JP5440442B2 - Optical scanning apparatus and image forming apparatus - Google Patents

Description

  The present invention is to form an electrostatic latent image on the surface of an image carrier such as a photoconductor in an image forming apparatus such as an electrophotographic printer, a facsimile machine, a copying machine, or a multi-function machine having at least two of these functions. The present invention relates to an improvement in the optical system of the optical scanning device, and further relates to an image forming apparatus equipped with the optical scanning device.

  In an image forming apparatus using a conventionally known electrophotographic system, an optical system for forming a desired electrostatic latent image is disposed on an image carrier such as a uniformly charged photoconductor. In the optical system, a light beam modulated in accordance with an image signal is emitted from a light source, and the emitted light beam passes through an appropriate optical member such as a coupling lens, an aperture, or a cylindrical lens, and a polygon mirror or the like. Is converged on an image carrier, converged or imaged on an image carrier by an imaging optical system such as an f-θ lens, and the desired electrostatic latent image is obtained. Can be formed on the image carrier. The optical path from the light source to the image carrier is generally folded by using a folding mirror or the like to reduce the size of the image forming apparatus, and further controls the modulation timing in the image carrier. Therefore, a photodiode called a synchronization detection sensor is provided on the upstream side of the scanning optical system, and an optical member such as a mirror is arranged so that the light beam from the light source reaches the synchronization detection sensor. It is common.

  Here, in this type of optical system, the light power or light quantity of incident light from a light source incident to form an electrostatic latent image on the image carrier depends on characteristics such as spectral sensitivity characteristics of the image carrier. The light output of the light source can be controlled, or the light use efficiency in the optical system from the light source to the image carrier can be controlled, or It is necessary to be able to control both of these, that is, the light emission output of the light source and the light utilization efficiency. However, the larger the light emission output of the light source, the better the light oscillation characteristics tend to be.Therefore, the image quality is better when the light source is operated within a range not exceeding the rated output but at a high output. It has been found that it is preferable to operate the light source in a high output state. Therefore, the conventionally known image forming apparatus employs a configuration in which a light source capable of generating a light amount higher than the light amount required on the image carrier is operated at a high output, while from the light source to the image carrier. It is often configured so that the light utilization efficiency of the light beam in the optical system can be adjusted.

  In addition, in this type of electrophotographic optical system, even if the light amount of the light beam from the light source is adjusted to a light amount according to the photoconductor characteristics such as spectral sensitivity characteristics at the time of shipment or assembly, for example, In general, the light quantity can be changed in a predetermined region in order to cope with the deterioration of the image carrier over time. Furthermore, in such an electrophotographic image forming apparatus, it is conventionally known to perform image or image quality adjustment for forming a high-quality image generally referred to as process control. This is done to prevent fluctuations in image quality such as the image density and gradation of the output image to be formed on the recording medium. In order to adjust the image density and gradation, a light source is also used. Is configured to be able to change in a predetermined region.

  On the other hand, the light utilization efficiency of the entire optical system from the light source to the image carrier is determined by multiplying the transmittance and reflectance of optical members such as a deflector, imaging optical system, and folding mirror in addition to the coupling efficiency. As a result, the light utilization efficiency of the entire optical system varies depending on the molding variation of each optical member. For this reason, if the change range of the predetermined light quantity required by the image carrier is wide or the variation in the light utilization efficiency of the entire optical system is wide, the adjustment range of the light quantity of the light beam emitted from the light source is accordingly widened. Therefore, as a result, the adjustment required range of the light amount emitted from the light source may exceed the rated output range of the light source. Therefore, in addition to the above-mentioned request to operate at high output from the viewpoint of the stability of the light source, also from the viewpoint of the adjustment range of the amount of light from the light source, the amount of light output higher than the amount of light required by the image carrier It is sometimes necessary to adjust the light utilization efficiency of the entire optical system in order to adjust the amount of light reaching the image carrier after using a light source that can emit light.

  In terms of the adjustment range of the amount of light from the light source, when a light source (for example, a semiconductor laser) that uses a single light source that has been frequently used in the past is employed, the light source has its properties. In addition, since a stable light beam can be emitted over a relatively wide range, it is possible to adjust the light amount over a wide range with relative ease. A multi-beam type light source that scans a scanning line at a time (see, for example, Patent Document 1) cannot adjust the amount of light beam in a wide range because of its nature. When adopting a light source having a light source, it is configured to adjust the light utilization efficiency of the optical system after adopting a high-output light source in order to provide a margin for the amount of light reaching the image carrier. Tend .

  Therefore, in the optical system from the light source to the image carrier in the conventional optical scanning device, the light utilization efficiency of the optical system is adjusted so that the light quantity from the light source finally becomes the light quantity required on the image carrier. Therefore, for example, a light amount adjusting element capable of limiting the light beam transmittance between the coupling lens and the cylindrical lens is detachable or selectable, and all the optical system components excluding the light amount adjusting element are configured. After arrangement, measures have been taken such as selecting and arranging a light quantity adjusting element having a transmittance corresponding to the required light quantity by measuring the light quantity actually reaching the image carrier. An example of an optical system that uses such a light amount adjusting element is disclosed in Patent Document 2. In Patent Document 2, a plurality of light amount adjusting elements that are coated on a substrate such as glass to reduce transmittance are provided. An arrangement is disclosed in which an appropriate light amount adjustment element can be switched in accordance with the light transmittance corresponding to the light amount required for the image carrier.

