JP2011098490A - Liquid ejector, liquid level calculation method and calibration method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To calculate a level of a liquid by limiting increase of the number of parts to a minimum also when a zero point of a pressure sensor shifts. <P>SOLUTION: The liquid ejector includes an ink jet head 2 which ejects ink liquid droplets, an ink tank 3 in which the ink is stored, the pressure sensor 6 which detects a pressure of the ink supplied to the ink jet head 2, a pump unit 7 which performs negative pressure control of an upper space S in the ink tank 3, and a control part 10. The control part 10 obtains a first pressure detected by the pressure sensor 6 when the upper space S is released to the atmosphere and a second pressure detected by the pressure sensor 6 when the upper space S is sent the air of a predetermined amount from the atmosphere-released state, and calculates the level of the ink by calculating a volume of the upper space S from a pressure rise value of the second pressure to the first pressure. Moreover, the control part calculates a true detection pressure of the pressure sensor 6 from the calculated level and calibrates the pressure sensor 6. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a liquid ejection device that ejects liquid droplets, a liquid level calculation method that calculates a liquid level of a liquid in the liquid ejection device, and a pressure sensor calibration method in the liquid ejection device.

  A liquid discharge apparatus such as an ink jet printer includes a liquid droplet discharge head that discharges liquid droplets and a liquid storage tank that stores liquid. By supplying liquid from the liquid storage tank to the liquid droplet discharge head, Droplets are ejected from the droplet ejection head. In order to make the liquid into a meniscus having a predetermined shape in the droplet discharge head, an appropriate water head value is designated.

  Therefore, in the on-carriage tank type liquid ejection device that scans the liquid storage tank integrally with the droplet discharge head, the arrangement of the liquid storage tank and the droplet discharge head is fixed. By connecting the units and controlling the negative pressure in the upper space of the liquid storage tank, the pressure of the liquid in the droplet discharge head is adjusted to a specified head value (see, for example, Patent Document 1).

JP 2006-088564 A

  By the way, in such a conventional liquid discharge apparatus, a liquid level sensor and a pressure sensor are used in order to appropriately control the negative pressure in the upper space.

  The method using the liquid level sensor, for example, obtains the liquid level (liquid level height) by a liquid level sensor installed in the liquid storage tank, and determines the upper space based on the water head value calculated from this liquid level. The liquid level is determined by a negative pressure control or a liquid level sensor installed in the liquid storage tank, and the liquid storage tank is replenished with liquid so that the liquid level is constant, and the upper space is negatively pressurized to a constant pressure. There is something to control. The liquid level sensor includes a float type liquid level sensor and a liquid level sensor using a capacitance. However, the float type liquid level sensor has low resolution and is less durable due to contact with liquid. There is a problem, and a liquid level sensor using a capacitance has a problem that it is large and expensive.

  On the other hand, as a method using a pressure sensor, for example, there is a method in which the pressure of a liquid is detected by a pressure sensor attached to a liquid flow path in the vicinity of the droplet discharge head, and the upper space is negatively controlled based on this pressure. The pressure sensor is small and has excellent resolution and durability, and can perform continuous measurement. Moreover, since the liquid level of the liquid stored in the liquid storage tank can be calculated from the detected pressure, near-end information and full tank information with a small amount of remaining liquid can also be obtained. For this reason, it is considered that it is more preferable to control the negative pressure in the upper space using a pressure sensor.

  However, the pressure sensor calibrates the zero point of the pressure sensor before using the liquid ejecting apparatus because a zero point shift (also referred to as zero drift) in which the zero point fluctuates with time occurs. There is a need. Normally, calibration of the pressure sensor is performed by opening the pressure sensor to the atmosphere and correcting the gauge pressure of the pressure sensor to zero. However, if the pressure sensor is opened to the atmosphere by blocking the liquid flow path with a valve or the like, the liquid may dry and solidify in the valve, leading to a malfunction of the valve. Therefore, it is conceivable to open the liquid storage tank to the atmosphere. However, since the liquid head is applied to the pressure sensor, it is necessary to obtain the liquid level in order to calibrate the pressure sensor.

  Therefore, the present invention provides a liquid ejection apparatus, a liquid level calculation method, and a calibration method that can calculate the liquid level of a liquid while minimizing an increase in the number of parts even when the zero point of the pressure sensor is shifted. The purpose is to provide.

