JPH11153767A - Optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease jitter caused by the plane tilt of a rotary polygon mirror or the like in an oblique-incident optical scanner. SOLUTION: This optical scanner is provided with a light source 1 for generating a light beam, a deflector 4 having plural deflecting surfaces for reflecting and deflecting the light beam made incident with an angle to the direction of subscanning from the light source 1, an optical scanning system 23 for making the light beam reflected and deflected by the reflecting surface 6 of the deflector 4 form a beam spot on the scanned surface for scanning, and light receiving element 33 for detecting the light beam reflected and deflected by the reflecting surface 6 of the deflector 4 before it scans a scanned surface 17 and generating a synchronous signal. In the scanner, the point that minimizes jitter caused by the plane tilt of the plural reflecting surfaces of the deflector 4 in the direction of sub-scanning is set within the region including the two points of the scanning center on the scanned surface 17 and the end point of the main scanning.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device used for a laser beam printer or the like, and more particularly, to an optical scanning device in which jitter due to surface tilt or the like is reduced.

[0002]

2. Description of the Related Art Conventionally, an image recording device such as a laser beam printer and an optical scanning device used for various image reading and measuring devices generally form a light beam emitted from a light source such as a semiconductor laser through a shaping optical system. The beam is deflected by a deflector such as a rotating polygon mirror as a deflecting means, and the deflected light beam is scanned by forming a beam spot on a surface to be scanned by an imaging lens system as an f · θ lens. ing.

In these apparatuses, a light beam is repeatedly scanned on a surface to be scanned in a straight line or a curved line.
The two-dimensional scanning is performed by relatively moving the medium to be scanned located on the surface to be scanned in a direction substantially orthogonal to the above-described scanning direction. The scanning direction of the former optical scanning device is referred to as a main scanning direction, and the latter direction of relative movement of the medium to be scanned is referred to as a sub-scanning direction.

In such an optical scanning device, in order to improve resolution and processing speed, a light beam emitted from a light source is incident on a rotary polygon mirror with a very small diameter in a main scanning direction and is deflected. A high-speed optical scanning device for re-inputting a light beam to a rotating polygon mirror via a transmission optical system is disclosed in
It has been proposed in 1-332340 and the like. In the optical scanning device in which the light beam is incident twice on the rotating polygon mirror, the diameter of the light beam in the main scanning direction when the light beam first enters the rotating polygon mirror is extremely smaller than when the light beam enters the second time. In addition, the transmission optical system is configured such that the light beam incident on the rotating polygon mirror for the second time follows the center point of the rotating reflecting surface in the main scanning direction.

On the other hand, in an optical scanning apparatus, a light beam is incident at an angle with respect to a scanning plane perpendicular to a rotation axis of a rotary polygon mirror to deflect the light beam.
No. 2 and the like.

In the present specification, the case where the light is incident twice on different reflecting surfaces of the rotary polygon mirror as described above is referred to as "double incidence". Further, letting the light beam enter the scanning plane of the rotating polygon mirror at an angle will be referred to as “oblique incidence”.

[0007]

In the above-mentioned obliquely incident optical scanning device, the timing shift in the main scanning direction (based on the tilt of the rotating polygon mirror) between the synchronizing signal generating light beam detection unit and the scanning optical system. Jitter), and the jitter becomes very large depending on the configuration. In an optical scanning device in which a light beam is made incident on a rotating polygon mirror within a scanning plane, a device in which a bus of a cylindrical lens of a light beam detector for generating a synchronization signal is made parallel to a main scanning direction in order to reduce jitter is particularly fair. As described in JP-A-7-43462, regarding the configuration for reducing the jitter due to the tilting in the case of the above-mentioned oblique incidence and the configuration of the light beam detection unit for generating the synchronizing signal, what has been studied in the past is as follows. Absent.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to reduce jitter due to tilting of a rotating polygon mirror and other causes in an obliquely incident optical scanning device. It is.

[0009]

According to the present invention, there is provided an optical scanning apparatus comprising: a light source for generating a light beam; and a plurality of light sources for reflecting and deflecting the light beam incident from the light source at an angle in the sub-scanning direction. A deflector having a reflecting surface, a scanning optical system for forming a beam spot on the surface to be scanned with the light beam reflected and deflected by the reflecting surface of the deflector, and scanning the light beam. A light receiving element that detects the light beam emitted before scanning on the surface to be scanned and generates a synchronization signal, wherein the plurality of reflecting surfaces of the deflector are tilted in the sub-scanning direction. The point where the jitter is minimized is set in an area between the two points including the scanning center and the scanning end point on the surface to be scanned.

In this case, a lens for guiding the light beam to the light receiving element can be arranged so that the jitter due to surface tilt on the light receiving element is minimized.

The lens for guiding the light beam to the light receiving element may be an anamorphic lens, and the lens may be arranged so that the direction in which the refracting power is strong and the direction in which the light beam is displaced due to the surface tilt substantially coincide.

The lens for guiding the light beam to the light receiving element is an anamorphic lens, and the principal axis of the light beam incident on the lens at the moment when the light beam is detected by the light receiving element is defined as a first axis. When the axis in the plane swept by the light beam and perpendicular to the first axis is the second axis, and the axis perpendicular to the first axis and the second axis is the third axis, the lens thereof Is preferably tilted about the first axis. In that case, it is desirable that the direction in which the refractive power of the lens is strong is tilted around the first axis so as to form an angle with the third axis.

The lens for guiding the light beam to the light receiving element is an anamorphic lens, and the principal axis of the light beam incident on the lens at the moment when the light beam is detected by the light receiving element is defined as a first axis. When the axis in the plane swept by the light beam and perpendicular to the first axis is the second axis, and the axis perpendicular to the first axis and the second axis is the third axis, the lens thereof May be tilted about a third axis and eccentric along the third axis.

Further, in the above, it is desirable that the light source and the light receiving element are arranged substantially conjugate in the main scanning direction.

