7 - Active Isolation of Vibrations

Abstract

This chapter deals with the application of active techniques to problems in vibration isolation. There are two classes of such problem; instances where one wish to isolate a vibrating body (such as a machine of some kind) from a “receiving structure” (such as a car body, ship hull, aircraft fuselage or building) and instances where one wish to isolate a body (such as sensitive equipment or a railway car) from vibrations imposed by another source (such as ground vibrations or railway track unevenness). In both classes of problem, the source of the vibrations may be either deterministic or random. Most problems that involve isolating machinery vibrations from a receiving structure have a deterministic source of vibrations. This is the case whenever the source of vibrations is a rotating or reciprocating machine. In these cases one can adopt what is essentially a feedforward control approach to the problem. Thus one only needs to know the frequency of the vibration source and the necessary control forces can be synthesized using the adaptive feedforward techniques. The second class of problem, which involves isolating a vibrating body from external sources of vibrations, is mostly dealt with using feedback techniques such as the design of active vehicle suspension systems. Thus the body to be isolated is the passenger cabin of the vehicle and the source of vibrations is the variable height of the road surface, the latter being a random process.