JPH0235666B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a method for measuring dampening water in a printing press, and in particular to a method for controlling the amount of dampening water applied to a plate surface attached to a plate cylinder of an offset printing machine. The present invention relates to a method for optically measuring the amount of dampening water on a printing plate.

[Prior art]

Conventionally, methods for measuring the amount of dampening water on the plate surface of a printing press include measuring the amount of infrared absorption of dampening water on the plate surface, measuring the humidity near the plate surface, and measuring the water film on the water supply roller. Although there are methods for measuring the electrical resistance of In addition to the above, when a parallel beam of light is incident on a thin film of water, the characteristics of the reflected light intensity with respect to the reflection angle depend on the thickness of the thin film, as described in Japanese Patent Application Laid-Open No. 47-4338. There is a known method that takes advantage of this change in dampening water by making light incident on the printing plate and measuring the reflected light from the printing plate.

[Problem to be solved by the invention]

However, in the method of measuring the reflected light from the printing plate, the light-receiving element was placed at a position at an angle of 60° to 80°, which is smaller than the specular reflection angle position, and the measurement was performed using diffused light. They had various problems such as weak directivity and large measurement errors.

[Means for solving the above problems]

This invention makes a laser beam emitted from a laser generator parallel to the plate surface of a printing press, and measures the intensity of the reflected light from the plate surface through an interference filter to measure the amount of dampening water on the plate surface. A method for measuring dampening water in a printing press, in which the intensity of specularly reflected light is detected by a first receiver that receives specularly reflected light from the printing plate, and a second receiver that receives diffused light from the printing plate. The method is characterized in that the intensity of the diffused light is detected by a light receiver, and the amount of dampening water on the printing plate is measured by dividing the intensity of the specularly reflected light by the intensity of the diffused light.

〔Example〕

Next, before explaining the configuration of the present invention, the relationship between the amount of water on the printing plate and the directivity of reflected light will be explained.

Figure 1 shows the relationship between the amount of water and the directionality of the intensity of reflected light. The broken line a in the figure shows the reflection when there is a lot of water when light i is incident on plate h at an incident angle θ. The broken line b shows the directionality of reflected light when there is a medium amount of water, and the broken line c shows the directionality of reflected light when there is little water. Arrow A indicates the direction of the specularly reflected light, and arrows B and C indicate the direction of the specularly reflected light.
This shows the direction of the two diffused lights. As can be seen from FIG. 1, when the amount of water is small, the reflected light from the printing plate is a strong diffused light, and as the amount of water increases, it becomes weaker and approaches specular reflection.

Figure 2 is a graph showing the relationship between the intensity of reflected light in the directions of arrows A, B, and C in Figure 1 (receiver output) and the water source roller rotation speed (amount of water supplied to the plate). . As can be seen from FIG. 2, the intensity of the reflected light in the A direction (specular reflected light) is saturated when the amount of water on the plate is large.

The reflected light in the B direction is diffused light at an angle close to specular reflection, and initially increases as the amount of water on the printing plate increases, reaches a peak, and then decreases. The conventional method described above corresponds to this case. In this case, the amount of light received relative to the amount of water on the plate becomes a bivalent function.

The reflected light in the C direction is diffused light at an angle away from specular reflection, and decreases as the amount of water on the plate increases.

From the above, it is considered that in order to increase the sensitivity of the measuring device and reduce measurement errors, it is better to measure the intensity of specularly reflected light. Furthermore, the relationship among the angle of incidence, unevenness of the plate, and measurement range can be considered as follows.

Figure 3 shows what happens when parallel light is applied to one of the grains on the plate. R is a light-receiving element placed at a position to receive specularly reflected light from the printing plate.

