JP2010274607A - Liquid feeding apparatus and liquid droplet discharging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid feeding apparatus and a liquid droplet discharging apparatus by which a pressure to be applied to the discharging port is maintained in a specified range even if the liquid level in a feeding tank changes, and the variation of a discharging liquid amount is kept within a specified range, and a high-accuracy liquid droplet discharge can be attained. <P>SOLUTION: This liquid feeding apparatus includes: a liquid level sensing means 4 which senses the liquid level of a liquid in the feeding tank 2; a pressure sensing means 31 which senses the pressure of an air layer in the feeding tank 2; an air pressure regulating means 32 which regulates the air pressure of the air layer in the feeding tank 2; and a control means 33 which controls the air pressure regulating means 32. The control means 33 controls the air pressure regulating means 32 in such a manner that the air pressure of the air layer which is sensed by the pressure sensing means 31 becomes a specified air pressure in response to the liquid level sensed by the liquid level sensing means 4 based on the value of the pressure sensed by the pressure sensing means 31 and the value of the liquid level sensed by the liquid level sensing means 4. By this way, the pressure applied to the discharging port is controlled to stay within the specified range. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a liquid supply device and a droplet discharge device, and more specifically, air pressure in a supply tank that supplies liquid to a droplet discharge head that performs droplet discharge of an inkjet printer or the like that performs image recording, display production, or the like. The present invention relates to a liquid supply device and a droplet discharge device that can appropriately control the flow rate.

  As a droplet discharge device that discharges liquid from a discharge port in the form of minute droplets, an ink jet printer that performs various image recording and display production using ink is known. A droplet ejecting apparatus that ejects an expensive functional liquid such as a liquid having an (Electro-Luminescence) function or bio-ink as a droplet has attracted attention.

  By the way, in such a droplet discharge device, a stable meniscus cannot be formed unless the pressure (back pressure) applied to the discharge port is within a specific range, and stable discharge becomes difficult. Conventionally, as a technique for paying attention to and controlling the pressure applied to the discharge port, there are those described in Patent Documents 1 to 3.

  In Patent Document 1, in the biological liquid droplet ejecting apparatus, when the biological fluid height level in the biological fluid cartridge is detected below a predetermined level, the biological fluid is replenished or the height level of the biological fluid cartridge is adjusted. Thus, it is disclosed that the biological fluid height level is kept constant and the meniscus position is kept constant.

  In Patent Document 2, air pressure in an ink cartridge that supplies liquid to a liquid ejecting head is detected by a pressure sensor, and a pressure control valve and a pump are controlled based on the detection signal to maintain the air pressure within a predetermined range. Thus, it is disclosed that the air pressure in the ink cartridge is maintained at a constant negative pressure.

  In Patent Document 3, in an ink jet recording apparatus configured to supply ink in a main tank to a recording head via a sub tank, the air pressure in the sub tank is maintained at a constant negative pressure by a negative pressure air pump and a pressure gauge. Thus, it is disclosed that when the remaining amount detection sensor senses that the ink in the sub tank has decreased due to the drawing operation, ink is replenished from the main tank to the sub tank.

Japanese Patent No. 405040 JP-A-2005-41048 JP 2003-182104 A

  According to the inventor's research, in order to form a meniscus capable of stably discharging droplets at the discharge port of the droplet discharge head, a negative pressure of about −5.0 cmAq to −15.0 cmAq is maintained on the discharge port surface. It turns out to be good.

  However, it has been found that even within this range of conditions, there is actually a difference in the appropriate amount of liquid to be discharged. This is because even if the pressure in the supply tank is kept constant, the liquid surface height gradually decreases due to liquid consumption due to the discharge operation, and the water head pressure changes accordingly. This is considered to be due to a gradual change (decompression) and a slight change in the shape of the meniscus.

  FIG. 7 shows the water head pressure (cmAq) and discharge liquid amount (droplet mass) applied to the discharge outlet when cationic UV ink (Black) is discharged at a head temperature of 50 ° C., a drive pulse of 11.0 μs, and 7.1 kHz. , Ng). As the water head pressure decreases, the amount of discharged liquid also decreases. Precisely, when the water head pressure decreases by 1 cmAq, the discharge liquid amount decreases by 0.42 ng. Here, when the amount of discharged liquid in a state where a water head pressure of −5.0 cmAq that can maintain a meniscus suitable for droplet discharge is applied, the value is 50.0 ng. Accordingly, if the liquid level is changed and the water head pressure is reduced by 5.0 cmAq, the discharge liquid amount is reduced by about 4%.

