JP7099083B2 - An optical scanning device and an image forming apparatus provided with the optical scanning device. - Google Patents

Description

The present invention relates to an optical scanning device and an image forming apparatus including the optical scanning device.

Conventionally, optical scanning devices used in laser printers, copiers, and the like have been known. This optical scanning device deflects the laser light emitted from the light source by the rotation of the polygon mirror and scans it on the scanned surface. A rectangular imaging lens is arranged between the polygon mirror and the surface to be scanned (see, for example, Patent Document 1). The imaging lens forms an image of the light deflected by the polygon mirror on the surface to be scanned.

In the optical scanning apparatus shown in Patent Document 1, the laser light emitted from the light source is incident from a direction inclined by a predetermined angle in the sub-scanning direction with respect to the normal direction of the reflecting surface of the polygon mirror. In an optical scanning device that employs such an obliquely incident optical system, the central portion of the light beam passing through the imaging lens in the main scanning direction is curved in the sub-scanning direction with respect to both ends.

Japanese Unexamined Patent Publication No. 2015-225139

In the optical scanning device shown in Patent Document 1, the imaging lens has a rectangular shape even though the passing trajectory of the light beam is curved. Therefore, the distances from the edges on both sides of the image pickup lens in the sub-scanning direction to the light beam may differ from each other. That is, in the example of FIG. 15, the distance from one side edge 200a in the sub-scanning direction of the imaging lens 200 to one marginal line 201 of the light beam is A, and from the other side edge 200b to the other marginal line 202. When the distance is B, A <B at the left end of the imaging lens and A> B at the center position of the imaging lens.

At locations where the distances from the edge 200a and 200b on both sides of the imaging lens 200 in the sub-scanning direction to the light beam are different (locations A> B or A <B), the light component passing through one side in the sub-scanning direction The refractive index may differ from that of the light component passing closer to the other side, and the imaging performance may deteriorate. That is, when the imaging lens 200 is made of, for example, a resin material, water gradually permeates from the surface of the imaging lens 200 toward the inside, so that the contour lines shown in FIG. 16 are inside the imaging lens 200. A shape-like refractive index distribution is generated (reference numeral 203 in FIG. 16 indicates an equal refractive index line). As a result, as shown in FIG. 17, the number of equal refractive index lines through which each light component passes differs between the light component passing through one side of the image pickup lens 200 in the sub-scanning direction and the light component passing through the other side. In the end (difference in refractive index occurs), the above-mentioned deterioration of imaging performance is caused.

If this deterioration in imaging performance occurs to the same extent at any position in the main scanning direction, it will not be noticeable even if an image defect occurs. However, in the optical scanning device shown in FIG. 15, the distances A and B from the both side edges 200a and 200b of the imaging lens 200 in the sub-scanning direction to the light beam are A <B, A = depending on the position in the main scanning direction. It changes as B, A> B. For this reason, the image quality of the image lens 200 is good (A = B) and poor (A <B or A> B), and image defects due to deterioration of the image quality are conspicuous. There is a problem that it is easy.

The present invention has been made in view of this point, and an object thereof is an image caused by a moisture absorption phenomenon of an imaging lens in an optical scanning apparatus and an image forming apparatus provided with an imaging lens made of resin. The purpose is to make defects as inconspicuous as possible.

The optical scanning device according to one aspect of the present invention includes a light source that emits a light beam, a rotating multi-sided mirror that reflects the light beam emitted from the light beam to perform deflection scanning, and light that is deflected and scanned by the rotating multi-sided mirror. A resin imaging lens provided in the optical path of the beam, extending in the main scanning direction, and forming an image of a light beam deflected and scanned by the rotating polymorphic mirror on the surface to be scanned, and reflecting the rotating polymorphic mirror. The incident angle of the light beam with respect to the surface is inclined in the sub-scanning direction with respect to the normal direction of the reflecting surface.
The passage trajectory of the light beam in the imaging lens has a curved shape in which the central portion in the main scanning direction swells in the sub-scanning direction with respect to both ends, and the edge edges on both sides in the sub-scanning direction in the imaging lens. At least one of the edges has a curved shape along the passage trajectory of the light beam in the imaging lens.

The optical scanning apparatus according to another aspect of the present invention includes a plurality of light sources that emit light beams, a rotating multi-sided mirror that reflects and deflects a plurality of light beams emitted from the plurality of light sources, and the rotation thereof. Each light path of a plurality of light beams deflected and scanned by a multi-sided mirror is provided with a resin imaging lens for forming an image of each light beam on the surface to be scanned, and each light on the reflecting surface of the rotating multi-sided mirror. The incident angle of the beam is inclined at a different angle in the sub-scanning direction with respect to the normal direction of the reflecting surface.
The plurality of light beams emitted from the plurality of light sources include a plurality of light beams reflected on the same side in the sub-scanning direction by the reflection surface of the rotating polymorphic mirror, and a plurality of light beams reflected on the same side. The outer shape of each imaging lens provided in the optical path of the light beam is the same, and at least one of the edges on both sides in the sub-scanning direction of the imaging lens passes through the imaging lens. The light beam is curved in the same direction as the passing locus of the light beam, and the bending amount is equal to the average value of the curving amounts of both passing trajectories.

