JP3367313B2 - Optical scanning device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a light source section for emitting a plurality of light beams, and simultaneously scans a surface to be scanned with a plurality of scanning lines to record an image at high speed.
The present invention relates to an optical scanning device for reading an image. Specifically, by devising the arrangement of an image forming optical system, it is possible to correct a plurality of image forming position shifts in the main scanning direction on a surface to be scanned. The present invention relates to an optical scanning device.

[0002]

2. Description of the Related Art Conventionally, an optical scanning device applied to a laser beam printer or a digital copying machine includes a laser diode assembly for emitting a light beam according to an image signal and a range of a predetermined scanning angle for the incident light beam. An optical deflector for deflecting light, a photosensitive drum having a surface to be scanned coated with a photosensitive material on which an image is recorded by the deflected light beam, and a light beam deflected in the vicinity of the photosensitive drum. And an image forming optical system for forming an image. Usually, the optical deflector has a deflecting surface for reflecting a light beam on its side surface, and is configured as a rotary polygon mirror that is rotated around a predetermined rotation axis by a motor or the like. Deflect.

However, when the light beam is incident vertically on the surface to be scanned on the photosensitive drum, the following problems occur.
That is, a part of the light beam incident on the surface to be scanned, which is a bright surface that generally reflects light, is reflected, returns to the optical deflector and is reflected as secondary reflected light, returns to the surface to be scanned again, and is a ghost. An image is formed and the image quality of a recorded image is deteriorated, or an error in reading image data occurs.

Therefore, as disclosed in JP-A-56-122006 (FIG. 2 of the same publication) and JP-A-6-118319 (FIG. 3 of the same publication), a light beam is applied to a surface to be scanned. There is proposed an optical scanning device configured such that a light beam is incident on a surface to be scanned from a direction that forms a predetermined angle in the sub-scanning direction with respect to the vertical direction, instead of being incident perpendicularly to the sub-scanning direction. . In such an optical scanning device, since the reflected light from the surface to be scanned is reflected in a direction different from the direction returning to the optical deflector, the light returning to the surface to be scanned is reduced and image deterioration and the like are effectively performed. Can be prevented.

By the way, in the optical scanning device, it is also a problem to increase the recording speed or the reading speed or the resolution of an image without increasing the rotation speed of the optical deflector (polygon mirror). .

Therefore, the conventional optical scanning device scans the surface to be scanned with one light beam.
As disclosed in JP-A-110960, a method is proposed in which a semiconductor laser array (hereinafter referred to as an LD array) is used to simultaneously scan a surface to be scanned with a plurality of light beams to increase the speed. ing. An example of simultaneously scanning the surface to be scanned with two light beams is shown in FIGS. 6A and 6B.

As shown in FIG. 6 (a), the interval in the sub-scanning direction between two light spots formed by imaging two light beams on the surface to be scanned is three times the interval between scanning lines. Therefore, the scanning is skipped over two scanning lines. On the other hand, in the example of FIG. 6B, two light spots scan two adjacent scanning lines. In both cases of scanning, the two light spots are aligned in the sub-scanning direction without their positions in the main scanning direction being displaced from each other.

On the other hand, many methods have been proposed in which a plurality of light spots are not aligned in the sub-scanning direction by inclining the LD array with respect to the direction corresponding to the sub-scanning direction. However, because it is difficult to set the tilt angle accurately, and it is necessary to have a synchronization signal for determining the write timing in each beam, two LD arrays are not tilted in the sub-scanning direction. It is desirable to align the light spots in the sub-scanning direction.

[0009]

However, in the above-described conventional optical scanning device, the generation of a ghost image is prevented by making the deflected light beam incident on the surface to be scanned in an oblique direction, and the LD array. If it is attempted to simultaneously satisfy the requirement of speeding up by using, the following problems will occur.

That is, when a plurality of light beams separated by a predetermined distance in the direction corresponding to the sub-scanning direction are incident perpendicularly to the surface to be scanned, the optical path lengths of the plurality of light beams to the surface to be scanned are almost the same. The light spots are equal, and the plurality of light spots are aligned in the sub-scanning direction without being displaced from each other in the main scanning direction. However, the two light beams (light beam A and light beam B) deflected by the optical deflector and transmitted through the imaging optical system are made incident at a predetermined angle in the sub-scanning direction with respect to the normal line of the surface to be scanned. In the case where the two light beams are arranged, the optical path lengths of the two light beams to the surface to be scanned differ. Therefore, as the scanning angle formed by the light beam in the main scanning direction with respect to the direction of reaching the central portion of the scanning line becomes larger, the two light spots a and b formed on the surface to be scanned are in the main scanning direction. The problem arises that the position shifts.

The positional deviation of the light spots a and b in the main scanning direction will be described below with reference to FIGS. 4 (a) and 4 (b).

When the optical paths of the two light beams are viewed from the main scanning direction as shown in FIG. 4B, the two light beams A and B deflected by the polygon mirror 10 are fθ lens 20.
The light is incident on the fθ lens 20 so as to have a height symmetrical with respect to the optical axis 50 of. Then, the light beams A and B pass through the f.theta. Lens 20 and cross at the focal position 46 of the f.theta. Lens, and thereafter, the image forming position 52 on the scanned surface 32 of the photosensitive drum 28.
a and 52b, respectively.

