JPH11242174A - Optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical scanner which resolves a difference in level of beam diameters in a joint even at the time of adopting a split scan system of an over field optical system. SOLUTION: A generating line M of a cylindrical lens 22 constituting at least one first optical system is rotated at a prescribed angle to an optical axis L to resolve the difference in level of beam diameters in a joint. For example, the generating line M of the cylindrical lens 22 where the angle of incidence in the subscanning direction is larger is rotated so as to be inclined at an ideal angle (this is such angle that the beam diameter in the main scanning direction is mainly reduced as the whole), and then, beam diameters in both of the main scanning direction and the subscanning direction in the joint are reduced to reduce the difference in level from the beam whose angle of incidence in the subscanning direction is smaller.

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 an image recording apparatus for recording an image by scanning and exposing a laser beam on a photosensitive member according to image information.

[0002]

2. Description of the Related Art The applicant of the present invention has responded to the demand for higher speed and higher resolution of an image processing apparatus, and has also been required to obtain a wide scanning width without increasing the focal length (optical path length). An optical scanning device employing an optical system (overfilled) division scanning method has been proposed (Japanese Patent Application No. 8-338636).
issue).

[0003] As shown in Fig. 7, the basic structure of the light source device includes two light source units 40A and 40B, two first optical systems 42A and 42B provided for each light source unit, and a laser beam modulated by an image signal. And a polygon mirror 12 (rotating polygon mirror) which repeatedly deflects the image signal for each line of the image signal, makes the deflected laser beam substantially uniform at the photoconductor 46 (scanning surface), and One imaging optical system 48 for converging a laser beam near 46 is provided.

When the scanning angle to be deflected is ± 2α, the angle of incidence on the same reflecting surface of the polygon mirror 12 is defined with respect to a center line CL connecting the center of rotation of the polygon mirror 12 and the center of the photosensitive member 46. Each in the main scanning direction
α, + α, and the rotation angle of the polygon mirror 12 is
If α (± α / 2) is the same as the incident angle of the two laser beams and n is the number of surfaces of the polygon mirror 12, α is 3
The configuration is such that 60 ° × 0.6 / n <α <360 ° / n.

[0005] The two laser beams have a range from a laser beam A shown by a dotted line at a scanning angle of -2α,
The laser beam B indicated by the solid line simultaneously scans the range from the scanning angle of + 2α.

As a result, a phenomenon that occurs when divided scanning is performed by an overfilled optical system, that is, FNo
(F number, the "brightness" in the camera) is suppressed from a phenomenon in which the uniformity of the beam diameter on the photoconductor 46 is deteriorated.

However, as shown in FIG. 8, when an overfilled optical system is adopted, the incident light beam width (Do) of the laser beam is larger than the surface width of the polygon mirror 12, so that
Adjacent surface a (rotation start side) in front of reflection surface b and adjacent surface c after
The beam incident on the (rotation end side) is also reflected, and unnecessary light N
Will be.

[0008] As shown in FIG. 7, unnecessary light N _A is, scans the range of from at the same time to scan the range of the laser beam A is unnecessary light N _B is, when scanning a range of the laser beam B At the same time, the range is scanned and double writing is performed.

In order to avoid double writing due to this unnecessary light, as shown in FIGS. 9 and 10, a polygon mirror is used so that the two laser beams A and B are incident at different angles β1 and β2 in the sub-scanning direction. An optical scanning device in which the laser beam is incident on the laser beam 12 and reflection mirrors 50A and 50B are provided for each laser beam has been proposed (see Japanese Patent Application No. 9-014139).

With this configuration, the laser beams deflected by the polygon mirror 12 are emitted at different angles in the sub-scanning direction. At the positions where the reflection mirrors 50A and 50B are arranged, both laser beams are sufficiently separated in the sub-scanning direction. , unnecessary light N _a, N _B is not to be reflected by the other reflecting mirror.

That is, the unnecessary light N of the laser beam A
_A (indicated by a thin dotted line) does not hit the reflecting mirror 50B that reflects the laser beam B and is not reflected.
Since nor even unnecessary light N _B of the laser beam B is reflected by the reflecting mirror 50A, it is possible to avoid the double writing.

