JP7851284B2 - Image forming apparatus - Google Patents

Description

This invention relates to an image forming apparatus.

In recent years, electrophotographic and inkjet printing methods have been gaining traction in the commercial printing market, where offset printing was previously dominant. For electrophotographic and inkjet printers to become even more widespread in the commercial printing market, they must achieve image quality equivalent to that of offset printing. Therefore, such image forming apparatuses are equipped with a reading device to read test sheets used for calibration of the image forming apparatus as they are transported along a transport path.

The image forming apparatus described in Patent Document 1 forms a test image on a sheet, reads the test image using an image reading device, and performs registration adjustment to correct the registration misalignment (misalignment of the image formation position) of the image formed on the sheet based on the reading result.

Japanese Patent Publication No. 2004-167990

However, if the reading mechanism is mounted at an angle perpendicular to the transport direction, the image detected by the reading mechanism will be distorted into a parallelogram shape, making it impossible to perform calibration with high accuracy. Therefore, the present invention aims to correct the tilt of the reading mechanism.

The present invention, for example,
A conveying means having a belt that is stretched and rotated on two or more rollers, and carrying a sheet on the outer surface of the belt for transport,
A forming means for forming an image on the sheet supported on the belt ,
A reading means that reads the sheet on which the first test image has been formed by the forming means while it is being transported by the belt ,
An acquisition means that acquires the inclination of the reading means with respect to the transport direction of the transport means based on the reading result of the first test image by the reading means,
The present invention provides an image forming apparatus having the following features.

According to the present invention, it becomes possible to correct the tilt of the reading means.

Schematic diagram of an image forming apparatus Diagram explaining the printed circuit board. Diagram explaining the belt unit Perspective view illustrating the structure of the recording head. Diagram illustrating the positioning of the recording head. Diagram illustrating the positioning structure Diagram illustrating an inline scanner. Diagram explaining position correction and magnification correction. Diagram illustrating the test image. A diagram illustrating how to obtain the tilt of an inline scanner. A diagram illustrating how to obtain the tilt of an inline scanner. Diagram explaining the controller Diagram explaining the correction unit Diagram explaining the tilt acquisition section. Diagram illustrating the image processing board. A flowchart showing how to obtain the tilt of an inline scanner. Diagram illustrating the test image. Diagram illustrating the test image. A flowchart showing how to obtain the tilt of an inline scanner. A flowchart showing how to obtain the tilt of an inline scanner.

The embodiments will be described in detail below with reference to the attached drawings. Note that the following embodiments do not limit the invention as defined in the claims. While multiple features are described in the embodiments, not all of these features are essential to the invention, and the features may be combined in any way. Furthermore, in the attached drawings, identical or similar configurations are given the same reference numerals, and redundant descriptions are omitted.

<Example 1>
(1) Image forming apparatus Figure 1 is a schematic diagram showing an example of the general configuration of an inkjet recording apparatus 100. The Z direction is the height direction of the inkjet recording apparatus 100. The Y direction is parallel to the sheet transport direction. The X direction is the width direction of the sheet S. The X direction may also be perpendicular to the sheet S transport direction (Y direction). The width direction of the sheet S is sometimes called the main scanning direction. The direction parallel to the sheet S transport direction is sometimes called the sub-scanning direction.

The inkjet recording device 100 is a sheet-fed image forming apparatus that forms an ink image on a sheet S using two liquids: a reaction solution and ink. The sheet S on which the ink image is formed may be called a recording, output, or deliverable. The ink contains, for example, a resin component, water, a water-soluble organic solvent, a colorant, a wax, and additives. However, this is only an example.

The inkjet recording device 100 includes a feeding module 1000, a printing module 2000, a drying module 3000, a fixing module 4000, a cooling module 5000, a reversing module 6000, and a discharge and loading module 7000. Cut sheets S supplied from the feeding module 1000 are transported along the transport path, processed in each module, and then discharged to the discharge and loading module 7000.

The feeding module 1000 has three storage compartments 1100a to 1100c for accommodating sheets S. Storage compartments 1100a to 1100c are retractable from the front side of the inkjet recording device 100. Sheets S are fed one by one from storage compartments 1100a to 1100c by a separation belt and transport rollers, and then transported to the print module 2000. Note that there may be one or more storage compartments 1100a to 1100c.

The print module 2000 includes a sheet correction unit 2100, a belt unit 2200, and a recording unit 2300. The sheet correction unit 2100 corrects the tilt and position of the sheet S conveyed from the feed module 1000 and conveys the sheet S to the belt unit 2200. The recording unit 2300 is positioned opposite the belt unit 2200 across the conveyance path. The recording unit 2300 performs a recording process (printing) on the conveyed sheet S from above using a recording head to form an image. The sheet S is carried by the belt unit 2200 by suction. This ensures an appropriate clearance between the recording head and the sheet S. In addition, multiple recording heads may be arranged along the conveyance direction. In this embodiment, four line-type recording heads corresponding to four colors (Y: yellow, M: magenta, C: cyan, Bk: black) inks and one line-type recording head that ejects the reaction liquid C0 are provided. The number of colors and recording heads are not limited to five. For example, three additional line-type recording heads may be added for special colors C1, C2, and C3, which are different from Y, M, C, and Bk. Inkjet recording methods include, for example, methods using heating elements, piezoelectric elements, electrostatic elements, or MEMS elements. MEMS is an abbreviation for Micro-Electromechanical Systems.

Each of the four inks is supplied to the recording head from an ink tank (not shown) via an ink tube. The belt unit 2200 further transports the sheet S, on which the image has been printed by the recording unit 2300, downstream. An inline scanner 1 may be positioned downstream of the recording unit 2300. The inline scanner 1 detects the misalignment and color density of the image formed on the sheet S. The detection results are used to correct subsequent printed images.

