JP2000267031A - Optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical scanner constituted so that a color slippage and color irregularity caused by a bow of the scanning lines of plural luminous fluxes can be suppressed on a surface to be scanned while maintaining the uniformity of the beam diameter. SOLUTION: Since the producing directions of the occurrence of a bow are different in the inclining direction of (fθ) lenses in a front incident optical system, when the direction of the luminous flux with respect to a deflector is changed among the plural luminous fluxes or a symmetric image is formed by reflection, the directions of the bow can be aligned. Besides, the expression of βi×(-1)Ni/(βj×(-1)Nj>0 is satisfied by the relation of the inclined angles βi and βj and the number of reflection times Ni and Nj of the (fθ) lenses 22A and 22B. Therefore, when the inclined angles of the (fθ) lenses are reversed to left and right (the code β is identical), the difference of the number of reflection times on and after the deflector becomes zero or the relation of an even number. When the inclined angles of the lenses are identical to left and right (the code β is different), the number of reflecting times becomes the relation of an odd number. Thus, the directions of the bow on the surface to be scanned can be made identical.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a laser printer,
The present invention relates to an optical scanning device used in a digital copying machine or the like, and in particular, an optical scanning device that scans a plurality of photoconductors or different positions of the same photoconductor using a plurality of light beams and scans the light beams when forming images in different colors. About.

[0002]

2. Description of the Related Art As a scanning exposure apparatus of a printer or a digital copying machine for recording a multicolor image, there is known an optical scanning apparatus which deflects and scans a plurality of light beams using different reflecting surfaces of a single deflector to expose different photosensitive members. (Japanese Patent Laid-Open No. 59-18861).
No. 6).

[0003] In this technique, as shown in FIG. 8, in an optical scanning device for exposing and scanning a plurality of photoconductors 140 and 142 with a plurality of light beams L1 and L2, light beams from a plurality of light sources are respectively provided by the same rotary polygon mirror or the like. A plurality of image forming lenses 120 which perform deflection scanning by different reflection surfaces of the deflector 110 and correspond to each light beam,
The plurality of photoconductors 140 and 142 formed by the image forming unit 122 are exposed and scanned. As described above, since the plurality of photosensitive members 140 and 142 are exposed and scanned only by the single deflector 110, the cost and size of the apparatus can be reduced. In this technique, a luminous flux is incident on a plane perpendicular to the deflecting / reflecting surface at an angle so that reflected light (ghost light) from the photoconductor is not re-imaged on the photoconductor. The angle between the reflection surface of each light beam and the surface perpendicular to the deflecting reflection surface is configured to be substantially opposite so that the so-called Bow) is the same between a plurality of light beams scanned by different reflection surfaces.

However, since each light beam enters the fθ lens at a predetermined angle, the light beam is twisted and the field curvature occurs, so that a uniform light beam diameter (a so-called beam diameter) cannot be obtained. In addition, the angle of incidence on the rotary polygon mirror is set in the opposite direction so that the scanning line curvature (Bow) is in the same direction to suppress the difference. However, the reflection from the deflector to the surface to be scanned is reduced. Depending on the number of folds, the scanning line curvature may be in a different direction, and the degree of freedom in optical design is small.

In the technique described in Japanese Patent Application Laid-Open No. 3-264970, a plurality of reflection surfaces of a single deflecting means are used, the difference in the number of folds of each light beam is made an odd number, and the exposure distance of each light beam is defined. There has been proposed an optical scanning device which eliminates color shift by setting the pitch unevenness due to the surface tilt of the deflector, that is, the fluctuation direction of the scanning line which changes with time in the same direction. However, in this technique, the color shift due to the scan line curvature is larger, and the color shift that does not fluctuate over time, such as the scan line curve difference, cannot be eliminated.

Incidentally, there is a so-called front-incident / double-pass scanning optical system which is advantageous in terms of miniaturization of the size of a deflector such as a rotary polygon mirror represented by a polygon mirror and securing left-right symmetry of optical performance. Known (Japanese Unexamined Patent Publication No.
No. 96773). In this technology, an fθ lens having a curvature only in the main scanning direction is arranged at an angle to prevent stray light due to the reflection of the incident light on the fθ lens surface, which is a problem of the double-pass optical system, and secure inexpensive and good optical performance. Possible points are also disclosed.

In such a front incidence scanning optical system, in order to separate an incident light beam and an outgoing light beam, it is necessary to make the light enter the deflection surface at a predetermined angle in the sub-scanning direction.
Occurs. This BOW is hardly recognized up to about several hundred μm in the entire image area in the case of a monochrome recording apparatus, and there is no problem in practical use.

As shown in FIGS. 9 and 10, photoconductors 140 and 14 differ depending on the symmetrically arranged front incidence scanning optical system.
In order to form a multicolor image by exposing and scanning a plurality of light beams L1 and L2 simultaneously on a plurality of reflecting surfaces of the same deflector 110, and exposing and scanning different photosensitive members 140 and 142 to form a multicolor image. I do. However, multiple photoconductors 14
The direction of Bow is different in each of the scanning lines 0 and 142.

For this reason, for example, as shown in FIG. 11A, when the scanning line position is adjusted at the vertex of the scanning line where Bow occurs, the scanning line curvature difference (△) which is twice as large as Bow is maximum.
X) occurs. In addition, as shown in FIG.
Even when w is overlapped and the scanning line position is adjusted to minimize the color shift, the same amount of scanning line curvature difference ΔX as Bow occurs. Therefore, when an image is formed in different colors, the image is recognized as a color shift and the amount of the color shift changes between the center and the end of the image, so that color unevenness occurs and a good multicolor image cannot be obtained. .

Japanese Patent Application Laid-Open No. 2-289816 discloses a technique for correcting a bow by rotating a parallel flat plate in a direction corresponding to sub-scanning. However, in this technique, the rotation of the plane-parallel plate changes the fθ characteristic, causing a color shift in the main scanning direction and further requiring a rotation adjustment mechanism.

