Image forming apparatus

Abstract

An image forming apparatus according to an embodiment includes a print head, a detection unit, a controller, and a power supply unit. The print head includes one or more light emitting element columns each of which includes a plurality of light emitting elements. The detection unit detects a number of the light emitting elements that emit light according to image data. The controller controls a driving voltage for driving the light emitting elements based on a detection result. The power supply unit supplies the driving voltage to the print head.

Description

Technical Field

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

[0002] Electrophotographic printers (hereinafter, printers) equipped with printheads are widely used. Printheads contain multiple light-emitting elements, such as LEDs (Light Emitting Diodes) or OLEDs (Organic Light Emitting Diodes). For example, a printhead may have light-emitting elements equivalent to 15,400 pixels, arranged along the main scanning direction, with directions orthogonal to the main scanning direction corresponding to the sub-scanning directions. The printer exposes a photosensitive drum by light emanating from these multiple light-emitting elements, and prints an image corresponding to the latent image formed on the photosensitive drum onto a sheet of recording paper. Summary of the Invention

[0003] An image forming apparatus according to one embodiment includes: a printhead including one or more rows of light-emitting elements composed of a plurality of light-emitting elements; a detection unit for detecting the number of light-emitting elements that emit light according to image data; a controller for controlling the driving voltage for driving the light-emitting elements based on the detection result; and a power supply unit for supplying the driving voltage to the printhead.

[0004] An image forming apparatus according to one embodiment includes: a plurality of printheads corresponding to each color, each printhead including one or more rows of light-emitting elements composed of a plurality of light-emitting elements; a detection unit for detecting the number of light-emitting elements in each printhead that emit light according to image data corresponding to each color; a controller for controlling the driving voltage for driving the light-emitting elements for each printhead based on the detection result; and a power supply unit for supplying the driving voltage to each printhead. Attached Figure Description

[0005] 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 according to an embodiment.

[0006] Figure 2 This is a diagram showing an example of a transparent substrate constituting the printhead according to the embodiment.

[0007] Figure 3 This is a diagram illustrating an example of the layout of the light-emitting elements and driving circuitry of the printhead according to the embodiment.

[0008] Figure 4 This is a diagram showing an example of a cross-section of the transparent substrate of the printhead according to the embodiment.

[0009] Figure 5This diagram illustrates an example of the connection between the control board and the printhead according to the embodiment.

[0010] Figure 6 This is a diagram illustrating an example of the structure of the light-emitting element of the printhead according to the embodiment.

[0011] Figure 7 This diagram illustrates an example of a circuit comprising a DRV circuit for driving the light-emitting element according to the embodiment, a light-emitting element that emits light from the DRV circuit, and a circuit for switching the current supply to the light-emitting element.

[0012] Figure 8 This is a diagram illustrating an example of the head circuit block of the printhead according to the embodiment.

[0013] Figure 9 This is a diagram illustrating an example of an image forming apparatus using the printhead described in the first embodiment.

[0014] Figure 10 This is a block diagram illustrating an example of a control system for an image forming apparatus according to an embodiment.

[0015] Figure 11 This is a flowchart illustrating an example of drive voltage control based on the embodiment of the image forming apparatus.

[0016] Figure 12 This is a graph showing the relationship between the number of light-emitting elements in the optical head of the image forming apparatus according to the embodiment and the light reduction rate.

[0017] Figure 13 This is a diagram illustrating the relationship between a halftone image (where the number of light-emitting elements is constant) formed by the image forming apparatus according to the embodiment and the voltage and drive current supplied to the print head in relation to the formation of the halftone image.

[0018] Figure 14 A diagram illustrating an undesirable use case for the drive voltage control involved in the implementation.

[0019] Figure 15 This is a diagram illustrating an application example of the drive voltage control involved in the embodiment.

[0020] Figure 16 This figure illustrates an example of the effect of suppressing the reduction in light intensity caused by an increase in the voltage of the optical head of the image forming apparatus according to the embodiment.

[0021] Figure 17 This is a block diagram illustrating a modified example of the control system of the image forming apparatus according to the embodiment.

