Robust trajectory tracking control of cable-driven parallel robots

In this paper, a robust tracking controller is designed for fully constrained cable-driven parallel robots (CDPRs). One of the main challenges of controller design for this type of robotic systems is that the cables should always be in tension, where this tension is generally generated through an actuator mechanism coupled with gearboxes. On the other hand, the presence of parametric and nonparametric modeling uncertainties is a common problem in designing a precise nonlinear tracking controller for these manipulators. To deal with these problems, in this paper two separate controllers are designed for the subsystems of the robot. First, an adaptive robust feedback controller with an adaptive feedforward term is designed for the dynamics of the CDPR, constituting the outer-loop dynamics. This controller is robust with respect to the modeling uncertainties of the system. Furthermore, the output of this controller is bounded, which guarantees a saturated desired input for the inner-loop dynamics. Next, a high-gain robust controller is developed for the inner-loop dynamics, which include the actuator-gearbox model. The stability of the overall system is analyzed through a theory of cascaded systems, and it is shown that the system is uniformly practically asymptotically stable. Finally, the effectiveness of the proposed control scheme is validated through simulations on a 4-cable planar robot in both nominal and perturbed conditions.