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Falling leaves flutter from side to side due to passive and intrinsic fluid-body coupling. Exploiting the dynamics of passive fluttering could lead to fresh perspectives for the locomotion and manipulation of thin, planar objects in fluid environments. Here, we show that the time-varying density distribution within a thin, planar body effectively elicits minimal momentum control to reorient the principal flutter axis and propel itself via directional fluttery motions. We validated the principle by developing a swimming leaf with a soft skin that can modulate local buoyancy distributions for active flutter dynamics. To show generality and field applicability, we demonstrated underwater maneuvering and manipulation of adhesive and oil-skimming sheets for environmental remediation. These findings could inspire future intelligent underwater robots and manipulation schemes.

Customization is an important issue for assistive gloves because it affects glove performance. In this letter, we propose an assembly based customizable soft pneumatic assistive glove, named Exo-Glove PM. Pneumatic soft robots generally consist of a single structure with embedded actuators. However, when assembled, the region where the assemblies are connected easily undergoes large stress concentration that leads to failure. To overcome this issue, we have developed a hybrid actuator module that combines a soft actuation structure and rigid joining methods. In general, rigid joining methods require a bulky design to enable easy assembly, but Exo-Glove PM is designed to create pathways for assembly tools to access the bolt heads by bending certain parts. This novel way of joining assemblies allows soft robots to be built of multiple parts while minimizing the volume. It ensures small module size and enables modules to cover a wide range of hand sizes; the distance between each module is matched to the length of the user's phalanges using spacers. This approach allows users to customize the glove by assembly of standardized modules and maximizes the comfort and the performance of the glove without custom manufacturing and, thus, reduces costs.

Haptic systems render virtual reality by providing kinesthetic, tactile senses to an operator through a haptic device. Previous researchers analyzed haptic systems’ stability and performance issues. On haptic frameworks, a virtual coupling network that provides compliance between the haptic device and the virtual proxy for passivity distorts realistic interaction with virtual environment. That is, the operator will experience resistance even when the environment simulates free-motion. This paper suggests a virtual coupling triggering algorithm for improving free-motion performance of a haptic interface. A 1DOF exoskeleton for a knee joint is designed, and admittance control is used instead of compensating device dynamics to enable wide implementation of the haptic interface, up to a heavy and bulky haptic device. The algorithm utilizes surface EMG (sEMG) signal, which is easily collected from operators. Proper virtual coupling is designed according to previously derived guidelines for unconditional stability criteria. A method for pattern recognition of sEMG signal and a triggering algorithm corresponding to the recognized patterns are explained. The suggested algorithm successfully reduces peak of interaction force between the device and the operator by about half when the haptic interface simulates free-motion. Corresponding simulations and experiments are presented.

A wheel drive mechanism is simple, stable, and efficient, but its mobility in unstructured terrain is seriously limited. Using a deformable wheel is one of the ways to increase the mobility of a wheel drive robot. By changing the radius of its wheels, the robot becomes able to pass over not only high steps but also narrow gaps. In this article, we propose a novel design for a variable-diameter wheel using an origami-based soft robotics design approach. By simply folding a patterned sheet into a wheel shape, a variable-diameter wheel was built without requiring lots of mechanical parts and a complex assembly process. The wheel's diameter can change from 30 to 68 mm, and it is light in weight at about 9.7 g. Although composed of soft materials (fabrics and films), the wheel can bear more than 400 times its weight. The robot was able to change the wheel's radius in response to terrain conditions, allowing it to pass over a 50-mm gap when the wheel is shrunk and a 50-mm step when the wheel is enlarged.

A high aspect-ratio foil is known to be advantageous in terms of both thrust and efficiency in flapping propulsion. However, many species of fish have evolved a low aspect-ratio hydrofoil, which naturally leads one to search for its physical advantages in locomotion. Here we study the flow physics of a hydrofoil in angular reciprocating motion with negligible free-stream velocity to reveal the effects of an aspect ratio on hydrodynamic performance. By establishing a scaling law for the thrust of a foil of general shapes and corroborating it experimentally, we find that the thrust of an angularly reciprocating foil is maximized at a low aspect ratio of 0.7 while hydromechanical efficiency continuously increases with an aspect ratio. This result suggests that a low aspect-ratio foil can improve thrust produced by the foil when they start from rest, but at the expense of efficiency.

