JP2007183492A - Scanning optical apparatus and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a scanning optical apparatus capable of acquiring a stable optical characteristic and an accurate image quality by suppressing the tilt of a rotating shaft even when a creep deformation occurs at a fixed part when the scanning optical apparatus reaches a high temperature. <P>SOLUTION: The typical structure of the scanning optical apparatus 200 of the present invention has: a deflector 8 provided with a rotating polygon mirror 1 which deflects and scans a light beam emitted from a light source; and an optical box 4 in which a deflector 8 is fixed at a plurality of fixing parts 15. The scanning optical apparatus is characterized in that the fixing parts 15 include: first fixing parts 15a and 15b in the vicinity of the rotating center of the rotating polygon mirror 1; and a second fixing part 15c provided at a position apart from the rotating center of the rotating polygon mirror 1, wherein a region 17 exists in the vicinity of the second fixing part 15c, where the strength is lower than that of other parts. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a laser beam printer, a digital copying machine, and a digital FAX, and a scanning optical apparatus used for these.

  In recent years, a scanning optical device used as an optical system is required to have a more compact and low-cost configuration. A configuration in which a deflection device is attached to an optical box in a scanning optical device is disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 11-218718). In the invention described in Patent Document 1, uneven load is prevented from being applied depending on the screwing position.

  Specifically, as shown in FIG. 8, land portions 116 and 117 for attaching a fixing member 115 to fix the deflecting device 114 to the optical box 113 are provided. The fixing member 115 is composed of an elastic member 119 such as rubber for pressing the circuit board 118 of the deflecting device with a uniform load and a metal plate 120, and is fixed to the land portions 116 and 117 with screws 121, whereby the deflecting device 114 is fixed. Is attached to the optical box 113.

Japanese Patent Laid-Open No. 11-218718

  However, the use of an elastic member such as rubber increases the cost. In addition, due to the downsizing of the circuit board of the deflection device, the area occupied by the control unit on which the driving ICs and connectors are mounted is larger than the circuit board area, and the space for the land and screw fixing parts is limited. Therefore, it is difficult to fix the deflection device to the optical box with a uniform pressing force against the rotation center of the deflection device.

  And there exists a possibility that the rotating shaft of a deflection | deviation apparatus may incline by the uneven pressing force with respect to a rotation center. When the rotation axis is tilted and the reflecting surface of the rotating polygon mirror is tilted, the position of the laser beam is shifted up and down, and a desired beam shape is not formed on the irradiated body, resulting in an image defect.

  Even when the deflecting device is fixed to the optical box by the pressing force of the elastic member, the optical box is thermally expanded when the scanning optical device is at a high temperature. At this time, in the optical box made of resin, due to the difference in linear expansion coefficient between the seating surface of the fixed part and the drive circuit board of the deflecting device, the optical box is thermally expanded non-uniformly to cause creep deformation in the fixed part.

  When creep deformation occurs, the deformation of the plurality of fixing portions is inclined in different directions. For this reason, there is a possibility that the drive circuit board attached to the fixed part deforms unevenly following the fixed part, and the rotation shaft of the deflecting device is inclined. When the rotation axis is tilted and the reflecting surface of the rotating polygon mirror is tilted, the position of the laser beam is shifted up and down, and a desired beam shape is not formed on the irradiated body, resulting in an image defect.

  Therefore, the present invention can prevent the rotation shaft from tilting even when the scanning optical device becomes high temperature and creep deformation occurs in the fixed portion. Accordingly, an object of the present invention is to provide a scanning optical device that can obtain stable optical characteristics and can obtain highly accurate image quality.

  In order to solve the above problems, a typical configuration of a scanning optical device according to the present invention includes a deflection device including a rotating polygon mirror that deflects and scans a light beam emitted from a light source, and a plurality of fixing units. In the scanning optical device having the optical box attached at the position, the fixed portion is provided at a position apart from the first fixed portion near the rotation center of the rotary polygon mirror and the rotation center of the rotary polygon mirror. And a second fixing portion, and a region having a weaker strength than others is provided in the vicinity of the second fixing portion.

