JP4998055B2 - Exposure apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an exposure apparatus that performs optical writing in an image forming apparatus such as a printer or a copying machine.

As a color image forming apparatus employing an electrophotographic system such as a printer or a copying machine, a tandem type image forming apparatus having a plurality of photosensitive drums is known. As an exposure device used in this type of tandem image forming apparatus, a plurality of light beams emitted from a plurality of light sources are deflected on the same surface of a rotating polygon mirror, and a plurality of deflected light beams are spatially separated. In addition, there is known one that exposes each of a plurality of photosensitive drums via a plurality of imaging lenses. In such an exposure apparatus, in order to spatially separate the deflected light beams, the incident angles of the light beams on the polygon mirror are different from each other.
However, when such a configuration is adopted, a difference occurs in the inclination of the scanning line of the light imaged on each photosensitive drum, and as a result, the toner images formed on the respective color photosensitive drums are superimposed. In some cases, color misregistration may occur. For this reason, for example, a technique for setting the lens shape of the imaging lens so as to absorb the inclination of the scanning line is disclosed (for example, see Patent Document 1).

JP 2003-215486 A

  An object of the present invention is to enable easy adjustment of misalignment due to a difference in inclination of a plurality of emitted lights.

According to the first aspect of the present invention, a light source that emits a plurality of lights and a plurality of the lights emitted from the light sources are incident at different angles in the sub-scanning direction, and the plurality of the lights are A deflecting member that deflects in the main scanning direction orthogonal to the sub-scanning direction, and a plurality of the light deflected by the deflecting member are arranged side by side in the sub-scanning direction, and each is arranged along the main scanning direction. A plurality of individual lenses having a lens shape that is symmetrical with respect to the main scanning direction and has a refractive power in the sub-scanning direction, and a plurality of the individual lenses arranged side by side in the sub-scanning direction. Among these, for the individual lenses arranged oddly in the sub-scanning direction, the one end side in the main scanning direction is used as an axis, and for the individual lenses arranged even-numbered in the sub-scanning direction. As an axis the other end of the main scanning direction, a holding member each rotatably holding a plurality of the individual lenses at the light in the plane perpendicular to the optical axis passing through the plurality of the individual lenses, the holding member And a fixing means for fixing the plurality of individual lenses held rotatably to the holding member.
According to a second aspect of the present invention, the holding member holds the one end side in the main scanning direction of the plurality of individual lenses outside a plurality of the light scanning regions , and the fixing means includes the plurality of the light beams. The exposure apparatus according to claim 1 , wherein the other end side in the main scanning direction of the plurality of individual lenses is fixed outside the scanning region .
According to a third aspect of the invention, the holding member holds the four individual lenses side by side in the sub-scanning direction, and the four individual lenses have a plurality of symmetry with respect to the sub-scanning direction. Of the four individual lenses that are configured so that the light is incident and are arranged side by side in the sub-scanning direction, an individual lens that is arranged first in the sub-scanning direction and an individual lens that is arranged fourth are The individual lens having the common lens shape and held by the holding member in a state in which the direction with respect to the main scanning direction is reversed, and the second and third individual lenses arranged in the sub-scanning direction are: 3. The holding member having a common lens shape and reversed in the direction with respect to the main scanning direction. It is of the exposure apparatus.
The invention according to claim 4 further includes a single common lens on which the plurality of light beams deflected by the deflecting member enter and emit the plurality of light beams toward the plurality of individual lenses, and the common lens The light incident surface of the lens is formed of an anamorphic aspheric surface, the light output surface of the common lens is formed of a y toric surface, and the light incident surface of each of the plurality of individual lenses is a y toric surface. 4. The light emission surface of each of the plurality of individual lenses is a surface whose curvature in the sub-scanning direction changes along the main scanning direction. 5. An exposure apparatus according to claim 1.

The invention according to claim 5 includes a plurality of image carriers and an exposure unit that exposes the plurality of image carriers, and the exposure unit emits a plurality of lights corresponding to the plurality of image carriers. And a plurality of the light beams emitted from the light source are incident at different angles in the sub- scanning direction, and deflect the plurality of light beams in the main scanning direction orthogonal to the sub- scanning direction. A member and a plurality of the light deflected by the deflecting member , arranged side by side in the sub-scanning direction , each extending along the main scanning direction and symmetrical with respect to the main scanning direction. there comprises a lens shape having a refracting power in the sub-scanning direction, a plurality of individual lens for forming a plurality of the light in each of a plurality of the image carrier, a plurality of the disposed side by side in the sub scanning direction Individual lens The individual lenses arranged oddly in the sub-scanning direction are centered on one end side in the main scanning direction, and the individual lenses arranged even-numbered in the sub-scanning direction are the other end side in the main scanning direction. A holding member that rotatably holds the plurality of individual lenses in a plane perpendicular to the optical axis of the light that passes through the plurality of individual lenses, and a plurality that is rotatably held by the holding member A fixing unit that fixes the individual lens to the holding member.
According to a sixth aspect of the invention, the holding member holds the one end side in the main scanning direction of the plurality of individual lenses outside a plurality of the light scanning regions, and the fixing means includes the plurality of the light beams. The image forming apparatus according to claim 5, wherein the other end side in the main scanning direction of the plurality of individual lenses is fixed outside the scanning region.
In the seventh aspect of the invention, the holding member holds the four individual lenses side by side in the sub-scanning direction, and the four individual lenses have a plurality of symmetry with respect to the sub-scanning direction. Of the four individual lenses that are configured so that the light is incident and are arranged side by side in the sub-scanning direction, an individual lens that is arranged first in the sub-scanning direction and an individual lens that is arranged fourth are The individual lens having the common lens shape and held by the holding member in a state in which the direction with respect to the main scanning direction is reversed, and the second and third individual lenses arranged in the sub-scanning direction are: 7. The holding member according to claim 5, wherein the holding member has a common lens shape and is reversed in direction with respect to the main scanning direction. Which is the image forming apparatus.

