ESDU 10019:2011

$89.05

Effect of Link Length Tolerances on the Performance of Four-Bar Linkages

Published By	Publication Date	Number of Pages
ESDU	2011-08	34

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Category: ESDU

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Description

ESDU 10019 explores the effects of tolerances in the link
lengths on the performance of four-bar linkages. This Item presents
an analysis of the four-bar chain mechanism, which includes
derivation of:

the coupler and rocker angles in terms of the link lengths,

errors in the link angles due to changes in the link lengths
from their nominal values

and position errors of the offsets from the coupler and
rocker.

Many applications require careful control of the magnitude of
tolerance that is allowable in order that the performance of a
linkage is not degraded. The four-bar chain is possibly the most
commonly-used linkage because of the diversity of outputs that can
be generated by suitable sizing of links.

An example of a simple four-bar crank-rocker linkage illustrates
the analysis process, together with the error in the coupler and
rocker angles resulting from small changes in the link lengths. The
error in the position of the coupler point from small changes in
the link lengths only is also shown. A second example illustrates
the steering linkage of a vehicle, known as the Ackermann linkage,
which is driven by the action of a four-bar linkage.

In an Appendix the equations of kinematic constraint are
derived. This approach is an alternative to the approach used in
the main body of the Item.

Additional information