Printhead and image forming apparatus

Abstract

The present application provides a print head and an image forming apparatus. The print head includes a light emitting element column including a plurality of light emitting elements, a plurality of drive circuits, a memory, and a light quantity correction control circuit. The plurality of drive circuits drive the light emitting elements of the light emitting element column, and a capacitor included in each drive circuit holds a voltage between terminals of the capacitor, which determines a light emitting light quantity of each light emitting element. The memory stores a voltage value (a correction value) set between the terminals of the capacitor included in the drive circuit, and stores, as the voltage value within a predetermined range including a target light quantity, a voltage value when the voltage between the terminals of the capacitor and the light quantity of the light emitting element have a correlation and the light emitting element can emit light with a light quantity within the predetermined range including the target light quantity, and stores a voltage value that does not affect the voltage set between the terminals of the other capacitor when the voltage between the terminals of the capacitor and the light quantity of the light emitting element have no correlation and the light emitting element cannot emit light with a light quantity within the predetermined range including the target light quantity. The light quantity correction control circuit controls the light quantity of the plurality of light emitting elements in accordance with the voltage value.

Description

Technical Field

[0001] Embodiments of the present invention relate to a printhead and an image forming apparatus. Background Technology

[0002] Electronic photo printers (hereinafter referred to as printers) are widely used. A printer has a printhead, which contains multiple light-emitting elements. These light-emitting elements can be LEDs (Light Emitting Diodes) or OLEDs (Organic Light Emitting Diodes). For example, a printhead may have light-emitting elements equivalent to 5,120 pixels, arranged along the main scanning direction, with the direction orthogonal to the main scanning direction being the sub-scanning direction. The printer uses light emanating from these multiple light-emitting elements to expose a photosensitive drum, printing an image corresponding to the latent image formed on the photosensitive drum onto a sheet of recording paper.

[0003] The image density corresponds to the light intensity of each light-emitting element, and the light intensity of each light-emitting element is determined by the voltage between the terminals of the capacitors included in the driving circuit of each light-emitting element. The voltage supply unit (D / A) controls the voltage between the terminals of each capacitor to ensure uniform light intensity of each light-emitting element.

[0004] While achieving uniform light intensity from all light-emitting elements, there are instances where the target voltage value for some capacitor terminals differs significantly from the target voltage value for others. For example, some light-emitting elements may contain defective elements, sometimes preventing the acquisition of sufficient light from these defective elements. Light intensity correction functions to address such defective elements, and there are cases where the target voltage value for the capacitor terminals corresponding to the defective element becomes extremely high. Thus, if the target voltage value for some capacitor terminals becomes extremely high, it becomes impossible to set an appropriate voltage between connected capacitor terminals, resulting in excessive light intensity and a degraded image quality. Summary of the Invention

[0005] The purpose of this invention is to provide a printhead and image forming apparatus that prevent image quality degradation.

[0006] The printhead of this embodiment includes a row of light-emitting elements, multiple drive circuits (including capacitors), a memory, and a light intensity correction control circuit. The row of light-emitting elements includes multiple light-emitting elements. The multiple drive circuits drive each light-emitting element in the row. The capacitors included in the multiple drive circuits maintain a voltage across their terminals that determines the amount of light emitted by each light-emitting element. The memory stores voltage values ​​(correction values) set between the terminals of the capacitors included in the drive circuits. When the voltage between the capacitor terminals is correlated with the amount of light emitted by the light-emitting element and can emit light within a predetermined range, the memory stores a voltage value (correction value) that represents the amount of light within the predetermined range. When the voltage between the capacitor terminals is not correlated with the amount of light emitted by the light-emitting element and cannot emit light 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 intensity correction control circuit controls the amount of light emitted by the multiple light-emitting elements according to the voltage values ​​(correction values) stored in the memory.

[0007] Another embodiment of the image forming apparatus includes the above-described printhead. Attached Figure Description

[0008] Figure 1 This is a diagram illustrating an example of the positional relationship between the photosensitive drum and the printhead in an image forming apparatus applied to an embodiment.

[0009] Figure 2 This is a diagram showing an example of a transparent substrate constituting the printhead of an embodiment.

[0010] Figure 3 This is a diagram illustrating an example of the layout of the light-emitting elements and DRV circuitry of a printhead in an embodiment.

[0011] Figure 4 This is a diagram showing an example of a cross-section of the transparent substrate of the printhead in an embodiment.

[0012] Figure 5 This is a diagram showing a DRV circuit for driving a light-emitting element in an implementation method, and an example of a light-emitting element that emits light through the DRV circuit.

[0013] Figure 6 This is a diagram illustrating an example of a circuit block of a printhead in an implementation method.

[0014] Figure 7 This is a diagram illustrating an example of an image forming apparatus with a printhead employing an embodiment.

[0015] Figure 8 This is a block diagram illustrating an example of a control system for an image forming apparatus according to an embodiment.

[0016] Figure 9 This is a diagram illustrating the light quantity control within the light-emitting element group of the printhead in an embodiment.

[0017] Figure 10 This is a timing diagram illustrating an example of the potential setting between the capacitor terminals of the printhead in an embodiment.

[0018] Figure 11 This is a timing diagram illustrating an example of the relationship between light intensity control and emission time control of the printhead in an implementation method.

[0019] Figure 12 This is a simplified diagram of a calibration data generation apparatus for illustrating a method of generating calibration data for causing the light-emitting elements of the printhead in the embodiment to emit light with uniform light intensity.

[0020] Figure 13 This is a graph showing the relationship between the correction value of the light-emitting element in the printhead of the embodiment and the amount of light.

[0021] Figure 14 This is a flowchart illustrating an example of light quantity correction for a printhead in an implementation method.

[0022] Figure 15 This is a timing diagram illustrating an example of optical quantity correction without defective components.

[0023] Figure 16 This is an illustration showing an example of a printhead containing defective components in an embodiment.

[0024] Figure 17 This is a diagram illustrating an example of optical quantity measurement results for a case where a defective element is present in the printhead.

[0025] Figure 18 This is a diagram illustrating an example of a correction value calculated using the first light quantity correction when a defective element is present in the printhead.

[0026] Figure 19 This is a diagram illustrating an example of the amount of light after applying the first light quantity correction in the case of a printhead containing defective elements.

[0027] Figure 20 This is a diagram used to illustrate the effects of setting an inappropriate voltage based on the first light quantity correction.

[0028] Figure 21 This is a diagram illustrating the effect on an image when a first light intensity correction is applied to a printhead containing defective elements.

[0029] Figure 22 This is a flowchart illustrating an example of second light quantity correction for a printhead in an embodiment.

[0030] Figure 23 This is a diagram illustrating an example of the correction value calculated using the second optical quantity correction when a defective element is present in the printhead.

[0031] Figure 24 This is a diagram illustrating an example of the amount of light after applying a second light quantity correction in the case of a printhead containing defective elements.

[0032] Figure 25 This is a diagram illustrating the effect on an image when a second light intensity correction is applied to a printhead containing defective elements.

[0033] Figure 26 This is a diagram illustrating an example where the array of light-emitting elements in the printhead of an embodiment is longer than the array of rod lenses, and the measured light intensity corresponding to the light-emitting elements at both ends is a very small value.

[0034] Figure 27 This is a diagram illustrating an example of light quantity measurement results in a printhead containing a light-emitting element outside the lens area.

[0035] Figure 28 This is a diagram illustrating an example of a correction value calculated using a first light quantity correction when a light-emitting element is included outside the lens area in the printhead.

