JP2018036438A - Optical scanner and image forming apparatus including the optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical scanner comprising an optical device that is provided on a light path of a light beam reflected by a light deflection part and reflects the light beam, and to maintain a fixed reflectance of the light beam irrespective of an incident angle of the light beam with respect to the optical device.SOLUTION: An optical device 50 is formed of a prism, and reflection of a light beam in the optical device 50 is total reflection of the light beam in the prism.SELECTED DRAWING: Figure 3

Description

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

  2. Description of the Related Art Conventionally, an optical scanning device that is mounted on an electrophotographic image forming apparatus and irradiates the surface of a photosensitive drum with a light beam corresponding to image data to scan in the main scanning direction is known.

  The optical scanning device includes a light source, a light deflecting unit that reflects and scans a light beam emitted from the light source, and an imaging lens that forms an image of light reflected by the light deflecting unit on a surface to be scanned. It has. The light deflection unit is configured by, for example, a rotating polygon mirror or a vibrating mirror unit.

  In the optical scanning device, in order to increase the degree of freedom of the optical path layout, a folding mirror may be provided in the optical path from the rotary polygon mirror to the scanned surface (see, for example, Patent Document 1). The folding mirror has a rectangular column shape that is long in the main scanning direction, reflects the light beam from the rotary polygon mirror, and guides it to the photosensitive drum. The reflection surface of the folding mirror is formed by depositing a thin film on the surface of the mirror material.

JP 09-015523 A

  However, in the folding mirror (optical element) in which a thin film is deposited on the surface of the mirror material as described above, the reflectance changes depending on the incident angle of the light beam with respect to the folding mirror. For this reason, the reflectance of the light beam differs between the central portion and both end portions of the folding mirror in the main scanning direction. As a result, there is a problem that uneven density in the main scanning direction occurs in the printed image.

  The present invention has been made in view of the above points, and an object of the present invention is to provide an optical scanning provided with an optical element that is provided in the optical path of the light beam reflected by the light deflection unit and reflects the light beam. In the apparatus, the reflectance of the light beam is to be kept constant regardless of the incident angle of the light beam with respect to the optical element.

  An optical scanning device according to one aspect of the present invention includes a light source, a light deflection unit including a rotary polygon mirror or a vibrating mirror that reflects and scans the light beam emitted from the light source in the main scanning direction, and the light deflection. And an optical element that is provided so as to extend in the main scanning direction on the optical path between the light beam reflected by the unit and the surface to be scanned.

  The optical element is constituted by a prism, and the reflection of the light beam by the optical element is total reflection of the light beam by the prism.

  An image forming apparatus according to another aspect of the present invention includes the optical scanning device.

  According to the present invention, in an optical scanning device including an optical element that is provided in an optical path of a light beam reflected by a light deflecting unit and reflects the light beam, light is incident regardless of an incident angle of the light beam with respect to the optical element. The reflectivity of the beam can be kept constant.

FIG. 1 is an overall view illustrating an image forming apparatus including an optical scanning device according to the first embodiment. FIG. 2 is a schematic view of the polygon mirror showing the scanning optical system in the optical scanning device as seen from the rotational axis direction. FIG. 3 is a schematic view of the scanning optical system in the optical scanning device viewed from the main scanning direction. FIG. 4 is a schematic view seen from the main scanning direction showing how the light beam is reflected by the optical element. FIG. 5 is a view corresponding to FIG. 4 showing a modification of the first embodiment. FIG. 6 is a view corresponding to FIG. FIG. 7 is a view corresponding to FIG. FIG. 8A is an explanatory diagram for explaining that the reflection direction of the light beam does not change even if rotational vibration occurs in the folding mirror section. FIG. 8B is an explanatory diagram for explaining that the reflection direction of the light beam does not change even if rotational vibration occurs in the folding mirror section. FIG. 8C is an explanatory diagram for explaining that the reflection direction of the light beam does not change even if rotational vibration occurs in the folding mirror section. FIG. 8D is a perspective view illustrating an example of a support structure for an optical element. FIG. 8E is a perspective view showing an example of a support structure of the optical element. FIG. 9A is a view corresponding to FIG. 8A showing a first modification of the second embodiment. FIG. 9B is a view corresponding to FIG. 8B, illustrating a first modification of the second embodiment. FIG. 9C is a view corresponding to FIG. 8C showing the first modification of the second embodiment. FIG. 9D is a view corresponding to FIG. 6 and illustrating a first modification of the second embodiment. FIG. 10A is a view corresponding to FIG. 8A showing a second modification of the second embodiment. FIG. 10B is a view corresponding to FIG. 8B, showing a second modification of the second embodiment. FIG. 10C is a view corresponding to FIG. 8C, showing a second modification of the second embodiment. FIG. 11A is a view corresponding to FIG. 8A showing a third modification of the second embodiment. FIG. 11B is a perspective view illustrating a support structure for an optical element according to Embodiment 2. FIG. 11C is a view in the XIC direction of FIG. 11B. FIG. 11D is a diagram corresponding to FIG. 8A and showing a fourth modification of the second embodiment. FIG. 11E is a view corresponding to FIG. 8A and showing a fifth modification of the second embodiment. FIG. 12 is a view corresponding to FIG. 7 showing a fourth modification of the second embodiment. FIG. 13 is a view corresponding to FIG. 7 and showing a fifth modification of the second embodiment.

