Optical scanning device and image forming device

Abstract

To provide an optical scanner that can reduce the size of a condensing lens and establish a required beam size, and provide an image forming apparatus.SOLUTION: An optical scanning unit 10 scans light beams B emitted from a laser diode LD in a main scanning direction by using a polygon mirror PGM. In an optical system of the optical scanning unit 10, the laser diode LD, a collimator lens COL, an aperture AP, a first lens 11, the polygon mirror PGM, and a condensing lens FL are arranged in order. The laser diode LD emits the light beams in which the divergent angle is different between two intersecting directions, and the direction with a larger divergent angle of the light beam is aligned with a sub-scanning direction, and the direction with a smaller divergent angle of the light beam is aligned with the main scanning direction. The first lens 11 has a first function to collect the beams in the sub-scanning direction, and a second function to disperse the beams in the main scanning direction.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an optical scanning device and an image forming apparatus using the same. [Background technology]

[0002] In image forming devices such as multifunction peripherals, optical scanning devices are used to write latent images onto image carriers (photosensitive drums). Such optical scanning devices are equipped with an optical system consisting of a light source, a deflection unit, and various optical lenses (see, for example, Patent Document 1).

[0003] FIG. 5 is a diagram showing a schematic configuration of an optical system in a conventional optical scanning device. FIG. 6 shows an example of a layout of the optical system in an optical scanning device viewed from the sub-scanning direction. The optical system shown in FIGS. 5 and 6 includes a laser diode LD as a light source, a collimator lens COL, an aperture AP, a cylindrical lens CYL, a polygon mirror PGM, and a condenser lens FL. The collimator lens COL converts the light beam B emitted from the laser diode LD into parallel light. The aperture AP is an opening that cuts out a portion of the light beam B and shapes it into a rectangular beam. The cylindrical lens CYL is a lens that has a condensing function only in the sub-scanning direction. The polygon mirror PGM is a deflection means that scans (deflects) the light beam B in the main scanning direction. The condenser lens FL condenses the light beam B deflected by the polygon mirror PGM toward an image plane (the surface of a photosensitive drum).

[0004] Furthermore, the light beam B emitted from the laser diode LD is generally elliptical, with different divergence angles in the two intersecting directions. In a conventional optical system, as shown in Figure 5, the major axis of the ellipse (the direction with the larger divergence angle) is aligned with the main scanning direction, and the minor axis of the ellipse (the direction with the smaller divergence angle) is aligned with the sub-scanning direction. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 3-80213 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, efforts have been made to reduce the number of lenses in optical scanning devices and to miniaturize the lenses in order to reduce material costs and make the units more compact. One method for achieving this is to shorten the distance between the polygon mirror PGM and the condenser lens FL (PGM-FL distance) and thereby reduce the size of the condenser lens FL. That is, as shown in Figure 6, the condenser lens FL requires a length in the main scanning direction because the light beam B scanned by the polygon mirror PGM is incident on it. However, by shortening the PGM-FL distance, the length of the condenser lens FL in the main scanning direction can be reduced.

[0007] On the other hand, shortening the PGM-FL distance reduces the ray width of the light beam B incident on the condenser lens FL in the sub-scanning direction in which divergent light is incident on the condenser lens FL. The ray width of the light beam incident on the condenser lens affects the spot diameter of the condensed light beam, and it is known that the larger the ray width, the smaller the spot diameter (the more the beam can be narrowed). In other words, if the ray width of the light beam B incident on the condenser lens FL becomes small, the beam cannot be narrowed on the image plane, and the required beam size on the image plane cannot be obtained (the beam size becomes too large).

[0008] The present invention has been made in view of the above-mentioned problems, and has an object to provide an optical scanning device and an image forming device that enable miniaturization of the condenser lens and establishment of the required beam size. [Means for solving the problem]

[0009] In order to solve the above problems, a first aspect of the present invention is an optical scanning device that scans a light beam emitted from a light-emitting element in a main scanning direction using a deflection means, and is characterized in that it comprises: a collimator lens that is arranged between the light-emitting element and the deflection means and converts the light beam emitted from the light-emitting element into parallel light; an aperture that cuts out a portion of the light beam and shapes it into a rectangular beam; a focusing lens that is arranged downstream of the light beam with respect to the deflection means and focuses the light beam deflected by the deflection means toward a scanned body; and a focusing and diffusing member that is arranged between the aperture and the deflection means and has a first function of focusing the beam in the sub-scanning direction and a second function of diffusing the beam in the main scanning direction, and the light-emitting element has different divergence angles in two intersecting directions of the emitted light beam, and the direction with the larger divergence angle of the light beam is aligned with the sub-scanning direction and the direction with the smaller divergence angle of the light beam is aligned with the main scanning direction.

