JP4413652B2 - Light beam scanning apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a light beam scanning device for forming an electrostatic latent image by scanning a light beam based on image data on the surface of an image carrier, and to form an electrophotographic image using the light beam scanning device. The present invention relates to an electrophotographic image forming apparatus such as a printer, a facsimile machine, and a copying machine.

  Image forming apparatuses such as printers, facsimile machines, and copiers are equipped with a light beam scanning device, and an image carrier in which a light beam such as a laser beam modulated in a signal based on input image data or read image data is charged in advance. An electrostatic latent image is formed by scanning the surface of the body. Thereafter, a developer image (toner image) obtained by developing (developing) the electrostatic latent image is transferred to a recording medium (hereinafter referred to as paper).

  A light beam scanning apparatus that scans an image carrier by modulating a light beam as described above is generally used because the modulation speed of the light beam is high and the scanning speed can be increased. .

  In addition, in an image forming apparatus that performs color image formation, a plurality of light beam scanning devices provided for each component color of image data are used to scan each surface of a plurality of image carriers with a light beam of each component color. It was.

  However, since the light beam scanning apparatus includes a deflecting unit (polygon mirror) for deflecting the light beam at a constant angular velocity, a light correcting unit (fθ lens) for deflecting the light beam at a constant angular velocity at a constant speed, and the like. In the configuration of the image forming apparatus provided with the light beam scanning apparatus, there is a problem that the apparatus becomes large and the cost increases.

  Therefore, in order to reduce the size and cost of the image forming apparatus, recent image forming apparatuses include a single deflecting unit that deflects a plurality of light beams emitted from a light source provided for each component color at an equal angular velocity. There is a configuration including a single optical scanning device that also uses a light beam of each component color as a (polygon mirror) and a light correction means (fθ lens) that deflects a plurality of light beams of equal angular velocity at equal speeds. (For example, refer to Patent Document 1 and Patent Document 2.) The plurality of light beams deflected by the deflecting unit are deflected at an equal angular velocity by the light correcting unit, and then separated by the separating unit toward the image carrier of each component color.

  In the configuration of Patent Document 1, as shown in FIG. 7, a plurality of light beams deflected at a uniform angular velocity by a polygon mirror 150 are deflected by a cylindrical lens 151 into light parallel to the sub-scanning direction. Thereafter, the fθ is corrected by the fθ lens 152 and deflected at a constant speed.

On the other hand, in the configuration of Patent Document 2, a plurality of light beams are deflected at a constant speed by a toric fθ lens composed of a plurality of lenses such as an fθ lens.
JP 2000-347116 A JP-A-5-142495

  However, in the configuration of Patent Document 1 described above, since a plurality of light beams are deflected in parallel in the sub-scanning direction using the cylindrical lens 151 and then deflected at a constant speed using the fθ lens 152, There is a problem in that the size in the main scanning direction becomes larger than necessary, and the cost of the fθ lens 152 increases.

  That is, in order to accurately separate a plurality of light beams deflected at the same speed and make them incident on the image carriers 154a to 154d, a predetermined interval must be provided between the plurality of light beams. This is because if this interval is narrow, the deflecting mirrors (separating means) 153a to 153d reflect not only a single light beam but also a part of the other light beams together.

  In addition, in order to deflect a plurality of light beams parallel to the sub-scanning direction with a predetermined interval, the plurality of light beams deflected at a constant angular velocity by the polygon mirror 150 must be diffused to some extent. Therefore, the cylindrical lens 151 must be separated from the reflection (incident) position of the plurality of light beams on the reflection surface of the polygon mirror 150 by a predetermined distance.

  Further, the plurality of light beams incident on the polygon mirror 150 finally scan the surfaces of the image carriers 154a to 154d in the main scanning direction. Therefore, in the optical path of the plurality of light beams from the polygon mirror 150 to the surfaces of the image carriers 154a to 154d, the main scanning through which the plurality of light beams pass as the distance from the reflection position of the polygon mirror 150 becomes longer. The range of directions increases.

  Therefore, the fθ lens 152 located on the downstream side of the cylindrical lens 151 on the optical path has a longer distance from the reflection position of the plurality of beams of the polygon mirror 150 than the cylindrical lens 151 and has a large size in the main scanning direction. It was. In other words, the size in the main scanning direction of the fθ lens 152 that is not related to the diffusion state of the plurality of light beams has become larger than necessary due to the arrangement of the cylindrical lens 151.

