Optical scanning apparatus and image forming apparatus equipped therewith

Abstract

To provide an optical scanner that can reduce the occurrence of color unevenness and obtain a high-quality image despite use of a plurality of laser beams, and an image forming apparatus including the same.SOLUTION: An optical scanner 1 is configured such that a plurality of laser beams 1a are incident on a reflecting surface 116a of a polygon mirror 116 obliquely in a sub scanning direction Y1, and comprises: a semiconductor laser 111 that emits the laser beams 1a; a polygon mirror 116 that has the polygon mirror 116 reflecting the laser beams 1a, and changes the direction of the polygon mirror 116 to change the direction of radiation of the laser beams 1a; a cylindrical lens 113 that focuses the laser beams 1a into an image on a surface of the polygon mirror 116; and an aperture 115 that is installed between the cylindrical lens 113 and the polygon mirror 116 and closer to the polygon mirror 116 than the cylindrical lens 113 so as to focus the laser beams 1a incident on the reflecting surface 116a.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to an optical scanning device and an image forming apparatus such as a copying machine, a multifunction peripheral, a printer, and a facsimile apparatus including the same.

Background Art

[0002] An electrophotographic image forming apparatus includes an image carrier, a charging device that charges the surface of the image carrier to a predetermined potential, an optical scanning device that forms an electrostatic latent image by irradiating and scanning the surface of the image carrier with laser light, a developing device that develops the electrostatic latent image into a toner image, a transfer device that transfers the toner image onto a sheet of paper, and a fixing device that fixes the toner image onto the sheet of paper. Here, the optical scanning device includes a light source and a polygon mirror that deflects the laser light emitted from the light source.

[0003] The configuration of a conventional optical scanning device will be described. For example, as disclosed in Patent Document 1, the optical scanning device includes a light source means that emits a plurality of laser lights, a collimator lens, a cylindrical lens, an aperture, a polygon mirror, and an fθ lens.

[0004] The plurality of laser lights emitted from the light source means pass through the collimator lens, the cylindrical lens, and the aperture in this order and enter the reflecting surface of the polygon mirror. The polygon mirror has a reflecting surface on an outer peripheral surface formed in a regular polygon, and reflects and deflects the laser light incident on the reflecting surface. The laser light deflected by the polygon mirror passes through the fθ lens and is irradiated onto the surface (scanned surface) of the photosensitive drum, which is an image carrier, for scanning to form an electrostatic latent image.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In recent years, there has been a trend towards increasing the number of laser beams in optical scanning devices. In other words, there has been a trend towards increasing the number of light-emitting elements in the light source. Here, each light-emitting element is arranged in a row, but because of the increasing number of light-emitting elements, the distance between the ends of the arranged multiple light-emitting elements increases, which in turn increases the optical axis difference of the laser beam incident on the reflective surface.

[0007] Furthermore, in order to share polygon mirrors and fθ lenses and to miniaturize the optical scanning device, a configuration is sometimes used in which the laser beam is incident on the reflective surface from an oblique direction to the sub-scanning direction. In such a configuration, in particular, as described above, if the difference in the optical axis of the laser beam incident on the reflective surface becomes large, the amount of deviation of the optical axis of the reflected laser beam in the sub-scanning direction will differ greatly depending on whether the laser beam is reflected at the reflective surface during incident-side image formation or during anti-incident-side image formation. Therefore, when attempting to adjust the deviation of the optical axis, if the adjustment is made to match the state in which the beam is reflected during incident-side image formation, the deviation of the optical axis will become large when the beam is reflected during anti-incident-side image formation, and conversely, if the adjustment is made to match the state in which the beam is reflected during anti-incident-side image formation, the deviation of the optical axis will become large when the beam is reflected during incident-side image formation, which may result in color unevenness in the image formed on the paper.

[0008] This disclosure is an invention made in view of the above circumstances, and its object is to provide an optical scanning apparatus and an image forming apparatus equipped therewith that can obtain high-quality images with less color unevenness despite using multiple laser beams. [Means for solving the problem]

[0009] An optical scanning apparatus according to one aspect of the present disclosure is an optical scanning apparatus in which a plurality of laser beams are obliquely incident on the reflective surface of a deflection mirror in a sub-scanning direction, comprising: a light source that emits the laser beams; a deflection mirror having a reflective surface that reflects the laser beams, and changing the irradiation direction of the laser beams by changing the orientation of the reflective surface; a cylindrical lens that focuses the laser beams and images them onto the surface of the deflection mirror; an aperture located between the cylindrical lens and the deflection mirror, closer to the deflection mirror than the cylindrical lens, for focusing the laser beams incident on the reflective surface; and a housing portion that covers the deflection mirror, wherein the housing portion has a wall portion arranged on its side, the distance between the aperture and the deflection mirror is greater than the distance between the wall portion and the deflection mirror, and the aperture is located outside the housing portion. The laser light, narrowed by the aperture, is incident on the deflection mirror. It is characterized by the following:

[0010] Thus, because the aperture is positioned between the cylindrical lens and the deflection mirror, and closer to the deflection mirror than the cylindrical lens, even in a configuration where multiple laser beams are obliquely incident on the reflective surface of the deflection mirror in the sub-scanning direction, the misalignment of the optical axes of the multiple laser beams reflected by the reflective surface can be suppressed. In particular, the amount of misalignment of the optical axis of the reflected laser beam in the sub-scanning direction can be suppressed in both cases: when the laser beam is reflected on the reflective surface during incident-side image formation and when the laser beam is reflected on the reflective surface during anti-incident-side image formation. As a result, the amount of misalignment is easily adjusted, differences in the amount of misalignment in the sub-scanning direction are easily suppressed, color unevenness is less likely to occur, and high-quality images can be obtained.

