Anti-windup design for saturation management during piezo-actuated vibration attenuation of the high-speed parallel robot Par2

The two degrees of freedom parallel robot Par2 is designed for high-speed and high-accuracy industrial pick-and-place operation tasks. As a result of high acceleration trajectories, its end-effector undergoes some undesirable vibrations after reaching the stop position, compromising precision and leading to an increase in the operation cycle time. Accelerometer sensors placed on the end-effector and piezoelectric patch actuators wrapped around the robot arms are employed in order to actively reduce these vibrations. Without taking into account saturation limitations, a robust controller is designed, minimizing vibrations for the robot nominal operating point but failing for some extreme operating points, due to high control efforts. An anti-windup strategy is then employed to deal with the saturation of the actuator. Such a strategy presents the advantage, with respect to the strategy which would consider a controller with smoother control efforts, to maintain a good level of vibration attenuation on the whole operation domain. Simulations and experimental results attest the adequacy of the proposed solution.