JP2011186202A - Optical scanner and image forming apparatus equipped with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner and an image forming apparatus that attain reduction in cost while a high-speed/high-definition image output is maintained and that can achieve a high angle of a view while synchronous detection is performed at an incident side of luminous flux to a deflector. <P>SOLUTION: The optical scanner includes: a light source; an incident optical system that guides, to a deflector, luminous flux emitted from the light source; a deflector that has multi-reflecting surfaces to deflect the luminous flux guided from the incident optical system; a scanning optical system that makes the luminous flux obliquely incident on the rotary axis of the deflector and guides the luminous flux deflected by the deflector to a surface to be scanned; and a synchronizing detecting means for performing the synchronizing detection of the deflected luminous flux. The incident optical system is characterized in that it has a luminous flux splitting means arranged between the light source and the deflector to split the luminous flux and it has an incident mirror for making incident the luminous flux split by the luminous flux splitting means on the deflector so as to have an aperture angle of π/2 mutually. The synchronizing detecting means is characterized in that it has a first synchronizing detecting part for receiving the luminous flux reflected from the deflector to the incident mirror to perform synchronizing detection. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical scanning device and an image forming apparatus including the optical scanning device.

  In electrophotographic image forming apparatuses used in laser printers, laser plotters, digital copiers, plain paper facsimiles, or complex machines of these, in recent years, colorization and speeding-up have progressed, and photoconductors as 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 with a developing means with different color developers (for example, yellow, magenta, cyan, and black toners) to be visualized. 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.

  An electrophotographic color image forming apparatus has only one photoconductor, rotates the photoconductor by the number of colors, and sequentially superimposes and transfers a visible image (monochromatic toner image) onto an intermediate transfer member. In addition, there is a so-called 1-drum-intermediate transfer system in which a color image is formed on an intermediate transfer member and then transferred to a recording material at once. Therefore, it is necessary to rotate the photoconductor 4 times for each image formation, which is inferior in productivity 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.
Moreover, deterioration of the semiconductor laser can be cited as a cause of the failure of the writing unit. For this reason, when the light reduction number increases, the probability of failure increases and the recyclability deteriorates.

  Therefore, there is an example in which a device that does not increase the number of light sources is used in an optical scanning device (as a writing unit) used in a tandem image forming apparatus (see, for example, Patent Document 1). In the technique described in Patent Document 1, a scanned 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 the technique described in Patent Document 2, polygon mirrors stacked in two stages with a phase shift are used as means for scanning a surface to be scanned with different beams from a common light source. The polygon mirror is not a general-purpose product, and there is a concern about increased costs. Further, the workability of the polygon mirror is also required, and there is a concern that the image quality is deteriorated because the surface inclination of each step is different and the surface accuracy is also different.

Further, in order to solve the above problem, one light beam from the light source is divided in the main scanning direction by the light beam dividing means, and is incident on a deflector having four reflecting surfaces with an opening angle of 90 degrees. In addition, an optical scanning device has been proposed in which two light beams split through an incident mirror are incident and a surface to be scanned with different beams from a common light source is scanned (see, for example, Patent Document 3). .
The technique described in Patent Document 3 can solve the above problem because a general-purpose polygon mirror having four reflecting surfaces can be used. However, the deflector has an opening angle of 90 degrees and two light beams. Therefore, the angle of the scanning image center and the incident beam with respect to the deflector is limited to approximately 45 degrees. When the angle of the incident beam is limited to 45 degrees, the angle at which the image can be scanned from the center of the scanned image to the image end on the incident beam side is limited to within 45 degrees. That is, it can be said that the angle of view decreases. Further, if the synchronous detection for detecting the image writing timing between the incident beam and the image edge portion is performed, the angle of view is further reduced.
In particular, in recent years, there has been a demand for enlargement of the angle of view in order to make the writing unit (optical scanning device) compact, and the reduction in the angle of view is also a problem in the configuration according to Patent Document 3.

  The present invention has been made in view of the above circumstances, enables cost reduction while maintaining high-speed and high-quality image output, and achieves a high angle of view while performing synchronous detection on the light beam incident side to the deflector. An object of the present invention is to provide an optical scanning device that can perform the above, and further to provide an image forming apparatus including the optical scanning device.

Therefore, in order to solve the above problems, the optical scanning device according to the present invention and the image forming apparatus including the optical scanning device have technical features described in the following (1) to (8).
(1): a light source, an incident optical system for guiding a light beam emitted from the light source to a deflector, a deflector having a multi-surface reflecting surface and deflecting the light beam guided by the incident optical system, and the deflection A scanning optical system that guides the light beam that is incident obliquely to the rotation axis of the device and deflected by the deflector to the surface to be scanned, and synchronization detection means that performs synchronous detection of the light beam deflected by the deflector, The incident optical system includes a light beam dividing unit that is disposed between the light source and the deflector and divides a light beam, and the light beams divided by the light beam dividing unit have an opening angle of π / 2. An incident mirror that is incident on a deflector, and the synchronization detection unit includes a first synchronization detection unit that receives a light beam reflected from the deflector to the incident mirror and detects synchronization. This is an optical scanning device.