[0022] Explanation of reference numerals in the attached figures

[0023] 1…Print head; 10…Light-emitting unit; 11…Transparent substrate; 12…Bar lens array; 13…Light-emitting element array; 14…Circuit array; 16…Connector; 17…Photosensitive drum; 100…Image forming apparatus; 101…Control board; 102…Power supply unit; 103…Transfer belt; 104…Wire harness; 118…Transfer roller pair; 119…Fixing unit; 120…Fixing roller; 121…Spacer; 131…Light-emitting element; 140…Drive circuit; 142…Capacitor; 144…Switch; 145…Wiring; 151…Light-emitting element address counter; 152…Decoding 153…Coder; 154…Conversion circuit; 155…Light correction memory; 171…Indicator circuit; 172…Image reading unit; 173…Image processing unit; 174…Image forming unit; 175…Controller; 176…Non-volatile memory; 177…Communication interface; 178…Control panel; 179…Color deviation sensor; 180…Mechanical control driver; 181…Light emission controller; 182…Image data bus; 201, 202…Paper; 1001, 1002, 1003, 1004…Print head; 1011, 1012, 1013, 1014…Print head 14…Light-emitting unit; 1021, 1022, 1023, 1024…Image forming assembly; 1101…Reference plane; 1102…Sealing glass; 1121, 1122, 1123, 1124…Charger with power; 1131, 1132, 1133, 1134…Developer; 1141, 1142, 1143, 1144…Transfer roller; 1161, 1162, 1163, 1164…Cleaner; 1171, 1172…Paper tray; 1201, 1202, 1203, 1204…Rod lens array; 1301…The… 1302… Second light-emitting element column; 1311… Hole transport layer; 1312… Light-emitting layer; 1313… Electron transport layer; 1321… Electrode (+); 1322… Insulating layer; 1323… Electrode (-); 1401… First driving circuit column; 1402… Second driving circuit column; 1701, 1702, 1703, 1704… Photosensitive drum; 1741… Driving voltage controller; 1801, 1802, 1803, 1804… Page memory; 1831… Light-emitting element quantity detection unit; 1832… Driving voltage controller. Detailed Implementation

[0024] The image forming apparatus according to the embodiment includes a printhead, a detection unit, a controller, and a power supply unit. The printhead includes one or more rows of light-emitting elements, each composed of multiple light-emitting elements. The detection unit detects the number of light-emitting elements that emit light according to image data. The controller controls the driving voltage for driving the light-emitting elements based on the detection result. The power supply unit supplies the driving voltage to the printhead.

[0025] 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 label the same components. 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.

[0026] [Printhead Structure]

[0027] Reference Figures 1 to 8 This illustrates an example of the configuration of the printhead applied to the image forming apparatus according to the embodiments.

[0028] 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 according to an embodiment.

[0029] Image forming apparatus has Figure 1 The photosensitive drum 17 and printhead 1 are shown. The printhead 1 is configured opposite to the photosensitive drum 17.

[0030] 17-directional photosensitive drum Figure 1 The direction of rotation indicated by the arrow is called the sub-scanning direction, and the direction orthogonal to the sub-scanning direction is called the main scanning 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. That is, the image forming apparatus controls the emission of light from the printhead 1, forming 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 de-emission (non-emission) of the printhead 1.

[0031] 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. For example, the transparent substrate 11 is a light-transmitting glass substrate. A plurality of light-emitting element rows 13, composed of multiple light-emitting elements of LEDs or OLEDs, are formed on the transparent substrate 11.

[0032] like Figure 1 As shown, the first light-emitting element column 1301 and the second light-emitting element column 1302 are arranged in parallel. The rod lens array 12 concentrates the light from each light-emitting element 131 in the first and second light-emitting element columns 1301 and 1302 onto the photosensitive drum 17. Thus, image rows corresponding to the emission of the light-emitting elements 131 are formed on the photosensitive drum 17. Furthermore, in this embodiment, the case where the print head 1 has multiple light-emitting element columns 13 is described, but it is also assumed that the print head 1 has a single light-emitting element column 13. Additionally, the print head 1 includes a spacer 121. The spacer 121 maintains a predetermined distance between the transparent substrate 11 and the photosensitive drum 17.

[0033] Figure 2 This is a diagram showing an example of a transparent substrate constituting the printhead according to the embodiment.

[0034] like Figure 2 As shown, two rows of light-emitting elements 13 (a first row of light-emitting elements 1301 and a second row of light-emitting elements 1302) are formed along the long side of the transparent substrate 11 at the center. Near the rows of light-emitting elements 13, rows of driving circuits 14 (a first driving circuit 1401 and a second driving circuit 1402) are formed for driving (emitting light) each light-emitting element. Hereinafter, "driving" will be referred to as "DRV". Figure 2 In this configuration, DRV circuit columns 14 for driving (lighting out) the light-emitting elements are arranged on both sides of the two light-emitting element columns 13, but the DRV circuit columns 14 can also be arranged on one side.

[0035] An IC (Integrated Circuit) 15 is disposed at one 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 transfer. A sealed substrate is mounted on the transparent substrate 11 to prevent the light-emitting element array 13, DRV circuit array 14, and other components from contacting external air. Alternatively, when it is difficult to install the connector to the transparent substrate, an FPC (Flexible Printed Circuit) can be connected to the transparent substrate and electrically connected to the control system.

[0036] Figure 3 This is a diagram illustrating an example of the layout of the light-emitting elements and driving circuitry of the printhead according to the embodiment.

[0037] like Figure 3 As shown, the light-emitting section 10 of the printhead 1 includes a row 13 of light-emitting elements 131 arranged in a plurality of light-emitting elements 131 and a row 14 of drive circuits 140 arranged in a plurality of drive circuits 140. The drive circuits 140 cause the light-emitting elements 131, which are respectively connected based on the signals of the wiring 145 (corresponding to the sample / hold signal 21, the light emission level signal 22, the light emission on (ON) signal 26, and the light emission off (OFF) signal 27 described later), to emit light.

