JP4779447B2 - Image forming apparatus and image forming method - Google Patents

Description

  The present invention relates to an image forming apparatus and method for forming a latent image by irradiating a latent image carrier driven in the sub-scanning direction with a light beam in a main scanning direction substantially orthogonal to the sub-scanning direction. .

  This type of image forming apparatus includes a photoreceptor, an exposure unit, and a developing unit, and forms a toner image on the photoreceptor as follows. That is, the light source of the exposure unit is controlled based on the image data indicating the toner image, and the light beam from the light source is scanned in the main scanning direction by the deflector of the exposure unit, so that a latent image corresponding to the image data is formed on the photoconductor. To form. The latent image is developed with toner to form a toner image.

  Further, in order to reduce the size and speed of the deflector, it has been conventionally proposed to use the deflecting mirror surface as a deflector by vibrating the surface (see Patent Document 1). That is, in this apparatus, the deflection mirror supported by the torsion bar is oscillated, and the deflection mirror is irradiated with the light beam from the light source to reciprocate the light beam on the surface of the photosensitive member.

JP 2002-182147 A (the third page and FIGS. 9 and 10)

  In such an image forming apparatus, it is possible to selectively switch between a double-sided scanning mode in which a light beam from a light source is scanned on the photoreceptor in both the forward path and the backward path, and a single-sided scanning mode in which only one of them is scanned. Thus, it is possible to form an image according to the printing mode. For example, when printing characters etc. that do not require high resolution, a light beam is scanned on the photoconductor only on either the forward path or the backward path to form an image with low resolution, and photographs etc. are beautiful When it is desired to print on the photosensitive member, it is preferable to increase the resolution by scanning the light beam from the light source on the photosensitive member in both the forward pass and the return pass.

  However, when the latent image formed on the photoconductor is developed in the double-side scan mode in the configuration in which the single-side scan mode and the double-side scan mode can be switched as described above, the toner adheres to the photoconductor surface more than necessary. This has the problem of causing image damage. The reason will be described in detail. In order for the lines formed in the sub-scanning direction to be uninterrupted in the one-side scanning mode, the beam width in the sub-scanning direction on the photosensitive member surface needs to be at least equal to or larger than the scanning pitch in the sub-scanning direction in the one-side scanning mode. . This is because when the light beam width in the sub-scanning direction on the surface of the photoconductor is less than the scanning pitch in the sub-scanning direction, the latent image formed by irradiating the light beam forms a continuous line without being connected between adjacent scanning lines. It is not possible. As described above, the light beam width in the sub-scanning direction on the surface of the photosensitive member needs to satisfy the condition that it is equal to or larger than the scanning pitch in the sub-scanning direction in the one-side scanning mode. On the other hand, when switching to the double-sided scanning mode, the scanning pitch becomes narrower than the scanning pitch in the single-sided scanning mode. Therefore, when the surface of the photosensitive member is scanned in the double-sided scanning mode, the region where the light beam scans the photosensitive member surface between adjacent scanning lines excessively overlaps. As a result, the latent images formed on the adjacent scanning lines are excessively overlapped with each other, so that the toner is attached more than necessary, resulting in an image detrimental effect that the line becomes thicker and the color density becomes too dark. was there.

  The present invention has been made in view of the above problems, and forms a latent image by irradiating a light beam for forming a latent image in the main scanning direction by a deflection mirror that vibrates on a latent image carrier driven in the sub-scanning direction. In the image forming apparatus and method, the single-sided scanning mode and the double-sided scanning mode can be selectively switched, and when developing a latent image formed on the photoconductor in the double-sided scanning mode, an excessive amount of toner is required. An object of the present invention is to provide a technique for preventing adhesion and forming a good image.

In order to achieve the above object, an image forming apparatus according to the present invention is provided with an effective image area having a predetermined width in the main scanning direction on the surface, and a latent image carrier whose surface is driven in the sub-scanning direction. The latent image forming light beam is configured to be able to scan the scanning region including the effective image region in the main scanning direction by the deflection mirror that vibrates the light beam emitted from the light source driven by the light source driving unit. A latent image forming means for forming a latent image on the effective image area, a one-side scanning mode for scanning the latent image forming light beam only in the first direction of the main scanning direction, and the first direction. And a scanning mode control means for selectively switching between both-side scanning modes for scanning in both directions in the second direction opposite to the first direction, the beam width in the sub-scanning direction of the latent image forming light beam is Has a length of more scanning pitch in the sub-scanning direction during mode, the light source driving section, the amount of latent image forming light beam on both sides scanning mode is higher than the light quantity of the latent image forming light beam of one scanning mode The light source is driven so that the number of the light sources is reduced, and the latent image forming light in the double-sided scanning mode is determined according to the ratio of the beam width in the sub-scanning direction and the scanning pitch of the latent image forming light beam in the single-sided scanning mode. It is characterized in that the light quantity of the beam is set .

