Patent Publication Number: US-7585064-B2

Title: Apparatus to remove bubbles in an inkjet printer

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of Korean Patent Application No. 10-2005-0115845, 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 
   The present general inventive concept relates to an apparatus to remove bubbles from a printhead of an inkjet printer, and more particularly, to a bubble removing apparatus usable with a line printing type array printhead. 
   2. Description of the Related Art 
   Generally, an inkjet printer is a device that prints a desired image by ejecting droplets of ink onto paper.  FIGS. 1 and 2  illustrate a conventional inkjet printer. Referring to  FIG. 1 , the conventional inkjet printer includes a printhead  10  ejecting ink droplets through nozzles  11   a , feed rollers  20  feeding paper (P) below the printhead  10 , and ejecting rollers  30  ejecting the paper (P) to a tray  40  after printing. When the feed rollers  20  feed the paper (P) below the printhead  10 , the printhead  10  ejects the ink droplets through nozzles  11   a  formed in a chip  11  to print the desired image, and the ejecting rollers  30  eject the paper (P) to the tray  40  after printing. 
   Examples of the printhead  10  include a shuttle type printhead and a line printing type printhead. The shuttle type print head prints each lateral line of the desired image while reciprocating in a width direction of paper (P). The line printing type printhead has a width corresponding to the width of paper (P), such that the line printing type printhead can simultaneously print one line of an image at a fixed position. The line printing type printhead is also referred to as an array type printhead, is preferred over the shuttle type print head because the array type printhead provides a high speed printing characteristic. 
   In the conventional inkjet printer, the ink droplets are ejected through the nozzles  11   a  formed in the chip  11  of the printhead  10 . Therefore, if the nozzles  11   a  are clogged by bubbles, the ink droplets are not properly ejected, and thus the desired image is not properly formed. To solve this problem, various conventional methods are used to remove the bubbles from ink. In a representative method of the various conventional approaches, a suction cap is put on the chip  11  of the printhead  10 , and the nozzles  11   a  are sucked using a pump to remove the bubbles from the nozzles  11   a  together with a little amount of the ink. Although this method can be effectively used for the shuttle type printhead having a small number of the chips  11  and a small size, it is difficult to use this method for the array type printhead since the chips  11  of the array type printhead are widely arranged across the width of the paper (P). That is, since the array type printhead includes a plurality of the chips  11  with the nozzles  11   a  arranged in the width direction of the paper (P) to entirely cover the width of the paper (P), it is difficult to precisely put caps on all the chips  11  for a hermetic or airtight seal. Further, it is difficult to apply a uniform pressure to the nozzles  11   a  to suck the bubbles from the nozzles  11   a . To solve these problems, another method illustrated in  FIG. 2  is used to remove the bubbles from the array type printhead. Referring to  FIG. 2 , an ink circulation line  60  is provided between the printhead  10  and an ink tank  50 , and if necessary, ink is circulated between the printhead  10  and the ink tank  50  using a diaphragm pump  70 . That is, when the ink reaches the ink tank  50  during circulation, the bubbles are removed from the ink due to a specific gravity difference between the bubbles and the ink. 
   Although the bubbles can be removed from a channel of the printhead  10  using the ink circulation method of  FIG. 2 , that is, although the bubbles can be removed from the ink before the ink flows into the chips  11  of the printhead  10 , the bubbles cannot be removed from the ink that has already entered the chips  11  of the printhead  10  since the ink that has entered the chips  11  is not circulated through the ink circulation line  60 . The bubbles are removed from the ink that has entered the chips  11  through purging. In a purge process, a valve  80  of the ink circulation line  60  is closed, and the diaphragm pump  70  is intensively operated two or three times to apply a large pressure to the printhead  10 , such that the bubbles can be pushed out of the chips  11  of the printhead  10  together with a little amount of the ink. That is, both the circulation and purging must be performed to remove the bubbles from the ink in the array type printhead  10 . 