[0038] Figure 4 This is a diagram showing an example of a cross-section of the transparent substrate of the printhead according to the embodiment.

[0039] like Figure 4As shown, the light-emitting portion 10 of the printhead 1 includes a plurality of light-emitting elements 131, a plurality of driving circuits 140, and wiring 145 arranged opposite to the reference surface 1101 of the transparent substrate 11. Additionally, the light-emitting portion 10 includes a sealing glass 1102. The plurality of light-emitting elements 131, the plurality of driving circuits 140, and the wiring 145 are arranged within 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.

[0040] Figure 5 This diagram illustrates an example of the connection between the control board and the printhead according to the embodiment.

[0041] like Figure 5 As shown, the image forming apparatus includes a control board 101, and the control board 101 includes a power supply unit 102. The power supply unit 102 supplies a power supply voltage VDDa to both ends of the print head 1 via a wiring harness 104. The relationship between the number of light-emitting elements 131 and the light intensity reduction rate will be explained below.

[0042] Figure 6 This diagram illustrates an example of the structure of the light-emitting element of the printhead according to the embodiment. Furthermore, in Figure 6 In the text, the sealing glass 1102 is omitted.

[0043] For example, the light-emitting element 131 is an organic EL (Organic Electroluminescence). (e.g.) Figure 6 As shown, the light-emitting element 131 includes a hole transport layer 1311, a light-emitting layer 1312, and an electron transport layer 1313, and is sandwiched in contact with electrodes (+) 1321 and (-) 1323, which are insulated by an insulating layer 1322. Furthermore, in the first embodiment, the light-emitting layer 1312 is, for example, an organic EL. The electrode (-) 1323 has a structure that reflects the light emitted by the light-emitting layer 1312. With this structure, the light emitted by the light-emitting layer 1312 is output to the transparent substrate 11 side.

[0044] Figure 7 This is a diagram illustrating an example of a circuit configuration including a DRV circuit for driving the light-emitting element according to the embodiment, a light-emitting element that emits light based on the DRV circuit, and a switch for switching the current supply to the light-emitting element.

[0045] The DRV circuit is constructed from low-temperature polysilicon thin-film transistors. The sample / hold signal 21 becomes "L" level when it causes a change in the luminous intensity of the light-emitting element 131 connected to the DRV circuit 140. When the sample / hold signal 21 becomes "L", the voltage of capacitor 142 changes according to the voltage of the luminous level signal 22. That is, capacitor 142 maintains a potential that changes according to the correction data described later.

[0046] When the sample / hold signal 21 is "H", the voltage of capacitor 142 is maintained. Even if the voltage of the light emission level signal 22 changes, the voltage level of capacitor 142 remains unchanged. A current corresponding to the voltage maintained in capacitor 142 flows through the light-emitting element 131, which is connected to signal line I of the DRV circuit 140. That is, the light-emitting element 131 emits light according to the potential of the capacitor. By using the sample / hold signal 21, a predetermined light-emitting element 131 can be selected from the plurality of light-emitting elements 131 included in the light-emitting element row 13, and the light emission intensity can be determined and maintained according to the light emission level signal 22.

[0047] Additionally, a switch 144 is connected to the DRV circuit 140. Switch 144 toggles the supply of current to the light-emitting element 131 (current supply on or off). When switch 144 is closed based on the light-on signal 26, current flows through the light-emitting element 131, causing it to emit light. When switch 144 is opened based on the light-off signal 27, no current flows through the light-emitting element 131, causing it to turn off.

[0048] Figure 8 This is a diagram illustrating an example of the head circuit block of the printhead according to the embodiment.

[0049] like Figure 8 As shown, the light-emitting unit 10 includes a head circuit block comprising IC 15. IC 15 includes a light-emitting element address counter 151, a decoder 152, a D / A (digital to analog) conversion circuit 153, a light intensity correction memory 154, and a light emission on / off indicator circuit 155, etc. These components supply the previously described sample / hold signal 21, light emission level signal 22, light emission on signal 26, and light emission off signal 27 to the DRV circuit 140, etc.

[0050] like Figure 8 As shown, each DRV circuit 140 is connected to a light-emitting element 131. Each independent DRV circuit 140 supplies an independent current to its own independent light-emitting element 131. A D / A conversion circuit 153 is connected to the first DRV circuit column 1401 connected to the first light-emitting element column 1301. Similarly, a D / A conversion circuit 153 is connected to the DRV circuit column 1402 connected to the second light-emitting element column 1302.

[0051] The light intensity correction memory 154 stores correction data corresponding to the current flowing through each light-emitting element 131. A horizontal synchronization signal 24 and an image data writing clock C are input to the light-emitting element address counter 151 via connector 16. The horizontal synchronization signal 24 resets the count value of the light-emitting element address counter 151. The light-emitting element address counter 151 displays a light-emitting element address signal 25 synchronized with the image data writing clock C.

