InsPulp-I# : An on-line visual inspection system for the pulp industry Pascual Campoy a, * , Javier Canaval b,1 , Daniel Pen ˜a c,2 a Universidad Politecnica Madrid, Jose ´ Gutierrez Abascal 2, 28006 Madrid, Spain b Research and Technology Center of ENCE Group, Ctra. Campan ˜o ´, Ribero-Vao, 36157 Pontevedra, Spain c Innovacio ´n Inspeccio ´n Industrial Imagenes S.L., spin-off U.P.M., Centro de Empresas LA ARBOLEDA, Local 51, Campus Sur UPM., Ctra. Valencia Km. 7, 3, 28031 Madrid, Spain Received 1 December 2004; received in revised form 31 March 2005; accepted 31 May 2005 Available online 12 October 2005 Abstract This paper presents a Machine Vision System developed for on-line visual pulp inspection under the critical lighting requirements of the UNE-ISO 5350-2 standard. These requirements typically result in a very low dynamic range in the electronic images due to the following: high-speed displacement of the product (up to 2.7 m/s), very high resolution (0.004 mm 2 /pixel), and the backlight requirement. This problem has been solved using TDI technology in the acquisition system, made up of several parallel CCD lines that shift their electrical charges in synchronization with the product movement, therefore producing a single line-image with several times more dynamic range. The obtained image has a cross light non-uniformity that is resolved by an image processing algorithm that divides the image into several sub-images that are processed in parallel. The system has been tested in on-line production plants, and has been proven to provide a great improvement over the objectivity and sampling rate limitations of human inspection, thereby realizing a more reliable and trustworthy quality control measurement. # 2005 Elsevier B.V. All rights reserved. Keywords: Automated visual inspection; On-line image processing; Web defect detection; Time delay integration technology 1. Introduction In the pulp industry is important to determine the cleanliness of the final product by counting number and the size of the impurities. After a final drying process, the pulp comes out continuously as a web product several meters wide and few mm. thick, which is cut into sheets, piled up in bales and sold in units made up of several bales. Depending on the raw material and on the overall chemical and mechanical process, the final product can have different degrees of cleanliness that highly influence the quality of the product and can therefore be sold for different applications and clients at different prices. www.elsevier.com/locate/compind Computers in Industry 56 (2005) 935–942 * Corresponding author. Tel.: +34 91336 3061; fax: +34 91336 3010. E-mail addresses: campoy@etsii.upm.es (P. Campoy), jcanaval@ence.es (J. Canaval), danipena@tiscali.es (D. Pen ˜a). 1 Tel.: +34 98687 2303; fax: +34 98687 3364. 2 Tel.: +34 65488 5112. 0166-3615/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.compind.2005.05.018