JP2001033722A - Optical scanning optical system and image forming device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make an optical scanning optical system compact by arranging a position where luminous flux for detecting a wiring start position passes through a scanning lens system and the position of a light source on opposite sides with respect to the optical axis of an image-formation optical system and making a part of optical devices constituting the scanning lens system have asymmetric shape with respect to the optical axis of the image-formation optical system in a main scanning direction. SOLUTION: The position where the BD luminous flux 14 passes through the scanning lens system 23 and the position of a semiconductor laser 1 are arranged on the opposite sides with respect to the optical axis M of the image-formation optical system 22. The 2nd scanning lens 8 is formed so that its shape may be asymmetric with respect to the optical axis M of the optical system 22 in the main scanning direction so as to prevent the luminous flux of an incident optical system 21 from interfering in the lens 8 even when it is transmitted near the lens 8 and to make a reflecting angle α by a reflecting mirror 6 small. Namely, the shape of the lens 8 is made asymmetric with respect to the optical axis M so that length (a) from the optical axis M to the end of the lens 8 on a side where the BD luminous flux 14 passes may be longer than length (b) from the optical axis M to the end of the lens 8 on a side where the luminous flux at the time of finishing writing scanning passes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning optical system and an image forming apparatus using the same, and more particularly, to a light beam emitted from a light source means being incident on a deflection surface from substantially the center of the deflection angle of an optical deflector (front incidence). ), And after deflecting on the deflecting surface, optically scans the surface to be scanned through a scanning lens system having fθ characteristics to record image information. For example, a laser beam printer having an electrophotographic process ( It is suitable for an image forming apparatus such as an LBP) or a digital copying machine.

[0002]

2. Description of the Related Art Conventionally, in an optical scanning optical system used in an image forming apparatus such as a laser beam printer or a digital copying machine, a light beam modulated and emitted from a light source means in accordance with an image signal is output to, for example, a rotating polygon mirror (polygon). mirror)
The light is periodically deflected by an optical deflector made of light, focused by an imaging optical system (scanning lens system) having fθ characteristics into a spot on a photosensitive recording medium (photosensitive drum) surface, and optically scanned on the surface. Image recording.

In recent years, in order to reduce the size of the optical scanning optical system, an optical scanning optical system of a system in which a light beam emitted from a light source means is incident on the deflection surface from substantially the center of the deflection angle of the optical deflector (front incidence). Various proposals have been made.

FIG. 4 is a schematic view of a main part of an optical scanning optical system proposed in, for example, JP-A-8-122676. In the figure, a light beam (laser light) emitted from the light source 41 in the main scanning direction substantially parallel to the bottom surface of the casing is converted into a substantially parallel light beam by a collimator lens 42, and a cylindrical lens 43 having power only in the sub-scanning direction; The light enters a light deflector (polygon mirror) 45 via a mirror 44. The first separation angle θ1 in the sub-scanning direction by the optical deflector 45
The light flux reflected and deflected by the mirror is turned back to the optical deflector 45 side by the curved mirror 46 in the sub-scanning direction at the second separation angle θ2, and passes through the anamorphic lens 47 mainly having power in the sub-scanning direction. The light beam transmitted through the anamorphic lens 47 is reflected by the optical path refracting mirror 48 to form a spot on the photosensitive drum surface 49 for scanning in the main scanning direction which is the generatrix direction of the photosensitive drum. The light flux forms an image once in the sub-scanning direction near the deflection surface of the optical deflector 45 by the cylindrical lens 43,
The image is re-formed on the photosensitive drum surface 49 mainly by the power of the anamorphic lens 47.

In FIG. 1, a light beam emitted from the light source 41 is emitted between the curved mirror 46 and the optical deflector 45 in the main scanning direction because a curved mirror 46 is used instead of the scanning lens. It is configured to be bent at 90 ° by the plane mirror 44.

On the other hand, an optical scanning optical system having a configuration using a scanning lens has been proposed in, for example, JP-A-9-96773. FIG. 5 is a schematic view of a main part of an optical scanning optical system proposed in the publication. FIG. 1 shows a general example of the configuration of an optical system for front incidence (on-axis incidence) using a scanning lens.

