Patent Description:
Conventionally, an inkjet image forming apparatus (hereinafter, referred to as an image forming apparatus) that forms (records) an image on a recording medium by ejecting ink from a plurality of nozzles provided in an inkjet head to the recording medium conveyed by a conveyance device has been known.

Some image forming apparatuses include an ink supply mechanism that supplies ink to the inkjet head while circulating ink between a supply tank supplying ink, an inkjet head, and a collection tank collecting ink (e.g., see Patent Literature (hereinafter, referred to as "PTL") <NUM> and PTL <NUM>).

In the above-described ink supply mechanism, the supply tank supplying ink to the inkjet head is disposed above the inkjet head. The supply tank and the inkjet head are connected to each other through an ink supply path.

Negative pressure (negative pressure for meniscus) is applied to the supply tank, and this negative pressure forms an appropriate meniscus pressure at the ejection opening of the inkjet head. An appropriate control of the meniscus pressure can form a meniscus having an appropriate shape in the ejection opening of the inkjet head.

Further, in the above-described ink supply mechanism, the collection tank collecting ink from the inkjet head is disposed above the inkjet head and at a position lower than the supply tank. Negative pressure that is the same as that applied to the supply tank is also applied to this collection tank, and the ink having been supplied to the inkjet head is guided through an ink collection path due to the height difference (water head difference) between the supply tank and the collection tank. The flow rate of ink flowing to the inkjet head is adjusted due to the height difference between the supply tank and the collection tank.

A configuration in which the negative pressure having the same magnitude is applied to the supply tank and the collection tank will be described hereinafter. The supply tank and the collection tank each communicate with a pressure reduction tank (buffer tank) configured to be capable of accommodating a predetermined volume of gas. A vacuum pump is connected to the pressure reduction tank through a vacuum path. Then, the pressure in the pressure reduction tank is reduced to a predetermined pressure by the driving control of the vacuum pump, and the pressure in the supply tank and the collection tank, which communicate with the pressure reduction tank, is also reduced to a predetermined pressure (negative pressure is applied).

Note that the collection tank and the supply tank are connected to each other through a circulation path in which a pump is provided. When a level sensor disposed in the supply tank detects that the ink level in the supply tank has fallen below a predetermined level, the pump is driven, and the ink having being collected in the collection tank is returned to the supply tank through the circulation path.

<CIT> relates to an ink circulation mechanism that circulates ink in a circulation path including an inkjet head and a printing apparatus incorporating the ink circulation mechanism. While an ink circulation mechanism that circulates ink in order to prevent ejection failure of an ink jet head due to ink thickening or the like is known, <CIT> provides an ink circulation mechanism and a printing apparatus including a check valve to restrict the flow of ink, which can suppress ink deterioration.

However, in the above-described ink supply mechanism, the flow rate of ink flowing to the inkjet head can be increased by an increase of the height difference between the supply tank and the collection tank; however, in order to increase the height difference, the height position of the supply tank and the height position of the collection tank need to be widely separated from each other, which results in an increase in the size of the apparatus.

To solve the problem, a configuration is conceivable in which the height difference between the supply tank and the collection tank is eliminated, the negative pressures of different magnitudes are applied to the supply tank and the collection tank, and the pressure difference (atmospheric pressure difference) between the supply tank and the collection tank guides the ink having been supplied to the inkjet head to the collection tank. However, when a plurality of supply tanks and collection tanks are provided to the plurality of inkjet heads, respectively, it is necessary to prepare the number of negative pressure generating sources (pressure reduction tanks and vacuum pumps) for the number of the plurality of the inkjet heads, consequently, for the number of the plurality of supply tanks and collection tanks, which involves another problem in that the apparatus cost increases.

An object of the present invention is to provide an image forming apparatus capable of adjusting a flow rate of ink flowing through a plurality of inkjet heads without involving an increase in the apparatus cost. Solution to Problem.

