Abstract:
An ink cartridge used with an ink jet printer. The ink cartridge has an ink reservoir and a housing to cover the ink reservoir with a negative pressure maintenance unit therebetween to maintain the inner pressure of the ink reservoir under a negative pressure. Since the negative pressure maintenance unit does not contact ink in the ink reservoir, the negative pressure maintenance unit does not corrode. In addition, the negative pressure maintenance unit is installed between the housing and the ink reservoir while occupying a small space, and thus improving the filling efficiency of ink in the ink reservoir.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application claims the benefit of Korean Application No. 2001-68632, filed Nov. 5, 2001, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to an ink cartridge used with an ink jet printer, and more particularly, to an ink cartridge used to maintain the inside of an ink reservoir under a proper negative pressure.  
           [0004]    2. Description of the Related Art  
           [0005]    An ink cartridge used with an ink jet printer generally reserves ink to discharge ink droplets through a print head so that a colored image is printed on a sheet.  
           [0006]    The ink cartridge requires a device to maintain the inside of an ink reservoir under a negative pressure in order to prevent an excessive amount of ink from leaking through the print head in a printing state, or a wetting occurrence at the print head in an idle state.  
           [0007]    [0007]FIG. 1 illustrates an ink cartridge disclosed in U.S. Pat. No. 5,541,632. Referring to FIG. 1, the ink cartridge includes a housing and an ink reservoir arranged in the housing to reserve ink, while having a negative pressure maintenance unit  30 . The housing includes a frame  10 , and side plates  12  and  14  to seal both sides of the frame  10 . The ink reservoir is sealed by flexible walls  22  and  24 , which may be transformed while maintaining the inside of the ink reservoir in a sealed state. The negative pressure maintenance unit  30  maintains the inside of the ink reservoir under a proper negative pressure. Thus, ink is prevented from dripping through a print head  13  when discharging the ink from the ink reservoir through the print head  13  by passing through a filter  18  or when reserving the ink in the ink reservoir. In this case, the negative pressure maintenance unit  30  has a bow spring  31  and plates  32  and  34  to support the bow spring  31 .  
           [0008]    In the ink cartridge of the above configuration, since the bow spring  31  directly contacts the ink reserved in the ink reservoir, the bow spring  31  may corrode by chemical reaction with the ink.  
           [0009]    Accordingly, preventing the bow spring  31  from corroding is required. However, forming the bow spring  31  by using a material which does not react with inks limits the range of materials for the bow spring  31  and increases the price of the selected material. An alternative plan for changing the main element and additives of the ink also limits the selecting range for ink and increases the price of the ink.  
         SUMMARY OF THE INVENTION  
         [0010]    Accordingly, it is an objective of the present invention to provide an ink cartridge used with an ink jet printer, which prevents a negative pressure maintenance unit from corroding and improves the filling efficiency of ink.  
           [0011]    Additional objects and advantages of the invention 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.  
           [0012]    The foregoing and other objects of the present invention are achieved by providing an ink cartridge used with an ink jet printer having an ink reservoir to reserve ink, a housing to cover the ink reservoir, and a negative pressure maintenance unit to maintain the inner pressure of the ink reservoir under a negative pressure. The reservoir includes a base plate, a cover plate separated from the base plate, and flexible walls interposed between the base plate and the cover plate to form a sealed space to reserve ink. Here, the negative pressure maintenance unit includes at least one elastic member to be interposed between the housing and the cover plate.  
           [0013]    In an aspect of the invention, the elastic member is a leaf spring to maintain the inner pressure of the ink reservoir under the negative pressure by applying an elastic restoring force in a pulling direction of the cover plate.  
           [0014]    The leaf spring has a housing fixing portion fixed to the housing, plate fixing portions fixed to the cover plate, and connecting portions to integrally connect the housing fixing portion and plate fixing portion.  
           [0015]    In another aspect of the invention, the housing is formed by fixing first and second body portions that are facing each other or by fixing a wall body having a through hole and a cover to seal one side of the wall body, so that the housing is coupled with the base plate to cover the ink reservoir. In another aspect of the invention, the housing is formed of one selected from a sheet metal and structural polymer. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    These and other objects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:  
         [0017]    [0017]FIG. 1 is a separate perspective view illustrating a conventional ink cartridge;  
         [0018]    [0018]FIG. 2 is a sectional view illustrating an ink cartridge according to an embodiment of the present invention;  
         [0019]    [0019]FIG. 3 is a sectional view illustrating the ink cartridge according to the embodiment of FIG. 2 along the cutting plane line II-II of FIG. 2;  
         [0020]    [0020]FIGS. 4A through 4C illustrate an aspect of a leaf spring used in the ink cartridge according to the embodiment of FIG. 2, in particular, an initial state, and before and after the operation of the leaf spring;  
         [0021]    [0021]FIGS. 5A through 5C illustrate the leaf spring used in the ink cartridge according to another aspect of the present invention, in particular, an initial state, and before and after the operation of the leaf spring, respectively;  
         [0022]    [0022]FIGS. 6A through 6C illustrate another aspect of the leaf spring used in the ink cartridge according to the embodiment of FIG. 2, in particular, an initial state, and before and after the operation of the leaf spring, respectively;  
         [0023]    [0023]FIG. 7 illustrates a housing used in the ink cartridge according to another embodiment of the present invention; and  
         [0024]    [0024]FIG. 8 illustrates a housing used in the ink cartridge according to yet another embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]    Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures.  
