Image forming apparatus and image forming method

Abstract

To perform shading correction according to real-time reading characteristics without using a white reference member.SOLUTION: An image forming apparatus comprises: a conveyance mechanism that conveys a recording medium; an image sensor that can detect the position of the recording medium; and a control unit that controls the conveyance mechanism and the image sensor. The control unit causes the conveyance mechanism to convey the recording medium to a place below the image sensor, causes the image sensor to acquire read data obtained by reading a white background part of the recording medium conveyed to the place below the image sensor, and executes shading correction for the image sensor based on the read data.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus and an image forming method. [Background technology]

[0002] In image forming devices such as printers and copiers, the position of the recording medium is read using, for example, an image sensor on the transport path of the recording medium, and the attitude of the recording medium is corrected based on the result. In order to obtain a good read image of the recording medium, shading correction is sometimes performed using a white reference member to remove uneven brightness from the read image.

[0003] For example, in Patent Document 1, a plurality of shading data are stored in advance, and shading correction is performed by reading out a given shading data as appropriate, thereby making it possible to perform shading correction without using a white reference member. Summary of the Invention [Problem to be solved by the invention]

[0004] However, the technology of Patent Document 1 requires that multiple pieces of shading data be obtained in advance, and only data selected from the shading data prepared in advance can be used. Therefore, the amount of data becomes enormous, and there is a risk that the correction accuracy will decrease.

[0005] The present invention has been made in consideration of the above, and aims to provide an image forming apparatus and an image forming method that can perform shading correction according to real-time reading characteristics without using a white reference member. [Means for solving the problem]

[0006] In order to solve the above problems and achieve the object, the present invention provides a recording medium recording apparatus comprising: a conveying mechanism for conveying a recording medium; an image sensor capable of detecting a position of the recording medium; and a control unit for controlling the conveying mechanism and the image sensor, the transport mechanism includes a sub-scanning direction transport mechanism that transports the recording medium in a sub-scanning direction connecting a paper feed unit and a paper discharge unit, and a main scanning direction transport mechanism that transports the recording medium in a main scanning direction perpendicular to the sub-scanning direction, and the image sensor is a line sensor that extends in the main scanning direction beyond an end position of the recording medium in the main scanning direction so as to be able to detect the end position of the recording medium in the main scanning direction; The control unit causes the conveying mechanism to convey the recording medium below the image sensor, causes the image sensor to acquire read data obtained by reading a white background portion of the recording medium conveyed below the image sensor, and performs shading correction of the image sensor based on the read data. When the image sensor acquires the read data used for the shading correction, the recording medium is moved in the main scanning direction by the main scanning direction transport mechanism, and at least a reading area corresponding to a maximum use area of ​​the image sensor is covered with the recording medium. . Effect of the Invention

[0007] According to the present invention, shading correction can be performed in accordance with real-time reading characteristics without using a white reference member. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating an example of a configuration of an image forming apparatus according to an embodiment. [Diagram 2] FIG. 2 is a diagram illustrating an example of the configuration of a registration mechanism and an image sensor according to the embodiment. [Diagram 3] FIG. 3 is a block diagram illustrating an example of a hardware configuration of the image forming apparatus according to the embodiment. [Figure 4] FIG. 4 is a block diagram showing an example of a configuration for realizing the registration adjustment function according to the embodiment. [Diagram 5] FIG. 5 is a diagram illustrating an example of an operation performed when the image forming apparatus according to the embodiment obtains a read value of the white level. [Figure 6] FIG. 6 is a diagram illustrating an example of an operation of acquiring a read value of a white level by the image forming apparatus according to the embodiment. [Figure 7] FIG. 7 is a diagram illustrating shading correction of the image sensor according to the embodiment. [Figure 8]FIG. 8 is a diagram illustrating an example of an operation of correcting the attitude of a recording medium by the image forming apparatus according to the embodiment. [Figure 9] FIG. 9 is a diagram illustrating an example of an operation of correcting the attitude of a recording medium by the image forming apparatus according to the embodiment. [Figure 10] FIG. 10 is a diagram illustrating an example of a timing chart of each unit when the image forming apparatus according to the embodiment performs an operation to correct the attitude of the recording medium. [Figure 11] FIG. 11 is a flowchart illustrating an example of a procedure of a white level reading process performed by the image forming apparatus according to the embodiment. [Figure 12] FIG. 12 is a flowchart illustrating an example of a procedure for correcting the attitude of the recording medium by the image forming apparatus according to the embodiment. [Figure 13] FIG. 13 is a diagram illustrating an example of an operation of acquiring a read value of a white level by the image forming apparatus according to the first modification of the embodiment. [Figure 14] FIG. 14 is a diagram illustrating an example of an operation of acquiring a read value of a white level by an image forming apparatus according to the second modification of the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, the best mode for carrying out the invention will be described with reference to the drawings.

[0010] (Example of configuration of image forming device) 1 is a diagram showing an example of the configuration of an image forming apparatus 100 according to an embodiment. The image forming apparatus 100 is configured as, for example, an on-demand line-scan inkjet recording apparatus.

[0011] The recording medium W1 is conveyed in conveying directions 400a to 400i, which are sub-scanning directions, along a conveying path indicated by a dashed line in Fig. 1. The recording medium W1 is a target for image formation by the image forming apparatus 100, that is, a sheet of paper or the like on which printing is to be performed. A number of pairs of rollers arranged above and below the conveying path assist in conveying the recording medium W1.

[0012] As shown in FIG. 1, the image forming apparatus 100 includes a liquid ejection section 210, a paper feed section 220, a registration adjustment section 230, a drying section 240, an inversion section 250, a paper discharge section 260, and a control section 270. Of these components, the paper feed section 220, the registration adjustment section 230, the liquid ejection section 210, the drying section 240, and the paper discharge section 260 are arranged in this order in the image forming apparatus 100. The inversion section 250 is arranged inside the drying section 240 and the liquid ejection section 210. The control section 270 is arranged inside the housing of the image forming apparatus 100 or near the outside of the housing of the image forming apparatus 100. However, the control section 270 may be configured to be able to remotely control the image forming apparatus 100 and arranged in a place away from the image forming apparatus 100.

[0013] The paper feed unit 220 includes a paper feed stack 221 and an air separation unit 222. The paper feed stack 221 is configured to be able to stack the recording media W1. The air separation unit 222 blows air from the side of the recording media W1 stacked on the paper feed stack 221, thereby picking up the recording media W1 one by one and transporting them toward the liquid ejection unit 210.

[0014] The registration adjustment unit 230 includes a registration mechanism 231. The registration mechanism 231 includes various driving mechanisms described below, and is configured to perform registration adjustment to correct the attitude of the recording medium W1, such as lateral shift and skew.

[0015] The liquid discharge section 210 as an image forming section includes a drum 211, a gripper 212, and an empty discharge receiver 213. Furthermore, in the liquid discharge section 210, liquid discharge head modules 28 (28K to 28P) are arranged.

[0016] The drum 211 has a cylindrical shape and is configured to be rotatable. The grippers 212 are provided, for example, at a plurality of positions on the surface of the drum 211, and grip the leading end of the recording medium W1 transported on the drum 211.

[0017] The liquid ejection head modules 28K-28P as liquid ejection head units are arranged at angles radially along the surface of the drum 211, and eject ink by an inkjet method toward the recording medium W1 on the drum 211. The liquid ejection head modules 28K-28P are filled in order with predetermined inks of the four basic colors of CMYK: black, cyan, magenta, and yellow, as well as other colors such as gold and transparent. An image is formed on the recording medium W1 by the predetermined liquid ejection head modules 28K-28P ejecting the predetermined ink.

[0018] The blank discharge receiver 213 is provided on the surface of the drum 211, and receives ink discharged by the liquid discharge head module 28 as blank discharge to an area outside the recording medium W1.

[0019] The drying section 240 includes a drying unit 241. The drying unit 241 is a heating mechanism such as a heater, and evaporates moisture from the recording medium W1 passing below the drying unit 241 to dry the recording medium W1.

