Image forming apparatus

Abstract

The image forming apparatus includes a photoreceptor, a light-emitting element, a developing device, a fixing device, and a control unit. The photoreceptor is charged. In order to form an electrostatic latent image on the photoreceptor, a plurality of light-emitting elements are provided and form light spots on the photoreceptor by emitting light, and have a first distance from each other in the main scanning direction. The developing device develops the electrostatic latent image on the photoreceptor into a toner image. The fixing device fixes the toner image onto a sheet. After the light-emitting element forms a first light spot on the photoreceptor, the control unit moves the photoreceptor relative to the light-emitting element by a second distance smaller than the first distance in the sub-scanning direction orthogonal to the main scanning direction, and then the light-emitting element forms a second light spot on the photoreceptor.

Description

Technical Field

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

[0002] In recent years, in image forming apparatuses that form images on paper, small exposure devices typified by LEDs (Light Emitting Diodes) have been widely used.

[0003] LED print heads have a complex structure and are limited in terms of positional accuracy and the like because they are manufactured by arranging chips. Therefore, exposure devices using organic EL (Electroluminescence) that can be manufactured by cutting out from a large area panel have attracted attention.

[0004] The shorter the life of an organic EL light emitting element is when the amount of light per unit area during light emission is larger. Therefore, the area of the organic EL light emitting element is formed larger than that of the LED light emitting element.

[0005] However, if the area of the organic EL light emitting element is simply increased, the light spot formed on the photoreceptor also increases, and the reproducibility of isolated points and thin lines decreases. Summary of the Invention

[0006] An image forming apparatus according to an embodiment includes: a charged photoreceptor; a plurality of light emitting elements that form electrostatic latent images on the photoreceptor by emitting light and have a first distance from each other in a main scanning direction; a developing device that develops the electrostatic latent image on the photoreceptor into a toner image; a fixing device that fixes the toner image to paper; and a control unit that, after causing the light emitting elements to form a first light spot on the photoreceptor, moves the photoreceptor relative to the light emitting elements by a second distance smaller than the first distance in a sub-scanning direction orthogonal to the main scanning direction, and then causes the light emitting elements to form a second light spot on the photoreceptor. Brief Description of the Drawings

[0007] Figure 1 The figure which shows an example of the positional relationship between the photoreceptor and the print head used for the image forming apparatus which concerns on one Embodiment.

[0008] Figure 2 The figure which shows an example of the transparent substrate of the print head which comprises this image forming apparatus.

[0009] Figure 3 The figure which shows an example of the light emitting element array of this image forming apparatus.

[0010] Figure 4This is a diagram showing an example of the image forming apparatus.

[0011] Figure 5 This is a block diagram showing an example of the control system of the image forming apparatus.

[0012] Figure 6 This is a diagram showing the correspondence between the exposure position and the light spots of the photoreceptor in the image forming apparatus.

[0013] Figure 7 This is a diagram showing the correspondence between the exposure position and the light spots of the photoreceptor in the image forming apparatus.

[0014] Figure 8 This is a diagram showing the correspondence between the exposure position and the light spots of the photoreceptor in the image forming apparatus.

[0015] Figure 9 This is a flowchart showing an example of the light emission control and image formation in the image forming apparatus. Detailed Embodiment

[0016] The image forming apparatus includes a photoreceptor, a light emitting element, a developing device, a fixing device, and a control unit. The photoreceptor is charged. In order to form an electrostatic latent image on the photoreceptor, the light emitting element forms light spots on the photoreceptor by emitting light, and a plurality of light emitting elements are arranged with a first distance from each other in the main scanning direction. The developing device develops the electrostatic latent image on the photoreceptor into a toner image. The fixing device fixes the toner image on the paper. After the control unit makes the light emitting element form a first light spot on the photoreceptor, the control unit moves the photoreceptor relative to the light emitting element by a second distance smaller than the first distance in the sub-scanning direction orthogonal to the main scanning direction, and then makes the light emitting element form a second light spot on the photoreceptor.

[0017] Hereinafter, the embodiments will be described with reference to the accompanying drawings.

[0018] First, with reference to Figures 1 to 5 , the structure of the print head and the image forming apparatus including the print head according to the embodiment will be described. Next, with reference to Figure 6 and Figure 9 , the light emission control of the light emitting element of the print head according to the embodiment will be described.