(2): The light beam guided by the incident optical system to one reflecting surface of the deflector when the first synchronization detector receives the light beam reflected by the incident mirror and performs synchronization detection. The angle formed by the angle at which the first reflecting surface reflects the light beam to the incident mirror is not 0 ° in a plane perpendicular to the rotation axis of the deflector. The optical scanning device according to (1) above.

(3) The optical scanning device according to (1) or (2), wherein the deflector has four reflective surfaces.

According to the configuration described in (1) to (3) above, the state in which the return light from the deflector just returns to the light source (however, the state shifted in the sub-scanning direction because of oblique incidence) is applied to the deflector. Two beams (light beams) separated by the light beam splitting means incident on the light beam are reflected toward the incident mirror by the reflecting surfaces of different deflectors, and the beam reflected by the incident mirror to the light source side is further reflected by the light beam separating means. Will overlap and return. That is, since the beams reflected from the reflecting surfaces of different deflectors are overlapped, synchronous detection cannot be performed.
If the return light from the deflector is in a state where the deflector is slightly rotated (a state where the angle formed between the incident light and the reflected light is not 0) than the state in which the return light just returns to the light source, the return light from a different reflecting surface However, the difference in angle makes it possible to separate the return light from different reflecting surfaces.
Therefore, the synchronization detection is performed in a state where the return light from the deflector is slightly rotated from the rotation angle at which the return light just returns to the light source, so that it is possible to detect the return light only on the surface that needs to be detected.

(4): The deflecting surface of the deflector has four reflecting surfaces, and the first synchronization detector has a scanning start end by one of the light beams having an opening angle of π / 2. (2), wherein the timing of (2) is performed based on synchronous detection by the other light flux among the light fluxes having an opening angle of π / 2 that is 5 lines before the scanning line that is the scanning start end. It is an optical scanning device as described in above.

  According to the configuration described in (4) above, after 5 lines are drawn from the synchronous detection detected by the light beam reflected from the deflector to the incident mirror, the reflecting surface of the deflector used in the synchronous detection is Rotate to the scanning start position on the scanning surface on the opposite side with the deflector interposed between the scanning surface where the line drawn at this time exists. Therefore, if the synchronization detection on the opposite side is performed based on the synchronization detection five lines before, the synchronization detection can be accurately performed. Furthermore, by arranging the synchronization detection plate only on the light source side, the electrical components are concentrated on the light source side, and the scanning optical unit becomes compact.

(5): a correction unit that corrects the main scanning magnification based on the scanning time from the scanning start end to the scanning end end, wherein the synchronization detection unit detects the timing of the scanning start end and the timing of the scanning end, and The synchronization detection unit 1 detects the timing of the scanning start end by one of the beams having an opening angle of π / 2 and the timing of the scanning end by the other beam. The optical scanning device according to any one of (1) to (4).

  According to the configuration described in (5) above, the deflector reflection at the scanning end on the opposite side can be performed with the same reasoning as in the configurations (1) to (3) (return light from different reflecting surfaces can be separated). The timing detection by the return light from the surface and the tip synchronization can be performed by the same synchronization detection unit. In other words, the timing of the scanning start end by one light flux among the light fluxes having an opening angle of π / 2 and the timing of the scanning end end by the other light flux can be performed by a single synchronization detection unit. . There is a cost reduction effect by using the same sensor for the rear end detection and the front end detection.

(6): The synchronization detection unit includes a second synchronization detection unit that receives the light beam reflected by the deflector without passing through the incident mirror and performs synchronization detection. The optical scanning device according to any one of (1) to (5) above, further comprising a dimming unit between the optical paths to the synchronization detection unit.

  According to the configuration described in (6) above, the intensity of the synchronization light that returns to the synchronization detection unit (first synchronization detection unit) on the light source side is divided twice by the light beam splitting means, so the amount of light is small. On the other hand, since the synchronization detection unit (second synchronization detection unit) on the side opposite to the light source is only divided once by the light beam dividing means, the amount of light is relatively large. Therefore, the amount of light is reduced by the ND filter in order to align the amount of light entering the different synchronization detection units. As a result, the light amount can be made uniform between the light source side synchronization detection unit (first synchronization detection unit) and the counter light source side synchronization detection unit (second synchronization detection unit).

(7) In the optical scanning device according to any one of (1) to (6), an opening is provided between optical paths from the light beam splitting unit to the first synchronization detection unit. is there.

