Small-Amplitude Vibrations of the Four-Bar Linkage Chain

Abstract

Experimental and theoretical work is described dealing with the small-amplitude dynamic characteristics of plane four-bar linkages with prismatical links, one link being fixed in space. The object is to devise methods by which a design can be investigated as a vibrating system, given that it is already kinematically suited to its task. The theoretical work is based on the assumption that only flexural vibrations are important, and uses the method of receptances to establish frequency equations which are then solved numerically to compare with the experimental results. The fundamental natural frequencies of the linkage were studied by free vibration tests and fundamental resonant response curves were obtained under conditions of forcing. The input was a mechanical scotch yoke drive when the links were flexible and an electro-magnetic exciter when the links were rigid. Comparison of experiment and theory shows extremely good agreement for natural frequencies over wide ranges of configuration and acceptable agreement for the forced response curves.