Optical element and optical scanner

Abstract

To provide an optical element excellent in characteristics.SOLUTION: The optical element includes a first surface and a second surface facing each other and extending along a longitudinal axis in a rectangle shape. The first surface has a pair of first lens regions for imparting optical action to a light beam passing therethrough and the second surface has a pair of second lens regions for imparting optical action to a light beam passing therethrough Both the first lens region and the second lens region extend along the longitudinal axis in the rectangle shape. The first lens region has a first extreme value of curvature on a first opposite side extending parallel to the longitudinal axis while the second lens region has a second extreme value of curvature on a second opposite side extending parallel to the longitudinal axis. The dimension of the first lens region in a direction perpendicular to the longitudinal axis is smaller than the dimension of the second lens region. The pair of second lens regions is smoothly continuous on the second opposite sides adjacent to each other.SELECTED DRAWING: Figure 15

Description

Technical Field

[0001] Embodiments of the present invention relate to an optical element and an optical scanning device.

Background Art

[0002] An electrophotographic image forming apparatus placed in a workplace scans a light beam to form an electrostatic latent image on a photoreceptor. The image forming apparatus includes an optical scanning device that scans the light beam. The optical scanning device includes an optical element that forms an image of the light beam on the photoreceptor.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The problem to be solved by the present invention is to provide an optical element and an optical scanning device with excellent characteristics.

Means for Solving the Problems

[0005] The optical element according to the embodiment has a first surface and a second surface that face each other and extend in a rectangle along the longitudinal axis. The first surface has a pair of first lens regions that exert an optical action on the passing light beam. The second surface has a pair of second lens regions that exert an optical action on the passing light beam. Both the first lens region and the second lens region extend in a rectangle along the longitudinal axis. The first lens region has a first extreme value of curvature at a first pair of sides extending parallel to the longitudinal axis. The second lens region has a second extreme value of curvature at a second pair of sides extending parallel to the longitudinal axis. The dimension of the first lens region in the direction perpendicular to the longitudinal axis is smaller than the dimension of the second lens region. The pair of second lens regions are smoothly continuous at a second pair of adjacent sides.

[0006] The optical scanning device according to the embodiment includes a first light source that emits a first light beam, a second light source that emits a second light beam, a third light source that emits a third light beam, a fourth light source that emits a fourth light beam, an optical deflector that dynamically deflects the first light beam, the second light beam, the third light beam, and the fourth light beam on the same reflecting surface and scans in the main scanning direction, a first pre-deflection optical system that guides the first light beam emitted from the first light source to the reflecting surface, a second pre-deflection optical system that guides the second light beam emitted from the second light source to the reflecting surface, a third pre-deflection optical system that guides the third light beam emitted from the third light source to the reflecting surface, a fourth pre-deflection optical system that guides the fourth light beam emitted from the fourth light source to the reflecting surface, a first optical element that imparts optical characteristics to the first light beam and the second light beam scanned by the optical deflector, a second optical element that cooperates with the first optical element to form an image of the first light beam, a third optical element that cooperates with the first optical element to form an image of the second light beam, a first post-deflection optical system having the above; a fourth optical element that imparts optical characteristics to the third light beam and the fourth light beam scanned by the optical deflector, a fifth optical element that cooperates with the second optical element to form an image of the third light beam, and a sixth optical element that cooperates with the second optical element to form an image of the fourth light beam, and a second post-deflection optical system having the above. In a projection onto a plane parallel to the main scanning direction, the first light source and the second light source are arranged so as to have a first opening angle, and the third light source and the fourth light source are arranged so as to have a second opening angle. In the sub-scanning direction perpendicular to the plane, the first light source, the second light source, the third light source, and the fourth light source are arranged at different positions. The first pre-deflection optical system, the second pre-deflection optical system, the third pre-deflection optical system, and the fourth pre-deflection optical system each guide the first light beam, the second light beam, the third light beam, and the fourth light beam to different positions in the sub-scanning direction with respect to the reflecting surface. The first optical element and the fourth optical element are arranged at the same position in a projection onto the plane and are arranged overlappingly in the sub-scanning direction.

Brief Description of the Drawings

[0007]

Figure 1

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Figure 15

Embodiments for Carrying Out the Invention

[0008] [Image Forming Apparatus] Hereinafter, the image forming apparatus according to the embodiment will be described with reference to the drawings. Note that in each of the drawings used in the following description of the embodiment, the scale of each part may be changed as appropriate. Also, in each of the drawings used in the following description of the embodiment, the configuration may be shown with omissions for the sake of explanation.

[0009] FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus 100 according to an embodiment. The image forming apparatus 100 is a device having a printing function, such as, for example, an MFP (multifunction peripheral), a copier, a printer, or a facsimile. However, hereinafter, the image forming apparatus 100 will be described as an MFP.

[0010] The image forming apparatus 100 includes, for example, a printing function, a scanning function, a copying function, an erasing function, and a facsimile function. The printing function is a function of forming an image on an image forming medium P or the like using a recording material such as toner. The image forming medium P is, for example, sheet-like paper or the like. The scanning function is a function of reading an image from an original on which an image is formed or the like. The copying function is a function of printing an image read from an original or the like using the scanning function on the image forming medium P using the printing function. The erasing function is a function of erasing an image formed of an erasable recording material on the image forming medium P.

[0011] The image forming apparatus 100 includes a printer 101, a scanner 102, and an operation panel 103.

[0012] The printer 101 is a device having a printing function. The printer 101 includes a paper feed tray 111, a manual feed tray 112, a paper feed roller 113, four toner cartridges 1141, 1142, 1143, 1144, four image forming units 1151, 1152, 1153, 1154, an optical scanning device 116, a transfer belt 117, a secondary transfer roller 118, a fixing unit 119, a duplex unit 120, and a paper discharge tray 121.

[0013] The paper feed tray 111 accommodates the image forming medium P used for printing.

[0014] The manual feed tray 112 is a platform for manually feeding the image forming medium P.

[0015] The paper feed roller 113 is rotated by a motor to selectively carry out the image forming medium P stored in the paper feed tray 111 and the manual feed tray 112 from either the paper feed tray 111 or the manual feed tray 112.

[0016] The toner cartridges 1141 to 1144 store the recording materials to be supplied to the image forming units 1151 to 1154 respectively. For example, the recording material is toner. The toner cartridge 1141 stores the yellow (Y) recording material. The toner cartridge 1142 stores the magenta (M) recording material. The toner cartridge 1143 stores the cyan (C) recording material. The toner cartridge 1144 stores the black (K) recording material. The combination of the colors of the recording materials is not limited to CMYK, and other color combinations may also be used. Further, the recording material may be a recording material that fades at a temperature higher than a predetermined temperature.

[0017] The image forming units 1151 to 1154 receive the supply of the recording materials from the toner cartridges 1141 to 1144 respectively and form images of different colors. The image forming unit 1151 forms a yellow (Y) image. The image forming unit 1152 forms a magenta (M) image. The image forming unit 1153 forms a cyan (C) image. The image forming unit 1154 forms a black (K) image.

[0018] [Image forming unit] The image forming units 1151 to 1154 have the same configuration except for the difference in the recording materials. Here, with reference to FIG. 2, the image forming unit 1151 will be typically described. FIG. 2 is a schematic diagram showing the schematic configuration of the image forming unit 1151.

