JP2006293178A - Light beam scanner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light beam scanner in which the deviation of a focusing position of a light beam in an optical path direction due to the thermal expansion of a constant speed deflection means is reduced. <P>SOLUTION: An exposure unit E is provided with semiconductor lasers 1A to 1D, collimator lenses 2A to 2D, spacers 40A to 40D, a polygon mirror 6, a first fθ lens 7, a second fθ lens 8 and a case 60 or the like. The respective spacers 40A to 40D support the semiconductor lasers 1A to 1D, the collimator lenses 2A to 2D with predetermined gaps in an optical path direction of laser beams L1 to L4. The spacers 40A to 40D are made of aluminum and have thermal expansion characteristic with which the gap between the semiconductor lasers 1A to 1D and the collimator lenses 2A to 2D are reduced so that the deviation of the focusing points of the laser beams L1 to L4 which are to be focused on the surface of photoreceptor drums 101A to 101D in the optical path direction due to the thermal expansion of the first fθ lens 7 and the second fθ lens 8 in a thermal change is reduced. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a light beam scanning apparatus that scans a surface to be scanned with a light beam emitted from a light source.

  An image forming apparatus that performs electrophotographic image formation uses light that irradiates the surface of an image carrier (scanning target) with a light beam modulated based on image data read from a document or image data input from an external device. A beam scanning device is provided. The surface of the image carrier is uniformly charged in advance by charging means, and an electrostatic latent image is formed on the surface of the image carrier by irradiation with a light beam. The electrostatic latent image is visualized as a developer image (toner image) by the developer supplied from the developing means, and then transferred to a recording medium such as paper directly or via an intermediate transfer carrier. The toner image transferred to the recording medium is finally fixed on the recording medium by fixing means such as a thermal fixing device, and an image formed product is obtained.

  FIG. 1A is a plan view schematically showing an optical path of a laser beam (light beam) in a conventional light beam scanning apparatus 50, and FIG. 1B is a side view thereof. The light beam scanning device 50 includes a semiconductor laser (light source) 51, a collimator lens (optical means) 52, a cylindrical lens 53, a polygon mirror (constant angular velocity deflecting means) 54, an fθ lens (constant velocity deflecting means) 55, and the like. ing. The spread angle of the laser beam emitted from the semiconductor laser 51 is changed by the collimator lens 52 so as to become parallel light, and the laser beam is reduced in one direction by the cylindrical lens 53. The laser beam is deflected at a constant angular velocity by the polygon mirror 54 and further deflected at a constant velocity in the main scanning direction along the surface of the image carrier 56 by the fθ lens 55.

  In the conventional light beam scanning device 50, the housing that supports the semiconductor laser 51, the collimator lens 52, the cylindrical lens 53, the polygon mirror 54, and the fθ lens 55 is formed of BMC resin and does not thermally expand when the heat changes.

  In the conventional light beam scanning apparatus 50, the fθ lens 55 is formed of resin instead of glass for cost reduction and productivity improvement. For this reason, the fθ lens 55 is likely to thermally expand when the temperature changes due to an increase in the internal temperature due to the heat generated by the heat fixing device. When the fθ lens 55 is thermally expanded, the thickness of the fθ lens 55 increases from the thickness K1 to the thickness K2 (K1 <K2). When the fθ lens 55 is thermally expanded, as shown by a broken line in FIG. 2, the curved surface on the emission side of the laser beam approaches a plane, so that the focal length is extended. When the focal length is extended, the focal position of the laser beam to be connected to the surface of the image carrier 56 is shifted in the optical path direction, and the accuracy of the electrostatic latent image formed on the surface of the image carrier 56 is lowered.

Here, there is a technique that can correct the shift of the focal position due to thermal expansion of the collimator lens by changing the collimator lens itself when the heat changes (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 3-179420

  However, the technique of Patent Document 1 is a technique for correcting the shift of the focal position due to the thermal expansion of the collimator lens by moving the collimator lens itself that has undergone thermal expansion, and is based on the thermal expansion of the fθ lens 55. It does not correct the deviation of the focal position.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a light beam scanning apparatus capable of reducing the deviation in the optical path direction of the focal position of the light beam due to thermal expansion of the constant velocity deflection means.

  The light beam scanning apparatus of the present invention is configured as follows in order to solve the above-described problems.

  (1) A light source that emits a light beam, an optical unit that changes a spread angle of the light beam emitted from the light source, and the light source and the optical unit are supported at a predetermined interval in the optical path direction of the light beam. A first support means, a constant angular velocity deflecting means for deflecting a light beam passing through the optical means, a light beam deflected by the constant angular velocity deflecting means at a constant angular velocity in a predetermined scanning direction, etc. A velocity deflection unit; and the first support unit, the constant angular velocity deflection unit, and a casing that supports the uniform velocity deflection unit, wherein the first support unit is the uniform velocity deflection unit during a heat change. A thermal expansion characteristic of changing a distance between the light source and the optical means in a direction to reduce a deviation in a light path direction of a focal position of the light beam to be connected to a surface of a scanning target due to thermal expansion of That.

  In this configuration, the light source and the optical means are supported by the first support means. The light beam emitted from the light source is irradiated onto the surface to be scanned via the optical means, the constant angular velocity deflecting means, and the constant speed deflecting means. The first support means thermally expands when the heat changes, thereby changing the distance in the optical path direction between the light source and the optical means in a predetermined direction. When the distance in the optical path direction between the light source and the optical means is changed in a predetermined direction, the incident angle of the light beam incident on the optical means changes, and the focal position to be connected to the surface of the scanning target due to thermal expansion of the constant velocity deflection means The deviation is reduced.

