Norske Skog (Lysaker, Norway; www.norskeskog.com), a producer of paper for newsprint and magazines, has 22 paper mills around the world. Its Tasman mill at Kawerau, New Zealand, produces more than 300,000 tons per year, enough for all the country's newsprint and telephone directories, plus 25% of Australia's newsprint needs. Paper is manufactured in wide rolls and then slit while rewinding onto cardboard tubes, called cores. These shorter rolls are sized specifically for printing presses. Keeping the rolls balanced as they are rewound onto the cores is a significant control challenge. Excessive eccentricity-the distance between the core center and the roll center-can cause vibration and web breaks on customer's printing presses.
Norske Skog was using a manual measurement technique for detecting rolls with excessive off-center cores. This procedure was both time-consuming and subjective, with different operators achieving different results. The company turned to Control-Vision (Auckland, New Zealand; www.controlvision.co.nz) to provide an automated inspection solution. Limited space on the production line meant cameras and lighting needed to be mounted within 2 m of the roll surface. The imaging solution developed by ControlVision was based on 6-Mpixel cameras from PixeLINK (Ottawa, ON, Canada; www.pixelink.com) and Fujinon (Wayne, NJ, USA; www.fujinon.com) lenses. Safety concerns prevented the use of standard lighting, so large-diameter infrared ringlights from Spectrum Illumination (Montague, MI, USA; www.spectrumillumination.com), each comprising 48 LEDs, were used. Image calibration, pattern-matching, and edge-finding are performed in PC-based VisionPro software from Cognex (Natick, MA, USA; www.cognex.com). Combined with ControlVision's VisionServer deployment environment, this vision system was developed and installed without the need to develop custom software.
