Unmanned planetary rovers have traversed kilometers of Lunar and Martian terrain while performing valuable science. However, they still face mobility challenges including steep slopes and unstable soil that can entrap vehicles, as demonstrated by NASA's Spirit rover. Vehicles on Earth can depend on a human operator or rescue vehicle to tow them out of an entrapment, but remote rovers cannot, limiting their route to highly conservative path selections. To increase rover mobility on slopes and unstable soils, we present a resettable anchor launcher for independent self-rescue. The device launches a tethered land anchor away from the rover and then uses a winch to tow the rover up a hill or out of an entrapment. This paper presents the design of the launcher and its integration into a half-meter-long rover mobility platform with field testing at the NASA Glenn Research Center SLOPE Lab. We demonstrate repeatable launching and winching to help the rover climb a 17° slope of loose GRC-1 Lunar regolith simulant that it otherwise could not climb. Our work presents an alternative method to increase rover mobility, especially up slopes, and enables independent rover rescue, which could eventually increase mission duration and reduce risk of entrapment during extraterrestrial exploration.

Robot performance has advanced considerably both in and out of the factory, however in tightly constrained, unknown environments such as inside a jet engine or the human heart, current robots are less adept. In such cases where a borescope or endoscope can’t reach, disassembly or surgery are costly. One promising inspection device inspired by plant growth are "vine robots" that can navigate cluttered environments by extending from their tip. Yet, these vine robots are currently limited in their ability to simultaneously steer into tight curvatures and apply substantial forces to the environment. Here, we propose a plant-inspired method of steering by asymmetrically lengthening one side of the vine robot to enable high curvature and large force application. Our key development is the introduction of an extremely anisotropic, composite, wrinkled film with elastic moduli 400x different in orthogonal directions. The film is used as the vine robot body, oriented such that it can stretch over 120% axially, but only 3% circumferentially. With the addition of controlled layer jamming, this film enables a steering method inspired by plants in which the circumference of the robot is inextensible, but the sides can stretch to allow turns. This steering method and body pressure do not work against each other, allowing the robot to exhibit higher forces and tighter curvatures than previous vine robot architectures. This work advances the abilities of vine robots–and robots more generally–to not only access tightly constrained environments, but perform useful work once accessed.

Research in the area of photo-actuation is growing rapidly, yet there are few examples of photo-actuators with practical use cases. One potential application is for the control of intelligent electromagnetic surfaces, or two-dimensional arrays that could shape and control an incident electromagnetic field in ideally any manner. A promising concept to realize such a surface leverages signal refraction via antenna edges, but requires non-metal actuation, large antenna rotations, and high antenna angular accuracy for long periods of time. Here, we present a nonmetal, light-controlled, multi-position inchworm actuator array that can rotate an antenna 88 degrees in incremental steps of less than 3.4 degrees with zero-power shape-persistence. The design is modular and rapidly manufacturable via a layered laser-cutting technique, such that the actuator can be tiled into an array to control the rotation of many antennas. We control the array with a single focused IR light that rasters across the actuators to precisely control all antenna positions. We characterize the response time, accuracy, and repeatability of a single actuator, and demonstrate the array achieving diverse antenna configurations. This work advances the precision and scalability of photothermal actuation not only for use in intelligent electromagnetic surfaces but for any application benefitting from light-controlled actuation.

A new subclass of soft robot, known as tip-extending or "vine" robots, consists of long inflatable devices that move through the environment by extending from the tip. A key requirement for many applications of these robots is a working channel-a hollow tube through the core of the robot for passing tools, sensors, fluids, etc. While working channels have been proposed in a few vine robots, it remains an open challenge to create miniaturized vine robots (diameter < 1 cm) with working channels that enable continuous access through the core. In this paper, we analyze the growth models of current vine robot designs and show that the working channel greatly increases required pressure to grow at small scales due to internal friction. Based on this insight, we propose the concept of storing scrunched material at the tip of the vine robot to circumvent this frictional force. We validate our models and demonstrate this concept via prototypes down to diameters of 2.3 mm. Overall, this work enables the creation of miniaturized vine robots with working channels, which significantly enhances their practicality and potential for impact in applications such as minimally invasive surgery.

Latch-mediated spring-actuation (LaMSA) is utilized in a majority of jumping robots for its ability to slowly load and quickly release energy to generate high-power movement. Such mechanisms are found in robots that jump off of solid surfaces and even off of water. However, no robot currently employs LaMSA to jump on air. This paper presents the design, modeling, and fabrication of the first LaMSA-driven air jumper, capable of jumping mid-air. Our model informs prototype design and provides insight into the scaling properties of the wing area, wing and fuselage mass, and energy. By successfully applying LaMSA to a new domain, this work lays the foundation for future investigations into high-power airreaction maneuvers, such as in fixed-wing unmanned aerial vehicle (UAV) flight, by enabling instantaneous changes in altitude without the addition of extra on-board motors.

