JP3324161B2 - Laser scanning device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser scanning apparatus used in an image forming apparatus such as a laser printer or a digital copying machine for recording an image by scanning and exposing a laser beam on a photosensitive member in accordance with image information. About.

[0002]

2. Description of the Related Art In an image forming apparatus for printing a plurality of colors using a plurality of laser beams, a plurality of beams are scanned on a photosensitive member using a conventional laser scanning device which deflects and scans one beam. For this purpose, a method is conceivable in which a plurality of parallel beams having a predetermined interval are incident on the rotating polygon mirror in a direction perpendicular to the scanning direction. If it is desired to make a plurality of beams incident on the photoreceptor at a certain distance by using this method, the beams after the imaging lens can be separated by reflecting the beams after the imaging lens in different directions from each other. It is desirable that the vertical spacing be large. On the other hand, it is a well-known fact that it is desirable that the interval between the beams to be incident on the rotating polygon mirror is narrower, because the power consumption is smaller when the rotating polygon mirror is thinner.

An fθ lens is used as an imaging lens in a laser scanning device using a rotary polygon mirror. As this fθ lens, for example,
As disclosed in Japanese Patent Application Laid-Open No. 6444, there is known a two-lens type of a single lens having a negative refractive power and a single lens having a positive refractive power. In general, in the case of an fθ lens composed of a combination of a single lens having a negative refractive power and a single lens having a positive refractive power, the negative refractive power or the positive refractive power is the power of the lens in the scanning direction. Means
The vertical direction is either not specified or is the same as the scanning direction.

FIG. 11 is an explanatory view showing a main part of a laser scanning apparatus having an fθ lens of the type shown in the above-mentioned Japanese Patent Publication No. 62-26444. In this example, a laser beam emitted from a light source unit (not shown) is deflected and scanned by a rotating polygon mirror 100, and a pair of fθs of a single lens 101 having a negative refractive power and a single lens 102 having a positive refractive power is formed. The light passes through the lens 103, is reflected by the plane reflection mirror 104, and forms an image on the photoconductor 105. In the example shown in FIG. 11, each single lens 101, 10
Reference numeral 2 denotes a spherical surface 106 on both sides, which has the same refractive power in the vertical direction as in the scanning direction.

[0005]

However, the fθ of the type disclosed in Japanese Patent Publication No. Sho 62-26444 is disclosed.
Using a laser scanning device having a lens, when a plurality of parallel beams having a predetermined interval in the vertical direction with respect to the polygon mirror to make the plurality of beams scan on the photoconductor as described above, The interval after passing through the fθ lens becomes narrower than the vertical interval of the beam incident on the polygon mirror. Therefore, unless the interval between the incident beams is made considerably large and a configuration is adopted in which the polygon mirror has a sufficient thickness,
There is a problem that a desired interval for separating beams cannot be obtained after passing through the fθ lens.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a rotary polygon mirror which, when a plurality of laser beams are made incident on the rotary polygon mirror in a direction perpendicular to the scanning direction, does not greatly increase the thickness of the rotary polygon mirror after passing through the fθ lens. It is an object of the present invention to provide a laser scanning device capable of widening the interval between laser beams.

[0007]

According to the first aspect of the present invention ,
Is (i) a photosensitive member, the photoconductor (b) a plurality of light beams
Emit parallel light at a predetermined interval in the main scanning direction and the vertical direction
A light source unit, these emitted from (c) the light source unit
And one of the rotating polygon mirror for deflecting and scanning a plurality of light beams on a photosensitive member, the surface for diverging light only in a direction perpendicular to the direction of scanning and has a negative refractive power disposed to the rotary polygonal mirror side (D) And a single lens having a positive refractive power disposed on the photoreceptor side to correct the scanning speed of the light beam deflected and scanned by the rotating polygon mirror and to emit the light beam near the photoreceptor. The imaging lens to form an image and the photoreceptor side of this imaging lens to correct the tilt of the rotating polygon mirror
Separately arranged for each of the multiple light beams described above
And has a positive refractive power in the direction perpendicular to the scanning direction.
Each light beam emitted from the imaging lens
And a cylindrical mirror for guiding a distant point on the body
The laser scanning device is provided with the lens scanning device .

