Cable robots are an important class of both parallel and serial robots. Since this kind of robot inherits nonlinear dynamics, designing a nonlinear suboptimal controller such that the robot tracks time-varying trajectories in complex missions to achieve optimal performance is of great importance. In this paper, a nonlinear suboptimal controller is suggested to track time-varying desired trajectories by the cable-suspended planar parallel robots (CSPPRs). For this aim, the mechanical and electromechanical models of the CSPPRs based on Newton’s second law are derived. After that, the controller is designed by taking three main steps. At first, a reference model is formulated by paying attention to the desired trajectory. Next, the pseudo-linearization technique is used to rewrite the state-space representation of an augmented system consisting of the robot and the reference model. Finally, a state-dependent Riccati equation is numerically solved to achieve the control law. The effectiveness of the proposed controller is verified by both simulation results and experimental results. The results show that the proposed controller is able to stabilize the closed-loop system while the tracking error converges asymptotically to zero and robust tracking performance is obtained.
