Optical scanner and image forming apparatus

Abstract

To provide an optical scanner that prevents a return beam reflected in an aperture from being incident on a light source.SOLUTION: An optical scanner according to an aspect of the present disclosure comprises: a light source section; a deflection scanning unit; and an incident optical system that is provided on an optical path reaching the deflection scanning unit from the light source section, and makes a beam radiated from the light source section incident on the deflection scanning unit. The incident optical system includes: a cylindrical lens that is provided between the light source section and the deflection scanning unit and condenses the beam toward the deflection scanning unit; and an aperture that is provided between the cylindrical lens and the deflection scanning unit, and has an opening narrowing the beam in a second direction orthogonal to a first direction, the first direction being the direction of travel of the beam along the optical path. The perpendicular of the aperture is provided inclined with respect to the first direction when seen from a third direction orthogonal to the first direction and the second direction.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present disclosure relates to an optical scanning device and an image forming apparatus. [Background technology]

[0002] Conventionally, an image forming apparatus has been disclosed that uses an optical scanning optical system having a light source means equipped with multiple light sources, a collimator lens that converts multiple divergent light beams emitted from the light source means into approximately parallel light beams or convergent light beams, a cylindrical lens that focuses the light beam converted into the approximately parallel light beam or convergent light beam, an aperture that limits the light beam width of the focused light beam, and a polygon mirror that reflects and deflects the multiple light beams in the main scanning direction (see, for example, Patent Document 1).

[0003] In the optical scanning optical system described in Patent Document 1, the cylindrical lens emits the incident light beam without refracting it in the direction corresponding to the main scanning direction of the surface to be scanned, and refracts it in the direction corresponding to the sub-scanning direction of the surface to be scanned so that it converges toward the deflection surface of the polygon mirror. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2001-228422 A Summary of the Invention [Problem to be solved by the invention]

[0005] In such an optical scanning optical system, the aperture (stop) faces the cylindrical lens in the direction of beam propagation, so that a portion of the beam emitted from the cylindrical lens is specularly reflected by the aperture (stop), and the specularly reflected return beam may be incident on the exit surface of the cylindrical lens.

[0006] For example, referring to FIG. 11, a return light in a light scanning optical system having four light sources corresponding to four colors, black (Bk), cyan (C), magenta (M) and yellow (Y), will be described.

[0007] Fig. 11A is a view seen from the direction of the rotation axis of the polygon mirror 4. As shown in Fig. 11A, a part of the beam BM emitted from the cylindrical lens 2 is guided toward the polygon mirror 4 through an opening 3a formed in the aperture 3, and the remaining part is specularly reflected by the aperture 3 to become a return beam RBM.

[0008] Fig. 11B is a view seen from a direction perpendicular to the rotation axis direction of the polygon mirror 4. In the optical scanning optical system shown in Fig. 11B, beams BM from light sources corresponding to each color are incident on the cylindrical lens 2 at different positions in the vertical direction. For example, the beam BM located at the top is a beam BM from a light source corresponding to black (Bk), the beam BM located second from the top is a beam BM from a light source corresponding to cyan (C), the beam BM located second from the bottom is a beam BM from a light source corresponding to magenta (M), and the beam BM located at the bottom is a beam BM from a light source corresponding to yellow (Y).

[0009] As shown in FIG. 11B, when the beam BM from the light source corresponding to black (Bk) is specularly reflected by the aperture 3, the specularly reflected return beam RBM is incident on the point Q near the point P where the beam BM from the light source corresponding to yellow (Y) is emitted, and the return beam RBM incident on the point Q may be incident on the light source corresponding to yellow (Y) along the optical path corresponding to yellow (Y). Similarly, when the beam BM from the light source corresponding to yellow (Y) is specularly reflected by the aperture 3, the specularly reflected return beam RBM may be incident on the light source corresponding to black (Bk). Similarly, when the beam BM from the light source corresponding to cyan (C) is specularly reflected by the aperture 3, the specularly reflected return beam RBM may be incident on the light source corresponding to magenta (M). Similarly, when the beam BM from the light source corresponding to magenta (M) is specularly reflected by the aperture 3, the specularly reflected return beam RBM may be incident on the light source corresponding to cyan (C).

[0010] The above describes the return beam in an optical scanning optical system equipped with a light source that supports multiple colors, but even in the case of a light source that supports a single color, it is possible that the beam emitted from the cylindrical lens is specularly reflected by the aperture, and the specularly reflected return beam is incident on the light source.

[0011] In an optical scanning device equipped with an optical scanning optical system as described above, when an APC (Automatic Power Control) control method is adopted in which the optical output (light emitting power) of the light source is monitored and the drive current of the light source is controlled based on the monitored light output, as described above, if the beam from the light source is specularly reflected by the aperture and a return beam is incident on the light source, the optical output of the light source cannot be accurately monitored, and the light emitting power of the light source may become unstable.

[0012] Therefore, one aspect of the present disclosure has an object to provide, for example, an optical scanning device that suppresses a return beam reflected by an aperture from being incident on a light source, and an image forming apparatus including the optical scanning device. [Means for solving the problem]

[0013] An optical scanning device according to one embodiment of the present disclosure comprises a light source unit, a deflection scanning unit which deflects and scans a beam from the light source unit, and an incident optical system which is arranged on an optical path from the light source unit to the deflection scanning unit and causes the beam irradiated from the light source unit to be incident on the deflection scanning unit, wherein the incident optical system includes: a cylindrical lens which is arranged between the light source unit and the deflection scanning unit and which focuses the beam toward the deflection scanning unit; and an aperture which is arranged between the cylindrical lens and the deflection scanning unit and which has an opening which narrows the beam in a second direction perpendicular to a first direction when the direction of propagation of the beam along the optical path is defined as a first direction, and a normal to the aperture is arranged at an angle with respect to the first direction when viewed from a third direction perpendicular to the first direction and the second direction.

