JPS6328649A - Control method of dot gain value in offset calibrator - Google Patents

Abstract

PURPOSE:To obtain printed matter of stable quality by obtaining an approximation formula for the representation of a relationship between a printing rate and a dot gain value, and calculating a printing rate for the obtaining of a desired dot gain value based on the approximation formula to perform a printing. CONSTITUTION:A pedestal is allowed to run at a speed V by rotating a motor 22 with a drive unit 66 to measure a dot gain value Da on a printed matter using a densitometer 72. Following this procedure, the motor 22 is caused to rotate at high speed to run the pedestal at a speed Vb for the measurement of a dot gain value Db. Next an approximation formula for the representation of a relationship between printing rates Va, Vb and dot gain values Da, Db is formulated by an arithmetic part 58 based on function data written into ROM 44, When a desired dot gain value Dn is entered by a keyboard 70, and a printing rate Vn is calculated by the arithmetic unit 58 on the basis of the earlier obtained approximation formula, outputting the printing rate to the drive unit 66 for printing.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an offset proofing machine that performs proof printing of printing plates, and more particularly to a method for controlling the amount of dot gain in printed matter printed by the offset proofing machine.

[Conventional technology]

One of the causes of variations in the quality of printed matter is changes in dot gain. Dot gain is a phenomenon in which the halftone dots that make up the printed image become thicker on the printed matter than on the printing plate.1For example, a halftone dot with an area ratio of A% on the printing plate becomes A+ on the printed matter.
If the area ratio becomes ΔA%, it means that there is a gain of ΔA%.

Dot gain occurs in all offset printing including proof printing, and the amount of dot gain varies depending on printing conditions.

When performing proof printing with a proofing machine, it is necessary to change the dot gain amount as necessary, but conventionally the dot gain amount is adjusted to the desired value by adjusting ink selection, temperature, roller pressure, etc. are doing. (For more information on the above, please refer to "Photolithographic Handbook 2 Multicolor Plate Making/Plate Making/Proofing Edition" published by the Japan Printing Technology Association)
Pages 128-130, edited by Printing Technology Association, 1932
(Refer to the first edition published on August 10, 2005) [Problems to be solved by the invention] The method for adjusting the dot gain amount described above relies on the experience of the operator, and not only does the work require skill. , which requires trial-and-error work and is not efficient.

[Means for solving problems]

This invention focuses on the fact that the amount of dot gain changes depending on the printing speed, that is, the slower the printing speed, the more the amount of dot gain increases, and attempts to control the amount of dot gain by controlling the printing speed. The dot gain data on each printed matter when printing was performed at different speeds was measured, and an approximate expression expressing the relationship between printing speed and dot gain amount was determined based on each dot gain data and the printing speed at that time, and the approximate expression The present invention provides a method for controlling the amount of dot gain in an offset proofing machine, which calculates the printing speed to obtain a desired amount of dot gain based on a formula, and controls the printing speed based on the calculated value.

[For production]

The relationship between the printing speed and the amount of dot gain can be determined by calculating the values of each speed and dot gain data at at least two points when printing at different speeds, and connecting these points using a function input in advance. Find an approximate expression representing . Then, by inputting the desired dot gain amount into this approximation formula, the printing speed to obtain the dot gain amount is calculated, and by printing based on the calculated value, a printed matter having the required dot gain amount is obtained. be able to.

〔Example〕

Embodiments of the present invention will be described below, but first an offset calibration machine for carrying out the present invention will be described.

Fig. 2 is a perspective view of the offset proofing machine, and Fig. 3 is a schematic side view thereof. is the motor 22
is configured to reciprocate on the frame 6 in the left-right direction in FIG. 3 by driving. This pedestal 8 has
A blanket cylinder 10, a dampening water roller 12, and an ink roller 14 are supported so as to rotate in synchronization with the movement of the pedestal 8. On the other hand, a damping device 16 for supplying dampening water is provided at one end of the frame 6, and an ink supply roller 2 is provided at the other end.
An inking device 18 having a number 0 is provided in each case.

