JPH0995028A - Printing inspection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a printing inspection device with improved ease of operation which can attain high-speed printing inspection at a low cost by processing the image data of printing to be inspected with high efficiency, and can facilitate maintenance such as data storage work. SOLUTION: This printing inspection device processes the image of printing to be inspected for each character string. The image in a measuring range KL enclosing the character string is obtained from the initial image GL of printing, and inspection ranges S1 , S2 are set at the prescribed position of the measuring range K1 . The number of dots existing in the inspection ranges S1 , S2 is compared with the prescribed reference value for judgement of good or bad printing. It is desirable to set the inspection ranges S1 , S2 to a range including the outmost dot string of dots which constitute printing. It is possible to add the processing for comparing the longitudinal width L1 and transverse width L2 of the measuring range K1 with a prescribed reference value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a print inspection device, and more particularly to a print inspection device suitable for inspecting dot printing of an inkjet printer attached to a product package or the like by image processing. .

[0002]

2. Description of the Related Art In recent years, products and packaging forms have been diversified and diversified, and high-speed printing of manufacturing dates, manufacturing numbers, etc. on product packages, parts and the like has been performed by an ink jet printer. Along with this, the printing inspection method is also automatically inspected visually using the image processing device.
In terms of quality control, such as displaying the expiration date, more accurate inspection methods are required. The conventional print inspection device stores in advance the characteristics (dot positional relationship, inclination, size, etc.) of each character to be inspected, and the image acquired at the time of inspection and the characteristic data of the stored characters. The print is recognized by comparing (pattern matching). According to such a conventional print inspection apparatus, since it is a processing method of recognizing an image for each character and inspecting the print, it is possible to make a discrimination close to human recognition and realize a highly accurate print inspection. .

[0003]

However, when using such a conventional print inspection device, there are the following problems. Since the character comparison is performed for each character in the print character string, if the number of print characters is large, the amount of data to be handled becomes huge and the time required for image processing becomes long. Therefore, in order to shorten the processing time, a high-speed unit is needed, and the manufacturing cost of the inspection device becomes excessive. Since it is necessary to store the characteristics of each character in advance, the greater the number of characters to be printed, the more time consuming the input work becomes, and the heavier the operator of the apparatus becomes.

Therefore, the present invention has been made in view of the above circumstances, and makes it possible to realize a high-speed print inspection at a low cost by efficiently processing the image data of the print to be inspected. It is an object of the present invention to provide a print inspection device that simplifies maintenance of the above and improves the handleability.

[0005]

[Means for Solving the Problems]

(First Invention) Therefore, a print inspection apparatus according to the first invention of the present invention is a print inspection apparatus for processing an image of a print to be inspected for each character string, and enclosing the character string from an initial image of the print. An image of the measurement area is acquired, an inspection area is set at a predetermined position of the measurement area, and then the number of dots existing in the inspection area is compared with a predetermined reference value to determine whether the printing is good or bad. And It is desirable that the inspection area is set to an area including the outermost dot row of the dots forming the printing.

The measuring area can be acquired by, for example, capturing the smallest rectangular area surrounding the character string from the image of the printed character string recognized by the imaging camera. When printing on products, etc., the same character string is often applied on a large number. For normal printing, the number of characters and the size of characters on products etc. are the same, and the size of the character strings is also almost the same. . Therefore, when the smallest rectangular area is fetched as described above, the measurement area becomes a substantially constant range for each character string. Regarding the acquisition method of the measurement region, other acquisition methods can be set according to the rule that a normal print character string can always be acquired within a certain range.

Regarding the method of setting the inspection area, it is advisable to select a certain area within the range of the measurement area where printing errors are likely to occur. In particular, in the case of inspecting the print of the inkjet printer, it is desirable to set the inspection region in a region including the outermost dot row of the dots forming the print, and more specifically, the upper portion of the measurement region and It is desirable to set it in two places, the lower part.

