JP2022011529A - Image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize low-resolution and high-resolution image formation at low cost in the case of a configuration in which a distance between scanning lines of laser light in a sub-scanning direction on a photosensitive drum is determined according to an arrangement of a plurality of laser diodes. At low resolution, the photosensitive drum is rotated at the first peripheral speed (S2), and the rotating polymorphic mirror is rotated at the first speed (S3). The control unit outputs image data having a resolution of 600 dpi from a plurality of laser diodes using the entire image data line (S4). In this case, two lines of the 600 dpi image are drawn at the same time. At high resolution, the photosensitive drum is rotated at a second peripheral speed slower than the first peripheral speed (S5), and the rotating polymorphic mirror is rotated at a second speed faster than the first peripheral speed (S6). The control unit outputs the image data converted from the resolution of 600 dpi to the resolution of 1200 dpi from one laser diode using only one image data line (S7, S8). In this case, the lines of the 1200 dpi image are drawn line by line. [Selection diagram] FIG. 9

Description

The present invention relates to an image forming apparatus using an electrophotographic method such as a printer, a copying machine, a facsimile or a multifunction device.

In an image forming apparatus using an electrophotographic method, an electrostatic latent image is formed on a charged photosensitive drum by an exposure apparatus, and an electrostatic latent image formed on the photosensitive drum is subjected to toner by a developing apparatus using a developer. It is developed into an image. The exposure device is an optical scanning device, which has a light source that emits laser light and a rotating multi-sided mirror, and scans the laser light emitted from the light source in the main scanning direction while being reflected by the rotating multi-sided mirror. An electrostatic latent image is formed on the photosensitive drum. As the light source, a semiconductor laser light source or the like having a plurality of light emitters (for example, a laser diode), each of which can emit a laser beam, is used. In such a light source, a plurality of light emitters are arranged at intervals corresponding to the reference resolution in the sub-scanning direction so that an image having a reference resolution (for example, 600 dpi) can be formed when a plurality of laser beams are emitted at the same time. There is. In the present specification, the direction in which the laser beam emitted from the light source is scanned by the rotating polymorphic mirror is referred to as the main scanning direction, and the scanning line of the laser beam moves due to the rotation of the photosensitive drum perpendicular to the main scanning direction. The direction to go is called the sub-scanning direction. In addition, dpi (dots per inch) means dot density, that is, resolution.

In the case of an exposure device capable of simultaneously scanning a plurality of laser beams emitted by the above-mentioned plurality of light emitters, the spacing between scanning lines in the sub-scanning direction on the photosensitive drum is determined according to the arrangement of the plurality of light emitters. It is difficult to form an image with a resolution higher than the resolution. Therefore, a proposal for forming an image having a resolution higher than the reference resolution has been conventionally made. For example, by lowering the peripheral speed of the photosensitive drum from the standard resolution and not emitting the laser beam to the light emitting body arranged at the most downstream in the rotation direction of the photosensitive drum among the plurality of light emitters, the laser beam is doubled from the standard resolution. An apparatus for forming a high-resolution image has been proposed (Patent Document 1).

Japanese Unexamined Patent Publication No. 2018-163213

In the apparatus described in Patent Document 1 above, when an image having a resolution twice higher than the reference resolution is formed, the odd-numbered lines of the image data having twice the high resolution are scanned by the "nth scan", and the "nth scan" is used. The so-called interlaced scanning, in which the even-numbered lines are scanned at the "n + 1th scan", is performed. Conventionally, in order to perform interlaced scanning, low-resolution image data is converted into twice as high-resolution image data. In order to convert and temporarily store image data, an "ASIC (Application Specific Integrated Circuit)" having a large buffer memory capacity and high processing capacity is used. However, since "ASIC" is expensive, it is difficult to adopt it due to the recent demand for cost reduction. Therefore, in the case of a configuration in which the interval between the scanning lines of the laser beam in the sub-scanning direction on the photosensitive drum is determined according to the arrangement of a plurality of light emitters, a low-resolution image is obtained even with an inexpensive configuration without using "ASIC". And a device capable of forming a high-resolution image has been desired. However, such a device has not yet been proposed.

The present invention forms a low-resolution image and a high-resolution image when the spacing between the scanning lines of the laser beam in the sub-scanning direction on the photosensitive drum is determined according to the arrangement of a plurality of light emitters emitting the laser beam. It is an object of the present invention to provide an image forming apparatus that can be realized with an inexpensive configuration.

The image forming apparatus of the present invention is an electrophotographic image forming apparatus, and is a plurality of light sources capable of emitting light for exposing a photoconductor that is rotationally driven and whose surface is charged and a surface of the charged photoconductor. The plurality of light sources are provided, and when light is emitted from the plurality of light sources at the same time, the distance between the plurality of exposure positions in the rotation direction of the photoconductor is the distance corresponding to the first resolution. A light source in which light emitters are arranged, a rotating polymorphic mirror that can rotate and scan the light emitted from the light source in the direction of the rotation axis of the photoconductor, and a multifaceted mirror that rotationally drives the rotating polymorphic mirror at a variable speed. A first mode in which the rotating polymorphic mirror is rotated at the first speed and light is emitted to all of the plurality of light emitters in order to form a drive source and the first resolution image, and the first resolution. In order to form a second resolution image having a higher resolution, the rotating polymorphic mirror is rotated at a second speed higher than the first speed, and light is emitted to one of the plurality of light sources. The second mode is provided with a control unit that can be selectively executed.