  It is considered that such a difference in the discharge liquid amount caused by the change in the liquid surface height is a slight one that does not cause any trouble when droplet discharge for normal image recording is performed. However, in recent years, in the field of EL display production and the like that require higher image quality printing and higher resolution, there has been an increasing demand for highly accurate and high-definition droplet discharge. There is a growing concern about the effect on images and products obtained even with a slight difference. For example, in the former printing field, if droplets are smaller than expected, printing unevenness and white spots may be caused. In some cases, the printed color may be lighter than the target color. In the latter EL display manufacturing field, if coating unevenness occurs due to variations in the amount of discharged liquid, it causes light emission unevenness or light emission defects.

  Patent Document 1 discloses a technique for keeping the liquid level constant. According to this method, a problem due to a change in the water head pressure is less likely to occur, but in order to realize this, it is necessary to supply liquid into the cartridge or adjust the height of the cartridge each time a droplet is discharged. The liquid supply operation or cartridge height adjustment must be performed frequently. The liquid surface cannot be stabilized under the influence of the pressure wave generated at this time, and as a result, it is difficult to maintain the shape of the meniscus of the discharge port, and it is difficult to continuously discharge droplets having a stable shape. There's a problem.

  Japanese Patent Application Laid-Open No. 2004-228561 attempts to keep the amount of liquid ejected constant by always keeping the air pressure in the ink cartridge constant, and does not consider changes in the liquid level. Therefore, the problem that the pressure applied to the discharge port changes minutely due to the change of the water head pressure due to the liquid level cannot be solved.

  Patent Document 3 is to keep the air pressure in the sub-tank at a constant negative pressure, and this method also does not consider the change in liquid level as in Patent Document 2, and depends on the liquid level. The problem that the pressure applied to the discharge port changes minutely due to the change in the water head pressure cannot be solved. Here, it is shown that the remaining amount in the sub tank is detected, but this is only used to determine the timing of supplying ink from the main tank to the sub ink, and the air pressure in the sub tank is determined. When controlling, there is no description of performing control based on the signal which detected this remaining amount.

  Therefore, the present invention can maintain the pressure applied to the discharge port within a certain range even if the liquid level in the supply tank that supplies the liquid to the droplet discharge head changes, thereby reducing the discharge liquid amount. It is an object of the present invention to provide a liquid supply device capable of maintaining a change within a certain range and realizing highly accurate droplet discharge in a droplet discharge head and a droplet discharge device including the liquid supply device.

  Other problems of the present invention will become apparent from the following description.

  The above problems are solved by the following inventions.

According to a first aspect of the present invention, there is provided a supply tank for storing a liquid to be supplied to a droplet discharge head for discharging a droplet from a discharge port, and controlling a pressure of an air layer in the supply tank to thereby discharge the droplet. In a liquid supply device having a pressure control device for controlling the pressure applied to the ejection port of the head,
With a liquid level detection means for detecting the liquid level of the liquid in the supply tank,
The pressure control device includes pressure detecting means for detecting the pressure of the air layer in the supply tank, air pressure adjusting means for adjusting the air pressure of the air layer in the supply tank, and control means for controlling the air pressure adjusting means. With
The control means detects the air pressure of the air layer detected by the pressure detection means based on the pressure value detected by the pressure detection means and the liquid level height value detected by the liquid level height detection means. The pressure applied to the discharge port is controlled within a certain range by controlling the air pressure adjusting means so that a predetermined air pressure corresponding to the liquid level detected by the liquid level detecting means is obtained. This is a liquid supply device.

  According to a second aspect of the present invention, the air pressure of the air layer detected by the pressure detecting means is reduced to a constant pressure value with respect to the air pressure after the adjustment immediately before the air layer in the supply tank. When it is detected, the adjusted air pressure value corresponding to the liquid level detected by the liquid level detector at that time is obtained, and the air pressure of the air layer becomes the adjusted air pressure. 2. The liquid supply apparatus according to claim 1, wherein the air pressure adjusting means is controlled as described above.

The invention according to claim 3 is that the liquid level height of the liquid in the supply tank is higher than the height of the discharge port of the droplet discharge head,
The constant pressure value <the adjusted air pressure ≦ the atmospheric pressure,
The air pressure adjusting means is composed of a communication path that connects the air layer in the supply tank and the atmosphere, and a valve that opens and closes the communication path.
The control means opens the valve to control the inflow amount of outside air, thereby controlling the air pressure of the air layer in the supply tank to the positive pressure side, whereby the air pressure of the air layer is adjusted to the adjusted air pressure. 3. The liquid supply apparatus according to claim 2, wherein the air pressure adjusting means is controlled so that

In the invention according to claim 4, the liquid level height of the liquid in the supply tank is at a position lower than the height of the discharge port of the droplet discharge head,
Atmospheric pressure ≦ the constant pressure value <the adjusted air pressure,
The air pressure adjusting means is constituted by a pump for supplying air to the air layer in the supply tank,
The control means controls the air pressure in the supply tank by driving the pump to control the air supply amount, thereby controlling the air pressure in the air tank to the positive pressure side. 3. The liquid supply apparatus according to claim 2, wherein the air pressure adjusting means is controlled so as to be.

