Patent Description:
A liquid discharge device including a liquid discharge head (ink jet head) for discharging liquid (ink) and a liquid circulation device for circulating the liquid in a circulation path including the liquid discharge head is known.

The liquid circulation device includes a liquid detection sensor at a specific location in a flow path in order to detect a state of filling the liquid discharge head with the liquid. For example, the liquid detection sensor is an electrostatic capacitance type or float type sensor.

However, an installation place of the electrostatic capacitance type liquid detection sensor is limited because the electrostatic capacitance type liquid detection sensor is large in size. The float type liquid detection sensor has low reliability because a moving part thereof may be stuck by liquid.

<CIT> discloses a liquid circulation device comprising a buffer tank and sensor configured to measure pressure in the buffer tank. Further each of <CIT>, <CIT> and <CIT> discloses a liquid ejecting apparatus.

In order to solve the above-cited problems, , a liquid circulation device, a liquid discharge device ink jet recording apparatus according to appended claims.

Embodiments provide a liquid circulation device and a liquid discharge device for effectively detecting that a liquid discharge head is filled with liquid.

In general, according to one embodiment, there is provided a circulation device configured to be connected to a liquid discharge head, including a pressurizing pump, a depressurizing pump, a buffer tank, a sensor, and a processor. The pressurizing pump is configured to supply liquid from a tank (replenishment tank) to the liquid discharge head. The depressurizing pump is configured to collect the liquid from the liquid discharge head. The buffer tank is connected in parallel with the liquid discharge head between the pressurizing pump and the depressurizing pump, and configured to store the liquid. The sensor is configured to measure pressure in the buffer tank. The processor is configured to determine whether a pressure chamber included in the liquid discharge head is filled with the liquid based on the measured pressure.

According to the present invention, the processor is configured to acquire the pressure from the sensor in time series, and determine whether the pressure chamber is filled with the liquid based on the pressure acquired in time series.

According to the present invention, the processor is configured to determine that the pressure chamber is filled with the liquid, when detecting that the pressure reaches lower limit pressure, the pressure reaches upper limit pressure, and the pressure is stable.

Preferably, the processor is configured to determine that the pressure reaches the lower limit if a minimum value of the pressure is not updated for a predetermined period of time, determine that the pressure reaches the upper limit if a maximum value of the pressure is not updated for a predetermined period of time, and determine that the pressure is stable based on variance of the pressure.

Preferably, the processor is configured to acquire a plurality of the pressures from the sensor in a predetermined time period to calculate the variance of the acquired pressures.

Preferably, the processor is configured to count the number of times the variance falls below a predetermined threshold, and determine that the pressure is stable when the counted number exceeds a predetermined threshold.

There is also provided a liquid discharge device which comprises a liquid discharge head comprising a pressure chamber and the liquid circulation device as described above.

There is also provided an ink jet recording apparatus comprising a plurality of the liquid discharge devices as described above.

Hereinafter, a liquid circulation device and a liquid discharge device according to an embodiment will be described with reference to the drawings.

Hereinafter, a liquid discharge device <NUM> according to the embodiment and an ink jet recording apparatus <NUM> including the liquid discharge device <NUM> will be described with reference to <FIG>. For the sake of illustration in each figure, the configuration is appropriately enlarged, reduced, or omitted. <FIG> is a side view illustrating a configuration of the ink jet recording apparatus <NUM>. <FIG> is an explanatory diagram illustrating a configuration of the liquid discharge device <NUM>. <FIG> is an explanatory diagram illustrating a configuration of a liquid discharge head <NUM>. <FIG> is an explanatory diagram illustrating a configuration of a first circulation pump <NUM> and a second circulation pump <NUM>.

The ink jet recording apparatus <NUM> illustrated in <FIG> includes a plurality of liquid discharge devices <NUM>, a head support mechanism <NUM> that movably supports the liquid discharge devices <NUM>, a medium support mechanism <NUM> that movably supports a recording medium S, and a host control device <NUM>.

As illustrated in <FIG>, the plurality of liquid discharge devices <NUM> are arranged in parallel in a predetermined direction and supported by the head support mechanism <NUM>. The liquid discharge device <NUM> integratedly includes the liquid discharge head <NUM> and a circulation device <NUM>. The liquid discharge device <NUM> forms a desired image on the recording medium S arranged to face the liquid discharge device <NUM> by discharging, for example, ink as liquid from the liquid discharge head <NUM>.

The plurality of liquid discharge devices <NUM> discharge a plurality of colors, for example, cyan ink, magenta ink, yellow ink, black ink, and white ink, respectively, but are not limited in the color or characteristics of the ink used. For example, instead of white ink, transparent glossy ink, special ink that develops a color when irradiated with infrared rays or ultraviolet rays, and the like can be discharged. The plurality of liquid discharge devices <NUM> have the same configuration although the inks respectively used are different from each other.