Japanese Patent Application Laid-Open No. Sho 59-188616 discloses that the angles of incidence on a plurality of deflecting / reflecting surfaces are tilted in the opposite direction with respect to the rotation axis of a rotating polygon mirror, and the optical system arranged symmetrically on the surface to be scanned. A technique is disclosed in which scanning lines are curved in the same direction to obtain an image without color shift. However, since each light beam is incident on the fθ lens at a predetermined angle, the light beam is twisted and a uniform beam diameter cannot be obtained. This is particularly noticeable when a front-incident optical system is applied to a scanning optical system that performs simultaneous scanning using a plurality of reflecting surfaces, because the angle of incidence on the fθ lens is large, and significant nonuniform beam diameter occurs.

Further, as described above, when the incident light beam is made incident at a predetermined angle in the sub-scanning direction, the light beam that scans the scanning end when reflected by the deflecting / reflecting surface is more twisted, and the beam diameter is reduced. Is different between the scanning center portion and the scanning end portion, which is not practical. The tilt angle of the fθ lens and the beam diameter uniformity have a relationship. By tilting the fθ lens, the beam diameter over the entire scanning area can be made uniform. However, even when the fθ lens is tilted, Does not always match the beam diameter in the main scanning direction.

Also, there is a relationship between the tilt angle of the fθ lens and Bow on the surface to be scanned. That is, fθ
The angle of inclination of the lens and the angle at which Bow on the scanned surface generated by the incident angle of the light beam on the deflecting and reflecting surface in the sub-scanning direction does not always coincide, for example, the light beam without tilting the fθ lens Generated when tilting the incident angle of
Bow larger than w may occur in the opposite direction.

As a result, Bow on the photoreceptor changes depending on the tilt angle of the fθ lens. Depending on the lens tilt angle, each beam is incident on the deflector at an incident angle in the opposite direction. In some cases, Bow occurs in the reverse direction and color shift cannot be corrected.

Further, the degree of freedom of the optical arrangement, particularly the limitation on the difference in the number of mirrors such as a flat mirror, is a major problem. Generally, a plurality of photoconductors are arranged on the same side with respect to a plane perpendicular to the rotation axis of the deflector. At this time, the size of the exposure scan is substantially determined by the optical path length and the number of folds by a mirror such as a plane mirror. In order to increase the number of folds to reduce the size and reduce the difference in the number of folds to zero or an even number, two mirrors must be added, which increases the cost.

Further, when a cylindrical mirror (cylindrical mirror) is used as the tilt correction optical system of a scanning device having a curved scanning line, the position of incidence and the angle of incidence on the cylindrical mirror by the light beam at the center of scanning and the light beam at the scanning end. Therefore, depending on the folding direction of the cylindrical mirror, the curvature of field in the sub-scanning direction or the shift of the conjugate point occurs, and the beam diameter in the sub-scanning direction becomes non-uniform or the pitch becomes uneven, so that a good image cannot be obtained.

[0017]

SUMMARY OF THE INVENTION In view of the above, the present invention provides an optical scanning system capable of suppressing color misregistration and color unevenness due to scanning line curvature of a plurality of light beams on a surface to be scanned while maintaining uniform beam diameter. The purpose is to get the device.

[0018]

In order to achieve the above object, an optical scanning apparatus according to the present invention comprises at least a plurality of reflecting surfaces, and intersects a main scanning direction toward a different one of the plurality of reflecting surfaces. Deflecting means for deflecting and scanning each of the plurality of light beams incident in such a manner that the optical axis is inclined by a predetermined angle in the sub-scanning direction in the main scanning direction, and corresponding to each of the plurality of light beams and each of which is deflected and scanned. A plurality of scanning optical systems for focusing the light beam on the surface to be scanned such that the light spot is scanned, and a plurality of folding means corresponding to each of the plurality of light beams and folding the light beam deflected and scanned. In the optical scanning device, one of the plurality of light beams is set as a reference light beam, an angle between the optical axis of the scanning optical system corresponding to the reference light beam and a plane perpendicular to the rotation axis of the deflecting unit is set as βi, Hand deflected in optical path The number of folds by the fold means between the scan light and the scanned surface is Ni, one of the plurality of light beams other than the reference light beam is a target light beam, and the optical axis of the scanning optical system corresponding to the target light beam and the rotation of the deflecting means are rotated. When the angle formed by the plane perpendicular to the axis is βj, and the number of folds by the fold means between the deflecting unit and the scanned surface in the optical path of the target luminous flux is Nj, the following relationship is established between the reference luminous flux and the target luminous flux. It is characterized by being configured to satisfy.

(Βi × (−1) ^Ni ) / (βj × (−1) ^Nj )> 0 where the angle has a positive sign in the counterclockwise direction and a negative sign in the clockwise direction. That is, in the optical path projected on the sub-scan section, the sign of the clockwise rotation angle from the optical axis of the scanning optical system such as the fθ lens toward the vertical plane is negative, and the sign of the counterclockwise angle is positive.

According to the present invention, Bow on the surface to be scanned caused by, for example, tilting of the fθ lens as the deflecting means and the scanning optical system is in the same direction, and the amount of color shift on the surface to be scanned can be reduced or matched. Become.

In the optical scanning device of the present invention, the light beam incident on the deflecting means is a light beam focused in the sub-scanning direction by an anamorphic optical system for forming a long line image in the main scanning direction near the reflecting surface. In addition, the absolute value of the conjugate magnification between the deflecting reflection surface and the surface to be scanned in the sub-scanning direction on the light beam side where the absolute values of the angles βi and βj are large can be set small.

When the angle between the optical axis of the scanning optical system such as the fθ lens and the plane perpendicular to the rotation axis of the deflector such as a rotary polygon mirror is large, the amount of Bow generated increases. Therefore,
The conjugate magnification of a light beam having a large Bow is set smaller than the conjugate magnification of a light beam having a small Bow. As a result, as shown in FIG. 6, the generated Bow difference can be reduced or the Bow difference can be set to 0, and the scanning lines can be made substantially coincident with each other on the surface to be scanned, thereby suppressing color shift. .

