Abstract:
A pump for an inkjet printer applying a negative pressure to an inkjet head nozzle, includes: a tube connected to the inkjet head nozzle and being U-shaped; a plurality of rollers which contact an inner arch of the tube and having a tapered shape; and a rotor to which the plurality of rollers are rotatably mounted. When the rotor rotates in a direction, at least one of the plurality of rollers rotate and squeeze the tube. When the rotor stops rotating, the plurality of rollers return to a state in which the plurality of rollers do not squeeze the tube due to a recovering force of the tube. The squeezing of the tube generates the negative pressure in the inkjet head nozzle.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of Korean Application No. 2002-83522, filed Dec. 24, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a pump for an inkjet printer, and more particularly, to a pump for an inkjet printer which squeeze a tube to generate a suction force, thereby sucking ink from an inkjet head nozzle. 
   2. Description of the Related Art 
   An inkjet printer using a permanent head, which can be permanently used and refilled (replenished) with ink, and a semi-permanent head, generally includes a pump. The pump for the inkjet printer performs a sucking operation in order to remove air that may enter during the replenishing of the ink and to open a head nozzle when the head nozzle is blocked by dried ink. 
   Pumps used in inkjet printers are generally divided into piston type pump apparatuses and rotor type pump apparatuses. The rotor type is more commonly used. The rotor type utilizes the rotation of a rotor to squeeze a plastic tube and thus generate a pressure difference which causes ink to be ejected from an inkjet head nozzle. 
   Several inventions relating to such a rotor type pump apparatus have been patented and have been put to practical use, one example of which is disclosed in U.S. Pat. No. 5,910,808. Operation of that pump apparatus as disclosed will be briefly described with reference to  FIG. 1 . 
   As a rotor of the pump apparatus rotates in a counterclockwise direction, a roller  14  squeezes a tube  10 . Due to a pressure difference to an atmosphere pressure occurring as the tube  10  is squeezed, the squeezing results in a negative pressure differential relative to the ambient. This negative pressure differential causes ink in an inkjet head nozzle (not shown) to be sucked into the tube  10  an end of which is connected to the inkjet head nozzle. 
   After the suction of the ink, when the rotor rotates in a clockwise direction, the roller  14  comes into contact with a damper plate  16  made of rubber as shown in  FIG. 2 . This contact moves the roller inward along a cam groove  12 . In this state, the roller  14  does not squeeze the tube  10  so as to allow the tube  10  to return to its original (i.e. uncompressed) state. That is, the conventional rotor type pump apparatus varies the position of the roller  14  within the cam groove  12  by using the damper plate  16  when the rotor is rotated in the counterclockwise and the clockwise directions, whereby the tube  10  is squeezed and relaxed and thus the sucking operation is performed. 
   However, since in the conventional rotor type pump apparatus the position of the roller  14  is changed within the cam groove  12  by using the rubber-made damper plate  16  when the tube  10  is contracted and relaxed, the damper plate  16  is periodically subjected to an alternate shock load. Accordingly, when the pump apparatus is used for a long time, the properties of the rubber-made damper plate  16  such as elasticity and surface friction coefficient are deteriorated and thus reliability of the sucking operation is reduced. 
   Also, the collision of the roller  14  with the damper plate  16  when the damper plate  16  changes the position of the roller  14  in the cam groove  12  causes noise. When the tube  10  is disposed on a right-angled wall, the rotation of the roller  14  causes the tube  10  to ascend. 
   Still further, since the conventional pump apparatus requires many parts such as a plurality of gears, the damper plate, and the like manufacture and/or assembly can be complicated. 
   SUMMARY OF THE INVENTION 
   The present invention has been developed in order to solve the above problems in the related art. Accordingly, an aspect of the present invention is to provide a pump apparatus for an inkjet printer capable of preventing a reliability of sucking operation from being lessened even in the case that it is used for a long time. 
   Also, another aspect of the present invention is to provide a pump apparatus for an inkjet printer capable of preventing a collision noise from occurring during the rotation of a roller and a tube from ascending. 