First, the liquid discharge head <NUM> will be described.

The liquid discharge head <NUM> illustrated in <FIG> is an inkjet head, and includes a supply port 20a through which ink flows in, a collection port 20b through which ink flows out, a nozzle plate <NUM> having a plurality of nozzle holes 21a, a substrate <NUM>, and a manifold <NUM> joined to the substrate <NUM>.

The substrate <NUM> is joined to face the nozzle plate <NUM> and is configured in a predetermined shape to form a predetermined ink flow path <NUM> including a plurality of ink pressure chambers <NUM> with the nozzle plate <NUM>. The substrate <NUM> is provided with partition walls arranged between a plurality of ink pressure chambers <NUM> in the same row. An actuator <NUM> provided with electrodes 24a and 24b is provided at a portion of the substrate <NUM> facing each ink pressure chamber <NUM>.

The actuator <NUM> is disposed to face the nozzle hole 21a, and the ink pressure chamber <NUM> is formed between the actuator <NUM> and the nozzle hole 21a. The actuator <NUM> is connected to a drive circuit. The liquid discharge head <NUM> discharges liquid from the nozzle hole 21a arranged to face the actuator <NUM> by deforming the actuator <NUM> according to a voltage under the control of the module control unit <NUM>.

Next, the circulation device <NUM> (liquid circulation device) will be described.

As illustrated in <FIG>, the circulation device <NUM> is integratedly connected to a top portion of the liquid discharge head <NUM> by a metal connecting component. The circulation device <NUM> includes a predetermined circulation path <NUM> configured to allow liquid to circulate through the liquid discharge head <NUM>, a first circulation pump <NUM>, a bypass flow path <NUM>, a buffer tank <NUM>, a second circulation pump <NUM>, an on-off valve <NUM>, and a module control unit <NUM> that controls a liquid discharge action.

The circulation device <NUM> includes a cartridge <NUM> as an ink replenishment tank (liquid replenishment tank) provided outside the circulation path <NUM>.

The cartridge <NUM> is configured to be able to hold ink, and an air chamber inside the cartridge <NUM> is open to the atmosphere.

First, the circulation path <NUM> will be described.

The circulation path <NUM> includes a first flow path 31a, a second flow path 31b, a third flow path 31c, and a fourth flow path 31d. The first flow path 31a connects the cartridge <NUM>, which is an ink replenishment tank, and the first circulation pump <NUM>. The second flow path 31b connects the first circulation pump <NUM> and the supply port 20a of the liquid discharge head <NUM>. The third flow path 31c connects the collection port 20b of the liquid discharge head <NUM> and the second circulation pump <NUM>. The fourth flow path 31d connects the second circulation pump <NUM> and the cartridge <NUM>. The first flow path 31a and the fourth flow path 31d include a pipe made of a metal or resin material and a tube covering an outer surface of the pipe. The tube covering the outer surface of the pipes of the first flow path 31a and the fourth flow path 31d is, for example, a PTFE tube.

The ink circulating in the circulation path <NUM> reaches the inside of the liquid discharge head <NUM> from the cartridge <NUM> through the first flow path 31a, the first circulation pump <NUM>, the second flow path 31b, and the supply port 20a of the liquid discharge head <NUM>. The ink circulating in the circulation path <NUM> reaches the cartridge <NUM> from the liquid discharge head <NUM> through the collection port 20b of the liquid discharge head <NUM>, the third flow path 31c, the second circulation pump <NUM>, and the fourth flow path 31d.

Next, the first circulation pump <NUM> and the second circulation pump <NUM> will be described.

The first circulation pump <NUM> is a pump that sends out liquid. The first circulation pump <NUM> sends out the liquid from the first flow path 31a toward the second flow path 31b. That is, the first circulation pump <NUM> is a pressurizing pump that sucks up ink from the cartridge <NUM>, which is an ink replenishment tank, and supplies the ink to the liquid discharge head <NUM> by the action of the actuator.

The second circulation pump <NUM> is a pump that sends out liquid. The second circulation pump <NUM> sends out the liquid from the third flow path 31c toward the fourth flow path 31d. That is, the second circulation pump <NUM> is a depressurizing pump that collects the ink from the liquid discharge head <NUM> and replenishes the ink to the cartridge <NUM> by the action of the actuator.

The first circulation pump <NUM> and the second circulation pump <NUM> are configured as a piezoelectric pump <NUM>, for example, as illustrated in <FIG>. The piezoelectric pump <NUM> includes a pump chamber <NUM>, a piezoelectric actuator <NUM> that is provided in the pump chamber <NUM> and vibrates by a voltage, and check valves <NUM> and <NUM> arranged at an inlet and outlet of the pump chamber <NUM>. The piezoelectric actuator <NUM> is configured to be vibratable at a frequency of, for example, about <NUM> to <NUM>. The first circulation pump <NUM> and the second circulation pump <NUM> are connected to the drive circuit by wiring and are configured to be controllable by the control of the module control unit <NUM>.