[0014] An image forming apparatus according to an aspect of the present disclosure includes the optical scanning device described above. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an image forming apparatus. [Diagram 2] FIG. 2 is a schematic plan view showing an optical system of the optical scanning device. [Diagram 3] FIG. 2 is a schematic side view showing an optical system of the optical scanning device. [Figure 4A] 2 is a diagram of a light source in the optical scanning device as viewed from the beam emission side in the optical axis direction. [Figure 4B] 2 is a diagram showing a light source in the optical scanning device as viewed from a direction perpendicular to the optical axis direction. [Diagram 5] FIG. 2 is a perspective view showing a state in which an upper cover of the optical scanning device is removed. [Figure 6] FIG. 2 is a plan view showing the internal structure of the optical scanning device. [Figure 7] 4 is a cross-sectional view of the optical scanning device showing the internal structure of a case. [Figure 8]2 is a perspective view of the optical scanning device, showing an optical path from a cylindrical lens to a deflection scanning unit. FIG. [Figure 9] FIG. 13 is a schematic diagram showing the inclination of a second aperture with respect to the beam propagation direction. [Figure 10] 11 is a table showing measurement results of sound pressure level versus distance from a deflection scanning unit. [Figure 11A] FIG. 1 is a schematic diagram showing an incident optical system of a conventional optical scanning device. [Figure 11B] FIG. 1 is a schematic diagram showing an incident optical system of a conventional optical scanning device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the drawings, the same or equivalent elements are denoted by the same reference numerals, and duplicated descriptions will be omitted.

[0017] An image forming apparatus 1 according to one embodiment of the present disclosure will be described below with reference to Fig. 1. Fig. 1 is a schematic cross-sectional view showing the image forming apparatus 1. In the following description, the side on which the device body 10 is placed is defined as the lower side, the opposite side (the image reading device 20 side) as the upper side, the side on which the transport path R1 for transporting paper is provided in the device body 10 is defined as the right side, and the opposite side is defined as the left side.

[0018] The image forming apparatus 1 is, for example, a multifunction machine having a copying function, a printer function, a scanner function, a facsimile function, etc. The image forming apparatus 1 transmits image data read by the image reading device 20 to an external device, and also forms an image on an original document in single color or multiple colors based on the image data of the read original document or image data received from an external device.

[0019] The image forming apparatus 1 includes an apparatus main body 10 and an image reading device 20. The apparatus main body 10 forms a monochromatic or multicolor image on a recording medium such as paper, based on image data read by the image reading device 20 or image data transmitted from an external terminal.

[0020] The image reading device 20 includes an original placement table 21 made of a transparent material, an original pressing cover 22 that is attached to the original placement table 21 so as to be freely opened and closed, and an image reading unit 23 that has a light source, multiple mirrors, an imaging lens, a line sensor, etc., and generates image data based on an image of the original surface. A display operation unit (not shown) that accepts input operations by a user is provided in front of the original placement table 21.

[0021] The apparatus main body 10 includes a paper feed section 110, a pair of transport rollers 120, a pair of registration rollers 130, an image forming section 140, a pair of discharge rollers 150, and a discharge tray 160. Inside the image forming apparatus 1, a transport path R1 is formed for sending a sheet fed from the paper feed section 110 to the discharge tray 160 via the pair of transport rollers 120, the pair of registration rollers 130, the image forming section 140, and the pair of discharge rollers 150.

[0022] The paper feed section 110 includes a cassette 111 arranged below the image forming section 140, a paper feed tray 112 on which paper is loaded, a pickup roller 113 provided above one end of the paper feed tray 112, a paper feed roller 114 arranged downstream of the pickup roller 113 in the paper transport direction, and a separation roller 115 pressed against the paper feed roller 114.

[0023] In the paper feed section 110, a pickup roller 113 picks up paper from a paper feed tray 112 and guides it to a paper feed roller 114. The paper passes between the paper feed roller 114 and a separation roller 115 to separate the paper one by one, and the paper is transported to a transport path R1 by a pair of transport rollers 120.

[0024] The pair of registration rollers 130 feeds the paper in accordance with the timing of the toner image formation. The pair of registration rollers 130 temporarily stops the paper, aligns the leading edge of the paper, and then conveys the paper in accordance with the timing of the transfer of the toner image in the nip area between the intermediate transfer belt 145a and the transfer roller 146, which will be described later.

[0025] The image forming section 140 includes a photoconductor drum 141, a charger 142, an optical scanning device 200, a developing unit 143, a cleaner unit 144, an intermediate transfer belt unit 145, a transfer roller 146, a fixing unit 147, and the like.

[0026] The image data handled by the image forming unit 140 corresponds to color images of four colors: black (Bk), cyan (C), magenta (M), and yellow (Y). For this reason, four photoconductor drums 141, chargers 142, developing units 143, and cleaner units 144 are provided so as to form four types of latent images corresponding to the respective colors, and these constitute four image forming stations. Four toner cartridges are provided so as to supply toner corresponding to each image forming station.

[0027] The photoconductor drum 141 is an electrostatic latent image carrier in which a photosensitive layer is formed on the surface of a cylindrical base body having electrical conductivity. The charger 142 charges the surface of the photoconductor drum 141 to a predetermined potential. The optical scanning device 200 is a laser scanning unit equipped with a laser emission unit, a reflecting mirror, and the like. The optical scanning device 200 exposes the charged surface of the photoconductor drum 141 to light, thereby forming an electrostatic latent image on the surface of the photoconductor drum 141 according to image data. The developing unit 143 visualizes the electrostatic latent image formed on the surface of the photoconductor drum 141 with four color toners. The cleaner unit 144 removes and collects toner remaining on the surface of the photoconductor drum 141 after development and image transfer.

