JP4682758B2 - Droplet discharge device - Google Patents

Description

  The present invention relates to a droplet discharge device that discharges droplets.

  In a droplet discharge apparatus such as an ink jet recording apparatus, bubbles present in a droplet discharge head and in a liquid channel cause discharge failure and increase in channel resistance. For this reason, conventionally, a liquid is circulated between a tank open to the atmosphere and a droplet discharge head, and bubbles are collected in the tank and released to the atmosphere (for example, Patent Documents 1 to 3). 3).

  By the way, when a droplet discharge head unit having a droplet discharge area longer than the width of the recording medium (the length in the direction orthogonal to the transport direction) is formed by connecting a plurality of droplet discharge heads There is. In this case, the liquid supply from the tank to each droplet discharge head and the liquid reflux from each droplet discharge head to the tank may be performed by individual liquid flow paths for each droplet discharge head. In order to suppress the variation in the circulation amount of the liquid for each droplet discharge head, it is desirable to carry out with a common liquid flow path for the plurality of droplet discharge heads.

Here, a common liquid flow path capable of circulating the liquid between the tank and the plurality of liquid droplet ejection heads is divided into a main flow path connected to the tank and the main flow path, and each liquid droplet ejection head. However, there is a problem that bubbles are stagnated at the branch point between the main channel and the branch channel and cannot be removed. This occurs when the buoyancy of bubbles in the branch channel extending in the vertical direction and the pressure of the liquid flowing downward in the branch channel are balanced. This problem can be solved by increasing the amount of liquid circulation. However, when the amount of liquid circulation is increased, the pressure in the liquid flow path increases and bubbles are sucked from the nozzles.
JP-A-8-276604 JP 2000-33714 A Japanese Patent Laid-Open No. 2003-19816

  The present invention has been made in consideration of the above facts, and prevents bubbles from staying in the branch flow path without increasing the amount of liquid circulation.

The droplet discharge device according to claim 1 is a plurality of droplet discharge heads for discharging droplets, a tank for storing liquid, a first main channel having one end inserted into the tank, and the first A plurality of first branch channels that branch off from the main channel and extend downward to insert each tip into each droplet discharge head; and one end portion is inserted into the tank; A second main flow path in which the other end is joined to the first main flow path, and a plurality of second branch flow paths that branch downward from the second main flow path and extend downward to be inserted into each droplet discharge head. And a liquid flows from the droplet discharge head to the tank in the first liquid channel and from the tank to the droplet discharge head in the second liquid channel. Circulating means for circulating liquid between the droplet discharge head and the tank , Bei example, the circulating means is provided in the first main flow path, the negative pressure generating means for circulating a liquid by generating a negative pressure, and, upstream and downstream of the circulating direction from said negative pressure generating means The flow rate of the liquid is reduced while the liquid is circulated by controlling the on / off of the negative pressure generating means and the opening / closing of the on / off valve. It is characterized by making it.

  In the liquid droplet ejection apparatus according to claim 1, the plurality of liquid droplet ejection heads are communicated with the tank storing the liquid by the first liquid channel and the second liquid channel, and the first unit is provided by the circulation unit. The liquid is circulated between the droplet discharge head and the tank by flowing the liquid from the droplet discharge head to the tank in the liquid channel and from the tank to the droplet discharge head in the second liquid channel. Thereby, the bubbles in the first liquid channel and the second liquid channel are collected in the tank.

  The first liquid channel is composed of a first main channel having one end inserted into the tank, and a first branch channel branched from the first main channel and having the tip inserted into each droplet discharge head. Similarly, the second liquid flow path includes a second main flow path having one end inserted therein, and a second branch flow path branched from the second main flow path and having a tip portion inserted into each droplet discharge head. It consists of In addition, the other end of the second main channel joins the first main channel. For this reason, when the circulation means is operated, the liquid flows from each droplet discharge head to the first main flow path via each first branch flow path, and then flows to the tank. Further, the liquid branches from the tank to each second branch channel via the second main channel, flows to each droplet discharge head, and flows to the first main channel via the second main channel. To do.

  By the way, each of the second branch channels extends downward from the second main channel, and the tip portion is inserted into each droplet discharge head. For this reason, when the pressure of the liquid flowing downward in the second branch channel exceeds the buoyancy of the bubble, the bubble moves in the order of the droplet discharge head and the first branch channel. Each first branch channel extends downward from the first main channel and has a tip inserted into each droplet discharge head. Therefore, the bubbles flowing from the droplet discharge head to the first branch flow path receive the buoyancy of the bubbles and the pressure of the liquid flowing upward, move to the first main flow path, and pass through the first main flow path. And move to the tank.

