Image forming apparatus

Abstract

To provide an image forming apparatus that enables accurate image inspection. [Solution] An image forming apparatus according to one embodiment of this technology comprises a printing unit and an inspection unit. The printing unit has a plurality of nozzles for ejecting ink and forms an actual image so that an expected image is printed on a sheet. The inspection unit compares whether the actual image and the expected image match based on two different first and second rules. When the printing unit forms the actual image on the sheet, it performs a gradation correction predetermined based on the ejection characteristics of the plurality of nozzles, and the inspection unit performs a comparison based on the first rule in the correction region, which is the area on the actual image where the gradation correction has been performed, and performs a comparison based on the second rule in the area other than the correction region.

Description

Technical Field

[0001] The present technology relates to an image forming apparatus applicable to a printer or the like.

Background Art

[0002] Patent Document 1 discloses a recording apparatus that acquires a correction value for correcting the positional deviation between two nozzle arrays and a conveyance error of a test pattern by reading the test pattern. In this recording apparatus, the correction value is changed based on the conveyance error. This makes it possible to accurately correct the positional deviation of the nozzle arrays.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] [[ID=~]] In such an apparatus for forming an image, a technology that enables accurate inspection of the image of a printed matter is required.

[0005] In view of the above circumstances, an object of the present technology is to provide an image forming apparatus that enables accurate image inspection.

Means for Solving the Problems

[0006] To achieve the above object, an image forming apparatus according to one aspect of the present technology includes a printing unit and an inspection unit. The printing unit has a plurality of nozzles that eject ink and forms a real image so that an expected image is printed on a sheet. The inspection unit compares whether the real image and the expected image match based on two different first rules and second rules. When the printing unit forms the actual image on the sheet, it performs gradation correction based on a predetermined amount of ejection characteristics of the plurality of nozzles. The inspection unit performs a comparison based on the first rule in the correction region, which is the area on the actual image where the gradation correction has been performed, and performs a comparison based on the second rule in the area other than the correction region.

[0007] In this image forming apparatus, when forming a real image on a sheet, gradation correction is performed based on the nozzle's ejection characteristics. Furthermore, a comparison based on a first rule is performed in the correction area, and a comparison based on a second rule, which differs from the first rule, is performed in the area outside the correction area. This makes it possible to perform image inspection with high accuracy.

[0008] The printing unit may identify a defective nozzle among the plurality of nozzles that is exhibiting poor ejection characteristics, and perform the grayscale correction by changing the ejection amount of the nozzle adjacent to the defective nozzle.

[0009] The sheet is transported along a predetermined transport direction, and when the direction perpendicular to the transport direction is defined as the width direction, the inspection unit may identify the correction area based on the position of the defective nozzle and nozzle range information, which is the range in the width direction of the plurality of nozzles corresponding to sheet range information, which is the range of the sheet in the width direction.

[0010] The first rule may have more relaxed comparison conditions than the second rule.

[0011] The inspection unit may compare the actual image and the expected image using a plurality of pixels as units. In this case, the number of pixels included in the unit in the first rule may be greater than the number of pixels included in the unit in the second rule.

[0012] The sheet may be a single-fed sheet. In this case, the printing unit may obtain the sheet range information for each sheet by reading the edges of each sheet in the width direction, and calculate the nozzle range information for each sheet based on the sheet range information.

[0013] The printing unit may form a range image including the nozzle range information in an area of ​​the sheet where the actual image is not formed. In this case, the inspection unit may acquire the nozzle range information by reading the range image formed on the sheet.

[0014] The inspection unit may acquire the nozzle range information by communicating with the printing unit.

[0015] The inspection unit may read each of the actual images formed on the plurality of sheets and acquire an image as the expected image by combining the images obtained by removing the correction region from each of the actual images. [Brief explanation of the drawing]

[0016] [Figure 1] This is a schematic diagram showing an example of the configuration of an image forming apparatus according to one embodiment of this technology. [Figure 2] This is a schematic diagram showing an example of the configuration of the reading unit. [Figure 3] This is a schematic diagram showing an example of a head configuration. [Figure 4] This is a flowchart related to printing and inspection. [Figure 5] This is a schematic diagram illustrating the overview of ejection defects and grayscale correction. [Figure 6] This is a schematic diagram showing an example of a range image. [Figure 7] This is a flowchart related to the generation of the expected image. [Figure 8] This is a schematic diagram showing nozzle range information, etc. [Figure 9] This is a schematic diagram illustrating the process of combining real images. [Modes for carrying out the invention]

[0017] <First Embodiment> Hereinafter, embodiments of the present technology will be described with reference to the drawings.

[0018] [Image Forming Apparatus] FIG. 1 is a schematic diagram showing a configuration example of an image forming apparatus 1 according to an embodiment of the present technology. The image forming apparatus 1 is a printer that forms an image on a sheet 2 by an inkjet method. The image forming apparatus 1 may be other types of printers, fax machines, copiers, or multifunction peripherals.