However, the two laser beams A and B are directed to a plane orthogonal to the rotation axis of the polygon mirror 12.
Is incident on the polygon mirror 12 such that the incident angles β1 and β2 in the sub-scanning direction are different from each other, the state of the beam diameter on the photoconductor 46 changes including uniformity.

Specifically, the incident angles β1 and β2 in the sub-scanning direction with respect to the fθ lens 48 are two laser beams A,
Since the beam diameter differs between B and B, the beam diameter on the scanning surface changes in characteristics from the beginning to the end, and a step occurs in the beam diameter between the beginning and the end.

Here, how much a step difference occurs in the beam diameter will be described with reference to specific figures with reference to FIGS.

The incident angle β1 of the beam A in the sub-scanning direction =
1.2 °, incident angle β1 of beam A in the sub-scanning direction = 2.
7 °, the number of faces of the polygon mirror 12 is n = 24, the diameter of the polygon mirror is Φ = 46 mm, the wavelength λ of the semiconductor laser as the light source is 780 nm, and the fθ lenses 48A and 48B
Is as follows.

The distance between the polygon mirror 12 and the fθ lens 48A is 18.5 mm, and the radius of curvature (only in the main scanning direction) of the surface of the fθ lens 48A on the polygon mirror 12 side is 170.
43 mm, the surface of the fθ lens 48A farther from the polygon mirror 12 is flat, and the thickness of the fθ lens 48A is 9 mm.
The refractive index of the fθ lens 48A is 1.609110, and the distance between the fθ lens 48A and the fθ lens 28 is 25.998 m.
m, the surface of the fθ lens 48B on the polygon mirror 12 side is Δ, the radius of curvature of the surface of the fθ lens 48B farther from the polygon mirror 12 is 122.67 mm, and the fθ lens 48B
Is 10 mm, and the refractive index of the fθ lens 48B is 1.7.
12268.

Next, the distance from the surface of the fθ lens 48B farther from the polygon mirror 12 to the reflection mirror 50 (cylindrical mirror) is set as follows.
The beam B is 271 mm, the incident / emission angle of the reflecting mirror 50 is 62 °, the beam A is 65.6 °, the distance from the reflecting mirror 50 to the photoconductor 46 is 9 mm.
Assuming that the beam B is 6.2 mm and the beam B is 101.3 mm, the beam diameter in the main scanning direction / sub-scanning direction is 68 μm / 59 μm at the position as shown in FIGS.
103 μm / 1 at the position of 1.5 μm / 68.5 μm
70 μm / 65 μm at the position of 05 μm.

As described above, a large step is formed in the beam diameter in the case of (1), which has a serious adverse effect on the image quality. (Generally, if there is a discontinuous step in the beam diameter, a streak is drawn on the portion. Will be).

[0019]

In consideration of the above facts, the present invention can prevent double writing due to unnecessary light even if the division scanning method of the overfilled optical system is employed, and can prevent the central portion (seam) of scanning. It is an object of the present invention to provide an optical scanning device which can eliminate the step of the beam diameter.

[0020]

According to the first aspect of the present invention, two beams are applied from the two first optical systems provided for each light source to the same reflecting surface of the rotary polygon mirror in the main scanning direction and the sub-scanning direction. At different angles.

Then, while the rotary polygon mirror rotates, the two beams are each deflected in the main scanning direction within a predetermined angle range. The beam deflected in the main scanning direction is individually reflected by two reflecting mirrors through a single imaging optical system, and scans one line of the surface to be scanned in two.

Since these two beams are sufficiently separated in the sub-scanning direction at the position of the reflecting mirror, unnecessary light is not reflected by the other reflecting mirror, and as a result, double writing can be avoided.

Further, by rotating the generating line of the cylindrical lens constituting at least one of the first optical systems by a predetermined angle with respect to the optical axis, the step of the beam diameter at the joint can be eliminated.

According to the second aspect of the present invention, the predetermined angle is an ideal angle. For example, with respect to the optical axis, the generatrix of the cylindrical lens having the larger incident angle in the sub-scanning direction becomes an ideal angle (an angle at which the beam diameter in the main scanning direction becomes smaller as a whole). By rotating, the beam diameter at the joint becomes smaller in both the main scanning direction and the sub-scanning direction, and the step difference from the beam having the smaller incident angle in the sub-scanning direction can be reduced.

