Torque-velocity control algorithm for on-line obstacle avoidance for mobile manipulators

The paper deals with obstacle avoidance for a mobile manipulator. Mobile manipulator consists of a velocity controlled mobile platform and a torque controlled robot manipulator. Therefore combined torque-velocity control is used. In spite of a combined control the system maintains dynamic compensation. The proposed algorithm enables obstacle avoidance in real time. The platform has integrated ultrasonic sensors that detect obstacles. Obstacles near the platform generate virtual repulsive velocity in the null space and the platform moves away from the obstacles. The manipulator avoids the obstacles using the action-reaction principle without using any sensors. If an obstacle collides with the manipulator, the manipulator consequently moves away from the obstacle because the control assures high compliance of the mobile manipulator in the null space. The behaviour of the end-effector in the task space is stiff. The advantage of the manipulator placed on a mobile platform over the fixed-base manipulator is grater workspace while the other motion properties such as accuracy and dynamic properties are preserved.