JP5723610B2 - Inkjet recording device - Google Patents

Description

  The present invention relates to an ink jet recording apparatus that performs recording on a recording medium by discharging ink from an ink jet head.

  2. Description of the Related Art Conventionally, an ink circulation type ink jet recording apparatus that performs recording on a recording medium such as paper by discharging ink from nozzles of an ink jet head while circulating ink in an ink circulation path is known.

  Patent Documents 1 and 2 disclose an ink circulation type ink jet recording apparatus that sends ink from an ink tank to an ink jet head by an ink pump and collects ink that has not been consumed by the ink jet head into the ink tank.

  In order to perform normal ink ejection with an ink jet recording apparatus, it is necessary to maintain the pressure applied to the nozzles at an appropriate negative pressure to maintain the meniscus. In the ink jet recording apparatuses described in Patent Documents 1 and 2, the pressure in the ink tank is made negative by the pressure generated by the force of sucking out the ink in the ink tank by the ink pump, and thereby the pressure applied to the nozzles of the ink jet head is made negative. ing.

Japanese Patent Application Laid-Open No. 2004-230652 JP 2008-162285 A

  However, in the ink jet recording apparatuses described in Patent Documents 1 and 2, due to the pulsation of the ink pump, the negative pressure of the nozzle cannot be stably maintained, and ink ejection abnormality may occur.

  The present invention has been made in view of the above, and an object of the present invention is to provide an ink circulation type ink jet recording apparatus capable of suppressing ink ejection abnormality.

In order to achieve the above object, a first feature of an ink jet recording apparatus according to the present invention is that an ink jet head for discharging ink, a first tank for storing ink to be supplied to the ink jet head, and consumption by the ink jet head. A second tank for storing ink that has not been formed, a circulation path for circulating ink between the first tank, the inkjet head, and the second tank; An adjusting unit that adjusts the volume of the first air layer formed on the ink and the volume of the second air layer formed on the ink in the second tank; the first air layer; When the ink is circulated through the air path connected to the second air layer and the circulation path, the first and second tanks are sealed from the atmospheric pressure, and While controlling the adjustment portion such that the first air layer must maintain state volume is greater than the second air layer, sending air to the first air layer from the second air layer by the air pump And a control unit that controls the absolute value of the negative pressure in the second tank to be larger than the positive pressure in the first tank .

  A second feature of the ink jet recording apparatus according to the present invention is that it has an internal space communicating with the first air layer, and the volume of the internal space can be changed according to the change in the volume of the first air layer. A second air buffer unit having an internal space communicating with the first air buffer unit and the second air layer, the volume of the internal space being variable in accordance with a change in the volume of the second air layer It is in providing further.

  A third feature of the ink jet recording apparatus according to the present invention is that the first and second tanks are arranged such that the liquid level of the stored ink is lower than the ink discharge surface of the ink jet head. There is.

According to the first feature of the ink jet recording apparatus of the present invention, the control unit is configured such that the first air layer is the second airtight state from the atmospheric pressure of the first and second tanks during the ink circulation. While maintaining a state where the volume is larger than that of the air layer, by sending air from the second air layer to the first air layer, the negative pressure in the second tank is higher than the positive pressure in the first tank. The absolute value is controlled to be larger . Thus, to maintain a state in which the applied negative pressure to the nozzle of Lee inkjet head can be suppressed abnormal discharge of the ink.

  According to the second feature of the ink jet recording apparatus according to the present invention, the first and second air buffers can suppress the pressure fluctuation in the first and second tanks, and the negative pressure applied to the nozzles of the ink jet head 2. Therefore, ink can be ejected more stably.

  According to the third feature of the ink jet recording apparatus of the present invention, the first and second tanks are arranged such that the liquid level of the stored ink is lower than the ink discharge surface of the ink jet head. Therefore, it is possible to avoid overflow of ink from the nozzles of the inkjet head during standby.

1 is a schematic configuration diagram of an ink jet recording apparatus according to an embodiment. FIG. 2 is a detailed explanatory diagram of an upstream tank and a downstream tank in the ink jet recording apparatus shown in FIG. 1. FIG. 2 is a block diagram illustrating a configuration of a control system of the ink jet recording apparatus illustrated in FIG. 1. 3 is a flowchart for explaining an operation when ink circulation is performed in the ink jet recording apparatus shown in FIG. 1. 3 is a flowchart for explaining an operation when ink circulation is performed in the ink jet recording apparatus shown in FIG. 1. 3 is a flowchart for explaining an operation when ink circulation is performed in the ink jet recording apparatus shown in FIG. 1. 3 is a flowchart for explaining an operation when ink circulation is performed in the ink jet recording apparatus shown in FIG. 1. 3 is a flowchart for explaining an operation when ink circulation is performed in the ink jet recording apparatus shown in FIG. 1. It is a schematic block diagram of the inkjet recording device which concerns on the modification of embodiment.

  Embodiments of the present invention will be described below with reference to the drawings. Throughout the drawings, the same or equivalent parts and components are denoted by the same or equivalent reference numerals. However, it should be noted that the drawings are schematic and different from the actual ones.

  Further, the embodiment described below exemplifies an apparatus or the like for embodying the technical idea of the present invention, and the technical idea of the present invention is to arrange the components and the like as follows. It is not something specific. The technical idea of the present invention can be variously modified within the scope of the claims.

