JP5471999B2 - Optical scanning apparatus and image forming apparatus - Google Patents

Description

  The present invention includes an optical scanning device that deflects and scans a light beam such as a laser beam from a light source by a rotating polygon mirror (hereinafter also referred to as a “polygon mirror”) of a deflecting means, and the optical scanning device is mounted on the optical scanning device. Images are formed by writing images (electrostatic latent images) on the scanned surfaces (peripheral surfaces) of a plurality of image carriers with a plurality of light beams, and visualizing and synthesizing these images. The present invention relates to an image forming apparatus such as a tandem digital copying machine, a digital multi-function peripheral (MFP), a facsimile machine, and a printer.

As an electrophotographic image forming apparatus such as a digital copying machine, a tandem type image forming apparatus having a plurality of photoconductors as an image carrier is becoming popular due to colorization and speeding up.
In such a tandem type image forming apparatus, it is necessary to irradiate each of the plurality of photoconductors with a light beam. Therefore, as the number of photoconductors increases, the number of light sources increases. This increase in the number of light sources increases the cost due to an increase in the number of components, and further causes a color shift due to a wavelength difference between a plurality of light sources. Further, when the number of light sources increases, the failure probability of the optical scanning device due to deterioration of the light emitting element (for example, a semiconductor laser) also increases, and the recyclability decreases.

  In order to solve this problem, as an optical scanning device mounted on a tandem type image forming apparatus, for example, as seen in Patent Document 1, the angle of the reflecting surface is shifted up and down by rotating the angle of the reflecting surface in the rotation direction with respect to a common rotation axis. A deflector (deflection means) having two polygon mirrors (also simply referred to as “mirrors”) provided in a stage, and a light beam from a light source is divided into a plurality of light beams, and each of the divided light beams is different. Light beam splitting means for entering the stage mirror, and periodically deflecting each of the light beams by the upper and lower stage mirrors, respectively, so that the plurality of scanned surfaces rotating in the sub-scanning direction are each in the sub-scanning direction. It has been proposed to perform image writing on each surface to be scanned by scanning in the main scanning direction orthogonal to the main scanning direction.

  However, with such an optical scanning device, high-speed image writing is possible while reducing the number of light sources. However, a light beam that is deflected and scanned by two upper and lower mirrors is detected and a synchronization detection signal is output. Each synchronization detection signal corresponding to each mirror output from the synchronization detection sensor is provided with a common synchronization detection sensor (detection means), and main scanning (main scanning direction) of the light beam with respect to each scanned surface by each mirror Therefore, there is a problem in that it is not possible to electrically distinguish each mirror, and feedback control for correcting the image writing timing by scanning each mirror cannot be performed. The synchronization detection sensor is usually disposed outside the surface to be scanned (effective scanning area) of the photoconductor, and detects the light beam when the light beam scanned by the mirror is incident, and the light beam is detected. A synchronization detection signal (a signal for determining image writing timing) used as a reference signal for scanning is output.

  Therefore, in order to solve the problem, for example, as seen in Patent Document 2, the angle in the rotation direction of each of the upper and lower two mirror reflecting surfaces is slightly shifted from the shift amount in which the scanning cycle is shifted by a half cycle, Using the fact that the detection timing (synchronization detection timing) of each light beam from each mirror reflection surface is shifted, each output from the synchronization detection sensor by the incidence of each light beam from each mirror reflection surface There has also been proposed one that can determine the synchronization detection signal.

  In the device described in Patent Document 2, when the number of reflecting surfaces of each mirror in the upper and lower two stages is 4, the phase difference (angle difference) in the rotation direction of the reflecting surface of each mirror is exactly 45 °. The output intervals of the synchronization detection signals (synchronization detection pulses) from the synchronization detection sensors by the light beams respectively scanned by the mirror reflecting surfaces are equal intervals, and the synchronization detection signals are discriminated on the control unit side. Since the angle difference in the rotation direction of each mirror reflecting surface is not exactly 45 °, it is slightly shifted to 45 ° 1 ′, 44 ° 59 ′, etc. Each synchronization detection signal is discriminated using the fact that a long and short time difference occurs in the output interval of the detection signal.

  However, even if the effective scanning period is limited by performing the light beam splitting by the light beam splitting means (using the beam splitting method), the mirror reflecting surface described in Patent Document 2 is used. Since the phase difference of the scanning period due to this shifts from a half period, there is a problem that the effective scanning period is further shortened by the mirror on the side where the scanning period becomes shorter. In other words, in the case of the beam splitting method, the effective scanning period for scanning the surface to be scanned of the photosensitive member with respect to the scanning period is theoretically 50% or less, and synchronization detection (except for the timing for scanning the surface to be scanned of the photosensitive member) The output of the synchronization detection signal from the synchronization detection sensor) and the APC (auto power control) for automatically adjusting the light quantity of the light source also require the light source to be turned on. Cannot be used for scanning the scanning surface.

Therefore, in order to discriminate each synchronization detection signal output from the synchronization detection sensor by the incidence of each light beam from each mirror reflection surface, the angle in the rotation direction of each mirror reflection surface is shifted from a half cycle. As a result, the effective scanning time is reduced, and there is a problem in that sufficient time for performing synchronization detection and APC cannot be secured.
Therefore, if the shift amount of the angle difference in the rotation direction of each mirror reflecting surface is made as small as possible, the time required for shortening the effective scanning period is reduced. However, from the synchronization detection sensor due to the incidence of each light beam from each mirror reflecting surface. There is a problem that it is difficult to determine each synchronization detection signal output.