[0019] The image forming unit 1151 includes a photosensitive drum 11511, a charging unit 11512, a developing unit 11513, a primary transfer roller 11514, a cleaner 11515, and a discharge lamp 11516.

[0020] The photosensitive drum 11511 is irradiated with a light beam BY emitted from the optical scanning device 116. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 11511.

[0021] The charging unit 11512 charges the surface of the photosensitive drum 11511 with a predetermined positive charge.

[0022] The developing unit 11513 develops the electrostatic latent image on the surface of the photosensitive drum 11511 using the recording material D supplied from the toner cartridge 1141. As a result, an image using the recording material D is formed on the surface of the photosensitive drum 11511.

[0023] The primary transfer roller 11514 is disposed at a position facing the photosensitive drum 11511 with the transfer belt 117 interposed therebetween. The primary transfer roller 11514 generates a transfer voltage between itself and the photosensitive drum 11511. As a result, the primary transfer roller 11514 transfers (primary transfer) the image formed on the surface of the photosensitive drum 11511 onto the transfer belt 117 that is in contact with the photosensitive drum 11511.

[0024] The cleaner 11515 removes the recording material D remaining on the surface of the photosensitive drum 11511.

[0025] The discharge lamp 11516 removes the charges remaining on the surface of the photosensitive drum 11511.

[0026] In FIG. 1, the optical scanning device 116 is also called an LSU (laser scanning unit). The optical scanning device 116 irradiates the image forming units 1151, 1152, 1153, and 1154 with light beams BY, BM, BC, and BK, respectively, according to the input image data. The light beams BY, BM, BC, and BK are for forming images of colors Y, M, C, and K, respectively. The optical scanning device 116 controls the light beam BY according to the Y component of the image data to form an electrostatic latent image on the surface of the photosensitive drum 11511 of the image forming unit 1151. Similarly, the optical scanning device 116 controls the light beams BM, BC, and BK according to the M, C, and K components of the image data to form electrostatic latent images on the surfaces of the photosensitive drums of the image forming units 1152, 1153, and 1154.

[0027] The input image data is, for example, image data read from a document or the like by the scanner 102. Alternatively, the input image data is image data transmitted from another device or the like and received by the image forming apparatus 100.

[0028] The transfer belt 117 is, for example, an endless belt and is rotatable by the action of rollers. By rotating, the transfer belt 117 conveys the images transferred from the image forming units 1151 to 1154 to the position of the secondary transfer roller 118.

[0029] The secondary transfer roller 118 includes two rollers facing each other. The secondary transfer roller 118 transfers (secondary transfer) the image formed on the transfer belt 117 onto the image forming medium P passing between the secondary transfer rollers 118.

[0030] The fixing unit 119 heats and presses the image forming medium P onto which the image has been transferred. Thereby, the image transferred onto the image forming medium P is fixed. The fixing unit 119 includes a heating unit 1191 and a pressure roller 1192 facing each other.

[0031] 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.

[0032] The pressure roller 1192 presses the image forming medium P passing between the pressure roller 1192 and the heating unit 1191.

[0033] The duplex unit 120 makes the image forming medium P printable on the back side. For example, the duplex unit 120 reverses the front and back of the image forming medium P by switching back the image forming medium P using a roller or the like.

[0034] The paper output tray 121 is a platform on which the printed image forming medium P is discharged.

[0035] The scanner 102 is a device having a scanning function. The scanner 102 is, for example, an optical reduction method including an imaging element such as a CCD (charge-coupled device) image sensor. Alternatively, the scanner 102 is a CIS (contact image sensor) method including an imaging element such as a CMOS (complementary metal-oxide-semiconductor) image sensor. Alternatively, the scanner 102 may be another known method. The scanner 102 reads an image from a document or the like. The scanner 102 includes a reading module 131 and a document feeder 132.

[0036] The reading module 131 converts the incident light into a digital signal by an image sensor. Thereby, the reading module 131 reads an image from the surface of the document.

[0037] The original document feeder 132 is also called, for example, an ADF (auto document feeder). The original document feeder 132 successively conveys the original documents placed on the original document tray. The conveyed original documents have their images read by the scanner 102. Also, the original document feeder 132 may be provided with a scanner for reading an image from the back side of the original document. Note that the surface from which the image is read by the scanner 102 is the front side.

[0038] The operation panel 103 includes, for example, a man-machine interface for performing input and output between the image forming apparatus 100 and the operator of the image forming apparatus 100. The operation panel 103 includes, for example, a touch panel 1031 and an input device 1032.

[0039] The touch panel 1031 is, for example, a device in which a display such as a liquid crystal display or an organic EL display and a pointing device by touch input are laminated. The display included in the touch panel 1031 functions as a display device for displaying a screen for notifying various information to the operator of the image forming apparatus 100. Also, the touch panel 1031 functions as an input device for receiving a touch operation by the operator.

[0040] The input device 1032 receives an operation by the operator of the image forming apparatus 100. The input device 1032 is, for example, a keyboard, a keypad, or a touch pad.

[0041] [Circuit Configuration of Main Components] Next, the circuit configuration of the main components of the image forming apparatus 100 will be described with reference to FIG. 3. FIG. 3 is a block diagram showing an example of the circuit configuration of the main components of the image forming apparatus 100. The image forming apparatus 100 includes, as an example, a processor 141, a ROM (read-only memory) 122, a RAM (random-access memory) 123, an auxiliary storage device 144, a communication interface 145, a printer 101, a scanner 102, and an operation panel 103. And a bus 146 or the like connects these components.

[0042] Processor 141 corresponds to the central part of a computer that performs processes such as operations and controls necessary for the operation of the image forming apparatus 100. Based on programs such as system software, application software, and firmware stored in the ROM 142 or the auxiliary storage device 144, etc., the processor 141 controls each part to realize various functions of the image forming apparatus 100. Note that part or all of the program may be incorporated in the circuit of the processor 141. The processor 141 is, for example, a CPU (central processing unit), MPU (micro processing unit), SoC (system on a chip), DSP (digital signal processor), GPU (graphics processing unit), ASIC (application specific integrated circuit), PLD (programmable logic device), or FPGA (field-programmable gate array), etc. Alternatively, the processor 141 is a combination of a plurality of these.

[0043] ROM 142 corresponds to the main storage device of a computer centered on the processor 141. The ROM 142 is a non-volatile memory used exclusively for reading data. The ROM 142 stores, for example, firmware among the above programs. Also, the ROM 142 stores data or various setting values used by the processor 141 when performing various processes.

[0044] RAM 143 corresponds to the main storage device of a computer centered on the processor 141. The RAM 143 is a memory used for reading and writing data. The RAM 143 is used as a so-called work area that stores data temporarily used by the processor 141 when performing various processes. The RAM 143 is, for example, a volatile memory.

[0045] The auxiliary storage device 144 corresponds to the auxiliary storage device of a computer centered around the processor 141. The auxiliary storage device 144 is, for example, an EEPROM (electric erasable programmable read-only memory), an HDD (hard disk drive), or a flash memory. The auxiliary storage device 144 stores, among the above programs, for example, system software and application software. Further, the auxiliary storage device 144 stores data used by the processor 141 to perform various processes, data generated by the processes in the processor 141, or various setting values. Note that the image forming apparatus 100 may include an interface into which a storage medium such as a memory card or a USB (universal serial bus) memory can be inserted as the auxiliary storage device 144. The interface reads and writes information to and from the storage medium.