  FIG. 1 is a schematic configuration diagram of an ink jet recording apparatus according to an embodiment of the present invention, and FIG. 2 is a detailed explanatory diagram of an upstream tank and a downstream tank in the ink jet recording apparatus shown in FIG. In addition, the up-down direction in the following description is a vertical direction, and shall show the up-down direction shown in FIG.

  As shown in FIG. 1, an ink jet recording apparatus 1 according to the present embodiment includes an ink jet head 2, an upstream tank 3, a downstream tank 4, an ink bottle 5, an ink pump 6, an air pump 7, and an ink conduit. 8a-8d and air conduits 9a-9d.

  The inkjet head 2 records an image by ejecting ink supplied from the upstream tank 3 onto a recording medium such as paper. The inkjet head 2 includes a plurality of unit heads 21, a distributor 22, and an aggregator 23.

  The unit head 21 includes a plurality of nozzles, an ink chamber, and an ink ejection mechanism (none of which are shown). The ink ejection mechanism ejects ink from nozzles by, for example, deforming an ink chamber using a piezo element.

  The distributor 22 distributes the ink supplied from the upstream tank 3 through the ink conduit 8 a to each unit head 21.

  The aggregator 23 collects ink that has not been consumed by the ink ejection operation in each unit head 21. The ink collected by the collector 23 is collected into the downstream tank 4 through the ink conduit 8b.

  The upstream tank 3 stores ink to be supplied to the inkjet head 2. The ink in the upstream tank 3 is supplied to the inkjet head 2 through the ink conduit 8a. Ink is supplied to the upstream tank 3 from the downstream tank 4 through the ink conduit 8 c by driving the ink pump 6. The upstream tank 3 corresponds to the first tank of the claims.

  In the upstream tank 3, an air layer 32 is formed on the liquid surface 31 of the ink stored inside. The air layer 32 corresponds to a first air layer in the claims. The upstream tank 3 is configured to be open to the atmospheric pressure through an air conduit 9 a communicating with the air layer 32.

  The upstream tank 3 is provided at substantially the same height as the downstream tank 4, and is lower (lower) than the ink discharge surface (nozzle surface) 21 a of the unit head 21 of the inkjet head 2 even when the ink liquid level 31 is the highest. Position).

  The upstream tank 3 is provided with an upstream lower limit sensor 33 and an upstream upper limit sensor 34. The upstream side lower limit sensor 33 outputs a signal indicating ON when the height HA of the ink liquid surface 31 in the upstream tank 3 is equal to or higher than the height Ha1 that is the lower limit value, and is less than the height Ha1. A signal indicating OFF is output. The upstream upper limit sensor 34 outputs a signal indicating ON when the height HA of the liquid level 31 is equal to or higher than the upper limit height Ha2, and outputs a signal indicating OFF when the height HA is less than the height Ha2. To do. Here, Ha2> Ha1.

  The downstream tank 4 stores ink that has not been consumed by the ejection operation by the inkjet head 2. The downstream tank 4 stores ink supplied from the ink bottle 5 through the ink conduit 8d. The downstream tank 4 corresponds to the second tank of the claims.

  In the downstream tank 4, an air layer 42 is formed on the liquid level 41 of ink stored inside. The air layer 42 corresponds to a second air layer in the claims. The downstream tank 4 is configured to be open to atmospheric pressure through an air conduit 9 b communicating with the air layer 42.

  The downstream tank 4 is provided at substantially the same height as the upstream tank 3, and is disposed so as to be lower than the ink discharge surface 21 a of the inkjet head 2 even when the ink liquid level 41 is the highest. Further, the downstream tank 4 is disposed below the ink bottle 5.

  The downstream tank 4 is provided with a downstream lower limit sensor 43 and a downstream upper limit sensor 44. The downstream side lower limit sensor 43 outputs a signal indicating ON when the height HB of the ink liquid level 41 in the downstream tank 4 is equal to or higher than the lower limit height Hb1, and is lower than the height Hb1. A signal indicating OFF is output. The downstream upper limit sensor 44 outputs a signal indicating ON when the height HB of the liquid level 41 is equal to or higher than the upper limit height Hb2, and outputs a signal indicating OFF when the height HB2 is less than the height Hb2. To do. Here, Hb2> Hb1.

  In the present embodiment, the upstream tank 3 and the downstream tank 4 are constituted by tanks having substantially the same shape. Therefore, for example, if the height HA of the liquid surface 31 of the upstream tank 3 and the height HB of the liquid surface 41 of the downstream tank 4 are the same, the volume of ink stored in both tanks and the air layers 32 and 42 are stored. Are equal in volume. In the present embodiment, as will be described later, the heights HA and HB of the liquid surfaces 31 and 41 are maintained while the air layer 32 of the upstream tank 3 has a larger volume than the air layer 42 of the downstream tank 4 during ink circulation. Is adjusted to maintain a constant value. The above-described upstream lower limit sensor 33, upstream upper limit sensor 34, downstream lower limit sensor 43, and downstream upper limit sensor 44 adjust the heights HA and HB of the liquid surfaces 31 and 41 as described above. And is used for adjusting the volume of the air layers 32 and 42. For this reason, each sensor is arrange | positioned so that it may become Hb2> Hb1> Ha2> Ha1.

