JP2009220505A - Liquid jet apparatus, method for removing bubbles therein, and inkjet printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid jet apparatus for spraying liquid, in which bubbles causing poor injection of a nozzle can be effectively removed. <P>SOLUTION: The liquid jet apparatus includes a pressure chamber 13 for filling ink, a pressurizing means for pressurizing the ink in the pressure chamber 13, a piezoelectric element 17 for changing the volume in the pressure chamber 13, a nozzle 15 for discharging the ink, and a control unit 50 for generating drive pulses for controlling the piezoelectric element 17. The control unit 50 controls the pressurizing means to pressurize the ink in the pressure chamber 13 and generate maintenance drive pulses for discharging unnecessary air bubbles with the ink from the pressure chamber 13. The maintenance drive pulses comprise a first pulse portion for controlling the piezoelectric element 17 to expand the pressure chamber 13 to shift it to an expanding state, a second pulse portion for holding the expanding state for a predetermined time, and a third pulse portion for shrinking the pressure chamber 13 from the expanding state. The pulse width of the first pulse portion is set to a value based on the Helmholtz resonance period of the ink in the pressure chamber 13. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a liquid ejecting apparatus, a method for removing bubbles, and an ink jet printer, and is particularly useful when discharging bubbles in a pressure chamber.

  The ink jet printer performs printing by ejecting (jetting) ink droplets from a nozzle toward a paper surface. In such an ink jet printer, the ink droplets are absorbed by the bubbles due to the increase in viscosity of the ink at the nozzle opening due to natural evaporation or the change in pressure in the ink chamber due to the mixing of bubbles in the ink chamber filled with ink. In some cases, ejection failure may occur.

  Until now, various maintenance-related techniques have been proposed in order to perform ink droplet ejection successfully and continuously (see, for example, Patent Document 1). For example, in Patent Document 1, the nozzle is temporarily sealed with a cap and negative pressure is generated by a pump, and pressure is applied to the ink chamber by a pressure generating element to eject ink droplets, thereby increasing the viscosity of the ink. And a technique for performing bubble removal.

  However, even when the above maintenance process is performed, a force that works to discharge bubbles, such as pressure, can be sufficiently applied to bubbles having a small diameter (for example, bubbles having a diameter of several tens of micrometers). Therefore, it is difficult to completely remove the bubbles. Such a problem is not limited to an ink jet printer, and may occur in a liquid ejecting apparatus that ejects fluid other than ink (including liquid and liquid material in which particles of functional material are dispersed). Until now, it has been the actual situation that such a problem has not been sufficiently devised.

JP 2007-136989 A JP 59-131464 A

  An object of the present invention is to provide a liquid ejecting apparatus, a method for removing the air bubble, and an ink jet printer that can effectively remove bubbles that cause nozzle ejection failure in a liquid ejecting apparatus that ejects liquid.

An aspect of the present invention that achieves the above object is a liquid ejecting apparatus for ejecting a liquid, a pressure chamber filled with the liquid, and a pressurizing unit that pressurizes the liquid in the pressure chamber from its supply side. A pressure generating element that is provided on a wall surface of the pressure chamber and that changes the volume of the pressure chamber by deforming the wall surface, a nozzle that is in communication with the pressure chamber and ejects the liquid, and the pressure The liquid ejecting apparatus includes a control unit that controls a driving pulse for the generating element and the pressurizing unit.
According to this aspect, since the liquid in the pressure chamber is pressurized from the supply side during the flushing, the flow of the liquid is generated in the pressure chamber. As a result, the bubbles grown in the pressure chamber ride on the flow from the nozzle. Easily discharged outside. As a result, the bubbles in the pressure chamber can be reliably discharged to the outside, and liquid discharge defects can be prevented satisfactorily.

  Here, the control unit controls the pressurizing unit to pressurize the liquid in the pressure chamber, and at the same time, generates a maintenance drive pulse for discharging unnecessary bubbles together with the liquid from the pressure chamber. The maintenance driving pulse causes the pressure generating element to be driven to move the pressure chamber to the expanded state and hold the expanded state for a predetermined time. A second pulse portion and a third pulse portion for contracting the pressure chamber from the expanded state, wherein the pulse width of the first pulse portion is the Helmholtz resonance period of the liquid filled in the pressure chamber It is desirable that the value is set based on. As a result, the pressure applied to the liquid in the pressure chamber by the pressure generating element at the time of flushing can be further increased by utilizing Helmholtz resonance. As a result, the force generated by the pressure wave acting on the bubbles mixed in the pressure chamber Can be further increased, and the bubble diameter can be further increased, so that the bubbles can be easily discharged.