The drying module 3000 reduces the liquid content of the ink applied to the sheet S by the recording unit 2300, thereby improving the adhesion between the sheet S and the ink. The drying module 3000 includes a decoupling unit 3200, a drying belt unit 3300, and a hot air blowing unit 3400. The sheet S, on which an image has been printed by the recording unit 2300 of the print module 2000, is transported to the decoupling unit 3200 located within the drying module 3000. The decoupling unit 3200 holds the sheet S with upward air pressure and the frictional force of the belt, while transporting the sheet S further downstream. This suppresses displacement of the sheet S on the belt unit 2200. The sheet S is then transported from the decoupling unit 3200 to the drying belt unit 3300. The drying belt unit 3300 transports the sheet S while adsorbing it. The hot air blowing unit 3400 is located above the drying belt unit 3300. The hot air blowing unit 3400 applies hot air to the sheet S, drying the ink-applied surface of the sheet S. The drying belt unit 3300 transports the sheet S to the fixing module 4000.

The drying module 3000 heats and dries the liquid components of the reaction solution and ink applied to the sheet S. This promotes the evaporation of water from the reaction solution and ink, suppressing cockling of the sheet S.

The drying module 3000 can be any device capable of performing heat drying. For example, the drying module 3000 may have a hot air dryer or a heater. There are no particular restrictions on the type of heater. For example, an electric heating element heater or an infrared heater may be used as the heater.

The fixing module 4000 has a fixing belt unit 4100. The fixing belt unit 4100 has an upper belt unit and a lower belt unit. The upper and lower belt units are heated, and the sheet S passes between them. This allows the ink solvent to sufficiently penetrate the sheet S.

The cooling module 5000 has a plurality of cooling units 5100 that cool the high-temperature sheet S conveyed from the fixing module 4000. The cooling units 5100, for example, draw outside air into the cooling box with a fan to increase the pressure inside the cooling box and blow the air onto the sheet S through nozzles formed in the conveying guide. This cools the sheet S. The cooling units 5100 are arranged on both sides of the conveying path in the height direction. This cools both sides of the sheet S. A switching unit 5200 may be provided inside the cooling module 5000 to switch the conveying path. The switching unit 5200 switches between conveying the sheet S to the reversing module 6000 and conveying the sheet S to the double-sided conveying path used during double-sided printing. During double-sided printing, the sheet S is conveyed to the double-sided conveying path 5300 provided below the cooling module 5000. Furthermore, the sheet S is transported through the fixing module 4000, drying module 3000, print module 2000, and feed module 1000. This transports the sheet S back to the sheet correction unit 2100, belt unit 2200, and recording unit 2300 of the print module 2000. The recording unit 2300 then prints the image on the second surface of the sheet S.

The double-sided transport path of the fixing module 4000 may be provided with a reversal unit 4200 for reversing the front and back sides of the sheet S. The reversal module 6000 also has a reversal unit 6400. The reversal unit 6400 reverses the front and back sides of the transported sheet S. This allows for the free selection of the front and back sides (face down/face up) of the discharged sheet S.

The discharge and loading module 7000 has a top tray 7200 and a loading section 7500. The top tray 7200 and the loading section 7500 align and load the sheets S that have been transported from the inversion module 6000.

(2) Print Module Figure 2 is a schematic cross-sectional view of the print module 2000. The print module 2000 is an image forming unit that performs recording processing on a conveyed sheet S from above using five recording heads 10 (eight recording heads 10 if special color recording heads are used) to form an ink image on the sheet S. The sheet S needs to be conveyed stably in the image forming unit. In particular, the sheet S that passes directly under the recording heads 10 needs to be conveyed stably. Therefore, the belt unit 2200 picks up and conveys the sheet S.

The print belt 25 of the belt unit 2200 is stretched over tension rollers 21 to 24. The belt surface (conveying surface) stretched over tension rollers 21 and 24 is called the image forming surface 26. The recording head 10 ejects ink (droplets) onto the sheet S conveyed by the image forming surface 26 to form an image. The print belt 25 has a plurality of suction holes (not shown) for attracting the sheet S. By attracting the sheet S through the plurality of suction holes on the image forming surface 26, the sheet S is firmly adsorbed to the image forming surface 26, and the sheet S is conveyed stably. Note that the print belt 25 is not limited to a configuration in which the sheet S is attracted to the print belt 25 by attracting the sheet S through the suction holes of the print belt 25. For example, a charge-applying part that applies an electric charge to the surface of the print belt 25 may be added. In this way, the sheet S may be electrostatically attracted to the print belt 25. In this way, the print belt 25 functions as a sheet-carrying member that carries the sheet S. The printed belt 25 is manufactured from a single strip of PET sheet wound into a roll. PET stands for polyethylene terephthalate. Multiple suction holes are formed in the PET sheet. Next, the PET sheet is cut to a predetermined length. The leading and trailing ends of the PET sheet are joined by laser welding. This produces an endless printed belt 25.

(3) Belt Unit Figure 3 shows the belt unit 2200. The printed belt 25 is stretched over tension rollers 21 to 24. In particular, the tension roller 21 is a drive roller that rotates the printed belt 25. The rotation axis of the tension roller 21 is rotatably supported by a bearing 40a. The motor M2a moves the bearing 40a in the X direction, thereby moving the tension roller 21 in the X direction.

The tension roller 22 is a tension roller that tensions the print belt 25 by pressing it from the inner circumferential surface towards the outer circumferential surface. The tension roller 23 is a steering roller. Motor M1 moves one end of the tension roller 23, tilting it. This suppresses meandering of the print belt 25.

The tension roller 24 is a driven roller that rotates in accordance with the rotation of the printed belt 25. The rotation axis of the tension roller 24 is rotatably supported by a bearing 40b. The motor M2b moves the bearing 40b in the X direction, thereby moving the tension roller 24 in the X direction.

The sheet S is adsorbed onto the image forming surface 26 and integrated with the print belt 25. Therefore, by precisely positioning the image forming surface 26, the accuracy of the image formed on the sheet S (e.g., right angles) is also improved. Two tension rollers 21 and 24 form the image forming surface 26.

Belt sensor 30a is positioned near the tension roller 21 and detects the detection shape 35 located at the end of the printed belt 25. Belt sensor 30b is positioned near the tension roller 24 and detects the detection shape 35 located at the end of the printed belt 25. The detection results from belt sensors 30a and 30b are used to determine the passage position of the end of the printed belt 25 and the conveying direction of the printed belt 25. Based on the detection results from belt sensors 30a and 30b, motors M2a and M2b independently move the tension rollers 21 and 24 in the X direction, thereby adjusting the position of the printed belt 25.