  (2) Image forming means for forming an image of the light beam deflected at a constant speed by the constant speed deflecting means on the surface of the scanning target, and the constant speed deflecting means and the image forming means in the optical path direction of the light beam. A second support means for supporting the optical beam at a distance, and the second support means has a focal point of the light beam to be connected to the surface of the scanning target due to thermal expansion of the constant velocity deflection means during a heat change. It has a thermal expansion characteristic that changes the interval between the constant velocity deflection means and the imaging means in a direction to reduce the deviation of the position in the optical path direction.

  In this configuration, the constant velocity deflection unit and the imaging unit are supported by the second support unit. The second support means has a predetermined thermal expansion characteristic. The second support means thermally expands when the heat changes, thereby changing the distance in the optical path direction between the constant velocity deflection means and the imaging means in a predetermined direction. When the distance in the optical path direction between the constant velocity deflection means and the imaging means is changed to a predetermined direction, the incident angle of the light beam incident on the imaging means changes, and the surface of the object to be scanned due to the thermal expansion of the constant velocity deflection means The shift of the focal position that should be connected to is reduced.

  (3) The first support means and the second support means are formed of the same material.

  In this configuration, since the same material can be used for the first support means and the second support means, the design is facilitated. Further, both the first support means and the second support means are formed of, for example, aluminum, and the first support means and the second support means are arranged to reduce the shift of the focal position to be connected to the surface to be scanned due to the thermal expansion of the constant velocity deflection means. The support means and the second support means each thermally expand.

  (4) A plurality of light sources that emit light beams corresponding to different hues, and a plurality of optical means corresponding to the plurality of light sources, respectively, wherein the first support means includes the plurality of light sources. The plurality of optical means are supported at predetermined intervals in the optical path direction of the light beam emitted from each of the plurality of light sources.

  In this configuration, the light beam scanning device includes a plurality of light sources and a plurality of optical means corresponding to the light sources. The plurality of light sources and the plurality of optical means are supported by the first support means. Since the plurality of light sources and the plurality of optical means are supported by the first support means, the intervals between the light sources and the optical means corresponding to the light sources are uniformly changed during the heat change.

  (5) The first support means is provided as a single unit.

  In this configuration, all light sources and optical means are supported by a single first support means. Since all the light sources and the optical means are supported by the single first support means, the intervals between the light sources and the optical means corresponding to the light sources are uniformly changed during the heat change.

  (6) The first support means includes a first material portion, and a second material portion formed of a material having a smaller coefficient of thermal expansion than the first material portion, and the first material. And the second material portion are divided by a boundary line along the optical path direction of the light beam emitted from each of the plurality of light sources, and the first material portion is emitted from each of the plurality of light sources. A light source that emits light beams positioned at the upper end and the lower end of the plurality of light beams incident on the constant velocity deflecting unit and an optical unit corresponding to the light source; and the second material unit includes the first material unit. The light source and the optical means other than the light source and the optical means supported by the material portion are supported.

  At the time of heat change, the upper end and the lower end of the constant velocity deflecting unit thermally expand larger than the portions other than the upper end and the lower end, and conventionally, the focal position of the light beam incident on the upper end and the lower end of the constant velocity deflecting unit is It is farther from the focal position of the light beam incident on the part other than the lower end.

  In this configuration, the first material portion thermally expands more than the second material portion when the heat changes. For this reason, the distance between the light source that emits the light beam positioned at the upper end and the lower end of the plurality of light beams incident on the constant velocity deflecting unit and the optical unit corresponding to the light source is the same as that of the other light sources and the light source. The distance is greatly changed from the distance from the corresponding optical means. Therefore, the focal position of the light beam emitted from each light source is brought close to a single position.

  (7) Among the plurality of light sources, a light source that emits a light beam incident on an upper end or a lower end of the constant velocity deflection unit emits a light beam corresponding to a yellow hue.

  In this configuration, the light beam that is incident on the upper end or the lower end of the constant velocity deflecting unit and tends to have a large focal position shift is a light beam corresponding to the yellow hue. The yellow hue is the least noticeable hue compared to other hues.

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

  (1) By using the first support means having a predetermined thermal expansion characteristic, it is possible to reduce the deviation in the optical path direction of the focal position to be connected to the surface of the scanning target due to the thermal expansion of the constant velocity deflection means. . Therefore, it is possible to form an electrostatic latent image on the surface to be scanned with high accuracy.

  (2) By using the second support means having a predetermined thermal expansion characteristic, the deviation in the optical path direction of the focal position to be connected to the surface of the scanning target due to the thermal expansion of the constant velocity deflection means is further reduced. Can do. Therefore, an electrostatic latent image can be formed on the surface to be scanned with higher accuracy.

  (3) By forming both the first support means and the second support means with the same material (for example, aluminum), the design is facilitated, and the first support means and the second support means are provided. Appropriate thermal expansion can be achieved.

  (4) Since the distance between each light source and the optical means corresponding to the light source is changed uniformly during a heat change, the accuracy of scanning the surface to be scanned can be made uniform between hues. .

  (5) Since the distance between each light source and the optical means corresponding to the light source is uniformly changed between all the light sources and the optical means at the time of heat change, the accuracy of scanning the surface to be scanned is improved. It can be made more uniform between each hue.