Tendon drives are widely used in robotics. The compliance of the tendon in such drives suits them for soft robots, including soft wearable robots, but several issues impede their use. Generally, the tendon should always maintain tension to prevent derailment from the spool. However, in soft robots, tendon tension induces high friction forces owing to the absence of ball bearings. Because the kinematics of the soft robot is basically nonlinear and changed by the deformation of the structure, the kinematic difference between the soft structure and the spool causes derailment of the tendon. Moreover, continuously maintained tension in soft wearable robots causes safety issues. The linear actuator can be an option. However, the need to increase the length of the linear actuator to accommodate the excursion length of its tendon is a barrier to its use in small-scale applications. To preclude this issue, a slack-enabling actuator that employs a spool is proposed. The space efficiency of the spool enables the mechanism to be small, and a one-way clutch applies unidirectional friction force to the tendon to tighten the tendon around the spool. This paper describes the design concept for the slack-enabling mechanism, its design optimization, and system identification for force control.

Small mobile robots with transformable wheels have recently emerged thanks to their increased mobility and maneuverability. When a high payload is applied to these robots, however, wheel transformation becomes difficult because they must directly overcome the payload’s weight. In this paper, we propose a wheel that can be transformed from its starting circular shape (radius, 56 mm) to a wheel with three legs (radius, 99 mm) under a high payload with low operating force. The key design principle of this wheel is to kinematically decoupled legs and passive locking. Its legs are kinematically decoupled but operated by a single air pump using a pneumatic channel connected to soft pneumatic actuators installed at each leg. Application of pressure causes the legs to behave like a coupled system through the pneumatic channel. With pressurization, the two legs that are not in contact with the ground easily emerge from body, and the leg in contact with the ground emerges once the wheel rotates. Once emerged, each leg is supported by a rigid pawl instead of by the soft pneumatic actuators. This setup enables the legs to be transformed independently with low air pressure, even under high payloads. It reduces system weight and the energy required to maintain the transformed shape. This legged wheel can overcome obstacles up to 2.9 times the radius of the wheel in its circular form, and wheel transformation can be accomplished with 85 kPa air pressure for payloads up to 1115 g.

Manufacturing paradigms have historically been shaped by social, economic, and technological aspect, including limitations and needs. Design for manufacturing (DFM) has been the main paradigm for last three decades since design is defined by the limitations of available manufacturing processes. Since reducing the time required for the development of new products has been one of the key issues for businesses, removing the gap between designers and manufacturers has been one of today’s main goals. Many methods were developed to reduce this gap including information and communication technologies (ICT). However, current issues have been shifting towards design-related issues such that researchers have been trying to make products desired by the customers rather than that which is cheaper to manufacture. In this article, hybrid manufacturing (HM) and the concept of smart factory are introduced as key technologies for the future paradigm of manufacturing: Manufacturing for Design (MFD). Issues related to the development of HM process and examples of HM process are explained, and the importance of smart factories for the implementation of MFD is shown. Finally, future trends of HM and smart factory are predicted at the end of this article.

As a steerable needle or robotic manipulator, the concentric-tube robot shows good potential for use in minimally invasive medical procedures. However, the torsional deformation of the precurved tubes comes at the price of instability, which not only limits the workspace and tool path but also potentially creates danger of tissue rupture when external load is applied. In this paper, we propose anisotropic patterning of tubes to solve the instability problem. Hole-patterning can tune the mechanical properties of the tubes so that the ratio of the torsional rigidity to the bending rigidity becomes higher. This study investigates the effect of pattern design parameters by building a lumped analytical model and examining it with finite-element analysis. The pattern is engraved via laser machining and we experimentally verify that material anisotropy reduces instability.

To improve the multi-functionality of a structure, a foldable or deployable structure with variable stiffness is needed. This article presents dual-stiffness structures with two stiffness states: a stiff state and a flexible state for a multi-mission capability. This dual-stiffness structure is based on a hybrid structure that combines rigid and flexible segments; when the rigid segments are rearranged, the bending motion of the compliant material is constrained by the rigid segments, which varies the stiffness of the structure. Instead of continuously changing the stiffness, the dual-stiffness structure abruptly changes the stiffness state with a simple reconfiguring mechanism. We developed two reconfiguring mechanisms: a sliding mechanism and a folding mechanism. Using a layering process, the dual-stiffness structure with a two-dimensional multi-layer design was manufactured. To verify the behavior of the structure, a simplified structure with no sliding mechanism was designed and simulated using a finite element method. The ratio of the length of a rigid segment to the length of a compliant segment determined the stiffness of the structure. This dual-stiffness structure with the reconfiguring mechanism can be effective for applications that require a big change in stiffness, such as for a deployable solar panel, or flexible display.

