JP4374493B2 - Optical scanning apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an optical scanning device such as a digital color copying machine or a color laser printer, and an image forming apparatus using the same.

  In recent years, with the increase in the speed of color image forming apparatuses, for example, four photosensitive drums are arranged in the recording paper conveyance direction, and a latent image is exposed simultaneously by a plurality of scanning optical systems corresponding to the respective photosensitive drums. These latent images are visualized by developing devices using different color developers such as yellow (Y), magenta (M), cyan (C), and black (K). A so-called 4-drum tandem type digital color copying machine, a color laser printer, or the like, which obtains a color image by sequentially superimposing and transferring an image on the same recording paper, has been put into practical use.

The 4-drum tandem system is advantageous for high-speed printing because a color image can be output at the same speed as monochrome with respect to the 1-drum system.
Further, sharing the deflecting means among the plurality of scanning optical systems is advantageous for cost reduction.
Further, the size can be reduced by arranging a folding mirror between the scanning optical system and the surface to be scanned. Here, as an arrangement form of the folding mirror, for example, there are a case where it is arranged after passing through two scanning lenses and a case where it is arranged in the optical path of the two scanning lenses. However, the imaging performance (optical characteristics) of the light beam is deteriorated in the configuration in which the folding mirror is disposed between the two scanning lenses as compared with the configuration in which the folding mirror is folded after passing through the two scanning lenses (for example, , See Patent Document 1).
In addition, there is a configuration in which a mirror is disposed between the light source and the deflecting unit, but the imaging performance of the light beam in this configuration is slightly deteriorated compared to a configuration in which no mirror is disposed between the light source and the deflecting unit (for example, (See Patent Document 2).
JP 2002-196271 A JP 2003-15066 A

  The present invention minimizes deterioration of the imaging performance of the light beam as a whole by effectively using an optical path bending means such as a folding mirror or a prism between the plurality of optical elements of the scanning optical system comprising a plurality of optical elements. It is an object of the present invention to provide an optical scanning device and an image forming apparatus that can be reduced in size while suppressing the above.

In the optical scanning device according to the present invention, each of the plurality of scanning optical systems is provided with an optical path bending means in the optical path between the deflector and the surface to be scanned, and the optical path bending means disposed in each of the scanning optical systems. Among them, the optical path bending means arranged closest to the deflector on the optical path is arranged in the optical path between the imaging optical system and the surface to be scanned in one scanning optical system and formed in the other scanning optical system. A plurality of incident light beams from a plurality of light sources to a deflector, which are arranged in an optical path of the optical system, have an opening angle in a deflection rotation plane, and light is out of optical path bending means arranged in each of the scanning optical systems. The optical path bending means arranged closest to the deflector on the path is an imaging optical system and a scanned object in a scanning optical system in which the average incident angle to the deflecting / reflecting surface in the deflecting rotation surface is larger than that of other scanning optical systems. Other scans placed in the optical path with the surface Characterized in that it is disposed in the optical path of the imaging optical system in the academic system.

In the optical scanning device according to the present invention, at least one of the plurality of scanning optical systems includes a second optical path bending means in the optical path between the light source and the deflector, and is disposed in each of the scanning optical systems. Among the optical path bending means, the optical path bending means arranged closest to the deflector on the optical path is in the optical path between the imaging optical system and the surface to be scanned in the scanning optical system having the second optical path bending means. The other scanning optical system is characterized by being disposed in the optical path of the imaging optical system.

In the optical scanning device according to the present invention, the second optical path bending means is a mirror or a prism.

In the optical scanning device according to the present invention, the optical path bending means is a mirror or a prism.

An image forming apparatus according to the present invention is an apparatus that performs optical writing from an optical writing device to an image carrier and forms an electrostatic latent image on the image carrier by electrophotography. The insertion device is an optical scanning device according to the present invention.