[0020] The reversing unit 250 includes a reversing mechanism 251, a reversing conveying mechanism 252, and a registration mechanism 253. The reversing mechanism 251 allocates the conveying destination of the recording medium W1. Specifically, the reversing mechanism 251 switches the conveying path so that the recording medium W1 is conveyed to the paper discharge unit 260 during single-sided printing. Also, the reversing mechanism 251 switches the conveying path so that the recording medium W1 is conveyed to the reversing conveying mechanism 252 during double-sided printing. The recording medium W1 is conveyed again to the liquid discharge unit 210 via the reversing conveying mechanism 252.

[0021] The recording medium W1 that has passed through the reversing conveying mechanism 252 reaches the registration mechanism 253. The registration mechanism 253 has a function similar to that of the registration mechanism 231 described above, and corrects the posture of the recording medium W1. Thereafter, the recording medium W1 reaches the drum 211 with the back side of the printed side facing outward, and printing is performed on the back side.

[0022] The paper discharge section 260 includes a paper discharge stack 261. The paper discharge stack 261 is configured to be capable of stacking the recording medium W1. The recording medium W1 that has completed single-sided printing or double-sided printing is stacked in the paper discharge stack 261 in an aligned state.

[0023] The control unit 270 is configured as a computer equipped with, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), etc., and controls each of the liquid ejection unit 210, the paper feed unit 220, the resist adjustment unit 230, the drying unit 240, the inversion unit 250, and the paper discharge unit 260.

[0024] In a printing operation by the image forming apparatus 100, the control unit 270 controls each unit, and the recording media W1 stacked inside the paper feed unit 220 are transported one by one toward the liquid ejection unit 210. The recording media W1 that reach the registration adjustment unit 230 are subjected to registration adjustment inside the registration adjustment unit 230 and then sent to the liquid ejection unit 210. In the liquid ejection unit 210, ink is ejected onto only one side of the recording medium W1 or onto both sides at a time by the liquid ejection head module 28, and the recording medium W1 is stacked inside the paper ejection unit 260 after being dried by the drying unit 240.

[0025] 2, the registration mechanism 231 of the image forming apparatus 100 and the configuration associated with the registration mechanism 231 will be described in detail. Note that the registration mechanism 253 included in the above-mentioned reversing unit 250 may also have a configuration similar to that of the registration mechanism 231 described below, and the registration mechanism 253 may be accompanied by a configuration similar to that of the registration mechanism 231.

[0026] FIG. 2 is a diagram showing an example of the configuration of the registration mechanism 231 and the image sensor 30 according to the embodiment.

[0027] 2, the registration mechanism 231 includes a registration roller 231a, a rotation drive unit 231b, and a shift drive unit 231c. In the vicinity of the registration mechanism 231, a transport roller 232 and a plurality of image sensors 30 are disposed.

[0028] The transport rollers 232 are a pair of rollers provided above and below the transport path 410, and are disposed upstream of the registration mechanism 231, that is, closer to the paper feed unit 220 than the registration mechanism 231. The transport rollers 232 rotate to send out the recording medium W1 in the transport direction 400a, thereby transporting the recording medium W1 to the registration mechanism 231. In this manner, the transport rollers 232 are configured to be rotatable by a rotation mechanism (not shown).

[0029] Further, the conveying rollers 232 are configured so that the distance between the pair of conveying rollers 232 can be changed by a driving mechanism (not shown). By narrowing the distance between the conveying rollers 232, the conveying rollers 232 can pinch the recording medium W1 passing between the conveying rollers 232. By widening the distance between the conveying rollers 232, the conveying rollers 232 can be separated from the recording medium W1 passing between the conveying rollers 232.

[0030] The multiple image sensors 30 are provided above the transport path 410, and are arranged, for example, on both the upstream and downstream sides of the registration mechanism 231. In the example of Fig. 2, three image sensors 31, 32, and 33 are arranged in this order from the upstream side. Of these, the image sensors 31 and 32 are arranged on the upstream side of the registration mechanism 231, and the image sensor 33 is arranged on the downstream side of the registration mechanism 231.

[0031] More specifically, each image sensor 30 extends from near one end of the transport path 410 in the main scanning direction 420 toward the center along the main scanning direction 420 perpendicular to the transport direction 400a as the sub-scanning direction.

[0032] These image sensors 30 are, for example, a line sensor in which a plurality of CISs (Contact Image Sensors) as light receiving elements and a plurality of LEDs (Light Emitting Diodes) as light emitting elements are arranged in a line, etc. The CIS of the image sensor 30 receives the reflected light from the recording medium W1 of the light irradiated from the LEDs, thereby detecting the end position of the recording medium W1.

[0033] The CIS uses a complementary metal-oxide semiconductor (CMOS) and is also called a CMOS image sensor. However, the image sensor 30 may include a charge coupled device (CCD) or the like as a light receiving element instead of the CIS.

[0034] As described above, by each of the multiple image sensors 30 detecting the end position of the recording medium W1, it is possible to know the posture of the recording medium W1, such as whether the recording medium W1 is shifted laterally or skewed in the conveying path 410.

[0035] When the image sensor 30 detects a lateral deviation or a skew of the recording medium W1, the registration mechanism 231 performs a registration adjustment to correct the attitude of the recording medium W1.

[0036] The registration rollers 231a included in the registration mechanism 231 are a pair of rollers provided above and below the conveying path 410. The registration rollers 231a are configured to be rotatable by a rotation mechanism (not shown). The registration rollers 231a are also configured to be able to change the distance between the pair of registration rollers 231a by a drive mechanism (not shown). By narrowing the distance between the registration rollers 231a, the registration rollers 231a can pinch the recording medium W1 passing between the registration rollers 231a. By widening the distance between the registration rollers 231a, the registration rollers 231a can be separated from the recording medium W1 passing between the registration rollers 231a.

[0037] The rotation drive unit 231b is provided, for example, at the center of the registration roller 231a, and tilts the registration roller 231a arranged along the main scanning direction 420 toward the conveying direction 400a. As a result, the rotation drive unit 231b corrects the posture of the skewed recording medium W1. The shift drive unit 231c is provided, for example, at one end of the conveying path 410, and shifts (moves laterally) the registration roller 231a along the main scanning direction 420. As a result, the shift drive unit 231c corrects the posture of the recording medium W1 that has shifted laterally.

[0038] In the image forming apparatus 100 of the embodiment, the drum 211 and gripper 212 provided in the liquid ejection section 210, the inversion mechanism 251 and inversion conveying mechanism 252 provided in the inversion section 250, and multiple roller pairs arranged above and below the conveying path 410 are included in a sub-scanning direction conveying mechanism that conveys the recording medium W1 in the conveying direction 400a as the sub-scanning direction.

[0039] Furthermore, the registration mechanism 231 provided in the registration adjustment unit 230 is included in a main scanning direction transport mechanism that transports the recording medium W1 in the main scanning direction 420. However, the registration mechanism 253 provided in the reversing unit 250 may be included in the main scanning direction transport mechanism.

[0040] (Example of hardware configuration of image forming device) Next, the hardware configuration of the image forming apparatus 100 according to the embodiment will be described with reference to FIGS.

[0041] Fig. 3 is a block diagram showing an example of a hardware configuration of the image forming apparatus 100 according to the embodiment. As shown in Fig. 3, the control unit 270 of the image forming apparatus 100 includes a CPU 11, a ROM 12, a RAM 13, a memory 14, an ASIC (Application Specific Integrated Circuit) 15, a host I / F (Interface) 16, a head drive control unit 17, a motor control unit 18, and a sensor control unit 19.

[0042] The CPU 11 is the main controller in the control unit 270 that controls the image forming apparatus 100. The ROM 12 stores computer programs executed by the CPU 11 and other fixed data. The RAM 13 temporarily stores print data and the like. The memory 14 is a rewritable non-volatile memory that retains data even while the power to the image forming apparatus 100 is cut off. The ASIC 15 executes image processing for the print data and other input / output signal processing for controlling the entire image forming apparatus 100.