The optical scanning apparatus according to another aspect of the present invention includes a plurality of light sources that emit light beams, a rotating multi-sided mirror that reflects and deflects a plurality of light beams emitted from the plurality of light sources, and the rotation thereof. Each light path of a plurality of light beams deflected and scanned by a multi-sided mirror is provided with a resin imaging lens for forming an image of each light beam on the surface to be scanned, and each light on the reflecting surface of the rotating multi-sided mirror. The incident angle of the beam is inclined at a different angle in the sub-scanning direction with respect to the normal direction of the reflecting surface.
The plurality of light beams emitted from the plurality of light sources include a plurality of light beams reflected on the same side in the sub-scanning direction by the reflection surface of the rotating polymorphic mirror, and a plurality of light beams reflected on the same side. The shape of each imaging lens provided in the optical path of the light beam is the same, and at least one of the edges on both sides in the sub-scanning direction of the imaging lens passes through the imaging lens. The path of the light beam is the same as the path with the largest amount of curvature, and the other edge is the same as the path of the light beam passing through each imaging lens with the smallest amount of curvature. be.

The image forming apparatus according to the present invention includes the above-mentioned optical scanning apparatus.

According to the present invention, in an optical scanning device and an image forming apparatus provided with an imaging lens made of a resin member, image defects due to moisture absorption of the imaging lens can be made as inconspicuous as possible.

FIG. 1 is a schematic view showing the overall configuration of an image forming apparatus including the optical scanning apparatus according to the first embodiment. FIG. 2 is a plan view showing a schematic configuration of the optical scanning device according to the first embodiment. FIG. 3 is a schematic side view showing the optical path from the polygon mirror of the optical scanning device according to the first embodiment to the second imaging lens, as viewed from the main scanning direction. FIG. 4 is a schematic diagram showing a passing locus of a light beam passing through the second imaging lens. FIG. 5 is a view of the second imaging lens as viewed from the optical axis direction. FIG. 6 is a diagram corresponding to FIG. 5 showing a modification 1 of the first embodiment. FIG. 7 is a diagram corresponding to FIG. 5 showing a modification 2 of the first embodiment. FIG. 8 is a schematic view showing the overall configuration of the image forming apparatus including the optical scanning apparatus according to the second embodiment. FIG. 9 is a plan view showing a schematic configuration of the optical scanning device according to the second embodiment. FIG. 10 is a schematic view showing an optical path from the light source of the optical scanning device according to the second embodiment to the polygon mirror. FIG. 11 is a diagram corresponding to FIG. 3 showing the second embodiment. FIG. 12 is a diagram corresponding to FIG. 4 showing the second embodiment. FIG. 13A is a view of two second imaging lenses on one side in the sub-scanning direction in the second embodiment as viewed from the optical axis direction. FIG. 13B is a view of two second imaging lenses on the other side in the sub-scanning direction of the second embodiment as viewed from the optical axis direction. FIG. 14A is a diagram corresponding to FIG. 13A showing a modified example of the second embodiment. FIG. 14B is a diagram corresponding to FIG. 13B showing a modified example of the second embodiment. FIG. 15 is a view of the imaging lens in the conventional example as viewed from the optical axis direction. FIG. 16 is an explanatory diagram for explaining a change in the refractive index inside the lens caused by the hygroscopic phenomenon of the imaging lens in the conventional example. FIG. 17 schematically shows the upper and lower marginal lines and the main ray of the light beam passing through each of the one-sided end portion and the central portion of the image pickup lens in the main scanning direction in the conventional example, as viewed from the main scanning direction. It is a schematic diagram.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the following embodiments.

<< Embodiment 1 >>
FIG. 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus 100 according to the present embodiment. The image forming apparatus 100 includes a box-shaped apparatus main body 102, a manual paper feeding unit 106, a cassette paper feeding unit 107, an image forming unit 108, a fixing unit 109, and a paper ejection unit 110. Then, the image forming apparatus 100 is configured to form an image on the paper based on the image data transmitted from a terminal (not shown) or the like while conveying the paper along the transport path H in the apparatus main body 102. Has been done.

The manual paper feed unit 106 has a manual feed tray 104 that can be opened and closed on one side of the device main body 102, and a manual paper feed roller 105 that is rotatably provided inside the device main body 102. ing.

The cassette paper feed unit 107 is provided at the bottom of the apparatus main body 102. The cassette paper feed unit 107 separates the paper feed cassette 111 for accommodating a plurality of stacked papers, the pick roller 112 for taking out the paper in the paper feed cassette 111 one by one, and the taken out paper one by one. It is provided with a feed roller 113 and a retard roller 114 that are sent out to the transport path H.