According to the first aspect of the present invention, compared to the case where the present configuration is not provided, for example, when adjusting the positional deviation between two adjacent individual lenses, adjustment of one individual lens and adjustment of the other individual lens are performed. Can be performed in parallel .
According to invention of Claim 2 , compared with the case where it does not have this structure, the situation where the optical path of light is obstructed by the holding member and the individual lens held by the holding member is avoided, and each individual lens It is possible to secure a wide adjustment range of the position .
According to the third aspect of the present invention, compared to the case where this configuration is not provided, the types (shapes) of the individual lenses necessary for forming the four optical paths are two, which is half the number of optical paths. Can be realized.
According to the fourth aspect of the present invention, the surface shape of each individual lens can be simplified as compared with the case where this configuration is not provided.
According to the fifth aspect of the present invention, compared to the case where the present configuration is not provided, for example, when adjusting the positional deviation between two adjacent individual lenses, adjustment of one individual lens and adjustment of the other individual lens are performed. Can be performed in parallel .
According to the sixth aspect of the present invention, it is possible to avoid a situation in which the optical path of light is obstructed by the holding member and the individual lens held by the holding member, and to ensure a wide adjustment range of the position of each individual lens. it can.
According to the seventh aspect of the present invention, compared to the case where this configuration is not provided, the types (shapes) of the individual lenses necessary for forming the four optical paths are two, which is half the number of optical paths. Can be realized.

The best mode for carrying out the present invention (hereinafter referred to as an embodiment) will be described below in detail with reference to the accompanying drawings.
<Embodiment 1>
FIG. 1 is a diagram illustrating an example of a configuration of an image forming apparatus 1 to which the exemplary embodiment is applied. An image forming apparatus 1 shown in FIG. 1 is a so-called tandem type digital color printer using an electrophotographic system, and an image forming process unit 70 that forms an image corresponding to image data of each color, and the entire image forming apparatus 1. An image processing unit 81 that performs predetermined image processing on image data received from, for example, an image reading device 4 such as a personal computer (PC) 3 or a scanner, a processing program, and image data are stored. For example, a main storage unit 82 realized by a hard disk drive (Hard Disk Drive) is provided.

The image forming process unit 70 has four image forming units 10Y, 10M, 10C, and 10K (in the following description, sometimes collectively referred to as “image forming unit 10”) at regular intervals in the vertical direction (substantially vertical direction). Are arranged in parallel. The image forming unit 10 includes a photosensitive drum 11 as an image holding member, a charging roll 12 that charges the surface of the photosensitive drum 11, and a developing device that develops the electrostatic latent image formed on the photosensitive drum 11 with toner of each color. 13. A drum cleaner 14 for cleaning the surface of the photosensitive drum 11 after transfer is provided.
Each image forming unit 10 is configured to be detachable from the main body of the image forming apparatus 1. For example, when the toner in the developing device 13 is consumed or the photosensitive drum 11 reaches the end of its life, the image forming unit 10 Exchanged in units of 10 forming units.

The charging roll 12 is composed of a roll member in which a conductive elastic layer and a conductive surface layer are sequentially laminated on a conductive core metal such as aluminum or stainless steel. Then, a charging bias voltage is supplied from a charging power source (not shown), and the surface of the photosensitive drum 11 is uniformly charged at a predetermined potential while being driven to rotate relative to the photosensitive drum 11.
The developing device 13 holds a two-component developer composed of yellow (Y), magenta (M), cyan (C), and black (K) toners and a magnetic carrier in each of the image forming units 10, and is photosensitive. The electrostatic latent image formed on the body drum 11 is developed with each color toner.
The drum cleaner 14 brings a plate-like member formed of a rubber material such as urethane rubber into contact with the surface of the photosensitive drum 11 to remove toner, paper dust, and the like attached on the photosensitive drum 11.

Further, the image forming apparatus 1 of the present embodiment is provided with a laser exposure device 20 as an example of an exposure unit (exposure device) that exposes the photosensitive drum 11 provided in each image forming unit 10. Yes. The laser exposure unit 20 acquires image data for each color from the image processing unit 81, and scans and exposes the photosensitive drum 11 of each image forming unit 10 with laser light whose lighting is controlled based on the acquired image data. To do.
Further, a paper transport belt 30 that transports the paper P as a recording material is disposed so as to move while being in contact with the photosensitive drum 11 of each image forming unit 10. The paper transport belt 30 is formed of a film-like endless belt that electrostatically attracts the paper P. Then, the sheet P is circulated and moved between the drive roll 32 and the idle roll 33, and a sheet conveyance path M <b> 1 is formed between the photosensitive drum 11 and the sheet P being conveyed from the lower side to the upper side in the substantially vertical direction. Yes.