As shown in the figure, since the light beams A and B are incident on the surface 32 to be scanned at a predetermined angle in the sub-scanning direction, the light beams A and B are emitted from the f.theta. The optical path lengths to the image forming positions 52a and 52b are different from each other. That is, as shown in FIG.
The optical path length from a to the imaging position 52a is longer than the optical path length from the emission point 51b of the light beam B to the imaging position 52b. Here, the optical path length is the distance from the emission point to the image forming position, but the optical path lengths from the deflection surface 11 may be compared.

On the other hand, when the optical paths of the two light beams are viewed from the sub-scanning direction as shown in FIG. 4A, when the scanning angle φ formed by the deflected beam with respect to the optical axis 50 is 0 degree, that is, When the beams reach the centers of the scanning lines l _a and l _b , the two light beams do not travel in the main scanning direction and are incident perpendicularly to the surface 32 to be scanned, so that the total optical path length is long. Is absorbed by the difference in optical path length in the sub-scanning direction, and the two image forming positions do not shift in the main scanning direction.

However, as the absolute value of the scanning angle φ increases, the two light beams form an angle according to the scanning angle φ not only in the sub-scanning direction but also in the main scanning direction.
It is obliquely incident on 2. As a result, the light beam also travels in the main scanning direction, and the image forming positions of the two light beams having different optical path lengths are displaced in the main scanning direction. That is, the light beam A travels a longer optical path length than the light beam B, but since the light beam A travels outward in the main scanning direction by the length of the optical path length, the image forming position 52a ′ (52) of the light beam A is moved.
a ”) is located outside the image forming position 52b ′ (52b ″) of the light beam B in the main scanning direction. Therefore, FIG.
As shown in (b), the light spots a and b are not aligned in the sub-scanning direction.

In order to solve the above problem, it is possible to deal with the difference by providing the frequencies of the clocks for modulating the respective light beams, but it is necessary to have a plurality of clocks which are originally one, and A new problem arises that it is difficult to align the phases of the beams.

In consideration of the above facts, the present invention is an optical scanning device which makes a plurality of light beams incident on a surface to be scanned at a predetermined angle, and makes it possible to use a plurality of light beams by extremely easy means without using complicated means. An object of the present invention is to provide an optical scanning device in which image forming positions of beams are aligned in the sub-scanning direction.

[0018]

In order to achieve the above-mentioned object, the invention according to claim 1 emits a plurality of light beams separated by a predetermined distance in a direction corresponding to the sub-scanning direction, and emits light from the light source. Deflecting means for simultaneously deflecting the plural light beams thus deflected in a direction corresponding to the main scanning direction, and the plural light beams deflected by the deflecting means make a predetermined incident angle with respect to the normal line in the sub-scanning direction. An object to be scanned having a surface to be scanned and a plurality of light beams which are interposed between the deflecting means and the object to be deflected and are deflected by the deflecting means to form an image on the surface to be scanned. Together with the plurality
Decentered with respect to the optical beam of
At least one of the tilting causes the plurality of lights to
The beam is incident on the surface to be scanned at a specified angle.
Imaging in which the positional deviation of the light spots in the main scanning direction is corrected and the scanning lengths of the plurality of light beams incident on the object to be scanned on the surface to be scanned are the same or substantially the same. And an optical system.

According to the first aspect of the invention, the light source emits a plurality of light beams separated by a predetermined distance in the direction corresponding to the sub-scanning direction. Then, the deflecting means simultaneously deflects the plurality of emitted light beams in a direction corresponding to the main scanning direction. Then, the plurality of deflected light beams are imaged on the surface to be scanned by the imaging optical system interposed between the deflecting means and the object to be scanned. At this time, the deflected light beams are incident on the surface to be scanned of the object to be scanned at a predetermined incident angle with respect to the normal line in the sub-scanning direction. Although a part of the light beam is reflected on the surface to be scanned, the light beam is incident at a predetermined incident angle, so that the reflected light can be prevented from returning to the deflecting means and returning to the surface to be scanned. Further, the imaging optical system is decentered with respect to the plurality of light beams, and
By at least one of being tilted with respect to the optical axis,
The plurality of light beams are incident on the surface to be scanned at a predetermined angle.
Position deviation of the light spot in the main scanning direction caused by
Since the plurality of light beams that are corrected and incident on the object to be scanned are arranged so that the scanning lengths on the surface to be scanned are the same or substantially the same, the plurality of light beams separated by a predetermined distance in the sub-scanning direction. Even when the scanning angle of the beam is larger than 0 degree and travels in the main scanning direction, the image forming position in the main scanning direction is not displaced.
As a result, for example, it is possible to prevent the image quality of the recorded image on the object to be scanned from deteriorating and the image data reading error.

The invention of claim 2 is characterized in that the image forming optical system of claim 1 has a power in a direction corresponding to the sub-scanning direction.

According to the second aspect of the invention, since the image forming optical system has power in the direction corresponding to the sub-scanning direction, for example, when the deflecting means is composed of a polygon mirror or the like, the deflecting surface is troublesome. The positional deviation in the sub-scanning direction due to this can be prevented at the same time.

According to a third aspect of the present invention, the image forming optical system according to the second aspect is arranged so as to be decentered with respect to the plurality of light beams.
In this case, the plurality of deflected light beams are eccentrically arranged so as to be incident at a height asymmetric with respect to the optical axis of the imaging optical system.