  On the other hand, when the buoyancy of the bubbles exceeds the pressure of the liquid flowing downward in the second branch flow path, or the flow of the liquid stops, the bubbles move from the second branch flow path to the second main flow path. .

  Further, when the buoyancy of the bubbles and the pressure of the liquid flowing downward are balanced in the second branch channel, the bubbles stagnate and adhere to the second branch channel.

Here, in the present invention, the circulation means is provided in the first main flow path, generates negative pressure to circulate the liquid, and the upstream and downstream sides in the circulation direction from the negative pressure generation means. The flow rate of the liquid can be reduced during the circulation of the liquid by controlling on / off of the negative pressure generating means and opening / closing of the on / off valve. Decrease. As a result, when the buoyancy of the bubble and the pressure of the liquid flowing downward are balanced in the second branch flow channel while the liquid is being circulated, this equilibrium relationship is lost and the buoyancy of the bubble is reduced. Since the pressure downward due to the liquid is overcome, the bubbles move from the second branch channel to the second main channel. And it moves to a 1st main flow path from a 2nd main flow path, and is collect | recovered by a tank.

  Accordingly, it is possible to prevent the bubbles from staying in the second branch flow path without increasing the liquid circulation amount, thereby preventing further bubbles from being mixed from the droplet discharge head.

Further , a negative pressure is generated by the negative pressure generating means provided in the first main flow path, so that the liquid flows from the droplet discharge head to the tank in the first liquid flow path, and from the tank in the second liquid flow path. The liquid flows to the droplet discharge head or the first main channel.

  Here, the circulation of the liquid by the negative pressure increases the volume of the bubbles stagnating in the first liquid channel and the second liquid channel, so that the bubbles are easily subjected to the pressure due to the flow of the liquid. Air bubbles easily move in the liquid channel and the second liquid channel. Therefore, the bubble removability is improved.

The apparatus according to claim 2 is the liquid droplet ejecting apparatus according to claim 1, wherein the circulation means, said on-off valve closed, a first step of turning on the negative pressure generator After the first step, the on-off valve is opened, the second step of turning off the negative pressure generating means, and after the second step, the on-off valve is closed and the negative pressure generating means is turned on. A third step and a fourth step of opening the on-off valve and turning off the negative pressure generating means after the third step are performed.

In the droplet discharge device according to the second aspect, first, in the first step, the on-off valve is closed and the negative pressure generating means is turned on. As a result, the flow rate of the liquid becomes maximum, the bubbles in the first liquid channel and the second liquid channel move toward the tank, and adhere to the inner walls of the first liquid channel and the second liquid channel. Air bubbles are peeled off.

  Note that the time from the start of the first step to the start of the second step is longer than the time for the liquid to make a round of the first liquid channel and the second liquid channel, and all the bubbles peeled off from the inner wall are in the first step. In this step, the bubbles may be removed from the inner wall by shortening the time.

  In the second step after the first step, the on-off valve is opened and the negative pressure generating means is turned off. This stops the liquid flow downward in the second branch flow path, so that if the bubbles are stagnant in the second branch flow path, the bubbles move to the second main flow path by buoyancy.

  In a third step after the second step, the on-off valve is closed and the negative pressure generating means is turned on. As a result, the bubbles moved from the second branch flow path to the second main flow path in the second step move from the second main flow path to the first main flow path, and move to the tank via the first main flow path. Further, the bubbles peeled off from the inner walls of the first liquid channel and the second liquid channel in the first step also move to the tank via the second liquid channel and the first liquid channel.

  In the fourth step after the third step, the on-off valve is opened, the negative pressure generating means is turned off, and the liquid circulation is stopped.

The apparatus according to claim 3 is the liquid droplet ejecting apparatus according to claim 1, wherein the circulation means, on the negative pressure generator, a first step of the on-off valve in the closed A second step of opening the on-off valve after the first step; a third step of closing the on-off valve after the second step; and a third step of closing the on-off valve after the third step. Opening, and a fourth step of turning off the negative pressure generating means.

In the droplet discharge device according to the third aspect, first, in the first step, the negative pressure generating means is turned on and the on-off valve is closed. As a result, the flow rate of the liquid becomes maximum, the bubbles in the first liquid channel and the second liquid channel move toward the tank, and adhere to the inner walls of the first liquid channel and the second liquid channel. Air bubbles are peeled off.

