The ability to grasp objects broadens the application range of unmanned aerial vehicles (UAVs) by allowing interactions with the environment. The difficulty in performing a midair grasp is the high probability of impact between the UAV's foot and the target. For a successful grasp, the foot must smoothly absorb the energy of impact and simultaneously engage with the target in a short period of time. We present a bioinspired passive dynamic foot in which the claws are actuated solely by the impact energy. Our gripper simultaneously resolves the issue of smooth absorption of the impact energy and fast closure of the claws by linking the motion of an ankle linkage and the claws through soft tendons. We study the dynamics of impact and use the stiffness of the tendon as our design/control parameter to adjust the mechanics of the gripper for smooth recycling of the impact energy. Our gripper closes within 45 ms after initial contact with the impacting object without requiring any controller or actuation energy. An electroadhesive locking mechanism attached to the tendon locks the claws within 20 ms after reaching closed configuration. We demonstrated the effectiveness of our gripper by integrating it in an UAV and performing a variety of passive dynamic perching and grasping tasks.

As the burst buffer is being widely deployed in the HPC (High-Performance Computing) systems, the distributed file system layer is taking the role of campaign storage where scalability and cost-effectiveness are of paramount importance. However, the centralized metadata management in the distributed file system layer poses a scalability challenge. The object storage system has emerged as an alternative thanks to its simplified interface and scale-out architecture. Despite this, the HPC communities are used to working with the POSIX interface to organize their files into a global directory hierarchy and control access through access control lists.In this paper, we present ArkFS, a near-POSIX compliant and scalable distributed file system implemented on top of the object storage system. ArkFS achieves high scalability without any centralized metadata servers. Instead, ArkFS lets each client manage a portion of the file system metadata on a per-directory basis. ArkFS supports any distributed object storage system such as Ceph RADOS or S3-compatible system with an appropriate API translation module. Our experimental results indicate that ArkFS shows significant performance improvement under metadata-intensive workloads while showing near-linear scalability. We also demonstrate that ArkFS is suitable for handling the bursty I/O traffic coming from the burst buffer layer to archive cold data.

Existing technologies for patients with respiratory insufficiency have focused on providing reliable assistance in their breathing. However, the need for assistance in other everyday respiratory functions, such as coughing and speaking, has remained unmet in these patients. Here, we propose Exo-Abs, a wearable robotic system that can universally assist wide-ranging respiratory functions by applying compensatory force to a user's abdomen in synchronization with their air usage. Inspired by how human abdominal muscles transmit pressure to the lungs via abdominal cavity compression, a biomechanically interactive platform was developed to optimally utilize the abdominal compression while aligning the assistance with a user's spontaneous respiratory effort. In addition to the compact form factor, thorough analytic procedures are described as initial steps toward taking the human respiratory system into the scope of robotics technology. We demonstrate the validity of the overall human–system interaction with the assistance performance under three essential respiratory functions: breathing, coughing, and speaking. Our results show that the system can significantly improve the performance of all these functions by granting on-demand and self-reliant assistance to its users.

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.

Soft actuators have been widely studied in recent years because of their ability to adapt to diverse environments and safely interact with humans. Their softness broadens their potential range of medical applications since they can provide inherent safety. Among the various motions a soft robot can perform, "torsion" can maximize the efficiency of motion in confined spaces like the human abdominal cavity. This paper presents a fully soft actuator with a double-helix tendon routing path for large-angle torsional motions. The double-helix tendon routing enables the actuator to generate large twisting deformations, while also avoiding buckling generally associated with the torque imbalance in small diameter soft cylinder structures. A sequential casting method was developed for cylindrical structures with internal double-helix pathing. A parametric study of the actuator’s twisting angle and the axial contraction with respect to different design parameters was conducted, including the wire tension and path pitch. From the results, when the tendon was pulled with 40 N after the pitch was decreased, the axial contraction of the soft actuator was reduced by half and the torsional angle was doubled up to 600° without buckling.

