Optical scanner and image forming apparatus

Abstract

To provide an optical scanner that can reduce the angle of a beam emitted from a polygon mirror to obtain a good beam diameter.SOLUTION: An optical scanner comprises: a cylindrical lens 83 that makes a beam LB radiated from a laser diode 81 incident on a polygon mirror 86, and on which the beam LB radiated from the laser diode 81 is incident; and a curved surface lens 85 that is arranged between the cylindrical lens 83 and the polygon mirror 86, and changes the angle of emission of the incident beam.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present disclosure relates to an optical scanning device and an image forming apparatus that cause a beam emitted from a light source to be incident on a rotating polygon mirror. [Background technology]

[0002] Conventionally, image forming devices such as digital copiers, laser printers, and facsimiles use optical scanning devices that scan a laser beam. When forming an image using an image forming device, a photoconductor is charged by a charging device, and then writing is performed according to image information using an optical scanning device to form an electrostatic latent image on the photoconductor. The electrostatic latent image on the photoconductor is then visualized using toner supplied from a developing device. The toner image visualized on the photoconductor is transferred to paper by a transfer device, and then fixed to the paper by a fixing device, thereby obtaining a desired image.

[0003] In optical scanning devices, a configuration in which multiple light sources are provided is used, but the imaging position of the light beam from the light source may shift. Therefore, a method for reducing the shift in the imaging position has been proposed (for example, see Patent Document 1). [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] Conventional image forming devices include a light source means having a plurality of light sources spaced apart in the main scanning direction, a collimator lens that converts the plurality of divergent light beams emitted from the light source means into a converging light beam, a deflection means (polygon mirror) that reflects and deflects the plurality of light beams in the main scanning direction, an aperture that is disposed between the collimator lens and the deflection means and that limits the beam width of the incident light beam, and an imaging optical system that images the plurality of light beams reflected and deflected by the deflection means on a scanned surface.

[0006] In the above-mentioned image forming apparatus, since a diaphragm (aperture) is provided between the collimator lens and the polygon mirror, there is a problem in that the amount of light from the light source reaching the surface to be scanned is reduced.

[0007] In recent years, image forming devices have been made smaller, and the shortening of the optical path of the incident system from the light source to the polygon mirror has been considered. However, if the degree of focusing at the lens is increased simply to shorten the optical path, there is a problem that the angle of emission from the polygon mirror becomes large and the width of the light beam becomes large. If the width of the light beam becomes large, the beam diameter when it is incident on the scanned surface becomes extremely small due to the characteristics of the light, and there is a risk of causing problems in image formation.

[0008] The present disclosure has been made to solve the above-mentioned problems, and aims to provide an optical scanning device and an image forming device that can reduce the emission angle of the beam from the polygon mirror and obtain a good beam diameter. [Means for solving the problem]

[0009] The optical scanning device disclosed herein is an optical scanning device that causes a beam emitted from a light source to be incident on a rotating polygon mirror, and is characterized in that it comprises a cylindrical lens onto which the beam emitted from the light source is incident, and a curved lens that is positioned between the cylindrical lens and the rotating polygon mirror and changes the exit angle of the incident beam.

[0010] In the optical scanning device according to the present disclosure, the curved lens may have a preset curvature in the sub-scanning direction.

[0011] In the optical scanning device according to the present disclosure, the curved lens may be a concave lens.

[0012] In the optical scanning device according to the present disclosure, the curved lens may be arranged at a position closer to the cylindrical lens than a focal point of the cylindrical lens.

[0013] In the optical scanning device according to the present disclosure, the curved lens may be a convex lens.

[0014] In the optical scanning device according to the present disclosure, the curved lens may be arranged at a position farther from the cylindrical lens than a focal point of the cylindrical lens.

[0015] In the optical scanning device according to the present disclosure, the curvature of the curved lens may be smaller than the curvature of the cylindrical lens.

