Page 230 - Cam Design Handbook

THB8 9/19/03 7:25 PM Page 218

218 CAM DESIGN HANDBOOK

a p = pressure angle, deg
b = cam angle rotation for rise, h, radians
d = deflection, in
m = coefficient of friction
q = cam angle rotation, radians
w = cam rotational speed, rad/sec

8.1 INTRODUCTION

We shall discuss the cam-follower system forces driven by constant speed cam. The
forces listed are generally superimposed on each other during the cam-follower system
action.
• working loads
• impact forces
• inertia forces
• vibratory forces
• frictional forces
• spring forces
• operating forces (braking, start/stop, and overload shock actions)
Information on these forces is necessary to determine (at a designed speed) the struc-
tural sizes of the machine moving parts for strength and rigidity, the proper choice of and
life materials, the bearing sizes, the spring sizes and loads, and the system performance
and power consumption, among other things. Note that impact forces may produce farces
that far exceed all others. Also, a torque analysis of the system is usually necessary to
understand the transfer of energy throughout the system under conditions of operation.
Often the follower system is remotely located with reference to the cam (cam modu-
lated system) and the dynamic analysis becomes quite complex. For dynamic analysis of
these cam modulated systems, see Paul (1979) (1996) and Sandor and Erdman (1984).

8.2 WORKING LOADS

Working loads, or applied loads, represent the useful work performed by a machine.
Working loads may be classified in these relative categories: gradually applied, suddenly
applied, and impact forces.
Note that these three categories may not be directly related to the speed of the cam.
For example, a slow-speed cam mechanism, having a large flywheel, punching holes in
tough sheet metal may have an impact load, while a high-speed system pumping chemi-
cally processed air can have gradually applied loads. It is the responsibility of the engi-
neer to make an experienced judgment about the designed effect of the working load on
the system. Also, the application of working loads in a positive drive cam follower may
augment or reduce the other forces in a system. For example, if applied during the initial
cam stroke, they add to the inertia forces during the positive acceleration period. During
the negative acceleration period they tend to reduce the load by absorbing some of the
energy stored in the follower mechanism.