JP2002182143A - Optical scanner, multibeam scanner and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical scanner, a multibeam scanner and an image forming device by which illuminance distribution is made nearly uniform on a surface to be scanned even in the case of using a scanning optical system having a wide viewing angle and even in the case of rotating the polarization direction of a laser beam emitted from a light source means. SOLUTION: This optical scanner is provided with the light source means 1 emitting the laser beam being linearly polarized light, an incident optical system 11 making the laser beam emitted from the light source means incident on a deflection means 5, and a scanning optical system by which the laser beam deflected by the deflection means is formed into an image on the surface to be scanned 8 through a reflection member 7 reflecting the laser beam in a subscanning direction. In the scanner, the reflection surface of the reflection member is set so that reflectance may be nearly equal in P polarized light and S polarized light and it may be different according to the incident angle of the incident laser beam, whereby the illuminance distribution on the surface to be scanned is made nearly uniform.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning apparatus, a multi-beam scanning apparatus, and an image forming apparatus. The present invention is suitable for a laser beam printer or a digital copying machine having an electrophotographic process, for example, in which image information is recorded by optically scanning the upper side.

[0002]

2. Description of the Related Art Conventionally, in an optical scanning device such as a laser beam printer, image information is written by optically scanning a recording medium surface such as a photosensitive drum using a laser beam.

FIG. 41 is a schematic view of a main part of a conventional optical scanning device.

In FIG. 1, a laser beam emitted from a laser oscillator 91 is converted into a substantially parallel beam by a collimator lens 92, which is a condenser lens, and the width of the laser beam is restricted by an aperture stop 93 to form a cylindrical lens 94.
Incident on Of the substantially parallel light beam incident on the cylindrical lens 94, it is emitted as it is in the main scanning plane, converges in the sub-scanning plane, and is substantially linearly imaged on a deflecting plane (deflecting / reflecting surface) 95a of the deflecting means 95 composed of a polygon mirror. As an image.

[0005] The laser beam deflected by the deflecting plane 95a of the polygon mirror 95 has fθ characteristics, and after passing through a scanning optical system 96 comprising two fθ lenses 96a and 96b,
The light is reflected by the folding mirror 97 and is guided on the recording medium surface (scanned surface) 98. And polygon mirror 9
5 is rotated at substantially constant angular velocity in the direction of arrow A by a driving means (not shown), thereby optically scanning the recording medium surface (photosensitive drum surface) 98 in the direction of arrow B at a substantially constant speed, and the potential difference due to the potential difference. Forming an image.

Recently, plastic lenses are used for each of the fθ lenses 96a and 96b constituting the scanning optical system 96 from the advantages of cost reduction and freedom of shape. It is difficult to coat an anti-reflection film on the surface of a plastic lens, and it is generally not coated. Therefore, there is a problem that the surface reflectance varies depending on the angle of incidence on the lens surface, and the transmittance of the scanning optical system 96 varies depending on the angle of view, and the illuminance distribution on the recording medium surface 98 becomes non-uniform. For example, when optical scanning is performed with a laser beam linearly polarized in a direction parallel to the deflection plane, the illuminance is low at the center of the effective scanning area on the recording medium surface 98, and the illuminance distribution is high at the peripheral portion.

As a means for solving this problem, for example, Japanese Patent Publication No. 2727572 discloses a method in which a laser beam is incident on an optical member while the polarization direction is polarized in the P polarization direction. Xp and Xs are set so that Xp <Xs, and conversely, when incident on the optical member while being polarized in the S polarization direction, Xp
An optical scanning device in which the reflection property or the transmission property of an optical member is configured to satisfy> Xs is disclosed.

[0008]

In order to reduce the size of the optical scanning device, for example, when a scanning optical system 96 having a wide angle of view is used, the light beam deflected to the polygon mirror is f
The surface reflectance greatly varies depending on the angle of incidence on the surfaces of the θ lenses 96a and 96b.
The difference in light amount loss between the center and the periphery of the upper effective scanning area also increases, and the non-uniformity of the illuminance distribution on the recording medium surface 98 increases. There is a problem that it is difficult to uniformly correct the illuminance distribution using only the difference in the characteristics.

In a multi-beam scanning apparatus using a monolithic multi-laser for emitting a plurality of linearly polarized laser beams as a light source means, in addition to the above-mentioned problem, the scanning line spacing in the sub-scanning direction on the recording medium surface is increased. In order to set a value corresponding to the pixel density, the interval between light emitting points in the sub-scanning direction is adjusted by rotating the light source means. At this time, the polarization direction of each laser beam is completely The light is not polarized in the direction of P-polarized light or S-polarized light, and has a uniform inclination according to the adjustment amount. As a result, there is a problem that the illuminance distribution becomes asymmetrical in the left and right directions with respect to the center of the effective scanning range on the recording medium surface.

Further, a plurality of laser beams emitted from the above-mentioned light source means (multi-laser) have an angle difference in the direction of linearly polarized light due to a manufacturing error of the light source means. Another problem is that the shape of the illuminance distribution is different.

A first object of the present invention is to make the illuminance distribution substantially uniform on the surface to be scanned even in a scanning optical system having a wide angle of view, and even when the polarization direction of the laser beam emitted from the light source means is rotated. It is an object of the present invention to provide an optical scanning device capable of performing such operations.

A second object of the present invention is to provide a multi-beam scanning device having no uneven illuminance distribution on the surface to be scanned.

A third object of the present invention is to provide an image forming apparatus which can make the illuminance distribution substantially uniform on the surface to be scanned by using the above-described optical scanning device or multi-beam scanning device.

[0014]

According to a first aspect of the present invention, there is provided an optical scanning apparatus comprising: a light source for emitting a linearly polarized laser beam; and an incident optical system for causing the laser beam emitted from the light source to enter a deflection unit. A scanning optical system that forms an image on a surface to be scanned via a reflecting member that folds the laser beam deflected by the deflecting means in the sub-scanning direction, wherein the reflecting surface of the reflecting member is a P-polarized light. And the S-polarized light, and the reflectance is made different depending on the incident angle of the incident laser beam so that the illuminance distribution on the surface to be scanned is made substantially uniform.

According to a second aspect of the present invention, in the first aspect of the present invention, the reflectances of the P-polarized light and the S-polarized light are substantially equal within a range of an incident angle of 25 ° to 40 °.
It is characterized by being within 3%.

According to a third aspect of the present invention, in the first aspect of the present invention, the illuminance distribution is substantially uniform when the illuminance distribution on the surface to be scanned is on the axis within the effective scanning area over the entire effective scanning area.
It is characterized by the fact that it is within 3%.

According to a fourth aspect of the present invention, when the fθ coefficient of the scanning optical system is k and the effective scanning width of the scanned surface is W, the condition of k / W ≦ 0.6 is satisfied. It is characterized by satisfaction.

According to a fifth aspect of the present invention, in the first aspect of the present invention, an angle at which a laser beam toward a center of an effective scanning area on the surface to be scanned is incident on the reflecting member is βo (deg),
When the angle at which the laser beam directed to the end of the effective scanning area on the surface to be scanned enters the reflecting member is βi (deg), the condition of 8 (deg) ≦ βi−βo ≦ 20 (deg) is satisfied. It is characterized by doing.

A multi-beam scanning apparatus according to a sixth aspect of the present invention is a multi-beam scanning device, comprising: a light source means for emitting a plurality of linearly polarized laser light beams; an incident optical system for causing the plurality of laser light beams emitted from the light source means to enter a deflection means; A scanning optical system for imaging a plurality of laser beams deflected by the deflecting means on the surface to be scanned via a reflecting member that is turned back in the sub-scanning direction. The reflectance is substantially equal between the polarized light and the S-polarized light, and the reflectance is made different depending on the incident angle of the incident laser beam so that the illuminance distribution on the surface to be scanned is made substantially uniform.

According to a seventh aspect of the present invention, in the sixth aspect, the reflectance of the P-polarized light and the S-polarized light is substantially equal within a range of an incident angle of 25 ° to 40 °.
It is characterized by being within 3%.

According to an eighth aspect of the present invention, in the sixth aspect of the present invention, the illuminance distribution on the surface to be scanned is substantially uniform when the illuminance distribution on the scanned surface is ±
It is characterized by the fact that it is within 3%.

According to a ninth aspect of the present invention, when the fθ coefficient of the scanning optical system is k and the effective scanning width of the surface to be scanned is W, the condition of k / W ≦ 0.6 is satisfied. It is characterized by satisfaction.

According to a tenth aspect of the present invention, in the invention of the sixth aspect, an angle at which a laser beam toward the center of the effective scanning area on the surface to be scanned is incident on the reflecting member is βo (deg),
When the angle at which the laser beam directed to the end of the effective scanning area on the surface to be scanned enters the reflecting member is βi (deg), the condition that 8 ≦ βi−βo ≦ 20 (deg) is satisfied. Features.

According to an eleventh aspect of the present invention, in the sixth aspect, the light source means is rotatable around an optical axis of the incident optical system.