The detection shape 35 may be, for example, multiple holes with a major axis of about 1 mm. The multiple holes may be, for example, spaced about 6 mm apart, around the circumference of the printed belt 25. The line connecting the center positions of each of the multiple holes is a straight line, and this straight line is parallel to the end of the printed belt 25. The belt sensors 30a and 30b may be contact image sensors (CIS). The center positions of the holes read by the belt sensors 30a and 30b may be used for calculation. If the center position of the hole detected by belt sensor 30a in the X direction coincides with the center position of the hole detected by belt sensor 30b, then the printed belt 25 is parallel to the Y direction. Furthermore, when the printed belt 25 is moved in the X direction, the amount of movement of the center position of the hole detected by belt sensor 30a in the X direction and the amount of movement of the center position of the hole detected by belt sensor 30b are calculated. If the two amounts of movement are equal, then the printed belt 25 has moved in the X direction. By intentionally making the two movement amounts different, it becomes possible to change the conveying direction of the print belt 25.

(4) Recording Head Figure 4 is a perspective view of the recording head 10. As shown in Figure 4, the recording head 10 has a plurality of nozzle plates 103 arranged in the X direction. Each of the plurality of nozzle plates 103 has a plurality of nozzles for ejecting ink (droplets). Positioning parts 101L and 101R are located at both ends of the recording head 10 and position the recording head 10 in the X, Y, and Z directions. The bottom surface of the positioning part 101L is provided with a first contact part 101a. The first contact part 101a has a recess with a conical slope. The bottom surface of the positioning part 101R is provided with a second contact part 101b and a third contact part 101c. The second contact part 101b has a groove. The Z-Y cross section of the groove is approximately V-shaped. The third contact part 101c has a flat surface.

One end of the recording head 10 in the longitudinal direction (X direction) is provided with a first pin 107a extending in the X direction. The other end of the recording head 10 in the longitudinal direction (X direction) is provided with a second pin 107b and a third pin 107c extending in the X direction. The straight line connecting the center of the first contact portion 101a and the center of the second contact portion 101b is parallel to the arrangement direction of the multiple nozzle plates 103.

(5) Support structure of recording heads Figure 5(A) shows four recording heads 10 and a positioning member 811a provided on the housing 81 of the belt unit 2200. Figure 5(B) shows the state in which the four recording heads 10 are positioned relative to the housing 81. The positioning member 811a has a shape corresponding to the first contact portion 101a. In this example, the positioning member 811a is a hemispherical convex portion. As the recording heads 10 descend toward the housing 81, the positioning member 811a fits onto the first contact portion 101a. This positions the recording heads 10 relative to the housing 81.

Figure 6(A) shows one end of the recording head 10. Figure 6(B) shows the other end of the recording head 10. Figure 6(C) is a perspective view of the recording head 10. The head holders 106R and 106L are support members that support the recording head 10. As the head holders 106R and 106L descend from the retracted position towards the printing position, the recording head 10 also descends. This causes the first contact portion 101a to engage with the positioning member 811a. The second contact portion 101b engages with the positioning member 811b provided on the housing 81. The third contact portion 101c contacts or engages with the positioning member 811c. This firmly positions both ends of the recording head 10 in the longitudinal direction.

The head holder 106R is provided with an opening 161 having a larger area than the cross-sectional shape of the first pin 107a. A first groove 161a is provided at the bottom of the opening 161, into which the first pin 107a of the recording head 10 engages.

The head holder 106L is provided with roughly U-shaped openings 162 and 163. A second groove 162a is provided at the bottom of opening 162. A third groove 163a is provided at the bottom of opening 163. The second pin 107b of the recording head 10 engages with the second groove 162a. The third pin 107c of the recording head 10 engages with the third groove 163a.

In this way, the recording head 10 is positioned in the Z and Y directions by the first pin 107a engaging with the first groove 161a, the second pin 107b engaging with the second groove 162a, and the third pin 107c engaging with the third groove 163a.

(6) In-line scanner Figure 7 shows the in-line scanner 1. The in-line scanner 1 is an image reading device installed downstream of the recording head 10 in the conveying direction (Y direction) of the sheet S. The in-line scanner 1 can read images formed on the sheet S that is conveyed by the print belt 25.

The housing 2 of the inline scanner 1 contains an optical box 3, a reading glass 4, and an image processing substrate 7. The optical box 3 reads the shape of the sheet S itself and a test image via the reading glass 4. The optical box 3 is movable in the Y direction. The reading position 5 of the optical box 3 can move between a position for reading the sheet S and a shading sheet 6. The reading result of the shading sheet 6 is used to correct the shading of the image acquired by the optical box 3. The shading sheet 6 is sometimes called a white reference plate. The inline scanner 1, like the recording head 10, may be positioned by contacting a positioning member provided on the housing 81 of the belt unit 2200.

Incidentally, the optical box 3 has a reduction optical system that includes a CMOS-type image sensor and a lens. CMOS is an abbreviation for complementary metal-oxide-semiconductor. When the ambient temperature of the inline scanner 1 rises, the temperature of the optical box 3 also rises. This temperature rise causes thermal expansion in the holding member that holds the lens within the optical box 3, and also in the lens itself. As a result, the reading position 5 of the optical box 3 changes. In particular, the reading positions 5, which are aligned linearly in the X direction, may no longer be perpendicular to the transport direction. This can occur when the temperature change at each position of the optical box 3 in the X direction is not uniform. Therefore, it may be necessary to correct the tilt of the image read by the inline scanner 1 (hereinafter referred to as the tilt of the inline scanner 1).