  (6) Since the focal position of the light beam emitted from each light source can be brought close to a single position, the accuracy of scanning the surface to be scanned can be made more uniform between hues.

  (7) By making the light beam that tends to have a large focus position shift into a light beam that corresponds to the yellow hue that is most inconspicuous, it is possible to make the reduction in the accuracy of scanning the surface of the scanning object inconspicuous.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 is an explanatory diagram showing a schematic configuration of an image forming apparatus 100 including an exposure unit E which is a light beam scanning apparatus according to an embodiment of the present invention. The image forming apparatus 100 forms multicolor and single color images on a sheet based on the read image data of the original or image data transmitted via a network or the like. The image forming apparatus 100 includes an exposure unit E, photosensitive drums 101A to 101D, developing devices 102A to 102D, charging rollers 103A to 103D, cleaning units 104A to 104D, an intermediate transfer belt 11, primary transfer rollers 13A to 13D, and secondary transfer. A 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 are provided.

  The image forming apparatus 100 applies black (K) and four hues of cyan (C), magenta (M), and yellow (Y), which are three subtractive primary colors obtained by color separation of a color image. Image formation is performed in the image forming sections PA to PD using the corresponding image data. The image forming units PA to PD are configured in the same manner. For example, the black image forming unit PA includes a photosensitive drum 101A, a developing device 102A, a charging roller 103A, a transfer roller 13A, a cleaning unit 104A, and the like. The image forming portions PA to PD are arranged in a line in the moving direction of the intermediate transfer belt 11 (the sub-scanning direction that is orthogonal to the main scanning direction that is the scanning direction of the present invention).

  However, although not shown in FIG. 3, the photosensitive drum 101A has a larger diameter than the photosensitive drums 101B to 101D. In monochrome image formation performed using only the black image forming unit PA, there is a high demand for speeding up, and the frequency of use is higher than color image formation performed using all of the image forming units PA to PD. This is because the photosensitive drum 101A provided in the black image forming portion PA needs to have a longer life than the photosensitive drums 101B to 101D. The photosensitive drums 101B to 101D have the same diameter. For this reason, the interval between the rotation shaft of the photosensitive drum 101A and the rotation shaft of the photosensitive drum 101B is longer than the interval between the rotation shafts of the photosensitive drums 101B to 101D.

  The charging roller 103A is a contact-type charger that uniformly charges the surface of the photosensitive drum 101A, which is an image carrier as a scanning target of the present invention, to a predetermined potential. Instead of the charging roller 103A, a contact type charger using a charging brush or a non-contact type charger using a charging charger may be used. Each of the charging rollers 103B to 103D is configured similarly to the charging roller 103A.

  An exposure unit E which is a light beam scanning apparatus of the present invention includes a semiconductor laser, a polygon mirror 6, a first fθ lens 7, a second fθ lens 8, and the like (not shown), and images of each hue of black, cyan, magenta and yellow. Each of the photosensitive drums 101A to 101D is irradiated with a laser beam (which is a light beam of the present invention) modulated according to data. On each of the photosensitive drums 101A to 101D, an electrostatic latent image is formed based on image data of each hue of black, cyan, magenta, and yellow. Details of the exposure unit E will be described later.

  The developing device 102A stores black toner, supplies black toner to the surface of the photosensitive drum 101A on which the electrostatic latent image is formed, and visualizes the electrostatic latent image into a developer image. Each of the developing devices 102B to 102D stores toner of each hue of cyan, magenta, and yellow, and the electrostatic latent images of each hue formed on each of the photosensitive drums 101B to 101D are cyan, magenta, and yellow. To develop a developer image of each hue.

  The cleaning unit 104A removes and collects toner remaining on the surface of the photosensitive drum 101A after development and image transfer. As with the cleaning unit 104A, each of the cleaning units 104B to 104D removes and collects toner remaining on the surfaces of the photosensitive drums 101B to 101D after development and image transfer.

  The intermediate transfer belt 11 is stretched between the driving roller 11A and the driven roller 11B to form a loop-shaped moving 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.

  In order to transfer the developer images carried on the surfaces of the photosensitive drums 101A to 101D onto the intermediate transfer belt 11, primary transfer biases having a polarity opposite to the charging polarity of the toner are applied to the primary transfer rollers 13A to 13D. Applied by control. As a result, the developer images of the respective colors formed on the photosensitive drums 101 </ b> A to 101 </ b> D are sequentially superimposed on the outer peripheral surface of the intermediate transfer belt 11, and a full-color developer image is formed on the outer peripheral surface of the intermediate transfer belt 11. The

  However, when image data of only a part of the hues of yellow, magenta, cyan, and black is input, only a part corresponding to the hue of the input image data among the four photosensitive drums 101A to 101D. In step S1, an electrostatic latent image and a developer image are formed. For example, when forming a monochrome image, an electrostatic latent image and a developer image are formed only on the photosensitive drum 101A corresponding to the black hue, and only the black developer 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.

  The developer image transferred to the outer peripheral surface of the intermediate transfer belt 11 at each primary transfer position is conveyed to a secondary transfer position that is a position facing the secondary transfer roller 14 by the rotation of the intermediate transfer belt 11. The secondary transfer roller 14 is in pressure contact with 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 (recording medium) 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 charging polarity of the toner is applied to the secondary transfer roller 14. A high voltage having a polarity opposite to that of is applied. As a result, the developer image is transferred from the outer peripheral surface of the intermediate transfer belt 11 to the surface of the sheet.

