JP6614419B2 - Optical scanning device and image forming apparatus including the optical scanning device - Google Patents

Description

  The present invention relates to an optical scanning device and an image forming apparatus including the optical scanning device.

  Conventionally, as an optical scanning device mounted on an electrophotographic color image forming apparatus, light beams emitted from a plurality of light sources are deflected in the same direction by a common rotating mirror, and simultaneously on different scanning surfaces. What is made to scan is known.

  In this type of optical scanning device, for example, an upper light source and a lower light source arranged at different heights are provided, and a light beam is emitted from each light source along a preset upper optical path and lower optical path. A plurality of light beams are separated in the height direction (sub-scanning direction) and are incident on different scanned surfaces (see, for example, Patent Document 1). As the rotating mirror, an upper and lower two-stage configuration corresponding to the upper optical path and the lower optical path may be employed, or a thicker structure than usual may be employed.

  The upper light source and the lower light source are arranged at different phase positions when viewed from the axial direction of the rotary mirror. For this reason, the incident opening angle is different between the light beam incident on the rotating mirror from the upper light source and the light beam incident on the rotating mirror from the lower light source. If the incident opening angle is different, the reflection point of each light beam on the reflecting surface of the rotating mirror is also different. For this reason, there is a problem that the optical performance deteriorates due to variations in the beam diameter of each light beam on the surface to be scanned.

  In order to solve this problem, for example, in the optical scanning device disclosed in Patent Document 1, the incident open angle is corrected between the upper light source, the lower light source, and the rotating mirror in addition to the cylindrical lens having power in the sub-scanning direction. Optical performance is stabilized by arranging bending elements such as prisms. Further, in the optical scanning device disclosed in Patent Document 2, optical performance is improved by disposing two non-common imaging lenses on the downstream side of the optical path of the rotating mirror of the upper optical path and the lower optical path.

JP 2006-171317 A JP 2006-301205 A

  However, the optical scanning device disclosed in Patent Document 1 requires a refractive element such as a prism in addition to the cylindrical lens, which causes a problem of increasing costs. Further, in the optical scanning device shown in Patent Document 2, it is necessary to provide two imaging lenses for each of the upper optical path and the lower optical path, which increases the number of imaging lenses and causes an increase in cost. There's a problem.

  The present invention has been made in view of such a point, and the object of the present invention is to scan the light beams that are incident on the rotating mirror from the upper light source and the lower light source because of different incident open angles. It is to suppress a difference in the light diameter of each light beam on the surface by an inexpensive configuration.

  An optical scanning device according to the present invention includes a rotating mirror, an upper light source and a lower light source that are arranged at different heights and emit a light beam toward the rotating mirror, and an optical path of the light beam emitted from the upper light source And an upper image forming unit for forming an image of each light beam reflected by the rotating mirror on the surface to be scanned, provided on the upper optical path and the lower optical path which is the optical path of the light beam emitted from the lower light source. And a lower imaging unit.

  The light beam emitted from the upper light source and the light beam emitted from the lower light source have different incident open angles with respect to the reflecting surface of the rotating mirror, and the upper imaging unit and the lower imaging The imaging unit through which the light beam having the larger incident opening angle with respect to the reflecting surface passes constitutes the imaging unit compared to the imaging unit through which the light beam having the smaller incident opening angle passes. The number of imaging lenses is increased.

  An image forming apparatus according to the present invention includes the optical scanning device.

  According to the present invention, it is inexpensive to produce a difference in the light diameter of each light beam on the scanned surface due to the difference in the incident opening angle of each light beam incident on the rotating mirror from the upper light source and the lower light source. This can be suppressed by a simple configuration.

FIG. 1 is an overall view illustrating a schematic configuration of an image forming apparatus including an optical scanning device according to the present embodiment. FIG. 2 is a plan view of the optical scanning device viewed from the axial direction of the rotating mirror. 3 is a cross-sectional view taken along line III-III in FIG. FIG. 4 is an enlarged plan view showing the rotating mirror and its periphery in FIG. 2 in an enlarged manner. FIG. 5 is a side view of the optical scanning device viewed from the main scanning direction. FIG. 6 is a view corresponding to FIG. 5 showing another embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the following embodiment.