[0036] Figure 29 This is a diagram illustrating an example of the light quantity after applying the first light quantity correction when the light-emitting element is included outside the lens area in the printhead.

[0037] Figure 30 This diagram illustrates the effect on an image when a first light intensity correction is applied to a printhead containing light-emitting elements outside the lens region.

[0038] Figure 31 This is a diagram illustrating an example of a correction value calculated using a second light quantity correction when a light-emitting element is included outside the lens area in the printhead.

[0039] Figure 32 This is a diagram illustrating an example of the light quantity after applying a second light quantity correction when the light-emitting element is included outside the lens area in the printhead.

[0040] Figure 33 This diagram illustrates the effect on an image when a second light intensity correction is applied to a printhead containing light-emitting elements outside the lens region.

[0041] Explanation of reference numerals in the attached figures

[0042] 1…Printhead; 10…Light-emitting unit; 11…Transparent substrate; 12…Bar lens array; 13…Light-emitting element array; 14…Circuit array; 16…Connector; 17…Photosensitive drum; 18…Light intensity correction memory; 19…Light intensity measurement sensor; 100…Image forming apparatus; 101…Control board; 103…Transfer belt; 118…Transfer roller pair; 119…Fixing unit; 120…Fixing roller; 131…Light-emitting element; 140…DRV circuit; 141…Switch; 142…Capacitor; 144…Switch; 145…Wiring; 151…Light intensity correction control circuit; 152…SH 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 unit; 174…Controller; 177… Non-volatile memory; 179…Control panel; 181…Color shift sensor; 182…Mechanical control driver; 183…Light emission controller; 184…Image data bus; 200…Controller; 201, 202…Paper; 1001~1004…Print head; 1011~1014…Light emission unit; 1021~1024…Image forming unit; 1101…Reference plane; 1102…Sealed glass; 1121~1124… Charger; 1131~1134… Developer; 1141~1144… Transfer roller; 1161~1164… Tape cleaner; 1171, 1172… Paper tray; 1201~1204… Rod lens array; 1411~1418… Switch; 1421~1428… Capacitor; 1701~1704… Photosensitive drum; 1801~1804… Page memory. Detailed Implementation

[0043] Hereinafter, an example of an image forming apparatus according to an embodiment will be described using the accompanying drawings. In each drawing, the same reference numerals are used to denote the same structure. The image forming apparatus is a printer, copier, or multifunction printer (MFP). In this embodiment, an image forming apparatus equivalent to an MFP will be described.

[0044] [Structure of the print head]

[0045] Reference Figures 1-6 An example of the structure of the print head of the image forming apparatus used in the implementation will be described.

[0046] Figure 1 This is a diagram illustrating an example of the positional relationship between the photosensitive drum and the printhead in an image forming apparatus applied to an embodiment.

[0047] Image forming apparatus has Figure 1The photosensitive drum 17 and printhead 1 are shown. The printhead 1 and the photosensitive drum 17 are arranged opposite each other.

[0048] 17-directional photosensitive drum Figure 1 The direction of rotation indicated by the arrow is called the sub-scanning direction (Y-axis direction), and the direction orthogonal to the sub-scanning direction is called the main scanning direction (X-axis direction). The photosensitive drum 17 is uniformly charged by a charge carrier and exposed to light from the printhead 1, causing the potential of the exposed portion to decrease. In other words, the image forming apparatus controls the emission of light from the printhead 1 to form an electrostatic latent image on the photosensitive drum 17. Controlling the emission of light from the printhead 1 involves controlling the timing of the emission and extinguishing (non-emission) of the printhead 1 and controlling the amount of light.

[0049] The printhead 1 includes a light-emitting section 10 and a rod-shaped lens array 12. The light-emitting section 10 includes a transparent substrate 11 disposed opposite to the rod-shaped lens array 12. For example, the transparent substrate 11 is a glass substrate that allows light to pass through. A row of light-emitting elements 13, consisting of multiple light-emitting elements, is formed on the transparent substrate 11. Alternatively, the printhead 1 may also include multiple rows of light-emitting elements.

[0050] The rod lens array 12 focuses the light from each light-emitting element 131 of the light-emitting element array 13 onto the photosensitive drum 17. As a result, image lines corresponding to the emission of the light-emitting elements 131 are formed on the photosensitive drum 17. The light-emitting elements 131 are formed on the transparent substrate 11. The light intensity at the position opposite the rod lens array 12 across the light-emitting elements 131 is controlled by current to meet a reference and fall within a predetermined range. However, sometimes a portion of the light-emitting elements 131 (defective elements or elements outside the light transmission area of ​​the lenses arranged in the rod lens array 12) may deviate from the predetermined range at the position opposite the rod lens array 12 due to current control; this will be described later.

[0051] Figure 2 This is a diagram showing an example of a transparent substrate constituting the printhead of an embodiment. Figure 2 This is an example of a transparent substrate corresponding to a column of light-emitting elements arranged in one column. The printhead can also be a multi-column arrangement of light-emitting elements.

[0052] like Figure 2 As shown, a row of light-emitting elements 13 is formed on a transparent substrate 11 along its long side. A drive circuit row 14 for driving each light-emitting element (making each light-emitting element emit light) and wiring 145 for supplying signals to the drive circuit row 14 are arranged near the row of light-emitting elements 13. Hereinafter, "drive" will be labeled "DRV". Figure 2In this configuration, the wiring 145 used to drive the light-emitting elements 131 (to make each light-emitting element 131 emit light) is concentrated on one side of the light-emitting element column 13, but the wiring 145 can also be distributed on both sides.

[0053] An integrated circuit (IC) 15 and a light correction memory 18 are disposed at the end of the transparent substrate 11. Additionally, the transparent substrate 11 includes a connector 16. The connector 16 electrically connects the printhead 1 to the control system of a printer, copier, or multifunction printer. This connection enables power supply, printhead control, and image data transmission. A sealing substrate is mounted on the transparent substrate 11 in a manner that prevents the light-emitting element array 13, wiring 145, and DRV circuit 140 from contacting external air. Furthermore, when it is difficult to mount the connector to the transparent substrate, an FPC (Flexible Printed Circuit) can be connected to the transparent substrate for electrical connection to the control system.

[0054] Figure 3 This is a diagram illustrating an example of the layout of the light-emitting elements and DRV circuitry of a printhead in an embodiment. Figure 3 This is an example of a DRV circuit corresponding to one column of light-emitting elements, but the printhead can also have DRV circuits corresponding to multiple columns of light-emitting elements.

[0055] like Figure 3 As shown, the light-emitting section 10 of the printhead 1 includes a light-emitting element column 13 composed of multiple light-emitting elements 131 and a DRV circuit column 14 composed of multiple DRV circuits 140. The DRV circuit 140 causes the light-emitting elements 131 connected to each other to emit light based on signals from the wiring 145 (equivalent to the sample-and-hold signal (SH signal) 21, the light emission level signal 22, and the PWM (Pulse Width Modulation) signal 32 described later).

[0056] Figure 4 This is a diagram showing an example of a cross-section of the transparent substrate of the printhead in an embodiment. Figure 4 This is an example of a cross-section of a transparent substrate corresponding to one column of light-emitting elements, but the printhead can also be multiple columns of light-emitting elements.

[0057] like Figure 4As shown, the light-emitting section 10 of the printhead 1 includes a plurality of light-emitting elements 131, a plurality of DRV circuits 140, and wiring 145 arranged opposite to the reference surface 1101 of the transparent substrate 11. Additionally, the light-emitting section 10 also includes a sealing glass 1102. The plurality of light-emitting elements 131, the plurality of DRV circuits 140, and the wiring 145 are arranged in the 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 illuminates the photosensitive drum 17.

