ВУЗ:
Составители:
Рубрика:
103
the center of the roller follower and the R
max
circle through the highest
position as shown. The different points on the pitch curve are now
located. Point 6'", for instance, is found by stepping off the y
6
ordinate
of the displacement diagram on arc 6' starting at the R
min
circle.
Pressure Angle and Radius of Curvature.— The pressure angle at any
point on the profile of a cam may be defined as the angle between the
direction where the follower wants to go at that point and where the cam
wants to push it. It is the angle between the tangent to the path of
follower motion and the line perpendicular to the tangent of the cam
profile at the point of cam-roller contact. The size of the pressure angle
is important because:
1) Increasing the pressure angle increases the side thrust and this
increases the forces exerted on cam and follower.
2) Reducing the pressure angle increases the cam size and often this is
not desirable because:
A) The size of the cam determines, to a certain extent, the size of
the machine.
B) Larger cams require more precise cutting points in
manufacturing and, therefore, an increase in cost.
C) Larger cams have higher circumferential speed and small
deviations from the theoretical path of the follower cause additional
acceleration, the size of which increases with the square of the cam
size.
Fig. 8. (a) Time-Displacement Diagram for Cam to be Laid Out;
(b) Construction of Contour of Cam With Swinging Roller Follower
Страницы
- « первая
- ‹ предыдущая
- …
- 101
- 102
- 103
- 104
- 105
- …
- следующая ›
- последняя »
