JP2003211728A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus in which the cost is reduced by standardizing the components being used in a plurality of optical scanners even when the plurality of optical scanners are applied to a multicolor imaging apparatus where the exposing positions are not coplanar. <P>SOLUTION: In the imaging apparatus 30, optical path length (conjugate magnification) of YMCK beams must be equalized but the diameter of a photosensitive body 44K is larger than that of other photosensitive bodies 44Y-44C. Even such a case can be dealt with by adjusting the position of turn back mirrors 60 and 64 or a cylindrical mirror 62 in the housing. Even if the distance from the housing to the photosensitive body is different from color to color, housings 50YM and 50CK of identical shape can be used and the cost can be reduced. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine or a laser printer which scans a laser beam to form an image, and more particularly, an image forming apparatus for forming an image of a plurality of colors by a plurality of optical scanning devices. Regarding the device.

[0002]

2. Description of the Related Art An image forming apparatus for forming a multicolor image at a high speed by simultaneously scanning and exposing a plurality of objects to be scanned has been known.

For example, in Japanese Patent Laid-Open No. 2000-35702, as shown in FIG. 12, four photoconductors 100A-10A are used.
Rotating polygon mirrors 104A to 104D for 0D
Independent optical scanning devices 102A-102 with
As shown in FIG. 13, one using D (hereinafter, referred to as 4BOX type) and an optical scanning device 102 sharing four rotary lasers 104 with the same four laser beams for four photoconductors 100A to 100D. What to use (hereinafter 1BOX
Type) is disclosed.

The 4BOX type has four optical scanning devices 1
Since 02A to 102D are completely independent, the same optical scanning device can be used for single color and multicolor, and the housings 105A to 105D for accommodating each optical scanning device can be downsized and the manufacturing is easy. The advantage is that there are four optical scanning devices, so four high-cost rotary polygon mirrors are required. Even if each optical scanning device is small, it requires four images. The disadvantage is that the forming apparatus as a whole becomes large.

On the other hand, since the 1BOX type is shared by four scanning optical systems, one rotary polygon mirror 104 can be used, and a plurality of optical systems share a space in the same housing 105, so that the entire apparatus is used. It can be miniaturized. However, if the arrangement intervals of the objects to be scanned 100A to 100D are large, the size of the optical scanning device (housing 105) becomes large, and when manufactured with low-cost plastic, the accuracy of mounting optical components is ensured by distortion or thermal deformation. There is a problem that it becomes difficult to do so, and it is difficult to share it with a black-and-white machine (when it is used as a black-and-white machine, the space where the three scanning optical systems that are not used become unnecessary space).

Furthermore, these 4BOX type and 1BO
The 2BOX type, which is the intermediate of the X type, has also been proposed in Japanese Patent Laid-Open No. 10-228148. As shown in FIG. 14, the 2BOX type means four photoconductors 100A.
Two optical scanning devices 102E, 10 for ~ 100D
2F, each optical device (housing 105E, 10E,
5F) accommodates two sets of scanning optical systems each sharing the rotary polygon mirrors 104E and 104F.

The number of rotary polygon mirrors (cost) and the size of the housing of the 2BOX type are between those of 4BOX and 1BOX, but it is said that there is little wasted space even if one optical scanning device is applied to a monochrome machine. In terms of points, it has an advantage close to 4BOX.

The realization of an image forming apparatus using a plurality of photoconductors as described above facilitates the output of a full-color image at a higher speed than in the past. However, full-color output by the image forming apparatus has come to be used not only for simple coloring of black and white documents but also for printing of photographs and the like, so that the image forming apparatus is required to have higher image quality.

As a result, the optical scanning device is required to have an improved scanning line density, and as a measure therefor, it has been proposed to use a surface emitting laser array as a light source.

The surface emitting laser array can be easily formed into an array due to the structure of the device, and can generate several tens of laser beams. Japanese Patent Laid-Open No. 8-330661 discloses an optical scanning device using a surface emitting laser. The surface emitting laser has an advantage that it can output a plurality of beams, but unlike the conventional edge emitting laser, there is no back beam emitted to the rear of the laser element. Therefore, as shown in FIG. Light amount detection sensor 1 by separating a part of the
A structure for detecting the amount of light by making the light incident on 14 must be taken.

