JPS58214805A - Measuring device of pattern area rate - Google Patents

Abstract

PURPOSE:To improve stability and accuracy in the measurement of pattern area rate in a light room by an apparatus wherein a spherical interference filter selectively transmissible for only the light of laser wavelength is provided in front of a photo detector for detecting the intensity of the reflected light from a printed plate. CONSTITUTION:An interference filter 11 having a characteristic as shown by a curve A is provided in front of a light receiving part 10 of a photo detector 7 to make only the light of laser wavelength transmissible therethrough. The interference filter is shaped into the spherical form which has a radius (r) with the light receiving surface being as the origin. This permits the reflected light to enter the interference filter at a nearly right angle even when a laser spot is scanned over a printed plate from one end to the other end, whereby a shift amount of the spherical characteristic can be restrained to the minimun and the intensity of the reflected laser beam can be made uniform all over the surface of the printed plate. Thus, only the light near the laser wavelength is allowed to pass through the filter and enter the light receiving part 10 without suffering significant influence from the external light, so that the measurement may be always carried out with stability and high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for measuring the pattern area ratio of a printing plate using laser scanning, and in particular, even when working in a relatively bright room with fluorescent lights etc. Regarding the area ratio measuring device, this device is characterized by the fact that it is bright and can be operated indoors.

Hereinafter, the present invention will be explained in detail based on the drawings.

FIG. 1 is a schematic explanatory diagram of a picture area ratio measuring device of the present invention.

The laser beam (4) from the laser beam (2) is adjusted to a certain beam diameter (for example, a 2 x 8M round beam) by a collimator lens (3), and is further reflected by a mirror (5) to the printing plate (1). ) is irradiated.

The irradiated t''L laser beam (4) is applied to the printing plate (11).
A part of the light is absorbed by the handle, and a part of the light is diffusely reflected and enters the light-receiving portion uO) of the light-receiving element (7).

The light-receiving element (7) (for example, a photomultiplier) has a light-receiving section 0.
0) is incident on n y, - the amount of incident light is converted into an electrical signal,
This signal ycpU (enters 91).

CPU t9) processes the electric signal and prints the printing plate (1
) picture area ratio? :'S is out.

However, the maximum dimensions of the printing plate (1) are 1200 x 1360
m, so the galvanometer (6) is used to measure the mirror (5
) To scan the printing plate (1) by rotating it, the distance from the printing plate m1 to the light receiving element (7) is the mirror (5).
If the swing angle is 50° to 60°, 1220 to 146
01EII+, which is quite high.

When determining the image area ratio of the printing plate (1) using such a large device, it is likely to be easily affected by external light for illumination, such as a fluorescent lamp, and therefore the laser scanned printing plate ( The light receiving element (force) receives the reflected light amount including the light (outside light) from outside the area of 11 and converts it into an electrical signal level. There is a drawback that it is difficult to measure accurately at all times as it tends to contain a lot of light. °C is not a desirable condition from the viewpoint of the structure of the equipment and workability.

This is because the time it takes to measure a printing plate is usually about 30 seconds. Doing it for a long time reduces work efficiency, and also in terms of installation and maintenance, it is difficult to completely shut off the outside for a long time, and it is not economical.

In view of the above, the present inventor provides an apparatus that can always measure the picture area ratio stably and accurately under normal working conditions, that is, indoors and with the lights inside the apparatus turned on.

That is, as mentioned above, the laser beam from the laser (2) is adjusted to a certain beam diameter by the collimator lens (3).
The printing plate (1) is irradiated with a 2×8 film beam every other day, which is reflected by a mirror (5) whose rotation is controlled by a galvanometer (6). Here, we will discuss in more detail the configuration for scanning the printing plate (1). It is set so that it comes to (・ru).

The laser beam starts from the origin U21 and rotates the mirror (5) slightly downward using a galvanometer (6) to produce a pitch (for example, 1 m) in the lateral direction of the printing plate (1).
Send and rescan.

Then, the origin force scans the printing plate (1) to the lateral edge, and then the pulse motor (8) is driven to move the gallenometer (6) and mirror (5). : The disk is rotated and fed at a certain pitch (for example, 5 mm) in the vertical direction of the printing plate (1).

At this time, the laser beam is simultaneously rotated by a galvanometer (6) to move the mirror (5) to the p end on the origin side of the printing plate.

Then, like last time, the printing plate is scanned in the horizontal direction at a certain pitch (for example, one step).

Scan the entire print version repeatedly.

As described above, the laser beam that scans the printing plate is partially absorbed by the surface of the printing plate, and part is diffusely reflected and placed above the printing plate (1). Human radiation is emitted onto the light receiving section (10) of the light receiving section (10).

Here, the color of the photosensitive layer of the printing plate (mainly a photosensitive type PS plate) is mainly cyan or green.