[0058] Figure 5 This is a diagram showing an example of a DRV circuit for driving a light-emitting element in an implementation method and a light-emitting element that emits light through the DRV circuit.

[0059] The DRV circuit 140 consists of low-temperature polycrystalline silicon thin-film transistors 141, 143, and 144, and a capacitor 142. The SH signal 21 is low when it causes a change in the luminous intensity of the light-emitting element 131 connected to the DRV circuit 140. When the SH signal 21 is low, transistor 141 is ON, and the voltage between the terminals of capacitor 142 connected to transistors 141 and 143 changes according to the voltage of the luminous level signal 22. In other words, the voltage between the terminals of capacitor 142 changes according to a correction value described later, and the current supplied to the light-emitting element 131 is determined by this voltage.

[0060] If the SH signal 21 is high, the transistor 141 is in the OFF state, maintaining the voltage between the terminals of the capacitor 142. Even if the voltage of the light emission level signal 22 changes, the voltage level between the terminals of the capacitor 142 will not change. In the light-emitting element 131 connected to the signal line I of the DRV circuit 140, a current flows corresponding to the voltage maintained between the terminals of the capacitor 142. That is, the light-emitting element 131 emits light with an intensity corresponding to the voltage between the terminals of the capacitor 142 within the DRV circuit 140. Using the SH signal 21, a predetermined DRV circuit 140 and light-emitting element 131 can be selected from the plurality of DRV circuits 140 and the plurality of light-emitting elements 131 included in the DRV circuit row 14 and the light-emitting element row 13. Using the light emission level signal 22, the light emission intensity can be determined and maintained. Hereinafter, the voltage between the terminals of the capacitor will sometimes be described as the voltage of the capacitor.

[0061] Transistor 144 in DRV circuit 140 switches the current supply to the light-emitting element 131 to either power on or power off (current supply is turned on or off). A PWM signal 32 connected to transistor 144 controls the illumination and de-illumination of the light-emitting element 131 (determining the illumination time per line cycle). If transistor 144 is turned on by PWM signal 32, current flows in the light-emitting element 131, causing it to illuminate. If transistor 144 is turned off by PWM signal 32, no current flows in the light-emitting element 131, causing it to de-illuminate.

[0062] Figure 6 This is a diagram illustrating an example of a circuit block of a printhead in an implementation method. Figure 6 This represents an example of a printhead circuit block corresponding to one column of light-emitting elements, but the printhead can also have multiple columns of light-emitting elements.

[0063] like Figure 6 As shown, the light-emitting unit 10 includes a head circuit block comprising an IC 15, a light intensity correction memory 18, and N groups 161 of light-emitting elements from the first to the Nth (e.g., N=640). Each group 161 of light-emitting elements includes M DRV circuits 140 from the first to the Mth (e.g., M=8). Figure 6 As shown, the M DRV circuits 140 contained in a light-emitting element group 161 are labeled as DRV1~8. IC15 includes a light intensity correction control circuit 151, an SH signal output circuit 152, a D / A (digital to analog) conversion circuit 153, and an on / off control circuit 155, etc.

[0064] The light intensity correction memory 18 stores correction values ​​(first correction values) for causing each light-emitting element 131 to emit light at a predetermined intensity within a predetermined range. For light-emitting elements 131 that cannot emit light at a predetermined intensity within the predetermined range for any correction value, a separately determined correction value (second correction value) is stored. The light intensity correction memory 18 outputs the correction values ​​to the light intensity correction control circuit 151. The light emission controller of the image forming apparatus, described later, can read the correction values ​​from the light intensity correction memory 18 and write the correction values ​​into the light intensity correction control circuit 151.

[0065] A level synchronization signal 24 and an image data writing clock C are input to the light intensity correction control circuit 151 via connector 16. Additionally, a level synchronization signal 24, an image data writing clock C, and image data 31 are input to the on / off control circuit 155 via connector 16. The level synchronization signal 24 resets the count values ​​of the light intensity correction control circuit 151 and the on / off control circuit 155.

[0066] The light intensity correction control circuit 151 outputs a signal synchronized with the image data writing clock C. That is, the light intensity correction control circuit 151 outputs a correction value to the D / A conversion circuit 153 synchronously with the image data writing clock C. Consequently, the D / A conversion circuit 153 outputs a voltage according to the correction value. The SH signal output circuit 152 supplies the previously described SH signal 21 to the DRV circuit 140. Furthermore, the on / off control circuit 155 controls the on / off state of the PWM signal 32, and the PWM signal output circuit 160 supplies the PWM signals 32 (321, 322, ..., 328) to the DRV circuit 140. Based on 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, the voltage between the capacitor terminals is set sequentially. In other words, the SH signal output circuit 152 and the D / A conversion circuit 153 function as voltage setting units.

[0067] The DRV circuit 140 generates a drive signal to make the light-emitting element 131 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 IC15. The DRV circuit 140 supplies the drive signal (current) to the light-emitting element 131.

[0068] [Structure of the image forming apparatus]

[0069] Figure 7 This is a diagram illustrating an example of an image forming apparatus with a printhead employing an embodiment. Figure 7 This is an example of a four-in-one color image forming apparatus, but the printhead 1 of the embodiment can also be applied to a monochrome image forming apparatus.

[0070] like Figure 7 As shown, for example, the image forming apparatus 100 includes an image forming unit 1021 for forming a yellow (Y) image, an image forming unit 1022 for forming a magenta (M) image, an image forming unit 1023 for forming a cyan (C) image, and an image forming unit 1024 for forming a black (K) image. The image forming units 1021, 1022, 1023, and 1024 form yellow, magenta, cyan, and black images respectively, and transfer them to a transfer belt 103. Thus, a panchromatic image is formed on the transfer belt 103.

[0071] The image forming unit 1021, which forms a yellow (Y) image, includes a printhead 1001, which includes a light-emitting unit 1011 and a rod lens array 1201. Furthermore, the image forming unit 1021 includes a charger 1121, a printhead 1001, a developer 1131, a transfer roller 1141, and a tape cleaner 1161 around a photosensitive drum 1701. The printhead 1001 corresponds to printhead 1, the light-emitting unit 1011 corresponds to light-emitting unit 10, the rod lens array 1201 corresponds to rod lens array 12, and the photosensitive drum 1701 corresponds to photosensitive drum 17; further descriptions of these components are omitted.

[0072] The image forming unit 1022, which forms an image of magenta (M), includes a printhead 1002, which includes a light-emitting unit 1012 and a rod lens array 1202. Furthermore, the image forming unit 1022 includes a charger 1122, a printhead 1002, a developer 1132, a transfer roller 1142, and a tape cleaner 1162 around a photosensitive drum 1702. The printhead 1002 corresponds to the printhead 1, the light-emitting unit 1012 corresponds to the light-emitting unit 10, the rod lens array 1202 corresponds to the rod lens array 12, and the photosensitive drum 1702 corresponds to the photosensitive drum 17; further descriptions of these components are omitted.

[0073] The image forming unit 1023, which forms a cyan (C) image, includes a print head 1003, which includes a light-emitting unit 1013 and a rod lens array 1203. Furthermore, the image forming unit 1023 includes a charger 1123, a print head 1003, a developer 1133, a transfer roller 1143, and a tape cleaner 1163 around a photosensitive drum 1703. The print head 1003 corresponds to print head 1, the light-emitting unit 1013 corresponds to light-emitting unit 10, the rod lens array 1203 corresponds to rod lens array 12, and the photosensitive drum 1703 corresponds to photosensitive drum 17; further descriptions of these components are omitted.