For example, by changing the voltage applied to the piezoelectric actuator <NUM>, the piezoelectric actuator <NUM> deforms in the direction in which the pump chamber <NUM> is contracted or in the direction in which the pump chamber <NUM> is expanded, as illustrated in the upper and lower parts of <FIG>. With this configuration, the volume of the pump chamber <NUM> changes. For example, if the piezoelectric actuator <NUM> is deformed in the direction of expanding the pump chamber <NUM>, the check valve <NUM> at the inlet of the pump chamber <NUM> opens and ink is drawn into the pump chamber <NUM>. For example, if the piezoelectric actuator <NUM> is deformed in the direction of contracting the pump chamber <NUM>, the check valve <NUM> at the outlet of the pump chamber <NUM> opens, and the ink in the pump chamber <NUM> is sent out to the other side. By repeating this action, the first circulation pump <NUM> and the second circulation pump <NUM> each draw ink from one side and send out ink from the other side.

The maximum change amount of the piezoelectric actuator <NUM> depends on the voltage applied to the piezoelectric actuator <NUM>. As the voltage applied to the piezoelectric actuator <NUM> increases, the maximum change amount of the piezoelectric actuator <NUM> increases. If the voltage applied to the piezoelectric actuator <NUM> becomes smaller, the maximum change amount of the piezoelectric actuator <NUM> becomes smaller. A liquid feeding capacity of the piezoelectric pump <NUM> depends on the maximum change amount of the piezoelectric actuator <NUM>. That is, the module control unit <NUM> controls the liquid feeding capacity of the piezoelectric pump <NUM> by controlling the voltage applied to the piezoelectric actuator <NUM>.

Next, the bypass flow path <NUM> and the buffer tank <NUM> will be described.

The bypass flow path <NUM> is a flow path connecting the second flow path 31b and the third flow path 31c. The bypass flow path <NUM> connects the supply port 20a which is the primary side of the liquid discharge head <NUM> and the collection port 20b which is the secondary side of the liquid discharge head <NUM> in the circulation path <NUM> in a short-circuit manner without passing through the liquid discharge head <NUM>.

The buffer tank <NUM> is connected to the bypass flow path <NUM>. Specifically, the bypass flow path <NUM> includes a first bypass flow path 34a connecting a predetermined location on a lower portion of one side wall of a pair of side walls of the buffer tank <NUM> and the second flow path 31b, and a second bypass flow path 34b connecting a predetermined location on a lower portion of the other side wall of the pair of side walls of the buffer tank <NUM> and the third flow path 31c.

For example, the first bypass flow path 34a and the second bypass flow path 34b have the same length and the same diameter, and the first and second bypass flow paths are configured to have a smaller diameter than that of the circulation path <NUM>. For example, the diameter of the circulation path <NUM> is set to be about <NUM> to <NUM> times the diameter of the first bypass flow path 34a and the second bypass flow path 34b. The first bypass flow path 34a and the second bypass flow path 34b are provided so that a distance between a connection position between the second flow path 31b and the first bypass flow path 34a and the supply port 20a of the liquid discharge head <NUM> and a distance between a connection position between the third flow path 31c and the second bypass flow path 34b and the collection port 20b of the liquid discharge head <NUM> are equal.

The buffer tank <NUM> is connected in parallel with the liquid discharge head <NUM> between the first circulation pump <NUM> and the second circulation pump <NUM>. The buffer tank <NUM> has a flow path cross-sectional area larger than the flow path cross-sectional area of the bypass flow path <NUM>, and is configured to be able to store liquid. The buffer tank <NUM> has, for example, an upper wall, a lower wall, a rear wall, a front wall, and a pair of left and right side walls, and is configured in a rectangular box shape forming a storage chamber 35a for storing the liquid inside thereof. The connection position between the first bypass flow path 34a and the buffer tank <NUM> and the connection position between the second bypass flow path 34b and the buffer tank <NUM> are set to be at the same height. Ink flowing through the bypass flow path <NUM> is arranged in the lower region of the storage chamber 35a in the buffer tank <NUM>, and an air chamber is formed in the upper region of the storage chamber 35a. That is, the buffer tank <NUM> can store a predetermined amount of liquid and air. The buffer tank <NUM> is provided with the on-off valve <NUM> configured to open the air chamber in the buffer tank <NUM> to the atmosphere and the pressure sensor <NUM>.

The on-off valve <NUM> is a normally closed solenoid on-off valve that opens if a power source is turned on and closes if the power source is turned off. The on-off valve <NUM> is configured to be able to open and close the air chamber of the buffer tank <NUM> with respect to the atmosphere by being opened and closed under the control of the module control unit <NUM>.

