Soft robotic wearables, with lightweight and flexible actuation, have shown promising results in assistive applications. However, it remains unclear whether they can be made fully comfortable and suitable for everyday use. In this study, we introduce a clothing-type soft robotic wearable embedded with shape memory alloy (SMA) based artificial muscle fibers for ankle plantarflexion assistance. We conducted force characterization of SMA wires, analyzing the effects of thickness, strain, applied current, and number of wires. The actuator was designed to achieve assistive force of 80 N and implemented a closed-loop controller with a PI controller to enable precise force and displacement control. Last, we demonstrate that the developed system can deliver controlled and repeatable forces in bench tests and modulate peak force according to target assistive levels on the ankle during walking in a user study.

Shape memory alloy (SMA) has superior actuation capability over the limit of the scale. However, inherently low controllability is a primary issue that hinders practical usage. To address this challenge, this paper presents an SMA-based artificial muscle actuator capable of the displacement sensing through the capacitive sensor. To realize sensing capability, the theoretical model-based design and fabrication process are proposed. Here, we show that the actuator can be controlled at intervals of 100 μm as well as maintaining sensing capability while lifting 90 times heavier than its weight. To exhibit the usefulness of the actuator to an optical device, we integrate the actuator into the mirror tilting device, which has 20 degrees tilting angle. We expect that the proposed actuator can overcome the scale limit of meso-scale devices, which require payload capacity and controllability, simultaneously.

Miniaturization of robotic grippers enables precise manipulation of small-size objects. However, most microgrippers are actuated by rigid actuators, and thus retain challenges such as micro-fabrication, complex structure, and lack of compliance. Here, we present a compliant microgripper driven by a soft polymer actuator. The proposed millimeter-scale soft polymer actuator can produce a linear displacement and output force with a fast operation. Then, we designed the gripper linkage to convert the linear displacement of the actuator into a gripping motion. Fabricated compliant microgripper has a size of$\boldsymbol{10\times 10\times 10}\ \mathbf{mm}^{3}$and a weight of 0.36 g, with a maximum gripping width of 8 mm. Demonstration of the gripper shows the feasibility of gripping various sub-millimeter scale objects regardless of their shape owing to its compliance.

Robotic manipulators require contact force sensing capabilities to sense the contact force between the manipulator and an object. Specifically, for humans and robots to coexist in the work environment, the robot must be able to detect an external force applied by a human. This study presents a new intrinsic force sensing method for robot manipulators that can obtain accurate information of the external force applied by a human during human–robot interaction. The method employs a robot cover, which is typically utilized in robot manipulators. Unlike conventional force sensing methods, a six-axis force/torque sensor is placed between the cover and the link of the robot manipulator. As a result, the proposed method provides information of the three-axis contact force applied to the cover surface and its contact location. Therefore, the cover itself becomes a sensorized cover based on the intrinsic force sensing method. To evaluate its sensing performance, the sensorized cover is experimentally validated using reference sensors. Finally, an experiment is performed in which the robot successfully recognizes letters written on the cover, indicating a high level of contact force sensing performance.

Origami provides a unique tool for the design of robotic frames owing to its simple shaping principle by “folding.” However, achieving the fast and reversible activeness of a highly reconfigurable structure remains challenging owing to the limitations of accessible actuators. In particular, it is difficult to find an actuator that can realize a simultaneously large, rapid, reversible, and stable movement while leading to a favorable form factor for the origami. To overcome this, in this article, we propose a 3-D shape-shifting system consisting of a morphing origami block that complements the stability problem of shape memory alloy wire actuators by tuning its structural characteristics. This cooperative scheme improves the reversibility and stability of the shape-shifting system, which enables the rapid transformation with high degrees of freedom unlike in existing programmable origami. As a stand-alone unit of transformation, morphing block equipped with deployable mechanism and actuators weighs 6 g and has a volume change factor of ten. Furthermore, the transformation time in both directions is less than 5 s, and the block can carry more than 120 g of payload in the deployed state. The proposed system composed of multiple origami blocks can reconfigure itself into diverse 3-D target shapes.

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.

In this paper, we propose a new shape-shifting system. Shape-shifting is achieved by the integration of arranged identical transformable units. These are self-folding origami modules that transform their shape from a cubic to a flat shape, and vice versa, similarly to a three-dimensional (3D) morphing pixel. By changing the shape of individual modules, the system can generate desired shapes. Each module is based on a modified Kresling pattern, which has bi-stability during deployment so that it can maintain its shape in both states without any actuator force. Also, it can rapidly and reversibly transform its shape via folding and unfolding motions that are generated by a low-profile torsional SMA wire actuator positioned at fold lines. This approach is a hybrid of the modular and folding approaches so that the system can generate shape-shifting without complicated communication methodology between modules and bulky infrastructure, and has fast, compact and lightweight hardware. We demonstrate performance with a 3×3 matrix form of this module (40 mm side length) that can make five different shapes and it required only 15 seconds per transformation. This new shape-shifting system could be applied to design multi-functional self-folding origami such as a morphing 3D map.