In FIG. 1, a light beam emitted from a light source 51 is converted into a substantially parallel light beam by a collimator lens 52, and the light beam is restricted by an aperture stop 53 before being incident on a cylindrical lens 54. Here, of the substantially parallel light beams incident on the cylindrical lens 54, in the sub-scanning cross section, the light beams converge and pass through the second and first scanning lenses 57 and 56 via the return mirror 55, and are deflected by an optical deflector (polygon). (Mirror) 58 is incident on the deflecting surface 58a, and is substantially a line image (a line image elongated in the main scanning direction) near the deflecting surface 58a.
As an image. At this time, the light beam incident on the deflecting surface 58a is a plane perpendicular to the rotation axis of the optical deflector 58 (of the optical deflector) in the sub-scanning section including the rotation axis of the optical deflector 58 and the optical axis of the scanning lens system. (A rotation plane) from an oblique direction.

On the other hand, in the main scanning section, the light beam passes through the second and first scanning lenses 57 and 56 via the turning mirror 55 in a state as it is, and is deflected from substantially the center of the deflection angle of the optical deflector 58. The light is incident on the surface 58a (front incidence).

The light beam deflected by the deflecting surface 58a of the light deflector 58 is guided to the photosensitive drum surface 61 via the first and second scanning lenses 57 and 56 and the return mirror 59 and the cylindrical mirror 60. And the optical deflector 58
Is rotated in the direction of arrow A, thereby optically scanning the photosensitive drum surface 61 in the direction of arrow B (main scanning direction). Thus, an image is recorded on the photosensitive drum surface 61 as a recording medium.

At this time, before optical scanning on the photosensitive drum surface 61, a BD light beam (write start) which is a part of the light beam deflected by the optical deflector to adjust the timing of the scanning start position on the photosensitive drum surface 61 is adjusted. The position detecting light flux 62 is reflected by a BD mirror (synchronous detection mirror) 63 and guided to a BD sensor (photodetector) 64. The timing of the scanning start position of the image recording on the photosensitive drum surface 61 is adjusted using the BD signal (synchronization signal) obtained by detecting the output signal from the BD sensor 64.

Since the photodetector 64 in FIG. 1 can be arranged on the light source 61 side, it is easy to put together the wiring of the photodetector and the light source and the substrate circuit, and since it is not necessary to route the wiring unnecessarily, it is excellent in noise and response characteristics. There are advantages such as.

[0012]

In the conventional optical scanning optical system (Japanese Patent Laid-Open No. 8-122676), the light beam emitted from the light source 41 is directed in the main scanning direction.
The light is deflected by 0 ° and is incident on the optical deflector 45. Further, the angle of separation in the sub-scanning direction is configured by inclining the reflection surface of the optical deflector 45.
The luminous flux towards 5 must be parallel to the casing bottom. When a light beam from the light source 41 toward the plane mirror 44 or a light beam from the plane mirror 44 to the light deflector 45 is angled with the bottom surface, a long focal line formed in the vicinity of the light deflector 45 in the main scanning direction is moved with respect to the bottom surface. There is a problem that the image forming performance due to the inclination and the curved mirror 46 or the cylindrical mirror 48 is remarkably deteriorated. Since the occurrence of angular errors due to assembly tolerances and component tolerances is unavoidable, it is desirable to minimize the sensitivity of tilting the focal line, and it is necessary to configure the plane mirror 44 to be bent as acutely as possible.

On the other hand, in a conventional configuration using a scanning lens (Japanese Patent Application Laid-Open No. 9-96773), the light source 51 and the light beam 62 for detecting the writing start position are located on opposite sides of the optical axis of the scanning lens system 71. 5 can be read from FIG. 5, but there is no description of the shape of the scanning lens and the positional relationship with respect to the components of the incident system, particularly the positional relationship between the light source 51 and the folding mirror 55 and the optical deflector 58, and the folding angle of the folding mirror 55. There is no disclosure of a compact configuration or its effect.

An object of the present invention is to provide an optical scanning optical system capable of reducing the size of the entire apparatus by appropriately setting each element constituting the optical scanning optical system, and an image forming apparatus using the optical scanning optical system. I do.