  In the second step after the first step, the on-off valve is opened. As will be described in detail later, a part of the liquid circulates in the bypass flow path, and the amount of liquid circulation in the first liquid flow path and the second liquid flow path decreases. When the bubbles are stagnant, the bubbles move to the second main flow path by buoyancy.

  Then, in the third step after the second step, the on-off valve is closed, and contrary to the second step, the circulation amount of the liquid in the first liquid channel and the second liquid channel increases, Bubbles that have moved from the branch flow path to the second main flow path move from the second main flow path to the first main flow path, and then move to the tank via the first main flow path. Further, the bubbles peeled off from the inner walls of the first liquid channel and the second liquid channel in the first step also move to the tank via the second liquid channel and the first liquid channel.

  Here, in the second step, the flow of the liquid is not stopped, and the bubbles that have moved from the second branch flow path to the second main flow path are directed to the first main flow path without stopping in the second main flow path. Therefore, the time required to move the bubbles to the tank can be shortened, and the time required for the third step can be shortened.

  In the fourth step after the third step, the on-off valve is opened, the negative pressure generating means is turned off, and the liquid circulation is stopped.

The droplet discharge device according to claim 4 is the droplet discharge device according to claim 1 , wherein the circulation unit is configured to turn on the negative pressure generation unit and close the on-off valve. After the first step, the second step of turning off the negative pressure generating means, the third step of turning on the negative pressure generating means after the second step, and the third step, And performing a fourth step of turning off the negative pressure generating means and opening the on-off valve.

In the droplet discharge device according to the fourth aspect, first, in the first step, the negative pressure generating means is turned on and the on-off valve is closed. As a result, the flow rate of the liquid becomes maximum, the bubbles in the first liquid channel and the second liquid channel move toward the tank, and adhere to the inner walls of the first liquid channel and the second liquid channel. Air bubbles are peeled off.

  Then, in the second step after the first step, the negative pressure generating means is turned off. This stops the liquid flow downward in the second branch flow path, so that if the bubbles are stagnant in the second branch flow path, the bubbles move to the second main flow path by buoyancy.

  Here, in the second step, since the bypass flow path is closed by the on-off valve, the negative pressure in the first liquid flow path is released compared to the state in which the bypass flow path is opened by the on-off valve. The time until the liquid flow is stopped. This makes it difficult for bubbles to adhere to the inner walls of the first liquid channel and the second liquid channel.

  Then, in the third step after the second step, the negative pressure generating means is turned on, the flow of the liquid is restarted, and the bubbles that have moved from the second branch flow path to the second main flow path are removed from the second main flow path. It moves to one main flow path and moves to the tank via the first main flow path. Further, the bubbles peeled off from the inner walls of the first liquid channel and the second liquid channel in the first step also move to the tank via the second liquid channel and the first liquid channel.

  In the fourth step after the third step, the on-off valve is opened, the negative pressure generating means is turned off, and the liquid circulation is stopped.

  Since the present invention is configured as described above, it is possible to prevent bubbles from staying in the second branch flow path without increasing the amount of liquid circulation.

  Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 shows an ink jet recording apparatus 12 of the present embodiment. A paper feed tray 16 is provided in the lower part of the casing 14 of the ink jet recording apparatus 12, and the sheets P stacked in the paper feed tray 16 can be taken out one by one by a pickup roll 18. The taken paper P is transported by a plurality of transport roller pairs 20 constituting a predetermined transport path 22.

  Above the paper feed tray 16, an endless transport belt 28 stretched around a drive roll 24 and a driven roll 26 is disposed. A recording head array 30 is disposed above the conveyor belt 28 and faces the flat portion 28F of the conveyor belt 28. This opposed area is an ejection area SE where ink droplets are ejected from the recording head array 30. The sheet P transported along the transport path 22 is held by the transport belt 28 and reaches the discharge area SE, and ink droplets corresponding to image information are attached from the recording head array 30 in a state of facing the recording head array 30. The

  In this embodiment, the recording head array 30 has a long shape in which the effective recording area is equal to or larger than the width of the paper P (the length in the direction orthogonal to the transport direction), and is yellow (Y) and magenta (M). , Sian (S), and four inkjet recording head units (hereinafter referred to as head units) 32 corresponding to the four colors of black (K) are arranged along the transport direction so that a full-color image can be recorded. It has become.

  Each head unit 32 is controlled by a head controller 60 (see FIG. 5). For example, the head controller 60 is configured to determine an ink droplet ejection timing and an ink ejection port (nozzle) to be used according to image information and send a drive signal to the head unit 32.