(7) Position Correction and Magnification Correction Figure 8 shows position correction and magnification correction in the inkjet recording device 100. Position correction includes, for example, sheet position correction and image position correction. Sheet position correction means correcting the position (transport position) of the sheet S relative to the recording head 10 in the width direction (X direction) of the print belt 25. Image position correction means correcting the position of the image 800 relative to the sheet S (position in the main scanning direction and position in the sub-scanning direction). Magnification correction means correcting the magnification of the image 800 in the sub-scanning direction and the magnification in the main scanning direction. These correction processes are performed based on correction values obtained by reading the test image described later with the inline scanner 1.

(8) Test Image Figure 9 shows a sheet S on which a test image has been formed. The test image may be four cross marks, one at each of the four corners of the sheet S. It may be used to correct the transport position of the sheet S relative to the recording head 10. This test image may be used to correct the write position in the main scanning direction relative to the sheet S and the write position in the sub-scanning direction relative to the sheet S. This test image may be used to adjust the magnification of the image in the sub-scanning direction and the magnification of the image in the main scanning direction. Furthermore, the test image can also be used to obtain the tilt θ of the inline scanner 1. Here, the tilt θ of the inline scanner 1 is used to correct the image read by the inline scanner 1. The test image is printed on the sheet S by the recording head 10 located at the downstream end in the transport direction (Y direction) in which the sheet S is transported. The test image described in this embodiment is printed by a black recording head 10.

According to Figure 9, the coordinates of the first corner of sheet S are defined as (X1, Y1). The coordinates of the second corner of sheet S are defined as (X2, Y2). The coordinates of the third corner of sheet S are defined as (X3, Y3). The coordinates of the fourth corner of sheet S are defined as (X4, Y4). The coordinates of the first mark are defined as (X5, Y5). The coordinates of the second mark are defined as (X6, Y6). The coordinates of the third mark are defined as (X7, Y7). The coordinates of the fourth mark are defined as (X8, Y8).

Note that the direction parallel to the transport direction (Y direction) is sometimes called the sub-scanning direction. The X direction perpendicular to the transport direction is sometimes called the main scanning direction. (X1, Y1) to (X8, Y8) are calculated from the reading results of the inline scanner 1 of the sheet S on which the test image has been formed.

Sheet position correction, image position correction, and magnification correction are performed from (X1, Y1) to (X8, Y8). However, since the specific methods for these corrections are already known, their explanation is omitted here.

(9) How to determine the tilt If the inline scanner 1 is tilted with respect to the transport direction of the sheet S, the reading result of the inline scanner 1 will also be tilted. The inline scanner 1 can reduce the influence of the tilt θ on the reading result by rotating the reading result (reading image) according to the tilt θ. This rotation process may be performed in the inline scanner 1, or it may be performed in an image processing device provided outside the inline scanner 1.

Figure 10 shows how to determine the inclination θ. Here, it is assumed that the perpendicularity of the image is ensured beforehand by adjusting the transport direction of the print belt 25 and the mounting angle of the recording head 10. Figure 10 shows that the inline scanner 1 is tilted with respect to a direction perpendicular to the transport direction of the sheet S. This inclination is expressed as θ.

Correction chart S0 is sheet S on which four test images have been accurately formed. Figure 11 shows the reading results (read images) of correction chart S0.

The print belt 25 transports the correction chart S0, and the inline scanner 1 reads the correction chart S0. The tilt θ of the inline scanner 1 is measured from the coordinates of the four test images included in the reading result of the correction chart S0. In this case, the correction value, tilt θ, is calculated using the following formula.

θ = (θa + θb)/2 (1)
As shown in Figure 11, the inclination θa is the inclination of the inline scanner 1 determined from two test images on the downstream side (front end side) in the transport direction. The inclination θb is the inclination of the inline scanner 1 determined from two test images on the upstream side (rear end side) in the transport direction. The inclinations θa and θb are calculated from the following equations.

θa = arctan((Y6-Y5)/(X6-X5))...(2)
θa represents the measured tilt of the image on the leading edge side in the conveying direction of the sheet S.

θb = arctan((Y8-Y7)/(X8-X7))...(3)
θb represents the measured tilt of the image at the rear end in the transport direction of the sheet S.
Thus, the slope θ is calculated from the statistical values (e.g., the mean) of the measured values θa and θb. For simplification of the calculation, the following calculation may be used: That is, the slope θ may be calculated from two test images at the front end, or from two test images at the rear end.

θ = θa...(4)
θ = θb...(5)
The tilt θ obtained in this way is used as a tilt correction value for the inline scanner 1. The tilt θ obtained using equation (1) is stored in the memory device of the inline scanner 1. θ may also be obtained by having an inkjet recording device 100, installed in the customer's room, form a test image on a sheet S. In this case, the sheet S may be called a correction chart. Alternatively, as described in Example 2, θ may be obtained using a non-ejection detection chart printed on the sheet S to detect ink non-ejection.

(10) Controller Figure 12 shows the controller 1200 of the inkjet recording device 100. The controller 1200 has a CPU 1201 and a memory 1210. The CPU 1201 realizes various functions by executing control programs stored in the memory 1210. All or part of the functions realized by the CPU 1201 may be realized by other hardware circuits such as a DSP, ASIC or FPGA. DSP is an abbreviation for digital signal processor. ASIC is an abbreviation for application-specific integrated circuit. FPGA is an abbreviation for field-programmable gate array. The memory 1210 is a storage device that may include volatile memory (e.g., RAM), non-volatile memory (e.g., ROM), hard disk drive (HDD) and solid-state drive (SSD). The controller 1200 may be connected to an input device 1451 for receiving user input and a display device 1452 for displaying information to the user.

The test unit 1202 controls the inkjet recording device 100 to form a test image on the sheet S. The image acquisition unit 1203 controls the inline scanner 1 to read the test image formed on the sheet S. The image acquisition unit 1203 then acquires the reading result of the test image. The correction unit 1204 determines the position correction value of the sheet S, the image position correction value, and the magnification correction value from the test image reading result, and performs position correction and magnification correction according to these correction values. The tilt acquisition unit 1205 acquires the tilt θ of the inline scanner 1 based on the test image reading result.