According to the present invention, according to the arrangement of a plurality of light emitters that emit light for exposing the surface of the photoconductor, the distance between the plurality of exposure positions in the rotation direction of the photoconductor is the distance corresponding to the first resolution. In some cases, it is possible to realize the formation of a low-resolution image and a high-resolution image with an inexpensive configuration.

The schematic diagram which shows the structure of the image forming apparatus of this embodiment. The schematic which shows the image formation part. The schematic diagram which shows the structure of an exposure apparatus. An exploded perspective view showing an exposure apparatus. Top view showing an exposure apparatus. The schematic which shows the semiconductor laser light source. A control block diagram for explaining a control unit. The figure which shows an example of the resolution setting screen. A flowchart showing an exposure control process. The scanning mode of the laser beam when there are two laser diodes is shown, (a) when the resolution is low, and (b) when the resolution is high. The scanning mode of the laser beam in the case of four laser diodes is shown, (a) in the case of low resolution, and (b) in the case of high resolution.

<Image forming device>
Hereinafter, the image forming apparatus of this embodiment will be described. First, the configuration of the image forming apparatus of this embodiment will be described with reference to FIGS. 1 and 2. The image forming apparatus 100 shown in FIG. 1 is a tandem type intermediate transfer type full-color printer including a plurality of yellow, magenta, cyan, and black image forming portions PY, PM, PC, and PK along the intermediate transfer belt 30. Although not shown, the image forming apparatus 100 is attached to the recording material P according to image information from an external device such as a document reading apparatus connected to the apparatus main body or a personal computer communicably connected to the apparatus main body. Form an image. Examples of the recording material P include various types of sheet materials such as plain paper, thick paper, rough paper, uneven paper, coated paper and the like, plastic films, cloth and the like.

In the present embodiment, as shown in FIG. 1, the intermediate transfer device 5 is provided above the image forming portions PY to PK. The intermediate transfer device 5 is configured such that the endless intermediate transfer belt 30 is stretched on a plurality of rollers (31, 32) and moves in the direction of arrow H. A secondary transfer roller 65 is provided at a position facing the roller 32 on which the intermediate transfer belt 30 is stretched across the intermediate transfer belt 30, and a toner image supported on the intermediate transfer belt 30 is recorded as a recording material as described later. The secondary transfer portion T2 to be transferred to P is formed. The secondary transfer unit T2 is a transfer nip unit formed by the roller 32 and the secondary transfer roller 65, and the secondary transfer voltage is applied to the secondary transfer roller 65 by a high voltage power source (not shown). The toner image is secondarily transferred onto the recording material P.

The process of forming, for example, a four-color full-color image by the image forming apparatus 100 will be described. However, the four image forming units PY, PM, PC, and PK included in the image forming apparatus 100 have substantially the same configuration except that the developed colors are different. Therefore, here, the black image forming portion PK will be described as a representative, and the description of other image forming portions will be omitted.

As shown in FIG. 2, the image forming unit PK has a photosensitive drum 1K as a photoconductor. The photosensitive drum 1K is rotated in a variable peripheral speed in the direction of arrow R2 by a drum drive motor 70 as a photoconductor drive source. A charging device 2K, a developing device 4K, a primary transfer roller 5K, and a cleaning device 6K are provided around the photosensitive drum 1K.

When the image forming operation is started, the surface of the rotating photosensitive drum 1K is uniformly charged by the charging device 2K. Next, the surface of the charged photosensitive drum 1K is exposed by the laser beam L corresponding to the image signal emitted from the exposure apparatus 3 (for example, a laser scanner or the like). As a result, an electrostatic latent image corresponding to the image signal is formed on the photosensitive drum 1K. The electrostatic latent image formed on the photosensitive drum 1K is developed into a toner image by the developer contained in the developing apparatus 4K. In the case of the present embodiment, as shown in FIG. 1, one exposure device 3 is provided below the image forming unit PY, PM, PC, and PK, and only one exposure device 3 is used to provide a plurality of photosensitive drums 1Y to. 1K is exposed. That is, one exposure device 3 is shared by a plurality of image forming units PY to PK for exposure. The exposure apparatus 3 will be described later (see FIGS. 3 to 6).

The toner image formed on the photosensitive drum 1K is primarily transferred to the intermediate transfer belt 30 by the primary transfer unit T1 configured between the primary transfer rollers 5K arranged with the intermediate transfer belt 30 interposed therebetween. At this time, the primary transfer voltage is applied to the primary transfer roller 5K. The intermediate transfer belt 30 carries and conveys the toner image transferred from the photosensitive drum 1K. The deposits such as toner remaining on the surface of the photosensitive drum 1K after the primary transfer are removed by the cleaning device 6K.