According to the third aspect of the invention, the predetermined angle is different from the ideal angle. As described above, by rotating the generating line of the cylindrical lens, the beam diameter at the joint can be further reduced in both the main scanning direction and the sub-scanning direction to eliminate a step.

By making the angle different from the ideal angle, the beam diameter on the side opposite to the seam of the scanning lines (on the scanning start side or on the scanning end side) becomes large. It is possible to adjust to a level without problems.

According to the fourth aspect of the invention, the slits constituting the first optical system have different opening widths in the sub-scanning direction.

If the generatrix of the cylindrical lens is rotated as in the first to third aspects of the present invention, it is possible to eliminate a step in the beam diameter in the main scanning direction at the joint. However, since the movement of the beam diameter in the sub-scanning direction is independent, the step may not be so small depending on the degree of adjustment.

Therefore, by changing the opening width of one of the slits in the sub-scanning direction, a step in the beam diameter can be eliminated in the sub-scanning direction. Utilizing the phenomenon that the beam diameter becomes smaller).

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, an optical scanning device 10 according to the present embodiment has a center line CL connecting a rotation center of a polygon mirror 12 and a scanning center position of a photosensitive member 14 with respect to a center line CL.
The two light source units 16A and 16B are symmetrically arranged.
The light source units 16A and 16B are composed of semiconductor lasers that emit a laser beam having a substantially Gaussian distribution.

Hereinafter, the laser beam emitted from the light source 16A is distinguished from the beam A (indicated by a broken line), and the laser beam emitted from the light source 16B is distinguished from the beam B (indicated by a solid line). Then, as shown in FIG.
The beam A is directed to the reflection surface 12 a of the polygon mirror 12 with respect to a plane H orthogonal to the rotation axis M of the polygon mirror 12.
At an incident angle of 2 °, the light source unit 16B transmits the beam B to the reflecting surface 12a of the polygon mirror 12 at 2.7 ° with respect to the plane H.
At an angle of incidence.

On the other hand, beams emitted from the light source sections 16A and 16B and having different divergent angles in the vertical and horizontal directions are made substantially collimated by the collimator lenses 18A and 18B, but the collimator lenses 18A and 18B and the light source sections 16A and 16B Is about 1 mm smaller than the focal length of the collimator lenses 18A and 18B.
The beams that have passed through A and 18B become loosely divergent light.

Immediately thereafter, the slit 20 for beam shaping is used.
A, 20B allows only the center of the divergent light to pass through,
The light converges in the sub-scanning direction near the reflecting surface of the polygon mirror 12 by the cylindrical lenses 22A and 22B.

The beams passing through the cylindrical lenses 22A and 22B are reflected by reflection mirrors 24A and 24B symmetrically arranged with respect to the center line CL. Reflection mirror 2
4A shows the beam A at an incident angle of + α (12.8 °) in the main scanning direction and 1.2 ° in the sub-scanning direction with respect to the center line CL, and the reflecting mirror 24B shows the beam B with the center line. C
L at an incident angle of -α (-12.8 °) in the main scanning direction and 2.7 ° in the sub-scanning direction,
To the same reflection surface.

Between the reflecting mirrors 24A and 24B and the polygon mirror 12, there is a power source 2 having power only in the main scanning direction.
A set of fθ lenses 26 and 28 is provided.
Beams A and B passing through θ lenses 26 and 28 are
The light enters as substantially parallel light (Do) wider than the surface width of the polygon mirror 12 (see FIG. 8).

The beams A and B deflected by the polygon mirror 12 pass through the fθ lenses 26 and 28 again. The beam A is reflected by the cylindrical mirror 30A, and the beam B is reflected by the cylindrical mirror 30B.
Image on 4.

The cylindrical mirrors 30A and 30B
Corrects a scan position shift (called a surface tilt error) caused by a variation in the inclination of each reflection surface of the polygon mirror 12 in the sub-scanning direction.

On the other hand, due to the action of the fθ lenses 26 and 28, the spot of the beam generated on the photoconductor 14 due to the image formation is such that the spot of the beam A goes from the surface of the photoconductor 14 to the spot of the beam B, The surface of the photoconductor 14 is divided and scanned at a substantially constant speed in the main scanning direction from the surface.