According to a twelfth aspect of the present invention, there is provided an optical scanning device, comprising: light source means for emitting a linearly polarized laser light beam having a polarization direction substantially parallel to the deflection plane; and a laser light beam emitted from the light source means to the deflection means. An optical scanning device comprising: an incident optical system for incidence; and a scanning optical system for imaging a laser beam deflected by the deflecting means on a surface to be scanned via a reflecting member that folds in a sub-scanning direction. Is characterized in that the reflectance of P-polarized light and that of S-polarized light are substantially equal, and the reflectance of S-polarized light or P-polarized light decreases as the incident angle of the incident laser beam increases. And

According to a thirteenth aspect of the present invention, in the twelfth aspect, the illuminance distribution on the surface to be scanned is made substantially uniform by reducing the reflectance of the S-polarized light or the P-polarized light. .

According to a fourteenth aspect, in the thirteenth aspect, the illuminance distribution is substantially uniform when the illuminance distribution on the surface to be scanned is within ± 3% with respect to the axis over the entire effective scanning area. It is characterized by

According to a fifteenth aspect, in the twelfth aspect, when the fθ coefficient of the scanning optical system is k and the effective scanning width of the scanned surface is W, the condition that k / W ≦ 0.6 is satisfied. It is characterized by satisfaction.

According to a sixteenth aspect of the present invention, in the twelfth aspect, an angle at which a laser beam toward the center of an effective scanning area on the surface to be scanned is incident on the reflecting member is βo (deg), and When the angle at which the laser beam directed toward the end of the effective scanning area enters the reflecting member is βi (deg), a condition of 8 (deg) ≦ βi−βo ≦ 20 (deg) is satisfied. And

An optical scanning device according to a seventeenth aspect of the present invention provides a light scanning device which emits a linearly polarized laser beam having a polarization direction substantially perpendicular to a deflection plane, and a laser beam emitted from the light source to the deflection unit. An optical scanning device comprising: an incident optical system for incidence; and a scanning optical system for imaging a laser beam deflected by the deflecting means on a surface to be scanned via a reflecting member that folds in a sub-scanning direction. Is characterized in that the reflectivity of the P-polarized light and the S-polarized light is substantially equal, and the reflectivity of the P-polarized light or S-polarized light increases as the incident angle of the incident laser beam increases. And

The invention of claim 18 is characterized in that, in the invention of claim 17, the illuminance distribution on the surface to be scanned is made substantially uniform by increasing the reflectance of the P-polarized light or the S-polarized light. .

According to a nineteenth aspect of the present invention, in the invention of the eighteenth aspect, the substantially uniform means that the illuminance distribution on the surface to be scanned is within ± 3% with respect to the axis over the entire effective scanning area. Features.

According to a twentieth aspect of the present invention, when the fθ coefficient of the scanning optical system is k and the effective scanning width of the scanned surface is W, the condition that k / W ≦ 0.6 is satisfied. It is characterized by satisfaction.

According to a twenty-first aspect of the present invention, in the seventeenth aspect, an angle at which a laser beam toward a center of an effective scanning area on the surface to be scanned is incident on the reflecting member is βo (deg), and When the angle at which the laser beam directed toward the end of the effective scanning area enters the reflecting member is βi (deg), a condition of 8 (deg) ≦ βi−βo ≦ 20 (deg) is satisfied. And

According to a twenty-second aspect of the present invention, there is provided a multi-beam scanning apparatus, comprising: a light source means for emitting a plurality of linearly polarized laser light beams having a polarization direction substantially parallel to a deflection plane; and a plurality of laser light beams emitted from the light source means. Multi-beam scanning apparatus, comprising: an incident optical system that causes light to enter a deflecting unit; and a scanning optical system that forms an image on a surface to be scanned via a reflecting member that folds a laser beam deflected by the deflecting unit in a sub-scanning direction. In the above, the reflection surface of the reflection member is formed such that the reflectances of the P-polarized light and the S-polarized light are substantially equal, and the reflectance of the S-polarized light or the P-polarized light decreases as the incident angle of the incident laser beam increases. It is characterized by having.

According to a twenty-third aspect, in the twenty-second aspect, the illuminance distribution on the surface to be scanned is made substantially uniform by reducing the reflectance of the S-polarized light or the P-polarized light. .

According to a twenty-fourth aspect, in the twenty-third aspect, the illuminance distribution is substantially uniform when the illuminance distribution on the surface to be scanned is within ± 3% with respect to the axis over the entire effective scanning area. It is characterized by

According to a twenty-fifth aspect of the present invention, when the fθ coefficient of the scanning optical system is k and the effective scanning width of the surface to be scanned is W, the condition that k / W ≦ 0.6 is satisfied. It is characterized by satisfaction.

According to a twenty-sixth aspect of the present invention, in the twenty-second aspect, an angle at which a laser beam directed toward the center of an effective scanning area on the surface to be scanned enters the reflecting member is βo (deg), and When the angle at which the laser beam directed toward the end of the effective scanning area enters the reflecting member is βi (deg), a condition of 8 (deg) ≦ βi−βo ≦ 20 (deg) is satisfied. And

In a twenty-seventh aspect, in the twenty-second aspect, the light source means is rotatable around the optical axis of the incident optical system.

A multi-beam scanning apparatus according to a twenty-eighth aspect of the present invention provides a multi-beam scanning device, comprising: a light source means for emitting a plurality of linearly polarized laser light beams having a polarization direction substantially perpendicular to a deflection plane; and a plurality of laser light beams emitted from the light source means. Having a plurality of laser beams deflected by the deflecting unit, and a scanning optical system for forming an image on a surface to be scanned through a reflecting member that folds the plurality of laser beams in the sub-scanning direction. In the scanning device, the reflecting surface of the reflecting member is P-polarized light and S-polarized light.
P-polarized light or S-polarized light as the reflectance with the polarized light is substantially equal and the incident angle of the incident laser beam increases.
It is characterized in that it is formed so as to increase the reflectance of polarized light.

According to a twenty-ninth aspect, in the twenty-eighth aspect, the illuminance distribution on the surface to be scanned is made substantially uniform by increasing the reflectance of the P-polarized light or the S-polarized light. .

The invention according to claim 30 is the invention according to claim 29, wherein the illuminance distribution is substantially uniform when the illuminance distribution on the surface to be scanned is within ± 3% with respect to the axis over the entire effective scanning area. It is characterized by

According to a thirty-first aspect of the present invention, the condition that k / W ≦ 0.6 is satisfied, where k is the fθ coefficient of the scanning optical system and W is the effective scanning width of the surface to be scanned. It is characterized by satisfaction.

The invention of claim 32 is the invention of claim 28, wherein the angle at which the laser beam directed to the center of the effective scanning area on the surface to be scanned is incident on the reflecting member is βo (deg), When the angle at which the laser beam directed toward the end of the effective scanning area enters the reflecting member is βi (deg), a condition of 8 (deg) ≦ βi−βo ≦ 20 (deg) is satisfied. And

A thirty-third aspect of the present invention is based on the twenty-eighth aspect, wherein the light source means is rotatable around the optical axis of the incident optical system.

According to a thirty-fourth aspect of the present invention, there is provided an image forming apparatus comprising: the optical scanning device according to any one of the first to thirty-third aspects;
Alternatively, a multi-beam scanning device, a photoconductor disposed on the surface to be scanned of the optical scanning device or the multi-beam scanning device, and an electrostatic latent image formed by scanning a light beam on the photoconductor are formed as toner images. And a transfer unit for transferring the developed toner image to a sheet of paper, and a fixing unit for fixing the transferred toner image to the sheet of paper.

An image forming apparatus according to a thirty-fifth aspect of the present invention provides the optical scanning device according to any one of the first to thirty-third aspects,
Alternatively, it is characterized by having a multi-beam scanning device and a printer controller that converts code data input from an external device into an image signal and inputs the image signal to the optical scanning device.

[0049]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [Embodiment 1] FIG. 1A is a cross-sectional view of main parts in the main scanning direction (main scanning cross-sectional view) of an optical scanning device according to Embodiment 1 of the present invention, and FIG. FIG. 2 is a sectional view (sub-scan sectional view) of a main part in the sub-scan direction of FIG.

In the present specification, the main scanning direction is defined as a laser beam (also simply referred to as a "beam") by a deflecting means.
Refers to a direction in which deflection scanning is performed, and the sub-scanning direction refers to a direction including the optical axis of the scanning optical system and orthogonal to the main scanning direction. The polarization plane refers to a plane on which the laser beam is deflected by the deflecting means, and is parallel to the main scanning direction in this embodiment.

In the drawing, reference numeral 1 denotes a light source means, which is composed of, for example, a semiconductor laser having one light emitting portion, and emits a linearly polarized laser beam having a polarization direction substantially parallel to the deflection plane. Reference numeral 2 denotes a condenser lens (collimator lens), which converts a linearly polarized divergent light beam emitted from the light source means 1 into a substantially parallel light beam. Reference numeral 3 denotes an aperture stop, which restricts a passing light beam (light amount). Reference numeral 4 denotes a cylindrical lens which has a predetermined refractive power only in the sub-scanning direction, and deflects a laser beam which has passed through the aperture stop 3 in an optical deflector (deflecting means) 5 described later in a sub-scanning section.
The image is substantially formed as a line image on a.

The collimator lens 2, aperture stop 3,
Each element such as the cylindrical lens 4 constitutes one element of the incident optical system 11.

Reference numeral 5 denotes an optical deflector comprising a polygon mirror (rotating polygon mirror) as a deflecting means, which is rotated at a constant speed in a predetermined direction by a driving means such as a motor (not shown).