[0019] Here, for convenience, an XYZ coordinate system is defined with respect to the drawings. When viewed from the direction in which the positive side of the Z axis is the upper side and the positive side of the X axis is the right side, the positive side of the Y axis is the back side (that is, a right-handed coordinate system). In the present embodiment, with the Z direction being the vertical direction (gravity direction) and the X and Y directions being horizontal directions, the image forming apparatus 1 is arranged as shown in FIG. 1. Note that the orientation in which the image forming apparatus 1 is used is not limited with respect to the application of the present technology.

[0020] The image forming apparatus includes a paper feeding unit 3, a printing unit 4, a drying unit 5, and an inspection unit 6. In FIG. 1, these ranges are indicated by a rectangular broken line. The image forming apparatus also has a control unit 7, a communication unit 8, and a storage unit 9. Although the control unit 7 etc. are illustrated as one block in FIG. 1, the control unit 7 etc. are each configured separately for each of the paper feeding unit 3, the printing unit 4, the drying unit 5, and the inspection unit 6.

[0021] The control unit 7 is a functional block that controls the operations of various mechanisms of the image forming apparatus 1. The communication unit 8 is a module for performing network communication, short-range wireless communication, etc. For example, a wireless LAN module such as WiFi or a communication module such as Bluetooth (registered trademark) is used. Through the communication unit 8, communication between the mechanisms within the image forming apparatus 1 and communication with external devices etc. are realized.

[0022] The memory unit 9 is a storage device such as non-volatile memory, for example, an HDD (Hard Disk Drive) or SSD (Solid State Drive). Alternatively, any non-transient storage medium readable by a computer may be used. Various information, such as the expected image described later, is stored in the memory unit 9. Other devices, such as a display unit and an operation unit, may also be configured within the image forming apparatus 1.

[0023] The paper feeding unit 3 includes a paper feeding cassette 10, a paper feeding roller 11, a tilt adjustment unit 12 (12a, 12b), and a resist sensor 13. The paper feeding cassette 10 is a cassette that holds the paper 2. In Figure 1, the paper feeding cassette 10 is schematically shown in a flat shape, but its specific shape is not limited.

[0024] Paper 2 is a sheet of paper that has been pre-cut into a rectangular shape. The specific shape of Paper 2 is not limited, and its shape may be changed as appropriate within the scope that makes this technology feasible. The material of Paper 2 is also not limited, and any type of Paper 2 that can form an image on its surface may be used. Paper 2 corresponds to one embodiment of the sheet relating to this technology.

[0025] Paper 2 is placed in the paper cassette 10, stacked so that the longer side of the rectangle is parallel to the X direction (left-right direction in Figure 1), and the shorter side is parallel to the Y direction (depth direction). Hereafter, the length of the longer side of paper 2 may be simply referred to as "length," and the length of the shorter side as "width" (see Figure 2A).

[0026] Inside the image forming apparatus 1, there are multiple rollers 14, indicated by thin circular lines. The paper 2 is transported towards the left side of Figure 1 by the driving of the rollers 14 and each mechanism.

[0027] Figure 1 shows the portion of the paper transport path excluding the transport belt 23 as a dashed line. Hereafter, this portion will be referred to as the transport path 15. In the transport path 15, the paper 2 is transported by being gripped and fed out by rollers 14. In reality, in addition to the rollers 14 shown in Figure 1, many other rollers 14 are provided along the transport path 15. Also, in Figure 1, only one roller 14 is represented by a reference numeral. Hereafter, if multiple identical mechanisms are configured, one of them may be represented by a reference numeral.

[0028] The paper feed roller 11 picks up the top sheet of paper 2 from the stack of paper 2 stored in the paper feed cassette 10 and sends it to the transport path 15. The tilt adjustment unit 12 adjusts the horizontal tilt of the paper 2. Specifically, as the paper 2 rotates in the horizontal plane due to transport, its long side and short side may no longer be parallel to the X and Y directions, respectively. The tilt adjustment unit 12 corrects the tilt of the paper 2 so that its long side and short side become parallel again. The resist sensor 13 detects whether or not a sheet of paper 2 is directly beneath it.

[0029] The printing unit 4 includes a pre-suction roller 18, a paper sensor 19, a transport belt unit 20, a reading unit 21, and a head 22 (22b, 22c, 22m, 22y). The pre-suction roller 18 rotates when the paper 2 is detected by the resist sensor 13, pressing the paper 2 against the upper surface 28 of the transport belt 23 of the transport belt unit 20. The paper sensor 19 is a timing sensor that detects the leading and trailing edges of the paper 2.