Soft wearable robots are good alternatives to rigid-frame exoskeletons because they are compact and lightweight. This article describes a soft wearable hand robot called the Exo-Glove that uses a soft tendon routing system and an underactuation adaptive mechanism. The proposed system can be used to develop other types of soft wearable robots. The glove part of the system is compact and weighs 194 g. The results conducted using a healthy subject showed sufficient performance for the execution of daily life activities, namely a pinch force of 20 N, a wrap grasp force of 40 N, and a maximum grasped object size of 76 mm. The use of an underactuation mechanism enabled the grasping of objects of various shapes without active control. A subject suffering from paralysis of the hands due to a spinal cord injury was able to use the glove to grasp objects of various shapes.

Recently, there have been many researches about applications of origami to mechanical engineering, which realizes a 3D sturcture by folding a 2D plane material. With this simple manufacturing process, origami was even adopted by some roboticists as a way to build an entirely new robot with benefits in terms of cost, weight, and structural simplicity. In this paper, we propose a new type of a walking robot based on origami structure. Because all the components of the robot that generate gait motion are mechanically connected, it can actually walk forward with only a single actuator. We also showed the similarity of gait trajectories between a kinematic analysis and the actual gait motion measured by video tracking. This result proved the possibility of designing an origami-based robot with the identical gait trajectory as we plan.

Pneumatic artificial muscles (PAMs) are frequently used actuators in soft robotics due to their structural flexibility. They are generally characterized by the tensile force due to the axial contraction and the radial force with volume expansion. To date, most applications of P AMs have utilized axial contractions. In contrast, we propose a novel way to control radial expansions of particular P AMs using anisotropic behaviors. P AMs generally consist of a cylindrical rubber bladder that expands with injection of air and multiple flexible but inextensible strings or mesh that surround the bladder to generate axial contraction force. We propose methods of generating radial expansion force in two ways. One is to control the spatial density of the strings that hold the bladder, and the other is to give asymmetric patterns directly to the bladder for geometrical anisotropy. To evaluate the performance of the actuators, soft sensors made of a hyperelastic material and a liquid conductor were attached to the P AMs for measuring local strains and pressures of the PAMs. We also suggest use of the proposed PAMs to a wearable therapeutic device for treating text neck symptoms as an application. The P AMs were used to exert a pressure to the back of the neck to recover the original spinal alignment from the deformed shape.

In this paper, we propose a new tendon routing method using branching tendon for driving a revolute joint. Unlike conventional tendon (or wire) widely used in the tendon transmission, the branching tendon splits into sub-tendons, and the end points of the sub-tendons are located on the same link but different positions. Thus, without using any complicated and bulky mechanism, the branching tendon can transmit the tendon force through the alternative path depending on the rotating angle of the joint. Based on this concept, the design of the branching tendon with two sub-tendons is proposed. Also, an analysis of the tension transmission path of this branching tendon is performed to increase force transmitting efficiency. By applying this branching tendon, a finger joint with a compact tendon routing path was constructed. And we have verified that the branching tendon can be used to develop robotic fingers or hand prosthetics.

Field of soft robotics has been widely researched. Modularization of soft robots is one of the effort to expand the field. In this paper, we introduce a magnet connection for modularized soft units which were introduced in our previous research. The magnet connector was designed with off the shelf magnets. Thanks to the magnet connection, it was simpler and more intuitive than the connection method that we used in previous research. Connecting strength of the magnet connection and bending performance of a soft bending actuator assembled with the units were tested. Connecting strength and air leakage prevention of the connector was affordable in a range of actuating pneumatic pressure. We hope that this magnet connector enables modularized soft units being used as a daily item in the future.

A critical issue for Bowden-cable transmission is bending-dependent hysteresis that degrades control performance and limits the application. The relationship between input and output of the Bowden-cable varies with the changing bending angle of the cable. This paper proposes a novel method that can compensate the varying hysteresis of the Bowden-cable using an embedded auxiliary wire, called a sensing wire. The accumulated bend angle of the Bowden-cable can be estimated by measuring the displacement change of the sensing wire and the input tension of the actuation wire. The estimated bending angle of the sheath can be used to compensate the hysteresis of the Bowden-cable with a feedforward control scheme, even though it is subject to the varying shape of the Bowden-cable. The proposed system has a simple and fully embedded design inside the sheath and does not require any external shape sensor or output tension sensor, which keeps the size and complexity of the system low. The results show that the control error of output tension decreased from 4.22 N to 0.69 N when the bend angle of the Bowden-cable changes from 0° to 560°.

We report on the design, optimization, and performance evaluation of a new wheel-leg hybrid robot. This robot utilizes a novel transformable wheel that combines the advantages of both circular and legged wheels. To minimize the complexity of the design, the transformation process of the wheel is passive, which eliminates the need for additional actuators. A new triggering mechanism is also employed to increase the transformation success rate. To maximize the climbing ability in legged-wheel mode, the design parameters for the transformable wheel and robot are tuned based on behavioral analyses. The performance of our new development is evaluated in terms of stability, energy efficiency, and the maximum height of an obstacle that the robot can climb over. With the new transformable wheel, the robot can climb over an obstacle 3.25 times as tall as its wheel radius, without compromising its driving ability at a speed of 2.4 body lengths/s with a specific resistance of 0.7 on a flat surface.

