JP4626247B2 - Line head and image forming apparatus - Google Patents

Description

  The present invention relates to a line head and an image forming apparatus.

There is a line head as a device that is incorporated in an electrophotographic image forming apparatus such as a copying machine or a printer and forms (exposes) an electrostatic latent image on the surface of a photoreceptor. In this line head, a large number of light-emitting elements are arranged in a one-dimensional manner on a substrate, and each light-emitting element is driven through wiring patterned on the substrate. As the light emitting element of such a line head, a light emitting diode (LED), an organic EL element or the like is used. For example, the following publicly known documents disclose a light emitting element array and an image forming apparatus corresponding to such a line head.
JP 11-27469 A

  By the way, in an organic EL panel used for such a line head, data lines and control signal lines are usually wired along the arrangement of light emitting elements. Therefore, since the wiring length of these wirings reaches, for example, several tens of centimeters, there is a problem that static electricity is likely to be superimposed and electrostatic breakdown easily occurs in circuits other than the input buffer. Also, it is necessary to take countermeasures against electrostatic breakdown in the input section.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a line head and an image forming apparatus capable of preventing electrostatic breakdown of a circuit connected to a data line and a control signal line. It is to provide.

  In order to solve the above-described problem, in the present invention, as a first means related to a line head, a light emitting element line in which a plurality of light emitting elements are arranged in one line is provided and a data signal is supplied to the light emitting element. A line head provided along the light-emitting element line and a control signal line for transmitting a control signal for controlling light emission of the light-emitting element and the light-emitting element, at least at the end of the data line and / or the control signal line. The solution of providing an electric protection circuit is adopted. According to the present invention, electrostatic breakdown of a circuit connected to a data line and / or a control signal line can be prevented.

  Further, as a second means related to the line head, a solution means is adopted in which the electrostatic protection circuit is further provided in the preceding stage of the input buffer inserted in the data line in the first means. According to the present invention, electrostatic breakdown of a circuit connected to a data line or / and a control signal line can be prevented more reliably.

  As a third means related to the line head, a solution means is provided in which the electrostatic protection circuit is further provided in the subsequent stage of the input buffer inserted in the data line in the first or second means. According to the present invention, electrostatic breakdown of a circuit connected to a data line or / and a control signal line can be prevented more reliably.

  As a fourth means related to the line head, in any of the first to third means, when the light emitting element is driven by a thin film transistor formed by a thin film process, the electrostatic protection circuit is formed by a thin film process. The solution means that the thin film transistor is diode-connected. According to this invention, the abnormal voltage protection circuit can be easily formed by the same thin film process as the thin film transistor for driving the light emitting element.

  On the other hand, in the present invention, as a first means related to the image forming apparatus, a photoconductor, a charging unit for uniformly charging the photoconductor, and any one of the first to fourth line heads are provided, and the photoconductor An exposure unit that forms an electrostatic latent image of an image to be formed on the photoconductor by exposing the photoconductor; a developing unit that develops the electrostatic latent image on the photoconductor as a toner image; and A solution means is provided which comprises a transfer means for transferring a toner image onto a transfer material and a fixing means for fixing the toner image on the transfer material. According to such an invention, the electrostatic breakdown of the clock signal line can be prevented, so that it is possible to prevent the occurrence of a malfunction and realize a stable operation.

  As a second means related to the image forming apparatus, a solution means for forming a color image in the first means is adopted. According to this invention as well, it is possible to prevent electrostatic breakdown of the clock signal line in the line head for forming a color image, so that it is possible to prevent the occurrence of trouble and realize stable operation.

  Hereinafter, a line head and an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a circuit diagram showing a partial circuit configuration of a line head according to an embodiment of the present invention. In FIG. 1, the data line of the land head 1 and one light emitting element are shown. In FIG. 1, only one light emitting element 321 is shown, but the actual land head 1 has n (for example, 5120) light emitting elements arranged in a line.

