Introduction
A cam is a mechanism that makes a cam follower move with a reciprocating motion.
There are two main categories of cams:
- cams that move with a rotary motion.
- cams that move with a linear motion.
Cams that move with a rotary motion
Cams that move with a rotary motion are fixed on a shaft called a camshaft. The camshaft may have lots of cams on it. A row of cams on a camshaft may:
- all have the same shape (profile) and be in line, so that the cam followers rise and fall at exactly the same time and with the same motion
- all have the same profile and have various degrees of rotation on the camshaft, so that the cam followers rise with the same motion but at different times
- have different profiles and be in line, so that the cam followers rise and fall with various motions at approximately the same time
- have different profiles and have various degrees of rotation on the camshaft, so that the cam followers rise and fall with different motions at various times.
A complete rotation of the camshaft is called a cycle.
Linear cams
Linear cams move backwards and forwards with a reciprocating motion. The cam follower slides or rolls over the linear cam as the cam passes the follower. The cam profile makes the follower rise and fall as the cam passes it.
Cam profile
The shape of the cam is called its profile. The cam profile determines how the cam follower will move. Each cam profile is designed to make a cam follower move in a particular way, e.g. a wheel or circular cam with an off-set centre is called eccentric. It causes the cam follower to gradually rise and gradually fall with a smooth rise and fall action.
Cam follower
A cam follower is forced onto the cam, usually by a spring and rises and falls as the cam passes it.
The part of the cam profile that causes the cam follower to lift is called the rise.
The part of the cam profile that causes the cam follower to fall is called the fall.
The part of the cam profile that causes the cam follower to remain stationary is called the dwell.
The distance between the highest part of the rise and the lowest part of the fall is called the stroke.
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