JP6322945B2 - Defect detection device - Google Patents

Description

  The present invention relates to a defect detection apparatus.

  Patent Document 1 discloses a print confirmation sheet creating apparatus that creates a print confirmation sheet for confirming whether or not a two-dimensional code encoded with information is properly printed: A two-dimensional code creation unit that creates a two-dimensional code, an enlarged two-dimensional code creation unit that expands the created two-dimensional code to obtain an enlarged two-dimensional code, and the created two-dimensional code is deteriorated to be difficult to read. A deteriorated two-dimensional code generating unit that generates a deteriorated two-dimensional code; a sheet image generating unit that generates a confirmation sheet image by arranging the two-dimensional code, the enlarged two-dimensional code, and the deteriorated two-dimensional code; and the sheet There is disclosed a printing confirmation sheet creating apparatus including a printing unit that prints an image.

  Japanese Patent Application Laid-Open No. 2003-259542 discloses a dot dropout detecting device that detects dot dropout in a liquid ejecting head by recognizing a liquid landing area and a non-landing area on the surface of a landing target, and generates detection light and detects the detection light. A light irradiating means for spot-irradiating the surface of the landing object; a light receiving means for receiving the detection light reflected by the surface of the landing object; a landing detection means for receiving a detection signal from the light receiving means; And the landing detection means recognizes the liquid landing area and the non-landing area based on the difference in the degree of light scattering caused by the surface fine state of the landing target. Is disclosed.

  Patent Document 3 discloses a test pattern printing method using a printing head in which a plurality of printing elements for forming dots on a recording medium are arranged and forming an image on the recording medium. A main scanning step that scans along the main scanning direction, and during the scanning in the main scanning step, a plurality of print elements in the print head are selectively driven to form dots on the recording medium. A pattern printing step for printing a test pattern, wherein the pattern printing step forms a predetermined number of dots along the main scanning direction by the selected printing element, and sets the dots formed by the printing elements. A test pattern printing method characterized in that the density is higher than the density of dots formed during the image forming operation. It is.

JP 2007-261166 A JP 2004-314362 A Japanese Patent Laid-Open No. 2000-043382

  An object of the present invention is to provide a defect detection apparatus that detects the presence or absence of defects when a code image composed of a plurality of dots is formed.

In order to achieve the above object, according to the first aspect of the present invention, a code image representing specific information based on the presence / absence of dot arrangement with respect to a plurality of dot arrangement areas periodically arranged at predetermined intervals is recorded on a recording medium. before forming, the test images are dots dot arrangement region all disposed that might dots are arranged, and an image forming means for forming on said recording medium, which is formed on the recording medium A reading means for reading a test image, and a read image obtained by the reading means are divided into a plurality of areas, and the coverage by the image forming material is obtained for each of the plurality of areas, and an area having a different coverage from the other areas is defined as a defect. And a detection means for detecting.

  A second aspect of the present invention is the defect detection apparatus according to the first aspect, further comprising display means for displaying the read image.

  The invention according to claim 3 is the defect detection apparatus according to claim 2, wherein when a defect is detected by the detection means, the display means enlarges and displays a defective portion of the read image.

The invention according to claim 4 is the defect detection apparatus according to any one of claims 1 to 3 , wherein the code image and the test image are images formed on a recording medium with an infrared absorbing material. It is.

  According to the first aspect of the present invention, the presence / absence of a defect when a code image composed of a plurality of dots is formed is detected.

  According to invention of Claim 2, a defect location is confirmed visually.

  According to invention of Claim 3, a defect location is observed in detail.

According to the fourth aspect of the present invention, the presence or absence of a defect is detected even in an infrared read image.

1 is a schematic diagram showing the overall configuration of an image forming system (A) is the elements on larger scale which expand and show a part of code image. (B) is a schematic diagram which shows an example of a unit pattern. (C) is a schematic diagram showing an example of a code pattern. (A) is a schematic diagram which shows an example of a code image. (B) is a schematic diagram showing an example of a test image. 1 is a schematic diagram illustrating an example of a configuration of an image forming apparatus. 2 is a block diagram illustrating an electrical configuration of the image forming apparatus. FIG. It is a flowchart which shows the processing routine of "defect detection processing." (A) is a figure which shows an example of the test image read by the infrared rays. (B) is a diagram showing an example of an image obtained by binarizing the test image shown in (A).

  Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.

<Image forming system>
First, an example of an image forming system according to the present embodiment will be described.
FIG. 1 is a schematic diagram showing the overall configuration of the image forming system. As shown in FIG. 1, the image forming system 10 includes a terminal device 20, an image forming device 30, and a document management server 40. The terminal device 20, the image forming apparatus 30, and the document management server 40 are connected by a communication line 90 such as a LAN (Local Area Network). The terminal device 20 is an information processing device such as a computer used by a user and a peripheral device. The image forming apparatus 30 is a printing apparatus or the like that forms an image on a sheet. The document management server 40 is an information processing apparatus such as a computer that manages electronic documents. The configuration of the image forming system is an example, and the present invention is not limited to this. “Paper” is an example of a recording medium, and is not limited thereto.

  For example, the terminal device 20 acquires an electronic document from the document management server 40 and instructs the image forming apparatus 30 to print the electronic document. The image forming apparatus 30 forms a document image of an electronic document on a sheet in response to a print instruction from the terminal device 20, and outputs a printed matter on which the document image is formed. Note that the terminal device 20 may acquire an electronic document from the storage unit of the terminal device 20. Further, the terminal device 20 may acquire an electronic document from an external device other than the document management server 40 via the communication unit of the terminal device 20. Alternatively, the image forming apparatus 30 may read a document image on a document by an image reading unit of the image forming apparatus 30 and form the read document image on a sheet.

  In the present embodiment, the image forming apparatus 30 forms a code image on a sheet as a document image, and outputs a printed matter 50 on which the code image is printed. Alternatively, a superimposed image in which a document image and a code image are superimposed is formed on a sheet, and a printed matter 60 on which the superimposed image is printed is output. Here, the “code image” is an image including code information including a plurality of dots and representing specific information as a code pattern (code). “Dot” refers to a halftone dot image. As the code pattern (code), a two-dimensional code (dot pattern) in which a plurality of dots are two-dimensionally arranged, such as a QR code (registered trademark) or a glyph code, is used. The specific information is decoded (decoded) by reading the code pattern of the code image.

  The code image may be an infrared image formed of an infrared absorbing material. Here, the “infrared image” is an image that is difficult to be visually recognized by the naked eye under natural light or white light, and is read by detecting the reflected infrared light by irradiating the infrared light. Infrared images are read using a dedicated infrared imaging device such as an infrared camera. As the infrared absorbing material, a material having a light absorption peak in an infrared region from a wavelength of 750 nm to a wavelength of 1000 nm is used. Therefore, infrared rays having a wavelength corresponding to the absorption characteristics of the infrared absorbing material are used for reading the infrared image.

  In the code image in which the two-dimensional code is formed, since the dots are irregularly arranged, it is difficult to know whether there is an image defect. For example, even if the dot is enlarged or the density is increased to improve the visibility, it is difficult to visually determine the presence or absence of defects such as missing dots. The code image includes code information in which specific information is represented by a code pattern, and has a different dot arrangement depending on the specific information. Therefore, it is difficult to collate the code information of the formed code image with the original code information.

  In this embodiment, when a code image is formed, a “defect detection process” described later is executed in advance. In “defect detection processing”, a test image for a code image is formed on a sheet, and a defect in the formed test image is detected. By executing this “defect detection process”, it is confirmed in advance whether or not the code image is formed without a defect in the image forming apparatus which is to form the code image. That is, the presence or absence of a defect when a code image is formed is detected.

  Note that the pen device 70 may be used to read a code image from the printed material 50 or the printed material 60. The pen-type device 70 is configured to acquire the handwritten information that has been added while reading the code image. For example, when writing on the printed matter 60 using the pen-type device 70, handwriting information is acquired by the pen-type device 70 and transmitted to the document management server 40. The handwriting information for the printed material 60 is managed by the document management server 40 in association with the electronic document printed on the printed material 60.