  Further, the pressurizing means has a pressure regulating valve disposed in the middle of a flow path that communicates the reservoir portion of the pressurized liquid and the pressure chamber, and the control unit controls the opening of the pressure regulating valve. It can comprise so that the pressurization force of a pressurized liquid may act on the liquid of the said pressure chamber. In this case, the pressure gradient of the liquid toward the pressure chamber can be easily formed by controlling the pressure regulating valve, and the above-described effects can be easily obtained.

  Furthermore, the control unit may be configured to supply the maintenance drive pulse to the pressure generating element in a state where the liquid is pressurized via the pressurizing unit. In this case, since the liquid in the pressure chamber is pressurized before the vibration of the pressure generating element, a liquid flow is already formed during the vibration. As a result, bubbles can be quickly discharged from the nozzle.

  The controller may be configured such that the pressurizing unit pressurizes the liquid in a state where the maintenance drive pulse is supplied to the pressure generating element. In this case, since the bubble is grown by the vibration of the pressure generating element and the liquid in the pressure chamber is pressurized to form a liquid flow, the liquid consumption due to the idle ejection can be reduced.

  Further, the apparatus further includes a liquid discharge detection unit that detects a missing dot including a discharge failure, and the control unit selects the nozzle row in which the missing dot is detected by the discharge detection unit, and sends the maintenance driving pulse to the pressure generating element. And the pressurizing means may be controlled to pressurize the liquid in the pressure chamber. In this case, the predetermined flushing operation can be performed only for the nozzles causing the ejection failure, so that the liquid consumption due to the idle ejection associated with the flushing can be reduced as much as possible.

  It is desirable that the control unit repeatedly generates at least some of the maintenance drive pulses having different waveforms from each other in a predetermined order. In this case, a pulse group composed of maintenance drive pulses having different waveforms can be repeatedly generated at a constant period. Therefore, various variations of pulse groups effective for removing bubbles can be generated.

  Further, the maintenance drive pulses that are different from each other may have different pulse widths in the second pulse portion. In this case, the removal of bubbles having different natural diameters corresponding to the pulse width of the second pulse portion can be repeatedly performed in a predetermined order. Therefore, it is possible to execute the removal of bubbles corresponding to bubbles having various diameters.

  Further, the control unit generates a plurality of drive pulse groups in which the maintenance drive pulses are repeated at a constant cycle, and each set of drive pulse groups has the same waveform of the maintenance drive pulse, The set of drive pulse groups may include two or more sets of drive pulse groups in which the waveforms of the maintenance drive pulses are different from each other. In this case, it is possible to sequentially execute the removal of the types of bubbles corresponding to the waveforms of the maintenance drive pulses of two or more different drive pulse groups. Accordingly, it is possible to remove various bubbles and to effectively discharge the bubbles.

  Further, the two or more sets of driving pulse groups can be configured such that the pulse widths of the second pulse portions are different from each other. In this case, the removal of bubbles having different natural diameters corresponding to the pulse width of the second pulse portion can be sequentially executed by two or more sets of drive pulses. Therefore, it is possible to execute the idle discharge of the liquid corresponding to each of the bubbles having various diameters.

Another aspect of the present invention is an ink jet printer that includes the liquid ejecting apparatus as described above.
According to this aspect, it is possible to perform printing while ensuring high print quality by reducing dot dropout as much as possible by complete bubble removal flushing.

Still another aspect of the present invention includes a pressure chamber filled with a liquid, a pressure generating element that is provided on a wall surface of the pressure chamber and changes a volume of the pressure chamber by deforming the wall surface, and the pressure chamber. A bubble removal method for a liquid ejecting apparatus, comprising: a nozzle for communicating and ejecting the liquid through the nozzle, wherein the liquid in the pressure chamber is pressurized while the pressure In the bubble removing method of the liquid ejecting apparatus, the driving pulse for discharging the liquid from the chamber is supplied to the pressure generating element.
According to this aspect, since pressure is applied to the liquid in the pressure chamber during the flushing, the bubbles can be reliably discharged outside the nozzle along the flow of the liquid formed by the pressure. As a result, poor liquid discharge can be prevented satisfactorily.

  Here, while pressurizing the liquid in the pressure chamber, a maintenance driving pulse for discharging unnecessary bubbles together with the liquid from the pressure chamber is supplied to the pressure generating element to perform bubble removal flushing, and The maintenance driving pulse at the time of bubble removal flushing drives the pressure generating element to inflate the pressure chamber so as to shift to an expanded state, and the expansion state is set to a predetermined value. A second pulse portion for holding for a period of time and a third pulse portion for contracting the pressure chamber from the expanded state, wherein the pulse width of the first pulse portion is that of the liquid filled in the pressure chamber. It is desirable that the value is set based on the Helmholtz resonance period. In this case, bubbles can be grown by flushing simultaneously with pressurization of the liquid in the pressure chamber, and the grown bubbles can be reliably discharged out of the nozzle on the flow of liquid formed by the pressurization. Because it can.