  In the configuration of Patent Document 2 described above, a plurality of light beams are not deflected in parallel to the sub-scanning direction in a toric fθ lens composed of a plurality of lenses such as an fθ lens. Although it is illustrated as being deflected in parallel, it is unclear at which position it is deflected. For this reason, the position for deflecting a plurality of light beams in parallel in the sub-scanning direction is not taken into consideration, and the same problem as in Patent Document 1 may occur.

  An object of the present invention is to provide a light beam scanning device capable of reducing the size of the light correction means in the main scanning direction to reduce the size of the device and reducing the cost, and an image forming apparatus provided with the light beam scanning device. There is to do.

  In order to solve the above problems, the present invention has the following configuration.

(1) a plurality of light beams having a deflection means for deflecting the constant angular velocity in the main scanning direction, each incident of the plurality of light beams emitted at different angles from each other from said deflecting means in a plane perpendicular to the main scanning direction A plurality of light correcting means arranged in order in the optical path direction on the optical path to the surface of the plurality of scanned objects, and deflecting the plurality of light beams deflected at a constant angular velocity at a constant speed in the main scanning direction And separating means for separating the plurality of light beams deflected at the same speed from each other, and using the plurality of light beams separated by the separating means, the surfaces of the plurality of objects to be scanned are in the main scanning direction. In the light beam scanning device that scans
Among the plurality of light correction units, the light correction unit closest to the separation unit on the optical path is substantially provided with a certain interval between the plurality of light beams in a plane orthogonal to the main scanning direction. It is characterized by being deflected in parallel.

  In this configuration, the plurality of light beams deflected at the uniform angular velocity by the deflecting unit are deflected at the uniform velocity in the main scanning direction by the plurality of light correcting units. Further, on the optical path from the deflecting means to the surfaces of the plurality of scanning objects, the light correcting means closest to the separating means among the plurality of light correcting means arranged in order in the optical path direction is deflected by the deflecting means. A plurality of light beams in a diffused state are deflected substantially parallel to the sub-scanning direction at intervals.

  In other words, the plurality of light beams deflected at a constant angular velocity by the plurality of light correction units start to be deflected at a constant speed before entering the light correction unit closest to the separation unit. Thereafter, the plurality of light beams emitted from the light correction means closest to the separation means are directed to the separation means in a state where they are deflected substantially parallel to the sub-scanning direction at a constant speed and at intervals. Here, the plurality of light beams are deflected substantially parallel to each other in the sub-scanning direction with a space between them, and if there is no space between each other, the separation means separates the plurality of light beams in a state where the light beams are completely separated. This is because the light cannot enter the scanning body.

  In order to deflect a plurality of light beams at a distance from each other and to be substantially parallel to the sub-scanning direction, it is necessary to carry out at a position where the plurality of light beams deflected by the deflecting means are diffused to some extent on the optical path. In other words, it is necessary to deflect at a position somewhat away from the incident positions of the plurality of light beams in the deflecting means on the optical path. Note that the diffusion state of the plurality of light beams does not cause a problem in order to deflect the plurality of light beams having the same angular velocity at the same speed. In addition, since the surface of the object to be scanned is scanned in the main scanning direction by the plurality of light beams deflected by the deflecting means, the longer the distance from the incident position, the more the light beams pass in the main scanning direction. The range will expand.

  Accordingly, among the plurality of light correction units on the optical path, the plurality of light beams are deflected substantially parallel to the sub-scanning direction at intervals from each other by the light correction unit closest to the separation unit, in other words, the farthest from the deflection unit. Therefore, the size of the plurality of light correction units in the main scanning direction is smaller than the size of the light correction unit farthest from the incident position.

  (2) At least one of the plurality of light correction units other than the light correction unit closest to the separation unit deflects the plurality of light beams in the sub-scanning direction.

  In this configuration, the plurality of light beams are deflected in the sub-scanning direction by at least one of the light correction unit closest to the separation unit and the plurality of light correction units other than the light correction unit closest to the separation unit.

(3) The plurality of light correction units are a plurality of fθ lenses,
Of the surfaces of the plurality of light correction means through which the plurality of light beams pass, the surfaces other than the light beam emission surfaces of the light correction means closest to the separation means have a rotationally symmetric aspheric shape, and the emission The surface is a free-form surface shape.

  In this configuration, a plurality of fθ lenses, which are a plurality of light correction means, are sequentially arranged in the optical path direction on the optical path. Of the surfaces through which the plurality of light beams of the plurality of fθ lenses pass, the surfaces other than the plurality of light beam exit surfaces of the fθ lens closest to the separating means are formed in a rotationally symmetric aspherical shape. The exit surface is formed in a free-form surface shape. That is, the surface of the fθ lens is formed in a rotationally symmetric aspherical shape as much as possible.

