JP2013076995A - Optical scanner and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical scanner that prevents a light beam generated by reflection from each scanned face from reaching a scan imaging optical system and is able to prevent an occurrence of image defect resulting from the reach of light reflected by the scan imaging optical system to other scanned faces.SOLUTION: In an optical element composing the scan imaging optical system, if the angle between a light beam LB1 near the center in a main scanning direction which has been emitted from an optical element (long toroidal lens 10) having refractive power in a sub-scanning direction and located nearest to a scanned surface 5a and a light beam LB2 after the light beam LB1 that has been reflected by the scanned face is represented as θ1, and the angle between the light beam LB1 and a line connecting the end 10a of the long toroidal lens 10 in the sub-scanning direction and a reflection point 5b at which the light beam LB1 is reflected by the scanned face is represented as θ2, light reflected by each scanned face satisfies a condition expressed by θ1>θ2, and travels away from a plane perpendicular to the rotation shaft of a light deflector.

Description

  The present invention relates to an optical scanning apparatus, a copier having the optical scanning apparatus, a printer, a facsimile machine, a plotter, and an image forming apparatus such as a multifunction machine including at least one of them.

In general, an optical scanning device used in a laser printer or the like deflects a light beam from a light source side by an optical deflector and condenses the light beam toward a scanned surface by a scanning imaging optical system such as an fθ lens. A light spot is formed on the top.
The surface to be scanned is optically scanned (main scan) with this light spot.
What forms the surface to be scanned is a photosensitive surface of a photosensitive medium such as a photoconductive photosensitive member.

As an example of a full-color image forming apparatus, four photoconductors (hereinafter referred to as “photosensitive drums”) are arranged in the recording paper conveyance direction, and light beams emitted from a plurality of light source devices corresponding to the photoconductors. There is known a configuration in which the light beam is deflected and scanned by one deflecting means (optical deflector).
In this apparatus, a plurality of scanning imaging optical systems corresponding to each photoconductor are simultaneously exposed to each photoconductor to form a latent image.
These latent images are visualized by developing devices using developers of different colors such as yellow, magenta, cyan, and black.

These visible images are sequentially superimposed and transferred onto the same recording paper, and fixed to obtain a color image.
An image forming apparatus that obtains a two-color image, a multi-color image, a color image, or the like by using two or more combinations of optical scanning devices and photoreceptors is known as a “tandem image forming apparatus”.
In a full-color image forming apparatus, there is an increasing need for high image quality, and density fluctuations due to ghost light and image defects are problems as one cause of image defects.

The light beam reflected by the photosensitive member as the surface to be scanned reaches the scanning imaging optical system again and is reflected again by hitting the optical surface and the rib structure, and the light is irradiated again as ghost light. Sometimes.
As a result, an unintended image is generated, and the image quality is greatly affected, such as a change in density caused by a change in the amount of light in the ghost light irradiated portion.
In particular, there is a problem in an optical scanning device used for an image forming apparatus of a type that shares an optical deflector with light beams corresponding to a plurality of colors, such as a tandem image forming apparatus.

That is, as compared with a conventional monochrome machine, there is a high possibility that ghost light will be incident on a photoconductor having a color different from the color from which ghost light is generated, which is a big problem.
In this case, unlike a monochrome machine, a phenomenon of color unevenness also occurs, and the image defect becomes more conspicuous.

As a low-cost scanning optical system suitable for a tandem image forming apparatus, there is an oblique incidence system in which the light is incident with an angle in the sub-scanning direction with respect to the normal line of the deflecting reflection surface of the optical deflector.
In this system, a plurality of light beams are obliquely incident toward the center of the sub-scanning section of the deflecting / reflecting surface.
Accordingly, there is an advantage that a low-cost optical deflector in which the height of the deflecting reflection surface in the sub-scanning direction is reduced can be adopted instead of the high-cost two-stage polygon mirror or the thick polygon mirror.

However, in the oblique incidence method, the light beams directed to different photoconductors are often close in the sub-scanning direction on the deflection reflection surface of the optical deflector.
When ghost light is incident on the optical deflector, it easily reaches the photoconductors of other colors, and the above-mentioned problem of image quality deterioration tends to occur.
As an optical scanning device for removing a ghost image, for example, the one described in Patent Document 1 is known.