  The recording head array 30 may be stationary in a direction orthogonal to the transport direction. However, if the recording head array 30 is configured to move as necessary, an image with higher resolution can be obtained by multi-pass image recording. Can be recorded, or troubles of the head unit 32 can be prevented from being reflected in the recording result.

  Four maintenance units 34 corresponding to the respective head units 32 are arranged on both sides of the recording head array 30. As shown in FIG. 2, when performing maintenance on the head unit 32, the recording head array 30 moves upward, and the maintenance unit 34 moves into the gap formed between the conveyance belt 28 and enters. Then, a predetermined maintenance operation (suction, wiping, capping, etc.) is performed while facing the nozzle surface 33N (see FIG. 8).

  As shown in FIG. 3, the maintenance unit 34 includes a cap 88 that receives ink from the nozzle surface 33 </ b> N during the recovery operation of the inkjet recording apparatus 12, and a drain line 92 that discharges the ink received by the cap 88. . A waste ink tank 96 is provided at the downstream end of the drain line 92 in the discharge direction via a valve 94. In addition, the ink jet recording apparatus 12 includes a pump 98 that provides an ink feeding output (ink suction force) from the cap 88 to the drainage line 92. The pump 98 is controlled by a controller 56 (see FIG. 5) that controls the entire inkjet recording apparatus 12, as is the pump 74 described later.

  In this embodiment, the four maintenance units 34 are divided into two sets of two, and are arranged on the upstream side in the transport direction and the downstream side in the transport direction of the recording head array 30 during image recording.

  As shown in FIG. 4, a charging roll 36 connected to a power source 38 is disposed on the upstream side of the recording head array 30. The charging roll 36 is driven while sandwiching the conveyance belt 28 and the paper P with the driven roll 26, and moves between a pressing position for pressing the paper P against the conveyance belt 28 and a separation position separated from the conveyance belt 28. It is possible. At the pressing position, a predetermined potential difference is generated between the grounded driven roll 26 and the sheet P can be charged and electrostatically attracted to the transport belt 28. Further, a peeling plate 40 is disposed on the downstream side of the recording head array 30, and the paper P is peeled from the transport belt 28 by the peeling plate 40.

  Between the conveyance belt 28 and the paper discharge tray 46, an ink tank 54 for storing each of the four colors of ink and a reservoir tank 64 connected to the ink tank 54 are provided. The reservoir tank 64 is provided with an atmosphere release portion 65 (see FIG. 6), and the liquid level of the reservoir tank 64 is at atmospheric pressure. The ink in the reservoir tank 64 is supplied to each head unit 32 via a first ink channel 69 and a second ink channel 70 (both see FIG. 6) described later. As the ink, various known inks such as water-based ink, oil-based ink, and solvent-based ink can be used.

  As shown in FIG. 5, the entire inkjet recording apparatus 12 is controlled by a controller 56, and operations including image recording, discharging, and maintenance from feeding of a sheet P are controlled. Various data relating to the recorded image is sent from the image controller 58 to the controller 56. An ink jet recording head 33 (see FIG. 6; hereinafter referred to as a recording head), which will be described later, is controlled by a head controller 60, and a signal is transmitted from the controller 56 to the head controller 60. The controller 56, the head controller 60, and the charging roll 36 are supplied with power from a power source 38.

  In the ink jet recording apparatus 12 of the present embodiment configured as described above, the paper P taken out from the paper feed tray 16 is transported to the transport belt 28 as described above. The paper P is pressed against the conveyance belt 28 by the charging roll 36 and is attracted and held by the conveyance belt 28 by the voltage applied from the charging roll 36. In this state, while the paper P passes through the ejection area SE by the rotation of the transport belt 28, ink droplets are ejected from the recording head array 30, and an image is recorded on the paper P. Then, the paper P is peeled off from the transport belt 28 by the peeling plate 40, transported by a plurality of discharge roller pairs 42 constituting the discharge path 44 on the downstream side of the peeling plate 40, and discharged at the upper part of the housing 14. It is discharged to the paper tray 46.

  Here, the configuration of the head unit 32 will be described. Here, only one head unit 32 is illustrated and described, but all the head units 32 have the same configuration.

  As shown in FIGS. 6 and 7, the head unit 32 includes a plurality of (eight in the present embodiment) recording heads 33 that are shorter than the width of the paper P along the width direction of the paper P. Has been. As shown in FIG. 8, the recording heads 33 are attached to the lower surface of the support plate 35 extending along the width direction of the paper P so as to form a staggered arrangement.