  Here, the exit surface of the plurality of light beams of the fθ lens closest to the separating means is not formed in a rotationally symmetric aspherical shape, in addition to deflecting the plurality of light beams at a constant speed in the main scanning direction on the exit surface. This is because it is necessary to deflect a plurality of diffused light beams positioned in the sub-scanning direction into parallel light. For this reason, the exit surface needs to be an aspherical shape having a different effect in the main scanning direction and the sub-scanning direction, that is, a free-form surface shape.

  On the other hand, the surface of the plurality of fθ lenses through which a plurality of light beams other than the exit surface passes has an effect in the main scanning direction and the sub-scanning direction that only deflects the plurality of light beams at a constant speed in the main scanning direction. Equal rotationally symmetric aspheric shape.

(4) In an image forming apparatus for forming an image by transferring a toner image obtained by developing an electrostatic latent image formed on the surface of a plurality of image carriers onto a recording medium,
(1) to (3) including the light beam scanning device according to any one of
The electrostatic latent images are formed by scanning the surfaces of the plurality of image carriers using the plurality of light beams.

  In this configuration, in the light beam scanning device described in any of (1) to (3) above, the surfaces of the plurality of image carriers are scanned by the plurality of light beams modulated based on the image data. An electrostatic latent image is formed.

  According to the present invention, the following effects can be obtained.

  (1) Among a plurality of light correction means on the optical path, the light correction means closest to the separation means, that is, the farthest from the deflection means, is used to deflect a plurality of light beams at a distance from each other and substantially parallel to the sub-scanning direction. By doing so, the size of the plurality of light correcting units in the main scanning direction can be made smaller than the size of the light correcting unit farthest from the deflecting unit in the main scanning direction. Therefore, the size of the light correction means in the main scanning direction can be made smaller than the conventional structure in which a plurality of light beams are deflected substantially parallel to each other in the sub-scanning direction and then deflected at a constant speed, and the cost of the light correction means is reduced. Can be reduced. Thereby, the apparatus can be made compact and the cost can be reduced.

  (2) By deflecting a plurality of light beams in the sub-scanning direction using at least one of a light correction unit closest to the separation unit and a plurality of light correction units other than the light correction unit closest to the separation unit, After the plurality of light beams deflected by the deflecting means are diffused to such an extent that they can be easily separated, it can be adjusted so as not to diffuse further.

  In addition, when a plurality of light beams are gradually deflected substantially parallel to the sub-scanning direction by a plurality of light correction means, compared to a configuration in which a plurality of light beams are deflected in the sub-scanning direction using only a single light correction means. Since the deflection rate (refractive index) for deflecting in the sub-scanning direction can be dispersed, the design of the light correction means can be facilitated and high-precision optical characteristics can be obtained.

  (3) By forming the surface of the fθ lens as much as possible in a rotationally symmetric aspherical shape, the molding accuracy of the lens surface is improved as compared with the case of forming a free-form lens surface, and molding close to the ideal state (design value) is achieved. enable. Furthermore, the relative positional deviation between the lens surfaces (incident surface and outgoing surface) can be reduced, and the deflection of a plurality of light beams can be performed more accurately.

  The rotational accuracy of the rotationally symmetric aspherical lens is higher than the processing accuracy of the rotationally curved aspherical lens compared to the free curved surface shaped lens. This is because the machining accuracy is higher. For example, a plastic molded lens is formed by creating a mold and press-fitting a plastic material into the mold. Therefore, the lens surface depends on the mold accuracy. In this case, the processing of the free-form lens mold is performed in three axes.

  On the other hand, the processing of the rotationally symmetric aspherical lens mold is performed with two axes since one axis is the rotation axis. That is, as compared with the processing of the mold of the lens having a free-form surface shape, the processing of the mold of the lens having a rotationally symmetric aspherical shape has a higher mold accuracy with one processing axis being less.

  (4) The light beam scanning device according to any one of (1) to (3) is provided, and the surfaces of a plurality of image carriers are scanned and statically scanned with a plurality of light beams modulated based on image data. By forming the electrostatic latent image, the apparatus can be made compact while maintaining the image quality, and the cost can be reduced.