  Further, the maintenance driving pulse can be supplied to the pressure generating element in a state where the liquid is pressurized, and the liquid is pressurized in a state where the maintenance driving pulse is supplied to the pressure generating element. You can also. In the former case, since the liquid in the pressure chamber is pressurized before the vibration of the pressure generating element, the liquid flow is already formed at the time of vibration, and as a result, the bubbles can be quickly discharged from the nozzle. In the latter case, since the bubble is grown by the vibration of the pressure generating element and then the liquid in the pressure chamber is pressurized to form a liquid flow, the liquid consumption due to idle ejection can be reduced.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic view showing the configuration of an ink jet printer according to an embodiment of the present invention. As shown in the figure, the ink jet printer 100 is an ink jet printing apparatus that forms an image by ejecting ink droplets of a plurality of colors on a paper surface in accordance with print data transmitted from the outside. The ink jet printer 100 includes a print head unit 10, a head drive unit 20, a paper transport unit 30, a cap unit 40, and a control unit 50.

  The print head unit 10 is detachably mounted with four color ink cartridges 11 (C, M, Y, K) composed of cyan, yellow, magenta, and black. The print head unit 10 repeats reciprocating movement along the direction perpendicular to the conveyance direction PD of the printing paper 200 (the arrow X direction in the drawing) when the inkjet printer 100 performs printing, and drops the ink droplets of each color on the paper surface. It discharges toward. Note that the number of colors of the ink cartridge attached to the print head unit 10 is not limited to four colors, and may be any number such as one color or six colors.

  Although not shown in FIG. 1 to be described later in detail, the ink in each ink cartridge 11 (C, M, Y, K) is configured to be supplied to the print head unit 10 via a pressure adjustment valve. is there. Ink in each ink cartridge 11 (C, M, Y, K) is pressurized with a predetermined pressure.

  The head drive unit 20 includes first and second pulleys 21 and 22 and a head drive belt 23. The two pulleys 21 and 22 are provided at positions facing each other with the paper transport unit 30 in between, and the head drive belt 23 is stretched between the two pulleys 21 and 22. The first pulley 21 is rotationally driven by a motor (not shown) controlled by the control unit 50, and the second pulley 22 rotates following the first pulley 21 via the head drive belt 23. . The print head unit 10 is fixed to the head drive belt 23, so that the print head unit 10 reciprocates on the printing surface of the printing paper 200 in accordance with the rotation drive of the first pulley 21.

  The sheet conveying unit 30 includes first and second sheet conveying rollers 31 and 32 and a sheet conveying belt 33 stretched between the two sheet conveying rollers 31 and 32. The first paper transport roller 31 is driven to rotate by a motor (not shown) controlled by the control unit 50, and the second paper transport roller 32 is connected to the first paper transport roller 31 via the paper transport belt 33. Rotate following. As a result, the printing paper 200 is transported on the paper transport belt 33 in the transport direction PD during printing.

  The cap unit 40 is disposed in parallel with the paper transport unit 30 in the movable area of the print head unit 10. The print head unit 10 is configured so that the nozzle 15 provided on the bottom surface (the surface facing the printing paper 200) of the print head unit 10 can be sealed by the cap unit 40 when performing a maintenance process described later. Move to the placement area. The position of the print head unit 10 at this time is referred to as “maintenance position MP”. Details of the cap unit 40 will be described later.

  Examples of the ink discharge detection unit 70 include one that electrically detects ink discharge. Specifically, when the print head unit 10 is at the maintenance position MP, ink is discharged in a state where electric charges are charged between the nozzle surface 15p (see FIG. 2A) and the lid body 41 of the cap unit 40. And a change in the amount of charge is detected by the sensor. If the amount of ejected ink is small, the change in the amount of charge becomes less than a predetermined value. In this case, it can be determined that dot missing has occurred. The ink discharge detection unit 70 may detect ink droplets discharged by an optical sensor, or may be detected by other methods.

  The control unit 50 is configured as a logic circuit centered on a microcomputer, and includes a central processing unit (not shown), a storage device (not shown), and the like. The control unit 50 is connected to the above-described print head unit 10 and the like via a signal line, and controls the operation of the inkjet printer 100.

  FIG. 2A is a schematic cross-sectional view showing the internal structure of the ink droplet ejection mechanism of the print head unit 10. FIG. 2A illustrates the vicinity of an arbitrary nozzle 15 of the print head unit 10 when viewed along the direction of the arrow Y shown in FIG. The print head unit 10 has a common ink chamber 12 and a pressure chamber 13 which are internal spaces filled with ink for each ink color.

  Any one of the ink cartridges 11 (C, M, Y, K) is mounted on the upper part of the common ink chamber 12, and pressurized ink flows from the ink cartridge 11 (C, M, Y, K). The common ink chamber 12 communicates with the pressure chamber 13 through the ink flow path 14. The ink filled in the common ink chamber 12 enters and exits the pressure chamber 13 through the ink flow path 14. That is, the common ink chamber 12 functions as an ink buffer region with respect to the pressure chamber 13.

