Patent Publication Number: US-6213601-B1

Title: Ink-jet printer and method of controlling the same

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an ink-jet printer which prints an image onto a print medium held on a rotary drum with ink jetted from a print head, and particularly, to an ink-jet printer in which ink is supplied from an ink tank apart from the print head. 
     Hitherto, serial-type ink-jet printers are widely spreading. In the serial-type ink-jet printer, a print head and an ink tank of a relatively small capacity are mounted on a carriage, and the carriage is movably attached to a guide bar extending across a paper sheet to be printed. The paper sheet is fed in a direction perpendicular to the guide bar at a constant pitch, and the carriage is moved along the guide bar each time paper sheet is fed by the pitch. During the movement of the carriage, the print head jets ink droplets. In a serial-type color ink-jet printer, a plurality of print heads are employed and are supplied with ink of different colors from the respective ink tanks. The plurality of print heads are beforehand filled with ink when the printer is shipped. In the structure as described above, a color image of A4 size is printed out at a relatively low speed. 
     Thereto in recent years, a drum rotation type ink-jet printer capable of printing a color image at a high speed has been known. This ink-jet printer includes a rotary drum rotating in one direction and a print head disposed to face a paper sheet held on the rotary drum. The print head has a plurality of line-type nozzle units which are arranged along the peripheral surface of the rotary drum, corresponding to cyan(C), yellow(Y), magenta(M) and black(B). Each nozzle unit has a plurality of ink-jet nozzles disposed across the paper sheet in the axial direction of the rotary drum. This ink-jet printer jets ink droplets from nozzle units in response to image signals to print a color image on the paper sheet rotating together with the rotary drum. In this structure, a color image of A4 size can be printed extremely faster than the above-described serial-type printers. 
     In this drum-rotation type ink-jet printer, a plurality of ink tanks are placed apart from the print head and store ink of different colors to be supplied to the nozzle units of the print head. Each ink tank is connected to a corresponding nozzle unit via a supply tube, and is filled with ink supplied from an ink supplement bottle detachably attached thereto. The ink is conveyed from the ink tank to an ink pressure chamber of the nozzle unit by a supply pump having a valve function and interposed in the supply tube. At the time of printing, the supply pump is stopped in a valve-open state, and the nozzle unit is driven to jet ink. Upon consumption of ink for jet, ink is supplemented to the ink pressure chamber through the supply tube by a capillary action. 
     In the above-described drum rotation type ink-jet printer, the nozzle unit is empty when the printer is shipped and is filled with ink at a user side when the printer is used. A foreign matter such as a lump of dried ink may exist in the nozzle unit at the beginning of ink-supply. Thus, ink-jet nozzles of the nozzle unit is apt to be clogged by the foreign matter and the quality of printing carried out by such a nozzle unit is deteriorated. 
     BRIEF SUMMARY OF THE INVENTION 
     An object of the present invention is to carry out a high quality printing on a print medium by ink jet printer. 
     Still another object of the present invention is to prevent a lump of dried ink from entering into a plurality of ink-jet nozzles of an ink-jet printer. 
     Another object of the present invention is to provide an ink-jet printer which can has a unique ink supply system. 
     According to the present invention, there is provided an ink-jet printer which comprises: a print head for jetting ink, the print head having an upstream side and a downstream side; an ink tank for storing the ink; a tube member connected between the ink tank and the print head; a pump mechanism including a plurality of pumps located at the upstream side and the downstream side of the print head, respectively, the pump mechanism being in fluid. communication with the print head and the ink tank through the tube member; and a controller for controlling the pump mechanism in a filling mode in which the print head is filled with ink flowing from the ink tank. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a view showing the internal structure of an ink-jet printer according to an embodiment of the present invention; 
     FIG. 2 is a perspective view showing a positional relationship between the rotary drum and the print head shown in FIG. 1; 
     FIG. 3 is a schematic view showing an ink supply system of the ink-jet printer shown in FIG. 1; 
     FIG. 4 is a view showing one example of an ink supply pump of the ink supply system shown in FIG. 3; 
     FIG. 5 is a block diagram illustrating a detailed control unit shown in FIG. 1; and 
     FIG. 6 is a flow chart showing an ink filling mode controlled by the control unit shown in FIG.  5 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An ink-jet printer according to an embodiment of the present invention is described with reference to FIGS. 1 to  6 . 
