JP2011158496A - Optical scanner and image forming apparatus equipped with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner in which a beam diameter can be optimized with a single aperture for a plurality of beam wavelengths without incurring cost increase. <P>SOLUTION: The optical scanner includes: a light source; a deflector which deflects a light beam L emitted from a light source; the aperture 29 having an aperture stop which stops down the light beam L on an optical path between the deflector and the light source; and an fθ lens which focuses the light beam L deflected with the deflector on a face to be scanned at a constant speed. In the optical scanner, a mounting part 30 for mounting the aperture 29 is provided, the angle of the face 30a on the side of the light source and the angle of the face 30b on the side opposite to the light source in the mounting part 30 are made to be different from each other in a main-scanning direction and/or a sub-scanning direction, and the aperture 29 is selectively mounted on either one of the faces 30a and 30b. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical scanning device that scans a surface to be scanned with a focused spot of a light beam, and an image forming apparatus such as a copying machine and a printer equipped with the optical scanning device.

  In an image forming apparatus such as a copying machine or a printer, an image carrier whose surface is uniformly charged by a charger is exposed and scanned by an optical scanning device, and an electrostatic latent image corresponding to image information is formed on the surface. The The electrostatic latent image is developed by a developing device using toner as a developer to be visualized as a toner image. The toner image is transferred onto a sheet by a transfer device and then heated and heated by a fixing device. A series of image forming operations is completed by discharging the sheet having the toner image fixed thereon by being pressed and fixed on the sheet.

  In such an image forming apparatus, an optical scanning device that exposes and scans an image bearing member converts a light beam emitted from a light source such as a laser diode into a collimated beam by a collimator lens, and deflects the collimated beam such as a polygon mirror that rotates at high speed. The light beam is reflected and deflected by a detector, and the deflected light beam is condensed by an fθ lens to form a condensed spot on an image carrier that is a surface to be scanned.

  By the way, the optimum spectral sensitivity characteristics differ depending on the type of image carrier (organic semiconductor (OPC) or amorphous silicon photoreceptor), and the optimum beam diameter varies depending on the specifications. The best one is selected. The appearance of an optical scanning device that uses a blue laser to obtain a higher resolution image is also conceivable.

  However, when light beams having different wavelengths are condensed using the same imaging optical system, the beam spot diameter on the image carrier varies due to the difference in wavelength.

  Therefore, normally, prepare a plurality of apertures (apertures) having an aperture stop of a size corresponding to the wavelength of the light beam to be used, and select an aperture having an aperture stop of the optimum size for the wavelength of the light beam. Assembling this into an optical scanning device has been performed. For this reason, it is necessary to prepare as many apertures as the number of wavelengths of the light beam to be used.

  In order to solve the above-described problem, Patent Document 1 discloses that the aperture stop through which a light beam passes is changed by rotating and bending a plate-like aperture in which an aperture stop (beam shaping hole) is formed to collect light. An optical scanning device that adjusts the beam diameter at a position has been proposed.

JP-A-6-265802

  However, in the optical scanning device proposed in Patent Document 1, since it is necessary to adjust the cross-sectional area of the aperture stop while rotating the aperture, it takes time to assemble and the adjustment mechanism requires many members. There is a problem that the cost increases.

  The present invention has been made in view of the above problems, and its objective is to perform optical scanning that can optimize the beam diameter with a single aperture for a plurality of beam wavelengths without increasing the cost. The present invention provides an apparatus and an image forming apparatus including the apparatus.

  In order to achieve the above object, an invention according to claim 1 includes a light source, a deflector for deflecting a light beam emitted from the light source, and an aperture for narrowing the light beam in an optical path between the deflector and the light source. In an optical scanning apparatus including an aperture having an aperture and an fθ lens that forms an image of the light beam deflected by the deflector on the surface to be scanned at a constant speed, a mounting portion for mounting the aperture is provided. The angle between the surface on the light source side and the surface on the opposite light source side is made different in the main scanning direction and / or the sub-scanning direction, and the aperture is selectively attached to any one of these surfaces.

  According to a second aspect of the present invention, in the first aspect of the invention, one surface of the mounting portion is perpendicular to the light beam emitting direction, and the other surface is inclined obliquely with respect to the light beam emitting direction. It is characterized by that.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the mounting portion is formed integrally with the housing.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the aperture is attached to any one surface of the attachment portion.

  An image forming apparatus according to a fourth aspect includes the optical scanning device according to any one of the first to third aspects.

