Trajectory Tracking Control Scheme for a Mobile Welding Manipulator driven by Differential Drive Steering Units

Mobile manipulators extend the workspace of industrial manipulators by mounting them on mobile platforms. In this paper we present a trajectory control scheme for a special class of mobile manipulators. The mobile manipulator consists of a mobile platform driven by two Differential Drive Steering Units (DDSUs) and a robotic arm with 6 Degrees of Freedom (DoF). The mobile platform provides additional 3 DoF in motion. This results in a total of 9 DoF in the configuration space for the entire mobile manipulator. This paper develops a trajectory control scheme for mobile platforms driven by DDSUs that incorporates the kinematic motion constraints of the system. We propose a control and sensing scheme for high accuracy tracking relative to the workpiece. The proposed trajectory control scheme is evaluated by experimental analysis, which shows that the tracking control scheme can achieve end-effector mm accuracy relative to the workpiece.