JPH1164759A - Light scanning optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the fluctuation of light quantity within one line on the surface to be scanned by providing luminous flux dividing means in an optical path so that the incident direction of luminous flux at a center scanning to the deflection plane of a deflection means is almost matched with the normal direction of the deflection plane when the luminous flux is projected to a main scanning cross section. SOLUTION: A cylindrical lens 2 has a prescribed refractive power only in a subscanning cross section to roughly form a luminous flux passing through an aperture 1c on the deflection plane 4a of an optical deflector 4 as a line image in the subscanning cross section. In this case, the width of the luminous flux emitted from the lens 2 is formed so as to become wider than that of a deflection plane 4a. Moreover, the luminous flux dividing means are constituted so that the incident direction of the luminous flux at a center scanning to the deflection plane 4a is almost matched with the normal direction of the deflection plane 4a when the incident luminous flux is projected to the main scanning cross by a half mirror 3. Thus, the amount of change in the width of the luminous flux to be generated in accordance with the revolution of the optical deflector 4 can be suppressed small.

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, and more particularly to a scanning optical device having an f.theta. Characteristic after deflecting and reflecting a light beam emitted from a light source means after being modulated by an optical deflector comprising a rotary polygon mirror. The present invention relates to an optical scanning optical device suitable for an apparatus such as a laser beam printer or a digital copying machine having an electrophotographic process, in which image information is recorded by optically scanning the surface to be scanned via an fθ lens). is there.

[0002]

2. Description of the Related Art Conventionally, a laser beam printer (LB) has been used.
In an optical scanning optical device such as P), a light beam emitted from a light source unit after being light-modulated in accordance with an image signal is periodically deflected by an optical deflector composed of, for example, a rotating polygon mirror (polygon mirror) to have fθ characteristics. The light is converged in the form of a spot on a photosensitive recording medium (photosensitive drum) surface by scanning optical means (fθ lens), and the surface is optically scanned to record an image.

FIG. 6 is a schematic view of a main part of a conventional optical scanning optical device. In the figure, a divergent light beam that has been light-modulated and emitted from the light source means 61 is converted into a substantially parallel light beam (or a divergent light beam or a convergent light beam) by a collimator lens 62, and the light beam (light amount) is converted by a stop (aperture) 63.
And is incident on a cylindrical lens 64 as an incident optical means having a predetermined refractive power only in the sub-scan section. Of the substantially parallel light beams that have entered the cylindrical lens 64, they are emitted as they are in the state of substantially parallel light beams in the main scanning section. In the sub-scan section, the light is converged and formed as a substantially linear image on the deflecting surface 65a of the optical deflector 65 composed of a rotating polygon mirror. The light beam deflected and reflected by the deflecting surface 65a of the optical deflector 65 is passed through a scanning optical unit 66 having fθ characteristics to a photosensitive drum surface 67 as a surface to be scanned.
By guiding the light upward and rotating the optical deflector 65 in the direction of arrow A, the photosensitive drum surface 67 is optically scanned in the direction of arrow B (main scanning direction) to record image information.

The refractive power of the scanning optical means 66 in the sub-scanning direction is appropriately set so that the deflecting surface 65a of the optical deflector 65 and the surface to be scanned 67 have a conjugate image relationship.
Thereby, the angle error when the deflection surface of the optical deflector is tilted with respect to the rotation axis, that is, the surface tilt is corrected, so that the pitch unevenness of the scanning line does not occur.

Such optical scanning optical devices are required to be able to perform higher-speed scanning by increasing the speed and definition of laser beam printers. However, the number of rotations of a motor as a driving means and the light as a deflecting means are required. Deflector (rotating polygon mirror)
The high-speed scanning is limited by the number and size of the surfaces.

Therefore, in the related art, the light beam width in the direction corresponding to the main scanning direction of the light beam incident on the light deflector is smaller than the width in the rotation direction (main scanning direction) of the deflecting surface of the light deflector, which is the deflecting means. A so-called overfilled type optical scanning optical device in which is set large is proposed, for example, in Japanese Patent Application Laid-Open No. Hei 8-17169. Such an overfilled type optical scanning optical device has features that it is suitable for high speed and high definition and that the diameter of the optical deflector can be reduced.

