JP4922118B2 - Optical scanning apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an optical scanning device provided in an electrophotographic image forming apparatus, and an image of a laser printer, a laser plotter, a digital copying machine, a plain paper facsimile, or a composite machine of these equipped with the optical scanning device. The present invention relates to a forming apparatus.

  In electrophotographic image forming apparatuses used in laser printers, laser plotters, digital copying machines, plain paper facsimiles, or multi-function machines of these types, in recent years, colorization and high speed have been advanced, and photoconductors that are image carriers. An image forming apparatus compatible with a tandem method having a plurality of (usually four) is widely used. In this tandem image forming apparatus, for example, four photoconductors are arranged side by side along a transfer belt (or intermediate transfer belt) that conveys a recording material, and each photoconductor is charged by a charging unit and then written by a writing unit. A latent image is formed on each photoconductor, and the latent image on each photoconductor is developed and visualized with developers of different colors (for example, yellow, magenta, cyan, and black toners) of the developing means. The color images are transferred onto a recording material (or an intermediate transfer belt) conveyed by a transfer belt so as to form a color image.

  The electrophotographic color image forming apparatus has only one photoconductor, rotates the photoconductor by the number of colors, and sequentially superimposes and transfers the image onto the intermediate transfer member. There is also a so-called one-drum-intermediate transfer method in which the image is formed and transferred onto the recording material in a lump. In this case, if there are four colors and one drum, the photoconductor is formed every time one image is formed. Must be rotated four times, and productivity is inferior compared to the tandem method.

As described above, the tandem image forming apparatus can increase the speed and improve the productivity of color image formation as compared with the one-drum-intermediate transfer system. However, in the case of the tandem image forming apparatus, optical scanning is possible. In order to perform optical writing on a plurality of photoconductors by a writing unit using the apparatus, the number of light sources of the optical scanning device inevitably increases (for example, when there are four photoconductors, four light sources are usually required). As a result, problems such as an increase in the number of components, a color shift due to a wavelength difference between a plurality of light sources, and an increase in cost occur.
Further, deterioration of the semiconductor laser is cited as a cause of the failure of the writing unit. For this reason, if the number of light sources increases, the probability of failure increases and the recyclability deteriorates.

In view of this, there is an example in which the optical scanning device used in the tandem image forming apparatus is devised so as not to increase the number of light sources (see, for example, Patent Document 1). In this prior art, a scanning surface with different beams from a common light source is scanned using a pyramid mirror or a flat mirror. However, with this method, the number of light sources can be reduced, but the number of deflecting mirrors is limited to a maximum of two, and there remains a problem with speeding up.
In order to solve the above problem, one light beam from the light source is split into two light beams shifted in the sub-scanning direction by the light beam splitting means, and two polygon mirrors that are overlapped at different angles are coaxial. There has been proposed an optical scanning device that is configured to scan with two different scanning surfaces by using a deflecting means that is rotated in order (see, for example, Patent Document 2).

  In this prior art, as means for scanning the surface to be scanned with different beams from a common light source, a polygon mirror with two phases shifted and shifted is used. It is not a general-purpose product and there is a concern about cost increase. In addition, the workability of the polygon mirror is also required, and the surface tilt of each step is different and the surface accuracy is different.

Japanese Patent Laid-Open No. 2002-23085 JP 2006-284822 A

  The present invention has been made in view of the above circumstances, and provides an optical scanning device having a configuration capable of further reducing costs while maintaining high-speed and high-quality image output and further improving layout. Another object of the present invention is to provide an optical scanning device having a configuration capable of improving the separation between the incident beam and the scanning beam while maintaining high-speed and high-quality image output. An object is to provide an image forming apparatus provided.

In order to achieve the above object, the present invention adopts the following means.
According to a first aspect of the present invention, there is provided an optical scanning apparatus including a light source to be modulated and driven, a deflecting unit having a multi-surface reflecting mirror, and a scanning optical system for guiding a beam scanned by the deflecting unit to a surface to be scanned. A beam splitting unit that splits a beam from the light source between the light source and the deflecting unit, the deflecting unit having four reflecting surfaces, and the beams split by the beam splitting unit at the same timing Are incident on different reflecting surfaces of the deflecting means, and the angle formed by the divided beams when entering the deflecting means is approximately π / 2 .
The second means of the present invention is characterized in that in the optical scanning device of the first means, an incident mirror is provided for setting an incident angle of the beam divided by the light beam dividing means to the deflecting means. .

According to a third means of the present invention, in the optical scanning device of the second means, the incident mirror is disposed at a position substantially equal to the scanning lens of the scanning optical system.
According to a fourth means of the present invention, in the optical scanning device of the third means, the incident mirror and a part of the scanning lens are in contact with each other.
Further, the fifth means of the present invention is characterized in that, in the optical scanning device of the third or fourth means, the end face of the incident mirror is subjected to antireflection treatment.

According to a sixth means of the present invention, in the optical scanning device of the first or second means,
An end in the main scanning direction on the incident surface of the scanning lens of the optical scanning optical system closest to the deflecting unit has a flat part, and the flat part is provided with a reflective coating, and the light beam dividing unit The beam divided by is reflected by the flat portion and is incident on the reflecting surface of the deflecting means.

According to a seventh means of the present invention, in the optical scanning device of any one of the first to sixth means, scanning in a direction away from the light source side in the main scanning direction of the beams divided by the light beam dividing means. Synchronous detection means for receiving at least one of the incident beams is arranged on the opposite side of the scanning direction of the at least one beam with the incident beam to the deflecting means of the at least one beam as a boundary. It is characterized by.
The eighth means of the present invention is characterized in that, in the optical scanning device of any one of the first to sixth means, the light source side synchronization detection is performed by a light receiving means for controlling the light amount of the light source. To do.