  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 embodiment.

Embodiment 1
FIG. 1 is a cross-sectional view showing a schematic configuration of a laser printer 1 as an image forming apparatus in the present embodiment.

  As shown in FIG. 1, the laser printer 1 includes a box-shaped printer main body 2, a manual paper feed unit 6, a cassette paper feed unit 7, an image forming unit 8, a fixing unit 9, and a paper discharge unit 10. It has. Thus, the laser printer 1 is configured to form an image on a sheet based on image data transmitted from a terminal (not shown) while conveying the sheet along a conveyance path H in the printer body 2. ing.

  The manual paper feed unit 6 includes a manual feed tray 4 that can be opened and closed on one side of the printer body 2, and a manual feed roller 5 that is rotatably provided inside the printer body 2. ing.

  The cassette paper feeding unit 7 is provided at the bottom of the printer main body 2. The cassette paper feed unit 7 separates the paper feed cassette 11 that stores a plurality of papers stacked on each other, a pick roller 12 that takes out the paper in the paper feed cassette 11 one by one, and the paper that is taken out one by one. The feed roller 13 and the retard roller 14 are fed to the transport path H.

  The image forming unit 8 is provided above the cassette paper feeding unit 7 in the printer main body 2. The image forming unit 8 includes a photosensitive drum 16, a charger 17, a developing unit 18, a transfer roller 19, a cleaning unit 20, a toner hopper 21, and an optical scanning device 30. The image forming unit 8 forms a toner image on a sheet supplied from the manual sheet feeding unit 6 or the cassette sheet feeding unit 7.

  The transport path H is provided with a pair of registration rollers 15 that supply the fed sheet to the image forming unit 8 at a predetermined timing after temporarily waiting.

  The fixing unit 9 is disposed on the side of the image forming unit 8. The fixing unit 9 includes a fixing roller 22 and a pressure roller 23 that are pressed against each other and rotate. The fixing unit 9 fixes the toner image transferred to the sheet by the image forming unit 8 on the sheet.

  The paper discharge unit 10 is provided above the fixing unit 9. The paper discharge unit 10 includes a paper discharge tray 3, a paper discharge roller pair 24 for transporting paper to the paper discharge tray 3, and a plurality of transport guide ribs 25 for guiding paper to the paper discharge roller pair 24. . The paper discharge tray 3 is formed in a concave shape at the top of the printer body 2.

  When the laser printer 1 receives the image data, the photosensitive drum 16 is rotationally driven in the image forming unit 8, and the charger 17 charges the surface of the photosensitive drum 16.

  Then, based on the image data, a light beam is emitted from the optical scanning device 30 to the photosensitive drum 16. An electrostatic latent image is formed on the surface of the photosensitive drum 16 by irradiation with a light beam. This electrostatic latent image is visualized as a toner image by being developed with toner charged in the developing unit 18.

