JPH03162959A - Method of detecting printing error - Google Patents

Abstract

PURPOSE:To make it possible to detect a printing error being produced during a printing process of various printing matters by detecting the printing errors on the basis of a ratio, the number of error points to the whole number of measuring points, namely, a fraction defective. CONSTITUTION:A plurality of photo-sensing element 18 are arranged so as to cross the whole width of a printing surface. Analog signals continuously outputted from the photo-sensing elements 18 are time divided by moving the printing surface and converted to digital signals which are respectively stored into a memory as reference values. The reference values are compared with digital signals corresponding to the whole measuring points of another printing surface. Each of the measuring points is regarded as an error point when each value of the differences between the reference values and the digital signals corresponding to the whole measuring points of the printing surface exceeds a predetermined level, thereby detecting the printing errors resulting from the ratio, the number of such error points to the whole number of the measuring points, namely, a fraction detective. Consequently, it is possible to desirably inspect a wide variety of printing errors according to the content of the printing.

Description

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

Conventional technology 4 When detecting printing errors, a commonly used method is to convert the state of reflected light from the printing 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 the product 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 the entire print surface like 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, when operating the comparison circuit, the sensitivity of the sensor must have a considerable range5, and depending on the type of printed matter, the detection sensitivity may be insufficient, making it difficult to judge. There will be things you can't do.

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

SUMMARY OF THE INVENTION To achieve this object, the present invention is disclosed in claim 1.
The gist is the printing error detection method described in Section 1.

Means to solve problems The above problem is solved by the following (1).

2) to 6) indicate preferred embodiments.

(1) While moving the printing surface, light from a large number of light emitting elements provided at predetermined intervals across the entire width of the printing surface is irradiated and reflected onto the entire printing surface, and the light emitting elements A large number of correspondingly installed light receiving elements receive reflected light from the entire printing surface, and the amount of light received by each light emitting element is converted into an analog electrical signal.
These analog electrical signals are converted into digital electrical signals by time division to obtain digital electrical signals corresponding to the entire measurement points on the printing surface, and each of these digital electrical signals is stored as a reference value, and the The reference value is compared with the digital electrical signals of the corresponding measurement points on the entire printing surface, and when the difference at each measurement point on the entire printing surface exceeds the allowance setting value, it is determined to be an error point and the A printing error detection method characterized by detecting printing defects based on the ratio of the number of error points to the total number of measurement points, that is, the defective ratio (2) The defective ratio actually measured is set in advance. The above-described printing error detection method determines a printing defect when the defective ratio setting value exceeds a predetermined defective ratio setting value.

(3) The printing error detection method described above, in which 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, calculate the bell allowance and point allowance at each measurement point, store them as allowance settings, and then detect them. Shine light on all corresponding measurement points on the printed surface, measure the amount of reflected light from the detected printed surface, calculate the difference between the reference value of the standard printed surface and the amount of reflected light from the detected printed surface for each measurement point, and calculate the difference. When the value exceeds the allowance setting value, the error point is calculated as 8, and the point where the error points are continuous is considered as the 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 levels of error blocks, and P is the number of error points in the error blocks. Printing error detection method described in Section 1 (5) When the previously detected printed surface is determined to be good, the previously described printing error detection method updates the reference value by setting the previously detected printed surface as the standard printed surface. Method.

(6) The above-described printing error detection method in which the allowance setting value and/or the defective ratio setting value are arbitrarily set depending on the printing contents and detection accuracy.

Embodiment 9 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 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.

If the comparison at each measurement point was simply performed as E1-E+'=0 10 (E+ is the signal of the standard printed surface measured at one point, and E1' is the signal of the detected printed surface), it would be Unevenness in the printing surface, errors in measurement points, deviations in measurement points, etc. may all be judged as printing defects. Therefore, it is assumed that El - El'<±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 an allowance M includes a detection width allowance,
There are ink density allowances, point limit allowances, error limit allowances, density sensitivity allowances, etc., and multiple allowances can be set separately (or one
1) Set the allowance to any desired allowance setting value in advance. Allowance settings can also be automated.

