Checking the web25 June 2002
Web inspection technology keeps pace with press development
Efficient web inspection is essential for peace of mind in modern printing and converting. In line with the continuing advances in print processes, manufacturers of web inspection systems have been working hard to ensure that their equipment will do the job efficiently and cost effectively.
One area of innovation TecScan has been examining in detail is the gearless flexo press. Malcolm Lear says: "While this technology offers faster makeready, more productive press time and greater productivity, the 'downside' is that any corrective action must be carried out at 'double fast' – if not, the high press speed will result in an unacceptable level of waste". He adds: "More than at any time, the operator of a gearless flexo press requires faster feedback on print quality and guaranteed colour registration. In effect, a high resolution video inspection and a high speed automatic registration control system.
"The video system must be competent enough to allow for excellent colour rendition to assist with ink adjustment. It must also offer high speed camera traverse, high speed image transfer and storage of regions of interest, instant re-positioning of the camera to regions of interest – and control of all of these functions from a user friendly operator interface. This interface should also be designed to assist in the makeready process. To support this, the system must have a high speed automatic registration capability that ensures the registration is accurate, and in specification – and within a few turns of the CI," he says.
To meet these requirements, TecScan has developed the Avis Combi - a dual video inspection and machine vision platform – "able to go beyond the disciplines of conventional systems with added service and maintenance advantages", the company claims.
At start-up, the Avis Combi acts as a high speed registration system to correct any errors within a few turns of the CI. It then automatically moves to video inspection mode to assist in makeready and normal monitoring. The system can be pre-set to alternate between registration and video inspection, as necessary.
The user friendly interface has been designed to assist flexo press makeready procedures. During makeready, the areas of interest selected by the operator can be recalled at the touch of a key to the exact co-ordinates, anywhere on the repeat length – either for straight visual comparison or to compare in split screen mode with the last stored image.
Also focusing on solutions to cut makeready time and waste, AVT says: "The major components of colour control of flexo presses relate to cylinder pressure and ink viscosity, hence any change of these control parameters will result in a colour variation."
Currently under development is ReColor, a closed loop solution using viscosity and cylinder control to achieve required colour in set-up quickly and ensure stable colour during run time. During set-up, ReColor helps to bring the press quickly to the required colour by checking and analyzing the printed image and comparing it to previously stored data of a similar job. During the run, it can control plate pressure and viscosity settings of all colours, by analyzing and identifying the cause of any colour variation on the printed image.
In addition, AVT has developed Delta E colour measurement capabilities to resolve workflow requirements. They are: intra-repeat measurements of left-right for controlling left-right pressure balance on each cylinder, during make ready; and a quality assurance measurement tool for the operator to help achieve consistency in different packages on the same repeat, during makeready and run time. Delta E also provides the user with an effective communication tool with the customer, who defines the job requirements in 'Delta E' language.
Eltromat introduced three new products at IPEX, including IMCOM-3 - a CCD camera based print quality control system adaptable to all web-fed offset presses. It provides a central, compact man-machine interface with the ability to control ink fountain settings. Detailed examination of the conditions on the web is possible through the 17-fold zoom camera.
Also new was the DGC750 CCD camera based register control system. It is capable of working with small micro dot registration marks for gravure printing, and with the typical wedge shaped registration marks used on existing cylinders. It can interface to Eltromat's MIS600 management information system.
Completing the IPEX trio was Accu-Colour, a CCD camera based system that examines images to provide precise, non contact colour measurement at print speeds of up to 500m/min. It takes real time measurements of the job on-the-run, analyzes the results obtained against the job standard, and provides the operator with a guidance screen and an alarm if the colour varies outside of the predefined tolerance levels. Immediate adjustments can then be made on the press to ensure colour accuracy throughout the print run.
Tectonic claims its K1 system has the industry's smallest camera case and most compact control box, able to fit into the smallest space. Its special board, combined with the latest high speed cameras, provides a high resolution picture and user friendliness without the support of a Windows operating system, the company says.
In addition to low cost and low maintenance, the system is claimed to be particularly effective for use in hazardous environments or extreme temperatures.
The K1 follows in the footsteps of Tectonics' Lynx system, which offers "exceptional picture quality" with standard memory functions such as programmable positioning and a visual retrieval system that stores the master image onto a floppy disk. Features include a constant scan function that allows the printer to automatically scan back and forth along and across the web at pre-determined, regular intervals. A double camera system is also available to allow both sides of the web to be viewed.