<Code image>
Next, a code image used in the present embodiment will be described. Here, an example of a dot code using a specific unit pattern called “9C2 pattern” will be described. FIG. 2A is a partially enlarged view showing a part of the code image in an enlarged manner. FIG. 2B is a schematic diagram illustrating an example of a unit pattern. FIG. 2C is a schematic diagram illustrating an example of a code pattern. The code image may be printed on the entire surface of the paper, or may be printed on a specific area of the paper such as an image forming area where the image is formed by the image forming apparatus 30 or a peripheral area around the image forming area. . Also, code images may be printed on both the front and back sides of the paper.

  As shown in FIG. 2A, the code image printed on the portion 50A of the printed matter 50 includes a plurality of code patterns 52 arranged two-dimensionally. Each of the plurality of code patterns 52 includes a plurality of unit patterns 54 arranged two-dimensionally. The code pattern 52 is a minimum reading unit for decoding specific information such as position information and identification information. For example, a QR code (registered trademark) corresponds to one QR code (registered trademark). The specific information is decoded for each code pattern 52. The unit pattern 54 is the minimum unit constituting the code pattern 52 and expresses 1-bit or multiple-bit information.

  In the present embodiment, a two-dimensional code (dot pattern) in which a plurality of dots are two-dimensionally arranged is used as the code pattern 52 and the unit pattern 54. In this example, “dot” is a portion printed using a printing color material, and is represented by a black square (■) in FIG. Although FIG. 2A illustrates a dot having a size of “2 pixels × 2 pixels”, the size of the dot is not limited to this. For example, the size of one dot of the unit pattern 54 may be “7 pixels × 7 pixels”. When a code image having the unit pattern 54 is printed using an image forming apparatus having a resolution capable of printing 2400 pixels per inch, the size of one dot of the unit pattern 54 is “75 μm × 75 μm”. .

  The size (length or diameter of one side) of one dot constituting the unit pattern 54 is 50 μm or more and 100 μm or less in consideration of the amount of information to be expressed, reading accuracy, resolution of the image forming apparatus, and the like. A range is good. The smaller the dot size, the greater the amount of information per unit area. However, if the dot size is too small, the reading accuracy will decrease. In particular, when the code image is an infrared image, the visibility increases and the image quality deteriorates as the dot size increases. By setting the size of the dots to 100 μm or less, the visibility is lowered and the deterioration of the image quality is reduced. A suitable range of the dot size of the code image will be described later in detail.

As shown in FIG. 2B, the unit pattern 54 is divided into a dot arrangement area where dots are arranged and a non-arrangement area where dots are not arranged. The black area 56A indicates that dots are arranged in the dot arrangement area. The gray area 56B indicates that no dot is arranged in the dot arrangement area. The white area 56C indicates a non-arranged area where no dots are arranged. In the unit pattern 54, there are nine dot arrangement areas, and dots are arranged in two places selected from the nine places. Since there are 36 combinations (= ₉ C ₂ ) to select, there are 36 types of unit patterns 54. For example, by using 32 types of unit patterns 54 among them, 5-bit information is expressed.

  As shown in FIG. 2C, the code pattern 52 has a plurality of unit patterns 54 arranged therein. Here, the position where the unit pattern 54 is arranged is referred to as a “unit block”. In this example, 25 (= 5 × 5) unit blocks are arranged, and any unit pattern 54 is arranged in each unit block. In this example, four types of unit patterns 54 are used as synchronization codes 54 for detecting image rotation. The remaining 32 types of unit patterns 54 are used as an X position code 54B representing the X coordinate, a Y position code 54C representing the Y coordinate, and an identification code 54D. FIG. 2C shows an example of the layout of the unit pattern 54, and the layout of the code pattern 52 is not limited to this.

  In the above description, the “code pattern” including a plurality of unit patterns has been described as the reading unit. However, the “unit pattern” may be the reading unit. The reading unit may be a size or an area necessary for decoding the specific information, and may be set according to the information amount of the specific information. For example, even when the “unit pattern” according to this embodiment is used as a reading unit, specific information of 5 bits or more is held as described above.

