Optical scanning device and image forming device

Abstract

An optical scanning device and an image forming device use a plurality of prisms with different numbers of faces. The optical scanning device includes a first and a second light source, a first and a second aperture section, and a deflector. The first light source emits a first light beam. The second light source emits a second light beam having an aperture angle relative to the first light beam in the main scanning direction, and is located more upstream in the main scanning direction than the first light source. The first aperture section shapes the first light beam so that the length from the optical axis to the upstream end in the main scanning direction is a first length and the length from the optical axis to the downstream end in the main scanning direction is a second length greater than the first length. The second aperture section shapes the second light beam so that the length from the optical axis to the upstream end in the main scanning direction is a third length and the length from the optical axis to the downstream end in the main scanning direction is a fourth length less than the third length. The deflector deflects the first and second light beams passing through the first and second aperture sections at positions offset in the sub-scanning direction of the same surface.

Description

Technical Field

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

[0002] The image forming device of the electrophotographic method forms an electrostatic latent image on the image plane by scanning the beam. At this time, in order to improve the image quality, the image forming device shapes the cross-sectional shape of the beam through the aperture. The beam shaped by the aperture is reflected by the rotating polygonal mirror and scans the image plane through the scanning optical system. Summary of the invention

[0003] Technical problem that the invention aims to solve

[0004] If an image forming apparatus can use multiple types of polygonal mirrors with different numbers of faces, a housing etc. can be shared, which can reduce costs. However, when the number of faces of a polygonal mirror is increased, vignetting occurs in the beam.

[0005] The technical problem to be solved by the embodiments of the present invention is to provide an optical scanning device and an image forming device that can use multiple types of polygonal mirrors with different numbers of faces.

[0006] Means for solving technical problems

[0007] The optical scanning device of the embodiment includes a first light source, a second light source, a first aperture section, a second aperture section, and a deflector. The first light source emits a first light beam. The second light source emits a second light beam having an aperture angle relative to the first light beam in the main scanning direction, and the second light source is located at a position more upstream of the first light source in the main scanning direction. The first aperture section shapes the shape of the first light beam in such a manner that the length from the optical axis to one end on the upstream side of the main scanning direction becomes a first length, and the length from the optical axis to one end on the downstream side of the main scanning direction becomes a second length greater than the first length. The second aperture section shapes the shape of the second light beam in such a manner that the length from the optical axis to one end on the upstream side of the main scanning direction becomes a third length, and the length from the optical axis to one end on the downstream side of the main scanning direction becomes a fourth length less than the third length. The deflector deflects the first light beam and the second light beam passing through the first aperture section and the second aperture section at positions offset in the sub-scanning direction of the same surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 FIG. 1 is a diagram showing an example of an outline of the configuration of the image forming apparatus according to the embodiment.

[0009] Figure 2 It is shown Figure 1 A diagram showing an example of an outline of the configuration of an image forming unit in FIG.

[0010] Figure 3 It is shown Figure 1 A block diagram showing an example of the circuit configuration of a main part of an image forming apparatus in FIG.

[0011] Figure 4 It is shown Figure 1 FIG. 1 is a diagram of an example of an optical scanning device.

[0012] Figure 5 Yes Figure 1 An example of an optical system of a light scanning device in FIG. 1 is developed on a plane.

[0013] Figure 6 Yes Figure 5 A local enlarged image obtained by locally enlarging the main part.

[0014] Figure 7 Observed from the side Figure 6 The structure obtained by the diagram.

[0015] Figure 8 It is shown Figure 5 FIG. 1 is a diagram of an example of a main scanning aperture.

[0016] Fig. 9 It is shown Figure 5 FIG. 1 is a diagram of an example of a main scanning aperture.

[0017] Fig.10 It is a diagram showing a comparative example of the main scanning aperture.

[0018] Fig.11 This is a diagram for explaining the main scanning aperture.

[0019] Fig.12 This is a diagram for explaining the main scanning aperture.

[0020] Fig.13 This is a diagram for explaining the main scanning aperture.

[0021] Fig.14 This is a diagram for explaining the main scanning aperture.

[0022] Fig.15 This is a diagram for explaining the main scanning aperture.

[0023] Fig.16 This is a diagram for explaining the main scanning aperture.

[0024] Fig.17 This is a diagram for explaining the main scanning aperture.

[0025] Fig.18This is a diagram for explaining the main scanning aperture.

[0026] Fig.19 It is a diagram showing a modified example of the main scanning aperture.

[0027] Fig. 20 It is shown Figure 5 FIG. 1 is a diagram of an example of a main scanning aperture.

[0028] Fig.21 It is shown Figure 5 FIG. 1 is a diagram of an example of a main scanning aperture.

[0029] Fig. 22 It is a diagram showing a modified example of the main scanning aperture.

[0030] Description of Reference Numerals

[0031] 100 ... image forming device; 101 ... printer; 102 ... scanner; 115, 115C, 115K, 115M, 115Y ... image forming unit; 116 ... optical scanning device; 151, 151-7, 151-8 ... polygonal mirror; 152 ... motor; 153 ... light source; 161, 162 ... scanning optical system; 170 ... pre-deflection optical system; 171 ... collimating lens; 172 ... secondary scanning aperture; 173 ... cylindrical lens; 174, 174a, 174b, 174c, 174d, 200, 210, 300 ... main scanning aperture; 175a, 175b, 176a, 176b, 201, 202a, 202b, 221...opening; 220...second main scanning aperture; 222...protrusion; 230...fixing component; 231...groove; 1151...photosensitive drum; 1152...charging unit; 1153...developing unit; 1154...primary transfer roller; 1155...cleaner; 1156...anti-static lamp; 1511...reflecting surface; BY, BM, BC, BK, Ba, Bb, Bc, Bd...beam; OAM, OAY, OAa, OAb, OAc, OAd...optical axis. DETAILED DESCRIPTION

[0032] The following is an explanation of the image forming apparatus according to the embodiment using the accompanying drawings. It should be noted that the scales of the various parts of the drawings used to explain the following embodiment may be appropriately changed. In addition, for the sake of convenience, the drawings used to explain the following embodiment may be shown in a manner that omits the structure.

[0033] Figure 1 FIG. 1 is a diagram showing an example of an outline of the configuration of the image forming apparatus 100 according to the embodiment.

[0034] The image forming apparatus 100 is, for example, an MFP (multifunction peripheral), a copier, a printer, or a fax machine. However, the image forming apparatus 100 is described below as an MFP. The image forming apparatus 100 has, for example, a printing function, a scanning function, a copying function, a decolorizing function, and a fax function. The printing function is a function of forming an image on an image forming medium P, etc., using a recording material such as a toner. The image forming medium P is, for example, a sheet of paper, etc. The scanning function is a function of reading an image from an original on which an image is formed. The copying function is a function of using the printing function to print an image read from an original using the scanning function on the image forming medium P. The decolorizing function is a function of decolorizing an image formed on the image forming medium P using a decolorizable recording material. As an example, the image forming apparatus 100 includes a printer 101, a scanner 102, and an operation panel 103.

[0035] The printer 101 is a device having a printing function and includes, for example, a paper feed tray 111 , a manual paper feed tray 112 , a paper feed roller 113 , a toner cartridge 114 , an image forming unit 115 , an optical scanning device 116 , a transfer belt 117 , a secondary transfer roller 118 , a fixing unit 119 , a double-sided unit 120 , and a paper discharge tray 121 .

[0036] The paper feed tray 111 accommodates image forming media P for printing.

[0037] The manual paper feeding tray 112 is a stand for manually feeding the image forming medium P.

[0038] The paper feed roller 113 is rotated by the action of a motor, thereby feeding the image forming medium P stored in the paper feed tray 111 or the manual paper feed tray 112 out of the paper feed tray 111 or the manual paper feed tray 112 .

[0039] The toner cartridge 114 stores recording materials such as toner to be supplied to the image forming unit 115. The image forming apparatus 100 includes a plurality of toner cartridges 114. Figure 1As shown, the image forming device 100 has four toner cartridges 114, namely, a toner cartridge 114C, a toner cartridge 114M, a toner cartridge 114Y, and a toner cartridge 114K. The toner cartridges 114C, the toner cartridges 114M, the toner cartridges 114Y, and the toner cartridges 114K respectively store recording materials corresponding to the colors of CMYK (cyan, magenta, yellow, and basic colors). That is, the toner cartridge 114C stores recording materials of cyan (C). The toner cartridge 114M stores recording materials of magenta (M). The toner cartridge 114Y stores recording materials of yellow (Y). The toner cartridge 114K stores recording materials of black (K). It should be noted that the colors of the recording materials stored in the toner cartridges 114 are not limited to the colors of CMYK, but may be other colors. In addition, the recording materials stored in the toner cartridges 114 may also be special recording materials. For example, the toner cartridge 114 stores a decolorizable recording material that is decolorized at a temperature higher than a predetermined temperature and becomes invisible.