Recent advances in the rapidly growing field of soft robotics highlight the potential for innovations in wearable soft robotics to meet challenges and opportunities affecting individuals, society, and the economy. Some of the most promising application areas include wearable haptic interfaces, assistive robotics, and biomedical devices. Several attributes of soft robotic systems make them well-suited for use in human-wearable applications. Such systems can be designed to accommodate the complex morphology and movements of the human body, can afford sufficient compliance to ensure safe operation in intimate proximity with humans, and can provide context-appropriate haptic feedback or assistance to their wearers. Many soft robotic systems have been designed to resemble garments or wearables that are already widely used today. Such systems could one day become seamlessly integrated into a myriad of human activities and environments. Here, we review emerging advances in wearable soft robotic technologies and systems, including numerous examples from prior research. We discuss important considerations for the design of such systems based on functional concerns, wearability, and ergonomics. We describe an array of design strategies that have been adopted in prior research. We review wearable soft robotics applications in diverse domains, survey sensing and actuation technologies, materials, and fabrication methods. We conclude by discussing frontiers, challenges, and future prospects for soft, wearable robotics.

Continuum and soft robots can leverage complex actuator shapes to take onuseful shapes while actuating only a few of their many degrees of freedom. Continuum robotsthat alsogrow increasethe range of potential shapes that can be actuated and enable easier access to constrained environments. Existing models for describing the complex kinematics involved in general actuation of continuum robots rely on simulation or well-behaved stress–strain relationships, but the nonlinear behavior of the thin-walled inflated-beams used in growing robots makes these techniques difficult to apply. Here, we derive kinematic models of single, generally routed tendon paths on a soft pneumatic backbone of inextensible but flexible material from geometric relationships alone. This allows for forward modeling of the resulting shapes with only knowledge of the geometry of the system. We show that this model can accurately predict the shape of the whole robot body and how the model changes with actuation type. We also demonstrate the use of this kinematic model for inverse design, where actuator designs are found based on desired final robot shapes. We deploy these designed actuators on soft pneumatic growing robots to show the benefits of simultaneous growth and shape change.

Modular soft robots combine the strengths of two traditionally separate areas of robotics. As modular robots, they can show robustness to individual failure and reconfigurability; as soft robots, they can deform and undergo large shape changes in order to adapt to their environment, and have inherent human safety. However, for sensing and communication these robots also combine the challenges of both: they require solutions that are scalable (low cost and complexity) and efficient (low power) to enable collectives of large numbers of robots, and these solutions must also be able to interface with the high extension ratio elastic bodies of soft robots. In this work, we seek to address these challenges using acoustic signals produced by piezoelectric surface transducers that are cheap, simple, and low power, and that not only integrate with but also leverage the elastic robot skins for signal transmission. Importantly, to further increase scalability, the transducers exhibit multi-functionality made possible by a relatively flat frequency response across the audible and ultrasonic ranges. With minimal hardware, they enable directional contact-based communication, audible-range communication at a distance, and exteroceptive sensing. We demonstrate a subset of the decentralized collective behaviors that these functions make possible with multi-robot hardware implementations. The use of acoustic waves in this domain is shown to provide distinct advantages over existing solutions.

As robotic technologies advance and robots move out of factories and labs into the real world, grip on a variety of surfaces (e.g. smooth or rough) in a variety of conditions (e.g. dry or wet) becomes increasingly important. Bioinspired "microspines" have been previously explored, but primarily for vertical climbing applications or for small-scale robots applying low forces (less than 1 N). Further, these works primarily focused on rough surfaces. To advance this area of research, we present a composite material comprising high- friction rubber and compliant nitinol microspines which can passively retract below the surface of the rubber. We show that the composite can support large loads (greater than 75 N) with a high coefficient of friction on both smooth and rough surfaces (p > 1.1), outperforming microspines alone on smooth surfaces and rubber alone on rough surfaces, especially when wet and oily. Further, due to the retraction of the microspines, the composite does not damage relatively soft, smooth surfaces, like wood flooring. We also test durability, and show that it is improved by microspine compliance, and test the effects of varying microspine diameter, angle, and tip shape. Finally, we demonstrate that a small RC car can climb steeper slopes and stop more quickly in wet conditions with microspines.

Many soft robots are capable of significantly changing their shape, an ability that can offer advantages in many applications. For instance, such a robot can flatten its body to fit under small gaps and expand to move over large obstacles. Further, because these shape changes are usually driven by a pressurized fluid, if they act over a large area, they have the potential to apply large forces to the world. However, when these same shape changes are used for the locomotion of an untethered robot, they tend to result in slow forward movement. Here we present a hybrid soft-rigid elongated-sphere robot that decouples shape change from locomotion. Pairing a compliant, inflatable outer skin, which changes volume by 15x to both fit under and roll over obstacles and can lift objects up to 30 kg, with a wheeled internal carriage, we obtain relatively fast locomotion. A new two-sided controllable adhesive between the internal carriage and the skin enables the carriage to climb vertically inside the skin, allowing the robot to climb external obstacles. We present the design of the robot, simple modeling of its behavior, and experimental testing. Our work advances the area of hybrid soft-rigid robotics by demonstrating how leveraging the strengths of both soft and rigid systems can have quantifiable performance benefits.

