JPS60125509A - Detection for print defect - Google Patents

Abstract

PURPOSE:To detect accurately defects of printed matters by processing electrically the sensitivity characteristic to variable density of a photodetector and correcting the sensitivity characteristic to variable density before comparison and discrimination. CONSTITUTION:The pattern of a printed face A is read by a sensor 10, and the output is inputted to an A/D converter E through an amplifier D and is converted to a digital signal. This digital signal is sent to a variable density sensitivity corrector P to correct the sensitivity characteristic to variable density of a photodetector 18, and thereafter, the signal is compared with a standard digital signal from a memory F by an operating circuit H. The output of the operating circuit H is compared with an allowance value from an allowance setter I by a comparing circuit J to discriminate error points. The output of the circuit J is given to a counter K, and a fraction defective is calculated by an operating circuit L and a fraction defective setter U.

Description

[Detailed description of the invention]

The present invention relates to a printing defect detection method that can detect printing defects in a wide variety of printed matter. When detecting printing errors, the 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 to determine pass/fail. It is the one that lowers the. 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. In such a conventional method, when operating the comparison circuit, the sensitivity of the sensor must be increased to a considerable degree of 11, and depending on the type of printed material, the detection sensitivity may be insufficient and some may not be able to be determined. Furthermore, conventional methods have the disadvantage that printing defects cannot be detected appropriately because they are directly influenced by the sensitivity characteristics of the sensor. SUMMARY OF THE INVENTION An object of the present invention is to minimize such inconveniences, provide flexibility in accordance with the edges of printed matter, and increase detection capability. The gist of the present invention to achieve this object is as follows. While moving the printing surface, light is irradiated and reflected from a large number of light emitting elements provided at predetermined intervals across the entire width of the printing surface in the direction across the printing surface, and the light is reflected from the light emitting elements corresponding to the light emitting elements. A large number of light receiving elements receive reflected light from the entire printing surface, the light received by each light emitting element is converted into analog electrical signals, and these analog electrical signals are converted into digital electrical signals by time division. Obtain digital electrical signals corresponding to all measurement points on the printing surface, store each digital electrical signal as a reference value,
These reference values are compared with the digital electrical signals of the corresponding measurement points on the entire other printing surface, and when the difference at each measurement point on the entire printing surface exceeds the allowance setting value, it is determined as an error point. , a printing defect detection method that determines printing defects based on the error points,
A printing defect detection method comprising electrically processing the density sensitivity characteristics of a light-receiving element to correct the density characteristics before comparison and judgment. Now, to briefly explain the printing defect detection method of the present invention,
A large number of measurement points 1 to 1 are created on the entire printing surface, for example, like eyes on the substrate, so as to detect the entire printing surface. 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 A-burlap 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 + -E +' -0 (E+ indicates the signal of the standard printed surface measured at one point, and E+' indicates the signal of the detected printed surface). Slight unevenness in the printing surface, errors in measurement points, deviations in measurement points, etc. may all be judged as printing defects. Therefore, E+ −E+′<±M. M is 70 once (tolerable error) that is thought to occur when measuring the amount of reflected light at the same measurement point or changing the ink density. Only when this allowance M is exceeded is a determination that it is an error point made. Such an allowance M includes a detection width allowance,
Ink 111170 Once, Point Limited Epidemic Once,
There are error limit allowances, density sensitivity allowances, etc., and a plurality of allowances can be set in advance to an arbitrary 70-once setting value separately (or all at once) depending on the type of printing, etc. Allowance settings can also be automated. Since the sensitivity characteristics of the light-receiving element and the sensitivity characteristics of humans are different, the gradation sensitivity is corrected in order to approximate the defect judgment of humans (though this may not necessarily be the case depending on the case). Depending on the type of printing, the points that become error points are further aggregated, and the ratio of the total number of error points to the number of all measurement points 1, that is, the defective ratio (this is treated as the number of error points among all measurement points). good)
I put it on. Then, when it exceeds a preset failure ratio setting value, it is determined that the detected printing surface is a printing failure. 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 percent. Note that it would be convenient to be able to set the pure black level, pure white level, print size, etc. in advance. Hereinafter, the present invention will be described in detail 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 section 10a, a movable panel section 10b provided on both sides of the sensor section 10b for adjusting the detection width, and a sensor section 10a.
A pro-adduct 10C is provided along the entire length of the sensor part 10a and is used to cool the sensor part 10a with air to keep the temperature constant. A tube 10e, a drive unit l-1Of, and a support arm 100 are provided. As shown in FIG. 1B, the sensor section 10a described above has a frame 11, and a large rectangular opening 11a is formed at the upper center of the frame 11, to which a transparent plate G is attached. 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.