According to the third aspect of the present invention, since the imaging optical system having power in the sub-scanning direction is decentered, the deflected light beams have heights asymmetric with respect to the optical axis of the imaging optical system. Incident on. By arranging the imaging optical system by adjusting the asymmetric heights so that the scanning lengths of the plurality of light beams on the surface to be scanned are the same or substantially the same, a plurality of light beams generated in the main scanning direction on the surface to be scanned can be obtained. The deviation of the image forming position of the light beam can be corrected.

The invention of claim 4 relates to claim 1 to claim 3.
The imaging optical system of any one of, with respect to the optical axis
It is characterized in that the plurality of deflected light beams are arranged so as to be incident at a predetermined angle in the sub-scanning direction with respect to the optical axis of the imaging optical system when arranged at an angle.

In the invention of claim 4, a plurality of deflected light beams are incident on the optical axis of the imaging optical system at a predetermined angle in the sub-scanning direction. By arranging the imaging optical system by adjusting the angle of incidence with respect to the optical axis so that the scanning lengths of a plurality of light beams on the surface to be scanned are the same or substantially the same, the scanning surface is moved in the main scanning direction. It is possible to correct the deviations of the imaging positions of the plurality of light beams that occur. According to the invention of claim 4, a plurality of light beams may be incident at a predetermined angle and at an asymmetric height with respect to the imaging optical system, and the deviations are corrected by the actions of both. You can

The invention of claim 5 is the invention of claim 1 or claim 2.
The imaging optical system of the above forms an image of a plurality of deflected light beams.
Incident at a predetermined angle in the sub-scanning direction with respect to the optical axis of the optical system
And is arranged so as to be incident at a height symmetrical with respect to the optical axis of the imaging optical system.

According to the present invention, a plurality of deflected light beams are incident on the optical axis of the imaging optical system at a predetermined angle in the sub-scanning direction and symmetrical with respect to the optical axis of the imaging optical system. Incident at any height. And by arranging the imaging optical system by adjusting the angle of incidence with respect to the optical axis so that the scanning lengths of the plurality of light beams on the surface to be scanned are the same or substantially the same,
It is possible to correct the deviation of the image forming positions of the plurality of light beams which occurs in the main scanning direction on the surface to be scanned. Further, since the plurality of light beams are incident at symmetrical heights, it is possible to maintain good optical performance during image formation.

[0028] The invention of claim 6 is from claim 1 to claim 5.
2. The image forming optical system according to any one of 1 above is composed of a first group optical system having a power only in the main scanning direction and a second group optical system having a power only in the sub-scanning direction. Is characterized by.

In the invention of claim 6, the deflected light beam is composed of a first group of optical systems having a power only in the main scanning direction and a second group of optical systems having a power only in the sub-scanning direction. An image is formed on the surface to be scanned by the image forming optical system. By configuring the image forming optical system in this way, the shapes of the optical components forming the image forming optical system are simplified, and the manufacturing cost can be reduced.

The invention of claim 7 is from claim 1 to claim 6.
The invention according to any one of the aspects 1 to 3, wherein the plurality of light beams are incident in a state in which the plurality of light beams are not parallel to the imaging optical system.

According to the seventh aspect of the invention, the plurality of deflected light beams are incident in a state not parallel to the image forming optical system. As a result, in addition to the effects of the inventions of claims 1 to 6, the positional relationship of the optical member such as the imaging optical system with respect to the surface to be scanned, particularly the traveling direction of the light beam is deviated due to a mounting error or the like. It is possible to prevent the fluctuation of the interval between the two beams in the sub-scanning direction on the surface.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 shows the schematic arrangement of an optical scanning apparatus according to the first embodiment. As shown in FIG. 1, the present optical scanning device is provided with a polygon mirror 10 as a light beam deflecting means. The polygon mirror 10 has the shape of a flat regular polygonal prism, and each deflecting surface forming the side surface of the polygon mirror 10 is a flat mirror surface. Further, the polygon mirror 10 is configured to be rotatable around a rotation center axis O in a substantially vertical direction, and the polygon mirror 10 is provided below the polygon mirror 10 at a substantially constant angular velocity around the rotation center axis O. A motor 12 for rotating the motor is arranged.

A laser diode assembly 26 used as a light source is arranged on the side of the optical scanning device. This laser diode assembly 26
The semiconductor laser array 14 is composed of two light sources 14a and 14b which are separated from each other by a predetermined distance d ₀ in the direction 27 corresponding to the sub-scanning direction. Light sources 14a and 14b
Is a semiconductor laser that emits a divergent light beam, and is controlled to be turned on / off in accordance with an image signal by a modulator (not shown).

Further, the laser diode assembly 26
Is composed of a collimator lens 16 for converging two divergent light beams emitted from the semiconductor laser array 14, and an aperture stop 17 for beam shaping.

Further, at the position adjacent to the collimator lens 16 on the exit side of the aperture stop 17, the transmitted light beam is converged on the deflecting surface 11 of the polygon mirror 10 or in the vicinity thereof only in the direction corresponding to the sub-scanning direction. Thus, the cylindrical lens 18 for forming an elongated line image in the direction corresponding to the main scanning direction is arranged.

