JP2006035550A - Image forming apparatus and image formation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form images by a uniform density at all times in an apparatus equipped with a latent image forming part for each toner color which scans light beams from a light source by an oscillating deflection mirror face. <P>SOLUTION: For any of color components. the light beams from a laser light source are enabled to scan back and forth in a main scanning direction by deflecting the light beams by the oscillating deflection mirror face. However, only the light beam SL scanned in a first direction (+X) of the main scanning direction illuminates an effective image region of a photoreceptor here to form a latent image. A toner image is formed by developing the latent image. Image formation is thus carried out by using only the light beam SL scanned in the first direction (+X), and therefore the images can be formed by the uniform density regardless of kinds of the images. Moreover, since a scanning direction of the light beam SL is unified to the first direction (+X) for all of the color components, the image density can be kept uniform among toner images of each color component. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called tandem image forming apparatus and method, and more particularly to an apparatus equipped for each toner color with a latent image forming unit that scans a light beam from a light source using a vibrating deflection mirror surface. .

  This type of image forming apparatus includes a so-called tandem in which an image forming unit having a photoreceptor, an exposure unit, and a developing unit is provided for each of four different colors, for example, yellow, magenta, cyan, and black. Conventional image forming apparatuses are known. In this tandem apparatus, a toner image of each color component is formed on the photoreceptor as follows. That is, for each color component, the light source of the exposure unit is controlled based on the image data indicating the toner image of the color component, and the light beam from the light source is scanned in the main scanning direction by the deflector of the exposure unit. A latent image corresponding to the component image data is formed on the photoreceptor. The latent images are developed with corresponding color toners to form a plurality of color toner images, and the plurality of color toner images are superimposed on a transfer medium to form a color image.

  In addition, in order to reduce the size and speed of the deflector, it has been conventionally proposed to use a vibrating mirror that sinusoidally vibrates the deflecting mirror surface as the deflector (see, for example, Patent Document 1). That is, in this apparatus, the frequency of the drive signal applied to the vibration mirror is matched with the natural resonance frequency of the vibration mirror, so that the vibration mirror is resonated and a relatively large amplitude is obtained. Then, the light beam from the light source is irradiated to the vibration mirror that is oscillating at resonance to scan the light beam back and forth. As a result, latent images are formed in both the forward scan and the backward scan.

JP-A-9-230276 (pages 8 and 9 and FIG. 5)

  By the way, in each image forming unit, a two-dimensional latent image is formed by reciprocating the light beam in the main scanning direction while rotating the photosensitive member in a direction substantially orthogonal to the main scanning direction. For this reason, as will be described in detail later, depending on the type of image, light and shade of the image may occur on the forward and backward sides in the main scanning direction. As a result, there is a problem that the image quality is deteriorated.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and in an apparatus equipped with a latent image forming section for each toner color that scans a light beam from a light source by a vibrating deflection mirror surface, an image is always formed with a uniform density. The purpose is to do.

  The image forming apparatus according to the present invention includes a plurality of image forming units that form toner images of different colors, and forms a color image by superimposing the toner images formed by the respective image forming units on a transfer medium. In order to achieve the above object, each of the plurality of image forming means is provided with an effective image area having a predetermined width in the main scanning direction on the surface, and the surface is substantially in the main scanning direction. The latent image carrier driven in the orthogonal sub-scanning direction and the oscillating deflecting mirror surface are configured to scan the first scanning region corresponding to the effective image region in the main scanning direction with the light beam from the light source, And a latent image forming unit configured to irradiate the effective image area with only the light beam for scanning the first scanning area in the first direction of the main scanning direction and form a latent image in the effective image area.

  The image forming method according to the present invention also has a latent image carrier in which an effective image area having a predetermined width is provided on the surface thereof in the main scanning direction and the surface is driven in the sub-scanning direction substantially orthogonal to the main scanning direction. An image forming method for forming a color image on a transfer medium by using a plurality of image forming means to form a toner image by forming a latent image on the top and developing the latent image with different color toners. In order to achieve the above object, in each of the plurality of image forming means, the light beam from the light source is irradiated to the effective image area of the latent image carrier in the first direction of the main scanning direction by the vibrating deflection mirror surface. The latent image is formed in the effective image area, and the latent image is developed to form a toner image, and the toner image formed by each of the plurality of image forming units is superimposed on the transfer medium. It is characterized by comprising a transfer step of forming a color image.