Such an operation is sequentially performed in each of the image forming portions of yellow, magenta, cyan, and black, and the toner images of four colors are superimposed on the intermediate transfer belt 30. After that, the recording material stored in the cassette 9 is conveyed to the secondary transfer unit T2 at the timing of forming the toner image (see FIG. 1).

Returning to FIG. 1, a cassette 9 containing the recording material P is arranged below the main body of the image forming apparatus 100. The recording material P supplied from the cassette 9 is conveyed toward the registration roller 92 by the transfer roller 91. The tip of the recording material P abuts against the registration roller 92 in the stopped state, and a loop is formed to correct the skew of the recording material P. After that, the registration roller 92 is started to rotate in synchronization with the toner image on the intermediate transfer belt 30, and the recording material P is transferred to the secondary transfer unit T2. Then, when the secondary transfer voltage is applied to the secondary transfer roller 65 by a high voltage power source (not shown), the toner image on the intermediate transfer belt 30 is secondarily transferred onto the recording material P.

The recording material P on which the toner image is secondarily transferred is conveyed to the fixing device 20. The fixing device 20 heats and pressurizes the recording material P while transporting the recording material P to fix the toner image on the recording material P. The recording material P on which the toner image is fixed by the fixing device 20 is discharged to the outside of the machine body by the discharging roller 93.

As described above, in the image forming apparatus 100, in order to form a full-color image on the recording material P, the exposure apparatus 3 exposes each photosensitive drum 1Y to 1K at a predetermined timing according to the image information of each color, and the photosensitive drum An electrostatic latent image is formed on 1Y to 1K. Regardless of whether it is a low-resolution image or a high-resolution image, the exposure device 3 forms an electrostatic latent image that accurately reproduces the position of the image of each color on the photosensitive drums 1Y to 1K, and as a result, the recording material. An image of good quality is formed in P.

<Exposure device>
The exposure apparatus 3 used in this embodiment will be described with reference to FIGS. 1 and 6 with reference to FIGS. 1. FIG. 3 shows an example of forming an electrostatic latent image on the photosensitive drum 1K. In the following, in order to make the explanation easier to understand, a case where the photosensitive drum 1K is exposed to form an electrostatic latent image will be described as an example.

As shown in FIG. 3, the exposure apparatus 3 includes a laser drive circuit board 11, a semiconductor laser light source 12, a collimating lens 13, a cylindrical lens 14, a rotary multifaceted mirror 15, a multifaceted mirror drive motor 16, an fθ lens 17, and a reflection mirror 18. Have. Each part other than the laser drive circuit board 11 is provided with the same number (4 in this embodiment) as the number of photosensitive drums 1Y to 1K. The semiconductor laser light source 12 is mounted on the laser drive circuit board 11, and each receives power from a power source (not shown) via the laser drive circuit board 11, and individually modulates the laser beam L according to the image information of each color. Can be emitted to.

In FIG. 3, for convenience of illustration, only two semiconductor laser light sources 12 are shown. A collimating lens 13, a cylindrical lens 14, a rotating multi-sided mirror 15, a multi-sided mirror drive motor 16, an fθ lens 17, and a reflection mirror 18 are provided for each of the semiconductor laser light sources 12. By doing so, it is possible to form an electrostatic latent image for each photosensitive drum 1Y to 1K by the laser beam L emitted from each semiconductor laser light source 12.

The cylindrical lens 14 and the collimating lens 13 guide the laser beam L emitted from one corresponding semiconductor laser light source 12 to the rotating polymorphic mirror 15. The rotating multi-sided mirror 15 is, for example, a quadrangular (four-sided) multi-sided mirror having four reflectors 15a that reflect and deflect light on outer edges corresponding to four sides, and is a multi-sided mirror drive source. It is rotationally driven at a variable speed by the mirror drive motor 16. The laser beam L deflected by the rotating multi-sided mirror 15 is guided by an optical member such as an fθ lens 17 or a reflection mirror 18 and travels on a predetermined path. Then, the laser beam L is passed through a transmissive member 40 (see FIG. 1) provided at the irradiation port of the main body of the apparatus, and is scanned on the photosensitive drum 1K in the rotation axis direction (main scanning direction, arrow X direction). It forms an electrostatic latent image (this is called exposure). The laser beam L emitted from the semiconductor laser light source 12 scans the photosensitive drum 1Y once from one end side to the other end side in the rotation axis direction for each surface of the reflecting mirror 15a of the rotating polymorphic mirror 15. That is, when a rotating multi-sided mirror 15 having four reflecting mirrors 15a is used, the photosensitive drum 1K is scanned four times by the laser beam L each time the rotating multi-sided mirror 15 makes one rotation.