[0046] The communication interface 145 is an interface for the image forming apparatus 100 to communicate via a network or the like.

[0047] The bus 146 includes a control bus, an address bus, a data bus, etc., and transmits signals exchanged between each part of the image forming apparatus 100.

[0048] [Optical Scanning Device According to the First Example] With reference to FIGS. 4 to 8, the optical scanning device 116 will be further described. FIG. 4 is a diagram showing an optical scanning device 116 according to a first example applicable to the image forming apparatus 100 shown in FIG. 1. FIG. 5 is a diagram showing the optical system of the optical scanning device 116 according to the first example shown in FIG. 4 developed on a plane. FIG. 6 is an enlarged view showing the pre-deviation optical system shown in FIG. 5. FIG. 7 is an X-X cross-sectional view of the pre-deviation optical system shown in FIG. 6. FIG. 8 is a Y-Y cross-sectional view of the pre-deviation optical system shown in FIG. 6.

[0049] The optical scanning device 116 includes four light sources 1531, 1532, 1533, 1534 and a light deflector 170.

[0050] The light sources 1531, 1532, 1533, and 1534 each emit light beams BY, BM, BC, and BK.

[0051] The light deflector 170 dynamically deflects the light beams BY, BM, BC, and BK emitted from the light sources 1531, 1532, 1533, and 1534 to scan the light beams BY, BM, BC, and BK.

[0052] For example, the light deflector 170 is composed of a polygon mirror scanner and includes a polygon mirror 171 and a motor 175.

[0053] The polygon mirror 171 is a regular polygonal prism-shaped mirror with each side surface being a reflecting surface 172. The polygon mirror 171 shown in FIGS. 4 to 9 is a regular heptagonal prism-shaped mirror having seven reflecting surfaces 172. The polygon mirror 171 is rotatable about a rotation axis parallel to each reflecting surface 172. Also, for example, the rotation axis 176 of the motor 175 is orthogonal to the rotation axes of the photoreceptor drums 11511, 11521, 11531, and 11541.

[0054] The motor 175 rotates the polygon mirror 171 in the counterclockwise (CCW) direction at a predetermined speed. For example, the rotation axis 176 of the motor 175 is parallel to the reflecting surface 172 of the polygon mirror 171.

[0055] The optical scanning device 116 also includes four pre-deflection optical systems 1601, 1602, 1603, and 1604 and two post-deflection optical systems 1801 and 1803.

[0056] As shown in FIGS. 5 to 8, the pre-deflection optical systems 1601, 1602, 1603, and 1604 each guide the light beams BY, BM, BC, and BK emitted from the light sources 1531, 1532, 1533, and 1534 to the light deflector 170. Specifically, the pre-deflection optical systems 1601, 1602, 1603, and 1604 each guide the light beams BY, BM, BC, and BK to the same reflecting surface 172 of the polygon mirror 171 of the light deflector 170.

[0057] The pre-deviation optical system 1601 includes a collimator lens 1621, a diaphragm 1631, and a cylinder lens 1641. Similarly, the pre-deviation optical system 1602 includes a collimator lens 1622, a diaphragm 1632, and a cylinder lens 1642, respectively.

[0058] The pre-deviation optical system 1603 includes a collimator lens 1623, a diaphragm 1633, a cylinder lens 1643, and a folding mirror 1653. Similarly, the pre-deviation optical system 1604 includes a collimator lens 1624, a diaphragm 1634, a cylinder lens 1644, and a folding mirror 1654.

[0059] The collimator lenses 1621, 1622, 1623, 1624 change the light beams BY, BM, BC, BK emitted from the light sources 1531, 1532, 1533, 1534 into parallel beams, respectively.

[0060] The diaphragms 1631, 1632, 1633, 1634 shape the light beams BY, BM, BC, BK passing through the collimator lenses 1621, 1622, 1623, 1624, respectively.

[0061] The cylinder lenses 1641, 1642, 1643, 1644 change the light beams BY, BM, BC, BK passing through the diaphragms 1631, 1632, 1633, 1634 into flat light beams on the reflecting surface 172 of the polygon mirror 171, respectively.

[0062] The folding mirrors 1653, 1654 reflect the light beams BC, BK passing through the cylinder lenses 1643, 1644 toward the light deflector 170, respectively.

[0063] Here, for the sake of convenience, regarding the pre-deviation optical systems 1601, 1602, 1603, 1604, the light deflector 170, and the post-deviation optical systems 1801, 1803, the direction parallel to the short side of the paper surface of FIG. 5 is defined as the main scanning direction, and the direction perpendicular to the paper surface of FIG. 5 is defined as the sub-scanning direction.

[0064] The light sources 1531 and 1532 are arranged such that the directions of their respective optical axes are different in the projection onto a plane parallel to the main scanning direction (i.e., the plane of the paper in FIG. 5). Here, the direction of the optical axis is the direction in which the light beam is emitted. Specifically, the light sources 1531 and 1532 are arranged so as to have an opening angle θ. Here, that the light sources 1531 and 1532 have an opening angle θ means that the optical axis of the light source 1531 and the optical axis of the light source 1532 form an angle θ. In other words, the difference in the angles of the emission directions of the light beam BY of the light source 1531 and the light beam BM of the light source 1532 is the angle θ.

[0065] Similarly, the light sources 1533 and 1534 are arranged such that the directions of their respective optical axes are different in the projection onto a plane parallel to the main scanning direction (i.e., the plane of the paper in FIG. 5). Specifically, the light sources 1533 and 1534 are arranged so as to have an opening angle θ.

[0066] Also, as can be seen by comparing FIG. 7 which is the X-X cross-sectional view of FIG. 6 and FIG. 8 which is the Y-Y cross-sectional view of FIG. 6, the light sources 1531 and 1532 are arranged at slightly different positions in the sub-scanning direction. For example, when the upper side of the paper in FIG. 6 is taken as the top, the light source 1532 is arranged at a higher position than the light source 1531.

[0067] Therefore, the beam BY emitted from the light source 1531 and the beam BM emitted from the light source 1532 enter the same reflecting surface 172 of the polygon mirror 171 of the optical deflector 170 at positions slightly shifted in the sub-scanning direction. For example, with respect to the reflecting surface 172, the beam BY enters at a higher position than the beam BM.

[0068] Also, both the beam BY and the beam BM enter perpendicularly to the reflecting surface 172 of the polygon mirror 171 of the optical deflector 170. In other words, the pre-deflection optical systems 1601 and 1602 are each configured to cause the beams BY and BM emitted from the light sources 1531 and 1532 to enter perpendicularly to the reflecting surface 172 of the polygon mirror 171 of the optical deflector 170. For this reason, the pre-deflection optical systems 1601 and 1602 can be configured relatively simply.

[0069] Note that the incident positions of the beams BY and BM on the reflecting surface 172 of the polygon mirror 171 of the light deflector 170 may be shifted or the same in the main scanning direction.

[0070] Here, the light sources 1531 and 1532 and the pre-deviation optical systems 1601 and 1602 have been described with reference to FIGS. 6 to 8, but the same applies to the light sources 1533 and 1533 and the pre-deviation optical systems 1603 and 1604.

