JPH0424228B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a printing error detection method capable of detecting printing defects in a wide variety of printed matter.

Conventional technology When detecting printing errors, the commonly used method is to convert the state of reflected light from the printed surface into an electrical signal, and compare this with the electrical signal from the paper surface to be detected. It is used to judge whether it is good or bad. The following methods have been proposed for this method.

(1) A static method in which optical sensors are installed at several points on the paper and the signals are taken while both the paper and the sensors are stationary.

(2) A static method that captures an entire image of the printed surface, similar to a television camera.

(3) A dynamic method in which the sensor or paper surface is moved to extract changes in reflected light within a certain zone of the paper surface as a signal.

Problems to be Solved by the Invention In such conventional methods, the sensitivity of the sensor must have a considerable range when operating the comparison circuit, and depending on the type of printed matter, the detection sensitivity may be insufficient. There will be things that cannot be determined.

OBJECTS OF THE INVENTION It is therefore an object of the present invention to minimize such inconveniences, provide flexibility depending on the type of printed material, and increase detection ability.

Means for Solving the Problem The above problem is solved by the following (1). (2) to (6) indicate preferred embodiments.

(1) While moving the printing surface, light is irradiated onto the printing surface from a large number of light emitting elements provided at predetermined intervals in a direction across the printing surface and reflected, and a large number of light receiving elements are provided corresponding to the light emitting devices. receives multiple reflected lights in an overlapping form, converts the amount of light received by each light-receiving element into an analog electrical signal, and converts these analog electrical signals into digital electrical signals by time-sharing. Obtain digital electrical signals corresponding to all measurement points on the printed surface, store these digital electrical signals as reference values, compare these reference values with digital electrical signals at corresponding measurement points on other printed surfaces, When the difference at each measurement point on the printing surface exceeds the allowance setting value, it is determined to be an error point, and printing defects are detected based on the ratio of the number of such error points to the total number of measurement points, that is, the defect ratio. A printing error detection method characterized by:

(2) The above-mentioned printing error detection method that determines a printing defect when the defective ratio actually measured exceeds a preset defective ratio setting value.

(3) The printing error detection method described above, wherein the allowance setting value includes a setting value for ink density allowance and a setting value for detection width allowance.

(4) First, shine light on all measurement points on the printed surface that has been determined to be good, measure the amount of reflected light at each measurement point, use it as a reference value, and calculate plus and minus level allowances and point allowances from these reference values. Calculate each measurement point at all measurement points and store it as an allowance setting value.
After that, light is applied to all the corresponding measurement points on the printed surface to be detected and the amount of reflected light from the detected printed surface is measured, and the difference between the reference value of the standard printed surface and the amount of reflected light from the detected printed surface is calculated for each measurement. Take each point, define it as an error point when the difference exceeds the allowance setting value, define the point where the error points are consecutive as an error block, and calculate the following formula: L+S/P (where L is the peak value of the error block, S
is the sum of the levels of the error blocks, and P is the number of error points of the error blocks. The printing error detection method according to item 1.

(5) The aforementioned printing error detection method in which when the previously detected printed surface is determined to be good, the reference value is updated by setting the previously detected printed surface as the standard printed surface.

(6) The aforementioned printing error detection method in which the allowance setting value and/or defect ratio setting value are arbitrarily set depending on the printing content and detection accuracy.

Embodiment Now, first, to briefly explain the printing error detection method of the present invention, a large number of measurement points are created, for example, in a grid pattern on the entire printing surface so that the entire printing surface can be detected. At that time, a large number of light receiving elements are arranged across the entire width of the printed surface, and the printed surface is moved to time-divide and convert the continuous analog electrical signals emitted by each light receiving element into digital electrical signals, making it possible to perform a large number of measurements. Obtain digital electrical signals corresponding to the points.

At each measurement point, each light-receiving element receives reflected light from the printed surface, and at this time, each light-receiving element receives the light in an overlapping manner.
The degree of overlap can be adjusted by adjusting the arrangement interval of the light receiving elements, the shape of the lens, the method of time division, etc.

