California blackworms constitute a recently identified animal system exhibiting unusual collective behaviors, in which dozens to thousands of worms entangle to form a “blob” capable of actions like locomotion as an aggregate. In this paper we describe a system of pneumatic soft robots inspired by the blackworms, intended for the study of collective behaviors enabled and mediated by such physical entanglement. Both the robots and worms have high aspect ratio ($\gtrsim 1: 50$), intertwine in complex 3D configurations, operate both in air and underwater, and can locomote both individually and as a collective. We demonstrate and characterize locomotion for both individual robots and entangled blobs, explore the tunability of entanglement strength, and compare these to the analogous versions in living worms. The robots provide a testbed for studying mechanisms underlying behaviors observed in worm blobs, as well as serving as a platform for studies of novel collective behaviors based on physical entanglement.

Osmosis-driven actuation offers a promising strategy for developing untethered, environmentally responsive soft and shape shifting mechanisms and robots. In this work, we explore the use of superabsorbent polymer (SAP) pellets as large-scale, shape-morphing actuators. Upon exposure to water, these approximately 2mm diameter spherical pellets undergo a dramatic volumetric expansion, up to 300 times their initial volume, generating actuation forces of approximately 10 N under constrained conditions. We further demonstrate reversible cyclic actuation via controlled swelling-deswelling using ethanol-water solutions. Finally, we integrate these systems into a shape-morphing wheel design to enable adaptive locomotion that passively transitions between terrestrial and aquatic environments. Our findings demonstrate SAP-based osmotic actuators as an environmentally-driven solution for soft robotics, and shape-shifting soft hybrid mechanisms.

Soft, wearable systems hold promise for a wide variety of new or enhanced applications in the realm of human-computer interaction, physiological monitoring, wear-able robotics, and a host of other human-centric devices. Soft sensor systems have been developed concurrently in order to allow these wearable systems to respond intelligently with their surroundings. A recently reported sensing mechanism based on the strain-mediated contact in anisotropically resistive structures (SCARS) is an attractive solution due to its high sensing resolution, low-profile nature, and high mechanical resilience. Furthermore, the resistance-based output provides a simple electronic readout, facilitating its use in a wide variety of applications. However, previous iterations of the sensing mech-anism have exhibited stress relaxation and hysteretic behaviors that limit the scope of its use. Here, we report an iteration of the SCARS mechanism that uses silicone-based materials with low mechanical loss in order to improve the sensor signal stability and bandwidth. A new fabrication approach is developed which permits the incorporation of a liquid elastomer adhesive layer while also preserving the SCARS sensing functionality. The silicone-based SCARS sensors exhibited fast stress relaxation response (< 1 s) and reduced cyclic drift properties by more than half that of previously reported designs. A physiological monitoring demonstration is presented, validating that the new sensor design is mechanically resilient to such applications and has potential for use in real-world wearable use cases.

Soft robotics has seen an exponential growth in the past decade, in part because the transition to soft materials has made a wider range of applications possible. Tasks involving contact with fragile objects or unstructured environments are particularly amenable to devices based on soft materials. To date, research has primarily focused on the development of soft analogs to traditional sensors and actuators while controllers for soft robots have tended to rely on common rigid electronic components. We aspire to create a library of elastomer-based devices that can evolve soft controllers beyond component-level demonstrations and towards system-level completeness taking inspiration from electronic microcontrollers. Our approach combines microfluidic circuit designs with soft robotic fabrication techniques to create fluidic microcontroller components that are composed of soft materials and are of minimal size. We have identified the shift register, oscillator, and demultiplexer as key circuit elements for both individual functionality and for multi-component systems that can mimic microcontroller behaviors. In this paper, we present a review of fluidic circuits, fabrication processes, and implementation of these circuits into soft robotic platforms. In this work, we demonstrate a shift register, demultiplexer, and oscillator. They contain characteristics such as memory storage, data communication, and timing capabilities.

This paper describes the development of a modular end-effector system (MEES) for autonomous robotic maintenance and repair tasks. The design consists of the following major components: Robot Side Mating Socket Module (RSMS), End-Effector Side Mating Socket Module (EEMS), the Modular Camera System (MCS), and Tool Holder/Changer unit. Multiple prototypes for each component have been manufactured, tested, and evaluated resulting in the final concept. Existing robotic tool-changer systems on the market were evaluated and features were built into the Modular End-Effector System to overcome the current limitations of those systems. A notable advantage to the MEES is that it is a robot agnostic system and simply uses an ISO standard bolt mounting pattern to physically attached to the robot of choice along with an ethernet connection. No external cables are required that could restrain the workspace of the robot manipulator. Additionally, it is compatible with customized wrist-mounted sensors and end-effectors without any modification of the actual robot circuitry. The MEES is demonstrated working with three different end-effectors and two different robots.

In this paper, we discuss the role of gripper compliance in successful grasping and manipulation of thin, flexible materials. We show, both conceptually and empirically, that each axis of compliance in a planar gripper provides unique benefits in this domain. Vertical compliance allows robust grasping of thin materials in the presence of large uncertainty in positioning. Lateral compliance increases opportunity to respond to unexpected snags by increasing the time window over which tensile forces are applied. Rotational compliance avoids damage to objects by decreasing the maximum tensile forces applied during snags. We explore these three benefits through empirical tests comparing a rigid gripper to a soft gripper, evaluating the level of vertical uncertainty each can handle for prehensile and non-prehensile manipulation, as well as the forces and displacements incurred during snags. The results show how a soft gripper's three-axis compliance provides a passive ability to prevent damage to delicate materials.

As robots begin to move from structured industrial environments to the real world, they must be equipped to not only safely interact with the environment, but also reason about how to leverage contact to perform tasks. In this work, we develop a modeling and motion planning framework for continuum robots that accounts for contact anywhere along the robot. We first present an analytical model for continuum manipulators under contact and discuss the ideal choice of generalized coordinates given properties of the manipulator and task specifications. We then demonstrate the utility of our model by developing a motion planning framework that can solve a diverse set of tasks. We apply our framework to end effector path planning for a soft arm in an obstacle-rich environment, and grasp planning for soft robotic grippers, where contact can happen anywhere on the arm or gripper. Finally, we verify the utility of our model and planning framework by planning a grasp with a desired contact force for a soft antipodal gripper and testing this grasp in a hardware demonstration. Overall, our model and planning approach further enhance soft and continuum robots where they already excel: utilizing contact with the world to achieve their goals with a gentle touch.

Proprioception, or the perception of the configuration of one's body, is challenging to achieve with soft robots due to their infinite degrees of freedom and incompatibility with most off-the-shelf sensors. This work explores the use of inertial measurement units (IMUs), sensors that output orientation with respect to the direction of gravity, to achieve soft robot proprioception. A simple method for estimating the shape of a soft continuum robot arm from IMUs mounted along the arm is presented. The approach approximates a soft arm as a serial chain of rigid links, where the orientation of each link is given by the output of an IMU or by spherical linear interpolation of the output of adjacent IMUs. In experiments conducted on a 660mm long real-world soft arm, this approach provided estimates of its end effector position with a median error of less than 10% of the arm's length. This demonstrates the potential of IMUs to serve as inexpensive off-the-shelf sensors for soft robot proprioception.

To deploy robots outside of laboratory environments, they must be able to locomote on natural, unstructured terrain. While perception and control strategies for terrain navigation and obstacle avoidance have been developed for human-scale robots, microrobots are often too small to carry the sensors, computing power, and energy required to implement such techniques. Instead, this work presents passive foot designs for improving open-loop, quasi-static locomotion of a 1.6 g, 45 mm quadruped robot over rough terrains. The feet were evaluated by tracking the distance travelled on an uneven terrain of progressively increasing feature heights. Our insect tarsi inspired rigid foot designs improved performance somewhat, and by adding passive compliance via a viscoelastic hinge on the heel and toe, we increased the distance travelled by 168% over the original design. By exploring the design space of foot geometries and compliance, this work lays the foundation for understanding how passive foot design facilitates locomotion over uneven terrains.

Insects can locomote readily in challenging environments, such as over steep inclines and across obstacle-laden terrains, which still frustrate robots of similar size. In this work, inspired by the passive compliant properties of insect limbs, we use the insect-scale Harvard Ambulatory Microrobot and multilayer microfabrication techniques as platform to study the ability of passive mechanisms to improve open-loop running in rough terrains. We tested the performance of different limb designs in vivo, exploring how the magnitude, directionality, and distribution of compliance incorporated into the leg impacted robot performance. Limbs were evaluated on both a featureless substrate and an increasingly-adversarial 3D-printed terrain designed to mimic natural environments. We tested the limbs using a trotting gait in the quasi-static (2 Hz) and body dynamics (25 Hz) stride frequency regimes. Performance was reported as bodylengths traveled per gait cycle on the featureless substrate, and as the largest feature height the robot was able to overcome in the terrain. The work presented here provides design principles for a passive limb that expands the terrain accessible to small robot; we find a limb with a single asymmetrical joint is able to improve quasi-static terrain traversal by 203% relative to a rigid limb.

Mantis shrimp produce one of the fastest strikes in the animal kingdom, their striking appendages reaching tip velocities of tens of meters per second underwater. Their ultrafast movement is capable of crushing the shells of prey and generating cavitation bubbles, and has long raised interest from the scientific community. To study the underlying mechanisms and operating principles behind these behaviors, prior research has developed physical models that mimic the motions and speeds of mantis shrimp. That microrobot demonstrated speeds of approximately 5 m/s in water and 26 m/s in air. Here we utilize an accurate dynamical model of the four-bar mechanism and geometric latch observed in biological shrimp in a numerical trajectory optimization approach to find the design changes that can maximize the microrobot's striking velocities. Through a suboptimization problem maximizing the energy loaded in the mechanism's spring, we manage to improve the performance of the microrobot by over 58%, reaching tip velocities of$41.2 \pm 0.6$m/s.

In-hand manipulation is challenging for soft robotic hands, especially in the real world where robots encounter a variety of object sizes and shapes. As such, the role of the palm is crucial, providing stabilizing contact to objects during grasping and manipulation, and controlling the position of objects with respect to the fingertips. We demonstrate an actuated palm capable of enhancing the in-hand manipulation capabilities of a soft hand by better-utilizing limited finger dexterity. With a combination of physical and virtual experiments, we explore the effects of palm diameter and height on in-hand manipulation performance over a variety of object shapes and sizes, and three key manipulation primitive motions. The results of these experiments show that maintaining manipulation capabilities over a large range of object sizes requires the palm’s diameter to decrease as a function of its height to prevent interference between the fingers and palm. Based on these insights, we design an actuated palm mechanism that achieves the desired relationship between palm height and diameter using one actuated degree of freedom. Finally, we show that this adjustable palm enables the hand to manipulate a larger range of object sizes and aspect ratios, and its utility is demonstrated in a mid-air shelving in-hand manipulation task.

Engineers and scientists often rely on their intuition and experience when designing soft robotic systems. The development of performant controllers and motion plans for these systems commonly requires time-consuming iterations on hardware. We present the SoMo (Soft Motion) toolkit, a software framework that makes it easy to instantiate and control typical continuum manipulators in an accurate physics simulator. SoMo introduces a standardized and human-readable description format for continuum manipulators. It leverages this description format and the Bullet physics engine to enable fast and accurate simulations of soft and soft-rigid hybrid robots in environments with complex contact interactions. This allows users to vary design and control parameters across simulations with minimal effort. We compare the capabilities of SoMo to other physics simulators and highlight the benefits and accuracy of SoMo by demonstrating the agreement between simulation and real-world experiments on several examples; these include an in-hand manipulation task with continuum fingers, an automated exploration of how to design soft fingers for precision grasping, and a brief snake locomotion study. Overall, SoMo provides an accessible way for designers of soft robotic hardware and control systems to gain access to a simulation-accelerated workflow.

The need for robotic hands capable of gentle in-hand manipulation is growing rapidly as robots enter the real world. In this work, we show that the arrangement of digits in a soft robotic hand has a strong effect on in-hand manipulation capabilities. Introducing task-based performance metrics which quantify the range of motion, repeatability, and accuracy of in-hand manipulation tasks, we investigate hand designs with finger arrangements ranging from axisymmetric-circular to anthropomorphic. Using an open-source soft robot simulator, the effect of object size and aspect ratio on the in-hand manipulation performance is studied for a variety of finger arrangements, and findings are validated using a physical hardware platform. We found that the ideal finger arrangement is task-dependent; anthropomorphic arrangements excel at lateral translations, and axisymmetric arrangements are best suited for rotations. The aspect ratio of the object also has a strong effect on in-hand manipulation, with anthropomorphic designs performing best on objects of high aspect ratio, and axisymmetric arrangements doing well on objects of low aspect ratio. These findings are further confirmed in a real-world task with delicate pastries, where gentle in-hand manipulation is critical. Overall, our results suggest that active control of digit arrangement is necessary for soft robotic hands to maximize in-hand manipulation capabilities with arbitrary objects.

Here we present HAMR-Jr, a 22.5mm, 320mg quadrupedal microrobot. With eight independently actuated degrees of freedom, HAMR-Jr is, to our knowledge, the most mechanically dexterous legged robot at its scale and is capable of high-speed locomotion (13.91bodylengthss-1) at a variety of stride frequencies (1-200Hz) using multiple gaits. We achieved this using a design and fabrication process that is flexible, allowing scaling with minimum changes to our workflow. We further characterized HAMR-Jr's open-loop locomotion and compared it with the larger scale HAMR-VI microrobot to demonstrate the effectiveness of scaling laws in predicting running performance.

