Patent Description:
A fluid circulation apparatus for circulating fluid through a fluid ejection head in a circulation path is known. The fluid ejection apparatus includes a tank having an air layer upstream of the fluid ejection head in the circulation path to alleviate fluctuations in the fluid pressure flowing into the fluid ejection head. Thus fluctuations in the fluid pressure of a nozzle are reduced.

<CIT> discloses a liquid circulation module comprising a tank to store fluid to be supplied to a fluid ejection head and a circulation path including a first flow path portion to provide fluid from the tank to a supply port of the fluid ejection head, and a second flow path portion to return fluid from a collection port of the fluid ejection head to the tank. <CIT> discloses a fluid circulation apparatus according to the preamble of claim <NUM>.

To solve such problem, there is provided a fluid circulation apparatus, according to claim <NUM>.

Preferably, the buffer tank has a flow path cross-sectional area that is larger than a flow path cross-sectional area of the bypass flow path between the buffer tank and at least one of the supply port and the collection port.

Preferably still, the fluid circulation apparatus further comprises:
an accommodating chamber in the buffer tank having a deformable wall.

Suitably, the fluid circulation apparatus further comprises:.

Suitably still, the fluid circulation apparatus further comprises:.

Suitably yet, the bypass flow path comprises a first bypass flow path portion fluidly connecting the first flow path portion to the buffer tank and a second bypass flow path portion fluidly connecting the buffer tank to the second flow path portion, and
the first bypass flow path portion and the second bypass flow path portion are identical to each other in length and a flow path cross-sectional area that is less than a flow path cross-sectional area of the circulation path.

The present invention also relates to a fluid ejection apparatus, comprising:.

Preferably still, the fluid ejection apparatus further comprises:
an accommodating chamber in the buffer tank having a deformable wall.

The fluid ejection apparatus further comprises:
an opening/closing valve connected to an air chamber of the buffer tank and configured to selectively open the air chamber to the atmosphere.

Suitably, the fluid ejection apparatus further comprises:.

Suitably stll, the fluid ejection apparatus further comprises:.

Suitably yet, the fluid ejection apparatus further comprises:.

The present invention also concerns a fluid ejection apparatus, comprising:.

Suitably still, the fluid ejection apparatus further comprises:.

The present invention further relates to a control method for a fluid circulation apparatus according to claim <NUM>, the control method comprising;.

The present invention further concerns a non-transitory computer readable medium storing a program causing a computer to execute the method described above.

The above and other objects, features and advantages of the present invention will be made apparent from the following description of the preferred embodiments, given as non-limiting examples, with reference to the accompanying drawings, in which:.

In general, according to one embodiment, a fluid circulation apparatus includes a first tank to store fluid to be supplied to a fluid ejection head, a circulation path including a first flow path portion to provide fluid from the first tank to a supply port of the fluid ejection head, and a second flow path portion to return fluid from a collection port of the fluid ejection head to the first tank, a bypass flow path that connects the supply port to the collection port outside of the fluid ejection head, and a buffer tank in the bypass flow path.

Hereinafter, an inkjet recording apparatus <NUM> and a fluid ejection apparatus <NUM> according to a first embodiment will be described with reference to <FIG>. It should be noted that the drawings are schematic and are drawn with exaggeration and omissions for purposes of explanatory convenience. In general, components are not drawn to scale. In addition, the number of components, the dimensional ratio between different components, or the like, does not necessarily match between different drawings or to actual devices. <FIG> is a side view of the inkjet recording apparatus <NUM>. <FIG> is an explanatory view of the fluid ejection apparatus <NUM>. <FIG> and <FIG> are a partial perspective view and a partial front view of the configuration of the fluid ejection apparatus <NUM>. <FIG> is an explanatory view of a fluid ejection head <NUM>. <FIG> is an explanatory view of a first circulation pump <NUM>, a second circulation pump <NUM>, and a replenishing pump <NUM>. <FIG> is a block diagram of the fluid ejection apparatus <NUM>.

The inkjet recording apparatus <NUM> shown in <FIG> includes a plurality of the fluid ejection apparatuses <NUM>, a head support mechanism <NUM> for movably supporting the fluid ejection apparatus <NUM>, a medium support mechanism <NUM> for movably supporting a recording medium S, and a host control device <NUM>.

As shown in <FIG>, the plurality of fluid ejection apparatuses <NUM> is arranged in parallel in a predetermined direction and supported by the head support mechanism <NUM>. The fluid ejection apparatus <NUM> integrally includes a fluid ejection head <NUM> and a circulation device <NUM>. The fluid ejection apparatus <NUM> ejects, for example, an ink I from the fluid ejection head <NUM> as fluid, thereby forming a desired image on the recording mediums S arranged opposite to each other.

The plurality of fluid ejection apparatuses <NUM> ejects multiple colors such as a cyan ink, a magenta ink, a yellow ink, a black ink, and a white ink, respectively, but the color or characteristic of the ink I to be used is not limited. For example, in place of a white ink, a transparent glossy ink, a specialty ink that develops a color when irradiated with infrared rays or ultraviolet rays, or the like may be ejected. The plurality of fluid ejection apparatuses <NUM> have the same configuration although fluid to be ejected is different.