The deflector comprises a rotary polygon mirror, and has a transmission optical system for transmitting and entering the light beam reflected and deflected by the first reflection surface of the rotary polygon mirror to the second reflection surface of the rotary polygon mirror. The light beam reflected and deflected by the reflection surface may be configured to scan by forming a beam spot on the surface to be scanned by the scanning optical system.

In the present invention, the point that the jitter due to the tilt of the plurality of reflecting surfaces of the deflector in the sub-scanning direction is minimized is as follows.
These include the center of the scan on the scanned surface and the end point of the scan.
Since it is set in the region between the points, the maximum value of the total jitter that combines the jitter due to surface tilt and the jitter due to factors other than surface tilt can be suppressed to a small value. Can be reduced.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an optical scanning device according to the present invention will be described in detail with reference to the drawings. First, a basic embodiment of the optical scanning device of the present invention will be described. FIG. 1 is a plan view showing the configuration of the optical scanning device of the present basic embodiment, FIG. 2 is a side view thereof, FIG. 3 is a perspective view of a main part thereof, and FIG. 4 is a side view of the main part thereof. Hereinafter, in the present invention, at an arbitrary position of the optical system, a plane including the optical axis of the optical system at that position and being parallel to the rotation axis 41 of the rotary polygon mirror 4, which is a deflector, is defined as a sub-scanning plane. And a plane perpendicular to the sub-scanning plane is defined as a main scanning plane. Further, in the main scanning plane, a direction perpendicular to the optical axis is defined as a main scanning direction, and in the sub-scanning plane,
The direction perpendicular to the optical axis is defined as the sub-scanning direction.

A light beam emitted from a semiconductor laser 1 as a light source is shaped by passing through an aperture 61 (FIG. 5), a first shaping lens 2 and a second shaping lens 3, and is formed by a rotating polygon mirror 4 as a deflector. The light enters the first reflection surface 5 and is deflected for the first time. At this time, the light beam is transmitted to the rotating polygon mirror 4.
Is incident on the first reflection surface 5 at an angle with respect to a plane perpendicular to the rotation axis 41 of the light source, and the incident light beam and the reflected light beam do not interfere with each other. The light beam reflected by the first reflection surface 5 passes through the first transmission lens 7, the second transmission lens 8, and the third transmission lens 9 and is reflected by the first transmission mirror 10, and is reflected by the fourth transmission lens 11, 5 through the transmission lens 12 and the second
The light is reflected by the transmission mirror 13, re-enters the second reflection surface 6 of the rotary polygon mirror 4, and is deflected a second time. Also at this time, since the light beam is incident on the second reflecting surface 6 at an angle with respect to the plane perpendicular to the rotation axis 41 of the rotary polygon mirror 4, the incident light beam and the reflected light beam do not interfere with each other. .

The light beam reflected by the second reflecting surface 6 is formed as a light beam spot on the surface 17 to be scanned by the first scanning lens 14, the second scanning lens 15 and the third scanning lens 16, and is scanned. You. The number of surfaces of the rotary polygon mirror 4 is 12 (even number). The third scanning lens 16 is decentered in the sub-scanning direction, which is the direction of the arrow in FIG.
The reason why the third scanning lens 16 is decentered in this manner is that the light beam reflected and deflected by the second reflecting surface 6 of the rotary polygon mirror 4 draws a conical trajectory, and the coordinate system of the cross section of the light beam is deflected. This is because the image formation spot on the scanned surface 17 is distorted due to the rotation depending on the angle, but the decentering of the third scanning lens 16 can prevent the dislocation.

Incidentally, the light is reflected by the second reflecting surface 6 and
The light beam c scanned through the scanning lens 14 and the second scanning lens 15 is incident on and reflected by the mirror 31 of the main scanning (horizontal) synchronization signal generating light beam detecting unit 30 immediately before scanning the effective scanning area. The light is introduced into the light receiving element 33 via the lens 32. The start of scanning on the surface to be scanned 17 is synchronized with the time when the light beam c is detected by the light receiving element 33. The lens 32 is a cylindrical lens having a refractive power only in the sub-scanning direction.
The reflecting surface 6 and the light receiving element 33 are configured to be substantially conjugate, and in the main scanning direction, the semiconductor laser 1
And the light receiving element 33 are substantially conjugated.

By the way, the optical system between the semiconductor laser 1 and the first reflecting surface 5 is formed by the shaping optical system 21 and the first reflecting surface 5.
The optical system between the second reflecting surface 6 and the transmission optical system 22,
If the optical system between the reflecting surface 6 and the surface to be scanned 17 is called a scanning optical system 23, the first reflecting surface 5 of the rotary polygon mirror 4
And the second reflective surface 6 are mutually parallel reflective surfaces facing each other across the rotation axis 41, and the optical axes of the shaping optical system 21, the transmission optical system 22, and the scanning optical system 23 include the rotation axis 41. Are arranged in the sub-scanning plane. Therefore, this optical scanning device has a symmetrical configuration with respect to the sub-scanning surface, while being incident twice and obliquely incident. With such an arrangement, the optical axes of the shaping optical system 21, the transmission optical system 22, and the scanning optical system 23 are arranged in a straight line when viewed in the main scanning plane. Each element constituting the optical system can be arranged with high accuracy on a plane. In addition, since the optical axis of the transmission optical system 22 partially overlaps the optical axes of the shaping optical system 21 and the scanning optical system 23 when viewed on the main scanning plane, the optical axis can be arranged in a small space, and the installation area of the optical scanning device can be reduced. The size of the device can be reduced. With such an arrangement, it is possible to prevent a position change of the scanning line in the sub-scanning direction due to the eccentricity of the rotating shaft 41 of the rotating polygon mirror 4.

FIG. 5 shows an optical path diagram (a) in the main scanning direction of the shaping optical system 21 and an optical path diagram (b) in the sub-scanning direction. A light beam b emitted from the semiconductor laser 1 having a bonding surface perpendicular to the main scanning surface and parallel to the sub-scanning surface and having a cover glass so as to spread in the main scanning direction as compared with the sub-scanning direction is supplied to the first shaping lens 2. The peripheral portion is shielded by an aperture 61 having a rectangular opening arranged at the position of the incident surface of the lens, and is converted into a parallel light beam by the first shaping lens 2 constituting the aspherical collimator lens. The second shaping lens 2 is a positive cylindrical lens having a positive refractive power only in the sub-scanning direction.
Therefore, the light beam transmitted through the second shaping lens 2 is incident on the first reflection surface 5 as a parallel light beam on the main scanning surface, and forms an image (convergence) near the first reflection surface 5 on the sub-scanning surface. .