In this optical scanning device, as shown in FIG. 9, an angle α formed by the optical axis of the light beam incident on the optical deflector 3 and the optical axis of the scanning imaging optical system 4 having the fθ lens is scanned. Certain restrictions are applied according to the effective scanning width W of the surface 5a and the distance D from the principal point of the scanning imaging optical system 4 to the surface to be scanned 5a.
Thereby, the ghost image Pg is formed outside the effective scanning width W of the surface to be scanned 5a.

According to the optical system disclosed in Patent Document 1, a ghost image generated in the main scanning direction by the optical deflector 3 can be prevented.
However, as shown in FIG. 10, it is difficult to prevent a ghost image generated by the optical system after the optical deflector 3, particularly a ghost image generated in the sub-scanning direction.
In FIGS. 9 and 10, reference numeral L denotes an incident light beam to the photosensitive member 5, P denotes an incident point, Lg denotes a reflected light beam, and 10 denotes an optical element of the scanning imaging optical system.

As an optical scanning device for preventing a ghost image generated in the sub-scanning direction, for example, the one described in Patent Document 2 is known.
In this optical scanning device, the content is defined so that the reflected light from the photosensitive member does not face the dust-proof glass.

However, in the apparatus described in Patent Document 2, the incident angle with respect to the normal line of the photosensitive member is increased.
For this reason, problems such as the beam diameter of the light beam imaged on the photoconductor becoming larger in the sub-scanning direction and the scanning line being curved are likely to occur.

  The present invention has been made in view of the circumstances as described above, and the surface to be scanned on which the light reflected by the surface to be scanned is incident on the scanning imaging optical system and the light reflected by the scanning imaging optical system is scanned. Alternatively, the main object of the present invention is to provide an optical scanning device that can prevent the occurrence of image defects caused by being incident as ghost light on another surface to be scanned.

In order to achieve the above object, the present invention comprises a plurality of light source devices, and light beams from each light source device are deflected by an optical deflector and then condensed on different surfaces to be scanned by a scanning optical system. In the scanning device, a first light beam emitted from the scanning lens and reaching the scanned surface of a light beam passing through the vicinity of the center in the main scanning direction of the scanning lens located closest to the scanned surface in the scanning optical system The angle between the first light beam and the second light beam generated by reflection at the reflection point on the surface to be scanned is θ1, and the first light beam, the reflection point, and main scanning of the scanning lens are performed. When the angle formed by the line connecting the sub-scanning end near the center of the direction is θ2,
θ1> θ2
And the reflected light on the scanned surface is deployed between the optical deflector and the scanned surface, and is developed without considering the reflection on the folding mirror that folds the optical path in the sub-scanning direction. The light deflector is directed in a direction far from a plane perpendicular to the rotation axis of the optical deflector.

  According to the present invention, it is possible to prevent the reflected light beam from the surface to be scanned from being incident on the scanning imaging optical system, reflected, and re-imaged on the surface to be scanned. ) In the sub-scanning direction can also be suppressed, and a high-quality and high-quality image can be formed.

1 is a perspective view illustrating an outline of a configuration of an optical scanning device according to an embodiment of the present invention. It is sectional drawing in the subscanning direction for demonstrating the conditions for prescribing | regulating the course of the light beam reflected by the to-be-scanned surface. It is sectional drawing in the subscanning direction of the example with the same absolute value of the angle with respect to the normal line of a to-be-scanned surface of the light beam which injects into a to-be-scanned surface. It is sectional drawing in the subscanning direction which shows the example of the compact structure using a reflective mirror. It is sectional drawing in the subscanning direction which shows the other example of the compact structure using a reflective mirror. It is sectional drawing in the subscanning direction in the example of a counter scanning system. It is sectional drawing in the subscan direction in the other example for demonstrating the conditions for prescribing | regulating the path | route of the light beam reflected by the to-be-scanned surface. 1 is a schematic configuration diagram of an image forming apparatus. It is a block diagram in the main scanning plane of the conventional optical scanning device. It is a figure for demonstrating the problem in the past. It is sectional drawing in a subscanning direction for demonstrating generation | occurrence | production of a ghost image when the optical element near an optical polarizer has power in a subscanning direction. It is sectional drawing in the subscanning direction for demonstrating generation | occurrence | production of a ghost image when the optical element near an optical polarizer does not have power in a subscanning direction.