The object is solved by an image forming apparatus according to claim <NUM>, Advantageous embodiments are described in the dependent claims. An image forming apparatus includes among others: an inkjet head; an ink storage section that stores ink circulating between the inkjet head and the ink storage section; a pressure generating section that communicates with the inkjet head and generates a first pressure so that an internal pressure of the ink storage section becomes the first pressure; and a first fluid resistance section that gives resistance to a fluid flowing through a communication path between the ink storage section and the pressure generating section so that the internal pressure of the ink storage section becomes a second pressure different from the first pressure.

According to the present invention, it is possible to adjust a flow rate of ink flowing to a plurality of inkjet heads without increasing a device cost.

<FIG> illustrates an overview configuration of inkjet image forming apparatus <NUM>. Inkjet image forming apparatus <NUM> includes sheet feeding section <NUM>, image forming section <NUM>, sheet discharging section <NUM>, and control section <NUM> (see <FIG>).

Inkjet image forming apparatus <NUM> (functioning as an "image forming apparatus" of the present invention), under the control of control section <NUM>, conveys recording medium P stored in sheet feeding section <NUM> to image forming section <NUM>, forms an image on recording medium P in image forming section <NUM>, and conveys recording medium P on which the image has been formed to sheet discharging section <NUM>. As recording medium P, in addition to a paper such as a plain paper and a coated paper, various media capable of fixing ink landed on the surface, such as a fabric or a sheet-like resin, can be used.

Sheet feeding section <NUM> includes sheet feeding tray <NUM> for storing recording medium P, and medium supply section <NUM> for conveying and supplying recording medium P from sheet feeding tray <NUM> to image forming section <NUM>. Medium supply section <NUM> includes an annular belt whose inner side is supported by two rollers, and conveys recording medium P from sheet feeding tray <NUM> to image forming section <NUM> by rotating the rollers with recoding medium P placed on the belt.

Image forming section <NUM> includes conveyance section <NUM>, passing unit <NUM>, heating section <NUM>, head unit <NUM>, fixing section <NUM>, delivery section <NUM>, and the like.

Conveyance section <NUM> performs a conveyance operation that holds recording medium P placed on conveyance surface 211a (placing surface) of conveyance drum <NUM> and conveys recording medium P placed on conveyance drum <NUM> in the conveyance direction (Y direction) by rotating and moving conveyance drum <NUM> on a rotation axis (cylindrical axis) extending in X direction (the direction perpendicular to the sheet surface of <FIG>).

Conveyance drum <NUM> includes a claw portion (not illustrated) and an intake portion (not illustrated) for holding recording medium P on conveyance surface 211a. Recording medium P is held on conveyance surface 211a by the claw portion holding the end of recording medium P and the intake portion suctioning recording medium P to conveyance surface 211a. Conveyance section <NUM> is connected to a conveyance drum motor (not illustrated) for rotating conveyance drum <NUM>. Conveyance drum <NUM> rotates by an angle proportional to the rotation amount of the conveyance drum motor.

Passing unit <NUM> transfers recording medium P conveyed from medium supply section <NUM> of sheet feeding section <NUM> to conveyance section <NUM>. Passing unit <NUM> is provided between medium supply section <NUM> of sheet feeding section <NUM> and conveyance section <NUM>, holds and takes up one end of recording medium P conveyed from medium supply section <NUM> by swing arm section <NUM>, and transfers recording medium P to conveyance section <NUM> through passing drum <NUM>.

Heating section <NUM> is provided between the placing position of passing drum <NUM> and the placing position of head unit <NUM>, and heats recording medium P so that recording medium P conveyed by conveyance section <NUM> has a temperature within a predetermined temperature range. Heating section <NUM> includes, for example, an infrared heater or the like, and energizes the infrared heater based on a control signal supplied from control section <NUM> (see <FIG>) to generate heat of the infrared heater.

Head unit <NUM> forms an image by ejecting ink to recording medium P from a nozzle opening provided in an ink ejecting surface facing conveyance surface 211a of conveyance drum <NUM> at an appropriate timing corresponding to the rotation of conveyance drum <NUM> on which recording medium P is held. Head unit <NUM> is placed so that the ink ejecting surface and conveyance surface 211a are separated from each other by a predetermined distance.

