JP6074737B2 - Tandem scanning optical system - Google Patents

Description

  The present invention relates to a tandem scanning optical system that scans a scanning surface of a corresponding color after deflecting a light beam composed of light beams for a plurality of colors on the same polarization plane.

  In a tandem scanning optical system, a light beam deflected by the same polarization plane is composed of a light beam for a plurality of colors, and is spatially distributed to each color light beam in the middle of the optical path to the scanned surface of the corresponding color. To be separated. For separation, a plurality of light beams are not spatially separated from each other in the luminous flux, but need to be separated from each other with a very small space.

  As an optical beam separation method, there is an oblique incidence optical system. In the oblique incidence optical system, the light beams for a plurality of colors are incident on the polarization plane with an angle in the sub-scanning direction (hereinafter referred to as an oblique incidence angle) with respect to the normal line of the polarization plane. The oblique incidence optical system includes one-side deflection and both-side deflection. Among these, in both-side deflection, a light beam of a plurality of colors constitutes a light beam and enters the polarization plane, and the remaining light beams of a plurality of colors constitute another light flux and enter a different polarization surface. In a general oblique incidence optical system, after deflection, the light beams of a plurality of colors pass through a common scanning lens shared by the plurality of colors, and are then separated into individual light beams by a separating unit.

  A common scanning lens for imaging a plurality of light beams after separating a plurality of light beams scanned by an optical deflector is disclosed in Patent Document 1 below for an oblique incidence optical system having a general configuration. An optical scanning device comprising

JP 2011-95383 A

  When the sub-scanning direction of the common scanning lens is constituted by one surface, the surfaces need to have shapes symmetrical to each other in the sub-scanning direction. When a plurality of light beams are allowed to pass through the common scanning lens, the plurality of light beams after passing are closer to each other than before passing. Therefore, it is necessary to increase the oblique incidence angle in order to spatially separate these light beams. However, when the oblique incident angle is increased, scanning line bending occurs or the light beam is twisted and incident on the scanning optical lens. As a result, there is a problem that it becomes difficult to correct aberrations with the scanning optical lens.

  SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a tandem scanning optical system that facilitates aberration correction with a scanning optical lens.

To achieve the above object, according to one aspect of the present invention, there is provided a plurality of scanned surfaces and a light beam provided to each of the plurality of scanned surfaces and to be irradiated to the corresponding scanned surface. A plurality of light sources to be emitted, and a plurality of light beams emitted from the plurality of light sources have a surface on which an oblique incident angle is incident in the sub-scanning direction, with an axis parallel to the sub-scanning direction as a center A polarizer that rotates and scans a plurality of light beams incident on the surface in the main scanning direction, and a plurality of light beams that are scanned by the polarizer and that have not passed through the scanning lens Separating means for separating the beam into individual light beams and one corresponding to each of the plurality of scanned surfaces are provided, and the light beams separated by the separating means are converged to correspond to the corresponding scanned surface. A plurality of scanning lenses emitting toward the It is provided.

  One surface of each scanning lens has an asymmetric shape in the sub-scanning direction, one surface of each scanning lens has an asymmetric shape in the main scanning direction, and the optical axis of each scanning lens is , And eccentric with respect to a plane perpendicular to the rotation axis of the polarizer.

  According to the above aspect, it is an object of the present invention to provide a tandem scanning optical system that facilitates aberration correction with a scanning optical lens.

It is a perspective view which shows the structure of the upstream of each optical path of the tandem scanning optical system which concerns on 1st embodiment. FIG. 2 is a cross-sectional view illustrating a downstream configuration of each optical path of the tandem scanning optical system in FIG. 1. It is a schematic diagram which shows the relationship of the light beam in the separation position of a light beam. It is a schematic diagram showing that the distance from the center of the deflection point to the incident surface of the scanning lens varies depending on the image height in the main scanning direction. It is a schematic diagram showing that the incident position (the height in the sub-scanning direction) of the light beam on the scanning lens varies depending on the image height in the main scanning direction. It is a schematic diagram which shows the core thickness and subscanning direction height of a scanning lens. FIG. 2 is a top view when one optical path in the tandem scanning optical system of FIG. 1 is developed in the X-axis direction. FIG. 7B is a side view of the tandem scanning optical system shown in FIG. 7A. It is a schematic diagram which shows the relationship between an oblique incident angle and the amount of eccentricity. It is a top view when one optical path is developed in the X-axis direction in the tandem scanning optical system according to the modification. FIG. 9B is a side view of the tandem scanning optical system shown in FIG. 9A. It is a top view when one optical path in the tandem scanning optical system according to the second embodiment is developed in the X-axis direction. FIG. 10B is a side view of the tandem scanning optical system shown in FIG. 10A.