[0040] The image forming apparatus 100 includes a plurality of image forming units 115. For example, Figure 1 As shown, the image forming apparatus 100 includes four image forming units 115, namely, an image forming unit 115C, an image forming unit 115M, an image forming unit 115Y, and an image forming unit 115K. The image forming unit 115C, the image forming unit 115M, the image forming unit 115Y, and the image forming unit 115K form images using recording materials corresponding to the respective colors of CMYK. That is, the image forming unit 115C forms a cyan image. The image forming unit 115M forms a magenta image. The image forming unit 115Y forms a yellow image. The image forming unit 115K forms a black image.

[0041] use Figure 2 The image forming unit 115 will be further described. Figure 2 1 is a schematic diagram showing an example of an outline of the configuration of the image forming unit 115. As an example, the image forming unit 115 includes a photosensitive drum 1151, a charging unit 1152, a developing unit 1153, a primary transfer roller 1154, a cleaner 1155, and a neutralizing lamp 1156.

[0042] The photosensitive drum 1151 is irradiated with the beam B irradiated from the optical scanning device 116 . As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 1151 .

[0043] The charging unit 1152 charges the surface of the photosensitive drum 1151 with a predetermined positive charge.

[0044] The developing unit 1153 develops the electrostatic latent image on the surface of the photosensitive drum 1151 using the recording material D supplied from the toner cartridge 114 . Thus, an image formed by the recording material D is formed on the surface of the photosensitive drum 1151 .

[0045] The primary transfer roller 1154 is disposed at a position opposite to the photosensitive drum 1151 with the transfer belt 117 interposed therebetween. The primary transfer roller 1154 generates a transfer voltage between the primary transfer roller 1154 and the photosensitive drum 1151. Thus, the primary transfer roller 1154 transfers (primary transfer) the image formed on the surface of the photosensitive drum 1151 onto the transfer belt 117 in contact with the photosensitive drum 1151.

[0046] The cleaner 1155 removes the recording material D remaining on the surface of the photosensitive drum 1151 .

[0047] The anti-static lamp 1156 removes the charge remaining on the surface of the photosensitive drum 1151 .

[0048] The optical scanning device 116 is also called an LSU (laser scanning unit) or the like. The optical scanning device 116 controls the beam B based on the input image data to form an electrostatic latent image on the surface of the photosensitive drum 1151 of each image forming unit 115 under the control of the processor 141. The image data input here is, for example, image data read from an original document or the like by the scanner 102. Alternatively, the image data input here is image data sent from another device or the like and received by the image forming device 100.

[0049] It should be noted that the beam B irradiated by the light scanning device 116 to the image forming unit 115Y is set to beam BY, the beam B irradiated to the image forming unit 115M is set to beam BM, the beam B irradiated to the image forming unit 115C is set to beam BC, and the beam B irradiated to the image forming unit 115K is set to beam BK. Therefore, the light scanning device 116 controls the beam BY according to the Y (yellow) component of the image data. The light scanning device 116 controls the beam BM according to the M (magenta) component of the image data. The light scanning device 116 controls the beam BC according to the C (cyan) component of the image data. The light scanning device 116 controls the beam BK according to the K (key: basic color) component of the image data. The light scanning device 116 will be further described later.

[0050] The transfer belt 117 is, for example, an endless belt, and can rotate by the operation of a roller. The transfer belt 117 rotates to convey the image transferred from each image forming unit 115 to the position of the secondary transfer roller 118 .

[0051] The secondary transfer roller 118 includes two rollers facing each other and transfers (secondary transfer) the image formed on the transfer belt 117 onto the image forming medium P passing through the gap between the secondary transfer rollers 118 .

[0052] The fixing unit 119 heats and pressurizes the image forming medium P to which the image has been transferred. Thus, the image transferred to the image forming medium P is fixed. The fixing unit 119 includes a heating unit 1191 and a pressure roller 1192 facing each other.

[0053] The heating unit 1191 is, for example, a roller provided with a heat source for heating the heating unit 1191. The heat source is, for example, a heater. The roller heated by the heat source heats the image forming medium P.

[0054] Alternatively, the heating section 1191 may be a component having an endless belt hung on a plurality of rollers. For example, the heating section 1191 includes a plate-shaped heat source, an endless belt, a belt conveyor roller, a tensioning roller, and a pressure roller. The endless belt is, for example, a film-shaped component. The belt conveyor roller drives the endless belt. The tensioning roller applies tension to the endless belt. The pressure roller has an elastic layer formed on its surface. The heat generating portion side of the plate-shaped heat source contacts the inner side of the endless belt and is pressed in the direction of the pressure roller, thereby forming a fixing roller gap of a predetermined width between the plate-shaped heat source and the pressure roller. Since the plate-shaped heat source is configured to heat while forming the roller gap area, its responsiveness when powered on is higher than that in the case of heating by a halogen lamp.

[0055] The pressure roller 1192 presses the image forming medium P passing between the pressure roller 1192 and the heating unit 1191 .

[0056] The double-side unit 120 enables printing on the back side of the image forming medium P. For example, the double-side unit 120 reverses the image forming medium P by using rollers or the like to turn the front side and the back side of the image forming medium P.

[0057] The paper discharge tray 121 is a platform from which the image-formed medium P after printing is discharged.

[0058] The scanner 102 is a device having a scanning function. The scanner 102 is, for example, an optical reduction method having an imaging element such as a CCD (charge-coupled device) image sensor. Alternatively, the scanner 102 is a contact sensor (CIS (contact image sensor)) method having an imaging element such as a CMOS (complementary metal-oxide-semiconductor) image sensor. Alternatively, the scanner 102 may be other known methods. The scanner 102 reads an image from a manuscript or the like. The scanner 102 includes a reading module 131 and a manuscript conveying device 132.

[0059] The reading module 131 converts the incident light into a digital signal through an image sensor, thereby reading an image from the surface of the document.

[0060] The document conveying device 132 is also called ADF (auto document feeder) or the like. The document conveying device 132 continuously conveys the document placed on the document tray. The image of the conveyed document is read by the scanner 102. In addition, the document conveying device 132 may also include a scanner for reading an image from the back side of the document. It should be noted that the surface on which the image is read by the scanner 102 is the front side.

[0061] The operation panel 103 includes a human-machine interface and the like for performing input and output between the image forming apparatus 100 and an operator of the image forming apparatus 100. The operation panel 103 includes, for example, a touch panel 1031 and an input device 1032.

[0062] The touch panel 1031 is a component formed by stacking a display such as a liquid crystal display or an organic EL display and a pointing device based on touch input. The display provided in the touch panel 1031 functions as a display device that displays a screen for notifying the operator of the image forming apparatus 100 of various information. In addition, the touch panel 1031 functions as an input device that receives touch operations performed by the operator.

[0063] The input device 1032 receives an operation performed by an operator of the image forming apparatus 100. The input device 1032 is, for example, a keyboard, a keypad, or a touch panel.

[0064] Next, use Figure 3 The main circuit configuration of the image forming apparatus 100 will be described. Figure 3 1 is a block diagram showing an example of the circuit configuration of the main parts of the image forming apparatus 100. As an example, the image forming apparatus 100 includes a processor 141, a ROM (read-only memory) 142, a RAM (random-access memory) 143, an auxiliary storage device 144, a communication interface 145, a printer 101, a scanner 102, and an operation panel 103. In addition, a bus 146 or the like connects these parts.

[0065] The processor 141 is equivalent to the central part of the computer that performs the calculation and control required for the operation of the image forming device 100. The processor 141 controls various parts for realizing various functions of the image forming device 100 based on the programs such as system software, application software and firmware stored in the ROM 142 or the auxiliary storage device 144. It should be noted that part or all of the program can also be incorporated into the circuit of the processor 141. The processor 141 is, for example, a CPU (central processing unit), an MPU (micro processing unit), an SoC (system on a chip), a DSP (digital signal processor), a GPU (graphics processing unit), an ASIC (application specific integrated circuit), a PLD (programmable logic device) or an FPGA (field-programmable gate array). Alternatively, the processor 141 is a combination of multiple of these.

[0066] ROM 142 is equivalent to the main storage device of the computer with processor 141 as the core. ROM 142 is a non-volatile memory dedicated to data reading. ROM 142 stores the above-mentioned programs such as firmware. In addition, ROM 142 stores data or various setting values ​​used by processor 141 when performing various processes.

