Design of target trajectories for the detection of joint clearances in parallel robot based on the actuation torque measurement

This paper proposed a design method of trajectories for detecting the excessive clearances of passive joints in a DELTA robot on the basis of the phenomenon that the actuation torque waveform fluctuates due to the collision between joint elements. We introduced Joint Impact Index, as an index to evaluate the magnitude of actuation torque fluctuation due to the collision at the passive joints with clearances. In order to simplify the problem of the clearance detection, this paper proposed to use a trajectory specially designed for the detection of each joint's clearance, called target trajectory. For the design of the target trajectory, objective functions were defined based on the Joint Impact Index. Target trajectories obtained by solving the multi-objective optimization problem were applied to an industrial robot, and experiments were conducted. The relation between the detection performance in the experiments and the distribution of Joint Impact Index for the designed target trajectories was investigated and the effectiveness of the proposed method was discussed. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

This paper proposed a trajectory design method for detecting excessive clearances in passive joints of a DELTA robot. By introducing the Joint Impact Index and designing target trajectories, the problem of clearance detection was simplified. The method was experimentally validated on an industrial robot, with the effectiveness of the proposed approach discussed in relation to the distribution of Joint Impact Index for the designed target trajectories.