Pneumatic Relaxation Oscillator with Passive Components for Continuous Toes Movement.

Continuous passive motion of the toes improves blood circulation and may help ankle injuries heal faster. Soft devices are more appropriate than rigid devices to accommodate a variety of foot shapes. Most conventional pneumatic soft robots are actuated cyclically by solenoid valves, which require large amounts of power for valves and controllers. In this paper, we introduce a pneumatic oscillator comprised only of passive elements.The device is implemented with a relaxation oscillator based on RC filters from pneumatic components and connected to an inflatable soft actuator. We measured the input and output pressure to verify the RC filter and the oscillation characteristics. Then, we attached the toes CPM device to a participant and measured the toes bending angle and flexing torque. The low-pass and oscillation characteristic of the pneumatic RC circuit was verified. The toes CPM device could bend the toe angle between 15° and 30° with a torque of 1.5 Nm in a 15 s period. Compared to existing solutions, the proposed method allows for toe CPM using only passive pneumatic components which consumes less power and does not require active participation from the user.