Further, the polygon mirror 1 of the present optical scanning device
A photoconductor drum 28 is arranged at the end opposite to 0. The photoconductor drum 28 has a shape of an elongated cylinder having a light-sensitive photosensitive material applied to the surface 32 to be scanned, and the scanning direction (main scanning direction) indicated by an arrow 30 is the same. The photoconductor drums 28 are arranged so as to be substantially aligned with the longitudinal direction thereof. In the following, the direction orthogonal to the main scanning surface formed by the light beam reflected and deflected by the polygon mirror 10 is defined as the sub-scanning direction.

The photosensitive drum 28 has a rotary shaft W
Is configured so as to rotate in the direction of arrow Q at a predetermined constant rotation speed by a driving unit (not shown) as a center, and this rotation moves the scanning line in the sub-scanning direction orthogonal to the main scanning direction.

Further, between the photosensitive drum 28 and the polygon mirror 10, the light beam reflected and deflected by the polygon mirror 10 is focused on the scanned surface 32 of the photosensitive drum 28 as a light spot in the main scanning direction. An fθ lens 20 is provided for moving the light spot on the surface of the photoconductor drum 28 at a constant speed while forming an image. The fθ lens 20 has power in the sub-scanning direction in order to correct the positional deviation of the light spot on the surface to be scanned 32 in the sub-scanning direction due to so-called surface tilt of the deflecting surface 11 of the polygon mirror. There is.

Further, as shown in FIG. 2, the light beam 40 deflected by the polygon mirror 10 and transmitted through the fθ lens 20 is directed to the normal 42 of the surface 32 to be scanned in order to prevent deterioration of image quality due to returning light. Angle θ in the sub-scanning direction
The respective constituent members are arranged so as to enter the surface 32 to be scanned.

Further, as shown in FIG. 3B, the fθ lens 20 shifts the position of a light spot, which will be described later, in the main scanning direction caused by the light beam entering the surface 32 to be scanned at a predetermined angle θ. It is eccentrically arranged with respect to the two light beams for correction. In FIG. 3B, f
It shows a case where the θ lens 20 is viewed from the main scanning direction,
Since the fθ lens 20 has power in the sub-scanning direction, the emission surface of the light beam has a curvature.

Since the fθ lens 20 is eccentrically arranged in this way, for example, the light beam A shown by the dotted line passes through the fθ lens 20 at the same height as the optical axis 50 and is shown by the solid line. The light beam B passes through the fθ lens 20 at a predetermined height with respect to the optical axis 50. That is, the two light beams are transmitted at a height that is asymmetric with respect to the optical axis 50. Here, the height refers to the distance h of the light beam B from the optical axis 50 in the direction corresponding to the sub-scanning direction as shown in FIG. 3B. In the following, the optical path of the light beam A is shown by a dotted line, and the optical path of the light beam B is shown by a solid line.

Further, the fθ lens 20 and the photosensitive drum 2
8, a plane mirror 58 for reflecting the light beam emitted from the fθ lens 20 upward is disposed,
Above the plane mirror 58, a surface tilt correction cylindrical mirror 60 having power only in the sub-scanning direction is arranged. Further, a dustproof window 62 is interposed between the cylindrical mirror 60 and the photosensitive drum 28.

A plane mirror 64 for reflecting the SOS beam to the opposite end is arranged between the plane mirror 58 and the fθ lens 20 on the optical path of the SOS beam. An SOS sensor 66 that detects the SOS beam is arranged. Further, the plane mirror 6 for reflecting the light beams A and B emitted from the laser diode assembly 26 in the direction of incidence on the polygon mirror 10.
8 are installed.

The fθ lens 20 having a power in the sub-scanning direction is also applied to the optical system having the tilt correcting cylindrical mirror 60 as described above, but as shown in FIG. The aspherical fθ lens 20 can also be applied to an optical system without a cylindrical mirror.

Next, the operation of this embodiment will be described. Two light sources 14a and 1 of the semiconductor laser 14
4b emits a light beam A and a light beam B, which are divergent lights, in accordance with an image signal by a modulator (not shown). The two divergent lights emitted are collimator lens 16
To form a substantially parallel light beam, and the aperture stop 17 limits the beam width in the direction corresponding to the sub-scanning direction.

Next, the light beams A and B that have passed through the aperture stop 17 are converged by the cylindrical lens 18 near the surface of the deflecting surface 11 of the polygon mirror 10 only in the direction corresponding to the sub-scanning direction.

Light beams A, B converged by the deflecting surface 11
Is reflected and deflected by the deflecting surface 11 and enters the fθ lens 20. The two light beams incident on the fθ lens 20 are
By the power of the fθ lens 20 in the main scanning direction, the light spots a and b having a predetermined irradiation beam diameter K are converged in the main scanning direction in the vicinity of the surface of the photosensitive drum 28 (see FIG. 6).

At this time, the light beam 40 is incident on the scan surface 32 at a predetermined angle with respect to the normal 42 of the scan surface 32. As a result, the reflected light from the surface 32 to be scanned is reflected in a direction different from the direction returning to the polygon mirror 10, so that the light returning to the surface 32 to be scanned is avoided and deterioration of the image quality of the recorded image is prevented. You can

Here, since the polygon mirror 10 is rotating in the direction of arrow P, the traveling direction of the light beam reflected by the deflecting surface 11 is changed in the main scanning direction, and accordingly, the photosensitive drum 28 is scanned. A light spot a radiated on the surface 32,
The position of b also changes.

