2-DOF state control scheme for the motion control of a parallel kinematic machine

In this article a state control scheme for the end effector motion control of a 6-DOF parallel kinematic machine is presented. The control scheme complies with a two degrees of freedom (DOF) structure: A feed forward path based on the nonlinear inverse dynamics ensures a good tracking behavior, while disturbances are compensated for via a constant state feedback path. The constant feedback matrix is designed solving the Riccati regulator equation, using a linearized system representation. In contrast to established approaches, this allows the consideration of the actuator coupling within the controller design. Its stability over the entire workspace is evaluated through an examination of the eigenvalues of the closed-loop path. The required knowledge of the system states is obtained by means of a Kalman filter. Simulations with a dynamic model of a hydraulically actuated 6-DOF Stewart- Gough platform demonstrate the effectiveness of the control design approach.