JP3904764B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus that performs electrophotographic image formation based on image light modulated by a plurality of image data.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as a color image forming apparatus that forms an image of a plurality of colors using electrophotographic image formation, a photosensitive member on which an electrostatic latent image is formed is rotated once for each color of developer. is there. For example, when a full-color image is formed using developers of four colors of yellow, magenta, cyan, and black, the photosensitive member is rotated four times.
[0003]
As shown in FIG. 13, such a four-rotation type image forming apparatus includes a charging roller 102, a laser writing unit 115, a developing unit 118 (118 a to 118 d), a transfer drum 122, and a photosensitive drum 107. The cleaning unit 123 and the like are arranged in this order in the rotation direction of the photosensitive drum 107, and the fixing unit 105, the contact roller 108, the paper feed roller 117, and the like are arranged at predetermined positions.
[0004]
In the four-rotation type image forming apparatus configured as described above, the above-described units are controlled by a control unit (not shown), and the following image forming process is executed.
[0005]
(1) The paper P is fed to the transfer drum 122 when the paper feed roller 117 rotates. The fed paper P is charged by the contact roller 108 connected to the power source 121 and is electrostatically attracted to the transfer drum 122. The contact roller 108 can be brought into contact with and separated from the surface of the transfer drum 122.
[0006]
(2) The surface of the photosensitive drum 107 is uniformly charged with a single polarity by the charging roller 102, and then irradiated with the first image light from the laser writing unit 115. An electrostatic latent image is formed on the surface of the body drum 107. The first image light is irradiated with light according to image data corresponding to the color of the developer stored in the developing unit 118a.
[0007]
(3) Developer is supplied from the developing unit 118a to the surface of the photosensitive drum 107 on which the electrostatic latent image is formed, and a developer image that visualizes the electrostatic latent image is carried on the surface of the photosensitive drum 107. Is done.
[0008]
(4) The developer image carried on the surface of the photosensitive drum 107 faces the sheet P electrostatically attracted to the surface of the transfer drum 122. At this time, the developer image is electrostatically transferred onto the surface of the paper P due to the potential difference between the photosensitive drum 107 and the transfer drum 122.
[0009]
(5) The developer remaining on the surface of the photosensitive drum 107 after the transfer process is completed is removed by the cleaning unit 123.
[0010]
(6) By sequentially switching the image light irradiated from the laser writing unit 115 and the developing units 118b to 118d for supplying the developer, the processes (2) to (5) are repeatedly executed. That is, the processes (2) to (5) are repeated based on the second to fourth image lights corresponding to the colors of the developers stored in the developing units 118b to 118d, respectively, and the surface of the paper P The four color developer images are transferred in sequence.
[0011]
(7) The paper P is peeled off from the surface of the transfer drum 122 by the peeling claw 109 a and the peeling charger 109 b, and heated and pressurized by the fixing unit 105. The four-color developer images transferred to the paper P are melted by being heated, and are then firmly fixed on the surface of the paper P by being pressurized.
[0012]
As described above, in the four-rotation type color image forming apparatus, the electrostatic latent image and the developer image corresponding to the image data for the four colors are displayed on the surface of the photosensitive member while the single photosensitive member rotates four times. Since they are formed in order, it is sufficient to provide a single laser writing unit (exposure scanning optical system), adjustment of errors of optical components constituting the exposure scanning optical system, and operation for exposure scanning. There is an advantage that the timing can be easily controlled. However, the four-rotation type color image forming apparatus has a drawback in that it is necessary to repeat the image forming process four times when forming a color image, and the image forming speed becomes slow.
[0013]
On the other hand, as a conventional color image forming apparatus, an individual process unit is provided for each developer color, and images are formed by conveying paper so as to sequentially face a plurality of photoconductors. There is a tandem type color image forming apparatus in which the formation time is shortened. For example, in a case where a full color image is formed using four color developers of yellow, magenta, cyan, and black, four process units are provided.
[0014]
In this tandem type color image forming apparatus, as shown in FIG. 14, a conveyance belt 171 stretched by a pair of rollers 172 and 173 between a paper feed tray 160 containing paper P and a fixing unit 180 is provided. Four process units 150a to 150d are arranged along the conveyance path to be configured. Developer images of four colors of yellow, magenta, cyan, and black are individually formed in each of the process units 150a to 150d, and sequentially transferred onto the surface of the paper P that is transported in the transport path by the transport belt 171. The paper P on which the four color developer images are transferred is heated and pressurized in the fixing unit 180, and the four color developer images are firmly fixed on the surface of the paper P.
[0015]
The process units 150a to 150d have the same configuration. As an example, a process unit 150 a that forms a yellow developer image includes a charging roller 152, a laser writing unit 153, a developing unit 155, a transfer roller 155, and a cleaner 156 around the photosensitive drum 151, and the photosensitive drum 151. Are arranged in this order along the rotation direction. Image data corresponding to a yellow image is input to the laser writing unit 153, and the developing unit 155 stores a yellow developer. The transfer roller 155 is disposed to face the photosensitive drum 151 with the conveyance belt 171 interposed therebetween. In the process units 150b to 150d, image data corresponding to images of magenta, cyan, and black are input to the laser writing unit 153, and the developing unit 155 stores developers of magenta, cyan, and black. is doing.
[0016]
In the tandem type color image forming apparatus configured as described above, since the developer images of four colors are formed almost simultaneously in the individual process units, the color image is formed in a time substantially corresponding to one image forming process time. This is advantageous in that the image forming time can be shortened. However, in a tandem type color image forming apparatus, it is necessary to provide a separate process unit for each color, which requires a plurality of exposure scanning optical systems, adjustment of errors in optical components constituting the exposure scanning optical system, and There is a drawback that control of operation timing for exposure scanning is complicated.
[0017]
Therefore, by sharing the optical components that make up the exposure scanning optical system in multiple process units, it is possible to simplify the adjustment of errors in the optical components that make up the exposure scanning optical system and the control of the operation timing for exposure scanning. A tandem type color image forming apparatus has been proposed. As an example, in Japanese Patent Laid-Open No. 5-100540, polygon mirrors, which are optical components constituting an exposure scanning optical system, are arranged in two stages on the same axis, and the upper and lower polygon mirrors are driven by a single motor. However, a configuration and a control method are disclosed in which four image lights are irradiated through two surfaces of the upper and lower two-stage polygon mirrors.
[0018]
Japanese Patent Application Laid-Open No. 5-270051 discloses a configuration in which three laser beams having different wavelengths are separated from each other by an optical filter via a single polygon mirror.
[0019]
Further, JP-A-6-286226 discloses a single f-θ correction means after deflecting laser light irradiated very close from a laser array in the main scanning direction via a single polygon mirror. Discloses a configuration in which the scanning speed is made uniform, and the light is separated and irradiated in the respective directions of the four photoconductors via the beam separation means.