   Also, still another aspect of the present invention is to provide a pump apparatus for an inkjet printer providing an effect that the number of parts can be decreased. 
   Additional aspects and/or 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 of the invention. 
   According to an aspect of the present invention there is providing a pump for an inkjet printer applying a negative pressure to an inkjet head nozzle, including: a tube connected to the inkjet head nozzle and being U-shaped; a plurality of rollers which contact an inner arch of the tube and having a tapered shape; and a rotor to which the plurality of rollers are rotatably mounted. When the rotor rotates in a direction, at least one of the plurality of rollers rotate and squeeze the tube. When the rotor stops rotating, the plurality of rollers return to a state in which the plurality of rollers do not squeeze the tube due to a recovering force of the tube. The squeezing of the tube generates the negative pressure in the inkjet head nozzle. 
   The plurality of rollers may be tapered. Also, the plurality of rollers may be a pair of rollers disposed symmetrically to each other. 
   According to another aspect of the present invention there is a pump for an inkjet printer applying a negative pressure to an inkjet head nozzle, including: a fixing shaft; a driving gear rotatably assembled to the fixing shaft; a stopper protruding from a side of the driving gear; a ratchet wheel rotatably assembled to the fixing shaft, having a driving ratchet formed in a lower end thereof and a cam recess; a rotor assembled to the fixing shaft, movable in an axial direction, and having a driven ratchet formed in an upper end thereof which is engagable with the driving ratchet; a plurality of rollers rotatably disposed at the rotor and having tapered sides; and a tube disposed to contact the plurality of rollers and connected to the inkjet head nozzle. The driving gear is rotatable in a direction and rotation of the driving gear causes the rotor to move along the fixing shaft so that at least one of the plurality of rollers squeezes the tube. 
   When the driving gear stops rotating or is rotated in the reverse direction, the rotor may move along the driving shaft in a reverse direction due to a recovering force of the tube to return the tube to an original state. 
   The plurality of rollers a pair of rollers disposed symmetrically to each other. 
   The tube may be disposed in a housing accommodating the rotor, the ratchet wheel and the driving gear, and the housing may be provided with a rotor stopper protruding from an inner side thereof which encourages the plurality of rollers to maintain contact with the tube when the rotor is not rotating. 
   The driving ratchet and the driven ratchet may be inclined and cooperate so that a load of the plurality of rollers applied to the tube by the driving ratchet when the ratchet wheel rotates in a reverse direction opposite the direction is smaller than the recovering force of the tube. 
   According to still another aspect, there is provided a pump which pumps ink from an ink source, including: a shaft; a driving gear surrounding the shaft and rotatable in a direction about the shaft; a stopper integrally formed on a side of the driving gear and having at least one protrusion; a ratchet rotatable about the shaft, movable about an axial direction, having one or more cam recesses formed on an upper side each of which receive a projection, and having a driving ratchet formed at a lower side; a rotor rotatable about the fixing shaft, movable about an axial direction, and having a driven ratchet formed on an upper side; and two or more rollers extending from a lower side of the rotor and which orbit the shaft when the rotor rotates. 
   Also, according to the pump apparatus of the present invention, the collision noise does not occur during the operation, and the tube is prevented from ascending over the rollers. 
   Also, according to the pump apparatus of the present invention, the number of the components of the apparatus can be reduced. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above aspects and/or other advantages of the present invention will be more apparent by describing a preferred embodiment of the present invention, in which: 
       FIG. 1  is a cross-sectional view showing a conventional pump apparatus for an inkjet printer; 
       FIG. 2  is a cross-sectional view showing the damper plate of the pump apparatus for the inkjet printer of  FIG. 1 ; 
       FIG. 3  is a perspective view showing a pump apparatus for an inkjet printer according to a first embodiment of the present invention; 
       FIG. 4  is a perspective view showing the housing assembled with the pump apparatus for the inkjet printer of  FIG. 3 ; 
       FIG. 5  is an exploded perspective view showing the pump apparatus for the inkjet printer of  FIG. 4 ; 
       FIG. 6  is a perspective view showing the ratchet wheel of the pump apparatus for the inkjet printer of  FIG. 4 ; 
       FIG. 7  is a cross sectional view showing the pump apparatus for the inkjet printer of  FIG. 4  in the non-operation; 
       FIG. 8  is a cross sectional view showing the pump apparatus for the inkjet printer of  FIG. 4  when it rotates in a direction of squeezing the tube. 
