This paper presents the design of a computed torque controller for a two-degree-of-freedom (two-dot) cable-suspended parallel mechanism. Unlike fully constrained cable-driven parallel mechanisms, cable-suspended parallel mechanisms are not redundantly actuated and usually have the same number of actuated cables as the degrees of freedom. Compared with rigid-link parallel mechanisms, the control of cabled parallel mechanisms is more challenging in that the cable tensions are unidirectional. Taking the input constraints into account, the method of computed torque control is applied to the two-dof planar cable robot. The sufficient conditions and necessary & sufficient conditions of the controller's parameters are obtained, under which the positiveness of the tensions is always maintained during the point-to-point motion within the cable robot's static workspace. Numerical simulations show that the controller is computationally efficient and the end-effector of the robot could converge to desired final positions with exponential stability.
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