  According to the configuration described in (7) above, each light beam split by the light beam splitting unit returns from the deflector and is separated at the opening before returning to the synchronization detection unit (first synchronization detection unit). As a result, synchronization detection can be performed with high accuracy.

(8): In an image forming apparatus including a writing unit that forms a latent image by irradiating a light beam from a light source onto an image carrier that is a surface to be scanned, the image forming apparatus includes a plurality of the image carriers. Developing means for developing latent images formed on a plurality of image carriers in a unit with developers of different colors and developing the images, and direct or intermediate transfer of each color image formed on the plurality of image carriers Transfer means for forming a multicolor or full-color image by superimposing and transferring on a recording material via a body, and the writing unit is any one of (1) to (7) above An image forming apparatus including an optical scanning device.

  According to the configuration described in (8) above, it is possible to provide an image forming apparatus in which the scanning optical unit is compact.

  According to the present invention, an optical scanning apparatus capable of reducing the cost while maintaining high-speed and high-quality image output and further achieving a high angle of view while performing synchronous detection on the light beam incident side to the deflector. And an image forming apparatus including the optical scanning device.

1 is a schematic diagram illustrating a configuration in an embodiment of an image forming apparatus according to the present invention. It is a schematic perspective view which shows the structure in 1st Embodiment of the optical scanning device based on this invention. It is the schematic which shows the structure of the half mirror as a light beam splitting means in 1st Embodiment in the optical scanning device based on this invention. It is a figure for demonstrating the optical scanning by a division | segmentation light. It is a timing chart of exposure for multiple colors. It is a timing chart in the case of varying the exposure amount depending on the color in the exposure for a plurality of colors. It is a schematic perspective view which shows the structure in 2nd Embodiment of the optical scanning device based on this invention. It is a schematic diagram which shows the reflected light when the incident angle to the black polygonal deflector 7 is −1 °. It is a schematic perspective view which shows the structure in 3rd Embodiment of the optical scanning device based on this invention. 6 is a timing chart in the case where black and yellow exposure is performed by a common light source 1 and all lights are turned on in an effective scanning region.

The optical scanning device according to the present invention has a light source 1, an incident optical system (2 to 5) for guiding a light beam emitted from the light source 1 to the deflector 7, and a multi-surface reflecting surface. A deflector 7 for deflecting the guided light beam, and a scanning optical system (8 to 9) for guiding the light beam incident on the rotation axis of the deflector 7 at an angle and deflected by the deflector 7 to the surface 11 to be scanned. Synchronization detecting means 10 for performing synchronous detection of the light beam deflected by the deflector 7, and the incident optical system (2 to 5) is disposed between the light source 1 and the deflector 7. A beam splitting unit 4 for splitting the beam and an incident mirror 2 for allowing the beams split by the beam splitting unit 4 to enter the deflector 7 so as to have an opening angle of π / 2. The detecting means 10 receives the light beam reflected twice from the deflector 7 to the incident mirror. And having a first synchronization detection unit 10a for performing period detection.
The image forming apparatus according to the present invention includes a writing unit 30 that forms a latent image by irradiating a light beam from a light source onto an image carrier 31 that is a surface to be scanned, and includes a plurality of the image carriers 31. The developing unit 4 that develops the latent images formed on the plurality of image carriers 31 by the writing unit 30 with developers of different colors and visualizes them, and is formed on the plurality of image carriers 31. Transfer means 6 for forming a multi-color or full-color image by transferring a visible image of each color on a recording material directly or via an intermediate transfer member, and the writing unit 30 according to the present invention. An optical scanning device is provided.

Next, the optical scanning device according to the present invention and the image forming apparatus including the optical scanning device will be described in more detail.
Although the embodiments described below are preferred embodiments of the present invention, various technically preferable limitations are attached thereto, but the scope of the present invention is intended to limit the present invention in the following description. Unless otherwise described, the present invention is not limited to these embodiments.

FIG. 1 is a diagram showing a basic configuration of a multicolor image forming apparatus.
In FIG. 1, reference numeral 31 denotes a photosensitive member as an image carrier (scanned surface), 2 denotes a charger, 4 denotes a developing device (developing means), 5 denotes a cleaning means, 6 denotes a transfer charging means (transfer means), and 32. Denotes a transfer belt, 40 denotes a fixing unit, and 30 denotes a writing unit whose details will be described later. Y, M, C, and K represent image colors, and indicate yellow, magenta, cyan, and black, respectively.
The photoconductors 31Y, 31M, 31C, and 31K rotate in the clockwise direction in FIG. 1, and in the order of rotation, the chargers 2Y, 2M, 2C, and 2K, the developers 4Y, 4M, 4C, and 4K, the transfer charging units 6Y, 6M, 6C, 6K and cleaning means 5Y, 5M, 5C, 5K are provided.