FIG. 6 shows an optical path diagram (a) in the main scanning direction of the transmission optical system 22 and an optical path diagram (b) in the sub-scanning direction. Each of the first transmission lens 7, the second transmission lens 8, and the third transmission lens 9 is a cylindrical lens having a refractive power only in the main scanning direction, and the first transmission lens 7 and the second transmission lens 8 are positive cylindrical lenses. The third transmission lens 9 is a negative cylindrical lens, and these three lenses form a main scanning direction positive refractive power transmission lens group 24. The fourth transmission lens 11 is a positive cylindrical lens having a positive refractive power only in the sub-scanning direction, and the fifth transmission lens 12 is a spherical lens having a positive refractive power. In these operations, the light beam reflected by the first reflection surface 5 is once formed on the main scanning surface by the main scanning direction positive refractive power transmission lens group 24. The image-side focal point of the transmission lens group 24 and the object-side focal point of the fifth transmission lens 12 coincide, and constitute an afocal optical system on the main scanning plane. Therefore, on the main scanning surface, the main refractive power transmitting lens group 24 in the main scanning direction constitutes a front group of the afocal optical system, and the fifth transmission lens 12 constitutes a rear group of the afocal optical system. Therefore, the light beam is converted into a parallel light beam again in the main scanning plane by the fifth transmission lens 12 and is incident on the second reflection surface 6. On the sub-scanning surface, the fourth transmission lens 11 and the fifth transmission lens 1
2 and the first reflecting surface 5 and the second reflecting surface 6
Has a conjugate relationship, and the convergence point near the first reflecting surface 5 is imaged again near the second reflecting surface 6.

FIG. 7 shows an optical path diagram (a) of the scanning optical system 23 in the main scanning direction and an optical path diagram (b) of the scanning optical system 23 in the sub-scanning direction. The first scanning lens 14 is a spherical lens having a positive refractive power. The second scanning lens 15 is a prism having a refracting action only in the sub-scanning direction, and the third scanning lens 16 is a long lens made of resin and long in the main scanning direction. The entrance surface of the third scanning lens 16 has a concave shape with a large radius of curvature in the main scanning direction and a convex shape with a small radius of curvature in the sub-scanning surface direction. This is a surface formed by rotating around an axis parallel to the main scanning direction, which is located closer to the scanned surface 17 than the incident surface. Such a surface is also called a saddle-shaped toric surface. The exit surface of the third scanning lens 16 has a convex non-arc shape having a large radius of curvature in the main scanning direction, and has a linear cross section in the sub-scanning direction and has no refractive power. Scanning optical system 23 having such a configuration
Makes the second reflection surface 6 and the surface to be scanned 17 conjugate in the sub-scanning surface, and forms an image of a convergence point near the second reflection surface 6 near the surface to be scanned 17. In the main scanning plane, the second
The parallel light beam reflected from the reflecting surface 6 is scanned by the scanning surface 17.
An image is formed in the vicinity.

Next, the operation of the transmission optical system 22 will be described. FIG. 8 is an expanded sectional view of the main scanning surface of the transmission optical system 22. The main scanning direction positive refractive power transmitting lens group 24 composed of the first transmitting lens 7, the second transmitting lens 8, and the third transmitting lens 9 is simplified and shown as a single lens. The fourth transmission lens 11 has no refractive power in the main scanning direction, and is not shown. FIGS. 8A and 8B show the state of the light beam when the rotary polygon mirror 4 rotates. by the way,
As shown in FIGS. 1 to 4 and the like, the optical path of the transmission optical system 22 is
The light is reflected twice by the transmission mirrors 10 and 13. That is, the light is reflected an even number of times. In FIG. 8, since the reflections are developed for these even-numbered reflections, the rotation directions of the first reflection surface 5 and the second reflection surface 6 are the same as in FIG. 8B.

The diameter of the parallel light beam incident on the first reflecting surface 5 is w _i . Since the transmission optical system 22 forms an afocal optical system in the main scanning plane, the light beam incident on the second reflection surface 6 is also parallel, and the diameter of the light beam is w _o.
It is. Assuming that the focal length of the transmission lens group 24 is f ₁ and the focal length of the fifth transmission lens 12 is f ₂ , the ratio of the diameter of the light beam obtained by dividing w _o by w _i is f ₂ divided by f ₁ . Is equal to

As shown in FIG. 8B, when the rotary polygon mirror 4 rotates by the angle θ ₁ , the light beam is deflected by the first reflection surface 5 by the angle 2θ ₁ . The deflected light beam passes through the transmission lens group 24 and the fifth transmission lens 12 and has an angle θ ₂
Is only deflected. This light beam intersects the optical axis at point Q. On the second reflecting surface 6, the distance between the deflected light beam and the optical axis is d, the rotary polygon mirror 4 is rotated by an angle theta _1, so that also the second reflecting surface 6 moves by the same distance d Is set to a proper positional relationship. Therefore, the movement amount of the light beam and the movement amount of the second reflection surface 6 match, and the light beam does not protrude from the second reflection surface 6.

At this time, the deflected light beam is deflected to the side where the incident angle is increased by an angle θ _{2 with} respect to the second reflection surface 6, so that the light beam reflected by the second reflection surface 6 is scanned. The angle θ _s is represented as θ _s = 2θ ₁ + θ ₂ .

Since the transmission optical system 22 of the present embodiment is an afocal optical system on the main scanning plane, its optical magnification β is a value obtained by dividing the focal length f ₂ by the focal length f _1. , Equal to the ratio of the diameters of the light beams, w _o / w _i . The light beam transmitted through the transmission optical system 22 has an angle 2
Since the deflection angle is changed from theta ₁ to the angle theta _2, the optical magnification β
Can also be expressed as 2θ ₁ / θ ₂ . Therefore, the optical magnification β is expressed by the following equation.