Soft strain sensors have been explored as an unobtrusive approach for wearable motion tracking. However, accurate tracking of multi degree-of-freedom (DOF) noncyclic joint movements remains a challenge. This paper presents a soft sensing shirt for tracking shoulder kinematics of both cyclic and random arm movements in 3 DOFs: adduction/abduction, horizontal flexion/extension, and internal/external rotation. The sensing shirt consists of 8 textile-based capacitive strain sensors sewn around the shoulder joint that communicate to a customized readout electronics board through sewn micro-coaxial cables. An optimized sensor design includes passive shielding and demonstrates high linearity and low hysteresis, making it suitable for wearable motion tracking. In a study with a single human subject, we evaluated the tracking capability of the integrated shirt in comparison with a ground truth optical motion capture system. An ensemble-based regression algorithm was implemented in post-processing to estimate joint angles and angular velocities from the strain sensor data. Results demonstrated root mean square errors (RMSEs) less than 4.5° for joint angle estimation and normalized root mean square errors (NRMSEs) less than 4% for joint velocity estimation. Furthermore, we applied a recursive feature elimination (RFE)-based sensor selection analysis to down select the number of sensors for future shirt designs. This sensor selection analysis found that 5 sensors out of 8 were sufficient to generate comparable accuracies.

Movement in bio-inspired robots typically relies on the use of a series of actuators and transmissions with one or more degrees of freedom (DOF), allowing asymmetrical ellipsoidal gaits for use in walking, running, swimming, and crawling. In an effort to simplify these multi-component systems, we present a novel, modular, soft, bi-stable, one DOF dome actuator platform that is capable of complex gaits through mechanical programming, driven by simple periodic fluid input. With a modular, reconfigurable design, the end effectors of these bi-stable dome actuators can be quickly modified for use on a variety of surfaces for specific applications. In the present study, we describe the finite element modeling, manufacturing, and characterization of different end effectors and outline a workflow for the implementation of these soft bi-stable dome actuators for the production of functional robotic prototypes.

We present a novel paradigm and algorithm for optimal design of underactuated robot platforms in highly-constrained nonconvex parameter spaces. We apply this algorithm to two variants of the mature RoboBee platform, numerically demonstrating predicted performance improvements of over 10% in some cases by algorithmically reasoning about variable effective-mechanical-advantage (EMA) transmissions, higher aspect ratio (AR) wing designs, and force-power tradeoffs. The algorithm can currently be applied to any underactuated mechanical system with one actuated degree of freedom (DOF), and can be easily extended to arbitrary configuration spaces and dynamics.

Soft robotics has yielded numerous examples of soft grippers that utilize compliance to achieve impressive grasping performances with great simplicity, adaptability, and robustness. Designing soft grippers with substantial grasping strength while remaining compliant and gentle is one of the most important challenges in this field. In this paper, we present a light-weight, vacuum-driven soft robotic gripper made of an origami “magic-ball” and a flexible thin membrane. We also describe the design and fabrication method to rapidly manufacture the gripper with different combinations of low-cost materials for diverse applications. Grasping experiments demonstrate that our gripper can lift a large variety of objects, including delicate foods, heavy bottles, and other miscellaneous items. The grasp force on 3D-printed objects is also characterized through mechanical load tests. The results reveal that our soft gripper can produce significant grasp force on various shapes using negative pneumatic pressure (vacuum). This new gripper holds the potential for many practical applications that require safe, strong, and simple grasping.

Flapping-wing micro-aerial vehicles rely on subtle changes in the kinematics of high-frequency wing flapping to produce roll, pitch, and yaw torques. To generate yaw torque, the Harvard RoboBee changes the ratio of upstroke to downstroke speed (“split-cycling”) by applying a second harmonic to the fundamental flapping signal for each wing. However, since flapping typically occurs near resonance (for efficiency), these higher harmonics are filtered out by the transmission and actuator dynamics. Therefore, reliable yaw control authority has proven elusive. We propose a method to generate yaw torque sufficient for in-flight control by using split-cycle flapping in an “iso-lift” regime, to mitigate resonant filtering by decreasing the flapping frequency and increasing the drive voltage, which produces lift identical to typical flight conditions. We model the expected torque at iso-lift conditions and apply this method to the physical RoboBee, achieving reliable, controllable yaw torque. Finally, we demonstrate yaw control with a simple heading controller, achieving a step response with a time constant an order of magnitude faster than previous attempts.

Remoras employ their adhesive discs to rapidly attach to and detach from a wide range of marine surfaces. By analyzing high-speed images of remoras' (Echeneis naucrates) hitchhiking behavior, we describe the fish's detachment mechanism as a lip curling up to break the seal between the disc and substrate. By mimicking the kinematic and morphological properties of the biological disc, we fabricated a multi-material biomimetic disc (whose stiffness spans four orders of magnitude) that is capable of both attachment and detachment. Detachment is realized by a flexible cable-driven mechanism that curls the anterior region of the silicone soft lip, allows leakage under the disc, and equalizes the internal pressure to the external pressure. The disc lamellae with attached carbon fiber spinules can be rotated by hydraulic soft actuators whose internal pressure is precisely tuned to the ambient underwater pressure. During attachment, increasing the rotational angle of the lamellae and the preload of the disc significantly enhanced the adhesive forces. We found that curling up the soft lip and folding down the lamellae rapidly reduced the pulling force of the disc by a factor of 254 compared to that under the attached state, which lead to detachment. Based on these mechanisms, underwater maneuvers involving repeated attachment and detachment were demonstrated with an integrated ROV unit that had a self-contained actuation and control system for the disc. This study lays a foundation for the development of fully untethered robotic systems for underwater hitchhiking in real-world marine environments.

A hybrid manufacturing process combining abrasive jet and laser micromaching enables the creation of living hinges in nitinol that retain the superelastic properties of the bulk material. The former selectively etches through the thickness of a workpiece and the latter defines the part's final geometry. Because the majority of the material removal is done with the room-temperature mechanical etching procedure, thermal damage to the part is minimized. Processing parameters to achieve desired geometries are described, a bending stiffness model for the living hinges is provided, and validation experiments are presented. Lastly, to demonstrate the usefulness of these components to millimeter-sized robotic systems and medical devices, we show their integration in two prototype devices: an endoscopic camera wrist and a simple laser beam steering system.

Laryngeal cancer treatments, while curative, often lead to voice impairment. Minimally invasive surgical methods that facilitate greater preservation of healthy tissue have recently emerged, but they are still limited in important ways. In this work, we describe a device that combines the advantages of the two primary minimally invasive approaches: the high quality incision and reduced post-operative pain achievable with transoral laser microsurgery and the superior visualization and tissue manipulability afforded by transoral robotic surgery. Our 11 mm diameter scanning system connects to focusing optics and a fiber optic laser source and can direct a laser beam across a 18×10 mm plane with controllable trajectories at speeds up to 7m/s. We describe its design and benchtop validation and present avenues for further development within a clinical environment. While oncological treatment is a natural first application area for this technology, we anticipate that it may also yield important benefits for the minimally invasive treatment of benign laryngeal diseases.

Robotic artificial muscles are a subset of artificial muscles that are capable of producing biologically inspired motions useful for robot systems, i.e., large power-to-weight ratios, inherent compliance, and large range of motions. These actuators, ranging from shape memory alloys to dielectric elastomers, are increasingly popular for biomimetic robots as they may operate without using complex linkage designs or other cumbersome mechanisms. Recent achievements in fabrication, modeling, and control methods have significantly contributed to their potential utilization in a wide range of applications. However, no survey paper has gone into depth regarding considerations pertaining to their selection, design, and usage in generating biomimetic motions. In this paper, we discuss important characteristics and considerations in the selection, design, and implementation of various prominent and unique robotic artificial muscles for biomimetic robots, and provide perspectives on next-generation muscle-powered robots.

The development of soft, compliant force sensors is greatly sought after in areas such as soft robotics and prosthetics. Nevertheless, solutions for measuring forces in multiple axes, while being mechanically compliant, have been few and far between. Here we present a compliant sensor able to detect forces tangential and normal to the sensor surface. The transduction mechanism is based on the deformation of laser-machined carbon fiber composite (CFC) micro-scale meanders, encapsulated within elastomers layers. Strains in the elastomer are transmitted to the meanders, causing changes in the electrical resistance of the sensor contact mechanics. Configuring the meanders in a radial pattern, segmenting them into quadrants (two antagonist pairs) and biasing the center of the sensor out-of-plane enables detection of forces in multiple axis via differential measurement. Sensors were manufactured using a custom fabrication process and exhibited high mechanical compliance with a very low form factor. The sensors were experimentally characterized and demonstrated large differential changes in resistance (up to 26 kΩ for tangential forces applied to the sensor surface). We integrated our sensor onto a soft robotic gripper finger and demonstrated the ability to detect changes in friction at the actuator surface, thus demonstrating their potential for real world applications.

In this paper we present the design of a fin-like dielectric elastomer actuator (DEA) that drives a miniature autonomous underwater vehicle (AUV). The fin-like actuator is modular and independent of the body of the AUV. All electronics required to run the actuator are inside the 100 mm long 3D-printed body, allowing for autonomous mobility of the AUV. The DEA is easy to manufacture, requires no pre-stretch of the elastomers, and is completely sealed for underwater operation. The output thrust force can be tuned by stacking multiple actuation layers and modifying the Young's modulus of the elastomers. The AUV is reconfigurable by a shift of its center of mass, such that both planar and vertical swimming can be demonstrated on a single vehicle. For the DEA we measured thrust force and swimming speed for various actuator designs ran at frequencies from 1 Hz to 5 Hz. For the AUV we demonstrated autonomous planar swimming and closed-loop vertical diving. The actuators capable of outputting the highest thrust forces can power the AUV to swim at speeds of up to 0.55 body lengths per second. The speed falls in the upper range of untethered swimming robots powered by soft actuators. Our tunable DEAs also demonstrate the potential to mimic the undulatory motions of fish fins.

Dynamic tactile displays represent a class of haptic devices of particular interest to the blind and visually impaired. Despite many years of research and development efforts, the low-cost, low-power, compact tactile display remains elusive. This paper describes a low-cost electromechanical actuator array based on low-force, low-displacement bistable actuators that can be realized using inexpensive, commercially available components and high-volume manufacturing processes. The array is applicable to several types of tactile displays; as an initial proof of concept, we demonstrate a 6-dot Braille cell with a 3mm pitch that requires less than 50mJ per actuator per transition.

Nascent endoscopic therapeutic procedures, such as endoscopic submucosal dissection, enable unparalleled access to and removal of mid-size cancerous neoplasia from within the gastrointestinal tract. However, the remote locations of these lesions often incur substantial distal dexterity which imparts appreciable cognitive loading on the clinician and opens up the possibility of adverse events such as intestinal perforation due to limited dexterity and a lack of sensory feedback. In this work, we introduce a mm-scale, tip-mounted robotic system, EndoMODRA (Endoscopic Module for On-Demand Robotic Assistance), which interfaces with commercially-available endoscopic tools and provides additional dexterity and feedback sensing using on-board actuators and sensors, decoupling tool motion from endoscope motion. Leveraging alternative high-energy-density actuation strategies and monolithic, printed-circuit-inspired manufacturing processes, all actuation and sensing is fully contained within the distally-mounted module, obviating the need for a continuous mechanical transmission to a proximal motor package. We develop a fuzzy-tuned PID/PWM controller for closing the loop distally to enable closed-loop position-controlled trajectory execution using onboard actuation and sensing, realizing fully -distal loop closure in an endoscope-mounted robotic module with no proximal actuation or sensing component. Controller performance is validated on a fully-integrated module with on-board sensing, demonstrating the ability to execute pre-determined trajectories as well as real-time rate-based teleoperation.

Force feedback during robotic surgery is critical in order to minimize potential injury to the patient and decrease recovery time from surgical procedures. Here we describe the use of a novel strain gauge printing method to apply low profile, low cost sensors directly to the surface of da Vinci surgical robot end effectors (Intuitive Surgical, Inc.) to sense deflection and provide force feedback. This additive, vapor-deposition-based sensor fabrication method is used to deposit strain gauges directly onto the surfaces of the end effectors with minimal disruption to the device and without the need for adhesives or machining operations. Initial experiments characterize sensor performance and indicate the applicability of the proposed approach for force feedback during minimally invasive procedures.

In this work, we show that sensors based on soft, intentionally-lossy optical waveguides are well-suited for soft robotic grasping applications in the deep-sea. Each finger of a soft robotic hand is outfitted with a 2×1 array of optical sensing elements to enable proprioception and contact force sensing. Curvature sensing elements are integrated directly into the structure of a finger, while contact force sensors are fabricated as standalone units and attached afterward. Along with considerations for interfacing with deep-sea remotely operated vehicles (ROVs), models for the effect of bending on light loss and the effect of normal force on strain were used to inform sensor design decisions. Our sensors show sensitivity to curvature over a range of diameters from 8 mm to 76 mm, and sub-Newton force sensitivity. Additionally, sensors were characterized in simulated deep-sea environments at temperatures from -10°C to 50°C and hydrostatic pressures up to 4000 psi. The sensitivity of our curvature sensors is invariant to the temperatures and pressure ranges tested, though contact force sensors decreased in sensitivity as temperatures decreased. Finally, we successfully demonstrate that sensors onboard soft finger actuators can provide informative state feedback during grasping operations in air and water.