  According to the present invention, an optical scanning device capable of realizing a reduction in size while dispersing deterioration of the imaging performance of the light beam in a well-balanced manner among the scanning optical systems and minimizing deterioration of the imaging performance of the light beam as a whole. Can be obtained. Further, by using this optical scanning device, it is possible to obtain an image forming apparatus that can form an image with good quality.

  Embodiments of an optical scanning device and an image forming apparatus according to the present invention will be described below with reference to the drawings.

First, an optical scanning device according to the present invention will be described.
FIG. 1 is an optical arrangement diagram developed in a plane parallel to a deflection rotation plane showing an embodiment of an optical scanning device according to the present invention. Here, a multi-beam scanning optical system including two scanning optical systems A and B is shown as an example. However, the number of scanning optical systems included in the optical scanning device according to the present invention is not limited to two. It may be 3 or more.
Reference numerals 1a and 1b are semiconductor lasers which are light sources, 5 is a polygon mirror which is a deflector having a deflecting reflecting surface for deflecting light beams from the semiconductor lasers 1a and 1b, and 2a and 2b are light beams from the semiconductor lasers 1a and 1b, respectively. Coupling lenses 3a and 3b for coupling the light beams from the coupling lenses 2a and 2b to the polygon mirror 5, 4a and 4b are virtual mirrors, and 6 is a parallel plate. Glass 10 is the surface of the photoconductor which is the surface to be scanned, and 7 and 8 are the first scanning which is an optical element constituting a scanning imaging optical system for condensing the light beam from the polygon mirror 5 onto the surface 10 to be scanned. The lens and the second scanning lens 9 are dust-proof glass.
Here, the direction in which the light beam scans on the surface to be scanned 10 is the main scanning direction, and the direction orthogonal to the main scanning direction is the sub-scanning direction.

  The soundproof glass 6 is arranged in an incident / exit optical path of a laser beam with respect to the polygon mirror 5 between the polygon mirror 5 and the scanning imaging optical system (between the polygon mirror 5 and the first scanning lens 7 in the example of FIG. 1). It is installed. More specifically, the soundproof glass 6 is disposed in a window hole provided in a case for housing the polygon mirror 5 and a motor that rotationally drives the polygon mirror 5. The soundproof glass 6 is provided in order to prevent noise caused by the polygon mirror 5.

  The dust-proof glass 9 is disposed on the exit window of the plastic case in order to prevent dust from entering the optical scanning device housed in a plastic case or the like and sealed.

Optical scanning by the optical scanning device will be described for each scanning optical system.
First, the scanning optical system A will be described.
The semiconductor laser 1a is modulated and driven based on an image signal and emits a divergent light beam. The divergent light beam emitted from the semiconductor laser 1a is coupled into a beam form suitable for the subsequent optical system by the coupling lens 2a. Note that each of the coupled light beams is a parallel beam having the same beam form.
The light beam that has passed through the coupling lens 2a passes through the cylindrical lens 3a, is reflected by the virtual mirror 4a, is converged only in the sub-scanning direction by the cylindrical lens 3a, and is main-scanned in the vicinity of the deflection reflection surface of the polygon mirror 5. It forms as a line image of the direction.
The polygon mirror 5 is rotated in a clockwise direction on a plane parallel to the paper surface in FIG. 1 at a substantially constant speed by a motor (not shown), and deflects an incident light beam at an equal angular velocity.
The light beam emitted from the semiconductor laser 1 a and deflected by the polygon mirror 5 passes through the soundproof glass 6, the first scanning lens 7, and the second scanning lens 8, and acts by the first scanning lens 7 and the second scanning lens 8. The light beam is focused on the surface to be scanned 10 to be focused and imaged as a beam spot, and the first scanning lens 7 and the second scanning lens 8 have the fθ function to scan the light beam at a substantially constant speed. Optical scanning is performed on the surface 10 from the upper side to the lower side in FIG.

  Similarly, in the scanning optical system B, the light beam emitted from the semiconductor laser 1b is coupled to the coupling lens 2b, the cylindrical lens 3b, the virtual mirror 4b, the polygon mirror 5, the soundproof glass 6, the first scanning lens 7, and the second scanning lens. 8 is condensed on the surface 10 to be scanned and focused as a beam spot, and optically scanned on the surface 10 to be scanned at a substantially constant speed.