On the other hand, an image forming apparatus using a plurality of photoconductors is capable of outputting an image of many colors, but in an actual use state, there are many outputs of a single color (especially black and white).
There is a problem that the frequency of use of the black photoconductor becomes higher than that of the photoconductors of other colors, and the life of the black photoconductor becomes shorter than that of the photoconductors of other colors (premature deterioration). .
Therefore, in Japanese Unexamined Patent Publication No. 2000-242057, as shown in FIG. 16, the diameter of the photoconductor 100K used for black is changed to the photoconductors 100Y, 100M, 100C (hereinafter, 10) of other colors.
0Y to 100C) to extend the life of the photoconductor 100K and increase the black photoconductor 100
It has been proposed to prevent early deterioration by K.

[0012]

[Problems to be Solved by the Invention] Japanese Patent Laid-Open No. 2000-242
The configuration of No. 057 prevents early deterioration of the black photoconductor 100K and averages the life of the photoconductors of the respective colors. However, since the diameter of the black photoconductor 100K is larger than that of the other photoconductors 100Y to 100C, 4 Exposure (scanning) positions PY, PM, PC, PK on the photoconductor of the book (hereinafter referred to as PY to PK)
Are not on the same plane (see FIG. 16). On the other hand, in this prior art example, the LED array heads 116Y to 116Y are used as exposure devices.
K is used, which corresponds to the above-mentioned 4BOX type. In the 4BOX type, since the respective optical scanning devices are completely independent, even if the diameters of the photoconductors 100Y to 100K are different, they can be arranged according to the respective exposure positions PY to PK. There is no. However, when an optical scanning device using a laser is used as the exposure device instead of the LED array head, the 4BOX type has a problem that the entire image forming device becomes large because each optical scanning device has a rotary polygon mirror. .

Further, when applied to the 1BOX type, there are drawbacks that the housing of the optical scanning device becomes large and it is difficult to share it with a monochrome machine.

Further, when applied to the 2BOX type, since the black exposure position PK is not on the same plane as the other color exposure positions PY to PC, an optical scanning device (an optical scanning device including an optical system including the black optical system ( (Casing) and an optical scanning device (housing) in which only optical systems of other colors are configured have different configurations. That is, a plurality of types of optical scanning devices (housings) are required, which causes a problem that the manufacturing cost of the image forming apparatus increases.

Furthermore, in a full-color image forming apparatus, when a surface emitting laser is used as a light source to achieve high image quality, each surface emitting laser of each color is controlled in order to control the light amount of each surface emitting laser. It requires a half mirror and a light amount detection sensor. Therefore, there is a problem that the inside of the device becomes more complicated than that using the conventional edge emitting laser.

In order to solve the above inconvenience, the present invention provides
Even when a plurality of optical scanning devices are applied to a multicolor image forming device whose exposure positions are not on the same plane, the components used for the plurality of optical scanning devices are made common, and an image forming device with low cost is provided. The purpose is to Further, according to the present invention, when a surface emitting laser array is applied to a light source of an optical scanning device in which a plurality of optical systems are arranged, the number of light quantity monitors and half mirrors are reduced, the configuration is simplified and the cost is reduced. It is also an object to provide an image forming apparatus designed.

[0017]

In order to solve such a problem, the invention according to claim 1 has at least one M (M is a natural number of 3 or more) scanning lines which are not on the same plane. On the surface to be scanned N (N is smaller than M (N <
M) a natural number of 2 or more) optical scanning devices, and a housing having the same shape in which the optical scanning devices are configured, and at least one optical scanning device is different from other optical scanning devices. An optical system is provided.

The operation of the invention according to claim 1 will be described.

In the optical scanning device, it is possible to adjust the arrangement of the optical components of the optical system arranged in the housing of the same shape. Therefore, different optical systems corresponding to the respective optical scanning devices that form scanning lines that are not on the same plane as the surface to be scanned can be configured in the same housing. Therefore, in the image forming apparatus, it is possible to share a housing or the like used for a plurality of optical scanning devices and reduce costs.

According to a second aspect of the invention, in the first aspect of the invention, a plurality of optical systems are housed in each of the optical scanning devices, and at least one optical system of the plurality of optical systems is It is characterized in that it is the same for all optical scanning devices.

The operation of the invention according to claim 2 will be described.

Even if the exposure positions are not on the same plane, if one of a plurality of optical systems housed in the same optical scanning device (housing) is positioned as a reference with respect to the object to be scanned, a plurality of optical systems can be obtained. It is not necessary for all optics to be separate between enclosures, and at least one set of optics can be the same for multiple, preferably all, optical scanning devices.