According to a ninth means of the present invention, in the optical scanning device of any one of the first to eighth means, a pitch adjusting means for adjusting the pitch in the sub-scanning direction of the plurality of scanning lines formed on the scanned surface. And the pitch adjusting means is disposed between the light beam dividing means and the deflecting means.
According to a tenth means of the present invention, in the optical scanning device of any one of the first to ninth means, the plurality of light sources are provided, and the plurality of light sources are arranged at different positions in the sub-scanning direction. It is characterized by being.

According to an eleventh means of the present invention, in the optical scanning device according to any one of the first to tenth means, when a common light source scans different scanned surfaces, the scanned surfaces differ from each other. The amount of light is set.
According to a twelfth means of the present invention, in the optical scanning device of any one of the first to eleventh means, a surface emitting semiconductor laser is used as the light source.

According to a thirteenth aspect of the present invention, in an image forming apparatus including a writing unit that forms a latent image by irradiating a beam from a light source onto an image carrier that is a surface to be scanned. An optical scanning device according to any one of the twelfth means is provided.
According to a fourteenth aspect of the present invention, in the image forming apparatus of the thirteenth aspect, a plurality of the image carriers are provided, and the latent images formed on the plurality of image carriers by the writing unit are developed in different colors. Developing with a developer to form a visible image, and forming a multicolor or full-color image by transferring the visible images of each color formed on the plurality of image carriers onto a recording material directly or via an intermediate transfer member. Features.

In the optical scanning device of the first means, a light beam splitting means for splitting the beam from the light source is provided between the light source and the deflecting means, and the deflecting means has four reflecting surfaces, and at the same timing. Each of the beams split by the light beam splitting unit is incident on different reflecting surfaces of the deflecting unit, and an angle formed by the split beams when entering the deflecting unit is approximately π / 2. Accordingly, it becomes possible to scan different scanning surfaces with one light source, and it is possible to realize a scanning device capable of achieving cost reduction by reducing the number of light sources while maintaining high speed. Also it is possible to realize an optical scanning apparatus capable of improving the layout properties.

In the optical scanning device of the second means, in addition to the configuration and effects of the first means, the optical scanning device has an incident mirror for setting the incident angle of the split beam to the deflection means, and the optical scanning of the third means In the apparatus, in addition to the configuration of the second means, the incident mirror is arranged at a position substantially equal to the scanning lens of the scanning optical system, so that the separation between the incident beam and the scanning beam can be improved. Become.
Further, in the optical scanning device of the fourth means, in addition to the configuration and effect of the third means, the incident mirror and the scanning lens are in contact with each other, so that the incident beam and the scanning beam are separated. It becomes possible to improve, and the setting of the arrangement position of the incident mirror becomes easy.
Further, in the fifth optical scanning device, in addition to the configuration and effect of the third or fourth means, the end face of the incident mirror is subjected to antireflection treatment, thereby preventing reflection of the scanning beam and preventing ghost. It becomes possible to do.

In the optical scanning device of the sixth means, in addition to the configuration and effect of the first or second means, the end in the main scanning direction on the incident surface of the scanning lens of the optical scanning optical system closest to the deflecting means is flat. A reflection coating is applied to the flat portion, the beam divided by the light beam dividing means is reflected by the flat portion, and is incident on the reflection surface of the deflecting means, Since the reflective coating replaces the incident mirror, the cost can be reduced in addition to the effects of the third means.

In the optical scanning device of the seventh means, in addition to the configuration and effect of any one of the first to sixth means, the direction away from the light source in the main scanning direction of the beams divided by the light beam dividing means Synchronous detection means for receiving at least one of the beams incident so as to scan in the direction is arranged on the opposite side of the scanning direction of the at least one beam with the incident beam to the deflecting means of the at least one beam as a boundary. As a result, the degree of freedom in layout can be further improved.
Further, in the optical scanning device of the eighth means, in addition to the configuration and effect of any one of the first to sixth means, the light source side synchronization detection is performed by using a light receiving means (for example, a semiconductor) for controlling the light amount of the light source. Since the number of synchronization detection means can be reduced by using a light-receiving element that monitors the light output of the laser, it is possible to realize an optical scanning device that can achieve further cost reduction.

In the optical scanning device of the ninth means, in addition to the configuration and effect of any one of the first to eighth means, a pitch for adjusting the pitch in the sub-scanning direction of the plurality of scanning lines formed on the surface to be scanned By having an adjusting unit and the pitch adjusting unit is disposed between the light beam dividing unit and the deflecting unit, it is possible to accurately correct the scanning line interval in the sub-scanning direction on the surface to be scanned.
Further, in the optical scanning device of the tenth means, in addition to the configuration and effect of any one of the first to ninth means, the plurality of light sources are provided, and the plurality of light sources are arranged at different positions in the sub-scanning direction. As a result, different light beams in the sub-scanning direction can be divided by one light beam dividing element, and further cost reduction can be achieved.

In the optical scanning device of the eleventh means, in addition to the configuration and effect of any one of the first to tenth means, when a common light source scans different scanned surfaces, each scanned surface is scanned. Since different amounts of light can be set, the amount of light of each color can be adjusted by adjusting the amount of light, and a high-quality image with excellent color reproducibility can be output.
In the optical scanning device of the twelfth means, in addition to the configuration and effect of any one of the first to eleventh means, a high-speed optical scanning device is realized by using a surface emitting semiconductor laser as the light source. It becomes possible to do.