[0071] Further, the optical paths of the pre-deviation optical systems 1603 and 1604 are different from the optical paths of the pre-deviation optical systems 1601 and 1602 and are bent by the folding mirrors 1653 and 1654. Thereby, the light source substrates 1541 and 1542 holding the light sources 1531 and 1532 and the light source substrates 1543 and 1544 holding the light sources 1533 and 1534 are satisfactorily prevented from interfering with each other in the sub-scanning direction.

[0072] This facilitates bringing the incident positions of the light beams BC and BK emitted from the light sources 1533 and 1534 closer to the incident positions of the beams BY and BM emitted from the light sources 1531 and 1532 with respect to the sub-scanning direction on the same reflecting surface 172 of the polygon mirror 171 of the light deflector 170.

[0073] As described above, the pre-deviation optical systems 1601, 1602, 1603, and 1604 guide the light beams BY, BM, BC, and BK emitted from the light sources 1531, 1532, 1533, and 1534, respectively, to the same reflecting surface 172 of the polygon mirror 171 of the light deflector 170.

[0074] The light deflector 170 reflects the light beams BY, BM, BC, and BK by the same reflecting surface 172 of the polygon mirror 171. Further, as the polygon mirror 171 rotates, the light deflector 170 scans the light beams BY, BM, BC, and BK in the main scanning direction. The light beams BY, BM, BC, and BK are scanned along a plane perpendicular to the rotation axis 176 of the motor 175, respectively.

[0075] As shown in FIG. 4, the post-deflection optical system 1801 guides the light beams BY and BM scanned by the light deflector 170 to the image forming units 1151 and 1152, respectively. The post-deflection optical system 1803 guides the light beams BC and BK deflected by the light deflector 170 to the image forming units 1153 and 1154, respectively.

[0076] As shown in FIGS. 4 and 5, the post-deflection optical system 1801 has an imaging optical system that forms an image of the light beam BY on the photoreceptor drum 11511, and this imaging optical system has an fθ lens 1811 and an fθ lens 1821. Further, the post-deflection optical system 1801 has an imaging optical system that forms an image of the light beam BM on the photoreceptor drum 11521, and this imaging optical system has an fθ lens 1811 and an fθ lens 1822.

[0077] Similarly, the post-deflection optical system 1803 has an imaging optical system that forms an image of the light beam BC on the photoreceptor drum 11531, and this imaging optical system has an fθ lens 1813 and an fθ lens 1823. Further, the post-deflection optical system 1803 has an imaging optical system that forms an image of the light beam BK on the photoreceptor drum 11541, and this imaging optical system has an fθ lens 1813 and an fθ lens 1824.

[0078] The fθ lens 1811 and the fθ lens 1821 cooperate to deflect the light beam BY so that it is incident perpendicularly to the surface of the photoreceptor drum 11511 and to form an image of the light beam BY on the surface of the photoreceptor drum 11511. The fθ lens 1811 and the fθ lens 1822 cooperate to deflect the light beam BM so that it is incident perpendicularly to the surface of the photoreceptor drum 11521 and to form an image of the light beam BM on the surface of the photoreceptor drum 11521.

[0079] Similarly, the fθ lens 1813 and the fθ lens 1823 cooperate to deflect the light beam BC so as to be incident perpendicularly to the surface of the photoreceptor drum 11531 and to form an image of the light beam BC on the surface of the photoreceptor drum 11531. The fθ lens 1813 and the fθ lens 1824 cooperate to deflect the light beam BK so as to be incident perpendicularly to the surface of the photoreceptor drum 11541 and to form an image of the light beam BK on the surface of the photoreceptor drum 11541.

[0080] That is, the fθ lens 1811, the fθ lens 1813, the fθ lens 1821, the fθ lens 1822, the fθ lens 1823, and the fθ lens 1824 are all imaging optical elements.

[0081] As shown in FIG. 5, the two fθ lenses 1811 and 1813 have the same structure and are arranged at the same position in a projection onto a plane parallel to the main scanning direction (i.e., the plane of the paper in FIG. 5). For this reason, in FIG. 5, the two fθ lenses 1811 and 1813 are drawn overlapping each other. Although the four fθ lenses 1821, 1822, 1823, and 1824 are not arranged at the same position in the aforementioned projection, for the sake of convenience, they are drawn overlapping each other in FIG. 5.

[0082] The fθ lens 1811 provides a positive optical power in the sub-scanning direction over the entire main scanning direction with respect to the passing light beams BY and BM. Thereby, the light beams BY and BM are focused between the fθ lens 1811 and the fθ lenses 1821 and 1822. Similarly, the fθ lens 1813 provides a positive optical power in the sub-scanning direction over the entire main scanning direction with respect to the passing light beams BC and BK. Thereby, the light beams BC and BK are focused between the fθ lens 1813 and the fθ lenses 1823 and 1824.

[0083] For example, in FIG. 5, the light beams BY and BM are focused on the curve FL by the fθ lens 1811. Also, the light beams BC and BK are focused on the curve FL by the fθ lens 1813. The focal positions of the light beams BY, BM, BC, and BK are different in the sub-scanning direction.

[0084] As a result, a separation position between the light beams BY, BM and BC, BK in the sub-scanning direction can be created at a position immediately after passing through the fθ lenses 1811 and 1813.

[0085] Also, as shown in FIG. 4, the post-deflection optical system 1801 has three folding mirrors 1831, 1841, and 1851 for bending the optical path of the light beam BY between the two fθ lenses 1811 and 1821. Further, the post-deflection optical system 1801 has two folding mirrors 1831 and 1842 for bending the optical path of the light beam BM between the two fθ lenses 1811 and 1822. Since the folding mirror 1831 is common to the light beams BY and BM, the post-deflection optical system 1801 has a total of four folding mirrors 1831, 1841, 1842, and 1851.

[0086] The post-deflection optical system 1803 has four folding mirrors 1833, 1843, 1853, and 1863 for bending the optical path of the light beam BC between the two fθ lenses 1813 and 1823. Further, the post-deflection optical system 1803 has three folding mirrors 1833, 1843, and 1854 for bending the optical path of the light beam BK between the two fθ lenses 1813 and 1824. Since the folding mirrors 1833 and 1843 are common to the light beams BC and BK, the post-deflection optical system 1803 has a total of five folding mirrors 1833, 1842, 1853, 1854, and 1863.

[0087] The post-deflection optical system 1801 also has a synchronization optical system for synchronizing the light beam BY, and this synchronization optical system includes a photodetector 1871, an optical path correction element 1881, and a folding mirror 1891.

[0088] In other words, the optical scanning device 116 has a first scanning optical system and a second scanning optical system. The first scanning optical system scans the light beams BY and BM and guides them to the image forming units 1151 and 1152. The second scanning optical system scans the light beams BC and BK and guides them to the image forming units 1153 and 1154.

[0089] The first scanning optical system includes light sources 1531 and 1532, pre-deviation optical systems 1601 and 1602, a light deflector 170, and a post-deviation optical system 1801. The second scanning optical system includes light sources 1533 and 1534, pre-deviation optical systems 1603 and 1604, the light deflector 170, and a post-deviation optical system 1803. That is, the first scanning optical system and the second scanning optical system commonly have one light deflector 170.