When scanning of one line is performed in this manner, the beams A and B are deflected by the next reflection surface of the polygon mirror 12, and scanning of the next line is performed.

Then, in order to set a write start position where image recording is performed on these lines, the SOS (St) is set on the path of the beam A passing through the fθ lenses 26 and 28.
(ArtOfScan) 32 is provided. This SO
S32 is connected to the control unit, and the control unit executes SOS3
After a lapse of a predetermined time from the time when the output signal of No. 2 is detected,
The modulation of the image signal is started.

The beam B is the SOS 32 of the beam A.
At the point in time when a predetermined time elapses in synchronization with the output signal, the modulation of the image signal is started, and at the same time, the beam A scans in the forward direction and simultaneously performs the divided scanning in the backward direction.

Next, the operation of the optical scanning device according to this embodiment will be described. As shown in FIG. 1, the beam A and the beam B have an angle range of ± 2α with respect to a center line CL passing through the scanning center position.
The light is incident on the polygon mirror 12 so as to form an angle ± α of （of the (scan angle).

Further, the scanning angle of the polygon mirror 12 (the angle at which the polygon mirror 12 rotates while the beam scans within the range of the scanning angle ± 2α) is the same as the incident angle of the beams A and B (α / 2). That is, while the polygon mirror 12 rotates by the angle α, the scanning is performed from the incident beam A to the incident beam B.

In this embodiment, the incident angle in the sub-scanning direction is set to 1.2 ° for the beam A and 2.7 ° for the beam B. Hardly deteriorates. However, the cylindrical mirror 30A is cylindrical mirror 30B unnecessary light N _A
To avoid the double writing reflects unnecessary light N _B,
When mounting a cylindrical mirror, beam A
Therefore, it is necessary to determine the incident angle in the sub-scanning direction in consideration of two conditions.

Next, the step of the beam diameter at the joint will be described with reference to specific figures. The number n of surfaces of the polygon mirror 12 is 24, the incident angle = scanning angle / 2 = α = 12.8.
°, incident angle of beam A in the sub-scanning direction of 1.2 °, beam B
Angle of incidence in the sub-scanning direction of 2.7 °, diameter of polygon mirror 12 = 46 mm, wavelength input of semiconductor laser as light source = 7
80 mm and the fθ lenses 26 and 28 are as follows.

The distance between the polygon mirror 12 and the fθ lens 26 is 18.5 mm, and the polygon mirror 1 of the fθ lens 26 is
The radius of curvature of the surface on the second side (only in the main scanning direction) is 170.43
mm, the surface of the fθ lens 26 remote from the polygon mirror 12 is flat, the thickness of the fθ lens 26 is 9 mm, the refractive index of the fθ lens 26 is 1.609110, and the distance between the fθ lens 26 and the fθ lens 28 is 25.998 mm. , Fθ lens 28 at the polygon mirror 12 side
The radius of curvature of the surface farther from the polygon mirror 12 is 12
2.67 mm, thickness of fθ lens 28 is 10 mm, fθ
The refractive index of the lens 28 is 1.712268.

The polygon mirror 1 of the fθ lens 26
The distance from the cylindrical mirror on the side farther from 2 to the cylindrical mirror was 276.8 mm for beam A / 271 mm for beam B, the incident / exit angle of the cylindrical mirror was 62 ° /
The beam B is 65.6 °, the distance from the cylindrical mirror to the photoconductor, the beam A is 96.2 mm / the beam B is 101.3 mm, and the opening width N of the slit in the sub-scanning direction is 1. 8 mm.

Under the above conditions, as shown in FIG.
The rotation angle θ of the generating line M of the cylindrical lens 22 with respect to the optical axis L is an ideal angle (0.5 ° for the beam A and 1.0 ° for the beam B) with respect to the initial set position of the cylindrical lens 22.

As a result, as shown in FIGS. 4 and 5,
The beam diameter at the joint is such that the beam A is 62 μm in the main scanning direction.
m: 59 μm in the sub-scanning direction, the beam B is 68 μm in the main scanning direction
m: 70 μm in the sub-scanning direction, and the step is reduced.

The rotation angle θ of the generatrix M of the cylindrical lens 22 with respect to the optical axis L is different from the ideal angle with respect to the initial set position of the cylindrical lens 22 (the beam A is 0.2 ° and the beam B is 1 °). .1 °).

