Printhead

Abstract

To provide a print head which prevents image quality deterioration.SOLUTION: A print head includes a light emission element array, a plurality of drive circuits (including a capacitor), a memory, and a light quantity correction control circuit. The capacitor included in the plurality of drive circuits maintains a voltage determining a light emission quantity of each light emission element between terminals. The memory stores a voltage value (a correction value) set between capacitor terminals included in the drive circuits. The memory stores the voltage value as a light quantity in a predetermined range when a voltage between the capacitor terminals and the light quantity of the light emission element are correlated and light can be emitted at the light quantity in a predetermined range including a target light quantity, and stores the voltage value which does not affect voltage setting between the other capacitor terminals when the voltage between the capacitor terminals and the light quantity of the light emission element are not correlated and the light cannot be emitted at the light quantity in the predetermined range including the target light quantity. The light quantity correction control circuit controls the light quantity of the plurality of light emission elements according to the voltage value stored in the memory.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] SUMMARY OF THE DISCLOSURE The present invention relates to a printhead. [Background technology]

[0002] Electrophotographic printers (hereinafter, printers) are widely used. Printers are equipped with a print head, which is equipped with multiple light-emitting elements. The light-emitting elements can be LEDs (Light Emitting Diodes) or OLEDs (Organic Light Emitting Diodes). For example, a print head is provided with light-emitting elements equivalent to 5,120 pixels, with the arrangement of the light-emitting elements in the main scanning direction and the direction perpendicular to the main scanning direction being the sub-scanning direction. The printer exposes a photosensitive drum to light emitted from the multiple light-emitting elements, and prints an image corresponding to the latent image formed on the photosensitive drum onto a sheet of recording paper.

[0003] The density of an image corresponds to the amount of light emitted by each light-emitting element, and the amount of light emitted by each light-emitting element is determined by the voltage across the terminals of a capacitor included in the drive circuit of each light-emitting element. A voltage supply unit (D / A) controls the voltage across the terminals of each capacitor to make the amount of light emitted by each light-emitting element uniform. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2007-283599 A Summary of the Invention [Problem to be solved by the invention]

[0005] In obtaining a uniform amount of light from each light-emitting element, the set voltage value (target value) between some capacitor terminals may differ greatly from the set voltage value between other capacitor terminals. For example, a defective element may be included among a number of light-emitting elements, and a sufficient amount of light may not be obtained from this defective element. The light amount correction may function for such a defective element, and the set voltage value between the capacitor terminals corresponding to the defective element may become extremely large. In this way, when the set voltage value between some capacitor terminals becomes extremely large, an appropriate voltage cannot be set between adjacent capacitor terminals, and as a result, the amount of light may become too large, which may lead to a deterioration in image quality.

[0006] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide a print head which prevents degradation of image quality. [Means for solving the problem]

[0007] The print head according to the embodiment includes a light-emitting element row, a plurality of driving circuits (including a capacitor), a memory, and a light amount correction control circuit. The light-emitting element row includes a plurality of light-emitting elements. The plurality of driving circuits drive each of the light-emitting elements in the light-emitting element row. The capacitors included in the plurality of driving circuits hold a voltage between their terminals that determines the amount of light emitted by each of the light-emitting elements. The memory stores a voltage value (correction value) to be set between the capacitor terminals included in the driving circuit. When there is a correlation between the voltage between the capacitor terminals and the amount of light emitted by the light-emitting element and the light amount can be emitted within a predetermined range, the memory stores a voltage value (correction value) that results in a light amount within the predetermined range, and when there is no correlation between the voltage between the capacitor terminals and the amount of light emitted by the light-emitting element and the light amount cannot be emitted within the predetermined range, the memory stores a voltage value (correction value) that does not affect the voltage setting between other capacitor terminals. The light amount correction control circuit controls the light amount of the plurality of light-emitting elements according to the voltage value (correction value) stored in the memory. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing an example of the positional relationship between a photoconductor drum and a print head applied to an image forming apparatus according to an embodiment. [Diagram 2] FIG. 2 is a diagram showing an example of a transparent substrate constituting the print head according to the embodiment. [Diagram 3] FIG. 3 is a diagram showing an example of the layout of light emitting elements and a DRV circuit of a print head according to the embodiment. [Figure 4] FIG. 4 is a diagram showing an example of a cross section of a transparent substrate of a print head according to an embodiment. [Diagram 5] FIG. 5 is a diagram showing an example of a DRV circuit for driving a light-emitting element according to an embodiment, and a light-emitting element that emits light by the DRV circuit. [Figure 6] FIG. 6 is a diagram showing an example of a circuit block of the print head according to the embodiment. [Figure 7] FIG. 7 is a diagram showing an example of an image forming apparatus to which the print head according to the embodiment is applied. [Figure 8] FIG. 8 is a block diagram showing an example of a control system of the image forming apparatus according to the embodiment. [Figure 9] FIG. 9 is a diagram for explaining light amount control within a light emitting element group of a print head according to an embodiment. [Figure 10] FIG. 10 is a timing chart showing an example of potential setting between capacitor terminals of the print head according to the embodiment. [Figure 11] FIG. 11 is a timing chart showing an example of the relationship between light amount control and light emission time control of the print head according to the embodiment. [Figure 12] FIG. 12 is a schematic diagram of a correction data generating device for explaining a method of generating correction data for causing the light emitting elements of the print head according to the embodiment to emit a uniform amount of light. [Figure 13] FIG. 13 is a graph showing the relationship between the correction value and the amount of light of the light emitting element in the print head according to the embodiment. [Figure 14] FIG. 14 is a flowchart showing an example of light amount correction for the print head according to this embodiment. [Figure 15]FIG. 15 is a timing chart showing an example of light amount correction in the case where there is no defective element. [Figure 16] FIG. 16 is a diagram showing an example of exposure in the case where the print head according to the embodiment includes a defective element. [Figure 17] FIG. 17 is a diagram showing an example of the light quantity measurement result when a defective element is included in the print head. [Figure 18] FIG. 18 is a diagram showing an example of the correction value calculated by the first light amount correction in a case where the print head includes a defective element. [Figure 19] FIG. 19 is a diagram showing an example of the amount of light after the first light amount correction is applied in a case where a defective element is included in the print head. [Figure 20] FIG. 20 is a diagram for explaining the influence of an inappropriate voltage setting due to the first light amount correction. [Figure 21] FIG. 21 is a diagram for explaining the effect on an image when the first light amount correction is applied to a print head including a defective element. [Figure 22] FIG. 22 is a flowchart showing an example of the second light amount correction for the print head according to this embodiment. [Diagram 23] FIG. 23 is a diagram showing an example of the correction value calculated by the second light amount correction in a case where the print head includes a defective element. [Figure 24] FIG. 24 is a diagram showing an example of the amount of light after the second light amount correction is applied in a case where the print head includes a defective element. [Diagram 25] FIG. 25 is a diagram for explaining the effect on an image when the second light amount correction is applied to a print head including a defective element. [Figure 26] FIG. 26 is a diagram showing an example of a case where the light emitting element row of the print head according to the embodiment is longer than the rod lens array, and the measured light quantities corresponding to the light emitting elements at both ends are very small values. [Figure 27] FIG. 27 is a diagram showing an example of the light quantity measurement result in the case where a light emitting element is included outside the lens area in the print head. [Figure 28] FIG. 28 is a diagram showing an example of the correction value calculated by the first light amount correction in a case where the print head includes a light emitting element outside the lens area. [Figure 29] FIG. 29 is a diagram showing an example of the amount of light after the first light amount correction is applied in a case where a light emitting element is included outside the lens area in a print head. [Diagram 30] FIG. 30 is a diagram for explaining the effect on an image when the first light amount correction is applied to a print head including a light emitting element outside the lens region. [Diagram 31] FIG. 31 is a diagram showing an example of the correction value calculated by the second light amount correction in a case where the print head includes a light emitting element outside the lens area. [Diagram 32] FIG. 32 is a diagram showing an example of the amount of light after the second light amount correction is applied in a case where a light emitting element is included outside the lens area in the print head. [Diagram 33] FIG. 33 is a diagram for explaining the effect on an image when the second light amount correction is applied to a print head including a light emitting element outside the lens region. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] An example of an image forming apparatus according to an embodiment will be described below with reference to the drawings. In each drawing, the same components are given the same reference numerals. The image forming apparatus is a printer, a copier, or a multi-function peripheral (MFP: Multi-Functional Peripheral). In this embodiment, an image forming apparatus equivalent to an MFP will be described.