In order to achieve the above object, the image forming method according to the present invention is provided with an effective image area having a predetermined width in the main scanning direction on the surface, and a latent image carrier whose surface is driven in the sub-scanning direction. The latent image forming light beam is configured to be able to scan the scanning region including the effective image region in the main scanning direction by the deflection mirror that vibrates the light beam emitted from the light source driven by the light source driving unit. One-sided scanning in which the latent image forming light beam is scanned only in the first direction of the main scanning direction in an image forming apparatus provided with latent image forming means for forming a latent image in the effective image region by irradiating the effective image region An image forming method for forming a latent image in a selected scanning mode by selectively switching between a mode and a double-sided scanning mode for scanning in both the first direction and a second direction opposite to the first direction, The beam width in the sub-scanning direction of the image forming light beam, and sets the above scanning pitch in the sub-scanning direction of the one-side scanning mode length, the amount of latent image forming light beam on both sides scan mode is one scanning The light source is driven so that the amount of light beam of the latent image forming light beam in the mode is smaller and the ratio of the beam width in the sub-scanning direction of the latent image forming light beam in the one-sided scanning mode to the scanning pitch The light quantity of the latent image forming light beam in the double-sided scanning mode is set .

  In the invention thus configured (image forming apparatus and method), the one-side scanning mode in which the latent image forming light beam is scanned only in the first direction of the main scanning direction, and the first direction and the reverse of the first direction. The double-sided scanning mode for scanning in both directions of the second direction can be selectively switched. For example, when a line latent image is formed on the latent image carrier as shown in FIG. 6, a line latent image LI () is formed in the effective image area by a latent image forming light beam scanned in the first direction of the main scanning direction. + X) is formed, while the line latent image LI (−X) is formed by the light beam scanned in the second direction opposite to the first direction. Therefore, in the double-sided scanning mode in which the light beam used for forming the latent image is scanned in the first direction and the second direction, the line latent images LI (+ X) and LI (−X) are alternately formed in the sub-scanning direction. In contrast, in the one-side scanning mode in which the latent image forming light beam is scanned only in either the first direction or the second direction, only one of the line latent images LI (+ X) and LI (−X) is present. It is formed in the sub-scanning direction. In the present invention, the light beam width in the sub-scanning direction on the surface of the latent image carrier, that is, the beam width in the sub-scanning direction of the latent image forming light beam is equal to or larger than the scanning pitch in the sub-scanning direction in the one-side scanning mode. It is configured to have a length. In such a configuration, as described above, the latent images formed on the adjacent scanning lines in the double-sided scanning mode excessively overlap each other, so that the toner adheres more than necessary, and the lines become thicker or the color density becomes darker. There is a problem that an image detrimental effect such as the image becomes too dark occurs. However, according to the present invention, the light source is driven so that the light amount of the latent image forming light beam applied to the surface of the latent image carrier is smaller in the double-sided scanning mode than in the single-sided scanning mode. For this reason, in the double-sided scanning mode, the amount of light of the latent image forming light beam is suppressed even when the area where the latent image forming light beam scans is excessively overlapped between adjacent scanning lines. Yes. Therefore, it is possible to suppress the amount of toner adhering when developing the latent image. Therefore, it is possible to prevent an adverse effect of the image such that the toner adheres more than necessary and the line becomes thicker or the color density becomes too dark, and a good image can be formed.

  According to the present invention, the light source driving unit is configured to form a latent image in the double-sided scanning mode in accordance with a ratio between the beam width in the sub-scanning direction of the latent image forming light beam and the scanning pitch in the sub-scanning direction during single-sided scanning. The light source is driven so that the light amount of the light beam for use is smaller than the light amount of the light beam for forming a latent image in the one-side scanning mode. With this configuration, the light amount of the latent image forming light beam in the double-sided scanning mode can be further optimized. That is, for example, the beam width in the sub-scanning direction of the latent image forming light beam is relatively large with respect to the scanning pitch in the sub-scanning direction during single-sided scanning, and the latent-image forming light between adjacent scanning lines in the single-sided scanning mode. When the areas scanned by the beams are largely overlapped, the areas scanned by the latent image forming light beams are greatly overlapped between adjacent scanning lines even in the double-sided scanning mode. Therefore, in such a case, a good image can be formed by sufficiently reducing the light amount of the latent image forming light beam in the double-sided scanning mode to prevent excessive toner adhesion. On the other hand, for example, the beam width in the sub-scanning direction of the light beam for forming a latent image is approximately the same as the scanning pitch in the sub-scanning direction during one-side scanning, and latent image formation is performed between adjacent scanning lines in the one-side scanning mode. In the case where the overlap of the area scanned by the light beam is relatively small, the overlap of the area scanned by the latent image forming light beam between the adjacent scan lines is relatively small even in the double-sided scanning mode. Therefore, in such a case, the amount of toner adhesion can be reduced by excessively suppressing the light amount of the latent image forming light beam by preventing the light amount of the latent image forming light beam in the double-sided scanning mode from being too small. Is reduced excessively, and the adverse effect of the image that the line formed in the sub-scanning direction is interrupted in the double-sided scanning mode can be prevented, and a good image can be formed.

<First Embodiment>
FIG. 1 is a diagram showing a first 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 is provided in the apparatus main body 5. 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 print an image corresponding to the print command on a sheet (recording medium) S such as a copy sheet, a transfer sheet, a sheet, 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, the drive motor MT is mechanically connected to one end of the photoreceptor 2Y. The motor control unit 105 electrically connected to the drive motor MT 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, the scanning light beam Ly is irradiated 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. 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 photoconductor 2Y becomes visible 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 Is desirable.

