JP5614052B2 - Optical scanning apparatus and image forming apparatus - Google Patents

Description

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

  Conventionally, an image forming apparatus having an optical scanning device that forms an image by irradiating a photosensitive member with a laser beam is known. In this optical scanning device, a reflection mirror (folding mirror) for bending an optical path is used, and the folding mirror is often fixed at both ends by a leaf spring or the like.

  In that case, bending vibration of the folding mirror occurs with the fixed point as a supporting point. If there is an excitation force in the bending vibration frequency band, for example, an excitation force due to rotation of the polygon mirror or a gear meshing frequency, a striped pattern called banding may appear in the output image at that frequency. .

  In general, it is said that the change in density in the range of spatial frequency 0.2 to 2.0 (line / mm) is most easily noticeable from the characteristics of the human visual system. Considering the rotational speed of the photoconductor and the conveyance speed of the paper, it is necessary to avoid or suppress the vibration of the laser beam in the frequency range of several Hz to several hundred Hz.

  Therefore, by providing a plurality of mirror support portions other than both ends of the reflecting mirror and supporting the folding mirror at three or more points, the natural frequency of the folding mirror is made higher than the frequency band where the banding pattern called banding appears. A configuration has been proposed (see, for example, Patent Document 1 and Patent Document 2).

  The optical box (housing) that holds the optical components vibrates using the part of the optical box that becomes a node when the optical box (housing) vibrates, and a holding member for fixing the folding mirror is attached to the node and the folding mirror is lifted from the housing. In this way, a configuration is proposed in which the excitation force is not easily transmitted to the folding mirror (see, for example, Patent Document 3).

  However, in the inventions of Patent Document 1 and Patent Document 2, since the support part must be provided also in the center part of the mirror, the structure of the mirror support part becomes complicated, and in particular, an optical system for multicolor is provided in one optical box. In what is accommodated in the inside, adopting a structure in which a plurality of mirror support portions are provided in addition to both ends of the reflection mirror, the size of the optical box is left as it is, and when trying to secure an optical path of laser light of any one color, The optical path of the remaining color laser light is obstructed, and in order to avoid this, there is a disadvantage that the optical box must be enlarged.

  On the other hand, the invention of Patent Document 3 has a problem that banding or the like is likely to occur when the excitation force due to other than the vibration of the optical box matches the natural frequency of the folding mirror.

  Therefore, an object of the present invention is to have a configuration in which the natural frequency can be changed so that the excitation frequency deviates from the vicinity of the natural frequency of the folding mirror when there is an external excitation force with a simple configuration, and the output It is an object of the present invention to provide an optical scanning device and an image forming apparatus capable of suppressing image degradation caused by banding or the like on a formed image.

In order to achieve the object of the present invention, a light source, an optical deflector that scans a light beam emitted from the light source, and a reflection that reflects the light beam deflected and scanned by the deflector toward a surface to be scanned. An optical scanning device having a mirror, wherein the light source, the optical deflector, and the folding mirror are placed in an optical box,
An additional member having a surface for attaching the seat to the seat for determining and holding the angle of the folding mirror and a surface for attaching to the optical box is provided, and the rigidity of the seat is changed by the additional member. It is characterized by.

According to the present invention, an additional member having a surface for attaching the seat and a surface for attaching to the optical box is provided for the seat that determines and holds the angle of the folding mirror, and the rigidity of the seat is changed by the additional member. Because the natural frequency of the folding mirror can be changed, the natural frequency of the folding mirror vibration can be shifted to a high level even when there is an excitation force with a frequency that excites the folding mirror vibration. Image deterioration such as banding can be suppressed.

FIG. 1 is a plan view showing a configuration of an optical scanning device according to an embodiment of the present invention. FIG. 2 is a perspective view showing a folding mirror support portion of the optical scanning device shown in FIG. FIG. 3 is a side view of the rigidity adding jig and the folding mirror shown in FIG. FIG. 4 is a perspective view showing the relationship between the rigidity adding jig and the seat surface shown in FIG. FIG. 5 is a graph showing the relationship between the transfer function and the frequency of the folding mirror shown in FIG. 2, and is an explanatory diagram when the excitation frequency is in the vicinity of the natural frequency of the folding mirror. FIG. 6 is a graph showing the relationship between the transfer function and the frequency of the folding mirror shown in FIG. 2, and is an explanatory diagram when there is no excitation frequency in the vicinity of the natural frequency of the folding mirror. FIG. 2 is a schematic view of an image forming apparatus in which the optical scanning device shown in FIG. 1 is incorporated.

