JP6429641B2 - Image forming apparatus and data processing apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus and a data processing apparatus that generate image data for forming images at different resolutions.

  2. Description of the Related Art Conventionally, there has been known an image forming apparatus that forms a nip portion between a photosensitive member and an intermediate transfer member, and transfers a toner image from the photosensitive member to the intermediate transfer member by forming an electric field in the nip portion. In the image forming apparatus, a phenomenon occurs in which the relative speed between the surface speed of the photosensitive member and the surface speed of the intermediate transfer member differs depending on whether or not toner is present in the nip portion. Due to this phenomenon, the frictional force between the photosensitive member and the intermediate transfer member fluctuates. For example, the rotational speed of the photosensitive member when there is no toner in the nip portion is higher than the rotational speed when there is toner in the nip portion. The phenomenon of becoming faster occurs. If the rotational speed of the photoconductor changes due to the presence or absence of toner in the nip portion, color misregistration occurs in a color image forming apparatus, or the intermediate transfer body rotates in a monochrome image forming apparatus and a color image forming apparatus. There has been a problem that the length of the image in the direction is different from the ideal length. For such a problem, Patent Document 1 proposes an image forming apparatus that forms a predetermined number of minute dots that are difficult to visually recognize per unit area so that toner is always present in the nip portion. .

JP 2004-117602 A

  It is desirable that the data processing unit for adding minute dots can generate image data having a common number of bits regardless of the resolution, and can add minute dots to the image data.

The image forming apparatus of the present invention includes a first resolution mode for forming an image with a first resolution, a second resolution mode for forming an image with a second resolution higher than the first resolution, In the image forming apparatus capable of switching between, a rotating photoconductor, a light source for emitting a light beam for forming an electrostatic latent image on the photoconductor, and a light beam emitted from the light source on the photoconductor A nip part is formed between the deflecting means for deflecting the light beam, the developing means for developing the electrostatic latent image formed on the photoconductor with toner, and the photoconductor, A transfer means for transferring the toner image transferred on the intermediate transfer belt to a recording medium; and an intermediate transfer belt for transferring the developed toner image on the photoconductor in the nip portion; Resolution mode and previous The deflecting unit is controlled so that the scanning speed of the light beam on the photoconductor is the same in the second resolution mode, and the rotational speed of the photoconductor in the first resolution mode is the second resolution. So that the rotational speed of the intermediate transfer belt becomes a speed corresponding to the rotational speed of each of the photosensitive bodies in the first resolution mode and the second resolution mode. A control means for controlling the photosensitive member and the intermediate transfer belt; and generating N-bit (N ≧ 2) image data for one pixel in the first resolution in the first resolution mode; A first data processing means for generating N-bit image data for a plurality of pixels at the second resolution in the resolution mode; And N bit image data obtained by adding the N bit additional data to the N bit image data generated in the first resolution mode. And second data processing means for generating N-bit image data obtained by adding the N-bit additional data to the N-bit image data generated in the second resolution mode; Conversion means for converting the N-bit image data to which data has been added into drive data composed of binary values of data that emits the light beam and data that does not emit the light beam, wherein the first resolution mode The N-bit image data to which the additional data is added based on the first conversion table corresponding to the first resolution in Conversion that converts the N-bit image data to which the additional data is added into the driving data based on a second conversion table corresponding to the second resolution in the second resolution mode. And drive means for driving the light source based on the drive data converted by the conversion means.

Further, the data processing apparatus of the present invention includes a first resolution mode for forming an image with a first resolution and a second resolution mode for forming an image with a second resolution higher than the first resolution. An image forming apparatus capable of switching between: a rotating photosensitive member; a light source that emits a light beam for forming an electrostatic latent image on the photosensitive member; and a light beam emitted from the light source. A nip portion between a deflecting unit that deflects the light beam so as to scan the photoconductor, a developing unit that develops the electrostatic latent image formed on the photoconductor with toner, and the photoconductor. A transfer means for transferring the toner image transferred onto the intermediate transfer belt onto a recording medium, and an intermediate transfer belt to which the toner image developed on the photoconductor is transferred at the nip portion. The first resolution mode In the second resolution mode, the deflecting unit is controlled so that the scanning speed of the light beam on the photoconductor is the same, and the rotational speed of the photoconductor in the first resolution mode is the second resolution mode. And the rotation speed of the intermediate transfer belt becomes a speed corresponding to the rotation speed of each of the photoconductors in the first resolution mode and the second resolution mode. As described above, in the data processing apparatus provided in the image forming apparatus including the photosensitive member and the control unit that controls the intermediate transfer belt, N bits for one pixel in the first resolution in the first resolution mode ( N ≧ 2) image data is generated, and a plurality of pixels in the second resolution are generated in the second resolution mode. First data processing means for generating N-bit image data, storage means for storing N-bit additional data for forming minute dots, and the N-bit image generated in the first resolution mode N-bit image data obtained by adding the N-bit additional data to the data is generated, and the N-bit additional data is added to the N-bit image data generated in the second resolution mode. The second data processing means for generating N-bit image data, and the N-bit image data to which the additional data is added are composed of binary values of data for emitting the light beam and data for not emitting the light beam. Conversion means for converting the drive data into drive data based on a first conversion table corresponding to the first resolution in the first resolution mode. Then, the N-bit image data to which the additional data is added is converted into the drive data, and the additional data is converted based on a second conversion table corresponding to the second resolution in the second resolution mode. A conversion unit that converts the added N-bit image data into the drive data, and a drive unit that drives the light source based on the drive data converted by the conversion unit.

  According to the present invention, it is possible to realize the formation of minute dots corresponding to the resolution.