  As shown in FIGS. 6 and 7, the recording head 33 is formed with a plurality of ink chambers 72 and ejection nozzles 78 (see FIG. 8) communicating with the ink chambers 72. Ink droplets are ejected at an increased pressure. That is, as shown in FIG. 8, the lower surface side of the recording head 33 is a discharge surface, and a large number of discharge nozzles 78 are arranged along the width direction of the paper P.

  As shown in FIGS. 6 and 7, the ink jet recording apparatus 12 is provided with a first ink channel 69 and a second ink channel 70 that connect the ink chamber 72 and the reservoir tank 64. A pump 74 and an on-off valve 76 are connected in parallel to the first ink channel 69.

  The pump 74 generates a negative pressure on the ink chamber 72 side to apply a fluid force from the ink chamber 72 to the reservoir tank 64 to the ink. That is, when the pump 74 is operated, the ink flows from each recording head 44 to the first main flow path 79 via each first branch flow path 81 and then flows to the reservoir tank 64. Further, the ink branches from the reservoir tank 64 via the second main flow path 80 to the respective second branch flow paths 82 and flows to the respective recording heads 33, and the first main flow via the second main flow path 80. It flows to the main flow path 79.

  Here, the circulation of the ink by the negative pressure increases the volume of the bubbles stagnating in the first ink channel 69 and the second ink channel 70, so that the bubbles are easily subjected to the pressure due to the flow of the ink, Air bubbles easily move in the first ink channel 69 and the second ink channel 70. Therefore, the bubble removability is improved.

  The pump 74 is controlled by the controller 56 as described above. The on-off valve 76 is provided in a bypass flow path 77 that bypasses the upstream side in the circulation direction and the downstream side in the circulation direction from the pump 74 of the first main flow path 79, and is controlled by the controller 56.

  The first ink channel 69 has a first main channel 79 with one end inserted into the reservoir tank 64 and a first main channel 79 branched downward from the first main channel 79 and extending downward into each ink chamber 72. 1 branch channel 81. The second ink flow path 70 is branched from the second main flow path 80 having one end inserted into the reservoir tank 64 and the other end merged with the first main flow path 79 and the second main flow path 80. And a second branch channel 82 having a leading end inserted into each ink chamber 72.

  At the time of ink ejection shown in FIG. 6, the pump 74 is stopped and the on-off valve 76 is opened. Then, the ink chamber 72 is depressurized by the ejection of ink droplets, so that the ink flows from the reservoir tank 64 to the ink chamber 72 in both the first ink channel 69 and the second ink channel 70. As a result, the ink flows into the ink chamber 72 from the two ink flow paths, so that the pressure loss is reduced by half compared to the case of one ink flow path, and the allowable pressure loss value by each ink flow path is reduced to about It becomes possible to set to 2 times. Therefore, the volume of the pipe can be reduced, and thus the apparatus can be reduced in size and cost. In addition, when the ink is circulated, which will be described later, the flow rate becomes faster, and the pump 74 does not need excessive performance, so the pump 74 can be downsized.

  Here, a first embodiment of a method for controlling the pump 74 and the on-off valve 76 during ink circulation shown in FIG. 7 will be described with reference to the flowchart of FIG.

  First, in step 100, it is determined whether there is an ink circulation command. If the determination is affirmative, the process proceeds to step 102. In step 102, the head unit 32 is raised, the maintenance unit 34 is moved to the maintenance position, and the nozzle surface 33N of the recording head 33 is capped.

  Next, in step 104, the pump 74 is turned on, the on-off valve 76 is closed, and is maintained for 10 [sec]. Due to the circulation of the ink for 10 [sec], the ink flow rate (flow velocity) is maximized, the bubbles in the first ink channel 69 and the second ink channel 70 move toward the reservoir tank 64, and Bubbles attached to the inner walls of the first ink channel 69 and the second ink channel 70 are peeled off. Further, the bubbles in the first branch flow path 81 are moved into the first main flow path 79 in response to the pressure of the bubble buoyancy and the flow of ink, and are moved to the reservoir tank 64.

  Note that the time from the start of step 104 to the start of the next step 106 is made longer than the time for the ink to make a round of the first ink flow path 69 and the second ink flow path 70, and all the bubbles peeled off from the inner wall are removed. It may be collected in the reservoir tank 64 in this step, or the time may be shortened until the bubbles are peeled off from the inner wall in this step.