         [0026]    [0026]FIG. 2 is a sectional view illustrating an ink cartridge according to an embodiment of the present invention, and FIG. 3 is a sectional view illustrating the ink cartridge along the cutting plane line II-II of FIG. 2. Referring to FIGS. 2 and 3, the ink cartridge includes an ink reservoir  120 , a housing  110 , and a leaf spring  130  as a negative pressure maintenance unit.  
         [0027]    The ink reservoir  120  contains a base plate  100 , a cover plate  102 , and flexible walls  104  to seal a space between the plates  100  and  102 . In this case, the cover plate  102  moves vertically according to the amount of ink in the ink reservoir  120 . The flexible walls  104  formed of a flexible material are attached to the edges of the base plate  100  and the cover plate  102  that face each other, so that a sealed space is formed.  
         [0028]    The housing  110  has an opening in the area of which the housing  110  is coupled with the base plate  100  by welding, i.e., a thermal or ultrasonic welding, or by using a combining unit, i.e., a screw or hook, so that the housing  110  with the base plate  100  covers the ink reservoir  120 .  
         [0029]    The housing  110  and the cover plate  102  of the ink reservoir  120  are arranged with the leaf spring  130  therebetween . The initial state and before and after operation states of the leaf spring  130  are illustrated in FIGS. 4A through 4C. Referring to FIGS. 4A through 4C, the leaf spring  130  includes a housing fixing portion  130   a  fixed to the housing  110 , plate fixing portions  130   b  fixed to the cover plate  102 , and connecting portions  130   c  to connect the fixing portions  130   a  and  130   b . In this case, the housing and plate fixing portions  130   a  and  130   b  are fixed to the housing  110  and the cover plate  102  by a welding method or by using a combining unit like a screw or hook, respectively. The leaf spring  130  is flat in the initial state. When installing the leaf spring  130  in the ink cartridge, the leaf spring  130  is transformed toward an operation direction by a small amount, as illustrated in FIG. 4B. Since strain energy accumulates in the leaf spring  130  due to the transformation, the strain energy generates an elastic restoring force to pull the cover plate  102  of the ink reservoir  120 . Consequently, a negative pressure, under an external atmospheric pressure, is formed in the ink reservoir  120 . As the ink is discharged through a print head  114  and the amount of ink in the ink reservoir  120  decreases, the flexible walls  104  contract toward an inner direction, as illustrated by dotted lines in FIGS. 2 and 3. Accordingly, the cover plate  102  moves toward the base plate  100 . In this case, the transformation of the leaf spring  130  increases to move the cover plate  102 , so that the negative pressure in the ink reservoir  120  is maintained within a predetermined range. FIG. 4C illustrates the final state of the leaf spring  130 .  
         [0030]    [0030]FIGS. 5A through 5C illustrate another aspect of a leaf spring used in the ink cartridge according to an embodiment of the present invention, in particular, an initial, uninstalled state of the leaf spring, and states of the leaf spring before and after operation, respectively. Prior to installation, the leaf spring  140  is transformed by a small amount in an opposite direction from the operation direction in, as illustrated in FIG. 5A. When installing the leaf spring  140  in the ink cartridge, the leaf spring  140  is transformed toward an operation direction, as illustrated in FIG. 5B. Accordingly, a stronger restoring force than that of the leaf spring  130  shown in FIG. 4B is generated to pull the cover plate  102 . FIG. 5C illustrates the final state of the leaf spring  140 .  
         [0031]    [0031]FIGS. 6A through 6C illustrate another aspect of a leaf spring used in the ink cartridge according to an embodiment of the present invention. The leaf spring is formed by overlapping two identical leaf springs  150  and  160  inversely facing each other. The leaf springs  150  and  160  are overlapped in the state illustrated in FIG. 6B so that a restoring force is applied to pull the cover plate  102 . FIG. 6C illustrates the final state of the leaf springs  150  and  160 .  
         [0032]    Although a few types of leaf springs used in the ink cartridge are described above, various types of leaf springs may be used without departing from the scope of the present invention.  
         [0033]    In addition, another housing, other than an integral type housing, may be formed by coupling corresponding portions of the housing, as illustrated in FIGS. 7 and 8. FIG. 7 illustrates the housing formed by coupling first and second body portions  110   a  and  110   b  that are facing each other, to cover the ink reservoir  120  in FIG. 2. The first body portion  110   a  has an opened side and an upper surface with an opened portion. The second body portion  110   b  is formed in a shape to seal the opened side and the opened portion of the upper surface of the first body portion  110   a . The first and second body portions  110   a  and  110   b  are coupled to form the housing having an opened lower surface. The first and second body portions  110   a  and  110   b  are coupled by a welding method, such as thermal welding or ultrasonic welding, or by a mechanical coupling method using a screw or hook. In this case, the housing is formed of a processed sheet metal or structural polymer. In FIG. 8, a housing is formed by coupling a wall body  110   c  having a through hole and a cover  110   d  to seal the upper portion of the wall body  110   c.  In this case, the material and coupling method for the wall body  110   c  and the cover  110   d  are the same as those for the housing illustrated in FIG. 7. Although a few types of housings used in the ink cartridge according to the present invention are described above, various types of housings may be formed without departing from the range of the present invention.  
         [0034]    Since the ink is filled only in the ink reservoir of the ink cartridge according to the present invention, changes in the physical property of the ink by vaporization of the ink are prevented. Since the inner pressure of the ink reservoir does not vary while storing the ink cartridge for a long time or at a high or low temperature, it is unlikely that the ink drips. Moreover, the leaf spring is located outside of the ink reservoir, so that the leaf spring does not corrode while having the possibility to freely select the ink and the material for the leaf spring. The leaf spring occupies a small space between the housing and ink reservoir, so that the filling efficiency of ink improves.  
         [0035]    Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.