Patent Publication Number: US-2007120940-A1

Title: Image drum and method of manufacturing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application claims the right of priority under 35 U.S.C. § 119(a)-(d) of Korean Patent Application No. 10-2005-0115866, filed on Nov. 30, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      Apparatuses and methods consistent with the present invention relate to an image drum for use in a printing apparatus, and more particularly to an image drum and a method of manufacturing the image drum, in which an image drum including a ring conductor can be easily fabricated and associated manufacturing costs can be reduced.  
      2. Description of the Related Art  
       FIG. 1  is a schematic perspective view illustrating a conventional image-forming element according to the conventional art, and  FIG. 2  is an enlarged cross-sectional view illustrating a portion of the circumferential wall of the image-forming element according to the conventional art. The image-forming element shown in  FIGS. 1 and 2  is disclosed in U.S. Pat. No. 6,014,157 by reference.  
      Referring to  FIGS. 1 and 2 , the conventional image-forming element  10  comprises a hollow cylindrical drum body  12  which is made of metal, preferably aluminum or an aluminum alloy. A plurality of circumferentially extending electrodes  14  are formed on the outer circumferential surface of the drum body  12 . These electrodes  14  are electrically insulated from one another and from the drum body  12  and are covered by a thin layer of dielectric material. The ring-shaped electrodes  14  may generally be designed variously depending on the desired resolution of the images to be formed, but are preferably provided densely over the whole length of the drum body  12  in such a fashion as to be arranged with a pitch of, for example, about 40 μm in order to realize a resolution of approximately 600 dpi.  
      An elongate-shaped control unit  16  is mounted inside of the hollow drum body  12  such that a terminal array  18  formed at a longitudinal edge of the control unit  16  adjoins the internal wall of the drum body  12 . The control unit  16  is arranged for individually applying a suitably high voltage to each of the electrodes  14  via the terminal array  18  in accordance with the image formation. As shown in  FIG. 2 , the individual electrodes  14  are formed as grooves separated by adjacent insulating ridges  20  and are filled internally with electrically conductive material  32 . Since the electrically conductive material  32  fills in a small-diameter hole  24  and a large-diameter hole  26 , together constituting a through-hole  22 , the electrodes  14  are electrically connected to zebra-strips  36  disposed at the inner wall surface of the drum body  12  via the through-hole  22 . In this case, an anodized surface layer  34  is present at the outer circumferential surface of the drum body  12  and at the internal wall of the through-holes so as to electrically insulate the drum body  12  and the electrodes  14  from each other.  
      In order to manufacture the image-forming element  10 , the cylindrical drum body  12  is provided. The grooves are cut into the outer circumferential surface of the drum body, for example, by means of a diamond chisel in such a fashion as to have a pitch of approximately 40 μm and a width of approximately 20 μm in order to form the electrodes  14 . Alternatively, these grooves may be formed on the outer circumferential surface of the drum body by means of a laser beam or an electron beam.  
      In the next step, the large-diameter holes  26  are cut into the wall of the drum body  12  from the inside by, for example, a laser beam. The small-diameter holes  24  may also be formed with a laser beam, either from the inside or outside of the drum body, to thereby form the through-holes  22 . After the through-holes  22  including the small-diameter holes  24  and the large-diameter holes  26  have been formed, the whole drum body  12  is anodized so as to form the insulating metal oxide layer  34  on the whole surface of the drum body. Thereafter, the electrically conductive material  32  fills in the grooves  14  and the through-holes  22 . The outer or inner circumferential surface of the drum body  12  is cut to a predetermined depth through grinding so as to effectuate the electrodes  14  and electrical connection portions inside of the through-holes  22 . An insulating layer is formed on the outer circumferential surface of the drum body  12  and the control unit  16  is disposed inside of the drum body  12  so as to complete the manufacture of the image-forming element  10 .  