  Here, the suction pressure of the pump 74 is set so that the pressure in the first ink channel 69 and the second ink channel 70 becomes a pressure at which bubbles are not sucked from the discharge nozzle 78 (so-called meniscus holding pressure). ing. In this embodiment, the nozzle diameter of the discharge nozzle 78 is 25 μm, the surface tension of the ink is 30 mN / m, and the meniscus holding pressure is −3.7 kPa.

  For this reason, it is not essential to circulate ink while the nozzle surface 33N of the recording head 33 is capped.

  Next, in step 106, the on-off valve 76 is opened, the pump 74 is turned off, and is maintained for 6 [sec]. In this state, the upstream side in the circulation direction of the first ink channel 69 from the pump 74 is communicated with the reservoir tank 64 by the bypass channel 77, so that the negative pressure in the first ink channel 69 is immediately released, The flow of ink in the first ink channel 69 and the second ink channel 70 is stopped.

  Here, when the pressure P due to the flow of ink and the buoyancy S of the bubbles H are balanced, the bubbles H are stagnating in the second branch flow path 82 (see FIG. 10A), 6 [ In the second branch flow path 82, the downward flow of ink stops in the second branch flow path 82, and the equilibrium relationship is broken and the buoyancy S overcomes the pressure P. 2 Moves to the main channel 80 (see FIG. 10B).

  Next, in step 108, the on-off valve 76 is closed, the pump 74 is turned on, and is maintained for 24 [sec]. Due to the circulation of the ink during 24 [sec], the bubbles moved from the second branch flow path 82 to the second main flow path 80 in Step 106 move from the second main flow path 80 to the first main flow path 79, It moves to the tank via the first main flow path 79 (see FIG. 10C). In addition, the bubbles peeled off from the inner walls of the first ink channel 69 and the second ink channel 70 in step 104 also move to the reservoir tank 64 via the second liquid channel and the first liquid channel.

  Next, at step 110, the on-off valve 76 is opened, the pump 74 is turned off, the ink circulation is stopped, and the routine proceeds to step 112. In step 112, the maintenance unit 34 is moved from the maintenance position to the non-maintenance position, the head unit 32 is lowered, and the cap of the nozzle surface 33N of the recording head 33 is released. Then, the processing routine ends.

  Next, a second embodiment of a method for controlling the pump 74 and the on-off valve 76 during ink circulation will be described with reference to the flowchart of FIG.

  First, in step 200, it is determined whether there is an ink circulation command. If the determination is affirmative, the process proceeds to step 202. In step 202, the head unit 32 is raised, the maintenance unit 34 is moved to the maintenance position, and the nozzle surface 33N of the recording head 33 is capped.

  Next, in step 204, the pump 74 is turned on, and the routine proceeds to step 206. In step 206, the on-off valve 76 is closed and maintained for 10 [sec]. As a result, the ink flow rate becomes maximum, the bubbles in the first ink flow path 69 and the second ink flow path 70 move toward the reservoir tank 64, and the first ink flow path 69 and the second ink flow path. Bubbles adhering to the inner wall of the path 70 are peeled off.

  Next, in step 208, the on-off valve 76 is opened and maintained for 10 [sec]. During this 10 [sec], a part of the ink circulates in the bypass channel 77 as shown in FIG. In addition, the entire ink flow path constituted by the first ink flow path 69 and the second ink flow path 70 and the recording head 33 and the bypass flow path 77 have the same flow path resistance. As shown by the equation (1), the ink circulation amount Q2 in the ink flow path is about ½ compared with the case where the bypass flow path 77 is closed by the on-off valve 76.

Q2 = (R2 / (R1 + R2)) × Q1 (1)
Q1: Ink flow rate when the on-off valve 76 is closed Q2: Ink flow rate when the on-off valve 76 is open R1: Consists of the first ink channel 69 and the second ink channel 70 and the recording head 33 The flow path resistance of the entire ink flow path R2: the flow path resistance of the bypass flow path 77 By this, the pressure P caused by the flow of the ink and the buoyancy S of the air bubbles H are balanced, so that the air bubbles H Is stagnant (see FIG. 10A), the flow rate of the ink downward in the second branch flow path 82 is reduced, the equilibrium relationship is broken, and the buoyancy S overcomes the pressure P. The buoyancy S moves to the second main channel 80 (see FIG. 10B).

  If the flow path resistance of the ink flow path changes greatly due to the opening and closing of the bypass flow path 77, the flow rate of the pump 74 fluctuates and the above equation (1) is not satisfied. As a result, the flow rate of the ink in the ink flow path cannot be controlled, so that the change in the flow path resistance of the ink flow path due to the opening and closing of the bypass flow path 77 is suppressed to the extent that the pump flow rate does not fluctuate.

