JP2011025446A - Optical writing apparatus and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical writing apparatus securing an optical path of synchronous light in the optical writing apparatus while reducing the number of components of the optical writing apparatus. <P>SOLUTION: The optical writing apparatus 20 includes semiconductor lasers 30a, 30b; a polygon mirror 22 deflecting optical beams emitted from the semiconductor lasers 30a, 30b: a scanning optical system 23 having a plurality of long-sized optical elements including a dichroic mirror 38 and converging the deflected optical beams on a photoconductor drum 9 to form an electrostatic latent image; and a photodiode 24 receiving optical beams for synchronous detection. The dichroic mirror 38 reflects the optical beams for synchronous detection toward the other end inside the dichroic mirror 38 by a reflecting surface formed at one longitudinal end and transmits the optical beams in a main scanning direction inside the dichroic mirror 38, and the photodiode 24 receives the optical beams for synchronous detection transmitted inside the dichroic mirror 38. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical writing apparatus, and more particularly, to an optical writing apparatus in an image forming apparatus such as a copying machine, a printer, a facsimile machine, and a multifunction machine that employs an electrophotographic system.

  In recent years, market demands for image forming apparatuses include size reduction, weight reduction, and cost reduction. Particularly, a desktop type color image forming apparatus has a large number of components, and therefore tends to be very large as compared with a conventional monochrome image forming apparatus, and the market demand for downsizing is high. One factor for the increase in the size of such an image forming apparatus is that an optical writing apparatus applied to an image forming apparatus that has been commercially available has increased in the thickness direction.

  That is, such a conventional optical writing apparatus irradiates laser beams from a plurality of light sources onto the scanning surfaces of the respective image carriers by turning the optical paths three-dimensionally using a plurality of reflecting mirrors. For this reason, the above-described optical writing device tends to increase in the thickness direction. In particular, in a color tandem type image forming apparatus, the laser beam corresponding to each photoconductor is shifted in the sub-scanning direction to prevent interference of each optical path or optical element. It has become. For this reason, in order to avoid an increase in the size of the optical writing device as described above, an optical writing device that has been made thinner and smaller has been proposed.

  In general, an optical writing apparatus includes a light source, a deflecting unit that deflects laser light from the light source, a scanning optical system that guides the laser light deflected by the deflecting unit to a surface to be scanned of the image carrier, and a deflecting unit. A reflection mirror that reflects a part of the laser beam deflected by the reflection light as a synchronization light, and a synchronization detection means that detects the synchronization light reflected by the reflection mirror, and the synchronization detection means detects the synchronization light. There is also known an apparatus in which a writing position for forming an electrostatic latent image on an image carrier is determined. In such an optical writing device, a reflection mirror for synchronization detection for reflecting the synchronization light is required as a component, and a layout space for holding the reflection mirror for synchronization detection is also required. . For this reason, in such an optical writing device, in addition to the above-described factors of increasing the size of the optical writing device, from the viewpoint of increasing the number of components and securing the layout space for holding the synchronous mirror for detecting synchronization. However, there is a problem that an increase in the size of the optical writing device cannot be avoided.

  Therefore, conventionally, as an optical writing apparatus that responds to such a problem, one surface of a mirror holding member that holds an optical path folding mirror that is one of optical elements constituting a scanning optical system is used as a mirror surface, and the laser is reflected by this mirror surface. It is known that the light is guided to the synchronization detection means, thereby increasing the degree of freedom of the installation position of the synchronization detection mirror and the synchronization detection means and contributing to the miniaturization of the optical writing device (for example, , See Patent Document 1).

  Also, as an optical writing device that reduces the number of components, the laser light emitted from the light source is deflected by the deflecting means and deflected via the scanning optical system including the first scanning lens, the second scanning lens, and dust-proof glass. The irradiated laser beam is irradiated onto the surface to be scanned of the image carrier, and a part of the deflected laser beam is reflected on the first surface facing the deflection unit of the dust-proof glass as the synchronization light, and the reflected synchronization light is reflected. Is also known that is detected by synchronization detection means (see, for example, Patent Document 2).

  In the conventional optical writing device described in Patent Document 2, the dust-proof glass functions as a scanning optical system that guides the changed laser light to the surface to be scanned, and as a reflection mirror for synchronization detection for reflecting the synchronization light. By combining this function, the number of components is reduced.

  However, in any of the optical writing apparatuses described in Patent Document 1 and Patent Document 2 described above, a part of the component parts is provided with a function as a reflection mirror for synchronization detection, thereby reducing the number of component parts. However, since many scanning optical elements such as scanning imaging elements and long mirrors are arranged, the space in the optical writing device is limited. Therefore, it is difficult to arrange the optical path of the synchronization light in such a limited space so as to pass between these scanning imaging elements and scanning optical elements.

  In particular, as described above, as the optical writing device becomes thinner and smaller, the degree of freedom in optical design decreases, and it becomes extremely difficult to secure the optical path of the synchronous light in the optical writing device. It is coming.

  The present invention has been made in view of the above-described conventional problems, and is capable of ensuring the optical path of the synchronous light in the optical writing apparatus while reducing the number of components of the optical writing apparatus. An object is to provide an apparatus.

