Patent Publication Number: US-6220690-B1

Title: Ink jet printer

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a serial-type ink jet printer and more particularly to an ink jet printer so configured that printing functions of a printing head are restored by sucking out thickened ink, dust and the like from a clogged nozzle through the use of negative pressure. 
     2. Description of the Related Art 
     A conventional serial-type ink jet printer is known wherein ink is discharged from a nozzle formed on a nozzle forming face of a printing head to perform printing. 
     In the conventional ink jet printer of this kind, image information covering one line is printed on paper while a printing head scans to and from once or more than one time in the direction of the width and, when the printing covering one line is terminated, it is started on a new line again by scanning in the direction of the width. 
     The ink jet printer can provide printed images with high quality and has an advantage that its printing head produces comparatively less noise while being printed. 
     However, the conventional ink jet printer presents a problem in that a nozzle of the printing head, when not in use, may get clogged up with dried ink, dust and floating materials in the air. Solidified ink, adhered dust and the like may cause defective discharging of ink (so-called “dot omission”) and interfere with normal printing. To prevent this, when the nozzle is not in use, the printing head is taken off from the ink jet printer to be housed in a keeping box or a nozzle forming face of the printing head is sealed to prevent drying of ink, adherence of dust and the like. However, it is inconvenient for a user to take the printing head off from the ink jet printer and to house it in the keeping box in every use and, in many cases, such storing of the printing head in the keeping box is not put into practice accordingly. 
     Another method for solving the problem of clogging of the nozzle of the printing head is to provide the ink jet printer with a nozzle restoring mechanism in which printing functions of the printing head are restored by using suction processes. 
     The conventional nozzle restoring mechanism is so configured that caps surrounding a group of nozzles in a closed contact with a nozzle forming face of a printing head are provided and air within a sealed cap chamber formed by the cap and the nozzle forming face is sucked so that solidified ink, dust and the like within the nozzle are sucked out forcedly together with air. The nozzle restoring mechanism, unlike in the case of using the keeping box, has an advantage that there is no need for intervention of users. That is, the ink jet printer is provided with a nozzle restoring section on the side of its printing section and, when the nozzle is not in use, the printing head is automatically brought to the position of the nozzle restoring section. 
     However, the conventional nozzle restoring mechanism using suction processes presents a problem in that waste ink residing in the cap after the suction has been carried out (or waste ink residing within a path of ink discharged by the suction) invades backward into the nozzle by residual negative pressure within the nozzle of the printing head, causing the nozzle to be contaminated with waste ink. 
     The influence by the contamination remarkably shows up in a color ink jet printer in particular. Recently, users tend to prefer the color ink jet printer that can provide color printing. In response to these demands, the recent ink jet printer can use multicolor ink and is provided with a printing head with nozzles that can be operated in use with such various color ink. In such a color ink jet printer, if waste ink is present even in trace amounts, it causes a color image to be degraded. Especially, for example, if bright color ink such as yellow ink or the like is mixed with dark color ink such as black ink, the resulting color image decreases in the quality, causing a feeling of visual strangeness. 
     Such a malfunction caused by the mixing of ink having different components does not always occur only in ink jet color printers. For example, in the case of an ink jet printer using black ink only, the printing head with different specifications uses black ink having different components. In any case, therefore, mixing of ink must be avoided in the operation of printers. 
     SUMMARY OF THE INVENTION 
     In view of the above, it is an object of the present invention to provide an ink jet printer provided with a mechanism to restore at least one nozzle by suction which can prevent the contamination and clogging of the nozzle of a printing head caused by waste ink, dust and the like. It is another object of the present invention to provide an ink jet printer being able to restore functions of nozzles of the printing head without using a keeping box. 
     According to an aspect of the present invention, there is provided an ink jet printer having a mechanism to restore at least one nozzle by suction, comprising: 
     a carrier on which a printing head is mounted; 
     a guide shaft to guide the carrier; 
     a guide frame; 
     a nozzle restoring unit including a frame, a capping unit supported by a frame, a negative pressure generating unit and an air releasing unit; and 
     a driving shaft; 
     whereby the nozzle forming face of a printing head is sealed with a cap when the nozzle is not in use and printing function of the printing head are restored, with the air releasing unit closed, by sucking ink and/or dust from the nozzle by negative pressure applied to a sealed space formed by the printing head and the cap; 
     the air releasing unit being used to release the sealed space to the atmosphere, with the air releasing unit opened, while ink is being discharged from the nozzle of the printing head at a terminal stage of the suction process by negative pressure. 
