Patent Publication Number: US-6663220-B2

Title: Ink jet printer

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is based on Japanese Priority Document 2000-257238 filed Aug. 28, 2000, the content of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an ink jet printer which performs printing by discharging ink supplied from nozzle head ink tank having plural ink jet nozzles from selected ink jet nozzles, on a print medium. 
     2. Discussion of the Background 
     Conventionally known is a line type ink jet printer which performs printing at a greatly-improved printing speed in comparison with a so-called serial type ink jet printer and performs continuous print operation on a large number of print sheets. This line type ink jet printer can perform continuous printing on, e.g., 500 or more sheets. 
     In the continuous printing on a large number of print sheets, if only an unincreasable-sized ink cassette (i.e. a small ink cassette) is used as in the case of the conventional serial type ink jet printer where the size of the ink cassette cannot be increased due to a reciprocating movement in a line direction, the ink becomes short. 
     In the ink jet printer that performs continuous print operation on e.g. 500 or more print sheets, a removable large-capacity ink cartridge is provided, and ink is supplied from the ink cartridge to the ink tank whenever necessary, thereby frequent ink cassette change as in the case of the conventional small ink cassette is unnecessitated and continuous print operation for a long period is realized. 
     In addition, in this ink jet printer, a removable waste ink tank is provided in a fixed position, and upon maintenance of a nozzle head, ink discharged from the nozzle head is collected into the waste ink tank. 
     In this large-capacity line type ink jet printer, attachment of ink tank and piping are complicated, assembly thereof is troublesome and the number of processes is large. Accordingly, the ink tank cannot be easily changed. If the printer is used for a long period without changing the ink tank, impurities such as dirt mixed in ink supplied from the ink cartridge to the ink tank and chemical compound of the ink itself (hereinbelow referred to as “impurities”) are deposited on the bottom of the ink tank. 
     As the impurities supplied from the ink tank to the nozzle head cause clogging in the nozzle head, the conventional ink jet printers have various arrangements to prevent the entry of the impurities into the nozzle head. 
     As an example of arrangement to prevent the entry of the impurities into the nozzle head, an ink supply port from the ink tank to the nozzle head is provided in a position higher than the bottom surface of the ink tank such that the impurities are deposited in a predetermined area. In this case, the impurities reach the supply port in time and the impurities are supplied to the nozzle head. To prevent this inconvenience, the capacity of the ink tank may be increased so as to increase the impurity depositing area. However, if the capacity of the ink tank is increased, the ink jet printer itself is enlarged. Therefore, this arrangement cannot be the best solution. 
     Further, as another arrangement to prevent the entry of the impurities into the nozzle head, a filter is provided inside the ink tank. However, in this case, as the impurities are deposited inside the filter, the inside space of the filter is filled with the impurities in time, and ink supply to the nozzle head might be disturbed. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the present invention is to provide an ink jet printer which reliably prevents clogging in a nozzle head due to impurities. 
     The object of the present invention is achieved by the novel ink jet printer head of the present invention. 
     According to the novel ink jet printer of the present invention, a discharge port formed in the bottom surface of ink tank is connected by a connecting member to a waste ink tank to collect waste ink produced upon nozzle head maintenance, and a part of the connecting member is freely opened/closed by a valve. 
     Another aspect of the novel ink jet printer head of the present invention, the discharge port formed in the bottom surface of ink tank is connected by connecting means to waste ink tank for collecting waste ink produced upon nozzle head maintenance, and a part of the connecting means is freely opened/closed by a valve. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the present invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
     FIG. 1 is an explanatory view of a printing method of an ink jet printer according to a first embodiment of the present invention; 
     FIG. 2 is a block diagram showing electrical connection among respective elements of the ink jet printer; 
     FIG. 3 is an explanatory view of ink flow path in the ink jet printer; 
     FIG. 4 is a flowchart schematically showing the flow of impurity discharge processing; 
     FIG. 5 is an explanatory view of the ink flow path in the ink jet printer according to a second embodiment of the present invention; and 
     FIG. 6 is an explanatory view of the ink flow path in the ink jet printer according to a third embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will now be described in detail in accordance with the accompanying drawings. 
