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A medical equipment manufacturer wanted to use a spring that provided (1) compression, (2) torsion, (3) lateral bending and (4) lateral translation rates, all within one individual spring having an easy attachment method. They also requested three other springs with the same criteria except for different rates. All of this, and the springs must be lightweight and relatively inexpensive.
Just being able to hit one elastic rate can be challenging, but four! Since the lateral translation rate needed to be as high as possible, it became the starting point for analysis. It is known that triple start HELI-CAL Flexures are very high in lateral stiffness. Next, came the remaining three rates. Using first-class finite element analysis software, these three were quantified. A trend also appeared, showing that as the number of starts increased, the ratio of the remaining three rates converged. In fact, at five starts, the ratio was near perfect. At six or more, divergence was experienced, hence no benefit. All that was left was to select a coil thickness, and OD to ID ratio that best fit the customer's needs. Combine the use of 7075-T6 aluminum for light weight and lower machining cost, and it's a done deal. (It needs to be said that this application died on the operating table due to medical reasons. But the ability to ratio elastic rates remains a solution looking for a sophisticated application.)
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901 W.
McCoy Lane · P.O. Box 1069 · Santa Maria, CA 93456-1069 Phone: 805-928-3851 · Fax: 805-928-2369 sales@heli-cal.com · engineering@heli-cal.com |
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