     In the foregoing, a preferable mode is one wherein the negative pressure generating mean is used to generate negative pressure to be applied to the sealed space, and the negative pressure generating means and air releasing means are individually driven by first and second cam members each having a different phase, which are both mounted on the same cam axis. 
     Also, a preferable mode is one wherein phases of the first and second cams are set so that, before a nose of the first cam points to the lowest point representing the termination of the negative pressure generating operation of a pump driving unit, or when it points to a position where an angle of θ is formed with respect to the lowest point, a flat face of the second cam points to the direction of the lowest point. 
     Also, a preferable mode is one wherein the air releasing unit is composed of the tube, one end of which is communicated with the cap and the other end of which is used to release air, a crushing member formed on the frame and used to crush the tube using the second cam to cut off air and a receiving member used to support the tube when crushed. 
     Also, a preferable mode is one wherein the air releasing means is activated to release the nozzle to the atmosphere while the discharging of ink from the nozzle continues. 
     Furthermore, a preferable mode is one wherein the suction by the negative pressure and releasing of air are performed by a predetermined timing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The above and other objects, advantages and features of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is a perspective view showing a nozzle restoring unit of an ink jet printer of the present invention; 
     FIG. 2A is a schematic diagram, seen from below, of a printing head of the ink jet printer shown in FIG.  1  and FIG. 2B is an enlarged view of a portion encircled by a circular shown in FIG. 2A; 
     FIGS. 3A and 3B are cross-sectional views, seen from the front, of a capping unit of the ink jet printer shown in FIG. 1, and FIG. 3A showing the state before being capped and FIG. 3B showing the state being capped; 
     FIGS. 4A and 4B are cross-sectional views showing operations of a negative pressure generating unit of the ink jet printer shown in FIG. 1; 
     FIGS. 5A and 5B are also cross-sectional views showing operations of the negative pressure generating unit of the ink jet printer shown in FIG. 1; 
     FIG. 6 is an exploded perspective view of a nozzle restoring unit shown in FIG. 1; 
     FIGS. 7A and 7B are cross-sectional views, seen from the side, showing an air releasing unit of the ink jet printer of the present invention and FIG. 7A showing the state when air is cut off and FIG. 7B showing the state when the unit is released to the atmosphere; 
     FIG. 8 is a schematic diagram illustrating the deviation of phases between a first cam and a second cam in the nozzle restoring unit shown in FIG. 1; and 
     FIG. 9 is a timing chart showing operations of the nozzle restoring unit shown in FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Best modes of carrying out the present invention will be described in further detail using various embodiments with reference to the accompanying drawings. 
     As shown in FIG. 1, the ink jet printer of the present invention is provided with a carrier  1  on which a printing head  11  is mounted, a guide shaft  2  to guide the carrier  1 , a guide frame  3 , a nozzle restoring unit  4  and a driving shaft  5 . 
     The nozzle restoring unit  4  consists of a frame  41 , a capping unit  42  supported by the frame, a negative pressure generating unit  43  and an air releasing unit  44 . 
     The carrier  1  has a hole through which the guide shaft  2  comes and a sliding member (not shown) and is supported by the guide frame  3  through the guide shaft  2  and the sliding member. The carrier  1  is so configured that it can move along the guide shaft  2  in the direction of an axial line by a belt conveying means (not shown) driven by an external driving motor (not shown). 
     As depicted in FIG. 3, the printing head  11  is disposed below the carrier  1 . 
     FIG. 2A is a bottom view approximately showing a nozzle forming face  12  of the printing head  11 . Referring to FIG. 2A, a frame  120  shown by the dotted lines illustrates a contact portion between the top end of the capping unit  42  of the nozzle restoring unit  4  and the nozzle forming face  12 . 
     On the nozzle forming face  12  of the printing head  11  are formed a black ink nozzle  121 , a cyan ink nozzle  122 , a light cyan ink nozzle  123 , a Magenta ink nozzle  124 , a light Magenta ink nozzle  125  and a yellow ink nozzle  126  and, as shown in an enlarged view of FIG. 2B, two or more nozzle rows are arranged at equal intervals vertically in the drawing. 
     An ink drop, as a shape of a piezo device (not shown) disposed at the back of the nozzle changes, is pushed and discharged out of the nozzle. 
     As in the case of known ink jet printers, the ink jet printer of the present invention is also so configured that printing information to be printed on printing media such as paper is performed by discharging ink out of the nozzle formed on the nozzle forming face  12  of the printing head  11 . 
