Link 2, designed as an internal double rack, has two vertical straight sections connected at top and bottom by semicircular internal gears. Keyed to driving shaft 7 is pinion 1 which rotates about fixed axis A and meshes with internal rack 2, engaging the vertical sections alternately, so that rack 2 travels up and down. Rack 2 carries four rollers 6 which engage cam 5 at the bottom and top of the stroke. This cam throws over the rack at the end of each stroke, enabling pinion 1 to mesh with the semicircular gears and reversing the direction of travel of the rack. An extension of rack 2 carries guide plate 3 which contacts roller 4 with its outer surface in the downstroke and inner surface in the upstroke. Roller 4 and guide plate 3 keep pinion 1 in mesh with first one and then the other vertical section of rack 2. The right-hand view shows roller contact with the outer surface; in the left-hand view, roller 4 is passing across the bottom portion of plate 3 and will make contact next with the outer surface.
$2805$CmG,FD$