[I am a cook,
Three through holes 14a are formed, and the lens 13 passes 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 2 (1 m). If the arrangement is shifted in this way, the resolution will be high. It is also possible to arrange the light-receiving elements at narrower intervals, but In this case, there is a possibility that the cost will be unnecessarily increased even though the resolution will not improve much.Of course, the probability of detection or discrimination errors will vary depending on the type of printed surface being measured.
It is not possible to make a general statement. If the entire length of the frame 11 is made integral 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 may be a photodiode, for example, a photodiode ΔF T 1001W 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. 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, 1
Four light emitting elements 21 are arranged for each of the four light receiving elements 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. Furthermore, it is preferable to use a non-directional light emitting element 21 in order to reduce variations in the optical axis and light intensity.If the light emitting element 21 is yellow-green, more colors of the printed surface can be detected, Practical advantage 1 increases.Also, the light emitting diode A is inferior in durability and stability.The print board 20 is provided with necessary electrical wiring, and the light receiving element 189, the light emitting element 21, Resistance (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 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 e-nocer 10 according to this embodiment also has the overall configuration shown in FIG.
1. Holder 12. Transparent plate G (with lens 13 on part of it)
are integrally formed), a light receiving element 18, a light emitting element 21, a printed board 20, etc. As clearly shown in FIG. 5, the frame 11 has a large opening 11a formed in its upper center. frame 1
1 is made of a material that blocks light from the outside. The holder 12 has a shape that accommodates the frame 11 therein. (The frame 11 is a coin that includes the holder 12.) The holder 12 is slidable within the frame 11 in its longitudinal direction. The upper edge of the boulder 12 to which it is attached has ten inward folding pieces 12a. 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 has a mirror finish. The width of the plate G is the same as the frame 11, 11, and 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. A plurality of light receiving elements 18 are fixed in a row at regular intervals in the center of the printed board 20. These light receiving elements 18 have a field of view diameter of 15ml.
1, they are arranged at a distance of 10 mm from each other. Pairs of light emitting elements 21 are arranged 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 space. In the illustrated example, a hole 20a is formed in the printed board 2o, and the light emitting element 21 is fixed in a slightly embedded manner. One light receiving element 18 and the light emitting elements 21 on both sides thereof form a set, and a large number of phases are arranged in a line (this is used in a broad sense and includes staggered patterns, etc.). Necessary electrical wiring is provided on the board 20 to the printer 1, and the light receiving element 181, 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 signals 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. (On the contrary, 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 to the printing surface as referred to in the water statement includes both of these aspects, and the relative relative to the sensor 10 (to refer to something) In other words, 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 arranged.
will exist throughout the inside of the 11th side of the seal,
As illustrated in FIG.
A large number of measurement points (pixels) will be arranged like the eyes of the base. Note that, in reality, the measurement points naturally overlap each other by a distance corresponding to 1] vertically, horizontally, and horizontally due to the characteristics of the reflected light. For simplicity of 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 content of printing on the printing surface (that is, the amount of light received) that is 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 the A/D converter E, where it is converted into a digital electrical signal. The A/D converter E performs sampling at a constant time using a signal from the clock circuit Q (or encoder). In other words, it covers time division. Therefore, when the printing surface A is moved at a constant speed, digital electrical signals are outputted at measurement points at regular intervals along the moving direction of the printing surface A one after another. FIG. 8 shows one zone (corresponding to the hatched part in FIG. 14) when the printing surface A is moved in this way and the distance from the front edge to the rear edge of the printing surface A is measured using one light receiving element 18. An example of an analog electrical signal and a digital electrical signal is shown. Digital electrical signal from A/D converter E to IIVA
It is sent to a sensitivity corrector P, where the density sensitivity is corrected and then stored in the first memory F and second memory C. 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. Referring to FIG. 16, the density sensitivity corrector P will be explained. 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 IH of the sensitivity characteristic of the light-receiving element 18 between T1 and T2, a negative correction is made between T2 and T3, and in the intermediate region between black and white levels. The difference in Ul lightness is made to appear as a larger voltage difference. In other words, complementary curve S
3 is suitable for detecting printing defects with high sensitivity in intermediate density regions. 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. After correcting the density sensitivity in this manner, the digital electrical signals are stored in the first memory F and the second memory C, respectively, and the corresponding digital electrical signals are extracted and input into the arithmetic circuit 1-1. This arithmetic circuit H takes out the absolute value of the difference between the corresponding digital electric signals of the first memory 1: 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 ■, in which an arbitrary allowance is set in advance according to the printing content, and the digital electric signal of the first memory 1= 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 the error point is 1 or more, 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 a detection allowance, an ink density allowance, a point limit allowance, an error limit allowance, and others. Regarding the detection rli allowance, allowances are 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 70 once for a 111 degree change in ink. Especially when updating the standard values, there is a possibility that the desired density limit will be exceeded and some printing will occur. It is desirable to set the ink density allowance independently of the "11a1" once. The point limit allowance is 70 degrees of displacement in the front-rear direction to the printing surface relative to 1 degree of the sensor. This point limit allowance is set when the output of the print feed mechanism is low. , If the point limit allowance setting value is large, the detection judgment will be lenient. The error limit allowance is an allowance for deviation in the left and right (horizontal) direction from the sensor 10 to the printing surface. The setting value is determined especially in relation to the detection quality. For example, as shown in FIG.