The comparison at each measurement point was simply made as E ₁ −E ₁ ′=0 (E ₁ is the signal of the standard printing surface measured at one point, and E ₁ ′ is the signal of the detected printing surface). In this case, there is a risk that slight unevenness in the printing surface, errors in measurement points, deviations in measurement points, etc., may all be judged as printing defects. Therefore, E ₁ −E ₁ ′<±M. M is an allowance (tolerable error) that is thought to occur when measuring the amount of reflected light or changing the ink density at the same measurement point. It is determined that an error point has occurred only when this allowance M is exceeded.

Such allowances M include detection width allowance, ink density allowance, point limit allowance, error limit allowance, density sensitivity allowance, etc., and multiple allowances can be set separately (or all at once) depending on the type of printing, etc. Set the allowance to an arbitrary setting value in advance. Allowance settings can also be automated.

Depending on the type of printing, the points that become error points are further aggregated and calculated as the ratio of the total number of error points to the number of all measurement points, that is, the defective ratio (this is treated as the number of error points among all measurement points). (also good). Then, when it exceeds a preset failure ratio setting value, it is determined that the detected printing surface has a printing error.

Depending on the type of printing, in order to increase detection accuracy, it may be necessary to determine a printing error if even one error point appears. Generally, the defective ratio is
Set arbitrarily between 0.1 and 100%.

Note that it would be convenient to be able to set the pure black level, pure white level, print size, etc. in advance.

Illustrated Examples Hereinafter, embodiments of the present invention will be described with reference to the drawings.

First, to explain the light emitting element and light receiving element of the sensor, as shown in FIG. 10b, a blower duct 10c that is provided along the entire sensor 10a and cools the sensor 10a by applying air to keep the temperature constant; Tube 1 for supplying
0e, a drive unit 10f, and a support arm 10g.

As shown in FIG. 1B, the aforementioned sensor section 10
A has a frame 11, and a large rectangular opening 11a is formed in the upper central part of the frame 11, and a transparent plate G is attached to the opening 11a. This plate G is preferably made of transparent acrylic or transparent glass. The outer surface of the plate G has a diffused reflection shape, and the inner surface of the plate G has a mirror finish.

The frame 11 is made of a material that blocks light from the outside. Of course, the frame 11 may be constructed in various other shapes.

The lens 13 is preferably made of transparent acrylic or glass and has a mirror finish. The lens 13 is rod-shaped and typically has a circular cross section. Depending on the situation, the cross-sectional shape of the lens 13 may be oval, egg-shaped, semicircular, etc.

The lens 13 for the light receiving element 18 is mainly for adjusting the field of view, and the lens 13 for the light emitting element 21 is mainly for adjusting the level.
Therefore, the lens for the light receiving element 18 and the lens for the light emitting element 21 can have different cross-sectional shapes.

In the illustrated example, the support 14 is a rectangular parallelepiped block, and has three through holes 14a formed therein, into which the lens 13 is passed. The support 14 thereby supports the three lenses 13.

The printed board 20 is an example of a board, and a normal electric circuit board can be used. Print board 2
A plurality of light-receiving elements 18 are fixed in a row at regular intervals in the center of the photodetector 0 .

For example, these light receiving elements 18 are arranged at a distance of 10 to 20 mm. Such an arrangement provides high resolution. It is also possible to arrange the light receiving elements at narrower intervals, but in that case, the resolution may not improve much but the cost may increase unnecessarily. Of course, the probability of a detection error or discrimination error occurring varies depending on the type of printed surface to be measured, and cannot be definitively determined.

If the entire length of the frame 11 is constructed in one piece and the printed board 20 is made by combining a plurality of small units, the versatility will be increased, especially regarding the detection width.

Furthermore, the length of the sensor can be made variable by making the entire frame and other parts into a unit and connecting a plurality of units. In that case, each unit becomes compatible.

The light receiving element 18 can be a photodiode, for example, a photodiode AFT1001W manufactured by Siemens. Since this photodiode has a built-in amplifier, it has the characteristic of being resistant to noise in the detection signal, and is also of a flat type, which has the advantage of minimizing the installation volume.