[0015]

According to a first aspect of the present invention, there is provided an optical scanning optical system comprising: a light beam emitted from a light source unit including light source means; From the center to the deflection surface of the optical deflector,
A light beam deflected by the optical deflector is imaged on a surface to be scanned by an image forming optical system including a scanning lens system, and the light deflector is used in an optical scanning optical system for optically scanning the surface to be scanned. A part of the deflected light flux is passed through the scanning lens system as a light flux for writing start position detection, guided to writing start position detection means, and scanned on the surface to be scanned using an output from the writing start position detection means. Control means for controlling the timing of the start position, wherein the position at which the light beam for writing start position detection passes through the scanning lens system and the position of the light source means are mutually relative to the optical axis of the imaging optical system; At least a part of the optical elements which are arranged on the opposite side and constitute the scanning lens system are characterized by being formed in an asymmetric shape with respect to the optical axis of the imaging optical system in the main scanning direction.

According to a second aspect of the present invention, in the first aspect of the present invention, a distance from the light source means to the return mirror is shorter than a distance from the return mirror to a deflection surface of the optical deflector.

According to a third aspect of the present invention, in the first aspect, an angle at which the light beam emitted from the light source unit is turned back toward the optical deflector by the turning mirror is less than 45 °.

According to a fourth aspect of the present invention, in the first aspect of the present invention, a line segment from the reflection point of the return mirror to an end located at the farthest position of the light source unit, and the light deflection from the reflection point of the return mirror. The distance when projecting the line segment to the end located at the farthest position on the sub-scanning section is L
When 1, L2, the condition of L1 <L2 is satisfied.

According to a fifth aspect of the present invention, in the first aspect of the present invention, the light flux for detecting the writing start position is １ ／ of the scanning field angle.
It is characterized by passing through a larger range.

According to a sixth aspect of the present invention, in the first aspect, the scanning lens system also forms a part of the incident optical system.

According to a seventh aspect of the present invention, in the first aspect, the light beam emitted from the incident optical system is obliquely incident on the deflection surface of the optical deflector in the sub-scan section.

According to an eighth aspect of the present invention, there is provided an image forming apparatus for forming an image using the optical scanning optical system according to any one of the first to seventh aspects.

According to a ninth aspect of the present invention, in the optical scanning optical system, the light beam emitted from the light source means is made to enter the deflection surface of the optical deflector from substantially the center of the deflection angle of the optical deflector via the folding mirror.
A light beam deflected by the light deflector is imaged on a surface to be scanned by an image forming optical system, and in a light scanning optical system for optically scanning the surface to be scanned, a distance from the light source means to the turning mirror; Is characterized by being shorter than the distance from the folding mirror to the deflection surface of the optical deflector.

According to a tenth aspect of the present invention, in the optical scanning optical system, the light beam emitted from the light source means is made to enter the deflection surface of the optical deflector from the approximate center of the deflection angle of the optical deflector via the turning mirror. The light beam deflected by the deflector is imaged on the surface to be scanned by the imaging optical system, and the light beam emitted from the light source means is reflected by the folding mirror in the optical scanning optical system for optically scanning the surface to be scanned. The turning angle is less than 45 °.

According to an eleventh aspect of the present invention, in the optical scanning optical system, the light beam emitted from the light source unit including the light source means is incident on the deflection surface of the optical deflector from the approximate center of the deflection angle of the optical deflector via the return mirror. Then, the light beam deflected by the optical deflector is imaged on the surface to be scanned by the imaging optical system, and the light is scanned on the surface to be scanned. The distance between the line segment from the reflection point of the folding mirror to the end portion at the farthest position of the optical deflector and the line segment to the farthest end of the light source unit is projected on the sub-scan section. When L1 and L2 are respectively set in order, L1 <L
It is characterized by satisfying the following two conditions.

An image forming apparatus according to a twelfth aspect of the present invention is characterized in that an image is formed using the optical scanning optical system according to any one of the ninth to eleventh aspects.

[0027]

[First Embodiment] FIG. 1 is a sectional view of a main portion in a main scanning direction when an optical scanning device according to a first embodiment of the present invention is applied to an image forming apparatus such as a laser beam printer or a digital copier. FIG. 2 is a sectional view (sub-scanning sectional view) of a main part in the sub-scanning direction of FIG.

1 and 2, reference numeral 1 denotes a light source means,
For example, it consists of a semiconductor laser. Reference numeral 2 denotes a converging lens which converts a divergent light beam emitted from the light source means 1 into a substantially divergent light beam. The light source 1 and the converging lens 2 are integrated and housed in the same light source unit 3.