In the image forming apparatus of the thirteenth means, the optical scanning device of any one of the first to twelfth means is provided in the writing unit, so that image formation capable of reducing cost while maintaining high speed and high quality is achieved. An apparatus can be realized.
In addition to the configuration and effect of the thirteenth means, the image forming apparatus of the fourteenth means includes a plurality of the image carriers, and the latent image formed on each of the plurality of image carriers by the writing unit is colored. Developing with different developers to make visible images, and transferring the visible images of each color formed on the plurality of image bearing members onto a recording material directly or via an intermediate transfer member to form a multicolor or full color image As a result, it is possible to realize a color image forming apparatus capable of reducing costs while maintaining high speed and high quality.

[Embodiment 1]
Hereinafter, the configuration, operation, and effects of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic perspective view of an optical scanning device showing an embodiment of the present invention. In the figure, reference numerals 1 and 1 'are semiconductor lasers (LD) as light sources, 2, 2' are incident mirrors, 3 and 3 'are coupling lenses, 4 is a half mirror prism as light beam splitting means, 5a and 5b, 5c and 5d are cylindrical lenses, 6 is a soundproof glass, 7 is a deflector as a deflecting means (for example, a polygon mirror having four deflecting reflecting surfaces), 8 (8a and 8b) is a first scanning lens, and 9 is for optical path folding. , 10 (10a, 10b) are second scanning lenses, 11 (11a, 11b) are photoreceptors as scanning surfaces, and 12 is an aperture stop (aperture).

  The two divergent light beams emitted from the semiconductor lasers 1, 1 'are converted into weak convergent light beams, parallel light beams, or weak divergent light beams by the coupling lenses 3, 3'. The beam that has exited the coupling lens 3, 3 ′ passes through the aperture stop 12 for stabilizing the beam diameter on the surface to be scanned and enters the half mirror prism 4. The beams from the common light source incident on the half mirror prism 4 are each divided into two beams, and the beams emitted from the half mirror prism 4 become a total of four beams. In this case, since the arrangement of the light sources 1 and 1 ′ is different only in the sub-scanning direction, the half mirror prism 4 can be used in common, and two beams that are different in the sub-scanning direction are divided into four beams.

FIG. 2 shows a half mirror prism 4 according to an embodiment of the present invention. The half mirror prism 4 functions as a beam splitting means, and 4a is a half mirror, which separates transmitted light and reflected light at a ratio of 1: 1. The separation ratio in the half mirror 4a does not need to be 1: 1, and may be set according to the conditions of other optical systems.
The beam emitted from the half mirror prism 4 is converted into a line image that is long in the main scanning direction in the vicinity of the deflection reflection surface of the polygon mirror 7 by cylindrical lenses 5a, 5b, 5c, and 5d provided in the upper and lower stages.

  In FIG. 1, out of the light beams divided in two directions by the half mirror prism 4, incident light on one side incident on one side of the deflector 7 via the cylindrical lenses 5a and 5b and the incident mirror 2 ′ is deflected. Only the scanning optical system (the first scanning lenses 8a and 8b, the optical path folding mirror 9, and the second scanning lenses 10a and 10b) that deflects by the device 7 and scans the two photoconductors 11a and 11b is illustrated. Actually, a scanning optical system similar to the optical system shown in the figure is disposed with the deflector 7 interposed therebetween, and the other light beam divided by the half mirror prism 4 is also a cylindrical lens. The light is incident and deflected to the other side of the deflector 7 via the incident mirror 2 and 5c, 5d, and scans two photosensitive members (not shown) via a scanning optical system (not shown) having the same configuration.

  FIG. 3 is a diagram for explaining the optical scanning by the divided light. As shown in FIG. 4A, the incident light from the common light source divided by the half mirror prism 4 (incident light x and incident light y in the figure) is adjusted by the incident mirrors 2 and 2 ', respectively. Thus, the light is incident on different surfaces of a deflector (polygon mirror having four deflecting reflecting surfaces in the illustrated example), and has a phase difference of approximately π / 2 (about 90 °). If the phase difference is near 90 °, the divided light beams do not scan the effective scanning area at the same time. As an example, the lower reflected light when scanning the upper effective scanning region x shown in FIG. 3A (when the reflected light a is scanned into the reflected light b and reflected light c) will be described. .

  When the upper incident light x becomes the reflected light a, the lower reflected light does not enter the scanning region because the phase difference of the lower reflected light is 90 ° as shown in FIG. When the deflector 7 rotates and the upper incident light becomes the reflected light b, the lower reflected light becomes b 'as shown in FIG. 3C and does not enter the scanning region. Further, when the deflector 7 further rotates and the upper incident light becomes the reflected light c, the lower reflected light becomes c ′ as shown in FIG. 3D and does not enter the scanning region. That is, it can be seen that the reflected light on the lower side does not enter the scanning region from FIG. 3B through FIG. 3C to FIG. 3D. This is because the phase difference of incident light is 90 ° and the number of reflecting surfaces of the deflector 7 is four, so that the above relationship is established when the phase difference of reflected light is always 90 °. When the upper incident light (incident light x) scans within the effective scanning region x, the lower incident light y scans outside the effective scanning region y, and there is no relationship on the surface of the photoconductor. It is self-evident from the above relationship that it is established even if the phase difference is slightly shifted from 90 °. Conversely, when the lower incident light y scans the effective scanning area y, the upper incident light x scans outside the effective scanning area x, and it does not scan on the photosensitive surface. This is self-evident.

  When the upper incident light x scans within the effective scanning region x, the light source is modulated and driven based on image information of the corresponding color (for example, magenta). Further, when the lower incident light y scans within the effective scanning region y, the light source is driven to modulate the image information of the corresponding color (for example, black), so that an image for two colors with a common light source. Can be scanned.