The pressure sensor <NUM> measures the pressure in the air chamber of the buffer tank <NUM>, and sends pressure data indicating a pressure value to the module control unit <NUM>. If the on-off valve <NUM> is open and the air chamber of the buffer tank <NUM> is open to the atmosphere, pressure data measured by the pressure sensor <NUM> is equal to the atmospheric pressure. The pressure sensor <NUM> measures the pressure in the air chamber of the buffer tank <NUM> if the on-off valve <NUM> is closed and the air chamber of the buffer tank <NUM> is not open to the atmosphere.

The pressure sensor <NUM> outputs the pressure as an electric signal by using, for example, a semiconductor piezoresistive pressure sensor. The semiconductor piezoresistive pressure sensor includes a diaphragm that receives external pressure and a semiconductor strain gauge formed on a surface of the diaphragm. The semiconductor piezoresistive pressure sensor measures the pressure by converting a change in electrical resistance due to a piezoresistive effect that occurs in the strain gauge accompanied by the deformation of the diaphragm due to external pressure into an electric signal.

Next, the module control unit <NUM> will be described.

<FIG> is an explanatory diagram illustrating a configuration example of the module control unit <NUM>.

The module control unit <NUM> controls the action of the liquid discharge head <NUM>, the first circulation pump <NUM>, the second circulation pump <NUM>, and the on-off valve <NUM>. The module control unit <NUM> includes a processor <NUM>, a memory <NUM>, a communication interface <NUM>, a circulation pump drive circuit <NUM>, a valve drive circuit <NUM>, and a liquid discharge head drive circuit <NUM>.

The processor <NUM> is a computing element (for example, a central processing unit (CPU)) that executes computation processing. The processor <NUM> performs various processing based on data such as a program stored in the memory <NUM>. The processor <NUM> functions as a control circuit capable of executing various controls by executing the program stored in the memory <NUM>.

The memory <NUM> is a memory device for storing various information. The memory <NUM> includes, for example, a read only memory (ROM) 72a and a random access memory (RAM) 72b.

The ROM 72a is a read-only non-volatile memory. The ROM 72a stores a program, data used in the program, and the like. For example, the ROM 72a stores various setting values such as a calculation formula for calculating ink pressure of the nozzle hole 21a, a target pressure range, and an adjustment maximum value of each pump as control data used for pressure control.

The RAM 72b is a volatile memory that functions as a working memory. The RAM 72b temporarily stores data and the like in processing by the processor <NUM>. The RAM 72b temporarily stores a program executed by the processor <NUM>.

The communication interface <NUM> is an interface for communicating with another device. The communication interface <NUM> relays, for example, communication with the host control device <NUM> that transmits print data to the liquid discharge device <NUM>.

The circulation pump drive circuit <NUM> applies a drive voltage to the piezoelectric actuator <NUM> of the piezoelectric pump <NUM> based on the control of the processor <NUM> to drive the piezoelectric pump <NUM>. With this configuration, the circulation pump drive circuit <NUM> circulates ink in the circulation path <NUM>. The circulation pump drive circuit <NUM> is provided for each circulation pump. The circulation pump drive circuit <NUM> connected to the first circulation pump <NUM> applies a drive voltage to the piezoelectric actuator <NUM> of the first circulation pump <NUM>. The circulation pump drive circuit <NUM> connected to the second circulation pump <NUM> applies a drive voltage to the piezoelectric actuator <NUM> of the second circulation pump <NUM>.

The valve drive circuit <NUM> drives the on-off valve <NUM> based on the control of the processor <NUM> to open the air chamber of the buffer tank <NUM> to the atmosphere.

The liquid discharge head drive circuit <NUM> applies a voltage to the actuator <NUM> of the liquid discharge head <NUM> to drive the liquid discharge head <NUM> based on the control of the processor <NUM>, and causes ink to be discharged from the nozzle hole 21a of the liquid discharge head <NUM>.

In the configuration described above, the processor <NUM> receives various information such as action conditions by communicating with the host control device <NUM> through the communication interface <NUM>. Various information acquired by the processor <NUM> is sent to the host control device <NUM> of the ink jet recording apparatus <NUM> through the communication interface <NUM>.

The processor <NUM> acquires a measurement result from the pressure sensor <NUM>, and controls the action of the circulation pump drive circuit <NUM> and the valve drive circuit <NUM> based on the acquired measurement result. For example, the processor <NUM> controls the liquid feeding capacity of the first circulation pump <NUM> and the second circulation pump <NUM> by controlling the circulation pump drive circuit <NUM> based on the measurement result of the pressure sensor <NUM>. With this configuration, the processor <NUM> adjusts the ink pressure of the nozzle hole 21a.