  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 configured in the same manner as yellow, and magenta toner images, cyan toner images, and black toner images are formed on the photoreceptors 2M, 2C, and 2K, respectively, and primary transfer is performed. Primary transfer is performed on the intermediate transfer belt 71 in the regions 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 rotating the roller 72. ). In addition, a secondary transfer roller 74 is provided at a position facing the roller 73 with the intermediate transfer belt 71 interposed therebetween. The secondary transfer roller 74 is configured to be brought into contact with and separated from the surface of the belt 71 by an electromagnetic clutch (not shown). Yes. When a color image is transferred 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 to be intermediate. The color image is secondarily transferred onto the sheet S conveyed to the secondary transfer region TR2 between the transfer 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 primary transfer of the toner image to the intermediate transfer belt 71 is reset by a neutralizing unit (not shown), and the toner remaining on the surface is further removed. Is removed by the cleaning unit, and then charged 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 is in contact with 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. Reference numeral 108 denotes an FRAM (ferroelectric memory) for storing information on the usage status of each part of the engine.

  FIG. 3 is a main scanning sectional view showing the configuration of the exposure unit provided in the image forming apparatus of FIG. 1, and FIG. 4 is a view showing the scanning region of the light beam in the exposure unit of FIG. 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.

  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. As shown in FIG. 4, the laser light source 62Y is electrically connected to the light source driving unit 1021 of the exposure control unit 102Y. 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, two types of line buffers 116A and 116B, a scanning mode switching unit 116C, a pulse modulation unit 117, a gradation correction table 118, and a correction table calculation unit 119. It has.

  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 such gamma characteristic variations 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.

  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.

  For the corrected gradation data corrected in this way, the image processing unit 115 forms a halftone dot using a plurality of pixels and determines the size of the halftone dot by a dither method, an error diffusion method, a screen method, or the like. The halftoning process for realizing the gradation by growing is performed, and halftone gradation data of 8 bits per halftone dot color is input to the two types of line buffers 116A and 116B. The contents of the halftoning process vary 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 photographic image, the optimum processing content for the image is selected and executed.

  These line buffers 116A and 116B are common in that they store halftone gradation data (image information) constituting one line image data output from the image processing unit 15, but the readout order of gradation data is the same. Is different. That is, the forward line buffer 116A outputs halftone gradation data constituting one line image data in the forward direction from the head, whereas the reverse line buffer 116B outputs in the reverse direction from the end. is there.

  The halftone gradation data thus output is input to the scanning mode switching unit 116C, and only the halftone gradation data output from one line buffer based on the scanning mode switching signal is scanned at an appropriate timing. 116C is output to pulse modulation section 117. The main reason why the two types of line buffers 116A and 116B are provided in this manner is to cope with the difference in the scanning mode of the latent image forming light beam depending on the printing mode, as will be described later. In addition, the gradation data is input to the pulse modulation unit 117 at the timing and order corresponding to each color component by the scanning mode switching unit 116C. Thus, in this embodiment, the line buffers 116A and 116B and the scanning mode switching unit 116C correspond to the “scanning mode control means” of the present invention.

  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 1021 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 area SR that can be scanned by the deflector 65 is set wider than the effective image area, as shown in FIG. The effective image area IR is located substantially at the center of the scanning area SR 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 60 described below. Is shown.

  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. . As described above, the gradation data constituting one line image data is temporarily stored in the storage unit (line buffers 116A and 116B), and the scanning mode switching unit 116C performs gradation data at an appropriate timing and order. Is supplied to the pulse modulation unit 117. For example, when the direction is changed to the (+ X) direction, as shown in FIG. 6A, the beam spot is read out from the line buffer 116A in the order of gradation data DT1, DT2,. Is irradiated onto the photoconductor 2 in the first direction (+ X) to form a line latent image LI (+ X). On the other hand, when the direction is switched to the (−X) direction, as shown in FIG. 6B, the grayscale data DTn, DT (n−1),. A beam spot is irradiated onto the photoconductor 2 in the second direction (−X) based on each gradation data, and a line latent image LI (−X) is formed. Therefore, the light beam for forming a latent image (corresponding to the “latent image forming light beam” of the present invention) can be made different for each printing mode or for each line as follows. More specifically, in this embodiment, information about the resolution (resolution information) included in the print command is temporarily stored in the RAM 107. When high resolution printing is instructed, an operation of scanning the effective image area IR in the (+ X) direction with the light beam SL1 as a latent image forming light beam to form a latent image in the effective image area IR; A so-called double-sided scanning mode is executed in which the light beam SL2 is scanned as the latent image forming light beam in the (-X) direction to scan the effective image area IR and the latent image is formed alternately in the effective image area IR. A latent image is formed. On the other hand, when low resolution printing is instructed, a latent image is formed by executing a so-called one-side scanning mode in which only the latent image forming light beam SL1 is repeated. Thus, in this embodiment, the scanning mode of the latent image forming light beam is switched between high resolution printing and low resolution printing based on the resolution information. This point will be described in detail later.