  However, when the light amount adjusting element is arranged, the most inexpensive shape of the light amount adjusting element is a flat plate shape. Therefore, it is most cost effective to use the flat light amount adjusting element. When a light beam is incident on the adjusting element, the type of light source employed (for example, a light source having a single light source such as a semiconductor laser, or a light source having a plurality of light sources such as a multi-beam system) Regardless of whether the interference is caused by internal multiple reflection between the incident surface and the exit surface of the light amount adjusting element, that is, inside the light amount adjusting element. When such interference due to multiple reflection occurs, the light amount incident on the light amount adjusting element does not change even if the wavelength of the light beam emitted from the light source varies only slightly due to, for example, fluctuations in the installation environment temperature. As a result, the amount of light emitted from the light amount adjusting element varies, and as a result, a predetermined transmittance required for the light amount adjusting element varies. If the transmittance of the light amount adjusting element fluctuates from a desired value, the amount of light reaching the image carrier naturally varies with respect to the amount of light required by the image carrier, resulting in an image to be formed. This causes problems such as density unevenness or the formation of an abnormal image called a streak image by those skilled in the art. Therefore, it is desirable to prevent interference with the formed image due to transmittance fluctuations caused by this type of internal multiple reflection. However, if light enters and passes through the plate-shaped light amount adjusting element, it is between the entrance surface and the exit surface. Inevitably, multiple internal reflections occur, and as a result, for example, due to fluctuations in the temperature of the installation environment, transmittance fluctuations can occur due to minute fluctuations in the wavelength of the light beam emitted from the light source. Is inevitable.

  Here, the influence or interference of the transmittance variation due to this type of internal multiple reflection on the electrostatic latent image to be formed on the image carrier becomes more significant as the transmittance of the light amount adjusting element is smaller. To explain this further, assuming that the transmittance variation with respect to the incident light beam due to internal multiple reflection is constant, if the transmittance of the light amount adjusting element required by the optical system is high, the amount of transmitted light is large. The effect on the formed image due to the transmittance variation caused by the value of is relatively small with respect to the transmitted light beam. However, when the transmittance is low, the amount of transmitted light is small, so the transmittance variation caused by the predetermined value The effect on the formed image is relatively large for the transmitted light beam. Specifically, assuming that the transmittance fluctuation rate due to internal multiple reflection with respect to a predetermined transmittance is 3%, the transmittance fluctuates when the transmittance of the light quantity adjusting element is 90%. While the light quantity of the emitted light is between 87 to 93%, when the transmittance of the light quantity adjusting element is 20%, the light quantity of the emitted light whose transmittance has fluctuated is 17 to 23%. It will be in between. In this case, when the transmittance of the light amount adjusting element is 90%, the contribution ratio of the transmittance fluctuation to the transmittance is 1-87 / 90 = 0.034 when the amount of transmitted light is 87%. On the other hand, the contribution rate of the transmittance variation due to multiple reflection when the light amount of the emitted light at 17% is 17% while the desired light amount to be emitted is 1%. 17/20 = 0.15, which is as large as 15% with respect to the desired amount of light to be emitted, and as a result, the variation with respect to the amount of light required on the image carrier becomes large. The effect on the image is increased.

  Therefore, in order to minimize the influence on the formed image caused by the transmittance variation due to the internal multiple reflection in the light amount adjusting element, it is preferable to set the transmittance of the light amount adjusting element as high as possible. However, on the other hand, as described above, the light source wants to operate at the highest possible output, or because it is required to operate at the higher output, so the light utilization efficiency in the optical system from the light source to the image carrier. In particular, there is a light source having a plurality of surface light sources that is a multi-beam type light source described above and that cannot greatly change the light amount of the emitted light beam. When it is adopted, it is difficult to adjust the amount of light emitted on the light source side in a wide range, so that the necessity of setting the light utilization efficiency to a low transmittance is increased. Therefore, in the configuration in which the light use efficiency of the optical system is controlled using only the conventional light amount adjusting element, the transmittance of the light amount adjusting element may be inevitably lowered. To cope with such a case, Although various configurations for suppressing the internal multiple reflection and reducing the variation in transmittance have been considered, such a configuration for suppressing the internal multiple reflection is expensive or the arrangement configuration becomes complicated. In addition to having many drawbacks, in particular, when the transmittance of the light quantity adjusting element has to be set to 20% or less, the light quantity adjusting element formed in a flat plate shape alone, for example, emits light from a light source. There is a problem that the transmittance fluctuation due to the internal multiple reflection of the light amount adjusting element starting from the minute fluctuation of the beam wavelength cannot be reduced to the extent that it does not affect the image quality. It was.

  In view of the above-described problems, the present invention is an optical scanning device that uses a light amount adjusting element to reduce the amount of light from a light source, and is particularly employed even in an optical scanning device that requires low transmittance. It is an object of the present invention to provide an optical scanning device capable of reducing interference with a formed image due to transmittance variation caused by internal multiple reflection at a light amount adjusting element at low cost and easily regardless of the type of An object of the present invention is to provide an image forming apparatus provided with this optical scanning device.

In order to achieve the above object, the present invention provides:
A light source having at least one light source;
A first lens array comprising at least one lens for forming a light beam generated from the light source substantially parallel;
A second lens array composed of at least one lens for forming a substantially parallel light beam that has passed through the first lens array in a non-parallel manner for condensing the deflector;
In an optical scanning device having a light amount adjustment element provided between the first lens array and the second lens array,
The light amount adjustment element is formed in a flat plate shape, and either the incident surface or the emission surface of the light amount adjustment element is provided with a light amount adjustment element transmittance reduction coating for reducing the transmittance.
Furthermore, a second lens array transmittance reduction coating for reducing the transmittance is applied to either the entrance surface or the exit surface of at least one lens in the second lens array,
The light amount adjusting element transmittance reducing coating has a higher transmittance than the second lens array transmittance coating, and proposes an optical scanning device.