[0011] Furthermore, the optical scanning device described above may be equipped with a collimator lens for shaping the laser beam, and the light source, the collimator lens, the cylindrical lens, and the aperture may be arranged in that order, with the aperture positioned closer to the deflection mirror than the cylindrical lens, and the aperture positioned such that the light intensity of the laser beam after passing through the aperture is 30% or more of the light intensity on the optical axis of the laser beam.

[0012] Thus, since the aperture is positioned such that the light intensity of the laser beam after passing through the aperture is 30% or more of the light intensity (peak value) on the optical axis of the laser beam, even in a configuration where multiple laser beams are obliquely incident on the reflective surface of the deflection mirror in the sub-scanning direction, the misalignment of the optical axes of the multiple laser beams reflected by the reflective surface can be suppressed. As a result, the difference in the amount of misalignment in the sub-scanning direction can be suppressed, making it less likely for color unevenness to occur and allowing for the acquisition of high-quality images.

[0013] Furthermore, the optical scanning device described above may be equipped with a collimator lens for shaping the laser beam, and the light source, the collimator lens, the cylindrical lens, and the aperture may be arranged in that order, with the aperture positioned closer to the deflection mirror than the cylindrical lens, and satisfying the following equation.

[0014] (w / 2+(pt×((d / f)-1))) / ((f×tan(α / 2)) / 0.59)≦0.77 however, w: Aperture width in the main scanning direction of the aperture. pt: Pitch in the main scanning direction of the multiple laser beams d: Distance between the collimator lens and the aperture f: focal length of the collimator lens α: Angle of view of the collimator lens Let's assume that.

[0015] This makes it possible to suppress the misalignment of the optical axes of the multiple laser beams reflected by the reflective surface, even when multiple laser beams are incident obliquely on the reflective surface of the deflection mirror in the sub-scanning direction. As a result, differences in the amount of misalignment in the sub-scanning direction can be suppressed, making it less likely for color unevenness to occur and enabling the acquisition of high-quality images.

[0016] Furthermore, in the optical scanning apparatus described above, the aperture may be positioned at a distance of 10 mm or more from the deflection mirror.

[0017] This can suppress the aperture from generating abnormal noise due to the influence of the air flow generated by the rotation of the deflection mirror.

[0018] Further, in the above-described optical scanning device, it may have a housing portion that covers the deflection mirror, the housing portion has a wall portion disposed on the side surface, and the distance between the aperture and the deflection mirror may be larger than the distance between the wall portion and the deflection mirror.

[0019] This can suppress the aperture from generating abnormal noise due to the influence of the air flow generated by the rotation of the deflection mirror.

[0020] Further, in the above-described optical scanning device, it may have a housing portion that covers the deflection mirror, the housing portion has a wall portion disposed on the side surface, and the aperture may be disposed integrally with the wall portion.

[0021] This can suppress the aperture from generating abnormal noise due to the influence of the air flow generated by the rotation of the deflection mirror. Also, since the aperture is integrally formed with the wall portion, manufacturing is easy.

[0022] Further, in the above-described optical scanning device, it may have a housing portion that covers the deflection mirror, the housing portion has a wall portion disposed on the side surface, a part of the wall portion is a transparent body through which the laser light is incident, and the aperture may be disposed in contact with the transparent body.

[0023] This can suppress the aperture from generating abnormal noise due to the influence of the air flow generated by the rotation of the deflection mirror. Also, since the aperture is integrally formed with the transparent body, the manufacturing process can be simplified.

[0024] Further, an image forming apparatus according to an aspect of the present disclosure is characterized by including the above-described optical scanning device.

[0025] This makes it possible to suppress the misalignment of the optical axes of the multiple laser beams reflected by the reflective surface, even when multiple laser beams are obliquely incident on the reflective surface of the deflection mirror in the sub-scanning direction. In particular, it is possible to suppress the amount of misalignment of the optical axis of the reflected laser beam in the sub-scanning direction, both when the laser beam is reflected on the reflective surface during image formation on the incident side and when the laser beam is reflected on the reflective surface during image formation on the reverse side. As a result, the amount of misalignment is easy to adjust, differences in the amount of misalignment in the sub-scanning direction are easily suppressed, and high-quality images can be obtained with less color unevenness. [Effects of the Invention]

[0026] According to this disclosure, it is possible to provide an optical scanning apparatus and an image forming apparatus equipped therewith that can obtain high-quality images with minimal color unevenness despite using multiple laser beams. [Brief explanation of the drawing]