[0043] The host I / F 16 transmits and receives print data and control signals to and from the host side via a cable or a network. Examples of hosts connected to the image forming apparatus 100 include information processing devices such as client PCs (Personal Computers), and management servers that manage print jobs received from the client PCs 101.

[0044] The head drive control unit 17 is connected to the liquid ejection head module 28 and drives and controls the liquid ejection head module 28. More specifically, the head drive control unit 17 generates a drive waveform used when ejecting droplets from the liquid ejection head module 28 based on the print data. In addition, the head drive control unit 17 inputs the generated drive waveform and the like to a drive circuit inside the liquid ejection head module 28.

[0045] The motor control unit 18 is connected to various motors M, such as a pair of conveying rollers provided on the conveying path 410 and a motor that rotates the drum 211, and drives these motors M. The motors M also include a motor provided in the registration mechanism 231, as described later.

[0046] The sensor control unit 19 is connected to various sensors S, such as a temperature and humidity sensor that detects the temperature and humidity inside the image forming apparatus 100 and other sensors, and controls these sensors S and acquires detection signals from these sensors S. The sensors S include the image sensors 31 to 33 described above.

[0047] FIG. 4 is a block diagram showing an example of a configuration for realizing the registration adjustment function according to the embodiment.

[0048] As shown in FIG. 4, the configuration for realizing the registration adjustment function includes image sensors 31 to 33, encoders 21b and 21c, controllers 18b and 18c, motor drivers 22b and 22c, a rotation motor 23b, and a shift motor 23c.

[0049] The encoder 21b, the motor driver 22b, and the rotary motor 23b are included in a rotary drive unit 231b of the registration mechanism 231.

[0050] The rotation motor 23b tilts the registration roller 231a toward the conveying direction 400a. The encoder 21b is installed on the rotation motor 23b or a cam of the rotation motor 23b, and counts the rotation amount of the registration roller 231a from the initial position as the encoding count number. When the image sensors 31 to 33 detect skew of the recording medium W1, the encoder 21b calculates the correction amount required to correct the skew of the recording medium W1 as the encoding count number. For example, the controller 18b, which is a part of the motor control unit 18, controls the motor driver 22b based on the encoding count number required to correct the skew calculated by the encoder 21b, and drives the rotation motor 23b.

[0051] The encoder 21c, the motor driver 22c, and the shift motor 23c are included in a shift drive unit 231c of the registration mechanism 231.

[0052] The shift motor 23c shifts the registration roller 231a along the main scanning direction 420. The encoder 21c is installed on the shift motor 23c or a cam of the shift motor 23c, and counts the shift amount of the registration roller 231a from the initial position as an encoding count number. In addition, when the image sensors 31 to 33 detect a lateral deviation of the recording medium W1, the encoder 21c calculates the correction amount required to correct the lateral deviation of the recording medium W1 as an encoding count number. For example, the controller 18c, which is a part of the motor control unit 18, controls the motor driver 22c based on the encoding count number required to correct the lateral deviation calculated by the encoder 21c, and drives the shift motor 23c.

[0053] Incidentally, in order to correctly detect the end position in the main scanning direction of the recording medium W1 by the above-mentioned image sensor 30, shading correction of the image sensor 30 may be performed. The shading correction is a technique for calculating a correction amount from the read values ​​of the black level and the white level acquired in advance, and reducing the luminance unevenness between the pixels of the image sensor 30 using the calculated correction amount.

[0054] The black level is the luminance level of the darkest part or the part without reflected light in the reading area of ​​the image sensor 30. As the reading value of the black level, for example, the reading value when the image sensor 30 performs reading with the LED of the image sensor 30 turned off is obtained.

[0055] The white level is the luminance level of the brightest part or the part where the strongest reflected light is obtained in the reading area of ​​the image sensor 30. In this embodiment, the white level reading value is obtained by reading a recording medium placed below the image sensor 30 with the LED of the image sensor 30 turned on.

[0056] (Example of shading correction in action) An example of the shading correction operation in the image forming apparatus 100 of the embodiment will be described with reference to FIGS.

[0057] 5 and 6 are diagrams showing an example of an operation of acquiring a white level reading value by the image forming apparatus 100 according to the embodiment. As shown in Fig. 5 and Fig. 6, when acquiring a white level reading value, a recording medium W2 is used in the image forming apparatus 100 according to the embodiment.

[0058] The recording medium W2 is, for example, a blank sheet of paper that is white and has no printing thereon, that is, blank paper, etc. The same type of paper as the recording medium W1 to be printed on may be used as the recording medium W2.

[0059] As shown in FIG. 5(a), the recording medium W2 is conveyed out of the above-mentioned paper feed stack 221, and is further conveyed by conveying rollers 232 toward the registration mechanism 231, in the same manner as the recording medium W1 to be normally printed.

[0060] When the recording medium W2 passes under the image sensors 31 and 32 on the upstream side of the registration mechanism 231, the image sensors 31 and 32 read the end positions of the recording medium W2. Based on the reading positions of the image sensors 31 and 32, the encoder 21c of the registration mechanism 231 mainly calculates the encoding counter number required to shift the recording medium W2 to the end of the conveying path 410 on the image sensors 31 to 33 side in the main scanning direction 420.

[0061] However, at this time, the end position of the recording medium W2 may be read only by the image sensor 31. In this case, the end position of the recording medium W2 can be read at least when the recording medium W2 reaches a position below the image sensor 31.

[0062] As shown in FIG. 5(b), when the recording medium W2 reaches the registration mechanism 231, the motor driver 22c mainly drives the shift motor 23c based on the encoding counter number calculated by the encoder 21c, and shifts the registration roller 231a holding the recording medium W2 toward the image sensors 31-33 in the main scanning direction 420 of the conveying path 410.

[0063] As shown in FIG. 5(c), the recording medium W2 is brought into contact with the end of the conveying path 410 on the image sensors 31-33 side in the main scanning direction 420 by the above-mentioned operations of the encoder 21c, the motor driver 22c, and the shift motor 23c.

[0064] However, depending on the detection results of the image sensors 31 and 32, the above-mentioned encoder 21b, motor driver 22b, and shift motor 23b may rotate the registration roller 231a in a predetermined direction to correct the skew of the recording medium W2, while the above-mentioned encoder 21c, motor driver 22c, and shift motor 23c are operated.

[0065] During the time when the registration rollers 231a are moved to shift the recording medium W2 or to correct the skew of the recording medium W2, the conveying rollers 232 are kept separated from the recording medium W2.

[0066] 6, the recording medium W2 is further conveyed in the conveying direction 400a by the registration rollers 231a etc., and the recording medium W2 is positioned below all of the image sensors 31 to 33. At this time, the recording medium W2 is conveyed in a state of contact with the end of the conveying path 410 on the image sensors 31 to 33 side in the main scanning direction 420. Therefore, the reading areas corresponding to all pixel areas of the image sensors 31 to 33 are covered by the recording medium W2.

[0067] In this way, when the reading area corresponding to all pixel areas of the image sensors 31-33 is covered by the recording medium W2 and the LEDs of each of the image sensors 31-33 are turned on, the CIS or the like of each of the image sensors 31-33 receives the reflected light of the LED from the recording medium W2 and obtains a reading value of the white level.

[0068] It should be noted that the acquisition of the white level reading value begins after the leading end of the recording medium W2 in the transport direction 400a reaches the position of the image sensor 33, and ends before the trailing end of the recording medium W2 in the transport direction 400a passes the position of the image sensor 31.

[0069] However, the read values ​​by each of the image sensors 31-33 may be obtained after the recording medium W2 reaches its lower position and before it passes its lower position. That is, for example, the read values ​​by the image sensors 31 and 32 may be obtained immediately after the recording medium W2 abuts against the end of the image sensors 31-33, that is, after the state of FIG. 5(c) is reached, without waiting for the recording medium W2 to reach the lower position of the image sensor 33.

