Density measurement has proven to be a measurement technique suitable for printing color control. After all, the amount of ink has a close relationship with the corresponding density value measured on the printed sheet. According to this constant principle, manroland, the pioneer of color control, has perfected measurement equipment, control technology, and control algorithms as much as possible for the past 25 years.
So far, the printing industry has used colorimetry to evaluate print quality for several years. This method is usually used in conjunction with the standardization and color management of all processes in the digital production process. Because the color analysis can be used to better determine the final color effect, especially for spot color printing, it makes color measurement particularly important in more complex printing types, such as packaging printing.
The requirement for printing color control has driven the development of ColorPilot, an automatic ink supply and control device. ColorPilot is a new system installed on manroland sheetfed offset press that is used to comprehensively control the density and color of inks. For more than two decades, printers have used measurement and control techniques to obtain print quality that is faithful to the original and has a stable quality. Density measurement plays an integral role in it. Because the density of the ink film on the surface of the substrate can be measured optically, the ColorPilot system is used to determine if the measured area is to be reduced or increased. For the problem area, the sophisticated control algorithm finally achieved the precise switching operation of the ink dispensing device. The ink is supplied to this area accordingly, obtaining the desired color effect on the printed sheet.
Manroland launches groundbreaking ink monitor
As a pioneer in the field of color control, Manroland introduced the first generation Roland CCI ink control system as early as 1977. Since then, Manroland has continuously improved the speed, measurement accuracy and reliability of the CCI ink control system. In the late 1980s, the introduction of the third generation ColorPilot control system significantly reduced measurement time. It can measure a length of 1,020 mm measuring strip in about 14 seconds. The bar is only 3 mm wide. Measuring more areas in the bar means that more information can be printed (340 pages in medium format).
The Roland 700 press, introduced in 1990, drastically reduced the time to select the ink slider. Prior to this, a six-color printer took at least six seconds to make the selection, and this time has been greatly reduced.
When the fourth-generation Roland CCI system was introduced in 1998, Manroland once again set new standards. The measuring head can now measure printing strips that are only 4 mm wide.
ColorPilot system that combines density measurement and colorimetry
The ColorPilot system first appeared in the IPEX2002 exhibition, and its introduction is the most important step in the development of technology so far. As a corollary of previous developments, this well-known density control method and colorimetric measurement technology are combined into the same system.
In addition to measuring and controlling using the well-known test method of the ink density principle, the ColorPilot system can simultaneously measure the colorimetric value of each measurement area (only 3Ã—4 mm in size) on the printed control strip without additional time. . Target color patches can be input to each printing unit and each ink slider area.
Record and statistics ink difference
The ink measurement results are recorded as a plot of the ink density difference (Î”E value) or in a digital form. Choosing this form of visualization allows the deviation range of the ink (permissible ink difference) and the value beyond this range to be clear at a glance.
Each printing unit can choose to enlarge the display and mark the independent components (for example, â–³L, â–³a, Î”b) of each ink supply area. In a square measurement zone, the difference between the target value and the actual value can be displayed in numerical or graphical form, corresponding to the true color of the visual inspection.
Using the "Statistical Protocol" function, the ColorPilot system can count the value of ink delta E based on all recorded measurements in a job and plot a histogram.
In the "Statistics" function, the ColorPilot system calculates and displays the minimum, maximum, and median differences in numbers or drawings. This is based on the results of all measurements made on each slider zone included in the measurement zone. In the â€œHistogramâ€ function, the system calculates and displays the minimum, maximum, and average ink differences for all ink ribbons on each printed sheet in digital or graphical form. The records of these drawings or numbers can be printed in the form of reports.
The basis of color control: density measurement
Density measurement is still an ideal technique for ink control because these density values â€‹â€‹are closely related to the thickness of the ink film on the printed sheet. In the range of printing ink film thickness (as small as one-thousandth of a millimeter) common in multi-color overprinting, there is a nearly linear relationship between the density value and the ink film thickness. Therefore, the density value is very suitable for measuring and controlling the ink film thickness on the sheet. The measured value is directly affected by the ink slider setting, which is affected by the ink film thickness. By measuring the density through a polarizer, the effect of scattered light from the dried ink film surface can be eliminated. This virtually eliminates the density difference between wet ink and dry ink. In contrast, the use of polarimetry for colorimetric measurements is difficult.
The automatic control of the slider position makes the job of the press operator easier. He only takes samples at intervals and measures and confirms whether or not he meets the recommended control values. The ink measurement during the operation of the machine is left to the control program to complete. The quality of production operations is recorded by statistical evaluation.
The control of the thickness of the ink film, an important process element, ensures the stability of the printing process. Once a certain printing effect is achieved, stable printing quality can be maintained without difficulty by density control.
Commercial printers print most typical halftone images using a four-color process. For most of them, pure density measurement and control systems are sufficient. Because spot colors are rarely used in such production. Standardization of production processes before printing (including reproductions) and printing improves the productivity and efficiency of the entire printing system.
Color measurement, perfect color control
Packaging printers require extra help because packaging printing places very high demands on the color appearance of printed products. According to the requirements of the manufacturer or product, it is usually necessary to measure large areas of spot colors. The objective evaluation of printed sheets requires a measurement and evaluation system that can imitate the visual impression of the human eye. Colorimetry is such a system. If only the density value is used, the accuracy of the ink cannot be completely determined. For example, depending on the density value, it cannot be determined whether the hue of the color is correct. In such a case, it is meaningless to adjust the position of the slider.
Moreover, due to the different substrates used, the same amount of ink supply will produce different visual effects on printed sheets. The difference may be the thickness, absorbency, and apparent color of the substrate. The color of the substrate is one of the important reasons leading to different, defective color effects.
To solve the process problems in the production process, it is required to change the process with the press sheets of different parameters. For example, ink balance or changes in temperature can result in a large number of process adjustments.
In such cases, supplementing density measurements with colorimetry is the ideal solution. The ColorPilot system can provide this method with the following important features:
â— High-precision measurement and control based on ink density â— Spectral measurement of color patches using independent sensing technology under the same head â— Functions connecting color measurement values â€‹â€‹to density control process
Source: "Global Box Industry"
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