JP2007041235A - Exposure apparatus, image forming apparatus and method of exposure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exposure apparatus in which the structure is more simplified than a conventional apparatus and an equivalent scanning speed is realized. <P>SOLUTION: An exposure apparatus 2 is provided with a multibeam light source apparatus 11, a collimator lens 12, a deflection mirror 13, an Fθ lens 14, a mirror 15 and a control part 16. A plurality of beams emitted from the multibeam light source apparatus 11 is parallelized by the collimator lens 12. The deflection mirror 13 is provided with a single reflecting face 13s and the plurality of beams are deflected by the reflecting face 13s. The plurality of beams deflected by the reflecting face 13s are focused by the Fθ lens 14 and reflected by the mirror 15 and radiated on different positions on the surface of a photoreceptor drum 3 which is an object to be exposed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exposure apparatus, an image forming apparatus, and an exposure method mounted on a laser beam printer, a copying machine, and the like, and more particularly, to an exposure apparatus that performs scanning by deflecting a beam with a reflecting surface.

  Conventionally, an exposure apparatus having a configuration as shown in FIG. 8 is known. FIG. 8 is a schematic view of a conventional exposure apparatus. 8 includes a light source 81 that emits a single beam (that is, one beam), a collimator lens 82, a cylindrical lens 83, a polygon mirror 84, an Fθ lens 85, and a mirror 86. The polygon mirror 84 includes a plurality of continuous reflecting surfaces. More specifically, the polygon mirror 84 has a polygonal column shape in which each side surface is a reflecting surface, and is a mirror that rotates in the direction of arrow A in the drawing around the rotation axis. Hereinafter, an optical system including the Fθ lens 85 and the mirror 86 is referred to as a scanning optical system.

  The beam emitted from the light source 1 is first converted into parallel light by the collimator lens 82. The beam that has become parallel light is reduced in diameter by the cylindrical lens 83 in the rotation axis direction of the polygon mirror 84. The beam having a smaller beam diameter in the direction of the rotation axis of the polygon mirror 84 is then reflected by the polygon mirror 84. The beam reflected by the polygon mirror 84 is further collected by the Fθ lens 85 and then reflected by the mirror 86. The beam reflected by the mirror 86 is irradiated onto the surface of the photosensitive drum 87 that is an exposure target.

  The beam irradiated onto the surface of the photosensitive drum 87 in this way is accompanied by the rotation of the polygon mirror 84 in the direction of the arrow A in the drawing (hereinafter referred to as the main scanning direction). ) Is scanned over the surface of the photosensitive drum 87.

  As the polygon mirror 84 rotates, the photosensitive drum 87 also rotates in the direction of arrow C in the drawing. Therefore, by the rotation of the photoconductor drum 87, the beam reflected by the mirror 86 is scanned on the surface of the photoconductor drum 87 in the direction of arrow D (hereinafter referred to as the sub-scanning direction) in the drawing.

  When the beam is reflected by one reflecting surface of the polygon mirror 84, the beam is reflected by the reflecting surface adjacent to the reflecting surface. In this case, the scanning start positions on the surface of the photosensitive drum 87 in the main scanning direction by the beams reflected by the respective reflecting surfaces are the same positions.

  By using the polygon mirror 84 in this way, the beam emitted from the cylindrical lens 83 can be similarly reflected by each reflection surface of the polygon mirror 84, and the beam is continuously reflected by the plurality of reflection surfaces. Can do.

  Therefore, the configuration including the polygon mirror 84 can usually perform high-speed exposure (scanning) than the configuration including only one reflecting surface.

In recent years, there has also been proposed a system that uses a reflecting mirror having a single reflecting surface instead of using a polygon mirror and can be exposed (scanned) at high speed (for example, see Patent Document 1). In this system, although there is a single reflecting surface, a plurality of scanning optical systems are arranged. In this system, the beam reflected by the reflecting surface enters each scanning optical system as the reflecting surface rotates.
Japanese Patent Laid-Open No. 11-290442 (published on September 17, 1999)

  However, the conventional configuration causes the following problems.

  That is, in the configuration of FIG. 8, the polygon mirror 84 has a polygonal column shape in which each side surface is a reflection surface as described above, and rotates in the direction of the arrow A in the drawing around the rotation axis. When the angle formed by the rotation axis and the reflection surface, the length of the reflection surface in the rotation axis direction, the reflectance of the reflection surface, and the like are different among the plurality of reflection surfaces, the beam spot formed on the photosensitive drum 87 , Positional deviation and light quantity fluctuations occur. Therefore, in order to prevent the positional deviation and the fluctuation of the light amount, it is necessary to manufacture the polygon mirror 84 with very high processing accuracy. For this reason, the manufacturing cost of the polygon mirror 84 is high.

  Further, in order to reduce problems caused by the difference between the angles of the rotation axis and the reflection surface for each reflection surface, it is necessary to reduce the beam diameter in the rotation axis direction of the polygon mirror. Therefore, it is essential to use the cylindrical lens 83.

  On the other hand, if a reflecting mirror having a single reflecting surface is used instead of the polygon mirror 84, such a problem does not occur. However, if the rotational speed of the reflecting surface is the same as that of the conventional exposure apparatus, the scanning speed (image area scanned per unit time) is compared with, for example, a conventional polygon mirror having six reflecting surfaces. (Length in the sub-scanning direction) is reduced to 1/6. In order to make the scanning speed the same, the rotational speed of the reflecting surface needs to be six times that of the conventional one. However, even in the present situation, the reflecting surface rotates at a sufficiently high speed of tens of thousands of rpm, and it is difficult to increase the speed further.

  In this regard, according to the method of Patent Document 1, for example, by arranging six scanning optical systems, even if the rotational speed of the reflecting surface is the same as that of the polygon mirror having six reflecting surfaces, The scanning speed can be the same.

