JPH0563310B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method for detecting the amount of dampening water on a plate surface in an offset printing press and a device for displaying the detected amount of water.

[Background technology and its problems]

Offset printing requires accurate control of the amount of dampening water on the plate surface. This control was carried out by an operator visually observing the plate surface and determining the amount of light reflected from the plate surface by the dampening water, or by visually observing the printed material to determine whether the amount of dampening water was appropriate. .

However, in such a method that depends on the operator, the influence of individual differences among operators directly appears, and the reproducibility is poor, and the amount of dampening water cannot be managed by automatic control.

Therefore, there is a need for a method for detecting the amount of dampening water on a plate surface without relying on an operator, and methods that detect the amount of reflected light from the water surface and methods that utilize infrared absorption have been proposed.

However, when implementing these methods, it is necessary to install the detection means near the plate cylinder of the printing press, so there are major restrictions such as installation space and measures against ink mist stains. As a result, environmental resistance,
It has not been put into practical use due to workability, size, versatility, price, etc.

In particular, regarding environmental resistance, optical sensors are constantly exposed to dust floating in the air and ink mist scattered from inking rollers, and the sensor's output can be reduced by half in about two weeks. Therefore, how to prevent contamination of the sensor and how to correct the sensor gain is the key to putting the dampening water amount detection device into practical use.

[Purpose of the invention]

The present invention has been made in consideration of the above points, and
It is an object of the present invention to provide a method and a device that can accurately detect the amount of dampening water on a printing plate even when used in a bad environment where the output of an optical sensor is reduced.

[Summary of the invention]

In order to achieve this objective, in the present invention, in the light reflected from the printing plate when light is projected onto the printing plate at a predetermined angle,
The present invention provides a method and apparatus for detecting the amount of dampening water by detecting specularly reflected light and diffusely reflected light separately, and correcting the amount of specularly reflected light using the amount of diffusely reflected light as a reference value.

〔Example〕

An embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows the principle of detecting the amount of dampening water on a printing plate according to the present invention. In other words, the plate surface 2 when light is irradiated from the projector 1 onto the plate surface 2 at a projection angle a.
Of the reflected light from the plate, the first light receiver 3 detects the specularly reflected light that appears at the acceptance angle a' set equal to the projection angle a, and the second light receiver 4 detects the diffusely reflected light in the direction perpendicular to the plate surface 2. To detect.

Here, the projection angle a (=reception angle a') can be chosen arbitrarily, but if practical issues are ignored, from Fresnel's equation and experimental results, the larger the projection and reception angle, the greater the amount of reflected light and the better the detection performance. This has been confirmed. Furthermore, the wavelength of the light beam used for light transmission and reception can be arbitrarily selected.

Figure 2 shows the output characteristics of the first light receiver 3 and the second light receiver 4 in the configuration shown in Figure 1, with the amount of dampening water on the horizontal axis and the output of the light receiver on the vertical axis. There is. 3A is the output curve of the first light receiver 3, which changes in proportion to the amount of dampening water on the plate surface, whereas the output curve 4A of the second light receiver 4 shows a constant value almost regardless of the amount of dampening water on the plate surface. . Although only the relationship between the amount of dampening water on the plate surface and the outputs of both light receivers is shown here, the outputs of both light receivers change in response to changes in the reflected light from the plate surface 2. Contamination caused by ink mist, dust, etc. is the cause of this change, that is, disturbance.
There are changes in the light source over time, misalignment of the sensor, etc., and these appear in the same way for both light receivers.

Therefore, by correcting the output of the first light receiver with the output of the second light receiver, the amount of dampening water on the printing plate can be accurately measured.

The output of the first receiver before receiving any disturbance is A, the output of the second receiver is B, the output of the first receiver during disturbance is A', the output of the second receiver is B', If the rates of change in the outputs of the first and second light receivers due to disturbance are respectively α and β, the outputs at the time of disturbance are A'=αA B'=βB, respectively. Here, assuming that the influence of the disturbance on the first and second receivers is equal, α=β
Then, B′=αB. Therefore, A=(B/B')A', and the influence of disturbance can be canceled out.