As a result, the beam diameter at the joint is as follows: beam A is 65 μm in the main scanning direction: 64 μm in the sub-scanning direction, and beam B is 65 μm in the main scanning direction: 66.5 μm in the sub-scanning direction.
The step in the main scanning direction is eliminated, and the step in the sub-scanning direction is further reduced.

As described above, by rotating the bus M,
The step of the beam diameter at the joint can be eliminated.
Therefore, two first optical systems (cylindrical lens,
(A collimator lens and a slit) can be constituted by a common member.

Here, if the opening width N of the slit 20A on the beam A side in the sub-scanning direction is changed to 1.7 mm, the beam diameter at the joint becomes 65 μm (in the main scanning direction) as shown in FIG. (See FIG. 5): 66.5 μ in the sub-scanning direction
m and the beam B are 65 μm in the main scanning direction (see FIG. 5): 66.5 μm in the sub-scanning direction, and a step between the main scanning direction and the sub-scanning direction can be eliminated.

It is a matter of course that the step can also be eliminated by increasing the opening width of the slit 20B on the beam B side in the sub-scanning direction.

[0055]

According to the present invention, the overfilled optical system is employed in the present invention to increase the speed and resolution of the apparatus without increasing the diameter of the polygon mirror. , And by adopting the split scanning method,
A wide scanning width can be ensured without increasing the focal length (optical path length).

In addition to this, the problem of double writing can be solved, and furthermore, the step of the beam diameter at the joint of two beams can be solved.

According to the second aspect of the present invention, by setting the rotation angle of the cylindrical lens to an ideal angle, a step with a beam having a smaller incident angle in the sub-scanning direction can be reduced.

According to the third aspect of the invention, by setting the rotation angle of the cylindrical lens to an angle different from the ideal angle, the beam diameter at the joint can be further reduced in both the main scanning direction and the sub-scanning direction to eliminate a step. Can be.

According to the fourth aspect of the present invention, by changing the opening width of the slit, a step in the beam diameter in the sub-scanning direction can be eliminated.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical scanning device according to an embodiment of the present invention.

FIG. 2 is a schematic side view of an optical scanning device according to an embodiment of the present invention.

FIG. 3 is a perspective view showing a first optical system of the optical scanning device according to the embodiment of the present invention.

FIG. 4 is a graph showing how a beam diameter changes in the sub-scanning direction.

FIG. 5 is a graph showing how the beam diameter changes in the main scanning direction.

FIG. 6 is a graph showing a relationship between an opening width of a slit and a beam diameter.

FIG. 7 is a configuration diagram of a conventional optical scanning device.

FIG. 8 is a conceptual diagram illustrating unnecessary light.

FIG. 9 is a schematic side view of another conventional optical scanning device.

FIG. 10 is a schematic plan view of another conventional optical scanning device.

FIG. 11 is a plan view showing beams entering and exiting a polygon mirror.

FIG. 12 is a side view showing beams entering and exiting a polygon mirror.

[Explanation of symbols]

 12 polygon mirror (rotating polygon mirror) 16A light source (first optical system) 16B light source (first optical system) 18A slit (first optical system) 18B slit (first optical system) 22A cylindrical lens (first optical system) 22B Cylindrical lens (first optical system) 30A Cylindrical mirror (reflection mirror) 30B Cylindrical mirror (reflection mirror) M Bus bar

Claims (4)

[Claims] 1. Two light sources, two first optical systems provided for each light source, and two beams incident from the first optical system at different angles in the main scanning direction and the sub-scanning direction are the same. A rotating polygon mirror that deflects on the reflecting surface, and two reflecting mirrors that individually reflect the two beams deflected by the rotating polygon mirror through a single imaging optical system and divide and scan the surface to be scanned. An optical scanning device comprising: an optical scanning device, wherein at least one of the cylindrical lenses constituting the optical system is arranged in a state where its generating line is rotated by a predetermined angle with respect to an optical axis. 2. The optical scanning device according to claim 1, wherein the predetermined angle is an ideal angle. 3. The optical scanning device according to claim 1, wherein the predetermined angle is different from an ideal angle. 4. The optical scanning device according to claim 1, wherein the slits constituting the first optical system have different opening widths in the sub-scanning direction.