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.

Soft robotics, a concept contrary to conventional “hard” robotics, is a robot design methodology that uses soft materials inspired by nature. In contrast to a hard robot, a soft robot is composed of soft and flexible materials that blur the distinction between an actuator and a structure, which leads to unique characteristics that cannot be found in a conventional hard robot. This paper presents our approach to the issues that arise when the concept of soft robotics is applied to a wheeled robot. The compliance of the wheel diversifies its potential movement and allows for a high degree of adaptability to the environment. Although the wheel radius of the robot is 50 mm, it can pass through a 30 mm gap and climb a 45 mm step. While soft robotics displays properties whose performance can be challenging to implement, it also enables us to create complex forms of movement in a cheaper and simpler way. We expect that this kind of approach can provide a new design method for a deformable wheel.

This paper proposes three design concepts for developing a crawling robot inspired by an inchworm, called the Omegabot. First, for locomotion, the robot strides by bending its body into an omega shape; anisotropic friction pads enable the robot to move forward using this simple motion. Second, the robot body is made of a single part but has two four-bar mechanisms and one spherical six-bar mechanism; the mechanisms are 2-D patterned into a single piece of composite and folded to become a robot body that weighs less than 1 g and that can crawl and steer. This design does not require the assembly of various mechanisms of the body structure, thereby simplifying the fabrication process. Third, a new concept for using a shape-memory alloy (SMA) coil-spring actuator is proposed; the coil spring is designed to have a large spring index and to work over a large pitch-angle range. This large-index-and-pitch SMA spring actuator cools faster and requires less energy, without compromising the amount of force and displacement that it can produce. Therefore, the frequency and the efficiency of the actuator are improved. A prototype was used to demonstrate that the inchworm-inspired, novel, small-scale, lightweight robot manufactured on a single piece of composite can crawl and steer.

In order to operate a search and rescue robot in hazardous area, the robot requires high mobility and adaptable locomotion for moving in unpredictable environments. In this paper, we propose the deformable soft wheel robot that can produce three kinds of driving modes; caterpillar driving mode, normal wheel driving mode, legged-wheel driving mode. The robot changes its driving mode as it faces the various obstacles such as a small gap, stairs etc. Soft film and composite materials are used for fabrication of deformable wheel structure and Shape Memory Alloy (SMA) coil spring actuators are attached on the structure as an artificial muscle. Film lamination and an composite manufacturing process is introduced and the robot design is required to be modified and compromised to applying the manufacturing process. The prototype is developed and tested for verifying feasibility of the deformable wheel locomotion.

Legged locomotion has been widely researched due to its effectiveness in overcoming uneven terrains. Due to previous efforts there has been much progress in achieving dynamic gait stability and as the next step, mimicking the high speed and efficiency observed in animals has become a research interest. The main barrier in developing such a robotic platform is the limitation in the power efficiency of the actuator: the use of pneumatic actuators produce sufficient power but are heavy and big; electronic motors can be compact but are disadvantageous in producing sudden impact from stall which is required for high speed legged locomotion. As a new attempt in this paper we suggest a new leg design for a mobile robot which uses the slider-crank mechanism to convert the continuous motor rotation into piston motion which is used to impact the ground. We believe this new mechanism will have advantage over conventional leg mechanism designs using electronic motors since it uses the continuous motion of the motor instead of sudden rotation movements from stall state which is not ideal to draw out maximum working condition from an electronic motor. In order to control impact timing from the periodic motion of the piston a mechanical passive clutch trigger mechanism was developed. Dynamic analysis was performed to determine the optimal position for the mechanical switch position of the clutch trigger mechanism, and the results were verified through simulation and experiment. Development of a legged locomotion with two degrees of freedom, slider-crank mechanism for impact and additional actuation for swing motion, is proposed for future work.

`Multi-scale mass-deployable cooperative robots` is a next generation robotics paradigm where a large number of robots that vary in size cooperate in a hierarchical fashion to collect information in various environments. While this paradigm can exhibit the effective solution for exploration of the wide area consisting of various types of terrain, its technical maturity is still in its infant state and many technical hurdles should be resolved to realize this paradigm. In this paper, we propose to develop new design and manufacturing methodologies for the multi-scale mass-deployable cooperative robots. In doing so, we present various fundamental technologies in four different research fields. (1) Adaptable design methods consist of compliant mechanisms and hierarchical structures which provide robots with a unified way to overcome various and irregular terrains. (2) Soft composite materials realize the compliancy in these structures. (3) Multi-scale integrative manufacturing techniques are convergence of traditional methods for producing various sized robots assembled by such materials. Finally, (4) the control and communication techniques for the massive swarm robot systems enable multiple functionally simple robots to accomplish the complex job by effective job distribution.