In inkjet image forming apparatus <NUM> according to the present embodiment, four head units <NUM> corresponding to four colors of inks: white (W), yellow (Y), magenta (M), cyan (C), and black (K), respectively, are arranged in the order of W, Y, M, C, and K from the upstream side in the conveyance direction of recording medium P at predetermined intervals.

<FIG> is a schematic diagram illustrating a configuration of head unit <NUM>. Here, in head unit <NUM>, a surface facing conveyance surface 211a of conveyance drum <NUM> is illustrated.

Head unit <NUM> includes four inkjet heads <NUM> attached to attachment member <NUM>. Each of inkjet heads <NUM> is provided with a plurality of image forming elements (recording elements) each including a pressure chamber for storing ink, a piezoelectric element provided on the wall surface of the pressure chamber, and nozzle <NUM>. When a driving signal to deform the piezoelectric element is input, the deformation of the piezoelectric element deforms the pressure chamber to change the pressure inside the pressure chamber, and thus the image forming element ejects ink from the nozzle communicating with the pressure chamber.

In inkjet head <NUM>, two nozzle arrays are formed by nozzles <NUM> arranged at equal internals in the direction intersecting the conveyance direction of recording medium P (in the present embodiment, the direction orthogonal to the conveyance direction, that is, X direction). These two nozzle arrays are provided so that the arrangement positions of nozzles <NUM> are shifted from each other by one-half of the arrangement interval of nozzle <NUM> in each nozzle array in the X direction.

Four inkjet heads <NUM> are arranged in a zigzag pattern so that the arrangement ranges of the nozzle arrays in the X direction are connected with each other without any breaks. The arrangement ranges of nozzles <NUM> included in head unit <NUM> in the X direction covers the width of the area where an image is formed on recording medium P conveyed by conveyance section <NUM> in the X direction, and the position of head unit <NUM> is fixed with respect to the rotation axis of conveyance drum <NUM> when the image is formed. That is, head unit <NUM> includes a line head capable of ejecting ink over an image-formable-width in the X direction with respect to recording medium P, and inkjet image forming apparatus <NUM> is a single-pass inkjet image forming apparatus.

Note that the number of nozzle arrays included in inkjet head <NUM> may not be two, and may be one, three or more. Further, the number of inkjet heads <NUM> included in head unit <NUM> may not be four, and may be three or less, or five or more.

As the ink ejected from nozzle <NUM> of the image forming element, ink containing a pigment, for example, a white ink containing titanium dioxide or the like as a pigment is used. Further, as the ink ejected from nozzle <NUM> of the image forming element, gel ink containing a gelling agent and having a property of being phase-changed to a gel state or a sol state depending on the temperature and being cured by the irradiation with an energy ray such as ultraviolet rays is used. In the present embodiment, gel ink is used as the ink ejected from nozzle <NUM> of the image forming element.

Head unit <NUM> includes an ink heating section (not illustrated) that heats the ink stored in head unit <NUM>. The ink heating section operates under the control of control section <NUM> and heats the ink to the temperature at which the ink is in a sol state.

Inkjet head <NUM> ejects the ink that has been heated to be in a sol state. When the sol-state ink is ejected to recording medium P, the ink droplet is landed on recording medium P, immediately is in a gel state by natural cooling, and solidifies on recording medium P.

Fixing section <NUM> includes a light-emitting section disposed over the width of conveyance section <NUM> in the X direction, and irradiates recording medium P placed on conveyance section <NUM> with the energy rays such as ultraviolet rays from the light-emitting section to cure and fix the ink (gel ink) ejected on recording medium P. The light-emitting section of fixing section <NUM> is disposed between the placing position of head unit <NUM> and the placing position of transferring drum <NUM> of delivery section <NUM> in the conveyance direction so as to face conveyance surface 211a.

