Cam 1 rotates about fixed axis A and has two working surfaces. The outer surface is composed of portion acb and circular arc e of radius R. The inner cam surface is composed of grooves d and f, and circular arc k of radius r. Cross-shaped follower 3 rotates about fixed axis B and carries rollers 2, 4, 5 and 6 which roll along the inner and outer working surfaces of cam 1. When cam 1 rotates clockwise, portion ac acts against roller 2 and begins to turn follower 3. At this, roller 5 enters groove d and roller 4 enters groove f. When these rollers come out of the grooves, follower 3 has been turned one-fourth of a revolution and rollers 5 and 4 begin to roll around concentric outer and inner surfaces e and k, locking follower 3 in its long dwell position. Positive motion is achieved because the rollers simultaneously roll along the corresponding portions of the working surfaces.
$3080$SmC,ML$