[0030] The conveyor belt unit 20 includes a conveyor belt 23, a drive roller 24, a speed detection roller 25, a meandering correction roller 26, and a number of fans 27. The conveyor belt 23 has a strip shape, and its width in the Y direction is greater than the width of the paper 2. The conveyor belt 23 also has holes of a predetermined size provided at predetermined intervals. The conveyor belt 23 is supported at its four corners by the drive roller 24, the speed detection roller 25, the meandering correction roller 26, and the normal roller 14, so that it is held in a state without bending, so that it is roughly rectangular when viewed from the Y direction.

[0031] The drive roller 24 drives the conveyor belt 23 by rotating. In this embodiment, the drive roller 24 rotates counterclockwise when viewed from the negative side of the Y direction, and consequently the conveyor belt 23 also rotates counterclockwise. That is, the upper surface 28 of the conveyor belt 23 moves toward the left side of the figure.

[0032] The speed detection roller 25 rotates as it receives frictional force from the conveyor belt 23 as the conveyor belt 23 rotates, and detects the speed of the conveyor belt 23 based on the speed of its rotation. The meandering correction roller 26 corrects the deviation of the conveyor belt 23 if it deviates to the positive or negative side in the Y direction as it rotates.

[0033] The fan 27 is a mechanism for drawing in air and is positioned directly below the upper surface 28 of the conveyor belt 23. In this embodiment, five fans 27 are shown, but the specific number and arrangement are not limited. After the paper 2 is pressed against the upper surface 28 by the pre-suction roller 18, it is attracted to the upper surface 28 by negative pressure through holes opened in the upper surface 28 when driven by the fan 27. As a result, the paper 2 is conveyed to the left while in close contact with the upper surface 28.

[0034] Figure 2 is a schematic diagram showing an example of the configuration of the reading unit 21. Figure 2 shows a view from above of the paper 2 passing below the reading unit 21. Figure 2 shows the state just before the paper 2 enters directly below the reading unit 21, and Figure 2B shows the state after the paper 2 has entered. The transport direction is indicated by a thick arrow.

[0035] The reading unit 21 has two CIS (Contact Image Sensor) 31 (31a, 31b). CIS 31a and 31b each have a rod shape and are arranged to extend in the Y direction. CIS 31a is located on the right side and CIS 31b is located on the left side, and there is an overlapping portion where parts of CIS 31a and 31b are present at the same position in the Y direction. In Figure 2, this overlapping portion is shown by a dashed line. The width of the overlapping portion in the Y direction is, for example, about 3 mm, but is not limited to this.

[0036] Here, due to transport errors and other factors, the position of each sheet of paper 2 in the width direction (Y direction) when it is transported will differ. In this example, sheet 2 is located approximately in the center of the entire CIS31, but sheet 2 may also be transported shifted upwards or downwards. Taking into account the possible range of such shifts, the Y-direction width of the entire CIS31 is set to a value with a certain margin so that the entire surface of sheet 2 passes directly beneath the CIS31 regardless of how it is shifted.

[0037] The CIS31 detects the paper 2 based on the difference in the amount of reflected light between the paper 2 and the transport belt 23. In overlapping areas, a method may be used that uses the detection result from either CIS31, or the average of the detection results from each CIS31. By using two CIS31s, it is possible to reduce manufacturing costs compared to using a single CIS31. Of course, a single CIS31 or three or more connected CIS31s may also be used.

[0038] Figure 3 is a schematic diagram showing an example of the configuration of the head 22. Figures 1 and 3 illustrate printheads 22b, 22c, 22m, and 22y, which eject black, cyan, magenta, and yellow inks, respectively. Each printhead 22 and the ink it ejects are illustrated with a different pattern.

[0039] Figure 3 shows the state where the paper 2 has entered directly beneath the head 22b. The head 22b consists of three heads 29a, 29b, and 29c, which are arranged in a staggered pattern extending in the Y direction, with overlapping portions, similar to the CIS 31. The head 22b also has a width with a margin so that the entire surface of the paper 2 passes directly beneath it.

[0040] Multiple nozzles are arranged on the lower surface of head 22b. Each nozzle is assigned a number corresponding to its position in the Y direction. For example, the nozzle on the far negative side in the Y direction of head 22b (located on head 29a) is assigned number 1, and the nozzle on the far positive side (located on head 29c) is assigned number 15000. The nozzles are arranged in a grid pattern when viewed from the Z direction, for example, but the arrangement and number are not limited.

[0041] The configuration of heads 22c, 22m, and 22y is the same as that of head 22b. The heads 22 are arranged from right to left in the order of heads 22b, 22c, 22m, and 22y. With the paper 2 positioned directly beneath each head 22, ink is ejected from the nozzles, forming a color image on the top surface of the paper 2. Hereinafter, this formed image may be referred to as the actual image.