Detection allowances are set above and below 00, and electrical signals 201.202 of the detection rlz allowance setting value are set, and electrical signals @203.204 of the ink density allowance setting value are independently set above and below 00. After this, the printed surface is detected and the electricity obtained by measurement (No. 0 205) is used to set the detection width allowance setting value 202 at the measurement point SE, and the ink density allowance setting value 204 at the measurement point L-SG.
If both are exceeded, an error point 1- will appear in either case. 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 one, the second one, the third one, and so on from the starting edge to the ending edge of the printing surface. Compare and contrast as described above until you reach the first (last measurement point). Then, the number of error points 1- is counted by a counter. When the contents of the first memory F and the second memory C are completely compared, the data in the counter is input to the arithmetic circuit. Then, the percentage ratio between the total number of measurement points (m pieces) and the actual count number on the counter is determined. Defective ratio setting IIU using percentage as judgment standard in advance
By comparing the calculation result of *pole radius with the percentage (defect ratio) set in advance, it is finally determined whether or not the printing is defective for the entire printing surface. That's what I do. In the failure ratio setting device U, the error point count is 1.
Although all of the above values may be set, normally the defective ratio is set arbitrarily within the range of 0.1 to 100%. In this invention, a large number of light receiving elements 1 are arranged across the moving direction of the printing surface A over the entire length of the printing surface A.
The above-mentioned comparative judgment is performed for each of the items 8 and 8. 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. Also, (a) (
B)-(C)...(G) is the encoder 84 (12th
13) shows the positions of a series of a plurality of measurement points along the direction of movement of one light receiving element 18 toward the printing surface. Since measurement points similar to ゛C are taken for each light-receiving element 18, a large number of measurement points 1- are burlaped over the entire printing surface A and are arranged vertically and horizontally at regular intervals in a 1C shape as shown in Fig. 7. The distribution will be J. For convenience of explanation, only one light receiving element 18 will be explained. In FIG. 9, a signal 100 represents an analog electrical signal of a standard printing surface, and a signal 100a is an analog electrical signal obtained by adding a level allowance M' to the signal 100. , signal 100b is an analog electrical signal obtained by subtracting the level allowance M' from 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 E1' to obtain E+ - (E+ ' ±α)〈±M, and then comparison is performed to correct the difference in the amount of reflected light before making a judgment. put down. For example, if 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 will approach the line Y as a whole due to the influence of the paper quality. If the signal 101 is compared with the signal 100 as it is, there is a possibility that the detected printing surface will be determined to be a printing error, so the correction level α is added to the signal 101 to make the signal 101' and then the comparison is made. This kind of level allowance mainly deals with paper quality, printing unevenness, and sensor drift, but the point allowance explained next mainly deals with Koninkoda 8.
4 (FIGS. 12 and 13) and printing 11nA. 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 tolerance range will be a square centered around 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, level allowance only (Figure 9) or a combination of level allowance and point door 1'' once (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)...The number of error points is set among all measurement points* (This corresponds to the failure rate setting value)
If it exceeds the limit, 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 if the next calculated value exceeds the failure rate setting value and it is an IC, it is determined as a printing error. L+S/P L is the peak value of the error block S is the total sum of levels of the error block P is the number of error points of the error block Next, the 12th
A more specific embodiment of the method of the present invention will be described with reference to the figure.
1...N o, n light receiving elements 18 are provided. The sensor 10 is constructed so that the light from each light emitting element 21 is reflected onto the printing surface A, and the reflected light is received by each light receiving element 18 and converted into an analog quantity of electricity. The output of each light-receiving element 18 is amplified by an amplifier 72. The two amplifiers 72 are preferably buffer amplifiers that perform impedance conversion in order to prevent noise from being mixed in. The amplified tc analog electrical signal is passed through the △D sicon converter 7.
Sent to 1. It is desirable to provide various components after the AD converter 71 for each light receiving element 18 from the viewpoint of detection speed, but in the case of low speed printing etc.
It can also be used in combination to cover the set number. The converter 71 samples the analog electrical signal and converts it into a digital electrical signal in response to the measurement pulse 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 or the like, and generates a signal pulse at the same time as printing starts. Sampling is performed in a time-division manner by pulses from encoder 84. The 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 1ml light sensitivity corrector 73, where the sensitivity correction for J and uni shading, which has already been explained with reference to FIG. 16, is performed. Then, according to the instructions from the memory controller 74, the measurement points are stored in the memory circuit 75 for each measurement point. The memory circuit 75 is largely a standard memory 75 due to its role.
a and detection memory 75b.

