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A Roberts linkage
A Sarrus linkage
Peaucellier–Lipkin linkage:
bars of identical colour are of equal length
Cardan straight line mechanism

In the late seventeenth century, before the development of the planer and the milling machine, it was extremely difficult to machine straight, flat surfaces. For this reason, good prismatic pairs without backlash were not easy to make. During that era, much thought was given to the problem of attaining a straight-line motion as a part of the coupler curve of a linkage having only revolute connection. Probably the best-known result of this search is the straight line mechanism development by Watt for guiding the piston of early steam engines. Although it does not generate an exact straight line, a good approximation is achieved over a considerable distance of travel.


Nearly straight line linkagesEdit

Perfect straight line linkagesEdit

Eventually, several linkages were discovered that produced perfect linear output:

Rotary straight line mechanismsEdit

See alsoEdit


  • Theory of Machines and Mechanisms, Joseph Edward Shigley

External linksEdit