Force/Position Control of Manipulators in Task Space with Dominance in Force

Abstract

The increased demand on robotic manipulator performance leads to the use of advanced control structures. The general task of a robot control system is to enable the manipulator end-effector to follow prescribed motion trajectories, planned in a suitable coordinate frame related to the manipulator task space, and to exert prescribed forces when the end-effector impacts the environment. During latest years several control schemes have been proposed in the literature, such as pure force control, compliance control, impedance control, and hybrid control. Hybrid control is the only control strategy which allows for simultaneous control of motion and force; the structure of this control system is modified by means of opportune selection matrices which are defined according to the task requirement. This paper presents a new force control method which may be thought as logically derived from compliance control and impedance control for which only a reference position is usually assigned. The attractive feature of the proposed control is that it also allows for a reference force to be assigned. In this way one may obtain analogous performance to hybrid control without adopting selection matrices. The advantage gained with this choice lies in the achievement of a degree of robustness of the control scheme to inaccurate environment modeling.