  In order to achieve the above object, an optical writing device according to the present invention includes a plurality of laser light sources that emit laser beams having different wavelengths, and a deflector that deflects the laser beams emitted from the laser light sources in a main scanning direction. A scanning optical system having a plurality of long optical elements elongated in the main scanning direction, and condensing the laser beam deflected by the deflector onto an image carrier to form an electrostatic latent image; An optical writing device comprising: a synchronization detection unit configured to receive laser light deflected by a deflector as synchronization light and detect a writing start position in a main scanning direction in the image carrier; Among the long optical elements, any one of the long optical elements has a reflecting surface for synchronization detection formed at one end portion in the longitudinal direction, and the synchronous light incident inside the long optical element is synchronized with the sync light. The main scanning direction due to the reflective surface for detection Reflecting and transmitting the inside of the long optical element in the main scanning direction toward the other end in the longitudinal direction, and the synchronization detection unit is disposed in the vicinity of the other end of the long optical element And receiving the synchronized light transmitted through the long optical element in the main scanning direction.

  With this configuration, according to the present invention, any one of the plurality of long optical elements has a reflection detection surface for synchronization detection at one end portion in the longitudinal direction, and the long optical element is provided inside the long optical element. The incident sync light is reflected by the sync detection reflecting surface in the main scanning direction and transmitted through the long optical element in the main scanning direction toward the other end in the longitudinal direction. Since it is arranged in the vicinity of the other end of the long optical element so as to receive the synchronized light transmitted through the inside of the long optical element in the main scanning direction, it is arranged in the main scanning direction inside the long optical element that is not originally used. The optical path of the synchronization light can be arranged over the entire area. Therefore, even when the optical writing device is made thinner and smaller, the optical path of the synchronous light in the optical writing device can be ensured while reducing the number of components of the optical writing device.

  In the optical writing device according to the present invention, the optical path length of the synchronization light emitted from the light source and received by the synchronization detection unit via the deflector is emitted from the light source and passed through the deflector. The long optical element and the synchronization detection unit are arranged so as to have an optically equivalent distance to the optical path length of the scanning light that is a laser beam condensed on the image carrier.

  With this configuration, in the present invention, the long optical element and the synchronization detection unit are arranged so that the optical path length of the synchronization light and the optical path length of the scanning light have an optically equivalent distance. The optical path length of the synchronized light and the optical path length of the scanning light condensed on the image carrier can be made substantially coincident. For this reason, the synchronization light is received by the synchronization detection unit at a position narrowed to a beam diameter substantially equal to the beam diameter of the scanning light condensed on the image carrier. Therefore, on the light receiving surface of the synchronization detection unit, the synchronization light having a beam diameter substantially equal to the beam diameter of the scanning light on the image carrier can be received, and the synchronization detection accuracy can be improved.

  In the optical writing device according to the present invention, the scanning optical system is arranged so that at least the laser light deflected by the deflector is incident as the plurality of long optical elements, and the laser light is incident thereon. A first long optical element that transmits or reflects the laser light according to a direction, and a second long optical that transmits or reflects the laser light after passing through the first long optical element according to a wavelength. An element, and a third long optical element that reflects the laser light that has passed through the second long optical element toward the image carrier.

  With this configuration, according to the present invention, any one of the first long optical element, the second long optical element, and the third long optical element has one end in the longitudinal direction. The synchronous light that is incident on the inside of the long optical element is reflected in the main scanning direction by the synchronous detection reflective surface and is directed toward the other end in the longitudinal direction. The inside of the element is transmitted in the main scanning direction, and the synchronization detection unit is disposed in the vicinity of the other end of the long optical element so as to receive the synchronous light transmitted through the inside of the long optical element in the main scanning direction. Therefore, the optical path of the synchronous light can be arranged in the main scanning direction inside the long optical element that is not originally used. Therefore, even when the optical writing device is made thinner and smaller, the optical path of the synchronous light in the optical writing device can be ensured while reducing the number of components of the optical writing device.

  Further, in the optical writing device according to the present invention, the reflection surface for synchronization detection causes the synchronization light incident from the entrance surface of the long optical element facing the deflector to pass through the inside of the long optical element. It comprises a mirror surface portion that reflects in the main scanning direction and an antireflection portion that prevents reflection of laser light other than the synchronizing light.

  With this configuration, according to the present invention, the synchronization detection reflection surface includes a mirror surface portion that reflects the synchronization light in the main scanning direction inside the long optical element, and an antireflection portion that prevents reflection of laser light other than the synchronization light. The mirror surface part can reflect only the sync light toward the sync detection part and reflect the inside of the long optical element in the main scanning direction, and the anti-reflection part reflects the laser light other than the sync light. It is possible to prevent the laser light other than the synchronization light from being reflected and become ghost light.

  In the optical writing device according to the present invention, the long optical element on which the synchronization detection reflecting surface is formed has an end surface of the other end facing the synchronization detection unit orthogonal to the main scanning direction. The synchronous detection unit is formed with a convex curved surface so that the beam diameter of the synchronous light is reduced in the sub-scanning direction.

