Use of Spatial Four-Bar Mechanism for the Synthesis of Mechanisms with Large Dwell

摘要

In several design applications there is a need for mechanisms having long periods of dwell. If the output is to remain completely stationary cam, geneva or intermittent gear mechanisms are used. When an approximate dwell is sufficient, this is usually achieved by mechanisms with lower kinematic pairs or with cycloidal motion mechanisms utilizing gear pairs. There exists several examples in the literature where a cam is conveniently replaced by a six-link planar dwell mechanism. However, in cases where large output stroke and/or large proportion of dwell period is required, such a solution may not provide an acceptable solution in terms of link proportions, force transmission and kinematic characteristics or due to the excessive oscillations during the dwell period. In this study, spatial and planar four-bar mechanisms have been used in series to obtain mechanisms having long periods of dwell. A modular approach accompanied by a heuristic synthesis procedure is used, and a six-link mechanism is obtained where the axes of the input and output shafts are skew and at right angle. The resulting mechanisms have long dwell periods with large output swing angles, possessing acceptable link dimensions and favorable dynamic and kinematic parameters that define the quality of motion. Such a dwell mechanism may find application in rapier weaving machines, where the rapiers are required to remain outside the weaving zone for up to the half of the working cycle.