ORUS - Automatisation par la Vision

The writing is on the box:
A young machine vision company is taking on the challenges of print inspection
Advanced Imaging

05/2003 - Each time we set foot in a store, we are bombarded with hundreds of packaged products, many contained in printed cardboard boxes. From an aesthetic point-of-view, the boxes have to be in pristine condition; after all, a manufacturer does not want to see poor print quality on his package. For certain industries, however, the packaging plays an even greater role. When the consumer purchases extra-strength pain medication, for example, that particular medication must be contained in the box.

Founded in 2000, Orus Integration of Laval, Quebec, Canada, developed the PL series of print inspection systems for local box manufacturers who print cartons for pharmaceutical companies. The PL-1100 is an inspection machine that segregates pharmaceutical boxes to prevent insertion of a drug in the wrong package. The PL- 1100 is a periscope configured to fit underneath a conveyor so it can scan the printed cartons as they pass between conveyors. A light source illuminates the 1" gap between the conveyors, and a line-scan camera acquires 100% of the box's printed surface as it passes between the conveyors at a rate of 120,000 products/hour.

The operator's console of the PL-1100 includes a vision server running a FalCOM HMI. Based on the Matrox Imaging Library, FalCOM requires the operator to first specify a model box, to which the remaining boxes in the batch will be compared. Sheets that fail are rejected using the PL-1100's tracking system, which is tied onto the production line's existing reject mechanism. FalCOM allows the user to adjust the sensitivity with many parameters, as well as provide statistical data analysis with Microsoft Excel compatibility .To ensure system reliability, the PL-1100 system rejects all boxes that do not conform to the specified model. That is, not only are incorrect sheets rejected (for example, an extra-strength batch containing a regular strength package), but contaminated sheets and those with printing defects as well.

The components

Depending on the actual system, the PL series inspection systems use the DALSA Piranha2 line of linescan cameras for monochrome systems which range from 1K to 8K; color systems use either a DALSA Trillium or a Basler L301kc. Two dual LED linear front lights project a 1mm line on the scanning axis from two different directions, which improves the quality of the scanned image. A Camera Link frame grabber is then inserted inside the Orus multiprocessors' vision server.

The PL series also includes a tracking system that runs on an independent 1.7 GHz processor; this provides away to monitor the server activity and report any malfunctions. The resulting system is intrinsically safe, as needed by the pharmaceutical industry.

Project Manager Louis Dicaire says careful decisions were made when choosing the system's components. "In this type of application, line-scan technology was the only practical solution. We just couldn't get the whole sheet surface with an area-scan camera." Moreover, achieving 33 inspections a minute requires bandwidth and hardware optimization. "With the Camera Link standard, we have not only increased system performance, but also increased robustness," he adds. The Camera Link-compliant components also contribute to the ease of installing the PL system.

Read outside the box

When an image is scanned, proprietary algorithms are used for "automatic learning" and pre-processing. This involves qualifying the printing, determining the sheet size and locating the model on the printed surface. These algorithms also compensate for normal occurrences in the entire production process: cutting errors, surface bumpiness, vibration during transfers between conveyors and rotation and translation from sheet to sheet. The pre-processing and automatic learning is performed before the start of the production run, and uses a single first scan. Dicaire notes, "We optimized the real-time algorithm to take full advantage of memory and multiprocessor architecture. So, after the learning phase, the software knows exactly what to expect and uses pre-computed information in memory specific to the actual sheet. Using this strategy more than doubled the speed of the scanning process."

MIL's pattern-matching algorithms locate the printed pattern on each sheet. Bit-wise operations and filters are used to manipulate the images. The blob analysis module locates and sorts the defects. Prior to inspection, the user can specify the tone difference threshold; when scanning in color, this can be used to control discoloration or saturation of the printed logo. Spots, streaks, and haze detection are also configured - for example, to set the tolerance for maximum spot size or discoloration threshold.

"Being truly generic was the real challenge," explains Dicaire. The software has to be flexible enough to support a varied number of images and sizes. "Finding a mathematical model that could predict a suitable portion of the sheet was very difficult." The dimensions of the model, search region and levels of accuracy had to be fine-tuned to achieve the best possible performance, and still be processed under thirty ms for the complete inspection cycle. For this reasons, the company uses double-buffering and PCI bus-mastering to take full advantage of the Camera Link hardware.

The pharmacode reader used to be the preferred method of inspecting cartons for pharmaceutical products. The drawback to this method is that well-printed bar code will still pass inspection, even if portions of the package are printed badly. The PL series resolves many of the problems that occur with traditional barcode reading. Some products cannot be coded at all due to their geometry, such as fifth panel boxes, which leaves a manufacturer very few options. Another advantage is reliability. Oil drops, ink bubbles, and even squashed insects can all be found on one sheet.

Since the system segregates the sheets based on their appearance, and not on bar codes that are unreadable by human eyes, the PL inspection system prevents those contaminated boxes from ever reaching the customer. This is the primary advantage of scanning the entire surface of each sheet. Furthermore, users find the touch-screen panel very intuitive, which facilitates the set-up; the inspection process itself can be engaged by a single button. Finally, the system's learning process is completely automatic, so it is even simpler to use than traditional pharmacode readers.

A look at the future

Orus Integration has installed over twenty systems during the last two years, all of them in manufacturing plants. The company has developed inspection systems for many sectors, including bakeries, military industries, opto-electronic components, plastics and pharmaceuticals. In development is a system for cylindrical, or tubular products that are impossible to inspect using area scan cameras. By adapting the PL system, Orus hopes to improve precision at detecting defects on printed squeeze-dispensing plastics or aluminium tubes.

(By Sarah Sookman)

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