JP5017973B2 - Image forming apparatus and image forming method - Google Patents

Description

  The present invention relates to an image forming apparatus including a plurality of image forming stations each having a line head in which a plurality of light emitting elements are arranged in a line, and an image forming method thereof.

  In a conventional electrophotographic image forming apparatus, an electrostatic latent image is formed on the surface of a photoconductor by scanning and exposing the surface of the photoconductor with a convergent light beam or laser light using a lamp as a light source. Is visualized with a developer (toner) to form an image. However, in recent years, light-emitting elements such as LEDs (light-emitting diodes) and organic EL (electroluminescence) elements that have a small size and can obtain a sufficient amount of light have been developed, and these light-emitting elements are used as exposure light sources. Therefore, a technique for eliminating the scanning optical system and reducing the size of the apparatus and the process speed has been studied. For example, in the image forming apparatus described in Patent Document 1, a line head having a large number of LED elements arranged in a row is arranged opposite to a photosensitive member, and each LED element is turned on all at once, thereby latent potential for one dot line. Form an image.

JP 2004-249549 A (FIG. 1)

  In the image forming apparatus described in Patent Document 1, an I / F controller that separates and outputs data for each toner color from print data sent from an external device such as a personal computer, and corresponds to each toner color And an LED head control circuit for controlling the line head. Data given from the I / F controller to the LED head control circuit is transmitted via a communication line provided for each toner color.

  However, the following problems remain in the above prior art. That is, with the recent demand for image formation speed and image quality, it is necessary to increase the data communication speed. In the above-described prior art, a plurality of communication lines having substantially the same communication speed are provided. Therefore, there is a possibility that these communication clocks are complicated inside the apparatus and interfere with each other to cause a communication error or a malfunction of the apparatus. This problem becomes more prominent as the communication speed increases. In addition, since individual communication lines are provided for each of a plurality of sets of line heads, there is a problem that the number of communication lines increases and the cost of the apparatus increases.

  The present invention has been made in view of the above problems, and an image forming apparatus including a plurality of image forming stations each having a line head in which a plurality of light emitting elements are arranged in a row and an image forming method thereof increase communication lines. It is an object to perform data communication for controlling the line head at high speed and stably while suppressing.

In order to achieve the above object, an image forming apparatus according to the present invention has a photosensitive member charged to a predetermined surface potential and a line head in which a plurality of light emitting elements are arranged in a row, and exposes the surface of the photosensitive member. A plurality of image forming stations each having an exposure unit that forms an electrostatic latent image and a developing unit that visualizes the electrostatic latent image with toner, and each of the image forming stations based on video data. A lighting control unit that controls lighting of the line head provided, and signal processing that performs signal processing on an image signal to generate the video data corresponding to each of the image forming stations and transmits the video data to the lighting control unit and means, the lighting control means has a function of repeatedly transmitting a serial signal to a word a predetermined number of bits with respect to the signal processing means, prior By assigning each of a plurality of request signals for requesting the signal processing means to start transmission of the video data for each of a plurality of image forming stations to each bit in one word of the serial signal, the plurality of request signals are The signal processing means has a function of repeatedly transmitting a serial signal having a predetermined number of bits to one word to the lighting control means while being multiplexed with one serial signal and transmitted to the signal processing means . The video data to be transmitted to the plurality of image forming stations is assigned to each of a plurality of sections into which one word of the serial signal is divided, thereby corresponding to the request signal of each of the plurality of image forming stations. the lighting multiplexed to one of the serial signal video data It is characterized by transmitting to the control means.

The image forming method according to the present invention corresponds to each of a plurality of image forming stations each having a line head in which a plurality of light emitting elements are arranged in a row by performing signal processing on an image signal by a signal processing unit. Video data is generated and transmitted to the lighting control means, and the lighting of each line head provided in each image forming station is controlled based on the video data by the lighting control means, thereby electrostatic latent images on the surface of the photoreceptor. An image forming method for forming an image and forming the image by developing the electrostatic latent image with toner, and in order to achieve the above object, a periodic serial signal having a predetermined number of bits as one word Each of the plurality of request signals for requesting the start of transmission of the video data for each of the plurality of image forming stations is assigned to each of the plurality of image forming stations. The plurality of request signals are multiplexed into one serial signal and transmitted from the lighting control means to the signal processing means, and in accordance with the request signal, a periodic serial signal having a predetermined number of bits as one word By assigning the video data corresponding to the plurality of image forming stations to each of the plurality of sections into which one word is divided, the video data corresponding to the request signal of each of the plurality of image forming stations is assigned to one section. The serial signal is multiplexed and transmitted from the signal processing means to the lighting control means.

In the invention configured as described above, since request signals and video data corresponding to a plurality of image forming stations are multiplexed and transmitted, the waveform becomes dull when the clock speed is increased, and these data are individually transmitted. There is no clock interference that may occur in transmission, and high-speed and stable data transmission can be performed. Further, since the request signals transmitted from the plurality of image forming stations and the data to be transferred to the plurality of image forming stations are respectively transmitted as one multiplexed serial signal, the number of signal lines can be reduced.

Here, the signal processing means time-division-multiplexes the video data by allocating video data corresponding to a plurality of image forming stations to each of a plurality of sections obtained by dividing one word of a periodic serial signal . The This makes it easier to handle especially digitized video data.

  More specifically, each image forming station is configured to form a toner image as an aggregate of a large number of dots, and the signal processing means outputs one frame of a signal to be transmitted to the lighting control means to the image. The time slot divided by the number of forming stations may be configured to allocate data for one dot.

  Further, for example, each image forming station is configured to form a toner image as an aggregate of a large number of dots, and the signal processing unit uses data corresponding to one dot as one channel, and The channels corresponding to each may be multiplexed and transmitted as one frame to the lighting control means.

  According to these configurations, it is possible to multiplex and transmit dot information to be formed by a plurality of image forming stations in one frame of data word. In addition, the lighting control means that has received the multiplexed signals as described above can easily extract data embedded in one frame.

Further, the toner images arranged in the moving direction of the transfer medium that moves in the respective image forming stations in a predetermined direction and visualized in the image forming stations are sequentially transferred to the transfer medium at different transfer positions. The lighting control means transmits the request signal generated at a different timing for each of the image forming stations due to the difference in the transfer position to the signal processing means as the serial signal each time, The signal processing means multiplexes the video data by synchronous time division multiplexing, and the video data to be transmitted to each of the image forming stations is timed according to the request signal corresponding to the image forming station. May be output respectively .

  In this way, data to be transferred to each image forming station can be transmitted at an arbitrary timing, that is, regardless of whether or not there is data corresponding to another image forming station.

  In this type of apparatus, a monochrome operation mode in which only one of a plurality of image forming stations is operated to form an image, and a plurality of image forming stations having different color toners are operated to generate a color image. And a color operation mode for forming a color. In such an apparatus, there is no data to be sent to an image forming station corresponding to a color other than the monochrome color when the monochrome operation mode is executed. In such a case, the signal processing means may multiplex the video data by synchronous time division multiplexing when executing either the monochrome operation mode or the color operation mode. For example, dummy data may be applied to data other than the monochrome color to multiplex video data. In this case, the data format in transmission / reception is the same in both modes, and transmission / reception processing can be unified.

  On the other hand, the signal processing means multiplexes the video data by synchronous time division multiplexing at the time of execution of the color operation mode, and does not perform multiplexing at the time of execution of the monochrome operation mode. Video data corresponding to only the video signal may be transmitted to the lighting control means as the serial signal. In this case, in the monochrome operation mode, the capacity of the communication line can be occupied exclusively by the monochrome color, so that a larger amount of data can be communicated at a higher speed.

  The lighting control unit that has received such a signal includes a demultiplexing processing unit that demultiplexes the serial signal received from the signal processing unit and develops the video signal for each image forming station. Thus, the video data corresponding to each image forming station can be restored from the received signal.