In the optical scanning device of the present invention, the angle βi,
The angle between the optical axis of the light beam incident on the deflecting means and the plane perpendicular to the rotation axis of the deflecting means corresponding to βj is α
When i and αj, the reference light beam and the target light beam are ｛| α
When i |> | αj |, | βi | <| βj |｝ can be satisfied.

As described above, Bow generated by setting a small inclination angle of a scanning optical system such as an fθ lens corresponding to a light beam having a large incident angle in the sub-scanning direction of the light beam is generated.
Can be made the same, and a good image with less color shift can be obtained.

An optical scanning device according to another aspect of the present invention includes at least a plurality of reflecting surfaces, and an optical axis is provided at a predetermined angle in a sub-scanning direction crossing the main scanning direction toward a different one of the plurality of reflecting surfaces. A deflecting unit that deflects and scans each of the plurality of light beams incident so as to be inclined in the main scanning direction, so that the light spots are scanned with the light beams corresponding to each of the plurality of light beams and each of which is deflected and scanned. An optical scanning device comprising: a plurality of scanning optical systems for converging on a surface to be scanned; and a plurality of folding units corresponding to each of the plurality of luminous fluxes, and a plurality of folding-back means for folding the deflected and scanned light fluxes. The incident light beam is a light beam focused in the sub-scanning direction by an anamorphic optical system that forms a long line image in the main scanning direction in the vicinity of the reflection surface. Song And at least one of a cylindrical mirror having power only in the sub-scanning direction and having a tilt correction function, so that at least one of the plurality of light beams is deflected by the deflection means. The angle between the optical axis when the light is incident on the plane perpendicular to the rotation axis of the deflecting means is α, and the angle between the optical axis of the corresponding scanning optical system and the plane perpendicular to the rotation axis of the deflecting means is β. When the incident angle of the light beam to at least one of the cylindrical mirror and the cylindrical lens is γ, and the number of turns between the deflecting means and at least one of the cylindrical mirror and the cylindrical lens is M, ｛α × β < 0 and β × γ × (−1) ^M > 0, where the angle has a positive sign in the counterclockwise direction and a negative sign in the clockwise direction. That is, in the optical path projected on the sub-scanning cross section, α is positive in the counterclockwise direction from the incident light beam toward a plane perpendicular to the rotation axis, negative in the clockwise direction, and γ is from the incident light beam to the normal to the cylindrical mirror incident position. The counterclockwise direction is positive and the clockwise direction is negative. ｝ It is characterized in that it is configured to satisfy the relationship.

According to the present invention, by inclining the incident angle of the light beam to the deflecting means and the direction of the inclination of the optical axis of the fθ lens in different directions, the light beam incident on the deflecting means has an angle in the sub-scanning direction. In addition to preventing the beam diameter from becoming non-uniform due to the torsion of the lens, the bending direction of the scanning line on the cylindrical mirror caused by the tilt of the fθ lens is determined by the angle of incidence of the scanning end beam relative to the sub-scanning incident angle of the scanning central beam on the cylindrical mirror. By setting the direction to be smaller, the curvature of the sub-scanning image on the surface to be scanned can be suppressed, and the shift of the conjugate position of the deflecting reflection surface can be prevented.

In the optical scanning device according to the present invention, the angle between the angle α and the angle β is (−0.2> α / β> −0.4).
Can be configured to satisfy the following relationship.

As a result, the light beam incident on the deflecting means at the light beam incident angle α is deflected and scanned, and the light beam is fed to the fθ lens by (α
+ Β). At this time, the angles α and β
Is set so as to satisfy the above expression, it is possible to suppress the nonuniformity of the beam diameter due to the twist of the light beam caused by entering the deflection means at an angle in the sub-scanning direction to a range where there is no problem in practical use. it can.

As described above, according to the present invention, inexpensive / compact, the scanning lines of a plurality of luminous fluxes have the same direction and substantially the same amount of curvature on the surface to be scanned, thereby preventing color shift due to a Bow difference and reducing the beam diameter. It is possible to provide a multicolor image recording apparatus capable of obtaining a good image in which pitch unevenness is prevented while maintaining uniformity. Further, according to the present invention, the present invention is particularly effective for color misregistration which is easily recognized by humans, and the scanning lines of a plurality of luminous fluxes can be bowed in the same direction and substantially the same amount of curvature on the surface to be scanned without adding a special optical element. At the same time, the color shift or the color unevenness due to the difference can be reduced, and the beam diameter on the surface to be scanned can be kept constant over the entire scanning area.

Also, it is possible to provide an optical scanning device capable of correcting the curvature of field in the sub-scanning direction and reducing the shift of the conjugate point to obtain good tilt correction performance.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[First Embodiment] FIGS. 2 and 1 show a schematic configuration of an optical scanning device according to an embodiment of the present invention. FIG. 2 is a perspective view of the optical scanning device, and FIG. 1 is a view of the optical scanning device as viewed from the direction corresponding to the sub-scanning direction (a view as viewed from the direction of arrow X in FIG. 2). Table 1 below shows main optical data of the deflecting surface 24X and thereafter of the present embodiment.

[0033]

[Table 1]

In the following description, a surface formed by the trajectory of the light beam (laser beam) reflected and deflected by the rotary polygon mirror 24 is defined as a main scanning surface, and the main scanning surface and the photosensitive member surface are formed so as to intersect with each other. Is defined as a main scanning direction, and a direction intersecting (particularly orthogonal to) the main scanning plane is defined as a sub-scanning direction. In addition, the surface of the photoreceptor is a surface to be scanned.