A more detailed configuration of the exposure apparatus 3 described above is shown in FIGS. 4 and 5. FIG. 4 is an exploded perspective view showing the exposure apparatus 3, and FIG. 5 is a top view showing the exposure apparatus 3 as seen from the intermediate transfer apparatus 5 side (see FIG. 1). As shown in FIGS. 4 and 5, the exposure apparatus 3 includes four semiconductor laser light sources 12Y, 12M, 12C, 12K and two cylindrical lenses 14a, 14b. In addition, a collimating lens (not shown here) is also provided. The semiconductor laser light sources 12Y and 12M are mounted on the laser drive circuit board 11a. The semiconductor laser light sources 12C and 12K are mounted on the laser drive circuit board 11b.

Explaining with reference to FIG. 1, the semiconductor laser light source 12Y emits the laser beam LY irradiated on the photosensitive drum 1Y. The semiconductor laser light source 12M emits a laser beam LM that is applied to the photosensitive drum 1M. The semiconductor laser light source 12C emits a laser beam LC that irradiates the photosensitive drum 1C. The semiconductor laser light source 11K emits the laser beam LK irradiated on the photosensitive drum 1K. As will be described later, each of these semiconductor laser light sources 12Y to 12K has two laser diodes and is configured to be capable of emitting two laser beams at the same time (see FIG. 6).

The exposure device 3 includes a rotating multi-sided mirror 15 having a plurality of (for example, 5) reflecting mirrors 15a that reflect the laser beams LY, LM, LC, and LK emitted from the semiconductor laser light sources 12Y, 12M, 12C, and 12K, and rotation. A multi-sided mirror drive motor 16 for rotationally driving the multi-sided mirror 15 is provided. The multi-sided mirror drive motor 16 rotates the rotating multi-sided mirror 15 by the rotor 16a.

Further, the exposure apparatus 3 is an fθ lens 17a for forming an image of the laser beams LY, LM, LC, and LK deflected by the rotary multifaceted mirror 15 on the surfaces of the photosensitive drums 1Y, 1M, 1C, and 1K which are the scanned surfaces. , 17b. Further, the exposure apparatus 3 includes a reflection mirror 18 that reflects the laser beams LY, LM, LC, and LK deflected by the rotary multifaceted mirror 15 and guides them to the photosensitive drums 1Y, 1M, 1C, and 1K. The optical member included in the exposure apparatus 3 described so far is housed in the optical box 101 shown in FIG.

Next, the basic operation of the exposure apparatus 3 will be described. First, the laser beams LY, LM, LC, and LK emitted from the semiconductor laser light sources 12Y, 12M, 12C, and 12K are transmitted through the cylindrical lenses 14a and 14b, and are converged only in the sub-scanning direction. The image is formed (incident) as a line image on the reflecting mirror 15a of the above.

Here, the exposure apparatus 3 of the present embodiment employs an oblique incident optical system. That is, the laser beams LY and LM emitted from the semiconductor laser light sources 12Y and 12M are orthogonal to the rotation axis direction of the rotary polymorphic mirror 15 and are in the rotation axis direction with respect to the virtual plane overlapping with the reflector 15a of the rotary multifaceted mirror 15. It is incident on the reflecting mirror 15a of the rotating multi-sided mirror 15 from one side and the other side. The incident angles of the laser beams LY and LM with respect to the virtual plane are θ1 and θ2, and the relationship is “θ1 = θ2”. Although the relationship between the semiconductor laser light sources 12Y and 12M has been described here, the relationship between the semiconductor laser light sources 12C and 12K is also the same.

Next, the laser beams LY, LM, LC, and LK imaged by the reflecting mirror 15a of the rotating multi-sided mirror 15 are reflected by the reflecting mirror 15a when the rotating multi-sided mirror 15 is rotated by the driving force of the multi-sided mirror drive motor 16. Be biased. The deflected laser beams LY, LM, LC, and LK pass through the fθ lenses 17a and 17b, are reflected by the reflection mirror 18, and form an image on the surface (scanned surface) of the photosensitive drums 1Y, 1M, 1C, and 1K. ..

In this way, the exposure apparatus 3 scans the laser beams LY, LM, LC, and LK on the surfaces of the photosensitive drums 1Y, 1M, 1C, and 1K to form an electrostatic latent image. Specifically, the rotation of the rotating polymorphic mirror 15 changes the deflected angles of the laser beams LY, LM, LC, and LK, and the spot image in which the laser beams LY, LM, LC, and LK are imaged is mainly used. It is scanned in the scanning direction. Further, by rotating the photosensitive drums 1Y, 1M, 1C, and 1K, the spot image formed by the laser beams LY, LM, LC, and LK is scanned in the sub-scanning direction.

Although only one laser beam L is shown in FIG. 3 described above, in the case of the present embodiment, it is possible to emit not only one laser beam L but also a plurality of laser beams L from one semiconductor laser light source 12 (12Y to 12K). There is. When a plurality of laser beams L are simultaneously emitted from one semiconductor laser light source 12, a plurality of lines can be scanned on the photosensitive drum 1K by the above-mentioned one scan. FIG. 6 shows a semiconductor laser light source 12 capable of emitting a plurality of laser beams L. However, here, a semiconductor laser light source 12 capable of emitting two laser beams L is shown as an example.