  FIG. 1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a view showing the arrangement of image forming stations in the image forming apparatus of FIG. FIG. 3 is a diagram showing an electrical configuration of the image forming apparatus of FIG. This apparatus uses a color mode in which four color toners of yellow (Y), magenta (M), cyan (C) and black (K) are superimposed to form a color image, and only black (K) toner. Thus, the image forming apparatus can selectively execute a monochrome mode for forming a monochrome image. In this image forming apparatus, when an image forming command is given from an external device such as a host computer to a main controller MC having a CPU, a memory and the like, the main controller MC gives a control signal to the engine controller EC, and based on this, the engine controller EC The controller EC controls each part of the device, such as the engine unit EG and the head controller HC, to execute predetermined image forming operations, and responds to image forming commands on sheets that are recording materials such as copy paper, transfer paper, paper, and OHP transparent sheets. The image to be formed is formed.

  In the housing main body 3 of the image forming apparatus according to this embodiment, an electrical component box 5 is provided that incorporates a power circuit board, a main controller MC, an engine controller EC, and a head controller HC. An image forming unit 2, a transfer belt unit 8, and a paper feed unit 7 are also disposed in the housing body 3. In FIG. 1, a secondary transfer unit 12, a fixing unit 13 and a sheet guide member 15 are disposed on the right side in the housing body 3. The paper feed unit 7 is configured to be detachable from the housing body 3. The paper feeding unit 7 and the transfer belt unit 8 can be removed and repaired or exchanged.

  The image forming unit 2 includes four image forming stations 2Y (for yellow), 2M (for magenta), 2C (for cyan) and 2K (for black) that form a plurality of images of different colors. In FIG. 1, since the image forming stations of the image forming unit 2 have the same configuration, only some of the image forming stations are denoted by reference numerals for convenience of illustration, and the reference numerals are omitted for other image forming stations. To do.

  Each image forming station 2Y, 2M, 2C, and 2K is provided with a photosensitive drum 21 on which a toner image of each color is formed. Each photosensitive drum 21 is connected to a dedicated drive motor and is driven to rotate at a predetermined speed in the direction of arrow D21 in the figure. A charging unit 23, a line head 29, a developing unit 25, and a photoconductor cleaner 27 are disposed around the photoconductive drum 21 along the rotation direction thereof. Then, a charging operation, a latent image forming operation, and a toner developing operation are executed by these functional units. When the color mode is executed, the toner images formed by all the image forming stations 2Y, 2M, 2C, and 2K are superimposed on the transfer belt 81 provided in the transfer belt unit 8 to form a color image. When the monochrome mode is executed, only the image forming station 2K is operated to form a black monochrome image.

  The charging unit 23 includes a charging roller whose surface is made of elastic rubber. The charging roller is configured to rotate in contact with the surface of the photosensitive drum 21 at the charging position, and is driven to rotate as the photosensitive drum 21 rotates. The charging roller is connected to a charging bias generator (not shown). The charging roller is supplied with the charging bias from the charging bias generator and is charged at the charging position where the charging unit 23 and the photosensitive drum 21 come into contact with each other. The surface of 21 is charged to a predetermined surface potential.

  The line head 29 includes a plurality of light emitting elements arranged in the axial direction of the photosensitive drum 21 (a direction perpendicular to the paper surface of FIG. 1), and is disposed to face the photosensitive drum 21. Then, light is emitted from these light emitting elements toward the surface of the photosensitive drum 21 charged by the charging unit 23 to form an electrostatic latent image on the surface.

  FIG. 4 is a diagram showing the structure of the line head. In the following description, the direction from the back of the drawing to the near side in FIG. That is, the X direction is a direction parallel to the rotation axis of the photosensitive drum 21 and is orthogonal to the moving direction of the surface of the photosensitive drum 21 and the moving direction D81 of the transfer belt 81. In the line head 29, an LED array 293 in which a plurality of LED (light emitting diode) elements serving as exposure light sources are arranged in the X direction is held in a long housing. The LED array 293 on the base substrate 294 is driven by a driver IC 295 formed on the same base substrate 294. When a video signal is supplied from the head controller HC, the driver IC 295 is operated based on the video signal, and the LED elements provided in the LED array 293 are turned on. The gradient index rod lens array 296 constitutes an imaging optical system, and a gradient index rod lens 297 disposed on the front surface of the LED element is stacked. The housing covers the periphery of the base substrate 294, and the side facing the photosensitive drum 21 is open. In this way, light is emitted from the gradient index rod lens 297 to the photosensitive drum 21. Thereby, an electrostatic latent image is formed on the photosensitive drum 21 corresponding to the video signal.

  Returning to FIG. 1, the description of the apparatus configuration will be continued. The developing unit 25 has a developing roller 251 on which toner is carried. The charged toner is developed at a developing position where the developing roller 251 and the photosensitive drum 21 come into contact with each other by a developing bias applied to the developing roller 251 from a developing bias generator (not shown) electrically connected to the developing roller 251. Moves from the developing roller 251 to the photosensitive drum 21, and the electrostatic latent image formed on the surface thereof is visualized.

  The toner image made visible at the developing position is conveyed in the rotational direction D21 of the photosensitive drum 21, and then is transferred to the transfer belt 81 at a primary transfer position TR1 where the photosensitive belt 21 comes into contact with the transfer belt 81 described later in detail. Primary transcription.

  A photoreceptor cleaner 27 is provided in contact with the surface of the photoreceptor drum 21 on the downstream side of the primary transfer position TR1 in the rotation direction D21 of the photoreceptor drum 21 and on the upstream side of the charging unit 23. The photoconductor cleaner 27 abuts on the surface of the photoconductor drum to remove the toner remaining on the surface of the photoconductor drum 21 after the primary transfer.

  The transfer belt unit 8 includes a driving roller 82, a driven roller 83 (blade facing roller) disposed on the left side of the driving roller 82 in FIG. 1, and an arrow D81 illustrated in FIG. And a transfer belt 81 that is circulated in the direction (conveyance direction). Further, four transfer belt units 8 are arranged on the inner side of the transfer belt 81 so as to be opposed to each of the photosensitive drums 21 included in the image forming stations 2Y, 2M, 2C, and 2K when the cartridge is mounted. Primary transfer rollers 85Y, 85M, 85C and 85K. Each of these primary transfer rollers is electrically connected to a primary transfer bias generator (not shown).

  When the color mode is executed, as shown in FIGS. 1 and 2, all the primary transfer rollers 85Y, 85M, 85C, and 85K are positioned on the image forming stations 2Y, 2M, 2C, and 2K, so that the transfer belt 81 is imaged. A primary transfer position TR1 is formed between each photosensitive drum 21 and the transfer belt 81 by being pushed and brought into contact with the photosensitive drum 21 included in each of the forming stations 2Y, 2M, 2C, and 2K. Then, by applying a primary transfer bias from the primary transfer bias generating unit to the primary transfer roller 85Y or the like at an appropriate timing, the toner images formed on the surface of each photosensitive drum 21 are respectively transferred to the corresponding primary transfer positions. Transfer is performed on the surface of the transfer belt 81 in TR1. That is, in the color mode, the single color toner images of the respective colors are superimposed on the transfer belt 81 to form a color image.

  In the so-called tandem image forming apparatus, the primary transfer position where the toner image is primarily transferred from the photosensitive drum 21 to the transfer belt 81 is different for each image forming station. In this embodiment, the yellow image forming station 2Y, the magenta image forming station 2M, the cyan image forming station 2C, and the black image forming station 2K are arranged in this order along the moving direction of the transfer belt 81. . Accordingly, the yellow primary transfer position TR1y and the magenta primary transfer position TR1m are the distance Lym, the magenta primary transfer position TR1m and the cyan primary transfer position TR1c are the distance Lmc, and the cyan primary transfer position TR1c and the black primary transfer position TR1k are only the distance Lck. Separated.

  On the other hand, when executing the monochrome mode, among the four primary transfer rollers, the primary transfer rollers 85Y, 85M, and 85C are separated from the image forming stations 2Y, 2M, and 2C that face each other, and the primary transfer rollers corresponding to the black color are used. By bringing only 85K into contact with the image forming station 2K, only the monochrome image forming station 2K is brought into contact with the transfer belt 81. As a result, the primary transfer position TR1k is formed only between the primary transfer roller 85K and the image forming station 2K. Then, by applying a primary transfer bias to the primary transfer roller 85K from the primary transfer bias generator at an appropriate timing, a black toner image formed on the surface of the photosensitive drum 21 provided in the image forming station 2K is obtained. A monochrome image is formed by transferring to the surface of the transfer belt 81 at the primary transfer position TR1k.