As shown in FIGS. 2 and 1, the optical scanning device according to the first embodiment includes a light source 10A for emitting a light beam LA as a laser beam (laser light) and a light source 10B for emitting a light beam LB. ing. The light flux L is on the emission side of the light source 10A.
A collimating lens 12A that makes A substantially parallel, and an opening 14A that makes the passing light beam LA a desired spot diameter are sequentially provided. A shaping optical system 16A, a reflecting mirror 18A, and a deflector 24 such as a rotating polygon mirror are sequentially provided on the emission side of the light beam LA of the opening 14A. The luminous flux LA is
The light beam is shaped by the shaping optical system 16A so that the light beam is focused in the sub-scanning direction and becomes a long line image in the main scanning direction. The light beam LA emitted from the shaping optical system 16A is guided toward the deflection reflection surface 24X of the deflector 24 by the reflection mirror 18A. The deflecting reflection surface 24X is provided in the vicinity of the above-described line image, that is, the position of the light beam focused in the sub-scanning direction by the shaping optical system 16A.

In the present embodiment, the deflector 24 is used as a single deflector for deflecting and scanning each of the light beams LA and LB. For this reason, in the following description, the deflecting / reflecting surfaces 24X corresponding to the light beams LA and LB will be referred to as 24A and 24B for convenience.
B will be described.

The light beam L deflected and scanned by the deflector 24
A is imaged on the photoreceptor 34A by the fθ lens 22A, that is, on the surface to be scanned. fA lens 22A has a function of converting a light beam LA deflected at a constant angular velocity by the deflector 24 into a constant velocity so that a focused spot is scanned at a constant velocity on the surface to be scanned, as is well known. I have. The light beam LA is incident on the deflector 24 from substantially the front after being converged in the sub-scanning direction by the shaping optical system 16A. At this time, the light beam LA is divided into a plane V perpendicular to the rotation axis CL of the deflector 24 in order to separate the incident light beam and the output light beam.
And a predetermined angle is set.

An fθ lens 22A, a plane mirror 26A, a cylindrical mirror 28A, a plane mirror 30A, an opening 32A, and a photoreceptor 34A are provided in this order on the light exit side of the deflector 24.

The light beam LA reflected by the deflecting / reflecting surface 24A passes through the fθ lens 22A and passes through the plane mirror 26A.
Is folded back by Thereafter, the cylindrical mirror 28A receives refracting power in the sub-scanning direction, is turned by the plane mirror 30A, passes through the opening 32A, and scans the photosensitive member 34A by exposure. Note that the cylindrical mirror 28A mainly has an image forming action in the sub-scanning direction, and forms a light beam converged linearly on the deflecting / reflecting surface 24A on the surface to be scanned by a combined refracting power with the fθ lens 22A. belongs to.

Similarly, a collimating lens 12B, an opening 14B, a shaping optical system 16B, a reflecting mirror 18B, and a deflector 24 are sequentially provided on the emission side of the light source 10B. The light beam LB emitted from the shaping optical system 16B is guided by the reflecting mirror 18B toward the deflecting / reflecting surface 24X of the deflector 24, and the light beam LB scanned by the deflector 24 is scanned by the fθ lens 22B, the plane mirror 26B, An image is formed on the photosensitive member 34B, that is, on the surface to be scanned, via the cylindrical mirror 28B, the plane mirror 30B, and the opening 32B.

Accordingly, the light beams LA and LB are reflected by the deflecting / reflecting surface 24.
A, after being reflected by 24B, its optical axis is deflector 24
After passing through the fθ lenses 22A and 22B arranged at a predetermined angle with respect to a plane V perpendicular to the rotation axis CL of the optical axis, and being turned back by the plane mirrors 26A and 26B, it has an image forming function mainly in the sub-scanning direction. Cylindrical mirror 28 provided for each light beam that forms a light beam condensed linearly on the deflecting reflection surface on the surface to be scanned by the combined refracting power with fθ lenses 26A and 26B.
A, 28B receive the refracting power in the sub-scanning direction and are folded back by the plane mirrors 30A, 30B, and the photoconductors 34A, 34B
Is exposed and scanned.

The photoconductors 34A and 34B form a latent image by being exposed to light, and are developed in different colors corresponding to the latent images on the photoconductors 34A and 34B to form a multicolor visible image. can get. By transferring this visible image to the same recording medium, a multicolor print can be obtained.

Here, the luminous fluxes LA, L for each optical element
The angle formed by the optical path of B will be described. In the present embodiment, as shown in FIG. 1, the light beam LA is incident on the deflecting / reflecting surface 24A at an angle αi from above (upper side of the paper surface of FIG. 1), and the light beam LB is downward at an angle αj (the paper surface of FIG. 1). From the lower side). The sign of each angle is negative when the direction toward the plane V perpendicular to the rotation axis CL of the deflector 24 is clockwise with respect to the optical path of the light beam, and positive when the direction is counterclockwise. In the present embodiment, the incident angle αi of the light beam LA to the deflector 24 in the sub-scanning direction in the sub-scanning direction is + 2.4 °, and the incident angle αj of the light beam LB to the deflector 24 in the sub-scanning direction is both positive. Is set to

In this embodiment, the fθ lens 22
In order to avoid a difference in beam diameter between the scanning center portion and the scanning end portion due to A and 22B, the optical axes of the fθ lenses 22A and 22B are installed so as to be inclined with respect to a plane perpendicular to the deflecting surfaces 24A and 24B. I have. Incidentally, there is a relationship between the tilt angle of the fθ lens and the uniformity of the beam diameter.

FIG. 3 shows the relationship between the tilt angle of the fθ lens and the uniformity of the beam diameter. As can be understood from FIG. 3, as shown in the beam diameter uniformity when the fθ lens tilt angle β = 0, the intensity is 1 / e ² at the incident angle α = 2.4 ° in the sub-scanning direction. The resulting width (the so-called beam diameter) differs by 70 μm between the central scanning portion and the scanning end portion, which is not practical. In this case, the beam diameter in the entire scanning area can be made uniform by tilting the fθ lens. However, in FIG. 3, the beam diameter difference in the sub-scanning direction (Tan) is obtained at the tilt angle β = −8 ° of the fθ lens. 6 μm in the main scanning direction (Sa
The beam diameter difference of g) is 0 μm, and beam non-uniformity cannot be avoided. On the other hand, as understood from FIG.
If the inclination angle of the fθ lens is around 6.8 °, the beam diameter difference can be kept to 5 μm or less. This is a practical number.

