Image inspection equipment

Abstract

To appropriately determine whether to stop image formation when a defect occurs in an image formed on a recording medium.SOLUTION: An image inspection device has: a reading unit that reads information on an image formed by performing image formation on a recording medium based on image information; an inspection unit that compares the image read by the reading unit with the image information being the source of the read image to detect a defect in an image in the formed image; and a printing stop determination unit. When a plurality of defects occur, the printing stop determination unit obtains the distance between the defects, determines if the obtained distance is the integral multiple of the peripheral length of a photoconductor drum, and determines whether to stop the image formation based on a result of the determination. When determining to stop the image formation, the image inspection device displays, to a user, information representing a photoconductor drum whose peripheral length is the integral multiple for the defects causing to stop the image formation.SELECTED DRAWING: Figure 16

Description

[Technical Field]

[0001] The present invention relates to an image inspection technique for inspecting an image formed on a recording medium or inspecting a recording medium before an image is formed thereon. [Background technology]

[0002] Devices that inspect printed materials are known as a post-processing step for offset printing. In these inspection devices, a reference master image is generated by manually selecting scanned images of printed materials with few or no image defects. During inspection, the scanned image of the printed material being inspected is compared with the master image, and the presence or absence of image defects in the printed material is determined based on the difference between the two. However, plateless printing devices, such as electrophotography, often print small runs, and the printed content may vary from page to page, as in variable printing. Therefore, the method of generating a master image from printed materials and then performing inspection, as with offset printing machines, is not necessarily desirable. To address this issue, generating a master image from print data allows for efficient support of variable printing.

[0003] In inspections that involve comparing images, image formation and output is temporarily halted depending on the inspection results to avoid continuing image formation and output when the defect rate is high. In this case, frequent printing suspensions reduce the productivity of image formation and output, so it is important not to halt printing unnecessarily. Patent Document 1 discloses a technique in which the presence or absence of defects is determined for each page, and printing is stopped if defects are found on multiple consecutive pages. Furthermore, Patent Document 1 discloses a method for determining whether an image to be inspected is an image that is unlikely to have defects based on information about an image to be formed and output. This allows for the exclusion of pages that are determined to be images that are unlikely to have defects when determining whether defects occur on multiple consecutive pages, and for the interruption of image formation and output to be suitably controlled in accordance with the inspection results. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-118050 Summary of the Invention [Problem to be solved by the invention]

[0005] Patent Document 1 assumes that if image data for each color is present across the entire surface of the printing paper, image defects will necessarily occur consecutively on every page. However, depending on the combination of the size of the printing paper and the circumference of the image forming components that cause the defects, defects may not occur consecutively on multiple pages, but may occur every few pages. In this case, using the method of Patent Document 1, which stops printing if defects occur consecutively on multiple pages, can make it difficult to accurately determine whether defects have occurred.

[0006] In view of the above problems, an object of the present invention is to appropriately determine whether to stop image formation when a defect occurs in an image formed on a recording medium. [Means for solving the problem]

[0007] The image inspection device of the present invention comprises a reading means for reading a recording medium on which an image is formed by an image forming means, and a control means for comparing the image read by the reading means with a reference image and inspecting the read image, wherein when there are multiple defective images in the image read during the inspection, the control means calculates an inter-image distance between a first defective image and a second defective image in the conveyance direction of the recording medium, compares the inter-image distance with a component distance corresponding to a component of the image forming means, and displays information on a display means as to whether the inter-image distance is an integer multiple of the component distance, The distance between the defective images is a distance in a conveying direction of the recording medium in an image forming device including the image forming means, and the part distance is a circumferential length of a rotating part of an image forming element that configures the image forming device and includes a rotating part, and the image forming device executes a second print job different from the first print job after executing a first print job, and the control means calculates the inter-image distance for the first defective image formed in the first print job and the second defective image formed in the second print job by using a rotation distance of the rotating part after executing the first print job and a rotation distance of the rotating part before executing the second print job as an inter-recording medium distance. It is characterized by the following. [Effects of the Invention]

[0008] According to the present invention, when a defect occurs in an image formed on a recording medium, it is possible to appropriately determine whether to stop image formation. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus in which an image inspection device is performed. [Figure 2] FIG. 2 is a functional block diagram showing the hardware configuration of the image forming apparatus. [Figure 3] Functional block diagram of the RIP unit. [Figure 4] FIG. 2 is a schematic diagram of a touch panel unit. [Figure 5] FIG. 6 is an explanatory diagram of an example of a setting screen of a printer driver. [Figure 6] FIG. 10 is an explanatory diagram of an example of a property setting screen. [Figure 7] FIG. 2 is a cross-sectional view showing the schematic configuration of a reading unit as viewed from the front. [Figure 8] Left side of the reading unit. [Figure 9] 10A to 10E are explanatory diagrams of the circumferential length of a rotating part of an image forming part, the length of a sheet in the conveying direction, and the distance between sheets of paper. [Figure 10] FIG. 10 is an explanatory diagram of an examination content setting screen. [Figure 11] FIG. 2 is a functional block diagram showing the functional configuration of a master image processing unit. [Figure 12] FIG. 2 is an explanatory diagram of the functional configuration of an MFP control unit. [Figure 13] An explanatory diagram of a comparison test. [Figure 14] 10(a) and 10(b) are explanatory diagrams of defects that occurred on the page being inspected. [Figure 15] FIG. 10 is a diagram illustrating the result of defect feature extraction. [Figure 16] 10A to 10C are explanatory diagrams of a process for determining whether to cancel printing. [Figure 17] 10 is a flowchart showing processing executed by an MFP control unit. DETAILED DESCRIPTION OF THE INVENTION

[0010] The following description of the preferred embodiments of the present invention will be given with reference to the accompanying drawings. The embodiments described below are subject to various limitations that are technically preferable for carrying out the present invention, but the scope of the invention is not limited to the following embodiments and illustrated examples.

[0011] (Image forming system) FIG. 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus that also functions as an image inspection apparatus. A multifunction peripheral device 100 (hereinafter referred to as MFP 100) serving as an image forming apparatus is an electrophotographic image forming apparatus. As shown in FIG. 1, the MFP 100 has a scanner unit 110, a laser exposure unit 120, and an image creating unit 130. The image creating unit 130 has four photosensitive drums 131-134 corresponding to respective colors, chargers for each photosensitive drum, four developing units arranged in the order of yellow (Y), magenta (M), cyan (C), and black (K), and an intermediate transfer body 11. The MFP 100 also has a fixing unit 140, a paper feed / transport unit 150, a manual paper feed unit 155, and a printer control unit 160 that controls each of the components.

[0012] The scanner unit 110 optically reads the image of a document placed on a document table by illuminating the document and converts the read image into an electrical signal to create image data. The laser exposure unit 120 causes a beam of light, such as a laser beam, modulated according to the image data created by the scanner unit 110 to be incident on a rotating polygon mirror 121 that rotates at a constant angular velocity, and irradiates the beam as reflected scanning light onto photosensitive drums 131 to 134 via an optical system.