  The data line 312 transmits a data signal via the protective resistor 310 and the input buffer 311. The data signal is supplied from the data line 312 via the lead line 313 to the holding transistor TFT1 formed as a thin film transistor. Further, such a data signal is synchronized with a selection signal transmitted through the gate line 306. In the data line 312, the ESD protection element 60 is provided at the front stage of the input buffer 311, and the ESD protection element 61 is provided at the tip. These ESD protection elements 60 and 61 are composed of thin film transistors TFT-A and TFT-B connected in series to each other and connected in diodes, and operate as an electrostatic protection circuit.

  The holding transistor TFT1 is turned on / off according to a selection signal supplied via the gate line 306, and switches the driving transistor TFT2. Light emission / non-light emission of the light emitting element 321 is controlled according to the ON / OFF state of the driving transistor TFT2 and the L (low) / H (high) state of the data signal.

  That is, the selection signal is generated by inputting a start signal to a shift register described later and transferring the start signal in synchronization with the clock signal. The selection signal thus generated is supplied to the holding transistor TFT1 through the gate line 306 to select the light emitting element 321. Then, when the data signal is input to the drive transistor TFT2 via the holding transistor TFT1, the light emitting element 321 selected by the selection signal is turned on / off.

  As shown in FIG. 2, an ESD protection element 62 may be provided after the input buffer 311. The ESD protection element 62 includes thin film transistors TFT-A and TFT-B that are connected in series and diode-connected, like the ESD protection elements 60 and 61 described above, and operate as an electrostatic protection circuit.

  Next, FIG. 3 is a schematic diagram showing a circuit layout of the line head 1. In addition, the same code | symbol is attached | subjected to the part corresponding to FIG. As shown in FIG. 3, the shift register 303 is arranged between a start signal line 304 and a clock signal line 305 which are control signal lines. Further, adjacent to the start signal line 304, the data line 312 and the holding transistor TFT1 are arranged along the arrangement direction of the light emitting elements 321. Further, the light emitting element 321 and the driving transistor TFT2 are arranged in a line adjacent to the data line 312 and the holding transistor TFT1.

  A power supply wiring 301 is disposed adjacent to the light emitting element 321 and the driving transistor TFT 2, and a ground wiring 302 is disposed adjacent to the power supply wiring 301. Further, on the back side of the light emitting element 321 and the driving transistor TFT2, a ground contact portion 302a for drawing out the ground wiring 302 to the back side and a back cathode 302b are arranged. The ESD protection element 60 is disposed adjacent to the input buffer 311, and the ESD protection element 61 is disposed near the end of the data line 312.

  A characteristic point in the configuration of the line head 1 is that ESD protection elements 60, 61, 62 are provided at various locations on the data line 312. As shown in FIG. 3, since the data line 312 is provided long along the arrangement direction of the light emitting elements 321, the impedance increases as the distance from the tip of the data line 312 increases, and a high voltage is generated when static electricity is superimposed. . Therefore, by providing the ESD protection element 61 at least at the tip of the data line 312, it is possible to prevent electrostatic breakdown of a circuit connected to the data line 312. Further, by providing the ESD protection elements 60 and 62 in addition to the ESD protection element 61, electrostatic breakdown can be more reliably prevented.

  Next, an image forming apparatus according to the present embodiment, that is, an image forming apparatus using the above-described line head 1 as four line heads 11K, 11C, 11M, and 11Y will be described.

  First, with reference to the block diagram shown in FIG. 4, a functional configuration relating to image data processing of the image forming apparatus will be described. The overall control unit that controls the overall operation of the image forming apparatus is provided with a data processing unit 9 including a CPU, an image processing circuit, and the like, and a storage unit 10 that stores original image data and the like. The image forming apparatus forms a color image in addition to a black and white image, and corresponds to the primary colors “black”, “cyan”, “magenta”, and “yellow” when forming the image. Two line heads 11K, 11C, 11M, and 11Y are provided.

  Here, alphabets K, C, M, and Y attached to the end of the reference numerals of the line heads 11K, 11C, 11M, and 11Y mean black, cyan, magenta, and yellow, which are primary colors for forming an image, respectively. is doing. The addition of the alphabets K, C, M, and Y is the same for the other members described below.

  The data processing unit 9 reads the original image data (bitmap data) transmitted from the external host computer to the image forming apparatus and stored in the storage unit 10, and performs screen processing, color conversion processing, data conversion processing, data Transfer processing is performed. Screen processing is performed for the purpose of ensuring gradation reproducibility by matching with the process conditions of the image forming apparatus, and combining line patterns, error diffusion patterns, dot patterns, etc. It is processing.