Among the incident lights, the light received by R is light δ that hits the crests of the grain, and lights α, β, and γ that hit the valleys of the water surface. The surface of the water has a shape similar to that of a sphere due to surface tension, and while the surface is relatively smooth, the ridges of grain are prominent. Therefore, it is thought that most of the light received comes from the water surface in the valley. The light reflected and received by this valley portion is the light incident on the range X in FIG. The size of X increases as the radius of curvature of the water surface increases. For this reason, it is thought that when the amount of dampening water on the printing plate increases, the unevenness of the water surface becomes smaller, the radius of curvature of the water surface becomes larger, X increases, and the amount of light received increases. From the above estimation, it is considered that if the incident angle θ is made too large, the unevenness of the plate blocks the light α and γ hitting the edge of the area X, and the measurement range becomes narrower. In addition, the energy reflectance on the water surface increases as the incident angle increases, and since a large amount of received light energy can be obtained, the incident angle θ is preferably set appropriately large within a range that is not affected by the unevenness of the plate.

The dampening water measuring device used to carry out the present invention is composed of a sensor section and a processing section, and the sensor section is a section that measures the reflection directivity of the printing plate, and includes a light source and a light receiver. It consists of the sensor body. For example, a laser device that can provide high-intensity, nearly monochromatic light is suitable as the light source, and parallel light rays are made to be incident on the printing plate. In addition, the receiver is
It consists of a photoelectric conversion element such as a silicon photodiode and a photoelectric conversion circuit, and there is a first receiver for receiving specularly reflected light and a second receiver for receiving diffused light. This was added to compensate for the effects of output fluctuations.

The processing section is a section that calculates a value corresponding to the amount of water on the printing plate based on the signal from the sensor section.

The present invention will be explained below based on the embodiments shown in the drawings of FIGS. 4 and 5.

In Fig. 4, the sensor section will be explained first.
The emitted light from the helium-neon laser device 1 with an output of 0.5 mW passes through the optical fiber 2 and is reciprocated in the axial direction above the outer peripheral surface of the plate cylinder 10 by a drive device (not shown). The light is guided to a collimator 3 attached to the plate, and is made incident on the plate at an incident angle θ of about 75 degrees with respect to the normal to the plate.

The sensor 29 is equipped with light receivers 4 and 4', which detect the light reflected in the direction of the specularly reflected light θ and the direction of the diffused light with a reflection angle of 0 degrees, respectively. Receiver 4,
4' is the laser wavelength of approximately 633mm, as shown in Figure 5.
Interference filter that passes only nearby light (for example, IFW type interference filter manufactured by Nippon Vacuum Optical Co., Ltd.) 5 and diameter 20
The light source section 9, 9' consists of a silicon photodiode 6 of mm and a MOS FET with a small input bias current.
Photoelectric conversion circuit 8, 8' using operational amplifier 7 as input
It consists of

In the synchronization signal generation section, a detection signal is inputted to a comparator 13 from an encoder 11 and a detection position register 12 attached to the plate cylinder 10, and a synchronization signal is output from the comparator 13 to a processing section 14. 15 is a detection position setting switch.

The processing unit 14 consists of a division circuit 16 and a sample-and-hold circuit 17, and the division circuit 16 calculates (specular reflection light intensity)/(diffuse light intensity), and samples the result of division according to the synchronization signal. It is something that has become popular. The reason for calculating and sampling the ratio of the specularly reflected light intensity and the diffused light intensity in this way is that fluctuations in this ratio occur only due to changes in the amount of water on the printing plate, and changes in the reflected light intensity due to changes in the light intensity of the light source. This is because the fluctuations are canceled out and there is no influence from external disturbances.

FIG. 6 shows an example of the configuration of a dampening water control system using the dampening water measuring device shown in FIG.
22 is a rubber cylinder, 23 is a water roller, and 24 is an ink roller. The dampening water 21 is supplied from the water source roller 25 to the water supply rollers 26, 27 and the water roller 2.
The water source roller 25 is rotated by a water supply motor 28.

The sensor 29 is connected to the plate cylinder 10 as shown in FIG.
It is designed to be reciprocated along the axis of the

The processing unit 14 is connected to a position detection encoder 11 attached to the plate cylinder 10 via a synchronization signal generation unit 18.
The sensor 9 receives signals from the sensor 9, and outputs measured values to the differential amplifier 30 and the display 37.

