On Thermal Positioning Error of a Planar Robot Arm over Entire Workspace

Robot links are typically subjected to larger thermal deformations than machine-tool structures. In this study, the thermal effect on the two-dimensional (2D) positioning error of a planar robot arm over its entire workspace was investigated. It was experimentally verified that the Denavit–Hartenberg (DH) parameters, namely the link lengths and angular offset of the rotary axis, could be the key contributors to the thermal variation in the 2D positioning error. The experiment revealed that the variation in the angular positioning deviations of the rotary axes was marginal. This paper presents an on-machine test to identify the link lengths and the angular offset by probing an artifact bar of a pre-calibrated length. To compensate for the thermal influence, it is effective to identify the DH parameters by periodically performing the proposed test.