  A liquid ejection apparatus according to the present invention detects a liquid droplet ejection head that ejects liquid droplets, a liquid storage container that stores liquid to be supplied to the liquid droplet ejection head, and a pressure of the liquid that is supplied to the liquid droplet ejection head A liquid discharge apparatus comprising: a pressure sensor that controls the pressure in the upper space in the liquid storage container; and a control unit that drives and controls the negative pressure control unit based on the pressure detected by the pressure sensor. The controller obtains the first pressure detected by the pressure sensor when the upper space is opened to the atmosphere by driving the negative pressure control unit, and the upper space is opened to the atmosphere by driving the negative pressure control unit. The second pressure detected by the pressure sensor when the pressure is changed from the state is acquired, the volume of the upper space is calculated based on the pressure fluctuation value of the second pressure with respect to the first pressure, and the liquid is calculated based on the volume of the upper space. of And calculates the position.

  According to the liquid ejection device according to the present invention, the liquid supplied from the liquid storage container is ejected as droplets from the droplet ejection head. At this time, the negative pressure control unit uses the pressure detected by the pressure sensor. By performing negative pressure control of the upper space, the liquid in the droplet discharge head can be maintained in a predetermined negative pressure state. At this time, the pressure fluctuation value of the first pressure detected by the pressure sensor when the upper space is opened to the atmosphere and the second pressure detected by the pressure sensor when the pressure of the upper space is changed from the open atmosphere is calculated, By calculating the volume of the upper space from this pressure fluctuation value, the volume of the upper space can be correctly calculated even if a zero point shift occurs in the pressure sensor. Therefore, by subtracting the volume of the upper space calculated from the capacity of the liquid storage container and calculating the liquid level of the liquid in the liquid storage container, even if a zero point shift occurs in the pressure sensor, The liquid level can be calculated without providing a special sensor such as a liquid level sensor.

  The negative pressure control unit includes a metering pump that sends out a predetermined amount of air, and the control unit detects a second pressure as a pressure sensor when a predetermined amount of air is sent from the negative pressure control unit into the upper space. It is preferable to acquire the detected pressure. In this way, the pressure detected by the pressure sensor when the predetermined amount of air is fed into the upper space from the negative pressure control unit equipped with the metering pump is set as the second pressure, so that the predetermined amount of air is released from the open atmosphere. The pressure increase value of the upper space that is fed and pressurized can be obtained. For this reason, since the pressure increase value when the predetermined amount of air increases is inversely proportional to the volume of the upper space, the volume of the upper space can be calculated based on the obtained pressure increase value.

  The negative pressure control unit is a constant pressure unit that sends out air at a predetermined pressure, and the control unit sends air at a predetermined pressure as a second pressure to the upper space for a predetermined time by drive control of the negative pressure control unit. It is preferable to acquire the pressure detected by the pressure sensor. In this way, the pressure detected by the pressure sensor when air of a predetermined pressure is fed into the upper space for a predetermined time from a negative pressure control unit equipped with a constant pressure pump is used as the second pressure, so that the air is released from the atmosphere for a predetermined time. It is possible to obtain the pressure increase value of the upper space where constant pressure air is fed and pressurized. Since the pressure increase value when constant-pressure air is fed for a predetermined time is inversely proportional to the volume of the upper space, the volume of the upper space can be calculated based on the obtained pressure increase value.

  And it is preferable that a control part calibrates a pressure sensor with the pressure corresponding to the calculated liquid level. In this way, the accurate pressure detected by the pressure sensor can be obtained based on the liquid level obtained without being affected by the zero point shift of the pressure sensor, so the number of parts can be minimized. The pressure sensor can be calibrated.

  The liquid level calculation method according to the present invention includes a droplet discharge head that discharges droplets, a liquid storage container that stores liquid to be supplied to the droplet discharge head, and a pressure of liquid supplied to the droplet discharge head. A liquid level calculation method in a liquid ejection device comprising a pressure sensor to detect and a negative pressure control unit for adjusting the pressure in a liquid storage container, wherein the negative pressure control unit is driven and controlled to open the upper space to the atmosphere A first pressure acquisition step for acquiring a first pressure detected by the pressure sensor, and a second pressure detected by the pressure sensor when the negative pressure control unit is driven and controlled to change the pressure of the upper space from the open atmosphere. A second pressure acquisition step for calculating the volume of the upper space based on the pressure fluctuation value of the second pressure with respect to the first pressure, and a liquid level calculation step for calculating the liquid level of the liquid based on the volume of the upper space When Characterized in that it has a.