  In the invention thus configured (image forming apparatus and method), the light beam from the light source is deflected by the vibrating deflection mirror surface in each of the image forming means, and the light beam can be reciprocated in the main scanning direction. It has become. However, in the present invention, only the light beam scanned in the first direction of the main scanning direction is irradiated on the effective image area of the latent image carrier to form a latent image. Then, the latent image is developed to form a toner image. As described above, since the image formation is performed using only the light beam scanned in the first direction, the image can be formed with a uniform density regardless of the type of the image. Further, since the scanning direction of the light beam is unified in the first direction for all the image forming units, the image density can be kept uniform between the toner images formed by the respective image forming units.

Further, in this type of image forming apparatus, in order to control the latent image forming operation in each image forming unit, each latent image forming unit has the main beam in the second scanning region wider than the first scanning region. The image forming unit is scanned in the scanning direction, and each image forming unit is provided with a detection unit for detecting the scanning light beam. That is, in the image forming apparatus, a driving unit is provided to drive the surface of the latent image carrier in the sub scanning direction. In particular, in order to reduce the size of the apparatus, a driving means is mechanically connected to one end of the latent image carrier in the main scanning direction, and the driving means drives to one end of the latent image carrier. In many cases, the latent image carrier is driven by the transmission of force. For this reason, one end of the latent image carrier is more susceptible to mechanical vibration than the other end. Therefore, the following conditions:-The opposite side of the driving means in the main scanning direction (the other end side of the latent image carrier),
In the second scanning area and outside the first scanning area,
It is also possible to improve the image quality by suppressing the influence of mechanical vibration by disposing the detection unit at a position satisfying these two conditions.

  Furthermore, the drive unit may be disposed on the downstream side in the first direction, while the detection unit may be disposed on the upstream side in the first direction. As a result, the latent image writing position by the light beam is on the other end side of the driving means, and is less susceptible to mechanical vibration. As a result, the latent image writing position is aligned in the sub-scanning direction, and the image quality can be further improved.

  FIG. 1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus of FIG. This image forming apparatus is a so-called tandem type color printer, and yellow (Y), magenta (M), cyan (C), and black (K) four-color photoconductors 2Y, 2M, and 2C as latent image carriers. 2K are arranged in the apparatus main body 5 side by side. The apparatus forms a full-color image by superimposing the toner images on the photoreceptors 2Y, 2M, 2C, and 2K, or forms a monochrome image using only the black (K) toner image. That is, in this image forming apparatus, when a print command is given to the main controller 11 from an external device such as a host computer in response to an image formation request from the user, an engine controller is responded to the print command from the CPU 111 of the main controller 11. 10 controls each part of the engine unit EG to form an image corresponding to a print command on a sheet S such as copy paper, transfer paper, paper, and an OHP transparent sheet.

  In the engine unit EG, a charging unit, a developing unit, an exposure unit, and a cleaning unit are provided for each of the four photoconductors 2Y, 2M, 2C, and 2K. As described above, for each toner color, an image forming unit is provided that includes a photoreceptor, a charging unit, a developing unit, an exposure unit, and a cleaning unit, and forms a toner image of the toner color. The configuration of these image forming means (photosensitive member, charging unit, developing unit, exposure unit, and cleaning unit) is the same for all color components. Therefore, the configuration relating to yellow will be described here, and the other color components will be described. Are denoted by corresponding reference numerals, and description thereof is omitted.