The chargers 2Y, 2M, 2C, and 2K are charging members that constitute a charging device for uniformly charging the surface of the photoreceptor 31. The surface of the photosensitive member 31 between the charger 2 and the developing devices 4Y, 4M, 4C, and 4K is irradiated with a beam (light beam) from the light source of the writing unit (optical scanning device) 30, and the electrostatic latent image is applied to the photosensitive member 31. An image is formed. Then, based on the electrostatic latent image, a toner image that is visualized with different color developers is formed on the surface of the photoreceptor 31 by the developing device 4. Further, the respective transfer toner images are sequentially transferred onto the recording paper S (not shown; one form of recording material) by the transfer charging means 6Y, 6M, 6C, 6K, and finally the recording test S is performed by the fixing means 40. The image is fixed on the screen.
The image forming apparatus according to the present invention is not limited to the configuration shown in FIG. 1 as long as it has a configuration including an optical scanning device used in a writing unit 30 described later. That is, a well-known and commonly used technique may be appropriately employed. For example, a configuration including an intermediate transfer belt can be used to form a so-called intermediate transfer type full-color image forming apparatus.

Next, the configuration of the optical scanning device used in the writing unit 30 will be described in more detail with a specific example.
(First embodiment)
FIG. 2 is a schematic perspective view showing the configuration of the optical scanning device according to the first embodiment of the present invention.
In FIG. 2, reference numerals 1 and 1 'denote semiconductor lasers as light sources (not directly visible in FIG. 2 but soldered to the substrate), 3 and 3' are coupling lenses, and 4 is a beam splitting means. Half mirrors (part of the incident optical system), 5a, 5b, 5c and 5d are cylindrical lenses (part of the incident optical system), 7 is a polygon mirror as a deflector, and 8a and 8b are scanning lenses (of the scanning optical system). (Part), 9 is a mirror (a part of the scanning optical system), 11a, 11b, 11c, and 11d are photoconductors as scanning surfaces, and 12 and 12 'are aperture stops.
In the present specification, the rotational axis direction of the polygon mirror 7 will be described as the sub-scanning direction, and the direction perpendicular to the sub-scanning direction and the optical axis will be described as the main scanning direction. Optically, the main scanning direction coincides with the axial direction of each of the photoconductors 11a, 11b, 11c, and 11d, and the sub-scanning direction coincides with the circumferential direction of each of the photoconductors 11a, 11b, 11c, and 11d.

  The two divergent light beams emitted from the semiconductor lasers 1 and 1 'are converted into weak convergent light beams, parallel light beams, or weak divergent light beams by the coupling lenses 3 and 3'. A beam (light beam) exiting the coupling lens 3, 3 ′ passes through the aperture stop 12 for stabilizing the beam diameter on the scanned surface 11 and enters the half mirror prism 4. The beam (light beam) from the common light source incident on the half mirror 4 is divided into two beams, and the beam emitted from the half mirror becomes a total of four beams (light 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 can be used in common, and two beams that are different in the sub-scanning direction are divided into four beams.

  These four light beams (light beams) enter the cylindrical lenses 5a, 5b, 5c, and 5d, and are condensed in the sub-scanning direction by the action of the cylindrical lenses. An image is formed as a “line image long in the main scanning direction”. The incident beam is incident obliquely with respect to the rotation axis of the polygon mirror deflector 7. In this embodiment, the half mirror prism 4, the cylindrical lens 5, and the incident mirror 2 described later constitute an incident optical system.

Four light beams from the light sources 1 and 1 ′ are emitted to the scanning imaging optical (scanning optical system) side of the polygon mirror deflector 7.
The polygon mirror type deflector 7 is configured to be rotated around a rotation axis in a rotation direction (clockwise direction) shown in FIG. 2 by a drive motor.
Reference numerals 8a and 8b denote scanning lenses, and reference numeral 9 denotes an optical path bending mirror, which constitute a scanning optical system. Reference numerals 11a, 11b, 11c, and 11d denote photoconductive photoreceptors (corresponding to the photoreceptor 31 shown in FIG. 1).

  The scanning lens 8a and the optical path bending mirror 9 guide the two light beams deflected by the polygon mirror of the polygon mirror deflector 7 to the photoconductive photoconductor 11 which is the corresponding optical scanning position, A spot is formed. Since the beam entering the polygon mirror deflector 7 is incident obliquely with respect to the rotation axis, the two light beams reflected from the polygon mirror deflector 7 and directed to the scanning lens 8a are separated in the sub-scanning direction. The light is further separated in the sub-scanning direction by a bending mirror and guided to the corresponding photoreceptors 11a and 11b. Similarly, the two light beams on the opposite side across the polygon mirror deflector 7 are separated in the sub-scanning direction by the scanning lens 8b and the optical path bending mirror 9, and are guided to 11c and 11d.

