Patent Publication Number: US-7911488-B2

Title: Ion print head and image forming apparatus using the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from Korean Patent Application No. 2004-72076, filed on Sep. 9, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein its entirety by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present general inventive concept relates to an ion print head and an image forming apparatus using the same, and more particularly, to an ion print head in which a discharge cell array structure having microelectrodes is employed, and a image forming apparatus using the same. 
     2. Description of the Related Art 
     In a conventional image forming apparatus, a charged photoconductor is exposed to a laser beam, thereby forming a latent image on an image forming part. A toner is supplied between the photoconductor and a development roller to selectively adhere the toner on the image forming part according to an electrostatic property thereof. Herein, the development roller engages the photoconductor but has a different electrostatic potential than the photoconductor. Since the conventional image forming apparatus uses laser beams, a laser scanning unit is required to expose the photoconductor. However, the laser scanning unit requires a precise optical arrangement. Additionally, the laser scanning unit is expensive. 
     In an attempt to avoid these disadvantages associated with the conventional image forming apparatus that used the laser scanning unit, a printer with a conventional ion print head is disclosed in U.S. Pat. No. 5,406,314. The printer with the conventional ion print head of U.S. Pat. No. 5,406,314 is illustrated in  FIGS. 1 and 2 . 
       FIG. 1  is a schematic sectional view illustrating a printer that uses a conventional ion print head. Referring to  FIG. 1 , the printer includes an image cylinder  15  having a conductive layer  17  and a dielectric layer  16 , and erase lamp  14 , an electronic writing head  30  for charging the image cylinder  15  to have a predetermined pattern that corresponds to a latent image according to control exerted by a controller, an ink-supply roller  12  in contact with the image cylinder  15  for supplying ink while rotating, a transfer roller  18  for transferring the latent image formed on the image cylinder  15  to a printing medium  10 , and a heating element  21  and a hot roller  23  for fusing the transferred image on the printing medium  10 . A printing operation performed by the printer is as follows: the electronic writing head  30  forms the latent image having the predetermined pattern on the image cylinder  15 , the ink-supply roller  12  supplies ink to the image cylinder  15 , the supplied ink adheres on a latent image area of an outer surface of the image cylinder  15  to form an ink image thereon. The transfer roller  18  then transfers the ink image of the image cylinder  15  to the printing medium  10 , which passes between the image cylinder  15  and the transfer roller  18 . The heating element  21  and the hot roller  23  then fuse the transferred image on the printing medium  10 . 
       FIG. 2  is a schematic sectional view illustrating the electronic writing head  30  of the conventional ion print head of  FIG. 1 . 
     Referring to  FIG. 2 , the electronic writing head  30  includes an insulating body  31 , a needle electrode  35 , a wraparound electrode  37 , and a power supply  39  for supplying voltage pulses to the needle electrode  35 . The insulating body  31  is spaced apart from the dielectric layer  16  in a perpendicular direction and has a tunnel  31   a  disposed therein. The needle electrode  35  is formed on an inside wall of the tunnel  31   a  and has a leading end pointing toward an opposite inner wall of the tunnel  31   a . The wraparound electrode  37  is formed at a portion of the tunnel  31   a  that is adjacent to the dielectric layer  16 . 
     Accordingly, when a voltage pulse is applied to the needle electrode  35 , gas molecules in the proximity of the needle electrode  35  lose at least one electron under the influence of a strong electrostatic field created by the needle electrode  35 . The electrons are then absorbed by the needle electrode  35 . Positive ions from the gas molecules that lose at least one electron tend to migrate away from the needle electrode  35  to a lower electrical potential at a bottom portion of the tunnel  31   a  where the positive ions encounter and are neutralized by the wraparound electrode  37 . The positive ions are more strongly attracted to the conductive layer  17  than by the wraparound electrode  37  because an electric potential of the conductive layer  17  is more negative than is an electric potential of the wraparound electrode  37 . Thus, the positive ions can be accumulated on the dielectric layer  16  to form the latent image thereon. 
     The disadvantage of the conventional ion print head of the printer is that the needle electrode  35  in the insulating body  31  is arranged in a radial direction of the image cylinder  15  and the wraparound electrode  37  is additionally provided at the bottom of the tunnel  31   a , thereby increasing complexity of the electronic writing head  30 . Additionally, the process of accumulating the positive ions on the dielectric layer  16  of the image cylinder  15  is complicated. 