  With this configuration, according to the present invention, the end surface of the other end of the long optical element on which the synchronization detection reflecting surface is formed is a curved surface having power in the sub-scanning direction, and is convex toward the synchronization detection unit. Since it is configured by a curved surface, the beam diameter of the synchronization light received by the synchronization detection unit can be reduced in the sub-scanning direction by this curved surface, and the light intensity of the synchronization light incident on the synchronization detection unit can be increased. Therefore, it is not necessary to provide a separate optical element for synchronization detection for condensing the synchronization light on the synchronization detection unit, and the optical path of the synchronization light in the optical writing apparatus while reducing the number of components of the optical writing apparatus. Can be secured.

  The optical writing device according to any one of claims 1 to 5, wherein the deflector is used as a common deflector, and the plurality of light sources and the scanning device are used. The optical system and the synchronization detection unit are respectively arranged substantially symmetrically on both sides of the deflector, and each of the plurality of laser beams emitted from the plurality of light sources is condensed on the four image carriers, An electrostatic latent image is formed on the four image carriers.

  With this configuration, the present invention is configured even when the optical writing device applied to the image forming apparatus capable of forming a full-color image having four image carriers is thinned and downsized. While reducing the number of parts, the optical path of the synchronous light in the optical writing device can be secured.

  The image forming apparatus according to the present invention includes a plurality of image carriers, an optical scanning unit that individually scans the image carriers and forms an electrostatic latent image on the image carrier, and the image A plurality of developing means for individually developing the electrostatic latent images formed on the carrier to make visible images, and the visible images obtained on the image carrier by the development are superimposed on the transfer body, respectively. An image forming apparatus including the optical writing device according to any one of claims 1 to 6 as the optical scanning unit.

  With this configuration, the present invention secures the optical path of the synchronous light in the optical writing device while reducing the number of components of the optical writing device even when the optical writing device is reduced in thickness and size. It is possible to provide an image forming apparatus including an optical writing device that can perform the above operation.

  The image forming apparatus according to the present invention has a configuration that is a tandem type full-color image forming apparatus in which the plurality of image carriers are composed of four image carriers corresponding to different colors.

  With this configuration, the present invention secures the optical path of the synchronous light in the optical writing device while reducing the number of components of the optical writing device even when the optical writing device is reduced in thickness and size. It is possible to provide a tandem type full-color image forming apparatus provided with an optical writing device capable of performing the above.

  According to the present invention, it is possible to provide an optical writing device that can secure the optical path of synchronous light in the optical writing device while reducing the number of components of the optical writing device.

1 is a cross-sectional configuration diagram illustrating an example of an image forming apparatus including an optical writing device according to an embodiment of the present invention. It is a perspective view which shows the principal part structure of the optical writing device which concerns on embodiment of this invention. It is a top view which shows the principal part structure of the optical writing device which concerns on embodiment of this invention. 1 is a cross-sectional view showing an optical writing device according to an embodiment of the present invention. It is a figure which shows a part of scanning optical system of the optical writing device which concerns on embodiment of this invention, and the optical path of synchronous light, Comprising: (a) is a top view, (b) is a side view. It is a partial enlarged view of the dichroic mirror in the optical writing device concerning an embodiment of the invention, (a) is a top view showing one end, and (b) shows one end. It is a side view.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing an embodiment of an image forming apparatus to which an optical writing apparatus according to the present invention is applied, and shows an example in which the image forming apparatus is applied to a direct transfer tandem type full-color printer. The image forming apparatus is not limited to the direct transfer method, and may be an intermediate transfer method in which the toner image on the photosensitive member is primarily transferred to the intermediate transfer member and then secondarily transferred to the transfer medium. It may be a copying machine, a facsimile machine, or a multifunction machine having a plurality of these functions. The optical writing apparatus according to the present invention is not limited to a full-color machine of four colors, but can be applied to an image forming apparatus including a multi-color machine using a plurality of colors, for example, two colors of toner.

First, the configuration of the image forming apparatus will be described.
As shown in FIG. 1, a tandem type full-color printer 1 as an image forming apparatus employs a direct transfer system that directly transfers a toner image on a photosensitive member to a transfer medium as a transfer system. Four image forming units 3Y, 3C, 3M, and 3K (hereinafter simply referred to as image forming units 3) corresponding to magenta and black are provided at the center of the apparatus main body 2. The image forming units 3 are arranged side by side along the upper circumferential surface of the direct transfer belt 4 as a transfer unit.

  The direct transfer belt 4 is wound around support rollers 5 and 6 and is driven to rotate counterclockwise in the drawing by a driving means (not shown). A registration roller 7 is provided on the side of the support roller 6 arranged on the right side in the drawing, and a fixing device 8 is provided on the side of the support roller 5 arranged on the left side in the drawing. Yes.

  Each image forming unit 3 has the same configuration except for the color of the toner to be handled. The photosensitive drums 9Y, 9C, 9M and 9K (hereinafter simply referred to as photosensitive drums) as image carriers corresponding to the respective colors. Body drum 9). Around the photosensitive drum 9, a charging roller 10 as a charging unit and a developing device 11 are arranged.

