A cam and follower mechanism is a machine element that converts rotary motion into a planned back and forth or up and down motion. It is used when a machine needs a part to move at the right distance, speed, and time during each rotation. Cams are important in engines, pumps, textile machines, packaging equipment, and automatic tools.
The shape of the cam is the main control feature, because it decides how the follower moves.
Key Facts
- One full cam rotation is 360 degrees of timing.
- Follower displacement s depends on cam angle theta, so s = f(theta).
- Rise is the part of the cycle where follower displacement increases.
- Dwell is the part of the cycle where follower displacement stays constant.
- Return is the part of the cycle where the follower moves back toward its starting position.
- Average follower velocity during a rise is v_avg = h / t, where h is lift and t is rise time.
Vocabulary
- Cam
- A cam is a rotating shaped part that pushes or guides a follower to create a specific motion pattern.
- Follower
- A follower is the moving part that stays in contact with the cam and responds to the cam profile.
- Cam profile
- The cam profile is the outer shape or surface of the cam that determines the follower displacement at each angle.
- Lift
- Lift is the maximum distance the follower moves from its lowest position during a cam cycle.
- Dwell
- Dwell is an interval of cam rotation during which the follower remains at the same displacement.
Common Mistakes to Avoid
- Confusing cam rotation with follower motion, because the cam turns continuously while the follower may rise, dwell, and return in separate parts of the cycle.
- Assuming a circular cam always produces follower motion, because a centered circular cam with no offset can rotate without changing follower displacement.
- Ignoring dwell angles, because many real mechanisms need the follower to pause so actions like valve opening or part holding occur at the correct time.
- Treating lift and velocity as the same quantity, because lift is displacement while velocity depends on how quickly that displacement occurs.
Practice Questions
- 1 A cam rotates at 600 rpm. How many complete cam cycles occur each second?
- 2 A cam gives a follower a lift of 12 mm during a rise that lasts 90 degrees of cam rotation. If the cam rotates at 300 rpm, find the rise time and the average follower velocity during the rise.
- 3 An engine valve must stay fully open for part of a cycle before closing. Explain which part of the cam motion diagram represents this requirement and why the cam profile must include it.