  The ink bottle 5 holds ink used for recording in the ink jet recording apparatus 1. The ink bottle 5 is provided above the upstream tank 3 and the downstream tank 4. An air layer 52 is formed on the ink liquid surface 51 in the ink bottle 5. The ink bottle 5 is configured to be openable to atmospheric pressure through an air conduit 9 c communicating with the air layer 52. When the ink supply atmosphere release valve 93 provided in the air conduit 9c is opened and the inside of the ink bottle 5 is opened to the atmospheric pressure, the ink in the ink bottle 5 is supplied to the downstream tank 4 via the ink conduit 8d. .

  The ink pump 6 moves ink between the upstream tank 3 and the downstream tank 4 via the ink conduit 8c. The ink pump 6 is provided in the middle of the ink conduit 8c. The ink pump 6 sends ink from the downstream tank 4 to the upstream tank 3 when driven in the forward direction, and sends ink from the upstream tank 3 to the downstream tank 4 when driven in the reverse direction. The ink pump 6 adjusts the volume of the air layers 32 and 42 by adjusting the heights HA and HB of the liquid surfaces 31 and 41 of the upstream tank 3 and the downstream tank 4. The ink pump 6 corresponds to an adjustment unit in claims.

  The air pump 7 sends air from the air layer 42 of the downstream tank 4 to the air layer 32 of the upstream tank 3 during ink circulation. The air pump 7 is connected to the air layer 32 of the upstream tank 3 and the air layer 42 of the downstream tank 4 via the air conduit 9d.

  The ink conduit 8 a connects the upstream tank 3 and the distributor 22 of the inkjet head 2. Ink flows from the upstream tank 3 toward the distributor 22 in the ink conduit 8a.

  The ink conduit 8 b connects the collector 23 of the inkjet head 2 and the downstream tank 4. Ink flows from the collector 23 toward the downstream tank 4 in the ink conduit 8b.

  The ink conduit 8 c connects the upstream tank 3 and the downstream tank 4. Ink that moves between the upstream tank 3 and the downstream tank 4 flows through the ink conduit 8 c by driving the ink pump 6.

  The ink conduits 8 a to 8 c constitute an ink circulation path 10 for circulating ink between the upstream tank 3, the inkjet head 2, and the downstream tank 4. During the ink circulation, the ink flows in the direction indicated by the arrow A through the ink circulation path 10.

  The ink conduit 8 d connects the ink bottle 5 and the downstream tank 4. Ink supplied from the ink bottle 5 to the downstream tank 4 flows through the ink conduit 8d.

  One end of the air conduit 9a is connected to the air layer 32 of the upstream tank 3, and the other end communicates with the atmosphere. The air conduit 9a is provided with an upstream air release valve 91 that opens and closes the air flow path in the pipe. When the upstream air release valve 91 is opened, the upstream tank 3 is opened to atmospheric pressure.

  One end of the air conduit 9b is connected to the air layer 42 of the downstream tank 4, and the other end communicates with the atmosphere. The air conduit 9b is provided with a downstream air release valve 92 that opens and closes the air flow path in the pipe. When the downstream air release valve 92 is opened, the downstream tank 4 is opened to atmospheric pressure.

  One end of the air conduit 9c is connected to the air layer 52 of the ink bottle 5, and the other end communicates with the atmosphere. The air conduit 9c is provided with an ink supply atmosphere release valve 93 that opens and closes an air flow path in the pipe. When the ink supply atmosphere release valve 93 is opened, the ink bottle 5 is opened to the atmospheric pressure.

  One end of the air conduit 9 d is connected to the air layer 32 of the upstream tank 3, and the other end is connected to the air layer 42 of the downstream tank 4. An air pump 7 is provided in the middle of the air conduit 9d. Air flows through the air conduit 9 d from the air layer 42 of the downstream tank 4 toward the air layer 32 of the upstream tank 3 by driving the air pump 7.

  FIG. 3 is a block diagram showing the configuration of the control system of the inkjet recording apparatus 1. As shown in FIG. 3, the ink jet recording apparatus 1 includes a control unit 11.

  The control unit 11 includes a CPU, a ROM, a RAM (all not shown), and the like. The control unit 11 controls the operations of the inkjet head 2, the ink pump 6, the air pump 7, the upstream atmosphere release valve 91, the downstream atmosphere release valve 92, and the ink supply atmosphere release valve 93. Outputs from the upstream lower limit sensor 33, the upstream upper limit sensor 34, the downstream lower limit sensor 43, and the downstream upper limit sensor 44 are guided to the control unit 11.

  The control unit 11 closes the upstream side air release valve 91 and the downstream side air release valve 92 during the ink circulation (at the time of the recording operation) so that the upstream tank 3 and the downstream tank 4 are sealed from the atmospheric pressure. Then, the control unit 11 controls the ink pump 6 so that the air layer 32 of the upstream tank 3 maintains a larger volume than the air layer 42 of the downstream tank 4, while the air pump 7 controls the air layer 32 from the air layer 42. Control to send air to. Thereby, ink circulation is performed while the negative pressure applied to the nozzles of the inkjet head 2 is properly maintained.

  Next, the operation of the inkjet recording apparatus 1 will be described.

  4 to 8 are flowcharts for explaining the operation when the ink circulation is performed in the ink jet recording apparatus 1.

  The ink jet recording apparatus 1 performs ink circulation when performing a recording operation. The processing in the flowcharts of FIGS. 4 to 8 is started when the inkjet recording apparatus 1 is instructed to start recording. Note that while the ink jet recording apparatus 1 is not performing ink circulation, the upstream atmosphere release valve 91 and the downstream atmosphere release valve 92 are opened, and the ink supply atmosphere release valve 93 is closed.