According to a third aspect of the present invention, in the first aspect of the invention, a plurality of optical systems are housed in each of the optical scanning devices. Is deflected and scanned by the same rotating polygon mirror.

The operation of the invention according to claim 3 will be described.

By sharing the rotary polygon mirror among a plurality of optical systems housed in the same optical scanning device (housing), the cost and size of the optical scanning device can be reduced. In particular,
It is more preferable in terms of downsizing if light beams from a plurality of optical systems are made incident on the same reflecting surface of the rotary polygon mirror.

In other words, as a method of sharing the rotary polygon mirror, it is conceivable that the light beam is made incident on two reflecting surfaces which are substantially opposed to the rotation axis. In this case, a plurality of optical systems rotate the rotary polygon mirror. Since the light sources are arranged symmetrically with respect to the axis, multiple light sources are placed in front and rear or left and right positions of the optical scanning device, which complicates the routing of the signal line to the light source, and scanning by multiple light beams There is a problem that a memory for inverting the image is required because the scanning direction of the surface is the reverse direction. However, these problems are solved by making a plurality of light beams incident on the same reflecting surface.

According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the plurality of optical systems housed in the N optical scanning devices respectively emit a plurality of light beams. And the conjugate magnification between the respective light sources and the surface to be scanned is the same.

The operation of the invention according to claim 4 is shown in FIG.
Will be described with reference to.

In an optical system used in a general optical scanning device, as shown in FIG. 11A which is a sectional view in the sub-scanning direction, a divergent light beam emitted from a light source 10 is converted into a substantially parallel light beam by a collimator lens 12. The cylindrical lens 14 collects light only in the sub-scanning direction, and the reflecting surface 1 of the rotary polygon mirror
6 is imaged. Further, the divergent light reflected by the reflecting surface 16 is condensed again by the tilt correction optical system 18 and condensed on the surface of the scanned object 20.

As shown in FIG. 11 (A), when there is one light beam, the magnification between the light source 10 and the surface to be scanned 20 can be set relatively freely, but as shown in FIG. 11 (B), When the light source 10 emits a plurality of light beams, the magnification of the optical system is determined by the distance L1 between the plurality of light emitting portions of the light source and the scanning line interval L on the surface 20 to be scanned.
Specified by 2.

If the optical magnification between the light sources of the plurality of types of optical systems used in the N optical scanning devices and the surface to be scanned differs for each optical system, in order to expose the surface to be scanned at the same scanning line density, The distance between the light beams emitted from the light source must be different. That is, different light sources have to be used. However, if the magnification (L2 / L1) between the light source and the surface to be scanned is the same as in the present invention, the same light source can be used even if the optical system is different.

According to a fifth aspect of the present invention, in the fourth aspect of the present invention, the plurality of optical systems have different optical magnifications for correcting surface tilts of a plurality of reflecting surfaces of a rotary polygon mirror for polarization-scanning each light beam. Is characterized by.

FIG. 1 shows the operation of the invention according to claim 5.
This will be described with reference to FIG.

The light source 10 is shown in FIGS. 11 (B) and 11 (C).
Although the conjugate magnification (L2 / L1) between the scanning surface 20 and the scanned surface 20 is the same, an example in which the optical magnification for correcting the surface tilt of the plurality of reflecting surfaces of the rotary polygon mirror is different is shown. That is, FIG. 11 (B) and FIG.
In (C), L1 and L2 have the same value, and the conjugate magnification between the light source and the surface to be scanned is the same. However, light source 1
0 and the conjugate magnification between the reflecting surface 16 of the rotary polygon mirror and the conjugate magnification between the reflecting surface 16 of the rotary polygon mirror and the scanned surface 20 are different. That is, comparing the arrangements of the optical components in FIGS. 11B and 11C, it can be seen that the positions of the cylinder lens 14 and the surface tilt correction optical system 18 are displaced. When the two optical systems share the same reflecting surface 16 of the same rotary polygon mirror, the two optical systems are arranged one above the other, but in this way the light source 10 and the reflecting surface of the rotary polygon mirror are arranged. 16 and between the reflecting surface 16 of the rotary polygon mirror and the surface to be scanned 20 are set to different values, the cylinder lens 14 and the surface tilt correction optical system 18 are arranged on the optical path in the optical systems that are vertically stacked. They can be arranged so as to be shifted forward and backward, and can be easily attached to the housing.