     First Embodiment 
     A first embodiment of the present invention will be described with reference to FIGS. 1 to  4 . 
     An ink jet printer according to the present embodiment is applied to a line type color ink jet printer which performs line-directional printing by discharging ink from respective color ink jet nozzles on a rotating print medium, and performs column-directional printing by utilizing the rotation of drum during forward-movement by an ink jet nozzle pitch. 
     Note that FIG. 1 is an explanatory view of printing method of an ink jet printer  1 , and FIG. 2, a block diagram showing electrical connection among respective elements of the ink jet printer. As shown in FIG. 1, the ink jet printer  1  has respective color nozzle heads  2 C,  2 M,  2 Y and  2 K integrated as a nozzle unit  2  along the length of the unit in a main-scanning (X) direction (or integrated plural nozzle head elements arrayed in the line direction). The line-directional printing on a rotating print medium (e.g., a print sheet P) is performed by supplying respective color ink to the respective color ink jet nozzles while resiprocatively moving the nozzle unit by the ink jet nozzle pitch and discharging the ink from selected ink jet nozzles, and the column-directional printing is performed by utilizing the rotation of a rotary member  3  in a direction R on an axial line Z during forward-movement by the ink jet nozzle pitch. That is, in the ink jet printer  1  capable of simultaneously performing the low-directional printing and the column-directional printing, the print speed can be greatly improved. Note that in the present embodiment, the nozzle unit  2  has nozzle heads for 4 colors (cyan (C), yellow (Y), magenta (M) and black (K)), however, it may be arranged such that the nozzle unit  2  has only a nozzle head for 1 color (e.g., black (K)). 
     As shown in FIG. 2, the ink jet printer  1  formed with an image processor  4  and an engine  5  performs print processing on print data generated in the image processor  4  based on a print command generated in the image processor  4 . Note that it may be arranged such that the ink jet printer  1  constructs an ink jet print system where print processing is performed on print data, transmitted from an external computer  7  via a data communication line (e.g. LAN)  6 , based on a print command from the computer. 
     The image processor  4  includes a CPU (Central Processing Unit)  8  which controls the respective elements, a ROM (Read Only Memory)  9  for storing control programs and the like, a RAM (Random Access Memory)  10  for rewritably storing variable data, an operation panel  11 , a display unit  12 , an interface (I/F)  13 , a timer T for time measurement, and the like. The image processor  4  performs processing to convert print data into bitmap data and outputs the data to an engine  5 , and the like, and drive controls the ink jet printer  1  by an appropriate amount at appropriate timing. 
     Note that in FIG. 1, head drivers  2 DC,  2 DM,  2 DY and  2 DK of the nozzle unit  2  ( 2 C,  2 M,  2 Y and  2 K), a driver  14 D for a rotation mechanism  14  to drive the rotary member  3 , another mechanism  15  to be described later, and the like, are arranged in the image processor  4  for the sake of convenience. 
     The engine  5  has the rotary member  3  which holds a print medium (print sheet P) fed from print medium feeding means (not shown) on its peripheral surface, the rotation mechanism  14  which rotates the rotary member  3  at a predetermined rotational speed (e.g. 120 rpm), the print medium feeding means and print medium discharge means (not shown), and another mechanism  15  including a maintenance mechanism (not shown) and the like, as well as the above-described nozzle unit  2 . The engine  5  is capable of performing color printing and monochrome printing. Note that another mechanism  15  also includes a drive mechanism (not shown) which drives a tube pump  20  of ink supply means  16  for supplying the respective color ink to the nozzle unit  2 , a suction pump  29  of waste ink collection means  23  and a tube pump  28  (all shown in FIG. 3) to be described in detail later. 
     More specifically, the print medium (print sheet P), transmitted from the print medium supply means in a main body case, is supplied to the rotary member  3  side rotating in the direction R at predetermined timing, and held around the peripheral surface of the rotary member  3  by utilizing e.g. electrostatic attraction. Note that in a feeding path from the print medium feeding means to the rotary member  3 , up to  2  print sheets can be held in waiting before delivery of print sheet to the rotary member  3 . Further, the rotary member  3  holds one print medium (print sheet P). 