Schematic sectional view of an image forming apparatus according to the present embodiment The principal part enlarged view of the image forming apparatus which concerns on a present Example Schematic of the optical scanning device according to the present embodiment The figure which shows the spot diameter of the laser beam on the photosensitive drum Control block diagram of the image forming apparatus according to the present embodiment Block diagram of the image processing unit according to the present embodiment Block diagram of the PM control unit according to the present embodiment Block diagram of the DM control unit according to the present embodiment The figure which shows the bit pattern structure in 600 dpi mode and 1200 dpi mode The figure which shows the output circuit based on a present Example Clock signal timing chart Control flow executed by the controller according to this embodiment The figure which shows the bit pattern structure of image data and additional data The figure which divided the unit area (25.4 mm x 25.4 mm) by the pixel unit of each resolution, and showed the lighting state of the light beam in each pixel Conversion table used by the controller according to this embodiment A comparative example in which a unit area (25.4 mm × 25.4 mm) is divided in units of pixels of each resolution and the lighting state of the light beam in each pixel Comparative example for the conversion table used by the controller according to this embodiment Explanation of the cause of blank pixels

(Example 1)
(Image forming device)
FIG. 1 is a schematic sectional view of the image forming apparatus 100. The image forming apparatus 100 is a color image forming apparatus that forms an image using toners of yellow (Y), magenta (M), cyan (C), and black (Bk). The image forming apparatus 100 according to the present exemplary embodiment is an apparatus capable of forming an image at a plurality of resolutions, that is, 600 dpi and 1200 dpi.
The image forming apparatus 100 includes optical scanning devices 101Y, 101M, 101C, and 101Bk that are exposure units that expose a photosensitive drum, which will be described later, and 102Y, 102M, 102C, and 101Bk that are image forming units. In addition, toner storage units 103Y, 103M, 103C, and 103Bk that store toner to be supplied to each image forming unit are provided.

  As an apparatus for transferring a toner image formed on a photosensitive drum included in each image forming unit, the image forming apparatus 100 is a transfer roller 104Y, 104M, 104C, 104Bk, which is a primary transfer apparatus, an intermediate transfer belt 105, a roller. 106, 120, 121, and a secondary transfer device 107 are provided.

  The intermediate transfer belt 105 is stretched around a plurality of rollers 106, 120, and 121, and rotates in the direction of the arrow in FIG. The toner image formed in each image forming unit is transferred onto the intermediate transfer belt 105 by the primary transfer devices 104Y, 104M, 104C, and 104Bk. A recording medium is conveyed between the rollers 106 and the secondary transfer device 107 from the paper feed trays 108 and 109 and the manual feed tray 110. The toner images of the respective colors transferred onto the intermediate transfer belt 105 are transferred to a recording medium conveyed between the roller 106 and the secondary transfer device 107 by the secondary transfer device 107.

  The recording medium on which the toner image is transferred is conveyed to the fixing device 111. The fixing device 111 includes a heating roller 112 and a pressure roller 113. The toner image to which the toner image has been transferred is fixed on the recording medium by passing between the heating roller 112 and the pressure roller 113. The recording medium subjected to the fixing process is discharged to the paper discharge unit 114 or 115.

  The image forming apparatus 100 according to the present exemplary embodiment includes a reading device 116. The reading device 116 includes a document table 122 on which a document is placed, and a document pressure plate 117 that sandwiches the document between the document table 122 and the document table 122. Light is irradiated on the document placed on the document table 122. The reading device 116 includes a light receiving element 118 (CCD or CMOS) that receives reflected light from a document. Note that the reading device 116 may include an ADF (Automatic Document Feeder).

  Next, the respective color image forming units 102Y, 102M, 102C, and 101Bk will be described with reference to FIG. Since the configurations of the image forming units for the respective colors in this embodiment are the same, the subscripts Y, M, C, and Bk that indicate colors are omitted in the following description.

  As shown in FIG. 2, the image forming unit 102 includes a photosensitive drum 201 that is a photosensitive member, a charging device 202, a developing device 203, a cleaning device 205, and a pre-exposure device 206. The charging device 202 charges the surface of the photosensitive drum 201. The photosensitive drum 201 charged by the charging device 202 is exposed by the light beam emitted from the optical scanning device 101. By exposure with the light beam, an electrostatic latent image is formed on the photosensitive drum 201 (on the photosensitive member).

  The developing device 203 includes a toner carrying roller 204 that carries toner. The electrostatic latent image is developed with toner carried on the toner carrying roller 204. The toner image developed on the photosensitive drum is transferred from the photosensitive drum 201 to the intermediate transfer belt 105 at the primary transfer portion by a bias applied by the transfer roller 104. The toner transferred to the photosensitive drum 201 (on the photosensitive member) without being transferred to the intermediate transfer belt 105 is collected by a cleaning device. The pre-exposure device 206 is provided to remove the potential on the photosensitive drum 105 on which the electrostatic latent image is formed.

  The transfer roller 104 is a sponge rubber member. The transfer roller 104 is pressed against the photosensitive drum 201 via the intermediate transfer belt 105 with a linear pressure of 70 g / cm or less. As a result, the transfer roller 104 is deformed, and as shown in FIG. 2, a transfer nip portion T <b> 1 is formed between the photosensitive drum 201 and the intermediate transfer belt 105 of this embodiment so as to sandwich the toner image. The width of the transfer nip T1 in the rotation direction of the intermediate transfer belt 105 is about 5 mm.

  Next, the optical scanning device will be described with reference to FIG. Since the configurations of the optical scanning devices for the respective colors in this embodiment are the same, the subscripts Y, M, C, and Bk indicating the colors are omitted in the following description.

  As shown in FIG. 3, the optical scanning device 101 of this embodiment includes a semiconductor laser 301 as a light source, a collimator lens 302, and a polygon mirror (rotating polygonal mirror) 303 as a deflecting unit. The optical scanning device 101 also includes a beam detector 304 (hereinafter referred to as BD 304), an fθ lens (scanning lens) 305, and a folding mirror 306.

  The semiconductor laser 301 of this embodiment has one light emitting point. A light beam (laser light) is emitted from one light emitting point. The light beam emitted from the semiconductor laser 301 is converted into parallel light by the collimator lens 302. The polygon mirror 303 rotates in the direction of the arrow in FIG. The light beam that has passed through the collimator lens 302 is deflected by the rotated polygon mirror 304 and enters the fθ lens 305. The fθ lens 305 is a lens for converting the scanning speed of the light beam on the photosensitive drum 201 to be substantially constant regardless of the exposure position. The light beam that has passed through the fθ lens 305 is guided onto the photosensitive drum 201 by the folding mirror 306. The light beam is deflected by the polygon mirror 303 to scan the photosensitive drum 201 in the arrow direction (longitudinal direction of the photosensitive drum 201 / main scanning direction). A BD 304 is a sensor for defining an image writing position in the scanning direction in which the light beam scans on the photosensitive drum 201. A BD signal is generated by receiving the light beam deflected by the polygon mirror 304. A controller to be described later controls the output timing of image data in accordance with the generation timing of the BD signal.