According to a sixth aspect of the present invention, in an optical scanning device in which a plurality of optical systems are housed in the same housing, each optical system has a surface emitting laser which is a light source and emits light from the surface emitting laser. The light quantity detection sensor having a plurality of optical systems, the light quantity detection sensor having a beam separation means for separating a part of the beam and a light quantity detection sensor for detecting an output of the beam separated by the beam separation means. It is characterized by sharing.

The operation of the invention according to claim 6 will be described.

By sharing the light amount detecting sensor required when the surface emitting laser is used as the light source with a plurality of optical systems, the number of light amount detecting sensors required when using the surface emitting laser is reduced. be able to.

According to a seventh aspect of the invention, in the sixth aspect of the invention, the plurality of beams emitted from the plurality of surface emitting lasers are incident on the same reflecting surface of the same rotary polygon mirror, and the plurality of beams of the plurality of beams are emitted. It is characterized in that it has an optical synchronization sensor for detecting one of the beams to detect the scanning start timing, and that the light amount detection sensor and the optical synchronization sensor are arranged on the same substrate.

The operation of the invention according to claim 7 will be described.

The optical scanning device is usually provided with an optical synchronization sensor for detecting the timing of deflection scanning by the rotary polygon mirror. When light beams from a plurality of optical systems are made incident on the reflecting surface of the same rotary polygon mirror, it is known to reduce the number of optical synchronization sensors by using the optical synchronization sensor for only one optical system of the plurality of optical systems. However, according to the present invention, the number of parts is reduced by providing the light synchronization sensor and the light amount detection sensor, which is a unique structure of the surface emitting laser, on the same substrate.

According to an eighth aspect of the invention, in the seventh aspect of the invention, the light amount detecting sensor and the light synchronizing sensor are also used as the same sensor.

The operation of the present invention will be described.

When the surface emitting laser is used as the light source of the optical scanning device, the surface emitting laser can be used without increasing the number of sensors by using the light synchronizing sensor and the light amount detecting sensor as one sensor. It will be possible.

[0044]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An image forming apparatus to which an optical scanning device according to an embodiment of the present invention is applied will be described with reference to FIGS.
Will be described with reference to.

The image forming apparatus 30, as shown in FIG.
An electrophotographic unit 32 that forms four color toner images of Y (yellow) M (magenta) C (cyan) K (black).
Y, 32M, 32C, 32K (hereinafter, referred to as 32Y to 32K; other reference numerals are also the same), and a transfer device 34 described later.
The intermediate transfer belt 36 on which the toner images are stacked by Y to 34K, the transfer device 40 that transfers the toner image transferred on the intermediate transfer belt 36 to the paper supplied from the tray 38, and the transfer device 40 that transfers the toner image on the paper. It basically comprises a fixing device 42 for fusing and fixing a toner image.

The electrophotographic unit 32Y includes a photoconductor 44Y.
A charging device 46Y, an optical scanning device 48YM, a developing device 50Y, a transfer device 34Y, and a cleaning device 52Y around
Are arranged. The same applies to the electrophotographic units 32M to 32K.

The optical scanning device 48YM is composed of the photoconductor 4
4Y and the photosensitive member 44M are scanned and exposed, and similarly, the optical scanning device 48CK is configured to scan and expose the photosensitive member 44C and the photosensitive member 44K.

Further, the diameter of the K photoconductor 44K is made larger than the diameter of the YMC photoconductors 44Y to 44M, and it is possible to prevent only the K photoconductor 44K from being prematurely deteriorated by the output of the monochrome image. ing.

Two optical scanning devices 48YM, 48CK
Uses the same shape of the casings 50YM and 50CK, but the casings 5YM and 50CK have different diameters.
The distance from 0YM to the photoconductor 44M and the distance from the housing 50CK to the photoconductor 44K are different, and the optical systems of M and K are partially different. Since the photoconductors 44Y and 44C have the same diameter, Y and C have the same optical system. That is, the casing 50YM and the casing 50CK are arranged so as to have the same positional relationship with respect to the photoconductors 44Y and 44C so that Y and C are formed as the same optical system.

The optical scanning device 48YM will now be described with reference to FIGS. 2 and 3. First, the description will be given along the optical path of the Y beam LY.