[0067] RAM 143 is equivalent to the main storage device of the computer with processor 141 as the core. RAM 143 is a memory for reading and writing data. RAM 143 is used as a so-called working storage area for storing data temporarily used when processor 141 performs various processes in advance. RAM 143 is, for example, a volatile memory.

[0068] The auxiliary storage device 144 is equivalent to the auxiliary storage device of the computer with the processor 141 as the core. The auxiliary storage device 144 is, for example, an EEPROM (electric erasable programmable read-only memory), an HDD (hard disk drive), an SSD (solid state drive) or an eMMC (embedded MultiMediaCard). The auxiliary storage device 144 stores the above-mentioned programs, such as system software and application software. In addition, the auxiliary storage device 144 saves the data used by the processor 141 when performing various processes, the data generated by the processing in the processor 141, or various setting values. It should be noted that the image forming device 100 can also have an interface that can insert a storage medium such as a memory card or a USB (universal serial bus) memory as an auxiliary storage device 144. The interface reads and writes information to the storage medium.

[0069] The communication interface 145 is an interface for the image forming apparatus 100 to communicate via a network or the like.

[0070] The bus 146 includes a control bus, an address bus, a data bus, and the like, and transmits signals transmitted and received in each unit of the image forming apparatus 100 .

[0071] Next, use Figures 4 to 7 The optical scanning device 116 will be further described. Figure 4 1 is a diagram showing an example of the optical scanning device 116 . Figure 5 This is a diagram in which an example of the optical system of the optical scanning device 116 is developed on a plane. Figure 6 Yes Figure 5 A local enlarged image obtained by locally enlarging the main part. Figure 7 Observed from the side Figure 6 As an example, the optical scanning device 116 includes a polygon mirror 151, a motor 152, a light source 153, and a plurality of optical elements.

[0072] The polygon mirror 151 is a regular polygonal cylindrical mirror (deflector) whose side surfaces are reflection surfaces 1511 for reflecting laser light. Figures 4 to 7 The polygonal mirror 151 shown is a regular seven-sided cylindrical mirror having seven side surfaces (reflection surfaces 1511). The reflection surfaces 1511 of the polygonal mirror 151 are arranged along the rotation direction CCW ( Figure 5The polygonal mirror 151 is continuous with the photosensitive drum 1151 in the counterclockwise direction and constitutes the outer peripheral surface of the polygonal mirror 151. The polygonal mirror 151 can rotate around a rotation axis parallel to each reflection surface 1511. In addition, the rotation axis of the polygonal mirror 151 is orthogonal to the rotation axis of each photosensitive drum 1151. It should be noted that Figure 6 The paper plane is a plane perpendicular to the rotation axis of the polygonal mirror 151.

[0073] The optical scanning device 116 can be equipped with a plurality of types of polygonal mirrors 151 having different numbers of reflection surfaces 1511. For example, in addition to Figures 4 to 7 The light scanning device 116 may also be equipped with a regular heptagonal polygonal prism 151 having a regular octagonal polygonal prism 151 with a reflection surface 1511 having 8 faces. In addition, the light scanning device 116 may also be equipped with a polygonal prism 151 with a face number of less than 6 or more than 9. However, preferably, the polygonal prisms 151 installed in the light scanning device 116 all have the same inscribed circle radius and the same rotation axis. This is because, by using the polygonal prisms 151 with the same inscribed circle radius and the same rotation axis, regardless of the number of faces of the polygonal prism, the same face can be used for reflection without changing the optical path length of the beam B, thereby suppressing the focus position change on the image plane.

[0074] It should be noted that, when it is necessary to distinguish the number of faces of the prism 151, the prism 151 with 7 faces is referred to as prism 151-7, and the prism 151 with 8 faces is referred to as 151-8, and like this, "-number of faces" is added at the end.

[0075] The motor 152 rotates the polygon mirror 151 in the rotation direction CCW at a predetermined speed. As an example, the rotation axis of the motor 152 and the rotation axis of the polygon mirror 151 are coaxial. However, the rotation axis of the motor 152 and the rotation axis of the polygon mirror 151 may not be coaxial.

[0076] The light source 153 emits a beam B such as a laser. The light source 153 includes, for example, a plurality of laser diodes. That is, the beam B is a multi-beam composed of beams emitted from a plurality of laser diodes. It should be noted that the plurality of laser diodes maintain a distance in the main scanning direction. Therefore, the beams included in the beam B also maintain a distance in the main scanning direction. As an example, the optical scanning device 116 includes four light sources 153, namely, a light source 153C, a light source 153M, a light source 153Y, and a light source 153K. For example, the light source 153Y emits a beam BY corresponding to the Y component, the light source 153M emits a beam BM corresponding to the M component, the light source 153C emits a beam BC corresponding to the C component, and the light source 153K emits a beam BK corresponding to the K component.

[0077] The optical scanning device 116 irradiates each beam B onto the surface of each photosensitive drum 1151 through an optical path formed by a predetermined scanning optical system set according to each beam B. The scanning optical system includes a plurality of optical elements. Figure 4 and Figure 5 As shown in FIG. 1 , two beams B are set as one group, and a scanning optical system is arranged on the left and right sides of the polygon mirror 151. In other words, Figure 4 and Figure 5 As shown, the optical scanning device 116 is centered on a single polygonal prism 151, and has two scanning optical systems 161 and a scanning optical system 162, each of which includes a plurality of optical elements, on both sides (left and right sides in the figure). It should be noted that the polygonal prism 151 is included in each of the scanning optical system 161 and the scanning optical system 162. That is, the polygonal prism 151 included in each of the scanning optical system 161 and the scanning optical system 162 is the same polygonal prism 151.

[0078] The scanning optical system 161 on the left side of the figure includes a scanning optical system for scanning the beam BY and a scanning optical system for scanning the beam BM. The scanning optical system 161 uses the same reflection surface 1511 of the polygonal mirror 151 rotating in the rotation direction CCW to reflect the beam BY emitted from the light source 153Y and the beam BM emitted from the light source 153M. As a result, the beam BY and the beam BM are deflected in the main scanning direction along the rotation direction CCW, and scan the surfaces of the two photosensitive drums 1151Y and the photosensitive drum 1151M respectively. The scanning optical system 161 includes the polygonal mirror 151, the light source 153Y, the light source 153M, the pre-deflection optical system 170Y, the pre-deflection optical system 170M, and the post-deflection optical system 180YM. It should be noted that the pre-deflection optical system 170Y is an optical system for the beam BY. In addition, the pre-deflection optical system 170M is an optical system for the beam BM. Furthermore, the post-deflection optical system 180YM is an optical system for the beam BY and the beam BM.

[0079] It should be noted that beam BY is an example of a first light beam. In addition, beam BM is an example of a second light beam. Furthermore, light source 153Y that emits beam BY as a first light beam is an example of a first light source. Light source 153M that emits beam BM as a second light beam is an example of a second light source.

[0080] It should be noted that, here, the direction in which each beam B is deflected (scanned) by the polygonal mirror 151 as a deflector (the circumferential direction of the polygonal mirror 151) is defined as the "main scanning direction". In addition, the direction perpendicular to the main scanning direction and perpendicular to the optical axis direction of the beam B is defined as the "sub-scanning direction" of the beam B. Figure 5 and Figure 6In FIG. 1 , the rotation axis direction of the polygon mirror 151 is the sub-scanning direction. Figure 5 and Figure 6 In FIG. 1 , a direction that is orthogonal to the rotation axis direction of the polygon mirror 151 and to the optical axis direction of the beam B is a main scanning direction of the beam B. In FIG.

[0081] The scanning optical system 162 on the right side of the figure includes a scanning optical system for scanning the beam BC and a scanning optical system for scanning the beam BK. The scanning optical system 162 uses the same reflection surface 1511 of the polygonal mirror 151 rotating in the rotation direction CCW to reflect the beam BC emitted from the light source 153C and the beam BK emitted from the light source 153K. As a result, the beam BC and the beam BK are deflected in the main scanning direction along the rotation direction CCW, and scan the surfaces of the two photosensitive drums 1151C and 1151K respectively. The scanning optical system 162 includes the polygonal mirror 151, the light source 153C, the light source 153K, the pre-deflection optical system 170C, the pre-deflection optical system 170K, and the post-deflection optical system 180CK.

[0082] It should be noted that the beam BK is an example of a first light beam. In addition, the beam BC is an example of a second light beam. Furthermore, the light source 153K that emits the beam BK as the first light beam is an example of a first light source. The light source 153C that emits the beam BC as the second light beam is an example of a second light source.