Embodiments of the present invention will be described below with reference to the drawings.
First, the outline of the configuration of the optical scanning device according to the present embodiment will be described with reference to FIG.
A divergent light beam (light beam) emitted from the semiconductor laser 1 as a light source is converted into a light beam form suitable for the subsequent optical system in the coupling lens 6 of the imaging optical system 2.

The form of the light beam converted by the coupling lens 6 can be a parallel light beam, or a light beam with weak divergence or weak convergence.
The coupling lens 6 can be adjusted in the optical axis direction, the main scanning corresponding direction, and the sub-scanning corresponding direction, and converts the convergence state of the light flux into a desired light flux form by the adjustment.
The light beam passes through the aperture 7 and is deflected and reflected by an optical deflector (hereinafter also referred to as “polygon mirror”) 3 in a state where it is condensed only in the sub-scanning direction by the cylindrical lens 8 (a state of a line image long in the main scanning direction). It is incident on the surface.

This is because the tilting of the deflection surface can be corrected by the scanning imaging optical system 4.
The “main scanning direction” refers to the direction in which the deflecting / reflecting surface of the optical deflector 3 scans the beam on the photosensitive drum 5 as the image carrier, and the “sub-scanning direction” refers to the rotation axis of the optical deflector 3. The directions parallel to each other are represented.
The position of the optical element (coupling lens, cylindrical lens) of the imaging optical system 2 is adjusted so that the beam waist diameter and beam waist position of the scanning light beam are balanced in the scanning region.

The light beam reflected by the deflecting and reflecting surface is deflected at a constant angular velocity along with the constant speed rotation of the polygon mirror 3 and passes through the scanning imaging optical system 4 including the fθ lens 9 and the long toroidal lens 10.
Then, the light enters the photosensitive drum 5 having the surface to be scanned 5 a directly or via the folding mirror 11.
Reference numeral 13 denotes a synchronization detection unit.

In this embodiment, the optical path is folded back by the folding mirror 11 and finally condensed on the scanned surface 5a (on the photosensitive drum).
Thereby, the deflected light beam forms a light spot on the surface to be scanned, and performs optical scanning of the surface to be scanned.

Here, before describing the features of the present invention, problems when the conditions of the present invention are not set will be described using an oblique incidence optical system as an example.
FIG. 11 and FIG. 12 depict the sub-scan section from the optical deflector to the scanned surface, and explain the reason why the reflected light from the scanned surface becomes ghost light.
In FIG. 11, in the scanning imaging optical system, a lens close to the optical deflector 3 (here, fθ lens 9) is a so-called shared lens that is used in common for two scanned surfaces.

The fθ lens 9 as a shared lens has power in the main scanning direction and the sub-scanning direction. Hereinafter, the fθ lens 9 is also referred to as a “common lens 9”.
Lenses close to the surface to be scanned (here, the long toroidal lens 10) exist corresponding to the number of surfaces to be scanned, have power mainly in the sub-scanning direction, and have a surface tilt correction function.
The light beam reflected by the deflecting reflecting surface (shown by a solid line in the figure) passes through the scanning imaging optical system and is finally condensed on the surface to be scanned 5a (on the photosensitive drum 5).

However, as indicated by the broken line, the light beam may be directed again toward the scanning imaging optical system due to reflection on the surface to be scanned.
First, by passing through the long toroidal lens 10 positioned closest to the surface to be scanned, it is influenced by the refractive power in the sub-scanning direction, and goes toward the shared lens 9 close to the optical deflector.
At that time, light hitting the optical surface of the shared lens 9 or the rib portion structure is reflected on the surface. In the figure, the light reflected by the second surface of the shared lens 9 is directed upward in the figure.

On the other hand, the light reflected by the first surface of the shared lens 9 is directed downward in the figure and is incident on another surface to be scanned.
That is, the light reflected by the photosensitive drum 5A forms an image as ghost light on the photosensitive drum 5B. Reference numerals 5A and 5B simply indicate different surfaces to be scanned, and have no relationship with colors (the same applies to other examples).

In FIG. 12, the fθ lens 9 close to the optical deflector 3 in the scanning imaging optical system is a so-called shared lens that is used in common for two scanned surfaces, and has power only in the main scanning direction.
The long toroidal lens 10 close to the surface to be scanned exists corresponding to the number of surfaces to be scanned, has power mainly in the sub-scanning direction, and has a surface tilt correction function.
The light beam reflected by the deflecting reflection surface of the optical deflector 3 passes through the scanning imaging optical system and is finally condensed on the surface to be scanned (photosensitive member).