Therefore, in this embodiment, the fθ lens 2
As the inclination angles βi and βj of 2A and 22B, βi = −7 ° and βj = − so that Bow of light beam LA and light beam LB become the same amount and the main scanning beam diameter difference becomes 10 μm or less.
It is set to 7.3 °. The sign of each angle is negative when the direction from the optical axis to the plane V perpendicular to the rotation axis CL of the deflector 24 is clockwise, and positive when the direction is counterclockwise.

In this embodiment, the fθ lenses 22A, 22A
The angles βi and βj for inclining each of the lenses 2B are set to be negative, and oblique incidence on the deflector 24 and the fθ lens 22
Plane mirror 26 generated by the tilt angle of A, 22B
Bow on A and 26B has an inverted shape such that the light beam LA has a mountain shape and the light beam LB has a valley shape. For this reason, in order to eliminate the color shift due to Bow on the surface to be scanned, the number of folds of the light beams LA and LB after the deflector is set to three when Ni and Nj, respectively. Thus, Bow can be set in the same direction on the surface to be scanned.

With this configuration, the photosensitive member 34
When the fθ lenses 22A and 22B are not tilted, Bow on A and 34B has a light beam LA of −55 μm and a light beam LB of −73.
With the inclination of the fθ lenses 22A and 22B with respect to μm, Bow becomes +172 μm for both the light fluxes LA and LB, eliminating color shift and reducing the beam diameter difference between the scanning center and the scanning end.

By tilting the fθ lenses 22A and 22B as in the present embodiment, the problem that the surface reflection of the incident light beam by the lens surface in the double-pass optical system becomes stray light and enters the surface to be scanned can be solved. You can also.

The fθ lenses 22A and 22B described above
The relationship between the inclination angles βi, βj and the number of turns Ni, Nj can be expressed by the following equation (1). If this expression (1) is satisfied, Bow on the surface to be scanned can be set in the same direction.

Βi × (−1) ^Ni ) / (βj × (−1) ^Nj )> 0 (1) Equation (1) expresses a relationship in which Bow on the surface to be scanned is directed in the same direction. I have. That is, in the front-incidence optical system, the direction in which Bow occurs differs depending on the direction in which the fθ lens is inclined. For this reason, if the direction of the light beam with respect to the deflector is changed or a symmetric image is formed by reflection among a plurality of light beams, the Bow direction can be matched. Therefore, the inclination angle of the fθ lens is reversed left and right (the sign of β is the same sign)
In this case, the difference between the number of folds after the deflector is set to 0 or an even number, and when the lens tilt angle is the same on the left and right (β code is a different sign), the number of folds is set to an odd number, so that Bo on the surface to be scanned is set.
w can be in the same direction.

In the present embodiment, the cylindrical mirror 28
A and 28B form an image in the sub-scanning direction and constitute a tilt correction optical system. The cylindrical mirror 2 at this time
The signs of the incident angles γi and γj on the light beams 8A and 28B are negative when the direction from the optical path of the light beam to the normal line of the cylindrical mirrors 28A and 28B is clockwise, and positive when the counterclockwise direction is positive. is there. As a result, as shown in FIG. 1, the light beam LA is folded back (downward in the plane of FIG. 1), and the light beam LB is folded upward (upward in the plane of FIG. 1).

In the present embodiment, the turning angle by the cylindrical mirror (the angle of incidence γi on the cylindrical mirrors 28A and 28B,
By setting γj) to be positive to each other,
Due to the curvature of the scanning line on the cylindrical mirror, the incident angle of the cylindrical mirror due to the light beam at the scanning end can be made smaller than the incident angle of the cylindrical mirror due to the light beam at the scanning center, and the field curvature in the sub-scanning direction can be corrected. As a result, the conjugate point shift when the reflection surface fell 120 seconds was about 0.2 mm.

In this case, the relationship among the incident angle α of the light beam, the inclination angle β of the fθ lens, the incident angle γ of the cylindrical mirror, and the number of turns M between the deflector and the cylindrical mirror is expressed by the following equation (2). Can be represented by If this expression (2) is satisfied, the curvature of field in the sub-scanning direction can be corrected.

Β × β <0, β × γ × (−1) ^M > 0 (2) That is, when α × β is negative, the angle of incidence of the light beam on the deflector and the angle of inclination of the fθ lens are It is to have an angle in the opposite direction. As described above, by inclining the inclination angle β of the fθ lens in the reverse direction with respect to the incident angle α in the sub-scanning direction on the deflecting reflection surface, the nonuniformity of the beam diameter due to oblique incidence on the deflector is reduced to f.
It can be corrected by tilting the θ lens.

In this case, the inclination angle β of the fθ lens that minimizes the difference between the beam diameter at the scanning center and the beam diameter at the scanning end (beam diameter difference) differs depending on the incident angle α in the sub-scanning direction to the deflector. That is, when the absolute value (| α |) of the incident angle α is large, the absolute value (| β
|) Also increases. Therefore, in order to suppress the beam diameter difference to a predetermined value which does not cause a problem in practical use, for example, about 10 μm, as shown in FIG.
The ratio of the lens inclination angle β (α / β) is -0.2 to -0.0.
It is desirable to set between 4.

Further, the fact that the sign of β × γ × (−1) ^M is positive means that the cylinder of the light beam at the center of scanning and the light beam at the scanning end generated when the fθ lens is inclined at an angle to prevent beam nonuniformity. This is to take advantage of the fact that there is a difference in the scanning line curvature on the mirror, that is, the incident position. That is, by folding back in the direction in which the incident angle of the light beam at the scanning end in the sub-scanning direction is smaller than the incident angle of the light beam at the scanning center in the sub-scanning direction,
The power of the light beam at the scanning end can be made smaller than the power of the cylindrical mirror for the light beam at the scanning center, and the curvature of the image field in the sub-scanning direction that is negatively curved can be corrected to reduce the displacement of the conjugate point. And good tilt correction performance can be obtained.