Further, in the present invention, the light amount adjustment element transmittance coating is provided on the incident surface side of the light beam from the light source in the light amount adjustment element, and the emission surface side opposite to the incident surface side of the light amount adjustment element It is preferable that a light amount adjustment element antireflection coating for preventing reflection of the light beam is provided.
Furthermore, in the present invention, the second lens array transmittance coating is provided on the incident surface side of the light beam from the light source in the second lens array, and is opposite to the incident surface side of the second lens array. It is preferable that a second lens array antireflection coating for preventing the reflection of the light beam is provided on the light exit surface side.

Furthermore, it is proposed that the light amount adjusting element transmittance reducing coating and / or the second lens array transmittance coating is composed of a single metal film or dielectric film.
Furthermore, in the present invention, the light amount adjusting element transmittance reducing coating and / or the second lens array transmittance coating may be configured as a multilayer film of a metal film and / or a dielectric film.

Furthermore, in the present invention, it is proposed that the light amount adjusting element transmittance reducing coating is configured by sequentially laminating a dielectric multilayer film, a metal film, and a dielectric multilayer film.
Furthermore, in the present invention, it is proposed that the second lens array transmittance reduction coating is configured by sequentially laminating a dielectric multilayer film and a metal film.

  In the present invention, a dielectric film or a dielectric multilayer film is used for the light amount adjusting element transmittance reduction coating, while a metal film or a metal multilayer film is used for the second lens array transmittance coating. Is preferably used.

  Furthermore, it is preferable that the second lens array transmittance coating is applied to the non-planar side of at least one lens in the second lens array.

  Furthermore, in the present invention, in order to achieve the above object, an image forming apparatus provided with the optical scanning device according to any one of claims 1 to 9 is proposed.

  According to the present invention, since the light amount adjusting element on which the light beam from the light source having at least one light source is incident is configured in a flat plate shape, it is possible to employ the light amount adjusting element that is the cheapest and simplest shape. In addition, a light quantity adjusting element transmittance reducing coating for reducing the transmittance is applied to either the incident surface or the exit surface of the light quantity adjusting element, and the second lens is composed of at least one lens. Either the entrance surface or the exit surface of at least one lens in the array is provided with a second lens array transmittance reduction coating that reduces the transmittance, and further, the transmittance of the light amount adjusting element transmittance reduction coating is: Since it is configured to have a higher transmittance than the second lens array transmittance coating, the transmittance variation due to internal multiple reflection is not achieved because it is not configured as a flat plate. Adopting a transmittance-reducing coating with a relatively low transmittance for the lenses in the second lens array that do not significantly affect the image to be formed, and having a flat plate shape, transmittance variation due to internal multiple reflection Even if a low transmittance is sought by being able to adopt a transmittance-reducing coating having a relatively high transmittance for the light amount adjusting element that greatly affects the image to be formed, The light quantity adjustment element adopting a flat plate shape that is inexpensive and simple while achieving the low transmittance in the entire optical system transmits to the extent that the transmittance variation due to internal multiple reflection does not affect the formed image. Since the rate can be increased, the influence of the transmittance variation due to the internal multiple reflection on the light amount adjusting element on the image to be formed with an inexpensive and simple configuration. It is possible to reduce.

1 is a schematic perspective view showing an example of an optical scanning device to which the present invention is applied. In order to explain the optical path from the light source to the deflector, which is an optical path of the optical scanning device, it is an explanatory diagram schematically extracting the optical path from the light source to the deflector, and FIG. A) is a top view of the optical path FIG. B) shows a side view of the optical path. It is a schematic sectional drawing for demonstrating the internal multiple reflection in a light quantity adjustment element and a 2nd lens arrangement | sequence, and is also a figure for showing the structure of the light quantity adjustment element of this invention, and a 2nd lens arrangement | sequence. The example which showed the arrangement | positioning method of a light quantity adjustment element is shown with a schematic perspective view. FIG. 5 is a front view showing an example of an arrangement configuration in which a plurality of light amount adjustment elements having light transmittance adjustment coatings with different transmittances are arranged and the light amount adjustment elements can be selected. . An example of an image forming apparatus provided with the optical scanning device of the present invention is shown in a schematic sectional view.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  First, the configuration of the image forming apparatus 100 provided with the optical scanning device 502 of the present invention will be described with reference to FIG. Here, FIG. 6 shows a schematic cross-sectional view of a full-color printer as an example of the image forming apparatus. The image forming apparatus 100 as shown in FIG. Since the image forming apparatus is conventionally well known to those skilled in the art except for the configuration and operation of the second lens array 104 including the light amount adjusting element 120 and at least one lens, the configuration and operation thereof will be schematically described. .

  An image forming apparatus 100 shown in FIG. 6 includes four electrophotographic image forming units 1a, 1b, 1c, and 1d. Although the first to fourth image forming units 1a, 1b, 1c and 1d have the same configuration, only the corresponding toner colors are different. In these image forming units, for example, a black toner image and a magenta toner are used. An image, a cyan toner image, and a yellow toner image are formed. Since these image forming units have the same configuration except for the difference in developer (toner) color, in the following description, the subscripts a, b, c, and d are appropriately omitted as necessary. .

  In the image forming means 1 shown here, a drum-shaped photoconductor 11 as an image carrier is rotatably arranged in a counterclockwise direction. Around the photoconductor 11, a charging member 12 and a developing device are arranged. 13 and a cleaning means 18 are provided. Further, the surface of the photoconductor 11 to be rotationally driven can be uniformly charged by applying a predetermined bias voltage to the charging member 12. The charging member 12 shown here employs a roller-shaped member that contacts the photoreceptor 10, but a non-contact type utilizing corona discharge or the like can also be employed.

