Design and Development of Oblique-Incident Interferometer for Form Measurement of Hand-Scraped Surfaces

Precision flat surfaces finished by hand-scraping are extensively used in the sliding parts of precision positioning systems or the surface plates of precision measuring instruments.These hand-scraped surfaces are employed to improve the flatness of the machined surfaces and the motion accuracy of the instruments.The numerous depressions of micrometer-scale depth on a scraped surface are thought to prevent wringing and improve the lubrication properties by forming oil pockets.Form measurement of the micrometer-scale features of a hand-scraped surface is one of the reasonable methods for investigating its effect on the motion accuracy of the positioning systems or the lubrication properties of the sliding parts.Because a hand-scraped surface is a rough surface composed of micrometric complex features,it is difficult to conduct precision measurement of the three-dimensional surface form using conventional measurement instruments,such as vertical-incident interferometers or stylus-type profilometers.In this study,an oblique-incident interferometer based on Abramson interferometry is introduced to measure the form of a rough surface produced by hand-scraping.Because this technique can detect high-intensity reflected light on a rough surface,it allows the measurement of the form of the hand-scraped surface in noncontact condition.In order to shorten the measurement time,the form calculation based on a five-step phase shifting method was introduced.