  According to the liquid ejection method of the present invention, the first pressure detected by the pressure sensor when the upper space is opened to the atmosphere and the second pressure detected by the pressure sensor when the pressure of the upper space is changed from the open state to the atmosphere. By calculating the pressure fluctuation value and calculating the volume of the upper space from this pressure fluctuation value, the volume of the upper space can be correctly calculated even if a zero point shift occurs in the pressure sensor. Therefore, by subtracting the volume of the upper space calculated from the capacity of the liquid storage container and calculating the liquid level of the liquid in the liquid storage container, even if a zero point shift occurs in the pressure sensor, The liquid level can be calculated without providing a special sensor such as a liquid level sensor.

  In the second pressure acquisition step, it is preferable to acquire the pressure detected by the pressure sensor when a predetermined amount of air is sent into the upper space by the drive control of the negative pressure control unit as the second pressure. In this way, the pressure detected by the pressure sensor when the predetermined amount of air is fed into the upper space from the negative pressure control unit equipped with the metering pump is set as the second pressure, so that the predetermined amount of air is released from the open atmosphere. The pressure increase value of the upper space that is fed and pressurized can be obtained. For this reason, since the pressure increase value when the predetermined amount of air increases is inversely proportional to the volume of the upper space, the volume of the upper space can be calculated based on the obtained pressure increase value.

  Moreover, it is preferable that a 2nd pressure acquisition step acquires the pressure which the pressure sensor detected when air of predetermined pressure was sent into upper space only for predetermined time by drive control of a negative pressure control unit as 2nd pressure. In this way, the pressure detected by the pressure sensor when the predetermined amount of air is fed into the upper space from the negative pressure control unit equipped with the metering pump is set as the second pressure, so that the predetermined amount of air is released from the open atmosphere. The pressure increase value of the upper space that is fed and pressurized can be obtained. For this reason, since the pressure increase value when the predetermined amount of air increases is inversely proportional to the volume of the upper space, the volume of the upper space can be calculated based on the obtained pressure increase value.

  The calibration method according to the present invention includes a calibration step for calibrating the pressure sensor based on the liquid level calculated by any one of the above methods.

  According to the calibration method according to the present invention, the accurate pressure detected by the pressure sensor can be obtained based on the liquid level obtained without being affected by the zero point shift of the pressure sensor. The pressure sensor can be calibrated with minimal addition.

  According to the present invention, even when the zero point of the pressure sensor is shifted, the liquid level of the liquid can be calculated while minimizing the increase in the number of parts.

1 is a schematic configuration diagram of an inkjet printer according to an embodiment. It is a sequence diagram which shows the processing operation of negative pressure control. It is a figure for demonstrating operation | movement of an inkjet printer. It is a figure which shows the flow of air when sending air into an ink tank. It is a figure which shows the flow of the air in the case of attracting | sucking air from an ink tank. It is a sequence diagram which shows a calibration process. It is a figure which shows the flow of the air at the time of open | releaseing upper space to air | atmosphere. It is a figure for demonstrating the view of calculation of the liquid level height of an ink. It is a figure for demonstrating the calculation method of the liquid level height of an ink.

  Hereinafter, preferred embodiments of a liquid ejection apparatus, a liquid level calculation method, and a calibration method according to the present invention will be described in detail with reference to the drawings. In this embodiment, the liquid ejection device, the liquid level calculation method, and the calibration method according to the present invention are applied to an ink jet printer that is a droplet ejection device. The same or equivalent parts are denoted by the same reference numerals.

  FIG. 1 is a schematic configuration diagram of an inkjet printer according to an embodiment. As shown in FIG. 1, the inkjet printer 1 includes an inkjet head 2, an ink tank 3, a supply channel 4, a reduction channel 5, a pressure sensor 6, a pump unit 7, an alarm device 8, and a control. Part 10.

  The inkjet head 2 ejects ink droplets. The inkjet head 2 is formed with a common ink flow path 2a through which ink flows and a number of nozzles 2b communicating with the common ink flow path 2a. The inkjet head 2 is mounted on a carriage (not shown) that is mounted so as to be movable in the scanning direction. The inkjet head 2 is scanned by ejecting ink droplets when the carriage moves in the scanning direction.

  The ink tank 3 is an ink container that stores ink to be supplied to the inkjet head 2. The ink tank 3 is mounted on a carriage (not shown) similarly to the ink jet head 2, and scanning is performed integrally with the ink jet head 2.

