In 2020, the ratio of the Japanese elderly became more than 26 %. Under these circumstances, various as sisting and rehabilitation devices to help welfare work for the elderly and disabled using pneumatic soft actuators have been actively developed. A pneumatic soft actuator is useful for, not only power assisted system but also a rehabilitation device. In the previous study, the washable portable rehabilitation device using Extension type Flexible Pneumatic Actuators (we call it “EFPA” for short) that can provide passive exercise was proposed and tested. The attitude control of the device based on the model without position sensor was carried out. As a reha bilitation device using the same EFPA, W. Tian developed the Tetrahedral-shaped Soft Actuator (we call it “TSA” for short) for wrist rehabilitation was developed. Usually, a pneumatic actuator was often used for wear able and rehabilitation devices because it has advantage of compliance based on air compressibility. Especially, a pneumatic soft actuator is more suitable because it has more advantages such as lighter-weight and more com pliance based on flexibility. In the next step, it is necessary to investigate fundamental characteristics of the TSA. In this paper, the improved TSA and the shape of restraint PET sheets with the setting angle of EFPA of 45 and 60 deg. from the base stage were proposed and tested. In order to get higher stiffness and generated force, the shorter EFPA with the original longitudinal length of 180 mm was used for TSA. Each TSA has 10 restraint PET sheets. The setting position of each EFPA is changed so that the setting angle of EFPA from the base can keep 45 and 60 deg. Each PET sheet is installed every three pitches. The experimental setup to investigate the stiff ness and the generated torque of the TSAs as a fundamental characteristic was also reported. As a result, it can be concluded that the TSA with EFPA setting angle of 60 deg. is suitable to any rehabilitation equipment from view point of almost same bending stiffness and larger generated torque. In addition, we confirmed that TSA with the setting angle of 60 deg. can give larger bending angle and displacement from preliminary experiments. In addition, we also confirmed that a TSA can lift up the load with more than 130 N, that is enough lifting force for the target robot, under the condition when three EFPAs are pressurized.