[0020]
[Problems to be solved by the invention]
However, in the configuration disclosed in Japanese Patent Laid-Open No. 5-80631, an individual f-θ correction unit is required for each color of image light, and the error adjustment of the f-θ correction unit becomes complicated. In addition, it is necessary to adjust the error between the upper and lower polygon mirrors. Furthermore, since the two image lights are scanned in the opposite direction to the other two image lights through the two upper and lower polygon mirrors, scanning unevenness occurs in the direction opposite to the rotation unevenness of the polygon mirror, resulting in a large defect on the image. It becomes.
[0021]
Further, in the configuration disclosed in Japanese Patent Laid-Open No. 5-270051, when the optical paths of the respective laser beams are matched or when the respective laser beams are separated and deflected, the amount of the laser beam is reduced by the optical filter. Further, when the wavelengths of the laser beams of the respective colors are close to each other, it is necessary to use an optical filter capable of separating and deflecting a plurality of laser beams having close wavelengths, which is generally expensive and increases the cost. On the other hand, when the wavelengths of the laser beams of the respective colors are separated from each other, a relatively inexpensive optical filter can be used. However, an imaging correction unit such as an f-θ correction unit having a different design value for each specific wavelength can be used. Design and manufacture are difficult, and the imaging correction means must be expensive, and in any case, an increase in cost cannot be avoided.
[0022]
Furthermore, in the configuration disclosed in Japanese Patent Laid-Open No. 6-286226, four positions of the laser array, the reflection surface of the polygon mirror, the beam separation means, and the surface of the photosensitive member must be optically conjugate, This is a great limitation in designing the exposure scanning optical system. Further, the beam separating means needs to separate very close laser beams, and high accuracy is required for the shape and arrangement position of the components. Further, since the laser beam is incident obliquely on the f-θ correction unit, the shape of the f-θ correction unit is complicated. The f-θ correction means having a complicated shape cannot easily identify deformation due to a temperature change, and it is difficult to form a high-quality image.
[0023]
Further, the most serious problem in a color image forming apparatus is color misregistration for each color. This color shift is caused by the fact that the image formation for each color by a plurality of laser beams is shifted from a prescribed position in image formation (resist failure). This resist failure is caused by the positional deviation of the laser beam in the main scanning direction and the positional deviation in the sub-scanning direction.
[0024]
The positional deviation in the main scanning direction is caused by the deviation of the incident position of each laser beam on the reflecting surface of the polygon mirror from the predetermined position in the main scanning direction, which causes an error in the scanning range of the laser beam in the scanning plane. However, as shown in FIG. 15, by detecting the scanning start position of each laser beam by a single start sensor 193, it is relatively easy to achieve a general positional deviation tolerance of 1/8 dots or less. realizable.
[0025]
However, since the start sensor 193 cannot detect the positional deviation in the sub-scanning direction due to the deviation of the incident position of each laser beam on the reflecting surface of the polygon mirror 191 from the predetermined position in the sub-scanning direction, If an error occurs on the surface of the body 195 and a positional deviation of one or more dots in the sub-scanning direction occurs for a plurality of laser beams, the developer images of a plurality of colors cannot be superimposed on each other, and the images are faithfully reproduced. Cannot be reproduced.
[0026]
For this reason, in the configuration shown in FIG. 15, there is a configuration in which the irradiation position of the laser beam with respect to the surface of the photoconductor 195 in the sub-scanning direction is corrected by changing the reflection angle of the deflection mirror 194. In addition to the adjustment of the −θ correction means 192, it is necessary to adjust the deflection mirror 194, which complicates the control mode.
[0027]
An object of the present invention is to allow an exposure scanning optical system including an optical component such as a polygon mirror and f-θ correction means to be shared between a plurality of image lights when an image is formed by a plurality of image lights. An object of the present invention is to provide a tandem-type image forming apparatus that can realize downsizing and can easily adjust the positional deviation of image light for forming a highly accurate image.
[0028]
[Means for Solving the Problems]
The present invention has the following configuration as means for solving the above problems.
[0029]
  A first means for focusing a plurality of image lights on the polygon mirror in the sub-scanning direction;singleImage light deflected at a constant angular velocity in the main scanning direction by a polygon mirror,A single conversion means for converting light into parallel light in the sub-scanning direction;Deflection at constant speed in the main scanning directionsingleThrough correction meanspluralA second means for forming an image on the surface of the photoreceptor;,In an image forming apparatus comprising:
  The first means includesIt has the same configuration for a plurality of image lights,A plurality of image lights are focused at positions close to each other in the sub-scanning direction on the same reflecting surface of a single polygon mirror, and the beam waists of the plurality of image lights are partially or entirely in the sub-scanning direction. When the beam waist of each image light is ω, the difference W in the sub-scanning direction of the incident position of each image light on the polygon mirror is set to be smaller than ω.And
The second means has the same configuration for a plurality of image lights after the single correction means.It is characterized by being.
[0030]
In this configuration, a plurality of image lights are reflected from the light source at positions close to each other on the reflection surface of the single polygon mirror, and each image light from the light source to the surface of the photoconductor via the reflection surface of the polygon mirror is reflected. In this optical path, the reflection position of the polygon mirror and the irradiation position of the photosensitive member have an optical conjugate relationship. Therefore, the irradiation position shift (resist failure) on the photoconductor between the plurality of image lights is reduced.
[0031]
In addition, the irradiation position on the photoconductor is displaced in the same manner for a plurality of image lights in response to the displacement of the reflection position in the single polygon mirror, and the plurality of image lights are adjusted by adjusting only the reflection position in the single polygon mirror. The irradiation position on the photoconductor is simultaneously adjusted. Therefore, when correcting the resist defect, it is only necessary to adjust the inclination angle of the rotation axis of the single polygon mirror (polygon mirror surface tilt correction). There is no need to consider a combination of adjustment states.
[0032]
Furthermore, the distortion state of the reflection position is substantially the same for a plurality of image lights. Therefore, a large resist failure does not occur between the plurality of image lights due to the difference in the state of the reflection position.
[0033]
In addition, only one polygon mirror for deflecting image light in the main scanning direction is provided for a plurality of image lights. Therefore, the number of parts is reduced, and the size and cost of the apparatus can be reduced.
[0035]
  Also,In this configuration, the errors in the sub-scanning direction of the reflection positions of the plurality of image lights at the polygon mirror are within the range of the beam waist of each image light. Therefore, the resist failure between the plurality of image lights is within a range of 1 dot or less, and the image is not significantly displaced.
[0037]
  Also,By irradiating image light from a plurality of light sources to a position close to the reflecting surface of the polygon mirror, the optical path ranges in the main scanning direction of the plurality of image lights substantially coincide. For this reason, the length of the reflection surface of the polygon mirror in the main scanning direction is utilized to the maximum by the plurality of image lights constituting the image.