     FIG. 1 shows the internal structure of the ink-jet printer. The ink-jet printer is used to perform a multicolor printing on a paper sheet P cut as a printing medium. The paper sheet P may be a plain paper, a coated paper or an OHP sheet. 
     The ink-jet printer comprises a rotary drum  10 , a print head  20 U, a manual-feed tray T 1 , a paper cassette T 2 , a sheet feed-in mechanism FM 1 , a sheet feed-out mechanism FM 2 , an ink supply system SP and a control unit CNT. The rotary drum  10  rotates at a predetermined circumferential speed, with a paper sheet P held thereon. The print head  20 U performs a multicolor printing on the paper sheet P. The manual-feed tray T 1  places thereon paper sheets P for feeding one by one. The paper cassette T 2  stores therein a stack of paper sheets P. The sheet feed-in mechanism FM 1  feeds each paper sheet P from the paper cassette T 2  or the manual-feed tray T 1  onto the rotary drum  10 . The sheet feed-out mechanism FM 2  feeds out the paper sheet P printed at the rotary drum  10 . The ink supply system SP performs an ink supply. The control unit CNT controls the overall operation made by the components or circuits of the ink jet printer. The control unit is construed as a controller. 
     As shown in FIG. 1, the rotary drum  10  is located near the central position within a housing  1 . The manual-feed tray T 1  is located below the rotary drum  10  and extends externally from a side wall face of the housing  1 , and the paper cassette T 2  is located under the rotary drum  10 . The sheet feed-in mechanism FM 1  is placed upstream of the rotary drum  10 . The print head  20 U is located above the rotary drum  10 . The sheet feed-out mechanism FM 2  is located downstream of the rotary drum  10 . 
     The rotary drum  10  is supported about the axis X, and causes the paper sheet P to be wound around a peripheral surface  11  thereof in accordance with its rotation indicated by an arrow R in FIG.  2 . The rotational position of the rotary drum  10  is detected by a rotational position detector DT disposed near the peripheral surface  11  of the rotary drum  10 . The print head  20 U includes four nozzle units  20  (C, Y, M, and B) which are arranged in order along the peripheral surface  11  of the rotary drum  10  from the upstream side to the downstream side so as to perform a printing on the paper sheet P with inks of cyan(C), yellow(Y), magenta(M), and black(B). The nozzle units  20  (C, Y, M, and B) receive ink of corresponding colors from the ink supply system SP. Each of the nozzle units  20  (C, Y, M, and B) has a plurality of ink-jet nozzles  23  which are arranged in the axial direction X of the rotary drum  10  to have a span corresponding to the width of the paper sheet P of A 4  size and jet the corresponding color ink to the paper sheet P. The plurality of ink-jet nozzles  23  are provided with heaters acting as an energy generator and thus, ink is jetted from nozzles  23  when heaters are selectively energized in a print mode. Piezo-electric element may be used, instead of the heater, to jet ink. 
     The nozzle units  20  (C, Y, M, and B) are constructed in structures identical to each other. The nozzle segments  20 A and  20 C are mounted on a first surface of the connection plate, and the nozzle segments  20 B and  20 D are mounted on a second surface of the connection plate opposed to the first surface, for example. As shown in FIG.3, each of the nozzle segments  20 A to  20 D is constituted by ink-jet nozzles  23  and an ink pressure chamber  22  for directly applying ink to the ink-jet nozzles  23 . The ink pressure chambers  22  of the nozzle segments  20 A to  20 D are connected in series such that ink flows there-through as shown in FIG.  3 . Each of the ink pressure chambers  22  has a capacity of 0.55 ml. The pitch of the ink-jet nozzles  23  is set up to {fraction (1/150)} inch, for example, in the case where the printing resolution is 300 dpi in the main scanning direction X. 