  According to the present invention, even when the scanning optical device becomes high temperature and the deflection device fixing portion is deformed, it is possible to suppress the tilt of the rotation shaft of the deflection device. Thereby, stable optical characteristics for forming a desired beam shape on the irradiated object can be obtained even at high temperatures, and highly accurate image quality can be obtained.

  An embodiment of the present invention will be described. However, the dimensions, materials, relative arrangements, and the like of the component parts described in the following embodiments are not intended to limit the scope of the present invention only to those unless otherwise specified.

[First embodiment]
A first embodiment of a scanning optical device according to the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of a scanning optical device according to the present embodiment.

(Scanning optical device)
The scanning optical device 200 includes a semiconductor laser (not shown) that is a light source, a rotating polygon mirror 1, imaging lenses 2 and 3, a light source unit 5, a collimator lens 6, and a cylindrical lens 7. The rotary polygon mirror 1, the imaging lenses 2, 3, and the lenses 6, 7 are accommodated in an optical box 4 that is a casing. The light source unit 5 holding the semiconductor laser is assembled to the side wall of the optical box 4 or the like.

  Laser light generated from the semiconductor laser of the light source unit 5 is collimated by the collimator lens 6. Then, the light is condensed linearly on the reflecting surface of the rotary polygonal mirror 1 by the cylindrical lens 7 and deflected and scanned by the rotary polygonal mirror 1. The laser beam deflected and scanned passes through the imaging lenses 2 and 3, passes through the window of the optical box 4, and forms an image on the photosensitive member 213 (see FIG. 7). The scanning light that forms an image on the photosensitive member 213 forms an electrostatic latent image along with the main scanning by the rotary polygon mirror 1 and the sub-scanning by the rotation of the photosensitive member 213.

  A motor 8 that is a drive unit that rotates the rotary polygon mirror 1 includes a rotating shaft 9, a rotor 10, a washer 31, and a stator coil 34.

  As shown in FIG. 4A, the rotating shaft 9 is supported on the optical box 4 via a bearing 30 such as an oil bearing. The washer 31 is integral with the rotating shaft 9. The rotor 10 includes a yoke 32 and a rotor magnet 33 coupled to a washer 31. The stator coil 34 is fixed to the circuit board 11 that is integral with the bearing housing.

  The rotary polygon mirror 1 is pressed against a washer 31 by an elastic member (not shown), and is integrated with the rotary shaft 9 and the rotor 10 via the washer 31. On the circuit board 11, a control circuit and the like for controlling the drive current supplied to the stator coil 34 are mounted. When the stator coil 34 is excited, the rotor 10 rotates at a high speed together with the rotary polygon mirror 1 to deflect and scan the laser light applied to the rotary polygon mirror 1.

  The circuit board 11 is a substantially rectangular plate-like body, and includes a motor unit on which the stator coil 34 is mounted and a control unit on which a driving IC 13 and a connector 14 for controlling the rotation of the motor unit are mounted.

  The circuit board 11 is fixed to fixing portions 15a, 15b, 15c provided at the bottom of the optical box 4 with screws 16a, 16b, 16c. The fixing portions 15a and 15b are provided in the vicinity of the rotor 10, and the fixing portion 15c is provided at a position away from the vicinity of the rotor 10. The fixing portions 15a to 15c are provided on the optical box 4 as circular seating surfaces. The fixing portion 15c has a region 17 whose strength is weaker than others in the vicinity thereof.

  In the present embodiment, the description has been given of the case where there are two fixing portions in the vicinity of the rotor and one fixing portion provided at a position away from the rotor 10. However, the present invention is not limited with respect to the number of fixing portions.

