An extremely lightweight pneumatic soft actuator is an actuator made of non-expansion and contraction material such as the plastic film. It can be driven low pressure and has unique characteristic which are flexibility and lightweight. As for contraction type extremely lightweight pneumatic soft actuator by pleats structure, it has the characteristic that up to approximately 40% shrink axially by opening the pleats of air cell surface at the time of pressurization. The purpose of this study is to clarify relationship between the design parameter, contraction force and the shape of pressurized state. Therefore, we produced the actuator which changed the film ratio (the ratio of the film length of the radial direction for the axial direction) or the magnification of the air cell and measured contraction force for air pressure using a force gauge. In addition, we measured the expansion magnitude of the radial direction at the time of the pressurization. It became clear that there was a positive correlation between contraction force and magnification of the air cell, and a negative correlation between contraction force and the film ratio. As for the expansion magnitude of air cell at the time of the pressurization, it was confirmed that the expansion magnitude was close to the calculated value of the model approximated from the design parameters. Finally, we made the graph that showed relationship between contraction force and cross-sectional area in each pressure.
Wearable robots are desired to be lightweight from the viewpoint of safety and load reduction, so compressed air source is required to have high portability in order to install it in a wearable robot. The portable air supply system for wearable robot had been developed in previous works. The proposed system constructed with a compressor and a variable volume tank, which has been developed in our previous works, and has a mechanism of recompressing exhausted air. The developed tank can accumulate pneumatic energy converted into elastic energy. In addition, this tank can mitigate pressure change even when inflow or outflow of compressed air. The previous system can decrease energy consumption by the pressure mitigation characteristics of the variable volume tank. However, this tank had been made by trial and error to realize ideal characteristic. In this study, the model of variable volume tank is proposed to design the tank which has ideal deformation and energy characteristics. Moony-Rivlin function is introduced in the proposed model to calculate the deformation of rubber material. The energy characteristic is simulated based on this calculated deformation characteristic. In this paper, the accuracy of the proposed model is verified by comparing it with the characteristics of the variable volume tank manufactured based on the model.