Proceedings of the ASME 2013 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference IDETC/CIE 2013 August 4-7, 2013, Portland, Oregon, USA DETC2013-13091 WRENCH RECONFIGURABILITY VIA ATTACHMENT POINT DESIGN IN MOBILE CABLE ROBOTS Xiaobo Zhou Automation Robotics and Mechatronics Laboratory Department of Mechanical and Aerospace Engineering State University of New York at Buffalo Buffalo, New York 14260 Email: xzhou9@buffalo.edu Seung-kook Jun Venkat Krovi ∗ Automation Robotics and Mechatronics Laboratory Department of Mechanical and Aerospace Engineering State University of New York at Buffalo Buffalo, New York 14260 Email: seungjun,vkrovi@buffalo.edu ABSTRACT In our previous paper [1], we examined enhancing manip- ulation 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 feasi- ble 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 me- chanical averaging behavior. Further, by using the notion of vir- tual 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 ex- plored via both simulation and experiments. 1 INTRODUCTION Cable robots have gained immense popularity in the past decade in bringing together benefits such as high payload ca- ∗ Address all correspondence to this author. pacity, significant workspace, low inertia, high energy efficiency and ease of construction. Most of the past research efforts, how- ever, focused mainly on two major classes: (i) conventional cable robots with winches fixed in the inertial frame [2–7]; (ii) towing robots with fixed length cables on mobile bases [8, 9], with one notable exception of [10]. In our previous paper [1], we examined enhancement of ma- nipulation capabilities of cable robots, by addition of base mo- bility (sliders, mobile-platforms) to the spooling-winches. Mul- tiple individual mobile cable-robot platforms could now attach themselves to a common payload and cooperatively manipulate the composite system. The characteristic feature was the recon- figurability and redundancy both within the individual mobile- cable-robot subchains as well as within the composite system. The benefits of this reconfigurability can be realized by careful selection of: (i) mobility, numbers of articulations and type of actuation within each subchain; together with (ii) the number of subchains and nature of attachment to the common payload. For example, one immediate benefit of the addition of redun- dancy was the ability to change tension direction. Cable robots can sustain only tension along the length of the cable which can be quite limiting, especially one seeks to achieve a large wrench- feasible workspace [11]. Multiple methods for altering and reg- ulating the tension-direction are illustrated in Fig. 1. For exam- ple, in Case (a), attaching two cables to the same payload attach- ment point creates an analog to the “friction cone” in grasping 1 Copyright c  2013 by ASME