Transfer rolls 31 are arranged at positions inside the paper conveyance belt 30 and facing the respective photosensitive drums 11. Each transfer roll 31 forms a transfer electric field with the photosensitive drum 11, so that each color toner image formed by each image forming unit 10 is formed on the paper P held and transported by the paper transport belt 30. Transfer sequentially. Further, on the outer side of the paper conveying belt 30 and on the downstream side of each transfer roll 31, a static elimination lamp 15 for neutralizing the photosensitive drum 11 after the transfer is provided.
An adsorption roll 34 that charges the paper transport belt 30 is disposed at the most upstream portion of the paper transport belt 30 on the photosensitive drum 11 side. The surface of the paper transport belt 30 is electrostatically attracted to the paper P by being charged to a predetermined potential by the suction roll 34.
A fixing device 40 is provided on the downstream side of the paper transport belt 30 along the paper transport path M1 to perform a fixing process using heat and pressure on an unfixed toner image on the paper P.

Further, as a paper transport system other than the paper transport belt 30, a paper storage unit 50 that stores the paper P on the paper feed side, and a pickup that picks up and transports the paper P stored in the paper storage unit 50 at a predetermined timing. A roll 51, a transport roll 52 that transports the paper P fed by the pickup roll 51, and a registration roll 53 that feeds the paper P to the paper transport belt 30 in accordance with the image forming operation are provided.
On the other hand, on the paper discharge side, a paper discharge roll 54 that conveys the paper P fixed by the fixing device 40, and in the case of single-sided printing, the paper P is directed to a paper discharge stacking unit 90 provided in the upper part of the apparatus main body. In the case of double-sided printing, the paper P on which one side is fixed by the fixing device 40 is reversed at a predetermined timing from the rotation direction toward the paper discharge stacking unit 90 in the reverse direction. A reversing roll 55 is disposed to be sent out toward the head. In addition, the double-sided conveyance path M2 is provided with a plurality of conveyance rolls 56 along the double-sided conveyance path M2.

  In the image forming apparatus 1 of the present embodiment, the image forming process unit 70 performs an image forming operation under the control of the control unit 80. That is, the image data input from the PC 3 or the image reading device 4 is subjected to predetermined image processing by the image processing unit 81 and supplied to the laser exposure unit 20. For example, in the black (K) image forming unit 10 </ b> K, the surface of the photosensitive drum 11 uniformly charged at a predetermined potential by the charging roll 12 is based on the image data from the image processing unit 81 by the laser exposure unit 20. Then, scanning exposure is performed with the laser light whose lighting is controlled, and an electrostatic latent image is formed on the photosensitive drum 11. The formed electrostatic latent image is developed by the developing device 13, and a black (K) toner image is formed on the photosensitive drum 11. Similarly, in the image forming units 10Y, 10M, and 10C, yellow (Y), magenta (M), and cyan (C) toner images are formed.

On the other hand, when the formation of each color toner image in each image forming unit 10 is started, the paper P taken out from the paper storage unit 50 is supplied to the paper transport belt 30 by the registration roll 53 in accordance with the toner image formation timing. Is done. The surface of the paper transport belt 30 is charged to a predetermined potential by the suction roll 34. As a result, the paper P is electrostatically attracted onto the paper transport belt 30 and is transported along the paper transport path M1 by the paper transport belt 30 that circulates and moves in the direction of the arrow in FIG. In the middle of the process, the color toner images are sequentially transferred onto the paper P by the transfer electric field formed by the transfer roll 31.
The sheet P on which each color toner image is electrostatically transferred is peeled from the sheet conveying belt 30 downstream of the image forming unit 10K and conveyed to the fixing device 40. When the paper P is conveyed to the fixing device 40, the unfixed toner image on the paper P is fixed to the paper P by receiving a fixing process using heat and pressure. The paper P on which the color toner images are fixed is stacked on a paper discharge stacking unit 90 provided in a discharge unit of the image forming apparatus 1. On the other hand, during double-sided printing, the same image forming operation is performed again via the double-sided conveyance path M2, and then the paper is stacked on the paper discharge stacking unit 90.

Next, the laser exposure device 20 used in the present embodiment will be described.
FIG. 2 is a side sectional view for explaining a schematic configuration of the laser exposure device 20 of the present embodiment. As shown in FIG. 2, the laser exposure device 20 includes a light source 21 composed of, for example, four semiconductor lasers. Further, four collimator lenses 22 and cylinder lenses 23 provided corresponding to each laser beam from the light source 21, for example, a rotating polygon mirror (polygon mirror) 24 as an example of a deflecting member formed of a regular hexagonal body, A common fθ lens 25 as a common lens through which laser beams pass in common, a plurality of folding mirrors 26, and four individual fθ lenses 27K, 27C, 27M, 27Y through which each laser beam passes individually (in the following description, “individual (sometimes collectively referred to as an fθ lens 27). In the present embodiment, the common fθ lens 25 and the individual fθ lens 27 constitute an fθ lens. Further, the laser exposure device 20 is configured in the housing 28 to suppress leakage of laser light to the outside and adhesion of dust or the like to each optical member. Further, the laser exposure device 20 includes a support shaft 28a provided integrally with a housing 28 for installation in the image forming apparatus 1, and individual fθ lenses 27K, 27C, 27M, and 27Y as an example of a plurality of individual lenses. A lens fixing frame 29 as a holding member to be fixed is provided.

  In this laser exposure device 20, the four divergent laser beams LK, LC, LM, and LY as a plurality of lights emitted from the light source 21 are converted into parallel lights by the collimator lenses 22 and are converted in the sub-scanning direction. The cylinder lens 23 having only the refractive power forms an image as a line image that is long in the main scanning direction in the vicinity of the deflection reflection surface 24a of the polygon mirror 24. The laser beams LK, LC, LM, and LY are reflected by the deflecting / reflecting surface 24a of the polygon mirror 24 that rotates at a high speed and a constant speed, and are scanned at an equal angular velocity.

