SEED Unit Design - Cam Mechanisms < >

As shown in Figure 1, the design process continues by determining the forces acting on the mechanism. Knowledge of the operating speed, spring force, external load and lumped mass of the following system at the roller centre, together with the cam geometry, enables the contact stress in the cam disc and the required dynamic load capacity of the roller to be calculated (assuming it does not slip on the cam profile). Both involve complex analyses. Since the reaction force between the cam and roller varies continuously during rise and fall actions the position of maximum contact stress is unlikely to co-incide with that of the maximum load, maximum pressure angle or least profile curvature. Likewise, accurate analysis of the dynamic loading of the roller must allow for the combination of continuously-varying force and rotational speed.

Hence a hardenable, stable material having good fatigue and wear properties, such as a spheroidal graphite cast iron or a hardened steel of different composition to the roller is needed for the cam. Needle bearing cam rollers are commercially available, they should be selected by reference to a current catalogue to meet the computed static and dynamic load capacities within the limiting speed quoted by the manufacturer.