Design of Small Isolator Units for the Suppression of Low-Frequency Vibration

Abstract

The customary linear vibration isolators are unsuitable for the suppression of low-frequency vibration in applications where, in addition to steady-state vibration, the danger of shock excitation exists. Linear suspensions which ensure a low natural frequency are necessarily very soft and, as a result, excessive large deflections will arise during steady accelerations or shock excitation. These undesirable features are not encountered with symmetrical nonlinear suspensions, which under steady state vibration excitation behave like linear springs, but when suffering large deflections from their ‘working point’ become progressively stiffer. One of the spring elements which has the required spring characteristic is the ‘sine spring’. The properties of this spring element are summarized and the various ways of coupling sine springs and ordinary springs are discussed. Several designs of isolator units, incorporating sine springs for the vertical degree of freedom and leaf springs for the horizontal degree of freedom are described. The Appendices contain a short discussion of various ‘constant-force’ springs suitable for low-frequency suspensions, a description of the experimental equipment used, and some experimental results regarding the behaviour of sine spring suspensions.