[0010] [Print head configuration] An example of the configuration of a print head that is applied to an image forming apparatus according to an embodiment will be described with reference to FIGS. FIG. 1 is a diagram showing an example of the positional relationship between a photoconductor drum and a print head applied to an image forming apparatus according to an embodiment. The image forming apparatus includes a photoconductor drum 17 and a print head 1 shown in FIG.

[0011] Photoconductor drum 17 rotates in the direction of the arrow shown in Fig. 1. The rotation direction of photoconductor drum 17 is called the sub-scanning direction (Y-axis direction), and the direction perpendicular to the sub-scanning direction is called the main scanning direction (X-axis direction). Photoconductor drum 17 is uniformly charged by a charger and exposed to light from print head 1, lowering the potential of the exposed area. In other words, the image forming apparatus controls the light emission of print head 1 and forms an electrostatic latent image on photoconductor drum 17. Controlling the light emission of print head 1 means controlling the timing of when print head 1 emits light and when it is turned off (non-emits light), and controlling the amount of light.

[0012] The print head 1 includes a light-emitting unit 10 and a rod lens array 12. The light-emitting unit 10 includes a transparent substrate 11 disposed opposite the rod lens array 12. For example, the transparent substrate 11 is a glass substrate that transmits light. A light-emitting element row 13 consisting of a plurality of light-emitting elements is formed on the transparent substrate 11. Note that the print head 1 may include a plurality of light-emitting element rows.

[0013] The rod lens array 12 focuses light from each light-emitting element 131 in the light-emitting element row 13 onto the photosensitive drum 17. As a result, an image line is formed on the photosensitive drum 17 according to the light emitted by the light-emitting elements 131. The light-emitting elements 131 are formed on the transparent substrate 11. The light amount of the light-emitting elements 131 at the opposing positions across the rod lens array 12 satisfies the standard and becomes a value within a predetermined range due to current control. Note that, as will be described later, some of the light-emitting elements 131 (defective elements or out-of-area elements arranged outside the light passing area of ​​the lens of the rod lens array 12) may not satisfy the standard and may become a value outside the predetermined range at the opposing positions across the rod lens array 12 due to current control.

[0014] Fig. 2 is a diagram showing an example of a transparent substrate constituting a print head according to an embodiment. Fig. 2 shows an example of a transparent substrate corresponding to a single row of light emitting elements, but the print head may have multiple rows of light emitting elements.

[0015] As shown in Fig. 2, a light emitting element row 13 is formed on a transparent substrate 11 along the longitudinal direction of the transparent substrate 11. A drive circuit row 14 for driving (causing light to be emitted) each light emitting element and wiring 145 for supplying signals to the drive circuit row 14 are arranged near the light emitting element row 13. Hereinafter, "drive" is abbreviated as "DRV." In Fig. 2, the wiring 145 for driving (causing light to be emitted) the light emitting elements 131 is gathered on one side of the light emitting element row 13, but the wiring 145 may be divided into two.

[0016] An IC (Integrated Circuit) 15 and a light quantity correction memory 18 are disposed on an end of the transparent substrate 11. The transparent substrate 11 also includes a connector 16. The connector 16 electrically connects the print head 1 to a control system of a printer, copier, or multifunction device. This connection enables power supply, head control, image data transfer, and the like. A substrate is attached to the transparent substrate 11 to seal the light emitting element row 13, wiring 145, DRV circuit 140, and the like so that they do not come into contact with the outside air. If it is difficult to attach a connector to the transparent substrate, an FPC (Flexible Printed Circuits) may be connected to the transparent substrate and electrically connected to the control system.

[0017] 3 is a diagram showing an example of the layout of light emitting elements and a DRV circuit of a print head according to an embodiment. Although FIG. 3 shows an example of a DRV circuit corresponding to one row of light emitting elements, the print head may be provided with DRV circuits corresponding to multiple rows of light emitting elements.

[0018] 3, the light-emitting section 10 of the print head 1 includes a light-emitting element row 13 in which a plurality of light-emitting elements 131 are arranged, and a DRV circuit row 14 in which a plurality of DRV circuits 140 are arranged. The DRV circuits 140 cause the light-emitting elements 131 connected thereto to emit light based on signals from wiring 145 (corresponding to a sample-and-hold signal (SH signal) 21, a light-emitting level signal 22, and a PWM (Pulse Width Modulation) signal 32, which will be described later).

[0019] Fig. 4 is a diagram showing an example of a cross section of a transparent substrate of a print head according to an embodiment. Fig. 4 shows an example of a cross section of a transparent substrate corresponding to one row of light emitting elements, but the print head may have multiple rows of light emitting elements. 4, the light-emitting unit 10 of the print head 1 includes a plurality of light-emitting elements 131, a plurality of DRV circuits 140, and wiring 145, which are arranged to face a reference surface 1101 of the transparent substrate 11. The light-emitting unit 10 also includes a sealing glass 1102. The plurality of light-emitting elements 131, the plurality of DRV circuits 140, and wiring 145 are arranged in a space surrounded by the transparent substrate 11 and the sealing glass 1102. Light from the light-emitting elements 131 passes through the transparent substrate 11 and is irradiated towards the photoconductor drum 17.

[0020] FIG. 5 is a diagram showing an example of a DRV circuit for driving a light-emitting element according to an embodiment, and a light-emitting element that emits light by the DRV circuit. The DRV circuit 140 is composed of low-temperature polysilicon thin-film transistors 141, 143, 144 and a capacitor 142. The SH signal 21 goes low when changing the light emission intensity of the light-emitting element 131 connected to the DRV circuit 140. When the SH signal 21 goes low, the transistor 141 goes ON, and the terminal voltage of the capacitor 142 connected to the transistor 141 and the transistor 143 changes according to the voltage of the light-emission level signal 22. In other words, the terminal voltage of the capacitor 142 changes according to a correction value, which will be described later, and the current supplied to the light-emitting element 131 is determined by the terminal voltage.

[0021] When the SH signal 21 becomes high level, the transistor 141 is turned off and the voltage between the terminals of the capacitor 142 is held. Even if the voltage of the light emission level signal 22 changes, the voltage level between the terminals of the capacitor 142 does not change. A current corresponding to the voltage held between the terminals of the capacitor 142 flows through the light emitting element 131 connected to the signal line I of the DRV circuit 140. That is, the light emitting element 131 emits light with an amount of light corresponding to the voltage between the terminals of the capacitor 142 in the DRV circuit 140. A predetermined DRV circuit 140 and a light emitting element 131 are selected from the multiple DRV circuits 140 and the multiple light emitting elements 131 included in the DRV circuit row 14 and the light emitting element row 13 by the SH signal 21, and the light emission intensity is determined by the light emission level signal 22, and the light emission intensity can be maintained. Hereinafter, the voltage between the terminals of the capacitor may be referred to as the voltage of the capacitor.