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.

An active needle is proposed for the development of magnetic resonance imaging (MRI)-guided percutaneous procedures. The needle uses a low-transition-temperature shape memory alloy (LT SMA) wire actuator to produce bending in the distal section of the needle. Actuation is achieved with internal optical heating using laser light transported via optical fibers and side coupled to the LT SMA. A prototype, with a size equivalent to a standard 16-gauge biopsy needle, exhibits significant bending, with a tip deflection of more than 14° in air and 5° in hard tissue. A single-ended optical sensor with a gold-coated tip is developed to measure the curvature independently of temperature. The experimental results in tissue phantoms show that human tissue causes fast heat dissipation from the wire actuator; however, the active needle can compensate for typical targeting errors during prostate biopsy.

Jumping locomotion has been widely employed in milliscale mobile robots to help overcome their size limitations by extending their range and enabling them to overcome obstacles. During jumping, the robot's legs experience acceleration that is up to an order of magnitude greater than the gravitational acceleration. This large force results in bending of the jumping legs. In this paper, we study how the bending of the leg affects the jumping performance of a flea-inspired jumping robot. To judge the effect of the leg compliance, the amount of energy lost during jumping is determined by examining the ratio of kinetic energy to input energy, which we define as the mechanical efficiency. The bending leg is dynamically modeled using a pseudo-rigid-body model in order to precisely analyze the energy transfer. Jumping experiments are performed for five different legs, each with a different stiffness. Shape memory polymer rivets, which are lightweight and compact, were used to easily switch out the legs. The mechanical efficiency of the robot with appropriately chosen leg compliance was 41.27% compared with 36.93% for the rigid case and 21.51% for the much more compliant case. The results show that optimizing the compliance of a jumping leg can improve the performance of a jumping robot.

Fleas have a unique catapult mechanism with a special muscle configuration. Energy is stored in an elastic material, resilin, and the extensor muscle. Force is applied by the extensor muscle to generate a torque. Energy is released as a small triggering muscle reverses the direction of the aforementioned torque. A flea can jump 150 times its body length using this elastic catapult mechanism. In this paper, a flea-inspired catapult mechanism is presented. This mechanism can be categorized as an active storage and active release elastic catapult. Owing to its unique stiffness change characteristic, a shape-memory-alloy coil spring actuator enables the mimicking of the flea's catapult mechanism. Two types of flea-inspired jumping mechanisms were developed for verifying the feasibility of applying the concept to an efficient jumping robot. The first prototype has a flea-like appearance and the second is simplified to contain just the essential components of the flea-inspired catapult mechanism. The two prototypes are 20-mm- and 30-mm-long and can jump 64 cm and 120 cm, respectively. This unique catapult mechanism can be used not only for jumping robots but also for other small-sized robots to generate fast-releasing motion.

In this paper, we verify the scalability of an underactuated mechanism based on flexural buckling by applying the mechanism to multi-scale adaptive grippers. For verification, we design and fabricate two grippers having different sizes and install the grippers to a manipulator. As a result, the scalability of the mechanism will be shown by grasping from small electronic parts to large wine drinking glasses.

This paper describes a novel rivet fastener made with shape memory polymer (SMP). Shape recovery and modulus change are main two properties of SMPs that enable themselves to be promising base materials for fasteners. The new type of fastener was used to join two composite parts of a meso-scale robot. The fabrication procedure includes macro molding and subsequent laser machining in order to enhance manufacturability, and change size and design on demand. By pull-off experiment it was demonstrated that one single rivet can endure 8N of disengagement force. We applied this fastener to meso-scale flea robot and verified its feasibility.

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.

In gripping devices, adapting to highly unstructured environments such as irregularly shaped objects and surfaces continues to be challenging. To achieve safe and reliable gripping, many researchers have employed various underactuated mechanisms such as differential and compliant mechanisms. All these mechanisms have demonstrated successful gripping performances. They, however, have hardly considered scalability issues of underactuated mechanisms originating from additional force transmissions and onerous mechanism assembly. In this paper, we propose a structurally simple and scalable underactuated mechanism. The mechanism is demonstrated on a gripping device called the “Buckling gripper.” The Buckling gripper achieves adaptive gripping on rugged, uneven, and undulating surfaces typically found in the natural world. The key design principle of the Buckling gripper is inspired by a caterpillar's proleg that highly deforms depending on the shape of the contact surface. This key principle is applied to the gripper via flexural buckling. Normally, buckling is avoided in mechanical designs, but the buckling behavior of a flexure with an adequately selected length provides wide gripping range with a narrow range of force variation, which provides a sufficient number of contacts with even contact forces. As a result, the Buckling gripper achieves adaptive gripping on various surfaces, similar to a caterpillar.