[0042] The printing unit 4 forms an actual image so that the expected image is printed on the paper 2. The expected image is the image that is the target of printing, for example, the image that a user of the image forming apparatus 1 wishes to be printed on the paper 2. The expected image is stored in advance in the storage unit 9 of the printing unit 4. In the overlapping area of ​​the head 22b, control is performed such as ejecting ink by either the head 29a or 29b so that the expected image is printed appropriately.

[0043] The drying unit 5 in Figure 1 includes a dryer 35 and a reversing mechanism 36. The dryer 35 dries the ink adhering to the upper surface of the paper 2 by blowing hot air onto it. If printing is performed on only one side of the paper 2, the paper 2 is immediately transported to the inspection unit 6 after drying. On the other hand, if double-sided printing is performed, the paper 2 is transported to the reversing mechanism 36.

[0044] The reversal mechanism 36 has a reading unit 37. When the paper 2 reaches the position of the reading unit 37, the paper 2 switches back and is transported along the lower transport path 15 of the transport belt unit 20 with the pre-formed surface where the actual image has already been formed facing upwards. The paper 2 then passes through the tilt adjustment unit 12b with the unformed surface where the actual image has not yet been formed facing upwards, and the paper 2 passes directly under the head 22 again, thereby forming the actual image on the unformed surface. After that, the paper 2 is transported to the inspection unit 6.

[0045] The inspection unit 6 includes reading units 40 (40a, 40b), an output tray 41, and a waste tray 42. The reading units 40a and 40b are arranged on either side of the transport path 15. The reading unit 40a reads the actual image formed on the paper 2. In the case of double-sided printing, the reading unit 40b also reads the actual image.

[0046] The control unit 7 of the inspection unit 6 compares whether the actual image and the expected image match. If a match is determined, the paper 2 is ejected to the output tray. If a match is determined, the paper 2 is ejected to the waste tray and subsequently discarded by the user.

[0047] [Processing flow] Figure 4 is a flowchart related to printing and inspection. In this embodiment, the process shown in this flowchart is executed once for each sheet of paper 2. While this example describes single-sided printing, the process for double-sided printing is generally similar.

[0048] Paper 2 is read (step 101). The shape of paper 2 is acquired as an image by the CIS31 shown in Figure 2.

[0049] Paper size information is obtained (step 102). Paper size information is information indicating the range of paper 2 in the Y direction. Paper size information is obtained, for example, as a range of coordinate values ​​in the Y direction in real space, but the specific format is not limited. The paper range information corresponds to one embodiment of the sheet range information related to this technology.

[0050] The control unit 7 of the printing unit 4 detects the coordinate values ​​of the leading edge 32, trailing edge 45, and the Y-direction edges, the right edge 46 and left edge 47, of the paper 2, based on the image of the paper 2 shown in Figure 2. Then, based on the coordinate values ​​of the right edge 46 and left edge 47, it generates paper range information. In other words, the printing unit 4 can be said to acquire paper range information by reading the Y-direction edges of the paper 2.

[0051] The control unit 7 calculates the length of the paper 2 based on the coordinate values ​​of the front end 32 and the rear end 45, and calculates the width of the paper 2 based on the coordinate values ​​of the right end 46 and the left end 47.

[0052] Furthermore, the control unit 7 obtains the travel speed of the transport belt 23 from the speed detection roller 25 when the tip 32 is detected. Based on this travel speed, the control unit 7 calculates the time it takes for the paper 2 to pass through each head 22 and determines the ink ejection timing of each head 22.

[0053] Nozzle range information is calculated (step 103). Nozzle range information indicates the range in the Y direction of the nozzles that the paper 2 passes directly beneath. Nozzle range information is expressed using the numbers assigned to the nozzles, for example, as a range such as "348:14380". In this case, the paper 2 passes through the range from directly beneath nozzle number 348 to directly beneath nozzle number 14380. In other words, the right edge 46 of the paper 2 passes almost directly beneath nozzle number 348, and the left edge 47 passes almost directly beneath nozzle number 14380. The specific format of the nozzle range information is not limited.

[0054] The control unit 7 of the printing unit 4 calculates nozzle range information based on the paper range information. Specifically, the Y-coordinate values ​​of each nozzle number are stored in advance in the storage unit 9, and the nozzle range information is calculated by matching these coordinate values ​​with the coordinate values ​​of the paper range information.

[0055] For example, if the nozzle range information is "348:14380" and paper 2 moves a predetermined amount to the positive side in the Y direction, the nozzle range information changes to "355:14387". These are some possible explanations.

[0056] Printing, including gradation correction, is performed (step 104). Figure 5 is a schematic diagram illustrating the overview of ejection defects and grayscale correction. In the image forming apparatus 1 according to this embodiment, the nozzle ejection characteristics may change with use. Specifically, there may be cases where the nozzle does not eject any ink at all, or ejects ink poorly. Hereinafter, nozzles exhibiting ejection defects may be referred to as defective nozzles.

