Investigation of Controllable Modes in Active Vibration Cancellation Induced by Piezoelectric Patches

Piezoelectric (PZT) patches are widely preferred for actuators and sensors for achieving active vibration cancellation (AVC). When PZT actuators and sensors are placed at the region of maximum strain energy for structural modes, there are still uncontrollable and controllable modes in the actual application. When an uncontrollable mode is excited, the structural vibration problem may not be solved by AVC, and may even be aggravated. However, a few studies have specifically targeted this problem. In this study, the controllable modes of a plate with free boundaries are investigated to ensure the AVC effect. To specify the controllable modes in advance, a criterion for controllable modes is proposed. The proposed criterion is firstly obtained by defining the ratio of the open-loop and closed-loop energies of AVC, and then simplified by considering the dominating modes. Corresponding simulations and experiments are conducted on a smart plate consisting of PZT patches to verify the correctness of the theoretical analysis. Results show that the proposed criterion is reliable to specify the controllable modes. The vibration response of the plate is significantly attenuated at the selected controllable mode, and conversely enlarged at a specified uncontrollable mode. It is verified that controllable modes can be effectively predicted by the proposed criterion, which promotes the application of AVC.

Active Wide-Band Vibration Rejection for Semiconductor Manufacturing Robots

Currently, the semiconductor manufacturing industries over the world are upgrading from processing 300mm wafers to processing 450mm wafers. In order to satisfy the requirements of producing and processing 450mm wafers, vibration control of wafer handling tools has to make new breakthroughs. This paper introduces an active wide-band vibration rejection method with a vibrotactile actuator and applies it to a wafer transfer robot. Compared to conventional methods based on motor control of the robot, active vibration cancellation with a separate actuator does not risk compromising the tracking accuracy of wafer transfer motions. A three-step controller synthesis scheme is developed by analyzing and combining the strengths of several control strategies. Experimental validation shows a vibration reduction of more than 40% in energy and 30% in amplitude.

Active Control of the Longitudinal-Lateral Vibration of a Shaft-Plate Coupled System

The coupled longitudinal-lateral vibration of a shaft-plate system and its suppression by means of a feedback control scheme are discussed. A simplified model of the system is established through synthesis of frequency response functions (FRFs) and verified with the finite element method (FEM). This analytical model describes the coupled longitudinal-lateral vibration of the system induced by longitudinal periodic excitation at the free end of the shaft. Based on this model, vibration control via longitudinal actuation on the shaft and active vibration cancellation are studied. The active control scheme is based on an adaptive feedback scenario and a novel mechanism of adaptation of the controller’s gain, which is proposed for time-varying dynamics induced by the variation of the axial spring stiffness. Simulation results have demonstrated that the control scheme is effective in attenuating vibration of the system. Furthermore, axial actuation on the shaft is able to cancel the effect of the longitudinal disturbance acting at the free end of the shaft and consequently reduces the internal forces as well as the vibration in the plate. However, deviation of the actuation force from the shaft axis will deteriorate control of the lateral vibration and sufficiently small deviation needs to be guaranteed.