As shown in FIG. 2, the light source 72Y and the light source 7
Between the rotary polygon mirror 54 that deflects the beam LY emitted from 2Y, a collimating lens 74Y that makes the beam emitted from the surface emitting laser array, which is the light source 72Y, substantially parallel light, and the collimated beam are sub-scanned. A cylindrical lens 78Y that condenses light only in a direction and a half mirror 80 that separates a part of the beam and reflects the beam to a light amount detection sensor 82 are provided. The beam LY that has passed through the half mirror 80 is incident on the rotary polygon mirror 54.

The beam LY deflected by the reflecting surface of the rotary polygon mirror 54 is, as shown in FIG.
At 6, an image is formed in the main scanning direction so that the photoconductor is scanned at a constant speed. That is, the beam LY that has passed through the Fθ lens 56 is reflected by the return mirrors 66 and 68, and is imaged on the photoconductor 44Y in the sub scanning direction by the cylindrical mirror 70 having power in the sub scanning direction.
The cylindrical mirror 70 also functions as a surface tilt correction optical system of the rotary polygon mirror 54.

Next, description will be given along the optical path of the M beam LM.

As shown in FIG. 2, the path between the rotary polygon mirrors 54 for deflecting the beam LM emitted from the light source 72M is the same as the optical path of the beam LY of Y, but the collimator lens 7 is used.
Reflection mirror 7 between 4M and cylindrical lens 78M
6M is provided, and by being reflected by the reflection mirror 76M, the beam LM and the beam LY are located at a position where they overlap with each other in plan view (shifted in the vertical direction), and reach the rotary polygon mirror 54.

As shown in FIG. 3, the beam LM deflected by the rotary polygon mirror 54 is reflected by the folding mirrors 58 and 60 via the Fθ lens 56, and the beam LY reflected by the cylindrical mirror 62 is finally reflected. The light is reflected by the folding mirror 64 and reaches the photoconductor 44M. The cylindrical mirror 62 is also a rotary polygon mirror 54.
It also functions as an optical compensating optical system.

On the other hand, the optical scanning device 48CK also has a housing 50Y.
The housing 50CK having the same shape as M is arranged in substantially the same manner. That is, the photoconductors 44 located on the same plane
Since the housing 50YM and the housing 50CK are arranged so as to have the same positional relationship with the scanning positions PY and PC of Y and 44C, the optical system of Y is exactly the same as the optical system of C. On the other hand, the diameter of the photosensitive member 44K is smaller than that of the other photosensitive member 44K.
Since the scanning positions PK are larger than the diameters of Y to 44C, the scanning positions PK do not lie on the plane of the scanning positions PY to PC (see FIG. 1), and the K optical system and the M optical system cannot be configured the same ( (See FIG. 3).

Further, Y, M accommodated in the housing 50YM
Since the optical system of (1) shares the Fθ lens 56, the optical path lengths from the rotary polygon mirror 54 to the photoconductor 44 are the same for the Y and M optical systems. Further, since the same Fθ lens 56 is used for the two housings 50CK and 50YM,
The optical path lengths of all the optical systems of MCK are the same. However, the diameter of the photoconductor 44K is different from that of the other photoconductors 44Y to 44Y.
Since it is larger than the diameter of C, the photosensitive member 44
The distance K is the same shape from the housing 50YM to the photoconductor 44.
It becomes shorter than the distance to M, and the beam L in the housing
The optical path length of K must be longer than the beam LM. Therefore, in the case 50CK, the positions of the folding mirrors 60, 64 and the cylindrical mirror 62 are slightly changed from those in the case 50YM, and the beam LK and the beam L are changed.
The difference in the optical path length of M is absorbed (see the broken line portion in FIG. 3).

The housing 50 is provided with a mounting portion which can be mounted by adjusting or selecting the positions of the mirrors 60, 62 and 64 (solid line position and broken line position). The mounting part should not interfere with other mirrors or light beams.

That is, the positions of the folding mirrors 60 and 64 and the cylindrical mirror 62 are adjusted in the housings 50YM and 50CK so that the housing 5 can be used for the Y and C optical systems.
By configuring the optical path length of the M optical system in 0YM and 50CK to be long and the optical path length of the K optical system to be short, different optical systems can be configured in the same-shaped housings 50YM and 50CK.

