DESIGNING A CAM

In low-speed ,low-weight ,cam-follower linkages , the design of the cam may be very simple to construct , requiring little understanding of contours .As either the mass , speed , are elasticity of the follower linkage increases , a detailed study must be made of the contour on its characteristic velocity and acceleration curves .Thus ,pertinent information relating to cam size ,vibrations, dynamic loads ,noise , wear ,stresses etc. ,is obtained

The final choice of cam-follower system is generally an intelligent compromise of the following important factors which should never be forgotten and applied as much as possible, when designing a cam are:

i) The cam almost always runs at constant speed which is established by the desirable values of the follower displacement, velocity, and acceleration.

ii) The radial cam is usually employed.

iii) The cam contour should be made smooth with no abrupt changes in its curvature.

iv) The minimum curvature or sharpness of a convex cam contour is dependent upon the value of maximum negative acceleration of the follower .That is, the larger the maximum negative acceleration, the sharper must be the cam surface.

v) The cam size should be as small as possible to minimize the cam-follower sliding velocity, surface wear, and torque .Also, improved balance of the cam will result.

vi) The pressure angle or steepness of the cam contour should be kept to a minimum.

vii) Basic popular curves are available that will fulfill the requirements for most machines.

ix) At high speeds, the noise, surface wear and vibration of a cam-follower system is largely dependent upon the shape of the follower acceleration curve; smoothness and continuity are essential.

x) Scribing lines on the template or cam blank, as a cam fabrication method, is acceptable only for low-speed action. Calculated profiles to establish location for cutter or grinder are necessary for higher cam speeds.

xi) Manufacturing methods and accuracy of cutting and inspection are of paramount importance in assuring the anticipated performance. Required surface and profile accuracy depend upon the cam speed and the follower displacement.

Xii) The moving parts of the cam-follower mechanism should be made as light in weight and as rigid as possible (with no backlash in the system, especially at high speeds).

This helps to keep the inertia forces, noise and wear at a minimum.