  According to the present invention, by changing the mounting angle (tilt angle) of a single aperture, the aperture area of the aperture stop portion of the aperture can be adjusted, so that it depends on the wavelength of the light beam emitted from the light source. By adjusting the aperture angle and adjusting the aperture area of the aperture stop, it is possible to optimize the aperture for the wavelength of the light beam and optimize the diameter of the beam spot formed on the scanned surface. Can do. For example, one of the light source side and anti-light source side surfaces of the mounting portion is a surface perpendicular to the light beam emission direction, and the other surface is a surface inclined obliquely with respect to the light beam emission direction. If the aperture is attached at right angles to the light beam emission direction, the aperture area of the aperture stop of the aperture can be maximized, and the aperture can be used for light beams of short wavelengths. If it is mounted obliquely with respect to the beam emission direction, the aperture area of the aperture stop of the aperture can be adjusted to be small.

  Then, the aperture area of the aperture stop of the aperture is adjusted to the optimum size with respect to the wavelength of the light beam simply by mounting the aperture on the light source side or the non-light source side surface of the mounting portion according to the wavelength of the light beam. Therefore, a complicated adjustment mechanism and adjustment work are not required, and the beam diameter can be optimized with a single aperture for a plurality of beam wavelengths without increasing the cost. In this case, the wavelength of the light beam emitted from the light source being used can be easily identified by visually observing the mounting angle of the aperture.

1 is a side sectional view of an image forming apparatus (color laser printer) according to the present invention. 1 is a perspective view of an optical scanning device according to the present invention. It is a figure explaining the principle which adjusts the aperture area of the aperture stop by the attachment angle of an aperture. It is a main scanning sectional view of the aperture mounting portion of the optical scanning device according to the present invention. It is a sub-scan sectional view of the aperture mounting portion of the optical scanning device according to the present invention.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

[Image forming apparatus]
FIG. 1 is a side sectional view of a color laser printer as an embodiment of an image forming apparatus according to the present invention. The illustrated color laser printer is a tandem type, and a magenta image is formed at the center in the main body 100. The unit 1M, the cyan image forming unit 1C, the yellow image forming unit 1Y, and the black image forming unit 1K are arranged in tandem at regular intervals.

  Each of the image forming units 1M, 1C, 1Y, and 1K is provided with photosensitive drums 2a, 2b, 2c, and 2d, which are image carriers, and a charger 3a is disposed around each of the photosensitive drums 2a to 2d. , 3b, 3c, 3d, developing devices 4a, 4b, 4c, 4d, transfer rollers 5a, 5b, 5c, 5d and cleaning devices 6a, 6b, 6c, 6d are arranged, respectively.

Here, the photosensitive drums 2a to 2d are drum-shaped photosensitive members, and are rotationally driven at a predetermined process speed in a direction indicated by an arrow (counterclockwise) by a drive motor (not shown). The chargers 3a to 3d uniformly charge the surfaces of the photosensitive drums 2a to 2d to a predetermined potential by a charging bias applied from a charging bias power source (not shown).
Further, the developing devices 4a to 4d contain magenta (M) toner, cyan (C) toner, yellow (Y) toner, and black (K) toner, respectively, and are formed on the photosensitive drums 2a to 2d. In addition, the toner of each color is attached to each electrostatic latent image to visualize each electrostatic latent image as a toner image of each color.

  The transfer rollers 5a to 5d are arranged so as to be able to contact the photosensitive drums 2a to 2d via the intermediate transfer belt 7 in the respective primary transfer portions. Here, the intermediate transfer belt 7 is stretched between the driving roller 8 and the tension roller 9 and is disposed on the upper surface side of each of the photosensitive drums 2a to 2d. The driving roller 8 is a secondary roller. The transfer unit is disposed so as to be in contact with the secondary transfer roller 10 via the intermediate transfer belt 7. An optical density sensor 11 is disposed at a position facing the intermediate transfer belt 7 in the vicinity of the driving roller 8.

  Further, below the image forming units 1M, 1C, 1Y, and 1K in the printer main body 100, a total of four optical scanning devices 12 according to the present invention corresponding to the image forming units 1M, 1C, 1Y, and 1K are provided. The paper feed cassette 13 is detachably installed at the bottom of the printer main body 100 below each of these. A plurality of sheets (not shown) are stacked and accommodated in the sheet feeding cassette 13. In the vicinity of the sheet feeding cassette 13, the sheets are taken out from the sheet feeding cassette 13 and transported to the transport path S one by one. A feed roller pair 14 is provided.