[0038]
Further, the plurality of light sources are arranged at different positions in the sub-scanning direction. Therefore, the light emitted from each light source is emitted from the reflecting surface of the polygon mirror toward different positions in the sub-scanning direction. For this reason, the plurality of image lights constituting the image are easily separated after being reflected by the polygon mirror.
[0040]
In this configuration, the plurality of image lights reflected by the polygon mirror are made parallel to each other by the conversion means, and then deflected at a constant speed in the main scanning direction by the correction means. Therefore, after the plurality of image lights are reflected by the polygon mirror, they are irradiated onto the photoconductor in a state of being reliably separated. In addition, the incident angles of the plurality of image lights with respect to the correcting means are the same, and the resist defects occurring between the plurality of image lights are the same.
[0041]
Furthermore, one conversion unit and one correction unit are provided for each of the plurality of image lights. Therefore, the conversion state in the conversion unit and the correction state in the correction unit are constant for a plurality of image lights constituting the image, and the configuration is simplified.
[0042]
  Also,An optical path setting unit for irradiating a plurality of image lights to the same position on the surface of the photoconductor is provided between the correction unit and the photoconductor.It is also possible.
[0043]
In this configuration, a plurality of image lights deflected at a constant speed in the main scanning direction by the correcting unit are irradiated to the same position on the surface of the photosensitive member by the light setting unit. Accordingly, the plurality of image lights that have been converted into light parallel to each other in the sub-scanning direction by the conversion unit are deflected at a constant speed in the main scanning direction and then irradiated to the same position on the surface of the photoconductor in a state of being separated from each other. The electrostatic latent image formed by each image light is visualized by a developer corresponding to each image light, whereby a plurality of developers are superimposed to form an image.
[0044]
  Also,In the plurality of image lights, with respect to two image lights a and b adjacent to each other in the sub-scanning direction, the width of the image light a in the sub-scanning direction is Ba, and the width of the image light b in the sub-scanning direction is Bb. When the interval between the image light a and the image light b in the sub-scanning direction is L, the error in the sub-scanning direction of the reflection position of the polygon mirror is W, and the maximum error in the sub-scanning direction due to the tilt of the polygon mirror is D,
  L- (Ba / 2)-(Bb / 2) -WD> 0
The plurality of light sources and conversion means are arranged so as to satisfy the above relationship.
[0045]
  In this configuration, for two image lights a and b adjacent to each other in the sub-scanning direction, from (interval L in the sub-scanning direction) to (a value of ½ of the width Ba of the image light a in the sub-scanning direction). , (The value of ½ of the width Bb of the image light b in the sub-scanning direction), (the error W in the sub-scanning direction of the focal point position in the polygon mirror), and The value obtained by subtracting D) is made positive. Therefore, even if an error occurs in the reflection position of the image light a and the image light b on the polygon mirror or the inclination of the rotation axis of the polygon mirror, the optical paths of the image light a and the image light b overlap in the sub-scanning direction. The plurality of image lights can be reliably separated.
  The first means includes a first optical system that focuses each of the plurality of image lights at a position close to the sub-scanning direction on the same reflecting surface of a single polygon mirror,
  The second means includes, after the correcting means, a second optical system having the same configuration for each of the plurality of image lights, and the same number of deflection mirrors for each of the plurality of image lights. ,
  The second optical system converts the plurality of image lights into parallel light in the sub-scanning direction,
  The deflecting mirror may separate the light from the second optical system into a plurality of image lights and deflect the light toward the photoconductor.
[0050]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a diagram showing a configuration of a color image forming apparatus according to an embodiment of the present invention. In the image forming apparatus 40 according to this embodiment, a conveyance belt 71 stretched between a pair of rollers 72 and 73 is disposed between the paper feeding unit 60 and the fixing unit 80. The conveying belt 71 conveys a recording medium, for example, a sheet P, supplied from the sheet feeding unit 60 to the fixing unit 80 on the upper surface. The process units 50 a to 50 d that form developer images of each color of yellow (Y), magenta (M), cyan (C), and black (B) face the upper surface of the conveyance belt 71 and move the upper surface of the conveyance belt 71. Are arranged along the sub-scanning direction.
[0051]
Each of the process units 50a to 50d has the same configuration. As an example, a process unit 50a for forming a yellow developer image has a charging roller 52a, a developing unit 54a, and a transfer roller 55a around a cylindrical photosensitive drum 51a that rotates at a constant speed in a direction indicated by an arrow in the drawing. And a cleaner 56a and the like. The developing unit 54a stores a yellow developer, and the process unit 50a forms a yellow developer image by the following process.
[0052]
The surface of the photoconductive drum 51a is uniformly charged with a charge opposite to the charged polarity of the developer from the charging roller 52a, and then irradiated with image light corresponding to a yellow image from the laser writing unit 10, An electrostatic latent image is formed by the photoconductive action. The electrostatic latent image formed on the surface of the photosensitive drum 51a is visualized as a yellow developer image by the developer supplied from the developing unit 54a.
[0053]
In synchronization with the rotation of the photosensitive drum 51a, the paper P fed from the paper feeding unit 60 is conveyed between the photosensitive drum 51a and the transfer roller 55a by the conveying belt 71. The transfer roller 55a is disposed in contact with the inner surface of the conveyance belt 71, and a bias voltage having a polarity opposite to the charging polarity of the developer is applied thereto. As a result, the yellow developer image formed on the surface of the photosensitive drum 51 a is transferred to the surface of the paper P. The developer remaining on the surface of the photosensitive drum 71 that has passed through the position facing the transfer roller 55a is collected by the cleaner 56a.
[0054]
The above process is similarly executed in the process units 50b to 50d in which magenta, cyan, and black developers are stored in the developing units 54b to 54d, respectively. Each of the photosensitive drums 51 b to 51 d is irradiated with image light corresponding to magenta, cyan, and black images from the laser writing unit 10. As a result, magenta, cyan, and black developer images are formed on the respective surfaces of the photosensitive drums 51b to 51d. Accordingly, the paper P fed from the paper feed unit 60 is sequentially conveyed to the process units 50a to 50d by the conveyance belt 71, whereby yellow, magenta, cyan, and black developer images are sequentially transferred onto the surface. The
[0055]
The paper P that has passed through the process units 50 a to 50 d is guided to the fixing unit 80. The fixing unit 80 is constituted by a pair of upper and lower rollers, and the paper P is heated and pressurized while passing through the fixing unit 80. As a result, the four color developers are melted and firmly fixed on the surface of the paper P on the surface of the paper P, and a color image is formed.
[0056]
2 and 3 are diagrams showing a configuration of the laser writing unit 10 provided in the image forming apparatus 40. FIG. 2 is a side view, and FIG. 3 is a plan view. The laser writing unit 10 includes laser diodes 11a to 11d as light sources, lenses 12a to 12d, a polygon mirror 13, a first cylindrical lens (hereinafter referred to as CY) lens 14 as conversion means, and an f− as correction means. A θ lens 15, deflection mirrors 16 a to 16 d as optical path setting means, and second CY lenses 17 a to 17 d are provided, and optical paths to the photosensitive drums 51 a to 51 d are formed for the respective image lights irradiated from the laser diodes 11 a to 11 d. is doing.
