JPH0411804B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring the amount of dampening water on a non-image area of a printing plate surface of a lithographic printing press.

In planographic printing, excessive or insufficient amount of dampening water supplied onto the non-image area of the plate has a significant effect on the quality of printed matter. Furthermore, recently there has been a strong demand for higher printing speeds, and the speed of sheet-fed lithographic offset printing machines and the spread of lithographic offset rotary printing machines are rapidly progressing. In these high-speed printing machines, it is necessary to constantly control the amount of dampening water during printing, and if the amount of dampening water is too much or too little even for a short period of time, a large amount of defective printed matter will be produced. Conventionally, printing press operators have been able to determine the amount of dampening water by empirically determining the amount of dampening water from the amount of light reflected, gloss, etc. on the non-image areas of the plate, or by frequently inspecting printed matter. However, there is a great demand for automatic control of the amount of dampening water due to issues such as individual differences, judgment accuracy, and time from judgment to correction.

As a method for detecting the amount of dampening water on the non-printing area of the printing plate, a method is known in which the amount of light reflected from the dampening water is photoelectrically converted (Japanese Patent Publication No. 52-17761).
Due to problems with accuracy and reproducibility, it has not been widely used or put into practical use.

Generally, in order to accurately and quantitatively measure the amount of water contained on or in a sample, a method that utilizes the absorption of infrared rays by water is suitable. A filter wheel equipped with two types of filters, ie, a filter that transmits only infrared rays of wavelengths near which there is no absorption by water, is rotated (chipped) in the optical path of a continuous light beam emitted from a light source containing infrared rays. After the measurement sample is alternately irradiated with infrared rays of two wavelengths that have passed through the filter wheel, an infrared detector detects the intensity of the infrared rays of two wavelengths that are reflected from the sample, and The infrared intensity of one wavelength attenuated by absorption,
The principle of measuring the amount of water by determining the difference between the infrared intensity of the other wavelength that has not undergone absorption attenuation by water and converting this difference into the amount of water is well known.

Here, an interference filter is generally used as a filter that transmits infrared rays of a specific wavelength. In addition, the wavelength suitable for water absorption is
There are 1.2μ, 1.45μ, 1.93μ, and 2.95μ, but 1.93μ and 2.95μ are mainly used because it is more advantageous in terms of sensitivity and accuracy to use wavelengths with large absorption. Also,
As an infrared detector, a so-called photoconductive cell such as PbS or PbSe is used.

In addition, a measuring device that uses the above measurement principle to measure the amount of dampening water on the non-image area of a printing plate has been awarded a West German patent.
It is disclosed in No. 2412234. The outline of these measuring devices will be explained using FIGS. 1 and 2. A continuous beam of light emitted from a light source 1 is focused by a lens 2, and filtered by two types of filters 8 and 9 in a filter wheel 4 driven and rotated by a motor 3. The light rays reflected from the plate are guided by a light guide tube 5 having a material on the inner wall and illuminate the plate surface 6, and reach an infrared detector 7 via a light guide tube 5'. Converts infrared intensity into an electrical signal and outputs it. This electrical signal is further processed by an electrical circuit, and the amount of absorption and attenuation of infrared rays depending on the amount of water is converted into an amount of voltage. Here, using a previously determined calibration curve, that is, a curve that shows the relationship between the voltage and the moisture content obtained from several measurement samples with different known moisture contents, we calculate the moisture content on the plate surface. You can know.

As explained above, in these devices, it is necessary to chop a continuous beam using a filter wheel, and the rotation speed of the filter wheel is extremely large, and generally the rotation speed is 10,000 per minute in order to perform chopping at several 100 Hz. It becomes more than rotation. Therefore, in a high-speed printing machine where the printing plate moves at a high speed and the area to be measured is narrow in the printing direction, the area under measurement can be measured under the spot of the measurement light within an extremely short period of time during which the area to be measured passes through. It is necessary to irradiate infrared rays with two different wavelengths, and for this purpose,
Although it is necessary to increase the rotational speed of the filter wheel, a problem arises in terms of reliability of the device, that is, the durability of the high-speed rotating drive part of the filter wheel. In addition, when the installation space for the device is narrow, such as in recent printing presses that are assembled compactly, the measuring device needs to be small and lightweight, and for this purpose, it is necessary to The volume occupied by the filter wheel and drive is a hindrance.