[0019] [Structure]

[0020] Figure 1 This is a diagram showing an example of the positional relationship between the photoreceptor (image carrier) 111 used in the image forming apparatus 100 according to the embodiment and the print head 1. For example, the image forming apparatus 100 such as a printer, a copier, or a multifunction machine includes Figure 1The photoreceptor 111 shown, and the print head 1 is an organic EL print head using an organic EL light-emitting material, which is disposed opposite to the photoreceptor 111.

[0021] The photoreceptor 111 rotates Figure 1 in the direction of the arrow shown. This rotation direction is referred to as the sub-scanning direction SD. The photoreceptor member 111 is uniformly charged by a charger and is exposed to light from the print head 1, so that the potential of the exposed portion thereof decreases. That is, by controlling the light emission and non-light emission of the print head 1, an electrostatic latent image can be formed on the photoreceptor 111.

[0022] The print head 1 includes a light-emitting portion 10 and a lens array 12. In addition, the light-emitting portion 10 includes a transparent substrate 11. For example, the transparent substrate 11 is a glass substrate that transmits light. An array of light-emitting elements 13, which is composed of, for example, a plurality of light-emitting elements, is formed on the transparent substrate 11. In Figure 1 shows an example in which two columns of a first light-emitting element array (first array) 13L1 and a second light-emitting element array (second array) 13L2 are formed in parallel with each other.

[0023] Figure 2 is a diagram showing an example of the transparent substrate constituting the print head 1 according to the embodiment. As Figure 2 shown, at the central portion on the transparent substrate 11, two light-emitting element arrays 13 (a first light-emitting element array 13L1 and a second light-emitting element array 13L2) are formed along the long side direction of the transparent substrate 11. Near the light-emitting element array 13, a DRV circuit row 14 (a first DRV circuit row 14L1 and a second DRV circuit row 14L2) for driving each light-emitting element (to make it emit light) is formed.

[0024] In Figure 2 DRV circuit rows 14 for driving the light-emitting elements (to make them emit light) are arranged on both sides of the two light-emitting element arrays 13, but the DRV circuit rows 14 may also be arranged on one side.

[0025] An IC (Integrated Circuit) 15 is disposed at the end of the transparent substrate 11. The IC 15 will be described in detail later. In addition, the transparent substrate 11 includes a connector 16. The connector 16 is electrically connected to the control systems of the print head 1 and a printer, a copier, or a multifunction machine. Through this connection, power supply, print head control, transmission of image data, etc. can be performed. A substrate for sealing the light-emitting element array 13, the DRV circuit row 14, etc. so that they do not come into contact with external air is mounted on the transparent substrate 11.

[0026] Figure 3 is a diagram showing an example of the light-emitting element array (two-column head) according to the embodiment. As Figure 3As shown, each light-emitting element array 13 (the first light-emitting element array 13L1 and the second light-emitting element array 13L2) includes a plurality of light-emitting elements 131 arranged along the main scanning direction MD that is perpendicular to the moving direction (sub-scanning direction SD) of the photoreceptor 111. That is, the plurality of light-emitting elements 131 forming the first column of the light-emitting element array 13 and the plurality of light-emitting elements 131 forming the second column of the light-emitting element array 13 are parallel to the main scanning direction MD. The light-emitting element array may also be three columns or more.

[0027] In addition, the light-emitting element 131 is formed, for example, as a rectangle whose width in the main scanning direction MD is larger than the width in the sub-scanning direction SD. The arrangement interval (first distance) D11 between the light-emitting centers of the light-emitting elements 131 is, for example, a pitch (first pitch) of approximately 42.3 μm at a resolution of 600 dpi.

[0028] In addition, the first column of the light-emitting element array 13 and the second column of the light-emitting element array 13 are arranged at an interval of distance D12 with respect to the sub-scanning direction SD. Furthermore, the light-emitting centers of the respective light-emitting elements 131 forming the first column of the light-emitting element array 13 and the light-emitting centers of the respective light-emitting elements 131 forming the second column of the light-emitting element array 13 are arranged to be offset by a predetermined pitch D13 with respect to the main scanning direction MD. For example, the predetermined pitch D13 is 1 / 2 of the arrangement interval D11. Thus, the two light-emitting element arrays 13 are arranged in a staggered manner in the main scanning direction MD and the sub-scanning direction SD.