  The photoreceptor 2Y is rotatably provided in the arrow direction (sub-scanning direction) in FIG. More specifically, a drive motor MT is mechanically connected to one end of the photoreceptor 2Y. When a drive command is given from the CPU 101 to the motor control unit 105 electrically connected to the drive motor MT, the motor control unit 105 controls the drive motor MT. As a result, the photoreceptor 2Y rotates. Thus, in this embodiment, the photoconductor 2Y is driven by transmitting the driving force from the drive motor MT only to one end side of the photoconductor 2Y. In this embodiment, the arrangement position of the drive motor MT, the horizontal synchronization sensor 60 described later, and the scanning direction of the light beam are set to satisfy a predetermined relationship. This point will be described in detail later.

  A charging unit 3Y, a developing unit 4Y, and a cleaning unit (not shown) are arranged around the photosensitive member 2Y driven in this way along the rotation direction. The charging unit 3Y is composed of, for example, a scorotron charger, and uniformly charges the outer peripheral surface of the photoreceptor 2Y to a predetermined surface potential by applying a charging bias from the charging control unit 103. Then, a scanning light beam Ly is emitted from the exposure unit 6Y toward the outer peripheral surface of the photoreceptor 2Y charged by the charging unit 3Y. As a result, an electrostatic latent image corresponding to the yellow image data included in the print command is formed on the photoreceptor 2Y. Thus, the exposure unit 6Y corresponds to the “latent image forming unit” of the present invention, and operates in accordance with a control command from the exposure control unit 102Y (FIG. 4). The configuration and operation of the exposure unit 6 (6Y, 6M, 6C, 6K) and the exposure control unit 102 (102Y, 102M, 102C.102K) will be described in detail later.

  The electrostatic latent image formed in this way is developed with toner by the developing unit 4Y. The developing unit 4Y contains yellow toner. When a developing bias is applied from the developing device controller 104 to the developing roller 41Y, the toner carried on the developing roller 41Y partially adheres to each surface portion of the photoreceptor 2Y according to the surface potential. As a result, the electrostatic latent image on the photoreceptor 2Y is visualized as a yellow toner image. As the developing bias applied to the developing roller 41Y, a DC voltage or a voltage obtained by superimposing an AC voltage on the DC voltage can be used. In particular, the photosensitive member 2Y and the developing roller 41Y are spaced apart from each other. In a non-contact development type image forming apparatus that develops toner by flying toner with a voltage waveform in which an alternating voltage such as a sine wave, a triangular wave, or a rectangular wave is superimposed on a direct current voltage in order to efficiently fly the toner It is preferable that

  The yellow toner image developed by the developing unit 4Y is primarily transferred onto the intermediate transfer belt 71 of the transfer unit 7 in the primary transfer region TRy1. The color components other than yellow are also configured in exactly the same way as yellow, and a magenta toner image, a cyan toner image, and a black toner image are formed on the photoreceptors 2M, 2C, and 2K, respectively, and a primary transfer region. Primary transfer is performed on the intermediate transfer belt 71 by TRm1, TRc1, and TRk1, respectively.

  The transfer unit 7 includes an intermediate transfer belt 71 stretched between two rollers 72 and 73, and a belt driving unit (not shown) that rotates the intermediate transfer belt 71 in a predetermined rotation direction R2 by driving the roller 72 to rotate. ). Further, a secondary transfer roller 74 is provided at a position facing the roller 73 with the intermediate transfer belt 71 interposed therebetween, and is configured to be able to contact and separate with respect to the surface of the belt 71 by an electromagnetic clutch (not shown). Yes. When transferring a color image to the sheet S, the primary transfer timing is controlled to superimpose the toner images to form a color image on the intermediate transfer belt 71, and the color image is taken out from the cassette 8 and transferred to the intermediate transfer belt 71. The color image is secondarily transferred onto the sheet S conveyed to the secondary transfer region TR2 between the belt 71 and the secondary transfer roller 74. On the other hand, when a monochrome image is transferred to the sheet S, only the black toner image is formed on the photoreceptor 2K, and the monochrome image is secondarily transferred onto the sheet S conveyed to the secondary transfer region TR2. In addition, the sheet S that has received the secondary transfer of the image in this way is conveyed toward the discharge tray portion provided on the upper surface portion of the apparatus main body via the fixing unit 9.