  Further, in the image forming apparatus shown in FIG. 6, four optical scanning devices 502 (to be described later) are provided above the four image forming units 1. The optical scanning device 502 includes appropriate optical components such as a polygon mirror, an f-θ lens, and a reflection mirror configured as a light source, a rotating polygon mirror as a deflector, and includes image data of each color toner. Based on the image information formed accordingly, each photoconductor 11 charged by the charging member 12 is optically scanned or exposed, and is provided to create a desired electrostatic latent image on each photoconductor 11. The electrostatic latent image formed on the photoconductor 11 using the optical scanning device 502 is developed and visualized by applying each color toner when passing through the developing device 13 by the rotation of the photoconductor 11. The

  Further, an endless belt-like intermediate transfer belt 14 configured as an intermediate transfer member is disposed so as to face and abut on the photoreceptor 11 of each image forming unit 1. The intermediate transfer belt 14 shown in FIG. 5 is configured to be circumscribed and inscribed on a plurality of intermediate transfer belt support rollers 31, 32, 33, 34. One of these support rollers is a drive (not shown). It is configured as a drive roller by being connected to a drive motor as a source. Then, when the driving roller is rotated by the driving force transmitted by driving the driving motor, the intermediate transfer belt 14 is rotated counterclockwise in the drawing, and is a support roller that can be driven and rotated other than the driving roller. Is driven to rotate as the intermediate transfer belt 14 rotates. A primary transfer roller (not shown) is disposed on the back surface of the intermediate transfer belt 14 so as to face the photoreceptor 11 with the belt interposed therebetween. A primary transfer bias is also applied to the primary transfer roller from a high voltage power supply (not shown), and the toner image visualized by the developing device 13 is primarily transferred to the intermediate transfer belt 14. The primary transfer residual toner left on the photoconductor 11 without being primary transferred is removed by the cleaning device 18 in preparation for the next image forming operation by the photoconductor 11, and the toner on the photoconductor 11 is completely removed. Removed.

  Furthermore, in the illustrated image forming apparatus 100, a secondary transfer roller as a constituent member of the secondary transfer device is located at a position facing the roller 31, which is one of the above-described intermediate transfer support rollers, with the intermediate transfer belt 14 interposed therebetween. A predetermined voltage is applied to the secondary transfer roller 48 in order to transfer the toner image on the intermediate transfer belt 14 to a recording medium. Note that the secondary transfer roller 48 exemplified here is wound around a transport belt 44 by a roller 49 that is paired with the secondary transfer roller 48, and the transported recording medium is transported downstream in the transport direction via the transport belt 44. It also functions as a transport roller for transporting. Further, the image forming apparatus 100 includes a registration roller pair 56 and the like in addition to the paper feed cassette 60 and the feed roller 54 for loading the recording medium, and also transports the recording medium as viewed from the secondary transfer roller 48. A fixing device 50 including a roller pair of a pressure roller and a heating roller is disposed on the downstream side in the direction in order to apply heat and pressure to the recording medium to fix the unfixed toner image on the recording medium. The recording medium that has exited 50 is discharged to a recording medium discharge section (not shown).

  Next, an image forming operation in this image forming apparatus will be described. Also in this image forming operation, the configuration in which a toner image is formed on each photoconductor 11 and the toner image is transferred to the intermediate transfer belt 14 is substantially the same except that the color of the toner image is different. Subscripts a, b, c and d are omitted as appropriate.

  First, in an image forming apparatus that has received an image forming signal from a personal computer (not shown), the photosensitive member 11 is started to rotate in a counterclockwise direction by a driving source (not shown). Again, light from a static eliminator (not shown) is irradiated to initialize the surface potential. The surface of the photoconductor 11 whose surface potential has been initialized is now uniformly charged to a predetermined polarity by the charging member 12. The charged surface of the photoconductor 11 is irradiated with laser light from an optical scanning device 502 described later, whereby a desired electrostatic latent image is formed on the surface of the photoconductor 11. Note that image information that is exposed or optically scanned from the optical scanning device 502 to each photoconductor 11 is single-color image information obtained by separating a desired full-color image into toner color information of yellow, cyan, magenta, and black. The electrostatic latent image formed on the photoconductor 11 in this way is visualized as a visualized toner image by being supplied with each color toner (developer) from the developing device 13 when passing through the developing device 13. The

  Here, the intermediate transfer belt 14 is driven to run counterclockwise in the figure, but the primary transfer roller (not shown) has a primary polarity opposite to the toner charging polarity of the toner image formed on the photoreceptor 11. A transfer voltage is applied. By the action of the primary transfer voltage, a primary transfer electric field is formed between the photoconductor 11 and the intermediate transfer belt 14, and the toner image on the photoconductor 11 is rotated in synchronization with the photoconductor 11. Primary transfer is electrostatically performed on the transfer belt 14. The respective color toner images that are primarily transferred in this way are superimposed on the intermediate transfer belt 14 at sequential timing from the upstream side in the conveyance direction of the intermediate transfer belt 14, and a desired full-color toner image is formed on the intermediate transfer belt 14. The

  On the other hand, the recording medium on which an image is to be formed is separated one by one from the recording medium bundle loaded in the paper feeding cassette 60 to the registration roller pair 56 by the action of an appropriate conveying member such as the feeding roller 54. Then, the sheet is fed to the nip portion of the registration roller pair 56 that has not yet started to rotate. At that time, in the registration roller pair 56, the leading edge of the conveyed recording medium hits the nip portion of the registration roller pair 56 to form a so-called loop, thereby registering the recording medium. Thereafter, at the timing of the full-color toner image carried on the intermediate transfer belt 14, the rotational driving of the registration roller pair 56 is started, and the secondary transfer roller 48 faces the intermediate transfer belt 14 via the intermediate transfer belt 14. A recording medium is sent out to a secondary transfer portion constituted by the intermediate transfer belt support roller 31. In this embodiment, a predetermined transfer voltage is applied to the secondary transfer roller 48, whereby the full-color toner image formed on the surface of the intermediate transfer belt 14 is collectively transferred onto the recording medium and is undetermined on the recording medium. It is carried as a toner image. The recording medium to which the toner image has been transferred is further conveyed to the fixing device 50, and when passing through the fixing device 50, heat and pressure are applied by the fixing device 50 to form a semi-permanent full-color image on the recording medium. It is fixed. The recording medium on which the image has been fixed by the fixing device 50 is further conveyed and discharged to a recording medium discharge unit such as a discharge tray via a pair of conveyance rollers (not shown), thereby completing the image forming operation. The residual toner remaining on the intermediate transfer belt 14 without being transferred at the secondary transfer portion where the secondary transfer roller 48 is disposed is removed and collected by an intermediate transfer belt cleaning unit (not shown).