[0029] When the light-emitting elements 131 of the first column and the second column of the light-emitting element arrays 13 emit light at the same timing, an interleaved exposure pattern is formed on the photoreceptor 111. Regarding the moving direction of the photoreceptor 111, the upstream side is set as the first column and the downstream side is set as the second column. The control unit ( Figure 5 the control unit 174 described later) causes the first column of the light-emitting element array 13 and the second column of the light-emitting element array 13 to emit light at different timings according to the moving speed of the photoreceptor 111 and the distance D12.

[0030] That is, the control unit 174 causes the light-emitting timing of the second column of the light-emitting element array 13 to be delayed by a certain time with respect to the light-emitting timing of the first column of the light-emitting element array 13 according to the moving speed of the photoreceptor 111 and the distance D12. In other words, the control unit 174 outputs the first light-emitting element image data to the first column of the light-emitting element array 13 and outputs the second light-emitting element image data to the second column of the light-emitting element array 13 at different timings according to the moving speed of the photoreceptor 111 and the distance D12. Here, the first light-emitting element image data and the second light-emitting element image data correspond to the image data of one row amount in the main scanning direction. Thus, a latent image is formed on the photoreceptor 111 at a resolution of 1200 dpi.

[0031] Hereinafter, the highest resolution of the pixels that the print head can form is referred to as the print head resolution, and the resolution of the pixels actually formed by the print head by controlling the print head is referred to as the set resolution.

[0032] Accordingly, the control unit 174 can achieve high density of the image by controlling the light emission timing (image data transfer timing) of the plurality of light emitting element arrays 13. In the case of two light emitting element arrays 13, high density of the image can be achieved with a density twice that of each column of light emitting elements 131, and in the case of n (n≥3, n: integer) light emitting element arrays 13, high density of the image can be achieved with a density n times that of each column of light emitting elements 131.

[0033] The lens array 12 focuses the light emitted from the light emitting element 131 to form a light beam. The light beam forms a light spot on the photoreceptor 111. Hereinafter, the light spot refers to the portion exposed by the energy of 1 / e or more of the peak energy of the light beam in the photoreceptor 111. 2 The above energy part.

[0034] The print head 1 is configured such that the width of the light spot formed by one light emitting element 131 in the main scanning direction MD is greater than the arrangement interval D11. That is, the print head 1 is configured such that the width of the light spot of the photoreceptor 111 in the main scanning direction MD is at least the pitch of the resolution of 1 / 2 of the print head resolution.

[0035] Figure 4 It is a diagram showing an example of an image forming apparatus to which the print head according to the present embodiment is applied. Figure 4 It is an example of a four-color tandem type color image forming apparatus, but the print head 1 of the present embodiment can also be applied to a monochrome image forming apparatus.

[0036] As Figure 4 shown, for example, the image forming apparatus 100 includes: an image forming unit 102-Y that forms a yellow (Y) image, an image forming unit 102-M that forms a magenta (M) image, an image forming unit 102-C that forms a cyan (C) image, and an image forming unit 102-K that forms a black (K) image. The image forming units 102-Y, 102-M, 102-C, and 102-K form yellow, magenta, cyan, and black images respectively and transfer them to the transfer belt 103. Accordingly, a full-color image is formed on the transfer belt 103.

[0037] The image forming unit 102-Y includes a charging charger 112-Y, a print head 1-Y, a developing device 113-Y, a transfer roller 114-Y, and a cleaner 116-Y around the photoreceptor 111-Y. The image forming units 102-M, 102-C, and 102-K also have the same structure.

[0038] In addition, in Figure 4 the structure of the image forming unit 102-Y for forming a yellow (Y) image is labeled with the symbol "-Y". The structure of the image forming unit 102-M for forming a magenta (M) image is labeled with the symbol "-M". The structure of the image forming unit 102-C for forming a cyan (C) image is labeled with the symbol "-C". The structure of the image forming unit 102-K for forming a black (K) image is labeled with the symbol "-K".

[0039] The charging chargers 112-Y, 112-M, 112-C, and 112-K uniformly charge the photoreceptors 111-Y, 111-M, 111-C, and 111-K, respectively. The print heads 1-Y, 1-M, 1-C, and 1-K expose the respective photoreceptors 111-Y, 111-M, 111-C, and 111-K by the emission of the light-emitting elements 131 of the respective first light-emitting element arrays 13L1 and second light-emitting element arrays 13L2, and form electrostatic latent images on the photoreceptors 111-Y, 111-M, 111-C, and 111-K. The developers 113-Y, 113-M, 113-C, and 113-K attach yellow toner, magenta toner, cyan toner, and black toner to the electrostatic latent image portions (develop) of the respective photoreceptors 111-Y, 111-M, 111-C, and 111-K, respectively.