[0052] The light intensity correction memory 154 receives an input light source address signal 25 from image data 31 and an output light source address counter 151. The decoder 152 receives the light source address signal 25 from the output light source address counter 151. The decoder 152 outputs a sample / hold signal 21 corresponding to the light source 131 specified by the light source address signal 25. The light intensity correction memory 154 outputs correction data 33 corresponding to the light source 131 specified by the light source address signal 25. The D / A conversion circuit 153 receives the correction data 33 output from the light intensity correction memory 154. The D / A conversion circuit 153 outputs a voltage of the light emission level signal 22 based on the correction data 33. The voltage of the light emission level signal 22 is sampled and held in capacitor 142 of the DRV circuit 140. Sampling and holding of capacitor 142 is performed periodically.

[0053] [Composition of the image forming apparatus]

[0054] Figure 9 This is a diagram illustrating an example of an image forming apparatus using the printhead described in the first embodiment. Figure 9 This is an example of a color image forming apparatus with four connected in series. The printhead 1 of this embodiment can also be applied to a monochrome image forming apparatus.

[0055] like Figure 9 As shown, for example, the image forming apparatus 100 includes an image forming component 1021 for forming a yellow (Y) image, an image forming component 1022 for forming a magenta (M) image, an image forming component 1023 for forming a cyan (C) image, and an image forming component 1024 for forming a black (K) image. The image forming components 1021, 1022, 1023, and 1024 form yellow, cyan, magenta, and black images respectively, and transfer them to a transfer belt 103. Thus, a full-color image is formed on the transfer belt 103.

[0056] The image forming assembly 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 assembly 1021 includes a charger 1121, a printhead 1001, a developer 1131, a transfer roller 1141, and a 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.

[0057] The image forming assembly 1022, which forms a magenta (M) image, includes a printhead 1002, which includes a light-emitting unit 1012 and a rod lens array 1202. Furthermore, the image forming assembly 1022 includes a charger 1122, a printhead 1002, a developer 1132, a transfer roller 1142, and a 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.

[0058] The image forming assembly 1023, which forms a cyan (C) image, includes a printhead 1003, which includes a light-emitting unit 1013 and a rod lens array 1203. Furthermore, the image forming assembly 1023 includes a charger 1123, a printhead 1003, a developer 1133, a transfer roller 1143, and a cleaner 1163 around a photosensitive drum 1703. The printhead 1003 corresponds to printhead 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.

[0059] The image forming assembly 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 assembly 1024 includes a charger 1124, a printhead 1004, a developer 1134, a transfer roller 1144, and a 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.

[0060] Chargers 1121, 1122, 1123, and 1124 uniformly charge photosensitive drums 1701, 1702, 1703, and 1704, respectively. Printheads 1001, 1002, 1003, and 1004 expose each photosensitive drum 1701, 1702, 1703, and 1704 by the light emission of light-emitting elements 131 in the first light-emitting element column 1301 and the second light-emitting element column 1302, respectively, and form electrostatic latent images on the photosensitive drums 1701, 1702, 1703, and 1704. The developer 1131 applies (develops) yellow toner to the electrostatic latent image portion of the photosensitive drum 1701, the developer 1132 applies magenta toner to the electrostatic latent image portion of the photosensitive drum 1702, the developer 1133 applies cyan toner to the electrostatic latent image portion of the photosensitive drum 1703, and the developer 1134 applies black toner to the electrostatic latent image portion of the photosensitive drum 1704.

[0061] Transfer rollers 1141, 1142, 1143, and 1144 transfer the toner image developed on photosensitive drums 1701, 1702, 1703, and 1704 to transfer belt 103. Cleaners 1161, 1162, 1163, and 1164 remove any untransferred toner residue from photosensitive drums 1701, 1702, 1703, and 1704, preparing the drums for the next image formation.

[0062] The first-size (small-size) paper (image forming medium) 201 is contained in the paper box 1171, which serves as a paper supply mechanism. The second-size (large-size) paper (image forming medium) 202 is contained in the paper box 1172, which serves as a paper supply mechanism.

[0063] In the paper 201 or 202 taken from paper trays 1171 or 1172, a toner image is transferred from the transfer belt 103 by a transfer roller 118, which serves as a transfer mechanism. The paper 201 or 202 with the toner image transferred is heated and pressurized by the fixing roller 120 of the fixing unit 119. Through the heating and pressing of the fixing roller 120, the toner image is firmly fixed to the paper 201 or 202. By repeating the above processing steps, the image forming operation is carried out continuously.

[0064] Figure 10 This is a block diagram illustrating an example of a control system for an image forming apparatus according to an embodiment.

