Achieving fine absolute positioning accuracy in large powerful manipulators

High accuracy is generally unattainable in manipulators capable of producing high task forces due to such factors as high joint, actuator, and transmission friction and link elastic and geometric distortions. A method called base sensor control has been developed to compensate for nonlinear joint characteristics, such as high joint friction, to improve system repeatability. A method to identify and compensate for system geometric and elastic distortion positioning errors in large manipulators has also been proposed to improve absolute accuracy in systems with good repeatability using a wrist force/torque sensor. This technique is called geometric and elastic error compensation. Here, it is shown experimentally that the two techniques can be effectively combined to enable strong manipulators to achieve high absolute positioning accuracy while performing tasks requiring high forces.