Cam 1 rotates about fixed axis A and has a contour of which portions a-a and b-b are concentric circular arcs of radii R and r. Follower 2 reciprocates in fixed guides B-B and carries two rollers, 3 and 4, which roll along the working curve (profile) of cam 1. When cam 1 rotates continuously, follower 2 has long dwells at the extreme positions where rollers 3 and 4 contact portions a-a and b-b of the cam. Positive motion is achieved because the sums of all opposing radius vectors of the theoretical curve of cam 1 are equal to the distance between the centres of rollers 3 and 4.
$2999$SmC,3L$