[0065] like Figure 10As shown, the image forming apparatus 100 includes a control board 101. The control board 101 includes a power supply unit 102, 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 deviation sensor 181 and a mechanical control driver 182. Additionally, the image forming unit 173 includes image forming components 1021, 1022, 1023, and 1024. The power supply unit 102 supplies driving voltage to both ends of the printheads 1001, 1002, 1003, and 1004 of the image forming unit 173 via the wiring harness 104.

[0066] The controller 174 is connected to a ROM 175, RAM 176, non-volatile memory 177, communication I / F 178, control panel 179, color deviation sensor 181, mechanical control driver 182, and light-emitting controller 183.

[0067] 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 the forms Y, M, C, or K, respectively. A light-emitting controller 183 is connected to page memories 1801, 1802, 1803, and 1804, and receives image data 31 in the forms Y from page memory 1801, M from page memory 1802, C from page memory 1803, and K from page memory 1804. Printheads 1001, 1002, 1003, and 1004 are connected to the light-emitting controller 183 corresponding to each image data 31. The light-emitting controller 183 inputs each image data 31 to the print head 1001, 1002, 1003 or 1004 corresponding to each image data 31.

[0068] 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.

[0069] Additionally, the controller 174 inputs image data of the test pattern to page memories 1801, 1802, 1803, and 1804, and forms the test pattern. The color deviation sensor 181 detects the test pattern formed on the transfer belt 103 and outputs a detection signal to the controller 174. Based on the input from the color deviation sensor 181, the controller 174 can identify the positional relationship of the test patterns for each color. Furthermore, the controller 174 selects the paper tray 1171 or 1172 that provides the paper for forming the image via the mechanical control driver 182.

[0070] The ROM175 stores various programs required for controlling the controller 174. These programs include the printhead illumination control program. The illumination control program is a program that controls the timing of illumination and de-illumination (non-illumination) based on image data.

[0071] RAM 176 temporarily stores data required for control by controller 174. Non-volatile memory 177 stores part or all of various programs and various parameters, etc.

[0072] 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 also inputs various information from the outside. For example, the communication I / F 178 acquires image data including multiple image lines. The image forming apparatus 100 prints the image data acquired via the communication I / F 178 using the printing function. The control panel 179 receives operation input from users and service personnel.

[0073] Image reading unit 171 optically reads the image of the original document, acquires image data including 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 on page memories 1801, 1802, 1803, and 1804 in a manner corresponding to the printing position or printhead. 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 light emission (light emission and off states) of each light-emitting element 131 corresponding to the image data.

[0074] The light-emitting controller 183 is composed of one or more processors and controls the light emission of the light-emitting element 131 based on image data according to various programs stored in at least one of the ROM 175 and the non-volatile memory 177. The light-emitting controller 183 includes a light-emitting element quantity detection unit 1831 and a drive voltage controller 1832.

[0075] The light-emitting element quantity detection unit 1831 detects the number of light-emitting elements 131 that emit light according to image data before the light-emitting elements 131 emit light according to the image data. For example, the light-emitting element quantity detection unit 1831 detects the proportion of emitting light-emitting elements in one or more light-emitting element rows. Taking the case where all light-emitting elements 131 in light-emitting element row 13 (first light-emitting element row 1301 and second light-emitting element row 1302) are emitting light as 100%, it detects whether the proportion of emitting light-emitting elements is 20% or less, 40% or less, 60% or less, or 80% or less. Furthermore, the detected proportion is just one example; any proportion can be applied. Additionally, the light-emitting element quantity detection unit 1831 can also detect the number of simultaneously emitting light-emitting elements 131 based on image data and the arrangement position of the emitting light-emitting elements 131 when the emission timing (phase) of the light-emitting elements 131 differs due to their arrangement position in the main scanning direction. Moreover, it can also detect the proportion of emitting light-emitting elements based on the number of simultaneously emitting light-emitting elements 131.

[0076] The drive voltage controller 1832 controls the drive voltage of the drive element 131 based on the detection result of the number of light-emitting elements. That is, the drive voltage controller 1832 controls the drive voltage supplied from the power supply unit 102 to both ends of the print head 1 based on the detection result of the number of light-emitting elements. For example, the drive voltage controller 1832 changes (increases or decreases) the drive voltage supplied to the print head 1 based on the proportion of light-emitting elements.

[0077] [Drive Voltage Control]

[0078] Figure 11 This is a flowchart illustrating an example of drive voltage control based on the embodiment of the image forming apparatus.

[0079] The communication interface 178 receives image data and outputs the received image data. Alternatively, the image reading unit 171 reads the original image and outputs the read image data.

[0080] Controller 174 performs printing based on image data (ACT101, yes).

[0081] For example, when receiving image data corresponding to each color (i.e., in the case of color printing), the image processing unit 172 converts the image data corresponding to each color into raster data and expands the converted raster data to page memories 1801, 1802, 1803, and 1804. Page memories 1801, 1802, 1803, and 1804 output image data corresponding to one row.

