An Obstacle Avoidance Method for Action Support 7-DOF Manipulators Using Impedance Control

An obstacle avoidance method of action support 7-DOF manipulators is proposed in this paper. The manipulators are controlled with impedance control to follow user's motions. 7-DOF manipulators are able to avoid obstacles without changing the orbit of the end-effector because they have kinematic redundancy. A joint rate vector is used to change angular velocity of an arbitrary joint with kinematic redundancy. The priority of avoidance is introduced into the proposed method, so that avoidance motions precede follow motions when obstacles are close to the manipulators. The usefulness of the proposed method is demonstrated through obstacle avoidance simulations and experiments. 1. Introduction The application of robot technology extends from the manufacturing industry to our homes. In particular, applied research on robot technology is widely carried out in the field of medical treatment and welfare, such as operation support robots and meal support robots. The authors focus on an action support manipulator which supports humans with poor muscle strength. One application of this manipulator is a meal support manipulator. The manipulator grasps a spoon, and a user attaches the hand to the spoon. The spoon moves to the desired direction according to the minute force applied by the user. Obstacle avoidance is necessary to use the manipulator safely under the environment where humans and other objects exist. A 7-DOF manipulator is used as an action support in this paper. 7-DOF manipulators have kinematic redundancy. 7-DOF manipulators are able to avoid obstacles without changing the position and the attitude of the end-effector by using their redundant degree of freedom. Various methods on obstacle avoidance for redundant manipulators are proposed in [1–6]. A joint rate vector [1, 2] is adopted to avoid obstacles in this paper. Impedance control [7–10] is used to make the manipulator follow the user’s motion in this paper. Though the methods of impedance control for redundant manipulators are proposed in [7, 8], the obstacle avoidance is not handled. The methods of impedance control for redundant manipulators considering the obstacle avoidance are presented in [9, 10]. Though the manipulator avoids the obstacle while the end-effector follows the fixed reference path in [9, 10], cooperative works of manipulators and humans are not considered. An obstacle avoidance method for redundant manipulators using impedance control is proposed in this paper. Priority of avoidance is introduced into the proposed method, so that avoidance motions precede follow motions when