[0028] The intermediate transfer belt unit 145 includes an intermediate transfer belt 145a, a driving roller 145b, a driven roller 145c, and four intermediate transfer rollers 145d. The intermediate transfer belt unit 145 is disposed above the photosensitive drums 141. The intermediate transfer belt 145a is provided so as to contact each of the photosensitive drums 141, and the toner images of each color formed on the corresponding photosensitive drum 141 are sequentially transferred to the intermediate transfer belt 145a in a superimposed manner using each of the intermediate transfer rollers 145d, thereby forming a toner image on the intermediate transfer belt 145a.

[0029] The transfer roller 146 is disposed in the vicinity of the drive roller 145b on the conveying path R1. When a sheet of paper passes through a nip area between the transfer roller 146 and the intermediate transfer belt 145a, the toner image formed on the intermediate transfer belt 145a is transferred to the sheet of paper.

[0030] The fixing unit 147 includes a heat roller 147a and a pressure roller 147b. The fixing unit 147 is disposed above the transfer roller 146, in other words, downstream in the paper conveying direction, on the conveying path R1. When the paper passes through the nip region between the heat roller 147a and the pressure roller 147b, the toner image transferred to the paper is melted, mixed, and pressed against the paper, and the toner image is thermally fixed to the paper. The paper with the fixed toner image is conveyed to the discharge tray 160 by the discharge roller pair 150.

[0031] When an image is to be formed on the back side of the paper in addition to the front side, the paper is conveyed in the opposite direction from the discharge roller pair 150 to the reversal path R2. In the reversal path R2, the paper is turned over by the reversal roller pair 170 and guided again to the registration roller pair 130. After that, the paper, on whose back side an image has been formed in the same manner as on the front side, is conveyed to the discharge tray 160.

[0032] Next, an overview of the optical scanning device 200 will be described with reference to Fig. 2 to Fig. 4. Fig. 2 is a schematic plan view showing an optical system of the optical scanning device 200. Fig. 3 is a schematic side view showing an optical system of the optical scanning device 200. Fig. 4A is a view of the light source 211 in the optical scanning device 200 as seen from the beam emission side in the optical axis direction. Fig. 4B is a view of the light source 211 in the optical scanning device 200 as seen from a direction perpendicular to the optical axis direction. In the following, the main scanning direction in which the polygon mirror 222 is rotated to scan the beam is defined as X, the direction perpendicular to the main scanning direction X is defined as Y (the direction in which the beam is emitted from the light source), and the height direction and sub-scanning direction in the axial direction of the rotation axis 223a that rotates the polygon mirror 222 are defined as Z.

[0033] As shown in Figures 2 and 3, the optical scanning device 200 includes a light source section 210, a deflection scanning unit 220 that deflects and scans the beam from the light source section 210, an incident optical system 230 that is provided on the optical path from the light source section 210 to the deflection scanning unit 220 and causes the beam BM irradiated from the light source section 210 to be incident on the deflection scanning unit 220, an exit optical system 240 that is provided between the deflection scanning unit 220 and the photosensitive drum 141 and emits the beam BM deflected and scanned by the deflection scanning unit 220 to the photosensitive drum 141, and a detection section 250 for controlling the writing timing (hereinafter referred to as scanning timing) of an image on the scanned surface F (surface of the photosensitive drum 141) of the beam BM.

[0034] 2, the light source unit 210 includes a plurality of light sources 211. In this embodiment, four light sources 211 are provided corresponding to four colors, namely black (Bk), cyan (C), magenta (M), and yellow (Y).

[0035] As shown in FIGS. 4A and 4B, light source 211 includes a plurality of light-emitting elements LD(1)-(n) (n is an integer of 2 or more, in this embodiment, n=8) such as laser diodes, a substrate 211a on which the plurality of light-emitting elements LD(1)-(n) are mounted, and a housing case 211b that houses the plurality of light-emitting elements LD(1)-(n).

[0036] 4B, the light source 211 emits beams BM(1)-(n) (n is an integer of 2 or more, n=8 in this embodiment) modulated according to image data. The number of beams emitted from the light source 211 corresponds to the number of light-emitting elements.

[0037] The light-emitting elements LD(1)-(n) emit beams BM(1)-(n) (n is an integer of 2 or more, n=8 in this embodiment) to different positions in the sub-scanning direction Z of the scanned surface F (surface of the photosensitive drum 141). The light-emitting elements LD(1)-(n) are housed in a housing case 211b that is circular when viewed from the optical axis direction. The light-emitting elements LD(1)-(n) are arranged in a row with the emission ports of the beams BM(1)-(n) spaced at regular intervals from each other, centered on a rotation axis α of the housing case 211b that is aligned along the optical axis direction.

[0038] The optical scanning device 200 has, for example, a photodiode (PD: Photo Diode) built into the laser diode (light source 211) as a light amount detection unit (not shown). The photodiode (not shown) is a light receiving element for monitoring the light emission power of the laser diode (light source 211). The photodiode (not shown) detects the optical output (light emission power) of the laser diode (light source 211) on the opposite side to the emission port from which the beam BM is emitted to the laser diode (light source 211).

[0039] The optical scanning device 200 employs an APC (Automatic Power Control) control method that monitors the optical output (light emission power) of the laser diode (light source 211) detected by a light amount detection unit (not shown) and automatically controls the drive current of each laser diode (light source 211) to a constant value according to the level of a reference voltage signal (Vref) so that the optical output becomes a target light amount.

[0040] As shown in FIG. 2, the deflection scanning unit 220 includes a deflection scanning substrate 221 (see FIGS. 7 and 8), a polygon mirror 222 (a rotating polygon mirror), and a drive motor 223 that drives the polygon mirror 222 to rotate.