The image forming unit 108 is provided above the cassette feeding unit 107 in the apparatus main body 102. The image forming unit 108 includes a photoconductor drum 116 which is an image carrier rotatably provided in the apparatus main body 102, a charger 117 arranged around the photoconductor drum 116, a developing unit 118, and a transfer roller. It includes a 119 and a cleaning unit 120, an optical scanning device 130 arranged above the photoconductor drum 116, and a toner hopper 121. Then, the image forming unit 108 forms an image on the paper supplied from the manual feeding unit 106 or the cassette feeding unit 107.

The transport path H is provided with a pair of resist rollers 115 that temporarily wait for the fed paper and then supply it to the image forming unit 108 at a predetermined timing.

The fixing portion 109 is arranged on the side of the image forming portion 108. The fixing portion 109 includes a fixing roller 109a and a pressure roller 109b that are pressed against each other and rotate. Then, the fixing unit 109 fixes the toner image transferred to the paper by the image forming unit 108 to the paper.

The paper ejection unit 110 is provided above the fixing unit 109. The paper ejection unit 110 includes a paper ejection tray 103, a paper ejection roller pair 124 for transporting the paper to the paper ejection tray 103, and a plurality of transport guide ribs 125 for guiding the paper to the paper ejection roller pair 124. .. The output tray 103 is formed in a concave shape on the upper part of the apparatus main body 102.

When the image forming apparatus 100 receives the image data, the photoconductor drum 116 is rotationally driven in the image forming unit 108, and the charger 117 charges the surface of the photoconductor drum 116.

Then, based on the image data, the laser beam is emitted from the optical scanning device 130 to the photoconductor drum 116. An electrostatic latent image is formed on the surface of the photoconductor drum 116 by irradiating the surface with a laser beam. The electrostatic latent image formed on the photoconductor drum 116 is developed by the developing unit 118 to become a visible image as a toner image.

The paper then passes between the transfer roller 119 and the photoconductor drum 116. At this time, the toner image on the photoconductor drum 116 is moved to the paper and transferred by the transfer bias acting on the transfer roller 119. The paper on which the toner image is transferred is heated and pressed by the fixing roller 109a and the pressure roller 109b in the fixing portion 109. As a result, the toner image is fixed on the paper.

FIG. 2 is a schematic configuration diagram inside the housing 131 of the optical scanning device 130. The optical scanning device 130 includes a light source 132, a polygon mirror 133, a first imaging lens 134, and a second imaging lens 135. The light source 132 is a laser light source having, for example, a laser diode. The light source 132 emits one light beam toward the polygon mirror 133. A collimator lens 136 and a cylindrical lens 137 are arranged in this order between the light source 132 and the polygon mirror 133. The polygon mirror 133 is a regular polygonal rotating multifaceted mirror having a plurality of reflecting surfaces 133a on its peripheral surface. The polygon mirror 133 is rotationally driven by a motor (not shown). The rotating polygon mirror 133 reflects the light beam emitted from the light source 132 and causes deflection scanning in the main scanning direction.

The first imaging lens 134 and the second imaging lens 135 are arranged so as to extend in the main scanning direction on the side of the polygon mirror 133. The second imaging lens 135 is arranged radially outside the first imaging lens 134. The first imaging lens 134 and the second imaging lens 135 are made of a highly hygroscopic resin material. An example of this resin material is PMMA resin.

In the optical scanning device 130 configured as described above, the light beam emitted from the light source 132 is converted into a parallel light flux by the collimator lens 136 and then focused on the reflecting surface 133a of the polygon mirror 133 by the cylindrical lens 137. The light beam focused on the polygon mirror 133 is reflected by the reflecting surface 133a of the polygon mirror 133 and is incident on the first imaging lens 134 as scanning light. After passing through the second imaging lens 135, the scanning light that has passed through the first imaging lens 134 is reflected toward the photoconductor drum 116 outside the housing 131 by a reflection mirror (not shown). In this way, the scanning light is imaged on the surface of the photoconductor drum 116 (corresponding to the surface to be scanned). The scanning light imaged on the surface of the photoconductor drum 116 scans the surface of the photoconductor drum 116 in the main scanning direction by the rotation of the polygon mirror 133, and scans in the sub-scanning direction by the rotation of the photoconductor drum 116. An electrostatic latent image is formed on the surface of the body drum 116.

Here, the oblique incident method is adopted as the incident optical system of the light beam with respect to the polygon mirror 133. That is, the light beam emitted from the light source 132 is incident on the reflection surface 133a of the polygon mirror 133 from a direction inclined in the sub-scanning direction rather than the normal direction. Therefore, as shown in FIG. 3, the light beam is reflected in a direction inclined in the sub-scanning direction from the normal direction of the reflection surface 133a of the polygon mirror 133.