[0010] According to the above configuration, when the distance between the deflection means and the condenser lens is shortened to reduce the size of the condenser lens, the required beam size in the sub-scanning direction can be obtained by aligning the direction with the largest divergence angle of the light beam with the sub-scanning direction. Furthermore, the required beam size in the main scanning direction can be obtained by the second function of the light collecting / diffusing member. This allows for both a compact condenser lens and the establishment of the required beam size for the scanned object.

[0011] Furthermore, in the optical scanning device, the light collecting and diffusing member may be configured to collect the beam toward the deflection means and then expand the beam toward the collecting lens by the first function.

[0012] According to the above configuration, the spot diameter of the light beam in the sub-scanning direction can be narrowed on the reflecting surface of the deflecting means, and a desired beam width can be obtained when the light beam is incident on the condenser lens.

[0013] The optical scanning device may be configured such that the light beam has a width wider in the sub-scanning direction than in the main scanning direction when it passes through the collimator lens.

[0014] In the optical scanning device, the opening width of the aperture may be larger in the sub-scanning direction than in the main scanning direction.

[0015] In the optical scanning device, the light collecting / diffusing member may be a single lens having a cross-sectional shape of a concave lens in the main scanning direction and a cross-sectional shape of a convex lens in the sub-scanning direction.

[0016] According to the above configuration, by using a single lens as the light collecting and diffusing member, the number of lenses can be reduced, which contributes to the miniaturization of the optical scanning device. In addition, using a single lens has the advantages of shortening the optical path length of the incident system and increasing the transmittance of the entire optical system.

[0017] The optical scanning device may be configured so that the shortest distance between the deflection means and the condenser lens is in the range of 20 to 30 mm.

[0018] In addition, in the above optical scanning device, the condensing lens can be configured to be a lens that does not have the function of causing the light beam, which is scanned at an equal angle in the main scanning direction by the deflection means, to scan at a constant speed on the image plane of the scanned object.

[0019] In order to solve the above problem, an image forming apparatus according to a second aspect of the present invention is characterized by including the optical scanning device described above. [Effects of the Invention]

[0020] The optical scanning device and image forming device of the present invention achieve the effect of shortening the distance between the deflection means and the focusing lens, thereby miniaturizing the focusing lens, while still achieving the required beam size, by aligning the direction of the larger divergence angle of the light beam with the sub-scanning direction, making the width dimension of the light beam narrowed by the aperture larger in the sub-scanning direction than in the main scanning direction, and by using the second function of the focusing / diffusing member which diffuses the beam in the main scanning direction. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a plan view illustrating an example of a layout of an optical system inside an optical scanning unit as viewed from the sub-scanning direction side, illustrating one embodiment of the present invention. FIG. [Figure 2] 1 is a diagram showing a schematic configuration of an optical system in an optical scanning unit according to a first embodiment. [Figure 3] 4A and 4B are perspective views showing examples of the shape of a first lens. [Figure 4] FIG. 10 is a diagram showing a schematic configuration of an optical system in an optical scanning unit according to a second embodiment. [Figure 5] FIG. 1 is a diagram showing a schematic configuration of an optical system in a conventional optical scanning device. [Figure 6] 10 is a diagram illustrating an example of a layout of an optical system in an optical scanning device as viewed from the sub-scanning direction side. DETAILED DESCRIPTION OF THE INVENTION

[0022] First Embodiment Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Fig. 1 is a plan view showing an example of the layout of an optical system inside an optical scanning unit 10 according to the first embodiment, as seen from the sub-scanning direction side. Fig. 2 is a diagram showing a schematic configuration of the optical system in the optical scanning unit 10. Such an optical scanning unit 10 is used as an optical scanning device that writes a latent image onto an image carrier (photosensitive drum) in an image forming apparatus such as a multifunction peripheral.

