Calibration of industrial robots with spherical joint using single wire encoder

Demands for affordable robot calibration are increasing recently due to collaborative robots and virtual manufacturing. This study proposes a method using a single wire encoder as an affordable device. Unlike previous studies focused on compensating errors from wire sagging and fixture itself, this method utilizes the alignment between spherical joint and wire end by finding minimum wire length. After the optimal joint angles #4 and #5 are found by grid search and polynomial least-square regression, closed-loop kinematic chain and linear least square are utilized to find calibration parameters. With 576 datasets, the position error was reduced from 2.43 mm to 0.78 mm.