Small mobile robots which use round wheels are suitable for driving on a flat surface, but it cannot climb the obstacle whose height is greater than the radius of wheels. As an alternative, legged-wheels have been proposed by many researchers due to its better climbing performance. However, driving and climbing performances have a trade-off relationship so that their driving performance should be sacrificed. In this study, in order to achieve both driving and climbing performances, a new transformable wheel was developed. The developed transformable wheel can have a round shape on a flat surface and change its shape into legged-wheel when it makes a contact with an obstacle. For design of the transformable wheel, the performance of legged-wheel was analyzed with respect to the number and curvature of the leg, and then the new transformable wheel was designed based on the analysis. Contrary to the existing transformable wheels that contain additional actuators for the transformation, the developed transformable wheel can be unfolded without any additional actuator. In this study, in order to validate the transformable wheel, a simple robot platform was fabricated. Consequently, it climbed the obstacle whose height is 2.6 times greater than the wheel radius.

In this paper, we propose a self-deployable origami structure and its application to a gliding wing module for jump-gliding. Generally, origami structures are composed of flat rigid facets. By using curved compliant facets instead of flat rigid facets, we endowed the origami structure with the ability to self-deploy and self-lock. When the origami structure is folded, the curved facets gradually flatten, and potential energy is stored on the flattened facets. By using the stored energy, the structure can rapidly deploy without an actuator. The geometry of the curved facet generates a notably high joint stiffness in the deployed state, which can be used as a self-locking mechanism. In jump-gliding, the gliding wing should be foldable and lightweight for efficient jumping and capable of rapid deployment for efficient gliding. By applying the suggested origami structure as a basic frame, the deployable gliding wing module can satisfy these requirements. The wing span of the module is 44.7 cm, and it weighs 20.3 g including a battery and a servo motor. The module can be folded in 1/8.1 of the deployed area, and it deploys within 350 ms when it needs to glide.

In this paper, a soft continuum manipulator is introduced. We tried to hybrid element technologies of soft robotics and traditional hard material based continuum robots. The soft continuum manipulator was composed of urethane rubber based soft and flexible modules. These modules gave the manipulator softness and adaptiveness. Additionally, the manipulator could be inflated with air pressure to change length and stiffness of the manipulator. Tendon driven mechanism, which is widely used for continuum robots and manipulators, was chosen as an actuating method for the soft continuum manipulator. 500 g of weight lifting tests was performed with this manipulator. Stiffness of the manipulator was varied with 69 kPa of air pressure while lifting the weight. The experiments showed feasibility of variable stiffness concept of this soft continuum manipulator.

In this paper, the force characteristics of the rolling contact joint are studied. Design parameters affecting performance of the rolling contact joint are considered, and the effects of tension and compression are shown by analysis. The rolling contact joint is compared to the pin joint by modeling, and it is shown that the force capability of the rolling contact joint is higher than that of the pin joint at a small scale. Finally, to explore the feasibility of using the rolling contact joint in prosthetics, a prototype hand prosthetic is developed using rolling contact joints.

In this paper, we propose a trajectory-adjustable integrated milli-scale jumping-crawling robot with improved ability to overcome obstacles compared to a robot that can only crawl. The robot employs a novel jumping module with enhanced energy storing-capacity and a height-adjustable active trigger. To increase the energy-storing capacity, latex rubber and knee-like joints are employed to utilize large displacement of the elastic material. The active trigger is based on a single DC motor and can release stored energy at any state, enabling the robot to control the take-off speed of jumping. The jumping module is integrated with the lightweight Dash crawler. The integrated jumping-crawling robot weighs 59.4 g and controls its moving trajectory by adjusting both its crawling speed and its jumping take-off speed.

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.

Bend sensors have been developed based on conductive ink, optical fiber, and electronic textiles. Each type has advantages and disadvantages in terms of performance, ease of use, and cost. This study proposes a new and low-cost bend sensor that can measure a wide range of accumulated bend angles with large curvatures. This bend sensor utilizes a Bowden-cable, which consists of a coil sheath and an inner wire. Displacement changes of the Bowden-cable's inner wire, when the shape of the sheath changes, have been considered to be a position error in previous studies. However, this study takes advantage of this position error to detect the bend angle of the sheath. The bend angle of the sensor can be calculated from the displacement measurement of the sensing wire using a Hall-effect sensor or a potentiometer. Simulations and experiments have shown that the accumulated bend angle of the sensor is linearly related to the sensor signal, with an R-square value up to 0.9969 and a root mean square error of 2% of the full sensing range. The proposed sensor is not affected by a bend curvature of up to 80.0 m(-1), unlike previous bend sensors. The proposed sensor is expected to be useful for various applications, including motion capture devices, wearable robots, surgical devices, or generally any device that requires an affordable and low-cost bend sensor.