FIG. 3 is a schematic diagram showing a configuration of a half mirror as a light beam splitting unit in the first embodiment of the optical scanning device according to the present invention.
The half mirror prism 4 functions as a beam splitting means, and 4a is a half mirror (separation surface), which separates (divides) the transmitted light and reflected light at a ratio of 1: 1. The ratio of separation (division) of the half mirror is not necessarily 1: 1, and may be set according to the conditions of other optical systems.

FIG. 4 is a diagram for explaining the optical scanning by the divided light.
As shown in FIG. 4, incident light from a common light source (1 or 1 ′) is incident on different surfaces of the deflector 7, and the angle difference between the incident light is 90 ° (FIG. 4). Incident light x, incident light y). If the angle difference between the incident lights is approximately 90 °, the divided light beams do not simultaneously scan the effective scanning area (A, B).

As an example, when the upper effective scanning area A shown in FIG. 4A is scanned (when the reflected light a is scanned in the order of reflected light b and reflected light c), the lower side shown in FIG. The reflected light will be described.
When the upper incident light x becomes the reflected light a, as shown in FIG. 4B, the lower reflected light a ′ has an angular difference of 90 ° between the incident light x and the incident light y, so that the effective scanning region B is entered. not enter. When the polarizer 7 rotates and the upper incident light x becomes the reflected light b, the lower reflected light becomes b ′ and does not enter the effective scanning region B as shown in FIG. Further, when the polarizer 7 further rotates and the upper incident light x becomes the reflected light c, the lower reflected light becomes c ′ and does not enter the effective scanning region B as shown in FIG. .

That is, it can be seen that the reflected light (a ′ to b ′ to c ′) on the lower side from FIG. 4B to FIG. 4D through FIG. This is because the angle difference between the incident light x and the incident light y is 90 °, and the number of surfaces of the polarizer 7 is 4, so that the angle difference of the reflected light is always 90 °, so that the effective scanning area A And the effective scanning area B are not scanned simultaneously.
When the upper incident light (incident light x) scans within the effective scanning area A, the lower incident light y scans outside the effective scanning area B and is on the surface to be scanned of the photoconductor 11. However, such a configuration does not require that the angle difference between the incident light x and the incident light y is strictly π / 2, and may be slightly shifted. (It is obvious from the arrangement shown in FIG. 4.)
Conversely, when the lower incident light y scans the effective scanning area B, the upper incident light x scans outside the effective scanning area A and does not scan the surface to be scanned of the photoconductor 11. This is obvious because of the vertically symmetrical arrangement.

  The modulation driving of the light source (1 or 1 ') performs the modulation driving of the light source based on the image information of the corresponding color (for example, black) when the upper incident light x is scanning the effective scanning area A. Further, when the lower incident light y scans within the effective scanning area B, the light source (1 or 1 ') is modulated and driven to the image information of the corresponding color (for example, yellow), thereby providing a common light source. Thus, it is possible to scan an image for two colors.

FIG. 5 is a timing chart of exposure for a plurality of colors. In FIG. 5, the vertical axis represents the amount of light, and the horizontal axis represents time.
FIG. 5 shows a time chart in the case where black and yellow exposure is performed with a common light source (1 or 1 ′) and all of the effective scanning areas A and B are lit. A solid line indicates a portion corresponding to black, and a dotted line indicates a portion corresponding to yellow. The writing timing in black and yellow is determined by detecting the scanning beam with a synchronous light receiving means arranged outside the effective scanning areas A and B. Although the synchronous light receiving means is not shown, 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 amount is set to be the same in the black region and the yellow region. However, since the transmittance and reflectance of the optical element are actually different, the light amount of the light source is the same. The light amount of the beam reaching the photoconductor 11 is different. Therefore, as shown in FIG. 6, when the scanning surfaces of the different photoconductors 11 are scanned, the light amounts of the beams reaching the scanning surfaces of the different photoconductors 11 can be made equal by making the set light amounts different from each other.

  Usually, a semiconductor laser used in an image forming apparatus performs automatic light amount control (Auto Power Control: hereinafter referred to as APC) to stabilize light output. APC is a system in which the light output of a semiconductor laser is monitored by a light receiving element, and the forward current of the semiconductor laser is controlled to a desired value by a detection signal of a light receiving current proportional to the light output of the semiconductor laser.

When the semiconductor laser is an edge emitting semiconductor laser, the light receiving element often uses a photodiode for monitoring light emitted in the direction opposite to the direction emitted toward the coupling lens. However, when performing APC, it is unnecessary. When 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 upper reflecting mirror is 0 °, the reflecting surface of the reflecting mirror faces the light source direction. When APC is performed at this position, the reflected beam returns to the light source and receives light. The amount of light detected by the element increases. Therefore, it is set so that APC is not performed when the incident angle is 0 °. By adopting this configuration, it is possible to output an image with an appropriate density and with little density unevenness.