[0027] [Figure 1] This is a perspective front view showing a schematic configuration of an image forming apparatus according to the first embodiment of this disclosure. [Figure 2] This is a schematic plan view showing the general configuration of each part of the optical scanning device according to the first embodiment of this disclosure. [Figure 3] This is a perspective view showing the schematic configuration of each part of the optical scanning apparatus according to the first embodiment of this disclosure. [Figure 4] This is a schematic enlarged plan view of the area around the semiconductor laser of an optical scanning apparatus according to the first embodiment of this disclosure. [Figure 5] This is a schematic side view illustrating the incidence of laser light onto a reflective surface in an optical scanning device according to the first embodiment of this disclosure. [Figure 6] This is a Gaussian intensity distribution diagram of laser light in an optical scanning device according to the first embodiment of this disclosure. [Figure 7] This is a schematic perspective view showing the configuration of a housing that covers a polygon mirror of an optical scanning device according to the first embodiment of this disclosure. [Figure 8]This is a schematic plan view illustrating the arrangement of the housing, aperture, and polygon mirror covering the polygon mirror of the optical scanning apparatus according to the first embodiment of this disclosure. [Figure 9] This is a schematic plan view illustrating the arrangement of the housing, aperture, and polygon mirror covering the polygon mirror of the optical scanning apparatus according to the second embodiment of this disclosure. [Figure 10] This is a schematic plan view illustrating the arrangement of the housing, aperture, and polygon mirror covering the polygon mirror of the optical scanning apparatus according to the third embodiment of this disclosure. [Figure 11] This is a schematic plan view illustrating the arrangement of the housing, aperture, and polygon mirror covering the polygon mirror of the optical scanning apparatus according to the fourth embodiment of this disclosure. [Modes for carrying out the invention]

[0028] Embodiments relating to this disclosure will be described with reference to the drawings.

[0029] (First Embodiment) An image forming apparatus according to the first embodiment of this disclosure will be described with reference to the drawings. Figure 1 is a perspective front view showing the schematic configuration of the image forming apparatus according to the first embodiment of this disclosure.

[0030] The image forming apparatus 100 is a multifunction device having copying, scanning, facsimile, and printing functions, and transmits the image of the original document G read by the image reading device 102 to an external source. The image forming apparatus 100 also forms an image on a sheet P of paper or the like in color or monochrome from the image of the original document G read by the image reading device 102 or from an external source.

[0031] Above the image reading unit 130, a document feeder 160 (automatic document feeder (ADF)) is provided, which is supported so as to be openable and closable relative to the image reading unit 130. The image reading unit 102 is equipped with the document feeder 160. The document feeder 160 transports one or more documents G one by one in sequence. The image reading unit 102 reads the documents G that are transported one by one from the one or more documents G by the document feeder 160. The image reading unit 102 is equipped with a document tray 130a on which documents G are placed, and a document reading function that reads documents placed on the document tray 130a. When the document feeder 160 of the image forming apparatus 100 is opened, the document tray 130a above the image reading unit 130 is opened, allowing documents G to be placed manually. The document feeder 160 also includes a document tray 161 on which the document G is placed and a document output tray 162 for loading the document G that has been discharged to the outside. The image reader 102 has a document reading function that reads the document G transported by the document feeder 160. The document feeder 160 transports the document G placed on the document tray 161 onto the document reading unit 130b of the image reader unit 130. The image reader unit 130 generates image data by scanning the scanning optical system 130c to read the document placed on the document table 130a or by reading the document G transported by the document feeder 160.

[0032] The image forming apparatus main body 101 includes an image transfer unit 50, an optical scanning device 1, an intermediate transfer belt device 70, a secondary transfer device 11, a fixing device 12, a sheet transport path S, a paper feed cassette 18, and a sheet discharge tray 141.

[0033] The image forming apparatus 100 handles image data corresponding to color images using black (K), cyan (C), magenta (M), and yellow (Y), or monochrome images using a single color (for example, black).

[0034] The image transfer unit 50 of the image forming apparatus 100 has four image stations Pa, Pb, Pc, and Pd, corresponding to black, cyan, magenta, and yellow. Each of these image stations Pa, Pb, Pc, and Pd is equipped with a developer 2, a photoreceptor drum 3, a drum cleaning device 4, and a charger 5, and these image stations Pa, Pb, Pc, and Pd form four types of toner images. In other words, there are four of each of the developer 2, photoreceptor drum 3, drum cleaning device 4, and charger 5, each corresponding to black, cyan, magenta, and yellow.

[0035] The optical scanning device 1 exposes the surface of the photoreceptor drum 3 to form an electrostatic latent image. Specifically, laser light 1a is irradiated onto the photoreceptor drum 3 from the fθ lens 117 of the optical scanning device 1. Details of the optical scanning device 1, including the fθ lens 117, will be described later.

[0036] The developing device 2 develops the electrostatic latent image on the surface of the photoreceptor drum 3 to form a toner image on the surface of the photoreceptor drum 3. The drum cleaning device 4 removes and collects residual toner from the surface of the photoreceptor drum 3. The charger 5 uniformly charges the surface of the photoreceptor drum 3 to a predetermined potential. Through the above series of operations, toner images of each color are formed on the surface of each photoreceptor drum 3.

[0037] The intermediate transfer belt device 70 comprises an intermediate transfer roller 6, an endless intermediate transfer belt 71, an intermediate transfer drive roller 72, an intermediate transfer driven roller 73, and a cleaning device 9. The intermediate transfer belt 71 is an endless belt that can move around and is wrapped around the intermediate transfer drive roller 72 and the intermediate transfer driven roller 73. In other words, the intermediate transfer drive roller 72 and the intermediate transfer driven roller 73 tension the intermediate transfer belt 71. Four intermediate transfer rollers 6 are provided inside the intermediate transfer belt 71 to form four different toner images corresponding to each color. The intermediate transfer rollers 6 transfer the toner images of each color formed on the surface of the photoreceptor drum 3 to the intermediate transfer belt 71.

