Machinery's Handbook, 31st Edition
2374
CAMS AND CAM DESIGN
R 0
k tan τ 1
y 1 = y 2 R y 1 h
k tan τ 2
E 1
E 2 α ” 2 α 2
R y 2
α 1
α ” 1
R max
R u
R min
e
O 1
O 3
O 2
A
F 2
F 1
Fig. 15. Finding Proportions of Cam; Offset Translating Follower The angle α 2 is laid out at E 2 as shown, and another ray E 2 F 2 is determined. Similarly, any point on this ray chosen as the cam shaft center will proportion the cam so that the pressure angle at a point on the cam profile corresponding to point P 2 of the displacement diagram will be exactly α 2 . Any point chosen within the cross-hatched area A as the cam center will yield a cam whose pressure angles at points corresponding to P 1 and P 2 will not exceed the specified values α 1 and α 2 respectively. If O 1 is chosen as the cam shaft center, the pressure angles on the cam profile corresponding to points P 1 and P 2 are exactly α 1 and α 2 , respectively. Selection of point O 1 also yields the smallest possible cam for the given requirements and requires an offset follower in which e is the offset distance. If O 2 is chosen as the cam shaft center, a radial translating follower is obtained (zero offset). In that case, the pressure angle α 1 for the rise is unchanged, whereas the pressure angle for the return is changed from α 2 to α ′ 2 . That is, the pressure angle on the return stroke is reduced at the point P 2 . If point O 3 had been selected, then α 2 would remain unchanged but α 1 would be decreased and the offset e increased.
360°
0°
e
300°
α 1
O 1
100°
α 2
120°
Fig. 16. Construction of Cam Contour; Offset Translating Follower
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