[0090] As shown in FIG. 5, the first scanning optical system scans the light beams BY and BM emitted from the light sources 1531 and 1532 in the direction indicated by the arrow SD within the range of the image area IA. As shown in FIG. 4, the first scanning optical system also forms images of the light beams BY and BM on the surfaces of the photoreceptor drums 11511 and 11521 of the image forming units 1151 and 1152, respectively. As a result, the light beams BY and BM linearly move on the surfaces of the photoreceptor drums 11511 and 11521, respectively. Further, the surfaces of the photoreceptor drums 11511 and 11521 are moved by the rotation of the photoreceptor drums 11511 and 11521. As a result, an electrostatic latent image is formed on the surfaces of the photoreceptor drums 11511 and 11521.

[0091] Also, the second scanning optical system scans the light beams BC and BK emitted from the light sources 1533 and 1534 in the direction indicated by the arrow SD within the range of the image area IA. As shown in FIG. 4, the second scanning optical system also forms images of the light beams BC and BK on the surfaces of the photoreceptor drums 11531 and 11541 of the image forming units 1153 and 1154, respectively. As a result, the light beams BC and BK linearly move on the surfaces of the photoreceptor drums 11531 and 11541, respectively. Further, the surfaces of the photoreceptor drums 11531 and 11541 are moved by the rotation of the photoreceptor drums 11531 and 11541. As a result, an electrostatic latent image is formed on the surfaces of the photoreceptor drums 11531 and 11541.

[0092] The scanning directions of the light beams BY, BM, BC, and BK, i.e., the direction indicated by the arrow SD, are parallel to the rotation axes of the photoreceptor drums 11511, 11521, 11531, and 11541. Therefore, the moving direction of the surfaces of the photoreceptor drums 11511, 11521, 11531, and 11541 is perpendicular to the scanning direction of the light beams BY, BM, BC, and BK. The surfaces of the photoreceptor drums 11511, 11521, 11531, and 11541 are the surfaces to be scanned.

[0093] Hereinafter, the scanning direction of the light beams BY, BM, BC, and BK is referred to as the main scanning direction, and the direction perpendicular to the scanning direction of the light beams BY, BM, BC, and BK is referred to as the sub-scanning direction.

[0094] The optical scanning device 116 includes a first cover glass 1911, a second cover glass 1921, and third cover glasses 1931, 1932, 1933, and 1934.

[0095] The first cover glass 1911 is disposed on the optical paths of the pre-deflection optical systems 1601 to 1604. The second cover glass 1921 is disposed on the optical paths of the post-deflection optical systems 1801 and 1803. The third cover glasses 1931 to 1934 are disposed on the optical paths of the post-deflection optical systems 1801 and 1803.

[0096] The first cover glass 1911 is disposed between the cylindrical lenses 1641 to 1644 and the optical deflector 170. The second cover glass 1921 is disposed between the optical deflector 170 and the fθ lenses 1811 and 1813. The third cover glasses 1931 to 1934 are respectively disposed between the fθ lenses 1821 to 1824 and the image forming units 1151 to 1154.

[0097] The first cover glass 1911 and the second cover glass 1921 are provided to prevent the leakage of the wind noise when the polygon mirror 171 rotates. The third cover glasses 1931 to 1934 cover the outlets from which the light beams BY, BM, BC, and BK are emitted in the housing of the optical scanning device 116.

[0098] [Two fθ lenses 1811, 1813] Next, with reference to FIGS. 9 to 11, the fθ lenses 1811, 1813 will be described. FIG. 9 is a perspective view of the fθ lenses 1811, 1813 as viewed from the incident surface side. FIG. 10 is a perspective view of the fθ lenses 1811, 1813 as viewed from the exit surface side. FIG. 11 is a longitudinal sectional view of the fθ lenses 1811, 1813. The longitudinal section shown in FIG. 11 is, for example, the section of the fθ lenses 1811, 1813 at the center in the main scanning direction.

[0099] Here, for convenience of explanation, as shown in FIGS. 9 and 10, an XYZ orthogonal coordinate system is set. That is, the X-axis is set in the main scanning direction, the Y-axis is set in the sub-scanning direction, and the Z-axis is set perpendicular to the X-axis and the Y-axis. The X-axis corresponds to the longitudinal axis of the fθ lenses 1811, 1813.

[0100] The two fθ lenses 1811, 1813 are similar structures, and are arranged at the same position in the ZX plane and are arranged overlappingly in the Y direction.

[0101] The fθ lenses 1811, 1813 each have a pair of first surfaces 210, 230 and second surfaces 220, 240 facing each other. The first surfaces 210, 230 and the second surfaces 220, 240 extend in a rectangle along the X-axis. The first surface 210 is the incident surface of the light beams BY, BM, and the second surface 220 is the exit surface of the light beams BY, BM. Also, the first surface 230 is the incident surface of the light beams BC, BK, and the second surface 240 is the exit surface of the light beams BC, BK.

[0102] The first surfaces 210, 230 each have a first lens region 211, 231, and the second surfaces 220, 240 each have a second lens region 221, 241.

[0103] The first lens region 211 and the second lens region 221 have an optical effect on the passing light beams BY, BM. The first lens region 211 and the second lens region 221 as a whole give a positive optical power to the light beams BY, BM.

[0104] The first lens region 231 and the second lens region 241 exert an optical action on the passing light beams BC, BK. The first lens region 231 and the second lens region 241, as a whole, provide positive optical power to the light beams BC, BK.

[0105] The first lens regions 211, 231 and the second lens regions 221, 241 extend rectilinearly along the X-axis. The first lens region 211 has a first extreme value of curvature at the first pair of opposite sides 212, 213 that extend parallel to the X-axis. Similarly, the first lens region 231 has a first extreme value of curvature at the first pair of opposite sides 232, 233 that extend parallel to the X-axis. Also, the second lens region 221 has a second extreme value of curvature at the second pair of opposite sides 222, 223 that extend parallel to the X-axis. Similarly, the second lens region 241 has a second extreme value of curvature at the second pair of opposite sides 242, 243 that extend parallel to the X-axis.

[0106] The first surface 210 has a pair of first outer extreme value extension surfaces 214, 215 that extend along the Y-axis while maintaining the first extreme value. The outer extreme value extension surfaces 214, 215 extend from the first pair of opposite sides 212, 213 of the first lens region 211 to the opposite sides 216, 217 of the first surface 210 that extend parallel to the X-axis. Similarly, the first surface 230 has a pair of first outer extreme value extension surfaces 234, 235 that extend along the Y-axis while maintaining the first extreme value. The outer extreme value extension surfaces 234, 235 extend from the first pair of opposite sides 232, 233 of the first lens region 231 to the opposite sides 236, 237 of the first surface 230 that extend parallel to the X-axis.

[0107] Further, the second surface 220 has a pair of first outer extreme value extension surfaces 224, 225 that maintain the second extreme value and extend along the Y-axis. The outer extreme value extension surfaces 224, 225 extend from the second opposite sides 222, 223 of the second lens region 221 to the opposite sides 226, 227 of the second surface 220 that are parallel to the X-axis. Similarly, the second surface 240 has a pair of second outer extreme value extension surfaces 244, 245 that maintain the second extreme value and extend along the Y-axis. The outer extreme value extension surfaces 244, 245 extend from the second opposite sides 242, 243 of the second lens region 241 to the opposite sides 246, 247 of the second surface 240 that are parallel to the X-axis.

