Machine Vision ensures Excellence in Paper Processing
Anyone who processes paper and print knows the name Hunkeler as a byword for excellence. It stands for Excellence in Paper Processing , the company´s constant claim. Working for the printing industry since 1922, Hunkeler is an independent, owner-managed family business which today has some 280 employees around the world.
With their headquarters in Wikon in the northern part of Switzerland, Hunkeler is concentrating on two business areas. “In the digital segment we supply advanced pre- and post solutions for high performance digital printing systems, print on demand, data centers, security printing and direct mails”, says Nicola Bologna, Product Manager Inspection and Tracking Solutions. “Our Hunkeler Control Platform supplies scalable solutions for quality and production inspection and tracking.”
Innovative systems are an obligation
Innovation matters at Hunkeler: Continuous investment in advanced equipment and an appropriate infrastructure are a core principle at Hunkeler. This also applies to the machine vision systems that are an essential element in almost every Hunkeler system: “With the always increasing production speeds and quality demands in this field, print quality inspection as well as production integrity monitoring and tracking is getting more and more important and is a must in most of the high-end projects which Hunkeler is providing solutions for”, Bologna explains.
For that reason, the Swiss company has already been cooperating with STEMMER IMAGING as their machine vision partner since 2010. At that time, line scan cameras and contact image sensor technology had been used for Hunkeler´s web inspection systems. STEMMER IMAGING had supplied all the necessary vision hardware for these systems at that time.
“After various problems with color rendering and speed with the previously used contact image sensor technology, we started searching for an alternative, and after a phase of intensive testing and with the help of STEMMER IMAGING we finally decided to use the new Mitsubishi Electric Line Scan Bars for our future web inspection systems”, Bologna remembers.
The new web inspection generation was demonstrated at the Hunkeler Innovation Days 2013 for the first time, with integration into the company´s DP6 Dynamic Perforators. These machines, as an example, are able to dynamically produce longitudinal and cross perforations onto the paper such as vouchers, coupons, payments slips, checks selectively enabled by specific activation codes usually embedded into the production or tracking code. The DP6 dynamic perforator is only one of the many highly flexible and scalable modules form the POPP6 family of devices, available since more than a decade which is now getting replaced from the new POPP8 family of devices, which are providing wider, faster, better and even more complex functionalities.
Two years later, Line Scan Bars were already used as standard components in Hunkeler machines. Bologna mentions one example: “In the last quarter of 2015 we designed a web inspection WI6 version for integration into Canon color stream printers based on Mitsubishi Electric AX3 sensors which have been installed in several printing lines starting from Q1/2016.”
At that time, his team also started testing the new high speed CX versions of the Mitsubishi Electric Line Scan Bars and demonstrated their developments for the first time at DRUPA 2016, the world´s leading international show for printing, media and packaging production, as a preview of their future WI8 web inspection system integrated into the latest DP8 Dynamic Perforator machines.
“Now we are in the final developing phase for this WI8 web inspection systems that are exclusively based on the high speed CX Line Scan Bar models. These systems are typically integrated into our POPP8 family of finishing equipment, which will be officially deployed on the market in early 2018”, Bologna says. “These real time digital printing quality inspection systems detect printer oriented and user oriented defects, integrated with our tracking platform for end to end production monitoring and tracking.”
Challenges in different industries
Until today, Hunkeler has more than two hundred WI6 web inspection systems installed all over the world in many field of application such as transactional, trans-promo, direct mailing, publishing, lotteries, pharma, security printing and many more. Depending on the application, the risks and consequences of not detecting a defect are varying: In lotteries and pharmaceutical for example, an undetected defect or a duplicate could mean loss of money or in the worst case, putting somebody´s life at risk. In other fields such as direct mailing, transactional or trans-promotional the risk is more the contract incompliance of Hunkeler´s customers (typically the printing service companies) which is also unwanted.
In many applications, the challenges for the inspection and tracking systems are mainly related to speed: The machines and imaging systems have to deal with up to 350 meters per minute, with web widths of up to 42”, in combination with the need to perform controls on 100% of pages in real-time, especially when running production tracking. “Further arguments to keep in mind are accuracy, ease of use, reliability, cost effectiveness and always trying to adapt to main market and customer needs. These are the reasons why we are always looking for flexible, modular standard products when designing solutions”, Bologna states.