In addition, the amount of dampening water on the non-image area of the printing plate, which is the object to be measured, is extremely small, and under normal printing conditions,
The amount of water vapor in the air existing in the light guide tube from the light source to the infrared detector and its fluctuations also affect the measurement results, causing problems with the accuracy and reproducibility of the measurement values ^. There are some drawbacks.

In order to eliminate the above problems and drawbacks, the inventors of the present invention,
In order to develop a measuring device that does not use a mechanical drive part inside the device, has high reliability, has excellent measurement accuracy and reproducibility, and is capable of measuring small areas to be measured even on high-speed printing machines. As a result of extensive research, we have arrived at the present invention. That is, the present invention irradiates infrared rays emitted from a light source onto a non-image area of a plate surface of a rotating lithographic printing machine, and uses the infrared rays reflected from the non-image area to detect specific wavelengths absorbed by dampening water. In this method, a xenon discharge tube is used as a light source, a synchronization signal from a rotating lithographic printing plate is extracted, and this signal is transferred to a xenon discharge tube. By using the discharge tube as a trigger signal to irradiate only the dampening water amount measurement point on the non-printing area of the plate surface of the lithographic printing machine, an instantaneous discharge is generated, and the infrared rays reflected from the non-printing area are transferred to water. One filter transmits infrared rays in a region that includes wavelengths that are absorbed by water, and the other filter transmits infrared rays in a region that includes wavelengths that are not absorbed by water. This is a method for measuring the amount of dampening water on a plate surface of a lithographic printing press, which is characterized by detecting the amount of attenuation of infrared rays of a specific wavelength in response to the received light. Furthermore, there is a signal generator for instantaneously discharging the xenon discharge tube at the point where the amount of dampening water is measured in the non-image area of the plate surface of the lithographic printing machine.
A light guide tube for irradiating the infrared rays from the xenon discharge tube to the measuring point of the amount of dampening water, a light guide tube for guiding the reflected infrared rays from the printing plate to the semi-transparent mirror, and a light guide tube for directing the reflected infrared rays guided by the light guide to the dampening water amount measurement point. A semi-transparent mirror for splitting, a filter for transmitting infrared rays in a region that includes wavelengths that are absorbed by water for one of the reflected light beams that are split into two by the semi-transparent mirror, and a filter for transmitting infrared rays in a region that includes wavelengths that are absorbed by water for the other. This is an apparatus for measuring the amount of dampening water on the plate surface of a lithographic printing press, which is composed of a filter for transmitting infrared rays in a region that includes wavelengths that are not detected, and a set of detectors for the infrared rays that have passed through each filter.

The xenon discharge tube used as a light source in the present invention momentarily flows electrical energy stored in a capacitor into the discharge tube in response to a trigger signal.
This is a flash type xenon discharge tube used for general stroboscopes that produce instantaneous discharge or for strobe photography. The flash time of this type of xenon discharge tube is extremely short, less than 1 μsec. For example, in a lithographic offset printing machine where the peripheral speed of the printing plate is 5 m/sec. When a xenon discharge tube with time is used as the light source of the dampening water amount measuring device of the present invention, the distance on the printing plate that moves in 1 μsec is only 0.005 mm, which is almost the same as the spot of the measurement light irradiated on the printing plate. Non-print areas of the same size can be measured. Therefore, there is no need to provide a special non-print area with a large area on the printing plate for measuring the amount of dampening water, and as long as the non-print area is the same size as the spot of the measurement light beam, it can be used to measure the amount of dampening water. It is possible to easily measure any location. In addition, in order to instantaneously discharge the xenon discharge tube so as to measure an arbitrary point, a mechanical This is accomplished by extracting a synchronizing signal using a conventional method such as an optical method or an electromagnetic method, and using this signal as a trigger signal for instantaneous discharge of the xenon discharge tube.
In addition, the emission spectrum distribution of a xenon discharge tube includes visible light and infrared light, and it responds to changes in electrical input.
The change in light intensity is almost uniform at any wavelength, and this property hardly changes during the life of the discharge tube. Furthermore, the xenon gas sealed in the discharge tube has properties suitable for use in the present invention, such as having a small heat capacity and a quick start-up during lighting.

