JPS60100710A - Measuring device for pattern area rate of print plate of offset printing machine - Google Patents

Abstract

PURPOSE:To take an accurate measurement speedily and easily after a print plate is mounted on a print drum by making light from a high-brightness homogeneous light source incident to the print surface of the print plate mounted on the print drum, and measuring the intensity of reflected light from the print surface and detecting the pattern area rate of the print plate. CONSTITUTION:A screw shaft 3 is rotated by a motor 2 synchronously with the rotation of the print drum 1 and a case 4 is moved in the axial direction of the print drum 1 to scan on the print plate 1'; and the density on the print surface is sampled and stored in a density-area rate converter 18 corresponding to sampling positions X and Y. Then, the density at the sampling position is converted into an area rate per unit area on the basis of the stored density value of a reference mark 27 at a predetermined position (reference mark density in Malay. Davis equation). The value aXY per unit area detected as mentioned above is obtained by dividing the width of the plate drum in the axial direction equally into (n) widths X1, X2...Xn and calculating the area rate SK of a width (XK, XK+1).

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a measuring device for measuring the picture area ratio of the image area of a printing plate attached to the plate cylinder of an offset printing machine.
In particular, the present invention relates to a measuring device that measures area ratio based on the intensity of reflected light from the image area of a printing plate.

When printing with an offset printing machine, in order to keep the print density constant or to obtain the desired print density, it is necessary to adjust the ink supply amount according to the area ratio of the image area to the printing plate area. There is.

Conventionally, the method of measuring the area ratio of the image area of such a printing plate is to measure it from the plate surface before mounting the printing plate on the plate cylinder (
For example, Dai Nippon Printing Co., Ltd. (Demia), film (manuscript)
Measurements were taken from. However, the former method takes a lot of time to print, and there are problems such as the difficulty of measuring printing plates with curls, while the latter method makes it difficult for printers to obtain the film. This has caused problems such as cases in which measurements cannot be made.

This invention was made in order to solve the above-mentioned problems in measuring the picture area ratio of the image area of the printing plate. It is an object of the present invention to provide a printing plate pattern area ratio measuring device that can accurately measure the area ratio of an image area.

Here, printing plate (28 plates) 1' used for offset printing machine
As shown in FIG. 3, a hydrophilic (grained) non-image area 101 and a lipophilic (ungrained) image area 102 are combined. Then, during printing, dampening water is applied to the non-image area 101, ink is applied to the image area 102, and printing is performed. The image area 102 is colored in a post-development process.

This invention allows light to enter the plate surface of a printing plate, measures the intensity of specularly reflected light and diffusely reflected light, and detects changes in the light source. By compensating for [111] and measuring the halftone dot density of a colored printing plate and comparing it with the density of a solid area at a predetermined position, the picture area ratio of the image area to the area of the printing plate is measured. This is what I am trying to do.

Hereinafter, the present invention will be explained based on an embodiment shown in the drawings. The printing plate pattern area ratio measuring device in this offset printing machine includes a sensor section, a sensor driving section, a printing plate driving section, a sensor position detection section, a printing plate It consists of a plate rotation angle detection section and a processing section. The sensor section is a section that detects the intensity of reflected light from the printing plate, and consists of a sensor body including a light source and a light receiving section. The light source is a device that can provide high-intensity, nearly monochromatic light, such as a laser device, and parallel light rays are made incident on the printing plate. In addition, the receiver is
A device for receiving diffused light consists of a photoelectric conversion element such as a silicon photodiode and a photoelectric conversion circuit, and includes a first light receiver for receiving specularly reflected light and a second receiver for receiving diffusely reflected light. This is added to compensate for the effects of fluctuations in the output of the light source. The processing section is a section that calculates the value of the picture area ratio of the image area of the printing plate based on the signals from the sensor section, the sensor position detection section, and the rotational position detection section of the printing plate.

In FIG. 1, the sensor section will be explained first. The optical fiber 9 emits light from the light source of the helium-neon laser device 8.
is guided to a collimator 10 attached to a case 4, which is configured to scan above the outer circumferential surface of the plate cylinder l along the axial direction of a screw shaft 3 rotated by a motor 2. The light is made incident on plate 1'. The case 4 has light receiving elements 11 and 11' mounted at positions corresponding to the direction of specularly reflected light and the direction of diffusely reflected light with a reflection angle of 0 degrees, respectively. are each equipped with an amplifier 12.12'
is connected.

The processing section includes a divider 13 and an arithmetic unit 14, and the divider 13 calculates the ratio between the specularly reflected light intensity and the diffusely reflected light intensity, and inputs this result as a signal B to the arithmetic unit 14. . The reason for calculating the ratio of the specularly reflected light intensity and the diffusely reflected light intensity in this way is that the value of this ratio is determined only by the density of the image area on the printing plate, and the reflected light intensity varies due to changes in the light source. This is because it is sealed and is not affected by external disturbances.