Here, as a beam incident method to the polygon mirror 24, a tangential offset incident method in which a plurality of beams are incident at an angle in the main scanning direction, or a sagittal in which a plurality of beams are incident at different angles in the sub-scanning direction. -There are offset incidence methods. In this embodiment, as shown in FIG. 2, the laser beams LK, LC, LM, and LY incident on the deflecting / reflecting surface 24a of the polygon mirror 24 have angles in the sub-scanning direction, and the sagittal direction. The sagittal offset incidence method is adopted in which the incident angles are offset from each other. The laser beams LK, LC, LM, and LY incident on the polygon mirror 24 are set so that the reflection positions on the deflection reflection surface 24a coincide with the sub-scanning direction.
However, in this embodiment, since the emission wavelengths of the laser beams LK, LC, LM, and LY emitted from each light source 21 are the same, the laser beams LK, LC, LM, and LY emitted from each light source 21 are used. In order to guide the light onto each photosensitive drum 11, it is necessary to spatially separate the laser beams LK, LC, LM, and LY. For example, if the laser beams LK, LC, LM, and LY are incident on the deflection reflection surface 24a from an oblique direction in the sub-scan section, the target spatial separation can be achieved. However, if the laser exposure unit 20 is downsized, the spatial separation is achieved. Therefore, the incident angle with respect to the deflecting / reflecting surface 24a must be increased, and problems such as scanning line bending on the photosensitive drum 11 and degradation of imaging performance occur. In order to cope with this, in the present embodiment, the surface shapes of the common fθ lens 25 and the individual fθ lenses 27 are set as described later.

The laser beams LK, LC, LM, and LY deflected by the polygon mirror 24 pass through the common fθ lens 25, and the direction thereof is changed toward the surface of the photosensitive drum 11 by the plurality of folding mirrors 26, and each individual fθ. The surface of the photosensitive drum 11 of each image forming unit 10 is scanned and exposed through the lenses 27K, 27C, 27M, and 27Y. Here, the common fθ lens 25 and the individual fθ lenses 27K, 27C, 27M, and 27Y constituting the fθ lens have a function of equalizing the scanning speed of the laser light spot on the photosensitive drum 11, respectively. Yes.
Further, the above-described line image is formed in the vicinity of the deflecting / reflecting surface 24a of the polygon mirror 24, and the fθ lens links the light spot on the surface of the photosensitive drum 11 with the deflecting / reflecting surface 24a as an object point in the sub-scanning direction. Since this image is formed, this scanning optical system has a function of correcting the tilting of the deflecting / reflecting surface 24a.

By the way, in the digital color printer according to the present embodiment, when the exposure position on each photoconductor drum 11 is shifted in the main scanning direction or the sub-scanning direction, the color toner images superimposed on the paper P are shifted. . In this digital color printer, the allowable amount of misregistration is less than 1 dot in the main scanning direction and the sub-scanning direction (42.3 μm when the output resolution is 600 dpi (dot per inch)). In order to correct such misalignment of the exposure position, it is effective to adjust the attachment positions of various lenses and mirrors in the laser exposure unit 20.
However, when the adjustment for improving the deviation of the exposure position in the main scanning direction is performed, the deviation in the sub scanning direction becomes large, or conversely, when the adjustment for improving the deviation of the exposure position in the sub scanning direction is performed. It is not preferable that the scanning direction shift becomes large.
Therefore, in the present embodiment, the individual fθ lens 27 is selected as an adjustment target, and the surface for adjusting the characteristics in the sub-scanning direction has a surface shape that does not have characteristics that affect the performance in the main scanning direction. In addition, the surface for adjusting the characteristics in the main scanning direction has a surface shape that does not have characteristics that affect the performance in the sub-scanning direction.

FIG. 3 is a diagram for explaining the lens shape of the common fθ lens 25.
When the surface on which the laser light is incident on the common fθ lens 25 is an incident surface S1, and the surface to be emitted is an output surface S2, the incident surface S1 is an anamorphic aspheric surface, and the output surface S2 is a y toric surface. ing.
Here, the exit surface S2 which is the y toric surface has a constant curvature in the x direction, that is, the sub-scanning direction, and is a surface shape formed by rotating the shape represented by z (y) below around the y axis. It has become.
That is,
CUY: curvature in the main scanning direction of the optical axis origin
K: Conic constant
A, B, C, D: Assuming higher-order coefficients in the y-axis direction,
The exit surface S2 of the common fθ lens 25 is expressed by the following equation.

Also,
CUX: curvature in the sub-scanning direction of the optical axis origin
CUY: curvature in the main scanning direction of the optical axis origin
Kx: Sub-scanning direction conic constant
Ky: Main scanning direction conic constant
AR, BR, CR, DR: Even-order coefficients of rotational symmetry
AP, BP, CP, DP: Assuming odd-order coefficients with rotational symmetry,
The incident surface S1 of the common fθ lens 25 is expressed by the following equation.

FIG. 4 is a diagram for explaining the lens shape of the individual fθ lens 27.
When the surface on which the laser light is incident on the individual fθ lens 27 is an incident surface S3 and the surface to be emitted is an output surface S4, the incident surface S3 is a y-toric surface, and the exit surface S4 is x1 (y ) As a vertex, and a curvature radius R (y) is a surface formed by connecting arcs determined by a position y in the main scanning direction. The exit surface S4 is a surface in which the generatrix is curved and the curvature in the sub-scanning direction changes along the main scanning direction.
The incident surface S3 is represented by the same equation as the exit surface S2 of the common fθ lens 25 described above.
On the other hand, the exit surface S4 of the individual fθ lens 27 is expressed by the following equation.