Β = w _o / w _i = f ₂ / f ₁ = 2θ ₁ / θ
_{In the two} basic examples, the optical magnification β is set to 1 <β <20.

In the optical scanning device in which the light beam is deflected twice by the rotary polygon mirror 4 as in the present basic embodiment, the scanning speed is increased as compared with the conventional optical scanning device in which the light beam is deflected only once. Can be. This will be described below.

In a conventional optical scanning device that deflects only once, the reflection surface moves when the rotary polygon mirror rotates, so
In order to always put the entire light beam on the same reflecting surface in each scanning, the size of the reflecting surface must be larger than the size of the light beam incident on the rotary polygon mirror in the main scanning direction. Therefore, the number of reflecting surfaces of the rotary polygon mirror cannot be increased so much.

In this basic embodiment, a light beam parallel to the first reflecting surface 5 is incident on the main scanning surface. Also, β> 1
Therefore, the diameter w _i of the light beam on the first reflection surface 5 in the main scanning direction is smaller than the diameter w _o of the light beam on the second reflection surface 6 in the main scanning direction. Therefore, even if the size of the first reflecting surface 5 is smaller than that of the conventional optical scanning device, the entire light beam can always enter the same reflecting surface in one scan. The smaller the value of w _i , the smaller the size of the first reflecting surface 5 can be.
In the second deflection, the moving amount of the light beam when the rotary polygon mirror 4 rotates and the moving amount of the second reflecting surface 6 match, so that the size of the second reflecting surface 6 in the main scanning direction is It is sufficient that the size is at least as large as the size of the incident light beam.

Therefore, in comparison with the conventional optical scanning device which deflects only once, the optical scanning device which deflects twice in the present basic embodiment has the diameter of the light beam on the second reflecting surface 6 in the main scanning direction. By reducing the diameter w _i of the light beam in the main scanning direction on the first reflecting surface 5 with respect to w _o , the reflecting surface of the rotary polygon mirror 4 can be reduced. More can be done, and the scanning speed can be increased accordingly.

Table 1 shows a numerical example of a specific basic embodiment of the optical scanning device thus configured. In Table 1, the radius of curvature of the cylindrical surface and the toric surface in the sub-scanning direction and the main scanning direction are _rix and _riy (i indicates the surface number from the light source 1 to the surface 17 to be scanned). For the aspherical surface, the radius of curvature indicates a value on the optical axis. The unit of the length is mm.

[0036] Note) S _i: the surface of the surface number i, r _i: curvature of the surface number i radius, d _i: surface distance between the surface of number i and i + 1, n _i: wavelength 780nm of the medium between the surface number i and i + 1 Is the refractive index of

Second shaping lens 2 and third scanning lens 16
The expression representing the aspherical surface of is given by z _i = (y ² / r _i ) / [1+ ｛1− (K _i +1) (y
/ R _i) ^{2} 1/2]} a ^{_{+ A i y 4 + B i}} y 6 + C i y 8, showing the aspherical coefficients in the following Table 2.

[0038] Note) S ₄ : Aspherical surface coefficient of surface number 4, S _26y : Aspherical surface coefficient of surface number 26 in the main scanning direction.

In this specific example, the third scanning lens 16
Of the incident surface S ₂₅ is a toric surface formed by an arc of r _25y = -1475.39378 rotated at r _25x = 37.95675. The second scanning lens 15 and the third
When the optical path is refracted, such as when passing through the scanning lens 16, the optical axis is refracted in the same manner as the principal ray. , Always coincides with the principal ray of the beam that scans the scanning center.

The number of faces of the rotary polygon mirror 4 is 12, and the diameter of the inscribed circle is 38.64 mm.
The incident angle of the light beam on the reflecting surface 5 and the second reflecting surface 6 in the sub-scanning direction is 6 °, and the incident angle of the light beam on the first transmitting mirror 10 and the second transmitting mirror 13 in the sub-scanning direction. Is 3 °. Also, the exit surface S ₂₄ of the second scanning lens 15
Is inclined by 13 ° in the sub-scan section, and the incident surface S ₂₅ of the third scanning lens 16 is 8.7503 in the sub-scan section.
The exit surface S ₂₆ of the third scanning lens 16 is inclined by 2.875374 ° in the sub-scan section. See FIGS. 2 and 4 for the directions of these inclination angles.

Further, in accordance with the first shaping lens incident surface S ₃ , the main scanning direction is 0.7154 mm, and the sub-scanning direction is 1.05 mm.
A 26 mm rectangular aperture 61 is arranged. Then, in the sub-scanning direction, the light emitting point 1 and the first reflecting surface 5 of the rotary polygon mirror 4 are out of the geometrical conjugate relationship. However, since the first reflecting surface 5, the second reflecting surface 6, and the scanned surface 17 of the rotary polygon mirror 4 are all in a conjugate relationship with each other, the tilting of the rotary polygon mirror 4 is corrected. . Therefore, the light emitting point 1 and the scanned surface 17 are out of the conjugate relationship. However, the position where the light beam becomes minimum (beam waist) is shifted from the geometrical optical imaging point due to the influence of diffraction, and the scanned surface 17 is located at the position where the light beam becomes substantially minimum (beam waist). Are located. This will be described later.

The optical magnification β in the main scanning direction of the transmission optical system 22 in the above specific example is 8.24, the optical magnification β _t in the sub-scanning direction is 1.12, and the optical magnification β of the scanning optical system 23 in the sub-scanning direction. β _s is 0.406.