  First, in step S10, the control unit 11 determines that the condition that “the upstream side lower limit sensor 33 and the downstream side lower limit sensor 43 are ON and the upstream side upper limit sensor 34 and the downstream side upper limit sensor 44 are OFF” Judgment) is satisfied. When it is determined that the liquid level condition is satisfied (step S10: YES), the control unit 11 proceeds to step S20. When it is determined that the liquid level condition is not satisfied, the control unit 11 proceeds to step S170 in FIG. Here, when the liquid level condition is satisfied, Ha1 ≦ HA <Ha2 and Hb1 ≦ HB <Hb2.

  In step S <b> 20, the control unit 11 controls to close both the upstream atmosphere release valve 91 and the downstream atmosphere release valve 92. Thereby, the upstream tank 3 and the downstream tank 4 will be in the sealing state from atmospheric pressure.

  Next, in step S <b> 30, the control unit 11 starts driving the air pump 7. As a result, air is sent from the air layer 42 of the downstream tank 4 to the air layer 32 of the upstream tank 3, so that the air layer 32 of the upstream tank 3 becomes pressurized and the air layer 42 of the downstream tank 4 becomes decompressed. Become. As a result, the circulation of the ink from the upstream tank 3 to the downstream tank 4 via the ink conduit 8a, the inkjet head 2, and the ink conduit 8b starts.

  Here, when the upstream atmosphere release valve 91 and the downstream atmosphere release valve 92 are closed when the liquid level condition is satisfied, the air layer 32 of the upstream tank 3 has a volume larger than the air layer 42 of the downstream tank 4. Becomes a large state. In this state, when air moves from the air layer 42 to the air layer 32 by driving the air pump 7, the absolute value of the negative pressure PB in the downstream tank 4 becomes larger than the positive pressure PA in the upstream tank 3. . Since the pressure VN applied to the nozzles of the inkjet head 2 is expressed by the following equation (1), the pressure VN is a negative pressure when the absolute value of the negative pressure PB is larger than the positive pressure PA.

VN = (RB / (RA + RB)) × (PA + PB) (1)
Here, RA is a flow path resistance from the upstream tank 3 to the nozzle of the inkjet head 2, and RB is a flow path resistance from the nozzle of the inkjet head 2 to the downstream tank 4.

  Accordingly, the positive pressure PA and the negative pressure PB are set appropriately by setting the heights Ha2, Ha1, Hb2, Hb1, the rotation speed of the air pump 7 (the air flow rate by the air pump 7), and the like, and are applied to the nozzles of the inkjet head 2. Negative pressure can be set appropriately. Thereby, normal ink discharge from the nozzles of the inkjet head 2 becomes possible.

  Next, in step S40, the control unit 11 starts an operation of ejecting ink from the inkjet head 2 based on the image data. Ink is supplied from the upstream tank 3 to the inkjet head 2 via the ink conduit 8a, and ink that has not been consumed by the ink discharge operation of the unit head 21 flows to the downstream tank 4 via the ink conduit 8b.

  During the ink circulation, the ink moves from the upstream tank 3 to the downstream tank 4. As a result, the height HA of the liquid surface 31 of the upstream tank 3 is decreased, and the height HB of the liquid surface 41 of the downstream tank 4 is varied to be increased. Due to such fluctuations in the heights HA and HB of the liquid surfaces 31 and 41, the positive pressure PA in the upstream tank 3 becomes smaller and the absolute value of the negative pressure PB in the downstream tank 4 becomes larger than when the ink circulation is started. Fluctuate as follows. If the heights HA and HB of the liquid surfaces 31 and 41 deviate from the initial ranges of Ha1 ≦ HA <Ha2 and Hb1 ≦ HB <Hb2, the pressure VN applied to the nozzles of the inkjet head 2 will not be appropriate.

  Further, the amount of circulating ink is reduced by the ink ejection operation in the inkjet head 2. For this reason, ink replenishment may be required during ink circulation.

  Therefore, the control unit 11 maintains the heights HA and HB of the liquid surfaces 31 and 41 in the range of Ha1 ≦ HA <Ha2 and Hb1 ≦ HB <Hb2 during the ink circulation. In addition, the ink replenishment atmosphere release valve 93 is controlled.

  In step S50, the control unit 11 determines whether or not the downstream side upper limit sensor 44 is ON.

  When it is determined that the downstream upper limit sensor 44 is ON (step S50: YES), in step S60, the control unit 11 starts the forward rotation driving of the ink pump 6. As a result, ink is sent from the downstream tank 4 to the upstream tank 3. Thereafter, the control unit 11 returns to step S50.

  When it is determined that the downstream upper limit sensor 44 is OFF (step S50: NO), in step S70, the control unit 11 determines whether or not the ink pump 6 is being driven.

  When it is determined that the ink pump 6 is being driven (step S70: YES), the control unit 11 stops the ink pump 6 in step S80. Thereby, the movement of the ink from the downstream tank 4 to the upstream tank 3 is completed. Thereafter, the control unit 11 proceeds to step S90. If it is determined that the ink pump 6 is not being driven (step S70: NO), the controller 11 proceeds directly to step S90.