  FIG. 4A is a diagram showing the scanning position relationship between the Nth and N + 1th laser spots on the photosensitive drum 201 at a resolution of 600 dpi (first resolution mode). FIG. 4B is a diagram showing a scanning positional relationship between the Nth scanning and N + 1th scanning laser spots on the photosensitive drum 201 in a resolution of 1200 dpi (second resolution mode).

  When an image is formed with a resolution of 600 dpi, it is necessary to form 600 scanning lines within one inch. Therefore, as shown in FIG. 4A, the photosensitive drum is set so that the distance between the scanning lines is about 42.3 μm. The rotation speed 201 (surface movement speed) and the rotation speed of the polygon mirror 303 are set. On the other hand, when forming an image with a resolution of 1200 dpi, since it is necessary to form 1200 scanning lines within 1 inch, as shown in FIG. 4B, the spacing between the scanning lines is about 21.3 μm. The rotational speed of the photosensitive drum 201 and the rotational speed of the polygon mirror 303 are set. In the image forming apparatus 100 according to the present exemplary embodiment, when a controller described later sets the rotation speed of the photosensitive drum 201 to 117 mm / sec when an image is formed at a resolution of 600 dpi and forms an image at 1200 dpi, the controller of the photosensitive drum 201 The rotation speed is set to 58.5 mm / sec. On the other hand, the controller described later sets the rotation speed of the polygon mirror 303 to be the same at a resolution of 600 dpi and a resolution of 1200 dpi.

  Since the same optical system (lens and mirror) is used when forming an image with a resolution of 600 dpi and when forming an image with a resolution of 1200 dpi, the diameter of the light beam guided onto the photosensitive drum 201 is either 600 dpi or 1200 dpi. In this case, it is about 70 μm.

  Next, a control block diagram of the image forming apparatus 100 in this embodiment will be described with reference to FIG. The image forming apparatus 100 according to the present exemplary embodiment includes a controller 500 (control unit), a crystal oscillator 501, an operation unit 502, a data reception unit 505, a ROM 506, and a RAM 507. The image forming apparatus 100 according to the present exemplary embodiment includes a DM driver 512, a DM driver 514, a motor 514 (M514), a motor 515 (M515), an encoder 516 (EC516), and an encoder 517 (EC517). Each optical scanning device includes a PM driver 508, an LD driver 509, a BD 304, an LS motor 510, and an LD 511.

  The controller 500 controls each unit based on information stored in the ROM 506 and the RAM 507 which are storage units. The controller 500 controls each unit based on information supported by the user from the touch panel 502 provided in the operation unit 502. Further, the controller 500 operates the reading device 116 and the image forming apparatus 100 when the start button 504 is pressed by the user.

  A read signal read by the CCD 118 of the reading device 116 is input to the controller 500. The data receiving unit 505 receives image data and resolution data (resolution information) from an external information device such as a PC. The controller 500 receives image data and resolution data from the data receiving unit 505. The controller 500 generates image data by performing image processing on signals input from the CCD 118 and the data receiving unit 505.

  The controller 500 includes a PM control unit 701 shown in FIG. The optical scanning device 101 includes an LS motor 304 that rotates the polygon mirror 303 and a PM driver 509 (polygon mirror motor driver) for driving the LS motor 304. The LS motor 304 is a DC motor, and the PM driver 509 controls the rotational speed of the LS motor 304, that is, the rotational speed of the polygon mirror 303, by controlling the current value.

  The PM control unit 701 is a unit (module) that controls the PM driver 509 corresponding to the polygon mirror 303 of each color. Data PM_tgt indicating the target rotational speed of the polygon mirror 303 is input from the ROM 506 to the PM control unit 701. PM_tgt is reference cycle data for comparison with the cycle of the BD signal. Further, the PM control unit 701 receives the target phase difference information Phase_tgt of rotation of the polygon mirror 304 of each color from the RAM 507. In this embodiment, PM_tgt uses common data with a resolution of 600 dpi and a resolution of 1200 dpi.

  Phase_tgt is a target value that is set based on the result of color misregistration detection after executing known color misregistration correction control. Phase_tgt is data for controlling the rotational phase relationship of the polygon mirrors of the respective colors. By controlling the phase between the polygon mirrors based on the data, the color shift in the rotational direction (sub-scanning direction) of the photosensitive drum is reduced to 1. Control can be performed in units of less than pixels. In this embodiment, Phase_tgt uses separate data with a resolution of 600 dpi and a resolution of 1200 dpi.

  The PM control unit 701 receives a BD signal from each of the BDs 304Y, 304M, 304C, and 304Bk. The PM control unit 701 compares the period of each BD signal with PM_tgt. Then, according to the comparison result, an acceleration signal is transmitted to the PM driver corresponding to the polygon mirror requiring acceleration, and a deceleration signal is transmitted to the PM driver corresponding to the polygon mirror requiring deceleration. Further, the PM control unit 701 compares the phase difference of each BD signal with Phase_tgt, and transmits an acceleration signal or a deceleration signal to the PM driver when phase adjustment is necessary. Each PM driver controls a current value supplied to the corresponding LS motor in accordance with an acceleration signal or a deceleration signal from the PM control unit 701.

  The controller 500 includes a DM control unit 702 shown in FIG. The DM control unit 702 is a unit (module) that controls the DM driver 512 and the DM driver 513 shown in FIG. The image forming apparatus 100 according to this embodiment includes a motor 514 for rotating the photosensitive drum 201Bk and the intermediate transfer belt 105, and a motor 515 for rotating the photosensitive drums 201Y, 201M, and 201Bk. The photosensitive drum 201Bk and the intermediate transfer belt 105 are driven to rotate by a common motor 514, but have different gear ratios. Therefore, in the image forming apparatus 100 of this embodiment, the rotation speed of the intermediate transfer belt 105 (the surface carrying the toner image) is about 0.20% faster than the rotation speed of the photosensitive drum 201Bk (surface speed). . By configuring in this way, “missing” of the image is suppressed.