  Here, as shown in FIG. 4, incident light (incident light x, incident light y in the figure) from the common light source divided by the half mirror prism 4 is incident on the same reflecting surface of the deflector 7. However, it is necessary to fold the light beam with a mirror across the scanning area, which deteriorates the layout. Further, if the light beam is incident on the same reflecting surface of the deflector 7, the divided light beams need to be incident on the deflector 7 at different positions in the sub-scanning direction. You have to change the position. Therefore, as shown in FIG. 1 and FIG. 3, the layout is improved when the divided light beams are incident on different reflecting surfaces of the deflector 7.

FIG. 5 is a timing chart of exposure for a plurality of colors. In the figure, the vertical axis represents the amount of light and the horizontal axis represents time.
As described above, the beam from the common light source divided by the half mirror prism 4 is deflected and scanned by the deflector 7 to expose the two photoconductors 11a and 11b (for example, black and magenta photoconductors), In addition, a time chart in the case where all the lights are lit in the effective scanning region is shown in FIG. A solid line indicates a portion corresponding to black, and a dotted line indicates a portion corresponding to magenta. The timing of writing in black and magenta is determined by detecting the scanning beam with a synchronization detection means (synchronization detection sensor) arranged outside the effective scanning width. Although the synchronization detection means is not shown in FIG. 1, a synchronization detection sensor using a light receiving element such as a photodiode is usually used.

  FIG. 6 is a timing chart for varying the exposure amount depending on the color. In FIG. 5, the light amounts in the black and magenta regions are set to be the same. However, since the transmittance and reflectance of the optical element are actually different, if the light amount of the light source is the same, the photoconductor The amount of light reaching the beam will be different. Therefore, as shown in FIG. 6, when the different photoconductor surfaces are scanned, the light amounts of the beams reaching the different photoconductor surfaces can be made equal by making the set light amounts different from each other.

By the way, each beam emitted from the two light sources 1 and 1 'shown in FIG. 1 is divided by the half mirror prism 4 and exposed to two different photoconductors 11a and 11b. , 11b, two scanning lines are formed in one scan. At this time, it is necessary to adjust the pitch of the scanning lines in the sub-scanning direction according to the pixel density. As a method often used as a pitch adjustment method in the sub-scanning direction, the light source unit (the light sources 1, 1 ′, the coupling lenses 3, 3 ′, and the aperture stop 12 as one unit) is used as the main scanning direction and the sub-scanning. There is a method of rotating about an axis perpendicular to the direction. In this case, a certain photosensitive member can have a desired pitch, but the other photosensitive member has a light beam splitting means (half mirror prism) 4. Pitch errors occur due to subsequent optical element shape errors, mounting errors, and the like.
In order to solve this problem, it is necessary to provide means for adjusting the pitch in the sub-scanning direction between the light beam splitting element (half mirror prism) 4 and the deflecting means (deflector) 7.

Here, FIG. 7 is a diagram showing an example of the pitch adjusting means. FIG. 4A is a diagram showing one-side adjustment means, and FIG. 4B is a diagram showing both-side adjustment means.
Here, as an example, a case where pitch adjusting means is provided in the optical element 5 (for example, the cylindrical lenses 5a, 5b, 5c, 5d in FIG. 1) disposed between the half mirror prism 4 and the deflector 7 will be described.
The cylindrical lens 5 is attached to a housing (not shown) of the optical scanning device via an intermediate member 21a (or 21b, 21c). A curable resin (for example, a photocurable resin) is previously applied to each mounting surface. At this time, the intermediate member 21a (or 21b, 21c) can be “adjusted eccentrically about an axis parallel to the main scanning direction” and “adjusted in the optical axis direction” with respect to the housing, and the cylindrical lens 5 is connected to the intermediate member 21a. (Or 21b, 21c) can be adjusted “eccentric adjustment around an axis parallel to the optical axis” and “position adjustment in the sub-scanning direction”, and the intermediate member 21a (or 21b, 21c) can be adjusted with respect to the housing. At least one of the possible directions is different from at least one of the adjustable directions of the cylindrical lens 5 with respect to the intermediate member 21a (or 21b, 21c). By adopting such a configuration, a plurality of optical characteristics (thickening the beam waist diameter, reducing beam waist position deviation, and beam spot position deviation) can be secured simultaneously, and the cylindrical lens 5 is decentered around the optical axis. By making the adjustment possible, the scanning line interval in the sub-scanning direction can be set optimally. Further, the surface of the intermediate member 21a that is in contact with the cylindrical lens 5 and the surface that is in contact with the housing are flat and easy to adjust. When the adjustment is completed, the mutual position is fixed by curing the curable resin by a predetermined method (for example, ultraviolet irradiation).

FIG. 8 is a diagram for explaining an example of an actual adjustment method. FIG. 4A shows an example of one-side adjustment, and FIG. 4B shows an example of both-side adjustment.
The cylindrical lens 5 is held by a jig, and the cylindrical lens 5 is moved in the direction to be adjusted (here, the position in the optical axis direction, the eccentricity around the axis parallel to the optical axis, the position in the sub-scanning direction). Thereafter, the intermediate member 21a (or 21b, 21c) coated with a curable resin (for example, an ultraviolet curable resin) is pressed against the cylindrical lens 5 and the pedestal 22 of the housing, and the cylindrical lens 5 is fixed by irradiating ultraviolet rays. With such a configuration, adjustment in a plurality of directions can be easily performed with a simple structure. Here, by making the intermediate member 21a (or 21b, 21c) transparent, it becomes easier to fix with the ultraviolet curable resin.
Although it is possible to hold an optical element (such as the cylindrical lens 5) using one intermediate member 21a as shown in FIG. 7A, a plurality of intermediate members 21b, 21c are arranged on opposite sides of the light beam. By adopting such a configuration, for example, when the linear expansion coefficients of the housing and the intermediate member 21 (assuming resin) are different, even if the temperature rises, the optical axis Since stress is generated symmetrically with respect to the optical element, the posture change of the optical element is reduced.