[0041] The deflection scanning substrate 221 is fixed to the bottom surface of a housing 260 of the optical scanning device 200, which will be described later. The polygon mirror 222 is an example of a deflection mirror. The polygon mirror 222 is a rotating polygonal mirror having a polygonal shape (a heptagon in this embodiment). The polygon mirror 222 is fixed to a rotation shaft 223a of a drive motor 223. The polygon mirror 222 has a plurality of mirror surfaces 222a along the rotation shaft 223a on its periphery. The drive motor 223 rotates at a constant rotation speed in a constant rotation direction. This allows the polygon mirror 222 to deflect and scan the beam BM incident on the mirror surface 222a in the main scanning direction X.

[0042] As shown in FIG. 2, the incident optical system 230 causes the beam BM emitted from the light source section 210 to be incident on the mirror surface 222a of the deflection scanning unit 220 (polygon mirror 222).

[0043] The incident optical system 230 includes a collimator lens 231 that approximately collimates the beams BM(1)-(n) emitted from the light source unit 210, a first aperture 232 that narrows the beam diameter of the parallel light beams BM(1)-(n) in the sub-scanning direction Z on the scanned surface F, a first reflecting mirror 233 that is capable of reflecting the beams BM(1)-(n) with narrowed beam diameters, a cylindrical lens 234 that collects the beams BM(1)-(n) reflected by the first reflecting mirror 233, a second reflecting mirror 235 that reflects the beams BM(1)-(n) emitted from the cylindrical lens 234, and a second aperture 236 that narrows the beam diameter of the beams BM(1)-(n) reflected by the second reflecting mirror 235 in the main scanning direction X on the scanned surface F.

[0044] Four collimator lenses 231 are provided in accordance with the number of light sources 211. The collimator lenses 231 are optical components that shape the beams BM emitted from the light sources 211 into parallel beams.

[0045] Four first apertures 232 are provided in accordance with the number of light sources 211. The first aperture 232 is a plate-like member in which an opening (not shown) is formed. The first aperture 232 is a member for narrowing the beam diameter of the beam BM in the sub-scanning direction Z on the scanned surface F. In other words, the first aperture 232 is a member for shaping the cross-sectional shape of the passing beam BM. In this embodiment, the first aperture 232 narrows the beam diameter of the beam BM in the sub-scanning direction Z on the scanned surface F by forming a slit-shaped opening that is long in the main scanning direction X.

[0046] Four first reflecting mirrors 233 are provided in accordance with the number of light sources 211. In this embodiment, one of the four first reflecting mirrors 233 does not reflect the beam BM from the corresponding first aperture 232, but makes the beam BM directly incident on the cylindrical lens 234. The remaining three of the four first reflecting mirrors 233 reflect the beam BM from the corresponding first aperture 232 toward one first reflecting mirror 233. Then, the beam BM reflected by one first reflecting mirror 233 is made incident on the cylindrical lens 234.

[0047] The cylindrical lens 234 is an optical component for concentrating the beam BM, which has been collimated by the collimator lens 231, so as to converge on the mirror surface 222a of the polygon mirror 222. The cylindrical lens 234 focuses the beam BM so as to converge only in the sub-scanning direction Z on the scanned surface F. In this embodiment, the cylindrical lens 234 focuses the beam BM passing through it in the sub-scanning direction Z, thereby concentrating the beam BM in the sub-scanning direction Z on the scanned surface F.

[0048] The cylindrical lens 234 includes an incident surface 234a on which the beam BM is incident, and an exit surface 234b from which the beam BM is exited (see FIG. 8). The incident surface 234a has no curvature in the main scanning direction X, but has a curvature in the sub-scanning direction Z. The exit surface 234b is a flat surface facing the incident surface 234a. This causes the beam BM passing through the cylindrical lens 234 to be condensed in the sub-scanning direction Z.

[0049] The beams BM from the four light sources 211 are incident at different heights on the incident surface 234a of the cylindrical lens 234. In this embodiment, from the top, the beam BM from the light source 211 corresponding to yellow (Y), the beam BM from the light source 211 corresponding to magenta (M), the beam BM from the light source 211 corresponding to magenta (M), and the beam BM from the light source 211 corresponding to black (Bk) are incident on the incident surface 234a. These beams BM are refracted by the cylindrical lens 234 and are collected in the sub-scanning direction Z.

[0050] The second reflecting mirror 235 is an optical component for reflecting the beam BM emitted from the cylindrical lens 234 and guiding it to the mirror surface 222a of the polygon mirror 222. Note that the incident optical system 230 has the second reflecting mirror 235, but is not limited to this, and the second reflecting mirror 235 may be omitted.

[0051] The second aperture 236 is a plate-like member having an opening 236a formed in the center (see FIG. 8). The second aperture 236 is a member for narrowing the beam diameter of the beam BM in the main scanning direction X on the scanned surface F. In other words, the second aperture 236 is a member for shaping the cross-sectional shape of the beam BM passing through it.

[0052] As shown in FIGS. 2 and 3, the emission optical system 240 reflects and bends the beam BM, which is repeatedly scanned in the main scanning direction X, and irradiates the beam onto a scanned surface F (the surface of the photosensitive drum 141).

[0053] The output optical system 240 includes a first fθ lens 241 , a plurality of folding mirrors 242 , and a plurality of second fθ lenses 243 .

[0054] The first fθ lens 241 is an optical member that corrects the beam BM, which is emitted from the mirror surface 222a of the deflection scanning unit 220 (polygon mirror 222) and moves at a constant angular velocity, so that it moves at a constant velocity on the scanned surface F. The multiple folding mirrors 242 are optical members that reflect the beam BM that has passed through the first fθ lens 241 and guide it to the second fθ lens 243. The multiple second fθ lenses 243 are optical members that converge the beam BM on the scanned surface F.