Soft, tip-extending, pneumatic "vine robots" that grow via eversion are well suited for navigating cluttered environments. Two key mechanisms that add to the robot’s functionality are a tip-mounted retraction device that allows the growth process to be reversed, and a tip-mounted camera that enables vision. However, previous designs used rigid, relatively heavy electromechanical retraction devices and external camera mounts, which reduce some advantages of these robots. These designs prevent the robot from squeezing through tight gaps, make it challenging to lift the robot tip against gravity, and require the robot to drag components against the environment. To address these limitations, we present a soft, pneumatically driven retraction device and an internal camera mount that are both lightweight and smaller than the diameter of the robot. The retraction device is composed of a soft, extending pneumatic actuator and a pair of soft clamping actuators that work together in an inch-worming motion. The camera mount sits inside the robot body and is kept at the tip of the robot by two low-friction interlocking components. We present characterizations of our retraction device and demonstrations that the robot can grow and retract through turns, tight gaps, and sticky environments while transmitting live video from the tip. Our designs advance the ability of everting vine robots to navigate difficult terrain while collecting data.

A key challenge in robotics is to create efficient methods for grasping objects with diverse shapes, sizes, poses, and properties. Grasping with hand-like end effectors often requires careful selection of hand orientation and finger placement. Here, we present a fingerless soft gripper capable of efficiently generating multiple grasping modes. It is based on a soft, cylindrical accordion structure containing coupled, parallel fluidic channels, which are controlled via pressure supplied from a single fluidic port. Inflation opens the gripper orifice for enveloping an object, while deflation allows it to produce grasping forces. The interior is patterned with a gecko-like skin that increases friction, enabling the gripper to lift objects weighing up to 20 N. Our design ensures that fragile objects, such as eggs, can be safely handled, by virtue of a wall buckling mechanism. In reverse, the gripper can be deflated to reach into an opening or orifice then inflated to grasp objects with handles or cavities. The gripper may also integrate a lip that enables it to form a seal and, upon inflating, to generate suction for lifting objects with flat surfaces. In this article, we describe the design and fabrication of this device and present an analytical model of its behavior when operated from a single fluidic port. In experiments, we demonstrate its ability to grasp diverse objects, and show that its performance is well described by our model. Our findings show how a fingerless soft gripper can efficiently perform a variety of grasping operations. Such devices could improve the ability of robotic systems to meet applications in areas of great economic and societal importance.

Soft robotic pneumatic grippers have been shown to be versatile, robust to impacts, and safe for use on delicate objects. One type, fluidic elastomer grippers, are characterized by fingers with an inextensible gripping surface backed by extensible pneumatic chambers; when inflated, this mismatch in extensibility results in the finger curling. However, one drawback of these simple fingers is that they have one preprogrammed grasp, usually a simple constant-curvature wrap. While well-suited for finger-sized round objects, they do not grasp flat or small objects well. Here, we present an adaptable tri-stable soft robotic finger that can form either a pinch or wrap grasp based on the shape of the grasped object. We enable this by incorporating two bi-stable springs into the inextensible layer. The three stable positions are: i) open (unpressurized), ii) pinch (with only the proximal section bending), and iii) wrap (with the entire finger bending). We present a simple model of the behavior of our finger and experimental results verifying the model. Further, we apply forces and moments to grasped objects, and show that the tri-stable finger increases the grasping performance when compared to a control gripper with equal gripping force. Our work presents a novel design modification that is unobtrusive, simple, and passive. Our introduction of inexpensive programmable hardware advances the versatility and adaptability of soft grippers.

The field of soft robotics is grounded on the idea that, due to their inherent compliance, soft robots can safely interact with the environment. Thus, the development of effective planning and control pipelines for soft robots should incorporate reliable robot-environment interaction models. This strategy enables soft robots to effectively exploit contacts to autonomously navigate and accomplish tasks in the environment. However, for a class of soft robots, namely vine-inspired, tip-extending or "vine" robots, such interaction models and the resulting planning and control strategies do not exist. In this paper, we analyze the behavior of vine robots interacting with their environment and propose an obstacle-interaction model that characterizes the bending and wrinkling deformation induced by the environment. Starting from this, we devise a novel obstacle-interaction planning method for these robots. We show how obstacle interactions can be effectively leveraged to enlarge the set of reachable workspace for the robot tip, and verify our findings with both simulated and real experiments. Our work improves the capabilities of this new class of soft robot, helping to advance the field of soft robotics.

Soft, tip-extending "vine" robots offer a unique mode of inspection and manipulation in highly constrained environments. For practicality, it is desirable that the distal end of the robot can be manipulated freely, while the body remains stationary. However, in previous vine robots, either the shape of the body was fixed after growth with no ability to manipulate the distal end, or the whole body moved together with the tip. Here, we present a concept for shape-locking that enables a vine robot to move only its distal tip, while the body is locked in place. This is achieved using two inextensible, pressurized, tip-extending, chambers that "grow" along the sides of the robot body, preserving curvature in the section where they have been deployed. The length of the locked and free sections can be varied by controlling the extension and retraction of these chambers. We present models describing this shape-locking mechanism and workspace of the robot in both free and constrained environments. We experimentally validate these models, showing an increased dexterous workspace compared to previous vine robots. Our shape-locking concept allows improved performance for vine robots, advancing the field of soft robotics for inspection and manipulation in highly constrained environments.