The invention according to claim 5 has pressure fluctuation mitigation means that communicates with the air layer in the supply tank and relieves pressure fluctuation of the air layer,
The liquid supply device according to claim 1, wherein the air pressure adjusting unit communicates with an air layer in the supply tank via the pressure fluctuation reducing unit.

  According to a sixth aspect of the present invention, there is provided a liquid droplet ejection apparatus comprising: a liquid droplet ejection head that ejects liquid droplets from an ejection port; and the liquid supply device according to any one of the first to fifth aspects. .

  The invention according to claim 7 is characterized in that the supply tank of the liquid supply device is arranged in the vicinity of the droplet discharge head in a one-to-one correspondence with the droplet discharge head. It is a droplet discharge device of description.

  According to the present invention, even when the liquid level in the supply tank for supplying the liquid to the droplet discharge head changes, the pressure applied to the discharge port can be maintained within a certain range, thereby reducing the discharge liquid amount. It is possible to provide a liquid supply device capable of maintaining a change within a certain range and realizing highly accurate droplet discharge in a droplet discharge head, and a droplet discharge device including the liquid supply device.

Explanatory drawing explaining the outline | summary of the droplet discharge apparatus provided with the liquid supply apparatus which concerns on this invention Explanatory drawing explaining the outline | summary of the droplet discharge apparatus which has a liquid supply apparatus provided with the pressure fluctuation relaxation means. Schematic cross section of pressure fluctuation mitigation means Diagram showing an example of a liquid supply system Timing chart for explaining the pressure adjustment operation in the droplet supply system shown in FIG. The figure which shows another example of a liquid supply system A graph showing the relationship between water head pressure and discharge fluid volume Graph showing the relationship between control pressure and liquid level

  Embodiments of the present invention will be described below.

  First, an outline of a liquid supply apparatus according to the present invention and a droplet discharge apparatus including the liquid supply apparatus will be described with reference to FIG.

  The droplet discharge apparatus includes a droplet discharge head 1 that discharges droplets from the discharge port 11 and a liquid supply device 100 that supplies liquid to the droplet discharge head 1. The liquid supply apparatus 100 controls the pressure applied to the discharge port 11 of the droplet discharge head 1 by controlling the pressure of the supply tank 2 storing the liquid W therein and the air layer 21 in the supply tank 2. Pressure control device 3.

  The supply tank 2 stores a predetermined amount of the liquid W so as to form an air layer 21 in the upper part of the supply tank 2 and directly supplies the liquid W to the droplet discharge head 1. Direct supply means that the internal liquid W is supplied to the droplet discharge head 1 without interposing a storage means such as another tank between the droplet discharge head 1.

  The supply tank 2 is formed of, for example, a synthetic resin such as polypropylene, a metal such as stainless steel, glass, or the like, and does not substantially change its shape even when a control pressure (positive pressure or negative pressure) is applied to the inside. It has rigidity. The specific material can be determined by the relationship with the stored liquid W. For example, when bio-ink is used as the liquid W, a material formed of polypropylene is preferable. Although the supply tank 2 by a syringe is illustrated in FIG. 1, the shape is not particularly limited.

  The number of the supply tanks 2 corresponds to the number of the droplet discharge heads 1 to 1 and is arranged in parallel in the vicinity of the droplet discharge heads 1 so as to be integrated when the droplet discharge heads 1 are moved. Move. The arrangement position of the supply tank 2 may be higher or lower than the discharge port 11 exposed on the lower surface of the droplet discharge head 1. FIG. 1 shows an example in which the liquid W is disposed at a high position, and is connected to the droplet discharge head 1 by a straight tubular supply flow path 22 that hangs down from the bottom thereof. Supply directly. The supplied liquid W is discharged as droplets from the discharge port 11 by driving the droplet discharge head 1.

  By arranging the supply tank 2 in the vicinity of the droplet discharge head 1 in this manner, the supply flow path 22 of the liquid W can be shortened. In particular, the liquid W is expensive such as bio ink or silver nano paste. Even when a rare liquid or a valuable liquid that can be prepared only in a small amount in an experiment or the like is used, the residual liquid in the supply channel 22 can be reduced and waste can be eliminated. In particular, with bio ink, the supply channel 22 can be short, so that the risk of contamination can be reduced.

  When the supply tank 2 is provided at a position higher than the discharge port 11, it is necessary to limit the liquid level height h so that no liquid leaks from the discharge port 11 when the liquid W is filled. The liquid level height h causing liquid leakage from the discharge port 11 varies depending on the surface tension and density of the liquid W and the diameter of the discharge port 11, but according to the experiments of the present inventors, the supply tank 2 is as shown in FIG. When installed, liquid leakage from the discharge port 11 was observed when the liquid level height h with respect to the discharge port 11 was 35 to 40 cm. In this case, in order to prevent liquid leakage from the discharge port 11, the liquid level height h may be less than 35 cm. However, a certain margin is provided for safety, for example, 30 cm or less. It is preferable to adjust to.