This paper presents an end-to-end approach to automate the design and fabrication process for self-folding origami structures. Self-folding origami structures are robotic sheets composed of rigid tiles and joint actuators. When they are exposed to heat, each joint folds into a preprogrammed angle. Those folding motions transform themselves into a structure, which can be used as body of 3-D origami robots, including walkers, analog circuits, rotational actuators, and microcell grippers. Given a 3-D model, the design algorithm automatically generates a layout printing design of the sheet form of the structure. The geometric information, such as the fold angles and the folding sequences, is embedded in the sheet design. When the sheet is printed and baked in an oven, the sheet self-folds into the given 3-D model. We discuss, first, the design algorithm generating multiple-step self-folding sheet designs, second, verification of the algorithm running in O(n2) time, where n is the number of the vertices, third, implementation of the algorithm, and finally, experimental results, several self-folded 3-D structures with up to 55 faces and two sequential folding steps.

Many areas of robotics, particularly locomotion and grasping, can benefit from the ability to modulate friction on surfaces that come into contact with objects in the environment. Previous research has tried to address the challenge of tunable friction; however, those efforts only provide modest gains or are difficult to integrate. We propose a tunable friction mechanism that relies on pneumatic actuation and is easily integrated into pre-existing soft actuators. We characterize the performance of our friction mechanism with quantitative force data for varying preload forces, substrate materials, and inflation pressures. Testing results show that our tunable friction mechanism achieves an order of magnitude differentiation in friction forces between high and low friction states. We demonstrate its potential application in a one degree-of-freedom soft crawler and a soft gripper with actuatable finger friction pads. The crawler successfully propelled itself forward by leveraging asymmetric strokes and the gripper achieved a factor of five differentiation of grip force between engaged and disengaged states of the friction tuning mechanism.

We present an off-board phase estimator and controller for leg position near the resonance of the Harvard Ambulatory MicroRobot's (HAMR) two degree-of-freedom transmission. This control system is a first step towards leveraging the significant increase in stride length at transmission resonance for faster and more efficient locomotion. We experimentally characterize HAMR's transmission and determine that actuator phase is a sufficient proxy for leg phase across the range of useful operating frequencies (1-120Hz). An estimator is developed to determine actuator phase using off-board position sensors and it converges within a cycle on average. We also fit a nonlinear dynamic model of the transmission to the experimental data, and utilize the model to determine a suitable open-loop resonant leg trajectory and define feed forward control inputs. This resonant (100Hz) trajectory is theoretically 50% more efficient than pre-resonant high speed running trajectories. The controller converges to this trajectory in 0.05 ± 0.02 seconds (5.3 ± 2.4 cycles) in air, and in 0.05 ± 0.01 seconds (4.7 ± 0.6 cycles) under perturbations that approximate ground contact.

A multilayer fabrication method has been used to create crawling soft robots based on dielectric elastomer actuators. These actuators are created without the need for pre-stretch, eliminating the need for rigid components. A four-legged, multi-gait capable crawler can be fabricated in a matter of hours and shows promise for future untethered systems. Studies on inchworm robots show them to be the fastest dielectric elastomer actuator-based systems reported to date, capable of traveling faster than 1 body length/second for the best elastomer available. Most importantly, the devices are primarily soft and deformable, with few rigid attachments.

`Snap-On' robotic modules that can integrate distally with existing commercially-available endoscopic equipment have the potential to provide new capabilities such as enhanced dexterity, bilateral manipulation and feedback sensing with minimal disruption of the current clinical workflow. However, the desire for fully-distal integration of sensors and actuators and the resulting form factor requirements preclude the use of many off-the-shelf actuators capable of generating the relevant strokes and forces required to interact with tools and tissue. In this work, we investigate the use of millimeter-scale, optimally-packed helical shape memory alloy (SMA) actuators in an antagonistic configuration to provide distal actuation without the need for a continuous mechanical coupling to proximal, off-board actuation packages to realize a truly plug-and-play solution. Using phenomenological modeling, we design and fabricate antagonistic helical SMA pairs and implement them in an at-scale roboendoscopic module to generate strokes and forces necessary for deflecting tools passed through the endoscope working port, thereby providing a controllable robotic `wrist' inside the body to otherwise passive flexible tools. Bandwidth is drastically improved through the integration of targeted fluid cooling. The integrated system can generate maximum lateral forces of 10N and demonstrates an additional 96 degrees of distal angulation, expanding the reachable workspace of tools passed through a standard endoscope.

This paper presents an off-board trajectory controller for a range of stride frequencies (2-45 Hz) that enables zero-radius turns and holonomic control on one of the smallest and fastest legged robots, the Harvard Ambulatory MicroRobot (HAMR). An experimental model is used as the basis for control to capture the highly nonlinear response of the robot to input signals. Closed-loop trajectories are performed with an RMS position error at or below 0.3 body lengths (BL) using gaits at speeds up to 6.5 BL/s (29.4 cm/s) for straight-line and sinusoidal trajectories.

Onboard vision sensing is a current challenge in micro-scale robotics. Small flapping-wing robots such as the RoboBee present significant constraints on power, weight, and image quality for an onboard vision sensor. Here we report the integration of a 1 × 1 × 1.7 mm camera capable of video capture in flight. Inspired by gaze stabilization in insects, we designed and fabricated a one degree of freedom mechanism attached to the top of the RoboBee that achieves output angles of -41° to +60°. We perform open-loop roll maneuvers and demonstrate initial control of the gaze angle during flight. This represents the first use of a camera in free flight at this scale.

Flexible endoscopes are still the gold standard in most natural orifice translumenal endoscopic surgery (NOTES) procedures; however their flexibility (necessary for navigating through the GI tract) limits their capabilities in terms of distal manipulation and stability. We propose a deployable endoscopic add-on aimed at locally counteracting forces applied at the tip of an endoscope. We analyze different designs: a fully soft version and two hybrid soft-folded versions. The hybrid designs exploit either an inextensible structure pressurized by a soft actuator or the stiffness provided by the unfolded “magic cube” origami structure. We focus on the fabrication and experimental characterization of the proposed structures and present some preliminary designs and integration strategies to mount them on top of current flexible endoscopes.

Piezoelectric materials are an attractive option for electromechanical transduction on the mesoscale due to their intrinsic high force production, large bandwidth, and favorable scaling characteristics. However, the small displacements they inherently produce are typically too small to be directly used in robotic systems, and thus displacement amplification is needed. Here we present a piezoelectric actuator that uses geometric amplification to achieve 20 × the nominal piezoelectric displacement. Actuator performance is described in terms of blocked force (20 mN), displacement (115 μm), bandwidth (3 kHz), and power density (172 W/kg). The actuator is fabricated using printed circuit MEMS, an emerging mesoscale manufacturing paradigm. Expected applications include locomotion for terrestrial crawling robots and flapping wing micro-air vehicles.

Wearable robotic systems which aid or enhance human performance are the subject of substantial ongoing research efforts. Soft exosuits to assist with walking represent one class of system that leverage textiles and apparel to provide a lightweight and nonrestrictive means to interface to the lower extremity and apply assistive joint torques via a cable that applies a force across a biological joint. Current embodiments of the soft exosuit use off-the-shelf load cells attached to the distal end of a Bowden cable to measure and control the delivered force. As these systems evolve, we envision replacing all rigid components with compliant, textile-based components. Here we present a new force sensing concept suitable for exosuit applications. The approach is based on micro-machined carbon fiber composite structures encapsulated in elastomer materials as the transducer element, and high-strength, stiff textiles as the load bearing element. The transduction mechanism uses the Poisson effect in the encapsulating elastomer to create electrical contact between the carbon fiber structures. This method allows the sensor to be sensitive in tension while remaining insensitive to bending deformation. We fabricate a prototype sensor capable of detected forces up to 300 N, yet weighing just 2.15 g. The compliant nature of the materials used in fabrication allow the sensor to be flexible. The sensor output is qualitatively very repeatable, yet exhibits moderate drift at peak load. However this drift begins to stabilize over the test duration. These preliminary results demonstrate the promising potential of this sensor technology for soft exosuit systems.

Numerous therapeutic transendoscopic procedures exist to treat lesions in the GI tract. However, these procedures are limited by their difficulty and the amount of training required to successfully perform them. The surgeon is tasked with simultaneously steering the distal tip of the endoscope, applying tension to tissue to retract it, and manipulating electro-cautery tools with limited dexterity. We propose a device designed to assist with anchoring and tissue retraction during endoscopic surgical procedures. The designed solution decouples the tissue-grasping function from the movement of the endoscope tip, leaving the surgeon free to use the endoscope tip solely for positioning of electro-cautery or biopsy tools deployed through the endoscope working channel. The anchoring and retraction device uses pop-up book MEMS techniques, allowing for a “flat” structure to expand into a 3-D structure. The proposed device has three main integrated components: a rigid expandable geometric structure, inflatable pneumatic actuators, and a vacuum gripper. These inflatable actuators include internal rigid discs, allowing for resistance to buckling while maintaining the benefits of the established lightweight, low profile actuator design scheme. Proof-of-concept ex vivo testing demonstrates that the integrated device can be used to retract tissue to a height of 13.5 mm, providing access for endoscopy tools to contact a sample of porcine stomach tissue.

This paper develops a custom motion capture system that uses vision-based methods to rapidly and accurately track the body and leg position/orientation of a 1.43g legged microrobot, the Harvard Ambulatory MicroRobot (HAMR). Two new generalized metrics for quantifying locomotion performance are defined: amplitude-normalized stride correlation, and percent ineffective stance. Six different gaits are run on HAMR to validate the experimental setup and establish baseline performance. Furthermore, HAMR is compared with the cockroach, Blaberus Discoidalis, and with other legged robots. Future studies can leverage the experimental setup to study gait selection and transitions for small legged systems.

Burgeoning transendoscopic procedures, such as endoscopic submucosal dissection (ESD), provide a promising means of treating early-stage gastric neoplasia in a minimally-invasive way. However, the remote locations of these lesions, coupled with their origination in the submucosal layers of the gastrointestinal tract, often lead to extreme technical, cognitive and ergonomic challenges which combat the widespread applicability and adoption of these techniques. Among these challenges is achieving the in vivo dexterity required to retract and dissect tissue. By leveraging workspace and force data obtained through clinical studies, we developed a modular, disposable, distally-mounted actuator (an `active endcap') that can augment an endoscopist's distal dexterity in ways that are not achievable with the endoscope's built-in degrees-of-freedom. The device consists of a flexible articulating `exoskeleton' manufactured via printed-circuit MEMS (PCMEMS) which engages and deflects electrosurgical tools that are passed through the endoscopic working channel. Embedded proprioceptive sensing is implemented on-board using distributed LED/phototransistor pairs and the principle of light intensity modulation (LIM). The distal degree-of-freedom is actuated using shape memory alloy (SMA) technology, and the actuation transmission system is fully contained within a 1-inch-long end cap that can be mounted on the distal end of the endoscope, thereby obviating the need for a mechanical connection to a proximal source. Proof-of-concept tests demonstrate that the actuator adds over 50 degrees of distal articulation to existing tools and can generate 450 mN of lateral force which has been clinically determined to be sufficient for performing circumferential incisions in ESD.

Small, lightweight micro-aerial vehicles (MAVs) must rely on a limited number of actuators for flight stability and control. A method for six-degree of freedom control in a dual-actuator MAV has been previously proposed which employs stroke amplitude, bias, and split-cycle timing modulation. This control scheme is the basis of actuation for stable, controlled flapping wing flight of the Harvard Robobee. The role of passive wing pitching dynamics are currently unexplored in their effects on yaw-dynamics during free flight. Here we demonstrate in simulation and experiment the critical role wing pitching dynamics play in yaw control of a dual-actuated MAV using the split-cycle control scheme. We find that yaw-authority sensitively depends on the functional form of the wing hinge joint and that pitching dynamics of wing hinges with linear stiffness may compromise yaw control. To solve this we present a design method for laminate based non-linear hinges and demonstrate that non-linear hinge stiffness improves yaw torque generation during split-cycle actuation.

Insect-scale flying robots are currently unable to carry the power source and sensor suite required for autonomous operation. To overcome this challenge, we developed and experimentally verified a non-linear damping model of actuation-limited flapping-wing vehicles with passively rotating wing hinges. In agreement with studies on the wing dynamics of honey bees, we found that the optimal angle of the passive wing hinge in mid-stroke is about 70 ° rather than 45-50 ° as previously assumed. We further identified a narrow actuation force window in which the occurrence of a sharp resonance can be used to achieve both higher lift and efficiency. The findings from our model informed design changes to the Harvard Dual-Actuator Robobee, which resulted in a 130% increase in mean lift from ~140mg to 320mg (with a vehicle mass increase of only 5 - 8%), along with a corresponding expected payload increase of 330 - 470% (30 - 40mg to 170mg). The power consumption only increased by ~55%, making the new prototype 50% more efficient at lift production. Our model provides a greater understanding of the dynamics of this complex system, and the resulting lift and efficiency improvements are expected to bring insect-scale flying robots closer to autonomy.