In this embodiment, the case where two photosensitive members are used has been described. However, a scanning device and a photosensitive member having the same configuration are added, or as shown in FIG. A four-color full-color recording apparatus can be formed by configuring the scanning device that scans a light beam on the left and right as in this embodiment.

Although the illustration of the optical scanning device in FIG. 4 is omitted,
Light fluxes LA, La, LB. A light source for emitting Lb, a collimating lens, an opening, and a shaping optical system are provided in this order.
Light beams LA and L emitted from a shaping optical system (not shown)
a, the light beams LB and Lb are reflected by the reflecting mirror 18A.
It is guided to a single deflector 24 by the reflection mirror 18B, and is deflected and scanned. The luminous fluxes LA and La are the fθ lenses 2
An image is formed on each of the photoconductors 34A and 34a by 2A. Similarly, the light beams LB and Lb are imaged on the photoconductors 34B and 34b by the fθ lens 22B. The plane mirrors 26A and 26a, the cylindrical mirrors 28A and 28a, and the plane mirrors 30A and 30a are sequentially provided between the deflector 24 and the photoconductors 34A and 34a.

Therefore, each of the light beams LA, La, LB, and Lb is deflected and scanned by the deflector 24,
2A and 22B, and pass through the plane mirrors 26A, 26a and 26
B, 26b, the cylindrical mirrors 28A,
The photosensitive members 34A, 34A, 34B, and 34B receive refracting power in the sub-scanning direction by 28A, 28B, and 28B and are turned back by the plane mirrors 30A, 30A, 30B, and 30B to expose and scan the photosensitive members 34A, 34A, 34B, and 34B.

Each of the photoconductors 34A, 34a, 34B and 34b is exposed to form a latent image corresponding to each color, and a different color corresponding to the latent image on each photoconductor 34A, 34a, 34B and 34b. Is carried out to obtain a multicolor visible image. By transferring this visible image to the same recording medium, a multicolor print can be obtained.

[Second Embodiment] An optical scanning device according to an embodiment of the present invention has the same configuration as that of the above-described embodiment, and differs only in optical data. For this reason, the same components are denoted by the same reference numerals, and detailed description is omitted. Table 2 below shows main optical data after the deflection surface 24X of the present embodiment.

[0063]

[Table 2]

Each of the light beams A and B emitted from the shaping optical system is f
The light passes through the θ lenses 22A and 22B and enters the deflector. At this time, the sub-scanning incident angle to the deflector is the same as in the first embodiment, when the light beam LA is αi = + 2.4 ° and αj = + 1.5.
°. The light beam reflected by the deflector 24 passes through the fθ lenses 22A and 22B again, and is returned to the mirrors 26A and 26A.
B is reflected. lenses 22A and 22B have an inclination angle of βi = −8 ° and βj = −5.8 °, and an angle at which the uniformity of the beam diameter becomes the best according to the incident angle α of each light beam to the deflector 24. did.

The light beam L reflected by the plane mirror 26A
A is reflected by the cylindrical mirror 28A, is imaged on the photoreceptor 34A, and is exposed and scanned. Incident angle γi of cylindrical mirror 28A =
+ 10 °, the radius of curvature is 154.32, and the conjugate magnification of the light beam LA is −0.3.

The light beam L reflected by the plane mirror 26B
B is reflected by the cylindrical mirror 28B, is imaged on the photoreceptor 34B, and is exposed and scanned. Incident angle γj of cylindrical mirror 28B =
The curvature radius is 169.41 and the conjugate magnification of the light beam LB is -0.35.

In this embodiment, the inclination angle β of the fθ lens
Signs of i and βj, number of folds Ni and N after deflector 24
j satisfies the expressions (1) and (2) as in the first embodiment, and the bow directions on the surface to be scanned coincide.
The sign of the incident angle α, the deflector 24 and the cylindrical mirror 2
8 is also the same as in the first embodiment, and satisfies the expression (2). The folding angle γ of the cylindrical mirror is folded in the direction in which the field curvature in the sub-scanning direction becomes smaller. .

FIG. 5 shows the relationship between the tilt angle of the fθ lens and Bow on the surface to be scanned. Luminous flux L
Since the inclination angle of the fθ lens 22A of A is larger than the light beam LB, as shown in FIG. 5, the occurrence of Bow on the light beam LA side increases. Therefore, in the present embodiment, the conjugate magnification between the deflection reflecting surface of the light beam LA and the surface to be scanned is -0.3, and the light beam LB
By setting the conjugate magnification of −0.35 to −0.35, the amount of Bow on the surface to be scanned is the same as 120 μm for both the light beam LA and the light beam LB. By doing so, the direction and size of Bow on the surface to be scanned can be matched.

By the way, there are several methods for making the conjugate magnification different. In this embodiment, the distance from the deflector to the cylindrical mirror and the distance from the cylindrical mirror to the surface to be scanned are made different from each other. The magnification was set by adjusting the radius of curvature of the cylindrical mirror so as to form an image on the surface.

In the present embodiment, the bow amounts are the same. However, it is not necessary to make them completely coincide with each other, and the bow difference is reduced to a size that can be recognized as color misregistration by human eyes, for example, a half pixel or less. A sufficient effect can be obtained even if the conjugate magnification is made different as described above. In the present embodiment, if the conjugate magnification is different between the light beam LA and the light beam LB, the same vignetting amount may cause the beam diameter on the scanned surface to be different between the light beam LA and the light beam LB. 14
The same beam diameter can be obtained by changing the aperture width of B or changing the magnification of the shaping optical system so that the total magnification is matched between the light beam LA and the light beam LB.