  Next, the configuration and operation of the optical scanning device 502 mounted on the image forming apparatus 100 shown as an example in FIG. 6 will be further described with reference to FIGS. 1 and 2. The optical scanning device 502 shown here is also a configuration well known to those skilled in the art except for the configuration and operation of the second lens array 104 including a light amount adjusting element 120 and at least one lens, which will be described later. The overall configuration of the optical scanning device 502 will be described briefly.

  FIG. 1 is a schematic perspective view showing an example of an optical scanning device 502 to which the present invention is applied. FIG. 2 shows an optical path of the optical scanning device 502, which is a polygon mirror as a deflector from the light source 101. In order to explain the optical path up to 105, the optical path from the light source 101 to the polygon mirror 105 is schematically extracted. FIG. A) is a top view of the optical path, and FIG. A side view is shown.

  As shown in FIGS. 1 and 2, an optical scanning device 502 of the present invention includes a light source 101, a collimating lens 102 as a first lens array for making light beams emitted from the light source substantially parallel, An aperture 103 having an aperture for restricting the size of the light beam substantially paralleled by the collimating lens 102 and a substantially parallel and size-controlled light beam having passed through the collimating lens 102 and the aperture 103 are converted by a deflector. In order to condense in the sub-scanning direction on a certain polygon mirror 105, a cylindrical lens 104 as a second lens array for forming the light beam non-parallel and a polygon mirror 105 as a deflector described above are first provided. It consists of In the illustrated example, in order to facilitate understanding of the invention, the first lens array 102 is an example in which a single collimator lens is used. However, the present invention is not limited to this, and the first lens array 102 includes a plurality of lenses. The lens array 102 can also be configured. Similarly, in the illustrated example, the second lens array 104 is configured by a single cylindrical lens, but the second lens array 104 is configured by a plurality of lenses. You can also In other words, in the present invention, the first lens array 102 and the second lens array 104 may have at least one lens. Furthermore, the second lens array 104 can be applied to a lens other than a cylindrical lens, and may be composed of, for example, a diffractive lens having a diffractive surface.

  Next, the light beam deflected and scanned by the polygon mirror 105 serving as a deflector passes through appropriate optical members such as the f-θ lens 106 and the surface tilt correction lens 107, and passes through the first folding mirror 108, the second folding mirror 109, and the like. The optical path is folded by the third folding mirror 110 to reach the image carrier 11, and the image carrier 11 is scanned to form a desired electrostatic latent image on the image carrier 11.

  Here, in the present invention, the light amount adjusting element 120 is provided between the collimating lens 102 that is the first lens array and the cylindrical lens 104 that is the second lens array. As described above, the light amount adjusting element 120 is configured to change the light amount of the light beam from the light source 101 that is desired to be operated at a high output as much as possible or to be operated at a high output on the image carrier 11. It is provided for adjusting to a desired light quantity, and is arranged with a predetermined light transmittance in order to adjust the light use efficiency in the optical system from the light source 101 to the image carrier 11. Therefore, the light amount adjusting element 120 has a base material such as glass or transparent resin, and is a coating that reduces the transmittance on either the incident surface or the output surface of the base material, such as ND (neutral density) for those skilled in the art. A coating 121 called a film is applied. The light amount adjusting element transmittance reducing coating 121 for reducing the transmittance may be a metal film such as aluminum, titanium, or an oxide of these metals, or a dielectric film made of resin or the like. May be. Furthermore, the metal film or the dielectric film can be configured as a multilayer film, or can be configured as a heterogeneous multilayer film in which the metal film and the dielectric film are laminated. In summary, the light amount adjusting element transmittance reducing coating may be formed of a metal film or a dielectric film alone, or may be formed of a multilayer film of a metal film and / or a dielectric film.

  In the case of a metal film, there is no dependency on the wavelength, the incident angle, and the like, and the transmittance can be uniformly reduced according to the film thickness, while the dielectric film has the wavelength of the incident light beam and the like. Since it depends on the incident angle, it is necessary to select the optimum film thickness and material. However, although the dielectric film in the present invention can be constituted alone, it can be designed according to the purpose of use or usage conditions such as transmittance and incident angle, in particular by using a dielectric multilayer film. In the case of using a dielectric film, there is an advantage that the degree of design freedom is high. The configuration of the light amount adjusting element transmittance reduction coating 121 to be used is determined depending on the use situation or through an experiment with an actual machine, or the like, or a laminated configuration of a metal film or a dielectric film. Choose the best one. The light quantity adjusting element transmittance reduction coating 121 in the example shown here is configured by laminating a dielectric multilayer film, a metal film, and a dielectric multilayer film in order from the upstream side of the optical path.