  Thereafter, the sheet supplied from the sheet feeding cassette 11 passes between the transfer roller 19 and the photosensitive drum 16. At this time, the toner image carried on the surface of the photosensitive drum 16 receives the electrostatic attraction from the transfer roller 19 and moves to the printing surface of the paper. As a result, the toner image on the photosensitive drum 16 is transferred to the paper. The sheet on which the toner image is transferred is heated and pressed by the fixing roller 22 and the pressure roller 23 in the fixing unit 9. As a result, the toner image is fixed on the paper.

  Next, the details of the optical scanning device 30 will be described with reference to FIGS. The optical scanning device 30 includes a housing (not shown), a polygon mirror 35 that is housed in the housing and deflects and scans the light beam from the light source 32, and reflects the light beam deflected and scanned by the polygon mirror 35. The optical element 50 as an optical element to perform, and the imaging lens 36 that forms an image of the light beam reflected by the optical element 50 are provided.

  The polygon mirror 35 is attached to the housing via a polygon motor 40. The polygon mirror 35 is a rotary polygon mirror and is driven to rotate by a polygon motor 40.

  The light source 32 is disposed on the side wall of the housing. The light source 32 is a laser light source having a laser diode, for example. The light source 32 emits a laser beam (light beam) toward the polygon mirror 35. A collimator lens 33 (see FIG. 3) and a cylindrical lens 34 are disposed between the light source 32 and the polygon mirror 35.

  As shown in FIG. 2, the imaging lens 36 extends in the main scanning direction on the side of the polygon mirror 35.

  The optical element 50 is provided on the opposite side of the imaging lens 36 from the polygon mirror 35 side. The optical element 50 is composed of a columnar member extending in the main scanning direction. The cross section perpendicular to the main scanning direction of the optical element 50 has a right-angled isosceles triangle shape. The optical element 50 includes an entrance surface 50a perpendicular to the optical path of the light beam from the polygon mirror 35, an exit surface 50b perpendicular to the entrance surface 50a, and an edge of the exit surface 50b from the edge of the entrance surface 50a. And a reflecting surface 50c extending up to. The reflection surface 50 c is inclined at 45 ° with respect to the light beam incident from the polygon mirror 35. The optical element 50 totally reflects the light beam from the polygon mirror 35 on the reflection surface 50c and turns it back.

  Laser light emitted from the light source 32 when the optical scanning device 30 is operated is converted into a parallel light beam by the collimator lens 33 (see FIG. 2) and then condensed on the reflection surface of the polygon mirror 35 by the cylindrical lens 34. The light beam condensed on the polygon mirror 35 is reflected by the reflection surface of the polygon mirror 35. The light beam reflected by the polygon mirror 35 passes through the imaging lens 36 and is then reflected by the optical element 50 to return its optical path. The light beam is imaged on the surface of the photosensitive drum 16. The scanning light imaged on the surface of the photosensitive drum 16 scans the surface of the photosensitive drum 16 in the main scanning direction by the rotation of the polygon mirror 35, and scans in the sub-scanning direction by the rotation of the photosensitive drum 16. An electrostatic latent image is formed on the surface of the body drum 16.

Next, the principle of reflection of the light beam by the optical element 50 will be described with reference to FIG. The light beam reflected by the polygon mirror 35 passes through the incident surface 50 a of the optical element 50 at an incident angle of 0 ° and enters the optical element 50. The entered light beam reaches the reflecting surface 50c of the optical element 50 at an incident angle of 45 °. Here, the refractive index of glass is generally around 1.5, and when the incident angle of the light beam is below the critical angle at the boundary between the medium having a high refractive index and the medium having a low refractive index, the light beam is transmitted through the boundary. If is greater than the critical angle, total reflection occurs at the boundary (from Snell's law). In this embodiment, the refractive index of the medium used for the optical element 50 is 1.5, for example, and the critical angle is 41.8 ° (= sin ⁻¹ (sin 90 ° / 1.5)). The incident angle (= 45 °) with respect to 50c is larger than the critical angle. As a result, the light beam is totally reflected by the reflection surface 50c at the same reflection angle (= 45 °) as the incident angle. Since the totally reflected light beam reaches the exit surface 50b at an incident angle of 0 °, the light beam passes through the exit surface 50b at a refraction angle of 0 °.