At this time, as shown in FIG. 9, the light spot a scans the surface of the photosensitive drum 28 in the direction of arrow 30 (main scanning direction) at a substantially constant speed from the scanning start point to the scanning end point. It is scanned on the line l _a. Further, the light spot b is scanned on the scanning line l _b of the surface of the photosensitive drum 28 from the scanning start point at a substantially uniform speed in a direction of the arrow 30 until the scanning end point. The scanning line l _a and the scanning line l _b
May be adjacent to each other in the sub-scanning direction as shown in FIG. 6B, or as shown in FIG.
A plurality of scan lines may be separated for scanning.

Then, as described above, the photosensitive drum 2
8 rotates about the axis W in the direction of arrow Q at a predetermined constant rotation speed, so that the photosensitive material on the photoconductor drum 28 is scanned in a predetermined direction not only in the main scanning direction but also in the sub-scanning direction. It will be scanned at speed. In addition, the modulation of the image signal of each line unit is performed by the SOS sensor 66.
It is started after a predetermined time has elapsed from the time when the S beam was detected.

By the way, in the present embodiment, when the two light beams A and B are transmitted through the fθ lens 20, they are arranged so as to be incident at an asymmetric height with respect to the optical axis 50 of the fθ lens 20. However, FIG. 5A shows the image forming positions of the light beams A and B in the main scanning direction when such an arrangement is adopted.
An explanation will be given using (b).

As shown in FIG. 5B, the light beam A is f
The light beam B is transmitted at the same height as the optical axis 50 of the θ lens 20, and the light beam B is transmitted through the fθ lens 20 at a height off the optical axis 50. The light beams A and B that have passed through the fθ lens 20 intersect at a focal position 46 and then form an image forming position 54 on the scanned surface 32.
a and 54b, respectively.

If the f.theta. Lens 20 is not eccentrically arranged, as shown in FIG. 4A, the lengths (52a 'to 52a ", 52b' of the light beams A and B on the surface to be scanned are scanned.
.About.52b ″), the light beam A is longer than the light beam B.

However, in the present embodiment, as shown in FIG. 5B, the light beam A is transmitted at the same height as the optical axis 50 so that the optical path length becomes shorter, and the light beam B is transmitted. The fθ lens 20 is arranged so that the scanning length of the light beam on the surface to be scanned is the same or substantially the same at an arbitrary scanning angle φ by making the light incident on the asymmetric height so that the optical path length becomes longer. ing.

As described above, since the scanning lengths of the two light beams are the same or substantially the same, as shown in FIG. 5A, the image forming positions 54a 'and 5a are formed at arbitrary scanning angles φ.
4b ', 54a "and 54b" are aligned in the sub-scanning direction,
Positional deviation in the main scanning direction can be avoided.

The decentering of the fθ lens 20 as described above to prevent the displacement in the main scanning direction can be explained as follows.

That is, as shown in FIG. 4A, when the light beam is incident on the surface 32 to be scanned at a predetermined angle in the sub-scanning direction, the image forming positions 52a ', 52a of the light beam A are formed.
a ″ tends to shift outside the imaging positions 52b ′ and 52b ″ of the light beam B in the main scanning direction, and the shift increases as the absolute value of the scanning angle φ increases.

However, as shown in FIG. 3 (a), the light beam B incident on the fθ lens 20 at an asymmetric height is higher than the light beam A transmitted at the same height as the optical axis 50. The angle of refraction in the scanning direction becomes smaller. In the example of FIG. 3A, the light beam B is emitted from the emission point 78b of the light beam A, which is further outside in the main scanning direction than the emission point 78a, and outward from the fθ lens 20. Thus, considering only the effect of eccentricity, the light beam A is
On the contrary to the positional deviation due to the oblique incidence, an image is formed at a position inside the light beam B in the main scanning direction. Moreover, this deviation increases as the absolute value of the scanning angle φ increases. The magnitude of this positional deviation can be adjusted by the amount of eccentricity, which is the height at which the fθ lens 20 is eccentric with respect to the two light beams A and B.

Therefore, the positional deviation caused by incidence on the surface 32 to be scanned at a predetermined angle in the sub-scanning direction is
By adjusting the amount of eccentricity so as to cancel out the positional deviation caused by decentering the fθ lens 20, FIG.
As shown in, it is possible to eliminate the deviation of the image forming position in the main scanning direction.

As described above, in the first embodiment, 2
By the extremely simple method of arranging the fθ lens 20 eccentrically so that the two light beams are incident on the asymmetric height, it is possible to eliminate the positional deviation in the main scanning direction without using a complicated electric circuit or the like. .

In FIGS. 3 and 5, the light beam A is f
Although the case where the θ lens 20 is transmitted at the same height as the optical axis 50 has been described, one light beam does not necessarily have to be arranged so as to be transmitted at the same height as the optical axis 50. This is because it is similarly possible to correct the deviation in the main scanning direction by making the two light beams asymmetrically incident so that the heights with respect to the optical axis 50 are different from each other.

(Second Embodiment) In the first embodiment, by decentering the fθ lens 20, the directions in which the two light beams are emitted are shifted to prevent displacement in the main scanning direction. It was On the other hand, the same effect can be obtained by arranging the fθ lens 20 in a tilted manner without decentering it. This is shown below as a second embodiment. The configuration of the optical scanning device according to the second embodiment is almost the same as that of the first embodiment, and the same constituents are designated by the same reference numerals and the description thereof will be omitted.