As described above, in this embodiment, the latent image forming light beam having a constant spot diameter can be scanned on the surface of the effective image region IR on the surface of the photosensitive member 2 by switching between the double-sided scanning mode and the single-sided scanning mode. is there. Further, in this embodiment, the beam width Wb in the sub-scanning direction of the latent image forming light beam is configured to be equal to or larger than the scanning pitch PT in the one-side scanning mode. The reason for this will be described below with reference to FIG. However, in FIG. 7, the alternate long and short dash line is an imaginary line indicating the trajectory of the scanning line in the one-side scanning mode, and the solid line represents the latent image forming light beam. When the beam width Wb in the sub-scanning direction is smaller than the scanning pitch PT in the one-side scanning mode in the one-side scanning mode, the latent images formed by irradiation with the light beam are adjacent to each other as shown in FIG. A continuous line cannot be formed because the scanning lines are not connected. Therefore, the line formed in the sub scanning direction is interrupted. Therefore, in order for the lines formed in the sub-scanning direction to be uninterrupted, as shown in FIG. 7B or 7C, the light beam width Wb in the sub-scanning direction on the surface of the photoconductor is set in the one-side scanning mode. Must be greater than or equal to the scanning pitch PT in the sub-scanning direction. Further, in this specification, the light beam width Wb in the sub-scanning direction is 1 / e ² (with respect to the peak value in the light intensity distribution of the light beam at the photosensitive member surface position (hereinafter referred to as “beam profile”). “E” is the width in the sub-scanning direction of a region having an intensity equal to or greater than the base of the natural logarithm. Further, the beam width Wb in the sub-scanning direction of the latent image forming light beam can be measured, for example, by the following method. As a measuring device, a BeamScan Model 2180 manufactured by Photon, Inc. can be used. Then, the beam width Wb in the sub-scanning direction can be obtained by measuring the beam profile at a position assumed to be the surface of the photoconductor when the laser is continuously lit at a laser power of 1 mW. The spot diameter of the light beam is generally proportional to the product of the wavelength of the light beam and the F value in the effective image area IR on the surface of the photoreceptor. Therefore, by adjusting the wavelength or F value of the light beam, the beam width Wb in the sub-scanning direction measured by the above method can be adjusted to be equal to or larger than the scanning pitch PT in the one-side scanning mode.

  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. That is, 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 scanning region SR on the upstream side in the scanning direction (+ X), and moves on the upstream side in the scanning direction (+ X) within the scanning region SR and outside the effective image region IR. The scanning light beam to be guided 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, a latent image forming operation in the apparatus according to the present embodiment will be described.

  FIG. 8 is a flowchart showing the operation of the image forming apparatus in the first embodiment. FIG. 9 is a diagram showing a latent image formed by the latent image forming operation of the present embodiment. In FIG. 9, the alternate long and short dash line is a virtual line indicating the trajectory of the scanning line, and the thick arrow indicates the latent image forming light beam.

  When a print command is input from an external device such as the host computer 100, a latent image is formed on each photoconductor according to the flowchart shown in FIG. 8, and a color image is formed based on each latent image. That is, in step S10, resolution information included in the print command is acquired (information acquisition step). Then, based on the resolution information, it is determined whether the print command requests high resolution printing or low resolution printing (step S11).

  If “YES” is determined in the step S11, that is, if it is determined that the low-resolution printing is performed, steps S16 to S19 are executed to form an image with a low resolution, and the image is transferred to the sheet S and the printing process is ended. First, in step S16, the one-side scanning mode is set (scanning mode setting step). Next, the level of the light source drive signal given to the laser light source 62 from the light source drive unit 1021 included in the exposure control unit 102 is set to the one-side scanning drive level (step S17). Thereby, in step S19 described later, the latent image forming light beam scanned on the photosensitive member 2 has a light amount corresponding to the driving level during one-side scanning. Further, a scanning mode switching signal corresponding to the scanning mode determined as described above is given to the scanning mode switching unit 116C of the main controller 11 (step S18). On the other hand, the scanning mode switching unit 116C that has received these instructions forms a latent image line by line by fixing the read timing and order of gradation data from the line buffer. That is, the data is read out from the forward line buffer 116A at an appropriate timing and forward direction (that is, the order of the gradation data DT1, DT2,... DTn) and optically modulated based on each gradation data, as shown in the lower part of FIG. Only the latent image forming light beam SL1 scanned in one direction is scanned on the photosensitive member 2 to form a latent image (step S19). In this way, a so-called one-side scanning mode is executed, and a latent image is formed at a low resolution. Further, the latent image formed in this way is developed with toner to form a four-color toner image, and is superimposed on the intermediate transfer belt 71 to form a color image, and then the color image is formed on the sheet S. The image is transferred and the low resolution printing is completed.

  If “NO” is determined in the step S11, that is, it is determined that high resolution printing is performed, steps S12 to S15 are executed to form an image with high resolution, transferred to the sheet S, and the printing process is ended. First, in step S12, the double-sided scanning mode is set (scanning mode setting step). Next, the level of the light source drive signal given from the light source drive unit 1021 of the exposure control unit 102 to the laser light source 62 is set to a drive level at the time of double-sided scanning that is smaller than the drive level at the time of single-sided scanning (step S13). Thereby, in step S15 described later, the latent image forming light beam scanned on the photosensitive member 2 has a light amount smaller than the light amount in the one-side scanning mode. Further, a scanning mode switching signal corresponding to the scanning mode determined as described above is given to the scanning mode switching unit 116C of the main controller 11 (step S14). On the other hand, upon receiving these instructions, the scanning mode switching unit 116C alternately switches the timing and order of reading out the gradation data from the line buffer for each line. Thereby, a high-resolution latent image is formed as follows. That is, as shown in the upper part of FIG. 9, the light beam SL1 is used as a latent image forming light beam to scan the effective image area IR in the (+ X) direction to form a latent image in the effective image area IR, The operation of forming the latent image in the effective image area IR by scanning the effective image area IR in the (−X) direction using the beam SL2 as a latent image forming light beam is alternately repeated (step S15). Thus, a so-called double-sided scanning mode is executed to form a latent image with high resolution. Further, the latent image formed in this way is developed with toner to form a four-color toner image, and is superimposed on the intermediate transfer belt 71 to form a color image, and then the color image is formed on the sheet S. The image is transferred and high-resolution printing ends.