     Next, the nozzle unit  2 , the ink supply means  16 , the waste ink collection means  23  and its peripheral portion will be described in detail with reference to FIG. 3 showing an ink flow path in the ink jet printer  1 . As shown in FIG. 3, the ink supply means  16  that supplies respective color ink to the respective nozzle heads  2 C,  2 M,  2 Y and  2 K forming the nozzle unit  2  (FIG. 3 shows only the nozzle head  2 Y) is constructed with ink tanks  17  (FIG. 3 shows only a yellow ink tank), a removably-provided ink cartridge  18  for ink replenishing, a connection tube  19  to replenish ink in the ink cartridge  18  to the ink tanks  17  when necessary, the tube pump  20  having a valve function for selecting an open state or a closed state of the connection tube  19 , a supply tube  21  as a first connection member to supply ink in the ink tank  17  to ink chambers (not shown) of the nozzle heads  2 C,  2 M,  2 Y and  2 K forming the nozzle unit  2 , and the like. Note that the capacity of the ink cartridge  18  is larger (e.g. 200 cm 3  or greater) than that of the conventional small ink cassette (10 to 20 cm 3 ). Further, the supply tube  21  is connected to an ink supply port  22  provided in a side surface of the ink tank  17  in a position higher than a bottom surface  17   a  of the ink tank  17  by a predetermined distance. Further, the respective color ink tanks  17  (specifically ink liquid surfaces) are set in positions lower than ink discharge orifices of the respective color nozzle heads  2 C,  2 M,  2 Y and  2 K of the nozzle unit  2 . In this arrangement, a constant negative pressure is applied to ink in the ink chambers (not shown) of the respective color nozzle heads  2 C,  2 M,  2 Y and  2 K of the nozzle unit  2 , thereby ink leakage can be prevented by the tare. 
     Further, the respective distances in heights between the respective color ink tanks  17  (specifically ink liquid surfaces) and the respective color nozzle heads  2 C,  2 M,  2 Y and  2 K of the nozzle unit  2  are fine adjusted in accordance with respective ink characteristics for performing printing in higher quality in a stable manner by uniforming ink jet characteristics (meniscus). 
     Note that the ink liquid surface in the ink tank  17  is always adjusted in a constant state by liquid surface stabilizing means (not shown). 
     Note that the ink jet printer  1  is further provided with the maintenance mechanism (not shown) for maintaining excellent ink discharge characteristics in the respective color nozzle heads  2 C,  2 M,  2 Y and  2 K of the nozzle unit  2 . The maintenance mechanism is connected to the waste ink collection means  23 . The waste ink collection means  23  has a cap  24  to cover the respective color nozzle heads  2 C,  2 M,  2 Y and  2 K of the nozzle unit  2  upon maintenance, a suction tube  25 , the suction pump  29  and a waste ink tank  26 . The waste ink collection means  23  collects the ink in the respective color nozzle heads  2 C,  2 M,  2 Y and  2 K of the nozzle unit  2  by driving the suction pump  29  to suck the ink while the nozzle unit  2  is covered with the cap  24 , and collects the sucked ink (waste ink) into the waste ink tank  26  communicating with the cap  24  via the suction tube  25 . Note that the waste ink tank  26  is removably provided in a predetermined position. 
     In addition, a discharge port  17   b  is provided in the bottom surface  17   a  of the ink tank  17  of the ink jet printer  1  for discharging impurities deposited inside the ink tank  17  to the above-described waste ink tank  26 . The discharge port  17   b  communicates with the waste ink tank  26  via a connection tube  27  as second connection member and connection means. 
     Further, the connection tube  27  is provided with the tube pump  28  having a valve function of selecting an open state or a closed state of the connection tube  27 . 
     In the present embodiment, the tube pumps  20  and  28  provided in two positions have structures where projections  20   b  and  28   b  are provided in  3  positions around cylindrical base portions  20   a  and  28   b , and the base portions  20   a  and  28   b  are rotate-driven. In the tube pumps  20  and  28 , the projections  20   b  and  28   b  press the connection tubes  19  and  17  by the rotation of the base portions  20   a  and  28   b , thereby the connection tubes  19  and  17  are changed from the open state to the closed state. 