[0057]
The optical path length between the f-θ lens 15 and the photosensitive drums 51a to 51d in the optical path of each image light is made equal to each other by a mirror (not shown).
[0058]
The laser diodes 11a to 11d irradiate image light La to Ld corresponding to each color of YMCB according to the image data. The lenses 12 a to 12 d collect the image lights La to Ld emitted from the laser diodes 11 a to 11 d and form an image on the reflection surface of the polygon mirror 13. Therefore, the image lights La to Ld are focused on the reflection surface of the polygon mirror 13 in a direction (sub-scanning direction) orthogonal to the rotation direction (main scanning direction) of the polygon mirror 13. The laser diodes 11a to 11d and the lenses 12a to 12d are arranged side by side in the sub-scanning direction, and the incident angles of the image light La to Ld with respect to the reflection surface of the polygon mirror 13 are different from each other.
[0059]
The polygon mirror 13 is a rotating polygon mirror that rotates in the main scanning direction indicated by an arrow in the drawing, and reflects the image light La to Ld incident from the lenses 12a to 12d while rotating. As a result, the image lights La to Ld are irradiated while being deflected at a constant angular velocity within a predetermined range in the main scanning direction of the photosensitive drums 51a to 51d. The laser diodes 11a to 11d and the lenses 12a to 12d are arranged at the same position in the main scanning direction. Therefore, the image lights La to Ld are irradiated and reflected on the same reflecting surface of the polygon mirror 13.
[0060]
The first CY lens 14 has a lens effect only in the sub-scanning direction, and converts the image light La to Ld reflected by the polygon mirror 13 into light parallel to each other in the sub-scanning direction. The f-θ lens 15 deflects the image light La to Ld converted to light parallel to each other by the first CY lens 14 after being deflected at a constant angular speed by the polygon mirror 13 at a constant speed. Therefore, the image lights La to Ld scan the surfaces of the photosensitive drums 51s to 51d at a constant speed over the entire area in the main scanning direction.
[0061]
The deflection mirrors 16a to 16d change the optical paths of the image lights La to Ld deflected at a constant speed by the f-θ lens 15 in the direction of the photosensitive drums 51a to 51d. The second CY lenses 17a to 17d collect the image lights La to Ld reflected by the deflection mirrors 16a to 16d and form images on the surfaces of the photosensitive drums 51a to 51d. Accordingly, the image lights La to Ld are focused on the surfaces of the photosensitive drums 51a to 51d over the entire region in the main scanning direction.
[0062]
As described above, in the laser writing unit 10, the image lights La to Ld irradiated from the laser diodes 11a to 11d are focused on the reflection surface of the polygon mirror 13 and are formed on the surfaces of the photosensitive drums 51a to 51d. It is configured to focus. That is, the reflection surface of the polygon mirror 13 and the surfaces of the photosensitive drums 51a to 51d are in an optically conjugate relationship in the sub-scanning direction.
[0063]
FIG. 4 is a diagram showing the relationship between the polygon mirror 13 of the laser writing unit 10 and the photoconductors 51a to 51d (in the figure, the case of the image light La is shown as an example). As described above, the reflective surface of the polygon mirror 13 and the surfaces of the photosensitive drums 51a to 51d are in an optically conjugate relationship in the sub-scanning direction. Therefore, when the rotation axis of the polygon mirror 13 is tilted from the proper state shown in FIG. 4A as shown in FIG. 4B and the polygon mirror 13 is so-called face-down, the reflection of the polygon mirror 13 is reflected. Although the incident positions of the image light La to Ld on the surface in the sub-scanning direction change, the positions of the image light La to Ld on the surfaces of the photosensitive drums 51a to 51d are maintained in an appropriate state.
[0064]
In this way, the incident positions of the image light La to Ld in the sub-scanning direction on the surfaces of the photosensitive drums 51a to 51d do not change due to the surface tilt of the polygon mirror 13, and no resist failure occurs. Therefore, it is not necessary to correct the surface tilt of the polygon mirror 13 in order to prevent the resist failure of the image light La to Ld on the surfaces of the photosensitive drums 51a to 51d.
[0065]
However, when the image light La to Ld is focused in the main scanning direction on the surface of the polygon mirror 13, the image light La to Ld is defective on the reflection surface of the polygon mirror 13 due to the surface tilt of the polygon mirror 13. Is incident on the surface of the photosensitive drums 51a to 51d, the image light La to Ld is irregularly reflected at the defective portion, and is not irradiated to the predetermined positions on the surfaces of the photosensitive drums 51a to 51d. Therefore, in the laser writing unit 10 of the color image forming apparatus according to this embodiment, the image lights La to Ld are not focused on the reflection surface of the polygon mirror 13 in the main scanning direction.
[0066]
FIG. 5 is a view for explaining the incident position of the image light on the polygon mirror 13 of the laser writing unit 10. FIG. 5A is a sectional view in the sub-scanning direction in the vicinity of the reflecting surface of the polygon mirror 13. B) is a sectional view in the main scanning direction. FIG. 5 shows only two image lights La and Lb adjacent to each other among a plurality of image lights for easy understanding. The plurality of image lights La to Ld are incident on substantially the same position on the same surface of the polygon mirror 13.
[0067]
In particular, the difference W in the sub-scanning direction of the incident positions of the image light La to Ld on the reflection surface of the polygon mirror 13 is set to be smaller than the beam waist ω of each of the image light La to Ld. As a result, on the reflecting surface of the polygon mirror 13, the beam waists ω of the two color image lights adjacent to each other in the plurality of image lights La to Ld at least partially overlap, and resist defects are suppressed.
[0068]
The error in the sub-scanning direction of the reflection positions of the image light La to Ld at the polygon mirror 13 causes an error (registration defect) in the incident positions of the image light La to Ld on the surfaces of the photosensitive drums 51a to 51d. When the incident position of any image light causes an error of one dot or more with respect to the incident position of the other image light on the surface of the photosensitive drums 51a to 51d, the developer image formed by these image lights. Therefore, there is a case where a predetermined color cannot be reproduced in a color image or color turbidity may occur, resulting in a reduction in image quality. Therefore, in order to maintain the color image formation state satisfactorily, it is necessary to suppress the error of the incident position between the plurality of image lights on the surfaces of the photosensitive drums 51a to 51d to one dot or less.
[0069]
As shown in FIG. 6, for example, the error W ′ of the incident positions of the image light La and Lb on the photosensitive drums 51a and 51b is W on the reflection surface of the polygon mirror 13, and the polygon mirror 13 and the photosensitive drums 51a and 51b. The optical magnification of the first CY lens 14, the f-θ lens 15, the deflection mirrors 16a and 16b, and the second CY lenses 17a and 17b located between the first CY lens 14 and the second CY lens 17a and 17b is expressed by the following first formula.