  Further, the transfer belt unit 8 includes a downstream guide roller 86 disposed on the downstream side of the black primary transfer roller 85K and on the upstream side of the driving roller 82. The downstream guide roller 86 is common to the primary transfer roller 85K and the black photosensitive drum 21 (K) at the primary transfer position TR1 formed by the primary transfer roller 85K contacting the photosensitive drum 21 of the image forming station 2K. It is configured to contact the transfer belt 81 on the tangent line.

  A patch sensor 89 is provided opposite to the surface of the transfer belt 81 wound around the downstream guide roller 86. The patch sensor 89 is composed of, for example, a reflection type photosensor, and optically detects a change in the reflectance of the surface of the transfer belt 81, so that the position and density of the patch image formed on the transfer belt 81 as necessary. Is detected.

  The sheet feeding unit 7 includes a sheet feeding unit having a sheet feeding cassette 77 capable of stacking and holding sheets and a pickup roller 79 that feeds sheets one by one from the sheet feeding cassette 77. The sheet fed from the sheet feeding unit by the pickup roller 79 is adjusted in sheet feeding timing by the registration roller pair 80, and then the drive roller 82 and the secondary transfer roller 121 abut along the sheet guide member 15. Paper is fed to the secondary transfer position TR2.

  The secondary transfer roller 121 is provided so as to be able to come into contact with and separate from the transfer belt 81 and is driven to come into contact with and separate from a secondary transfer roller drive mechanism (not shown). The fixing unit 13 includes a heating roller 131 that includes a heating element such as a halogen heater and is rotatable, and a pressure unit 132 that presses and biases the heating roller 131. The sheet on which the image is secondarily transferred is guided to the nip formed by the heating roller 131 and the pressure belt 1323 of the pressure unit 132 by the sheet guide member 15, and in the nip, a predetermined value is formed. The image is heat-fixed at temperature. The pressure unit 132 includes two rollers 1321 and 1322 and a pressure belt 1323 stretched between them. A nip portion formed by the heating roller 131 and the pressure belt 1323 is formed by pressing the belt tension surface stretched by the two rollers 1321 and 1322 out of the surface of the pressure belt 1323 against the peripheral surface of the heating roller 131. Is configured to be widely taken. Further, the sheet thus subjected to the fixing process is conveyed to a paper discharge tray 4 provided on the upper surface portion of the housing body 3.

  The drive roller 82 circulates and drives the transfer belt 81 in the direction of the arrow D81 in the figure, and also serves as a backup roller for the secondary transfer roller 121. A rubber layer having a thickness of about 3 mm and a volume resistivity of 1000 kΩ · cm or less is formed on the peripheral surface of the drive roller 82, and secondary transfer is omitted by grounding through a metal shaft. A conductive path of a secondary transfer bias supplied from the bias generation unit via the secondary transfer roller 121 is used. Thus, by providing the driving roller 82 with a rubber layer having high friction and shock absorption, image quality deterioration caused by transmission of the impact to the transfer belt 81 when the sheet enters the secondary transfer position TR2. Can be prevented.

  Further, in this apparatus, a cleaner portion 71 is disposed to face the blade facing roller 83. The cleaner unit 71 includes a cleaner blade 711 and a waste toner box 713. The cleaner blade 711 removes foreign matters such as toner and paper dust remaining on the transfer belt 81 after the secondary transfer by bringing the tip of the cleaner blade 711 into contact with the blade facing roller 83 via the transfer belt 81. The foreign matter removed in this way is collected in a waste toner box 713. Further, the cleaner blade 711 and the waste toner box 713 are integrally formed with the blade facing roller 83.

  In this embodiment, the photosensitive drum 21, the charging unit 23, the developing unit 25, and the photosensitive cleaner 27 of each of the image forming stations 2Y, 2M, 2C, and 2K are unitized as a unit. The cartridge is configured to be detachable from the apparatus main body. Each cartridge is provided with a nonvolatile memory for storing information related to the cartridge. Then, wireless communication is performed between the engine controller EC and each cartridge. Thus, information about each cartridge is transmitted to the engine controller EC, and information in each memory is updated and stored. Based on these pieces of information, the usage history of each cartridge and the lifetime of consumables are managed.

  In this embodiment, the main controller MC, the head controller HC, and each line head 29 are configured as separate blocks, and are connected to each other via a serial communication line as described below. Although it is conceivable to configure the head controller HC integrally with the main controller MC or the line head 29, the following advantages are produced by configuring them separately.

  First, by making the function of the head controller HC independent of the line head 29, the line head 29 can be significantly downsized, and the engine unit EG and the entire apparatus can be downsized. In addition, by separating the processing function depending on the structure of the line head from the main controller MC and making it a dedicated block, the main controller MC can perform only more versatile signal processing without considering the head configuration. become able to. If the communication between the main controller MC and the head controller HC is standardized, the head controller corresponding to the head to be used can be used without changing the main controller even when using a head having a different configuration. It will be necessary to prepare only. As a result, a common main controller MC can be used in common for apparatuses having differently configured heads, and multi-model development using one controller is facilitated.

  The cooperative operation of each part of the apparatus configured as described above will be described with reference to FIG. 3 again. When an image formation command is given from the external device to the main controller MC, the main controller MC transmits a control signal for starting the engine unit EG to the engine controller EC via a UART (general purpose asynchronous transmission / reception) communication line. Further, the image processing unit 100 provided in the main controller MC performs predetermined signal processing on the image data included in the image formation command, and generates video data for each toner color.

  On the other hand, the engine controller EC receiving the control signal starts initialization and warm-up of each part of the engine part EG. When these are completed and the image forming operation can be executed, the engine controller EC sends a synchronization signal Vsync that triggers the start of the image forming operation to the head controller HC that controls each line head 29 via the UART communication line. To output. In addition, in the communication between the engine controller EC and the head controller HC via the UART communication line, various control parameters for controlling the line head 29 are exchanged, and details thereof will be described later.

  The head controller HC is provided with a head control module 400 that controls each line head and a head-side communication module 300 that controls data communication with the main controller MC. On the other hand, the main communication module 200 is also provided in the main controller MC. From the head-side communication module 300 to the main-side communication module 200, a vertical request signal VREQ indicating the head of an image for one page and a horizontal request for requesting video data for one line among the lines constituting the image. Signal HREQ is transmitted. On the other hand, the video data VD is transmitted from the main communication module 200 to the head communication module 300 in response to these request signals. More specifically, after receiving the vertical request signal VREQ indicating the head of the image, each time the horizontal request signal HREQ is received, video data is sequentially output for each line from the head portion of the image.

  FIG. 5 is a diagram illustrating communication between the main controller and the head controller. An image of one page is positioned little by little in a direction perpendicular to the line in which a large number of dots are arranged in a line along the X direction (the light emitting element arrangement direction of the line head 29), that is, in the moving direction D81 of the transfer belt 81. It is formed while differentiating. A request signal VREQ output from the head controller HC indicates the head of the page. The main controller MC validates the request signal HREQ received after receiving the request signal VREQ, and transmits video data VD for one line to the head controller HC every time the request signal HREQ is received.

  In this embodiment, the maximum number of dots constituting one line is 6828. The resolution is 600 dpi (dots per inch), and the dot pitch is equal to this. Thus, the maximum length of one line is approximately 11.4 inches (289 mm). This length corresponds to the short side dimension of Japanese Industrial Standard A3 size paper. The image data of each dot is expressed in multi-gradation with 8 bits, and one line of video data VD is a predetermined specific value (here 55h) of head data followed by 8 bits × 6828 dots. Image data string. The head data is for indicating the head of the data string, and the head controller that receives the video data can recognize the head of the data from the head data received after the value 00h. In other words, if a value other than 00h received first after receiving the vertical request signal VREQ is different from that determined as the head data, it can be determined that a communication error has occurred.

  After outputting the video data for one line in this way, when the request signal HREQ is subsequently given, the main controller MC outputs the data for the next one line. By repeating this, video data VD corresponding to an image for one page is transferred from the main controller MC to the head controller HC. When there is an image of the next page to be formed, the vertical request signal VREQ is transmitted again from the head controller HC to the main controller MC after the data communication of the previous page is completed.