A fundamental challenge in the field of modular and collective robots is balancing the trade-off between unit-level simplicity, which allows scalability, and unit-level functionality, which allows meaningful behaviors of the collective. At the same time, a challenge in the field of soft robotics is creating untethered systems, especially at a large scale with many controlled degrees of freedom (DOF). As a contribution toward addressing these challenges, here we present an untethered, soft cellular robot unit. A single unit is simple and one DOF, yet can increase its volume by 8x and apply substantial forces to the environment, can modulate its surface friction, and can switch its unit-to-unit cohesion while agnostic to unit-to-unit orientation. As a soft robot, it is robust and can achieve untethered operation of its DOF. We present the design of the unit, a volumetric actuator with a perforated strain-limiting fabric skin embedded with magnets surrounding an elastomeric membrane, which in turn encompasses a low-cost micro-pump, battery, and control electronics. We model and test this unit and show simple demonstrations of three-unit configurations that lift, crawl, and perform plate manipulation. Our untethered, soft cellular robot unit lays the foundation for new robust soft robotic collectives that have the potential to apply human-scale forces to the world.

Soft, tip-extending devices, or “vine robots,” are a promising new paradigm for navigating cluttered and confined environments. Because they lengthen from their tips, there is little relative movement of the body with the environment, and the compressible nature of the device allows it to pass through orifices smaller than its diameter. However, the interaction between these devices and the environment is not well characterized. Here we present a comprehensive mathematical model that describes vine robot behavior during environmental interaction that provides a basis from which informed designs can be generated in future works. The model incorporates transverse and axial buckling modes that result from growing into obstacles with varying surface normals, as well as internal path-dependent and independent resistances to growth. Accordingly, the model is able to predict the pressure required to grow through a given environment due to the interaction forces it experiences. We experimentally validate both the individual components and the full model. Finally, we present three design insights from the model and demonstrate how they each improve performance in confined space navigation. Our work helps advance the understanding of tip-extending, vine robots through quantifying their interactions with the environment, opening the door for new designs and impactful applications in the realms of healthcare, research, search and rescue, and space exploration.

Energy harvesting is an attractive alternative to carrying onboard power for mobile robots, especially for long duration missions. While solar is a powerful option, alternatives are needed for situations where direct sunlight is unavailable. One intriguing concept was proposed in the 17thcentury to power clocks: energy harvesting based on temporal, rather than spatial, temperature gradients, using a low boiling point fluid that vaporizes at ambient temperatures. This concept has many strengths: it offers all-in-one energy harvesting and storage; direct high-force and large displacement mechanical output, eliminating the need for a motor; and temporal gradients are ubiquitous, due to diurnal thermal fluctuations. The challenge for robotic applications, however, is to create large enough amounts of work in a small enough package to power a mobile device while using a non-toxic and readily available working fluid. Here we present a simple, low-cost energy harvesting actuator, powered by the vaporization of butane and isobutane, with an isobaric energy density of up to 38000 J/m3(i.e. energy extracted per total volume expansion) each time the temperature fluctuates 13.1°C, enough to power a small car to drive 10m. Two principles enable this: i) precompression of the working fluid, allowing us to tune the boiling point and choose among many non-toxic fluids that do more work than non-compressed fluids; and ii) a constant force profile of the return springs, allowing more work than a linear spring. We present a simple model of the actuator and experimental results characterizing its behavior. Our work lays the foundation for energy harvesting across temporal temperature gradients using vaporization as a viable option for powering mobile robots.

Soft robotics and pneumatic actuation present opportunities for lightweight wearable haptic devices that provide distributed touch feedback to the skin. Ideally, such devices would be easily donned and doffed, since permanent coverage of a large area of the skin is undesirable. Here we present the design and evaluation of a concept device called HapWRAP: a growing haptic device constructed from flexible low density polyethylene. Controlled air flow through tubes and pouches allows HapWRAP to grow out of a compact housing unit and provide a combination of directional and force feedback to a user. When activated, HapWRAP grows up and around the forearm; its loops form a temporary sleeve. After growth, pneumatic actuators inflate and deflate to stimulate mechanoreceptors in the skin at distinguishable locations. This paper describes the design and manufacturing of HapWRAP, reports its performance metrics, and tests its suitability as a haptic feedback device. Participants were able to interpret force and direction cues from HapWRAP with 92.5% accuracy. These findings suggest that HapWRAP can be successfully used for applications where both force and direction cues are necessary.