[0082] The light-emitting element quantity detection unit 1831 detects the number of light-emitting elements 131 that emit light based on image data corresponding to one row (ACT102). That is, the light-emitting element quantity detection unit 1831 detects the number of light-emitting elements 131 that emit light corresponding to each color. In addition, the drive voltage controller 1832 controls the drive voltage of the light-emitting elements 131 (ACT103 to ACT111) based on the detection result of the number of light-emitting elements 131.

[0083] For example, if the proportion of light-emitting elements 131 is below 20% (first proportion) (ACT103, yes), the drive voltage controller 1832 controls the drive voltage to the reference voltage (VDD) and supplies the reference voltage. If the drive voltage is already controlled to the reference voltage, the drive voltage controller 1832 does not change the drive voltage. If the drive voltage is controlled to be higher than the reference voltage, the drive voltage is reduced to the reference voltage (ACT104).

[0084] If the proportion of light-emitting elements 131 that emit light exceeds 20% (ACT103, No) and is below 40% (second proportion) (ACT105, Yes), the drive voltage controller 1832 changes the drive voltage to a first drive voltage that is 2% higher than the reference voltage and supplies the first drive voltage (ACT106).

[0085] When the proportion of light-emitting elements 131 that emit light exceeds 40% (ACT105, No) and is below 60% (third proportion) (ACT107, Yes), the drive voltage controller 1832 changes the drive voltage to a second drive voltage that is 4% higher than the reference voltage and supplies the second drive voltage (ACT108).

[0086] When the proportion of light-emitting elements 131 that emit light exceeds 60% (ACT107, No) and is below 80% (fourth proportion) (ACT109, Yes), the drive voltage controller 1832 changes the drive voltage to a third drive voltage that is 6% higher than the reference voltage and supplies the third drive voltage (ACT110).

[0087] When the proportion of light-emitting elements 131 exceeds 80% (ACT109, No), the drive voltage controller 1832 controls the drive voltage to a fourth drive voltage that is 8% higher than the reference voltage, and supplies the fourth drive voltage (ACT111).

[0088] The light emission controller 183 repeatedly performs ACT102 to ACT111 from the image data corresponding to the first row to the image data corresponding to the last row. If the light emission control based on the image data corresponding to the last row ends (ACT112, yes) and there is image formation processing for the next page, then the light emission control based on the image data of the next page is executed. If there is no image formation processing for the next page, then the light emission control ends.

[0089] Figure 12 This is a graph showing the relationship between the number of light-emitting elements and the light reduction rate in the driving voltage control according to the embodiment.

[0090] exist Figure 5 The diagram illustrates an example of the connection between the control board and the printhead. Figure 5 The power supply unit 102, as shown, supplies a power supply voltage VDDa to both ends of the print head 1 via the wiring harness 104. As the number of light-emitting elements 131 increases and the current increases, a voltage drop occurs in the wiring harness 104 and within the print head 1. As a result, the power supply voltage VDDa supplied from the power supply unit 102 drops to the power supply voltage VDDb within the print head 1. The larger the voltage drop in the wiring within the print head 1, the higher the proportion of light reduction in the central portion of the light-emitting element row 13 of the print head 1. The higher the illumination rate, the higher the proportion of light reduction. This phenomenon affects the image differently in the main scanning direction and the sub-scanning direction. Figure 12 As shown, the decrease (change) in light intensity along the main scanning direction is smooth regardless of the illumination rate. Therefore, the image density change caused by the change in light intensity along the main scanning direction is not significant. On the other hand, the change in light intensity per row depends on the number of light-emitting elements in that row. Therefore, when rows with fewer light-emitting elements and rows with more light-emitting elements are adjacent, a sharp change in light intensity occurs along the sub-scanning direction. For example, when the difference in light intensity between rows becomes 3% or more, the density difference becomes significant.

[0091] Figure 13 This is a diagram illustrating the relationship between a halftone image (where the number of light-emitting elements is constant) formed by the image forming apparatus according to the embodiment and the voltage and drive current supplied to the print head in relation to the formation of the halftone image.

[0092] like Figure 13As shown, when the number of light-emitting elements 131 that emit light changes at fixed intervals each time an image row is formed, the driving current supplied to the print head 1 also changes at fixed intervals. If the driving current changes at fixed intervals, the voltage supplied to the light-emitting elements 131 also changes at fixed intervals, without changing on a row-by-row basis. If the voltage supplied to the light-emitting elements 131 changes at fixed intervals, the light-emitting elements 131 emit light at a fixed amount of light. If the light-emitting elements 131 emit light at a fixed amount of light, the image density in each image row is fixed (there is no density change in the sub-scanning direction). Furthermore, although a change in light intensity occurs in the main scan direction, as previously explained, its rate of change is very smooth and is at a level that cannot be perceived as a density difference.

