13.8 DISCUSSION

In cam-follower systems, follower vibrations are always induced. At low speeds, they are rarely a factor for concern, but at high speeds, they can become great enough to significantly degrade system performance. At very high speeds the vibration may be sufficient to destroy the system or at least stop it from functioning.

Vibrations arise from many sources:

1. Vibrations due to the shape of the follower acceleration curve (the main source addressed in this chapter).

2. Vibrations resulting from separation of the cam and the follower. With positive-drive cams with backlash, impact of the roller on the cam is produced as the contact force changes direction. This is called cross-over shock. With spring-loaded followers separation is due to the jump condition that occurs when the preload force is insufficient to maintain a positive contact force.

3. Vibrations due to surface irregularities caused by deficiencies in cam and/or follower manufacturing.

4. Vibrations due to variations in the external load. For example, a cam-driven punch indexing mechanism has its load applied suddenly as the punch starts into the work-piece. This quick-load application cannot be eliminated, and, therefore, the ultimate design must account for it.

5. Miscellaneous sources. One of these sources is camshaft unbalance. In this case, intelligent practical design of the cam structure and the body to reduce the offset mass and maximize camshaft stiffness and support will keep this vibration to a minimum. Vibration may be transmitted to the cam surface from the driving mechanism through the frame...