A cascaded sliding mode hybrid force/position controller

This paper presents a novel method for controlling force and position simultaneously using a sliding-mode position controller and a sliding-mode position error estimator for the position controller according to force error (which is used to control force essentially). The main advantage of this method is that there is no explicit control mode switching between distinct force and position controllers, but one sliding-mode position controller, for which the force error affects the position error by means of a sliding-mode position error estimator, is used for both cases. With experimental results on a voltage-driven piezo actuator, submicron accuracy (a maximum position error of 0.2 μm) for position control and a maximum force error of 0.02 N are achieved. Also, it is shown that with this approach, the jump of control input (the main stability problem of using separate force and position controllers) is removed without losing control power.