  However, the method of Patent Document 1 requires a plurality of scanning optical systems. Further, as many photosensitive drums as the number of scanning optical systems are required. Furthermore, a transport system for passing the printing paper through all scanning optical systems is also required. For this reason, the manufacturing cost of an apparatus increases and the problem that an apparatus size also arises arises. Furthermore, the fact that there are a plurality of scanning optical systems naturally causes a positional deviation of a beam spot formed on the surface of the photosensitive drum between the scanning optical systems. For this reason, it is necessary to make the precision and assembly precision of each component high, and the merit of using a single reflecting surface is impaired. Therefore, the method of Patent Document 1 has not been a sufficient solution.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an exposure apparatus, an image forming apparatus, and an exposure method capable of realizing a scanning speed not inferior to the conventional one while simplifying the apparatus configuration as compared with the conventional one. It is to provide.

  In order to solve the above-described problems, an exposure apparatus according to the present invention includes: a beam emitting unit that emits a beam; and a deflecting unit that deflects the beam emitted from the beam emitting unit with a rotatable reflecting surface. In the exposure apparatus that exposes the surface of the photosensitive material by scanning the surface of the photosensitive material with the deflected beam as the reflecting surface rotates, the deflecting unit includes a single reflecting surface as the reflecting surface, The plurality of beams after being deflected by the single reflecting surface are irradiated to different positions on the surface of the photosensitive material.

  According to said structure, the reflective surface which a deflection | deviation means has is a single reflective surface. Therefore, the deflecting means itself has a simpler configuration than the polygon mirror. In addition, since there is only one reflecting surface, the angle formed by the reflecting surface and the rotation axis of the reflecting surface does not differ for each reflecting surface. For this reason, it is not necessary to provide a cylindrical lens for reducing a problem due to a difference between the reflecting surfaces and the angle formed by the reflecting surfaces and the rotation axes of the reflecting surfaces. For the above reasons, the apparatus configuration can be simplified compared to the configuration in which the beam is deflected by the polygon mirror.

  Further, since the plurality of beams deflected by the reflecting surface are irradiated to different positions on the surface of the photosensitive material, the surface of the photosensitive material can be simultaneously scanned by the plurality of beams. Therefore, it is possible to realize a scanning speed not inferior to the configuration in which the beam is deflected by the polygon mirror.

  Therefore, according to said structure, the exposure apparatus which can implement | achieve the scanning speed not inferior to the past can be provided, simplifying an apparatus structure compared with the past.

The exposure apparatus according to the present invention is the above exposure apparatus, wherein the photosensitive material is a rotatable photosensitive drum, and the circumference of the photosensitive drum is L, and the rotational speed per unit time of the photosensitive drum. B, the scanning direction when the deflected beam scans the surface of the photosensitive drum with the rotation of the reflecting surface is the main scanning direction, and the direction opposite to the rotating direction of the photosensitive drum is the auxiliary direction. the scanning direction, number of rotations per above the photoreceptor length in the sub-scanning direction of the image area formed on the surface of the drum and d _1, the unit of the reflective surface time by one scanning in the main scanning direction a is the same as the unit of L and d ₁ ,
a <L × b / d ₁
The structure shown by may be sufficient.

According to the above configuration, the time required for one rotation of the single reflecting surface of the deflecting unit is longer than the time required for the surface of the photosensitive drum to rotate by the length d _1. . Therefore, an image area formed on the surface of the photosensitive drum by one scanning in the main scanning direction and an image formed on the surface of the photosensitive drum by the next scanning in the main scanning direction. There is no overlap between the areas. That is, the same area on the surface of the photosensitive drum is not continuously exposed. Therefore, it is possible to prevent a deterioration in the quality of the electrostatic latent image formed on the surface of the photosensitive drum.

The exposure apparatus according to the present invention is the above-described exposure apparatus, wherein the plurality of beams are images formed on the surface of the photosensitive drum along the main scanning direction, and the photosensitive drums of adjacent images are formed. The distance in the sub-scanning direction along the surface is constant, and when the distance is d ₂ , the rotation speed a is the same when the units of d ₁ and d ₂ are the same:
a = L × b / (d ₁ + d ₂ )
The structure shown by may be sufficient.

According to the above configuration, the plurality of beams are images formed on the surface of the photosensitive drum along the main scanning direction, and adjacent images in the sub-scanning direction along the surface of the photosensitive drum. interval is a constant value d _2, and the main by one scanning in the scanning direction and an image region formed on the surface of the photosensitive drum, the photosensitive drum by the following one scan in the main scanning direction spacing between the image area to be formed on the surface of the is equal to the d _2. Therefore, the intervals in the sub-scanning direction along the surface of the photosensitive drum are constant for all the images formed on the surface of the photosensitive drum along the main scanning direction. Therefore, scanning in the sub-scanning direction by rotation of the photosensitive drum can always be performed at regular intervals. Therefore, a high-quality electrostatic latent image without unevenness can be formed on the surface of the photosensitive drum.

  The exposure apparatus according to the present invention further comprises output control means for switching whether to turn on or off the output of the plurality of beams from the beam emitting means in the exposure apparatus, wherein the output control means comprises: The structure may be such that the output of the beam from the beam emitting means is turned off during a period when there is no reflecting surface of the deflecting means on the optical path of the plurality of beams.

  While there is no reflecting surface of the deflecting unit on the optical path of the beam, turning off the beam output from the beam emitting unit can prevent the beam from being reflected by a portion other than the reflecting surface. Therefore, the beam reflected by the portion other than the reflecting surface is not irradiated on the surface of the photosensitive material. Therefore, it is possible to prevent the quality of the electrostatic latent image from deteriorating due to an unnecessary beam incident on the surface of the photosensitive material.

  In the exposure apparatus according to the present invention, in the exposure apparatus described above, a portion other than the reflection surface of the deflecting unit, where the plurality of beams are incident as the reflection surface rotates, reflects the beam. Surface treatment to prevent may be made.

  According to the above configuration, the portion other than the reflection surface of the deflecting unit, on which the plurality of beams are incident as the reflection surface rotates, is subjected to surface treatment for preventing the reflection of the beams. Thus, it is possible to prevent the beam from being reflected by a portion other than the reflecting surface. Therefore, the beam reflected by the portion other than the reflecting surface is not irradiated on the surface of the photosensitive material. Therefore, it is possible to prevent the quality of the electrostatic latent image from deteriorating due to an unnecessary beam incident on the surface of the photosensitive material.