[0013] The image forming unit 130 rotates and drives the photosensitive drums 131-134, charges them with chargers, and develops the latent images formed on the photosensitive drums 131-134 by the laser exposure unit 120 with toner. The developed toner images are then transferred onto the intermediate transfer body 11 (also referred to as ITB). Any small amounts of toner remaining on the photosensitive drums 131-134 that were not transferred are collected. The intermediate transfer body 11 is composed of an intermediate transfer belt suspended between three rollers. The toner image is transferred by the secondary transfer device 14 to paper conveyed from the paper feed / transport unit 150 in synchronization with the toner image on the intermediate transfer body 11. The fixing unit 140 is composed of a combination of rollers and belts and incorporates a heat source such as a halogen heater. It uses heat and pressure to melt and fix the toner on the paper onto which the toner image has been transferred by the image forming unit 130.

[0014] Paper feed / transport unit 150 has one or more paper storage containers 151, such as a paper cassette or a paper deck, and in this embodiment has two. Paper feed / transport unit 150 separates one sheet from the multiple sheets stored in paper storage container 151 in response to instructions from printer control unit 160, and transports it to image creation unit 130 and fixing unit 140. Note that when paper is fed from manual paper feed unit 155, the fed paper is also transported to image creation units 130 and 140.

[0015] When a sheet of paper is transported to the image forming unit 130, a toner image of each color is formed on the photosensitive drums 131 to 134 in each of the developing units, and then transferred from the photosensitive drums 131 to 134 onto the intermediate transfer body 11. The toner images of each color are then transferred from the intermediate transfer body 11 onto the sheet of paper, so that a full-color toner image is finally formed on the sheet of paper. When images are to be formed on both sides of the sheet of paper, the paper feed / transport unit 150 controls each unit so that the sheet that has passed through the fixing unit 140 is transported to the double-sided reversing unit 152, and after being reversed, passes through a double-sided transport path 153 and a double-sided standby storage 154, which transport the sheet again to the image forming unit 130.

[0016] The printer control unit 160 communicates with the MFP control unit 210 (described later in FIG. 2), which controls the entire MFP 100, and executes various controls in response to its instructions. The printer control unit 160 also manages the status of the scanner unit 110, laser exposure unit 120, image creation unit 130, fixing unit 140, and paper feed / transport unit 150, and issues instructions to ensure smooth, harmonious operation of the entire unit. As shown in FIG. 1, the MFP 100 also includes a reading unit 170 between the fixing unit 140 and the double-sided inversion unit 152 of the paper feed / transport unit 150, which reads an image (hereinafter referred to as an output image) formed on a recording medium, i.e., paper. The reading unit 170 includes a CIS device 50 (described later in FIG. 8), which detects and reads the output image in response to a user instruction and transmits the read image to the MFP control unit 210. The reading unit 170 will be described in detail later.

[0017] Next, the printer control unit 160 will be described. When the MFP 100 is powered on from a power-off state, the printer control unit 160 first instructs the scanner unit 110, laser exposure unit 120, image creation unit 130, fixing unit 140, and paper feed / transport unit 150 to start preparatory operations. The printer control unit 160 then waits for the start of communication with the MFP control unit 210, which manages the entire MFP 100. Once communication with the MFP control unit 210 is established, the printer control unit 160 exchanges device specification information with the MFP control unit 210. Thereafter, when the preparatory operations of each unit of the MFP 100 are completed and image formation operation is possible, the printer control unit 160 notifies the MFP control unit 210 that it is in an operable state. The printer control unit 160 notifies the MFP control unit 210 of the device status of each unit of the MFP 100.

[0018] Next, in the state where MFP 100 is ready to start operation, the operation of each component from when MFP control unit 210 notifies printer control unit 160 of an operation instruction for each component until the end of a series of printing operations will be described with reference to Fig. 1. MFP control unit 210 is shown in Fig. 2, which will be described later.

[0019] First, the MFP control unit 210 sends an operation start command to the printer control unit 160. Upon receiving the operation start command, the printer control unit 160 instructs the laser exposure unit 120, the image creation unit 130, the paper feed / transport unit 150, and the fixing unit 140 to start a print operation. The laser exposure unit 120 starts rotating the motor (polygon motor) that drives the polygon mirror 121. The image creation unit 130 drives and rotates the photosensitive drums 131 to 134, charging the photosensitive drums 131 to 134. The fixing unit 140 turns on the fixing heater, raising the temperature to a level at which the toner on the paper can be fixed to the paper. The paper feed / transport unit 150 puts the driving means (motor) into a startable state. When each unit of the MFP 100 is ready to operate, the printer control unit 160 notifies the MFP control unit 210 that preparations are complete.

[0020] When the MFP control unit 210 receives a preparation completion notification from the printer control unit 160, it instructs the printer control unit 160 to perform the next print operation on a page-by-page basis. For example, if the print job is for 20 copies of 10 pages, the MFP control unit 210 issues a print operation instruction for 200 pages. When the printer control unit 160 receives the print operation instruction, it issues a paper feed instruction to the paper feed / transport unit 150. If paper can be fed, the paper feed / transport unit 150 feeds and transports one sheet of paper, and when the paper reaches a predetermined position, it notifies the printer control unit 160 that the paper has reached the predetermined position. If paper cannot be fed, for example, if there is no paper in the paper storage 151, the paper feed / transport unit 150 notifies the printer control unit 160 that paper cannot be fed.

[0021] Furthermore, paper feed / transport unit 150 may have a double feed detection sensor that detects when paper is being transported in an overlapping state (double feed state) on the transport path, a thickness detection sensor that detects the thickness of the paper, etc. In this case, when these sensors detect a double feed or an abnormal state, paper feed / transport unit 150 suspends the paper feed operation and transport operation and notifies printer control unit 160 of the abnormality. When printer control unit 160 receives the abnormality notification, it notifies MFP control unit 210 of the reason for the operation suspension, the position of any paper remaining in the device, etc.

[0022] When the paper is transported normally and reaches the predetermined position, the printer control unit 160 instructs the image forming unit 130 to start image formation in response to a notification from the paper feed / transport unit 150 that the paper has reached the predetermined position. This timing control causes a toner image to be transferred onto the paper. The fixing unit 140 monitors its temperature and controls it to maintain an appropriate fixing temperature. While the fixing unit 140 controls its temperature in this way, if the paper absorbs a large amount of heat from the fixing unit 140, the temperature of the fixing unit 140 may drop. In this case, the fixing unit 140 notifies the printer control unit 160 of the drop in temperature of the fixing unit 140. Upon receiving this notification, the printer control unit 160 increases the interval between paper transports to prevent the temperature of the fixing unit 140 from dropping any further. If the temperature of the fixing unit 140 still does not return to normal, the printer suspends the printing operation and controls the operation to resume once the temperature of the fixing unit 140 returns to normal. When all the sheets have been ejected, printer control unit 160 instructs each unit to stop operation, receives operation stop notifications from each unit, and notifies MFP control unit 210 that operation has ended.