In this laser scanning device, a plurality of light beams emitted from the light source section are deflected and scanned by a rotating polygon mirror, and are imaged near a photoreceptor by an imaging lens. When a plurality of light beams are made incident on the rotary polygon mirror at a certain interval along a direction perpendicular to the scanning direction using this laser scanning device, the scanning of a single lens having a negative refractive power is formed. By the action of the surface that diverges light only in the direction perpendicular to the direction, the interval between the plurality of light beams after passing through the imaging lens is widened.

According to a second aspect of the present invention, there is provided a laser scanning device.
The surface that diverges light only in a direction perpendicular to the scanning direction in the invention according to claim 1 is a cylindrical surface formed on the first surface when viewed from the rotating polygon mirror side of a single lens having a negative refractive power. Things.

According to a third aspect of the present invention, there is provided a laser scanning device.
According to the first aspect of the present invention, the surface that diverges light only in the direction perpendicular to the scanning direction is a cylindrical surface formed on the second surface when viewed from the rotating polygon mirror side of the single lens having a negative refractive power. Things.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 8 relate to a first embodiment of the present invention.

FIG. 1 is a plan view showing a schematic configuration of a laser scanning device according to this embodiment, and FIG. 2 is a front sectional view of FIG.

As shown in these figures, a laser scanning device according to the present embodiment includes a light source unit 1 for emitting a laser beam modulated in accordance with image information, and a laser beam emitted from the light source unit 1 for sensitizing the laser beam. Rotating polygon mirror 2 for deflecting and scanning on body 5
The fθ lens 3 as an imaging lens for correcting the scanning speed of the laser beam deflected and scanned by the rotary polygon mirror 2 to form a laser beam near the photoreceptor 5 and the tilting of the rotary polygon mirror 2 And a cylindrical mirror 4 as a one-way converging optical member for correcting a beam shake in a direction perpendicular to the scanning direction due to the above. The light source unit 1
Has an optical system that forms a laser beam on the surface of the rotary polygon mirror 2 in a linear shape in the same direction as the scanning direction. Also,
The light source unit 1 may include a gas laser such as a He-Ne laser and a modulator such as an acousto-optic modulator that modulates a laser beam emitted from the gas laser according to image information. It may have a semiconductor laser that emits a laser beam modulated accordingly.

Lens 3 has a single lens 31 having a negative refractive power (hereinafter referred to as a negative lens) disposed on the rotating polygon mirror 2 side and a positive refractive power disposed on the cylindrical mirror 4 side. And a single lens 32 (hereinafter referred to as a positive lens). In the present embodiment, the second surface 31 of the negative lens 31 as viewed from the rotating polygon mirror 2 side.
₂ , a cylindrical surface having a curvature for diverging light only in a direction perpendicular to the scanning direction is formed. The first surface 31 ₁ of the negative lens 31 is spherical when viewed from the rotating polygon mirror 2 side, and the first surface 32 ₁ is flat and the second surface 32 ₁ of the positive lens 32 viewed from the rotating polygon mirror 2 side. ₂ is a spherical surface.

Table 1 below shows the specifications of the laser scanning apparatus of this embodiment when the wavelength of the light source is 632.8 nm.
Show.

[0016]

[Table 1]

In Table 1, the unit is mm. Further, D ₀ refers to the portion of the rotating polygon mirror 2 surface as shown in FIG. 2 to the first surface 31 ₁ of the negative lens 31.
Further, each ~, as shown in FIG. 2, the first side 31 ₁ of the negative lens 31, a second surface 31 _2, the first side 32 ₁ of the positive lens 32, a second surface 32 _2, a cylindrical mirror 4
Refers to the reflective surface. Further, the thickness and the material refer to the thickness and the material from each surface to the next surface, respectively.