[0016] The image forming apparatus according to the present disclosure is characterized by including the optical scanning device according to the present disclosure. Effect of the Invention

[0017] According to the present disclosure, by providing a curved lens that changes the beam emission angle, the beam emission angle from the polygon mirror can be reduced to obtain a good beam diameter. In addition, since the beam emission angle is adjusted by the curved lens, the curvature of the cylindrical lens can be increased to shorten the optical path and reduce the size of the unit. [Brief description of the drawings]

[0018] [Figure 1] 1 is a schematic side view of an image forming apparatus according to a first embodiment of the present disclosure. [Diagram 2] 1 is a perspective view showing an optical scanning device according to a first embodiment of the present disclosure. [Diagram 3]1 is a plan view showing an optical scanning device according to a first embodiment of the present disclosure. [Figure 4] FIG. 2 is a schematic perspective view showing the positional relationship of optical components in an optical scanning device. [Diagram 5] FIG. 2 is a schematic plan view showing the positional relationship of optical components in the optical scanning device. [Figure 6] 1 is a schematic explanatory diagram showing a part of the optical path of a beam in Comparative Example 1. FIG. [Figure 7] 11 is a schematic explanatory diagram showing a part of the optical path of a beam in Comparative Example 2. FIG. [Figure 8] FIG. 2 is a schematic explanatory diagram showing a part of an optical path of a beam in the first embodiment of the present disclosure. [Figure 9] 9 is an enlarged explanatory diagram showing a part of the optical path of the beam in the vicinity of the curved lens in FIG. 8. [Figure 10] FIG. 11 is a schematic explanatory diagram showing a part of an optical path of a beam in a second embodiment of the present disclosure. [Figure 11] 11 is an enlarged explanatory diagram showing a part of the optical path of the beam in the vicinity of the curved lens in FIG. 10. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] (First embodiment) Hereinafter, an image forming apparatus according to a first embodiment of the present disclosure will be described with reference to the drawings.

[0020] FIG. 1 is a schematic side view of an image forming apparatus according to a first embodiment of the present disclosure.

[0021] Image forming device 100 is a multifunction device having a scanner function, a copy function, a printer function, a facsimile function, etc., and transmits an image of an original document read by an image reading device to the outside (corresponding to the scanner function), and also forms an image of the read original document or an image received from the outside on paper in color or monochrome (corresponding to the copy function, printer function, and facsimile function).

[0022] An original transport device 50 (ADF) is provided above the image reading unit 41 and is supported so as to be freely opened and closed relative to the image reading unit 41. When the original transport device 50 is opened, an original placement table 44 above the image reading unit 41 is opened, allowing an original to be placed manually. The original transport device 50 automatically transports the placed original onto the image reading unit 41. The image reading unit 41 reads the placed original or the original transported from the original transport device 50 to generate image data.

[0023] The image forming apparatus 100 includes an optical scanning device 1, a developing device 2, a photosensitive drum 3, a drum cleaning device 4, a charger 5, an intermediate transfer belt 7, a fixing unit 12, a paper transport path Sm, a paper feed cassette 10, a loading tray 15, and the like.

[0024] Image forming apparatus 100 handles image data corresponding to color images using the colors black (K), cyan (C), magenta (M), and yellow (Y), or monochrome images using a single color (e.g., black). Image forming apparatus 100 is provided with four developing devices 2, four photoconductor drums 3, four drum cleaning devices 4, and four chargers 5 for forming four types of toner images, each corresponding to black, cyan, magenta, and yellow, constituting four image stations Pa, Pb, Pc, and Pd.

[0025] The drum cleaning device 4 removes and collects residual toner on the surface of the photosensitive drum 3. The charger 5 uniformly charges the surface of the photosensitive drum 3 to a predetermined potential. The optical scanning device 1 exposes the surface of the photosensitive drum 3 to light to form an electrostatic latent image. The developing device 2 develops the electrostatic latent image on the surface of the photosensitive drum 3 to form a toner image on the surface of the photosensitive drum 3. Through the above-mentioned series of operations, a toner image of each color is formed on the surface of each photosensitive drum 3. The detailed structure of the optical scanning device 1 will be described later with reference to FIG. 2 and FIG. 3.

