Cam System Design

MAE 342 – Kinematics & Dynamics of Machinery

Typical Problem• Design a cam system to:

1. Open a valve 0.05 inches in 0.0025 seconds2. Stay open for 0.0050 seconds3. Close in 0.0025 seconds, and 4. Stay closed for 0.02 seconds.5. Repeat continuously.

2

0.05

y (in)

t (s)0

0 0.001

0.0025 0.0075

0.002 0.003

• Use a roller follower.

• Make accelerations as small as possible.

0.0325

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Classification of Cams

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Classification of Followers

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Reciprocating vs. Oscillating

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Offset vs. Radial Follower

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Mechanical Constraint Cam Systems

Ducati desmodromic camImage from MECH 324 Colorado State University

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Designing Cam Systems

1. Create a displacement diagram

2. Select geometric parameter values

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Creating Displacement Diagram

• Lift and dwell are usually application-dependent (given by application requirements)

• Therefore mainly need to design transitions:� Full-rise

� Half-rise

� Full-return

� Half-return

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Designing Transitions• Select an equation to meet maximum

velocity, acceleration and jerk rate requirements:

� Parabolic motion

� Simple harmonic motion

� Cycloidal motion

� Polynomial

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Selecting Geometric Parameters

• Geometric parameter values need to be chosen to avoid problems such as:

� Interference/undercuts

� High pressure angles

� Large enough face on follower

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• Select values of R0, e, etc. to avoid high pressure angles

� To obtain pressure angles, draw cam with follower in each position and measure or use nomograph (Fig. 6.28) to find maximum φ if possible.

Parameter selection: Roller Follower

Φ

pressure angle

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Parameter selection: Roller Follower

• Select values of R0, e, etc. to avoid undercuts

� Minimum curvature (ρmin) must be greater than 0.

� To obtain ρmin draw cam and measure it or use Fig.s 6.30 – 6.34 if possible.

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Parameter selection: flat face follower

• Select R0, e, etc. to avoid undercutting

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Parameter selection: flat face follower

• Select face size & position so that face stays on cam