     As shown in FIG. 1, the nozzle restoring unit  4  is placed at a nozzle restoring section disposed at the outside of a printing section where printing is performed by moving the carrier  1  in the direction of an axial line of the guide shaft, and when the printer is not in use, the carrier  1  is returned back to the nozzle restoring section so as to stand ready for subsequent printing. 
     Referring to FIGS. 3A and 6, the capping unit  42  is provided with a cap  421  to seal the nozzle forming face and a pressing means to press the cap  421  to the nozzle forming face. The pressing means consists of a cap holder  422 , a compressed spring  423 , a bracket  424 , a cap lever  425  and a tension spring  426 . The cap  421  is so configured that it is surrounded by an enclosure with a uniform height to make its cross-section concave and is opened on its side opposite to the nozzle forming face  12 . The cap  421  is made of an elastic material such as rubber and, when the top end of the enclosure is contacted, by pressure, with the nozzle forming face  12 , a sealed cap air chamber  4213  (see FIG. 3B) is formed. 
     As shown in FIG. 6, in the position opposite to the black ink nozzle  121  and in the position opposite to the yellow ink nozzle  126  at the bottom of the cap  421  are formed a sucking port  4211  and an air communicating port  4212  respectively. By this arrangement, the ink collected in the cap air chamber  4213  flows from a bright color position to a dark color position therein. The cap holder  422  is disposed below the cap  421 . Communicating paths to communicate the sucking port  4211  of the cap  421  with a first tube  46  and communicate the air communicating port  4212  with a second tube  47  respectively are provided. The cap  421  is pressed against the nozzle forming face  12  by a protrusion formed at the lower portion of the carrier  1 . 
     Referring FIGS. 3A and 6, the capping unit  42  is composed of the cap lever  425  which swings with respect to a rotary axis  413  to lift the bracket  424  by being contacted by the protrusion  13  of the carrier  1 , the cap holder  422  used to hold the cap  421 , by pressure, to the contacting section  120  (see FIG. 2) surrounding the nozzle forming face  12  and to press up the compressed spring  423  so that its loads are imposed uniformly on the contacting section  120 , and the bracket  424  to hold the cap holder  422  through the compressed spring  423 . The bracket  424  is pulled, by the tension spring  426 , toward the hook  414  of the tensile spring mounted on the frame  41  and held by holding sections  411  and  412  of the capping unit formed on the frame  41 . 
     By referring to FIGS. 4A,  4 B and  6 , the negative pressure generating unit  43  is hereafter described. The negative pressure generating unit  43  contains a diaphragm pump communicating with the cap  421  by the first tube  46  and a pump driving unit to transfer external driving power to the diaphragm pump. The diaphragm pump is provided with a cover  4311 , a diaphragm  4312 , a pump frame  4313 , a shaft cover  4314 , a shaft  4315  and a loading ring  4316 . 
     The cover  4311  has a cap communicating port  43110  into which the tube  46  is inserted to be connected thereto. The diaphragm  4312  co-operates with the cover  4311  to form a pump chamber  4310  having variable volume. 
     The pump frame  4313  is used to seal and hold the cover  4311  and the diaphragm  4312  against the cover lock section  415  formed by the frame  41 . 
     The shaft cover  4314  is used to supply a force that acts on a bottom surface  43120  of the diaphragm  4312  and push the same in the direction to reduce the volume of the pump chamber  4310 . 
     The shaft  4315  has a disc-shaped valve section  43150  within the pump chamber  4310  and have the pump chamber cut off from air by bringing the disc-shaped valve section  43150  into intimate contact with the bottom surface of the diaphragm  4312 . 
     The loading ring  4316  is located between a pump frame holding section  416  formed by the frame  41  and the pump frame  4313 . The loading ring  4316  is used to impose loads on the shaft cover  4314  when the shaft cover accomplishes up-and-down movements. 
     The pump driving unit has a swinging pump lever  4320 , a first gear  4321  and a second gear  4324  engaged with the first gear  4321 . The second gear  4324  is constructed so as to be integral with a cam shaft  4322  and the former drives the latter to be rotated. The cam shaft  4322  has a first cam  43220  and a second cam  43221 . The swinging pump lever  4320  of the pump driving unit is coupled to the shaft  4315  of the pump with a pin  4323 . 
     The pump lever  4320  is supported so as to be swung by a shaft  43200  connected to the bearing  417  at its hinged support. The first gear  4321  is coupled, by the application of pressure, to the driving shaft  5  in the direction of the axis line and is made rotatable integrally with the driving shaft  5 . The second gear  4324  is adapted to engage with the first gear  4321 . As described above, the second gear  4324  is constructed so as to be integral with the cam shaft  4322  equipped with the first cam  43220  and the second cam  43221 . 