PC Industries has developed new software features for its Viper print inspection system to provide narrow and wide web printers with 100 per cent print defect detection. It is said to be capable of continuously monitoring 100 per cent of the web and automatically alerting operators to costly print defects. After detecting a defect, the system can insert a flag, mark the web or stop the press or inspection rewinder.
Fully automated inspection, image archiving and data collection is offered by Futec Europe in the QC-EasyMax MC. Designed to inspect even the most complex patterns on paper, film, foil, laminates and non wovens, it also detects a wide range of repeating or random flaws, from individual splashes and missing ink, to fine streaks and blade marks. An associate system is the QC-FMax, for surface inspection of material on laminators, film extrusion lines, and in paper manufacturing.
Futec's use of line scan technology eliminates the need for strobe lighting systems, and manual or motorized traversing. The company also designs its own cameras and high speed flaw detection hardware.
Says Ray Scragg: "A key feature is that minimal operator intervention is required. Throughout the inspection, the operator console unit captures and shows the flaws in full colour, making it easy to identify the nature and source of the fault. Data for reporting and analysis purposes is collected and the integrated printer produces hard copy of flaw data for use in job evaluation and for future reference."
The system employs independent flaw detect- ion algorithms that can be set to look for flaws of a particular size and contrast. It also includes enhanced streak and low contrast smear detection algorithms. Job require-ments can be stored for easy recall when required.
Ray Scragg adds: "A feature of the EasyMax is that it provides for a 'full' width snapshot of the web to facilitate easy alignment of the inspection to the web edges. The web view is subdivided into a number of lanes and flaw data is then collected and analyzed by its lane position across the web. This is particularly useful in that flaw information can be aligned correctly depending upon the number of streams into which the web will be slit. Also, output devices such as alarms, labellers, and print reports can now be individually controlled by severity of defect."
Vigitek claims its VigiPrint PVI-200X is the only 100 per cent colour print inspection system designed specifically for flexible packaging. Using 'golden master' techniques, it inspects every repeat, the complete width and length. The system 'learns' the complete print repeat and then checks every copy against that master. It detects all common print defects, including spots, colour, register, missing print, streaks, hazing and cold seal or varnish skips..
This system is self adapting - automatically setting limits dependent on colour and frequency of copy. It interfaces to commercial databases to provide flexible production reports, and can be extended to include standard video cameras for lacquer and cold seal inspection, as well as systems to track and remove waste on a roll to roll basis, and other on-line colour measurement tools. Modular design allows the system to be configured to inspect web widths from 100mm-2m, at line speeds up to 700m/min.
Fife-Tidland believes its InPrint video web inspection system meets many users' demands for simplicity and compact design. "Simplicity seems to become an issue," the company states, "as numerous conversations with buyers and operators alike have concluded that too often equipment is purchased at high expense, then used to not even a fraction of its capabilities."
Reasons for this phenomenon, the company says, are complexity of use, performance mistrust by the printer/operator in comparison with their own capability and experience, and/or system limitations versus expectations. Definitions for current 'must-have' features – 100 per cent inspection, automatic defect detection and automatic register control - for example, vary heavily from supplier to supplier and user to user, and could lead to disappointment once the equipment is in use.
"While even the most complex and cost intensive, image processing system will sooner or later have its payback, even if mainly used as a web viewer, this stage is reached faster, and therefore more cost effectively, with basic equipment, provided its functionality suffices for the application and operator. Lower cost not only originates from the actual purchasing cost, but also from considerably reduced periods required for installation, maintenance and operator training, all commonly equalling machine downtime," says Fife-Tidland.
The InPrint meets the basic demand for web viewing - creation of a stable image of the web running at full production speed and its display on a monitor. A motorized lens assembly allows control of zoom, focus and brightness. Split screen, vertical auto-scroll, 180 degree image turn and image freeze are further basic features.
Originally designed for narrow web and label applications, the system combines camera, control panel and CPU in a single, compact housing. The absence of a separate PC based CPU and thus fewer cables and connectors is said to simplify installation and increase reliability.
Instead of the camera used in traditional web viewers, the InPrint uses a high resolution RGB module. This, combined with purely hardware based image processing on the spot, is said to result in a sharper image and improved reliability.