[0026] A transfer belt device 8 is provided above the photosensitive drums 3, and intermediate transfer rollers 6 are arranged with an intermediate transfer belt 7 interposed therebetween. The intermediate transfer belt 7 is stretched around a transfer drive roller 21 and a transfer driven roller 22, and moves in a circular motion in the direction of arrow C. Residual toner is removed and collected by a belt cleaning device 9, and the toner images of each color formed on the surface of each photosensitive drum 3 are transferred in sequence and superimposed on top of each other to form a color toner image on the surface of the intermediate transfer belt 7.

[0027] A nip area is formed between the transfer roller 11a of the secondary transfer unit 11 and the intermediate transfer belt 7, and the paper conveyed through the paper conveying path Sm is sandwiched in the nip area and conveyed. When the paper passes through the nip area, the toner image on the surface of the intermediate transfer belt 7 is transferred to the paper, and the paper is conveyed to the fixing unit 12.

[0028] The fixing unit 12 includes a fixing roller 31 and a pressure roller 32 that rotate while sandwiching the paper. The fixing unit 12 sandwiches the paper, onto which the toner image has been transferred, between the fixing roller 31 and the pressure roller 32 and applies heat and pressure to fix the toner image to the paper.

[0029] The paper feed cassette 10 is a cassette for storing paper to be used for image formation, and is provided below the optical scanning device 1. The paper is pulled out from the paper feed cassette 10 by a paper pickup roller 16, transported through a paper transport path Sm, passed through a secondary transfer unit 11 and a fixing unit 12, and discharged to a stack tray 15 via a paper discharge roller 17. On the paper transport path Sm, there are arranged a paper registration roller 14 that temporarily stops the paper, aligns the leading edge of the paper, and starts transporting the paper in accordance with the transfer timing of the color toner image in the nip area between the intermediate transfer belt 7 and the transfer roller 11a, a transport roller 13 that promotes the transport of the paper, and a paper discharge roller 17.

[0030] When an image is to be formed on the back side of the paper in addition to the front side, the paper is transported in the opposite direction from the paper discharge rollers 17 to the paper inversion path Sr. In the paper inversion path Sr, the paper is inverted by the inversion rollers 18 and guided again to the paper registration rollers 14. Thereafter, an image is formed on the back side in the same manner as on the front side, and the paper is conveyed to the stacking tray 15.

[0031] FIG. 2 is a perspective view showing the optical scanning device according to the first embodiment of the present disclosure, and FIG. 3 is a plan view showing the optical scanning device according to the first embodiment of the present disclosure.

[0032] The optical scanning device 1 according to the embodiment of the present disclosure includes a rectangular housing 60, and optical components are attached to each part of the housing 60. In addition, in Fig. 2 and Fig. 3, in consideration of ease of viewing the drawings, some members such as the top surface of the housing 60 are removed so that the inside of the housing 60 can be seen. For the sake of explanation below, the direction along one side surface of the housing 60 (for example, the mounting side surface 61) may be referred to as the width direction X, the direction along the side surface adjacent to the mounting side surface 61 may be referred to as the length direction Y, and the direction perpendicular to the width direction X and the length direction Y may be referred to as the height direction Z.

[0033] A plurality of laser diodes 81 (an example of a light source) are attached to the mounting side surface 61 of the housing 60. In the present embodiment, four laser diodes 81 are attached to the housing 60. The four laser diodes 81 (first diode 81a to fourth diode 81d) are arranged side by side in the height direction Z.

[0034] In addition to the laser diode 81, optical components such as a collimator lens 82, a cylindrical lens 83, a reflecting mirror 84, a curved lens 85, a polygon mirror 86 (rotating polygonal mirror), and an fθ lens 87 are attached to the housing 60. However, the housing 60 may also be equipped with various components such as mirrors, lenses, and sensors. The relationship between the beam LB emitted from the laser diode 81 and the optical components will be described with reference to Figs. 4 and 5, which will be described later.