  In the color conversion process, the screen-processed image data is converted into data separated into colors corresponding to the line heads 11K, 11C, 11M, and 11Y. The data conversion process is a process of converting the image data subjected to the color conversion process into a data signal for transmission to each of the line heads 11K, 11C, 11M, and 11Y. The data transfer process is a process for transferring the transmission data to the line heads 11K, 11C, 11M, and 11Y.

  FIG. 5 is a longitudinal side view showing a mechanism configuration of the image forming apparatus according to the present embodiment. In this image forming apparatus, four line heads 11K, 11C, 11M, and 11Y having the same configuration are arranged at the exposure positions of four corresponding photosensitive drums 12K, 12C, 12M, and 12Y, respectively. And is configured as a tandem image forming apparatus.

  This image forming apparatus is provided with a driving roller 13, a driven roller 14, and a tension roller 15, and is tensioned by the tension roller 15 to be stretched and circulated and driven in the direction indicated by the arrow (counterclockwise). A transfer belt 16 is provided. Photosensitive members 12K, 12C, 12M, and 12Y having photosensitive layers are arranged on the outer peripheral surface as four image carriers arranged at predetermined intervals with respect to the intermediate transfer belt 16.

  The photosensitive drums 12K, 12C, 12M, and 12Y are driven to rotate in the direction indicated by the arrow (clockwise) in synchronization with the driving of the intermediate transfer belt 16. Further, around the photosensitive drums 12K, 12C, 12M, and 12Y, corona chargers 17K, 17C, 17M, and 17Y for uniformly charging the outer peripheral surfaces of the photosensitive drums 12K, 12C, 12M, and 12Y; The outer peripheral surfaces of the photosensitive drums 12K, 12C, 12M, and 12Y uniformly charged by the corona chargers 17K, 17C, 17M, and 17Y are synchronized with the rotation of the photosensitive drums 12K, 12C, 12M, and 12Y. Thus, line heads 11K, 11C, 11M, and 11Y that sequentially scan the lines are provided.

  Further, around each of the photosensitive drums 12K, 12C, 12M, and 12Y, a toner that is a developer is added to the electrostatic latent images formed by the line heads 11K, 11C, 11M, and 11Y to form toner images. Development devices 18K, 18C, 18M, and 18Y, and primary transfer rollers 19K as transfer means for sequentially transferring the toner images developed by the development devices 18K, 18C, 18M, and 18Y to the intermediate transfer belt 16 that is a primary transfer target. 19C, 19M, and 19Y, and cleaning devices 20K, 20C, 20M, and 20Y that remove toner remaining on the surfaces of the photosensitive drums 12K, 12C, 12M, and 12Y after being transferred are provided.

  Here, the line heads 11K, 11C, 11M, and 11Y are fixed so that the arrangement direction of the organic EL light-emitting elements described above is parallel to the buses of the photosensitive drums 12K, 12C, 12M, and 12Y. Further, the peak wavelength of the light emission energy of each of the line heads 11K, 11C, 11M, and 11Y and the sensitivity peak wavelength of each of the photosensitive drums 12K, 12C, 12M, and 12Y are set so as to substantially match.

  The developing devices 18K, 18C, 18M, and 18Y use, for example, non-magnetic one-component toner as a developer, and the developer that is conveyed to the developing roller by, for example, a supply roller and adhered to the surface of the developing roller. Is regulated by a regulating blade, and the developing roller is brought into contact with or increased in thickness on each of the photosensitive drums 12K, 12C, 12M, and 12Y, thereby depending on the potential level of each of the photosensitive drums 12K, 12C, 12M, and 12Y. The toner is developed as a toner image by attaching a developer.

  The black, cyan, magenta, and yellow toner images formed by the four-color single-color toner image forming station are transferred to the intermediate transfer belt 16 by the primary transfer bias applied to the primary transfer rollers 19K, 19C, 19M, and 19Y. The toner image that has been firstly transferred onto the intermediate transfer belt 16 and superimposed on the intermediate transfer belt 16 to become a full color is secondarily transferred to a recording medium P such as a sheet by the secondary transfer roller 21, and a fixing roller pair as a fixing unit. The sheet is fixed on the recording medium P by passing through 22 and discharged onto a discharge tray 24 formed on the upper part of the apparatus by a pair of discharge rollers 23. The secondary transfer roller 21 forms a secondary transfer portion with the intermediate transfer belt 16.