     SUMMARY OF THE INVENTION 
     The present general inventive concept provides an ion print head and an image forming apparatus using the same including at least one discharge cell array structure having microelectrodes. The ion print head and the image forming apparatus using the same can be simply constructed. 
     Additional aspects of the present general inventive concept will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the general inventive concept. 
     The foregoing and/or other aspects of the present general inventive concept may be achieved by providing an ion print head to form an electrostatic latent image on an insulation layer of an electrostatic drum by selectively applying charged particles to the insulation layer. The ion print head includes at least one discharge cell provided with a plurality of discharge elements to emit the charged particles, and each of the discharge elements includes a base, a microelectrode disposed on the base to emit the charged particles toward the insulation layer, and a control electrode spaced apart from the base and having a hole therein through which the emitted charged particles pass and to control the emission of the charged particles from the microelectrode. The ion print head further includes a controller to control the plurality of discharge elements of the at least one discharge cell. 
     The foregoing and/or other aspects of the present general inventive concept may also be achieved by providing an image forming apparatus including: an electrostatic drum on which a latent image is formed, an ion print head having a structure of at least one discharge cell having a base, a microelectrode, and a control electrode to form a latent image on an insulation layer of the electrostatic drum by selectively applying charged particles to the insulation layer, a development unit to apply a developer to the charged insulation layer of the electrostatic drum to form a developer image that corresponds to the latent image, a transfer unit to transfer the developer image of the electrostatic drum to a printing medium, and a fuse to fuse the transferred image on the printing medium. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects of the present general inventive concept will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a schematic sectional view illustrating a printer that uses a conventional ion print head. 
         FIG. 2  is a schematic sectional view illustrating an electronic wiring head of the conventional ion print head of  FIG. 1 ; 
         FIG. 3  is a schematic perspective view illustrating an ion print head according to an embodiment of the present general inventive concept; 
         FIG. 4  is a schematic plain view illustrating a discharge cell array of the ion print head of  FIG. 3 ; 
         FIG. 5  is a schematic sectional view illustrating a discharge element of the ion print head of  FIG. 3 ; and 
         FIG. 6  is a schematic view illustrating an image forming apparatus employing an ion print head according to an embodiment of the present general inventive concept. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the embodiments of the present general inventive concept, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present general inventive concept while referring to the figures. 
       FIG. 3  is a schematic perspective view illustrating an ion print head according to an embodiment of the present general inventive concept. 
     Referring to  FIG. 3 , an ion print head selectively applies charged particles on an insulation layer  55  of an electrostatic drum  50 , such that the selectively charged insulation layer  55  forms a latent image. The ion print head includes a discharge cell array  60  including a discharge cell  70  (or a plurality of discharge cells  70 ) having a plurality of discharge elements  70   a  to emit the charged particles and a controller  79  to control the discharge elements  70   a . The ion print head may include the discharge cell array  60  including a plurality of groups of discharge cells  70  each having a plurality of discharge cells  70  in one or more directions. 
     The electrostatic drum  50  includes a conductor  51  and the insulation layer  55  coated on an outer surface of the conductor  51 . The conductor  51  provides electric stability for the electrostatic drum  50  and lowers sensitivity of the electrostatic drum  50  against humidity, temperature, etc. Additionally, the conductor  51  receives a bias voltage from the controller  79  to form an electric field. The insulation layer  55  holds the charged particles that are selectively applied by the ion print head on a surface thereof. 
       FIG. 4  is a schematic plain view illustrating the discharge cell array  60  of the ion print head of  FIG. 3 . 
     Referring to  FIGS. 3 and 4 , the discharge cell  70  having the plurality of discharge elements  70   a  may include a plurality of discharge cells  70 . The discharge cells  70  are arranged in a longitudinal direction of the electrostatic drum  50  to form the discharge cell array  60 . Each of the discharge cells  70  independently emits the charged particles toward a corresponding surface portion of the electrostatic drum  50  to form the latent image (i.e., an electrostatic latent image) on the electrostatic drum  50 . The plurality of discharge elements  70   a  of each of the discharge cells  70  may be arranged in both the longitudinal and transverse directions of the electrostatic drum  50  to form a multi-line latent image at a particular time. In other words, the discharge elements  70   a  of each of the discharge cells  70  may be arranged in two dimensions to be capable of forming more than one line of the latent image at the particular time (i.e., at one time). 