(Introduction)
Prior to the description of the tandem scanning optical system according to each embodiment of the present invention, terms are defined. In some drawings, the X, Y, and Z axes are shown. The X axis indicates the horizontal direction (lateral direction) in the tandem scanning optical system. The Y axis indicates the front-rear direction (depth direction) in the tandem scanning optical system and the direction in which the light beam is scanned on each surface to be scanned (hereinafter referred to as the main scanning direction). The Z axis indicates the vertical direction (height direction) of the image forming apparatus. The Z-axis indicates the sub-scanning direction of the light beam when the tandem scanning optical system is developed in the X-axis direction.

  In addition, in some of the configurations, subscripts a, b, c, and d are added after reference numerals in some configurations. a, b, c, and d mean yellow (Y), magenta (M), cyan (C), and black (Bk). For example, the scanned surface 1a means the scanned surface 1 for Y. In addition, when the subscript is not added to the reference code, this reference code is a generic term for each color. For example, the scanned surface 1 is a generic term for scanned surfaces 1a to 1d for each color of Y, M, C, and Bk.

(First embodiment)
Hereinafter, the tandem scanning optical system according to the first embodiment will be described with reference to the drawings. First, FIG. 1 and FIG. 2 are referred. The tandem scanning optical system is mounted on an image forming apparatus such as a full-color copying machine or printer. In the image forming apparatus, the scanned surfaces 1a to 1d are juxtaposed corresponding to each color of YMCK. The tandem scanning optical system irradiates the scanned surfaces 1a to 1d with light beams Ba to Bd modulated with image data of the corresponding color, and forms electrostatic latent images of the corresponding color on the scanned surfaces 1a to 1d. .

The tandem scanning optical system employs a so-called double-sided deflection system, and in addition to the scanned surfaces 1a to 1d, the light sources 2a to 2d, the collimator lenses 3a to 3d, the stops 4a to 4d, the folding mirror 5b, 5c, synthetic mirrors 6 ₁ and 6 ₂ , cylindrical lenses 7 ₁ and 7 ₂ , deflector 8, separation mirrors 9 ₁ and 9 ₂ , scanning lenses 10 a to 10 d, and upstream folding mirrors 11 a to 11 d And downstream folding mirrors 12a to 12d.

  The scanned surface 1 is provided at the most downstream position of the optical path of the corresponding color. The surface 1 to be scanned is a peripheral surface of the corresponding photosensitive drum, and is rotated in the sub-scanning direction by a driving force from a motor (not shown). A corresponding color light beam B is sequentially scanned on the rotating scanned surface 1 line by line in the main scanning direction.

  The light source 2 is provided at the most upstream position of the corresponding color optical path, and emits the corresponding color light beam B. More specifically, when the image data for Y is input to the light source 2a, the light source 2a emits a light beam Ba modulated by the input image data. When the corresponding color image data is input, the light sources 2b to 2d emit light beams Bb to Bd modulated by the input image data.

  The collimator lenses 3a to 3d are provided immediately downstream of the light sources 2a to 2d, and convert the light beams Ba to Bd emitted from the light sources 2a to 2d into parallel light. The diaphragms 4a to 4d are provided immediately downstream of the collimator lenses 3a to 3d, and shape the light beams Ba to Bd that have become parallel lights so as to have a predetermined width in the Z-axis direction (sub-scanning direction).

The folding mirrors 5b and 5c are provided immediately downstream of the stops 4b and 4c. The light beams Bb and Bc that have passed through the apertures 4b and 4c are incident on the folding mirrors 5b and 5c. The folding mirrors 5b and 5c reflect the incident light beams Bb and Bc toward the combining mirrors 6 ₁ and 6 ₂ .