  The supply flow path 4 is configured by an elongated tubular member (tube), and the flow path for connecting the ink tank 3 and the inkjet head 2 to supply the ink stored in the ink tank 3 to the inkjet head 2. It is.

  The reduction flow path 5 is configured by an elongated tubular member (tube), and the flow path for reducing the ink stored in the inkjet head 2 to the ink tank 3 by communicating the inkjet head 2 and the ink tank 3. It is.

  The pressure sensor 6 is a sensor that is disposed in the ink flow path near the inkjet head 2 and detects the pressure of the ink supplied to the inkjet head 2. In addition, when the regulator which hold | maintains the ink supplied to the inkjet head 2 below a designated water head value is provided, you may incorporate the pressure sensor 6 in this regulator.

  The pump unit 7 is driven by the control of the control unit 10 and performs negative pressure control of the upper space S. The pump unit 7 is connected to the upper space S of the ink tank 3, and includes a pump 71 that sends out air, a valve 72, a valve 73, a first pipe 74, a second pipe 75, and a third pipe 76. The fourth pipe 77 and the valve 78 are provided.

  The pump 71 is a metering pump capable of sending a predetermined amount of air.

  The valve 72 is an electromagnetic switching valve in which two switching ports and one discharge port are formed, and one of the switching ports communicates with the discharge port. The valve 72 selectively switches between the two switching ports based on the control of the control unit 10.

  The valve 73 is an electromagnetic switching valve formed with one suction port and two switching ports, and communicates the suction port with one of the switching ports. The valve 72 selectively switches between the two switching ports based on the control of the control unit 10.

  The first pipe 74 is a pipe connected to the upper part of the ink tank 3 and the discharge port of the valve 72.

  The second pipe 75 is a pipe connected to the intake port of the pump unit 7, one switching port of the valve 72, and one switching port of the valve 73.

  The third pipe 76 is a pipe connected to the exhaust port of the pump unit 7, the other switching port of the valve 72, and the other switching port of the valve 73.

  The fourth pipe 77 is a pipe connected to the intake port of the valve 73 and opened to the atmosphere.

  The valve 78 is an electromagnetic valve that opens and closes the first pipe 74.

  The pump unit 7 configured in this manner is configured to supply air to the upper space S by pressurizing the pump 71 and switching the valve 72, the valve 73, and the valve 78 to pressurize the upper space S, The upper space S can be decompressed by sucking air from the air, the upper space S can be opened to the atmosphere, and the upper space S can be sealed.

  The alarm device 8 is configured to issue an alarm by sound or video when the ink stored in the ink tank 3 is near-end or when the ink is full based on a command from the control unit 10. It is.

  The control unit 10 is connected to the pressure sensor 6, the pump unit 7, and the alarm device 8, and performs negative pressure control of the upper space S, calculation of the ink level, calibration of the pressure sensor 6, alarm processing, and the like. Is what you do. In addition, the control part 10 is comprised mainly by the computer containing CPU, ROM, and RAM, for example. And each function which the control part 10 performs is implement | achieved by reading predetermined computer software (program) on CPU or RAM, and making it operate | move under control of CPU.

  Next, the operation of the inkjet printer 1 will be described. The processing operation of the inkjet printer 1 described below is performed under the control of the control unit 10. That is, in the control unit 10, a processing unit (not shown) configured by a CPU or the like performs overall management of each function according to a program recorded in a storage device such as a ROM, whereby the following processing is performed.

  First, ink stored in the ink tank 3 is supplied to the inkjet head 2 through the supply flow path 4, whereby ink droplets are ejected from the inkjet head 2.

  At this time, in order to adjust the pressure of the ink in the inkjet head 2 to the designated head value, the control unit 10 uses the pressure of the ink supplied to the inkjet head 2 detected by the pressure sensor 6 to use the negative pressure in the upper space S. Take control.

  Here, with reference to FIG.2 and FIG.3, the process operation | movement of the negative pressure control of the upper space S by the control part 10 is demonstrated. FIG. 2 is a sequence diagram showing the processing operation of the negative pressure control, and FIG. 3 is a diagram for explaining the operation of the ink jet printer. In FIG. 3, A of the valve 72 indicates the other switching port connected to the third piping 76, and B of the valve 72 indicates one switching port connected to the second piping 75. Yes. Further, A of the valve 73 indicates the other switching port connected to the third piping 76, and B of the valve 73 indicates one switching port connected to the second piping 75.