1 depending on the type of printing.Furthermore, the points that become error points are totaled, and the ratio of the total number of error points to the number of all measurement points, that is, the defective ratio (this can be treated as the number of error points among all measurement points). good)
seek. 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 arbitrarily set between 0.1 and 100%.

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

Embodiments of the present invention will be described below with reference to the drawings.

First, to explain the light emitting element and light receiving element of the sensor, as shown in FIG.
A sensor part 10a, a movable panel part 10b provided on both sides of the sensor part 10a for adjusting the detection width, and the sensor 10
A pro-adduct 10C is provided along the entire length of the sensor part 10a to keep the temperature constant by cooling the sensor part 10a with air, and to supply air thereto via an air connector 10d. It includes a tube 10e, a drive unit 101, and a support arm 10g.

As shown in FIG. 1B, the aforementioned sensor part 10a 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 thereto.

This plate G is preferably made of transparent acrylic or transparent glass. The outer surface of the plate G has a diffusely reflective 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 are different from each other.
4 It is also possible to have a curved cross-section.

The support 14 is a rectangular parallelepiped block in the illustrated example, and has 3
Two through holes 14a are formed, and the lens 13 is passed through them.

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. A plurality of light receiving elements 18 are fixed in a row at regular intervals in the center of the printed board 20.

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 will vary depending on the type of printed surface to be measured, and cannot be definitively determined.

If the entire length of the frame 11 is integrated and the printed board 20 is made by combining a plurality of small units, the versatility will increase, 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 AFTIOOIW manufactured by Siemens. This photodiode has a built-in amplifier, which makes it resistant to noise in the detection signal.Furthermore, the photodiode is flat, so it has the advantage of minimizing installation space.

Pairs of light emitting elements 21 are arranged at equal distances from each other 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,
In order to save installation space, it is preferable to use a flat type light emitting diode, as shown in the example shown, 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 practical benefits.

Light emitting diodes also have excellent durability and stability.

The printed board 20 is provided with necessary electrical wiring, to which the light receiving element 18, the light emitting element 2171, a resistor (not shown), etc. are electrically connected. Various types of wiring can be arranged in the lower space of the printed board 20 as required.

It is preferable that each light-receiving element 18 incorporate an integrated IC amplifier, such as the aforementioned photodiode made by Siemens, to amplify the electric signal for each light-receiving element 18 before noise enters.

The sensor 10 has a temperature compensation mechanism (for example, Japanese Patent Application No. 57-2
07744) is preferably provided.

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

The printed surface monitoring sensor 1o according to this embodiment also has the overall configuration shown in FIG.
It includes a holder 12, a transparent plate G (a part of which is integrally formed with a lens 13), 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 in the upper central part. frame 1
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 mounted so as to be slidable in the longitudinal direction of the frame 11.

An inward folding piece 12a 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. By making the outer surface of the plate G have 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 folded piece 12a on the upper edge of the holder 12 is attached to the frame 11.
It is designed to be held integrally with the

The printed board 20 is an example of a board, and a normal electric circuit board can be used. A plurality of light receiving elements 8 are fixed in a row at regular intervals in the center of the printed board 20. These light receiving elements 18 are arranged at a distance of 10 mm from each other, assuming that the diameter of the field of view is 15 mm.

Light-emitting elements 21 are arranged in pairs at equal distances on both sides of each of the light-receiving elements 18. 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 20 20a is formed in the printed board 20, and the light emitting element 21 is fixed therein by being slightly embedded therein.

One light-receiving element 18 and the light-emitting elements 21 on both sides thereof constitute one set, and many sets are arranged in a line (this is used in a broad sense and includes a staggered pattern, 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 of these aspects, and the movement of the printing surface A relative to the sensor 10 is ).

Then, since the sensor 10 is arranged across the entire width of the printing surface A, a large number of light emitting elements 21 and light receiving elements 18 are present over the entire width of the printing surface A.
As illustrated in FIG. 4, a large number of measurement points (pixels) are arranged like a checkerboard over the entire printing surface A. 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 shown hatched in FIG.

