Pint-Sized Hardness Tester Gets Its Finesse from Compact Servodrive

Feb. 1, 2011
A miniature dc servomotor from the Faulhaber Group in Germany controls the vertical measuring movement of a super-fine needle on a hardness testing machine
MICROMO Electronics Inc., Clearwater, Fla., U.S. distributor for Faulhaber motors and drives,

It’s now possible to more easily check the hardness of tiny elastomer part, thanks to a novel testing instrument with supersmall motor-driven probes.

Ordinary Shore A hardness testers use a conically shaped needle for probing samples 4 to 6-mm thick with a bearing surface of approximately 18 mm in diameter. But the probe on ordinary machines is too big to handle supersmall samples, and particularly so for soft materials, as sometimes needed for special applications.

Developers at Q-TEC GmbH in Germany scaled down the geometry of a conventional probe to produce one having a point which corresponds to the diameter of a human hair. The resulting instrument can work with samples no thicker than 0.5 mm. The small needle is not prestressed, so the instrument can measure soft materials.

A laser-positioning reticle defines the penetration point regardless of the test item’s geometry. This lets it take measurements at different positions, such as wave crests or troughs. Once the laser pinpoints the position of the test area, a miniature dc servomotor from the Faulhaber Group in Germany controls the vertical movement of the needle.

The servomotor is compact and sports an integrated motion controller to minimize the load on the instrument electronics. Motor output torque is 50 mNm on the shaft and the power rating is up to 90 W. The controller provides speed control, precise speed profiles, and incorporates both a stepper-motor mode and a positioning mode.

The controller resolves moves of up to 1/3,000 revolution and has the option of accounting for reference marks and limit switch positions. An RS-232 interface enables communication with the external logic. The controller also manages overload and overvoltage conditions.

© 2011 Penton Media, Inc.

About the Author

Leland Teschler

Lee Teschler served as Editor-in-Chief of Machine Design until 2014. He holds a B.S. Engineering from the University of Michigan; a B.S. Electrical Engineering from the University of Michigan; and an MBA from Cleveland State University. Prior to joining Penton, Lee worked as a Communications design engineer for the U.S. Government.

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