  In order to prevent color mixing in the next process, the toner remaining on the intermediate transfer belt 11 without being transferred onto the paper from among the toner adhering to the intermediate transfer belt 11 from some or all of the photosensitive drums 101A to 101D. It is collected by the cleaning unit 12.

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

  In the image forming apparatus 100, a substantially vertical direction for feeding the paper stored in the paper feed 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. Paper transport path P1 is provided.

  In the paper transport path P1, the pickup roller 16A and paper feed roller 16B that feed out the paper in the paper feed cassette 16 one by one into the paper transport path P1, and the uppermost position when a plurality of papers are fed out in a superimposed manner. A paper pad 16C for scooping the paper so that only the paper to be conveyed is transported, and a transport roller R capable of changing the rotational speed for transporting the fed paper along the paper transport path P1 are arranged.

  A paper detector 30 is disposed immediately after the separation pad 16C of the paper transport path P1. The paper detector 30 detects the presence or absence of paper passing between the paper feed roller 16B and the scooping pad 16C. That is, the paper detector 30 detects whether or not one sheet is properly fed from the paper feed cassette 16 to the paper transport path P1 by the pickup roller 16A. Further, the paper detector 30 outputs a detection result to a control unit (not shown).

  In the paper conveyance path P1, a registration roller 19 that guides the conveyed paper between the secondary transfer roller 14 and the intermediate transfer belt 11 at a predetermined timing, and a paper discharge roller that discharges the paper to the paper discharge tray 18 18A is arranged.

  In the image forming apparatus 100, a sheet conveyance path P <b> 2 is formed between the manual sheet feeding tray 17 and the registration roller 19. Similarly to the configuration of the paper transport path P1, the paper transport path P2 includes a pick-up roller 17A, a paper feed roller 17B, and a separating pad 17C for feeding the papers placed on the manual feed tray 17 one by one into the paper transport path P2. Is arranged.

  Further, a sheet conveyance path P3 is formed between the paper discharge roller 18A and the upstream side of the registration roller 19 in the sheet conveyance path P1. The paper discharge roller 18A is rotatable in both forward and reverse directions. When forming a single-sided image for forming an image on one side of a sheet, and when 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, at the time of forming the first surface image 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 only on 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 performs secondary transfer of paper fed from the paper feed cassette 16 or the manual paper feed tray 17 or transported via the paper transport path P3 at a timing synchronized with the rotation of the intermediate transfer belt 11. Guided between the roller 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 of being in contact with (chucked) 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, and the front end portion of the sheet and the front end portion of the developer image formed on the intermediate transfer belt 11 face each other. To start rotation.

  At the time of full color image formation in which image formation is performed in all of the image forming portions PA to PD, the primary transfer rollers 13A to 13D press the intermediate transfer belt 11 against all the photosensitive drums 101A to 101D. On the other hand, at the time of monochrome image formation in which image formation is performed only in the image forming unit PA, only the primary transfer roller 13A presses the intermediate transfer belt 11 against the photosensitive drum 101A.

  FIG. 4 is a side view showing a schematic configuration of the exposure unit E. As shown in FIG. FIG. 5 is a plan view showing a schematic configuration of the exposure unit E. In FIG. 5, the arrow XX direction, which is a direction parallel to the rotation axis of the photosensitive drum 101 and is the scanning direction of the laser beams L1 to L4, is the scanning direction of the present invention, and is the main scanning direction. That's it. In FIG. 4, the arrow Y-Y direction, which is the direction orthogonal to the main scanning direction within the deflection surface 6A, is referred to as the sub-scanning direction.

  The exposure unit E includes semiconductor lasers 1A to 1D, collimator lenses 2A to 2D, mirrors 3B to 3D, first cylindrical lens 4, mirror 5, polygon mirror 6, first fθ lens 7, second fθ lens 8, and second cylindrical lens 9A. To 9D, mirrors 21, 22A to 22C, 23A, 23B, 24A to 24C, optical components such as the synchronization lens 10A and the BD sensor 10, and a housing 60 that supports these optical components. The housing 60 is made of aluminum.

  Each semiconductor laser 1A-1D is equivalent to the light source of this invention. Each collimator lens 2A-2D is equivalent to the optical means of this invention. The polygon mirror 6 corresponds to the equiangular velocity deflecting means of the present invention. The first fθ lens 7 and the second fθ lens 8 correspond to constant velocity deflection means of the present invention. Each of the second cylindrical lenses 9A to 9D corresponds to the image forming means of the present invention. Moreover, in this embodiment, the housing | casing 60 is corresponded to the 2nd support means of this invention.

  As shown in FIG. 6, the semiconductor laser 1A and the collimator lens 2A corresponding to the semiconductor laser 1A are provided with a predetermined interval SA in the optical path direction of the laser beam L1 emitted from the semiconductor laser 1A, and a single spacer 40A. Is supported by. Similarly, the semiconductor laser 1B and the collimator lens 2B are supported by a single spacer 40B with a predetermined interval SB in the optical path direction of the laser beam L2 emitted from the semiconductor laser 1B, and the semiconductor laser 1C and the collimator lens 2C. Means a laser beam L3 emitted from the semiconductor laser 1D and provided with a predetermined interval SC in the optical path direction of the laser beam L3 emitted from the semiconductor laser 1C and supported by a single spacer 40C. A predetermined interval SD is provided in the optical path direction of the beam L4 and is supported by a single spacer 40D.