  Hereinafter, an image forming apparatus according to the best embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is an explanatory diagram showing a configuration of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus 100 forms multicolor and single color images on a sheet in accordance with image data transmitted from the outside. Therefore, the image forming apparatus 100 includes a light beam scanning device E, a photosensitive drum (corresponding to the image carrier of the present invention) 101 (101a to 101d), a developing unit 102 (102a to 102d), and a charging roller 103 ( 103a to 103d), cleaning unit 104 (104a to 104d), intermediate transfer belt (corresponding to the endless belt of the present invention) 11, primary transfer roller (corresponding to the transfer roller of the present invention) 13 (13a to 13d) A secondary transfer roller 14, a fixing device 15, paper transport paths P1, P2, and P3, a paper feed cassette 16, a manual paper feed tray 17, a paper discharge tray 18, and the like.

  The image forming apparatus 100 includes four component colors obtained by adding black (K) to yellow (Y), magenta (M), and cyan (Y), which are three subtractive primary colors obtained by color separation of a full-color image. Image formation is performed using image data corresponding to the above. The photosensitive drum 101 (101a to 101d), the developing unit 102 (102a to 102d), the charging roller 103 (103a to 103d), the primary transfer roller 13 (13a to 13d) and the cleaning unit 104 (104a to 104d) Four each is provided according to the color, and constitutes four image forming portions Pa to Pd. The image forming portions Pa to Pd are arranged in a line in the moving direction (sub-scanning direction) of the intermediate transfer belt 11 which is a direction orthogonal to the main scanning direction.

  The charging roller 103 is a contact-type charger that uniformly charges the surface of the photosensitive drum 101 to a predetermined potential. Instead of the charging roller 103, a contact type charger using a charging brush or a non-contact type charger using a charging charger may be used. The light beam scanning device E includes a semiconductor laser (not shown), a polygon mirror 26, a reflection mirror 33, and the like, and each of a plurality of light beams modulated by image data of black, cyan, magenta, and yellow component colors. Irradiate each of the photosensitive drums 101a to 101d. On each of the photosensitive drums 101a to 101d, an electrostatic latent image is formed by image data of each component color of black, cyan, magenta, and yellow. Details will be described later.

  The developing unit 102 supplies a developer to the surface of the photosensitive drum 101a on which the electrostatic latent image is formed, and visualizes (develops) the electrostatic latent image into a toner image. Each of the developing units 102a to 102d contains a developer of each component color of black, cyan, magenta, and yellow, and an electrostatic latent image of each component color formed on each of the photosensitive drums 101a to 101d is stored. The toner image is visualized as a toner image of each component color of black, cyan, magenta, and yellow. The cleaning unit 104 removes and collects toner remaining on the surface of the photosensitive drum 101 after development and image transfer.

  The intermediate transfer belt 11 disposed above the photosensitive drum 101 is stretched between the driving roller 11a and the driven roller 11b to form a loop-shaped movement path. The outer peripheral surface of the intermediate transfer belt 11 faces the photosensitive drum 101d, the photosensitive drum 101c, the photosensitive drum 101b, and the photosensitive drum 101a in this order. Primary transfer rollers 13a to 13d are arranged at positions facing the respective photosensitive drums 101a to 101d with the intermediate transfer belt 11 interposed therebetween. Each of the positions where the intermediate transfer belt 11 faces the photosensitive drums 101a to 101d is a primary transfer position.

The intermediate transfer belt 11 is formed endlessly using a film having a thickness of about 100 μm to 150 μm, and has a volume resistivity of 1.0 × 10 ^{11 to} 1.0 × 10 ¹² Ω · cm. When the volume resistivity of the intermediate transfer belt 11 is lower than this level, a leak occurs from the intermediate transfer belt 11 and sufficient transfer power cannot be maintained during primary transfer, and the volume resistivity of the intermediate transfer belt 11 is not maintained. If this level is higher than this level, it is necessary to separately provide means for neutralizing the intermediate transfer belt 11 after passing through each transfer position.

  In order to transfer the toner images carried on the surfaces of the photosensitive drums 101a to 101d onto the intermediate transfer belt 11, primary transfer biases (in the present invention, primary transfer rollers 13a to 13d) have a polarity opposite to that of the toner. Corresponding to transfer power) is applied by constant voltage control. As a result, the toner images of the respective component colors formed on the photosensitive drum 101 (101a to 101d) are sequentially superimposed on the outer peripheral surface of the intermediate transfer belt 11, and a full-color toner image is formed on the outer peripheral surface of the intermediate transfer belt 11. It is formed.