The agility and ease of control make a quadrotor aircraft an attractive platform for studying swarm behavior, modeling, and control. The energetics of sustained flight for small aircraft, however, limit typical applications to only a few minutes. Adding payloads - and the mechanisms used to manipulate them - reduces this flight time even further. In this paper we present the flying monkey, a novel robot platform having three main capabilities: walking, grasping, and flight. This new robotic platform merges one of the world's smallest quadrotor aircraft with a lightweight, single-degree-of-freedom walking mechanism and an SMA-actuated gripper to enable all three functions in a 30 g package. The main goal and key contribution of this paper is to design and prototype the flying monkey that has increased mission life and capabilities through the combination of the functionalities of legged and aerial robots.

This paper presents a biologically inspired, 3.2g untethered vehicle capable of both active (flapping) and passive (gliding) flight. We discuss the overall vehicle design, as well as its validation with thrust data from benchtop testing, simulation, and flight test results. The vehicle has one pair of flapping wings for thrust generation, making it a good analogue for insects of the same scale. Flight energetics and control can be thoroughly explored through the array of simulation and testing that have been implemented. Integrated electronics provide wireless communication, sensing, and basic open-loop flight control, making flight test iteration fast and providing additional dynamics data. All of the testing setups and the physical vehicle working together have created a robust development environment for future iterations on the vehicle. The successful flight of the vehicle, including the data collection from onboard sensors and an external motion capture arena, show that this platform is ideal to study flight energetics and control schemes at an insect scale.

This paper introduces a manufacturing technique which enables the integration of soft materials and soft fluidic micro-actuators in the Pop-up book MEMS paradigm. Such a technique represents a promising approach to the design and fabrication of low cost and scalable articulated mechanisms provided with sensing capabilities and on-board actuation with potential applications in the field of minimally invasive surgery. Design and integration of soft components in the rigid-flex laminates is described along with the resulting soft pop-up mechanisms realized at different scales. Prototype characterization is presented, demonstrating forces and dexterity in a range suitable for surgical applications, as well as the possibility to integrate sensing capabilities. Based on these results, a multi-articulated robotic arm is fabricated and mounted on top of an endoscope model to provide a proof of concept of simple robotic mechanisms that could be useful in a surgical scenario.

Here we experimentally quantify the effects of wing morphological and inertial parameters on flapping flight performance. Through running at-scale, passive pitching experiments with different wing designs, we compare the relative importance of wing inertia, wing shape, and wing-actuation pairing. We find wing inertia strongly influences the coupling between stroke and pitch dynamics, which directly impacts lift production and efficiency. Flapping resonance frequency is reduced as wing aspect ratio or area moment increases. Further, wing leading edge design strongly influences chordwise center of pressure, which further impacts pitching dynamics. Based on our experimental results we propose a new wing design and measure 37% increase in mean lift relative to a previous work.

Self-folding provides an efficient way of creating complex 3D geometries from 2D composites. However, the precision of self-folding structures is often limited by the use of open-loop folding mechanisms. In this paper we demonstrate feedback-controlled self-folding using a shape memory polymer and optical sensors to accurately control folding angles. We present a method of quickly and inexpensively fabricating large collectives of self-folding autonomous robots that can be transported in flat configurations prior to autonomous deployment at target destinations. To demonstrate this, we build a collective of robots that is manufactured in one continuous laminar composite. Individual robots in the collective detach from one other, self-fold into pre-programmed configurations and navigate by phototaxis. This method could be applied to a broad range of applications where logistics necessitate compact transport and where external manipulation is difficult or expensive, such as in space applications or delivering search-and-rescue robots in cluttered environments.

Self-assembling robots can be transported and deployed inexpensively and autonomously in remote and dangerous environments. In this paper, we introduce a novel self-assembling method with a planar pneumatic system. Inflation of pouches translate into shape changes, turning a sheet of composite material into a complex robotic structure. This new method enables a flat origami-based robotic structure to self-fold to desired angles with pressure control. It allows a static joint to become dynamic, self-actuate to reconfigure itself after initial folding. Finally, the folded robot can unfold itself at the end of a robotic application. We believe this new pneumatic approach provides an important toolkit to build more powerful and capable self-assembling robots.

Full autonomy remains a challenge for miniature robotic platforms due to mass and size requirements of on-board power and control electronics. This paper presents a solution to these challenges with a 2.3g autonomous legged robot. An off-the-shelf optical mouse sensor is adapted for use on the Harvard Ambulatory Microrobot (HAMR) by reducing the sensor weight by 36% and achieving a position error below 11% when suspended 3mm above a cardstock surface. The position data is combined with data from a gyroscope for feedback control of both position and orientation. A microcontroller processes the sensor data and commands a controlled gait to HAMR that is powered by a battery, a boost converter and high voltage drive electronics. Solar cells are used as an alternative source providing enough power for autonomous operation of the robot. The resulting deviation for a controlled straight-line walk using both sensors to minimize lateral deviation and angular error is only 4.6%, compared to an error of 31% in an uncontrolled, straight-line walk.

Here we present a suite of theoretical, computational, and experimental studies culminating in the first aerial and aquatic capable insect-scale robot. We develop a computational fluid dynamics (CFD) simulation to model fluid-wing interaction in air and water. From CFD and a system dynamics analysis we predict that a multi-modal flapping strategy will enable locomotion in both air and water for a single device. We validate the CFD predictions by running at-scale, robotic wing-flapping experiments. Finally, we demonstrate for the first time a flying and swimming capable flapping-wing insect-like robot.

Despite having achieved unconstrained stable flight, the insect-scale flapping-wing robot is still tethered for power and control. Towards the goal of operating a biologically-inspired robot autonomously outside of laboratory conditions. In this paper, we simulate outdoor disturbances in the laboratory setting and investigate the effects of wind gusts on the flight dynamics of a millimeter-scale flapping wing robot. Simplified models describing the disturbance effects on the robot's dynamics are proposed, together with two disturbance rejection schemes capable of estimating and compensating for the disturbances. The proposed methods are experimentally verified. The results show that they reduced the root mean square position errors by approximately 50% when the robot was subject to 60 cm·s-1horizontal wind.

This paper presents the design and control of a teleoperated robotic system for dexterous micromanipulation tasks at the meso-scale, specifically open microsurgery. Robotic open microsurgery is an unexplored yet potentially a high impact area of surgical robotics. Microsurgical operations, such as microanastomosis of blood vessels and reattachment of nerve fibers, require high levels of manual dexterity and accuracy that surpass human capabilities. A 3-DoF robotic wrist is designed and built based on a spherical five-bar mechanism. The wrist is attached to a 3-axis commercial off-the-shelf linear stage, achieving a fully dexterous system. Design requirements are determined using motion data collected during a simulated microanastomosis operation. The wrist design is optimized to maximize workspace and manipulability. The system is teleoperated using a haptic device, and has the required bandwidth to replicate microsurgical motions. The system was successfully used in a micromanipulation task to stack 1 mm-diameter metal spheres. The micromanipulation system presented here may improve surgical outcomes during open microsurgery by offering better accuracy and dexterity to surgeons.

This paper presents a non-linear, dynamic model of the flexure-based transmission in the Harvard Ambulatory Microrobot (HAMR). The model is derived from first principles and has led to a more comprehensive understanding of the components in this transmission. In particular, an empirical model of the dynamic properties of the compliant Kapton flexures is developed and verified against theoretical results from beam and vibration theory. Furthermore, the fabrication of the piezoelectric bending actuators that drive the transmission is improved to match theoretical performance predictions. The transmission model is validated against experimental data taken on HAMR for the quasi-static (1–10 Hz) operating mode, and is used to redesign the transmission for improved performance in this regime. The model based redesign results in a 266% increase in the work done by the foot when compared to a previous version of HAMR. This leads to a payload capacity of 2.9g, which is ∼ 2× the robot's mass and a 114% increase. Finally, the model is validated in the dynamic regime (40–150 Hz) and the merits of a second order linear approximation are discussed.

The Harvard Robobee is a fly-sized aerial vehicle that can perform controlled flight maneuvers. But this robot is unable to control its yaw or heading angle to a desired value. Motivated by this deficiency, we propose a new method to produce yaw-axis rotations. Termed wriggle-steering, it consists of driving body oscillations around its two other rotational axes. Because no torque is applied directly around the controlled axis, it therefore constitutes an alternative control method for under-actuated designs. Oscillations are driven around pitch and roll axes at the same frequency but 90 degrees out of phase, resulting in a small change in yaw angle after each cycle because of nonlinearity in attitude dynamics. We propose two wing kinematics perturbations that produce the necessary actuation. The predictions are validated with a quasi-steady aerodynamics model, free-body simulations, and flight tests on a fly-sized hovering aerial robot. The results suggest that wriggle-steering can save mass and reduce complexity by eliminating the need for additional actuators in flapping-wing robots or other aircraft.

Without sufficient payload capacity to carry necessary electronic components, flying robots at the scale of insects cannot fly autonomously. Using a simple scaling heuristic to determine a few salient vehicle properties, we develop a vehicle design that possesses the requisite payload capacity for the full suite of required components for control autonomy. We construct the vehicle using state-of-the-art methods, producing a 380 mg vehicle with a 115 mg payload capacity, and demonstrate controlled hovering of the fully-loaded vehicle. The payload-capable vehicle demonstrated here establishes a scalable vehicle design and validates current fabrication methods, laying a foundation for an eventual, fully-integrated robotic system.

Self-folding is a promising technique for assembling robots from flat sheets. However, existing implementations do not include reliable methods for sensing the folding angle, making feedback control impossible. In this paper, we present novel angle sensors for foldable robots and machines. They are inkjet printed and fully integrated into robots' laminate. This additional sensor layer tracks the angle motion of robot hinges, to better guide robot assembling by folding and to perform more complicated tasks that requires feedback control, making folded robots more capable in real world applications. We introduce the fabrication process, property assessments, and demonstrate sensor performance by measuring folding angles of a cube and controlling folds on a gripper.

Soft fluidic actuators consisting of elastomeric matrices with embedded flexible materials are of particular interest to the robotics community because they are affordable and can be easily customized to a given application. However, the significant potential of such actuators is currently limited as their design has typically been based on intuition. In this paper, the principle of operation of these actuators is comprehensively analyzed and described through experimentally validated quasi-static analytical and finite-element method models for bending in free space and force generation when in contact with an object. This study provides a set of systematic design rules to help the robotics community create soft actuators by understanding how these vary their outputs as a function of input pressure for a number of geometrical parameters. Additionally, the proposed analytical model is implemented in a controller demonstrating its ability to convert pressure information to bending angle in real time. Such an understanding of soft multimaterial actuators will allow future design concepts to be rapidly iterated and their performance predicted, thus enabling new and innovative applications that produce more complex motions to be explored.

This paper presents an end-to-end approach for creating 3D shapes by self-folding planar sheets activated by uniform heating. These shapes can be used as the mechanical bodies of robots. The input to this process is a 3D geometry (e.g. an OBJ file). The output is a physical object with the specified geometry. We describe an algorithm pipeline that (1) identifies the overall geometry of the input, (2) computes a crease pattern that causes the sheet to self-fold into the desired 3D geometry when activated by uniform heating, (3) automatically generates the design of a 2D sheet with the desired pattern and (4) automatically generates the design files required to fabricate the 2D structure. We demonstrate these algorithms by applying them to complex 3D shapes. We demonstrate the fabrication of a self-folding object with over 50 faces from automatically generated design files.

We implement a 2D computational model to investigate the unsteady aerodynamic effects not captured by classical quasi-steady models. We compare numerical simulation results, experimental measurements and quasi-steady predictions to demonstrate the strength of the numerical tool in identifying unsteady fluid mechanisms and improving propulsive efficiency of flapping wing robots. In particular, this study quantifies the effect of the relative phase between wing degrees of freedom δ on lift and drag production. The computational model also identifies unsteady effects such as wake capture and downwash that are not accounted for in classical quasi-steady models. To examine the accuracy of our computational model, we fabricate millimeter-scale wings through the SCM fabrication processes and measure flapping kinematics and dynamics. The experiments show 2D computational model is 44% more accurate than the quasi-steady model and can be further used to improve wing morphology for better aerodynamic performance.

Inspired by the agility of flying insects and the recent development on an insect-scale aerial vehicle, we propose a single-loop adaptive flight control suite designed with an emphasis on the ability to track dynamic trajectories as a step towards the goal of performing acrobatic maneuvers as observed in real insects. Instead of the conventional approach of having cascaded control loops, the proposed controller directly regulates the commanded torques to stabilize the attitude and lateral position in a single loop. The method is verified by performing trajectory following flights with the insect-like robot. The results show that the position errors during trajectory following flights are comparable to those observed from steady hovering flights.

Transmissions play a vital role in machines by transforming the torque and speed of a motor into a desired output. They are often necessary for operating a motor at peak efficiency or power. The majority of variable transmissions are mechanically complex, large, and expensive, which limits scalability and is often cost prohibitive. As an alternative, we propose an origami-wheel design that is capable of varying its own transmission ratio between motor torque and ground reaction force, effectively creating a passive, continuously variable transmission. The wheel responds to an increase in torque by reducing its radius through the spring-like properties of the origami structure, increasing the force applied by the wheel to the ground. We demonstrate that the wheel is able to match the speed of a 55 mm fixed-radius wheel when unloaded, and can also tow loads as high as a 25 mm wheel without stalling. This design could be used to provide smaller, cheaper robots with an effective means to vary their output while maintaining motor efficiency.