      As described above, in order to form the electrodes  14  on the outer circumferential surface of the drum body  12 , the grooves are densely formed over the whole length of the drum body  12  using a precise cutting tool and the through-holes  22  must be formed at regular intervals either from the inside or outside of the drum body  12 . Also, after the formation of the anodized surface layer on the outer circumferential surface of the drum body  12  and at the internal wall of the through-holes  22 , the electrically conductive material  32  is filled into the grooves and the through-holes and is removed until a desired thickness of the drum body  12  remains. Specifically, since it is very difficult to evenly form the grooves on the outer circumferential surface of the drum body  12  in such a fashion as to have a pitch of approximately 40 μm and a width of approximately 20 μm and to fabricate the through-holes  22 , the manufacturing cost of the image-forming element  10  is very high and a defects regularly occur. As mentioned above, there is at present a disclosed direct-induction-type, image-forming method and apparatus using a ring conductor such as the image-forming element as described above. However, the conventional image-forming method and apparatus entails a problem in that a printer made by using such a method and apparatus is high priced, which makes it difficult for the printer to be popularized.  
     SUMMARY OF THE INVENTION  
      Accordingly, the present invention has been made in view of the aforementioned problems occurring in the conventional art. An exemplary embodiment of the present invention provides an image drum which can be easily fabricated and can enable an excellent quality of printing, and a method of manufacturing the image drum.  
      Another exemplary embodiment of the present invention provides an image drum which can be rapidly and easily fabricated, is advantageous for mass production, and can reduce manufacturing costs, and a method of manufacturing the image drum.  
      A further exemplary embodiment of the present invention provides an image drum which can effectively discharge heat generated in the image drum so that it can be utilized for a long time period without inconvenience.  
      To accomplish the above, according to one exemplary embodiment of the present invention, there is provided a image drum which has long-lasting, good heat conductive characteristics.  
      According to an exemplary embodiment of the present invention, the novel image drum includes a drum body and an electrode member. The electrode member includes a flexible substrate, ring-shaped electrodes for a ring conductor, and a control unit. The ring-shaped electrodes are formed on the flexible substrate and the control unit is joined to the flexible substrate. An image drum for selectively adsorbing a toner on the image drum so as to form an image in a printing apparatus may include, for example, a hollow cylindrical drum body and an electrode member. The electrode member may include a flexible substrate adapted to surround an outer circumferential surface of the drum body, a plurality of ring-shaped electrodes formed circumferentially on a top surface of the flexible substrate so as to be electrically insulated from one another, and a control unit disposed on a bottom surface of the flexible substrate for independently applying a voltage to each of the ring-shaped electrodes. The electrode member may be disposed on the outer circumferential surface of the drum body.  
      As mentioned above, a conventional image drum is constructed such that grooves are formed on the outer circumferential surface of the drum body by using a diamond cutting tool, etc., and an electrically conductive material is filled into the grooves so as to form ring-shaped conductors. Further, through-holes are formed in the drum body using a laser beam, etc., so as to electrically interconnect an inside and an outside of the drum body, and an electrically conductive material fills in the through-holes to form an electrical connection portion.  
      However, in the present invention, ring-shaped electrodes may be formed on the flexible substrate and the control unit may be joined to the flexible substrate to correspond to each of the ring-shaped electrodes so as to form the electrode member. Generally, a conventional flexible printed circuit board (“FPCB”) technology may be used, and it is possible to form a copper line having a width of approximately 20 μm in FPCB. Thus, in the electrode member of the present invention, a copper pattern having a pitch of approximately 40 μm and a width of approximately 20 μm may also be formed on the flexible substrate. An application-specific integrated circuit (“ASIC”) chip may be used as the control unit. In this case, a needed number of ASIC chips can be joined to the flexible substrate by means of bonding, for example. The electrode member including the ring-shaped electrodes and the control unit is disposed on the outer circumferential surface of the drum body so as to form an image drum. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other features and advantages of the present invention will be apparent from the following detailed description of the exemplary embodiments of the invention in conjunction with the accompanying drawings, in which:  
       FIG. 1  is a schematic perspective view illustrating a conventional image-forming element according to a conventional art;  
       FIG. 2  is an enlarged cross-sectional view illustrating a portion of the circumferential wall of the image-forming element according to the conventional art;  
       FIG. 3  is a schematic cross-sectional view illustrating the inner construction of a printer using an image drum according to an exemplary embodiment of the present invention;  
       FIG. 4  is a partially enlarged perspective view illustrating the image drum shown in  FIG. 3 ;  
       FIG. 5  is a partially enlarged side cross-sectional view illustrating the image drum shown in  FIG. 3 ;  
       FIG. 6  is a partially enlarged perspective view illustrating a process of manufacturing the image drum shown in  FIG. 3 ;  
       FIG. 7  is a perspective view illustrating an image drum according to an exemplary embodiment of the present invention;  
       FIG. 8  is a partially enlarged perspective view illustrating the image drum shown in  FIG. 7 ; and  
       FIG. 9  is a graph illustrating the relationship between the power per one chip and the junction temperature of a chip when a gear module of  FIG. 7  is employed. 