Combining mirror ₆₁ is provided immediately downstream of the throttle 4a and folding mirror 5b. Combining mirror 6 ₂ is provided immediately downstream of the throttle 4d and folding mirror 5c. The light beams Bb and Bc reflected by the folding mirrors 5b and 5c are incident on the combining mirrors 6 ₁ and 6 ₂ . Further, the combining mirror _61, as is aligned with the traveling direction of the light beam Ba having passed through the aperture 4a, it reflects incident light beam Bb. As a result, a light beam B ₁ composed of the light beams Ba and Bb is formed. In the light beam B ₁ , the light beams Ba and Bb travel in the same direction, are aligned in the sub-scanning direction, and are not spatially separated (in other words, spatially coupled). Similarly, the combining mirror 6 _2, as aligned in the traveling direction of the light beam Bd that has passed through the aperture 4d, reflects incident light beam Bc. As a result, a light beam B ₂ composed of the light beams Bc and Bd is formed. In the light beam B ₂ , the light beams Bc and Bd travel in the same direction, are aligned in the sub-scanning direction, and are not spatially separated.

The cylindrical lenses 7 ₁ and 7 ₂ converge the incident light beams B ₁ and B ₂ at least in the sub-scanning direction. More specifically, the cylindrical lens 7 ₁ focuses the light beams Ba and Bb constituting the incident light beam B ₁ on the polarization plane 8 ₁ of the deflector 8. The cylindrical lens 7 ₂ forms an image of the light beams Bc and Bd constituting the incident light beam B ₂ on the polarization plane 8 ₂ of the deflector 8.

The deflector 8 includes a polygon mirror and a motor (not shown). The polygon mirror has a polarization plane 8 ₁ and a polarization plane 8 ₂ . The polarization plane 8 _1, 8 _2, the cylindrical lens _71, 7 _two beams B ₁ that has passed through, B ₂ is incident.

Here, the center in the Z-axis direction of the polygon mirror is defined as the sub-direction center. Further, a plane that is perpendicular to the rotation axis of the polygon mirror and includes the center in the sub direction is set as a reference plane. Light beams Ba, Bb is incident on the polarizing surface ₈₁ at a predetermined oblique angle of incidence and symmetrically with respect to the reference plane (oblique incidence optical system). Similarly, the light beams Bc, Bd is incident on the polarizing surface ₈₂ at a predetermined oblique angle of incidence and symmetrically with respect to the reference plane.

The polygon mirror receives the driving force of the motor and rotates in parallel with the reference plane about the rotation axis. Thus, the polygon mirror reflects and deflects the incident light beams Ba and Bb on the polarization plane 8 ₁ toward the separation mirror 9 ₁ and scans in the main scanning direction. Similarly, the polygon mirror, the incident light beam Bc to the polarization plane _82, while reflection and deflected towards the Bd the separation mirror 9 _2, is scanned in the main scanning direction.

The separation mirror 9 ₁ is disposed on the optical path of the light beam Bb and between the deflector 8 and the scanning lens 10b. Specifically, the separation mirror 9 ₁ includes the light beam Bb out of the light beam B ₁ reflected by the polarization plane 8 ₁ , but the light beam Ba is not incident on the separation mirror 9 _1. Be placed. Separation mirror 9 ₁ reflects the incident light beam Bb on the scanning lens 10b. The light beam Ba illustratively in this embodiment, and passes toward the immediate above of the separation mirror 9 ₁ in the direction of the scanning lens 10a. In this way, the separation mirror 9 ₁ spatially separates the incident light beam B ₁ into the light beams Ba and Bb. The light beam Ba is directed to the scanning lens 10a, and the light beam Bb is directed to the scanning lens 10b.

Separation mirror 9 ₂ is an optical path of the light beam Bc, is arranged between the deflector 8 and the scanning lens 10c. Specifically, the separation mirror 9 ₂ includes the light beam Bc out of the light beam B ₂ reflected by the polarization plane 8 ₂ , but the light beam Bd does not enter the separation mirror 9 _2. Be placed. Separation mirror 9 _2, reflects the incident light beam Bc on the scanning lens 10c. The light beam Bd illustratively in this embodiment, and passes toward the immediate above of the separation mirror 9 ₂ in the direction of the scanning lens 10d. In this way, the separation mirror 9 ₂ spatially separates the incident light beam B ₂ . The light beam Bc goes to the scanning lens 10c, and the light beam Bd goes to the scanning lens 10d.

  The scanning lens 10a is provided on the optical path of the light beam Ba. Similarly, the scanning lenses 10b to 10d are provided on the optical paths of the light beams Bb to Bd. The scanning lenses 10a to 10d image the light beams Ba to Bd scanned by the deflector 8 on the scanned surfaces 1a to 1d. More specifically, in the scanning lenses 10a to 10d, the scanning speeds of the light beams Ba to Bd in the main scanning direction are constant on the scanned surfaces 1a to 1d, and the beam diameters of the light beams Ba to Bd are uniform. It has such optical characteristics.