  On the bottom surface of the pressure chamber 13, a plurality of nozzles 15 for discharging ink are provided in parallel along the paper transport direction (arrow Y direction). Hereinafter, the bottom surface of the print head unit 10 is referred to as a “nozzle surface 15p”. Each nozzle 15 is provided as a minute through hole having a tapered shape in which the diameter gradually decreases from the pressure chamber 13 toward the nozzle surface 15p.

  In the pressure chamber 13, a diaphragm 16 and a piezoelectric element 17 are provided to face each nozzle 15. The vibration plate 16 is a plate-like member having a thick portion with which the piezoelectric element 17 abuts and a thin portion having elasticity on the outer periphery thereof, and the thick portion vibrates according to the expansion and contraction of the piezoelectric element 17. In the drawing, the division of the thick portion and the thin portion of the diaphragm 16 is omitted.

  The piezoelectric element 17 is a laminated piezoelectric vibrator configured by alternately laminating piezoelectric bodies and internal electrodes, and in a vertical direction (illustrated by an arrow) perpendicular to the laminating direction according to an applied voltage. It is a piezoelectric vibrator in a longitudinal vibration mode that can be expanded and contracted. The piezoelectric element 17 is fixed to the fixed base material 18. The fixed base 18 is formed of a member having sufficient rigidity to efficiently transmit the vibration of the piezoelectric element 17 to the diaphragm 16. With such a configuration, the piezoelectric element 17 applies pressure to the ink filled in the pressure chamber 13 via the vibration plate 16 and ejects the ink from the nozzle 15.

  By the way, bubbles may be mixed in the ink in the pressure chamber 13 when the ink is initially filled from the ink cartridge or when the printing process is continued. In addition, since the bubbles absorb the pressure change in the pressure chamber 13 applied by the piezoelectric element 17, ink droplets are not properly ejected from some nozzles, so-called missing dots may occur. is there. Further, there is a case where nozzle clogging occurs in which the ink 15 thickens and adheres due to natural evaporation and the nozzle 15 is clogged. In view of this, in the inkjet printer 100, various maintenance processes for appropriately discharging ink droplets from the nozzles are executed in addition to the execution of the printing process.

  As the maintenance process, for example, there is a so-called flushing in which ink is ejected from the nozzles 15 and bubbles and thickened ink are ejected from the nozzles 15 together with ink droplets. Here, “empty ejection” means ejection performed for purposes other than the original use (that is, printing) of ink droplets.

  FIG. 2B is a diagram when the ink jet printer 100 when the print head unit 10 is moved to the maintenance position MP (FIG. 1) for maintenance processing is viewed along the direction of the arrow Y in FIG. It is. In FIG. 2B, the components of the inkjet printer 100 other than the print head unit 10 and the cap unit 40 are not shown for convenience.

  The cap unit 40 includes a lid body 41, an ink discharge pipe 42, a pump 43, and a drive mechanism 45. The lid body 41 is a saucer-like member disposed so as to cover the nozzle surface 15p. The lid 41 can receive the waste ink ejected from the nozzle 15 during flushing.

  A through hole 41h is provided in the center of the bottom surface of the lid body 41, and the ink discharge pipe 42 is connected to the through hole 41h. A pump 43 is provided in the ink discharge pipe 42, and the discharged ink accumulated in the lid body 41 can be sucked. The waste ink is guided to a waste ink processing unit (not shown) for processing the waste ink through the ink discharge pipe 42. The drive mechanism 45 is for raising the lid 41 and closely contacting the nozzle surface 15p during ink suction using the pump 43. During the flushing, the lid body 41 is kept away from the nozzle surface 15p.

  In the present embodiment, an ink flow is formed in the common ink chamber 12 and the pressure chamber 13 during flushing. More specifically, as shown in FIG. 3, in the ink jet printer 100 according to the present embodiment, a pressure adjustment valve 24 is provided between the ink cartridge 11 (C, M, Y, K) and the print head unit 10. It is. Here, the ink in the ink cartridge 11 (C, M, Y, K) is pressurized, and the pressure is applied to the pressure adjusting valve 24. The pressure adjustment valve 24 functions as a self-sealing valve that maintains the closed state by balancing the internal pressure of the common ink chamber 12 of the print head unit 10 and the pressure applied by the ink in a normal state. That is, when ink droplets are ejected through the nozzle 15 by driving the piezoelectric element 17, the common ink chamber 12 becomes negative pressure, and the pressure adjustment valve 24 is opened by this negative pressure to meet the negative pressure. Ink is supplied to the common ink chamber 12. Therefore, the pressure adjusting valve 24 is opened by a control signal from the control unit 50, whereby the pressure applied to the ink in the ink cartridge 11 can be applied to the ink in the pressure chamber 13 via the common ink chamber 12. . In the present embodiment, when performing bubble removal flushing, the pressure adjustment valve 24 is opened prior to flushing.