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
      Reference will now be made in detail to exemplary embodiments of the present invention, 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 invention by referring to the figures.  
       FIG. 3  is a schematic cross-sectional view illustrating the inner construction of a printer using an image drum  100  according to an exemplary embodiment of the present invention, and  FIG. 4  is a partially enlarged perspective view illustrating the image drum  100  shown in  FIG. 3 .  
      Referring to  FIGS. 3 and 4 , the image drum  100  comprises a cylindrical drum body  110  and an electrode member  120 . A toner feed roller  210 , a magnetic cutter  220 , and an image transfer section  230  are disposed around the outer circumferential surface of the image drum  100 . A toner  1  from a toner storage section (not shown) is supplied to the toner feed roller  210  and is transferred to the image drum  100  from the toner feed roller  210  while moving on the outer circumferential surface of the toner feed roller  210 . At this time, the toner is kept in an electrically charged state, and it is moved toward the magnetic cutter  220  while maintaining contact with an insulating layer formed on the outermost circumferential portion of the image drum  100 .  
      The magnetic cutter  220  includes a rotary sleeve  224 , and a magnet  222  disposed within the magnetic cutter  220  for applying an attractive magnetic force to the toner  1 . The magnet  222  is positioned adjacent to the image drum  100 , and can attract the toner  1  adhered to the surface of the image drum  100  using the magnetic force. The magnet  222  has a sufficient magnetic force so that it can collect the toner  1  from the electrodes of the image drum  100  that is not attracted to the image drum  100  by a voltage. The toner  1  collected by the magnet  222  is fed back to the toner storage section or the toner feed roller  210  via the rotary sleeve  224 .  
      The toner  1  that is not fed back to the toner storage section or the toner feed roller  210  by the magnetic cutter  220  is transferred to the image transfer section  230  from the outer circumferential surface of the image drum  100 . Then, the toner  1  transferred to the image transfer section  230  is moved to a printing paper sheet which is in turn heat-treated so as to allow the toner to be adhered to the surface of the printing paper sheet. To this end, the image drum  100  controls the voltage applied to the electrodes to conform to an image signal. Then, the image drum  100  generates a electrostatic force larger than the magnetic force of the magnet  222  so as to prevent the toner  1  from being collected to the magnetic cutter  220 .  
      Approximately five thousand electrodes are controlled independently so as to represent a two dimensional image on the image drum  100 . The image represented on the image drum  100  through the toner  1  can be transferred to the printing paper sheet by using the image transfer section  230  as a relay means. After the toner  1  has been adhered to the surface of the printing paper sheet, the printing paper sheet passes through a heat-treatment apparatus. At this time, the toner is adsorbed to the surface of the printing paper sheet to complete a corresponding printing.  
      As shown in  FIGS. 3 and 4 , the drum body  100  is formed in a hollow cylindrical shape, and may be formed of a material having excellent heat conductivity and mechanical strength. Also, an electrode member  120  including the flexible substrate  125  is provided on the outer circumferential surface of the drum body  110 .  
      The electrode member  120  includes the flexible substrate  125 , ring-shaped electrodes  130  formed on the top surface of the flexible substrate  125 , and the control chip  140  formed beneath the bottom surface of the flexible substrate  125 . The electrode member  120  may be formed of a thin insulating film made of a material such as polyimide, etc. Conductive patterns may be circumferentially formed on the outer circumferential surface of the flexible substrate  125 . The conductive patterns are evenly formed as ring-shaped electrodes  130  in such a fashion as to have a pitch of approximately 40 μm and a width of approximately 20 μm. The ring-shaped electrodes  130  covering the circumference of the drum body  110  are formed to have a width corresponding to the printing width of the printing paper sheet. For example, assuming the printing paper sheet is of A4 size, the drum body  110  is formed to have a length of at least 20 cm to 22 cm over its whole width. At this time, each of the ring-shaped electrodes  130  may be formed to have a pitch of approximately 40 μm in order to achieve about five thousand lines. The ring-shaped electrodes can be formed in a ring structure which is closed as one piece or partially opened. That is, both ends of each of the ring-shaped electrodes  130  may be electrically interconnected to form a closed ring structure, but it is possible to electrically insulate both ends of the each ring-shaped electrode  130  according to circumstances.  