Here, the second scanning lens 15 is a prism having a refraction function only in the sub-scanning direction, as described above. The operation of the prism will be described. The light beam reflected and deflected by the reflecting surface 6 of the rotary polygon mirror 4 draws a conical trajectory, and when the prism of the second scanning lens 15 is not disposed, the beam is curved on the long lens of the third scanning lens 16. It becomes a trajectory. As schematically shown in FIG. 9, the prism 16 forms a trajectory of the conical light beam a on the incident surface of the third scanning lens 16 in a linear beam trajectory A.
Has the effect of converting to

FIG. 10 is a diagram showing a beam locus on the incident surface of the third scanning lens 16 in the above specific example, and the beam locus is shown by a solid line. In the drawing, the Y direction indicates the main scanning direction, and the X direction indicates the sub scanning direction. For comparison, the third reflection surface 6 to the third reflection surface 6
The trajectory of the beam on the incident surface of the third scanning lens 16 when only the second scanning lens 15 is removed without changing the distance to the scanning lens 16 is indicated by a broken line. From FIG.
It can be seen that the prism function of the second scanning lens 15 has the function of correcting the beam trajectory into a straight line.

FIG. 11 shows the sub-scanning cross section of the third scanning lens 16 at several (5) positions in the main scanning direction, and shows the error of the measured value with respect to the design value of the cross-sectional shape. Things. In the drawing, X, Y, and Z are the sub-scanning direction, the main scanning direction, and the optical axis direction, respectively. As shown in FIG. 11, the shape error of a lens having a saddle-shaped toric surface such as the third scanning lens 16 shows substantially the same state regardless of the position in the main scanning direction, but changes periodically in the sub-scanning direction. There are features. As described above, by the prism action of the second scanning lens 15, the beam trajectories on the third scanning lens 16 linearly A, and the beam is always shape error of point regardless of the position in the main scanning direction B ₁ .about.B ₅ is It is incident on the convex part. At any position in the main scanning direction, when the light beam is incident on a portion where the shape error of the third scanning lens 16 is convex, the imaging position in the sub-scanning direction is shifted forward from the designed position, but the entire scanning region , The third scanning lens 1
Correction can be made by adjusting the optical system such as by adjusting the position of 6, and such adjustment does not cause curvature of field.

Now, the jitter generated in the obliquely incident optical scanning device as described above will be examined. First, a reference axis in the main scanning synchronization signal generating light beam detector 30 is defined. The principal axis of the light beam c incident on the lens 32 at the moment when the light beam c is detected by the light receiving element 33 is defined as a first axis, is in a plane swept by the light beam c, and is perpendicular to the first axis. The axis is a second axis, and an axis perpendicular to the first axis and the second axis is a third axis.

First, the rotary polygon mirror 4 is positioned at the position of the light receiving element 33.
The following describes that jitter occurs due to the surface tilting. FIG.
FIG. 2 is a diagram showing the lens 32 of the above-mentioned basic embodiment in the direction of travel of the light beam c. The trajectory of the light beam c is along the second axis 51, and the light beam c moves in the direction of the arrow as the rotating polygon mirror rotates. In the rotary polygon mirror, the reflecting surface is tilted due to a manufacturing error, but the light beam c is displaced as indicated by points D ₀ , D ₁ , and D ₂ due to the tilting of the reflecting surface. The direction 53 in which the light beam c is displaced by the surface falling
Are angled with respect to the third axis 52. As described above, in the case of oblique incidence, the third axis 52 does not coincide with the direction 53 in which the light beam c is displaced due to surface tilt.

As shown in FIG. 12, when the light beam detecting lens 32 is tilted around the first axis and the generatrix 34 is arranged so as to be perpendicular to the direction 53 in which the light beam c is displaced by the surface inclination. The light beams c incident on the points D ₀ , D ₁ , and D ₂ form an image on the same point E on the light receiving element 33, and no jitter occurs in the light receiving element 33. The imaged light beam spot moves in the direction of the arrow in parallel with the generating line 34 with the rotation of the rotating polygon mirror.

However, as shown in FIG. 13, unless the direction 53 in which the light beam is displaced due to the surface inclination and the direction 53 in which the light beam is displaced is not perpendicular, the light beams incident on the points D ₀ , D ₁ and D ₂ will 33, points F ₀ , F ₁ and F
₂ is formed, and the formed light beam spot is
, In the direction of the arrow, a deviation of the distance e occurs at the maximum, and the writing start timing on the surface 17 to be scanned is deviated by that amount, thereby causing jitter. As described above, the lens 32 disposed in the main scanning synchronization signal generating light beam detector 30 is used.
, The amount of jitter generated due to surface tilt in the light receiving element 33 varies. However, this is not particularly limited to oblique incidence.

Next, the occurrence of jitter due to surface tilt in the scanning optical system 23 will be described. Generally, at oblique incidence, jitter occurs due to surface tilt in the scanning optical system. FIG. 14 shows the trajectory of the deflected light beam before it enters the scanning optical system 23 in the traveling direction of the light beam. If there is a tilt, the light beam at the scanning center will be at the point G ₀ , Displaced as shown by points G ₁ and G ₂ , and at the start of scanning, points H ₀ , H ₁ ,
Displaced like point H ₂ , and at the end point of the scan J ₀ , point J ₁ ,
Displaced as a point J _2.

At the center of the scanning, the light beam does not displace in the main scanning direction even if the surface is tilted.
There is displacement in the main scanning direction, and the light beam spot on the surface to be scanned is also displaced in the main scanning direction, causing jitter. On both sides of the center of scanning, displacements in the main scanning direction are opposite to each other, and the displacement increases as the distance from the scanning center increases. In the present basic embodiment, the trajectory of the light beam is linearized by the second scanning lens 15 as a prism.
As shown in FIG. 5, displacement of the light beam in the main scanning direction due to surface tilt exists.

However, if the amount of eccentricity of the third scanning lens 16 is appropriately selected, it is possible to prevent the scanning optical system 23 from causing jitter due to surface tilt. Further, depending on the amount of eccentricity of the third scanning lens 16, before entering the third scanning lens 16, the direction of displacement of the light beam displaced by the surface tilt in the main scanning direction and the light beam spot on the scanned surface 17 are different. The direction of displacement may be reversed. In the present basic embodiment, as described above, the amount of eccentricity of the third scanning lens 16 is determined in order to prevent the shape of the image spot on the scanned surface 17 from being deformed. Since the amount of eccentricity is different from the amount of eccentricity to prevent the occurrence, jitter occurs due to surface tilt in the scanning optical system 23.