  In this embodiment, the above-described signals, that is, request signals VREQ and HREQ sent from the head controller HC to the main controller MC and video data VD sent from the main controller MC to the head controller HC correspond to four sets corresponding to each color of YMCK. Exists. In the following, the colors are distinguished by attaching a hyphen and a code representing the color to each signal as necessary. For example, the vertical synchronizing signal, horizontal synchronizing signal, and video data for yellow are represented as VREQ-Y, HREQ-Y, and VD-Y, respectively.

  FIG. 6 is a diagram showing the communication timing for each color. More specifically, this figure shows the exchange of signals between the main controller and the head controller when two pages of color images are continuously formed. As shown in FIG. 2, the primary transfer positions TR1y, TR1m, TR1c and TR1k at which the image forming stations 2Y, 2M, 2C and 2K transfer the toner image onto the transfer belt 81 are different from each other. Therefore, in order to superimpose the toner images formed at the respective image forming stations at the same position on the transfer belt 81, a buffer memory for temporarily storing video data to absorb the difference in the primary transfer position is used as a head. It is necessary to provide the video data transmission timing for each toner color depending on the distance between the primary transfer positions provided in the controller HC. In the former case, a large-capacity memory is required for each toner color, resulting in a significant increase in apparatus cost.

This embodiment employs the latter method that does not require a large-capacity buffer memory. In other words, by providing a time difference in the video data transmission timing in accordance with the arrangement of the image forming stations, the toner image formation positions on the transfer belt 81 are made to coincide between the toner colors. More specifically, the timing for transmitting the request signals VREQ and HREQ output from the head controller HC is different for each toner color. For example, the time difference Tym between the yellow vertical request signal VREQ-Y and the magenta vertical request signal VREQ-M is obtained when the moving speed of the transfer belt 81 is Vtb.
Tym = Lym / Vtb
The output timing of the request signal is adjusted so that As a result, a similar time difference is generated between the yellow video signal VD-Y and the magenta video signal VD-M. As a result, the toner image formation positions of both toner colors are the same on the transfer belt 81. . Similarly, the distance between the primary transfer positions is also between the magenta video signal VD-M and the cyan video signal VD-C, and between the cyan video signal VD-C and the black video signal VD-K. The time differences Tmc and Tck according to the above are provided.

  At this time, it is the request signal output from the head controller HC that sets the time difference according to the distance between the primary transfer positions, and the main controller MC simply receives the video signal at the timing requested by the given request signal. Is simply output. In this way, it is not necessary to manage the distance between the primary transfer positions on the main controller MC side, and the main controller MC can perform only processing independent of the configuration of the engine unit EG.

  By the way, in such a communication system, at least three signal lines of request signals VREQ and HREQ and video data VD are required for each color. As the number of colors increases, the number of signal lines also increases. Further, as apparent from FIG. 6, there is a timing at which signals of two or more colors are simultaneously transmitted / received, so that it is difficult to adopt a bus communication system via a common bus line.

  Therefore, in this embodiment, the request signal is encoded as described below. Thus, the vertical and horizontal request signals VREQ and HREQ for each toner color are multiplexed in a time division manner so that request signals for four colors can be transmitted through one set of serial signal lines. Also, video data VD can be transmitted through one set of serial signal lines by multiplexing four colors into one signal in a time division manner. Therefore, in this embodiment, the number of colors is determined by a set of signal lines including a signal line for transmitting from the main controller MC to the head controller HC and a signal line for transmitting from the head controller HC to the main controller MC. It is possible to perform necessary data communication regardless of the case.

  When data is multiplexed in this way, data transmission at higher speed is required. In this embodiment, a clock for data transmission is generated on the transmission module side, and the clock component is superimposed on the data for transmission, thereby eliminating the clock transmission lines and further reducing the number of signal lines, and at a higher speed. Stable data communication is possible.

  Hereinafter, the data communication system in the present embodiment will be described in detail. In this embodiment, the request signals for four colors sent from the head controller HC to the main controller MC and the video data for four colors sent from the main controller MC to the head controller HC are both 32-bit serial signals. Sending and receiving.

  FIG. 7 shows the contents of data transmitted from the head controller. The 32-bit data transmitted from the head controller HC is composed of four sections of data in units of 8 bits, and each bit of each section includes Y, M, C, and K color vertical request signals VREQ and horizontal requests. One of the signals HREQ is assigned. There are eight types of request signals sent from the head controller HC to the main controller MC for two colors, that is, a vertical request signal VREQ and a horizontal request signal HREQ for each color. These 8 types of signals are assigned to each of 8 bits constituting one section. Here, it is assumed that the request signals VREQ-Y, HREQ-Y, VREQ-M, HREQ-M, VREQ-C, HREQ-C, VREQ-K, and HREQ-K are assigned in order from the upper bit. The main controller MC that has received this information can restore the request signal for each color that has been multiplexed into the serial signal by taking out each bit information and rearranging it in time series.

  FIG. 8 is a timing chart showing an example of a request signal. FIG. 9 is a diagram showing the result of encoding the pattern of FIG. A method of transmitting eight types of request signals as one serial signal will be described with reference to these drawings. Note that the patterns shown in FIGS. 8 and 9 are virtual ones created for convenience of explanation, and do not necessarily match the patterns that can actually occur in the operation of the apparatus. When the request signal is encoded, the H level is represented by a value 0 and the L level is represented by a value 1.

  In the head controller HC, the request signal to be transmitted is sampled and encoded at a sampling period corresponding to 1/4 of the transfer period for one word, that is, the transfer period per section. When the time t = 0 is set as the start point, since all the eight types of request signals are at the H level in the first sampling period, this state can be expressed by “00000000d”, that is, “00h”. Here, symbols d and h represent binary notation and hexadecimal notation, respectively. This value becomes the value of the first section (bits 31 to 24) of the first word. Similarly, the second sampling period can be expressed as “00h”, which is the value of the second section (bits 23 to 16).

  Since only the vertical request signal VREQ-Y corresponding to yellow is at the L level in the third sampling period, this state can be represented by “10000000d”, that is, “80h”. Therefore, the value of the third section (bits 15 to 8) is “80h”. In the fourth sampling period, all the signals are again at the L level, and therefore can be represented by “00h”. From the above, the sampling result of the first to fourth sampling periods can be expressed as “00000000h” in one word (32 bits long). In this way, each request signal in this period can be multiplexed and encoded.

  The request signal thus encoded is transmitted from the head controller HC to the main controller MC as a serial signal in units of one word. In the main controller MC that has received this signal, by applying the above-described encoding rule in the reverse direction, from the received data “00000000h”, “the yellow request signal VREQ-Y is at the L level in the third sampling period, etc. Can restore the pre-sampling state. The same can be done for each of the subsequent sampling periods, whereby the change pattern of the request signal shown in FIG. 8 is represented as a data string shown in FIG. In this way, the head controller HC can multiplex and transmit eight types of request signals into one serial signal, and the main controller MC that has received this can restore the change in the original request signal without excess or deficiency.

  FIG. 10 is a diagram showing the contents of data transmitted from the main controller. From the main controller MC to the head controller HC, video data represented by 8 bits for each color is time-division multiplexed into a 32-bit serial signal and transmitted. The 32-bit data is composed of four sections in units of 8 bits, and one toner color is assigned to one section. Each section represents information (2 bits) indicating a position such as whether the dot to be formed is top aligned or bottom aligned, information indicating the type of screen to be applied (1 bit), and the gradation value of the dot to be formed It consists of information (5 bits).

  Thus, 8-bit × 4-color video data is serially transmitted to the head controller HC as 32-bit data. Then, the head controller HC that has received this can restore the video data of each color by dividing the received data into sections. In each section, null data or predetermined dummy data is inserted into a section corresponding to a toner color for which a request signal is not output from the head controller HC. That is, in this embodiment, even when there is no video data to be transmitted, the assignment of sections to predetermined toner colors does not change. That is, in this embodiment, video data is synchronously time-division multiplexed.

  As described above, in this embodiment, the video data for four colors sent from the main controller MC to the head controller HC and the eight types of request signals for four colors sent from the head controller HC to the main controller MC are all used. It is transmitted and received as one serial signal. Next, a hardware configuration for enabling the above communication method will be described.

  FIG. 11 shows the connection between the main controller and the head controller. The main controller MC is provided with a 7-pin plug 201 (hereinafter referred to as “host plug”) electrically connected to the main communication module 200. The head controller HC is also provided with a 7-pin plug 301 (hereinafter referred to as “device plug”) that is electrically connected to the head-side communication module 300. The two plugs are connected to each other by a communication cable 700 having 7-pin connectors 701a and 701b fitted to the host plug 201 and the device plug 301, respectively.