Now, as the printing surface A moves, the printed content (that is, the amount of light received) on the printing surface A that is captured by the light receiving element 1228 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 determined by the light receiving element 1.
8 into an analog electrical signal. 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 outputted one after another along the moving direction of the printing surface A.

FIG. 8 shows one zone (corresponding to the hatched area in FIG. 14) when the printing surface A is moved in this way and the distance from the front end to the rear end of the printing surface A is measured using one light receiving element 18. 23 An example of an analog electrical signal and a digital electrical signal is shown.

Such a digital electrical signal is stored in the first memory F. 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 〇. 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 is based on differences in the material of printed matter (paper, metal, etc.), screen shape, and other 24 shading configurations. In order to cope with the differences in the following, it is possible to arbitrarily set a large number of correction characteristics 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, a gradation sensitivity corrector P is provided to correct the gradation sensitivity characteristics as shown in the correction curves 81 to S4, for example. Taking the correction curve S3 as an example, a positive correction is made to the line R of the sensitivity characteristic of the light-receiving element 18 between T1 and T2, and a negative correction is made between T2 and T3 to create an intermediate area between black and white levels. The difference in shading is made to appear as a larger voltage difference. In other words, the correction curve S
3 is suitable for detecting printing defects with high sensitivity in intermediate density regions.

The correction curves Sl 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, the corresponding digital electric signals from the first memory F and the second memory C are taken out and input into the arithmetic circuit H. 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 〇 as a voltage difference. This voltage difference is compared in a comparator circuit J based on the allowance setting value from the 726 rowance setting device I, which has an arbitrary allowance set in advance according to the printing content, and is compared with the digital electric signal in the first memory F and the second memory. If the difference from the digital electric signal of C 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 detection width allowance, allowance is set above and below the reference value. It is determined that an error point has occurred when the value exceeds the set value below.

The ink density allowance is an allowance for changes in ink density. Particularly when updating the reference value 27, 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 the allowance for the displacement of the printing surface A in the front-rear direction with respect to the sensor 10. This point limit allowance is set when the accuracy of the printing material 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.
Detection width allowances are set above and below 00, and electrical signals 201 and 202 of detection width allowance set values are set.
, 204 are set. After that, if the electrical signal 205 obtained by detecting and measuring the printed surface exceeds the detection width allowance setting value 202 at the measurement point SE and the ink density allowance setting value 204 at the measurement point SG, In either case, an error point is generated.

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

These operations are performed on all the digital electrical signals stored in the first memory F and the second memory C in the same order, and the first signal is applied to each other, the second signal is obtained from each other, and the third signal is processed from the beginning to the end of the printing surface. The measurement is performed up to the m-th (last measurement point). Then, the number of error points is counted by 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 as a judgment standard is set in advance by the defective ratio setting machine U, and the calculation result of the calculation circuit L is compared with the preset percentage (defective ratio).
Ultimately, it is determined whether or not the printing is defective on the entire printing surface.

In the failure ratio setting device U, the error point count is 1.
It may be possible to set all of the above values, but normally the defective ratio is 0. Set it arbitrarily within the range of 1 to 100%.

30 In the present invention, the above-mentioned comparative judgment is performed for each of the large number of light receiving elements 18 arranged throughout 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 printing surface,
Line Y indicates the level of the completely black printed surface. In addition, (a) (gu) (c)... (g) are encoders 84 (12th to 1st
3) shows a series of positions of a plurality of measurement points along the moving direction of the printing surface A by one light receiving element 18. Since similar measurement points are taken for each light-receiving element 18, a large number of measurement points are distributed over the entire printing surface A in an overlapping manner vertically and horizontally at regular intervals as shown in FIG.

31 For convenience of explanation, only one light receiving element 18 will be explained. In FIG. 9, the signal 100 represents an analog electrical signal of a standard printing surface, and the signal 100a is an analog electrical signal obtained by adding a level allowance M1 to the signal 100. The signal 100b is an analog electrical signal obtained by subtracting the level allowance M' from the signal 100. Measure the detection printing surface,
By performing the comparison judgment described above, the signal 100a and the signal 100b are
If no measurement point falls between the two, it is determined that it is an error point.