[0074] The image forming unit 1024, which forms a black (K) image, includes a printhead 1004, which includes a light-emitting unit 1014 and a rod lens array 1204. Furthermore, the image forming unit 1024 includes a charger 1124, a printhead 1004, a developer 1134, a transfer roller 1144, and a tape cleaner 1164 around a photosensitive drum 1704. The printhead 1004 corresponds to printhead 1, the light-emitting unit 1014 corresponds to light-emitting unit 10, the rod lens array 1204 corresponds to rod lens array 12, and the photosensitive drum 1704 corresponds to photosensitive drum 17; further descriptions of these components are omitted.

[0075] Chargers 1121, 1122, 1123, and 1124 uniformly charge each photosensitive drum 1701, 1702, 1703, and 1704. Printheads 1001, 1002, 1003, and 1004, through the illumination of light-emitting elements 131, expose each photosensitive drum 1701, 1702, 1703, and 1704, forming an electrostatic latent image on each of the drums. Developer 1131 applies yellow toner to photosensitive drum 1701, developer 1132 applies magenta toner to photosensitive drum 1702, developer 1133 applies cyan toner to photosensitive drum 1703, and developer 1134 applies black toner to the electrostatic latent image portion of photosensitive drum 1704 (for development).

[0076] Transfer rollers 1141, 1142, 1143, and 1144 transfer the toner image developed on photosensitive drums 1701, 1702, 1703, and 1704 to transfer belt 103. Cleaning belts 1161, 1162, 1163, and 1164 clean any remaining toner on the photosensitive drums 1701, 1702, 1703, and 1704 that has not been transferred, preparing them for the next image formation.

[0077] The first-size (small-size) paper (which forms the image medium) 201 is stored in the paper box 1171, which serves as a paper supply unit. The second-size (large-size) paper (which forms the image medium) 202 is stored in the paper box 1172, which serves as a paper supply unit.

[0078] The toner image is transferred from the transfer belt 103 to the paper 201 or 202 taken from the paper tray 1171 or 1172 via the transfer roller 118, which serves as a transfer unit. The paper 201 or 202 with the transferred toner image is heated and pressed by the fixing roller 120 of the fixing unit 119. Through the heating and pressing of the fixing roller 120, the toner image is reliably fixed to the paper 201 or 202. By repeating the above process, the image forming operation is performed continuously.

[0079] Figure 8 This is a block diagram illustrating an example of a control system for an image forming apparatus according to an embodiment.

[0080] like Figure 8As shown, the image forming apparatus 100 includes a control board 101. The control board 101 includes an image reading unit 171, an image processing unit 172, an image forming unit 173, a controller 174, a ROM (Read Only Memory) 175, a RAM (Random Access Memory) 176, a non-volatile memory 177, a communication I / F 178, a control panel 179, page memories 1801, 1802, 1803, and 1804, a light-emitting controller 183, and an image data bus 184. Furthermore, the image forming apparatus 100 includes a color shift sensor 181 and a mechanical control driver 182. Additionally, the image forming unit 173 includes image forming units 1021, 1022, 1023, and 1024.

[0081] The controller 174 is connected to a ROM 175, RAM 176, non-volatile memory 177, communication I / F 178, control panel 179, color shift sensor 181, mechanical control driver 182, and light emission controller 183.

[0082] An image reading unit 171, an image processing unit 172, a controller 174, and page memories 1801, 1802, 1803, and 1804 are connected to the image data bus 184. Page memories 1801, 1802, 1803, and 1804 output image data 31 in Y, M, C, or K formats, respectively. A light-emitting controller 183 is connected to page memories 1801, 1802, 1803, and 1804, and receives image data 31 in Y format from page memory 1801, M format from page memory 1802, C format from page memory 1803, and K format from page memory 1804. Printheads 1001, 1002, 1003, and 1004 are connected to the light-emitting controller 183. The light-emitting controller 183 inputs image data 31 in Y, M, C, or K formats to printheads 1001, 1002, 1003, or 1004.

[0083] The controller 174 consists of one or more processors, and controls actions such as image reading, image processing and image formation according to various programs stored in at least one of the ROM 175 and the non-volatile memory 177.

[0084] Additionally, the controller 174 inputs the 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 identify the positional relationship of various color test patterns based on the input from the color shift sensor 181. Furthermore, the controller 174 selects the paper tray 1171 or 1172 that supplies paper for forming the image via a mechanical control driver 182.

[0085] The ROM175 stores various programs required for controlling the controller 174. These programs include the printhead's light-emitting control program. The light-emitting control program is a program that controls the timing of light emission and extinguishing (non-illumination) based on image data.

[0086] RAM 176 temporarily stores the data required for control by controller 174. Non-volatile memory 177 stores part or all of various programs and various parameters, etc.

[0087] The mechanical control drive 182 controls the operation of motors and other components required for printing, according to the instructions of the controller 174. The communication I / F 178 outputs various information to the outside and inputs various information from the outside. For example, the communication I / F 178 acquires image data containing multiple image lines. The image forming apparatus 100 prints the image data acquired via the communication I / F 178 using its printing function. The control panel 179 accepts operation input from users and service personnel.

[0088] Image reading unit 171 optically reads the image of a document placed on a document tray (not shown), acquires image data containing multiple image lines, and outputs the image data to image processing unit 172. Image processing unit 172 performs various image processing operations, such as correction, on the image data input via communication I / F 178 or from image reading unit 171. Page memories 1801, 1802, 1803, and 1804 store the image data processed by image processing unit 172. Controller 174 edits the image data in page memories 1801, 1802, 1803, and 1804 in accordance with the print position and print head. Image forming unit 173 forms an image based on the image data stored in page memories 1801, 1802, 1803, and 1804. That is, image forming unit 173 forms an image based on the emission (emitting and extinguishing states) of each light-emitting element 131 corresponding to the image data.

[0089] The light-emitting controller 183 is composed of one or more processors, and controls the light-emitting element 131 based on image data to emit light according to various programs stored in at least one of ROM 175 and non-volatile memory 177. That is, the light-emitting controller 183 outputs a drive signal to the light-emitting element 131 to emit light at a predetermined time.

[0090] [Light control]

[0091] Figure 9 This is a diagram illustrating the light quantity control within the light-emitting element group 161 of the printhead in the embodiment.

[0092] like Figure 6 As described in the text, a light-emitting element group 161 includes, for example, eight DRV circuits 140 (DRV1~8) and light-emitting elements 131 connected to them. Figure 5 The transistor 141 and capacitor 142 of the DRV140 described herein are in Figure 9 The diagram shows eight switches 1411-1418 and eight capacitors 1421-1428 corresponding to DRV1-8 respectively. The SH signals 211-218 output by the SH signal output circuit 152 are signals that open and close the switches 1411-1418 (ON / OFF, connected or disconnected), equivalent to... Figure 5 The SH signal 21 is explained in the text. The light intensity control of the printhead is performed in units of light-emitting element groups (8 DRV circuits).

[0093] use Figure 10 The timing diagram is used to illustrate the light intensity settings for the eight DRV circuits DRV1 to DRV8 included in the light-emitting element group 161.

[0094] When the SH signal 211 goes low, switch 1411 of DRV1 closes (is on). Simultaneously, D / A conversion circuit 153 outputs a light level signal 22 suitable for the amount of light the light-emitting element 131 connected to DRV1 should output, and sets this voltage in capacitor 1421 (sample). If the SH signal 211 goes high, switch 1411 opens (is off), and the voltage of the light level signal 22 remains held in capacitor 1421. After switch 1411 opens (is off), even if the voltage of the light level signal 22 changes, the voltage of capacitor 1421 will not change.