  The present invention has been made in view of the above points, and divides a light beam from a light source into a plurality of light beams, and each of the divided light beams is reflected on a reflecting surface in a rotation direction about a rotation axis of a deflecting unit. Even when deflection scanning is performed by each polygon mirror provided in a plurality of stages at different angles, the effective scanning period that can be used for scanning each light beam is not shortened, and each light from the reflection surface of each polygon mirror It is an object to make it possible to discriminate each detection signal output from a detection means (synchronous detection sensor) by the incidence of a beam.

In order to achieve the above object, the present invention provides the following optical scanning device and an image forming apparatus equipped with the same.
An optical scanning device according to the present invention includes a deflecting unit having a plurality of rotary polygon mirrors provided in a plurality of stages on a common rotation axis with the angles of reflection surfaces shifted from each other in the rotation direction, and a light beam from a light source. The light beams are split into a plurality of light beams, and the divided light beams are incident on the rotary polygon mirrors at different stages, and deflected and scanned by the rotary polygon mirrors at the stages of the deflection means. A plurality of scanned surfaces rotating in the sub-scanning direction by periodically deflecting each of the light beams by the rotary polygon mirrors of the respective stages. An optical scanning device that scans in a main scanning direction orthogonal to the sub-scanning direction and writes an image on each surface to be scanned based on a detection timing by the detection means. An optical element for guiding each of the light beams deflected and scanned by a mirror to the detection means, and the timing at which the light beams scan the detection means with respect to the timing at which the scanning surfaces are scanned. Among the rotary polygon mirrors of the stage, the rotary polygon mirror of one stage and the rotary polygon mirror of the other stage are provided differently.

The optical element is constituted by a reflecting mirror for each stage arranged to guide each light beam deflected and scanned by the rotary polygon mirror at each stage to the detecting means. It is preferable to arrange one of the reflecting mirrors so that one of the reflecting mirrors differs in angle with respect to the main scanning direction with respect to the other reflecting mirror. Also, when the multi-stage rotary polygon mirror is a two-stage rotary polygon mirror, the vertex of the other stage rotary polygon mirror overlaps the vertical bisector of the reflecting surface of the one stage rotary polygon mirror. It is good to arrange in. Furthermore, you may provide the measurement means which measures the time difference of the interval of the detection signal output from the said detection means.
An image forming apparatus according to the present invention includes the above-described optical scanning device and a plurality of image carriers each having a scanned surface on which each of the light beams is scanned.

  According to the present invention, the optical element for guiding each light beam deflected and scanned by the rotary polygon mirror provided in a plurality of stages on the rotation shaft of the deflecting means of the optical scanning device to the detecting means, The timing at which the detecting means scans the scanning surface is made different between the rotating polygon mirror of one stage and the rotating polygon mirror of the other stage with respect to the timing of scanning each surface to be scanned. Since the light beam from the light source is divided into a plurality of light beams and each of the divided light beams is deflected and scanned by the rotary polygon mirrors at each stage, the light beams can be used for scanning each light beam. The effective scanning period is not shortened, and each detection signal output from the detection means can be determined by the incidence of each light beam from the reflecting surface of each stage of the rotating polygon mirror.

It is a block diagram showing a configuration example of an image forming mechanism of a color image forming apparatus equipped with a light beam scanning device according to the present invention. It is a perspective view which shows the structural example of the optical system of the optical scanning device 22 of FIG. It is explanatory drawing with which it uses for description of an effect | action of the half mirror prism 4 of FIG. It is explanatory drawing with which it uses for description of the scanning of the light beam by each polygon mirror 71,72 of FIG. An explanation for explaining an example in which the light amounts of the semiconductor lasers 1 and 1 ′ are changed by the polygon mirrors 71 and 72 in FIG. 2 when writing black images and magenta images on the scanned surfaces of the photosensitive drums 11a and 11b, respectively. FIG.

It is a block diagram which shows the structural example of the principal part containing the control part with which the optical scanning device 22 shown in FIG. 1, FIG. 2 is provided. It is explanatory drawing which looked at the angle difference to the rotation direction of the reflective surface of the polygon mirrors 71 and 72 of the upper and lower two stages which the deflector 7 of FIG. 2 has seen from the rotating shaft direction. FIG. 8 is a timing diagram showing control timing by a control unit that controls a deflector having two upper and lower polygon mirrors 71 and 72 shown in FIG. 7. FIG. 3 is a perspective view showing a configuration example of a characteristic part related to the present invention in the optical system of the optical scanning device 22 shown in FIG. 2. It is explanatory drawing which looked at the angle difference to the rotation direction of the reflective surface of the polygon mirror of the upper and lower two steps | paragraphs which the deflector by a prior art had seen from the rotating shaft direction. FIG. 11 is a timing diagram showing control timings by a control unit that controls a deflector having upper and lower two-stage polygon mirrors 71 ′ and 72 ′ shown in FIG. 10.

Hereinafter, embodiments for carrying out the present invention will be specifically described with reference to the drawings.
In the following embodiments, the light beam from the light source is divided into a plurality of light beams, and each of the divided light beams is moved up and down by shifting the angle of the reflecting surface in the rotation direction with respect to the rotation axis of the deflector serving as the deflecting means. Optical element for guiding each light beam deflected and scanned by a polygon mirror at each stage to a synchronous detection sensor as a detection means in a beam splitting type optical scanning apparatus that performs deflection scanning by polygon mirrors provided in stages. (The reflection mirror for each stage), with respect to the timing at which each of the light beams scans the synchronization detection sensor scans the surface to be scanned of each image carrier, the polygon mirror on one stage and the mirror on the other stage Provided to be different from the polygon mirror (one reflection mirror is arranged so that the angle with respect to the main scanning direction is slightly different from the other reflection mirror) Thus, only the detection timing of the light beam by the synchronization detection sensor can be shifted without changing the timing of scanning the surface to be scanned of the image carrier, so that each light beam from the reflection surface of the polygon mirror at each stage can be shifted. Each synchronization detection signal (synchronization detection pulse) that is output from the synchronization detection sensor when incident is given a time difference so that it is possible to determine which synchronization detection signal is generated by detecting the light beam from the reflecting surface of the polygon mirror. It is characterized by that.