     In the arrangement, the ink in the ink cartridge  18  is replenished to the ink tanks  17  by the tube pump  20 . When ink is discharged by control of the CPU  8  from the respective color nozzle heads  2 C,  2 M,  2 Y and  2 K of the nozzle unit  2  on a print medium (print sheet P), the ink in the ink tanks  17  is automatically supplied to the ink chambers of nozzle head that discharged ink via a supply tube  21  from the ink tank  17  by a capillary phenomenon by the decrement due to the ink discharge. 
     On the other hand, impurities mixed with the ink supplied from the ink cartridge  18  to the ink tank  17  are deposited on the bottom surface  17   a  of the ink tank  17 . 
     Next, as a function executed by the CPU  8  based on the control program stored in the ROM  9 , characteristic of the ink jet printer  1  of the present embodiment, impurity discharge processing to eliminate impurities deposited on the bottom surface  17   a  of the ink tank  17  will be described. 
     FIG. 4 is a flowchart schematically showing the flow of the impurity discharge processing. As shown in FIG. 4, in the impurity discharge processing, first, reception of “tube pump ‘open’ signal” to rotate the tube pump  28  to set the connection tube  27  to the open state is waited (step S 1 ). The “tube pump ‘open’ signal” is generated when a maintenance operation is performed in the nozzle unit  2 , when a predetermined number of print sheets have been print-outputted, when the impurity discharge processing is declared by operation at the operation panel  11 , or the like. 
     When the “tube pump ‘open’ signal” has been received (Y at step S 1 ), the tube pump  28  is rotated to set the connection tube  27  to the open state (step S 2 ). When the connection tube  27  is in the open state, the impurities deposited on the bottom surface  17   a  of the ink tank  17  flow with ink from the discharge port  17   b  provided in the bottom surface  17   a  of the ink tank  17  via the connection tube  27  into the waste ink tank  26 . Note that the open state of the connection tube  27  is maintained until it is determined by time measurement of the timer T that a predetermined period has elapsed (Y at step S 3 ). 
     Then, if the predetermined period has elapsed (Y at step S 3 ), the tube pump  28  is rotated to set the connection tube  27  to the closed state (step S 4 ), to stop the discharge of the impurities from the discharge port  17   b.    
     That is, in the impurity discharge processing at steps S 1  to S 4 , the function of the opening/closing selection means is performed. 
     If the impurities are deposited on the bottom surface  17   a  of the ink tank  17 , as the tube pump  28  is rotated to set the connection tube  27  to the open state, the impurities can be discharged with the ink from the discharge port  17   b  of the ink tank  17  to the waste ink tank  26 . As the impurities are not supplied to the respective color nozzle heads  2 C,  2 M,  2 Y and  2 K of the nozzle unit  2 , clogging in the respective color nozzle heads  2 C,  2 M,  2 Y and  2 K of the nozzle unit  2  due to impurities can be reliably prevented. Further, as the impurities discharged from the discharge port  17   b  of the ink tank  17  are collected in the waste ink tank  26  to collect ink (waste ink) sucked from the respective color nozzle heads  2 C,  2 M,  2 Y and  2 K of the nozzle unit  2  upon maintenance of the nozzle unit  2 , it is unnecessary to provide another tank to collect impurities. Thus the size of the printer itself is not increased, and the manufacturing costs can be saved. 
     Further, the maintenance to maintain excellent ink discharge characteristics of the respective color nozzle heads  2 C,  2 M,  2 Y and  2 K of the nozzle unit  2  is executed whenever the nozzle unit  2  comes to a home position, for example. Accordingly, if the tube pump  28  is rotated to set the connection tube  27  to the open state at timing of the maintenance operation, depositing of large amount of impurities on the bottom surface  17   a  of the ink tank  17  with elapse of time can be prevented. 
     Further, in the present embodiment, as frequent ink cassette change operation as in the case of conventional small ink cassette can be omitted by replenishing ink from the ink cartridge  18  to the ink tank  17 , a long-period continuous print operation can be performed. 
     Next, the ink jet printer according to a second embodiment of the present invention will be described with reference to FIG.  5 . Note that elements corresponding to those in the above-described first embodiment have the same reference numerals and the explanations of the elements will be omitted. The difference between the present embodiment and the first embodiment is that the ink tank  17  in the first embodiment is replaced with an ink tank  30 . 
