PWM control of semi-active dampers

The positioning and tracking control problems of a Stewart hexapod platform are investigated in the present paper by the use of six optimal semi-active pulse-width modulated brakes. The control in PWM (Pulse Width Modulation) of the damping coefficients of the actuators constitutes a novelty. Indeed, it differs from the most common active control methods adopted in literature to change the position and orientation of the Stewart manipulator. Furthermore, thanks to the on-off variation of the damping coefficients, the proposed semi-active control strategy can result in a substantial gain in terms of energy saving and power supply, without losing in performance and accuracy. After the derivation of the equations of motion of the system, its dynamics is linearized and the LQR (Linear Quadratic Regulator) approach is systematically applied. The optimal control solution, provided in terms of optimal damping coefficients, is then opportunely converted into the required PWM laws to allow the platform to pursue the prescribed behaviour.