Reference numeral 4 denotes an aperture stop, which shapes a light beam emitted from the converging lens 2 into a desired optimum beam shape.
Reference numeral 5 denotes an incident type cylindrical lens which has a predetermined refractive power only in the sub-scanning direction, and deflects a substantially parallel light beam having passed through the aperture stop 4 in a sub-scanning cross section on a deflecting surface of an optical deflector 12 described later. (Reflection surface) 11 is formed as a substantially linear image. Reference numeral 6 denotes a turning mirror. In the present embodiment, the angle α at which the light beam emitted from the light source means 1 is turned toward the optical deflector 12 by the turning mirror 6 is set to 40 °.
Note that the folding angle α may be less than 45 °.

The light beam reflected by the turning mirror 6 passes through the scanning lenses 8 and 7 and is converted into a substantially parallel light beam in the main scanning section, and a plurality of deflecting surfaces (reflection surfaces) of the optical deflector are started from substantially the center of the deflection angle. Is irradiated.

The light source 1, the converging lens 2, the aperture stop 4, the cylindrical lens 5, the folding mirror 6, and the scanning lenses 7, 8 constitute one element of the incident optical system 21.

Reference numeral 12 denotes an optical deflector, which comprises, for example, a polygon mirror (rotating polygon mirror) and is rotated at a constant speed in a direction indicated by an arrow A in the figure by driving means (not shown) such as a motor.

Reference numeral 22 denotes an imaging optical system having a light condensing function and fθ characteristics, and a first optical system 22 having a predetermined power in the main scanning direction.
The optical deflector 12 includes a scanning lens system (fθ lens system) 23 having second scanning lenses 7 and 8 and a cylindrical lens (long lens) 9 having a predetermined power only in the sub-scanning direction. The deflected light flux is imaged on the surface to be scanned 10 and the deflecting surface 11 of the optical deflector 12 and the surface to be scanned 10 are made to have a substantially conjugate relationship in the sub-scanning cross section. The fall has been corrected. In the present embodiment, the shape of the second scanning lens 8 is formed to be asymmetric with respect to the optical axis M of the imaging optical system 22 in the main scanning direction.

Reference numeral 10 denotes a photosensitive drum surface as a surface to be scanned.

Reference numeral 13 denotes a synchronization detection mirror (hereinafter, also referred to as a “BD mirror”), which is a light beam for writing start position detection (hereinafter, “BD light beam”) for adjusting the timing of the scanning start position on the photosensitive drum surface 10. 14) is reflected to the synchronization detecting means side.

Reference numeral 15 denotes an optical sensor (hereinafter also referred to as a “BD sensor”) as a synchronization detecting means. In this embodiment, a synchronization signal (hereinafter, referred to as “BD sensor”) obtained by detecting an output signal from the BD sensor 15 is provided. The timing of the scanning start position of the image recording on the photosensitive drum surface 10 is adjusted by the control unit 16 by using the control signal 16.

In the present embodiment, the position where the BD light beam 14 passes through the scanning lens system 23 and the position of the light source means 1 are arranged so as to be located on opposite sides with respect to the optical axis M of the imaging optical system 22. ing.

In this embodiment, the light beam emitted from the semiconductor laser 1 is converted into a substantially divergent light beam by the converging lens 2, and the light beam is restricted by the aperture stop 4 before being incident on the cylindrical lens 5. Here, of the substantially divergent light beams incident on the cylindrical lens 5, the light beams converge in the sub-scanning cross-section and pass through the return mirror 6 to the second and first light beams.
Of the optical deflector 12 through the scanning lenses 8 and 7
1 and is formed as a nearly linear image (a linear image elongated in the main scanning direction) near the deflection surface 11. At this time, the deflection surface 1
The light beam incident on the optical deflector 1 is a plane perpendicular to the rotation axis of the optical deflector 12 (the rotation plane of the optical deflector) in the sub-scan section including the rotation axis of the optical deflector 12 and the optical axis M of the imaging optical system 22. ) At an oblique incidence angle β / 2.
That is, the light beam emitted from the incident optical system 21 is obliquely incident on the deflecting surface 11 of the optical deflector 12 in the sub-scan section at an oblique incident angle β /
2 is incident.

The light beam deflected by the deflecting surface 11 of the light deflector 12 is deflected by the same angle β / 2 as when it is incident,
The light is guided onto the photosensitive drum surface 10 via the first and second scanning lenses 7 and 8 and the cylindrical lens 9, and is rotated on the photosensitive drum surface 10 by rotating the optical deflector 12 in the direction of arrow A. Is optically scanned in the direction of arrow B (main scanning direction). Thus, an image is recorded on the photosensitive drum surface 10 as a recording medium.