Then, the light beam is directed again to the scanning imaging optical system by reflection on the surface to be scanned.
The light reflected by the surface to be scanned first passes through the long toroidal lens 10 close to the surface to be scanned, and is affected by the refractive power in the sub-scanning direction, and may be directed to the common lens 9 close to the optical deflector.
Thereafter, the light hitting the optical surface or rib structure portion of the shared lens 9 is reflected by the surface and is incident on the other surface to be scanned (lower side in the figure).
That is, the light reflected by the photosensitive drum 5A forms an image as ghost light on the photosensitive drum 5B.

As described with reference to FIGS. 11 and 12, when the reflected light from the surface to be scanned is incident on the lens near the surface to be scanned again, the possibility of reaching the scanning lens (shared lens) on the side near the optical deflector increases. .
Then, the light hitting the optical surface or rib structure portion of the shared lens is reflected by the surface, and the possibility that the light enters the other scanned surface as a ghost image (ghost light) increases.
The deflecting reflection surface of the optical deflector and the surface to be scanned have a conjugate relationship, but even a shared lens close to the optical deflector has a conjugate relationship.

For this reason, the light beam reflected by the shared lens and directed toward the scanning surface is likely to be collected, and the intensity of the ghost image is increased, which tends to adversely affect the image.
The description here is based on an oblique incidence optical system (oblique incidence method).
The possibility of ghost light going to another photosensitive drum is higher in the oblique incidence optical system.

  However, even in a normal horizontal incidence optical system, there is a sufficient possibility that the ghost light is reflected to the photosensitive drum itself or another color photosensitive drum depending on the reflection angle from the photosensitive drum as the surface to be scanned. Needless to say, the issues are the same.

The features of the present invention will be described below.
FIG. 2 shows the sub-scanning section from the optical deflector 3 to the scanned surface 5a.
In practice, another set of scanning optical systems that are directed toward the photosensitive drum as another surface to be scanned are arranged symmetrically (line symmetric) with respect to a virtual surface L0 described later, but this is not shown.
At this time, the fθ lens 9 close to the optical deflector is shared by the upper and lower light beams across the virtual plane L0.
The long toroidal lens 10 located closest to the surface to be scanned is individually disposed corresponding to the surface to be scanned.

In the scanning imaging optical system 4, a lens (optical element; fθ lens 9) close to the optical deflector 3 is a so-called shared lens that is commonly used for two scanned surfaces, and is only in the main scanning direction. Has power and no power in the sub-scanning direction.
In the scanning imaging optical system 4, lenses (optical elements; long toroidal lenses 10) close to the scanning surface exist corresponding to the number of scanning surfaces, have power mainly in the sub-scanning direction, and correct surface tilt. It has a function.

The reason why the lens close to the optical deflector 3 has almost no power in the sub-scanning direction is that the field curvature correction in the sub-scanning direction is performed only by the lens close to the surface to be scanned. This is to achieve both reduction in the amount of bending in the direction.
The long toroidal lens 10 closest to the surface to be scanned 5a is an optical element having a refractive power in the sub-scanning direction.

In the present embodiment, an optical element (scanning lens) which is an angle in the sub-scanning section and has the refractive power in the sub-scanning direction and is closest to the scanned surface 5a among the optical elements constituting the scanning imaging optical system 4. A light beam LB1 (first light beam) emitted from the long toroidal lens 10 as a light beam near the center in the main scanning direction, and a light beam LB2 (second light beam) after the light beam LB1 is reflected by the scanned surface 5a. The angle formed by θ1,
Similarly, the angle in the sub-scanning section is the light beam LB1, the end 10a in the sub-scanning direction near the center of the long toroidal lens 10 in the main scanning direction, and the reflection point 5b at which the light beam LB1 is reflected by the scanned surface 5a. The angle formed by the connected line L is θ2,
And when
The reflected light from each scanned surface is
θ1> θ2
It is set to satisfy the conditions.
However, the scanning imaging optical system 4 is an optical system excluding reflecting members such as the folding mirror 11.