  The upstream folding mirrors 11a to 11d and the downstream folding mirrors 12a to 12d reflect the light beams Ba to Bd that have passed through the scanning lenses 10a to 10d and guide them to the scanned surfaces 1a to 1d. More specifically, the light beam Ba is reflected by the mirrors 11a and 12a, passes through a dustproof window (not shown), and forms an image on the scanned surface 1a. Similarly, the light beams Bb to Bd are reflected by the mirrors 11b to 11d and 12b to 12d, and then pass through corresponding dustproof windows (not shown) to form images on the scanned surfaces 1b to 1d. .

(About the details of the issue)
For example, when the light beam is separated in the sub-scanning direction by the separation mirror, as shown in FIG. 3, light beams for a plurality of colors (for example, light beams Ba and Bb) included in the light beam are separated in the X-axis direction position. Xs must be separated by an interval Δ ₁ . This interval Δ ₁ is determined by the interval Δ ₂ between the principal rays of the plurality of light beams (Ba, Bb) and the widths Wa, Wb in the sub-scanning direction of the respective light beams (Ba, Bb). In the oblique incidence optical system, the distance Δ ₂ between the principal rays depends on the oblique incidence angle of each light beam (Ba, Bb). However, if the light beam is separated after passing through the scanning lens, the scanning lens converges the light beam in the sub-scanning direction, and the plurality of principal rays are refracted in a direction approaching each other. Therefore, each oblique incident angle needs to be designed to be a relatively large angle in consideration of the amount of refraction by the scanning lens in advance. However, as is well known, in an oblique incidence optical system, scanning line bending (so-called Bow) occurs on the surface to be scanned. This scan line bending increases as the oblique incident angle increases. Hereinafter, scanning line bending will be described.

  Here, FIG. 4 and FIG. 5 are referred. As shown in FIG. 4, unless the shape of the scanning lens 101 in the main scanning direction P is an arc shape centered on a reflection point (hereinafter referred to as a deflection point center) 103 of the principal ray on the polarization plane 102, the main scanning direction P The distance d from the deflection point center 103 to the incident surface 104 of the scanning lens 101 differs depending on the image height. In the oblique incidence optical system, the light beam is incident on the polarization plane with an oblique incident angle. Therefore, as shown in FIG. 5, the incident position of the light beam on the scanning lens 101 (specifically, the height in the sub-scanning direction Q) is lower at the end 106 than at the center 105 in the main scanning direction. The refractive power that the light beam receives in the sub-scanning direction Q when passing through such a scanning lens 101 varies depending on the image height. This causes scanning line bending in the light flux.

  Further, since the light beam deflected by the deflector has a width in the main scanning direction, it is incident on the scanning lens in a twisted state. As a result, the wavefront aberration of the light beam that has passed through the scanning lens deteriorates, and the light beam contained in the light beam becomes thick.

  The above-described scanning line bending and twist are generally corrected by changing the tilt in the sub-scanning direction for each image height in the main scanning direction on the surface of the scanning lens. However, since the correction parameters of the scanning lens are fixed, it is impossible to completely correct both scanning line bending and twisting. Therefore, in order to reduce scanning line bending and twist, it is necessary to reduce the oblique incident angle.

(Relationship between separation mirror and scanning lens)
In order to solve the above problems, in the tandem type scanning optical system according to the present embodiment, as shown in FIG. 2, immediately upstream side of the scanning lens 10 a to 10 d, the light flux B1, B ₂ is the individual light beams Ba~ Spatial separation into Bd. Thereafter, the light beam Ba is incident on the scanning lens 10a. Similarly, the light beams Bb to Bd are incident on the scanning lenses 10b to 10d. As described above, in the tandem scanning optical system, only the light beams Ba to Bb directed to the scanned surfaces 1a to 1d of the corresponding colors pass through one scanning lens 10a to 10d. Therefore, it is not necessary to consider that a plurality of light beams approach after passing through the scanning lenses 10a to 10d. Therefore, the oblique incident angle can be reduced.