       FIG. 9A  is a perspective view showing the pump apparatus for the inkjet printer of  FIG. 3  in a non-operational mode; 
       FIG. 9B  is a perspective view showing the driving ratchet and the driven ratchet engaged with each other when the pump apparatus for the inkjet printer of  FIG. 9A  rotates; and 
       FIG. 9C  is a perspective view showing the plurality of rollers squeezing the tube when the pump apparatus for the inkjet printer of  FIG. 9A  rotates further than the state of  FIG. 9B . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Reference will now be made in detail to 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. 
   Hereinafter, a pump apparatus for an inkjet printer according to an embodiment of the present invention will be described with reference to the accompanying drawings. 
   Referring concurrently to  FIGS. 3 to 6 , the pump apparatus for the inkjet printer according to a first embodiment of the present invention includes a fixing shaft  30 , a driving gear  40 , a ratchet wheel  50 , a rotor  60 , a tube  80 , and a housing  90 . 
   The fixing shaft  30  is fixed to a frame  20  of the inkjet printer in which the pump apparatus is disposed, and guides the rotation of the driving gear  40  and the rotor  60 . 
     FIG. 5  shows that the driving gear  40  is rotatably disposed on the fixing shaft  30  and engaged with a driving force transmitting gear  22  for transmitting a driving force from a motor (not shown). A stopper  42  protrudes from one end of the driving gear  40 . The stopper  42  is formed in a hollow shape to be assembled with the fixing shaft  30  and has a projection  44  protruding from a sidewall thereof. The stopper includes two projections  44 . However, while two projections are shown and described, more projections may be provided and, when multiple projections  44  are provided in pair, they are symmetrically disposed to each other as shown in  FIG. 5  for smooth operation. 
   The ratchet wheel  50  is hollow-shaped as shown in  FIG. 6  and has a driving ratchet  54  at one end thereof (the upper end in  FIG. 6 ) and a cam recess  52  at the other end (the lower end in  FIG. 6 ) thereof. The ratchet wheel  50  has an inner diameter sufficient to smoothly rotate with respect to an outer diameter of the stopper  42 . The cam recess  52  is defined in a circumference of the lower end of the ratchet wheel  50  and has a bottom gradually inclined from one side  52   a  to the other side  52   c . The projection  44  of the stopper  42  is inserted into the cam recess  52  and the rotation of the stopper  42  causes the bottom of the cam recess  52  to be pushed, so that the ratchet wheel  50  moves in a lengthwise direction on the stopper  42 . When the projection  44  is positioned at side  52   a  of the cam recess  52 , the driving ratchet  54  is disengaged from the driven ratchet  64  so that the roller  70  does not squeeze the tube  80 . On the other hand, when the projection  44  is positioned at the other side  52   c  of the cam recess  52 , the driving ratchet  54  is engaged with the driven ratchet  64  so that the roller  70  squeezes the tube  80 . When the projection  44  is positioned at the other side  52   a  of the cam recess  52 , the driving ratchet  54  is not in contact with the driven ratchet  64 . That is, the lower surface of the driving ratchet  54  and the upper surface of the driven ratchet  64  are spaced apart by a gap so that the driving ratchet  54  avoids coming into contact with the driven ratchet  64 . The rotor  60  rises due to a recovering force of the squeezed tube  80  on the non-operation of the driving gear  40 , causing the ratchet wheel  50  to be rotated in the reverse direction. The gap is to prevent the reverse rotation of the rotor  60  caused by the reverse rotation of the ratchet wheel  50 . The reverse rotation of the rotor  60  may causes a noise and abrasion. 