[0083] Here, the polygonal mirror 151, the light source 153, and the pre-deflection optical system 170 are further described by taking the scanning optical system 161 on the left side of the figure as an example. The polygonal mirror 151 rotates while reflecting the two beams B, the beam BY emitted from the light source 153Y and the beam BM emitted from the light source 153M, using the same reflection surface 1511. As a result, the two image planes respectively arranged at predetermined positions, that is, the surfaces of the corresponding photosensitive drum 1151Y and the photosensitive drum 1151M are scanned in the main scanning direction (the direction of the rotation axis of the photosensitive drum 1151) at a predetermined linear speed. At this time, the image forming device 100 rotates the photosensitive drum 1151Y and the photosensitive drum 1151M in the sub-scanning direction. As a result, an electrostatic latent image corresponding to the Y component is formed on the surface of the photosensitive drum 1151Y. In addition, an electrostatic latent image corresponding to the M component is formed on the surface of the photosensitive drum 1151M.

[0084] like Figure 5 and Figure 6As shown, the light source 153Y and the light source 153M of the scanning optical system 161 are arranged at different angular positions when viewed from the front side of the paper. That is, the two light sources 153Y and the light source 153M are arranged so that the directions in which the beam BY and the beam BM are incident on the reflecting surface 1511 have an aperture angle θ. In other words, the two light sources 153Y and the light source 153M are arranged so that the beam BY and the beam BM have an aperture angle θ in the main scanning direction. In addition, the light source 153Y of the two light sources 153 is located at a position more downstream than the light source 153M along the rotation direction CCW of the polygonal mirror 151. Relatively speaking, the light source 153M is located at a position more upstream than the light source 153Y along the rotation direction CCW.

[0085] In addition, if Figure 7 As shown in FIG. 1 , the two light sources 153Y and the light source 153M are located at positions slightly offset in the sub-scanning direction. The light source 153M is located at a higher position than the light source 153Y. That is, the light source 153M is located closer to the light source 153Y. Figure 5 and Figure 6 In addition, the optical axes (light traveling directions) of the pre-deflection optical systems 170Y and 170M are orthogonal to the rotation axis 131b of the polygonal mirror 151. Therefore, the beam BY and the beam BM emitted from the light source 153Y and the light source 153M are incident on the same reflecting surface 1511 at positions slightly offset in the sub-scanning direction.

[0086] The scanning optical system 161 is provided with a pre-deflection optical system 170 on the optical path between the light source 153 and the polygonal mirror 151. That is, the scanning optical system 161 is provided with two pre-deflection optical systems 170, namely, a pre-deflection optical system 170Y and a pre-deflection optical system 170M. The pre-deflection optical system 170Y is arranged on the optical path between the light source 153Y and the polygonal mirror 151. The pre-deflection optical system 170M is arranged on the optical path between the light source 153M and the polygonal mirror 151. Each pre-deflection optical system 170 includes a collimating lens 171, a sub-scanning aperture 172, a cylindrical lens 173, and a main scanning aperture 174. The pre-deflection optical system 170Y includes a collimating lens 171Y, a sub-scanning aperture 172Y, a cylindrical lens 173Y, and a main scanning aperture 174YM. In addition, the pre-deflection optical system 170M includes a collimating lens 171M, a sub-scanning aperture 172M, a cylindrical lens 173M, and a main scanning aperture 174YM. It should be noted that the collimating lens 171Y and the collimating lens 171M are the collimating lens 171. In addition, the sub-scanning aperture 172Y and the sub-scanning aperture 172M are the sub-scanning aperture 172. And, the cylindrical lens 173Y and the cylindrical lens 173M are the cylindrical lens 173. Furthermore, the main scanning aperture 174YM is the main scanning aperture 174 for the beam BY and the beam BM. It should be noted that the main scanning aperture 174YM included in the pre-deflection optical system 170Y and the pre-deflection optical system 170M is the same main scanning aperture 174YM.

[0087] The collimator lens 171 applies a predetermined convergence to the beam B emitted from the light source 153. The collimator lens 171 makes the beam B parallel light.

[0088] The sub-scanning aperture 172 shapes the shape of the beam B that has passed through the collimator lens 171 in the sub-scanning direction. For example, the sub-scanning aperture 172 shapes the width of the beam B in the sub-scanning direction to a predetermined width.

[0089] The cylindrical lens 173 applies a predetermined convergence in the sub-scanning direction to the beam B that has passed through the sub-scanning aperture 172. Thus, the width of the beam B that has passed through the cylindrical lens 173 in the sub-scanning direction becomes narrower as it approaches the reflection surface 1511. Therefore, it is possible for a plurality of beams B to be incident on the same reflection surface 1511 at positions that are offset in the sub-scanning direction without overlapping.

[0090] The main scanning aperture 174 shapes the shape of the beam B passing through the cylindrical lens 173 in the main scanning direction. For example, the sub-scanning aperture 172 shapes the width of the beam B in the main scanning direction to a predetermined width. The main scanning aperture 174 will be further described later. It should be noted that the main scanning aperture 174 is an example of a third aperture.

[0091] Furthermore, the polygonal mirror 151, the light source 153, and the pre-deflection optical system 170 of the scanning optical system 162 shown on the right side of the figure are also explained. The polygonal mirror 151 rotates while reflecting the two beams B, the beam BC emitted from the light source 153C and the beam BK emitted from the light source 153K, using the same reflection surface 1511. As a result, two image planes respectively arranged at predetermined positions, that is, the surfaces of the corresponding photosensitive drum 1151C and the photosensitive drum 1151K are scanned in the main scanning direction (the direction of the rotation axis of the photosensitive drum 1151) at a predetermined linear speed. At this time, the image forming device 100 rotates the photosensitive drum 1151C and the photosensitive drum 1151K in the sub-scanning direction. As a result, an electrostatic latent image corresponding to the C component is formed on the surface of the photosensitive drum 1151C. In addition, an electrostatic latent image corresponding to the K component is formed on the surface of the photosensitive drum 1151K.

[0092] The two light sources 153C and 153K of the scanning optical system 162 are similar to the light sources 153Y and 153M of the scanning optical system 161. Figure 5 and Figure 6 The two light sources 153C and 153K are arranged at different angular positions when observed from the front side of the paper. That is, the two light sources 153C and 153K are arranged so that the directions in which the beams BC and BK are incident on the reflecting surface 1511 have an aperture angle θ. In other words, the two light sources 153C and 153K are arranged so that the beams BC and BK have an aperture angle θ in the main scanning direction. In addition, the light source 153C of the two light sources is located at a position closer to the upstream side than the light source 153K along the rotation direction CCW of the polygonal mirror 151. Relatively speaking, the light source 153K is located at a position closer to the downstream side than the light source 153C along the rotation direction CCW.

[0093] In addition, the light source 153C and the light source 153K are located at slightly different positions in the sub-scanning direction. The light source 153C is located at a higher position than the light source 153K. Therefore, the beam BC and the beam BK emitted from the light source 153C and the light source 153K are incident on the same reflection surface 1511 at slightly different positions in the sub-scanning direction.

[0094] The scanning optical system 162 includes a pre-deflection optical system 170 on the optical path between the light source 153 and the polygonal mirror 151. That is, the scanning optical system 162 includes two pre-deflection optical systems 170, namely, a pre-deflection optical system 170C and a pre-deflection optical system 170K. The pre-deflection optical system 170C is arranged on the optical path between the light source 153C and the polygonal mirror 151. The pre-deflection optical system 170K is arranged on the optical path between the light source 153K and the polygonal mirror 151. The pre-deflection optical system 170C includes a collimating lens 171C, a sub-scanning aperture 172C, a cylindrical lens 173C, and a main scanning aperture 174CK. In addition, the pre-deflection optical system 170K includes a collimating lens 171K, a sub-scanning aperture 172K, a cylindrical lens 173K, and a main scanning aperture 174CK. It should be noted that the collimating lens 171C and the collimating lens 171K are the collimating lens 171. In addition, the sub-scanning aperture 172C and the sub-scanning aperture 172K are the sub-scanning aperture 172. Furthermore, the cylindrical lens 173C and the cylindrical lens 173K are the cylindrical lens 173. Furthermore, the main scanning aperture 174CK is the main scanning aperture 174. It should be noted that the main scanning aperture 174CK included in the pre-deflection optical system 170C and the pre-deflection optical system 170K is the same main scanning aperture 174CK. As described above, the scanning optical system 162 has the same components as the scanning optical system 161.

