JP5664001B2 - Liquid ejection device - Google Patents

Description

  The present invention relates to a liquid ejection device that ejects liquid from ejection ports.

  In an inkjet head that ejects ink droplets from a plurality of ejection openings, forcibly supplying ink to the ink flow path in the inkjet head using a pump, air bubbles and increase in the ink flow path in the vicinity of the ejection opening. A technique for discharging the viscous ink and cleaning the discharge port is known (for example, see Patent Document 1). In Patent Document 1, after closing the three-way valve and closing the discharge path, the supply pump is operated to pressurize the ink in the flow path in the inkjet head for a predetermined time, and the ink is discharged from the nozzle to clean the nozzle. Yes.

JP 2009-29111 A

  In order to reliably discharge ink from all the ejection ports and clean the ejection ports, it is necessary to increase the ink pressure applied to the ink flow path. However, if it takes time for the ink pressure in the ink flow path to reach the desired pressure after the pump is started, the ink is discharged in order from the discharge port having the lowest ink discharge resistance (flow path resistance). Ink cannot be instantaneously discharged from the discharge port. For this reason, ink is wasted from the ejection ports when cleaning the ejection ports.

  An object of the present invention is to provide a liquid ejecting apparatus that can efficiently discharge bubbles and foreign substances together with liquid from an ejection port and suppress wasteful consumption of liquid.

The liquid discharge apparatus according to the present invention includes an inflow port through which a liquid flows in, an outflow port through which the liquid flows out, an internal flow path that connects the inflow port and the outflow port, and a plurality of discharge ports for discharging the liquid. A liquid discharge head comprising: a plurality of individual liquid channels that branch from the internal channel to the plurality of discharge ports; and a pressure applying unit that applies pressure to the liquid in the plurality of individual liquid channels. A tank for storing the liquid to be supplied to the liquid discharge head, a supply channel for communicating the inside of the tank and the inlet, and a return channel for communicating the interior of the tank and the outlet Supply means for forcibly supplying the liquid stored in the tank to the internal flow path through the supply flow path, and a flow resistance value in the return flow path is set to a predetermined minimum value and a predetermined maximum value. Adjusting means adjustable between values, and the pressure applying hand , And a said supply means and control means for controlling said adjusting means. The control means drives the supply means while reducing the flow path resistance value below the predetermined maximum value by adjusting the adjustment means, thereby supplying the liquid in the tank to the supply flow path, the internal flow path, and Circulate so as to be transferred in the order of the return flow path, during the circulation, by adjusting the adjustment means to increase the flow path resistance value, to discharge the liquid from the plurality of discharge ports, During the discharge, the adjustment means is adjusted to reduce the flow path resistance value, thereby controlling the discharge of the liquid from the plurality of discharge ports, and the control means further performs the discharge. the same time as the start, the controls the pressure applying means, the plurality of by applying pressure oscillations to the liquid in the individual liquid flow path, and, stopping the application of the pressure oscillations prior to the discharge is stopped As before To control the pressure applying means.

According to the present invention, by performing circulation, it is possible to discharge bubbles, foreign matters, and the like remaining in the internal flow path into the tank while preventing liquid from leaking from the discharge port. In this state, by increasing the channel resistance value by adjusting the adjusting means, the pressure in the internal channel instantaneously increases, and the liquid in the internal channel flows into the individual liquid channel. Thereby, the liquid is discharged from the discharge port. At this time, a high pressure is applied to all the discharge ports from the start of discharge, and the liquid is discharged. Therefore, it is possible to efficiently discharge the thickened liquid, bubbles and foreign matter in the discharge port,
It is possible to suppress the wasteful discharge of the liquid. Furthermore, the same time as the discharge is initiated, in order to apply pressure vibration to all liquid in the individual liquid flow path, easily discharged peeled off from the wall surface air bubbles or foreign matters adhered to the wall surface of the individual liquid channels Thus, the discharge characteristics at each discharge port can be made uniform. For this reason, it is possible to efficiently discharge bubbles and foreign matters together with the thickened liquid in the discharge port while further suppressing the wasteful discharge of the liquid. In addition, since the pressure vibration also works in the direction in which the liquid is not discharged, by stopping the application of the pressure vibration before the liquid discharge is completed, the wall surface of the individual liquid flow path is applied by applying the pressure vibration. It is possible to efficiently remove the bubbles and foreign matters that have been peeled off after the application of pressure vibration has stopped, while reliably removing the air bubbles and foreign matters adhering to the wall.

In the present invention, when the discharge is started , the control unit applies a pressure for discharging one droplet from the plurality of discharge ports to the liquid in the plurality of individual liquid flow paths. Further, it is preferable to control the pressure applying means .

In the present invention, when the discharge is started , the control unit applies a pressure for discharging two or more droplets from the plurality of discharge ports to the liquid in the plurality of individual liquid channels. Thus, it is preferable to control the pressure applying means. According to this, since the discharge of the liquid from the plurality of discharge ports is promoted when the discharge is started, the discharge characteristics at each discharge port can be further uniformed.

  In the present invention, the control means may control the pressure applying means so as to apply the pressure vibration without discharging liquid from the plurality of discharge ports after stopping the discharge. preferable. According to this, after the discharge of the liquid from the discharge port is stopped, the flow of the liquid in the individual liquid channel can be quickly adjusted. Thereby, it can further suppress that the liquid leaks from a discharge outlet uselessly.

  Furthermore, in the present invention, it is preferable that the pressure applying unit is a piezo actuator that applies a pressure for discharging liquid from the plurality of discharge ports to the liquid in the plurality of individual liquid channels. According to this, since the pressure applying means has a function of discharging liquid from the discharge port and a function of performing liquid vibration, it is not necessary to separately provide a mechanism having a function of performing pressure vibration. The cost of the discharge head can be reduced.