Next, a configuration for minimizing the jitter due to such tilting will be described. The jitter due to the surface tilt is a combination of the amount generated at the position of the light receiving element 33 (FIG. 13) and the amount generated at the scanning optical system 23 (FIG. 15). When there is a tilt in a certain direction, the light receiving element 3
If the direction of the shift of the light beam spot in 3 is the same as the direction of the shift of the light beam spot on the surface to be scanned generated by the scanning optical system 23, those shifts are canceled each other, and the jitter is reduced. However, if their directions are opposite, their shifts are added to each other and the jitter increases.

When there is a certain amount of tilt, the scanning optical system 2
It is assumed that the displacement of the light beam spot on the surface 17 to be scanned, which occurs in 3, is as shown by the solid line in FIG. 16 with the scanning direction of the light beam spot being positive. The scanning start point is L ₀ , the scanning center is L ₁ , and the scanning end point is L ₂ . At this time, if there is no displacement of the spot of the light beam due to the surface falling at the light receiving element 33, the displacement generated at the position of the light receiving element 33 and the displacement generated at the scanning optical system 23 are also obtained by combining FIG.
Becomes the solid line. Since the jitter represents the deviation width by the magnitude, the jitter at this time is as shown by the solid line in FIG.
It becomes 0 at the center L ₁ scan.

Here, when the displacement at the position of the light receiving element 33 is set to be the same amount in the same direction as the scanning start point L ₀ ,
The displacement at the scanning start point L ₀ is canceled out to be 0, and is added at the scanning end point L ₂ , as shown by the broken line in FIG. The jitter is as shown by the broken line in FIG. Conversely, if the displacement at the position of the light receiving element 33 is made the same only in the direction opposite to the scanning start point L ₀ , the shift is as shown by the dashed line in FIG. 16 and the jitter is as shown by the dashed line in FIG. Become.

Therefore, if no jitter due to surface tilt is caused in the light receiving element 33, the jitter due to surface tilt becomes as shown by the solid line in FIG. 17, and the maximum value in the scanning area can be minimized.

The jitter is caused not only by the tilting of the rotating polygon mirror 4 described above, but also by the uneven rotation of the motor rotating the rotating polygon mirror 4 and the flatness error of the reflection surface of the rotating polygon mirror 4. And so on. Jitter due to these factors, since the basis of the detection of the light beam c of the light receiving element 33, but the scanning very small in the starting point L ₀ of tends to increase substantially in proportion toward the end point L ₂ of the scanning .

FIG. 18 shows a total of the jitter caused by the tilting and the jitter caused by other factors. As shown in FIG. 17, the lens 3 for detecting a light beam
By appropriately arranging 2 and appropriately selecting the amount of shift generated in the light receiving element 33, it is possible to change the jitter due to surface tilt. Therefore, it is considered that the maximum value of the jitter in the scanning area on the scanned surface 17 is minimized in accordance with the magnitude of the jitter due to factors other than the surface tilt.

[0059] FIG. 18 (a), when a jitter 92 due to factors other than troublesome is small, by the point where the jitter 91 by the surface tilt of 0 on the center L ₁ of approximately scanning, the jitter in the scanning region The maximum value can be minimized. FIG. 18 (b), in the case of the degree jitter 92 are the same due to factors other than are cumbersome and jitter 91 by tilt, the point where the jitter 91 by the surface tilt is 0 and the center L ₁ scan scanning end point L ₂ By setting the interval between the two, the jitter at the starting point and the ending point of the scanning becomes the same value, and the maximum value of the jitter in the scanning area can be minimized. FIG. 18C shows a case where the jitter 92 due to a factor other than the surface tilt is larger than the jitter 91 due to the surface tilt.
By the point where the end point L ₂ of the scanning, it is possible to minimize the maximum value of the jitter in the scan area.

As described above, by setting the point where the jitter due to the surface tilt becomes 0 in the area between the two points including the scanning center L ₁ and the scanning end point L ₂ , the jitter in the scanning area is reduced. The maximum value can be minimized. In addition, when there is unevenness in the rotation of the scanner motor or the surface accuracy error of the reflecting surface, the jitter caused by factors other than surface tilt varies depending on the individual optical scanning devices. by setting in the area between those two points including the center L ₁ and scanning end point L _2, it is possible to reduce the maximum value of the jitter in the scan area.

As described above, the third scanning lens 1
If the amount of eccentricity of 6 is appropriately selected, it is possible to prevent the scanning optical system 23 from causing jitter due to surface tilt. In this case, if the setting is made so that the jitter due to the surface tilt does not occur even at the position of the light receiving element 33, the jitter due to the surface tilt becomes zero in the entire scanning area.

In an actual optical scanning device, the allowable amount of jitter is about 30 μm, and if it is larger than this, the jitter can be visually recognized. Hereinafter, several embodiments of the optical scanning device of the present invention based on the above-described basic embodiment will be described.

(Embodiment 1) In FIG. 1, the horizontal synchronizing signal
The light beam c for generation enters the lens 32 perpendicularly. Les
The bus 34 of the cylindrical surface of the lens 32 is
The light beam is arranged perpendicular to the direction 53
(FIG. 12). Therefore, the light receiving element 33 is troublesome.
This does not cause jitter. The bus bar 34 is connected to the second axis 51
About the first axis in the traveling direction of the light beam c.
Counterclockwise with an inclination of θ = 1.01 °. No.
The three-scan lens 16 is 5.77 in the direction indicated by the arrow in FIG.
mm eccentric. This is the third scanning lens of the basic embodiment
16 incident surfaces S_{twenty five}, Exit surface S ₂₆Corresponds to the inclination of.

In this embodiment, since the light receiving element 33 does not cause jitter due to surface tilt, the jitter due to surface tilt is only generated by the scanning optical system 23. Shows the value of jitter due to surface tilt. In all of the following examples, the trouble
As shown in FIG. 19, the value of the jitter at the time of seconds is 0 at the center of the scanning, increases toward the both ends of the scanning, takes the same value at the both ends of the scanning, and its value is 11 μm.