Further, the reflected light (second light beam) from the surface to be scanned is away from the surface perpendicular to the rotation axis of the optical deflector in the rotation axis direction of the optical deflector, in other words, away from the sub-scanning direction. It is set to go to.
Here, a plane perpendicular to the rotation axis of the optical deflector is defined as a virtual plane L0.
The virtual surface L0 is located within the height h of the deflecting / reflecting surface of the optical deflector 3 in the height direction (the rotational axis direction of the optical deflector) as shown in FIG.
In the present embodiment, the virtual plane L0 passes through the center of the deflection reflection point in the optical deflector of a plurality of light beams. The purpose is not limited to this, and the deflection reflection surface may pass through the center of the height h.

When the reflected light from the surface to be scanned is directed to the virtual surface L0, the light other than the optical element having refractive power in the sub-scanning direction closest to the surface to be scanned is entered by entering the reflected light inside the scanning optical system. There is a high possibility of entering the element.
Specifically, there is a high possibility that the light enters an optical element corresponding to another color adjacent in the sub-scanning direction, and a possibility that the light reaches the photosensitive member by reflection from the other optical element is increased.

In the full-color optical scanning device, since the optical scanning device corresponding to a plurality of photoconductors is arranged, the number of optical elements in the optical box in which the optical elements are arranged is large, and further in the sub-scanning direction. Arranged side by side.
For this reason, since the direction in which the reflected light returns is an important point in a full-color optical scanning device, the direction in which the reflected light is separated from the virtual plane L0 (the direction in which the reflected light is separated in the sub-scanning direction) as in this embodiment. Is important.
When the reflected light travels in a direction far from the virtual surface L0 as in the present embodiment, the possibility of further reflection by another optical element is low.

Even when the light is reflected, it is possible to prevent the light from entering the inside of the scanning optical system and moving toward the photoconductor corresponding to another color.
The present invention is also characterized in that the reflected light is removed in the optical box.
This is because when the reflected light is removed outside the optical box, the reflected light may reach the photosensitive member due to the layout of other modules outside the optical box in which the optical scanning device is disposed. Other modules will be described later.

The end in the sub-scanning direction of the optical element having refractive power in the sub-scanning direction closest to the surface to be scanned does not mean only the optical surface of the optical element, but a rib that covers the outer periphery of the optical surface. Structures and the like are also included.
Here, the scanning imaging optical system 4 is exemplified as having two scanning lenses, but a single-lens configuration, a three-lens configuration, and the like are also possible.
With the above configuration, it is possible to prevent the reflected light from each scanned surface from entering an optical element having refractive power in the sub-scanning direction closest to the scanned surface.

For this reason, it is possible to prevent ghost light generated when entering the optical element, and light generated by reflection on the optical element does not enter the photosensitive drum again.
As a result, no ghost image is generated at a position in the sub-scanning direction.
In particular, as shown in FIG. 12, the common lens is often configured not to have refractive power in the sub-scanning direction, and when reflected light from the surface to be scanned reaches, it becomes easy to form a ghost image on another photoconductor. .
However, generation of a ghost image can be suppressed with the above configuration. In FIG. 2, reference numeral 3a indicates the rotation axis of the polygon mirror.

Furthermore, it is desirable that the absolute value of the angle of the light beam incident on the scanned surface with respect to the normal of the scanned surface is the same.
In order to set the reflected light as described above, it is necessary to appropriately set the incident angle to the photosensitive member.
The incident angle on the photosensitive member may be equal to or larger than a set angle for satisfying the above-described conditions.

However, when the incident angle is smaller, the bending of the scanning line can be suppressed, and the size of the beam spot diameter in the sub-scanning direction can also be reduced.
As shown in FIG. 3, by making the absolute values of the incident angles equal on the photoconductors corresponding to the respective colors, the beam spot diameter on the scanned surface can be made uniform for each color.
In FIG. 3, in the photosensitive drums 5 </ b> A and 5 </ b> B, the inorganic of the reflected light indicated by the dotted line is opposite in the right and left sides of the incident light, but the absolute angle of the incident light beam with respect to the normal line of the surface to be scanned is The value is the same.

  Needless to say, it is preferable that the variation in the beam spot diameter for each color is small. In order to improve the image quality, it is desirable that the absolute value of the angle with respect to the normal line of the scanned surface is the same.

FIG. 4 is another example showing a scanning optical system provided with a folding mirror.
The apparatus can be miniaturized by providing a folding mirror between the scanning imaging optical system and the surface to be scanned.
In the example shown in FIG. 4, the folding mirror 11 is disposed between the optical element 10 having a refractive power in the sub-scanning direction close to the scanning surface and the scanning surface.
In the oblique incidence optical system, the scanning line bends. However, in the case of the tandem optical system, the bending of the scanning line formed on each scanned surface must be substantially the same.