  Further, in the transport path S extending in the vertical direction on the side portion of the printer main body 100, a secondary portion which is a contact portion between the driving roller 8 and the secondary transfer roller 10 at a predetermined timing after the paper is temporarily waited. A registration roller pair 15 is provided to be supplied to the transfer unit.

  By the way, the conveyance path S arranged in the vertical direction on one side portion in the printer main body 100 extends to the paper discharge tray 16 provided on the upper surface of the printer main body 100, and the fixing device 17 and the discharge path are disposed in the middle. A paper roller pair 18 is provided.

  Next, an image forming operation by the color laser printer having the above configuration will be described.

  When an image formation start signal is issued, the respective photosensitive drums 2a to 2d are driven to rotate in a direction indicated by an arrow (counterclockwise) in the image forming units 1M, 1C, 1Y, and 1K at a predetermined process speed. 2a to 2d are uniformly charged by the chargers 3a to 3d. Further, each optical scanning device 12 emits a light beam modulated by a color image signal for each color, irradiates the surface of each photosensitive drum 2a to 2d, and each color is applied to each photosensitive drum 2a to 2d. The electrostatic latent images corresponding to the color image signals are respectively formed.

  First, magenta toner is attached to the electrostatic latent image formed on the photosensitive drum 2a of the magenta image forming unit 1M by the developing device 4a to which a developing bias having the same polarity as the charged polarity of the photosensitive drum 2a is applied. The electrostatic latent image is visualized as a magenta toner image. This magenta toner image is moved in the direction of the arrow in the figure by the action of the transfer roller 5a to which a primary transfer bias having a polarity opposite to that of the toner is applied in the primary transfer portion (transfer nip portion) between the photosensitive drum 2a and the transfer roller 5a. Primary transfer is performed on the intermediate transfer belt 7 that is rotationally driven.

  The intermediate transfer belt 7 on which the magenta toner image has been primarily transferred as described above moves to the next cyan image forming unit 1C. In the cyan image forming unit 1C as well, the cyan toner image formed on the photosensitive drum 2b is transferred to the magenta toner image on the intermediate transfer belt 7 in the primary transfer portion in the same manner as described above.

  Similarly, yellow and black toners respectively formed on the photosensitive drums 2c and 2d of the yellow and black image forming units 1Y and 1K on the magenta and cyan toner images superimposed and transferred on the intermediate transfer belt 7, respectively. The images are sequentially superimposed at each primary transfer portion, and a full-color toner image is formed on the intermediate transfer belt 7. The transfer residual toner that is not transferred onto the intermediate transfer belt 7 and remains on the photosensitive drums 2a to 2d is removed by the cleaning devices 6a to 6d, and the photosensitive drums 2a to 2d are prepared for the next image formation. .

  Then, in accordance with the timing at which the front end of the full-color toner image on the intermediate transfer belt 7 reaches the secondary transfer portion (transfer nip portion) between the drive roller 8 and the secondary transfer roller 10, the pair of transport rollers 14 from the paper feed cassette 13. Thus, the sheet fed to the transport path S is transported to the secondary transfer portion by the registration roller pair 15. Then, a full-color toner image is collectively transferred from the intermediate transfer belt 7 to the sheet conveyed to the secondary transfer unit by the secondary transfer roller 10 to which a secondary transfer bias having a polarity opposite to that of the toner is applied. .

  Thus, the sheet on which the full-color toner image has been transferred is conveyed to the fixing device 17, where the full-color toner image is heated and pressurized and thermally fixed on the surface of the sheet, and the sheet on which the toner image is fixed Then, the paper is discharged onto the paper discharge tray 16 by the paper discharge roller pair 18, and a series of image forming operations is completed.

[Optical scanning device]
Next, the optical scanning device 12 according to the present invention will be described with reference to FIGS. Since all the four optical scanning devices 12 have the same configuration, only one optical scanning device 13 will be described below.

  2 is a perspective view of the optical scanning device according to the present invention, FIG. 3 is a diagram for explaining the principle of adjusting the aperture area of the aperture stop according to the aperture mounting angle, FIG. 4 is a main scanning sectional view of the aperture mounting portion, and FIG. It is a sub-scanning sectional view of an aperture mounting portion.

  As shown in FIG. 2, a laser diode 20 as a light source is provided in the housing 19 of the optical scanning device 12, and the housing 19 is not shown along the emission direction of the light beam L from the laser diode 20. The collimator lens 21, the cylindrical lens 22, and the polygon mirror 23 as a deflector are arranged on a straight line.

