Jeff Weisbeck
Enidine Inc.
www.enidine.com

David Catanzarite
Lord Corp.
www.lord.com

HOW DOES VIBRATION CONTROL OR LACK THEREOF AFFECT PRODUCTIVITY AND THROUGHPUT IN INDUSTRIAL MOTION SYSTEMS?

Jeff • Enidine: Vibration control affects productivity through its impact on the accuracy and repeatability of manufactured parts. Motion within a machine will inherently excite the natural frequencies of its components and the part being manufactured. These natural frequencies will lead to unwanted relative motions. Imagine a controlled conveyor moving parts into a delicate wafer-handling system. A force is generated when the part is stopped in the desired location. This force has the possibility of exciting natural frequencies in both the machine and the part itself.

If speed is increased in an effort to increase throughput, then the force required to stop the part must also increase, leading to greater relative motion. The relative motion created this way by inherently non-rigid systems limits the accuracy and repeatability of a motion control system. This may also force a part in production to dwell at a given location to allow these relative motions to decay. The same mechanism is at work in larger systems as well, such as heavy punch presses.

David • Lord Corp.: Vibration can affect productivity in a number of ways. Not only are machines and foundations adversely impacted by vibration, but also humans and their productivity.

Controlling unwanted vibration in high-speed grinding, for instance, or the chatter of a cutting bit not only allows for faster operations, but also achieves greater accuracy. As the vibration is reduced, more and better parts start coming off the line.

Large punch presses designed to produce high-volume precision parts at low cost, such as aluminum beverage can production, benefit greatly from reduced vibration. At rates of 450 CPM, for example, any unwanted vibration can cause the machine to produce scrap, at a very high rate. Controlling the vibration, such as the ram motion, can allow the press to run at even faster speeds, thereby improving productivity.

Man/machine interface is another area where controlling vibration pays off. Exposure to vibrations generated by operating equipment from handheld pneumatic tools and jackhammers to vehicles such as dozers and class 8 trucks can have negative effects on operator health and productivity. The exposure a human can have to vibration is time-limited; the higher the vibration, the shorter the operating time. This relates to decreased productivity, as well as operator fatigue.

WHAT ARE THE MAIN CHALLENGES IN OVERCOMING VIBRATION AND WHAT ARE SOME OF THE ADVANTAGES AND DISADVANTAGES TO DEALING WITH VIBRATION EITHER BEFORE OR AFTER IT HAS OCCURRED?

Jeff • Enidine: Careful design of a motion control system can address relative motions early in the design stage. Computing a system s natural frequencies can be accomplished with many finite element packages, but the real challenge is to account for damping in the system. These values tend to be non-linear and difficult to predict.

Empirical measurement and monitoring of existing systems provide actual in-situ machine vibration levels. However, modifications to existing systems can be costly. One approach is to design vibration control elements into a system during the early design stages. These vibration control elements can then be modified or eliminated during system checkout. The key is to reserve space early in the design process for motion control elements.

To control vibrations in an existing system, a number of motion control devices and approaches can be used. Active vibration control measures problematic vibrations, and then applies an equal but out of phase frequency force to cancel or minimize the vibration. Passive vibration control absorbs or attenuates vibrations by using products such as shock absorbers and vibration isolation mounts.