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FLEXO Magazine : April 2011
Technologies & Techniques Print Inspection The new Frontier For Press Productivity By John D. Thome Imagine, for a moment, everything you know about inspect- ing the printed web. Now imagine that everything you know is no longer accurate. Imagine that technology and systems have changed so dramatically in the last 2 or 3 years that the only rule is that all the rules have changed. Welcome to inspection of the printed web in 2011. In a striking worldwide trend, converters of all materials and web widths are taking their print inspection up a notch. Yet inspec- tion systems are evolving so rapidly, it can be tough to keep track of the most recent developments. TYPES OF INSPECTION Three types of inspection systems are common today, video, print process management and 100-percent. Video inspection systems are purely visual systems that use cameras with optical lenses for magnification. They use area scan cameras that take pictures of the moving web and dis- play them on a monitor. Tens of thousands of video inspection systems are in use today. Print process management systems are video inspection systems capable of performing tasks such as defect detec- tion, color monitoring, barcode verification, register- and pressure-setting and more. They, too, use area scan cameras with optical lenses. Many provide press operators with full visual inspection capabilities, as well. The 100-percent inspection systems inspect all of the mate- rial going through the machine, including material going through the press or rewinder, at high speeds. Instead of con- ducting an area scan, these systems use line scan cameras that inspect one line of pixels across the web, but at speeds up to 24,000 lines per second. (See Figure 1.) They have fixed lenses, which means limited visual capabilities and digital im- age magnification, and they offer print process management to varying degrees. NEW STANDARDS Converters across the industry are ratcheting up their stan- dards. Leaders are installing systems comprised of both area scan and line scan cameras as converters strive to improve customer satisfaction and gain competitive advantage. For example, basic visual inspection has been the standard in narrow web flexo for years but this is no longer the case. Narrow web converters are now adding print defect detection systems, 100-percent inspection systems, color monitoring capabilities and much more. Having no inspection or only a video inspection system on the press places a printer behind the curve. BST Pro Mark recently installed a 100-percent inspection system on a 16-inch press, in combination with a video system with Virtual Repeat technology,, automatic color monitoring and a 26-inch high-definition (HD) display. All aspects of the system are linked to a workflow solution on a rewinder 300 feet away and to the company's quality control department. The trend toward multiple systems is even stronger in wide web flexo. (See Photo 1.) Here the standard for the last 6 to 8 years has been print process management with defect detec- tion as a minimum. For example, BST Pro Mark is currently outfitting both new and older presses with packages that include a 100-percent inspection system combined with a print process management system to perform automatic register and pressure setting, automatic color monitoring to a standard of 1.0 DE, barcode verification of 2D barcodes and separate video systems down stream for inspection of front-to-back print and cold seal. These systems use HD thin-film transistor (TFT) displays and large touch screens, and they are often augment- ed with 42-inch displays as a visual tool for the operators. DRIVERS Package sophistication, customer demands and the con- verters’ need for competitive advantage are driving the trend toward cutting-edge print inspection. FIguRE 1. Area scan vs. line scan. 18 FLeXO APril 2011 www.flexography.org Keeping Pace With Technology • Three types of inspection systems are common today, video, print process management and 100-percent. • The use of multiple systems is gaining popularity in both narrow and wide web flexo. • Area scan camera technology, line scan camera technology, mathematics and software and integrat- ed workflow have experienced rapid evolution. • Camera space requirements, operator skills and equipment costs must be addressed for implementa- tion to be a success. • Current inspection technology is driving improve- ments in press productivity, throughput and quality. It is generating sizeable savings in time and materials and improving press “up” time.