   However, the conventional inkjet printer requires two motors, a circulation motor (M 1 )  71  and a purging motor (M 2 )  72 , in the diaphragm pump  70  to perform the circulation and purging since the circulation and purging requires different operating conditions.  FIGS. 3A and 3B  are characteristic graphs respectively illustrating a pump output in the circulation process for removing the bubbles and a pump output in the purge process for removing bubbles for the conventional bubble removing apparatus. During the circulation process, the diaphragm pump  70  is slowly operated to continuously generate a pressure of about 2 kpa as illustrated in  FIG. 3A . However, during the purging process, the diaphragm pump  70  is operated one or two times to generate an instantaneous pressure larger than 7 kpa, as illustrated in  FIG. 3B . For this reason, the two motors  71  and  72  with different output powers are used. 
   However, because of the two motors and power transmitting structures for connecting the two motors to the diaphragm pumps, the inkjet print has a complicated structure and a heavy weight. Therefore, there is a need for an apparatus that has a more simplified structure and can smoothly perform the circulation and purging processes. 
   SUMMARY OF THE INVENTION 
   The present general inventive concept provides a bubble removing apparatus usable in an inkjet printer that performs circulation and purging operations using a single motor. 
   Additional aspects and advantages 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 and utilities of the present general inventive concept may be achieved by providing a bubble removing apparatus usable in an inkjet printer, including an ink circulation line to connect an ink tank and a printhead, and a pumping unit to apply a pressure to the ink circulation line to remove bubbles from a channel and a chip of the printhead, wherein the pumping unit includes a housing including an inlet and an outlet that are connected to the ink circulation line, a vibration unit installed to the housing and capable of vibrating, the vibration unit to generate pressure variations to move ink from the intake to the outlet, a motor to drive the vibration unit, a circulation cam to vibrate the vibration unit while rotated by the motor in a circulation mode, to circulate the ink contained in the channel of the printhead along the ink circulation line, a purging cam installed coaxially with the circulation cam, the purging cam to vibrate the vibration unit while rotated by the motor in a purge mode, to discharge the ink contained in the chip of the printhead through a nozzle, and a clutch unit to transmit power of the motor to one of the circulation cam and the purging cam in a selective manner. 
   The circulation cam may include a cam surface to cause the vibration unit to vibrate in a gentle manner, and the purging cam may include a cam surface to cause the vibration unit to vibrate in an abrupt manner. 
   The clutch unit may include a first ratchet wheel having a first tooth orientation to engage a first ratchet surface formed on the circulation cam to transmit a driving force in one direction, a second ratchet wheel having a second tooth orientation opposite to the first tooth orientation of the first ratchet wheel, to engage a second ratchet surface formed on the purging cam to transmit the driving force in a direction opposite to the one direction, a first elastic member to apply a first elastic force in a first direction to allow the first ratchet wheel to engage the ratchet surface of the circulation cam, and a second elastic member to apply an elastic force in a second direction to allow the second ratchet wheel to engage the ratchet surface of the purging cam. 
   The first ratchet wheel, the second ratchet wheel, the circulation cam, and the purging cam may be coaxially installed on a driving shaft. 
   The vibration unit may include a piston installed to the housing and capable of reciprocating, the piston being vibrated according to the cam surface of the rotating circulation cam or the cam surface of the rotating purging cam, and an elastic diaphragm to repeatedly deform and return to its original shape to interlock with the piston to generate pressure variations in the housing to suck the ink through the intake and to discharge the ink through the outlet. 
   The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing an apparatus to remove bubbles in an inkjet printer, including a housing having an inlet, an outlet, and a vibration unit connected between the inlet and the outlet, a circulation cam having a first shape to control the vibration unit in a circulation mode, a purging cam having a second shape to control the vibration unit to move ink between the inlet and the outlet in a purging mode, and a single motor to selectively control one of the circulating cam and the purging cam. 