Delivery section <NUM> includes transferring drum <NUM> having a cylindrical shape and transferring recording medium P from conveyance section <NUM> to belt loop <NUM>, and belt loop <NUM> including an annular belt whose inner side is supported by two rollers. Transferring drum <NUM> transfers recording medium P from conveyance section <NUM> to the surface of belt loop <NUM>, and belt loop <NUM> conveys and discharges recording medium P to sheet discharging section <NUM>.

Sheet discharging section <NUM> includes sheet discharging tray <NUM> having a plate shape on which recording medium P transferred from image forming section <NUM> by delivery section <NUM> is placed.

<FIG> is a block diagram illustrating a main functional configuration of inkjet image forming apparatus <NUM>. Inkjet image forming apparatus <NUM> includes heating section <NUM>, head driving section <NUM> and inkjet head <NUM>, fixing section <NUM>, control section <NUM>, conveyance driving section <NUM>, operation display section <NUM>, input/output interface <NUM>, and the like.

Head driving section <NUM> supplies a driving signal to deform the piezoelectric element to the image forming element of inkjet head <NUM> at an appropriate timing in accordance with the image data, and causes nozzle <NUM> of inkjet head <NUM> to eject ink of the amount corresponding to the pixel value of the image data.

Control section <NUM> includes Central Processing Unit (CPU) <NUM>, Random Access Memory (RAM) <NUM>, Read Only Memory (ROM) <NUM>, and storage section <NUM>.

CPU <NUM> reads out various control programs and setting data stored in ROM <NUM>, causes RAM <NUM> to store the programs and the data, and executes the program to perform various arithmetic processes. Further, CPU <NUM> performs overall control of the entire operation of inkjet image forming apparatus <NUM>.

RAM <NUM> provides a working memory space to CPU <NUM> and stores temporary data. RAM <NUM> may include a non-volatile memory.

ROM <NUM> stores various control programs executed by CPU <NUM>, and/or setting data or the like. Note that, instead of ROM <NUM>, a rewritable non-volatile memory such as an Electrically Erasable Programmable Read Only Memory (EEPROM) and a flash memory may be used.

Storage section <NUM> stores a printing job (image forming command) input from external device <NUM> via input/output interface <NUM>, and image data related to the printing job and/or the like. Among these, the printing job includes, in addition to information specifying image data related to the image to be formed, information related to the type of recording medium P (e.g., the size and thickness of recording medium P) on which the image is formed. As storage section <NUM>, a Hard Disk Drive (HDD) may be used, and a Dynamic Random Access Memory (DRAM) or the like may be used in combination.

Conveyance driving section <NUM> supplies a driving signal to a conveyance motor of conveyance drum <NUM> based on a control signal supplied from control section <NUM>, and rotates conveyance drum <NUM> at a predetermined speed and timing.

Further, conveyance driving section <NUM> supplies a driving signal to a motor for operating medium supply section <NUM>, passing unit <NUM>, and delivery section <NUM> based on the control signal supplied from control section <NUM>, and causes medium supply section <NUM>, passing unit <NUM>, and delivery section <NUM> to supply recording medium P to conveyance section <NUM> and to discharge recording medium P from conveyance section <NUM>.

Operation display section <NUM> includes a display device such as a liquid crystal display and an organic EL display, and an input device such as an operation key and a touch panel placed to be superposed on a screen of the display device. Operation display section <NUM> displays various types of information on the display device, and converts an input operation input to the input device by the user into an operation signal to output the operation signal to control section <NUM>.

Input/output interface <NUM> mediates transmission and reception of data between external device <NUM> and control section <NUM>. Input/output interface <NUM> includes, for example, any of various serial interfaces and various parallel interfaces, or a combination thereof.

External device <NUM> is, for example, a personal computer, and supplies a printing job, image data, and the like to control section <NUM> via input/output interface <NUM>.

Next, a configuration of ink supply mechanism <NUM> that supplies ink to inkjet heads <NUM> in inkjet image forming apparatus <NUM> will be described with reference to <FIG>. Ink supply mechanism <NUM> supplies ink to the inkjet head while circulating ink between the supply tank supplying ink, the inkjet head, and the collection tank collecting ink.