  As shown in FIG. 1 and FIG. 2, the light quantity adjustment element 120 configured in this way is configured in a flat plate shape as the least expensive configuration, and the cost of the optical scanning device and the image forming apparatus on which the optical scanning device is mounted is configured. Is preferable. However, when the light amount adjusting element 120 is configured in a flat plate shape, as indicated by arrows in the left diagram of FIG. 3, internal multiple reflection is caused on the incident surface and the exit surface, that is, inside the light amount adjusting element 120. Inevitable. FIG. 3 is a schematic cross-sectional view for explaining internal multiple reflection in the light amount adjusting element 120 and the cylindrical lens 104 as the second lens array, and the light amount adjusting element of the present invention and the second lens array. It is also a figure for showing the structure. This internal multiple reflection is generated by repeating the reflection on the exit surface and the reflection on the incident surface of the light amount adjustment element 120. The light amount of the light beam emitted from the light amount adjustment element 120 through the internal multiple reflection is the light beam. As a result, the amount of light emitted from the light amount adjusting element 120 varies depending on the wavelength variation of the incident light beam. Under the influence of reflection, it may become stronger or weaker. That is, the transmittance of the light quantity adjusting element 120 varies from a predetermined transmittance according to the wavelength variation of the incident light beam.

  Here, as described above, in order to stabilize the light beam from the light source 101 or due to the type of the light source, the light beam must be emitted as high as possible or a high-power light source. When it must be used, it may be necessary to reduce the light utilization efficiency of this optical system to about 20%, for example. In particular, in light sources such as semiconductor lasers that have been used very well in the past, it has been possible to generate a relatively stable light beam in a wide output range. In a multi-beam method using a surface emitting laser having a light source, the light amount of the light source often has a narrow output range due to its configuration. It is necessary to adjust the utilization efficiency.

  However, as described above, when the light quantity adjustment element 120 is configured in a flat plate shape having the most cost advantage, particularly when the transmittance required for the light quantity adjustment element 120 is low, the light output from the light quantity adjustment element. There is a problem that the influence of transmittance fluctuation due to internal multiple reflection in incident light becomes large. If the influence of the transmittance variation is increased only by a minute change in the wavelength of the light source 101, an image to be easily formed on the image carrier 11 only by a minute change in the installation environment temperature or the like. In some cases, density unevenness occurs, or abnormal images such as streak images occur.

  An example of such a phenomenon is explained in the background art section. The influence of the transmittance variation due to the internal multiple reflection on the electrostatic latent image to be formed on the image carrier is the transmittance variation. Assuming that the rate is 3% with respect to the amount of incident light, when the transmittance of the light amount adjusting element is 90%, the amount of emitted light whose transmittance has fluctuated is 87 to 93%. On the other hand, when the transmittance of the light amount adjusting element is 20%, the light amount of the emitted light whose transmittance has fluctuated is between 17 to 23%. In this case, the light amount adjustment When the transmittance of the element is 90%, the contribution ratio of the transmittance fluctuation to the transmittance is 1-87 / 90 = 0.034 when the amount of the emitted light is 87%, and is desired to be emitted. Is about 3% of the light intensity of the light, while the output light with a transmittance of 20% When the amount is 17%, the influence of the transmittance variation due to the internal multiple reflection on the emitted light is 1-17 / 20 = 0.15, which is as large as 15% with respect to the desired light amount to be emitted. As a result, the electrostatic latent image to be formed on the image carrier 11 is greatly affected. This is because, when the transmittance is 90%, the influence of the transmittance variation due to the internal multiple reflection is only about 3% with respect to the desired light quantity to be emitted, so that the image to be formed is further affected. However, in the case where the transmittance is 20%, the transmittance fluctuation affects the desired amount of light to be emitted by as much as 15%. Therefore, the electrostatic latent to be formed on the image carrier 11 is not affected. This means that the image may be affected to cause image defects such as density unevenness and streak images. For this reason, many attempts have been made in the past to reduce the transmittance variation by reducing the internal multiple reflectivity in the light quantity adjusting element 120, but the configuration for reducing this type of internal multiple reflectivity is generally expensive. Or the optical system is complicated, and there are many drawbacks. Further, even in actual actual experiments, when the transmittance of the light amount adjusting element 120 has to be set as low as about 20%, the light source It has been found that the effect of density unevenness and streak images on the image to be formed can be produced only by minutely changing the wavelength of the light. This is considered to be due to the large influence on the image to be obtained.

  Accordingly, in order to reduce the influence of the transmittance variation on the formed image as much as possible, it is actually desirable to set the transmittance of the light amount adjusting element 120 as high as possible. The amount of light from the light source 101 cannot be reduced to the amount of light required by the body 11.

  Therefore, in the present invention, the cylindrical lens 104 as the second lens array first focuses on the fact that the lens is not configured in a planar shape so as to collect the incident light beam onto the polygon mirror 105 as the deflector. It has been devised to apply a coating for reducing the transmittance to the second lens array 104. Here, as also shown on the right side of FIG. 4, the cylindrical lens 104 which is the second lens array has a curved surface, that is, a non-planar surface. The reflected light from the light beam exit surface that has entered the lens array 104 is dispersed within the second lens array or travels again to the focusing point, and therefore, it is difficult to be affected by transmittance fluctuations due to internal multiple reflection. have.

  Therefore, in an optical system that particularly requires low transmittance, at least one of the second lens arrangements composed of at least one lens is applied at the same time that the light amount adjusting element transmittance reducing coating 121 is applied to the light amount adjusting element 120. At least one of the entrance surface and the exit surface of the two lenses is provided with a second lens array transmittance reduction coating 131 that lowers the transmittance. Further, the light amount adjusting element transmittance reduction coating 121 is a second lens array transmittance coating 131. And having a higher transmittance than the light source 101 to the image carrier 11, the entire optical system from the light source 101 to the image carrier 11 can be adjusted to a desired light amount required by the image carrier 11, and at the same time, the internal multiple reflection can be achieved. The light amount adjusting element 120 that is easily affected by the transmittance fluctuation due to the light transmission causes a transmittance fluctuation due to some internal multiple reflection. Also, the effect on the image to be formed further figured out to set the or acceptably high permeability does not occur.