According to the present invention, by performing circulation, it is possible to discharge bubbles, foreign matters, and the like remaining in the internal flow path into the tank while preventing liquid from leaking from the discharge port. In this state, by increasing the channel resistance value by adjusting the adjusting means, the pressure in the internal channel instantaneously increases, and the liquid in the internal channel flows into the individual liquid channel. Thereby, the liquid is discharged from the discharge port. At this time, a high pressure is applied to all the discharge ports from the start of discharge, and the liquid is discharged. Therefore, it is possible to efficiently discharge the thickened liquid, bubbles, and foreign matters in the discharge port, and it is possible to suppress the wasteful discharge of the liquid. In addition, during the discharge, pressure vibrations are applied to the liquids in all the individual liquid flow paths, so that bubbles and foreign matters fixed to the wall surfaces of the individual liquid flow paths are easily peeled off from the wall surfaces and discharged. The discharge characteristics can be made uniform. For this reason, it is possible to efficiently discharge bubbles and foreign matters together with the thickened liquid in the discharge port while further suppressing the wasteful discharge of the liquid. In addition, since the pressure vibration also works in the direction in which the liquid is not discharged, by stopping the application of the pressure vibration before the liquid discharge is completed, the wall surface of the individual liquid flow path is applied by applying the pressure vibration. It is possible to efficiently remove the bubbles and foreign matters that have been peeled off after the application of pressure vibration has stopped, while reliably removing the air bubbles and foreign matters adhering to the wall.

1 is a schematic plan view of an ink jet printer according to an embodiment of the present invention. It is sectional drawing of the inkjet head and ink supply unit which are shown in FIG. FIG. 3 is a plan view of the head main body shown in FIG. 2. It is an enlarged view of the area | region enclosed with the dashed-dotted line shown in FIG. It is sectional drawing of the VV line shown in FIG. 6 is a partially enlarged cross-section of the actuator unit shown in FIG. It is a graph which shows the operating characteristic of the purge pump shown in FIG. It is a functional block diagram of the control apparatus shown in FIG. (A) It is a wave form diagram of the ejection drive signal which a head control part shown in Drawing 8 generates. FIG. 9B is a waveform diagram of an ink vibration signal generated by the head controller shown in FIG. FIG. 9 is a diagram illustrating an ink flow when the circulation / purge control unit illustrated in FIG. 8 performs ink circulation. It is a figure which shows the operation | movement sequence of the inkjet printer shown in FIG. It is a graph which shows the change of the ink flow rate in the purge operation | movement by the circulation and purge control part shown in FIG.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, the inkjet printer 101 includes a transport unit 20 that transports a sheet P from the upper side to the lower side of FIG. 1, and black, magenta, cyan, and yellow inks on the sheet P transported by the transport unit 20. Four inkjet heads 1 that respectively eject droplets, four ink supply units 10 that supply ink to the inkjet head 1, a maintenance unit 31 that performs maintenance of the inkjet head 1, and a control device 16 that controls the entire inkjet printer 101 And have. In the present embodiment, the sub-scanning direction is a direction parallel to the transport direction when the paper P is transported by the transport unit 20, and the main scanning direction is a direction orthogonal to the sub-scanning direction and along the horizontal plane. Direction.

  The transport unit 20 includes two belt rollers 6 and 7 and an endless transport belt 8 wound around the rollers 6 and 7. The belt roller 7 is a driving roller, and rotates when a driving force is applied from a conveyance motor (not shown). The belt roller 6 is a driven roller and rotates as the conveyor belt 8 travels due to the rotation of the belt roller 7. The paper P placed on the outer peripheral surface of the transport belt 8 is transported downward in FIG.

  The four inkjet heads 1 each extend along the main scanning direction and are arranged in parallel to each other in the sub-scanning direction. That is, the ink jet printer 101 is a line type color ink jet printer in which a plurality of ejection openings 108 for ejecting ink droplets in the main scanning direction are arranged. The lower surface of each inkjet head 1 is an ejection surface 2a in which a plurality of ejection ports 108 are arranged (see FIGS. 2 to 4).

  The outer peripheral surface of the upper loop of the conveyor belt 8 and the discharge surface 2a are parallel to each other while facing each other. When the paper P transported by the transport belt 8 passes below the four ink jet heads 1, ink droplets of each color are sequentially ejected from the respective ink jet heads 1 toward the upper surface of the paper P, and are desired on the paper P. The color image is formed.

  The ink supply unit 10 is connected to the vicinity of the left end of FIG. 1 on the lower surface of the inkjet head 1 and supplies ink to the connected inkjet head 1.

  The maintenance unit 31 has four wiper members 32. The four wiper members 32 are elastic members that wipe the ejection surface 2a of the inkjet head 1 in a wipe operation related to a maintenance operation described later, and can be reciprocated along the main scanning direction by an actuator (not shown). (See arrow in FIG. 1).

  Next, the inkjet head 1 will be described in detail with reference to FIG. As shown in FIG. 2, the inkjet head 1 includes a reservoir unit 71 and a head body 2.

  The reservoir unit 71 is a flow path forming member that is fixed to the upper surface of the head body 2 and supplies ink to the head body 2. In addition, the reservoir unit 71 has an ink inflow channel 72, ten ink outflow channels 75, and an exhaust channel 73 formed therein. In FIG. 2, only one ink outflow channel 75 appears.