In this paper we have rapidly prototyped customized, highly-sensitive, mm-scale multi-axis force sensors for medical applications. Using a composite laminate batch fabrication process with biocompatible constituent materials, we have fabricated a fully-integrated, 10×10 mm three-axis force sensor with up to 5 V/N sensitivity and RMS noise on the order of ~1.6 mN, operational over a range of -500 to 500 mN in the x- and y-axes, and -2.5 to 2.5 N in the z-axis. Custom foil-based strain sensors were fabricated in parallel with the mechanical structure, obviating the need for post-manufacturing alignment and assembly. The sensor and its custom-fabricated signal conditioning circuitry fit within a 1×1×2 cm volume to realize a fully-integrated force transduction platform with potential haptics and control applications in minimally-invasive surgical tools. The form factor, biocompatibility, and cost of the sensor and signal conditioning makes this method ideal for rapid-prototyping low-cost, mm-scale distal force sensors. Sensor performance is validated in a simulated tissue palpation task using a robotic master-slave platform.

Mesoscale robots are devices with characteristic dimensions in the centimeter to millimeter scale, with feature sizes ranging from millimeters to micrometers. Due to the physics involved in scaling down conventional motors, such robots frequently require novel approaches to actuation. Actu- ation can have a very significant effect on robot performance, particularly at small scales where locomotion becomes ener- getically expensive; however, existing options for small-scale actuation are quite limited. We present a mesoscale voice coil actuator (VCA) with favorable scaling characteristics and a design that minimizes costly frictional effects at small scales while allowing fast, linear, high-displacement motion. The VCA is fabricated using planar manufacturing techniques, making it well-suited for integration into a number of mesoscale robotic platforms and for mass production. The designed VCA has a mass of 310mg, maximum force of 11.8mN, bandwidth of 51Hz, and a stroke of 4mm.

The Harvard RoboBee was the first fly-sized vehicle to lift its own weight. This vehicle has previously demonstrated controlled flight maneuvers, but this required an array of external cameras to precisely track its trajectory. Developing flight-worthy sensors to eliminate the need for external motion capture is an area of active study. In this paper, we consider an onboard analog magnetometer. We show that the sensor meets the size, weight, and power requirements for the RoboBee and can provide feedback on angular position for pitch and yaw angle control. We show that this sensor can provide an accurate angle reading despite proximity to the piezoelectric actuators of this vehicle. This is likely because the actuators are driven by electrostatic forces rather than the electromagnetic forces that drive the electric motors of larger aircraft. This sensor provided sufficient bandwidth to enable rapid pitch angle maneuvers within 200ms on a RoboBee constrained to rotate only about its pitch axis. We also show it operating in a feedback loop to control heading angle, the first demonstration of controlling yaw orientation at this scale.

Onboard power remains a major challenge for miniature robotic platforms. Locomotion at small scales demands high power densities from all system components, while limited payload capacities place severe restrictions on the size of the energy source, resulting in integration challenges and short operating times when using conventional batteries. Wireless power delivery has the potential to allow microrobotic platforms to operate autonomously for extended periods when near a transmitter. This paper describes the first demonstration of RF wireless power transfer in an insect-scale ambulatory robot. A wireless power transmission system based on magnetically coupled resonance is designed for the latest iteration of the Harvard Ambulatory MicroRobot (HAMR), a piezoelectrically driven quadruped that had previously received power through a tether. Custom power and control electronics are designed and implemented on lightweight printed circuit boards that form a part of the mechanical structure of the robot. The integration of the onboard receiver, power and control electronics, and mechanical structure yields a 4cm, 2.1g robot that can operate autonomously in two wireless power transmission scenarios.

We present a method for setting the pressure of multiple chambers using a single pressure source when they are interconnected via band-pass valves. These valves can be constructed from simple passive devices that behave like leaky check valves. We present the theory of operation and design parameters for individual valves, give a control strategy for serial connections of pressure chambers, and demonstrate the approach by building prototype valves and using them to control serially connected soft-robotic actuators from a single pressure source.

Transmission and actuator selection are crucial for robot locomotion at any scale. This is especially true at small scales where actuation choices are limited and locomotion is energetically expensive. These components control the payload capacity and determine the height of the obstacles the robot can navigate over. In this study, we analyze the drivetrain of the new Harvard Ambulatory MicroRobot (HAMR-V) to improve its walking performance. We modeled several transmission and actuator design concepts and investigated their force and displacement outputs. The results led to the selection of improved actuator and transmission designs. Using these new insights, we constructed a miniature quadruped with a payload capacity of 63% of its weight that can be used for on-board electronics for sensing, control, and power.

We present the design of a soft wearable robotic device composed of elastomeric artificial muscle actuators and soft fabric sleeves, for active assistance of knee motions. A key feature of the device is the two-dimensional design of the elastomer muscles that not only allows the compactness of the device, but also significantly simplifies the manufacturing process. In addition, the fabric sleeves make the device lightweight and easily wearable. The elastomer muscles were characterized and demonstrated an initial contraction force of 38N and maximum contraction of 18mm with 104kPa input pressure, approximately. Four elastomer muscles were employed for assisted knee extension and flexion. The robotic device was tested on a 3D printed leg model with an articulated knee joint. Experiments were conducted to examine the relation between systematic change in air pressure and knee extension-flexion. The results showed maximum extension and flexion angles of 95° and 37°, respectively. However, these angles are highly dependent on underlying leg mechanics and positions. The device was also able to generate maximum extension and flexion forces of 3.5N and 7N, respectively.

Self-assembled structures and machines can be made using origami-inspired manufacturing methods. In particular, self-folding of two-dimensional materials using shape memory polymers and embedded electrical circuits has been utilized to build robots and structures in an inexpensive and rapid manner. In order to build increasingly complex and functional self-folding machines, however, methods for interaction with the environment are necessary. This paper presents and characterizes three types of self-folding sensors: a mechanical switch, a capacitive contact sensor, and a velocity sensor. We utilize specialized fold patterns to create cyclic mechanical linkages as well as additional composite layers such as magnetic sheets to build these sensors. We demonstrate the integration of two of these sensors, the switch and the contact sensor, into a lamp that can self-fold and immediately begin responding to its surroundings.

The design of flapping wing robots and the study of flapping wing flyers requires a detailed knowledge of how wings interact with the surrounding fluid. However, the unsteady nature of fluid-structure interactions during flapping wing flight render analytical design of wing shapes and motion kinematics difficult. We propose that flapping wing micro aerial vehicle (MAV) design will benefit from a complimentary, datadriven approach in which wing shape, material properties, and stroke-kinematics may be varied rapidly. Here, we present a high-throughput experimental apparatus for fabrication and optimization of MAV wings for flapping flight. This apparatus incorporates the collection and analysis of multiple sensor modalities including force, electrical power, resultant fluid flow, and wing kinematics into the experiment control loop. This “analysis-in-the-loop” methodology enables multivariate optimization routines for flapping flight of unmanned aerial vehicles. We demonstrate the validity of this approach through optimization experiments on wing kinematics, fluid flow, lift and power consumption.

The ability to measure human hand motions and interaction forces is critical to improving our understanding of manual gesturing and grasp mechanics. This knowledge serves as a basis for developing better tools for human skill training and rehabilitation, exploring more effective methods of designing and controlling robotic hands, and creating more sophisticated human-computer interaction devices which use complex hand motions as control inputs. This paper presents work on the design, fabrication, and experimental validation of a soft sensor-embedded glove which measures both hand motion and contact pressures during human gesturing and manipulation tasks. We design an array of liquid-metal embedded elastomer sensors to measure up to hundreds of Newtons of interaction forces across the human palm during manipulation tasks and to measure skin strains across phalangeal and carpal joints for joint motion tracking. The elastomeric sensors provide the mechanical compliance necessary to accommodate anatomical variations and permit a normal range of hand motion. We explore methods of assembling this soft sensor glove from modular, individually fabricated pressure and strain sensors and develop design guidelines for their mechanical integration. Experimental validation of a soft finger glove prototype demonstrates the sensitivity range of the designed sensors and the mechanical robustness of the proposed assembly method, and provides a basis for the production of a complete soft sensor glove from inexpensive modular sensor components.

Articulation based on flexure hinges is increasingly popular in microrobotics because of the absence of Coulomb friction, ease of manufacturability, fluid motion, durability, and large angular ranges. However, the inherent flexibility of these hinges makes modeling very complex and specific to the particular engineering applications for which they were developed. In this paper we describe the development and testing of a simplified, versatile method for modeling the stress on a flexure hinge under multi-axis loads in order to maximize hinge lifespan. We also discuss other stress concentration reducing features and design rules that can be applied to more general flexure hinge designs to further extend hinge lifespan.

Locomoting soft robots typically walk or crawl slowly relative to their rigid counterparts. In order to execute agile behaviors such as jumping, rapid actuation modes are required. Here we present an untethered soft-bodied robot that uses a combination of pneumatic and explosive actuators to execute directional jumping maneuvers. This robot can autonomously jump up to 0.6 meters laterally with an apex of up to 0.6 meters (7.5 times it's body height) and can achieve targeted jumping onto an object. The robot is able to execute these directed jumps while carrying the required fuel, pneumatics, control electronics, and battery. We also present a thermodynamic model for the combustion of butane used to power jumping, and calculate the theoretical maximum work output for the design. From experimental results, we find the mechanical efficiency of this prototype to be 0.8%.

This paper presents the design, analysis, and characterization of a compliant thoracic mechanism that saves inertial power for flapping-wing micro air vehicles. Lightweight polyimide film hinges were previously integrated into a compliant flapping-wing mechanism to reduce friction. However, these were not stiff enough to fully recover wing's inertial energy into elastic energy. To store adequate elastic energy using film hinges, we develop a compliant thoracic mechanism with nonlinear stiffness characteristics by mimicking a Dipteran insect's flight thorax. This thoracic mechanism consists of rigid plates and polyimide film hinges connected to form a closed shell structure. It has a nonlinearly increasing stiffness so that it can slow the wings down rapidly toward the end stroke and subsequently help reverse the wings. It demonstrates almost full recovery of inertial power for 10-cm span flapping wings up to 25 Hz. As a result, it only expends 2% of the total mechanical power on inertial power at 25 Hz. In contrast, the rigid-body mechanism with no elastic storage expends 23% of the total mechanical power on inertial power when the same wings beat at the same frequency. With the capability of elastic energy storage, this compliant thoracic mechanism saves power expenditure ranging from 20 up to 30% to produce the same thrust, in comparison with the rigid-body flapping mechanism. This study shows that power saving is effective only if elastic energy storage is well tuned to recover the wing inertial power.

A novel robotic sensor is proposed to measure both the contact angle and the force acting between the tip of a surgical robot and soft tissue. The sensor is manufactured using a planar lithography process that generates microchannels that are subsequently filled with a conductive liquid. The planar geometry is then molded onto a hemispherical plastic scaffolding in a geometric configuration enabling estimation of the contact angle (angle between robot tip tangent and tissue surface normal) by the rotation of the sensor around its roll axis. Contact force can also be estimated by monitoring the changes in resistance in each microchannel. Bench top experimental results indicate that, on average, the sensor can estimate the angle of contact to within ±2° and the contact force to within ±5.3 g.

Experimentally collected flight dynamics data of flapping-wing microrobots reveals several characteristics that cannot be captured by the information gathered from static experiments. For an insect-sized flapping-wing micro air vehicle with air dampers, we show that a physics-based quasi-steady aerodynamic model is able to predict the flight dynamics with reasonable accuracy. The proposed model is optimized for the vehicle of interest through the use of learning algorithms. The identified model demonstrates the potential for future use in control applications.

Printing and folding are fast and inexpensive methods for prototyping complex machines. Self-assembly of the folding step would expand the possibilities of this method to include applications where external manipulation is costly, such as micro-assembly, mass production, and space applications. This paper presents a method for self-folding of printed robots from two-dimensional materials based on shape memory polymers actuated by joule heating using embedded circuits. This method was shown to be capable of sequential folding, angle-controlled folds, slot-and-tab assembly, and mountain and valley folds. An inchworm robot was designed to demonstrate the merits of this technique. Upon the application of sufficient current, the robot was able to fold into its functional form with fold angle deviations within six degrees. This printed robot demonstrated locomotion at a speed of two millimeters per second.

This paper discusses recent developments in sensors for the Harvard RoboBee. The RoboBee is a sub-100 mg flapping-wing micro-aerial vehicle that is able to lift its own weight under external power, but, like flying insects, is unstable in flight without active feedback. We discuss design and characterization of two low-latency insect-inspired sensors for flight control: an antenna to sense airspeed and light-sensing ocelli to estimate attitude angle relative to a luminous sky. We demonstrate accurate wind velocity estimation in a wind tunnel despite the effect of nearby flapping wings.We also demonstrate pitch angle control using the ocelli on a wire-mounted RoboBee that is free to rotate about its pitch axis. These flight-weight sensors are essential first steps toward autonomous upright stability and controlled forward motions.

Motion sensing has played an important role in the study of human biomechanics as well as the entertainment industry. Although existing technologies, such as optical or inertial based motion capture systems, have relatively high accuracy in detecting body motions, they still have inherent limitations with regards to mobility and wearability. In this paper, we present a soft motion sensing suit for measuring lower extremity joint motion. The sensing suit prototype includes a pair of elastic tights and three hyperelastic strain sensors. The strain sensors are made of silicone elastomer with embedded microchannels filled with conductive liquid. To form a sensing suit, these sensors are attached at the hip, knee, and ankle areas to measure the joint angles in the sagittal plane. The prototype motion sensing suit has significant potential as an autonomous system that can be worn by individuals during many activities outside the laboratory, from running to rock climbing. In this study we characterize the hyperelastic sensors in isolation to determine their mechanical and electrical responses to strain, and then demonstrate the sensing capability of the integrated suit in comparison with a ground truth optical motion capture system. Using simple calibration techniques, we can accurately track joint angles and gait phase. Our efforts result in a calculated trade off: with a maximum error less than 8%, the sensing suit does not track joints as accurately as optical motion capture, but its wearability means that it is not constrained to use only in a lab.

