JP2009066834A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device capable of maintaining good image quality at low cost since a beam with a desired output intensity can be emitted on a photosensitive member even when a disturbance temperature is raised/lowered or a light emitting source is replaced. <P>SOLUTION: This image forming device comprises a light scanner for deflecting and scanning by guiding beams from light sources 1-1, 1-2 to the light sensitive surface of a light sensitive medium 9 through an optical system including a deflection means 5. A latent image is formed on the light sensitive surface by the light scanner, and visualized by a developing means to provide an image. The image forming device further comprises a light source drive means for maintaining constant the intensities of light of the light sources, a light quantity controlling means for continuously changing the transmission rate of beam, and a detection means for detecting the density of the image. The intensity of light of the beam is variable according to the output of the detection means. Consequently, even when the disturbance temperature is raised/lowered or a light emitting source is replaced, the beam with a desired output intensity can be emitted on the light sensitive surface, and excellent image quality can be maintained at low cost. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a laser beam printer, a facsimile machine, or a complex machine including an optical scanning device.

  In recent electrophotographic image forming apparatuses such as a copying machine, a laser beam printer, a facsimile machine, or a complex machine thereof, electronic information is converted into optical information, and the optical information is hidden on a photosensitive medium by an optical scanning device. The image is fixed as an image, and the fixed latent image is developed with toner or the like to form an image. The optical scanning device comprises an optical system including a light source, a cylindrical lens, a deflecting means such as a rotating polygonal mirror, an imaging lens, and a mirror. The light beam from the light source is adjusted by the cylindrical lens and deflected and scanned by the rotating polygonal mirror. Then, the deflected beam is imaged on the photosensitive surface of the photosensitive medium by an imaging lens, a mirror or the like to form an electrostatic latent image.

  In general, in the image forming apparatus having the above configuration, a laser diode (hereinafter referred to as LD) is used as a light source. The oscillation of the LD does not rise immediately with respect to the drive current, and as shown in FIG. 2, the LED oscillates up to the threshold defined for each LD, and the LD light intensity is linear with respect to the drive current in the range exceeding the threshold. It has an increasing characteristic (hereinafter referred to as IL characteristic). Because of such oscillation characteristics, when LD oscillation is performed at a low intensity, there is a problem that the linearity of the light quantity is deteriorated in the vicinity of the threshold value, and a desired light intensity cannot be obtained. In addition, since the dynamic characteristics (droop characteristics) of the LD are poor at low strength, there is a problem that the time response of oscillation is poor.

  Conventionally, an optical system that removes LED light before LD oscillation using a half mirror or the like is conventionally known as a conventional technique described in Patent Document 1 for these problems. However, if an element with a constant light attenuation, such as a half mirror, is used, the LED light cannot be removed sufficiently when the IL characteristics change with temperature changes. However, it is necessary to replace the light source according to the characteristics of the new light source, and lacks versatility.

  There is also a case where the light emission intensity of the LD is actively modulated using a liquid crystal element as in the prior art described in Patent Document 2. However, in this configuration, when the IL characteristics change due to temperature fluctuations and the transmittance of the liquid crystal element fluctuates, it is necessary to control both the output intensity of the LD and the transmittance of the liquid crystal element. There is a concern about the increase in the cost of peripheral devices due to the above.

JP-A-11-242173 JP 7-159748 A

  The present invention has been made in view of the problems of the prior art described above, and is desired on the surface to be scanned (photoreceptor) even when the disturbance temperature rises or falls and the light source is replaced. An optical scanning device that can irradiate a beam with a high output intensity and maintain good image quality at low cost, and can improve image quality compared to the conventional technology. An object is to provide a forming apparatus.

In order to achieve the above object, the present invention employs the following solutions.
According to a first aspect of the present invention, there is provided an optical scanning device that guides a beam from a light source to a photosensitive surface of a photosensitive medium through an optical system including a deflecting unit, and deflects and scans the photosensitive surface of the photosensitive medium by the optical scanning device. In an image forming apparatus for forming a latent image on the surface and visualizing the latent image with a developing unit to obtain an image, a light source driving unit that keeps the light intensity of the light source constant, and a transmittance of the beam are continuously changed. It has a light amount adjusting means and a detecting means for detecting the density of the image, and the light intensity of the beam is varied according to the output of the detecting means.