[0070] Thereafter, the recording medium W2 passes through the liquid ejection unit 210 and the drying unit 240 and is stored in a discharged paper stack 261 of a paper discharge unit 260.

[0071] The characteristics of the image sensors 31 to 33 change over time due to a decrease in the amount of light caused by deterioration of the LEDs, etc. For this reason, it is preferable to acquire the white level readings shown in Fig. 5 and Fig. 6 and the black level readings with the LEDs turned off as described above at a predetermined timing.

[0072] In order to detect the end position of the recording medium W1 to be printed, it is preferable that, for example, each time the image sensors 31-33 read the recording medium W1, shading correction is performed on the read value of the recording medium W1 using the most recently obtained white level and black level read values.

[0073] FIG. 7 is a diagram illustrating shading correction of the image sensor 30 according to the embodiment.

[0074] 7A is a graph showing the results of reading before shading correction by a given image sensor 30. The horizontal axis of the graph represents the pixel position of each pixel of the image sensor 30, and the vertical axis represents the luminance value of each pixel.

[0075] 7(a), the read luminance of the recording medium W1 read by the image sensor 30 has a relatively large luminance unevenness before shading correction. The recording medium W1 here is the recording medium whose end position is to be detected by the image sensor 30. In this state, there is a risk that the image sensor 30 will not be able to correctly detect the end position of the recording medium W1.

[0076] Therefore, shading correction is performed on the image sensor 30 based on the white level read value of each pixel and the black level read value of each pixel. The correction formula when correcting the read luminance of the recording medium W1 using the white level and black level read values ​​is shown in Figure 7(c).

[0077] 7B is a graph showing the results of reading after shading correction by the same image sensor 30. The horizontal axis of the graph represents the pixel position of each pixel of the image sensor 30, and the vertical axis represents the luminance value of each pixel.

[0078] 7(b), the luminance unevenness in the read luminance of the recording medium W1 read by the image sensor 30 is suppressed to within a predetermined range by the shading correction, thereby improving the detection accuracy of the edge position of the recording medium W1 by the image sensor 30.

[0079] In addition, the registration mechanism 253 arranged in the inversion section 250 and the image sensor (not shown) associated with the registration mechanism 253 may also be configured to be capable of reading the white level using the recording medium W2, similar to the registration mechanism 231 and image sensor 30 arranged in the registration adjustment section 230.

[0080] Similarly to the image sensor 30 associated with the registration mechanism 231, the image sensor associated with the registration mechanism 253 may also be subjected to shading correction based on the read value of the white level obtained by reading the recording medium W2.

[0081] (Example of recording medium posture correction operation) Next, an example of the operation of correcting the attitude of the recording medium W1 in the image forming apparatus 100 of the embodiment will be described with reference to FIGS.

[0082] 8 and 9 are diagrams showing an example of an operation of correcting the posture of the recording medium W1 by the image forming apparatus 100 according to the embodiment. In Fig. 8 and Fig. 9, the recording medium W1 at the beginning of conveyance is assumed to be inclined counterclockwise in a top view. Also, the recording medium W1 at the beginning of conveyance is assumed to be laterally shifted toward the image sensor 30 side of the conveyance path 410 in the main scanning direction 420.

[0083] 8(a), when the conveying roller 232 conveys the recording medium W1 in the conveying direction 400a, the recording medium W1 that reaches a position below the image sensors 31 and 32 is sequentially read by the image sensors 31 and 32. When reading the recording medium W1, shading correction is performed on the image sensors 31 and 32.

[0084] In this way, the multiple image sensors 30 read the recording medium W1 and detect the end positions of the recording medium W1 in the main scanning direction 420, making it possible to determine the attitude of the recording medium W1.

[0085] That is, when each image sensor 30 detects the end position of the recording medium W1 at a different position in the main scanning direction 420, it is found that the recording medium W1 is skewed with respect to the conveying direction 400a. Even when each image sensor 30 detects the end position of the recording medium W1 at the same position in the main scanning direction 420, if the actual detection position is shifted from the position where the end position of the recording medium W1 should be detected on the conveying path 410, it is found that the recording medium W1 is shifted laterally with respect to the center position of the conveying path 410.

[0086] In the example of FIG. 8(a), based on the readings of the image sensors 31 and 32, it is determined that the recording medium W1 is shifted laterally and is skewed.

[0087] 8(b), before the recording medium W1 reaches the registration roller 231a, the rotation motor 23b rotates the registration roller 231a so that the long axis direction of the registration roller 231a is parallel to the leading end of the skewed recording medium W1 in the conveying direction 400a. Also, the shift motor 23c shifts the registration roller 231a in the main scanning direction 420 so that the center position of the registration roller 231a in the long axis direction is the center position of the width of the recording medium W1 in the main scanning direction 420 that has shifted laterally.

[0088] As described above, the operation of moving the registration rollers 231a from the initial position to a predetermined position in accordance with the initial position of the recording medium W1 is called the welcoming operation.

[0089] 8(c), when the recording medium W1 reaches the registration rollers 231a, the recording medium W1 is sandwiched between the registration rollers 231a. In this state, the rotation motor 23b rotates the registration rollers 231a so that the major axis direction of the registration rollers 231a is aligned with the main scanning direction 420. This corrects the skewed position of the recording medium W1.

[0090] Further, the shift motor 23c shifts the registration roller 231a in the main scanning direction 420 so that the central position of the registration roller 231a in the major axis direction is located at the central position of the conveying path 410 in the main scanning direction 420. This corrects the laterally shifted attitude of the recording medium W1.

[0091] As described above, the operation of returning the registration roller 231a, which has been moved to a predetermined position by the pick-up operation, to the initial position is called a return operation.

[0092] 9(a), the registration rollers 231a continue to convey the recording medium W1 in the conveying direction 400a. Then, the recording medium W1 that has reached a position below the image sensor 33 is read by the image sensor 33. When reading the recording medium W1, shading correction is performed on the image sensor 33.

[0093] On the other hand, when the recording medium W1 is being read by the image sensor 33, detection of the recording medium W1 by at least the image sensor 32 is also continuing. Therefore, based on the read values ​​of these image sensors 32 and 33, it is determined whether or not the attitude of the recording medium W1 has been correctly corrected.

[0094] If the correction is insufficient, the rotation of the registration roller 231a by the rotation motor 23b and the shift of the registration roller 231a by the shift motor 23c are appropriately repeated to correct the posture of the recording medium W1 again.

[0095] 9(b), the registration roller 231a is then separated from the recording medium W1, and returned to its initial position before the next recording medium W1 is conveyed. The operation of returning the registration roller 231a to its initial position is called a return operation.

[0096] During the return operation of the registration rollers 231a and the readjustment of the posture of the recording medium W1, the conveying rollers 232 are kept separated from the recording medium W1 while the registration rollers 231a are moved to correct the posture of the recording medium W1.

[0097] FIG. 10 is a diagram showing an example of a timing chart of each part when the image forming apparatus 100 according to the embodiment performs an operation to correct the attitude of the recording medium W1.

[0098] In Fig. 10, when the rotating motor 23b rotates forward CW, the registration roller 231a rotates counterclockwise in a top view. When the rotating motor 23b rotates reverse CCW, the registration roller 231a rotates clockwise in a top view. When the shift motor 23c rotates forward CW, the registration roller 231a shifts toward the image sensor 30 in the main scanning direction 420. When the shift motor 23c rotates reverse CCW, the registration roller 231a shifts to the opposite side of the image sensor 30 in the main scanning direction 420.

[0099] Section A in Figure 10 corresponds to the section shown in Figure 8(a) above, and is the section from the start of reading of the recording medium W1 by the image sensor 31 to the end of the process of calculating the lateral deviation and skew amount of the recording medium W1 based on the reading values ​​by the image sensors 31 and 32.

[0100] The recording medium W1 is conveyed in the conveying direction 400a on the conveying path 410 by the conveying rollers 232. Then, when the recording medium W1 reaches a position below the image sensor 31, the image sensor 31 receives reflected light from the recording medium W1 and turns on. In other words, the image sensor 31 turns on when it starts reading the recording medium W1, and remains on until the recording medium W1 has completely passed below the image sensor 31.