The semiconductor laser light source 12 shown in FIG. 6 has two laser diodes 121 and 122 capable of emitting laser light as a light emitting body. When these two laser diodes 121 and 122 emit laser light at the same time, the distance between the two scanning lines, which is the exposure position in the rotation direction of the photosensitive drum 1K, is, for example, the reference resolution "600 dpi" (first resolution). They are arranged so that the intervals correspond to. That is, in the semiconductor laser light source 12, the laser diodes 121 and 122 are arranged so that the distance between the lines in the sub-scanning direction (rotation direction of the photosensitive drum 1K) is the reference resolution "600 dpi" so as not to move mechanically. It is fixed.

In the present embodiment, when forming a 600 dpi image, all of the two laser diodes 121 and 122 are controlled to emit light, and the laser diode 121 is used for the first line of the 600 dpi image and the laser diode 122 is used for the second line of the 600 dpi image. Scan. In this case, two lines are scanned on the photosensitive drum 1K by one surface of the reflecting mirror 15a of the rotating multi-sided mirror 15 described above. Therefore, when the rotating multi-sided mirror 15 makes one rotation, eight lines (2 beams × 4 surfaces) are scanned on the photosensitive drum 1K. On the other hand, when forming an image of "1200 dpi" (second resolution), which is twice as high resolution, one of the two laser diodes 121 and 122 is controlled to emit light, and only one is formed. The 1200 dpi image is scanned line by line. In this case, when the rotary multifaceted mirror 15 makes one rotation, four lines (1 beam × 4 planes) are scanned on the photosensitive drum 1K. Details of this point will be described later.

<Control unit>
Further, as shown in FIG. 1, the image forming apparatus 100 includes a control unit 200 capable of generally controlling the operation of the image forming apparatus 100. The control unit 200 will be described here with reference to FIG. 7 with reference to FIGS. 1 and 2 with respect to an exposure control system that mainly exposes the photosensitive drums 1Y to 1K by the exposure apparatus 3. In addition to the illustrations, the control unit 200 is connected to various parts constituting the image forming apparatus 100 and various devices such as a drive source (motor, power supply, etc.) for operating each part. However, since it is not the main purpose of the invention, the illustration and description thereof will be omitted.

The control unit 200 controls various operations related to image formation, and includes, for example, a CPU 201 (Central Processing Unit), a memory 202, and an image control unit 210. The memory 202 is composed of, for example, a ROM (Read Only Memory), a RAM (Random Access Memory), or the like. The memory 202 is an image acquired from various programs such as "exposure control processing" (see FIG. 9 described later) that controls exposure to the photosensitive drums 1Y to 1K by the exposure device 3 during an image forming job, a document reading device, or an external device. It can store information, image data in various formats for exposure, and the like. The CPU 201 can execute various programs stored in the memory 202, and can execute these various programs to control the operation of each part of the image forming apparatus 100. The memory 202 can also temporarily store the calculation processing results and the like associated with the execution of various programs.

The image forming job is a series of operations from the start of the image forming operation to the completion of the image forming operation based on the print signal for forming an image on the recording material P. That is, after starting the preliminary operation (so-called forward rotation) required for performing image formation, the preliminary operation required for completing image formation (so-called backward rotation) is completed through the image forming step. It is a series of operations up to. Specifically, it refers to the period from the front rotation (preparatory operation before image formation) after receiving the print signal (input of the image formation job) to the rear rotation (operation after image formation), and the image formation period. , Including between papers.

The operation unit 220 is connected to the control unit 200 via the UI control unit 221. The operation unit 220 is, for example, a touch panel or the like, which has an input unit such as various keys for the user to operate, a display unit for displaying various information, and the like. The UI control unit 221 is an interface device for managing data input / output between the operation unit 220 and the control unit 200, and for realizing control (screen display, etc.) of the operation unit 220 by the control unit 200.

<Resolution setting screen>
Here, FIG. 8 shows an example of the “resolution setting screen” displayed on the operation unit 220 based on the control by the control unit 200. The “resolution setting screen” shown in FIG. 8 is a screen displayed on the operation unit 220 as a user interface that assists the user in setting the resolution of the image formed on the recording material P. In the example shown in FIG. 8, two selection buttons are displayed according to the resolution so that the user can select and set either a low resolution of 600 dpi or a high resolution of 1200 dpi. The user can set the resolution of the image to either "low resolution" or "high resolution" by touching the selection button displayed on the "resolution setting screen".