  FIG. 4 is a flowchart showing the bubble removal flushing process in the present embodiment. Here, “bubble removal flushing” means flushing specifically for removing bubbles among the flushing.

  As shown in the figure, in step S10, the control unit 50 opens the pressure regulating valve 24. As a result, a pressure gradient caused by the pressure of ink is formed from the ink cartridges 11 (C, M, Y, K) toward the common ink chamber 12. In such a state, each of the nozzles 15 is continuously discharged with 3000 ink drops. Hereinafter, this continuous ink droplet ejection process is referred to as “continuous flushing set”. In step S20, the control unit 50 closes the pressure regulating valve 24 and waits for a predetermined interval (for example, about 1 second). Here, the reason for setting the interval in step S20 is to converge the vibration of the ink and the pressure chamber 13 due to the continuous flushing set in the previous process. This makes it possible to effectively execute the subsequent continuous flushing set.

  Subsequently, in step 30, as in step 10, the pressure regulating valve 24 is opened and a continuous flushing set is performed. Thereafter, in step 40, as in step 20, the pressure regulating valve 24 is closed to enter a standby state. Hereinafter, in the bubble removal flushing, a series of steps including a continuous flushing set and an interval are repeated an arbitrary predetermined number of times.

  Note that such “bubble removal flushing” can also be selectively performed with respect to a nozzle row in which missing dots are detected. That is, since the missing dot can be detected by the ink discharge detection unit 70 (see FIG. 1), the nozzle row in which the missing dot is detected by the ink discharge detection unit 70 is selected by the control unit 50 and shown in FIG. What is necessary is just to process.

  FIG. 5 is a graph showing a driving pulse 300 that the control unit 50 transmits to the piezoelectric element 17 of each nozzle 15 for discharging one ink droplet in a continuous flushing set of bubble removal flushing. In this graph, the vertical axis represents voltage and the horizontal axis represents time.

  The drive pulse 300 is a substantially trapezoidal pulse signal, and includes a first pulse portion Pwc, a second pulse portion Pwh, and a third pulse portion Pwd. In the first pulse portion Pwc, the voltage value of the piezoelectric element 17 increases at a constant rate from the ground state (voltage value 0) to Vh between time t0 and time t1. In the second pulse portion Pwh, the voltage value of the piezoelectric element 17 is kept constant at Vh from time t1 to time t2. In the third pulse portion Pwd, between time t2 and time t3, the voltage value of the piezoelectric element 17 returns from Vh to the ground state at a constant ratio.

  Note that the frequency of the drive pulse 300 in the continuous flushing set (FIG. 5; the frequency corresponding to the period from time t0 to time t4) is preferably 1 KHz to 5 KHz.

  6A to 6C are schematic views schematically showing the operation of the print head unit 10 by the drive pulse 300. FIG. 6A to 6C show the pressure chamber 13 in the print head unit 10 shown in FIG. 2A in an enlarged manner, and the piezoelectric element 17 and the common ink chamber 12 are not shown. Yes.

  FIG. 6A shows the state of the pressure chamber 13 before receiving the drive pulse 300 (before time t0). The pressure chamber 13 is filled with ink 400, and bubbles 500 are mixed in the ink 400. Note that the bubble 500 tends to stay in a region on the upper side of the pressure chamber 13 in the gravity direction and facing the ink flow path 14.

  FIG. 6B shows the state of the pressure chamber 13 from time t0 to time t2 in FIG. When the piezoelectric element 17 receives the first pulse portion Pwc between time t0 and time t1, the piezoelectric element 17 contracts as the applied voltage increases. Then, as shown in FIG. 6B, the diaphragm 16 curves toward the outside (in the direction of the arrow) of the pressure chamber 13, and negative pressure is generated in the ink 400 in the pressure chamber 13. At this time, the meniscus 401 generated in the nozzle 15 increases the degree of curvature in the same direction as the diaphragm 16. Then, the bending of the diaphragm 16 is maintained from time t1 to time t2. Between time t0 and time t2, the diameter of the bubble 500 increases as the pressure in the pressure chamber 13 decreases.

  FIG. 6C shows the state of the pressure chamber 13 from time t2 to time t3. By the third pulse portion Pwd of the drive pulse 300, the applied voltage value of the piezoelectric element 17 returns to the base value (see FIG. 5), and the piezoelectric element 17 expands and returns to the ground state. That is, the diaphragm 16 returns from a curved state to a flat state. As a result, the ink 400 in the pressure chamber 13 is discharged from the nozzle 15 while being given pressure from the diaphragm 16. At this time, the bubble 500 gradually approaches the nozzle 15 as ink is discharged, and is finally discharged from the nozzle 15 to the outside. FIG. 6C shows a trajectory in which the bubble 500 moves to the nozzle 15 in response to the generation of a large number of drive pulses 300.