Then, the light beam reflected by the polygon mirror 133 and passing through the first imaging lens 134 and the second imaging lens 135 has a curved shape. FIG. 4 shows the schematic shape of the passage locus X1 of the light beam passing through the second imaging lens 135. In FIG. 4, the second imaging lens 135 is simplified and drawn in a rectangular shape. The detailed shape of the second imaging lens 135 will be described later. The passing locus X1 of the light beam has a curved shape in which the central portion in the main scanning direction swells in the sub-scanning direction (lower side in FIG. 4) with respect to both ends.

FIG. 5 is a schematic plan view of the second imaging lens 135 as viewed from the optical axis direction (V direction in FIG. 2). The second imaging lens 135 has a lens surface 135a (mirror surface) and a non-lens surface 135b that surrounds the outside of the lens surface 135a. In FIG. 5, reference numeral X0 indicates a bus, reference numeral X1 schematically shows a passing locus of the main ray of the light beam, and reference numeral X2 schematically shows a passing locus of the marginal line of the light beam. In the following description, the passing locus of the light beam means the passing locus X1 of the main ray.

Both side edges T1 and T2 of the second imaging lens 135 in the sub-scanning direction are curved in the same direction as the curved shape of the passing locus X1 of the light beam passing through the second imaging lens 135. Both side edges T1 and T2 of the second imaging lens 135 in the sub-scanning direction have the same curved shape as the passing locus X1 of the main light beam of the light beam. The bus X0 does not match the outer shape of the lens, the lens surface 135a is not curved, and only the outer shape is curved.

The curved shapes of the both end edges T1 and T2 are not only the same shape as the passing locus X1, but also a shape along the passing locus X1 (for example, 0.5 times or more and 1.5 times or more the bending amount of the passing locus X1). It may be a curved shape having a bending amount of twice or less). Further, in the present specification, the “curvature amount” means the amount of misalignment in the sub-scanning direction at each position in the main scanning direction with respect to a straight line passing through the apex of the curved shape and extending in the main scanning direction.

-Action effect-
As described above, in the present embodiment, the edge T1 and T2 on both sides of the second imaging lens 135 in the sub-scanning direction form a curved shape along the passing locus X1 of the light beam in the imaging lens 135. ing.

Therefore, the distances A and B (see FIG. 5) from the side edges T1 and T2 in the sub-scanning direction of the second imaging lens 135 to the light beam are equal regardless of the position in the main scanning direction (A = B). Satisfy the relationship). Therefore, even if the refractive index inside the lens changes in a contour line due to the moisture absorption phenomenon of the second imaging lens 135, the refractive index of the light beam is maintained substantially constant at each position in the main scanning direction of the second imaging lens 135. can do. Therefore, it is possible to prevent image defects from becoming conspicuous due to variations in the refractive index of the light beam at each position in the main scanning direction.

In the present embodiment, both the side edge T1 and T2 of the second imaging lens 135 in the sub-scanning direction have a curved shape along the passing locus X1 of the light beam, but one end edge T1 ( Alternatively, only T2) may have a curved shape along the passage locus X1, and the other edge T2 (or T1) may be formed, for example, in a straight line. Even in this case, the magnitude relation of the distances A and B from the both edge edges T1 and T2 in the main scanning direction to the light beam is higher than that in the case where both edge edges T1 and T2 are formed in a straight line. Variation can be suppressed. Therefore, it is possible to suppress image defects caused by the variation in the magnitude relationship between the distances A and B.

-Modification example 1-
FIG. 6 is a diagram corresponding to FIG. 5 showing a modified example 1 of the first embodiment. In this modification, a rectangular plate-shaped lens mounting portion 135e is provided outside the lens surface 135a of the second imaging lens 135 in the main scanning direction. According to this configuration, it is possible to obtain the same effect as that of the first embodiment while improving the mountability of the second imaging lens 135.

-Modification example 2-
FIG. 7 is a diagram corresponding to FIG. 5 showing a modification 2 of the first embodiment. In this modification, the second imaging lens 135 is formed asymmetrically in the main scanning direction.

That is, in this modification, the light beam is inclined in the main scanning direction and incident on the normal line of the reflection surface 133a of the polygon mirror 133. Therefore, the passing locus X1 of the light beam passing through the second imaging lens 135 becomes asymmetric in the main scanning direction. Therefore, the curved shapes of the edge T1 and T2 on both sides of the second imaging lens 135 in the sub-scanning direction are asymmetrically formed in the main scanning direction corresponding to the passing locus X1 of the light beam. According to this configuration, the same effect as that of the first embodiment can be obtained.

<< Embodiment 2 >>
FIG. 8 shows an image forming apparatus 1 provided with the optical scanning apparatus 4 according to the second embodiment. This image forming apparatus 1 is a tandem color printer, and is an intermediate transfer belt 7, a primary transfer unit 8 and a secondary transfer unit 9, a fixing unit 11, an optical scanning device 4, and four image forming devices. The units 16a to 16d and the first to fourth paper transport units 21 to 24 are provided.

