Abstract
Pneumatic servo system is expected to be applied for the contact tasks because of its function of impact force absorption and the possibility of minute force control due to air compressibility. An impedance control, unified approach to control the dynamic relation between the external force and displacement, has been confirmed to be effective for the contact tasks. However, it requires a force sensor, which makes the structure of control system intricate.
We propose an impedance control method without force sensor and applied it to a pneumatic servo system comprising a bellophram type cylinder and PCM control valves. A control system using a disturbance observer which estimate the external force is constructed in an internal position control loop.
There exists a dead time element in most of the pneumatic servo systems, so a Smith's method is introduced to increase the stability margin. Then an estimation function, which is a realization indicator of the setting impedance, is proposed. By using this estimation function, the stability of the control system also can be inspected so the control parameters can be chosen rationally with considering the stability of the control system simultaneously. Through some experiments, the proposed control method is confirmed to be available for the pneumatic servo system.