As illustrated in <FIG>, ink supply mechanism <NUM> includes pressure reduction tank <NUM>, vacuum pump <NUM>, opening/closing valve <NUM>, pressure detection section <NUM>, first supply tank <NUM>, opening/closing valve <NUM>, first collection tank <NUM>, opening/closing valve <NUM>, second supply tank <NUM>, opening/closing valve <NUM>, second collection tank <NUM>, and the like.

Note that first supply tank <NUM>, first collection tank <NUM>, second supply tank <NUM>, and second collection tank <NUM> function as an "ink storage section" of the present invention that stores ink communicating between the inkjet head and the ink storage section. Further, opening/closing valves <NUM>, <NUM>, and <NUM> function as an "opening/closing section" of the present invention.

First supply tank <NUM> stores ink supplied to inkjet head 242A (functioning as a "first inkjet head" of the present invention) through ink supply path <NUM>. In the present embodiment, first supply tank <NUM> is disposed above inkjet head 242A.

Although not illustrated, first supply tank <NUM>, first collection tank <NUM>, and inkjet head 242A are provided corresponding to each of four colors of ink: yellow (Y), magenta (M), cyan (C), and black (K). Then, inkjet head 242A ejects ink of the yellow (Y), magenta (M), cyan (C), or black (K) supplied from first supply tank <NUM>.

Negative pressure (negative pressure for meniscus) of, for example, -<NUM> kPA is applied to first supply tank <NUM>, and this negative pressure forms an appropriate meniscus pressure to the ejection opening of inkjet head 242A. An appropriate control of a meniscus having an appropriate shape at the ejection opening of inkjet head 242A.

Atmosphere communication path <NUM> (an atmosphere releasing pipe) communicable with the atmosphere is connected to first supply tank <NUM>. Opening/closing valve <NUM> (e.g., a solenoid valve) opens and closes atmosphere communication path <NUM> upon reception of the control of control section <NUM>, and adjusts the amount of air in the atmosphere suctioned into first supply tank <NUM> through atmosphere communication path <NUM> to adjust (increase) the pressure inside first supply tank <NUM> toward the atmospheric pressure.

First collection tank <NUM> stores the ink collected from inkjet head 242A through ink collection path <NUM>. In the present embodiment, a metal container having a capacity of about <NUM> liters is used as first collection tank <NUM>. In the present embodiment, first collection tank <NUM> is disposed above inkjet head 242A and at the position lower than first supply tank <NUM>.

Negative pressure having the same magnitude (e.g., -<NUM> kPa) as that applied to first supply tank <NUM> is applied to first collection tank <NUM>, and the ink that has been supplied from first supply tank <NUM> to inkjet head 242A is guided to first collection tank <NUM> through ink collection path <NUM> due to the height difference (water head difference indicated by H in <FIG>) between first supply tank <NUM> and first collection tank <NUM>. The flow rate of ink flowing to inkjet head 242A is adjusted due to the height difference between first supply tank <NUM> and first collection tank <NUM>.

Atmosphere communication path <NUM> (an atmosphere releasing pipe) communicable with the atmosphere is connected to first collection tank <NUM>. Opening/closing valve <NUM> (e.g., a solenoid valve) opens and closes atmosphere communication path <NUM> upon reception of the control of control section <NUM>, and adjusts the amount of air in the atmosphere suctioned into first collection tank <NUM> through atmosphere communication path <NUM> to adjust (increase) the pressure in first collection tank <NUM> toward the atmospheric pressure.

Note that first supply tank <NUM> and first collection tank <NUM> are connected to each other through a circulation path (not illustrated) in which a pump is provided. When the level sensor disposed in first supply tank <NUM> detects that the ink level in first supply tank <NUM> has fallen below the predetermined level, the pump is driven, and the ink collected in first collection tank <NUM> is returned to first supply tank <NUM> through the circulation path.

Second supply tank <NUM> stores the ink supplied to inkjet head 242B (functioning as a "second inkjet head" of the present invention) through ink supply path <NUM>. In the present embodiment, second supply tank <NUM> is disposed above inkjet head 242B. Inkjet head 242B ejects white (W) ink supplied from second supply tank <NUM>.