  The surface potential of each of the photoreceptors 2Y, 2M, 2C, and 2K after the toner image is primarily transferred to the intermediate transfer belt 71 is reset by a neutralizing unit (not shown), and the toner remaining on the surface is cleaned. Then, the next charging is performed by the charging units 3Y, 3M, 3C, and 3K.

  In the vicinity of the roller 72, a transfer belt cleaner 75, a density sensor 76 (FIG. 2), and a vertical synchronization sensor 77 (FIG. 2) are arranged. Among these, the cleaner 75 can be moved toward and away from the roller 72 by an electromagnetic clutch (not shown). Then, the blade of the cleaner 75 abuts on the surface of the intermediate transfer belt 71 that is stretched over the roller 72 while moving to the roller 72 side, and the toner that remains on the outer peripheral surface of the intermediate transfer belt 71 after the secondary transfer. Remove. The density sensor 76 is provided to face the surface of the intermediate transfer belt 71 and measures the optical density of the patch image formed on the outer peripheral surface of the intermediate transfer belt 71. Further, the vertical synchronization sensor 77 is a sensor for detecting the reference position of the intermediate transfer belt 71, and is a synchronization signal output in association with the rotational drive of the intermediate transfer belt 71 in the sub-scanning direction, that is, a vertical synchronization signal. It functions as a vertical sync sensor for obtaining Vsync. In this apparatus, the operation of each part of the apparatus is controlled based on the vertical synchronization signal Vsync in order to align the operation timing of each part and to superimpose toner images of each color accurately. Further, a color misregistration sensor 78 is disposed between the rollers 72 and 73, and detects the color misregistration amount of each color toner image.

  In FIG. 2, reference numeral 113 denotes an image memory provided in the main controller 11 for storing image data given from an external device such as a host computer via the interface 112, and reference numeral 106 is executed by the CPU 101. A ROM for storing calculation data, control data for controlling the engine unit EG, and the like, and a reference numeral 107 are RAMs for temporarily storing calculation results in the CPU 101 and other data.

  3 is a main scanning sectional view showing the structure of the exposure unit equipped in the image forming apparatus of FIG. 1, FIG. 4 is a view showing the scanning region of the light beam in the exposure unit of FIG. 3, and FIG. FIG. 3 is a diagram illustrating a signal processing block in one image forming apparatus. Hereinafter, the configurations and operations of the exposure unit 6 and the exposure control unit 102 will be described in detail with reference to these drawings. The configuration of the exposure unit 6 and the exposure control unit 102 is the same for all color components, so the configuration relating to yellow will be described here, and the other color components will be denoted by corresponding reference numerals and description thereof will be omitted.

  The exposure unit 6Y (6M, 6C, 6K) has an exposure housing 61. A single laser light source 62Y is fixed to the exposure housing 61, and a light beam can be emitted from the laser light source 62Y. The laser light source 62Y is electrically connected to a light source driving unit (not shown) of the exposure control unit 102Y shown in FIG. Then, the light source driving unit controls ON / OFF of the laser light source 62Y according to the image signal as follows, and a light beam modulated in accordance with the image data is emitted from the laser light source 62Y. Hereinafter, a description will be given with reference to FIG.

  In this image forming apparatus, when an image signal is input from an external device such as the host computer 100, the main controller 11 performs predetermined signal processing on the image signal. The main controller 11 includes functional blocks such as a color conversion unit 114, an image processing unit 115, a line buffer 116, a pulse modulation unit 117, a gradation correction table 118, and a correction table calculation unit 119.

  In addition to the CPU 101, the ROM 106, the RAM 107, and the exposure control unit 102 shown in FIG. 2, the engine controller 10 detects a gradation characteristic that detects a gradation characteristic indicating the gamma characteristic of the engine unit EG based on the detection result of the density sensor 76. Part 123 is provided. In the main controller 11 and the engine controller 10, these functional blocks may be configured by hardware, or may be realized by software executed by the CPUs 111 and 101.