Usually, a semiconductor laser used in an image forming apparatus performs automatic light quantity control (hereinafter referred to as APC) to stabilize light output. With APC, the optical output of a semiconductor laser is monitored by a light receiving element such as a photodiode (PD), and the forward current of the semiconductor laser is controlled to a desired value by a detection signal of the received light current proportional to the optical output of the semiconductor laser. It is a method.
When the semiconductor laser is an edge-emitting type semiconductor laser, the light receiving element often uses a photodiode that monitors light emitted in the direction opposite to the direction emitted toward the coupling lens. When a ghost light is incident, the amount of light detected by the light receiving element increases.

  For example, when the incident angle of the beam to the reflecting surface of the deflector 7 is 0, the reflecting surface faces the light source direction. Therefore, when APC is performed at this position, the reflected beam returns to the light source and is used for monitoring. The amount of light detected by the light receiving element increases. Therefore, it is set so that APC is not performed when the incident angle is zero. By adopting this configuration, it is possible to output an image with an appropriate density and with little density unevenness.

Next, as an example of the arrangement of the synchronization detection means, as shown in the lower side of FIG. 9, it is possible to detect the scanning light by placing a synchronization detection sensor such as a photodiode outside the effective scanning area on the side opposite to the light source. However, since there is incident light in the vicinity of the effective scanning area on the light source side, there is no room for installing a synchronous detection sensor. Therefore, as shown in the upper side of FIG. 9, the light source side synchronous detection uses reflected light on the light source side for the synchronous detection with the incident light as a boundary.
In place of the above method, the APC light receiving element may be used to perform synchronous detection using the light output of the light receiving element when the incident angle of the beam to the reflecting surface of the deflector 7 is zero. Is possible. This is because, when the incident angle is 0, the reflected light from the reflecting surface of the deflector 7 returns to the LD as it is, so that the light returned to the LD is also detected by the APC light receiving element, and this signal is used to detect synchronization. It is used as a signal. Thus, by performing synchronization detection with a light receiving element for APC, the number of sensors dedicated to synchronization detection can be reduced, the number of parts can be reduced, and a cost reduction effect can be expected.

  The above-described technology of the present invention is also effective when an integrated surface emitting semiconductor laser is used as a light source. For example, when a 40 channel surface emitting semiconductor laser is used, two light sources and four colors and 40 channels are used. Thus, the cost of the light source can be reduced while maintaining the high speed of 40-beam writing.

[Embodiment 2]
In the optical scanning device of the first embodiment described above, the beam from the light source is divided between the light source (semiconductor laser) 1, 1 ′ and the deflector 7, and each divided beam is directed to the deflector 7 by approximately π / 2 is provided with a light beam splitting means (half mirror prism) 4 that enters with a phase difference of about 2 (about 90 °), and the deflector 7 has four reflecting surfaces, so that different scanning surfaces can be obtained with one light source. It is possible to scan, and it is possible to realize a scanning device capable of achieving cost reduction by reducing the number of light sources while maintaining high speed.
However, in the configuration of the first embodiment, the incident angle to the deflector 7 is as narrow as π / 4, and it may be difficult to separate the incident beam and the scanning beam. Therefore, the present embodiment realizes an optical scanning device that improves the separation between the incident beam and the scanning beam while maintaining high-speed and high-quality image output.

  That is, in this embodiment, as shown in FIG. 11, the beam from the light source is divided between the light sources (semiconductor lasers) 1 and 1 ′ and the deflector 7, and the divided beams are directed to the deflector. In an optical scanning device having a light beam splitting means (half mirror prism) 4 that makes an incident with a phase difference of approximately π / 2 and the deflector 7 has four reflecting surfaces, the incident angle to the deflector 7 is set. The incident mirror 2 ′ is arranged at a position substantially equal to the scanning lens 8 (8a, 8b).

In the optical scanning device of FIG. 11, the second scanning lens 10 (10a, 10b) is not shown, but the basic configuration is the same as that of FIG.
Also in FIG. 11, of the light beams divided in two directions by the half mirror prism 4, incident light on one side incident on one side of the deflector 7 via the cylindrical lenses 5a and 5b and the incident mirror 2 'is shown. Only the scanning optical system that deflects with the deflector 7 and scans the two photoconductors 11a and 11b is shown, but actually, the scanning optical system similar to the illustrated optical system is substantially symmetrical with the deflector 7 interposed therebetween. The other light beam divided by the half mirror prism 4 is also incident on the other side of the deflector 7 through the cylindrical lenses 5c and 5d and the incident mirror 2, and is deflected. Two photosensitive members (not shown) are scanned via a scanning optical system (not shown) having the same configuration. Therefore, the incident mirror 2 on the other side in FIG. 11 is also arranged at a position substantially equal to a scanning lens (not shown).

Here, the reason for the above configuration will be described.
FIG. 12 shows the relationship between incident light and scanning light (shown as reflected light in the figure).
In an ordinary optical system, the incident angle (incident angle: defined as the angle between the direction perpendicular to the surface to be scanned and the incident light) is about 55 ° to 70 °, whereas the phase difference of 90 ° in the present embodiment is set. In the attaching method, the incident angle is 45 °. The half angle of view is about 35 ° to 40 ° in a normal scanning optical system. Therefore, the angle between the incident light and the scanning light closest to the incident light, that is, the difference between the incident angle of the scanning light and the half angle of view is 15 ° to 35 ° in a normal optical system, but a phase difference of 90 ° is added. In the system, an angle difference of only 5 ° to 10 ° can be obtained. It is necessary to separate incident light and scanning light by the narrow angle difference.
However, since the angle difference between the incident light and the scanning light is small, it is difficult to separate the incident light and the scanning light at the position A close to the deflector 7 as shown in FIG. If it is arranged near 7, the scanning light may be kicked by the incident mirror.