The fluid ejection head <NUM> shown in <FIG> is an inkjet head and includes a nozzle plate <NUM> having a plurality of nozzles 21a, a substrate <NUM>, and a manifold <NUM> joined to the substrate <NUM>. The substrate <NUM> is mounted so as to face the nozzle plate <NUM> and is configured in a predetermined shape to form a flow path <NUM> including a plurality of fluid pressure chambers <NUM> in between the substrate <NUM> and the nozzle plate <NUM>. An actuator <NUM> is provided on a portion of the substrate <NUM> facing each fluid pressure chamber <NUM>. The substrate <NUM> has partition walls between adjacent fluid pressure chambers <NUM> in the same row. The actuator <NUM> is disposed to face the nozzle 21a, and the fluid pressure chamber <NUM> is formed between the actuator <NUM> and the nozzle 21a.

The fluid ejection head <NUM> includes the flow path <NUM>, with the ink pressure chamber <NUM> thereon, as formed by the nozzle plate <NUM>, the substrate <NUM>, and the manifold <NUM>. The actuator <NUM> having electrodes 24a and 24b is provided at a portion of the substrate <NUM> facing the fluid pressure chamber <NUM>. The actuator <NUM> is connected to a drive circuit. In the fluid ejection head <NUM>, the actuator <NUM> deforms according to applied voltages under the control of a module control unit <NUM> (depicted in <FIG>), thereby causing fluid to be ejected from the opposing nozzle 21a.

As shown in <FIG>, the circulation device <NUM> is connected to, or integrated with, the upper part of the fluid ejection head <NUM> by metal connecting parts. The circulation device <NUM> includes a circulation path <NUM> through which fluid circulates through the fluid ejection head <NUM>, an intermediate tank <NUM> provided in the circulation path <NUM>, the first circulation pump <NUM>, a bypass flow path <NUM>, a buffer tank <NUM> (as a buffer device <NUM>), the second circulation pump <NUM>, a plurality of opening/closing valves 37a and 37b, and the module control unit <NUM> that controls a fluid ejection operation. In general, a buffer tank is a buffer device and may be a discrete component connected to a flow path or may be an integral portion of the flow path formed or shaped to function as a flow buffer within the flow path.

The circulation device <NUM> includes a cartridge <NUM>, functioning as a supply tank (a first tank) provided outside the circulation path <NUM>, a supply path <NUM>, and the replenishing pump <NUM>. The cartridge <NUM> is configured to hold the fluid to be supplied to the intermediate tank <NUM>, and the internal air chamber of the cartridge <NUM> is open to the atmosphere. The supply path <NUM> is a flow path connecting the intermediate tank <NUM> and the cartridge <NUM>. The replenishing pump <NUM> is provided in the supply path <NUM> and delivers the fluid from the cartridge <NUM> to the intermediate tank <NUM>.

The circulation path <NUM> includes a first flow path 31a connecting the intermediate tank <NUM> and a supply port 20a (of the fluid ejection head <NUM>) and a second flow path 31b connecting a collection port 20b (of the fluid ejection head <NUM>) and the intermediate tank <NUM>. The circulation path <NUM> passes from the intermediate tank <NUM> through the first flow path 31a to the supply port 20a and passes from the collection port 20b through the second flow path 31b to the intermediate tank <NUM>. In the first flow path 31a, the first circulation pump <NUM> is provided. In the second flow path 31b, the second circulation pump <NUM> is provided. The first flow path 31a is provided with a first pressure sensor 39a (also referred to as a first pressure detector) that detects the fluid pressure in the first flow path 31a. The second flow path 31b is provided with a second pressure sensor 39b (also referred to as a second pressure detector) that detects the fluid pressure in the second flow path 31b.

The intermediate tank <NUM> is connected to the fluid ejection head <NUM> by the circulation path <NUM> and is configured to store fluid. The intermediate tank <NUM> is provided with the opening/closing valve 37a configured to open the air chamber of the intermediate tank <NUM> to the atmosphere. A fluid level sensor <NUM> is provided to detect the fluid level in the intermediate tank <NUM>.

The bypass flow path <NUM> is a flow path that connects the downstream side of the first circulation pump <NUM> on the first flow path 31a and the upstream side of the second circulation pump <NUM> on the second flow path. The bypass flow path <NUM> connects the primary side of the fluid ejection head <NUM> and the secondary side of the fluid ejection head <NUM> in the circulation path <NUM> in a short circuiting manner (that is, without passing through the fluid ejection head <NUM>). The buffer tank <NUM> is connected to the bypass flow path <NUM>. That is, the bypass flow path <NUM> includes a first bypass flow path 34a connecting the buffer tank <NUM> and the first flow path 31a and a second bypass flow path 34b connecting the buffer tank <NUM> and the second flow path 31b.

According to the invention, the first bypass flow path 34a and the second bypass flow path 34b have the same length and the same diameter, both of which have a smaller diameter than the circulation path <NUM>. For example, in the first embodiment, the diameter of the circulation path <NUM> is set to about <NUM> to <NUM> times the diameter of the first bypass flow path 34a or the second bypass flow path 34b. As an example, the flow path diameter ϕ1 of the bypass flow path <NUM> is set to <NUM> or less, and the flow path diameter ϕ2 of the circulation path <NUM> is set to about <NUM>. The first bypass flow path 34a and the second bypass flow path 34b are each configured to have a length L1 of about <NUM>.

According to the invention, the buffer tank <NUM> is provided at a midpoint of the bypass flow path <NUM>. In the circulation path <NUM>, the distance from a branch point at which the bypass flow path <NUM> branches from the first flow path 31a to the supply port 20a is the same as the distance from the collection port 20b to the junction point of the second bypass flow path 34b.

