A cam and follower is a mechanical system that converts the rotation of a shaped cam into a controlled back and forth or up and down motion of a follower. In robotics and automation, this is useful when a machine must repeat a precise motion at a precise time. The cam profile acts like a physical program that tells the follower when to rise, pause, return, or dwell.
This makes cams important in grippers, feeders, valves, packaging machines, and timing mechanisms.
As the cam rotates, different radii of the cam surface push the follower to different heights. A displacement graph shows follower position versus cam angle, so the graph directly represents the motion created by the cam shape. Steep changes in the graph mean rapid motion, while flat sections mean dwell where the follower stays still.
Engineers choose the cam profile, rotation speed, and follower type to control timing, force, smoothness, and wear.
Key Facts
- Follower displacement is the distance the follower moves from its lowest position.
- One full cam rotation is 360 degrees, so cam timing is often described by angle.
- Angular speed is omega = 2 pi f, where f is rotations per second.
- For constant cam speed, time for a motion segment is t = theta / omega, with theta in radians.
- Follower velocity can be found from v = ds/dt, where s is displacement.
- Dwell occurs when the cam radius is constant over a range of angles, so follower displacement stays constant.
Vocabulary
- Cam
- A rotating shaped part that drives another part by its changing surface radius.
- Follower
- The moving part that stays in contact with the cam and follows its profile.
- Displacement
- The change in position of the follower measured from a chosen reference point.
- Dwell
- A part of the cam rotation during which the follower remains at the same position.
- Cam profile
- The outline or shape of the cam that determines the follower motion.
Common Mistakes to Avoid
- Confusing cam angle with time. Cam angle only becomes time when the rotation speed is known.
- Assuming a bigger cam always creates more lift. Lift depends on the change in cam radius, not the overall size alone.
- Ignoring dwell sections on the displacement graph. A flat graph segment means the follower is not moving even though the cam is still rotating.
- Using degrees directly in formulas that require radians. Convert with theta radians = theta degrees times pi / 180 before using t = theta / omega.
Practice Questions
- 1 A cam rotates at 120 rpm. How long does one full rotation take, and how long does a 90 degree rise segment take?
- 2 A follower rises 18 mm during a 60 degree cam rotation. If the cam speed is 2 revolutions per second and the rise is approximately uniform, what is the follower's average upward speed?
- 3 A displacement graph has a flat section from 150 degrees to 230 degrees, followed by a steep downward slope. Explain what the follower is doing during these two parts and why this might be useful in a robot mechanism.