Kinematically Controllable Cable Robots with Reconfigurable End-effectors
Nan Zhang
TL;DR
Problem: Expanding the translational and rotational workspace of cable-driven robots is hampered by cable interference reducing rotation and by non-unique tension distributions complicating control. Approach: Introduces passive, reconfigurable end-effectors that convert linear cable actuation into rotation using a compression spring, a $helical\text{-}grooved$ shaft, and a matching spline nut, with a bearing providing an extra rotational DoF; the end-effector has $6$ DoF, plus $2$ additional relative DoFs, totaling $8$, matched by $8$ cables for purely kinematic control. Contributions: Describes two designs—one enabling large workspace transformations and a rotatable gripper—and analyzes interference minimization and applicability to underwater and VR contexts. Impact: Delivers cable-length–based, non-torque-sensing control with large translational and rotational capabilities, enabling tasks such as grinding/polishing/cleaning, VR flight simulation, and underwater grasping.
Abstract
To enlarge the translational workspace of cable-driven robots, one common approach is to increase the number of cables. However, this introduces two challenges: (1) cable interference significantly reduces the rotational workspace, and (2) the solution of tensions in cables becomes non-unique, resulting in difficulties for kinematic control of the robot. In this work, we design structurally simple reconfigurable end-effectors for cable robots. By incorporating a spring, a helical-grooved shaft, and a matching nut, relative linear motions between end-effector components are converted into relative rotations, thereby expanding the rotational workspace of the mechanism. Meanwhile, a bearing is introduced to provide an additional rotational degree of freedom, making the mechanism non-redundant. As a result, the robot's motion can be controlled purely through kinematics without additional tension sensing and control.