[0055] As shown in FIG. 2, the detection section 250 includes a detection reflecting mirror 251 that reflects the beam BM emitted from the mirror surface 222a of the deflection scanning unit 220 (polygon mirror 222), a focusing lens 252 that focuses the beam BM reflected by the detection reflecting mirror 251, and a semiconductor sensor 253 that photoelectrically converts the beam BM focused by the focusing lens 252.

[0056] The detection reflecting mirror 251 is disposed on the optical path of the beam BM reflected from the light source unit 210 through the incident optical system 230 and the deflection scanning unit 220, outside the scanning area of ​​the beam group BG that is scanned onto the scanned surface F. The condenser lens 252 is disposed on the optical path of the beam BM emitted from the detection reflecting mirror 251, between the detection reflecting mirror 251 and the semiconductor sensor 253. The beam BM emitted from the condenser lens 252 is incident on the semiconductor sensor 253.

[0057] The optical scanning device 200 further includes a housing 260 that houses the light source section 210, the deflection scanning unit 220, the entrance optical system 230, the exit optical system 240, and the detection section 250. The housing 260 is formed in a box shape.

[0058] The following describes the optical path of the beam BM from the light source unit 210 until it is incident on the photosensitive drum 141. The beam BM from the light source unit 210 passes through the collimator lens 231 to be converted into a substantially parallel beam, narrowed by the first aperture 232, passes through the cylindrical lens 234, is incident on the second reflecting mirror 235 and is reflected, narrowed by the second aperture 236, and is incident on the mirror surface 222a of the deflection scanning unit 220 (polygon mirror 222). The deflection scanning unit 220 is rotated in a predetermined rotational direction at a constant angular velocity by the driving motor 223, and successively reflects the beam BM at each mirror surface 222a, and repeatedly deflects the beam BM in the main scanning direction X at a constant angular velocity. The first fθ lens 241 focuses the beam BM to a predetermined beam diameter on the surface of the photosensitive drum 141 in both the main scanning direction X and the sub-scanning direction Z. Further, the first fθ lens 241 converts the beam BM, which is deflected at a constant angular velocity in the main scanning direction X by the deflection scanning unit 220, so that it moves at a constant linear velocity on the photosensitive drum 141. This allows the beam BM to repeatedly scan the surface of the photosensitive drum 141 in the main scanning direction X.

[0059] Further, the optical scanning device 200 detects the main scanning start timing of the beam BM emitted from the light source unit 210 and deflected and scanned in the main scanning direction X by the deflection scanning unit 220 by the detection unit 250. The detection unit 250 receives the beam BM reflected by the detection reflection mirror 251 immediately before the main scanning (writing) of the photosensitive drum 141 is started. The detection unit 250 receives the beam BM at the timing immediately before the main scanning of the surface of the photosensitive drum 141 is started, and outputs a BD signal indicating the timing immediately before the start of the main scanning. The start timing of the main scanning of the photosensitive drum 141 at which a toner image is formed is set according to this BD signal, and writing of the beam BM according to the image data is started. Then, the two-dimensional surface (circumferential surface) of the photosensitive drum 141, which is rotated and charged, is scanned by the beam BM, and each electrostatic latent image is formed on the surface of the photosensitive drum 141.

[0060] A specific configuration of the second aperture 236 in the optical scanning device 200 will be described with reference to Figs. 5 to 9. Fig. 5 is a perspective view showing a state in which the upper cover 261 of the optical scanning device 200 is removed. Fig. 6 is a plan view showing the internal structure of the optical scanning device 200. In Fig. 6, the upper cover 261 and some of the optical components are omitted. Fig. 7 is a cross-sectional view of the optical scanning device 200 showing the internal structure of the case 263. Fig. 7 is a cross-sectional view cut along a horizontal plane passing through the case 263. Fig. 8 is a perspective view of the optical scanning device 200 showing the optical path from the cylindrical lens 234 to the deflection scanning unit 220.

[0061] 5, the housing 260 of the optical scanning device 200 has an upper cover 261 and a lower cover 262. Various optical components are attached to the lower cover 262.

[0062] The lower cover 262 accommodates the light source section 210, the deflection scanning unit 220, the entrance optical system 230, the exit optical system 240, and the detection section 250. Note that the exit optical system 240 is not shown in FIG.

[0063] 6, a case 263 that covers the deflection scanning unit 220 is formed on the bottom surface of the lower cover 262. The polygon mirror 222, the drive motor 223, and the second aperture 236 are arranged inside the case 263 (see FIGS. 2, 6, and 7).

[0064] The case 263 is provided so as to protrude upward from the bottom surface of the lower cover 262. The outer shape of the case 263 is a substantially rectangular shape with rounded corners when viewed from above. The case 263 has an upper surface 263a that covers the upper side of the deflection scanning unit 220, and a side surface 263b that surrounds the periphery of the deflection scanning unit 220.

[0065] 7 and 8, an opening 263c for passing the beam BM is provided on a side surface 263b of the case 263 at a position overlapping with the optical path from the second reflecting mirror 235 to the mirror surface 222a of the polygon mirror 222. A light-transmitting member 264 for transmitting the beam BM is provided in the opening 263c. The light-transmitting member 264 is attached so as to cover the opening 263c from the outside.

[0066] 7 and 8, an opening 263d for passing the beam BM is provided on a side surface 263b of the case 263 at a position overlapping with the optical path from the mirror surface 222a of the polygon mirror 222 to the first fθ lens 241. The first fθ lens 241 is attached to the side surface 263b of the case 263 so as to cover the opening 263d from the outside.

[0067] 7 and 8, second aperture 236 is disposed inside case 263. Second aperture 236 is disposed on the optical path from second reflecting mirror 235 to mirror surface 222a of polygon mirror 222. When second reflecting mirror 235 is omitted, second aperture 236 may be disposed on the optical path from cylindrical lens 234 to mirror surface 222a of polygon mirror 222.

