Spatial Curve Tracing Control of Industrial Robots

Abstract

This paper describes an adaptive tracing control of industrial robots for arc welding, inspection and other manufacturing processes, wherein the end effectors mounted at the tips of robot hands are required to move along spatial curves on the objects. First, the tracing control systems are described. A parameter on a given spatial curve is introduced to indicate the progress of tracing action, and a local coordinate system which moves along the curve together with the end effector is used to describe the relative position and attitude between the effector and the object surface. Then some proper variables suitable for evaluating control performance are derived. These variables are called job variables and the control specification about them is determined. Second, a sensor feedback control system to meet the specification is designed. Usually, the required control accuracy for each job variable is different, for example, in arc welding, the gap between an electrode and a welding groove should be controlled more accurately than its attitude. In the proposed control scheme, the sensor feedback loops are constructed for important job variables and are tuned with high gains. As for the auxiliary job variables which have not much influence upon the job, loop gains are tuned low enough to reduce the burden on the actuators. The compensator for independent tuning about job variables is derived from off-line data of the spatial curve to be traced, and is varied being syncronized with the progress of tracing action on the execution phase. Finally, experiments verify the theoretical results.