Therefore, when the incident mirror 2 ′ is disposed at a position substantially equal to the first scanning lens 8 (8a, 8b) which is the farthest position from the deflector 7, the optical system of this embodiment has a small angle difference between the incident light and the scanning light. In addition, the incident beam can be incident on the deflector 7 without the scanning light being kicked. Further, in this case, if the incident mirror 2 ′ and the first scanning lens 8 (8a, 8b) are arranged so as to be in contact with each other, alignment, assembly, and the like are facilitated.
Further, there is a concern that the scanning beam is incident on the end face of the incident mirror 2 ′, and the light reflected by the end face of the incident mirror 2 ′ becomes a ghost and enters the effective scanning area, and streaks due to the ghost enter the image. It is better to apply an antireflection coating to the end face of the incident mirror 2 '.

Instead of disposing the incident mirror 2 ′ in the vicinity of the first scanning lens 8 (8a, 8b), as shown in FIG. 13, the incident light side (first scanning) of the first scanning lens 8 (8a, 8b) is used. A plane portion may be provided near the intersection with the incident light of the lens, and a reflective coating 2 ″ may be applied to the plane portion, the incident light may be reflected by the reflective coating portion 2 ″, and the incident light may be guided to the deflector 7. In this case, since the reflective coating portion 2 ″ provided on the plane portion of the first scanning lens 8 functions as an incident mirror, it is not necessary to separately provide the incident mirror 2 ′, and the incident mirror can be omitted, thereby reducing the cost. There is also.
In the above description, the incident mirror 2 ′ on one side has been described as an example, but the same applies to the incident mirror 2 on the other side.

  In the optical scanning device of the second embodiment described above, the basic configuration is the same as that in FIG. 1, and the arrangement positions of the incident mirrors 2 and 2 ′ are substantially equal to the first scanning lens, or the first scanning A flat part is provided on the incident light side of the lens (near the intersection with the incident light of the scanning lens), a reflective coating 2 "is applied to the flat part, and the incident light is reflected by the reflective coating part 2" and enters the deflector 7. The only difference is that light is guided, and the other configuration (the configuration described with reference to FIGS. 2 to 9) is the same as that of the first embodiment, and thus the description thereof is omitted here.

[Embodiment 3]
Next, an embodiment of an image forming apparatus provided with the above-described optical scanning device of the present invention in a writing unit will be described.
FIG. 10 is a schematic configuration diagram of a multicolor image forming apparatus showing an embodiment of the present invention. In the figure, reference numeral 31 is a photoconductor as an image carrier, 32 is a charger for charging the photoconductor, 33 is an electrostatic latent image formed by exposing each charged photoconductor to a beam modulated in accordance with an image signal. A writing unit using the above-described optical scanning device for forming the image; 34, a developing unit for developing the latent image on the photoconductor with each color toner to make it visible; and 35, cleaning the transfer residual toner on the photoconductor Cleaning means 36 is a transfer charging means for transferring the visible image on the photosensitive member to the recording material, 37 is a transfer belt for carrying and transporting the recording material, 38a and 38b are driven by a driving roller on which the transfer belt is stretched. 40, a fixing means for fixing the image transferred to the recording material, 40, a paper feed cassette containing a sheet-like recording material (for example, recording paper) S, and 41, a paper feeding roller for feeding the recording material S , 42 indicates a recording material S fed by a paper feed roller. Separating rollers for separating the recording materials one after another, 43 and 44 are conveying rollers for conveying the recording material, and 45 is a registration roller for feeding the recording material S to the transfer belt 37 in synchronization with image formation on each photoconductor. . Further, Y, M, C, and K attached to the reference numerals represent the colors of the image, and indicate Y: yellow, M: magenta, C: cyan, and K: black, respectively.

  The four photoconductors 31Y, 31M, 31C, and 31K are juxtaposed along the transfer belt 37, rotate in the clockwise direction, and in the order of the rotation direction, the chargers 32Y, 32M, 32C, and 32K, the developing devices 34Y, 34M, 34C, 34K, transfer charging means 36Y, 36M, 36C, 36K, and cleaning means 35Y, 35M, 35C, 35K are provided.

  The chargers 32Y, 32M, 32C, and 32K constitute a charging device for uniformly charging the surface of the photosensitive member. The charger includes a charging member of a contact charging method such as a roller or brush. There are non-contact charging types such as charging chargers. The writing unit 33 irradiates the photosensitive member surfaces between the chargers 32Y, 32M, 32C, and 32K and the developing devices 34Y, 34M, 34C, and 34K with the writing unit 33, and electrostatically applies to the photosensitive members 31Y, 31M, 31C, and 31K. A latent image is formed. Then, based on the electrostatic latent image, toner images of respective colors Y, M, C, and K are formed on the photoreceptor surface by the developing units 34Y, 34M, 34C, and 34K. Further, after the toner images of the respective colors are sequentially superimposed and transferred onto the recording material S conveyed by the transfer belt 37 by the transfer charging units 36Y, 36M, 36C, and 36K, the recording material S is finally transferred by the fixing unit 39. The image is fixed on the screen.

  In the optical scanning device shown in FIG. 1 (or FIG. 11), only the figure corresponding to the two photoconductors 11a and 11b is shown, but in the writing unit 33 of the image forming apparatus shown in FIG. In addition to the same configuration as that of the optical scanning device shown in FIG. 1 (or FIG. 11), as described in the first and second embodiments, the scanning optical system similar to the optical system shown in FIG. The system is arranged at symmetrical positions so that optical scanning corresponding to the above-described four photoconductors 31Y, 31M, 31C, and 31K can be performed.