  Here, in the conventional optical scanning device 30, the optical element that reflects the light beam is formed by depositing a thin film on the surface of the material. For this reason, the reflectivity varies depending on the incident angle of the light beam with respect to the optical element 50, and the reflectivity of the light beam differs between both ends and the center of the optical element 50 in the main scanning direction. There is a problem that density unevenness occurs in the main scanning direction.

  On the other hand, in the present embodiment, the optical element 50 that reflects the light beam from the polygon mirror 35 is configured by a prism, and the light beam is reflected by utilizing total reflection by the prism. Accordingly, the reflectance of the light beam can be maintained constant regardless of the incident angle of the light beam with respect to the optical element 50. Therefore, it is possible to suppress the occurrence of density unevenness in the printed image.

<Modification>
FIG. 5 shows a modification of the first embodiment. In this modification, the incident angle of the light beam with respect to the optical element 50 is different from that of the above embodiment.

  That is, in this modification, the light beam reflected by the polygon mirror 35 reaches the incident surface 50a of the optical element 50 at an incident angle of 30 ° and is transmitted at a refraction angle of 19.5 °. Thus, the light beam that has entered the optical element 50 reaches the reflecting surface 50c at an incident angle of 64.5 °. Since this incident angle is larger than the critical angle, the light beam is totally reflected at the reflection surface 50c at the same reflection angle as the incident angle. The totally reflected light beam reaches the exit surface 50b at an incident angle of 19.5 °, and the light beam is transmitted at a refraction angle of 30 °.

  Also in the first modification, the optical element 50 is configured by a prism as in the first embodiment. Therefore, the same effect as the first embodiment can be obtained.

<< Embodiment 2 >>
6 and 7 show the second embodiment. The present embodiment is different from the first embodiment and the modification in that the light beam is totally reflected twice by the optical element 50.
That is, in the present embodiment, the optical element 50 is formed of a columnar body having an isosceles triangle shape when viewed from the main scanning direction. The optical element 50 includes an incident / exit surface 50d perpendicular to the optical path of the light beam reflected by the polygon mirror 35, a first reflecting surface 50e inclined downward from the upper end of the incident / exit surface 50d toward the right side, It has the 2nd reflective surface 50f which inclines below from the lower end of the 1st reflective surface 50e toward the left side.
As shown in FIGS. 6 and 7, the light beam reflected by the polygon mirror 35 enters the optical element 50 from the incident / exit surface 50d and is totally reflected by the first reflecting surface 50e and the second reflecting surface 50f, respectively. After that, the light is emitted from the incident / exit surface 50d to the outside of the optical element 50 and applied to the surface of the photosensitive drum 16 (see FIG. 7).

By the way, in the conventional optical scanning device 30, the rotational vibration of the polygon mirror 35 is transmitted to the optical element 50, whereby the optical element 50 vibrates alternately in the clockwise direction and the counterclockwise direction when viewed from the main scanning direction. (Hereinafter referred to as rotational vibration). When this rotational vibration occurs, the light beam incident on the imaging surface (the surface of the photosensitive drum 16) may vibrate in the sub-scanning direction, and image defects such as jitter may occur in the printed image.
On the other hand, in the present embodiment, since the first reflecting surface 50e and the second reflecting surface 50f of the optical element 50 are formed as one prism, the light beam greatly oscillates in the sub-scanning direction on the imaging surface. Can be prevented. The reason will be described with reference to FIGS. 8A and 8B.

  8A and 8B show a case where the angle formed by the first reflecting surface 50e and the second reflecting surface 50f is 90 °. In each figure, the first reflection surface 50e and the second reflection surface 50f and the rotation axis A of the optical element 50 are schematically shown for the sake of simplicity. In the present embodiment, the rotation axis A is located on a plane L1 that bisects the angle formed by the first reflecting surface 50e and the second reflecting surface 50f. The axis of rotation A and the intersection line L2 between the reflecting surfaces 50e and 50f are separated by a predetermined distance.

