Quadruplanar inversor

Animation to derive a Quadruplanar Inversor from Hart's first inversor.[Note 1]

The Quadruplanar inversor of Sylvester and Kempe is a generalization of Hart's inversor. Like Hart's inversor, is a mechanism that provides a perfect straight line motion without sliding guides.

The mechanism was described in 1875 by James Joseph Sylvester in the journal Nature.[1]

Like Hart's inversor, it is based on an antiparallelogram but the rather than placing the fixed, input and output points on the sides (dividing them in fixed proportion so they are all similar), Sylvester recognized that the additional points could be displaced sideways off the sides, as long as they formed similar triangles. Hart's original form is simply the degenerate case of triangles with altitude zero.


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  1. ^ Sylvester, J.J. (15 July 1875). "History of the Plagiograph". Nature. XII (298): 214–216. Bibcode:1875Natur..12..214S. doi:10.1038/012214b0.