Active-passive vibration isolation devices for automation and precision equipment applications

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Active-passive vibration isolation devices for automation and precision equipment applications


Author: Yung, Chung-sheung
Title: Active-passive vibration isolation devices for automation and precision equipment applications
Degree: M.Phil.
Year: 2006
Subject: Hong Kong Polytechnic University -- Dissertations.
Piezoelectric materials.
Shock (Mechanics)
Department: Dept. of Applied Physics
Pages: xvii, 204 leaves : ill. (some col.) ; 30 cm.
Language: English
InnoPac Record:
Abstract: Vibration isolation of sensitive and sophisticated parts (e.g., visual-inspection, micro-sensing, and mechatronic apparatuses, etc.) from highly accelerated moving parts (i.e., X-Y motion stages) is an urgently needed technology for the advance of automation and precision equipment. Specifically, the rapid decrease in feature sizes and increase in complexity and volume production of microelectronics components and products have called for a technological breakthrough in increasing both the speed and accuracy of microelectronics manufacturing equipment. While the modern motion technology can enable the moving parts of equipment to attain a high acceleration so as to reach the target speed, an increase in acceleration leads to an increase in dynamic forces. These forces act as a source of disturbance to transmit mechanical vibrations to other functional parts of the equipment due to structural coupling. The higher the acceleration of the motion, the more serious the vibrations that are generated, and the less accuracy the motion that can be obtained. Traditional vibration isolation devices based on high-loss viscoelastic materials are essentially passive in nature, while those based on pneumatic technology suffer from slow response, large reposition error, and bulkiness. Therefore, a compromise between fast response, high repositionability, and small size has urged to increase the intelligence, adaptability, and compactness of isolation devices so that highly integrated devices incorporating active sensoriactuation function with passive isolation function are deemed necessary. In this study, a novel class of active-passive vibration isolation devices, called PiTAPaT (Piezoelectric Trapodizal Active Passive Table), was developed, based on the piezoelectric materials and compliant structure technologies, to provide a reliable tabletop for isolating sensitive and sophisticated parts from their underneath disturbance sources. The active-passive isolation performance of PiTAPaT was demonstrated in a state-of-the-art microelectronics wire bonder. The basic form of PiTAPaT consisted of a metallic compliant frame and two lead zirconate titanate (PZT) piezoceramic patches. To acquire significant passive isolation performance, the compliant frame was bent to form an open trapezoid having a central saddle-like unit and two slanting legs. The saddle-like unit was used to increase the compliance of the frame so as to improve the flexibility of PiTAPaT in the vertical direction even though the two slanting legs were rigidly mounted on the ground. To facilitate active sensoriactuation function, each slanting leg was attached with a PZT patch. In operation, when an electric field was applied across the thickness of the PZT patches, the induced longitudinal deformations of the PZT patches resulted in a bending motion of the slanting legs. This drove the central saddle-like unit to provide a linear vertical motion.
A physical model was derived to predict the free displacement, stiffness, and blocked force of the basic PiTAPaT with different combinations of geometric parameters and material properties. Three characteristic types of basic PiTAPaT were obtained for given material properties, including: TYPE (A) the one with large displacement; TYPE (B) the one with large stiffness and force; and TYPE (C) the one with moderate performance. For given geometric parameters, the use of a high-stiffness alloy and a high piezoelectric d₃₁ coefficient PZT was able to enhance PiTAPaT's performance in general. An ANSYS finite-element model was implemented to further validate the physical model, and the computed results were compared, in good agreement, with the theoretical predications. Three basic PiTAPaT's, each representing one of the three characteristic types of design, were fabricated and characterized. The measured free displacements and stiffnesses of the PiTAPaT's coincided well with those predicted by the physical and finite-element models. Besides, the hysteresis, step response, DC voltage stiffening effect, sensibility, vibration isolatability, and other frequency responses of the PiTAPaT's were measured to provide a full design and operation guide. To demonstrate the modularity of the basic PiTAPaT's, a hybrid PiTAPaT comprising two identical basic PiTAPaT's arranged in orthogonal directions was fabricated and characterized. Without reducing the available displacement output, this hybrid PiTAPaT not only doubled the stiffness and force of its basic PiTAPaT but also enhanced the horizontal stability. In particular, the four distributed PZT patches, when excited independently, were able to provide complex motions involving rolling and pitching motions. Finally, the active-passive vibration isolation performance of the hybrid PiTAPaT was evaluated in-situ on an ASM AB559A wire bonder. It was found that the hybrid PiTAPaT can generally provide a 15-dB isolation with less than ±3-μm reposition accuracy for the isolated parts in the frequency range of 0-150 Hz. A number of publications were produced during the course of this study, elucidating the originality and practical applications of the present work.

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