[0040] The transfer rollers 114-Y, 114-M, 114-C, and 114-K transfer the toner images developed on the photoreceptors 111-Y, 111-M, 111-C, and 111-K to the transfer belt 103. The cleaners 116-Y, 116-M, 116-C, and 116-K clean the toner remaining untransferred on the photoreceptors 111-Y, 111-M, 111-C, and 111-K, and enter the standby state for the next image formation.

[0041] Sheets (image forming media) P1 of the first size (small size) are accommodated in the paper cassette 117-1 as a paper supply unit. Sheets (image forming media) P2 of the second size (large size) are accommodated in the paper cassette 117-2 as a paper supply unit.

[0042] It is necessary to change the image formation position (image formation range in the main scanning direction MD) according to the paper size. The change of the image formation position will be described in detail later.

[0043] The toner image is transferred from the transfer belt 103 to the paper P1 or P2 taken out from the paper cassette 117-1 or 117-2 by the transfer roller pair 118 serving as a transfer unit. The paper P1 or P2 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 firmly fixed on the paper P1 or P2. By repeating the above processing operations, the image forming operation is continuously performed.

[0044] Figure 5 is a block diagram showing an example of the control system of the image forming apparatus according to the embodiment. As Figure 4 shown, the image forming apparatus 100 includes: an image reading unit 171, an image processing unit 172, an image forming unit 173, a control unit 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 180-Y, 180-M, 180-C, 180-K, a color shift sensor 181, a mechanical control driver 182, and an image data bus 183. In addition, the image forming unit 173 includes: image forming units 102-Y, 102-M, 102-C, and 102-K.

[0045] The ROM 175, the RAM 176, the non-volatile memory 177, the communication I / F 178, the control panel 179, the color shift sensor 181, and the mechanical control driver 182 are connected to the control unit 174.

[0046] The image reading unit 171, the image processing unit 172, the control unit 174, the page memories 180-Y, 180-M, 180-C, and 180-K are connected to the image data bus 183. The print heads 1-Y, 1-M, 1-C, and 1-K are respectively connected to the page memories 180-Y, 180-M, 180-C, and 180-K.

[0047] The control unit 174 is composed of one or more processors and controls operations such as image reading, image processing, and image formation (including the light emission control of light emitting elements) according to various programs stored in at least one of the ROM 175 and the non-volatile memory 177.

[0048] The ROM 175 stores various programs and the like required for the control of the control unit 174.

[0049] The RAM 176 temporarily stores the data required for the control of the control unit 174. The non-volatile memory 177 stores the updated programs and various parameters, etc. In addition, the non-volatile memory 177 may also store a part or all of various programs.

[0050] The mechanical control driver 182 controls the operations of motors, etc. required during printing according to the instructions of the control unit 174. The communication I / F 178 outputs various information to the outside or inputs various information from the outside. For example, the image forming apparatus 100 uses the printing function to print the image data input via the communication I / F. The control panel 179 accepts operation inputs from users and service personnel.

[0051] The image reading unit 171 optically reads the image of the original document to obtain image data, and then outputs the image data to the image processing unit 172. The image processing unit 172 performs various image processes (including correction, etc.) on the image data input via the communication I / F 178 or the image data from the image reading unit 171. The page memories 180-Y, 180-M, 180-C, and 180-K store the image data processed by the image processing unit 172. The control unit 174 controls the image data on the page memories 180-Y, 180-M, 180-C, and 180-K to match the printing position and the print head. The image forming unit 173 forms an image based on the image data stored in the page memories 180-Y, 180-M, 180-C, and 180-K. In addition, the image forming unit 173 includes: print heads 1-Y, 1-M, 1-C, and 1-K.

[0052] In addition, the control unit 174 inputs a test pattern to the page memories 180-Y, 180-M, 180-C, and 180-K to form a test pattern. The color shift sensor 181 detects the test pattern formed on the transfer belt 103 and outputs a detection signal to the control unit 174. The control unit 174 can identify the positional relationship of the test patterns of various colors based on the input of the color shift sensor 181.

