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Online optical method for real-time surface measurement using line-of-light triangulation
Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Real time paper surface-web measurement is one of the challenging research fields. The traditional laboratory method has many limitations and is unable to measure the entire tambour during the manufacturing process. It has been necessary to develop an online technique that could measure the surface topography in real time. An optical technique was developed, based on laser triangulation, and is applied to develop a new prototype device, which characterizes high speed paper-web surfaces over a wide scale of spatial wavelengths spectrum and computes the surface roughness in real time. The used multi channel pulsed laser diode, source of illumination onto the paper-web, is of benefit due to its low coherence length and is capable to deliver a powerful burst of light beam over a 1 µs duration, which delivers energy of 100 µJ per pulse. The short exposure time avoids blurriness in the acquired images which could possible due to the high speed and vibrations on the paper-web.

The laser beam is shaped into a narrow line-of-light using cylindrical lenses and is projected onto a paper-web surface, which covers a physical length of about 210 mm. The created line-of-light cross section full width at half maximum, FWHM Gaussian distribution, is 2-3 pixels on the image. The line-of-light is projected onto the paper-web perpendicular to the plane of the surface. The low angled, low specular, reduced coherence length, scattered reflected laser line is captured by the 3 CCD sensors, which are synchronized with the laser source. The low specular light ensures to avoid saturation of the imaging sensors if the surface is very smooth, and obliquely captures the z-directional fine feature of the surface.

The scattered phenomenon of the reflected light is responsible for the surface irregularity measurements. The basic image processing algorithm is applied in order to remove noise and cropped the images widthwise so that only pixels above a preset threshold gray level can be processed, which enables efficient real time measurement. The image is transformed into a 1D array using the center of gravity, COG. The accuracy and precision of the COG depends on the line-of-light FWHM, which, in turn, is responsible for the accuracy, noise and the resolution of the developed technique. The image subpixel resolution achieved is 0.01 times a pixel and uuncertainty in the raw data is 0.43 µm while it is 0.05 µm in the rms roughness.

The signal processing steps combining the B-Spline filter and the filter in the spatial frequency domain were employed in order to separate roughness, waviness, and form and position error in the raw profile. The prototype is designed to measure online surface roughness and to characterize surface in a spatial wavelength spectrum from 0.09 to 30 mm, which is extendable to any required spatial range in order to cover a wide scale surface feature such as micro roughness, macro roughness and waviness. It is proven that exploitation of a simple laser triangulation technique could lead to an improvement in the overall quality and efficiency in the paper and paperboard industries and it can also be of potential interest for the other surface characterization problems.

Place, publisher, year, edition, pages
Sweden Sundsvall: Mid Sweden University , 2013. , 151 p.
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 171
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:miun:diva-20449Local ID: STCISBN: 978-91-87557-17-0 (print)OAI: oai:DiVA.org:miun-20449DiVA: diva2:675731
Public defence
2013-12-16, L111, Mittuniversitetet, Sundsvall, 13:15 (English)
Supervisors
Available from: 2013-12-06 Created: 2013-12-04 Last updated: 2016-10-19Bibliographically approved
List of papers
1. Investigation of the surface topographical differences between the Cross Direction and the Machine Direction for newspaper and paperboard
Open this publication in new window or tab >>Investigation of the surface topographical differences between the Cross Direction and the Machine Direction for newspaper and paperboard
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2011 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 26, no 4, 468-475 p.Article in journal (Refereed) Published
Abstract [en]

Paper and paperboard surface quality is constantly being improved by the industry. This improvement work deals with the essential fact that the surface topography must be measured, both in relation to offline and online measurements for the manufactured products. Most measurements relating to surface topography (especially online) are performed either in the machine direction (MD) or in the cross direction (CD). It has been the opinion of SCA Ortviken AB and Iggesund Paperboard AB that the surface topography amplitudes are almost always higher in the CD than in the MD, for their products which consist of newspaper and paperboard. This article aims to investigate the rela-tionship between the CD and the MD surface topography amplitudes for a wide range of spatial wavelength for both newspaper and paperboard. The tests and investiga-tions have been conducted using an FRT Microprof profilometer within the range 20 μm up to 8 mm, and the results confirm that the surface topography amplitudes are higher in the CD for most of the shorter spatial wavelength within this range. The results also show significant differences between measurements for different paper qualities, suggesting a requirement to investigate the relationship between the CD and the MD topography for all paper and paperboard qualities of interest for a paper or paperboard mill, before a decision is made in relation to a measurement method.

Keyword
Paper surface measurement, Roughness measurement, Surface topography, Optical measurement, spectral analysis, Cross Direction (CD), Machine Direction (MD), Paperboard, Newspaper
National Category
Embedded Systems
Identifiers
urn:nbn:se:miun:diva-15060 (URN)000298868000014 ()2-s2.0-84855528544 (Scopus ID)STC (Local ID)STC (Archive number)STC (OAI)
Available from: 2011-12-11 Created: 2011-12-06 Last updated: 2016-10-17Bibliographically approved
2. Online surface roughness characterization of paper and paperboard using a line of light triangulation technique
Open this publication in new window or tab >>Online surface roughness characterization of paper and paperboard using a line of light triangulation technique
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2012 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, no 3, 662-670 p.Article in journal (Refereed) [Artistic work] Published
Abstract [en]

Within both the paper and paperboard industries, real time monitoring and measurement of surface roughness of a paper moving at high velocities is an important and challenging area of research. The uniform surface, for an entire production, can be effectively achieved by monitoring and controlling the paper surface roughness, in real time during the manufacturing steps. Presently the majority of paper industries rely on traditional laboratory profilometers. The obvious limitations of lab profilometers are that these are slow, do not measure the quality of entire reels but rather deal with only a few small pieces of samples taken from the end of the reels and it is difficult to make any possible correction in the productionlines without knowing the online roughness data. To eradicate the disadvantages associated with conventional measurements, an online prototype instrument has been developed that measures the surface roughness during the manufacturing steps, and is based on a line of lighttriangulation technique. The prototype technique will be of assistance in ensuring tight process control in order to maintain both a better and auniform quality throughout the entire production. It measures the whole reel, meter by meter, in traditional units of roughness and is also capable of characterizing the topography in a wide range of wavelength spectra. The article presents the online analyses results obtained from the developed prototype. The real time measurements, in a paperboard pilot mill, have successfully characterized and distinguished 16 different grades of newspaper and paperboard reels including reels which have the same family of quality grades and materials.

Keyword
Laser application; Line of light triangulation; Newspaper; Online surface measurement; OnTop; Optical measurement; Paper; Paper roughness; Paper smoothness; Paperboard
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-15969 (URN)10.3183/NPPRJ-2012-27-03-p662-670 (DOI)000311020100018 ()2-s2.0-84862525400 (Scopus ID)STC (Local ID)STC (Archive number)STC (OAI)
Available from: 2012-02-29 Created: 2012-02-29 Last updated: 2016-10-20Bibliographically approved
3. Online surface characterization of paper and paperboards in a wide-range of the spatial wavelength spectrum
Open this publication in new window or tab >>Online surface characterization of paper and paperboards in a wide-range of the spatial wavelength spectrum
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2012 (English)In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 258, no 20, 7928-7935 p.Article in journal (Refereed) Published
Abstract [en]

In the paper industry, surface topography is the essence of both paper and paperboard, and accurate topographical measurements are equally essential in order to achieve a uniform smooth surface. The traditional laboratory methods measure only a few samples from the entire tambour and there are other obvious limitations to this approach. Online measurements may be of significant value to improve the surface quality throughout the production. Roughness is one of the topography components and the majority of techniques measure paper by means of a single predictor of average roughness, R a which is inadequate in providing a comprehensive characterization of the surface. Measurements, in a wide range ofwavelengths, can characterize topography components such as roughness, waviness, cockling, etc. Online measurements were taken for various grades of 8 paper reels, containing the wireside and topsides for newspaper, and uncoated and coated sides of paperboards. Their surfacecharacterization, in the spatial wavelength spectrum, from 0.1 to 10 mm was obtained. This article presents the online characterizationresults which have efficiently distinguished the surfaces of same family materials including the edge and the middle position reels of fine coatedpaperboard. Online measurements were taken, at Iggesund Paperboard Pilot Coater in Sweden, by using a recently developed OnlineTopography (OnTop) device which is based on the principle of light triangulation. © 2012 Elsevier B.V. All rights reserved.

Keyword
Newspaper; Online paper measurements; Online topography; Paper spectral topography; Paperboard; Surface characterization
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-15970 (URN)10.1016/j.apsusc.2012.04.136 (DOI)000305940700022 ()2-s2.0-84862524529 (Scopus ID)STC (Local ID)STC (Archive number)STC (OAI)
Available from: 2012-02-29 Created: 2012-02-29 Last updated: 2016-10-20Bibliographically approved
4. Real time surface measurement technique in a wide range of wavelengths spectrum
Open this publication in new window or tab >>Real time surface measurement technique in a wide range of wavelengths spectrum
2014 (English)In: IEEE Sensors Journal, ISSN 1530-437X, E-ISSN 1558-1748, Vol. 14, no 1, 285-294 p.Article in journal (Refereed) Published
Abstract [en]

Real time surface topography measurement in the paper and paperboard industries is a challenging research field. The existing online techniques measure only a small area of paper surface and estimate topographical irregularities in a narrow scale as a single predictor. Considering the limitations and complications in measuring the surface at high speed, a laser line triangulation technique is explored to measure surface topography in a wide scale. The developed technique is new for the paper and paperboard application that scans a line onto the paper-web surface up to 210 mm in length in the cross machine direction. The combination of a narrow laser linewidth imaging, a subpixel resolution, and the selection of a unique measurement location has made it possible to measure roughness and simultaneously characterize paper surface topography from 0.1 to 30 mm spatial wavelength. This spatial range covers wide scale surface properties such as roughness, cockling, and waviness. The technique clearly distinguishes and characterizes the surface of newspaper, and lightweight coated, coated, and uncoated paperboard in real time during the paper manufacturing process. The system temporal noise for the average roughness is estimated as 37 dB. The signal to noise ratio found is from 5.4 to 8.1 in the short spatial wavelength up to 1 mm, whereas it is more than 75 in the long spatial wavelength from 5 to 10 mm.

Keyword
Laser line triangulation; Narrow laser linewidth imaging; Optical online surface topography, Paper and paperboard topography, Surface measurements techniques
National Category
Engineering and Technology
Identifiers
urn:nbn:se:miun:diva-20447 (URN)10.1109/JSEN.2013.2281913 (DOI)000327248100009 ()2-s2.0-84888147725 (Scopus ID)STC (Local ID)STC (Archive number)STC (OAI)
Available from: 2013-12-04 Created: 2013-12-04 Last updated: 2017-03-06Bibliographically approved
5. Limitation of a line-of-light online paper surface measurement system
Open this publication in new window or tab >>Limitation of a line-of-light online paper surface measurement system
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2014 (English)In: IEEE Sensors Journal, ISSN 1530-437X, E-ISSN 1558-1748, Vol. 14, no 8, 2715-2724 p.Article in journal (Refereed) [Artistic work] Published
Abstract [en]

A new prototype device has been developed based on a laser triangulation principle to measure online surface topography in the paper and paperboard industries. It characterizes the surface in a wide spatial scale of topography from 0.09-10 mm. The prototype's technique projects a narrow line-of-light perpendicularly onto the moving paper-Web surface and scattered reflected light is collected at a low angle, low specular, and reduced coherent length onto the CCD sensors synchronized with the laser sources. The scattering phenomenon determines surface deviations in the z-direction. The full-width, at half-maximum of a laser line in cross section is sensitive in computation of the surface topography. The signal processing aspect of the image processing, for example, threshold and filtering algorithms are also sensitive in estimating the accurate surface features. Moreover, improper light illumination, intensity, reflection, occlusion, surface motion, and noise in the imaging sensor, and so forth, all contribute to deteriorate the measurements. Optical techniques measure the surface indirectly and, in general, an evaluation of the performance and the limitations of the technique are both essential and challenging. The paper describes the accuracy, uncertainty, and limitations of the developed technique in the raw profiles and in terms of the rms roughness. The achieved image subpixel resolution is 0.01 times a pixel. Statistically estimated uncertainty (2σ) in the laboratory environment was found 0.05 μm for a smooth sample, which provides a 95% confidence level in the rms roughness results. The depth of field of the prototype is ~2.4 mm.

Keyword
accuracy, calibration, Laser triangulation, limitation, online surface measurement, optical profiler, paper-web topography, uncertainty
National Category
Engineering and Technology
Identifiers
urn:nbn:se:miun:diva-20448 (URN)10.1109/JSEN.2014.2314753 (DOI)000340103500004 ()2-s2.0-84904362184 (Scopus ID)STC (Local ID)STC (Archive number)STC (OAI)
Note

Correction to this article published: 

IEEE SENSORS JOURNAL, 14 (10):3726-3726; 10.1109/JSEN.2014.2345891 OCT 2014 

Scopus: 2-s2.0-84961153977

Available from: 2013-12-04 Created: 2013-12-04 Last updated: 2017-07-04Bibliographically approved

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