     Further, each of the discharge cells  70  may be replaced independently such that the discharge cell array  60  can be easily formed, replaced, and repaired. The controller  79  and the discharge cell array  60  are electrically connected. Herein, the electrical connection is constructed such that each of the discharge cells  70  can be replaced independently. A detailed description of the electrical connection will not be provided, since electrical connections should be well known to one skilled in the art. 
       FIG. 5  is a schematic sectional view illustrating a discharge element  70   a  of the ion print head of  FIG. 3 . 
     Referring to  FIGS. 4 and 5 , each of the discharge elements  70   a  of the discharge cell  70  includes a base  71 , a microelectrode  73 , and a control electrode  77  spaced above the base  71 . Additionally, a spacer  75  is disposed between the base  71  and the control electrode  77  to provide a space therebetween. 
     The microelectrode  73  is disposed on the base  71  and between the spacer  75  to emit charged particles toward the insulation layer  55  of the electrostatic drum  50 . Although an emission of negatively charged particles is illustrated in  FIG. 5 , it should be understood that the polarity of the charged particles can be controlled to have a positive or a negative charge by adjusting a voltage applied by the controller  79 . Herein, a polarity of a developer (e.g., toner or ink) can determine the polarity of the charged particles. 
     The microelectrode  73  may have an aspect ratio (H/W) that satisfies the equation below in order to maximize an electric field around an end of the microelectrode  73 .
 
 H/W =10  [Equation]
 
where H and W represent a height and a width of the microelectrode  73 , respectively.
 
     A large aspect ratio enables the microelectrode  73  to create a high electric field around the end thereof, thereby ionizing surrounding air. The microelectrode  73  may have a rod, a pyramid, or a needle shape that has a large aspect ratio.  FIG. 5  illustrates the microelectrode  73  having the needle shape. 
     Further, the microelectrode  73  may be made of a carbon nanotube, silicon, molybdenum, gallium arsenide, or diamond, which can easily generate ions through a corona discharge. Also, it can be appreciated that the ion print head may include one or more microelectrodes extending from the base toward the hole of the control electrode. Additionally, one or more microelectrodes may include first and second microelectrodes having different lengths. 
     The control electrode  77  is spaced apart from the base  71  by the spacer  75  to control the charge particle emission of the microelectrode  73 . The charge particles are emitted by the electric field formed between the microelectrode  73  and the control electrode  77  according to the control exerted by the controller  79 . 
     The control electrode  77  includes a hole  77   a  through which the charged particles pass. A spreading angle at which the charged particles are projected toward the electrostatic drum  50  is determined according to a size of the hole  77   a . That is, a smaller hole makes the spreading angle of the charged particles smaller, which can be used for a high-resolution printing operation. Additionally, the controller  79  is capable of applying a voltage to each of the discharge elements  70   a  independently. 
     The controller  79  includes a control power supply  79   a  to supply a control voltage of a predetermined waveform to the control electrode  77 , and a bias power supply  79   b  to supply a bias voltage to the conductor  51  of the electrostatic drum  50  and the microelectrode  73  through the base  71  thereof. An amount of the charged particles is controlled by adjusting one or more properties and an application time of the control voltage. The bias voltage supplied to the electrostatic drum  50  and the microelectrode  73  increases a speed of the charged particle emission after the control voltage is supplied to the control electrode  77 , thereby reducing time required to form the latent image on the electrostatic drum  50 . 
     In the ion print head of various embodiments of the present general inventive concept, one discharge element  70   a  can be used to form one unit pixel, or a combination of discharge elements  70   a  can be used to form one unit pixel (See unit pixels A and B in  FIG. 4 ). 
     Operation of the ion print head according to an embodiment of the present general inventive concept will now be described with reference to  FIGS. 3 through 5 . 
     A voltage is applied between the microelectrode  73  and the control electrode  77 , thereby forming a strong electric field around the microelectrode  73  as a result of the large aspect ratio of the microelectrode  73 . The strong electric field around the microelectrode  73  ionizes surrounding air, and another electric field that is formed between the microelectrode  73  and the electrostatic drum  50  (i.e., the conductor  51 ) forces the ions to migrate to the insulation layer  55  of the electrostatic drum  50 , thereby forming the latent image on the insulation layer  55 . Herein, each control electrode  77  of the discharge elements  70   a  of the discharge cell  70  and the discharge cell array  60  can be provided with the control voltage independently such that the control voltage can be turned on or off according to image signals that correspond to the discharge elements  70   a  that are provided to the controller  79 . Therefore, the amount of the charged particles to be applied on the electrostatic drum  50  can be controlled using the control electrode  77  and thus an intensity (and resolution) of the latent image can also be controlled. For example, when ten thousand discharge elements  70   a  are arranged in one line in a widthwise direction of an A4 size print medium, a resolution of 600 dpi (dots per inch) is obtained by using two discharge elements  70   a  for one unit pixel. Similarly, a resolution of 1200 dpi is obtained by using one discharge element  70   a  for one unit pixel. In this manner, printing can be performed with desired resolutions. Additionally, the discharge elements  70   a  can be arranged in matrix form (two-dimensional) to form a plurality of lines of the latent image at a particular time (i.e., at one time) to increase printing speed. 