Light-emitting elements 21 are arranged in pairs at equal distances on both sides of each of the light-receiving elements 18.
In the illustrated example, four light emitting elements 21 are arranged on each light receiving element 18. The light emitting element 21 can be composed of a light emitting diode, and in order to save installation space, it is preferable to use a flat type light emitting diode, as shown in the illustrated example, without a light bulb or lens on the outside.

Further, it is preferable to use a non-directional light emitting element 21 in order to reduce variations in the optical axis and the amount of light.

When the light-emitting element 21 is yellow-green, more colors can be detected on the printed surface, which increases the practical merit.

Light emitting diodes also have excellent durability and stability.

The printed board 20 is provided with necessary electrical wiring, and the light receiving element 18, the light emitting element 21, a resistor (not shown), etc. are electrically connected. Various types of wiring can be placed in the space below the printed board 20 as required.

It is preferable that each light-receiving element 18 incorporates an IC amplifier integrally, such as the photodiode manufactured by Siemens, and amplifies the electric signal for each light-receiving element 18 before noise enters.

The sensor 10 has a temperature compensation mechanism (for example,
57-207744) is preferably provided.

Other embodiments of the sensor used in the present invention will be described with reference to FIGS. 4 to 6.

The print surface monitoring center 10 according to this embodiment also has the overall configuration shown in FIG. 1A, and has a sensor section 1a.
However, frame 11, holder 12, transparent plate G
(a lens 13 is integrally formed in a part thereof), a light receiving element 18, a light emitting element 21, a printed board 20, and the like.

As clearly shown in FIG. 5, the frame 11 has a large opening 11a formed in its upper center. The frame 1 is made of a material that blocks light from the outside.

The holder 12 is shaped to accommodate the frame 11 therein. (The frame 11 includes the holder 12 in a broad sense.) The holder 12 is adapted to be slidably mounted within the frame 11 in its longitudinal direction. A folded piece 12a facing inward is formed on the upper edge of the holder 12.

The transparent plate G is attached to the opening 11a of the frame 11. It is preferable that the plate G is made of transparent acrylic or transparent glass. When the outer surface of the plate G has a diffused reflection shape, stable detection is possible even on a glossy printed surface. A lens 13 is integrally formed on the inner surface of the plate G. The surface of this lens 13 is given a mirror finish. The width of the plate G is the same as that of the frame 11, and the plate G is held integrally with the frame 11 by a folded piece 12a at the upper edge of the holder 12.

The printed board 20 is an example of a board, and a normal electric circuit board can be used. Print board 2
A plurality of light-receiving elements 18 are fixed in a row at regular intervals in the center of the photodetector 0 . These light receiving elements 18 are arranged at a distance of 10 mm from each other when the diameter of the field of view is 15 mm.

Pairs of light emitting elements 21 are arranged on both sides of each of the light receiving elements 18 at equal distances from each other.
The light emitting element 21 can be composed of a light emitting diode, and is preferably a small light emitting diode in order to save installation space. In the illustrated example, a hole 20a is formed in the printed board 20, and the light emitting element 21 is fixed in a slightly embedded manner.

One light receiving element 18 and light emitting elements 21 on both sides thereof
A large number of sets are arranged in a line (this is used in a broad sense and includes staggered patterns, etc.).

The printed board 20 is provided with necessary electrical wiring, and the light receiving element 18, the light emitting element 21, etc. are electrically connected to terminals of a connector (not shown), respectively.

Next, a detailed description will be given of how to process the electrical signal obtained by the sensor 10 as described above to determine a printing error.

In FIG. 7, the sensor 10 is fixed and the printing surface A is moved in the direction of the arrow B. In FIG. (Conversely, it is also possible to move the sensor 10 and make the printing surface A stand still.The present invention may be used in either manner, and the movement of the printing surface A in this specification includes both modes, and the movement of the printing surface A relative to the sensor 10 is (say something)

Then, sensor 1 crosses the entire width of printing surface A.
0 is arranged, a large number of light emitting elements 21 and light receiving elements 18 are present over the entire width of the printing surface A, and as illustrated in FIG.
A large number of measurement points (pixels) are arranged like a checkerboard over the entire print surface A. Note that, in reality, the measurement points naturally overlap each other by a considerable width in the vertical and horizontal directions due to the characteristics of reflected light.

