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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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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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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