[0095] Next, the SH signal 218 goes low, and the switch 1418 of the DRV8 closes (is on). Simultaneously, the D / A conversion circuit 153 outputs a light emission level signal 22 suitable for the amount of light the light-emitting element 131 connected to the DRV8 should output, and sets this voltage in the capacitor 1428 (samples it). If the SH signal 218 goes high, the switch 1418 opens (is off), and the voltage of the light emission level signal 22 remains held in the capacitor 1428. After the switch 1418 opens (is off), even if the voltage of the light emission level signal 22 changes, the voltage of the capacitor 1428 will not change.

[0096] Next, the same operation is performed in the order of DRV2, DRV7, DRV3, DRV6, DRV4 and DRV5 to set the light intensity of the eight DRV circuits contained in the light-emitting element group 161.

[0097] In this way, the timing of the opening and closing (on / off) of switches 1411-1418 is different by SH signals 211-218, and the signal output level of D / A conversion circuit 153 is changed synchronously with SH signals 211-218, thereby controlling the amount of light emitted by the light-emitting elements 131 connected to DRV1-8.

[0098] Figure 11 This is a timing diagram illustrating an example of the relationship between light intensity control and emission time control of the printhead in an implementation method.

[0099] like Figure 11 As shown, when capacitor 142 holds the set voltage, if PWM signal 32 is input, the light-emitting element 131 emits light at the set amount. That is, SH signal 21 and PWM signal 32 are output synchronously. Furthermore, the length of PWM signal 32 controls the light emission time per line cycle. In addition, PWM signal 32, like SH signal 21, is also output to DRV1~8 at independent timings.

[0100] Furthermore, 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 to the capacitor whose voltage is set first (hereinafter referred to as the pre-stage) and the capacitor whose voltage is continuously set with the pre-stage (hereinafter referred to as the post-stage) is too large, there will not be enough time to charge (or discharge) the post-stage capacitor 142, and sometimes it will be impossible to set the accurate voltage (light emission level) as the target in the post-stage capacitor 142. That is to say, in Figure 10In the control sequence shown, for example, sometimes the set voltage of the capacitor 1421 in the preceding stage cannot be set to the accurate target voltage for the capacitor 1428. If the accurate target voltage cannot be set, the amount of light emitted by the light-emitting element 131 will be affected, which may lead to a decrease in image quality. In this embodiment, image quality degradation is prevented by light quantity correction, which will be described later.

[0101] In addition, according to Figure 10 The sequence of DRV1, DRV8, DRV2, DRV7, DRV3, DRV6, DRV4, DRV5, DRV1… shown is used to perform a series of light intensity controls and light emission actions to ensure the continuity of light emission timing between adjacent light-emitting element groups 161. For example, since DRV1 and DRV8 are adjacent to each other, it is desirable to have continuous light intensity controls and light emission actions for DRV1 and DRV8 as described above.

[0102] Figure 12 This is a simplified diagram of a calibration data generation apparatus for illustrating a method of generating calibration data for causing the light-emitting element 131 of the printhead 1 to emit light in a uniform amount of light.

[0103] The calibration data generation device includes a light intensity measurement sensor 19 and a controller 200. The light intensity measurement sensor 19 is a sensor that receives light output from the light-emitting element 131 of the printhead 1 after passing through the lens 12, and outputs a voltage proportional to the intensity (light intensity) of the light as a detection signal.

[0104] like Figure 12 As shown, the light intensity measurement sensor 19 is located on the opposite side of the transparent substrate 11, separated by the rod lens array 12.

[0105] The controller 200 has the same printhead control function as the previously described light-emitting controller 183, and has calculations for obtaining correction data and control functions for moving the sensor.

[0106] In order to measure the light intensity of all light-emitting elements 131 of the printhead 1, the controller 200 can move the light intensity measurement sensor 19 to the position of the light-emitting element to be measured by a light intensity measurement sensor moving device (not shown), and make the light-emitting element to be measured emit light, thereby measuring the light intensity of the light-emitting element to be measured based on the detection signal from the light intensity measurement sensor 19.

[0107] 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 causes the light-emitting elements 131 to emit light sequentially while the light intensity measurement sensor 19 is moved. The light intensity measurement sensor 19 detects the light intensity of the light-emitting elements 131 and outputs a detection signal. Based on the detection signal from the light intensity measurement sensor 19, the controller 200 sequentially measures the light intensity of the emitting elements 131.

[0108] When measuring light intensity, the controller 200 writes an arbitrary value into the light intensity correction memory 18 of the print head 1, and then sends the image data 31 of the light-emitting element being measured to the print head 1, thereby enabling any light-emitting element to emit light at any light level. Furthermore, although... Figure 6 Although not illustrated, the controller 200 can also directly access the light correction circuit 151 without going through the light correction memory 18, thereby emitting light at any light level.

[0109] Figure 13 This is a graph representing the amount of light emitted by the light-emitting element relative to the correction value. Figure 13 In the example, the relationship between the correction value and the light intensity is shown for normally emitting elements A and B and abnormally emitting element C.

[0110] First, let's explain the components A and B that emit light normally.

[0111] like Figure 13 As shown, compared to the case where both components A and B are set to the first reference value as the correction value, the amount of light is larger when the second reference value is set. Figure 13 The horizontal level indicated by the dashed line represents the target light intensity. Elements A and B both have light intensities lower than the target light intensity at the first reference value. At the second reference value, elements A and B both have light intensities higher than 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 and second reference values ​​for elements A and B. The correction value for outputting the target light intensity can be calculated. It can be seen that as long as a straight line is drawn connecting the point representing the light intensity relative to the first reference value and the point representing the light intensity relative to the second reference value, and the point where the line intersects with the target light intensity is found, the correction value for outputting the target light intensity can be calculated. Furthermore, even if the correction value for outputting the target light intensity is not between the first and second reference values, as long as the point where the aforementioned straight line intersects with the target light intensity exists within the range of the settable correction value, the correction value for outputting the target light intensity can be calculated. In this way, elements A and B are elements whose light intensity at the position opposite the rod lens array 12 across the correction value setting (current control) satisfies the reference and becomes a value within a predetermined range.

[0112] Component C is a component that causes the light-emitting element 131 to not emit light normally due to defects in the DRV circuit 140 and / or the light-emitting element 131, or even if the light-emitting element 131 emits light, the light will not come out of the lens.

[0113] The first and second reference values ​​of element C, and the first and second measured light quantities corresponding to the first and second reference values, are not proportional. For element C, even if the voltage between the capacitor terminals is increased by increasing the correction value, the light quantity will not increase. Or, even if the light quantity increases, the target light quantity will not be reached. Therefore, in the case of element C, the straight line connecting the point representing the light quantity relative to the first reference value and the point representing the light quantity relative to the second reference value does not intersect with the target light quantity. In other words, element C is an element whose light quantity at the position opposite the rod lens array 12, set by the correction value (current control), does not meet the reference and deviates from the predetermined range.

[0114] For components that cannot emit light at the target intensity regardless of the set correction value, it is sometimes impossible to calculate an appropriate correction value to achieve the target light intensity, resulting in an inappropriate correction value. For example, because the light intensity is lower than the target light intensity, the maximum value is calculated as the correction value. Inappropriate correction values ​​may affect the light emission of other light-emitting components, leading to a decrease in image quality. Components exhibiting characteristics like component C will be referred to as defective components.

[0115] Figure 14 This is a flowchart illustrating an example of light intensity correction implemented to enable the printhead of an embodiment to emit light with uniform light intensity.