   The driving ratchet  54  is formed of a series of triangular teeth with one side  54   a  being right-angled to a parallel line and disposed along the circumference of one end of the ratchet wheel  50 . An inclined surface  54   b  of the driving ratchet  54  is formed in a manner so that it allows the ratchet wheel  50  to move in a lengthwise direction of the stopper  42  as the rotor  60  moves upwardly due to a recovering force of the tube  80  on the non-operation of the driving gear  40  and thus the driven ratchet  64  pushes the driving ratchet  54 . Also, the inclined surface  54   b  of the driving ratchet  54  is formed in a manner so that when the driving gear  40  rotates in a direction that it does not squeeze the tube  80 , a force the driving ratchet  54  applies to the driven ratchet  64  is not greater than a force applied to the driven gear  64  due to the recovering force of the tube  80 . 
   Turning back to  FIG. 5 , the rotor  60  is shaped as a hollow cylinder and one end  62  thereof moves in an axial direction with respect to the fixing shaft  30 . Around an outer circumference of the hollow cylinder is formed the driven ratchet  64  to be engaged with the driving ratchet  54 . At the other end of the rotor  60  are provided two rollers  70 . The two rollers  70  are tapered, orbit the rotor  60  as it rotates, and freely and independently rotate with respect to the rotor  60 . However, while two rollers are shown and described, it is to be understood that more than two rollers may be provided. A tapered portion of the roller  70  completely squeezes the tube  80  as the rotor  60  is moved to the maximum degree by the stopper  42 . Also, the size of the driven ratchet  64  is identical to that of the driving ratchet  54 . At a center portion of the other end of the rotor  60  may be provided a guide shaft  66  for supporting the rotation of the rollers  70  and guiding the straight forwarding movement of the rotor  60  with respect to the fixing shaft  30 . One end of the guide shaft  66  is inserted into the housing  90  to guide the straight forwarding movement of the rotor  60 . 
   The tube  80  is disposed at a position to come into contact with at least one of the rollers  70  that orbit as the rotor  60  rotates. Although not shown, one end of the tube  80  is connected to an inkjet head nozzle. Generally, the tube  80  is disposed around the rollers  70  to come into contact with one roller  70  in a half orbiting circle of the plural rollers  70 . Accordingly, when the rotor  60  is rotated by the driving gear  40 , only one roller  70  rotates, squeezing the tube  60 . The tube  80  is made of material having a high elasticity so that it easily recovers its original state from a squeezed state. That is, the tube  80  has to have a recovering force powerful enough to push the rotor  60  and the ratchet wheel  50  toward the driving gear  40 . 
   As  FIG. 4  shows, the housing  90  accommodates the above-described components to prevent foreign materials from going into the pump apparatus, and especially firmly secures the tube  80  thereto. The housing  90  is provided with a guide hole  92  formed in one end thereof. Into the guide hole  92  is inserted the guide shaft  66  of the rotor  60 . Also, the housing  90  is provided with a rotor stopper  94  (shown in  FIG. 7 ) protruding from an inner side thereof. The rotor stopper  94  supports one end of the rotor  60  in order for the roller  70  to preload upon the tube  80  when the driving gear  40  is in the non-operation. The roller  70  preloads upon the tube  80  to prevent the rotor  60  from idle-rotating when the rotor  60  is rotated due to the ratchet wheel  50 . Accordingly, the degree of preload is set to an extent so that the tube  80  is not squeezed so as to generate a negative pressure and a friction force is generated between the roller  70  and the tube  80  (shown in  FIG. 7 ). 
   Hereinafter, operation of the pump apparatus for the inkjet printer according to an embodiment of the present invention will be described in detail with reference to  FIGS. 7 to 9C . 