  The ink inflow channel 72 is a channel through which ink from the ink supply unit 10 flows through an inflow port 72 a that opens to the lower surface of the reservoir unit 71. The ink inflow channel 72 has a function as an ink reservoir for temporarily storing the inflowed ink. A hole 72 b that penetrates to the outer wall surface of the reservoir unit 71 is formed in the inner wall surface of the ink inflow channel 72. A resin film 76 having flexibility seals the hole 72 b from the inner wall surface side of the ink inflow channel 72. That is, the resin film 76 is sealed from the outer wall surface side of the reservoir unit 71. The resin film 76 functions as a damper that suppresses fluctuations in the ink pressure because the resin film 76 is displaced with fluctuations in the ink pressure in the ink inflow channel 72. By using the resin film 76, the damper can be realized with an inexpensive configuration. During normal printing, the resin film 76 is slightly convex toward the ink inflow channel 72. A plate-shaped restricting member 77 is fixed to the outer wall surface of the reservoir unit 71 so as to cover the hole 72 b, and restricts the resin film 76 from being excessively convex toward the outside of the reservoir unit 71. . Thus, when the ink pressure in the ink inflow channel 72 becomes abnormally high, the resin film 76 is prevented from being excessively displaced and damaged. An air communication hole 77 a is formed in the restriction member 77, and the atmospheric pressure is always between the restriction member 77 and the resin film 76. Thereby, the resin film 76 becomes easy to displace.

  The ink outflow channel 75 communicates with the ink inflow channel 72 through the filter 75a and also communicates with the ink supply port 105b formed on the upper surface of the channel unit 9 of the head body 2 (FIG. 3). reference). The filter 75a extends along the direction of ink flow (the left-right direction in FIG. 2) in the ink inflow channel 72. During normal printing, the ink from the ink supply unit 10 flows into the ink inflow channel 72, passes through the ink outflow channel 75, and is supplied from the ink supply port 105 b to the channel unit 9.

  The exhaust passage 73 communicates with the ink inflow passage 72 on the upstream side of the filter 75 a in the ink inflow passage 72, and communicates with the ink supply unit 10 through the outflow port 73 a formed on the lower surface of the reservoir unit 71. It is connected.

  A hole 73 b that penetrates to the outer wall surface of the reservoir unit 71 is formed in the lower inner wall surface of the exhaust passage 73. Further, the resin film 78 having flexibility is sealed from the outer wall surface below the reservoir unit 71. That is, the resin film 78 is a part of the inner wall surface of the exhaust passage 73. The resin film 78 is displaced as the ink pressure in the exhaust passage 73 varies, and thus functions as a damper that suppresses the variation in ink pressure. By using the resin film 78, the damper can be realized with an inexpensive configuration. During normal printing, the resin film 78 is slightly convex toward the exhaust passage 73. A plate-shaped restricting member 79 is fixed to the lower outer wall surface of the reservoir unit 71 so as to cover the hole 73b, and restricts the resin film 78 from being excessively convex toward the outside of the reservoir unit 71. ing. Thereby, when the ink pressure of the exhaust flow path 73 becomes abnormally high, the resin film 78 is prevented from being excessively displaced and damaged. An air communication hole 79 a is formed in the regulating member 79, and the atmospheric pressure is always between the regulating member 79 and the resin film 78. Thereby, the resin film 78 becomes easy to displace. During ink circulation, which will be described later, ink from the ink supply unit 10 flows into the ink inflow channel 72 through the inflow port 72a, passes through the exhaust channel 73 from the ink inflow channel 72, and flows out the outlet 73a. To the ink supply unit 10 (see FIG. 10).

  Further, the head main body 2 will be described with reference to FIGS. In FIG. 4, for convenience of explanation, the pressure chamber 110, the aperture 112, and the discharge port 108 that are to be drawn by broken lines below the actuator unit 21 are drawn by solid lines.

  As shown in FIG. 3, the head main body 2 includes a flow path unit 9 and four actuator units 21 fixed to the upper surface of the flow path unit 9. As shown in FIG. 4, the flow path unit 9 has an ink flow path including a pressure chamber 110 and the like formed therein. The actuator unit 21 includes a plurality of unimorph actuators corresponding to the pressure chambers 110 and has a function of selectively applying ejection energy to the ink in the pressure chambers 110.

  As shown in FIG. 5, the flow path unit 9 is formed by stacking metal plates 122 to 130 made of stainless steel while aligning them with each other. The laminate is formed with a flow path that reaches the discharge port 108 via the. As shown in FIG. 3, a total of ten ink supply ports 105 b communicating with the ink outflow channel 75 (see FIG. 2) of the reservoir unit 71 are opened on the upper surface of the channel unit 9. As shown in FIG. 4, a manifold channel 105 communicating with the ink supply port 105 b and a plurality of sub manifold channels 105 a included in the manifold channel 105 are formed inside the channel unit 9. Further, as shown in FIG. 5, a plurality of individual inks that branch from the respective sub-manifold channels 105 a and reach the discharge port 108 that opens to the discharge surface 2 a through the pressure chamber 110 are provided in the flow channel unit 9. A flow path 132 is formed. A plurality of discharge ports 108 are arranged in a matrix on the discharge surface 2a.

  The ink flow in the flow path unit 9 will be described. As shown in FIGS. 3 to 5, during normal printing, the ink supplied from the ink outflow channel 75 of the reservoir unit 71 to the ink supply port 105 b is distributed to the sub-manifold channel 105 a of the manifold channel 105. The The ink in the sub-manifold flow path 105 a flows into the individual ink flow paths 132 via the apertures 112 and reaches the discharge ports 108 via the pressure chambers 110.