The signal transmission method is LVDS (Low Voltage Differential), which allows high-speed transmission.
Signaling (low voltage differential transmission) interface is employed, and differential signal lines, each consisting of two lines, are used for transmission from the main controller MC to the head controller HC and transmission in the opposite direction. One of the two signal line pairs includes a transmission TX + terminal and a TX− terminal, which will be described later, provided in the main communication module 200 and a reception RX + terminal and RX−, provided in the head communication module 300. The terminals are electrically connected to each other through a connector. The other pair electrically connects the RX + and RX- terminals for reception provided in the main-side communication module 200 and the TX + and TX- terminals for transmission provided in the head-side communication module 300, respectively. Connecting. That is, the main side communication module 200 and the head side communication module 300 are point-to-point connected. Each signal line pair is shielded, and the shield conductor and the GND line are also connected to the connectors 701a and 701b, respectively, with the signal line pair interposed therebetween. These shield conductors and the GND line are grounded in both communication modules. As described above, in this embodiment, data transmission from the main controller MC to the head controller HC and data transmission from the head controller HC to the main controller MC are performed bidirectionally by a set of communication cables. In addition, the wiring from the TX + terminal to the RX + terminal and the wiring from the TX− terminal to the RX− terminal have the same length including the communication cable 700 and the wiring pattern on the board, and stable communication is possible even at high speed. It can be done.

  FIG. 12 is a diagram showing the configuration of the main controller. The main controller MC includes an image processing unit 100 that performs signal processing necessary for image data included in an image formation command given from an external device, and a main-side communication module 200. The image processing unit 100 includes a color conversion processing block 101 that develops RGB image data into CMYK image data corresponding to each toner color, and an image memory 102 for temporarily storing the image data. Further, the image processing unit 100 is provided with image processing blocks 103Y, 103M, 103C, and 103K for each toner color, which generate video data VD by performing processing such as screen processing and gamma correction on the image data. Yes. Each image processing block 103Y or the like starts signal processing for the image for one page triggered by the input of the vertical request signal VREQ-Y or the like, and sequentially outputs the generated video data for each line to the main communication module 200. .

  Next, the configuration of the main communication module 200 will be described. The main-side communication module 200 multiplexes four-color video data VD-Y, VD-M, VD-C, and VD-K output from the image processing unit 100 based on the above principle, and serially transmits them to the head controller HC. A block 210; a reception block 220 that receives the vertical and horizontal request signals VREQ and HREQ of each color that are multiplexed based on the above principle and sent from the head controller HC; And a clock generation block 230 for generating a clock for this purpose.

  The transmission block 210 is provided with a FIFO buffer 211 for aligning the timing for multiplexing the video data VD of each color. The FIFO buffer 211 receives 8-bit video data VD-Y output from each color image processing block in response to the restored vertical request signals VREQ-Y, VREQ-M, VREQ-C, and VREQ-K for each color. VD-M, VD-C, and VD-K are output as 32-bit parallel data while being latched by horizontal request signals HREQ-Y, HREQ-M, HREQ-C, and HREQ-K, respectively. The 32-bit data output from the FIFO buffer 211 is input to an 8b / 10b encoder 212 that adds 2 additional bits to 8 bits of data to form 10-bit data, and is processed into 40-bit data. When an error correction code such as a CRC (Cyclic Redundancy Check) code is used as the additional bit data, the reliability of the transmission data can be further improved.

  The 40-bit data is input to the serializer 214 via the FIFO buffer 213 and sent to the transmission buffer 215 as serial data. The transmission buffer 215 embeds the transmission clock generated by the transmission clock generation unit 232 based on the reference clock (REFCLK) 231 provided in the clock generation block 230, that is, modulates the transmission clock with the transmission data, The modulation signal is output as a differential serial signal from the TX + and TX− terminals. As described above, in this embodiment, the video data for four colors are multiplexed into one serial signal, and the serial signal is output as a differential signal in which the clock component is embedded. That is, in this embodiment, video data for four colors is transmitted through a pair of differential signal lines.

  FIG. 13 is a diagram schematically showing video data on a signal line. In this embodiment, the frequency of the reference clock (REFCLK) is 75 MHz, and the frequency of the data transmission clock (word clock) obtained by dividing the frequency by 2 is 37.5 MHz. Therefore, the transmission period of one word data is about 26.7 nsec, which is twice the reference clock period Tref, and four color time slots are provided therein. Since the data (frame) length is 40 bits, the data transfer rate is 1.5 Gbps (bits per second). The breakdown of 40-bit data (one frame) is 10 bits × 4 channels per color (channel) obtained by adding 2-bit additional data to 8-bit video data. The clock component is embedded in the data, and the illustrated clock signal is not transmitted separately.

  Returning to FIG. 12, the configuration and operation of the reception block 220 will be described. As described above, the signal transmitted from the head side communication module 300 is also a differential signal in which a clock component is embedded. This differential signal is input between the RX + terminal and the RX− terminal, and the received 40-bit serial data is input to the reception buffer 221. The clock component embedded in the signal is demodulated by the reception clock demodulation unit 233, and data is received based on the demodulated clock.

  The received 40-bit serial data is parallelized by the deserializer 222. Then, the additional bit data is removed by the 10b / 8b decoder 223 and converted to 32-bit data. At this time, error correction is performed as necessary. The 32-bit data is input to the buffer 224 and supplied to the distributor 225 in synchronization with an output clock 234 provided separately.

  In the distributor 225, each bit information of 32-bit data is cut out and output in time series, thereby restoring eight types of request signals. Among them, the vertical request signals VREQ-Y, VREQ-M, VREQ-C, and VREQ-K are given to the image processing blocks 103Y, 103M, 103C, and 103K, respectively, to notify the start timing of the image processing. The horizontal request signals HREQ-Y, HREQ-M, HREQ-C, and HREQ-K are used as FIFO data signals as data latch timing signals to multiplex the video data VD output from each image processing block at a predetermined timing. The buffer 211 is given.

  FIG. 14 is a diagram showing the configuration of the head controller. The head controller HC includes a head side communication module 300 and a head control module 400. The configuration of the head side communication module 300 is similar to that of the main side communication module 200. That is, the head-side communication module 300 receives the video data multiplexed and transmitted from the main controller MC and restores it to video data for each color, and multiplexes the request signal and transmits it to the main controller MC. The transmission block 310 and the clock generation block 330 are provided. The serial signal transmitted from the main communication module 200 is received based on the clock demodulated from the signal by the reception clock demodulator 333 and input to the reception buffer 321. Then, it is converted into 40-bit parallel data by the deserializer 322, and additional bits are removed by the 10b / 8b decoder 323, converted into 32-bit parallel data, and input to the buffer 324. The 32-bit data input to the buffer 324 is given to the distributor 325 in synchronization with the output clock 334. The distributor 325 divides the data into sections, restores 8-bit video data for each color, and outputs the video data to the head control module 400. That is, the head side communication module 300 demultiplexes the four-color video data multiplexed and sent from the main controller MC, and develops the video data for each color.

  The head control module 400 includes a Y head control block 410Y, an M head control block 410M, a C head control block 410C, and a K head that individually control the line heads 29 provided in the image forming stations 2Y, 2M, 2C, and 2K. A control block 410K is provided. The video data divided for each color is input to the corresponding color head control block. Further, the vertical request signal VREQ and the horizontal request signal HREQ are input to the head side communication module 300 from each head control block at independent timings.

  The transmission block 310 of the head side communication module 300 encodes and multiplexes request signals input from each head control block as needed, and outputs them to the main side communication module 200. The multiplexer 311 provided in the transmission block 310 outputs a total of eight types of request signals VREQ and HREQ output from each head control block as 32-bit data of 8 bits × 4 sections. The 8-bit / 10-b encoder adds 2 bits of additional data per 8 bits to the 32-bit data and converts it into 40-bit data. The 40-bit data obtained in this way is sent to the serializer 314 via the FIFO buffer 313, and the serially converted data is sent to the transmission buffer 315.