  Further, when the scanning lenses are arranged on the downstream side of the separation mirror, these scanning lenses need to be separated from the deflector to some extent. Therefore, the thickness deviation of the scanning lens in the main scanning direction increases. That is, the thickness of the scanning lens in the light beam passing direction varies depending on the image height in the main scanning direction. Therefore, if the thickness of the end portion of the scanning lens is to be ensured, the core thickness increases. In this case, the molding cycle of the scanning lens becomes long and the manufacturing cost increases. However, as shown in FIG. 6, by making the height h in the sub-scanning direction Q of the scanning lens 10 disposed closest to the deflector 8 smaller than the core thickness t of the scanning lens 10, the molding cycle is It is determined by the height h. Here, the height h is the height in the sub-scanning direction in the portion of the scanning lens 10 that passes through the optical axis Ao. The core thickness t is a distance between the surface vertex Vi of the incident surface of the scanning lens 10 and the surface vertex Vo of the output surface. As a result, the manufacturing cost of the scanning lens 10 can be suppressed even when the core thickness t is increased.

(Surface shape of optical element in tandem scanning optical system)
Reference is now made to FIGS. 7A and 7B. 7A is a top view when one optical path in the tandem scanning optical system is developed in the X-axis direction, and FIG. 7B is a side view of the tandem scanning optical system in FIG. 7A. 7A and 7B typically show one optical path, that is, the deflector 8, the scanning lens 10, and the surface 1 to be scanned.

  Here, for convenience of the following description, it is assumed that the X coordinate value, the Y coordinate value, and the Z coordinate value of the deflection point center in the deflector 8 are (0, 0, 0). Further, the shape of the polarization plane of the deflector 8, the surface vertex coordinates, and the components of the local X vector are as shown in the top row (surface number 1) in Table 1 below. As the surface vertex coordinates, coordinate values of the rotation center of the polygon mirror are shown.

  The scanning lens 10 has at least one surface that is asymmetric in the main scanning direction and one surface that is asymmetric in the sub-scanning direction. Here, the asymmetric surface in the main scanning direction and the asymmetric surface in the sub scanning direction may be the same or different from each other. Such a scanning lens 10 has an entrance surface and an exit surface, each of which is a free-form surface. The surface vertex coordinates of the incident surface and the components of the local X vector are shown in surface number 2 (second stage) in Table 1. The exit surface is indicated by surface number 3 (third stage). The refractive index of the scanning lens 10 is as illustrated at the right end of Table 1.

  The entrance surface and the exit surface have free-form surface coefficients as shown in Table 2. As is apparent from Table 2, in the first embodiment, both the entrance surface and the exit surface are asymmetric in the main scanning direction (Y-axis direction) and the sub-scanning direction (Z-axis direction). By having this surface shape, it is possible to correct asymmetry on the scanned surface 1. Moreover, by using the scanning lens 10 having this surface shape, one scanning lens 10 on each optical path can be used. This makes it possible to reduce the manufacturing cost and the like of the tandem scanning optical system.

  Further, specifically, the image plane of the scanned surface 1 has the surface vertex coordinates and the local X vector component values shown in the bottom row (surface number 4) of Table 1.

(Scanning lens optical axis)
Further, as shown in FIG. 8, each of the scanning lenses 10 is decentered by a predetermined amount Δ ₃ with respect to the reference plane Fr perpendicular to the rotation axis Ar of the deflector 8. It is arranged on the optical path. Here, the predetermined amount Δ ₃ is set to be equal to the oblique incident angle, for example. This makes it possible to reduce the degree to which the distance from the polarization plane of the deflector 8 to the incident surface of the corresponding scanning lens 10 varies depending on the image height in the main scanning direction P. Furthermore, the degree to which the incident position of the light beam B on the scanning lens 10 (specifically, the height in the sub-scanning direction Q) varies depending on the image height in the main scanning direction P is also reduced. As a result, the scanning line bending is also reduced. Further, since the scanning line bending is reduced by the eccentric arrangement of the scanning lens 10, the optical performance of the scanning lens 10 can be distributed to the torsion correction.

(Other)
In the present embodiment, the plurality of light beams incident on the polarization planes 8 ₁ and 8 ₂ shown in FIG. 2 are preferably convergent lights in the main scanning direction. Thereby, since it is possible to have a convergence effect near the light source 2, it is possible to reduce the power (specifically, the convergence force) of the scanning lens 10. Thereby, it is possible to reduce the thickness deviation of the scanning lens 10. Thereby, since the core thickness of the scanning lens 10 can be reduced, the cost can be reduced by shortening the molding cycle. For example, as shown in Table 3 below, when it is assumed that the scanning lens 10 is not provided, the condensing position is a position 500 mm from the center of the deflection point.

