Trajectory Design Based on Joint Impact Index for Detecting Joint Clearance in Parallel Robot
This paper proposes a method to detect the existence of excessive clearance in passive joints of a parallel robot based on the measurement of torque fluctuation for preliminarily selected trajectories. A Joint Impact Index (JII) was introduced to evaluate the magnitude of collisions between joint elements. Two constraint models of spherical joints with clearances were introduced to facilitate the investigation of the behavior of joint elements. A multi-objective optimization problem was formulated with objective functions based on JII and constraints on the maximum acceleration and the workspace of the robot so that specific trajectory for detecting the existence of excessive clearance at each joint is obtained. Optimization of trajectories was done for a DELTA parallel robot, and its result was experimentally evaluated using a Support Vector Machine classifier. With high true positive rates (more than 80%) and low false positive rates (less than 10%), the effectiveness of the proposed method was confirmed.
KeywordsParallel robot Failure detection Clearance joints Trajectory design Multi-body dynamics Joint Impact Index
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