  However, when image data of only a part of component colors of yellow, magenta, cyan, and black is input, one of the four photosensitive drums 101a to 101d corresponding to the component color of the input image data. The electrostatic latent image and the toner image are formed only on the photosensitive member 101 of the portion. For example, when a monochrome image is transferred, an electrostatic latent image and a toner image are formed only on the photosensitive drum 101a corresponding to the black component color, and only the black toner image is formed on the outer peripheral surface of the intermediate transfer belt 11. Is transcribed.

  Each of the primary transfer rollers 13a to 13d is configured by covering the surface of a shaft made of a metal (for example, stainless steel) having a diameter of 8 to 10 mm with a conductive elastic material (for example, EPDM, urethane foam, or the like). A high voltage is uniformly applied to the intermediate transfer belt 11 by the elastic material. Instead of the intermediate transfer roller 103, a brush-like intermediate transfer member can be used.

  Each of the primary transfer rollers 13a to 13d is in a direction different from the normal direction at the contact position of the intermediate transfer belt 11 on the peripheral surfaces of the photosensitive drums 101a to 101d with respect to the photosensitive drums 101a to 101d. It is energized.

  The toner image transferred to the outer peripheral surface of the intermediate transfer belt 11 at each primary transfer position is conveyed to a position facing the secondary transfer roller 14 by the rotation of the intermediate transfer belt 11. The secondary transfer roller 14 is pressed against the outer peripheral surface of the intermediate transfer belt 11 whose inner peripheral surface is in contact with the peripheral surface of the driving roller 11a at a predetermined nip pressure during image formation. When the paper fed from the paper feed cassette 16 or the manual paper feed tray 17 passes between the secondary transfer roller 14 and the intermediate transfer belt 11, the polarity of the toner charged on the secondary transfer roller 14 is opposite to that of the toner. The high voltage is applied. As a result, the toner image is transferred from the outer peripheral surface of the intermediate transfer belt 11 to the surface of the sheet.

  In order to maintain the nip pressure between the secondary transfer roller 14 and the intermediate transfer belt 11 at a predetermined value, either the secondary transfer roller 14 or the driving roller 11a is made of a hard material (metal or the like) and remains. The other is made of a soft material such as an elastic roller (such as an elastic rubber roller or a foaming resin roller).

  Further, of the toner adhering to the intermediate transfer belt 11 from the photosensitive drum 101, the toner remaining on the intermediate transfer belt 11 without being transferred onto the sheet is removed by the cleaning unit 12 in order to prevent color mixing in the next process. Collected.

  The sheet on which the toner image has been transferred is guided to the fixing device 15, and passes between the heating roller 15a and the pressure roller 15b to be heated and pressurized. As a result, the toner image is firmly fixed on the surface of the paper. The paper on which the toner image is fixed is discharged onto the paper discharge tray 18 by the paper discharge roller 18a.

  In the image forming apparatus 100, a substantially vertical direction for feeding the paper stored in the paper cassette 16 to the paper discharge tray 18 between the secondary transfer roller 14 and the intermediate transfer belt 11 and via the fixing device 15. A paper transport path P1 is provided. In the paper transport path P1, a pickup roller 16a that feeds the paper in the paper cassette 16 one by one into the paper transport path P1, a transport roller r that transports the fed paper upward, and the transported paper is predetermined. A registration roller 19 that guides between the secondary transfer roller 14 and the intermediate transfer belt 11 at the timing and a paper discharge roller 18 a that discharges the paper to the paper discharge tray 18 are disposed.

  Further, inside the image forming apparatus 100, a paper conveyance path P2 in which a pickup roller 17a and a conveyance roller r are arranged is formed between the manual paper feed tray 17 and the registration roller 19. Further, a paper transport path P3 is formed between the paper discharge roller 18a and the upstream side of the registration roller 19 in the paper transport path P1.

  The paper discharge roller 18a is rotatable in both forward and reverse directions, and is used for forming a single-sided image for forming an image on one side of a sheet and for forming a second-side image in forming a double-sided image for forming an image on both sides of a sheet. Driven in the forward direction, the paper is discharged to the paper discharge tray 18. On the other hand, when the first side image is formed in the double-sided image formation, the discharge roller 18a is driven in the normal rotation direction until the rear end of the paper passes through the fixing device 15, and then reversely rotated with the rear end of the paper sandwiched. Driven in the direction, the sheet is guided into the sheet conveyance path P3. As a result, the paper on which the image is formed on only one side when the double-sided image is formed is guided to the paper transport path P1 with the front and back surfaces and the front and rear ends reversed.