Reference numeral 6 denotes a scanning optical system (fθ lens system) having fθ characteristics, and the first and second scanning optical systems are made of synthetic resin.
It has fθ lenses (scanning lenses) 6a and 6b, forms a laser beam based on image information deflected by the optical deflector 5 into a spot on the surface 8 to be scanned, and emits light in a sub-scanning cross section. Deflection plane 5a of deflector 5 and scanned surface 8
By having a conjugate relationship between the two, a tilt correction function is provided.

Reference numeral 7 denotes a folding mirror as a reflecting member, which is provided between the optical deflector 5 and the surface 8 to be scanned, and folds a laser beam passing through the scanning optical system 6 in the sub-scanning direction. The reflection surface 7a of the folding mirror 7 in the present embodiment has substantially the same reflectance for P-polarized light and S-polarized light,
Further, it is formed so that the reflectance of S-polarized light or P-polarized light decreases as the incident angle of the incident laser beam increases. Here, that the reflectances of the P-polarized light and the S-polarized light are substantially equal means that the reflectance difference between the two is within ± 3% within the range of the incident angle of 25 ° to 40 °.

In this embodiment, the illuminance distribution on the surface 8 to be scanned is made substantially uniform by reducing the reflectance of S-polarized light or P-polarized light. Note that the substantially uniform illuminance distribution means that the illuminance distribution on the surface 8 to be scanned is within ± 3% of the axis over the entire effective scanning area.

Reference numeral 8 denotes a photosensitive drum surface as a surface to be scanned.

In this embodiment, the divergent light beam of linearly polarized light emitted from the semiconductor laser 1 after being modulated in accordance with image information is converted into a substantially parallel light beam by the collimator lens 2, the amount of light is restricted by the aperture stop 3, and the cylindrical lens 4 is incident. The laser light beam incident on the cylindrical lens 4 is emitted as it is in the main scanning section. Further, in the sub-scan section, the light converges and forms a substantially linear image (a linear image elongated in the main scanning direction) on the deflection plane 5a of the optical deflector 5.

The laser beam deflected by the deflecting plane 5a of the optical deflector 5 receives the first and second fθ lenses 6a and 6a.
b, light is guided onto the photosensitive drum surface 8 via the folding mirror 7, and the light deflector 5 is rotated in a predetermined direction to optically scan the photosensitive drum surface 8 in a predetermined direction (main scanning direction). ing. Thus, an image is recorded on the photosensitive drum surface 8 as a recording medium.

In this embodiment, in order to reduce the size of the scanning optical system 6, the scanning angle of view is set to a wide angle of view of ± 56.2 degrees, and the laser beam is directed toward the center of the effective scanning area on the surface 8 to be scanned. The first and second fθ lenses 6a and 6b are arranged so that the optical axis 9 of the scanning optical system 6 overlaps with the first lens.

FIG. 2 is a diagram showing the illuminance distribution after passing through the scanning optical system 6. The ordinate indicates the illuminance ratio when the illuminance on the optical axis 9 is 1, and the abscissa indicates the image height. The plus side of the image height is the scanning start side.

In the present embodiment, the laser beam emitted (oscillated) from the semiconductor laser 1 is linearly polarized in a direction parallel to the deflection plane 5a, and the first and second fθ lenses 6a,
6b, where the angle of incidence is small, the Fresnel reflectivity is high, the angle of view is widened, and the first and second fθ lenses 6
The Fresnel reflectivity decreases where the angle of incidence on the surfaces a and 6b increases. Therefore, the illuminance distribution after passing through the scanning optical system 6 is the lowest on the axis and the highest at the end of the effective scanning area on the surface 8 to be scanned, and the light amount ratio is 1.06 times.

In this embodiment, as described above, the laser beam emitted from the semiconductor laser 1 is linearly polarized in a direction parallel to the deflection plane, and is directed to the return mirror 7 on the optical axis 9 of the scanning optical system 6 in the S polarization direction. Laser beam polarized to α
It is incident at an angle of o = 25 deg.

The laser beam traveling toward the end of the effective scanning area on the surface 8 to be scanned enters the folding mirror 7 at an angle of θi = 35.6 deg in the main scanning direction and αi = 25 deg in the sub-scanning direction. From the following formula (1) to the return mirror 7
It is incident at an angle of i = 42 deg.

Cos β = cos α × cos θ (1) FIG. 3 shows the ratio of the P-polarized light component and the S-polarized light component on the reflecting surface 7a of the turning mirror 7 at each image height (angle of view) at this time.

The relationship between the image height Y and the angle of view ε is as follows: Y = k × ε (2) where k is the fθ coefficient (k = 109 mm / rad in the present embodiment). Upper effective scanning width W and scanning optical system 6
The relationship of the fθ coefficient k is as follows: k / W = 109 (mm / rad) / 214 (mm) = 0.51 (3), and a wide angle of view scanning optics satisfying k / W ≦ 0.6. Indicates a system.

As shown in FIG. 3, the S-polarized light component shows 100% on the optical axis 9, the P-polarized light component increases as the image height increases, and the P-polarized light component and the S-polarized light component near the image height ± 70 mm. Hereinafter, also referred to as “PS polarization component”), the S-polarized light at the image height Y = ± 107 mm (angle of view ± 56.2 deg) corresponding to the end of the effective scanning area on the surface 8 to be scanned. The component is about 39%, and the P-polarized component is about 61%, which is the opposite point.

FIG. 4 is a diagram showing the angle characteristics of the reflectance for each of the P-polarized light component and the S-polarized light component on the reflecting surface 7a of the folding mirror 7 according to the present invention.

In this embodiment, the reflectivity of the PS polarization component is substantially the same, the reflectivity of the laser beam incident on the return mirror 7 is 25 °, the reflectivity is 60.0%, and the reflectivity of the laser beam is 42 °. The rate is set to be 56.5%. That is, as shown in FIG. 4, the reflection surface 7 is designed so that the reflectance of the S-polarized light or the P-polarized light decreases as the incident angle of the laser beam incident on the return mirror 7 increases.
a. As a result, as shown in FIG. 5, the illuminance distribution on the scanned surface 8 can be corrected to be substantially uniform so as to fall within a difference of 0.9% over the entire effective scanning area.

Here, as Comparative Example 1, an example in which the illuminance distribution on the surface 8 to be scanned is made substantially uniform using the difference in the reflectance of the conventional PS polarization component will be described. The difference from the present embodiment in Comparative Example 1 is that P ·
The point is that the reflectance of the S-polarized component is different.

FIG. 6 shows the reflectance of the PS polarization component on the reflection surface of the folding mirror in Comparative Example 1. The reflectance of the P-polarized light component is 54.degree. When the incident angle .beta.
0%, and the reflectance of the S-polarized light component is 60.0%. As a result, as shown in FIG. 7, the illuminance distribution on the scanned surface 8 has a difference of 1.7% over the entire effective scanning area.

As can be seen from this difference, the surface 8 to be scanned is obtained by utilizing the difference in the reflectance of the PS polarization component described as Comparative Example 1.
The method of changing the reflectance according to the incident angle β of the laser beam incident on the return mirror 7 can correct the illuminance distribution on the surface 8 to be scanned more uniformly than the method of correcting the above illuminance distribution. . Therefore, if the effects of the present embodiment are used, the illuminance distribution on the surface 8 to be scanned can be corrected to be substantially uniform with higher accuracy.

The semiconductor laser 1 as the light source means may be rotated from a state where the polarization direction is parallel or perpendicular to the deflection plane due to a manufacturing error or an assembly error. For example, if the polarization direction of the laser beam emitted from the semiconductor laser 1 is rotated by 5 degrees from the deflection plane, the scanning optical system 6 is slightly symmetrically transmitted with respect to the optical axis 9 under the influence of the rotation of the polarization direction. As the ratio changes, the ratio of the PS polarization component on the reflection surface of the folding mirror differs between the right and left sides of the optical axis 9.

In this embodiment, since the reflectance of the PS mirror component on the reflection surface 7a of the return mirror 7 is substantially the same, the illuminance distribution on the surface 8 to be scanned is not affected by the rotation of the polarization direction. . However, when the reflectance is made different between the P-polarized component and the S-polarized component as in Comparative Example 1, asymmetry occurs in the reflectance of the reflecting surface of the folding mirror. As a result, in the optical scanning device according to the present embodiment, as shown in FIG. 8, the illuminance distribution on the surface 8 to be scanned has a difference of 1.0% over the entire effective scanning area, whereas in the comparative example 1, FIG. As shown, the illuminance distribution on the surface 8 to be scanned has a difference of 3.0% over the entire effective scanning area, and the uniformity of the illuminance distribution deteriorates due to the rotation of the polarization direction of the laser beam.

When the polarization direction is further rotated by 10 degrees, in this embodiment, as shown in FIG.
The above illuminance distribution falls within the difference of 1.1% in the entire effective scanning area, whereas in Comparative Example 1, the difference becomes 4.6% as shown in FIG. 11, and the illuminance distribution is changed by rotating the polarization direction of the laser beam. Is significantly deteriorated.

From this, it is understood that the uniformity of the illuminance distribution on the scanned surface 8 can be maintained even if the polarization direction of the laser beam emitted from the light source means 1 is rotated by the effect of the present embodiment. Therefore, it is possible to provide an optical scanning device that can always obtain a good image.