The mobility of a wheeled robot in various terrains is basically limited by the size of the wheel. If the size of the wheel is fixed, the robot can only pass through a hole bigger than the wheel size. Furthermore, the robot cannot climb stairs much higher than the wheel size. Therefore, for a wheeled robot that has fixed dimensions, it is hard to improve the mobility depending on unexpected situations such as passing through a hole smaller than the original robot size and climbing stairs much higher than the original wheel size. To deal with the scale problem, we propose a deformable wheeled robot that can change the shape of the wheel depending on the obstacles. It improves the mobility the wheeled robot. In order to make the simple and robust robot, we employ smart structures and actuators such as composite flexure linkages, deformable polymers and shape memory alloy actuators. The robot shows three kinds of motion with combination of the motor and the SMA coil actuator. The motor is used for driving the wheel and the SMA coil actuators deform the wheel to produce a caterpillar-like motion. Using both actuators, the legged wheel motion can be produced. The light weight and the multimodal locomotion of the robot enhance the mobility for the search and rescue robot application.

Fleas can jump more than 200 times their body length. They do so by employing a unique catapult mechanism: storing a large amount of elastic energy and releasing it quickly by torque reversal triggering. This paper presents a flea-inspired catapult mechanism for miniature jumping robots. A robotic design was created to realize the mechanism for the biological catapult with shape memory alloy (SMA) spring actuators and a smart composite microstructure. SMA spring actuators replace conventional actuators, transmissions, and the elastic element to reduce the size. The body uses a four-bar mechanism that simulates a flea's leg kinematics with reduced degrees of freedom. Dynamic modeling was derived, and theoretical jumping was simulated to optimize the leg design for increased takeoff speed. A robotic prototype was fabricated with 1.1-g weight and 2-cm body size that can jump a distance of up to 30 times its body size.

We propose a biomimetic gripper, inspired by a caterpillar's proleg, that can reliably grip dusty and rough terrain. A caterpillar's proleg makes this possible by using a retractor muscle that opens and closes the proleg, and a planta that gives compliance to the proleg. We implement these components with shape memory alloy (SMA) coil actuators and flexure joints. The gripper is fabricated using composite links and flexure joints. This method replaces metal-based joints and links with flexure joints and composite-based rigid links. The composite-based design provides a simple, light weight, and compact structure that enables the gripper to be applied to small-scale robots. Modeling and experiments are used to analyze the gripping force. The results show how the gripping force changes depending on the length of the flexure joint. A prototype was built to demonstrate reliable gripping on a rough-surfaced block using an adaptive mechanism.

This paper presents a second prototype of the flytrap robot which mimics the fast snap-through motion of the Venus flytrap, the previous version of the robot. This second prototype employs a new type of unsymmetrically laminated carbon fiber reinforced prepreg (CFRP) structure which has two different curvatures, and an SMA spring actuator. To estimate the force of snap-through the structure, a linear beam bending model is introduced and a force-displacement experiment is demonstrated. Based on the numerical and experimental results, the flytrap robot can be closed rapidly and opened for re-load. The closure time is about 100ms.

In this video, composites and a polymer flexure joint are used to design mechanical elements. This composite structure can be applied to endoskeleton structures of biomimetic meso-scale robot. The basic active unit of the structure is a revolute joint with an SMA spring actuator that imitates a joint and muscle formation. The conventional mechanical element is replaced by composite structures design on 2D pattern. Using these elements, prototypes of a robot are fabricated to verify feasibility of application of the robot.

In this paper, we describe the design, fabrication processes, and control of a new biomimetic robot inspired by the inchworm, Ascotis Selenaria. The robot, called Omegabot, is named after the omega (Ω) shape of the crawling motion of the inchworm. This type of inchworm can travel approximately its body length per stroke along rough surfaces, leaf edges, and boughs of trees. The robot is built with smart composite microstructures (SCM), a fabrication method that uses laser micromachining to cut composites and assemble them into micro structures. We suggest a special pattern design for SCM to generate a two-dimensional turning motion, crawling motion, and a proleg design for climbing a tree. The robot is actuated with a shape memory alloy coil actuator activated by a PWM (pulse-width modulation) signal control electric current. As a result, Omegabot can crawl, turn, and grip a tree bough. This robot can be used for search and rescue or gathering useful information in an area where only small-scale robots can penetrate.