Generally, when printing is performed by an ink jet printer, the ink is clogged in the outermost nozzle of the nozzle row for ejecting the ink due to the structure of the printer. Therefore, the outermost dot row of the dot printing is printed. Defects are likely to occur. In other words, printing defects rarely occur only in the middle part of the character string. For example, FIG.
As shown in the concrete example of FIG. 3, the printing defects of the outermost dot row are defective dots such as missing dots (B), dot irregularities (C), and missing lines (D). Is likely to occur. Therefore, when inspecting the printing by the ink jet printer, the printing inspection is performed for each character string by setting the inspection area in the area including the outermost dot row among the dots forming the printing in the measurement area. It can be done efficiently. The reason for setting the inspection areas above and below the measurement area is that the structure of an inkjet printer is generally such that the nozzles are arranged in a row in the vertical direction of the character. This is because the outermost dot rows are present at the upper and lower portions of the measurement area that surrounds the character string, and printing defects are likely to occur in these areas.

The reason for comparing the inspection areas with the number of dots is that it is a factor for relatively easily identifying the characteristics of the printed character string. Dot printing on products is
Usually it is a constant character string such as date or serial number, so
When a dot drop or dot disorder occurs, the number of dots increases or decreases, and it can be easily identified as a normal product. For these reasons, it is possible to inspect all the characters (character strings) by inspecting a certain area of the measurement area instead of recognizing each character one by one.

The method for measuring the number of dots in the inspection area can be carried out by labeling each dot in the area. For example, it is preferable to add only dots of a certain size based on the dot diameter or the like. It should be noted that for the feature comparison of the character strings, it is possible to compare the dot positional relationship in the inspection area, but the processing time tends to be long because the data processing amount in the inspection increases. On the other hand, when comparing the numbers of dots in the inspection areas, the amount of processed data is small and the amount of data for storing the character string features is small.

Regarding the dot number comparison method, feature comparison with a reference value stored in advance (pattern matching)
By. It is desirable to set the reference value to the number of dots in the inspection area corresponding to the normal print character string. If the difference between the reference value and the measured value is within the allowable range, it is determined that the printing is good, and if it is outside the allowable range, it is determined that the printing is defective.

Regarding the allowable range of the difference between the reference value and the measured value, the most preferable numerical value can be set according to the print or the conveyance line to be inspected.

In addition, in addition to the process of comparing the number of dots existing in the inspection area with a predetermined reference value, the process of comparing the vertical width and the horizontal width of the measurement area with a predetermined reference value is added. You may make it pass / fail judgment. This is to increase the accuracy of pattern matching by increasing the number of inspection items. The vertical width and the horizontal width of the measurement area are set as the inspection items because these measurement values serve as indices indicating the size of the measurement area and the characteristics of the entire character string are represented by simple numerical values.

(Second Aspect) A print inspecting apparatus according to a second aspect of the present invention for solving the above-mentioned problems is a print inspecting apparatus for processing an image of a print to be inspected for each character string.
An image of a measurement area surrounding the character string is acquired from the initial image of the printing, and then the number of dots existing in the measurement area is compared with a predetermined reference value to determine whether the printing is good or bad. .

Regarding the method of acquiring the image of the measurement area, it can be acquired by setting, for example, the minimum rectangular area surrounding the character string, as in the first invention. Also,
The dot number measuring method can also be measured by labeling each dot in the measurement region as in the first aspect of the invention.

When the second invention is compared with the first invention,
In the first invention, the print inspection is performed in the inspection area set in a part of the measurement area, whereas in the second invention, the print inspection is performed in the entire measurement area. Therefore, according to the second aspect, the number of dots in the entire character string is inspected in a wider measurement area, and the accuracy of pattern matching is increased.

