- Email: [email protected]
The development of user-friendly software measurement standards for surface topography software assessment
Available online at www.sciencedirect.com
Wear 264 (2008) 389–393
The development of user-friendly software measurement standards for surface topography software assessment Liam Blunt a,∗ , Xiang Jiang a , Richard Leach b , Peter Harris b , Paul Scott c a
School of Computing and Engineering, University of Huddersfield, Queensgate, Huddersfield HD1 3DH, UK b National Physical Laboratory, Hampton Road, Teddington, Middlesex TW11 0LW, UK c Taylor Hobson Ltd., PO Box 36, 2 New Star Road, Leicester LE4 9JQ, UK Accepted 28 August 2006 Available online 27 February 2007
Abstract The development of user-friendly reference data sets (softgauges) and reference software algorithms for validating the software aspects of surface profile measuring instruments is described. A framework for the software measurement standards, and the form of the reference data (Type F1 softgauges) and reference software (Type F2) that were developed is discussed. This work was carried out as part of the UK National Measurement System Length Programme (2002–2005) and involved collaboration between University of Huddersfield, Taylor Hobson Ltd. and the National Physical Laboratory. © 2007 Elsevier B.V. All rights reserved. Keywords: Surface profile; Surface texture; Softgauges; Software validation; Software measurement standard
1. Introduction As in many areas of metrology, instruments that measure surface texture generally interface to a computer that collects, filters and analyses the measurement data. As part of this analysis, parameters are calculated that allow surfaces to be described quantitatively in order to gain information concerning a manufacturing process or to draw some inference on the functionality of a surface. There is a wealth of calibration artefacts that are used to calibrate surface measuring instruments but such artefacts do not allow specific validation or verification of the numerical correctness of the software that is used to filter and analyse the data. ISO 5436-2 [1] specifies two Type F software measurement standards for verification purposes: Type F1 (reference data sets) and Type F2 (reference software). Recently the National Institute of Standards and Technology (NIST) in the USA have reported on the development of a beta version of a “Surface Metrology Algorithm Testing System” [2] and the Physikalisch-Technische Bundesanstalt (PTB) ∗
Corresponding author. E-mail addresses: [email protected] (L. Blunt), [email protected] (X. Jiang), [email protected] (R. Leach), [email protected] (P. Harris), [email protected] (P. Scott). 0043-1648/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.wear.2006.08.044
in Germany has developed reference software for roughness analysis [3]. Both of these developments include Type F1 and Type F2 software measurement standards, but they were developed using a different methodology to those reported here. The UK Softgauges project focused on providing mathematically well-defined and unambiguous specifications of surface profile parameters, together with comprehensive Type F1 and Type F2 software measurement standards to support the implementation of these specifications. The National Physical Laboratory (NPL) web site will be used as the primary delivery mechanism for the reference data sets and reference software. 2. Consultation exercise Prior to the software development phase of the Softgauges project, and in order to guide its development and implementation, an industrial consultation exercise was undertaken between August 2003 and January 2004. Industry was consulted and asked to describe current practice in terms of surface metrology and, in particular, to list the parameters that were considered to be the most important. Information on participant’s current awareness of software measurement standards was also requested. The majority of the respondents were from the automotive sector, followed by metrology instrument manufacturers and educational
390
L. Blunt et al. / Wear 264 (2008) 389–393
Fig. 1. Most critical processes requiring surface metrology.
Fig. 3. Percentage use of roughness parameters (note total could exceed 100% as respondents may use more than one parameter).
3. Software measurement standards basic framework institutes. The respondents represented a good coverage across a number of industrial sectors including aerospace, bioengineering, sheet product and more general precision engineering. A full description of the consultation exercise (and more information regarding the development of the software measurement standards) is given elsewhere [4]. In summarising the results it was clear that precision finishing of metal was highlighted as the main manufacturing process for the majority of the respondents, with grinding and lapping/polishing of steels appearing to be the most critical in terms of the need for surface metrology, see Fig. 1 and Ref. [4]. Fig. 2 summaries how the respondents approach the use of specification standards. For two-dimensional surface metrology, contacting stylus instruments remain the key tool. The majority of the respondents were already using specification standards, particularly ISO 4287 [5]. A significant number of instrument users that responded, however, employ no specification standards and have no knowledge of the standards to which their companies work. Most respondents were aware of the possibility of software giving incorrect results. A wide variety of surface texture parameters were reported as being used with the most frequent being Ra , Rsk , Rv , Rp , Rz , Rt and RSm , see Fig. 3. The critical functional properties identified by the respondents were wear properties and lubricant retention.