To simplify the illustration, only one light-receiving element 18 is shown in FIG. 7, and one zone consisting of a series of measurement points is correspondingly hatched in FIG. 14.

Now, as the printing surface A moves, the print content (that is, the amount of light received) on the printing surface A captured by the light receiving element 18
changes. In other words, each light-receiving element 18 exhibits a change in the amount of light received depending on the print content. The amount of light received is converted into an analog electrical signal by the light receiving element 18. This analog electrical signal is amplified by an amplifier D, then enters an A/D converter E, where it is converted into a digital electrical signal. A/D converter E performs sampling at a constant time using a signal from clock circuit Q (or encoder). In other words, it is time-divided. Therefore, if the printing surface A is moved at a constant speed, digital electrical signals of measurement points at regular intervals are output one after another along the moving direction of the printing surface A.

FIG. 8 shows how the printing surface A is moved and one light-receiving element 18 is used from the front end to the rear end of the printing surface A.
An example of an analog electrical signal and a digital electrical signal of one zone (corresponding to the hatched area in FIG. 14) when measured by .

Such digital electrical signals are stored in the first memory F.
to be memorized. If the standard printing surface A is inserted, the digital electrical signal of the standard printing surface A is stored in the first memory F.

Next, the digital electrical signal obtained by moving the printed surface A to be compared and judged is input into the second memory C.

Also, instead of sending the digital electrical signal to memories F and C immediately, it is sent from the A/D converter E to the gradation sensitivity corrector P, where the gradation sensitivity is corrected and then stored in the first memory F and second memory C. You can also do that.

The shading sensitivity corrector P corrects the discrepancy between the comparison of the input value by the sensor 10 and the comparison by human vision, and it compensates for differences in the material of printed matter (paper, metal, etc.), screen shape, and other shading configurations. In order to accommodate the differences, a large number of correction characteristics can be arbitrarily set depending on the intended use.

The gray scale sensitivity corrector P will be explained with reference to FIG. 16. The vertical axis shows the black and white level (that is, the amount of received light), and the horizontal axis shows the electrical signal (voltage in this example). The line R shows the density sensitivity characteristic of the light receiving element 18 (this is ideal, but there are errors in reality), and the black and white level and the voltage are directly proportional and form a straight line. However, since human shading sensitivity characteristics vary depending on the type of printing and other factors, they are usually different from the shading sensitivity characteristics of the light receiving element 18. Therefore, for example, correction curves S1 to S4
A gradation sensitivity corrector P is provided to correct the gradation sensitivity characteristics as shown in FIG. Taking the correction curve S3 as an example, between T1 and T2, a positive correction is made to the line R of the sensitivity characteristic of the light receiving element 18, and T
Negative correction is performed between T2 and T3 so that the difference in shading appears as a larger voltage difference in the intermediate region between black and white levels. In other words, the correction curve S3 is suitable for detecting printing defects with high sensitivity in the intermediate density region.

The correction curves S1 and S4 are suitable for detecting printing defects with high sensitivity in dark and light areas close to black and white, respectively. The correction curve S2 is suitable for detecting printing defects with high sensitivity in dark and light areas close to both black and white.

Now, each digital electric signal corresponding to the first memory F and second memory C is extracted and the arithmetic circuit H
Put it in. This arithmetic circuit H extracts the absolute value of the difference between the corresponding digital electric signals of the first memory F and the second memory C as a voltage difference. This voltage difference is compared in a comparator circuit J based on the allowance setting value from the allowance setting device I, which has an arbitrary allowance set in advance according to the printing content, and compares the digital electric signal in the first memory F with the digital electric signal in the second memory C. If the difference from the digital electric signal is greater than or equal to the allowance setting value, it is determined that it is an error point. When it is determined that it is an error point, only the result of failure is entered into the counter K. If it is good, it is not counted.

The allowances to be set include detection width allowance, ink density allowance, point limit allowance, error limit allowance, and others.

Regarding the detection width allowance, an allowance is set above and below a reference value, and when the above and below set values are exceeded, it is determined that it is an error point.