   The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing an inkjet printer, including feed rollers to feed the printing medium to the inkjet printhead, ejecting rollers to remove the printing medium after an image has been formed thereon, an inkjet printhead to form images on a printing medium, an ink tank to supply ink to the inkjet printhead, and a pump to circulate the ink from the ink tank to the inkjet printhead, the pump including a housing having an inlet, an outlet, and a vibration unit connected between the inlet and the outlet, a circulation cam having a first shape to control the vibration unit in a circulation mode, a purging cam having a second shape to control the vibration unit to move ink between the inlet and the outlet in a purging mode, and a single motor to selectively control one of the circulating cam and the purging cam. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and/or other aspects and advantages 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  illustrates a structure of a conventional inkjet printer; 
       FIG. 2  illustrates a schematic structure of a conventional bubble removing apparatus; 
       FIGS. 3A and 3B  are characteristic graphs respectively illustrating a pump output in a circulation process for removing bubbles and a pump output in a purge process for removing bubbles of a conventional bubble removing apparatus; 
       FIG. 4  is a view illustrating a bubble removing apparatus according to an embodiment of the present general inventive concept; 
       FIGS. 5 and 6  are views illustrating a pump unit of the bubble removing apparatus of  FIG. 4 ; 
       FIGS. 7A through 7C  are views illustrating a circulation cam and a purging cam of the pump unit of  FIG. 5 ; and 
       FIGS. 8A and 8B  are views illustrating an operation of the pump unit of  FIGS. 4 and 5 . 
   

   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 by referring to the figures. 
     FIG. 4  is a view illustrating a bubble removing apparatus according to an embodiment of the present general inventive concept. 
   Referring to  FIG. 4 , the bubble removing apparatus includes an ink circulation line  600  to connect a printhead  100  and an ink tank  500 , and a pumping unit  700  to circulate ink. When the pumping unit  700  operates in an open state of a valve  800 , a circulation mode starts. In the circulation mode, the ink is moved from a channel (not shown) of the printhead  100  to the ink tank  500  through the ink circulation line  600  and the valve  800  and returned to the channel from the ink tank  500  through the ink circulation line  600  and the pumping unit  700 . During the circulation mode, bubbles contained in the ink are separated from the ink in the ink tank  500  owing to a specific gravity difference therebetween to thereby remove the bubbles from the ink in the printhead  100 . In a purge mode, the valve  800  is closed, and a large pressure is instantaneously applied from the pumping unit  700  through the ink circulation line  600  to remove the bubbles from the ink contained in chips  110  of the printhead  100  by discharging the bubbles to an outside through nozzles  111 . 
     FIGS. 5 and 6  are views illustrating the pumping unit  700  of the bubble removing apparatus of  FIG. 4 . Referring to  FIGS. 4-6 , the pumping unit  700  is configured to perform the circulation and purge modes using a single motor (M)  710 .  FIGS. 5 and 6  are views illustrating a pump unit of the bubble removing apparatus of  FIG. 4 .  FIGS. 7A through 7C  illustrate a circulation cam  720  and a purging cam  730  of the pump unit  700  of  FIG. 4 . Referring to  FIGS. 5 and 6 , the pumping unit  700  includes the motor  710 , the circulation cam  720 , and the purging cam  730  that are installed on a driving shaft  711  connected with the motor  710  to receive driving power from the motor  710 . The circulation cam  720  has a circular shape with an axis of rotation displaced from a center thereof. That is, the radius of the circulation cam  720  is eccentric so that one side extends further than other sides thereof, In addition, the circulation cam has a gently profiled cam surface  721  as illustrated in  FIG. 7A . The purging cam  730  has a steeply profiled cam surface  731  with a cutout as illustrated in  FIG. 7B . When the two cams  720  and  730  are overlapped as illustrated  FIG. 7C , a portion  730 ′ of the purging cam  730  is protruded from the profile of the circulation cam  720 , such that a stroke of a piston  751  is changed by the rotation of the purging cam  730  more than by the rotation of the circulation cam  720 . 