In the arithmetic unit 14, the signal B is converted to the picture area ratio (SK, S).
Convert to This arithmetic unit 14 can be configured only with analog circuits, but considering the compensation of instrumental errors,
As shown in FIG. 2, it is desirable to configure it with a hybrid circuit of analog and digital.

In FIG. 2, 15 is a compensator, 16 is a logarithmic amplifier, 1
7 is an analog-to-digital converter, 18 is a concentration-to-area ratio converter using a microprocessor, signal B from the divider 13 is input to the compensator 15, and ζ is a light receiving element t.
The characteristics of t, i and i' are compensated. Then, it is input to a logarithmic field width converter 16, where it is converted into a concentration value, then input to an analog-to-digital converter 17, where it is converted to a digital value, and further, a unit area It is converted to the winning pattern area ratio.

Here, as an example of calculation of this concentration-area ratio conversion, the area ratio a can be calculated from the well-known Murray-Davis formula (%):1::.

Since the sensor section scans the printing plate 1' attached to the plate cylinder 1, the scanning in the circumferential direction of the printing plate 1' is performed in conjunction with the movement of the case 4, that is, the scanning in the axial direction of the plate cylinder 1. A drive device (not shown) is attached to rotate the plate cylinder 1 so as to perform the following operations. Furthermore, reference marks 27 for solid area density are provided on the printing plate 1' at predetermined positions. Further, an encoder 20 is attached to the plate cylinder 1 to detect the rotation angle of the plate cylinder 1, and an encoder 21 is attached to the screw shaft 3 to detect the rotation angle of the screw shaft 3, that is, the axial direction of the plate cylinder 1. The measuring position (x, y) on the plate surface of the printing plate 1' is detected by two encoders 20 and 21, and a position signal (X, Y) is output.

Next, to explain the measurement method using the picture area ratio measuring device described above, the motor 2 drives the screw shaft 3 in synchronization with the rotation of the plate cylinder 1.
The printing plate 1 is rotated to move the case 4 in the axial direction of the plate cylinder l.
sample the density of the printing plate and store it in the density-to-area ratio converter 18 in correspondence with the sample position (x, y);

Next, using the stored density value of the reference mark 27 at a predetermined position as a reference (reference mark density D in the Murray-Davis equation), the density at the sample position is calculated as the area ratio 'xy Convert to

The area ratio value a per unit area detected in this way
xy divides the width of the plate cylinder in the axial direction X into n equal parts x, , x
2. . . . Area ratio at the width of (XK, XK+,) is 5K in Xn. Yn: Obtained by calculating the width of the printing plate 1' in the circumferential direction. Also, the average area ratio g is calculated by θ
Ru. The information regarding the area ratios SK and S obtained here is as follows:
This relates to the ink supply amount in the ink supply device of an offset printing machine.

Note that in order to integrate the area ratio 'xy, instead of scanning a set of sensor sections as in the above embodiment, a plurality of sensor sections may be arranged.

Furthermore, the pattern area ratio measuring device in the above embodiment can also be used as a dampening water measuring device for a printing press, and has advantages such as reducing the cost of reeds, printing presses, and improving cost performance. .

As described above, the present invention allows light from a high-intensity monochromatic light source to enter the plate surface of a printing plate mounted on a plate cylinder, measures the intensity of the reflected light from the plate surface, and determines the picture area ratio of the printing plate by measuring the intensity of the reflected light from the plate surface. By detecting this, it is possible to perform quick, easy, and accurate measurements after the printing plate is mounted on the plate cylinder. This method has excellent effects such as saving labor and making it possible to preset the amount of ink, thereby enabling quick printing.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment of the present invention, and FIG. 2 is a block diagram showing an example of the configuration of the arithmetic unit 14 in the embodiment.
FIG. 3 is a sectional view showing the state of the plate surface of the printing plate. 1... Plate cylinder 1'... Print plate 2... Motor 3... Screw shaft 4... Case B... Laser M [10... Collimator 11, 11'... Light receiving element 13...Divider 14...Arithmetic unit

Claims (1)

[Claims] 1. A picture area ratio measuring device for a printing press that measures the picture area ratio by making light incident on the plate surface of a printing plate mounted on the plate cylinder of the printing press and measuring the intensity of reflected light from the plate surface. , a light source device that inputs parallel light rays, a first light receiving device that receives specularly reflected light from the plate, a second light receiving device that receives diffused light from the plate, and specular reflection detected by the first light receiving device. It is equipped with an arithmetic device that calculates and outputs the picture area ratio by scanning the entire surface of the printing plate using the solid area of the printing plate as a reference mark based on the intensity of the light and the intensity of the diffused light detected by the second light receiving device. A device for measuring the pattern area ratio of printing plates in offset printing presses.