Next, specific implementation data of the optical system of the optical scanning apparatus having the configuration shown in Embodiment 1 (FIG. 1) or Embodiment 2 (FIG. 11) is shown below.
-Wavelength of light source 1, 1 ': 655nm
-Focal length of coupling lens 3, 3 ': 15mm
-Coupling action: Collimating action-Polygon mirror 7: Number of deflecting reflecting surfaces: 4
Inscribed circle radius: 7mm
Further, cylindrical lenses 5 and 5 ′ having a focal length of 110 mm are arranged between the half mirror prism 4 which is a light beam splitting means and the deflector (polygon mirror) 7, and in the main scanning direction near the reflecting surface of the deflector 7. A long line image is formed.

Lens data after the deflector is shown below.
The first surfaces of the first scanning lenses 8a and 8b and both surfaces of the second scanning lenses 10a and 10b are expressed by the following equations (1) and (2).

Main scanning non-arc type The surface shape in the main scanning surface is a non-arc shape, the paraxial radius of curvature in the main scanning surface on the optical axis is Rm, the distance in the main scanning direction from the optical axis is Y, and the cone When the constant is K and the higher-order coefficients are A1, A2, A3, A4, A5, A6,..., The depth in the optical axis direction is X and is expressed by the following polynomial (1).
X = (Y2 / Rm) / [1 + √ {1- (1 + K) (Y / Rm) 2}
+ A1 ・ Y + A2 ・ Y ² + A3 ・ Y ³ + A4 ・ Y ⁴ + A5 ・ Y ⁵ + A6 ・ Y ⁶ + ・ ・
... (1)
Here, when a numerical value other than zero is substituted for the odd-order coefficients A1, A3, A5,..., It has an asymmetric shape in the main scanning direction.
In this embodiment, only the even order is used, and it is a symmetric system in the main scanning direction.

Sub-scanning curvature formula The following formula (2) shows a formula in which the sub-scanning curvature changes according to the main scanning direction.
Cs (Y) = 1 / Rs (0)
+ B1 · Y + B2 · Y ² + B3 · Y ³ + B4 · Y ⁴ + B5 · Y ⁵ + ··
... (2)
Here, when a value other than zero is substituted for the odd odd power coefficients B1, B3, B5,..., The radius of curvature of sub-scanning becomes asymmetric in the main scanning direction.
Further, the second surface of the first scanning lens is a rotationally symmetric aspheric surface, and is expressed by the following equation (3).

A rotationally symmetric aspheric surface The paraxial radius of curvature of the optical axis is R, the distance from the optical axis in the main scanning direction is Y, the cone constant is K, the higher order coefficients are A1, A2, A3, A4, A5, A6,. When represented by the following polynomial, the depth in the optical axis direction is X.
X = (Y2 / R) / [1 + √ {1- (1 + K) (Y / Rm) 2}
+ A1 • Y + A2 • Y ² + A3 • Y ³ + A4 • Y ⁴ + A5 • Y ⁵ + A6 • Y ⁶ + ••
... (3)

The shape of the first surface of the first scanning lens Rm = −279.9, Rs = −61.0
K = -2.900,000E + 01
A4 = 1.755765E-07
A6 = −5.491789E-11
A8 = 1.087700E-14
A10 = -3.183245E-19
A12 = −2.6635276E-24
B1 = −2.066347E-06
B2 = 5.727737E-06
B3 = 3.1252201E-08
B4 = 2.280241E-09
B5 = −3.729852E-11
B6 = −3.283274E-12
B7 = 1.765590E-14
B8 = 1.732929E-15
B9 = −2.889722E-18
B10 = -1.984531E-19
In the above, “E + 01” means “× 10 ⁰¹ ” and “E-07” means “× 10 ^-07 ”, and the same applies to the following.

Shape of second surface of first scanning lens R = −83.6
K = −0.549157
A4 = 2.748446E-07
A6 = −4.502346E-12
A8 = -7.366455E-15
A10 = 1.803003E-18
A12 = 2.727900E-23

The shape of the first surface of the second scanning lens Rm = 6950, Rs = 110.9
K = 0.000000 + 00
A4 = 1.549648E-08
A6 = 1.292741E-14
A8 = −8.811446E-18
A10 = −9.182312E-22
B1 = −9.593510E-07
B2 = −2.135322E-07
B3 = −8.079549E-12
B4 = 2.390609E-12
B5 = 2.881396E-14
B6 = 3.693775E-15
B7 = -3.258754E-18
B8 = 1.814487E-20
B9 = 8.72085E-23
B10 = −1.3340807E-23

The shape of the second surface of the second scanning lens Rm = 766, Rs = −68.22
K = 0.000000 + 00
A4 = -1.150396E-07
A6 = 1.096926E-11
A8 = −6.5542135E-16
A10 = 1.9844381E-20
A12 = −2.411512E−25
B2 = 3.644079E-07
B4 = −4.847051E-13
B6 = −1.666159E-16
B8 = 4.534859E-19
B10 = −2.819319E-23
Note that the refractive index of the scanning lens at the operating wavelength is 1.52724.

The optical arrangement is shown below.
Distance d1: 64 mm from the deflection reflection surface of the deflector to the first surface of the first scanning lens
Center wall thickness d2 of the first scanning lens: 22.6 mm
The distance d3 from the second surface of the first scanning lens to the first surface of the second scanning lens: 75.9 mm
Center wall thickness d4 of second scanning lens: 4.9 mm
Distance d2: 158.7 mm from the second surface of the second scanning lens to the surface to be scanned

In the optical scanning device shown in FIG. 1, a soundproof glass 6 and a dustproof glass (not shown) having a refractive index of 1.514 and a thickness of 1.9 mm are arranged, and the soundproof glass 6 generates ghost light. In order to prevent this, it is installed at an angle of 10 deg with respect to the direction parallel to the main scanning direction in the deflection rotation plane.
Moreover, although not shown about dustproof glass, it is arrange | positioned between the 2nd scanning lenses 10a and 10b and the to-be-scanned surfaces 11a and 11b.