  An exposure apparatus according to the present invention is the above exposure apparatus, wherein the beam emitting means is a light source that emits a single beam, and a division that divides the single beam emitted from the light source into the plurality of beams. Means.

  According to the above configuration, a plurality of beams can be obtained by dividing the single beam emitted from the light source by the dividing unit.

  The exposure apparatus according to the present invention may be configured such that in the exposure apparatus described above, the beam emitting means includes a plurality of light emitting units, and each light emitting unit emits a single beam.

  According to said structure, a beam emission means is provided with the several light emission part, and each light emission part inject | emits a single beam, A multiple beam can be obtained by simple structure.

  In the exposure apparatus according to the present invention, in the exposure apparatus described above, the dividing unit includes a plurality of light modulation elements, and all the light modulation elements reflect a single beam emitted from the light source. Thus, the light modulation element may be divided into the plurality of beams, and each of the light modulation elements may be configured to switch between reflecting and transmitting a single beam emitted from the light source.

  According to the above configuration, all the light modulation elements switch whether to reflect or transmit the single beam emitted from the light source, so that the beam output from the beam emitting means is turned on or off. This can be switched for each beam.

  In the exposure apparatus according to the present invention, in the exposure apparatus, the beam emitting unit includes a condensing unit that condenses the plurality of beams divided by the dividing unit. Each of the collected beams is provided with a light modulation element that switches between reflecting and transmitting a beam incident on the element, and the reflected or transmitted beam is deflected by the reflecting surface. There may be.

  According to the above configuration, the beam emitting means includes the condensing means for condensing the plurality of beams divided by the dividing means, and for each beam condensed by the condensing means, Since the light modulation element that switches whether the beam incident on the element is reflected or transmitted is individually provided, the beam output from the beam emitting means is switched on or off for each beam. Can do. In addition, since the light modulation element is irradiated with a beam having a beam diameter reduced by being condensed by the light condensing means, the light modulation element can be reduced in size according to the reduced beam diameter. By miniaturizing the light modulation element, switching between reflecting and transmitting the beam becomes faster, so switching between turning on and off the output of each beam is performed at higher speed. Can do.

  Further, in the exposure apparatus according to the present invention, in the above exposure apparatus, the dividing unit may be a diffraction grating.

  By using a diffraction grating as the dividing means, a plurality of beams can be obtained with a simple configuration.

  In order to solve the above-described problems, an image forming apparatus according to the present invention includes the above-described exposure apparatus.

  According to the above configuration, by providing the above-described exposure apparatus, it is possible to realize an image forming apparatus including an exposure apparatus that can realize a scanning speed that is not inferior to that of the prior art while simplifying the configuration of the apparatus.

  In order to solve the above problems, an exposure method according to the present invention includes a beam emitting step for emitting a beam and a deflection step for deflecting the emitted beam by a rotatable reflecting surface. Accordingly, in the exposure method of scanning the surface of the photosensitive material with the deflected beam to expose the photosensitive material, the beam emitting step simultaneously emits a plurality of beams, and the deflection step includes the plurality of beams. It is characterized in that the beam is simultaneously deflected by a single reflecting surface.

  According to said method, the reflective surface which a deflection | deviation means has is a single reflective surface. Therefore, the deflecting means itself has a simpler configuration than the polygon mirror. In addition, since there is only one reflecting surface, the angle formed by the reflecting surface and the rotation axis of the reflecting surface does not differ for each reflecting surface. For this reason, it is not necessary to provide a cylindrical lens for reducing a problem due to a difference between the reflecting surfaces and the angle formed by the reflecting surfaces and the rotation axes of the reflecting surfaces. For the above reasons, the apparatus configuration can be simplified compared to the configuration in which the beam is deflected by the polygon mirror.

  Furthermore, since a plurality of beams are irradiated to different positions on the surface of the photosensitive material, the surface of the photosensitive material can be simultaneously scanned by the plurality of beams. Therefore, it is possible to realize a scanning speed not inferior to the configuration in which the beam is deflected by the polygon mirror.

  Therefore, according to said structure, the exposure method which can implement | achieve the scanning speed not inferior to the past can be provided, simplifying an apparatus structure compared with the past.

  In the exposure apparatus according to the present invention, as described above, the deflecting unit includes a single reflecting surface as the reflecting surface, and the plurality of beams after being deflected by the single reflecting surface are subjected to the photosensitive. Since different positions on the surface of the material are irradiated, it is possible to provide an exposure apparatus that can realize a scanning speed not inferior to that of the prior art while simplifying the configuration of the apparatus as compared with the prior art.

  Moreover, since the image forming apparatus according to the present invention includes the exposure apparatus according to the present invention as described above, an exposure apparatus capable of realizing a scanning speed not inferior to the conventional one while simplifying the apparatus configuration as compared with the conventional one. The provided image forming apparatus can be realized.

  In the exposure method according to the present invention, as described above, in the beam emission step, a plurality of beams are simultaneously emitted, and in the deflection step, the plurality of beams are simultaneously deflected by a single reflecting surface. Therefore, it is possible to provide an exposure method capable of realizing a scanning speed not inferior to the conventional one while simplifying the apparatus configuration as compared with the conventional one.

  An embodiment of the present invention will be described with reference to FIGS. 1 to 7 as follows.

  First, an image forming apparatus provided with the exposure apparatus of the present embodiment will be described with reference to FIG. FIG. 1 is a schematic view of an image forming apparatus provided with the exposure apparatus of the present embodiment.

  The image forming apparatus 1 includes an exposure device (optical scanning device) 2 and a photosensitive drum 3. The exposure apparatus 2 includes a multi-beam light source device (beam emitting means) 11, a collimator lens 12, a deflecting mirror (deflecting means) 13, an Fθ lens 14, a mirror 15, and a control unit (rotation control unit, output control unit) 16. ing.

  The multi-beam light source device 11 is a device that emits six beams simultaneously. A specific configuration of the multi-beam light source device 11 will be described later. The collimator lens 12 is a lens that collimates each beam emitted from the multi-beam light source device 11.

