JPH0586339B2 - - Google Patents

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to an inspection device for printed matter, and in particular, for determining the quality of printed matter in sheet-fed printing presses, rotary printing presses, rewinding machines, etc., and detecting defects when defects occur. The present invention relates to a device that performs notification.

[Prior art and its problems]

Print quality inspection during printing differs depending on the type of printing machine. In the case of offset sheet-fed printing presses and offset rotary printing presses, operators conduct sampling visual inspections, and in the case of gravure rotary printing presses, visual inspections are carried out by flashing a strobe in synchronization with the quality of printed matter. Furthermore, after printing is completed, only the surface of the printed matter is inspected using a rewinding machine.

Attempts have been made to shift from such visual inspection to automatic inspection, such as a method in which a laser light source scans the width of the printed paper and the reflected light is received by a photoelectric conversion device such as a camera, an image pickup tube, a CCD sensor, etc. There are inspection methods using image sensors such as:

However, in any of these methods, only good detection accuracy has been obtained in the laboratory stage, and none of these methods can be put to practical use in printing sites.

For example, in the laser method, the adjustment of the optical system is complicated and requires precision, so detection accuracy cannot be maintained in a harsh environment with vibrations or heat near the printing machine. Further, in the image scanner method, when inspecting the entire width of a wide original, a long optical path from the object to be inspected to the imaging section is required, and the detection section becomes large-sized. Furthermore, when inspecting flowing printed matter, the accuracy of the conveyance system affects the detection performance, especially speed fluctuations in the flow direction.
Misalignment of the object to be inspected, such as meandering in the width direction and fluttering in the vertical direction, cannot be inspected by these methods.

[Purpose of the invention]

The present invention has been made in consideration of the above points, and
An object of the present invention is to provide a printed matter inspection device capable of inspecting a running printed matter in a printing press or a rewinding machine without being affected by positional deviation.

[Summary of the invention]

In order to achieve this objective, in the present invention, the pixels for inspecting the printed paper surface are set to overlap each other, and the non-defective data is first taken in as reference data, and then the data to be inspected is taken in and compared with the reference data. Moreover, this comparison is made so that each pixel is compared and then the added data are compared with each other.

As a result, accurate inspection can be performed without being affected by the inevitable positional deviation of printed matter while it is running.

〔Example〕

The present invention will be explained in detail below based on illustrated embodiments.

FIG. 4 is an explanatory diagram showing a state in which the inspection device according to the present invention is installed in the offset rotary printing press 1.

Strip-shaped printing paper 2 fed out from take-up roll 3
is continuously printed and discharged by each printing unit. The signals detected by the signal detecting section 100 are synchronized with pulses from the rotary encoder 110 attached to the folding saw barrel 10 and subjected to inspection processing by the signal processing means 600. In addition, the fourth
In the figure, only the signal detection means 100 and signal processing means 600 corresponding to the front side of the printing paper 2 are shown for simplicity, but similar signal detection means and signal processing means are also provided on the back side. ing.

First, the structure of the signal detection section 100 and the signal detection means will be explained.