  Each spacer 40 </ b> A to 40 </ b> D is formed of the same material as that of the housing 60. That is, the spacers 40A to 40D are made of aluminum in this embodiment. Each of the spacers 40A to 40D corresponds to the first support means of the present invention.

  Each of the semiconductor lasers 1A to 1D emits laser beams L1 to L4 modulated based on black, cyan, magenta, and yellow image data, respectively. Each of the laser beams L1 to L4 is a light beam of the present invention. The laser beams L1 to L4, which are diffused lights emitted from the semiconductor lasers 1A to 1D, are changed into parallel lights by changing the spread angles by the collimator lenses 2A to 2D, and become mirrors 3B to 3D, the first cylindrical lens 4 and the mirror. 5, the light enters the reflecting surface 61 of the polygon mirror 6 at different incident angles within a plane including the rotation axis of the polygon mirror 6. The semiconductor lasers 1A to 1D, the collimator lenses 2A to 2D, and the mirrors 3B to 3D are provided with a height difference so that the laser beams L1 to L4 do not pass through the corresponding mirrors 3B to 3D. Has been placed.

  The polygon mirror 6 includes seven reflecting surfaces 61 as an example. The polygon mirror 6 rotates in the direction of arrow A and deflects the laser beams L1 to L4 at the respective reflecting surfaces 61 in the direction of arrow B at a constant angular velocity.

  The first fθ lens 7 and the second fθ lens 8 deflect the laser beams L1 to L4 deflected at a constant angular velocity by the polygon mirror 6 to the respective surfaces of the photosensitive drums 101A to 101D at a constant velocity in the direction of arrow C in the main scanning direction. To do. As a result, the respective surfaces of the photosensitive drums 101A to 101D are scanned in the direction of arrow C. As an example, both the entrance surface and the exit surface of the first fθ lens 7 are aspherical surfaces. Further, the incident surface of the second fθ lens 8 is constituted by a free-form surface, and the exit surface is constituted by an aspheric surface.

  The mirrors 21, 22A to 22C, 23A, 23B, and 24A to 24C separate the laser beams L1 to L4 so that the laser beams L1 to L4 are distributed on the respective surfaces of the photosensitive drums 101A to 101D. reflect. The laser beam L1 that has passed through the second fθ lens 8 forms an image on the surface of the photosensitive drum 101A via the mirror 21 and the second cylindrical lens 9A. The laser beam L2 that has passed through the second fθ lens 8 forms an image on the surface of the photosensitive drum 101B via the mirrors 22A to 22C and the second cylindrical lens 9B. The laser beam L3 that has passed through the second fθ lens 8 forms an image on the surface of the photosensitive drum 101C via the mirrors 23A and 23B and the second cylindrical lens 9C. The laser beam L4 that has passed through the second fθ lens 8 forms an image on the surface of the photosensitive drum 101D via the mirrors 24A to 24C and the second cylindrical lens 9D.

  The laser beams L 1 and L 2 and the laser beams L 3 and L 4 pass through the second fθ lens 8, and are positioned above and below the deflection surface 6 A that is a horizontal plane including the normal direction of each reflection surface 61 of the polygon mirror 6. Is deflected in a plane parallel to the deflection surface 6A.

  As the first fθ lens 7, the second fθ lens 8, and the second cylindrical lens 9, plastic molded products are used for cost reduction and productivity improvement.

  The BD sensor 10 detects any one of the laser beams L1 to L4 outside the effective exposure region F in the main scanning direction. That is, any of the laser beams L1 to L4 reflected by the reflecting surface 61 of the polygon mirror 6 does not reach the surface of the photosensitive drum 101 in the main scanning direction, and the light receiving surface of the BD sensor 10 through the synchronization lens 10A. To form an image. When receiving any one of the laser beams L1 to L4, the BD sensor 10 outputs a signal for determining the modulation start timing based on the image data of each of the laser beams L1 to L4 in the semiconductor lasers 1A to 1D.

  In this embodiment, since the laser beams L1 to L4 are reflected so that all the laser beams L1 to L4 are substantially overlapped by the same reflecting surface 61 of the polygon mirror 6, the BD sensor 10 receives one laser beam. Only by this, it is possible to control the modulation start timing of all the laser beams L1 to L4. Since the detection is performed by the BD sensor 10 using the laser beam L1 that forms a black image with the least bending distortion of the scanning line, highly accurate detection can be performed.

  FIG. 7A is a plan view schematically showing the optical paths of the laser beams L1 to L4 when the spacers 40A to 40D are thermally expanded during the heat change in the exposure unit E, and FIG. FIG.

  The first fθ lens 7 and the second fθ lens 8 are conceptually shown as an fθ lens 78. The same applies to FIGS. 8 and 9 shown below. Although the semiconductor laser 1A and the collimator lens 2A are described here, the same applies to the semiconductor lasers 1B to 1D and the collimator lenses 2B to 2D.

  As described above, the semiconductor laser 1A and the collimator lens 2A are supported by the spacer 40A. The spacer 40A is made of aluminum and thermally expands when the heat changes due to heat generated by the semiconductor laser 1A or the like. When the spacer 40A is thermally expanded, the interval M1 between the semiconductor laser 1A and the collimator lens 2A is expanded to the interval M2 (M1 <M2).

