Construction of Cam and Follower Systems

The following are links to constructions on how to construct radial plate cams from displacement diagrams.

Understanding these constructions:

Probably the best way to understand the following constructions is to imagine the exact opposite to what actually happens. As we all know in the case of cam and follower systems the cam rotates imparting a displacement on the follower. When constructing these systems it is imagined that the cam remains fixed and the follower is drawn in different positions around the cam, in effect the follower is imagined to travel around the cam.

Important note before considering the constructions:

The minimum cam radius is the smallest radius of the cam, the maximum follower displacement is the maximum distance travelled by the follower and the radius maximum follower displacement circle is equal to the minimum cam radius + the maximum follower displacement.

مثال هاااااااااااااااااااااااااااااام

Given the cam profile and the axis of revolution (shown below), construct a displacenent diagram for the follower as the cam rotates through 360�. Also given the minimum cam radius and the maximum follower displacement

الحل

خطوات الحل

Step 1	Given the cam profile and the centre of revolution, draw the minimum cam radius circle and the maximum follower displacement circle with the axis of revolution as centre. The minimum cam radius and the maximum follower displacement are given in the question.
Step 2	Divide the circles in 30� divisions and project the intersections between these division and the cam profile onto the displacement diagram to intersect the corresponding angular displacement.
Step 3	Join all the points of intersection on the displacement diagram between the projections form the cam profile and the angular displacements.

استكمال انواع الكامات والتابع

Disc Cam with Roller Follower

The diagram above shows the an animation of a rotating cam and roller follower. As the cam rotates the the follower is pushed up and down.

There is some external force pushing the cam back down, so that it remains in contact with the cam profile.

The cam shown above is also known as a plate cam.

Disc Cam with Flat Follower

The diagram above shows the an animation of a rotating cam and flat follower. As the cam rotates the the follower is pushed up and down.

There is some external force pushing the cam back down, so that it remains in contact with the cam profile.

The cam shown above is also known as a plate cam.

This type of follower can be found in the cam and follower system used to open and close inlet and exhaust valves in an engine.

Drum Cam and Roller Follower

This cam and follower system is slightly different to the plate cams. This type of cam is cylindrical in shape with a profile machined onto it

Different Types of Cam and Follower Systems

Different Types of Cam and Follower Systems
The variety of different types of cam and follower systems that one can choose from is quite broad. The following is a list of these different types (each type is linked to more an image of the system, these images can be accesses by clicking on the name of the system

Plate Cam with

knife-edge follower

roller follower

flat follower

Clyindrical Cam with

roller follower

knife-edge follower

Disc Cam with Knife Edge Follower

Displacement Diagrams

Displacement Diagrams

Displacement diagrams are merely a plot of two different displacements (distances). These two dispalcements are:
1 the distance travelled up or down by the follower and
2 the angular displacement (distance) rotated by the cam
In the diagram shown
we can see the two different displacements represented by the two different arrows. The green arrow representing the displacement of the follower i.e. the distance travelled up or down by the follower. The mustard arrow (curved arrow) shows the angular displacement travelled by the cam.

Note: Angular displacement is the angle through which the cam has rotated

If we examine the diagram shown below we can see the relationship between a displacement diagram and the actual profile of the cam. Note only half of the displacement diagram is drawn because the second half of the diagram is the same as the first. The diagram is correct from a theoretical point of view but would have to changed slightly if the cam was to be actually made and used. We will consider this a little more in the the following section - Uniform Velocity.

cam and follower system

What is a cam and follower system?

A cam and follower system is system/mechanism that uses a cam and follower to create a specific motion. The cam is in most cases merely a flat piece of metal that has had an unusual shape or profile machined onto it. This cam is attached to a shaft which enable it to be turned by applying a turning action to the shaft. As the cam rotates it is the profile or shape of the cam that causes the follower to move in a particular way. The movement of the follower is then transmitted to another mechanism or another part of the mechanism.

If we examine the image below we can see how the profile of the cam imparts a particular motion on the follower. In this case the motion is an up and down motion.

Examining the diagram shown above we can see that as some external turning force is applied to the shaft (for example: by motor or by hand) the cam rotates with it. The follower is free to move in the Y plane but is unable to move in the other two so as the lobe of the cam passes the edge of the follower it causes the follower to move up. Then some enternal downward force (usually a spring and gravity)pushes the follower down making it keep contact with the cam. This external force is needed to keep the follower in contact with the cam profile. This is probably best displayed in the animation