[You can There is no functional difference between the standard memory 758 and the detection memory 751). The standard memory 7ba stores information on the standard printing surface, and the detection memory 75b stores information on the detected printing surface. The contents of the memory 75b are stored in the memory 75a by the arithmetic unit 81.
The allowance setting (if there is a difference of 1 or more is determined by error point 1 - binding).In other words, the information of the first measurement point on the standard printing surface of the memory 75a (hereinafter referred to as E+) is calculated. It is guided to the vessel 81. Subsequently, information on the 11rth measurement point (hereinafter referred to as E1') on the detected printing surface in the memory 75b is led to the computing unit 81. Then, in the arithmetic unit 81, by determining the absolute value of (E T -E +')〈M,
This overrides the determination as to whether E+' is a defective point. Among the setting values of the allowance M, the setting value of the detector allowance is arbitrarily set by the detection 1JA [coance setting device 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 setting value of the ink degree allowance is arbitrarily set by the ink density allowance setting device 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 51 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 I~ on the detected printed surface (
E2') is similarly compared to determine whether E2' is an error point signal. This operation is performed for all measurement points. When all the measurement points t have been compared, 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 defective ratio, which is the ratio of the error point signal to the total number of measurement points. For example, when the defective ratio setting device 42 is set to 0.2% and the total number of measurement points 1- is 1000 points, the limit of the number of error points is 2 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 is compared with the information sent from the defective rate setting device 42. Also, normally, the judgment result of printing defects is displayed on a display (not shown). or alarm I! (not shown). If necessary, printed matter determined to be defective can be automatically ejected. Setting of the ink density allowance setting value in the ink 1 degree allowance setting device 92, detection 1] Setting of the detector allowance setting value in the 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/
A separate stopper 50 for calculating the value of P) may be provided to perform the determination method (2). Excluding the imposter 5o [
The embodiment shown in FIGS. 1' and 3 has the same construction as the embodiment shown in 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 summing, comparison, and judgment 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 at a speed that matches 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 sequentially follow and update the density curve of printed matter. However, even in that case, the ink density allowance setting value can be set in conjunction with (or without) the update of the reference value in order to have a certain limit. The once set value of the detector 70 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 setting can be made in consideration of printing accuracy, there will be many practical benefits. It is also possible to make settings to correct the discrepancy between the comparison of the sensor's 1) IF and the comparison of the human visual sense. Printed matter (
The correction characteristics can be carefully selected and set depending on the application in order to correspond to differences in paper, metal, etc.), screen shapes, and m-degree configurations. Note that not only inline real-time processing but also offline batch processing is possible.

