Shadow Technique Improves Measurement of Micro Holes

Jun 02, 2005
Shadow Technique Improves Measurement of Micro Holes

Sometimes seeing a shadow can be as good or better than seeing the real thing. A new measurement method* developed by researchers working at the National Institute of Standards and Technology (NIST) is a case in point. The method uses the shadow cast by a small glass probe to infer the dimensions of tiny, microscale holes or other micrometer-sized components. The technique may provide an improved quality control method for measuring the interior dimensions of fuel nozzles, fiber optic connectors, biomedical stents, ink jet cartridges and other precision-engineered products.

Image: NIST researchers and collaborators have developed a new method for measuring the interior dimensions of small holes with an uncertainty of only 35 nanometers. Here, a glass probe is inserted into an optical "ferrule," a device for connecting optical fibers used in communications systems. NIST Photo

Designed to be implemented with the type of coordinate measuring machine (CMM) routinely used in precision manufacturing settings, the method uses a flexible glass fiber with a microsphere attached on one end. The glass probe is attached to the CMM's positioning system, inserted into the part to be measured, and systematically touched to the part's interior walls in multiple locations. A light-emitting diode is used to illuminate the glass fiber.

While the microsphere inside the part is not visible, the shadow of the attached fiber—with a bright band of light at its center—shows the amount of deflection in the probe each time the part's interior is touched. A camera records the shadow positions. Based on prior calibration of the force required to bend the probe a specific distance, the part's dimensions can be determined with an uncertainty of about 35 nanometers (nm). The method can be used for holes as small as 100 micrometers in diameter.

"Our probe has a much smaller measurement uncertainty than other available methods and it is very cost effective to make," says Bala Muralikrishnan, a NIST guest researcher from the University of North Carolina at Charlotte.

The thin, glass fiber is about 20 millimeters long and 50 micrometers in diameter, making it especially useful for measuring relatively deep holes not easily measured with other methods. Replacement probes cost about $100 compared to about $1,000 for those manufactured using silicon micromachining techniques.

*B. Muralikrishnan, J.A. Stone and J. R. Stoup. Measuring internal geometry of fiber ferrules. Presented at the SME MicroManufacturing Conference, Minneapolis, Minn., May 4-5, 2005.

Source: NIST

Explore further: Art of Science 2014: Princeton launches online galleries of prize-winning images and video

add to favorites email to friend print save as pdf

Related Stories

A global view of oceanic phytoplankton

Jul 18, 2014

University of Maine oceanographer Ivona Cetinic is participating in a NASA project to advance space-based capabilities for monitoring microscopic plants that form the base of the marine food chain.

From thin silicate films to the atomic structure of glass

Jun 05, 2014

Glass ranks as one of the most important materials of our age. You have only to think about smartphones, or drinking glasses, or look out of the window to realise that glass in its various forms is omnipresent. ...

Skin with high rust protection factor

Jun 04, 2014

In industrialized countries, corrosion guzzles up to 4 percent of economic performance annually. Substances that protect metals effectively from its ravages are often damaging to the environment or have other ...

Recommended for you

Ultra high definition TVs boost LG Display profit

5 hours ago

(AP)—LG Display Co. said profit for the April-June quarter more than doubled as a stronger won reduced the value of its foreign debt and the World Cup boosted demand for ultra-high-definition TVs.

Drugmaker GSK slashes annual profits forecast

5 hours ago

British drugmaker GlaxoSmithKline on Wednesday slashed its 2014 profits forecast as second-quarter earnings sank on the back of weak US trade, adverse currency moves and a Chinese bribery probe.

Perthites wanted for study on the Aussie lingo

6 hours ago

We all know that Australians speak English differently from the way it's spoken in the UK or the US, and many of us are aware that Perth people have a slightly different version of the language from, say, Melbournians - but ...

User comments : 0