Even if the variables C ₀ , B _2n , X ₀ , A _2n, etc. used in this equation are changed, the characteristics in the main scanning direction are not affected at all.
As described above, by defining the surface shape of the exit surface S4, adjusting the characteristics in the main scanning direction will affect the performance in the sub-scanning direction, or adjusting the characteristics in the sub-scanning direction. It is less likely that the performance in the scanning direction will be affected.
That is, the surface in order to satisfy the characteristics in the sub-scanning direction (for example, scanning line curvature correction at the time of sagittal offset and field curvature correction in the sub-scanning direction), that is, the exit surface S4 of the individual fθ lens 27 has performance in the main scanning direction. A surface shape that does not have an influencing characteristic is set, and conversely, a surface for satisfying characteristics in the main scanning direction (linearity correction, field curvature correction in the main scanning direction), that is, the incident surface S3 of the individual fθ lens 27 is provided. By setting a surface shape that does not have characteristics that affect the performance in the sub-scanning direction, it is possible to pursue the lens performance independently in the main scanning direction / sub-scanning direction.

Incidentally, as one of the exposure position shifts as described above, there is a so-called skew in which the exposure position for one line in the main scanning direction is inclined with respect to the sub-scanning direction.
FIG. 5 is a diagram for explaining the cause of such a skew.
FIG. 5A is a view of the laser beam deflected by the rotating polygon mirror 24 as seen from a direction orthogonal to the rotation direction of the polygon mirror 24. It is assumed that the polygon mirror 24 rotates in the direction of the arrow in the figure about the rotation axis 24b. Further, incident light (laser light) LI is irradiated onto the deflecting / reflecting surface 24a of the polygon mirror 24.
In this example, when the rotating polygon mirror 24 reaches the position indicated by the solid line in the figure, scanning for one line in the main scanning direction is started, and when the deflection reflection surface 24a reaches the state indicated by the broken line in the figure. Complete the scan. In the figure, the deflecting / reflecting surface 24a (S) indicates the position of the deflecting / reflecting surface 24a at the start of scanning, and the deflecting / reflecting surface 24a (E) indicates the position of the deflecting / reflecting surface 24a at the completion of scanning. .

At the start of scanning, the incident light LI is regularly reflected by the deflecting / reflecting surface 24a (S) and output as reflected light LR (S). On the other hand, when scanning is completed, the input light LI is regularly reflected by the deflecting / reflecting surface 24a (E) and output as reflected light LR (E). Between these, the incident light LI is incident on the rotating polygon mirror 24 and its regular reflection is performed, and optical writing for one line in the main scanning direction is performed on the photosensitive drum 11.
Here, referring to FIG. 5A, it can be seen that the reflection position of the deflecting reflection surface 24a with respect to the input light LI differs between when scanning is started and when scanning is completed. More specifically, the reflection position at the completion of scanning is further away from the photosensitive drum 11 than the reflection position at the start of scanning.

FIG.5 (b) is the figure which looked at Fig.5 (a) from the Vb direction.
In the present embodiment, as described above, the sagittal offset incidence method is adopted in which the incident angles of the respective laser beams with respect to the polygon mirror 24 are made different in the sub-scanning direction. For this reason, the incident light LI is incident on the deflecting / reflecting surface 24a in a state inclined in the sub-scanning direction as shown in the figure. Then, as described above, since the position of the deflection reflection surface 24a is different between the start of scanning and the end of scanning, the exposure position of the reflected light LR (S) on the photosensitive drum 11 at the start of scanning, The exposure position on the photosensitive drum 11 of the reflected light LR (E) upon completion of scanning is shifted in the sub-scanning direction.
As a result, as shown in FIG. 5C, when optical writing for one line in the main scanning direction is performed, a so-called skew occurs in which the start point and the end point of the line are shifted by Δ in the sub scanning direction. It will be.

  Such a skew can be corrected by adjusting the mounting angle of the individual fθ lens 27. For this reason, in the present embodiment, the setting angle of the individual fθ lens 27 is set in the manufacturing process at the factory. Specifically, the laser exposure device 20 is installed in the measurement device, and the laser beam is actually emitted, and the exposure position of the laser beam emitted from the individual fθ lenses 27K, 27C, 27M, and 27Y is measured and individually measured. Fine adjustments are made to the set angles of the fθ lenses 27K, 27C, 27M, and 27Y, and adjustments are made to match the design values. Finally, the individual fθ lenses 27K, 27C, 27M, and 27Y are fixed to the housing 28 with an adhesive as fixing means in a state where the exposure position matches the design value. Thereby, the exposure position of the laser exposure device 20 in the main scanning direction and the sub-scanning direction is set with high accuracy.

  FIG. 6 is a diagram for explaining the configuration of the individual fθ lens 27. 6A is a front view of the individual fθ lens 27, FIG. 6B is a longitudinal side view of the individual fθ lens 27, and FIG. 6C is a rear view of the individual fθ lens 27. Each is shown. The basic configuration of the individual fθ lens 27 shown in FIG. 6 is common to the individual fθ lenses 27K, 27C, 27M, and 27Y.

The individual fθ lens 27 includes a lens portion 271 extending along the main scanning direction, a frame portion 272 surrounding the lens portion 271, and a first protruding portion 273 formed to protrude from one end portion in the longitudinal direction of the frame portion 272. And a second projecting portion 274 formed to project from the other longitudinal end portion of the frame portion 272. And the V-shaped groove 275 which goes to a back side from the front side is formed in the edge part of the 1st protrusion part 273. As shown in FIG. The lens portion 271, the frame portion 272, the first projecting portion 273, and the second projecting portion 274 are formed by integrally molding a synthetic resin such as an annular polyolefin that is transparent to the laser light emitted from the light source 21. Composed.
As shown in FIGS. 6B and 4, the lens portion 271 in the present embodiment has a lens shape that is symmetrical in the longitudinal direction, that is, the main scanning direction. The lens portion 271 has power, that is, refractive power, in the sub-scanning direction orthogonal to the main scanning direction.