Line Scan Bars meet the challenges
With the Mitsubishi Electric Line Scan Bars, Hunkeler has found their favorite solution for a powerful, reliable and flexible machine vision component. Due to its technical design, these products are perfectly suited for the paper industry: They use the same concept as office desktop scanners, but make sure all industrial requirements are met. The image formation is achieved via a double-row lens array, using gradient index rod lenses, matched to a colour tri-linear CMOS sensor. Each individual rod lens captures an image of a very small region of the target. Thanks to some overlap in the individual images, a clear, sharp, combined image is produced along the narrow line of the sensor at a resolution of 600 dpi.
Rod lenses are designed for a working distance of 12 mm and allow a depth of field of approximately +/- 0.5 mm which makes this technology only suitable for objects with a height deviation of less than 1 mm, which perfectly is the case in the printing industry. Thanks to their compact design, Line Scan Bars are easy to install and can be mounted directly above the surface of interest at a fixed height of 12 mm, with all LED illumination and optics already built-in. “These modules can be installed in just a few minutes, and it is very easy to carry out the adjustment directly above the object”, Bologna explains his experiences. He also likes the flexibility that comes with them: “The high-speed CX models we use in our current web inspection machines are available in different widths of 367 mm, 587 mm and 807 mm, with a resolution of up to 19,008 pixels. For seamless scanning of different or larger material widths we can arrange several sensors next to one another.”
As mentioned before, speed is one of the main challenges Hunkeler has to manage in their machines. The powerful CX models of Line Scan Bars are especially designed for very high inspection speeds, allowing for extremely fast data output via one or two CoaxPress interfaces depending on the size of the sensor. This setup allows the scanning of paper at a speed of 138 meters per minute with a maximum resolution of 600 dpi. The commonly used resolution of 300 dpi enables reliable inspection of up to 450 meters per minute, and inspections with 150 dpi resolution even allow speeds of 1,200 meters per minute. “With these enormous speeds we are able to deliver high-quality and reliable surface inspection systems that meet our customer´s requirements”, Bologna happily says.
The current web inspection system provides a lot of functionalities running in real-time on 100% of the printed pages. Some examples are standard inspections of up to five A4 pages in parallel (called 5-UP in the printing industry) duplex independent pages, presence, size and position measurements for graphical objects on the page, the detection of smearing and streaks, print registration verification down to 40 microns with standard 300 dpi resolution, color grading, 1D, 2D ANSI and postal code grading, decoding and data validation or optional dynamic real-time marking and I/O driving based on the inspection status, which is usually used for inline lottery or label inspection applications. Above that, there are many more applications Hunkeler can address with their Line Scan Bar based machines.
The following example gives a better idea of what these machines are able to do: A 42“ web press has a printable width of 1.066 mm. On that space it is possible to print five A4 pages in parallel which allows increasing the overall productivity. Running at 240 meters per minute, 42“ presses are producing 67 duplex A4 pages per second or 4.020 A4 sheets per minute printed on both sides, which is also the reason why an automated web inspection is mandatory to verify punctually each page and each document for quality and integrity.
Mitsubishi Electric´s sales channel for their Line Scan Bars is Europe’s largest imaging technology provider, STEMMER IMAGING. “This partner first introduced this interesting technology to us, and we are very glad that we can rely on the expertise we get from them”, Bologna emphasizes. “STEMMER IMAGING not only assisted us when selecting the right machine vision technology for our demanding applications, but also supported our team when it came to designing the machines. After having received an appropriate introduction to the components and the technology, we had no trouble to integrate the Line Scan Bars into our systems.”
“We see a significant number of appropriate applications for these products", states Jan Friedrich, Machine Vision Sales Engineer at STEMMER IMAGING.
“This is not only true for the paper industry, but also in other areas where flat objects need to be inspected, like in the electronics industry and many others. With Mitsubishi Electric, we can rely on a very powerful, global partner supplying this type of product which is an important element of our comprehensive machine vision product range.”
For many years Mitsubishi Electric has offered solutions for the development of compact optical colour readers with the highest scan rates. The KD series of contact image sensors (CIS) are the first sensors Mitsubishi Electric have produced targeted at the machine vision industry.