  The registration roller 19 feeds a sheet fed from the sheet cassette 16 or the manual feed tray 17 or conveyed via the sheet conveying path P 3 at a timing synchronized with the rotation of the intermediate transfer belt 11. 14 and the intermediate transfer belt 11. For this reason, the registration roller 19 stops rotating when the operation of the photosensitive drum 101 and the intermediate transfer belt 11 is started, and the sheet fed or conveyed prior to the rotation of the intermediate transfer belt 11 has the front end at the registration roller 19. The movement in the sheet conveyance path P1 is stopped in a state where the sheet 19 is in contact with the sheet 19. Thereafter, the registration roller 19 is a position where the secondary transfer roller 14 and the intermediate transfer belt 11 are in pressure contact with each other, at a timing when the front end portion of the sheet and the front end portion of the toner image formed on the intermediate transfer belt 11 face each other. Start spinning.

  2 and 3 are a side view and a plan view showing a simple configuration of the light beam scanning device provided in the image forming apparatus according to the embodiment of the present invention. The light beam scanning device E includes an incident optical system 20, a polygon mirror 26, an output optical system 30, and the like. The incident optical system 20 includes semiconductor lasers 21a to 21d, collimator lenses 22a to 22d, apertures 23a to 23d, a reflection mirror 24, a first cylindrical lens 25, and the like, and is emitted based on image data as shown in FIG. The plurality of light beams are guided to the same reflecting surface 26 a of the polygon mirror 26.

  The semiconductor lasers 21a to 21d are arranged at different positions in the sub-scanning direction, and emit light beams based on the component colors (yellow, magenta, cyan, black) of the image data. The collimator lenses 22a to 22d make each light beam a parallel beam. Apertures 24a to 24d are openings, and define the passable range of each incident light beam. The reflection mirror 24 reflects each light beam and guides it to the first cylindrical lens 25 and the polygon mirror 26 so that the distance in the main scanning direction until each light beam enters the reflection surface 26 a of the polygon mirror 26 becomes the same. .

  The distances in the main scanning direction are the same because the light beams of the respective component colors are not incident on the polygon mirror 26 at the same timing, and the plurality of light beams deflected to the polygon mirror 26 are each photosensitive drum 101a. This is because the light does not enter the same position on the surface of −101 d, but enters a different position. The first cylindrical lens 25 deflects a plurality of light beams in the main scanning direction and the sub-scanning direction orthogonal to the main scanning direction, and condenses them on the same location on the reflection surface 26 a of the polygon mirror 26.

  The polygon mirror 26 is a rotating polygon mirror, and reflects a plurality of light beams emitted from the semiconductor lasers 21a to 21d while rotating on each reflecting surface 26a. As a result, the plurality of light beams are deflected at a uniform angular velocity as shown in FIG.

  The emission optical system 30 includes a first fθ lens 31, a second fθ lens 32, a reflection mirror 33, second cylindrical lenses 34a to 34d, and the like, and is deflected by a polygon mirror 26 as indicated by an optical path L (La to Ld). A plurality of light beams are deflected and separated at equal speeds and irradiated onto a predetermined range in the main scanning direction on the surfaces of the photosensitive drums 101a to 101d.

  The first fθ lens 31 and the second fθ lens 32, which are a plurality of light correction means of the present invention, correct a plurality of light beams deflected at a constant angular velocity by fθ and deflect them at a constant velocity in the main scanning direction. Further, as shown in FIG. 5, the second fθ lens 32 deflects a plurality of light beams substantially parallel to the sub-scanning direction with a predetermined interval d.

  Here, the reason why the plurality of light beams are deflected substantially parallel to the sub-scanning direction with a predetermined interval d using the second fθ lens is to separate the plurality of light beams accurately by the reflection mirror 33. This is for the purpose of downsizing. That is, if the predetermined distance d is narrow, when a single light beam is separated by being reflected by the reflection mirror 33, a part of the other light beam may be reflected together. Further, if the plurality of light beams are not made substantially parallel to the sub-scanning direction, the range of arrangement positions of the plurality of reflecting mirrors 33 is sub-scanned in order to diffuse as shown in the optical paths L′ a to L′ d shown in FIG. This is because the size of the light beam scanning device E increases.

  In the second fθ lens 32, a plurality of light beams are deflected substantially in parallel with a predetermined distance d from each other, but it is not necessary that they are all equally spaced. Even if they are different from each other, it is only necessary to ensure an interval at which a plurality of light beams can be accurately separated. Further, the plurality of light beams are deflected substantially in parallel, but being substantially parallel means that some errors are included.