(Detailed specifications of this tandem scanning optical system)
An example of detailed specifications of the tandem scanning optical system of the present embodiment is described in the left column of Table 3 below.

(Modification)
9A is a top view when one optical path in the tandem scanning optical system according to the modification is developed in the X-axis direction, and FIG. 9B is a side view of the tandem scanning optical system of FIG. 9A. 9A and 9B differ from FIGS. 7A and 7B in that parallel light is incident on the polarization planes 8 ₁ and 8 ₂ . Since there are no other differences in configuration between the modified example and the first embodiment, in FIG. 9A and FIG. 9B, the same reference numerals are given to those corresponding to the configurations shown in FIG. 7A and FIG. 7B. In addition, explanation of each is omitted.

  The shape of the polarization plane, the surface vertex coordinates, and the components of the local X vector of the deflector 8 according to the modification are as shown in the uppermost stage (surface number 1) in Table 4 below.

  The scanning lens 10 is the same as in the first embodiment, but the surface vertex coordinates of the incident surface and the components of the local X vector are different as shown in surface number 2 (second stage) in Table 4. Further, the exit surface is different as indicated by surface number 3 (third stage). The refractive index of the scanning lens 10 is as illustrated at the right end of Table 4.

  In this modification, the incident angle and the outgoing angle have free-form surface coefficients as shown in Table 5.

  Further, specifically, the image plane of the scanned surface 1 has the surface vertex coordinates and the local X vector component values shown in the bottom row (surface number 4) of Table 4.

  An example of detailed specifications of the tandem scanning optical system of this modification is described in the center column of Table 3.

(Second embodiment)
10A is a top view when one optical path in the tandem scanning optical system according to the modification is developed in the X-axis direction, and FIG. 10B is a side view of the tandem scanning optical system in FIG. 10A. 10A and 10B are provided with an upstream scanning lens 13 and a downstream scanning lens 14 which are different from FIG. 7A and FIG. 7B in that at least two scanning lenses are provided in place of the scanning lens 10. Is different. Since there is no difference in configuration other than that, in FIGS. 10A and 10B, components corresponding to those shown in FIGS. 7A and 7B are denoted by the same reference numerals, and description thereof is omitted.

  The shape of the polarization plane, the surface vertex coordinates, and the components of the local X vector of the deflector 8 according to the second embodiment are as shown in the uppermost stage (surface number 1) in Table 6 below.

  The entrance surface and the exit surface of the upstream scanning lens 13 are free-form surfaces, respectively. The surface vertex coordinates of the incident surface and the components of the local X vector are shown in surface number 2 (second stage) of Table 6. The exit surface is indicated by surface number 3 (third stage). The refractive index of the upstream scanning lens 13 is as illustrated at the right end of Table 6.

  Here, the entrance surface and the exit surface of the upstream scanning lens 13 are asymmetric in the main scanning direction Y, but have a symmetrical shape in the sub-scanning direction Z. The entrance surface and the exit surface have free-form surface coefficients as shown in Table 7. As apparent from Table 7, regarding the upstream scanning lens 13, since the odd-order (primary) in the sub-scanning direction Z is zero, both the entrance surface and the exit surface are asymmetric in the main scanning direction (Y-axis direction). is there.

  Further, the entrance surface and the exit surface of the downstream scanning lens 14 are free-form surfaces. The surface vertex coordinates of the incident surface and the components of the local X vector are shown in surface number 4 (fourth row) in Table 6. The exit surface is indicated by surface number 5 (fifth stage). The refractive index of the downstream scanning lens 14 is as illustrated at the right end of Table 6.

  Here, the entrance surface and the exit surface of the downstream scanning lens 14 are symmetric in the main scanning direction Y, but asymmetric in the sub-scanning direction Z. The entrance surface and the exit surface have free-form surface coefficients as shown in Table 8. As is apparent from Table 8, regarding the downstream scanning lens 14, since the odd order in the main scanning direction Y is zero, both the incident surface and the exit surface are asymmetric in the sub-scanning direction (Z-axis direction).

