JP6669991B2 - Optical scanning device and image forming apparatus provided with 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.

  2. Description of the Related Art Conventionally, as an optical scanning device mounted on an electrophotographic color image forming apparatus, a plurality of light sources opposed to respective colors of yellow, magenta, cyan and black, and deflection scanning of light beams emitted from the plurality of light sources. A rotating polygon mirror is known. The rotating polygon mirror separates the light beams emitted from the plurality of light sources and reflects the light beams toward the image carrier corresponding to each color.

  In this type of optical scanning device, a rotating polygon mirror may be provided in a plurality of stages in order to facilitate separation of a light beam. For example, in an optical scanning device disclosed in Patent Literature 1, rotating polygon mirrors are arranged vertically in two stages. The two rotating polygon mirrors are fixed to a shaft, and the shaft is rotatably supported by a bearing.

JP 2007-304624 A

  However, in the optical scanning device disclosed in Patent Literature 1, the rotation polygonal mirror located farther from the bearing unit has a larger deflection and tilting during rotation than the rotary polygonal mirror located closer to the bearing. Therefore, the position of the light beam passing through the optical path (second optical path) farther from the bearing portion than the light beam passing through the optical path closer to the side (first optical path) in the sub-scanning direction in the sub-scanning direction. Becomes larger. As a result, there is a problem that an image defect such as jitter occurs in the printed image due to a positional shift of the light beam in the sub-scanning direction. This problem can occur even if the rotary polygon mirror is configured not as a plurality of stages but as one stage as long as it has two optical paths separated in the axial direction.

  In order to solve the above problem, the reflecting surface of the rotating polygon mirror is processed with high precision in consideration of the deflection and the shaft tilt during rotation of the shaft, or the shaft is tilted by a jig or the like during assembly of the optical scanning device. May be adjusted, but in that case, there is a problem that the processing cost and the operation cost at the time of assembly are significantly increased.

  The present invention has been made in view of such a point, and an object of the present invention is to displace a light beam passing through a second optical path located on a side farther from the bearing than the first optical path in the sub-scanning direction. Is suppressed by an inexpensive configuration.

An optical scanning device according to the present invention includes a rotary polygon mirror, a shaft supporting the rotary polygon mirror, a bearing rotatably supporting the shaft, and a first light beam directed toward the rotary polygon mirror. And a second light source that emits a second light beam toward the rotating polygon mirror, and a light incident side of the second light beam emitted from the second light source with respect to the rotating polygon mirror. the second incident side optical path Ru optical path der is, the first light beam the rotary remote from the bearing section than that of the first incident side optical path is an optical path of the light incident side with respect to polygonal mirror emitted from the first light source located in a first imaging unit for imaging the provided first reflection side optical path is an optical path of the light reflecting side for the first light beam of the rotating polygon mirror of the first light beam on the scanned surface , the second reflection side optical an optical path of the light reflecting side with respect to the rotating polygon mirror of the second light beam Provided by further comprising a second imaging section for imaging the second light beam on the scanned surface.

The first imaging unit includes only one imaging lens having power in the sub-scanning direction and the main scanning direction, and the second imaging unit includes a main imaging lens having power in the sub-scanning direction and the main scanning direction. an imaging lens, and the rotating polygon mirror side with respect to the main imaging lens is provided on the opposite side, seen contains and one or more auxiliary imaging lens having power in at least a sub-scanning direction, said first The optical path length from the rotary polygon mirror to the surface to be scanned in the two reflection side optical path is shorter than the optical path length from the rotary polygon mirror to the surface to be scanned in the first reflection side optical path,

  According to the present invention, the displacement of the light beam passing through the second optical path located farther from the bearing portion than the first optical path in the sub-scanning direction can be suppressed by an inexpensive configuration.

FIG. 1 is an overall view showing a schematic configuration of an image forming apparatus provided with an optical scanning device according to the present embodiment. FIG. 2 is a plan view showing the optical scanning device, as viewed from an axial direction of a rotating mirror unit. FIG. 3 is a side view showing the optical scanning device as viewed from the main scanning direction. FIG. 4 is a sectional view taken along line IV-IV of FIG. FIG. 5 is a diagram corresponding to FIG. 3 showing another embodiment.

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

  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 a recording sheet P based on image data transmitted from an external device such as a computer connected to a network. An optical scanning device 4 for irradiating 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 for storing the recording paper P is disposed below the optical scanning device 4, and a manual paper feed unit 7 is disposed beside the paper storage unit 6. A fixing unit 8 that performs a fixing process on an image transferred and formed on the recording paper P is disposed on an upper side of the transfer belt 5. Reference numeral 9 denotes a paper discharge unit that is disposed above the casing 2 and discharges the recording paper P on which the fixing process has been performed 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 photoconductor drum 11. A charging device 12 is disposed directly 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 disposed immediately above each photoconductor drum 11. A cleaning unit 15 for cleaning the peripheral surface of the photoconductor drum 11 is disposed on the other side of each photoconductor drum 11.