Further, the degree of influence of the disturbance on each light receiver is different, and in the case of α≠β, the influence of the disturbance can be canceled by calculating the relationship between the two in advance and correcting it.

To correct this disturbance, the relationship between α and β is α=f
(β), the output of each receiver at the time of disturbance is A'=f(β)A, B'=βB, and the output of the first receiver after canceling the disturbance is A=A'/f (B'/B).

Now, regarding the specific method of displaying the amount of water, in this apparatus, the amount of water is expressed as a relative value, with the plate dry state being 0% and the saturated output in the water excess state being 100%.
The reference states are V _nio and V _nax in Fig. 2, respectively.
It is shown in

In this device, even when there is no water, there is some reflection on the plate surface and the output does not become 0. Therefore, if the detected value calibrated using the above method is V _e , the amount of water is finally given by the relative value of the following equation. It will be done.

V _e −V _nio /V _nax −V _nio Figure 3 a, b, and c show the first and second receivers with dampening water attached to the plate surface in order to detect non-image areas on the plate surface. This is an example showing the state of scanning when a printing plate is scanned by a light receiver and the output of each light receiver. In this example, as shown in FIG. Scanning is performed in the XX direction until The outputs of the respective receivers thus obtained are as shown in figures b and c, and the output waveforms of the second receiver, which detects diffusely reflected light, are shown in figure b, and those of the first receiver, which detects specularly reflected light, are as shown in figures b and c. The output waveform of the device is shown in Figure c.

And the output 9 of the second photoreceiver shown in FIG.
shows a decrease in output according to the pattern area of the plate without being affected by the amount of water on the plate. Therefore, the maximum output V _nax is always generated for the non-print area where there is no pattern.

Therefore, an appropriate tolerance range is set for the maximum output value V _nax of the second receiver per one rotation of the plate cylinder, and if the second receiver produces an output within this tolerance range, it is considered a non-printing area. If the water amount signal 10 of the first light receiver is sampled only at the position corresponding to the image area, the water amount measurement signal will be obtained only for the non-image area.

Further, the measurement of the printing speed necessary to determine the sampling interval can be obtained by performing calculations using the vice output of the second light receiver.

FIG. 4 shows the external configuration of a device according to the present invention installed in an offset sheet-fed printing press 11. The device according to the invention has a sensor 12 and a display section 13, which are connected to a printing press 11, respectively.
installed at a designated location. That is, the sensor 12 is installed near the plate cylinder 14 in each unit of the printing press. The plate cylinder 14 is supplied with ink from an inking roller 15 and dampening water from a dampening water supply device 16, and cooperates with a blanket cylinder 17 and an impression cylinder 18 to perform printing. The display unit 13 displays printing colors (B,
A dampening water amount signal is given from the printing unit for each of C, M, and Y), and these signals are displayed all at once.

Note that the non-printing area may be recognized in the following manner. That is, a rotary encoder is provided in the plate cylinder drive system, and the position of the non-printing portion is determined by comparing the output of the rotary encoder with data inputted in advance by the operator.

FIG. 5 is a flowchart showing an example of the operation performed by the display unit 13 of FIG. 4, and this will be explained. During the first rotation of the plate cylinder, the light amount data of the first light receiver and the second light receiver in the sensor 12 are taken into the memory at regular intervals on the plate surface (S1).
In the second rotation of the plate cylinder, first, among the data in the memory, the data of the second light receiver that is not affected by the amount of water is read out, the peak data is searched (S2), and the data with a width of -a from this value is averaged. (S3),
Let it be x. Next, among the data of the first light receiver that changes depending on the amount of water, the data at the same location where the data was used to obtain x is read out, and the average value thereof is set as y (S4). The amount of water is calculated from these x and y (S5), and the value is displayed on the LED. By repeating the above steps, the amount of water per rotation can be reduced.
Displayed on the LED (S6).