Therefore, the feature will be described in detail.
[Overall configuration of image forming apparatus]
First, an image forming mechanism of a tandem color image forming apparatus equipped with a light beam scanning apparatus according to the present invention will be described with reference to FIG.
FIG. 1 is a configuration diagram showing a configuration example of an image forming mechanism of the color image forming apparatus.
This color image forming apparatus is an image forming apparatus such as a tandem digital color copying machine, a digital color multifunction peripheral, a color facsimile apparatus, and a color printer.

  This color image forming apparatus includes four photosensitive drums 11a to 11d, four charging units 12a to 12d, four toner cartridges 13a to 13d as developing units, four transfer rollers 14a to 14d, and a photosensitive member. Four cleaners (not shown) for removing toner on the drums 11a to 11d, an intermediate transfer belt 15, an intermediate transfer roller 16, an intermediate transfer belt cleaning device 17, a transfer device 18, a registration roller pair 19, and a fixing device. 20, a paper discharge device 21, and an optical scanning device 22.

  When the start button on the operation unit of the color image forming apparatus is pressed, or when a print job start signal from an external device such as a personal computer is validated, the optical scanning device 22 uses a timing-controlled light beam. The scanned surfaces of the photosensitive drums 11a to 11d are exposed. In this optical scanning device 22, each polygon mirror, which is a rotary polygon mirror in two upper and lower stages, is rotated by a drive motor (polygon motor) (not shown) so that each light beam from a scanning optical system, which will be described later, is a polygon mirror in a different stage. By periodically scanning the scanned surfaces of the photosensitive drums 11a to 11d rotated in the sub-scanning direction in the main scanning direction orthogonal to the sub-scanning direction, the respective scanned surfaces are electrostatically charged. A latent image is formed (image writing is performed). The scanned surfaces of the photosensitive drums 11a to 11d are charged in advance by the charging units 12a to 12d before exposure.

The electrostatic latent images formed on the respective scanned surfaces are developed with the toner supplied from the toner cartridges 13a to 13d, and monochromatic images are formed on the scanned surfaces of the photosensitive drums 11a to 11d. In the embodiment shown in FIG. 1, first, black (K) toner is adhered to the first photosensitive drum 11a to form a black image (black image), which is transferred onto the intermediate transfer belt 15 by the transfer roller 14a. The
On the next photosensitive drum 11b, magenta (M) toner is adhered, a magenta image is formed, and is transferred onto the intermediate transfer belt 15 by the transfer roller 14b. Since a black image has already been transferred onto the intermediate transfer belt 15, a magenta image is transferred thereon.

Further, on the next photosensitive drum 11c, cyan (C) toner is adhered, a cyan image is formed, and is transferred onto the intermediate transfer belt 15 by the transfer roller 14c. Since the black image and the magenta image have already been transferred onto the intermediate transfer belt 15, the cyan image is further transferred onto them.
On the last photoconductor drum 11d, yellow (Y) toner is adhered, and a yellow image (yellow image) is formed and transferred onto the intermediate transfer belt 15 by the transfer roller 14d. A yellow image is further transferred onto the already transferred black image, magenta image, and cyan image on the intermediate transfer belt 15.

The intermediate transfer belt 15 is driven to rotate using the intermediate transfer roller 16 as a driving roller, thereby conveying the transferred toner images of the respective colors in the directions indicated by the arrows.
As described above, the toner images of the respective colors are superimposed on the intermediate transfer belt 15 to form a composite color image. Here, images are formed in the order of black, magenta, cyan, and yellow, but the order of colors to be formed is not limited to this.

  On the other hand, when the job start signal is validated, this color image forming apparatus separates and feeds the transfer sheets S one by one from a sheet feeding device (not shown) and is disposed in front of the registration roller pair 19. When the transfer sheet S is detected by a sheet feeding registration sensor (not shown), the sheet feeding is temporarily stopped in a state where the leading end of the transfer sheet S is held between the pair of registration rollers 19. Then, the registration roller pair 19 is rotated in synchronization with the conveyance of the composite color image on the intermediate transfer belt 15, and the transfer sheet S is sent between the intermediate transfer belt 15 and the transfer device 18. The transfer device 18 transfers the composite color image to the transfer paper S, and the fixing device 20 applies heat and pressure to the transfer paper S on which the conveyed composite color image is transferred to fix it. The fixed transfer sheet S is discharged by a pair of paper discharge rollers of the paper discharge device 21 and stacked on a paper discharge tray (not shown).

[Configuration of optical system of optical scanning device]
Next, the configuration of the optical system of the optical scanning device 22 in FIG. 1 will be described with reference to FIGS. For convenience of explanation, among the optical systems for scanning the scanned surfaces of the photosensitive drums 11c and 11d in FIG. 1 with a light beam, the optical system for scanning the scanned surfaces of the photosensitive drums 11a and 11b. Except for the common parts, the illustration is omitted.