In the present invention, the purpose of constantly filling the cylinder which guides the irradiated light from the light source to the printing plate and the reflected light from the printing plate to the infrared detection section with constant humidity, preferably low humidity gas, is as described above. The purpose is to eliminate the influence of the amount of water vapor in the air existing in the pipe and its fluctuations on the measured value of the amount of dampening water. For example, the amount of water vapor in the air at 25°C and 60% RH is approximately
0.14mg/The volume inside the light guide tube is 20cm ² (cross-sectional area 1
cm ² and length 20 cm), the amount of water vapor present in the light guide tube is 0.28 mg, which is compared to the amount of dampening water (0.2 mg/cm ² ) that normally exists on the non-image area as described above. It becomes impossible to ignore. In particular, if the humidity of the air guiding the light differs greatly between calculating the calibration curve and the actual measurement as described above, or if the humidity changes significantly during the measurement, it is difficult to determine the exact moisture content. Measurement becomes impossible. Note that the constant low humidity gas used in the present invention is generally used for industrial purposes and has a moisture content of several
Nitrogen gas at ppm is suitable from the viewpoint of handling, but there is no particular restriction as long as it is a constant humidity gas and can be stably and safely supplied. In addition, if the gas is supplied excessively into the light guide tube, the gas ejected from the end of the light guide will dry the dampening water on the non-image area of the printing plate, so the supply flow rate of the gas is A very small flow rate is sufficient to prevent humid air from entering the light guide tube, and dirt, dust, etc. floating in the air adheres to the inner wall of the light guide tube, causing infrared reflection on the inner wall. It is also possible to prevent the rate from changing.

The purpose of using an optical fiber cable as a light guide in the present invention is to prevent highly humid air from entering the light guide as described above, making it impossible to obtain an accurate measurement value of the amount of dampening water. Furthermore, by using two or more optical fibers, the measurement light beam can be transmitted from one xenon discharge tube to multiple measurement points on the printing plate using multiple optical fibers. After simultaneously guiding the reflected light from each measurement point to multiple infrared detection units using multiple optical fibers, the amount of dampening water on the non-printing areas of multiple locations on the printing plate is measured simultaneously. It becomes possible to do so. In addition, if measurements are repeated by moving these multiple optical fibers in a direction perpendicular to the printing direction, it is possible to repeat the measurement by moving multiple optical fibers in a direction perpendicular to the printing direction. The amount of dampening water in this direction on the printing plate can be easily measured in a short time. In addition, the amount of dampening water in each area on the printing plate corresponding to each divided area of the already known various dampening water amount divided supply adjustment mechanisms of printing machines is constantly measured, and each of these measurement data is applied to the area. It is also possible to continuously adjust the amount of dampening water supplied to each divided area of the adjustment mechanism by feedback to the adjustment mechanism, so that the amount of dampening water supplied to each area on the printing plate can always be controlled to an appropriate amount. In addition, as the optical fiber used in the present invention, quartz fiber with good infrared transmittance is suitable, but materials other than quartz may also be used to improve measurement sensitivity.
There is no particular restriction as long as it does not affect accuracy.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 3 is a sectional view schematically showing an apparatus showing one embodiment of the present invention. In FIG. 3, the light rays emitted by the instantaneous discharge of the xenon discharge tube 10 are condensed by a lens 11 and then guided to a printing plate 13 by a light guide tube 12. Note that a reflecting mirror may be used instead of the lens 11. The reflected light from the printing plate is passed through a light guide tube 12' to a semi-transparent mirror 15 of an infrared detection section.
guided by. Note that the insides of the light guide tubes 12 and 12' are filled with nitrogen gas supplied from a nitrogen gas cylinder 14. The reflected light beam is split into two by a semi-transparent mirror 15, and reaches infrared detectors 18, 19 through two types of interference filters 16, 17, respectively. As for the semi-transparent mirror 15, interference filters 16 and 17, and infrared detectors 18 and 19, conventionally known ones can be used as they are. The interference filters 16 and 17 can normally transmit light with a wavelength width of about 0.1μ, and although it varies depending on the conditions, for example, the interference filters include a region of 2.95μ as a wavelength that is absorbed by water. One that transmits infrared rays and one that transmits infrared rays that include a wavelength range of 2.5μ that is not absorbed by water are used.

