Design of a return spring for a cam-follower arm

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Reference no: EM131469833

Case Study

Problem: Design an extension spring for a cam-follower as shown in figure 1. Figure 2 shows the whole test fixture.

The follower arm is loaded against the cam by an extension spring with loops at each end. The spring constant is 25 lb/in. and a preload of 25 lb, which will keep the follower force positive between values of 13 and 110 lb., at the design speed of 180 rpm. The length of the spring should be suitable to the package as shown in the figure. i.e., of the same order as cam diameter, which has 8 in. max. dia. and 6 in. min. dia. The attachment point of spring to frame is adjustable.

**Given: The spring rate is 25 lb/in. with a preload load of 25 lb. The spring dynamic deflection is 1.50 in.

**Assumptions: The spring operates in an oil bath whose temperature is below 250o F. Infinite life is required. Use ASTM A228 music wire and standard loop on each end.

You need to determine d, D, N, Nt, Lf, Sn and FS for the extension spring.

Note: First calculate analytically, then use software of your choice to verify your answers.

Figure 1: Cam-Follower Arm with Helical Extension Spring

Figure 2: General Design Scheme of a Cam Dynamic Test Fixture

What is Required?

- Detailed solution with assumptions listed.
- MATLAB or Excel analysis to verify solution.
- Fatigue curve.

Clearly show all the required values of the extension spring, such as: d, D, N, Nt, Lf, Sn, and Safety Factor.

Show step by step calculations and output of software analysis. Draw scaled fatigue curve for the spring and identify clearly all pertinent points/lines.

Reference no: EM131469833

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