     As shown in FIG. 5, the ink tank  30  has a discharge port  31  in a bottom surface  30   a  to discharge impurities deposited inside the ink tank  17  to the waste ink tank  26 . The discharge port  31  is communicated with the waste ink tank  26  via the connection tube  27 . 
     Further, an ink supply port  32  connected to the supply tube  21  is formed in a side surface of the ink tank  30  in a position near the bottom surface  30   a  of the ink tank  30 . Further, a cylindrical filter  33  having a length approximately the same as that of the ink tank  30  is provided in the ink tank  30 . The filter  33  eliminates impurities mixed with supplied ink passing through the filter. Note that the discharge port  31  is positioned inside the filter  33 . 
     That is, as the ink tank  30  of the present embodiment has the filter  33  to prevent supply of impurities to the nozzle unit  2  side, the impurity depositing area as described in the first embodiment is unnecessary and the ink supply port  32  is formed in the side surface of the ink tank  30  in a position near the bottom surface  30   a  of the ink tank  30 . 
     In this construction, the ink in the ink cartridge  18  is replenished by the tube pump  20  through the filter  33  to the ink tank  30 . When the ink is discharged by control of the CPU  8  from the respective color nozzle heads  2 C,  2 M,  2 Y and  2 K of the nozzle unit  2  to a print medium (print sheet P), the ink in the ink tank  30  is automatically supplied to the ink chambers of nozzle head that discharged ink via a supply tube  21  from the ink tank  30  by a capillary phenomenon, by the decrement due to the ink discharge. 
     On the other hand, the impurities mixed with the ink supplied from the ink cartridge  18  to the ink tank  30  are caught inside the filter  33  and deposited on the bottom surface  30   a  of the ink tank  30  positioned inside the filter  33 . 
     Then, the impurities deposited on the bottom surface  30   a  of the ink tank  30  positioned inside the filter  33  are discharged to the waste ink tank  26  by the impurity discharge processing as described in the first embodiment. 
     Next, the ink jet printer according to a third embodiment of the present invention will be described with reference to FIG.  6 . Note that elements corresponding to those in the above-described first or second embodiment have the same reference numerals and the explanations of the elements will be omitted. The difference between the present embodiment and the first and second embodiments is that the ink tank  17  in the first embodiment is replaced with an ink tank  40  as a modification to the ink tank  30  used in the second embodiment. 
     As shown in FIG. 6, the ink tank  40  of the present embodiment has a shape different from that of the ink tank  30  of the second embodiment. A discharge port  41  provided in a bottom surface  40   a  of the ink tank  40  has approximately the same shape of a cross section of the filter  33 , and connected to the connection tube  27  via a conical-shaped impurity depositing portion  42 . 
     That is, in the ink tank  40 , impurities mixed with ink supplied from the ink cartridge  18  are caught inside the filter  33  and deposited in the impurity depositing portion  42 . 
     Then, the impurities deposited in the impurity depositing portion  42  are discharged to the waste ink tank  26  by the impurity discharge processing as described in the first embodiment. 
     Note that in the second and third embodiments, the filter  33  is provided, and the ink supply port  32  is formed in the side surface of the ink tanks  30  and  40  in positions near the bottom surfaces  30   a  and  40   a  of the ink tanks  30  and  40 , however, the ink supply port  32  may be provided in a position above the bottom surfaces  30   a  and  40   a  of the ink tanks  30  and  40  by a predetermined distance as in the case of the first embodiment. In this case, even if impurities cannot be eliminated by the filter  33 , as the impurities are deposited in a position lower than the ink supply port  32 , supply of the impurities to the respective color nozzle heads  2 C,  2 M,  2 Y and  2 K of the nozzle unit  2  can be prevented. 
     Further, in the respective embodiments, the ink jet printer of the present invention is applied to an ink jet printer which performs low-directional printing by discharging ink from respective color ink jet nozzles on a rotating print medium and performs column-directional printing by utilizing the rotation of drum upon forward movement by ink jet nozzle pitch. However, the ink jet printer is not limited to this printer, but the present invention is applicable to a so-called serial type ink jet printer. 
     Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specially described herein.