Returning to the description of FIG. 7, the image control unit 210 performs conversion processing of the image data to be output, and has a resolution conversion processing unit 211 and a VIDEO output unit 212. The resolution conversion processing unit 211 generates image data having a reference resolution (600 dpi), stores the generated reference resolution image data in the memory 202, and can output the generated reference resolution image data to the VIDEO output unit 212. Further, the resolution conversion processing unit 211 can convert the reference resolution (low resolution) image data stored in the memory 202 into high resolution (1200 dpi) image data and output the converted high resolution image data VIDEO output unit 212. Is. The resolution conversion processing unit 211 outputs the image data of the resolution set in the above-mentioned "resolution setting screen" (see FIG. 8) or the like to the VIDEO output unit 212. That is, when "low resolution" is set, the resolution conversion processing unit 211 outputs image data having a resolution of 600 dpi to the VIDEO output unit 212. When "high resolution" is set, the resolution conversion processing unit 211 converts the image data having a resolution of 600 dpi into the image data having a resolution of 1200 dpi and outputs the image data to the VIDEO output unit 212.

The VIDEO output unit 212 outputs these image data to the laser drive circuit board 11 via the image data lines 213 and 214. As a result, the light emission of the semiconductor laser light source 12 mounted on the laser drive circuit board 11 is controlled. In the case of the present embodiment, when the resolution is "low resolution", the VIDEO output unit 212 can scan two lines in one scan by the two laser diodes 121 and 122 of the semiconductor laser light source 12, and the image data line 213. , 214 are used to output image data. On the other hand, when the resolution is "high resolution", the VIDEO output unit 212 can scan one line in one scan by any one of the laser diodes 121 and 122, and only one of the image data lines 213 and 214 can be scanned. Output the used image data.

For example, in the case of "high resolution", the image data is output only to the image data line 213 by the VIDEO output unit 212, and the laser diode 121 of the laser drive circuit board 11 is controlled to emit light according to the image data, but the laser. The diode 122 is not lit. That is, when forming a "low resolution" image, laser light is emitted from all of the laser diodes 121 and 122, and when forming a "high resolution" image, one of the laser diodes 121 and 122 is emitted. The laser beam is emitted from. This is due to the following reasons.

<Exposure control processing>
As described above, the laser diodes 121 and 122 of the semiconductor laser light source 12 are arranged so that the distance between the scanning lines on the photosensitive drum 1K corresponds to the reference resolution "600 dpi" when the laser light is emitted at the same time. Has been done. Therefore, when forming a high-resolution (1200 dpi) image, simply controlling the emission of both the laser diodes 121 and 122 according to the high-resolution image data has a pitch substantially equivalent to the resolution of 600 dpi in the sub-scanning direction. Image formation is performed at intervals. Therefore, in the present embodiment, when forming an image having a resolution of 1200 dpi, only one of the laser diodes 121 and 122 is used, and all the lines are drawn in the order of the first line and the second line of the 1200 dpi image. I have to.

Hereinafter, when forming a high-resolution image, refer to FIGS. 2 to 7 for the “exposure control process” of the present embodiment in which the laser diode that emits laser light is limited to one and the photosensitive drum is exposed. However, it will be described with reference to FIGS. 9 to 10 (b). The "exposure control process" is started by the control unit 200 at the start of the image formation job.

As shown in FIG. 9, the control unit 200 determines whether the resolution of the image formed on the recording material P is low resolution (600 dpi) or high resolution (1200 dpi) according to the start of execution of the image formation job. Select (S1). The control unit 200 forms an image at "low resolution" or an image at "high resolution" according to the resolution of the image formed on the recording material P set by the user from the "resolution setting screen" (see FIG. 8), for example. Selectively decide whether to do it.

When "low resolution" is selected (low resolution of S1), the control unit 200 executes the "low resolution mode" (first mode) shown below to expose the photosensitive drum 1K. In the "low resolution mode", the control unit 200 first controls the drum drive motor 70 to rotate the photosensitive drum 1K at the first peripheral speed (D1: for example, 150 mm / sec) (S2). In the "low resolution mode", the peripheral speed of the photosensitive drum 1K is maintained at the first peripheral speed. Next, the control unit 200 controls the multi-side mirror drive motor 16 to rotate the rotary multi-side mirror 15 at the first speed (P1: for example, 25000 rpm) (S3). Then, the control unit 200 outputs the image data having a resolution of 600 dpi generated by the resolution conversion processing unit 211 from the VIDEO output unit 212 using both the image data lines 213 and 214 (S4). In this case, since the laser light is simultaneously emitted from both the laser diodes 121 and 122 of the semiconductor laser light source 12, two 600 dpi image lines are simultaneously drawn on the photosensitive drum 1K.

FIG. 10A shows the scanning mode of the laser beam by the two laser diodes 121 and 122 when "low resolution" is selected. As shown in FIG. 10A, when forming an image having a resolution of 600 dpi, two laser diodes 121 and 122 are used for image formation in one scan cycle, and the line scanned at the nth scan. Are two lines shown by solid lines (LD1, LD2). Then, the photosensitive drum 1K is rotated at the first peripheral speed (D1), and the rotary multifaceted mirror 15 is rotated at the first speed. Then, the line scanned in the "n + 1" scan is shown by a solid line, and the line scanned in the nth scan is as shown by the broken line. In this way, when forming an image having a resolution of 600 dpi, the 600 dpi image is formed on the photosensitive drum 1K by drawing two lines (LD1 and LD2) of the 600 dpi image at the same time.