FIGS. 8A and 8B show the arrangement of the fθ lens 20 according to the second embodiment with respect to two light beams, as viewed from the main scanning direction and the sub-scanning direction, respectively. As shown in FIG. 8B, the fθ lens 20
Are arranged so that the light beams A and B are not parallel to the optical axis 50 and are inclined so as to enter the fθ lens 20 at a predetermined angle θ ′. Also, the light beams A and B are
Although it is arranged so that the light enters at a height symmetrical with respect to the optical axis 50, it is important to tilt the fθ lens 20 in the present embodiment, and naturally, it is also applied to the case where light enters at an asymmetric height. it can.

By arranging the fθ lens 20 in a tilted manner as described above, the emission points 80a and 80 of the light beams A and B are obtained.
Since the height of b from the optical axis 50 is different, the refraction angle in the main scanning direction is different. In the example of FIG. 8A, the light beam B is emitted outward from the light beam A in the main scanning direction. Thus, considering only the effect of tilting the angle θ ′, the light beam A is imaged at a position inside the light beam B in the main scanning direction, which is opposite to the displacement due to oblique incidence. Moreover, this deviation increases as the absolute value of the scanning angle φ increases. Then, the magnitude of this positional deviation can be adjusted by the tilt angle θ ′.

Therefore, the positional deviation caused by incidence on the surface 32 to be scanned at a predetermined angle in the sub-scanning direction is
By adjusting the angle θ ′ so as to cancel out the positional deviation caused by tilting the fθ lens 20, it is possible to eliminate the deviation of the image forming position in the main scanning direction as shown in FIG. 7A.

As described above, in the second embodiment, 2
By a very simple method of arranging the fθ lens 20 so that two light beams are incident at a predetermined angle with respect to the optical axis, a positional deviation in the main scanning direction is eliminated without using a complicated electric circuit or the like. be able to.

(Third Embodiment) In the first and second embodiments, the fθ lens 20 having power in the sub-scanning direction is used, but the fθ lens 20 has power in the sub-scanning direction. A cylinder lens that is not included may be used. This will be disclosed below as a third embodiment. The same components as those in the above-described embodiment are designated by the same reference numerals and the description thereof will be omitted.

The operation of this embodiment will be described with reference to FIGS. It is deflected by the polygon mirror 10 and f
The light beams A and B transmitted through the θ lens 20 are reflected upward by the plane mirror 58, further reflected by the cylindrical mirror 60, reach the photosensitive drum 28, and are scanned on the scanning line. At this time, the cylindrical mirror 6
With the power of 0 in the sub-scanning direction only, the positional deviation in the sub-scanning direction caused by the tilt of the deflecting surface of the polygon mirror 10 with respect to the vertical direction is corrected.

Since the positional deviation in the sub-scanning direction is corrected by the cylindrical mirror 60, it is not necessary for the fθ lens 20 to also serve as a plane tilt correction optical system, and FIG.
As shown in, the fθ lens 20 can be configured as a flat cylinder lens that has no power in the sub-scanning direction, and the entire apparatus can be downsized.

Furthermore, the fθ lens 20 of the present embodiment
As shown in FIG. 10 (b), the light beams A and B are aligned with the optical axis 50.
Is arranged so as to be incident at a predetermined angle θ ″ with respect to the light beam B. Therefore, the light beam B is emitted outward from the light beam A as shown in FIG.
Moreover, the angle of refraction in the main scanning direction can be adjusted by the tilt angle θ ″.

Therefore, the positional deviation caused by incidence on the surface 32 to be scanned at a predetermined angle in the sub-scanning direction is
By adjusting the angle θ ″ so as to cancel the positional deviation caused by tilting the fθ lens 20, it is possible to eliminate the deviation of the image forming position in the main scanning direction as shown in FIG. 7A.

As described above, also in the third embodiment, the position shift in the main scanning direction can be performed without using a complicated electric circuit by the extremely simple method of arranging the flat cylinder lens in a tilted manner. It can be lost.

In addition, there is a disadvantage that the cylindrical mirror 60 as the surface tilt correction optical system is required,
The fθ lens 20 can be a cylinder lens that is easy to manufacture, and the optical system in the sub-scanning direction can be used as the tilt correction optical system so that the fθ lens 20 can function as a tilt correction optical system as in the first and second embodiments. It is possible to reduce the distance between the two light beams on the surface 32 to be scanned, which is advantageous for high resolution.

Although the two light beams are incident on the fθ lens 20 at symmetrical heights in FIG. 10, they may be incident at asymmetrical heights.

(Fourth Embodiment) In each of the above embodiments, the two parallel light beams A and B are fed to the f.theta.
However, it is rare that two light beams (hereinafter, referred to as two beams) are parallel to each other when entering the fθ lens 20, and an optical path having a symmetric angle with respect to the optical axis 50 is taken. Therefore, an optical scanning device in which this angle is optimally set is shown below as a fourth embodiment.

First, referring to FIG. 11, the imaging optical system (fθ
The optical path in the sub-scanning direction when the two beams are incident on the lens 20) in parallel with each other will be described. Note that in FIG. 11 and FIG. 12 described later, the lens optical system is shown as a quadrangle, and the mirror is shown as a line segment.
The same reference numerals are given and the description is omitted.