The recording unit 2300 includes a head control unit 1230. The head control unit 1230 controls the recording head 10 according to the image signal output from the CPU 1201. The head control unit 1230 drives the motor M3 according to the control commands output from the CPU 1201 to adjust the mounting angle of the recording head 10. The motor M3 is optional. Furthermore, the head control unit 1230 adjusts the ejection timing of the recording head 10 and selects which of the multiple nozzles included in the recording head 10 to use, according to the control commands output from the correction unit 1204. This corrects the image position.

The belt unit 2200 includes a belt control unit 1220. The belt control unit 1220 controls motor M1 to reduce meandering of the print belt 25. The belt control unit 1220 controls belt sensors 30a and 30b to detect the transport direction of the print belt 25. The belt control unit 1220 may also control motors M2a and M2b according to control commands from the CPU 1201. This corrects the transport direction of the print belt 25, and thus corrects the transport position of the sheet S relative to the recording head 10.

Figure 13 shows details of the correction unit 1204. The sheet position correction unit 1301 calculates a correction value for the position of sheet S, for example, so that the coordinates (X1, Y1) in the reading result of sheet S match the target coordinates. The accuracy of the position correction is improved by also utilizing coordinates (X2, Y2), (X3, Y3), and (X4, Y4). The belt adjustment unit 1306 sends a control command to the belt control unit 1220 to control the transport direction of the print belt 25 according to the sheet position correction value.

The image position correction unit 1302 corrects the sub-scan position and main scan position of the image based on the coordinates (X5, Y5) obtained from the reading results of the test image. For example, the image position correction unit 1302 corrects the image write position in the main scan direction and the image write position in the sub-scan direction so that the coordinates (X5, Y5) become the target coordinates. The image write position in the main scan direction is achieved by correcting the transport position of the sheet S, or by selecting the nozzle to be ejected from among the multiple nozzles in the recording head 10. In other words, the image position correction value is set in the bed adjustment unit 1307 or the timing adjustment unit 1308. Alternatively, the image position correction may be achieved by deforming the original image using the image deformation unit 1309. In this case, the image position correction value is set in the image deformation unit 1309.

The magnification correction unit 1303 corrects the image magnification in the main scanning direction and the image magnification in the sub-scanning direction. For example, the magnification correction unit 1303 measures the current sub-scanning magnification and the current main scanning magnification from the reading results of a test image. The magnification correction unit 1303 determines the correction value for the main scanning direction magnification from the error between the measured value in the main scanning direction and the target value in the main scanning direction. Similarly, the magnification correction unit 1303 determines the correction value for the sub-scanning direction magnification from the error between the measured value in the sub-scanning direction and the target value in the sub-scanning direction. The image deformation unit 1309 deforms the original image based on the correction value for the main scanning direction magnification and the correction value for the sub-scanning direction magnification. This corrects the magnification in the main scanning direction and the sub-scanning direction. This process of pre-deforming the original image (document image) may be called pre-distortion.

Figure 14 shows details of the tilt acquisition unit 1205. The tilt acquisition unit 1205 acquires the tilt θ from the reading result of the test image formed on the sheet S. The tilt acquisition unit 1205 may also calculate the tilt θ using, for example, equation (1).

The θa calculation unit 1402 calculates the slope θa from the reading result of the test image by the inline scanner 1. For example, the θa calculation unit 1402 may calculate the slope θa using equation (2).

The θb calculation unit 1403 calculates the slope θb from the reading result of the test image by the inline scanner 1. For example, the θb calculation unit 1403 may calculate the slope θb using equation (3).

The statistics unit 1404 calculates statistical values (e.g., the average of slopes θa and θb) based on slopes θa and θb. The θ calculation unit 1405 calculates the slope θ (corrected value θ) from the statistical values of slopes θa and θb. For example, the θ calculation unit 1405 may calculate the slope θ by applying equation (1) to the statistical values of slope θa and slope θb.

Figure 15 shows the image processing board 7 of the inline scanner 1. The image processor 1502 is composed of a CPU or ASIC, etc. The image processor 1502 generates image data from the reading results of the inline scanner 1 and transmits it to the controller 1200. The image processor 1502 has an image data generation unit 1503 and a tilt correction unit 1504. The image data generation unit 1503 generates image data from the image signal output from the image sensor 1501. The tilt correction unit 1504 rotates the image data in the reverse direction by tilt θ, based on the tilt θ acquired by the tilt acquisition unit 1205 and stored in the memory 1505. This reduces the influence of tilt θ on the image data. Since the influence of tilt θ is reduced from the reading results of the test image, the reading accuracy of the test image is improved.

(11) Flowchart Figure 16 is a flowchart showing the control method executed by the CPU 1201.

In step S1601, the CPU 1201 (test unit 1202) controls the inkjet recording device 100 to form a test image on the sheet S. For example, the feed module 1000 starts feeding and transporting the sheet S according to the feed command from the CPU 1201. The print module 2000 forms the test image on the sheet S while transporting it according to the command from the CPU 1201.

In step S1602, the CPU 1201 (image acquisition unit 1203) reads the test image using the inline scanner 1. This acquires the reading result (image data) of the test image.

In S1603, the CPU 1201 (correction unit 1204) acquires the coordinates of the test images based on the reading results of the test images. As shown in Figure 8, the coordinates (X5, Y5) to (X8, Y8) of the four test images are acquired.

In S1604, the CPU 1201 (θa calculation unit 1402, θb calculation unit 1403) obtains the slopes θa and θb from the coordinates (X5, Y5) to (X8, Y8) of the four test images. For example, equations (2) and (3) may be used to calculate the slopes θa and θb.

In S1605, the CPU 1201 (statistical unit 1404) performs statistical processing on the slopes θa and θb. As shown in equation (1), the statistical processing may be a process to calculate the average value of the slopes θa and θb. Furthermore, if there are reading results for N sheets S, the average value of the N average values obtained from the N sheets S may be calculated.

In S1606, the CPU 1201 (θ calculation unit 1405) determines the slope θ based on the statistical values of the slopes θa and θb. This is as explained in relation to equation (1).