[0007]

In the above overfilled optical scanning optical device, as the optical deflector rotates, the width of the deflection surface of the optical deflector facing the incident optical means (cylindrical lens) changes. . As a result, the light beam width of the light beam used for actual image formation also changes as the optical deflector rotates, and the light beam width on the photosensitive drum surface, which is the surface to be scanned, is changed.
There is a problem that the amount of light fluctuation in the line cannot be ignored. In the above-mentioned Japanese Patent Application Laid-Open No. Hei 8-17169, the light beam is obliquely incident on the deflection surface of the optical deflector within the scanning deflection surface (in the main scanning section). At this time, the amount of light in the peripheral portion with respect to the central portion of the scan varies by 10% or more. Further, the light amount ratio on the photosensitive drum surface includes many factors such as the transmittance of the lens and the angle dependency of the mirror reflectivity, so that the light amount ratio further increases. When the light amount ratio increases, a density difference occurs between the central portion and the peripheral portion of the output image, and as a result, a problem arises in that a good image cannot be obtained.

According to the present invention, the width of the light beam emitted from the incident optical means is formed to be wider than the width of the deflecting surface of the deflecting means (optical deflector) in the main scanning section, and the light beam is scanned in the main scanning direction. By providing the light beam splitting means in the optical path such that the direction of incidence of the light beam in the center scan on the deflection surface of the deflection means when projected onto the cross section substantially coincides with the normal direction of the deflection surface, It is an object of the present invention to provide an optical scanning optical apparatus capable of suppressing a change amount of a light beam width according to the rotation, thereby suppressing a light amount fluctuation amount within one line on a surface to be scanned.

[0009]

The light scanning optical device according to the present invention comprises: (1) converting the state of a light beam emitted from a light source means into another state by a conversion optical element, and obtaining a light beam cross section of the converted light beam; The shape is shaped by an aperture, condensed by the incident optical means, focused on the deflecting surface of the deflecting means via the light beam splitting means to form an image in the form of a long line in the main scanning direction, and the light flux deflected and reflected by the deflecting means In the form of a spot on the surface to be scanned by the scanning optical means via the light beam dividing means, and optically scans the surface to be scanned, wherein the center of the light source means, the center of the conversion optical element The optical axis, the center of the aperture, and the optical axis of the incident optical means are arranged in a plane perpendicular to the main scanning section and on the central axis of the full scanning angle; The beam width of the beam passing through is within the main scanning section. When the light beam is projected onto the main scanning section, the incident direction of the light beam in the center scan on the deflection surface of the deflecting means and the width of the deflecting surface The light beam splitting means is provided in the optical path so that the normal direction substantially coincides with the normal direction.

In particular, (1-1) the light beam splitting means reflects the light beam passing through the incident optical means toward the deflecting means, and transmits the light beam deflected and reflected by the deflecting means to the scanning optical means. (1-2) Of the light beams deflected and reflected by the deflecting surface of the deflecting device, (1-2) a sub-light beam reflected by the light beam splitting device toward the light source unit is more than half vignetted by the aperture. The inclination angle of the light beam splitting means with respect to the normal of the deflecting surface in the scanning section is set, (1-3) the light beam splitting means is formed of a half mirror, and (1-4) the half mirror is The mirror surface may be a flat surface, (1-5) the mirror surface of the half mirror may be a curved surface, or (1-6) the conversion optical element may convert the state of the light beam emitted from the light source means into a substantially parallel light beam. Or converted to a convergent or divergent beam And that and that, (1-7)
The light beam incident on the deflecting means is obliquely incident on the deflecting surface of the deflecting means in the sub-scan section.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic view of a main part of a first embodiment of the present invention, FIG. 2 is a cross-sectional view of a main part (sub-scan cross-sectional view) of a main part in a sub-scanning direction of the first embodiment of the present invention, FIG. 3 is a cross-sectional view (main scanning cross-sectional view) of a main part of a main part in the main scanning direction according to the first embodiment of the present invention.

