National Aperture’s micro mini stages are used in labs around the world and in instruments such as spectrometers, chemistry analyzers, microscopes, and optical systems.

In sharp contrast to the dust, heat, and even caustic chemicals that industrial motion control systems must endure, the cool, clean environment of a typical lab or cleanroom seems like it should make automation easy. Far from it. What a typical scientific application lacks in environmental challenges it makes up for in terms of performance demands.

They may not take place on a hot, dirty factory floor, but applications like DNA testing or flip-chip bonding require spatial positioning on the order of microns, not millimeters. Motion needs to be carefully controlled to produce reliable, duplicable results. The systems must produce repeatable action, even when subjected to the heavy duty cycles that commercial labs can impose. As if that isn't enough, they need to provide all of that performance in the smallest possible package.

Miniaturized linear and rotary positioning stages by Salem, NH-based National Aperture (naimoton.com) are meeting these challenges.

Tiny but mighty

High spatial resolution in a small form factor is the specialty of National Aperture, whose micro mini stages show up in labs around the world and in instruments such as spectrometers, chemistry analyzers, microscopes, and optical systems.

When the company's engineering team set out to build a line of miniaturized devices, they wanted to design linear stages capable of achieving micron-scale accuracy with kilogram-level loads and rotary stages with sub-100 arcsec accuracy.

To meet size and performance requirements, the motors powering the stages needed to be no more than 13 mm in diameter and provide consistent performance. The most accurate, repeatable stage in the world is useless unless it can carry the load required, however. The challenge for the National Aperture design team was finding sufficiently small motion components that could produce not only the consistency but the torque needed, while ensuring the kind of reliability scientific applications require. The challenge was met by Clearwater, FL-based MicroMo (micromo.com), member of the Faulhaber Group.

The motor packages consist of precious-metalcommutated servo motors operating at high enough speed that they can be integrated with planetary gearheads to increase torque and still achieve the desired motion characteristics. The subassembly also includes an optical encoder to ensure accuracy. Currently, the linear stages can position loads of up to 3 kg with ±0.5 µm repeatability and a linear accuracy of ±1.0 µm per 25 mm of travel. The rotary stages can carry 2-kg axial loads with 80 arcsec accuracy and 15 arcsec repeatability. Of course, it is important to remember that accuracy and repeatability numbers increase as reduction ratio rises.

Although National Aperture offers standard products, where they really excel is in tailoring their motion platforms to meet the specifications of a project. “We look at the customer's application and then we build to meet his need, depending on the load, the speed, or the torque requirements,” says William Grenier, president and general manager of National Aperture. He gives MICROMO credit for that flexibility. “MICROMO offers a good variety of gearheads with different gear ratios. They have a very small footprint and very high accuracy.”

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