Cost-Effective Calibration of Collaborative Robot Arm with Single Wire Encoder

초록

With its flexibility of a collaboration robot and demands for maintaining virtual model's fidelity in cyber-physical system of robotic manufacturing, frequent calibration is required. This paper proposes a cost-effective calibration method of a collaborative robot using a single wire encoder. First, DH (Denavit-Hartenberg) convention-based kinematics of the robot are analyzed. Then, a mathematical relation between distance errors between robot's end effector and wire encoder and the kinematic parameters are presented. In the experiment, turning-in-place-based measurement methodology is applied. Also, in order to reduce error caused by wire bending at the point where a wire is hooked in previous studies, a rotatable wire hanger which has 2-DoF (Degree of Freedom) rotary joint is fabricated and applied. Next, identifiable parameters are analyzed through SVD (Singular value decomposition), then 21 parameters are calculated via Levenberg-Marquardt algorithm. The estimated parameters were validated by comparing fidelity of the calibrated and nominal model against actual physical system measured by a robot arm type measurement device. As a result, feasibility of the proposed method was checked by confirming 64.3% better fidelity of the calibrated model using the proposed method. Furthermore, the performance of the method also shows better results than camera-based robot's internal calibration function provided by manufacturer.

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