[0023] Furthermore, apart from the above basic operations, MFP 100 is configured to be able to perform image inspection of the output image using reading unit 170. Image inspection of the output image using reading unit 170 is performed by printer control unit 160 performing a detection process to detect the output image and transmitting the detected image to MFP control unit 210. The image inspection method for the output image will be described later.

[0024] Next, the hardware configuration of MFP 100 will be described with reference to Fig. 2. Fig. 2 is a functional block diagram showing the hardware configuration of MFP 100.

[0025] As shown in FIG. 2, the MFP 100 includes an MFP control unit 210, an input image processing unit 220, a NIC unit 231, a RIP unit 232, a memory unit 240, and an operation unit 250. The MFP 100 also includes an output image processing unit 260, a printer unit 270, a post-processing unit 271, a master image processing unit 280, and the reading unit 170 shown in FIG. 1. The input image processing unit 220 reads an original document, such as a paper document, using an image reading device such as a scanner and performs image processing on the read image data. The NIC (Network Interface Card) unit 231 passes image data (mainly PDL data) input via a network to the RIP unit 232 and transmits image data and device information within the MFP 100 to the outside via the network. The RIP (Raster Image Processor) unit 232 decodes input PDL (Page Description Language) data, performs RIP processing, and converts the data into bitmap data.

[0026] The MFP control unit 210 receives image data input via the input image processing unit 220 or the NIC unit 231. The MFP control unit 210 acts as a traffic controller, controlling the input data and output data. The MFP control unit 210 also temporarily stores the input image data in the memory unit 240. The memory unit 240 temporarily stores image data and calls up the stored image data as needed. The output image processing unit 260 performs image processing on the image data to output the image, and sends it to the printer unit 270.

[0027] The printer unit 270 sequentially forms images on paper sheets based on the image data generated by the output image processing unit 260. The printer unit 270 includes the image creating unit 130, fixing unit 140, paper feed / transport unit 150, printer control unit 160, etc. shown in FIG. 1. The paper sheets on which the images have been formed by the printer unit 270 are sent to a post-processing unit 271. The post-processing unit 271 performs processes such as sorting the paper sheets and finishing the paper sheets.

[0028] Next, the RIP unit 232 of the MFP 100 will be described with reference to Figure 3. Figure 3 is a functional block diagram showing the configuration of the RIP unit 232 of the MFP 100. The RIP is a processor that develops object information for each of vector information, or image scan line information such as colors, patterns, and photographs, into a bitmap (raster image) in memory in order to simultaneously reproduce this information on a page. Vector information includes characters, line drawings, and figures written in PDL (Page Description Language). Originally, RIPs were installed as hardware on the output device side, but now, with the increasing speed of CPUs, they are implemented as software.

[0029] The RIP unit 232 generally comprises two parts: an interpreter unit 310 and a rendering unit 320. The interpreter unit 310 comprises a PDL interpretation unit 311 that translates the PDL, and a DL (Display List) generation unit 312 that generates an intermediate file called a display list from the interpreted PDL data. The rendering unit 320 comprises a CMM (Color Matching Module) unit 321 that performs color matching on the display list, and a DL development unit 322 that develops the display list into a bitmap (raster image).

[0030] The PDL interpretation unit 311 analyzes various types of input PDL data. Well-known input data formats include Adobe Systems' PostScript (registered trademark) language and HP's (Hewlett-Packard's) PCL (Printer Control Language). These are written in printer control codes for creating page-by-page images, including simple character codes as well as graphics and photographic image codes. The PDF (Portable Document Format), a document display file format developed by Adobe Systems, is also widely used in various industries. The PDL interpretation unit 311 also analyzes data in this format that is input directly to the MFP 100 without using a driver. The PDL interpretation unit 311 also supports a format for VDP (Variable Data Print) called PPML (Personalized Print Markup Language). It also supports JPEG (Joint Photographic Experts Group) and TIFF (Tagged Image File Format). PPML and other formats are compression formats for color images.

[0031] The CMM unit 321 can input image data using various color representation methods, such as grayscale, RGB, and CMYK. For other color representation methods, the CMM unit 321 first converts the data to CMYK representation using a CRD (Color Rendering Dictionary) and then performs color matching. The CMM unit 321 performs color matching using an ICC profile. ICC profiles include a source profile and a printer profile. The source profile converts image data in RGB or CMYK representation (RGB image data or CMYK image data) into image data in L*a*b* representation, a standardized color representation method (L*a*b* image data). This L*a*b* image data is then converted back into CMYK image data suitable for the image forming device that will be the output destination. The source profile consists of an RGB profile and a CMYK profile. When the input image is an RGB image, an RGB profile is selected, and when the input image is a CMYK image, a CMYK profile is selected. Printer profiles are created to match the color characteristics of the image forming device to which they are output. For RGB images, it is preferable to select color characteristics that prioritize color tone or vividness, while for CMYK images, color characteristics with minimal color difference are often selected to output the optimal image.

[0032] Furthermore, ICC profiles are generally created in the form of a lookup table. When RGB or CMYK image data is input into a source profile, the input RGB or CMYK image data is uniquely converted into L*a*b* image data. In contrast, a printer profile converts L*a*b* image data into CMYK image data that is compatible with the destination printer. In a printer profile, RGB image data that does not require color matching is converted into CMYK image data using default color conversion settings and output, while CMYK image data that does not require color matching is output as is. The DL development unit 322 develops the output image data as 8-bit CMYK image data with a resolution of 600 dpi.

[0033] Next, operation unit 250 of MFP 100 will be described with reference to Fig. 4. Fig. 4 is a diagram showing a schematic configuration of a touch panel unit provided in operation unit 250 of MFP 100. As shown in the figure, operation unit 250 of MFP 100 includes touch panel unit 400. In the following explanation, explanations of basic buttons such as the start key and numeric input unit will be omitted.

[0034] Touch panel unit 400 is a touch panel display made up of a liquid crystal display (LCD) and transparent electrodes attached thereon that correspond to the various keys. Operation unit 250 is pre-programmed to detect when a finger touches the transparent electrodes that correspond to the various keys displayed on the LCD of touch panel unit 400 and display a different operation screen. FIG. 4 shows the initial screen displayed on touch panel unit 400 in standby mode, and operation unit 250 can display various operation screens on touch panel unit 400 in accordance with user settings.

[0035] In Fig. 4, copy tab 401 is a tab key for switching the display screen to an operation screen for copy operations, and send tab 402 is a tab key for transitioning to an operation screen for instructing transmission operations such as faxing or e-mail transmission. Box tab 403 is a tab key for switching to an operation screen for inputting and outputting jobs to a box, which is a storage means for storing jobs for each user. Expansion tab 404 is a tab key for setting expansion functions such as scanner settings. System monitor key 405 is a key for displaying the status and condition of MFP 100. By selecting each of the above tabs on touch panel unit 400, the user can switch the operation mode of MFP 100 to the respective operation mode.