The reflecting surface 7 of the folding mirror 7 of the present embodiment
a is formed by depositing an Al compound or a Cr compound on a vapor-deposited film, and attaching a protective film on the upper surface thereof. The difference between the reflectances of the P-polarized light component and the S-polarized light component is preferably within ± 3% within the range of the incident angle of 25 ° to 40 °, but a difference of ± 5% is acceptable.

In this embodiment, the effective scanning area on the scanned surface 8 is W = 214 mm (± 107 mm), and the angle of view ε = ± 56.
Although the scanning optical system 6 having a wide angle of view and deg is used as an example, the illumination distribution can be sufficiently substantially uniformly corrected using the effect of the present invention even if a scanning optical system having a larger angle of view is used. .

FIG. 12 is a schematic view of a main part of the folding mirror 7 used in this embodiment. The folding mirror 7 shown in the figure chamfers only four ridges in the longitudinal direction to prevent an operator from being injured when the folding mirror 7 is incorporated in an optical box (not shown), and to make a ridge in the short direction. The eight mirrors eliminate the chamfering and reduce the cost of the folding mirror 7.

In this embodiment, the deflection plane is 4
When a linearly polarized laser beam having a polarization direction of 5 ° is used, P
What is necessary is just to set the reflectance of the polarized light and the S-polarized light to be substantially the same regardless of the incident angle. In the present embodiment, the folding mirror is constituted by one mirror. However, the present invention is not limited to this. For example, the folding mirror may be constituted by a plurality of mirrors if the reflectance of the reflecting surface of the folding mirror is appropriately set. In the present embodiment, the scanning optical system is configured by two lenses, but is not limited thereto, and may be configured by, for example, a single lens or three or more lenses.

[Embodiment 2] FIG. 13A is a sectional view (main scanning sectional view) of a main portion in the main scanning direction in an optical scanning device according to Embodiment 2 of the present invention, and FIG. 13B is a sectional view of FIG. 3) is a sectional view (sub-scan sectional view) of a main part in the sub-scan direction. FIG.
1A and 1B, the same elements as those shown in FIGS. 1A and 1B are denoted by the same reference numerals.

This embodiment is different from the first embodiment in that the angle of the laser beam incident on the return mirror 7 and polarized in the S-polarized direction in the sub-scanning direction (return angle).
Is set to αo = 48 deg. Other configurations and optical functions are substantially the same as those of the first embodiment, and thus, similar effects are obtained.

That is, in the present embodiment, on the optical axis 9, the incident angle θ in the main scanning direction of the S-polarized laser beam incident on the return mirror 7 in the main scanning direction is θ = 0 deg. The incident angle βo of the turning mirror 7 is directly obtained (βo = αo).

In the present embodiment, the laser beam traveling toward the end (image height ± 107 mm) of the effective scanning area on the surface 8 to be scanned is in the main scanning direction with respect to the turning mirror 7 in the first embodiment.
Similarly to the above, θi = 35.6 deg and the sub-scanning direction is incident at an angle of αi = 48 deg.
Is incident at βi = 57 deg.

As described above, by changing the incident angle α of the laser beam incident on the return mirror 7 in the sub-scanning direction, the angle difference Δβ (= βi) of the angle β of the laser beam incident on the return mirror 7 at the entire view angle. -Βo) and PS
Of the polarized light component also changes.

In this embodiment, the angle at which the laser beam directed toward the center of the effective scanning area on the surface to be scanned enters the return mirror 7 is βo (deg), and the laser beam toward the end of the effective scanning area on the surface 8 to be scanned. Assuming that the angle at which the light beam enters the return mirror 7 is βi (deg), the following condition is satisfied: 8 (deg) ≦ βi−βo ≦ 20 (deg) (A).

The above-mentioned conditional expression (A) defines a range in which the illuminance distribution on the surface to be scanned can be easily made uniform. In particular, when the rotation of the polarization direction occurs, the effect of the present invention is larger than that of the comparative example. This is related to the range in which it is exerted. If the range is out of the range of the conditional expression (A), it is difficult to uniformly correct the illuminance distribution on the surface to be scanned.

Each image height of the optical scanning device in this embodiment
P on the reflection surface 7a of the return mirror 7 at (angle of view)
FIG. 14 shows the ratios of the polarization component and the S polarization component.

In the present embodiment, the angle difference Δβ of the laser beam incident on the return mirror 7 is 9 degrees,
On the optical axis 9, the S-polarized light component shows 100%, and as the angle of view increases, the P-polarized light component increases. High ± 1
07 mm), the S-polarized component is about 78%, and the P-polarized component is about 2%.
2%.

FIG. 15 shows the folding mirror 7 according to the present invention.
FIG. 9 is a diagram showing the angle characteristics of the reflectance for each of the P-polarized light component and the S-polarized light component on the reflection surface 7a.

In the present embodiment, the reflectivity of the PS polarization component is substantially the same, the reflectivity of the laser beam incident on the return mirror 7 is 48 °, the reflectivity is 60.0%, and the reflectivity is 57 °. The rate is set to be 56.6%. That is, as shown in FIG. 15, as the incident angle of the laser beam incident on the return mirror 7 increases, the reflection surface 7 decreases so that the reflectance of S-polarized light or P-polarized light decreases.
a. As a result, as shown in FIG. 16, the illuminance distribution on the surface 8 to be scanned can be corrected to be substantially uniform so as to be within a difference of 0.8% in the entire effective scanning area.

Here, as Comparative Example 2, an example in which the illuminance distribution on the surface 8 to be scanned is made substantially uniform by utilizing the difference in the reflectance of the conventional PS polarization component as in Comparative Example 1 described above. . Comparative Example 2 is different from the present embodiment in that the reflectance of the PS polarization component on the reflection surface of the folding mirror 7 is different.

FIG. 17 shows the reflectance of the PS polarization component on the reflection surface of the folding mirror in Comparative Example 2. The reflectance of the P-polarized component is 4 when the incident angle β is in the range of 48 to 57 degrees.
3.1%, and the reflectance of the S-polarized light component is 60.0%. As a result, as shown in FIG. 18, the illuminance distribution on the scanned surface 8 has a difference of 1.0% over the entire effective scanning area.

At this time, similarly to the first embodiment, the angle of view is ± 56.2 d.
The transmittance of the scanning optical system 6 has a large distribution of 1.06 times at the peripheral portion (angle of view ± 56.2 deg) with respect to the axis 9 by the scanning optical system 6 having a wide angle of view with eg. In order to substantially uniformly correct the illuminance distribution on the surface 8 to be scanned, it is difficult to provide a large difference in the reflectance of the PS polarization component as large as 16.9% (71.8% in ratio) and to correct it. You can see that.

As can be seen from this difference, the surface to be scanned 8 is utilized by utilizing the difference in the reflectance of the PS polarization component mentioned as Comparative Example 2.
The method of changing the reflectance according to the incident angle β of the laser beam incident on the return mirror 7 can correct the illuminance distribution on the surface 8 to be scanned more uniformly than the method of correcting the above illuminance distribution. . Therefore, if the effects of the present embodiment are used, the illuminance distribution on the surface 8 to be scanned can be corrected to be substantially uniform with higher accuracy.

In some cases, the polarization direction of the semiconductor laser 1 as the light source means is rotated from a state parallel or perpendicular to the deflection plane due to a manufacturing error or an assembly error. For example, if the polarization direction of the laser beam emitted from the semiconductor laser 1 is rotated by 5 degrees from the deflection plane, the scanning optical system 6 is slightly symmetrically transmitted with respect to the optical axis 9 under the influence of the rotation of the polarization direction. The P.S. on the reflection surface 7a of the return mirror 7 is not only changed, but also changed.
The ratio of the polarization component differs between the left and right sides of the optical axis 9.

In the present embodiment, the reflectance of the PS mirror component on the reflection surface 7a of the return mirror 7 is substantially the same, so that the illuminance distribution on the surface 8 to be scanned is not affected by the rotation of the polarization direction. . However, when the reflectance difference is made larger than that of Comparative Example 1 by the P-polarized light component and the S-polarized light component as in Comparative Example 2, the asymmetry of the reflectance of the reflecting surface of the folding mirror also occurs. As a result, in the optical scanning device according to the present embodiment, as shown in FIG. 19, the illuminance distribution on the surface 8 to be scanned has a difference of 0.9% over the entire effective scanning area. As shown, the scanned surface 8
The above illuminance distribution is 4.7% difference over the entire effective scanning area,
Rotation of the polarization direction of the laser beam deteriorates the uniformity of the illuminance distribution.

When the polarization direction is further rotated by 10 degrees, in this embodiment, as shown in FIG.
The illuminance distribution above is a difference of 1.0% in the entire effective scanning area, whereas the comparative example 2 has a difference of 8.6% as shown in FIG. It becomes a problem far beyond.

From this, it can be seen that the uniformity of the illuminance distribution on the surface 8 to be scanned can be maintained even if the polarization direction of the laser beam emitted from the light source means 1 is rotated by the effect of the present embodiment. Therefore, it is possible to provide an optical scanning device that can always obtain a good image.

According to the present embodiment, the return mirror 7
Without limiting the angle α (turnback angle) in the sub-scanning direction, the degree of freedom in configuring the optical scanning device can be increased.

When the same scanning optical system 6 is used, the angle β at which the laser beam is incident on the return mirror 7 is determined by the angle α of the return mirror 7 in the sub-scanning direction. In addition, the same folding mirror 7 can be used for a plurality of main body arrangements, and cost can be reduced.

