Cam and Follower Systems

As a cam rotates it imparts a particular motion on the follower in contact with it.  From the image shown below we can see that as the cam shaft rotates the follower will be forced to move up and down.  That is of course provided that there is an external downward force on the follower that makes it keep contact with the cam.

The next consideration is the type of the upward and downward motion of the cam and follower system.  The are three different types of motion that could have been imparted on the follower.  These are:

1. Uniform Velocity

2. Simple Harmonic Motion

3. Acceleration/Retardation

Uniform Velocity:

Velocity is the rate of change of displacement with respect to time.   This change may be a change of speed or a changein direction.  From the definition uniform velocity therefore means that the change in displacement is a steady change.  Or to put it differently it means that the change in displacement in the first second of the uniform velocity motion is the same as the change in displacement in any other second in that motion. 

Simple Harmonic Motion:

The motion of a follower is simple harmonic motion if its acceleration towards a particular point if its acceleration towards a particular point is proportional to its displacement from that point.

The best way to understand this non-uniform motion is to imagine a pendulum swinging.

If you examine the pendulum as it swings you can see that as it swings towards A it slows down until it finally stops at A.  Then it starts to swing back in the other direction.  As it does so it starts to gain speed until it reaches it max speed at O.   Once the pendulum passes O it starts to slow down on its approach to B.  At B the pendulum stops and begins to swing back.  Again it speed up as it approaches O, reaches its maximum speed at O, then slows down on its approach to A, stops at A and then swings back in the other direction.  This cycle then keeps repeating itself.  If you watch the swinging pendulum shown later in the site you should be able to notice the non-unifromity of its motion.

Displacement Diagram for Simple Harmonic Motion.

Acceleration/Retardation:

Acceleration is the rate of change of velocity with respect to time.   This motion is used where the follower is required to rise or fall with uniform acceleration, that is it's velocity is changing at a constant rate.

Summary:

In cam and follower systems, the motion of the follower is usually perpendicular to the axis around which the cam is rotating.  Three types of motion that the follower cam experience are;

1. Uniform velocity;

2. Simple harmonic motion;

3. Uniform accelaration and retardation.