[0101] On the other hand, when the image sensor 31 detects the recording medium W1 and turns on, the registration rollers 231a are lowered to a position where they can pinch the recording medium W1 at that timing. The registration rollers 231a are maintained in the lowered position until the end of a section E, which will be described later.

[0102] Next, when the recording medium W1 reaches a position below the image sensor 32, the image sensor 32 receives the reflected light from the recording medium W1 and turns on. After this, the image sensor 32 is maintained in the on state until the recording medium W1 has completely passed below the image sensor 32.

[0103] When the image sensors 31 and 32 each read the recording medium W1, the above-mentioned sensor control unit 19 (see FIG. 3) calculates the end positions of the recording medium W1 in the main scanning direction 420 based on these read values. In addition, the sensor control unit 19 calculates the amount of lateral deviation and the amount of skew of the recording medium W1 from the calculated end positions of the recording medium W1.

[0104] Section B in FIG. 10 corresponds to the section shown in FIG. 8(b) described above, and is a section in which a pick-up operation is performed to move the registration roller 2231a from the initial position to a predetermined position.

[0105] In the pick-up operation, the rotating motor 23b rotates forward CW or reverse CCW according to the amount and direction of skew of the recording medium W1, and rotates the registration roller 231a so as to tilt in a predetermined direction with respect to the main scanning direction 420. Here, following the example of Fig. 8(b), the rotating motor 23b rotates forward CW and tilts the registration roller 231a counterclockwise when viewed from above.

[0106] In parallel with this, the shift motor 23 rotates forward CW or reverse CCW according to the amount and direction of lateral deviation of W1 of the recording medium, and shifts the registration roller 231a to either end side of the main scanning direction 420 of the conveying path 410. Here, following the example of FIG. 8(b), the shift motor 23c rotates forward CW to shift the registration roller 231a to the image sensor 30 side.

[0107] Section C in FIG. 10 corresponds to the section shown in FIG. 8(c) above, and is a section in which the posture of the recording medium W1 is corrected by a return operation that returns the registration roller 231a, which is in a predetermined position by a pick-up operation.

[0108] In order to correct the attitude of the recording medium W1, the rotation motor 23b rotates forward CW or reverse CCW depending on the amount and direction of inclination of the registration roller 231a tilted by the pick-up operation, and returns the registration roller 231a to be aligned with the main scanning direction 420. In the example of Fig. 10, the rotation motor 23b rotates forward CW in section B, so here, the rotation motor 23b is rotated reverse CCW.

[0109] In order to correct the posture of the recording medium W1, the shift motor 23c rotates forward CW or reverse CCW depending on the shift amount and shift direction of the registration roller 231a shifted by the pick-up operation, and returns the registration roller 231a to the center position in the main scanning direction 420 of the conveying path 410. In the example of Fig. 10, the shift motor 23c rotates forward CW in section B, so here the shift motor 23c is rotated reverse CCW.

[0110] Section D in Figure 10 corresponds to the section shown in Figure 9(a) above, and is the section from the start of reading of the recording medium W1 by the image sensor 33 to the end of the process of calculating the lateral shift amount and skew amount of the recording medium W1 based on the read values ​​by the image sensors 32 and 33.

[0111] The recording medium W1 continues to be conveyed in the conveying direction 400a by the conveying roller 232 and the registration roller 231a. Then, when the recording medium W1 reaches a position below the image sensor 33, the image sensor 33 receives reflected light from the recording medium W1 and turns on. After this, the image sensor 33 is maintained in the on state until the recording medium W1 has completely passed below the image sensor 33.

[0112] The sensor control unit 19 calculates the end position of the recording medium W1 in the main scanning direction 420 based on the read values ​​by the image sensor 32 that is still continuing reading and the image sensor 33 that has just started reading. The sensor control unit 19 also determines the attitude of the recording medium W1 from the calculated end position of the recording medium W1.

[0113] 10 is a reserve section in which the attitude of the recording medium W1 is re-corrected as necessary based on the attitude of the recording medium W1 determined by the sensor control unit 19.

[0114] If it is determined that the recording medium W1 is skewed, the rotation motor 23b rotates forward CW or reverse CCW depending on the amount and direction of skew of the recording medium W1, and rotates the registration roller 231a so that it is inclined in a predetermined direction with respect to the main scanning direction 420.

[0115] If it is determined that the recording medium W1 is misaligned laterally, the shift motor 23c rotates forward CW or reverse CCW depending on the amount and direction of the lateral deviation of the recording medium W1, shifting the registration roller 231a to either end side of the conveying path 410 in the main scanning direction 420.

[0116] In this manner, by appropriately repeating the reading of the recording medium W1 by the image sensors 32 and 33 and the feedback by the rotation motor 23b and the shift motor 23c, the attitude of the recording medium W1 is corrected with high accuracy.

[0117] Section F in FIG. 10 corresponds to the section shown in FIG. 9(b) described above, and is a section in which a return operation is performed to return the registration roller 231a to its initial position.

[0118] When the return operation starts, the registration roller 231a rises from the lowered position in which the recording medium W1 is sandwiched, and is separated from the recording medium W1. The recording medium W1, while maintaining the correct posture after the correction, is taken up by, for example, a pair of rollers (not shown) arranged further downstream in the conveying direction 400a, and conveyance continues.

[0119] In order to return the registration roller 231a to its initial position, the rotary motor 23b rotates forward CW or reverse CCW depending on the tilt amount and tilt direction of the registration roller 231a at that time, and moves the registration roller 231a along the main scanning direction 420.

[0120] At the same time, in order to return the registration roller 231a to its initial position, the shift motor 23c rotates forward CW or reverse CCW depending on the shift amount and shift direction of the registration roller 231a at that time, moving the registration roller 231a to the center position in the main scanning direction 420 of the conveying path 410.

[0121] By the above-mentioned returning operation, the registration roller 231a returns to the initial position by the time the next recording medium W1 reaches at least a position below the image sensor 31. After this, for example, a plurality of recording media W1 are conveyed in sequence, and the attitude correction operation by the registration mechanism 231 is repeated.

[0122] In addition, the registration mechanism 253 arranged in the inversion section 250 and the image sensor associated with the registration mechanism 253 may be configured to perform posture correction of the recording medium W1 to be printed on the back side, similar to the registration mechanism 231 and image sensor 30 arranged in the registration adjustment section 230.

[0123] (Processing method for image forming device) Next, a predetermined processing method in the image forming apparatus 100 according to the embodiment will be described with reference to FIGS.

[0124] FIG. 11 is a flowchart showing an example of a procedure of a white level reading process performed by the image forming apparatus 100 according to the embodiment.

[0125] As shown in FIG. 11, the control unit 270 of the image forming apparatus 100 rotates the conveying roller 232 and multiple roller pairs arranged above and below the conveying path 410 to start conveying the recording medium W2 used for reading the white level (step S101).

[0126] When the recording medium W2 reaches a position below the image sensor 31, the image sensor 31 detects the recording medium W2 (step S102). When the recording medium W2 reaches a position further below the image sensor 32, the image sensor 32 detects the recording medium W2 (step S103).

[0127] More specifically, the sensor control unit 19 detects the end position of the recording medium W2 based on the results of reading the recording medium W2 by the image sensors 31 and 32. In addition, the sensor control unit 19 calculates the relative position of the detected end position of the recording medium W2 on the conveying path 410 in the main scanning direction 420.

[0128] Based on the above calculation result, the motor control unit 18 calculates the shift amount to the position where the recording medium W2 is read for use in shading correction (step S104). More specifically, the motor control unit 18 causes the encoder 21c associated with the shift motor 23c to calculate the necessary shift amount as an encoding count number.

[0129] The motor control unit 18 drives a drive mechanism (not shown) associated with the registration rollers 231a to narrow the distance between the pair of registration rollers 231a and bring the registration rollers 231a into contact with the recording medium W2 (step S105).