     The sheet feed-in mechanism FM 1  has a sheet loader LD for loading the paper sheet P to the rotary drum  10  such that the width direction of the paper sheet P corresponds with the axial direction X of the rotary drum  10 . The paper sheet P is taken out of either the manual feed tray T 1  or the paper cassette T 2  by the sheet feed-in mechanism FM 1 . The paper loader LD is controlled to load the paper sheet P toward the rotary drum  10  when the position detector DT detects the rotary drum  10  at a predetermined rotating position. The paper sheet P is then wound around the peripheral surfacell of the rotary drum  10  when the rotary drum  10  has made one rotation. The print head  20 U prints a color image on the paper sheet P as the rotary drum  10  rotates. 
     The paper loader LD includes at least a pair of loading rollers Rl and R 2  extending in the axial direction X of the rotary drum  10  to load the paper sheet P fed from the manual-feed tray T 1  or paper cassette T 2  to the rotary drum  10  at a predetermined timing. The feeding speed of the paper of the paper sheet P is set at a speed corresponding to the circumferential speed of the rotary drum  10 . The peripheral surface  11  of the rotary drum  10  is about 220 mm wide in the axial direction X and 408 mm long in the rotational direction R. Therefore, the rotary drum  10  can fully hold the A4 size paper sheet P having a width of 210 mm and a length of 297 mm. 
     After the print is completed, the paper sheet P is removed from the peripheral surface  11  of the rotary drum  10  by a sheet separator PL and fed in a predetermined direction by the sheet feed-out mechanism FM 2 . Driving of the sheet feed-in mechanism FM 1  and the sheet feed-out mechanism FM 2  are performed by a sheet feed motor FM. The paper separator PL includes a separation claw to be contacted with the peripheral surface  11  of the rotary drum  10  at the time of sheet removal. A discharge switch SEL guides the paper sheet P to either a rear discharge tray RT or an upper discharge tray UT. The rear discharge tray RT receives the paper sheet P with the print surface facing upward, and the upper discharge tray UT receives the paper sheet P with the print surface facing downward. 
     The print head  20 U is capable of being reciprocally shifted by {fraction (1/75)} inch in the main scanning direction parallel to the axial direction X of the rotary drum  10 . The rotary drum  10  holds the paper sheet P, and rotates in a sub-scanning direction perpendicular to the main scanning direction X. The rotary drum  10  is maintained at a constant rotation rate of 120 rpm and makes one rotation every 0.5 second, for example. In the printing operation, the print head  20 U is shifted in the main scanning direction X at a constant rate of ½ nozzle pitch each time the rotary drum  10  makes one rotation, so that it move for a distance equal to a nozzle pitch PT while the rotary drum  10  makes two rotations. 
     As shown in FIG. 1, the ink-jet printer further includes an elevation mechanism  90  for automatically adjusting the height of the print head  20 U, an ink collection tray  30  for collecting ink flowed out of the print head  20 U during a non-printing time, and a reciprocating rotation mechanism  46  for rotating reciprocally the ink collection tray  30  along the peripheral surface  11  of the rotary drum  10  such that the ink collection tray  30  can face the print head  20 U. At the time of printing, the elevation mechanism  90  moves the print head  20 U to a lower limit position (print position) near the peripheral surface  11  of the rotary drum  10 . After the print is completed. the elevation mechanism  90  moves the print head  20 U to an upper limit position spaced from the rotary drum  10 , and then to a non-print position wherein print head  20 U is located between the upper and lower limit positions. The elevation mechanism  90  sets the print head  20 U in a state where the print head  20 U is disposed at the upper limit position at the non-printing time, so that the ink collection tray  30  is inserted between the print head  20 U and the rotary drum  10 . The print head  20 U is further moved to the non-print position after insertion of the ink collection tray  30 . In this state, a top end  24  of the ink-jet nozzle  23  of the nozzle unit  20  (C, Y, M, and B) is disposed close to the ink collection tray  30  without making contact with the tray  30 , so that the ink collection try  30  can be used in common to collect inks flowed out of each the nozzle units  20  (C, Y, M, and B). Collected ink is drained as waste ink to a detachable waste ink cassette (not shown) from the ink collection tray  30 . 
