Moving-Platform Pose Estimation for Cable-Driven Parallel Robots

Cable-Driven Parallel Robots (CDPRs) are parallel robots with rigid links replaced by cables. As for most parallel robots the determination of the analytical solutions to the direct geometrico-static model (DGSM) is a difficult task that is often not feasible online. However, the knowledge of the moving-platform (MP) pose is necessary in order to control the CDPR, e.g. with visual servoing. When the MP pose measurement is not available, an estimation can be sufficient. This paper compares three estimation methods: (a) control-based; (b) image-based; and (c) model-based. The three methods are implemented experimentally with an open-loop velocity controller and a closed-loop visual servoing controller. Overall, very good results are shown with model-based and control-based methods for both controllers. Finally, it is shown that the visual servoing controller leads to a better accuracy of the robot than the velocity controller.