  When the interval M1 between the semiconductor laser 1A and the collimator lens 2A is widened to the interval M2, as shown by a broken line in FIG. 7, a laser beam having a small divergence angle is emitted from the laser beam L1 emitted from the semiconductor laser 1A. 2A enters, and the focal length is shortened. For this reason, the deviation in the optical path direction of the laser beam L1 of the focal position of the laser beam L1 to be connected to the surface of the photosensitive drum 101A due to the thermal expansion of the fθ lens 78 is reduced.

  Note that, as shown in FIG. 7B, the focal position of the laser beam L1 when viewed from the side surface direction during a heat change is substantially the same as that before the heat change.

  FIG. 8 is a side view schematically showing an optical path of the laser beam L1 when the housing 60 is thermally expanded at the time of heat change in the exposure unit E. Although the optical path of the laser beam L1 will be described here, the same applies to the optical paths of the laser beams L2 to L4.

  As described above, the fθ lens 78 (the first fθ lens 7 and the second fθ lens 8) and the second cylindrical lens 9A are supported by the housing 60. Moreover, since the housing | casing 60 is a product made from aluminum, it thermally expands at the time of the heat change by the heat which generate | occur | produced from the laser beams L1-L4. When the housing 60 is thermally expanded, the interval N1 between the fθ lens 78 and the second cylindrical lens 9A in the optical path direction of the laser beam L1 is expanded to the interval N2 (N1 <N2).

  When the interval N1 between the fθ lens 78 and the second cylindrical lens 9A is increased to the interval N2, the focal length of the laser beam L1 incident on the second cylindrical lens 9A is reduced as indicated by a broken line at 87. For this reason, the deviation in the optical path direction of the laser beam L1 of the focal position of the laser beam L1 to be connected to the surface of the photosensitive drum 101A due to the thermal expansion of the fθ lens 78 is reduced.

  FIG. 9 is an explanatory diagram showing the positional relationship between the optical paths of the laser beams L1 to L4 and the fθ lens 78. As shown in FIG. Each of the laser beams L <b> 1 to L <b> 4 is incident on the fθ lens 78 in parallel planes whose positions are different in the vertical direction. When the fθ lens 78 expands during a heat change, the expansion coefficients at the upper and lower ends increase with respect to the center of the fθ lens 78. Therefore, the deviation in the optical path direction of the focal positions of the laser beams L1 and L4 incident on the upper and lower ends of the fθ lens 78 is considered to be larger than the deviation in the optical path direction of the focal positions of the other laser beams L2 and L3. It is done.

  The laser beam L4 modulated by the image data of yellow hue is incident on the lower end of the fθ lens 78. Note that the laser beam L4 modulated by the image data of yellow hue may be incident on the upper end of the fθ lens 78.

  Here, the laser beams L2 and L3 incident on the center of the fθ lens 78 are called inner laser beams (or inner beams), and the laser beams L1 and L4 incident on the upper and lower ends of the fθ lens 78 are outer laser beams ( Or an outer beam).

10 to 15 are experimental data showing the beam diameters of the laser beams L1 to L4 at the respective positions in the main scanning direction when the housing 60 and the spacers 40A to 40D are thermally changed to 50 degrees. 10 and 11 show the case 60 and the spacers 40A to 40D made of aluminum (linear expansion coefficient: 25 × 10 ⁻⁶ / ° C.), and FIGS. 12 and 13 show the case 60 and the spacer 40A. ˜40D is made of polycarbonate (linear expansion coefficient: 40 × 10 ⁻⁶ / ° C.), and FIGS. 14 and 15 show the casing 60 and the spacers 40A to 40D as BMC resin (linear expansion coefficient: 15 × 10). ^-6 / ° C). 10, 12 and 14 show the beam diameters of the inner laser beams L2 and L3, and FIGS. 11, 13 and 15 show the beam diameters of the outer laser beams L1 and L4.

  10 to 15, the upper stage shows the horizontal beam diameter (μm), and the lower stage shows the vertical beam diameter (μm). The positions (mm) of the photosensitive drums 101A to 101D are set so that the direction of approaching the semiconductor lasers 1A to 1D with respect to the reference position (0) is -1 (mm) to -3 (mm) in consideration of mounting errors. The direction away from the semiconductor lasers 1A to 1D with respect to the reference position (0) is indicated by 1 (mm) to 3 (mm).

  10-15, the beam diameter in the appropriate range is underlined with the appropriate range of the beam diameter in the horizontal direction being 50 μm or more and less than 65 μm, and the vertical beam diameter being 55 μm or more and less than 70 μm. Yes.

  When the casing 60 and the spacers 40A to 40D are formed of BMC resin having the smallest linear expansion coefficient among the three types of materials, the photosensitive drums 101A to 101D are used for the inner laser beams L2 and L3 as shown in FIG. In the range of −1 to +1, all the beam diameters are within the appropriate range. However, as shown in FIG. 15, for the outer laser beams L1 and L4, when the positions of the photosensitive drums 101A to 101D are −1 mm, some of the horizontal beam diameters are not within the proper range.

  In contrast, when the casing 60 and the spacers 40A to 40D are formed of aluminum having the second largest linear expansion coefficient among the three types of materials, as shown in FIGS. 10 and 11, the photosensitive drum 101A is formed. It can be seen that all beam diameters are within the appropriate range when the position of −101D is in the range of −1 to +1, and that the correction effect as intended by the present invention is obtained. This is probably because the correction is realized in such a manner that the region in which the beam diameter of the outer beam is within the appropriate range in FIG. 11 moves upward (in the direction in which the negative value of the position of the photosensitive drum increases). .

