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Coming Age of Surface Metrology with Optical Instruments

Contact-Type Measurement

Surface irregularities can significantly impact the quality and performance of industrial products; these irregularities can then impact the value of such products. Industrial manufacturing requires advanced machining technologies, product quality testing, and machining process management. When creating a surface, there will be a target range, an instrument for seeing that range, and a required method. The method for examining this quality is measurement, and the contact-type instrument (contact stylus) is the tool most typically used to perform this measurement.  Contact-type measurement detects irregularities by moving the tip of a stylus directly across the measured surface, which leads to highly reliable measurement data. The standards developed for such measurement have helped improve the supply and reliability of industrial products.

From Contact-Type to Light

Contact-type techniques achieve measurement with high reliability, but as the stylus touches the measured surface, it is limited in reaching the bottom of the valleys in the surface texture due to the size of the tip,  in addition the tip is further rounded by friction. Also, measurement pressure can damage the measured surface. As a result, the measurement can differ from actual surface roughness. Today, diamonds with high friction resistance are used as styli, with tip shapes made as narrow as possible, allowing fine adjustment of measurement pressure. The precision of the instruments themselves has dramatically increased, and progress is being made in standardizing the precision of contact-type instruments, which contributes to higher quality in industrial products. However, not all problems associated with contact-type measurement have been overcome. As higher product quality is expected, the development of finer surface roughness assessment methods continues, along with an emerging shift from “line” to “area” roughness. Today’s manufacturers have increase expectations about the use of “light” in place of contact-type styli as the core of the next generation of surface roughness measurement.

Industry Turning to Light

About 30 years ago, when standardization of contact-type measurement was underway, we encountered our first measuring instrument that used light. The advantages of light are that it is eternally free of friction, does not damage the measured surface, measures rapidly, and utilizes easy-to-use instrumentation. These benefits, combined with the novelty of the technology, raised high expectations. Initial measurement results, however, were very different from measurement data obtained with contact-type instruments. It became clear that the discrepancy in measurement data was due to light-specific phenomena, such as variations in light scattering and the amount of reflected light. Today, measurement with light has become more precise and the measurement data obtained with light closer to that obtained from contact-type instruments.
The advantages of light are that it is non-contact, capable of areal measurement, and can measure at high speed. Non-contact and areal measurement make it possible to quickly measure the full area of industrial products that are soft, thin, or wide without damaging them. Measurement with light is becoming essential for mass-produced industrial products that are expected to be uniform and homogeneous.
Light is used for displays, electronics, films, and similar products where destruction during measurement is a concern, and also for more robust samples such as diesel engine nozzles. Measurement with light also has a number of environmental advantages.

Delivering Satisfactory Reliability

The Japanese Industrial Standard (JIS) for areal roughness measurement only regulates two-dimensional parameters, and no clear standards exist for three-dimensional parameters. Work by European research groups on the standardization of three-dimensional parameters is progressing, and it now appears that the wider use of three-dimensional parameters, and the provision of adequately reliable information on three-dimensional analysis, are necessary.
Machining precision continues to improve with recent advances in machining technology, and there is demand for high-precision roughness measurement instruments. There are laser microscopes today that can measure surface roughness with light condensed into the extremely small spot diameter of a laser beam, achieving nanometer-level resolution in the vertical direction, and areal rather than linear assessment is becoming the mainstream in measurement assessment. We are now in an age where high-speed areal and full-area measurement with light can deliver satisfactory reliability.

Dr_Yanagi Dr. Kazuhisa Yanagi is a professor of faculty of engineering, department of mechanical engineering at Nagaoka University of Technology.

Publications by Prof. Kazuhisa Yanagi with Olympus LEXT Laser Scanning Confocal Microscope

  • Akihiro Fujii, Shinichi Hayashi, Shintaro Fujii, Kazuhisa Yanagi, "Analytical study on optically measured surface profiles of referential geometry using a FDTD method", 14th International Conference on Metrology and Properties of Engineering Surfaces, June 2013.
  • M. F. Ismail, K. Yanagi, H. Isobe, A H M Rozalee, "Effect of Diamond Electrodeposited Tool Surface Topography to Ultrasonic Vibration Assisted Grinding", "14th International Conference on Metrology and Properties of Engineering Surfaces.", June 2013.
  • Akihiro Fujii, Shinichi Hayashi, Shintaro Fujii, Kazuhisa Yanagi, " Analytical study on optically measured surface profiles of referential geometry using a FDTD method ", The Japan Society for Precision Engineering (JSPE) Spring Meeting 2013 (in Japanese)
  • Kazuya Shimizu, Hidetake Tanaka, Kazuhisa Yanagi, "Analytical study of planetary drilling tools for CFRP and its wear observation", The Japan Society for Precision Engineering (JSPE) Spring Meeting 2012 (in Japanese)
  • Koichi Nishinaka, Hidetake Tanaka, Kazuhisa Yanagi, "Development of Hydraulic Diamond Burnishing Tool for Interrupt Surface Finishin", The Japan Society for Precision Engineering (JSPE) Spring Meeting 2012 (in Japanese)
  • Mohd F. Ismail , Kazuhisa Yanagi, Hiromi Isobe, "Geometrical transcription of diamond electroplated tool in ultrasonic vibration assisted grinding of steel", International Journal of Machine Tools & Manufacture 62(2012) 24-31
  • Hidetake Takanaka, Koichi Nishinaka, Kazuhisa Yanagi, "Development of Hydraulic Burnishing Tool for Discontinuous Surface Finishing -Machining Characteristics of Hydrostatic Burnishing Tool with Single Crystal Diamong Tip-", Journal of The Japan Society for Technology of Plasticity Vol53,621 (2012) (in Japanese)
  • Kazuhisa Yanagi, Akihiro Fujii, "A study on short-wavelength measurement limit for surface texture measuring instruments by optical methods", 3rd International Conference on surface metrology, Annecy (poster session)、2012.
  • Akihiro Fujii, Kazuhisa Yanagi, " A study on short-wavelength measurement limit for surface texture measuring instruments by optical methods ", The Japan Society for Precision Engineering (JSPE) Spring Meeting 2012 (in Japanese)
  • Mohd F. Ismail, Kazuhisa Yanagi,, Akihiro Fujii, "An outlier correction procedure and its application to areal surface data measured by optical instruments", Measurement Science and Technology 21 (105105) (2010) 11 pp.
  • Akihiro Fujii, Hitoshi Suzuki, Kazuhisa Yanagi, "Development of measurement standards for verifying functional performance of surface texture measuring instruments", Journal of Physics : Conference Series311(2011)012009
  • Hidetake Takanaka, Wataru Ishii, Kazuhisa Yanagi, "Optimal Burnishing Conditions and Mechanical Properties of Surface Layer by Surface Modification Effect Incuced of Applying Burnishing Process to Stanless Steel and Aluminum Alloy", Journal of The Japan Society for Technology of Plasticity Vol52,605 (2011) (in Japanese)
  • Akihiro Fujii, Hitoshi Suzuki, and Kazuhisa Yanagi, "A study on response properties of surface texture measuring instruments in terms of surface wavelength", ASPE Summer Topical Meeting 2010 Ashvill
  • Akihiro Fujii, Kazuhisa Yanagi, " A study on response properties of surface texture measuring instruments in terms of surface wavelength ", The Japan Society for Precision Engineering (JSPE) Spring Meeting 2009 (in Japanese)

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