  FIG. 1 is a schematic configuration diagram of an image forming apparatus 1 according to the embodiment. The image forming apparatus 1 is a tandem type color printer, and includes an image forming unit 3 in a box-shaped casing 2. The image forming unit 3 transfers and forms an image on the recording paper P based on image data transmitted from an external device such as a computer connected to a network. An optical scanning device 4 that irradiates a light beam (laser light) is disposed below the image forming unit 3, and a transfer belt 5 is disposed above the image forming unit 3. A paper storage unit 6 that stores the recording paper P is disposed below the optical scanning device 4, and a manual paper feed unit 7 is disposed on the side of the paper storage unit 6. A fixing unit 8 that performs a fixing process on the image transferred and formed on the recording paper P is disposed on the upper side of the transfer belt 5. Reference numeral 9 denotes a paper discharge unit that is disposed on the casing 2 and discharges the recording paper P that has been subjected to fixing processing by the fixing unit 8.

  The image forming unit 3 includes four image forming units 10 arranged in a line along the transfer belt 5. These image forming units 10 have a photosensitive drum 11. A charger 12 is disposed immediately below each photoconductor drum 11, a developing device 13 is disposed on one side of each photoconductor drum 11, and a primary transfer roller is directly above each photoconductor drum 11. 14 is arranged, and on the other side of each photosensitive drum 11, a cleaning unit 15 for cleaning the peripheral surface of the photosensitive drum 11 is arranged.

  Each photosensitive drum 11 is uniformly charged on the peripheral surface by the charger 12, and each color based on image data input from the computer or the like is applied to the peripheral surface of the charged photosensitive drum 11. Corresponding laser light is irradiated from the optical scanning device 4, and an electrostatic latent image is formed on the peripheral surface of each photosensitive drum 11. Developer is supplied to the electrostatic latent image from the developing device 13, and a yellow, magenta, cyan, or black toner image is formed on the peripheral surface of each photosensitive drum 11. These toner images are respectively transferred to the transfer belt 5 by a transfer bias applied to the primary transfer roller 14.

  Reference numeral 16 denotes a secondary transfer roller disposed below the fixing unit 8 so as to be in contact with the transfer belt 5, and is a recording sheet conveyed through the sheet conveyance path 17 from the sheet storage unit 6 or the manual sheet feeding unit 7. P is sandwiched between the secondary transfer roller 16 and the transfer belt 5, and the toner image on the transfer belt 5 is transferred onto the recording paper P by a transfer bias applied to the secondary transfer roller 16.

  The fixing unit 8 includes a heating roller 18 and a pressure roller 19. The recording paper P is sandwiched and heated by the heating roller 18 and the pressure roller 19, and the toner image transferred to the recording paper P is transferred. Fix to recording paper P. The recording paper P after the fixing process is discharged to the paper discharge unit 9. Reference numeral 20 denotes a reversing conveyance path for reversing the recording paper P discharged from the fixing unit 8 during double-sided printing.

  Next, the details of the optical scanning device 4 will be described with reference to FIGS. As shown in FIG. 2, the optical scanning device 4 has a housing C that houses the optical deflector 40 therein. The casing C is open to the upper side, and the upper side of the casing C is closed by a lid member (not shown).

  The optical deflector 40 is disposed at the center of the bottom wall of the housing C. The optical deflector 40 includes a rotating mirror 41 and a motor 43 that rotates and has a shaft 42 to which the rotating mirror 41 is fixed.

  As shown in FIG. 3, the motor 43 includes a cylindrical motor 43 and a rotor portion 43 b disposed concentrically with respect to the stator portion 43 a. A shaft 42 is inserted and fixed to the rotor portion 43b. A coil portion 43c is provided on the inner peripheral portion of the stator portion 43a, and a magnet portion 43d is fixed on the outer peripheral portion of the rotor portion 43b with a gap from the coil portion 43c. The rotor portion 43b rotates together with the shaft 42 by energizing the coil portion 43c and applying a magnetic force to the magnet portion 43d. The shaft 42 extends in the vertical direction, and the rotating mirror 41 is fixed to the upper end portion thereof. A lower end portion of the shaft 42 is rotatably supported by the bearing portion 50. The bearing portion 50 is press-fitted and fixed in a hole formed in the bottom wall portion of the housing C.

  The rotating mirror 41 is provided between the upper polygon mirror 41a and the lower polygon mirror 41b, which are arranged at intervals in the vertical direction (axial direction of the shaft 42), and the polygon mirrors 41a and 41b. And a connecting portion 41c to be fixed.