The processor <NUM> controls the valve drive circuit <NUM> to cause the on-off valve <NUM> to be opened and closed. With this configuration, the processor <NUM> adjusts a liquid level of the buffer tank <NUM>.

The processor <NUM> acquires a measurement result from the pressure sensor <NUM>, and controls the liquid discharge head drive circuit <NUM> based on the acquired measurement result to cause ink droplets to be discharged from the nozzle hole 21a of the liquid discharge head <NUM> to the recording medium. Specifically, the processor <NUM> inputs an image signal corresponding to image data to the liquid discharge head drive circuit <NUM>. The liquid discharge head drive circuit <NUM> drives the actuator <NUM> of the liquid discharge head <NUM> in response to the image signal. If the liquid discharge head drive circuit <NUM> drives the actuator <NUM> of the liquid discharge head <NUM>, the actuator <NUM> is deformed and ink pressure (nozzle surface pressure) of the nozzle hole 21a at a position facing the actuator <NUM> changes. The nozzle surface pressure is pressure given by ink in the ink pressure chamber <NUM> to a meniscus Me formed by ink in the nozzle hole 21a. If the nozzle surface pressure exceeds a predetermined value determined by the shape of the nozzle hole 21a, the characteristics of the ink, and the like, the ink is discharged from the nozzle hole 21a. With this configuration, the processor <NUM> forms an image corresponding to the image data on the recording medium.

Next, the pressure in the buffer tank <NUM> will be described.

Here, a change in pressure in the buffer tank <NUM> between the time when the ink pressure chamber <NUM> is in an empty state and the time when the ink pressure chamber <NUM> is filled with ink will be described.

<FIG> is a graph illustrating the change in pressure in the buffer tank <NUM> between the time when the ink pressure chamber <NUM> is in the empty state and the time when the ink pressure chamber <NUM> is filled with the ink. That is, <FIG> illustrates the change in pressure measured by the pressure sensor <NUM>. In <FIG>, the horizontal axis represents the time and the vertical axis represents the pressure in the buffer tank <NUM>.

In the example illustrated in <FIG>, it is assumed that the liquid discharge head <NUM> and the circulation path <NUM> are not filled with ink at a time point T1. It is assumed that the on-off valve <NUM> is closed. It is assumed that the pressure in the buffer tank <NUM> at the time point T1 is "<NUM> kPa".

At the time point T1, the processor <NUM> starts circulation of ink from the cartridge <NUM> using the first circulation pump <NUM> and the second circulation pump <NUM>.

If the supply of ink from the cartridge <NUM> starts, the pressure in the buffer tank <NUM> is reduced. The pressure in the buffer tank <NUM> continues to decrease until the ink flows into the first flow path 31a and the second flow path 31b and flows into the ink pressure chamber <NUM> of the liquid discharge head <NUM>, the first bypass flow path 34a, and the buffer tank <NUM>. Here, it is assumed that at a time point T2, the plurality of nozzle holes 21a are filled with ink, and ink starts to flow into the buffer tank <NUM>. That is, the pressure in the buffer tank <NUM> becomes the minimum at the time point T2.

If the plurality of nozzle holes 21a are filled with ink and the ink flows into the buffer tank <NUM>, the pressure in the buffer tank <NUM> rises. The pressure in the buffer tank <NUM> continues to rise until the ink reaches the second circulation pump <NUM>. Here, it is assumed that at a time point T3, the ink reaches the second circulation pump <NUM>. That is, at the time point T3, the pressure in the buffer tank <NUM> reaches the peak thereof.

If the ink reaches the second circulation pump <NUM>, the pressure in the buffer tank <NUM> decreases again. After that, air bubbles in the ink pressure chamber <NUM> and the circulation path <NUM> are discharged, and the liquid level of the buffer tank <NUM> is stabilized. If the liquid level in the buffer tank <NUM> is stabilized, the pressure in the buffer tank <NUM> is also stabilized. Here, it is assumed that at a time point T4, the pressure in the buffer tank <NUM> is stable. That is, in the vicinity of the time point T4, the change in pressure in the buffer tank <NUM> becomes small.

It is assumed that at the time point T4, the ink pressure chamber <NUM> is filled with ink.

Next, a function realized by the circulation device <NUM> will be described. The function realized by the circulation device <NUM> is realized by the processor <NUM> executing the program stored in the memory <NUM> or the like.

The processor <NUM> has a function of determining whether the ink pressure chamber <NUM> is filled with ink based on the pressure in the buffer tank <NUM>.

The processor <NUM> acquires the pressure in the buffer tank <NUM> in time series. The processor <NUM> determines whether the ink pressure chamber <NUM> is filled with ink based on the pressure acquired in time series.