  The two scanning optical systems A and B constituting the optical scanning device are arranged with an arbitrary interval in the sub-scanning direction. Here, the arbitrary interval is an interval determined by the pixel density. Therefore, two parallel scanning lines having a distance in the sub-scanning direction are simultaneously formed on the scanned surface 10.

  In the two scanning optical systems A and B, an incident light beam from the semiconductor laser 1a to the polygon mirror 5 and an incident light beam from the semiconductor laser 1b to the polygon mirror 5 (hereinafter referred to as "one set of incident light beams") are deflected and rotated. It arrange | positions so that it may have an opening angle in a surface. FIG. 1 shows that, of a set of incident light beams, a light beam emitted from the semiconductor laser 1b has an average incident angle (deflection) on the deflecting / reflecting surface in the deflection rotation plane as compared with a light beam emitted from the semiconductor laser 1a. It shows that the angle formed between the incident direction on the reflecting surface and the normal direction of the deflecting reflecting surface is large.

  Hereinafter, the configuration of the optical scanning device according to the present invention will be specifically described with reference to optical system data.

1) Semiconductor laser 1a
Light source wavelength: 655 nm
Average incident angle to the deflecting / reflecting surface within the deflecting rotation surface: 37.275 degrees
2) Semiconductor laser 1b
Light source wavelength: 655 nm
Average incident angle to the deflecting / reflecting surface within the deflecting rotation surface: 28.225 degrees
3) Coupling lens 2
Focal length: 27mm
Coupling action: Collimating action 4) Polygon mirror 5
Number of deflecting reflecting surfaces: 6
Inscribed circle radius: 18mm
5) Soundproof glass 6
Refractive index: 1.514
Thickness: 1.9mm
Inclination in the main scanning direction within the deflection rotation plane: 16 degrees
Inclination in the sub-scanning direction within the deflection rotation plane: 1.3 degrees
6) Dust-proof glass 9
Refractive index: 1.514
Thickness: 1.9mm

  Next, lens data after the polygon mirror 5 is shown below.

The first scanning lens 7 and both surfaces of the second scanning lens 8 have a non-arc shape in the main scanning direction. The depth X in the optical axis direction of each surface is expressed by the following equation.
X = (Y ^ 2 / Rm) / [1 + √ {1- (1 + K) (Y / Rm) ^ 2}]
+ A1 ・ Y + A2 ・ Y ^ 2 + A3 ・ Y ^ 3 + A4 ・ Y ^ 4
+ A5 · Y ^ 5 + A6 · Y ^ 6 + (Formula 1)
Here, Y is a distance in the main scanning direction from the optical axis, Rm is a radius of curvature, K is a conical constant, and An (n = 1, 2, 3,...) Is a higher-order coefficient. In Formula 1, when a numerical value other than zero is substituted for odd-order coefficients A1, A3, A5,..., The shape has an asymmetric shape in the main scanning direction. In the embodiment described below, only the even order is used, and the system is symmetrical in the main scanning direction.

Further, assuming that a curvature radius (sub-scanning curvature radius) in a plane perpendicular to the deflection direction with Y as a variable is Cs (Y), Cs (Y) is expressed by the following equation.
Cs (Y) = 1 / Rs (0) + B1 · Y + B2 · Y ^ 2 + B3 · Y ^ 3
+ B4 · Y ^ 4 + B5 · Y ^ 5 + (Formula 2)
Here, Rs (0) is a radius of curvature in the sub-scanning direction at the optical axis position, and Bn (n = 1, 2, 3,...) Is a high-order coefficient. In equation 2, when a numerical value other than zero is substituted for odd-order coefficients B1, B3, B5,..., The radius of curvature in the sub-scanning direction becomes asymmetric in the main scanning direction.