   The circulation and purging cams  720  and  730  have different shapes to cause different pressure changes in the ink depending on which of the circulation or purging cam  720  and  730  contacts the piston  751 . The gently profiled surface  721  of the circulation cam  720  may have a first radius r 1  that is greatest for the circulation cam  720  and a second radius r 2  that is smallest for the circulation cam  720 . The purging cam  730  may also have a portion of its radius be equal to the first radius r 1  of the circulation cam  720 . The purging cam  730  may have a third radius r 3  that is a radius for the protruded portion  730 ′ that is greater than the first radius of the circulation cam  720  and a fourth radius r 4  for the cutout that is smaller than any of the first, second, and third radii r 1 , r 2 , and r 3 . When the circulation and purging cams  720  and  730  are overlapped as illustrated in  FIG. 7C , the profile thereof demonstrates that the third radius r 3  is greatest, the first radius r 1  is larger than the second radius r 2 , and that the fourth radius r 4  is smallest. In addition, an angle a 2  formed by a width of the protruding portion  730 ′ of the purging cam  730  is smaller than an angle a 1  formed by a width of the cam surface  721  of the circulation cam. Thus, a vibration caused by the circulation cam  720  builds steadily while a vibration caused by the purging cam  730  builds quickly. In addition, the purging cam  730  causes a greater pressure to be formed within the pumping unit  700 . 
   The piston  751  is installed on a housing  750  to elastically reciprocate in a motion determined by the cam surfaces  721  and  731  having different shapes. By the reciprocating motion of the piston  751 , an elastic diaphragm  752  that is installed under the piston  751  is repeatedly deformed and returned to its original shape. Through the reciprocating motion, the piston  751  and the elastic diaphragm  752  make up a vibration unit to generate pressure variations to suck and discharge the ink. The pressure inside the housing  750  varies according to a vibration of the vibration unit, such that the ink can be sucked into a pressure generating space  752   a  through an intake  750   a  and a first check valve  771  and pushed to the outside through a second check valve  772  and an outlet  750   b.    
   In the circulation mode, the circulation cam  720  is rotated to vibrate the piston  751  of the vibration unit, and in the purging mode, the purging cam  730  is rotated to vibrate the piston  751 . A clutch unit is provided to transmit the power of the motor  710  to one of the circulation cam  720  and the purging cam  730  in a selective manner as described above. The clutch unit includes a first ratchet wheel  741  and a second ratchet wheel  742 , and a first spring  761  and a second spring  762 . The first and second ratchet wheels  741  and  742  are installed on the driving shaft  711  to couple with respective ratchet surfaces  723  and  733  formed on the circulation cam  720  and the purging cam  730 . The first and second springs  761  and  762  provide elastic forces to couple the ratchet wheels  741  and  742  and the ratchet surfaces  723  and  733 , respectively. The first and second springs  761  and  762  ensure contact between the respective first and second ratchet wheels  741  and  742  and the ratchet surfaces  723  and  733 . The rotation direction of the circulation cam  720  when coupled with the first ratchet wheel  741  is different from the rotation direction of the purging cam  730  when coupled with the second ratchet wheel  742 . That is, ratchet engagement directions of the ratchet surfaces  723  and  733  are opposite to each other. For example, when the driving shaft  711  is rotated counterclockwise, the circulation cam  720  is rotated by the engagement with the first ratchet wheel  741 , and when the driving shaft  711  is rotated clockwise, the purging cam  730  is rotated by the engagement with the second ratchet wheel  742 . 
   The first and second ratchet wheels  741  and  742  are fixed to the driving shaft  711  using pins  741   a  and  742   a , such that the first and second ratchet wheels  741  and  742  always rotate with the driving shaft  711 . However, the circulation cam  720  and the purging cam  730  are rotatably coupled to the driving shaft  711  using bearings  722  and  733 , and may be slightly movable in an axis direction of the driving shaft  711 . That is, when the elastic forces from the first and second spring  761  and  762  are received by the circulation cam  720  and the purging cam  730 , the respective circulation and purging cams  720  and  730  are moved along the axis of the driving shaft  711  to be selectively engaged. Therefore, the circulation cam  720  and the purging cam  730  can be rotated with the driving shaft  711  when the driving power of the motor  710  is transmitted thereto by the coupling between the ratchet surfaces  723  and  733  and the first and the second ratchet wheels  741  and  742 . Otherwise, only inner rims of the bearings  722  and  732  are rotated together with the driving shaft  711 , and the circulation cam  720  and the purging cam  730  coupled to outer rims of the bearings  722  and  732  are not rotated. 
   An operation of the above-described bubble removing apparatus will now be described. 