  Resolution data is input to the DM control unit 702. The DM control unit 702 receives DM_tgt indicating the target rotational speed of the photosensitive drum corresponding to each resolution from the ROM 506 based on the input resolution data. In the image forming apparatus 100 of this embodiment, the target rotational speed of each photosensitive drum when an image is formed at a resolution of 600 dpi is 117 mm / sec, and the target rotational speed of each photosensitive drum when an image is formed at a resolution of 1200 dpi is It is 58.5 mm / sec.

  An encoder 516 is attached to the photosensitive drum 201Bk. The encoder 516 outputs a signal EC_1 having a period corresponding to the rotation speed of the photosensitive drum 201Bk. On the other hand, an encoder 517 is attached to at least one of the photosensitive drums 201Y, 201M, and 201C. The encoder 517 outputs a signal EC_2 having a period corresponding to the rotation speed of the attached photosensitive drum.

  The DM control unit 702 outputs DMdrive_1, which is an acceleration signal or a deceleration signal, to the DM driver 512 based on the comparison result between EC_1 and DM_tgt. Also, the DM control unit 702 outputs DMdrive_2, which is an acceleration signal or a deceleration signal, to the DM driver 513 based on the comparison result between EC_2 and DM_tgt. The DM driver 512 drives the motor 514 based on DMdrive_1, and the DM driver 513 drives the motor 514 based on DMdrive_2.

  With the above configuration, when the photosensitive drum 201Bk rotates at 117 mm / sec, the intermediate transfer belt 105 rotates at 119.4 mm / sec depending on the gear ratio. On the other hand, when the photosensitive drum 201Bk rotates at 58.5 mm / sec, the intermediate transfer belt 105 rotates at 59.7 mm / sec according to the gear ratio.

  With this configuration, the image forming apparatus 100 according to the present exemplary embodiment can control the rotation speed of the photosensitive drum 201 and the intermediate transfer belt 105 according to the resolution.

  Next, an image processing unit (image processing module) included in the controller 500 will be described with reference to FIGS. 6, 9, 10, and 11.

  FIG. 6 is a control block diagram of the image processing unit. The image processing unit includes a data processing unit 601 (data processing unit I), a data processing unit 602 (data processing unit II), a PLL circuit 603, an output circuit 604Y, an output circuit 604M, an output circuit 604C, and an output circuit 604Bk. The data processing unit 601 receives RGB data (Data_R, Data_G, Data_B) from the CCD 118 or the data receiving unit 505. Resolution data is input to the data processing unit 601, and processing of input image data corresponding to the resolution data is executed. For example, the data processing unit 601 converts RGB data into 8-bit multi-value data indicating the densities of yellow, magenta, cyan, and black in accordance with the resolution data, and performs known γ correction according to engine characteristics. Run. The data processing unit 601 generates 4-bit image data Data_Y1, Data_M1, Data_C1, and Data_Bk1 by executing multi-value dither processing or error diffusion processing.

  The data processing unit 601 is a first IC (Integrated Circuit), and the data processing unit 602 is a second IC (Integrated Circuit). The controller 500 in this embodiment is an interface including four data buses for transferring density data from the data processing unit 601 to the data processing unit 602, and the 4-bit unit (N bits) is used regardless of the resolution using the interface. The density data is transferred in units (N ≧ 2). That is, the data processing unit 601 is configured to transmit 4-bit data in parallel to the data processing unit 602 in synchronization with the reference clock (reference CLK) input from the crystal oscillator 501. Note that the data processing unit 601 and the data processing unit 602 may be different modules provided in the same IC.

  In response to such an interface configuration, the data processing unit 601 varies the number of bits of image data allocated per pixel according to the resolution.

  FIG. 9 is a diagram illustrating image data Data_Y1, Data_M1, Data_C1, and Data_Bk1 (controller image) generated by the data processing unit 601 according to the resolution. As shown in FIG. 9A, when an image is formed at a resolution of 600 dpi (600 dpi mode), the data processing unit 601 generates a 4-bit bit pattern for one pixel. That is, in the image forming apparatus 100 of the present embodiment, when an image is formed at a resolution of 600 dpi, the density of one pixel is defined by a 4-bit bit pattern. Accordingly, the density of one pixel having a resolution of 600 dpi is defined by 16 gradations.

  On the other hand, as shown in FIG. 9B, when an image is formed at a resolution of 1200 dpi (1200 dpi mode), the data processing unit 601 generates 1-bit image data for one pixel. That is, as shown in FIG. 9B, the density of the first pixel is defined by binary data of bit 2 and is adjacent to the first pixel in the scanning direction of the light beam on the downstream side in the scanning direction. The pixel density is defined by binary data of bit0. Bit3 and bit1 are always “0” data, and are not used for density expression. Therefore, in the image forming apparatus 100 of this embodiment, when forming an image with a resolution of 1200 dpi, the density of one pixel with a resolution of 1200 dpi is defined by two gradations (0 or 1). Therefore, the 4-bit bit pattern generated by the data processing unit 601 indicates one of the values 0/1/4/5 in decimal.

  The data processing unit 602 receives image data Data_Y1, Data_M1, Data_C1, and Data_Bk1 output from the data processing unit 601 in units of 4 bits. Then, the 4-bit image data Data_Y1, Data_M1, Data_C1, and Data_Bk1 are converted into 16-bit binary PWM data Data_Y2, Data_M2, Data_C2, and Data_Bk2 using the data conversion table shown in FIG.

  15A shows a data conversion table (first conversion table) used by the data processing unit 602 in the resolution 600 dpi mode, and FIG. 15B shows data used by the data processing unit 602 in the resolution 1200 dpi mode. It is a conversion table (second conversion table). The vertical axis of the table indicates a value obtained by converting the value of 4-bit data output by the data processing unit 601 into a decimal number, and the horizontal axis of the table indicates the binary bit after conversion output by the data processing unit 602. A pattern column is shown. As the conversion table, a table common to each color may be used, or a conversion table unique to each color may be used according to the characteristics of the semiconductor laser.