  In this mechanism configuration, reference numeral 25 denotes a paper feeding cassette in which a large number of recording media P are stacked and held, 26 denotes a pickup roller that feeds the recording media P from the paper feeding cassette 25 one by one, and 27 denotes a secondary roller. A pair of gate rollers 28 that regulates the supply timing of the recording medium P to the secondary transfer portion of the transfer roller 21 is a cleaning blade that removes toner remaining on the surface of the intermediate transfer belt 16 after the secondary transfer.

  According to such an image forming apparatus, since the line head 1 according to the present embodiment is used, it is possible to prevent electrostatic breakdown of various circuits in the line head 1, thereby preventing occurrence of malfunction and stability. The operation can be realized.

In addition, this invention is not limited to the said embodiment, For example, the following modifications can be considered.
(1) In the embodiment described above, the ESD protection elements 60 and 61 are provided on the data line 312 to prevent electrostatic breakdown of various circuits connected to the data line 312. In addition, there are control signal lines such as a start signal line 304 and a clock signal line 305 as wirings provided long along the arrangement direction of the light emitting elements 321. Therefore, by providing an ESD protection element in such a control signal line, it is possible to prevent electrostatic breakdown of a circuit connected to the control signal line.

(2) In the above embodiment, the ESD protection elements 60 to 62 are formed of thin film transistors in the same manner as the holding transistor TFT1 and the driving transistor TFT2. This is to enable the ESD protection elements 60 to 62 to be formed on the substrate in the same manner as the holding transistor TFT1 and the driving transistor TFT2, but the present invention is not limited to this.
(3) Although the tandem image forming apparatus has been described in the above embodiment, the present invention is not limited to the tandem method.

It is a circuit diagram which shows the partial circuit structure of the line head concerning one Embodiment of this invention. It is a circuit diagram which shows the partial circuit structure of the line head concerning the modification of one Embodiment of this invention. It is a schematic diagram which shows the circuit layout of the line head concerning one Embodiment of this invention. FIG. 3 is a block diagram relating to image data processing of the image forming apparatus according to an embodiment of the present invention. 1 is a cross-sectional view showing a mechanism configuration of an image forming apparatus according to an embodiment of the present invention.

Explanation of symbols

1 line head, 60 to 62 ESD protection element, 311 input buffer, 301 power supply wiring, 302 ground wiring, 302b backside cathode, 303 shift register, 304 start signal line, 305 clock signal line, 306 gate line, 310 protection resistor, 312 Data line, 313 lead line, 321 light emitting element,

Claims (6)

A light emitting element line in which a plurality of light emitting elements are arranged in one line is provided, and a data line for supplying a data signal to the light emitting element and a control signal line for transmitting a control signal for controlling light emission of the light emitting element are emitted. A line head provided along the element line,
An electrostatic protection circuit is provided at least at a terminal of the data line and / or the control signal line.   The line head according to claim 1, wherein the electrostatic protection circuit is further provided in a stage preceding the input buffer interposed in the data line.   3. The line head according to claim 1, wherein the electrostatic protection circuit is further provided at a stage subsequent to the input buffer inserted in the data line. 4.   4. When the light emitting element is driven by a thin film transistor formed by a thin film process, the electrostatic protection circuit is a diode-connected thin film transistor formed by a thin film process. The line head described. A photoreceptor,
Charging means for uniformly charging the photoreceptor;
An exposure unit comprising the line head according to claim 1, and exposing the photosensitive member to form an electrostatic latent image of an image to be formed on the photosensitive member;
Developing means for developing the electrostatic latent image on the photoreceptor as a toner image;
Transfer means for transferring a toner image on the photoreceptor to a transfer material;
An image forming apparatus comprising: a fixing unit that fixes the toner image on the transfer material. 6. The image forming apparatus according to claim 5, wherein a color image is formed.

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