SEED Unit Design - Cam Mechanisms <

APPENDIX A. BLENDED MOTIONS

One means of reducing the prime circle radius without increasing the maximum pressure angle is to blend portions of two complete motion segments so that the maximum follower velocity is displaced towards outer dwell. The displacement diagrams of two DRD segments forming a blended motion are shown in Figure 20. (The lines AB and CD were generated by the spreadsheet: they should be ignored!) The portion beginning at inner dwell has the same prime circle radius as the actual cam; that of the portion leading to the maximum follower displacement is (with zero offset)

APPENDIX B. OFFSET TRANSLATING FOLLOWER

If the cam angle for one direction of follower movement is much smaller than that for the converse action then the critical pressure angle can be reduced by offsetting the follower path as shown in Figure 7. Equations (16) & (18) for the pressure angle and radius of pitch curve curvature apply. The pressure angle for a DRDF motion with varying degrees of offset defined by the non-dimensional parameter E/H is shown in Figure 22 and the improvement obtained by increasing the segment angle for the adverse condition in Figure 23. In this case the follower displacement, velocity and acceleration continue to be represented by Figures. 11 to 13. Offsetting the follower path affects every motion segment.

APPENDIX C. INCREASED ROLLER RADIUS

Since the magnitudes of both the pressure angle and the profile radius depend upon the pitch curve radius another way to minimize the swept volume for a given prime circle radius is to increase the roller radius.

Conversely, using a larger roller with a given cam has the beneficial effect of reducing the pressure angle since the prime circle radius is increased but not that of the reference circle. The larger roller is more expensive and, having greater mass moment of inertia, is more prone to slip on the cam profile.

APPENDIX D. 4-5-6-7 POLYNOMIAL MOTION.

This motion is designed for zero jerk at every position of zero acceleration. The non-dimensional form of the displacement equation is

The apparent attractions of this motion must be balanced against high peak accelerations and the very gradual start and finish of the displacement curve requiring precision manufacture if the theoretical potential is to be achieved in practice.

APPENDIX E. CRITICAL VALUES OF FOLLOWER DISPLACEMENT, VELOCITY AND ACCELERATION.

Non-dimensional values for a rise motion.

NOTE: Whilst every effort has been made to ensure that the information given is correct and up-to-date, SEED, the publishers and authors cannot be held responsible for any errors or omissions that might occur in this Guide. Use of the methods or data on projects for application outside the academic environment should be justified and validated during the course of the designer's normal professional duties. Copyright © SEED