  In step S90, the control unit 11 determines whether or not the upstream side lower limit sensor 33 is in an OFF state for a preset specified time or more.

  If it is determined that the upstream side lower limit sensor 33 is in the OFF state for the specified time or longer (step S90: YES), the control unit 11 controls to open the ink supply atmosphere release valve 93 in step S100. As a result, replenishment of ink from the ink bottle 5 to the downstream tank 4 via the ink conduit 8d is started. Thereafter, the control unit 11 returns to step S50.

  When it is determined that the upstream lower limit sensor 33 is not in the OFF state for a predetermined time (step S90: NO), the control unit 11 determines whether or not the ink supply atmosphere release valve 93 is opened in step S110 of FIG. Judging.

  When it is determined that the ink supply atmosphere release valve 93 is open (step S110: YES), in step S120, the control unit 11 controls the ink supply atmosphere release valve 93 to be closed. As a result, the ink supply from the ink bottle 5 to the downstream tank 4 is stopped. Thereafter, the control unit 11 proceeds to step S130. When it is determined that the ink supply atmosphere release valve 93 is closed (step S110: NO), the control unit 11 proceeds to step S130 as it is.

  In step S130, the control unit 11 determines whether ink ejection based on the image data has been completed.

  If it is determined that ink ejection has not ended (step S130: NO), the controller 11 returns to step S50 in FIG. When it is determined that ink ejection has been completed (step S130: YES), the control unit 11 stops the air pump 7 in step S140.

  Next, in step S150, the control unit 11 performs control to open the upstream air release valve 91. Thereafter, in step S160, the control unit 11 performs control to open the downstream side air release valve 92. Thus, the ink circulation is completed.

  On the other hand, when it is determined in step S10 that the liquid level condition is not satisfied (step S10: NO), the control unit 11 opens the ink pump 6 and the ink supply atmosphere before the ink circulation starts as described below. By adjusting the valve 93, the liquid level condition is adjusted.

  When it is determined that the liquid level condition is not satisfied (step S10: NO), in step S170 of FIG. 6, the control unit 11 determines whether or not the upstream upper limit sensor 34 and the downstream upper limit sensor 44 are ON. to decide.

  When it is determined that the upstream upper limit sensor 34 and the downstream upper limit sensor 44 are ON (step S170: YES), the control unit 11 ends the process as an error. In this case, even if ink is moved between the upstream tank 3 and the downstream tank 4 by the ink pump 6, it cannot be adjusted so that the liquid level condition is satisfied.

  If it is determined that at least one of the upstream upper limit sensor 34 and the downstream upper limit sensor 44 is OFF (step S170: NO), in step S180, the control unit 11 determines whether the upstream lower limit sensor 33 is OFF. Judge whether or not.

  When determining that the upstream lower limit sensor 33 is ON (step S180: NO), the controller 11 proceeds to step S320 in FIG.

  When it is determined that the upstream side lower limit sensor 33 is OFF (step S180: YES), in step S190, the control unit 11 starts the forward rotation driving of the ink pump 6. As a result, ink is sent from the downstream tank 4 to the upstream tank 3.

  Next, in step S200, the control unit 11 determines whether or not the upstream side lower limit sensor 33 is ON.

  When it is determined that the upstream lower limit sensor 33 is OFF (step S200: NO), in step S210, the control unit 11 determines whether the downstream lower limit sensor 43 is OFF.

  When determining that the downstream side lower limit sensor 43 is ON (step S210: NO), the control unit 11 returns to step S200. When it is determined that the downstream lower limit sensor 43 is OFF (step S210: YES), in step S220, the control unit 11 controls to open the ink supply atmosphere release valve 93. As a result, replenishment of ink from the ink bottle 5 to the downstream tank 4 via the ink conduit 8d is started. Thereafter, the control unit 11 returns to step S200.

  When it is determined in step S200 that the upstream side lower limit sensor 33 is ON (step S200: YES), the control unit 11 stops the ink pump 6 in step S230. Thereby, the movement of the ink from the downstream tank 4 to the upstream tank 3 is completed.

  Next, in step S240, the control unit 11 determines whether or not the downstream side lower limit sensor 43 is OFF.

  When it is determined that the downstream lower limit sensor 43 is OFF (step S240: YES), in step S250, the control unit 11 determines whether or not the ink supply atmosphere release valve 93 is open.

  When it is determined that the ink supply atmosphere release valve 93 is closed (step S250: NO), in step S260, the control unit 11 controls to open the ink supply atmosphere release valve 93. As a result, replenishment of ink from the ink bottle 5 to the downstream tank 4 via the ink conduit 8d is started. Thereafter, the control unit 11 proceeds to step S270. When it is determined that the ink supply atmosphere release valve 93 is open (step S250: YES), the control unit 11 proceeds to step S270 as it is.

  In step S270, the control unit 11 determines whether or not the downstream side lower limit sensor 43 is ON.

  When it is determined that the downstream lower limit sensor 43 is OFF (step S270: NO), the control unit 11 repeats the process of step S270. When it is determined that the downstream side lower limit sensor 43 is ON (step S270: YES), the control unit 11 determines that the liquid level condition is satisfied, and in step S280, the ink supply atmosphere release valve is set. 93 is controlled to close. As a result, the ink supply from the ink bottle 5 to the downstream tank 4 is stopped. Thereafter, the control unit 11 proceeds to step S20 in FIG. 4 and performs the subsequent processing.