[0036] Furthermore, color selection setting key 406 is a key for preselecting color copying, black and white copying, or automatic selection, and magnification setting key 407 is a key for switching to a screen for setting magnification such as same size, enlargement, or reduction. Post-processing setting key 408 is a key for switching to a screen for setting various post-processing settings such as sorter selection, presence / absence of stapling and punching, the number and position, etc. Duplex setting key 409 is a key for switching to a screen for selecting single-sided printing or double-sided printing, and paper setting key 410 is a key for switching to a screen for selecting a paper feed tray, paper size, and paper type. Image mode setting key 411 is a key for selecting an image mode suitable for the original image, such as text mode or photo mode, and density setting key 412 is a key for adjusting the darkness or lightness of the output image.

[0037] The status display unit 413 is a display unit that simply displays the status of the MFP 100, such as whether copying is possible, in standby mode, warming up, a jam has occurred, or an error has occurred, and the magnification display unit 414 displays the magnification set by the magnification setting key 407.

[0038] The paper display unit 415 displays the paper size and paper type set using the paper setting keys 410, and the number of copies display unit 416 displays the number of copies specified using a numeric keypad (not shown) provided on the operation unit 250, and also displays which copy is being printed during the copy operation.

[0039] An interrupt key 417 is a key for interrupting another job during a copy operation, and an application mode key 418 is a key for switching to a screen for setting various image processing and layouts such as continuous page copying, cover and inserting sheet settings, reduced layout, image movement, etc. In addition, the application mode selectable by the application mode key 418 includes a key for executing an image inspection of the output image, which will be described later.

[0040] Next, the printer driver will be described. It is used as a means for outputting a proof from a printing application to a printing device such as an MFP, or for outputting final image data. The printer driver is installed, for example, in a personal computer (PC) or the like that is communicably connected to the MFP control unit 210.

[0041] When a user prints an image using a printing device such as an MFP, the printer driver setting screen is generally displayed on the display unit of a PC by selecting a print menu of a printing application.

[0042] Fig. 5 is an explanatory diagram of an example of a printer driver setting screen displayed on the display unit of a PC. On the setting screen shown in Fig. 5, the user can switch the display screen to a property setting screen, which will be described later in Fig. 6, by pressing a property button 501. The user can set more detailed print attributes on this property screen. Furthermore, when the user has completed the desired settings on the printer driver setting screen, the user can print the image data to be printed by MFP 100 or output it to a desired file by pressing an OK button 502. Furthermore, the user can stop printing or file output by pressing a cancel button 503.

[0043] Figure 6 is an explanatory diagram of an example of a property setting screen in the printer driver setting screen. The property setting screen shown in Figure 6 is an example of a property setting screen for setting characteristics related to the finishing process of the printer driver. As shown in Figure 6, this property setting screen has an inspection content setting key 601 located in the lower left. When performing image inspection of the output image, which will be described later, the desired inspection can be performed by pressing this inspection content setting key 601 and selecting / modifying / changing detailed setting items. When the inspection content setting key 601 is pressed, the inspection content setting screen shown in Figure 10, which will be described later, is displayed.

[0044] (Reading unit) Next, the reading unit 170 will be described with reference to Figures 7 and 8. Figure 7 is a cross-sectional view showing the schematic configuration of the reading unit 170 as seen from the front, and Figure 8 is a view of the reading unit 170 as seen from the left side.

[0045] 7 and 8, the reading unit 170 includes a horizontally disposed transport roller pair 37, a horizontally disposed transport roller pair 38 below the transport roller pair 37, and a CIS device 50 disposed between the transport roller pairs 37, 38. The transport roller pairs 37 and 38 are disposed so that their nip portions face each other in the vertical direction, and transport a sheet of paper (indicated by P in the drawings) on which an image has been formed in the paper feed direction (the direction of arrow K in FIG. 7). The CIS device 50 is disposed below the transport roller pair 37 and above the transport roller pair 38, along the paper feed direction.

[0046] Furthermore, in the reading unit 170, an opposing plate 51 is disposed to the right of the CIS device 50 so as to face the right side of the CIS device 50 across the paper path. Specifically, as shown in FIG. 8 , in the CIS device 50, the CIS device 50 is disposed opposite the opposing plate 51 in an area surrounded by the pairs of transport rollers 37 and 38. A gap G of a fixed distance is formed between the CIS device 50 and the opposing plate 51. When the paper discharged from the fixing roller of the fixing unit 140 passes through this gap G, the CIS device 50 detects the output image on the paper.

[0047] The CIS device 50 incorporates an LED array 60 that illuminates the output image on the paper and a contact glass 61 that protects the interior of the CIS device 50 from paper abrasion and paper dust. It also incorporates a SELFOC® glass 62 that guides the projected light beam from the paper and a photodiode 63 that reads the projected light beam as a projected image. The photodiode 63 is configured to have a resolution of 1800 dpi in the main scanning direction and 1800 dpi in the sub-scanning direction. Also, RGB filters are arranged in order above the light-receiving surface of the photodiode 63. Therefore, the photodiode 63 actually has a full-color reading resolution of 600 dpi. While the photodiode 63 cannot resolve the output image down to the individual toner particles, the 600 dpi resolution of the RIP unit 232 makes it easy to compare the output image with the input image without requiring resolution conversion during output image inspection. Furthermore, the CIS device 50 can obtain output image information as 8-bit 256-level luminance signal information using the photodiode 63, and therefore can also make precise determinations regarding gradation.

[0048] The following describes an image inspection method for an output image in the MFP 100. In this example, if there is a damaged part (or a defective part) in a rotating part of an image forming part such as photosensitive drums 131-134, and if the damaged part is positioned on a sheet of paper, a defect will inevitably appear in the printed image on the sheet. Note that the image forming part is an element that constitutes an image forming apparatus, and is also referred to as an image forming element. Figures 9(a) to (e) show explanatory diagrams of the circumferential length of the rotating parts of the image forming parts (L-Parts), the length of the paper in the transport direction (L-sheet), and the distance between sheets of paper (L-Space) in relation to defects in printed images. 9(a) shows the case where (L-Parts)≦(L-Sheet). In this case, the perimeter of the image forming parts is equal to or less than the length of the paper in the transport direction, so as shown in the figure, defects occur continuously on each page. 9(b) shows the case where (L-Sheet)<(L-Parts)<(L-Sheet)+(L-Space). In this case, the perimeter of the image forming parts is longer than the length of the paper in the transport direction, and shorter than the sum of the length of the paper in the transport direction and the distance between sheets of paper, which means that there are cases where defects occur consecutively on every page, and cases where they do not. Figure 9(c) shows the case where (L-Parts) = (L-Sheet) + (L-Space). In this case, the circumference of the image forming parts is equal to the sum of the length of the paper in the transport direction and the distance between the sheets. As shown in the figure, if the image defect is on the paper, the defect will occur continuously on every page. However, if the defect is located between the sheets, the defect will continue to appear at the sheet-to-sheet position, so it can be seen that no defect will occur in the printed product.