[Third Embodiment] Next, a third embodiment of the present invention will be described.

The difference between this embodiment and the first embodiment is that the light source means is constituted by a monolithic multi-beam light source (multi-laser array) having a plurality (two in this embodiment) of light-emitting portions (light-emitting points). The point is that the light source means 1 is rotated around the optical axis of the condenser lens 2 in order to set the interval between the scanning lines on the surface 8 to be scanned to a desired value. Other configurations and optical functions are substantially the same as those of the first embodiment, and thus, similar effects are obtained.

In the present embodiment, a plurality of laser beams emitted from the monolithic multi-beam light source means 1 have substantially one polarization direction. This light source means 1
In the multi-beam scanning device using the
In order to set the interval between the upper scanning lines to a value corresponding to the pixel density, it is necessary to rotate the light source means 1 around the optical axis of the condenser lens 2 to adjust the interval between the plurality of light emitting points to a desired value. The angle γ (de) for rotating the light source means 1 around the optical axis of the condenser lens 2
g) is given by the following equation.

Sin γ = t / βs / La where t is the scanning line interval corresponding to the pixel density, βs is the lateral magnification in the entire sub-scanning direction, and La is the interval between light emitting points.

In this embodiment, the pixel density is 600 dpi.
Therefore, the scanning line interval t is 42.3 μm, the overall lateral magnification βs in the sub-scanning direction is βs = 6.8 (times), and the light emitting point interval L
a is La = 90.0 μm, and the angle γ for rotating the light source means 1 around the optical axis of the condenser lens 2 is γ = 3.95 deg.

At this time, the polarization direction of the laser beam is also rotated by an angle γ from a direction substantially parallel to the deflection plane. As a result, the laser beam traveling toward the center of the effective scanning area on the surface 8 to be scanned is directed to the return mirror 7 from the S polarization direction by an angle γ.
It is rotating and incident. In addition, the laser beam that is completely polarized in the S-polarized direction and enters the return mirror 7 is located at a position shifted to the left or right from the center of the effective scanning area.
If the reflectance of the PS polarization component is provided on the reflection surface 7a of the return mirror 7, the illuminance distribution on the scanned surface 8 will be asymmetric with respect to the center of the effective scanning area.

Therefore, in the present embodiment, the reflectance of the P-polarized light component and that of the S-polarized light component are made substantially the same using the folding mirror
The illuminance distribution on the surface 8 to be scanned is corrected substantially uniformly by forming the reflecting surface 7a so that the reflectance of S-polarized light or P-polarized light decreases as the incident angle β of the laser beam incident on the surface becomes larger. ing.

FIG. 23 is a diagram showing the illuminance distribution on the surface to be scanned in this embodiment.

Since the light source means 1 is rotated by an angle γ around the optical axis of the condenser lens 2 in order to adjust the interval between the scanning lines of the multi-beam on the surface 8 to be scanned, the scanning optical system 6 has a light transmittance. It changes by a small amount substantially symmetrically with respect to the axis 9,
Since the reflection surface 7a of the reflecting mirror 7 has substantially the same reflectance for the P-polarized light component and the S-polarized light component, it is not affected by the rotation of the polarization direction. Therefore, the illuminance distribution on the scanned surface 8 can be suppressed to a difference of 1.0% over the entire effective scanning area,
This makes it possible to satisfactorily correct the uniformity of the illuminance distribution.

Here, as Comparative Example 3, an example in which the illuminance distribution on the surface 8 to be scanned is made substantially uniform using the difference in the reflectance of the conventional PS polarization component will be described. Comparative Example 3 is different from the present embodiment in that the P.S.
The point is that the reflectance of the polarized light component is different.

In the optical scanning device of Comparative Example 3, the same folding mirror as that of Comparative Example 1 is used. The reflectance of the P-polarized light component is 54.0% when the incident angle β is in the range of 25 to 42 deg.
The reflectance of the polarized light component is 60.0%. In Comparative Example 1, as shown in FIG. 7, the illuminance distribution on the scanned surface 8 has a difference of 1.7% over the entire effective scanning area. In Comparative Example 3, the scanning line interval on the scanned surface 8 is corrected. Therefore, the light source means 1 is rotated 3.95 degrees around the optical axis of the condenser lens 2, so that the illuminance distribution on the surface 8 to be scanned has a difference of 2.6% over the entire effective scanning area as shown in FIG. Becomes

As can be seen from this difference, the surface 8 to be scanned is obtained by utilizing the difference in the reflectance of the PS polarization component described as Comparative Example 3.
The method in which the reflectance is changed according to the incident angle β of the laser beam incident on the return mirror 7 can correct the illumination distribution on the surface 8 to be scanned more uniformly than the method in which the above illumination distribution is corrected. I understand. Therefore, by using the effect of the present embodiment, it is possible to substantially uniformly correct the illuminance distribution on the surface 8 to be scanned without causing asymmetry in the multi-beam scanning apparatus using the monolithic multi-beam as the light source 1. it can.

Further, the two laser beams have variations in the direction of polarization, and some have a relative difference of 15 degrees. At this time, the polarization direction of one laser beam (for example, A laser beam) is rotated from the deflection plane by 3.95 deg tilted to adjust the scanning line interval, while the other laser beam (for example, B laser beam) is rotated. The light beam has a polarization direction rotated by 18.95 degrees from the deflection plane. Therefore, the two laser beams that scan the same position on the surface 8 to be scanned have greatly different proportions of the PS polarization components on the reflection surface 7 a of the return mirror 7.

In the present embodiment, since the reflectance of the P-polarized light component and the reflectance of the S-polarized light component on the reflecting surface 7a of the return mirror 7 are substantially the same, it is not affected by the rotation of the polarization direction of the laser beam. Since the desired reflectance can always be set, the difference in the amount of light between the two laser beams on the scanned surface 8 is 1.5%, and the illuminance distribution of the A laser beam is 1.0% over the entire effective scanning area as shown in FIG. , B laser beam can be suppressed to a light amount difference of 1.8%. In contrast,
In Comparative Example 3, since the reflectance is different between the PS polarization components, the reflectances of the two laser beams differ greatly due to the difference in the ratio of the PS polarization components. That is, as shown in FIG. 26, the difference between the light amounts of the two laser beams on the scanned surface 8 is 2.7% at the maximum, the illuminance distribution of the A laser beam is 2.6%, and 18.95 degrees from the deflection plane. B light beam which is largely rotated is 7.2% in the entire effective scanning area on the surface 8 to be scanned.
Light amount difference. On the surface 8 to be scanned, which is the photosensitive drum surface, the A laser beam and the B laser beam are alternately optically scanned, and the scanning line drawn by the B laser beam has high illuminance while sandwiching the optical axis 9. On the other hand, there is a problem that the illuminance is low and the image is dark on the one hand and light on the other. A
Since there is a large difference in the amount of light from the laser beam, shading may occur on every other scanning line on the image.

Therefore, if the effects of the present embodiment are used, even if the polarization directions of the two laser beams emitted from the multi-beam light source 1 vary, the illuminance distribution can be made substantially uniform on the surface 8 to be scanned. Accordingly, it is possible to provide a multi-beam scanning device capable of always obtaining a good image.

In this embodiment, a multi-beam scanning device using two laser beams has been described as an example.
The present invention is not limited to this.
Even if the number of beams is increased to four or four, the same effect as in the present embodiment can be obtained.

In this embodiment, it is desirable that the illuminance distribution on the surface to be scanned be within ± 3% (6% difference) over the entire effective scanning area as described above in order to obtain a good image.

[Fourth Embodiment] Next, a fourth embodiment of the present invention will be described.

This embodiment is different from the third embodiment in that the angle (folding angle) of the laser beam incident on the folding mirror 7 in the sub-scanning direction, which is polarized in the S-polarized direction, is αo = similar to the second embodiment. This is a point set at 48 deg, and the reflectance of the reflection surface 7a of the return mirror 7 is set in the same manner as in the second embodiment. Other configurations and optical functions are substantially the same as those of the third embodiment, and thus, similar effects are obtained.

That is, the present embodiment uses a monolithic multi-laser array 1 that emits two laser beams similarly to the above-described third embodiment, and adjusts the scanning line interval on the surface 8 to be scanned. 3.95 deg around the optical axis of the condenser lens 2 with the monolithic multi-laser array 1
Rotating.

In the present embodiment, the same scanning optical system 6 and folding mirror 7 as those of Embodiment 2 are used, and the angle of the laser beam, which is incident on the folding mirror 7 and is polarized in the S-polarized direction, in the sub-scanning direction, as in Embodiment 2. Since αo is set to αo = 48 deg, the reflectance of the reflecting surface 7a of the return mirror 7 is not affected by the rotation of the polarization direction of the laser beam, and the transmittance of the scanning optical system 6 slightly changes. As shown in FIG. 27, the illuminance distribution on the scanned surface 8 is 0.9% over the entire effective scanning area.
Can be corrected so as to be substantially uniform.

Here, as Comparative Example 4, a description will be given of an example in which the illuminance distribution on the surface 8 to be scanned is made substantially uniform using the difference in the reflectance of the conventional PS polarization component. The difference from the present embodiment in Comparative Example 4 is that P · S on the reflecting surface of the folding mirror is different.
The point is that the reflectance of the polarized light component is different.