Further, in the first invention and the second invention, it is possible to judge the quality of the printing by comparing the printing areas of the character strings instead of the number of dots. In this way, when the print area is to be inspected, detailed inspection such as partial dot missing can be performed. The first
Both the invention and the second invention are suitable for use in the inspection of dot printing of an inkjet printer, but as other application examples, they can be applied to printing by other printing methods such as stamps and engraving. is there.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. A print inspection apparatus according to the first aspect of the present invention is shown in FIGS. As shown in FIGS. 2 and 3, the configuration of the print inspection device 1 includes an imaging camera 2, a photoelectric sensor 3, an image processing device 4, a monitor device 5, a teach unit 6, and a sequencer 7. The image processing device 4, the monitor device 5, and the teach unit 6 are housed in a device box 8 shown in FIG. Product W to be inspected
Are transported in a fixed direction on the transport line. Dot printing such as the manufacturing date is attached to the side surface of the product W. Product W
When the photoelectric sensor 3 passes the predetermined inspection position, the photoelectric sensor 3
Is detected, and the imaging camera 2 captures the print image of the product W based on the detection signal. The print image is processed by the image processing device 4, and the quality of printing is notified to the administrator through the monitor device 5. When there is an error such as a printing error, the sequencer 7
Is working so that the transportation line is stopped.

The image pickup camera 2 is fixed at a fixed position on a side of the carrying line with a predetermined distance, and is installed so that the axis of incident light of the lens is substantially horizontal.
The focus of the imaging camera 2 is adjusted so as to coincide with the center of the printed character string when the product W comes to the front position. The focal position of the image pickup camera 2 is illuminated with a strobe light or the like in order to capture a printed image more clearly.

The photoelectric sensor 3 detects the product W flowing on the conveying line, and is installed behind the image pickup camera 2 in the conveying direction. The light emitted from the photoelectric sensor 3 is the product W.
When blocked by, a detection signal is sent to the image processing device 4. The image processing device 4 performs a predetermined process on the print image when the product W passes through the front of the imaging camera 2 based on this detection signal. That is, the photoelectric sensor 3 is a sensor that acquires the timing of starting the inspection.

As shown in FIG. 4, the image processing apparatus 4 has M
PU (Micro Processing Unit) 12, DSP (Digital
Signal Processor, 13, AGDC (Advanced Graphi)
csDisplay Controller) 14, a memory 15 and an interface unit 16. Parallel processing is performed by the MPU 12 and the DSP 13 to perform high-speed processing of the printed image.

The MPU 12 controls image processing, and executes arithmetic operations such as addition and subtraction, logical operations such as logical sum, and branch judgment according to a program stored in the memory 15. The DSP 13 is equipped with a high speed multiplier, and processes the image signal at high speed and with high accuracy. AGDC
14 is an LSI for bit map graphics
Then, the characters or lines to be output are displayed on the monitor device 5. The main functions are a drawing function, a display function, a CRT / printer synchronization signal control function, and a display memory / refresh function.

The memory 15 stores various programs relating to inspection programs and character characteristics. These data are input in advance by the administrator. Further, the interface unit 16 includes the monitor device 5,
It is connected to an external device such as the teach unit 6, the sequencer 7, etc., and as shown by the arrow in FIG. 3, inputs or outputs a signal with the external device.

The monitor device 5 has a monochrome CRT display and displays the image from the image pickup camera 2 and the determination result. It is also possible to display input data such as reference values for comparison inspection on the screen.

The teach unit 6 is a control panel used when storing various data required for print inspection in the memory 15. It is possible to change each data by operating the keys on the control panel.

The image processing procedure of the print inspection device 1 is as follows.
As shown in FIG. 1, first, the measurement region K1 is acquired from the initial image G1 captured by the imaging camera 2. The measurement area K1 is acquired by enclosing the entire character string in a rectangular frame having vertical and horizontal sides parallel to the frame line of the initial image G1, and defining the area inside the frame when this rectangular frame is the minimum as the measurement area K1. To do. Next, an upper region S1 and a lower region S2 are set as inspection regions at the upper end and the lower end of the measurement region K1. Upper area S
The widths of 1 and the lower region S2 in the vertical direction in FIG. 1 are set so that the dot rows at the uppermost end and the lowermost end among the dots constituting the printing are included in each region.