The software measurement standards basic framework consists of three parts as shown in Fig. 4. The first part is the general conditions for reference data sets, including the Ls filtering, uniform sampling conditions and form removal. The second provides the filtration definitions for obtaining the different components. The third part specifies the definitions and methods of calculation of the surface texture parameters (field and feature parameters). 4. Unambiguous specifications All the parameter definitions outlined in the relevant ISO standards were investigated and ambiguities in the definitions were addressed. An example of an unambiguous specification, for the definition and implementation of the Rp parameter, is shown in Fig. 5. Specifications for the complete set of parameters considered will be available via the NPL web site and are used within the reference algorithms. 5. Reference data sets The reference data sets that were developed are divided into three types (see Table 1): • Mathematically defined profiles: numerically generated sine wave profiles, isosceles triangular profiles, square waves, random profiles, steps and impulses. • Simulated manufacturing profiles: providing numerically modelled turning, milling and ground surfaces. Table 1 Types of F1 softgauges available within the software measurement standards
Fig. 2. Percentage of respondents using roughness specification standards (note total could exceed 100% as some respondents use more than one standard). Also, note that “NAMAS lab 0026” refers to an in-house document.
Type of profile
Number of profiles available
Mathematically generated profiles sine, saw, noise, pulse and step Simulated manufacturing ground, milled, distribution based Masterpiece measurements milled, EDM, ground, honed lapped, polished
18 8 15
L. Blunt et al. / Wear 264 (2008) 389–393
Fig. 4. Software measurement standards framework.
Fig. 5. An example of the specification of the feature parameter Rp .
391
392
L. Blunt et al. / Wear 264 (2008) 389–393
6. Reference software
Fig. 6. Procedure for comparing software.
• Masterpiece measurements: including typical manufacturing processes such as EDM, ground and honed surfaces.
To test the numerical correctness of software, a common data set is input into both the software under test and the reference software. The results delivered by the software under test and those obtained from the reference software are compared, see Fig. 6. The algorithms implemented in the reference software have been designed according to the set of unambiguous specifications as indicated above. A key task in the evaluation of the parameters is to produce a continuous representation of the underlying profile. A natural cubic spline that interpolates the discrete measured data values has been used for this purpose [6]. The algorithms are intended to deliver mathematically correct values of the parameters for this natural cubic spline. The reference software is implemented in the Java programming language, which ensures that it is portable across operating systems. The reference software does not provide the uncertainties associated with the calculated reference values for the surface texture parameters. 7. Software measurement standards system
The reference data sets with numerically correct results for their accompanying profile parameters will be available for download via the NPL web site. Users can then use these reference data sets to validate filter implementations or calculations of surface texture parameters.
Fig. 7 illustrates the facilities that will eventually be made available via the NPL web site. These include documentation giving mathematically well defined and unambiguous specifications of the computations addressed, reference data sets with
Fig. 7. Software measurement standards’ system for surface profile metrology.
L. Blunt et al. / Wear 264 (2008) 389–393
393
corresponding reference results, reference software and a facility for converting between common data formats used by industry.
2002–2005. Thanks are due to Graeme Parkin (NPL) for help in developing the Type F2 software measurement standards.
8. Conclusions
References
The Softgauges project has delivered a full range of reference data sets and cross-platform reference software implementing unambiguous specifications of surface texture parameters. The outputs of the project provide a credible way to test the numerical correctness of surface profile software for industry, academia and measurement institutes. The software measurement standards are now under validation and will eventually be hosted on the NPL web site. Further work will include a comparison with NIST and PTB software measurement standards.
[1] ISO 5436: Part 2: 2002 Geometrical product specification (GPS) – Surface texture: profile method – Measurement standards – Software measurement standards, International Organization for Standarization. [2] S.H. Bui, T.B. Reneger, T.V. Vorburger, Virtual surface calibration database, in: Proceedings of the International Colloquium on Surfaces, Chemnitz, Germany, February, 2004. [3] L. Jung, B. Stranger, R. Kr¨uger-Sehm, L. Koenders, M. Krystek, Reference software for roughness analysis—features and results, in: Proceedings of the International Colloquium on Surfaces, Chemnitz, Germany, February, 2004. [4] Final Report: Development and dissemination of softgauges for surface topography NMS Project Ref. No: 4.4, Programme for Length Metrology, 2005. [5] ISO 4287: 1997 Geometrical product specification (GPS) – Surface texture: profile method – Terms, definitions and surface texture parameters, International Organization for Standarization. [6] J.K. Brennan, A. Crampton, X. Jiang, R. Leach, P. Harris, Reconstruction of continuous surface profiles from discretely sampled data, in: Proceedings of the 5th Euspen International Conference, Montpellier, France, May, 2005.