  FIG. 8A shows a basic state in which no rotational vibration occurs in the optical element 50. The incident angle θ1 of the light beam reflected by the polygon mirror 35 and incident on the first reflecting surface 50e is 45 °, and the light beam is folded at a right angle by the first reflecting surface 50e. The folded light beam is incident on the second reflecting surface 50f. The incident angle θ2 of the light beam with respect to the second reflecting surface 50f is 45 °, and the light beam is again folded at a right angle by the second reflecting surface 50f. That is, the light beams reflected by the first reflecting surface 50e and the second reflecting surface 50f are folded back 180 ° (= 2θ1 + 2θ2 = 90 ° + 90 °), so that the light beam incident on the optical element 50 is reflected by the optical element 50. Is parallel to the light beam.

  FIG. 8B shows a state in which the optical element 50 is rotated by β ° in the clockwise direction from the state shown in FIG. 8A due to rotational vibration. In this state, assuming that the incident angle θ1 ′ of the light beam on the first reflecting surface 50e is θ1 ′ = θ1-β, the light beam is folded at an angle of 90 ° −2β on the first reflecting surface 50e. The folded light beam is incident on the second reflecting surface 50f. Assuming that the incident angle θ2 ′ of the light beam with respect to the second reflecting surface 50f is θ2 ′ = θ2 + β, the light beam is folded at an angle of 90 ° + 2β on the second reflecting surface 50f. Therefore, the light beam is folded 180 ° (= 2θ1 ′ + 2θ2 ′ = 90 ° -2β + 90 ° + 2β) by two reflections, so that the direction of the reflected light beam by the optical element 50 is maintained in the same direction before and after the occurrence of rotational vibration. can do.

  Therefore, even if rotational vibration occurs in the optical element 50, it is possible to avoid the light beam from greatly shaking in the sub-scanning direction with the incident position as a fulcrum. As a result, it is possible to suppress the occurrence of image defects such as jitter in the printed image.

  Here, the position of the rotation axis A of the optical element 50 is determined by the support position of the optical element 50 by a plurality of support pins. 8D and 8E show an example of the support structure of the optical element 50 in the present embodiment. FIG. 8D shows an example in which the optical element 50 is supported from the front side, and FIG. 8E shows an example in which the optical element 50 is supported from the back side. The support position 71 in each figure is located on a plane L1 that bisects the first reflection surface 50e and the second reflection surface 50f, and the support positions 72 and 73 are arranged symmetrically across the plane L1. . The optical element 50 is supported by support pins (not shown) at the respective support positions 71 to 73. Thus, in the present embodiment, the rotation axis A is located on a plane L1 that bisects the first reflecting surface 50e and the second reflecting surface 50f. Therefore, as shown in FIG. 8C, the positional deviation amount δ in the sub-scanning direction of the light beam reflected by the optical element 50 can be reduced as compared with the case where the rotation axis A is separated from the plane L1. Therefore, it is possible to more reliably suppress image defects caused by the rotational vibration of the optical element 50.

<Modification 1>
9A to 9C show the optical element 50 according to the first modification of the first embodiment. The first modification differs from the first embodiment in that the angle formed between the first reflecting surface 50e and the second reflecting surface 50f is an obtuse angle. The state of reflection of the light beam by the optical element 50 of the first modification is shown. Also in the first modification, as in the first embodiment, it is possible to prevent the light beam from greatly vibrating in the sub-scanning direction on the imaging plane. The reason will be described below.

  FIG. 9A shows a basic state in which no rotational vibration is generated in the optical element 50. In the drawing, the angle formed by the first reflecting surface 50e and the second reflecting surface 50f is indicated by 90 ° + η. The angle formed by the plane L1 that bisects the angle formed by the reflecting surfaces 50e and 50f and the light beam incident on the first reflecting surface 50e when viewed from the main scanning direction (perpendicular to the paper surface) is 2η1, and the second reflecting surface If the angle between the light beam reflected at 50f and the plane L1 is 2η2, the incident angle θ1 of the light beam incident on the first reflecting surface 50e is 45 ° + η1, and the light beam is reflected on the first reflecting surface 50e. At 90 ° + 2η1. The incident angle θ2 of the light beam that is folded at the first reflecting surface 50e and incident on the second reflecting surface 50f is 45 ° + η2, and the light beam is folded at an angle of 90 ° + 2η2 at the second reflecting surface 50f. That is, since the light beam incident on the optical element 50 is folded back at 180 ° + 2η (= 2θ1 + 2θ2 = 90 ° + 2η1 + 90 ° + 2η2), the angle formed between the incident light beam and the reflected light beam is 2η = 2η1 + 2η2. That is, when the light beam is incident on the optical element 50 in which the angle α formed by the two reflecting surfaces 50e and 50f is 90 ° + η, the angle formed by the incident light beam and the reflected light beam is always 2η.