[0068] As shown in FIG. 7, a pair of ribs 265 supporting the second aperture 236 is provided on the inside of the side surface 263b of the case 263. The pair of ribs 265 extends from the inner side surface of the case 263 toward the inside (polygon mirror 222). The pair of ribs 265 are located on both sides of the opening 263c. The distance between the pair of ribs 265 is approximately the same as the length of the second aperture 236. Groove portions 265a that hold both ends of the second aperture 236 are provided at the tips of the pair of ribs 265. The second aperture 236 is held by the tips of the pair of ribs 265 by inserting both ends of the second aperture 236 into the groove portions 265a from above.

[0069] As shown in Figs. 7 and 8, the second aperture 236 is a plate-like member having an opening 236a formed in the center. The second aperture 236 has a diaphragm surface 236b that narrows the beam diameter of the beam BM emitted from the second reflecting mirror 235 (or the cylindrical lens 234) in a second direction D2 perpendicular to the first direction D1. The first direction D1 is the traveling direction of the beam BM along the optical path. More specifically, it is the traveling direction of the beam BM collected by the cylindrical lens 234. The second direction D2 is a direction perpendicular to the first direction D1 and corresponds to the main scanning direction X on the scanned surface F. In this embodiment, the second direction D2 is a direction perpendicular to the first direction D1 and the sub-scanning direction Z.

[0070] The diaphragm surface 236b is a flat surface having a substantially rectangular shape with an opening 236a at the center. The diaphragm surface 236b is an entrance surface on which the beam BM is incident along the optical path. When the beam passes through the second aperture 236, a part of the beam is reflected by the diaphragm surface 236b, and the remaining part passes through the opening 236a, thereby narrowing the beam diameter of the passing beam BM in the second direction D2. In other words, the cross-sectional shape of the passing beam BM is shaped in the second direction D2.

[0071] As described above, by arranging the second aperture 236 on the optical path from the second reflecting mirror 235 to the mirror surface 222a of the polygon mirror 222, the pitch of the multiple beams BM in the main scanning direction X can be narrowed when the multiple beams BM emitted from the light source 211 are incident on the first fθ lens 241, and therefore it is possible to stabilize the performance of each beam. Therefore, when the multiple beams BM emitted from the light source 211 are irradiated onto the scanned surface F, the pitch of the multiple beams BM in the sub-scanning direction Z can be made closer to uniform, and therefore it is possible to reduce the occurrence of density unevenness.

[0072] The following describes the inclination of the perpendicular line N of the second aperture 236 with respect to the first direction D1, which is the traveling direction of the beam BM, with reference to Fig. 9. Fig. 9 is a schematic diagram showing the inclination of the perpendicular line N of the second aperture 236 with respect to the first direction D1, which is the traveling direction of the beam BM. In Fig. 9, the second reflecting mirror 235 is omitted from the illustration. The perpendicular line N of the second aperture 236 is a straight line that intersects with the diaphragm surface 236b of the second aperture 236 at a right angle.

[0073] 9, the normal N of the second aperture 236 (aperture surface 236b) is inclined with respect to the first direction D1, which is the traveling direction of the beam BM, when viewed from a third direction D3 perpendicular to the first direction D1 and the second direction D2. The third direction D3 is a direction perpendicular to the first direction D1 and the second direction D2, and corresponds to the sub-scanning direction Z on the scanned surface F. In this embodiment, the third direction D3 is the height direction Z.

[0074] The inclination angle of the perpendicular N of the second aperture 236 (aperture surface 236b) with respect to the first direction D1 when viewed from the third direction D3 is an angle at which the return beam RBM reflected by the aperture surface 236b is not incident on the exit surface 234b of the cylindrical lens 234. In other words, the inclination angle is an angle at which the return beam RBM reflected by the aperture surface 236b is incident on an outer region located outside the exit surface 234b on the same plane as the exit surface 234b. In FIG. 9, it is assumed that the return beam RBM is incident on the boundary between the exit surface 234b of the cylindrical lens 234 and the outer region of the exit surface 234b.

[0075] As shown in FIG. 9, if the inclination angle at which the perpendicular line N of the second aperture 236 (aperture surface 236b) when viewed from the third direction D3 intersects with the first direction D1 is θ, the width in the second direction D2 of the beam BM incident on the second aperture 236 (aperture surface 236b) is W1, the width in the second direction D2 of the cylindrical lens 234 is W2, and the distance in the first direction D1 between the cylindrical lens 234 and the second aperture 236 (aperture surface 236b) is L1, then the perpendicular line N of the second aperture 236 (aperture surface 236b) is inclined with respect to the first direction D1 so as to satisfy the following relational expression (1). θ≧{ArcTAN((W1 / 2+W2 / 2) / L1)} / 2···(1)

[0076] Note that θ1 shown in FIG. 9 is the angle obtained by adding the incident angle of the beam BM to the aperture surface 236b and the reflection angle of the beam BM to the aperture surface 236b. When the beam BM is reflected specularly from the aperture surface 236b, the incident angle and the reflection angle are the same angle, and therefore the inclination angle θ corresponds to 1 / 2 of the angle θ1.

[0077] In this embodiment, the width W1 is 8.8 mm, the width W2 is 9.5 mm, and the distance L1 is 101 mm. Therefore, when applying the above relational expression (1), it is preferable that the inclination angle θ is approximately 2.6 degrees or more.

[0078] As described above, by providing the normal N of the second aperture 236 (aperture surface 236b) at an incline with respect to the first direction D1 when viewed from the third direction D3, it is possible to prevent the return beam RBM reflected by the aperture surface 236b from being incident on the cylindrical lens 234. Therefore, it is possible to prevent the power of the light source 211 from becoming unstable due to the return beam RBM being incident on one or other light source 211 via the cylindrical lens 234.