FIG. 2 is a perspective view showing a configuration example of the optical system of the optical scanning device 22.
The optical scanning device 22 constitutes a beam splitting type scanning optical system.
The semiconductor lasers 1 and 1 ′ are two light emitting sources constituting one light source, and each emits one light beam (laser beam). These semiconductor lasers 1 and 1 ′ are held by the holder 2 in a predetermined positional relationship.

Each light beam emitted from each of the semiconductor lasers 1 and 1 'is converted into a light beam form (parallel light beam or weakly divergent or weakly convergent light beam) suitable for the subsequent optical system by the coupling lenses 3 and 3'. Is done. In this example, the light beams coupled by the coupling lenses 3 and 3 'are both parallel light beams.
Each of the light beams emitted from the coupling lenses 3 and 3 ′ and having a desired light beam shape is light beam splitting means after being shaped through the opening of the aperture 12 that regulates the light beam width. The light enters the half mirror prism 4 and is divided into two in the sub-scanning direction by the action of the half mirror prism 4 and is divided into two light beams.

This situation is shown in FIG. Here, for convenience of illustration, the light beam L1 emitted from the semiconductor laser 1 is shown as a representative. Although the vertical direction in FIG. 3 is the sub-scanning direction, the half mirror prism 4 includes a half mirror (semi-transparent mirror) 4a that separates an incident light beam into transmitted light and reflected light at a ratio of 1: 1, and a light beam. And a total reflection surface 4b having a function of changing the direction in which the light travels in parallel in the sub-scanning direction.
When the light beam L1 is incident on the half mirror prism 4, the light beam L1 is incident on the half mirror 4a, and part of the light beam L1 passes straight through the half mirror 4a to become the light beam L11, and the rest is reflected to the total reflection surface 4b. Incident light is totally reflected by the total reflection surface 4b to become a light beam L12.

In this example, since the half mirror 4a and the total reflection surface 4b are parallel to each other, the light beams L11 and L12 emitted from the half mirror prism 4 are parallel to each other.
In this way, the light beam L1 emitted from the semiconductor laser 1 is divided into two in the sub-scanning direction as two light beams L11 and L12. The light beam from the semiconductor laser 1 'is also divided into two in the same manner.
Therefore, two light beams are emitted from one light source, and these two light beams are divided into two in the sub-scanning direction, thereby obtaining four light beams.

  In this embodiment, a half mirror prism that divides a light beam (light beam) that travels straight at a ratio of 1: 1 and a light beam that is shifted downward and passed is used, but a single half mirror is generally used. An optical system device having the same function can be configured by other means such as using a mirror to be used. Further, the light separation ratio by the half mirror is not limited to the above 1: 1, and can be appropriately set according to the conditions of other optical system devices.

With reference to FIG. 2 again, the optical scanning device 22 will be described. In addition to the scanning optical system described above, the optical scanning device 22 includes cylindrical lenses 5a and 5b, soundproof glass 6, a deflector 7, first scanning lenses 8a and 8b, optical path bending mirrors 9a and 9b, and a second scanning lens 10a, 10b.
The four light beams exiting the half mirror prism 4 are subjected to main scanning in the vicinity of a reflection surface (deflection reflection surface) described later of the deflector 7 by cylindrical lenses 5a and 5b arranged in accordance with the upper and lower stages. After being converted into a line image that is long in the direction, the light beam is incident on the deflector 7 via the soundproof glass 6, and the light beam deflected by the deflector 7 is emitted to the scanning imaging optical system side via the soundproof glass 6. .

The deflector 7 is a deflecting means having two polygon mirrors 71 and 72 provided in two upper and lower stages by shifting the angle of the reflecting surface in the rotational direction to a common rotating shaft (not shown), and the rotating shaft is driven by a driving motor (not shown). It can be rotated around.
The upper polygon mirror (hereinafter also referred to as “upper polygon mirror”) 71 and the lower polygon mirror (hereinafter also referred to as “lower polygon mirror”) 72 have four reflecting surfaces in this example. The reflection surface of the lower polygon mirror 72 is shifted from the reflection surface of the upper polygon mirror 71 by a predetermined angle: θ (= 45 °) in the rotation direction. The upper and lower polygon mirrors may be integrally formed.

  The first scanning lens 8a, the second scanning lens 10a, and the optical path bending mirror 9a are two light beams (emitted from the semiconductor lasers 1 and 1 'that are deflected by the upper polygon mirror 71 of the deflector 7 and are half mirrors). A pair of scanning images forming two light spots separated in the sub-scanning direction by guiding the two light beams transmitted through the half mirror 4a of the prism 4 to the scanning surface of the corresponding photosensitive drum 11a. Configure the optical system.

  The first scanning lens 8b, the second scanning lens 10b, and the optical path bending mirror 9b are two light beams (emitted from the semiconductor lasers 1, 1 'that are deflected by the lower polygon mirror 72 of the deflector 7 and are half mirrors). A set of scans for guiding two light beams reflected by the total reflection surface 4b of the prism 4 to the surface to be scanned of the corresponding photosensitive drum 11b to form two light spots separated in the sub-scanning direction. An imaging optical system is configured.

  Since the reflecting surfaces of the upper polygon mirror 71 and the lower polygon mirror 72 of the deflector 7 are shifted from each other by a phase difference of 45 ° in the rotational direction, the scanning optical system after the polygon mirrors 71 and 72 is shifted by exactly half a cycle. The surface to be scanned of the two photosensitive drums 11a and 11b is scanned by the first scanning lenses 8a and 8b, the optical path bending mirrors 9a and 9b, and the second scanning lenses 10a and 10b.