  The deflecting mirror 13 includes a single reflecting surface 13s that can rotate in the direction of arrow A in the figure, and deflects the beams collimated by the collimator lens 12 simultaneously by the reflecting surface 13s. The Fθ lens 14 is a lens for condensing each beam deflected by the deflection mirror 13. The mirror 15 is a mirror for irradiating the surface of the photosensitive drum 3 as an exposure target with each beam condensed by the Fθ lens 14.

  The photosensitive drum 3 is a cylindrical member whose surface is coated with a photosensitive material. The photosensitive drum 3 is configured to be rotatable in the direction C in the drawing with a line passing through the center of each circular bottom as a rotation axis. The photosensitive drum 3 is charged by a charger (not shown).

  The control unit 16 is a member that controls the rotation of the reflecting surface 13 s and the rotation of the photosensitive drum 3. The control unit 16 is a member that controls whether the output from the multi-beam light source device 11 is turned on or off based on the rotation angle of the reflecting surface 13s detected by a sensor (not shown).

  The six beams emitted from the multi-beam light source device 11 are first converted into parallel light by the collimator lens 12. Each beam that has become parallel light is then reflected by the deflection mirror 13.

  Each beam reflected by the deflection mirror 13 is collected by the Fθ lens 14. Thereafter, each beam is reflected by the mirror 15 to form six beam spots at different positions on the surface of the photosensitive drum 3 (more specifically, positions different from each other in the sub-scanning direction described later).

  The six beams irradiated on the surface of the photosensitive drum 3 are photosensitized in the direction of arrow B (hereinafter referred to as the main scanning direction) in the drawing as the reflecting surface 13s of the deflection mirror 13 rotates. The surface of the body drum 7 is scanned.

  Further, along with the rotation of the reflecting surface 13s, the photosensitive drum 3 also rotates in the direction of arrow C in the drawing. Therefore, by the rotation of the photosensitive drum 3, the beam reflected by the reflecting surface 13s is scanned on the surface of the photosensitive drum 3 in the direction of arrow D (hereinafter referred to as the sub-scanning direction) in the drawing.

  Due to the scanning in the main scanning direction by the rotation of the reflecting surface 13s and the scanning in the sub-scanning direction by the rotation of the photosensitive drum 3, the electrostatic latent image is formed on the surface of the exposed photosensitive drum 3. An image is formed.

  The electrostatic latent image formed in this manner is visualized by a developing device (not shown) and then transferred to a recording material such as paper by a transfer device (not shown).

In the exposure apparatus 2 of the present embodiment, the six simultaneously irradiated beams are images formed on the surface of the photosensitive drum 3 along the main scanning direction, and the photosensitive drums of adjacent images are formed. The interval in the sub-scanning direction along the surface 3 is constant. Further, this interval is d ₂ (mm), the circumferential length of the photosensitive drum 3 is L (mm), the rotational speed of the photosensitive drum 3 per minute is b (rpm), and 1 in the main scanning direction. Assuming that the length of the image region formed on the surface of the photosensitive drum 3 by the scanning of the sub scanning direction is d ₁ (mm), the number of rotations a (rpm) per minute of the reflecting surface 13s is as follows. It is controlled by the control unit 16 so as to satisfy the relationship represented by Expression (1).

a = L × b / (d ₁ + d ₂ ) (1)
When the relationship represented by the above equation (1) is satisfied, the time 1 / a (minute) required for the reflecting surface 13s to make one rotation is represented by the following equation (2).

1 / a = (d ₁ + d ₂ ) / L × b (2)
Here, L × b indicates the rotational speed of the surface of the photosensitive drum 3. Therefore, from the above equation (2), (reflecting surface 13s is time required for one rotation) = (surface of the photosensitive drum 3 is by the length obtained by adding the distance d ₂ in the length d ₁ The relationship of time required for rotation) is derived. Therefore, the period in which the reflecting surface 13s is rotated 1, the surface of the photosensitive drum 3, it can be seen that rotation by the length obtained by adding the distance d ₂ in the length d _1. At this time, an image area formed on the surface of the photosensitive drum 3 by one scanning in the main scanning direction and a surface formed on the surface of the photosensitive drum 3 by the next scanning in the main scanning direction. spacing between the image area is equal to the d ₂ that. Therefore, the intervals in the sub-scanning direction along the surface of the photosensitive drum 3 are constant for all the images formed on the surface of the photosensitive drum 3 along the main scanning direction.

  As described above, the six beams simultaneously irradiated are images formed on the photosensitive drum 3 along the main scanning direction, respectively, and sub-scanning along the surface of the photosensitive drum 3 is performed for adjacent images. Along the main scanning direction, the control unit 16 controls the number of rotations a per minute of the reflecting surface 13s so that the direction interval is constant and the relationship of the above expression (1) is satisfied. Thus, the intervals in the sub-scanning direction along the surface of the photosensitive drum 3 are constant for all the images formed on the surface of the photosensitive drum 3. Therefore, scanning in the sub-scanning direction due to rotation of the photosensitive drum 3 can always be performed at regular intervals. Therefore, a high-quality electrostatic latent image without unevenness can be formed on the surface of the photosensitive drum 3.

  In this embodiment, in order to ensure the same scanning speed (length in the sub-scanning direction of the image area scanned per unit time) as the configuration using the polygon mirror having six reflecting surfaces, The case where the number of beams emitted from the multi-beam light source device 11 is six is described. However, the number of emitted beams is not limited to six. As the number of beams increases, the length in the sub-scanning direction of the image area scanned while the reflecting surface 13s rotates once increases, so that higher-speed scanning can be performed.

  Moreover, in this Embodiment, the control part 16 is controlling the rotation speed a per minute of 13 s of reflective surfaces so that the relationship shown by said Formula (1) may be satisfy | filled. However, the control part 16 may control the said rotation speed a so that the relationship shown by the following formula | equation (3) may be satisfy | filled.

a <L × b / d ₁ (3)
When the relationship represented by the above formula (3) is satisfied, the time 1 / a (minute) required for the reflecting surface 13s to make one rotation is represented by the following formula (4).