Negative pressure (negative pressure for meniscus) of, for example, -<NUM> kPA is applied to second supply tank <NUM>, and this negative pressure forms an appropriate meniscus pressure to the ejection opening of inkjet head 242B. An appropriate control of meniscus pressure can form a meniscus having an appropriate shape at the ejection opening of inkjet head 242B.

Atmosphere communication path <NUM> (an atmosphere releasing pipe) communicable with the atmosphere is connected to second supply tank <NUM>. Opening/closing valve <NUM> (e.g., a solenoid valve) opens and closes atmosphere communication path <NUM> upon reception of the control of control section <NUM>, and adjusts the amount of air in the atmosphere suctioned into second supply tank <NUM> through atmosphere communication path <NUM> to adjust (increase) the pressure inside second supply tank <NUM> toward the atmospheric pressure.

Second collection tank <NUM> stores the ink collected from inkjet head 242B through ink collection path <NUM>. In the present embodiment, a metal container having a capacity of about <NUM> liters is used as second collection tank <NUM>. In the present embodiment, second collection tank <NUM> is disposed above inkjet head 242B and at the same height as second supply tank <NUM>.

Negative pressure different from that applied to second supply tank <NUM> (e.g., -<NUM> kPA) is applied to second collection tank <NUM>, and a difference between the negative pressures applied respectively to second supply tank <NUM> and second collection tank <NUM> guides the ink that has been supplied from second supply tank <NUM> to inkjet head 242B to second collection tank <NUM> through ink collection path <NUM>. The flow rate of ink flowing to inkjet head 242B is adjusted by the difference between the negative pressures applied respectively to second supply tank <NUM> and second collection tank <NUM>.

Note that second supply tank <NUM> and second collection tank <NUM> are connected to each other through a circulation path (not illustrated) in which a pump is provided. When the level sensor disposed in second supply tank <NUM> detects that the ink level in second supply tank <NUM> has fallen below the predetermined level, the pump is driven, and the ink collected in second collection tank <NUM> is returned to second supply tank <NUM> through the circulation path.

Next, a specific configuration of applying the negative pressures to first supply tank <NUM>, first collection tank <NUM>, second supply tank <NUM>, and second collection tank <NUM> will be described.

First supply tank <NUM> communicates with pressure reduction tank <NUM> (buffer tank) through communication paths <NUM> and <NUM>. Further, first collection tank <NUM> communicates with pressure reduction tank <NUM> through communication paths <NUM> and <NUM>. Furthermore, second supply tank <NUM> communicates with pressure reduction tank <NUM> through communication paths <NUM> and <NUM>, and second collection tank <NUM> communicates with pressure reduction tank <NUM> through communication paths <NUM> and <NUM>.

Pressure reduction tank <NUM> is configured to be capable of accommodating a predetermined volume of gas. Vacuum pump <NUM> is connected to pressure reduction tank <NUM> through vacuum path <NUM>. Upon reception of the control of control section <NUM>, vacuum pump <NUM> suctions the air in pressure reduction tank <NUM> through vacuum path <NUM> to reduce the pressure (atmospheric pressure) in pressure reduction tank <NUM>. Pressure detection section <NUM> detects the pressure in pressure reduction tank <NUM> and outputs the detection data to control section <NUM>. Under the control of control section <NUM>, opening/closing valve <NUM> (e.g., a solenoid valve) opens and closes vacuum path <NUM> to adjust the amount of air suctioned into vacuum pump <NUM> in accordance with the detection result of pressure detection section <NUM> so that the pressure in pressure reduction tank <NUM> becomes a predetermined pressure (e.g., -<NUM> kPa).