FIG. 6 is a block diagram of an electronic circuit for realizing these processes.

The number of locations where water volume measurement is required is not limited to one location.
A plurality of sensors are installed in the width direction of the plate cylinder, and in a multicolor printing press, a sensor is often installed for each color unit.
Therefore, this electronic circuit has a configuration in which a plurality of sensors 12 can be connected.

The sensor 12 is a first light receiver 12 for measuring water amount.
a, a second photoreceiver 12b for correcting the output and automatically detecting the position of the non-image area, and these output signals are passed through photocurrent-voltage conversion circuits 20a and 20b, respectively, and input to multiplexers 21a and 21b, respectively. Connected. Multiplexer 21a, 21
Of the input lines b, one each is selected by the channel selection signal 32 from the CPU 51, and the input lines are passed through the buffer amplifiers 22a and 22b.
The sample and hold circuits 23a and 23b are entered.

On the other hand, the output of the second light receiver 12b is input to the printing speed measurement circuit 27, which measures the printing speed from the vise part signal, and from that value, the sampling frequency calculation circuit 28 calculates the printing speed at constant distance intervals regardless of the printing speed. A sampling frequency for sampling is calculated, and a sampling pulse of this frequency is generated by the pulse generator 29. This pulse is passed through the latch 30 to the sample hold circuit 23.
a and 23b, and simultaneously hold the signals of the first light receiver 12a and the second light receiver 12b. The held signal is sequentially switched between the two signals by the multiplexer 24, and sent to the A/V via the sample hold 25.
The signal is sent to the D converter 26, becomes a digital signal, and is stored in the memory 32.

The CPU 51 issues instructions for A/D conversion, etc., in accordance with the flowchart shown in FIG. In FIG. 7, the CPU first initializes the channels of multiplexers 21a, 21b, 24 (S11, S12) and clears the sample-hold latch 30 (S13), and then monitors the output line 33. , when it is recognized that it has been held (S14), the multiplexer 21a,
22b is switched to the next channel (S15). At this time, the multiplexer 24 selects the first photoreceiver output, and the CPU 51 selects the A/D output.
Sends a conversion start signal 34 to the converter 26 (S1
6). Next, the CPU 51 switches the channel of the multiplexer 24 to the signal of the second optical receiver (S1
7) The conversion end signal 35 is monitored, and as soon as the conversion is completed (S18), the first light receiver data is taken into the memory 52 (S19). At this point, the signal from the second receiver has already appeared at the A/D input, so immediately
A D conversion start signal 34 is sent (S20). next
The CPU 51 sends a clear signal 36 to the sample hold latch 30 (S21), and the multiplexer 2
After switching the channel No. 4 to the signal of the first photoreceiver (S22), the conversion end signal 35 is monitored, and as soon as the conversion is completed (S23), the second photoreceiver data is taken into the memory 32 (S24). The CPU 51 repeats this process sequentially, but a vise signal 37 is output from the printing speed measurement circuit 27, and when one revolution of data has been captured, the CPU 51 is interrupted by this vise signal 37. Proceed to water amount calculation processing.

The amount of water calculated by the CPU 51 is D/A converted and then sent to the LED, but as shown in Figure 6, display on multiple LED units can be realized with one D/A converter. It uses a so-called dynamic lighting method. That is, water amount data is written in the display memory 39, and this data is sequentially read out as a memory address using the value of the counter 40 running at high speed, and the D/A converter 4
1, buffer 42, demultiplexer 43
It is sent to LED45 via. The channel signal of the demultiplexer 43 also uses the same value as the memory address, and is synchronized with the reading of memory data.

Data in the display memory 39 is updated by switching the address lines 48 and 49 to the CPU side 49 using the selector signal input 50 of the address selector and sending a write signal 47 and new data 48 to the display memory 39. By the above method,
Realizes dynamic LED lighting.

