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Molded Plastic Gears Find Niche in Glucose Monitors, Magnetic Imaging Devices

Originally Published MPMN September 2002

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Molded Plastic Gears Find Niche in Glucose Monitors, Magnetic Imaging Devices

Compact, lightweight components are suited for mobile devices

Because they are made entirely of plastic, Wave Drive gears can benefit magnetic imaging equipment in which the use of metallic components may be problematic.

Although they can be as small as 12 mm OD and weigh less than 1 g, molded plastic gears can achieve reduction ratios up to 8000:1. Wave Drive technology, developed by Oechsler AG (Ansbach, Germany), has numerous applications, but the components' compact size and light weight make them particularly suitable for use in medical devices, according to project manager Frank Poehlau. In addition, because they are nonmetallic, the gears may have a material advantage in magnetic-based medical imaging applications.

"The gears weigh as little as 0.97 g," stresses Poehlau, "making them ideal for mobile units in which every gram counts." He cites portable pumps and glucose monitors as the type of medical equipment that could benefit from Wave Drive gears. The gears can be attached to compatible motors to form a compact drive unit; custom linear drives can also be designed.

Magnetic imaging, where the use of metallic components may be problematic, represents another potential application for the components, according to Poehlau. "Any imaging system with magnetic features would benefit," he says, "because the gears provide high reduction ratios, precision, durability, and reasonably good torque without generating artifacts." Gear can measure between 10 and 50 mm in diameter, and produce up to 10 N∙m of torque.

Unlike planetary and worm gears that rely on several groups of engaged cogs, Wave Drive gears use an elliptical core that is enveloped by a pulsator wheel and a flexible gear ring. The flexible ring's external grooves mesh with the grooves in a stationary, rigid ring that has two more teeth than its flexible counterpart. The rotation of the input shaft causes a deformation in the pulsator wheel, which, in turn, alters the shape of the flexible ring. The variance in the number of teeth produces a slow rotation of the flexible ring. By varying teeth parameters between the outer and inner rings, a wide range of reduction ratios can be achieved.

The components are very cost- effective, adds Poehlau, because the gears are injection molded. "When you get into large quantities—for example, we anticipate producing about 3 million units annually for use in a glucose monitor—they cost pennies per unit," says Poehlau.

The gears do have one limitation for medical applications, notes Poelhau: they cannot withstand temperatures above 80°C. That is the next challenge, he adds, noting that Oechsler is "investigating the feasibility of molding sterilizable materials to manufacture the gears."

Norbert Sparrow

Oechsler AG, Matthias-Oechsler-Str. 9, Ansbach, Germany D-91522; phone: +49 981 18070; fax: +49 981 1807234; www.oechsler-ag.de

Copyright ©2002 Medical Product Manufacturing News

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