  FIG. 9B shows a state in which the optical element 50 is rotated by β ° from the state of FIG. 9A in the clockwise direction of the drawing due to rotational vibration. In this state, if the incident angle of the light beam on the first reflecting surface 50e is θ1 ′, θ1 ′ = θ1−β, and the light beam is folded at an angle of 90 ° + 2η1-2β on the first reflecting surface 50e. It is. Assuming that the incident angle θ2 ′ of the light beam that is folded back by the first reflecting surface 50e and incident on the second reflecting surface 50f is θ2 ′ = θ2 + β, the light beam is folded by the second reflecting surface 50f at an angle of 90 ° + 2η2 + 2β. It is. Accordingly, the light beam is folded back 180 ° + 2η (= 2θ1 ′ + 2θ2 ′ = 90 ° + 2η1-2β + 90 ° + 2η2 + 2β) by two reflections. Therefore, the light beam emission direction from the optical element 50 can be maintained in the same direction before and after the occurrence of rotational vibration.

  Further, since the rotation axis A of the optical element 50 is located on a plane L1 that is equal to the first reflection surface 50e and the second reflection surface 50f, the rotation axis A is separated from the plane L1 as shown in FIG. 9C. Compared to the case where the optical elements 50 are separated from each other, the positional deviation amount δ in the sub-scanning direction of the reflected light beam by the optical element 50 can be reduced. Therefore, the same effect as the first embodiment can be obtained.

  FIG. 9D is a design example of the optical element 50 of the first modification. As shown in the figure, in this modification, it is not necessary to set the incident / exit angle of the light beam with respect to the incident / exiting surface 50d of the light beam to 90 °, so that the degree of freedom in design increases.

<Modification 2>
10A to 10C show the optical element 50 of Modification 2 of Embodiment 1. FIG. Modification 2 is different from Embodiment 1 and Modification 1 in that the angle formed by the first reflection surface 50e and the second reflection surface 50f is an acute angle. Also in the second modification, similarly to the first embodiment and the first modification, it is possible to prevent the light beam from greatly vibrating in the sub-scanning direction on the imaging surface. The reason will be described below.

  FIG. 10A shows a basic state in which no rotational vibration is generated in the optical element 50. In the drawing, the angle formed by the first reflecting surface 50e and the second reflecting surface 50f is indicated by 90 ° −η. When viewed from the main scanning direction (perpendicular to the paper surface), the angle formed by the plane L1 that bisects the angle formed by the reflecting surfaces 50e and 50f and the light beam incident on the first reflecting surface 50e is 2η1, and the second reflecting surface. If the angle formed between the light beam reflected at 50f and the plane L1 is 2η2, the incident angle θ1 of the light beam incident on the first reflecting surface 50e is 45 ° −η1, and the light beam is reflected on the first reflecting surface. It is folded at an angle of 90 ° -2η1 at 50e. The incident angle θ2 of the light beam that is folded back at the first reflecting surface 50e and incident on the second reflecting surface 50f is 45 ° −η2, and the light beam is folded back at an angle of 90 ° −2η2 at the second reflecting surface 50f. It is. That is, the light beam incident on the optical element 50 is folded at 180 ° −2η (= 2θ1 + 2θ2 = 90 ° −2η1 + 90 ° −2η2), and the angle formed by the incident light beam and the reflected light beam is 2η = 2η1 + 2η2. That is, when the light beam is incident on the optical element 50 having the relative angle α = 90 ° −η between the two reflecting surfaces 50e and 50f, the relative angle between the incident light beam and the reflected light beam is always 2η.

