Industrial Robot Forward Calibration Method and Results

This paper presents a forward calibration method for serial link manipulators. The procedure uses a model whose parameters represent link lengths, joint encoder offsets, the relative orientations of consecutive axes, and experimentally observed effects of joint compliance, backlash, and gear transmission errors. A least squares numerical search algorithm uses theodolite measurements of tool position and the robot’s joint encoder readings to estimate the complete model’s parameters. The calibrated robot model predicts theodolite readings with an rms error of 5.7 × 10−5 rad (0.13 mm). Other tests show that this technique improves the robot model from as much as 4.8 mm error to 0.3 mm error.