[0035] Fig. 4 is a schematic perspective view showing the positional relationship of optical components in an optical scanning device, and Fig. 5 is a schematic plan view showing the positional relationship of optical components in an optical scanning device. In Fig. 4 and Fig. 5, some of the optical components in the optical scanning device 1 are extracted and shown for ease of viewing.

[0036] As described above, optical components such as a laser diode 81 (first diode 81a to fourth diode 81d), a collimator lens 82, a cylindrical lens 83, a reflecting mirror 84, a curved lens 85, a polygon mirror 86, and an fθ lens 87 are attached to the housing 60 of the optical scanning device 1.

[0037] In FIG. 4, a part of the beam LB emitted from the laser diode 81 (particularly the second diode 81b) is indicated by a dashed line. Although omitted in FIG. 4, the beam LB is also emitted from the laser diodes 81 other than the second diode 81b. The main scanning direction S and the sub-scanning direction H attached to the beam LB are the directions in which the beam LB is scanned and correspond to the directions in which the light spreads. In the optical path of the beam LB, between the laser diode 81 and the reflection mirror 84, the main scanning direction S is approximately parallel to the width direction X, and the sub-scanning direction H is approximately parallel to the height direction Z. For the sake of explanation, in the optical path of the beam LB, the part from the laser diode 81 to the polygon mirror 86 may be referred to as the incident system, and the part from the polygon mirror 86 to the scanned surface (for example, the photosensitive drum 3) may be referred to as the emission system.

[0038] Four collimator lenses 82 are provided corresponding to the four laser diodes 81, and are disposed on the optical path of the beam LB emitted from the laser diodes 81. The collimator lens 82 converts the incident beam LB into parallel light and emits it.

[0039] The cylindrical lens 83 is disposed on the optical path of the beam LB emitted from the collimator lens 82. In this embodiment, one cylindrical lens 83 is provided corresponding to the four laser diodes 81. Specifically, the cylindrical lens 83 is a lens that is long in the height direction Z according to the four laser diodes 81 arranged side by side in the height direction Z, and all the beams LB emitted from the four laser diodes 81 are incident on the cylindrical lens 83. The cylindrical lens 83 changes the way light spreads in a predetermined direction (magnification), and in this embodiment, it acts on the incident beam LB to widen the irradiation range in the main scanning direction S and narrow it in the sub-scanning direction H.

[0040] Furthermore, the cylindrical lens 83 adjusts the direction (irradiation angle) at which the beam LB passes through in the sub-scanning direction H. The four beams LB that have passed through the cylindrical lens 83 change their direction of emission so that the beams LB converge to each other in the sub-scanning direction H. When the four beams LB reach the polygon mirror 86, they are most convergent to each other in the sub-scanning direction H, and after passing through the polygon mirror 86, the beams LB diffuse to each other in the sub-scanning direction H.

[0041] The reflecting mirror 84 is disposed on the optical path of the beam LB emitted from the cylindrical lens 83 , and guides the reflected beam LB so that it passes through a curved lens 85 and enters a polygon mirror 86 .

[0042] The curved lens 85 is disposed on the optical path between the reflecting mirror 84 and the polygon mirror 86, and acts on the incident beam LB to change the irradiation range (output angle) in the sub-scanning direction H. The actions of the cylindrical lens 83 and the curved lens 85 on the beam LB will be described later with reference to FIG.

[0043] The polygon mirror 86 is, for example, a polygonal mirror having multiple reflective surfaces, and has a rotation axis that rotates by a drive unit such as a motor.The beam LB incident on the reflective surface is reflected while rotating, causing the beam LB to scan the surface of the photosensitive drum 3.

[0044] The fθ lens 87 is provided at a position opposite to the polygon mirror 86, and the beam LB emitted from the polygon mirror 86 is incident on the fθ lens 87. Although not shown, optical components such as lenses and mirrors may be provided in the optical path beyond the fθ lens 87, and the beam LB may scan the surface of the photosensitive drum 3 via these components.

[0045] Next, the behavior of the beam LB in the optical path of the incident system will be described with reference to FIGS. 6 to 9 in order to compare this embodiment with Comparative Example 1 and Comparative Example 2 based on conventional structures.