     The first cam  43220  of the cam shaft  4322  is placed at a position where it can engage with a cam curving surface  43201  of the pump lever  4320 . The first cam  43220  is adapted to transfer movements, by sliding the cam curving surface  43201  of the pump lever  4320 , to the shaft  4315  coupled to the pump lever  4329  with the pin  4323 . 
     The force given by the second cam  43221  acts on the air releasing unit  44 . Since the first cam  43220  and the second cam  43221  are adapted to rotate around the same rotary axis, they rotate in synchronization with each other. 
     As depicted in FIG. 8, phases of the first cam  43220  and the second cam  43221  are set so that, before a nose  32200  of the first cam  43220  points to the lowest point representing the termination of a negative pressure generating operation of the pump driving unit, i.e., when it points to a position where an angle of θ is formed with respect to the lowest point, the flat face  432210  of the second cam points to the direction of the lowest point. 
     Referring to FIG. 7, the air releasing unit  44  is provided with the tube  47 , one end of which is communicated with the cap  421  and the other end of which is used to release air, a crushing member  418  formed on the frame  41  and used to crush the tube  47  using the second cam  43221  to cut off air and a receiving member  419  used to support the tube when crushed. The tube  47  is held by the crushing member and the receiving member  419 . 
     Next, operations for restoring the nozzle of the ink jet printer of the present invention are described below by referring to a timing chart shown in FIG.  9 . 
     The carrier  1 , during standby for printing, has been carried to the position shown in FIG. 3B past the position shown in FIG. 3A to protect the nozzle forming face  12  of the printing head supported by the carrier  1  and is standing ready for a subsequent printing in the nozzle restoring unit  4 . That is, the carrier  1  moves from the left to the right direction while a right lower portion  130  of the protrusion  13  of the carrier  1  is sliding on a upper slope  4250  of the cap lever  425 . The cap lever  425  rotates around a hinged support  413  in a clockwise direction and a right protrusion  4251  of the cap lever  425  lifts the bracket  424  upward. The bracket  424  lifts a cap holder  422  used to hold the cap  421  through the compressed spring  423  and presses the cap  421  against the nozzle forming face  12  as shown in FIG.  3 B. At this point, a cap air chamber (i.e., sealed space)  4213  is formed by the nozzle forming face  12  and the cap  421 . 
     To restore a clogged nozzle, the negative pressure generating unit  43  is activated. That is, an external driving force (not shown) is transferred, through the driving shaft  5 , to the first gear  4321 . Then, the cam shaft  4322  is rotated through the second gear  4323 . When the cam shaft  4322  is rotated, the first cam  43220  is rotated, for example, from a lowest point  432200  where the first cam  43220  now exists, to the direction of an arrow mark (in a clockwise direction) as shown in FIG. 4A and, at the first rotation position  432201  shown by chain lines, the nose  432200  of the first cam  43220  is contacted with the cam curving surface  43201  of the pump lever  4320  (at first rotation position in FIG.  9 ). 
     When the first cam  43220  is further rotated, it drives the pump lever  4320  while contacting with the cam curving surface  43201  of the pump lever  4320 . This causes the pump lever  4320  to swing around the rotary axis  43200  in a counterclockwise direction and to begin to lift the shaft  4315  through the pin  4323 . When the first cam  43220  is rotated from the rotation position  432201  to the other position  432202 , as shown in FIG. 4B, because the disc-shaped valve section  43150  of the shaft  4315  leaves a bottom face  43120  of the diaphragm  4312 , air is allowed to enter or go out of, the pump chamber  4310  through a clearance  43140  between the shaft cover  4314  and the shaft  4315 . At the rotation position  432202  of the first cam  43220 , a right upper face  43202  of the pump lever  4320  comes into contact with the shaft cover  4314  in a bumped state (see FIG. 4B) and from this point, an exhaust stroke starts (see FIG.  9 ). 
     When the pump lever  4320  is further swung, a right upper face  43202  of the pump lever  4320  lifts the shaft cover  4314 , and in response to this action, the shaft cover  4314  lifts a bottom face  43120  of the diaphragm  4312 . When the first cam  43220  is rotated from the rotation position  432202  to a position  432203 , the pump moves from the position of the bottom dead center where the volume of the pump chamber  4310  is maximized to the position of the top dead center where the volume of the pump chamber  4310  is minimized (refer to FIGS.  5 A and  9 ). This causes the pump chamber  4310  to release air within the chamber into the atmosphere through the clearance  43140  and to reduce its volume. Because of this, waste ink collected in the pump chamber  4310  is discharged downward through the clearance  43140  and flows into a waste ink container (not shown). 