On the other hand, the second surface of the first scanning lens 7 is a coaxial aspheric surface, and the depth X in the optical axis direction is expressed by the following equation.
X = (Y ^ 2 / R) / [1 + √ {1- (1 + K) (Y / Rm) ^ 2}] +
+ A1 ・ Y + A2 ・ Y ^ 2 + A3 ・ Y ^ 3 + A4 ・ Y ^ 4
+ A5 · Y ^ 5 + A6 · Y ^ 6 + (Formula 3)
Here, R is a paraxial radius of curvature in the optical axis, Y is a distance in the main scanning direction from the optical axis, K is a cone constant, An (n = 1, 2, 3,...) Is a high-order coefficient, It is.

The optical system data of the first surface of the first scanning lens 7 is as follows.
Rm = −279.9
Rs = −61.0
K = -2.900000E + 01
A4 = 1.755765E-07
A6 = −5.491789E-11
A8 = 1.087700E-14
A10 = -3.183245E-19
A12 = −2.6635276E-24
B1 = −2.066347E-06
B2 = 5.727737E-06
B3 = 3.152201E-08
B4 = 2.280241E-09
B5 = −3.729852E-11
B6 = -3.283274E-12
B7 = 1.765590E-14
B8 = 1.3729295E-15
B9 = -2.889722E-18
B10 = -1.984531E-19

The optical system data of the second surface of the first scanning lens 7 is as follows.
R = −83.6
K = -0.549157
A4 = 2.748446E-07
A6 = −4.502346E-12
A8 = −7.366655E-15
A10 = 1.803003E-18
A12 = 2.727900E-23

The optical system data of the first surface of the second scanning lens 8 is as follows.
Rm = 6950
Rs = 110.9
K = 0.000000E + 00
A4 = 1.549648E-08
A6 = 1.292741E-14
A8 = −8.811446E-18
A10 = −9.182312E-22
B1 = −9.593510E-07
B2 = -2.135322E-07
B3 = −8.079549E-12
B4 = 2.390609E-12
B5 = 2.881396E-14
B6 = 3.693775E-15
B7 = -3.258754E-18
B8 = 1.814487E-20
B9 = 8.72085E-23
B10 = −1.3340807E-23

The optical system data of the second surface of the second scanning lens 8 is as follows.
Rm = 766
Rs = −68.22
K = 0.000000E + 00
A4 = -1.150396E-07
A6 = 1.096926E-11
A8 = −6.5542135E-16
A10 = 1.9844381E-20
A12 = −2.411512E−25
B2 = 3.644079E-07
B4 = −4.847051E-13
B6 = −1.666159E-16
B8 = 4.534859E-19
B10 = −2.819319E-23

  Note that the refractive index of the scanning lens at the operating wavelength is 1.52724.

Next, optical system data relating to the optical arrangement will be shown.
Distance d1 = 64 mm from the deflection reflection surface to the first surface of the first scanning lens 7
Center wall thickness d2 of the first scanning lens 7 = 22.6 mm
The distance d3 from the second surface of the first scanning lens 7 to the first surface of the second scanning lens 8 = 75.9 mm
Center thickness d4 of the second scanning lens 8 = 4.9 mm
The distance d5 = 158.7 mm from the second surface of the second scanning lens 8 to the surface to be scanned

The F numbers in the sub-scanning direction at the re-periphery and the central image height are shown below.
Image height = 150 mm: 41.5
Image height = 0 mm: 40.4
Image height = −150 mm: 41.0

In each of the scanning optical systems A and B, an optical path bending means is disposed in the optical path between the polygon mirror 5 and the scanned surface 10.
FIG. 2 is a sub-scan sectional view after the deflector of the optical scanning device shown in FIG. 1 for explaining the optical path of the light beam reflected by the deflecting reflecting surface and traveling toward the scanned surface.
In the scanning optical system A, reflection mirrors 11a, 11a ′, 11a ″ as optical path bending means are arranged in this order in the optical path from the polygon mirror 5 toward the scanned surface 10.
In the scanning optical system B, reflection mirrors 11b, 11b ′, 11b ″ as optical path bending means are arranged in this order in the optical path from the polygon mirror 5 toward the scanned surface 10.