When the light beam deflected by the upper polygon mirror 71 scans the surface to be scanned of the photosensitive drum 11a, the light beam deflected by the lower polygon mirror 72 is not guided to the surface to be scanned of the photosensitive drum 11b. When the light beam deflected by the lower polygon mirror 72 scans the surface to be scanned of the photosensitive drum 11b, the light beam deflected by the upper polygon mirror 71 is not guided to the surface to be scanned of the photosensitive drum 11a. .
That is, the scanning of the light beam with respect to the surface to be scanned of the photosensitive drums 11a and 11b is alternately performed with a time shift.

FIG. 4 is a diagram for explaining this situation. For convenience of illustration, light beams (in reality, four beams) incident on the deflector 7 are shown as “incident light”.
In FIG. 4A, each light beam from the cylindrical lenses 5a, 5b is incident on the deflector 7, and the light beam B1 reflected and deflected by the upper polygon mirror 71 passes through the surface to be scanned of the photosensitive drum 11a. It shows the situation when scanning. At this time, the light beam B2 reflected and deflected by the lower polygon mirror 72 is shielded by the light shielding member 30 so as not to reach the surface to be scanned of the photosensitive drum 11b. FIG. 4B shows a situation when the light beam B2 reflected and deflected by the lower polygon mirror 72 scans the surface to be scanned of the photosensitive drum 11b. At this time, the light beam B1 reflected and deflected by the upper polygon mirror 71 is shielded by the light shielding member 30 so as not to reach the surface to be scanned of the photosensitive drum 11a.

  Thus, in this embodiment, the scanning of the light beam with respect to each of the photosensitive drums 11a and 11b is performed alternately. For example, when the scanning with respect to the photosensitive drum 11a is performed, the light amount (light intensity) of the light source is set to black. When modulated with the image signal of the image and when the optical scanning of the photosensitive drum 11b is performed, the electrostatic latent image of the black image is photosensitive on the photosensitive drum 11a by modulating the light quantity of the light source with the image signal of the magenta image. An electrostatic latent image of a magenta image can be written on the body drum 11b.

  FIG. 5 shows writing of a black image and a magenta image on the scanned surfaces (effective scanning areas) of the photosensitive drums 11a and 11b by the common light source (semiconductor lasers 1 and 1 'in FIG. 2) and the polygon mirrors 71 and 72, respectively. FIG. 6 shows a timing chart when the light source is fully turned on during the effective scanning period (light beam scanning period with respect to the surface to be scanned of the photosensitive drums 11a and 11b). A solid line indicates a portion corresponding to writing of a black image, and a broken line indicates a portion corresponding to writing of a magenta image.

  In this embodiment, each light beam obtained by dividing a light beam emitted from a common light source (semiconductor laser 1, 1 ′) into two by the half mirror prism 4 is scanned once by the polygon mirrors 71, 72, so that FIG. As shown in FIG. 4, black images and magenta images can be written on the scanned surfaces of the photosensitive drums 11a and 11b, respectively. The writing to each scanned surface is exactly half a cycle because the reflecting surfaces of the polygon mirrors 71 and 72 are shifted from each other by a phase difference of 45 ° in the rotational direction. The timing of writing out the black image and the magenta image is to detect the light beam toward the scanning start position by the synchronization detection sensor arranged outside the scanned surface (effective scanning area) of each of the photosensitive drums 11a and 11b. Determined by. The synchronization detection sensor is not shown here, but normally a photodiode is used.

  In FIG. 5, the light amount of the light source is set differently in the time region for writing the black image and the time region for writing the magenta image. This is because, in each optical path from the light source to the photosensitive drums 11a and 11b, when there is a relative difference in the transmittance and reflectance of the optical element, the light amount of the light source is set to the photosensitive drums 11a and 11b. If they are the same, the amount of light beams reaching the photosensitive drums 11a and 11b will be different. Therefore, in this example, as shown in FIG. 5, when the scanned surfaces of the different photosensitive drums 11a and 11b are scanned, the scanned surfaces of the different photosensitive drums 11a and 11b are changed by changing the light amount of the light source. It is possible to equalize the light amount of the light beam that reaches.

  Instead of setting the light amount of the light source differently for each photosensitive drum, for example, the ratio between the transmittance and the reflectance is adjusted without setting the transmittance / reflectance of the half mirror in the half mirror prism to 1: 1. By doing so, it is possible to equalize the amount of light beams that reach the scanned surfaces of different photosensitive drums. Also, in order to equalize the amount of light beams that reach different scanned surfaces, the amount of light from the light source is varied and the adjustment of the ratio of the transmittance and reflectance of the half mirror in the half mirror prism is combined. Is also possible.

[Configuration of control system of optical scanning device]
Next, the configuration of the main part including the control unit provided in the optical scanning device 22 shown in FIGS. 1 and 2 and the scanning control performed by the control unit will be described with reference to FIG.
FIG. 6 is a block diagram illustrating a configuration example of a main part including a control unit included in the optical scanning device 22.
The control unit 50 included in the optical scanning device 22 includes a light source control unit 51, a data selection unit 52, and a mirror determination unit 53.
The mirror determination unit 53 includes a synchronization detection measurement unit 53a and a comparison determination unit 53b.

  The light source controller 51 outputs an image signal (modulation signal) to each light source in order to control each light beam emitted from the two light sources to the upper polygon mirror 71 and the lower polygon mirror 72. The light beam emitted from each light source is incident on the reflecting surface of the upper polygon mirror 71 and the reflecting surface of the lower polygon mirror 72. The light beams are scanned in the main scanning direction by the rotation of the polygon mirrors 71 and 72, and the first scanning lenses 8a and 8b, the second scanning lenses 10a and 10b, and the optical path bending mirrors 9a and 9b shown in FIG. The scanned surfaces of the photosensitive drums 11a to 11d are scanned via the scanning imaging optical system including the scanning imaging optical system.