[0046] 6 to 9 show the portion of the optical path of the beam LB from the cylindrical lens 83 to the fθ lens 87. Also, in Fig. 6 to 9, the behavior of the beam LB in the sub-scanning direction H in one of the four laser diodes 81 is shown as a representative, and the beam LB in the other laser diodes 81 behaves in the same way. Note that the reflecting mirror 84 is omitted because it does not affect the optical path length of the beam LB and the angle of the beam LB in the sub-scanning direction H.

[0047] FIG. 6 is a schematic explanatory diagram showing a part of the optical path of the beam in Comparative Example 1. As shown in FIG.

[0048] In Comparative Example 1 based on a conventional structure, the emission angle (first emission angle θ1) of the beam LB from the cylindrical lens 83 is set small, and the beam LB gradually converges. The polygon mirror 86 is disposed at the focal position of the cylindrical lens 83, and the optical path length (first optical path length NL1) from the cylindrical lens 83 to the polygon mirror 86 is long according to the first emission angle θ1.

[0049] The polygon mirror 86 reflects the beam LB at the same angle as the incident angle, so that the beam LB diverging at the same angle as the first emission angle θ 1 enters the fθ lens 87 .

[0050] In comparison example 1, the width of the beam LB when it enters the fθ lens 87 is small, so there is no problem with the beam diameter becoming small on the scanned surface. However, the first optical path length NL1 is long, which is disadvantageous in terms of miniaturizing the device.

[0051] FIG. 7 is a schematic explanatory diagram showing a part of the optical path of a beam in Comparative Example 2. As shown in FIG.

[0052] In Comparative Example 2, the optical path length is changed to be shorter than in Comparative Example 1. Specifically, in Comparative Example 2, the emission angle (second emission angle θ2) of the beam LB from the cylindrical lens 83 is set large, and the beam LB is sharply converged. The optical path length (second optical path length NL2) from the cylindrical lens 83 to the polygon mirror 86 is shortened according to the second emission angle θ2. Accordingly, the emission angle from the polygon mirror 86 is also increased.

[0053] In Comparative Example 2, the width of the beam LB when it is incident on the fθ lens 87 is large, which causes a problem that the beam diameter on the scanned surface becomes small.

[0054] FIG. 8 is a schematic explanatory diagram showing a part of the optical path of a beam in the first embodiment of the present disclosure.

[0055] In the present embodiment, unlike Comparative Examples 1 and 2, a curved lens 85 is disposed between a cylindrical lens 83 and a polygon mirror 86, and the emission angle of the incident beam LB is changed by the curved lens 85. Therefore, the behavior of the beam LB in the vicinity of the curved lens 85 will be described with reference to FIG.

[0056] FIG. 9 is an enlarged explanatory diagram showing a part of the optical path of the beam in the vicinity of the curved lens of FIG.

[0057] The curved lens 85 is a concave lens having a curvature in the sub-scanning direction H. In Fig. 9, a focal point FP indicates the focal position of the cylindrical lens 83, and the curved lens 85 is disposed at a position closer to the cylindrical lens 83 than the focal point FP. The polygon mirror 86 is disposed at the focal position of the curved lens 85.

[0058] In this embodiment, the emission angle (third emission angle θ3) of the beam LB from the cylindrical lens 83 is set large, but the emission angle is changed by the curved lens 85, and the beam is incident on the polygon mirror 86 at a small angle (fourth emission angle θ4). In addition, the optical path length (third optical path length NL3) from the cylindrical lens 83 to the polygon mirror 86 is shortened according to the third emission angle θ3. In this way, by providing the curved lens 85 that changes the emission angle of the beam LB, the emission angle of the beam from the polygon mirror 86 can be reduced to obtain a good beam diameter. In addition, since the emission angle of the beam LB is adjusted by the curved lens 85, the curvature of the cylindrical lens 83 can be increased to shorten the optical path, thereby achieving a compact unit.