  First, the control part 10 acquires the pressure of the ink supplied to the inkjet head 2 detected by the pressure sensor 6 (step S1).

  Next, the control part 10 compares the pressure acquired by step S1 with setting pressure (step S2). In step S <b> 2, the set pressure is a pressure detected by the pressure sensor 6 when the ink pressure in the inkjet head 2 becomes the designated head value. For this reason, when the pressure sensor 6 is disposed above the inkjet head 2, the set pressure becomes a value slightly lower than the designated head value, and the pressure sensor 6 is disposed below the inkjet head 2. In this case, the set pressure is slightly higher than the specified head value.

  If it is determined in step S2 that the pressure acquired in step S1 is within a predetermined range centered on the set pressure (step S2: the same), the control unit 10 seals the ink tank 3 (step S3). That is, in step S3, the ink tank 3 is sealed by turning off the valve 78 and closing the first pipe 74.

  If it is determined in step S2 that the pressure acquired in step S1 is lower than a predetermined range centered on the set pressure (step S2: low), the control unit 10 sends air into the ink tank 3 (step S4). That is, in step S4, the valve 78 is turned on to open the first pipe 74, the valve 72 is switched to B, the valve 73 is switched to A, and the pump 71 is driven. As a result, the suction port of the pump 71 is opened to the atmosphere, and the discharge port of the pump 71 is communicated with the ink tank 3, so that air is sent into the ink tank 3 by driving the pump 71. The air flow at this time is shown in FIG.

  If it is determined in step S2 that the pressure acquired in step S1 is higher than a predetermined range centered on the set pressure (step S2: high), the controller 10 sucks air from the ink tank 3 (step S5). That is, in step S5, the valve 78 is turned on to open the first pipe 74, the valve 72 is switched to A, the valve 73 is switched to B, and the pump 71 is driven. As a result, the suction port of the pump 71 communicates with the ink tank 3 and the discharge port of the pump 71 is opened to the atmosphere, so that air is sucked from the ink tank 3 by driving the pump 71. The air flow at this time is shown in FIG.

  And the pressure of the ink in the inkjet head 2 is adjusted to the designated head value by performing the negative pressure control of the ink tank 3 by repeating the steps S1 to S5 described above.

  Next, the zero point shift calibration process of the pressure sensor 6 will be described with reference to FIGS. FIG. 6 is a sequence diagram illustrating the calibration process.

  The calibration process is performed when the ink jet printer 1 is started up or every predetermined operation time.

  First, the control unit 10 capping the inkjet head 2 (step S11). As will be described later, in the calibration process, since the ink tank 3 is opened to the atmosphere, the ink head is covered with the ink jet head 2 and the ink leaks from the nozzle 2b. Therefore, in order to prevent ink from leaking from the nozzles 2b in the calibration process, the ink jet head 2 is capped in step S11 prior to the calibration process.

  Next, the control unit 10 opens the upper space S of the ink tank 3 to the atmosphere (step S12). That is, in step S12, the valve 78 is turned on to open the first pipe 74, the valve 72 is switched to A, and the valve 73 is switched to A. Thereby, the upper space S is opened to the atmosphere through the third pipe 76 without passing through the pump 71. The air flow at this time is shown in FIG.

  Next, the control part 10 acquires the pressure of the ink supplied to the inkjet head 2 detected by the pressure sensor 6 (step S13). Note that the pressure acquired in step S13 is referred to as a first pressure for convenience.

  Next, the control unit 10 sends a predetermined amount of air into the ink tank 3 (step S14). That is, in step S14, the valve 78 is turned on to open the first pipe 74, the valve 72 is switched to B, the valve 73 is switched to A, and the pump 71 is driven. As a result, the suction port of the pump 71 is opened to the atmosphere, and the discharge port of the pump 71 is communicated with the ink tank 3, so that air is sent into the ink tank 3 by driving the pump 71. Note that the air flow at this time is shown in FIG. Then, when a predetermined amount of air is sent out from the pump 71 and a predetermined amount of air is injected into the upper space S after a predetermined time has elapsed, the valve 78 is turned OFF to close the piping and stop the pump 71 from being driven. Let As a result, a predetermined amount of air is injected into the upper space S of the ink tank 3 from the open state to the pressurized state.

  Next, the control unit 10 acquires the pressure of the ink supplied to the inkjet head 2 detected by the pressure sensor 6 (step S15). Note that the pressure acquired in step S15 is referred to as a second pressure for convenience.

