Robust Impedance Control of a Single-Link Flexible Robot Interacting with the Unknown Environment using Sliding Mode Control Method

In this paper, a novel scheme based on sliding mode control method for impedance control of a single link flexible robot arm when it comes into contact with unknown environment, is presented. The proposed control strategy is robust against the changes of the environment parameters (such as stiffness and damping coefficient), the unknown Coulomb friction disturbances, payload and viscous friction variations. The proposed scheme is also valid for both constrained and unconstrained motions. In our new approach, the controller automatically switches from a free to a constrained motion mode therefore it does not need an algorithm to detect collision between the link and the environment. In this regard, impedance control is proposed with the inner loop position. This means that in the free motion, the applied force to the environment is zero and the reference trajectory for the inner loop position is the desired trajectory. In the constrained motion, the reference trajectory for the inner loop is determined by the desired impedance dynamic. Feasibility and effectiveness of the proposed control scheme are demonstrated via numerical simulations.