[0038] The image forming apparatus 100 sequentially transfers and superimposes the toner images of each color formed on the surface of each photoreceptor drum 3 to form a color toner image on the surface of the intermediate transfer belt 71 stretched over the intermediate transfer drive roller 72 and the intermediate transfer driven roller 73. The cleaning apparatus 9 removes and collects waste toner that remains on the surface of the intermediate transfer belt 71 without being transferred to the sheet P.

[0039] The secondary transfer device 11 forms a transfer nip region TN between the secondary transfer roller 11a and the intermediate transfer belt 71, and transports the sheet P that has been transported through the sheet transport path S by sandwiching it in the transfer nip region TN. As the sheet P passes through the transfer nip region TN, the toner image on the surface of the intermediate transfer belt 71 is transferred to the sheet P and it is then transported to the fixing device 12.

[0040] The fixing device 12 is equipped with a fixing roller 31 and a pressure roller 32 that rotate with the sheet P in between. The fixing device 12 heats and pressurizes the sheet P, on which the toner image has been transferred, by sandwiching it between the fixing roller 31 and the pressure roller 32, thereby fixing the toner image to the sheet P. A heater, which is a heat source, is located inside the fixing roller 31.

[0041] The paper feed cassette 18 is a cassette for storing sheets P used for image formation and is located on the lower side of the optical scanning device 1. The sheets P are pulled out of the paper feed cassette 18 by the pickup roller 16 and transported to the sheet transport path S. The sheets P transported to the sheet transport path S pass through the secondary transfer device 11 and the fixing device 12, are transported to the discharge roller 17, and discharged to the sheet discharge tray 141 in the discharge section 140. The sheet transport path S is equipped with a transport roller 13, a registration roller 14, and a discharge roller 17. The transport roller 13 facilitates the transport of the sheets P. The registration roller 14 temporarily stops the sheets P and aligns the leading edge of the sheets P. The registration roller 14 then transports the temporarily stopped sheets P in sync with the timing of the color toner image on the intermediate transfer belt 71. The color toner image on the intermediate transfer belt 71 is transferred to the sheets P in the transfer nip region TN between the intermediate transfer belt 71 and the secondary transfer roller 11a.

[0042] Although Figure 1 shows only one paper feed cassette 18, the system is not limited to this configuration. Multiple paper feed cassettes 18 may be provided, each loaded with a different type of sheet P.

[0043] Furthermore, if the image forming apparatus 100 is to perform image formation not only on the front surface but also on the back surface of the sheet P, it transports the sheet P in the reverse direction from the discharge roller 17 to the sheet reversal path Sr. The image forming apparatus 100 reverses the front and back surfaces of the sheet P that has been transported in the reverse direction and guides it back to the register roller 14. The image forming apparatus 100 then forms an image on the back surface of the sheet P guided to the register roller 14 in the same way as the front surface, and transports it to the sheet discharge tray 141.

[0044] Next, the configuration of the optical scanning device 1 will be described in detail with reference to the drawings. Figure 2 is a schematic plan view showing the schematic configuration of each part of the optical scanning device according to the first embodiment of this disclosure. Figure 3 is a perspective view showing the schematic configuration of each part of the optical scanning device according to the first embodiment of this disclosure. Figure 4 is a schematic enlarged plan view of the area around the semiconductor laser of the optical scanning device according to the first embodiment of this disclosure. The optical scanning device 1 scans the photoreceptor drum 3 by irradiating it with laser light 1a. As a result, an electrostatic latent image is formed on the surface of the photoreceptor drum 3.

[0045] Each of the four image stations Pa, Pb, Pc, and Pd is equipped with a photoreceptor drum 3. Therefore, laser light 1a is irradiated onto each of these four photoreceptor drums 3. However, this explanation will focus on the configuration in which laser light 1a is irradiated onto one photoreceptor drum 3, and the configuration in which laser light 1a is irradiated onto the other three photoreceptor drums 3 will not be explained. The other photoreceptor drums can be configured similarly.

[0046] As shown in Figure 2, the optical scanning device 1 includes a semiconductor laser 111, a collimator lens 112, a cylindrical lens 113, a reflective mirror 114, an aperture 115, a polygon mirror 116, and an fθ lens 117. The laser light 1a emitted from the semiconductor laser 111 passes through or is reflected by the collimator lens 112, cylindrical lens 113, reflective mirror 114, aperture 115, polygon mirror 116, and fθ lens 117 in that order, and is then irradiated onto the photoreceptor drum 3. Here, as shown in the figure, the sub-scanning direction Y1 is perpendicular to the main scanning direction X1.

[0047] The semiconductor laser 111 is a light source and emits laser light 1a. The collimator lens 112 adjusts the focal position of the laser light 1a emitted from the semiconductor laser 111, converting (shaping) the laser light 1a into parallel light. The laser light 1a, converted into parallel light by the semiconductor laser 111, is focused by the cylindrical lens 113 and incident on the reflective mirror 114. The laser light 1a is then focused by the cylindrical lens 113 and imaged onto the surface of the polygon mirror 116.

[0048] The laser beam 1a incident on the reflective mirror 114 is reflected in the direction of the aperture 115. Since the aperture 115 has a slit-shaped opening, the laser beam 1a reflected by the reflective mirror 114 is focused by the aperture 115 and incident on the polygon mirror 116.