     As shown in FIG. 3 the ink supply system SP includes ink supply sections  40  for nozzle units  20  (C, Y, M, and B), respectively. Since the ink supply sections  40  for the nozzle units  20  have the same construction with one another, only one of the ink supply sections  40  will be described. 
     The ink supply section  40  includes an ink tank TK which is located apart from the nozzle unit  20  and stores ink, an ink reserve bottle CT for supplying ink to the ink tank TK, an ink supply tube  41  for guiding ink from the ink tank TK to an upstream side of the nozzle unit  20 , and an ink return tube  47  for guiding ink from a downstream side of the nozzle unit  20  to the ink tank TK. The ink supply section  40  further includes a push type ink supply pump  42  interposed in the ink supply tube  41  and a pull type ink return pump  48  interposed in the ink return tube  47 . The ink supply pump  42  performs an ink supply operation in which ink is forcibly pushed from the ink tank TK to the nozzle unit  20  through the ink supply tube  41  at a rate of 0.7 ml/sec. The ink return pump  48  performs an ink suction operation in which an excessive ink is forcibly pulled from the nozzle unit  20  to the ink tank TK through the ink return tube  47  at a rate of 0.35 ml/sec. The ink suction operation is construed as an ink return operation. The ink supply tube  41  and the ink return tube  47  are made of a soft synthetic resin. 
     As shown in FIG. 4, the ink supply pump  42  is a conventional rotary type in which four press rollers  42 RL are located at a predetermined interval on a circular locus. The ink supply tube  41  is located between the press rollers  42 RL and the ink supply pump guide  42 G which is formed in a semi-circular shape. The press rollers  42 RL press the ink supply tube  41  against the ink supply pump guide  42 G to act as a valve. The ink supply tube  41  is repeatedly set at a selected one of open and closed state as the press rollers  42 RL are rotated by an ink supply pump motor  42 M. Thus ink in the ink supply tube  41  pressed by adjacent press rollers  42 RL is conveyed from an upstream side to a downstream side of the ink supply pump  42 . Since construction and operation of the ink return pump  48  is the same as those of ink supply pump  42  and therefore, the explanation of these are omitted. As described above, when both pump motors are driven, ink is supplied between the ink tank TK and the nozzle unit  20 , and is circulated. The ink supply tube  41  and the ink return tube  47  are construed as a tube member, the ink supply pump  42  and the ink return pump  48  are construed as a pump mechanism. 
     Further, as shown in FIG.3 a heating unit is located downstream of the ink supply pump  42  in the ink supply tube  41 . The heating unit includes a heater  51  for heating ink supplying to nozzle unit  20  and an ink temperature detector  55 . The ink temperature detector  55  detects temperature of ink heated by the heater  51 . 
     As show in FIG. 5, the control unit CNT includes a CPU (Central Processing Unit)  61  for performing a processing control, a ROM (Read Only Memory)  62  for storing a control program for the CPU  61 , a RAM (Random Access Memory)  63  for temporarily storing data items input into and output from the CPU  61 , a display unit  64  for displaying the status of the ink-jet printer, a keyboard unit  65  for entering various mode (print mode, filling mode ) settings, and an input and output port (or I/O port)  66  serving as an interface for external components of the control unit CNT. The CPU  61  is connected to the ROM  62 , the RAM  63 , the display unit  64 , the keyboard unit  65 , and the I/O port  66  through a system bus SB. The I/O port  66  is connected to the print head  20 U, the rotational position detector DT, the ink temperature detector  55 , the heater  51 , the ink supply pump motor  42 M, the ink return pump motor  48 M, the elevation mechanism  90 , the reciprocating rotation mechanism  46  and the sheet feed motor FM. 