FIG. 4 shows an example of an electric circuit when using the dampening water amount measuring device of the present invention for detecting the intensities of two types of infrared rays obtained by two infrared detectors as a difference in voltage amount. 1 is a schematic block diagram shown in FIG. Trigger signal generator 21 from the plate cylinder 20
The trigger signal is extracted from the timing logic circuit 22, and this circuit first generates a sampling signal and sends it to the peak hold circuit 2.
After resetting 3 and 24, the xenon discharge tube 10
A trigger signal for instantaneous discharge is sent to the xenon discharge tube 10, causing the xenon discharge tube 10 to flash. Thereafter, the infrared detectors 18 and 19 convert the intensity of the infrared rays incident on each into an electrical signal, and the electrical signal is transmitted to the amplifier circuits 25 and 26.
The peak hold circuits 23 and 24 are amplified and reset, and the maximum signals are held in these circuits.The maximum signals each enter a logarithm circuit 27, which outputs the difference between the two maximum signals.
The output is displayed on the display 28 and recorded on the pen recorder 29 at the same time.

Figure 5 shows how the device for measuring the amount of dampening water on the non-image area of a printing plate according to the present invention is attached to a lithographic offset printing machine, and the measurement position with respect to the plate cylinder is as shown in this figure. Although the location is preferred, the location is not particularly limited. For the dampening water, use the Mizumoto roll 41 and the calling roll 42 from the Mizufune 40.
The dampening water is supplied to the printing plate through a group of rollers 43, 44, and 45 attached to the printing cylinder 51 for supplying dampening water to the printing plate. The dampening water amount measuring device 46 measures the amount of dampening water on the non-image area of the printing plate immediately after the dampening water is supplied. The printing plate is further inked by roll group 4.
Ink is supplied by 7, 48, 49, and 50.

FIG. 6 explains another embodiment of the present invention. The light rays emitted by the flashing of the xenon discharge tube 10 are condensed by the lens 11 and guided by the optical fiber cable 30 to reach the printing plate 13. The reflected light from the printing plate is guided by an optical fiber cable 30', reaches a semi-transparent mirror 15 of the infrared detection section, and is divided into two directions by the semi-transparent mirror, and two types of interference filters 16, 17 are applied to each direction. through the infrared detector 18,1
Reach 9. Hereinafter, using the electrical circuit explained in FIG. 4, an electrical output corresponding to the amount of dampening water is obtained, and the amount of dampening water is measured. Although a semi-transparent mirror 15 is used in FIGS. 3 and 6 to divide the reflected infrared rays into two, conventionally known means such as optical fibers may be used instead of the semi-transparent mirror.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view schematically showing a device for measuring the amount of dampening water on the non-image area of a plate surface of a conventional lithographic printing machine, and FIG. FIG. 3 is a plan view of the wheel. FIG. 3 is a sectional view illustrating an embodiment of a device for measuring the amount of dampening water on a non-image area of a plate surface of a lithographic printing machine according to the present invention, and FIG. This is an example of a block diagram of an electric circuit section of a device for measuring the amount of dampening water on a non-image area of a printing plate. Fifth
The figure is a cross-sectional view illustrating an example of a part where a dampening water amount measuring device on a non-image area of a printing plate according to the present invention is attached to a printing machine. FIG. 6 is a sectional view showing another embodiment of the present invention. The main symbols in the drawings are 10...xenon discharge tube, 12, 12'... light guide tube, 15... semi-transparent mirror,
16, 17... filter, 18, 19... infrared detector, 46... device for measuring the amount of dampening water on the plate surface of a lithographic printing machine, respectively.

Claims (1)

[Claims] 1. Infrared rays emitted from a light source are irradiated onto the non-printing area of the plate surface of a rotating lithographic printing machine, and the infrared rays reflected from the non-printing area attenuate the infrared rays of a specific wavelength that have been absorbed by the fountain solution. In the method of measuring the amount of dampening water in the non-image area, a xenon discharge tube is used as a light source, a synchronizing signal is extracted from the plate surface of a rotating lithographic printing machine, and this signal is transmitted to the lithographic printing plate of the xenon discharge tube. By using it as a trigger signal to irradiate only the dampening water amount measurement point in the non-printing area of the printing press plate, an instantaneous discharge is generated, and one side of the infrared rays reflected from the non-printing area is absorbed by water. A filter that transmits infrared rays in a range that includes wavelengths and a filter that transmits infrared rays in a range that includes wavelengths that are not absorbed by water are passed through each filter. A method for measuring the amount of dampening water on the plate surface of a lithographic printing press, characterized by detecting the amount of attenuation of infrared rays of wavelength.