Control section <NUM> controls vacuum pump <NUM> and opening/closing valve <NUM> to reduce the pressure in pressure reduction tank <NUM> to a predetermined pressure (corresponding to a "first pressure" of the present invention), thereby controls the pressures in first supply tank <NUM>, first collection tank <NUM>, second supply tank <NUM>, and second collection tank <NUM> each communicating with pressure reduction tank <NUM> to reduce the pressures to the predetermined pressure (negative pressure application). Note that control section <NUM>, pressure reduction tank <NUM>, vacuum pump <NUM>, opening/closing valve <NUM>, and pressure detection section <NUM> function as a "pressure generating section" of the present invention generating the first pressure so that the internal pressures of first supply tank <NUM>, first collection tank <NUM>, second supply tank <NUM>, and second collection tank <NUM> become the first pressure.

Incidentally, in the conventional ink supply mechanism, increasing the flow rate of ink flowing to the inkjet head can be achieved by an increase of the height difference (water head difference) between the supply tank and the collection tank. However, the height of the supply tank and the height of the collection tank need to be widely separated from each other to increase the height difference, which results in an increase in the size of the apparatus.

To solve the problem, a configuration is conceivable in which the height difference between the supply tank and the collection tank is eliminated and the negative pressure of different levels is applied to the supply tank and the collection tank, and the pressure difference (atmospheric pressure difference) between the supply tank and the collection tank guides the ink having been supplied to the inkjet head to the collection tank. However, when a plurality of supply tanks and collection tanks are provided to each of a plurality of inkjet heads, it is necessary to prepare negative pressure generating sources (pressure reduction tanks and vacuum pumps) for the number of the plurality of inkjet heads, consequently, for the number of the plurality of the supply tanks and the collection tanks, which arises another problem that the device cost is increased.

Therefore, in the present embodiment, ink supply mechanism <NUM> adopts a configuration in which the flow rate of ink flowing to a plurality of inkjet heads can be adjusted without increasing the device cost.

That is, in communication path <NUM>, first fluid resistance section <NUM> is provided to give resistance, that is, to generate a pressure loss, to a fluid (e.g., air) flowing through communication path <NUM> so that the internal pressure of first supply tank <NUM> becomes a predetermined pressure (e.g., -<NUM> kPa, corresponding to a "second pressure" of the present invention) different from the pressure (e.g., -<NUM> kPa) in pressure reduction tank <NUM>. More specifically, when first supply tank <NUM> is open to the atmosphere, first fluid resistance section <NUM> gives resistance to the fluid flowing through communication path <NUM> so that the difference between the pressure in pressure reduction tank <NUM> and the internal pressure of first supply tank <NUM> is equal to or higher than a predetermined pressure (e.g., <NUM> kPa).

In the present embodiment, first fluid resistance section <NUM> is an element that reduces the pressure fluctuation in first supply tank <NUM> against the pressure fluctuation in pressure reduction tank <NUM> caused by the control of vacuum pump <NUM> and opening/closing valve <NUM>, and is configured with, for example, an orifice. The fluid resistance value of first fluid resistance section <NUM> can be optionally adjusted by the adjustment of the aperture diameter of the orifice. That is, in the case where first fluid resistance section <NUM> is not provided, the same pressure fluctuation as in pressure reduction tank <NUM> is caused in first supply tank <NUM> with time after the pressure fluctuation in pressure reduction tank <NUM> starts; however, providing first fluid resistance section <NUM> allows the adjustment of the internal pressure of first supply tank <NUM> to a predetermined pressure (e.g., -<NUM> kPa).

Note that, when it is difficult to adjust the internal pressure of first supply tank <NUM> to a predetermined pressure only by first fluid resistance section <NUM> (e.g., when the pressure value in pressure reduction tank <NUM>, consequently, the negative pressure value applied to first supply tank <NUM>, is very large), control section <NUM> may control opening/closing valve <NUM> and adjust the amount of air in the atmosphere suctioned into first supply tank <NUM> through atmosphere communication path <NUM> to adjust the pressure in first supply tank <NUM>.