1 / a> d ₁ / L × b (4)
As described above, L × b indicates the rotational speed of the surface of the photosensitive drum 3. Therefore, from the above equation (4), the relationship (time reflecting surface 13s is required for one revolution)> (the time the surface of the photosensitive drum 3 is required to rotate by the amount of the length d ₁₎ Led. At this time, an image area formed on the surface of the photosensitive drum 3 by one scanning in the main scanning direction and a surface formed on the surface of the photosensitive drum 3 by the next scanning in the main scanning direction. There is no overlap between the image area. That is, the same area on the surface of the photosensitive drum 3 is not continuously exposed. Accordingly, it is possible to prevent the deterioration of the quality of the electrostatic latent image formed on the surface of the photosensitive drum 3.

  In the present embodiment, as shown in FIG. 1, the images formed by the six beams on the surface of the photosensitive drum along the main scanning direction are arranged at equal intervals in the sub-scanning direction. . According to this configuration, there is an advantage that unevenness generated in the electrostatic latent image formed on the surface of the photosensitive drum 3 is reduced. However, the images formed by the six beams on the surface of the photosensitive drum along the main scanning direction are not necessarily arranged at equal intervals in the sub-scanning direction.

In the above description, the photosensitive drum is used as the photosensitive material. However, the photosensitive material is not limited to this and may be, for example, photographic paper. When photographic paper is used, a transport system for transporting the photographic paper is separately provided. At this time, it is preferable that the six beams simultaneously irradiated are images formed on the surface of the photographic paper, and the interval between adjacent images in the conveyance direction of the photographic paper is constant. In addition, this constant interval is d ₄ (mm), the conveyance speed of the photographic paper is v (mm / min), and the six beams irradiated on the surface of the photographic paper are scanned by one scan. When the length of the photographic paper in the image area formed on the surface is d ₃ (mm), the control unit 16 reflects the reflecting surface 13s so as to satisfy the relationship represented by the following expression (5). It is preferable to control the rotation speed a per minute.

a = v / (d ₃ + d ₄ ) (5)
When the relationship represented by the above equation (5) is satisfied, the time 1 / a (minute) required for the reflecting surface 13s to make one rotation is represented by the following equation (6).

1 / a = (d ₃ + d ₄ ) / v (6)
The formula (6) is (time reflecting surface 13s is required for one rotation) = (photographic paper the time required in order to be conveyed by the length obtained by adding the distance d ₄ to the length d ₃ ). Therefore, the period for rotating the reflecting surface 13s is 1, photographic paper, it can be seen that is conveyed to the length d ₃ of the distance d ₄ min length only plus. At this time, there is an interval between an image area formed by six beams on the surface of the photographic paper by one scanning and an image area formed by six beams on the surface of the photographic paper by the next scanning. the spacing, equal to the _{d 4.} Therefore, since the interval in the conveyance direction of the photographic paper is constant for all the images formed on the surface of the photographic paper, scanning by the conveyance of the photographic paper can always be performed at a constant interval. Therefore, a high-quality electrostatic latent image without unevenness can be formed on the surface of the photographic paper.

  When photographic paper is used as the photosensitive material, the control unit 16 may control the rotational speed a so as to satisfy the relationship represented by the following formula (7).

a <v / d ₃ (7)
When the relationship represented by the above formula (7) is satisfied, the time 1 / a (minute) required for the reflecting surface 13s to make one rotation is represented by the following formula (8).

1 / a> d ₃ / v (8)
The equation (8) shows the relationship (time reflecting surface 13s is required for one revolution)> (the time required for photographic paper is conveyed by the amount of the length d _3). At this time, there is an interval between an image area formed by six beams on the surface of the photographic paper by one scanning and an image area formed by six beams on the surface of the photographic paper by the next scanning. In addition, there is no overlap. That is, the same area on the surface of the photographic paper is not continuously exposed. Accordingly, it is possible to prevent the deterioration of the quality of the electrostatic latent image formed on the surface of the photographic paper.

  In the above description, the control unit 16 of the exposure apparatus 2 controls the number of rotations a per minute of the reflecting surface 13s, but instead of or together with this, the control unit (not shown) of the image forming apparatus 1 The number of revolutions b per minute of the photosensitive drum 3 or the conveyance speed v of the photographic paper may be controlled.

  In addition, each unit used by said description is an illustration, You may use a unit different from the above, as long as the same unit is used for the same kind of quantity.

  Next, the multi-beam light source device 11 will be described with reference to FIGS. In addition, the same reference number is attached | subjected to the member which has the same function, and the description is abbreviate | omitted.

  FIG. 2 is a schematic diagram illustrating a configuration example of the multi-beam light source device 11. The multi-beam light source device 11 shown in FIG. 2 includes a light source 21 and a light modulation element array 24.

  The light source 21 is a member that emits a single light beam.

  The light modulation element array 24 includes eight light modulation elements 30 as shown in FIG. Each of the light modulation elements 30 is a light modulation element for switching whether to reflect or transmit a single beam emitted from the light source 21 according to a voltage applied to itself.

  In FIG. 3, each light modulation element 30 reflects a beam when a voltage is applied to itself, and transmits a beam when a voltage is not applied.

    In FIG. 3, the light modulation element array 24 includes eight light modulation elements 30. However, the number of light modulation elements 30 is not particularly limited as long as a plurality of light modulation elements 30 are provided so that a plurality of beams can be emitted from the multi-beam light source device 11.

  In FIG. 3, the light modulation elements 30 are aligned on a straight line as a configuration for aligning the images formed by the beams on the surface of the photosensitive drum 3 along the main scanning direction at equal intervals in the sub-scanning direction. They are arranged at equal intervals. However, the arrangement of the light modulation elements 30 is not limited to this. FIG. 4 is a diagram illustrating another arrangement example of the light modulation elements 30. For example, as shown in FIG. 4, the light modulation elements 30 may be arranged in a matrix and tilted by a predetermined angle θ. Also in this case, by appropriately adjusting the distance between the light modulation elements 30 and the predetermined angle θ, an image formed on the surface of the photosensitive drum 3 along the main scanning direction by each beam in the sub-scanning direction, etc. It can be arranged at intervals.

  The multi-beam light source device 11 shown in FIG. 2 is configured to output the beam reflected by the light modulation element 30 to the outside of the device. Therefore, whether or not to output the beam from the multi-beam light source device 11 can be switched by controlling the controller 16 of the exposure apparatus 2 whether or not to apply a voltage to each light modulation element 30. .