  Here, as described in FIG. 6B, according to the drive pulse 300, the diameter of the bubble 500 can be increased between the time t0 and the time t1, and as the diameter increases, A larger force can be applied to the bubble 500 from the diaphragm 16. Therefore, according to the driving pulse 300, even a bubble having a small diameter can be easily discharged.

  By the way, as can be understood from the above description, by reducing the pressure in the pressure chamber 13 and increasing the diameter of the bubble 500 as much as possible, the bubble 500 can be discharged and removed more reliably. . Here, the pulse width of the first pulse portion Pwc (see FIG. 5) of the drive pulse 300 is preferably set to ½ or less of the Helmholtz resonance period Tc of the ink 400 in the pressure chamber 13. The “Helmholtz resonance period Tc” is a natural vibration period when the vibration wave generated by the increase / decrease in the volume of the pressure chamber 13 propagates through the ink 400 in the pressure chamber 13. The value is determined by the shape of the nozzle 15.

  FIG. 7 is a graph showing how ink vibration follows the Helmholtz resonance period Tc. Theoretically, it can be understood that when the pressure in the pressure chamber 13 is decreased over a period of about ½ of the Helmholtz resonance period Tc from the time t0, the amplitude of the ink becomes maximum. Therefore, by setting the pulse width of the first pulse portion Pwc to ½ or less of the Helmholtz resonance period Tc, a large negative pressure can be generated in the pressure chamber 13 and the diameter of the bubble 500 can be increased. Is possible.

  As described above, in the present embodiment, since the pulse width of the first pulse portion Pwc is a value corresponding to the Helmholtz resonance cycle Tc, the contraction cycle of the piezoelectric element 17 is the pulse width of the second pulse portion Pwh. It is preferable to adjust to a value corresponding to the natural frequency of the bubbles. As a result, in the subsequent third pulse portion Pwd, it is possible to eject ink droplets at the timing when the diameter of the bubble is greatly increased. The pulse width of the second pulse portion Pwh can be interpreted as a waiting time until the bubble resonance is started.

  By the way, in this embodiment, the pulse width of the second pulse portion Pwh is set to a different value for each continuous flushing set (steps S20, S40, etc. in FIG. 4). More specifically, the pulse width of the second pulse portion Pwh of the drive pulse 300 generated in step S40 is made shorter than that generated in step S20, and thereafter, it is shortened for each continuous flushing set. That is, this means that the bubble diameter to be removed is reduced each time the continuous flushing set is repeated. As a result, it is possible to more reliably execute the bubble removal by the bubble removal flushing as described above.

  Furthermore, the pulse width of the third pulse portion Pwd of the drive pulse 300 (see FIG. 5) is preferably set to be approximately equal to the natural frequency Ta of the piezoelectric element 17. This is because, by setting the pulse width of the third pulse portion Pwd to such a value, the piezoelectric element 17 after receiving the driving pulse 300 can be prevented from continuing excessive vibration. Because. If the piezoelectric element 17 continues to vibrate more than necessary, there is a possibility that minute droplets of ink may be ejected from the nozzle 15 due to the vibration, which is not preferable.

  In the inkjet printer 100 that performs bubble removal flushing using the drive pulse 300 in this manner, minute bubbles existing in the pressure chamber 13 can also be discharged from the nozzle 15 with an increased diameter. In addition, since the drive pulses 300 corresponding to the bubbles having different diameters are sequentially generated, it is possible to execute the bubble removal more effectively.

  Bubbles 500 whose diameter increases in the bubble removal flushing are better discharged from the nozzles 15 when there is a flow in the common ink chamber 12. In other words, when bubble removal flushing is performed in a state where there is no flow in the common ink chamber 12, depending on the size of the bubble 500 and the location where it stays, it is not discharged from the nozzle 15 and is not discharged into the pressure chamber 13. It may remain. In this case, cap cleaning is required separately. Therefore, in this embodiment, a large flow from the common ink chamber 12 toward the pressure chamber 13 is formed by using the pressure of the pressurized ink sealed in the ink cartridges 11 (C, M, Y, K). .

  This point will be described in detail with reference to the schematic diagram shown in FIG. FIG. 8A conceptually shows a case where the above-described bubble removal flushing is performed with the pressure regulating valve 24 (see FIG. 3, the same applies hereinafter) being closed. As shown in the figure, in this case, since the pressure is adjusted by the pressure adjustment valve 24, the pressure of the pressure ink sealed in the ink cartridge 11 (C, M, Y, K) is the common ink. The ink 400 is not transmitted to the ink 400 in the chamber 12 and the flow in the common ink chamber 12 and the pressure chamber 13 is also small. For this reason, the bubbles 500 floating in the ink flow path 14 and the pressure chamber 13 may not be discharged well and may stay.