[0070]
W ′ = m · W 1st formula
The size of one dot on the surfaces of the photosensitive drums 51a and 51b is a value obtained by multiplying the beam waist ω on the reflecting surface of the polygon mirror 13 by the optical magnification m. For these reasons, if the error in the reflection position in the sub-scanning direction between the image light La and Lb on the reflection surface of the polygon mirror 13 is equal to or less than the beam waist ω, the error in the incident position on the surface of the photoconductive drums 51a and 51b is. It is suppressed within one dot, and the color image formation state can be maintained well.
[0071]
As shown in FIG. 7, the beam waist ω refers to the beam width at the focal position of the image light La to Ld. The laser writing unit 10 provided in the color image forming apparatus 40 according to this embodiment condenses the image lights La to Ld emitted from the laser diodes 11a to 11d by the lenses 12a to 12d and reflects the reflecting surface of the polygon mirror 13. Is incident on. The intensity of the laser light emitted from the laser diodes 11a to 11d generally has a Gaussian distribution. For this reason, the beam waist ω of the image light La to Ld, which is laser light, is obtained by the following second formula, where λ is the wavelength of the laser light and NA is the aperture angle of the lenses 12a to 12d.
[0072]
π ・ ω ・ NA = λ 2nd formula
Therefore, in the color image forming apparatus 40, the difference in incident position of the image light La to Ld in the polygon mirror 13 in the sub-scanning direction is set to be smaller than λ / (π · NA).
[0073]
FIG. 8 is a view showing a state of image light in the vicinity of the first CY lens 14 and the f-θ lens 15 in the laser writing unit 10. In the laser writing unit 10 of the color image forming apparatus 40 according to this embodiment, four image lights are incident on the first CY lens 14 in a state of being separated at positions that do not overlap each other in the sub-scanning direction. The first CY lens 14 converts the image light La to Ld into light parallel to each other while maintaining a state where they are separated from each other. Therefore, the separated state of the image light La to Ld is maintained even when passing through the f-θ lens 15.
[0074]
For example, for the image light La and the image light Lb that are adjacent to each other after being emitted from the first CY lens 14, the interval between the image light La and the image light Lb in the sub-scanning direction is L, and each of the image light La and the image light Lb. When the width in the sub-scanning direction is Ba and Bb, the error in the sub-scanning direction of the reflection position at the polygon mirror 13 is W, and the maximum error in the sub-scanning direction due to the tilting of the polygon mirror is D, the relationship of the following equation (3) is satisfied. To meet.
L- (Ba / 2)-(Bb / 2) -WD> 0 (3rd formula)
The interval L between the image lights La and Lb in the sub-scanning direction is an ideal design value (see FIG. 8A). From this state, when an error W occurs in the reflection position of the image light Lb on the reflection surface of the polygon mirror 13, the image light Lb when passing through the f-θ lens 15 moves to the position of Lb ′, and the image light La and The gap in the sub-scanning direction of Lb is
L- (Ba / 2)-(Bb / 2) -W
(See FIG. 8B).
[0075]
Further, when the polygon mirror 13 is tilted from this state and the image lights La and Lb are moved to the positions of La ″ and Lb ″, the difference between the movement amounts Da and Db of the image lights La and Lb is set to the maximum error D. The gap H in the sub-scanning direction of the image light La and Lb is
H = L- (Ba / 2)-(Bb / 2) -WD
(See FIG. 8C).
[0076]
Therefore, even when the image light is displaced and the polygon mirror 13 is tilted, the value of the interval H between the image light La and Lb in this state is positive, and the relationship of the above-described third formula is satisfied. The separated state of the light La to Ld is maintained. This relationship can be realized by making the arrangement positions of the laser diodes 11a to 11d, the lenses 12a to 12d, the polygon mirror 13 and the first CY lens 14 appropriate.
[0077]
FIG. 9 illustrates a method for irradiating the surfaces of the photoconductors 51 a to 51 d with a plurality of image lights using a single reflecting surface of the polygon mirror 13. In the tandem type color image forming apparatus 40 including this embodiment, as shown in FIG. 1, the paper P is constituted by a photosensitive member such as the photosensitive drums 51a to 51d and a transfer unit such as the transfer rollers 55a to 55d. The developer image formed on the surface of the photoreceptor is sequentially transferred to the surface of the paper P at each transfer position.
[0078]
In FIG. 9, a photoreceptor belt is used as an example of a photoreceptor, and the interval between transfer positions of two adjacent photoreceptor belts n (photoreceptor a) and n ′ (photoreceptor b) is G (m). The distance (Ta) between the exposure position E and the transfer position F on the surface of the belt n is T (m), and the distance (Tb) between the exposure position E ′ and the transfer position F ′ on the surface of the photosensitive belt n ′. ) Is T '(m), the conveyance speed (process speed) of the paper P is v (m / s), and the rotation speed of the polygon mirror is q (rpm). In order to form a high-quality color image on the paper P by superimposing the two color developer images N and N ′ formed on the surfaces of the photoreceptor belts n and n ′, It is necessary to transfer the two-color developer images N and N ′ in a state where the positions of the two colors coincide with each other.
[0079]
That is, after the developer image N is transferred from the photosensitive belt n to the paper P being conveyed at a constant conveyance speed v (m / s) at the transfer position F of the photosensitive belt n, development is performed at the transfer position F ′. The developer image N ′ must be transferred from the photosensitive belt n ′ to the same position on the paper P to which the agent image N has been transferred. At this time, the time required for the developer image N, which visualizes the electrostatic latent image formed at the exposure position E of the photosensitive belt n, to reach the transfer position F ′ of the photosensitive belt n ′ via the paper P, is (G + T) / v until the developer image N ′ obtained by visualizing the electrostatic latent image formed at the exposure position E ′ of the photosensitive belt n ′ reaches the transfer position F ′ of the photosensitive belt n ′. Is T ′ / v.
[0080]
Therefore, the exposure on the photosensitive drum n ′ is started at a timing delayed by the time t = (G + T−T ′) / v from the exposure start timing for the photosensitive belt n, whereby the development on the sheet P is performed at the transfer position F ′. The developer image N ′ is transferred from the photosensitive drum n ′ to the position where the agent image N is transferred. Here, the time t is set to be equal to a value obtained by multiplying the time 60 / q required for one rotation of the polygon mirror rotating at the rotation number q (rpm) by an arbitrary integer (k), that is, By satisfying Equation 4,
(G + T−T ′) / v = k · 60 / q
G + T−T ′ = k · 60 · v / q (4th formula)
An image formed by a plurality of colors of image light reflected by the same reflecting surface of the polygon mirror, that is, a dot at the same position in a plurality of developer images is transferred within a range of one dot on the paper P. As a result, a plurality of color developer images can be transferred to the same position on the paper P to form a high-quality color image.
