Page 241 - Cam Design Handbook

THB8 9/19/03 7:25 PM Page 229

CAM MECHANISM FORCES 229

• mechanisms having heavy masses or loads such as an indexing turret mechanism
• mechanisms having high-speed and thus high-inertia loads
• mechanisms having high pressure angles.

Let
N = normal component of velocity, ips
ÿ = follower acceleration in/sec 2
F n = force normal to cam surface, lb
a p = pressure angle, deg
W = cam rotational speed, rad/sec
T = torque, lb-in
b = angle of cam rotation for maximum rise, h rad
h = maximum rise of follower, in
q = cam angle rotation, rad
˙ y = follower velocity, ips
L = external load on cam, lb
L 0 = mÿ + L = total load on cam, lb
(friction is negligible)
2
m = mass of follower, lb sec /in
Figure 8.8 shows a radial cam with a roller follower. The normal component

N = rw sin a p
also the follower velocity
˙ y = rw tana (8.4)
p
and the torque load
L = F cosa
o n p
also the torque
T = F r sina p
n
combining yields

T = L r tana . (8.5)
o p
Substituting Eq. (8.4) in Eq. (8.5) we find torque
Ly ˙
T = o (8.6)
w
+ ˙˙ ˙
(Lmy )y
= . (8.7)
w
From Eq. (8.7) we see for the dwell-rise-dwell action that the torque is continually
changing, being proportional to the follower velocity and the load. Also, if these cams are