  The upper polygon mirror 41a and the lower polygon mirror 41b are formed in a regular hexagonal column shape having six reflecting surfaces on the side surfaces. The upper polygon mirror 41a and the lower polygon mirror 41b are driven to rotate at a predetermined speed by the motor 43, thereby reflecting and deflecting and scanning the light beams emitted from the left and right light source units 44.

  The left and right light source sections 44 are arranged symmetrically with respect to a straight line that passes through the axis of the optical deflector 40 and extends in the front-rear direction. Each light source unit 44 includes an upper laser light source 44a (see FIGS. 2 and 4) that emits a light beam toward the upper polygon mirror 41a, and a lower laser light source 44b that emits a light beam toward the lower polygon mirror 41b. And have. The optical scanning device 4 has two optical paths, an upper optical path La that is an optical path of the light beam emitted from the upper laser light source 44a and a lower optical path Lb that is an optical path of the light beam emitted from the lower laser light source 44b. Have.

  As shown in FIG. 4, the light beam emitted from the upper laser light source 44a is incident on the reflecting surface of the upper polygon mirror 41a (open laser angle on the reflecting surface and the optical axis AX of the imaging lens 46a). The light beam incident at an angle α and emitted from the lower laser light source 44b is incident on the reflecting surface of the lower polygon mirror 41b (the incident laser light on the reflecting surface and the imaging lens). 47a is incident with an angle (β) formed with the optical axis AX. In the present embodiment, α> β.

  A collimator lens (not shown) and a cylindrical lens 45 are disposed on the upstream side of the optical path of the rotating mirror 41 in the upper optical path La and the lower optical path Lb, respectively. In addition, an upper image forming unit 46 and a lower image forming unit that form an image of a light beam on the surface to be scanned (the surface of the photosensitive drum 11) on the downstream side of the optical path of the rotating mirror 41 in the upper optical path La and the lower optical path Lb, respectively. A portion 47 is provided.

  As shown in FIG. 5, the upper imaging unit 46 is provided on the downstream side of the optical path of the main imaging lens 46a and the main imaging lens 46a having power in the sub-scanning direction and the main scanning direction, and only in the sub-scanning direction. And an auxiliary imaging lens 46b having power. The auxiliary imaging lens 46b corrects the light diameter difference on the surface to be scanned of the light beam caused by the difference in the incident open angles α and β of the light beams emitted from the light sources 44a and 44b. Each of the main imaging lens 46a and the auxiliary imaging lens 46b is composed of a crescent-shaped fθ lens in which the central portion in the main scanning direction bulges to the downstream side of the optical path with respect to both ends.

  The lower imaging unit 47 includes one imaging lens 47a having power in the sub-scanning direction and the main scanning direction. The imaging lens 47a is a saddle-shaped fθ lens in which the central portion in the main scanning direction bulges downstream of the optical path with respect to both ends.

  As shown in FIGS. 2 and 5, when the optical scanning device 4 is operated, the light beam emitted from the upper laser light source 44a of the left and right light source sections 44 is deflected and scanned by the upper polygon mirror 41a, and then the main imaging lens. 46a and the auxiliary imaging lens 46b in this order, and then reflected by the reflecting mirror 48a and imaged on the surface of the photosensitive drum 11. Further, the light beam emitted from the lower laser light source 44b of the left and right light source sections 44 is deflected and scanned by the lower polygon mirror 41b, passes through the lower imaging lens 47a, and then reflected by the reflecting mirror 48b to be photosensitive. An image is formed on the surface of the body drum 11.

  As described above, in the optical scanning device 4 of the present embodiment, the incident opening angle between the light beam incident on the rotating mirror 41 from the upper laser light source 44a and the light beam incident on the rotating mirror 41 from the lower laser light source 44b. α and β are different. If the incident opening angles α and β are different, the reflection position of each light beam on the reflection surface of the rotary mirror 41 is shifted in the mirror rotation direction. For this reason, there is a possibility that the optical performance is deteriorated due to variations in the beam diameter of each light beam on the scanned surface (on the surface of the photosensitive drum 11).

  On the other hand, in the present embodiment, among the upper imaging unit 46 and the lower imaging unit 47, the imaging unit 46 through which the light beam having the larger incident opening angle with respect to the reflecting surface of the rotating mirror 41 passes is incident. Compared with the imaging unit 47 through which the light beam having a smaller opening angle passes, the number of imaging lenses is increased. In other words, the lower imaging unit 47 is composed of one imaging lens 47a, while the upper imaging unit 46 has two imaging lenses including an auxiliary imaging lens 46b in addition to the main imaging lens 46a. It consists of As a result, the light diameter of the light beam having the larger incident opening angles α and β can be corrected to suppress variations in the light diameter on the surface to be scanned.