A transfer roller 12 as a transfer unit is disposed inside the direct transfer belt 4 and at a position facing the photosensitive drum 9 with the direct transfer belt 4 interposed therebetween. Note that the direct transfer belt 4 is adapted to the case where image formation is performed only in black (K), such as monochrome printing, by a transfer roller 12 with respect to the photosensitive drum 9K corresponding to black (K). It is configured to always contact. On the other hand, the transfer belt 4 directly contacts and separates from the other photosensitive drums 9Y, 9C, and 9M by the function of a movable tension roller.
Further, a toner storage container 14 is provided in the upper part of the developing device 11, and developer corresponding to each color, so-called toner, is stored in the toner storage container 14.

An optical writing device 20 is provided above the four image forming units 3 and at the top of the apparatus main body 2. This optical writing device 20 corresponds to the tandem full-color printer 1 capable of forming full-color images of four colors, and forms an optical beam L corresponding to each color as a laser beam light-modulated based on image information. The surface of the photosensitive drum 9 of the unit 3 is irradiated with each. Here, the photosensitive member to be scanned is not limited to a drum-like one such as the photosensitive drum 9, but may be a belt-like photosensitive member, for example.
Details of the optical writing device 20 will be described later.

  A paper feed tray 16 is disposed below the direct transfer belt 4 and at the lowermost part of the apparatus body 2, and sheets are stacked on the paper feed tray 16. Further, a separation sheet feeding unit 17 is disposed on the side of the sheet feeding tray 16 and upstream of the registration roller 7 in the sheet conveying direction. The separation sheet feeding unit 17 is connected to the sheet feeding tray 16. The uppermost sheet is separated from the stacked sheet bundle and fed.

Next, an image forming operation in the tandem type full color printer 1 configured as described above will be described.
In the image forming operation, first, each photosensitive drum 9 of the image forming unit 3 is rotationally driven in the clockwise direction in the drawing by a driving unit (not shown), and the surface of each photosensitive drum 9 is predetermined by the charging roller 10 in accordance with the rotational driving. It is uniformly charged to the polarity. The surface of each photosensitive drum 9 charged in this way is irradiated with a light beam based on single-color image information that is color-separated into yellow, magenta, cyan, and black by the optical writing device 20, respectively. Thereby, an electrostatic latent image is formed on the surface of each photosensitive drum 9. The electrostatic latent image formed in this manner is provided with toner of each color from each developing device 11, and is visualized as a toner image.

  On the other hand, the paper is separated and fed from the paper feed tray 16 by the separation paper feeding unit 17. The fed paper is once abutted against the registration roller 7 and then sent directly to the transfer belt 4 in synchronism with the above-described visualization. Next, the sheet is directly sucked and conveyed by the transfer belt 4. At this time, the toner images of the respective colors are sequentially transferred and transferred onto the conveyed paper by the action of the transfer rollers 12 at the transfer positions where the photosensitive drums 9 and the transfer rollers 12 are in contact with each other. As a result, a full-color toner image is carried on the paper.

  The paper carrying the full-color toner image is directly separated from the transfer belt 4 and sent to the fixing device 8. Thereafter, in the fixing device 8, the toner image is melt-fixed on the paper by heat and pressure. The sheet on which the toner image is fixed is discharged out of the apparatus and stacked on a discharge tray (not shown).

  Further, residual toner adhering to the surface of the photosensitive drum 9 after the toner image is transferred is removed from the surface of the photosensitive drum 9 by a cleaning unit (not shown). Next, the surface potential on the surface of the photosensitive drum 9 is removed by a static eliminator (not shown) to prepare for the next image formation.

  In the image forming operation described above, the case of forming a full-color image of four colors has been described. However, the present invention is not limited to this. For example, a single-color image is formed using any one of the image forming units 3. It is also possible to form a two-color or three-color image. In the case of monochrome printing, image formation is performed using only the image forming unit 3K corresponding to black (K).

Next, the optical writing device 20 according to the present embodiment will be described.
As shown in FIGS. 2 to 4, the optical writing device 20 includes a light source unit 21, a polygon mirror 22 as a deflector, a scanning optical system 23, and a photodiode 24 as a synchronization detection element. These components are arranged in the housing 27, respectively. The optical writing device 20 includes one light source unit 21, a scanning optical system 23, and two photodiodes 24, each having a single polygon mirror 22 in common. The light source unit 21 scans on both sides around the polygon mirror 22. The optical system 23 and the photodiode 24 are arranged substantially symmetrically. Further, as shown in FIGS. 2 and 4, the optical writing device 20 scans the four photosensitive drums 9 as scanning objects.

  In addition, since the structure and function of the light source unit 21, the scanning optical system 23, and the photodiode 24 arranged on both sides of the polygon mirror 22 are the same, each component arranged on the left side in the drawing will be described below. For each component arranged on the right side in the figure, components having the same configuration and function are denoted by the same reference numerals and description thereof is omitted.