<Test image for code image>
Next, a test image (test chart) for code images will be described.
FIG. 3A is a schematic diagram illustrating an example of a code image. FIG. 3B is a schematic diagram illustrating an example of a test image. As shown in FIG. 3A, as a result of expressing the specific information by a code pattern, dots are irregularly arranged in the code image. As shown in FIG. 3B, in the test image, dots are formed at all positions where dots may be formed. The dots formed in the test image are arranged according to the dot size and arrangement interval of the code image. In this example, rectangular dots having a dot size (length of one side) of “L” are periodically arranged in a two-dimensional manner at an arrangement interval “d”.

  When the test image shown in FIG. 3B is formed on a sheet, a defect in which dots are not formed becomes clear, for example, one dot at the center is missing. The defect in the test image may be confirmed visually or detected optically. For example, in the case of visual confirmation, the cause of the occurrence of a defect, such as a missing dot or a deformed dot (partially missing state), can be understood by enlarging and displaying the defective part.

  For example, when a defect is detected optically, the test image is divided into small areas, and the coverage (toner coverage) is calculated for each small area. If there is no defect, the coverage is constant. On the other hand, the coverage varies in a region where a defect has occurred. That is, a defect is detected by the variation in coverage. Normal dots are not formed in areas where defects are detected in the test image. Therefore, whether or not the code image is formed without a defect is determined according to the set criteria such as the presence / absence of a defect in the test image, the degree of occurrence of the defect, and the position where the defect occurs. In other words, the presence or absence of a defect when a code image is formed is detected.

<Configuration of image forming apparatus>
Next, an example of the configuration of the image forming apparatus 30 will be described. In the present embodiment, an electrophotographic image forming apparatus that forms an image on a sheet using an electrophotographic developer (including toner) will be described. FIG. 4 is a schematic diagram illustrating an example of the configuration of the image forming apparatus. FIG. 5 is a block diagram showing an electrical configuration of the image forming apparatus.

  In the present embodiment, a case where the code image and the test image are infrared images will be described. In this case, the image forming apparatus 30 forms an infrared image on a sheet by using an infrared absorbing material such as ink or toner having absorption mainly in the infrared region. The infrared absorbing material has low absorption sensitivity to light in the visible region, that is, is transparent to light in the visible region.

  As shown in FIGS. 4 and 5, the image forming apparatus 30 according to the present embodiment includes a control unit 300, an operation display unit 310, an image reading unit 320, an image forming unit 330, a paper supply unit 340, and a paper discharge unit 350. A test image reading unit 360, a communication unit 370, and a storage unit 380. Each of the image forming unit 330, the paper supply unit 340, the paper discharge unit 350, and the test image reading unit 360 includes a paper supply unit 340, an image forming unit 330, and a test image reading unit along a paper conveyance path illustrated by dotted lines. 360 and the paper discharge unit 350 are arranged in this order.

  The test image reading unit 360 includes an image reading device that optically reads the test image formed on the paper by the image forming unit 330. The test image reading unit 360 is disposed between the image forming unit 330 and the paper discharge unit 350. The test image reading unit 360 is disposed so as to face the image forming surface of the supplied paper.

  In this embodiment, since the test image is an infrared image, an infrared image reading device such as an infrared camera is used for the test image reading unit 360. As the infrared absorbing material, a material having a light absorption peak in an infrared region from a wavelength of 750 nm to a wavelength of 1000 nm is used. Therefore, infrared rays having a wavelength corresponding to the absorption characteristics of the infrared absorbing material are used for reading the infrared image. The test image reading unit 360 reads a test image on a sheet and generates image information of the test image.

  The control unit 300 is configured as a computer that controls the entire apparatus and performs various calculations. That is, the control unit 300 includes a CPU (Central Processing Unit) 300A, a ROM (Read Only Memory) 300B storing various programs, a RAM (Random Access Memory) 300C used as a work area when executing the programs, A nonvolatile memory 300D for storing various information and an input / output interface (I / O) 300E are provided. Each of CPU 300A, ROM 300B, RAM 300C, nonvolatile memory 300D, and I / O 300E is connected via bus 300F.