  In the main controller 11 to which the image signal is given from the host computer 100, the color conversion unit 114 converts the RGB gradation data indicating the gradation level of the RGB component of each pixel in the image corresponding to the image signal into the corresponding CMYK. Conversion into CMYK gradation data indicating the gradation level of the component. In this color conversion unit 114, the input RGB gradation data is, for example, 8 bits per pixel per color component (that is, representing 256 gradations), and the output CMYK gradation data is similarly 8 bits per pixel per color component ( That is, it represents 256 gradations). The CMYK gradation data output from the color conversion unit 114 is input to the image processing unit 115.

  The image processing unit 115 executes the following processing for each color component. That is, gradation correction and halftoning processing are performed on the gradation data of each pixel input from the color conversion unit 114. That is, the image processing unit 115 refers to the gradation correction table 118 registered in advance in the non-volatile memory, and in accordance with the gradation correction table 118, the input gradation data of each pixel from the color conversion unit 114 is Conversion to corrected gradation data indicating the corrected gradation level is performed. The purpose of the gradation correction is to compensate for the change in the gamma characteristic of the engine unit EG configured as described above, and to keep the overall gamma characteristic of the image forming apparatus always ideal. In other words, in this type of image forming apparatus, the gamma characteristic of the apparatus varies from apparatus to apparatus, and even in the same apparatus, depending on the usage status. Therefore, in order to eliminate the influence of the variation in gamma characteristics on the image quality, a gradation control process is executed to update the contents of the gradation correction table 118 based on the actual measurement result of the image density at a predetermined timing. To do.

  In this gradation control process, for each toner color, a gradation patch gradation image prepared in advance for measuring the gamma characteristic is formed on the intermediate transfer belt 71 by the engine unit EG, and each gradation patch is obtained. The image density of the image is read by the density sensor 76, and based on a signal from the density sensor 76, the gradation characteristic detection unit 123 associates the gradation level of each gradation patch image with the detected image density ( The gamma characteristics of the engine unit EG are created and output to the correction table calculation unit 119 of the main controller 11. Then, the correction table calculation unit 119 compensates the actually measured gradation characteristic of the engine unit EG based on the gradation characteristic given from the gradation characteristic detection unit 123 to obtain an ideal gradation characteristic. The tone correction table data is calculated, and the content of the tone correction table 118 is updated to the calculation result. Thus, the gradation correction table 118 is changed and set. By doing so, this image forming apparatus can form an image with stable quality regardless of variations in gamma characteristics of the apparatus and changes over time.

  The image processing unit 15 performs halftoning processing such as an error diffusion method, a dither method, and a screen method on the corrected gradation data thus corrected, and lines halftone CMYK gradation data of 8 bits per pixel. Input to buffer 116. The gradation data stored in the line buffer 116 provided for each color component is input to the pulse modulator 117 at an appropriate timing. The content of the halftoning process varies depending on the type of image to be formed. That is, based on a determination criterion such as whether the image is a monochrome image, a color image, a line drawing, or a graphic image, the optimum processing content for the image is selected and executed.

  The gradation data after halftoning input to the pulse modulation unit 117 is a multilevel signal indicating the size and arrangement of toner dots of each color to be attached to each pixel, and the pulse modulation unit 117 that has received such data. Uses the halftone gradation data to create a video signal for pulse width modulating the exposure laser pulse of each color image of the engine unit EG, and outputs it to the engine controller 10 via a video interface (not shown). . Upon receiving this video signal, the light source driving unit (not shown) of the exposure control unit 102Y performs ON / OFF control of the laser light source 62Y of the exposure unit 6. The same applies to the other color components.

  Next, returning to FIGS. 3 and 4, the description will be continued. In the exposure housing 61, a collimator lens 631, a cylindrical lens 632, a deflector 65, and a scanning lens 66 are provided to scan and expose the light beam from the laser light source 62Y onto the surface (not shown) of the photoreceptor 2Y. It has been. That is, the light beam from the laser light source 62Y is shaped into collimated light of an appropriate size by the collimator lens 631, and then incident on the cylindrical lens 632 having power only in the sub-scanning direction Y. Then, by adjusting the cylindrical lens 632, the collimated light is imaged in the vicinity of the deflection mirror surface 651 of the deflector 65 in the sub-scanning direction Y. Thus, in this embodiment, the collimator lens 631 and the cylindrical lens 632 function as the beam shaping system 63 that shapes the light beam from the laser light source 62Y.