[0057] For example, if the image forming apparatus 1 is not used for a long period of time, or if it is used but some nozzles are located outside the printing range and ink ejection by those nozzles is not required, ink may solidify inside the nozzles and clog, causing ejection failure. Also, paper fibers 2 may get stuck inside the nozzles, causing ejection failure. Such ejection failures often cannot be improved by cleaning, and the faulty nozzles may become unusable permanently.

[0058] Figure 5A shows the expected image 49 of a night landscape. In this example, this expected image 49 is the image that should be printed. Figure 5B shows the actual image 50 that would occur if printed without any correction while a defective nozzle is present. Because insufficient ink is ejected from the defective nozzle, a linear white streak 51 appears on the actual image 50 at a position in the Y-direction that is the same as the position of the defective nozzle.

[0059] Figure 5C shows the actual image 50 after grayscale correction. In this embodiment, the printing unit 4 performs grayscale correction based on the nozzle ejection characteristics when forming the actual image 50 on the paper 2. Specifically, the control unit 7 of the printing unit 4 identifies defective nozzles that are causing ejection problems in terms of ejection characteristics.

[0060] Whether a nozzle is defective can be determined, for example, by driving a piezoelectric element in the head 22 and basing the determination on the degree of vibration generated within the head 22. The number of the determined defective nozzle is stored in the storage unit 9 and referenced by the control unit 7 during printing.

[0061] The control unit 7 performs gradation correction by changing the discharge volume of nozzles adjacent to the defective nozzle. Specifically, it increases the discharge volume of two nozzles adjacent to the defective nozzle in the Y direction to make the white streaks less noticeable. For example, if nozzle 1027 of head 22b is experiencing a discharge malfunction, control is performed to increase the discharge volume of nozzles 1026 and 1028 of head 22b.

[0062] As a result, the area corresponding to the white streak 51 in Figure 5B is corrected and becomes less noticeable, as shown in Figure 5C. Hereafter, this area will be referred to as the corrected area 52. The corrected area 52 is the area on the actual image 50 where gradation correction has been performed. Although Figure 5C illustrates the corrected area 52, in reality, it blends in with the surrounding area to such an extent that it is not noticeable to the human eye that it has been corrected.

[0063] Furthermore, gradation correction may be performed by changing the discharge volume of nozzles located at a certain distance away from the defective nozzle. Also, it is conceivable that the discharge volume of a nozzle may unintentionally increase as a discharge characteristic. In such cases, processing to reduce the discharge volume of other nozzles may be performed. The content of the discharge characteristics and the method of gradation correction are not limited.

[0064] The printing unit 4 performs printing, including gradation correction, based on nozzle range information and ejection timing. Here, the position of the defective nozzle does not change, but the position of the paper 2 changes each time, so the position of the correction area 52 on the actual image 50 will be different each time. For example, if the paper 2 is transported at a position to the right (negative side in the Y direction) than in the example in Figure 5C, the correction area 52 will be located to the left of Figure 5C, as shown in Figure 5D.

[0065] The inspection unit 6 acquires nozzle range information (step 105). In this embodiment, the inspection unit 6 acquires nozzle range information by communicating with the printing unit 4. Specifically, the communication unit 8 of the printing unit 4 transmits the nozzle range information wirelessly, and the communication unit 8 of the inspection unit 6 acquires it. Alternatively, the printing unit 4 and the inspection unit 6 may be connected by a cable or the like, and transmission may be performed via wired connection. Note that the processes in steps 105 and 106 may be executed immediately after step 103 and in parallel with step 104.

[0066] The inspection unit 6 identifies the correction area (step 106). The control unit 7 of the inspection unit 6 identifies the correction area 52 based on the position of the defective nozzle and the nozzle range information, which are stored in the storage unit 9 beforehand. Since the nozzle range information also represents the position range in the Y direction where the paper 2 is located, it is possible to identify the position of the correction area 52 by offsetting the position of the defective nozzle with the nozzle range information.

[0067] The actual image 50 and the expected image 49 are compared (step 107). First, the reading unit 40 reads the actual image 50 formed on the paper 2. In this embodiment, the expected image 49 is pre-stored in the storage unit 9 of the inspection unit 6. The control unit 7 of the inspection unit 6 compares whether the actual image 50 and the expected image 49 match based on two different rules, a first rule and a second rule. Here, in the correction region 52, a comparison based on the first rule is performed, and in regions other than the correction region 52, a comparison based on the second rule is performed.

[0068] In this embodiment, the control unit 7 compares the actual image 50 and the expected image 49 using multiple pixels as units. Specifically, for example, a unit consisting of an arbitrary n x n square group of pixels is defined in a grid, the average value of the color tone of the pixels in that unit is calculated, and the average values ​​are compared for each unit. If there is a unit where the difference in average values ​​is greater than or equal to a predetermined threshold, it is determined that the actual image 50 and the expected image 49 do not match. If the difference in average values ​​for all units is less than the threshold, it is determined that the actual image 50 and the expected image 49 match.