(Example 1)
Embodiment 1 of the present invention will be described below with reference to FIGS.
FIG. 1 is a plan view illustrating the configuration of the optical scanning device according to the first embodiment.
In FIG. 1, 11 is an optical box, 12 is a light source unit that emits a laser beam, 13 is a cylinder lens that condenses the laser beam from the light source unit 12 in the sub-scanning direction, and 14 is a deflection scan that deflects and scans the laser beam. Is a unit. The optical box 11 is made of metal, for example.

  The deflection scanning unit 14 is roughly composed of a polygon mirror 14a that reflects the laser beam L and a drive motor 14b that rotationally drives the polygon mirror 14a. The laser beam L emitted from the light source unit 12 is reflected and deflected toward the scanning lens 15a by the mirror surface 14c of the polygon mirror 14a, and is guided to the folding mirror 101 through the scanning lenses 15a and 15b. The scanning lenses 15a and 15b are configured by an fθ lens, a surface tilt correction lens, or the like.

  The optical box 11 is provided with a light detection mirror 16 and a light detection unit 17 for detecting the laser light L2 reflected by the light detection mirror 16. The light detection mirror 16 has a laser beam L1 as a photosensitive drum (not shown). The laser beam L2 is reflected toward the light detection unit 17, and the light detection unit 17 detects the laser beam L2 and determines the writing timing of the laser beam L1 on the photosensitive drum. .

The folding mirror 101 is arranged in parallel with the main scanning direction, reflects the laser beam L1 toward the photosensitive drum, and the laser beam L1 is irradiated to the photosensitive drum. Both ends of the folding mirror 101 are supported by seats 102a and 102b.
The pedestals 102a and 102b are formed integrally by cutting and raising the sheet metal constituting the optical box 11, or formed separately from the optical box 11 and fixed integrally to the optical box 11 with screws not shown. Has been.

The pedestals 102a and 102b can be provided with rigidity adding jigs 104a and 104b on both side surfaces thereof.
FIG. 2 is a perspective view of the pedestals 102a and 102b showing the support state of both end portions 101a and 101b of the folding mirror 101 and the rigidity adding jigs 104a and 104b arranged on the side surfaces of the pedestals 102a and 102b. 3 is a perspective view showing a pedestal 102a that supports one end 101a of the folding mirror 101 and a rigidity adding jig 104a arranged on the side surface thereof, and FIG. 4 shows a state in which the folding mirror 101 is removed. It is a perspective view which shows the base 102a shown and the rigidity addition jig | tool 104a arrange | positioned at the side surface.

Plate spring mounting surfaces 102c are formed on the upper surfaces of the pedestals 102a and 102b, and the inclined surfaces are inclined seat surfaces 102a ′ and 102a ′ for supporting the folding mirror 101. The seats 102a and 102b have positioning contact surfaces 102a ".
A screw hole 102d is formed in the leaf spring mounting surface 102c, and the screw 102e shown in FIGS. 1 to 3 is screwed into the screw hole 102d. The leaf springs 103a and 103b are fixed to the leaf spring mounting surface 102c by the screw 102e.

The folding mirror 101 is pressed and urged toward the inclined seating surfaces 102a ′ and 102a ′ by the leaf springs 103a and 103b, whereby the inclination angle of the folding mirror 101 with respect to the reference plane (horizontal plane) is determined.
Screw holes (not shown) are formed on the side surfaces of the pedestals 102a and 102b.
The rigidity of the pedestals 102a and 102b can be changed by the rigidity adding jigs 104a and 104b.

The rigidity adding jig 104a (104b) has a mounting plate portion 104c and an upright plate portion 104d as shown in FIG. The upright plate portion 104d is formed with an elliptical long hole 106a at a position corresponding to the screw hole formed on the side surface of the seats 102a and 102b, and the mounting plate portion 104c is formed with an elliptical long hole 106b.
In the optical box 11, screw holes (not shown) are formed at locations corresponding to the elliptical long holes 106b.

The attachment plates 104c of the rigidity adding jigs 104a and 104b are fixed to the optical box 11 by screws 105b. The rigidity adding jigs 104a and 104b are integrally fixed to the pedestal 102a on the upright plate portion 104d by screws 105a.
The rigidity of the pedestals 102a and 102b is made variable by attaching the rigidity adding jigs 104a and 104b. The rigidity adding jigs 104a and 104b reinforce the pedestals 102a and 102b in the optical box 11, It functions as means for adding rigidity to the seats 102a and 102b. That is, the rigidity adding jigs 104a and 104b function as an additional member having a surface for attaching the base 102a and a surface for attaching the optical box 11 to the base 102a that determines and holds the angle of the folding mirror 101. .