[0079] Furthermore, by setting the inclination angle of the normal N of the second aperture 236 (aperture surface 236b) with respect to the first direction D1 to an angle at which the return beam RBM reflected by the aperture surface 236b is not incident on the exit surface 234b of the cylindrical lens 234, the return beam RBM can be prevented from being incident on one or other light source 211 via the cylindrical lens 234, thereby preventing the power of the light source 211 from becoming unstable.

[0080] In the above configuration, the inclination of second aperture 236 (aperture surface 236b) with respect to first direction D1 is compared between perpendicular line N and first direction D1, but this is not limiting, and for example, second aperture 236 (aperture surface 236b) may be compared with imaginary plane P perpendicular to first direction D1. In this case, the inclination angle θ is the inclination angle of aperture surface 236b with respect to imaginary plane P when viewed from third direction D3.

[0081] Moreover, the second aperture 236 is preferably formed such that the direction in which the opening 236a penetrates is the first direction D1. As a result, even if the normal N of the second aperture 236 (stop surface 236b) is arranged at an angle from the first direction D1, the opening 236a penetrates along the first direction D1, and therefore, it is possible to prevent the beam BM passing through the opening 236a from being obstructed.

[0082] 7, the second aperture 236 is provided inside a case 263 that covers the deflection scanning unit 220. This makes it possible to prevent the return beam RBM reflected by the second aperture 236 from becoming stray light.

[0083] 7, the second aperture 236 is disposed on the optical path closer to the deflection scanning unit 220 than the cylindrical lens 234. That is, the distance L2 between the second aperture 236 and the deflection scanning unit 220 on the optical path is smaller than the distance L1 between the cylindrical lens 234 and the second aperture 236.

[0084] As described above, the distance L1 is the separation distance in the first direction D1 on the optical path between the second aperture 236 and the cylindrical lens 234. In this embodiment, the distance L1 is the distance from the second aperture 236 to the cylindrical lens 234 via the second reflecting mirror 235.

[0085] Distance L2 is a distance on the optical path between second aperture 236 and deflection scanning unit 220. Specifically, distance L2 is a distance in first direction D1 between second aperture 236 and a circumscribing circle passing between vertices of a polygon (in this embodiment, a heptagon) of polygon mirror 222.

[0086] As described above, by arranging the second aperture 236 closer to the deflection scanning unit 220 than the cylindrical lens 234 on the optical path, the pitch of the multiple beams BM in the main scanning direction X can be narrowed when the multiple beams BM emitted from the light source 211 are incident on the first fθ lens 241, and therefore the performance of each beam can be effectively stabilized. Therefore, when the multiple beams BM emitted from the light source 211 are irradiated onto the scanned surface F, the pitch of the multiple beams BM in the sub-scanning direction Z can be made more uniform, and thus the occurrence of density unevenness can be effectively reduced.

[0087] The relationship between the sound pressure level and the distance from the deflection scanning unit 220 will be described below with reference to Fig. 10. Fig. 10 is a table showing the measurement results of the sound pressure level versus the distance from the deflection scanning unit 220. In Fig. 10, the vertical lines represent the sound pressure level of the sound emitted by the deflection scanning unit 220, and the horizontal lines represent the distance from the deflection scanning unit 220.

[0088] The deflection scanning unit 220 was placed on a designated installation stand, and the sound pressure level of the sound emitted by the deflection scanning unit 220 was measured at each designated distance from the deflection scanning unit 220, and the measurement results were represented by an approximation curve (the dashed line shown in Figure 10).

[0089] 10, it has been confirmed that when the distance from the deflection scanning unit 220 is between 5 mm and 15 mm, the sound pressure level of the sound generated by the deflection scanning unit 220 decreases with an increase in the distance, and when the distance from the deflection scanning unit 220 is 15 mm or more, the sound pressure level of the sound generated by the deflection scanning unit 220 remains substantially constant regardless of an increase in the distance. It has also been confirmed that when the distance from the deflection scanning unit 220 is 15 mm or more, the wind noise generated by the deflection scanning unit 220 is reduced.

[0090] From the above, it is preferable that the distance L2 on the optical path between the second aperture 236 and the deflection scanning unit 220 is 15 mm or more. This makes it possible to reduce wind noise generated by the deflection scanning unit 220.

[0091] In this embodiment, the optical scanning device 200 is configured to guide the beam BM from the cylindrical lens 234 to the polygon mirror 222 via the second reflecting mirror 235, but the present invention is not limited to this, and the beam BM may be directly guided from the cylindrical lens 234 to the polygon mirror 222. Even in this case, the same effect as that described above can be achieved by arranging the second aperture 236 on the optical path from the cylindrical lens 234 to the polygon mirror 222 and setting the perpendicular line N of the diaphragm surface 236b of the second aperture 236 to be inclined with respect to the first direction D1, which is the traveling direction of the beam BM, when viewed from the third direction D3.

[0092] In the above configuration, the optical scanning device 200 includes a light source section 210, a deflection scanning unit 220 that deflects and scans the beam BM from the light source section 210, and an incident optical system 230 that is provided on an optical path from the light source section 210 to the deflection scanning unit 220 and causes the beam BM irradiated from the light source section 210 to be incident on the deflection scanning unit 220. The incident optical system 230 includes a cylindrical lens 234 that is provided between the light source section 210 and the deflection scanning unit 220 and focuses the beam BM toward the deflection scanning unit 220, and an aperture (second aperture 236) that is provided between the cylindrical lens 234 and the deflection scanning unit 220 and has an opening 236a that narrows the beam BM in a second direction D2 perpendicular to the first direction D1, when the traveling direction of the beam BM along the optical path is a first direction D1. A perpendicular line N of the aperture (second aperture 236) is provided at an angle with respect to the first direction D1 when viewed from a third direction D3 perpendicular to the first direction D1 and the second direction D2.