Soft robotics deals with interaction with environments that are uncertain and vulnerable to change, by easily adapting to the environment with soft materials. However, softness inherently has large degrees of freedom which greatly complicates the motion generation. There has been no underlying principle for understanding the motion generated of soft robots. A big gap between rigid robots and soft robots has been that the kinematics of rigid robots can be defined using analytical methods, whereas the kinematics of soft robots were hard to be defined. Here, I suggest to use the minimum energy path to explain the kinematics of soft robots. The motion of soft robots follow the path where minimum energy that is required to create deformation. Hence, by plotting an energy map of a soft robot, we can estimate the motion of the soft robot and its reaction to external disturbances. Although it is extremely difficult to plot the energy map of a soft robot, this framework of using energy map to understand the motion of a soft robot can be a basis for unifying the method of explaining the motion generated by soft robots as well as rigid robots. A concept of physically embodied intelligence is a way to simplify the motion generate by soft robots by embodying intelligence into the design. Better performance can be achieved with a simpler actuation by using this concept. In nature, there are few example that exhibit this property. Flytrap, for example, can close its leaves quickly by using bistability of the leaves instead of just relying on the actuation. Inchworm achieves adaptive gripping with its prolegs by using the buckling effect. In this talk, I will give an overview of various soft robotic technologies, and some of the soft robots with physically embodied intelligence that are being developed at SNU Biorobotics Lab and Soft Robotics Research Center. These examples will show that the concept of physically embodied intelligence simplifies the design and enables better performance by exploiting the characteristics of the material and the minimum energy path concept can be a powerful tool to explain the motion generated by these robots.

Variable stiffness enables the safe and effective operation of the minimally invasive surgical instruments. In this article, we propose a continuously variable stiffness mechanism of the scalable tubular structure. The mechanism consists of multiple coaxial nitinol tubes, and each tube has an anisotropic distribution of flexural stiffness created by nonuniform through-hole patterning. The stiffness of the mechanism is varied by relative rotation and translation among the tubes, resulting in flexural stiffness difference up to 7.2 times in the direction of load. Its flexural stiffnesses along principal axes are independently controlled by the suggested counterrotation algorithm. The stiffness change is validated through analytical modeling, FEM simulation, and the experiments. Thanks to its physically embodied intelligence, the mechanism has a simple scalable structure and the response time is immediate. We applied this mechanism to control the stiffness of the steerable needle. Varying the stiffness grants the additional degree of freedom to control the needle's trajectory, which can expand the workspace of the steerable needle.

This paper introduces soft LEGO for bottom-up design platform of soft robotics that can be used for various purposes, ranging from research and fast prototyping of soft robots to toys and entertainment. We integrated the interlocking mechanism of LEGO into a modular soft robot. With this design, soft robots could be built by a simple and play-like assembling process. Three kinds of components were proposed to make soft robotics compatible with LEGO: pneumatically inflatable soft brick, flexible bending brick, and channel brick. The soft brick has an air chamber and can generate motions when inflated. The bending brick has flexure and is bendable for generating motion when the assembled soft bricks are pneumatically actuated. The air channel brick has an air channel inside and works as an interface between air hoses and soft LEGO bricks. Detailed design parameters of the soft brick were optimized based on the Taguchi method with finite-element analysis to improve robustness. Design of the bending brick was selected based on experimental results to enhance the robustness of the flexure. Thanks to the multi-material 3-dimensional printer, the soft LEGO bricks could be fabricated with a single printing process. To see the feasibility of soft LEGO as a bottom-up design platform, a simple toy robot for children and a gripper that had a hybrid mechanism of hard and soft materials were built and tested. We hope this soft LEGO could lower the hurdle of soft robotics for children, researchers from other fields, and the public interest in robotics.

In this paper, we propose an omnidirectional jumper with expanded locomotion capabilities. The mechanisms for four functions-jumping, steering, self-righting and take-off angle adjustment-are designed using only two motors to maximize the jumping performance. Jumping uses the modified active triggering mechanism with one motor. Steering shares this motor and uses the wheel touching the ground. The take-off angle is adjusted by changing the angle between the body and the foot using another motor. Self-righting is possible by utilizing combinations of the movements that occur in the energy storing and angle adjustment processes. With these four functions, the robot is capable of jumping in all directions and can jump anywhere in between the maximum height and maximum distance. It can also jump multiple times by self-righting. The robot, with a mass of 64.4 g, jumps up to 113 cm in vertical height, and 170 cm in horizontal distance. This robot can be deployed to explore various environments. Moreover, the design method to implement more functions than the number of motors can be applied to design other small-scale robots.