For many types of robots, avoiding obstacles is necessary to prevent damage to the robot and environment. As a result, obstacle avoidance has historically been an important problem in robot path planning and control. Soft robots represent a paradigm shift with respect to obstacle avoidance because their low mass and compliant bodies can make collisions with obstacles inherently safe. Here we consider the benefits of intentional obstacle collisions for soft robot navigation. We develop and experimentally verify a model of robot-obstacle interaction for a tip-extending soft robot. Building on the obstacle interaction model, we develop an algorithm to determine the path of a growing robot that takes into account obstacle collisions. We find that obstacle collisions can be beneficial for open-loop navigation of growing robots because the obstacles passively steer the robot, both reducing the uncertainty of the location of the robot and directing the robot to targets that do not lie on a straight path from the starting point. Our work shows that for a robot with predictable and safe interactions with obstacles, target locations in a cluttered, mapped environment can be reached reliably by simply setting the initial trajectory. This has implications for the control and design of robots with minimal active steering.

We present a pneumatic actuator capable of changing length by 1000%, applying both pushing and pulling forces, and independently modulating its length and stiffness. These characteristics are enabled by individually addressable internal and external chambers that work antagonistically against one another. The high deformation with low hysteresis is achieved by wrinkling of thin materials that are assumed to be inextensible but flexible, as opposed to stretchable. A model for the actuator is presented and validated with experimental results, showing capabilities of high strain, pushing and pulling, and independent control of length and stiffness. These characteristics are motivated by the application of a compliant truss robot. Accordingly, we show a simple grounded tetrahedron with three actuator elements and three static elements. We demonstrate motion of the tetrahedron apex against external loads and the ability of the structure to vary its stiffness. The actuator offers a unique set of characteristics that could increase the capabilities of soft robotic devices.

Mobility by growth is a new paradigm in robotic systems design and their applications in the real world. Soft, tip-extending, or “growing”, robots have potential applications including inspection and navigation in disaster scenarios. However, due to their growing capability, such robots create unique challenges for intuitive human control. In this paper, a new flexible interface is proposed to intuitively map human bending commands into movements of the growing robot while providing shape information of the robot in order to improve situational awareness. Several command mappings are proposed, and a subjective study was conducted to assess the intuitiveness of the developed interface and mappings compared with other commercially available interfaces. The interfaces were evaluated using four metrics in two virtual task scenarios. The proposed interface with shape mapping performed better than the other interfaces, especially when the vine robot rolls over unintentionally during complex tasks.

Mobile robots of all shapes and sizes move through the air, water, and over ground. However, few robots can move through the ground. Not only are the forces resisting movement much greater than in air or water, but the interaction forces are more complicated. Here we propose a soft robotic device that burrows through dry sand while requiring an order of magnitude less force than a similarly sized intruding body. The device leverages the principles of both tip-extension and granular fluidization. Like roots, the device extends from its tip; the principle of tip-extension eliminates skin drag on the sides of the body, because the body is stationary with respect to the medium. We implement this with an everting, pressure-driven thin film body. The second principle, granular fluidization, enables a granular medium to adopt a dynamic fluid-like state when pressurized fluid is passed through it, reducing the forces acting on an object moving through it. We realize granular fluidization with a flow of air through the core of the body that mixes with the medium at the tip. The proposed device could lead to applications such as search and rescue in mudslides or shallow subterranean exploration. Further, because it creates a physical conduit with its body, electrical lines, fluids, or even tools could be passed through this channel.

Grasping objects that are too large to envelop is traditionally achieved using friction that is activated by squeezing. We present a family of shear-activated grippers that can grasp such objects without the need to squeeze. When a shear force is applied to the gecko-inspired material in our grippers, adhesion is turned on; this adhesion in turn results in adhesion-controlled friction, a friction force that depends on adhesion rather than a squeezing normal force. Removal of the shear force eliminates adhesion, allowing easy release of an object. A compliant shear-activated gripper without active sensing and control can use the same light touch to lift objects that are soft, brittle, fragile, light, or very heavy. We present three grippers, the first two designed for curved objects, and the third for nearly any shape. Simple models describe the grasping process, and empirical results verify the models. The grippers are demonstrated on objects with a variety of shapes, materials, sizes, and weights.

Free-flying robots have the potential to autonomously fulfill a wide range of tasks involving manipulation of objects in space. In this paper we study the design of a wrist mechanism for free-flying robots that are equipped with an adhesive gripper for attaching to objects and surfaces. The wrist and gripper allow the robots to apply moments in addition to forces, which increases their versatility for object manipulation. We apply grasp optimization to establish limitations on the forces/moments that the wrist can impart, subject to adhesion capabilities. Building on these results, we present considerations for tuning a passive wrist mechanism, or controlling an active wrist, to broaden the range of forces and moments that the robot can exert. Our theoretical insights and wrist designs are validated in simulations and on a planar micro-gravity test bed.