  The upper part of the supply tank 2 is sealed by the lid member 23 after storing the liquid W, and is substantially sealed except that it is connected to a means for adjusting the air pressure of the air layer 21 such as the pressure control means 3. . Thereby, it isolate | separates from air | atmosphere except when the air pressure of the air layer 21 is adjusted.

  Further, the supply tank 2 is provided with a liquid level detecting means 4 for detecting the liquid level height h of the liquid W inside. The liquid level detection means 4 only needs to be able to detect the liquid level height h of the liquid W. For example, a float sensor or a capacitance sensor provided in the supply tank 2 can be used. As the float sensor, there is a float type level sensor (YF / FL type) manufactured by Yamamoto Electric Industry Co., Ltd. Examples of the capacitance sensor include a capacitance level meter (MHL series) manufactured by Yamamoto Electric Industry Co., Ltd. From the viewpoint of detection accuracy, a capacitance sensor is preferable.

  The pressure control means 3 controls the air pressure of the air layer 21 in the supply tank 2. The pressure control means 31 detects the air pressure of the air layer 21 in the supply tank 2 and the air layer 21 in the supply tank 2. An air pressure adjusting means 32 for adjusting the air pressure and a control means 33 for controlling the air pressure adjusting means 32 are provided.

  The pressure detection means 31 detects the air pressure of the air layer 21 by communicating with the air layer 21 in the supply tank 2 through a communication path 311 that passes through the lid member 23. Since the pressure detection means 31 only needs to detect the air pressure of the air layer 21, it is not necessary to directly contact the liquid W. Therefore, it is not necessary to use an expensive pressure detecting unit 31 that does not affect the liquid W even if it is touched, and a general air pressure sensor can be used. A detection signal from the pressure detection means 31 is constantly sent to the control means 33.

  The air pressure adjusting means 32 communicates with the air layer 21 of the supply tank 2 through the communication path 321 that penetrates the lid member 23 and adjusts the air pressure of the air layer 21. The communication path 321 is closed except when adjusting the air pressure.

  When the supply tank 2 is disposed at a position higher than the discharge port 11 as shown in FIG. 1, the pressure applied to the discharge port 11 of the droplet discharge head 1 is maintained in a predetermined negative pressure state necessary for stable discharge. Therefore, a predetermined negative pressure (initial standard pressure) is applied to the air layer 21 at the initial setting after the liquid W is stored. Further, when the supply tank 2 is disposed at a position lower than the discharge port 11, the liquid applied to the discharge port 11 of the droplet discharge head 1 is maintained in a predetermined negative pressure necessary for stable discharge. At the time of initial setting after storing W, a predetermined positive pressure (initial standard pressure) is applied to the air layer 21 as necessary.

  Here, if the pressure applied to the discharge port 11 is P, the air pressure of the air layer 21 in the supply tank 2 is Pa, and the pressure applied to the discharge port 11 by the liquid level height h of the liquid W in the supply tank 2 is Ph. P = Pa + Ph. In the present invention, the control means 33 in the pressure control device 3 adjusts Pa by controlling the air pressure adjusting means 32 so that P is within a certain range. When the liquid W in the supply tank 2 is consumed by continuing to discharge the liquid droplets, the liquid level height h decreases and Pa increases to the negative pressure side. The air pressure adjusting means 32 adjusts the air layer 21 to the positive pressure side regardless of whether the arrangement position with respect to 11 is high or low.

  Therefore, when the air pressure of the air layer 21 is set to a negative pressure, the air pressure adjusting means 32 may simply release the communication passage 321 to the atmosphere to allow the outside air to naturally flow in using the negative pressure. A valve mechanism such as an electromagnetic valve that opens and closes the communication path 321 can be used. In this case, it is preferable to use a flow path resistance valve such as a leak adjustment valve or a speed controller that can easily adjust the inflow amount of outside air.

  In addition, when the air pressure of the air layer 21 is set to a positive pressure, the air pressure adjusting means 32 needs to perform pressurization for forcing the outside air through the communication path 321, Pumps such as a tube pump and a diaphragm pump for performing can be used.

  The control means 33 controls the air pressure adjusting means 32. Further, the detection signal of the liquid level detection means 4 is constantly sent to the control means 33. In the present invention, the pressure detected by the pressure detecting unit 31 is detected by the control unit 33 based on the pressure value detected by the pressure detecting unit 31 and the liquid level detected by the liquid level detecting unit 4. However, by controlling the air pressure adjusting means 32 so that the predetermined air pressure corresponding to the liquid level detected by the liquid level detecting means 4 is maintained, the pressure applied to the discharge port 11 is kept within a certain range. Control and maintain the discharge liquid amount within a certain range.