[0023] As shown in FIG. 1, the optical scanning unit 10 includes an internal optical system including a laser diode (light-emitting element) LD, a collimator lens COL, an aperture AP, a polygon mirror (deflection means) PGM, and a condenser lens FL. The collimator lens COL converts the light beam B emitted from the laser diode LD into parallel light. The aperture AP is an opening that cuts out a portion of the light beam B and shapes it into a rectangular beam. The polygon mirror PGM is a deflection means that scans (deflects) the light beam B in the main scanning direction. The condenser lens FL is a lens that condenses the light beam B deflected by the polygon mirror PGM toward an image plane (the surface of a photosensitive drum, which is the scanned object). The optical scanning unit 10 may also include a reflecting mirror 12 that changes the direction of the optical axis of the light beam B. The deflection means is not limited to the polygon mirror PGM, and a MEMS (Micro Electro Mechanical Systems) mirror or the like may also be used.

[0024] In the illustrated optical scanning unit 10, an F lens without θ-axis rotation is used as the condenser lens FL. Conventionally, an Fθ lens with θ-axis rotation was generally used as the condenser lens located downstream of the deflection unit (downstream of the light beam B). However, in recent years, a configuration has been proposed in which the θ-axis rotation is realized by electronic control of the light beam, and the condenser lens does not have θ-axis rotation. Using an F lens without θ-axis rotation as the condenser lens FL also contributes to the miniaturization of the condenser lens. However, the present invention is not limited to this. The condenser lens located downstream of the polygon mirror PGM may also be an Fθ lens with θ-axis rotation. An Fθ lens with θ-axis rotation is a lens that has the function of scanning the light beam B, which has been scanned at an equal angle by the polygon mirror PGM, at a constant speed on the image plane of the scanned object. In contrast, an F lens without θ-axis rotation is defined as a lens that does not have the above function. Even if the focusing lens FL does not have a θ characteristic, by electronically controlling the light beam B (controlling the timing of writing image data), writing can be performed on the image plane of the scanned object in the same way as when an Fθ lens is used for the focusing lens FL.

[0025] The optical scanning unit 10 of FIG. 1 differs from the conventional optical scanning unit shown in FIG. 5 in that it has the following (Feature 1) and (Feature 2). (Feature 1) As shown in Figure 2, the light beam B emitted from the laser diode LD has its major axis (the direction with the larger divergence angle) aligned with the sub-scanning direction, and its minor axis (the direction with the smaller divergence angle) aligned with the main scanning direction. As a result, the light beam width of the light beam B when it passes through the collimator lens COL is wider in the sub-scanning direction than in the main scanning direction. Accordingly, the opening width dimensions of the aperture AP (3.34 mm in the main scanning direction × 5.14 mm in the sub-scanning direction) are also made larger in the sub-scanning direction than in the main scanning direction. (Feature 2) Instead of the cylindrical lens CYL in FIG. 5, a first lens (light-condensing / diffusing member) 11 is provided between the aperture AP and the polygon mirror PGM. As shown in FIG. 2, the first lens 11 has a function of condensing the beam in the sub-scanning direction (cylindrical lens function: first function) and a function of diffusing the beam in the main scanning direction (expander lens function: second function). The cylindrical lens function of the first lens 11 in the sub-scanning direction is equivalent to that of a conventional cylindrical lens CYL. In other words, the focal length of the first lens 11 in the sub-scanning direction is equivalent to that of a conventional cylindrical lens CYL. The reason why the first lens 11 has a cylindrical lens function in the sub-scanning direction is to narrow the spot diameter of the light beam B in the sub-scanning direction on the reflecting surface of the polygon mirror PGM and to restrict the dimension of the polygon mirror PGM in the sub-scanning direction (height direction). The light beam B that is condensed in the sub-scanning direction by the first lens 11 is diffused after being reflected by the polygon mirror PGM, and is made to have a desired beam width when it is incident on the condenser lens FL.

[0026] The following distances are examples of the arrangement distances (distances in the optical axis direction) of the optical systems inside the optical scanning unit 10 in FIG.

[0027] Distance between LD and COL: 32 mm COL-AP distance: 5mm AP-(1st lens 11) distance: 10 mm Distance between (first lens 11) and (reflection mirror 12): 10 mm Distance between (Reflecting mirror 12) and PGM: 30 mm Distance between PGM and FL: 25 mm The width of the condenser lens FL (the dimension in the direction perpendicular to the optical axis) is set to 50 mm.

[0028] The optical scanning unit 10 according to the first embodiment has (Feature 1) and (Feature 2), which makes it possible to shorten the distance between PGM and FL and to downsize the condenser lens FL compared to conventional devices. Furthermore, even while shortening the distance between PGM and FL, it is possible to obtain the required beam size (approximately 60 μm in both the main scanning direction and the sub-scanning direction) on the image plane (the beam spot diameter can be sufficiently narrowed). Hereinafter, the optical action in the sub-scanning direction and the main scanning direction will be described with reference to FIG. 2.