  Next, the actuator unit 21 will be described. As shown in FIG. 6, the actuator unit 21 is a piezoelectric actuator composed of three piezoelectric sheets 141 to 143 made of a lead zirconate titanate (PZT) ceramic material having ferroelectricity. The uppermost piezoelectric sheet 141 is polarized in the thickness direction. A plurality of individual electrodes 135 are formed on the upper surface of the piezoelectric sheet 141. A common electrode 134 formed on the entire surface of the sheet is interposed between the piezoelectric sheet 141 and the lower piezoelectric sheet 142. A plurality of individual electrodes 135 and a common electrode 134 sandwich the piezoelectric sheet 141.

  The individual electrode 135 faces the pressure chamber 110. An individual land 136 electrically connected to the individual electrode 135 is provided at the tip of the individual electrode 135. When the electric field in the polarization direction is applied to the piezoelectric sheet 141 by setting the individual electrode 135 to a potential different from that of the common electrode 134, the electric field application portion of the piezoelectric sheet 141 functions as a drive active portion that is distorted by the piezoelectric effect. Correspondingly, a portion sandwiched between the individual electrode 135 and the pressure chamber 110 functions as an individual actuator. That is, the actuator unit 21 is a piezoelectric element in which a plurality of actuators corresponding to the number of pressure chambers 110 are built.

  The common electrode 134 is equally grounded in the region corresponding to all the pressure chambers 110. On the other hand, a drive signal is supplied to the individual electrode 135.

  Here, a driving method of the actuator unit 21 will be described. For example, if the polarization direction and the electric field application direction are the same, the drive active portion contracts in a direction (plane direction) orthogonal to the polarization direction. Here, the actuator unit 21 uses the upper one piezoelectric sheet 141 away from the pressure chamber 110 as a layer including the drive active portion, and deactivates the lower two piezoelectric sheets 142 and 143 close to the pressure chamber 110. It is a so-called unimorph type actuator made into a layer. Since the piezoelectric sheets 141 to 143 are fixed to the upper surface of the plate 122 that defines the pressure chamber 110, the electric field application portion (driving active portion) contracts in the plane direction and is flat between the piezoelectric sheets 142 and 143 below the electric field application portion. When a difference occurs in the strain in the direction, the entire piezoelectric sheets 141 to 143 are deformed so as to be convex toward the pressure chamber 110 (unimorph deformation). As a result, pressure (discharge energy) is applied to the ink in the pressure chamber 110, and an ink droplet is discharged from the nozzle 108.

  In the present embodiment, a predetermined potential is applied to the individual electrode 135 in advance, and the individual electrode 135 is once set to the ground potential every time there is an ejection request, and then the individual electrode 135 is again set to the predetermined potential at a predetermined timing. A drive signal for applying a potential is supplied (see FIG. 9). In this case, the piezoelectric sheets 141 to 143 return to the original state at the timing when the individual electrode 135 becomes the ground potential, and the volume of the pressure chamber 110 increases as compared with the initial state (a state in which a voltage is applied in advance). Ink is sucked from the manifold channel 105 a into the individual ink channel 132. After that, at the timing when a predetermined potential is applied to the individual electrode 135 again, the piezoelectric sheets 141 to 143 are deformed so that the portions facing the active region protrude toward the pressure chamber 110, and the ink is reduced due to the volume reduction of the pressure chamber 110. And the ink droplets are ejected from the nozzles 108.

  The ink supply unit 10 will be described in detail. As shown in FIG. 2, the ink supply unit 10 includes a sub tank 80, an ink supply pipe 81 connected to the sub tank 80, a supply pump 91 and a supply valve 92 provided in the ink supply pipe 81, and an ink supply pipe 82. And an ink return pipe 83, a purge pump 86 provided in the ink supply pipe 82, a circulation valve 87 provided in the ink return pipe 83, and an air communication valve 88 connected to the sub tank 80.

  The sub tank 80 stores ink supplied to the inkjet head 1. When the ink amount in the sub tank 80 decreases, the replenishment valve 92 is opened and the replenishment pump 91 is driven. The ink stored in 90 is supplied through the ink supply pipe 81. The atmosphere communication valve 88 communicates (hereinafter referred to as “open”) or blocks (hereinafter referred to as “close”) the atmosphere in the sub tank 80 and the atmosphere. At the time of normal printing, the atmosphere communication valve 88 is opened, and the inside of the sub tank 80 and the atmosphere are communicated. As a result, the atmospheric pressure in the sub tank 80 is always atmospheric pressure regardless of the amount of stored ink, enabling stable ink supply.

  One end of the ink supply pipe 82 is connected to the sub tank 80, and the other end is connected to the inlet 72a of the reservoir unit 71 via the joint 82a. As a result, the ink in the sub tank 80 is supplied to the ink inflow channel 72 of the reservoir unit 71 via the ink supply pipe 82. The purge pump 86 functions as supply means for forcibly supplying the ink in the sub tank 80 to the ink inflow channel 72 via the ink supply pipe 82 by being driven. The purge pump 86 functions as a check valve that prevents ink from flowing from the joint 82 a toward the sub tank 80 in the ink supply pipe 82. Even when the purge pump 86 is stopped, the ink in the sub tank 80 can be supplied to the reservoir unit 71 through the ink supply pipe 82. The purge pump 86 is a three-phase diaphragm pump, which is a positive displacement pump, and as shown in FIG. 7, the three diaphragms are driven at different phases to discharge ink, thereby suppressing pressure fluctuations during ink delivery. It is the composition to do.

  As shown in FIG. 2, one end of the ink return pipe 83 is connected to the sub tank 80, and the other end is connected to the outlet 73a of the reservoir unit 71 via the joint 83a. The circulation valve 87 is an adjusting means that can adjust the flow resistance value in the ink return pipe 83 between a predetermined minimum value (hereinafter referred to as “open”) and a predetermined maximum value (hereinafter referred to as “closed”). In the present embodiment, the circulation valve 87 is an open / close valve that switches between open, which is completely open, and closed, which is completely shut off (inhibition of ink passage). It may be a flow path control valve that can be adjusted by any value.