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 store fluid. The buffer tank <NUM> has, for example, an upper wall, a lower wall, a rear wall, a front wall, and a pair of right and left side walls and is configured to have a rectangular box shape forming an accommodating chamber 35a for storing fluid therein. The bypass flow path <NUM> is connected to predetermined portions of the lower portion of the pair of side walls of the buffer tank <NUM>, respectively. In the first embodiment, for example, the connection position of the first bypass flow path 34a on the inflow side to the buffer tank <NUM> and the connection position of the second bypass flow path 34b on the outflow side to the buffer tank <NUM> are set to the same height.

The buffer tank <NUM> has a flow path cross-sectional area <NUM> times to <NUM> times the flow path cross-sectional area of the bypass flow path <NUM>. For example, the buffer tank <NUM> is configured such that the dimensions in a height direction and a depth direction, which are two directions orthogonal to the bypass flow path <NUM>, are <NUM>, respectively and the dimension in a width direction parallel to the bypass flow path <NUM> is about <NUM>.

In the buffer tank <NUM>, the fluid flowing through the bypass flow path <NUM> is disposed in the lower region of the accommodating chamber 35a, and an air chamber is formed in the upper region of the accommodating chamber 35a. That is, the buffer tank <NUM> may store a predetermined amount of fluid and air. By this buffer tank <NUM>, the flow path cross-sectional area of the fluid flowing from the bypass flow path <NUM> is enlarged, whereby the accommodating chamber 35a acts as a spring, and fluctuations in the pressure in the circulation path <NUM> are absorbed.

The buffer tank <NUM> is configured so that the volume of the accommodating chamber 35a is variable. Specifically, a part of the wall forming the accommodating chamber 35a (<FIG>) of the buffer tank <NUM> is made of an elastically deformable material. Here, the front wall forming the accommodating chamber 35a of the buffer tank <NUM> is composed of a deformable film 35c made of, for example, polyimide or PTFE.

The opening/closing valve 37b is configured to open the air chamber of the buffer tank <NUM> to the atmosphere. That is, a connecting pipe 35d extending upward is provided on the upper wall of the buffer tank <NUM>, and the opening/closing valve 37b that opens and closes the flow path in the connecting pipe 35d is provided at the other end of the connecting pipe 35d.

The circulation path <NUM>, the bypass flow path <NUM>, and the supply path <NUM> include a pipe made of a metal or a resin material, and a tube that covers the outer surface of the pipe, for example, a PTFE tube.

The first pressure sensor 39a and the second pressure sensor 39b output pressure as an electric signal using a semiconductor piezoresistive pressure sensor, for example. The semiconductor piezoresistive pressure sensor includes a diaphragm that receives external pressure and a semiconductor strain gauge formed on the surface of the diaphragm. The semiconductor piezoresistive pressure sensor detects the pressure by converting the change in the electrical resistance caused by the piezoresistive effect generated in the strain gauge as the diaphragm deforms due to the pressure from the outside into an electric signal.

The fluid level sensor <NUM> is configured to include a float <NUM> floating on the fluid surface and moving up and down and Hall ICs 56a and 56b provided at two predetermined positions in the upper and lower portions. The fluid level sensor <NUM> detects the amount of fluid in the intermediate tank <NUM> by detecting the float <NUM> reaching an upper limit position and the lower limit position by the Hall ICs 56a and 56b to send the detected data to the module control unit <NUM>.

The opening/closing valves 37a and 37b are provided in the intermediate tank <NUM> and the buffer tank <NUM>. The opening/closing valves 37a and 37b are normally closed solenoid opening/closing valves which are opened when power is turned on and closed when the power is turned off. The opening/closing valves 37a and 37b are opened and closed under the control of the module control unit <NUM>, so that the air chamber of the intermediate tank <NUM> and the buffer tank <NUM> may be opened and closed with respect to the atmosphere.

The first circulation pump <NUM> is provided in the first flow path 31a of the circulation path <NUM>. The first circulation pump <NUM> is disposed between the primary side of the fluid ejection head <NUM> and the intermediate tank <NUM> and sends fluid toward the fluid ejection head <NUM> disposed downstream. The fluid in the first flow path 31a is distributed to the fluid flowing in the fluid ejection head <NUM> and the fluid flowing in the buffer tank <NUM> through the bypass flow path <NUM>, according to the flow resistance of the flow path through the fluid ejection head <NUM> and the flow path through the bypass flow path <NUM>. In the first embodiment, the bypass flow path <NUM> has a smaller diameter than the circulation path <NUM> so that the flow path resistance on the bypass flow path <NUM> side is <NUM> to <NUM> times the flow path resistance on the fluid ejection head <NUM> side.

The pressure in the circulation path <NUM> is such that the primary side of the fluid ejection head <NUM>, that is, the inflow side is at a higher pressure than the secondary side of the fluid ejection head <NUM>, that is, the outflow side due to the pressure loss due to the resistance of the fluid ejection head <NUM>. Therefore, in the circulation path <NUM> and the bypass flow path <NUM> passing through the fluid ejection head <NUM>, fluid flows from the high-pressure primary side to the low-pressure secondary side, as indicated by arrows in <FIG>.

The second circulation pump <NUM> is provided in the second flow path 31b of the circulation path <NUM>. The second circulation pump <NUM> is disposed between the secondary side of the fluid ejection head <NUM> and the intermediate tank <NUM> and sends fluid to the intermediate tank <NUM> disposed downstream.

The replenishing pump <NUM> is provided in the supply path <NUM>. The replenishing pump <NUM> sends the ink I held in the cartridge <NUM> toward the intermediate tank <NUM>.