  On the other hand, FIG. 8B conceptually shows the case where the above-described bubble removal flushing is performed with the pressure regulating valve 24 opened. In this case, the pressure of the pressurized ink sealed in the ink cartridge 11 (C, M, Y, K) via the pressure adjustment valve 24 is applied to the ink 400 in the common ink chamber 12 as shown in FIG. As a result, a large flow of ink 400 is formed in the common ink chamber 12 and the pressure chamber 13. For this reason, the bubbles 500 floating in the pressure chamber 13 are well discharged from the nozzles 15 along with the flow of the ink 400.

  Here, in the present embodiment, the pressure regulating valve 24 is first opened to perform the above-described bubble removal flushing, but this may be reversed. Although the effects of both of the bubble removal processes are finally about the same, the bubble 500 can be removed more quickly in the case of this embodiment in which the flow of the ink 400 is made first and the bubble removal flushing is performed. it can. However, in the latter case where the bubble removal flushing is performed first to form the ink flow in the state where the bubbles 500 are grown, it is possible to reduce the amount of ink that is wasted due to the idle ejection associated with the bubble removal flushing. it can. This is because when the pressure regulating valve 24 is opened, ink leakage from the nozzles 15 due to the action of the pressure of the pressurized ink begins.

  Note that such “bubble removal flushing” can also be selectively performed with respect to a nozzle row in which missing dots are detected. That is, since the missing dot can be detected by the ink discharge detection unit 70 (see FIG. 1), the nozzle row in which the missing dot is detected by the ink discharge detection unit 70 is selected by the control unit 50 and shown in FIG. If the processing is performed, ink leakage accompanying the bubble removal flushing can be minimized.

  The present invention is not limited to the above-described embodiment, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

(Modification 1)
In the above embodiment, the ink jet printer has been described. However, the present invention can also be applied to a liquid ejecting apparatus that ejects another liquid.

(Modification 2)
In the above embodiment, the bubble 500 is discharged smoothly by applying the pressure of the pressurized ink to the pressure chamber 13 via the pressure adjustment valve during the bubble removal flushing. However, the present invention is not limited to this. At least during the bubble removal flushing, the ink flow may be generated by applying pressure to the common ink chamber 12 by some pressure means.

(Modification 3)
In the above embodiment, the pulse width of the second pulse portion Pwh of the drive pulse 300 (see FIG. 5) is set according to the natural period of the bubble. However, an arbitrary pulse width may be set. Further, the outside air temperature may be detected when the bubble removal flushing is performed, and the pulse width of the second pulse portion Pwh may be set according to the detected outside air temperature.

(Modification 4)
In the above embodiment, the ink droplets are ejected 3000 times as a continuous flushing set (see FIG. 4), but the ink droplets may be ejected any number of times. Further, in each continuous flushing set, the drive pulse 300 is continuously generated in the same cycle, but it may be generated by changing the cycle.

(Modification 5)
In the above embodiment, the pulse width of the second pulse portion Pwh of the drive pulse 300 (see FIG. 5) is changed for each continuous flushing set. However, the continuous flushing set may be repeated with the same pulse width. .

(Modification 6)
In the above embodiment, each continuous flushing set is configured by a plurality of drive pulses 300 having the same waveform, but at least some of the waveforms may include different drive pulses. For example, each continuous flushing set may include a drive pulse 300 having a different pulse width of the second pulse portion Pwh, a drive pulse 300 having a different voltage value Vh, and the like together with the drive pulse 300.

1 is a schematic diagram illustrating a configuration of an inkjet printer according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view illustrating a configuration of a print head unit and a cap unit according to the embodiment of FIG. 1. The block diagram which shows the part relevant to the flushing in embodiment of FIG. The flowchart which shows the process sequence of bubble removal flushing. The graph which shows the drive pulse which a control part generate | occur | produces in bubble removal flushing. The schematic diagram explaining the mechanism of bubble removal in bubble removal flushing. The graph for demonstrating the suitable pulse width of a 1st pulse part. FIG. 5 is a schematic diagram for explaining the flow of ink during bubble removal flushing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Print head part, 11 (C, M, Y, K) Ink cartridge, 12 Common ink chamber, 13 Pressure chamber, 14 Ink flow path, 15 Nozzle, 16 Diaphragm, 17 Piezoelectric element, 24 Pressure adjustment valve, 50 Control Part, 400 ink, 500 bubble Tc Helmholtz resonance period

Claims (15)