In FIG. 1, reference numeral 1a denotes light source means, which is made of, for example, a semiconductor laser. A conversion optical element 1b converts, for example, a light beam (light beam) emitted from the light source 1a into a divergent light beam (or a convergent light beam or a substantially parallel light beam). Reference numeral 1c denotes an aperture (aperture) for shaping the light beam cross section. Each element such as the semiconductor laser 1a, the conversion optical element b, and the aperture 1c constitutes one element of the light source unit 1.

Reference numeral 2 denotes a cylindrical lens as incident optical means, which has a predetermined refractive power only in the sub-scanning section, and converts a light beam passing through the aperture 1c into a light as a deflecting means which will be described later in the sub-scanning section. Deflector (rotating polygon mirror) 4
Are formed as substantially linear images (linear images elongated in the main scanning direction) on the deflecting surface (reflective surface) 4a. In the present embodiment, the light beam width of the light beam emitted from the cylindrical lens 2 is formed to be wider than the width of the deflection surface of the light deflector 4 in the main scanning section.

The center of the light source means 1a, the conversion optical element 1
The optical axis b, the center of the aperture 1c, and the optical axis of the cylindrical lens 2 are arranged in a plane perpendicular to the main scanning section and on the central axis of the full scanning angle.

Numeral 3 denotes a half mirror as a light beam splitting means, which has a mirror surface formed of a flat surface, and which is located at 45.degree. With respect to the normal L of the deflecting surface 4a of the optical deflector 4 in the sub-scanning section.
It is arranged at an angle of 5 °. The half mirror 3 converts the light beam emitted from the cylindrical lens 2 into a deflecting surface 4 of an optical deflector 4.
The light flux reflected on the a side and deflected and reflected by the deflecting surface 4a is transmitted and made incident on an fθ lens 5 as scanning optical means described later. At this time, in the main scanning section, when the incident light beam is projected onto the main scanning section, the incident direction of the light beam in the center scanning on the deflecting surface 4a of the optical deflector 4 substantially coincides with the normal L direction of the deflecting surface 4a. The light beam is incident on the light deflector 4 so that the light beam is obliquely incident on the light deflector 4 at an angle of 1 ° with respect to the normal L of the deflection surface 4a in the sub-scan section. I have.

The optical deflector 4 as a deflecting means is composed of, for example, a rotating polygon mirror (polygon mirror), and is rotated at a constant speed in a direction indicated by an arrow A in the figure by a driving means (not shown) such as a polygon motor. .

The fθ lens 5 as scanning optical means forms a light beam based on image information deflected and reflected by the deflecting surface 4a of the optical deflector 4 on a photosensitive drum surface 7 as a surface to be scanned.

Reference numeral 6 denotes a return mirror as light guide means, which returns the light flux passing through the fθ lens 5 to the photosensitive drum surface 7 side.

In the present embodiment, the light beam emitted from the semiconductor laser 1a is converted into a substantially parallel light beam by the conversion optical element 1b, and the light beam cross-sectional shape of the light beam is shaped by the aperture 1c to be incident on the cylindrical lens 2. As shown in FIG. 3, when the incident light beam is projected onto the main scanning cross section by the half mirror 3 in the state of substantially parallel light beam in the main scanning cross section of the substantially parallel light beam incident on the cylindrical lens 2, the light deflector 4 The light beam enters the optical deflector 4 in such a manner that the incident direction of the light beam in the central scanning on the deflecting surface 4a substantially coincides with the direction of the normal L of the deflecting surface 4a, and converges in the sub-scan section. As shown in FIG. 2, the light is obliquely incident on the light deflector 4 by the half mirror 3 at an angle of 1 ° with respect to a normal L of the deflection surface 4a of the light deflector 4.

The light beam deflected and reflected by the deflecting surface 4a of the light deflector 4 passes through the half mirror 3 and is formed into an image on the photosensitive drum surface 7 by the fθ lens 5 via the return mirror 6 in the form of a spot. By rotating the optical deflector 4 in the direction of arrow A, the photosensitive drum surface 7 is optically scanned in the direction of arrow B (main scanning direction). Thus, an image is recorded on the photosensitive drum surface 7 as a recording medium.