  Resolution data is input to the data processing unit 602. The data processing unit 602 selects a conversion table to be used based on the resolution data.

  When an image is formed at a resolution of 600 dpi, the density per pixel is defined by using all 4-bit bit patterns, and therefore, as shown in FIG. 15A, the conversion table contains 0 (“0000”) to 15 ( 16-bit binary PWM data is set for all gradation values of “1111”). On the other hand, when an image is formed with a resolution of 1200 dpi, the value indicated by the 4-bit bit pattern is within 3 bits even when processing for adding minute dots, which will be described later, is considered. The binary PWM data is set. “1” of the 16-bit binary PWM data is data for turning on (turning on) the semiconductor laser 301. “0” in the 16-bit binary PWM data is data for controlling the semiconductor laser 301 to a non-lighting (off) state.

  For example, consider a case where the data processing unit 602 converts 4-bit data “0110” into PWM data in a mode for forming an image with a resolution of 600 dpi. This 4-bit data is “6” when converted to decimal. Therefore, the data processing unit 602 converts the 4-bit “0110” bit pattern into 16-bit “1111111,000,000,000” using the data conversion table of FIG. On the other hand, consider a case where the data processing unit 602 converts 4-bit data of “0001” into PWM data in a mode for forming an image with a resolution of 1200 dpi. This 4-bit data is “1” when converted to decimal. Therefore, the data processing unit 602 converts the 4-bit “0001” bit pattern to 16-bit “1111111100000000” using the data conversion table of FIG.

  As described above, the data processing unit 602 generates the PWM data Data_Y2, Data_M2, Data_C2, and Data_Bk2 using the conversion table corresponding to each resolution. The data processing unit 602 outputs 16-bit PWM data Data_Y2, Data_M2, Data_C2, and Data_Bk2 to the output circuits 604Y, 604M, 604C, and 604Bk in parallel with the reference CLK.

  FIG. 10 is a diagram illustrating a schematic circuit configuration of the output circuits 604Y, 604M, 604C, and 604Bk. Hereinafter, the output circuit 604 will be described. The output circuit 604 is a parallel-serial conversion circuit that converts 16-bit data output in parallel from the data processing unit 602 into a PWM signal that is a serial signal.

  The output circuit 604 includes an OR circuit 1001, flip-flops 1002-0 to 15, AND circuits 1003-1 to 15-15, and an OR circuit 1005. As shown in FIG. 11A, the OR circuit 1001 and the flip-flops 1002-0 to 15 generate 16 timing signals (0) to (15) having different phases by 1 CLK of the high frequency CLK using the high frequency CLK. To do. The high frequency CLK is generated by the PLL 603 (Phase Locked Loop) shown in FIG. 6 multiplying the reference CLK by 16. A timing signal input to the OR circuit 1001 is a signal generated by the PLL 603 (Phase Locked Loop) shown in FIG. 6 in synchronization with the rising edge of the reference CLK.

  As shown in FIG. 10, PWM data Data_Y2, Data_M2, Data_C2, and Data_Bk2 of bits 0 to 15 (horizontal axis of the conversion table) output in parallel by the data processing unit 602 are input to the corresponding AND circuits 1003-0 to 1003-15, respectively. Is done. Further, as shown in FIG. 10, the 16 timing signals are input to the corresponding AND circuits 1003-0 to 1003-15, respectively. The OR circuit 1005 outputs a PWM signal (PWM_Y, PWM_M, PWM_C, PWM_Bk) to each LD driver (see FIG. 3) based on the outputs from the AND circuits 1003-0 to 1003-15. Each LD driver supplies a current to the LD when the PWM signal is at a high level, and stops supplying the current to the LD when the PWM signal is at a low level. Thus, by generating a PWM signal from the PWM data and performing on / off control of the LD according to the PWM signal, it is possible to perform light emission control of the semiconductor laser according to the image data generated by the data processing unit 602.

  Here, a method of adding minute dot data to the 4-bit image data output from the data processing unit 601 will be described. A nip portion T1 having a width of about 5 mm is formed between the intermediate transfer belt 105 and the photosensitive drum 201 in the belt conveyance direction. A speed difference of about 0.20% is provided between the photosensitive drum 201 and the intermediate transfer belt 105. In such a configuration, when the leading end of the image that is the toner image on the photosensitive drum 201 enters the nip portion T1 from the state where there is no toner image in the nip portion T1, the frictional force between the intermediate transfer belt 105 and the photosensitive drum 201 is obtained. Decrease. The intermediate transfer belt 105 and the photosensitive drum 201Bk are configured to be driven by the same motor. However, when the frictional force between the intermediate transfer belt 105 and the photosensitive drum 201 is reduced, the photosensitive drum 201Bk is rotated by an amount corresponding to the backlash of the gear. Speed is reduced. On the other hand, since the intermediate transfer belt 105 and the photosensitive drums 201Y, M, and C are driven by different motors, the frictional force between the intermediate transfer belt 105 and the photosensitive drums 201Y, M, and C is reduced, so that The rotational speeds of the drums 201Y, M, and C are instantaneously decreased. When the rotational speed of the photosensitive drum 201 is decreased, a portion where the interval between the scanning lines is narrowed is generated, and the density of the image of the portion becomes higher than necessary.

  In order to suppress such a phenomenon, there is a method of reducing a variation in frictional force between the photosensitive drum 201 and the intermediate transfer belt 105 by dispersing and forming a predetermined number of minute dots that are difficult to see per unit area. It is disclosed in Japanese Patent Application Laid-Open No. 2004-117602. Japanese Patent Application Laid-Open No. 2004-117602 discloses an image forming apparatus in which the formation rate of fine dots per unit area in a high image quality mode for forming an image with high resolution is lower than the formation rate of fine dots per unit area in a normal mode. doing.

  Hereinafter, a method for forming minute dots in a configuration in which the data output configuration of the data processing unit 601 is the same regardless of the resolution, which is a feature of the image forming apparatus of the present embodiment will be described.