[0049] The polygon mirror 116, which is a deflection mirror, is a polyhedron and has multiple reflective surfaces 116a. In this first embodiment, there are six reflective surfaces 116a, which are arranged in a regular hexagon when viewed from above. The polygon mirror 116 has a rotation axis 116b and rotates around the rotation axis 116b. As a result, each reflective surface 116a rotates in the rotation direction C around the rotation axis 116b. Laser light 1a is incident on the reflective surfaces 116a and reflected. Furthermore, as the reflective surfaces 116a rotate in the rotation direction C, the reflection direction of the laser light 1a reflected by the reflective surfaces 116a changes. This allows the laser light 1a to be irradiated onto the photoreceptor drum 3 for scanning. Although not shown in Figures 2 and 3, the polygon mirror 116 is covered by a housing 120 (see Figure 7). The housing 120 prevents the polygon mirror 116 from becoming contaminated with dust, etc. Details of the housing 120 will be described later.

[0050] The laser beam 1a reflected by the reflective surface 116a passes through the fθ lens 117 and is adjusted to irradiate the photoreceptor drum 3 perpendicularly. Specifically, the fθ lens 117 focuses the laser beam 1a onto a plane with a substantially constant spot size across the entire scanning surface. This allows for uniform irradiation of the entire photoreceptor drum 3, which is the object to be scanned, with the laser beam 1a.

[0051] Although simplified in Figure 2, the optical scanning device 1 uses a multi-beam configuration that irradiates the photoreceptor drum 3 with multiple laser beams 1a for scanning. As shown in Figure 3, multiple semiconductor lasers 111 (111a to 111d) are arranged. In addition, collimator lenses 112a to 112d are installed in the optical scanning device 1, corresponding to these semiconductor lasers 111a to 111d. In other words, the laser beams 1a emitted from each semiconductor laser 111a to 111d are incident on the collimator lenses 112a to 112d. Furthermore, optical waveguides 119a to 119d are installed, corresponding to each of these, and the laser beams 1a emitted from the collimator lenses 112a to 112d are guided to the cylindrical lens 113 via the optical waveguides 119a to 119d.

[0052] Furthermore, as shown in Figure 4, the semiconductor laser 111a (111b-111d) has four additional light-emitting elements 21, from which laser light 1a is emitted. The optical axis center 22 of this semiconductor laser 111a (111b-111d) is the same as the optical axis center 22 of the collimator lens 112a (112b-112d).

[0053] As described above, in the optical scanning device 1, the aperture 115 is installed between the cylindrical lens 113 and the polygon mirror 116. Furthermore, the aperture 115 is positioned closer to the polygon mirror 116 side than to the cylindrical lens 113 side.

[0054] Here, the distance d = d1 + d2 is the sum of the distance d1 between the collimator lens 112 and the reflective mirror 114 and the distance d2 between the reflective mirror 114 and the aperture 115 (see Figure 2). Also, in the semiconductor laser 111, the distance (pitch) in the main scanning direction X1 from the optical axis center 22 to the light-emitting element 22 for each of the semiconductor lasers 111a to 111d is the pitch pt in the main scanning direction X1 for the laser beam 1a (see Figure 4).

[0055] Here, with reference to the drawings, the incident direction of the laser beam 1a to the reflective surface 116a will be described. Figure 5 is a schematic side view illustrating the incident of laser beam to the reflective surface in an optical scanning apparatus according to the first embodiment of this disclosure.

[0056] As shown in Figure 5, the laser beam 1a is incident on the reflective surface 116a at an angle, not perpendicular to the sub-scanning direction Y1. Note that in Figure 5, for simplicity, only one laser beam 1a is shown, but there are actually multiple laser beams 1a (see Figure 3). In this configuration, where the laser beam 1a is incident on the reflective surface 116a at an angle to the sub-scanning direction Y1, the misalignment of the optical axes of the multiple laser beams 1a reflected by the reflective surface 116a tends to increase as the pitch value pt increases.

[0057] However, in the optical scanning apparatus 1 according to this first embodiment, as described above, the aperture 115 is installed between the cylindrical lens 113 and the polygon mirror 116, and the aperture 115 is positioned closer to the polygon mirror 116 side than to the cylindrical lens 113 side, so that the amount of optical axis misalignment can be suppressed. Specifically, since the laser beam 1a is focused by the aperture 115 just before it enters the reflective surface 116a of the polygon mirror 116, the amount of optical axis misalignment in the multiple laser beams 1a that enter the reflective surface 116a is suppressed. As a result, the amount of optical axis misalignment in the multiple laser beams 1a reflected by the reflective surface 116a can be suppressed.

[0058] Specifically, the aperture 115 focuses the laser beam 1a, and each component should be set up so that the light intensity of the laser beam 1a emitted from the aperture 115 is 30% or more of the light intensity (peak value) of the laser beam 1a on its optical axis. For example, the arrangement of components such as the aperture 115 and the value of the aperture width w in the main scanning direction X1 of the aperture 115 can be set.

[0059] Figure 6 is a Gaussian intensity distribution diagram of laser light in an optical scanning apparatus according to the first embodiment of this disclosure. The laser light 1a, converted into parallel light by the collimator lens 112, has a Gaussian distribution as shown in Figure 6, and is focused by the aperture 115 to adjust the beam shape (diameter).

[0060] Generally, the light intensity of a Gaussian-distributed beam (laser light) can be expressed by the following formula.