A paper cassette 3 is arranged in the lower part of the inside of the main body 2 of the image forming apparatus 1. The paper feed cassette 3 is loaded with paper (not shown) such as cut paper before printing and accommodated therein. Then, this paper is separated and sent out one by one toward the upper right of the paper feed cassette 3 in FIG.

The first paper transport unit 21 is provided on the side of the paper feed cassette 3. The first paper transport unit 21 is arranged along the right side surface of the main body 2. Then, the first paper transport unit 21 receives the paper fed from the paper feed cassette 3 and transports the paper to the upper secondary transfer unit 9 along the right side surface of the main body 2.

A manual paper feed unit 5 is provided on the left side of the paper feed cassette 3. On the manual paper feed unit 5, paper of a size not contained in the paper feed cassette 3, thick paper, an OHP sheet, or the like is placed. A second paper transport unit 22 is provided on the right side of the manual paper feed unit 5. The second paper transport unit 22 extends substantially horizontally from the manual paper feed unit 5 to the first paper transport unit 21 and joins the first paper transport unit 21. Then, the second paper transport unit 22 receives the paper or the like sent out from the manual paper feed unit 5 and conveys it to the first paper transport unit 21.

The optical scanning device 4 is arranged above the second paper transport unit 22. Here, the image forming apparatus 1 receives the image data transmitted from the outside. This image data is stored in a temporary storage unit (not shown) and then sent to the optical scanning device 4 as needed. The optical scanning device 4 irradiates the image forming units 16a to 16d with a laser beam controlled based on the image data.

The image forming units 16a to 16d are provided above the optical scanning device 4. Each of the image forming units 16a to 16d has photoconductor drums 10a to 10d, respectively. Chargers 20a to 20d, developing devices 30a to 30d, and cleaning devices 35a to 35d are provided for each of the photoconductor drums 10a to 10d. The cleaning devices 35a to 35d are provided for cleaning the peripheral surfaces of the photoconductor drums 10a to 10d.

An endless intermediate transfer belt 7 is provided above each image forming unit 16a to 16d. The intermediate transfer belt 7 is wound around a plurality of rollers and is rotationally driven by a drive device (not shown).

As shown in FIG. 8, the four image forming units 16a to 16d are arranged in a row along the intermediate transfer belt 7 to form a yellow, magenta, cyan, or black toner image, respectively. That is, in each image forming unit 16a to 16d, the peripheral surface of the photoconductor drums 10a to 10d is irradiated with laser light by the optical scanning device 4 to form an electrostatic latent image of the original image, and the developing devices 30a to 30d form the electrostatic latent image. Toner images of each color are formed by developing the electrostatic latent image.

The primary transfer units 8a to 8d are arranged above the image forming units 16a to 16d, respectively. The primary transfer units 8a to 8d have primary transfer rollers 80a to 80d for primary transfer of the toner image formed by the image forming units 16a to 16d to the surface of the intermediate transfer belt 7. A transfer bias is applied to the primary transfer rollers 80a to 80d from a transfer bias power supply (not shown). The toner images of the image forming units 16a to 16d are transferred to the intermediate transfer belt 7 at a predetermined timing by the transfer bias applied to the primary transfer rollers 80a to 80d. Then, on the surface of the intermediate transfer belt 7, a color toner image in which four color toner images of yellow, magenta, cyan, and black are superimposed is formed.

The secondary transfer unit 9 has a secondary transfer roller 18 arranged on the right side of the intermediate transfer belt 7. A transfer bias is applied to the secondary transfer roller 18 by a transfer bias power supply. The secondary transfer roller 18 sandwiches the paper P with the intermediate transfer belt 7. Then, the toner image on the intermediate transfer belt 7 is transferred to the paper P by the transfer bias applied to the secondary transfer roller 18.

The fixing portion 11 is provided above the secondary transfer portion 9. A third paper transport section 23 is formed between the secondary transfer section 9 and the fixing section 11 to transport the paper P on which the toner image is secondarily transferred to the fixing section 11.

The fixing portion 11 has a rotating heating roller 11a and a pressure roller 11b, respectively. The fixing portion 11 sandwiches the paper P between the heating roller 11a and the pressure roller 11b to heat and pressurize the toner image transferred to the paper P and fix it on the paper P.

A branch portion 27 is provided above the fixing portion 11. When double-sided printing is not performed, the paper P discharged from the fixing unit 11 is discharged from the branch portion 27 to the paper ejection unit 28 formed on the upper portion of the image forming apparatus 1. The discharge port portion where the paper P is discharged from the branch portion 27 toward the paper discharge portion 28 functions as a switchback portion 29. When double-sided printing is performed, the transfer direction of the paper P discharged from the fixing unit 11 is switched in the switchback unit 29.