Control of insect-scale flapping-wing robots is challenging due to weight constraints and inherent instabilities. Instead of adding more actuators to increase the controllability of the flapping-wing robot, we use a single actuator to drive a system of mechanical linkages to cause bilaterally asymmetric changes in the wing hinge spring rest angle of the left and right wings. We show in simulation that such a control input can generate wing motions which produce yaw and roll torques. A kinematic model of the mechanism was developed and an at-scale prototype of this concept was built. High speed videos of its wing motions are consistent with the kinematic model and according to the simulation, are capable of generating adequate yaw and roll torques for attitude control.

In this paper we present a soft lower-extremity robotic exosuit intended to augment normal muscle function in healthy individuals. Compared to previous exoskeletons, the device is ultra-lightweight, resulting in low mechanical impedance and inertia. The exosuit has custom McKibben style pneumatic actuators that can assist the hip, knee and ankle. The actuators attach to the exosuit through a network of soft, inextensible webbing triangulated to attachment points utilizing a novel approach we call the virtual anchor technique. This approach is designed to transfer forces to locations on the body that can best accept load. Pneumatic actuation was chosen for this initial prototype because the McKibben actuators are soft and can be easily driven by an off-board compressor. The exosuit itself (human interface and actuators) had a mass of 3500 g and with peripherals (excluding air supply) is 7144 g. In order to examine the exosuit's performance, a pilot study with one subject was performed which investigated the effect of the ankle plantar-flexion timing on the wearer's hip, knee and ankle joint kinematics and metabolic power when walking. Wearing the suit in a passive unpowered mode had little effect on hip, knee and ankle joint kinematics as compared to baseline walking when not wearing the suit. Engaging the actuators at the ankles at 30% of the gait cycle for 250 ms altered joint kinematics the least and also minimized metabolic power. The subject's average metabolic power was 386.7 W, almost identical to the average power when wearing no suit (381.8 W), and substantially less than walking with the unpowered suit (430.6 W). This preliminary work demonstrates that the exosuit can comfortably transmit joint torques to the user while not restricting mobility and that with further optimization, has the potential to reduce the wearer's metabolic cost during walking.

Here we present the design of a 1.27g quadrupedal microrobot manufactured using “Pop-up book MEMS” the first such device capable of locomotion. Implementing popup assembly techniques enables manufacturing of the robot's exoskeleton and drivetrain transmissions from a single 23-layer laminate. Its demonstrated capabilities include payload capacity greater than 1.35g (106% of body mass), maneuverability on flat terrain, and high-speed locomotion up to 37cm/s. Additionally, locomotion performance is compared to a hand-assembled quadruped with similar design parameters. The results demonstrate that the pop-up manufacturing methodology enables more complex mechanisms while simultaneously increasing performance over hand-assembled alternatives.

Challenges for controlled flight of a robotic insect are due to the inherent instability of the system, complex fluid-structure interactions, and the general lack of a complete system model. In this paper, we propose theoretical models of the system based on the limited information available from previous work and a comprehensive adaptive flight controller that is capable of coping with uncertainties in the system. We have demonstrated that the proposed methods enable the robot to achieve sustained hovering flights with relatively small errors compared to a similar but non-adaptive approach. Furthermore, vertical takeoff and landing flights are also shown to illustrate the fidelity of the flight controller.

This paper presents a wing characterization method for insect-scale flapping-wing robots. A quasi-steady model is developed to predict passive wing pitching at mid-stroke. Millimeter scale wings and passive hinges are manufactured using the SCM fabrication processes. Flapping experiments at various frequencies and driving voltages are performed to extract kinematics for comparison with the quasi-steady predictions. These experiments examine the validity of the quasi-steady model and demonstrate the robustness of the wing characterization method. In addition, because time-averaged lift and drag are strongly correlated with flapping kinematics, quasi-steady prediction of wing kinematics directly leads to predictions of lift and drag generation. Given a flapping frequency and a driving voltage, the model computes the hinge stiffness that leads to optimal flapping kinematics. This reduces the number of flapping experiments required for wing characterization by a factor of four.

The small scale of minimally-invasive surgery (MIS) presents significant challenges to developing robust, smart, and dexterous tools for manipulating millimeter and sub-millimeter anatomical structures (vessels, nerves) and surgical equipment (sutures, staples). Robotic MIS systems offer the potential to transform this medical field by enabling precise repair of these miniature tissue structures through the use of teleoperation and haptic feedback. However, this effort is currently limited by the inability to make robust and accurate MIS end effectors with integrated force and contact sensing. In this paper, we demonstrate the use of the novel Pop-Up Book MEMS manufacturing method to fabricate the mechanical and sensing elements of an instrumented MIS grasper. A custom thin-foil strain gage was manufactured in parallel with the mechanical components of the grasper to realize a fully-integrated electromechanical system in a single manufacturing step, removing the need for manual assembly, bonding and alignment. In preliminary experiments, the integrated grasper is capable of resolving forces as low as 30 mN, with a sensitivity of approximately 408 mV/N. This level of performance will enable robotic surgical systems that can handle delicate tissue structures and perform dexterous procedures through the use of haptic feedback guidance.

This paper explores the use of mechanical redundancy to enhance robustness to leg failures in miniature ambulatory robots. Graceful degradation, rather than immediate catastrophic failure, is exhibited experimentally in 10-20 leg centipede-inspired millirobots as legs are removed without altering the gait, using speed and radius of curvature as performance metrics. Static stability retention is examined as a function of the nominal number of legs, and for cases where static stability is lost, two gait options are tested. The effect of location of missing legs on performance is also described.

The design and the fabrication of a mesoscale jumping robotic insect are presented. The basis of the robot is a torque reversal catapult mechanism, inspired by a flea's jumping leg. The current robot structure is 20mm in length, 2mm in height and weighs 34mg. The smart composite microstructures (SCM) process is used to developing the mesoscale structures and articulated, flexure-based mechanisms of the leg. Furthermore, the design is compatible with the pop-up book MEMS process, ameliorating the laborious assembly process of small components. The robot prototype can achieve jumps of approximately 30cm with a 2.7m/s initial velocity. It is 150 times its body height. The effect of air resistance is considered in order to improve jumping performance with the light weight body structure. The air resistance efficiency (Jumping height in air (hv) / Jumping height in vacuum (hv)) is computed to be 0.83 and the robot exhibits a drag coefficient of 1.8.

Insect-scale legged robots have the potential to locomote on rough terrain, crawl through confined spaces, and scale vertical and inverted surfaces. However, small scale implies that such robots are unable to carry large payloads. Limited payload capacity forces miniature robots to utilize simple control methods that can be implemented on a simple onboard microprocessor. In this study, the design of a new version of the biologically-inspired Harvard Ambulatory MicroRobot (HAMR) is presented. In order to find the most suitable control inputs for HAMR, maneuverability experiments are conducted for several drive parameters. Ideal input candidates for orientation and lateral velocity control are identified as a result of the maneuverability experiments. Using these control inputs, two simple feedback controllers are implemented to control the orientation and the lateral velocity of the robot. The controllers are used to force the robot to track trajectories with a minimum turning radius of 55 mm and a maximum lateral to normal velocity ratio of 0.8. Due to their simplicity, the controllers presented in this work are ideal for implementation with on-board computation for future HAMR prototypes.

Nature regularly uses self-folding as an efficient approach to automated fabrication. In engineered systems, however, the use of self-folding has been primarily restricted to the assembly of small structures using exotic materials and/or complex infrastructures. In this paper we present three approaches to the self-folding of structures using low-cost, rapid-prototyped shape memory laminates. These structures require minimal deployment infrastructure, and are activated by light, heat, or electricity. We compare the fabrication of a fundamental structure (a cube) using each approach, and test ways to control fold angles in each case. Finally, for each self-folding approach we present a unique structure that the approach is particularly suited to fold, and discuss the advantages and disadvantages of each approach.

This paper studies flapping-wing micro air vehicles (FWMAV) whose transmission mechanisms use flexures as energy storage elements to reduce needed input power. A distinguishing feature of the proposed four-bar mechanism is the use of rubber-based flexures in two of its joints. These lightweight and compact flexures have been used for the first time in the design of an FWMAV whose projected total weight is approximately 3 g. This paper discusses in detail how the flexures were designed and how the challenges associated with their fabrication were met. Flexure stiffnesses were chosen based upon a simple, computationally efficient model of the four-bar mechanism actuated by an electric motor to flap two wings at 18 Hz. An instrumented test stand was designed to easily replace the upper part of the four-bar flexure mechanism and wings, and it was used to experimentally determine the power savings associated with flexures of different stiffnesses. While the measured power savings (maximum of 20%) may seem modest, they were nevertheless significant, considering that the use of the rubber-based flexures produced approximately 0.3 g added thrust at a less than 1% cost in weight (0.02 g).

We present experimental results on the controlled vertical flight of a flapping-wing flying microrobot, in which for the first time an on-board sensing system is used for measuring the microrobot's altitude for feedback control. Both the control strategy and the sensing system are biologically inspired. The control strategy relies on amplitude modulation mediated by optical flow. The research presented here is a key step toward achieving the goal of complete autonomy for flying microrobots, since this demonstrates that strategies for controlling flapping-wing microrobots in vertical flight can rely on optical flow sensors.

This paper presents measurements of open-loop roll, pitch and yaw torques, and open-loop flight experiments for an insect-sized robotic bee. Torques are generated entirely with flapping wings via an actuation scheme that uses a single, central power actuator and two smaller control actuators that fine-tune wing motion. We present an initial 110mg design used for torque measurements and a lighter 83mg prototype that is capable of liftoff with external power and can execute open loop pitching and rolling maneuvers.

Micromanipulation methods used for complicated tasks such as microrobot assembly and microvascular surgery often lack the force reflection and contact localization capability necessary to achieve robust grasps of micro-scale objects without applying excessive forces. This absence of haptic feedback is especially prohibitive in cases where visual evidence of force application, such as object surface deformation, is imperceptible and where unstructured, dynamically changing environments require force sensing and modulation for safe, atraumatic object manipulation. This paper describes the design, fabrication, and experimental validation of a soft tactile sensor array for sub-millimeter contact localization and contact force measurement during micromanipulation. The geometry and placement of conductive liquid embedded channels within the sensor array are optimized to provide adequate sensitivity for representative micro-manipulation tasks. Mechanical testing of the sensor demonstrates a sensitivity of less than 50mN and contact localization resolution on the order of 100's of microns.

Alternating gliding and active propulsion is a potentially energy saving strategy for small-scale flight. With the goal of finding optimal wing shapes for flapping-gliding robots we evaluate the quasi-steady aerodynamic performance of four butterfly species (Monarch (Danaus plexippus), the Orange Aeroplane (Pantoporia consimilis), the Glasswing (Acraea andromacha) and the Four-barred Swordtail (Protographium Ieosthenes)). We fabricate at-scale wing models based on measured wing shapes and vary the forewing angle in nine steps to account for the ability of the butterfly to change the relative orientation of its forewing and hindwing during flight. For comparison we include twelve non-biological planforms as performance benchmarks for the butterfly wing shapes. We then test these 48 wing models at 2m/s, 3.5m/s and 5m/s (Reynolds number between 2597 and 12632) in a low speed wind tunnel which allows lift and drag force measurements of centimeter-size wings. The results indicate that the forewing orientation which maximizes the wing span offers the best gliding performance and that overall the gliding ratios are highest at 3.5m/s. The wing shapes with the best gliding ratio are found in the Glasswing butterfly with a maximum of 6.26 which is very high compared to the gliding performance of similarly sized flying robots. The results from this study are important for the development of novel biologically-inspired flying micro robots as well as for biomechanics studies in biology.

The split actuator microrobotic bee is the first flight-capable, insect-scale flapping-wing micro air vehicle that uses “split-cycle” constant-period frequency modulation to control body forces and torques. Building this vehicle is an intricate challenge, but by leveraging a maturing fabrication technology for microscale devices, we have developed a solution to tackle the design and fabrication difficulties. We show that the design is able to independently modulate the motions of both wings and produce roll, pitch, and yaw torques, as well as a peak lift force of 1.3 mN, in a 70mg package.

A proposed adaptive soft orthotic device performs motion sensing and production of assistive forces with a modular, pneumatically-driven, hyper-elastic composite. Wrapping the material around a joint will allow simultaneous motion sensing and active force response through shape and rigidity control. This monolithic elastomer sheet contains a series of miniaturized pneumatically-powered McKibben-type actuators that exert tension and enable adaptive rigidity control. The elastomer is embedded with conductive liquid channels that detect strain and bending deformations induced by the pneumatic actuators. In addition, the proposed system is modular and can be configured for a diverse range of motor tasks, joints, and human subjects. This modular functionality is accomplished with a decentralized network of self-configuring nodes that manage the collection of sensory data and the delivery of actuator feedback commands. This paper mainly describes the design of the soft orthotic device as well as actuator and sensor components. The characterization of the individual sensors, actuators, and the integrated device is also presented.

