Nonlinear robust control design for a 6 DOF parallel robot

A class of robust tracking controllers for a 6 DOF parallel robot in the presence of nonlinearites and uncertainties are proposed. The controls are based on Lyapunov approach and guarantees practical stability. The controls utilize the information of link displacements and its velocities rather than using the positions or angles of the 6 DOF platform. This can be done by constructing the linkspace coordinates and the workspace coordinates simultaneously by imposing geometric constraints. The controls utilize the possible bound of uncertainty, and the uniform ultimate ball size can be adjusted by a suitable choice of control parameters. The control performance of the proposed algorithms is verified through experiments.