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°.

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.

This paper presents the development of a polymer-based tendon-driven wearable robotic hand, Exo-Glove Poly. Unlike the previously developed Exo-Glove, a fabric-based tendon-driven wearable robotic hand, Exo-Glove Poly was developed using silicone to allow for sanitization between users in multiple-user environments such as hospitals. Exo-Glove Poly was developed to use two motors, one for the thumb and the other for the index/middle finger, and an under-actuation mechanism to grasp various objects. In order to realize Exo-Glove Poly, design features and fabrication processes were developed to permit adjustment to different hand sizes, to protect users from injury, to enable ventilation, and to embed Teflon tubes for the wire paths. The mechanical properties of Exo-Glove Poly were verified with a healthy subject through a wrap grasp experiment using a mat-type pressure sensor and an under-actuation performance experiment with a specialized test set-up. Finally, performance of the Exo-Glove Poly for grasping various shapes of object was verified, including objects needing under-actuation.

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.

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. In this study, a slack enabling mechanism was proposed to increase the efficiency and guarantee the safety of the soft tendon routing system. The proposed mechanism eliminates the pre-tension of the tendons and minimizes the friction induced by the pre-tension, which causes inefficiency and a lack of safety. Furthermore, the slack enabling mechanism mechanically prevents the derailing of the tendon from the spool. In order to verify the benefits of the proposed mechanism, a prototype was built and tested on the Exo-Glove, which is a soft wearable robot for the hand. The experiment results showed that the prototype could completely remove the pre-tension, whichproposed to apply a tendon drive to a soft wearable robot. In this study, a slack enabling mechanism was proposed to increase the efficiency and guarantee the safety of the soft tendon routing system. The proposed mechanism eliminates the pre-tension of the tendons and minimizes the friction induced by the pre-tension, which causes inefficiency and a lack of safety. Furthermore, the slack enabling mechanism mechanically prevents the derailing of the tendon from the spool. In order to verify the benefits of the proposed mechanism, a prototype was built and tested on the Exo-Glove, which is a soft wearable robot for the hand. The experiment results showed that the prototype could completely remove the pre-tension, which allowed the Exo-Glove to function well with the prototype.

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.

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).

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.

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.

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.

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

The concentric-tube continuum robot generates distal end motions by translating and rotating the proximal ends of pre-curved tubes that overlap concentrically. This robot does not require additional actuators along the tubes because the overall curvature and distal end position are determined solely by interactions between the inner and outer tubes. However, under certain conditions, the rotation of the distal end is hindered as the actuation energy accumulates into torsional energy of the tubes. As the distal ends are rotated further, the accumulated energy from the twisting is suddenly released, which makes the tubes snap to a remote position. This is called the snapping problem, and it considerably limits the performance of the robot. In this paper, we propose a novel design for the concentric tubes to eliminate the snapping problem. The new design creates groove patterns on superelastic nitinol tubes to make the tubes more flexible to bending than twisting. Simulations and experiments were performed to verify that the tubes with our groove patterns had anisotropic structural characteristics, and video image analysis verified that this structural property can eliminate the snapping problem. A concentric-tube robot with this new tube design can have a larger workspace area because tubes with greater curvatures can be used without the snapping problem.

The unique characteristics of origami to realize 3-D shape from 2-D patterns have been fascinating many researchers and engineers. This paper presents a fabrication of origami patterned fabric wheels that can deform and change the radius of the wheels. PVC segments are enclosed in the fabrics to build a tough and foldable structure. A special cable driven mechanism was designed to allow the wheels to deform while rotating. A mobile robot with two origami wheels has been built and tested to show that it can deform its wheels to overcome various obstacles.

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.