Such a construction is not limited to the case where the diameters of the photoconductors 44 are different as shown in FIG. 1, but the photoconductors 44Y to 44K are the same in diameter as shown in FIG.
It can also be applied to the case where the arrangement of ~ 44K is curved in a side view. Even in this case, Y
And the distance from the housing 50YM of the C to the photosensitive member 44Y and the distance from the housing 50CK to the photosensitive member 44C are the same,
Only the M and K optics need to be different, Y and C
The same optical system can be used for.

By the way, in this embodiment, since the surface emitting laser array which emits a plurality of beams is used as the light sources 72Y to 72K, the magnification of the optical system is as shown in FIGS. 11B and 11C.
As described above, it is determined from the light emitting point interval L1 of the laser array and the scanning line interval L2 on the photoconductor. Therefore, in order to use the laser arrays having the same arrangement for the four light sources, the magnification of the optical system must be the same in all the optical systems. Therefore, in the present embodiment, the light sources 72Y to 72Y.
The magnification between K and the rotary polygon mirror 54 and the magnification between the rotary polygon mirror 54 and the photoconductors 44Y to 44K are the same for the four colors. Specifically, the collimating lens 74, the cylindrical lens 78, and the cylindrical mirrors 62 and 70 have the same focal length in all optical systems. Although the position of the cylindrical mirror 62 is shifted between M and K in FIG. 3, the cylindrical mirror 62 and the photoconductors 44M and 44K are different from each other.
Have the same distance. Cylindrical mirror 62
Since the focal length of can be the radius of curvature and the reflection angle, M and K
The cylindrical mirror 62 has the same focal length in the optical system, but the radius of curvature of the mirror itself has another value.

As a method of making the magnifications of YC and MK the same, the YC cylindrical mirror 70 and the photosensitive member 4 are used.
4Y, 44C distance MK cylindrical mirror 62
And the distance between the photoconductors 44M and 44K should be the same,
Depending on the space in the image forming apparatus, it may not be possible to arrange such a mirror. In such a case, the present inventor proposes a Japanese Patent Application No. 2000-0284 as an optical system for multiple beams.
If an optical system using two cylindrical mirrors filed in No. 62 is used, it becomes possible to change the position of the cylindrical mirror while maintaining the magnification. In Figure 3,
Although the distances from the M and K and the Y and C cylindrical mirrors 62 and 70 to the photoconductors 44Y to 44K are different, the folding mirrors 58 and 66 are also cylindrical mirrors, so that the rotary polygon mirror 54 and the photoconductors 44Y to 44K. Magnification between them is the same.

In the above examples, since the magnifications between the light source and the photoconductor, between the light source and the rotary polygon mirror, and between the rotary polygon mirror and the photoconductor are all the same, the cylindrical lenses 78Y and 78M are used.
(78C, 78K) are in the vertically overlapping position (Fig. 2).
reference). Cylindrical lens 78Y, 78M (78
(C, 78K) may be difficult to attach to the housing when they are vertically stacked. In such a case, it can be solved by changing the magnification between the light source-rotating polygon mirror and between the rotating polygon mirror-photoreceptor between the optical systems. This is because if the magnification of the entire optical system is (magnification between the light source and the rotary polygon mirror) × (magnification between the rotary polygon mirror and the photoconductor), the two breakdowns need not be the same. . For example, in FIG.
In the above optical system, if the focal lengths of the cylindrical mirrors 62 and 70 are set so that the magnification between the rotary polygon mirror and the photoconductor is larger in the M optical system than in the Y optical system, the magnification of the entire optical system is maintained. Is a cylindrical lens 78M
Since the focal length of the cylindrical lens 78Y is made smaller than the focal length of the cylindrical lens 78Y, it is possible to shift the positions of the cylindrical lenses 78Y and 78M as shown in FIG. Is easy to install.

As described above, when the surface emitting laser is used as the light source 72, the light amount detecting sensor 82 is externally required. However, one sensor is not required for each surface emitting laser. Absent. As shown in FIG. 6, the optical path from the half mirror 80 to the light amount detection sensor 82 is shown in the sub-scanning direction.
By inserting the lens 84 between the two of Y and M
The beams LY and LM from the two optical systems can be collected at approximately one point. With this configuration, the two optical systems can also serve as one light amount detection sensor 82. Therefore, when controlling the light quantity, the two light sources 72
It is possible to control with one light amount detection sensor 82 by sequentially lighting Y and 72M.

