Identification and vibration attenuation for the parallel robot par2

Par2 is a parallel robot with two degrees of freedom designed for high-speed and high-accuracy industrial pick-and-place operation tasks. As a result of the high acceleration trajectories, the end-effector undergoes some undesirable vibrations after reaching the stop positions, compromising its 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 in a noncollocated closed-loop setting. After submitting the robot to an identification procedure, the obtained nominal model is used to synthesize a reduced order controller with the H_∞ loop-shaping technique. Performance analysis as well as simulation and experimental results show that vibration reduction is achieved around the nominal operating point, but fails 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, which allows achieving vibration attenuation on the whole operation domain, for a given configuration of the robot at the stop point.