We describe a new series pneumatic artificial muscle (sPAM) and its application as an actuator for a soft continuum robot. The robot consists of three sPAMs arranged radially round a tubular pneumatic backbone. Analogous to tendons, the sPAMs exert a tension force on the robot's pneumatic backbone, causing bending that is approximately constant curvature. Unlike a traditional tendon driven continuum robot, the robot is entirely soft and contains no hard components, making it safer for human interaction. Models of both the sPAM and soft continuum robot kinematics are presented and experimentally verified. We found a mean position accuracy of 5.5 cm for predicting the end-effector position of a 42 cm long robot with the kinematic model. Finally, closed-loop control is demonstrated using an eye-in-hand visual servo control law which provides a simple interface for operation by a human. The soft continuum robot with closed-loop control was found to have a step-response rise time and settling time of less than two seconds.

We present the design, modeling, and implementation of a novel pneumatic actuator, the Pneumatic Reel Actuator (PRA). The PRA is highly extensible, lightweight, capable of operating in compression and tension, compliant, and inexpensive. An initial prototype of the PRA can reach extension ratios greater than 16:1, has a force-to-weight ratio over 28:1, reach speeds of 0.87 meters per second, and can be constructed with parts totaling less than $4 USD. We have developed a model describing the actuator and have conducted experiments characterizing the actuator's performance in regards to force, extension, pressure, and speed. We have implemented two parallel robotic applications in the form of a three degree of freedom robot arm and a tetrahedral robot.

Stroke is the leading cause of adult disability. Many robots have been developed to administer movement therapies or provide physical assistance to stroke survivors suffering from movement deficits. One effective approach has been to support the weight of the arm, offloading shoulder abductor muscles that have become coupled to elbow muscles. However, patients have limited access to such robots due to the robots' complexity, cost, and bulk. To counter this problem, we developed a lightweight (350 g), inexpensive external actuator, which we call an exomuscle. We constructed a prototype exomuscle by reinforcing a plastic bladder with a fabric bag that is sewn to supporting straps. The bladder can then be inflated with pressurized air to provide expansive forces between the user's torso and arm, supporting shoulder abduction. A seam acting as a hinge joint connects the exomuscle to the torso. We demonstrate that our exomuscle reduces muscular effort by 74% in isometric tasks and 72% in dynamic reaching tasks while minimally affecting the range of motion of the shoulder and elbow (average 4% reduction) on three users ranging from 165 to 188 cm tall. Future studies will evaluate the exomuscle with users who have post-stroke motor impairments.

The twisted string actuator is an actuator that is gaining popularity in various engineering and robotics and applications. However, the fundamental limitation of actuators of this type is the uni-directional action, meaning that the actuator can contract but requires external power to return to its initial state. This paper proposes 2 novel passive extension mechanisms based on buckling effect to solve the uni-directional issue of the twisted string actuator. The proposed mechanisms are mechanically simple and compact and provide a nearly-constant extension force throughout the operation range. The constant force can fully extend the twisted string actuator with minimal loss of force during contraction. The designed mechanisms are evaluated in a series of practical tests, and their performances are compared and discussed.

Surgeries involving interaction with soft tissue like the brain need to minimize shear and normal forces that can cause tissue damage or hemorrhage. Other surgeries require the ability to follow a complex, curved path, such as through an intestine or to a kidney stone. This paper presents a soft catheter that has the potential to aid in these challenging cases. The soft catheter is capable of apical extension in which the tip extends while the rest of the catheter remains stationary. This limits shear forces with the environment, easing movement of a body's tip through a constrained space. The soft catheter is pre-formed to patient-specific trajectories, meaning that normal forces against tissue would only arise due to errors between the actual and desired paths; we show decrease in normal force applied to the environment on the order of 100 compared to a standard catheter in a 30 degree bend. Setting the internal pressure allows for control of catheter stiffness, with a 500 times difference over the range of tested pressures. Manual operation to reach a surgical site requires only holding the correct orientation at the entry point into the body and setting the internal pressure of the catheter. This soft catheter could offer two benefits: the ability to apply low tissue interaction forces and reach challenging locations within the body.

Perching can extend the useful mission life of a micro air vehicle. Once perched, climbing allows it to reposition precisely, with low power draw and without regard for weather conditions. We present the Stanford Climbing and Aerial Maneuvering Platform, which is to our knowledge the first robot capable of flying, perching with passive technology on outdoor surfaces, climbing, and taking off again. We present the mechanical design and the new perching, climbing, and takeoff strategies that allow us to perform these tasks on surfaces such as concrete and stucco, without the aid of a motion capture system or off-board computation. We further discuss two new capabilities uniquely available to a hybrid aerial-scansorial robot: the ability to recover gracefully from climbing failures and the ability to increase usable foothold density through the application of aerodynamic forces. We also measure real power consumption for climbing, flying, and monitoring and discuss how future platforms could be improved for longer mission life.

We explore the use of grippers with gecko-inspired adhesives for spacecraft docking and acquisition of tumbling objects in microgravity. Towards the goal of autonomous object manipulation in space, adhesive grippers mounted on planar free-floating platforms are shown to be tolerant of a broad range of incoming linear and angular velocities. Through modeling, simulations, and experiments, we characterize the dynamic “grasping envelope” for successful acquisition and derive insights to inform future gripper designs and grasping strategies for motion planning.