[0061] I(r) = I₀·exp(-(2r) 2 / ω0 2 )) I0: Light intensity of the laser beam along its optical axis ω0: This value is usually called the Gaussian beam radius, and the light intensity is 1 / e of the maximum value. 2 (Value at the position where it is 13.5%) r: Distance from the central axis of the laser beam Here, in order for the light intensity of the laser beam 1a emitted from aperture 115 to be 30% or more of the light intensity (peak value) of the laser beam 1a on the optical axis, the following equation must be satisfied.

[0062] exp(-(2r 2 / ω0 2 ))≧0.3 By rearranging this equation, we can derive the following equation, and it is preferable that the following equation is satisfied.

[0063] r / ω0≦0.77 Furthermore, if there are multiple laser beams 1a, the optical axis of the laser beam 1a shifts by an amount A of displacement of the optical axis center of the laser beam 1a passing through the aperture 115, according to the pitch pt of the main scanning direction X1 in the laser beam 1a, so the distance r increases. In this case, the amount A of displacement of the optical axis center of the laser beam 1a is approximately equal to the value obtained by multiplying the pitch pt by the value obtained by dividing the distance d, which is the distance between the collimator lens 112 and the aperture 115, by the focal length f of the collimator lens 112, and subtracting 1, so the following equation holds.

[0064] A = pt × ((d / f) - 1) Furthermore, since it is generally not possible to measure the edges of a laser beam, the portion corresponding to 50% of the maximum light intensity of the laser beam is defined as 1 / 2 full angle. This portion is calculated as f × tan(α / 2), which is the distance from the optical axis of the laser beam 1a when it passes through the collimator lens 112. This portion also corresponds to 50% of the maximum light intensity of the laser beam 1a after passing through the collimator lens 112. Due to the characteristics of a Gaussian beam, this position can also be expressed as 0.59 × ω0. Hereinafter, α is the divergence angle (full angle at half maximum) in the main scanning direction of the semiconductor laser 111, i.e., the field of view of the collimator lens 112. The following equation holds true.

[0065] f × tan(α / 2) = 0.59 × ω0 ω0 = (f × tan(α / 2)) / 0.59 Here, r = (w / 2) + A, and as mentioned above, A = pt × ((d / f) - 1), so the following equation holds.

[0066] r = (w / 2 + (pt × ((d / f) - 1))) As mentioned above, it is preferable that r / ω0 ≤ 0.77, and by substituting the above-mentioned ω0 and r into this equation, the following equation can be derived.

[0067] (w / 2+(pt×((d / f)-1))) / ((f×tan(α / 2)) / 0.59)≦0.77 Therefore, it is preferable that the optical scanning device 1 satisfies this equation.

[0068] By configuring the optical scanning apparatus 1 to satisfy the above formula, the image forming apparatus 100 can suppress the misalignment of the optical axes of the multiple laser beams 1a reflected by the reflective surface 116a, even when multiple laser beams 1a are obliquely incident on the reflective surface 116a of the polygon mirror 116 in the sub-scanning direction Y1. As a result, color unevenness is less likely to occur, and high-quality images can be obtained.

[0069] In particular, the amount of optical axis displacement of the reflected laser beam 1a in the sub-scanning direction Y1 can be suppressed when the laser beam 1a is reflected at the reflective surface 116a during incident-side image formation and when the laser beam 1a is reflected at the reflective surface during anti-incident-side image formation. As a result, the amount of displacement can be easily adjusted, the difference in the amount of displacement in the sub-scanning direction Y1 can be easily suppressed, and high-quality images can be obtained with less color unevenness.

[0070] Next, the housing portion 120 covering the polygon mirror 116 will be described with reference to the drawings. Figure 7 is a schematic perspective view showing the configuration of the housing covering the polygon mirror of the optical scanning device according to the first embodiment of this disclosure. Figure 8 is a schematic plan view for explaining the arrangement of the housing covering the polygon mirror, aperture, and polygon mirror of the optical scanning device according to the first embodiment of this disclosure. Note that in Figure 8, the top portion 121 shown in Figure 7 is omitted. Similarly, in Figures 9 to 11 thereafter, the top portion 121 is also omitted.

[0071] As shown in Figures 7 and 8, the housing portion 120 is installed to cover the polygon mirror 116 as described above. The housing portion 120 has a dustproof function to prevent the high-speed rotating polygon mirror 116 from being contaminated by dust, etc. The housing portion 120 comprises an upper surface portion 121 located on the upper side of the polygon mirror 116 and a wall portion 122 that covers the side of the polygon mirror 116. In addition, a transparent incident glass 118 that allows the laser beam 1a to pass through is installed in the housing portion 120 at the location where the laser beam 1a is incident, and the incident glass 118 and the wall portion 122 are formed continuously. Furthermore, a through hole, which is an exit port 123, is formed in a part of the wall portion 122 so that the laser beam 1a reflected from the reflective surface 116a is emitted from the housing portion 120. Note that a transparent material such as glass may be placed in the exit port 123.