  The deflector 65 is formed by using a micromachining technique in which a micromachine is integrally formed on a semiconductor substrate by applying a semiconductor manufacturing technique, and includes a vibrating mirror that resonates and oscillates. That is, in the deflector 65, the light beam can be deflected in the main scanning direction X by the deflecting mirror surface 651 that resonates and vibrates. More specifically, the deflecting mirror surface 651 is pivotally supported around a swing shaft (torsion spring) that is substantially orthogonal to the main scanning direction X, and responds to an external force applied from an operating portion (not shown). Swings sine around the swing axis. This actuating unit applies an electrostatic, electromagnetic or mechanical external force to the deflection mirror surface 651 based on a mirror drive signal from a mirror drive unit (not shown) of the exposure control unit 102 to mirror the deflection mirror surface 651. Swing at the frequency of the drive signal. Note that any driving method such as electrostatic adsorption, electromagnetic force, or mechanical force may be adopted as the driving method by the operating unit, and since these driving methods are well known, description thereof is omitted here.

  The light beam deflected by the deflecting mirror surface 651 of the deflector 65 is deflected toward the scanning lens 66 at the maximum amplitude angle θmax as shown in FIG. In this embodiment, the scanning lens 66 is configured so that the F values are substantially the same in the entire effective image region IR of the photoreceptor 2. Accordingly, the light beam deflected toward the scanning lens 66 is focused on the effective image area IR on the surface of the photosensitive member 2 through the scanning lens 66 with substantially the same spot diameter. As a result, a line-shaped latent image extending in the main scanning direction X is formed on the effective image area IR of the photosensitive member 2 by scanning the light beam in parallel with the main scanning direction X. In this embodiment, the scanning region (the “second scanning region” of the present invention) SR2 that can be scanned by the deflector 65 is used for scanning the light beam on the effective image region IR as shown in FIG. The scanning area (the “first scanning area” of the present invention) is set wider than SR1. Further, the first scanning region SR1 is located at a substantially central portion of the second scanning region SR2, and is substantially symmetric with respect to the optical axis. Further, the symbol θir in the figure indicates the amplitude angle of the deflection mirror surface 651 corresponding to the end of the effective image region IR, and the symbol θs indicates the amplitude angle of the deflection mirror surface 651 corresponding to the horizontal synchronization sensor described below. Show.

  Further, in the apparatus configured as described above, the light beam can be reciprocated in the main scanning direction, that is, the light beam can be scanned in both the (+ X) direction and the (−X) direction. . However, in this embodiment, as shown in FIG. 4, only the light beam SL that scans the first scanning region SR1 in the (+ X) direction is guided to the effective image region IR to form a latent image in the effective image region IR. To do. That is, the (+ X) direction is the scanning direction of the light beam SL for forming a latent image, and corresponds to the “first direction” of the present invention. In this embodiment, the scanning direction and the arrangement position of the drive motor MT are set in advance so as to satisfy the following relationship.

  The drive motor MT is disposed on the downstream side in the scanning direction (+ X). Also, as shown in FIG. 3, the end of the scanning path of the scanning light beam is guided to the horizontal synchronization sensor 60 by the folding mirror 69 on the upstream side in the scanning direction (+ X). The folding mirror 69 is disposed at the end of the second scanning region SR2 on the upstream side in the scanning direction (+ X). The folding mirror 69 is located in the second scanning region SR2 and on the first scanning region SR1 on the upstream side in the scanning direction (+ X). The scanning light beam that moves outside the position is guided to the horizontal synchronization sensor 60. A signal is output from the horizontal synchronization sensor 60 at a timing when the scanning light beam is received by the horizontal synchronization sensor 60 and passes through the sensor position (amplitude angle θs). Thus, in this embodiment, the horizontal synchronization sensor 60 is used as a horizontal synchronization reading sensor for obtaining a synchronization signal when the light beam scans the effective image area IR in the main scanning direction X, that is, the horizontal synchronization signal Hsync. The latent image forming operation is controlled based on the horizontal synchronization signal Hsync. Hereinafter, the latent image forming operation in the conventional apparatus and the latent image forming operation in the apparatus according to the present embodiment will be described with reference to the drawings.

