Straight line mechanism

Peaucellier–Lipkin linkage:
bars of identical colour are of equal length

A Sarrus linkage

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 linkages;

• Watt's linkage (1784)
• Hoekens linkage (Can trade off straightness and near constant velocity)
• Chebyshev linkage
• Roberts Mechanism

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

• Sarrus linkage (1853)
• Peaucellier–Lipkin linkage (1864)
• Hart's A-frame

See also

• Four-bar linkage
• Level luffing crane

Source

• Theory of Machines and Mechanisms, Joseph Edward Shigley

External links

• Cornell university - Straight-line mechanism models
• Cornell university - "How to Draw a Straight Line" by A.B. Kempe
• Cornell university - "How to Draw a Straight Line" - tutorial by Daina Taimina
• Simulations using the Molecular Workbench software
• bham.ac.uk - Hart's A-frame (draggable animation) 6-bar linkage