Fθ lens 5 as the above-mentioned scanning optical means
Is appropriately set so that the deflecting surface 4a of the optical deflector 4 and the photosensitive drum surface 7 have a conjugate imaging relationship, whereby the deflecting surface 4a of the optical deflector 4 is Is corrected with respect to the rotation axis, i.e., surface tilt, so that scanning line pitch unevenness does not occur.

As in the present embodiment, the half mirror 3 is replaced with the optical deflector 4 and the fθ lens 5 (and the cylindrical lens 2).
For example, when the light flux (return light) reflected by the half mirror 3 of the light flux deflected and reflected by the light deflector 4 returns to the semiconductor laser 1a as a light source, There is a problem that the output from the semiconductor laser 1a becomes unstable and the light quantity varies. Therefore, in this embodiment, the return light from the optical deflector 4 is the semiconductor laser 1a
In order to prevent the reflected light from entering the half mirror 3 in the sub-scanning section so that the return light is vibrated by an aperture (not shown) more than half as shown in FIG.
Is set to 45.5 ° as described above. That is, the light beam enters the deflecting surface 4a at an angle of 1 ° with respect to the normal line L of the deflecting surface 4a, whereby the light quantity fluctuation of the semiconductor laser 1a can be prevented.

In this embodiment, as described above, the light beam width of the light beam emitted from the cylindrical lens 2 is set to be wider than the width of the deflection surface 4a of the light deflector 4 in the main scanning section as shown in FIG. When the half mirror 3 projects the incident light beam onto the main scanning section, the incident direction of the light beam in the center scanning on the deflection surface 4a of the light deflector 4 and the normal L direction of the deflection surface 4a Are configured to substantially match. As a result, in this embodiment, the amount of change in the light beam width due to the rotation of the optical deflector, which cannot be avoided in the overfield type optical scanning optical device, is reduced, and the amount of light fluctuation within one line on the surface to be scanned is reduced. ing.

FIG. 4 is a graph showing a change in light beam width depending on the incident angle with respect to the deflection surface of the optical deflector. In the present embodiment, as described above, since the incident direction of the light beam in the center scanning on the deflection surface in the main scanning cross section and the normal direction of the deflection surface substantially coincide with each other, the light beam The angle of incidence corresponds to 0 °. As can be seen from the figure, when the incident angle is 30 ° or more, the light flux width changes by 20% or more in one scan, but is suppressed to 10% at the incident angle of 0 °. Here, in order to make the incident angle 0 to 30 °, the incident optical system must be arranged in the optical path between the optical deflector and the fθ lens, and the focal length of the fθ lens must be long. . This leads to an increase in the size of the entire apparatus and is not practical.

Therefore, in the present embodiment, when the incident light beam is projected onto the main scanning section using the half mirror 3 as described above, the incident direction of the light beam in the center scanning on the deflecting surface 4a of the light deflector 4 and the deflecting surface By configuring the normal line L of 4a to substantially coincide with the direction of the normal line L, it is possible to reduce the amount of light quantity fluctuation within one line on the photosensitive drum surface 7,
Thereby, a good image is obtained.

Since the light beam emitted from the semiconductor laser as a light source is a Gaussian beam, the amount of light varies depending on, for example, the position where the light beam is used, but the means of the present embodiment using the half mirror as described above is most effective. Clearly,

FIG. 5 is a schematic view of a main part of a second embodiment of the present invention. 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 the mirror surface of the half mirror as the light beam splitting means is formed of a curved surface. Other configurations and optical functions are substantially the same as those of the first embodiment, and thus the same effects are obtained.

That is, in the figure, reference numeral 53 denotes a half mirror having a curved mirror surface, which prevents the return light from the optical deflector 4 from being incident on the semiconductor laser 1a, and also controls the cylindrical lens 2 The emitted light beam is incident on the deflection surface 4a of the optical deflector 4 as a converged light beam.

In this embodiment, when the return light from the optical deflector 4 returns to the semiconductor laser 1a as described above, the output becomes unstable and the amount of light fluctuates. Therefore, the mirror surface of the half mirror 53 should be curved. As a result, as in the first embodiment, the return light is vignetted by half or more at the aperture (not shown). Even if the light beam returns to the semiconductor laser 1a, it returns as a divergent light beam, so that the light beam directly enters the semiconductor laser 1a. Light intensity of the light beam
As a result, it is possible to effectively prevent the light quantity fluctuation of the semiconductor laser 1a.