  On the other hand, when the casing 60 and the spacers 40A to 40D are formed of polycarbonate having the largest linear expansion coefficient among the three types of materials, the linear expansion coefficient is too large to obtain an appropriate correction effect. As shown in FIG. 13, the beam diameter is often not within the appropriate range. As shown in FIGS. 12 and 13, the region in which the beam diameter is within the appropriate range is greatly increased in the upward direction (the direction in which the negative value of the position of the photosensitive drum increases) in FIGS. It is considered that the desired result was not obtained by the correction.

  Therefore, from the experimental data shown in FIGS. 10 to 15, the case 60 and the spacers 40 </ b> A to 40 </ b> D are formed of aluminum as compared to the case of the case 60 and the spacers 40 </ b> A to 40 </ b> D formed of polycarbonate and BMC resin. It has been found that the deviation in the optical path direction of the focal positions of the laser beams L1 to L4 due to thermal expansion of the fθ lens 78 can be corrected more appropriately.

  According to the exposure unit E, the semiconductor lasers 1A to 1D and the collimator lenses 2A to 2D are supported by the spacers 40A to 40D made of aluminum, respectively, so that the fθ lens 78 (the first fθ lens 7 and the second fθ lens 8) at the time of thermal change. ) Due to thermal expansion of the photosensitive drums 101A to 101D can be reduced in the optical path direction. Therefore, electrostatic latent images can be formed with high accuracy on the surfaces of the photosensitive drums 101A to 101D.

  Further, the housing 60 that supports the fθ lens 78 (the first fθ lens 7 and the second fθ lens 8) and the second cylindrical lenses 9A to 9D is formed of aluminum, so that the fθ lens 78 (first fθ when the heat changes) is formed. The deviation in the optical path direction of the focal position to be connected to the surfaces of the photosensitive drums 101A to 101D due to the thermal expansion of the lens 7 and the second fθ lens 8) can be further reduced. Therefore, electrostatic latent images can be formed on the surfaces of the photoconductive drums 101A to 101D with higher accuracy.

  Furthermore, design is facilitated by forming the spacers 40A to 40D and the housing 60 from the same material (aluminum).

  Further, even when the deviation of the focal position of the laser beam incident on the upper end or the lower end of the fθ lens 78 (the first fθ lens 7 and the second fθ lens 8) in the optical path direction is large, the laser beam L4 corresponding to the yellow hue that is most inconspicuous. Is made incident on the upper end or the lower end of the fθ lens 78 (the first fθ lens 7 and the second fθ lens 8), the deterioration in the accuracy of scanning the surfaces of the photosensitive drums 101A to 101D can be made inconspicuous.

  The fθ lens 78 (the first fθ lens 7 and the second fθ lens 8) and the second cylindrical lenses 9A to 9D are supported at a predetermined interval in the optical path direction by an aluminum support base (second support means). Even when the support base is supported by the housing, the same effects as those of the exposure unit E can be obtained. In this case, the casing may be formed of BMC resin or the like.

  FIG. 16 is a plan view showing a part of the configuration of an exposure unit E2 which is a light beam scanning apparatus according to another embodiment. The exposure unit E2 according to this embodiment is formed in the same manner as the exposure unit E except that the semiconductor lasers 1A to 1D and the collimator lenses 2A to 2D are supported at predetermined positions by a single support member 41. ing. The support member 41 is made of aluminum.

  According to the exposure unit E2, the intervals between the semiconductor lasers 1A to 1D and the collimator lenses 2A to 2D corresponding to the semiconductor lasers 1A to 1D can be uniformly changed when the heat changes. Therefore, the accuracy of scanning the surfaces of the photosensitive drums 101A to 101D can be made uniform among the hues.

  As shown in FIG. 17, the support member 41 includes a first material portion 41A and a second material portion 41B formed of a material having a smaller coefficient of thermal expansion than the first material portion 41A. You can also. For example, the first material portion 41A is made of polycarbonate, and the second material portion 41B is made of aluminum. In this case, the first material portion 41A and the second material portion 41B are divided by boundary lines along the optical path direction of the laser beams L1 to L4 emitted from the respective semiconductor lasers 1A to 1D. The first material portion 41A is positioned at the upper and lower ends of the plurality of laser beams emitted from each of the plurality of semiconductor lasers 1A to 1D and entering the fθ lens 78 (the first fθ lens 7 and the second fθ lens 8). The semiconductor lasers 1A and 1D that emit the laser beams L1 and L4 and the collimator lenses 2A and 2D corresponding to the semiconductor lasers 1A and 1D are supported. The second material portion 41B supports the semiconductor lasers 1B and 1C and the collimator lenses 2B and 2C.

  According to this configuration, the first material portion 41A thermally expands more than the second material portion 41B during a heat change. For this reason, the intervals between the semiconductor lasers 1A and 1D and the collimator lenses 2A and 2D are changed to be larger than the intervals between the semiconductor lasers 1B and 1C and the collimator lenses 2B and 2C. For this reason, the focal positions of the laser beams L1 to L4 emitted from the semiconductor lasers 1A to 1D are brought close to a single position. Therefore, the accuracy of scanning the surfaces of the photosensitive drums 101A to 101D can be made more uniform between the hues.