Light beams A and B emitted in parallel from a light source
Crosses at the focal point 70 of the collimator lens 16 and then spreads to the cylindrical lens 18. By this cylindrical lens 18, the traveling directions of the two beams are changed to a substantially parallel state, and after passing through the fθ lens 20 having a two-piece configuration, the two beams reach the cylindrical mirror 60.

Here, as shown in FIG. 11, the object-side focal position of the cylindrical lens 18 and the collimator lens 1
By making the image-side focal positions of 6 coincide with each other, the fθ lens 20
Two beams can be made to enter in parallel to. However, when the fθ lens 20 has power only in the main scanning direction, or when the power in the sub scanning direction is small, the two beams travel to the cylindrical mirror 60 almost in parallel and intersect at the focal position 74 of the cylindrical mirror 60. Reach the surface 32 to be scanned.

Therefore, when two beams which are substantially parallel to each other are incident on the fθ lens 20 as described above, the two beams which are incident on the surface 32 to be scanned are not parallel but have an angular difference. Therefore, if the positional relationship of the optical member with respect to the scanned surface 32 is deviated, there arises a problem that the two-beam interval in the sub-scanning direction on the scanned surface 32 is displaced. Even when the fθ lens 20 has a power in the sub-scanning direction for the purpose of correcting the surface tilt and the cylindrical mirror 60 is not used, the two beams intersect at the focal position of the fθ lens 20 and have an angular difference. Since the light enters the scanning surface 32, the same problem as in the case of using the cylindrical mirror 60 occurs.

Next, the optical path in the sub-scanning direction of the optical system according to the fourth embodiment will be described with reference to FIG.

As shown in FIG. 12, the light beams A and B converged by the cylindrical lens 18 have an optical axis 50.
With respect to the fθ lens 20 with the angles of θ ₁ and θ ₂ , respectively.
Incident on. Note that normally, θ ₁ and θ ₂ are set to the same angle, but they may be set to different angles. Then, the two beams that have passed through the fθ lens 20 cross again at the focal position 72 of the fθ lens 20, and reach the cylindrical mirror 60.

The two beams reflected by the cylindrical mirror 60 are made substantially parallel and are incident on the surface 32 to be scanned. The second crossing position 72 is f in this example.
Although they intersect after passing through the θ lens 20, the crossing position 72 changes depending on the configuration of the fθ lens 20, and is not limited to after passing.

As described above, the optical system shown in FIG.
By arranging the optical components so that the two beams incident on the surface 32 to be scanned are substantially parallel to each other, the problem that occurred in the optical system of FIG. 11 can be solved. That is, even if the positional relationship of the optical member with respect to the surface to be scanned 32 (particularly with respect to the traveling direction of the light beam) is deviated due to an attachment error or the like, it is possible to prevent the fluctuation of the interval between the two beams in the sub-scanning direction on the surface to be scanned 32. You can

The optical scanning device according to the fourth embodiment can be applied to each of the first to third embodiments.

The above is the respective embodiments of the present invention.
The present invention is not limited to the above example. For example, in FIG.
As shown in FIG. 5, the fθ lens 20 of each embodiment is composed of a first group of lenses 90 having a power only in the main scanning direction and a second group of lenses 92 having a power only in the sub-scanning direction. You can With such a lens configuration, the same effect as that of the above-described embodiment can be obtained.

When the fθ lens having the two-group structure as shown in FIG. 13 or a plurality of lenses is eccentrically arranged or inclined as in the first to third embodiments, all of them are arranged. The lens may be decentered or tilted, or one lens, two
It is also possible to decenter or incline only a part of the lens such as a sheet.
Further, the eccentricity amount and the tilt angle may be set to be different for each lens. The important point is to eccentrically or tilt the two beams, which were arranged in parallel in the sub-scanning direction until they entered the fθ lens, so as to cancel the positional deviation in the main scanning direction at the time of exiting the fθ lens. is there.

The decentering of the fθ lens as in the first embodiment and the inclined placement of the fθ lens as in the second and third embodiments may be performed at the same time, If the positional deviation in the main scanning direction can be eliminated by the comprehensive action of the two types of arrangements, the same effect can be obtained.

Further, although two light beams have been described in the above example, even when three or more light beams are used, each of the above embodiments can be applied.

Although the example of the photosensitive drum used in an electrophotographic apparatus or the like as the medium to be scanned has been described, for example, a document on which characters and figures are recorded is scanned with a light beam, and the reflected light is detected by a photodetector. It can also be applied to an information reading device that detects information by reading with.

[0092]

As described above, according to the inventions of claims 1 to 7, in the optical scanning device for making a plurality of light beams incident on the surface to be scanned at a predetermined angle,
By the extremely easy method of arranging the image forming optical system such as the fθ lens so as to correct the positional deviation in the main scanning direction, the image forming positions of the plurality of light beams can be set in the main scanning direction without using complicated means. It is possible to obtain the effect of being aligned in the sub-scanning direction without being displaced.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical scanning device according to a first embodiment.

FIG. 2 is a diagram showing an optical path of a light beam which is incident so as to form a predetermined angle in a sub-scanning direction with respect to a normal line of a surface to be scanned.

FIG. 3A is a diagram of the optical paths of the light beams A and B that pass through the fθ lens according to the first embodiment, as viewed from the sub-scanning direction, and FIG. F according to the embodiment
FIG. 6 is a diagram of an eccentric arrangement of the θ lens with respect to the light beams A and B as viewed from the main scanning direction.