According to a second means of the present invention, in the image forming apparatus of the first means, the light amount adjusting means is composed of a liquid crystal element and a polarizer.
According to a third means of the present invention, in the image forming apparatus according to the second means, the liquid crystal element is inclined from 90 ° with respect to the straight traveling direction of the beam.
The fourth means of the present invention is the image forming apparatus of the second or third means, wherein the liquid crystal element has a plurality of electrodes for changing the transmittance in the deflection direction.

According to a fifth means of the present invention, in the image forming apparatus of the first means, a light amount adjusting means comprising a polarizer capable of continuously changing a beam transmittance between the light source and the deflecting means. It is provided with.
According to a sixth means of the present invention, in the image forming apparatus of the seventh means, the light amount adjusting means comprises a plurality of polarizers, and one of the polarizers has a rotation adjusting mechanism. To do.

According to a seventh means of the present invention, in the image forming apparatus of the fifth means, the light amount adjusting means comprises a polarizer and a phase shifter, and the polarizer has a rotation adjusting mechanism.
According to an eighth means of the present invention, in the image forming apparatus of the sixth or seventh means, one of the polarizers is tilted from 90 ° with respect to the straight traveling direction of the beam. And
Furthermore, a ninth means of the present invention is the image forming apparatus according to any one of the first to eighth means, wherein the light source has a plurality of light emitting points and is arranged with the polarization direction aligned. To do.

  In the image forming apparatus according to the present invention, the configuration of any one of the first to ninth means allows the surface to be scanned even when the disturbance temperature rises or falls or the light source is replaced. A beam with a desired output intensity can be irradiated onto the photosensitive surface of a photosensitive medium, and good image quality can be maintained at a low cost. Therefore, image quality can be improved over conventional technology, and high speed and high image quality can be achieved. Can be realized. Further, according to the present invention, it is possible to realize an image forming apparatus that can cope with high speed and high image quality, and can improve image quality and reduce environmental burden compared to the prior art.

First, an example of an optical scanning apparatus that can adopt the technical idea of the present invention and an image forming apparatus including the optical scanning apparatus will be described with reference to FIGS. 1 and 3.
FIG. 1 shows an embodiment of an optical scanning device according to the present invention. In the optical scanning device of FIG. 1, reference numerals 1-1 and 1-2 denote laser diodes (hereinafter referred to as LDs) as light sources. 2-1 and 2-2 are coupling lenses, 3 is an aperture, 4 is a cylindrical lens, 5 is a polygon mirror as a deflecting means, 6 is a first scanning lens, and 7 is a second scanning lens. 8 is a reflecting mirror, and 9 is a photosensitive drum serving as a surface to be scanned.

  Two light beams are emitted from the two LDs 1-1 and 1-2, respectively. The two light beams emitted from the two LDs 1-1 and 1-2 are coupled to the subsequent optical system by coupling lenses 2-1 and 2-2, shaped by the aperture 3 and then sub-scanned by the cylindrical lens 4. The light is condensed only in the direction, and a line image is formed near the reflection point of the polygon mirror 5. The polygon mirror 5 is formed with several deflecting reflection surfaces on the peripheral surface at regular intervals in the circumferential direction, and is driven to rotate at a high speed at a constant speed by a motor (not shown) as a drive source, so that the light beam is reflected and the like. Deflection in angular velocity. A total of four light beams deflected by the polygon mirror 5 are transmitted through the first scanning lens 6 and the second scanning lens 7, further reflected by the reflecting mirror 8, and guided to the photosensitive drum 9.