Further, in the optical scanning device 10 using the rotary polygon mirror 54, the photosensitive member 44 is formed on each reflecting surface of the rotary polygon mirror 54.
In order to match the timing when exposing Y to 44K, it is usual to provide a beam passage timing detection means before the start of scanning of the photoconductor. For example, as shown in FIG. 7, a pickup mirror 86 for reflecting the beam to the passage timing detection means is provided. Then, the beam reflected by the pickup mirror 86 is incident on a synchronizing optical sensor 88 provided on the same substrate as the light amount detecting sensor 82.

FIG. 8 shows a structure in which the light amount detecting sensor 82 and the synchronizing sensor 88 are mounted on the substrate. Board 90
Is provided with a light amount detection sensor 82 and a synchronization sensor 88, and the beam LA reflected by the half mirror 80 and condensed by the lens 84 enters the light amount detection sensor 82.
On the other hand, since the synchronization beam LB is reflected by the pickup mirror 86 after being deflected by the rotary polygon mirror 54, it moves as shown by the dotted line in the drawing and crosses the synchronization sensor 88, so that the write timing can be detected.

In the above structure, each sensor is provided,
It is also possible to perform light amount detection and synchronous detection with the same sensor. That is, as shown in FIG. 9, the sensor 92 provided on the substrate 90 has a beam LA reflected by the half mirror 80 and a beam L reflected by the pickup mirror 86.
Both B are incident. A method of performing light amount detection and synchronization detection in this configuration will be described with reference to FIG.

FIG. 10 shows a lighting signal for lighting the Y and M lasers and the sensor output at that time. In the figure, APC indicates the light amount control state, and SOS indicates the scanning start signal detection state. For example, when controlling the light amount with the optical scanning device 48YM, first, the light source 72Y is turned on. At that time, since the beam LYB deflected and reflected by the rotary polygon mirror 54 does not enter the sensor 92, only the Y beam LYA reflected by the half mirror 80 enters the sensor 92,
The light amount of Y is detected. When the light amount control of Y is completed, the M light source 72M is turned on next, and only the M beam LMA reflected by the half mirror 80 enters the sensor 92,
Is detected. When the light amount control ends, the beam LYB deflected by the rotary polygon mirror 54 comes to a position where it is incident on the sensor 92, so that Y laser is used for synchronization.
Turn on the laser. In order to detect the synchronization signal, the laser is turned on before the deflected beam LYB enters the sensor 92. That is, the Y beam LYA reflected by the half mirror 80 first enters the sensor 92, and the beam LB reflected by the pickup mirror 86 also enters the sensor 92. As a result, the sensor 9
The output of 2 further increases (see FIG. 10, sensor output). Therefore, the half mirror 8 is used for synchronization detection.
0 and both beams LY from the pickup mirror 86
The current or voltage level output only when A and LYB are incident may be used as the threshold value (see FIG. 10). Since the two light sources 72Y and 72M are turned on at the same time during image printing, a larger output is output from the sensor 92 than during light amount control, but no problem occurs because no control is performed during image printing.

In the present embodiment, each optical scanning device 4
Since 8YM and 48CK are configured with two optical systems for one housing 50YM and 50CK, the space for arranging the optical components forming one optical system is not required even when used in a monochrome machine. As a result, it can be efficiently shared with the color image forming apparatus.

Further, each optical scanning device 48YM, 48CK
Has a configuration in which two optical systems that share one rotary polygon mirror 54 are provided, the housings 50YM and 50CK are relatively small, and the housings 50YM and 50C are provided for cost reduction.
Even when plastic is used for K, it is possible to secure the mounting accuracy of the optical component. Further, since the beams of the plurality of optical systems are deflected on the same reflecting surface of the rotary polygon mirror 54, the housings 50YM and 50CK can be further downsized.

In this embodiment, the light sources 72Y to 72Y are used.
Although K has been described as a surface emitting laser, the present invention is not limited to this and can be applied to an edge emitting laser, for example. In this case, as described with reference to FIG.
Different optical systems can be provided in the housings 50YM and 50CK having the same shape only by keeping the optical magnifications of the light sources 72Y to 72K and the scanning positions PY to PK of the photoconductors 44Y to 44K constant.

[0072]

As described above, according to the present invention,
Even if the scanning lines formed on the plurality of surfaces to be scanned are not on the same plane, the plurality of optical scanning devices can be provided in the same shape housing, and the optical parts can be shared to reduce the cost.