The reflecting surface of the return mirror of Comparative Example 4 is the same as that of Comparative Example 2, and the reflectance of the P-polarized light component is 4 for the incident angle β.
It is 43.1% in the range of 8 to 57 degrees, and the reflectance of the S-polarized light component is 60.0%.

However, in the comparative example 4, the light source means 1 is connected to the condenser lens 2 in order to correct the scanning line interval on the surface 8 to be scanned.
28, the illuminance distribution on the surface 8 to be scanned has a difference of 3.8% over the entire effective scanning area as shown in FIG.

As in the third embodiment, the two laser beams have variations in the polarization directions, and the relative difference is 15 degrees.
In this embodiment, the reflectance of the folding mirror is not affected by the rotation of the polarization direction of the laser beam, and only the transmittance of the scanning optical system 6 is changed. The illuminance distribution of the light beam falls within a 0.9% difference over the entire effective scanning area, and the illuminance distribution of the B laser beam falls within a 1.5% difference over the entire effective scanning area. On the other hand, in Comparative Example 4, as shown in FIG. 30, the illuminance distribution of the A laser beam was 3.8% difference over the entire effective scanning area, and the illuminance distribution of the B laser beam was 15.2% over the entire effective scanning area. A difference occurs, and non-uniformity of the illuminance distribution cannot be tolerated.

Therefore, if the effect of the present embodiment is used, the angle α (return angle) in the sub-scanning direction of the laser beam incident on the return mirror 7 and polarized in the S-polarized direction is large, and P · S on the optical axis and in the peripheral portion. Even in the configuration of the optical scanning device in which the ratio of the polarized light component does not change much, the illuminance distribution on the surface 8 to be scanned can be corrected substantially uniformly, and the rotation of the laser beam in the polarization direction is affected. It is possible to provide a multi-beam scanning device that can maintain a substantially uniform illuminance distribution without any trouble and always obtain good images.

In this embodiment, the optical axis 9 of the scanning optical system 6 is
In the above description, the case where the laser beam whose main polarization direction is S-polarized light is incident on the folding mirror 7 is described as an example. Can be sufficiently corrected using the effect of the present invention even when the light is incident.

[Fifth Embodiment] Next, a fifth embodiment of the present invention will be described.

In this embodiment, the first and second embodiments are described.
The difference from the above is that the polarization direction of the laser beam emitted from the light source means is rotated by 90 degrees,
Is that the reflectance of the reflection surface 7a is different. Other configurations and optical functions are substantially the same as those of the first and second embodiments, and thus, similar effects are obtained.

That is, in this embodiment, the laser beam emitted from the semiconductor laser 1 is linearly polarized in a direction perpendicular to the deflection plane, and the incident angles on the first and second fθ lenses 6a and 6b are small. By the way, the Fresnel reflectivity is low,
Fresnel reflectivity increases where the angle of view is widened and the angles of incidence on the first and second fθ lenses 6a and 6b are large. Therefore, the illuminance distribution after passing through the scanning optical system 6 is highest on the optical axis 9 and lowest at the end of the effective scanning area (image height ± 107 mm) on the surface 8 to be scanned, as shown in FIG. The light quantity ratio is 0.91 times.

FIG. 32 shows a folding mirror 7 according to the present invention.
FIG. 9 is a diagram showing the angle characteristics of the reflectance for each of the P-polarized light component and the S-polarized light component on the reflection surface 7a.

In this embodiment, the reflectivity of the PS polarization component is substantially the same, the reflectivity is 60.0% when the incident angle β of the laser beam incident on the return mirror 7 is 25 °, and the reflectivity is 42 ° when the incident angle β is 42 °. The rate is set to be 65.5%. That is, as shown in FIG. 32, as the incident angle of the laser beam incident on the return mirror 7 increases, the reflection surface 7 increases so that the reflectance of P-polarized light or S-polarized light increases.
a. As a result, as shown in FIG. 33, the illuminance distribution on the scanned surface 8 can be corrected so as to be substantially uniform so as to be within a 2.3% difference over the entire effective scanning area.

Here, as Comparative Example 5, an example in which the illuminance distribution on the surface 8 to be scanned is made substantially uniform using the difference in the reflectance of the conventional PS polarization component will be described. The difference from the present embodiment in Comparative Example 5 is that P ·
The point is that the reflectance of the S-polarized component is different.

FIG. 34 shows the reflectance of the PS polarization component on the reflection surface of the return mirror in Comparative Example 5. The reflectance of the P-polarized component is 60 when the incident angle β is in the range of 25 to 42 deg.
0%, and the reflectance of the S-polarized light component is 69.3%. As a result, as shown in FIG. 35, the illuminance distribution on the scanned surface 8 has a difference of 3.5% over the entire effective scanning area.

As can be seen from this difference, the surface to be scanned 8 is obtained by utilizing the difference in the reflectance of the PS polarization component described as Comparative Example 5.
The method of changing the reflectance according to the incident angle β of the laser beam incident on the return mirror 7 can correct the illuminance distribution on the surface 8 to be scanned more uniformly than the method of correcting the above illuminance distribution. . Therefore, even when the laser beam emitted from the light source means 1 is linearly polarized perpendicular to the deflection plane, if the effect of the present embodiment is used, the illuminance distribution on the scanned surface 8 can be made more uniform with higher accuracy. Can be corrected.

When the polarization direction of the laser beam emitted from the semiconductor laser 1 is rotated by 5 degrees from a plane perpendicular to the deflection plane, in the present embodiment, the PS polarization component of the reflection surface 7a of the return mirror 7 is changed. Since the reflectance is substantially the same, the reflectance of the folding mirror 7 is not affected by the rotation of the polarization direction of the laser beam, and the scanning optical system 6
36 slightly changes, and as shown in FIG. 36, the illuminance distribution on the surface 8 to be scanned has a difference of 2.3% over the entire effective scanning area. On the other hand, in Comparative Example 5, since the reflectance differs between the P-polarized light component and the S-polarized light component of the reflection surface of the folding mirror, the illuminance distribution on the surface 8 to be scanned has an effective scanning area as shown in FIG. There is a 5.2% difference across the whole area.

Further, as shown in FIG. 38, when the polarization direction of the laser beam is rotated by 10 degrees from a plane perpendicular to the deflection plane, in this embodiment, the illuminance distribution on the surface to be scanned is 2. Although the difference is 5%, in Comparative Example 5 shown in FIG. 39, a difference of 7.5% occurs and exceeds the allowable value, which is a problem.

Thus, if the effects of the present embodiment are used,
Even in an optical scanning device in which the laser beam emitted from the light source means 1 is linearly polarized perpendicular to the deflection plane, the illuminance distribution on the surface 8 to be scanned is not affected by the rotation of the polarization direction of the laser beam. Can be kept uniform, and an optical scanning device that can always provide good images can be obtained.

[Embodiment 6] Next, Embodiment 6 of the present invention will be described.

In this embodiment, the above-described third and fourth embodiments are described.
The different point is that the polarization directions of a plurality of laser light beams emitted from the light source are rotated by 90 degrees, and the reflectance of the reflection surface 7a of the folding mirror 7 is different. Other configurations and optical functions are substantially the same as those of the third and fourth embodiments, and the same effects are obtained.

That is, in the present embodiment, the reflectance in the PS polarization component is made substantially the same by using the same folding mirror 7 as in the above-described fifth embodiment, and the angle of incidence of the laser beam incident on the folding mirror 7 is reduced. P-polarized as it gets larger,
Alternatively, the reflection surface 7a is formed such that the reflectance of S-polarized light increases. Thus, even in a multi-beam scanning apparatus in which a plurality of laser beams emitted from the light source means 1 are linearly polarized perpendicular to the deflection plane, the scanning surface is not affected by the rotation of the polarization direction of the laser beam. 8 can be kept substantially uniform, and a good image can always be provided.

[Image Forming Apparatus] FIG. 40 shows an embodiment of an image forming apparatus (electrophotographic printer) using any one of the optical scanning apparatuses according to the first to sixth embodiments or the multi-beam scanning apparatus. It is principal part sectional drawing of a direction.
In FIG. 40, reference numeral 104 denotes an image forming apparatus. Code data Dc is input to the image forming apparatus 104 from an external device 117 such as a personal computer. The code data Dc is converted into image data (dot data) Di by the printer controller 111 in the apparatus. This image data Di is transmitted to the optical scanning unit 10
Input to 0. Then, from this optical scanning unit (optical scanning device or multi-beam scanning device) 100,
Light beam (light flux) 1 modulated according to image data Di
The light beam 103 scans the photosensitive surface of the photosensitive drum 101 in the main scanning direction.

The photosensitive drum 101, which is an electrostatic latent image carrier (photoconductor), is rotated clockwise by a motor 115. Then, along with this rotation, the photosensitive surface of the photosensitive drum 101 moves in the sub-scanning direction orthogonal to the main scanning direction with respect to the light beam 103. Above the photosensitive drum 101, a charging roller 102 for uniformly charging the surface of the photosensitive drum 101 is provided so as to contact the surface.
The surface of the photosensitive drum 101 charged by the charging roller 102 is irradiated with a light beam 103 scanned by the optical scanning unit 100.

