JPH0560521A - Water screen sensor for printing plate of printer - Google Patents

Abstract

PURPOSE:To enable high-speed sampling to be performed for a zone having a small measurement area such as a water scale division by using a semiconductor laser beam as an illuminant. CONSTITUTION:Linearly polarized light 2 from a semiconductor laser 1 is converted to circularly polarized light 21 via a collimator 3 and a 1/4 wavelength plate 4. The circularly polarized light 21 passes a beam displacing prism 22, and becomes parallel laser beams 26 and 27 with optical axes relatively displaced for P- and S-polarized light. The laser beam 26 and 27 collides with the surface of a printing plate 6, and the quantity of regular reflected light for both P- and S-waves is branched into a half with a half-mirror 23, and separated into the light receiving side of the P-polarized light wave 26 and the light receiving side of the S-polarized light wave 27. Light receiving constitution for the P-wave interrupts the S-wave and, therefore, the voltage signal 31 of a P-wave component is obtained by a receiver lens 24 and a laser detecting element 25. Light receiving constitution for the S-wave also interrupts the P-wave and permit the passage of only the S-wave. The voltage signal 32 of a S-wave component is obtained by a receiver lens 7 and a laser detecting element 8. Also, the voltage signals 31 and 32 are calculated from the voltage signals of the P- and S-waves by a signal processor 9, thereby calculating the thickness of a water screen on the plate 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water film sensor applied to printing machines, iron making machines and the like.

[0002]

2. Description of the Related Art A conventional apparatus will be described with reference to FIG. Printing machines (ink / water roller groups 10, 11, 12 etc. and plates
With various cylinders), the print quality depends on the state of the water film on the plate surface 6. FIG. 8 is a block diagram of an apparatus for detecting this water. The infrared light emitted from the infrared light emitter 15 is condensed by the infrared condenser lens 16, and the interference filter 3 on the chopper 17 is collected.
The light having the reference wavelength and the light having the absorption wavelength of water are alternately selected. This light is guided by the optical conduit 18, and the light is absorbed by the water on the plate 6, and then the transmitted / reflected light is converted into a signal by the receiver lens 19 and the detection element 20. The position detector 31 of the interference filters 33 and 34 recognizes the signal of the element 20. Reference numeral 9 denotes a signal processor that takes in the signal from the detection element 20 and the signal from the position detector 31 and converts it into a water film thickness.

[0003]

The problem of print quality due to the state of the water film on the plate surface is as follows: Phenomenon 1 Water grain: A number of streaks (change in density) of 1.5 mm or less in the width direction occur in the flow direction. Phenomenon 2 of phenomenon 2: A part without a pattern (non-image area) is stained in a wide range. Etc. In the water film measurement of Phenomenon 2, even if the measurement area is large and the chopper speed is low, it is possible to measure by averaging the range of the dirt, and thus it is possible to measure with the conventional water film meter. But,
The water film measurement of phenomenon 1 has a small measurement area and requires a high-speed chopper.

With respect to the above-mentioned print quality trouble, the above-mentioned prior art has the following problems. (1) Since the infrared luminous body is not a point light source, it cannot be narrowed down to φ1.5 mm or less without reducing the light quantity. (2) If the measurement area becomes smaller, it is necessary to sample with a high-speed chopper. But not cope with the conventional mechanical chopper (0~100KH _Z).

It is an object of the present invention to provide a water film sensor for a printing plate, which is capable of performing high speed sampling on a region having a small measurement area such as a water drop.

[0006]

[Means for Solving the Problems] The water drop phenomenon, which is one of the problems in print quality, occurs because the ink transfer rate changes at the portion where the water pattern on the plate surface is rapid. A number of streaks (change in concentration) of 1.5 mm or less occur in the width direction in the flow direction. As a means for measuring this water grain, (1) a semiconductor laser that is effective in narrowing down is adopted in order to make a measurement area capable of measuring a water pattern change.
(2) P-wave and S-wave analog signals are used in order to obtain measurement data that is not delayed by changes in printing speed and water pattern. (3) Polarized waves (P-wave, S-wave), which is a property of laser, and an angle (Brewster angle) at which a special phenomenon occurs are used for measuring a water film.

[0007]

By using the semiconductor laser light as the light source, it is possible to cope with the measurement of the water film in a narrow region such as a water grain. High-speed capture of shooting data (0-
20MH _Z) perform. Phenomenon caused by Brewster's angle of water (directions of P and S polarized waves at water interface are different), that is, light reflected on the surface of water (S wave) and water surface attached to the plate surface The water film is measured by utilizing the property of the transmitted light (P wave).