FIG. 1 shows the optical system structure of the signal detection unit 100, in which a single light source is installed in the width direction of the printing paper 2 so as to illuminate the inspection area extending in the width direction of the surface of the printing paper 2. A plurality of photodiodes of channels 1 to n are provided with a cylindrical fluorescent lamp 21 and linearly arranged in the width direction of the printing paper 2.
It is composed of PDs (PD1, PD2, PD3,...PDn), and the light source 21 and photodiode PD are located at an angle θ with respect to the perpendicular line drawn from the photodiode PD to the surface of the printing paper 2. light source 21
The positional relationship is such that direct light from the photodiode does not hit the photodiode PD, and θ=45° is preferable. Here, the light source 21 is preferably a white light source with a large amount of light and a long life.Since signal processing is performed at extremely high speed, a commercial power supply
General fluorescent lamps, incandescent lamps, etc. whose light intensity changes depending on 60Hz cannot be used, and it is necessary to use fluorescent lamps with high frequency lighting or incandescent lamps, etc. that emit light with a constant voltage and constant current DC power source. . A light shielding box 22 and a slit 23 are provided in order to pass only the reflected light from the inspection area on the surface of the printing paper 2 and block light other than this reflected light, such as direct light from the light source 21. Make effective use of the amount of light from the
A reflecting plate 24 and a light shielding plate 25 are provided to block light from indoor lighting. The reflected light from the inspection area on the surface of the printing paper 2 passes through the slit 23, is received by the photodiode PD, and is converted into an electrical signal according to the amount of light received. The photodiode PD used has a luminous sensitivity characteristic as a spectral sensitivity characteristic. When inspecting a printed paper surface using such a photodiode, for example, a width of 1030 mm and a circumferential
An offset rotary printing press with a plate cylinder size of 685 mm and an operating speed of 700 [rpm] or 8000 [mm/sec]
The photodiode PD is installed at a pitch of 23 mm in the width direction of the printing paper (see Figure 1B and Figure 2).
(PD1, PD2,...PD45) are arranged as shown in Figure 1 B, and the inspection surface (field of view, pixel) a _ij of the printing paper by one photodiode is 28 mm on each side as shown in Figure 2. The inspection surface is square, and the pitch of the light-receiving elements is determined to be 23 mm so that adjacent fields of view (for example, _ai1 and _ai2 ) overlap by a distance of 5 mm, and a light-shielding box 22 and a slit 23 are provided. Furthermore, since the printing paper 2 itself is transported by the printing machine, the surface of the printing paper 2 is sequentially inspected line by line as shown in FIG. Inspection using a processing circuit that can inspect the surface of paper 2 line by line at a photodetector pitch of 23 mm, and in which adjacent fields of view (for example, a _i ′ ₂ and a _i ′ ₊₂ ) overlap by 5 mm in the Z direction. The entire surface of the printing paper 2 can be inspected.

Here, the procedure for determining the size of the visual field will be explained. In an offset rotary printing press, meandering of the web during running, that is, misalignment of the web in the printing width direction, and misalignment of the web in the running direction due to printing speed fluctuations of the printing machine, expansion and contraction of the web, etc., occur.
Furthermore, the color tone varies even within the original paper.

Therefore, assuming that the device of the present invention is installed in an actual offset rotary printing press, we conducted a simulation test to check the positional deviation of the web in regular paper, the variation in color tone, etc. The results showed that the effects of misalignment and color tone variations were large. Therefore, based on the measured positional deviation data, the size of the field of view was determined so that the density fluctuation within the sensor field of view due to positional deviation would be less than a few percent of the sensor output. The field of view was sized ² .

In addition, as shown in FIG. 5A, defects 3 such as water dripping, oil dripping, and ink dripping in the visual fields 31 to 36
If 7 occurs across the field of view,
Without overlapping fields of view, only a portion of the actual size defect will fall within one field of view.
Inspection performance clearly deteriorates. Therefore, Figure 5B
As shown in , the apparatus of the present invention has a structure in which the fields of view 38 to 45 in the printing paper flow direction and in the width direction overlap, and the size of the overlapping part of the fields of view is approximately the size of a defect that can be detected with a single field of view. , in the case of the device of the present invention, was set to 5 mm. This causes defect 46
allows the entire defect to be detected in each field of view.

The second image shows the field of view and the amount of overlap.
In the figure, the field of view in which the surface of the printing paper 2 is indicated by diagonal lines.
It shows how it is divided into a _i1 (one inspection area by the light receiving element) and inspected, and the visual field a _ij and the visual field
a _i2 overlaps by a distance b in the width direction of the printing paper 2, fields a _i ′ ₂ and fields a _i ′ ₊₁₂ overlap by a distance b in the printing paper flow direction, and in general, each field of view overlaps a distance b in the printing paper flow direction. , overlaps with eight fields of view adjacent in the width direction. Further, c1 indicates the light receiving element pitch, and c2 indicates the inspection pitch in the printing paper flow direction Z.

Note that the inspection using this photodiode is timed by a timing pulse from the rotary encoder 110, and inspection is performed line by line.

Next, the signal detection means for detecting printing defects based on the signals detected by the signal detection means 100 as described above will be explained.

FIG. 3 shows the configuration of this signal processing section.

A photodiode 401 that converts the reflected light from the object to be inspected obtained by the detection means into an electrical quantity.
A and a head amplifier 402 that converts the photocurrent obtained from the photodiode 401a into voltage to form an amount of electricity corresponding to the density of the printed matter.

The analog output from the head amplifier 402 is sent to a data conversion circuit shown surrounded by a broken line and converted into a digital signal. The conversion circuit includes a multiplexer 4 that selects the analog output from the head amplifier.
03, and the signal selected by this multiplexer 403 is sent to the calibration photodiode 4.
21, a sample and hold circuit 404 that samples the output of this correction circuit 422 at a certain time, and holds the data for the required time; It consists of an A/D converter 405 that converts analog signals to digital signals.

