Parallel manipulators have many attractive features, such as a high strength to weight ratio, with great potential for applications in manufacturing and construction industry. Cable actuated parallel manipulators are a special case of parallel robots, where the limbs are replaced by cables, offering increased scalability of the structure. However, cable actuated manipulators have larger errors in positioning because of cable extensions and changes in the effective spool diameter. Also, the direct kinematics solution is no longer meaningful once the robot crosses the workspace boundary. Finally, it is necessary to start from a pre-calibrated home position where the cable lengths are known. In this work we address the pose estimation and control for a cable robot using visual and inertial measurements as well as information from the direct kinematics. We demonstrate the algorithm on a prototype with a working volume of 2m × 4.6m × 6m.
Pose-estimation and control in a 3D visual servoing system