[0008]

【Example】

(First Embodiment) A first embodiment of the present invention will be described with reference to FIGS. In a printing machine composed of the ink / water roller groups 10, 11, 12 and the like and the plate / various cylinders as shown in FIG. 1, the print quality (grain of water) depends on the water film state on the plate surface 6. FIG. 1 shows a structure for detecting a water film pattern on the printing plate 6. The water film detecting member is composed of a laser projecting side and a laser receiving side. The laser projecting side and the laser receiving side are installed so that the projected light ray axis and the received light ray axis face and intersect at the Brewster's angle 5 of water on the plane perpendicular to the plate surface 6. The member on the laser projecting side uses the semiconductor laser 1 as the semiconductor laser driver 28.
And linearly polarized light 2 is projected. The linearly polarized light 2 becomes parallel light by the collimator 3, and is converted into circularly polarized light 21 when passing through the quarter wavelength plate 4. Further, when the circularly polarized light 21 passes through the beam dissipating prism 22, the circularly polarized light 21 is decomposed into a P polarized light wave 26 and an S polarized light wave 27, and at the same time, parallel laser light 26, 27 in which the optical axes of the P and S polarized light waves are relatively deviated. Yes (laser light = S polarized wave + P polarized wave).

The two laser beams of the P-polarized wave 26 and the S-polarized wave 27 hit the plate surface 6, and the specularly reflected light (P, S waves) on the plate surface 6 has a quantity of light at the half mirror 23 for both P and S waves. Divided in half, the receiving side of P-polarized wave 26 and S-polarized wave 2
The structure is divided into the light receiving side of 7. Since the P-wave receiving structure blocks the S-wave, a polarizer 30 is provided to pass only the P-wave.
A voltage signal 31 of the P wave component is obtained by the receiver lens 24 and the laser detection element 25. Similarly, the S-wave light receiving structure is provided with a polarizer 29 that blocks the P-wave and allows only the S-wave to pass therethrough, and the receiver lens 7 and the laser detection element 8 obtain the voltage signal 32 of the S-wave component. The voltage signals 31 and 32 are calculated by the signal processor 9 from the P-wave and S-wave voltage signals, and the water film thickness on the printing plate as shown in FIG. 2 is measured.

In the water film sensor for a plate according to the present invention, a phenomenon caused by Brewster's angle of water (the traveling directions of P and S polarized waves are different at the interface of water), that is, the light reflected on the surface of the water adhering to the plate ( The water film is measured by utilizing the property of the S wave) and the light (P wave) that is transmitted even on the surface of the water adhering to the plate surface, and the phenomenon at the Brewster angle of water is shown in FIG.

FIG. 4 shows the S-wave incident angle and reflectance, and FIG. 5 shows the P-wave incident angle reflectance. Fig. 2 shows the detection signals of the laser detection elements 8 and 25 and the water film thickness (difference in the amount of light received between S and P waves).
Shows the relationship. Here, the light transmitted on the surface of the water (P wave)
Is diffused due to the roughness of the plate surface, so the detected light amount is small. On the other hand, the light (S wave) reflected on the surface of the water is specularly reflected on the surface of the water, so the detected light amount is large. The reason for subtracting the received light amounts of the S wave and P wave is to cancel the plate surface roughness of the water film measuring unit.

The laser beam diameter projected on the plate surface can be narrowed down even on the order of several microns, and in this embodiment, φ1.0 was used. Further, although the conventional mechanical chopper in the range of 0H _Z ~100H _Z, the invention 0H _Z
It may be used in a range of ~20MH _Z, the water film sensor of this Example was applied by 30KH _Z. (Second Embodiment) A second embodiment of the present invention will be described with reference to FIGS.

In the second embodiment, the P-polarized wave and the S-polarized wave are decomposed on the light receiving side, which has been performed on the light projecting side in the first embodiment, and therefore the beam in the first embodiment is used. Polarizing beam splitter (PBS) 23 is used instead of display mirror 22 instead of Haar mirror 23.
Install a. The member on the laser projecting side is the semiconductor laser 1
Is driven by the semiconductor laser driver 28 to project linearly polarized light. The linearly polarized light 2 is collimated by the collimator 3 and is converted into a circularly polarized wave 21 when passing through the quarter wavelength plate 4. The circularly polarized wave 21 hits the plate surface 6, and the regularly reflected light on the plate surface 6 is split into a P polarized wave 26 and an S polarized wave 27 by a polarization beam splitter (PBS) 23a. The branched P wave is condensed by the condenser lens 30a, and the laser detection element 25 obtains the voltage signal 31 of the P wave component. Similarly, the S wave is also condensed by the condenser lens 29a, and the laser detection element 8 obtains the voltage signal 32 of the S wave component. The voltage signals 31 and 32 are calculated by the signal processor 9 from the P-wave and S-wave voltage signals to measure the water film thickness on the printing plate. In addition to the semiconductor laser, an LED may be used as the light source for measuring the water film thickness.