In S1607, the CPU 1201 (tilt acquisition unit 1205) stores the tilt θ in the memory 1505 of the inline scanner 1 and terminates the tilt θ acquisition process of the inline sensor 1. Next, the sheet position correction performed by the CPU 1201 using the tilt θ stored in the memory 1505 will be described. The CPU 1201 reads the shape of the sheet S itself using the inline scanner 1 while continuously forming images. The CPU 1201 rotates the reading result (image data) of the shape of the sheet S itself based on the tilt θ stored in the memory 1505. Then, the CPU 1201 corrects the position (transport position) of the sheet S being transported to the recording head 10 based on the rotated reading result (image data) of the shape of the sheet S itself. Note that the configuration for correcting the position (transport position) of the sheet S being transported to the recording head 10 may be a known configuration, for example, one in which rollers are used to correct the transport position of the sheet S. A detailed explanation of the configuration for correcting the position (transport position) of the sheet S being transported to the recording head 10 is omitted here.

According to this embodiment, the tilt θ of the inline scanner 1 is determined from the test image formed on the sheet S. This makes it possible to correct the tilt of the reading means. Furthermore, the influence of the tilt of the inline scanner 1 is reduced in position correction and magnification correction. As a result, the deviation of the printing position relative to the sheet S is also reduced.

<Example 2>
In Example 1, the tilt θ (correction value θ) of the inline scanner 1 is obtained from a dedicated correction chart S0. However, this is only one example. In Example 2, a case is described in which a test image for other purposes and a test image for determining the tilt θ (correction value θ) of the inline scanner 1 are formed on the same sheet S. In Example 2, the explanation of matters common to Example 1 will be based on the explanation of Example 1. Therefore, the parts specific to Example 2 will be explained in detail below.

(1) Correction Chart Figure 17 shows a non-discharge detection chart S1 with two test images for determining the tilt θ (correction value θ) of the inline scanner 1. The non-discharge detection chart S1 includes test images 1710 for detecting clogging of multiple nozzles included in the recording head 10.

The non-discharge detection chart S1 includes a test image 1710 for non-discharge detection, as well as two test images 1717 and 1718 for determining the tilt θ (correction value θ) of the inline scanner 1. In this case, the tilt θb is obtained from the coordinates (X7, Y7) and (X8, Y8) of the two test images 1717 and 1718 included in the image read by the inline scanner 1. Furthermore, the tilt θ (correction value θ) of the inline scanner 1 is equal to the tilt θb. Thus, the two test images 1717 and 1718 for determining the tilt θ (correction value θ) of the inline scanner 1 may be formed in the empty area on the rear end side of the non-discharge detection chart S1 in the transport direction.

Figure 18 shows another non-discharge detection chart S1 with four test images for determining the tilt θ (correction value θ) of the inline scanner 1. In this example, the non-discharge detection chart S1 has four test images 1717, 1718, 1805, and 1806 for determining the tilt θ (correction value θ) of the inline scanner 1, in addition to the test image 1710 for non-discharge detection. That is, by shifting the formation position of the test image 1710 for non-discharge detection in the non-discharge detection chart S1, an empty area is secured on the leading edge side of the non-discharge detection chart S1 in the transport direction. Then, test images 1805 and 1806 are formed in this empty area. As a result, the tilt θa is obtained from the coordinates (X5, Y5) and (X6, Y8) of the two test images 1805 and 1806 included in the image read by the inline scanner 1. Furthermore, similar to Example 1, the CPU 1201 determines the tilt θ (correction value θ) of the inline scanner 1 from the tilt θa and tilt θb.

(2) Flowchart (2-1) Case where the non-vomiting detection chart has two test images Figure 19 is a flowchart showing how to obtain the tilt θ (correction value θ) of the inline scanner 1 using the non-vomiting detection chart S1 shown in Figure 17.

In S1901, the CPU 1201 determines whether to start non-discharge detection based on the instruction received from the input device 1451. If the instruction indicates that non-discharge detection should be started, the CPU 1201 proceeds from S1901 to S1902. If the instruction does not indicate that non-discharge detection should be started, the CPU 1201 skips each process from S1902 to S1907.

In step S1902, the CPU 1201 controls the inkjet recording device 100 to form a non-discharge detection chart S1 with test images 1717 and 1718 on the sheet S.

In step S1903, the CPU 1201 controls the inline scanner 1 and reads the test images 1717 and 1718 of the non-ejaculation detection chart S1. This yields the reading results (read images) of the test images 1717 and 1718.

In S1904, the CPU 1201 obtains the coordinates of two test images 1717 and 1718 from the reading result (read image) of the test image. As illustrated in Figure 17, (X7, Y7) and (X8, Y8) are obtained.

In S1905, the CPU 1201 obtains the tilt θb based on the coordinates of the test image. For example, the CPU 1201 may calculate the tilt θb according to equation (3).

In S1906, the CPU 1201 obtains a correction value θ, which is the tilt of the inline scanner 1, based on the tilt θb. For example, the CPU 1201 substitutes the tilt θb into the correction value θ.

In S1907, CPU 1201 stores the correction value θ in memory 1210.

Furthermore, the series of processes from S1903 to S1907 may be repeated multiple times to calculate multiple correction values θ and obtain the average value of these correction values θ. This may reduce the influence of reading errors by the inline scanner 1.

(2-2) Case where the non-vomiting detection chart has four test images Figure 20 is a flowchart showing how to obtain the tilt θ (correction value θ) of the inline scanner 1 using the non-vomiting detection chart S1 shown in Figure 18.

In S2001, the CPU 1201 determines whether to start non-discharge detection based on the instruction received from the input device 1451. If the instruction indicates that non-discharge detection should be started, the CPU 1201 proceeds from S2001 to S2002. If the instruction does not indicate that non-discharge detection should be started, the CPU 1201 skips each process from S2002 onward.

In step S2002, the CPU 1201 controls the inkjet recording device 100 and forms a non-discharge detection chart S1 with test images 1717, 1718, 1805, and 1806 on the sheet S.

In S2003, CPU 1201 controls the inline scanner 1 and reads test images 1717, 1718, 1805, and 1806 of the non-ejaculation detection chart S1. This yields the reading results (read images) of test images 1717, 1718, 1805, and 1806.

