Adaptive force control of direct drive motor for force sensor stiffness compensation

Abstract

This paper deals with an adaptive control problem of direct drive (DD) robotic manipulators with force sensor stiffness. Since DD motor has advantages to force control in robotic application, so that many works have been reported so far in control problems. However, the dynamic compensation for the sensor stiffness has little been reported so far, even though the force sensor in DD robots decreases the stiffness of the overall DD robots. In order to make use of high stiffness of DD motors itself in the servo loop, it is necessary to take into account the sensor stiffness for the high gain dynamic control. Therefore, an adaptive dynamic compensation method is introduced here in the vein of the model reference adaptive control to widen the applicability of the DD robots, because the feedback with the constant gains may cause unstable behaviors, depending on objects dynamics. The applicability of the proposed method could be verified with some experiments. Then this method is applied to nonlinear objects, such as rotary channel. The experiments show the better performance by the proposed method for the nonlinear compensation than the conventional feed-back control method. Thus, it is shown that the DD motor can have much wider applicabilities by the proposed adaptive force control.