The ink density allowance is an allowance for changes in ink density. Particularly when updating the reference value, there is a possibility that printing exceeding the desired density limit may occur, so it is desirable to set the ink density allowance independently of the detection width allowance.

The point limit allowance is an allowance for the displacement of the printing surface A in the front-back direction with respect to the sensor 10, and this point limit allowance is set when the accuracy of the printed matter feeding mechanism is low. If the set value of the point limit allowance is large, the detection judgment will be lenient.

The error limit allowance is the allowance for the deviation of the printing surface A in the left-right (horizontal) direction with respect to the sensor 10. The setting value is determined particularly in relation to detection accuracy.

For example, as shown in FIG. 15, detection width allowances are set above and below the electrical signal 200 of the reference value, and the electrical signals 201 and 2 of the detection width allowance set value are
02, and electrical signals 203 and 204 of ink density allowance setting values are set above and below independently of this. After that, the electrical signal 205 obtained by detecting and measuring the printed surface is transmitted to the measurement point SE.
If the detection width allowance setting value 202 is exceeded at the measurement point SG, and the ink density allowance setting value 204 is exceeded at the measurement point SG, an error point is generated in both cases.

For example, between the pure black level and the pure white level.
The contents of the first memory F and the second memory are divided into 256 stages.
The contents of memory C are compared to determine the difference.

Such operations are stored in the first memory F and second memory C. All digital electrical signals are stored in the same order, and from the beginning to the end of the printing surface A
The measurement points are compared, the second measurement point is compared, the third measurement point is compared, and so on until the mth measurement point (the last measurement point). Then, the number of error points is counted by a counter K.

When the contents of the first memory F and the second memory C are completely compared, the data of the counter K is input to the arithmetic circuit L. Then, the percentage of the total number of measurement points (m pieces) and the actual count number of the counter K is calculated.

A percentage ratio as a judgment standard is set in advance by the defect ratio setting machine U, and the calculation result of the calculation circuit L is compared with the preset percentage ratio (defective ratio), and finally the printed surface is determined. It is determined whether the overall printing is defective or not.

The defective ratio setting device U may be configured to be able to set all values with an error point count of 1 or more, but normally the defective ratio can be set arbitrarily within the range of 0.1 to 100%.

In the present invention, the above-mentioned comparative judgment is performed for each of a large number of light receiving elements 18 arranged across the entire width of the printing surface A across the moving direction of the printing surface A.

Still another embodiment of the present invention will be described with reference to FIGS. 9 to 13.

In FIG. 9, the vertical axis indicates the black and white level of the printing surface, that is, the amount of reflected light. Line X indicates the level of the pure white printed surface, and line Y indicates the level of the pure black printed surface. In addition, A, B, H... are encoder 84
(FIGS. 12 and 13) shows the positions of a series of a plurality of measurement points along the moving direction of the printing surface A by one light receiving element 18. Each light receiving element 18
Since similar measurement points are taken for each print surface A, a large number of measurement points are distributed over the entire print surface A in an overlapping manner vertically and horizontally at regular intervals as shown in FIG.

For convenience of explanation, only one light receiving element 18 will be described. In FIG. 9, signal 100 represents an analog electrical signal of a standard printing surface;
a is an analog electrical signal obtained by adding level allowance M′ to signal 100, and signal 100b is signal 1
It is an analog electrical signal obtained by subtracting the level allowance M' from 00. The detected printed surface is measured and the comparison judgment described above is performed to determine the signal 100a and the signal 100b.
If no measurement point falls between the two, it is determined that it is an error point.

Now, even though the detected print surface is a good print, the amount of reflected light may vary due to differences in the material of the print surface, and the detected print surface may be determined to be an error point. To avoid such discrimination errors,
A correction level α is added or subtracted from E ₁ ′ to obtain E ₁ −(E ₁ ′±α)<±M, and then comparison is performed to correct the difference in the amount of reflected light and make a determination.

For example, when the paper quality of the detected printing surface A is dark, even if the printed content is exactly the same, the signal 101 of the detected printing surface approaches the line Y as a whole due to the influence of the paper quality. If signal 101 is compared with signal 100 as it is, there is a possibility that the detected printing surface will be judged as a printing error, so signal 101 is set to correction level α.
is added to obtain a signal 101', and then compared.

