Adaptive Position Control for Fully Constrained Parallel Wire Driven Systems

A parallel wire driven mechanism uses flexible wires instead of heavy rigid links. In this paper, we propose an adaptive position control method for the fully constrained parallel wire-driven systems that use the minimum number of wires under zero-gravity conditions. Unfortunately, conventional methods of adaptive control cannot be used directly because of the nonlinearity of an internal force term. To overcome such an impossibility, we incorporate a new idea into the conventional method to separate the internal force term linearly. Not only does this adaptive control method ensure precise positioning using external sensors; it enhances the robustness for uncertainty of the Jacobian matrix, which results from the error of actuator installation. First, we explain the linearization of the internal force term. Next, the adaptive control method for the parallel wire driven system using the uncertain Jacobian matrix is proposed; then we prove the motion convergence to desired points and discuss its robustness based on Lyapunov stability analysis. Finally, the usefulness of the proposed control scheme is demonstrated through both experiments and simulation