  By configuring in this way, a second lens array transmittance coating with low transmittance is applied to the second lens array that is less affected by the variation in transmittance due to multiple reflection, and the light amount adjusting element that is greatly affected by the transmittance variation due to multiple reflection 120 can be provided with a light transmittance adjusting element transmittance reducing coating having a high transmittance. Therefore, particularly when the light use efficiency from the light source 101 to the image carrier 11 is set to a low transmittance, The transmittance can be set as high as possible, and the adverse effect on the image to be formed due to the transmittance variation due to the internal multiple reflection can be reduced.

  The second lens array transmittance reduction coating 131 can employ the same coating as the light amount adjustment element transmittance reduction coating 121, and the configuration described above for the configuration of the light amount adjustment element transmittance reduction coating 121. Can be adopted. That is, the second lens array transmittance reduction coating 131 may be formed of a metal film or a dielectric film alone, or may be configured as a multilayer film of a metal film and / or a dielectric film. Further, the second lens array transmittance reduction coating 131 may be provided on either the incident surface or the exit surface of the second lens array. However, as shown in FIG. It is preferable that the cylinder surface on the flat side is provided because the reflected light by the second arrangement transmittance reduction coating can be prevented from being collected on the light source 101. In the example shown here, the second arrangement transmittance reduction coating 131 is formed by laminating a dielectric multilayer film and a metal film in order from the upstream side of the optical path.

  As a more preferred embodiment of the present invention, as shown in FIG. 3, a light amount adjusting element transmittance reduction coating 121 is applied on the incident surface side of the light amount adjusting element 120, and on the exit surface side of the light amount adjusting element 120. An antireflection coating 122 such as an AR (Anti Refect) film may be provided. By providing the light amount adjustment element antireflection coating 122 on the emission surface side in this way, the light beam reflected from the emission surface side to the incident surface side is reduced, so that the internal multiple reflection itself in the light amount adjustment element 120 is reduced. This is preferable.

Here, the antireflection coating is generally well known to those skilled in the art as an AR film, and is very similar in configuration to the ND film described above. The configuration and operation will be schematically shown. In general, the AR film is divided into light that reflects on the surface of the film and light that is transmitted and reflected in the back when external light is incident on the film. Using the property, the film is configured such that the thickness of the film is ¼ wavelength times that of the incident light so that the reflected light reflected from the surface and the reflected light reflected by the back surface is canceled. Typical examples of well-known materials constituting the film include Ta ₂ O ₅ , SiO ₂ , and MgF ₂ . Although it can be configured as a single metal layer or dielectric film layer, in practice the optimal thickness depends on the wavelength and angle of incident light, so it may be configured as a multilayer film for optimization. Many are also preferred. With regard to this antireflection film, the optimum material and film thickness can be optimized from experiments with actual machines.

  In the embodiment shown in FIG. 3, the light amount adjusting element antireflection coating 122 is configured as a dielectric multilayer film on the exit surface side opposite to the incident surface of the light amount adjusting element 120. A multi-layer, a metal film, and a dielectric multi-layer may be sequentially stacked from the upstream side of the optical path. Furthermore, in the embodiment shown in FIG. 3, the second lens antireflection coating 132 configured as a dielectric multi-layer is also provided on the exit surface side of the second lens array 104. As described above, the antireflection coating 132 may be provided on the emission surface side of the second lens array 104, and the second lens array antireflection coating 132 is a dielectric multi-film similarly to the light amount adjusting element antireflection coating. A layer, a metal film, and a dielectric multi-layer may be sequentially stacked from the upstream side of the optical path. Furthermore, as shown in the drawing, the light quantity adjusting element antireflection coating 122 and the second lens array antireflection coating 132 can be used in combination, or only one of them can be disposed.

  Furthermore, in the present invention, in the light amount adjusting element transmittance coating, by setting the transmittance as high as possible and setting the transmittance of the second lens array transmittance coating as low as possible, the light amount adjusting element 120 could not be dropped. The light quantity is characterized in that low transmittance can be achieved in the entire optical system, but the second lens array transmittance reduction coating 131 is required to set the transmittance low, so the film thickness is increased. Thus, it is preferable that the transmittance is uniformly reduced and the metal film or the multilayer film of the metal film that can easily achieve the low transmittance is suitable. On the other hand, the light amount adjusting element transmittance reduction coating 121 set to a transmittance higher than that of the second lens array transmittance reduction coating 131 has a high degree of design freedom with respect to the incident angle and wavelength of the incident light beam. It is preferable to use a dielectric film or a dielectric multilayer film.

  The light quantity adjustment element 120 described so far has been described using a single light quantity adjustment element 120. The light quantity adjustment element 120 is, for example, a light quantity required by the image carrier 11 at the time of shipment or assembly. Depending on the situation, they are sorted and arranged with various transmittances. Therefore, it is advantageous in terms of manufacturing cost that it is configured to be easily detachable. Conventionally, the light amount adjusting element 120 is fixed to the optical scanning device 502 by bonding and fixing using an adhesive or the like, but a configuration for easily detaching the light amount adjusting element 120 different from this fixing method is illustrated. 4. FIG. 4 is a perspective view for illustrating an example of attachment of the light amount adjustment element 120. The base 125 on which the light amount adjustment element 120 is arranged is connected to a flat plate 126, and screws or the like are fixed to holes provided in the flat plate 126. The example which fixes the flat plate 126 to an optical system by inserting and inserting the member 127 is shown. With this configuration, the light amount adjustment element 120 can be easily detachably disposed.