That is, the processor <NUM> detects that the pressure in the buffer tank <NUM> has reached (corresponding to time point T2) a lower limit (lower limit pressure), then has reached (corresponding to time point T3) an upper limit (upper limit pressure), and then is stable (corresponding to time point T4).

First, the processor <NUM> detects that the pressure in the buffer tank <NUM> has reached the lower limit pressure.

For example, the processor <NUM> receives a control signal for starting circulation of ink from the host control device <NUM> through the communication interface <NUM>. If the control signal is received, the processor <NUM> starts circulation of ink from the cartridge <NUM> by using the first circulation pump <NUM> and the second circulation pump <NUM>.

If the circulation of ink is started, the processor <NUM> causes the pressure sensor <NUM> to measure the pressure in the buffer tank <NUM>. Here, it is assumed that the on-off valve <NUM> is closed.

The processor <NUM> continues to acquire pressure data indicating a value of pressure from the pressure sensor <NUM>. The processor <NUM> sets a variable P_min_temp for storing a minimum value of pressure. Here, the processor <NUM> substitutes an initial value (for example, <NUM> Pa) into P_min_temp.

If pressure P measured by the pressure sensor <NUM> is smaller than P_min_temp, the processor <NUM> substitutes the pressure P into P_min_temp. If P_min_temp is not updated (that is, if P is greater than P_min_temp) for a predetermined period of time (for example, <NUM>), the processor <NUM> determines that the pressure in the buffer tank <NUM> has reached the lower limit (lower limit pressure).

If it is determined that the pressure in the buffer tank <NUM> has reached the lower limit (lower limit pressure), the processor <NUM> substitutes P_min_temp into a variable P_min for storing the lower limit pressure. If P_min _temp is substituted into P_min, the processor <NUM> sets a flag indicating that the pressure in the buffer tank <NUM> has reached the lower limit pressure.

Next, the processor <NUM> detects that the pressure in the buffer tank <NUM> has reached the upper limit pressure.

If the flag indicating that the lower limit pressure has been detected is set, the processor <NUM> sets a variable P_max_temp for storing a maximum value of the pressure. Here, the processor <NUM> substitutes P_min as an initial value into the variable P_max_temp.

If the pressure P measured by the pressure sensor <NUM> is greater than P_max_temp, the processor <NUM> substitutes the pressure P into P_max_temp. If P_max_temp is not updated (that is, if P is less than or equal to P_max_temp) for a predetermined period of time (for example, <NUM>), the processor <NUM> calculates a difference between P_max_temp and P_min.

If the difference is calculated, the processor <NUM> determines whether the calculated difference is greater than a predetermined threshold (for example, <NUM> kPa). If it is determined that the calculated difference is greater than the predetermined threshold, the processor <NUM> determines that the pressure in the buffer tank <NUM> has reached the upper limit (upper limit pressure).

If it is determined that the pressure in the buffer tank <NUM> has reached the upper limit (upper limit pressure), the processor <NUM> substitutes P_max_temp into a variable P_max for storing the upper limit pressure. If P_max_temp is substituted into P_max, the processor <NUM> sets a flag indicating that the pressure in the buffer tank <NUM> has reached the upper limit pressure.

If it is determined that the calculated difference is equal to or less than the predetermined threshold, the processor <NUM> returns to the action of determining whether the pressure P measured by the pressure sensor <NUM> is greater than P_max_temp.

Next, the processor <NUM> detects that the pressure in the buffer tank <NUM> is stable.

If the flag indicating that the upper limit pressure is detected is set, the processor <NUM> sets a counter (count_stb) that counts the number of times the variance of pressure falls below a predetermined threshold (for example, <NUM>).

If the counter is set, the processor <NUM> calculates the variance σm of pressure. Here, the processor <NUM> acquires the pressure every <NUM> in the past <NUM> and calculates the variance of the acquired pressure.

If the variance σm of pressure is calculated, the processor <NUM> determines whether the variance σm of pressure is smaller than the predetermined threshold (for example, <NUM>). If it is determined that the variance σm of pressure is smaller than the predetermined threshold, the processor <NUM> increments the count_stb (adds <NUM> to count_stb).

The processor <NUM> repeats the action described above for a predetermined period of time (for example, <NUM>). If the predetermined period of time elapses, the processor <NUM> determines whether the count_stb exceeds a predetermined threshold (for example, <NUM>). If it is determined that the count_stb exceeds the predetermined threshold, the processor <NUM> determines that the pressure is stable, and sets a flag indicating that the pressure in the buffer tank <NUM> is stable.

If it is determined that the count_stb is equal to or less than the predetermined threshold, the processor <NUM> returns to the action of calculating the variance of pressure again.

If the flag indicating that the pressure in the buffer tank <NUM> is stable is set, the processor <NUM> determines that the ink pressure chamber <NUM> is filled with ink. For example, if it is determined that the ink pressure chamber <NUM> is filled with ink, the processor <NUM> transmits a control signal indicating that the ink pressure chamber <NUM> is filled with ink to the host control device <NUM> through the communication interface <NUM>.