  The transmission buffer 315 performs differential communication on the 40-bit serial data in which the clock component is embedded based on the transmission clock generated by the transmission clock generation unit 332 in synchronization with the reference clock (REFCLK) 331 provided in the clock generation block 330. Output to line. In this way, the eight types of request signals are multiplexed into one serial signal and transmitted through a pair of differential communication lines.

As described above, the communication between the main controller MC and the head controller HC in this embodiment is bidirectional serial communication based on the LVDS method. Since the data of each color is multiplexed into one data, the transmission data from both can be transmitted only by one differential signal line pair. Therefore, only a minimum of four signal lines are required to connect the controllers, and the number of signal lines can be greatly reduced. In this embodiment, a 7-wire signal cable including a GND wiring and a shield conductor is used. This type of cable is a SATA (Serial Advanced Technology) which is one of the standards for interconnection between computer peripheral devices.
It is also adopted in the Attachment standard, and can be obtained at a low price on the market as the standard product. In addition, the use of the differential signal line enables high-speed transmission and is hardly affected by noise.

  In addition, a clock component based on a reference clock provided in the main controller MC is embedded in data transmitted from the main controller MC, while a reference clock provided separately in the head controller HC is included in data transmitted from the head controller HC. The clock component based on is embedded. Therefore, in this communication, the transmission side is always the master and the reception side is the slave. This provides the following advantages.

  In an image forming apparatus having a line head, lighting control of the light emitting element is performed at high speed. Therefore, it is desirable to generate a lighting control clock as close to the line head as possible in order to control the dot formation position with high accuracy. Therefore, in this embodiment, the lighting control clock is generated in each head control block as described below.

  Also, the video data transmitted from the main controller MC needs to be sequentially output in synchronization with the lighting control clock. In order to realize this, it is conceivable that a clock for video data transmission is supplied from the head controller HC side to operate the main controller MC as a slave. However, in such a case, there are problems that the high-speed clock is routed for a long time and the waveform becomes dull and the clock is not transmitted correctly, or that high-frequency noise is generated in the device and the operation of the device becomes unstable.

  In this embodiment, only the request signal for each page and each line is supplied from the head controller HC to the main controller MC, while the main controller MC generates a clock component generated from its own reference clock according to the request signal. The video data on which is superimposed is output. Therefore, data transfer errors due to clock dullness can be reduced. In particular, since differential signal lines are used for data transmission, there is little influence of waveform dullness and noise emission, and data transmission can be performed at high speed.

  Moreover, the reason why such a transmission method can be adopted for the transmission of the request signal is because the request signal is encoded. If the request signal is transmitted by changing the voltage level of the dedicated signal line as in the conventional technology, if the speed is increased, the timing may be shifted due to waveform dullness or interference between multiple clocks, or unsteady noise. Radiation increases. In addition, a malfunction may occur due to noise superimposed on the signal line. In contrast, in the present embodiment, since the request signal encoded by the signal in which the clock component is embedded is transmitted, the occurrence of such a problem is extremely reduced.

  FIG. 15 is a diagram showing the configuration of the head control block. Here, the Y head control block 410Y for yellow will be described, but the other blocks 410M, 410C, and 410K have the same structure. The main function of the Y head control block 410Y is to first generate request signals VREQ-Y and HREQ-Y at appropriate timing based on the synchronization signal Vsync given from the engine controller EC, and control the operation timing of each part. Second, the Y video data VD-Y given from the head side communication module 300 is subjected to signal processing required due to the structure of the line head 29 and supplied to the line head 29. .

  First, the first function will be described. The Y head control block 410Y is provided with a request signal generation unit 416 that generates request signals VREQ-Y and HREQ-Y based on a synchronization signal Vsync supplied from the engine controller EC. The request signal generation unit 416 starts counting an internal timer when receiving the synchronization signal Vsync, and outputs a vertical request signal VREQ-Y indicating the head of the page when a predetermined waiting time has elapsed. The synchronization signal Vsync from the engine controller EC is simultaneously applied to the head control blocks for each color, but the waiting time is set individually for each toner color. By setting the standby time according to the difference in the primary transfer position, the difference in data transfer timing for each color shown in FIG. 6 can be created.

  Subsequent to the output of the vertical request signal VREQ-Y, the request signal generation unit 416 repeatedly outputs the horizontal request signal HREQ-Y corresponding to the number of lines constituting one page image at a constant cycle. These request signals VREQ-Y and HREQ-Y are sent to the head-side communication module 300, multiplexed with request signals of other colors, and sent to the main controller MC.

  The horizontal request signal HREQ-Y is also input to the divided HREQ signal generation unit 417. The divided HREQ signal generation unit 417 multiplies the input request signal HREQ-Y by 16 times, for example, to generate a divided HREQ signal. To do. The divided HREQ signal is input to the gradation value control unit 413, the light emission order control unit 414, and the control signal generation unit 418, and the LED serving as the light source is controlled to turn on the light emission order and the light emission period finely based on the divided HREQ signal. Is done. Thereby, multi-tone dots can be formed with high positional accuracy, and as a result, high image quality can be obtained.

  Next, the second function will be described. In this embodiment, signal processing depending on the structure of the line head 29 is not performed by the main controller MC but by the head control block 410Y. In this way, even when line heads having different specifications are used, for example, it is only necessary to prepare a head control block that matches the specifications, and there is no need to change the processing contents in the main controller.

  The processing for the video data performed by the head control block 410Y is mainly correction processing for line head alignment and variations in light emission characteristics, and includes registration correction, skew correction, light amount correction, and curvature correction.

  FIG. 16 is a diagram showing alignment of the line head. As shown in FIG. 16A, the LED array 293 provided in the line head 29 has 37 LED chips 2931 in which 192 LED elements per chip are arranged in a line in the X direction, in the X direction. They are arranged. If there is a relative positional shift in the X direction among the LED array 293, the photosensitive drum 21, and the transfer belt 81, the position of the yellow toner image formed on the transfer belt 81 is shifted in the X direction. . It is resist correction that corrects this. The resist correction is performed as follows.

  The light emitting elements of the line head 29 are prepared for 7104 dots as shown in FIG. On the other hand, as described above, the maximum length of one line is 6828 dots. Therefore, it is not necessary for all light emitting elements to contribute to exposure. Therefore, among the 7104 dots prepared in advance, the light emitting element located at the end portion (hatched portion) is not turned on, but only the continuous 6828 dots in the central portion are turned on to contribute to the exposure, and the lighting range thereof. Is shifted in the X direction as necessary, so that the positional deviation in the X direction can be corrected.

  The misregistration amount (registration amount) can be obtained by a registration control process performed as necessary, for example, immediately after the apparatus is turned on. In the resist control, the Y image forming station 2Y is operated to form a resist mark having a predetermined image pattern on the transfer belt 81. Then, this registration mark is read by the patch sensor 89 and its position is detected. The amount of deviation between the position thus detected and the reference position of the registration mark is defined as the resist amount. The registration amount is managed by the engine controller EC, and is transmitted to the UART communication control unit 419 of the head control block 410Y as one of control parameters transmitted from the engine controller EC by UART communication. Thus, the resist correction unit 411 determines the lighting range of the LED array 293 according to the resist amount provided from the engine controller EC.

  Next, skew correction will be described. As shown in FIG. 16B, the arrangement direction of the line heads 29 may be inclined with respect to the original direction (X direction). The magnitude of this inclination is the skew amount, and the magnitude of the skew amount can also be obtained from the registration mark reading result. The skew correction for correcting this is performed by shifting the lighting timing of the LED element according to the amount of skew. In this embodiment, a skew correction unit 412 having line buffers for several lines is provided, and the skew correction unit 412 turns on each dot according to a skew amount given from the engine controller EC as one of the control parameters. Adjust timing.

  Next, light quantity correction will be described. As described above, the line head 29 is formed by arranging a plurality of chips. The light emission amounts of the LED elements are well aligned in each chip, but it is inevitable that the light emission amount varies among the chips. The process of correcting this and aligning the amount of light emission between the chips is light amount correction. The amount of light for each chip is written in advance as light amount information in an EEPROM 298 provided in the line head 29 at the stage of manufacturing the line head 29. The EEPROM communication control unit 421 provided in the head control block 410Y reads the light amount information stored in the EEPROM 298 and transmits it to the light amount correction value control unit 415. Based on this, the light amount correction value control unit 415 sets a light amount correction value and transmits it to the driver IC 295 provided in the line head 29. The driver IC 295 suppresses the light amount difference between the chips by adjusting the drive current amount of each chip based on the light amount correction value.

