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We have developed a pneumatic artificial rubber muscle using two shape-memory polymer (SMP) sheets. We attached the SMP sheets to a linear pneumatic artificial rubber muscle. Utilizing the large difference in the elastic modulus below and above the glass transition temperature, the shape fixity and shape recovery of SMPs, the bending direction and the initial shape can be changed. In this study, in order to increase the bending motion range, we developed a segmented SMP sheet with embedded electrical heating wires, and evaluated its mechanical properties using bending and tensile tests. Moreover, we attached such sheets to an artificial muscle and evaluated the bending motion. Bending tests showed that segmenting the SMP sheets greatly reduced their bending stiffness. In tensile tests at temperatures below the glass transition temperature, it was found that the artificial muscle with the attached sheet withstood high elongating loads without failure. Attachment of such segmented SMP sheets to an artificial muscle resulted in an increased bending angle. Through isotonic and isometric tests, we showed that the prototype actuator could bend in two directions.

We have developed a pneumatic artificial rubber muscle having a bending direction that can be changed using two shape-memory polymer (SMP) sheets, the stiffness of which depends on the temperature. In the present study, we attached two SMP sheets with embedded electrical heating wires to both sides of a pneumatic artificial rubber muscle in order to realize multidirectional actuation and evaluated the basic characteristics of the artificial muscle. The actuator is based on the design of a conventional curved-type artificial rubber muscle. Since only a heated SMP sheet becomes soft, the rigid SMP sheet inhibits the extension of the side of the actuator. Therefore, bending motion can be induced when air is supplied to the internal bladder. By controlling the temperature of the SMP sheets, the bending direction of the prototype actuator could be changed. Namely, three kinds of motions, such as two-directional bending and axial extension, became possible. Moreover, we improved the manufacturing method and the structure of the artificial muscle, such as the stitching method and the SMP sheet thickness, and evaluated the characteristics of the two-directional bending and the axial extension motions of the prototype actuator. We also calculated the theoretical values and compared these values with the experimental results. Furthermore, we examined the application of the actuators to a robot hand. Using the two-directional motion of the actuator, the proposed robot hand can grasp either small or large objects. The experimental results conducted using this prototype confirm the feasibility of the newly proposed actuator.

This paper proposes an upper-limb power assist machine driven by a single actuator to reduce the weight and cost. This assist machine is used to support the shoulder and elbow movements for viticulture operations, and upper-limb holding for load transport tasks. This assist machine consists of an arm part and a mounting part. The arm part is composed of a parallel link mechanism, which is driven by an actuator and a trapezoidal feed screw. To realize a natural upper-limb motion, the length of the arm part was designed based on the human upper-limb motion. The assist machine is controlled based on the user’s intention by applying bend sensors attached to the input device. By measuring the electromyography signal of five muscles, the effectiveness of the proposed upper-limb power assist machine was verified experimentally.

It is well known that fluid-powered systems are used practically in almost all industrial fields, including construction, manufacturing, transportation, among others. Nowadays, the rapid growth in the development of the mechanical elements in fluid-powered systems, such as control valves, actuators, and sensors, and the rapid growth in control strategies have given rise to pioneering in some novel application fields in ways that were thought to be impossible a decade ago. High-precision positioning control using the compressible fluid of pneumatic driving systems and multi-legged robots equipped with standalone hydraulic components are simple examples. Moreover, soft robotics based on fluid-powered technologies has attracted attention not only in academia but also in human support fields, which will become more important as Japan’s society ages. This special issue on “Fluid Powered System and its Application” includes one review paper and 22 other interesting papers related to the state of the art in the development of mechanical elements, total drive systems, motion control theory, and concrete applications of fluid-powered systems. We thank all of the authors and reviewers of the papers and hope this special issue helps readers to develop fluid powered systems that will contribute to developments in the academia and industry.

This study aims to use three-dimensional (3D) Finite Element Modeling (FEM) to establish a quantitative design optimization method forMcKibben-type pneumatic rubber artificial muscle. First, a simple 3D model that does not account for the friction between the tube and the fiber braid strands and or that between the strands themselves is developed. The model is validated through experimentation, and the usefulness of the model is examined. With this model, the effects of various parameters, e.g., the braid angle, on the operation of the artificial muscle is investigated. It is found that the characteristics of the artificial muscle can be predicted. Thus, the proposed analysis may be a useful design method for braided artificial muscles.

This paper proposes an upper-limb power-assist machine that is driven by a single actuator to reduce its weight and cost. The assist machine is intended for supporting shoulder and elbow movements during work in the field of viticulture. It consists of an arm part, a mounting part, and a drive part, the last of which contains an actuator and a worm gear. The arm part is equipped with a parallel link mechanism. In order to realize natural upper-limb motion, the length of the arm part is designed on the basis of human upper-limb motion. The assist machine is controlled by user intention through the use of bending sensors attached to the input device. The assistance effectiveness of the proposed assist machine is verified experimentally by measuring the EMG signals of the deltoid, biceps brachii, and triceps brachii muscles.

In this study, electromyography is applied to a subject’s forearm to discriminate between intended finger and wrist motions and the resulting signals are used to control a power assist glove. This glove is designed to assist with grasping. The fingers and wrist are moved when the corresponding muscles of the forearm contract simultaneously. Therefore, the intention to move either a finger or a wrist must be discriminated to enable assisting a finger movement by this glove. The introduction of Self-Organizing Maps (SOM) improves the ability to discriminate between these motions. In this study, the effectiveness of a discrimination method using SOM is verified experimentally.