In each of the embodiments, a half mirror of a dielectric film coating is used as a light beam splitting means. However, the present invention is not limited to this. For example, even if a prism type half mirror is used, the present invention is similar to the above embodiment. Can be applied.

[0032]

According to the present invention, as described above, the width of the light beam emitted from the incident optical means is formed to be wider than the width of the deflecting surface of the deflecting means (optical deflector) in the main scanning section. And a light beam splitting means provided in an optical path such that, when the light beam is projected onto the main scanning section, the incident direction of the light beam in the center scan on the deflection surface of the deflection means substantially coincides with the normal direction of the deflection surface. Thus, the amount of change in the light beam width according to the rotation of the deflecting means can be suppressed to a small amount, whereby the amount of light amount fluctuation within one line on the surface to be scanned can be suppressed to a small amount to obtain a good image. An optical device can be achieved.

[Brief description of the drawings]

FIG. 1 is a schematic view of a main part of a first embodiment of the present invention.

FIG. 2 is a sectional view of a sub-scanning area around a half mirror according to the first embodiment of the present invention;

FIG. 3 is a main scanning sectional view of a main part according to the first embodiment of the present invention.

FIG. 4 is a graph showing a change in a light beam width depending on an incident angle with respect to an optical deflector.

FIG. 5 is a schematic diagram of a main part of a second embodiment of the present invention.

FIG. 6 is a schematic view of a main part of a conventional optical scanning optical device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light source unit 1a Semiconductor laser 1b Conversion optical element 1c Aperture 2 Incident optical means (cylindrical lens) 3,53 Beam splitting means (half mirror) 4 Deflection means (rotating polygon mirror) 5 Scanning optical means (fθ lens) 6 Light guide means (Folding mirror) 7 Scanned surface (photosensitive drum surface)

Claims (8)

[Claims] 1. A state of a light beam emitted from a light source means is converted into another state by a conversion optical element, a light beam cross-sectional shape of the converted light beam is shaped by an aperture, and the light beam is condensed by an incident optical means. An image is formed linearly in the main scanning direction on the deflection surface of the deflecting means via the splitting means, and the light beam deflected and reflected by the deflecting means is scanned by the scanning optical means via the light beam splitting means onto the surface to be scanned. To form a spot
An optical scanning optical device that optically scans the surface to be scanned, wherein a center of the light source unit, an optical axis of the conversion optical element, a center of the aperture, and an optical axis of the incident optical unit are relative to a main scanning section. The light beam width of the light beam passing through the incident optical unit is wider than the width of the deflecting surface of the deflecting unit in the main scanning section in a vertical plane and on the central axis of the entire scanning angle. And in the optical path such that, when the light beam is projected onto the main scanning section, the direction of incidence of the light beam in the central scanning on the deflecting surface of the deflecting means substantially coincides with the normal direction of the deflecting surface. Wherein the light beam splitting means is provided. 2. The light beam splitting means reflects the light beam passing through the incident optical device to the deflecting device side, and transmits the light beam deflected and reflected by the deflecting device and causes the light beam to enter the scanning optical device. 2. The optical scanning optical device according to claim 1, wherein: 3. A light beam deflected and reflected by a deflecting surface of the deflecting means, the light beam reflected by the light beam splitting means toward the light source means being more than half vignetted by the aperture. 3. The optical scanning optical device according to claim 1, wherein an inclination angle of the light beam dividing means with respect to a normal line of the deflection surface is set. 4. The optical scanning optical device according to claim 1, wherein said light beam splitting means comprises a half mirror. 5. The optical scanning optical device according to claim 4, wherein a mirror surface of said half mirror is a flat surface. 6. The optical scanning optical device according to claim 4, wherein a mirror surface of said half mirror is a curved surface. 7. The optical scanning optical device according to claim 1, wherein said conversion optical element converts a state of a light beam emitted from said light source means into a substantially parallel light beam, a convergent light beam, or a divergent light beam. 8. The optical scanning optical apparatus according to claim 1, wherein the light beam incident on the deflecting means is incident on the deflecting surface of the deflecting means in an oblique direction in a sub-scan section.