[0069] The finer the grid and the fewer pixels are contained within each unit, the stricter the comparison conditions become. In other words, defects such as ink smudges, stains, fading, and ejection failures in the actual image 50 become easier to detect, and the likelihood of determining that the two images do not match increases.

[0070] The inspection unit 6 uses the above-mentioned unit-by-unit comparison as the first and second rules. Furthermore, the number of pixels included in the unit in the first rule is set to be greater than the number of pixels included in the unit in the second rule. These first and second rules are different from each other, and as described above, the first rule has more relaxed comparison conditions than the second rule. In other words, the comparison using the first rule is less likely to detect minor defects as defects than the comparison using the second rule.

[0071] The inspection unit 6 applies the first rule to the correction region 52 identified in step 106, and the second rule to regions other than the correction region 52. That is, in the regions corresponding to the correction region 52 of the actual image 50 and the correction region 52 of the expected image 49, the grid is made coarser, and a comparison is performed under relatively lenient conditions. In addition, in regions other than the correction region 52, the grid is made finer, and a comparison is performed under relatively strict conditions.

[0072] Since the correction region 52 does not cause any discomfort when viewed with the human eye, the actual image 50 including the correction region 52 should be judged as normal. However, from a microscopic perspective, differences in density occur due to gaps remaining between ink droplets, etc., so if the comparison criteria in the correction region 52 are the same as the criteria in other regions, the two images may be judged as not matching. To prevent such misjudgments, this technology applies a more lenient rule to the correction region 52 than to other regions.

[0073] There are no restrictions on how the units of multiple pixels are defined, nor are the comparison methods limited to comparing average values. Furthermore, another rule could be added, such as adding a condition to the first rule only: "Even if a difference in color tone is detected, it will not be considered defective unless such areas are continuous in streaks for a predetermined length or longer." In this case as well, the first rule differs from the second rule, and its conditions are relaxed.

[0074] Generally, when expressing the degree of pixel matching numerically, if the first rule is defined as "a match is determined if the degree of matching is 60 or higher" and the second rule is defined as "a match is determined if the degree of matching is 80 or higher," then the first rule is less stringent than the second rule.

[0075] The rules may be determined according to the color of the correction area 52, such as making the conditions stricter for conspicuous colors. The rules may also be determined according to the position of the correction area 52, such as making the conditions stricter for the central part of the actual image 50, as it is more conspicuous. The conditions may be made stricter if the user selects an area of ​​high importance and the correction area 52 is located within that area.

[0076] Furthermore, any comparison method may be used in which the first rule is applied in the correction region 52 and the second rule is applied in other regions, and in which the first rule and the second rule are different from each other. For example, the first rule does not necessarily have to be less restrictive than the second rule, as long as the effects of this technology are achieved. Also, the comparison method is not limited to comparing on a unit-by-unit basis.

[0077] If the actual image 50 and the expected image 49 match (Yes in step 108), paper 2 is ejected into the output tray 41 (step 109). If they do not match (No in step 108), paper 2 is ejected into the waste tray 42 (step 110).

[0078] In the image forming apparatus 1 according to this embodiment, when forming a real image 50 on the paper 2, gradation correction is performed based on the nozzle ejection characteristics. Furthermore, a comparison based on a first rule is performed in the correction region 52, and a comparison based on a second rule different from the first rule is performed in regions other than the correction region 52. This makes it possible to perform image inspection with high accuracy.

[0079] As mentioned earlier, although the correction region 52 does not cause any discomfort to the human eye, it may be judged as an abnormal image from a microscopic perspective. This technology prevents such misjudgments because the correction region 52 is judged according to different rules than other regions.

[0080] Furthermore, in this technology, the printing unit 4 identifies defective nozzles, and gradation correction is performed by changing the discharge amount of nozzles adjacent to the defective nozzles. This results in even higher precision gradation correction.

[0081] Furthermore, in this technology, the correction area 52 is identified based on the location and nozzle range information of the defective nozzle. For example, when roll paper is used, the position of the paper 2 in the width direction does not change, so as long as the location of the defective nozzle can be identified, it is possible to apply different rules in the correction area 52. However, when the paper 2 is a single sheet, the position of the paper 2 changes each time, so even if the location of the defective nozzle is known, it is not possible to determine the location of the correction area 52 on the paper 2 based on that alone.

[0082] This technology utilizes nozzle range information, making it possible to pinpoint the position of the correction area 52. This allows for the application of different rules to the correction area 52 while tracking changes in the position of the paper 2.

[0083] Furthermore, this technology uses a first rule with more relaxed conditions than the second rule. This makes it possible to prevent misjudgments even more reliably.