  The operation display unit 310, the image reading unit 320, the image forming unit 330, the paper supply unit 340, the paper discharge unit 350, the test image reading unit 360, the communication unit 370, and the storage unit 380 are the I / O 300E of the control unit 300. It is connected to the. The control unit 300 controls the operation display unit 310, the image reading unit 320, the image forming unit 330, the paper supply unit 340, the paper discharge unit 350, the test image reading unit 360, the communication unit 370, and the storage unit 380. In addition, the control unit 300 acquires image information of the read test image from the test image reading unit 360. Note that the image forming apparatus 30 includes a plurality of conveyance rollers 346. The plurality of transport rollers 346 are arranged along the paper transport path illustrated by dotted lines. The plurality of transport rollers 346 transport the paper according to the image forming operation.

  The operation display unit 310 includes various buttons such as a start button and a numeric keypad, a touch panel for displaying various screens such as a warning screen and a setting screen, and the like. With the above configuration, the operation display unit 310 receives user operations and displays various information to the user. Further, a test image read by the test image reading unit 360 or a partially enlarged image of the test image may be displayed on the operation display unit 310. The image reading unit 320 includes an image reading device that optically reads an image formed on a sheet, such as a CCD image sensor, and a scanning mechanism for scanning the sheet. With the above configuration, the image reading unit 320 reads an image on a document sheet placed on the image reading unit 320 and generates image information.

  The image forming unit 330 forms an image on a sheet by electrophotography. Here, a so-called tandem type and intermediate transfer type image forming unit is illustrated. The image forming unit 330 includes an image forming unit 332K that forms a K color toner image, an image forming unit 332C that forms a C color toner image, an image forming unit 332M that forms an M color toner image, and a Y color toner image. And an image forming unit 332I for forming a transparent toner image with toner containing an infrared absorbing material.

  The image forming unit 330 also intermediate transfer belt 336 wound around a plurality of rollers 334 so as to move in the direction of arrow B, and a secondary transfer device 338 that collectively transfers the toner image on the intermediate transfer belt 336 onto a sheet. The image forming apparatus includes a fixing device 339 that fixes the second-transferred toner image.

  Each of the image forming units 332K, 332C, 332M, 332Y, and 332I is arranged such that when the intermediate transfer belt 336 moves in the direction of arrow B, the Y, M, C, K, and transparent colors are transferred onto the intermediate transfer belt 336. The toner images are arranged in the order shown so that the toner images are formed in this order. Hereinafter, when it is not necessary to distinguish between the colors, they are collectively referred to as an image forming unit 332. The image forming unit 332 includes a photosensitive drum, a charging device, an exposure device, a developing device, a transfer device, a cleaning device, and the like. The photosensitive drum is configured to rotate in the direction of the arrow.

  Specifically, the image forming unit 330 forms an image according to the following procedure. The toner image of K color is transferred onto the intermediate transfer belt 336 by the image forming unit 332K. In the image forming unit 332K, the photosensitive drum is charged by the charging device. The exposure apparatus exposes the charged photosensitive drum with light corresponding to the K color image. As a result, an electrostatic latent image corresponding to the K-color image is formed on the photosensitive drum. The developing device develops the electrostatic latent image formed on the photosensitive drum with K color toner. The transfer device transfers the K color toner image formed on the photosensitive drum onto the intermediate transfer belt 336.

  Similarly, the C-color toner image is transferred onto the intermediate transfer belt 336 by the image forming unit 332C. Further, the toner image of M color is transferred onto the intermediate transfer belt 336 by the image forming unit 332M. Further, the Y-color toner image is transferred onto the intermediate transfer belt 336 by the image forming unit 332Y. Further, the transparent toner image is transferred onto the intermediate transfer belt 336 by the image forming unit 332I. On the intermediate transfer belt 336, the K, C, M, Y, and transparent toner images are superimposed to form an “overlapped toner image”. The secondary transfer device 338 collectively transfers the “superimposed toner image” on the intermediate transfer belt 336 onto the paper. The fixing device 339 fixes the “superimposed toner image” collectively transferred onto the sheet by heating or heating.

  When a code image and a test image are formed in this embodiment, only a transparent toner image is formed by the image forming unit 332I, and an infrared image is formed on a sheet by being transferred and fixed.