Comparing optical systems directed to adjacent scanning surfaces in the figure, the number of folding mirrors 11 is different in order to align the scanning line bending direction.
Light beams from a plurality of light source devices are deflected by the same deflecting / reflecting surface of the optical deflector or the deflecting / reflecting surfaces of the same phase arranged in the sub-scanning direction.
Further, in the sub-scanning direction, the sub-direction of the light beam deflected with respect to the virtual plane L0 passing through the center of the deflection reflection point of the light deflector of the plurality of light beams and perpendicular to the deflection reflection surface of the light deflector. It is desirable that the number of folding mirrors that fold the optical path in the sub-scanning direction differs between the odd and even numbers on the upper side and the lower side in the scanning direction.

As described above, the absolute value of the incident angle of the light beam to the photosensitive member should be the same on the scanned surface corresponding to each color.
Further, by adopting the above configuration, the direction of the incident angle of the light beam incident on the photoconductor can be matched with each color photoconductor.
As a result, it becomes easy to make the intervals between the photoconductors the same in the layout around various photoconductors such as charging and development other than the optical system.

Further, it is possible to realize a layout around the photosensitive member common to each color.
In addition, it is not necessary to secure a space through which the light beam that reaches the photosensitive member passes for each color, and it is advantageous for miniaturization of the image forming apparatus because it is easy to secure the minimum space.
An image forming apparatus that forms a full color using four colors of black, cyan, magenta, and yellow can be realized by using two optical scanning devices shown in FIG.

In another example shown in FIG. 5, a folding mirror 11 is disposed between the optical element 10 having refractive power in the sub-scanning direction close to the surface to be scanned and the scanning imaging element 9 on the side close to the optical deflector 3. ing.
Similar to FIG. 4, when the optical systems directed to adjacent scanning surfaces in the drawing are compared, the number of folding mirrors is different because the scanning line bending direction is aligned.

As still another embodiment, an example in which a common optical deflector for four colors is used is shown in FIG.
According to the present embodiment, two different deflection reflection surfaces facing each other by the same optical deflector deflect the light up and down in the sub-scanning direction, and the light beams are guided to the corresponding four photosensitive members.
At this time, the upper stage deflected by one deflection reflection surface, the number of folding mirrors corresponding to the lower light beam deflected by the other deflection reflection surface, the lower stage deflected by one deflection reflection surface, and The number of folding mirrors corresponding to the upper stage light beam deflected by the other deflecting / reflecting surface is desirably different between the odd number and the even number.

As described above, the light beams reflected by the respective deflection reflection surfaces pass through the center of the deflection reflection point of the optical deflector of the plurality of light beams in the sub-scanning direction and are perpendicular to the deflection reflection surface of the optical deflector. The number of folding mirrors that fold the optical path in the sub-scanning direction for guiding the deflected light beam to the corresponding scanned surface on the upper and lower sides of the deflected light beam with respect to the virtual surface L0 is odd and even. It has a different configuration.
However, in the method of sorting in the opposing direction as shown in FIG. 6, the number of folding mirrors corresponding to the upper stage light beam deflected by one deflection reflection surface and the lower stage light beam deflected by the other deflection reflection surface The number of folding mirrors corresponding to the lower stage light beam deflected by one deflecting reflection surface and the upper stage light beam deflected by the other deflecting reflection surface can be made different between odd and even numbers. The direction of the incident angle of the light beam on the body can be matched.

FIG. 7 explains conditions for preventing the reflected light from the surface to be scanned from reaching an optical element close to the optical deflector.
If the reflected light from the surface to be scanned passes through the optical element 10 having a refractive power in the sub-scanning direction close to the surface to be scanned, the possibility of reaching the optical element 9 close to the optical deflector 3 is increased. It is a condition of.
That is, it is close to the optical deflector so as to be within the extension line of the line L connecting the reflection point 5b on the surface to be scanned and the upper end portion 10a of the optical element having refractive power in the sub-scanning direction near the surface to be scanned. This is a condition for accommodating the size of the optical element 9.

As described above, the upper end portion here is an optical element in a direction opposite to the sub-scanning direction (upper side) with respect to the scanning plane including the normal line (virtual plane L0) of the deflection reflection point of the optical deflector. Means 10 ends.
A symbol X indicates the height of one side of the optical element 10 with respect to the virtual plane L0.