[0053] The control unit 174 selects the paper cassette 117-1 or the paper cassette 117-2 that feeds the paper for forming an image through the mechanical control driver 182.

[0054] [Luminescence control]

[0055] Next, with reference to Figures 6 to 8 , a method for controlling the light emission of the light emitting element 131 of the print head 1 when printing pixels at a resolution of 600 dpi in the image forming apparatus 100 will be described.

[0056] Figure 6 This is a reference example, which represents the following example: A 600 dpi print head having light-emitting elements arranged in a line in the main scanning direction forms light spots at the exposure positions on the photoreceptor 111 corresponding to the image data stored in the page memory. Figure 7 and Figure 8 represents the following situation: The print head 1 forms light spots at the exposure positions on the photoreceptor 111 corresponding to the image data stored in the page memory.

[0057] The image forming apparatus 100 can switch Figure 7 the light emission control method (first method) shown in Figure 8 and the light emission control method (second method) shown in

[0058] In the light emission control of the present embodiment, first, the control unit 174 maps the exposure positions to a matrix (pixel matrix) having the number of rows and columns corresponding to the print head resolution based on the image data stored in the page memory, as Figures 6 to 8 shown.

[0059] Next, the control unit 174 causes each light-emitting element arranged in the main scanning direction MD of the print head to correspond to each column arranged in the main scanning direction (row direction) MD of the matrix.

[0060] Next, the control unit 174 reads the exposure positions of each row arranged in the sub-scanning direction (column direction) SD in the matrix.

[0061] Next, the photoreceptor 111 is rotated in the sub-scanning direction SD, and the light-emitting element corresponding to the exposure position emits light at the timing corresponding to the exposure position, and light spots are formed on the photoreceptor 111.

[0062] Figure 6 (A) of Figure 6 represents a state in which only one block of the matrix MX corresponding to 600 dpi becomes an exposure position EP as an isolated point. Figure 6 The (B) of Figure 6 represents the light spot IA on the photoreceptor 111 corresponding to the exposure position EP of (A) of

[0063] Figure 7 In Figure 7 Figure 7 Figure 7 the (A) of Figure 7In [the figure], the print head 1 causes a light-emitting element 131 to emit light twice, and forms a light spot IB on the photoreceptor 111.

[0064] As Figure 7 shown in (B) of [], in the first method, when forming an isolated dot of 600 dpi, after forming the first light spot IB1, the photoreceptor 111 is moved a certain distance (second distance) D2 in the sub-scanning direction SD with respect to the light-emitting element 131, and the second light spot IB2 is formed. The distance D2 is a distance that is 1 / 2 of the arrangement interval D11. The distance D2 only needs to be less than the arrangement interval D11. The light spot IB has an overlapping portion IBO where the first light spot IB1 and the second light spot IB2 overlap.

[0065] Figure 8 (A) of [] shows a state where, in the matrix MX2 corresponding to 1200 dpi, four squares corresponding to the isolated dot of 600 dpi become the exposure positions EP. Figure 8 (B) of [] shows the light spot IC on the photoreceptor 111 corresponding to the exposure position EP of (A) of []. In Figure 8 (A), the print head 1 causes two adjacent light-emitting elements 131 separated by a predetermined pitch D13 in the main scanning direction MD to emit light twice respectively, and forms light spots IC on the photoreceptor 111. Figure 8 In [the figure], the print head 1 causes two adjacent light-emitting elements 131 separated by a predetermined pitch D13 in the main scanning direction MD to emit light twice respectively, and forms light spots IC on the photoreceptor 111.

[0066] As Figure 8 shown in (B) of [], in the second method, when forming an isolated dot of 600 dpi, while moving the photoreceptor 111, a first light spot IC1 and a third light spot IC3 are formed by one light-emitting element 131. In addition, a second light spot IC2 and a fourth light spot IC4 are formed by a light-emitting element 131 that is separated from the light-emitting element 131 forming the first light spot IC1 and the third light spot IC3 by a predetermined pitch D13 in the main scanning direction MD. The first light spot IC1 and the third light spot IC3 are separated by a distance D2 in the sub-scanning direction SD. The second light spot IC2 and the fourth light spot IC4 are separated by a distance D2 in the sub-scanning direction SD. The first light spot IC1 and the second light spot IC2 are formed at the same position in the sub-scanning direction SD. The light spot IC has an overlapping portion ICO where the first light spot IC1, the second light spot IC2, the third light spot IC3, and the fourth light spot IC4 overlap.