  The paper supply unit 340 includes a paper storage unit 342 that stores paper, a supply mechanism that supplies paper from the paper storage unit 342 to the image forming unit 330, and the like. The supply mechanism includes a take-out roller 344 that takes out paper from the paper storage unit 342, a transport roller 346, and the like. A plurality of paper storage portions 342 are provided according to the type and size of the paper. The paper supply unit 342 takes out the paper from one of the paper storage units 342 and supplies it to the image forming unit 330.

  The paper discharge unit 350 includes a discharge unit 354 from which paper is discharged, a discard unit 356 from which unnecessary paper is discarded, a discharge mechanism for discharging the paper onto the discharge unit 354, and the like. The discharge mechanism includes a conveyance path switching unit 352 that switches the sheet conveyance path outside the conveyance roller 346 so that unnecessary sheets are discarded by the discard unit 356. With the above configuration, the paper discharge unit 350 discharges the paper on which the image is formed by the image forming unit 330 to the discharge unit 354 when a document image is formed. Note that the paper on which the test image is formed may be discharged to the discharge unit 354 for visual confirmation, and may be discarded to the discarding unit 356 when visual confirmation on the paper is unnecessary.

  The communication unit 370 is an interface for communicating with an external device via a wired or wireless communication line. For example, it functions as an interface for communicating with a computer connected to a network such as a LAN (Local Area Network). The communication unit 370 acquires a print parameter together with a print instruction and electronic document image information from an external device such as the terminal device 20 or the document management server 40.

  The print parameter is a print attribute such as a page, the number of copies, a paper size, the number of pages to be printed on one sheet, and a margin. In the present embodiment, whether to use a code image is also included in the print parameters. For example, when a document image is superimposed and printed on a code image, the image forming apparatus 30 selects a code image corresponding to the print parameter, and the selected code image and the document image of the electronic document are superimposed. The superimposed image is formed on the paper, and the printed matter 60 on which the superimposed image is printed is output.

  The storage unit 380 includes a storage device such as a hard disk. The storage unit 380 stores various data such as log data, a control program, and the like. In the present embodiment, a case where a control program for “defect detection processing” to be described later is stored in the storage unit 380 in advance will be described. The control program stored in advance is read and executed by the CPU 300A. Various data and control programs may be stored in other storage devices such as the ROM 300B.

  In the present embodiment, the storage unit 380 stores in advance image data of a plurality of code images having different dot sizes and arrangement intervals. Further, in the storage unit 380, image data of a test image in which dots are periodically arranged according to the size and arrangement interval of the dots of the code image is stored in association with each other in correspondence with each of the plurality of code images. Has been. Therefore, the image data of the test image is uniquely specified according to the type of code image.

  Various drives may be connected to the control unit 300. Each type of drive is a device that reads data from a computer-readable portable recording medium such as a flexible disk, a magneto-optical disk, or a CD-ROM, and writes data to the recording medium. When various types of drives are provided, a control program may be recorded on a portable recording medium, and this may be read and executed by a corresponding drive.

<Defect detection process>
Next, the “defect detection process” will be described.
When the image forming apparatus 30 is instructed to print an electronic document, the image forming apparatus 30 acquires a print parameter together with the print instruction and image information of the electronic document. When “use of code image” is included in the print parameters, the image forming apparatus 30 executes “defect detection processing” described below before forming the code image on the paper. That is, the image forming apparatus 30 functions as a defect detection apparatus.

  FIG. 6 is a flowchart showing the processing routine of “defect detection processing”. The “defect detection process” is executed by the CPU 300A of the control unit 300. By this “defect detection processing”, the presence or absence of defects in the test image formed by the image forming apparatus is detected, and the presence or absence of defects when the code image is formed is detected.

  First, in step 100, image data of a test image corresponding to the code image is acquired. As shown in FIGS. 3A and 3B, in the test image, dots of a predetermined size are arranged at a predetermined arrangement interval according to the dot size and arrangement interval of the code image. Next, in step 102, the image forming unit 330 is instructed to form a test image on a sheet. The image forming unit 330 forms a test image (infrared image) on a sheet with transparent toner containing an infrared absorbing material based on the acquired image data of the test image.

  Next, in step 104, the test image reading unit 360 is instructed to read the test image formed on the paper. The test image reading unit 360 optically reads a test image formed on a sheet with infrared rays and generates image information. As shown in FIG. 7A, the test image (infrared image) read with infrared rays has a low contrast. Therefore, here, as shown in FIG. 7B, the infrared image may be binarized to clarify the defective portion.