  The first scanning lens 6 and the second scanning lens 7 constitute a scanning optical system, and each light beam is collected on the surface of the photosensitive drum 9 which is a surface to be scanned by the imaging function and the fθ function of the scanning optical system. At the same time, the surface of the photosensitive drum 9 is scanned at a constant speed in a direction parallel to the rotation axis direction (referred to as a main scanning direction). Each light beam emitted from the two LDs 1-1 and 1-2 is modulated by an image signal, and an image is written on the surface of the photosensitive drum 9 according to the modulation signal to form an electrostatic latent image. The

  FIG. 3 schematically shows an embodiment of an image forming apparatus according to the present invention. The image forming apparatus includes an image forming unit (printer unit) having an optical scanning device 120, an image forming apparatus main body 100 including a paper feeding unit (paper feeding tray 19 and the like), and an original image placed thereon. It is composed of a reading device 110 and has functions of a copying machine and a printer. Further, by connecting to a communication line, LAN, or the like, it can function as a facsimile machine or a digital multifunction machine.

In FIG. 3, four image forming units (or process cartridges) having the same configuration are arranged in parallel along the intermediate transfer belt 13 in the image forming unit (printer unit) of the image forming apparatus main body 100. In each image forming unit, the photosensitive drums 9Y, 9M, 9C, and 9K are drum-shaped images provided for the respective colors of yellow (Y), magenta (M), cyan (C), and black (K). It is a carrier. The photosensitive drums 9Y, 9M, 9C, and 9K have the same diameter, and are in pressure contact with the intermediate transfer belt 13 at equal intervals.
In the vicinity of the periphery of the photosensitive drums 9Y, 9M, 9C, and 9K, the charging devices 10Y, 10M, 10C, and 10K, the developing devices 11Y, 11M, 11C, and 11K, and the intermediate transfer belt 13 are arranged along the drum rotation direction. Drum cleaning devices 12Y, 12M, 12C, and 12K and a static elimination device (not shown) are provided.

The optical scanning device 120 has a configuration in which four optical scanning devices having the configuration shown in FIG. 1 are arranged corresponding to the photosensitive drums 9Y, 9M, 9C, and 9K. The mirror 5 is used in common, and there are a configuration in which four systems of light sources and scanning optical systems are arranged on the left and right sides or one side of the polygon mirror 5 to deflect and scan four systems of beams with one polygon mirror 5.
Further, each laser beam for writing from the optical scanning device 120 is placed on each photosensitive drum 9Y, 9M, 9C, 9K between the charging devices 10Y, 10M, 10C, 10K and the developing devices 11Y, 11M, 11C, 11K. Is irradiated.

  The charging devices 10Y, 10M, 10C, and 10K are roller-shaped devices that are arranged in a non-contact manner for the photosensitive drums 9Y, 9M, 9C, and 9K of the respective colors, and the charging drums 10Y, 9M, 9C, and 9K. Charge the surface uniformly. When the surface of the photosensitive drums 9Y, 9M, 9C, and 9K charged by the charging devices 10Y, 10M, 10C, and 10K is irradiated with a writing laser beam from the optical scanning device 120, the photosensitive drums 9Y, 9M, and 9C are used. , 9K, an electrostatic latent image corresponding to each color is formed.

  The developing devices 11Y, 11M, 11C, and 11K are devices that are arranged in such a manner that the developing rollers are in contact with the respective photosensitive drums 9, and toners of colors corresponding to the photosensitive drums 9Y, 9M, 9C, and 9K corresponding to the respective colors. (Developer) is retained. At the time of image formation, toner is supplied to the photosensitive drums 9Y, 9M, 9C, and 9K, and the electrostatic latent images formed on the photosensitive drums 9Y, 9M, 9C, and 9K are developed. The electrostatic latent image is developed with each color toner to be a toner image of each color.

  The drum cleaning devices 12Y, 12M, 12C, and 12K are devices that are disposed by bringing a blade (or cleaning blade) (or a brush roller or the like) into contact with each of the photosensitive drums 9Y, 9M, 9C, and 9K. 13 removes and collects residual toner, paper pieces, and the like remaining on the photosensitive drums 9Y, 9M, 9C, and 9K after the transfer of the toner image to 13, and cleans the surfaces of the photosensitive drums 9Y, 9M, 9C, and 9K. . Further, a neutralization device (not shown) is provided between the drum cleaning devices 12Y, 12M, 12C, and 12K and the charging devices 10Y, 10M, 10C, and 10K. The static eliminator neutralizes the surfaces of the photosensitive drums 9Y, 9M, 9C, and 9K.

