Machine Vision Ensures Quality in Bottle Tops
Ruth A. Mendonsa
Over 98 percent of bottles sold are returned, thanks to refundable deposits, and each one is refilled and reused by breweries 16 to 18 times. But, the wear and tear can sometimes produce almost undetectable cracks and chips in the bottle-top threads, making the cap hard to remove.
The IPS machine vision system inspects for beer bottle thread flaws.
Labatt and Image Processing Systems Inc. of Scarborough, Ontario, Canada, have embarked on a three-year collaboration to ensure quality bottle tops. They have developed an algorithm-driven machine vision system that inspects bottle threads -- not by looking at the threads themselves, but by examining the properties of the light reflected from them.
The joint project, supported by a grant from the National Research Council of Canada, resulted in the QVS Model 1500 -- so named because it inspects at speeds up to 1500 bottles a minute -- that now sits on the 950/min Labatt bottling line in London, Ontario. The system sees the reflected light of an imperfect bottle thread, and if the flaw's size is above the current threshold setting, sends a signal to reject it.
"Our first challenge was to develop a system that would not touch the bottle," said IPS Vice President Todd Richardson. "Our second challenge was the fact that glass, especially wet glass, tends to reflect light and frustrate attempts to examine the object."
In this application, the QVS 1500 is folded around, but is not part of, the bottling line between the washer and the filler. As the empties speed by, the system's halogen lights and four solid-state charge-coupled device (CCD) cameras with precision lenses provide overlapping coverage of the circumference of the bottles.
The cameras perform a three-stage inspection of the thread area in as little as 0.04 s. In the first stage, the IPS-developed intelligent tracking algorithm locates the bottle tops and then the threads as they sway and jiggle down the bottling line. The electronically shuttered cameras capture the light reflected off the bottles, with built-in progressive-scan CCD technology providing full vertical resolution. Next, two subsystems linked to the cameras and to the host central processing unit, digitize and analyze the reflected light. The system can detect disturbances to the light caused by erosion or chips as tiny as 1 mm2. In the final stage, the unit determines the exact nature of the defect and triggers the reject mechanism.
Success is prompting Labatt to install the QVS 1500 at all its facilities.
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