On the automatic calibration of redundantly actuated cable-driven parallel robots

Calibration is vital to improve robot accuracy. Automatic calibrations that require no extra devices have lots of conveniences, which is especially significant for cable-driven parallel robots that usually have the reconfigurable ability. This paper proposes a new automatic calibration method that is applicable for a general kind of redundantly actuated cable-driven parallel robots. The key point of this method is to establish the mapping between the unknown parameters to be calibrated and the parameters that could be measured by the inner sensors, and then use least squares algorithm to find the solutions. Specifically, the unknown parameters herein are the coordinates of the attachment points and the measured parameters are the lengths of the redundant cables. Simulations are performed on a 3-DOF parallel robot driven by 4 cables for validation. Results show the proposed calibration method could precisely find the real coordinate values of the attachment points, errors less than 10−12 mm. Trajectory simulations also indicate that the positioning accuracy of the CDPR could be greatly improved after calibration using the proposed method.