A Fiber Probe for CMM Measurements of Small Features
Jack A. Stone Jr., Balasubramanian Muralikrishnan, John R. Stoup
We report on performance of a new form of fiber probe, which can be used in conjunction with a coordinate measuring machine (CMM) for microfeature measurement. The probe stylus is a glass fiber with a small ball (?75 ?m diameter) glued to the end. When the ball is brought into contact with a surface, the fiber bends, and this bending is measured optically. The fiber acts as a cylindrical lens, focusing transmitted light into a narrow stripe that can be magnified by a microscope and detected by a camera, providing position resolution under 10 nm. In addition to the high resolution, the primary advantage of this technique is the large aspect ratio attainable. (Measurements 5 mm deep inside a 100 ?m diameter hole are practical.) Another potential advantage of the probe is that it exerts exceptionally low forces, ranging from a few micronewtons down to hundreds of nanonewtons. Furthermore, the probe is relatively robust, capable of surviving more than 1-mm over-travel, and the probe stylus should be inexpensive to replace if it is broken. To demonstrate the utility of the probe, we have used it to measure the internal geometry of a small glass hole and a fiber ferrule. Although the intrinsic resolution of the probe is better than 10 nm, there are many potential sources of error that could cause larger errors, and many of these errors are discussed in this paper. Our practical measurement capabilities for the hole geometry are currently limited to about 70 nm uncertainty. Hole measurements only requires a two-dimensional probe, but we have now extended the use of the probe from 2 d to 3-d measurements. Measurements of the z-height of a surface can be carried out by detecting buckling of the stylus when it is brought down into a surface.
Proceedings of SPIE
July 31, 2005
San Diego, CA
Recent Developments in Traceable Dimensional Measurements III
coordinate metrology, fiber probe, microfeature metrology, small hole