Based on the progress of Japanese aging society, development of rehabilitation devices and power as sistive devices has been required. In such devices, it is required to use human-friendly soft actuators. In ideal, the soft actuator with both a longer stroke and a larger generated force is required. However, a flexible actuator that can generate both larger force and longer displacement has not been developed on the market yet. It is also difficult to realize a flexible displacement sensor with long stroke while deforming its form according to the actuator’s shape. In the previous study, a various types of flexible linear stepping actuators that can push and pull the flexible rod while changing the gripping position of the tube have been proposed and tested. In this study, we proposed and tested a rehabilitation device for hip joint that using three PLSAs and one connecter connected with three flexible rods and a knee supporter. Also, to decrease uncertainness based on bending rods and influence of friction, a universal-joint-type stage for PLSA with a wire-type linear potentiometer was proposed and tested. The control system using PLSAs was also developed. The tracking position control of knee supporter based on an analytical model was carried out. However, the tested PLSA moves only every certain stroke. Therefore, the positioning accuracy depends on its stroke. Therefore, in this paper, a novel pneumatic linear stepping actuator that can change the stroke for one step freely was also proposed and tested. The construction and operating principle of the tested actuator are described in this paper. The tracking position control using rehabilitation devices with three previous PLSAs and renewed PLSAs for hip joint was carried out. As a result, it could be concluded that the con trolled length using the renewed PLSAs could trace the desired length well. The standard deviation of tracking control error was improved from 19.1 mm to 4.7 mm compared with the method using ordinal constant step motion.
