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.

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

Nearly straight line linkages

Perfect straight line linkages

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

Rotary straight line mechanisms
gollark: The grid here noticeably breaks for a few hours every year or so, presumably because there's a lot of redundancy due to lots of components in it. If we had a smaller-scale one, it would either have to be really overbuilt or fail when it was cloudy for too many weeks or something like that, but it would be free of cascading-failure-y problems.
gollark: Less area/stuff to spread problems over.
gollark: Dunbar's number is an incredibly handwavey estimate, but I think the concept is sound.
gollark: Revolutions have always worked well, so this is a good idea.
gollark: Maybe I should have documented this.

See also

Sources
  1. https://web.archive.org/web/20180418124753/http://kmoddl.library.cornell.edu/model.php?m=139 Reuleaux Collection, Cornell university
  • Theory of Machines and Mechanisms, Joseph Edward Shigley
  • Cornell university (archived) - Straight-line mechanism models
  • Alfred Kempe (1877). How to Draw a Straight Line (PDF). Macmillan – via University of California at Irvine.
  • Daina Taimina. "How to Draw a Straight Line - a tutorial". Cornell University.
  • Simulations using the Molecular Workbench software
  • bham.ac.uk - Hart's A-frame (draggable animation) 6-bar linkage


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