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Theauthors of such comparisons are often surprised by the results but, uponcloser inspection, most of the results can be explained. Often it is stated thatthe instruments do not compare because they have not been adequatelycalibrated. Whilst this may be a source of discrepancy, there are usually betterreasons for instruments with different operating principles not comparingwell. For example, a stylus acts as if a ball is rolled across the surface whilst anoptical instrument relies on the reflection of an electromagnetic wave.
Is itreally so difficult to appreciate that such instruments can produce differentresults? Also, different instruments will sample different spatial wavelengthbandwidths of the surface being measured and will have different physicallimitations.165166C H A P T ER 6 : Surface topography measurement instrumentationIn an early example [130] the measurement of groove depths wascompared, where this groove could be measured by optical, mechanical andeven AFM instruments (see chapter 7).
From this comparison it becameevident that grooves of some 40 nm could be measured with uncertainties inthe nanometre level, but, for a 3 mm depth the results scattered far more than1 %, even between NMIs. It is expected that since then, this situation hasimproved (see later).For example, the results of the measurements of a nickel sinusoid sample,with a period of 8 mm and an Ra of 152 nm, showed very different results fora number of different instruments (see Figure 6.36) [131]. The participants inthis comparison were all experienced in surface texture measurement. In thisexample, NS IV refers to the traceable instrument at NPL (see section 6.10.1),Stylus 1 and Stylus 2 are different stylus instruments on the same site, Inter 1and Inter 2 are the same model of CSI instrument on different sites and Confrefers to a confocal instrument.
It was later found out that Stylus 2 hadincorrectly applied a filter. A further triangulation instrument was also usedin the comparison and the result was an Ra value of 2955 nm – far too large toplot on this figure!Many of the discrepancies above were explained after the comparison butthe question remains: would a user in an industrial situation have the luxuryof the hindsight that is afforded in such a comparison?This section is not intended to scare the reader into complete distrust ofsurface topography instruments – its purpose is to make the reader vigilantwhen measuring and characterising surface topography.
Instruments shouldbe properly calibrated and performance verified, results should be scrutinisedand, where possible, different instruments should be used to measure thesame surface. Once a stable measurement procedure is set up in a givensituation, appropriate procedures should be in place to ensure that theFIGURE 6.36 Results of a comparison of different instruments used to measurea sinusoidal sample.Software measurement standardsinstrument is operated within its limits and results are properly interpreted.Due care should especially be given to the types of filtering that are applied,both physical and digital.On a happier note a recent comparison carried out by European NMIs[132] of profile measurements using types A, C, D and F1 calibration artefacts (see sections 6.10.2 and 6.13) gave results that were in relatively closeagreement.
This shows that it is possible for different instruments to getcomparable results. Note that many of the comparisons that are reported inthe literature are for profile measurements. To date there have been relativelyfew comparisons of areal measurements (but see [133]).6.13 Software measurement standardsAs can be seen from chapter 8, surface texture characterization involvesa large array of filtering methods and parameter calculations. The softwarepackages that are supplied with surface texture measuring instruments, andsome stand-alone software packages, usually offer a bewildering range ofoptions for characterization.
Where possible, these software packages shouldbe verified by comparing them to reference software. ISO 5436 part 2 [134]presents two types of software measurement standard for profile measurement and ISO/FDIS 25178 part 7 [135] presents the two areal counterparts.Only the profile software measurement standards will be discussed here butthe general principles also apply in the areal case.The two types of software measurement standards [134] are:Type F1 – reference data files.
These are digital representations of a profilethat are used as input to the software under test. The results from the software under test are compared with the certified results provided with the typeF1 software measurement standard. Type F1 software measurement standards are often referred to as softgauges.Type F2 – reference software. Reference software consists of traceablecomputer software against which software in a measuring instrument (orstand-alone package) can be compared.
Type F2 software measurementstandards are used to test software by inputting a common data set into boththe software under test and the reference software and comparing the results.Of course the type F1 and F2 software measurement standards arerelated. Type F1 standards can be generated as mathematically knownfunctions such as sinusoids, etc., for which parameters can be calculatedanalytically and independently. These can be input to candidate software,and if this software passes the acceptance test for many different type F1software measurement standards it can be considered as type F2 software.167168C H A P T ER 6 : Surface topography measurement instrumentationSoftware measurement standards are available from some NMI web sites;see for example [136–138].