[0093] As described above, the normal N of the aperture (second aperture 236) is inclined with respect to the first direction D1 when viewed from the third direction D3, thereby making it possible to prevent the return beam RBM reflected by the diaphragm surface 236b from being incident on the cylindrical lens 234. Therefore, it is possible to prevent the power of the light source 211 from becoming unstable due to the return beam RBM being incident on one or other light source 211 via the cylindrical lens 234.

[0094] When the inclination angle at which the perpendicular N to the aperture (second aperture 236) when viewed from the third direction D3 intersects with the first direction D1 is θ, the width in the second direction D2 of the beam BM incident on the aperture (second aperture 236) is W1, the width in the second direction D2 of the cylindrical lens 234 is W2, and the distance in the first direction D1 between the cylindrical lens 234 and the aperture (second aperture 236) is L1, the following equation (1) is satisfied. θ={ArcTAN((W1 / 2+W2 / 2) / L1)} / 2...Equation (1)

[0095] This allows the return beam RBM reflected by the diaphragm surface 236b to be angled so as not to be incident on the exit surface 234b of the cylindrical lens 234, thereby preventing the return beam RBM from being incident on one or other light source 211 via the cylindrical lens 234. Therefore, it is possible to prevent the power of the light source 211 from becoming unstable due to the return beam RBM being incident on one or other light source 211 via the cylindrical lens 234.

[0096] The incident optical system 230 is provided between the cylindrical lens 234 and an aperture (second aperture 236), and further includes a reflecting member (second reflecting mirror 235) that reflects the beam BM emitted from the cylindrical lens 234 toward the deflection scanning unit 220.

[0097] The optical scanning device 200 further includes a housing 260 that houses the deflection scanning unit 220 and the incident optical system 230. A case 263 that covers the deflection scanning unit 220 is provided inside the housing 260, and an aperture (second aperture 236) is disposed inside the case 263. This makes it possible to prevent the return beam RBM reflected by the second aperture 236 from becoming stray light.

[0098] The aperture (second aperture 236) is disposed on the optical path closer to the deflection scanning unit 220 than the cylindrical lens 234. This makes it possible to narrow the pitch of the multiple beams BM in the main scanning direction X when the multiple beams BM emitted from the light source 211 are incident on the first fθ lens 241, thereby effectively stabilizing the performance of each beam. Therefore, when the multiple beams BM emitted from the light source 211 are irradiated onto the scanned surface F, the pitch of the multiple beams BM in the sub-scanning direction Z can be made more uniform, thereby effectively reducing the occurrence of density unevenness.

[0099] The distance between the aperture (second aperture 236) and the deflection scanning unit 220 on the optical path is greater than 15 mm. This makes it possible to reduce wind noise generated by the deflection scanning unit 220.

[0100] The image forming apparatus 1 includes an optical scanning device 200 .

[0101] The present disclosure is not limited to the above-described embodiment, and various modifications are possible. For example, the above-described embodiment may be replaced with a configuration that is substantially the same as the configuration shown in the above-described embodiment, a configuration that provides the same effect, or a configuration that can achieve the same purpose. [Explanation of symbols]

[0102] 1 image forming apparatus, 200 optical scanning device, 210 light source section, 220 deflection scanning unit, 230 incident optical system, 234 cylindrical lens, 235 second reflecting mirror (reflecting member), 236 second aperture (aperture), 260 housing, 263 case, BM beam, D1 first direction, D2 second direction, D3 third direction, L1 distance between cylindrical lens and aperture surface, N perpendicular to aperture surface, W1 width of beam incident on aperture surface, W2 width of cylindrical lens, θ inclination angle

Claims

1. A light source unit; a deflection scanning unit that deflects and scans a beam from the light source unit; an incidence optical system that is provided on an optical path from the light source unit to the deflection scanning unit and causes the beam emitted from the light source unit to be incident on the deflection scanning unit; The incident optical system includes: a cylindrical lens provided between the light source unit and the deflection scanning unit and configured to focus a beam toward the deflection scanning unit; an aperture provided between the cylindrical lens and the deflection scanning unit, the aperture having an opening for narrowing the beam in a second direction perpendicular to a first direction in a case where a traveling direction of the beam along the optical path is defined as a first direction; An optical scanning device, wherein a normal to the aperture is inclined with respect to the first direction when viewed from a third direction perpendicular to the first direction and the second direction.

2. an inclination angle between a perpendicular line of the aperture when viewed from the third direction and the first direction is defined as θ; The width of the beam incident on the aperture in the second direction is W1, The width of the cylindrical lens in the second direction is W2, When the distance between the cylindrical lens and the aperture in the first direction is L1, The optical scanning device according to claim 1 , which satisfies the following formula (1): θ={ArcTAN((W1 / 2+W2 / 2) / L1)} / 2...Formula (1)

3. 3. The optical scanning device according to claim 1, wherein the incident optical system further comprises a reflecting member provided between the cylindrical lens and the aperture and configured to reflect the beam emitted from the cylindrical lens toward the deflection scanning unit.

4. a housing that houses the deflection scanning unit and the incident optical system, a case for covering the deflection scanning unit is provided inside the housing, The optical scanning device according to claim 1 , wherein the aperture is disposed inside the case.

5. 3. The optical scanning device according to claim 1, wherein the aperture is disposed on the optical path closer to the deflection scanning unit than the cylindrical lens.

6. The optical scanning device according to claim 5 , wherein a distance between the aperture and the deflection scanning unit on the optical path is greater than 15 mm.

7. 3. An image forming apparatus comprising the optical scanning device according to claim 1.

Images