       FIG. 6  is a schematic view illustrating an image forming apparatus employing an ion print head according to an embodiment of the present general inventive concept. 
     Referring to  FIG. 6 , the image forming apparatus includes a frame  110 , an electrostatic drum  150  provided in the frame  110 , an ion print head  160 , a development unit  120 , a transfer roller  117 , and a fusing roller  119 . 
     An electrostatic latent image that corresponds to an image to be printed on a printing medium (S) is formed on the electrostatic drum  150  by the ion print head  160 . The electrostatic drum  150  and the ion print head  160  may have the same structure illustrated in  FIGS. 3 through 5 . Thus, descriptions of the electrostatic drum  150  and the ion print head  160  will not be provided. 
     The development unit  120  includes a container  125  to contain a developer (T), an agitator  127 , a feed roller  124 , and a development roller  121 . The developer (T) of the container  125  is moved by the agitator  127 , the feed roller  124 , and the development roller  121  to the electrostatic latent image of the electrostatic drum  150  to form an image. According to electrophotography, the development roller  121  is supplied with a DC voltage from a power supply to apply the developer (T) to the electrostatic latent image of the electrostatic drum  150 . A regulating blade  123  is abutted on an outer surface of the development roller  121  to regulate the applied developer (T). In order words, the developer (T) on the development roller  121  has a uniform thickness after it passes between the regulating blade  123  and the development roller  121 . In addition, the development unit  120  is provided with a waste developer collector  129  to store a waste developer (W) that is collected from the electrostatic drum  150  by a cleaning blade  112  after the developing process. 
     The image formed on the electrostatic drum  150  by the development unit  120  is transferred to the printing medium (S) that passes between the electrostatic drum  150  and the transfer roller  117 . The transferred image of the printing medium (S) is then fused by the fusing roller  119 . 
     Further, the image forming apparatus includes a first cassette  131  and a second cassette  135  that hold the printing medium (S), a feed passage  141  along which the printing medium (S) is fed, and an output passage  45  along which the printing medium (S) is output after printing. Along the feed passage  141 , the image forming apparatus also includes pick-up rollers  132  and  136  to pick up the printing medium (S) one by one, a feed roller  133  to guide and feed the picked up printing medium (S), and a registration roller  142  to feed the printing medium (S) for printing the image to a desired area of the printing medium (S). Along the output passage  45 , the image forming apparatus also includes the fusing roller  119  and a plurality of ejection rollers  147 . 
     Therefore, the transfer roller  117  transfers the image of the electrostatic drum  150  to the printing medium (S), which is fed along the feed passage  141  from the first cassette  131  or the second cassette  135 . The transferred image is then fused by the fusing roller  119  to the printing medium (S). The printing medium (S) is then conveyed along the output passage  45  and is ejected to an output tray  149  provided at a top of the frame  110 , thereby completing a printing process. 
     As described above, an ion print head according to various embodiments of the present general inventive concept employs a discharge cell array structure using a microelectrode such that the ion print head has a simple structure to form a latent image on an electrostatic drum. Additionally, each discharge cell of the discharge cell array can be replaced independently such that maintenance of the discharge cell array can be easily performed. 
     Further, an image forming apparatus employing an ion print head according to the various embodiments of the present general inventive concept does not require a light scanning unit and a charger necessary to charge an electrostatic drum such that the image forming apparatus can be simply constructed. Additionally, the electrostatic drum merely requires a conductor and an insulation layer capable of holding charged particles such that the electrostatic drum can be more easily fabricated and can have an enhanced electric field that is influenced less by humidity and temperature when compared to a photoconductive drum of the conventional art. 
     Although a few embodiments of the present general inventive concept have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the general inventive concept, the scope of which is defined in the appended claims and their equivalents.