  The data processing unit 602 illustrated in FIG. 6 adds minute dot data to the 4-bit data output from the data processing unit 601. Resolution data is input to the data processing unit 602. When the resolution data indicates 600 dpi, a register (not shown) in the controller 500 is set so that the data processing unit 602 generates image data formed by one minute dot in 16 pixels square at a resolution of 600 dpi. On the other hand, when the resolution data indicates 1200 dpi, a register (not shown) in the controller 500 is set so that the data processing unit 602 generates image data in which one minute dot is formed in every 32 pixels at a resolution of 1200 dpi. The By setting the registers in this way, the number of minute dots per unit area can be made the same in the resolution 600 dpi mode and the resolution 1200 dpi mode. Further, since the spot diameter of the laser beam does not change depending on the resolution, the toner amount of minute dots per unit area is the same in the resolution 600 dpi mode and the resolution 1200 dpi mode.

  FIG. 13 is a diagram illustrating a data processing method of the data processing unit 602. FIG. 13A shows the 4-bit bit patterns Data_Y1, Data_M1, Data_C1, and Data_Bk1 output from the data processing unit 601. The bit pattern in FIG. 13A is image data indicating that the density value of one pixel is 5 when the resolution is 600 dpi mode, and forms a toner image for two pixels when the resolution is 1200 dpi mode. Is image data.

  FIG. 13B shows additional data corresponding to the minute dots to be added. The additional data is 4-bit data, and is used for both the resolution of 600 dpi and the resolution of 1200 dpi. The additional data in the present embodiment is a 4-bit bit pattern “0010”.

  The data processing unit 602 generates image data with additional data as shown in FIG. 13C by calculating the logical sum of each bit in FIGS. 13A and 13B. For example, since the data of bit 0 in FIG. 13A is “1” and the data of bit 0 in FIG. 13B is “0”, the data processing unit 602 performs the data of bit 0 in FIG. As a result, data of “1” which is the logical sum of them is generated. The data processing unit 602 performs the same calculation for the other bit1, bit2, and bit3. Therefore, when a 4-bit bit pattern “0101” is input from the data processing unit 601 shown in FIG. 13A to the data processing unit 602, the data processing unit 602 calculates the logical sum of the additional data and performs a 4-bit calculation. Image data “0111” is generated.

  Next, the data processing unit 602 converts the image data of FIG. 13C into PWM data (drive data) using the conversion tables shown in FIGS. When the input resolution data indicates 600 dpi, the data processing unit 602 selects the conversion table in FIG. On the other hand, if the input resolution data indicates 1200 dpi, the data processing unit 602 selects the conversion table in FIG. The data processing unit 602 sets the selected conversion table in a register (not shown). At this time, the same address is assigned to the 16 values on the vertical axis of FIGS. 15 (a) and 15 (b).

  When the data processing unit 602 receives the bit pattern “0000” from the data processing unit 601 in the resolution 600 dpi mode, the data processing unit 602 adds the additional data “0010” to generate image data “0010”. Since this image data “0010” is “2” on the vertical axis of FIG. 15A, the data processing unit 602 converts “0010” into PWM data “1110000000000” using the conversion table of FIG. Convert to One pixel data input from the data processing unit 601 to the data processing unit 602 does not have a density value, but PWM data including “1” that causes the laser to be turned on when the data processing unit 602 adds additional data. Is output from the data processing unit 602.

  On the other hand, in the resolution 1200 dpi mode, when the data processing unit 602 receives the bit pattern “0000” from the data processing unit 601, the data processing unit 602 adds the additional data “0010” to generate image data “0010”. . Since this image data “0010” is “2” on the vertical axis of FIG. 15B, the data processing unit 602 converts “0010” into PWM data “1110000000000” using the conversion table of FIG. Convert to One pixel data input from the data processing unit 601 to the data processing unit 602 does not have a density value, but PWM data including “1” that causes the laser to be turned on when the data processing unit 602 adds additional data. Is output from the data processing unit 602.

  As described above, the data processing unit 602 generates a PWM pattern based on the image data generated by adding the additional data to the bit pattern input from the data processing unit 601 and the conversion table according to the resolution. The generated PWM pattern is converted into a PWM signal by the output circuit 604.

  FIG. 12 is a control flow of an image forming operation executed by the controller 500. The controller 500 starts this control flow when image data is input to the controller 500. In step S1201, the controller 500 determines whether the output resolution is 600 dpi or 1200 dpi based on the resolution data added to the image data input to the controller 500. If it is determined in step S1201 that the output resolution is 600 dpi, the controller 500 sets the resolution 600 dpi mode in the register (step S1202). On the other hand, when it is determined in step S1201 that the output resolution is 1200 dpi, the controller 500 sets the resolution 1200 dpi mode in the register (step S1203).

  Next, the controller 500 executes an image formation preparation operation according to the mode set in the register in step S1202 or step S1203 (step S1204). Specifically, the controller 500 controls the rotational speed of the photosensitive drum 201 in accordance with the resolution, and executes a preparatory operation such as setting one of the conversion tables in FIGS. 15A and 15B in the register. . In step S1205, the controller 500 determines whether the image formation preparation operation is completed. If it is determined in step S1205 that the image formation preparation operation has not been completed, the controller 500 returns the control to step S1204.

  If it is determined in step S1205 that the image formation preparation operation has been completed, the controller 500 starts image formation (step S1206). Subsequently, the controller 500 determines in step S1207 whether or not the image formation on one recording medium is completed. If it is determined in step S1207 that image formation on one recording medium has not been completed, the controller 500 continues the image forming operation in step S1206. On the other hand, if it is determined in step S1207 that image formation on one recording medium has been completed, the controller 500 determines in step S1208 whether all image forming jobs have been completed. If it is determined in step S1208 that all image forming jobs have not ended, the controller 500 returns control to step S1201 to determine the resolution of the image to be formed on the next recording medium. If it is determined in step S1208 that all image forming jobs have been completed, the controller 500 ends this control.

  FIG. 14A-1 is a diagram illustrating a lighting state of a light beam in each pixel by dividing a unit area (25.4 mm × 25.4 mm) by a pixel unit having a resolution of 600 dpi. At a resolution of 600 dpi, the unit area (25.4 mm × 25.4 mm) is divided into 256 pixels (16 pixels × 16 pixels). 25.4 mm in the main scanning direction corresponds to 256 pulses of high frequency CLK (16 pixels × 16 CLK / pixel). FIG. 14A-2 is an enlarged view of the pixel in which the minute dots in FIG. 14A-1 are formed.