  Next, the control unit 10 calculates the ink level from the pressure fluctuation value between the first pressure acquired in step S13 and the second pressure acquired in step S15 (step S16).

  Here, a method for calculating the ink level in step S16 will be described.

  FIG. 8 is a diagram for explaining the concept of calculating the ink level. As shown in FIGS. 8A and 8B, for example, when the volume of the upper space S when the upper space S is opened to the atmosphere is 5, when air with a volume of 1 is injected into the upper space S, the upper space S The pressure in the space S increases 6/5 times. On the other hand, as shown in FIGS. 8C and 8D, for example, when the volume of the upper space S when the upper space S is opened to the atmosphere is 25, air with a volume of 1 is injected into the upper space S. The pressure in the upper space S rises 26/25 times. From this, the pressure of the upper space S when a predetermined amount of air (volume 1 air in the above example) is injected into the upper space S with respect to the pressure of the upper space S when the upper space S is opened to the atmosphere. By determining the rate of increase, that is, the pressure fluctuation value, the volume of the upper space S can be determined. Then, the liquid level height of the ink can be obtained from the relationship between the volume of the upper space S and the volume of the ink tank 3.

FIG. 9 is a diagram for explaining a method of calculating the liquid level of the ink. As shown in FIG. 9, in describing the method of calculating the ink level, the symbols representing the respective values are
St: Volume of ink tank 3 Si: Volume of ink stored in ink tank 3 Sa: Volume of upper space S A: Bottom area Pi1 of upper space S of ink tank 3 When upper space S is opened to the atmosphere First pressure Pi2 detected by the pressure sensor 6: second pressure Pa1 detected by the pressure sensor 6 when a predetermined amount of air is injected into the upper space S1: pressure Pa2 of the upper space S when the upper space S is opened to the atmosphere : Pressure Sj of the upper space S when a predetermined amount of air is injected into the upper space S: Volume Pab of air injected into the upper space S: Atmospheric pressure (absolute pressure)
ρ: ink density L: height from the pressure sensor 6 to the ink level (liquid level height)
La: height from the pressure sensor 6 to the bottom surface of the ink tank 3 Li: defined as the height from the bottom surface of the ink tank 3 to the ink surface. In addition, Sa is the volume in the ink tank 3, but to be exact, the volume in the pump unit 7 and the first pipe 74 is also included.

  At this time, pressures other than atmospheric pressure Pabs are expressed as gauge pressures, and the density of air is ignored. The injection air volume Sj indicates the volume at atmospheric pressure, and the atmospheric pressure and temperature do not change. The ink tank 3 has the same cross-sectional area in the height direction. The first pressure Pi1 and the second pressure Pi2 are values including an offset error due to the occurrence of a zero point shift of the pressure sensor 6. The atmospheric pressure Pabs may be a constant value, a value obtained by correcting the altitude of the installation point of the inkjet printer 1, or a barometer measurement value may be applied at the installation point of the inkjet printer 1. Good. In addition, the ink density ρ, the volume St of the ink tank 3, the bottom area A of the ink tank 3, the injection air volume Sj, and the height La from the pressure sensor 6 to the bottom surface of the ink tank 3 are obtained in advance by measurement or the like. be able to.

First, Sa is the volume of the upper space S of the ink tank 3.
Sa = St-Si (1)
It is represented by

When the upper space S is opened to the atmosphere in step S12, the first pressure Pi1 detected by the pressure sensor 6 and the pressure Pa1 of the upper space S are:
Pi1 = L * ρ (2)
Pa1 = 0 (3)
It is represented by The pressure Pa1 is 0 because it is a gauge pressure.

Next, when a predetermined amount of air is injected into the upper space S in step S14, the second pressure Pi2 detected by the pressure sensor 6 and the pressure Pa2 of the upper space S are:
Pa2 = Pa1 + ((Sa + Sj) / Sa) * Pabs (4)
Pi2 = Pi1 + (Pa2-Pa1) (5)
It is represented by

  The first pressure Pi1 and the second pressure Pi2 are values including an offset error, but Pi2-Pi1, which is the difference between them, is a correct value as the pressure increase before and after the air injection.

