Design and control optimization for hybrid-controlled overconstrained cable-driven parallel robots

In Cable-Driven Parallel Robots (CDPRs), multiple cables forming closed kinematic chains move the end-effector (EE). When the number of cables exceeds the degrees of freedom of the EE, the robot is overconstrained (OCDPR). This architecture helps keep cables taut but introduces actuation control challenges due to constraint redundancy. Hybrid Position-Force Control addresses this by using length-controlled cables to regulate the EE pose and force-controlled cables to manage force distribution. A hybrid control turns out to be a fast and intuitive solution in which, however, the choice of force-controlled cables influences the Wrench-Feasible Workspace. This article introduces the Wrench-Feasible Error-Insensitive Workspace (WFEIW), defined as the set of wrench-feasible poses that can be reached even in the presence of length- and tension-control errors. In particular, the paper shows how this workspace, which is inherently control-dependent, can be optimized. The WFEIW is analyzed for different 8-cable OCDPRs, demonstrating the method's efficacy and generality. Ultimately, the volume of the WFEIW is used as a cost function to optimize a robot geometry, thus showing how the presented method provides a practical synthesis tool for design.