The first circulation pump <NUM>, the second circulation pump <NUM>, and the replenishing pump <NUM> each include a piezoelectric pump <NUM> as shown in <FIG>, for example. The piezoelectric pump <NUM> includes a pump chamber <NUM>, a piezoelectric actuator <NUM> provided in the pump chamber <NUM> and vibrating by a voltage, and check valves <NUM> and <NUM> disposed at the inlet and outlet of the pump chamber <NUM>. The piezoelectric actuator <NUM> is configured to vibrate at a frequency of, for example, about <NUM> to <NUM>. The first circulation pump <NUM>, the second circulation pump <NUM>, and the replenishing pump <NUM> are connected to the drive circuit by wiring and are configured to be controllable under the control of the module control unit <NUM>. When an AC voltage is applied to the piezoelectric pump <NUM> and the piezoelectric actuator <NUM> is operated, the volume of the pump chamber <NUM> changes. In the piezoelectric pump <NUM>, when the applied voltage changes, the maximum change amount of the piezoelectric actuator <NUM> changes, and the volume change amount of the pump chamber <NUM> changes. Then, when the volume of the pump chamber <NUM> is deformed in a direction to increase, the check valve <NUM> at the inlet of the pump chamber <NUM> is opened and the fluid flows into the pump chamber <NUM>. On the other hand, when the volume of the pump chamber <NUM> changes in a direction to decrease, the check valve <NUM> at the outlet of the pump chamber <NUM> opens and the fluid flows out from the pump chamber <NUM>. The piezoelectric pump <NUM> repeats expansion and contraction of the pump chamber <NUM> to deliver the ink I to the downstream. Therefore, when the voltage applied to the piezoelectric actuator <NUM> is large, fluid delivery capability becomes strong, and when the voltage is small, the fluid delivery capability becomes weak. For example, in the first embodiment, the voltage applied to the piezoelectric actuator <NUM> is varied between <NUM> V and <NUM> V.

As shown in <FIG>, the module control unit <NUM> includes a CPU <NUM>, drive circuits 75a to 75e for driving each element, a storage unit <NUM> that stores various kinds of data, and a communication interface <NUM> for communication with an externally provided host control device (host computer) <NUM> on a control board integrally mounted on the circulation device <NUM>.

The module control unit <NUM> communicates with the host control device <NUM> in a state of being connected to the host control device <NUM> through the communication interface <NUM>, thereby receiving various information such as operation conditions and like.

An input operation by the user and an instruction from the host control device <NUM> of the inkjet recording apparatus <NUM> are transmitted to the CPU <NUM> of the module control unit <NUM> by the communication interface <NUM>. Various information acquired by the module control unit <NUM> is sent to the host control device <NUM> of the inkjet recording apparatus <NUM> via the communication interface <NUM>.

The CPU <NUM> corresponds to the central part of the module control unit <NUM>. The CPU <NUM> controls each unit to realize various functions of the fluid ejection apparatus <NUM> according to the operating system and the application program.

The various pumps <NUM>, <NUM>, and <NUM> of the circulation device <NUM>, the drive circuits 75a, 75b, 75c, 75d of the opening/closing valves 37a and 37b, the various sensors 39a, 39b, <NUM>, and the drive circuit 75e of the fluid ejection head <NUM> are connected to the CPU <NUM>.

For example, the CPU <NUM> has a function as circulation means for circulating the fluid by controlling the operations of the first and second circulation pumps <NUM> and <NUM>.

The CPU <NUM> has a function as replenishing means for replenishing fluid from the cartridge <NUM> to the circulation path <NUM> by controlling the operation of the replenishing pump <NUM> based on the information detected by the fluid level sensor <NUM> and the pressure sensors 39a and 39b.

The CPU <NUM> has a function as a pressure adjustment unit for adjusting the fluid pressure of the nozzle 21a by controlling the fluid delivery capability of the first circulation pump <NUM> and the second circulation pump <NUM> based on the information detected by the first pressure sensor 39a, the second pressure sensor 39b, and the fluid level sensor <NUM>.

The CPU <NUM> functions as fluid level adjusting means for adjusting the fluid level of the intermediate tank <NUM> and the buffer tank <NUM> by controlling the opening/closing of the opening/closing valves 37a and 37b.

The storage unit <NUM> includes, for example, a program memory and a RAM. The storage unit <NUM> stores an application program and various setting values. In the storage unit <NUM>, various setting values such as a calculation formula for calculating the fluid pressure of the nozzle 21a, a target pressure range, an adjustment maximum value of each pump, and the like are stored as control data used for pressure control, for example.

Hereinafter, a control method of the fluid ejection apparatus <NUM> according to the first embodiment will be described with reference to the flowchart of <FIG>.

In Act <NUM>, the CPU waits for an instruction to start circulation. For example, when an instruction to start circulation is detected with a command from the host control device <NUM> (Yes in Act <NUM>), the processing proceeds to Act <NUM>. As a printing operation, the host control device <NUM> forms an image on the recording medium S by performing a fluid ejecting operation while reciprocally moving the fluid ejection apparatus <NUM> in a direction orthogonal to the carrying direction of the recording medium S. Specifically, the CPU <NUM> carries a carriage 11a (<FIG>) provided in the head support mechanism <NUM> in the direction of the recording medium S to reciprocally move in the direction of an arrow A. The CPU <NUM> sends the image signal corresponding to the image data to the drive circuit 75e of the fluid ejection head <NUM>, selectively drives the actuator <NUM> of the fluid ejection head <NUM>, and ejects droplets of fluid from the nozzle 21a to the recording medium S.