  The light source unit 21 includes semiconductor lasers 30a and 30b as laser light sources, collimating lenses 31a and 31b, a beam combining prism 32 as a beam combining unit, and a cylindrical lens 33. The light source unit 21 may be provided with an aperture having an opening for shaping the laser light after passing through the collimating lenses 31a and 31b into a desired shape.

  The semiconductor lasers 30a and 30b are arranged side by side in the sub-scanning direction, and emit light beams as laser beams having different polarization directions and different wavelengths. Here, as a light beam emitted from the semiconductor lasers 30a and 30b, one having a wavelength band corresponding to a dichroic mirror described later is used.

  In the light source unit 21 having such semiconductor lasers 30a and 30b, the light beams emitted by the semiconductor lasers 30a and 30b are converted into parallel light beams by the collimating lenses 31a and 31b. Next, the light beams converted into parallel light beams by the collimating lenses 31 a and 31 b are combined on the same axis by the beam combining prism 32, and are emitted toward the deflecting surface of the polygon mirror 22 through the cylindrical lens 33.

  Note that, by using the beam combining prism 32 as described above, the optical path lengths of the two light beams emitted from the semiconductor lasers 30a and 30b are different on the upstream side of the polygon mirror 22. For example, the arrangement of a dichroic mirror described later is used. By adjusting the position, the optical path lengths of the two light beams up to the photosensitive drum 9 can be made the same.

  The polygon mirror 22 has a plurality of deflection surfaces and is rotated at a high speed by a polygon motor (not shown). In the polygon mirror 22 configured as described above, the light beams emitted by the semiconductor lasers 30a and 30b are deflected and scanned in the main scanning direction at an equal angle toward the scanning optical system 23 by the rotation of the polygon mirror 22.

  The scanning optical system 23 includes an fθ lens 35, a polarization beam splitter 36, a λ / 4 wavelength plate 37, a dichroic mirror 38, and a reflection mirror 39, and in particular, the polarization beam splitter 36, the dichroic. The mirror 38 and the reflection mirror 39 are long optical elements in the main scanning direction. In the present embodiment, the deflection beam splitter 36, the dichroic mirror 38, and the reflection mirror 39 described above constitute a plurality of long optical elements, and the deflection beam splitter 36 is the first long optical element, the dichroic mirror 38. Is a second long optical element, and the reflection mirror 39 is a third long optical element.

  The fθ lens 35 is disposed at a position closest to the polygon mirror 22 among the constituent elements constituting the scanning optical system 23, and optically corrects the light beam deflected and scanned by the polygon mirror 22 at equal intervals. ing.

The deflecting beam splitter 36 has a function of separating the light beam according to the polarization direction depending on the rotation angle of π / 2 of the light beam, and has a characteristic of transmitting or reflecting the light beam according to the incident direction of the light beam. ing.
The λ / 4 wavelength plate 37 is provided integrally with the deflecting beam splitter 36, and rotates the polarization direction of the light beam by π / 4.

  The dichroic mirror 38 is a multilayer dielectric mirror installed perpendicular to the light beam, and transmits or reflects the light beam according to the wavelength band of the light beam. The boundary between transmission and reflection of the light beam varies depending on the multilayer film added to the dichroic mirror. However, as the dichroic mirror 38 described above, it is preferable to use, for example, a boundary around the wavelength of 750 nm. In this case, it is necessary to select the above-described boundary, that is, a wavelength band around a wavelength of 750 nm, as a light beam emitted from the semiconductor lasers 30a and 30b. For this reason, for example, as the semiconductor lasers 30a and 30b, a semiconductor laser that emits visible light having a wavelength of about 650 nm and a semiconductor laser that emits infrared light having a wavelength of about 780 nm can be used. As the dichroic mirror 38, either a heat ray reflective type or a heat ray transmissive type can be applied.

In the scanning optical system 23 configured in this way, two light beams deflected and scanned by the polygon mirror 22 (light beams having the same polarization direction and different wavelengths) pass through the λ / 4 wavelength plate 37 through the fθ lens 35. pass. Then, the two light beams that have passed through the λ / 4 wavelength plate 37 are incident on the dichroic mirror 38 in a state where the light beams are rotated by π / 4 from the time of emission. At this time, the two light beams are transmitted by the dichroic mirror 38 for one light beam, reflected for the other light beam, and separated into transmitted light and separated light.
Then, the light beam that has passed through the dichroic mirror 38 is reflected by the reflection mirror 39 and irradiated onto the surface to be scanned of the photosensitive drum 9Y.

  On the other hand, the light beam reflected by the dichroic mirror 38 is returned again to the λ / 4 wavelength plate 37 and is incident on the polarization beam splitter 36 again. At this time, the light beam reflected by the dichroic mirror 38 passes through the λ / 4 wavelength plate 37 again to rotate the polarization direction again by π / 4, and is rotated by π / 2 from the time of emission. The light is incident on the polarization beam splitter 36 in the state of a beam. Then, the light beam incident on the polarization beam splitter 36 again is reflected by the deflection beam splitter 36 and is irradiated onto the surface to be scanned of the photosensitive drum 9C.