  In step 210, the on-off valve 76 is closed and maintained for 20 [sec]. As a result, in contrast to step 208, the ink flow rate increases, and the bubbles that have moved from the second branch flow path 82 to the second main flow path 80 move from the second main flow path 80 to the first main flow path 79. It moves to the reservoir tank 64 via the first main flow path 79. In addition, the bubbles peeled off from the inner walls of the first ink channel 69 and the second ink channel 70 in step 206 also move to the reservoir tank 64 via the second ink channel 70 and the first ink channel 69. .

  Here, in step 208, the flow of ink is not stopped, and the bubbles that have moved from the second branch flow path 82 to the second main flow path 80 do not stop in the second main flow path 80, so that the first main flow path Since it moves toward 79, the time required to move the bubbles to the reservoir tank 64 can be shortened, and the time required for step 210 can be shortened. In the first embodiment, it takes 24 [sec] to move the bubbles to the reservoir tank 64, but in the present embodiment, it can be shortened to 20 [sec].

  Next, at step 212, the on-off valve 76 is opened, and the routine proceeds to step 214. In step 214, the pump 74 is turned off and ink circulation is stopped. Then, the processing routine ends.

  Next, a third embodiment of a method for controlling the pump 74 and the on-off valve 76 during ink circulation will be described with reference to the flowchart of FIG.

  First, in step 300, it is determined whether there is an ink circulation command. If the determination is affirmative, the process proceeds to step 302. In step 302, the head unit 32 is raised, the maintenance unit 34 is moved to the maintenance position, and the nozzle surface 33N of the recording head 33 is capped.

  Next, in step 304, the pump 74 is turned on, and the routine proceeds to step 306. In Step 306, the on-off valve 76 is closed and maintained for 10 [sec]. As a result, the ink flow rate becomes maximum, the bubbles in the first ink flow path 69 and the second ink flow path 70 move toward the reservoir tank 64, and the first ink flow path 69 and the second ink flow path. Bubbles adhering to the inner wall of the path 70 are peeled off.

  Next, in step 308, the pump 74 is turned off and maintained for 8 [sec]. As a result, the flow of the ink in the downward direction in the second branch flow path 82 stops, so that if the air bubbles are stagnating in the second branch flow path 82, the air bubbles move to the second main flow path 80 by buoyancy. To do.

  Next, in step 310, the pump 74 is turned on and maintained for 24 [sec]. As a result, the flow of ink is resumed, and the bubbles that have moved from the second branch flow path 82 to the second main flow path 80 move from the second main flow path 80 to the first main flow path 79, and pass through the first main flow path 79. Then, it moves to the reservoir tank 64. Further, the bubbles peeled off from the inner walls of the first ink channel 69 and the second ink channel 70 in step 304 also move to the reservoir tank 64 via the second ink channel 70 and the first ink channel 69. .

  Here, in step 306, until the bypass flow path 77 is closed by the on-off valve 76, the negative pressure in the ink flow path is released compared to the state in which the bypass flow path 77 is opened by the on-off valve 76. The time will be longer. As a result, the time until the ink flow is stopped becomes longer, and bubbles are less likely to adhere to the inner walls of the first ink channel 69 and the second ink channel 70.

  Next, in step 308, the pump 74 is turned off to stop ink circulation, and the process proceeds to step 310. In step 310, the on-off valve is opened and the processing routine is terminated.

  As described above by taking this embodiment as an example, it is possible to prevent the bubbles from staying in the second branch flow path 82 without increasing the amount of ink circulation, so that further bubbles are mixed from the recording head 33. Can be prevented.

  In the present embodiment, negative pressure is generated in the ink flow path by the pump 74 and the ink is circulated. However, the flow rate (flow velocity) of ink from the reservoir tank 64 to the recording head 33 in the second ink flow path 70 is high. The present invention can also be applied to a configuration in which a positive pressure is generated in the ink flow path to circulate the ink.

  In the present embodiment, the present invention has been described by taking an inkjet recording apparatus as an example. However, the droplet ejection apparatus of the present invention is not limited to an inkjet recording head unit, and ejects colored ink on a polymer film or glass. Manufacturing color filters for display, forming bumps for component mounting by discharging molten solder onto the substrate, forming EL display panels by discharging organic EL solution onto the substrate, molten state It can be applied to general droplet discharge units intended for various industrial applications such as the formation of bumps for electrical mounting performed by discharging the solder on the substrate.