The compliance of a fin affects the thrust of underwater vehicles mimicking the undulatory motion of fish. Determining the optimal compliance of a fin to maximize thrust is an important issue in designing robotic fish using a compliant fin. We present a simple method to identify the condition for maximizing the thrust generated by a compliant fin propulsion system. When a fin oscillates in a sinusoidal manner, it also bends in a sinusoidal manner. We focus on a particular kinematic parameter of this motion: the phase difference between the sinusoidal motion of the driving angle and the fin-bending angle. By observing the relationship between the thrust and phase difference, we conclude that while satisfying the zero velocity condition, the maximum thrust is obtained when a compliance creates a phase difference of approximately π/2 at a certain undulation frequency. This half-pi phase delay condition is supported by thrust measurements from different compliant fins (four caudal-shaped fins with different aspect ratios) and a beam bending model of the compliant fin. This condition can be used as a guideline to select the proper compliance of a fin when designing a robotic fish.

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.

Tendon driven mechanism is one of the most popular mechanism for transmitting force and power from a distance. The energy efficiency of a tendon driven system can be improved if it can maintain actuation force while it is not moving without mechanical work. This could be achieved by a brake; a brake without an additional actuator is preferred for the compactness of the whole system. We present a novel passive brake mechanism, a capstan brake, which consists of a capstan and two one-way clutches. The friction between the capstan and the cable amplifies a small resisting force (originated from an inactive motor) to gain enough brake force. Because no additional actuator is involved, generation of the brake force does not consume energy. Also, the one-way clutches enable the capstan to rotate in the winding direction. Therefore, the brake force is exerted only when it is needed, and the performance of the whole device does not decrease owing to the use of the capstan brake. The performance of the proposed brake mechanism has been evaluated through several tests. The results show that the amount of the maximum brake force for the test condition is more than 55 N (and can be further increased by increasing the number of windings), and that the force loss from the brake is negligible.

In this paper, we present a novel stiffness adjustable structure that changes its stiffness by pulling a tendon. It adopts an endoskeleton structure where rigid segments and compliant segments are alternately connected in series. The stiffness of this structure is controlled by compressing the compliant segments with an axial force. A tendon that runs through the endoskeleton and is fixed at the tip provides the axial compression force when pulled. We analyze the structure using the cylindrical isolation bearing model. The bending stiffness of the proposed structure was simulated and compared with experimental results. The structure can be stiffened approximately fifty-times the original stiffness. This stiffness adjustable structure can be used to increase the efficiency of a system that uses compliance, e.g., a robotic fish that uses a compliant fin for its propulsion system.

Fish generates large thrust through an oscillating motion with a compliant joint of caudal fin. The compliance of caudal fin affects the thrust generated by the fish. Due to the flexibility of the fish, the fish can generate a travelling wave motion which is known to increase the efficiency of the fish. However, a detailed research on the relationship between the flexible joint and the thrust generation is needed. In this paper, the compliant joint of a caudal fin is implemented in the driving mechanism of a robotic fish. By varying the driving frequency and stiffness of the compliant joint, the relationship between the thrust generation and the stiffness of the flexible joint is investigated. In general, as the frequency increases, the thrust increases. When higher driving frequency is applied, higher stiffness of the flexible joint is needed to maximize the thrust. The bending angles between the compliant joint and the caudal fin are compared with the changes of the thrust in one cycle. This result can be used to design the robotic fish which can be operated at the maximum thrust condition using the appropriate stiffness of the compliant joint.

Reports on major areas of robotics research that focus on robotic mechanisms and design methodologies. Also reports on various workshops and social events in this area that brings together robotics engineers developing new and innovative robotic technologies.