Next, the measurement region K1 has a vertical width L1 and a horizontal width L2.
Is measured, and the upper area S1 and the lower area S2 are measured.
Then, the sum of the number of dots is calculated, and the difference between the measured values of these four items and the reference value set in advance for each item is calculated. If all the calculated results of the difference between the calculated value and the reference value are within the allowable range, it is determined that the printing is good, and if even one is outside the allowable range, it is determined that the printing is defective.

FIG. 5 shows a flow chart of the print inspection of the print inspection apparatus 1. First, in step 21, with respect to the measurement area K1 of the image processing apparatus 4, the vertical width L1, the horizontal width L2, the number of dots in the upper area S1 and the number of dots in the lower area S2 are four.
Measure one item. Next, it is sequentially determined whether the difference between each measured value and the reference value is within the allowable range. That is, the vertical width L1 is determined in step 22, and if it is within the allowable range, the process proceeds to step 23, and if it is outside the allowable range, it is stored in the memory 15 that the vertical width inspection is NG in step 31, and the step is stored. Proceed to 23. In step 23, the width L2
If it is within the allowable range, the process proceeds to step 24. If it is out of the allowable range, the fact that the width inspection is NG is stored in the memory 15 at step 32, and the process proceeds to step 24. In step 24, the number of dots in the upper area S1 is determined. If it is within the allowable range, the process proceeds to step 25. If it is outside the allowable range, the upper area S is stored in the memory 15 in step 33.
It is stored that the dot number inspection of 1 is NG, and the process proceeds to step 25. Further, in step 25, the lower region S2
The number of dots is determined. If it is within the allowable range, the process proceeds to step 26. If it is outside the allowable range, the lower dot number NG is stored in the memory 15 at step 34, and the process proceeds to step 26. Then, in step 26, it is judged whether or not each of the inspection items 1 to 3 has NG. If there is no NG, it is displayed in step 27 that the inspection result is non-defective, and at least one NG is present. For example, in step 28, it is displayed on the monitor that the inspection result is defective.

As described above, according to the print inspection apparatus 1,
Image processing of printing can be efficiently performed for each character string, and quick and accurate printing inspection can be performed without using a high-speed unit. Regarding the specific print inspection speed, it is possible to realize about 1/10 second per product. Also, for the data storage work required for comparing print characteristics, it is only necessary to enter the reference value and the numerical value within the allowable range for each inspection item, so the administrator's effort is reduced and the change of print type is quick. Can correspond to. Furthermore, it is not necessary to use an expensive image processing unit, and the manufacturing cost can be greatly reduced.

Next, a print inspection device 40 according to a second aspect of the present invention is shown in FIGS. 6 and 7. The print inspection apparatus according to the second aspect of the present invention counts the number of dots in the measurement area including the character string to be inspected to determine the quality of printing. The configuration of the print inspection device 40 includes an image pickup camera 2, a photoelectric sensor 3, an image processing device 4, a monitor device 5, a teach unit 6, and a sequencer 7, similarly to the print inspection device 1 of the first invention shown in FIG. The image processing of the image processing device 4 is performed by a dedicated program stored in the memory 15.

As shown in FIG. 6, the procedure of the print inspection by the print inspection apparatus 40 is as follows. First, from the initial image G2 containing the print character string of the inspection object captured by the imaging camera 2 to the measurement area K2.
To get. The measuring area K2 is acquired by enclosing the character string to be inspected with a rectangular frame having vertical and horizontal sides parallel to the frame line of the recognition image G2, as in the print inspection apparatus 1, and this rectangular frame is minimized. The area inside the frame at this time is defined as the measurement area K2.
Then, each dot in the entire measurement area K2 is labeled and the number of dots is measured. Then, the difference between this measured value and a preset reference value is calculated. If the calculated value is within the allowable range, it is determined that the printing is good, and if it is outside the allowable range, it is determined that the printing is defective.