  The first fθ lens 31 and the second fθ lens 32 of the present invention are plastic lenses formed by using a mold in order to improve mass productivity, but are not particularly limited thereto.

  Further, the incident surface and the exit surface of the first fθ lens 31 and the incident surface of the second fθ lens 32 in a plurality of light beams are formed in a rotationally symmetric aspherical shape. The exit surface of the second fθ lens 32 is formed in a free-form surface shape. This uses rotationally symmetric aspherical lens surfaces as much as possible to improve the molding accuracy of the lens surface compared to forming a free-form lens surface and enable molding close to the ideal state (design value). Because. Another reason for this is to reduce the relative positional deviation between the lens surfaces (incidence surface and exit surface) and more accurately deflect a plurality of light beams.

  Here, the exit surfaces of the plurality of light beams of the second fθ lens 32 are not formed in a rotationally symmetric aspherical shape, in addition to deflecting the plurality of light beams on the exit surface at a constant speed in the main scanning direction. This is because it is necessary to deflect a plurality of diffused light beams positioned in the direction into parallel light. For this reason, the exit surface needs to have an aspherical shape, that is, a free-form surface shape having different effects in the main scanning direction and the sub-scanning direction.

  On the other hand, the incident surface and the exit surface of the first fθ lens 31 and the incident surface of the second fθ lens 32 in the plurality of light beams are only in the main scanning direction and the sub-scanning direction that deflect the plurality of light beams at a constant speed in the main scanning direction. It is possible to make a rotationally symmetric aspherical shape with the same

  In addition, the rotational accuracy of the rotationally symmetric aspherical lens is higher than that of the free curved surface of the lens. This is because the mold machining accuracy is higher. For example, a plastic molded lens is formed by creating a mold and press-fitting a plastic material into the mold. Therefore, the lens surface depends on the mold accuracy. In this case, the processing of the free-form lens mold is performed in three axes.

  On the other hand, the processing of the rotationally symmetric aspherical lens mold is performed with two axes since one axis is the rotation axis. That is, as compared with the processing of the mold of the lens having a free-form surface shape, the processing of the mold of the lens having a rotationally symmetric aspherical shape has a higher mold accuracy with one processing axis being less.

  A plurality of reflecting mirrors 33 which are separation means of the present invention are arranged in the light beam scanning device E, reflect a plurality of light beams deflected at a constant speed, and each of the optical paths La to Ld has the same distance. It is guided to the photosensitive drums 101a to 101d. The reason why the optical paths La to Ld are made the same is that the relative formation positions of the electrostatic latent images on the surfaces of the photosensitive drums 101a to 101d are shifted due to the different optical path distances, and the toners of the component colors of the paper This is to prevent image transfer from shifting.

  The second cylindrical lenses 34a to 34d collect a plurality of light beams and form images on the surfaces of the photosensitive drums 101a to 101d. Thereby, electrostatic latent images are formed on the surfaces of the photosensitive drums 101a to 101d. A part of the plurality of light beams emitted from the second fθ lens 32 is incident on a BD sensor 36 including a synchronization lens 35 and a photo sensor, and the scanning timing of the photosensitive drums 101a to 101d is based on the detection timing. Is adjusted.

  As described above, by using the second fθ lens 32, a plurality of light beams are deflected substantially parallel to the sub-scanning direction with a predetermined interval d, so that the plurality of light beams are sub-scanned with a predetermined interval d. The size of the first fθ lens 31 and the second fθ lens 32 in the main scanning direction can be made smaller than the conventional configuration in which the deflection is performed at a constant speed after being deflected substantially parallel to the direction, and the cost of the light correction unit can be reduced. As a result, the light beam scanning device E can be made compact and the cost can be reduced.

  That is, in order to deflect a plurality of light beams at a predetermined distance d from each other and to be deflected substantially parallel to the sub-scanning direction, the plurality of light beams deflected to the polygon mirror 26 are diffused to some extent as shown in FIG. It is necessary to deflect with. In other words, it is necessary to deflect the light at a predetermined distance h from the reflection position of the plurality of light beams on the reflection surface 26a of the polygon mirror 26. Further, as shown in FIG. 3, since the surfaces of the photosensitive drums 101a to 101d are scanned in the main scanning direction by a plurality of light beams deflected by the polygon mirror 26, the distance from the polygon mirror 26 increases as the distance from the polygon mirror 26 increases. The range of the main scanning direction through which the light beam passes increases. Note that the diffusion state of the plurality of light beams does not cause a problem in order to deflect the plurality of light beams having the same angular velocity at the same speed.