As described above, the light beam 103 is
The light is modulated based on the image data Di, and by irradiating the light beam 103, an electrostatic latent image is formed on the surface of the photosensitive drum 101. This electrostatic latent image is further moved from the irradiation position of the light beam 103 to the photosensitive drum 101.
Is developed as a toner image by a developing device 107 disposed so as to contact the photosensitive drum 101 on the downstream side in the rotation direction of the photosensitive drum 101. As the toner particles used here, for example, those having a sign opposite to the charge charged by the charging roller 102 are used. Then, a portion (image portion) where the toner adheres to the non-exposed portion of the photosensitive drum is formed. That is, in the present embodiment, so-called regular development is performed. In this embodiment, reversal development in which toner adheres to the exposed portion of the photosensitive drum may be performed.

The toner image developed by the developing device 107 is transferred below the photosensitive drum 101 by a transfer roller 108 disposed opposite to the photosensitive drum 101 onto a sheet 112 as a material to be transferred. The paper 112 is stored in a paper cassette 109 in front of the photosensitive drum 101 (right side in FIG. 8), but can be fed manually. At the end of the paper cassette 109, a paper feed roller 11 is provided.
0 is provided, and the paper 11 in the paper cassette 109 is
2 to the transport path.

As described above, the sheet 112 on which the unfixed toner image has been transferred is further moved to the rear of the photosensitive drum 101 (FIG. 4).
0 (left side at 0). The fixing device has a fixing roller 113 having a fixing heater (not shown) therein.
And a pressure roller 114 disposed so as to be in pressure contact with the fixing roller 113. The paper 112 scattered from the transfer unit is transferred to the fixing roller 113 and the pressure roller 1.
The unfixed toner image on the paper 112 is fixed by heating while applying pressure at the pressure contact portion 14. Further, a paper discharge roller 116 is disposed behind the fixing roller 113, and discharges the fixed paper 112 to the outside of the image forming apparatus.

Although not shown in FIG. 40, the print controller 111 not only converts the explanation data, but also the motor 115 and other components in the image forming apparatus.
The control of the polygon motor and the like in the optical scanning unit 100 is performed.

[0149]

According to the first aspect of the present invention, by appropriately setting the reflectance of the reflecting surface of the reflecting member as described above, the light emitted from the light source means can be used even if a wide-angle scanning optical system is used. Even if the polarization direction of the laser beam rotates, it is possible to achieve an optical scanning device capable of making the illuminance distribution substantially uniform on the surface to be scanned.

According to the second aspect of the present invention, by appropriately setting the reflectivity of the reflecting surface of the reflecting member as described above, the laser beam emitted from the light source means can be used even if a wide-angle scanning optical system is used. Even if the polarization direction is rotated, it is possible to achieve a multi-beam scanning device in which the illuminance distribution is not uneven on the surface to be scanned.

According to the third aspect, as described above, by using the above-described optical scanning device or multi-beam scanning device,
An image forming apparatus capable of making the illuminance distribution substantially uniform on the surface to be scanned can be achieved.

[Brief description of the drawings]

FIG. 1 is a main-scan sectional view and a sub-scan sectional view of Embodiment 1 of the present invention.

FIG. 2 is an illuminance distribution diagram after passing through a scanning optical system according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a PS polarization component ratio on a reflection surface of a folding mirror according to the first embodiment of the present invention.

FIG. 4 is a diagram showing the reflectance of the PS polarization component according to the first embodiment of the present invention.

FIG. 5 is an illuminance distribution diagram according to the first embodiment of the present invention.

FIG. 6 is a diagram showing the reflectance of the PS polarization component of Comparative Example 1.

FIG. 7 is an illuminance distribution diagram of Comparative Example 1.

FIG. 8 is an illuminance distribution diagram when the light source unit according to the first embodiment of the present invention rotates.

FIG. 9 is an illuminance distribution diagram when the light source unit of Comparative Example 1 rotates.

FIG. 10 is an illuminance distribution diagram when the light source unit according to the first embodiment of the present invention rotates.

FIG. 11 is an illuminance distribution diagram when the light source unit of Comparative Example 1 rotates.

FIG. 12 is a perspective view showing a folding mirror according to the first embodiment of the present invention.

FIG. 13 is a main-scan sectional view and a sub-scan sectional view of Embodiment 2 of the present invention.

FIG. 14 is a diagram showing the PS polarization component ratio on the reflection surface of the folding mirror according to the second embodiment of the present invention.

FIG. 15 is a diagram showing the reflectance of the PS polarization component according to the second embodiment of the present invention.

FIG. 16 is an illuminance distribution diagram according to the second embodiment of the present invention.

FIG. 17 is a diagram showing the reflectance of the PS polarization component of Comparative Example 2.

FIG. 18 is an illuminance distribution diagram of Comparative Example 2.

FIG. 19 is an illuminance distribution diagram when the light source unit according to the second embodiment of the present invention is rotated.

FIG. 20 is an illuminance distribution diagram when the light source unit of Comparative Example 2 of the present invention rotates.

FIG. 21 is an illuminance distribution diagram when the light source unit according to the second embodiment of the present invention rotates.

FIG. 22 is an illuminance distribution diagram when the light source unit of Comparative Example 2 rotates.

FIG. 23 is an illuminance distribution diagram according to the third embodiment of the present invention.

FIG. 24 is an illuminance distribution chart of Comparative Example 3.

FIG. 25 is an illuminance distribution diagram when the light source unit according to the third embodiment of the present invention is rotated.

FIG. 26 is an illuminance distribution diagram when the light source means of Comparative Example 3 of the present invention rotates.

FIG. 27 is an illuminance distribution diagram according to the fourth embodiment of the present invention.

FIG. 28 is an illuminance distribution chart of Comparative Example 4.

FIG. 29 is an illuminance distribution diagram when the light source unit according to the fourth embodiment of the present invention is rotated.

FIG. 30 is an illuminance distribution diagram when the light source unit of Comparative Example 4 rotates.

FIG. 31 is an illuminance distribution diagram after passing through a scanning optical system according to the fifth embodiment of the present invention.

FIG. 32 is a diagram showing the reflectance of the PS polarization component according to the fifth embodiment of the present invention.

FIG. 33 is an illuminance distribution diagram according to the fifth embodiment of the present invention.

FIG. 34 is a view showing the reflectance of the PS polarization component of Comparative Example 5.

FIG. 35 is an illuminance distribution chart of Comparative Example 5.

FIG. 36 is an illuminance distribution diagram when the light source unit according to the fifth embodiment of the present invention rotates.

FIG. 37 is an illuminance distribution diagram when the light source unit of Comparative Example 5 rotates.

FIG. 38 is an illuminance distribution diagram when the light source unit according to the fifth embodiment of the present invention is rotated.

FIG. 39 is an illuminance distribution diagram when the light source unit of Comparative Example 5 rotates.

FIG. 40 is a schematic diagram of a main part in the sub-scanning direction showing a configuration example of an image forming apparatus (electrophotographic printer) using the scanning optical device of the present invention.

FIG. 41 is a perspective view showing a conventional optical scanning device.

[Explanation of symbols]

 Reference Signs List 1 light source means (semiconductor laser) 2 condenser lens (collimator lens) 3 aperture stop (aperture) 4 cylindrical lens 5 deflecting means (optical deflector) 6 scanning optical system 6a first fθ lens 6b second fθ lens 7 Reflecting member (return mirror) 7a Reflecting surface 8 Scanned surface (photosensitive drum surface) 11 Incident optical system 100 Optical scanning device 101 Photosensitive drum 102 Charging roller 103 Light beam 104 Image forming device 107 Developing device 108 Transfer roller 109 Paper cassette 110 Feed Paper roller 112 Transfer material (paper) 113 Fixing roller 114 Pressure roller 116 Discharge roller

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04N 1/113 H04N 1/04 104A F-term (Reference) 2C362 AA26 BA56 BA67 BA87 BA90 2H045 AA01 BA02 BA22 CA63 CB35 DA41 2H087 KA19 LA22 LA25 PA02 PA17 PB02 RA07 TA03 UA01 5C051 AA02 CA07 DB02 DB22 DB24 DB30 DC07 FA01 5C072 AA03 BA17 DA02 DA04 DA21 HA02 HA06 HA09 HA13 XA01 XA05

Claims (35)