[0049] Figure 9(d) shows the case where the condition (L-Sheet) + (L-Space) < (L-Parts) < 2 * {(L-Sheet) + (L-Space)} is satisfied. In this case, the perimeter of the image forming parts is longer than the sum of the length of the paper in the transport direction and the distance between the sheets of paper, but shorter than twice that sum, so it is possible that no defects will occur on the page. Figure 9(e) shows the case where the condition 2*{(L-Sheet)+(L-Space)}≦(L-Parts) is satisfied. In this case, the perimeter of the image forming parts is longer than twice the sum of the length of the paper in the transport direction and the distance between sheets, so defects occur on every other sheet or more. In this way, the longer the perimeter of the image forming parts that cause defects (L-Parts), the lower the frequency of defects. Also, the shorter the length of the paper in the transport direction (L-sheet), the lower the frequency of defects.

[0050] From the above explanation, for defects to occur consecutively on every page, the condition (L-Parts) ≦ (L-Sheet) or (L-Parts) = (L-Sheet) + (L-Space) must be satisfied. In other words, for other conditions, there will be pages without defects. Therefore, the method of stopping image formation when defects occur consecutively on each page does not appropriately determine whether to stop printing. For example, a drum with a diameter of approximately 80 mm is commonly used, and the drum circumference in this case is approximately 260 mm. Furthermore, the typical paper-to-paper distance is approximately 90 mm. Therefore, when printing A4-size paper (210 mm in the transport direction), the example in Figure 9(b) applies, and when printing 100 mm paper, such as official postcards, the example in Figure 9(e) applies. This shows that the method of stopping image formation when defects occur consecutively on each page is often inapplicable.

[0051] (Testing method) The image inspection method for the output image in the MFP 100 has the following six steps. Each step will be explained below.

[0052] (Step 1: Setting the inspection contents) Fig. 10 is an explanatory diagram of an inspection content setting screen that is displayed on the display unit of a PC when the inspection content setting key 601 is pressed on the property setting screen of Fig. 6. As shown in the figure, the inspection content setting screen has a check box 1001 for setting whether or not inspection is to be applied, a check box 1010 for setting the inspection level for point defects, and a check box 1011 for setting the inspection level for streak-like defects. For each type of defect (point defect, streak-like defect), the inspection application level can be selected from three levels: small, medium, and large. 10 is displayed on the touch panel unit 400 of the operation unit 250 by operating the application mode key 418 on the touch panel unit 400 of the operation unit 250 of the MFP 100 shown in FIG. 4. This allows the user to set the image inspection conditions in the same way as operating the printer driver described above.

[0053] (Step 2: Generate a master image to serve as the inspection standard) The functional configuration of the master image processing unit 280 will be described. FIG. 11 is a functional block diagram showing the configuration of the master image processing unit 280 shown in FIG. 2. As shown in FIG. 11, the master image processing unit 280 includes a color conversion processing unit 281 and a master image output processing unit 282. Note that the master image processing unit 280 according to this embodiment is realized by hardware configured as an ASIC or software control. When the user sends a print job with inspection application enabled, that is, with inspection being performed, 8-bit CMYK format image data with a resolution of 600 dpi is generated in the RIP unit 232 using the method described above. Color conversion processing unit 281 generates a master image in RGB format from CMYK format data input from RIP unit 232 via MFP control unit 210. By performing this processing, the image data formats of the master image and the inspection image are aligned, making them comparable. Note that the master image is not limited to one generated from a print job; a read image obtained by reading a previously output image using reading unit 170 may also be registered as the master image. Master image output processing unit 282 outputs the master image to MFP control unit 210. As a result, MFP control unit 210 acquires the master image.

[0054] (Step 3: Reading the inspection image) When a print job is received, printer control unit 160 forms an output image on paper. Then, reading unit 170 reads the output image to obtain a read image, which is an inspection image. Here, reading unit 170 reads the image of all printed output images, and performs the following processes from (Step 4: Determine whether there is a defect) to (Step 6: Determine whether printing can be stopped) for each page.

[0055] (Step 4: Determine if there are any defects) FIG. 12 is an explanatory diagram of the functional configuration of the MFP control unit 210 during inspection. As shown in FIG. 12, the MFP control unit 210 according to this embodiment includes an inspection result acquisition unit 1231, a print abort determination unit 1232, a defect feature extraction unit 1233, a print information acquisition unit 1234, an image forming component information acquisition unit 1235, and a printer control unit 160. The inspection result acquisition unit 1231 inputs the master image input from the master image processing unit 280 and the read image input from the reading unit 170 to the inspection unit 290, which then determines whether or not there is a defect and detects the defect. The inspection result acquisition unit 1231 also inputs the read image and the defect detection results from the inspection unit 290 to the print abort determination unit 1232. The defect feature extraction unit 1233 extracts feature values corresponding to each defect detected by the inspection unit 290.

[0056] The print information acquisition unit 1234 acquires the width of the printed paper in the transport direction (L-sheet) and the distance between the sheets (L-Space), and the image forming component information acquisition unit 1235 acquires the circumference information of each image forming component. The print abort determination unit 1232 determines whether to abort printing based on the master image input from the master image processing unit 280 and inputs from the inspection result acquisition unit 1231 and the image forming component information acquisition unit 1235. 13 is an explanatory diagram of a comparison inspection to determine the presence or absence of defects. When comparing a read image with a master image, the inspection unit 290 overlays the master image, which has been divided into predetermined ranges, on the read image corresponding to the divided ranges, and calculates the difference in pixel value of each pixel. This process is realized by the MFP control unit 210 acquiring images of the ranges to be overlaid from each of the master image and the read image, and inputting them to the inspection unit 290.

[0057] Furthermore, the inspection unit 290 determines the position where the calculated sum of the difference values is smallest as the accurate overlay position while shifting the position where the divided range is to be superimposed on the scanned image vertically and horizontally (i.e., while shifting the range of the image obtained from the scanned image vertically and horizontally).The inspection unit 290 then uses the calculated difference values of each pixel as the comparison result.As shown in FIG. 13, each square on the grid corresponds to a predetermined range for summing the difference values of each pixel.The size of each divided range shown in FIG. 13 can be determined arbitrarily, and is determined, for example, based on the range in which the inspection unit 290, which is configured by an ASIC as described above, can compare pixel values at one time.