This paper presents a kinematic analysis of the locomotion of a gecko, and experimental verification of the kinematic model. Kinematic analysis is important for parameter design, dynamic analysis, and optimization in biomimetic robot research. The proposed kinematic analysis can simulate, without iteration, the locomotion of gecko satisfying the constraint conditions that maintain the position of the contacted feet on the surface. So the method has an advantage for analyzing the climbing motion of the quadruped mechanism in a real time application. The kinematic model of a gecko consists of four legs based on 7-degrees of freedom spherical-revolute-spherical joints and two revolute joints in the waist. The motion of the kinematic model is simulated based on measurement data of each joint. The motion of the kinematic model simulates the investigated real gecko’s motion by using the experimental results. The analysis solves the forward kinematics by considering the model as a combination of closed and open serial mechanisms under the condition that maintains the contact positions of the attached feet on the ground. The motions of each joint are validated by comparing with the experimental results. In addition to the measured gait, three other gaits are simulated based on the kinematic model. The maximum strides of each gait are calculated by workspace analysis. The result can be used in biomimetic robot design and motion planning.

This paper reviews various processes for manufacturing new type of robots termed “soft biomimetic robots.” Most robots are made of rigid metallic materials. But in recent years, various biomimetic robots based on soft materials and compliant parts have been developed. New manufacturing processes are required to fabricate these types of robots, and the processes include Shape Deposition Manufacturing (SDM) and Smart Composite Microstructures (SCM). Since the design of robots are limited by the available material and manufacturing processes, it is important to develop new manufacturing processes that will enable development of novel soft biomimetic robots. In this paper, various manufacturing processes which can be applied to soft robot fabrication are summarized, and features of those processes are described. Processes are divided into three categories; soft robot body fabrication, actuators for soft robots and stretchable electronics. This review provides a guideline for selecting manufacturing processes for soft robots and developing new processes that will enable new type of robots to be designed.

Small multi-legged animals that can climb vertical walls with a rough surface have inspired research on climbing locomotion. Most robots that can climb a rough vertical wall are large and heavy due to the large number of actuators required to produce the complex locomotion. This paper proposes a novel design for a small and lightweight climbing robot that uses a single actuator. To guarantee reliable wall climbing, the contact phase of two tripods should overlap. A quick return leg is designed to enable phase overlap without requiring an extra actuator. Alternating tripods are also designed, and small spines with compliance are modeled based on the pseudo-rigid-body model. Layer-based fabrication is used to reduce weight. The resulting biomimetic platform is 10cm long and 10.8g in weight and can climb up a near-vertical brick wall at a rate of 5.57mm/sec.

Tendon drive is commonly used in various kind of machines. And, the spool is commonly used to wind and unwind the tendon because of its simplicity and compactness. However, the slack of the tendon causes the derailment of the tendon out of the spool and fails the system. In order to use the tendon drive with the spool without concerning about the derailment, the slack enabling actuator is previously proposed. In this paper, the performance criteria and the design parameters affecting the performance of the slack enabling actuator are discussed.

Tendon driven mechanism has been widely used in mechanical systems because of its versatility to mechanical systems requiring complex transmission. This paper proposes a control strategy of slack enabling tendon actuator using feedback linearization. The slack enabling actuator is a newly developed tendon actuator that does not fail although the tendon slacks (non-positive tension) at the outlet of the actuator which is an essential operating phase when the tendon driven is applied to the soft wearable robots. To deal with the dynamic nonlinearities of the slack enabling actuator, input-output feedback linearization was adopted and linear disturbance observer was used to estimate the output tension of the wire and reject position following error due to the external load. The results show that the estimated tension coincide with the measured tension and a proposed method have proper characteristics to control the position of the tendon while estimating the tension of the output tendon.

Friction along the Bowden-cable transmission degenerates control performance unless it is properly compensated. Friction is produced when the bending angle of the Bowden-cable changes as the relative position of the actuator and the end-effector changes. This study proposes a method, termed loop routing, to compensate friction along the Bowden-cable. Loop routing involves making a one-round loop along the sheath that continuously maintains the sheath's bending angle at 2π regardless of the end-effector's position in 2-D space. This minimizes the bending angle change of the sheath as the end-effector translates in a 3-D workspace, which minimizes the friction change and enables feedforward friction compensation of the Bowden-cable without employing a sensor. An experiment in open-loop tension control of the Bowden-cable was conducted to evaluate the performance of the proposed method. Results show that the output tension follows the reference tension well, with an RMS error of 4.3% and a peak error of 13.3% of maximum reference.

These days, many people suffer from impairments caused by diseases and accidents. Impaired arm function is one of the biggest problem interrupting the activities of daily living for these people. To assist these people with the activities of daily life, many assistive devices for arm motion have been developed. However, many issues arise in their use in actual life, such as the need for customization, costs, and appearance. We focus on the soft meal assistive exoskeleton to minimize the two main issues for typical rigid body devices, structural complexity and cost. We use soft materials and apply the concept of target-oriented rehabilitation to reduce complex arm motions to simple motions. Also, we apply the adjustable weight-bearing system to the soft meal assistive exoskeleton to reduce the required motor power, which is one of the main challenges to reducing running time, size and costs. To evaluate improvement, we measured motor current, which indicates the motor power when the soft meal assistive exoskeleton pulls the upper arm to generate the desired trajectory.