[0081]
FIG. 9 shows an example using a photosensitive belt, but the same applies to the color image forming apparatus 40 according to this embodiment using a photosensitive drum. That is, as shown in FIG. 10, the exposure positions of the photosensitive drums 51a and 51b having the radius R adjacent to each other with a gap G (m) are Ea and Eb, the transfer positions are Fa and Fb, and the exposure positions between the exposure position and the transfer position. When the rotation angle is Sa (rad) and Sb (rad), the circumference Ta (corresponding to T in the fourth equation) between the exposure position Ea and the transfer position Fa of the photosensitive drum 51a is R × Sa. The peripheral length Tb (corresponding to T ′ in the fourth equation) between the exposure position Eb and the transfer position Fb of the photosensitive drum 51b is R × Sb. Substituting this into the fourth equation above,
G + R * Sa-R * Sb = k * 60 * v / q (5th formula)
Accordingly, the rotation angle between the exposure position and the transfer position on the adjacent photosensitive drums 51a and 51b according to the gap G and radius R of the photosensitive drums 51a and 51b, the process speed v, and the rotational speed q of the polygon mirror 13. By setting Sa and Sb so as to satisfy the fifth formula, it is possible to reflect the image light of a plurality of colors on the same surface of the polygon mirror 13, so that the developer images of the plurality of colors are accurately reflected on the paper P. Can be superimposed on each other.
[0082]
Here, the operation of the laser writing unit 10 will be described. When image data of each color of yellow, magenta, cyan, and black is input, the controller of the laser writing unit 10 first forms an electrostatic latent image corresponding to the yellow image on the surface of the photosensitive drum 51a. Accordingly, a drive signal corresponding to yellow image data is output to the laser diode 11a, and the image light La is irradiated from the laser diode 11a. The image light La emitted from the laser diode 11a is received by the start sensor 20 (see FIG. 3) via the lens 12a, the polygon mirror 13 and the sensor mirror 19, and the position of the reflection surface of the polygon mirror 13 and the main scanning are received. The direction period is detected, and the start position in the main scanning direction is determined. As the start sensor 20, for example, a photodiode having a slit disposed on the light receiving surface can be used.
[0083]
The image light La irradiated from the laser diode 11a is irradiated to the polygon mirror 13 via the lens 12a, and after being reflected on the reflection surface of the polygon mirror 13, the first CY lens 14, the f-θ lens 15, the deflection mirror 16a, and the like. The light is incident on the surface of the photosensitive drum 51a that is uniformly charged by the charging roller 52a in advance through the second CY lens 17a. As a result, an electrostatic latent image corresponding to a yellow image is formed on the surface of the photosensitive drum 51a. The electrostatic latent image is visualized as a yellow developer image by the developing unit 54a, and transferred onto the surface of the paper P via the transfer roller 55a.
[0084]
Next, the control unit outputs drive data based on magenta image data to the laser diode 11b at a predetermined timing after the formation of the electrostatic latent image on the photosensitive drum 51a is started. As a result, image light Lb corresponding to magenta image data is irradiated from the laser diode 11b to the photosensitive drum 51b, and an electrostatic latent image corresponding to the magenta image is formed on the surface of the photosensitive drum 51b. At this time, the timing for starting the driving of the laser diode 11b is set so as to satisfy the relationship of the fifth equation. Therefore, the image light Lb corresponding to the magenta image data is reflected in the same state on the same reflecting surface as the reflecting surface that reflects the image light La corresponding to the yellow image data in the polygon mirror 13, and the image light Lb of the photosensitive drum 51b is reflected. The magenta developer image is transferred to the same position as the yellow developer image formed on the paper P at the transfer position. As shown in FIG. 5, the image lights La and Lb are incident on the polygon mirror 13 at positions close to each other.
[0085]
The control unit irradiates image light Lc corresponding to the cyan image data from the laser diode 11c based on the cyan image data so as to satisfy the relationship of the fifth formula and the relationship of the reflection position on the polygon mirror 13. Based on the timing and the black image data, the timing of irradiating the image light Ld corresponding to the black image data from the laser diode 11d is determined.
[0086]
In this manner, the control unit sequentially irradiates the image light La to Ld based on the image data of yellow, magenta, cyan, and black from the laser diodes 11a to 11d, so that each color formed on the photosensitive drums 51a to 51d. The developer image is transferred on the paper P in a state where the positions coincide with each other. As a result, a color image is formed on the paper P.
[0087]
As described above, in the color image forming apparatus 40 according to this embodiment, for four image lights, the reflection position on the polygon mirror 13 and the irradiation positions on the photosensitive drums 51a to 51d have an optical conjugate relationship in the sub-scanning direction. It is comprised so that it may become. Therefore, resist failure in the sub-scanning direction due to surface tilt of the polygon mirror 13 does not occur. As described above, since no resist failure occurs in the sub-scanning direction, it is necessary to provide an optical adjustment member such as a deflection mirror for adjusting the irradiation positions of the image light La to Ld on the photosensitive drums 51a to 51d. In other words, there is no need to adjust the relative positional relationship between the polygon mirror 13 and another adjustment member, and the manufacturing process of the image forming apparatus can be simplified to improve productivity. .
[0088]
Further, since the image lights La to Ld are incident on the same reflecting surface of the polygon mirror 13, it is caused by a difference in distortion of each reflecting surface that occurs when using a plurality of reflecting surfaces as in the prior art. Resist failure does not occur. Further, since the image lights La to Ld are incident on the positions close to each other on the reflection surface of the polygon mirror 13, resist failure caused by a difference in distortion in the reflection surface of the polygon mirror 13 is also suppressed. For this reason, it is possible to form a high-quality image with few resist defects even for a high-resolution image.
[0089]
In addition, since the polygon mirror 13, the first CY lens 14, and the f-θ lens 15 are provided for each of the four image lights La to Ld, the number of parts can be reduced to reduce the size and cost of the apparatus. Cost reduction can be realized. Further, there is no need to adjust errors of the plurality of f-θ lenses 15, and the manufacturing process can be further simplified.
[0090]
Further, since the laser diodes 11a to 11d that irradiate the four image lights La to Ld are arranged along the sub-scanning direction, each of the image lights La to Ld reflected by the polygon mirror 13 can be easily separated. Can do.
[0091]
Further, compared to the case where the laser diodes 11a to 11d are arranged along the main scanning direction, the scanning range common to the image light La to Ld can be maximized, and the use efficiency of the reflection surface of the polygon mirror 13 can be increased. Can be optimized. That is, when a plurality of laser diodes are arranged along the main scanning direction, the scanning range of each image light reflected by the polygon mirror is shifted in the main scanning direction, and the incident range of the plurality of image lights is reduced. Only overlapping portions can be used for image formation. For this reason, there are portions that cannot be used at both ends in the main scanning direction on the reflection surface of the polygon mirror, and the area of the reflection surface formed on the polygon mirror cannot be used effectively.