The user can either download type F1 standardsor upload data files for type F2 analyses.6.14 References[1] Leach R K 2001 The measurement of surface texture using stylus instruments NPL Good practice guide No. 37 (National Physical Laboratory)[2] Leach R K, Blunt L A, Brown L, Blunt R, Conroy M, Mauger D 2008 Guideto the measurement of smooth surface topography using coherence scanning interferometry NPL Good practice guide No. 108 (National PhysicalLaboratory)[3] Griffiths B 2001 Manufacturing surface technology (Penton Press: London)[4] Gilmozzi R, Spyromilio J 2007 The European Extremely Large Telescope(E-ELT) ESO Messenger 127 11–19[5] Shore P 2008 Ultra precision surfaces Proc.
ASPE, Portland, Oregon, USA,Oct. 75–78[6] Malacara D 2007 Optical shop testing (Wiley Series in Pure and AppliedOptics) 3rd edition[7] Whitehouse D J 2002 Handbook of surface and nanometrology (Taylor &Francis)[8] Mainsah E, Greenwood J A, Chetwynd D G Metrology and properties ofengineering surfaces (Kluwer Academic Publishers: Boston)[9] Smith G T Industrial metrology: surfaces and roundness (Springer-Verlag:London)[10] Blunt L A, Jiang X 2003 Advanced techniques for assessment surfacetopography (Butterworth-Heinemann: London)[11] Church E L 1979 The measurement of surface texture and topographyusing dynamic light scattering Wear 57 93–105[12] Stedman M 1987 Mapping the performance of surface-measuring instruments Proc.
SPIE 83 138–142[13] Stedman M 1987 Basis for comparing the performance of surfacemeasuring machines Precision Engineering 9 149–152[14] Jones C W, Leach R K 2008 Adding a dynamic aspect to amplitudewavelength space Meas. Sci. Technol. 19 055105[15] Shaw H 1936 Recent developments in the measurement and control ofsurface roughness J.
Inst. Prod. Engnrs. 15 369–391[16] Harrison R E W 1931 A survey of surface quality standards and tolerancecosts based on 1929–1930 precision-grinding practice Trans. ASME paperno. MSP-53-12[17] Hume K J 1980 A history of engineering metrology (Mechanical Engineering Publications Ltd)References[18] Reason R E, Hopkins M R, Garrod R I 1944 Report on the measurement ofsurface finish by stylus methods (Taylor, Taylor & Hobson: Leicester)[19] Schmaltz G 1929 Über Glätte und Ebenheit als physikalisches undphysiologisches Problem Zeitschrift des Vereines deutcher Ingenieure 731461[20] Abbott E J, Firestone F A 1933 Specifying surface quality MechanicalEngineering 55 569–773[21] Reason R E 1973 Stylus methods of surface measurement Bull. Inst. Phys.Oct.
587–589[22] ISO 4287: 2000 Geometrical product specification (GPS) - Surface texture:Profile method - Terms, definitions and surface texture parameters (International Organization of Standardization)[23] Evans C, Bryan J 1999 ‘‘Structured,’’ ‘‘textured,’’ or ‘‘engineered’’ surfacesAnn. CIRP 48 451–456[24] Bruzzone A A G, Costa H L, Lonardo P M, Lucca D A 2008 Advances inengineering surfaces for functional performance Ann. CIRP 57 750–769[25] ISO/FDIS 25178 part 6: Geometrical product specification (GPS) - Surfacetexture: Areal - Classification of methods for measuring surface texture(International Organization of Standardization)[26] ISO 3274: 1996 Geometrical product specification (GPS) - Surface texture:Profile method - Nominal characteristics of contact (stylus) instruments(International Organization of Standardization)[27] ISO/FDIS 25178 part 601: Geometrical product specification (GPS) Surface texture: Areal - Nominal characteristics of contact (stylus) instruments (International Organization of Standardization)[28] McCool J I 1984 Assessing the effect of stylus tip radius and flight onsurface topography measurements Trans.
ASME 106 202–209[29] DeVries W R, Li C -J 1985 Algorithms to deconvolve stylus geometry fromsurface profile measurements J. Eng. Ind. 107 167–174[30] O’Donnell K A 1993 Effects of finite stylus width in surface contact profilometry Appl. Opt. 32 4922–4928[31] Howard L P, Smith S T 1994 A metrological constant force stylus profilerRev. Sci. Instrum 65 892–902[32] Chetwynd D G, Liu X, Smith S T 1996 A controlled-force stylusdisplacement probe Precision Engineering 19 105–111[33] Leach R K, Flack D R, Hughes E B, Jones C W 2008 Development ofa new traceable areal surface texture measuring instrument Wear 266552–554[34] Garratt J, Mills M 1996 Measurement of the roughness of supersmoothsurfaces using a stylus instrument Nanotechnology 7 13–20[35] Leach R K 2000 Traceable measurement of surface texture at theNational Physical Laboratory using NanoSurf IV Meas.
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