A Study on task specification and control for two cooperating robot arms

Abstract

This thesis focuses on task specification and control for two cooperating robot arms. A new task specification is designed to allow a multi-robot system, in this case two cooperating industrial robots, to perform a cooperative task in a coordinated manner. The coordinated motion between the two robots is realized by feed forwarding the velocity trajectories of the first robot to the second robot, or vice versa. Unfortunately, this technique leads to a non-practical solution of having to specify tasks for both robots. Therefore, another task specification is introduced by exploiting the redundant properties of the multi-robot system. This specification is an extension of an existing task specification for a single robot arm. Redundancy is used mostly for executing tasks which consist of a relative motion between both robots. This method is straightforward, since the programmer only has to fOCllS on the contact and relative motion between the tool, held by one robot, and the manipulated object, held by the other robot. The utilization of redundant properties of the multi-robot system is studied. Redundant manipulator theory is applied to both cooperating robots so that during the task execution both robots stay within a reachable and comfortable workspace, keeping them away from their singular positions. Such an approach allows the multi-robot system to perform a complete operation in one step; even difficult tasks can he accomplished easily for which most single robot arms fail. The above theory is demonstrated using simulation studies which show very interesting results by utilizing redundancy of the multi-robot system. Finally some experiments were performed using two industrial robots, one of which was equipped with a six-dimensional force sensor. A comparison of some experimental results using a single robot arm and two cooperating robot arms has been made and an effective method for specifying the cooperative task based on redundancy is proven.