Of the optical path bending means arranged in the scanning optical system A, the optical path bending means arranged closest to the polygon mirror 5 on the optical path is the reflection mirror 11a. On the other hand, among the optical path bending means arranged in the scanning optical system B, the optical path bending means arranged closest to the polygon mirror 5 on the optical path is the reflection mirror 11b.
The reflection mirror 11a is disposed in the optical path between the imaging optical system and the surface to be scanned, that is, in the optical path between the second scanning lens 8a that is an optical element constituting the imaging optical system and the surface to be scanned 10. In other words, the light beam a emitted from the semiconductor laser 1a and deflected by the polygon mirror 5 passes through the first scanning lens 7a and the second scanning lens 8a, and is then folded back by the reflecting mirror 11a to be coupled onto the scanned surface 10. Image.
On the other hand, the reflection mirror 11b is disposed in the optical path of the imaging optical system, that is, in the optical path between the first scanning lens 7b and the second scanning lens 8b that are optical elements constituting the imaging optical system. . That is, the light beam b emitted from the semiconductor laser 1b and deflected by the polygon mirror 5 passes through the first scanning lens 7b and then is folded back by the reflecting mirror 11b, passes through the second scanning lens 8b, and is on the surface 10 to be scanned. To form an image.

  As shown in Patent Document 1, the arrangement of the reflection mirror with respect to the two scanning lenses affects the imaging performance of a light beam passing through these optical elements. That is, the imaging performance of the light beam passing through the imaging optical system configured by arranging a mirror in the optical path between the two scanning lenses is configured to be folded back by the mirror after passing through the two scanning lenses. Deteriorated in comparison with the imaging performance of the light beam passing through the imaging optical system. That is, in the example shown in FIG. 2, the imaging performance of the light beam b scanned by the scanning optical system B is deteriorated compared to the imaging performance of the light beam a scanned by the scanning optical system A. For example, when the surface accuracy of the reflecting mirror is 100 mR, the amount of variation in the field curvature in the main scanning direction at an image height of 0 is 0.308 mm for the reflecting mirror 11a and 0.657 mm for the reflecting mirror 11b. However, by configuring the optical scanning device so that the luminous flux a having poor imaging performance among the luminous fluxes a and b passes through the reflecting mirror 11a, the degradation of the imaging performance of the luminous flux as a whole is minimized. Therefore, it is possible to reduce the size of the optical scanning device.

  As described above, the optical scanning device according to the present invention has one optical path bending means disposed closest to the deflector on the optical path among the optical path bending means disposed in each of the plurality of scanning optical systems. The scanning optical system is arranged in the optical path between the deflector and the surface to be scanned, and the other scanning optical system is arranged in the optical path of the imaging optical system. By configuring the optical scanning device in this way, the degradation of the imaging performance of the light beam can be distributed in a balanced manner between the scanning optical systems, so that the degradation of the imaging performance of the entire optical scanning device is minimized. Can do.

FIG. 2 shows an example in which three reflection mirrors are arranged as optical path bending means in the scanning optical systems A and B, but the number of optical path bending means arranged in each scanning optical system is at least. It is sufficient that the number is 1, and it is not necessary to have the same number in each scanning optical system. Here, when there is one optical path bending means arranged in the scanning optical system, one optical path bending means arranged in the scanning optical system is “the most on the optical path among optical path bending means arranged in each of the scanning optical systems”. It corresponds to “optical path bending means arranged near the deflector”.
Further, as the optical path bending means, a prism may be used instead of the mirror.