  On the other hand, when it is determined in step S240 that the downstream side lower limit sensor 43 is ON (step S240: NO), in step S290 in FIG. 7, the control unit 11 determines whether or not the ink supply atmosphere release valve 93 is open. Judging.

  When it is determined that the ink supply atmosphere release valve 93 is open (step S290: YES), in step S300, the control unit 11 controls the ink supply atmosphere release valve 93 to close. As a result, the ink supply from the ink bottle 5 to the downstream tank 4 is stopped. Thereafter, the control unit 11 proceeds to step S310. If it is determined that the ink replenishment atmosphere release valve 93 is closed (step S290: NO), the controller 11 proceeds directly to step S310.

  In step S310, the control unit 11 determines whether or not the downstream side upper limit sensor 44 is OFF.

  When it is determined that the downstream upper limit sensor 44 is OFF (step S310: YES), the control unit 11 determines that the liquid level condition is satisfied, and proceeds to step S20 in FIG. Perform the process. When it is determined that the downstream upper limit sensor 44 is ON (step S310: NO), the control unit 11 ends the process as an error because the liquid level condition is not satisfied.

  In step S320 of FIG. 8, the control unit 11 determines whether or not the upstream side upper limit sensor 34 is ON. When it is determined that the upstream upper limit sensor 34 is ON (step S320: YES), the control unit 11 proceeds to step S330, and when it is determined that the upstream upper limit sensor 34 is OFF (step S320: NO), The process proceeds to step S360.

  In step S330, the control unit 11 starts reverse rotation driving of the ink pump 6. As a result, ink is sent from the upstream tank 3 to the downstream tank 4.

  Next, in step S340, the control unit 11 determines whether or not the upstream side upper limit sensor 34 is OFF. When it is determined that the upstream upper limit sensor 34 is ON (step S340: NO), the control unit 11 repeats the process of step S340.

  If it is determined that the upstream upper limit sensor 34 is OFF (step S340: YES), the control unit 11 stops the ink pump 6 in step S350. Thereby, the movement of the ink from the upstream tank 3 to the downstream tank 4 is completed. Thereafter, the control unit 11 proceeds to step S360.

  In step S360, the control unit 11 determines whether the downstream side upper limit sensor 44 is OFF.

  If it is determined that the downstream upper limit sensor 44 is ON (step S360: NO), the control unit 11 ends the process as an error because the liquid level condition is not satisfied.

  If it is determined that the downstream upper limit sensor 44 is OFF (step S360: YES), in step S370, the control unit 11 determines whether or not the downstream lower limit sensor 43 is OFF.

  When it is determined that the downstream side lower limit sensor 43 is ON (step S370: NO), the control unit 11 determines that the liquid level condition is satisfied, and proceeds to step S20 in FIG. Perform the process.

  If it is determined that the downstream side lower limit sensor 43 is OFF (step S370: YES), in step S380, the control unit 11 controls to open the ink supply atmosphere release valve 93. As a result, replenishment of ink from the ink bottle 5 to the downstream tank 4 via the ink conduit 8d is started.

  Next, in step S390, the control unit 11 determines whether or not the downstream side lower limit sensor 43 is ON. When it is determined that the downstream lower limit sensor 43 is OFF (step S390: NO), the control unit 11 repeats the process of step S390.

  If it is determined that the downstream side lower limit sensor 43 is ON (step S390: YES), the control unit 11 determines that the liquid level condition is satisfied, and in step S400, the ink replenishment atmosphere release valve. 93 is controlled to close. As a result, the ink supply from the ink bottle 5 to the downstream tank 4 is stopped. Thereafter, the control unit 11 proceeds to step S20 in FIG. 4 and performs the subsequent processing.

  As described above, in the ink jet recording apparatus 1 according to the present embodiment, when the ink circulation is started, the upstream side air release valve 91 and the downstream side air are satisfied in a state where Ha1 ≦ HA <Ha2 and Hb1 ≦ HB <Hb2. Open valve 92 is closed. As a result, the volume of the air layer 32 of the upstream tank 3 is larger than that of the air layer 42 of the downstream tank 4. In this state, air is moved from the air layer 42 to the air layer 32 by the air pump 7, so that the air layer 32 is in a pressurized state and the air layer 42 is in a reduced pressure state. At this time, the absolute value of the negative pressure PB in the downstream tank 4 is larger than that of the positive pressure PA in the upstream tank 3. As a result, a negative pressure is applied to the nozzles of the inkjet head 2. The ink jet recording apparatus 1 maintains the negative pressure applied to the nozzles of the ink jet head 2 by controlling Ha1 ≦ HA <Ha2 and Hb1 ≦ HB <Hb2 while driving the air pump 7 during ink circulation. can do. Thereby, in the ink-jet head 2, abnormal ink ejection can be suppressed and normal ink ejection can be achieved.

  Since the inkjet recording apparatus 1 does not generate a negative pressure in the downstream tank 4 by the suction / discharge pressure of the ink pump 6, the negative pressure applied to the nozzles of the inkjet head 2 is unstable due to the pulsation of the ink pump 6. Never become.

  Further, in the inkjet recording apparatus 1, the negative pressure applied to the nozzles of the inkjet head 2 can be properly maintained even if the rotation speed of the air pump 7 is fixed. For this reason, drive control of the air pump 7 is easy.