  6 is a diagram schematically showing the latent image forming operation, FIG. 7 is a diagram showing a latent image formed by the latent image forming operation of the conventional apparatus, and FIG. 8 is a diagram showing the latent image forming operation of the present embodiment. It is a figure which shows the latent image formed. 6 to 8 is an imaginary line indicating the locus of reciprocating scanning. In addition, a thick arrow in FIG. 6 indicates a scanning light beam SL for forming a latent image. Here, a case where a repeating pattern of 2 lines ON-2 lines OFF is formed will be described as an example.

  In the conventional apparatus, as shown in FIGS. 6 and 7, the scanning light beam SL is scanned in the forward path and the backward path to form a two-line latent image, and then the laser light source 62 is turned off for two lines. As a result, a latent image of 2 lines ON and 2 lines OFF is formed. Then, a desired repetitive pattern (two-dimensional latent image) is formed by repeating this latent image forming operation. Here, the problem is the density difference in the main scanning direction. That is, the two-dimensional latent image is formed by reciprocally scanning the scanning light beam SL in the main scanning direction X while rotating the photosensitive member 2 in the sub-scanning direction Y substantially orthogonal to the main scanning direction X. The latent image areas are different between the (+ X) direction side and the (−X) direction side, resulting in a difference in image density.

  In contrast, in this embodiment, although the light beam can be reciprocated in the main scanning direction X, only the light beam SL scanned in the first direction (+ X) of the main scanning direction X is exposed. A latent image is formed by irradiating the effective image area IR of the body 2. For this reason, as shown in FIG. 8, the latent image area is uniform in the main scanning direction X, and the image density is uniform. As a result, an image can be formed with excellent image quality.

  In this embodiment, since the scanning direction of the light beam SL for forming a latent image is unified in the first direction (+ X) for any color component, the image density is also between toner images of each color component. Can be kept uniform.

In this embodiment, the drive motor MT is mechanically connected to the end of the photoconductor 2 on the downstream side in the first direction (+ X) as shown in FIG. Therefore, one end portion of the photosensitive member 2 is more susceptible to mechanical vibration than the other end portion. Therefore, in the present embodiment, the following two conditions, that is,
The opposite side of the drive motor MT in the main scanning direction X (the other end side of the photoreceptor 2),
In the second scanning region SR2 and out of the first scanning region SR1,
The horizontal synchronization sensor 60 is disposed at a position satisfying these two conditions. As described above, since the sensor 60 corresponding to the “detection unit” of the present invention is disposed at a position that is not easily affected by mechanical vibration, a horizontal synchronization signal can be obtained in a state where the influence of mechanical vibration is suppressed. . As a result, the latent image can be formed satisfactorily and the image quality can be improved.

  Further, in this embodiment, the horizontal synchronization sensor 60 is arranged on the upstream side in the first direction (+ X), and the laser light source is ON / OFF controlled based on the output signal (horizontal synchronization signal) from the sensor 60. That is, since the latent image writing is performed in an area that is not easily subjected to mechanical vibration accompanying the rotational driving of the photosensitive member 2 by the drive motor MT, the latent image writing position is aligned in the sub-scanning direction Y, and the image quality can be further improved. .

  The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, in the above embodiment, the latent image is formed by scanning the light beam SL with the (+ X) direction as the “first direction” of the present invention, but the light beam SL is scanned in the (−X) direction. Needless to say, a latent image may be formed.