The intermediate transfer belt 13 is an endless belt for sequentially superimposing and transferring the toner images of the respective colors formed on the surfaces of the photosensitive drums 9Y, 9M, 9C, and 9K. A full color image is formed on the intermediate transfer belt 13 by sequentially superimposing the toner images of the respective colors.
The optical sensor 14 is an apparatus that is disposed in a non-contact manner on the intermediate transfer belt 13 and detects a toner pattern that is formed as a maintenance test pattern for the image forming apparatus 100. Specifically, “process control pattern”, “color matching pattern”, and the like. These toner patterns will be described in detail later.

  The transfer belt cleaning device 15 is a device that is disposed by bringing a blade (cleaning blade) or the like into contact with the intermediate transfer belt 13. The transfer belt cleaning device 15 remains on the intermediate transfer belt 13 after the transfer of the toner image to the recording paper to be fed. The remaining toner or toner pattern is removed and collected, and the surface of the intermediate transfer belt 13 is cleaned.

  The transfer roller 16 transfers the color image formed on the intermediate transfer belt 13 onto the recording paper conveyed from the paper feed tray 19. The fixing device 17 thermally fixes the color image transferred on the recording paper to the recording paper. The paper feed roller 18 feeds recording paper. The paper feed tray 19 stores recording paper for each recording paper size. The paper discharge roller 20 discharges the recording paper on which the color image is thermally fixed to the outside of the image forming apparatus 100. The paper discharge tray 21 is a tray on which the discharged recording paper is placed.

  The photosensitive drums 9Y, 9M, 9C, and 9K all rotate in the same direction. The intermediate transfer belt 13 moves in a direction opposite to the rotation direction of the photosensitive drums 9Y, 9M, 9C, and 9K, and the transfer roller 16 rotates in the direction opposite to the intermediate transfer belt 13 (photosensitive drum 9). In the same rotation direction). In FIG. 3, the photosensitive drums 9Y, 9M, 9C, 9K and the transfer roller 16 rotate counterclockwise, and the intermediate transfer belt 13 rotates clockwise.

  Next, a “process control pattern” formed as a test pattern for maintenance in the image forming apparatus of the present embodiment will be described. The process control pattern is a pattern used for adjusting the image density, and an example thereof is shown in FIG. As shown in FIG. 4, rectangular patches are formed along the conveyance direction of the intermediate transfer belt 13 so that the density is gradually changed for each color (the density is gradually increased). The patches are formed in different rows so that the patches of each color of yellow (Y), magenta (M), cyan (C), and black (K) do not overlap. This pattern for process control can be obtained by setting a main scanning start position to a main scanning end position / sub-scanning start position to a sub-scanning end position based on the main scanning counter and the sub-scanning counter.

  Next, in the optical scanning device and the image forming apparatus configured as described above, in the present invention, between the LD light source 1 (1-1, 1-2) of the optical scanning device and the polygon mirror 5 that is a deflection unit, or A light amount adjusting means capable of continuously changing the transmittance of the beam is provided between the polygon mirror 5 and the photoconductor 9 as the surface to be scanned. Hereinafter, the detail of the Example of the light quantity adjustment means which concerns on this invention is shown below.

[Example 1: When the light amount is adjusted by a polarizer and a liquid crystal element]
In this embodiment, the light amount adjusting means is constituted by a polarizer (deflecting plate) and a liquid crystal element, and FIG. 5 shows an embodiment using a TN (twisted nematic) mode by nematic liquid crystal as the light amount adjusting means. It is. A glass substrate 22, ITO (transparent electrode) 23, alignment film 24, liquid crystal 25, alignment film 24, ITO 23, glass substrate 22, and polarizing plate 27 are arranged in this order with respect to a beam from the LD light source (not shown). As the glass substrate 22, a highly transparent material such as white plate glass or BK7 (manufactured by Schott) can be used. The film is formed by applying an alignment film on the glass substrate 22 on which the ITO 23 is formed by spin coating and baking. For example, AL3046 manufactured by JSR Corporation can be used as the alignment film 24. Further, a predetermined cell gap is given by using the gap material 26 or the like. As the liquid crystal, ZLI-4792 manufactured by Chisso Corporation (Δn = 0.095 at a wavelength of 680 nm) was used. A gap material 26 having a diameter of 6.2 μm is used. As the polarizing plate 27, LLC 2-8218 manufactured by Sanritsu Co., Ltd. is used.