Subsequently, steps S1603 to S1607, as described in Example 1, are executed for test images 1717, 1718, 1805, and 1806. Then, the CPU 1201 generates correction data (correction conditions) for correcting the image formed on the sheet based on the corrected image data. Furthermore, based on this correction data (correction conditions), the CPU 1201 performs an affine transformation on the image formed on the sheet using image processing to correct the geometric characteristics of the image formed on the sheet.

As described above, in Example 2, the process of acquiring the tilt θ (correction value θ) of the inline scanner 1 is performed in parallel with the non-discharge detection process. This makes it possible to acquire the tilt θ (correction value θ) of the inline scanner 1 while suppressing a decrease in the productivity of the inkjet recording device 100.

<Technical concepts derived from the examples>
(Item 1)
The print belt 25 is an example of a transport means that sucks up the sheet S and transports it in a predetermined transport direction. The recording head 10 is an example of a forming means that forms an image on the sheet S transported by the transport means. The inline scanner 1 is an example of a reading means that reads the first test image formed by the recording head 10 from the sheet S transported by the print belt 25. The CPU 1201 and correction unit 1204 are an example of a correction means that corrects the inclination of the reading means relative to the transport means based on the reading result of the first test image. Thus, according to this embodiment, a rotating body having a position reference member as described in Patent Document 1 is unnecessary. Therefore, this embodiment makes it possible to correct the inclination of the reading means by a simpler method. In addition, the shape of the image in the image forming apparatus is maintained inexpensively and accurately.
(Item 2)
The CPU 1201 and the tilt acquisition unit 1205 are examples of acquisition means that acquire the tilt of the reading means based on at least two first test images formed on the sheet. By using the two first test images formed on the sheet S in this way, the tilt θ of the reading means can be acquired with high accuracy.
(Item 3)
The CPU 1201 and the θa calculation unit 1402 are an example of a first calculation means that calculates a first inclination θa at the leading edge of the sheet S based on two first test images formed at the leading edge of the sheet S in the conveying direction of the sheet S. The CPU 1201 and the θa calculation unit 1402 are an example of a second calculation means that calculates a second inclination θb at the rear end of the sheet S based on two first test images formed at the rear end of the sheet S in the conveying direction of the sheet S. The θ calculation unit 1405 is an example of a third calculation means that calculates the inclination θ of the reading means based on the first inclination and the second inclination. As a result, the inclination θ (correction value θ) is calculated accurately, and the alignment between the inline scanner 1 and the print belt 25 is accurately adjusted.
(Item 4)
The coordinates (X5, Y5) and (X6, Y6) are examples of first and second coordinates for two first test images formed on the leading edge of the sheet S. The θa calculation unit 1402 may calculate the first tilt θa by calculating the arctangent between the first and second coordinates. As a result, the tilt θ (correction value θ) is calculated accurately, and the alignment between the inline scanner 1 and the print belt 25 is precisely adjusted.
(Item 5)
The coordinates (X7, Y7) and (X8, Y8) are examples of the third and fourth coordinates for two first test images formed on the rear end side of the sheet S. The θa calculation unit 1402 may calculate the second inclination θb by calculating the arctangent between the third and fourth coordinates. This will allow the inclination θ between the inline scanner 1 and the print belt 25 to be acquired with high accuracy.
(Item 6)
The θ calculation unit 1405 may calculate the slope of the reading means using a statistical value (e.g., the average value) of the first slope and the second slope. This reduces the influence of reading errors, allowing the slope θ between the inline scanner 1 and the print belt 25 to be obtained with greater accuracy.
(Item 7)
As described in Example 2, the recording head 10 may form a second test image on the sheet S along with the first test image to detect image formation defects of the recording head 10. This allows the same sheet S to be used for tilt correction and non-discharge detection, thus reducing the number of sheets S. Furthermore, since the tilt θ can be acquired in parallel with non-discharge detection, the processing time is reduced.
(Item 8)
As illustrated in Figure 17, the recording head 10 may form at least two first test images on the rear end of the sheet S, and a second test image for detecting image formation defects may also be formed on the sheet S. This allows tilt correction and non-discharge detection to use the same sheet S, thus reducing the number of sheets S. Furthermore, since tilt θ can be acquired in parallel with non-discharge detection, processing time is reduced.
(Item 9)
As illustrated in Figure 18, the recording head 10 may form at least two first test images on the leading edge of the sheet S, as well as a second test image on the sheet for detecting image formation defects. This allows the same sheet S to be used for both tilt correction and non-discharge detection, thus reducing the number of sheets S required. Furthermore, since the tilt θ can be acquired in parallel with non-discharge detection, processing time is reduced.
(Item 10)
The CPU 1201 and the tilt acquisition unit 1205 may acquire the tilt θ of the reading means based on at least two first test images formed on the sheet S.
(Item 11)
As illustrated in Figure 18, the recording head 10 may form at least two first test images on the leading edge of the sheet S, at least two first test images on the trailing edge of the sheet S, and a second test image for detecting image formation defects on the sheet S. This allows tilt correction and non-discharge detection to use the same sheet S, thus reducing the number of sheets S. Furthermore, since tilt θ can be acquired in parallel with non-discharge detection, processing time is reduced. In addition, since four first test images are used, the accuracy of the tilt θ calculation will likely improve.
(Item 12)
As illustrated in Figure 11, the CPU 1201 and the correction unit 1204 may acquire the tilt θ of the reading means based on at least two first test images formed on the leading edge side of the sheet S and at least two first test images formed on the trailing edge side of the sheet S.
(Item 13)
The inline scanner 1 may be configured to read a third test image formed on a separate sheet. That is, the third test image may be a test image for position correction or magnification correction. In this embodiment, the test image for determining the tilt θ of the inline scanner 1 and the test image for position correction or magnification correction are the same, but this is just an example. These test images may be different. The CPU 1201, correction unit 1204, or tilt correction unit 1504 may be configured to correct (e.g., rotate) the reading result of the third test image according to the tilt θ. This may reduce the influence of the tilt θ of the inline scanner 1 on the reading result of the third test image. As a result, the accuracy of various controls using the reading result of the third test image will be improved.
(Item 14)
The sheet position correction unit 1301 or the belt adjustment unit 1306 may function as an adjustment means for adjusting the transport position of the print belt 25 or the sheet S based on the reading result of the third test image corrected according to the tilt θ.
(Item 15)
The print belt 25 is an example of an endless belt. The endless belt may be configured to rotate while being stretched over at least two rollers (e.g., tension rollers 21, 24). The sheet S is carried and transported on the outer surface (e.g., image forming surface 26) of the endless belt between the first roller (e.g., tension roller 21) and the second roller (e.g., tension roller 24) of the two or more rollers. The CPU 1201 and the correction unit 1204 move at least one of the first roller or the second roller in the rotation axis direction using adjustment means (e.g., belt adjustment unit 1306, motors M2a, M2b). This may correct the transport position of the print belt 25 or the sheet S.
(Item 16)
The image position correction unit 1302 or the magnification correction unit 1303, etc., are examples of adjustment means that adjust the formation position of the image formed on the sheet S by the recording head 10, or the magnification of the image, based on the reading result of the third test image corrected according to the tilt θ.
(Item 17)
As illustrated in Figure 4, the recording head 10 has multiple nozzles arranged along the longitudinal direction of the recording head 10, each of which ejects ink. The CPU 1201, correction unit 1204, and timing adjustment unit 1508 may adjust the formation position of the image formed on the sheet S by adjusting the ejection timing of the multiple nozzles.
(Item 18)
The CPU 1201 and the correction unit 1204 may correct the image data that forms the basis of the image formed by the recording head 10 based on the reading result of the third test image corrected according to the tilt θ. This may adjust the formation position of the image formed on the sheet S, or the magnification of the image.
(Item 19)
The inversion unit 4200 is an example of an inversion means for inverting a sheet S on which an image has been formed on the first surface. The double-sided transport path 5300 is an example of a transport path for transporting the sheet S, which has been inverted by the inversion means, to the transport means. The recording head 10 forms an image on the second surface of the sheet S on which an image has been formed on the first surface. By correcting the right angles of the image, the front-to-back misalignment is also reduced.