In daily life, arm motions are important for many activities. However, many people suffer from arm impairment because of such conditions as muscle disease and spinal cord injury and experience inconvenience in daily life. We present a new type of adjustable weight bearing system by considering the torque change by the 2-DOF system. In this system, we choose the tendon-driven mechanism for transmitting the weight bearing force from the weight bearing system to the upper arm. Also, we use soft materials such as fabric for the wearing part to minimize joint misalignment and avoid an unfamiliar appearance. In this paper, we suggest the design of the adjustable weight bearing system and simulate the joint torque on shoulder and elbow joint to show the effect of the system.

Patients with neuromuscular disorders experience problems with the activities of daily living (ADL) due to limited muscle strength. Upper limb weight-bearing orthoses have been developed to increase quality of life by enabling patients to move their arms freely. Most existing designs help patients lift their arm by compensating the gravitational force on the sagittal plane. However, the essential ADL for a patient's actual life, such as eating, drinking, scratching the face, and receiving phone calls, require motion in 3D space that is mainly performed by forearm movement. To assist forearm motion, weight should be compensated by elbow flexion/extension and shoulder medial/lateral rotation. In this study, a weight-bearing mechanism that compensates the weight in 3D space with only two zero-initial-length springs is presented. We built a 4 degree of freedom passive weight-bearing orthosis (WBO) with three rotational axes on the shoulder and one rotational axis on the elbow to mimic the natural movement of a human arm. To design the WBO, joint placement was considered, and a slider-crank mechanism was used to solve the joint misalignment problem caused by the overlapping of the joint between the WBO and the human arm. A prototype was built to verify the function of the proposed mechanism. It showed sufficient weight compensation performance to enable self-reliance in ADL by reducing the effort required to move the arm.

To treat patients suffering from dysfunction of the abdominal muscles, positive pressure devices that can inject air directly into a patient's mouth have been developed. But injection of air requires blocking of a patient's mouth with an air mask or air hose, which causes the patient additional inconvenience in talking and in breathing with their own mouth. The Respiratory Rehabilitation and Assistance Robot was developed to provide ventilation assistance without hindering patients from talking and breathing with their own mouth. The basic principle of the robot is a negative pressure assistance, using an abdomen pressuring part to push the abdomen of the user and help the user to exhale. The robot is mainly manipulated with an attached joystick. But without an additional control routine to govern the amount of force applied when the joystick is moved, usability and safety issues occur. In this research, linear, logarithmic, and exponential profiles that modify the joystick trajectory were tested to advance maneuverability of the robot conditioning the joystick signal. Through experiments, we found that logarithmic profiles with certain shape factors improve both usability and safety.

A soft wearable robot with a tendon drive is a promising technology that enables a wearable robot to be compact and lightweight. A soft tendon routing system was previously proposed to apply a tendon drive to a soft wearable robot.

One of the major problems in utilizing origami structures is ensuring variable stiffness; a deployable structure needs to become stiff or flexible according to the requirements of its use in an application. In this study, we present a self-deploying tubular origami mechanism that switches between two distinctive states: small and flexible at its normal state and rigid and stiffened at a locked state. By embedding compact torsional SMA actuators into the mechanism in a novel way through stitching, the process of deploying from the normal to the locked state proceeds in a simple and low-profile manner. With global heating, the torsional SMA wires activate a buckling effect that draws a radical change of folding line from one diagonal to another in every unit tile of the tube, creating axial stiffness. The activated structure, which weighs only 2.9 g, can endure a load of 2.7 kg or more. Additionally, since it does not require bulky actuators, this origami structure can be highly mobile and small in size. This novel origami mechanism is expected to be useful in a wide variety of applications, such as aerospace equipment, mobile architecture, and medical devices, especially those used in minimally invasive surgery (MIS).

A soft wearable robot, which is an emerging type of wearable robot, can take advantage of tendon-driven mechanisms with a Bowden cable. These tendon-driven mechanisms benefits soft wearable robots because the actuator can be remotely placed and the transmission is very compact. However, it is difficult to compensate the friction along the Bowden cable which makes it hard to control. This study proposes the use of a position-based impedance controller, which is robust to the nonlinear dynamics of the system and provides compliant interaction between robot, human, and environment. Additionally, to eliminate disturbances from unexpected tension of the antagonistic wire arising from friction, this study proposes a new type of slack enabling tendon actuator. It can eliminate friction force along the antagonistic wire by actively pushing the wire while preventing derailment of the wire from the spool.