Main goal of this research is to design and fabricate an exoskeleton type assistive device for polymyositis patients, which is extremely compact, lightweight and also comfortable. In order to achieve this goal, the target motion of the device is focused on eating motion which is one of the most important task of daily life. Also, the exoskeleton is designed with soft materials such as fabric, rubber, wire and other compliant materials. The most rigid component used in the exoskeleton is a supporting part made of flexible board. By adopting these materials and concentrating on specific target motion, the number and size of the actuators can be reduced so that total complexity, weight and size of the device decrease. Also, the characteristics of soft material allows comfortable wearing sensation, low cost and good appearance. Therefore, the device becomes affordable and convenient. Polymyositis patients are chosen as the target user since the characteristics of their symptom can reduce complexity of the exoskeleton. Also a special controller is designed to utilize the available motion of the polymyositis patients. Some experiments are conducted to evaluate the performance of the exoskeleton.

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.

A small mobile robot that uses round wheels has a stable ride ability on flat surfaces, but the robot cannot climb an obstacle whose height is greater than the length of its wheel radius. As an alternative, legged-wheel robots have been proposed for their better climbing performance. However, such legged-wheel robots have a poor driving performance on flat surfaces since their center of mass is vertically changed. Transformable wheels are used to make the robot drive with round wheels on flat surfaces and climb an obstacle with legged-wheels. However, the design of previously developed transformable wheels is complicated because it needs actuators for the transformation. Thus, it is not suitable for small robots. In this paper, a simple robot platform called Wheel Transformer that uses a new kind of transformable wheel is described. The transformation process is passively operated by an external frictional force, so it does not need any actuators. We fabricate the transformable wheel as well as the robot platform based on analysis of transformation mechanism. The robot can climb an obstacle whose height is 2.6 times greater than its wheel radius.

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.

Origami is the traditional Japanese art of paper folding. Due to its fascinating properties, several attempts are being actively made to expand applications of origami-inspired designs in engineering. This paper presents the design of a deformable wheel based on an origami structure that was integrated with a small-scale mobile robot. The wheel of the robot employs an origami structure proposed by Guest et al. All segments of the structure are connected by links-i.e., folding lines-and this linked structure provides advantages in terms of maintaining geometry and force transmissibility. These two advantages enable control of the shape or size of the wheel by activating a certain portion of the structure. With this property, the wheel diameter of the robot is reduced from 11 cm to 4 cm by four SMA coil spring actuators. Two plate springs are embedded in the wheel to maintain stiffness and allow the wheel to recover from contraction. With the deformable wheel, the robot can pass through a 5 cm gap despite having an 11 cm wheel in its normal state. This deformable wheel concept can be used to build mobile robots that can move quickly with large wheels and move through small gaps when required.

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.

Tendon-driven mechanisms are one of the most popular mechanisms for transmitting force and power from a distance. The energy efficiency of a tendon-driven system can be improved if it can maintain the actuation force while not moving, without mechanical work. This can be achieved by using a brake. A brake without an additional actuator is preferred for achieving compactness of the entire system. We present a novel passive brake mechanism - the capstan brake, which consists of a capstan, rollers, and one-way clutches. The friction between the capstan and tendon amplifies a small resisting force (originating from an inactivated motor) to gain enough brake force. Because no additional actuator is involved, no energy is consumed to generate the brake force. In addition, the one-way clutch enables the capstan to rotate in the winding direction. Therefore, the brake force is only exerted when needed, and the performance of the entire device does not decrease owing to the use of the capstan brake. The brake force of the system is limited to handling the safety issues. If the external load exceeds the maximum brake force, the brake becomes back-drivable again. The limit level can be controlled by changing the number of times the tendon is wound around the capstan. Another issue for a tendon-driven system is that the tendon escapes from a spooler when the tendon does not maintain proper tension. By implementing the rollers with the capstan brake, the tendon cannot escape from a spooler even though the tendon is not pulled by an external load in all actuating situations. The performance of the proposed brake mechanism was evaluated through several tests. The results showed that the capstan brake is suitable to be applied to the wearable robotic hand, which is one of the prospective applications of the brake. The force loss caused by the brake was negligible and the brake operated properly even though the tendon was not pulled by an external load in all actuating situations.

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.

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.

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.

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.