  In the above embodiment, the present invention is applied to an image forming apparatus that temporarily forms a color image on an intermediate transfer medium such as an intermediate transfer belt and then transfers the color image to the sheet S. The present invention is also applicable to an apparatus that forms a color image by directly superimposing toner images on a sheet. In this case, the sheet corresponds to the “transfer medium” of the present invention.

  In the above embodiment, the vibrating deflection mirror surface 651 is formed by using a micromachining technique. However, the method of manufacturing the deflection mirror surface is not limited to this, and the vibrating deflection mirror surface is used. The present invention can be applied to all so-called tandem type image forming apparatuses in which a light beam is deflected to scan the latent image carrier.

1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus in FIG. 1. FIG. 2 is a main scanning sectional view showing a configuration of an exposure unit in the image forming apparatus of FIG. The figure which shows the scanning area | region of the light beam in the exposure unit of FIG. FIG. 2 is a diagram showing a signal processing block in the image forming apparatus of FIG. 1. The figure which shows typically latent image formation operation | movement. The figure which shows the latent image formed by the latent image formation operation | movement of a conventional apparatus. FIG. 2 is a diagram illustrating a latent image formed by a latent image forming operation of the image forming apparatus in FIG. 1.

Explanation of symbols

  2, 2Y, 2M, 2C, 2K ... photosensitive member (latent image carrier), 4, 4Y, 4M, 4C, 4K ... developing unit (developing unit), 6, 6Y, 6M, 6C, 6K ... exposure unit (latent) (Image forming unit), 60 ... horizontal synchronization sensor (detector), 62, 62Y, 62M, 62C, 62K ... laser light source, 71 ... intermediate transfer belt (transfer medium), 651 ... deflection mirror surface, IR ... effective image area, Ly, Lm, Lc, Lk ... scanning light beam, MT ... drive motor (drive means), SL ... scanning light beam, X ... main scanning direction, Y ... sub-scanning direction

Claims (4)

In an image forming apparatus that has a plurality of image forming units that form toner images of different colors, and forms a color image by superimposing toner images formed by the respective image forming units on a transfer medium.
Each of the plurality of image forming units includes:
An effective image region having a predetermined width in the main scanning direction is provided on the surface, and the surface is driven in a sub-scanning direction substantially orthogonal to the main scanning direction;
The first scanning region corresponding to the effective image region can be scanned in the main scanning direction with the light beam from the light source by the oscillating deflection mirror surface, and in the first direction of the main scanning direction and the first scanning region. An image forming apparatus comprising: a latent image forming unit configured to irradiate the effective image region with only a light beam for scanning one scanning region to form a latent image in the effective image region. A drive unit that is mechanically connected to one end of the latent image carrier in the main scanning direction and drives the surface of the latent image carrier in the sub-scanning direction;
Each of the plurality of latent image forming units is configured to be able to scan a light beam in the main scanning direction in a second scanning region wider than the first scanning region,
Each of the plurality of image forming units detects a scanning light beam that moves within the second scanning region and outside the first scanning region on the opposite side of the driving unit in the main scanning direction. The image forming apparatus according to claim 1, further comprising: a detection unit that outputs a signal, and controlling a latent image forming operation based on the detection signal output from the detection unit.   The image forming apparatus according to claim 2, wherein the driving unit is disposed on the downstream side in the first direction, and the detection unit is disposed on the upstream side in the first direction. An effective image area having a predetermined width is provided on the surface in the main scanning direction, and the surface is driven in a sub-scanning direction substantially orthogonal to the main scanning direction to form a latent image on the latent image carrier and to each other. An image forming method for forming a color image on a transfer medium using a plurality of image forming means, wherein a toner image is formed by developing the latent image with different color toners,
In each of the plurality of image forming units, the effective image is irradiated by irradiating the effective image area of the latent image carrier with the light beam from the light source in the first direction of the main scanning direction by the vibrating deflection mirror surface. An image forming step of forming a latent image in the region and developing the latent image to form a toner image;
And a transfer step of superposing toner images formed by each of the plurality of image forming units on the transfer medium to form a color image.

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