Offline simulation of path deviation due to joint compliance and hysteresis for robot machining

Industrial robots offer a cost-effective and flexible machining alternative to the classic machining centers. One disadvantage is the significantly reduced working accuracy that results in considerable path deviation, particularly under load. To maximize the effectiveness of the robot and to derive suitable machining strategies, knowledge of the effects on the working accuracy is required. In this study, a model is presented in joint space that predicts the path deviation on the basis of joint stiffness and reversal error with high accuracy, with respect to the kinematic model and path planning. The identification of the model parameters of individual joints is carried out without disassembling the robot. The model is validated against the hysteresis occurring at the Tool Center Point and through the milling of circular contours. It is shown that the reversal error is mainly caused by hysteresis and not by backlash at zero crossing. The subsequent offline compensation strategy allows a considerable reduction of dimension and form deviations.