[0029] In the sub-scanning direction, the required beam size can be obtained by (Feature 1). That is, by aligning the major axis of the ellipse of the light beam B emitted from the laser diode LD in the sub-scanning direction, the light beam width in the sub-scanning direction of the light beam B (light beam B incident on the first lens 11) after passing through the collimator lens COL and the aperture AP can be made wider than before. If the light beam width of the light beam B incident on the first lens 11 is wider, the light beam width of the light beam B incident on the condenser lens FL can be made wider accordingly.

[0030] That is, in the sub-scanning direction, the reduction in the ray width of the light beam B incident on the condenser lens FL when the PGM-FL distance is shortened can be compensated for by the configuration of (Feature 1). As a result, even when the PGM-FL distance is shorter than before, the ray width of the light beam B incident on the condenser lens FL can be made approximately the same as before, and the required beam size on the image plane can be obtained.

[0031] Even in the conventional configuration shown in FIG. 5, it is possible to widen the beam width of the light beam B incident on the condenser lens FL by shortening the focal length of the cylindrical lens CYL. However, this approach increases the aberration of the cylindrical lens CYL, adversely affecting the performance of the optical scanning unit 10. Furthermore, the cylindrical lens CYL narrows the beam width of the emitted light beam B in the sub-scanning direction, resulting in a lens with a fairly short focal length. This makes it difficult to arrange the lens in conjunction with other expensive components. As described above, in the optical scanning unit 10, the focal length of the first lens 11 in the sub-scanning direction is approximately the same as that of the conventional cylindrical lens CYL, so the beam width of the light beam B incident on the condenser lens FL can be widened without causing these problems.

[0032] On the other hand, in the main scanning direction, opposite to the sub-scanning direction, the beam width of the light beam B incident on the first lens 11 is narrower than in the conventional case due to (Feature 1). Therefore, in the main / sub-scanning direction, the required beam size is obtained due to (Feature 2). That is, by converting parallel light into divergent light using the second function of the first lens 11, the beam width in the main scanning direction of the light beam B incident on the condenser lens FL can be ensured. As a result, the beam width of the light beam B incident on the condenser lens FL in the main scanning direction can be made approximately the same as in the conventional case, and the required beam size on the image plane can be obtained.

[0033] In the optical scanning unit 10, the distance between PGM and FL, which was conventionally about 40 to 50 mm, can be shortened to about 25 mm (more specifically, about 20 to 30 mm), and the condenser lens FL can be positioned closer to the polygon mirror PGM. This allows the length of the condenser lens FL in the main scanning direction to be significantly shorter than in the past, making it possible to reduce the size of the condenser lens FL. Furthermore, the reduction in the size of the condenser lens FL also makes it possible to reduce the size of the optical scanning unit 10 itself. Of course, shortening the distance between PGM and FL itself can also contribute to the miniaturization of the optical scanning unit 10. In this case, the distance between PGM and FL refers to the shortest distance between the polygon mirror PGM and the condenser lens FL.

[0034] In the first embodiment, a configuration is exemplified in which a single lens, namely, first lens 11, functions as a cylindrical lens in the sub-scanning direction and an expander lens in the main scanning direction. This configuration allows the number of lenses used to be reduced by providing first lens 11 with both a cylindrical lens function and an expander lens function, which can contribute to the miniaturization of optical scanning unit 10. Furthermore, using a single first lens 11 has the advantages of being able to shorten the optical path length of the incident system and increase the transmittance of the entire optical system.

[0035] FIG. 3 is a perspective view showing an example of the shape of the first lens 11 used. The first lens 11 has a cross-sectional shape of a concave lens with a center that is thinner than the peripheral portion in the main scanning direction to diffuse the beam. Furthermore, the first lens 11 has a cross-sectional shape of a convex lens with a center that is thicker than the peripheral portion in the sub-scanning direction to focus the beam. In the example shown in FIG. 3, the first lens 11 has a shape in which the incident side is concave (the exit side is convex) in the main scanning direction, so that it functions as a concave lens overall. Furthermore, the first lens 11 has a shape in which the incident side is convex (the exit side is concave) in the sub-main scanning direction, so that it functions as a convex lens overall. However, the present invention is not limited to this. In the main scanning direction of the first lens 11, either the exit side or the incident side may be concave, or both sides may be concave. Similarly, in the sub-scanning direction, either the exit side or the incident side may be convex, or both sides may be convex.