We present the inverse pneumatic artificial muscle (IPAM), a new soft actuator that is powered by pneumatics in a manner inverse to traditional pneumatic muscles: low pressure, rather than high, contracts the muscle. The IPAM improves on the 50-year-old standard in soft pneumatic actuators, the McKibben muscle, but retains many of the advantages that have drawn roboticists to this artificial muscle over the years. The McKibben muscle produces up to 40% strain, and has nonlinear control with friction and hysteresis, whereas the IPAM attains strains of over 300% and has a nearly linear mapping between input pressure and force/length output and no sliding friction. Crucially, the IPAM retains the soft structure, low weight, compliance, and robustness that the McKibben muscle boasts. We present a simple model to describe the behavior of the muscle, as well as force, displacement, pressure, and speed tests validating the model and characterizing the IPAM's performance. Further, we present two practical implementations using the IPAM: an active brace and a robotic finger.

The Wolverine is a mobile, wearable haptic device designed for simulating the grasping of rigid objects in a virtual reality interface. In contrast to prior work on wearable force feedback gloves, we focus on creating a low cost and lightweight device that renders a force directly between the thumb and three fingers to simulate objects held in pad opposition (precision) type grasps. Leveraging low-power brake-based locking sliders, the system can withstand over 100N of force between each finger and the thumb, and only consumes 0.24 mWh (0.87 joules) for each braking interaction. Integrated sensors are used both for feedback control and user input: time-of-flight sensors provide the position of each finger and an IMU provides overall orientation tracking. This paper describes the mechanical design, control strategy, and performance analysis of the Wolverine system and provides a comparison with several existing wearable haptic devices.

The controllable adhesives used by insects to both carry large loads and move quickly despite their small scale inspires the μTug robot concept. These are small robots that can both move quickly and use controllable adhesion to apply interaction forces many times their body weight. The adhesives enable these autonomous robots to accomplish this feat on a variety of common surfaces without complex infrastructure. The benefits, requirements, and theoretical efficiency of the adhesive in this application are discussed as well as the practical choices of actuator and robot working surface material selection. A robot actuated by piezoelectric bimorphs demonstrates fast walking with a no-load rate of 50 Hz and a loaded rate of 10 Hz. A 12 g shape memory alloy (SMA) actuated robot demonstrates the ability to load more of the adhesive enabling it to tow 6.5 kg on glass (or 500 times its body weight). Continuous rotation actuators (electromagnetic in this case) are demonstrated on another 12 g robot give it nearly unlimited work cycles through gearing. This leads to advantages in towing capacity (up to 22 kg or over 1800 times its body weight), step size, and efficiency. This work shows that using such an adhesive system enables small robots to provide truly human scale interaction forces, despite their size and mass. This will enable future microrobots to not only sense the state of the human environment in which they operate, but apply large enough forces to modify it in response.

The ability to carry large payloads could greatly increase the applications of small, low cost climbing robots. We present a linear inchworm gait that uses a single powerful actuator to climb. To make this gait possible, we leveraged two new methods of achieving controllable, anisotropic adhesion (one method produces over 200 times stronger adhesion in the preferred direction). With controllable, anisotropic adhesion, the gait is robust to missed steps. In addition, the gait provides a stance in which the robot can rest without requiring power. An autonomous 9 gram robot is able to climb a smooth vertical surface at 3 mm/s, while hoisting more than a kilogram. We also present a scaled down version of the robot, which is considerably smaller than any previous dry adhesive climbing mechanism. It is actuated by externally powered Shape Memory Alloy, weighs 20 mg, and is capable of hoisting 500 mg. These climbers show that a large hoisting ability while climbing can be achieved using dry adhesives, and the presented concepts could aid in the development of autonomous, highly functional, small robots.

Nearly all robotic grippers have one trait in common: they grasp objects with normal forces, either directly, or indirectly through friction. This method of grasping is effective for objects small enough for a given gripper to partially encompass. However, to grasp larger objects, significant grip forces and a high coefficient of friction are required. We present a new grasping method for convex objects, using almost exclusively shear forces. We achieve shear grasping with a gripper that utilizes thin film gecko-inspired fibrillar adhesives that conform to the curvature of the object. We present a verified model for grasping a range of curvatures and results that demonstrate the thin film fibrillar adhesives' increased contact area on textured surfaces when loaded in shear. Finally, the gripper is implemented on a robotic arm and grasps a variety of convex objects (at rest and ballistic).

As the number of rocket bodies and other debris in Earth's orbit increases, the need to capture and remove this space junk becomes essential to protect new satellites. A low cost solution may include gecko-inspired directional adhesives, which require almost no compressive preload to generate adhesion and are therefore suitable for surface grasping in space where objects are free floating. Current individual adhesive units with a pair of opposed pads achieve a limit of 13N normal to the surface. Instead of using a single large unit to generate high levels of adhesion, using multiple small gripper units is desirable to prevent single-point failures and to conform to higher curvatures. For this strategy to succeed, it is essential to distribute the overall force evenly, to minimize the overall preload normal to the surface, and to prevent local failures from propagating over the array. We present two load sharing mechanisms. The first uses nearly-constant force springs in parallel. The second uses a tendon and pulleys in series. Both allow a 4-unit gripper to maintain the same adhesive stress as a single unit. A normal adhesive load to compressive preload ratio of 100:1 is demonstrated. Zero gravity experiments and air bearing floor experiments demonstrate the gripper's functionality in a simulated space environment. Design considerations are discussed for further scaling, with the trade-offs among load sharing, suitability for different surfaces, and failure sensitivity.