  FIG. 10B shows a state in which the optical element 50 is rotated by β ° in the clockwise direction from the state of FIG. 10A due to rotational vibration. In this state, assuming that the incident angle θ1 ′ of the light beam to the first reflecting surface 50e is θ1 ′ = θ1-β, the light beam is folded at an angle of 90 ° −2η1-2β on the first reflecting surface 50e. . Assuming that the incident angle θ2 ′ of the light beam that is folded back at the first reflecting surface 50e and enters the second reflecting surface 50f is θ2 ′ = θ2 + β, the light beam has an angle of 90 ° −2η2 + 2β at the second reflecting surface 50f. Wrapped at Therefore, the light beam is folded 180 ° −2η (= 2θ1 ′ + 2θ2 ′ = 90 ° -2η1-2β + 90 ° -2η2 + 2β) by two reflections. Therefore, the direction of the reflected light beam reflected by the optical element 50 can be maintained in the same direction before and after the occurrence of rotational vibration.

  Further, since the rotation axis A of the optical element 50 is located on a plane L1 that bisects the first reflecting surface 50e and the second reflecting surface 50f when viewed from the main scanning direction, as shown in FIG. 10C. As compared with the case where the rotation axis A is separated from the plane L1, the positional deviation amount δ in the sub-scanning direction of the reflected light beam by the optical element 50 can be reduced. Therefore, the same effect as the first embodiment can be obtained.

<Modification 3>
11A to 11C show a third modification of the second embodiment. In the present modification, the position of the rotation axis A is different from those in the above embodiments and modifications.

  That is, in the present modification, the position of the rotation axis A coincides with the intersection line L2 between the first reflecting surface 50e and the second reflecting surface 50f when viewed from the main scanning direction.

  Here, as described above, the position of the rotation axis A is determined by the support position of the optical element 50 by the plurality of support pins 61 to 63 (see FIGS. 11B and 11C). With reference to FIG. 11B and FIG. 11C, the support structure of the optical element 50 by the some support pins 61-63 is demonstrated.

  The optical element 50 includes a prism main body 50g having a triangular prism shape and a pair of rectangular plate portions 50h protruding from both ends of the main body 50g in the main scanning direction. The optical element 50 is fixed to the pair of holding plates 60 using fixing bolts 65 that pass through the respective rectangular plate portions 50h in the thickness direction. The pair of holding plates 60 are supported by first to third support pins 61 to 63. That is, the optical element 50 is indirectly supported via the holding plate 60 by the first to third support pins 61 to 63.

  As shown in FIG. 11C, the first support pin 61 supports the base end portion of one holding plate 60, and the second and third support pins 62 and 63 support the base end portion of the other holding plate 60. Yes. The figure formed by connecting the support positions of the holding plate 60 by the support pins 61 to 63 has an isosceles triangle shape. A straight line passing through the support position of the holding plate 60 by the first support pin 61 and the midpoint of the support position of the holding plate 60 by the second and third support pins 62 and 63 is the rotation axis A of the optical element 50. The rotation axis A extends parallel to the main scanning direction, and in this embodiment, the holding plate is arranged so that the rotation axis A coincides with the intersection line L2 between the first reflection surface 50e and the second reflection surface 50f. The length of 60, the fixed position of the optical element 50 with respect to the holding plate 60, the support position of the optical element 50 by the support pins 61 to 63, and the like are determined.

  As described above, according to the optical scanning device 30 of the present embodiment, the rotation axis A at the time of the rotational vibration of the optical element 50 is the intersection line L2 between the first reflecting surface 50e and the second reflecting surface 50f when viewed from the main scanning direction. It matches. Therefore, as compared with the optical element 50 of the first embodiment, the positional deviation amount δ (see FIG. 11A) of the reflected light beam due to the rotational vibration of the optical element 50 in the sub-scanning direction is reduced. Therefore, the same effect as Embodiment 1 can be obtained more reliably.

  In the third modification, the example in which the angle formed by the first reflecting surface 50e and the second reflecting surface 50f is 90 ° has been described. However, the present invention is not limited to this. For example, as shown in FIG. Similar effects can be obtained even when is an obtuse angle or when the angle is an acute angle as shown in FIG. 11E.

