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KURTOSION - GETTING THE KURTOSIS INTO THE RESONANCES

Traditional random tests, using a Gaussian distribution, have not satisfactorily tested products in a realistic manner because the Gaussian distribution method fails to bring into the test the large peak accelerations which cause product failure. The key to bringing those large peak accelerations into the random vibration test is to use a kurtosis control method. Kurtosion , the patent-pending technique developed by Vibration Research Corporation, is a kurtosis control method that can effectively bring large peak accelerations into the random vibration test. This technique has been criticized by some who appeal to the Papoulis Rule a rule that indicates that all systems tend towards Gaussian distribution. However, while the Papoulis Rule indicates the output of highly filtered systems tend towards a Gaussian distribution, it does not claim they actually are Gaussian. Test results obtained at VRC with their newly developed kurtosis control technique clearly show that non-Gaussian distributions can indeed be created at product resonances, regardless of the Papoulis Rule.

Get the slides (pdf) or read the paper (pdf)

Examining the Dynamic Range of Your Controller

Dynamic range is one of the fundamental metrics describing the capability of a shaker controller. We all know that dynamic range describes the span of small-to-large acceleration amplitude that can be properly controlled during a test. Since modern controllers are digital instruments, we also know the dynamic range to be six times the number of bits in the analog/digital converter. But what do we really know? Lets examine the dynamic range of a vibration controller more scientifically.

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The Missing Knob on Your Random Vibration Controller

Random vibration testing is the industry workhorse for simulating the environment for a broad range of products. Tests are typically specified by defining a spectrum shape and overall RMS amplitude. The test controller then causes a measured reference acceleration to match these specified parameters. The controller forces a shaped-random response with a normal or Gaussian amplitude distribution. However, experience has shown that such tests may be too conservative for some product/environment combinations. The test does not produce the same damage statistics observed in the field. Adding a third control dimension provides more realistic random vibration tests that better match the damage potential of the actual environment. That third dimension is kurtosis control, which matches the amplitude distribution of the test to that of the environment.

This article appeared in Sound&Vibration
Page 2 - October 2005
Author: Philip Van Baren
Sound&Vibration 2-7.

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Kurtosis - The missing dashboard knob.

Many test personnel have recognized that random testing, while good, has shortcomings when it comes to simulating the real-world environment. As a result, over the years, there have been many vibration testing method modifications to address these shortcomings. In the automotive world, technicians often see that random tests do not find product faults that should show up when vibration testing. To make random testing more effective, they sometimes take the random spectrum, and increase the level accoreding to their own internal, home-cooked formula. The level may be increased so the random peak g levels match the real world.

This article appeared in Test Magazine
Page 14 - October/November 2005
Author: John Van Baren
Test Magazine 14-16

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Test your product using sine or random?

As you know, in the vibration world, there are quite a few test "types" to which you can expose your product. The major choices are Sine, Random, Classical Shock, Transient Shock, Field Recorded Time History, Sine-on-Random, Random-on-Random and Sine-and-Random-on-Random. Frequently, our customers will request advice on which of these types of test to run on their product, and in particular, how to choose between the two most common test types: sine or random. Their desire is to know which test, sine or random, is best to most quickly pinpoint flaws in their product. If they can only run one test, either sine or random, which should it be?
Recently, we received an even more specific request from a customer. This customer (Don) presented both a sine test and a random test and wanted to know, given both a sine test and a random test, how he could determine which is the most severe?

This article appeared in Test Magazine
June/July 2004
Authors: John Van Baren, Philip Van Baren

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Ask the IEST Testing Experts

How do I get the peak levels back up to 120 G peaks when running my random profile?
There are several solutions implemented in the real world to "solve" this issue.

