Point-to-point motion control of a pendulum-like 3-dof underactuated cable-driven robot

This paper presents a novel planar three-degree-of-freedom pendulum-like underactuated robot. The robot consists of an end-effector with an actuated arm suspended on a cable wound on a reel. The robot can achieve full planar point-to-point motion (position and orientation) with zero-velocity landing by swinging itself as children do on playground swings. The equations of motion of the underactuated cable-driven robot are first developed. Then, the actuated joint trajectory design for swing-up as well as an optimization technique used to control the behaviour of the passive joint are proposed. Finally, a prototype of the robot and its real-time controller are presented with experimental results for point-to-point trajectories. The proposed mechanism constitutes a low-cost solution for applications requiring large workspaces by combining the advantages of cable-driven systems and underactuation and, to the best of our knowledge, this is the first work presenting the real-time control of such a mechanism.