Next, an action example of the processor <NUM> will be described.

<FIG> is a flowchart illustrating the action example of the processor <NUM>.

First, the processor <NUM> starts circulation of ink from the cartridge <NUM> by using the first circulation pump <NUM> and the second circulation pump <NUM> (ACT <NUM>). If the circulation of ink is started, the processor <NUM> determines whether the pressure in the buffer tank <NUM> has reached a lower limit pressure (ACT <NUM>).

If it is detected that the pressure in the buffer tank <NUM> has reached the lower limit pressure, the processor <NUM> determines whether the pressure in the buffer tank <NUM> has reached an upper limit pressure (ACT <NUM>). If it is detected that the pressure in the buffer tank <NUM> has reached the upper limit pressure, the processor <NUM> determines whether the pressure in the buffer tank <NUM> is stable (ACT <NUM>).

If it is detected that the pressure in the buffer tank <NUM> is stable, the processor <NUM> determines that the ink pressure chamber <NUM> is filled with ink (ACT <NUM>). If it is determined that the ink pressure chamber <NUM> is filled with ink, the processor <NUM> ends the action.

If it is determined that the ink pressure chamber <NUM> is filled with ink, the processor <NUM> may cause ink to be discharged from the ink pressure chamber <NUM> according to the control of the host control device <NUM>.

Next, an action example (ACT <NUM>) in which the processor <NUM> detects that the pressure in the buffer tank <NUM> has reached the lower limit pressure will be described.

<FIG> is a flowchart illustrating the action example (ACT <NUM>) in which the processor <NUM> detects that the pressure in the buffer tank <NUM> has reached the lower limit pressure.

First, the processor <NUM> substitutes <NUM> Pa into P_min_temp (ACT <NUM>). If <NUM> Pa is substituted into P_min_temp, the processor <NUM> starts a timer t_min (ACT <NUM>).

If the timer t_min is started, the processor <NUM> determines whether the timer t_min is greater than <NUM> (whether <NUM> seconds have elapsed) (ACT <NUM>). If it is determined that the timer t_min is not greater than <NUM> (NO in ACT <NUM>), the processor <NUM> determines whether the pressure P, which is measured by the pressure sensor <NUM>, is less than P_min_temp (ACT <NUM>).

If it is determined that P is less than P_min_temp (YES in ACT <NUM>), the processor <NUM> substitutes P into P_min_temp (ACT <NUM>). If P is substituted into P_min_temp, the processor <NUM> resets the timer t_min (sets the timer t_min to <NUM>) (ACT <NUM>).

If it is determined that P is not less than P_min_temp (NO in ACT <NUM>), or if the timer t_min is reset (ACT <NUM>), the processor <NUM> returns to ACT <NUM>.

If it is determined that the timer t_min is greater than <NUM> (YES in ACT <NUM>), the processor <NUM> substitutes P_min_temp into P_min for storing the lower limit pressure (ACT <NUM>). If P_min_temp is substituted into P_min, the processor <NUM> sets a flag indicating that the pressure in the buffer tank <NUM> has reached the lower limit pressure (ACT <NUM>).

If the flag indicating that the pressure in the buffer tank <NUM> has reached the lower limit pressure is set, the processor <NUM> ends the action.

Next, an action example (ACT <NUM>) in which the processor <NUM> detects that the pressure in the buffer tank <NUM> has reached the upper limit pressure will be described.

<FIG> is a flowchart illustrating the action example (ACT <NUM>) in which the processor <NUM> detects that the pressure in the buffer tank <NUM> has reached the upper limit pressure.

First, the processor <NUM> substitutes P_min into P_max_temp (ACT <NUM>). If P_min is substituted into P_max_temp, the processor <NUM> starts the timer t_max (ACT <NUM>).

If the timer t_max is started, the processor <NUM> determines whether the timer t_max is greater than <NUM> (whether <NUM> seconds have elapsed) (ACT <NUM>). If it is determined that the timer t_max is not greater than <NUM> (NO in ACT <NUM>), the processor <NUM> determines whether the pressure P measured by the pressure sensor <NUM> is greater than P_max_temp (ACT <NUM>).

If it is determined that P is greater than P_max_temp (YES in ACT <NUM>), the processor <NUM> substitutes P into P_max_temp (ACT <NUM>). If P is substituted into P_max_temp, the processor <NUM> resets the timer t_max (sets the timer t_max to <NUM>) (ACT <NUM>).

If it is determined that P is not greater than P_max_temp (NO in ACT <NUM>), or if the timer t_max is reset (ACT <NUM>), the processor <NUM> returns to ACT <NUM>.