[0058] Through this process, the scanned image and the master image are aligned, and then a difference value between them is calculated. For example, even if there is a difference in scale between the entire scanned image and the entire master image, the inspection unit 290 can reduce the impact of the difference in scale by dividing the scanned image into ranges and aligning them as shown in FIG. 13 . Here, the inspection unit 290 calculates a difference value between each pixel constituting the scanned image and each pixel constituting the master image, and compares the difference value with a threshold value to determine whether each pixel constitutes a defect in the image. Then, among the pixels determined to constitute a defect, pixels that are consecutive vertically and horizontally are merged. The inspection unit 290 detects the merged pixels as a single defect. Note that in this embodiment, a defect that is consecutive vertically or horizontally over a length of 1 cm or more is considered a streak defect, and a defect that is 1 cm or less in size in both the vertical and horizontal directions is detected as a point defect.

[0059] 14(a) and 14(b) are explanatory diagrams of defects that occurred on a page to be inspected. FIG. 14(a) shows the page to be inspected, and FIG. 14(b) shows a differential image generated by calculating the difference between the scanned image and the master image during image comparison inspection. These four defects are detected by comparison inspection with the master image. In the example of FIGS. 14(a) and 14(b), point defects def0001, def0002, and def0004 and a streak defect def0003 have occurred. def0004 is a point defect caused by a thinned portion of the image. Therefore, def0004 is an example of a defect that appears in an output image when the defect is caused by an image forming component and the defect location of the image forming component overlaps with an area where image data exists. Below, as shown in FIG. 14, the following description will be given using a coordinate system in which the paper transport direction is the X direction and the direction perpendicular to the paper transport direction (the main scanning direction of the laser exposure unit 120) is the Y direction.

[0060] (Step 5: Extracting defect features) The following describes a method for extracting feature amounts corresponding to each defect, which is executed by defect feature amount extraction unit 1233 of MFP control unit 210. Fig. 15 is an explanatory diagram of the feature amount extraction results for each defect detected by inspection unit 290. In this embodiment, the feature amounts extracted for the defect include the type of defect (point defect or streak defect), defect area, defect difference value, page on which the defect occurred (Pagedef), X coordinate position of the defect (Xdef), Y coordinate position of the defect (Ydef), and image formation distance (X') of the defect position.

[0061] The defect area is information indicating the number of pixels that make up each defect, i.e., the number of pixels detected as a defect on the page. The defect difference value is the difference value between the pixel value of the pixel that makes up each defect and the pixel value of the corresponding pixel in the master image. Note that each defect contains multiple pixels, so the difference value is the average of the difference values for each of the multiple pixels. The page on which the defect occurred (Pagedef) is the page on which the defect occurred in the output image that is printed continuously. The Y coordinate position (Ydef) of the defect is the center position of the detected defect in the direction perpendicular to the paper transport direction (the main scanning direction of the laser exposure unit 120). Note that the front edge of the paper body is set as the reference position of Y=0 mm. The X coordinate position (Xdef) of the defect is the center position of the detected defect in the X direction, which is the paper transport direction. Note that the leading edge of the paper in the transport direction is set as the reference position of X=0 mm.

[0062] The image formation distance (X') of the defect position corresponds to the X coordinate position of the defect on a sheet of paper that is sufficiently long in the transport direction (X direction) when multiple consecutive output images are output onto the same sheet. Therefore, this distance also includes the distance between the sheets. The leading edge of the first sheet of consecutive output images in the transport direction is set as the reference position of X' = 0 mm. In this embodiment, the paper is A4 size, the width of the printed paper in the transport direction (L-sheet) = 210 mm, and the distance between the sheets (L-Space) = 90 mm. Therefore, the leading edge of the first page in the transport direction is X' = 0 mm, the leading edge of the second page in the transport direction is X' = (210 + 90) = 300 mm, and the leading edge of the third page in the transport direction is X' = (210 + 90 + 210 + 90) = 600 mm. Furthermore, the leading edge of the nth page in the transport direction is X' = 300 * (n - 1) mm. In this way, when one defect and the other defect are on different sheets of paper, the distance between the sheets of paper being transported can be calculated by taking into account the distance between the sheets of paper in the transport direction.

[0063] The defect feature extraction unit 1233 acquires the width of the printed paper in the transport direction (L-sheet) and the distance between the sheets (L-Space) from the print information acquisition unit 1234, and calculates the image formation distance (X') of the defect position by using the page on which the defect occurred (Pagedef). Using Pagedef, X' is expressed as follows: X'=(Pagedef-1){(L-sheet)+(L-Space)}+ Xdef In the above example, it is assumed that there is no speed difference between the speed of the image forming surface of the rotating parts of the image forming components involved in image formation (i.e., the peripheral speed of the rotating parts) and the paper conveyance speed. However, there may be a speed difference between the paper conveyance speed and the peripheral speed of the rotating parts of the image forming components. In this case, the defect position for each rotating part must be corrected according to this speed difference, and the corrected image formation distance (X'-Parts) must be calculated for each image forming component. For example, the corrected image formation distance (X'-Parts-A) for the defect position for image forming component A, which rotates a% faster than the paper, can be calculated as (X'-Parts-A) = (X') × (100 + a) ÷ 100. Note that if there is no difference between the paper conveyance speed and the peripheral speed of the rotating parts of the image forming components, a = 0, and (X'-Parts) = (X').

[0064] (Step 6: Determine whether to cancel printing) The following describes the process for determining whether to abort printing based on the defect feature extraction results obtained as described above. Figures 16(a) to 16(c) are explanatory diagrams of the process for determining whether to abort printing, executed by the print abort determination unit 1232 of the MFP control unit 210. The print abort determination unit 1232 determines whether to abort printing based on the defect feature extraction results, to which the feature extraction results obtained by the inspection result acquisition unit 1231 have been added, and the circumferential length information of each image forming component obtained by the image forming component information acquisition unit 1235. The defect feature amounts used here are the Y-coordinate position (Ydef) and the image forming distance (X') of the defect position. The circumferential length information of the image forming components used for the determination is the circumferential length of the photosensitive drum 131 (simply referred to as the drum in the drawings), which is 260 mm, and the circumferential length of the fixing roller of the fixing unit 140, which is 430 mm. Additionally, the peripheral length of the intermediate transfer body 11 (simply referred to as ITB in the drawing), 1000 mm, and the peripheral length of the developing sleeve of the developing unit, 85 mm, are also used as peripheral length information.

[0065] This determination process determines whether or not there are defects that periodically occur in the conveyance direction (X direction) due to one of the multiple image forming components. Here, the Y direction is the direction of the rotation axis of the image forming components, and defects that occur due to image forming components hardly change position in the Y direction. Therefore, if there are multiple defects whose Y coordinate positions (Ydef) match within a predetermined range (e.g., ±5 mm), a determination is made for each defect as to whether or not to stop printing. The Y coordinate positions (Ydef) of defects def2001, def2002, def2003, and def2004 shown in Figure 15 are within the predetermined range, and it is determined that these Y coordinate positions substantially match.