(Thermal deformation of optical box)
FIG. 2 is a diagram showing thermal deformation of a conventional optical box. As shown in FIG. 2, the optical box 54 is not provided with the region 17 having a lower strength than the others. When the optical box 54 reaches a high temperature and is thermally expanded and thermally deformed, the bottom of the optical box 54 is deformed into a concave shape. And the fixing | fixed part 15a-15c inclines in the different arrow a direction, the arrow b direction, and the arrow c direction, respectively.

  A position 54 a that is deformed to a concave shape at the bottom of the optical box 54 is between the fixed portions 15 a to 15 c and is displaced with respect to the rotation center 18. And the circuit board 11 attached to the fixing | fixed part 15a-15c deform | transforms unevenly following the thermal deformation of the fixing | fixed part 15a-15c.

  That is, the fixing portions 15a to 15c in the vicinity of the rotor are inclined in the directions of arrows a, b, and c. The position away from the rotation center 18 corresponding to the fixed portion 15c tends to be deformed the most, and a large stress C is applied to the position corresponding to the fixed portion 15c of the circuit board 11.

  Here, due to the stresses A and B generated at the positions corresponding to the fixing portions 15a and 15b of the circuit board 11, the rotational moment applied to the rotating shaft 9 cancels out. Therefore, a non-uniform rotational moment is applied to the rotating shaft 9 of the deflecting device due to the stress C, and the rotating shaft 9 is tilted.

  FIG. 3 is a diagram showing thermal deformation of the optical box 4 of the present embodiment. As shown in FIG. 3, the optical box 4 is provided with a region 17 having a lower strength than the others. The region 17 is a rectangular through hole whose longitudinal direction is a direction intersecting the direction connecting the rotation center 18 and the fixed portion 15c, and is provided in the vicinity of the fixed portion 15c.

  When the optical box 4 becomes hot and thermally expands and is thermally deformed, the bottom of the optical box 4 is deformed into a concave shape. And the fixing | fixed part 15a-15c inclines in the direction of the different arrows ac, respectively.

  By providing the region 17, the strength in the vicinity of the region 17 becomes weak. For this reason, creep deformation in the fixed portion 15c is reduced, and the inclination of the fixed portion 15c is reduced. Therefore, the stress C applied to the position corresponding to the fixed portion 15 c of the circuit board 11 is smaller than that of the conventional optical box 54.

  On the other hand, the stresses A and B are similarly applied to the positions corresponding to the fixing portions 15a and 15b of the circuit board 11. However, the fixing portions 15a and 15b are provided at positions that are symmetric with respect to the rotation center 18. Yes. And compared with these two stress A and B, the stress C concerning the position corresponding to the fixing | fixed part 15c is small.

  Accordingly, the rotational moment generated on the rotary shaft 9 by the stress C is reduced, and the rotational moment generated on the rotary shaft by the stresses A and B cancels each other. For this reason, it is possible to reduce the inclination generated in the rotating shaft 9 of the deflecting device. When the effect was verified using simulation for this embodiment, it was proved that the inclination of the rotating shaft 9 decreased by about 1/3.

  In addition, the area | region where intensity | strength is weaker than others is not limited to the area | region 17, It should just be provided in the position away from the rotor 10, and the fixing | fixed part 15c. Further, when there are a plurality of fixing portions provided at positions away from the rotor 10, the weaker area than the others is at least a fixing portion provided at a position away from the rotor 10 and at a position away from the rotor 10. It may be provided in the vicinity of one fixed part.

(Other forms of weaker areas than others)
FIG. 4 is a cross-sectional view showing a fixed portion of the deflection apparatus. 4 (a) to 4 (d) show other forms of regions where the strength is weaker than others. As shown in FIG. 4A, the region having a lower strength than the others may be a thin region 19 locally provided around the fixed portion 15c. Moreover, as shown in FIG.4 (b), the area | region where intensity | strength is weaker than others may be the recessed area | region 20 provided locally around the fixing | fixed part 15c.

  Further, as shown in FIG. 4C, in the weaker region than the others, the fixing portion 15 c provided at a position away from the vicinity of the rotor 10 and the rotation center 18 of the deflection device 8 are blocked by the through hole 21. It may be.