  In the housing 19, two fθ lenses 24 and 25 and a folding mirror 26 are disposed along the traveling direction of the light beam L deflected by the polygon mirror 23. Also, the effective scanning range R is deflected by the BD sensor 27 that is a light detection element and the polygon mirror 23 on the left and right of the position outside the effective scanning range (scanning range that is actually used as the print width) R of the light beam L. A BD mirror 28 that turns the light beam L1 that travels along the optical path off the path and guides it to the BD sensor 27 is disposed.

  By the way, a plate-like aperture 29 for focusing the light beam L is provided on the optical path between the laser diode 20 and the polygon mirror 23 in the housing 19 and between the collimator lens 21 and the cylindrical lens 22. 19 is attached. Here, as shown in FIG. 3, the aperture 29 is formed with an aperture stop 29 a for narrowing the light beam L.

  Thus, in the optical scanning device 12 shown in FIG. 2, when the laser diode 20 is ON / OFF controlled according to the image signal, the light beam L modulated in accordance with the image data is emitted from the laser diode 20. The light beam L is converted into a parallel light beam by the collimator lens 21, and the parallel light beam L is focused by the aperture stop 29 a of the aperture 29 and then the polygon mirror 23 by the cylindrical lens 22 having power only in the sub-scanning direction. The light is imaged on the reflecting surface and deflected by the polygon mirror 23 that rotates at high speed. The deflected light beam L is condensed at the same speed by the fθ lenses 24 and 25, and is folded by the folding mirror 26 to form a condensed spot on the photosensitive drum 2a (2b to 2d) that is the surface to be scanned. As a result, the photosensitive drums 2a (2b to 2d) are exposed and scanned in the main scanning direction, and electrostatic latent images corresponding to the color image signals of the respective colors are formed on the photosensitive drums 2a (2b to 2d). .

  Here, the light beam L1 is reflected by the BD mirror 28 and incident on the BD sensor 27 disposed outside the effective scanning range R, and the light beam L1 is detected by the BD sensor 27 so that the light beam L1 is photosensitive. The timing of starting exposure scanning (writing) on the drum 2a (2b to 2d) is determined.

  By the way, it is known that the spot diameter of the light beam condensed on the surface to be scanned is inversely proportional to the size of the diameter of the light beam incident on the fθ lens. That is, assuming that the spot diameter of the light beam on the surface to be scanned is W, the diameter of the light beam incident on the fθ lens is D, the wavelength of the light beam is λ, and the focal length of the fθ lens is f, The spot diameter W of the light beam is obtained by the following equation.

W = 2fλ / (πD)
From the above formula, the smaller the wavelength λ of the light beam, the smaller the spot diameter W of the light beam on the surface to be scanned. Therefore, the spot diameter W of the light beam on the surface to be scanned is set regardless of the wavelength λ of the light beam. In order to keep constant, the larger the wavelength λ of the light beam, the larger the diameter D of the light beam incident on the fθ lens. Conversely, the smaller the wavelength λ of the light beam, the smaller the diameter D of the light beam incident on the fθ lens. It needs to be small.

  Thus, even with a single aperture 29, the opening area of the aperture stop 29a of the aperture 29 can be adjusted by changing the mounting angle (inclination angle). Therefore, if the aperture area of the aperture stop 29a is adjusted by changing the attachment angle of the aperture 29 according to the wavelength of the light beam L emitted from the laser diode 20, an optimum stop for the wavelength of the light beam L can be obtained. This makes it possible to optimize the diameter of the beam spot formed on the photosensitive drum 2a (2b to 2d).

  That is, when the aperture 29 is attached at a right angle to the direction of emission of the light beam L as indicated by a broken line in FIG. 3, the aperture area of the aperture stop 29 a of the aperture 29 is maximized and passes through the collimator lens 21. The light beam (parallel light beam) L having the width b is narrowed to the illustrated width b1 by the aperture stop 29a of the aperture 29. On the other hand, when the aperture 29 is attached at an angle θ with respect to the emission direction of the light beam L as indicated by a solid line in FIG. 3, the aperture area of the aperture stop 29a of the aperture 29 is reduced. The light beam (parallel light beam) L having a width b that has passed through the collimator lens 21 is narrowed to the illustrated width b2 (<b1) by the aperture stop 29a of the aperture 29.