  As described above, in the first embodiment, the drive level during double-sided scanning is set to a level smaller than the drive level during single-sided scanning. Therefore, it is possible to prevent the toner from attaching more than necessary in the double-sided scanning mode and form a good image. The reason for this will be described below with reference to FIG. In FIG. 10, the one-dot chain line is a virtual line indicating the trajectory of the scanning line, and the ellipse surrounded by the solid line represents the latent image forming light beam. As described above, in the first embodiment, the beam width in the sub-scanning direction of the latent image forming light beam is configured to be equal to or larger than the scanning pitch in the one-side scanning mode. Therefore, when the single-side scanning mode is switched to the double-sided scanning mode, the scanning pitch becomes narrow, so in the region TR shown in FIG. 10, there is an excessive region where the latent image forming light beam scans the surface of the photoreceptor between adjacent scanning lines. Will overlap. As a result, in the double-sided scanning mode, the latent images formed on the adjacent scanning lines are excessively overlapped with each other, so that the toner adheres more than necessary and the lines become thicker or the color density becomes too dark. Bad image occurs.

  On the other hand, in the first embodiment, since the drive level at the time of both-side scanning is set to a level smaller than the drive level at the time of one-side scanning, the light amount of the light beam for forming a latent image in the both-side scanning mode is set to the latent image in the one-side scanning mode. The amount of light of the forming light beam can be reduced. The latent image formed by the latent image forming light beam having a small amount of light is developed with less toner. This is because, in general, when a latent image formed on the surface of a photoreceptor is developed with toner, the toner adheres according to the potential difference between the potential of the latent image portion and the developing bias potential. That is, the larger the potential difference, the larger the amount of toner that adheres. Further, the potential difference between the developing bias potential and the potential of the latent image portion becomes smaller as the latent image portion is formed with a smaller amount of light. Accordingly, as shown in FIG. 11, in the double-sided scanning mode, a smaller amount of toner adheres to the latent image formed with a smaller amount of light than in the single-sided scanning mode compared to that in the single-sided scanning mode. . Therefore, it is possible to prevent image detriment caused by excessive toner adhering in the double-sided scanning mode, and good image formation is possible. In addition, the dashed-dotted line in FIG. 11 is a virtual line which shows the locus | trajectory of a scanning line.

  Further, according to the first embodiment, the print resolution is switched by selectively switching between the double-sided scanning mode and the single-sided scanning mode based on the resolution information. In this manner, high resolution printing or low resolution printing can be selectively executed by simply switching the scanning mode of the latent image forming light beam without changing the vibration operation of the deflecting mirror surface 651. Therefore, it is possible to quickly change the resolution.

Second Embodiment
By the way, line drawings of characters and the like do not require so high resolution because they can be printed beautifully by continuously forming the lines without interruption. On the other hand, when a photograph or the like is printed neatly, it is preferable to increase the resolution because it is necessary to realize gradation reproducibility as described in detail later. Therefore, when printing line drawings such as characters, execute the one-sided scanning mode and print at a low resolution, while when printing pictures that require gradation reproducibility, execute the two-sided scanning mode. It is preferable to increase the resolution.

  As described above, when a photograph or the like is printed neatly, gradation reproducibility is required, and therefore it is necessary to increase the resolution. The reason will be described in detail with reference to FIG. As a means for realizing the gradation reproducibility, a means for realizing a gradation by forming a halftone dot using a plurality of pixels and growing the size of the halftone dot can be used. For example, in FIG. 12A, one halftone dot is formed using a total of 16 pixels of 4 vertical pixels × 4 horizontal pixels. Then, by increasing the number of pixels to be exposed toward (A) to (P), the size of the halftone dot corresponding to the exposed portion is grown according to a predetermined rule, and the gradation reproducibility in 16 levels. Is realized. It should be noted that the gradation corresponds to the darker as it goes to (A) to (P). Further, as shown in (A) to (D) of FIG. 12B, it is possible to give a plurality of gradations per pixel by exposing only one part of one pixel. . Therefore, for example, if 16 pixels are provided per pixel and one halftone dot is configured using 16 pixels, 256 gradations can be realized with 16 gradations × 16 gradations. . However, when many pixels are used to reproduce many gradations, there is a problem that the interval between adjacent halftone dots becomes large and the photograph becomes rough. Therefore, when printing a photograph, as shown in FIG. 12 (3), the double-sided scanning mode is executed to double the resolution in the sub-scanning direction, so that they are adjacent to each other as compared with the one-sided scanning mode. The distance between halftone dots can be halved in the sub-scanning direction. Therefore, higher-definition photo printing is possible. Therefore, in the second embodiment, it is determined whether or not gradation reproducibility is necessary. When gradation reproducibility is necessary, high-resolution printing is executed in the double-sided scanning mode and gradation reproducibility is not necessary. Is supposed to execute low-resolution printing in the single-sided scanning mode. Hereinafter, the operation of the apparatus that switches the scanning mode in accordance with the necessity of gradation reproducibility will be described in detail with reference to FIGS. 13 and 14. In addition, since the basic composition of the apparatus concerning 2nd Embodiment is the same as 1st Embodiment, it attaches | subjects the same and equivalent code | symbol, and abbreviate | omits description.