If it is determined that the timer t_max is greater than <NUM> (YES in ACT <NUM>), the processor <NUM> determines whether P_max _temp - P_min is greater than <NUM> kPa (ACT <NUM>). If it is determined that P_max_temp - P_min is not greater than <NUM> kPa (NO in ACT <NUM>), the processor <NUM> returns to ACT <NUM>.

If it is determined that P_max_temp - P_min is greater than <NUM> kPa (YES in ACT <NUM>), the processor <NUM> substitutes P_max_temp into P_max for storing the upper limit pressure (ACT <NUM>). If P_max_temp is substituted into P_max, the processor <NUM> sets a flag indicating that the pressure in the buffer tank <NUM> has reached the upper limit pressure (ACT <NUM>).

If the flag indicating that the pressure in the buffer tank <NUM> has reached the upper limit pressure is set, the processor <NUM> ends the action.

Next, an action example (ACT <NUM>) in which the processor <NUM> detects that the pressure in the buffer tank <NUM> is stable will be described.

<FIG> is a flowchart illustrating the action example (ACT <NUM>) in which the processor <NUM> detects that the pressure in the buffer tank <NUM> is stable.

First, the processor <NUM> starts a timer t_σ (ACT <NUM>). If the timer t_σ is started, the processor <NUM> calculates the variance σm of pressure (ACT <NUM>). If the variance σm of pressure is calculated, the processor <NUM> determines whether the variance σm of pressure is less than <NUM> (ACT <NUM>).

If it is determined that the variance σm of pressure is less than <NUM> (YES in ACT <NUM>), the processor <NUM> increments count_stb (ACT <NUM>).

If it is determined that the variance σm of pressure is not less than <NUM> (NO in ACT <NUM>) or if count_stb is incremented (ACT <NUM>), the processor <NUM> determines whether the timer t_σ is greater than <NUM> (whether <NUM> seconds have elapsed) (ACT <NUM>).

If it is determined that the timer t_σ is not greater than <NUM> (NO in ACT <NUM>), the processor <NUM> waits for <NUM> (ACT <NUM>). After waiting for <NUM>, the processor <NUM> returns to ACT <NUM>.

If it is determined that the timer t_σ is greater than <NUM> (YES in ACT <NUM>), the processor <NUM> determines whether count_stb is greater than <NUM> (ACT <NUM>). If it is determined that count_stb is not greater than <NUM> (NO in ACT <NUM>), the processor <NUM> resets the timer t_σ (sets the timer t_σ to <NUM>) (ACT <NUM>).

If the timer t_σ is reset, the processor <NUM> returns to ACT <NUM>.

If it is determined that count_stb is greater than <NUM> (YES in ACT <NUM>), the processor <NUM> sets a flag indicating that the pressure in the buffer tank <NUM> is stable (ACT <NUM>).

If the flag indicating that the pressure in the buffer tank <NUM> is stable is set, the processor <NUM> ends the action. The processor <NUM> determines that the pressure in the buffer tank <NUM> is stable based on the variance σm of pressure.

The liquid to be discharged is not limited to ink for printing, and application to, for example a device that discharges a liquid containing conductive particles for forming a wiring pattern of a printed wiring board, and the like, may also be contemplated.

In addition to the matters described above, the liquid discharge head <NUM> may have a structure in which a diaphragm is deformed by static electricity to discharge ink droplets, or a structure in which ink droplets are discharged from a nozzle by using thermal energy of a heater or the like.

In the embodiment, the liquid discharge head is illustrated as an example of being used in the ink jet recording apparatus or the like, but the exemplary embodiment is not limited thereto. The liquid discharge head can be used, for example, in a 3D printer, an industrial manufacturing machine, or a medical application.

Claim 1:
A liquid circulation device (<NUM>) configured to be connected to a liquid discharge head (<NUM>), comprising:
a pressurizing pump (<NUM>) configured to supply liquid from a tank (<NUM>) to the liquid discharge head (<NUM>);
a depressurizing pump (<NUM>) configured to collect the liquid from the liquid discharge head (<NUM>);
a buffer tank (<NUM>) connected in parallel with the liquid discharge head between the pressurizing pump (<NUM>) and the depressurizing pump (<NUM>), and configured to store the liquid;
a sensor (<NUM>) configured to measure pressure in the buffer tank (<NUM>); and
a processor configured to determine whether a pressure chamber (<NUM>) included in the liquid discharge head is filled with the liquid based on the measured pressure,
wherein
the processor is configured to acquire the pressure from the sensor in time series, and determine whether the pressure chamber is filled with the liquid based on the pressure acquired in time series, characterized in that
the processor is configured to determine that the pressure chamber (<NUM>) is filled with the liquid, when detecting that the pressure reaches lower limit pressure, the pressure reaches upper limit pressure, and the pressure is stable.