Now, even though the detected printing surface is a good print,
The amount of reflected light may vary due to differences in the material of the printing surface, and may be determined to be an error point. In order to avoid such discrimination errors, the correction level α is added or subtracted from El' to obtain E1-(E1'±α)〈±M 32, and then comparison is performed, and the difference in reflected light amount is corrected before judgment. Lower.

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

Such level allowances mainly deal with paper quality, printing unevenness, and sensor drift, but point allowances, which will be explained next, mainly deal with misalignment between the encoder 84 (Figures 12 and 13) and the printing surface A. belongs to.

Regarding the detection width allowance of a certain 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 tolerance range will be a square centered around the reference value. Of course, level allowances and point 1 allowances are 37. can be done.

In that case, the two may have different values. In that case, the permissible range is a rectangle.

Now, level allowance only (Figure 9) or a combination of level allowance and point allowance (Figure 10)
In any of the cases shown in the figure), if the sampled data exceeds the plus or minus allowance setting value, it is considered 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 34 points among all measurement points exceeds a set value (this corresponds to the defect ratio set value), it is determined that there is a printing error.

Judgment method (2): First, a location 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 determined as a printing error.

L+S/P 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, the first
A more specific embodiment of the method of the present invention will be described with reference to FIG.

The sensor 10 has the configuration as described above and is No. 1.
...NQ. It is equipped with n light receiving elements 18.

The sensor 10 is constructed so that the light from each light emitting element 21 is reflected on the printing surface A, and the reflected light is received by each light receiving element 35 and converted 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 and the like from entering.

The amplified analog electrical signal is sent to an AD converter 71
sent to. Although it is desirable 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 an analog electrical signal and converts it into a digital electrical signal in response to a measurement pulse from a 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 36, and generates a signal pulse at the same time as printing starts. Sampling is done in a time division manner by 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 to 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. According to instructions from the memory controller 74, the data is stored in the storage circuit 75 for each measurement point.

The memory circuit 75 is largely a standard memory 75 due to its role.
It can be divided into a detection memory 75b and a detection memory 75b. There is no functional difference between the standard memory 75a and the detection memory 75b. The standard memory 75a records information on the standard printing surface3.
7, and the detection memory 75b stores information on the detected printed surface.

The contents of the memory 75b are stored in the memory 75a by the arithmetic unit 81.
If there is a difference greater than or equal to the allowance setting value, it is determined as an error point. That is,
Information on the first measurement point on the standard printing surface in memory 758 (hereinafter referred to as E1) is derived to computing unit 81. Subsequently, information on the first measurement point (hereinafter referred to as E1') on the detected printing surface in the memory 75b is led to the computing unit 81.

Then, the arithmetic unit 81 determines whether E1' is a defective point by determining the absolute value <M of (E+-E+').

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 38 rowance and point allowance may be the same value, but they may 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. The defect rate detector 5l counts the number of pulses.

Next, information on the second measurement point on the standard printing surface (E
2) and the information of the second measurement point on the detected printing surface (
E2') is similarly compared to determine whether E2' is an error point signal.

This operation is performed for all measurement points.

39 When all the measurement points have been compared in this way, 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 defective ratio setting device 42 arbitrarily sets the ratio of the error point signal to the total number of measurement points, that is, the defective ratio. For example, if the defect ratio setting device 42 is set to 0.2% and all measurement points are iooo points, then
Two points is the limit for the number of error points. These two pieces of information are sent from the defective rate setter 42 to the defective rate detector 51.

Then, the number of error point signals and the information sent from the failure rate setting device 40 are compared.

Further, the determination result of printing defects is usually displayed on a display (not shown) or an alarm (not shown) is used to issue an alarm. 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.

Also, as shown in FIG. 13, the defective rate setter 42 and defective rate detector 51 are omitted, and instead, the above-mentioned (L+S/
An arithmetic unit 50 for calculating the value of 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, In this case, the processing of samples, comparisons, and judgments becomes faster, and the processing speed is improved.