-Details of optical scanning device-
Next, the details of the optical scanning apparatus 4 will be described with reference to FIGS. 9 to 11. FIG. 9 is a schematic view showing how the light beams D1 to D4 emitted from the light sources 40a to 40d of the light scanning apparatus 4 are reflected by the polygon mirror 44. FIG. 10 is a schematic diagram linearly showing an incident optical system from the light source unit 40 of the optical scanning device 4 to the reflecting surface 44a of the polygon mirror 44, and FIG. 11 is a schematic diagram showing the light beam reflected by the polygon mirror 44. It is a schematic diagram which shows the emission optical system which leads to the photoconductor drums 10a to 10d.

A polygon mirror 44 and a light source unit 40 (see FIGS. 9 and 10) that emits light beams D1 to D4 toward the polygon mirror 44 are arranged in a housing 43 (see FIG. 8) of the optical scanning device 4. Has been done. In the present embodiment, the polygon mirror 44 has a regular hexagonal shape having six reflecting surfaces 44a on the side surface. The polygon mirror 44 is rotated at a predetermined speed by a motor (not shown).

The light source unit 40 has light sources 40a to 40d corresponding to each color of yellow, magenta, cyan, and black. The four light sources 40a to 40d are arranged at intervals in the sub-scanning direction (the direction of the rotation axis of the polygon mirror 44 and the vertical direction in FIG. 10). Each of the light sources 40a to 40d emits light beams D1 to D4, respectively.

On the upstream side of the optical path from the polygon mirror 44, four collimator lenses 41a to 41d provided corresponding to each light source 40a to 40d and light beams D1 to D4 passing through the collimator lenses 41a to 41d have a predetermined optical path width. An aperture (not shown) and a cylindrical lens portion 42 for condensing the light beams D1 to D4 that have passed through the aperture on the reflection surface 44a of the polygon mirror 44 are arranged. A first imaging lens 45 and four second imaging lenses 46a to 46d (see FIG. 11) are arranged on the downstream side of the optical path from the polygon mirror 44. The four second imaging lenses 46a to 46d are arranged in the optical paths of the light beams D1 to D4 emitted from the light sources 40a to 40d, respectively. The first imaging lens 45 and the second imaging lenses 46a to 46d are made of a highly hygroscopic resin material. An example of this resin material is PMMA resin.

The light beams D1 to D4 incident on the reflecting surface 44a of the polygon mirror 44 are scanned at a constant angular velocity by the polygon mirror 44, and then converted into constant velocity scanning light by the first imaging lens 45. The light beams D1 to D4 that have passed through the first imaging lens 45 each pass through the second imaging lenses 46a to 46d and are formed on the surface (scanned surface) of each of the photoconductor drums 10a to 10d by a folded mirror (not shown). Be guided.

As shown in FIG. 10, the incident optical system of the light beam with respect to the polygon mirror 44 employs an oblique incident method. That is, the light beam emitted from each of the light sources 40a to 40d is incident on the reflection surface 44a of the polygon mirror 44 from a direction inclined in the sub-scanning direction from the normal direction thereof.

Then, as shown in FIG. 11, each of the light beams D1 to D4 reflected by the polygon mirror 44 is reflected in a direction inclined in the sub-scanning direction from the normal direction of the reflection surface 44a. Specifically, the light beams D1 and D2 emitted from the light sources 40a and 40b are reflected in the direction inclined upward in FIG. 10 with respect to the normal direction, and the light beams D3 and the light beams D3 emitted from the light sources 40c and 40d are reflected. D4 is reflected in a direction inclined downward in FIG. 10 with respect to the normal direction. The reflection angle θ1 of the light beam D1 is equal to the reflection angle θ4 of the light beam D4. Further, the reflection angle θ2 of the light beam D2 is equal to the reflection angle θ3 of the light beam D3.

When the incident optical system is an oblique incident optical system as described above, the light beams D1 to D4 that are reflected by the polygon mirror 44 and pass through the first imaging lens 45 and the second imaging lenses 46a to 46d are curved. It becomes a shape. FIG. 12 shows the schematic shape of the passage trajectories Y1 to Y4 of the light beams D1 to D4 passing through the second imaging lenses 46a to 46d. Each of the passing trajectories Y1 to Y4 of the light beams D1 to D4 has a curved shape in which the central portion in the main scanning direction swells in the sub-scanning direction with respect to both ends. The four light beams D1 to D4 are two light beams D1 and D2 reflected on one side in the sub-scanning direction by the reflecting surface 44a of the polygon mirror 44, and two lights reflected on the other side in the sub-scanning direction. It consists of beams D3 and D4.

The bending directions of the two light beams D1 and D2 reflected on one side of the sub-scanning direction and the bending directions of the two light beams D3 and D4 reflected on the other side of the sub-scanning direction are opposite to each other. There is.