Next, with regard to the configuration of the optical scanning device that can disperse the deterioration in the imaging performance of the luminous flux in a balanced manner between the scanning optical systems, the case where the relationship between the average incident angle on the deflecting reflecting surface and the imaging performance is considered. Explained as an example.
In FIG. 1, the average incident angles of the polygon mirror 5 on the deflection reflection surface within the deflection rotation surface are 28.225 degrees for the light beam a and 37.275 degrees for the light beam b. That is, the average incident angle on the deflecting / reflecting surface is larger in the scanning optical system B than in the scanning optical system A.
4A and 4B are diagrams showing the curvature of field of the optical scanning device, where FIG. 4A relates to the scanning optical system A and FIG. 4B relates to the scanning optical system B, the solid line is the sub-scanning direction, and the dotted line is the main scanning. Shows the direction. FIG. 4 shows that the amount of aberration of the light beam of the scanning optical system B shown in (b) is larger than that of the light beam of the scanning optical system A shown in (a).

In this case, the reflection mirror arranged closest to the polygon mirror 5 on the optical path is arranged in the optical path between the imaging optical system and the scanned surface 10 in the scanning optical system B, and in the scanning optical system A. The optical scanning device may be configured to be arranged in the optical path of the imaging optical system (configuration in which the arrangement positions of the folding mirrors 11a and 11b are exchanged in FIG. 2).
With this configuration, the scanning optical system A has a better imaging performance of the light beam deflected by the polygon mirror 5 and directed to the scanned surface 10 due to the arrangement relationship between the two scanning lenses and the reflection mirror. Deteriorated from the scanning optical system B.

Therefore, the imaging performance of the light beam of the scanning optical system A with a small average incident angle on the deflecting reflecting surface and a small amount of aberration is deteriorated from that of the scanning optical system B after the deflector. It is possible to disperse the optical system in a well-balanced manner, and it is possible to minimize degradation of the imaging performance of the entire optical scanning device.
In other words, among the optical path bending means arranged in the plurality of scanning optical systems, the optical path bending means arranged closest to the deflector on the optical path has an average incident angle on the deflection reflection surface within the deflection rotation surface of the other scanning. In a scanning optical system larger than the optical system, it is arranged in the optical path between the imaging optical system and the surface to be scanned, and in other scanning optical systems, it is arranged in the optical path of the imaging optical system. It is possible to minimize degradation of the imaging performance of the light beam as the entire optical scanning device.

Next, another embodiment of the optical scanning device according to the present invention will be described focusing on differences from the above-described embodiment.
In the present embodiment, among the plurality of scanning optical systems constituting the optical scanning device, at least one scanning optical system includes the second optical path bending means in the optical path between the light source and the deflector. This is different from the embodiment described above. Here, in addition to the mirror, a prism may be used as the second optical path bending means.

  FIG. 3 is an optical layout diagram developed in a plane parallel to the deflection rotation plane showing another embodiment of the optical scanning device according to the present invention. The scanning optical system A includes a folding mirror 12 as second optical path bending means in the optical path between the semiconductor laser 1a and the polygon mirror 5. The light beam a emitted from the semiconductor laser 1a passes through the coupling lens 2a and the cylindrical lens 3a, is bent by the folding mirror 12, and enters the polygon mirror 5.

The imaging performance of the light beams a and b incident on the polygon mirror 5 is slightly deteriorated with respect to the light beam b by the amount passing through the folding mirror 12 in consideration of the surface accuracy of the folding mirror 12. On the other hand, due to the arrangement relationship between the two scanning lenses and the reflection mirror described above, the scanning optical system B has the imaging performance of the light beam deflected by the polygon mirror 5 and directed to the scanned surface 10 in the scanning optical system A. More deteriorated. That is, the imaging performance of the light beam incident on the polygon mirror 5 is deteriorated in the scanning optical system A compared with the scanning optical system B, and the imaging performance of the light beam deflected by the polygon mirror 5 and directed toward the scanning surface is The scanning optical system B is deteriorated more than the scanning optical system A.
In this way, by configuring the optical scanning device in consideration of the deterioration of the imaging performance due to the optical path bending means and the second optical path bending means, the optical scanning device as a whole can suppress the deterioration of the imaging performance of the light flux to the minimum. Therefore, it is possible to reduce the size of the optical scanning device.