This level allowance is mainly due to paper quality,
Although it deals with printing unevenness and sensor drift, the point allowance explained next mainly affects the printing surface A of the encoder 84 (FIGS. 12 and 13).
This is to accommodate the discrepancy between the two.

Regarding the detection width allowance of one measurement point, the level allowance is the allowance (tolerable value) in the vertical direction, and the point allowance is the allowance (tolerable value) in the horizontal direction.

If the level allowance and point allowance are set to exactly the same value, the allowable range will be a square centered on the reference value. Of course, level allowances and point allowances can be made independent of each other. In that case, the two may have different values. In that case, the permissible range is a rectangle.

Now, in either case of level allowance alone (FIG. 9) or a combination of level allowance and point allowance (FIG. 10), if the sampled data exceeds the plus or minus allowance setting value, it is determined as an error point. Then, use one (or both) of the following methods to determine a printing error.

Judgment method (1): If the number of error points among all measurement points exceeds a set value (this corresponds to the defective ratio set value), it is determined that there is a printing error.

Judgment method (2): First, a place where error points are consecutive is defined as an error block, and when the next calculated value exceeds the defective ratio setting value, it is judged as a printing error.

L+S/PL L is the peak value of the error block S is the sum of the levels of the error block P is the number of error points of the error block Next, a more specific embodiment of the method of the present invention will be explained with reference to FIG. .

The sensor 10 has the configuration as already described.
It is provided with light receiving elements 18 of No.1...No.n.

The sensor 10 is made to reflect light from each light emitting element 21 onto the printing surface A, and receive the reflected light with each light receiving element 18 and convert it into an analog quantity of electricity.

The output of each light receiving element 18 is amplified by an amplifier 72. The amplifier 72 is preferably a buffer amplifier that performs impedance conversion in order to prevent noise from entering.

The amplified analog electrical signal is sent to AD converter 71. Although it is preferable from the viewpoint of detection speed to provide various components after the AD converter 71 for each light receiving element 18, in the case of low-speed printing, etc., a multiplexer 79 may be provided and used together.

The AD converter 71 samples analog electrical signals and converts them into digital electrical signals in response to measurement pulses from the measurement time controller 82. The measurement time controller 82 is activated by signal pulses from a starter 83. The starter 83 is attached to the power shaft of the printing machine, and is designed to generate a signal pulse at the same time as printing starts. Sampling is performed in a time division manner using pulses from encoder 84. Encoder 84 can be attached to the power shaft of the printing machine.

In the AD converter 71, the analog signal is converted into a digital signal, and the digital signal is sent to the gradation sensitivity corrector 73, where the gradation sensitivity correction is performed as already explained with reference to FIG. Memory controller 74
According to the instructions, the measurement points are stored in the storage circuit 75 for each measurement point.

The memory circuit 75 can be broadly divided into a standard memory 75a and a detection memory 75b depending on its role. Standard memory 75a and detection memory 75
b has no functional difference. Standard memory 75a
Detection memory 7 stores information on the standard printing surface.
5b stores information on the detected printed surface.

The contents of the memory 75b are compared with the contents of the memory 75a by an arithmetic unit 81, and any difference greater than the allowance setting value is determined as an error point. That is, the information (hereinafter referred to as E ₁ ) of the first measurement point on the standard printing surface in the memory 75a is derived to the computing unit 81. Next, memory 75b
Information on the first measurement point on the detected printed surface (hereinafter referred to as E ₁ ') is derived to the computing unit 81. Then, the arithmetic unit 81 determines whether E ₁ is a defective point by determining that the absolute value of (E ₁ -E ₁ ')<M.

Among the setting values of the allowance M, the setting value of the detection width allowance is arbitrarily set by the detection width allowance setter 90. In this case, the level allowance and point allowance may be set to the same value, but they may also be set to different values.

The set value of the ink density allowance is arbitrarily set by the ink density allowance setter 92.