[0067] In the first method, the exposure light amount of the light-emitting element 131 for one pixel is twice the exposure light amount of one light-emitting element 131 for one pixel in the second method.

[0068] In the second method, the light amount of one exposure of one light-emitting element 131 for one pixel is 1 / 4 of the exposure light amount of the light-emitting element in a 600-dpi print head for one pixel.

[0069] In the second method, the diameter CD of the light spot IC in the main scanning direction MD is larger than the diameter AD of the light spot IA of an isolated point of a print head with 600 dpi in the main scanning direction MD.

[0070] In the first method, the diameter BD of the light spot IB in the main scanning direction MD is equal to the diameter AD of the light spot IA of an isolated point of a print head with 600 dpi in the main scanning direction MD. In the first method, the total amount of light for exposing one pixel is the same as that in the second method. However, since the diameter BD of the light spot IB is smaller than the diameter CD of the light spot IC in the second method, the reproducibility of isolated points and thin lines is better than that in the second method.

[0071] In the first method, instead of making one light emitting element 131 of the print head 1 emit light twice, it may emit light continuously. In the first method, when making one light emitting element 131 of the print head 1 emit light continuously, the exposure light amount is set to four times the light amount of one exposure of one light emitting element 131 in the second method.

[0072] In the first method and the second method, the light amount of exposure is adjusted by adjusting the light emission duty ratio. The light emission duty ratio can also be adjusted within a range of 5% to 90%. In the first method and the second method, the light amount of exposure can be adjusted by adjusting the light amount of the light beam per unit area of the light emitting element 131.

[0073] In the first method and the second method, the light amount of the light beam required to form a pixel with a resolution of 600 dpi for one pixel of 600 dpi is preferably 50 nW or less.

[0074] Figure 9 It is a flowchart showing the light emission control method of the light emitting element 131 of the print head 1. Figure 9 The shown flowchart represents the process after the exposure position EP in the matrix MX2 is determined.

[0075] In step S11, the control unit 174 reads in the set value of the light emission duty ratio. The set value of the light emission duty ratio can be stored in advance in the ROM 175 or the like, or can be input by the user via the control panel 179 or the like. After the control unit 174 performs the process of step S11, it proceeds to step S12.

[0076] In step S12, the control unit 174 reads the selected value of the set resolution and determines whether the selected value is 1 / 2 of the print head resolution. If the selected value of the set resolution is 1 / 2 of the print head resolution, the control unit 174 proceeds to the following step S13 and performs the light emission control of the first method. The selected value of the set resolution is input by the user via the control panel 179 or the like. If the selected value of the set resolution is equal to the print head resolution, the control unit 174 proceeds to step S19 and performs the light emission control of the second method.

[0077] In step S13, the control unit 174 causes the light emitting elements 131 of the first light emitting element array 13L1 to correspond to every two columns in the sub-scanning direction MD adjacent to the matrix MX2 in the main scanning direction MD, respectively. After performing the process of step S13, the control unit 174 proceeds to step S14.

[0078] In step S14, the control unit 174 reads the exposure position EP of the foremost row in the main scanning direction MD arranged in the sub-scanning direction SD of the matrix MX2. After performing the process of step S14, the control unit 174 proceeds to step S15.

[0079] In step S15, the control unit 174 causes the light emitting elements 131 to emit light to the photosensitive member 111 rotating in the sub-scanning direction MD and forms a light spot IC. If at least any one of the two columns in the sub-scanning direction MD of the matrix MX2 corresponding to the light emitting element 131 is the exposure position EP, the control unit 174 causes the light emitting element 131 to emit light. After performing the process of step S15, the control unit 174 proceeds to step S16.

[0080] In step S16, the control unit 174 determines whether the exposure position EP of the last row in the main scanning direction MD arranged in the sub-scanning direction SD of the matrix MX2 has been read. If the exposure position EP of the last row in the main scanning direction MD has been read, the control unit 174 proceeds to the following step S17 and ends the process. If the exposure position EP of the last row in the main scanning direction MD has not been read, the control unit 174 proceeds to the following step S18.

[0081] In step S18, the control unit 174 reads the exposure position EP of the next row in the main scanning direction MD arranged in the sub-scanning direction SD of the matrix MX2. After performing the process of step S18, the control unit 174 returns to step S15.