Next, the operation of the laser scanning device of this embodiment will be described. The laser beam emitted from the light source unit 1 is deflected and scanned by the rotary polygon mirror 2, the scanning speed is corrected by the fθ lens 3, and an image is formed near the surface of the photoconductor 5. Further, the deflection of the beam in the direction perpendicular to the scanning direction due to the tilt of the rotary polygon mirror 2 is corrected by the cylindrical mirror 4.

FIG. 3 shows a laser scanner having the optical system shown in Table 1 deflecting and scanning two laser beams by one rotating polygon mirror and one set of fθ laser to form a two-color image. FIG. 2 is an explanatory diagram illustrating a configuration of a laser scanning device when applied to an image forming apparatus according to an exemplary embodiment. In the example shown in FIG. 3, two laser beams are made incident on the rotary polygon mirror 2 at a certain interval along a direction perpendicular to the scanning direction, and the beams after passing through the fθ lens 3 are respectively reflected by a plane reflection mirror. The light is separated at 61 and 62 and led to cylindrical mirrors 41 and 42, and these cylindrical mirrors 41 and 4 are separated.
The light is reflected on the photosensitive member 5 and irradiated onto the photoreceptor 5.
Each beam is modulated according to image information of a different color. The angle θ between the incident beam and the exit beam with respect to the cylindrical mirrors 41 and 42 is, for example, 8
6.5 degrees.

As shown in this figure, when a plurality of laser beams are made incident on the rotary polygon mirror 2 at a certain interval along a direction perpendicular to the scanning direction, the cylindrical surface formed on the negative lens 31 By the action, the interval between the plurality of laser beams after passing through the fθ lens 3 is widened.

Specifically, for example, as shown in FIG.
The interval A between the two beams after being reflected by the rotary polygon mirror 2 is 4 mm, and the second surface 32 ₂ of the positive lens 32 of the fθ lens 3
Assuming that the distance C from the mirror to the reflection position of each of the plane reflection mirrors 61 and 62 is 140 mm,
Is 9.3 mm, and the thickness of the rotary polygon mirror 2 is about 6 to 8 mm, so that separation of two beams and rotation of the rotary polygon mirror 2 are easy.

By the way, the negative lens 31 of the fθ lens 3
When second surface 31 ₂ of the planes rather than the cylindrical surface is of, A = 4 mm, when the C = 140mm, B = 2.
7 mm, and it is difficult to mount the reflection mirrors 61 and 62 for separating the two beams. The reason will be described below. The laser beam, which is a Gaussian beam, has a thickness. As shown in the light intensity distribution of FIG. 4, the beam diameter in the vertical direction in the vicinity of the reflection mirrors 61 and 62 also has an intensity of 1 / e ² in this embodiment. The width G of the distribution is about 1 mm. In order to secure 100% energy, 1 / e ²
Is required to be about twice as wide as the width of the intensity distribution. Here, as shown in FIG. 5, the beam deviation 111 is about 1 mm, the beam radius 112 is about 1 mm, and the reflection mirrors 61 and 62 are attached in consideration of the deviation of the beam direction due to the tolerance of parts. Assuming that the accuracy is about 0.5 mm, the ineffective portion 113 of the reflecting surface is about 1 mm, and the distance between the center between the two beams and the reflection position of one of the reflecting mirrors is E, E is at least about 3.5 mm. From E = (1/2) B, the distance B between the reflection positions of the plane reflection mirrors 61 and 62 needs to be at least about 7 mm.

Here, FIGS. 6 to 8 show the imaging performance of the optical system based on the specifications shown in Table 1. 6 shows the linearity characteristic, FIG. 7 shows the curvature of field in the scanning direction, and FIG. 8 shows the curvature of field in the direction perpendicular to the scanning direction. Note that these figures show the characteristics when A in FIG. 3 is 4 mm and the lens is used by offsetting the optical axis of the fθ lens 3 by 2 mm. In these figures, the image height corresponds to the beam position from the center of the photosensitive member 5 in the scanning direction.
In the example of these figures, the position of the scanning end of the beam is 200 m
m indicates that the deflection angle is 32.65 degrees. The linearity indicates a deviation of an actual beam position from an ideal position of the beam on the photoconductor 5, that is, a position that linearly changes with respect to the deflection angle.