A liquid ejecting apparatus for ejecting liquid,
A pressure chamber filled with the liquid;
Pressurizing means for pressurizing the liquid in the pressure chamber from the supply side;
A pressure generating element that is provided on a wall surface of the pressure chamber and changes a volume of the pressure chamber by deforming the wall surface;
A nozzle for injecting the liquid in communication with the pressure chamber;
A liquid ejecting apparatus comprising: a control unit that controls a driving pulse for the pressure generating element and the pressurizing unit. The liquid ejecting apparatus according to claim 1,
The control unit can control the pressurizing unit to pressurize the liquid in the pressure chamber and simultaneously generate a maintenance drive pulse for discharging bubbles from the pressure chamber together with the liquid. Yes,
The maintenance drive pulse includes a first pulse portion that causes the pressure chamber to transition to an expanded state by driving the pressure generating element, and a second pulse portion that maintains the expanded state for a predetermined time, A third pulse portion for contracting the pressure chamber from the expanded state,
The liquid ejecting apparatus according to claim 1, wherein a pulse width of the first pulse portion is set to a value based on a Helmholtz resonance period of the liquid filled in the pressure chamber. In the liquid ejecting apparatus according to claim 1 or 2,
The pressurizing means has a pressure regulating valve disposed in the middle of a flow path communicating the pressurized liquid storage section and the pressure chamber, and the control section is pressurized by controlling the opening of the pressure regulating valve. A liquid ejecting apparatus that controls the pressure of the liquid to act on the liquid in the pressure chamber. In the liquid ejecting apparatus according to claim 2 or 3,
The control unit is configured to supply the maintenance driving pulse to the pressure generating element in a state where the liquid is pressurized via the pressurizing unit. . In the liquid ejecting apparatus according to claim 2 or 3,
The liquid ejecting apparatus according to claim 1, wherein the controller controls the pressurizing unit to pressurize the liquid in a state where the maintenance driving pulse is supplied to the pressure generating element. The liquid ejecting apparatus according to any one of claims 2 to 5,
It further has a liquid discharge detection means for detecting missing dots including discharge defects,
The control means selects a nozzle row in which dot dropout is detected by the liquid discharge detection means, supplies the maintenance drive pulse to the pressure generating element, and controls the pressure means to control the liquid in the pressure chamber. A liquid ejecting apparatus configured to pressurize the liquid. The liquid ejecting apparatus according to any one of claims 2 to 6,
The liquid ejecting apparatus according to claim 1, wherein the controller repeatedly generates at least some of the maintenance drive pulses having different waveforms from each other in a predetermined order. The liquid ejecting apparatus according to claim 7,
The liquid ejection apparatus, wherein the maintenance drive pulses different from each other have different pulse widths of the second pulse portion. The liquid ejecting apparatus according to any one of claims 2 to 6,
The control unit generates a plurality of sets of driving pulse groups in which the maintenance driving pulses are repeated at a constant cycle,
Each set of drive pulse groups has the same drive pulse waveform for maintenance,
The plurality of sets of drive pulse groups include two or more sets of drive pulse groups in which waveforms of the maintenance drive pulses are different from each other. The liquid ejecting apparatus according to claim 9, wherein
In the liquid ejecting apparatus, the two or more sets of driving pulse groups have different pulse widths of the second pulse portion. An inkjet printer,
An ink jet printer comprising the liquid ejecting apparatus according to any one of claims 1 to 10. A pressure chamber filled with a liquid, a pressure generating element provided on a wall surface of the pressure chamber, which changes the volume of the pressure chamber by deforming the wall surface, and the liquid is ejected in communication with the pressure chamber. A bubble removing method for a liquid ejecting apparatus that ejects the liquid through the nozzle.
A method for removing bubbles from a liquid ejecting apparatus, wherein the liquid in the pressure chamber is pressurized and a driving pulse for discharging the liquid from the pressure chamber is supplied to the pressure generating element. The method of removing bubbles in a liquid ejecting apparatus according to claim 12,
While pressurizing the liquid in the pressure chamber, supplying a maintenance driving pulse for discharging unnecessary bubbles together with the liquid from the pressure chamber to the pressure generating element to perform bubble removal flushing,
The maintenance driving pulse at the time of the bubble removal flushing drives the pressure generating element to inflate the pressure chamber and transition to an expanded state, and a predetermined state of the expanded state. And a third pulse portion for contracting the pressure chamber from the expanded state, and the pulse width of the first pulse portion is the liquid filled in the pressure chamber. A method for removing bubbles in a liquid ejecting apparatus, wherein the value is set based on a Helmholtz resonance period. The method for removing bubbles in a liquid ejecting apparatus according to claim 13.
A method for removing bubbles in a liquid ejecting apparatus, wherein the maintenance driving pulse is supplied to the pressure generating element in a state where the liquid is pressurized. The method for removing bubbles in a liquid ejecting apparatus according to claim 13.
A method of removing bubbles in a liquid ejecting apparatus, comprising pressurizing the liquid in a state where the maintenance driving pulse is supplied to the pressure generating element.

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