Therefore, the image area has the color of the photosensitive layer, and the non-image area has the photosensitive layer removed and is grained, giving it the color of the aluminum substrate.

Therefore, as the laser light source (2), He-Ne (wavelength 63
28X), etc., the incident light amount of the laser beam is almost absorbed in the image area, and is diffusely reflected by the grained substrate in the non-mm area. Offset printing plates have color gradation based on the size of the halftone dots, so in the light and bright areas there are fewer halftone dots that correspond to the bright areas, so the amount of diffused reflection increases, and conversely, in the shadow areas, the amount of diffused reflection increases. Since the corresponding halftone dot area becomes larger, the amount of diffused reflection becomes smaller.

Therefore, if the amount of diffused reflection f is received by the light receiving element, J? F
n can be determined depending on the rate of printing.

Here, when receiving the amount of diffusely reflected light, in addition to the laser wavelength (for example, 6328;-' for 1 dHe-Ne), external light from the fluorescent lamp inside the device or indoors is also received, so it is not always stable. Therefore, it becomes impossible to trace accurately.

Therefore, in front of the light receiving portion tlol of the light receiving element (7), an interference filter having characteristics as shown in curve A in FIG. 2 is provided to selectively transmit only the laser wavelength.

Here, the shape of the interference filter is important.

If an interference filter with a characteristic spectral sensitivity distribution having a peak at wavelength 6528 ■) is incident at right angles to n
Regarding the amount of light, please refer to the song #! in Figure 2. Due to the spectral characteristics of A, laser wavelengths around 6328X are transmitted, but all other wavelengths are cut off.

As shown in Figure 3 fbl, for the light incident from the filter, the interference filter (old) shifts from the spectral characteristic of the song MA in Figure 2 (・, Figure 2 1
The spectral characteristics will be that of curve B.

In fact, since the laser spot moves from one end of the printing plate to the other, the reflected light from the printing plate force of the laser beam is incident on the interference filter as shown in Figure 3 (al). Rather, they are incident at various angles as shown in Figure 3 (bl).

Therefore, the spectral characteristics of the interference filter vary depending on the angle at which the light is incident, so that the interference filter has the disadvantage that it cannot accurately receive the amount of light reflected from the printing plate (1).

For example, when using an interference filter with a half-width of 80 to 100λ, if the incident angle of the diffusely reflected light from the printing plate that enters the interference filter is 45°, the spectroscopic customization will shift approximately 100 degrees to the short wavelength side. This causes the signal light of 6328'i, which is the signal light of the laser beam, to be attenuated to Yx% in the amount of reflected light.

Therefore, the shape of the interference filter is changed to a spherical shape with the light receiving surface as the origin and the radius r as shown in Figure 3 FC+.The shift of the spectral characteristics can be suppressed as much as possible, and the amount of reflected light of the laser beam can be reduced to the entire surface of the printing plate. can be made uniform over the entire range.

Therefore, the reading accuracy is improved, and since only light near the laser wavelength is transmitted through the light receiving section, the influence of external light (mainly fluorescent lamps) can be suppressed to a level that can be almost ignored. - It is possible to perform stable and accurate measurements again.

Furthermore, by covering external light such as from a fluorescent lamp with a cyan or green filter, it is possible to remove external light more completely.

Note that the radius r of the interference filter is determined by the mounting position, the size of the printing plate and the light-receiving portion of the light-receiving element, etc.

Since the present invention has the above structure, it has excellent effects as shown below.

That is, in the present invention, a laser light source is used to trace and determine the halftone dot area ratio on the printing plate surface, and to determine the density difference between the printed area and the non-printed area in a portion of the printing plate surface where the difference in density is quite small. The ratio can be measured with high accuracy.

Furthermore, by using a laser light source and an interference filter, it is possible to work in a relatively bright room (even in a normal work environment) without being affected by outside light. In addition, the interference filter has a spherical shape, so that the reflected light from the laser beam, which is the signal light, is transmitted uniformly over the entire surface of the printing plate. It is possible to further improve measurement accuracy.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention; FIG. 1 is a schematic explanatory diagram of the present device, FIG. 2 is a characteristic diagram of an interference filter,
FIG. 6 is an explanatory diagram of the interference filter. (1)...Printing plate (2)...Laser light source (31
... 11 meter lens (4) -... Laser beam +5) -°゛mirror 6)... Galvanometer
(7)...Photodetector (9)...cPU
QO) ... Light receiving section Old) ... Interference filter Patent applicant Toppan Printing Co., Ltd. Representative Aio Suzuki Goo +4\ (- Figure 1 Figure 2

Claims (1)

[Claims] In a device that measures the pattern surface at ratio of a printing plate by irradiating a laser beam onto a printing plate and receiving the amount of reflected light, a laser beam is placed in front of a light-receiving element that receives the amount of reflected light from the printing plate. A pattern area ratio measuring device characterized by being provided with a spherical interference filter that selectively transmits wavelengths of .