Returning to the description of FIG. 9, when "high resolution" is selected (high resolution of S1), the control unit 200 executes the "high resolution mode (second mode)" shown below to control the photosensitive drum 1K. To expose. In the "high resolution mode", the control unit 200 first controls the drum drive motor 70 to set the photosensitive drum 1K at a second peripheral speed (D2: for example, 70 mm /), which is slower than the first peripheral speed in the "low resolution mode". It is rotated by sec) (S5). In the "high resolution mode", the peripheral speed of the photosensitive drum 1K is maintained at the second peripheral speed. Next, the control unit 200 controls the multi-faceted mirror drive motor 16 to rotate the rotating multi-sided mirror 15 at a second speed (P2) faster than the first speed in the “low resolution mode” (S6). At this time, the second speed is obtained by Equation 1. That is, the second speed (P2) is "2 x N x D2 / D1" times the first speed (P1). Note that "N" in Equation 1 is the number of laser diodes (here, N = 2) possessed by one semiconductor laser light source 12.
P2 = P1 × (2 × N × D2 / D1) ・ ・ ・ Equation 1

Then, the control unit 200 converts the image data having a resolution of 600 dpi generated by the resolution conversion processing unit 211 into the image data having a resolution of 1200 dpi (S7). The control unit 200 outputs the converted image data having a resolution of 1200 dpi from the VIDEO output unit 212 using only one of the image data lines 213 and 214 (S8). For example, when the image data line 213 is used, the laser beam is emitted only from the laser diode 121 of the semiconductor laser light source 12, and the line of the 1200 dpi image is drawn line by line on the photosensitive drum 1K.

FIG. 10B shows the scanning mode of the laser beam by one laser diode 121 when "high resolution" is selected. As shown in FIG. 10B, when forming an image having a resolution of 1200 dpi, for example, only one laser diode 121 is used for image formation in one scan cycle, and the line scanned at the nth scan. Is only one indicated by a solid line (LD1). Then, the photosensitive drum 1K is rotated at the second peripheral speed (D2), and the rotary multifaceted mirror 15 is rotated at the second speed. Then, the line scanned in the "n + 1" scan is shown by a solid line, and the line scanned in the nth scan is as shown by the broken line. In this way, when an image having a resolution of 1200 dpi is formed, a 1200 dpi image is formed on the photosensitive drum 1K by drawing the lines of the 1200 dpi image line by line (LD1). The laser diode used to form the "high resolution" image may be either one of the plurality of laser diodes 121 and 122 included in the semiconductor laser light source 12.

As described above, in the present embodiment, when the high resolution mode is executed, only one of the two laser diodes 121 and 122 of the one semiconductor laser light source 12 is used, and the peripheral speed and rotational multifacet of the photosensitive drum 1K are used. The rotation speed of the mirror 15 is changed for exposure. According to this, it is possible to form a low-resolution image and a high-resolution image with an inexpensive configuration that does not use an "ASIC (Application Specific Integrated Circuit)" having a large capacity of a buffer memory and a high processing capacity.

Further, in the above-described embodiment, it is assumed that the peripheral speed (D2) of the photosensitive drum 1K in the high resolution mode is slower than the peripheral speed (D1) in the low resolution mode (D1> D2). If a high-resolution image is formed only by slowing the peripheral speed of the photosensitive drum 1K, the transport speed of the recording material P is slowed down, so that the productivity is lowered. In view of this point, in the present embodiment, the peripheral speed of the photosensitive drum K is slowed down, and the rotation speed of the rotary multifaceted mirror 15 is increased to realize high-resolution image formation while suppressing a decrease in productivity. I try to do it.

<Other embodiments>
In the above-described embodiment, the case where one semiconductor laser light source 12 has two laser diodes 121 and 122 has been described as an example, but the present invention is not limited to this. For example, one semiconductor laser light source 12 may have three or more laser diodes and simultaneously emit three or more laser beams so that one photosensitive drum 1K can be exposed. For example, when one semiconductor laser light source has four laser diodes, one surface (reflecting mirror 15a) of the rotating polymorphic mirror 15 can scan four lines on the photosensitive drum 1K. can. In this case, when the rotating multi-sided mirror 15 makes one rotation, 16 lines (4 beams × 4 surfaces) are scanned on the photosensitive drum 1K. Even in such a case, the above-mentioned "low-resolution mode" is executed when forming a low-resolution image (see S2 to S4 in FIG. 7), and the above-mentioned "high-resolution mode" is executed when forming a high-resolution image. (See S5 to S8 in FIG. 7). FIG. 11A shows the scanning mode of the laser beam by the four laser diodes when "low resolution" is selected. FIG. 11B shows the scanning mode of the laser beam by the four laser diodes when "high resolution" is selected.