  Then, the peripheral surface of each photoconductor drum 11 is uniformly charged by the charger 12, and the peripheral surface of the photoconductor drum 11 after the charging is applied to each color based on the image data input from the computer or the like. Corresponding laser light is emitted from the optical scanning device 4 to form an electrostatic latent image on the peripheral surface of each photosensitive drum 11. A developer is supplied from the developing device 13 to the electrostatic latent image, and a yellow, magenta, cyan, or black toner image is formed on the peripheral surface of each photoconductor drum 11. These toner images are transferred onto the transfer belt 5 in a superimposed manner by the transfer bias applied to the primary transfer roller 14.

  Reference numeral 16 denotes a secondary transfer roller disposed below the fixing unit 8 in contact with the transfer belt 5, and a recording sheet conveyed from the sheet storage unit 6 or the manual sheet feeding unit 7 through the sheet conveyance path 17. P is held 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, and heats and presses the recording paper P while nipping the recording paper P between the heating roller 18 and the pressure roller 19, and forms the toner image transferred on the recording paper P. It is fixed on the 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 duplex printing.

  Next, the optical scanning device 4 will be described in detail 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 housing C is open to the upper side, and the upper side of the housing C is closed by a cover member (not shown).

  The light 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 having a shaft 42 to which the rotating mirror 41 is fixed and which is driven to rotate.

As shown in FIG. 4 , the motor 43 has a cylindrical motor 43 and a rotor part 43b disposed concentrically inside the stator part 43a. The shaft 42 is inserted and fixed to the rotor portion 43b. A coil portion 43c is provided on an inner peripheral portion of the stator portion 43a, and a magnet portion 43d is fixed on an outer peripheral portion of the rotor portion 43b with a gap from the coil portion 43c. The rotor 43b rotates together with the shaft 42 when the coil 43c is energized and a magnetic force acts on the magnet 43d. The shaft 42 extends in the up-down direction, and the rotating mirror unit 41 is fixed to an upper end thereof. The lower end of the shaft 42 is rotatably supported by a bearing 50. The bearing part 50 is press-fitted into a hole formed in the bottom wall of the housing C and fixed.

The rotating mirror section 41 includes an upper polygon mirror 41a and a lower polygon mirror 41b which are arranged at intervals in the vertical direction (the direction of the axis of the shaft 42).
And a connecting portion 41c provided between the connecting portions 41b for connecting and fixing each other.

  The upper polygon mirror 41a and the lower polygon mirror 41b are formed as regular hexagonal prisms having six reflection surfaces on side surfaces. The upper polygon mirror 41a and the lower polygon mirror 41b are rotated and driven at a predetermined speed by a motor 43, so that the light beams emitted from the left and right light source units 44 are reflected and scanned.

  The left and right light source sections 44 are arranged symmetrically with respect to a straight line passing through the axis of the optical deflector 40 and extending in the front-rear direction. Each light source unit 44 has an upper laser light source 44a (see FIG. 2) 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. are doing. The optical scanning device 4 includes an upper optical path La (see FIG. 3), which is an optical path of a light beam emitted from the upper laser light source 44a, and a lower optical path Lb, which is an optical path of a light beam emitted from the lower laser light source 44b. Has two optical paths. The lower optical path Lb corresponds to the first optical path in the present invention, and the upper optical path La corresponds to a second optical path located farther from the bearing unit 50 than the first optical path.

  A collimator lens (not shown) and a cylindrical lens 45 are disposed in the optical path regions on the incident side of the rotating mirror section 41 in the upper optical path La and the lower optical path Lb, respectively. Further, in the upper optical path La and the lower optical path Lb, in the optical path areas on the reflection side of the rotating mirror section 41, the upper image forming section 46 and the lower image forming section 46 for forming a light beam on the surface to be scanned (the surface of the photosensitive drum 11), respectively. A side imaging section 47 is provided. The lower imaging section 47 corresponds to a first imaging section, and the upper imaging section 46 corresponds to a second imaging section.

As shown in FIG. 3 , the upper imaging unit 46 includes a main imaging lens 46 a having power in the sub-scanning direction and the main scanning direction, and a main imaging lens 46 a on a side opposite to the rotating mirror unit 41 with respect to the main imaging lens 46 a. And an auxiliary imaging lens 46b having power only in the sub-scanning direction. The auxiliary imaging lens 46b corrects a displacement of the light beam in the sub-scanning direction on the surface to be scanned caused by the reflection surface of the upper polygon mirror 41a falling in the radial direction due to the rotational vibration of the shaft 42. Both the main imaging lens 46a and the auxiliary imaging lens 46b are fθ lenses whose central portions in the main scanning direction bulge out from both ends to the opposite side to the rotating mirror portion 41 side.