Here, in the configuration example shown in FIG. 2, the synchronization detection is performed by a synchronization detection plate 10 b in which a photodiode (synchronization detection sensor) is installed outside the effective scanning area (A, B) on the side opposite to the light source (1, 1 ′). Although it is possible to detect the scanning light by placing the (second synchronization detection unit), since the light source (1, 1 ′) side has incident light in the vicinity of the effective scanning region (A, B), the synchronization detection is performed. There is no room to install the sensor.
In other words, of the deflected light from the polygon mirror 7, the side far from the incident light has a synchronization detection unit in the optical path leading to the surface to be scanned (however, outside the effective scanning area (A, B)). Although there is a sufficient space for installation, the side near the incident light has a space for installing the synchronization detection unit in the optical path leading to the surface to be scanned (however, outside the effective scanning area (A, B)). I can not afford to.

Therefore, in the present invention, synchronous detection is performed using a light beam reflected to the incident mirrors 2 and 2 '.
Specifically, a light beam (light beam) emitted from the light source 1 shown in FIG. 2 is incident on the coupling lens 3, shaped by the aperture stop 12, and guided to the yellow photoreceptor 11 a by the half mirror 4. And the light beam guided to the black photoconductor 11d is incident on the cylindrical lens 5c and reflected by the incident mirror 2. Then, the light enters the polyhedral mirror deflector 7. When the incident angle on the reflecting surface of the polygon mirror deflector 7 is 1 °, the reflected light from the polygon mirror deflector 7 returns to the incident mirror 2. The light beam re-reflected by the incident mirror 2 is incident on the cylindrical lens 5d while being shifted in the sub-scanning direction from the incident state, and returns to the half mirror 4. The light beam re-entering the half mirror 4 is divided into a light beam that returns to the light source 1 ′ while being shifted in the sub-scanning direction, and a light beam that travels toward the synchronization detection plate 10 a (first synchronization detection unit). The light beam traveling toward the synchronization detection plate 10a is incident on the synchronization detection plate 10a after being cut off by the aperture stop 12 ′. The synchronization detection plate 10a is disposed at a position deviated from the light (an alternate long and short dash line in FIG. 2) returning at an incident angle of 0 ° to the reflection surface of the polygon mirror deflector 7.

In the present embodiment, the light beam that is synchronously detected on the light source (1, 1 ′) side is reflected and returned when the incident angle to the reflecting surface of the polygon mirror deflector 7 is 0 °. Instead, the reason why light returning at 1 ° slightly deviated is used will be explained.
In the case of light having an incident angle to the polygon mirror deflector 7 of 0 °, in order to detect the synchronization of the light beam guided to the black photoconductor 11d, the reflection surface of the polygon mirror deflector 7 is detected. Of these, it is necessary to use the reflected light from the reflecting surface facing the scanning lens 8b. However, when the incident angle is 0 °, the reflected light from the reflecting surface facing the scanning lens 8a also simultaneously returns to the synchronization detection plate 10a.

This mechanism will be described in detail.
The light beam (light beam) emitted from the light source 1 is incident on the coupling lens 3, shaped by the aperture stop 12, and guided by the half mirror 4 to the yellow photoreceptor 11 a and the black photosensitive material. The light beam separated into the light beam guided to the body 11d and guided to the black photosensitive member 11d is incident on the cylindrical lens 5c, reflected by the incident mirror 2, and incident on the polyhedral mirror deflector 7. The reflecting surface of the incident polygon mirror deflector 7 is a surface facing the scanning lens 8b.
At the same time, the light beam guided to the yellow photoconductor 11 a is also incident on the cylindrical lens 5 a, reflected by the incident mirror 2 ′, and incident on the polygon mirror deflector 7. The reflecting surface of the incident polygon mirror deflector 7 is a surface facing the scanning lens 8a.

When the incident angle is 0 °, the light beam guided to the black photosensitive member 11d and the light beam guided to the yellow photosensitive member 11a are shifted only in the sub-scanning direction with respect to the incident light. Reflected in the state, reflected by the incident mirrors 2 and 2 ′ respectively, enters the cylindrical lenses 5 d and 5 b, and returns to the half mirror 4. Since the light beam returning to the half mirror 4 returns to the same position, the light beam is separated by the half mirror 4 and separated in the direction of the light source 1 ′ and the synchronization detection plate 10 a (dotted line in FIG. 2), The yellow light beams overlap and return.
In other words, when the incident angle is 0 °, the synchronization detection plate 10a receives the return light from the black light beam (from the surface facing the scanning lens 8b of the polygon mirror deflector 7) and the yellow light beam. Return light (from the surface facing the scanning lens 8a of the polygon mirror deflector 7) overlaps and enters from the reflecting surface facing the scanning lens 8b among the reflecting surfaces of the polygon mirror deflector 7. Since only reflected light cannot be extracted, black synchronization cannot be detected.