As is clear from the above explanation, according to this invention,
It is possible to automatically inspect all aspects of a large amount of printed matter. 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 the data of the printed side that was previously determined to be good is switched sequentially as the 42nd standard value and compared with the data of the next printed side, the standard value will be updated one after another, and as a result, the standard The value can be updated sequentially to follow the wave of density changes in printed matter. However, even in that case, the ink density allowance setting value can be set in conjunction with (or not in conjunction with) updating of the reference value in order to have a certain limit.

The detection width allowance setting value can be set arbitrarily. If you set it to a large value, it will be difficult to detect small error points.
On the other hand, if it is set too small, it will not be able to follow changes in printing accuracy. Therefore, if the settings can be made in consideration of printing accuracy, many practical benefits can be obtained.

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 43, density configurations, and the like.

In addition to inline real-time processing, offline batch processing is also possible.

[Brief explanation of the drawing]

FIG. 1A is a perspective view showing the appearance of a printed surface detection sensor according to the present invention. FIG. 1B is a plan view schematically 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. 44 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 and level allowance. FIG. 11 is a diagram showing the relationship between the reference value, level allowance, and point allowance. FIGS. 12 and 13 are block diagrams showing other embodiments of the printing error detection method of the present invention. FIG. 14 is a diagram showing the relationship among the printed surface, the light receiving element, and the measurement point. FIG. 15 is an explanatory diagram showing the interrelationship between the reference value, the ink density allowance 45, and the detection width allowance. FIG. 16 is a diagram showing the principle of density sensitivity correction. 10. -Sensor 11● -Frame 12. -Holder 13. -Lens plate 14.15.17..Support 16. -Base 18. -Light receiving element 20. -Printed board 21. -Light emitting element 72. -Amplifier 73.・AD converter 74・ ・Memory controller 75a
・Standard memory 75b ・Detection memory 46 ●Encoder・Failure rate setting device・Arithmetic unit・Failure rate detector・・・・・・・・・・・・・・・Print surface・・・・・・・・・
········amplifier··············
・A/D converter・・・・・・・・・・・・・・・First memory・・・・・・・・・・・・Second memory・
・・・・・・・・・・・・・・・Arithmetic circuit・・・・・・・
・・・・・・Allowance setting device・・・・・・・・・
・・・・・・Comparison circuit・・・・・・・・・・・・・・・
Counter・・・・・・・・・・・・Arithmetic circuit・・
・・・・・・・・・・・・Darkness sensitivity corrector・・・・・・
・・・・・・・・・Clock circuit・・・・・・・・・
・・・・・・Defective ratio setting device 47 100b 203 2 Compliance procedure amendment form (voluntary)

Claims (7)

[Claims] (1) While moving the printing surface, light is irradiated and reflected from a large number of light emitting elements arranged at predetermined intervals across the entire width of the printing surface in the direction across the printing surface, and corresponding to the light emitting elements. The reflected light is received from the entire printing surface by a large number of light-receiving elements installed at the same time, the amount of light received by each light-emitting element is converted into an analog electrical signal, and these analog electrical signals are converted into digital electrical signals by time-sharing. Obtain digital electrical signals corresponding to all measurement points on the printing surface, store those digital electrical signals as reference values, and use those reference values and digital electrical signals of all the corresponding measurement points on the other printing surface. When the difference at each measurement point on the entire printed surface exceeds the allowance setting value, it is determined to be an error point, and the ratio of the number of such error points to the total number of measurement points, that is, the defective ratio. A printing error detection method characterized by detecting printing defects based on. (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. Each measurement point is determined and stored as an allowance setting value, and then 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 to determine the reference value for the standard printed surface. The difference between the value and the amount of reflected light on 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 location where the error points are continuous is defined as 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 calculated value of this formula is the preset defect ratio setting value. 2. The printing error detection method according to claim 1, wherein the printing error is determined to be a printing defect when the value exceeds . (5) 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. The printing error detection method according to item 1. (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.