This data conversion circuit converts the analog signal from each photodiode into a digital signal,
The data is sent to the reference data memory 407 by the changeover switch 406 and stored therein. Further, by switching the switch 406, the reference data memory 407 is disconnected, and the data is sent to the subtraction circuit 409. Next, the subtraction circuit 409 subtracts the test data from the contents of the reference data memory corresponding to the test data to find a difference.

This difference is sent to the determination circuit 411 and compared with the tolerance value set in advance in the tolerance value setting circuit 410, and if it is determined to be larger than the tolerance value, then
It is determined that there is a defect on the surface to be inspected corresponding to this inspection data, and an error signal is sent to the alarm 412,
Indicates to the print operator that a defect has occurred. The allowable values used here will be explained.

If the same level of tolerance is given to all pixels regardless of whether the print density is high or low, detection performance will deteriorate for pixels with high density compared to pixels with low density. Therefore, in this device, in order to prevent deterioration of detection performance at pixels with high density, a smaller tolerance value is set for pixels with high density than for pixels with low density. The permissible value is a value obtained by multiplying the reference value data of each pixel by a certain ratio (relative permissible value). The ratio is set by adding the density variation due to positional deviation and the output variation due to the internal nozzle to a value that exceeds this, and further adding the amount of color tone variation that is allowable for each item.

When the density level is high and the sensor output is low, when the pixel data is multiplied by the above ratio, the permissible value becomes several levels, and erroneous determination is likely to occur due to the influence of noise and the like.

For example, if the pixel data is 20 levels and the ratio is 10%, the allowable value will be 2 levels.

Therefore, to prevent this, the allowable value L
(several levels) or less, the allowable value of those pixels is forcibly set to L level regardless of the ratio.

Multiplexer 403, sample & hold circuit 404, A/D converter 405, reference data memory 407, subtraction circuit 409, addition circuit 41
7. Judgment circuit 411, reference data addition memory 41
8. All operation timings of the test data addition memory 419 are performed by the timing generation circuit 413. This timing generation circuit 413 uses a phase detection circuit 414 to count the number of pulses from a rotary encoder 415 installed coaxially with the saw cylinder in order to detect the phase of the plate cylinder. It is generated and sent to the timing generation circuit 413 to control each circuit.

The above signal processing configuration performs the following processing to determine the quality of printed matter.

First, the rotary encoder 415 attached to the folding section saw cylinder 416 generates a pattern start pulse indicating that the leading edge of one pattern on the printed matter has reached the inspection area, and a signal generated when the saw cylinder rotates by a certain angle for one revolution. Outputs rotation pulse. After the picture start pulse is detected by the phase detection circuit 414, it is sent to the timing generation circuit 413, and this signal initializes each circuit so that it can be inspected at any time.

Next, when the timing generation circuit 413 receives the first pulse of the rotation pulses generated every time the saw barrel 416 rotates by a certain angle, the timing generation circuit 413
13 first switches the multiplexer 403 and sends the output signal of the photodiode 401a to the light amount fluctuation correction circuit 422. The light amount fluctuation correction circuit 422 performs analog calculations on the output signals of the calibration photodiode 421 and the photodiode 401a that detect the light amount of the light source, removes fluctuations in detected data due to light amount fluctuations, and sends the data to the sample & hold circuit 404. When the sample and hold circuit 404 receives the sampling signal from the timing generation circuit 413, it holds this time data and sends it to the A/D converter 405. A/D converter 405
receives the A/D conversion start signal from the timing generation circuit 413 and converts the analog data into digital data. A/D converter 40
When photodiode 5 finishes conversion, it sends an A/D conversion completion signal to timing generation circuit 413, and upon receiving this signal, timing generation circuit 413 switches the line of multiplexer 403 to receive the signal from the next photodiode 401b.

The digital output of the A/D converter 405 is sent to either the reference data memory 407 or the arithmetic circuit 409 by switching the switch 406 .

To write data to the reference data memory 407, for example, if the operator determines that the book is a good print after printing has started, the switch 406 sends the data to the reference data memory 407 and stores the reference data when an instruction is given to input the reference value. .