[0022] A transistor 144 in the DRV circuit 140 switches between supplying and not supplying current (turning the current supply on and off) to the light-emitting element 131. A PWM signal 32 connected to the transistor 144 controls the lighting and extinguishing of the light-emitting element 131 (determines the light-emitting time per line period). When the transistor 144 is turned on by the PWM signal 32, a current flows through the light-emitting element 131, causing the light-emitting element 131 to emit light. When the transistor 144 is turned off by the PWM signal 32, no current flows through the light-emitting element 131, causing the light-emitting element 131 to turn off.

[0023] Fig. 6 is a diagram showing an example of a circuit block of a print head according to an embodiment. Fig. 6 shows an example of a head circuit block corresponding to one row of light emitting elements, but the print head may have multiple rows of light emitting elements. As shown in Fig. 6, the light-emitting unit 10 includes an IC 15, a light intensity correction memory 18, and a head circuit block including N light-emitting element groups 161 from first to Nth (e.g., N=640). Each light-emitting element group 161 includes M DRV circuits 140 from first to Mth (e.g., M=8). As shown in Fig. 6, the M DRV circuits 140 included in each light-emitting element group 161 are denoted as DRV1 to 8. The IC 15 includes a light intensity correction control circuit 151, an SH signal output circuit 152, a D / A (digital to analog) conversion circuit 153, an ON / OFF control circuit 155, and the like.

[0024] The light quantity correction memory 18 stores a correction value (first correction value) for making each light emitting element 131 emit light in a predetermined range of light quantity. However, for light emitting elements 131 that cannot be made to emit light in a predetermined range of light quantity for any correction value, a separately determined correction value (second correction value) is stored. The light quantity correction memory 18 outputs the correction value to the light quantity correction control circuit 151. A light emission controller of the image forming apparatus, which will be described later, may read out the correction value from the light quantity correction memory 18 and write the correction value to the light quantity correction control circuit 151.

[0025] A horizontal synchronizing signal 24 and an image data writing clock C are input to the light quantity correction control circuit 151 via the connector 16. In addition, the horizontal synchronizing signal 24, the image data writing clock C, and image data 31 are input to the ON / OFF control circuit 155 via the connector 16. The horizontal synchronizing signal 24 resets the count values ​​of the light quantity correction control circuit 151 and the ON / OFF control circuit 155.

[0026] The light quantity correction control circuit 151 outputs a signal synchronized with the image data writing clock C. That is, the light quantity correction control circuit 151 outputs a correction value to the D / A conversion circuit 153 in synchronization with the image data writing clock C. As a result, the D / A conversion circuit 153 outputs a voltage according to the correction value. The SH signal output circuit 152 supplies the SH signal 21 described above to the DRV circuit 140, and the ON / OFF control circuit 155 controls the ON / OFF of the PWM signal 32, and the PWM signal output circuit 160 supplies the PWM signal 32 (321, 322, ..., 328) to the DRV circuit 140. The SH signal 22 from the SH signal output circuit 152 and the light emission level signal 22 from the D / A conversion circuit 153 set the voltage between the terminals of the capacitor in sequence. That is, the SH signal output circuit 152 and the D / A conversion circuit 153 function as a voltage setting means.

[0027] The DRV circuit 140 generates a drive signal for causing the light emitting element 131 to emit light based on the SH signal 21 (211, 212, ..., 218), the light emission level signal 22 (22001, 22002, ..., 22640), and the PWM signal 32 output by the IC 15. The DRV circuit 140 supplies a drive signal (current) to the light emitting element 131.

[0028] [Configuration of image forming device] Fig. 7 is a diagram showing an example of an image forming apparatus to which the print head according to the embodiment is applied. Fig. 7 shows an example of a four-tandem type color image forming apparatus, but the print head 1 according to the embodiment can also be applied to a monochrome image forming apparatus.

[0029] 7, for example, image forming apparatus 100 includes image forming unit 1021 that forms a yellow (Y) image, image forming unit 1022 that forms a magenta (M) image, image forming unit 1023 that forms a cyan (C) image, and image forming unit 1024 that forms a black (K) image. Image forming units 1021, 1022, 1023, and 1024 form yellow, cyan, magenta, and black images, respectively, and transfer them to transfer belt 103. As a result, a full-color image is formed on transfer belt 103.

[0030] Image forming unit 1021 which forms an image of yellow (Y) includes print head 1001, which includes a light emitting unit 1011 and a rod lens array 1201. Furthermore, image forming unit 1021 includes, around photoconductor drum 1701, a charger 1121, print head 1001, developer 1131, transfer roller 1141, and cleaner 1161. Print head 1001 corresponds to print head 1, light emitting unit 1011 corresponds to light emitting unit 10, rod lens array 1201 corresponds to rod lens array 12, and photoconductor drum 1701 corresponds to photoconductor drum 17, and their respective descriptions will be omitted.

[0031] Image forming unit 1022 which forms a magenta (M) image includes print head 1002, which includes a light emitting unit 1012 and a rod lens array 1202. Furthermore, image forming unit 1022 includes, around photoconductor drum 1702, a charger 1122, print head 1002, developer 1132, transfer roller 1142, and cleaner 1162. Print head 1002 corresponds to print head 1, light emitting unit 1012 corresponds to light emitting unit 10, rod lens array 1202 corresponds to rod lens array 12, and photoconductor drum 1702 corresponds to photoconductor drum 17, and their respective descriptions will be omitted.

[0032] Image forming unit 1023 which forms a cyan (C) image includes print head 1003, which includes light emitting section 1013 and rod lens array 1203. Furthermore, image forming unit 1023 includes charger 1123, print head 1003, developer 1133, transfer roller 1143, and cleaner 1163 around photosensitive drum 1703. Print head 1003 corresponds to print head 1, light emitting section 1013 corresponds to light emitting section 10, rod lens array 1203 corresponds to rod lens array 12, and photosensitive drum 1703 corresponds to photosensitive drum 17, and their respective descriptions will be omitted.

[0033] Image forming unit 1024 which forms a black (K) image includes print head 1004, which includes light emitting section 1014 and rod lens array 1204. Furthermore, image forming unit 1024 includes, around photoconductor drum 1704, electrostatic charger 1124, print head 1004, developer 1134, transfer roller 1144, and cleaner 1164. Print head 1004 corresponds to print head 1, light emitting section 1014 corresponds to light emitting section 10, rod lens array 1204 corresponds to rod lens array 12, and photoconductor drum 1704 corresponds to photoconductor drum 17, and their respective descriptions will be omitted.

[0034] Electrostatic chargers 1121, 1122, 1123, and 1124 uniformly charge photoconductor drums 1701, 1702, 1703, and 1704, respectively. Print heads 1001, 1002, 1003, and 1004 expose photoconductor drums 1701, 1702, 1703, and 1704 to light emitted by light-emitting element 131, and form electrostatic latent images on photoconductor drums 1701, 1702, 1703, and 1704. Developer 1131 deposits yellow toner, developer 1132 deposits magenta toner, developer 1133 deposits cyan toner, and developer 1134 deposits black toner onto the electrostatic latent image portions of photoconductor drums 1701, 1702, 1703, and 1704, respectively (to develop the images).

[0035] Transfer rollers 1141, 1142, 1143, and 1144 transfer the toner images developed on the photoconductor drums 1701, 1702, 1703, and 1704 onto the transfer belt 103. Cleaners 1161, 1162, 1163, and 1164 clean the photoconductor drums 1701, 1702, 1703, and 1704 to remove any toner that has not been transferred and remains thereon, and the system enters a standby state for the next image formation.

[0036] A first size (small size) paper (medium on which an image is formed) 201 is stored in a paper cassette 1171 which is a paper supply means. A second size (large size) paper (medium on which an image is formed) 202 is stored in a paper cassette 1172 which is a paper supply means.