In the present embodiment, the two light beams emitted from the semiconductor lasers 30 a and 30 b are both linearly polarized P waves, for example, and one light beam is π by the λ / 4 wavelength plate 37. After being rotated by / 4 and passing through the dichroic mirror 38 in the state of circularly polarized light, the photosensitive drum 9Y is irradiated. On the other hand, the other light beam is rotated by π / 4 by the λ / 4 wavelength plate 37 to become circularly polarized light, and then reflected by the dichroic mirror 38 and passes through the λ / 4 wavelength plate 37 again. Then, the polarization direction is again rotated by π / 4, and the photoconductor 9C is irradiated in the state of a linearly polarized S wave.
Therefore, the photosensitive drums 9Y and 9C are scanned by the light beams emitted from the semiconductor lasers 30a and 30b.

The photodiode 24 is disposed in the vicinity of the side portion of the dichroic mirror 38 and outside the writing range in the main scanning direction, and is irradiated with a light beam emitted from the semiconductor lasers 30a and 30b. That is, the photodiode 24 receives the light beam deflected by the polygon mirror 22 as synchronization light, and detects the writing start position in the main scanning direction on the surface to be scanned of the photosensitive drum 9. Therefore, since the optical writing device 20 can detect the position of the scanning line (light beam) by receiving the light beam emitted from the semiconductor lasers 30a and 30b as the synchronization light, the optical writing device 20 can detect the write timing. Can be controlled.
In the present embodiment, the photodiode 24 described above constitutes a synchronization detection unit.

  By the way, with the recent reduction in thickness and size of an optical writing device, in an optical writing device in which many optical elements are arranged, a light beam (synchronous light irradiated to a synchronous detection element such as a photodiode) Hereinafter, it has become difficult to secure an optical path of a synchronization detection light beam.

  Therefore, in the optical writing device 20 according to the present embodiment, as shown in FIGS. 1 and 2, a part of the optical path A of the synchronization detection light beam (hereinafter referred to as the synchronization detection light beam optical path A) is included. It is arranged inside the dichroic mirror 38. Thus, in the optical writing device 20 according to the present embodiment, the synchronization detection light beam optical path A can be suitably secured by utilizing a space that is not originally used.

Hereinafter, with reference to FIG. 1, FIG. 2, FIG. 5 and FIG. 6, a specific configuration for securing the synchronization detection light beam path A will be described in detail.
As shown in FIGS. 1 and 2, in this embodiment, a dichroic mirror 38 is used as the synchronization detection light beam path A among the plurality of optical elements constituting the scanning optical system 23.

  As shown in FIGS. 5A and 5B, the dichroic mirror 38 is a long optical element that is long in the main scanning direction, and has one end 38a and the other end at both ends in the longitudinal direction. 38b.

  As shown in FIG. 6A, at one end 38a, there is a reflecting surface 38d that is inclined at a predetermined angle θ with respect to a side surface 38c (incident surface) that faces the polarizing beam splitter 36 (see FIG. 1). Is formed. The reflection surface 38d reflects the synchronization detection light beams emitted from the semiconductor lasers 30a and 30b in the main scanning direction inside the dichroic mirror 38 (see FIG. 5A). Here, the predetermined angle θ, that is, the angle θ formed by the side surface 38c and the reflecting surface 38d is such that the synchronous detection light beam reflected by the reflecting surface 38d passes through the dichroic mirror 38 and the other end 38b side. The angle is set so as to be incident on the light receiving surface of the photodiode 24 arranged in the above. In the present embodiment, the reflection surface 38d described above constitutes a synchronization detection reflection surface.

Further, as shown in FIGS. 6A and 6B, the above-described reflecting surface 38d is composed of a mirror surface portion 40 that is mirror-finished and an antireflection portion 41 that is provided with an antireflection film. Yes.
The mirror surface portion 40 is provided so as to extend in a direction substantially perpendicular to the main scanning direction at a substantially central portion of the reflection surface 38d, and the synchronization detection light beam emitted from the semiconductor lasers 30a and 30b is transmitted to the dichroic mirror 38. Reflected in the main scanning direction inside (see FIG. 5A).

  The antireflection part 41 is made of an antireflection film, and is provided on both sides of the mirror surface part 40 on the reflection surface 38d. Therefore, the reflective surface 38d is configured by an antireflection film at portions other than the mirror surface portion 40. For this reason, it is possible to prevent a light beam other than the synchronization detection light beam incident on the reflecting surface 38d from becoming ghost light that adversely affects the image quality.

As the antireflection film, for example, a multilayer film in which a thin dielectric film is superimposed is used. The multilayer film is formed by forming a thin film such as a metal oxide by, for example, vacuum deposition. In addition, a single layer film made of MgF ₂ , SiO, CeF ₃ or the like may be used as the antireflection film in addition to the multilayer film described above.

  Further, as shown in FIG. 5B, the other end 38b is configured by a curved surface in which an end surface 38e facing the photodiode 24 is convex toward the photodiode 24 side. That is, the end surface 38e is processed to have a convex curved surface having a power such that the beam diameter is reduced in the sub-scanning direction and the light beam for synchronization detection is incident on the light receiving surface of the photodiode 24. Therefore, when the synchronous detection light beam reflected by the reflecting surface 38d and transmitted through the dichroic mirror 38 is emitted from the other end 38b, the beam diameter is reduced in the sub-scanning direction.