  FIG. 13 is a flowchart illustrating the operation of the image forming apparatus according to the second embodiment. FIG. 14 is a view showing a latent image formed by the latent image forming operation of the second embodiment. In addition, a one-dot chain line in FIG. 14 is an imaginary line indicating the trajectory of the scanning line, and a thick arrow indicates a latent image forming light beam. In the second embodiment, when a print command is input from an external device such as the host computer 100, a latent image is formed on each photoconductor according to the flowchart shown in FIG. Is formed. That is, in step 20, gradation information included in the print command is acquired (information acquisition step). Then, it is determined whether or not gradation reproducibility is necessary (step S21).

  If “NO” is determined in the step S21, that is, if it is determined that the gradation reproducibility is not necessary, an image is formed by executing the steps S26 to S29, transferred to the sheet S, and the printing process is ended. First, in step S26, the one-side scanning mode is set (scanning mode setting step). Next, the level of the light source drive signal given to the laser light source 62 from the light source drive unit 1021 included in the exposure control unit 102 is set to the one-side scanning drive level (step S27). Thereby, in step S29 described later, the latent image forming light beam scanned on the photosensitive member 2 has a light amount corresponding to the driving level at one-side scanning. Further, a scanning mode switching signal corresponding to the scanning mode determined as described above is given to the scanning mode switching unit 116C of the main controller 11 (step S28). On the other hand, the scanning mode switching unit 116C that has received these instructions forms a latent image line by line by fixing the read timing and order of gradation data from the line buffer. That is, the data is read out from the forward line buffer 116A at an appropriate timing and forward direction (that is, the order of the gradation data DT1, DT2,... DTn) and optically modulated based on each gradation data, as shown in the lower part of FIG. Only the latent image forming light beam SL1 scanned in one direction is scanned on the photosensitive member 2 to form a latent image (step S29). Thus, a so-called one-side scanning mode is executed to form a latent image. Further, the latent image formed in this way is developed with toner to form a four-color toner image, and is superimposed on the intermediate transfer belt 71 to form a color image, and then the color image is formed on the sheet S. The character is printed after being transferred.

  If “YES” is determined in the step S21, that is, if it is determined that gradation reproducibility is necessary, steps S22 to S25 are executed to form an image with high resolution, and the image is transferred to the sheet S and the printing process is ended. . First, in step S22, the double-sided scanning mode is set (scanning mode setting step). Next, the level of the light source drive signal given to the laser light source 62 from the light source drive unit 1021 included in the exposure control unit 102 is set to a drive level at the time of both-side scanning smaller than the drive level at the time of one-side scanning (step S23). Thus, in step S25 described later, the latent image forming light beam scanned on the photosensitive member 2 has a light amount smaller than the light amount in the one-side scanning mode. Further, a scanning mode switching signal corresponding to the scanning mode determined as described above is given to the scanning mode switching unit 116C of the main controller 11 (step S24). On the other hand, upon receiving these instructions, the scanning mode switching unit 116C alternately switches the timing and order of reading out the gradation data from the line buffer for each line. Thereby, a latent image is formed as follows. That is, as shown in the upper part of FIG. 14, the light beam SL1 is used as a latent image forming light beam to scan the effective image region IR in the (+ X) direction to form a latent image in the effective image region IR; The operation of scanning the effective image area IR in the (−X) direction using SL2 as a latent image forming light beam to form a latent image in the effective image area IR is alternately repeated (step S25). In this way, a so-called double-sided scanning mode is executed to form a latent image. Further, the latent image formed in this way is developed with toner to form a four-color toner image, and is superimposed on the intermediate transfer belt 71 to form a color image, and then the color image is formed on the sheet S. Transfer is completed and photo printing is completed.

  As described above, in the second embodiment, since photo printing that requires gradation reproducibility is performed by executing the double-sided scanning mode, the resolution in the sub-scanning direction is doubled compared to when the single-sided scanning mode is executed. High-definition photo printing becomes possible. Further, the drive level during double-sided scanning is set to a level smaller than the drive level during single-sided scanning. Therefore, it is possible to prevent the toner from adhering more than necessary in the double-sided scanning mode, and it is possible to perform photographic printing with a good image.

<Third Embodiment>
FIG. 15 is an explanatory diagram of the scanning pitch in the double-sided scanning mode. Note that the one-dot chain line in FIG. 15 is a virtual line indicating the trajectory of the scanning line. As indicated by symbols PT1 to PT3 in FIG. 15, the scanning pitch in the sub-scanning direction in the double-sided scanning mode is not constant. Therefore, if the light amount of the latent image forming light beam in the double-sided scanning mode is excessively reduced, the toner adhesion amount is excessively reduced, and the image defect that the line formed in the sub-scanning direction is interrupted at a wide scanning pitch. appear. Therefore, in the third embodiment, the drive level during double-sided scanning set in the light source drive unit 1021 in the double-sided scanning mode is determined according to the maximum value of the scanning pitch in the sub-scanning direction during the double-sided scanning mode. It is composed. That is, the drive level at the time of both-side scanning is determined so that the width of the toner image formed on the surface of the photoconductor 2 in the sub-scanning direction is equal to or greater than the maximum value of the scanning pitch in the both-side scanning mode. With this configuration, as shown in FIG. 15, even when the scanning pitch is maximum, the lines formed in the sub-scanning direction are not interrupted, and good image formation is possible. In addition, since the basic composition of the apparatus concerning 3rd Embodiment is the same as 1st Embodiment, it attaches | subjects the same and equivalent code | symbol, and abbreviate | omits description.

