An Experimental Investigation of Extra Measurements for Solving the Direct Kinematics of Cable-Driven Parallel Robots

Abstract

Solving the direct kinematics (DK) of cable-driven parallel robots (CDPR) based only on the cable length measurements is a demanding problem that is still not well mastered, especially for robots having sagging cables. A model-based approach may be used to solve this problem but the model parameters and measurements are uncertain, thereby leading to positioning inaccuracy. A possible way to improve the accuracy and speed up the solving is to add extra measurements. For that purpose a preliminary step is to determine what type of measurements are possible and then to estimate how accurate they are. For that purpose we have used a CDPR with 4 cables that has been instrumented with various types of extra measurements: cable tensions and orientations, platform orientation. Ground truth has been established and we have compared the data provided by the extra sensors with their real values. This work shows that cable tensions sensors and platform orientation sensors are not good candidates to be used for the DK while cable orientations may be obtained with a good accuracy both in static poses or during a quasi-static motion.