Impedance Control of Pneumatic Parallel Manipulator Using Disturbance Observer

In order to make a robot perform a contact task with an environment, robot must have an enough skillfulness and compliance simultaneously.Parallel manipulator has attracted an interest because of its features such as a multiple d.o.f. for its compact mechanism which is available for complicated tasks. In the meanwhile pneumatic actuator has a high power/weight ratio and an inherent compliance function due to the air compressibility which makes it possible to perform a minute force regulation. In this paper we apply an impedance control to the prototype of parallel manipulator driven by pneumatic cylinders and its control performances are investigated.There are 2 general impedance control strategies, one is force based type and the other is position based one. In the former one the influence of manipulator's dynamics such as inertia force and damping one affect on the control variable directly, while in the latter one applied external force works as a disturbance. Therefore we construct both types of control system based on the pressure control system to kill out the influence of these disturbances which are estimated with a dimension of a pressure by using a disturbance observer. Moreover we comprise an simplified position based impedance control system. The control performances are compared among the proposed three control systems analytically and the validity of them are proved by some experiments.