Cams and Motion
Definition
Cam
A mechanical part that converts rotational motion into linear motion.
How Cams Work
- Cam Profile: The shape of the cam determines the motion it imparts.
- Follower: A component that rides on the cam's surface, translating its shape into motion.
- Camshaft: The rotating axis on which the cam is mounted.
- Crank: In some systems, cams work alongside a crank, which converts rotary motion into reciprocating motion.
Types of Cams and Their Motion
Pear Cam
- Shape: Resembles a pear, with a rounded end and a tapered section.
- Motion: Provides a smooth rise and fall with a dwell period (no movement).
- Uses: Automated machinery where a pause in motion is needed, such as textile machines.
Example
In a sewing machine, a pear cam controls the needle's movement, allowing it to pause at the top and bottom of each stitch.
Circular Cam
- Shape: Perfect circle.
- Motion: Produces a constant, uniform motion.
- Uses: Simple applications where consistent motion is required, like rotary pumps.
Note
Circular cams are sometimes called eccentric cams when the rotation axis is offset from the center.
Triangular Cam
- Shape: Triangular, with rounded corners.
- Motion: Creates a sudden rise and fall, with sharp transitions.
- Uses: High-speed machinery where quick, repetitive actions are needed, such as printing presses.
Tip
- When analysing a cam, pay attention to the transition points.
- These are critical for understanding how the cam will impact the follower's motion.
Eccentric Cam
- Shape: Circular, but the rotation axis is offset.
- Motion: Produces a smooth, oscillating motion.
- Uses: Piston engines and valve systems, where precise control of movement is essential.
Analogy
- Think of an eccentric cam like a wobbling wheel.
- The offset center creates a gentle up-and-down motion as it rotates.
Oval Cam
- Shape: Elliptical or oval.
- Motion: Provides a gradual rise and fall, with varying speeds.
- Uses: Complex machinery where variable motion is needed, such as automated assembly lines.
Note
Oval cams are ideal for applications requiring smooth acceleration and deceleration.
Snail Cam
- Shape: Spiral or snail-like.
- Motion: Gradual rise followed by a sudden drop.
- Uses: Hammer mechanisms and timing devices, where a sudden release of energy is required.
Common Mistake
- Don't confuse snail cams with pear cams.
- While both have dwell periods, snail cams are designed for sudden drops, whereas pear cams provide smooth transitions.
Types of Followers
- Flat follower – Simple and stable; may wear unevenly
- Knife-edge follower – Precise point contact; high wear
- Roller follower – Reduces friction and wear; common in high-speed systems
- Spherical follower – Balanced contact for smoother motion
Analyzing Cam Motion
- Rise: The follower moves upward as the cam rotates.
- Fall: The follower moves downward.
- Dwell: The follower remains stationary.