[0059] When multiple light sources are provided, the degree of separation of the beams LB can be ensured by providing a curved lens 85 having a curvature in the sub-scanning direction H. In other words, by adjusting the emission angle of the beams LB with the curved lens 85, the width of the beams LB when they enter the fθ lens 87 can be reduced, and the interval between the beams LB emitted from the fθ lens 87 can be increased. Furthermore, by using a concave lens placed in front of the focal point, the emission angle of the beams LB can be easily changed and the position can be adjusted so that the polygon mirror 86 becomes the focal point.

[0060] Second embodiment Next, an image forming apparatus according to a second embodiment of the present disclosure will be described with reference to the drawings.

[0061] The second embodiment is different from the first embodiment in the configuration of the curved lens 85. Since the second embodiment has a configuration substantially similar to that of the first embodiment shown in Figures 1 to 9, a description thereof will be omitted and only the differences will be described.

[0062] FIG. 10 is a schematic explanatory diagram showing a part of an optical path of a beam in the second embodiment of the present disclosure.

[0063] The second embodiment differs from the first embodiment in that a convex lens is used as curved lens 85. In the present embodiment, as in the first embodiment, the output angle of the incident beam LB is changed by curved lens 85, and the behavior of the beam LB in the vicinity of curved lens 85 will be described with reference to FIG.

[0064] FIG. 11 is an enlarged explanatory diagram showing a part of the optical path of the beam in the vicinity of the curved lens of FIG.

[0065] 11, a focal point FP indicates the focal position of cylindrical lens 83, and curved lens 85 is disposed at a position farther away from the focal point FP than cylindrical lens 83. In this way, by disposing the convex lens behind the focal point FP, the beam LB that has begun to diverge can be refocused and the position can be adjusted so that the polygon mirror 86 becomes the focal point. The polygon mirror 86 is disposed at the focal position of the curved lens 85.

[0066] The curvature of the curved lens 85 is smaller than that of the cylindrical lens 83. In other words, the emission angle (fifth emission angle θ5) of the beam LB from the cylindrical lens 83 is set large, and the beam LB is diverged at the same angle after passing the focal point FP, but is focused at a smaller emission angle (sixth emission angle θ6) by the curved lens 85 and enters the polygon mirror 86. In this way, by using a convex lens with a smaller curvature than the cylindrical lens 83, the incidence angle on the polygon mirror 86 can be adjusted to be smaller.

[0067] It should be noted that the embodiments disclosed herein are illustrative in all respects and are not intended to provide a basis for a restrictive interpretation. Therefore, the technical scope of the present disclosure is not interpreted solely by the above-described embodiments, but is defined based on the claims. In addition, the present disclosure includes all modifications within the scope and meaning equivalent to the claims. [Explanation of symbols]

[0068] 1 Optical scanning device 81 Laser diode (example of light source) 82 Collimator lens 83 Cylindrical Lens 84 Reflective Mirror 85 Curved Lenses 86 Polygon Mirror 87 fθ lens 100 Image forming device S Main scanning direction H Sub-scanning direction

Claims

1. An optical scanning device that causes a beam emitted from a light source to be incident on a rotating polygon mirror, a cylindrical lens onto which the beam emitted from the light source is incident; a curved lens disposed between the cylindrical lens and the rotating polygon mirror for changing the exit angle of the incident beam; An optical scanning device comprising:

2. 2. The optical scanning device according to claim 1, The curved lens has a predetermined curvature in the sub-scanning direction. An optical scanning device comprising:

3. 2. The optical scanning device according to claim 1, The curved lens is a concave lens. An optical scanning device comprising:

4. 4. The optical scanning device according to claim 3, The curved lens is disposed at a position closer to the cylindrical lens than the focal point of the cylindrical lens. An optical scanning device comprising:

5. 2. The optical scanning device according to claim 1, The curved lens is a convex lens. An optical scanning device comprising:

6. 7. The optical scanning device according to claim 6, The curved lens is disposed at a position farther from the cylindrical lens than the focal point of the cylindrical lens. An optical scanning device comprising:

7. 7. The optical scanning device according to claim 6, The curvature of the curved lens is smaller than the curvature of the cylindrical lens. An optical scanning device comprising:

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

Images