It is a schematic perspective view of the optical scanning device which shows one Embodiment of this invention. It is a perspective view of the half mirror prism which shows one Embodiment of a light beam splitting means. It is a figure for demonstrating the optical scanning by a division | segmentation light. It is explanatory drawing of the problem at the time of dividing light entering into the same reflective surface of a deflector. It is a figure which shows the timing chart of the exposure for multiple colors. It is a figure which shows the timing chart for varying the exposure amount according to a color. It is a figure which shows an example of a pitch adjustment means. It is a figure for demonstrating an example of the actual pitch adjustment method. It is explanatory drawing of the arrangement position of a synchronous detection sensor. 1 is a schematic configuration diagram of a multicolor image forming apparatus showing an embodiment of the present invention. It is a schematic perspective view of the optical scanning device which shows another embodiment of this invention. It is a figure which shows the relationship between the incident light to the deflector by an incident mirror, and the scanning light (reflected light) of a deflector. It is a figure which shows the example which replaced with the incident mirror of FIG. 12, and gave the reflective coating to the scanning lens.

Explanation of symbols

1, 1 ': Light source (semiconductor laser (LD))
2, 2 ': incident mirror,
2 ": reflective coating 3, 3 ': coupling lens 4: beam splitting means (half mirror prism)
5 (5a, 5b, 5c, 5d): Cylindrical lens 6 is soundproof glass 7: Deflection means (deflector)
8 (8a, 8b): first scanning lens 9: mirror for turning back the optical path 10a, 10b: second scanning lens 11a, 11b: surface to be scanned 12: aperture stop (aperture)
31Y, 31M, 31C, 31K
32Y, 32M, 32C, 32K: Charger 33: Writing unit 34Y, 34M, 34C, 34K: Developer 35Y, 35M, 35C, 35K: Cleaning means 36Y, 36M, 36C, 36K: Transfer charging means 37: Transfer Belt 38a: Drive roller 38b: Driven roller 39: Fixing means 40: Paper feed cassette 41: Paper feed roller 42: Separation roller 43, 44: Conveyance roller 45: Registration roller S: Recording material

Claims (14)

In an optical scanning device having a light source to be modulated and driven, a deflecting unit having a multi-surface reflecting mirror, and a scanning optical system for guiding a beam scanned by the deflecting unit to a surface to be scanned.
A beam splitting unit that splits a beam from the light source between the light source and the deflecting unit, the deflecting unit having four reflecting surfaces, and the beams split by the beam splitting unit at the same timing Are incident on different reflecting surfaces of the deflecting means, and the angle formed by the divided beams when entering the deflecting means is approximately π / 2 . The optical scanning device according to claim 1,
An optical scanning apparatus comprising an incident mirror for setting an incident angle of the beam divided by the light beam dividing means to the deflecting means . Te second aspect of the optical scanning apparatus smell, the incident mirror, an optical scanning device characterized in that it is arranged substantially equal to a position between the scanning optical system of the scanning lens. The optical scanning device according to claim 3.
An optical scanning device, wherein the incident mirror and a part of the scanning lens are in contact with each other. The optical scanning device according to claim 3 or 4,
An optical scanning device, wherein an end face of the incident mirror is subjected to an antireflection treatment. The optical scanning device according to claim 1 or 2,
An end in the main scanning direction on the incident surface of the scanning lens of the optical scanning optical system closest to the deflecting unit has a flat part, and the flat part is provided with a reflective coating, and the light beam dividing unit The beam divided by is reflected by the flat part and enters the reflecting surface of the deflecting means. In the optical scanning device according to any one of claims 1 to 6,
Synchronous detection means for receiving at least one beam incident so as to scan in the main scanning direction away from the light source side in the main scanning direction among the beams divided by the light beam dividing means, and the deflection of the at least one beam. An optical scanning device, wherein the optical scanning device is disposed on the side opposite to the scanning direction of the at least one beam with a beam incident on the means as a boundary . In the optical scanning device according to any one of claims 1 to 6,
An optical scanning device characterized in that the light source side synchronization detection is performed by a light receiving means for controlling the light amount of the light source. In the optical scanning device according to any one of claims 1 to 8,
Pitch adjusting means for adjusting the pitch in the sub-scanning direction of the plurality of scanning lines formed on the surface to be scanned is provided, and the pitch adjusting means is disposed between the light beam dividing means and the deflecting means. An optical scanning device. The optical scanning device according to any one of claims 1 to 9,
An optical scanning device comprising a plurality of the light sources, wherein the plurality of light sources are arranged at different positions in the sub-scanning direction. In the optical scanning device according to any one of claims 1 to 10,
An optical scanning device characterized in that when a common light source scans different scanning surfaces, different light amounts are set for the respective scanning surfaces. In the optical scanning device according to any one of claims 1 to 11,
A surface-emitting type semiconductor laser is used as the light source. In an image forming apparatus including a writing unit that forms a latent image by irradiating an image carrier, which is a surface to be scanned, with a beam from a light source.
An image forming apparatus comprising the optical scanning device according to claim 1 in the writing unit. The image forming apparatus according to claim 13.
A plurality of the image carriers are provided, and latent images formed on the plurality of image carriers by the writing unit are developed with developers of different colors to be visualized, and each color formed on the plurality of image carriers is developed. An image forming apparatus for forming a multicolor or full color image by transferring an image on a recording material directly or via an intermediate transfer member.

Images