A plurality of the rigidity adding jigs 104a and 104b are prepared and can be exchanged for the bases 102a and 102b, and different rigidity can be imparted to the bases 102a and 102b.
For example, the rigidity of the rigidity adding jigs 104a and 104b can be changed by changing the material and size of the rigidity adding jigs 104a and 104b.

  When the bending vibration of the folding mirror 101 is large, in particular, when there is an excitation force generated at a frequency close to the natural frequency of the folding mirror 101, for example, due to gear meshing or the like, this is caused by the vibration of the laser beam based on the natural frequency. Since the drawn image is formed on the photosensitive drum, banding becomes conspicuous in the output image.

  In the first embodiment, since the rigidity adding jigs 104a and 104b are attached to the seats 102a and 102b with screws, the stiffness of the seats 102a and 102b is increased. As a result, the rigidity of the folding mirror 101 with respect to the bending vibration is increased. As a result, the natural frequency of the folding mirror 101 is set high.

FIG. 5 is a vibration curve diagram showing an example of the relationship between the frequency and the natural frequency of the folding mirror 101, where the horizontal axis represents frequency and the vertical axis represents the vibration output of the folding mirror 101.
In FIG. 5, a solid line Q1 indicates a transfer function of the folding mirror 101 before the rigidity adding jigs 104a and 104b are attached to the pedestals 102a and 102b, and a symbol Qf indicates a natural frequency in that case.

  In FIG. 5, reference sign Qf ′ indicates an excitation frequency in the vicinity of the natural frequency Qf of the folding mirror 101. For example, the frequency Qf ′ of the excitation force generated due to the gear meshing cycle is the natural frequency Qf. In the vicinity of, the spot position variation in the sub-scanning direction of the laser beam applied to the photosensitive drum becomes remarkable, and as a result, an image deterioration phenomenon such as banding occurs in the output image.

  On the other hand, when the rigidity adding jigs 104a and 104b are attached to the seats 102a and 102b, the natural frequency of the folding mirror 101 is shifted from Qf to Qf ″ higher as shown by the broken line Q1 ′ in FIG. The natural frequency Qf ″ can be separated from the frequency Qf ′ of the excitation force, and as a result, image deterioration phenomenon such as banding caused by bending vibration of the folding mirror 101 can be reduced. . Further, by changing the material and size of the rigidity adding jigs 104a and 104b, the natural frequency Qf of the folding mirror 101 also changes accordingly. Therefore, the natural frequency Qf can be shifted as necessary. it can.

FIG. 6 is a vibration curve diagram showing an example of the relationship between the frequency and the natural frequency Qf of the folding mirror 101, with the horizontal axis representing frequency and the vertical axis representing the vibration output of the folding mirror 101.
As shown in FIG. 6, when there is no frequency Qf ′ of the excitation force in the vicinity of the natural frequency Qf of the folding mirror 101, it is not necessary to attach the rigidity adding jigs 104a and 104b to the seats 102a and 102b. In this case, it is possible to prevent an image deterioration phenomenon such as banding from occurring in the output image without setting the rigidity adding jigs 104a and 104b in the optical box 11.

  As described above, according to the first embodiment, since the natural frequency Qf of the bending vibration of the folding mirror 101 can be changed as necessary, the natural frequency Qf of the bending vibration of the folding mirror 101 and the gear meshing, etc. It is possible to avoid the coincidence of the frequency Qf ′ of the external excitation force that is generated, and it is possible to suppress spot position fluctuations in the sub-scanning direction of the laser beam L1 irradiated to the photosensitive drum, and to reduce the output image. Banding can be reduced.

(Example 2)
The second embodiment of the present invention will be described below with reference to FIG. FIG. 7 shows an embodiment in which the optical scanning apparatus according to Embodiment 1 of the present invention is applied to an image forming apparatus.
In FIG. 7, reference numeral 200 denotes an image forming apparatus which is an electrophotographic apparatus. In this image forming apparatus 200, the image forming units 110, 120, 130, and 140 for each color are arranged in the traveling direction of the intermediate transfer belt 151.

  Four types of image forming units 110, 120, 130, and 140 are provided, and each includes a K developing unit having black toner, a C developing unit having cyan toner, an M developing unit having magenta toner, and a Y having yellow toner. The developing unit 140 is used.