Since the light beam enters the rotary polygon mirror 4 twice, the first reflection surface 5 and the second reflection surface 6
Of both sides affects. The main cause of the surface tilt is that the center axis of the rotary polygon mirror 4 is inclined with respect to the rotary shaft 41 of the scanner motor due to a manufacturing error when the rotary polygon mirror 4 is fitted to the scanner motor. Therefore, the first reflecting surface 5 and the second reflecting surface 6 facing each other are maintained in parallel,
It is assumed that the camera falls down to the same angle.

(Embodiment 2) The configuration differs from Embodiment 1 in the following points. The generatrix 34 of the cylindrical surface of the lens 32 has an inclination of θ = 0.15 ° counterclockwise with respect to the second axis 51 in the traveling direction of the light beam c around the first axis. I have. The jitter due to surface tilt is as shown in FIG. 20, and jitter due to surface tilt occurs in the light receiving element 33, and the jitter generated in the light receiving element 33 and the jitter generated in the scanning optical system 23 at the end point of scanning are canceled.

(Embodiment 3) The configuration differs from Embodiment 1 in the following points. The generatrix 34 of the cylindrical surface of the lens 32 has an inclination of θ = 0.47 ° counterclockwise around the first axis with respect to the second axis 51 in the traveling direction of the light beam c. . The jitter due to the surface tilt is as shown in FIG.
Zero jitter between the scan center and the scan end point
Becomes

(Embodiment 4) The configuration differs from Embodiment 1 in the following points. As shown in FIG. 22, the arrangement of the lens 32 is as follows.
Around a third axis 52 (an axis substantially perpendicular to the plane of FIG. 22), θ =
As shown in FIG. 23 viewed from the direction of the arrow in FIG. 22, it is eccentric along the third axis 52 by d = 0.38 mm. As described above, even if the lens 32 is tilted around the third axis 52 and is eccentric along the third axis 52, and the inclination angle and the amount of eccentricity are appropriately given, the light receiving element 33 causes the surface to tilt. Jitter can be made sufficiently small. However, it does not become completely zero, and the light receiving element 33
FIG. 24 shows the displacement of the position of the light beam spot. Since the slope of the curve is 0 when the surface tilt is 0 seconds, even if the surface tilt increases, the displacement of the position of the light beam spot is kept small. The jitter due to surface tilting is as shown in FIG. 25, and becomes minimum at the center of scanning but does not become zero. FIG. 26 shows the relationship between the angle of inclination of the lens 32 and the amount of eccentricity so that the positional deviation in FIG.
Shown in

(Embodiment 5) The configuration differs from Embodiment 1 in the following points. The arrangement of the lens 32 is tilted θ = 22.6 ° around the third axis 52 and d = 0.0 along the third axis 52.
It is eccentric by 6 mm. The jitter due to surface tilt is as shown in FIG. 27, and the jitter due to surface tilt becomes minimum at the end point of scanning.

(Embodiment 6) The configuration differs from Embodiment 1 in the following points. As the arrangement of the lens 32, it is inclined θ = 22.6 ° around the third axis 52, and d = 0.1 along the third axis 52.
It is eccentric by 8 mm. The jitter due to surface tilt is as shown in FIG. 28, and the jitter due to surface tilt between the center of scanning and the end point of scanning is minimized.

(Modification) In the above embodiment, the lens 32 is tilted around the first axis, or tilted around the third axis 52,
Either one of them is eccentric along the third axis 52, but these may be combined.

In order to prevent jitter, the tilt angle and the amount of eccentricity vary depending on the optical system. The incident angle of the light beam incident on the rotary polygon mirror 4 in the sub-scanning direction (incident angle of oblique incidence), the light receiving element It depends on the deflection angle when the light beam is detected by 33, the radius of curvature of the lens 32, the optical magnification of the transmission optical system 22 in the sub-scanning direction, the vertex angle of the second scanning lens 15 as a prism, and the like.

The lens 32 is not limited to a cylindrical lens, but may be any optical element having a strong refractive power in one direction, such as an anamorphic lens having a strong refractive power in one direction. In this case, in FIG. 12, in order to prevent the occurrence of jitter at the position of the light receiving element 33, the anamorphic lens 32 must be changed so that the direction of the strong refractive power coincides with the direction 53 in which the light beam c is displaced by the surface tilt. Is tilted about the first axis.

In the above embodiment, the case where a rotary polygon mirror is used as the deflector has been described. However, similar effects can be achieved in the case of a rotary dihedral mirror as well as a rotary polygon mirror. be able to. In addition, the present invention can be applied not only to a device which is reflected twice by the reflecting surface of the rotary polygon mirror but also to an optical scanning device which is incident only once and is reflected and deflected. As described above, the optical scanning device of the present invention has been described based on the embodiments, but the present invention is not limited to these, and various modifications are possible.

[0075]

As is clear from the above description, according to the optical scanning device of the present invention, the point that the jitter due to the tilt of the plurality of reflecting surfaces of the deflector in the sub-scanning direction is minimized is that the surface to be scanned is Since it is set in the area between these two points including the center of the upper scan and the end point of the scan, the maximum value of the total jitter combining the jitter due to the tilt and the jitter due to the factors other than the tilt is calculated. Therefore, the jitter can be reduced in the obliquely incident optical scanning device.

[Brief description of the drawings]

FIG. 1 is a plan view showing the configuration of a basic embodiment of an optical scanning device according to the present invention.

FIG. 2 is a side view of the optical scanning device of FIG.

FIG. 3 is a perspective view of a main part of the optical scanning device of FIG. 1;

FIG. 4 is a side view of a main part of the optical scanning device of FIG.

5 is an optical path diagram of a shaping optical system of the optical scanning device of FIG. 1 in a main scanning direction and a sub scanning direction.

6 is an optical path diagram of a transmission optical system of the optical scanning device of FIG. 1 in a main scanning direction and a sub scanning direction.

7 is an optical path diagram of a scanning optical system of the optical scanning device in FIG. 1 in a main scanning direction and a sub-scanning direction.

FIG. 8 is a sectional development view of a main scanning plane for explaining the operation of the transmission optical system.