Next, when the equations (1) to (5) are sequentially transformed,
Pi2-Pi1 = Pa2-Pa1
Pa2-Pa1 = (Sj / Sa) * Pabs
(Pa2-Pa1) / Pabs = Sj / Sa
((Pa2-Pa1) / Pabs) / Sj = 1 / Sa
Sj / ((Pa2-Pa1) / Pabs) = Sa
Sj * Pabs / (Pa2-Pa1) = Sa
Sj * Pabs / (Pi2-Pi1) = Sa (6)
Thus, the volume Sa of the upper space S is obtained from the equation (6).

The volume Si of the ink stored in the ink tank 3 is
Si = St-Sa (7)
The height Li from the bottom surface of the ink tank 3 to the ink surface is expressed as
Li = Si / A (8)
The height (liquid level height) L from the pressure sensor 6 to the ink level is expressed as follows:
L = Li + La (9)
Therefore, the height (liquid level height) L from the pressure sensor 6 to the ink level is determined from the formulas (7) to (9).

  Note that, when the ink stored in the ink tank 3 is near-end or full due to the liquid level calculated in step S <b> 16, the control unit 10 issues an alarm or sound from the alarm device 8.

Next, the controller 10 calculates the true detected pressure of the pressure sensor 6 from the ink level calculated in step S16 (step S17). The true detected pressure Pi1r of the pressure sensor 6 without an offset error is
Pi1r = L * ρ (10)
It is represented by Therefore, the true detected pressure Pi1r of the pressure sensor 6 is obtained by integrating the liquid level height L calculated in step S16 and the ink density ρ using Expression (10).

  Next, the control unit 10 performs offset correction of the pressure sensor 6 from the true detected pressure calculated in Step S10 (Step S18). That is, the offset correction value is changed so that there is no difference between the first pressure Pi1 detected in step S13 and the true detected pressure Pi1r calculated in step S17. Specifically, the upper space S is opened to the atmosphere, and the display of the pressure sensor 6 is offset-corrected so that the first pressure Pi1 detected by the pressure sensor 6 indicates the true detected pressure Pi1r calculated in step S18.

  As described above, according to the ink jet printer 1 according to the present embodiment, the ink supplied from the ink tank 3 is ejected as ink droplets from the ink jet head 2, and the pressure detected by the pressure sensor 6 at that time is detected. By performing negative pressure control of the upper space S by the pump unit 7 based on the above, the ink in the inkjet head 2 can be maintained in a predetermined negative pressure state. At this time, the first pressure detected by the pressure sensor 6 when the upper space S is opened to the atmosphere and the second pressure detected by the pressure sensor 6 when a predetermined amount of air is sent from the open space S to the atmosphere. When the pressure increase value is calculated, the pressure increase value when a predetermined amount of air increases is inversely proportional to the volume of the upper space S. Therefore, the volume of the upper space S can be calculated from the pressure increase value. As a result, even if a zero point shift occurs in the pressure sensor 6, the volume of the upper space S can be calculated correctly. Therefore, the volume of the upper space S calculated from the capacity of the ink tank 3 is subtracted to obtain the ink liquid. By calculating the position, the ink liquid level can be calculated without providing a special sensor such as a liquid level sensor in the ink tank 3 even if a zero point shift occurs in the pressure sensor 6.

  In addition, since the accurate pressure detected by the pressure sensor 6 can be obtained based on the ink level obtained without being affected by the zero point shift of the pressure sensor 6, the addition of the number of parts is minimized. The pressure sensor 6 can be calibrated with the limit.

  The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment. For example, in the above embodiment, a predetermined amount of air is sent to the upper space S by the pump unit 7 to obtain a pressure increase value when pressurized from the atmospheric release state, and the ink level is determined by this pressure increase value. Although it is calculated, the pump unit 7 sucks a predetermined amount of air from the upper space S to obtain a pressure drop value when the pressure is reduced from the atmospheric release state, and the ink level is determined by this pressure drop value. It may be calculated.

  In the above embodiment, the metering pump is used as the pump 71 of the pump unit 7 and a predetermined amount of air is sent into the upper space S. However, the constant pressure air that sends out the constant pressure air is used and It is good also as what sends in. In this case, when obtaining the pressure increase value of the upper space S, the first pressure detected by the pressure sensor 6 when the upper space S is opened to the atmosphere and the constant pressure air from the negative pressure control unit to the upper space S for a predetermined time. The pressure increase value is obtained by comparing with the second pressure detected by the pressure sensor 6 when it is fed. Until the atmospheric pressure in the upper space S rises to some extent, the time during which the constant pressure air is fed into the upper space S and the pressure rise value are in a proportional relationship. Since it is inversely proportional to the volume, the volume of the upper space S can be calculated based on the obtained pressure increase value.