  Next, in step 106, a coverage distribution is acquired from the read image (information). In step 108, a defect in the read image (test image) is detected based on the coverage distribution. Next, in step 110, it is determined whether or not there is a defect when the code image is formed. As described above, the presence / absence of a defect may be determined according to a set determination criterion instead of simply determining the presence / absence.

  If it is determined in step 110 that there is a defect, the process proceeds to step 112, where the defective part in the test image is displayed on the operation display unit, and the routine is terminated. At this time, the defect portion may be enlarged and displayed. On the other hand, if it is determined that there is no defect, the process proceeds to step 114 to display that there is no defect, and the routine is terminated.

<Modification>
Although an example using an electrophotographic image forming apparatus has been described above, the present invention is not limited to this. The present invention can be applied to any image forming apparatus that expresses light and shade based on the size and area ratio of dots. For example, a droplet discharge type image forming apparatus such as an ink jet printer or a printing apparatus that performs various types of printing such as offset printing may be used.

  In the above description, the code image is an infrared image with low visibility. However, the code image with low visibility is not limited to the infrared image, and may be a visible image. For example, it is sufficient if the visibility of the code image can be reduced, and the code image is made visible by reducing the size of the dots, reducing the color material density, using a color material with low visibility such as yellow, etc. You may form as.

  In the above description, an example of a dot code using a specific unit pattern called “9C2 pattern” has been described. However, the size of the unit pattern, the arrangement of dots, the number of dots to be selected, and the like can be changed as appropriate. Also good. Also, dot codes of different systems such as QR code (registered trademark), Anoto code, glyph code, etc. may be used.

  For example, in the Anoto code, a virtual lattice frame is arranged, and dots are arranged in any one of four regions divided by intersections of the lattice. As a result, four types of patterns can be expressed, and two bits can be expressed (Japanese Patent Publication No. 2003-511762). In the glyph code, one bit is expressed by right and left diagonal lines called glyphs (Japanese Patent Laid-Open No. 9-185669). Each of the right diagonal line and the left diagonal straight line is composed of a plurality of dots. Also in these cases, a defect detection process is performed by forming test images in which dots are formed at all positions where dots may be formed.

  In the above description, an example in which “defect detection processing” is executed before forming a code image on a sheet has been described. However, even if “defect detection processing” is executed regardless of whether there is an instruction to form a code image. Good. For example, when the test mode is selected, the above “defect detection process” may be executed.

  The device configurations described in the above embodiments are merely examples, and it goes without saying that the configurations may be changed without departing from the gist of the present invention. For example, the dot shape of the code image and the test image may be changed from a rectangle to a circle, and the order of each step in the flowchart may be changed. Needless to say, the procedure executed by software may be realized by hardware.

DESCRIPTION OF SYMBOLS 10 Image forming system 20 Terminal device 30 Image forming apparatus 40 Document management server 50 Printed matter 52 Code pattern 54 Unit pattern 60 Printed matter 70 Pen type device 90 Communication line 300 Control part 310 Operation display part 320 Image reading part 330 Image forming part 340 Paper supply Unit 350 paper discharge unit 360 test image reading unit 370 communication unit 380 storage unit

Claims (4)

Before forming a code image representing specific information on the presence or absence of dot arrangement for a plurality of dot arrangement areas periodically arranged at predetermined intervals on a recording medium, all dots may be arranged An image forming means for forming a test image in which dots are arranged in a dot arrangement region on the recording medium;
Reading means for reading a test image formed on the recording medium;
A detection unit that divides an image read by the reading unit into a plurality of regions, obtains a coverage by an image forming material for each of the plurality of regions, and detects a region having a coverage different from other regions as a defect ;
A defect detection apparatus.   The defect detection apparatus according to claim 1, further comprising display means for displaying the read image.   The defect detection apparatus according to claim 2, wherein when the defect is detected by the detection unit, the display unit enlarges and displays a defect portion of the read image. The defect detection apparatus according to any one of claims 1 to 3, wherein the code image and the test image are images formed on a recording medium with an infrared absorbing material.