An equal sided pentagon with curved sides generated as arcs at the vertices of the pentagon is a closed shape of constant width. Thus, as it rotates it will remain in contact with two parallel slides. Behind the slider, a crank turns the curved pentagon which, in turn, moves the slider back and forth with finite dwell periods similar to the other models in the Voigt ‘V’ series. While the curved triangle was widely used in positive-return cams to control steam engine valves before Reuleaux, he is the first to describe in depth how to generalize curves of constant width and this curved pentagon is used to illustrate the many possibilities of such shapes.

Francis Moon 2004-07-00