  In the ink jet recording apparatus 1, the upstream tank 3 and the downstream tank 4 are arranged such that the ink liquid levels 31 and 41 are below (lower position) than the ink ejection surface 21 a of the ink jet head 2. Thereby, even if both tanks are opened to the atmosphere during standby, it is possible to prevent ink from overflowing from the nozzles of the inkjet head 2.

  In the ink jet recording apparatus 1, as described above, control is performed to maintain Ha1 ≦ HA <Ha2 and Hb1 ≦ HB <Hb2 during ink circulation. However, a change in the heights HA and HB of the liquid surfaces 31 and 41 of the upstream tank 3 and the downstream tank 4 accompanying the ink circulation, and a pressure fluctuation in each tank corresponding thereto occur. In order to reduce such pressure fluctuation, for example, large tanks may be used as the upstream tank 3 and the downstream tank 4. As the volume is larger, changes in the heights HA and HB of the liquid surfaces 31 and 41 and fluctuations in pressure in each tank are suppressed to a smaller level.

  Further, by reducing the distance between the upstream lower limit sensor 33 and the upstream upper limit sensor 34 and the distance between the downstream lower limit sensor 43 and the downstream upper limit sensor 44, the height of the liquid surfaces 31, 41 is increased. The fluctuation range of the lengths HA and HB can be reduced, and as a result, the fluctuation of the pressure in each tank can be kept small.

(Modification)
FIG. 9 is a schematic configuration diagram of an ink jet recording apparatus according to a modification of the embodiment of the present invention.

  As shown in FIG. 9, the inkjet recording apparatus 1 </ b> A according to this modification is different from the inkjet recording apparatus 1 of FIG. 1 in that air conduits 9 e and 9 f, an upstream pressure adjustment unit 12, a downstream pressure adjustment unit 13, and It is the structure which added.

  One end of the air conduit 9e is connected to the air conduit 9a, and the other end is connected to the upstream pressure adjusting unit 12. One end of the air conduit 9e is connected to the air conduit 9a on the upstream tank 3 side from the upstream atmosphere release valve 91.

  The air conduit 9 f has one end connected to the air conduit 9 b and the other end connected to the downstream pressure adjusting unit 13. One end of the air conduit 9f is connected to the air conduit 9b on the downstream tank 4 side from the downstream side atmospheric release valve 92.

  The upstream pressure adjusting unit 12 is for suppressing the fluctuation of the pressure in the upstream tank 3 during ink circulation. The upstream pressure adjusting unit 12 is installed between a pair of fixed plates 14 and 15 fixed in the ink jet recording apparatus 1 </ b> A at a predetermined interval in the vertical direction. The upstream pressure adjustment unit 12 includes an air buffer unit 121 and a pressing spring 122.

  The air buffer unit 121 includes a bellows 123, a top plate 124 that closes the upper end of the bellows 123, and a bottom plate 125 that closes the lower end of the bellows 123. The air buffer unit 121 corresponds to a first air buffer unit of the claims.

  The top plate 124 is fixed to the upper fixing plate 14, and the other end side of the air conduit 9 e passes through the fixing plate 14 and the top plate 124, and the interior of the air buffer unit 121 formed by the bellows 123, the top plate 124, and the bottom plate 125. Open to space. As a result, the internal space of the air buffer 121 communicates with the air layer 32 of the upstream tank 3 via the air conduits 9e and 9a. The bellows 123 is made of an elastic member and can be expanded and contracted in the vertical direction. The volume of the internal space of the air buffer 121 varies according to the expansion and contraction of the bellows 123.

  The push spring 122 has one end connected to the bottom plate 125 and the other end connected to the lower fixing plate 15. The push spring 122 applies an elastic force in the contraction direction to the bellows 123.

  The downstream pressure adjusting unit 13 is for suppressing fluctuations in pressure in the downstream tank 4 during ink circulation. The downstream pressure adjusting unit 13 is installed between a pair of fixed plates 16 and 17 fixed in the ink jet recording apparatus 1 </ b> A at a predetermined interval in the vertical direction. The downstream pressure adjustment unit 13 includes an air buffer unit 131 and a tension spring 132.

  The air buffer unit 131 includes a bellows 133, a top plate 134 that closes the upper end of the bellows 133, and a bottom plate 135 that closes the lower end of the bellows 133. The air buffer 131 corresponds to the second air buffer of the claims.

  The top plate 134 is fixed to the upper fixed plate 16, and the other end side of the air conduit 9 f penetrates the fixed plate 16 and the top plate 134, and the inside of the air buffer unit 131 formed by the bellows 133, the top plate 134, and the bottom plate 135. Open to space. As a result, the internal space of the air buffer 131 communicates with the air layer 42 of the downstream tank 4 via the air conduits 9f and 9b. The bellows 133 is made of an elastic member and can be expanded and contracted in the vertical direction. The volume of the internal space of the air buffer 131 varies according to the expansion and contraction of the bellows 133.

  The tension spring 132 has one end connected to the bottom plate 135 and the other end connected to the lower fixing plate 17. The tension spring 132 imparts an elastic force in the extension direction to the bellows 133.

  The ink circulation operation of the ink jet recording apparatus 1A of the present modification is the same as that of the ink jet recording apparatus 1 of FIG. That is, when starting ink circulation, the ink jet recording apparatus 1A closes the upstream atmosphere release valve 91 and the downstream atmosphere release valve 92 in a state where Ha1 ≦ HA <Ha2 and Hb1 ≦ HB <Hb2.