The invention is not limited to the embodiments described above, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, the claims are attached to disclose the scope of the invention.

25: Print belt, 10: Recording head, 1: Inline scanner, 1201: CPU, 1502: Image processor

Claims (13)

A conveying means having a belt that is stretched and rotated on two or more rollers, and carrying a sheet on the outer surface of the belt for transport,
A forming means for forming an image on the sheet supported on the belt ,
A reading means that reads the sheet on which the first test image has been formed by the forming means while it is being transported by the belt ,
An acquisition means that acquires the inclination of the reading means with respect to the transport direction of the transport means based on the reading result of the first test image by the reading means,
An image forming apparatus having The first test image includes two first test images formed on the leading edge side of the sheet in the sheet transport direction, and two other first test images formed on the rear end side of the sheet in the sheet transport direction.
The image forming apparatus according to claim 1, wherein the acquisition means acquires the tilt of the reading means based on the reading results of the two first test images read by the reading means and the reading results of the other two first test images read by the reading means. The acquisition means is,
A first calculation means for calculating a first inclination at the leading edge of the sheet based on the two first test images formed on the leading edge of the sheet in the conveying direction of the sheet,
A second calculation means for calculating a second inclination at the rear end of the sheet based on the other two first test images formed on the rear end of the sheet in the sheet transport direction,
The image forming apparatus according to claim 2, further comprising: a third calculation means for calculating the inclination of the reading means based on the first inclination and the second inclination. The first calculation means calculates the first inclination by calculating the first coordinate of the first image among the two first test images formed on the leading edge of the sheet and the second coordinate of the second image among the other two first test images formed on the leading edge of the sheet , and by calculating the arctangent between the first coordinate and the second coordinate.
The image forming apparatus according to claim 3, wherein the second calculation means calculates the third coordinate of the third image among the other two first test images formed on the rear end side of the sheet and the fourth coordinate of the fourth image among the other two first test images formed on the rear end side of the sheet, and calculates the second inclination by calculating the arctangent between the third coordinate and the fourth coordinate . The image forming apparatus according to claim 3, wherein the third calculation means calculates the average value of the first slope and the second slope as the slope of the reading means. The image forming apparatus according to claim 1, wherein the forming means forms a second test image on the sheet, along with the first test image, for detecting image formation defects of the forming means. The reading means reads a third test image formed on a sheet different from the sheet on which the first test image was formed .
The image forming apparatus according to claim 1, further comprising a correction means for correcting the reading result of the third test image by the reading means according to the tilt acquired by the acquisition means. The image forming apparatus according to claim 7 , further comprising an adjustment means for adjusting the transport position of the transport means based on the reading result of the third test image corrected by the correction means. The aforementioned belt is stretched over at least two or more rollers and rotates ,
The sheet is carried on the outer surface of the belt between the first roller and the second roller among the two or more rollers, and is transported.
The image forming apparatus according to claim 8 , wherein the correction means adjusts the conveying position of the belt by moving at least one of the first roller or the second roller in the rotational axis direction using the adjustment means. The image forming apparatus according to claim 7 , further comprising an adjustment means for adjusting the magnification of an image formed on a sheet by the forming means based on the reading result of the third test image corrected by the correction means. The forming means has a plurality of nozzles that eject ink, arranged in a direction intersecting the transport direction,
The image forming apparatus according to claim 7, further comprising an adjustment means for adjusting the position of the image formed on a sheet by the forming means by adjusting the discharge timing of the plurality of nozzles based on the reading result of the third test image corrected by the correction means . The image forming apparatus according to claim 10, wherein the adjustment means adjusts the magnification by correcting the image data that will be the basis of the image formed by the forming means based on the reading result of the third test image corrected by the correction means. An inversion means for inverting a sheet on which an image has been formed on the first surface by the forming means,
The system further includes a transport path for transporting the sheet, which has been inverted by the inversion means, to the transport means,
The image forming apparatus according to claim 1, wherein the forming means forms an image on the second surface of the sheet on which an image is formed on the first surface.