[0116] The controller 200 sets first and second reference values ​​(first reference value < second reference value) as light quantity correction values ​​and measures the light quantity of all light-emitting elements 131. The light quantity measurement sensor 19 detects the light quantity from the light-emitting elements 131 corresponding to the light emission control of the controller 200 after passing through the lens and outputs a detection signal. Based on the detection signal from the light quantity measurement sensor 19, the controller 200 measures the light quantity (ACT1) from all light-emitting elements 131 after passing through the lens and located on the opposite side of the transparent substrate 11 across the rod lens array 12.

[0117] Next, the controller 200 calculates a correction value (ACT2) corresponding to the target light intensity of each light-emitting element 131 based on the measured light intensity corresponding to the first and second reference values. For example, in Figure 13 In the case of normally emitting components A and B as described in the text, the correction values ​​corresponding to the intersection points PA and PB are calculated. For... Figure 13 The defective element C described in the text cannot be calculated as a correction value for the target light intensity. Because the light intensity of element C is insufficient, the maximum value is calculated as the correction value.

[0118] Next, the controller 200 writes the correction values ​​of each light-emitting element into the light intensity correction memory 18 (ACT3). The printhead, having completed the light intensity correction, controls the current flowing in the light-emitting element 131 according to the correction values ​​written into the light intensity correction memory 18, and the light-emitting element 131 emits light at the target light intensity.

[0119] That is, the output voltage of the D / A conversion circuit 153 is controlled according to the correction value written into the light-emitting correction memory 18. The output voltage of the D / A conversion circuit 153 controls the voltage between the terminals of the capacitor 142. The voltage between the terminals of the capacitor 142 controls the current flowing in the light-emitting element 131, and the light-emitting element 131 emits light at the target light intensity. However, for defective elements such as element C, even if the correction value is set to the maximum value, it cannot emit light at the target light intensity.

[0120] Figure 15 This is a timing diagram illustrating an example of optical quantity correction without defective components.

[0121] For example, because the timing of the light emission of adjacent light-emitting elements 131 is continuous, IC15 is adjusted according to... Figure 10 and Figure 15 The voltage is set between the terminals of capacitor 142 in DRV circuit 140 in the sequence shown. That is, according to SH signal 21, the voltage is set between the capacitor terminals of each DRV circuit in the order of DRV1, DRV8, DRV2, DRV7, DRV3, DRV6, DRV4, DRV5, DRV1...

[0122] Furthermore, the D / A output voltage (dashed line) of the light emission level signal 22 from the D / A conversion circuit 153 changes according to the correction value during the timing allocated to each DRV circuit 140. The voltage between the capacitor terminals (solid line) becomes equal to the D / A output voltage during the time allocated to each DRV circuit 140 and is held during the rising timing of the SH signal. As a result, all light-emitting elements 131 are prepared to emit light with uniform intensity.

[0123] Figure 16 This is an illustration showing an example of a printhead containing defective components in an embodiment.

[0124] like Figure 16 As shown, if the array of light-emitting elements contains defective elements, the position on the photosensitive drum 17 corresponding to that element cannot be exposed. If by... Figure 12 The light intensity measurement method shown is used to measure such a printhead, and then... Figure 14As explained in the text, the measurement results corresponding to the defective element show very small values. In the light quantity correction for the defective element, for example, a correction value is calculated to maximize the light quantity, and therefore 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 other non-defective elements.

[0125] The following is a correction state in which there are defective elements in the light-emitting element column of the printhead, and the voltage set between the terminals of the capacitor 142 of the DRV circuit 140 corresponding to the defective element is significantly different from the voltage set between the terminals of the capacitor 142 of the DRV circuit 140 corresponding to other normal elements, is referred to as the first light quantity correction.

[0126] Figure 17 This is a diagram illustrating an example of the result of measuring light intensity using a second reference value when a defective element is present in the printhead. Figure 18 This is a diagram illustrating an example of a correction value calculated using the first light quantity correction when a defective element is present in the printhead. Figure 19 This is a diagram illustrating an example of the amount of light after applying the first light quantity correction in the case of a printhead containing defective elements.

[0127] like Figure 17 As shown, in the light quantity measurement results when the correction value is constant (second reference value), the light quantity measurement result corresponding to the defective element is significantly lower than the target light quantity. Therefore, as Figure 18 As shown, the calculated correction value corresponding to the defective component becomes a large value. However, as... Figure 19 As shown, the corrected light intensity corresponding to the defective element remains significantly lower than the target light intensity. Based on this, it affects the subsequent light-emitting elements of the defective element, and the light intensity of these subsequent light-emitting elements is higher than the target light intensity. In other words, both the defective element and its subsequent elements are in a state where they do not emit light at the target intensity.

[0128] Figure 20 This is a diagram used to illustrate the effects of setting an inappropriate voltage based on the first light quantity correction.

[0129] For example, the case where the potential between the capacitor terminals of DRV2 is extremely high will be explained. The output voltage (dashed line) of D / A conversion circuit 153 varies correspondingly to the correction value calculated based on each light quantity measurement result. When the light-emitting element 131 connected to DRV2 is a defective element, the light quantity measurement result is a very small value, and the correction value used for DRV2 (= output voltage of D / A conversion circuit 153) is at its maximum value. As a result, the voltage between the capacitor terminals of DRV2 is much larger than the voltage between the capacitor terminals of other DRVs.

[0130] If the correction value of DRV7, the stage following DRV2, is at an average level, then the voltage output by D / A conversion circuit 153 should change from maximum to average level. However, if the potential change (discharge) capability of D / A conversion circuit 153 is insufficient, its potential change will be untimely, resulting in a potential setting higher than the target value (creating a gap from the target value). As a result, the light intensity of the light-emitting element 131 connected to DRV7 is greater than the target level. In this way, during the first light intensity correction, light-emitting elements other than the defective element also emit light at a level different from the target level.

[0131] When the light intensity of the printhead is corrected by the first light intensity correction and a halftone image is output, the light-emitting element connected to DRV2 is non-emitting, thus becoming a white stripe, while the light intensity of the light-emitting element connected to DRV7 is greater, thus becoming a black stripe.

[0132] Figure 21 This is a diagram used to illustrate the effect on an image when a first light intensity correction is applied to a printhead containing defective elements.

[0133] In the case of halftone images, white stripes appear corresponding to defective elements based on the first light intensity correction, and black stripes appear corresponding to the effect of the correction value of the defective element. Furthermore, the positional relationship between the white and black stripes is determined based on the positional relationship between the defective element and the light-emitting elements following it. In other words, the positional relationship between the white and black stripes changes depending on the positional relationship between the defective element and the light-emitting elements following it. Figure 21 As an example, the left example shows a white stripe corresponding to DRV2 and a black stripe corresponding to DRV7, which is separated by a distance, and the right example shows a white stripe corresponding to DRV4 and a black stripe corresponding to the adjacent DRV5.

[0134] Figure 22 This is a flowchart illustrating an example of a second light intensity correction for a printhead in an embodiment. The second light intensity correction is a light intensity correction that suppresses the undesirable conditions of the first light intensity correction, namely, the light intensity correction that produces black stripes due to the influence of the correction value of defective elements.

[0135] The light-emitting controller 200 controls the emission of all light-emitting elements 131 using a first reference value. The light quantity measurement sensor 19 detects the light quantity from the light-emitting elements 131 corresponding to the light emission control of the light-emitting controller 200 and outputs a detection signal. The light-emitting controller 200 moves the light quantity measurement sensor 19 in coordination with the light-emitting elements emitting the printed hair and measures the light quantity from all light-emitting elements 131 (ACT101).