Based on FIG. 8, the configuration of an image forming apparatus to which the optical scanning device according to the present invention is applied will be described.
In the figure, reference numeral 21 is a charging charger, 20 is an optical scanning device, 22 is a developing device, 23 is a transfer charger, 24 is a cleaning device, 25 is a paper feed cassette, 26 is a paper feed roller, 27 is a transport roller, and 28 is A pair of registration rollers, 29 is a conveying belt, 30 and 31 are belt support rollers, 32 is a belt charging charger, 33 is a belt separation charger, 34 is a static elimination charger, 35 is a belt cleaning device, 36 is a fixing device, and 37 is a discharge roller. Reference numeral 38 denotes a paper discharge tray.
This embodiment is an example in which the optical scanning device 20 according to the present invention is applied to a tandem full-color laser printer.

A transport belt 29 for transporting the transfer paper S fed from the paper feed cassette 25 disposed in the horizontal direction is provided on the lower side in the apparatus.
On the conveyance belt 29, a photosensitive member 5Y for yellow Y, a photosensitive member 5M for magenta M, a photosensitive member 5C for cyan C, and a photosensitive member 5K for black K are sequentially arranged from the upstream side in the conveyance direction of the transfer sheet S. They are arranged at equal intervals.
Hereinafter, subscripts Y, M, C, and K are appropriately added to the reference numerals for distinction.

These photoconductors 5Y, 5M, 5C, and 5K are all formed to have the same diameter, and process members that perform each process according to the electrophotographic process are sequentially arranged around the photoconductors 5Y, 5M, 5C, and 5K.
Taking the photoconductor 5K as an example, a charging charger 21K, an optical scanning optical system 20K, a developing device 22K, a transfer charger 23K, a cleaning device 24K, and the like are sequentially arranged.
The same applies to the other photoconductors 5Y, 5M, and 5C.

In other words, in the present embodiment, the surfaces of the photoconductors 5Y, 5M, 5C, and 5K are set as scan surfaces or irradiated surfaces that are set for the respective colors, and each optical scanning optical system is applied to each photoconductor. (Optical scanning devices 20Y, 20M, 20C, and 20K) are provided in a one-to-one correspondence.
In the drawing, these optical scanning optical systems are collectively shown as one optical scanning device 20.

In the optical scanning device 20, the scanning lens on the left side in the figure is commonly used by 9K and 9C, and the scanning lens on the right side is commonly used by 9M and 9Y.
As shown in FIG. 4, individual optical elements having refractive power in the sub-scanning direction close to the surface to be scanned are provided for each photoconductor.
Around the conveyance belt 29, a registration roller pair 28 and a belt charging charger 32 are provided on the upstream side of the photoreceptor 5Y.
A belt separation charger 33, a charge removal charger 34, a belt cleaning device 35, and the like are provided in this order so as to be positioned downstream of the photosensitive member 5K in the rotation direction of the conveying belt 29.

A fixing device 36 is provided on the downstream side of the belt separating charger 33 in the transfer paper conveyance direction, and is connected to a paper discharge tray 38 by a pair of paper discharge rollers 37.
The fixing device 36 includes a fixing roller 36a and a pressure roller 36b.

In such a schematic configuration, for example, in the full color mode (multiple color mode), each of the photoconductors 5Y, 5M, 5C, and 5K is based on image signals of colors Y, M, C, and K, respectively. As a result of the optical scanning of the light beams by the optical scanning devices 20Y, 20M, 20C, and 29K, electrostatic latent images corresponding to the respective color signals are formed on the surfaces of the respective photosensitive members.
These electrostatic latent images are developed with color toners in the corresponding developing devices to become toner images, and are sequentially transferred onto the transfer paper S that is electrostatically attracted onto the transport belt 29 and transported. A full color image is formed on the transfer paper S by being superimposed.
This full-color image is fixed by the fixing device 36 and then discharged to a discharge tray 38 by a discharge roller pair 37.

This figure is a schematic diagram for explanation, and an optimal layout for miniaturization is not taken.
However, by using the optical scanning device of the present invention, there is no color misregistration, high-quality image reproducibility can be ensured, and low power consumption, low cost, compact image forming device, and full color image forming device are realized. can do.