At this time, a BD light flux 14 which is a part of the light flux deflected by the optical deflector 12 in order to adjust the timing of the scanning start position on the photosensitive drum face 10 before optically scanning the photosensitive drum face 10. Is passed through the first and second scanning lenses 7 and 8, reflected by the BD mirror 13, and guided to the BD sensor 15. The control unit 16 adjusts the timing of the scanning start position of the image recording on the photosensitive drum surface 10 using the BD signal obtained by detecting the output signal from the BD sensor 15.

Since the optical scanning optical system of the present embodiment is frontally incident (on-axis human radiation) as described above, the scanning range on the photosensitive drum surface 10 is symmetric about the optical axis M of the imaging optical system 22. Become. Further, in the present embodiment, the first and second scanning lenses 7 and 2 twice before the light beam emitted from the semiconductor laser 1 enters the optical deflector 12 and after the light beam is deflected by the optical deflector 12.
8 and a double pass.

In the present embodiment, as described above, the position where the BD light beam 14 passes through the scanning lens system 23 and the position of the semiconductor laser 1 are located on opposite sides with respect to the optical axis M of the imaging optical system 22. And the BD light flux 14 is set so as to pass through a range larger than 1/2 of the scanning angle of view.

The second scanning lens 8 needs an effective width a larger than the effective width b required for scanning as shown in FIG. For this reason, the second light is transmitted from the incident optical system 21 in the vicinity of the second scanning lens 8 so that the light does not interfere with the light and the return angle α by the return mirror 6 is minimized as described above.
Is formed so as to be asymmetrical with respect to the optical axis M of the imaging optical system 22 in the main scanning direction. That is, the length a to the end of the second scanning lens 8 on the side where the BD light beam 14 passes is equal to the end of the second scanning lens 8 on the side where the light beam at the end of the writing scan passes from the optical axis M. It is formed in an asymmetric shape with respect to the optical axis M so as to be longer than the length b.

In this embodiment, the folding mirror 6 is arranged at a position from the semiconductor laser 1 rather than an intermediate position of the optical path from the semiconductor laser 1 to the deflection surface 11 of the optical deflector 12. That is, the distance d2 from the semiconductor laser 1 to the turning mirror 6 is shorter than the distance d1 from the turning mirror 6 to the deflection surface 11 of the optical deflector 12.

By arranging the folding mirror 6 in this manner, the semiconductor laser 1 can be arranged in the main scanning direction without unnecessarily increasing the area of the optical box, whereby the entire apparatus can be made more compact. be able to.

In the present embodiment, the angle α at which the light beam emitted from the semiconductor laser 1 is returned by the return mirror 6 is set to 40 ° as described above. The angle α can be further reduced by disposing the folding mirror 6 further away from the semiconductor laser 1 or by making the shape of the second scanning lens 8 asymmetric, which contributes to downsizing.

Reducing the folding angle α can reduce the image forming performance on the surface of the photosensitive drum 10 caused by an angle error of the oblique incidence angle β / 2 in the sub-scanning cross section or an error of the light beam angle due to the inclination of the folding mirror 6. Can be reduced in sensitivity. Thereby, the optical performance can be stabilized.

As described above, in this embodiment, as described above, the position at which the BD light beam 14 passes through the scanning lens system 23,
The position of the semiconductor laser 1 is located on the opposite side to the optical axis M of the imaging optical system 22;
Is formed so as to be asymmetrical with respect to the optical axis M, so that the light beam passing through the incident optical system 21 does not interfere with the second scanning lens 8 and the light beam is reflected by the return mirror 6. Can be reduced, thereby reducing the size of the entire lens system and compensating the entire apparatus.

In this embodiment, the shape of the second scanning lens 8 is formed to be asymmetric with respect to the optical axis M.
If necessary, the shape of the first scanning lens 7 may be formed so as to be asymmetric with respect to the optical axis M.

[Embodiment 2] FIG. 3 shows Embodiment 2 of the present invention.
FIG. 3 is a cross-sectional view (main scanning cross-sectional view) of a main part in the main scanning direction when the scanning optical device is applied to an image forming apparatus such as a laser beam printer or a digital copying machine. In the figure, the same elements as those shown in FIG. 1 are denoted by the same reference numerals.

