Development of Flexible Pneumatic Spherical Actuator for Giving Passive Exercise with Simplification of its Attitude Control System and Simple Analysis for Evaluation

Abstract

With aging society, pneumatic soft actuators with human friendly features such as welfare support and virtual reality have been developed. In a previous study, a flexible pneumatic spherical actuator (FPSA) that could allow individuals to exercise passively while holding on to the top end of the actuator during motion was proposed. The actuator’s ability to improve the range of joints after surgery was tested. The FPSA comprises three extension-type flexible pneumatic actuators (EFPAs), shaped like a rugby ball through restraint by PET sheets. This paper introduces a non-contact bending/extension sensor composed of a Hall sensor and a ring-shaped magnet, proposed and tested as an attitude sensor. Recognizing that the FPSA’s bending direction depends on the pressurized EFPA, a simple measurement system was also proposed and tested. This system measures the bending angle and extensional displacement by measuring the displacement of the restraint plate at the center bottom of the FPSA. To simplify the attitude control system, a design reducing the number of valves from six to four was developed and tested. Results confirmed that the FPSA, equipped with this control system, could trace the desired bending angle even when the bending directional angle changed. Additionally, an analytical model was proposed to evaluate the effectiveness of passive exercise enabled by the spherical actuator. This model calculates the FPSA’s shape for various input pressures to the three EFPAs in open-loop attitude control. Results showed that the calculated attitude closely matched the actual actuator’s behavior.