[0072] As described above, it is preferable that the aperture 115 be positioned closer to the polygon mirror 116. However, if the aperture 115 is too close to the polygon mirror 116, the airflow generated around the polygon mirror 116 when the polygon mirror 116 rotates may interfere with the opening of the aperture 115, potentially causing abnormal noise. Therefore, it is preferable that the distance s1 (see Figure 8) between the aperture 115 and the polygon mirror 116 be such that such abnormal noise does not occur. For example, it is preferable that the distance s1 between the aperture 115 and the polygon mirror 116 be 10 mm. Furthermore, it is preferable that the distance s1 is greater than the distance s2 between the polygon mirror 116 and the wall portion 122. This makes the aperture 115 less susceptible to the effects of the airflow generated by the rotation of the polygon mirror 116, thereby suppressing the generation of abnormal noise.

[0073] The image forming apparatus 100 according to this first embodiment has been described above. As described above, since the image forming apparatus 100 is equipped with an optical scanning device 1, color unevenness is less likely to occur in the image formed on the sheet P, and a high-quality image can be obtained.

[0074] (Second Embodiment) According to the image forming apparatus 100 of the second embodiment of this disclosure, the aperture 115 in the optical scanning device 1 of the image forming apparatus 100 of the first embodiment is positioned differently from the aperture 115 in the optical scanning device 1 of the image forming apparatus 100 of the first embodiment, but the other configurations are the same as those of the image forming apparatus 100 of the first embodiment. Therefore, only the position of the aperture 115 will be described, and other descriptions will be omitted.

[0075] Referring to the drawings, the arrangement of the aperture 115 in the optical scanning apparatus 1 of the image forming apparatus 100 according to this second embodiment will be described. Figure 9 is a schematic plan view illustrating the arrangement of the housing covering the polygon mirror, the aperture, and the polygon mirror of the optical scanning apparatus according to the second embodiment of this disclosure.

[0076] As shown in Figure 9, the aperture 115 is positioned to contact the incident glass 118, which is formed continuously with the wall portion 122. This allows the wall portion 122, incident glass 118, and aperture 115 to be formed as a single unit, simplifying the manufacturing process. As a result, cost reduction is possible.

[0077] As described in the first embodiment above, it is preferable that the distance between the aperture 115 and the polygon mirror 116 be 10 mm. Furthermore, it is preferable that the distance between the aperture 115 and the polygon mirror 116 is greater than the distance between the polygon mirror 116 and the wall portion 122. This makes the aperture 115 less susceptible to the effects of airflow generated by the rotation of the polygon mirror 116, thereby suppressing the generation of abnormal noise.

[0078] (Third embodiment) The image forming apparatus 100 according to the third embodiment of this disclosure has a housing portion 120a with a different configuration from the housing portion 120 in the optical scanning device 1 of the image forming apparatus 100 according to the first embodiment, and the arrangement position of the aperture 115 is different, but the other configurations are the same as those of the image forming apparatus 100 according to the first embodiment. Therefore, only the arrangement position of the housing portion 120a and the aperture 115 will be described, and other descriptions will be omitted.

[0079] Referring to the drawings, the housing portion 120a of the optical scanning apparatus 1 of the image forming apparatus 100 according to this third embodiment will be described. Figure 10 is a schematic plan view illustrating the arrangement of the housing, aperture, and polygon mirror covering the polygon mirror of the optical scanning apparatus according to the third embodiment of this disclosure.

[0080] As shown in Figure 10, the housing portion 120a, which is installed to cover the polygon mirror 116, is provided with a wall portion 122a that covers the side portion of the polygon mirror 116. In addition, an aperture 115 is provided in the housing portion 120a where the laser beam 1a is incident, rather than an incident glass. The housing portion 120a of the image forming apparatus 100 according to the third embodiment of this disclosure does not have an incident glass. The aperture 115 and the wall portion 122a are formed continuously and are arranged integrally with each other.

[0081] This eliminates the need for an incident glass element, reducing the number of parts. As a result, cost reduction is possible.

[0082] As described in the first embodiment above, it is preferable that the distance between the aperture 115 and the polygon mirror 116 be 10 mm. Furthermore, it is preferable that the distance between the aperture 115 and the polygon mirror 116 is greater than the distance between the polygon mirror 116 and the wall portion 122a. This makes the aperture 115 less susceptible to the effects of airflow generated by the rotation of the polygon mirror 116, thereby suppressing the generation of abnormal noise.

[0083] (Fourth Embodiment) The image forming apparatus 100 according to the fourth embodiment of this disclosure includes a housing portion 120b with a different configuration from the housing portion 120 in the optical scanning device 1 of the image forming apparatus 100 according to the first embodiment, and the arrangement position of the aperture 115 is different, but the other configurations are the same as those of the image forming apparatus 100 according to the first embodiment. Therefore, only the arrangement position of the housing portion 120b and the aperture 115 will be described, and other descriptions will be omitted.

[0084] Referring to the drawings, the housing portion 120b of the optical scanning apparatus 1 of the image forming apparatus 100 according to this fourth embodiment will be described. Figure 11 is a schematic plan view illustrating the arrangement of the housing, aperture, and polygon mirror covering the polygon mirror of the optical scanning apparatus according to the fourth embodiment of this disclosure.

[0085] As shown in Figure 11, the housing portion 120b, which is installed to cover the polygon mirror 116, is provided with a wall portion 122b that covers the side portion of the polygon mirror 116. In addition, an aperture 115 is provided in the housing portion 120b where the laser beam 1a is incident, rather than an incident glass. The housing portion 120a of the image forming apparatus 100 according to the third embodiment of this disclosure does not have an incident glass.