[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 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. 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. Figure 11 shows the reference value, level allowance and point door [
It is a diagram showing the Cowans relationship. FIG. 12 and FIG. 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 printing surface, the light receiving element, and the measurement point. FIG. 15 is an explanatory diagram showing the interrelationship among m single chain, ink concentration allowance, and detection width allowance. FIG. 16 is a diagram showing the principle of gradation sensitivity correction. 10...Sensor 11...Frame 12...War/Holder 13...Lens plate 14.15.17...Support 16...Base 18... Light receiving element 20...Print board 21...Light emitting element 72...Amplifier 73...AD converter 74...Memory controller I~Roller 75a...
... Standard memory 75b ... Detection memory 84 ... Encoder 42 ... Defective rate setter 50 ... Calculator 51 ... Defective rate detector A ...・・・・・・・・・・・・Printing side D ・・・
・・・・・・・・・・・・Amplifier E ・・・・・・・・・
・・・・・・A/D converter F ・・・・・・・・・
・・・・・・・・・First memory C・・・・・・・・・・
・・・・Second memory H・・・・・・・・・・・・・
・・Arithmetic circuit■ ・・・・・・・・・・・Allowance setting device J ・・・・・・・・・・・Comparison circuit K ・・・・・・・・・・・・・・・・・・Counter L
・・・・・・・・・・・・・・・Arithmetic circuit P ・・・・
・・・・・・・・・・Darkness sensitivity corrector Q ・・・・・・・・・
・・・・・・・・・Clock circuit U ・・・・・・・・・
......Engraving of the drawing of the defective ratio setter (no changes to the contents) Fig. 1A Fig. 2 Fig. 10 Fig. 6 α oil 101' (1) 100] 1 blll. Figure 16 @ - Procedural amendment (voluntary) December 17, 1980 Commissioner of the Japan Patent Office Kazuo Wakasugi Tono 1, Indication of the case 52-2 Nidade'b Patent application filed on December 12, 1988 (3 ) 2. Method for detecting printing defects in the name of the invention 3. Relationship with the case of the person making the amendment Patent applicant address: 28-6 Iwabuchi-cho, Kita-ku, Tokyo Name: Kita Denshi Co., Ltd. 4, Agent address: 2-Toranomon, Minato-ku, Tokyo 8-1 Toranomon Electric Bill 5, drawings subject to amendment and power of attorney 7, details of amendment (1) The drawings will be amended as shown in the attached sheet. (2) Submit the power of attorney as shown in the attached document. I hereby refer to the attached power of attorney.

Claims (1)

[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 printed surface, store those digital electrical signals as reference values, and compare those reference values with the digital electrical signals at all measurement points on the other printed surface. In a printing defect detection method in which the signals are compared with each other, and when the difference at each measurement point of the entire printing surface exceeds an allowance setting value, it is determined as an error point, and a printing defect is determined based on the error point. A printing defect detection method comprising electrically processing the density sensitivity characteristics of a light-receiving element to correct the density characteristics before comparison and judgment.