  The image forming unit 110 includes a toner hopper that stores toner, a developing device 114 that includes a developing roller that forms a toner layer and supplies toner to the photosensitive drum 111, a drum cleaner 115 that cleans the photosensitive drum 111, and the photosensitive drum 111. A charging unit 112 for charging and an optical scanning unit 113 for writing an electrostatic latent image on the photosensitive drum 111 are configured.

  A toner hopper, a developing roller, a drum cleaner 115, a charger 112, and the like included in the image forming unit 110 are attached to a frame (not shown) and configured to be drawable from the main body of the image forming apparatus 200. The optical scanning device 113 uses the rigidity adding jigs 104a and 104b shown in the first embodiment. The remaining image forming units 120, 130, and 140 have substantially the same configuration.

  The intermediate transfer belt 151 is stretched around a plurality of rollers and passes through the secondary transfer roller 150. The belt cleaner 152 removes residual toner on the intermediate transfer belt 151. The primary transfer roller 150 ′ is disposed so as to face the photosensitive drum 111 and the like inside the intermediate transfer belt 151 so as to face the photosensitive drum 111 and the like.

  The sheet 171 is pulled out from the sheet feeding device 170 by a pickup roller, passes through a separation roller, contacts the intermediate transfer belt 151 while being sandwiched between the secondary transfer roller 150 and its opposite roller 150 ″, and the image is transferred to the sheet. The sheet is fed toward the fixing device 160 via 151 ′.

  The fixing device 160 includes a backup roller 163, an elastic roller 162, a heating roller 162 ', a fixing belt 161, and the like. The fixing belt 161 is stretched between the elastic roller 162 and the heating roller 162 ', and is conveyed by the rotation of the heating roller or other rollers. The sheet 171 is pressed against the elastic roller 162 side by the backup roller 163.

  The heating roller 162 ′ has heating means such as a halogen heater in a metal hollow shaft, and heats the fixing belt 161. The surface of the elastic roller 162 is formed of an elastic material such as silicon rubber, and the pressing force of the backup roller 163 makes the nip portion convex toward the elastic roller 162, thereby preventing the paper 171 from being wrapped around the fixing belt 161.

  When forming an image, the photosensitive drum 111 is charged by the charger 112, and the photosensitive drum 111 is exposed by the laser beam according to the image by the optical scanning device 113, and the potential on the photosensitive drum 111 is lowered. The exposed portion reaches the developing device 114 by the rotation of the photosensitive drum 111, the charged toner of the developing device 114 adheres to a position where an image is to be formed, and a toner image is formed on the photosensitive drum 111.

  The toner image formed on the photosensitive drum 111 is transferred to the intermediate transfer belt 151 when the primary transfer roller 150 ′ presses the intermediate transfer belt 151 against the photosensitive drum 111. Similarly, the toner images on the photosensitive drums 111 of the image forming units 110, 120, 130, and 140 are transferred to the intermediate transfer belt 151, thereby forming a color toner image.

  By the conveyance of the intermediate transfer belt 151, the toner image is transferred to the paper 171 conveyed at the site of the secondary transfer roller 150. The sheet 171 on which the toner image is transferred is conveyed to the fixing device 160 by the conveying belt 151 ′, and the toner is melted and fixed by heat and pressure to form a color image.

  As described above, in the image forming apparatus according to this embodiment, the beam spot position fluctuation due to the bending vibration of the folding mirror 101 by the optical scanning device 113 can be reduced, so that a high-quality image with little color shift can be obtained. Can do.

  In the optical scanning device of the present invention, it is possible to reduce the beam spot position fluctuation due to the bending vibration of the folding mirror 101, and it is possible to provide an image forming apparatus that obtains an image with higher image quality than before.

DESCRIPTION OF SYMBOLS 11 ... Optical box 101 ... Folding mirror 102a, 102b ... Seat 104a, 104b ... Stiffness addition jig

Japanese Patent Laid-Open No. 10-221627 Patent No. 3649934 Patent No. 4299103

Claims (4)

A light source; an optical deflector that scans the light beam emitted from the light source; and a folding mirror that reflects the light beam deflected and scanned by the deflector toward a surface to be scanned. An optical scanning device in which the device and the folding mirror are placed in an optical box,
An additional member having a surface for attaching the seat to the seat for determining and holding the angle of the folding mirror and a surface for attaching to the optical box is provided, and the rigidity of the seat is changed by the additional member. An optical scanning device. The optical scanning device according to claim 1, wherein the additional member is fixed to the base and the optical box by a fixture . The optical scanning device according to claim 2, wherein the fixture is a screw .   An image forming apparatus comprising the optical scanning device according to claim 1.

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