<Fourth embodiment>
Incidentally, as shown in FIGS. 7B and 7C, in the above embodiment, the beam width in the sub-scanning direction of the latent image forming light beam is set to be equal to or larger than the scanning pitch in the sub-scanning direction in the one-side scanning mode. . Accordingly, as shown in FIG. 7C, the latent image forming light beams overlap between adjacent scanning lines in the one-side scanning mode. Consider the influence of the overlap of the latent image forming light beams on the image formed in the double-sided scanning mode. When the overlap of the latent image forming light beams is relatively large, even in the double-sided scanning mode, the areas where the latent image forming light beams scan are greatly overlapped between adjacent scanning lines. On the other hand, when the overlap of the latent image forming light beams is relatively small, the overlap of the areas scanned by the latent image forming light beams between the adjacent scanning lines is relatively small even in the double-sided scanning mode. Therefore, if the light quantity of the latent image forming light beam in the double-sided scanning mode is made constant regardless of the degree of overlap of the latent image forming light beams, the following image problems may occur. That is, for example, when the degree of overlap is large, unnecessary toner may adhere to the overlapping portions of the latent image forming light beams in the double-sided scanning mode, and image defects may occur. On the other hand, when the degree of overlap is small, there is a case where an adverse effect on the image that the line formed in the sub-scanning direction is interrupted in the double-sided scanning mode may occur.

  Therefore, in the fourth embodiment, the driving level at the time of double-sided scanning set in the light source driving unit 1021 in the double-sided scanning mode is determined based on the beam width in the subscanning direction of the latent image forming light beam and the scanning in the subscanning direction at the time of single-sided scanning. It is configured so as to be determined according to the ratio with the pitch. That is, the drive level at the time of both-side scanning can be determined according to the degree of overlap of the above-described latent image forming light beams by determining the drive level at the time of both-side scanning according to such a ratio. is doing. More specifically, when the degree of overlap of the latent image forming light beams is large, the drive level during both-side scanning is set low so that the amount of light of the latent image forming light beams is relatively small, and latent image formation is performed. When the degree of overlap of the light beams for use is small, the drive level at the time of both-side scanning is set high so that the amount of light of the latent image forming light beam is relatively large. And the above-mentioned trouble is prevented by comprising in this way. That is, when the degree of overlap is relatively large, the amount of light of the latent image forming light beam is suppressed, so that excessive toner adhesion can be prevented and a good image can be formed. On the other hand, when the degree of overlap is relatively small, the latent image forming light beam is configured to have a certain amount of light. It is possible to prevent an image problem that the amount is excessively reduced and lines formed in the sub-scanning direction are interrupted in the double-sided scanning mode. Therefore, a good image can be formed. In addition, since the basic composition of the apparatus concerning 4th Embodiment is the same as 1st Embodiment, it attaches | subjects the same and equivalent code | symbol, and abbreviate | omits description.

<Fifth Embodiment>
Further, as shown in FIG. 16, a case is considered where the ratio of the effective image area to the scanning area (scanning efficiency) is small and the minimum scanning pitch and the maximum scanning pitch in the double-sided scanning mode can be regarded as substantially the same. A one-dot chain line in FIG. 16 is a virtual line indicating the trajectory of the scanning line. In such a case, the scanning pitch in the double-sided scanning mode can be regarded as approximately half the scanning pitch in the single-sided scanning mode. Therefore, in the fifth embodiment, the drive level during double-sided scanning set in the light source drive unit 1021 in the double-sided scanning mode is set, and the light amount of the latent image forming light beam in the double-sided scanning mode is the latent image formation in the single-sided scanning mode. It is configured so as to be determined to be less than the light amount of the light beam for use and more than half. In this way, by forming the light amount of the latent image forming light beam in the double-sided scanning mode to be more than half the light amount of the latent image forming light beam in the single-sided scanning mode, it is formed in the double-sided scanning mode. The width of the toner image in the sub-scanning direction is approximately half or more than the width of the toner image formed in the one-side scanning mode in the sub-scanning direction. Therefore, excessively suppressing the amount of the latent image forming light beam in the double-sided scanning mode excessively reduces the toner adhesion amount, and the image forming effect that the line formed in the sub-scanning direction is interrupted in the double-sided scanning mode. Can be prevented, and a good image can be formed. In addition, since the basic structure of the apparatus concerning 5th Embodiment is the same as 1st Embodiment, it attaches | subjects the same and equivalent code | symbol, and abbreviate | omits description.

<Others>
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 first or second embodiment, the double-sided scanning mode and the single-sided scanning mode are switched based on whether the required resolution or gradation reproducibility is necessary, but the criteria for switching the scanning mode are limited to these. However, the present invention can be applied to all image forming apparatuses configured to be switchable between the double-sided scanning mode and the single-sided scanning mode.

  In the above embodiment, the latent image forming operation is controlled based on the horizontal synchronization signal detected on the opposite side of the drive motor MT in the main scanning direction X. However, the number and arrangement of sensors are limited to this. It is not a thing. For example, as shown in FIG. 17, both ends of the scanning path of the scanning light beam may be guided to the horizontal synchronization sensors 60A and 60B by the folding mirrors 69a and 69b. In this apparatus, signals are output from the horizontal synchronization sensors 60A and 60B at the timing when the scanning light beams are received by the horizontal synchronization sensors 60A and 60B and pass the sensor position (amplitude angle θs). Therefore, the latent image forming operation may be controlled based on the output signals of the sensors 60A and 60B. In addition, since detection signals can be obtained on both sides in the main scanning direction X, latent image formation is performed based on detection signals output from a sensor (detection unit) disposed upstream in the scanning direction of the latent image forming light beam. The operation may be controlled. Further, as shown in FIG. 18, the scanning light beam may be detected by one horizontal synchronization sensor 60C and folding mirrors 69c to 69e.

