A Design of Force Control System Considering with Approach to Environment Using Virtual Environment Model

Abstract

Recently, to accomplish the contact control of the robot arm, many force control systems have been proposed, for example hybrid control and impedance control. In the literatures, it is not clarified how we can decide the control parameters for given environment, and the stability of force control system is not ensured sufficiently, because in the conventional approaches the control systems were designed for the robot arm and the environment separately. To overcome these problems, we should construct the force control system with consideration of the dynamics of the environment. Furthermore, it is necessary to operate the robot arm smoothly from free space to constraint space.In this paper, we propose a design method of force control system with consideration of the approach to the environment. The proposed method does not require the change of controllers in the transition from free space to constraint space. Firstly, the force control system using the model following servo controller is constructed and it is shown that the force in constraint space can be controlled and the robot arm move with constant velocity in free space. To reduce the impulsive force at collision, the approaching velocity must be controlled aggressively. So secondly, we introduce the concept of the virtual environment model. Using this model, the approaching velocity can be controlled by setting the virtual environment parameters, and the vibration of force can be reduced. Finally, experimental results demonstrate the effectiveness of the proposed controller.