This paper describes the development of a unique flapping-wing micro air vehicle (FWMAV) whose major components, i.e. the motor, transmission mechanisms, and wings, are rapidly interchangeable. When coupled with a test stand that includes a 6-axis force sensor, encoder, power-recording capabilities, and high speed video, the result is a highly versatile experimental platform on which system integration studies can be conducted. This paper provides a detailed description of the design and fabrication of this FWMAV whose interchangeability of parts is mostly accomplished through a novel system of tabs, slots, and retaining rods. Results of a study on energy saving elements in the transmission mechanism as well as an exploration of this effect for different wing sizes are also presented. Finally, the implications of interchangeable parts on the creation of customizable flyers are discussed.

The Harvard RoboBee is the first insect-scale cflapping-wing robot weighing less than 100 mg that is able to lift its own weight. However, when flown without guide wires, this vehicle quickly tumbles after takeoff because of instability in its dynamics. Here, we show that by adding aerodynamic dampers, we can can alter the vehicle's dynamics to stabilize its upright orientation. We provide an analysis using wind tunnel experiments and a dynamic model. We demonstrate stable vertical takeoff, and using a marker-based external camera tracking system, hovering altitude control in an active feedback loop. These results provide a stable platform for both system dynamics characterization and unconstrained active maneuvers of the vehicle and represent the first known hovering demonstration of an insect-scale flapping-wing robot.

A hyperelastic, thin, transparent pressure sensitive keypad is fabricated by embedding a silicone rubber film with conductive liquid-filled microchannels. Applying pressure to the surface of the elastomer deforms the cross-section of underlying microchannels and changes the electrical resistance across the affected channels. Perpendicular conductive channels form a quasi-planar network within an elastomeric matrix that registers the location, intensity and duration of applied pressure. Pressing channel intersections of the keypad triggers one of twelve keys, allowing the user to write any combination of alphabetic letters. A 5% change in channel output voltage must be achieved to trigger a key. It is found that approximately 100 kPa of pressure is necessary to produce a 5% change in voltage across a conductive microchannel that is 20 microns in height and 200 microns in width. Sensitivity of the keypad is tunable via channel geometry and choice of elastomeric material.

We present the design and fabrication of centimeter scale robots, which use inchworm-like motion and bidirectional claws. Two prototypes for different locomotion goals were built utilizing these two characteristics: Type I is designed particularly for horizontal surfaces utilizing two linear actuators and compliant claws. This robot is capable of steering and straight motion by utilizing directionally anisotropic friction. Type II is a variant of Type I that is designed for locomotion on ferromagnetic ceilings or vertical planes by using permanent magnets. The Smart Composite Microstructures (SCM) technique enables versatile and multi-jointed meso-scale devices suitable for such robots.

This work presents a technique which allows the application of 2-D fabrication methods to build 3-D robotic systems. The ability to print robots introduces a fast and low-cost fabrication method to modern, real-world robotic applications. To this end, we employ laser-engraved origami patterns to build a new class of robotic systems for mobility and manipulation. Origami is suitable for printable robotics as it uses only a flat sheet as the base structure for building complicated functional shapes, which can be utilized as robot bodies. An arbitrarily complex folding pattern can be used to yield an array of functionalities, in the form of actuated hinges or active spring elements. For actuation, we use compact NiTi coil actuators placed on the body to move parts of the structure on-demand. We demonstrate, as a proof-of-concept case study, the end-to-end fabrication and assembly of a simple mobile robot that can undergo worm-like peristaltic locomotion.

Here we present an autonomous 1.7g hexapod robot as a platform for research on centimeter-scale walking robots. It features six spherical five-bar linkages driven by high energy density piezoelectric actuators and onboard power and control electronics. This robot has achieved autonomous ambulation using an alternating tripod gait at speeds up to 0.9 body lengths per second, making this the smallest and lightest hexapod robot capable of autonomous locomotion.

Robot audition, which aims at multiple simultaneous human-robot communications in noisy environments, has undergone rapid development since last decade. For a common scenario, robot audition systems usually generate a huge amount of chronological data. These data fall into several categories: sound source locations and orientations, separated sound sources and recognized speeches. In order to efficiently assist people in understanding and analyzing the scenario, it is necessary to organize the data in a delicate way. To achieve this goal, we suggest Speech Arrow which conveys recognized speeches in animated arrow shaped frames. Speech Arrow is highly integrated, intuitive and vivid. In this paper, a single pane auditory scene visualizer is implemented to support Speech Arrow. The visualizer is 3D real-time virtual reality system based on the open source robot audition system HARK. It includes two versions, one of which restores original auditory scenes with offline raw data. The other analyzes and displays online instant data without any delay to help hearing impaired people. We demonstrate that our visualizer improves auditory awareness considerably with experiments.

Motivated by the need for torque sensing in the ¿Nm range for experiments with insect-sized flapping-wing robots, we present the design, fabrication and testing of a custom single-axis torque sensor. The micorobots in question are too large for MEMS force/torque sensors used for smaller live insects such as fruit flies, but too small to produce torques within the dynamic range of commercially available force/torque sensors. Our sensor consists of laser-machined Invar sheets that are assembled into a three dimensional beam. A capacitive displacement sensor is used to measure displacement of a target plate when the beam rotates, and the output voltage is correlated to applied torque. Sensor bandwidth, range, and resolution are designed to match the criteria of the robotic fly experiments while remaining insensitive to off-axis loads. We present a final sensor design with a range of ±130¿Nm, a resolution of 4.5nNm, and bandwidth of 1kHz.

Abstract — Flapping-wing robots typically include numerous nonlinear elements, such as nonlinear geometric and aerodynamic components. For an insect-sized flapping-wing micro air vehicle (FWMAV), we show that a linearized model is sufficient to predict system behavior with reasonable accuracy over a large operating range, not just locally around the linearization state. The theoretical model is verified against an identified model from a prototype robotic fly and implications for vehicle design are discussed. I.

The use of piezoelectric materials as actuators or sensors is widespread, and numerous actuator topologies and models have been developed. However, many of these applications do not place stringent requirements on actuator mass or energy density. Motivated by applications that do have strict requirements in these areas such as flapping-wing microrobots, a torsional piezoelectric actuator is developed. A model is presented that predicts output rotation, torque and energy density values; and allows optimization of these values based on actuator geometry. An emphasis is placed on actuator fabrication and testing for empirical validation of the model.

The performance of a swarm of robots depends on the hardware quality of the robots in the swarm. A swarm of robots with high-quality sensors and actuators is expected to out-perform a swarm of robots with low-quality sensors and actuators. This paper directly investigates the relationship between hardware quality and swarm performance. We take three common components of swarm algorithms (trail following, swarm expansion, and shape formation) and measure how they are affected by two common types of hardware inaccuracy (communication bearing reception error, and movement error) both in simulation and with E-Puck robots. We find that large amounts of both types of hardware error are required before performance appreciably decreases.

The design and modeling of a segmented myriapod millirobot with a compliant body is presented. A dynamic model is used to demonstrate how body undulations can result from only varying the phase difference in the stance change between adjacent segments - even with passive intersegmental connections - and how these gaits affect locomotion. Different gaits are demonstrated experimentally in a 20-leg, 2.2 gram millirobot, and the resulting motion is compared to that predicted by the simulation. Both simulation and experiments show that undulatory gaits can increase the average speed of straight-line locomotion as compared to non-undulatory gaits for the same stepping frequency. The model and the millirobot can be used concurrently with biological studies to understand aspects of myriapod locomotion. This robot is also a useful tool to gain insight into how flexibility can be introduced into robots at this scale to enhance locomotion.

We introduce a curvature sensor composed of a thin, transparent elastomer film (polydimethylsiloxane, PDMS) embedded with a microchannel of conductive liquid (eutectic Gallium Indium, eGaIn) and a sensing element. Bending the sensor exerts pressure on the embedded microchannel via the sensing element. Deformation of the cross-section of the microchannel leads to a change in electrical resistance. We demonstrate the functionality of the sensor through testing on a finger joint. The film is wrapped around a finger with the sensing element positioned on top of the knuckle. Finger bending both stretches the elastomer and exerts pressure on the sensing element, leading to an enhanced change in the electrical resistance. Because the sensor is soft (elastic modulus E ~ 1 MPa) and stretchable (>350%), it conforms to the host bending without interfering with the natural mechanics of motion. This sensor represents the first use of liquid-embedded elastomer electronics to monitor human or robotic motion.

Programmable materials based on robotic origami have been demonstrated with the capability to fold into 3D shapes starting from a nominally 2D sheet. This concept requires high torque density actuators, flexible electronics and an integrated substrate. We report on two types of stretchable circuitry that are directly applicable to robotic origami: meshed copper traces and liquid-metal-filled channels in an elastomer substrate. Both methods maintain conductivity even at large strains (during stretching) and curvatures (during folding). Both circuit designs are integrated with a tiled origami module actuated by a shape memory alloy actuator. We also integrate a soft curvature sensor into the robotic origami module that measures the full range of motion of the module in real-time.

We describe the design of an active soft ankle-foot orthotic device powered by pneumatic artificial muscles for treating gait pathologies associated with neuromuscular disorders. The design is inspired by the biological musculoskeletal system of a human foot and a lower leg, and mimics the muscle-tendon-ligament structure. A key feature of the device is that it is fabricated with flexible and soft materials that provide assistance without restricting degrees of freedom at the ankle joint. Three pneumatic artificial muscles assist dorsiflexion as well as inversion and eversion. The prototype is also equipped with various embedded sensors for gait training and gait pattern analysis. The prototype is capable of 12° dorsiflexion from a resting position of an ankle joint and a 20° dorsiflexion from plantarflexion. Results of early feedback control experiments show controllability of ankle joint angles. Ultimately, we envision a system that not only can provide physical support to improve mobility but also can increase safety and stability during walking, while enhancing muscle usage and encouraging rehabilitation.

The kinematic design of a multi-segment ambulatory microrobot inspired by centipedes is presented. The kinematics of five repeated segments joined by a flexible backbone of rigid links and flexures are described and simulated. The kinematic model was used to guide the design of an individual two degree of freedom segment, which was fabricated using the Smart Composite Microstructures process. Testing and analysis of a suspended segment displayed motion similar to that predicted by the model. Multiple segments can be joined to a flexible backbone to create a multi-segment structure capable of a variety of gaits. Due to its modular, multi-legged, and compact design, this robot has the potential to serve as a platform for swarm robotics applications, advance control techniques for ambulatory systems, and inspire batch fabrication of microrobots.

This paper presents a soft robotic platform that exhibits peristaltic locomotion. The design principle is based on the unique antagonistic arrangement of radial/circular and longitudinal muscle groups of Oligochaeta. Sequential antagonistic motion is achieved in a flexible braided mesh-tube structure with NiTi coil actuators. A numerical model for the mesh structure describes how peristaltic motion induces robust locomotion and details the deformation by the contraction of NiTi actuators. Several peristaltic locomotion modes are modeled, tested, and compared on the basis of locomotion speed. The entire mechanical structure is made of flexible mesh materials and can withstand significant external impacts during locomotion. This approach can enable a completely soft robotic platform by employing a flexible control unit and energy sources.

Here we present the design, modeling, and fabrication of a 2g mobile robot. By applying principles from biology and existing meso-scale fabrication techniques, a 5.7cm hexapod robot with sprawled posture has been created, and is capable of locomotion up to 4 body-lengths per second using the alternating tripod gait at 20Hz actuation frequency. Furthermore, this work proves the viability of a new mechanical linkage design, fabricated using the smart composite microstructure process, to provide desirable leg trajectories for successful ambulation at the insect-scale.

Wing motion in most flapping-wing micro air vehicles (MAVs) is restricted to a flat stroke plane in order to simplify analysis and mechanism design. An MAV actuation and transmission design capable of controlling flapping motions and deviations from the mean stroke plane using relatively simple modifications to a proven design is presented. This allows preliminary investigation into more power-efficient wing trajectories, an important concern for small MAVs. A theoretical quasi-steady model of flapping wing flight is used to predict wing motions, and these predicted trajectories are compared to empirically observed trajectories from a test device. The ratio of average lift to average aerodynamic power is used as an efficiency metric to compare stroke trajectories.

Flapping-wing mechanisms inspired by biological insects have the potential to enable a new class of small, highly maneuverable aerial robots with hovering capabilities. In order for such devices to operate without an external power source, it is necessary to address a complex system design challenge: the integration of all of the required components on board the robot. This paper discusses the flight energetics of flapping-wing robotic insects with the goal of selecting design parameters that enable power autonomy and maximize flight time. The subsystems of the robot are analyzed both from a broad perspective and using a detailed set of models for a piezoelectrically driven two-wing design. The models are used to perform a system-level optimization for the maximum flight time permitted by current technology, compare the resulting robot configurations to biological insects across several key metrics, and discuss the effect of performance gains in various subsystems of the robot.

Dielectric-elastomer minimum-energy structures (DEMES) form an emerging class of soft robotic systems. The appropriate materials and methods for rapidly fabricating DEMES prototypes are described. A DEMES component suitable for use in highly-deformable soft robots is presented and analyzed. Combinations of this component into snakelike robots are also presented. Calculations for determining the upper limit of a DEMES's mechanical work output, electromechanical efficiency, and energy density are described. The scope of the DEMES design-space and future research paths are discussed.