Comparing the passage trajectories Y1 and Y2 of the two light beams D1 and D2 reflected on one side in the sub-scanning direction, the light beam D1 has a reflection angle on the reflection surface 44a of the polygon mirror 44 more than the light beam D2. The larger the amount, the larger the amount of curvature. Further, when comparing the passage trajectories Y3 and Y4 of the two light beams D3 and D4 reflected on the other side in the sub-scanning direction, the light beam D4 is more reflected by the reflection surface 44a of the polygon mirror 44 than the light beam D3. The larger the angle, the larger the amount of curvature.

FIG. 13 is a plan view of the second imaging lenses 46a to 46d as viewed from the optical axis direction. The two second imaging lenses 46a and 46b on one side in the sub-scanning direction have the same (common) outer shape. The two second imaging lenses 46c and 46d on the other side in the sub-scanning direction have an outer shape that is vertically opposite to the other two second imaging lenses 46a and 46b.

FIG. 13A shows two second imaging lenses 46a and 46b on one side in the sub-scanning direction. Each imaging lens 46a, 46b has a lens surface 46A and a non-lens surface 46B that surrounds the outside of the lens surface 46A. The edges T3 and T4 on both sides of the two second imaging lenses 46a and 46b in the sub-scanning direction are the passage trajectories Y1 and Y2 of the light beams D1 and D2 passing through the second imaging lenses 46a and 46b (FIG. It is curved in the same direction as (see 12). The bending amount of the both end edges T3 and T4 is an average value (= (L1 + L2) / 2) of the bending amount L1 of the passing locus Y1 of the light beam D1 and the bending amount L2 of the passing locus Y2 of the light beam D2. Has been done.

FIG. 13B shows two second imaging lenses 46c, 46d on the other side in the sub-scanning direction. Each imaging lens 46a, 46b has a lens surface 46A and a non-lens surface 46B that surrounds the outside of the lens surface 46A. The edges T5 and T6 on both sides of the two second imaging lenses 46c and 46d in the sub-scanning direction are the passage trajectories Y3 and Y4 of the light beams D3 and D4 passing through the second imaging lenses 46c and 46d (FIG. It is curved in the same direction as (see 12). The bending amount of the both end edges T5 and T6 is an average value (= (L3 + L4) / 2) of the bending amount L3 of the passing locus Y3 of the light beam D3 and the bending amount L4 of the passing locus Y4 of the light beam D4. Has been done. In this embodiment, since L3 = L2 and L4 = L1, the relationship of (L3 + L4) / 2 = (L1 + L2) / 2 is satisfied. Therefore, by reversing the top and bottom of the two second imaging lenses 46a and 46b shown in FIG. 13A, the two second imaging lenses 46c and 46d shown in FIG. 13B can be used.

As described above, according to the second embodiment, each of the second imaging lenses 46a provided in the optical path of the two light beams D and D2 (or the two light beams D3 and D4) reflected on the same side in the sub-scanning direction. , 46b (or the second imaging lenses 46c, 46d) have the same shape, and both side edge T3, T4 (or both side edge T5, T6) in the sub-scanning direction in each of the imaging lenses 46a, 46b are Passage trajectories Y1 and Y2 (or passage trajectories Y3) of the light beams D and D2 (or two light beams D3 and D4) passing through the second imaging lenses 46a and 46b (or the second imaging lenses 46c and 46d). , Y4), the bending amount is equal to the average value of the bending amounts L1, L2 (or L3, L4) of both passing trajectories Y1, Y2 (or passing loci Y3, Y4).

According to this configuration, the second imaging lenses 46a and 46b (or the second imaging lens) are used for the two light beams D and D2 (or the two light beams D3 and D4) reflected on the same side in the sub-scanning direction. It is possible to obtain the same effect as that of the first embodiment while making the outer shapes of 46c and 46d) common.

-Modification example-
FIG. 14 shows a modified example of the second embodiment. In this modification, the amount of curvature of both side edges T3 to T6 in the sub-scanning direction of the second imaging lenses 46a to 46d is different from that of the second embodiment.

FIG. 14A shows two second imaging lenses 46a and 46b on one side in the sub-scanning direction. Both side edges T3 and T4 of the second imaging lenses 46a and 46b in the sub-scanning direction are the passage trajectories Y1 and Y2 of the light beams D1 and D2 passing through the second imaging lenses 46a and 46b (see FIG. 12). ) Is curved in the same direction. The one-sided edge T3 in the sub-scanning direction of each of the second imaging lenses 46a and 46b has the larger curvature amount L1 and L2 (the maximum) of the passage trajectories Y1 and Y2 of the two light beams D1 and D2. It has the same curved shape as the passing locus Y1. The other side edge T4 in the sub-scanning direction of each of the second imaging lenses 46a and 46b is the passage locus Y2 of the two light beams D1 and D2 having the smaller bending amount (minimum) of the passage loci Y1 and Y2. Has the same curved shape as.