     Then, the first cam  43220  rotates from the rotation position  432203  to a position  432204  shown by chain lines in FIG.  5  and again contacts the pump lever  4320 . 
     When the first cam  43220  is further rotated from the position  432204 , the pump lever  4320  begins to pull down the shaft  4315  through the pin  4323 . As shown in FIG. 5B, when the first cam  43220  is in the position  432205 , the disc-shaped valve section  43150  of the shaft  4315  comes into contact with the bottom face  43120  of the diaphragm  4312  to block the clearance  43140  so that the pump chamber  4310  is cut off from the atmosphere and sealed. This point is a starting point of sucking stroke of the pump (refer to FIG.  9 ). At this point, the printing head  11  is turned ON, ink discharging operation from the nozzle is started and ink drops are discharged into the cap air chamber  4213  (refer to FIG.  9 ). 
     When the first cam  43220  is rotated from the position  432205  to the position  432200  (i.e., the position immediately before the angle range of θ) by making the cam shaft  4322  rotate further, the pump lever  4320  swings to pull the shaft  4315  down further, causing the volume of the pumping chamber  4310  to be increased and the sucking stroke to start. As the volume of the pump chamber  4310  increases, negative pressure is generated within the pump chamber  4310 . The negative pressure is transferred to the cap air chamber  4213  through the communicating port  43110  of the cover  4311  and the tube  46 . 
     This negative pressure acts on each nozzle of the printing head  11  facing the cap air chamber. By the action of the negative pressure within the cap air chamber  4213 , in cooperation with actions of pressure of ink drops jetted from the nozzle, thickened ink, dust and the like within the nozzle are sucked out and collected in the cap air chamber  4213 . During this operation, since the pump moves from its top dead center to its bottom dead center, waste ink within the cap air chamber  4213  is sucked out and collected within the pump chamber  4310 . 
     When the first cam  43220  is rotated to the position  432200 , i.e., the position of immediately before the angle range of θ, because the flat face  432211  of the second cam  43221  having a phase being different from that of the first cam  43220  points to the lowest point, the air releasing unit  44  begins to perform air releasing operation to cause the pressure within the cap air chamber to be atmospheric pressure. 
     That is, as shown in FIGS. 7A and 7B, the flat face  432211  of the second cam  43221  points to the direction of the lowest point, the crushing member  418  crushing the tube  47  is released, allowing the atmosphere to come into the cap air chamber  4213  through the communicated tube  47 . At this point, the cap air chamber  4213  sucks air through the air communicating port  4212  and the pump sucks the waste ink and air combined with the waste ink within the cap air chamber  4213 . 
     As is apparent in FIG. 9, when the air releasing unit  44  allows the cap air chamber  4213  to accept air from the atmosphere, since discharging of ink from the nozzle still continues, after air is allowed to enter the cap air chamber  4213 , the nozzle jets ink under the atmospheric pressure. 
     The first cam  43220  further rotates to the front of the rotation position  432200 . At the front of the rotation position  432200 , the printing head  11  is turned OFF and the discharging of ink from the nozzle is terminated. At this point, as the cap air chamber  4213  is under the atmospheric pressure, at the time of termination of discharging of ink from the nozzle, no negative pressure acts on the nozzle. 
     When the first cam  43220  further rotates to the rotation position  432200 , the pump reaches its bottom dead center and sucks the waste ink and air combined with the waste ink within the cap air chamber  4213 , and the air releasing unit  44  crushes the tube  47  to cut off air and the air releasing operation is terminated. 
     As described above, according to the ink jet printer of the present invention, since, while the discharging of ink from the nozzle continues, the air releasing means is activated to release the nozzle to the atmosphere, there is no residue of the negative pressure within the nozzle after sucking process by negative pressure is terminated. Accordingly, the waste ink collected within the cap after being sucked in the sucking process does not flow backward to the nozzle, thus preventing the contamination and/or mixing of color of ink caused by the waste ink 
     Moreover, according to the present invention, because there is no need for using a keeping box, the clogging in the nozzle caused by the thickened ink, dust and the like can be prevented, thus providing restored normal printing capability. 
     Furthermore, according to a preferred embodiment, the negative pressure generating means and the air releasing means are individually driven by two cam members, each having a different phase, mounted on the same cam axis. 
     According to the present invention, the ink jet printer is so configured that the negative suction and air releasing can be performed by a predetermined timing in a simplest way. 
     It is thus apparent that the present invention is not limited to the above embodiment but may be changed and modified without departing from the scope and spirit of the invention.