When an error point signal is output, it is possible to immediately determine that there is a printing defect on the printed surface, but in order to make the determination more flexible, one pulse is sent from the arithmetic unit 81 to the failure rate detector 51. Defective rate detector 51
Now count the number of pulses.

Next, the information E ₂ of the second measurement point on the standard printing surface and the information E ₂ ′ of the second measurement point on the detected printing surface are compared in the same way to determine whether E ₂ ′ is an error point signal. It is determined.

This operation is performed for all measurement points.

When all measurement points have been compared in this manner, the defective rate detector 51 stores the number of error point signals. Whether printing is defective or not is determined based on the ratio of the number of error point signals to the total number of measurement points. In other words, the determination is made based on the number of error points among all points.

The defect ratio setting device 42 arbitrarily sets the ratio of the error point signal to the total number of measurement points, that is, the defect ratio. For example, when the defective ratio setting device 42 is set to 0.2% and the total number of measurement points is 1000, the limit for the number of error points is 2 points. These two pieces of information are used by the defective rate setting device 42.
from there to the defective rate detector 51. Then, the number of error point signals and the information sent from the defective rate setting device 42 are compared.

In addition, the judgment result of printing defects is usually displayed on a display (not shown) or an alarm (not shown) is displayed.
to issue a warning. If necessary, printed matter determined to be defective can be automatically ejected.

Setting of the ink density allowance setting value in the ink density allowance setting device 92, setting of the detection width allowance setting value in the detection width allowance setting device 90, and setting of the defective rate in the defective rate setting device 42 can also be performed automatically.

In addition, as shown in FIG.
2 and the defective rate detector 51 may be omitted, and instead, an arithmetic unit 50 for calculating the above-mentioned value of (L+S/P) may be separately provided to perform the determination method (2). Except for the arithmetic unit 50, the embodiment of FIG. 13 has the same configuration as the embodiment of FIG. 12.

In order to be compatible with high-speed printing presses, the sampling time at each measurement point must be kept as short as possible, but if the above-mentioned allowance (tolerable value) is stored in memory for all points, it is possible to In this case, the processing of samples, comparisons, and judgments becomes faster, and the processing speed is improved.

As is clear from the above description, according to the present invention, the entire surface of a large amount of printed matter can be automatically inspected. Moreover, a wide variety of printing errors can be checked flexibly depending on the printed content. This is a breakthrough for the printing industry.

In addition, it is easy to integrate it directly into a printing line and inspect all printed products according to the printing speed.

If you sequentially change the data of the printed side that was judged to be good last time as a reference value and compare it with the data of the next printed side, the reference value will be updated one after another, and as a result, the reference value will be It is possible to follow and update sequentially by riding the wave of concentration change. However, even in this case, the ink density allowance setting value can be set in association with (or not in association with) updating of the reference value in order to have a certain limit.

The detection width allowance setting value can be set arbitrarily. Setting it too large makes it difficult to detect small error points, and conversely, setting it too small makes it impossible to follow changes in printing accuracy. Therefore, in practice, if it is possible to set it by balancing printing accuracy,
You can get many benefits.

It is also possible to make settings to correct the discrepancy between the comparison of sensor input values and the comparison of human vision. Correction characteristics can be arbitrarily selected and set depending on the application to accommodate differences in printed matter (paper, metal, etc.), screen shapes, density configurations, etc.

Note that not only inline real-time processing but also offline batch processing is possible.

In addition, since a plurality of reflected lights are received by a large number of light receiving elements in an overlapping manner, the reflected light can be received in an appropriate state even if the position of the printed surface relative to the light receiving elements is slightly shifted.