The synchronization detection sensors 60a and 60b arranged at the scanning tip position detect the light beams scanned by the polygon mirrors 71 and 72, respectively, and output a synchronization detection signal indicating the main scanning start position. The respective synchronization detection signals are output to the mirror discrimination unit 53.
The synchronization detection measurement unit 53a in the mirror discrimination unit 53 is a measurement unit, and measures the output interval of each input synchronization detection signal, and outputs each measurement value to the comparison determination unit 53b.

The comparison determination unit 53b compares each measurement value input from the synchronization detection measurement unit 53a with a predetermined value set in advance, thereby outputting each synchronization detection signal DETP output from each synchronization detection sensor 60a, 60b. The time difference of the (synchronization detection pulse) is determined, the polygon mirror corresponding to each synchronization detection signal is determined, and the determination result is output to the data selection unit 52.
The data selection unit 52 selectively synthesizes and outputs the image signal (image data) from the image processing unit 65 based on the determination result from the comparison determination unit 53b.
The image processing unit 65 outputs four color image signals of black (K), magenta (M), cyan (C), and yellow (Y) to the data selection unit 52.

The toner color to be imaged by the light beam from each light source is determined by the arrangement of the optical scanning device 22 and the photosensitive drums 11a to 11d. Here, black and magenta image formation is performed with the light beam from one light source, and cyan and yellow image formation is performed with the light beam from the other light source. Therefore, the data selection unit 52 outputs from the comparison determination unit 53b. Based on the determination result, the black and magenta image signals are combined as an image signal for one light source, and the cyan and yellow image signals are combined for the other light source and output to the light source control unit 51. .
The light source control unit 51 outputs an image signal corresponding to each light source as a modulation signal.

Each light source is modulated (on / off) in accordance with the input modulation signal, and emits a corresponding light beam. Each light beam is divided into two by the half mirror prism 4, and the scanning surfaces of the photosensitive drums 11a to 11d are respectively exposed by deflection scanning with the polygon mirrors 71 and 72, thereby forming a desired electrostatic latent image. The
In this embodiment, two-color image formation is performed with one light source, and four-color image formation is performed with two light sources. However, the number of light sources is not limited to two. For example, in order to perform image formation at high speed, two light sources can be used for two-color image formation, and four-color image formation can be performed using a total of four light sources.

  By the way, when the angle difference (shift angle) in the rotation direction of the reflection surfaces of the polygon mirrors 71 and 72 is uniform, the angle difference is because the number N of reflection surfaces of the polygon mirrors 71 and 72 is four. It is 45 ° calculated by 360 ° / 4/2. For this reason, scanning is started by the upper polygon mirror 71 and thereafter scanning is started by the lower polygon mirror 72, and scanning is started by the lower polygon mirror 72, and thereafter scanning is started by the upper polygon mirror 71. , And the timing of the light beam reflected by the upper polygon mirror 71 and the timing of the beam reflected by the lower polygon mirror 72 cannot be determined.

  Therefore, in order to make this determination possible, in this embodiment, a reflection mirror for each stage for guiding each light beam deflected and scanned by the polygon mirrors 71 and 72 of each stage to the synchronization detection sensors 60a and 60b, respectively. The one reflection mirror is arranged so that the angle with respect to the main scanning direction is slightly different from the other reflection mirror. Hereinafter, the embodiment will be described. Before the description, for convenience of understanding, the upper and lower two-stage polygon mirrors of the deflector according to the prior art will be described with reference to FIGS. For convenience of explanation, the control unit 50 shown in FIG. 6 controls the deflector according to the prior art based on the synchronization detection signal from the synchronization detection sensor 60a, and the photosensitive drums 11a and 11b in FIG. Assume that the surface to be scanned is scanned.

FIG. 10 is an explanatory view of the angle difference in the rotation direction of the reflection surfaces of the upper and lower polygon mirrors of the deflector according to the prior art viewed from the rotation axis direction.
In the deflector according to the prior art shown in FIG. 10, the angle difference (phase difference) in the rotational direction of the reflection surfaces of the upper and lower polygon mirrors 71 ′ and 72 ′ is slightly shifted from 45 ° to 44 ° 59 ′ or the like. It is said.
FIG. 11 is a timing chart showing control timings by a control unit that controls the deflector having the upper and lower two-stage polygon mirrors 71 ′ and 72 ′ shown in FIG. 9.

In FIG. 11, the output timing of the synchronization detection signal (synchronization detection pulse) from the synchronization detection sensor 60a by each light beam scanned by each polygon mirror 71 ', 72' and the photosensitive by each polygon mirror 71 ', 72'. The scanning timing of the light beam with respect to the scanned surface (effective scanning area) of the body drums 11a and 11b is shown.
As can be seen from FIG. 11, the output of the synchronization detection signal DETP (synchronization detection pulse) is caused by the fact that the angle difference in the rotation direction of the reflecting surface of each of the polygon mirrors 71 ′ and 72 ′ is shifted from the half cycle. A time difference occurs.

  Therefore, the control unit 50 uses the time difference to generate a synchronization detection signal from the synchronization detection sensor 60a by each light beam scanned by each polygon mirror 71 ', 72' by the upper polygon mirror 71 '. Synchronization detection signal (synchronization detection signal for detecting the scanning timing by the polygon mirror 71 ') DETP_U by the scanned light beam and synchronization detection signal (lower polygon mirror by the light beam scanned by the lower polygon mirror 72') 72) and the synchronization detection signal DETP_D for detecting the scanning timing.