      Since the ring-shaped electrodes  130  can be formed by patterning copper or other thin conductive film in a flat state, a groove cutting step or a conductive material filling step employed in a conventional image drum manufacturing process can be eliminated in this exemplary embodiment. First of all, since it is possible to form the ring-shaped electrodes  130  on the planar flexible substrate  125 , the level of work difficulty is greatly lowered as compared to a formation of the ring-shaped electrodes  130  on the outer circumferential surface of the cylindrical drum body  110 , as well as remarkably reducing the generation rate of defective ring-shaped electrodes.  
      After the ring-shaped electrodes  130  have been formed on the flexible substrate  125 , the control chip  140  can be joined to the bottom surface of the flexible substrate  125 . The control chip  140  is connected to each ring-shaped electrode  130  on a one-to-one corresponding basis, and performs a kind of switch function so as to independently apply a necessary voltage to each electrode  130 . The control chips  140  may be mounted at various positions, but in this exemplary embodiment are mounted abuttingly along one end edge of the flexible substrate  125 . Owing to this arrangement of components, the present invention provides an advantageous structure for the manufacture of the image drum  100  since it is possible to eliminate interconnection of the control unit disposed inside of the cylindrical drum body  110  to the ring-shaped conductor disposed outside of the drum body  110  by through-holes, which causes problems in the conventional art.  
       FIG. 5  is a partially enlarged side cross-sectional view illustrating the image drum  100  shown in  FIG. 3 , and  FIG. 6  is a partially enlarged perspective view illustrating a process of manufacturing the image drum  100  shown in  FIG. 3 .  
      Referring to  FIGS. 5 and 6 , a recess  112  is longitudinally formed on the outer circumferential surface of the drum body  110 . The recess  112  has a depth corresponding to a height of the control chip  140  and the flexible substrate  125 , and is formed to have a width sufficient to accommodate the control chip therein. Therefore, a part of the electrode member  120  mounted with the control chip  140  is accommodated in the recess  112 , and the other end of the electrode member  120  opposite to the control chip  140  covers over the recess. Thus, the whole surface of the image drum  100  is surrounded by the flexible substrate  125 , and it can entirely cover the outer circumferential surface of the cylindrical drum body, although a partially overlapped portion exists.  
      As shown in  FIG. 5 , after one end of the flexible substrate  125  mounted with the control chip  140  has been disposed in the recess  112 , the flexible substrate  125  surrounds the circumference of the drum body  110  and another end of flexible substrate  125  covers over the recess  112 . At this time, a material of Epoxy Mold Compound (“EMC”), etc., may be used to fill an empty space defined between the control chip  140  and the flexible substrate  125 .  
      In addition, as the control chip  140  is made thinner, it becomes more favorable for mounting on the flexible substrate  125 . In additional, a thinner control chip  140  generally permits a slight bending of the control chip  140 . To this end, the control chip  140  initially may be designed to be thin, and may be formed so as to have a thickness of about 20 μm to 30 μm by partially removing the bottom portion of a conventional ASIC chip.  
      Now, a manufacturing method of the image drum  100  will be described hereinafter.  
      First, in order to manufacture the image drum  100 , the flexible substrate  125  formed with a plurality of ring-shaped electrodes  130  is fabricated. The flexible substrate  125  may be formed of polyimide material, and copper patterns may be formed on the surface of the flexible substrate  125  through a conventional photolithography, a screen printing, etc. The ring-shaped electrodes  130  are formed in a parallel linear shape on the surface of the flexible substrate  125  in such a fashion as to be regularly arranged while maintaining a width of approximately 20 μm prior to attachment of the flexible substrate  125  on the drum body  110 .  
      After provision of the flexible substrate  125  formed with the ring-shaped electrodes  130 , the control chip  140 , embodied as an ASIC chip, is joined to the bottom surface of the flexible substrate  125  along one end edge of the flexible substrate  125 . The control chip  140  is intended to independently apply a voltage to each of the ring-shaped electrodes  130 , and can be electrically connected to the ring-shaped electrodes  130  by means of general die bonding, soldering, or the like.  
