Initial Length and Pose Calibration for Cable-Driven Parallel Robots with Relative Length Feedback

Abstract

Feedback of cable lengths is commonly used in the determination of the robot pose for cable-driven parallel robots (CDPRs). As such, accurate information on the absolute cable length is important. However, for most CDPRs equipped with relative encoders, the absolute cable lengths depend on the system’s initial lengths. The initial cable length, and hence the robot’s initial pose, is typically unknown. In this paper, a forward kinematics based method to determine (calibrate) for the initial cable lengths and robot pose is proposed. The calibration problem is solved as a non-linear least squares optimisation problem, where only the relative lengths of cables over any random trajectory are required and measured. The proposed method is generic in the sense that it can be applied to any type of CDPR. The simulation and experimental results for various robots show that the method can effectively and efficiently determine the initial cable lengths and pose of the cable robot. This is useful in order to obtain more accurate cable length data to be used for forward kinematics to determine the robot’s pose.