FIG. 7 is a front view of the laser exposure device 20 shown in FIG. 2 as viewed from the image forming unit 10 side. As shown in FIG. 7, individual fθ lenses 27 </ b> K, 27 </ b> C, 27 </ b> M, and 27 </ b> Y are arranged on the image forming unit 10 side of the laser exposure device 20. Here, the lens fixing frame 29 is provided with a total of four shaft portions 29a alternately on each side. The individual fθ lenses 27K, 27C, 27M, and 27Y are fixed in a state in which the V-shaped grooves 275 provided in the individual fθ lenses 27K, 27C, 27M, and 27Y are fitted in the respective shaft portions 29a. The individual fθ lenses 27K, 27C, 27M, and 27Y are adhesively fixed to the lens fixing frame 29 in a state where the individual fθ lenses 27K, 27C, 27M, and 27Y are adjusted to predetermined setting angles θK, θC, θM, and θY, respectively.
Further, two through-holes 28b are formed in each of the side walls of the housing 28 that face the free end sides of the individual fθ lenses 27K, 27C, 27M, and 27Y. Here, FIG. 8 shows an enlarged side view of the laser exposure device 20. As shown in FIG. 8, each through-hole 28b has a rectangular shape.

  The individual fθ lenses 27K, 27C, 27M, and 27Y do not use lenses having different surface shapes, but have a structure in which the optical path of the present embodiment is symmetrical in the sub-scanning direction as shown in FIG. Therefore, two lenses having the same shape are used as a set. That is, the individual fθ lenses 27K and 27Y are lenses having the same shape with different arrangement positions and arrangement directions. Similarly, the individual fθ lenses 27C and 27M are lenses having the same shape with different arrangement positions and arrangement directions. As a result, the individual fθ lens 27 may be prepared as two types of two lenses for the entire apparatus.

  FIG. 9 is a diagram for explaining an angle adjusting device 100 for adjusting the angle of the individual fθ lens 27 and an angle adjusting procedure thereof. The angle adjusting device 100 is provided so as to be in contact with the first arm 101 provided so as to be in contact with one side end of the second projecting portion 274 of the individual fθ lens 27 and the other side end of the second projecting portion 274. And a second arm 102. The angle adjusting device 100 includes a holder (not shown) for fixing the laser exposure device 20.

  Each of the first arm 101 and the second arm 102 is configured to be movable forward and backward in the left-right direction in the drawing. The first arm 101 and the second arm 102 are inserted through the through hole 28b shown in FIG. 8, and the individual fθ lens 27 is pushed by the second projecting portion 274. In the initial state, as shown in FIG. 9A, the first arm 101 and the second arm 102 are in a state of being aligned. In addition, the first protrusion 273 and the second protrusion 274 of the individual fθ lens 27 are pressed by the leaf spring 110 from above. The leaf spring 110 presses the individual fθ lens 27 with such a strength that the individual fθ lens 27 can rotate.

  Then, the irradiation position of the laser light emitted from the individual fθ lens 27 is measured by the measuring device, and the set angle θ of the individual fθ lens 27 is finely adjusted by the angle adjusting device 100 based on the measured value. At this time, for example, as shown in FIG. 9B, the first arm 101 is advanced in the left direction in the figure, while the second arm 102 is retracted to the right side in the figure, so that the individual fθ lens 27 is pivoted. By rotating around the portion 29a, the individual fθ lens 27 moves in the negative direction (θ <0). Alternatively, as shown in FIG. 9 (c), the first arm 101 is retracted to the right side in the figure, while the second arm 102 is advanced to the left side in the figure, so that the individual fθ lens 27 is centered on the shaft portion 29a. And the individual fθ lens 27 moves in the positive direction (θ> 0). That is, the lens fixing frame 29 holds the individual fθ lenses 27 rotatably in a plane perpendicular to the optical axis of the light transmitted through the individual fθ lenses 27. Further, the lens fixing frame 29 rotatably holds each individual fθ lens 27 other than the lens portion 271 of each individual fθ lens 27, that is, outside the light scanning region.

  Then, as shown in FIG. 7, the individual fθ lens 27 </ b> K is set so that the skew of the exposure position in the main scanning direction and the sub-scanning direction in the laser exposure device 20 is set to a predetermined position (design value) of the photosensitive drum 11. Is adjusted to the angle θK, the individual fθ lens 27C is adjusted to the angle θC, the individual fθ lens 27M is adjusted to the angle θM, and the individual fθ lens 27Y is adjusted to the angle θY. After the adjustment is completed, the individual fθ lenses 27K, 27C, 27M, and 27Y are temporarily fixed to the lens fixing frame 29 using the leaf spring 110 and the like, and thereafter, these are bonded and fixed using an ultraviolet curable resin or the like.

  As described above, in the present embodiment, the individual fθ lens 27 is set to be rotatable by providing the individual fθ lens 27 with the V-shaped groove 275 and providing the lens fixing frame 29 with the shaft portion 29a. Then, by rotating the individual fθ lens 27 little by little around the shaft portion 29a, the mounting angle of the individual fθ lens 27 can be easily adjusted. As a result, it is possible to suppress the exposure position skew that occurs when the laser beams LK, LC, LM, and LY are incident on the polygon mirror 24 by the sagittal offset incidence method. As a result, a good image in which color misregistration of each color toner image is suppressed can be obtained.