[0037] A toner image is transferred from the transfer belt 103 to the paper 201 or 202 taken out of the paper cassette 1171 or 1172 by a pair of transfer rollers 118, which is a transfer means. The paper 201 or 202 to which the toner image has been transferred is heated and pressed by a fixing roller 120 in a fixing section 119. The toner image is firmly fixed to the paper 201 or 202 by the heating and pressure of the fixing roller 120. The image forming operation is performed continuously by repeating the above process operations.

[0038] FIG. 8 is a block diagram showing an example of a control system of the image forming apparatus according to the embodiment. 8, image forming apparatus 100 includes control board 101. Control board 101 includes image reading section 171, image processing section 172, image forming section 173, controller 174, ROM (Read Only Memory) 175, RAM (Random Access Memory) 176, non-volatile memory 177, communication I / F 178, control panel 179, page memories 1801, 1802, 1803, and 1804, light emission controller 183, and image data bus 184. Image forming apparatus 100 further includes color shift sensor 181 and mechanical control driver 182. Image forming section 173 includes image forming units 1021, 1022, 1023, and 1024.

[0039] To the controller 174, a ROM 175, a RAM 176, a non-volatile memory 177, a communication I / F 178, a control panel 179, a color shift sensor 181, a mechanical control driver 182, and a light emission controller 183 are connected.

[0040] The image reading unit 171, the image processing unit 172, the controller 174, and the page memories 1801, 1802, 1803, and 1804 are connected to the image data bus 184. The page memories 1801, 1802, 1803, and 1804 output Y, M, C, or K image data 31, respectively. The light emission controller 183 is connected to the page memories 1801, 1802, 1803, and 1804, and receives as input the Y image data 31 from the page memory 1801, the M image data 31 from the page memory 1802, the C image data 31 from the page memory 1803, and the K image data 31 from the page memory 1804. The print heads 1001, 1002, 1003, and 1004 are connected to the light emission controller 183. The light emission controller 183 inputs Y, M, C, or K image data 31 to the print heads 1001, 1002, 1003, or 1004.

[0041] The controller 174 is configured with one or more processors, and controls operations such as image reading, image processing, and image formation in accordance with various programs stored in at least one of the ROM 175 and the non-volatile memory 177 .

[0042] Furthermore, the controller 174 inputs image data of the test pattern into page memories 1801, 1802, 1803, and 1804 to form the test pattern. The color shift sensor 181 detects the test pattern formed on the transfer belt 103, and outputs a detection signal to the controller 174. The controller 174 can recognize the positional relationship of the test patterns of each color from the input of the color shift sensor 181. Furthermore, the controller 174 selects, via a mechanical control driver 182, paper cassette 1171 or 1172 that feeds paper on which an image is formed.

[0043] ROM 175 stores various programs and the like necessary for controlling controller 174. The various programs include a light emission control program for the print head. The light emission control program is a program that controls the timing of light emission and extinguishing (non-light emission) based on image data.

[0044] The RAM 176 temporarily stores data necessary for the control of the controller 174. The non-volatile memory 177 stores some or all of the various programs, various parameters, and the like.

[0045] Mechanical control driver 182 controls the operation of motors and the like required for printing according to instructions from controller 174. Communication I / F 178 outputs various information to the outside and also inputs various information from the outside. For example, communication I / F 178 acquires image data including multiple image lines. Image forming apparatus 100 prints the image data acquired via communication I / F 178 using a print function. Control panel 179 accepts operation inputs from users and service personnel.

[0046] The image reading unit 171 optically reads an image of a document set on a document table (not shown), obtains image data including a plurality of image lines, and outputs the image data to the image processing unit 172. The image processing unit 172 executes various image processes such as correction on the image data input via the communication I / F 178 or the image data from the image reading unit 171. The page memories 1801, 1802, 1803, and 1804 store the image data processed by the image processing unit 172. The controller 174 edits the image data on the page memories 1801, 1802, 1803, and 1804 so as to match the printing position and the print head. The image forming unit 173 forms an image based on the image data stored in the page memories 1801, 1802, 1803, and 1804. That is, the image forming unit 173 forms an image based on the light emission (light-on and off states) of each light-emitting element 131 according to the image data.

[0047] The light emission controller 183 is configured with one or more processors, and controls the light emission of the light emitting element 131 based on image data in accordance with various programs stored in at least one of the ROM 175 and the non-volatile memory 177. That is, the light emission controller 183 outputs a drive signal for causing the light emitting element 131 to emit light to the light emitting element 131 at a predetermined timing.

[0048] [Light control] FIG. 9 is a diagram for explaining light amount control within a light emitting element group 161 of a print head according to this embodiment. As described in Fig. 6, one light emitting element group 161 includes, for example, eight DRV circuits 140 (DRV1 to 8) and light emitting elements 131 connected thereto. The transistors 141 and capacitors 142 of the DRV 140 described in Fig. 5 are illustrated in Fig. 9 as eight switches 1411 to 1418 and eight capacitors 1421 to 1428 corresponding to the DRV1 to 8, respectively. The SH signals 211 to 218 output by the SH signal output circuit 152 are signals that open / close (ON / OFF) the switches 1411 to 1418, and correspond to the SH signal 21 described in Fig. 5. The light amount control of the print head is performed in units of light emitting element groups (eight DRV circuits).

[0049] The light intensity setting for the eight DRV circuits DRV1 to DRV8 included in the light emitting element group 161 will be described with reference to the timing chart of FIG.

[0050] The SH signal 211 goes to low level, and the switch 1411 of DRV1 closes (turns ON). In synchronization with this, the D / A conversion circuit 153 outputs the light emission level signal 22 appropriate for the amount of light that should be output by the light emitting element 131 connected to DRV1, and the voltage is set (sampled) in the capacitor 1421. When the SH signal 211 goes to high level, the switch 1411 opens (turns OFF), and the voltage of the light emission level signal 22 at this time is held (held) in the capacitor 1421. After the switch 1411 opens (turns OFF), the voltage of the capacitor 1421 does not change even if the voltage of the light emission level signal 22 changes.

[0051] Next, the SH signal 218 goes to low level, and the switch 1418 of the DRV8 closes (turns ON). In synchronization with this, the D / A conversion circuit 153 outputs the light emission level signal 22 appropriate for the amount of light to be output by the light emitting element 131 connected to the DRV8, and the voltage is set in the capacitor 1428 (sample). When the SH signal 218 goes to high level, the switch 1418 opens (turns OFF), and the voltage of the light emission level signal 22 at this time is held (held) in the capacitor 1428. After the switch 1418 opens (turns OFF), the voltage of the capacitor 1428 does not change even if the voltage of the light emission level signal 22 changes.

[0052] Thereafter, the same operation is executed in the order of DRV2, DRV7, DRV3, DRV6, DRV4, and DRV5, and the light intensity setting is performed for the eight DRV circuits included in the light emitting element group 161.

[0053] In this way, the timing of opening and closing (ON / OFF) of the switches 1411-1418 is varied by the SH signals 211-218, and the signal output level of the D / A conversion circuit 153 is changed in synchronization with the SH signals 211-218, thereby controlling the amount of light of the light-emitting elements 131 connected to DRV1-8.

[0054] FIG. 11 is a timing chart showing an example of the relationship between light amount control and light emission time control of the print head according to the embodiment. 11, when the PWM signal 32 is input while the capacitor 142 is holding a set voltage, the light emitting element 131 emits light with the set light intensity. That is, the SH signal 21 and the PWM signal 32 are output in synchronization. The light emission time per line period is controlled by the length of the PWM signal 32. Similarly to the SH signal 21, the PWM signal 32 is output to DRV1 to 8 at individual timings.