The differential amplifier 30 compares the set value inputted from the water volume set value output circuit 31 and the measured value inputted from the processing unit 14, and outputs the difference between the set value and the measured value to the motor rotation speed calculation circuit 32. . Based on the input from the differential amplifier 30, the motor rotation speed calculation circuit 32 controls the water supply motor 2 via the servo amplifier 33.
8 to operate the motor 28. 34 is a tachometer generator for speed feedback.

When measuring the amount of water on the plate, the sensor 29
is moved along the rail 40 in FIG. 7 to face the non-image area of the printing plate on the plate cylinder 10. Once the measurement position in the non-print area is determined, the sensor 29 is fixed, and the detection position storage switch 15 stores the detection position in the vertical direction of the plate in the detection position register 12. During the measurement operation, the comparator 13 compares the output of the encoder 11, that is, the value of the plate cylinder position detection position register 12, and when the two match, that is, when the plate has reached the detection position, a synchronization signal is sent to the processing unit 14. sample and hold 17.
The sample and hold 17 holds the output of the division circuit until the next synchronization signal arrives.

The amount of water on the printing plate is adjusted by controlling the rotational speed of the water supply motor 28 based on the measured value of the amount of water and a predefined reference value. Note that the amount of water is measured and controlled at all times during both actual printing and test printing. In the above embodiment, it is possible to improve the S/N ratio by inserting a filter 5 with break length selectivity into the light receiver 4, and furthermore, the light receiving portion is sufficiently larger than the diameter of the incident light. Therefore, even if the optical axis is relatively misaligned on the light receiving section, a certain degree of tolerance can be given to the positional relationship between the plate and the sensor.

Further, if sufficient parallel light can be obtained from the laser device 1, the collimator 3 can be omitted.

〔Effect of the invention〕

As described above, the present invention makes the laser beam emitted from the laser generator parallel to the plate surface of the printing press, and measures the intensity of the reflected light from the plate surface through an interference filter. A method of measuring dampening water in a printing press that measures the amount of dampening water, in which the intensity of the specularly reflected light is detected by a first receiver that receives specularly reflected light from the printing plate, and then the intensity of the specularly reflected light from the printing plate is detected. The intensity of the diffused light is detected by the second light receiver that receives the light, and the amount of dampening water on the printing plate is measured by dividing the intensity of the specularly reflected light by the intensity of the diffused light, which widens the measurement range. In addition, the measurement error can be reduced, and since the result of division is sampled, the influence of disturbance can be prevented. Furthermore, in the above process, a laser beam as a monochromatic light with higher brightness than white light is used, and since this laser beam is made parallel to the plate in order to increase the amount of light irradiated per unit area of the printing plate as much as possible, the first and second light receiving This has the excellent effect of significantly increasing the sensitivity of the detected value by the instrument.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram showing the relationship between the amount of water on the plate and the directivity of reflected light, Figure 2 is an explanatory diagram showing the relationship between the amount of water and the amount of reflected light received, and Figure 3 is an explanatory diagram showing the relationship between the amount of water on the plate and the directionality of reflected light. 4 is a schematic diagram showing an embodiment of the present invention, FIG. 5 is a circuit diagram of a light receiver of the same embodiment, and FIG. 6 is a diagram showing a dampening water measuring device according to the present invention. A block diagram showing the dampening water control system, and FIG. 7 is a detailed block diagram of the same. 1... Laser device, 4, 4'... Light receiver, 10
... plate cylinder, 14 ... processing section, 16 ... division circuit,
17... Sample and hold circuit, 25...
Mizumoto roller, 29...sensor.

Claims (1)

[Claims] 1. A laser beam emitted from a laser generator is made parallel to the plate surface of a printing press, and the intensity of the reflected light from the plate surface is measured through an interference filter, thereby determining the moisture content on the plate surface. This is a method for measuring the amount of dampening water in a printing press, in which the intensity of the specularly reflected light is detected by a first receiver that receives the specularly reflected light from the printing plate, and then the diffused light from the printing plate is detected. A printing machine characterized by measuring the amount of dampening water on the printing plate by detecting the intensity of the diffused light using a second light receiver that receives the light, and dividing the intensity of the specularly reflected light by the intensity of the diffused light. How to measure dampening water.