  In the present embodiment, as shown in FIGS. 4 and 5, the housing 19 is integrally formed with a wedge-shaped attachment portion 30, and the light source side surface 30 a of the attachment portion 30 is an emission direction of the light beam L. The surface 30b on the side opposite to the light source is perpendicular to the emission direction of the light beam L in both the main scanning direction and the sub-scanning direction. It is considered to be a good surface.

  Thus, in the present embodiment, for the long wavelength light beam L, the aperture 29 is shown on the surface 30b on the side opposite to the light source of the mounting portion 30 as shown by broken lines in FIGS. In this case, the aperture 29 is attached at right angles to the emission direction of the light beam L, and the aperture area of the aperture stop 29a of the aperture 29 is maximized as described in FIG. Can be reduced to an optimum size by the aperture stop 29a.

  On the other hand, when the aperture 29 is attached to the light source side surface 30a of the attachment portion 30 with a plurality of screws 31 as shown by the solid lines in FIGS. It is attached obliquely with respect to the emission direction of the beam L (angle θ1 in the main scanning direction and angle θ2 in the sub-scanning direction), and the aperture area of the aperture stop 29a of the aperture 29 is reduced as described in FIG. The light beam L having a short wavelength is narrowed to an optimum size by the aperture stop 29a having a small aperture area.

  As described above, in this embodiment, the aperture 29 is simply attached to the light source side surface 30a or the non-light source side surface 30b of the attachment portion 30 in accordance with the wavelength of the light beam L. Is adjusted to an optimum size with respect to the wavelength of the light beam L, so that a complicated adjustment mechanism and adjustment work are not required, and a single wavelength is not required for a plurality of beam wavelengths. The aperture 29 can optimize the beam diameter on the photosensitive drum 2a (2b to 2d). In this case, the wavelength of the light beam emitted from the light source used can be easily identified by identifying whether the attachment position of the aperture 29 is the light source unit side or the counter light source unit side.

  In the above embodiment, the aperture is inclined in the main scanning direction and the sub-scanning direction with respect to the light beam emission direction. However, the aperture is inclined in either the main scanning direction or the sub-scanning direction. May be. Although the present invention has been described with respect to a mode in which the present invention is applied to a color laser printer and an optical scanning device provided in the color laser printer, the present invention includes other arbitrary image forming apparatuses including a monochrome printer and a copying machine. Of course, the present invention can be similarly applied to the optical scanning device provided for this.

1M Magenta image forming unit 1C Cyan image forming unit 1Y Yellow image forming unit 1K Black image forming unit 2a to 2d Photosensitive drum 3a to 3d Charger 4a to 4d Developing device 5a to 5d Transfer roller 6a to 6d Cleaning device 7 Intermediate transfer belt 8 Drive roller 9 Tension roller 10 Secondary transfer roller 11 Optical density sensor 12 Optical scanning device 13 Paper feed cassette 14 Transport roller pair 15 Registration roller pair 16 Paper discharge tray 17 Fixing device 18 Paper discharge roller pair 19 Optical scanning device housing 20 Laser diode (light source)
21 Collimator lens 22 Cylindrical lens 23 Polygon mirror (deflector)
24, 25 fθ lens 26 Folding mirror 27 BD sensor 28 BD mirror 29 Aperture 29a Aperture aperture stop 30 Housing mounting portion 30a Mounting portion light source side surface 30b Mounting portion opposite light source side surface 31 Screw 100 Printer body L, L1 Light beam R Effective scanning range S Transport path

Claims (5)

A light source, a deflector for deflecting a light beam emitted from the light source, an aperture having an aperture stop for narrowing the light beam in an optical path between the deflector and the light source, and a light beam deflected by the deflector In an optical scanning device provided with an fθ lens that forms an image on a surface to be scanned at a constant speed,
An attachment portion for attaching the aperture is provided, and the angle of the surface on the light source side and the surface on the opposite light source side of the attachment portion is different from each other in the main scanning direction and / or the sub-scanning direction. An optical scanning device characterized by selectively attaching the optical scanning device.   2. The optical scanning device according to claim 1, wherein one surface of the mounting portion is a surface perpendicular to the light beam emitting direction and the other surface is inclined obliquely with respect to the light beam emitting direction.   3. The optical scanning device according to claim 1, wherein the mounting portion is formed integrally with the housing.   The optical scanning device according to claim 1, wherein the aperture is attached to any one surface of the attachment portion. An image forming apparatus comprising the optical scanning device according to claim 1.

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