[0055] In addition, in a series of light quantity control operations, if the voltage difference between the light emission level signal 22 output by the D / A conversion circuit 153 for the capacitor whose voltage is set first (hereinafter referred to as the front stage) and the capacitor whose voltage is set subsequently (hereinafter referred to as the rear stage) is too large, the charging (or discharging) of the rear stage capacitor 142 may not be in time, and the correct target voltage (light emission level) may not be set in the rear stage capacitor 142. That is, in the control sequence shown in FIG. 10, for example, the correct target voltage may not be set in the rear stage capacitor 1428 due to the influence of the set voltage for the front stage capacitor 1421. If the correct target voltage cannot be set, the amount of light emitted by the light emitting element 131 may be affected, and there is a risk of image quality degradation. In this embodiment, the image quality degradation is prevented by light quantity correction, which will be described later.

[0056] 10 in the order of DRV1, DRV8, DRV2, DRV7, DRV3, DRV6, DRV4, DRV5, DRV1... is to ensure continuity of light emission timing between adjacent light emitting element groups 161. For example, since DRV1 and DRV8 of adjacent light emitting element groups are adjacent to each other, it is desirable that the light amount control and light emission operation for DRV1 and DRV8 are continuous as described above.

[0057] FIG. 12 is a schematic diagram of a correction data generating device for explaining a method of generating correction data for making the light emitting elements 131 of the print head 1 emit light with a uniform amount of light.

[0058] The correction data generating device includes a light quantity measuring sensor 19 and a controller 200. The light quantity measuring sensor 19 is a sensor that receives light output from the light emitting element 131 of the print head 1 after passing through the lens 12, and outputs a voltage proportional to the intensity (amount of light) of the light as a detection signal.

[0059] As shown in FIG. 12, the light quantity measuring sensor 19 is located on the opposite side of the transparent substrate 11 with the rod lens array 12 interposed therebetween.

[0060] The controller 200 has a print head control function equivalent to that of the light emission controller 183 described above, and also has a calculation function for determining correction data and a control function for moving the sensor.

[0061] In order to measure the light quantity of all the light-emitting elements 131 of the print head 1, the controller 200 moves the light quantity measuring sensor 19 to the position of the light-emitting element to be measured using a light quantity measuring sensor moving device (not shown), and by causing the light-emitting element to be measured to emit light, the controller 200 can measure the light quantity of the light-emitting element to be measured from the detection signal of the light quantity measuring sensor 19.

[0062] For example, the controller 200 controls the output voltage of the light emission level signal 22 from the D / A conversion circuit 153 and the PWM signal 32 to be constant, and sequentially causes the light emitting elements 131 to emit light while moving the light quantity measuring sensor 19. The light quantity measuring sensor 19 detects the light quantity of the light emitting elements 131 and outputs a detection signal. Based on the detection signal from the light quantity measuring sensor 19, the controller 200 sequentially measures the light quantity of the light emitting elements 131 that have been made to emit light.

[0063] When measuring the amount of light, the controller 200 can cause any light-emitting element to emit light at any light emission level by writing an arbitrary value in the light amount correction memory 18 of the print head 1 and then sending image data 31 of the light-emitting element to be measured to the print head 1. Although not shown in Fig. 6, the controller 200 can also cause any light-emitting element to emit light at any light emission level by directly accessing the light amount correction circuit 151 without going through the light amount correction memory 18.

[0064] Fig. 13 is a graph showing the light amount of the light emitting element versus the correction value. Fig. 13 shows the relationship between the correction value and the light amount for elements A and B that emit light normally, and element C that does not emit light normally. First, elements A and B that emit light normally will be described. As shown in FIG. 13, for both element A and element B, the light intensity is greater when the second reference value is set as the correction value than when the first reference value is set. The level indicated by the dotted line in FIG. 13 is the target light intensity. For both elements A and B, the light intensity is smaller than the target light intensity at the first reference value. At the second reference value, both elements A and B exceed the target light intensity. Therefore, it can be seen that the correction value (first correction value) for outputting the target light intensity is between the first reference value and the second reference value for both elements A and B. The correction value for outputting the target value can be calculated. It can be seen that it is sufficient to connect the point showing the light intensity for the first reference value and the point showing the light intensity for the second reference value with a straight line and find the point where this line intersects with the target light intensity. The correction values ​​at the respective intersection points PA and PB are the correction values ​​for outputting the target light intensity. Even if the correction value for outputting the target light amount is not between the first and second reference values, if there is a point where the above line intersects with the target light amount within the range of settable correction values, the correction value for outputting the target light amount can be obtained. In this way, element A and element B are elements whose light amount at the opposing positions sandwiching the rod lens array 12 satisfies the standard and falls within a predetermined range by setting a correction value (current control).

[0065] The element C is an element in which the light emitting element 131 does not emit light normally due to a defect in the DRV circuit 140 or the light emitting element 131, or in which even if the light emitting element 131 emits light, the light does not exit from the lens. For element C, the first and second reference values ​​and the first and second measured light quantities corresponding to the first and second reference values ​​are not in a proportional relationship. For element C, the light quantity does not increase even if the correction value is increased to increase the voltage between the capacitor terminals. Or, even if the light quantity increases, it does not reach the target light quantity. Therefore, in the case of element C, the straight line connecting the point showing the light quantity for the first reference value and the point showing the light quantity for the second reference value does not intersect with the target light quantity. In other words, element C is an element in which the light quantity at the opposing positions sandwiching the rod lens array 12 does not satisfy the standard and becomes a value outside the specified range due to the correction value setting (current control).

[0066] In this way, for elements that cannot emit light at the target light amount no matter what correction value is set, it is not possible to calculate an appropriate correction value to make the emitted light amount the target light amount, and an inappropriate correction value may be calculated. For example, because the light amount is below the target light amount, the maximum correction value is calculated. An inappropriate correction value may affect the light emission of other light-emitting elements, resulting in a decrease in image quality. Hereinafter, an element that exhibits characteristics like element C will be referred to as a defective element.

[0067] FIG. 14 is a flowchart showing an example of light amount correction performed to make the print head according to the embodiment emit light with a uniform amount of light. The controller 200 sets first and second reference values ​​(first reference value<second reference value) as light amount correction values, and measures the light amounts of all the light-emitting elements 131. The light amount measuring sensor 19 detects the amount of light after passing through the lens from the light-emitting elements 131 corresponding to the light emission control of the controller 200, and outputs a detection signal. Based on the detection signal from the light amount measuring sensor 19, the controller 200 measures the amount of light on the opposite side of the transparent substrate 11 across the rod lens array 12 from all the light-emitting elements 131 after passing through the lens (ACT1).

[0068] Next, the controller 200 calculates a correction value corresponding to the target light amount of each light-emitting element 131 based on the measured light amounts corresponding to the first and second reference values ​​(ACT2). For example, in the case of element A and element B which emit light normally as described in Fig. 13, correction values ​​corresponding to the intersections PA and PB are calculated. For the defective element C described in Fig. 13, a correction value which becomes the target light amount cannot be calculated. Since the light amount of element C is insufficient, the maximum value is calculated as the correction value.

[0069] Next, the controller 200 writes the correction value of each light-emitting element to the light amount correction memory 18 (ACT3). After completing the light amount correction in this manner, the print head controls the current flowing through the light-emitting element 131 according to the correction value written to the light amount correction memory 18, and the light-emitting element 131 emits light at the target light amount.

[0070] That is, the output voltage of the D / A conversion circuit 153 is controlled according to the correction value written in the light emission correction memory 18, the voltage between the terminals of the capacitor 142 is controlled by the output voltage of the D / A conversion circuit 153, the current flowing through the light emitting element 131 is controlled by the voltage between the terminals of the capacitor 142, and the light emitting element 131 emits light at the target light amount. However, for a defective element such as element C, it is not possible to emit light at the target light amount even if the correction value is set to the maximum value.