  This will be further described with reference to FIG. 7. For example, when the liquid W having a specific gravity of 1 is used when the discharge liquid amount is kept at 50.0 ng, the pressure applied to the discharge port 11 at this time is As the height h increases by 1.0 cm, it increases by 1.0 cmAq. For example, when the liquid level height h is 30.0 cm, a pressure of 30.0 cmAq is applied to the discharge port 11. Therefore, in order for the discharge port 11 to maintain an appropriate meniscus, it is necessary to cancel the pressure of 30.0 cmAq and to set the pressure of the discharge port 11 to −5.0 cmAq to −15.0 cmAq necessary for stable discharge. There is. Therefore, if it is intended to maintain the pressure applied to the discharge port 11 at −5.0 cmAq in this situation, it is sufficient to apply a pressure of −35.0 cmAq, and the control means 33 can control the air layer 21 detected by the pressure detection means 31. Input the value of the air pressure and the value of the liquid level detected by the liquid level detection means 4, and the value of the adjusted air pressure appropriate for maintaining the pressure applied to the discharge port 11 at -5.0 cmAq from there. And the air pressure adjusting means 32 is controlled on the basis of the calculated adjusted air pressure value so that the air pressure of the air layer 21 in the supply tank 2 becomes the adjusted air pressure value. Thus, even if the liquid level height h changes, the pressure applied to the discharge port 11 is kept at -5.0 cmAq.

  Actually, since it is difficult to maintain the pressure applied to the discharge port 11 at a single value, control is performed so that the pressure applied to the discharge port 11 is maintained within a certain range. Therefore, the air pressure of the air layer 21 may be controlled so that the pressure applied to the discharge port 11 is within a certain range. For example, in the example of FIG. 7, when the hydraulic head pressure decreases by 1 cmAq, the discharge liquid amount decreases by 0.42 ng. Therefore, the ideal discharge liquid amount is set to 50.0 ng and it is desired to maintain it within a range of ± 2%. In this case, the water head pressure range (pressure upper limit and pressure lower limit) to be controlled may be ± 2.5 cmAq. FIG. 8 is a graph showing the relationship between the pressure value and the liquid level.

  As can be seen from this graph, the air pressure value of the air layer 21 in the supply tank 2 to be adjusted by the control means 33 controlling the air pressure adjusting means 32 in the present invention is not constant, and the liquid level height h is low. As it becomes, it becomes a value on the positive pressure side, and becomes a different value according to the liquid level height h. That is, the air layer 21 in the supply tank 2 is depressurized due to the decrease in the liquid level height h due to the droplet discharge, and the pressure applied to the discharge port 11 gradually decreases accordingly. The control means 33 of No. 3 has a liquid level height h detected by the liquid level height detection means 4 so that the air pressure of the air layer 21 in the supply tank 2 is maintained to maintain the pressure applied to the discharge port 11 within a certain range. The air pressure adjusting means 32 is controlled to adjust the air pressure of the reduced air layer 21 toward the positive pressure side so that a predetermined air pressure corresponding to the air pressure is obtained.

  Specifically, the control means 33 has adjusted the air pressure of the air layer 21 detected by the pressure detection means 31 immediately before the air layer 21 in the supply tank 2 (including adjustment to the initial standard value in the initial setting). When it is detected that the air pressure has decreased to a certain pressure value, the adjusted air pressure value corresponding to the liquid level height h detected by the liquid level detection means 4 at that time is obtained, and the air The air pressure adjusting means 32 is controlled so that the air pressure of the layer 21 becomes the air pressure after the adjustment.

  The fact that the pressure has decreased to a certain pressure value means that the value of the air pressure that decreases relative to the adjusted air pressure immediately before the air layer 21 in the supply tank 2 is necessary for stable discharge of the pressure applied to the discharge port 11. It is that it has fallen out of range. The reduction to the constant pressure value is detected by the fact that the air pressure that has decreased with respect to the air pressure after the previous adjustment has reached a constant reduction rate (%). The value of the reduction rate is preset in the control means 33 or a storage means (not shown).

  Further, the adjusted air pressure value corresponding to the liquid level height h detected by the liquid level height detecting means 4 is a table in which the relationship between the liquid level height h value and the adjusted air pressure value is defined in advance. And stored in the control means 33 or a storage means (not shown). Based on this stored data, the control means 33 adjusts the air pressure of the air layer 21 by controlling the air pressure adjusting means 32 so that the air pressure of the air layer 21 becomes the adjusted air pressure.

  In the present invention, it is preferable to have pressure fluctuation mitigating means 34 that communicates with the air layer 21 in the supply tank 2 to relieve the pressure fluctuation of the air layer 21.

  FIG. 2 shows an outline of a droplet discharge apparatus having the liquid supply apparatus 101 provided with such a pressure fluctuation relaxation means 34. Parts having the same reference numerals as those in FIG. 1 indicate parts having the same configuration.

