Auto-Calibration and Online-Adjustment of the Kinematic Uncertainties for Redundantly Actuated Cable-Driven Parallel Robots

Utilizing the encoders mounted on redundant actuators, the auto-calibration method of the kinematic uncertainties of cable-driven parallel robots (CDPRs) with redundant actuation is firstly discussed in this paper. According to the kinematic model, the relation between the structural parameters and the measurement errors is analyzed and the auto-calibration workflow is designed. In addition, due to the mechanical design of CDPRs and the characteristics of cables, the transmission ratio between the cable length and the actuator angle may change during the motion process and cannot be calibrated offline. To obtain the actual value of the ratio, the online-adjustment scheme using an extra camera is then presented. To validate the proposed auto-calibration method and online-adjustment scheme, the corresponding experiments are carried out on our 8-6 (6 DOFs with 8 cables) CDPR. The results of the experiments indicate that the auto-calibration method is very useful to enhance the structural accuracy. Meanwhile, the mechanical structure of our self-built CDPR is also reliable. Moreover, the online-adjustment scheme is also effective to improve the motion accuracy indirectly.