[0082] In step S19, the control unit 174 causes the light emitting elements 131 of the first light emitting element array 13L1 and the second light emitting element array 13L2 to correspond to every column in the sub-scanning direction MD arranged in the main scanning direction MD of the matrix MX2, respectively. After performing the process of step S19, the control unit 174 proceeds to step S20.

[0083] In step S20, the control unit 174 reads the exposure position EP of the foremost row in the main scanning direction MD arranged in the sub-scanning direction SD of the matrix MX2. After performing the process of step S20, the control unit 174 proceeds to step S21.

[0084] In step S21, the control unit 174 causes the light-emitting element 131 to emit light to the photoreceptor 111 rotating in the sub-scanning direction MD, and forms a light spot IB. If the column in the sub-scanning direction MD of the matrix MX2 corresponding to the light-emitting element 131 is the exposure position EP, the control unit 174 causes the light-emitting element 131 to emit light. The control unit 174 causes the light emission timing of the second light-emitting element array 13L2 to be delayed by a certain time with respect to the first light-emitting element array 13L1, and causes the light-emitting element 131 to emit light. After performing the process of step S21, the control unit 174 proceeds to step S22.

[0085] In step S22, the control unit 174 determines whether the exposure position EP of the last row in the main scanning direction MD arranged in the sub-scanning direction SD of the matrix MX2 has been read. If the exposure position EP of the last row in the main scanning direction MD has been read, the control unit 174 proceeds to step S17 below and ends the process. If the exposure position EP of the last row in the main scanning direction MD has not been read, the control unit 174 proceeds to step S23 below.

[0086] In step S23, the control unit 174 reads the exposure position EP of the next row in the main scanning direction MD arranged in the sub-scanning direction SD of the matrix MX2. After performing the process of step S23, the control unit 174 returns to step S21.

[0087] As described above, the image forming method according to the present embodiment has a first method in an image forming apparatus, the image forming apparatus having an image carrier to which a toner fixed to paper is attached and a print head, the print head having: a plurality of light-emitting elements arranged in a staggered manner in a main scanning direction and a sub-scanning direction, and a width in the main scanning direction being larger than a width in the sub-scanning direction, and a lens array that focuses light emitted from the light-emitting elements to form a light beam, and exposing the light beam emitted from the lens array at a position where the toner is attached to the image carrier, and making 1 / e of the peak energy of the light beam of one of the light-emitting elements 2The width in the main scanning direction at the light spots of the image carrier where a part of the above energy is exposed is more than the pitch of the resolution that is 1 / 2 of the print head resolution. In the first method, the resolution of the pixels formed at the plurality of light spots is set as the resolution that is 1 / 2 of the print head resolution, and the light emitting elements arranged at the pitch of the resolution that is 1 / 2 of the print head resolution in the main scanning direction respectively correspond to every two columns in the column direction adjacent to each other in the row direction of the pixel matrix corresponding to the print head resolution.

[0088] Alternatively, in the image forming method according to the present embodiment, the amount of light to be exposed is adjusted by changing the light emission duty ratio.

[0089] Alternatively, in the image forming method according to the present embodiment, there is a second method that can be switched with the first method. In the second method, the resolution of the pixels is set as the resolution that is 1 / 2 of the print head resolution, and each of the light emitting elements corresponds to each column in the sub-scanning direction arranged in the main scanning direction of the pixel matrix.

[0090] Alternatively, in the image forming method according to the present embodiment, the print head resolution is 1200 dpi and the resolution of the pixels is 600 dpi.

[0091] Alternatively, in the image forming method according to the present embodiment, the print head resolution is 2400 dpi and the resolution of the pixels is 1200 dpi.

[0092] Alternatively, in the image forming method according to the present embodiment, the amount of light for one-time exposure of one light emitting element is 50 nW or less.

[0093] Alternatively, in the image forming method according to the present embodiment, the light emitting elements are arranged adjacent to each other in the sub-scanning direction and are offset from each other in the main scanning direction by the pitch amount of the print head resolution along the main scanning direction.

[0094] Alternatively, in the image forming method according to the present embodiment, the width of the light emitting element in the main scanning direction is 22 μm or more, and the width in the sub-scanning direction is less than 22 μm.

[0095] Alternatively, in the image forming method according to the present embodiment, the range of the light emission duty ratio is 5% to 90%.