  Accordingly, the plurality of light beams are deflected substantially parallel to the sub-scanning direction by providing the predetermined distance d by the second fθ lens 32 closest to the reflecting mirror 33 on the optical paths La to Ld, in other words, farthest from the polygon mirror 33. Therefore, the size of the first fθ lens 31 in the main scanning direction can be made smaller than the size of the second fθ lens 32 in the main scanning direction.

  The first fθ lens 31 and the second fθ lens 32 may be used to deflect light substantially parallel to the sub-scanning direction. For example, as shown in FIG. 6, the first f.theta. Lens 31 and the second f.theta. Lens are used to gradually deflect substantially in the sub-scanning direction. This makes it possible to disperse the deflection rate (refractive index) for deflecting the plurality of light beams in the sub-scanning direction as compared to a configuration in which a plurality of light beams are deflected in the sub-scanning direction using only a single light correction unit (second fθ lens 32). Therefore, the design of the fθ lenses 31 and 32 is facilitated and high-precision optical characteristics can be obtained.

  It is also possible to adjust so that a plurality of light beams deflected by the polygon mirror 26 are diffused to such an extent that they can be easily separated and are not further diffused.

  In the embodiment of the present invention, the two fθ lenses 31 and 32 are used.

  As described above, by providing the image forming apparatus 100 of the present invention with the light beam scanning apparatus E, the apparatus can be made compact while maintaining the image quality, and the cost can be reduced.

  In the explanatory diagram of the present embodiment, the light beams are completely separated on the incident surfaces of the fθ lenses 31 and 32. However, it is not necessary to completely separate in this way. . It is only necessary that the plurality of light beams finally emitted from the second fθ lens 32 are accurately separated.

1 is an explanatory diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a side view showing a simple configuration of a light beam scanning device provided in the image forming apparatus. FIG. 2 is a plan view showing a simple configuration of a light beam scanning device provided in the image forming apparatus. FIG. 2 is an enlarged view of a part of a light beam scanning device provided in the image forming apparatus. FIG. 2 is an enlarged view of a part of a light beam scanning device provided in the image forming apparatus. FIG. 2 is an enlarged view of a part of a light beam scanning device provided in the image forming apparatus. It is the figure which expanded a part of conventional light beam scanning apparatus.

Explanation of symbols

26-polygon mirror 31-first f.theta. Lens 32-second f.theta. Lens 33-reflection mirror 100-image forming apparatus 101a-101d-photosensitive drum d-predetermined interval E-light beam scanning apparatus

Claims (4)

Has a deflecting means for deflecting a plurality of light beams in a constant angular velocity in the main scanning direction, a plurality of emitted at different angles from each other from said deflecting means in a plane perpendicular to the main scanning direction a plurality of respective light beam is incident A plurality of light correcting means arranged in order in the optical path direction on the optical path to the surface of the scanning object and deflecting the plurality of light beams deflected at the constant angular velocity at a constant speed in the main scanning direction; and Separating means for separating a plurality of light beams deflected at a constant velocity from each other, and using the plurality of light beams separated by the separating means, the surfaces of the plurality of scanning objects are scanned in the main scanning direction. In a light beam scanning device,
Among the plurality of light correction units, the light correction unit closest to the separation unit on the optical path is substantially provided with a certain interval between the plurality of light beams in a plane orthogonal to the main scanning direction. A light beam scanning device characterized by deflecting in parallel.   2. The light beam scanning according to claim 1, wherein at least one of the plurality of light correction units other than the light correction unit closest to the separation unit deflects the plurality of light beams in a sub-scanning direction. apparatus. The plurality of light correction means are a plurality of fθ lenses,
Of the surfaces of the plurality of light correction means through which the plurality of light beams pass, the surfaces other than the light beam emission surfaces of the light correction means closest to the separation means have a rotationally symmetric aspheric shape, and the emission The light beam scanning apparatus according to claim 1, wherein the surface has a free-form surface shape. In an image forming apparatus for forming an image by transferring a toner image obtained by developing an electrostatic latent image formed on the surface of a plurality of image carriers to a recording medium,
A light beam scanning device according to any one of claims 1 to 3,
An image forming apparatus characterized in that an electrostatic latent image is formed by scanning the surfaces of the plurality of image carriers using the plurality of light beams.

Images