  FIG. 14B-1 is a diagram illustrating a lighting state of a light beam in each pixel by dividing a unit area (25.4 mm × 25.4 mm) by a pixel unit having a resolution of 1200 dpi. At a resolution of 1200 dpi, the unit area (25.4 mm × 25.4 mm) is divided into 1024 pixels (32 pixels × 32 pixels). 25.4 mm in the main scanning direction corresponds to 256 pulses of high frequency CLK (32 pixels × 8 CLK / pixel). FIG. 14B-2 is an enlarged view of the pixel in which the minute dots in FIG. 14B-1 are formed.

  As shown in FIGS. 14 (a-1) and 14 (b-1), the controller 500 registers so that a minute dot is formed in one pixel per unit area (25.4 mm × 25.4 mm). Set. That is, the controller 500 provides pixels that form one minute dot for every 16 pixels in the main scanning direction and the sub-scanning direction in the resolution 600 dpi mode. The controller 500 also provides pixels that form one minute dot for every 32 pixels in the main scanning direction and the sub-scanning direction in the resolution 1200 dpi mode.

  The additional data for the minute dots uses the same data and the high frequency CLK for the resolution of 600 dpi and the resolution of 1200 dpi. Therefore, as shown in FIGS. 14 (a-2) and 14 (b-2), the minute dots in the main scanning direction are used. The lighting times of the semiconductor lasers for forming are the same. Further, the spot diameter of the light beam on the photosensitive drum does not change depending on the resolution. Therefore, in FIG. 14A and FIG. 14B, the toner amount of the minute dots is theoretically the same.

  Next, a comparative example for the present embodiment will be described. In FIG. 16A-1, similarly to FIG. 14A-1, the unit area (25.4 mm × 25.4 mm) is divided in units of pixels with a resolution of 600 dpi, and the lighting state of the light beam in each pixel is shown. It is a figure of the shown comparative example. In FIG. 16B-1, similarly to FIG. 14B-1, the unit area (25.4 mm × 25.4 mm) is divided in units of pixels with a resolution of 1200 dpi, and the lighting state of the light beam in each pixel is shown. It is a figure of the shown comparative example.

  FIG. 16A-1 shows that in the resolution 600 dpi mode, register setting is performed to form minute dots at a rate of 16 pixels (16 lines) in the sub-scanning direction. When this register setting is applied in the resolution 1200 dpi mode, one minute dot is formed in 16 pixels (16 lines) in the sub-scanning direction even in the resolution 1200 dpi mode. If the formation frequency of minute dots in the sub-scanning direction at a resolution of 600 dpi is also applied to a resolution of 1200 dpi, excessively fine dots are formed at a resolution of 1200 dpi. The formation of excessive fine dots causes problems such as a reduction in image quality and an increase in toner consumption.

  Therefore, in the image forming apparatus 100 according to the present embodiment, a register in which the fine dot formation frequency in the pixel unit in the resolution 1200 dpi mode in the sub-scanning direction is higher than the fine dot formation frequency in the pixel unit in the resolution 600 dpi mode. Settings are made. Specifically, the image forming apparatus 100 according to the present embodiment forms minute dots at a rate of 1 pixel per 16 pixels at a resolution of 600 dpi, and forms minute dots at a rate of 1 pixel per 32 pixels in the resolution 1200 dpi mode. Register settings are made.

  Further, a comparative example with respect to the present embodiment will be described. The conversion table shown in FIG. 17B is a comparative example for the conversion table shown in FIG. The conversion table in FIG. 15A and the conversion table in FIG. 17A are the same.

  In order to express 16 gradations with 4-bit image data of one pixel at a resolution of 600 dpi, all PWM data is assigned to 4-bit data. Therefore, it is not necessary to make the conversion table different between a model that needs to form minute dots and a model that does not need to be formed.

  However, the image data generated by the data processing unit 601 at a resolution of 1200 dpi shows only four values (see FIG. 9B). Therefore, when additional data is simply added to the image data generated by the data processing unit 601, there arises a problem that blank pixels are generated.

  FIG. 18A shows an image in which a space for three lines is provided between one line image having a resolution of 1200 dpi in the sub-scanning direction. The data processing unit 601 generates “0101” of 4 bits as a line image of 1 line as image data for the image of FIG. 18A and “0000” as image data of a space of 3 lines.

  Here, if the formation cycle of one line image and minute dots coincides, a blank pixel as shown in FIG. 18B is formed. When 4-bit “0101” is input to the data processing unit 602 for a line image of one line, the data processing unit 602 adds additional data “0010” to the data processing unit 602 to generate image data “0111”. This data corresponds to “8” on the vertical axis in FIG. 17B, but no PWM data is assigned to “8”. Therefore, the data processing unit 602 outputs “0000000000000000” as the PWM data for the pixel regardless of the pixel included in the line image. As a result, blank pixels as shown in FIG. 18C are formed.

  To deal with such a problem, as shown in FIG. 15B, the conversion table for the resolution of 1200 dpi is set so that no blank pixel is generated when additional data is added. That is, the data processing unit 602 uses a conversion table in which PWM data reflecting additional data is set to 2/3/6/7 in addition to 0/1/4/5 on the vertical axis in FIG. .

  Thus, by using a conversion table that considers additional data, the occurrence of blank pixels can be suppressed.

  As described above, by executing data processing in the image forming apparatus of the present embodiment, it is possible to realize formation of minute dots corresponding to the resolution.

  In the present embodiment, a color image forming apparatus including a plurality of photosensitive drums and an intermediate transfer belt (intermediate transfer body) is illustrated, but the embodiment is not limited thereto. The embodiment may be an image forming apparatus including a photosensitive drum and an intermediate transfer belt regardless of color or monochrome.

  In the embodiment, the intermediate transfer belt and the photosensitive drum may be rotationally driven by different motors.

  In this embodiment, an apparatus for forming minute dots on each photosensitive drum is illustrated. However, the embodiment is an apparatus for forming minute dots only on a photosensitive drum driven by a motor different from the intermediate transfer belt. There may be.