As described above, according to the present embodiment, fθ
When the angle between the optical axis of a scanning optical system such as a lens and the plane perpendicular to the rotation axis of a deflector such as a rotary polygon mirror is large, the conjugate magnification of the light beam with a large Bow is set to the value of the light beam with a small Bow. Set smaller than the conjugate magnification. As a result, as shown in FIG. 6, the generated Bow difference can be reduced or the Bow difference can be set to 0, and the scanning lines can be made substantially coincident with each other on the surface to be scanned, thereby suppressing color shift. .

[Third Embodiment] FIG. 7 shows a schematic configuration of an optical scanning device according to an embodiment of the present invention, as viewed from the direction of the sub-scan corresponding to the optical scanning device (arrow in FIG. 2). (View from the X direction). Further, Table 3 below shows main optical data of the deflecting surface 24X and thereafter of the present embodiment.

[0073]

[Table 3]

Each light beam LA, LB emitted from the shaping optical system
Pass through the fθ lenses 22A and 22B and enter the deflector 24. At this time, the sub-scanning incident angle αi of the light beam LA on the deflecting surface 24A and the sub-scanning incident angle αj of the light beam LB on the deflecting surface are both incident on the deflector from above the sheet. are doing.

The light beam reflected by the deflector 24 passes through the fθ lenses 22A and 22B again, and is returned to the turning mirrors 26A and 22A.
26B. In the present embodiment, the fθ lens 2
2A,. The inclination angle of 22B is βi = −6.8 °, βj =
Both angles are set so as to have an angle downward with respect to a plane V perpendicular to the rotation axis CL of the deflector 24 at + 6.8 °.

In this case, the scanning line curve on the plane mirrors 26A and 26B is a mountain shape in which the height of the scanning center is high for both the light beams LA and LB. In this case, by making the number of turns of the light beam LA and the light beam LB after the deflector 24 different so that the difference becomes an odd number, the curvature of the scanning line can be made the same direction on the surface to be scanned. In the present embodiment, the number of folds Ni on the light beam LA side is set to 2 and the number of folds Nj on the light beam LB side is set to 3, so that the Bow of the surface to be scanned is matched.

The light beam L reflected by the plane mirror 26A
A is reflected by the cylindrical mirror 28A, is imaged on the photoreceptor 34A, and is exposed and scanned. Incident angle γi of cylindrical mirror 28A =
+ 31.6 °, the radius of curvature is 220.71, and the conjugate magnification of the light beam LA is −0.49.

In the light beam LA, the sign of the angle α is positive and the sign of the angle β is negative, and the turn M between the deflector 24 and the cylindrical mirror is 1. By setting the turning angle γ of the cylindrical mirror to be positive, the light beam at the scanning end is turned in the direction in which the incident angle in the sub-scanning direction is smaller than the incident angle in the sub-scanning direction of the light beam at the center of the scanning direction. The curvature of field in the direction is corrected, and the conjugate point curvature is also reduced.

The light beam L reflected by the plane mirror 26B
B is reflected by the cylindrical mirror 28B to form an image on the photoreceptor 34B and is exposed and scanned. Incident angle γj of cylindrical mirror 28B =
25.87 °, radius of curvature of 8b is 208.6, and light beam LB
Has a conjugate magnification of -0.49.

In the light beam LB, the sign of the angle α is negative and the sign of the angle β is positive, and the number of turns M between the deflector 24 and the cylindrical mirror is two. By making the folding angle γ of the cylindrical mirror positive by this, the light beam at the scanning end is folded in a direction in which the incident angle in the sub-scanning direction is smaller than the incident angle in the sub-scanning direction of the light beam at the center of the scanning direction. The curvature of field is corrected, and the conjugate point curvature is also reduced.

In this embodiment, the angles α and β have opposite signs, but have the same absolute value. Therefore, B on the scanned surface
In order to make the amount of ow the same and to match the direction and the amount to eliminate the color shift, the conjugate magnification of both the light beam LA and the light beam LB is-
Assuming 0.49 as the Bow on the scanned surface, the light flux LA and the light flux L
B and 155 μm.

According to the present embodiment, the signs of the inclination angles βi and βj of the fθ lens, the number of turns Ni after the deflector,
Nj is different from that of the first embodiment, but by satisfying the expression (1), the bow directions on the surface to be scanned can be matched.

Also, the sign of the angle of incidence α to the deflector, the turn M between the deflector and the cylindrical mirror, and the turn angle γ of the cylindrical mirror are also different from those of the first embodiment.
As a numerical value, the curvature of field in the sub-scanning direction can be corrected by satisfying the expression (2).

[0084]

As described above, according to the present invention, f
The inclination angle of the scanning optical system such as the θ lens and the number of times of folding from the deflecting means to the surface to be scanned can be set so that Bow generated by the inclination of the scanning optical system bends in the same direction on the surface to be scanned. Thus, there is an effect that a good color image with little color shift can be obtained.

Further, by setting a small conjugate magnification from the deflecting means to the surface to be scanned with respect to a light beam having a large inclination angle of a scanning optical system such as an fθ lens, the amount of color misregistration can be further reduced. There is.

Also, by setting the inclination angle of the scanning optical system such as the fθ lens on the light beam side having a large incident angle in the sub-scanning direction on the deflection reflecting surface of the deflection means to be small, the amount of Bow on the surface to be scanned is reduced. And the amount of color misregistration can be further reduced.

Further, the tilt angle of the scanning optical system such as the fθ lens is set to an angle at which the beam uniformity can be ensured, and the turning direction of the cylindrical mirror is set such that the scanning center light beam is incident at the scanning end portion from the incident angle in the sub-scanning direction of the cylindrical mirror or the like. By folding back the light beam in the direction in which the incident angle of the light beam in the sub-scanning direction becomes smaller, the power of the light beam at the scanning end is made smaller than the power of the cylindrical mirror and the like for the light beam at the center of the scanning, thereby forming an image in the sub-scanning direction. There is an effect that both curvatures can be corrected.

By setting α / β between -0.2 and -0.4, the difference between the beam diameter of the light beam at the center of scanning and the beam diameter of the light beam at the scanning end is affected in actual use. And the stray light can be prevented from being generated in the double pass / front incidence optical system.

