Experiments in adaptive model-based force control

Abstract

Reports experiments with a class of model-based adaptive force control algorithms for robot arms. The problem addressed in this article is the control of robots whose motion is constrained by point contact between the robot tool and a smooth rigid environment or workpiece. Manufacturing applications for force control include a great variety of commonplace tasks, such as grinding, polishing, buffing, deburring, and assembly operations currently performed either manually or by fixed automation equipment. The force control algorithm provides asymptotically exact tracking of both end-effector position and contact-force. This force control algorithm utilizes a sliding-mode control technique of a type first espoused for the case of free (non-contact) robot motion. The stability of the new force control algorithm can be proven with respect to the commonly accepted nonlinear rigid body dynamical equations of motion. Moreover its adaptive extension can be shown to adaptively compensate for unknown plant parameters such as link and payload inertia, joint friction, and friction arising at the contact point between the tool tip and the surface. In Naniwa et al. (1993) and Arimoto and Naniwa (1992) the authors report satisfactory performance of this force control algorithm in numerical simulation studies. This article demonstrates the comparative advantages and disadvantages of this control algorithm under a variety of conditions in actual working implementations.