A cam and follower mechanism converts the continuous rotary motion of a cam into the repeated linear forward-and-back motion of a follower. This occurs because the changing radius of the cam profile pushes the follower through a controlled sequence of rise, dwell and fall.
The Mechanism
The cam is a shaped mechanical component fixed to a rotating shaft. The follower remains in contact with the cam's outer profile and usually moves along a constrained linear path.
As the cam rotates, the distance between its axis and the point of contact changes. An increasing radius pushes the follower outward; a decreasing radius allows it to return. A spring, gravity or a positive-drive arrangement maintains contact between the two components.
| Stage | Cam action and follower response |
|---|---|
| Rise | The cam radius increases, pushing the follower away from the cam axis. |
| Dwell | The radius remains constant, so the follower stays stationary even though the cam continues rotating. |
| Fall | The radius decreases, allowing the follower to move back toward the cam axis. |
| Return dwell | The follower remains in its starting position until the cycle repeats. |
One complete cam revolution normally produces one complete follower cycle, although the exact output depends on the number and arrangement of lobes. The cam profile determines the follower's displacement, timing, velocity and acceleration. Designers therefore select profiles to achieve outputs such as gradual motion, rapid return or a stationary dwell period.
Followers may be knife-edge, roller or flat-faced. A roller follower reduces sliding friction and wear, while a spring-loaded follower helps prevent loss of contact at higher rotational speeds.
A common misconception is that every cam produces reciprocating motion. A translating follower reciprocates, but a pivoted follower produces oscillating motion instead.
Exam Technique
For B3.3 Mechanical systems application and selection, identify the rotary input, follower output, contact method and cam profile. Explain the sequence using rise, dwell and fall, and justify component selection by referring to friction, wear, speed, accuracy and the required motion pattern.