  Specifically, the control unit 16 detects the rotation angle of the reflection surface 13s by a sensor (not shown), and the reflection surface 13s is on the optical path of the beam emitted from the multi-beam light source device 11 based on the detected rotation angle. Judge whether there is. During a period in which the reflection surface 13s is on the optical path of the beam emitted from the multi-beam light source device 11, the control unit 16 controls a voltage supply source (not shown) so as to apply a voltage to the light modulation element 30. . On the other hand, during a period when there is no reflecting surface 13 s on the optical path of the beam emitted from the multi-beam light source device 11, the control unit 16 controls a voltage supply source (not shown) so as not to apply a voltage to the light modulation element 30. .

  As a result, during the period in which the reflecting surface 13s is on the optical path of the beam emitted from the multi-beam light source device 11, the beam output from the multi-beam light source device 11 can be turned on and emitted from the multi-beam light source device 11. During a period when there is no reflecting surface 13s on the beam optical path, the beam output from the multi-beam light source device 11 can be turned off. As a result, the beam reflected by the portion other than the reflecting surface 13 s is not irradiated on the surface of the photosensitive drum 3, so that an unnecessary beam is incident on the surface of the photosensitive drum 3. Degradation of the latent image can be prevented.

  According to the configuration of FIG. 2, a single beam emitted from the light source 21 can be split into a plurality of beams by reflecting the plurality of light modulation elements 30. At that time, for each of the divided beams, whether the beam output is turned on or off can be individually switched, so that an exposure pattern can be formed by each beam.

  FIG. 5 is a schematic diagram illustrating another configuration example of the multi-beam light source device 11. The multi-beam light source device 11 shown in FIG. 2 is configured to output a beam reflected by the light modulation element 30 to the outside of the device. However, as shown in FIG. Also, it can be configured to output to the outside of the apparatus.

  By the way, as described above, the light modulation element 30 in the configuration of FIG. 3 reflects the beam when a voltage is applied to itself, and transmits the beam when a voltage is not applied. However, on the contrary, it is also possible to use a light modulation element configured to transmit a beam when a voltage is applied to itself and to reflect a beam when a voltage is not applied.

  FIG. 6 is a schematic diagram showing still another configuration example of the multi-beam light source device 11. The multi-beam light source device 11 shown in FIG. 6 includes a light source 21, a diffraction grating (dividing unit) 22, an optical lens (condensing unit) 23, and a light modulation element array 24. The member corresponding to the dividing means described in the claims is the diffraction grating 22 in the configuration of FIG.

  The diffraction grating 22 is a member that divides a single beam emitted from the light source 21 into a plurality of beams. The optical lens 23 is a member that condenses the beam divided by the diffraction grating 22.

  A single beam emitted from the light source 21 is first divided into a plurality of beams by the diffraction grating 22. Thereafter, the plurality of beams are condensed on the light modulation element array 24 by the optical lens 23. The beams condensed on the light modulation element array 24 are reflected or transmitted by the light modulation elements 30 corresponding to the respective beams one to one. The beam reflected by the light modulation element 30 enters the collimator lens 12.

  According to the configuration of FIG. 6, each beam after the division by the diffraction grating 22 is reflected or transmitted by the light modulation element 30 corresponding to the beam. It can be switched individually between on and off. Further, by condensing each beam after being divided by the diffraction grating 22 by the optical lens 23, the beam diameter of each beam is reduced. Therefore, the light modulation element 30 can be reduced in size according to the reduced beam diameter. Further, by downsizing the light modulation element 30, switching between reflecting and transmitting the beam becomes faster. Therefore, if the light modulation element 30 is reduced in size, switching between turning on or off the output of each beam can be performed at higher speed.

  FIG. 6 shows a case where the beam is divided into three beams by the diffraction grating 22 for simplification, but the beam may be divided by a member other than the diffraction grating. Further, the number of beams after the division is not limited to three, but may be two or four or more.

  If the beam is split using a diffraction grating, the number of optical elements through which the beam passes can be reduced as compared with a configuration in which a beam is split using a plurality of optical elements. Therefore, the light quantity loss of the beam can be reduced. In addition, when using a diffraction grating, it is preferable to optimize the grating groove depth and the grating cross-sectional shape so that the light quantity of each beam after division is uniform.

  In FIG. 6, the beam reflected by the light modulation element 30 is output to the outside of the apparatus. However, the beam transmitted through the light modulation element 30 may be output to the outside of the apparatus. .

  Further, as the multi-beam light source device 11, a light source device having two or more light emitting units such as a multi-beam laser or a surface emitting laser array (VCSEL) may be used. In the configuration using these light source devices, the control unit 16 of the exposure apparatus 2 turns on or off the output of the beam from the multi-beam light source device 11 by switching whether to apply a voltage to each light emitting unit. Can be switched. Furthermore, since an optical system for splitting the beam is not necessary, the multi-beam light source device 11 can be reduced in size.

  In addition, when a light source device having two or more light emitting units is used as the multi-beam light source device 11, the light emitting units are arranged in a matrix and are set at a predetermined angle θ as in the configuration shown in FIG. A tilted configuration may be used. Also in this case, by appropriately adjusting the interval between the light emitting sections and the predetermined angle θ, the images formed by the beams on the surface of the photosensitive drum 3 along the main scanning direction are equally spaced in the sub scanning direction. Can be lined up.

  FIG. 7 is a schematic diagram showing still another configuration example of the multi-beam light source device 11. The multi-beam light source device 11 shown in FIG. 7 includes light sources 41a and 41b, collimator lenses 42a and 42b, reflecting surfaces 43a and 43b, a polarizing beam splitter 44, and a photodetector 45.

  The two light sources 41a and 41b are members that each emit a single beam. The collimator lenses 42a and 42b are lenses that collimate the beams emitted from the light sources 41a and 41b, respectively. The reflecting surfaces 43a and 43b are members that reflect the beams that have become parallel light by the collimator lenses 42a and 42b, respectively.

  The polarization beam splitter 44 is a member that divides each beam incident on itself.

  The light detector 45 is a member that detects relative position information and light amount information of each light source from a beam incident thereon.