  At this time, in the ink jet recording apparatus 1 </ b> A, the sum of the volume of the air layer 32 of the upstream tank 3 and the volume of air in the air buffer unit 121 of the upstream pressure adjusting unit 12 is the volume of the air layer 42 of the downstream tank 4. It is made to be in a state larger than the sum of the volume of air in the air buffer part 131 of the downstream pressure adjusting part 13.

  In this state, the air pump 7 moves air from the air layer 42 to the air layer 32, so that the air layer 32 and the air buffer unit 121 communicating with the air layer 32 are in a pressurized state, and the air layer 42 and the air buffer communicating with the air layer 42. The inside of the part 131 is in a reduced pressure state, and ink circulation is started. At this time, as described above, the total of the volume of the air layer 32 and the volume of air in the air buffer unit 121 is larger than the total of the volume of the air layer 42 and the volume of air in the air buffer unit 131. The absolute value of the negative pressure PB in the downstream tank 4 is larger than that of the positive pressure PA in the upstream tank 3. As a result, a negative pressure is applied to the nozzles of the inkjet head 2. Then, the ink jet recording apparatus 1A performs control to maintain Ha1 ≦ HA <Ha2 and Hb1 ≦ HB <Hb2 while driving the air pump 7 during ink circulation.

  During the ink circulation, the inside of the air buffer 121 is pressurized together with the air layer 32 of the upstream tank 3, and the bellows 123 expands from the initial state. And the balance is maintained in the state where the force which the bellows 123 expand | extends by the inside of the air buffer part 121 being pressurized, and the elastic force of the pushing spring 122 balance.

  When the height HA of the liquid surface 31 of the upstream tank 3 decreases due to the ink circulation, the volume of the air layer 32 increases and the positive pressure PA in the upstream tank 3 decreases. However, since the bellows 123 contracts in accordance with this, the volume of the internal space of the air buffer unit 121 is reduced, so that the sum of the volume of the air layer 32 and the volume of air in the air buffer unit 121 is kept constant. As a result, the fluctuation of the positive pressure PA in the upstream tank 3 is suppressed to be small.

  On the other hand, on the downstream tank 4 side, during the ink circulation, the inside of the air buffer 131 is decompressed together with the air layer 42, and the bellows 133 contracts from the initial state. Then, the pressure in the air buffer 131 is reduced, and the balance is maintained in a state where the force of contracting the bellows 133 and the elastic force of the tension spring 132 are balanced.

  When the height HB of the liquid surface 41 of the downstream tank 4 increases due to ink circulation, the volume of the air layer 42 decreases. However, since the bellows 133 expands accordingly and the volume of the internal space of the air buffer unit 131 increases, the sum of the volume of the air layer 42 and the volume of air in the air buffer unit 131 is kept constant. As a result, the fluctuation of the negative pressure PB in the downstream tank 4 is suppressed to be small.

  As described above, according to the ink jet recording apparatus 1A of this modification, the upstream pressure adjusting unit 12 and the downstream pressure adjusting unit 13 cause the positive pressure PA in the upstream tank 3 and the negative pressure in the downstream tank 4 during ink circulation. The fluctuation of the pressure PB can be suppressed small. Thereby, it is possible to further reduce the fluctuation of the negative pressure applied to the nozzles of the inkjet head 2. As a result, the ink jet recording apparatus 1 </ b> A can eject ink more stably.

DESCRIPTION OF SYMBOLS 1,1A Inkjet recording device 2 Inkjet head 3 Upstream tank 4 Downstream tank 5 Ink bottle 6 Ink pump 7 Air pump 8a-8d Ink conduit 9a-9f Air conduit 10 Ink circulation path 11 Control unit 12 Upstream pressure adjustment unit 13 Downstream pressure Adjustment unit 31, 41 Liquid level 32, 42 Air layer 33 Upstream lower limit sensor 34 Upstream upper limit sensor 43 Downstream lower limit sensor 44 Downstream upper limit sensor 91 Upstream air release valve 92 Downstream air release valve 121, 131 Air buffer unit

Claims (3)

An inkjet head that ejects ink;
A first tank for storing ink to be supplied to the inkjet head;
A second tank for storing ink that has not been consumed by the inkjet head;
A circulation path for circulating ink between the first tank, the inkjet head, and the second tank;
An adjusting unit that adjusts the volume of the first air layer formed on the ink in the first tank and the volume of the second air layer formed on the ink in the second tank;
An air pump connected to the first air layer and the second air layer;
During the ink circulation through the circulation path, the first air layer maintains a larger volume than the second air layer in a sealed state from the atmospheric pressure of the first and second tanks. By controlling the adjustment unit and sending air from the second air layer to the first air layer by the air pump , the positive pressure in the second tank is compared with the positive pressure in the first tank. An ink jet recording apparatus, comprising: a control unit that controls the absolute value of the negative pressure to be larger . A first air buffer unit having an internal space communicating with the first air layer, the volume of the internal space being variable in accordance with a change in the volume of the first air layer;
A second air buffer section having an internal space communicating with the second air layer, the volume of the internal space being variable in accordance with a change in the volume of the second air layer. The inkjet recording apparatus according to claim 1.   3. The inkjet according to claim 1, wherein the first and second tanks are disposed so that a liquid level of ink to be stored is lower than an ink discharge surface of the inkjet head. Recording device.