[0093] Figure 14 This is a diagram illustrating an example of the drive voltage control involved in the embodiment that should not be used, and a halftone image formed by an image forming apparatus (where the number of light-emitting elements is not fixed depending on the block), and the relationship between the voltage supplied to the print head and the drive current corresponding to the formation of the halftone image. Furthermore, in Figure 14 To facilitate understanding, the diagram shows a scenario where the sub-scanning direction is divided into five blocks, from the first to the fifth, and the same image is printed in each block. Figure 14 The first, third, and fifth halftone images and Figure 13 The halftone images are the same. The second and fourth blocks are in... Figure 13 The center of the halftone image is set with a high-printability pure black image, and the pure black area of ​​the fourth block is larger than that of the second block.

[0094] like Figure 14 As shown, when each image block is formed, the second and fourth blocks have pure black areas in the center, thus increasing the number of light-emitting elements 131 and increasing the driving current supplied to the print head 1. When the driving current increases, a voltage drop occurs due to the resistivity of the wiring harness 104 and the wiring within the print head 1, resulting in a decrease in the driving voltage supplied to the light-emitting elements 131. When the driving voltage decreases, the light intensity of the light-emitting elements 131 decreases.

[0095] When the images of the first, third, and fifth blocks are formed, the number of light-emitting elements 131 is the same, therefore the light intensity of the light-emitting elements 131 is also the same, and the image density of the first, third, and fifth blocks becomes equal. When the image of the second block is formed, the number of light-emitting elements 131 corresponding to the pure black in the center of the second block increases, thus increasing the driving current. As the driving current increases, the voltage supplied to the light-emitting elements 131 decreases, and the light intensity of the light-emitting elements 131 decreases. The halftone at both ends of the second block is the same as the halftone of the first, third, and fifth blocks, but the light intensity of the light-emitting elements 131 decreases, thus reducing the halftone image density at both ends. Therefore, although the halftone images at both ends of the second block are the same as the halftone images of the first and third blocks, a density difference is generated at the block boundaries, and different halftones can be observed. When the image of the fourth block is formed, the number of light-emitting elements 131 corresponding to the pure black in the center of the fourth block further increases, thus further increasing the driving current. As the driving current further increases, the voltage supplied to the light-emitting elements 131 further decreases, and the light intensity of the light-emitting elements 131 further decreases. The halftones at both ends of the fourth block are the same as those of the first, third, and fifth blocks, as well as the halftones at both ends of the second block. However, the light intensity of the light-emitting element 131 is further reduced, resulting in a further reduction in the halftone image density at both ends. Therefore, although the halftone images at both ends of the fourth block are the same as those of the third and fifth blocks, a further greater density difference is generated at the block boundaries than in the case of the second block, and different halftones can be observed.

[0096] Therefore, as the number of light-emitting elements 131 increases, the light intensity of the light-emitting elements 131 decreases, resulting in a decrease in image density, and the density change becomes more pronounced at the block boundaries in the sub-scanning direction. Furthermore, depending on the development method, the relationship between the change in light intensity and the change in image density is sometimes inverse.

[0097] Figure 15 This is an application example of the drive voltage control involved in the implementation method. It is a diagram illustrating the relationship between a halftone image formed by an image forming apparatus (where the number of light-emitting elements is not fixed depending on the block) and the voltage and drive current supplied to the print head in relation to the formation of the halftone image.

[0098] like Figure 15 As shown, whenever an image row is formed, the drive voltage controller 1832 adjusts the voltage supplied to the print head 1 according to the number of light-emitting elements 131. Whenever an image row is formed, if there are many light-emitting elements 131, the drive voltage controller 1832 increases the supplied voltage to compensate for the voltage drop caused by the increased current and wiring resistance. When the voltage drop is suppressed, the light intensity drop is also suppressed (light intensity difference suppressed to below 3%), making density fluctuations less noticeable.

[0099] For example, when forming the first, third, and fifth images, if the proportion of light-emitting elements 131 exceeds 20% but is less than 40%, the drive voltage controller 1832 changes the drive voltage to a drive voltage 2% higher than the reference voltage. When forming the second image, if the proportion of light-emitting elements 131 exceeds 40% but is less than 60%, the drive voltage controller 1832 changes the drive voltage to a drive voltage 4% higher than the reference voltage. When forming the fourth image, if the proportion of light-emitting elements 131 exceeds 80%, the drive voltage controller 1832 changes the drive voltage to a drive voltage 8% higher than the reference voltage.

[0100] Figure 16 This diagram illustrates an example of the effect of suppressing the decrease in light intensity caused by an increase in the voltage of the optical head of the image forming apparatus according to the embodiment. By controlling the driving voltage, the following is obtained: Figure 16 The effect shown.