[0066] As shown in FIG. 16(a), the difference (ΔX') in the image formation position X' is calculated for all combinations of two image formation positions (X') selected from defects def2001, def2002, def2003, and def2004. This difference ΔX' is calculated as the distance between the two defects in the paper transport direction, that is, the distance between the defects. This process is performed for all combinations each time a new defect is detected. For defect def2001, the difference ΔX' between defect def2001 and defect def2002 is 260 mm, the difference between defect def2001 and defect def2003 is 1676 mm, and the difference between defect def2001 and defect def2004 is 2080 mm. Similarly, the difference ΔX′ between defect def2002 and defect def2003 is 1416 mm, the difference between defect def2002 and defect def2004 is 1820 mm, and the difference between defect def2003 and defect def2004 is 404 mm.

[0067] In this embodiment, the range of the image formation position (X') of the defective data used to determine whether printing can be stopped is set to 20,000 mm, which is 20 times the 1,000 mm circumference of the intermediate transfer body 11. In other words, once the reading unit 170 detects the output image, data from an image formation distance of 20,000 mm or more before can be erased. The range of the image formation position (X') of the defective data can be arbitrarily determined within a range that allows the output image to be inspected at any time, taking into account the memory and computing capacity of the MFP control unit 210.

[0068] As shown in Figure 16(b), when multiple defects occur at a defective image formation position X', the difference ΔX' between the image formation positions X' is calculated for each combination of two different defects. Each calculated difference ΔX' is then determined for each image forming component to determine whether it is an integer multiple of a predetermined value. This is because if multiple differences ΔX' are all integer multiples of a predetermined value, there is a high probability that the defects occur periodically at that predetermined value. In this embodiment, the circumferential length of each image forming component involved in image formation is used as the predetermined value, and the difference ΔX' is determined for each image forming component to be an integer multiple of that circumferential length. For the circumferential length of the intermediate transfer body 11 (1000 mm), the differences for defects def2001, def2002, def2003, and def2004 are 26%, 168%, 208%, 142%, 182%, and 40% of the circumferential length of the intermediate transfer body 11, which are not integer multiples. Therefore, it is determined that none of these defects are caused by defects in the intermediate transfer body 11. The predetermined value is not limited to the circumference of the image forming component, and any other value may be used. In this case, it is possible to appropriately determine whether to stop image formation even for defects that occur periodically but whose cause is unknown.

[0069] For the circumference of the photosensitive drum 131 (260 mm), the difference between defect def2001 and defect def2002 is 100% of the circumference of the photosensitive drum 131, the difference between defect def2001 and def2004 is 800%, and the difference between defect def2002 and def2004 is 700%, all of which are integer multiples of the circumference. Therefore, it can be seen that these defects occur at distances that are integer multiples of the circumference of the photosensitive drum 131. Similarly, it can be seen that no defects occur at the circumference of the fixing unit (430 mm) or the developing sleeve (85 mm). Note that, because there is also position detection error, an error within a predetermined range, for example, an error of 1% or less, is allowed. If there is a speed difference between the paper transport speed and the peripheral speed of the rotating parts of the image forming parts, as described above, the difference ΔX' in the image formation position X' of each defect must be corrected according to this speed difference, and the corrected difference (ΔX'-Parts) must be calculated. For example, the difference (ΔX'-Parts-A) in the corrected image formation position X' of the defect position for image forming part A, which rotates a% faster than on the paper, can be calculated as follows: (ΔX'-Parts-A) = (ΔX') × (100 + a) ÷ 100. If there is no difference between the paper transport speed and the peripheral speed of the rotating parts of the image forming parts, a = 0, and (ΔX'-Parts-A) = (ΔX').

[0070] 16(c) shows an example of a determination made by the print abort determination unit 1232 as to whether to abort printing. When defect def2001 is detected in the image of the first page, there is only one defect, and the difference ΔX' in the image formation position X' of the defect cannot be calculated at this point, so it is not possible to determine whether to abort printing, and so it is determined that printing should continue. When defect def2002 is detected on the second page, it is determined that there is one combination of defects where the distance between the defects, that is, the difference ΔX' in the image formation position X' of two different defects, is an integer multiple of the circumference of the photosensitive drum 131. This combination is defect def2001 and defect def2002 (ΔX' = 260 mm and the drum circumference = 260 mm, which is 100% of the circumference). However, for defects not caused by defects in the circumferential length of the photosensitive drum 131, the difference ΔX' in the image formation position X' may coincidentally be an integer multiple of the circumferential length of the photosensitive drum 131. Therefore, in this embodiment, in order to prioritize judgment accuracy, it is determined that printing should continue when there is only one combination of defects (defect def2001 and defect def2002) that have occurred at image formation distances that are integer multiples of the circumferential length of the image forming component. If the decision to stop printing is prioritized over judgment accuracy, it may be determined that printing should be stopped at this point.

[0071] When defect def2003 is detected on the seventh page, the defect combination for which the difference ΔX' is an integer multiple of the circumference of the image forming component remains the combination of defect def2001 and defect def2002, and the number of combinations remains 1. Therefore, the print abort determination unit 1232 determines to continue printing. When defect def2004 is detected on page 8, two new defect combinations (defect def2001 and defect def2004, and defect def2002 and defect def2004) have occurred in which the difference ΔX' is an integer multiple of the circumference of the image forming component. For defect def2001, two other defects, defect def2002 and defect def2004, have occurred at distances that are integer multiples of the circumference of the photosensitive drum 131. Because there are multiple defect combinations in which the distance between the defects is an integer multiple of a predetermined value (in this case, the circumference of the photosensitive drum 131), the print abort determination unit 1232 determines to abort printing. It can also be determined that defect def2001, defect def2002, and defect def2004 all occur periodically due to the same cause: the photosensitive drum 131.

[0072] In this example, the cause of defect def2003 is unknown, and defects def2001, def2002, and def2004 are defects that occur only when a defective portion of the photosensitive drum 131, which is the cause of the defect, overlaps with an area where image data exists. For example, this defect corresponds to a defect equivalent to a missing image, in which an image cannot be formed even when image data is present. Therefore, if a defective portion of the photosensitive drum 131 overlaps with an area where image data does not exist, no defect will occur in the output image. Conversely, for example, a defect may occur in the image in the area corresponding to the defective portion of the photosensitive drum 131, regardless of the image data. The print abort determination unit 1232 presents information to the user via the operation unit 250 indicating that defects def2001 and def2002 occur only when a defective portion of the photosensitive drum 131 overlaps with an area where image data exists. The print abort determination unit 1232 also presents information to the user via the operation unit 250 indicating that the cause of defect def2003 is unknown. In this way, information indicating the image forming part (in this case, the photosensitive drum 131) that caused the image defect is output, and if the cause is unknown, information indicating this is output and displayed on the operation unit 250, thereby making maintenance work more efficient when printing is stopped.