To perform proof printing with this apparatus, a printing plate is mounted on the plate platen 2, a printing paper is mounted on the paper platen 4, and the motor 22 is driven to cause the pedestal 8 to reciprocate. Then, at both ends of the reciprocating stroke of the pedestal 8, dampening water is applied to the dampening roller 12 from the damping device 16, and dampening water is applied to the ink roller 14.
Ink is supplied from the ink supply roller 20 of the inking device 18 to the printing plate 2, and dampening water and ink are supplied to the printing plate mounted on the platen 2. The ink on the printing plate surface is transferred to the circumferential surface of the blanket cylinder 10 when the pedestal 8 moves back (running from left to right in FIG. 3), and is printed on the surface of the printing paper mounted on the paper platen 4.

The above-mentioned configuration is disclosed in, for example, Japanese Patent Publication No. 59-53871, Japanese Patent Application Laid-Open No. 58-122870, and Japanese Patent Application Laid-open No. 54-15.
This is disclosed in Japanese Patent No. 4607 and the like.

Next, the configuration of the characteristic portion of this invention will be explained.

FIG. 1 is a block diagram of an embodiment of an apparatus according to the present invention. In this figure, 40 is an arithmetic processing unit, and has a control unit 56 and an arithmetic unit 58.
) 42, measured data storage means 48, specified data storage means 50, approximate formula storage means 52, speed data storage means 54, RAM 46, ROM 44, and input/output section 6.
Consists of 0. A drive unit 66 receives a signal from the input/output section 60 of the arithmetic processing unit 1W40 via the D/A converter 62 and amplifier 64, and rotates the motor 22 provided on the pedestal 8 at a desired speed. Further, 68 is an interface, which receives data regarding the halftone dot percentage measured by the densitometer 72 directly or via the keyboard 70, and receives data about the halftone dot percentage measured by the densitometer 72,
0 input/output unit 60.

Note that the ROM 44 in the arithmetic processing unit 40 described above has at least two types of setting speed data and function data to be described later written for rotating the motor 22 at two types of speeds, high speed and low speed.

Next, a printing method in the above-described apparatus will be explained.

First, by calling the set speed data written in the ROM 44 and rotating the motor 22 at a low speed by the drive unit 66, the gantry 8 is made to run at the speed Vu.
For example, a print management scale such as a step tablet consisting of various halftone percentages is printed. And the concentration meter 72
The dot gain amount Da at a predetermined position such as a halftone portion of the print management scale on the printed matter is measured, and the data is input into the interface 68 via the keyboard 70 or directly. This dot gain amount Da is
The measured data storage means 48 in the RAM 46 stores the measured data. Subsequently, another setting speed data written in the ROM 44 is called and the motor 22 is rotated at high speed, thereby causing the gantry 8 to run at the speed vb and printing is performed.

Then, as described above, the dot gain amount Db at that time is measured and the data is stored in the measured data storage means 48 in the RAM 46. Note that when performing the above-mentioned two printings, in order to make the data of the tonnage gains gDh and Db appropriate, it is necessary to print so that the solid density is constant in both printings. FIG. 4 shows the dot gain iDton, Db and printing speed V in the two printings mentioned above.
This is a graph showing the relationship between Q and Vb, with point A indicating data during low-speed printing, and point B indicating data during high-speed printing.

Next, based on the measurement results stored in the RAM 46 and the function data written in the ROM 44, the calculation unit 58 calculates an approximate expression representing the relationship between the printing speed and the dot gain amount. The above-mentioned function data is, for example, data for instructing what function should be used to connect points A and B in FIG. 4, and this data differs depending on the configuration of the proofreading machine and the like. Therefore, this function data is
It is determined experimentally in advance based on the relationship that exists between the printing speed and the amount of tont gain when printing is performed at various speeds. Based on the function data, the printing speed and dot gain amount can be adjusted by correcting the straight line connecting points A and B shown by the solid line in FIG. 4 to the line shown by the dashed-dotted line in FIG. Obtain an approximate expression expressing the relationship. Note that in cases where the dot gain amount may include a certain amount of error, the above-mentioned correction is not performed.
A straight line connecting points A and B may be used as the approximate expression.