  The lower imaging unit 47 is formed of one imaging lens having power in the sub-scanning direction and the main scanning direction. In the present embodiment, the lower imaging lens 47a is formed of an fθ lens whose central portion in the main scanning direction swells toward the opposite side of the rotating mirror portion 41 with respect to both ends. As the fθ lens, the same lens as the main imaging lens 46a of the upper imaging section 46 may be used. As a result, the parts can be shared and the product cost can be reduced.

  As shown in FIG. 3, during operation of the optical scanning device 4, after the light beam emitted from the upper laser light source 44a of the left and right light source units 44 is deflected and scanned by the upper polygon mirror 41a, the main imaging lens 46a and the auxiliary After passing through the imaging lens 46b in this order, the light is reflected by the reflection mirror 48a and is imaged on the surface of the photosensitive drum 11. 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, is reflected by the reflection mirror 48b, and is reflected by the photosensitive member. An image is formed on the surface of the drum 11.

  Here, since the upper polygon mirror 41a is located farther from the bearing 50 than the lower polygon mirror 41b, the swing and tilt of the shaft during rotation are larger than those of the lower polygon mirror 41b. For this reason, the position of the light beam deflected and scanned by the upper polygon mirror 41a in the sub-scanning direction on the surface to be scanned is not fixed, and as a result, image defects such as jitter occur in the printed image. is there.

  On the other hand, in the above embodiment, in addition to the main imaging lens 46a, the auxiliary imaging lens 46b having power in the sub-scanning direction is arranged on the upper optical path La located farther from the bearing unit 50. By doing so, it is possible to accurately correct the displacement of the light beam in the sub-scanning direction due to the rotational shake and the shaft tilt of the upper polygon mirror 41a. Further, since it is not necessary to process the reflecting surface of the rotating mirror portion 41 with high accuracy in consideration of the deflection and the shaft tilt during rotation of the shaft 42, the product cost can be reduced.

  Moreover, since the auxiliary imaging lens 46b has power only in the sub-scanning direction, the lens cost can be reduced as compared with 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-described embodiment, the optical scanning device 4 having the upper polygon mirror 41a and the lower polygon mirror 41b in which the rotating mirror unit 41 is arranged in two stages above and below has been described. However, the present invention is not limited to this. 41 may be configured in one stage, 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 at least in 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.

  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 (second optical path)
Lb Lower optical path (first optical path)
Reference Signs List 1 image forming device 4 optical scanning device 41 rotating mirror unit (rotating polygon mirror)
41a Upper polygon mirror (second rotating polygon mirror)
41b Lower polygon mirror (first rotating polygon mirror)
42 Shaft (shaft)
43 Motor 44a Upper laser light source 44b Lower laser light source 46 Upper imaging unit (second imaging unit)
46a Main imaging lens 46b Auxiliary imaging lens 47 Lower imaging unit (first imaging unit)
47a lower imaging lens

Claims (4)

A rotating polygon mirror, a shaft supporting the rotating polygon mirror, a bearing portion rotatably supporting the shaft, a first light source for emitting a first light beam toward the rotating polygon mirror, and A second light source that emits a second light beam toward the rotating polygon mirror,
Second incident side optical path Ru optical path der on the light incident side with respect to the rotating polygon mirror of the second light beam emitted from the second light source, the rotary polygon mirror of the first light beam emitted from the first light source Is located on the side farther from the bearing than the first incident side optical path, which is the optical path on the light incident side ,
A first imaging unit provided on a first reflection side optical path , which is a light reflection side optical path of the first light beam with respect to the rotary polygon mirror, to image the first light beam on a surface to be scanned,
A second imaging unit that is provided on a second reflection-side optical path that is a light reflection side optical path of the second light beam with respect to the rotary polygon mirror, and that forms an image of the second light beam on a surface to be scanned,
The first imaging unit includes only one imaging lens having power in the sub-scanning direction and the main scanning direction,
The second imaging unit is provided on the main imaging lens having power in the sub-scanning direction and the main scanning direction, and on the side opposite to the rotating polygon mirror with respect to the main imaging lens, and at least in the sub-scanning direction. see containing and one or more auxiliary imaging lens having power in,
An optical scanning device wherein an optical path length from the rotary polygon mirror to the surface to be scanned in the second reflection side optical path is shorter than an optical path length from the rotary polygon mirror to the surface to be scanned in the first reflection side optical path . The optical scanning device according to claim 1,
The rotating polygon mirror is provided with a first rotating polygon mirror that reflects the first light beam emitted from the first light source and an interval in the rotation axis direction with respect to the first rotating polygon mirror. And a second rotating polygon mirror for reflecting the second light beam emitted from the second light source. The optical scanning device according to claim 1,
The optical scanning device, wherein the auxiliary imaging lens has power only in the sub-scanning direction.   An image forming apparatus comprising the optical scanning device according to claim 1.

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