Media Contact: Claudia Kreiss
By Peter Griffin, President, EPG (Essex Products Group)
Material, labor, and energy costs are increasing but competitive pressures limit the opportunity for recovery through price increases. On top of that, in most market segments, run lengths are decreasing and makereadys per day are increasing. This combination is creating a serious squeeze on profits. Automatic registration systems now enable most printers to be in register very quickly after press startup. Waste, however, continues to pile up until color is set. If the paper, ink, and press time wasted during makeready can be reduced, these savings will flow directly to the bottom line. Finding an economical way to set color quickly has been generating increased interest in automatic ink presetting.
The basic premise of presetting is that there is a predictable relationship between the percentage of dot coverage on the plate and the ink key setting required to supply the correct volume of ink. The 1st step is to determine the coverage on the plate. Plate scanners were once the primary means of doing this. However, most printers are now composing digital image files for use by image setters or CTP systems. Presetting systems can use software running on standard PCs to analyze the image file for the film or plate and determine the percent coverage in each key zone. Some systems require CIP3/4 files as input, while others can accept a variety of image file formats. In most cases a low density file is desired to keep the total processing time reasonable.
A second software application is needed to convert the percent coverage in an ink zone to the correct key setting. There is a direct (but not linear) relationship between coverage and correct key setting. Presetting software uses this relationship together with the zone coverage data to calculate the required setting for each key on each fountain. Because fountains are not identical, most systems provide a means to account for these differences in the calculations. Some systems also provide a means of adjusting the key settings based on the characteristics of the paper being run.
Finally, the calculated key settings must be transferred to the ink desk controlling the keys on the press. Settings can be conveyed to the ink desk by a direct connection or by a variety of media. The ink desk’s computer will then accurately set the keys as required. However, the settings conveyed to the ink desk must be routed to the proper fountains. For a sheetfed press, color alone can identify the proper fountain. In web press applications, the specific web, side, and color must be identified for correct routing. Some systems can also use page number and color for routing.
The objective of the presetting system is to achieve uniform target density across the print as quickly as possible after startup. To accomplish this, other variables that affect proper key setting must be controlled. Ink key zero settings must be properly calibrated in order for the calculated key settings to accurately produce the expected blade opening. Fountain lock-ups must consistently close the fountain to the same position each time in order for zero settings to be accurate. Micro rollers, if used, must be set parallel and within manufacturers specifications for gap. Other variables that effect ink key settings at start up, such as ink ball speed, ductor settings, and water settings, must be standardized or under control of the presetting software.
The proper non-linear curves or formulas for converting percent coverage to key setting must be determined. To do this, test plates are run and their image files processed to preset the ink keys. Preset key settings are then adjusted to achieve uniform density at target value across the printed sheet for each color. In this process, color bars and quantitative density measurements will produce more accurate results than visual judgment. These “OK” settings are the basis for determining the correct conversion curves for the press. Creating curves to match the OK settings is done manually on some systems, automatically by software on others.
Achieving and maintaining optimum preset results requires periodic evaluation of preset performance. In this effort it is desirable to have a quantitative or graphical method of measuring the amount of correction the press operators need to make in order to achieve desired color. This requires capture of preset key settings as well as OK key settings. Because the objective is to quickly achieve desired color under startup conditions, it is more appropriate to capture OK settings as soon as desired color is achieved rather than at the conclusion of the run. It is useful to collect some printed sheets at the same time to allow later evaluation of the correctness of the OK settings. This information will enable the user to fine tune the conversion curves and minimize the need for additional adjustment after preset.
With the shift to more jobs of shorter run length, the impact of makeready waste reduction can be substantial. Reducing the number of current waste impressions by 20% to 50% is typically achievable. If, for example, a web press runs only one web, six days per week, seven makereadys per day, with 3000 waste impressions per makeready is generating 126,000 waste impressions per week. A 40% reduction in waste impressions through presetting will save 50,400 impressions per week. At a cost for paper and ink of $ .045 per impression, the saving is $ 2,268 per week. That’s $ 117,936 per year! While each web and sheetfed printer’s volume and potential saving is different, clearly there can be a substantial return and rapid payback of the investment. Run your own numbers to see how much presetting could benefit your shop.
About EPG: EPG (Essex Products Group) is a leader in the development of graphic arts technology, specializing in the design, manufacture, and service of integrated color control systems and software. EPG’s state-of-the-art KeyColor systems are integrated into original equipment by leading press manufacturers and installed worldwide as retrofits on newspaper, commercial, and package printing presses.
For more information about EPG and integrated color control systems, contact Helga Kollegger, Sales Administrator, email email@example.com, telephone +1-860-767-7130; fax +1-860-767-9137. EPG’s headquarters is located at 30 Industrial Park Road, Centerbrook, CT 06409. Visit the EPG web site at www.epg-inc.com/ICS/.