[0036] Second Embodiment In the optical scanning unit 10, the cylindrical lens function in the sub-scanning direction and the expander lens function in the main scanning direction do not need to be provided in a single lens, but may be provided in different lenses. Fig. 4 is a diagram showing a schematic configuration of an optical system in the optical scanning unit 10 according to the second embodiment.

[0037] The optical scanning unit 10 shown in FIG. 4 is configured to include a cylindrical lens CYL and a second lens 13 instead of the first lens 11 of the first embodiment. That is, the cylindrical lens CYL and the second lens 13 together constitute the light collecting and diffusing member described in the claims. The cylindrical lens CYL can be made of the same material as that of the conventional optical scanning unit shown in FIG. 5, and has a collecting function only in the sub-scanning direction. The second lens 13 has a diffusing function only in the main scanning direction and does not have a lens function in the sub-scanning direction. Both the cylindrical lens CYL and the second lens 13 are disposed between the aperture AP and the polygon mirror PGM, but the order in which the cylindrical lens CYL and the second lens 13 are disposed may be reversed.

[0038] 4, the cylindrical lens CYL has a cylindrical lens function in the sub-scanning direction, and the second lens 13 has an expander lens function in the main scanning direction. In this way, even with a configuration in which different lenses have the cylindrical lens function in the sub-scanning direction and the expander lens function in the main scanning direction, the same effects as in the first embodiment can be obtained.

[0039] The embodiments disclosed herein are illustrative in all respects and are not intended to be limiting. Therefore, the technical scope of the present invention should not be interpreted solely by the above-described embodiments, but should be defined by the claims. Furthermore, all modifications within the scope and meaning equivalent to the claims are included. [Explanation of symbols]

[0040] 10 Optical scanning unit (optical scanning device) 11 First lens (light-collecting / diffusing member) 12 Reflective mirror 13 Second lens (part of the light-collecting and diffusing member) LD Laser diode (light emitting element) COL Collimator Lens AP Aperture CYL Cylindrical lens (part of the light-collecting and diffusing component) PGM polygon mirror (deflection means) FL condenser lens

Claims

1. An under-field type optical scanning device that scans a light beam emitted from a light emitting element in a main scanning direction by a deflection means, a collimator lens disposed between the light emitting element and the deflection means, for converting the light beam emitted from the light emitting element into parallel light, and an aperture for cutting out a part of the light beam and shaping it into a rectangular beam; a condenser lens disposed downstream of the light beam with respect to the deflection means, for condensing the light beam deflected by the deflection means toward a scanned body; a light condensing / diffusing member disposed between the aperture and the deflection means, the light condensing / diffusing member having a first function of condensing the beam in the sub-scanning direction and a second function of diffusing the beam in the main scanning direction; the light emitting element emits a light beam having different divergence angles in two intersecting directions, the direction in which the divergence angle of the light beam is larger is aligned with a sub-scanning direction, and the direction in which the divergence angle of the light beam is smaller is aligned with a main scanning direction; 10. An optical scanning device according to claim 9, wherein the aperture has an opening width dimension larger in the sub-scanning direction than in the main scanning direction.

2. 2. The optical scanning device according to claim 1, The optical scanning device, wherein the light condensing / diffusing member, by means of the first function, condenses the beam toward the deflection means and then diverges the beam toward the condenser lens.

3. 3. The optical scanning device according to claim 1, an optical scanning device, characterized in that the light beam has a width wider in the sub-scanning direction than in the main scanning direction when passing through the collimator lens;

4. 4. The optical scanning device according to claim 1, The optical scanning device according to claim 1, wherein the light collecting and diffusing member is a single lens having a cross-sectional shape of a concave lens in the main scanning direction and a cross-sectional shape of a convex lens in the sub-scanning direction.

5. 5. The optical scanning device according to claim 1, An optical scanning device, characterized in that the shortest distance between the deflection means and the condenser lens is in the range of 20 to 30 mm.

6. 6. The optical scanning device according to claim 1, an optical scanning device characterized in that the condenser lens is a lens that does not have the function of causing the light beam, which is scanned at an equal angle in the main scanning direction by the deflection means, to scan at a constant speed on the image surface of the scanned object;

7. An image forming apparatus comprising the optical scanning device according to any one of claims 1 to 6.

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