  The pressure fluctuation relaxation means 34 is interposed in the communication path 321 of the air pressure adjustment means 32. Therefore, the air pressure adjusting means 32 communicates with the air layer 21 in the supply tank 2 via the pressure fluctuation mitigating means 34. Then, the fluctuation of the liquid level height h accompanying the droplet discharge of the droplet discharge head 1 and the influence of the sudden pressure wave at the time of adjusting the pressure of the air layer 21 by the air pressure adjusting means 32 are alleviated. A more stable discharge of droplets by the head 1 is enabled.

  As the pressure fluctuation mitigating means 34, one having a so-called damper function that has an air chamber that communicates with the air layer 21 of the supply tank 2 and that can mitigate pressure fluctuation as described above is preferably used.

  An example is shown in FIG. The pressure fluctuation reducing means 34 has a box-shaped casing 341 made of a relatively rigid body such as polypropylene or polyethylene. An opening 342 is formed on at least one wall surface of the casing 341, and a flexible film 343 made of a polymer material such as polyethylene terephthalate is provided so as to cover and close the opening 342. Yes. An air chamber 344 is formed inside the casing 341 and the flexible film 343.

  The flexible membrane 343 is in a state where the membrane surface is loosened without being strained with respect to the opening 342. In the air chamber 344, one end abuts against the inner surface side of the flexible membrane 343 and the other end abuts against the pressing member 346, and biasing means for urging the flexible membrane 343 outward. 345, and the flexible membrane 343 is maintained so as to protrude a predetermined amount outward from the opening 342.

  The air chamber 344 of the pressure fluctuation mitigating means 34 communicates with the air layer 21 in the supply tank 2 via the communication path 321 of the air pressure adjusting means 321, and has the same pressure as the pressure in the air layer 21. Therefore, when the supply tank 2 is disposed at a position higher than the discharge port 11 as shown in FIG. 2, the air chamber 344 is also in a predetermined negative pressure state, and the supply tank 2 is positioned lower than the discharge port 11. When it is disposed in a predetermined positive pressure state.

  In this state, when the air pressure of the air layer 21 in the supply tank 2 is adjusted to the positive pressure side by the air pressure adjusting means 32, and outside air flows in at once through the communication path 321, the inside of the air chamber 344 of the pressure fluctuation reducing means 34 When the protruding position of the flexible film 343 is changed, sudden pressure fluctuation is alleviated. Also, in the case of sudden pressure fluctuations in the air layer 21 due to fluctuations in the liquid level height h at the start of droplet discharge from the stationary state, the protrusions of the flexible film 343 are similarly mitigated by fluctuations. Is done.

  When the pressure fluctuation reducing means 34 is provided, the pressure detecting means 31 may detect the air pressure in the air chamber 344 of the pressure fluctuation reducing means 34 via the communication path 311 as shown in FIG. .

  Next, a method for actually performing pressure control will be described using a specific example.

  4 shows a liquid supply system including two sets of the liquid supply apparatus 101 and the droplet discharge head 1 shown in FIG. 2, and FIG. 5 shows a timing chart thereof. In FIG. 4, the control means 33 in the pressure control means 3 is not shown. Further, an air pressure sensor is used as the pressure detection means 31 and a capacitance sensor is used as the liquid level detection means 4.

  Further, since the two sets of the liquid supply device 101 and the droplet discharge head 1 shown in FIG. 4 perform the same operation, in FIG. 5, the two sets of the liquid supply device 101 and the droplet shown in FIG. Only the timing chart of one of the groups with the ejection head 1 (the group on the left side in FIG. 4) is shown.

  The following control operations are the same even when the combination of the liquid supply device 100 and the droplet discharge head 1 is performed, and the same is true even when the liquid supply device is the liquid supply device 100 shown in FIG. It is.

  In FIG. 4, 5 is a pump provided in the present embodiment, and communicates with the air layer 21 in each supply tank 2 via communication passages 51 and 52 that respectively penetrate the lid member 23. . Here, a tube pump capable of supplying and exhausting air to each air layer 21 by forward and reverse rotation driving is used.

  V1-1 is an electromagnetic valve that opens and closes the communication path 51 between the pump 5 and one supply tank 2, and V1-2 is an electromagnetic that opens and closes the communication path 52 between the pump 5 and the other supply tank 2. It is a valve.

  Further, V2-1 is an electromagnetic valve that opens and closes the communication path 321 between one flow path resistance valve 32 and the pressure fluctuation relaxation means 34, and V2-2 is the other flow path resistance valve 32 and the pressure fluctuation relaxation means 34. An electromagnetic valve 322 for opening and closing the communication path 321 between them is a flow path resistance valve for adjusting the flow path resistance of the communication path 321, and here, these electromagnetic valves V2-1 and V2-2 and the flow path resistance valve 322 Constitutes the air pressure adjusting means 32. The operations of these solenoid valves V1-1, V1-2, V2-1, V2-2 are also controlled by a control means 33 (not shown).