     The keyboard unit  65  is capable of setting a filling mode in which the nozzle unit  20  is filled with ink in the ink tank TK at the non-printing time. The ROM  62  stores a control program for starting the ink return pump motor  48 M a preset time, for example, 30 seconds, after the ink supply pump motor  42 M starts. It was experimentally confirmed beforehand that it took 30 seconds to fill ink into all of the ink-jet nozzles  23 . The ROM  62  stores numbers of rotation per minute of the ink supply pump motor  42 M and the ink return pump motor  48 M. Further the ROM  62  stores the control program for controlling a voltage supplied to the heater  51  and optimum temperature volumes of color inks heated by the heater  51 . Stored optimum temperature volumes are different from one another in terms of different color inks. The control unit CNT controls the heater  51  at a most pertinent temperature the range of which is 45° C. to 55° C. and therefore, nozzle unit  20  can be smoothly filled with ink by the supply system SP. 
     A filling mode operation of ink-jet printer is described in more detail with reference to FIG.  6 . 
     When the filling mode is requested through the keyboard unit  65 , the control unit CNT controls the reciprocating rotation mechanism  46  to insert the ink collection tray  30  between the print head  20 U and the rotation drum  10  as in step  101 . The print head  20 U is moved to the non-print position after insertion of the ink collection tray  30  in step  102 . Under this state, control unit CNT performs a pump drive process described below. The control unit CNT controls the flow of ink from the print head  20 U. In each ink supply section  40 , the ink supply pump motor  42 M and the ink return pump motor  48 M are controlled as described below by the control unit CNT. The ink supply pump motor  42 M is driven to supply ink from the ink tank TK to the nozzle unit  20  and the heater  51  is energized to heat ink at a most pertinent temperature of each color of inks in step  103 . All of the presser chamber  22  is filled with ink from the tank TK by the supply pump  42  and ink reaches each ink-jet nozzles  23 . 30 seconds after the ink supply pump motor  42 M is driven, as described before. Then, the ink return pump motor  48 M is driven. In other words, the ink return pump motor  48 M and the ink supply pump motor  42 M are not driven, simultaneously. At this time, the volume of ink supplied by the ink supply pump  42  is greater than that returned by the ink return pump  48  to increase the pressure of the ink pressure chamber  22  in step  104 . Thus ink in the nozzle unit  20  flows out of nozzle unit  20  through the ink-jet nozzles  23  by the difference in the ink volume between ink supply pump  42  and the ink return pump  48 . Therefore, a lump of dried ink and gas or air in the ink-jet nozzles  23  are discharged therefrom together with flowing ink and, in addition, gas or air outside the ink-jet nozzles  23  can be prevented from entering into the ink-jet nozzles  23 . After an elapse of a predetermined time, the ink supply pump motor  42 M and the ink return pump motor  48 M are stopped in step  105 . Namely, the ink supply tube  41 , the nozzle unit  20  and the ink return tube  47  are filled with ink. Ink flowing out of nozzle unit  20  is collected by the ink collection tray  30 , and is drained to the waste ink cassette as a waste ink. 
     In the ink-jet printer according to the present embodiment, the control unit CNT performs the pump drive process in the filling mode, so that a foreign matter in the ink-jet nozzles  23  of the print head  20 U can be discharged by the ink flowing out of the ink-jet nozzles  23 . Further the difference in ink flow rate between the ink supply pump  42  and the ink return pump  48  prevent gas or air outside the ink-jet nozzles  23  from entering into the ink-jet nozzles  23  in the pump drive process. 
     Furthermore, in the ink filling mode, the ink supply pump motor  42 M is driven prior to the operation of ink return pump motor  48 M, and the ink return pump motor  48 M is driven after ink in the ink-jet nozzles  23  has flowed. Thus, it can prevent a foreign matter which may float around the end surface  24  of the ink-jet nozzles  23  from entering into the ink-jet nozzles  23 . 
     Therefore, an ink-jet printer of the present embodiment can print images on a paper sheet with high quality and smoothness. 
     Moreover the ink-jet printer can fill the ink nozzle unit  20  with ink smoothly by heating ink flowing through the ink supply tube  41 . 
     The present invention has been described with respect to a specific embodiment. However, other embodiments based on the principles of the present invention should be obvious to those of ordinary skill in the art. Such embodiments are intended to be covered by the claims.