[Claims] 1. A light source for emitting a linearly polarized laser beam, an incident optical system for causing the laser beam emitted from the light source to enter a deflecting unit, and a laser beam deflected by the deflecting unit in a sub-scanning direction. A scanning optical system that forms an image on a surface to be scanned via a reflecting member that is turned back. The reflecting surface of the reflecting member has substantially the same reflectance for P-polarized light and S-polarized light, and the incident laser beam. An optical scanning device characterized in that the reflectance varies depending on the incident angle of a light beam, thereby making the illuminance distribution on the surface to be scanned substantially uniform. 2. The reflectances of the P-polarized light and the S-polarized light are substantially equal when the difference between the two reflectances is within ± 3% within an incident angle range of 25 ° to 40 °. 2. The optical scanning device according to 1. 3. The substantially uniform illuminance distribution means that the illuminance distribution on the surface to be scanned is within ± 3% of the on-axis effective scanning area over the entire effective scanning area. 2. The optical scanning device according to 1. 4. The apparatus according to claim 1, wherein a condition of k / W ≦ 0.6 is satisfied, where k is an fθ coefficient of the scanning optical system, and W is an effective scanning width of the surface to be scanned. Optical scanning device. 5. An angle βa at which a laser beam directed toward the center of an effective scanning area on the surface to be scanned enters the reflecting member.
(deg), the angle of incidence of the laser beam toward the end of the effective scanning area on the surface to be scanned on the reflecting member is βi (de).
2. The optical scanning device according to claim 1, wherein, when g), a condition of 8 (deg) ≦ βi−βo ≦ 20 (deg) is satisfied. 6. A light source for emitting a plurality of linearly polarized laser beams, an incident optical system for causing a plurality of laser beams emitted from the light source to enter a deflecting unit, and a plurality of laser beams deflected by the deflecting unit. A scanning optical system that forms an image on the surface to be scanned via a reflecting member that is turned back in the sub-scanning direction. The reflecting surface of the reflecting member has a reflectance of P-polarized light and S-polarized light that is substantially equal. A multi-beam scanning device, wherein the illuminance distribution on the surface to be scanned is made substantially uniform by making the reflectivity different depending on the incident angle of the incident laser beam. 7. The reflectivity of the P-polarized light and the S-polarized light is substantially equal when the difference between the two reflectances is within ± 3% within the range of the incident angle of 25 ° to 40 °. 7. The multi-beam scanning device according to 6. 8. The substantially uniform illuminance distribution means that the illuminance distribution on the surface to be scanned is within ± 3% of the on-axis effective scanning area over the entire effective scanning area. 7. The multi-beam scanning device according to 6. 9. The optical system according to claim 6, wherein the following condition is satisfied: k / W ≦ 0.6, where k is an fθ coefficient of the scanning optical system and W is an effective scanning width of the surface to be scanned. Multi-beam scanning device. 10. An angle β at which a laser beam directed to the center of an effective scanning area on the surface to be scanned enters the reflecting member.
o (deg), βi (de) is the angle of incidence of the laser beam toward the end of the effective scanning area on the surface to be scanned on the reflecting member.
7. The multi-beam scanning device according to claim 6, wherein, when g) is satisfied, a condition of 8 ≦ βi−βo ≦ 20 (deg) is satisfied. 11. The multi-beam scanning apparatus according to claim 6, wherein said light source means is rotatable around an optical axis of said incident optical system. 12. A light source means for emitting a linearly polarized laser beam having a polarization direction in a direction substantially parallel to a deflection plane;
An incident optical system for causing a laser beam emitted from the light source unit to enter a deflecting unit; and a scanning optical system for forming an image on a surface to be scanned via a reflecting member which folds the laser beam deflected by the deflecting unit in the sub-scanning direction. The reflection surface of the reflection member has substantially the same reflectance in P-polarized light and S-polarized light, and the reflectance of S-polarized light or P-polarized light increases as the incident angle of the incident laser beam increases. An optical scanning device, wherein the optical scanning device is formed so as to reduce the number of light beams. 13. The optical scanning device according to claim 12, wherein the illuminance distribution on the surface to be scanned is made substantially uniform by reducing the reflectance of the S-polarized light or the P-polarized light. 14. The illuminance distribution being substantially uniform means that the illuminance distribution on the surface to be scanned is within ± 3% over the entire effective scanning area with respect to the axis.
The optical scanning device according to claim 1. 15. The optical system according to claim 12, wherein the following condition is satisfied: k / W ≦ 0.6, where k is an fθ coefficient of the scanning optical system and W is an effective scanning width of the surface to be scanned. Optical scanning device. 16. An angle at which a laser beam toward the center of an effective scanning area on the surface to be scanned is incident on the reflecting member.
o (deg), βi (de) is the angle of incidence of the laser beam toward the end of the effective scanning area on the surface to be scanned on the reflecting member.
13. The optical scanning device according to claim 12, wherein, when g), a condition of 8 (deg) ≦ βi−βo ≦ 20 (deg) is satisfied. 17. A light source means for emitting a linearly polarized laser beam having a polarization direction substantially perpendicular to a deflection plane;
An incident optical system for causing a laser beam emitted from the light source unit to enter a deflecting unit; and a scanning optical system for forming an image on a surface to be scanned via a reflecting member which folds the laser beam deflected by the deflecting unit in the sub-scanning direction. The reflection surface of the reflection member has substantially the same reflectance in P-polarized light and S-polarized light, and the reflectance of P-polarized light or S-polarized light increases as the incident angle of the incident laser beam increases. An optical scanning device characterized by being formed so as to increase. 18. The optical scanning device according to claim 17, wherein the illuminance distribution on the surface to be scanned is made substantially uniform by increasing the reflectance of the P-polarized light or the S-polarized light. 19. The substantially uniform illuminance distribution means that the illuminance distribution on the surface to be scanned is within ± 3% with respect to the axis over the entire effective scanning area.
The optical scanning device according to claim 1. 20. The optical system according to claim 17, wherein a condition of k / W ≦ 0.6 is satisfied, where k is an fθ coefficient of the scanning optical system and W is an effective scanning width of the surface to be scanned. Optical scanning device. 21. An angle at which a laser beam toward the center of an effective scanning area on the surface to be scanned is incident on the reflecting member.
o (deg), βi (de) is the angle of incidence of the laser beam toward the end of the effective scanning area on the surface to be scanned on the reflecting member.
18. The optical scanning device according to claim 17, wherein, when g), a condition of 8 (deg) ≦ βi−βo ≦ 20 (deg) is satisfied. 22. A light source means for emitting a plurality of linearly polarized laser light beams having a polarization direction in a direction substantially parallel to the deflection plane, and an incident optical system for causing the plurality of laser light beams emitted from the light source means to be incident on the deflection means. A scanning optical system that forms an image on the surface to be scanned via a reflecting member that folds the laser beam deflected by the deflecting means in the sub-scanning direction, wherein the reflecting surface of the reflecting member is P The multi-beam scanning is characterized in that the reflectances of the polarized light and the S-polarized light are substantially equal, and the reflectance of the S-polarized light or the P-polarized light decreases as the incident angle of the incident laser beam increases. apparatus. 23. The multi-beam scanning apparatus according to claim 22, wherein the illuminance distribution on the surface to be scanned is made substantially uniform by reducing the reflectance of the S-polarized light or the P-polarized light. 24. The substantially uniform illuminance distribution means that the illuminance distribution on the surface to be scanned is within ± 3% with respect to the axis over the entire effective scanning area.
A multi-beam scanning device as described. 25. The optical system according to claim 22, wherein, when an fθ coefficient of the scanning optical system is k and an effective scanning width of the scanned surface is W, a condition of k / W ≦ 0.6 is satisfied. Multi-beam scanning device. 26. An angle at which a laser beam toward the center of an effective scanning area on the surface to be scanned is incident on the reflecting member.
o (deg), βi (de) is the angle of incidence of the laser beam toward the end of the effective scanning area on the surface to be scanned on the reflecting member.
23. The multi-beam scanning device according to claim 22, wherein, when g), a condition of 8 (deg) ≦ βi−βo ≦ 20 (deg) is satisfied. 27. The multi-beam scanning apparatus according to claim 22, wherein said light source means is rotatable around an optical axis of said incident optical system. 28. A light source means for emitting a plurality of linearly polarized laser light fluxes having a polarization direction substantially perpendicular to a deflection plane, and an incident optical system for causing the plurality of laser light fluxes emitted from the light source means to be incident on the deflection means. A scanning optical system for imaging a plurality of laser beams deflected by the deflecting means on a surface to be scanned via a reflecting member that is turned back in the sub-scanning direction. Is characterized in that the reflectivity of P-polarized light and that of S-polarized light are substantially equal, and the reflectivity of P-polarized light or S-polarized light increases as the incident angle of the incident laser beam increases. Beam scanning device. 29. The multi-beam scanning apparatus according to claim 28, wherein the illuminance distribution on the surface to be scanned is made substantially uniform by increasing the reflectance of the P-polarized light or S-polarized light. 30. The illuminance distribution being substantially uniform means that the illuminance distribution on the surface to be scanned is within ± 3% with respect to the axis over the entire effective scanning area.
A multi-beam scanning device as described. 31. The optical system according to claim 28, wherein k / W ≦ 0.6, where k is an fθ coefficient of the scanning optical system and W is an effective scanning width of the surface to be scanned. Multi-beam scanning device. 32. An angle at which a laser beam directed toward the center of an effective scanning area on the surface to be scanned is incident on the reflecting member.
o (deg), βi (de) is the angle of incidence of the laser beam toward the end of the effective scanning area on the surface to be scanned on the reflecting member.
29. The multi-beam scanning apparatus according to claim 28, wherein, when g), a condition of 8 (deg) ≦ βi−βo ≦ 20 (deg) is satisfied. 33. A multi-beam scanning apparatus according to claim 28, wherein said light source means is rotatable around an optical axis of said incident optical system. 34. An optical scanning device or a multi-beam scanning device according to claim 1, and a photoconductor disposed on a surface to be scanned of the optical scanning device or the multi-beam scanning device. Developing means for developing, as a toner image, an electrostatic latent image formed by scanning a light beam on the photoreceptor, transfer means for transferring the developed toner image to paper, and the transferred toner image An image forming apparatus, comprising: a fixing unit for fixing the sheet to a sheet. 35. The optical scanning device according to claim 1, further comprising: a multi-beam scanning device configured to convert code data input from an external device into an image signal and input the image signal to the optical scanning device. An image forming apparatus, comprising: