ME 5243:ADVANCED MECHANISM DESIGN

• Quiz• Cam Sizing Exercises

– Double Dwell– Conveyor Chase

Class #23Cam Sizing

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Notes

• Draft Report: Due Thursday, Nov 30

• Project Presentations: Dec 5 & 7– E-mail me with conflicts

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Questions from Video: Cam Sizing

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Double Dwell Cam Sizing

1. Cam motion profiles?

2. Pressure angle at 50º?– Acceptable?

3. Radius of curvature at 200°?– Acceptable?

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Double Dwell Cam Motion Profiles

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Double Dwell Cam Sizing

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Size the Cam and Follower

Download: camsize.m from course schedule page

Rp = 3; %base circle radiusRf = 0.5; %follower radiuse = 0; %eccentricity

% Polynomial cam segment coefficients (comment out if importing segments)s1 = [6 -15 10 0 0 0];s2 = [1];s3 = [20 -70 84 -35 0 0 0 1];s4 = [0];

Beta1 = 90/180*pi; %Rad Length of Segment 1Beta2 = 90/180*pi; %Rad Length of Segment 2Beta3 = 90/180*pi; %Rad Length of Segment 3Beta4 = 90/180*pi; %Rad Length of Segment 4

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Cam Sizing Rules of Thumb

• Start with = 3X cam lift (h)• Compute for all values of • Iterate to keep • Use eccentricity ( ) to correct asymmetry in

max and min • Check relative to RF

– Iterate RP and RF, considering forces & stresses

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Conveyor Chasing Cam• Construct polynomial segments in polycam.m• Save profiles as s1 and s2 (s1 = s;), set s3 and s4 = 0• Size cam and follower in camsize.m

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Conveyor Belt Chaser RP = 5 in, Rf = 2 in, ε = -1 in

0 50 100 150 200 250 300 350angle (deg)

-10

0

10

0 50 100 150 200 250 300 350angle (deg)

-5

0

5

0 50 100 150 200 250 300 350angle (deg)

-10

0

10

0 50 100 150 200 250 300 350angle (deg)

-20

0

20

-15 -10 -5 0 5 10 15-15

-10

-5

0

5

10

5 5 5 100 150 60

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• Size cam for:– Pressure angle– Radius of curvature– Forces / Stresses

• By adjusting:– Prime circle, RP– Eccentricity, – Follower radius, RF

Summary

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Cam Manufacturing Considerations

• Medium to high carbon steels, or cast ductile iron• Milled or ground• Heat treated for hardness (Rockwell HRC 50-55)• CNC machines often use linear interpolation (larger

accelerations)

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Actual vs. Theoretical Cam Performance• Larger acceleration

due to manufacturing errors, creating vibrations from jerk

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Practical Design Considerations

• Translating or oscillating follower?• Force or Form-Closed?

– Follower Jump vs. Crossover Shock• Radial or Axial Cam?• Roller or Flat-Faced Follower?• To Dwell or Not to Dwell?• To Grind or not to Grind?• To Lubricate or Not to Lubricate?