  The plane of polarization of the beam is parallel to the sub-scanning direction. The rubbing direction on the LD side is the main scanning direction, and the rubbing direction on the emission side substrate is the sub-scanning direction. Therefore, the twist angle of the liquid crystal 25 is 90 °. The transmission axis of the polarizing plate 27 is parallel to the main scanning direction. When the voltage difference between both ITOs 23 is 0, the light is efficiently transmitted through the polarizing plate 27 (approximately 82% of the incident light amount) with substantially linearly polarized light that vibrates in the main scanning direction in the exit side glass substrate. For example, when it is desired to reduce the transmittance, a predetermined voltage difference is applied. For example, in the case of 1/10, when an applied voltage of 3 V is applied, about 8.2% of the incident light is transmitted (assuming that it is desirable that the incident polarized light and the polarized light of the emitted light are parallel) A λ / 2 plate is disposed between the side glass plate 22 and the polarizing plate 27, the slow axis of the λ / 2 plate is inclined 45 ° with respect to the main scanning direction, and the transmission axis of the polarizing plate is set in the sub scanning direction. To be parallel to.)

  By controlling the voltage applied to the liquid crystal 25 in this way, an arbitrary transmittance can be realized. Accordingly, even in the LD light source 1 having the IL characteristics shown in FIG. 2, the light intensity (image density) can be controlled by changing the transmittance at the light intensity at which the LD stably oscillates. However, the transmittance of the liquid crystal 25 may fluctuate due to temperature changes or liquid crystal molecule state changes. Also, the LD characteristics may vary due to temperature changes in the LD. In such a case, the image density of each pattern is detected by the density detection means (optical sensor 14) from the process control pattern shown above, the LD drive current is fixed by the light source drive means (LD drive circuit), By finely adjusting the liquid crystal applied voltage of the light amount adjusting means, a desired light intensity can be obtained. FIG. 6 is a block diagram of the detection / control system, which has density detecting means (optical sensor 14) for detecting the density of the image, and the light intensity of the beam is varied by the light quantity adjusting means according to the output of the detecting means. An example of a detection / control system is shown. By adopting this configuration, the parameters controlled with respect to the prior art are reduced, and a desired light intensity can be obtained efficiently.

  In general, in an image forming apparatus using an LD as a light source, the light emission capability of the LD is often sufficiently high with respect to the light intensity necessary for forming a latent image on a photoconductor. Therefore, in order to oscillate the LD stably, there are many cases of outputting with high intensity. However, as a problem at the time of high intensity oscillation, there is a return light in the light amount adjusting element (in the present embodiment, a liquid crystal element). Therefore, in this embodiment, the entire liquid crystal element is shifted by 90 ° from the straight traveling direction of the beam to give an inclination, thereby preventing the return light in the liquid crystal element.

  Furthermore, as shown in FIG. 7, the liquid crystal 25 may have a structure in which a plurality of electrodes 28 are provided in the main scanning direction and the transmittance in the main scanning direction is different. This structure is preferable when a plurality of beams are used and each light intensity is controlled using a single liquid crystal element. Further, by adopting the structure shown in FIG. 7 between the polygon mirror 5 and the photosensitive drum 9 for a single light source, the image height between the cylindrical lens 4, the polygon mirror 5, the scanning lenses 6 and 7, and the reflection mirror 8 can be reduced. Intensity unevenness (shading) in the (main scanning direction) can be suppressed. For example, when the beam intensity at the image height end is weaker than the intensity at the center of the image height on the photoconductor, the image height is increased by increasing the transmittance at the end of the liquid crystal 25 in the main scanning direction or decreasing the transmittance at the center. The light intensity between them can be unified.

