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102
to the pitch curve. Thus, the difference in radii of these two circles is
equal to the maximum rise h of the follower.
The cam pitch curve is also the actual profile or working surface
when a knife-edged follower is used. To get the profile or working
surface for a cam with a roller follower, a series of arcs with centers on
the pitch curve and radii equal to the radius of the roller are drawn and
the inner envelope drawn tangent to these arcs is the cam working
surface or profile shown as a solid line in Fig. 7(b).
Swinging Roller Follower: Given the time-displacement diagram Fig.
8(a) and the length of the swinging follower arm L
f
, it is required that
the displacement of the follower center along the circular arc that it
describes be equal to the corresponding displacements in the time-
displacement diagram. If φ
0
is known, the displacement h of Fig. 8(a)
would be found from the formula
°
π
φ
=
180
0 f
Lh : otherwise the
maximum rise h of the follower is stepped off on the arc drawn with M
as a center and starting at a point on the R
min
circle. Point M is the actual
position of the pivot center of the swinging follower with respect to the
cam shaft center. It is again required that the rotation of the cam be
counterclock-wise and therefore M is considered to have been rotated
clockwise around the cam shaft center, whereby the points 2, 4, 6, etc.,
are obtained as shown in Fig. 8(b). Around each of the pivot points, 2,
4, 6, etc., circular arcs whose radii equal L
f
are drawn between the R
min
and R
max
circles giving the points 2', 4', 6', etc. The R
min
circle with
center at the cam shaft center is drawn through the lowest position of
Fig. 7. (a) Time-Displacement Diagram for Cam to be Laid Out;
(b) Construction of Contour of Cam With Radial Translating Roller Follower
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