In Act <NUM>, the CPU <NUM> drives the first circulation pump <NUM> and the second circulation pump <NUM> to start a fluid circulation operation. Here, the ink I in the first flow path 31a is distributed to the fluid flowing in the fluid ejection head <NUM> and the fluid flowing in the buffer tank <NUM> through the bypass flow path <NUM>, according to the flow resistance of the flow path through the fluid ejection head <NUM> and the flow path through the bypass flow path <NUM>. That is, a part of the ink I flows from the intermediate tank <NUM> to the fluid ejection head <NUM> through the first flow path 31a, passes through the second flow path 31b, and flows into the intermediate tank <NUM> again. The remaining part of the ink I passes through the bypass flow path <NUM> and the buffer tank <NUM> from the first flow path 31a, is sent to the second flow path 31b without passing through the fluid ejection head <NUM>, and flows into the intermediate tank <NUM> again. By this circulation operation, the impurities contained in the ink I are removed by the filter provided in the circulation path <NUM>.

In Act <NUM>, the CPU <NUM> opens the opening/closing valve 37a of the intermediate tank <NUM> and opens the intermediate tank <NUM> to the atmosphere. Since the intermediate tank <NUM> is open to the atmosphere and constantly has a constant pressure, pressure drop in the circulation path due to fluid consumption of the fluid ejection head <NUM> is prevented. Here, when the opening/closing valve 37a is opened for a long time to an extent that there is concern about temperature rise of the opening/closing valve 37a, the opening/closing valve 37a may be opened periodically for a short time. Even if the opening/closing valve 37a is closed, it is possible to keep the fluid pressure of the nozzle constant unless the circulation path is excessively reduced in pressure. The solenoid type opening/closing valve 37a is normally closed. Therefore, even if the power supply to the apparatus suddenly stops due to a power failure or the like, the opening/closing valve 37a may shut off the intermediate tank <NUM> from the atmospheric pressure by being closed instantaneously and seal the circulation path <NUM>. Therefore, it is possible to suppress leakage of the ink I from the nozzle 21a of the fluid ejection head <NUM>.

At the timing instructed by the host control device <NUM>, the CPU <NUM> opens the opening/closing valve 37b of the buffer tank <NUM> and opens the buffer tank <NUM> to the atmosphere. Since the buffer tank <NUM> is opened to the atmosphere and has atmospheric pressure, the fluid level of the buffer tank <NUM> is lowered.

In this fluid circulation operation, the pressure fluctuation accompanying the ejection operation of the fluid or the like is absorbed by the volume change of the buffer tank <NUM> and the spring action of the air of the accommodating chamber 35a, and the pressure variation is alleviated.

In Act <NUM>, the CPU <NUM> detects the pressure data transmitted from the first pressure sensor 39a. The CPU <NUM> detects the fluid level of the intermediate tank <NUM> based on the data transmitted from the fluid level sensor <NUM>.

In Act <NUM>, the CPU <NUM> starts fluid level adjustment. Specifically, the CPU <NUM> drives the replenishing pump <NUM> based on the detection results of the fluid level sensor <NUM>, thereby performing fluid replenishment from the cartridge <NUM> and adjusting the fluid level position to an appropriate range. For example, at the time of printing, the ink I is ejected from the nozzle 21a, the fluid amount of the intermediate tank <NUM> instantaneously decreases, and when the fluid level is lowered, the fluid is replenished. When the fluid amount increases again and the output of the fluid level sensor <NUM> is inverted, the CPU <NUM> stops the replenishing pump <NUM>.

In Act <NUM>, the CPU <NUM> detects the fluid pressure of the nozzle from the pressure data. Specifically, the fluid pressure of the nozzle 21a is calculated by using a predetermined arithmetic expression based on the pressure data on the upstream side and the downstream side transmitted from the first and second pressure sensors 39a and 39b.

For example, it is possible to obtain a fluid pressure Pn of the nozzle by adding a pressure ρgh generated by the water head difference between the height of the pressure measurement point and the head height of the nozzle surface height to the average value of a fluid pressure value Ph of the first flow path 31a and a fluid pressure value Pl of the second flow path 31b. Here, it is assumed that ρ is a density of the fluid, g is gravitational acceleration, and h is a distance between the pressure measurement point and the height direction of the nozzle surface.

As the pressure adjustment processing, the CPU <NUM> calculates a drive voltage based on the fluid pressure Pn of the nozzle calculated from the pressure data. Then, the CPU <NUM> maintains a negative pressure to an extent that the ink I does not leak from the nozzle 21a of the fluid ejection head <NUM> and bubbles are not sucked from the nozzle 21a and maintains a meniscus Me (<FIG>) by driving the first circulation pump <NUM> and the second circulation pump <NUM> so that the fluid pressure Pn of the nozzle becomes an appropriate value. Here, as an example, it is assumed that the upper limit of a target value is P1H and the lower limit is P1L.

In Act <NUM>, the CPU <NUM> determines whether the fluid pressure Pn of the nozzle 21a is within an appropriate range, that is, whether P1L≤Pn≤P1H. If Pn is out of the appropriate range (No in Act <NUM>), the CPU <NUM> determines whether or not the fluid pressure Pn of the nozzle 21a exceeds the upper limit of the target value P1H as Act <NUM>.

The fluid pressure at the nozzle 21a of the fluid ejection head <NUM> is pressurized when the driving of the first circulation pump <NUM> is relatively strong, and is depressurized when the driving of the second circulation pump <NUM> is relatively strong.

