関根 雅

The lightness and softness of pneumatic artificial muscles (PAMs) contribute to their safe use in mechanical devices involved with humans. However, a PAM has limited range of motion (ROM) and a stroke-dependent output force. In this paper, a mechanism combined with a PAM and a speed-increasing gear was developed to improve the tradeoff relationship between the ROM and output force and to verify its benefits in order to enhance the convenience of using PAMs. The gear enhanced the ROM and back-drivability of the PAM, which is beneficial for device safety in daily use. We first designed a mechanism consisting of an antagonistic system-driven PAM and the gear, and then simulated the relationship between the ROM and output force of the mechanism. The effectiveness of the mechanism including the gear was compared with a non-gear mechanism with multiple PAMs. We prototyped the PAM mechanism with and without the gear, and their ROMs, impact absorption, and viscoelasticity were experimentally investigated. Results showed that the gear effectively improved both ROM and output torque below a certain load moreover, the gear ratio and air pressure had large effects on the external static and dynamic forces, respectively. We confirmed comprehensively the effect and feasibility of the mechanism.

In developing a shoulder prosthesis, in addition to appropriate payload and range of motion under the constraints of weight and shape, impact absorption is very important for safe use. Hybridization of two different actuators (pneumatic elastic actuators with the features of lightness and intrinsic visco-elasticity, and servo motors that have stable torque and a large range of motion in combination with an antagonistic mechanism) was employed to achieve the development of the shoulder prosthesis. A two-link, two-degree-of-freedom arm was used to test the different hybridization configurations in order to investigate the impact absorption. A dynamic simulation platform based on four bimanual activities of daily living was established to obtain the required range of motion and torque for joints of a two-link, four-degree-of-freedom arm. The number of pneumatic elastic actuators required and the dimension of the antagonistic mechanism mechanical structures were optimized using the dynamic simulation platform. The best configuration of the two types of actuators was determined using the dynamic simulation based on the impact absorption results and other criteria. Moreover, a simplified prototype driven by hybrid actuation was made. It was shown that the pneumatic elastic actuator joint could improve impact absorption, and the actuator configuration of shoulder prostheses is activity of daily living dependent. The prototype could reproduce a certain activity of daily living motion, indicating its feasibility in daily living.

Unlike forearm amputees, transhumeral amputees have residual stumps that are too small to provide a sufficient range of operation for their prosthetic parts to perform usual activities of daily living. Furthermore, it is difficult for small residual stumps to provide sufficient impact absorption for safe manipulation in daily living, as intact arms do. Therefore, substitution of upper limb function in transhumeral amputees requires a sufficient range of motion and sufficient viscoelasticity for shoulder prostheses under critical weight and dimension constraints. We propose the use of two different types of actuators, ie, pneumatic elastic actuators (PEAs) and servo motors. PEAs offer high power-to-weight performance and have intrinsic viscoelasticity in comparison with motors or standard industrial pneumatic cylinder actuators. However, the usefulness of PEAs in large working spaces is limited because of their short strokes. Servo motors, in contrast, can be used to achieve large ranges of motion. In this study, the relationship between the force and stroke of PEAs was investigated. The impact absorption of both types of actuators was measured using a single degree-of-freedom prototype to evaluate actuator compliance for safety purposes. Based on the fundamental properties of the actuators identified, a four degree-of-freedom robotic arm is proposed for prosthetic use. The configuration of the actuators and functional parts was designed to achieve a specified range of motion and torque calculated from the results of a simulation of typical movements performed in usual activities of daily living. Our experimental results showed that the requirements for the shoulder prostheses could be satisfied.

Transhumeral and shoulder disarticulation amputees find it difficult to move their prostheses for goal-oriented movement using only their small residual limbs. Thus, spatial accessibility is especially important for shoulder prostheses. Moreover, because responding to external disturbances and absorbing impact using only the viscoelasticity and flexibility of the small residual limb is difficult, the intrinsic viscoelasticity of the shoulder prosthesis is indispensable for safety. In our previous work, we proposed a small pneumatic elastic actuator-driven parallel link mechanism for shoulder prostheses. In this paper, we propose two new devices, a sliding antagonistic mechanism and a soft backbone, to improve the spatial characteristics and disturbance responsiveness. We quantitatively evaluated a prosthetic arm with the two devices. The results showed that the two devices increased the arm's workspace and disturbance responsiveness.

Lightweight prostheses are preferred in terms of usability in daily living. However, this is not a property easy to realize, especially for shoulder prostheses. High portability, multiple degrees of freedom (DOFs) with an appropriate ROM (range of motion), sufficient end-effector power, and suitable viscoelasticity for the safe use in daily living, usually result in a heavy weight. In this paper, a hybrid shoulder prosthesis that combined servo motors and pneumatic elastic actuators, with a weight distribution scheme, was designed to meet the requirements. The prosthetic system was preliminarily tested by comparing its ADL (activities of daily living) motion data with that of an intact arm. The experiment results showed that the shoulder prosthesis could reproduce the motion of an intact arm, thus demonstrate its usability in daily living.

Human arms undertake most tasks in the activities of daily living (ADLs). When designing shoulder prostheses for high-level upper-limb amputees, we should consider not only how to realize high degrees of freedom under weight and shape constraints but also the user's individual task space in daily life. An appropriate mechanical structure that can make full use of state-of-the-art actuators and a scheme to optimize the structure's configuration to match users' spatial access and manipulability requirements are essential. In our previous research, a small pneumatic-actuator-driven parallel mechanism was studied as a shoulder prosthetic arm. In this paper, a systematic procedure is proposed to design the mechanism for a shoulder prosthesis considering force and spatial accessibility. This procedure includes ADL measurements to obtain the task spaces for individual subjects, indexes to evaluate the force and spatial accessibility and an optimization process based on kinematic and statics models. With this approach, the parallel mechanism was optimized for one important ADL task group, considering the trade-off between its required force and working space. Moreover, it was confirmed that the proposed design procedure could find solutions for various spatial specifications. That is, the approach could be used for individualized shoulder prosthesis design.

In this study, several indexes for spatial accessibility were proposed for evaluating the shoulder prosthesis with a small pneumatic actuator driven parallel mechanism in daily living use. Using the spatial accessibility indexes and manipulability indexes, the configuration of the parallel mechanism was optimized. Especially, the effect of biasing spacer and trunk motions on spatial accessibility were taken into consideration. The results showed that biasing spacers could improve the spatial accessibility by moving the center of the working space of the shoulder prosthesis towards the center of two specified spatial regions, which correspond to the expected frequently accessed area and the reachable area for an individual user's upper limb in daily living. And trunk motions could enlarge the working space thus further improve the spatial accessibility.

The shoulder prosthesis with a small pneumatic actuator driven parallel mechanism in daily living use, was suggested in this study. The configuration of the parallel link arm was optimized by means of the spatial accessibility and manipulability indexes for appraising the shoulder prosthesis. In particular, the effectiveness of biasing spacer was taken into consideration. The results showed that biasing spacers could improve the spatial accessibility. Eventually, the prototype was built on the basis of the optimal configuration, we validated the arm behavior and the availability of biasing spacers experimentally.