How does uniform velocity appear on a displacement diagram?

Uniform velocity appears as a straight sloping line. The follower moves equal distances for equal angles of cam rotation.

Why is pure uniform velocity a problem for a fast-running cam?

The follower changes speed instantly at the start and end of the rise. The sudden changes cause shock loads, noise and wear.

How does uniform acceleration and retardation appear on a displacement diagram?

Uniform acceleration and retardation gives a smooth S-shaped curve made of two parabolas. The follower speeds up steadily in the first half of the rise and slows steadily in the second.

How are the points for uniform acceleration plotted on a displacement diagram?

The displacements at equal angles grow in the ratio 1, 4, 9 through the first half of the rise. The second half mirrors these distances as the follower slows.

CCEA A-Level Technology and Design 8900

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Mechanical and Pneumatic Systems

Cam profiles and follower displacement diagrams

3 things to know
A2 1

Overview

Displacement diagrams and base circles, uniform velocity, uniform acceleration and simple harmonic motion, offset followers, constructing profiles and worked timing examples.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

How does the construction of a profile for a roller follower differ from one for a knife-edge follower?

Key term

What is a cam displacement diagram?

Key term

What is the base circle of a cam?

Questions from this subtopic

Each one with the model answer underneath.

1
What is a cam displacement diagram?
Model answer
A displacement diagram plots the follower's position against the angle turned by the cam. The horizontal axis covers one revolution, from 0° to 360°.
2
What is the base circle of a cam?
Model answer
The base circle is the smallest circle, centred on the camshaft, that touches the cam profile. The follower is at its lowest point while it rests on the base circle.
3
How does uniform velocity appear on a displacement diagram?
Model answer
Uniform velocity appears as a straight sloping line. The follower moves equal distances for equal angles of cam rotation.
4
Why is pure uniform velocity a problem for a fast-running cam?
Model answer
The follower changes speed instantly at the start and end of the rise. The sudden changes cause shock loads, noise and wear.
5
How does uniform acceleration and retardation appear on a displacement diagram?
Model answer
Uniform acceleration and retardation gives a smooth S-shaped curve made of two parabolas. The follower speeds up steadily in the first half of the rise and slows steadily in the second.
6
How are the points for uniform acceleration plotted on a displacement diagram?
Model answer
The displacements at equal angles grow in the ratio 1, 4, 9 through the first half of the rise. The second half mirrors these distances as the follower slows.

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