This paper presents a lightweight robotic hand that uses an SMA actuator array. The SMA wires are activated via joule heating, implementing SBC. A coordinate transformation architecture which reduces activation signal dimensionality, known as C-segmentation, is presented. A robotic hand with 16 controlled DOF and 32 independent SMA axes was developed to demonstrate the advantages of joule-heated SBC; the total weight of the robotic hand system was less than 800 grams. 16 different grasping postures were successfully recreated by using only 8 C-segments. It was concluded that a very lightweight robotic hand with simple controls can effectively reproduce the necessary configurations for conventional grasping situations.

This paper presents a cellular actuator design for a robotic hand. Although the motions of robotic hands are complex, a design of cellular actuator segmentation can be simplified by extracting the features of given postures and using them to design and control the actuator. A method of using captured hand posture data to design the actuator segmentation is proposed. Data from the eight most frequently used hand grips in a daily living, as defined in the sollerman hand function test, is used in this design. The gathered joint angle data is transformed into actuator displacement data and used to generate a segmentation design of the actuator. For segmentation design, feature extraction method, called non-negative matrix factorization with constraints is proposed. The actuator system has 12 SMA actuators each with eight segments, resulting in 96 configurable segments before the coupled segmentation design is applied. The coupling segmentation design effectively groups the segments into clusters which are simultaneously controlled. The segmentation design reduces 96 separately controlled segments to 8, while maintaining the ability to accomplish all desired postures. A robotic hand with five fingers, designed and fabricated using the FDM process, is driven with this actuator system, and eight hand postures are reproduced with the robotic hand

A new approach to artificial muscle actuator design is presented, and is implemented using shape memory alloys (SMA). An array of SMA actuators is segmented into many independently controlled, spatially discrete volumes, each contributing a small displacement to create a large motion. The segmented cellular architecture of SMA wires is extended to a multiaxis actuator array by arranging the segments in a two-dimensional (2-D) array. The multiaxis control is streamlined and coordinated using a 2-D segmentation method in order to activate multiple links of a robot mechanism in a coordinated manner. The basic principle of segmented binary control (SBC) is first presented, followed by multiaxis segmentation theory and a design procedure. The method is applied to a five-fingered robotic hand capable of taking a variety of postures. A 10-axis SMA actuator array is built, and SBC is implemented using Peltier-effect thermoelectric devices for selective local heating and cooling. Experiments demonstrate the feasibility and effectiveness of the new method.

A novel multi-axis Shape Memory Alloy (SMA) array actuator has been developed for driving five-fingered anthropomorphic robot hand. The new actuator array uses Segmented Binary Control (SBC), which controls the SMA wires segment by segment in a digital manner. Normally, SMA wires are hard to control and require nonlinear controllers to control each wire. SBC simplifies the control of SMA wire but increases the complexity of the design and the number of control loops. A multi-axis segmentation theory has been developed to reduce the design complexity and the number of control loops by reducing the number of segments. Segmentation architecture of an actuator array is designed for five-fingered robotic hand that performs fourteen different postures. The segmentation architecture is implemented with ten SMA wires sandwiched between a layer of thermoelectric modules embedded on a printed circuit board and a layer of acrylic substrate board with grooves. Initial results of the segmented binary controlled SMA wire are verified with minimum segment architecture of a single axis.

This paper describes a new approach to the control of highly nonlinear shape memory alloy (SMA) actuator systems, in which SMA wires are divided into many segments and their thermal states are controlled individually as a group of finite state machines. Instead of driving a current to the entire SMA wire and controlling the wire length based on the analogue strain-temperature characteristics, the new method controls the discrete state (austenite or martensite) of individual segments and thereby controls the total displacement proportional to the number of the austenite segments. Although the inherent property of SMA is highly nonlinear and uncertain with a prominent hysteresis, this Hysteresis Loop Control is robust and stable, providing characteristics similar to a stepping motor. Furthermore, this method can apparently eliminate the latency time associated with phase transition of SMA actuators. Coordination of the multitude of segments having independent thermal states allows for fast response with zero latency time even for thick SMA wires. The new control method is implemented using the Peltier effect thermoelectric devices for selective segment-by-segment heating and cooling. Experiments demonstrate effectiveness of the proposed method, which exploits the inherent hysteresis and nonlinearity of SMA rather than compensating for the nonlinearity.

