An external stabilization unit for high-precision applications of robot manipulators

Because of their large workspace, robot manipulators have the potential to be used for high precision non-contact manufacturing processes, such as laser cutting or welding, on large complex work pieces. However, most industrial manipulators are not able to provide the necessary accuracy requirements. Mainly because of their flexible structures, they are subject to point to point positioning errors and also vibration errors on a smaller scale. The vibration issues are especially hard to deal with. Many published solutions propose to modify the robot's own control system to deal with these problems. However, most modern control techniques require high fidelity models of the underlying system dynamics, which are quite difficult to obtain for robot manipulators. In this work, we propose an external stabilization unit with an additional set of actuators/sensors to stabilize the process tool, similar to Optical Image Stabilization systems. We show that, because of collocated control, a model of the robot's own dynamic behavior is not needed to achieve high tracking accuracy. We also provide testing results of a prototype stabilizing a dummy tool in two degrees of freedom on a UR10 robot, which reduced its tracking error by two orders of magnitude below 20 micrometers.