(A) is a top view which shows typically the optical path of the laser beam in the conventional light beam scanning apparatus, (B) is the side view. (A) is a top view which shows typically the optical path of the laser beam at the time of the heat change in the conventional light beam scanning apparatus, (B) is the side view. 1 is a side view showing a schematic configuration of an image forming apparatus including an exposure unit which is a light beam scanning apparatus according to an embodiment of the present invention. It is a side view which shows the schematic structure of the said exposure unit. It is a top view which shows the schematic structure of the said exposure unit. It is a side view which shows the spacer which supports a semiconductor laser and a collimator lens. (A) is a plan view schematically showing an optical path of a laser beam when a spacer is thermally expanded at the time of heat change in the exposure unit, and (B) is a side view thereof. It is a side view which shows typically the optical path of a laser beam when a housing | casing thermally expands at the time of a heat change in the said exposure unit. It is explanatory drawing shown about the positional relationship of the optical path of a several laser beam, and f (theta) lens. It is experimental data which shows the beam diameter of the inner side laser beam in each position of the main scanning direction at the time of forming a housing | casing and a spacer with aluminum. It is experimental data which shows the beam diameter of the outer side laser beam in each position of the main scanning direction at the time of forming a housing | casing and a spacer with aluminum. It is experimental data which shows the beam diameter of the inner side laser beam in each position of the main scanning direction at the time of forming a housing | casing and a spacer with a polycarbonate. It is experimental data which shows the beam diameter of the outside laser beam in each position of the main scanning direction at the time of forming a housing | casing and a spacer with a polycarbonate. It is experimental data which shows the beam diameter of the inner side laser beam in each position of the main scanning direction at the time of forming a housing | casing and a spacer with BMC resin. It is experimental data which shows the beam diameter of the outside laser beam in each position of the main scanning direction at the time of forming a housing | casing and a spacer with BMC resin. It is a top view which shows the structure of a part of exposure unit which is the light beam scanning apparatus which concerns on other embodiment. It is a top view which shows the structure of a part of exposure unit which is the light beam scanning apparatus which concerns on other embodiment.

Explanation of symbols

1A to 1D semiconductor laser (light source)
2A to 2D collimator lens (optical means)
6 Polygon mirror (equal angular velocity deflection means)
7 1st fθ lens (constant velocity deflection means)
8 Second fθ lens (constant velocity deflection means)
78 fθ lens (constant velocity deflection means)
9A to 9D Second cylindrical lens (imaging means)
40A to 40D spacer (first support means)
41 Support member (first support means)
41A 1st material part 41B 2nd material part 60 Case (2nd support means)
101A to 101D Photosensitive drum (scanning target)

Claims (7)

A light source that emits a light beam;
Optical means for changing the spread angle of the light beam emitted from the light source;
First support means for supporting the light source and the optical means at a predetermined interval in the optical path direction of the light beam;
Equal angular velocity deflecting means for deflecting the light beam that has passed through the optical means, at equal angular velocity;
Uniform velocity deflecting means for deflecting the light beam deflected at a uniform angular velocity by the uniform angular velocity deflecting device in a predetermined scanning direction;
A housing that supports the first support means, the constant angular velocity deflection means, and the constant velocity deflection means,
The first support means includes the light source and the optical means in a direction to reduce a deviation in a light path direction of a focal position of the light beam to be connected to a surface of a scanning target due to thermal expansion of the constant velocity deflection means at the time of thermal change. A light beam scanning device characterized by having a thermal expansion characteristic that changes a distance between the light beam and the light beam. Imaging means for imaging the light beam deflected at a constant speed by the constant speed deflection means on the surface of the scanning object;
A second support means for supporting the constant velocity deflection means and the imaging means at a predetermined interval in the optical path direction of the light beam,
The second support means and the constant velocity deflection means in a direction to reduce a deviation in the optical path direction of the focal position of the light beam to be connected to the surface of the scanning target due to thermal expansion of the constant velocity deflection means at the time of thermal change. The light beam scanning apparatus according to claim 1, wherein the light beam scanning apparatus has a thermal expansion characteristic that changes a distance from the imaging unit.   The light beam scanning apparatus according to claim 2, wherein the first support unit and the second support unit are formed of the same material. A plurality of light sources for emitting light beams corresponding to different hues, and a plurality of optical means corresponding to each of the plurality of light sources,
The first support means supports the plurality of light sources and the plurality of optical means at predetermined intervals in an optical path direction of a light beam emitted from each of the plurality of light sources. The light beam scanning device according to any one of 1 to 3.   The light beam scanning apparatus according to claim 4, wherein only one first support means is provided. The first support means includes a first material part, and a second material part formed of a material having a smaller coefficient of thermal expansion than the first material part,
The first material portion and the second material portion are divided by a boundary line along the optical path direction of the light beam emitted from each of the plurality of light sources,
The first material portion includes a light source that emits light beams positioned at an upper end and a lower end among a plurality of light beams emitted from each of the plurality of light sources and incident on the constant velocity deflection unit, and an optical corresponding to the light source. Support the means,
6. The light beam scanning apparatus according to claim 4, wherein the second material portion supports a light source and optical means other than the light source and optical means supported by the first material portion.   The light source that emits a light beam incident on the upper end or the lower end of the constant velocity deflecting unit among the plurality of light sources emits a light beam corresponding to a yellow hue. 2. A light beam scanning apparatus according to 1.

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