[0014]

EFFECTS OF THE INVENTION A water film sensor for a printing press plate according to the present invention includes (1) a semiconductor laser that emits linearly polarized light, a collimator that converts the linearly polarized light into parallel light, and a wavelength that converts the parallel light into circularly polarized light. A laser light projecting means comprising a plate and a prism for decomposing the circularly polarized light into P-polarized light and S-polarized light;
A half mirror that splits a polarized wave and an S polarized wave, a polarizer that blocks the S polarized wave of one of the split P polarized waves and an S polarized wave, and a passed P polarized wave is received to generate a voltage signal. P polarization wave detection means, a polarizer that blocks the P polarization wave of the other branched P polarization wave and the S polarization wave, and an S polarization wave detection that receives the passed S polarization wave and generates a voltage signal. By including means and means for calculating the water film thickness from the voltage signals of the P-polarized wave and the S-polarized wave, (2) a semiconductor laser which emits linearly polarized light, and the linearly polarized light is made parallel light. Collimator, convert parallel light into circularly polarized light 1
/ 4 wavelength plate laser light projecting means, a polarizing beam splitter that splits the specularly reflected light from the surface of the water film on the plate surface into P-polarized waves and S-polarized waves, and splits the P-polarized waves into voltage signals. A P-polarized wave detecting means for generating, an S-polarized wave detecting means for receiving an S-polarized wave and generating a voltage signal, and a means for calculating a water film thickness based on a difference between voltage signals of the P-polarized wave and the S-polarized wave. By having the following, the following effects can be obtained. (1) The measurement area of the water film can be reduced. (2) The sampling speed can be increased. (3) A semiconductor laser is cheaper and smaller than a mechanical chopper, and the entire device can be made smaller and cheaper. (4) It is also possible to measure a fine water film pattern at a halftone dot level (tens of μm).

[Brief description of drawings]

FIG. 1 is a configuration diagram of a first embodiment of the present invention.

FIG. 2 is a relationship diagram between a detection signal and a water film thickness of a non-image area of a printing plate in the first embodiment.

FIG. 3 is a diagram showing a phenomenon at a Brewster angle of water.

FIG. 4 is a relationship diagram of incident light and polarization energy ratio under the condition of the reflectance of S-polarized light.

FIG. 5 is a relationship diagram between incident light and polarization energy ratio under the condition of the reflectance of P-polarized light.

FIG. 6 is a configuration diagram of a second embodiment of the present invention.

FIG. 7 is a relationship diagram between a detection signal and a water film thickness of a non-image area of a printing plate in the second embodiment.

FIG. 8 is a configuration diagram of a conventional water film meter by an infrared absorption method.

[Explanation of symbols]

 1 semiconductor laser 3 collimator 4 1/4 wavelength plate 6 version 7 receiver lens (for S polarized wave) 8 laser detection element (for S polarized wave) 9 signal processor 22 beam displaying prism 23 half mirror 24 receiver lens (P Polarized wave) 25 Laser detector (for P polarized wave) 29 Polarizer 30 Polarizer

Claims (2)

[Claims] 1. A semiconductor laser for emitting linearly polarized light, a collimator for converting the linearly polarized light into parallel light, a quarter-wave plate for converting the parallel light into circularly polarized light, and a P-polarized wave for the circularly polarized light. And a laser light projecting means composed of a prism for decomposing into S-polarized waves, a half mirror for branching the P-polarized waves and S-polarized waves, and an S-polarized wave of one of the branched P-polarized waves and S-polarized waves. A polarizer for blocking, a P-polarized wave detecting means for receiving the P-polarized wave that has passed and generating a voltage signal, and a polarizer for blocking the P-polarized wave of the other branched P-polarized wave and S-polarized wave. , S-polarized wave detection means for receiving the passed S-polarized wave and generating a voltage signal, and means for calculating the water film thickness from the voltage signals of the P-polarized wave and the S-polarized wave Water film sensor for machine plate. 2. A semiconductor laser that emits linearly polarized light, a collimator that converts the linearly polarized light into parallel light, and a laser light projecting means that includes a quarter-wave plate that converts the parallel light into circularly polarized light. A polarization beam splitter that decomposes the specularly reflected light on the surface of the water film on the plate surface into P-polarized waves and S-polarized waves and splits it, P-polarized wave detection means that receives the P-polarized waves and generates a voltage signal, and S-polarized waves S-polarized wave detection means for receiving light and generating a voltage signal,
A water film sensor for a printing plate surface, comprising means for calculating a water film thickness based on a difference between voltage signals of P-polarized wave and S-polarized wave.