In this study, a fingertip force display device that uses negative pressure is developed. The device can control the resisting force against a finger’s motion by regulating the negative pressure in an air chamber processed in the device. Information about the position of a finger is obtained with a Web camera using AR-Toolkit library, and the resisting force is controlled based on the fingertip position (velocity), which shows the capability of the VR-oriented application and mechanical impedance task. The effectiveness of the proposed system is verified through experiments.

This research focuses on developing a safe, lightweight, power assist device that can be worn by people during lifting or static holding tasks to prevent them from experiencing Low Back Pain (LBP). In consideration of their flexibility, light weight, and large force to weight ratio, two types of pneumatic actuators are employed in assisting low back movement for their safety and comfort. Actuator A is an elongation-type pneumatic rubber artificial muscle that is installed in the outer layer of the garment. Its two ends are fixed on the shoulders and thighs. It can output contractile force, assisting the erector spinae muscles in the same direction. Compared to McKibben-type pneumatic rubber artificial muscle, the elongation type has a larger contraction rate. Actuator B is a layer-type of pneumatic actuator; it is composed of two balloons, and it is installed in the inner layer of the garment. By taking into account the biomechanic structure of the human spine, this device can provide support in two ways. Actuator A acts as an external muscle power generators to reduce the force requirement for the erector spinae muscles. As actuator B acts as a moment arm of the contractile force generated by actuator A, it will increase the effective amount of torque. The device can be worn directly on the body like normal clothing. Because there is no rigid exoskeleton frame structure, it is lightweight and user friendly. The system’s Inertial Measurement Unit (IMU), composed of accelerometer sensors and gyro sensors to measure the human motion signals, can monitor the angles of the human body in real-time mode. By measuring the EMG signal of the human erector spinae muscles, the assistance effectiveness of the proposed device has been proven through experiments.

This study focuses on developing a safe, lightweight, power assist device that can be worn by people who like caregivers during lifting or static holding tasks to prevent low back pain (LBP). Therefore in consideration of their flexibility, light weight, and large force to weight ratio we have developed a Wearable Power Assist Wear for caregivers, two types of pneumatic actuators are employed in assisting low back movement for their safety and comfort. The device can be worn directly on the body like normal clothing. Because there is no rigid exoskeleton frame structure, it is lightweight and user friendly. In this paper, we proposed the new type of the wearable power assist wear and improved the controller of control system.

This research focuses on developing a safe, lightweight, power assist device that can be worn by people during lifting or static holding tasks to prevent low back pain (LBP). In consideration of flexibility, light weight, and large force to weight ratio, two types of pneumatic actuators are employed in assisting low back movement for safety and comfort. The device can be worn directly on the body like normal clothing. Because there is no rigid exoskeleton frame structure, it is lightweight and user friendly.

Recently, the attention has been focused on developing a wearable power assist robot by installing an actuator, such as motors, in the body and assisting and enhancing muscular power; there has been a considerable increase in research and development in some institutes and companies worldwide. Various types of wearable power assist robots have been proposed to support the upper and lower limbs, waist, and so on, which are to be used for the operational support of elderly and disabled people, nursing care work, and heavy lifting work in production sites. Some of them have been commercialized and their promotions have been advanced. Their social needs are extremely high, and there is an expectation of further improvements of assisting effect, installation performance, safety and convenience and affordability. In this paper, after the current state of research and development of this kind of robot is outlined, and our researches on pneumatic rubber artificial muscles, exoskeleton type standing motion assist devices, and wearable, lightweight, and soft power assist robots without an exoskeleton are introduced.

A novel pneumatic artificial muscle actuator is presented which is based on the design of a conventional curved type pneumatic bellows actuator. By inhibiting the extension of one side with fiber reinforcement, bending motion can be induced when air is supplied to the internal bladder. In this study, we developed a new actuator by replacing the fiber reinforcement with a Shape-Memory Polymer (SMP). The SMP can be deformed above its glass transition temperature (Tg) and maintains a rigid shape after it is cooled below Tg. When next heated above Tg, it returns to its initial shape. When only part of our actuator is warmed above Tg, only that portion of the SMP is soft and can actuate. Therefore, the direction of the motion can be controlled by heating. Moreover, our actuator can be deformed by an external force above Tg and fixed by cooling it below Tg.

The purpose of this study is to develop a portable energy-saving type air supply system. A variable volume tank is developed in order to drive a pneumatic actuator with a low discharge pressure in a tank. The developed tank composed of flexible materials can store pneumatic energy by converting it to elastic energy. In this paper, the composition of the system, the structure and characteristic of a variable volume tank and experiment of driving actuator with constant and variable volume tanks are discussed. As a result, the variable volume tank can drive the actuator at a lower supply pressure than with the constant volume tank.

The purpose of this study is to develop a pneumatic artificial rubber muscle that has a high contraction rate in order to realize the required performance for a power assist device. In addition, a bilateral type pneumatic wearable master-slave training device is developed as an application of this muscle. The developed rubber muscle is constructed with two nylon bands and an expansion unit, which is put between the nylon bands. The generated force from the expansion unit is converted to a contraction force by the nylon band. This rubber muscle can realize the high contraction rate. The high contractile rubber is used in the form of actuators in the developed knee device because of the above feature. In this paper, the structure and characteristics of the developed rubber muscle are described and then the structure of the developed master-slave device is described. Finally, the validity of the proposed device is evaluated from an experiment that assumes rehabilitation.