[0096] Alternatively, in the image forming method according to the present embodiment, the width in the main scanning direction of the imaging is 42 μm or more and 68 μm or less.

[0097] According to the image forming apparatus 100, at a set resolution that is 1 / 2 of the print head resolution, one pixel can be formed by one light emitting element 131. Therefore, in the image forming apparatus 100, at a set resolution that is 1 / 2 of the print head resolution, the width of the light spot in the main scanning direction MD can be made the same as that in the case of a print head having a print head resolution that is 1 / 2 of the print head resolution of the image forming apparatus 100. Thus, in the image forming apparatus 100, when the set resolution is 1 / 2 of the print head resolution of the image forming apparatus 100, compared with the case of using a print head having a print head resolution that is 1 / 2 of the print head resolution of the image forming apparatus 100, a decrease in the reproducibility of isolated dots and thin lines can be suppressed.

[0098] Alternatively, in the image forming apparatus, the print head resolution of the print head may be set to 2400 dpi and the set resolution may be set to 1200 dpi.

[0099] [Examples]

[0100] Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples.

[0101] Image forming apparatuses 100 having different widths in the main scanning direction MD of the light emitting element 131 were prepared. Table 1 shows the width of the light spot in the main scanning direction MD for each width in the main scanning direction MD of the light emitting element 131 in the first method and the second method, the quality of unevenness during solid image formation, and the evaluation results of the reproducibility of vertical thin lines with a width of 600 dpi. The reproducibility of vertical thin lines with a width of 600 dpi was evaluated by comparing with vertical thin lines formed by a print head having a general print head resolution of 600 dpi.

[0102] [Table 1]

[0103]

[0104] As can be seen from Table 1, a good solid image can be obtained when the width of the light spot in the main scanning direction MD is approximately 42.3 μm or more (corresponding to a pitch of 600 dpi). The reproducibility of thin lines is good when the width of the light spot in the main scanning direction MD is approximately 63 μm or less (corresponding to a pitch of 400 dpi).

[0105] In addition, as can be seen from Table 1, in the second method, even when the width of the light-emitting element 131 in the main scanning direction MD is increased to 37 μm, the width of the light spot in the main scanning direction MD is 57 μm. It is understood that the element life can be taken into account while maintaining the width of the light spot in the main scanning direction MD to be small.

[0106] According to at least one of the embodiments described above, when 1 / 2 of the printhead resolution of the image forming apparatus 100 is the set resolution, compared with the case of using a printhead with 1 / 2 of the printhead resolution of the image forming apparatus 100 as the printhead resolution, it is possible to further suppress a decrease in the reproducibility of isolated dots and thin lines.

[0107] Although several embodiments have been described, these embodiments are presented only as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other ways, and various omissions, substitutions, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are similarly included in the invention described in the claims and its equivalents.

Claims

1. An image forming apparatus, comprising: a charged photoreceptor; a plurality of light-emitting elements that form light spots on the photoreceptor by emitting light and have a first distance from each other in a main scanning direction in order to form an electrostatic latent image on the photoreceptor; a developing device that develops the electrostatic latent image on the photoreceptor into a toner image; a fixing device that fixes the toner image onto a sheet; and a control unit that, after causing the light-emitting elements to form a first light spot on the photoreceptor, moves the photoreceptor relative to the light-emitting elements by a second distance smaller than the first distance in a sub-scanning direction orthogonal to the main scanning direction, and then causes the light-emitting elements to form a second light spot on the photoreceptor, the plurality of light-emitting elements are arranged in a first pitch in the main scanning direction to form a first array, and the first pitch has the same length as the first distance, the image forming apparatus further includes a second array disposed at a predetermined interval from the first array, and the second array includes light-emitting elements arranged in the first pitch in the main scanning direction, the second array includes a plurality of light-emitting elements having light-emitting centers at positions where the light-emitting centers of the plurality of light-emitting elements included in the first array do not overlap in the main scanning direction or in the sub-scanning direction, the control unit delays the light-emitting timing of the second array relative to the first array by a certain time according to the moving speed of the photoreceptor and the predetermined interval.

2. The image forming apparatus according to claim 1, wherein the second light spot has a portion overlapping with the first light spot.

3. The image forming apparatus according to claim 2, wherein the width of each of the plurality of light-emitting elements in the main scanning direction is longer than the width in the sub-scanning direction.

4. The image forming apparatus according to claim 3, wherein the second distance is half of the first distance.

Images