28.1 Introduction

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Industrialization, propelled by advances in science and technology in the last millennium, has led to the

development of mass-production equipment to satisfy man’s relentless pursuit for products such as

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© 2005 by Taylor & Francis Group, LLC

automobiles, air-conditioners, audio and video products, and so on. Today, apart from the consumer’s

demand for more functionality in new product lines, a miniaturization phenomenon is also clearly

evident where the physical size of the product can be smaller than its predecessor, even when it has

expanded performance. In addition, the ever shortening time-to-market of products and productivity

cost factors in today’s highly competitive world together pose tough and challenging requirements on the

manufacturing and automation systems that produce them. Thus, while high accuracy and precision in

production systems are necessary to produce highly delicate parts and products, a high production speed

must still be maintained even though speed and precision adversely affect each other. It is not difficult to

appreciate this dilemma since a high production speed can lead to excessive mechanical vibration (Fertis,

1995; Uicker et al., 2003), which means inevitably a loss in precision (Tan et al., 2001). This chapter will

seek to address the vibration issues in precision motion systems.

Different and numerous sources of vibration can be present in an industrial operating environment

(Adams, 2000; Kelly, 2000). Vibration may be generated by rotating or reciprocating machineries such as:

engines, motors, and compressors; impact processes such as drilling and PCB printing; the flow of fluid;

and many others (Raichel, 2000). The vibration level can reach an excessive level when abnormal operating

conditions occur due to unbalanced inertia, bearing failures in rotating systems such as turbines, motors,

generators, pumps, drives, and turbofans, component failure and operation outside prescribed load

ratings, and poor kinematical design (resulting in a nonrigid and nonisolating support structure).

Vibration, whether naturally occurring or induced under abnormal conditions, is undesirable as it usually

leads to dynamic stresses that, in turn, causes fatigue and deterioration of the machinery. Other adverse

consequences include unnecessary energy losses, deterioration in performance, and an unduly high level of

noise produced. These effects can be even more severe for high-precision motion systems with stringent

requirements on precision and accuracy, since vibration will lead directly to poor repeatability properties,

impeding any effort for systematic error compensation. Thus, it is even more essential that the vibration

level in such systems be suppressed as far as possible with an efficient mechanical design and that

functionality be included in the control to monitor and possibly adaptively reduce excessive vibration

when it occurs.

This chapter provides several possible approaches to this objective. The first approach will focus on a

proper mechanical design, based on the determinacy of the machine structure, to reduce the mechanical

vibration to a minimum. While the system design approach is certainly a first and key step to minimizing

vibration in mechanical systems, a parallel monitoring and suppression mechanism is necessary to cope

with additional and usually unpredictable sources of vibration seeping in during the course of

operations. An approach, utilizing an adaptive notch filter (narrow bandstop filter) in the control system,

will be presented as a means of continuously identifying resonant frequencies present and suppress signal

transmission into the system at these frequencies.

Finally, the development of a low-cost real-time vibration analyzer will be presented. This

analyzer can be implemented independently of the control system, and as such can be applied to

existing equipment without much retrofitting being necessary. A vibration signature is derived from

the vibration signal acquired using an accelerometer that is attached to the machine under normal

operating conditions. A pattern recognition template is used to compare real-time vibration signals

against the normal-condition signature and an alarm can be activated when the difference deviates

beyond an acceptable threshold. Actions of rectification can then be invoked before damage is done

to the machine. A case study will be provided at the end of the chapter to illustrate the effectiveness

of a remote vibration monitoring and control system for precision motion systems.

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