[Example 2: When adjusting the amount of light with a plurality of polarizers]
Next, in this embodiment, the light amount adjusting means is constituted by a plurality of polarizers (deflecting plates), and FIG. 8 shows an embodiment in which a fixed polarizing plate 29 and a polarizing plate 30 with a rotation adjusting mechanism are mounted. .
As shown in FIG. 8, the light amount adjusting means includes a polarizing plate 30 with a rotation adjusting mechanism such as a motor 31 and a fixed polarizing plate 29, and the incident polarization of a beam from an LD light source (not shown) is parallel to the paper surface. The transmission axis of the fixed polarizing plate 29 is parallel to the paper surface.

The maximum light utilization efficiency of the light amount adjusting means of this embodiment is about 50% (= 70% × 70) when the transmission axis of the polarizing plate 30 is parallel to the paper surface and a polarizing plate with a parallel transmittance of 70% is used. %). Further, when the light amount is, for example, 1/10 of the maximum light amount (light utilization efficiency 5%), the rotation angle of the polarizing plate 30 is set to cos ⁻¹ (1/10) = 84.3 °. Since the dependence on the temperature of the polarizing plate is sufficiently smaller than that of the liquid crystal element of Example 1, the density detection of the process control pattern is performed using the same detection / control system as in FIG. From the results, the light intensity can be adjusted by finely adjusting the rotation angle of the polarizing plate 30 with the motor 31. Further, as in the first embodiment, the polarizing plate 30 is shifted by 90 ° from the straight traveling direction of the beam to give an inclination, whereby return light in the polarizing plate can be prevented.

[Example 3: When the light amount is adjusted by a polarizer and a phase shifter]
Next, in this embodiment, the light amount adjusting means is constituted by a polarizer (deflection plate) and a phaser (phase difference plate). FIG. 9A shows a fixed phase difference plate 33, a motor 34 and the like. It is an Example at the time of mounting the polarizing plate 32 with a rotation adjustment mechanism.
When it is necessary to make circularly polarized light up to the polygon mirror 5 in the optical scanning optical system, the configuration of this embodiment is preferable. By using circularly polarized light, return light from the scanning lenses 6 and 7 can be prevented. The polarizing plate 32 and the phase difference plate (for example, λ / 4 plate) 33 are integrated (adhered), and are rotated and adjusted by the motor 34. Further, the slow axis (optical axis) of the λ / 4 plate 33 is inclined by 45 ° with respect to the transmission axis of the polarizing plate 32 as shown in FIG. In addition, the polarization of the light incident on the deflection plate 32 is parallel to the paper surface. A component parallel to the transmission axis of the polarizing plate 32 is transmitted and circularly polarized by the λ / 4 plate 33.

  The maximum light utilization efficiency in this configuration is substantially determined by the parallel transmittance of the polarizing plate 32. When a polarizing plate having a parallel transmittance of 70% is used, the maximum efficiency is approximately 70%. In order to make this light quantity 1/10, the polarizing plate 32 with the λ / 4 plate 33 is rotated by 84.3 °. When adjusting the density, the same detection / control system as in FIG. 6 is used as in the second embodiment, and the rotation angle of the polarizing plate 32 is finely adjusted by the motor 34 from the density detection result of the process control pattern. This is done by adjusting the strength. Further, by providing the tilt by shifting the polarizing plate 32 by 90 ° from the straight traveling direction of the beam, it is possible to prevent the return light in the polarizing plate 32.

  The second and third embodiments can be realized by arranging not only a single light source but also a plurality of light sources or a light source that emits a plurality of beams so that the polarization directions of the respective beams are aligned.

As described above, the image forming apparatus provided with the optical scanning device of the present invention has the light amount adjusting means having any one of the configurations of the first to third embodiments, thereby increasing or decreasing the disturbance temperature or emitting light. Even when the source is replaced, a beam having a desired output intensity can be irradiated onto the photosensitive surface of the photoconductor 9 as the surface to be scanned, and good image quality can be maintained at low cost.
And in the image forming apparatus of the present invention, by providing the optical scanning device having the light amount adjusting means of any configuration of the first to third embodiments, it is possible to improve the image quality over the prior art, An image forming apparatus corresponding to high speed and high image quality can be realized. In the present invention, it is possible to cope with high speed and high image quality, and to improve the image quality and reduce the environmental load compared to the prior art.