According to the present invention, it is possible to prevent the reflected light from the photosensitive member from entering the reflected photosensitive member itself or another photosensitive member again.
As a result, it is possible to provide a high-quality image forming apparatus that does not generate color unevenness, density unevenness, and abnormal images.
Further, in order to remove the reflected light from the outside of the optical scanning device, the reflected light can be removed within the optical box in which the optical scanning device is arranged.

That is, it is possible to solve the problem in the optical scanning device without considering the irradiation of the photosensitive member by reflection of other modules outside the optical box.
Furthermore, by limiting the number of folding mirrors for each color in order to eliminate reflected light, it is possible to unify the layout of other modules and to unify the layout of each color. This is also advantageous for downsizing the apparatus.

DESCRIPTION OF SYMBOLS 3 Optical deflector 3a Rotating shaft 4 Scanning imaging optical system 5 Photosensitive drum as an image carrier 5a Scanned surface 5b Reflection point 10 Long toroidal lens as a scanning lens 11 Return mirror 20 Optical scanning device 22 Developing device L Extension Line LB1 First light beam LB2 Second light beam L0 Virtual plane as a plane perpendicular to the rotation axis of the optical deflector S Recording medium

Japanese Patent Publication No. 3-5562 Japanese Patent No. 3699774

Claims (7)

In the optical scanning device comprising a plurality of light source devices, the light beam from each light source device is deflected by an optical deflector and then condensed on different scanned surfaces by a scanning optical system,
A first light beam emitted from the scanning lens and reaching the scanned surface, of the light beam passing through the vicinity of the center in the main scanning direction of the scanning lens located closest to the scanned surface in the scanning optical system; The angle between the light beam and the second light beam that is reflected by the reflection point on the scanned surface is θ1,
When the angle between the first light beam and the line connecting the reflection point and the sub-scanning end portion in the vicinity of the center of the scanning lens in the main scanning direction is θ2,
θ1> θ2
And the reflected light at the surface to be scanned is
When deployed between the optical deflector and the surface to be scanned without taking into account reflection by a folding mirror that bends the optical path in the sub-scanning direction, the optical deflector moves away from the plane perpendicular to the rotation axis of the optical deflector. An optical scanning device. The optical scanning device according to claim 1,
An optical scanning device characterized in that the absolute value of the angle of the first light beam incident on the surface to be scanned with respect to the normal line of the surface to be scanned is the same. The optical scanning device according to claim 1 or 2,
Light beams from a plurality of light source devices are deflected by the same deflection reflection surface of the optical deflector or the deflection reflection surfaces of the same phase aligned in the sub-scanning direction,
The number of folding mirrors that fold the optical path in the sub-scanning direction so as to guide the deflected light beam to the corresponding scanned surface on the upper and lower sides of the deflected light beam with respect to the plane perpendicular to the rotation axis of the optical deflector The optical scanning device is characterized in that the odd number and the even number are different. The optical scanning device according to claim 1 or 2,
The light beams from the plurality of light source devices are deflected to the upper side and the lower side in the sub-scanning direction with respect to the plane perpendicular to the rotation axis of the optical deflector by two different deflection reflection surfaces of the same optical deflector,
A folding mirror that folds the optical path in the sub-scanning direction to guide the deflected light beams to the corresponding scanned surfaces;
The number of folding mirrors corresponding to the light beam on the upper side deflected by one deflecting reflecting surface and the lower side deflected by the other deflecting reflecting surface;
An optical scanning device characterized in that the number of folding mirrors corresponding to the light beam on the lower side deflected by one deflection reflection surface and the upper side light beam deflected by the other deflection reflection surface is different between an odd number and an even number . In the optical scanning device according to any one of claims 1 to 4,
A plane perpendicular to the rotation axis of the optical deflector passes through a deflection reflection point of the optical deflector,
An optical scanning device characterized in that reflected light from each scanned surface is reflected toward the opposite side in the sub-scanning direction to a surface perpendicular to the rotation axis of the optical deflector. In the optical scanning device according to any one of claims 1 to 5,
The height in the sub-scanning direction of other optical elements in the scanning imaging optical system is lower than an extension line connecting the reflection point on the surface to be scanned and the end of the optical element in the sub-scanning direction. Image forming apparatus. An electrostatic latent image is formed on a plurality of image carriers having the scanned surface by an optical scanning device, the electrostatic latent image is visualized as a toner image by a developing device, and the toner image is recorded on a recording medium. In the image forming apparatus to
An image forming apparatus comprising the optical scanning device according to claim 1.

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