The CPU <NUM> further determines whether or not the drive voltage is within the adjustment range of the first circulation pump <NUM> and the second circulation pump <NUM> (Acts <NUM> and <NUM>) and pressurizes or depressurizes by using the first circulation pump <NUM> and the second circulation pump <NUM> when the drive voltage exceeds an adjustment maximum value Vmax of the first and second circulation pumps <NUM> and <NUM>.

More specifically, when the fluid pressure Pn of the nozzle 21a is out of the appropriate range (No in Act <NUM>) and the fluid pressure Pn of the nozzle 21a does not exceed the target value upper limit P1H (No in Act <NUM>), that is, when the fluid pressure Pn of the nozzle is lower than the target lower limit P1L, the CPU <NUM> determines whether or not a drive voltage V+ of the pressurizing side first circulation pump <NUM> is equal to or higher than the adjustment maximum value Vmax, that is, whether or not the drive voltage V+ exceeds the adjustable range of the first circulation pump <NUM> as Act <NUM>. When the drive voltage V+ of the pressurizing side first circulation pump <NUM> is equal to or higher than the adjustment maximum value Vmax (Yes in Act <NUM>), the CPU <NUM> pressurizes the voltage by lowering the voltage of the second circulation pump <NUM> as Act <NUM>. On the other hand, if the drive voltage V+ of the first circulation pump on the pressurizing side is lower than the adjustment maximum value Vmax, and within the adjustable range (No in Act <NUM>), the CPU <NUM> pressurizes the voltage by increasing the drive voltage of the first circulation pump <NUM> as Act <NUM>.

In Act <NUM>, when the fluid pressure Pn of the nozzle exceeds the target value upper limit P1H (Yes in Act <NUM>), the CPU <NUM> determines whether or not a drive voltage V- of the second circulation pump <NUM> on the depressurizing side is equal to or higher than the adjustment maximum value Vmax, that is, whether or not the drive voltage V-exceeds the adjustment range of the second circulation pump <NUM> as Act <NUM>. When the drive voltage V- of the second circulation pump <NUM> on the depressurizing side is equal to or higher than the adjustment maximum value Vmax (Yes in Act <NUM>), the CPU <NUM> depressurizes the voltage by lowering the voltage of the first circulation pump <NUM> as Act <NUM>. On the other hand, if the drive voltage V- of the second circulation pump <NUM> on the depressurizing side is lower than the adjustment maximum value Vmax, and within the adjustable range (No in Act <NUM>), the CPU <NUM> depressurizes the voltage by decreasing the drive voltage of the second circulation pump <NUM> as Act <NUM>. That is, the CPU <NUM> performs pressure adjustment in Acts <NUM> to <NUM>.

If Pn of the fluid pressure of the nozzle plate <NUM> is within the appropriate range (Yes in Act <NUM>), the CPU <NUM> proceeds to Act <NUM>. The CPU <NUM> performs feedback control of Acts <NUM> to <NUM> until a circulation end command is detected in Act <NUM>. Then, when detecting an instruction to end the circulation with a command from the host control device <NUM> (Yes in Act <NUM>), the CPU <NUM> closes the opening/closing valve 37a of the intermediate tank <NUM> and seals the intermediate tank <NUM> (Act <NUM>). The CPU <NUM> stops the first circulation pump <NUM> and the second circulation pump <NUM> and ends the circulation processing (Act <NUM>).

The fluid ejection apparatus <NUM> configured as described above may stabilize the ejection performance of the fluid ejection head <NUM> by connecting the flow paths on the upstream side and the downstream side of the fluid ejection head <NUM> with the bypass flow path <NUM> and providing the buffer tank <NUM>. That is, by connecting the flow paths on the upstream side and the downstream side of the fluid ejection head <NUM> with the bypass flow path <NUM> and disposing the buffer tank <NUM> and the fluid ejection head <NUM> in parallel, due to the change in the flow path cross-sectional area between the bypass flow path <NUM> and the buffer tank <NUM> and the action of an air layer in the buffer tank <NUM> as an air spring, the pressure fluctuation in the bypass flow path <NUM> is absorbed and the pulsation is absorbed, thereby stabilizing the ejection performance.

For example, when the circulation path <NUM> becomes negative pressure due to a large amount of fluid ejection, the volume of the buffer tank <NUM> is reduced and the fluid level of the buffer tank <NUM> is lowered so that the pressure fluctuation on the circulation path <NUM> side may be absorbed.

The bypass flow path <NUM> is configured to flow fluid without passing through the fluid ejection head <NUM>. Therefore, for example, if the pressure of the bypass flow path <NUM> is greatly decreased, the fluid level in the buffer tank <NUM> is lowered. Even if air bubbles are mixed, since the bubbles in the buffer tank <NUM> are sent to the intermediate tank <NUM> through the second bypass flow path 34b on the downstream side without passing through the fluid ejection head <NUM>, the air bubbles may be removed and the ejection performance is not affected.

The fluid ejection apparatus <NUM> may stabilize the fluid level of the buffer tank <NUM> at all times because the buffer tank <NUM> is configured to be openable to the atmosphere. In the fluid ejection apparatus <NUM>, a part of the buffer tank <NUM> is made of a material which may be elastically deformable, and the volume is variable, thereby ensuring the absorption amount of the pressure fluctuation.

The fluid ejection apparatus <NUM> appropriately sets the pipe resistance of the bypass flow path <NUM>, thereby appropriately maintaining the flow rate of the fluid passing through the fluid ejection head <NUM> and the fluid flowing through the bypass flow path <NUM>.