  The beam emitted from the light source 41a is collimated by the collimator lens 42a and then reflected by the reflecting surface 43a. The beam reflected by the reflecting surface 43 a is split into two beams by the polarization beam splitter 44. The polarization beam splitter 44 emits one of the two beams to the outside of the multi-beam light source device 11 by transmitting the beam without deflection. The polarization beam splitter 44 causes the other of the two beams to be incident on the photodetector 45 by being deflected.

  On the other hand, the beam emitted from the light source 41b is collimated by the collimator lens 42b and then reflected by the reflecting surface 43b. The beam reflected by the reflecting surface 43b is split into two beams by the polarization beam splitter 44. The polarization beam splitter 44 causes one of the two beams to pass through without being deflected so as to enter the photodetector 45. The polarization beam splitter 44 deflects the other of the two beams and emits it to the outside of the multi-beam light source device 11.

  In this way, a part of the beam emitted from the light source 41 a and a part of the beam emitted from the light source 41 b are emitted from the polarization beam splitter 44 to the outside of the multi-beam light source device 11. On the other hand, the photodetector 45 receives the other part of the beam emitted from the light source 41a and the other part of the beam emitted from the light source 41b. The light detector 45 detects the relative position information of the light sources 41a and 41b and the light amount information of each beam emitted from the light sources 41a and 41b based on the received beam.

  According to the configuration of FIG. 7, by appropriately changing the settings of the collimator lenses 42 a and 42 b, the reflecting surfaces 43 a and 43 b, and the deflection beam splitter 44, the beams emitted from the light sources 41 a and 41 b are changed to the multi-beam light source device 11. It is possible to arbitrarily set the interval between beams and the beam emission direction when the beam is emitted to the outside.

  Although a polarization beam splitter is used here, any means can be used as long as it can split a beam incident on itself, transmit at least one of the divided beams, and deflect at least another. Other means may be used.

  In the example shown in FIG. 7, the number of light sources is two, but the number of light sources may be three or more.

  In each configuration of the multi-beam light source device 11 described above, the output of the beam from the multi-beam light source device 11 is turned off during a period when there is no reflecting surface 13s on the optical path of the beam emitted from the multi-beam light source device 11. Yes. However, the present invention is not limited to this, and a surface treatment for preventing the reflection of the beam may be applied to a portion other than the reflection surface 13s of the deflecting mirror 13 and a portion where the beam is incident as the reflection surface 13s rotates. . As such a process, for example, a matte black coating or roughening the surface to reduce the amount of specularly reflected light, and diffracting reflected light up and down so that it does not enter the Fθ lens. A method of forming a diffraction grating having a wave-like or triangular shape in the vertical cross section of the reflecting surface 13 in the drawing or a light source wavelength order is mentioned. Even if the surface treatment for preventing the reflection of the beam is performed in this manner, the beam reflected by the portion other than the reflecting surface 13s is not irradiated on the surface of the photosensitive drum 3. It is possible to prevent the quality of the electrostatic latent image from deteriorating due to the incidence of an unnecessary beam on the surface.

  As described above, according to the exposure apparatus 2 of the present embodiment, the multi-beam light source device 11 emits a plurality of beams simultaneously, and the deflection mirror 13 includes a single reflecting surface 13s, and the plurality of beams Are simultaneously deflected by a single reflecting surface 13 s, so that the plurality of deflected beams are irradiated to different positions on the surface of the photosensitive drum 3.

  According to the above configuration, the reflecting surface 13s provided in the deflection mirror 13 is a single reflecting surface. Therefore, the deflection mirror 13 has a simpler configuration than the polygon mirror. In addition, since there is only one reflecting surface, the angle formed by the reflecting surface and the rotation axis of the reflecting surface does not differ for each reflecting surface. For this reason, it is not necessary to provide a cylindrical lens for reducing a problem due to a difference between the reflecting surfaces and the angle formed by the reflecting surfaces and the rotation axes of the reflecting surfaces. For the above reasons, the apparatus configuration can be simplified compared to the configuration in which the beam is deflected by the polygon mirror.

  Furthermore, since six beams are irradiated to different positions on the surface of the photosensitive drum 3, the surface of the photosensitive drum 3 can be simultaneously scanned by the six beams. Therefore, it is possible to realize a scanning speed not inferior to the configuration in which one beam is deflected by a polygon mirror having six reflecting surfaces. Furthermore, if the number of beams is increased to 12 or 24, the scanning speed can be doubled or quadrupled.

  Therefore, according to said structure, the exposure apparatus 2 which can implement | achieve the scanning speed which is not inferior to the past can be provided, simplifying an apparatus structure compared with the past.

  Below, the exposure process flow in the exposure apparatus 2 of this Embodiment is demonstrated.

  First, six beams are simultaneously emitted by the multi-beam light source device 11 (S1; beam emission step).

  Next, the six beams emitted from the multi-beam light source device 11 are simultaneously deflected by the single reflecting surface 13 s of the deflecting mirror 13, and the deflected six beams are at different positions on the surface of the photosensitive drum 3. (More specifically, irradiation is performed on different positions in the sub-scanning direction) (S2: deflection step).

  As a result of the above steps, the six beams irradiated on the surface of the photosensitive drum 7 are directed in the arrow B direction (main scanning direction) in FIG. 1 as the reflecting surface 13s of the deflection mirror 13 rotates. Then, the surface of the photosensitive drum 3 is scanned.

  Further, along with the rotation of the reflecting surface 13s, the photosensitive drum 3 also rotates in the direction of arrow C in FIG. Therefore, by the rotation of the photosensitive drum 3, the beam reflected by the reflecting surface 13s is scanned on the surface of the photosensitive drum 3 in the direction of arrow D (sub scanning direction) in the drawing.

  Due to the scanning in the main scanning direction by the rotation of the reflecting surface 13s and the scanning in the sub-scanning direction by the rotation of the photosensitive drum 3, the electrostatic latent image is formed on the surface of the exposed photosensitive drum 3. An image is formed.