1 is a schematic perspective configuration diagram showing an embodiment of an optical scanning device according to the present invention. It is a figure which shows the relationship between the drive current of LD light source, and light intensity. 1 is a schematic configuration diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 4 is a diagram illustrating an example of a process control pattern formed on an intermediate transfer belt. It is a schematic sectional drawing of the light quantity adjustment means which shows the 1st Example of this invention. It is a block diagram which shows an example of the detection and control system which varies the light intensity of a beam according to the output of a density | concentration detection means. It is a schematic perspective view which shows an example of the liquid crystal element which has a some electrode in the main scanning direction. It is a schematic block diagram of the light quantity adjustment means which shows the 2nd Example of this invention. It is structure explanatory drawing of the light quantity adjustment means which shows the 3rd Example of this invention.

Explanation of symbols

1 (1-1, 1-2): LD (light source)
2 (2-1, 2-2): Coupling lens 3: Aperture 4: Cylindrical lens 5: Polygon mirror (deflection means)
6: first scanning lens 7: second scanning lens 8: reflection mirror 9 (9Y, 9M, 9C, 9K): photosensitive drum 10Y, 10M, 10C, 10K: charging device 11Y, 11M, 11C, 11K: developing device 12Y, 12M, 12C, 12K: Drum cleaning device 13: Intermediate transfer belt 14: Optical sensor 16: Transfer roller 17: Fixing device 18: Paper feed roller 19: Paper feed tray 20: Paper discharge roller 21: Paper discharge tray 22: Glass substrate 23: ITO (transparent electrode)
24: Alignment film 25: Liquid crystal 26: Gap material 27: Polarizing plate (polarizer)
28: Multiple electrodes 29: Fixed polarizing plate (polarizer)
30: Polarizing plate with a rotation adjustment mechanism (polarizer)
31: Motor (rotation adjustment mechanism)
32: Polarizing plate with a rotation adjustment mechanism (polarizer)
33: Retardation plate (phaser)
34: Motor (rotation adjustment mechanism)
100: Image forming apparatus body 110: Reading apparatus 120: Optical scanning apparatus

Claims (9)

An optical scanning device that guides a beam from a light source to a photosensitive surface of a photosensitive medium through an optical system including a deflecting unit and performs deflection scanning, and forms a latent image on the photosensitive surface of the photosensitive medium by the optical scanning device; In an image forming apparatus that obtains an image by visualizing the image with a developing unit,
A light source driving means for keeping the light intensity of the light source constant, a light amount adjusting means for continuously changing the transmittance of the beam, and a detecting means for detecting the density of the image, and according to the output of the detecting means An image forming apparatus characterized in that the light intensity of the beam is varied. The image forming apparatus according to claim 1.
2. The image forming apparatus according to claim 1, wherein the light amount adjusting means includes a liquid crystal element and a polarizer. The image forming apparatus according to claim 2.
2. An image forming apparatus according to claim 1, wherein the liquid crystal element is tilted by shifting from 90 ° with respect to a straight traveling direction of the beam. The image forming apparatus according to claim 2 or 3,
The image forming apparatus, wherein the liquid crystal element has a plurality of electrodes for changing transmittance in the deflection direction. The image forming apparatus according to claim 1.
An image forming apparatus, comprising: a light amount adjusting unit made of a polarizer capable of continuously changing a beam transmittance between the light source and the deflecting unit. The image forming apparatus according to claim 5.
2. The image forming apparatus according to claim 1, wherein the light amount adjusting unit includes a plurality of polarizers, and one of the polarizers has a rotation adjusting mechanism. The image forming apparatus according to claim 5.
2. The image forming apparatus according to claim 1, wherein the light amount adjusting unit includes a polarizer and a phase shifter, and the polarizer has a rotation adjusting mechanism. The image forming apparatus according to claim 6 or 7,
An image forming apparatus according to claim 1, wherein one of the polarizers is tilted by shifting from 90 ° with respect to a straight traveling direction of the beam. The image forming apparatus according to any one of claims 1 to 8,
2. The image forming apparatus according to claim 1, wherein the light source has a plurality of light emitting points and is arranged with the polarization direction aligned.

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