  As described above, the optical path bending means arranged closest to the deflector on the optical path is arranged in the optical path between the imaging optical system and the scanned surface in the scanning optical system including the second optical path bending means. In other scanning optical systems, the optical scanning device can be reduced in size while minimizing deterioration of the light beam imaging performance of the entire optical scanning device by being disposed in the optical path of the imaging optical system. Can do.

Next, the image forming apparatus according to the present invention will be described.
FIG. 5 is a central sectional view showing an embodiment of the image forming apparatus according to the present invention. This image forming apparatus is a laser printer.
In addition to the optical scanning device 117, the laser printer 100 is a photoconductive photosensitive member, electrostatic latent image formed in a cylindrical shape as a latent image carrier 111 that is exposed by the optical scanning device 117 to form an electrostatic latent image. The image forming apparatus includes means for performing an electrophotographic process, such as developing means for developing the toner image with toner and transfer means for transferring the visualized toner image onto a recording sheet.

Around the latent image carrier 111, process members according to an electrophotographic method (process) such as a charging roller 112 as a charging unit, a developing device 113, a transfer roller 114, and a cleaning device 115 are sequentially arranged.
A corona charger can also be used as the charging means.

  The optical scanning device 117 is an optical writing device that performs optical writing on an image carrier, and performs an exposure process of an electrophotographic process. The optical scanning device 117 is a latent image carrier 111 that is uniformly charged by a charging roller 112. The surface is scanned to form an electrostatic latent image. The formed electrostatic latent image is a so-called negative latent image, and the image portion is exposed. This electrostatic latent image is reversely developed by the developing device 113, and a toner image is formed on the image carrier 111.

  The cassette 118 storing the transfer paper P is detachable from the main body of the laser printer 100, and when the transfer paper P is mounted as shown in the drawing, the uppermost sheet of the stored transfer paper P is fed by the paper feed roller 120. The leading edge of the fed transfer paper P is caught by the registration roller 119. The registration roller 119 sends the transfer paper P to the transfer unit in accordance with the timing at which the toner image on the image carrier 111 moves to the transfer position. The transferred transfer paper P is superimposed on the toner image at the transfer portion, and the toner image is electrostatically transferred by the action of the transfer roller 114.

The transfer paper P to which the toner image has been transferred is sent to the fixing device 116, where the toner image is fixed by the fixing device 116, passes through the conveyance path 121, and is discharged onto the tray 123 by the paper discharge roller 122.
The surface of the image carrier 111 after the toner image has been transferred is cleaned by a cleaning device 115 to remove residual toner, paper dust, and the like.

  By using the optical scanning device according to the present invention described above as the optical scanning device 117, it is possible to reduce the size of the optical scanning device while minimizing the deterioration of the imaging performance of the luminous flux. Deterioration of the imaging performance is suppressed to a minimum, and a good image can be formed.

  The above-described image forming process has been described assuming a single color image forming process. However, the present invention is not limited to this, and a color image forming apparatus that forms a plurality of color images in an overlapping manner is described. It is also possible to apply. In that case, the optical writing unit can be applied to an image forming apparatus sharing a plurality of colors. That is, it has one optical writing unit and an image carrier, performs optical writing with an image signal for each color, develops it with toner of the corresponding color, transfers this to transfer paper, and then another color The image signal is written with light, developed with the toner of the corresponding color, and transferred to the transfer paper, and image formation is performed for each color and transferred onto one transfer paper. This is an image forming apparatus of the type.

  The optical writing unit can also be applied to a so-called tandem type image forming apparatus in which this is used as an exposure unit for each color. In other words, it has a plurality of optical writing units and image carriers corresponding to each color, and an image is written on the corresponding image carrier by the corresponding optical writing unit with the image signal of each color, and developed with the toner of the corresponding color The toner images of the respective colors are transferred so as to overlap each other on one transfer sheet. The tandem type image forming apparatus is advantageous for light beam writing of images and high-speed image formation.