  By combining the two scanning lenses 13 and 14 as described above, it is possible to correct asymmetry on the surface 1 to be scanned. If two scanning lenses are provided on each optical path, the aberration correction level can be further improved. Further, as compared with the case where there is one scanning lens on the optical path, the power is distributed to each scanning lens 13, 14, and as a result, the degree of uneven thickness of each scanning lens 13, 14 is reduced. As a result, each of the scanning lenses 13 and 14 can be easily manufactured on the molding surface.

  Further, as described above, the shape of each surface of the upstream scanning lens 13 is symmetric only in the sub-scanning direction Z, and the shape of each surface of the downstream scanning lens 14 is symmetric only in the main scanning direction Y. is there. Therefore, the upstream scanning lens 13 and the downstream scanning lens 14 can be designed with a common design for each optical path. That is, one type of scanning lens constituting the tandem scanning optical system of the second embodiment can be provided on the upstream side and the downstream side.

  Further, specifically, the image plane of the scanned surface 1 has the surface vertex coordinates and the local X vector component values shown in the bottom row (surface number 6) of Table 6.

  An example of detailed specifications of the tandem scanning optical system of the second embodiment is described in the right column of Table 3.

(Appendix)
In the second embodiment, it has been described that the number of scanning lenses is two for each optical path. However, the present invention is not limited to this, and the tandem scanning optical system may include three or more scanning lenses for each optical path.

  The tandem scanning optical system according to the present invention facilitates aberration correction with a scanning optical lens, and is useful for a full-color copying machine, a printer, or a complex machine of these.

1a to 1d Scanned surface 2a to 2d Light source 8 Deflector 9 ₁ , 9 ₂ Separating mirror 10a to 10d Scan lens 13 Upstream scan lens 14 Downstream scan lens

Claims (5)

A plurality of scanned surfaces;
A plurality of light sources provided corresponding to each of the plurality of scanned surfaces, and emitting a light beam to be irradiated to the corresponding scanned surface;
The plurality of light beams emitted from the plurality of light sources have a surface that is incident with an oblique incident angle in the sub-scanning direction, and rotate about an axis parallel to the sub-scanning direction to A polarizer that scans a plurality of incident light beams in the main scanning direction;
Separating means for separating the plurality of light beams scanned by the polarizer and not passing through the scanning lens into individual light beams;
A plurality of scanning lenses provided one by one corresponding to each of the plurality of scanned surfaces, converging the light beams separated by the separating means, and emitting toward the corresponding scanned surface;
At least one surface of each of the scanning lenses has an asymmetric shape in the sub-scanning direction,
At least one surface of each scanning lens has an asymmetric shape in the main scanning direction,
The tandem scanning optical system in which the optical axis of each scanning lens is decentered with respect to a plane perpendicular to the rotation axis of the polarizer. 2. The tandem scanning optical system according to claim 1, wherein, in the scanning lens closest to the polarizer among the plurality of scanning lenses, a height in the sub-scanning direction is smaller than a core thickness. A plurality of scanned surfaces;
A plurality of light sources provided corresponding to each of the plurality of scanned surfaces and emitting a light beam to be irradiated on the corresponding scanned surface;
The plurality of light beams emitted from the plurality of light sources have a surface that is incident with an oblique incident angle in the sub-scanning direction, and rotate about an axis parallel to the sub-scanning direction to A polarizer that scans a plurality of incident light beams in the main scanning direction;
Separating means for separating a plurality of light beams scanned by the polarizer into individual light beams;
Two scanning lenses corresponding to each of the plurality of scanned surfaces, and a plurality of scanning lenses for converging the light beams separated by the separating unit and emitting toward the corresponding scanned surface,
Of each of the at least two scanning lenses, one surface of one scanning lens has an asymmetric shape in the sub-scanning direction, and both surfaces of the scanning lens have a symmetrical shape in the main scanning direction,
Of each of the at least two scanning lenses, one surface of the other scanning lens has an asymmetric shape in the main scanning direction, and both surfaces of the scanning lens have a symmetrical shape in the sub-scanning direction,
The tandem scanning optical system in which the optical axis of each scanning lens is decentered with respect to a plane perpendicular to the rotation axis of the polarizer. One surface of the scanning lens provided in front Kihen optical device side, when having the main scanning direction asymmetrically shaped, the surfaces of the scanning lens having a symmetric shape in the sub scanning direction, according to claim 3 Tandem scanning optical system. Wherein the plurality of light beams incident on the surface of the polarizer is convergent light in the main scanning direction, a tandem type scanning optical system according to any one of claims 1-4.

Images