The Harvard Microrobotics Lab has previously demonstrated the world's first at-scale robotic insect capable of vertical takeoff with external power. Both of the robot's wings were driven by a single power actuator and 1-DOF mechanical transmission-making independent control of both wings, and therefore asymmetric flapping and the generation of a net body torque, impossible. This paper presents a method to modulate body torques by altering the kinematics of each wing transmission independently, via the introduction of two additional control actuators. Theoretical kinematic and dynamic predictions based on a pseudo-rigid body model are compared to the observed wing trajectories. Controllable body torques are necessary for the development of control algorithms for eventual stable hovering and free flight.

Piezoelectric actuators can achieve high efficiency and power density in very small geometries, which shows promise for microrobotic applications, such as flapping-wing robotic insects. From the perspective of power electronics, such actuators present two challenges: high operating voltages, ranging from tens to thousands of volts, and a low electromechanical coupling factor, which necessitates the recovery of unused electrical energy. This paper explores the power electronics design problem by establishing the drive requirements of piezoelectric actuators, presenting circuit topologies and control methods suitable for driving different types of piezoelectric actuators in microrobotic applications, and demonstrating experimental realizations of sub-100 mg power electronics circuits.

This paper continues the exploration of the design space for an insect-sized autonomous flapping-wing MAV with the goal of stable hovering. Previous work has focused on the use of a large primary power actuator to generate flapping motion and smaller ¿control¿ actuators to asymmetrically alter wing kinematics. Here a new iteration of this concept is presented, merging the two actuator types to create a ¿hybrid¿ power-control actuator. Kinematic and dynamic models for wing motion are presented, and the predictions of these models are compared to experimental results from a prototype design. Controllable asymmetry in wing kinematics can be mapped into controllable body torques via an aerodynamic model, and this information can be used for the generation of control laws for stable hover and eventually highly agile aerial vehicles.

For a new class of soft robotic platforms, development of flexible and robust actuators is quintessential. Remarkable resilience, shape memory effect, high energy density, and scalability are attributed to nickel titanium (NiTi) making it an excellent actuator candidate for meso-scale applications. This paper presents a micro-muscle fiber crafted from shape memory alloy (NiTi) coiled springs. An enhanced spring NiTi model describes the combination of martensite deformation and spring effect due to its geometry. This paper also describes a manufacturing process and characterization for micro-scale NiTi coil actuators in various annealing temperatures. The presented fiber is 400µm in diameter and 0.5m in length exhibiting 50% contraction and 1226J/kg of energy density with 40g of force. By changing the geometry of the spring, force-displacement characteristics can be tuned. An enhanced-performance inverted-spring manufacturing method is also described and characterized. A method of discrete displacement control is presented. Taking advantage of the flexibility of micro-coil spring, we present a novel mesh-worm prototype that utilizes bio-inspired antagonistic actuation for its body deformation and locomotion.

In this paper, we present the design and fabrication of a centimeter-scale propulsion system for a robotic fish. The key to the design is selection of an appropriate actuator and a body frame that is simple and compact. SMA spring actuators are customized to provide the necessary work output for the microrobotic fish. The flexure joints, electrical wiring and attachment pads for SMA actuators are all embedded in a single layer of copper laminated polymer film, sandwiched between two layers of glass fiber. Instead of using individual actuators to rotate each joint, each actuator rotates all the joints to a certain mode shape and undulatory motion is created by a timed sequence of these mode shapes. Subcarangiform swimming mode of minnows has been emulated using five links and four actuators. The size of the four-joint propulsion system is 6 mm wide, 40 mm long with the body frame thickness of 0.25 mm.

Flapping-wing robotic insects require actuators with high power densities at centimeter to micrometer scales. Due to the low weight budget, the selection and design of the actuation mechanism needs to be considered in parallel with the design of the power electronics required to drive it. This paper explores the design space of flapping-wing microrobots weighing 1g and under by determining mechanical requirements for the actuation mechanism, analyzing potential actuation technologies, and discussing the design and realization of the required power electronics. Promising combinations of actuators and power circuits are identified and used to estimate microrobot performance.

Biology is a useful tool when applied to engineering challenges that have been solved in nature. Here, the emulous goal of creating an insect-sized, truly micro air vehicle is addressed by first exploring biological principles. These principles give insights on how to generate sufficient thrust to sustain flight for centimeter-scale vehicles. Here, it is shown how novel manufacturing paradigms enable the creation of the mechanical and aeromechanical subsystems of a microrobotic device that is capable of Diptera-like wing trajectories. The results are a unique microrobot: a 60 mg robotic insect that can produce sufficient thrust to accelerate vertically. Although still externally powered, this micromechanical device represents significant progress toward the creation of autonomous insect-sized micro air vehicles.

Significant advances in meso-scale prototyping are enabling rigid, articulated, and actuated microrobotic structures. Here, an elegant manufacturing paradigm is employed for the creation of a biologically- inspired flapping-wing micro air vehicle with similar dimensions to Dipteran insects. A novel wing transmission system is presented which contains one actuated and two passive degrees of freedom. The design and fabrication are detailed and the performance of the resulting structure is elucidated highlighting two key metrics: the wing trajectory and the thrust generated.

Up to this point, researchers working to artificially re-create hovering insect flight have not demonstrated an integrated micromechanical device that is able to lift its own weight. Inspiration from biological systems coupled with revolutionary breakthroughs in microfabrication technologies have now enabled the realization of insect- sized micro air vehicles (MAVs). This work describes a solution to the mechanical and aeromechanical components of an insect-scale MAV by demonstrating a 60 mg structure that can generate sufficient lift to takeoff with external power and constrained body degrees of freedom.

Insects of the order Diptera have evolved to become prolific flyers able to perform aerial maneuvers that far surpass anything man-made. The Harvard Micro robotics lab has recently demonstrated the first step towards recreating these evolutionary wonders with the world's first demonstration of an at-scale robotic insect capable of generating sufficient thrust to takeoff (with external power). The mechanics and aerodynamics of this device are quite similar to Dipteran insects. Biologists have recently quantified the complex nonlinear temporal phenomena that give insects their outstanding capabilities. Periodic wing motions consisting of a large stroke and pronation and supination about an axis parallel to the span-wise direction are characteristic of most hovering Dipteran insects. Previous microrobot designs have attempted to concisely control each wing trajectory in these two dimensions. The robot that is shown here has three degrees-of- freedom, only one of which is actuated. Here, a central power actuator drives the wing with as large a stroke as possible and passive dynamics allow the wing to rotate using flexural elements with joint stops to avoid over-rotation. There are four primary components to the mechanical system: the actuator (or 'flight muscle'), transmission (or 'thorax'), airframe (or 'exoskeleton') and the wings. Each is constructed using a meso- scale manufacturing paradigm called Smart Composite Microstructures. This entails the use of laminated laser-micromachined materials stacked to achieve a desired compliance profile. This prototyping method is inexpensive, conceptually simple, and fast: for example, all components of the fly can be created in less than one week. Additionally, the resulting structures perform favorably when compared to alternative devices: flexure joints have almost no loss, ultra-high modulus links have higher stiffness-to-weight than any other material, and the piezoelectric actuators have similar power density to the best DC motors at any scale. After integration, the fly is fixed to guide wires that restrict the motion so that the fly can only move vertically. The wings are then driven open loop to achieve a large angular displacement. This is done at resonance to further amplify the wing motion. The wings exhibit a trajectory nearly identical to biological counterparts. Finally, this 60 mg, 3 cm wingspan system is allowed to freely move in the vertical direction demonstrating thrust that accelerates the fly upwards. Bench-top thrust measurements show that this robotic fly has a thrust-to- weight ratio of approximately two. These results unequivocally confirm the feasibility of insect-sized MAVs. The remaining challenges involve the development of microelectronics appropriate for power conversion, sensing, communication, and control along with the choice of an appropriate power source.

This paper discusses the biomimetic design and assembly of a 3g self-contained crawling robot fabricated through the integrated use of various microrobot technologies. The hexapod structure is designed to move in an alternating tripod gait driven by two piezoelectric actuators connected by sliding plates to two sets of three legs. We present results of both the kinematic and static analyses of the driving mechanism that essentially consists of three slider cranks in series. This analysis confirmed the force differential needed to propel the device. We then review various other microrobot technologies that have been developed including actuator design and fabrication, power and control electronics design, programming via a finite state machine, and the development of bioinspired fiber arrays. These technologies were then successfully integrated into the device. The robot is now functioning and we have already fabricated three iterations of the proposed device. We hope with further design iterations to produce a fully operational model in the near future

In the following work, we develop a characterization method using miniature fiberoptic position sensors for the Micromechanical Flying Insect (MFI) 1, a centimeter sized micro aerial vehicle being developed at the University of California, Berkeley. Sensing the state of a structure of this scale is challenging due to limited sensor technology and difficulty in constraining the structure. We developed a unique fiberoptic reflection position sensor and associated circuitry that yields a high resolution (approximately 5 µ m of linear motion), appropriate scale, and real time method for sensing the state of the MFI. Also included is the development of a clamping technique for the 2 wing, 4 degree of freedom MFI designed to expose actuator surfaces to be sensed while properly grounding the MFI without introducing added compliance or stiffness to the airframe. We include characterization data for a 2 DOF (flapping and rotation for one wing) wing structure, a clamped 4 DOF motor core of the MFI, and one side of an entire 4 DOF MFI.

To keep pace with recent advances in micro robotic structures demands actuator technologies which can deliver high power and precise motion. For electroactive material based actuators, high power typically implies either high field or high current drives which may lead to greater nonlinearities such as saturation, softening, and increased loss. Physical modeling of actuators is normally taken to be linear since the range of displacements, applied loads, and applied fields is typically small. If extrapolated to high drive conditions, these linear models significantly over predict the power which can be delivered. For actuators driving dynamic systems, a complete nonlinear model of the system will improve controllability and give more accurate estimations of power delivery capabilities. Here static nonlinearities and dynamic linear and nonlinear parameters are derived for high performance piezoelectric bending actuators.

The use of high performance composite materials provides a substantial performance improvement for microrobotics. Such materials have great benefits over common MEMs materials such as better fracture toughness and fatigue properties than semiconductors, and higher stiffness to weight ratios than most metals. Composite structures yield remarkable improvements in microrobotic links and joints, as well as greater performance actuators while allowing complicated microrobotic mechanisms to be easily rapid prototyped. The use of such materials in the construction of the 4DOF, 26 joint Micromechanical Flying Insect has reduced the thorax inertia by a factor of 3 and given a 20% increase in resonant frequency over previous designs while cutting construction time from weeks to days.

Four prototypes of biomimetic sensors have been designed and implemented for flight control of a robotic flying insect. The ocelli use four photodiodes to detect changes in light intensity in the surrounding. The halteres use piezo-actuated vibrating structures to sense body rotational velocities via the Coriolis forces. The optic flow sensors consist of linear arrays of elementary motion detectors (EMDs) to register optic flows. The magnetic field sensor uses three metal loops to detect changes in the magnetic field. Despite simplicity and novelty, the preliminary tests on these devices showed promising performance for using such biomimetic sensors on a robotic flying insect.

This paper presents some recent improvements in the fabrication and control of the micromechanical flying insect (MFI), a centimeter sized aerial vehicle currently being developed at the University of California, Berkeley. We report a lift of 506 /spl mu/N from a single wing, which is sufficient for a 100 mg machine to lift itself off the ground. This lift matches very well with predictions based on quasi steady state models. We present some recent improvements in thorax fabrication leading to the development of a light weight platform (/spl sim/ 100 mg), which generates 400 /spl mu/N of lift with a single wing. We also present a new sensor mechanism, which makes it possible to sense the motion of the actuators without having to add anything to the structure itself.

This paper presents an analysis of the major mechanical component (the thorax) of the micromechanical flying insect (MFI), a centimeter sized aerial vehicle currently in development at UC Berkeley. We present a description of the kinematics of the mechanism which converts piezoelectric actuation into complex 3D wing motion. A complete non-linear modeling of the system based on the Lagrangian energy technique is presented. A design methodology is presented in order to achieve optimal matching conditions. Two kinds of sensors which are presently utilized on the MFI are described. Experimental results are presented which validate some of the modeled non-linear aspects of the mechanism.

The mechanism which-real flying insects use to detect body rotation has been simulated. The results show that an angular rate sensor can be made based on such a biological mechanism. Two types of biomimetic gyroscopes have been constructed using foils of stainless steel. The first device is connected directly to a compliant cantilever. The second device is placed on a mechanically amplifying fourbar structure. Both devices are driven by piezoelectric actuators and detect the Coriolis force using strain gages. The experimental results show successful measurements of angular velocities and these devices have the benefits of low power and high sensitivity.

Considers a 2 DOF resonant thorax structure signed and fabricated for the MFI project. Miniature piezoelectric PZN-PT unimorph actuators were fabricated and used to drive a four-bar transmission mechanism. The current thorax design utilizes two actuated four-bars and a spherical joint to drive a rigid wing. Rotationally compliant flexure joints have been tested with lifetimes over 10/sup 6/ cycles. Wing spars were instrumented with strain gauges for force measurement and closed-loop wing control.

Key to the success of the micromechanical flying insect (MFI) project is the development sensors for flight force measurement. At the lowest level of MFI control is the wing control system which relies on wing and thorax mounted force sensors. These sensors have a dual function of stroke by stroke force characterization and system identification as well as the use in feedback control for all levels. There are two methods for force sensing on a flying robotic insect: measurements directly on the thorax, and body force measurement with a trade-off in design between sensor bandwidth and sensitivity.