[0071] FIG. 15 is a timing chart showing an example of light amount correction in the case where there is no defective element. For example, in order to provide continuity in the light emission timing of adjacent light emitting elements 131, the IC 15 sets voltages between the terminals of the capacitors 142 of the DRV circuits 140 in the order shown in Fig. 10 and Fig. 15. That is, the SH signal 21 sets voltages between the capacitor terminals of the DRV circuits in the order of DRV1, DRV8, DRV2, DRV7, DRV3, DRV6, DRV4, DRV5, DRV1 ....

[0072] Furthermore, the D / A output voltage (dashed line) of the light emission level signal 22 from the D / A conversion circuit 153 changes at the timing assigned to each DRV circuit 140 according to the correction value. The capacitor terminal voltage (solid line) becomes equal to the D / A output voltage within the time assigned to each DRV circuit 140, and is held (held) at the rising edge of the SH signal. As a result, all the light emitting elements 131 are prepared to emit light with a uniform amount of light.

[0073] FIG. 16 is a diagram showing an example of exposure in the case where the print head according to the embodiment includes a defective element. As shown in Fig. 16, if a light-emitting element row contains a defective element, the position on the photoconductor drum 17 corresponding to that element cannot be exposed to light. When such a print head is measured using the light quantity measurement method shown in Fig. 12, the measurement result corresponding to the defective element shows a very small value as explained in Fig. 14. In the light quantity correction for the defective element, for example, a correction value is calculated to maximize the amount of light, so that the correction value shows a very large value. Therefore, the voltage value set between the terminals of the capacitor 142 corresponding to the defective element is larger than the voltage value set between the terminals of the capacitor 142 corresponding to the other non-defective elements.

[0074] Hereinafter, the correction state in which a defective element is present in the light-emitting element row of the print head and the voltage set across the terminals of capacitor 142 in DRV circuit 140 corresponding to the defective element is significantly different from the voltage set across the terminals of capacitor 142 in DRV circuit 140 corresponding to other normal elements will be referred to as the first light intensity correction.

[0075] Fig. 17 is a diagram showing an example of the result of measuring the light amount using, for example, the second reference value when the print head includes a defective element. Fig. 18 is a diagram showing an example of the correction value calculated by the first light amount correction when the print head includes a defective element. Fig. 19 is a diagram showing an example of the light amount after the first light amount correction is applied when the print head includes a defective element.

[0076] As shown in FIG. 17, in the light amount measurement results when the correction value is constant (second reference value), the light amount measurement result corresponding to the defective element is significantly lower than the target light amount. Therefore, as shown in FIG. 18, the correction value calculation result corresponding to the defective element is a large value. However, as shown in FIG. 19, the light amount after correction corresponding to the defective element remains significantly lower than the target light amount. Furthermore, the light emitting element downstream of the defective element is affected, and the light amount of the downstream light emitting element exceeds the target light amount. In other words, the defective element and the downstream element do not emit light at the target light amount.

[0077] FIG. 20 is a diagram for explaining the influence of an inappropriate voltage setting due to the first light amount correction. For example, let us consider a case where the potential set between the terminals of the capacitor of DRV2 is extremely large. The output voltage (dashed line) of the D / A conversion circuit 153 changes according to the correction value calculated from each light quantity measurement result. If the light emitting element 131 connected to DRV2 is a defective element, the light quantity measurement result will be a very small value, and the correction value for DRV2 (= the output voltage of the D / A conversion circuit 153) will be the maximum value. As a result, the voltage set between the capacitor terminals of DRV2 will be a voltage that is very large compared to the capacitor terminal voltages of the other DRVs.

[0078] If the correction value for DRV7 after DRV2 is at an average level, the voltage output by the D / A conversion circuit 153 next attempts to change from the maximum to the average level. However, if the potential change (discharge) capability of the D / A conversion circuit 153 is insufficient, the potential change will not be in time and the potential will be set higher than the target value (a gap will occur with respect to the target value). As a result, the light intensity of the light-emitting element 131 connected to DRV7 will be greater than the target level. Thus, in the first light intensity correction, light-emitting elements other than the defective element will also emit light at a level different from the target level.

[0079] When the light intensity of the print head is corrected using the first light intensity correction and a halftone image is output, the light-emitting element connected to DRV2 does not emit light, resulting in white streaks, and the light-emitting element connected to DRV7 has a high light intensity, resulting in black streaks.

[0080] FIG. 21 is a diagram for explaining the effect on an image when the first light amount correction is applied to a print head including a defective element. In the case of a halftone image, according to the first light intensity correction, white streaks appear corresponding to defective elements, and black streaks appear corresponding to the effect of the correction value of the defective element. The positional relationship between the white streaks and the black streaks is determined by the positional relationship between the defective element and the light emitting element subsequent to the defective element. In other words, the positional relationship between the white streaks and the black streaks changes depending on the positional relationship between the defective element and the light emitting element subsequent to the defective element. FIG. 21 shows, as an example, a case where a portion corresponding to DRV2 becomes a white streak and a portion corresponding to a distant DRV7 becomes a black streak (left), and a case where a portion corresponding to DRV4 becomes a white streak and a portion corresponding to the adjacent DRV5 becomes a black streak (right).

[0081] 22 is a flowchart showing an example of the second light amount correction of the print head according to the embodiment. The second light amount correction is a light amount correction that suppresses the occurrence of black streaks caused by a defect in the first light amount correction, that is, the effect of the correction value of a defective element.

[0082] The light emission controller 200 controls the light emission of all the light emitting elements 131 based on a first reference value. The light amount measuring sensor 19 detects the amount of light from the light emitting elements 131 corresponding to the light emission control of the light emission controller 200, and outputs a detection signal. The light emission controller 200 moves the light amount measuring sensor 19 to match the light emitting elements of the print head that emit light, and measures the amount of light from all the light emitting elements 131 (ACT101).

[0083] Furthermore, the light emission controller 200 controls the light emission of all the light emitting elements 131 based on a second reference value (second reference value>first reference value). The light amount measuring sensor 19 detects the amount of light from the light emitting elements 131 corresponding to the light emission control of the light emission controller 200, and outputs a detection signal. The light emission controller 200 moves the light amount measuring sensor 19 and measures the amount of light from all the light emitting elements 131 (ACT102).

[0084] As the reference value increases, the D / A output voltage from the D / A conversion circuit 153 increases. As the D / A output voltage increases, the voltage across the terminals of the capacitor 142 increases. As the voltage across the terminals of the capacitor 142 increases, the amount of light emitted by the light-emitting element 131 increases. Note that, although this embodiment describes a case in which the light emission controller 200 corrects the amount of light based on two reference values, the amount of light may also be corrected based on one or three or more reference values.

[0085] In order to perform light amount correction for all light emitting elements 131, the light emitting controller 200 sets an element number n (1 to 5120) of the light emitting elements 131 (ACT 103). For example, the light emitting controller 200 sets n=1 and performs light amount correction in order starting from the n-th element.

[0086] The light emission controller 200 judges whether the n-th element is capable of emitting light at the target light amount, based on the reference value and the measured light amount corresponding to the reference value, that there is a correlation between the voltage between the capacitor terminals and the light amount of the light-emitting element (ACT104). As described in FIG. 13, the judgment of whether the element is capable of emitting light at the target light amount is made by connecting the point showing the light amount for the first reference value and the point showing the light amount for the second reference value with a straight line, and judging whether the point where this line intersects with the target light amount is within the range of a settable correction value. That is, elements such as element A and element B in FIG. 13 are judged as elements capable of emitting light at the target light amount, and elements such as element C are judged as elements that cannot emit light at the target light amount.

