Precise robot motions using dual motor control

High motion performance, stiffness, and accuracy are crucial for industrial robot applications, but these requirements are in practice contradictory. Using a novel type of robot, the so called Gantry Tau, new combinations of stiffness and accuracy are in principle possible, except for the backlash in the drive-trains of each joint. Existing techniques for backlash reduction are either mechanically complex or limit the mechanical bandwidth. This paper presents an approach based on dual motors connected in parallel to the load, such that the entire robot structure can be made practically backlash free by means of software and feedback control. Different control strategies are presented and evaluated in experiments ranging from a lab servo process via a table-sized robot to a large industrial implementation with several meters of working range. Special emphasis was on a dual motor test rig with a linear high-resolution scale (not yet used for feedback) where the combined motor torque was fully utilized for high acceleration, while reducing backlash by over 96%.