[0136] Furthermore, the light emission controller 200 uses a second reference value (second reference value > first reference value) to control the emission of all light-emitting elements 131. The light quantity measurement 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 quantity measurement sensor 19 and measures the amount of light from all light-emitting elements 131 (ACT102).

[0137] If the reference value increases, the D / A output voltage from the D / A conversion circuit 153 increases. If the D / A output voltage increases, the voltage between the terminals of capacitor 142 increases. If the voltage between the terminals of capacitor 142 increases, the amount of light emitted by the light-emitting element 131 increases. Furthermore, in this embodiment, the light-emitting controller 200 is described based on two reference values ​​to correct the light amount, but it is also possible to correct the light amount based on one or more reference values.

[0138] In order to perform light intensity correction for all light-emitting elements 131, the light-emitting controller 200 sets the element number n (1~5120) of the light-emitting elements 131 (ACT103). For example, the light-emitting controller 200 sets n=1 and performs light intensity correction sequentially starting from the nth element.

[0139] The light-emitting controller 200, based on a reference value and the measured light intensity corresponding to the reference value, determines, for the nth element, whether it is an element whose voltage between the capacitor terminals is correlated with the light intensity of the light-emitting element and which can emit light at the target light intensity (ACT104). The determination of whether an element is an element whose voltage between the capacitor terminals is correlated with the light intensity of the light-emitting element and which can emit light at the target light intensity is as follows: Figure 13 As explained in the text, a straight line is used to connect the point representing the light quantity relative to the first reference value and the point representing the light quantity relative to the second reference value, and it is determined whether the point where the straight line intersects the target light quantity is within the range of the settable correction value. That is, Figure 13 Components like A and B are judged to be able to emit light at the target light intensity, while components like C are judged to be unable to emit light at the target light intensity.

[0140] When the light-emitting controller 200 determines that the nth element is an element whose voltage between capacitor terminals is correlated with the light intensity of the light-emitting element and which is capable of emitting light at the target light intensity (ACT104, Yes), it calculates a correction value as a first correction value to make the light intensity of the nth element reach the target light intensity based on a first reference value and a first measured light intensity relative to the first reference value, and a second reference value and a second measured light intensity relative to the second reference value (ACT105). The light-emitting controller 200 writes the calculated first correction value into the element number address n of the light intensity correction memory 18 (ACT106).

[0141] In addition, if the light-emitting controller 200 determines that the nth element is a component whose voltage between capacitor terminals is not related to the light intensity of the light-emitting element and which cannot emit light at the target light intensity (ACT104, No), the nth element is designated as a defective element and the element number and defect information are stored (ACT109).

[0142] If the light-emitting controller 200 has not yet determined whether all light-emitting elements 131 can emit light at the target intensity, that is, if n is not 5120 (ACT107, No), then the value of n is incremented by 1 (ACT110), and the processing of ACT104 and thereafter is repeated. If the light-emitting controller 200 has determined whether all light-emitting elements 131 can emit light at the target intensity, that is, if n = 5120 (ACT107, Yes), then the second correction value is stored in the element number address stored in the intensity correction memory 18 in ACT109 (ACT108). For example, the light-emitting controller 200 sets the second correction value between the maximum and minimum values ​​of the first correction value and writes it into the intensity correction memory 18. The second correction value can also be the average value of the first correction value, or a value within ±3% of the average value of the first correction value. In short, any correction value that does not affect the intensity of light emitted by subsequent light-emitting elements is acceptable. For example, the intensity variation affecting the image is a variation of ±3% or more. Therefore, any correction value that does not cause a change of more than ±3% in the amount of light emitted by the subsequent light-emitting element is acceptable.

[0143] Furthermore, the target light intensity and the allowable range of light intensity variation for subsequent components can be arbitrarily set during the design phase.

[0144] Thus, the light emission controller 200 performs a second light intensity correction. The light intensity correction memory 18 of the printhead, after performing the second light intensity correction, becomes as follows: In the address corresponding to a normal (not defective) light emission element 131, when that element emits light, a light intensity correction value (first correction value) as the target light intensity is stored. This first correction value is the value that determines the inter-terminal voltage of a predetermined capacitor included in the predetermined DRV 140, and is a value where the light intensity of the light emission element 131 at a position opposite the predetermined lens of the rod lens array 12 when viewed from the light emission element 131 connected to the predetermined DRV 140 is within a predetermined range. On the other hand, in the address corresponding to a defective element, a light intensity correction value (second correction value) that does not affect the light intensity of subsequent light emission elements is stored. This second correction value is the value that determines the inter-terminal voltage of a predetermined capacitor included in the predetermined DRV 140, and is a value where the inter-terminal voltage of the predetermined capacitor is within a predetermined range. Furthermore, this second correction value does not affect the terminal voltage setting of the next capacitor when the SH signal output circuit 152 and D / A conversion circuit 153 set the terminal voltage of the next capacitor (the capacitor located after the predetermined capacitor). Additionally, the emission of the defective element is light intensity that does not reach the target level.

[0145] Figure 23 This diagram illustrates an example of a correction value calculated using second light intensity correction when a defective element is present in the printhead. A correction value (second correction value) of the same level as other light-emitting elements is also set for the defective element. This setting value is stored in the light intensity correction memory 18 of the printhead where second light intensity correction has been implemented.

[0146] Figure 24 This is a diagram illustrating an example of the amount of light emitted by the light-emitting controller 183 of the control board 101 of the image forming apparatus 100 when the printhead contains defective elements, after applying second light quantity correction.

[0147] like Figure 24 As shown, the corrected light intensity corresponding to the defective element remains significantly lower than the target light intensity, but the light-emitting element after the defective element can emit light at the target light intensity.

[0148] Figure 25 This is a diagram illustrating the effect on an image when a second light intensity correction is applied to a printhead containing defective elements.

[0149] Will Figure 21 and Figure 25In comparison, in the case of a halftone image, white stripes appear corresponding to defective elements according to the second light intensity correction, just like the first light intensity correction. However, unlike the first light intensity correction, black stripes can be prevented from appearing corresponding to the influence of the correction value of the defective element.

[0150] Figure 26 This is a diagram illustrating an example where the array of light-emitting elements in the printhead of an embodiment is longer than the array of rod lenses, and the measured light intensity corresponding to the light-emitting elements at both ends is a very small value.

[0151] like Figure 26 As shown, if the light-emitting element array 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 array 13 will not pass through the lenses of the rod lens array 12, thus preventing the photosensitive drum 17 from being exposed. Furthermore, the measured light intensity of such a light-emitting element 131 will show a very small value, resulting in a very large correction value for such a light-emitting element 131. In other words, for light-emitting elements 131 outside the lens region of the rod lens array 12, even if the circuitry and components are without defects, the inability to measure the light intensity from these light-emitting elements 131 can sometimes lead to the same undesirable conditions as with defective elements.

[0152] Figure 27 This is a diagram illustrating an example of light quantity measurement results in a printhead containing a light-emitting element outside the lens area.

[0153] Components No. 1, 2, 3 and components No. 5, 118, 5, 119, 5, 120 are light-emitting elements located outside the lens area. Among each light-emitting element, DRV1, DRV2, DRV3 of the first group and DRV6, DRV7, DRV8 of the 640th group are connected as DRV circuits.

[0154] Figure 28 This is a diagram illustrating an example of a correction value calculated using a first light quantity correction when a light-emitting element is included outside the lens area in the printhead. Figure 29 This is a diagram illustrating an example of the light quantity after applying the first light quantity correction when the light-emitting element is included outside the lens area in the printhead.