  According to the above method, the reflecting surface 13s provided in the deflecting mirror 13 is a single reflecting surface. Therefore, the deflection mirror 13 has a simpler configuration than the polygon mirror. In addition, since there is only one reflecting surface, the angle formed by the reflecting surface and the rotation axis of the reflecting surface does not differ for each reflecting surface. For this reason, it is not necessary to provide a cylindrical lens for reducing a problem due to a difference between the reflecting surfaces and the angle formed by the reflecting surfaces and the rotation axes of the reflecting surfaces. For the above reasons, the apparatus configuration can be simplified compared to the configuration in which the beam is deflected by the polygon mirror.

  Furthermore, since six beams are irradiated to different positions on the surface of the photosensitive drum 3, the surface of the photosensitive drum 3 can be simultaneously scanned by the six beams. Therefore, it is possible to realize a scanning speed not inferior to the configuration in which one beam is deflected by a polygon mirror having six reflecting surfaces. Furthermore, if the number of beams is increased to 12 or 24, the scanning speed can be doubled or quadrupled.

  Therefore, according to the above method, it is possible to provide an exposure method capable of realizing a scanning speed not inferior to the conventional one while simplifying the apparatus configuration as compared with the conventional one.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims. That is, embodiments obtained by combining technical means appropriately changed within the scope of the claims are also included in the technical scope of the present invention.

  The present invention is applicable to an exposure apparatus in an image forming apparatus such as a copying machine or a printer, and an image forming apparatus provided with this exposure apparatus.

1 is a schematic diagram of an image forming apparatus including an exposure apparatus according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing one configuration example of a multi-beam light source device in the exposure apparatus of FIG. 1. FIG. 2 is a schematic view of a light modulation element array provided in a multi-beam light source device in the exposure apparatus of FIG. 1. FIG. 4 is a diagram illustrating another arrangement example of the light modulation elements in the light modulation element array of FIG. 3. It is the schematic which shows the other structural example of the multi-beam light source device in the exposure apparatus of FIG. FIG. 10 is a schematic view showing still another configuration example of the multi-beam light source device in the exposure apparatus of FIG. 1. FIG. 10 is a schematic view showing still another configuration example of the multi-beam light source device in the exposure apparatus of FIG. 1. It is the schematic of a conventional exposure apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Exposure apparatus 3 Photosensitive drum (photosensitive material)
11 Multi-beam light source device (beam emission means)
13 Deflection mirror (deflection means)
13s reflecting surface 16 control unit (output control means)
21 Light source 22 Diffraction grating (dividing means)
23 Optical lens (Condensing means)
30 Light modulation element (dividing means)
41a / 41b Light source (light emitting part)

Claims (12)

Beam emitting means for emitting a beam, and deflecting means for deflecting the beam emitted from the beam emitting means by a rotatable reflecting surface, and the deflected beam is moved to the surface of the photosensitive material as the reflecting surface rotates. In an exposure apparatus that scans up and exposes the surface of the photosensitive material,
The beam emitting means emits a plurality of beams simultaneously,
The deflection means includes a single reflecting surface as the reflecting surface,
An exposure apparatus for irradiating different positions on the surface of the photosensitive material with the plurality of beams deflected by the single reflecting surface. The photosensitive material is a rotatable photosensitive drum,
The circumferential length of the photosensitive drum is L,
The number of rotations per unit time of the photosensitive drum is b,
With the rotation of the reflecting surface, the scanning direction when the deflected beam scans the surface of the photosensitive drum is the main scanning direction,
The direction opposite to the rotation direction of the photosensitive drum is a sub-scanning direction,
When the length of the image area formed on the surface of the photosensitive drum by one scanning in the main scanning direction is d ₁ in the sub-scanning direction,
The rotation speed a per the unit time of the reflective surface, when the same units of L and d _1,
a <L × b / d ₁
The exposure apparatus according to claim 1, wherein Each of the plurality of beams is an image formed on the surface of the photosensitive drum along the main scanning direction, and an interval between adjacent images in the sub-scanning direction along the surface of the photosensitive drum is constant. If the interval is d ₂ ,
In the case where the unit of d ₁ and d ₂ is the same, the rotational speed a is
a = L × b / (d ₁ + d ₂ )
The exposure apparatus according to claim 2, wherein Output control means for switching whether to turn on or off the output of the plurality of beams from the beam emitting means,
4. The output control means according to claim 1, wherein the output control means turns off the output of the beam from the beam emitting means during a period when there is no reflecting surface of the deflecting means on the optical path of the plurality of beams. The exposure apparatus according to any one of the above.   The portion other than the reflecting surface of the deflecting means, where the plurality of beams are incident as the reflecting surface rotates, is subjected to surface treatment for preventing the reflection of the beams. The exposure apparatus according to any one of claims 1 to 3. The beam emitting means is
A light source that emits a single beam;
6. The exposure apparatus according to claim 1, further comprising a splitting unit that splits a single beam emitted from the light source into the plurality of beams.   6. The exposure apparatus according to claim 1, wherein the beam emitting unit includes a plurality of light emitting units, and each light emitting unit emits a single beam. The dividing means includes a plurality of light modulation elements, and all the light modulation elements reflect a single beam emitted from the light source, thereby dividing the plurality of beams,
7. The exposure apparatus according to claim 6, wherein each of the light modulation elements switches whether to reflect or transmit a single beam emitted from the light source. The beam emitting means includes a condensing means for condensing the plurality of beams divided by the dividing means, and reflects a beam incident on the element for each of the beams condensed by the condensing means. Individually equipped with light modulation elements that switch between transmission and transmission,
7. The exposure apparatus according to claim 6, wherein the reflected or transmitted beam is deflected by the reflecting surface.   10. The exposure apparatus according to claim 6, wherein the dividing unit is a diffraction grating.   An image forming apparatus comprising the exposure apparatus according to claim 1. A beam emitting step for emitting the beam, and a deflection step for deflecting the emitted beam by a rotatable reflecting surface, and the deflected beam is scanned on the surface of the photosensitive material as the reflecting surface rotates. In an exposure method for exposing the photosensitive material,
In the beam injection step, a plurality of beams are simultaneously emitted,
In the deflection step, the plurality of beams are simultaneously deflected using a single reflecting surface as the reflecting surface, so that the deflected plurality of beams are irradiated to different positions on the surface of the photosensitive material. An exposure method characterized by the above.

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