[0095] Next, the post-deflection optical system 180 is described. The post-deflection optical system 180 guides the beam B reflected by the reflection surface 1511 to the surface of the photosensitive drum 1151. The light scanning device 116 includes two post-deflection optical systems 180, namely, the post-deflection optical system 180YM and the post-deflection optical system 180CK. The post-deflection optical system 180 includes an fθ lens 181, an fθ lens 182, a light detector 183, a return mirror 184, an optical path correction element 185, and return mirrors 186 to 188.

[0096] The fθ lens 181 and the fθ lens 182 are a set of two imaging lenses that optimize the shape and position of the beam B deflected (scanned) by the polygon mirror 151 on the image plane.

[0097] One fθ lens 181 is provided for one post-deflection optical system 180 near the upstream side of the polygonal mirror 151. That is, the fθ lens 181 is located on the optical path of a set of two beams B. And, a set of two beams B pass through the same fθ lens 181. For example, the fθ lens 181YM is located at a position on the optical path of the beam BY and on the optical path of the beam BM. And, the beam BY and the beam BM pass through the fθ lens 181YM.

[0098] exist Figure 5In the figure, for each post-deflection optical system 180, there is an fθ lens 182 located on the downstream side close to the photosensitive drum 1151. Figure 4 As shown, an fθ lens 182 is separately provided on the optical path of each beam B. Figure 5 The fθ lens 182YM shown is Figure 4 The fθ lens 182Y and the fθ lens 182M are collectively shown. Figure 5 The fθ lens 182CK shown is Figure 4 The fθ lens 182C and the fθ lens 182K are collectively shown. It should be noted that the fθ lens 182Y, the fθ lens 182M, the fθ lens 182C, and the fθ lens 182K are the fθ lenses 182. Each beam B passes through the fθ lenses 182 on each optical path. The fθ lenses 182 are respectively located near the third cover glass 193 described later.

[0099] The photodetector 183 is located at the end (scanning position AA and scanning position AB) of the scanning start portion of the beam B. The photodetector 183 is provided to adjust the horizontal synchronization of the beam B that has passed through the fθ lens 181 and the fθ lens 182 .

[0100] The folding mirror 184 is located on the optical path from the fθ lens 182 toward the photodetector 183. The folding mirror 184 reflects the beam B to return the beam B toward the photodetector 183. Figure 5 In FIG. 1 , the optical path of the beam B and the light detector 183 , the reflecting mirror 184 and the optical path correction element 185 on the optical path are unfolded on a plane for illustration.

[0101] The optical path correction element 185 is located on the optical path between the folding mirror 184 and the photodetector 183. The optical path correction element 185 guides the beam B reflected by the folding mirror 184 to the detection surface of the photodetector 183.

[0102] The return mirrors 186 to 188 are a plurality of mirrors that reflect the beam B that has passed through the fθ lens 181 and thereby return the beam B toward the surface of each photosensitive drum 1151. The optical scanning device 116 includes two return mirrors 186, namely, a return mirror 186YM and a return mirror 186CK. The optical scanning device 116 includes four return mirrors 187, namely, a return mirror 187Y, a return mirror 187M, a return mirror 187C, and a return mirror 187K. The optical scanning device 116 includes two return mirrors 188, namely, a return mirror 188Y and a return mirror 188K. It should be noted that in Figure 5 In the figure, the illustration of the folding mirrors 186 to 188 is omitted.

[0103] In addition, the optical scanning device 116 includes a first cover glass 191 , a second cover glass, and a third cover glass 193 .

[0104] The first cover glass 191 is located between the pre-deflection optical system 170 and the polygonal mirror 151. The second cover glass 192 is located between the polygonal mirror 151 and the post-deflection optical system 180. The first cover glass 191 and the second cover glass 192 are provided to deal with wind noise when the polygonal mirror 151 rotates. The first cover glass 191 prevents the wind noise from leaking from the entrance of the beam B. The second cover glass 192 prevents the wind noise from leaking from the exit of the beam B.

[0105] The third cover glass 193 is located between the fθ lens 182 and the photosensitive drum 1151. The third cover glass 193 covers the exit in the housing of the optical scanning device 116 through which the beam B is emitted.

[0106] It should be noted that, as described above, the optical scanning device 116 is configured with the scanning optical system 161 and the scanning optical system 162 disposed on the left and right sides with the polygon mirror 151 as the center. Therefore, when the polygon mirror 151 is rotated in a certain direction, in the optical scanning device 116, the scanning direction of the photosensitive drum 1151 by the scanning optical system 161 and the scanning direction of the photosensitive drum 1151 by the scanning optical system 162 become opposite. Figure 5 In the figure, with the polygon mirror 151 as the center, the side (upper side on the paper) where the light sources 153Y, 153M, 153C, and 153K are depicted is assumed to be the positive side, and the opposite side (lower side on the paper) is assumed to be the negative side. In this case, the scanning optical system 161 scans the image plane from the positive side to the negative side as indicated by the arrow S. In contrast, the scanning optical system 162 scans the image plane from the negative side to the positive side as indicated by the arrow T.

[0107] use Figure 8 and Fig. 9 The main scanning aperture 174 will be described.

[0108] exist Figure 8 and Fig. 9 2 shows a main scanning aperture 174 a and a main scanning aperture 174 b as examples of the main scanning aperture 174 . Figure 8 and Fig. 9 They are diagrams showing examples of the main scanning aperture 174. It should be noted that Figure 8 and Fig. 9 The main scanning aperture 174 shown is the main scanning aperture 174YM. Figure 8 and Fig. 9 The main scanning aperture 174 shown is a plan view of the main scanning aperture 174 as viewed from the side where the light source 153 is located. Figure 8 and Fig. 9The main scanning aperture 174 shown is a plan view of the main scanning aperture 174 as viewed from the arrow U direction.

[0109] The main scanning aperture 174 is a plate-shaped member. The main scanning aperture 174 has an opening 175. Figure 8 The main scanning aperture 174 a shown has an opening 175 a as an example of the opening 175 . Fig. 9 The main scanning aperture 174b shown has an opening 175b as an example of the opening 175. The opening 175 is composed of two openings 176, namely, an opening 176a and an opening 176b. The shape of each opening 176 is a rectangle whose width in the sub-scanning direction is larger than the width of the beam B in the sub-scanning direction. The width of the opening 176 in the sub-scanning direction is such that the sub-scanning direction side (upper or lower side on the paper) of the beam B is not shielded even if the passing position of the beam B deviates in the sub-scanning direction due to device accuracy or the like.

[0110] In addition, Figure 8 and Fig. 9 , the optical axis OA of the beam B incident on the opening 176 is shown. Figure 8 and Fig. 9 In FIG. 1 , the optical axis OA of the beam BY is represented as the optical axis OAY, and the optical axis OA of the beam BM is represented as the optical axis OAM. Figure 8 and Fig. 9 , a bisector EL is shown as a straight line passing through the optical axis OA and parallel to the sub-scanning direction. Figure 8 and Fig. 9 , a bisector EL passing through the optical axis OAY is represented as ELY, and a bisector EL passing through the optical axis OAM is represented as ELM. The bisector EL is a straight line that divides the beam B into two equal parts in the main scanning direction.

[0111] The opening 176a is bounded by the bisector ELY, and the length on the downstream side in the main scanning direction is xY1, and the length on the upstream side in the main scanning direction is xY2. The relationship between the lengths of xY1 and xY2 is xY1>xY2. Regarding the beam BY passing through the opening 176a, the length from the optical axis OAY to one end on the upstream side in the main scanning direction is xY2, and the length from the optical axis OAY to one end on the downstream side in the main scanning direction is xY1. Therefore, the opening 176a is an example of a first aperture portion that shapes the beam BY as the first light beam. In addition, xY2 is an example of a first length. xY1 is an example of a second length.

[0112] The opening 176b is bounded by the bisector ELM, and the length on the upstream side in the main scanning direction is xM1, and the length on the downstream side in the main scanning direction is xM2. The relationship between the lengths of xM1 and xM2 is xM1>xM2. Regarding the beam BM passing through the opening 176b, the length from the optical axis OAM to one end on the upstream side in the main scanning direction is xM1, and the length from the optical axis OAY to one end on the downstream side in the main scanning direction is xM2. Therefore, the opening 176b is an example of a second aperture portion that shapes the beam BM as the second light beam. In addition, xM1 is an example of a third length. xM2 is an example of a fourth length.

[0113] exist Figure 8 In the opening 175a shown, the opening 176a and the opening 176b do not overlap each other. Therefore, the opening 175a is composed of two openings 176 that are not connected.

