Sliding-mode force control of manipulators

This paper presents robust motion and force control of a robotic manipulator to deal with system and environment using the sliding mode approach. The dynamic model is modified to contain two sets of state variables, where one describes the constrain motion and the other describes the unconstrained motion. This force control scheme is a position-based sliding mode technique and consists of two feedback loops. A simple force compensator in the outer loop modifies the end-effector position based on the sensed contact force and the desired force. A sliding mode controller in the inner loop produces the joint torque required to track the modified trajectory. This algorithm is able to achieve excellent position and force with unknown environmental stiffness. Simulation results are included to demonstrate the success of the proposed controller.