Combined Impedance/Direct Control of Robot Manipulators

In the basic impedance control structure, it is usually required to know the environment stiffness/impedance for precise force tracking. In addition, the performance may be degraded when the random external disturbances exist. By incorporating a PI-type compensator to the basic impedance control structure, this paper presents a combined impedance/direct control scheme for control of robot manipulators, which is characterized by high disturbance rejection, robustness to uncertainties, and simple structure for application. Moreover, it does not require to switch the control modes during the transition between the free space motion and the constrained motion. Therefore, the proposed controller combines the advantages of both the direct control and the impedance control. Computer simulations are performed to demonstrate the superiority of the proposed control scheme over the impedance control.