  Therefore, in this embodiment, the incident angle is set to 1 °. By shifting the incident angle from 0 °, the incident angle of the light beam returning to the incident mirrors 2 and 2 ′ to the reflecting surface of the deflector 7 is different between the black side and the yellow side. Therefore, since the return light from the incident mirrors 2 and 2 ′ is different in the main scanning direction by the half mirror 4, black and yellow can be separated as shown by the dotted line in FIG. Synchronization detection can be performed with reflected light from the reflecting surface.

  Furthermore, an aperture stop (opening) 12 ′ is disposed in front of the synchronization detection plate 10a (first synchronization detection unit) to restrict yellow reflected light from entering the synchronization detection plate 10a. Only the reflected light from the reflecting surface (of the deflector 7) facing the scanning lens 8b can be extracted at 10a.

  Further, in the present embodiment shown in FIG. 2, an ND filter (dimming means) 13 is disposed in front of the synchronization detection plate 10b (second synchronization detection unit) installed on the side opposite to the light source. This synchronization detection plate 10b determines the timing of yellow image writing. The yellow light beam incident on the synchronization detection plate 10b is incident after the light beam from the light source 1 is divided by the half mirror 4 once. The amount of light incident on the synchronization detection plate 10a on the light source 1 side is divided once when entering the deflector 7, and is further reflected from the deflector 7 and passes through the incident mirror 2 ′ and the cylindrical lens 5b. In order to enter the half mirror 4 again, the light quantity is divided twice. For this reason, the amount of light incident on the synchronization detection plate 10b is relatively large because the number of divisions is one. For this reason, in this embodiment, the ND filter 13 is arranged in front of the synchronization detection plate 10b (and after the deflector 7) so as to be equal to the amount of light incident on the synchronization detection plate 10a.

  In the above description, the configuration related to black and yellow in the optical scanning device has been described in detail. Needless to say, the present invention can also be implemented for magenta and cyan based on the same technical idea as black and yellow. Since the description is duplicated, details are omitted. The same applies to the embodiments described below.

(Second Embodiment)
FIG. 7 is a schematic perspective view showing the configuration of the optical scanning device according to the second embodiment of the present invention.
In the first embodiment, the synchronization detection plate 10a detects the black leading edge and determines the black scanning start timing, and the synchronization detection plate 10b performs the yellow leading edge detection and determines the yellow scanning start timing. It is the same as the form.
In this embodiment, in addition to the leading edge detection, the black scanning end timing is the synchronization detection plate 10c (third synchronization detection unit), and the yellow scanning end timing is the synchronization detection plate 10a (first synchronization detection unit). Detected by the detection unit). A method for detecting the timing of the end of scanning of yellow will be described in detail later.

By performing the rear end detection, the scanning time T1 from the front end detection to the rear end detection is measured, and based on the measurement result, a basic writing frequency f0 and a correction coefficient using T1 as variables are calculated. The write clock frequency is corrected by calculating the corrected write frequency f1 based on the function F (T1) and the equation f1 = f0 × F (T1). By this writing clock correction, the magnification in the main scanning direction can be corrected. (Correction means)
In this embodiment, the timing detection of the yellow scanning end is performed in the same manner as in the first embodiment, with black tip synchronization performed in a state where the incident angle to the polygon mirror deflector 7 is 1 °, and the incident angle − When the angle is 1 °, the timing at the end of scanning of yellow is detected.

FIG. 8 shows a schematic diagram of reflected light when the incident angle to the black polygonal deflector 7 is −1 °.
The arrows in FIG. 8 indicate black / yellow incident light, and the other solid lines indicate reflected light. As shown in FIG. 8, it can be seen that the yellow reflected light enters the synchronization detection plate 10a, exactly opposite to when the incident light is 1 ° (example shown in FIG. 2). Therefore, by performing synchronization detection at positions where the incident angles of the polygon mirror deflector 7 are different, the black rear end synchronization and the yellow front end synchronization are performed by one synchronization detection plate 10a (first synchronization detection unit). Can be done.
In addition, the ND filter 13 ′ (dimming means) is disposed in front of the synchronization detection plate 10c (third synchronization detection unit), but for the same reason as in the first embodiment, the synchronization detection plate 10a. This is because the amount of light incident on the light and the amount of light incident on the synchronization detection plate 10c are made uniform.