      Generally, an insulating layer is formed on the flexible substrate  125  and the ring-shaped electrodes  130 . The insulating layer may be formed of a dielectric material such as, for example, Aluminum Nitride (“AlN”), Al 2 O 3 , etc. The ring-shaped electrodes  130  can be electrically insulated from one another by the insulating layer. The insulating layer may be formed on the flexible substrate  125  before and/or after the control chip  140  is joined to the flexible substrate  125 .  
      After the ring-shaped electrodes  130  and the control chip  140  have been integrally formed on the flexible substrate  125 , the flexible substrate  125  is attached on the outer circumferential surface of the hollow cylindrical drum body  110 . At this time, a recess is formed on the outer circumferential surface of the drum body  110  to receive the control chip therein. Also, although the control chip  140  and the flexible substrate  125  are overlapped with each other in a vertical direction, it is possible to prevent any portion from projecting abnormally from the surface of the image drum.  
       FIG. 7  is a perspective view illustrating an image drum according to an exemplary embodiment of the present invention, and  FIG. 8  is a partially enlarged perspective view illustrating the image drum shown in  FIG. 7 .  
      Referring to  FIGS. 7 and 8 , after the flexible substrate  125  has been attached to the drum body  110 , a gear module  150  is mounted to both ends of the drum body  110 . The gear module  150  is intended to rotate the image drum. Gear teeth are formed on the outer circumferential surface of the gear module  150  so that the gear module can be functionally connected to an external gear motor drive and can be transmitted with a power necessary for the rotation of the image drum. The gear module  150  may be mounted to either one side or both sides of the drum body  110 .  
      The gear module  150  is centrally formed with a through-hole  152  for allowing the inside and outside of the drum body  110  to be exposed to air. According to this exemplary embodiment, since the control chip  140  is covered by the flexible substrate  125  and the heat-conductivity of polyimide material forming the flexible substrate  125  is relatively poor, heat accumulation phenomenon may occur within the image drum  101 . Of course, the drum body  110  is formed of aluminum having good heat-conductivity, but even though the inside of the drum body also is opened at both sides, heat may not be smoothly discharged to the outside.  
      Therefore, a plurality of blades  154  is radially formed inwardly from the through-hole  152  to improve smooth inflow or outflow of air. In order to rotate the image drum, the gear module must be rotated. At this time, a force may be generated for causing air flow from the blades  154  because of this rotation. By using a structural modification of forming the blades  154  integrally with one another, a forcible flow of air can be induced without power specifically allocated for air flow. In addition, since the structure of the blades is simple and a conventional connection structure can be used as is, it is not difficult to apply the blades to the novel image drum.  
       FIG. 9  is a graph illustrating the relationship between the power per one chip and the junction temperature of the chip when the gear module of  FIG. 7  is employed.  
      Referring to  FIG. 9 , there are shown respective cases of the gear module including and not including the blades. In the case of not using the blades, almost no flow of air is generated. In this situation, it can be seen that the temperature of the control chip sharply increases as time elapses. On the other hand, in the case of using the blades, it can be seen that an air flow of about 1 m/s is generated and the temperature of the control chip increases relatively slowly as time elapses. As a result, although a separate cooling fan is not used, generation of heat from the image drum can be relieved.  
      The image drum of the present invention can easily be manufactured in such a fashion that the control chip is joined to the flexible substrate by forming the FPCB, and the integrally formed FPCB is surrounded on the drum body. Since it is possible the electrodes, which are easily manufactured, have a reduced generation rate of defects and have relatively excellent quality, a superior printing quality can be expected.  
      In addition, manufacturing of the image drum can be rapidly performed due to its structural simplicity, and the image drum is very favorable for mass production due to easy facilitation of each manufacturing step. Since it is possible to utilize a processing technology which is conventionally well known in the art, the manufacturing cost is reduced and the product cost can be lowered accordingly.  
      Moreover, because blades are formed at the gear module so as to effectively discharge heat generated from the control chip to the outside, the image drum can be used for a long period without fault or inconvenience.  
      Although a few exemplary embodiments of the present invention have been shown and described, the present invention is not limited to the described exemplary embodiments. Instead, it would be appreciated by those skilled in the art that changes may be made to these exemplary embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.