  Then, based on the respective synchronization detection signals DETP_U and DETP_D, the respective photosensitive drums 11a and 11b are scanned with the light beams in accordance with the respective image signals DATA_U and DATA_D to form an image. In the example of FIG. The time that can be used for scanning by the upper polygon mirror 71 'is shortened by the amount that the polygon mirror 71' is shifted from the half cycle, and the surface to be scanned (effective scanning area) of the photosensitive drum 11a is scanned. In a region other than the time, it becomes difficult to secure time for turning on the light source for performing synchronization detection and turning on the light source for performing APC.

  Therefore, in order to solve the problem, if the shift amount from the angular difference (half cycle) in the rotation direction of the reflecting surface of each of the polygon mirrors 71 ′ and 72 ′ is made as small as possible, a decrease in the effective scanning time can be suppressed. It becomes difficult to reliably detect the time difference. For example, when the time difference is detected by counting with a counter circuit, the count clock must be advanced, the number of bits of the counter increases, and the circuit becomes larger.

Therefore, in order to solve the problem, in this embodiment, the following is performed.
FIG. 7 is an explanatory view of the angle difference in the rotation direction of the reflection surfaces of the upper and lower polygon mirrors 71 and 72 of the deflector 7 of FIG. 2 as viewed from the rotation axis direction.
In contrast to the two-stage upper and lower polygon mirrors 71 'and 72' of the deflector according to the prior art shown in FIG. 10, in this embodiment, as shown in FIG. The angle difference in the rotation direction of the reflecting surfaces 71 and 72 is set to 45 °. That is, they are arranged so that the vertex of the polygon mirror 72 at the other stage overlaps the vertical bisector of the reflection surface of the polygon mirror 71 at one stage.

FIG. 8 is a timing chart showing control timing by the control unit 50 (FIG. 6) that controls the deflector 7 having the upper and lower two-stage polygon mirrors 71 and 72 shown in FIG.
In FIG. 8, the output timing of the synchronization detection signal from the synchronization detection sensor 60a by each light beam scanned by each polygon mirror 71, 72 and the surface to be scanned of the photosensitive drums 11a, 11b by each polygon mirror 71, 72. The scanning timing of the light beam with respect to (effective scanning area) is shown.

  In this embodiment, the configuration described later makes it possible to slightly shift the timing at which the scanning light from the upper and lower polygon mirrors 71 and 72 scans the synchronization detection sensor 60a. As can be seen from FIG. The output (synchronization detection pulse) of the synchronization detection signal DETP from the synchronization detection sensor 60a is shifted, and the pulse interval alternately repeats a long interval and a short interval. That is, a time difference occurs in the pulse interval of the synchronization detection pulse. This time difference can be determined by measuring the output interval of the synchronization detection signal DETP by the synchronization detection measurement unit 53a in FIG. 6 and outputting the measured value to the comparison determination unit 53b, and which polygon mirror is used for scanning. Can be determined.

However, the scanning timing of the scanned surfaces of the photosensitive drums 11a and 11b is scanned by the polygon mirrors 71 and 72 having an angle difference of exactly 45 °, and thus the timing shown in FIG.
For this reason, the effective scanning time for the scanned surfaces of the photosensitive drums 11a and 11b by the upper and lower polygon mirrors 71 and 72 is the same as being equally divided, and the cycle of the synchronization detection pulse is shortened. The scannable period can also be used until the timing indicated by the broken line in FIG.

FIG. 9 is a perspective view showing a configuration example of a characteristic portion related to the present invention in the optical system of the optical scanning device 22 shown in FIG. For convenience of illustration, the first scanning lenses 8a and 8b, the second scanning lenses 10a and 10b, and the photosensitive drums 11a and 11b are collectively shown.
In this embodiment, for example, as shown in FIG. 9A, each light beam scanned in the main scanning direction A by the upper and lower polygon mirrors 71 and 72 is converted into one synchronization detection sensor (synchronization detection plate) 60a. Each of the light beams deflected by the polygon mirrors 71 and 72 passes through the second scanning lenses 10a and 10b and is reflected by the reflecting mirror 81 before scanning the scanned surfaces of the photosensitive drums 11a and 11b. After the reflection, the light is reflected by the two reflection mirrors 82a and 82b, which are optical elements in the area surrounded by the dotted line, and is incident on the synchronous detection sensor 60a.

  In the area, for example, as shown in an enlarged view in FIG. 9B, each of the reflection mirrors 82a and 82b for reflecting each light beam from the reflection mirror 81 and guiding it to the synchronous detection sensor 60a is provided on one side. The reflection mirror 82a is arranged so that the angle with respect to the main scanning direction is different from the other reflection mirror 82b. For this reason, the timing at which each light beam scans the synchronization detection sensor 60a is slightly shifted by the upper and lower polygon mirrors 71 and 72 with respect to the timing at which the scanned surfaces of the photosensitive drums 11a and 11b are scanned. At the timing as shown in FIG. 8, a synchronous detection pulse having a time difference between the upper and lower stages is obtained.

