Experiments on co-operating robot arms

When two robots manipulate a common object or perform a single task together, a closed-kinematic chain is formed. If both robots are controlled under position control only, at a certain phase during the manipulation, the interaction forces may become unacceptably high. The interaction forces are caused by the kinematic as well as the dynamic errors in the robot position controller. In order to avoid this problem, a synchronized motion between both robots has to be generated, not only by controlling the position (velocity) of the two end-effectors, but also by controlling the interaction forces between them. In order to generate a synchronized motion, the first robot controller continuously modifies the task frame velocity corresponding to the velocity of the other robot. This implies that the velocity of the other robot is used as feed-forward information in order to anticipate its motion. This approach results in a better tracking behaviour