  Next, the control device 16 will be described with reference to FIG. The control device 16 includes a CPU (Central Processing Unit), a program executed by the CPU, and an EEPROM (Electrically Erasable and Programmable Read Only Memory) that stores data used for these programs in a rewritable manner. It includes RAM (Random Access Memory) for temporary storage. Each functional unit constituting the control device 16 is constructed by cooperation of these hardware and software in the EEPROM. The control device 16 controls the entire inkjet printer 101, and includes a conveyance control unit 41, an image data storage unit 42, a head control unit 43, a non-ejection time detection unit 46, and a circulation / purge control unit 44. And a maintenance control unit 45.

  The transport control unit 41 controls the transport motor of the transport unit 20 so that the paper P is transported at a predetermined speed along the transport direction. The image data storage unit 42 stores image data relating to an image to be printed on the paper P.

  The head controller 43 supplies the generated ejection drive signal to the actuator unit 21 based on the image data during normal printing. As shown in FIG. 9A, the ejection drive signal is a signal including a pulse that changes from the potential V1 to the ground potential V0 for a predetermined time in one printing cycle. This pulse width is equal to the time during which the pressure wave propagates the distance AL (Acoustic Length) from the outlet of the sub manifold channel 105a to the discharge port 108. Note that the waveform in FIG. 9A is a waveform when a small ink droplet is ejected, and has one pulse. The waveform when ejecting medium ink droplets is configured by continuously arranging two pulses, and the waveform when ejecting large ink droplets is configured by sequentially arranging three pulses.

  In addition, the head control unit 43 vibrates the ink in all the individual ink flow paths 132 without causing the ink to leak out from the ejection port 108 (ink vibration) in a maintenance operation described later (ink vibration). To supply. As shown in FIG. 9B, the meniscus vibration signal is a signal in which a pulse that changes from the potential V1 to the ground potential V0 for a predetermined time is repeated at a predetermined cycle. This pulse width is preferably １ ／ or less of the time for the pressure wave to propagate through the AL length.

  The non-ejection time detection unit 46 detects the elapsed time from the last ejection of the ink droplet from the ejection port 108 to the present time for each inkjet head 1 from the past ejection history. Specifically, the elapsed time is detected based on the ejection drive signal output from the head control unit 43 or the data in the image data storage unit 42.

  The circulation / purge control unit 44 controls the operations of the purge pump 86, the circulation valve 87, and the atmosphere communication valve 88 of each ink supply unit 10 in a maintenance operation described later. Specific operation contents will be described later. The circulation / purge control unit 44 also controls the replenishment pump 91 and the replenishment valve 92 for replenishing ink, but is omitted in FIG.

  The maintenance control unit 45 controls the operation of the maintenance unit 31 in a maintenance operation described later.

  The maintenance operation will be described with reference to FIGS. The maintenance operation is an operation for performing maintenance of the inkjet head 1 and is started when the inkjet printer 101 is activated, when a standby time during which printing is not performed exceeds a certain time, or when an instruction is given from the user. Is done. During standby and normal printing, the purge pump 86 is stopped, the circulation valve 87 is closed, the air communication valve 88 is opened, and the supply pump 91 is stopped. 92 is closed (see FIG. 2).

  As shown in FIGS. 10 and 11, when the maintenance operation is started, the circulation / purge control unit 44 opens the circulation valve 87 and then closes the atmospheric communication valve 88 and simultaneously drives the purge pump 86. Start (start of circulation period). As a result, the ink in the sub tank 80 is forcibly supplied to the ink inflow channel 72 via the ink supply pipe 82. At this time, since the circulation valve 87 is open, the channel resistance in the path from the ink inflow channel 72 through the exhaust channel 73 and the ink return pipe 83 to the sub tank 80 is reduced from the ink inflow channel 72. It becomes smaller than the flow path resistance of the path reaching each discharge port 108 via the ink outflow flow path 75 and the manifold flow path 105. For this reason, the ink supplied to the ink inflow channel 72 does not flow into the ink outflow channel 75 but passes through the exhaust channel 73 and the ink return pipe 83 in order and returns to the sub tank 80 for ink circulation. By performing the ink circulation, the pressure of the ink in the flow path from the purge pump 86 to the sub tank 80 in the circulation path becomes high, and the ink flows due to the ink circulation and stays in the ink inflow flow path 72. The bubbles and foreign matters staying on the filter 75a are trapped in the sub-tank 80 through the exhaust passage 73 and the ink return pipe 83 in order with the ink.

  In order to efficiently move bubbles and foreign matter to the sub tank 80 in the ink circulation, the ink flow rate per unit time in the purge pump 86 is changed so that the ink meniscus formed at the discharge port 108 is broken (meniscus break). It is necessary to increase the flow rate within the range below the flow rate at which ink leaks out (meniscus break flow rate) (see FIG. 12). The meniscus break flow rate is a value calculated from the flow path structure of the inkjet head 1, the height relationship between the inkjet head 1 and the sub tank 80 in the inkjet printer 101, the viscosity of the ink, or the value obtained by actual measurement. It is. The ink flow rate per unit time in the purge pump 86 is less than the meniscus break flow rate, and when the ink is purged from the ejection port 108 later, the ink flow in the exhaust flow path 73 is abruptly blocked, thereby The ink pressure in the passage 73 and the ink inflow passage 72 suddenly rises, and the flow rate (recoverable flow rate) at which bubbles and foreign matters staying in the individual ink passage 132 can be discharged from the ejection port 108 together with the ink becomes higher. ing. The recoverable flow rate is a value obtained by actual measurement and is stored in advance. From another viewpoint, when the operation of the purge pump 86 is started with the circulation valve 87 closed so that the ink flow rate becomes a recoverable flow rate, bubbles and foreign matters staying in the individual ink flow path 132 are removed. The flow rate that can be discharged from all the ejection ports 108 together with the ink can also be called a recoverable flow rate. That is, when the purge pump 86 is driven at a flow rate less than the recoverable flow rate, the ink continues to be discharged only from the ejection port 108 related to the individual ink flow path 132 with less bubbles and thickened ink. Ink may not be discharged from all the ejection openings 108 together with air and foreign matter.