     FIGS. 8A and 8B  illustrate an operation of the pump unit of  FIG. 4 . To remove the bubbles from the ink contained in the channel of the printhead  100 , the valve  800  of the ink circulation line  600  is opened and the pumping unit  700  is operated in a circulation mode to circulate the ink from the channel to the ink tank  500  and then back to the channel. To circulate the ink in the circulation mode, the motor  710  of the pumping unit  700  rotates the driving shaft counterclockwise as illustrated in  FIG. 8A , and thus the first ratchet wheel  741  engages with the ratchet surface  722  of the circulation cam  720  to rotate the circulation cam  720 . In a case where the driving shaft is rotated counterclockwise, the second ratchet wheel  742  does not engage with the ratchet surface  733  of the purging cam  730  since the corresponding ratchets slip. Thus, only the inner rim of the bearing  732  rotates and the body of the bearing  732  does not rotate. Although the purging cam  730  may be slightly rotated while the second ratchet wheel  742  and the ratchet surface  733  slip, this rotation is negligible since the power of the motor  710  is not effectively transmitted through the slight rotation. Further, though the protruded portion  730 ′ (see  FIG. 7C ) of the purging cam  730  may press the piston  751  when the purging cam  730  is slightly rotated, the purging cam  730  cannot maintain a position to allow the protruded portion  730 ′ to continuously press the piston  751  since the piston  751  is elastically supported by an elastic plate  751   a  in an upward direction. Thus, the protruded portion  730 ′ is returned back or does not have enough power transmitted thereto to translate the piston  751  when the driving shaft is rotated counterclockwise. When the circulation cam  720  is rotated by the motor  710  in this state, the piston  751  is vibrated by the gently profiled cam surface  721  of the circulation cam  720 , and the elastic diaphragm  752  is repeatedly deformed and returned to its original shape in direct response to the vibration of the piston  751 , such that the ink can be sucked through the intake  750   a  and pushed to the outside through the outlet  750   b  as if the ink is sucked and dropped by a dropper. Therefore, by the driving force of the pumping unit  700 , the ink can be circulated between the channel of the printhead  100  and the ink tank  500 . In addition, the bubbles can float on the ink in the ink tank  500  owing to the specific gravity different between the bubbles and the ink, so that the bubbles can be removed from the ink. 
   When the bubble removing apparatus operates in a purging mode to remove the bubbles from the ink contained in the chips  110  of the printhead  100 , the valve  800  of the ink circulation line  600  is closed and the motor  710  is rotated in an opposite direction to rotate the driving shaft  711  clockwise as illustrated in  FIG. 8B . Then, the second ratchet wheel  742  engages the ratchet surface  733  of the purging cam  730  to rotate the purging cam  730 . In a case where the motor  710  is rotated in the clockwise direction, the circulation cam  720  is not rotated since the first ratchet wheel  741  and the ratchet surface  722  of the circulation cam  720  slip with each other. Accordingly, the piston  751  is vibrated by the steeply profiled cam surface  731 , and this vibration is converted into the large pressure through the elastic diaphragm  752  and transmitted to the chips  110 , so that the bubbles in the chips  110  are discharged to the outside of the nozzles  111  together with a little amount of the ink. Therefore, the bubbles can be clearly removed from the chips  110  and the possibility of clogging the nozzles can be eliminated. 
   As described above, in a bubble removing apparatus, proper pressures for a circulation mode and a purging mode can be obtained by changing a rotation direction of a motor, so that operations required to remove the bubbles can be smoothly performed. The pressure of the purging mode is higher than that of the circulation mode since an eccentric radius of the circulation cam  720  is smaller than a radius of the protruded portion  730 ′ of the purging cam  730 . 
   As described above, although a bubble removing apparatus is configured so that a purging mode is performed when a driving shaft is rotated in a clockwise direction and a circulation mode is performed when the driving shaft is rotated in a counterclockwise direction, the bubble removing apparatus can be configured in a reverse manner by changing a ratchet engagement direction. 
   As described above, a circulation mode and a purging mode are performed using a single motor to remove bubbles from a printhead channel and from printhead chips, so that a bubble removing apparatus can have a simple structure and a light weight. 
   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.