FIG. 4 is a diagram for explaining positional deviation in the main scanning direction,
(A) is a light beam A, B transmitted through a conventional fθ lens.
FIG. 6B is a diagram when the optical path of the is viewed from the sub-scanning direction,
[Fig. 6] is a view of the optical paths of the light beams A and B from the main scanning direction until they are imaged through the conventional fθ lens.

5A and 5B are diagrams illustrating a case where there is no positional deviation in the main scanning direction, and FIG. 5A is a positional deviation in the main scanning direction of the light beams A and B that pass through the fθ lens according to the first embodiment. 6B is a diagram when viewed from the sub-scanning direction, and FIG. 6B is a view from the main scanning direction of the optical paths of the light beams A and B until they are imaged after passing through the fθ lens according to the first embodiment. It is the figure seen.

FIG. 6 is a diagram illustrating a scanning line, in which (a) is a light spot a on which the light beams A and B are imaged on the surface to be scanned,
FIG. 9B is a diagram showing a case where the scanning line of b jumps over two scanning lines, and FIG. 9B is a diagram showing a case where the scanning lines of the light spots a and b are adjacent to each other in the sub-scanning direction.

7A shows a state in which the positions of light spots a and b on which the light beams A and B are imaged on the surface to be scanned are aligned in the sub-scanning direction, and FIG. 7B shows the light spots. It is a figure which shows the state which the position of a and b shifted | deviated in the main scanning direction, but was not aligned in the sub scanning direction.

FIG. 8A is a diagram when the optical paths of the light beams A and B that pass through the fθ lens according to the second embodiment are viewed from the sub-scanning direction, and FIG. F according to the embodiment
It is the figure which looked at the arrangement | positioning with respect to the light beams A and B of the (theta) lens from the main scanning direction.

FIG. 9 is a configuration diagram of an optical scanning device that does not use a cylindrical mirror as a tilt correction optical system.

FIG. 10A is a diagram when the optical paths of the light beams A and B that pass through the fθ lens according to the third embodiment are viewed from the sub-scanning direction, and FIG. FIG. 6 is a diagram of an arrangement in which the fθ lens according to the embodiment is tilted with respect to the light beams A and B as viewed from the main scanning direction.

FIG. 11 is a diagram of the optical paths of the light beams A and B of the optical scanning device according to the first to third embodiments as seen from the main scanning direction.

FIG. 12 is a view of the optical paths of light beams A and B of the optical scanning device according to the fourth embodiment as seen from the main scanning direction.

FIG. 13 is a diagram showing an fθ lens including a first group of optical systems 90 having a power only in the main scanning direction and a second group of optical systems 92 having a power only in the sub-scanning direction.

[Explanation of symbols]

10 Polygon mirror (deflecting means) 20 fθ lens (imaging optical system) 26 Laser diode assembly (light source) 28 Photosensitive drum (scanned object) 32 surface to be scanned

Claims (7)

(57) [Claims] 1. A light source that emits a plurality of light beams separated by a predetermined distance in a direction corresponding to the sub-scanning direction, and a deflection that simultaneously deflects the plurality of light beams emitted from the light source in a direction corresponding to the main scanning direction. Means for scanning, the plurality of light beams deflected by the deflecting means are incident on the surface to be scanned at a predetermined incident angle in the sub-scanning direction with respect to the normal line, and the deflecting means. A plurality of light beams, which are interposed between the object to be scanned and deflected by the deflecting means, are imaged on the surface to be scanned and are polarized with respect to the plurality of light beams.
Less to be cared for and tilted to the optical axis
At least one of the light beams is at a predetermined angle.
Of the light spot generated by incidence on the surface to be scanned.
An image forming optical system that is arranged so that the scanning lengths of the plurality of light beams incident on the scanned object are corrected to be the same or substantially the same by correcting the positional deviation in the main scanning direction. Optical scanning device including. 2. The optical scanning device according to claim 1, wherein the imaging optical system has a power in a direction corresponding to the sub-scanning direction. Wherein said imaging optical system, the plurality of light beams
Is arranged so as to be decentered with respect to, the plurality of deflected light beams are arranged so as to be decentered so as to be incident at a height asymmetric with respect to the optical axis of the imaging optical system. The optical scanning device according to claim 2. 4. The imaging optical system is tilted with respect to the optical axis.
2. When arranged so as to be offset, the plurality of deflected light beams are arranged so as to be incident on the optical axis of the imaging optical system at a predetermined angle in the sub-scanning direction.
The optical scanning device according to claim 3. 5. The imaging optical system has a plurality of deflected light beams in a sub-scanning direction with respect to an optical axis of the imaging optical system.
3. The optical scanning device according to claim 1 or 2, wherein the optical scanning device is arranged so as to be incident at an angle of 1 and at a height symmetrical with respect to the optical axis of the imaging optical system. 6. The image forming optical system includes a first group of optical systems having a power only in the main scanning direction and a second group of optical systems having a power only in the sub scanning direction. The optical scanning device according to any one of claims 1 to 5, which is characterized. 7. The light beam of any one of claims 1 to 6, wherein the plurality of light beams are incident in a state in which the light beams are not parallel to the image forming optical system. Optical scanning device of paragraph.