[0114] exist Fig. 9 In the opening 175b shown, the opening 176a and the opening 176b overlap each other. That is, the opening 175b is a single opening in a shape in which the two openings 176 communicate with each other.

[0115] The opening 176a is an example of a first aperture portion that shapes the beam BY as the first light beam, and the opening 176b is an example of a second aperture portion that shapes the beam BM as the second light beam.

[0116] As described above, in the optical scanning device 116 of the embodiment, since the beam BM and the beam BY are offset in the sub-scanning direction, the shapes of both the beam BM and the beam BY in the main scanning direction can be shaped into desired shapes by one main scanning aperture 174 .

[0117] In addition, if Figure 8 As shown in FIG. 1 , when the beam BM and the beam BY are sufficiently separated in the sub-scanning direction, the opening 176a and the opening 176b can be arranged separately in a non-overlapping manner. Fig. 9 As shown, when the distance separating beam BM and beam BY in the sub-scanning direction is small, opening 176a and opening 176b overlap. It should be noted that the farther beam BM and beam BY are separated in the sub-scanning direction, the larger the width of the polygonal mirror 151 in the sub-scanning direction needs to be. The smaller the width of the polygonal mirror 151 in the sub-scanning direction, the more likely it is that the light scanning device 116 can be miniaturized. In addition, the smaller the width of the polygonal mirror 151 in the sub-scanning direction, the shorter the time required from the start of rotation to the stable rotation at a specified rotation speed. Furthermore, the smaller the width of the polygonal mirror 151 in the sub-scanning direction, the shorter the time it takes to stop the rotation of the polygonal mirror 151.

[0118] use Fig.10 The main scanning aperture 200 used as a comparison target of the main scanning aperture 174 will be described. Fig.10 The main scanning aperture 200 shown is the main scanning aperture 200YM. The main scanning aperture 200YM is the same as the main scanning aperture 174YM, and is the main scanning aperture for the beam BY and the beam BM. The main scanning aperture 200 has an opening 201 instead of the opening 175 of the main scanning aperture 174. The opening 201 has two openings 202, namely, an opening 202a and an opening 202b, instead of the opening 176a and the opening 176b of the opening 175. With respect to the opening 202a and the opening 202b, the length of the upstream side in the main scanning direction is equal to the length of the downstream side in the main scanning direction, with the bisector EL as the boundary. As an example, the length of the opening 202a on the downstream side in the main scanning direction is xY1, and the length of the upstream side in the main scanning direction is xY1, with the bisector ELY as the boundary. Furthermore, the opening 202 b has a length xM1 on the upstream side in the main scanning direction and a length xM1 on the downstream side in the main scanning direction, with the bisector ELM as a boundary.

[0119] In addition, the main scanning aperture 174 is preferably close to the prism 151. As described above, beam B is a multi-beam composed of a plurality of beams. In addition, each beam included in beam B maintains a distance in the main scanning direction. Therefore, the farther each beam included in beam B passing through the main scanning aperture 174 is from the main scanning aperture 174, the easier it is to diffuse in the main scanning direction. If each beam included in beam B diffuses in the main scanning direction, it makes it easier for each beam to pass through a position deviated from the desired optical path. If each beam deviates from the desired optical path, it becomes easy for vignetting to occur when reflected by the polygonal mirror 151, or the respective focusing positions of each beam become different, etc., which becomes a cause of reduced image quality. Therefore, the closer the main scanning aperture 174 is to the polygonal mirror 151, the more the image plane curvature is reduced, etc., and the more the image quality of the image forming device 100 is improved. Therefore, as in the embodiment, by locating the main scanning aperture 174 at a position where the beam B passes through the cylindrical lens 173 and then passes through the main scanning aperture 174, the image quality of the image forming device 100 is improved. However, the closer the main scanning aperture 174 is to the prism 151, the more the positions of the beam BY and the beam BM in the main scanning direction overlap. Therefore, it becomes difficult to configure the aperture separately for each beam B as the sub-scanning aperture 172 does. As in the embodiment, by allowing two beams B, the beam BY and the beam BM, to pass through one main scanning aperture 174, it becomes possible to shape the shape in the main scanning direction near the polygonal mirror 151. It should be noted that in the conventional optical scanning device, an aperture for shaping the shape in both the main scanning direction and the sub-scanning direction is configured at the same position as the sub-scanning aperture 172.

[0120] The main scanning aperture 174 a and the main scanning aperture 174 b are formed in a shape in which the opening 175 is opened in a single plate-like member. Therefore, the cost can be reduced compared to using two main scanning apertures.

[0121] use Figures 11 to 18 The main scanning aperture 174 will be further described. Figures 11 to 18 is a diagram for explaining the main scanning aperture. Figures 11 to 18 In the embodiment, the upstream side of the rotation direction CCW of the polygon mirror 151 is defined as the positive side, and the downstream side is defined as the negative side. Figures 11 to 18 , the image plane IS is shown. The beam B deflected by the polygon mirror 151 scans the image plane IS from the positive side to the negative side. It should be noted that Figures 11 to 18 The area between the polygon mirror 151 and the image plane IS is partially omitted. Figures 11 to 18 Although the polygonal prism 151-8 is shown in FIG, the polygonal prism 151-7 is also shown by virtual lines for the convenience of comparison with the polygonal prism 151-8. It should be noted that the inscribed circle radius of the polygonal prism 151-7 is equal to that of the polygonal prism 151-8, and the inscribed circle radius is set to D.

[0122] Fig.11 This is a diagram showing a state in which the beam BM shaped by the main scanning aperture 200YM is deflected toward the negative scanning end.

[0123] Fig.12 This is a diagram showing a state in which the beam BM shaped by the main scanning aperture 200YM is deflected toward the positive scanning end.

[0124] like Fig.11 and Fig.12 As shown, regarding the beam BM shaped by the main scanning aperture 200YM, the width of the upstream side in the main scanning direction from the optical axis OAM is equal to the width of the downstream side in the main scanning direction from the optical axis OAM. It should be noted that the width of the upstream side in the main scanning direction from the optical axis OAM and the width of the downstream side in the main scanning direction from the optical axis OAM of the beam BM shaped by the main scanning aperture 200YM are both set to x1. And, as Fig.11 and Fig.12As shown, the beam BM is set so that the beam BM shaped by the main scanning aperture 200YM will not be vignetted by the polygonal mirror 151-7. However, when the polygonal mirror 151-8 is used, since the length of one side of the polygonal mirror 151-8 is shorter than the length of one side of the polygonal mirror 151-7, vignetting VM occurs at the positive scanning end. That is, a part of the beam BM exceeds the reflecting surface 1511. On the other hand, at the negative scanning end, since there is a margin from the position where the beam BM shines on the polygonal mirror 151-7 to the vertex on the upstream side of the position of the polygonal mirror 151-7, vignetting does not occur even with the polygonal mirror 151-8.

[0125] Fig.13 This is a diagram showing a state in which the beam BY shaped by the main scanning aperture 200YM is deflected toward the negative scanning end.

[0126] Fig.14 This is a diagram showing a state in which the beam BY shaped by the main scanning aperture 200YM is deflected toward the positive scanning end.

[0127] like Fig.13 and Fig.14 As shown, for the beam BY passing through the main scanning aperture 200YM, the width of the upstream side in the main scanning direction from the optical axis OAY is equal to the width of the downstream side in the main scanning direction from the optical axis OAY. It should be noted that the width of the upstream side in the main scanning direction from the optical axis OAY and the width of the downstream side in the main scanning direction from the optical axis OAY of the beam BM are both set to x3. And, as Fig.13 and Fig.14 As shown, the beam BY is set so that the beam BY shaped by the main scanning aperture 200YM will not be vignetted by the polygonal mirror 151-7. However, when the polygonal mirror 151-8 is used, since the length of one side of the polygonal mirror 151-8 is shorter than the length of one side of the polygonal mirror 151-7, vignetting VY occurs at the negative scanning end. That is, a part of the beam BY exceeds the reflecting surface 1511. On the other hand, at the positive scanning end, there is a margin from the position where the beam BY hits the polygonal mirror 151-7 to the vertex on the upstream side of the position of the polygonal mirror 151-7, so vignetting does not occur even with the polygonal mirror 151-8.

[0128] Fig.15 This is a diagram showing a state in which the beam BM shaped by the main scanning aperture 174YM is deflected toward the negative scanning end.

[0129] Fig.16 This is a diagram showing a state in which the beam BM shaped by the main scanning aperture 174YM is deflected toward the positive scanning end.

