COSMOS identifies motor frequencies to prevent severe vibration problems

Company Emerson Motor Company Advanced Motor Development Group Industry Electrical/Electronics Location U.S.A. Product Used COSMOSM Type of Analysis Linear Static More Details

The Challenge
We live in a noisy world. Planes scream overhead. Cars and trucks roar on the ground. When we enter our offices and homes, we long for the sound of silence. Or at least no more than a hum or purr from the appliances upon which we depend. Electric motors power those appliances. Emerson Electric Co., the world's leading manufacturer of motors and drives - with sales of over $10 billion in 1995 - makes many of those motors. The Advanced Motor Development (AMD) Group of Emerson Motor Company does research and development work on new motor technologies.

A recent study by Emerson estimates that every household in the United States could potentially use 48 electric motors in various applications. In view of that estimate, Don Williams, chief engineer for the Advanced Motor Development Group, who is responsible for mechanical development, including design, analysis and rapid prototyping said, "Customers are more and more sensitive to noise in their environment. Motors must be quiet and must not excite any of the resonances in the units."

The Solution
Recently, Williams and Jeffrey Mahn, development engineer responsible for mechanical design and analysis for electric motor components, undertook the analysis of an endshield for a general purpose line of motors. The endshields of an electric motor are made out of cast aluminum and are bolted to ends of the motor to provide support for the shaft and bearings and to protect people who handle the motor from contacting the moving parts inside.

Mahn said, "We knew the driving frequencies of the motor, and we wanted to design an endshield with natural frequencies outside of those ranges." Williams elaborated on the problems that would be caused by such a convergence of frequencies: "If the natural frequency of the structure was identical to the driving frequency of the motor, it would cause a severe vibration problem."

In the not too distant past, the AMD Group would not investigate noise problems until they encountered problems in the field. Mahn explained, "Even though we've had the ability to analyze parts for their natural frequencies, such analysis took too long to be a practical tool until COSMOS FFE came along."

For example, Mahn pointed out that "in the case of this endshield, it took the direct solver 48 hours to provide the frequency information, but COSMOS FFE took only 28 minutes." The dramatic difference in computation speeds "makes it practical to run several natural frequency analyses on a component. If we did find that that the natural frequencies of the endshield were the same as the driving frequencies of the motor, we could make changes in the endshield design to shift the natural frequencies and eliminate a vibration problem before was ever manufactured. In this case, we found out that redesign wasn't necessary, saving a great deal of time and money."

Summary and Metrics

• Using COSMOS FFE instead of direct solvers reduced analysis time from 48 hours to just 28 minutes