A High-Precision Non-contact Measurement System for Spatial Error Calibration of Industrial Robots Under Variable Loads

Spatial error obtained is a crucial process for industrial robot accuracy calibration. This study proposes an error measurement system for robot tool center point, comprising a novel non-contact measurement device based on R-test device, and an automated rotary device equipped with several standard spheres across different ranges. The geometric accuracy of the proposed system was calibrated by Coordinate Measurement Machine and a self-designed calibration stage. Spatial error measurement is established based on geometric modelling and error vector mapping, followed by a novel error identification and compensation algorithm incorporating the Least Squares Method, Cartesian stiffness identification and Ridge Estimation. The calibration experiment is conducted on EPSON C4-A901 industrial robot, with a radius varying from 50 mm to 100 mm under different loading conditions. The results indicates that the proposed measurement system and method effectively reduced average errors by 52% to 61%. A laser tracker is employed for validated the proposed system. The results exhibited trends consistent with those obtained by the laser tracker, with a standard deviation up to 0.06 mm.