[0130] like Fig.15 and Fig.16As shown, regarding the beam BM shaped by the main scanning aperture 174YM, the width on the upstream side of the main scanning direction from the optical axis OAM is x1, and the width on the downstream side of the main scanning direction from the optical axis OAM is x2. It should be noted that since the angle at which the beam BM enters the main scanning aperture 174YM is close to vertical, it can be considered that x1≈xM1 and x2≈xM2.

[0131] x2 is a value smaller than x1. That is, the width of the upstream side of the main scanning direction from the optical axis OAM of the beam BM shaped by the main scanning aperture 174YM is equal to the width of the upstream side of the main scanning direction from the optical axis OAM of the beam BM shaped by the main scanning aperture 200YM. In addition, compared with the beam BM shaped by the main scanning aperture 200YM, the width of the downstream side of the main scanning direction from the optical axis OAM of the beam BM shaped by the main scanning aperture 174YM is shorter. Therefore, as Fig.15 As shown in FIG. 1 , the beam BM shaped by the main scanning aperture 174YM is similar to the beam BM shaped by the main scanning aperture 200YM. In the negative scanning end, no vignetting occurs in the polygon mirror 151-7 and the polygon mirror 151-8. Fig.16 As shown, unlike the beam BM shaped by the main scanning aperture 200YM, the beam BM shaped by the main scanning aperture 174YM does not undergo vignetting in either the polygon mirror 151-7 or the polygon mirror 151-8.

[0132] Fig.17 This is a diagram showing a state in which the beam BY shaped by the main scanning aperture 174YM is deflected toward the negative scanning end.

[0133] Fig.18 This is a diagram showing a state in which the beam BY shaped by the main scanning aperture 174YM is deflected toward the positive scanning end.

[0134] like Fig.17 and Fig.18 As shown, regarding the beam BY shaped by the main scanning aperture 174YM, the width of the downstream side in the main scanning direction from the optical axis OAY is x3, and the width of the upstream side in the main scanning direction from the optical axis OAY is x4. It should be noted that since the angle at which the beam BY enters the main scanning aperture 174YM is close to vertical, it can be considered that x3≈xY1 and x4≈xY2.

[0135] x4 is a value smaller than x3. That is, the width of the beam BY shaped by the main scanning aperture 174YM on the downstream side of the main scanning direction from the optical axis OAY is equal to the width of the beam BY shaped by the main scanning aperture 200YM on the downstream side of the main scanning direction from the optical axis OAY. In addition, compared with the beam BY shaped by the main scanning aperture 200YM, the width of the beam BY shaped by the main scanning aperture 174YM on the upstream side of the main scanning direction from the optical axis OAY is shorter. Therefore, as Fig.17 As shown in FIG. 1 , unlike the beam BY shaped by the main scanning aperture 200YM, the beam BY shaped by the main scanning aperture 174YM does not undergo vignetting in either the polygon mirror 151-7 or the polygon mirror 151-8. Fig.18 As shown, the beam BY shaped by the main scanning aperture 174YM, like the beam BY shaped by the main scanning aperture 200YM, does not undergo vignetting in either the polygon mirror 151 - 7 or the polygon mirror 151 - 8 at the negative scanning end.

[0136] As described above, in the optical scanning device 116 , by using the main scanning aperture 174YM in which the lengths of xY1 , xY2 , xM1 , and xM2 are appropriately set, it is possible to prevent vignetting from occurring even when the polygon mirrors 151 having different numbers of faces are used.

[0137] In the above, the main scanning aperture 174 is described using the main scanning aperture 174YM, and the main scanning aperture 174CK is the same as the main scanning aperture 174YM. It should be noted that the main scanning aperture 174CK shapes the shapes of the beams BC and BK in the main scanning direction.

[0138] As described above, the image forming apparatus 100 of the embodiment can use the polygonal mirrors 151 with different numbers of faces. Therefore, the image forming apparatus 100 of the embodiment can use a common housing in different models using the polygonal mirrors 151 with different numbers of faces, thereby reducing manufacturing costs.

[0139] The above-mentioned embodiment may be modified as follows.

[0140] It can also be that Fig.19 Main scanning aperture 210 is shown in place of main scanning aperture 174 . Fig.19 2 is a diagram showing a modification of the main scanning aperture. It should be noted that the main scanning aperture 210 will be described by taking the main scanning aperture 210 for the beam BY and the beam BM as an example.

[0141] The main scanning aperture 210 includes a main scanning aperture 200 and a second main scanning aperture 220. It should be noted that: Fig.19In FIG. 2 , the second main scanning aperture 220 is shown in bold for easier understanding. The main scanning aperture 210 uses a main scanning aperture such as the main scanning aperture 200 that does not assume the use of multiple types of polygon mirrors 151 with different numbers of faces, thereby enabling the use of multiple types of polygon mirrors 151.

[0142] The main scanning aperture 210 is formed by overlapping the main scanning aperture 200 and the second main scanning aperture 220. It should be noted that the main scanning aperture 200 and the second main scanning aperture 220 can be closely attached to each other or there can be a gap between them. Fig.19 In the embodiment of the present invention, the second main scanning aperture 220 is located closer to the light source 153 than the main scanning aperture 200. However, the second main scanning aperture 220 may be located farther from the light source 153 than the main scanning aperture 200.

[0143] The second main scanning aperture 220 has an opening 221 and a protrusion 222 .

[0144] The opening 221 includes an opening for shaping the beam BY and an opening for shaping the beam BM. The opening for shaping the beam BY is bounded by the bisector ELY, and the length of the downstream side in the main scanning direction is greater than xY1, and the length of the upstream side in the main scanning direction is xY2. The opening for shaping the beam BM is bounded by the bisector ELM, and the length of the upstream side in the main scanning direction is greater than xM1, and the length of the downstream side in the main scanning direction is xM2. It should be noted that, as mentioned above, xY1>xY2, xM1>xM2.

[0145] In addition, the second main scanning aperture 220 is attached to, for example, a fixing member 230. The fixing member 230 includes a groove 231 for fitting the protrusion 222. The protrusion 222 is fitted into the groove 231, so that the position of the second main scanning aperture in the main scanning direction is determined by the protrusion 222 and the groove 231. In addition, the protrusion 222 and the groove 231 fix the second main scanning aperture to prevent it from moving in the main scanning direction.

[0146] In addition, the bottom portion 223 a and the bottom portion 223 b of the second main scanning aperture 220 contact the upper surface of the fixing member 230 , thereby determining the position of the second main scanning aperture 220 in the sub-scanning direction.

[0147] Therefore, the main scanning aperture 200 shapes the shape of the downstream side of the beam BY in the main scanning direction and the shape of the upstream side of the beam BM in the main scanning direction into desired shapes. The second main scanning aperture 220 shapes the shape of the upstream side of the beam BY in the main scanning direction and the shape of the downstream side of the beam BM in the main scanning direction into desired shapes. Thus, the shape of the beam B shaped by the main scanning aperture 210 becomes the same shape as the shape of the beam shaped by the main scanning aperture 174, and the occurrence of vignetting can be prevented.

[0148] The optical scanning device using the main scanning aperture 210 can be used with the main scanning aperture 210 installed when the polygonal mirror 151-8 is used, and can be used with the main scanning aperture 210 removed when the polygonal mirror 151-7 is used. Thus, the amount of light when the polygonal mirror 151-7 is used can be made higher than the amount of light when the polygonal mirror 151-8 is used.

[0149] It should be noted that the portion of the main scanning aperture 200 that shapes the downstream side of the beam BY in the main scanning direction is an example of the first portion. Also, the portion of the main scanning aperture 200 that shapes the upstream side of the beam BM in the main scanning direction is an example of the fourth portion. Also, the main scanning aperture 200 is an example of the first component including the first portion and the fourth portion.

[0150] In addition, the portion of the second main scanning aperture 220 that shapes the upstream side of the beam BY in the main scanning direction is an example of the third portion. In addition, the portion of the second main scanning aperture 220 that shapes the downstream side of the beam BM in the main scanning direction is an example of the third portion. In addition, the second main scanning aperture 220 is an example of the second member including the second portion and the third portion.

[0151] In the above embodiment, the main scanning aperture 174 has a shape in which the opening 175 is opened in a single member. However, the main scanning aperture 174 may be divided into two or more members.

[0152] Fig. 20 , the main scanning aperture 174c is shown as an example of the main scanning aperture 174 divided into two or more components. Fig. 20 17 is a diagram showing an example of the main scanning aperture 174. The main scanning aperture 174c has an opening 175c as an example of the opening 175. In the opening 175c, the opening 176a and the opening 176b do not overlap. Therefore, the opening 175c is composed of two openings 176 that are not connected. In addition, the main scanning aperture 174c is divided into two parts in the sub-scanning direction. That is, the main scanning aperture 174c is composed of two parts, a part 177a having the opening 176a and a part 177b having the opening 176b.