This article appeared in Test Magazine
August/September 2007
Author: John Van Baren

Read the Answer

A Comparison of Simultaneous and Sequential Single-axis Durability Testing

Multi-Axis Vibration Reduces Test Time

Reproducing real-world vibration environments for testing may introduce a higher level of product reliability.
Widely accepted as a method to improve product quality, vibration testing is used to qualify products for production. Either alone or combined with an environmental chamber, vibration testing is a critical step in the successful development of new products. Historically, single-axis, single-shaker testing is the method of choice. Vibration tests are conducted by sequentially applying single-axis vibration to a test article along the product’s X, Y, and Z axes. These tests are performed using a linear shaker and rotating the test product to the next axis after each test. However, complex, multi-axis motions are characteristic of field environments. The more a vibration test can replicate the field environment, the more realistically it can induce a vibration stress loading equivalent to that experienced by the product in the field. Testing all three axes simultaneously can reduce traditional test times by two-thirds and more closely duplicate real-world vibration environments.

This article appeared in Evaluation Engineering, June 2006
Authors: Clyde Harman, Team Corporation, and Michael B. Pickel, Spectrum Technologies

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This article appeared in the August 2000 issue of Shoreline Business Monthly and is reprinted by permission.

Good vibrations keeps shakers rolling at Hudsonville firm

HUDSONVILLE --- Shake, rattle and roll. Not only is that phrase part of one of the classic songs of the '50s, it also can be used to describe an important part of the manufacturing process: vibration testing.

Vibration Research Corporation (Vibration Research Corporation), a Hudsonville company founded six years ago by John Van Baren, is rolling unshakably as a major player in that segment of the manufacturing business. The firm's customer list includes such Michigan industrial stalwarts as Ford Motor Co., General Motors Corp. and BF Goodrich Aerospace along with more exotic clients like the Naval Research Laboratory in Washington, D.C. and firms in Canada, Taiwan, Brazil and Italy.

The purpose of Vibration Research Corporation is to help customers find fault with and flaws in what they produce before it reaches the customer. His primary market is described as "retro-fit," replacing the old with the new.

"Over the years vibration equipment has worked well, but big advances have been made in the instrumentation that goes on that equipment. It used to be very expensive, run with expensive analog computers and then expensive digital computers. But with the advent of digital signal processing and fast computers it's a natural fit to replace all that expensive, antiquated, hard to run equipment with less expensive, easy to use PC-based equipment," Van Baren told SBM. "Thanks to the computer revolution, we have taken the price to one-fourth of what it used to be and increased the capability ten-fold."

Vibration Research Corporation engineers and sells vibration analysis, testing, monitoring and controller systems for electro-dynamic and servo-hydraulic shakers. The firm has developed its signature product, the Vibration View system, which consists of an analog I/O box, a digital signal processing card, a personal computer and software to run the system. The system provides all standard types of tests including sine, random, sine-on-random and classical shock. It also provides a system check that can be used to test and calibrate a shaker system. Vibration Research Corporation's customers hook that system up to their own testing gear to analyze data on a product before it goes to market.

Van Baren, who cut his vibration testing teeth during a 15-year tenure at now competitor Thermotron Industries, operates two offices. Vibration Research Corporation's headquarters are in Hudsonville with a companion office in Ann Arbor. The latter was opened less than two years ago to better serve Vibration Research Corporation's automotive industry customers. That segment of the business is increasing in importance because the Japanese auto industry taught American car companies a valuable dollars-and-cents lesson about the need for vibration testing. "They (American automakers) will put cars together and actually shake them from the component level to whole cars," said Van Baren of the automakers demands. "They will vibrate it to see how it performs. And they are now doing what we call squeak and rattle testing just to see if it makes any noise. They measure the sound level."

In 1995 Vibration Research Corporation broke new ground in vibration research with the development of Field Data Replication (FDR). FDR has become very popular with the automotive industry. Said Van Baren, "This technology allows you to go out into the field and measure your vibration levels and then take that vibration back into the lab and repeat that exact waveform on your shaker." Vibration Research Corporation was the first first firm to make the technology available on a single-axis shaker system. "Since then all of our competitors have copied it or attempted to copy it. But we still do it better, and I can prove that," Van Baren stressed.

Vibration Research Corporation's founder offered a broad brush view of the company's future. "For any company to be successful it has to grow. That would naturally mean more offices, more people and more products."

He envisions an expansion of the Vibration Research Corporation product line based on new customer needs and demands, plans for which are already under development. Van Baren revealed he is also working on forming strategic alliances with companies that actually manufacture the shaker systems.