[0108] As shown in FIG. 11, the fθ lenses 1811, 1813 each have an optical axis 1812, 1814. Taking the positions of the optical axes 1812, 1814 of the fθ lenses 1811, 1813 as Y = 0 respectively, and based on the positions of the respective optical axes 1812, 1814, the positions along the Y-axis of each pair of opposite sides are as follows.

[0109] The positions of the first opposite sides 212, 232 of the first lens regions 211, 231 are Y = +L1. The positions of the first opposite sides 213, 233 of the first lens regions 211, 231 are Y = -L1. The positions of the second opposite sides 222, 242 of the second lens regions 221, 241 are Y = +L2. The positions of the second opposite sides 223, 243 of the second lens regions 221, 241 are Y = -L2. The positions of the opposite sides 216, 236 of the first surfaces 210, 230 are Y = +L0. The positions of the opposite sides 217, 237 of the first surfaces 210, 230 are Y = -L0. The positions of the opposite sides 226, 226 of the second surfaces 220, 240 are Y = +L0. The positions of the opposite sides 227, 247 of the second surfaces 220, 240 are Y = -L0. Here, |L1| < |L2| < |L0|. Therefore, the distance between the optical axes of the fθ lenses 1811, 1813 is 2L0.

[0110] [Optical Scanning Device According to the Second Example] Next, with reference to FIG. 12, the optical scanning device 116 according to the second example will be described. FIG. 12 is a diagram showing the optical scanning device 116 according to the second example applicable to the image forming apparatus 100 shown in FIG. 1. In FIG. 12, members denoted by the same reference numerals as those in FIG. 4 are the same members, and the description thereof will be omitted. Hereinafter, the description will focus on the differences. That is, the parts not mentioned in the following description are the same as those of the optical scanning device 116 according to the first example.

[0111] The optical scanning device 116 according to the second example has a single fθ lens 1810 instead of the two fθ lenses 1811 and 1813 of the optical scanning device 116 according to the first example. That is, the two post-deviation optical systems 1801 and 1803 commonly have the fθ lens 1810. The fθ lens 1810 combines the functions of the fθ lens 1811 and the fθ lens 1813. The dimension of the fθ lens 1810 in the sub-scanning direction is smaller than the combined dimension of the two fθ lenses 1811 and 1813 in the sub-scanning direction.

[0112] Accordingly, the dimension of the polygon mirror 171 of the optical deflector 170 in the sub-scanning direction is also reduced. Further, the interval in the sub-scanning direction between the two pre-deviation optical systems 1601 and 1602 and the two pre-deviation optical systems 1603 and 1604 is also reduced. As a result, the optical scanning device 116 according to the second example has a reduced dimension in the sub-scanning direction compared to the optical scanning device 116 according to the first example.

[0113] [Single fθ lens 1810] Next, with reference to FIGS. 13 to 15, the fθ lens 1810 will be described. FIG. 13 is a perspective view of the fθ lens 1810 as viewed from the incident surface side. FIG. 14 is a perspective view of the fθ lens 1810 as viewed from the exit surface side. FIG. 15 is a longitudinal sectional view of the fθ lens 1810. The longitudinal section shown in FIG. 15 is, for example, the section of the fθ lens 1810 at the center in the main scanning direction.

[0114] Here, for convenience of explanation, as shown in FIGS. 13 and 14, similar to FIGS. 9 and 10, an XYZ orthogonal coordinate system is set. That is, the X-axis is set in the main scanning direction, the Y-axis is set in the sub-scanning direction, and the Z-axis is set perpendicular to the X-axis and the Y-axis. The X-axis corresponds to the longitudinal axis of the fθ lens 1810.

[0115] The fθ lens 1810 has a pair of first surfaces 310 and second surfaces 330 facing each other. The first surface 310 and the second surface 330 extend in a rectangle along the X-axis. The first surface 310 is the incident surface of the light beams BY, BM, BC, BK, and the second surface 330 is the exit surface of the light beams BY, BM, BC, BK.

[0116] The first surface 310 has a pair of first lens regions 311, 315, and the second surface 330 has a pair of second lens regions 331, 335.

[0117] The first lens region 311 and the second lens region 331 exert an optical action on the passing light beams BY, BM. The first lens region 311 and the second lens region 331, as a whole, give positive optical power to the light beams BY, BM.

[0118] The first lens region 315 and the second lens region 335 exert an optical action on the passing light beams BC, BK. The first lens region 315 and the second lens region 335, as a whole, give positive optical power to the light beams BC, BK.

[0119] The first lens regions 311, 315 and the second lens regions 331, 335 extend in a rectangle along the X-axis. The first lens region 311 has a first extreme value of curvature at the first opposite sides 312, 313 extending parallel to the X-axis. Similarly, the first lens region 315 has a first extreme value of curvature at the first opposite sides 313, 317 extending parallel to the X-axis. Also, the second lens region 331 has a second extreme value of curvature at the second opposite sides 332, 333 extending parallel to the X-axis. Similarly, the second lens region 335 has a second extreme value of curvature at the second opposite sides 336, 337 extending parallel to the X-axis.

[0120] The dimension of the first lens regions 311 and 315 along the Y-axis is smaller than the dimension of the second lens regions 331 and 335 along the Y-axis. Also, the pair of second lens regions 331 and 335 are smoothly continuous at the second pair of opposite sides 333 and 336 adjacent to each other. That is, the position of the second pair of opposite sides 333 along the Y-axis coincides with the position of the second pair of opposite sides 336 along the Y-axis.

[0121] On the other hand, the first surface 310 has an extreme value extension surface 318 that extends along the Y-axis while maintaining the first extreme value between the first side 313 of the first lens region 311 and the first side 316 of the first lens region 315. The pair of first lens regions 311 and 315 are smoothly continuous with the extreme value extension surface 318.

[0122] The first surface 310 has a pair of first outer extreme value extension surfaces 314 and 319 that extend along the Y-axis while maintaining the first extreme value. The pair of first outer extreme value extension surfaces 314 and 319 extend from the first pair of opposite sides 312 and 317 of the pair of first lens regions 311 and 315 that are spaced apart from each other to the opposite sides 320 and 321 of the first surface 310 that extend parallel to the Y-axis.

[0123] Also, the second surface 330 has a pair of second outer extreme value extension surfaces 334 and 339 that extend along the Y-axis while maintaining the second extreme value. The pair of second outer extreme value extension surfaces 334 and 339 extend from the second pair of opposite sides 332 and 337 of the pair of second lens regions 331 and 335 that are spaced apart from each other to the opposite sides 340 and 341 of the second surface 330 that extend parallel to the Y-axis.

[0124] As can be seen by comparing FIG. 11 and FIG. 15, the dimension along the Y-axis of the structure in which two fθ lenses 1811 and 1813 are stacked along the Y-axis is 4L0, whereas the dimension along the Y-axis of a single fθ lens 1810 is 2L0 + 2L2. That is, the dimension along the Y-axis of a single fθ lens 1810 is reduced by (2L0 - 2L2) compared to the structure in which two fθ lenses 1811 and 1813 are stacked along the Y-axis.

[0125] Accordingly, the optical scanning device 116 according to the second example can be expected to have a reduced dimension along the Y-axis compared to the optical scanning device 116 according to the first example.