  Here, in the present embodiment, the lens shape of the individual fθ lens 27 is symmetric in the main scanning direction. As a result, even when the attachment angle of the individual fθ lens 27 is changed, the change in the refractive index in the main scanning direction can be suppressed, and the influence on the performance in the main scanning direction when the skew is improved can be suppressed.

  In the present embodiment, the individual fθ lens 27 is set in a rotatable state by providing the individual fθ lens 27 with the V-shaped groove 275 and the lens fixing frame 29 with the shaft portion 29a. I can't. That is, for example, as shown in FIG. 10A, a protrusion 276 is provided on the first protrusion 273 of the individual fθ lens 27, and a receiving part 29 b that receives the protrusion 276 is provided on the lens fixing frame 29. Good. For example, as shown in FIG. 10B, a circular through-hole 277 is provided in the first projecting portion 273 of the individual fθ lens 27, and a cylindrical shaft portion 29c that penetrates the through-hole 277 in the lens fixing frame 29 is provided. May be provided.

  In the present embodiment, the first arm 101 and the second arm 102 are used to adjust the mounting angle of the individual fθ lens 27 via the second protrusion 274. However, the present invention is not limited to this. Absent. For example, as shown in FIGS. 10 (a) and 10 (b), a gate portion 274a is formed to project from the end of the second projecting portion 274 to the side, and the gate portion 274a is directed upward or downward in the drawing. The angle of the individual fθ lens 27 may be adjusted by moving it.

  Further, in the present embodiment, the laser beams LK, LC, LM, and LY are incident on the polygon mirror 24 by the sagittal offset incidence method. However, the laser beams LK, LC are incident on the polygon mirror 24. Even when LM, LY are incident by the tangential offset incidence method, the skew amount of each laser beam LK, LC, LM, LY changes for the same reason. For this reason, the method used in the present embodiment may be applied to the laser exposure device 20 and the digital color printer that employ the tangential offset incidence method.

<Embodiment 2>
The present embodiment is substantially the same as the first embodiment, but in the first embodiment, the individual fθ lens 27 is rotated around one end portion in the main scanning direction of the individual fθ lens 27. In this embodiment, the individual fθ lens 27 is rotated around the central portion in the main scanning direction of the individual fθ lens 27 as an axis. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

FIG. 11 is a diagram for explaining the configuration of the individual fθ lens 27 used in the present embodiment.
The individual fθ lens 27 includes a lens portion 271 extending along the main scanning direction, a frame portion 272 surrounding the lens portion 271, and a central portion on one end side in the short side direction of the frame portion 272, that is, the main scanning of the lens portion 271. The first convex portion 278 formed to protrude laterally from the central portion in the direction and the first convex portion 278 from the central portion on the opposite side in the lateral direction of the frame portion 272, that is, from the central portion in the main scanning direction of the lens portion 271. And a second convex portion 279 that protrudes in the opposite direction. Here, each of the first convex portion 278 and the second convex portion 279 has an arcuate end surface shape.

  FIG. 12 is a front view of the laser exposure device 20 in the present embodiment as viewed from each image forming unit 10 side. As shown in FIG. 12, also in the present embodiment, individual fθ lenses 27K, 27C, 27M, and 27Y are arranged on the image forming unit 10 side of the laser exposure device 20. Further, in the present embodiment, in addition to the lens fixing frame 29 that bonds and fixes both ends of the individual fθ lenses 27K, 27C, 27M, and 27Y in the main scanning direction, the main scanning direction of the individual fθ lenses 27K, 27C, 27M, and 27Y. A holding portion 29d that rotatably holds the individual fθ lenses 27K, 27C, 27M, and 27Y is provided at the central portion. The holding portion 29d has a shape that sandwiches the first convex portion 278 and the second convex portion 279 provided in the individual θ lenses 27K, 27C, 27M, and 27Y, respectively.

  Also in the present embodiment, the individual fθ lenses 27K and 27Y are lenses having the same shape with different arrangement positions and arrangement directions, and the individual fθ lenses 27C and 27M have the same shape with different arrangement positions and arrangement directions. It is a lens. Therefore, the vertical relationship between the first convex portion 278 and the second convex portion 279 is reversed between the individual fθ lenses 27K and 27C and the individual fθ lenses 27M and 27Y.

  Also in the present embodiment, it is possible to adjust the mounting angle of the individual fθ lens 27 using the angle adjusting device 100 described in the first embodiment. However, in the present embodiment, when adjusting the mounting angle, the individual fθ lens 27 has the first convex portion 278 and the second convex portion 279 as the forming site, that is, the central portion in the main scanning direction of the individual fθ lens 27 as an axis. Rotate. For this reason, when skew correction of the exposure position is performed by adjusting the attachment angle, there is an advantage that the lead registration at the exposure position is less likely to be displaced than in the case of the first embodiment.