[0101] Figure 16 This shows the case where the light-emitting element 131, which has the largest light reduction rate, has a lamp luminance of 80% (see reference). Figure 12 An example of changing the drive voltage to 8% higher than the reference voltage. When the drive voltage is the reference voltage, approximately 6% light intensity reduction occurs at the end of printhead 1, and approximately 10% light intensity reduction occurs in the center. (Compared to...) Figure 12 same)

[0102] In contrast, when the drive voltage is changed to a voltage 8% higher than the reference voltage, such as Figure 16 As shown, the light intensity is +2% at the end of printhead 1 and -2% in the center. At the midpoint between the end and the center, the light intensity is ±0%. The drive voltage controller 1832 controls the drive voltage based on the illumination rate (number of light-emitting elements) of the light-emitting element 131, thereby converging the light intensity relative to the reference light intensity (0%) within a predetermined range (±3%), preventing density differences.

[0103] Here, an example of control for an 80% lighting rate is shown, but the same effect can be achieved for other lighting rates.

[0104] Additionally, the control panel 179 can also set the application or non-application of drive voltage control in accordance with the input indicating whether drive voltage control is applied or not. The non-volatile memory 177 stores the setting for the application or non-application of drive voltage control. When drive voltage control is set to be applied, the controller 174 and the light-emitting controller 183 detect the number of light-emitting elements 131 and change the drive voltage accordingly to the ratio of the number of light-emitting elements 131. When drive voltage control is set to be non-application, the controller 174 and the light-emitting controller 183 do not perform drive voltage control corresponding to the ratio of the number of light-emitting elements 131. When drive voltage control is applied, it is possible to prevent… Figure 12 Such a reduction in light and Figure 14 That would reduce image quality. Additionally, the drive voltage can be controlled so that it is not used to suppress power consumption.

[0105] Figure 17 This is a block diagram illustrating a modified example of the control system of the image forming apparatus according to the embodiment. Figure 10 In the control system of the image forming apparatus shown, the light-emitting controller 183 includes a drive voltage controller 1832 that controls the drive voltage of the print head, but... Figure 17 The difference in the control system of the image forming apparatus shown is that the controller 174 includes a drive voltage controller 1741. Figure 17 In the control system of the image forming apparatus shown, before the light-emitting element 131 emits light according to the image data, the light-emitting element quantity detection unit 1831 detects the number of light-emitting elements 131 emitting light according to the image data and outputs the detection result to the drive voltage controller 1741. The drive voltage controller 1741 controls the drive voltage of the light-emitting element 131 based on the detection result from the light-emitting element quantity detection unit 1831.

[0106] Furthermore, the driving voltage control described in the embodiments can be applied to either a monochrome image forming apparatus based on a single printhead or a color image forming apparatus based on printheads corresponding to each color. Additionally, although the case of using software to implement the detection of the number of light-emitting elements and the driving voltage control has been described, it can also be implemented in hardware.

[0107] In the image forming apparatus described above, when the number of transmitting elements that emit light corresponding to each image row increases, the image quality degradation can be suppressed by increasing the driving voltage according to the increase ratio.

[0108] 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. An image forming apparatus comprising: A printhead, comprising one or more rows of light-emitting elements consisting of multiple light-emitting elements; The detection unit detects the number of light-emitting elements that emit light according to the image data before the light-emitting elements emit light according to the image data. The controller controls the driving voltage of the light-emitting element based on the detection results; as well as The power supply unit supplies the driving voltage to the print head. The detection unit detects the proportion of light-emitting elements by using one or more rows of light-emitting elements as units, and sets the case where all the light-emitting elements in the row of light-emitting elements are emitting light as 100%. The controller adjusts the driving voltage supplied to the print head based on the ratio. When the proportion of light-emitting elements exceeding 20% ​​(as a first proportion) is reached, the controller changes the driving voltage from the reference voltage to a first voltage higher than the reference voltage.

2. The image forming apparatus according to claim 1, wherein, When the proportion of light-emitting elements that emit light exceeds a second proportion higher than the first proportion, the controller changes the driving voltage to a second voltage higher than the first voltage.

3. The image forming apparatus according to claim 1, wherein, When the proportion of light-emitting elements is below the first proportion, the controller controls the driving voltage to reach the reference voltage.

4. The image forming apparatus according to claim 1, wherein, The image forming apparatus includes an image forming unit that forms an image based on the light emitted by the print head corresponding to the image data.

5. An image forming apparatus comprising: Multiple printheads, each corresponding to a color, and each printhead includes one or more rows of light-emitting elements composed of multiple light-emitting elements. The detection unit detects the number of light-emitting elements in each printhead that emit light according to the image data corresponding to each color before the light-emitting elements emit light according to the image data. The controller, for each printhead, controls the driving voltage for driving the light-emitting element based on the detection results; and The power supply unit provides the driving voltage to each printhead. The detection unit detects the proportion of light-emitting elements by using one or more rows of light-emitting elements as units, and sets the case where all the light-emitting elements in the row of light-emitting elements are emitting light as 100%. The controller adjusts the driving voltage supplied to the print head based on the ratio. When the proportion of light-emitting elements exceeding 20% ​​(as a first proportion) is reached, the controller changes the driving voltage from the reference voltage to a first voltage higher than the reference voltage.

Images