Movement No. 138 demonstrates a simple yet effective cam-and-follower mechanism in which a cam positioned at the bottom drives a rod resting directly on its surface. As the cam rotates, its varying profile lifts the rod upward when a raised section or lobe passes beneath it, and allows the rod to fall back down when a lower section comes around. The rod rests on the cam surface under its own weight or with the assistance of a return spring, maintaining constant contact. Because the cam profile can be freely shaped — with gradual slopes, steep rises, flat dwells, or sharp drops — the resulting alternating rectilinear motion of the rod can be made variable in speed, stroke length, and timing to suit any desired application. This fundamental cam-follower principle is widely used in engine valve actuation, automatic machinery, textile equipment, and any system requiring programmable reciprocating motion from a rotating input.
138. On turning the cam at the bottom a variable alternating rectilinear motion is imparted to the rod resting on it.