[0092]
In this regard, in the color image forming apparatus 40 according to this embodiment, since the laser diodes 11a to 11d are arranged along the sub-scanning direction, the incident positions of the image lights La to Ld on the reflection surface of the polygon mirror 13 are as follows. Since all of them match, there are no unusable portions at both ends of the reflecting surface of the polygon mirror 13, and the entire reflecting surface formed on the polygon mirror 13 is effectively used to reduce the size of the polygon mirror 13. Can do.
[0093]
Further, in the color image forming apparatus according to this embodiment, the image lights La to Ld are made parallel to each other by the first CY lens 14 and are incident on the f-θ lens 15 at the same incident angle. For this reason, even when the f-θ lens 15 is deformed due to thermal expansion or the like, the same positional deviation occurs in the four image lights La to Ld after exiting the f-θ lens 15, and each image light La Difference in positional deviation between ~ Ld can be suppressed. In addition, the configuration of the f-θ lens 15 can be simplified.
[0094]
In the laser writing unit 10 of the color image forming apparatus 40 according to this embodiment, the configuration in which the image light La to Ld is emitted from the four laser diodes 11a to 11d is shown. The number of light sources arranged is not limited to four. For example, as shown in FIG. 11, two laser diodes 11a, 11a ', 11b, 11b', 11c, 11c ', 11d, 11d' and two lenses 12a, 12a for each image light. The present invention can be similarly implemented in a multi-beam laser writing unit having ', 12b, 12b', 12c, 12c ', 12d, 12d'.
[0095]
In this case, image light, for example, image light La and La ′, which is irradiated onto the same photosensitive drum, enters the beam waist range on the same surface of the polygon mirror 13 and is reflected by the polygon mirror 13. The photosensitive drum 51a is irradiated with the first CY lens 14, the f-θ lens 15, the deflection mirror 16a, and the second CY lens 17a. Similarly, for the other image lights, the two image lights emitted from the two laser diodes are combined into one and applied to the photosensitive drum.
[0096]
In the multi-beam laser writing unit, as shown in FIG. 12A, two image lights irradiated on the same photosensitive drum are separated from image lights irradiated on other photosensitive drums. However, it is also possible to enter the first CY lens 14 so as to overlap each other in the sub-scanning direction. For example, as shown in FIG. 12B, in the vicinity of the F-θ lens 15, the optical paths of the image light Lb and the image light Lb ′ are changed from the optical paths of the image light La ′ and the image light Lc that are adjacent in the sub-scanning direction. Can be configured to overlap each other in a separated state.
[0097]
Further, although the color image forming apparatus 40 according to this embodiment includes the cylindrical photosensitive drums 51a to 51d, a photosensitive belt constituted by an endless belt can also be used. In this case, in the laser writing unit 10, the developer image formed on each photosensitive belt is transferred onto the paper P without causing a positional deviation by performing the configuration and control satisfying the fourth formula. be able to.
[0098]
Furthermore, in the laser writing unit 10 of the color image forming apparatus 40 according to this embodiment, the first CY lens 14 that converts four image lights into parallel light, and the f-θ lens 15 that performs f-θ correction. However, it is also possible to provide a single conversion correction unit having a function of performing f-θ correction by converting four image lights into parallel light.
[0099]
Further, the resolution of the image improves as the aperture angle (angle α in FIG. 2) in the second CY lenses 17a to 17d increases. Therefore, it is desirable to increase the aperture angle of the second CY lenses 17a to 17 as much as possible.
[0100]
【The invention's effect】
According to the present invention, the following effects can be obtained.
[0101]
(1) A plurality of image lights are reflected from the light source at positions close to each other on the reflection surface of the single polygon mirror, and the optical path of each image light from the light source to the surface of the photoconductor via the reflection surface of the polygon mirror In this case, by making the reflection position of the polygon mirror and the irradiation position of the photoconductor optically conjugate, the deviation of the irradiation position (resist failure) in the photoconductor between a plurality of image lights can be reduced, and the image is clear. A color image can be formed.
[0102]
In addition, the irradiation position on the photoconductor can be displaced in the same manner for a plurality of image lights in response to the displacement of the reflection position in the single polygon mirror, and a plurality of images can be adjusted by adjusting only the reflection position in the single polygon mirror. The irradiation position on the photoconductor for image light can be adjusted simultaneously. Therefore, when correcting the resist defect, it is only necessary to adjust the inclination angle of the rotation axis of the single polygon mirror (polygon mirror surface tilt correction). Since it is not necessary to consider the combination of adjustment states, the assembly work of the optical component can be simplified.
[0103]
Furthermore, it is possible to substantially match the distortion state of the reflection position for a plurality of image lights. Therefore, it is possible to prevent a large resist failure between a plurality of image lights due to a change in the reflection state.
[0104]
In addition, only one polygon mirror for deflecting image light in the main scanning direction needs to be provided for a plurality of image lights. Therefore, it is possible to reduce the number of parts and reduce the size and cost of the apparatus.
[0105]
(2) The error in the sub-scanning direction of the reflection position of the plurality of image lights on the polygon mirror can be within the range of the beam waist of each image light. Therefore, resist defects between a plurality of image lights are within a range of 1 dot or less, and a clear image can be formed without causing a significant shift in the image.
[0106]
(3) By arranging a plurality of light sources for irradiating each image light to the polygon mirror at substantially the same position in the main scanning direction, the scanning ranges in the main scanning direction for the plurality of image lights are substantially matched, and the image The length of the reflecting surface of the polygon mirror in the main scanning direction can be utilized to the maximum by the plurality of image lights constituting the.
[0107]
In addition, by arranging a plurality of light sources at different positions in the sub-scanning direction, the light emitted from each light source is emitted from the reflecting surface of the polygon mirror toward different positions in the sub-scanning direction. . For this reason, the plurality of image lights constituting the image can be easily separated after being reflected by the polygon mirror.
[0108]
(4) A plurality of image lights reflected by the polygon mirror are made parallel to each other by the conversion means, and then deflected at a constant speed in the main scanning direction by the correction means, so that the plurality of image lights reflected by the polygon mirror are The image light can be irradiated onto the photoconductor in a reliably separated state. In addition, since the incident angles of the plurality of image lights with respect to the correcting means are the same, the resist defects occurring between the plurality of image lights are the same, and the adjustment work of the optical components can be simplified.
[0109]
Further, by providing one conversion means and correction means for each of the plurality of image lights, the conversion state in the conversion means and the correction state in the correction means can be made constant for the plurality of image lights constituting the color image. In addition, the configuration can be simplified.