[0130] The controller 18c drives the shift motor 23c by the motor driver 22c based on the encoding count number calculated by the encoder 21c based on the required shift amount, thereby moving the recording medium W2 to a reading position of the recording medium W2 (step S106).

[0131] When the recording medium W2 that has moved to the reading position reaches a position below the image sensor 33, the image sensor 33 detects the recording medium W2 (step S107). At this time, the upstream image sensors 31 and 32 are also continuing to read the recording medium W2.

[0132] The sensor control unit 19 acquires the values ​​read by the image sensors 31 to 33 on the recording medium W2 at the reading position (step S108). The sensor control unit 19 stores the read values ​​acquired from the image sensors 31 to 33 as white level read values ​​in, for example, the memory 14 (step S109).

[0133] As described above, the sensor control unit 19 may sequentially acquire the reading values ​​of the recording medium W2 by the image sensors 31-33 each time the recording medium W2 reaches a position below each of the image sensors 31-33 after the recording medium W2 abuts against the end of the image sensors 31-33.

[0134] With the above, the white level reading process by the image forming apparatus 100 according to the embodiment is completed.

[0135] Fig. 12 is a flow diagram showing an example of the procedure of the attitude correction process of the recording medium W1 by the image forming apparatus 100 according to the embodiment. Note that, before starting the process of Fig. 12, it is assumed that the white level reading value and the black level reading value have been stored in, for example, the memory 14 of the image forming apparatus 100. The white level reading value is obtained by the flow of Fig. 11 described above.

[0136] 12, the control unit 270 of the image forming apparatus 100 starts a conveying process of the recording medium W1 to be printed, and when the recording medium W1 reaches a position below the image sensor 31, the image sensor 31 reads the recording medium W1 (step S211). The sensor control unit 19 performs shading correction of the image sensor 31 using a value read by the image sensor 31 (step S212). However, the process of step S212 may be performed in parallel when the process of step S222 described later is performed.

[0137] More specifically, the sensor control unit 19 acquires the value read by the image sensor 31 of the recording medium W1 being conveyed. The sensor control unit 19 also reads the latest white level read value by the image sensor 31 and the latest black level read value by the image sensor 31 from the memory 14. The sensor control unit 19 also uses the read white level and black level read values ​​to perform shading correction on the read value by the image sensor 31 of the recording medium W1 being conveyed.

[0138] When the recording medium W1 reaches a position further below the image sensor 32, the image sensor 32 reads the recording medium W1 (step S221). The sensor control unit 19 performs shading correction of the image sensor 32 using the value read by the image sensor 32 (step S222).

[0139] More specifically, the sensor control unit 19 acquires the value read by the image sensor 32 of the recording medium W1 being conveyed. The sensor control unit 19 also reads the latest white level read value by the image sensor 32 and the latest black level read value by the image sensor 32 from the memory 14. The sensor control unit 19 also uses the read white level and black level read values ​​to perform shading correction on the read value by the image sensor 32 of the recording medium W1 being conveyed.

[0140] The sensor control unit 19 calculates the amount of skew of the recording medium W1 from the read values ​​by the image sensors 31 and 32 that have been subjected to shading correction (step S231).

[0141] The sensor control unit 19 determines whether the recording medium W1 is skewed (step S232). More specifically, if the amount of skew of the recording medium W1 is equal to or greater than a predetermined amount, the sensor control unit 19 determines that the recording medium W1 is skewed, and if the amount of skew of the recording medium W1 is less than the predetermined amount, the sensor control unit 19 determines that the recording medium W1 is not skewed.

[0142] If the recording medium W1 is skewed (step S232: Yes), the encoder 21b calculates the encoding count number required to correct the skew based on the amount of skew of the recording medium W1 (step S233).

[0143] The controller 18b rotates the rotary motor 23b by the motor driver 22b according to the encoding count number required to correct the skew. As a result, the controller 18b performs the pick-up operation of the registration roller 231a (step S234). Furthermore, the controller 18b rotates the rotary motor 23b in the opposite direction to the above by the motor driver 22b according to the movement amount in the pick-up operation while the registration roller 231a is in contact with the recording medium W1. As a result, the controller 18b performs the return operation of the registration roller 231a (step S235).

[0144] If the recording medium W1 is not skewed (step S232: No), the above processes of steps S233 to S235 are not performed.

[0145] In parallel with the calculation process of the skew amount of the recording medium W1 in step S231, the sensor control unit 19 calculates the lateral deviation amount of the recording medium W1 from the shading-corrected read values ​​by the image sensors 31 and 32 (step S241).

[0146] The sensor control unit 19 determines whether the recording medium W1 is laterally displaced (step S242). More specifically, if the amount of lateral displacement of the recording medium W1 is equal to or greater than a predetermined amount, the sensor control unit 19 determines that the recording medium W1 is laterally displaced, and if the amount of lateral displacement of the recording medium W1 is less than the predetermined amount, the sensor control unit 19 determines that the recording medium W1 is not laterally displaced.

[0147] If the recording medium W1 has shifted laterally (step S242: Yes), the encoder 21c calculates the encoding count number required to correct the lateral shift based on the amount of lateral shift of the recording medium W1 (step S243).

[0148] The controller 18c rotates the shift motor 23c by the motor driver 22c according to the encoding count number required to correct the lateral deviation. As a result, the controller 18c performs the pick-up operation of the registration roller 231a (step S244). In addition, the controller 18c rotates the shift motor 23c in the opposite direction to the above by the motor driver 22c according to the amount of movement in the pick-up operation while the registration roller 231a is in contact with the recording medium W1. As a result, the controller 18c performs the return operation of the registration roller 231a (step S245).

[0149] If the recording medium W1 is not laterally displaced (step S242: No), the above processes of steps S243 to S245 are not performed.

[0150] After the skew and lateral deviation of the recording medium W1 are corrected as necessary, when the recording medium W1 reaches a position below the image sensor 33, the image sensor 33 reads the recording medium W1 (step S251). The sensor control unit 19 performs shading correction of the image sensor 33 using the read value by the image sensor 33 (step S252).

[0151] More specifically, the sensor control unit 19 acquires the value read by the image sensor 33 of the recording medium W1 being conveyed. The sensor control unit 19 also reads the latest white level read value by the image sensor 33 and the latest black level read value by the image sensor 33 from the memory 14. The sensor control unit 19 also uses the read white level and black level read values ​​to perform shading correction on the read value by the image sensor 33 of the recording medium W1 being conveyed.

[0152] The sensor control unit 19 calculates the amount of skew of the recording medium W1 from the read values ​​by the image sensor 33 after shading correction and the image sensor 32 after the previous shading correction (step S261).

[0153] The sensor control unit 19 determines whether the recording medium W1 is skewed (step S262). If the recording medium W1 is skewed (step S262: Yes), the encoder 21b calculates the encoding count number required to correct the skew based on the amount of skew of the recording medium W1 (step S263).

[0154] The controller 18b rotates the rotary motor 23b by the motor driver 22b in accordance with the encoding count number required to correct the skew, and performs a re-correcting operation by the registration roller 231a (step S264).

[0155] If the recording medium W1 is not skewed (step S262: No), the above processes of steps S263 and S264 are not performed.

[0156] In parallel with the process of calculating the amount of skew of the recording medium W1 in step S261, the sensor control unit 19 calculates the amount of lateral deviation of the recording medium W1 from the shading-corrected read values ​​obtained by the image sensors 32 and 33 (step S271).

[0157] The sensor control unit 19 determines whether the recording medium W1 is laterally displaced (step S272). If the recording medium W1 is laterally displaced (step S272: Yes), the encoder 21c calculates the encoding count number required to correct the lateral displacement based on the amount of lateral displacement of the recording medium W1 (step S273).

[0158] The controller 18c rotates the shift motor 23c by the motor driver 22c according to the encoding count number required to correct the lateral deviation, and performs a re-correcting operation by the registration roller 231a (step S274).

