  Industrial robots play a vital role in automatic production, which have been
widely utilized in industrial production activities, like handling and welding.
However, due to an uncalibrated robot with machining tolerance and assembly
tolerance, it suffers from low absolute positioning accuracy, which cannot
satisfy the requirements of high-precision manufacture. To address this hot
issue, we propose a novel calibration method based on an unscented Kalman
filter and variable step-size Levenberg-Marquardt algorithm. This work has
three ideas: a) proposing a novel variable step-size Levenberg-Marquardt
algorithm to addresses the issue of local optimum in a Levenberg-Marquardt
algorithm; b) employing an unscented Kalman filter to reduce the influence of
the measurement noises; and c) developing a novel calibration method
incorporating an unscented Kalman filter with a variable step-size
Levenberg-Marquardt algorithm. Furthermore, we conduct enough experiments on an
ABB IRB 120 industrial robot. From the experimental results, the proposed
method achieves much higher calibration accuracy than some state-of-the-art
calibration methods. Hence, this work is an important milestone in the field of
robot calibration.