[0073] Fig. 17 shows a flowchart illustrating processing executed by MFP control unit 210 of MFP 100. When check box 1001 for setting whether or not inspection is applied is checked in Fig. 10 and the user inputs a print job from operation unit 250 of MFP 100, MFP 100 starts image formation (S1711). The output image formed by MFP 100 is read by inspection unit 290 and sent to MFP control unit 210 (S1712). Inspection unit 290 compares the read image with a reference image (S1713) and inspects the image by determining whether or not there is a defect in the read image (S1714). If there is no defect (S1714: N), printing continues (S1715). On the other hand, if there is a defect in the scanned image (S1714: Y), the defect feature extraction unit 1233 extracts the defect feature (S1716), and the print abort determination unit 1232 determines whether to abort printing (S1717). In this determination, it is determined whether there are two or more sets of defects for which the difference ΔX' is an integer multiple of the circumference of the image forming component. If there are two or more sets, it is determined that printing should be aborted. If it is determined that printing should be aborted (S1717: Y), the MFP control unit 210 aborts printing. Furthermore, as described above, since it is possible to identify the image forming component that is causing the defect in the output image, information about the identified image forming component, etc. is output to and displayed on the operation unit 250. This allows information such as the name of the identified image forming component to be displayed to the user, thereby improving the efficiency of maintenance work on the image forming device. If the difference ΔX' is not an integer multiple of the circumference of the image forming component and it is determined that the defect is not caused by the image forming component, the print abort determination unit 1232 determines not to abort printing (S1717: N). Thereafter, the print abort determination unit 1232 continues printing because it is highly likely that no defects will occur in the output image when printing is performed again (S1715). As described above, in this embodiment, MFP control unit 210 determines whether there is a defect in the image and determines whether to stop printing (image formation), and MFP control unit 210 executes the function of an image inspection device.

[0074] Note that the process shown in FIG. 17 does not need to be limited to one continuous print job. Below, we will explain an example in which, after a first print job is executed in response to a first image formation command, a second print job is executed in response to a second image formation command different from the first image formation command. After the first print job is executed, the rotating unit of the image forming components performs a post-rotation, and paper is not transported during this post-rotation. Therefore, the rotation distance of the rotating unit during this post-rotation corresponds to the paper-to-paper distance (recording medium distance). Furthermore, before the second print job is executed, the rotating unit of the image forming components performs a pre-rotation. Paper is not transported during this pre-rotation. Therefore, the rotation distance of the rotating unit during this pre-rotation also corresponds to the paper-to-paper distance. It is also possible to calculate the image formation distance X' described above by using the rotation distance of the rotating unit of the image forming components during the pre-rotation and post-rotation as the paper-to-paper distance. In this case, even for defects that occurred in the first print job and the second print job, which are different print jobs, the image formation distance X' at the defect position and the above-mentioned difference ΔX' can be calculated, and a determination can be made as to whether printing should be stopped.

[0075] As described above, when the paper size being printed is small or the circumference of the image forming component that is the cause of the defect is long, it is possible that an image defect will occur only once after printing multiple sheets, such as once every two or three sheets. Therefore, a method of stopping printing when a defect is found on multiple consecutive sheets of output images may not be able to appropriately determine whether to stop printing. Furthermore, a defect may occur only when the condition that the location of the image forming component that causes the defect in the output image overlaps with the area where image data exists is met. Since whether image data exists in the location that causes the defect is dependent on chance, whether a defect will occur in the output image is also dependent on chance. Therefore, it has been difficult to appropriately determine whether to stop printing.

[0076] On the other hand, according to this embodiment, by determining whether the difference ΔX' in the image forming distance between multiple defects in the output image is an integer multiple of the circumferential length of the image forming component, it is possible to appropriately determine whether printing is stopped if the defect is caused by the image forming component. Furthermore, if a defect in the image forming component is the cause, the difference ΔX' will be an integer multiple of the circumferential length of the image forming component, regardless of whether the above-mentioned condition is met. Therefore, for defects where the difference ΔX' is an integer multiple of the circumferential length of the image forming component, it is possible to determine that the defect is caused by a defect in the image forming component, and appropriately determine whether printing is stopped. Furthermore, if the circumferential length of the image forming component that caused the defect is small, multiple defects may occur in a single output image. Even in this case, according to this embodiment, it is possible to appropriately determine whether printing is stopped even from a single printed image based on whether the difference ΔX' is an integer multiple of the circumferential length of the image forming component. Furthermore, since the determination of whether printing is stopped is made using the circumferential length of the image forming component, identifying the image forming component that caused the defect can streamline maintenance work on the image forming device after printing is stopped.

Claims

1. a reading means for reading a recording medium on which an image is formed by an image forming means; a control means for comparing the image read by the reading means with a reference image and inspecting the read image; when there are a plurality of defective images among the images read in the inspection, the control means calculates an inter-image distance between a first defective image and a second defective image in the conveyance direction of the recording medium, compares the inter-image distance with a component distance corresponding to a component of the image forming means, and displays information on a display means as to whether the inter-image distance is an integer multiple of the component distance; the distance between the defective images is a distance in a conveyance direction of the recording medium in an image forming apparatus including the image forming unit, the component distance is a circumferential length of a rotating part of an image forming element that constitutes the image forming apparatus and has a rotating part, the image forming device executes a second print job different from the first print job after executing the first print job; The control means calculates the image-to-image distance for the first defective image formed in the first print job and the second defective image formed in the second print job by using the rotation distance of the rotating unit after execution of the first print job and the rotation distance of the rotating unit before execution of the second print job as the recording medium-to-recording medium distance.

2. the control means determines to stop image formation on the recording medium by the image forming means when the inter-image distance is an integer multiple of the component distance, and determines to continue image formation on the recording medium by the image forming means when the inter-image distance is not an integer multiple. The image inspection device according to claim 1 .

3. the component distance is a circumferential length of a rotating part of an image forming element that constitutes the image forming apparatus and has a rotating part, The image inspection device according to claim 1 .

4. The image forming element is any one of a photosensitive drum, an intermediate transfer body, a fixing roller, and a developing sleeve provided in the image forming apparatus. The image inspection device according to claim 3.

5. When it is determined that the image formation on the recording medium by the image forming unit is to be stopped, the control unit outputs information representing the image forming element in order to present the image forming element to a user.

5. The image inspection device according to claim 3 or 4.

6. When the first defective image and the second defective image are on different recording media, the inter-image distance is calculated including the inter-recording medium distance in the conveying direction between the different recording media conveyed by the image forming apparatus. The image inspection device according to any one of claims 1 to 5.

7. the control means determines to stop image formation by the image forming means when there are a plurality of combinations of the plurality of defective images in which the inter-image distance is an integer multiple of the component distance; The image inspection device according to any one of claims 1 to 5.

8. When there is a speed difference between the conveying speed of the recording medium and the peripheral speed of the rotating part, the control means corrects the inter-image distance in accordance with the speed difference.

5. The image inspection device according to claim 3 or 4.

9. The control means is characterized in that it causes a display means to display information regarding whether the inter-image distance is a natural number multiple of the component distance that is equal to or greater than two. The image inspection device according to claim 1 .

Images