FIG. 9 is a diagram for explaining a correcting operation of the refractive prism.

FIG. 10 is a diagram showing a beam trajectory on an incident surface of a third scanning lens according to one embodiment of the present invention.

FIG. 11 is a diagram for explaining the reason why field curvature does not occur in one specific example of the present invention.

FIG. 12 is a diagram illustrating a lens of a light beam detection unit according to a basic example in a traveling direction of a light beam.

FIG. 13 is a diagram for explaining the reason why jitter occurs on the light receiving element due to the arrangement of lenses.

FIG. 14 is a diagram showing a trajectory of a deflected light beam before it is incident on a scanning optical system in a traveling direction of the light beam.

FIG. 15 is a diagram illustrating a state in which a light beam is displaced in the main scanning direction due to surface tilt in the basic embodiment.

FIG. 16 is a diagram showing a shift of a light beam spot generated in the scanning optical system when there is a surface tilt.

FIG. 17 is a diagram illustrating jitter in the case of FIG. 16;

FIG. 18 is a diagram showing a total jitter including a jitter due to surface tilt and a jitter due to other factors.

FIG. 19 is a diagram showing the value of jitter when the tilting is 100 seconds in the basic example.

FIG. 20 is a diagram illustrating a state of jitter due to surface tilt in the second embodiment.

FIG. 21 is a diagram illustrating a state of jitter due to surface tilt in the third embodiment.

FIG. 22 is a view similar to FIG. 1, illustrating the arrangement of lenses in Example 4.

FIG. 23 is a view as seen from the direction of the arrow in FIG. 22;

FIG. 24 is a diagram illustrating a shift in the position of a light beam spot on a light receiving element due to surface tilt in the fourth embodiment.

FIG. 25 is a diagram illustrating a state of jitter due to surface tilt in the fourth embodiment.

FIG. 26 is a diagram illustrating the relationship between the angle of inclination of a lens and the amount of eccentricity in the arrangement of lenses according to a fourth embodiment.

FIG. 27 is a diagram illustrating a state of jitter due to surface tilt in the fifth embodiment.

FIG. 28 is a diagram illustrating a state of jitter due to surface tilt in the sixth embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser (light source) 2 ... 1st shaping lens 3 ... 2nd shaping lens 4 ... Rotation polygon mirror 5 ... 1st reflection surface of rotation polygon mirror 6 ... 2nd reflection surface of rotation polygon mirror 7 ... 1st transmission lens 8 second transmission lens 9 third transmission lens 10 first transmission mirror 11 fourth transmission lens 12 fifth transmission lens (rear group of transmission optical system) 13 second transmission mirror 14 first scanning lens 15 Second scanning lens (prism) 16 Third scanning lens (long lens) 17 Scanned surface 21 Shaping optical system 22 Transmission optical system 23 Scanning optical system 30 Main scanning (horizontal) synchronization signal generation Light beam detector for use 31 Mirror 32 Lens 33 Light receiving element 41 Rotating axis of rotary polygon mirror 51 Second axis 52 Third axis 53 Direction in which light beam is displaced due to surface tilt 61 Aperture 91 … Jick by trouble 92 ... center L ₂ ... the end point of the scanning start point L ₁ ... scan jitter L ₀ ... scanning due to factors other than being cumbersome

Claims (8)

[Claims] 1. A deflector having a light source for generating a light beam, a plurality of reflecting surfaces for reflecting and deflecting a light beam incident from the light source at an angle in a sub-scanning direction, and reflecting light by the reflecting surface of the deflector. A scanning optical system that scans the deflected light beam by forming a beam spot on the surface to be scanned, and detects the light beam reflected and deflected by the reflection surface of the deflector before scanning on the surface to be scanned. A light receiving element that generates a synchronization signal in the optical scanning device, wherein a point at which jitter due to surface tilt of the plurality of reflecting surfaces of the deflector in the sub-scanning direction is minimized is a center of scanning on the surface to be scanned. And an optical scanning device, wherein the optical scanning device is set in an area between the two points including the scanning end point. 2. The optical scanning device according to claim 1, wherein a lens for guiding a light beam to the light receiving element is arranged so as to minimize jitter due to the surface tilt on the light receiving element. . 3. A lens that guides a light beam to the light receiving element is an anamorphic lens, and is disposed such that a direction in which the refractive power is strong and a direction in which the light beam is displaced due to the surface tilt substantially coincide with each other. 3. The method according to claim 1, wherein
The optical scanning device according to claim 1. 4. A lens for guiding a light beam to the light receiving element is an anamorphic lens, and a principal ray of the light beam incident on the lens at a moment when the light beam is detected by the light receiving element is defined as a first axis. When an axis in a plane swept by the light beam and perpendicular to the first axis is a second axis, and an axis perpendicular to the first axis and the second axis is a third axis, 4. The optical scanning device according to claim 1, wherein the lens is tilted around a first axis. 5. The direction in which the refractive power of the lens is strong is the third direction.
The optical scanning device according to claim 4, wherein the optical scanning device is tilted around the first axis so as to form an angle with the axis. 6. A lens for guiding a light beam to the light receiving element is an anamorphic lens, and a principal axis of the light beam incident on the lens at a moment when the light beam is detected by the light receiving element is defined as a first axis. When an axis in a plane swept by the light beam and perpendicular to the first axis is a second axis, and an axis perpendicular to the first axis and the second axis is a third axis, 4. The optical scanning device according to claim 1, wherein the lens is tilted around a third axis and is decentered along the third axis. 7. The optical scanning device according to claim 1, wherein the light source and the light receiving element are arranged substantially conjugate in a main scanning direction. 8. The deflector comprises a rotary polygon mirror, and has a transmission optical system for transmitting a light beam reflected and deflected by a first reflection surface of the rotary polygon mirror to a second reflection surface of the rotary polygon mirror. 8. The scanning optical system according to claim 1, wherein the light beam reflected and deflected by the second reflecting surface is scanned by forming a beam spot on the surface to be scanned by the scanning optical system. The optical scanning device according to claim 1.