FIG. 14B shows two second imaging lenses 46c, 46d on the other side in the sub-scanning direction. The edges T5 and T6 on both sides of the two second imaging lenses 46c and 46d in the sub-scanning direction are the passage trajectories Y3 and Y4 of the light beams D3 and D4 passing through the second imaging lenses 46c and 46d (FIG. It is curved in the same direction as (see 12). Then, the one side edge T5 in the sub-scanning direction of each of the second imaging lenses 46a and 46b is the smaller (minimum) of the passage trajectories Y3 and Y4 of the two light beams D3 and D4. ) The curved shape is the same as that of the passing locus Y3, and the other side edge T6 in the sub-scanning direction is the larger (maximum) of the passing trajectories Y3 and Y4 of the two light beams D1 and D2. ) It has the same curved shape as the passing locus Y4. By reversing the top and bottom of the two second imaging lenses 46a and 46b shown in FIG. 14A, it can be used as the two second imaging lenses 46c and 46d shown in FIG. 14B.

According to this configuration, for each of the two light beams D and D2 (or the two light beams D3 and D4) reflected on the same side in the sub-scanning direction, the second imaging lenses 46a and 46b (or the second imaging) are formed. It is possible to obtain the same effect as that of the first embodiment while making the outer shapes of the lenses 46c and 46d) common.

<< Other Embodiments >>
In each of the above embodiments, a printer has been described as an example of the image forming apparatus 1, but the present invention is not limited to this. That is, the image forming apparatus 1 may be a copying machine, a facsimile, a multifunction device (MFP), or the like.

In the second embodiment, the outer shapes of the second imaging lenses 46a to 46d through which the light beams D1 to D4 pass are the same shape (common shape), but the present invention is not limited to this. That is, the shapes of the edges on both sides of the second imaging lenses 46a to 46d in the sub-scanning direction are made the same as the curved shapes of the passing trajectories Y1 to Y4 of the light beams D1 to D4, as in the first embodiment. May be good.

The light beam emitted from the light source 132 in the first embodiment and the light beams D1 to D4 emitted from the light sources 40a to 40d in the second embodiment are not limited to a single beam but may be a multi-beam. ..

Further, the present invention is not limited to each of the above embodiments and modifications, and the present invention includes a configuration in which each of these embodiments and modifications is appropriately combined.

As described above, the present invention is useful for an optical scanning device and an image forming apparatus provided with the optical scanning device, and particularly when applied to a printer, a facsimile, a copier, or a multifunction device (MFP). It is useful.

1: Image forming device 4: Optical scanning device 10a: Photoreceptor drum (scanned surface)
10b: Photoreceptor drum (scanned surface)
10c: Photoreceptor drum (scanned surface)
10d: Photoreceptor drum (scanned surface)
40a: Light source 40b: Light source 40c: Light source 40d: Light source 44: Polygon mirror 44a: Reflective surface 46a: Second imaging lens 46b: Imaging lens 46c: Second imaging lens 46d: Second imaging lens 130: Optical scanning Device 132: Light source 133: Polygon mirror (rotating multi-sided mirror)
135: Imaging lens D: Optical beam D1: Optical beam D2: Optical beam D3: Optical beam D4: Optical beam L1: Curved amount L2: Curved amount L3: Curved amount L4: Curved amount P: Paper T1: Paper T1: In the sub-scanning direction One side edge T2: Other side edge T3 in the sub-scanning direction: One side edge T4 in the sub-scanning direction: Other side edge T5 in the sub-scanning direction: One side edge T6 in the sub-scanning direction: In the sub-scanning direction Other side edge X1: Passing locus Y1: Passing locus Y2: Passing locus Y3: Passing locus Y4: Passing locus

Claims (3)

A plurality of light sources that emit light beams, a rotating polymorphic mirror that reflects and deflects and scans a plurality of light beams emitted from the plurality of light sources, and an optical path of a plurality of light beams that are deflected and scanned by the rotating polymorphic mirror. Each of the above is provided with a resin imaging lens for forming an image of each light beam on the surface to be scanned, and the incident angle of each light beam on the reflection surface of the rotating polymorphic mirror is in the normal direction of the reflection surface. It is an optical scanning device that is tilted at different angles in the sub-scanning direction.
The plurality of light beams emitted from the plurality of light sources include a plurality of light beams reflected on the same side in the sub-scanning direction by the reflecting surface of the rotating polymorphic mirror.
The shape of each imaging lens provided in the optical path of the plurality of light beams reflected on the same side is the same, and at least one of the edges on both sides in the sub-scanning direction of each imaging lens is The amount of curvature of the light beam passing through each imaging lens is the same as the path of the light beam having the largest curvature, and the other edge is the amount of curvature of the path of the light beam passing through each imaging lens. Is the same as the smallest passage trajectory, an optical scanning device. In the optical scanning apparatus according to claim 1 ,
Each of the above imaging lenses is an optical scanning device made of PMMA resin. An image forming apparatus comprising the optical scanning apparatus according to claim 1 or 2 .

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