[0126] [Effect] The optical scanning device 116 according to the embodiment scans all of the four light beams BY, BM, BC, and BK emitted from the four light sources 1531, 1532, 1533, and 1534 by reflecting them on the same reflecting surface 172 of the polygon mirror 171 of the light deflector 170. Therefore, color shift is less likely to occur compared to an optical scanning device configured to reflect the four light beams on different reflecting surfaces of the polygon mirror.

[0127] In an optical scanning device having such a configuration, it is necessary to use a plurality of synchronization optical systems to align the writing positions of the light beams. If the position of the sensor of the synchronization optical system is displaced due to a temperature change or the like, the writing position of the light beam is displaced and color shift occurs.

[0128] On the other hand, in the optical scanning device 116 according to the embodiment, only one necessary synchronization optical system is required. Therefore, even if a displacement occurs in the photodetector 1871, the writing positions of the light beams are equally displaced, so color shift is less likely to occur.

[0129] The fθ lens 1810 according to the embodiment has a first surface 310 having a pair of first lens regions 311 and 315, and a second surface 330 having a pair of second lens regions 331 and 335. The first lens regions 311 and 315 and the second lens regions 331 and 335 extend in a rectangle along the X-axis. The first lens region 311 has a first extreme value of curvature at the first opposite sides 312 and 313. The first lens region 315 has a first extreme value of curvature at the first opposite sides 313 and 317. The second lens region 331 has a second extreme value of curvature at the second opposite sides 332 and 333. The second lens region 335 has a second extreme value of curvature at the second opposite sides 336 and 337. The second lens regions 331 and 335 are smoothly continuous at the second opposite sides 333 and 336 adjacent to each other. The pair of first lens regions 311 and 315 are smoothly continuous at the extreme value extension surface 318.

[0130] As a result, an optical element and an optical scanning device with excellent characteristics are provided.

[0131] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalent scope thereof.

[0132] The invention disclosed in the embodiments is described below. [1] having a first surface and a second surface that face each other and extend in a rectangle along the longitudinal axis, the first surface having a pair of first lens regions that exert an optical action on a passing light beam, the second surface having a pair of second lens regions that exert an optical action on a passing light beam, both the first lens region and the second lens region extend in a rectangle along the longitudinal axis, the first lens region having a first extreme value of curvature at a first pair of sides extending parallel to the longitudinal axis, the second lens region having a second extreme value of curvature at a second pair of sides extending parallel to the longitudinal axis, the dimension of the first lens region in a direction perpendicular to the longitudinal axis is smaller than the dimension of the second lens region, the pair of second lens regions are smoothly continuous at the second pair of sides adjacent to each other, Optical element. [2] the pair of first lens regions are smoothly continuous with an extreme value extension surface that extends perpendicular to the longitudinal axis while maintaining the first extreme value between the first pair of sides adjacent to each other, The optical element according to [1]. [3] a first light source that emits a first light beam, a second light source that emits a second light beam, a third light source that emits a third light beam, a fourth light source that emits a fourth light beam, an optical deflector that dynamically deflects the first light beam, the second light beam, the third light beam, and the fourth light beam on the same reflecting surface and scans them in the main scanning direction, a first pre-deflection optical system that guides the first light beam emitted from the first light source to the reflecting surface, a second pre-deflection optical system that guides the second light beam emitted from the second light source to the reflecting surface, a third pre-deflection optical system that guides the third light beam emitted from the third light source to the reflecting surface, a fourth pre-deflection optical system that guides the fourth light beam emitted from the fourth light source to the reflecting surface, a first post-deflection optical system having a first optical element that imparts optical characteristics to the first light beam and the second light beam scanned by the optical deflector, a second optical element that cooperates with the first optical element to form an image of the first light beam, and a third optical element that cooperates with the first optical element to form an image of the second light beam, a second post-deflection optical system having a fourth optical element that imparts optical characteristics to the third light beam and the fourth light beam scanned by the optical deflector, a fifth optical element that cooperates with the second optical element to form an image of the third light beam, and a sixth optical element that cooperates with the second optical element to form an image of the fourth light beam, comprising, in a projection onto a plane parallel to the main scanning direction, the first light source and the second light source are arranged so as to have a first opening angle, and the third light source and the fourth light source are arranged so as to have a second opening angle, in a sub-scanning direction perpendicular to the plane, the first light source, the second light source, the third light source, and the fourth light source are arranged at different positions, The first pre-deviation optical system, the second pre-deviation optical system, the third pre-deviation optical system, and the fourth pre-deviation optical system each direct the first light beam, the second light beam, the third light beam, and the fourth light beam to different positions in the sub-scanning direction with respect to the reflecting surface. The first optical element and the fourth optical element are arranged at the same position in the projection onto the plane and are arranged overlapping in the sub-scanning direction. Optical scanning device. [4] The first post-deviation optical system and the second post-deviation optical system commonly have an integrally formed optical element in which the first optical element and the fourth optical element are integrally formed. The optical scanning device according to [3]. [5] The integrally formed optical element has a first surface and a second surface that face each other and extend in a rectangle along the longitudinal axis. The first surface has a pair of first lens regions that exert an optical action on the passing light beam. The second surface has a pair of second lens regions that exert an optical action on the passing light beam. Both the first lens region and the second lens region extend in a rectangle along the longitudinal axis. The first lens region has a first extreme value of curvature at a first pair of opposite sides that extend parallel to the longitudinal axis. The second lens region has a second extreme value of curvature at a second pair of opposite sides that extend parallel to the longitudinal axis. The dimension of the first lens region in the direction perpendicular to the longitudinal axis is smaller than the dimension of the second lens region. The pair of second lens regions are smoothly continuous at the second pair of opposite sides adjacent to each other. The optical scanning device according to [4]. [6] Twice the dimension of the second lens region in the direction perpendicular to the longitudinal axis is the distance between the optical axes of the pair of second lens regions. The optical element according to [1]. [7] The first surface has a pair of first outer extreme value extension surfaces that extend perpendicular to the longitudinal axis while maintaining the first extreme value from the first opposite sides of the pair of first lens regions that are spaced apart from each other to the opposite sides of the first surface that extend parallel to the longitudinal axis. The second surface has a pair of second extreme value extension surfaces that extend perpendicular to the longitudinal axis while maintaining the second extreme value from the second opposite sides of the pair of second lens regions that are spaced apart from each other to the opposite sides of the second surface that extend parallel to the longitudinal axis. The optical element according to [1]. [8] Each of the first optical element and the fourth optical element has a first surface and a second surface that face each other and extend rectangularly along the longitudinal axis. The first surface has a first lens region that optically acts on the passing light beam. The second surface has a second lens region that optically acts on the passing light beam. Both the first lens region and the second lens region extend rectangularly along the longitudinal axis. The first lens region has a first extreme value of curvature at the first opposite sides that extend parallel to the longitudinal axis. The second lens region has a second extreme value of curvature at the second opposite sides that extend parallel to the longitudinal axis. The first surface has a pair of first outer extreme value extension surfaces that extend perpendicular to the longitudinal axis while maintaining the first extreme value from the first opposite sides of the first lens region to the opposite sides of the first surface that extend parallel to the longitudinal axis. The second surface has a pair of second extreme value extension surfaces that extend perpendicular to the longitudinal axis while maintaining the second extreme value from the second opposite sides of the second lens region to the opposite sides of the second surface that extend parallel to the longitudinal axis. The optical scanning device according to [3]. [9] The optical axis distance between the pair of second lens regions of the integrally formed optical element is twice the dimension of the second lens region in the direction perpendicular to the longitudinal axis. The optical scanning device according to [5].