  The present invention can be applied to an image forming apparatus such as a digital color copying machine or a color laser printer, and the optical scanning apparatus as a whole can be miniaturized while minimizing the deterioration of the imaging performance of the light beam. Therefore, the image forming apparatus using the optical scanning device according to the present invention as the exposure process means can form a good image with the degradation of the imaging performance of the light beam being minimized.

FIG. 3 is an optical arrangement diagram developed in a plane parallel to a deflection rotation surface showing an embodiment of an optical scanning device according to the present invention. FIG. 2 is a sub-scanning sectional view after a deflector of the optical scanning device shown in FIG. 1 for explaining an optical path of a light beam reflected by a deflection reflection surface and traveling toward a surface to be scanned. FIG. 6 is an optical arrangement diagram developed in a plane parallel to a deflection rotation surface showing another embodiment of the optical scanning device according to the present invention. FIGS. 2A and 2B are diagrams showing curvature of field applied to each scanning optical system constituting the optical scanning device shown in FIG. 1, wherein FIG. 2A is a scanning optical system A having an average incident angle of 28.225 degrees, and FIG. A scanning optical system B having an angle of 37.275 degrees will be described. 1 is a central sectional view showing an embodiment of an image forming apparatus according to the present invention.

Explanation of symbols

1a, 1b Light source (semiconductor laser)
2a, 2b Coupling lenses 3a, 3b Cylindrical lenses 4a, 4b Virtual mirror 5 Deflector (polygon mirror)
6 Parallel flat plate (soundproof glass)
7 First scanning lens 8 Second scanning lens 9 Dust-proof glass 10 Scanned surfaces 11a and 11b Optical path bending means 12 Second optical path bending means

Claims (5)

An optical scanning device including a plurality of scanning optical systems,
Each of the scanning optical systems includes a light source, a deflector provided with a deflecting reflection surface for deflecting a light beam from the light source, a coupling lens for coupling the light beam from the light source, and a light beam from the coupling lens. A cylindrical lens for guiding the light beam to the deflector, and an imaging optical system composed of a plurality of optical elements for condensing the light beam deflected by the deflector on the surface to be scanned,
The deflector is common to the plurality of scanning optical systems,
In each of the plurality of scanning optical systems, an optical path bending means is disposed in an optical path between the deflector and the surface to be scanned.
Of the optical path bending means arranged in each of the scanning optical systems, the optical path bending means arranged closest to the deflector on the optical path is the distance between the imaging optical system and the surface to be scanned in one scanning optical system. Arranged in the optical path, and in other scanning optical systems, arranged in the optical path of the imaging optical system,
A plurality of incident light beams from the plurality of light sources to the deflector have an opening angle in a deflection rotation plane,
Among the optical path bending means arranged in each of the scanning optical systems, the optical path bending means arranged closest to the deflector on the optical path has an average incident angle with respect to the deflection reflection surface in the deflection rotation surface. In a scanning optical system larger than other scanning optical systems, it is arranged in the optical path between the imaging optical system and the surface to be scanned, and in the other scanning optical system, it is arranged in the optical path of the imaging optical system. Optical scanning device. At least one of the plurality of scanning optical systems includes second optical path bending means in the optical path between the light source and the deflector,
Of the optical path bending means arranged in each of the scanning optical systems, the optical path bending means arranged closest to the deflector on the optical path is an imaging optical system in the scanning optical system having the second optical path bending means. The optical scanning device according to claim 1, wherein the optical scanning device is disposed in an optical path between a scanning surface and a surface to be scanned, and is disposed in an optical path of an imaging optical system in another scanning optical system.   The optical scanning device according to claim 2, wherein the second optical path bending means is a mirror or a prism.   4. The optical scanning device according to claim 1, wherein the optical path bending means is a mirror or a prism. An apparatus that performs optical writing from an optical writing device to an image carrier and forms an electrostatic latent image on the image carrier by electrophotography,
The image forming apparatus according to claim 1, wherein the optical writing device is the optical scanning device according to claim 1.

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