FIG. 7 shows a flowchart of the print inspection of the print inspection device 40. First, in step 41, each dot in the measurement region K2 acquired by the image processing device 4 is labeled and the number of dots is measured. Next, in step 42, it is determined whether or not the difference between the measured value of the number of dots and the reference value is within the allowable range, and if it is within the allowable range, the process proceeds to step 43, and the inspection result of the monitor device 5 is a good product. Display that. If it is out of the allowable range, it is displayed in step 44 that the inspection result is defective.

As described above, the print inspection device 40 also
Since image processing is relatively simple and high-speed processing is possible, quick and accurate print inspection can be performed without using an expensive unit. Further, the labor for storing the data for comparing the printing characteristics is reduced, and the maintenance is simplified. Further, in the print inspection device 40, since the inspection items are smaller than those in the print inspection device 1, the device load of image processing is small, and the print inspection can be performed at a higher speed.

[0034]

As described above, according to the print inspection apparatus of the present invention, the print inspection is performed not by the conventional recognition for each character but by a predetermined inspection algorithm for each character (character string). Therefore, the following various effects can be obtained. (a) Since image processing can be performed efficiently and easily, the structure of the inspection device is simplified, and quick and accurate print inspection can be performed without using an expensive unit. (b) Since the amount of data used for pattern matching is reduced, the work of storing the characteristic data of the print to be inspected is reduced. (c) The handling of the device is improved because the operation of the device is easy and easy for the user to remember, and input errors are reduced. (d) The print inspection can be performed in a short time, which is useful for increasing the speed of the transfer line.

[Brief description of drawings]

FIG. 1 is a partially enlarged view showing a print image of a print inspection device according to a first aspect of the present invention.

FIG. 2 is a schematic configuration diagram showing a print inspection device according to a first invention of the present invention.

FIG. 3 is a block diagram showing a configuration of a print inspection device according to a first aspect of the present invention.

4 is a block diagram showing a configuration of an image processing apparatus of the print inspection apparatus shown in FIG.

FIG. 5 is a flowchart showing an inspection method of the print inspection apparatus according to the first aspect of the present invention.

FIG. 6 is a partially enlarged view showing a print image of the print inspection apparatus according to the second aspect of the present invention.

FIG. 7 is a flowchart showing an inspection method of the print inspection apparatus according to the second aspect of the present invention.

FIG. 8 is a partial enlarged view showing a specific example of an image of dot printing by an inkjet printer.

[Explanation of symbols]

 1 Print inspection device 2 Imaging camera 3 Photoelectric sensor 4 Image processing device 5 Monitor device 6 Teach unit 7 Sequencer G1, G2 Initial image K1, K2 Measurement area L1 Vertical width L2 Horizontal width S1 Upper area (inspection area) S2 Lower area (inspection area) )

Claims (5)

[Claims] 1. A print inspection device for processing a print image to be inspected for each character string, wherein an image of a measurement region surrounding the character string is acquired from an initial image of the print, and a predetermined position of the measurement region is obtained. An inspection area is set in, and the number of dots existing in the inspection area is compared with a predetermined reference value to determine whether the printing is good or bad. 2. The print inspection apparatus according to claim 1, wherein the inspection area is set to an area including an outermost dot row of dots forming the print. 3. The print inspection apparatus according to claim 1, further comprising a process of comparing a vertical width and a horizontal width of the measurement region with a predetermined reference value. 4. A print inspection device for processing a print image to be inspected for each character string, wherein an image of a measurement region surrounding the character string is acquired from the initial image of the print, and then this measurement region is set. A print inspecting device, characterized in that the number of existing dots is compared with a predetermined reference value to judge the quality of the printing. 5. The quality of the printing is determined by comparing the printing areas of the character strings instead of the number of dots, and the quality of the printing is determined. Print inspection device.