  Further, a plurality of light amount adjusting elements 120, 120 ′, 120 ″,... Having different transmittances may be arranged, and these light amount adjusting elements may be arranged so as to be selectable according to the light amount required by the image carrier. 5 shows an example in which three light quantity adjusting elements 120, 120 ′, 120 ″ having different transmittances are arranged in parallel on a single substrate 125 ′. . The base 125 ′ shown here is provided with, for example, a flat plate 126 ′ carrying the base 125 ′ with a long hole parallel to the arrangement direction (Y direction in FIG. 5) of the light amount adjusting elements 120, 120 ′, 120 ″. Then, by inserting and fixing a fixing member such as a screw into the elongated hole, the base 125 ′ can be easily shifted in the Y direction perpendicular to the X direction parallel to the optical path shown in FIG. It is configured so that desired light quantity adjustment elements 120, 120 ′, 120 ″ can be easily selected so as to be positioned in the optical path from the light source 101. A driving system capable of moving the flat plate 126 ′ in the Y direction is provided, and a desired light amount adjusting element is selected by automatically moving the flat plate 126 ′ in the Y direction by a signal from a control unit (not shown). You may comprise as follows.

  Here, the light amount adjusting element when adjusting the light use efficiency of the optical system from the light source 101 to the image carrier 11 using the three kinds of light amount adjusting elements 120, 120 ′, 120 ″ shown in FIG. An example of a structure with the 2nd lens arrangement | sequence 104 is shown.In the said example, when the light quantity of the emitted light beam of the light source 101 is 100%, the light utilization efficiency which reaches from the light source 101 to the image carrier 11 is 25%, In order to achieve this light utilization efficiency, first, the transmission of the second lens array transmittance reduction coating 131 applied to the cylindrical lens as the second lens array 104 is assumed. The light amount adjusting element transmittance reducing coating 121 applied to the light amount adjusting element 120 is applied to the light amount adjusting element 120 so as to be 90%. So that the adjustment element 120 ', the 72% was set to be the light amount adjustment device 120 "in 54%. With this configuration, in the light amount adjustment element that greatly receives the transmittance variation due to the internal multiple reflection, even if the transmittance variation occurs, the influence of the transmittance variation becomes larger as the formed image is affected. This can be effectively reduced.

  Finally, although the second lens array 104 has been described using an example of a single cylindrical lens, the second lens array 104 may be composed of a plurality of lenses in the present invention. In this case, if the second lens array transmittance reduction coating 131 applied to the second lens array 104 is applied to at least one of the plurality of second lens arrays 104 arranged, the object of the present invention is achieved. Is possible. Furthermore, the light source 101 may be a light source having a single light source such as a semiconductor laser, or may be a light source having a plurality of light sources such as those employed in a multi-beam method. . That is, the present invention can be applied to an optical scanning device including a light source having at least one light emitting source.

  The present invention relates to an optical scanning device for forming an electrostatic latent image on the surface of an image carrier such as a photoconductor, and in particular, simultaneously scans a plurality of light beams from a light source having a plurality of light emitting sources, and performs high-speed image scanning. Can be suitably used for an optical scanning device of a multi-beam scanning type that forms the image. Further, it can be suitably used for an image forming apparatus equipped with the optical scanning device.

11 Image carrier 101 Light source 102 First lens array (collimating lens)
103 Aperture 104 Second lens array (cylindrical lens)
105 Deflector (polygon mirror)
120 Light quantity adjustment element 121 Light quantity adjustment element transmittance reduction coating 131 Second lens arrangement transmittance reduction coating

JP 2009-47924 A JP 2010-55056 A

Claims (10)

A light source having at least one light source;
A first lens array comprising at least one lens for forming a light beam generated from the light source substantially parallel;
A second lens array composed of at least one lens for forming a substantially parallel light beam that has passed through the first lens array in a non-parallel manner for condensing the deflector;
In an optical scanning device having a light amount adjustment element provided between the first lens array and the second lens array,
The light amount adjustment element is formed in a flat plate shape, and either the incident surface or the emission surface of the light amount adjustment element is provided with a light amount adjustment element transmittance reduction coating for reducing the transmittance.
Furthermore, a second lens array transmittance reduction coating for reducing the transmittance is applied to either the entrance surface or the exit surface of at least one lens in the second lens array,
The light scanning device according to claim 1, wherein the light amount adjusting element transmittance reducing coating has a higher transmittance than the second lens array transmittance coating.   The light amount adjusting element transmittance coating is provided on the incident surface side of the light beam from the light source in the light amount adjusting element, and the light beam adjusting element has a light beam on the exit surface side opposite to the incident surface side. The optical scanning device according to claim 1, further comprising a light amount adjusting element antireflection coating for preventing reflection.   The second lens array transmittance coating is provided on the incident surface side of the light beam from the light source in the second lens array, and on the exit surface side opposite to the incident surface side of the second lens array, 3. The optical scanning device according to claim 1, further comprising a second lens array antireflection coating for preventing reflection of the light beam.   The light quantity adjusting element transmittance reducing coating and / or the second lens array transmittance coating is formed of a single metal film or a dielectric film, according to any one of claims 1 to 3. The optical scanning device described.   The light quantity adjusting element transmittance reduction coating and / or the second lens array transmittance coating is configured as a multilayer film of a metal film and / or a dielectric film. The optical scanning device according to one item.   6. The optical scanning device according to claim 5, wherein the light quantity adjusting element transmittance reduction coating is configured by sequentially laminating a dielectric multilayer film, a metal film, and a dielectric multilayer film.   6. The optical scanning device according to claim 5, wherein the second lens array transmittance reduction coating is configured by sequentially laminating a dielectric multilayer film and a metal film.   The light quantity adjusting element transmittance reduction coating uses a dielectric film or a dielectric multilayer film, while the second lens array transmittance coating uses a metal film or a metal multilayer film. The optical scanning device according to claim 1, wherein the optical scanning device is characterized in that:   9. The optical scanning device according to claim 1, wherein the second lens array transmittance coating is provided on a non-planar side of at least one lens in the second lens array. .   An image forming apparatus provided with the optical scanning device according to claim 1.

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