  Next, curvature correction will be described. As shown in FIG. 16C, in the line head 29, there is a slight variation in the mounting position between chips. The amount of deviation of each chip from the reference center line is the amount of bending here. Since the chip arrangement is fixed at the manufacturing stage of the line head 29, the bending amount of each chip measured in advance is written in the EEPROM 298 as bending information. Based on the bending information read from the EEPROM 298, the bending amount control unit 420 obtains the bending amount of each chip. The correction of the bending amount is performed by changing the lighting timing for each chip similarly to the skew correction. Therefore, the bending amount obtained by the bending amount control unit 420 is sent to the skew correction unit 412, and the skew correction unit 412. Then, the correction amount for each chip is determined by adding the given skew amount and bending amount.

  The corrected video data is input to the gradation value control unit 413. The gradation value control unit 413 converts the multi-gradation data into lighting intensity and lighting period length and transmits the converted data to the driver IC 295 of the line head 29. The driver IC 295 also receives a light amount correction value from the light amount correction value control unit 415 and a head control signal corresponding to the lighting control clock provided from the control signal generation unit 418, and the driver IC 295 is based on these signals. The IC 295 drives the LED array 293 to turn on. In this manner, the line heads 29 provided in the image forming stations 2Y, 2M, 2C, and 2K are appropriately controlled based on the image forming command to form an image.

  The above-described line head 29 of the present embodiment uses LED elements arranged in a row as an exposure light source. However, as described below, it is also possible to configure an image forming apparatus using a line head using an organic EL element as an exposure light source by using the same main controller MC and engine controller EC. When using an organic EL element as an exposure light source, it is necessary to use a head controller suitable for the organic EL element because the light emission principle and structure are different from those of the LED element.

  FIG. 17 is a diagram showing a configuration of a line head using an organic EL element. In this line head 290, an organic EL (electroluminescence) element is used as a light emission source instead of the LED element. That is, a glass substrate 2903 is attached on a base material 2901, and organic EL light emitting elements 2905 are arranged in three rows on the lower surface of the glass substrate 2903 (the surface in contact with the base material 2901) with the position slightly changed in the X direction. Are arranged in rows. That is, the light emitting elements 2905 have a so-called staggered arrangement. Light emitted from each light emitting element 2905 passes through the glass substrate 2903 and is emitted upward of the glass substrate 2903.

  A light shielding member 2907 is provided on the upper surface of the glass substrate 2903. In the light shielding member 2907, a plurality of light guide holes 2971 are formed one-on-one with respect to each light emitting element 2905. Further, the light guide hole 2971 is formed as a substantially cylindrical hole that penetrates the light shielding member 2907 with a line parallel to the normal line of the glass substrate 2903 as a central axis. Accordingly, light emitted from one light emitting element 2905 travels to the microlens array 2909 through the light guide hole 2971, and interference between light beams emitted from different light emitting elements 2905 is prevented by the light shielding member 2907. The light beam that has passed through the light guide hole 2971 formed in the light shielding member 2907 is imaged as a spot on the surface of the photosensitive drum 21 by the microlens array 2909, and is formed on the photosensitive drum 21 by the light beam. An electrostatic latent image is formed.

  FIG. 18 is a diagram showing a head control block suitable for a line head using organic EL elements. Although the Y head control block 510Y corresponding to the yellow toner color will be described here, the head control blocks corresponding to other colors also have the same structure. Further, the same components as those in the head control block suitable for the line head using the LED element shown in FIG.

  In this line head 290, since the EL light emitting elements 2905 are arranged in a staggered manner, a staggered arrangement correcting unit 513 for aligning dots formed by these in a line is provided. In addition, information regarding the skew amount given from the engine controller EC is input to the skew information control unit 515, and the skew information output therefrom is command data generation for generating command data for causing the EL element to emit light. This is input to the unit 517. Further, since a plurality of EL light emitting elements on one glass substrate 2903 are manufactured by the same manufacturing process, they are not curved as in the case of LED elements, and a function for correcting this is omitted. .

  Further, in the line head using EL elements, the variation in the light emission amount is small within one head, but the variation among individuals is relatively large. Current information related to the drive current value for correcting this is stored in an EEPROM 2908 provided in the line head 290. Further, information on the current value is also stored on the engine controller EC side, and the current value control unit 518 determines a drive current value from the stored current information, and sends it to the command data generation unit 517. The light emission data generation unit 514 generates light emission data for causing the EL element to emit light based on the corrected video data, the light amount correction value output from the light amount correction value control unit 516, and the command data output from the command data generation unit 517. Is transmitted to the driver IC 2906 provided in the line head 290. The driver IC 2906 drives the organic EL array based on the light emission data and the head control signal given from the control signal generation unit 418.

  Thus, in this embodiment, by using a head controller adapted to the configuration of the line head, the content of signal processing on the main controller MC side can be made independent of the configuration of the head. This means that, regardless of whether LED elements or organic EL elements are used, the same main controller MC can be used by preparing a head controller suitable for each. is doing.

  As described above, in this embodiment, the main controller MC that performs signal processing independent of the head configuration, the head controller HC that performs signal processing specific to the head configuration, and the LED array 293 that actually serves as the exposure light source are provided. The included line head 29 is configured as a separate body. By doing so, the line head 29 can be made compact, and the overall apparatus can be miniaturized by miniaturizing the image forming stations 2Y, 2M, 2C, and 2K. In addition, by separating the processing that depends on the configuration of the head from the main controller MC, it is possible to control line heads with different specifications with the same specification controller, reducing product development costs and facilitating multi-model deployment. be able to. For example, as described above, a line head using an LED element as a light source and a line head using an organic EL element as a light source can be controlled by the same main controller. When the specification of the line head is changed, only the head controller needs to be replaced with the line head.

  In this embodiment, request signals VREQ and HREQ transmitted from the head controller HC to the main controller MC for requesting video data are encoded. Therefore, the request signal can be transmitted at high speed without being affected by noise. Also, by encoding, a plurality of request signals can be multiplexed and combined into one signal, and all request signals can be transmitted through one set of signal lines. Therefore, an increase in signal lines can be suppressed even when the number of colors is large.

  Further, instead of transmitting video data from the main controller MC in synchronization with a request signal from the head controller HC, the head controller HC simply outputs request signals VREQ and HREQ at its own timing as a trigger for video data transmission. In response, the main controller MC also outputs video data at its own timing, that is, asynchronously with the request signal. Therefore, even in a tandem type image forming apparatus in which request signals are output in parallel from each image forming station according to the difference in the primary transfer position, video data of each color is multiplexed. Can be transmitted at the required timing. Further, since the head controller HC outputs a request signal for each line constituting the image at a necessary timing, it is not necessary to provide a large-capacity buffer for storing data on the head controller HC side. In addition, the main controller MC only needs to be configured to transmit data when requested, and it is necessary to manage the transmission timing due to the configuration of each image forming station and the difference in the primary transfer position. There is no.

  In this embodiment, when the video data VD is transmitted from the main controller MC to the head controller HC, the reference clock provided on the main controller MC side is modulated by the video data VD and output. By transmitting video data as a signal in which the clock component is embedded in this way, there is no need to transmit a separate clock signal, the number of signal lines can be reduced, and transmission errors caused by the slack of the clock waveform can be suppressed. it can. As a result, the transmission speed can be further increased, and it is possible to flexibly respond to the demands for higher image quality and more colors. In addition, by using the transmitting clock as a reference clock, it is possible to suppress the occurrence of problems caused by routing the high-frequency clock. In particular, by adopting the differential transmission method, it is possible to transmit data at high speed while suppressing the influence of noise.

  Further, in this embodiment, the signal processing required due to the configuration of the line head, more specifically, the manufacturing variation of the line head and the variation when assembling the device to the apparatus is consolidated in the head control block. I am trying to do it. The variation in the amount of emitted light determined at the manufacturing stage of the line head and the amount of displacement of the mounting position of the chip are stored in the EEPROM provided in the line head, while the amount of resist and the amount of skew generated during assembly to the apparatus are stored. A patch sensor is provided and managed by an engine controller EC that can detect these amounts, and the head control block reads out the information and performs necessary corrections. As a result, individual differences between line heads and devices can be absorbed only by the head control block, and there is no need to manage these individual differences on the main controller side.