[0084] Furthermore, in this technology, comparisons are performed using multiple pixels as units, and the number of pixels in the first rule is greater than the number of pixels in the second rule. This makes it possible to prevent misjudgments in the correction region 52 while reliably detecting defective areas in areas other than the correction region 52.

[0085] Furthermore, in this technology, paper range information is obtained by reading the edges of the paper 2 in the width direction, and nozzle range information is calculated based on the paper range information. This allows for even more accurate calculation of the nozzle range.

[0086] Furthermore, in this technology, the inspection unit 6 acquires nozzle range information through communication with the printing unit 4. This allows for high-speed acquisition of nozzle range information, thereby reducing the overall printing time.

[0087] <Second Embodiment> A more detailed embodiment of the image forming apparatus 1 relating to this technology will be described as a second embodiment. In the following description, parts that are similar to the configuration and operation of the image forming apparatus 1 described in the above embodiment will be omitted or simplified.

[0088] [Get nozzle range details] Figure 6 is a schematic diagram showing an example of a range image. In this embodiment, the printing unit 4 forms a range image including nozzle range information. Figure 6 shows the upper left portion of the paper 2 on which the actual image 50 is formed. In the area above the actual image 50, which is the margin where the actual image 50 is not formed, the range image of characters 55 and code 56 is formed.

[0089] A range image is an image containing nozzle range information. The character 55 is an image that directly displays the nozzle range information as text, with "348:14380" in character 55 representing the nozzle range information. Code 56 is a QR code (registered trademark), and by scanning code 56, it is possible to access a web page or other content that contains the nozzle range information.

[0090] Either character 55 or code 56 may be formed. Alternatively, another image containing nozzle range information may be formed. Furthermore, the range image may be formed in any area where the actual image 50 is not formed. Note that "PRINT-ID" in the figure is a number assigned to each print section. Code 56 may also contain information including the print ID.

[0091] The range image is formed simultaneously with the actual image 50, and the inspection unit 6 reads the range image simultaneously with the actual image 50. This allows the inspection unit 6 to acquire nozzle range information. After printing, the area where the range image was formed is cut off. This cutting may be performed automatically by the device, or manually by the user using a cutting machine or the like.

[0092] In this embodiment, nozzle range information is transmitted from the printing unit 4 to the inspection unit 6 via the paper 2 without using the communication unit 8. This makes the technology applicable even in offline systems where communication between the printing unit 4 and the inspection unit 6 is impossible.

[0093] <Third Embodiment> [Generating the expected image] Figure 7 is a flowchart showing the process for generating the expected image 49. Figure 8 is a schematic diagram showing nozzle range information, etc. Figure 9 is a schematic diagram illustrating the synthesis of the actual images 50. In this embodiment, the expected image 49 is not pre-stored in the storage unit 9 of the inspection unit 6. Furthermore, there is no communication unit 8, making it impossible to obtain the expected image 49 from the printing unit 4 via communication. In such cases, the inspection unit 6 generates the expected image 49 by reading multiple actual images 50.

[0094] Multiple copies of the actual image 50 are printed (step 201). In this example, as shown in Figure 8, two copies of the actual image 50 are printed, with multiple pages considered as one copy (print IDs 0349587, 0349588). Three or more copies of the actual image 50 may be printed.

[0095] The inspection unit 6 reads each of the actual images 50 (step 202). In addition, nozzle range information is acquired by the method via the range image in Figure 6, etc. Figure 8 shows an example of the acquired nozzle range information. "Page001", etc., represent the page number in the printing unit. "Correction" is the number of a known defective nozzle; in this example, nozzles 1027, 7891, and 10456 are defective.

[0096] It is determined whether the nozzle range information is identical or not (step 203). Specifically, the inspection unit 6 determines, page by page, whether the nozzle range information is identical between each unit. For example, on page 1, the nozzle range information is "348:14380" and "361:14395", so these are not identical. Similarly, they are not identical on pages 2 and 3. The same determination is repeated for pages 4 and beyond.

[0097] As indicated by the dashed frame and arrow, instead of focusing on the entire nozzle range information, it is also possible to determine whether or not they match by focusing only on the starting nozzle. Furthermore, if there are three or more copies, if the nozzle range information matches across all copies on a given page, it is determined that the nozzle range information is identical on that page.

[0098] If there is at least one page with identical nozzle range information, it is determined that the nozzle range information is identical (Yes in step 203), and the actual image 50 is reprinted (step 201). If there are no pages with identical nozzle range information, it is determined that the nozzle range information is not identical (No in step 203), and multiple actual images 50 are combined (step 204).

[0099] Figure 9A shows two real images 50 read in step 202. The two real images 50 have different part numbers, but the page number is the same, being page 1. Each real image 50 includes correction areas 52a and 52b, but because the paper transport positions are different, the positions of correction areas 52a and 52b are different.