[0087] When the light emission controller 200 determines that the nth element is an element capable of emitting light at the target light amount because there is a correlation between the voltage between the capacitor terminals and the light amount of the light-emitting element (ACT104, YES), it calculates a correction value for making the light amount of the nth element the target light amount from the first reference value and the first measured light amount corresponding thereto, and the second reference value and the second measured light amount corresponding thereto as a first correction value (ACT105).The light emission controller 200 writes the calculated first correction value to the element number address n of the light amount correction memory 18 (ACT106).

[0088] In addition, if the light emission controller 200 determines that the nth element has no correlation between the voltage between the capacitor terminals and the light intensity of the light-emitting element and cannot emit light at the target light intensity (ACT104, NO), it stores the element number and defect information of the nth element as a defective element (ACT109).

[0089] When the light emission controller 200 has not yet determined whether all the light emitting elements 131 can emit light at the target light amount, that is, when n=5120 is not satisfied (ACT107, NO), the light emission controller 200 increments the value of n (ACT110) and repeats the processes from ACT104 onward. When the light emission controller 200 has determined whether all the light emitting elements 131 can emit light at the target light amount, that is, when n=5120 is satisfied (ACT107, YES), the light emission controller 200 stores the second correction value in the element number address stored in ACT109 in the light amount correction memory 18 (ACT108). For example, the light emission controller 200 sets a second correction value between the maximum and minimum values ​​of the first correction value, and writes it to the light amount correction memory 18. The second correction value may be the average value of the first correction value, or may be a value within the range of ±3% of the average value of the first correction value. In short, it is sufficient if the correction value does not affect the light amount of the light emitting elements in the subsequent stage. For example, the light amount fluctuation that affects the image is a fluctuation of ±3% or more. Therefore, it is sufficient if the correction value does not cause a fluctuation of ±3% or more in the amount of light that should be emitted by the light emitting element in the subsequent stage.

[0090] The target light amount and the allowable range of fluctuation in the light amount of the subsequent elements can be set arbitrarily at the design stage.

[0091] In this way, the light emission controller 200 executes the second light quantity correction. The light quantity correction memory 18 of the print head where the second light quantity correction has been executed is in the following state. That is, a light quantity correction value (first correction value) that becomes a target light quantity when the element emits light is stored in an address corresponding to a normal (non-defective pixel) light emitting element 131. This first correction value is a value that determines the terminal voltage of a predetermined capacitor included in a predetermined DRV 140, and is a value that makes the light quantity of this light emitting element 131 at the facing position across a predetermined lens of the rod lens array 12 within a predetermined range as viewed from the light emitting element 131 connected to the predetermined DRV 140. On the other hand, a light quantity correction value (second correction value) that does not affect the light quantity of the light emitting element in the subsequent stage is stored in an address corresponding to a defective element. This second correction value is a value that determines the terminal voltage of a predetermined capacitor included in a predetermined DRV 140, and is a value that makes the terminal voltage of the predetermined capacitor within a predetermined range. Moreover, this second correction value is a value that does not affect the terminal voltage setting of the next capacitor (the capacitor located after the specified capacitor) when the SH signal output circuit 152 and the D / A conversion circuit 153 set the terminal voltage of the next capacitor. Note that the light emitted by the defective element is an amount of light that does not reach the target level.

[0092] 23 is a diagram showing an example of the correction value calculated by the second light quantity correction in the case where the print head includes a defective element. A correction value (second correction value) of the same level as that of the other light emitting elements is set for the defective element as well. Such a set value is stored in the light quantity correction memory 18 of the print head that has been subjected to the second light quantity correction.

[0093] FIG. 24 is a diagram showing an example of the amount of light emitted by the print head after the second light amount correction is applied in a case where the print head includes a defective element, when the print head is caused to emit light by the light emission controller 183 of the control board 101 of the image forming apparatus 100.

[0094] As shown in FIG. 24, the post-correction light amount corresponding to the defective element remains significantly below the target light amount, but the light-emitting element subsequent to the defective element can be made to emit light at the target light amount.

[0095] FIG. 25 is a diagram for explaining the effect on an image when the second light amount correction is applied to a print head including a defective element. Comparing Figures 21 and 25, in the case of a halftone image, the second light intensity correction causes white streaks to appear in response to defective elements, just like the first light intensity correction, but unlike the first light intensity correction, it is possible to prevent black streaks from appearing in response to the influence of the correction value of the defective element.

[0096] FIG. 26 is a diagram showing an example of a case where the light emitting element row of the print head according to the embodiment is longer than the rod lens array, and the measured light quantities corresponding to the light emitting elements at both ends are very small values. 26, if the light emitting element row 13 is longer than the rod lens array 12, the light from the light emitting elements 131 at both ends of the light emitting element row 13 does not pass through the lens of the rod lens array 12 and cannot expose the photosensitive drum 17. In addition, the measured light amount of such a light emitting element 131 will indicate a very small value, and as a result, the correction value of such a light emitting element 131 will indicate a very large value. In other words, the light emitting element 131 outside the lens area of ​​the rod lens array 12 may cause the same problem as a defective element, even if the circuit or element is not defective, because the light amount from that light emitting element 131 cannot be measured.

[0097] FIG. 27 is a diagram showing an example of the light quantity measurement result in the case where a light emitting element is included outside the lens area in the print head. The elements Nos. 1, 2, and 3 and the elements Nos. 5,118, 5,119, and 5,120 are light-emitting elements located outside the lens region. DRVs 1, 2, and 3 of the first group and DRVs 6, 7, and 8 of the 640th group are connected to the respective light-emitting elements as DRV circuits. Fig. 28 is a diagram showing an example of a correction value calculated by the first light amount correction in a case where a light emitting element is included outside the lens area of ​​the print head. Fig. 29 is a diagram showing an example of a light amount after the first light amount correction is applied in a case where a light emitting element is included outside the lens area of ​​the print head.

[0098] As shown in FIG. 27, in the light amount measurement results when the correction value is constant, the light amount measurement results corresponding to the light emitting elements outside the lens area (for example, the light emitting elements connected to DRV1, 2, 3 on the left side of FIG. 27 and DRV6, 7, 8 on the right side of FIG. 27) are significantly lower than the target light amount. Therefore, as shown in FIG. 28, the correction value calculation result corresponding to the light emitting elements outside the lens area is a large value. However, as shown in FIG. 29, the light amount after correction corresponding to the light emitting elements outside the lens area remains significantly lower than the target light amount. On the other hand, the light emitting elements inside the lens area (for example, the light emitting elements connected to DRV6, 7, 8 and 2, 3, 4) that are the latter stages of the light amount correction of the light emitting elements outside the lens area are affected, and the light amount of the latter stage light emitting elements exceeds the target light amount. This is because the setting order of the voltage between the capacitor terminals is DRV1, DRV8, DRV2, DRV7, DRV3, DRV6, DRV4, DRV5, DRV1. For example, the next stage of DRV1, 2, 3 is DRV8, 7, 6, and the next stage of DRV6, 7, 8 is DRV4, 3, 2.

[0099] FIG. 30 is a diagram for explaining the effect on an image when the first light amount correction is applied to a print head including a light emitting element outside the lens region. In the case of a halftone image, according to the first light intensity correction, even if the light emitting elements outside the lens area emit the maximum light intensity, there is no effect on the halftone image, but the light emitting elements inside the lens area are affected in response to the effect of the correction value of the light emitting elements outside the lens area, resulting in the appearance of black halftones (black streaks). Elements No. 6, 7, 8 and elements No. 5,114, 5,115, and 5,116 correspond to this.