  As shown in FIG. 10, when the ink is circulated, the ink pressure in the ink inflow channel 72 and the exhaust channel 73 is higher than that during normal printing. 76 is in close contact with the restricting member 77, and the resin film 78 of the exhaust passage 73 is in close contact with the restricting member 79.

  Further, during the period when the atmosphere communication valve 88 is closed, the pressure in the sub tank 80 is negative. The negative pressure in the sub tank 80 causes the ink in the ink inflow passage 72 to be sucked into the sub tank 80 through the exhaust passage 73 and the atmosphere communication valve 88 is opened compared with the case where the ink is opened. It becomes difficult for the ink to flow into the outflow channel 75. This makes it difficult for meniscus breaks to occur. Therefore, the ink flow rate per unit time is increased so that the pressure in the ink inflow channel 72 is closer to the pressure at which the meniscus break occurs (meniscus break pressure) than when the atmosphere communication valve 88 is open. can do. In other words, if the pressure inside the circulating ink inflow passage 72 is the same, the ink flow rate is higher when the atmospheric communication valve 88 is closed than when the atmospheric communication valve 88 is open. When the atmospheric communication valve 88 is closed, the pressure in the ink inflow channel 72 during the purge period can be made larger than when the atmospheric communication valve 88 is open. Air and foreign matter staying in the ink flow path can be efficiently discharged from the ejection port 108 together with the ink. The ink flow rate per unit time exceeds the maximum amount at which ink does not leak from the ejection port 108 when the atmospheric communication valve 88 is open during ink circulation, and the atmospheric communication valve 88 is closed. It is below the maximum amount at which ink does not leak from the ejection port 108 when it is. In FIG. 11, the solid line waveform indicating the pressure change in the flow path related to the ink inflow flow path 72 is the case where the air supply valve 88 is closed during the ink circulation and the ink supply amount is increased as described above (this embodiment). ), And the broken line waveform indicates the pressure change in the flow path when the atmosphere communication valve 88 is open in the ink circulation (the ink supply amount is not increased). .

  After the ink flow rate per unit time in the purge pump 86 is stabilized above the recoverable flow rate, the circulation / purge control unit 44 closes the circulation valve 87 and simultaneously opens the air communication valve 88. Thus, the ink circulation is stopped (end of the circulation period), and the ink supplied to the ink inflow channel 72 flows into the ink outflow channel 75 without flowing into the exhaust channel 73, and the manifold channel 105 and each The ink sequentially passes through the individual ink flow path 132 and is discharged from the discharge port 108 (start of the purge period). The discharged ink is received by a waste liquid tray (not shown).

  As described above, the purge operation is started (impact purge) by closing the circulation valve 87 in a state where the ink flow per unit time in the purge pump 86 is equal to or higher than the recoverable flow rate, and the circulation valve 87 is closed. Immediately after the start of the purge, the ink pressure in the ink inflow channel 72 becomes high, and the thickened ink, the remaining bubbles and foreign matter in the discharge port 108 can be efficiently discharged from the discharge port 108. In this regard, as shown in FIG. 12, when such an impact purge is not performed, that is, without causing the ink to circulate, the purge pump 86 starts to be driven with the circulation valve 87 closed, and the discharge port 108 In the case of the conventional example in which ink is discharged (without impact purge), the time required for the ink pressure in each individual ink flow path 132 to exceed the pressure at which ink is discharged from all the ejection ports 108 becomes longer, Until this arrival time is reached, ink is discharged from the ejection port 108 wastefully. That is, since ink is discharged only from the ejection port 108 related to the individual ink flow path 132 with less bubbles and thickened ink, the ink is discharged wastefully. In addition, since the atmospheric communication valve 88 is opened at the same time as the circulation valve 87 is closed, the inside of the sub tank 80 is forcibly set to atmospheric pressure, and the pressure in the sub tank 80 is reduced as ink is discharged. Can be suppressed. If the atmosphere in the sub tank 80 is shut off when the ink is discharged, the ink does not flow into the sub tank 80, so that the pressure in the ink suddenly becomes negative as the ink is discharged. Although it is conceivable that the operation is hindered, the possibility of hindering the operation of the purge pump 86 can be eliminated by allowing the sub tank 80 to communicate with the atmosphere when the ink is discharged.

  As shown in FIG. 11, the head control unit 43 starts continuous supply of the ejection drive signal relating to the small droplets to the actuator unit 21 at the same time as the purge operation is started (start of the ejection drive period). ). As a result, a pressure that allows ink droplets to be ejected from the ejection ports 108 is continuously applied to the ink in all the individual ink flow paths 132. For this reason, pressure vibration is applied to the ink in the individual ink flow path 132, and bubbles and foreign matters fixed to the wall surface of the individual ink flow path 132 are peeled off from the wall surface and float. Air bubbles and foreign matter peeled off from the wall surface are ejected from the ejection port 108 together with the ink in the flow of ink related to the purge operation. The head control unit 43 stops the continuous supply of the discharge drive signal to the actuator unit 21 after a predetermined time has elapsed since the start of the continuous supply of the discharge drive signal (end of the discharge drive period). The head controller 43 drives the actuator unit 21 for a drive signal (including a discharge drive signal and an ink vibration signal) during a period from when the discharge drive period ends until a predetermined purge amount of ink is discharged from the discharge port 108. Is stopped (driving stop period).