In addition to the method described above, as a method for obtaining an approximate formula, as shown in FIG. It is also possible to measure and find point C, and then use interpolation to obtain an approximate expression representing the relationship between printing speed and tonnage gain amount based on the data at points A, B, and C. The above-mentioned approximate formula is stored in the approximate formula storage means 52 in RAM 46.

Next, the user inputs the desired amount of gain using the keyboard 70. This value is stored in designated data storage means 50 in RAM 46.

Next, the previously obtained approximate formula and the desired dot gain amount D11 are called from the RAM 46, the printing speed V for obtaining the desired dot gain amount is calculated in the calculating section 58, and the data is stored in the speed data storage means 54. (See Figure 4).

When the above operations are completed, printing is performed. First, the desired dot gain fk[)n is stored in the speed data storage means 54.
Call the printing speed vr+ data to obtain
The data is output to a drive unit 66 via a D/A converter 62 and an amplifier 64.

Then, as the motor 22 rotates at a predetermined speed, the gantry 8 travels at a speed v1, and printing is performed in a state where the desired dot gain amount Dn is obtained.

In the above explanation, as dot gain data,
The case where the dot gain amount is measured and input has been described, but it is also possible to measure and input the halftone dot percentage. In that case, input the halftone dot percentage when the dot gain is zero into the RAM 46, and then input it. A similar effect to that described above can be obtained by subtracting the value from the actual dot percentage. It is also possible to input halftone dot density as dot gain data. In that case, the Murray-Davis equation or Neil-Nielsen equation for converting halftone dot density into halftone percentage can be stored in the ROM 44, and the halftone density can be converted into halftone percentage within the CPU 42. good. Similarly, instead of dot gain data, a value may be entered and the value converted to halftone percentage. That is, as the dot gain data, in addition to the dot gain amount itself, various types of data can be used as long as it can be converted into a dot gain amount.

In this sense, obtaining dot gain data by measurement or calculation is simply referred to as measurement in this specification.

Note that the speed control described above does not need to be performed over the entire travel stroke of the gantry 8, and may be configured to travel at a predetermined speed at least during printing.

Furthermore, although the above-mentioned embodiments have been described with reference to the case where the present invention is applied to a flatbed type proofing machine, it can be similarly applied to a rotary type offset proofing machine.

〔Effect of the invention〕

The method for controlling the amount of dot gain according to the present invention makes it possible to theoretically adjust the amount of dot gain by changing the printing speed, instead of adjusting the amount of dot gain, which was conventionally done by trial and error based on the operator's experience, thereby producing printed matter of stable quality. It becomes possible to obtain.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment device according to the present invention, and FIG.
FIG. 3 is a perspective view of the proofing machine, FIG. 3 is a schematic side view thereof, and FIGS. 4 and 5 are graphs showing the relationship between dot gain amount and printing speed. 2... plate plate, 4... paper plate. 8... Frame, 10... Blanket cylinder, 12... Dampening water roller, 14... Ink roller, 16... Damping device, 18... Inking device, 22... Motor, 40... Arithmetic processing unit, 42... Central processing unit, 44... ROM,
46・RAM, 56...control unit, 58...
Arithmetic unit, 66... Drive unit, 70
...keyboard, 72...densitometer. ";r=' Figure 2

Claims (1)

[Claims] The dot gain data on each printed matter when printing was performed at different speeds was measured, and an approximate expression expressing the relationship between printing speed and dot gain amount was determined based on each dot gain data and the printing speed at that time, and the above-mentioned A method for controlling a dot gain amount in an offset proofing machine, comprising calculating a printing speed to obtain a desired dot gain amount based on an approximate expression, and controlling the printing speed based on the calculated value.