  In addition, the “recording medium” that is the target of image recording in the droplet discharge device of the present invention includes a wide range of objects as long as the droplet discharge unit is a target that discharges droplets. Therefore, the recording medium includes a recording sheet, an OHP sheet, and the like, but also includes, for example, a substrate on which a wiring pattern or the like is formed.

1 is a diagram showing an outline of an ink jet recording apparatus according to an embodiment of the present invention. 1 is a diagram showing an outline of an ink jet recording apparatus according to an embodiment of the present invention. 1 is a diagram illustrating an outline of a maintenance unit of an ink jet recording apparatus according to an embodiment of the present invention. It is a figure which shows the outline of the printing part of the inkjet recording device of embodiment of this invention. FIG. 2 is a block diagram illustrating a configuration of a control system of the ink jet recording apparatus according to the embodiment of the present invention. It is a figure which shows the flow of the ink at the time of the ink discharge in the inkjet recording device of embodiment of this invention. It is a figure which shows the flow of the ink at the time of the ink circulation in the inkjet recording device of embodiment of this invention. It is a top view which shows the structure of the inkjet recording head unit of the inkjet recording device of embodiment of this invention. 3 is a flowchart for explaining a first embodiment of a pump and on / off valve control method during ink circulation in the ink jet recording apparatus according to the embodiment of the present invention. (A), (B) is a figure which shows the motion of the bubble in the ink flow path of the inkjet recording device of embodiment of this invention. It is a figure which shows the flow of the ink at the time of the ink circulation in the inkjet recording device of embodiment of this invention. 6 is a flowchart for explaining a second embodiment of a pump and on / off valve control method during ink circulation in the ink jet recording apparatus according to the embodiment of the present invention. 6 is a flowchart for explaining a third embodiment of a pump and on / off valve control method during ink circulation in the ink jet recording apparatus according to the embodiment of the present invention.

Explanation of symbols

12 Inkjet recording device (droplet ejection device)
28 Conveying belt (conveying means)
33 Inkjet recording head (droplet ejection head)
56 controller (first control means, second control means, third control means)
64 Reservoir tank (tank)
69 First ink channel (first liquid channel)
70 Second ink channel (second liquid channel)
74 Pump (circulation means, negative pressure generation means)
76 On-off valve (circulation means)
77 Bypass channel 79 First main channel 80 Second main channel 81 First branch channel 82 Second branch channel P Paper (recording medium)

Claims (4)

A plurality of droplet discharge heads for discharging droplets;
A tank for storing liquid;
A first main channel having one end inserted into the tank, and a plurality of first branch channels branching from the first main channel and extending downward and having tip portions inserted into each droplet discharge head A first liquid flow path,
One end is inserted into the tank, the other end is merged with the first main channel, the second main channel is branched from the second main channel, and the tip is inserted into each droplet discharge head. A plurality of second branched flow paths, and a second liquid flow path configured by:
By causing a liquid to flow from the droplet discharge head to the tank in the first liquid channel and from the tank to the droplet discharge head in the second liquid channel, the droplet discharge head and the tank A circulation means for circulating the liquid between,
Bei to give a,
The circulation means is provided in the first main flow path and generates negative pressure to circulate the liquid, and an on-off valve that bypasses the upstream side and the downstream side in the circulation direction from the negative pressure generation means The flow rate of the liquid is reduced during the circulation of the liquid by controlling on / off of the negative pressure generating means and opening / closing of the on-off valve. Droplet discharge device. The circulating means is
A first step of closing the on-off valve and turning on the negative pressure generating means;
A second step of opening the on-off valve and turning off the negative pressure generating means after the first step;
A third step of closing the on-off valve and turning on the negative pressure generating means after the second step;
After the third step, the on-off valve open, the liquid droplet ejecting apparatus according to claim 1, characterized in that to perform a fourth step of turning off the negative pressure generating means. The circulating means is
A first step of turning on the negative pressure generating means and closing the on-off valve;
A second step of opening the on-off valve after the first step;
A third step of closing the on-off valve after the second step;
After the third step, the on-off valve open, the liquid droplet ejecting apparatus according to claim 1, characterized in that to perform a fourth step of turning off the negative pressure generating means. The circulating means is
A first step of turning on the negative pressure generating means and closing the on-off valve;
A second step of turning off the negative pressure generating means after the first step;
A third step of turning on the negative pressure generating means after the second step;
After the third step, the negative pressure generating means off, The apparatus according to claim 1, characterized in that to perform a fourth step of the opening and closing valve opens.

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