A continuous terminal sliding mode algorithm for robot manipulators: an application to force control

Abstract

The problem of hybrid position/force control on rigid surfaces with high friction effects is considered in this letter. The controller is based on a Continuous Terminal Sliding Mode Algorithm (CTSMA), which allows to obtain a high tracking performance for industrial robot manipulators with DC motors. When the desired trajectory corresponds to the geometric constraint of a rigid surface, then an additional PI term can be included in the control law to achieve force tracking perpendicular to the surface, while friction effects are rejected by the CTSMA, thus leading to a notorious performance improvement. To the best of the authors' knowledge this is the first time that this technique is used for this particular goal. In case the robot manipulator does not own DC motors as actuators, the algorithm can be complemented with the knowledge of the inertia matrix to make the result applicable to any kind of rigid robots. Both simulation and experimental results are presented and the outcomes are compared with a GPI control/observer approach. The Root Mean Square Errors (RMSE) are computed to show objectively the advantages of the proposed solution.