[0153] in addition, Fig.21 , the main scanning aperture 174d is shown as an example of the main scanning aperture 174 divided into two or more components. Fig.2117 is a diagram showing an example of the main scanning aperture 174. The main scanning aperture 174d has an opening 175d as an example of the opening 175. In the opening 175d, the opening 176a overlaps with the opening 176b. That is, the opening 175d is an opening in a shape in which the two openings 176 are connected. In addition, the main scanning aperture 174d is divided into a part 178a and a part 178b in the main scanning direction. That is, the main scanning aperture 174d is divided into two parts by the opening 175d because its width in the sub-scanning direction is less than the width of the opening in the sub-scanning direction. In addition, a part of the opening 175d in the sub-scanning direction has no light-shielding part and is open.

[0154] In the above embodiment, the shape of the opening 176 is a rectangle. However, the shape of the opening 176 may be a shape other than a rectangle.

[0155] In the above embodiment, the optical scanning device 116 has a configuration in which the photosensitive drums 1151 and the light sources 153 of each color are separated into two groups on the left and right sides with the polygonal mirror 151 in the middle. However, the optical scanning device of the embodiment may also be configured such that three or more photosensitive drums 1151 and light sources 153 are arranged on one side of the polygonal mirror 151. In this case, the three or more beams B are reflected by the same reflection surface 1511. Fig. 22 An example of the shape of the main scanning aperture when four beams B are reflected by the same reflection surface is shown in FIG. Fig. 22 It is a diagram showing a modified example of the main scanning aperture. Fig. 22 The main scanning aperture 300 shown has an opening 301. The opening 301 is an opening in a shape in which four openings 301, namely, openings 302a to 302d, are connected. The shape of each opening 302 is a rectangle whose width in the sub-scanning direction is greater than the width of the beam B in the sub-scanning direction. The opening 302a partially overlaps with the opening 302b, thereby connecting the openings. The opening 302b partially overlaps with the opening 302c, thereby connecting the openings. The opening 302c partially overlaps with the opening 302d, thereby connecting the openings. However, at least one combination of the openings 302a and 302b, the openings 302b and 302c, and the openings 302c and 302d may not overlap. In this case, the opening 301 is an opening composed of a plurality of openings that are not connected. The openings 302a to 302d allow each beam B to pass through. That is, the opening 302a allows the beam Ba to pass through, the opening 302b allows the beam Bb to pass through, the opening 302c allows the beam Bc to pass through, and the opening 302d allows the beam Bd to pass through. Thus, the openings 302a to 302d shape the main scanning direction of the passing beams Ba to Bd.

[0156] The opening 302a is bounded by the bisector ELa passing through the optical axis OAa of the beam Ba, and has a length xa1 on the downstream side in the main scanning direction and a length xa2 on the upstream side in the main scanning direction.

[0157] The opening 302 b has a length xb1 on the downstream side in the main scanning direction and a length xb2 on the upstream side in the main scanning direction, with the bisector ELb passing through the optical axis OAb of the beam Bb as a boundary.

[0158] The opening 302c is bounded by a bisector ELc passing through the optical axis OAc of the beam Bc, and has a length xc1 on the upstream side in the main scanning direction and a length xc2 on the downstream side in the main scanning direction.

[0159] The opening 302d is bounded by a bisector ELd passing through the optical axis OAd of the beam Bd, and has a length xd1 on the upstream side in the main scanning direction and a length xd2 on the downstream side in the main scanning direction.

[0160] xa1 and xa2 have a relationship of xa1>xa2. Also, xd1 and xd2 have a relationship of xd1>xd2.

[0161] In addition, xb1, xb2, xc1, and xc2 have, for example, a relationship of xb1≥xb2, xc1≥xc2. Alternatively, xb1, xb2, xc1, and xc2 have a relationship of xb1≤xb2, xc1≥xc2. Alternatively, xb1, xb2, xc1, and xc2 have a relationship of xb1≥xb2, xc1≤xc2.

[0162] In the above embodiment, the image forming apparatus 100 uses four recording materials corresponding to the four colors of CMYK. However, the image forming apparatus of the embodiment may also be an apparatus using two, three, or five or more types of recording materials. In this case, the image forming apparatus of the embodiment, for example, has the same number of photosensitive drums 1151 and light sources 153 as the number of types of recording materials.

[0163] Although several embodiments of the present invention have been described, these embodiments are only presented as examples and are not intended to limit the scope of the invention. These new embodiments can be implemented in various other ways, and various omissions, substitutions, and changes can be made without departing from the scope of the purpose of the invention. These embodiments and their variations are included in the scope and purpose of the invention, and are also included in the invention described in the claims and their equivalents.

Claims

1. An optical scanning device comprising: A first light source emits a first light beam; a second light source that emits a second light beam having an aperture angle relative to the first light beam in the main scanning direction, the second light source being located more upstream in the main scanning direction than the first light source; a first aperture portion for shaping the shape of the first light beam so that a length from the optical axis to one end on the upstream side in the main scanning direction of the first light beam becomes a first length, and a length from the optical axis to one end on the downstream side in the main scanning direction becomes a second length greater than the first length; a second aperture portion that shapes the shape of the second light beam so that a length of the second light beam from the optical axis to one end on the upstream side in the main scanning direction becomes a third length, and a length from the optical axis to one end on the downstream side in the main scanning direction becomes a fourth length that is smaller than the third length; and a deflector for deflecting the first light beam passing through the first aperture portion and the second light beam passing through the second aperture portion at positions shifted in the sub-scanning direction on the same surface, The first aperture portion includes a first portion and a second portion, wherein the first portion shapes the shape of the first light beam in such a manner that a length from the optical axis to one end on the upstream side in the main scanning direction is a first length, and the second portion shapes the shape of the first light beam in such a manner that a length from the optical axis to one end on the downstream side in the main scanning direction is a second length greater than the first length. The second aperture portion includes a third portion and a fourth portion, the third portion shaping the shape of the second light beam in such a manner that a length from the optical axis to one end on the upstream side in the main scanning direction is a third length, and the fourth portion shaping the shape of the second light beam in such a manner that a length from the optical axis to one end on the downstream side in the main scanning direction is a fourth length that is smaller than the third length. The first portion and the fourth portion are formed on a first component, The second portion and the third portion are formed in a second component different from the first component.

2. The optical scanning device according to claim 1, wherein: The opening through which the first light beam passes through the first aperture portion communicates with the opening through which the second light beam passes through the second aperture portion.

3. The optical scanning device according to claim 1 or 2, wherein: The first aperture portion and the second aperture portion are formed in one integral member.

4. An image forming device comprising: A first light source emits a first light beam; a second light source that emits a second light beam having an aperture angle relative to the first light beam in the main scanning direction, the second light source being located more upstream in the main scanning direction than the first light source; a first aperture portion for shaping the shape of the first light beam so that a length from the optical axis to one end on the upstream side in the main scanning direction of the first light beam becomes a first length, and a length from the optical axis to one end on the downstream side in the main scanning direction becomes a second length greater than the first length; a second aperture portion for shaping the shape of the second light beam in such a manner that a length of the second light beam from the optical axis to one end on the upstream side in the main scanning direction becomes a third length, and a length of the second light beam from the optical axis to one end on the downstream side in the main scanning direction becomes a fourth length that is smaller than the third length; A deflector deflects the first light beam passing through the first aperture portion and the second light beam passing through the second aperture portion at positions offset in the sub-scanning direction on the same surface; as well as an image forming unit that transfers an electrostatic latent image formed by the first light beam and the second light beam deflected by the deflector to a medium as an image, The first aperture portion includes a first portion and a second portion, wherein the first portion shapes the shape of the first light beam in such a manner that a length from the optical axis to one end on the upstream side in the main scanning direction is a first length, and the second portion shapes the shape of the first light beam in such a manner that a length from the optical axis to one end on the downstream side in the main scanning direction is a second length greater than the first length. The second aperture portion includes a third portion and a fourth portion, the third portion shaping the shape of the second light beam in such a manner that a length from the optical axis to one end on the upstream side in the main scanning direction is a third length, and the fourth portion shaping the shape of the second light beam in such a manner that a length from the optical axis to one end on the downstream side in the main scanning direction is a fourth length that is smaller than the third length. The first portion and the fourth portion are formed on a first component, The second portion and the third portion are formed in a second component different from the first component.

Images