  In addition, the area | region where intensity | strength is weaker than others is not limited to this shape, It can be set as various shapes, such as the shape which opened several holes, and the shape which provided the several dent.

(Measurement of the relation between the thickness of the thin region 19 and the amount of inclination of the rotation axis)
FIG. 5 is a diagram showing the relationship between the thickness of the thin region 19 and the amount of inclination of the rotation axis. FIG. 4D is an enlarged view around the thin region 19 of FIG.

  The temperature of the scanning optical device 200 in which the circuit board 11 is fixed to the optical box 4 shown in FIG. 4D with screws is raised to 60 ° C. to 80 ° C., and the generated tilt amount [μm] of the rotating shaft 9 of the deflecting device is It was measured. The circuit board is made of iron, and the optical box is made of modified polyphenylene ether. The thickness of the thin region 19 was measured by changing from 0 mm to tmm.

  As shown in FIG. 5, it was confirmed by this measurement that the amount of inclination generated in the rotating shaft 9 of the deflecting device becomes smaller as the thickness t [mm] of the thin region 19 becomes thinner.

[Second Embodiment]
Next, a second embodiment of the scanning optical device according to the present invention will be described with reference to the drawings. FIG. 6 is a configuration diagram of the scanning optical device according to the present embodiment. About the part which overlaps with said 1st embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  As shown in FIG. 6, the scanning optical device 300 according to the present embodiment is provided with a region 23 instead of the region 17 of the first embodiment, and further adding a fixing portion 15 d.

  The region 23 whose strength is weaker than the others is provided in the vicinity of the fixed portion 15 c where the distance L to the rotation center 18 of the deflecting device 8 is the longest. The region 23 is a rectangular through hole whose longitudinal direction is a direction intersecting the direction connecting the rotation center 18 and the fixed portion 15c, and is provided in the vicinity of the fixed portion 15c. The region 23 is obtained by shifting the position of the region 17 and is perforated from the side wall of the optical box 4 to the center of the bottom of the optical box 4.

  By providing the region 23, the strength near the region 23 is weakened. For this reason, creep deformation in the fixed portion 15c is reduced, and the inclination of the fixed portion 15c is reduced. Therefore, the stress C applied to the position corresponding to the fixed portion 15 c of the circuit board 11 is smaller than that of the conventional optical box 54.

  The fixed portion 15d is provided on an extension line of a straight line T formed by connecting the fixed portion 15c and the rotation center 18 of the deflecting device 8. A stress D is generated at a position corresponding to the fixing portion 15d of the circuit board 11.

  Here, the moment generated in the rotating shaft 9 due to the stress D is configured to cancel the moment generated in the rotating shaft 9 due to the stress C. As a result, a uniform rotational moment acts on the rotating shaft 9, and the tilting of the rotating shaft 9 can be suppressed.

  In addition, in this embodiment, although the structure which has the area | region 17 whose intensity | strength is weaker than others was demonstrated only to the fixing | fixed part 15c vicinity, this invention is not limited to this structure. In other words, the region having a lower strength than the other region only needs to include at least a fixed portion having the longest distance L to the center of rotation, and may be provided in the vicinity of the other fixed portion 15d or the like.

[Third embodiment]
Next, an embodiment of an image forming apparatus according to the present invention will be described with reference to the drawings. FIG. 7 is a configuration diagram of the image forming apparatus.

  As shown in FIG. 7, the image forming apparatus includes a laser beam printer main body 201 and a scanning optical device 200. The scanning optical device 200 scans a laser beam modulated based on an image signal onto a photoconductor 213 that is an image carrier.

  The main body 201 includes a cassette 202, a feeding roller 205, a registration roller pair 206, a photoconductor 213 as an image forming unit, a primary charging roller 219, a developing device 220, and a cleaner 222. Further, the image forming apparatus includes a fixing device 209, a discharge roller 211, a stacking tray 212, and a transfer roller 221.