As described above, according to this embodiment, when a plurality of beams are incident on the rotary polygon mirror 2 at a certain interval in a direction perpendicular to the scanning direction, the intervals between the beams after passing through the fθ lens 3 are widened. Therefore, when it is desired to irradiate a plurality of beams to distant locations on the photoconductor 5, respectively, reflection mirrors 61 and 62 for reflecting and separating each beam in another direction.
Can be easily arranged, and it is not necessary to make the rotary polygon mirror 2 much thicker.

Further, since a cylindrical surface for widening the beam interval is formed on the negative lens 31 arranged on the rotary polygon mirror 2, the cost can be suppressed. This is because the lens on the side of the rotary polygon mirror 2 of the two-piece set of fθ lenses is generally small, so that the cylindrical surface, which is considered to be more expensive to manufacture than a spherical surface, can be small.

In general, in a pair of fθ lenses of a negative lens and a positive lens, from the rotary polygon mirror 2 to a surface having a negative refractive power of the negative lens (hereinafter referred to as a negative surface). Is shorter, and the longer the distance from the negative surface of the negative lens to the surface having a positive refractive power of the positive lens (hereinafter referred to as the positive surface), the performance as an fθ lens and the scanning direction Good field curvature characteristics. Therefore, as in the present embodiment, in particular by forming a cylindrical surface on the second surface 32 ₂ of the negative lens 31, to the negative side of the negative lens 31 from rotating polygon mirror 2 (the first surface 32 ₁₎ Can be shortened, and the performance as the above-mentioned fθ lens and the characteristics of the field curvature in the scanning direction are improved.

Further, the cylindrical surface is connected to a negative lens 31.
The second surface 32 is better to form the _2, this Rindorikaru surface curvature and the cylindrical combination by the curved image surface in a direction perpendicular to the performance and the scanning direction of the tilt correction of the rotary polygon mirror 2 of the curvature of the local mirror 4 of the Performance can be improved.

FIG. 9 is a plan view showing a schematic configuration of a laser scanning device according to a second embodiment of the present invention, and FIG. 10 is a front sectional view of FIG.

In this embodiment, the negative lens 3 of the fθ lens 3 is used.
Forming a cylindrical surface having a curvature diverging light only in a direction perpendicular to the direction of scanning the first surface 31 ₁ of 1, which has a second face 31 ₂ is spherical, other configurations and operations are the This is the same as in the first embodiment.

According to the present embodiment, similar to the first embodiment,
When a plurality of beams are incident on the rotary polygon mirror 2 at a certain interval in a direction perpendicular to the scanning direction, the interval between the beams after passing through the fθ lens 3 is widened. Mirrors 61 and 6 for reflecting and separating each beam in a different direction when it is desired to irradiate the beams.
2 can be easily arranged, and it is not necessary to make the rotary polygon mirror 2 much thicker.

Further, since a cylindrical surface for widening the beam interval is formed on the negative lens 31 disposed on the rotary polygon mirror 2, the cost can be suppressed. In particular, in this embodiment, since the form cylindrical surface on the first surface 31 ₁ of the negative lens 31, more can be reduced cylindrical surface can be suppressed more cost.

The laser scanning device of the present invention is not limited to a device that scans a plurality of laser beams, but can be used as a device that scans one laser beam.

[0033]

As described above, according to the first aspect of the present invention, of the imaging lens composed of a single lens having a negative refractive power and a single lens having a positive refractive power,
A single lens with negative refractive power has a surface that diverges light only in the direction perpendicular to the scanning direction, so multiple light beams are incident on the rotating polygon mirror along the direction perpendicular to the scanning direction. In this case, the distance between the light beams after passing through the fθ lens can be increased without greatly increasing the thickness of the polygon mirror, and there is an effect that separation of a plurality of light beams becomes easy. In addition, since the surface that diverges light only in the direction perpendicular to the scanning direction is formed as a single lens having a negative refractive power on the rotating polygon mirror side, this surface can be made small, and cost increase can be suppressed. This has the effect.

