On the Rotational Conditions of the Spatial Four-Bar Mechanisms

Abstract

This paper presents some methods to obtain easily the rotational conditions, i.e., the geometrical conditions under which the driving link can make a full rotation. The condition is expressed in terms of the limits of the lengths of the couplers for the spatial four-bar mechanisms whose driving links and couplers do not vary their lengths. The calculating and constructive methods to get the rotational conditions and their examples are presented for three mechanisms : A₁·2·1 mechanism having two revolute and two spheric pairs, A₁·2·2 mechanism having one revolute, one prismatic and two spheric pairs, and A₀·2·1 mechanism having two revolute, one cylindric and one spheric pairs.