[Variation example]

In the above embodiment, the measurement of the amount of dampening water on the printing plate was explained, but the present invention is configured to numerically grasp the nip pressure and skew adjustment of the dampening water roller, which are important in adjusting the amount of dampening water. You can also do it. To do this, the water amount sensor may be made movable or a plurality of water sensors may be installed in the width direction of the plate cylinder, and the output thereof may be used.

Further, the display section may be provided with a guideline that can be arbitrarily set by the operator as a guide for adjusting the amount of water, or may be configured to issue an alarm when the amount of water falls outside a predetermined range. Furthermore, this device may be used to automatically control the dampening water source roller rotation speed, nip pressure, skew, etc.

〔Effect of the invention〕

As described above, the present invention separately detects the specularly reflected light and the diffusely reflected light in the light reflected from the plate when light is projected at a predetermined angle to the plate, and corrects the amount of the specularly reflected light using the amount of the diffusely reflected light as a reference value. Since the amount of dampening water is detected by using an optical sensor near the printing machine, it is possible to sufficiently deal with dirt on the sensor when using an optical sensor near the printing machine, and to perform accurate measurement. Diffuse reflection light detection can also be used to detect non-print areas on the printing plate where dampening water should be applied, and to detect vise parts for measuring printing speed. All the signals necessary for correcting the water amount detection signal can be obtained.

As a result, the amount of dampening water on the printing plate can be measured very accurately, and even an unskilled operator can maintain the amount of dampening water at an appropriate value.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the principle of the present invention, Fig. 2 is an output characteristic diagram with respect to the amount of dampening water of each light receiver used in the configuration of Fig. 1, and Fig. 3 a, b, and c are each Output characteristic diagram with respect to time of photoreceiver, 4th
The figure is an external view of the apparatus of the present invention applied to an offset sheet-fed printing press, FIG. 5 is a flowchart showing the operation of the display section in FIG. 4, and FIG. 6 is a block diagram showing the electronic circuit of the display section. , FIG. 7 is a flowchart showing the operation of the electronic circuit. DESCRIPTION OF SYMBOLS 1... Emitter, 2... Offset plate surface, 3... First light receiver, 4... Second light receiver, 5... Vise part, 11... Printing machine, 12... Sensor, 13... Display part, 14... Plate cylinder,
15... Inking roller, 16... Dampening water supply device, 17... Blanket cylinder, 18... Impression cylinder, 20...
Photoelectric conversion circuit.

Claims (1)

[Claims] 1. A method for detecting the amount of dampening water supplied to a non-image area of a printing plate in an offset printing machine based on the level of reflected light from the printing plate, comprising: The specularly reflected light reflected from the plate surface at an angle corresponding to the projection angle and the diffusely reflected light reflected in the direction perpendicular to the plate surface are detected separately, and the detection signal of this diffusely reflected light is used to detect non-images on the plate surface. Distinguish the line part, correct level fluctuations due to disturbance in the detection signal of the specularly reflected light from the non-print area using the detection signal of the diffusely reflected light from the non-print area, and calculate the relative value of the amount of dampening water. A method for detecting the amount of dampening water on an offset plate surface. 2. A light projector that irradiates light at an appropriate angle to the offset printing plate, and a first light receiver that is installed relative to the printing plate at an angle corresponding to the irradiation angle of the projector and receives specularly reflected light from the printing plate. a second light receiver that is installed substantially perpendicularly to the plate surface and receives diffusely reflected light from the plate surface; and a non-image receiver that detects a non-image area of the plate surface based on the output of the second light receiver. a line part detection device, and the first
A device for measuring the amount of dampening water on an offset printing plate, comprising: a calculation device that calculates a relative value of the amount of dampening water from the outputs of a light receiver and a second photoreceiver; and a display unit that displays the calculation result of the calculation device as the amount of water on the printing plate. .