[Brief description of the drawings]

FIG. 1 is an image diagram illustrating an optical arrangement in an optical scanning device according to a first embodiment as viewed from a sub-scanning direction.

FIG. 2 is a perspective view illustrating a schematic configuration of the optical scanning device according to the first embodiment.

FIG. 3 is a diagram showing the relationship between the tilt angle of the fθ lens and the amount of change in the beam diameter difference.

FIG. 4 is an image diagram showing a modified example in which the optical scanning device according to the first embodiment is applied to a full-color recording device, and showing an optical arrangement viewed from a sub-scanning direction.

FIG. 5 is a diagram showing the relationship between the fθ tilt angle and Bow on the surface to be scanned.

FIG. 6 is an explanatory diagram of color shift due to Bow in the same direction.

FIG. 7 is an image diagram showing an optical arrangement of an optical scanning device according to a third embodiment as viewed from a sub-scanning direction.

FIG. 8 is a perspective view showing a schematic configuration of a conventional optical scanning device.

FIG. 9 is a perspective view showing another example of a schematic configuration of a conventional optical scanning device.

FIG. 10 is an image diagram showing an optical arrangement of the optical scanning device of FIG. 9 as viewed from a sub-scanning direction.

FIG. 11 is an explanatory diagram of color misregistration due to Bow occurring in the reverse direction.

[Explanation of symbols]

 10A, 10B: Light source 12A, 12B: Collimator lens 14A, 14B: Opening (slit) 16A, 16B: Shaping optical system (cylindrical lens) 18A, 18B: Plane mirror 22A, 22B: fθ lens 24: Deflector (rotation) 24X, 24A, 24B: Deflection / reflection surface 26A, 26B: Plane mirror 28A, 28B: Cylindrical mirror 30A, 30B: Plane mirror 34A, 34B: Photoconductor

Claims (5)

[Claims] 1. A plurality of reflecting surfaces having at least a plurality of reflecting surfaces, the plurality of reflecting surfaces being incident on different ones of the plurality of reflecting surfaces such that an optical axis is inclined by a predetermined angle in a sub-scanning direction intersecting a main scanning direction. Deflecting means for deflecting and scanning each of the light fluxes in the main scanning direction, and a plurality of light fluxes corresponding to each of the plurality of light fluxes and converging the light fluxes respectively deflected and scanned on the surface to be scanned so that the light spot is scanned. A scanning optical system, and an optical scanning device comprising: a plurality of folding units corresponding to each of the plurality of luminous fluxes and folding back the deflected and scanned luminous fluxes; wherein one of the plurality of luminous fluxes is a reference luminous flux; The angle between the optical axis of the scanning optical system corresponding to the reference light beam and the plane perpendicular to the rotation axis of the deflecting means is βi, and the number of folds by the fold means between the deflecting means and the surface to be scanned in the optical path of the reference light beam is Ni And said Of the several light beams, one light beam other than the reference light beam is defined as a target light beam, the angle between the optical axis of the scanning optical system corresponding to the target light beam and a plane perpendicular to the rotation axis of the deflecting means is defined as βj, and the angle is βj. An optical scanning device wherein the reference light flux and the target light flux are configured to satisfy the following relationship, where Nj is the number of turns by the turning means between the means and the surface to be scanned. (Βi × (−1) ^Ni ) / (βj × (−1) ^Nj )> 0 where the angle has a positive sign in the counterclockwise direction and a negative sign in the clockwise direction. 2. A light beam incident on the deflecting means is a light beam focused in the sub-scanning direction by an anamorphic optical system that forms a long line image in the main scanning direction in the vicinity of the reflecting surface, and the angle βi, 2. The optical scanning device according to claim 1, wherein the absolute value of the magnification between the deflecting reflection surface and the surface to be scanned in the sub-scanning direction on the light beam side where the absolute value of βj is large is set small. 3. A reference light flux, wherein αi and αj are angles at which an optical axis of a light beam incident on the deflecting means corresponding to the angles βi and βj forms a plane perpendicular to a rotation axis of the deflecting means. The optical scanning device according to claim 1, wherein the target light beam is configured to satisfy the following relationship. When | αi |> | αj |, | βi | <| βj | 4. A plurality of reflecting surfaces including at least a plurality of reflecting surfaces, the plurality of reflecting surfaces being incident on different ones of the plurality of reflecting surfaces such that an optical axis is inclined by a predetermined angle in a sub-scanning direction intersecting the main scanning direction. Deflecting means for deflecting and scanning each of the light fluxes in the main scanning direction, and a plurality of light fluxes corresponding to each of the plurality of light fluxes and converging the light fluxes respectively deflected and scanned on the surface to be scanned so that the light spot is scanned. An optical scanning device comprising: a scanning optical system; and a plurality of folding units corresponding to each of the plurality of luminous fluxes and folding back the deflecting-scanned luminous flux. A light beam converged in the sub-scanning direction by an anamorphic optical system that forms a long line image in the main scanning direction in the vicinity, and at least one of the folding means is constituted by a cylindrical mirror having a curvature only in the sub-scanning direction. It and thereby have at least one by inclination correcting function further comprises a cylindrical lens having a power only in the sub-scanning direction, for at least one light flux among the plurality of light beams,
The angle between the optical axis when entering the deflecting means and a plane perpendicular to the rotation axis of the deflecting means is α, and the angle between the optical axis of the corresponding scanning optical system and the plane perpendicular to the rotation axis of the deflecting means. Is β, the incident angle to the light beam to at least one of the cylindrical mirror and the cylindrical lens is γ, and the number of turns between the deflecting means and at least one of the cylindrical mirror and the cylindrical lens is M, An optical scanning device configured to satisfy the relationship. α × β <0 and β × γ × (−1) ^M > 0 where the angle has a positive sign in the counterclockwise direction and a negative sign in the clockwise direction. 5. The optical scanning device according to claim 1, wherein the angle α and the angle β satisfy the following relationship. −0.2> α / β> −0.4