According to the second aspect of the present invention, the cylindrical surface serving as a surface for diverging light only in the direction perpendicular to the scanning direction is replaced with the first surface of the single lens having a negative refractive power.
Since it is formed on the surface, in addition to the effect of the invention of claim 1,
There is an effect that the cylindrical surface can be made smaller and the cost can be further suppressed.

According to the third aspect of the present invention, the cylindrical surface as a surface for diverging light only in the direction perpendicular to the scanning direction is replaced with the second surface of the single lens having a negative refractive power.
Since it is formed on the surface, in addition to the effect of the invention of claim 1,
The performance as an imaging lens that corrects the scanning speed of a laser beam deflected and scanned by a rotating polygon mirror and forms an image of a laser beam near a photoconductor and the characteristics of field curvature in the scanning direction are improved. In combination with the converging optical member, there is an effect that the performance of correcting the tilt of the rotating polygon mirror and the performance of the field curvature in the direction perpendicular to the scanning direction are improved.

[Brief description of the drawings]

FIG. 1 is a plan view showing a schematic configuration of a laser scanning device according to a first embodiment of the present invention.

FIG. 2 is a front sectional view of FIG.

FIG. 3 is an explanatory diagram showing a configuration in a case where the laser scanning device of the first embodiment is applied to an image forming apparatus that forms a two-color image using two laser beams.

FIG. 4 is a characteristic diagram showing an intensity distribution of a laser beam.

FIG. 5 is an explanatory diagram showing an enlarged view of the vicinity of a plane reflecting mirror in FIG. 3;

FIG. 6 is a characteristic diagram showing a linearity characteristic as an imaging performance of the optical system in the first example.

FIG. 7 is a characteristic diagram illustrating a field curvature characteristic in a scanning direction as an imaging performance of the optical system in the first example.

FIG. 8 is a characteristic diagram showing a field curvature characteristic in a direction perpendicular to a scanning direction as an imaging performance of the optical system in the first example.

FIG. 9 is a plan view illustrating a schematic configuration of a laser scanning device according to a second embodiment of the present invention.

FIG. 10 is a front sectional view of FIG. 9;

FIG. 11 is an explanatory diagram showing a main part of a conventional laser scanning device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Light source part, 2 ... Rotating polygon mirror, 3 ... ftheta lens, 4 ... Cylindrical mirror, 5 ... Photoconductor, 31 ... Negative lens,
32 ... Positive lens

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G02B 9/00-17/08 G02B 21/02-21/04 G02B 25/00-25/04

Claims (3)

(57) [Claims] 1. A photoreceptor and a plurality of light beams directed in a direction perpendicular to a main scanning direction of the photoreceptor.
A light source unit which emits the light beams in parallel at predetermined intervals ; one rotary polygon mirror which deflects and scans the plurality of light beams emitted from the light source unit onto the photosensitive member; It consists of a single lens having a refractive power and a surface that diverges light only in a direction perpendicular to the scanning direction, and a single lens disposed on the photoreceptor side and having a positive refractive power, and is deflected by the rotating polygon mirror. Scanned
The scanning speed of the light beam is corrected, and an imaging lens for focusing the light beam in the vicinity of the photoreceptor, prior to the photoconductor side than the imaging lens in order to correct the tilt of the rotating polygon mirror
It is arranged individually corresponding to each of the plurality of light beams,
Has a positive refractive power in a direction perpendicular to the scanning direction;
Each light beam emitted from the imaging lens is
A lens scanning device having a cylindrical mirror for guiding to a remote location on the photosensitive member.
Laser scanning device . 2. A surface which diverges light only in a direction perpendicular to the scanning direction is a cylindrical surface formed on a first surface when viewed from a rotating polygon mirror side of a single lens having a negative refractive power. The laser scanning device according to claim 1, wherein: 3. A surface for diverging light only in a direction perpendicular to the scanning direction is a cylindrical surface formed on a second surface of the single lens having a negative refractive power when viewed from a rotating polygon mirror side. The laser scanning device according to claim 1, wherein: