University of Oulu

Paakkari, Jussi (1998) On-line flatness measurement of large steel plates using moiré topography. VTT Publications 350. URI:

On-line flatness measurement of large steel plates using moiré topography

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Author: Paakkari, Jussi
Format: ebook
Version: published version
Language: English
Published: Espoo : VTT Technical Research Centre of Finland, 1998
Publish Date: 2005-05-20
Thesis type: Doctoral Dissertation
Defence Note: Dissertation for the degree of Doctor of Technology to be presented, with the permission of the Department of Electrical Engineering of the University of Oulu, for public discussion in Auditorium L10, Linnanmaa, on June 5th, 1998, at 12 noon.


The quality demands for steel plate and strip products are increasing, and flatness and dimensional measurements performed on these products must fulfill quality standards, and above all the needs of the clients. Many quality assurance methods exist with regard to flatness and dimensional measurements in the steel industry. Manual gauging methods are often still used, but they are costly in terms of time and labour. Automated non- contact optical measurement systems are becoming more common due to their benefits over traditional methods.

In this thesis a projection moiré topography is applied for automatic measurement of the flatness of large steel plates and a fully automated system applicable to varying surface properties of large steel plates is implemented in a hostile industrial environment. The specifications, design and performance of the system are presented. The measurement area of the system is 3.5 metres x 1.0 metre (width x length), and it achieves a specified depth resolution of 0.3 mm. The system operates in real time on the production line at a speed of 1 m/s.

Experiences gained with the system and the different requirements applying to another measurement site then led to the invention of a novel multipurpose flatness measurement system, the design, laboratory prototype and performance of which are also described in this thesis. The usability and competitiveness of the novel system have been increased by adding 2D dimensional measurements such as edges, widths, lengths etc., and even surface quality inspection, to the same unit. The depth resolution of the laboratory system is better than 0.6 mm.

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Series: VTT Publications
ISSN: 1235-0621
ISSN-E: 1455-0849
ISSN-L: 1235-0621
ISBN: 951-38-5238-5
ISBN Print: 951-38-5237-7
Issue: 350