  In this way, each reflection mirror (optical element) for guiding each light beam deflected and scanned by the polygon mirror provided in two stages on the rotation axis of the deflector of the optical scanning device to the synchronous detection sensor, The timing at which each light beam scans the synchronization detection sensor is set to be different between the polygon mirror at one stage and the polygon mirror at the other stage with respect to the timing to scan each scanning surface (for each stage). The reflection mirror is arranged so that one reflection mirror has a different angle to the main scanning direction with respect to the other reflection mirror), so that the light beam from the light source is divided into a plurality of light beams, and each of the divided light beams When the beam is deflected and scanned by the polygon mirror at each stage, the effective scanning period that can be used for scanning each light beam is not shortened, and the polygon mirror at each stage is not shortened. Each synchronization detection signals output from the synchronization detection sensor by the incidence of the light beam from the elevation plane it is possible to easily determine. Therefore, it is possible to ensure a time outside the timing for scanning the surface to be scanned of the photosensitive drum, and to sufficiently ensure the lighting time of the light source for performing synchronization detection and APC.

In addition, as an optical element for guiding each light beam deflected and scanned by each stage of the polygon mirror to the synchronous detection sensor, elements other than the above-described reflection mirrors may be used.
Further, it is possible to easily determine which polygon mirror is used for scanning by measuring the time difference in the interval between detection signals output from the synchronization detection sensor.
Furthermore, if the angle of the reflection mirror for each stage with respect to the main scanning direction can be adjusted, the time difference of the synchronization detection pulse is increased, the measurement clock of the circuit for measuring the time difference is dropped, and the number of counter bits is reduced. It is also possible to do.

  Furthermore, the light beams are synchronized with an optical element for guiding each light beam deflected and scanned by a polygon mirror provided in three or more stages on the rotation axis of the deflector of the optical scanning device to the synchronization detection sensor. The scanning timing of the detection sensor is provided so that the polygon mirror of one stage differs from the polygon mirror of the other stage with respect to the timing of scanning each surface to be scanned (the reflection mirror for each stage is It is also possible to arrange one reflecting mirror so that the angle with respect to the main scanning direction differs from the other reflecting mirror. In this case, among the three or more stages of polygon mirrors, when the light beam scanned by the polygon mirrors at different stages of scanning the synchronization detection sensor is detected by the synchronization detection sensor, it is output from the synchronization detection sensor. Since it can be determined from the synchronization detection signal that scanning is performed with a polygon mirror at a stage where the synchronization detection sensor is scanned at a different timing, scanning with which polygon mirror is performed based on the synchronization detection signal output from the synchronization detection sensor thereafter. Can be determined.

  The present invention exposes a photosensitive member by scanning various types of image forming apparatuses such as copying machines, printers, facsimile machines, digital multi-function peripherals (MFPs), etc., from monochromatic to full color, particularly laser beams. The present invention can be used for a light beam scanning device and an image forming apparatus provided with the light beam scanning device.

DESCRIPTION OF SYMBOLS 1,1 ': Semiconductor laser 3, 3': Coupling lens 4: Half mirror prism 4a: Half mirror 4b: Total reflection surface 5a, 5b: Cylindrical lens 7: Deflector 8a, 8b: 1st scanning lens 9a, 9b : Optical path bending mirrors 10a and 10b: Second scanning lenses 11a to 11d: Photosensitive drums 12a to 12d: Charging units 13a to 13d: Toner cartridges 14a to 14d: Transfer roller 15: Intermediate transfer belt 16: Intermediate transfer roller 17: Intermediate Transfer belt cleaning device 18: Transfer device 19: Registration roller pair 20: Fixing device 21: Paper discharge device 22: Optical scanning device 30: Light shielding member 50: Control unit 51: Light source control unit 52: Data selection unit 53: Mirror discrimination unit 53a: Synchronization detection measurement unit 53b: Comparison determination unit 60a, 60b: Synchronization detection sensor 65: Image processing unit 71: Upper polygon mirror 72: Lower polygon mirror 81, 82a, 82b: Reflection mirror

JP 2005-92129 A JP 2008-58800 A

Claims (5)

Deflecting means having a plurality of rotating polygonal mirrors provided in a plurality of stages by shifting the angles of the reflecting surfaces to each other in the rotation direction on a common rotation axis, and dividing the light beam from the light source into a plurality of light beams; A light beam splitting means for making the split light beams enter the rotary polygon mirrors at different stages, and a common means for detecting the light beams deflected and scanned by the rotary polygon mirrors at the stages of the deflection means. A plurality of scanned surfaces that rotate in the sub-scanning direction are orthogonal to the sub-scanning direction. An optical scanning device that scans in a main scanning direction and writes an image on each scanned surface based on a detection timing by the detection unit,
An optical element for guiding each light beam deflected and scanned by the rotary polygon mirror at each stage to the detection means, and the timing at which each light beam scans the detection means scans each scanning surface. An optical scanning device, wherein the optical scanning device is provided so as to be different between a rotating polygon mirror of one stage and a rotating polygon mirror of another stage with respect to timing. The optical scanning device according to claim 1,
The optical element comprises a reflecting mirror for each stage arranged to guide each light beam deflected and scanned by the rotary polygon mirror of each stage to the detection means, respectively.
An optical scanning device characterized in that the reflecting mirrors for the respective stages are arranged so that one of the reflecting mirrors has a different angle with respect to the other scanning mirror with respect to the main scanning direction. The multi-stage rotary polygon mirror is a two-stage rotary polygon mirror;
3. The optical scanning device according to claim 1, wherein a vertex of the rotating polygon mirror of the other stage is arranged so as to overlap a perpendicular bisector of the reflecting surface of the rotating polygon mirror of one stage. 4. . In the optical scanning device according to any one of claims 1 to 3,
An optical scanning apparatus comprising: a measuring unit that measures a time difference between intervals of detection signals output from the detection unit.   5. The optical scanning device according to claim 1, and a plurality of image carriers each having a scanning surface on which each of the light beams is scanned by the optical scanning device. Image forming apparatus.

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