[Brief explanation of drawings]

FIG. 1A is a perspective view showing the appearance of a printed surface detection sensor according to the present invention. FIG. 1B is a schematic plan view showing a part of the printed surface detection sensor according to the present invention. FIG. 2 is a sectional view taken along the line X--X in FIG. 1. FIG. 3 is a sectional view taken along line Y--Y in FIG. 1. FIG. 4 is a perspective view showing an example of a printed surface monitoring sensor according to the present invention. FIG. 5 is an exploded view of the print surface monitoring sensor shown in FIG. 1. FIG. 6 is a sectional view of the print surface monitoring sensor shown in FIG. 1. FIG. 7 is a block diagram for explaining the principle of the method of the present invention. FIG. 8 is a waveform diagram showing the flow of the detection signal and the level at each detection point. FIG. 9 is an explanatory diagram of the principle of the printing error detection method of the present invention. FIG. 10 is a diagram showing the relationship between the reference value, level allowance, and point allowance in the method of the present invention. FIG. 11 is a diagram showing an error block. Figure 12 and 1
FIG. 3 is a block diagram showing another embodiment of the printing error detection method of the present invention. FIG. 14 is a diagram showing the relationship among the printing surface, the light receiving element, and the measurement point in the method of the present invention. 15th
The figure is an explanatory diagram showing the interrelationship among the reference value, ink density allowance, and detection width allowance. 16th
The figure is a diagram showing the principle of density sensitivity correction. 10...Sensor, 11...Frame, 12...
...Holder, 13...Lens plate, 14,1
5, 17...Support, 16...Base, 18...
...Photodetector, 20...Printed board, 21...
Light emitting element, 72...Amplifier, 73...AD converter, 74...Memory controller, 75
a...Standard memory, 75b...Detection memory,
84... Encoder, 42... Defective rate setting device,
50... Arithmetic unit, 51... Defective rate detector, A...
Printed surface, D...Amplifier, E...A/D converter, F...First memory, C...Second memory,
H...Arithmetic circuit, I...Allowance setting device, J...
...Comparison circuit, K...Counter, L...Arithmetic circuit,
P...Darkness sensitivity corrector, Q...Clock circuit, U
...Defective ratio setting device.

Claims (1)

[Scope of Claims] 1. While moving the printing surface, light is irradiated onto the printing surface from a large number of light emitting elements provided at predetermined intervals in a direction across the printing surface and reflected, and the light emitting elements are provided corresponding to the light emitting elements. Multiple reflected lights are received by multiple light receiving elements in an overlapping manner, the amount of light received by each light receiving element is converted into an analog electrical signal, and these analog electrical signals are time-divided into digital electrical signals. Convert it to obtain digital electrical signals corresponding to all measurement points on the printing surface, store each of these digital electrical signals as reference values,
These reference values are compared with the digital electrical signals of the corresponding measurement points on other printed surfaces, and when the difference at each measurement point on the printed surface exceeds the allowance setting value, it is determined to be an error point, and such A printing error detection method characterized by detecting printing defects based on a ratio between the number of error points and the total number of measurement points, that is, a defective ratio. 2. The printing error detection method according to claim 1, wherein a printing defect is determined when the defective ratio actually measured exceeds a preset defective ratio setting value. 3. The printing error detection method according to claim 1 or 2, wherein the allowance setting value includes a setting value for ink density allowance and a setting value for detection width allowance. 4 First, shine light on all measurement points on the printed surface that has been determined to be good, measure the amount of reflected light at each measurement point, use it as a reference value, and calculate the plus and minus level allowances and point allowances from these reference values. Calculate it at the measurement point and store it as the allowance setting value, then shine light on all the corresponding measurement points on the printing surface to be detected and measure the amount of light reflected from the detected printing surface, and compare it with the reference value for the standard printing surface. The difference between the amount of light reflected from the detected printing surface is taken for each measurement point, and when the difference exceeds the allowance setting value, it is considered an error point.The point where the error points are continuous is considered an error block, and the following formula is calculated, L+S/P (Here, L is the peak value of the error block, S is the sum of the levels of the error block, and P is the number of error points of the error block.) The value calculated by this formula exceeds the preset defect ratio setting value. The printing error detection method according to claim 1, wherein a printing error is determined when a printing error occurs. 5. Any one of claims 1 to 4, in which when the previously detected printed surface is determined to be good, the reference value is updated by setting the previously detected printed surface as the standard printed surface. Printing error detection method described in . 6. The printing error detection method according to any one of claims 1 to 5, wherein the allowance setting value is arbitrarily set depending on the content of printing and the accuracy of detection. 7. The printing error detection method according to any one of claims 1 to 6, wherein the defect ratio setting value is arbitrarily set.