ABSTRACT
566The performance of a precision machine depends on the attenuation of the environmental disturbances acting upon it, and considerable time and expense is invariably expended to isolate external and internal noise sources. The magnitude of these disturbances also influences the design of process controls (see Chapter 14). This chapter discusses the shock, vibration, thermal and acoustic isolation needed to protect precision machines. Vibration arises from dynamic machine motion, can be generated within the machine itself, transmitted through the floor, coupled in with direct linkages, or might be a result of vibrations and impacts in one machine generating acoustical noise that is absorbed by another. The attenuation of the impact of these perturbations on the machine can be achieved either by isolation or energy dissipation. Isolation refers to the process where the excitation magnitude is prevented from transmitting to the structure of the precision machine, while energy dissipation attenuates the excitation magnitude by dissipating the energy through heat or friction. In this chapter, an understanding of external excitations is first developed by reviewing and classifying different excitation sources. The impact of these excitations on the dynamic behaviour of a precision machine is investigated. Following the dynamic section, the focus is shifted to thermal isolation, where passive and active thermal isolation methods are introduced. In closing, the chapter outlines approaches to acoustic isolation. Different techniques and methods are discussed throughout the chapter to design appropriate isolation systems that ensure the minimisation of external impact on the application of precision machines.
