Wrench Reconfigurability via Attachment Point Design in Mobile Cable Robots

In our previous paper [1], we examined enhancing manipulation capabilities of cable robots by addition of base mobility to the spooling-winches. Base mobility facilitated the regulation of the tension-direction (via active repositioning of the mobile bases) and allowed for better conditioning of the wrench feasible workspace. In this paper, we explore design-modifications on the attachment to the common payload (merging multiple cables, attachment via pulleys) as alternate means to improve quality of the wrench-feasible workspace. Specifically we systematically examine the role played by attachment-modality and location, focusing on the benefits/drawbacks of the ensuing natural mechanical averaging behavior. Further, by using the notion of virtual cable subsystems, we illustrate the subsumption of this case into our previous mobile-cable-robot analysis framework. We seek improvement of the overall tension distribution by utilizing configuration space redundancy to shape the tension null-space. This is implemented computationally within the framework of a Tension Factor optimization problem over the workspace and explored via both simulation and experiments.