   When the driving force transmitting gear  22  (not shown) is rotated by the motor (not shown), the driving gear  40  surrounding the fixing shaft  30  is rotated in a direction on the fixing shaft  30 . In conjunction with the rotation of the driving gear  40 , the stopper  42  integrally formed with the driving gear  40  is rotated in the same direction. If the stopper  42  is rotated in a counterclockwise direction (an arrow direction of  FIG. 9A ), the ratchet wheel  50  is separated from the rotor  60  as shown in  FIG. 9A  is moved downwardly by the projection  44  of the stopper  42 . When the projection  44  is moved to a position  52   b  of the cam recess  60  (shown in  FIG. 6 ), the driving ratchet  54  of the ratchet  50  is engaged with the driven ratchet  64  of the rotor  60 . If the rotation of the projection  44  continues, the ratchet wheel  50  and the rotor  60  are pushed downwardly so that the plural rollers  70  squeeze the tube  80 . When the projection  44  reaches the other side  52   c  (shown in  FIG. 6 ) of the cam recess  52 , the tube  80  is completely squeezed by the roller  70  as shown in  FIGS. 8 and 9C . That is, the inner diameter of the tube  80  is completely compressed. If the projection  44  continues to rotate, the ratchet wheel  50  is also rotated in association with the projection  44 . The rotation of the ratchet wheel  50  causes the driven ratchet  64  engaged with the driving ratchet  54  of the ratchet wheel  50  to rotate. Accordingly, the rotor  60  is rotated so that the plural rollers  70  disposed at the rotor  60  orbit the rotor  60 , squeezing the tube  80 . The two rollers  70  are both initially pressing the tube  80 . However, when the rotor  60  is rotated, one roller of the two rollers  70  is rotated, squeezing the tube  80 , while the other one is rotated, about the rotor and away from a contact with the tube  80 . While the rotor  60  rotates, one roller is moved from the contact with the tube  80  as the other roller comes into contact with the tube  80 . Accordingly, as the rotation of the rotor  60  continues, the two rollers  70  rotate, alternately squeezing the tube  80 . When the roller  70  squeezes the tube  80 , there is generated a negative pressure in the tube  80 . Due to the pressure difference between the negative pressure and an atmosphere pressure, the tube  80  performs sucking operation of ink from the inkjet head nozzle. 
   After the sucking operation, the motor stops operating and thus the driving force transmitting gear  22  stops rotating. Accordingly, the driving gear  40  stops rotating. When the driving gear  40  stops rotating, the rotor  60  is released from the load applied by the projection  44  of the stopper  42  disappears. Then, due to the recovering force of the tube  80 , the tube  80  recovers its original state and pushes the rollers  70  upwardly. On receipt of the upward load, the rotor  60  is moved along the fixing shaft  40  in an axial direction. As the rotor  60  is moved upwardly, the driven ratchet  64  and the ratchet wheel  50  are concurrently moved upwardly to thus return to the initial state as shown in  FIG. 9A . That is, when the driving gear  40  stops rotating, the rotor  60  and the ratchet wheel  50  are moved upwardly due to the recovering force of the tube  80 , so that the tube  80  automatically recovers its original state in which it is not squeezed. 
   Alternatively, the motor is rotated in the reverse direction to move the ratchet wheel  50  and the rotor  60  upwardly, whereby the tube  80  returns to its original state. This embodiment requires the cam recess  52  of the ratchet wheel  50  to be modified so that when the stopper  42  is rotated in the reverse direction, the ratchet wheel  50  is upwardly moved. 
   As described above, since the pump apparatus for the inkjet printer according to the present invention does not require the damper plate, the reliability of the sucking operation is improved and the collision noise does not occur even in the case that the pump apparatus is used for a long time. Also, since the tapered rollers  70  is constantly in contact with the tube  80 , the tube  80  is prevented from ascending over the rollers  70 , and the number of the components can be reduced. 
   Although a few embodiments of the present invention have been shown and described, the present invention is not limited to the disclosed embodiments. Rather, it would be appreciated by those skilled in the art that changes and modifications may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.