(Third embodiment)
FIG. 9 is a schematic perspective view showing the configuration of the optical scanning device according to the third embodiment of the present invention.
The black detection is performed by the synchronization detection plate 10a (first synchronization detection unit), and the black scanning start timing is determined as in the first embodiment.
In the present embodiment, yellow tip detection is performed based on the result of black tip detection.
FIG. 10 is a timing chart of synchronization and exposure. In FIG. 10, the vertical axis represents the amount of light, and the horizontal axis represents time.
FIG. 10 shows a timing chart in the case where black and yellow exposure is performed with the common light source 1 and all lights are turned on in the effective scanning region. Polygon surface No. Indicates which surface of the reflecting surface of the deflector 7 is used for optical scanning. As described in the first embodiment, different reflection surfaces are used for the black image and the yellow image. Therefore, the black tip synchronization cannot be directly used for the yellow tip synchronization. Therefore, the yellow leading edge synchronization counts from the black synchronization detection of five images before the reflecting surface of the deflector 7 becomes equal to determine the yellow leading edge position. By doing so, it is possible to determine the image writing timing from the same reflecting surface.

(About Figure 1)
2Y, 2M, 2C, 2K chargers 4Y, 4M, 4C, 4K developing devices 5Y, 5M, 5C, 5K cleaning means 6Y, 6M, 6C, 6K transfer charging means,
31Y, 31M, 31C, 31K Photoconductor 32 Transfer belt 40 Fixing means 30 Writing unit (about FIGS. 2 to 10)
1, 1 'light source 2, 2' incident mirror 3, 3 'coupling lens 4 half mirror (light beam splitting means)
5a, 5b, 5c, 5d Cylindrical lens 7 Polygon mirror (deflector)
8a, 8b Scanning lens (part of scanning optical system)
9 Mirror (part of scanning optical system)
10a, 10b, 10c Sync detection plates 11a, 11b, 11c, 11d Photosensitive member (scanned surface)
12, 12 'is an aperture stop 13 ND filter

Japanese Patent Laid-Open No. 2002-23085 JP 2006-284822 A JP 2008-257169 A

Claims (8)

A light source;
An incident optical system for guiding a light beam emitted from the light source to a deflector;
A deflector having a multi-surface reflecting surface and deflecting a light beam guided by the incident optical system;
A scanning optical system that guides a light beam incident obliquely to the rotation axis of the deflector and deflected by the deflector to a surface to be scanned;
Synchronization detecting means for performing synchronous detection of the light beam deflected by the deflector,
The incident optical system includes a light beam dividing unit that is disposed between the light source and the deflector and divides a light beam, and the light beams divided by the light beam dividing unit have an opening angle of π / 2. An incident mirror that is incident on the deflector, and
The optical scanning device according to claim 1, wherein the synchronization detection unit includes a first synchronization detection unit that detects a synchronization by receiving a light beam reflected from the deflector to the incident mirror. When the first synchronization detector receives the light beam reflected by the incident mirror and performs synchronization detection,
The angle formed by the angle at which the light beam guided by the incident optical system is incident on one reflecting surface of the deflector and the angle at which the one reflecting surface reflects the light beam on the incident mirror is:
The optical scanning device according to claim 1, wherein the angle is not 0 ° in a plane perpendicular to the rotation axis of the deflector.   The optical scanning device according to claim 1, wherein the deflecting surface of the deflector includes four reflecting surfaces. The deflecting surface of the deflector has four reflecting surfaces,
The first synchronization detection unit sets the timing of the scanning start end by one of the light beams having an opening angle of π / 2 to each other that is 5 lines before the scanning line that is the scanning start end. 3. The optical scanning device according to claim 2, wherein the scanning is performed based on synchronous detection by the other light beam among the light beams having an opening angle of [pi] / 2. Correction means for correcting the main scanning magnification from the scanning time from the scanning start end to the scanning end end,
The synchronization detection means detects the timing of the scanning start end and the timing of the scanning end,
The first synchronization detection unit detects the timing of the scanning start end by one of the light beams having an opening angle of π / 2 and the timing of the scanning end by the other light beam. The optical scanning apparatus according to claim 1, wherein the optical scanning apparatus is characterized in that: The synchronization detection means includes a second synchronization detection unit that detects the synchronization by receiving the light beam reflected by the deflector without passing through the incident mirror,
The optical scanning device according to claim 1, further comprising a dimming unit between optical paths from the deflector to the second synchronization detection unit.   7. The optical scanning device according to claim 1, further comprising an opening between optical paths from the light beam splitting unit to the first synchronization detection unit. In an image forming apparatus including a writing unit that forms a latent image by irradiating a light beam from a light source onto an image carrier that is a scanned surface.
Comprising a plurality of the image carrier,
Developing means that develops the latent images formed on the plurality of image carriers by the writing unit with developers of different colors and visualizes the images of the respective colors formed on the plurality of image carriers directly. Or a transfer means for forming a multicolor or full-color image by superimposing and transferring on a recording material via an intermediate transfer member,
The image forming apparatus, wherein the writing unit includes the optical scanning device according to claim 1.