  As described above, in this embodiment, each of the image forming stations 2Y, 2M, 2C, and 2K corresponds to the “image forming station” of the present invention. In addition, the photosensitive drum 21, the line head 29, and the developing unit 25 provided in each image forming station function as the “photosensitive member”, “exposure unit”, and “developing unit” of the present invention, respectively. The transfer belt 81 functions as the “transfer medium” of the present invention.

  In this embodiment, the head controller HC and the main controller MC function as “lighting control means” and “signal processing means” of the present invention, respectively. In this embodiment, the reception block 320 provided in the head side communication module 300 functions as the “demultiplexing processing unit” of the present invention.

  The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, in the above embodiment, the data length of data exchanged between the main controller MC and the head controller HC is 32 bits, but the data length is not limited to this and is arbitrary.

  Further, for example, in communication between the main controller MC and the head controller HC in the above embodiment, data transmission is performed after converting 32-bit data into 40-bit data by adding 2 additional bits per 8 bits. . However, whether or not to perform such data conversion is arbitrary in the present invention, and data may be transmitted without adding additional bits. Further, error correction is also optional, and error correction may not be performed or other error correction methods may be employed.

  Further, in the image processing unit 100 provided in the main controller MC of the above embodiment, image data before image processing is stored in the image memory, and when requested by the head controller HC, each image processing block Is output as video data after performing necessary processing. However, the present invention is not limited to this. For example, when image data is received from an external device, image processing is performed and the processed image data is stored in the image memory. These may be read out sequentially and sent out.

  In the above embodiment, as data to be transmitted from the head controller HC to the main controller MC, 32-bit data is divided into 4 sections by 8 bits and 8 types of request signals are assigned to each bit. It is not limited to this. For example, another signal may be assigned to any bit. In the above embodiment, when a value of 1 is set for a bit in one section, it is considered that a request signal corresponding to the bit is output. It may be determined that the request signal is output for the first time when the value 1 is continuously raised.

  Further, in the transmission of video data from the main controller MC to the head controller HC in the above embodiment, 32-bit data is divided every 8 bits and assigned to each toner color. In addition, the color may be distinguished by adding a code indicating the toner color to the video data and transmitting it.

  In addition, since the communication between the main controller MC and the head controller HC in the above embodiment is configured to send the data for four colors at arbitrary timings, other toners are executed when the monochrome mode is executed. The data area allocated for the color will not be used at all. Therefore, in order to perform data transmission more efficiently, a communication protocol different from that in the color mode described above may be applied to the monochrome mode. For example, one data frame may be assigned to the monochrome color. In this way, a larger amount of data can be transmitted in the same communication time, and the communication time can be shortened or video data with higher definition can be transmitted.

  Furthermore, in the above embodiment, the present invention is applied to a color image forming apparatus using YMCK four-color toner, but the application target of the present invention is not limited to this, and the types of colors and the number of colors The present invention can also be applied to different image forming apparatuses.

1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a diagram illustrating an arrangement of image forming stations in the image forming apparatus of FIG. 1. FIG. 2 is a diagram illustrating an electrical configuration of the image forming apparatus in FIG. 1. The figure which shows the structure of a line head. The figure which shows the communication between a main controller and a head controller. The figure which shows the communication timing for every color. The figure which shows the content of the data transmitted from a head controller. The timing chart which shows the example of a request signal. The figure which shows the result of having encoded the pattern of FIG. The figure which shows the content of the data transmitted from a main controller. The figure which shows the connection of a main controller and a head controller. The figure which shows the structure of a main controller. The figure which shows typically the video data on a signal wire | line. The figure which shows the structure of a head controller. The figure which shows the structure of a head control block. The figure which shows alignment of a line head. The figure which shows the structure of the line head which uses an organic EL element. The figure which shows the head control block suitable for the line head by an organic EL element.

Explanation of symbols

  2Y, 2M, 2C, 2K ... image forming station (image forming station), 21 ... photoconductor drum (photoconductor), 25 ... developing unit (developing unit), 29 ... line head (exposure unit), 81 ... transfer belt ( Transfer medium), 320... Receiving block (demultiplexing processing unit), HC... Head controller (lighting control means), MC. Main controller (signal processing means)

Claims (7)

An exposure unit having a photosensitive member charged to a predetermined surface potential, a line head in which a plurality of light emitting elements are arranged in a line, and exposing the surface of the photosensitive member to form an electrostatic latent image; A plurality of image forming stations each having developing means for developing the latent image with toner;
Lighting control means for controlling lighting of the line heads provided in each of the image forming stations based on video data;
Signal processing means for performing signal processing on the image signal to generate the video data corresponding to each of the image forming stations, and transmitting to the lighting control means,
The lighting control unit has a function of repeatedly transmitting a serial signal having a predetermined number of bits to one word to the signal processing unit, and the signal processing starts the transmission of the video data for each of the plurality of image forming stations. By assigning each of a plurality of request signals requested to the means to each bit in one word of the serial signal, the plurality of request signals are multiplexed into one serial signal and transmitted to the signal processing means. ,
The signal processing means has a function of repeatedly transmitting a serial signal having a predetermined number of bits to one word to the lighting control means, and each of the plurality of sections into which one word of the serial signal is divided By assigning the video data to be transmitted to each of the image forming stations, the video data corresponding to the request signal of each of the plurality of image forming stations is multiplexed into one serial signal and transmitted to the lighting control means. An image forming apparatus. Each of the image forming stations is configured to form a toner image as an aggregate of a large number of dots,
The image forming apparatus according to claim 1 , wherein the signal processing unit assigns data for each dot to each section of the serial signal transmitted to the lighting control unit. The image forming stations are arranged along a moving direction of a transfer medium moving in a predetermined direction, and are configured to sequentially transfer the toner images visualized by the image forming station to the transfer medium at different transfer positions. And
The lighting control unit transmits the request signal generated at different timing for each of the image forming stations due to the difference in the transfer position to the signal processing unit as the serial signal each time,
The signal processing means multiplexes the video data by synchronous time division multiplexing, and the video data to be transmitted to each of the image forming stations is timed according to the request signal corresponding to the image forming station. in the image forming apparatus according to claim 1 or 2 outputs. A monochrome operation mode for forming an image by operating only one of the plurality of image forming stations, and a color operation mode for forming a color image by operating the plurality of image forming stations having different color toners. Is configured to run,
The image forming apparatus according to claim 3 , wherein the signal processing unit multiplexes the video data by synchronous time division multiplexing when executing either the monochrome operation mode or the color operation mode. A monochrome operation mode for forming an image by operating only one of the plurality of image forming stations, and a color operation mode for forming a color image by operating the plurality of image forming stations having different color toners. Is configured to run,
The signal processing means multiplexes the video data by synchronous time division multiplexing at the time of execution of the color operation mode, while not performing multiplexing at the time of execution of the monochrome operation mode. the image forming apparatus according to any one of claims 1 to send the corresponding video data to the lighting control means as said serial signal 3. It said lighting control means, to any one of claims 1 to 5 comprising a demultiplexing unit for developing the serial signal received from the signal processing unit demultiplexes the video data for each of the respective image forming stations The image forming apparatus described. Signal processing is performed on the image signal by the signal processing means, and video data corresponding to each of a plurality of image forming stations each having a line head in which a plurality of light emitting elements are arranged in a row is generated and transmitted to the lighting control means. Then, lighting of each line head provided in each image forming station is controlled based on the video data by the lighting control means, thereby forming an electrostatic latent image on the surface of the photosensitive member, and In an image forming method for forming an image by visualizing with toner,
By assigning each of a plurality of request signals for requesting the start of transmission of the video data for each of the plurality of image forming stations to each bit of a periodic serial signal having a predetermined number of bits as one word, the plurality of requests While the signal is multiplexed into one serial signal and transmitted from the lighting control means to the signal processing means,
In response to the request signal, by assigning the video data corresponding to the plurality of image forming stations to each of a plurality of sections obtained by dividing one word of a periodic serial signal having a predetermined number of bits as one word. An image forming method comprising: multiplexing the video data corresponding to the request signal of each of the plurality of image forming stations into one serial signal and transmitting the multiplexed signal from the signal processing unit to the lighting control unit.

Images