  As shown in FIGS. 1 and 2, in the optical writing device 20 having the dichroic mirror 38 configured as described above, the light beams emitted from the semiconductor lasers 30a and 30b are used as light beams for synchronous detection. The light is deflected and scanned by the polygon mirror 22 through the collimating lenses 31a and 31b, the beam combining prism 32, and the cylindrical lens 33. Then, the deflection-scanned light beam for synchronous detection passes through the fθ lens 35 and the polarization beam splitter 36, passes through the λ / 4 wavelength plate 37, and is side surface 38c of the dichroic mirror 38 (see FIG. 6A). To the inside of the dichroic mirror 38. Next, as shown in FIGS. 5A and 5B, the synchronous detection light beam incident on the dichroic mirror 38 is reflected by the mirror surface portion 40 (see FIG. 6A) of the reflecting surface 38d. Thus, the light passes through the dichroic mirror 38 in the main scanning direction. Thereafter, the light beam for synchronization detection is emitted toward the photodiode 24 from the other end 38b in a state where the beam diameter is narrowed in the sub-scanning direction by the end surface 38e formed of a convex curved surface. 24 is incident on the light receiving surface.

  Further, in the present embodiment, the dichroic mirror 38 and the photodiode 24 are configured so that the optical path length of the synchronization detection light beam and the light beam as the scanning light applied to the scanned surface of each photosensitive drum 9 (FIG. 1 and FIG. The optical path lengths shown in FIG. 2 are arranged in the housing 27 of the optical writing device 20 so as to have an optically equivalent distance.

  As described above, in the present embodiment, among the plurality of long optical elements constituting the scanning optical system 23, the dichroic mirror 38 has the reflecting surface 38d at one end 38a in the longitudinal direction, and the dichroic mirror The synchronous detection light beam incident on the inside of the laser beam 38 is reflected by the reflecting surface 38d in the main scanning direction and transmitted through the ichroic mirror 38 in the main scanning direction toward the other end 38b in the longitudinal direction. Let The photodiode 24 is disposed in the vicinity of the other end 38b of the dichroic mirror 38, and receives the synchronization detection light beam that has passed through the dichroic mirror 38 in the main scanning direction. Therefore, the optical writing device 20 according to the present embodiment can arrange the synchronization detection light beam optical path A in the main scanning direction inside the dichroic mirror 38 that is not originally used. Therefore, even when the optical writing device 20 is reduced in thickness and size, the synchronization detection light beam path A in the optical writing device 20 can be secured while reducing the number of components.

  In the present embodiment, the dichroic mirror 38 and the photodiode 24 are configured so that the optical path length of the light beam for synchronization detection and the optical path length of the light beam as scanning light are optically equivalent to each other. Accordingly, the optical path length of the synchronization detection light beam received by the photodiode 24 can be made substantially equal to the optical path length of the light beam as the scanning light. For this reason, the synchronization detection light beam is received by the photodiode 24 at a position narrowed to a beam diameter substantially equal to the beam diameter of the scanning light condensed on the photosensitive drum 9. Therefore, on the light receiving surface of the photodiode 24, the synchronization detection light beam having a beam diameter substantially equal to the beam diameter of the scanning light on the photosensitive drum 9 can be received, and the synchronization detection accuracy is improved. be able to.

  In the present embodiment, the reflecting surface 38d reflects the light beam other than the sync detection light beam and the mirror surface portion 40 that reflects the light beam for synchronization detection in the main scanning direction inside the dichroic mirror 38. Since the anti-reflection portion 41 is prevented, the mirror surface portion 40 can reflect only the light beam for synchronization detection toward the photodiode 24 and reflect the inside of the dichroic mirror 38 in the main scanning direction. Further, the reflection preventing unit 41 can prevent a light beam other than the synchronization detection light beam from being reflected, thereby preventing a light beam other than the synchronization detection light beam from being reflected and becoming ghost light. be able to.

  In the present embodiment, the end surface 38e of the other end 38b of the dichroic mirror 38 is a curved surface having power in the sub-scanning direction, and is formed by a curved surface convex toward the photodiode 24. With this curved surface, the beam diameter of the synchronization detection light beam received by the photodiode 24 is reduced in the sub-scanning direction, and the light intensity of the synchronization detection light beam incident on the photodiode 24 can be increased. Therefore, it is not necessary to separately provide an optical element for synchronization detection for condensing the light beam for synchronization detection on the photodiode 24, and the optical writing device 20 can be reduced while reducing the number of components of the optical writing device 20. It is possible to secure the optical beam path A for synchronization detection in the inside.

  In the present embodiment, the light beams emitted from the semiconductor lasers 30a and 30b are combined by the beam combining prism 32. However, the present invention is not limited to this. For example, the semiconductor lasers 30a and 30b are arranged so as to have a predetermined angle without using the beam combining prism 32, and two light beams are placed at the same position in the main scanning direction of the polygon mirror 22. It is also possible to combine the two light beams by configuring so that the light beam is irradiated.