[0155] like Figure 27 As shown, in the light quantity measurement results with a constant correction value, the light-emitting element outside the lens area (e.g., connected to...) Figure 27 DRV1, DRV2, DRV3 and on the left Figure 27 The light intensity measurement results for the light-emitting elements (DRV6, DRV7, and DRV8 on the right side) are significantly lower than the target light intensity. Therefore, as... Figure 28 As shown, the calculated correction value corresponding to the light-emitting element outside the lens area is a large value. However, as... Figure 29 As shown, the corrected light intensity corresponding to the light-emitting elements outside the lens area remains significantly lower than the target light intensity. On the other hand, the light-emitting elements within the lens area (e.g., those connected to DRV6, DRV7, DRV8, and DRV2, DRV3, DRV4) in the subsequent stage, which corrects the light intensity of the light-emitting elements outside the lens area, are affected, causing the light intensity of the subsequent stage's light-emitting elements to be higher than the target light intensity. This is because the voltage setting sequence between the capacitor terminals is DRV1, DRV8, DRV2, DRV7, DRV3, DRV6, DRV4, DRV5, DRV1. For example, the subsequent stage for DRV1, DRV2, DRV3 is DRV8, DRV7, DRV6, and the subsequent stage for DRV6, DRV7, DRV8 is DRV4, DRV3, DRV2.

[0156] Figure 30 This diagram illustrates the effect on an image when a first light intensity correction is applied to a printhead containing light-emitting elements outside the lens region.

[0157] In the case of halftone images, according to the first light intensity correction, even if the light-emitting elements outside the lens area emit light at maximum intensity, it will not have an impact on the halftone image. However, it will affect the light-emitting elements within the lens area in accordance with the correction value of the light-emitting elements outside the lens area, thus resulting in black halftones (black stripes). Components No. 6, 7, 8 and components No. 5, 114, 5, 115, 5, 116 belong to this category.

[0158] Figure 31 This diagram illustrates an example of a correction value calculated using second light intensity correction when light-emitting elements are included outside the lens area in the printhead. Correction values ​​(second correction values) at the same level as other light-emitting elements are also set for the light-emitting elements outside the lens area (elements No. 1, 2, 3 and elements No. 5, 118, 5, 119, 5, 120). These settings are stored in the light intensity correction memory 18 of the printhead that performs the second light intensity correction.

[0159] Figure 32 This is a diagram illustrating an example of the amount of light emitted by the printhead after the light-emitting controller 183 of the control board 101 of the image forming apparatus 100 applies a second light quantity correction when the printhead contains a light-emitting element outside the lens area.

[0160] like Figure 32As shown, it is possible to eliminate the influence of light-emitting elements outside the lens area (such as the light-emitting elements connected to DRV1, DRV2, DRV3 in the first group, and DRV6, DRV7, DRV8 in the 640th group) on the light-emitting elements of the subsequent stage (such as the light-emitting elements connected to DRV8, DRV7, DRV6 in the first group, and DRV4, DRV3, DRV2 in the 640th group), and enable the light-emitting elements of the subsequent stage (elements No. 6, 7, 8 and elements No. 5, 114, 5, 115, 5, 116) to emit light at the target amount.

[0161] Figure 33 This diagram illustrates the effect on an image when a second light intensity correction is applied to a printhead containing light-emitting elements outside the lens region. For a printhead with the second light intensity correction applied, the light intensity of the light-emitting element 131 within the lens region is constant.

[0162] If Figure 30 and Figure 33 In comparison, in the case of halftone images, the second light intensity correction, unlike the first light intensity correction, can prevent the appearance of black stripes.

[0163] According to the embodiments described above, a printhead and image forming apparatus that prevent image quality degradation can be provided. Specifically, the printhead and image forming apparatus select a first or a second correction value based on whether there is a correlation between a reference value and the measured light intensity corresponding to the reference value (whether light can be emitted within a predetermined range including the target light intensity). If there is a correlation (light can be emitted within a predetermined range including the target light intensity), the first correction value can be used to expose the latent image with the target light intensity. If there is no correlation (light cannot be emitted within a predetermined range including the target light intensity), the second correction value can be used to expose the latent image with a light intensity that reduces the impact on other light-emitting elements.

[0164] Furthermore, in the embodiment, an example is shown where, for instance, if the correction value increases, the voltage set between the capacitor terminals rises, and the light intensity increases. However, depending on the circuit structure, it is conceivable that the relationship between the correction value, the voltage set between the capacitor terminals, and the light intensity may differ. For example, it is also conceivable that if the correction value increases, the voltage set between the capacitor terminals decreases, and the light intensity increases. In such a case, the relationship between the correction value and the voltage set between the capacitor terminals is inverse.

[0165] While several embodiments have been described, these embodiments are merely illustrative and not intended to limit the scope of the invention. These embodiments can be implemented in various other ways, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included within the scope and spirit of the invention, and likewise within the scope of the invention as described in the claims and its equivalents.

Claims

1. A printhead, characterized in that, have: lens; A substrate is disposed opposite to the lens; A first light-emitting element is formed on the substrate, and the amount of light at the position opposite the lens is controlled by current to a value within a predetermined range; A second light-emitting element is formed on the substrate, and the amount of light at the position opposite the lens is controlled by current to deviate from a predetermined range. A first driving circuit is connected to the first light-emitting element and supplies current to the first light-emitting element; The first capacitor is included in the first driving circuit, and the current supplied to the first light-emitting element is determined by the voltage between the terminals of the first capacitor. The second driving circuit is connected to the second light-emitting element and supplies current to the second light-emitting element; The second capacitor is included in the second driving circuit, and the current supplied to the second light-emitting element is determined by the voltage between the terminals of the second capacitor; The memory stores a first correction value and a second correction value, wherein the first correction value determines the voltage between the terminals of the first capacitor and the second correction value determines the voltage between the terminals of the second capacitor. as well as The voltage setting unit sequentially sets the voltage between the capacitor terminals. The first correction value stored in the memory is a value that makes the amount of light at the position opposite the lens within a predetermined range when the first light-emitting element emits light. The second correction value stored in the memory is a value that makes the voltage between the terminals of the second capacitor within a predetermined range. The second correction value stored in the memory is as follows: when the voltage setting unit sets the inter-terminal voltage of the second capacitor and then sets the inter-terminal voltage of the first capacitor as the next capacitor, it does not affect the setting of the inter-terminal voltage of the first capacitor.

2. The printhead according to claim 1, characterized in that, The first light-emitting element is an element whose light intensity meets the reference. The second light-emitting element is the element whose light intensity does not meet the reference.

3. The printhead according to claim 1, characterized in that, The second light-emitting element is a light-emitting element disposed outside the light-passing area of ​​the lens.

4. The printhead according to claim 1, characterized in that, The second light-emitting element is a light-emitting element that has defects in itself.

5. The printhead according to claim 1, characterized in that, The second light-emitting element is a light-emitting element with a defect in the second driving circuit that supplies current to the second light-emitting element.

6. The printhead according to claim 4 or 5, characterized in that, Component numbers are assigned to the first light-emitting element and the second light-emitting element. The second light-emitting element is designated as a defective element, and its component number and defect information are stored in the memory.

7. The printhead according to claim 1, characterized in that, The second correction value is set between the maximum and minimum values ​​of the first correction value.

8. The printhead according to claim 1, characterized in that, The second correction value is a value within ±3% of the average of the first correction values.

9. An image forming apparatus, characterized in that, The image forming apparatus includes the printhead according to any one of claims 1 to 8.

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