  In the first to fifth embodiments, only the light beam SL1 scanned in the (+ X) direction is used as the latent image forming light beam in the one-side scanning mode, but the light beam SL2 scanned in the (−X) direction is used. You may make it use. In short, the latent image forming light beam may be configured to be unidirectionally scanned in the first direction (+ X) or the second direction (−X) of the main scanning direction X.

  In the above-described embodiment, the present invention is applied to a so-called tandem color printer, but the scope of the present invention is not limited to this. For example, only a so-called four-cycle printer or single color printing is used. The present invention can also be applied to a monochrome printer.

  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 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 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. 1. 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. FIG. 2 is a diagram showing a line latent image formed by the image forming apparatus of FIG. 1. The figure which shows the relationship between the beam width and scanning pitch at the time of the one-side scanning mode. 6 is a flowchart illustrating the operation of the image forming apparatus according to the first embodiment. The figure which shows the latent image formed by the latent image formation operation | movement of 1st Embodiment. FIG. 6 is a diagram illustrating overlapping of toner images in a double-sided scanning mode. FIG. 4 is a diagram illustrating a toner image formed according to the present invention. Explanatory drawing about the means to implement | achieve gradation reproducibility. 10 is a flowchart illustrating an operation of the image forming apparatus according to the second embodiment. The figure which shows the latent image formed by the latent image formation operation | movement of 2nd Embodiment. Explanatory drawing about the scanning pitch at the time of double-sided scanning mode. Explanatory drawing about the scanning pitch when scanning efficiency is low. FIG. 6 is a diagram showing another embodiment of the image forming apparatus according to the present invention. FIG. 5 is a diagram showing another embodiment of the image forming apparatus according to the present invention.

Explanation of symbols

  2, 2Y, 2M, 2C, 2K ... photosensitive member (latent image carrier), 6, 6Y, 6M, 6C, 6K ... exposure unit (latent image forming unit), 60, 60A to 60C ... horizontal synchronization sensor (detector) 62, 62Y, 62M, 62C, 62K ... laser light source, 71 ... intermediate transfer belt (transfer medium), 651 ... deflection mirror surface, DT1, DT2, DT (n-1), DTn ... gradation data (image information) ), IR ... effective image area, Ly, Lm, Lc, Lk ... scanning light beam, LI (+ X), LI (-X) ... line latent image, MT ... drive motor (drive means), PT, PT1, PT2 , PT3: scanning pitch, SL1, SL2: scanning light beam, SR: scanning region, X: main scanning direction, Y: sub-scanning direction

Claims (2)

An effective image area having a predetermined width in the main scanning direction is provided on the surface, and a latent image carrier in which the surface is driven in the sub-scanning direction;
The latent image forming light is configured to be able to scan the scanning region including the effective image region in the main scanning direction by a deflection mirror that oscillates the light beam emitted from the light source driven by the light source driving unit. A latent image forming means for irradiating the effective image area with a beam to form a latent image in the effective image area;
A one-sided scanning mode in which the latent image forming light beam is scanned only in the first direction of the main scanning direction, and a double-sided scanning mode in which scanning is performed in both the first direction and the second direction opposite to the first direction. Scanning mode control means for selectively switching,
The beam width in the sub-scanning direction of the latent image forming light beam has a length equal to or greater than the scanning pitch in the sub-scanning direction in the one-side scanning mode,
The light source driving unit drives the light source so that the light amount of the latent image forming light beam in the double-sided scanning mode is smaller than the light amount of the latent image forming light beam in the one-sided scanning mode; The light quantity of the latent image forming light beam in the double-sided scanning mode is set according to the ratio of the beam width in the sub-scanning direction and the scanning pitch of the latent image forming light beam in the one-sided scanning mode. image forming apparatus characterized by that. An effective image area having a predetermined width in the main scanning direction is provided on the surface, a latent image carrier whose surface is driven in the sub-scanning direction, and a light beam emitted from a light source driven by a light source driving unit. The scanning area including the effective image area can be scanned in the main scanning direction by the oscillating deflecting mirror, and the effective image area is irradiated with a light beam for forming a latent image on the effective image area. In the image forming apparatus including a latent image forming unit that forms a latent image, the one-side scanning mode that scans the latent image forming light beam only in the first direction of the main scanning direction, the first direction, and the first direction An image forming method for forming a latent image in a selected scanning mode by selectively switching between a double-sided scanning mode for scanning in both directions of the second direction opposite to the one direction,
The beam width in the sub-scanning direction of the latent image forming light beam is set to a length equal to or longer than the scanning pitch in the sub-scanning direction in the one-side scanning mode,
The light source is driven so that the light amount of the latent image forming light beam in the double-sided scanning mode is smaller than the light amount of the latent image forming light beam in the one-sided scanning mode, and in the one-sided scanning mode A light amount of the latent image forming light beam in the double-sided scanning mode is set according to a ratio between a beam width in the sub-scanning direction of the latent image forming light beam and a scanning pitch. Image forming method.

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