SEED Unit Design - Cam Mechanisms < >

From inspection of equation (16) the least cam size involves specifying the largest possible segment angle and least possible lift. These proportions also minimize the peak follower acceleration with attendant (desirable) implications for the force and contact stress at the camroller interface. Conversely, for given values of segment angle, lift and roller radius the maximum pressure angle can be reduced and the least radius of profile curvature increased by enlarging the prime circle radius, equation (1).

If necessary, the cam size can be reduced without exceeding the permitted pressure angle by:

1. blending the profile to displace the maximum velocity towards the maximum displacement position (Appendix A and Figures 20 & 21), or
2. offsetting the follower path (Appendix B and Figures 2b, 7, 22 & 23), or
3. increasing the prime circle radius for the same reference circle radius by using a larger roller (Appendix C).

Profile blending does not affect the remaining motions but has the disadvantage of increasing the maximum separating force and may also reduce the profile radius near the nose of the cam, both acting to increase the contact stress in this heavily-loaded region. Offsetting the follower path affects every part of the motion (including dwells). In particular this configuration requires a significantly larger segment angle for the converse action. Consider the possibilities of combining both procedures! Enlarging the roller radius with the same cam will improve the pressure angle but may affect profile curvature adversely (watch for undercutting!).

Hence the sensitivity of these constraints to each possibility needs to be investigated for the unique requirements of a specific design.