[0110]
(5) A plurality of image lights deflected at a constant speed in the main scanning direction by the correcting means are irradiated to the same position on the surface of the photosensitive member by the light setting means, so that the light is parallel to each other in the sub-scanning direction by the converting means. The plurality of image lights thus deflected at a constant speed in the main scanning direction can be irradiated to the same position on the surface of the photosensitive member in a state of being separated from each other. Therefore, an electrostatic latent image formed by each image light can be visualized by a developer corresponding to each image light, and an image can be formed by superimposing a plurality of developers.
[0111]
(6) With respect to two image light a and image light b adjacent to each other in the sub-scanning direction, (interval L in the sub-scanning direction) to (a value ½ of the width Ba of the image light a in the sub-scanning direction), ( (A value half of the width Bb in the sub-scanning direction of the image light b), (error W in the sub-scanning direction of the focal position of the polygon mirror), and (maximum error D in the sub-scanning direction due to the tilting of the polygon mirror) Even if an error occurs in the reflection position of the image light a and the image light b on the polygon mirror or the inclination of the rotation axis of the polygon mirror by making the value obtained by subtracting a positive value, the image light a and the image light The optical path of the light b can be reliably separated in the sub-scanning direction.
[0112]
(7) For the two photosensitive members a and b adjacent to each other, (the distance G between the transfer positions of the photosensitive member a and the photosensitive member b) and (the distance Ta between the exposure position and the transfer position of the photosensitive member a) The value obtained by subtracting (distance Tb between the exposure position and the transfer position of photoconductor b) from the sum of the above is an integral multiple of the value obtained by dividing (process speed v) by (number of rotations q of the polygon mirror). A plurality of image lights reflected on the same surface of the polygon mirror can be accurately irradiated to positions corresponding to the same dot of the image formed on each individual photoconductor, thereby reliably preventing the occurrence of resist failure. Therefore, it is possible to form a high-quality image without deviation.
[0113]
(8) For two adjacent photoconductors a and b, (the distance G between the transfer positions of the photoconductor a and the photoconductor b) and the radius R between the photoconductor a and the exposure position and transfer position. The value obtained by subtracting (the product of the radius R and the angle Sb between the exposure position and the transfer position) on the photoconductor b from the sum of the product of the angle Sa and the (process speed v) is the rotation speed of the polygon mirror. By using an integral multiple of the value divided by q), when a cylindrical photoconductor is used as a plurality of photoconductors for forming a developer image of a color corresponding to each image light, on the same surface of the polygon mirror Multiple reflected image lights can be accurately applied to the position corresponding to the same dot of the image on each individual photoconductor, reliably preventing the occurrence of resist failure and forming a high-quality image without deviation can do.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a color image forming apparatus according to an embodiment of the present invention.
FIG. 2 is a side view showing a configuration of a laser writing unit provided in the image forming apparatus.
FIG. 3 is a plan view showing a configuration of a laser writing unit provided in the image forming apparatus.
FIG. 4 is a diagram showing a relationship between a polygon mirror and a photosensitive member of the laser writing unit.
FIG. 5 is a diagram illustrating an incident position of image light on a polygon mirror of the laser writing unit.
FIG. 6 is a diagram illustrating a relationship between an error in an incident position of image light on a photosensitive drum and an error on a reflection surface of a polygon mirror.
FIG. 7 is a diagram illustrating a beam waist of image light.
FIG. 8 is a diagram illustrating a state of image light in the vicinity of the first CY lens and the f-θ lens in the laser writing unit.
FIG. 9 is a diagram illustrating a method of irradiating a surface of a photosensitive belt with a plurality of image lights using a single reflecting surface of a polygon mirror.
FIG. 10 is a diagram illustrating a method of irradiating a surface of a photosensitive drum with a plurality of image lights using a single reflecting surface of a polygon mirror.
FIG. 11 is a diagram showing an optical path of a laser beam in a multi-beam laser writing unit.
FIG. 12 is a diagram showing an optical path of a laser beam in a multi-beam laser writing unit.
FIG. 13 is a diagram illustrating the configuration and operation of a conventional four-rotation color image forming apparatus.
FIG. 14 is a diagram illustrating the configuration and operation of a conventional tandem type color image forming apparatus.
FIG. 15 is a perspective view showing a configuration of a laser writing unit in a conventional color image forming apparatus.
[Explanation of symbols]
10-Laser writing unit
11a to 11d-Laser diode (light source)
12a-12d-Lens
13-polygon mirror
14-first CY lens (conversion means)
15-f-θ lens (correction means)
16a-16d-deflection mirror (optical path setting means)
17a-17d-second CY lens (optical path setting means)
40-color image forming apparatus
51a to 51d-photosensitive drum

Claims (5)

For a plurality of image lights, the first means for focusing on the sub-scanning direction on the polygon mirror and the image light deflected at a constant angular velocity in the main scanning direction by a single polygon mirror are parallel to each other in the sub-scanning direction. a single conversion means for converting the light, in an image forming apparatus comprising a second means for forming on the surfaces of the photosensitive member, the through single correction means for deflecting the constant speed in the main scanning direction ,
The first means has the same configuration for a plurality of image lights , and the plurality of image lights are focused at positions close to the sub-scanning direction on the same reflecting surface of a single polygon mirror, and When the beam waists of the plurality of image lights partially or entirely overlap in the sub-scanning direction and the beam waist of each image light is ω, the difference in the incident position of each image light on the polygon mirror in the sub-scanning direction W is set to be smaller than ω ,
The image forming apparatus according to claim 2, wherein the second unit includes the same configuration for a plurality of image lights after the single correction unit . The image according to claim 1, further comprising an optical path setting unit that irradiates a plurality of image lights to the same position on the surface of each photoconductor between the correction unit and each of the plurality of photoconductors. Forming equipment. The image forming apparatus according to claim 2, wherein the optical path setting unit includes a lens for condensing the plurality of image lights at the same position on the surface of each photoconductor . In the plurality of image lights converted into parallel light and deflected in the main scanning direction, the width of the image light a in the sub-scanning direction is set to two image lights a and b adjacent to each other in the sub-scanning direction. Ba, the width of the image light b in the sub-scanning direction is Bb, the distance between the image light a and the image light b in the sub-scanning direction is L, the error of the focal position of the polygon mirror in the sub-scanning direction is W, the surface of the polygon mirror is tilted When the maximum error in the sub-scanning direction due to is D,
L- (Ba / 2)-(Bb / 2) -WD> 0
The image forming apparatus according to claim 1 , wherein the plurality of light sources and conversion means are arranged so as to satisfy the relationship . The first means includes a first optical system that focuses each of the plurality of image lights at a position close to the sub-scanning direction on the same reflection surface of a single polygon mirror,
The second means includes, after the correcting means, a second optical system having the same configuration for each of the plurality of image lights, and the same number of deflection mirrors for each of the plurality of image lights. ,
The second optical system converts the plurality of image lights into parallel light in the sub-scanning direction,
The deflection mirror, the image forming apparatus according to claim 1 for deflecting toward the photosensitive body with light separated into each of a plurality of image light from the second optical system.

Images