Design and optimization of voice coil motor for application in active vibration isolation

doi:10.1016/j.sna.2007.03.011

Sensors and Actuators A: Physical

Volume 137, Issue 2, 4 July 2007, Pages 236-243

https://doi.org/10.1016/j.sna.2007.03.011 Get rights and content

Abstract

To control the vibration transmitted from ground to the nano-precision measuring instruments has always been of great interest among the researchers. Vibration isolators typically reduce the vibration transmitted to the measuring instrument providing managed stiffness and damping through the transmitted path. Active isolators use control algorithms such as feedback or feed forward to provide the necessary control signal. In this paper, we propose optimized design of a voice coil motor (VCM) that can be used as an actuator to implement a suitable controller for active isolation using feedback control to attenuate the low frequency vibration of all six rigid body modes. Necessary force requirement has also been considered.

Introduction

Precision measuring instruments such as atomic force microscopes having resolution in nano-meter range are always adversely affected by seismic vibrations that have typical amplitude in sub micrometer region. Control of such vibration is thus a necessary requirement for accurate and precise measurement. A vibration isolation system reduces the effect of such disturbance to transmit to the measuring instrument usually by using a spring damper system with very low cut off frequency which works as a low pass filter for the disturbance. A passive system can be designed to provide the necessary attenuation to this vibration. To effectively attenuate low frequency ground vibration, a hybrid active passive system is necessary [1], [3].

The passive system attenuates high frequency disturbance with reasonable attenuation rate and then the active system works to attenuate the low frequency vibration effect. The active system implements active control using sensors and actuators. The actuator of active vibration isolator can be of several types: mechanical mechanisms, piezoelectric actuators, pneumatic springs, electromagnetic motors and electrical linear motors.

This research proposes implementation of a voice coil motor (VCM) on such an active vibration isolator which works to control the vibration typically in range from 0.1 to 100 Hz in all six degrees of freedom. VCM was used because of its ability to generate force with high acceleration and very high accuracy over a limited range of travel. The VCM was designed and optimized to provide necessary feedback force to nullify vibration effect. Necessary cost function was evaluated depending on passive isolation effect and system dynamics. Force generation was calculated using magnetic flux reluctance method. Optimized result was then evaluated comparing with electromagnetic FEM simulation result.

Section snippets

Design of the system

This isolation system is composed of four elastomer mounts to support upper plate with the instrument to be isolated (around 150 kg) along with three vertical and three horizontal VCMs mounted such that they can control all six rigid body modes using feedback control.

Feedback signal is provided from the accelerometers connected to the upper plate. Accelerometers measure transmitted vibration in the form of acceleration from ground to upper plate and send feedback signal to the actuators. The

Optimization of VCM

In order to optimize these VCMs, a cost function needs to be defined along with design parameters that can be varied to arrive at the desired optimization value. Force requirement depends on passive system dynamics as the actuators work against stiffness and damping of the passive elastomers to provide necessary dynamic force to attenuate vibration.

Complete system model with two inputs (control signal input, F_u(s) and vibration input, b(s)) contributing to output variable, p(s) is as follows: $([M$

Optimization results

Optimization was performed using the design variables and minimizing the cost function, where g(1), g(2) and g(3) are linear inequality constraints and g(4) is nonlinear inequality constraint.

To find the global converged value, we iterated the optimization process using many initial value combinations of the design parameters within the bound and then the cost function value was plotted as in Fig. 12 for all the iterations.

From Fig. 12, the global minima was found and optimized design

Simulation

To verify the optimization result, we performed FEM electromagnetic simulation and compared the result. The simulation model and result is shown in Fig. 15. Flux density distribution at the air gap is shown in Fig. 16.

Fig. 16 shows that the flux density is symmetric along the air gap and it does not exceed maximum allowable saturation flux. The comparison of simulation result with the optimization result is shown in Table 6.

From Table 6, we see that simulation result conforms to the

Conclusion

The optimized design of a voice coil motor was performed, which can be used as an actuator for the active vibration isolation system. Result of the optimization was verified using FEM simulation. This optimized VCM can easily be implemented to control the low frequency vibration typically within the range 0.1–100 Hz.

References (4)

Y.-D. Chen et al.
Application of voice coil motors in active dynamic vibration absorbers
IEEE Trans. magn.
(2005)
D.C. Hanselman
Brushless Permanent-Magnet Motor Design
(1994)

There are more references available in the full text version of this article.

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Rahul Banik is currently employed as PhD candidate, Nano-Opto Mechatronics Laboratory, Department of Mechanical Engineering, KAIST. He is pursuing doctor of philosophy (mechanical engineering) in Korea Advanced Institute of Science and Technology (KAIST), Republic of Korea (September 2003 till now). He received his master of engineering degree (mechatronics) from Asian Institute of Technology (AIT), Thailand (2003). He was an exchange student in Mechatronics, Technical University of Hamburg-Harburg (TUHH), Germany (September 2001–January 2003). He received his bachelor of science degree (electrical and electronics engineering) from Bangladesh Institute of Technology (BIT), Chittagong, Bangladesh (1999). His scientific interest include vibration isolation system design, automation, control and mechatronic system design.

Gweon Dae-Gab is currently employed as professor, Nano-Opto Mechatronics Laboratory, Department of Mechanical Engineering, KAIST. He completed his doctor of engineering (mechanical engineering) from University of Stuttgart, Germany (1987). He completed his MS (mechanical engineering) from Korea Advanced Institute of Science and Technology (KAIST), Republic of Korea (1977). He received his BS degree (mechanical engineering) from Hanyang University, Republic of Korea (1975). His scientific interest include nano-positioning, nano-measurement, nano-opto mechatronics system design.

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