SEED Guides Tutor's Guide - Cam Mechanisms < >

12.1 Compare the maximum force for spring force closure at outer dwell with the peak value of acceleration using alternative cam laws. Compare, say,:

SHM.

3-4-5 polynomial motion,

cycloidal motion,

modified trapezoidal acceleration motion,

modified sinusoidal acceleration motion.

Why is it adequate to use the data in Appendix E of 'Cam Mechanisms - Unit Design' guide ?

Explain the discrepancies between the relative peak accelerations and maximum spring forces in the results.

12.3 Determine the least reference circle radius [and least spring force to ensure force closure of the mechanism] for a disc cam driving a radial translating follower to suit, say, the following requirements:

Cycloidal motion throughout both rise and fall.

Lift 28mm

Segment angles:-

Rise 75š

Outer dwell 25š

Fall 150š

Inner dwell 110š

Roller radius* 12mm

Cam speed 940rev/min

Lumped mass of following
system at roller centre 0.8kg

* - Catalogue cites roller diameter!

COMMENT For academic purposes editing is clarified by avoiding duplication of the same numerical value in the input data.

12.4 Investigate means of reducing the reference circle radius of assignment 12.3 above by:-

12.4.1 offsetting the follower path,

12.4.2 blending the critical motion segment,

12.4.3 increasing the roller radius,

12.4.4 a combination of the above.

Discuss the results!

12.5 Investigate the value of blending the rise profile of example 12.3 to reduce the spring force by, say, 10%.

COMMENT - reduce the -ve acceleration so the peak follower velocity is displaced towards inner dwell. So, to keep the same maximum pressure angle, cam size is increased. What other consequences result?

12.6 The angle of lift is minimised by offsetting the follower path; investigate the value of profile blending for the fail motion of this cam to minimise the angle of fall.

12.7 A retro-fit change affecting a cam mechanism must have minimal consequences on the remainder of the machine. The angle of lift is reduced for the same lift and follower path. Redesign for the best possible follower motion. Data needed!

12.8 Superimpose an external load, varying, say, sinusoidally [zero at start and finish], on one of the above.

12.9 Analyse [and generate design data] for the driving torque of a cam driving an offset translating follower.