Adaptive fuzzy force control of manipulators with unknown environment parameters

This article proposes an adaptive fuzzy control scheme for explicit force control of a robot manipulator in contact with an environment whose parameters are unknown and vary considerably. The scheme consists of three main components: a reference force model describing the desired behavior of the force control system, a fuzzy force controller that determines the adjustment to the position control loop, and a fuzzy learning and adaptation mechanism that modifies the fuzzy force controller according to the difference between the actual and desired force responses. The modification is performed by shifting and contracting/expanding the membership functions of the fuzzy sets associated with the consequent rules of the fuzzy force controller. It is demonstrated, through simulations of a two-link manipulator and a 6-DOF industrial robot, that the scheme is capable of force tracking despite wide parameter variations, such as when the environment stiffness changes by several orders of magnitude. (C) 1997 John Wiley & Sons, Inc.