Page 491 - Cam Design Handbook

THB14 9/19/03 7:58 PM Page 479

SPECIAL CAM MECHANISMS 479

FIGURE 14.27. Triangular circular arc cam characteristics (translating follower).

If we consider the cycle in which q varies from 0° to 60° (the positive acceleration
period of the motion), the displacement

)
h -
y = (1 cosq in. (14.18)
This is simple harmonic motion for these 60° to a total lift equal to h/2.
The velocity and acceleration by differentiation
˙ y = w h sinq ips (14.19)
2
˙˙ y = w 2 h cosq in sec . (14.20)
The minus acceleration period is similar for the next rise portion h/2, the total lift occur-
ring in 120° of cam rotation. A dwell of 60° of cam rotation then follows. In Fig. 14.27b
we plot the curves of the complete action in which it is seen that the acceleration curve is
discontinuous.

14.24 SWASH PLATE CAM

The swash plate cam (Fig. 14.28) is an end cam having a flat-plane disk fixed at an acute
angle to a rotating shaft. This cam has been used for a multipiston pump whose piston rods
ride on the swash surface. If a knife edge or point contact were employed, the follower
would move with simple harmonic motion. However, with a more practical crowned roller
follower, the follower has approximate simple harmonic motion, if the roller diameter is
kept small. Swash-plate cams are feasible only under light loads, since the eccentricity
shown causes poor bearing operation due to excessive deflections of the cam and its shaft.