Long hours of driving cause the tissues to be pressurized for an extended period and result in considerable discomfort and driver fatigue. Periodically stimulating the tissues in contact with the car seat, as well as providing adequate ventilation and pressure relief may alleviate these problems. In this paper, we describe the design of a robotic car seat capable of actively redistributing the contact pressure on the tissue and thus providing relief to the weary driver. The distributed nature of the surface actuation and space limitations necessitate the use of a large number of actuators that must be confined to a small volume. We design and use Shape Memory Alloy actuator units, which can accomplish the above goals by virtue of their high power to weight ratio. Matrix architecture is used for the drive amplifier that can drive N/sup 2/ actuator units using only 2N switches and is thus suitable for vast degree of freedom systems in terms of scalability. The prototype car seat uses 16 SMA actuator units, which are driven in a matrix architecture using 8 switches. The actuators are compactly housed under the car seat and the force and displacements are transmitted to the flexible seat surface through a novel routing scheme. We create a distributed lifting motion of the seat surface in order to stimulate the tissue. A complementary distributed sinking motion of the seat surface is created in order to provide pressure relief and ventilation.

A new approach to the design and control of shape memory alloy (SMA) actuators is presented. SMA wires are divided into many segments and their thermal states are controlled individually in a binary manner. The Peltier effect is used for heating and cooling individual segments of the SMA. Unlike the traditional way of controlling the wire length by driving a current to the entire SMA wire, the new method controls the binary state (hot or cold) state of each segment. The total displacement is then proportional to the number of the segments having the heated state, i.e. austenite phase. This architecture has three salient features, which would overcome fundamental difficulties of SMA. 1) Although the inherent property of SMA is highly nonlinear and uncertain with a prominent hysteresis, the binary state/phase control does not depend on the complexity of SMA state transition. 2) With use of the Peltier effect thermoelectric devices the response of SMA becomes more controllable, stable, and more accurate compared to the traditional air cooling and electric wire heating. 3) By operating at the heated state, SMA shows considerable load disturbance rejection compared to traditional methods. First, the basic principle and architecture of the segmented SMA actuator system are described. Initial implementation and feasibility tests are then presented, followed by discussion of the experimental results.

A new approach to artificial muscle actuators assimilating the morphological and kinesiological structure of biological muscles is presented and is implemented using shape memory alloys. Like a biological muscle consisting of short muscle fibers arranged in an overlapping series, an array of SMA actuators are segmented into many independently controlled, spatially discrete volumes, each contributing a small displacement to create a large motion. Furthermore, the segmented architecture of SMA wires is extended to a multi-axis actuator array by arranging them in a two-dimensional array. The multi-axis control is streamlined and coordinated using a two-dimensional segmentation method in order to activate multiple bones (links) of a skeletal robot structure in a coordinated manner. Moreover, the 2-D segmentation is so designed that coordinated gross motion as well as independent fine movements may be generated with minimum complexity and minimum control loops.

Traditionally, a dedicated power amplifier is used for driving each actuator. For a system with a large number of actuator, this one-to-one architecture may be inefficient and costly. This paper presents a new, scalable architecture, called networked actuation architecture, for the power drive and control of large-scale actuation systems. The networked actuation architecture allows sharing of the drive amplifiers among many actuators, and thereby reducing the number of the drive amplifiers and wiring requirements. Since several actuators are sharing a drive amplifier, traditional control algorithms are not applicable. Several new control algorithms for large-scale actuation are presented and compared. Simulation is performed for different types of control algorithm for different types of inputs.

A new concept for an actuator array is presented where a vast number of actuators are contained within a small volume and are controlled in a scalable sense. This vast degree-of-freedom system utilizes an array of shape memory alloy wires embedded within a network of fluidic vessels. A matrix manifold and valve (MMV) system routes fluid from hot and cold reservoirs in order to control an array of N/sup 2/ SMA actuators using only 2N valves. A prototype MMV system containing a 4 by 4 array of wet SMA actuators is designed and implemented. Control strategies suitable for controlling MMV system that uses 2N valves to control N/sup 2/ actuators are presented. Two different protocols are presented and evaluated. The system error increases without bound under certain input conditions, since all the actuators cannot be activated at the same time. Simulations show that system error starts to go out of bound when the individual actuator is activated 25% of the time for the 4 by 4 arrays of the actuators.