[0100] Fig. 31 is a diagram showing an example of the correction value calculated by the second light quantity correction in the case where the print head includes light emitting elements outside the lens area. The same correction value (second correction value) as that of the other light emitting elements is set for the light emitting elements outside the lens area (element Nos. 1, 2, 3 and element Nos. 5, 118, 5, 119, 5, 120). Such a set value is stored in the light quantity correction memory 18 of the print head that has been subjected to the second light quantity correction.

[0101] Figure 32 shows an example of the amount of light when a print head including a light-emitting element outside the lens area is caused to emit light by the light emission controller 183 of the control board 101 of the image forming apparatus 100 after the second light amount correction has been applied.

[0102] As shown in Figure 32, it is possible to eliminate the influence of light-emitting elements outside the lens area (for example, light-emitting elements connected to DRVs 1, 2, 3 in the first group and DRVs 6, 7, 8 in the 640th group) on subsequent light-emitting elements (for example, light-emitting elements connected to DRVs 8, 7, 6 in the first group and DRVs 4, 3, 2 in the 640th group), and to cause the subsequent light-emitting elements (elements Nos. 6, 7, 8 and elements Nos. 5, 14, 5,115, 5,116) to emit light at the target light amount.

[0103] 33 is a diagram for explaining the effect on an image when the second light amount correction is applied to a print head including light emitting elements outside the lens area. In a print head to which the second light amount correction is applied, the light amount of the light emitting element 131 in the lens area is constant. Comparing FIG. 30 with FIG. 33, in the case of a halftone image, the second light amount correction can prevent the appearance of black streaks, unlike the first light amount correction.

[0104] According to the above-described embodiment, it is possible to provide a print head and an image forming device that prevent degradation of image quality. That is, the print head and the image forming device select a first or second correction value depending on whether there is a correlation between the reference value and the measured light amount corresponding to the reference value (whether it is possible to emit light at a light amount within a predetermined range including the target light amount). If there is a correlation (it is possible to emit light at a light amount within a predetermined range including the target light amount), the latent image can be exposed at the target light amount using the first correction value. If there is no correlation (it is not possible to emit light at a light amount within a predetermined range including the target light amount), the latent image can be exposed at a light amount that reduces influence on others using the second correction value. In addition, in the embodiment, for example, an example was shown in which, as the correction value increases, the voltage set between the capacitor terminals increases and the amount of light increases, but depending on differences in circuit configuration, there may be cases in which the relationship between the correction value, the voltage set between the capacitor terminals, and the amount of light is different. For example, a configuration may be considered in which, as the correction value increases, the voltage set between the capacitor terminals decreases and the amount of light increases. In such cases, the magnitude relationship between the correction value and the voltage set between the capacitor terminals is reversed.

[0105] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. The invention as described in the claims of the original application is set forth below. [C1] Lenses and A substrate disposed opposite the lens; a first light-emitting element formed on the substrate, the first light-emitting element being configured such that the amount of light emitted at a position facing the lens is within a predetermined range by current control; a second light emitting element formed on the substrate, the second light emitting element being adapted to have a light amount outside a predetermined range at a position facing the lens by current control; a first driving circuit connected to the first light emitting element and supplying a current to the first light emitting element; a first capacitor included in the first driving circuit, the current supplied to the first light emitting element being determined by a voltage across the first capacitor; a second driving circuit connected to the second light emitting element and configured to supply a current to the second light emitting element; a second capacitor included in the second drive circuit, the second capacitor determining a current supplied to the second light emitting element depending on a voltage between terminals of the second capacitor; a memory that stores a first correction value that determines a voltage between the terminals of the first capacitor and a second correction value that determines a voltage between the terminals of the second capacitor; having a first correction value stored in the memory that is a value that causes the amount of light at a facing position across the lens to fall within a predetermined range when the first light-emitting element emits light, and a second correction value stored in the memory that is a value that causes the voltage between the terminals of the second capacitor to fall within a predetermined range. [C2] the first light emitting element is an element whose light amount satisfies the standard, The print head described in [C1], wherein the second light-emitting element is an element whose light amount does not satisfy the standard. [C3] The print head described in [C1], wherein the second light-emitting element is a light-emitting element arranged outside the light passing area of ​​the lens. [C4] Further comprising a voltage setting means for sequentially setting the terminal voltages of the capacitors; The print head described in [C1], wherein the second correction value stored in the memory is a value that does not affect the terminal voltage setting of the first capacitor when the voltage setting means sets the terminal voltage of the first capacitor after the second capacitor. [Explanation of symbols]

[0106] 1. Print head 10…Light emitting part 11...Transparent substrate 12...Rod lens array 13...Light emitting element row 14...Circuit row 16…Connector 17...Photoconductor drum 18…Light intensity correction memory 19...Light quantity measurement sensor 100...Image forming apparatus 101...Control board 102...Power supply section 103...Transfer belt 104…Harness 118...Transfer roller pair 119…Fixation section 120...Fuser roller 131...Light emitting element 140…DRV circuit 141…Switch 142…Capacitor 144…Switch 145…Wiring 151...Light quantity correction control circuit 152...Signal output circuit 153...D / A conversion circuit 155…ON / OFF control circuit 161...Light emitting element group 171...Image reading unit 172...Image processing unit 173...Image forming section 174…Controller 177...Non-volatile memory 179…Control Panel 181...Color shift sensor 182…Mechanical control driver 183…Lighting controller 184...Image data bus 200…Controller 201, 202…Paper 1001~1004...Print head 1011~1014…Light emitting part 1021 to 1024: Image forming units 1101...Reference plane 1102...Sealing glass 1121~1124…Electric charger 1131~1134…Developer 1141~1144...Transfer roller 1161~1164…Cleaner 1171, 1172...Paper cassette 1201~1204...Rod lens array 1411~1418…Switch 1421~1428...Capacitor 1701~1704...Photoconductor drum 1801~1804...Page memory

Claims

1. Lenses and A substrate disposed opposite the lens; a first light-emitting element formed on the substrate, the first light-emitting element being configured to have a light amount within a predetermined range at a position facing the lens by current control; a second light emitting element formed on the substrate, the second light emitting element being adapted to have a light amount outside a predetermined range at a position facing the lens by current control; a first driving circuit connected to the first light emitting element and configured to supply a current to the first light emitting element; a first capacitor included in the first drive circuit, the current supplied to the first light emitting element being determined by a voltage across the first capacitor; a second driving circuit connected to the second light emitting element and configured to supply a current to the second light emitting element; a second capacitor included in the second drive circuit, the second capacitor determining a current supplied to the second light emitting element depending on a voltage between terminals of the second capacitor; a memory that stores a first correction value that determines a voltage between the terminals of the first capacitor and a second correction value that determines a voltage between the terminals of the second capacitor; having the first correction value stored in the memory is a value that causes a light amount at a facing position across the lens to fall within a predetermined range when the first light-emitting element emits light, and the second correction value stored in the memory is a value that causes a voltage between terminals of the second capacitor to fall within a predetermined range; a light emitting element row including a plurality of light emitting elements including the first and second light emitting elements is longer than a rod lens array that focuses light from the plurality of light emitting elements excluding the second light emitting element on a photosensitive drum; light from the plurality of light emitting elements excluding the second light emitting element passes through lenses of the rod lens array; a second light emitting element disposed at an end of the row of light emitting elements, the second light emitting element being arranged to be incident on the second light emitting element;

2. the first light-emitting element is an element whose light amount satisfies the standard, 2. The print head according to claim 1, wherein the second light emitting element is an element whose light amount does not satisfy the standard.

3. Further comprising a voltage setting means for sequentially setting the terminal voltages of the capacitors; 2. The print head according to claim 1, wherein the second correction value stored in the memory is a value that does not affect the setting of the terminal voltage of the first capacitor when the voltage setting means sets the terminal voltage of the first capacitor next to the second capacitor.

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