The use of linkages to generate straight-line motions goes back to Watt at the end of the 18th century in his improvements to the steam engine. This linkage is based on an extension of the four-bar linkage which was also the basis for the Watt straight-line mechanism in model S-24 or that due to Chebyshev shown in Model S-30. In this mechanism, the grounded link is part of the fixed support. The extension of the center link generates an approximate straight-line motion when one of the other links is rotated about its fixed point.

Francis Moon 2003-07-01