Acknowledgements The authors would like to acknowledge the financial support given by the UK Department of Trade and Industry through the National Measurement System Programme for Length
Wear 264 (2008) 389–393
The development of user-friendly software measurement standards for surface topography software assessment Liam Blunt a,∗ , Xiang Jiang a , Richard Leach b , Peter Harris b , Paul Scott c a
School of Computing and Engineering, University of Huddersfield, Queensgate, Huddersfield HD1 3DH, UK b National Physical Laboratory, Hampton Road, Teddington, Middlesex TW11 0LW, UK c Taylor Hobson Ltd., PO Box 36, 2 New Star Road, Leicester LE4 9JQ, UK Accepted 28 August 2006 Available online 27 February 2007
Abstract The development of user-friendly reference data sets (softgauges) and reference software algorithms for validating the software aspects of surface profile measuring instruments is described. A framework for the software measurement standards, and the form of the reference data (Type F1 softgauges) and reference software (Type F2) that were developed is discussed. This work was carried out as part of the UK National Measurement System Length Programme (2002–2005) and involved collaboration between University of Huddersfield, Taylor Hobson Ltd. and the National Physical Laboratory. © 2007 Elsevier B.V. All rights reserved. Keywords: Surface profile; Surface texture; Softgauges; Software validation; Software measurement standard
1. Introduction As in many areas of metrology, instruments that measure surface texture generally interface to a computer that collects, filters and analyses the measurement data. As part of this analysis, parameters are calculated that allow surfaces to be described quantitatively in order to gain information concerning a manufacturing process or to draw some inference on the functionality of a surface. There is a wealth of calibration artefacts that are used to calibrate surface measuring instruments but such artefacts do not allow specific validation or verification of the numerical correctness of the software that is used to filter and analyse the data. ISO 5436-2 [1] specifies two Type F software measurement standards for verification purposes: Type F1 (reference data sets) and Type F2 (reference software). Recently the National Institute of Standards and Technology (NIST) in the USA have reported on the development of a beta version of a “Surface Metrology Algorithm Testing System” [2] and the Physikalisch-Technische Bundesanstalt (PTB) ∗
Corresponding author. E-mail addresses: [email protected] (L. Blunt), [email protected] (X. Jiang), [email protected] (R. Leach), [email protected] (P. Harris), [email protected] (P. Scott). 0043-1648/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.wear.2006.08.044
in Germany has developed reference software for roughness analysis [3]. Both of these developments include Type F1 and Type F2 software measurement standards, but they were developed using a different methodology to those reported here. The UK Softgauges project focused on providing mathematically well-defined and unambiguous specifications of surface profile parameters, together with comprehensive Type F1 and Type F2 software measurement standards to support the implementation of these specifications. The National Physical Laboratory (NPL) web site will be used as the primary delivery mechanism for the reference data sets and reference software. 2. Consultation exercise Prior to the software development phase of the Softgauges project, and in order to guide its development and implementation, an industrial consultation exercise was undertaken between August 2003 and January 2004. Industry was consulted and asked to describe current practice in terms of surface metrology and, in particular, to list the parameters that were considered to be the most important. Information on participant’s current awareness of software measurement standards was also requested. The majority of the respondents were from the automotive sector, followed by metrology instrument manufacturers and educational
390
L. Blunt et al. / Wear 264 (2008) 389–393
Fig. 1. Most critical processes requiring surface metrology.
Fig. 3. Percentage use of roughness parameters (note total could exceed 100% as respondents may use more than one parameter).
3. Software measurement standards basic framework institutes. The respondents represented a good coverage across a number of industrial sectors including aerospace, bioengineering, sheet product and more general precision engineering. A full description of the consultation exercise (and more information regarding the development of the software measurement standards) is given elsewhere [4]. In summarising the results it was clear that precision finishing of metal was highlighted as the main manufacturing process for the majority of the respondents, with grinding and lapping/polishing of steels appearing to be the most critical in terms of the need for surface metrology, see Fig. 1 and Ref. [4]. Fig. 2 summaries how the respondents approach the use of specification standards. For two-dimensional surface metrology, contacting stylus instruments remain the key tool. The majority of the respondents were already using specification standards, particularly ISO 4287 [5]. A significant number of instrument users that responded, however, employ no specification standards and have no knowledge of the standards to which their companies work. Most respondents were aware of the possibility of software giving incorrect results. A wide variety of surface texture parameters were reported as being used with the most frequent being Ra , Rsk , Rv , Rp , Rz , Rt and RSm , see Fig. 3. The critical functional properties identified by the respondents were wear properties and lubricant retention.