  On the other hand, when a predetermined purge amount of ink is discharged from the discharge port 108 after the purge operation is started, the circulation / purge control unit 44 opens the circulation valve 87 and closes the air communication valve 88 again. This stops the purge operation (end of the purge period). Since the ink supply by the purge pump 86 continues, at the same time, the ink circulation is started again. The purge amount is determined by the ink flow rate per unit time in the purge pump 86 and the length of the purge period. The ink flow rate per unit time for discharging the predetermined purge amount and the length of the purge period are experimentally determined and stored in advance. The circulation / purge control unit 44 increases the circulation period as the temperature detected by the temperature sensor 35 increases or as the elapsed time detected by the non-ejection time detection unit 46 increases. Increase the purge amount.

  Further, the head controller 43 starts supplying the ink vibration signal at the same time as the purge period ends (start of the ink vibration period). Thereby, immediately after the purge operation is stopped, the flow of ink in the individual ink flow path 132 is quickly adjusted, and it is possible to prevent the ink from leaking wastefully from the ejection port 108.

  Thereafter, the circulation / purge control unit 44 stops the purge pump 86 and simultaneously opens the atmospheric communication valve 88. Thereby, ink circulation stops. At the same time, the head controller 43 stops supplying the ink vibration signal to the actuator unit 21 (end of the ink vibration period). Thereafter, the circulation / purge control unit 44 closes the circulation valve 87.

  As described above, by performing the ink circulation and the purge operation in order, the bubbles and foreign matters staying in the ink inflow passage 72 are removed from the downstream passage (the manifold passage 105 and the individual ink flow). The ink can be discharged out of the inkjet head 1 without flowing into the path 132 or the like.

  Next, when the wiping operation is started, the maintenance control unit 45 moves the four inkjet heads 1 upward by a moving mechanism (not shown), and then contacts the tips of the four wiper members 32 with the opposing ejection surface 2a. Each wiper member 32 is moved along the ejection surface 2a in the main scanning direction. As a result, excess ink adhering to the ejection surface 2a by the purge operation is removed, and the meniscus formed at the ejection port 108 is adjusted. After each discharge surface 2a is wiped, the maintenance control unit 45 returns the four wiper members 32 and each inkjet head 1 to their normal positions, and the circulation / purge control unit 44 opens the circulation valve 87. Thus, the wiping operation is completed.

  As described above, according to the ink jet printer 101 of the present embodiment, the pressure in the flow path from the purge pump 86 to the sub tank 80 in the circulation path is increased by performing ink circulation. By closing the circulation valve 87 in this state, the ink can be discharged from the ejection port 108 while instantaneously increasing the pressure in the flow path. As a result, since high pressure is applied to all the ejection openings 108 from the start of the purge and the ink is discharged, the thickened ink, bubbles and foreign matter in the ejection openings 108 can be efficiently discharged, and the ink can be discharged. Can be prevented from being discharged in vain. In addition, during the purge period, pressure vibration is applied to the ink in all the individual ink flow paths 132, so that bubbles and foreign matters fixed to the wall surfaces of the individual ink flow paths 132 are easily peeled off and discharged. The discharge characteristics at each discharge port 108 can be made uniform. For this reason, it is possible to efficiently discharge bubbles and foreign matter together with the thickened ink in the ejection port 108 while further suppressing the wasteful discharge of the ink.

  In addition, the circulation / purge control unit 44 closes the circulation valve 87 to stop the ink circulation, and at the same time, the head control unit 43 starts the continuous supply of the ejection drive signal to the actuator unit 21, so the purge operation is started. At the same time, application of pressure vibration to the ink in the individual ink flow path 132 is started. For this reason, from the beginning when ink is discharged from the ejection port 108, bubbles and foreign matters fixed to the wall surface of the individual ink flow path 132 are easily peeled off and discharged from the wall surface. As a result, it is possible to suppress the occurrence of the discharge ports 108 that are difficult to discharge ink, and to achieve uniform discharge characteristics at each discharge port 108. As a result, the liquid can be easily and stably discharged from all the discharge ports 108 from the beginning of discharge, and the ink can be further prevented from being discharged wastefully.

  Furthermore, since the drive stop period is provided after the discharge drive period ends in the purge period, the head controller 43 does not supply the discharge drive signal to the actuator unit 21 during the drive stop period, and the individual ink No new pressure vibration is generated in the flow path 132. For this reason, it is possible to suppress the pressure vibration from acting in a direction in which the ink in the individual ink flow path 132 is not discharged from the ejection port 108. Thereby, bubbles and foreign matters peeled off from the wall surface of the individual ink flow path 132 during the ejection drive period can be efficiently discharged from the ejection port 108 during the drive stop period.

  Further, since the head controller 43 supplies the actuator unit 21 with an ejection drive drive signal for ejecting a small ink droplet from the ejection port 108 in the ejection drive period, the ink from the ejection port 108 is ejected in the purge period. Discharge is promoted, and the discharge characteristics at each discharge port 108 can be made more uniform.

  Further, since the head controller 43 starts supplying the ink vibration signal to the actuator unit 21 at the same time as the purge period ends, the ink flow in the individual ink flow path 132 is quickly performed immediately after the purge operation is stopped. Thus, the ink is prevented from leaking wastefully from the ejection port 108.