  In the present embodiment, the case where the long optical element used as the synchronization detection light beam optical path A is the dichroic mirror 38 has been described. However, the present invention is not limited to this, and other long optical elements such as polarization The beam splitter 36 and the reflection mirror 39 may be used as the synchronization detection light beam path A. In this case, also for the polarizing beam splitter 36 and the reflection mirror 39, one end portion in the longitudinal direction is constituted by the reflection surface as described above, and the side surface of the other end portion in the longitudinal direction is formed as a convex curved surface as described above. To be configured.

  As described above, the optical writing device according to the present invention has an effect that the optical path of the synchronous light in the optical writing device can be secured while reducing the number of components of the optical writing device, and the electrophotography For example, it is useful as an optical writing device or the like in an image forming apparatus such as a copying machine, a printer, a facsimile machine, and a multi-function machine that employs the system.

1 Tandem type full color printer (image forming device)
3 Image forming unit (developing means)
4 Direct transfer belt (transfer means)
9 Photosensitive drum (image carrier)
12 Transfer roller (transfer means)
20 Optical writing device (optical scanning means)
21 Light source 22 Polygon mirror (deflector)
23 Scanning Optical System 24 Photodiode (Synchronous Detection Unit)
30a, 30b Semiconductor laser (light source)
36 Polarizing beam splitter (long optical element, first long optical element)
38 Dichroic mirror (long optical element, second long optical element)
38a One end portion 38b The other end portion 38c Side surface 38d Reflecting surface (reflection surface for synchronization detection)
38e End face 39 Reflection mirror (long optical element, third long optical element)
40 Mirror surface part 41 Antireflection part

Japanese Patent Laid-Open No. 11-183811 JP 2003-315708 A

Claims (8)

A plurality of laser light sources each emitting laser light having different wavelengths;
A deflector for deflecting laser light emitted from the laser light source in a main scanning direction;
A scanning optical system having a plurality of long optical elements elongated in the main scanning direction, and condensing the laser beam deflected by the deflector onto an image carrier to form an electrostatic latent image;
An optical writing device comprising: a synchronization detector that receives the laser beam deflected by the deflector as synchronization light and detects a writing start position in a main scanning direction in the image carrier,
Among the plurality of long optical elements, any one of the long optical elements has the reflection light for synchronization detection formed at one end in the longitudinal direction, and the synchronous light incident on the long optical element. Is reflected in the main scanning direction by the reflection surface for synchronization detection and is transmitted through the inside of the long optical element toward the other end in the longitudinal direction in the main scanning direction.
The synchronization detector is disposed in the vicinity of the other end of the long optical element, and receives the synchronous light transmitted through the long optical element in the main scanning direction. apparatus.   A laser beam emitted from the light source and received by the synchronization detection unit via the deflector is emitted from the light source and condensed on the image carrier via the deflector. 2. The optical writing apparatus according to claim 1, wherein the long optical element and the synchronization detection unit are arranged so as to have an optically equivalent distance to an optical path length of scanning light that is light. The scanning optical system is at least as the plurality of long optical elements,
A first long optical element that is arranged so that the laser beam deflected by the deflector is incident thereon and transmits or reflects the laser beam according to an incident direction of the laser beam;
A second long optical element that transmits or reflects the laser light after passing through the first long optical element according to a wavelength;
3. The optical writing according to claim 1, further comprising: a third long optical element that reflects the laser light transmitted through the second long optical element toward the image carrier. apparatus.   The reflection surface for synchronization detection includes a mirror surface portion that reflects the synchronization light incident from the incident surface of the long optical element facing the deflector in the main scanning direction inside the long optical element, and 4. The optical writing device according to claim 1, further comprising an antireflection portion that prevents reflection of laser light other than the synchronization light.   In the long optical element on which the synchronization detection reflecting surface is formed, the end surface of the other end facing the synchronization detection unit has a beam diameter of the synchronization light in a sub-scanning direction orthogonal to the main scanning direction. 5. The optical writing device according to claim 1, wherein the optical writing device is configured with a convex curved surface on the side of the synchronization detection unit so as to be narrowed down. The optical writing device according to any one of claims 1 to 5,
The deflector is used as a common deflector;
The plurality of light sources, the scanning optical system, and the synchronization detection unit are disposed substantially symmetrically on both sides of the deflector, respectively.
A plurality of laser beams emitted from the plurality of light sources are respectively condensed on the four image carriers to form electrostatic latent images on the four image carriers. Optical writing device. A plurality of image carriers, optical scanning means for individually scanning the image carriers to form an electrostatic latent image on the image carrier, and an electrostatic latent image formed on the image carrier An image comprising: a plurality of developing means that individually develops a visible image; and a transfer means that superimposes and transfers the visible image obtained on the image carrier by the development onto the transfer body. A forming device,
An image forming apparatus using the optical writing device according to claim 1 as the optical scanning unit.   The image forming apparatus according to claim 7, wherein the plurality of image carriers are tandem type full-color image forming apparatuses including four image carriers corresponding to different colors.

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