The software measurement standards basic framework consists of three parts as shown in Fig. 4. The first part is the general conditions for reference data sets, including the Ls filtering, uniform sampling conditions and form removal. The second provides the filtration definitions for obtaining the different components. The third part specifies the definitions and methods of calculation of the surface texture parameters (field and feature parameters). 4. Unambiguous specifications All the parameter definitions outlined in the relevant ISO standards were investigated and ambiguities in the definitions were addressed. An example of an unambiguous specification, for the definition and implementation of the Rp parameter, is shown in Fig. 5. Specifications for the complete set of parameters considered will be available via the NPL web site and are used within the reference algorithms. 5. Reference data sets The reference data sets that were developed are divided into three types (see Table 1): • Mathematically defined profiles: numerically generated sine wave profiles, isosceles triangular profiles, square waves, random profiles, steps and impulses. • Simulated manufacturing profiles: providing numerically modelled turning, milling and ground surfaces. Table 1 Types of F1 softgauges available within the software measurement standards
Fig. 2. Percentage of respondents using roughness specification standards (note total could exceed 100% as some respondents use more than one standard). Also, note that “NAMAS lab 0026” refers to an in-house document.
Type of profile
Number of profiles available
Mathematically generated profiles sine, saw, noise, pulse and step Simulated manufacturing ground, milled, distribution based Masterpiece measurements milled, EDM, ground, honed lapped, polished
18 8 15
L. Blunt et al. / Wear 264 (2008) 389–393
Fig. 4. Software measurement standards framework.
Fig. 5. An example of the specification of the feature parameter Rp .
391
392
L. Blunt et al. / Wear 264 (2008) 389–393
6. Reference software
Fig. 6. Procedure for comparing software.
• Masterpiece measurements: including typical manufacturing processes such as EDM, ground and honed surfaces.
To test the numerical correctness of software, a common data set is input into both the software under test and the reference software. The results delivered by the software under test and those obtained from the reference software are compared, see Fig. 6. The algorithms implemented in the reference software have been designed according to the set of unambiguous specifications as indicated above. A key task in the evaluation of the parameters is to produce a continuous representation of the underlying profile. A natural cubic spline that interpolates the discrete measured data values has been used for this purpose [6]. The algorithms are intended to deliver mathematically correct values of the parameters for this natural cubic spline. The reference software is implemented in the Java programming language, which ensures that it is portable across operating systems. The reference software does not provide the uncertainties associated with the calculated reference values for the surface texture parameters. 7. Software measurement standards system
The reference data sets with numerically correct results for their accompanying profile parameters will be available for download via the NPL web site. Users can then use these reference data sets to validate filter implementations or calculations of surface texture parameters.
Fig. 7 illustrates the facilities that will eventually be made available via the NPL web site. These include documentation giving mathematically well defined and unambiguous specifications of the computations addressed, reference data sets with
Fig. 7. Software measurement standards’ system for surface profile metrology.
L. Blunt et al. / Wear 264 (2008) 389–393
393
corresponding reference results, reference software and a facility for converting between common data formats used by industry.
2002–2005. Thanks are due to Graeme Parkin (NPL) for help in developing the Type F2 software measurement standards.
8. Conclusions
References
The Softgauges project has delivered a full range of reference data sets and cross-platform reference software implementing unambiguous specifications of surface texture parameters. The outputs of the project provide a credible way to test the numerical correctness of surface profile software for industry, academia and measurement institutes. The software measurement standards are now under validation and will eventually be hosted on the NPL web site. Further work will include a comparison with NIST and PTB software measurement standards.
[1] ISO 5436: Part 2: 2002 Geometrical product specification (GPS) – Surface texture: profile method – Measurement standards – Software measurement standards, International Organization for Standarization. [2] S.H. Bui, T.B. Reneger, T.V. Vorburger, Virtual surface calibration database, in: Proceedings of the International Colloquium on Surfaces, Chemnitz, Germany, February, 2004. [3] L. Jung, B. Stranger, R. Kr¨uger-Sehm, L. Koenders, M. Krystek, Reference software for roughness analysis—features and results, in: Proceedings of the International Colloquium on Surfaces, Chemnitz, Germany, February, 2004. [4] Final Report: Development and dissemination of softgauges for surface topography NMS Project Ref. No: 4.4, Programme for Length Metrology, 2005. [5] ISO 4287: 1997 Geometrical product specification (GPS) – Surface texture: profile method – Terms, definitions and surface texture parameters, International Organization for Standarization. [6] J.K. Brennan, A. Crampton, X. Jiang, R. Leach, P. Harris, Reconstruction of continuous surface profiles from discretely sampled data, in: Proceedings of the 5th Euspen International Conference, Montpellier, France, May, 2005.
Acknowledgements The authors would like to acknowledge the financial support given by the UK Department of Trade and Industry through the National Measurement System Programme for Length