[0159] If the recording medium W1 is not displaced laterally (step S272: No), the above processes of steps S273 and S274 are not performed.

[0160] After the skew and lateral deviation of the recording medium W1 are corrected as necessary, the controller 18b causes the motor driver 22b to rotate the rotary motor 23b, thereby carrying out the return operation of the registration roller 231a (step S281).

[0161] In parallel with the return operation by the rotation motor 23b in step S281, the controller 18c rotates the shift motor 23c by the motor driver 22c to perform the return operation of the registration roller 231a (step S291).

[0162] After the above process, the image forming apparatus 100 of the embodiment repeats the process from step S211 for the next recording medium W1.

[0163] (Comparative Example) The configuration of the image forming apparatus 100 according to the embodiment will be described below in comparison with the configuration of Patent Document 1 as a comparative example.

[0164] In an image forming apparatus, an image sensor is used to read the position of the recording medium in the transport path, and the posture of the recording medium is corrected according to the result. For example, in an image sensor equipped with multiple CISs, etc., brightness unevenness occurs between the pixels of the image captured by the CIS, so a technology is known that performs shading correction to reduce brightness unevenness.

[0165] In conventional shading correction, the amount of correction in shading correction is calculated from the white level reading value obtained by the CIS reading a white reference member such as a white board, and the black level reading value obtained by having the CIS read the image sensor with the LED turned off. This required a white reference member dedicated to shading correction to be prepared, and when reading with the image sensor, the white reference member had to be placed in a position corresponding to the entire pixel area of ​​the image sensor. This made the task of obtaining the white level reading value complicated.

[0166] For example, in the technology of Patent Document 1 (JP Patent Publication 2005-033457 A), multiple shading data are stored in advance in a memory, and appropriate data is read out from the memory and used for shading correction. This makes it possible to perform good shading correction without preparing a white reference member.

[0167] However, the technique of Patent Document 1 requires that a large amount of shading data be obtained in advance, which leads to an increase in the amount of data. In addition, only the shading data prepared in advance can be used, which may result in a decrease in the accuracy of shading correction.

[0168] According to the image forming apparatus 100 of the embodiment, a white level reading value is obtained by using a white recording medium instead of a white reference member. This eliminates the need to prepare a white reference member, and makes it possible to avoid cumbersome work of reading the white level.

[0169] According to the image forming apparatus 100 of the embodiment, the value read from the recording medium while the recording medium is being transported is used as the read value of the white level. This makes it possible to quickly obtain the read value of the white level while the recording medium is being transported.

[0170] Moreover, the read value of the white level can be updated at an appropriate timing as needed in response to changes over time in the performance of the image sensor 30. Therefore, highly accurate shading correction can be performed without increasing the amount of shading data.

[0171] (Variation 1) However, depending on the transport mechanism of the image forming device and the arrangement of the image sensor, it may be difficult to move the recording medium used to obtain the white level reading value to a position that covers the entire reading area corresponding to all pixel areas of the image sensor.

[0172] Modification 1 is an example of application of a method for reading a white level using a recording medium to the image forming apparatus described above. The image forming apparatus of Modification 1 will be described below with reference to FIG.

[0173] FIG. 13 is a diagram illustrating an example of an operation of acquiring a read value of a white level by the image forming apparatus according to the first modification of the embodiment.

[0174] 13, the image forming apparatus of the first modification includes a registration mechanism 331. The registration mechanism 331 includes a rotation drive unit 331b that rotates the registration roller 331a, and a shift drive unit 331c that shifts the registration roller 331a. In the image forming apparatus of the first modification, the image sensor 30 is disposed so as to protrude outward from one end of the conveying path 410 in the main scanning direction 420, for example.

[0175] In the image forming apparatus of the first modified example, the registration mechanism 331 is included in a main scanning direction transport mechanism that transports the recording media W1, W2, etc. in the main scanning direction 420. However, a registration mechanism provided in a reversing unit (not shown) may be included in the main scanning direction transport mechanism.

[0176] In the image forming apparatus of the first modification, even if the recording medium W2 is shifted as much as possible in the above configuration, it is difficult to cover the entire reading area corresponding to all the pixel areas of the image sensor 30 with the recording medium W2.

[0177] 13, for example, the recording medium W2 is shifted until the end position of the recording medium W2 in the main scanning direction 420 abuts against the end of the conveying path 410 in the main scanning direction 420. However, it is difficult to make the recording medium W2 reach a position below the image sensor 30 that protrudes from the end of the conveying path 410.

[0178] Therefore, in the image forming apparatus of the first modified example, the recording medium W2 is shifted to a position that covers at least the reading area of ​​the image sensor 30 that corresponds to the maximum usable area.

[0179] Fig. 13 shows an end position UE in the main scanning direction 420 of the maximum use area of ​​the image sensor 30. That is, the area from the end position UE in Fig. 13 toward the center in the main scanning direction 420 is the maximum use area of ​​the image sensor 30. In other words, among the multiple CISs of the image sensor 30, the CISs arranged on the outer side of the transport path 410 from the end position UE in Fig. 13 are not used for reading the recording media W1, W2, etc.

[0180] For example, in the example of Figure 13, the recording medium W2 is shifted until the end position of the recording medium W2 in the main scanning direction 420 abuts the end position of the conveying path 410 in the main scanning direction 420, so that the recording medium W2 covers the reading area corresponding to the maximum usage area of ​​the image sensor 30.

[0181] In the image forming apparatus of the first modified example, the reading value of the recording medium W2 by the image sensor 30 is obtained in a state in which the recording medium W2 covers at least a reading area of ​​the image sensor 30 that corresponds to the maximum usable area.

[0182] Of these readings, the readings of the CIS located in the area outside the maximum usage area of ​​the image sensor 30, i.e., the outer area of ​​the maximum usage area of ​​the image sensor 30, are excluded, and the readings of the recording medium W2 by the image sensor 30 are used as white level readings for shading correction.

[0183] According to the technique of the first modification, the CiS arranged in the use area of ​​the image sensor 30 is subjected to shading correction with high accuracy, so that the same effect as that of the above-described embodiment can be achieved.

[0184] (Variation 2) The conveying mechanism of the image forming apparatus may not include the conveying mechanism capable of correcting the attitude of the recording media W1, W2 such as the registration mechanisms 231, 331 described above.

[0185] Modification 2 is an example of application of a method for reading a white level using a recording medium to the image forming apparatus described above. The image forming apparatus of Modification 2 will be described below with reference to FIG.

[0186] FIG. 14 is a diagram illustrating an example of an operation of acquiring a read value of a white level by an image forming apparatus according to the second modification of the embodiment.

[0187] 14, the image forming apparatus of the second modification includes a registration roller 431a. The registration roller 431a does not include a drive unit for rotating or shifting the registration roller 431a. In the image forming apparatus of the second modification, the image sensor 30 is disposed so as to protrude outward from one end of the conveying path 410 in the main scanning direction 420, for example.

[0188] In the image forming apparatus of the second modification, the recording medium W2 cannot be shifted, and it is difficult to cover the entire pixel area or the reading area corresponding to the maximum use area of ​​the image sensor 30 with the recording medium W2.

[0189] Therefore, in the image forming apparatus of the modified example 2, in order to obtain a reading value of the white level, for example, a recording medium W3 larger in size than the recording medium W2 is used. Here, the conveying mechanism of the image forming apparatus of the modified example 2 is configured to be capable of conveying the large-sized recording medium W3.

[0190] The recording medium W3 is, for example, a blank sheet of paper that is white and has no printing thereon, i.e., a blank sheet of paper. The width of the recording medium W3 in at least the main scanning direction 420 is larger than that of the recording medium W2. More specifically, the width of the recording medium W3 in the main scanning direction 420 is large enough to cover at least the reading area corresponding to the maximum use area.

[0191] 13, for example, the end position in the main scanning direction 420 of the recording medium W3 is located outside the end position UE in the main scanning direction 420 of the maximum usable area of ​​the image sensor 30. In other words, the recording medium W3 covers the reading area corresponding to the maximum usable area of ​​the image sensor 30.