The present embodiment differs from the first embodiment in that a line segment from the reflection point 6a of the return mirror 6 to the end 3a at the farthest position of the light source unit 3 and a reflection point 6a of the return mirror 6 , L1 <L2, where L1 and L2 are the distances when a line segment from the optical deflector 12 to the end portion 12a at the farthest position is projected on the sub-scanning section, respectively. . Other configurations and optical functions are substantially the same as those of the first embodiment, and thus, similar effects are obtained.

That is, in this embodiment, a line segment from the reflection point 6a of the reflection mirror 6 to the end 3a at the farthest position of the light source unit 3 and the reflection point 6 of the reflection mirror 6
a, the distance when projecting a line segment from the light deflector 12 to the end 12a at the farthest position on the sub-scanning section is L
The configuration is such that when L1 and L2, the condition of L1 <L2 is satisfied.

In this embodiment, the semiconductor laser 1 and the converging lens 2 are configured as a light source unit 3 which is adjusted and integrated to a predetermined value in the same manner as in the first embodiment, so that the light source can be exchanged as a service part. Easy going.

As described above, in the present embodiment, since the light source unit 3 is disposed closer to the turning mirror 6 than the outer shape of the optical deflector 12 as described above, the size of the optical box is not limited, so that the main scanning section is not required. In this case, the size of the optical box in the direction orthogonal to the main scanning direction is not increased, and the arrangement of the optical system including the mechanical configuration can be made compact.

It should be noted that the components of the first embodiment and the components of the second embodiment may be combined.

[Other Embodiments] In another embodiment of the present invention, a light beam emitted from a light source means is deflected from substantially the center of the deflection angle of an optical deflector through an incident optical system including a return mirror. Optical scanning optics for causing the light beam deflected by the optical deflector to form an image on a surface to be scanned by an imaging optical system including a scanning lens system, and optically scanning the surface to be scanned. In the system, by using at least one of a plurality of means shown below, the entire apparatus is made compact.

The distance d2 from the light source means to the turning mirror is shorter than the distance d1 from the turning mirror to the deflection surface of the optical deflector.

The angle α at which the light beam emitted from the light source means is turned by the turning mirror is set to less than 45 °.

Sub-scanning is performed for a line segment from the reflection point of the folding mirror to the end of the light source unit at the farthest position and a line segment from the reflection point of the folding mirror to the end of the light deflector at the furthest position. The distance when projected on the cross section is L1,
When L2, L1 <L2.

[0060]

According to the present invention, as described above, in the optical scanning optical system and the image forming apparatus using the same, the position where the light beam for writing start position detection passes through the scanning lens system and the position of the light source means are connected. The scanning lens system is disposed on the side opposite to the optical axis of the image optical system, and at least a part of the optical elements constituting the scanning lens system has a shape asymmetric with respect to the optical axis of the imaging optical system in the main scanning direction. Accordingly, it is possible to achieve an optical scanning optical system and an image forming apparatus using the optical scanning optical system, in which the entire lens system can be downsized and the entire apparatus can be downsized.

Further, according to the present invention, as described above, the light emitted from the light source means is configured so that the distance from the light source means to the return mirror is shorter than the distance from the return mirror to the deflection surface of the optical deflector. The angle at which the light beam is turned by the turning mirror is set to less than 45 °. The line segment from the reflecting point of the turning mirror to the end located at the farthest position of the light source unit, and the farthest point of the optical deflector from the reflecting point of the turning mirror. When the distances when projecting the line segment to the position at the position on the sub-scanning section are L1 and L2, respectively, the configuration is such that L1 <L2, so that the entire apparatus can be made compact. It is possible to achieve an optical scanning optical system and an image forming apparatus using the optical scanning optical system.

[Brief description of the drawings]

FIG. 1 is a main scanning sectional view of a first embodiment of the present invention.

FIG. 2 is a sectional view in the sub-scanning direction according to the first embodiment of the present invention;

FIG. 3 is a main scanning cross-sectional view according to a second embodiment of the present invention.

FIG. 4 is a schematic view of a main part of a conventional scanning optical device.