<< Other embodiments >>
In each of the above embodiments and modifications, the optical element 50 is formed in a triangular prism shape extending in the main scanning direction. However, the present invention is not limited to this, and for example, as shown in FIG. As shown in FIG. 12, it may be a pentagonal prism. In the example of FIGS. 12 and 13, the bending angle when the light beam enters the optical element 50 and the bending angle when the light beam is emitted from the optical element 50 are both 0 °. By doing so, it is possible to simplify the optical path from the light beam reflected by the polygon mirror 35 to the imaging surface via the optical element 50 and to facilitate the optical path design of the entire optical scanning device 30. .

  In each of the above embodiments and modifications, the polygon mirror 35 has been described as an example of the light deflecting unit that deflects and scans the light beam. However, the light deflecting unit is, for example, a resonance-type vibrating mirror that is driven by a piezoelectric element or the like. There may be. When the light deflection unit is composed of a vibrating mirror, the length of the optical element 50 in the main scanning direction can be relatively short, so that the use of a prism for the optical element 50 increases the product cost. Can be suppressed.

  In the third modification of the second embodiment, the optical element 50 is indirectly supported by the plurality of support pins 61 to 63 via the holding plate 60. However, the present invention is not limited to this. You may make it support directly by the pins 61-63. Needless to say, the number of support pins that support the optical element 50 is not limited to three, but may be two or less, or may be four or more. For example, when there are four support pins, both ends of the optical element 50 in the main scanning direction may be supported by two support pins. In this case, the midpoint of the support position by two support pins provided at one end of the optical element 50 in the main scanning direction and the midpoint of the support position by two support pins provided at the other end in the main scanning direction. Is a rotation axis A of the optical element 50.

  In each of the above embodiments and modifications, a laser printer has been described as an example of an image forming apparatus on which the optical scanning device 30 is mounted. However, the present invention is not limited to this, and the image forming apparatus may be, for example, a multifunction peripheral (MFP). ), A copying machine, a facsimile, or the like.

  As described above, the present invention is useful for an optical scanning device and an image forming apparatus including the optical scanning device.

1 Laser printer (image forming device)
30 Optical scanning device 32 Light source 50 Optical element 51a First reflection surface 52a Second reflection surface L1 Plane L2 Intersection line

Claims (6)

Main scanning in the optical path between the light source, the light deflection unit that reflects and scans the light beam emitted from the light source in the main scanning direction, and the light beam reflected by the light deflection unit and the surface to be scanned An optical scanning device provided with an optical element that extends in a direction and reflects a light beam,
The optical element is composed of a prism,
The optical scanning device, wherein the reflection of the light beam by the optical element is total reflection of the light beam by the prism. The optical scanning device according to claim 1,
The prism constituting the optical element includes a first reflecting surface that totally reflects a light beam incident from the outside of the prism, and a second reflecting surface that totally reflects the light beam totally reflected by the first reflecting surface. An optical scanning device having a reflective surface. The optical scanning device according to claim 1 or 2,
The prism constituting the optical element has an incident angle of the light beam when the light beam is incident on the prism and an emission angle of the light beam when the light beam is emitted to the outside from the prism, as viewed from the main scanning direction. An optical scanning device in which both are zero. The optical scanning device according to claim 2,
A support pin for supporting the prism constituting the optical element;
The light deflection unit is a rotary polygon mirror,
The rotation axis of the prism when the prism rotates and vibrates with the rotation of the rotary polygon mirror is determined by the support position of the prism by the support pin,
The optical scanning device, wherein the rotation axis is located on a plane that bisects the first reflection surface and the second reflection surface when viewed in the sub-scan section of the prism. In the optical scanning device according to any one of claims 1 to 4,
A support pin for supporting the prism constituting the optical element;
The light deflection unit is a rotary polygon mirror,
The rotation axis of the prism when the prism rotates and vibrates with the rotation of the rotary polygon mirror is determined by the support position of the prism by the support pin,
The optical scanning device, wherein the rotation axis coincides with an intersection line of the first reflecting surface and the second reflecting surface as seen in a sub-scanning section of the prism.   An image forming apparatus comprising the optical scanning device according to claim 1.

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