[0192] In the image forming apparatus of the second modification, the reading value of the recording medium W3 by the image sensor 30 is obtained in a state in which the recording medium W3 covers at least a reading area of ​​the image sensor 30 that corresponds to the maximum usable area.

[0193] Of these readings, the readings from the area outside the maximum usage area of ​​the image sensor 30, i.e., the readings from the CIS located in the outer area of ​​the maximum usage area of ​​the image sensor 30, are excluded, and the readings from the recording medium W3 by the image sensor 30 are used as white level readings for shading correction.

[0194] However, in the image forming apparatus of the second modified example, similarly to the image forming apparatus of the above-mentioned embodiment, the image sensor 30 may be disposed inside the end position of the transport path 410 in the main scanning direction 420, and the read value of the recording medium W3 by the image sensor 30 may be acquired in a state in which the recording medium W3 covers a reading area corresponding to all pixel areas of the image sensor 30. In this case, shading correction can be performed on all CISs of the image sensor 30.

[0195] According to the method of the second modification, the CiS arranged in the use area of ​​the image sensor 30 is subjected to shading correction with high accuracy, and therefore the same effects as those of the above-described embodiment can be achieved.

[0196] In the above-described embodiment and modified examples 1 and 2, the image forming apparatus 100 is provided with three image sensors 30. However, the number of image sensors may be two, or four or more. Alternatively, the number of image sensors may be one. Even with one image sensor, it is possible to at least determine whether the attitude of the recording medium is proper or not by detecting the end position of the recording medium. For example, in a configuration such as modified example 2, if the attitude of the recording medium is improper, measures such as issuing an alarm to the user can be taken.

[0197] In the above-described embodiment and modified examples 1 and 2, the image sensor 30 detects the end position of the recording medium W1 and corrects the attitude of the recording medium W1. However, the image sensor may detect the image position on the recording medium and correct the image position. Also, the position of the recording medium may be indirectly determined from the detected image position, and the attitude of the recording medium may be indirectly corrected by correcting the image position. [Explanation of symbols]

[0198] 30(31,32,33) Image sensor 100 Image forming device 210 Liquid discharge part 230 Resist Adjustment Department 231,331,253 Resist mechanism 231a, 331a, 431a Registration roller 231b, 331b Rotation drive unit 231c,331c Shift drive unit 250 Reversal section 270 Control Unit 400a~400i Transport direction 420 Main scanning direction [Prior art documents] [Patent documents]

[0199] [Patent Document 1] JP 2005-033457 A

Claims

1. A conveying mechanism for conveying a recording medium; an image sensor capable of detecting the position of the recording medium; a control unit that controls the transport mechanism and the image sensor, The transport mechanism includes: a sub-scanning direction transport mechanism that transports the recording medium in a sub-scanning direction connecting a paper feed unit and a paper discharge unit; a main scanning direction transport mechanism that transports the recording medium in a main scanning direction perpendicular to the sub-scanning direction, The image sensor includes: a line sensor extending in the main scanning direction beyond an end position of the recording medium so as to be able to detect the end position of the recording medium in the main scanning direction; The control unit is causing the conveying mechanism to convey the recording medium below the image sensor; causing the image sensor to acquire read data obtained by reading a white background portion of the recording medium conveyed below the image sensor; performing shading correction of the image sensor based on the read data; when the image sensor acquires the read data to be used for the shading correction, the main scanning direction transport mechanism moves the recording medium in the main scanning direction, and at least a reading area corresponding to a maximum use area of ​​the image sensor is covered with the recording medium. Image forming device.

2. The control unit is when the image sensor acquires the read data to be used for the shading correction, the main scanning direction transport mechanism moves the recording medium in the main scanning direction, and a reading area corresponding to all pixel areas of the image sensor is covered with the recording medium. The image forming apparatus according to claim 1 .

3. A conveying mechanism for conveying a recording medium; an image sensor capable of detecting the position of the recording medium; a control unit that controls the transport mechanism and the image sensor, The image sensor includes: a line sensor that extends in a main scanning direction perpendicular to a sub-scanning direction connecting a paper feed unit and a paper discharge unit and is capable of detecting an end position of the recording medium in the main scanning direction; The control unit is causing the conveying mechanism to convey the recording medium below the image sensor; causing the image sensor to acquire read data obtained by reading a white background portion of the recording medium conveyed below the image sensor; performing shading correction of the image sensor based on the read data; when the image sensor acquires the read data used for the shading correction, the conveying mechanism conveys the recording medium having a width in the main scanning direction that is at least a size that covers a reading area corresponding to a maximum use area of ​​the image sensor. Image forming device.

4. The control unit is when the image sensor acquires the read data to be used for the shading correction, the conveying mechanism conveys the recording medium having a width in the main scanning direction that is large enough to cover a reading area corresponding to all pixel areas of the image sensor. The image forming apparatus according to claim 3 .

5. A conveying mechanism for conveying a recording medium; an image sensor capable of detecting the position of the recording medium; a control unit that controls the transport mechanism and the image sensor, The control unit is The conveying mechanism conveys a recording medium to be printed; causing the image sensor to obtain read data obtained by reading a white background portion of the recording medium conveyed below the image sensor, and executing shading correction of the image sensor based on the read data, and also causing the image sensor to detect an edge position of the recording medium to be printed, thereby determining whether or not lateral deviation has occurred in the recording medium to be printed. Image forming device.

6. the image sensor includes a plurality of image sensors; The control unit is The conveying mechanism conveys a recording medium to be printed; causing the plurality of image sensors to detect edge positions of the recording medium to be printed, and determining whether or not the recording medium to be printed is skewed; The image forming apparatus according to claim 1 .

7. A conveying mechanism for conveying a recording medium; an image forming method implemented in an image forming apparatus including an image sensor capable of detecting a position of the recording medium, The transport mechanism includes: a sub-scanning direction transport mechanism that transports the recording medium in a sub-scanning direction connecting a paper feed unit and a paper discharge unit; a main scanning direction transport mechanism that transports the recording medium in a main scanning direction perpendicular to the sub-scanning direction, The image sensor includes: a line sensor extending in the main scanning direction beyond an end position of the recording medium so as to be able to detect the end position of the recording medium in the main scanning direction; The recording medium is conveyed to a position below the image sensor by the conveying mechanism; The image sensor acquires read data obtained by reading a white background portion of the recording medium conveyed below the image sensor. performing shading correction of the image sensor based on the read data; When the image sensor acquires the read data to be used for the shading correction, the recording medium is moved in the main scanning direction so that at least a reading area corresponding to a maximum use area of ​​the image sensor is covered with the recording medium. Image forming method.

8. A conveying mechanism for conveying a recording medium; an image forming method implemented in an image forming apparatus including an image sensor capable of detecting a position of the recording medium, The image sensor includes: a line sensor that extends in a main scanning direction perpendicular to a sub-scanning direction connecting a paper feed unit and a paper discharge unit and is capable of detecting an end position of the recording medium in the main scanning direction; The recording medium is conveyed to a position below the image sensor by the conveying mechanism; The image sensor acquires read data obtained by reading a white background portion of the recording medium conveyed below the image sensor. performing shading correction of the image sensor based on the read data; when the read data used for the shading correction is obtained by the image sensor, the recording medium having a width in the main scanning direction of at least a size covering a reading area corresponding to a maximum use area of ​​the image sensor is conveyed by the conveying mechanism. Image forming method.

9. A conveying mechanism for conveying a recording medium; an image forming method implemented in an image forming apparatus including an image sensor capable of detecting a position of the recording medium, The conveying mechanism conveys a recording medium to be printed below the image sensor; a read data obtained by reading a white background portion of the recording medium conveyed below the image sensor by the image sensor, and a shading correction of the image sensor is performed based on the read data, and an end position of the recording medium to be printed is detected to determine whether or not a lateral shift has occurred on the recording medium to be printed. Image forming method.

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