As shown in FIG. 11A, when forming an image having a resolution of 600 dpi, all four laser diodes are used for image formation in one scan cycle, and the line scanned at the nth scan is a solid line. The number is 4 (LD1 to LD4). Then, the photosensitive drum 1K is rotated at the first peripheral speed (D1), and the rotary multifaceted mirror 15 is rotated at the first speed (P1). Then, the line scanned in the "n + 1" scan is shown by a solid line, and the line scanned in the nth scan is as shown by the broken line. In this way, when forming an image having a resolution of 600 dpi, the 600 dpi image is formed on the photosensitive drum 1K by simultaneously drawing four lines (LD1 to LD4) of the 600 dpi image.

On the other hand, as shown in FIG. 11B, when an image having a 1200 dpi resolution is formed, only one of the four laser diodes is used for image formation in one scan cycle, and the nth scan is used. There is only one line scanned in (LD1), which is indicated by a solid line. Then, the photosensitive drum 1K is rotated at the second peripheral speed (D2), and the rotary multifaceted mirror 15 is rotated at the second speed P2 (P1 × (2 × 4 × D2 / D1). The scanned lines are shown by solid lines, and the scanned lines at the nth scan are as shown by the broken lines. In this way, when forming an image with a resolution of 1200 dpi, the lines of the 1200 dpi image are shown. (LD1), an image of 1200 dpi is formed on the photosensitive drum 1K.

As described above, when the high resolution mode is executed, only one of the plurality of laser diodes possessed by one semiconductor laser light source 12 is used, and the peripheral speed of the photosensitive drum 1K and the rotation speed of the rotating multi-sided mirror 15 are changed for exposure. Let me. Especially when the number of laser diodes included in one semiconductor laser light source 12 is large, a low-resolution image and high resolution image can be obtained with an inexpensive configuration that does not use "ASIC", which has a large capacity of a buffer memory and a high processing capacity. It is easy to obtain the effect of forming an image with a resolution.

In the above-described embodiment, an example is shown in which the resolution of the image can be set to either "low resolution" (reference resolution) or twice "high resolution", but "high resolution" is doubled in resolution. Not limited to this, it may be possible to set a resolution of 2 times or more.

In the above-described embodiment, the peripheral speed of the photosensitive drum 1K is changed when the high-resolution mode is executed, but the peripheral speed of the photosensitive drum 1K is not changed when the high-resolution mode is executed. May be good. However, in such a case, it is preferable to rotate the rotary multifaceted mirror 15 in the double high image quality mode about "4" times faster than in the low image quality mode.

In the above-described embodiment, the image of the configuration in which the toner image of each color is first transferred from the photosensitive drums 1Y to 1K of each color to the intermediate transfer belt 51 and then the toner image of each color is collectively secondarily transferred to the recording material P. Although the forming device 100 has been described as an example, the present invention is not limited to this. For example, it may be a direct transfer type image forming apparatus that directly transfers from the photosensitive drums 1Y to 1K to the recording material P.

1Y (1M, 1C, 1K) ... Photoreceptor (photosensitive drum), 12 (12Y-12K) ... Light source (semiconductor laser light source), 15 ... Rotating multi-sided mirror, 15a ... Reflector, 16 ... Multi-sided mirror drive source (multi-sided mirror) Drive motor), 70 ... Photoreceptor drive source (drum drive motor), 100 ... Image forming device, 121, 122 ... Light emitter (laser diode), 200 ... Control unit, P ... Recording material

Claims (4)

It is an electrophotographic image forming device.
A photoconductor that is rotationally driven and whose surface is charged,
It has a plurality of light emitters capable of emitting light for exposing the surface of a charged photoconductor, and when light is emitted from the plurality of light emitters at the same time, a plurality of exposure positions in the rotation direction of the photoconductor. With a light source in which the plurality of light emitters are arranged so that the interval between the above is the interval corresponding to the first resolution.
A rotating polymorphic mirror that can rotate and scan the light emitted from the light source in the direction of the rotation axis of the photoconductor.
A multi-sided mirror drive source that drives the rotary multi-sided mirror to rotate at a variable speed,
In order to form the image of the first resolution, the first mode in which the rotating polymorphic mirror is rotated at the first speed and light is emitted to all of the plurality of light emitters, and the resolution is higher than that of the first resolution. A second mode in which the rotating polymorphic mirror is rotated at a second speed faster than the first speed and one of the plurality of light emitters emits light in order to form a high second resolution image. And, with a control unit that can be selectively executed,
An image forming apparatus characterized in that. A photoconductor drive source that rotationally drives the photoconductor in a variable peripheral speed is provided.
The control unit rotates the photoconductor at the first peripheral speed when the first mode is executed, and rotates the photoconductor at a second peripheral speed slower than the first peripheral speed when the second mode is executed.
The image forming apparatus according to claim 1. The second speed is the first speed when the number of light emitters is N (pieces), the first peripheral speed is D1 (mm / sec), and the second peripheral speed is D2 (mm / sec). Is "2 x N x D2 / D1" times
The image forming apparatus according to claim 2. The rotating polymorphic mirror has four reflecting mirrors that reflect light emitted from the plurality of light emitters.
The image forming apparatus according to any one of claims 1 to 3.

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