  An operation in the liquid supply system will be described.

(1) Filling liquid First, each supply tank 2 is filled with liquid W. For filling, the lid member 23 at the upper part of the supply tank 2 is removed, and the liquid level in each supply tank 2 is manually injected so that the liquid level from the discharge port 11 does not leak.

  After sealing with the lid member 23, the solenoid valves V1-1 and V1-2 are opened, the solenoid valves V2-1 and V2-2 are closed, and the pump 5 is driven to supply air. Pressurize. Thereby, the liquid W is filled in each droplet discharge head 1.

(2) Creation of negative pressure After completion of filling, the pump 5 is driven in the opposite direction so as not to cause liquid leakage, exhaust is performed, and the pressure in each supply tank 2 is reduced. The pressure at this time is detected by the air pressure sensor 31. When the supply tank 2 reaches a negative pressure (initial standard pressure P0) that satisfies the conditions for discharging liquid droplets without causing liquid leakage, the electromagnetic valve V1-1 or V1- that leads to the supply tank 2 is provided. 2 is closed, and when all the supply tanks 2 reach the initial standard pressure P0, the driving of the pump 5 is stopped. This is the initial adjustment after ink filling. After the adjustment is completed, each droplet discharge head 1 can discharge droplets.

(3) Discharge start By discharging droplets, the liquid W in each supply tank 2 is gradually consumed, and the liquid level decreases. Along with this, the value of the air pressure sensor 31 in each supply tank 2 also decreases according to the droplet discharge amount from the corresponding droplet discharge head 1, and thereby the discharge of each droplet discharge head 1. The pressure applied to the outlet 11 also decreases.

  In the timing chart shown in FIG. 5, it is assumed that the discharge is always continued after a while after the first negative pressure is created.

(4) Pressure adjustment By continuing the discharge, the air layer 21 in each supply tank 2 is depressurized according to the consumption of the droplet, and the value of the air pressure detected by the air pressure sensor 31 maintains the stable discharge of the droplet. When the pressure value P1 is reduced to a certain pressure value that cannot be obtained, the air pressure of each air layer 21 is adjusted to the positive pressure side so that the air pressure is in accordance with the liquid level. Here, it is assumed that the constant pressure value P1 is 5% lower than the adjusted air pressure P0 immediately before the air layer 21.

  Here, with reference to FIG. 5, the case of adjusting the pressure of one set (the left set in FIG. 4) will be described. First, the solenoid valve V2-1 is opened to adjust the pressure. The pressure adjustment of the air layer 21 is performed by opening the electromagnetic valve V2-1 based on the detection result by the pressure sensor 31 and the liquid level in the supply tank 2 detected by the capacitance sensor 4 at that time. The adjusted air pressure P2 due to the inflow of outside air is obtained, and the air pressure detected by the pressure sensor 31 is set to be the adjusted air pressure P2. The adjusted air pressure P2 is higher than the previous adjusted air pressure (in this case, the initial standard pressure P0) according to the amount of change in the liquid level, which is low. The adjusted pressure value is controlled by the opening time of the electromagnetic valve V2-1.

  Here, since the relationship of constant pressure value <adjusted air pressure ≦ atmospheric pressure is satisfied, the air layer 21 of the supply tank 2 is opened to the atmosphere, so that outside air flows in through the communication path 321, and the air layer 21. The air pressure is adjusted toward the positive pressure side, but at this time, since the flow resistance valve 322 is provided, the pressure does not change abruptly, and the pressure fluctuation mitigating means 34 is not burdened. It is possible to supply air with the pump 5, but by using only the opening and closing operation of the valve mechanism, the frequency of use of the pump 5 can be suppressed and the pump life can be extended.

  After that, when the air pressure of the air layer 21 becomes the air pressure P3 that is similarly reduced to a constant pressure value (5%) with respect to the previous air pressure P2, it is detected by the air pressure P3 and the capacitance sensor 4 at that time. The adjusted air pressure is obtained based on the liquid level height to be adjusted, and the air pressure P4 is adjusted to be higher than the immediately preceding air pressure P2 in accordance with the change in the liquid level height.

  Further, the same adjustment is performed every time the pressure value detected by the air pressure sensor 31 decreases to a certain pressure value. Thereby, the pressure applied to the discharge port 11 is always kept within a certain range even during the discharge of the droplet.

  The above-described operation for pressure adjustment can be similarly described for the right group in FIG. In this case, the solenoid valve V1-1 in the above description is replaced with the solenoid valve V1-2, and the solenoid valve V2-1 is replaced with the solenoid valve V2-2.

  Such a liquid supply system is configured to supply and exhaust air by a common pump 5 for a set of a plurality of droplet discharge heads 1 and the liquid supply apparatus 100 or 101. By doing in this way, the number of sets of the droplet discharge head 1 and the liquid supply apparatus 100 or 101 can be increased without increasing the number of pumps 5.