1 is a diagram illustrating an overall configuration of an image forming apparatus to which an embodiment is applied. It is a sectional side view explaining the schematic structure of a laser exposure device. It is a figure for demonstrating the lens shape of a common f (theta) lens. It is a figure for demonstrating the lens shape of an individual f (theta) lens. It is a figure for demonstrating the generation factor of a skew. It is a figure for demonstrating the structure of an individual f (theta) lens. It is the front view which looked at the laser exposure device from each image forming unit side. It is a side view of a laser exposure device. It is a figure for demonstrating the angle adjustment apparatus and angle adjustment procedure of an individual f (theta) lens. It is a figure for demonstrating the other structural example of an individual f (theta) lens. 6 is a diagram for explaining a configuration of an individual fθ lens used in Embodiment 2. FIG. It is the front view which looked at the laser exposure device used in Embodiment 2 from each image forming unit side.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 11 ... Photosensitive drum, 20 ... Laser exposure device, 21 ... Light source, 22 ... Collimator lens, 23 ... Cylinder lens, 24 ... Rotary polygon mirror (polygon mirror), 25 ... Common f (theta) lens, 26 ... Folding mirror, 27 ... individual fθ lens, 271 ... lens part, 272 ... frame part, 273 ... first protrusion part, 274 ... second protrusion part, 275 ... V-shaped groove, 276 ... protrusion part, 28 ... housing, 29 ... Lens fixing frame

Claims (7)

A light source that emits a plurality of lights;
A plurality of the light emitted from the light source are incident at different angles in the sub- scanning direction, and deflecting the plurality of the light in a main scanning direction orthogonal to the sub- scanning direction;
Corresponding to each of the plurality of lights deflected by the deflecting member, the light beams are arranged in the sub-scanning direction , each extends along the main scanning direction, and is symmetrical with respect to the main scanning direction. A plurality of individual lenses having a lens shape having refractive power in the sub-scanning direction;
Among the plurality of individual lenses arranged side by side in the sub-scanning direction, the odd-numbered individual lenses arranged in the sub-scanning direction are centered on one end side in the main scanning direction and are even-numbered in the sub-scanning direction. the other end of the main scanning direction as an axis for the individual lenses disposed respectively rotatably held plurality of the individual lenses at the light of the optical axis in a plane perpendicular to transmit multiple of the individual lenses Holding member to be
An exposure apparatus comprising: a fixing unit that fixes the plurality of individual lenses rotatably held by the holding member to the holding member. The holding member holds the one end side in the main scanning direction of the plurality of individual lenses outside a plurality of the light scanning regions ,
The exposure apparatus according to claim 1 , wherein the fixing unit fixes the other end side of the plurality of individual lenses in the main scanning direction outside a plurality of the light scanning regions . The holding member holds the four individual lenses side by side in the sub-scanning direction, and the four individual lenses are configured to receive a plurality of light beams that are symmetrical with respect to the sub-scanning direction. And
Of the four individual lenses arranged side by side in the sub-scanning direction, the first individual lens arranged in the sub-scanning direction and the fourth individual lens arranged in the sub-scanning direction have a common lens shape and the main lens. The individual lens arranged second and third in the sub-scanning direction, which are held by the holding member in a state in which the direction with respect to the scanning direction is reversed, have a common lens shape and the main lens. The exposure apparatus according to claim 1, wherein the exposure apparatus is held by the holding member in a state in which the direction with respect to the scanning direction is reversed. A plurality of the light deflected by the deflecting member is incident, and further includes a single common lens that emits the plurality of light toward the plurality of individual lenses,
The light incident surface of the common lens is configured with an anamorphic aspheric surface, and the light output surface of the common lens is configured with a y toric surface,
The light incident surface of each of the plurality of individual lenses is a y-toric surface, and the light emission surface of each of the plurality of individual lenses is a surface whose curvature in the sub-scanning direction changes along the main scanning direction. Consists of
The exposure apparatus according to any one of claims 1 to 3, wherein A plurality of image carriers;
Exposure means for exposing a plurality of the image carriers,
The exposure means includes
A light source that emits a plurality of lights corresponding to the plurality of image carriers;
A plurality of the light emitted from the light source are incident at different angles in the sub- scanning direction, and deflecting the plurality of the light in a main scanning direction orthogonal to the sub- scanning direction;
Corresponding to each of the plurality of lights deflected by the deflecting member, the light beams are arranged in the sub-scanning direction , each extends along the main scanning direction, and is symmetrical with respect to the main scanning direction. A plurality of individual lenses each having a lens shape having a refractive power in the sub-scanning direction, and each of which forms a plurality of the lights on the plurality of image holding bodies;
Among the plurality of individual lenses arranged side by side in the sub-scanning direction, the odd-numbered individual lenses arranged in the sub-scanning direction are centered on one end side in the main scanning direction and are even-numbered in the sub-scanning direction. the other end of the main scanning direction as an axis for the individual lenses disposed respectively rotatably held plurality of the individual lenses at the light of the optical axis in a plane perpendicular to transmit multiple of the individual lenses Holding member to be
An image forming apparatus including: a fixing unit configured to fix the plurality of individual lenses rotatably held by the holding member to the holding member. The holding member holds the one end side in the main scanning direction of the plurality of individual lenses outside a plurality of the light scanning regions,
The fixing means fixes the other end side in the main scanning direction of the plurality of individual lenses outside the plurality of light scanning regions.
The image forming apparatus according to claim 5. The holding member holds the four individual lenses side by side in the sub-scanning direction, and the four individual lenses are configured to receive a plurality of light beams that are symmetrical with respect to the sub-scanning direction. And
Of the four individual lenses arranged side by side in the sub-scanning direction, the first individual lens arranged in the sub-scanning direction and the fourth individual lens arranged in the sub-scanning direction have a common lens shape and the main lens. The individual lens arranged second and third in the sub-scanning direction, which are held by the holding member in a state in which the direction with respect to the scanning direction is reversed, have a common lens shape and the main lens. The image forming apparatus according to claim 5, wherein the image forming apparatus is held by the holding member in a state where the direction with respect to the scanning direction is reversed.

Images