Further, since the number of light amount detecting sensors peculiar to the surface emitting laser can be reduced, there is an effect that the structure of the device is simplified.

[Brief description of drawings]

FIG. 1 is a schematic explanatory diagram of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a partially omitted plan view of the optical scanning device according to the embodiment of the present invention.

FIG. 3 is a partially omitted side view of the optical scanning device according to the first embodiment of the present invention.

FIG. 4 is an explanatory view of a main part of an image forming apparatus according to another example of the first embodiment of the present invention.

FIG. 5 is a partially omitted plan view showing another example of the optical scanning device according to the second embodiment of the present invention.

FIG. 6 is a configuration diagram showing sensor input of an optical scanning device according to a second embodiment of the invention.

FIG. 7 is a partially omitted plan view of an optical scanning device according to another example of the present invention.

FIG. 8 is a perspective view showing a sensor arrangement according to another example of the present invention.

FIG. 9 is a perspective view showing a sensor arrangement according to another example of the present invention.

10 is a timing chart for performing light amount control and synchronization detection control in the sensor of FIG.

FIG. 11A is a sub-scanning direction cross section of an optical system applied to a general optical scanning device, and FIG. 11B is a sub-scanning direction cross section of an optical system when a light source that emits a plurality of light beams is used. 3C is a cross-sectional view, and FIG. 6C is a cross-sectional view in the sub-scanning direction of the optical system showing a case where the optical magnification for correcting the surface tilt of the rotating polygon mirror is different from FIG.

FIG. 12 is a schematic configuration diagram of an image forming apparatus according to a conventional example.

FIG. 13 is a schematic configuration diagram of an image forming apparatus according to a conventional example.

FIG. 14 is a schematic configuration diagram of an image forming apparatus according to a conventional example.

FIG. 15 is an explanatory diagram of a light amount detection mechanism of an optical scanning device according to a conventional example.

FIG. 16 is a schematic configuration diagram of an image forming apparatus according to a conventional example.

[Explanation of symbols]

30 ... Image forming apparatus 48 ... Optical scanning device 50 ... Case 54 ... Rotating polygon mirror 72 ... Light source 44 ... Photosensitive member (scanned surface) 80 ... Half mirror (beam separating means) 82 ... Sensor for detecting light amount 88 ... Optical synchronization sensor 92 ... Sensor

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Claims (8)

[Claims] 1. At least one M not coplanar
(M is a natural number of 3 or more) N scan lines are formed on the surface to be scanned (N is smaller than M (N <M) 2 or more natural number)
A plurality of optical scanning devices, and a housing having the same shape in which the optical scanning devices are configured, and at least one optical scanning device is provided with an optical system different from other optical scanning devices. An image forming apparatus characterized by the above. 2. A plurality of optical systems are housed in each of the optical scanning devices, and at least one optical system of the plurality of optical systems is the same in the plurality of optical scanning devices. The image forming apparatus according to claim 1. 3. A plurality of optical systems are housed in each of the optical scanning devices, and the light beams from the light sources of the plurality of optical systems in the optical scanning devices are deflected and scanned by the same rotary polygon mirror. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. 4. A plurality of optical systems housed in the N optical scanning devices each have a light source for emitting a plurality of light beams,
4. The image forming apparatus according to claim 1, wherein the respective light sources and the surface to be scanned have the same conjugate magnification. 5. The image forming apparatus according to claim 4, wherein the plurality of optical systems have different optical magnifications for correcting surface tilts of a plurality of reflecting surfaces of a rotary polygon mirror that performs polarization scanning of each light beam. 6. An optical scanning device in which a plurality of optical systems are housed in the same housing, each optical system including a surface emitting laser as a light source and a part of a beam emitted from the surface emitting laser. And a light amount detection sensor for detecting the output of the beam separated by the beam separation unit, and a plurality of optical systems share the same light amount detection sensor. Image forming apparatus. 7. A rotary polygon mirror in which a plurality of beams emitted from the plurality of surface emitting lasers are incident on the same reflecting surface, and one beam of the plurality of beams is detected to detect a scan start timing. 7. The image forming apparatus according to claim 6, further comprising: a light synchronization sensor for controlling the light intensity, and the light intensity detection sensor and the light synchronization sensor are disposed on the same substrate. 8. The image forming apparatus according to claim 7, wherein the light amount detecting sensor and the light synchronizing sensor are also used as the same sensor.