  FIG. 6 illustrates a liquid supply system when the supply tank 2 is disposed at a position lower than the discharge port surface of the droplet discharge head 1.

  In this case, since the air layer 21 in each supply tank 2 is in a predetermined positive pressure state, the relationship of atmospheric pressure ≦ constant pressure value <adjusted air pressure is established. I need to send air. The configuration for this can be performed by providing a common pump for each set of the droplet discharge head 1 and the liquid supply apparatus 102 in the same manner as the pump 5 of the liquid supply system of FIG. The required air supply amount varies depending on the droplet discharge amount in each group. When air is supplied by a common pump, there is a troublesome control of switching the air supply amount to each group by opening and closing an electromagnetic valve. Therefore, in this case, as shown in FIG. 6, it is preferable to provide the pumps 6 corresponding to the respective groups because it is not necessary to switch the supply of air to the respective groups by opening and closing the electromagnetic valves. Moreover, since the pump 6 can also be used as a pump for creating an initial standard pressure after the liquid W is injected into the supply tank 2, the initial standard is similar to the pump 5 seen in the liquid supply system of FIG. There is no need to prepare a separate pump for creating pressure.

DESCRIPTION OF SYMBOLS 1: Droplet discharge head 11: Discharge port 2: Supply tank 21: Air layer 22: Supply flow path 23: Lid member 3: Pressure control device 31: Pressure detection means 311: Communication path 32: Air pressure adjustment means 321: Communication path 33: Control means 34: Pressure fluctuation mitigation means 341: Casing 342: Opening 343: Flexible film 344: Air chamber 345: Biasing member 346: Pressing member 100, 101, 102: Liquid supply device

Claims (7)

The pressure applied to the discharge port of the droplet discharge head by controlling the pressure of the supply tank for storing the liquid supplied to the droplet discharge head for discharging the droplet from the discharge port and the air layer in the supply tank A liquid supply device having a pressure control device for controlling
With a liquid level detection means for detecting the liquid level of the liquid in the supply tank,
The pressure control device includes pressure detecting means for detecting the pressure of the air layer in the supply tank, air pressure adjusting means for adjusting the air pressure of the air layer in the supply tank, and control means for controlling the air pressure adjusting means. With
The control means detects the air pressure of the air layer detected by the pressure detection means based on the pressure value detected by the pressure detection means and the liquid level height value detected by the liquid level height detection means. The pressure applied to the discharge port is controlled within a certain range by controlling the air pressure adjusting means so that a predetermined air pressure corresponding to the liquid level detected by the liquid level detecting means is obtained. A liquid supply device.   When the control means detects that the air pressure of the air layer detected by the pressure detection means has decreased to a constant pressure value with respect to the adjusted air pressure immediately before the air layer in the supply tank, The adjusted air pressure value corresponding to the liquid level detected by the liquid level detecting means at that time is obtained, and the air pressure adjusting means is controlled so that the air pressure of the air layer becomes the adjusted air pressure. The liquid supply apparatus according to claim 1, wherein: The liquid level height of the liquid in the supply tank is at a position higher than the height of the discharge port of the droplet discharge head,
The constant pressure value <the adjusted air pressure ≦ the atmospheric pressure,
The air pressure adjusting means is constituted by a communication path that connects the air layer in the supply tank and the atmosphere, and a valve that opens and closes the communication path,
The control means opens the valve to control the inflow amount of outside air, thereby controlling the air pressure of the air layer in the supply tank to the positive pressure side, whereby the air pressure of the air layer is adjusted to the adjusted air pressure. The liquid supply apparatus according to claim 2, wherein the air pressure adjusting means is controlled so that The liquid level height of the liquid in the supply tank is at a position lower than the height of the discharge port of the droplet discharge head,
Atmospheric pressure ≦ the constant pressure value <the adjusted air pressure,
The air pressure adjusting means is constituted by a pump for supplying air to the air layer in the supply tank,
The control means controls the air pressure in the supply tank by driving the pump to control the air supply amount, thereby controlling the air pressure in the air tank to the positive pressure side. 3. The liquid supply apparatus according to claim 2, wherein the air pressure adjusting means is controlled so as to become. Communicating with the air layer in the supply tank, and having pressure fluctuation mitigating means for mitigating pressure fluctuation of the air layer;
5. The liquid supply apparatus according to claim 1, wherein the air pressure adjusting unit communicates with an air layer in the supply tank through the pressure fluctuation reducing unit.   6. A liquid droplet ejection apparatus comprising: a liquid droplet ejection head that ejects liquid droplets from an ejection port; and the liquid supply apparatus according to claim 1.   7. The droplet discharge device according to claim 6, wherein the supply tank of the liquid supply device is disposed adjacent to the droplet discharge head in a one-to-one correspondence with the droplet discharge head.

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