  The recording sheet S stored in the cassette 202 is fed to the registration roller pair 206 by the feeding roller 205. The fed recording sheet S is synchronously conveyed to the nip portion between the photosensitive member 213 and the transfer roller 221 by the registration roller pair 206.

  The photoconductor 213 forms a toner image on the recording sheet S based on the laser light from the scanning optical device 200. The primary charging roller 219 applies a voltage to the photoconductor 213 to uniformly charge it. The uniformly charged primary charging roller 219 is exposed to a laser beam to form an electrostatic latent image. The developer 220 applies toner to the electrostatic latent image to form a toner image. After transferring the toner image, the cleaner 222 removes residual toner remaining on the photoconductor 213 and cleans the photoconductor 213. The recording sheet S conveyed to the nip portion is transferred with a toner image to form an image.

  The recording sheet S on which an image is formed by the photoconductor 213 is conveyed to the fixing device 209. The recording sheet S conveyed to the fixing device 209 fixes the toner image by heating and pressing. The recording sheet S on which the toner image is fixed is discharged to the stacking tray 212 by the discharge roller 211 and stacked.

It is a block diagram of the scanning optical apparatus concerning 1st embodiment. It is a figure which shows the thermal deformation of the conventional optical box. It is a figure which shows the thermal deformation of the optical box of 1st embodiment. It is sectional drawing which showed the fixing | fixed part of the deflection | deviation apparatus of 1st embodiment. It is a figure which shows the relationship between the thickness of the thin area | region of 1st embodiment, and the inclination amount of a rotating shaft. It is a block diagram of the scanning optical apparatus concerning 2nd embodiment. It is a block diagram of the image forming apparatus concerning 3rd embodiment. It is a figure explaining the prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS S ... Recording sheet, T ... Straight line, 1 ... Rotary polygon mirror, 2, 3 ... Imaging lens, 4 ... Optical box, 5 ... Light source unit, 6 ... Collimator lens, 7 ... Cylindrical lens, 8 ... Deflection device, 9 ... Rotating shaft, 10 ... rotor, 11 ... circuit board, 13 ... driving IC, 14 ... connector, 15 ... fixed part, 17 ... area, 18 ... center of rotation, 19 ... thin area, 20 ... recessed area, 23 ... area, DESCRIPTION OF SYMBOLS 30 ... Bearing, 31 ... Washer, 32 ... Yoke, 33 ... Rotor magnet, 34 ... Stator coil, 54 ... Optical box, 200 ... Scanning optical apparatus, 201 ... Laser beam printer main body, 202 ... Cassette, 205 ... Feeding roller, 206: Registration roller pair, 211: Discharge roller, 212: Loading tray, 213 ... Photoconductor, 219 ... Primary charging roller, 220 ... Developer, 221 ... Transfer roller, 222 ... Cleaner 300 ... scanning optical device

Claims (5)

In a scanning optical device comprising: a deflection device comprising a rotating polygon mirror that deflects and scans a light beam emitted from a light source; and an optical box having the deflection device attached thereto by a plurality of fixed portions.
The fixed portion has a first fixed portion near the rotation center of the rotary polygon mirror, and a second fixed portion provided at a position away from the rotation center of the rotary polygon mirror,
A scanning optical device comprising a region having a weaker strength than the other in the vicinity of the second fixing portion.
The scanning optical apparatus according to claim 1, wherein the low-strength region is provided between the second fixed portion and the rotation center.
3. The scanning optical device according to claim 1, wherein the weak region is a thin region, a concave region, or a through hole locally provided in the optical box.
The said 2nd fixing | fixed part is provided in two places, The said rotation center exists on the straight line which connects the said 2nd 2nd fixing | fixed part, The Claim 1 characterized by the above-mentioned. The scanning optical device described.
A scanning optical device according to any one of claims 1 to 4,
An image forming apparatus comprising: an image forming unit that forms a toner image on a recording medium.

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