[0086] The aperture 115 and the wall portion 122b are formed continuously and are arranged as a single unit. Furthermore, the aperture 115 and the wall portion 122b have the same main surface.

[0087] This eliminates the need for an incident glass, reducing the number of parts. Furthermore, by forming a slit-shaped opening in the wall portion 122b, an aperture 115 integrated with the wall portion 122b can be easily formed. This allows for cost reduction.

[0088] As described in the first embodiment above, it is preferable that the distance between the aperture 115 and the polygon mirror 116 be 10 mm. Furthermore, it is preferable that the distance between the aperture 115 and the polygon mirror 116 is greater than the distance between the polygon mirror 116 and the wall portion 122b. This makes the aperture 115 less susceptible to the effects of airflow generated by the rotation of the polygon mirror 116, thereby suppressing the generation of abnormal noise.

[0089] This disclosure is not limited to the embodiments described above and can be implemented in various other ways. Therefore, such embodiments are merely illustrative in all respects and should not be constrained. The scope of this disclosure is defined by the claims and is not restricted by the text of the specification. Furthermore, any variations or modifications falling within the equivalent scope of the claims are all within the scope of this disclosure. [Explanation of symbols]

[0090] 1. Optical scanning device 1a Laser light 2. Developing device 3. Photoconductor drum 4. Drum cleaning device 5. Charger 6. Intermediate transfer roller 9. Cleaning device 11. Secondary transfer device 11a Secondary transfer roller 12 Fixing device 13 Conveyor rollers 14 Registrola 16 Pickup Roller 17 Discharge roller 18 Paper feed cassette 21 Light-emitting element 22 Optical axis center 31 Fixing roller 32 Pressure rollers 50 Image transfer section 70 Intermediate transfer belt device 71 Intermediate transfer belt 72 Intermediate transfer drive roller 73 Intermediate transfer driven roller 100 Image forming apparatus 101 Image forming apparatus main unit 102 Image reading device 111 Semiconductor laser (light source) 112 Collimator lens 113 Cylindrical Lens 111a~111d Semiconductor lasers 112a~112d Collimator lens 113a~113d Cylindrical Lens 114 Reflective mirror 115 Aperture 116 Polygon Mirror (Polarizing Mirror) 116a Reflective surface 116b Rotation axis 117 fθ lens 118 Incident glass (transparent material) 119a~119d Optical waveguide 120, 120a, 120b Enclosure 121 Top part 122, 122a, 122b wall 123 Outlet 130 Image reading unit 130a Manuscript placement stand 130b Manuscript reading unit 130c scanning optical system 141 Sheet ejection tray 160 Document feeder 161 Manuscript Tray 162 Document Output Tray G Manuscript P Sheet Pa, Pb, Pc, Pd Image Station S Sheet transport path Sr Sheet Reversal Path TN transfer nip region X1 Main scanning direction Y1 Sub-scanning direction w Opening width pt pitch C Rotation direction d, r, s1, s2 distance

Claims

1. An optical scanning device in which multiple laser beams are obliquely incident on the reflective surface of a deflection mirror in the sub-scanning direction, A light source that emits the aforementioned laser light, A deflection mirror having a reflective surface that reflects the laser light, and which changes the irradiation direction of the laser light by changing the orientation of the reflective surface, A cylindrical lens that focuses the laser light and forms an image on the surface of a deflection mirror, An aperture is located between the cylindrical lens and the deflection mirror, positioned closer to the deflection mirror than the cylindrical lens, for focusing the laser light incident on the reflective surface. It comprises a housing portion that covers the deflection mirror, The housing portion has a wall portion arranged on the side, The distance between the aperture and the deflection mirror is greater than the distance between the wall and the deflection mirror. The aperture is located on the outside of the housing portion. An optical scanning device characterized in that the laser light, narrowed by the aperture, is incident on the deflection mirror.

2. An optical scanning apparatus according to claim 1, The laser beam is provided with a collimator lens for shaping the laser beam. The light source, the collimator lens, the cylindrical lens, and the aperture are arranged in that order. The aperture is located closer to the deflection mirror than the cylindrical lens. An optical scanning device characterized in that the aperture is positioned at a location where the light intensity of the laser light after passing through the aperture is 30% or more of the light intensity on the optical axis of the laser light.

3. An optical scanning apparatus according to claim 1, The laser beam is provided with a collimator lens for shaping the laser beam. The light source, the collimator lens, the cylindrical lens, and the aperture are arranged in that order. The aperture is located closer to the deflection mirror than the cylindrical lens. An optical scanning device characterized by satisfying the following equation. (w / 2+(pt×((d / f)-1))) / ((f×tan(α / 2)) / 0.59)≦0.77 however, w: Aperture width of the aperture in the main scanning direction. pt: Pitch in the main scanning direction of the multiple laser beams d: Distance between the collimator lens and the aperture f: Focal length of the collimator lens α: Angle of view of the collimator lens Let's assume that.

4. An optical scanning apparatus according to claim 1, The optical scanning device is characterized in that the aperture is positioned at a distance of 10 mm or more from the deflection mirror.

5. An optical scanning apparatus according to claim 1, It has a housing portion that covers the deflection mirror, The housing portion has a wall portion arranged on the side, A portion of the wall is a transparent body into which the laser light is incident. A light scanning device characterized in that the aperture is positioned in contact with the transparent body.

6. An image forming apparatus characterized by comprising an optical scanning device according to any one of claims 1 to 5.

Images