The fluid ejection apparatus <NUM> may maintain the fluid pressure of the nozzle properly by detecting the pressure on both the upstream side and the downstream side of the fluid ejection head <NUM> and performing feedback control of the pressure with the first circulation pump <NUM> and the second circulation pump <NUM> that pressurize. Therefore, even when the pump performance changes over time, it is possible to realize appropriate pressure control.

In the fluid ejection apparatus <NUM>, since the piezoelectric pump <NUM> is used as the first circulation pumps <NUM> and <NUM>, the configuration is simple and material selection is easy. That is, the piezoelectric pump <NUM> does not require a large drive source such as a motor, a solenoid, and the like and may be made smaller than a general diaphragm pump, a piston pump, and a tube pump. For example, if a tube pump is used, there is a possibility that the tube and the fluid come into contact with each other, and therefore it is necessary to select a material that does not cause deterioration of the tube or fluid. On the other hand, it is easy to select a material by using piezoelectric pump <NUM>. For example, in the first embodiment, the fluid contact parts of the piezoelectric pump <NUM> may be made of SUS <NUM>, PPS, PPA, and polyimide which are excellent in chemical resistance.

In the first embodiment, by using the first circulation pump <NUM> on the upstream side which may be pressurized when the voltage is increased and depressurized when the voltage is lowered, and the second circulation pump <NUM> on the downstream side which may be depressurized when the voltage is increased and pressurized when the voltage is lowered, when the drive voltage exceeds the adjustable range, another pump may be used, thereby realizing highly accurate control. The functions required for controlling the first circulation pump <NUM>, the second circulation pump <NUM>, the replenishing pump <NUM>, the first and second pressure sensors 39a, 39b, the fluid level sensor <NUM>, the control board <NUM>, and other fluid supply, circulation, and pressure adjustment are concentrated in the circulation device <NUM>. Therefore, as compared with a large-sized stationary type circulation device, it is possible to simplify the connection and the electrical connection between the main body of the inkjet recording apparatus <NUM> and the carriage 11a. As a result, the inkjet recording apparatus <NUM> may be reduced in size, weight, and cost.

Hereinafter, a fluid ejection apparatus 10A according to a second embodiment will be described with reference to <FIG> is an explanatory view of the fluid ejection apparatus 10A. The fluid ejection apparatus 10A according to the second embodiment is the same as the fluid ejection apparatus <NUM> according to the first embodiment except that the cartridge <NUM> is used as the intermediate tank <NUM>. The same reference numerals are used for the components that are substantially the same as those of the first embodiment, and the description of repeated components may be omitted.

As shown in <FIG>, in the fluid ejection apparatus 10A according to the second embodiment, as the intermediate tank <NUM>, the intermediate tank <NUM> that is openable to the atmosphere is disposed in the circulation path <NUM> between the first flow path 31a and the second flow path 31b. That is, the cartridge <NUM> in the fluid ejection apparatus <NUM> is used as the intermediate tank <NUM>. The opening/closing valve 37a may control opening/closing of the intermediate tank <NUM> with respect to the atmosphere, or the intermediate tank <NUM> may be always opened to the atmosphere. In the second embodiment, the same effect as in the first embodiment may be obtained. The cartridge <NUM> is used as the intermediate tank <NUM>, and the configuration thereof may be omitted. In a fluid circulation apparatus and a fluid ejection apparatus having the above structure, the same effect as in the first embodiment may be obtained.

The configuration of the fluid ejection apparatus according to the example embodiments described above is not limited.

For example, the connection positions to the buffer tank <NUM> are set to the same height, but a height of the connection positions is not limited thereto. For example, the outflow port of the buffer tank <NUM> may be disposed above the inflow port. In this case, it is easy to guide the bubbles to the outflow side, and it is possible to promote discharge of bubbles.

The structure of the buffer device is not limited to those in the example embodiments described above. For example, in the example embodiments described above, the buffer tank <NUM>, as a buffer device has a rectangular parallelepiped box. However, in some embodiments, a buffer device <NUM> depicted in <FIG> may include a buffer tank <NUM> in which the flow path diameter gradually expands and contracts and an inner wall is formed in a curved surface shape. Even in this case, due to the change in the flow path cross-sectional area and the action of the air layer of the accommodating chamber 135a as an air spring, it is possible to obtain an effect of stabilizing the ejection performance by absorbing the pressure fluctuation in the bypass flow path <NUM> and absorbing the pulsation.

In some embodiments, the buffer device <NUM> depicted in <FIG> may include a plurality of buffer tanks <NUM> having a flow path cross-sectional areas enlarged in the bypass flow path <NUM>. The plurality of buffer tanks <NUM> is disposed in series in the bypass flow path <NUM>. That is, the bypass flow path <NUM> changes the cross-sectional area thereof so as to repeatedly expand and contract the flow path cross-sectional area multiple times. Even in this case, due to the change in the flow path cross-sectional area and the action of the air layer of an accommodating chamber 235a as an air spring, it is possible to obtain an effect of stabilizing the ejection performance by absorbing the pressure fluctuation in the bypass flow path <NUM> and absorbing the pulsation.

In some embodiments, the buffer device <NUM> depicted in <FIG> may be replaced with the buffer tank <NUM> in which the pipe wall of the bypass flow path <NUM> is formed of an elastically deformable material such as thin polyimide, thin PTFE or the like, and include a chamber <NUM> that constitutes an air chamber 335a on the outer periphery of the bypass flow path <NUM>. That is, the buffer device <NUM> surrounds the deformable bypass flow path <NUM> with the air chamber 335a. Even in this case, by forming the pipe wall of the bypass flow path <NUM> with an elastically deformable material, due to the change in the flow path cross-sectional area and the action of the air layer of the air chamber 335a as an air spring, it is possible to obtain an effect of stabilizing the ejection performance by absorbing the pressure fluctuation in the bypass flow path <NUM> and absorbing the pulsation.

