Control of generated force and stiffness in pneumatic air cylinder actuator

The authors developed an automatic choke valve where the unidirectional valve is arranged as bypassing so that the air of the high pressure will flow into the air cylinder and the piston can move at high velocity, and where the valve is automatically choked to decrease each flow so that a passive stiffness by spring effect or damping effect of the internal air is obtained. Then, we carried out experiments for evaluation of the system, using a humanoid robot arm with 7 degrees of freedom as double-acting air cylinder actuators with automatic choke valves and with I-PD control. The experimental results showed that an overshoot was approximately ten percents against the target angle but the joint was controlled with an error under one degree about follow-up to the target angle and with a time constant less than one second, even when five joints were simultaneously controlled under the influence of their respective motions.