  In the above embodiment, the reduction flow path 5 is provided in addition to the supply flow path 4, and the ink is circulated between the ink tank 3 and the inkjet head 2. However, only the supply flow path 4 is provided and the ink is circulated. A 1 WAY system in which ink is simply supplied from the tank 3 to the inkjet head 2 may be employed.

  In the above embodiment, the pressure level of the pressure sensor 6 is calibrated using the calculated ink level. However, the calculated ink level is used for various applications such as various alarms. be able to.

  In the above embodiment, the ink jet printer has been described as an example of the present invention. However, the present invention is applied to an industrial liquid droplet ejecting apparatus that ejects a high viscosity liquid such as edible oil or adhesive as liquid droplets. Also good.

DESCRIPTION OF SYMBOLS 1 ... Inkjet printer, 2 ... Inkjet head, 2a ... Common ink flow path, 2b ... Nozzle, 3 ... Ink tank, 4 ... Supply flow path, 5 ... Reduction flow path, 6 ... Pressure sensor, 7 ... Pump unit, 8 ... Alarm device, 10 ... control unit, 71 ... pump, 72 ... valve, 73 ... valve, 74 ... first piping, 75 ... second piping, 76 ... third piping, 77 ... fourth piping, 78 ... valve, S ... Upper space.

Claims (8)

A droplet discharge head for discharging droplets;
A liquid storage container for storing liquid to be supplied to the droplet discharge head;
A pressure sensor for detecting the pressure of the liquid supplied to the droplet discharge head;
A negative pressure control unit for adjusting the pressure of the upper space in the liquid storage container;
A control unit for driving and controlling the negative pressure control unit based on the pressure detected by the pressure sensor;
A liquid ejection device comprising:
The controller is
Obtaining the first pressure detected by the pressure sensor when the upper space is opened to the atmosphere by driving and controlling the negative pressure control unit;
Obtaining a second pressure detected by the pressure sensor when the negative pressure control unit is driven and controlled to change the pressure of the upper space from an open atmosphere;
The liquid ejecting apparatus, wherein the volume of the upper space is calculated based on a pressure fluctuation value of the second pressure with respect to the first pressure, and the liquid level is calculated based on the volume of the upper space. The negative pressure control unit includes a metering pump that sends out a predetermined amount of air,
The said control part acquires the pressure which the said pressure sensor detected when the predetermined amount of air was sent into the said upper space from the said negative pressure control unit as said 2nd pressure. Liquid discharge device. The negative pressure control unit is a constant pressure unit that sends out air of a predetermined pressure,
The control unit acquires, as the second pressure, a pressure detected by the pressure sensor when air of a predetermined pressure is sent into the upper space for a predetermined time by drive control of the negative pressure control unit. The liquid ejection device according to claim 1.   The liquid ejecting apparatus according to claim 1, wherein the control unit calibrates the pressure sensor with a pressure corresponding to the calculated liquid level. A droplet discharge head for discharging droplets, a liquid storage container for storing a liquid to be supplied to the droplet discharge head, a pressure sensor for detecting the pressure of the liquid supplied to the droplet discharge head, and the liquid A negative pressure control unit for adjusting the pressure in the storage container, and a liquid level calculation method in a liquid ejection device comprising:
A first pressure acquisition step of acquiring the first pressure detected by the pressure sensor when the negative pressure control unit is driven and controlled to open the upper space to the atmosphere;
A second pressure acquisition step of acquiring the second pressure detected by the pressure sensor when the negative pressure control unit is driven and controlled to change the pressure of the upper space from the open atmosphere;
A liquid level calculating step of calculating a volume of the upper space based on a pressure fluctuation value of the second pressure with respect to the first pressure, and calculating a liquid level of the liquid based on the volume of the upper space;
A liquid level calculation method characterized by comprising:   In the second pressure acquisition step, as the second pressure, the pressure detected by the pressure sensor when a predetermined amount of air is sent into the upper space by drive control of the negative pressure control unit is acquired. The liquid level calculation method according to claim 5.   The second pressure acquisition step acquires the pressure detected by the pressure sensor when air of a predetermined pressure is fed into the upper space for a predetermined time by the drive control of the negative pressure control unit as the second pressure. The liquid level calculation method according to claim 5, wherein: A calibration method comprising a calibration step of calibrating the pressure sensor based on the liquid level calculated according to any one of claims 5 to 7.

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