It is also possible to add elements such as a distributing plate or an impeller in the buffer tank <NUM>. In some embodiments, the buffer device <NUM> depicted in <FIG> may include a distributing plate inside the buffer tank <NUM> in which the flow path cross-sectional area is enlarged. Even in this case, due to the change in the flow path cross-sectional area of the bypass flow path <NUM> and the action of the air layer of an accommodating chamber 35a as an air spring, it is possible to obtain an effect of stabilizing the ejection performance by absorbing the pressure fluctuation in the bypass flow path <NUM> and absorbing the pulsation.

In the example embodiments described above, the flow path diameter of the bypass flow path <NUM> is smaller than the flow path diameter of the circulation path <NUM> which is the mainstream and the flow path resistance on the bypass flow path <NUM> side is increased. However, the flow path diameter of the bypass flow path <NUM> is not limited thereto. For example, when the flow rate may be secured, it is also possible to reduce the flow resistance on the bypass flow path <NUM> side by making the diameter of the bypass flow path <NUM> larger than the diameter of the circulation path <NUM>.

Here, the operation principle will be described. In <FIG>, the pressure of the supply port 20a of the first bypass flow path 34a and the fluid ejection head <NUM> is the same. The pressure of the collection port 20b of the second bypass flow path 34b and the fluid ejection head <NUM> is the same. If the diameter of the bypass flow path <NUM> is made larger than the diameter of the circulation path <NUM>, the amount of fluid flowing into the bypass flow path <NUM> and the buffer tank <NUM> is larger than the amount of fluid flowing in the fluid ejection head <NUM>. Then, the pressure of the bypass flow path <NUM> having a large amount of flowing fluid determines the pressure of the supply port 20a of the fluid ejection head <NUM> and the pressure of the collection port 20b of the fluid ejection head <NUM> more predominantly. Therefore, the pressure of the fluid ejection head <NUM> will be influenced more by the pressure of the bypass flow path <NUM>. The pressure fluctuation is absorbed by the change in the flow path cross-sectional area between the bypass flow path <NUM> and the buffer tank <NUM> and the action of the air layer in the buffer tank <NUM> as an air spring and is influenced more by the pressure of the bypass flow path <NUM> whose pulsation is absorbed, whereby the pulsation of the fluid ejection head <NUM> may be reduced, and the ejection performance is stabilized.

The fluid ejection apparatuses <NUM> and 10A may also eject fluid other than ink. As a fluid ejection apparatus that ejects fluid other than ink, for example, an apparatus that ejects fluid containing conductive particles for forming a wiring pattern of a printed wiring board, or the like may be used.

In some embodiments, the fluid ejection head <NUM> may have a structure in which droplets of fluid are ejected by deforming the diaphragm with static electricity, a structure in which droplets of fluid are ejected from a nozzle using thermal energy of a heater, or the like.

In the example embodiments described above, the fluid ejection apparatus is used for the inkjet recording apparatus <NUM>. However, the use of the fluid apparatus is not limited to this example. The fluid ejection apparatus may also be used, for example, in 3D printers, industrial manufacturing machines, and medical applications and may be reduced in size, weight, and cost.

As the first circulation pump <NUM>, the second circulation pump <NUM>, and the replenishing pump <NUM>, for example, a tube pump, a diaphragm pump, a piston pump or the like may be used instead of the piezoelectric pump <NUM>.

In the example embodiments described above, the circulation pumps <NUM> and <NUM> are provided on the upstream side and the downstream side, respectively. However, a single circulation pump may be used. Even in this case, it is possible to perform the same function as in the above embodiment by adjusting the positive and negative pressure states of the circulation path by pushing and pulling the fluid.

Claim 1:
A fluid circulation apparatus, comprising:
a first tank (<NUM>) to store fluid to be supplied to a fluid ejection head (<NUM>);
a circulation path (<NUM>) including a first flow path portion (31a) to provide fluid from the first tank (<NUM>) to a supply port (20a) of the fluid ejection head (<NUM>), and a second flow path portion (<NUM> b) to return fluid from a collection port (20b) of the fluid ejection head (<NUM>) to the first tank (<NUM>);
the fluid circulation apparatus further comprises:
a bypass flow path (<NUM>) that connects a primary side of the fluid ejection head (<NUM>) and a secondary side of the fluid ejection head (<NUM>) in the circulation path (<NUM>) in a short circuiting manner; and
a buffer tank (<NUM>) that is provided in the middle of the bypass flow path (<NUM>), wherein
the fluid flowing through the bypass flow path (<NUM>) is disposed in a lower region of an accommodation chamber (35a) of the buffer tank (<NUM>), and an air chamber is formed in an upper region of the accommodating chamber (35a),
the bypass flow path (<NUM>) includes a first bypass flow path (34a) connecting the buffer tank (<NUM>) and the first flow path (31a) and a second bypass flow path (34b) connecting the buffer tank (<NUM>) and the second flow path (31b), and
the fluid circulation apparatus further comprises an opening/closing valve (37b) connected to the air chamber of the buffer tank (<NUM>) and configured to selectively open the air chamber to the atmosphere;
characterized in that
the first bypass flow path (34a) and the second bypass flow path (34b) have the same length and the same diameter, the diameter being smaller than the diameter of the circulation path (<NUM>).