Perching on a vertical surface carries the risk of severe damage to the vehicle if the maneuver fails, especially if failure goes undetected. We present a detection method using an onboard 3-axis accelerometer to discriminate between perching success and failure. An analytical model was developed to calculate acceleration differences for success and failure and set decision times. Two distinct decision times were shown to be effective, corresponding to properly engaging the gripper and overloading the gripper's capabilities. According to a machine learning feature selection algorithm, the maximum Z axis acceleration of the quadrotor and the presence of near-zero readings are the most relevant features within these two time frames. Using these features, the detection algorithm discriminated between success and failure with a 91% accuracy at 40 ms, and 94% at 80 ms. Real-time detection and failure recovery experiments with a 20 g quadrotor verify the detection method. An improved approach that combines various decision times correctly identified success/failure for all 20 trials with an average total falling distance of 0.8m during recovery. We discuss the feasibility of extending our method to other quadrotor platforms.

Adhesion quality sensing is critical to the performance of any robot that utilizes gecko-inspired dry adhesives for climbing, perching, or grasping. We present a 3-axis tactile sensor designed for this application that demonstrates performance on par with a large commercial load cell while being compact enough to integrate into a robot foot. The sensor can measure spatially distributed force loads and demonstrates high sensitivity in both shear and normal components. Results showcase the sensor's ability to detect a variety of unreliable contact and loading conditions before the onset of adhesion failure.

We present a robot capable of both (1) dynamically perching onto smooth, flat surfaces from a ballistic trajectory and (2) successfully transitioning to a climbing gait. Merging these two modes of movement is achieved via a mechanism utilizing an opposed grip with directional adhesives. Critical design considerations include (a) climbing mechanism weight constraints, (b) suitable body geometry for climbing and (c) effects of impact dynamics. The robot uses a symmetric linkage and cam mechanism to load and detach the feet while climbing. The lengths of key parameters, including the distances between each the feet and the tail, are chosen based on the ratio of required preload force and detachment force for the adhesive mechanism.

Perching allows Micro Aerial Vehicles (MAVs) avoid the power costs and electrical and acoustic noise of sustained flight, for long-term surveillance and reconnaissance applications. This paper presents a dynamic model that clarifies the requirements for repeatable perching on walls and ceilings using an opposed-grip mechanism and dry adhesive technology. The model predicts success for perching over a range of initial conditions. The model also predicts the conditions under which other directional attachment technologies, such as microspines, will succeed. Experiments conducted using a launching mechanism for a range of different landing conditions confirm the predictions of the model and provide insight into future design improvements that are possible by modifying a few key damping and stiffness parameters.

Telerobotics has the potential to facilitate the repair of satellites in geosynchronous orbit by allowing human operators to interact naturally with remote objects. Time delays on the order of seconds make it difficult to provide immersive feedback to the operator, motivating the use of predictive visual and haptic displays of the robot and environment. A teleoperation framework developed for this scenario invokes a two-part environment model that predicts motion of objects in the environment, both in free space and during contact with the robot. When objects in the environment are in free space, a propagated model using delayed data provides predictive feedback to the operator. However, when the robot interacts with the environment, a local environment model that does not propagate delayed data is used. This reduces computational load and ensures stability during robot-environment interactions. Two experiments were carried out to test the teleoperation system. Results demonstrate the ability of the prediction algorithm to provide reliable feedback and improve operator performance before, during, and after robot-environment interactions.

Dynamic surface grasping is applicable to landing of micro air vehicles (MAVs) and to grappling objects in space. In both applications, the grasper must absorb the kinetic energy of a moving object and provide secure attachment to a surface using, for example, gecko-inspired directional adhesives. Functional principles of dynamic surface grasping are presented, and two prototype grasper designs are discussed. Computer simulation and physical testing confirms the expected relationships concerning (i) the alignment of the grasper at initial contact, (ii) the absorption of energy during collision and rebound, and (iii) the force limits of synthetic directional adhesives.

We present two foot mechanisms that allow relatively large patches of synthetic fibrillar dry adhesives applied inexactly by a climbing robot to perform at levels previously obtained only for small samples in precisely aligned and controlled bench-top tests. The mechanisms are inspired by the structures found in the toes of the gecko. The first mechanism uses ankles with roll and yaw flexures and a compliant structure behind the adhesive material to achieve approximately uniform pressures under nominal loading conditions on flat and curved surfaces. The second design uses a tendon-supported structure to achieve uniform loading and prevent premature peeling failures despite significant misalignment with a flat wall surface. The two designs are demonstrated on Stickybot III, an approximately 1 kg climbing robot, and can be scaled to larger areas and loads by tiling the basic structure.

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.