SEED Unit Design - Cam Mechanisms < >

The minimum size of the cam is determined by two independent kinematic constraints, pressure angle and profile curvature. The former also acts to magnify the normal force between the cam profile and the roller, the latter influences the magnitude of the contact stress at their interface. Therefore dimensions determined purely from the kinematic constraints are absolute minima which may need to be increased when the forces and stresses are determined.

Pressure Angle. If frictional effects are neglected then the thrust between the cam profile and the roller acts along the normal to the profile at the cam-roller interface, passing through the roller centre. For the general case of an offset translating follower, Figure 7, the pressure angle between the thrust and the follower path varies during rise and fall actions. It is given by:

Both these cases of interference between the roller (or cutter, whichever has the larger diameter) and the cam profile are known as undercutting.