[10] The first surface of the integrally formed optical element has a pair of first outer extreme value extension surfaces that extend perpendicular to the longitudinal axis while maintaining the first extreme value from the first opposite sides of the pair of first lens regions that are spaced apart from each other to the opposite sides of the first surface that extend parallel to the longitudinal axis. The second surface of the integrally formed optical element has a pair of second extreme value extension surfaces that extend perpendicular to the longitudinal axis while maintaining the second extreme value from the second opposite sides of the pair of second lens regions that are spaced apart from each other to the opposite sides of the second surface that extend parallel to the longitudinal axis. The optical scanning device according to [5].

Explanation of reference numerals

[0133] 100…Image forming apparatus, 101…Printer, 102…Scanner, 103…Operation panel, 111…Paper feed tray, 112…Manual feed tray, 113…Paper feed roller, 116…Optical scanning device, 117…Transfer belt, 118…Secondary transfer roller, 119…Fixing unit, 120…Duplex unit, 121…Paper output tray, 131…Reading module, 132…Original document feeder, 141…Processor, 142…ROM, 143…RAM, 144…Auxiliary storage device, 145…Communication interface, 146…Bus, 170…Optical deflector, 171…Polygon mirror, 172…Reflection surface, 175…Motor, 176…Rotation axis, 1810…fθ lens, 210…First surface, 211…First lens region, 212, 213…First pair of opposite sides, 214, 215…First outer extreme value extension surface, 216, 217…Opposite sides, 220…Second surface, 221…Second lens region, 222, 223…Second pair of opposite sides, 224, 225…Second outer extreme value extension surface, 226, 227…Opposite sides, 230…First surface, 231…First lens region, 232, 233…First pair of opposite sides, 234, 235…First outer extreme value extension surface, 236, 237…Opposite sides, 240…Second surface, 241…Second lens region, 242, 243…Second pair of opposite sides, 244, 245…Second outer extreme value extension surface, 246, 247…Opposite sides, 310…First surface, 311…First lens region, 312, 313…First pair of opposite sides, 314, 319…First outer extreme value extension surface, 315…First lens region, 316, 317…First pair of opposite sides, 318…Extreme value extension surface, 320…Opposite side, 321…Opposite side, 330…Second surface, 331, 335…Second lens region, 332, 333…Second pair of opposite sides, 334, 339…Second outer extreme value extension surface, 336, 337…Second pair of opposite sides, 340, 341…Opposite sides, 1031…Touch panel, 1032…Input device, 1141~1144…Toner cartridge, 1151~1154…Image forming unit, 1191…Heating unit, 1192…Pressing roller, 1531~1534…Light source, 1541~Light source substrate, 1601~1604…Pre-deviation optical system, 1621~Collimator lens, 1631~…Aperture, 1641~1644…Cylinder lens, 1653, 1654…Folding mirror, 1801, 1803…Post-deviation optical system, 1811, 1813…fθ lens, 1812, 1814…Optical axis, 1821~1824…fθ lens, 1831, 1833, 1841, 1842, 1843,1851, 1853, 1854, 1863... folding mirror, 1871... photodetector, 1881... optical path correction element, 1891... folding mirror, 1911, 1921... cover glass, 1931 - 1934... cover glass, 11512... charging unit, 11513... developing unit, 11514... secondary transfer roller, 11515... cleaner, 11516... charge elimination lamp, 11511 - 11541... photoreceptor drum.,

Claims

1. The plate has a first surface and a second surface that are opposed to each other and extend in a rectangular shape along a longitudinal axis, the first surface having a pair of first lens regions for providing an optical effect to a light beam passing therethrough; the second surface having a pair of second lens regions for providing an optical effect to a light beam passing therethrough; the first lens region and the second lens region both extend in a rectangular shape along the longitudinal axis; The first lens region has a first extremum of curvature at a first opposite side extending parallel to the longitudinal axis; the second lens region has a second extremum of curvature at a second opposite side extending parallel to the longitudinal axis; a dimension of the first lens region in a direction perpendicular to the longitudinal axis is smaller than a dimension of the second lens region; The pair of second lens regions are smoothly continuous with each other on the second opposite sides adjacent to each other. Optical elements.

2. The pair of first lens regions are smoothly connected to an extreme extension surface extending perpendicular to the longitudinal axis while maintaining the first extreme value between the adjacent first opposite sides. The optical element according to claim 1 .

3. a first light source that emits a first light beam; a second light source that emits a second light beam; a third light source that emits a third light beam; a fourth light source that emits a fourth light beam; an optical deflector that dynamically deflects the first light beam, the second light beam, the third light beam, and the fourth light beam on the same reflecting surface to scan in a main scanning direction; a first pre-deflection optical system that guides the first light beam emitted from the first light source to the reflecting surface; a second pre-deflection optical system that guides the second light beam emitted from the second light source to the reflecting surface; a third pre-deflection optical system that guides the third light beam emitted from the third light source to the reflecting surface; a fourth pre-deflection optical system that guides the fourth light beam emitted from the fourth light source to the reflecting surface; a first post-deflection optical system including a first optical element that imparts optical characteristics to the first light beam and the second light beam scanned by the optical deflector, a second optical element that cooperates with the first optical element to form an image of the first light beam, and a third optical element that cooperates with the first optical element to form an image of the second light beam; a second post-deflection optical system including a fourth optical element that imparts optical characteristics to the third light beam and the fourth light beam scanned by the optical deflector, a fifth optical element that cooperates with the second optical element to form an image of the third light beam, and a sixth optical element that cooperates with the second optical element to form an image of the fourth light beam; Equipped with When projected onto a plane parallel to a main scanning direction, the first light source and the second light source are disposed to have a first opening angle, and the third light source and the fourth light source are disposed to have a second opening angle, the first light source, the second light source, the third light source, and the fourth light source are disposed at different positions in a sub-scanning direction perpendicular to the plane, the first pre-deflection optical system, the second pre-deflection optical system, the third pre-deflection optical system, and the fourth pre-deflection optical system respectively guide the first light beam, the second light beam, the third light beam, and the fourth light beam to different positions in the sub-scanning direction with respect to the reflecting surface, the first optical element and the fourth optical element are disposed at the same position when projected onto the plane and are disposed to overlap in the sub-scanning direction. Optical scanning device.

4. the first post-deflection optical system and the second post-deflection optical system have in common an integrally formed optical element in which the first optical element and the fourth optical element are integrally formed; 4. The optical scanning device according to claim 3.

5. The integrally formed optical element has a first surface and a second surface that are opposed to each other and extend in a rectangular shape along a longitudinal axis, the first surface having a pair of first lens regions for providing an optical effect to a light beam passing therethrough; the second surface having a pair of second lens regions for providing an optical effect to a light beam passing therethrough; the first lens region and the second lens region both extend in a rectangular shape along the longitudinal axis; The first lens region has a first extremum of curvature at a first opposite side extending parallel to the longitudinal axis; the second lens region has a second extremum of curvature at a second opposite side extending parallel to the longitudinal axis; a dimension of the first lens region in a direction perpendicular to the longitudinal axis is smaller than a dimension of the second lens region; The pair of second lens regions are smoothly continuous with each other on the second opposite sides adjacent to each other.

5. The optical scanning device according to claim 4.

Images