[0100] As shown in Figure 9B, the inspection unit 6 performs the process of removing the correction region 52 from each actual image 50. The correction region 52 is identified by offsetting the defective nozzle using nozzle range information, as described above. Then, as shown in Figure 9C, the images with the correction region 52 removed are combined, and the resulting combined image is the expected image 49.

[0101] Of the expected image 49, the right-hand actual image 50 is used for the portion that was correction area 52a. Conversely, the left-hand actual image 50 is used for the portion that was correction area 52b. For the remaining portions, processing may be performed using either one of the actual images 50, or using the average value of the color tones of each actual image 50. Furthermore, if there are three or more copies, processing may also be performed using the average value of the color tones of the remaining actual images 50 for the portion that was correction area 52.

[0102] The expected image 49 generated in this way does not include the correction region 52, and is therefore almost identical to the expected image 49 data held by the printing unit 4. The inspection unit 6 repeats the same synthesis for each page to generate each expected image 49.

[0103] If there are pages with identical nozzle range information in step 203, when those pages are combined to generate the expected image 49, the actual image 50 used for the part corresponding to the correction region 52 does not exist, and the expected image 49 is generated without the correction region 52. To prevent this from happening, if there are pages with identical nozzle range information, reprinting is performed.

[0104] To reduce the likelihood of needing to reprint, you may print an increased number of copies in advance. This method is effective when there are many pages, as the probability of matching nozzle range information increases. Alternatively, instead of reprinting all pages, you may reprint only the pages with identical nozzle range information.

[0105] If the position of paper 2 does not change, the position of the correction area 52 on paper 2 will be the same each time, making it impossible to generate the expected image 49 by this synthesis. In this technology, the position of paper 2 changes, and this can be used to generate the expected image 49 by synthesis. As a result, even if the expected image 49 is not stored in advance on the inspection unit 6 side and the communication unit 8 is not present, the inspection unit 6 can acquire an expected image 49 with a high degree of fitness. [Explanation of Symbols]

[0106] 1…Image forming apparatus 4…Printing department 6…Inspection Department 7…Control Unit 8… Communications Department 21, 40... Reading section 22, 29... Head 31…CIS 46…Rightmost 47…Far left 49...Expected image 50…Actual image 52…Correction area 55... characters 56... Code

Claims

1. A printing unit having multiple nozzles for ejecting ink and forming an actual image so that the expected image is printed on the sheet, The system comprises an inspection unit that compares whether the actual image and the expected image match based on two different rules, namely a first rule and a second rule. When the printing unit forms the actual image on the sheet, it performs gradation correction that is predetermined based on the ejection characteristics of the plurality of nozzles. The inspection unit performs a comparison based on the first rule in the correction region, which is the area on the actual image where the gradation correction has been performed, and performs a comparison based on the second rule in the area other than the correction region. Image forming apparatus.

2. An image forming apparatus according to claim 1, The printing unit identifies a defective nozzle among the plurality of nozzles that is exhibiting poor ejection characteristics, and performs the grayscale correction by changing the ejection amount of the nozzle adjacent to the defective nozzle. Image forming apparatus.

3. An image forming apparatus according to claim 2, The sheet is transported along a predetermined transport direction, and when the direction perpendicular to the transport direction is defined as the width direction, The inspection unit identifies the correction area based on the location of the defective nozzle and the nozzle range information, which is the range in the width direction of the plurality of nozzles corresponding to the sheet range information, which is the range in the width direction of the sheet. Image forming apparatus.

4. An image forming apparatus according to claim 3, The first rule has more relaxed comparison conditions than the second rule. Image forming apparatus.

5. An image forming apparatus according to claim 4, The inspection unit compares the actual image and the expected image using multiple pixels as units. In the first rule, the number of pixels included in the unit is greater than the number of pixels included in the unit in the second rule. Image forming apparatus.

6. An image forming apparatus according to any one of claims 3 to 5, The aforementioned sheet is a single-sheet sheet, The printing unit reads the edges of each sheet in the width direction to obtain the sheet range information for each sheet, and calculates the nozzle range information for each sheet based on the sheet range information for each sheet. Image forming apparatus.

7. An image forming apparatus according to claim 6, The printing unit forms a range image including the nozzle range information in an area of ​​the sheet where the actual image is not formed. The inspection unit acquires the nozzle range information by reading the range image formed on the sheet. Image forming apparatus.

8. An image forming apparatus according to claim 6, The inspection unit acquires the nozzle range information by communicating with the printing unit. Image forming apparatus.

9. An image forming apparatus according to any one of claims 1 to 5, The inspection unit reads the actual images formed on the plurality of sheets, and acquires an image as the expected image by combining the images obtained by removing the correction region from each of the actual images. Image forming apparatus.

Images