  Further, the plurality of resolution modes described in this embodiment may not be limited to the combination of the 600 dpi mode and the 1200 dpi mode. For example, as the plurality of resolution modes, various combinations such as a combination of 1200 dpi mode and 2400 dpi and a combination of 600 dpi mode, 1200 dpi mode and 2400 dpi can be considered.

  Further, the semiconductor laser may have a plurality of light emitting points. In an image forming apparatus including a semiconductor laser having a plurality of light emitting points, an image is formed according to each resolution by setting the rotation speed of the polygon mirror and the rotation speed of the photosensitive drum according to the resolution. Is possible.

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 105 Intermediate transfer belt 201 Photosensitive drum 500 Controller 601 Data processing unit I
602 Data processing unit II

Claims (10)

In an image forming apparatus capable of switching between a first resolution mode for forming an image with a first resolution and a second resolution mode for forming an image with a second resolution higher than the first resolution. ,
A rotating photoreceptor,
A light source that emits a light beam for forming an electrostatic latent image on the photoreceptor;
Deflecting means for deflecting the light beam so that the light beam emitted from the light source scans on the photosensitive member;
Developing means for developing the electrostatic latent image formed on the photoreceptor with toner;
A nip portion is formed between the photosensitive member and an intermediate transfer belt to which a toner image developed on the photosensitive member is transferred at the nip portion, and the toner image transferred onto the intermediate transfer belt is recorded. Transfer means for transferring onto a medium;
The deflection means is controlled so that the scanning speed of the light beam on the photoconductor is the same in the first resolution mode and the second resolution mode, and the photoconductor is rotated in the first resolution mode. The rotation speed is higher than the rotation speed of the photoconductor in the second resolution mode, and the rotation speed of the intermediate transfer belt is the rotation speed of each of the photoconductors in the first resolution mode and the second resolution mode. Control means for controlling the photoreceptor and the intermediate transfer belt so as to achieve a speed according to
N-bit (N ≧ 2) image data for one pixel in the first resolution is generated in the first resolution mode, and N bits for a plurality of pixels in the second resolution in the second resolution mode. First data processing means for generating the image data;
Storage means for storing additional data of N bits for forming minute dots;
N bit image data obtained by adding the N bit additional data to the N bit image data generated in the first resolution mode is generated, and the N bit generated in the second resolution mode is generated. Second data processing means for generating N-bit image data obtained by adding the N-bit additional data to the image data;
Conversion means for converting the N-bit image data to which the additional data is added into drive data composed of binary values of data that emits the light beam and data that does not emit the light beam; In the resolution mode, the N-bit image data to which the additional data is added is converted into the drive data based on a first conversion table corresponding to the first resolution, and in the second resolution mode, the second data is converted to the second data. Conversion means for converting the N-bit image data to which the additional data is added into the drive data based on a second conversion table corresponding to the resolution of
An image forming apparatus comprising: a drive unit that drives the light source based on the drive data converted by the conversion unit.   The image forming apparatus according to claim 1, wherein the second resolution is twice the first resolution.   The image forming apparatus according to claim 2, wherein the first resolution is 600 dpi and the second resolution is 1200 dpi.   4. The N = 4, and the first data processing means can generate 16-gradation image data for one pixel in the first resolution mode. The image forming apparatus according to claim 1.   The first data processing means is a first IC, the second data processing means is a second IC, and the first IC is the second IC in units of N bits regardless of the resolution mode. 5. The image forming apparatus according to claim 1, wherein the generated image data is transmitted to the IC. An image forming apparatus capable of switching between a first resolution mode for forming an image with a first resolution and a second resolution mode for forming an image with a second resolution higher than the first resolution. A rotating photoreceptor, a light source that emits a light beam for forming an electrostatic latent image on the photoreceptor, and a light beam emitted from the light source that scans the photoreceptor. A nip portion is formed between the deflecting means for deflecting the light beam, the developing means for developing the electrostatic latent image formed on the photosensitive member with toner, and the photosensitive member, and the photosensitive member is formed in the nip portion. an intermediate transfer belt to which the toner image developed on the body is transferred, the transfer means for transferring the toner image transferred on the intermediate transfer belt onto a recording medium, the first resolution mode and the second To the resolution mode of The deflection means is controlled so that the scanning speed of the light beam on the photosensitive member is the same, and the rotational speed of the photosensitive member in the first resolution mode is set to be the photosensitive member in the second resolution mode. And the rotation speed of the intermediate transfer belt is a speed corresponding to the rotation speed of each of the photoconductors in the first resolution mode and the second resolution mode. A data processing apparatus provided in an image forming apparatus comprising: a control unit that controls the intermediate transfer belt;
N-bit (N ≧ 2) image data for one pixel in the first resolution is generated in the first resolution mode, and N bits for a plurality of pixels in the second resolution in the second resolution mode. First data processing means for generating the image data;
Storage means for storing additional data of N bits for forming minute dots;
N bit image data obtained by adding the N bit additional data to the N bit image data generated in the first resolution mode is generated, and the N bit generated in the second resolution mode is generated. Second data processing means for generating N-bit image data obtained by adding the N-bit additional data to the image data;
Conversion means for converting the N-bit image data to which the additional data is added into drive data composed of binary values of data that emits the light beam and data that does not emit the light beam; In the resolution mode, the N-bit image data to which the additional data is added is converted into the drive data based on a first conversion table corresponding to the first resolution, and in the second resolution mode, the second data is converted to the second data. Conversion means for converting the N-bit image data to which the additional data is added into the drive data based on a second conversion table corresponding to the resolution of
A data processing apparatus comprising: drive means for driving the light source based on the drive data converted by the conversion means.   The data processing apparatus according to claim 6, wherein the second resolution is twice the first resolution.   8. The data processing apparatus according to claim 7, wherein the first resolution is 600 dpi, and the second resolution is 1200 dpi.   9. N = 4, and the first data processing means can generate 16-gradation image data for one pixel in the first resolution mode. A data processing apparatus according to claim 1.   The first data processing means is a first IC, the second data processing means is a second IC, and the first IC is the second IC in units of N bits regardless of the resolution mode. The data processing apparatus according to claim 6, wherein the generated image data is transmitted to the IC.

Images