In the case of inspection, inspection data is always sent to the subtraction circuit 409 side. The subtraction circuit 409 reads the inspection data and the reference data that is the same as the position of the picture corresponding to the inspection data from the reference data memory 407, and subtracts the absolute value between the two.

The result of this subtraction is sent to the determination circuit 411 and compared with a tolerance value set in advance in the tolerance value setting circuit 410 for determination. If the subtraction value is larger than the set tolerance value, the inspection data is determined to be defective, and a defect occurrence signal is output to the alarm 412.

When the processing of one pixel is completed, the timing generation circuit 413 receives the next rotational pulse from the phase detection circuit and sends a sampling signal to the sample and hold circuit 404 to process the signal of the photodiode 401b. The generation cycle of this sampling signal is generated in synchronization with the speed of the printing press. Since this is generated by counting the number of pulses from the rotary encoder 415, the number of divisions within one picture is always the same even if the printing speed is different.

Next, the A/D converter 405 and the subtraction circuit 40
9. Processing is performed with the determination circuit 411. In this way, a pixel comparison judgment method is adopted in which the data of each pixel is compared one by one to determine whether the data is good or bad.

Also, the reference data and inspection data are stored in the adder circuit 41.
7 to the reference data addition memory 418,
The test data is stored in the test data addition memory 419, and after one picture is finished or when a certain number of additions is exceeded, the contents of the reference data addition memory 418 and the test data addition memory 419 are subtracted by the subtraction circuit 420, and the judgment circuit 411 The size is compared with the tolerance value set in the tolerance value setting circuit 410, and if the subtraction result is larger than the tolerance value, it is determined to be defective and a signal is output to the alarm 412. In this judgment method based on data addition, the density of the image is high or low over a rather wide range, but when comparing each pixel, it falls within the allowable density value, so by adding some data, it is possible to The purpose of this is to emphasize the tendency for the concentration to be high or low, thereby improving the detection ability. Therefore, even if there is no judgment function by this data addition, the apparatus can function satisfactorily even if the test is performed only by comparing each pixel.

When each pixel determination and addition determination for one picture are completed in this way, the timing generation circuit 413
receives a picture start pulse from the phase detection circuit 414 and repeatedly performs the above-described test.

The above description is only one embodiment of the present invention, and the present invention is not limited to this embodiment in any way, and may be implemented in various ways without departing from the spirit of the present invention. be able to.

〔Effect of the invention〕

As described above, the present invention includes a detection means whose field of view is set so that the pixels overlap each other when taking in pixel data of a printed matter to be inspected, and a detection means in which the pixel data extracted by this detection means is extracted in advance from a non-defective printed matter. Since each pixel is compared with the reference data and the added data is compared, even if a printed matter is displaced while it is running, the inspection can be carried out in accordance with the displacement, and the inspection accuracy is sufficiently high.

[Brief explanation of the drawing]

FIG. 1A is an explanatory diagram of the signal detection means in the flow direction with respect to the printed paper, FIG. 1B is an explanatory diagram of the width direction with respect to the printed paper, and FIG. 2 is an explanatory diagram showing the state of scanning of the printed material. , Fig. 3 is a block diagram showing the circuit configuration of the signal processing section, Fig. 4 is an explanatory diagram showing the state in which the inspection device of the present invention is attached to a printing press, and Fig. 5A is a block diagram showing the circuit configuration of the signal processing section. FIG. 5B is an explanatory diagram of the defect detection method shown in FIG. 5A. 1...Printing machine, 2...Printing paper, 3...Wrap paper,
100... Signal detection unit, 110... Rotary encoder, 10... Folding section saw barrel, 600... Signal processing means, 21... Light source, 22... Light shielding box, 23...
...slit, 24...reflector.

Claims (1)

[Scope of Claims] 1. Light sources that uniformly illuminate the surface of a printed matter, each having a visibility characteristic, arranged in a line in a direction perpendicular to the traveling direction of the printed matter, and arranged so that their visual fields partially overlap each other. a detection means for extracting pixel data in a state in which pixels overlap each other in the traveling direction from the traveling printed matter, the detection means having a plurality of light receiving elements that form a signal according to the reflected light from the printed matter; a reference pixel data memory in which the means stores image data extracted from a non-defective printed product as reference data; and a subtraction device in which the detection means compares the inspection data extracted from the inspected printed material and the stored content of the reference data memory to extract a difference. A printed matter inspection device comprising: a circuit; and a determination circuit that compares the output of the subtraction circuit with a preset tolerance value to determine quality.