  In addition, since the actuator unit 21 is a piezo-type actuator that generates ejection energy for ejecting ink droplets from the ejection port 108 and vibration energy that vibrates the ink in the individual ink flow path 132, vibration energy is reduced. There is no need to separately provide another mechanism for generating the ink jet head 1, and the cost of the inkjet head 1 can be reduced.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made as long as they are described in the claims. In the above-described embodiment, the head control unit 43 is configured to supply the ejection drive signal to the actuator unit 21 only in the ejection drive period from when the purge period starts until the predetermined time elapses. May be started after the purge period is started, may be ended simultaneously with the purge period, and further, the discharge drive period may coincide with the purge period.

  In the above-described embodiment, the head control unit 43 is configured to supply the ejection drive signal to the actuator unit 21 during the ejection drive period. In this period, the head control unit 43 supplies the ink vibration signal to the actuator unit 21. Alternatively, both the ejection drive signal and the ink vibration signal may be supplied.

  Furthermore, in the above-described embodiment, the head control unit 43 is configured to continuously supply an ejection drive signal that causes the actuator unit 21 to eject small ink droplets during the ejection drive period. It may be configured to continuously supply a discharge drive signal for discharging large ink droplets, or may be configured to supply any one of the discharge drive signals only once.

  Furthermore, in the above-described embodiment, the head controller 43 does not supply a drive signal to the actuator unit 21 in the circulation period before the purge period. However, in the circulation period before the purge period, the ink is supplied to the actuator unit 21. It may be configured to supply a vibration signal. Thereby, since the ink in the individual ink flow path 132 can be vibrated during the circulation period, bubbles and foreign matters fixed to the wall surface of the individual ink flow path 132 can be peeled off.

  In addition, in the above-described embodiment, the head control unit 43 is configured to supply the ink vibration signal to the actuator unit 21 at the same time as the purge period ends, but supplies the ink vibration signal after the purge period ends. Alternatively, the ink vibration signal may not be supplied.

  In the above-described embodiment, the actuator unit 21 includes an actuator that generates ejection energy for ejecting ink droplets from the ejection port 108, and an actuator that applies pressure vibration to the liquid in the individual ink flow path 132. Although it is the structure which serves also, the structure which provides actuators other than the actuator unit 21 separately and provides a pressure vibration with the said actuator may be sufficient.

  Further, in the above-described embodiment, the actuator unit 21 is a piezo actuator, but may be another type of actuator such as a thermal actuator.

  The present invention is also applicable to a recording apparatus that ejects liquid other than ink. Further, the present invention is not limited to a printer, and can be applied to a facsimile, a copier, and the like.

DESCRIPTION OF SYMBOLS 1 Inkjet head 16 Control apparatus 43 Head control part 44 Circulation / purge control part 72 Ink inflow path 72a Inlet 73 Exhaust path 73a Outlet 75 Ink outflow path 80 Sub tank 81 Ink supply pipe 82 Ink supply pipe 83 Ink return pipe 86 Purge pump 87 Circulation valve 88 Atmospheric communication valve 90 Ink tank 101 Inkjet printer 108 Discharge port 132 Individual ink flow path

Claims (5)

An inflow port through which the liquid flows in, an outflow port through which the liquid flows out, an internal flow path that connects the inflow port and the outflow port, a plurality of discharge ports for discharging the liquid, and a branch from the internal flow path A liquid discharge head having a plurality of individual liquid channels reaching the plurality of discharge ports, and pressure applying means for applying pressure to the liquid in the plurality of individual liquid channels;
A tank for storing therein the liquid supplied to the liquid discharge head;
A supply flow path communicating the inside of the tank and the inlet;
A return flow path communicating the inside of the tank and the outlet;
Supply means for forcibly supplying the liquid stored in the tank to the internal flow path via the supply flow path;
An adjusting means capable of adjusting a flow path resistance value in the return flow path between a predetermined minimum value and a predetermined maximum value;
Control means for controlling the pressure applying means, the supply means and the adjusting means,
The control means drives the supply means while reducing the flow path resistance value below the predetermined maximum value by adjusting the adjustment means, thereby supplying the liquid in the tank to the supply flow path, the internal flow path, and Circulate so as to be transferred in the order of the return flow path, during the circulation, by adjusting the adjustment means to increase the flow path resistance value, to discharge the liquid from the plurality of discharge ports, During the discharge, by adjusting the adjustment means to reduce the flow path resistance value, control to stop the discharge of the liquid from the plurality of discharge ports,
Further, the control means, at the same time when the discharge is started, the control the pressure applying means, to apply pressure vibration in the liquid in the plurality of individual liquid flow path, and the discharge is stopped The liquid ejecting apparatus is characterized in that the pressure applying means is controlled so as to stop applying the pressure vibration before the pressure is applied. When the discharge is started, the control means applies the pressure so as to apply a pressure when discharging one droplet from the plurality of discharge ports to the liquid in the plurality of individual liquid channels. The liquid ejecting apparatus according to claim 1, wherein the means is controlled.   When the discharge is started, the control means applies the pressure when discharging two or more droplets from the plurality of discharge ports to the liquid in the plurality of individual liquid channels. The liquid ejecting apparatus according to claim 1, wherein the applying unit is controlled.   The control means controls the pressure applying means so as to apply the pressure vibration without discharging liquid from the plurality of discharge ports after stopping the discharge. 4. The liquid ejection device according to any one of items 3.   5. The piezoelectric actuator according to claim 1, wherein the pressure applying unit is a piezo-type actuator that applies pressure for discharging liquid from the plurality of discharge ports to the liquid in the plurality of individual liquid channels. The liquid discharge apparatus according to claim 1.

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