FIG. 5 is a schematic view of a main part of a conventional scanning optical device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light source means (semiconductor laser) 2 Convergent lens 3 Light source unit 4 Aperture stop 5 Cylindrical lens 6 Folding mirror 7 First scanning lens 8 Second scanning lens 9 Cylindrical lens 10 Scanned surface (photosensitive drum surface) 11 Deflection surface 12 Optical deflector (rotating polygon mirror) 13 Synchronous detection mirror 14 Light flux for writing start position detection 15 Synchronous detection means 16 Control means 21 Incident optical system 22 Imaging optical system 23 Scanning lens system

Claims (12)

[Claims] 1. A light beam emitted from a light source unit including a light source means is incident on a deflection surface of the light deflector from substantially the center of a deflection angle of the light deflector via an incident optical system including a return mirror, and the light is deflected. The light beam deflected by the light deflector is focused on the surface to be scanned by an imaging optical system including a scanning lens system, and the light deflected by the light deflector in the optical scanning optical system for optically scanning the surface to be scanned. A part of the light beam is passed through the scanning lens system as a light beam for writing start position detection, guided to writing position detection means, and the output of the writing position detection means is used to determine the scanning start position on the surface to be scanned. Control means for controlling timing, wherein the position where the light beam for writing start position detection passes through the scanning lens system and the position of the light source means are opposite to each other with respect to the optical axis of the imaging optical system. Are arranged and constitute the scanning lens system. Ku and a part of the optical element in the main scanning direction,
An optical scanning optical system, wherein the optical scanning optical system has an asymmetric shape with respect to the optical axis of the imaging optical system. 2. The optical scanning optical system according to claim 1, wherein a distance from said light source means to said return mirror is shorter than a distance from said return mirror to a deflection surface of said optical deflector. 3. An angle at which the light beam emitted from the light source unit is turned back toward the optical deflector by the turning mirror is 4 degrees.
2. The optical scanning optical system according to claim 1, wherein the angle is less than 5 [deg.]. 4. A line segment from a reflection point of the folding mirror to a farthest end of the light source unit and a line segment from a reflection point of the folding mirror to a furthest end of the light deflector. 2. The optical scanning optical system according to claim 1, wherein when a distance when the line segment is projected on the sub-scanning section is L1 and L2, respectively, a condition of L1 <L2 is satisfied. 5. The optical scanning optical system according to claim 1, wherein the light beam for writing start position detection passes through a range larger than 走 査 of a scanning angle of view. 6. The optical scanning optical system according to claim 1, wherein said scanning lens system also constitutes a part of said incident optical system. 7. The optical scanning optical system according to claim 1, wherein the light beam emitted from the incident optical system is obliquely incident on a deflection surface of the optical deflector in a sub-scan section. 8. An image forming apparatus for forming an image using the optical scanning optical system according to claim 1. Description: 9. A light beam emitted from the light source means is incident on the deflection surface of the light deflector from substantially the center of the deflection angle of the light deflector via a turning mirror, and the light beam deflected by the light deflector is imaged. In an optical scanning optical system which forms an image on a surface to be scanned by an optical system and optically scans the surface to be scanned, a distance from the light source means to the turning mirror is determined by deflecting the light deflector from the turning mirror. An optical scanning optical system characterized by being shorter than a distance to a surface. 10. A light beam emitted from a light source means is made to enter a deflection surface of the light deflector from a substantially center of a deflection angle of the light deflector via a turning mirror, and the light beam deflected by the light deflector is imaged. In an optical scanning optical system which forms an image on a surface to be scanned by an optical system and optically scans the surface to be scanned, an angle at which a light beam emitted from the light source means is folded by the folding mirror is less than 45 °. Optical scanning optical system characterized. 11. A light beam emitted from a light source unit including a light source means is made to enter the deflection surface of the optical deflector from a substantially center of the deflection angle of the optical deflector via a folding mirror, and is deflected by the optical deflector. In a light scanning optical system that forms a light beam on a surface to be scanned by an image forming optical system and optically scans the surface to be scanned, an end located at a farthest position of the light source unit from a reflection point of the folding mirror. L1 and L2, respectively, when a line segment from the reflection mirror of the folding mirror to a line segment from the reflection point of the return mirror to the end located at the farthest position of the optical deflector is projected on the sub-scanning section, respectively. <L2. An optical scanning optical system characterized by satisfying the following condition: 12. An image forming apparatus, wherein an image is formed using the optical scanning optical system according to claim 9.