  Here, the upper image forming unit 46 forms an image of the light beam reflected by the upper polygon mirror 41a on the surface to be scanned. Since the upper polygon mirror 41a is located on the side farther from the bearing portion 50 (upper side) than the lower polygon mirror 41b, the deflection and axial tilt during rotation are greater than those of the lower polygon mirror 41b. For this reason, it is difficult for the light beam deflected and scanned by the upper polygon mirror 41a to have a fixed position in the sub-scanning direction on the surface to be scanned.

  On the other hand, in the present embodiment, the upper imaging unit 46 is configured by two imaging lenses, the main imaging lens 46a and the auxiliary imaging lens 46b, so that the touch and axis when the upper polygon mirror 41a is rotated are arranged. The scanning position of the light beam due to the tilt can be corrected. In this way, the auxiliary imaging lens 46b of the upper imaging unit 46 is not only used as a lens for correcting a difference in light diameter caused by the difference in the incident opening angles α and β of the respective light beams, but also the upper polygon mirror 41a. The optical performance can be enhanced as much as possible while reducing the number of imaging lenses as much as possible by using the lens as a correction lens for correcting the positional deviation of the light beam in the sub-scanning direction caused by touching and axis tilting during rotation. .

  In addition, since the auxiliary imaging lens 46b has power only in the sub-scanning direction, the lens cost can be reduced compared to the case where an imaging lens having power in the main scanning direction and the sub-scanning direction is used. .

<< Other embodiments >>
In the above embodiment, the optical scanning device 4 having the upper polygon mirror 41a and the lower polygon mirror 41b in which the rotary mirrors 41 are arranged in two upper and lower stages has been described, but the present invention is not limited to this. For example, as shown in FIG.

  In the above embodiment, the auxiliary imaging lens 46b has power only in the sub-scanning direction. However, the present invention is not limited to this, and the auxiliary imaging lens 46b may have power in both the sub-scanning direction and the main scanning direction. Good. That is, the auxiliary imaging lens 46b only needs to have power in at least the sub-scanning direction.

  In the above embodiment, only one auxiliary imaging lens 46b is provided, but a plurality of auxiliary imaging lenses 46b may be provided.

  In the above embodiment, the relationship α> β is satisfied, but the relationship is not limited to this, and β> α may be satisfied. In this case, the number of imaging lenses constituting the lower imaging unit 47 may be larger than the number of imaging lenses constituting the upper imaging unit 46.

  As described above, the present invention is useful for an optical scanning device and an image forming apparatus including the optical scanning device.

La Upper optical path Lb Lower optical path 1 Image forming apparatus 4 Optical scanning apparatus 41 Rotating mirror 42 Shaft (shaft)
44 Light Source 44a Upper Laser Light Source (Upper Laser Light Source)
44b Lower laser light source (lower laser light source)
45 Cylindrical lens 46 Upper imaging unit 47 Lower imaging unit

Claims (3)

A rotating mirror, an upper light source and a lower light source that are arranged at different heights and emit a light beam toward the rotating mirror, an upper optical path that is an optical path of the light beam emitted from the upper light source, and the lower light source An upper imaging unit and a lower imaging unit that are provided in a lower optical path that is an optical path of a light beam emitted from the light beam and that images each of the light beams reflected by the rotating mirror on a surface to be scanned. An optical scanning device,
The light beam emitted from the upper light source and the light beam emitted from the lower light source have different incident open angles with respect to the reflecting surface of the rotating mirror,
Of the upper imaging unit and the lower imaging unit, the imaging unit through which the light beam with the larger incident opening angle with respect to the reflecting surface passes is the imaging unit through which the light beam with the smaller incident opening angle passes. Compared with the optical scanning device, the optical scanning device is configured to increase the number of imaging lenses constituting the imaging unit. The optical scanning device according to claim 1,
A shaft portion extending in the vertical direction and supporting the rotating mirror;
A bearing portion that rotatably supports the shaft portion below the rotating mirror;
The imaging unit through which the light beam having the larger incident opening angle with respect to the reflecting surface passes is the upper imaging unit, and the imaging unit through which the light beam having the smaller incident opening angle passes is the lower imaging unit. An optical scanning device. An image forming apparatus comprising the optical scanning device according to claim 1.

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