Further, in communication path <NUM>, first fluid resistance section <NUM> is provided to give resistance, that is, to generate a pressure loss, to a fluid (e.g., air) flowing through communication path <NUM> so that the internal pressure of first collection tank <NUM> becomes a predetermined pressure (e.g., -<NUM> kPa, corresponding to a "second pressure" of the present invention) different from the pressure (e.g., -<NUM> kPa) in pressure reduction tank <NUM>. More specifically, when first collection tank <NUM> is open to the atmosphere, first fluid resistance section <NUM> gives resistance to a fluid flowing through communication path <NUM> so that the difference between the pressure in pressure reduction tank <NUM> and the internal pressure of first collection tank <NUM> is equal to or higher than a predetermined pressure (e.g., <NUM> kPa).

In the present embodiment, first fluid resistance section <NUM> is an element that reduces the pressure fluctuation in first collection tank <NUM> against the pressure fluctuation in pressure reduction tank <NUM> caused by the control of vacuum pump <NUM> and opening/closing valve <NUM>, and is configured with, for example, an orifice. The fluid resistance value of first fluid resistance section <NUM> can be optionally adjusted by the adjustment of the aperture diameter of the orifice. That is, in the case where first fluid resistance section <NUM> is not provided, the same pressure fluctuation as in pressure reduction tank <NUM> is caused in first collection tank <NUM> with time after the pressure fluctuation in pressure reduction tank 61starts; however, providing first fluid resistance section <NUM> allows the adjustment of the internal pressure of first collection tank <NUM> to a predetermined pressure (e.g., -<NUM>.

Note that, when it is difficult to adjust the internal pressure of first collection tank <NUM> to a predetermined pressure only by first fluid resistance section <NUM> (e.g., when the pressure value in pressure reduction tank <NUM>, consequently, the negative pressure value applied to first supply tank <NUM>, is very large), control section <NUM> may control opening/closing valve <NUM> and may adjust the amount of air in the atmosphere suctioned into first collection tank <NUM> through atmosphere communication path <NUM> to adjust the pressure in first collection tank <NUM>.

Further, in communication path <NUM>, first fluid resistance section <NUM> is provided to give resistance, that is, to generate a pressure loss, to a fluid (e.g., air) flowing through communication path <NUM> so that the internal pressure of second supply tank <NUM> is a predetermined pressure (e.g., -<NUM> kPa, corresponding to a "second pressure" of the present invention) different from the pressure (e.g., -<NUM> kPa) in pressure reduction tank <NUM>. More specifically, when second supply tank <NUM> is open to the atmosphere, first fluid resistance section <NUM> gives resistance to a fluid flowing through communication path <NUM> so that the difference between the pressure in pressure reduction tank <NUM> and the internal pressure of second supply tank <NUM> is equal to or higher than a predetermined pressure (e.g., <NUM> kPa).

In the present embodiment, first fluid resistance section <NUM> is an element that reduces the pressure fluctuation in second supply tank <NUM> against the pressure fluctuation in pressure reduction tank <NUM> caused by the control of vacuum pump <NUM> and opening/closing valve <NUM>, and is configured with, for example, an orifice. The fluid resistance value of first fluid resistance section <NUM> can be optionally adjusted by the adjustment of the aperture diameter of the orifice. That is, in the case where that first fluid resistance section <NUM> is not provided, the same pressure fluctuation as in pressure reduction tank <NUM> is caused in second supply tank <NUM> with time after the pressure fluctuation in pressure reduction tank <NUM> starts; however, providing first fluid resistance section <NUM> allows the adjustment of the internal pressure of second supply tank <NUM> to a predetermined pressure (e.g., -<NUM> kPa).

Note that, when it is difficult to adjust the internal pressure of second supply tank <NUM> to a predetermined pressure only by first fluid resistance section <NUM> (e.g., when the pressure value in pressure reduction tank <NUM>, consequently, the negative pressure value applied to second supply tank <NUM>, is very large), control section <NUM> may control opening/closing valve <NUM> and may adjust the amount of air in the atmosphere suctioned into second supply tank <NUM> through atmosphere communication path <NUM> to adjust the pressure in second supply tank <NUM>.

Note that communication path <NUM> does not include the first fluid resistance section that gives resistance, that is, generates a pressure loss, to a fluid (e.g., air) flowing through communication path <NUM>; therefore, the internal pressure of second collection tank <NUM> becomes the same pressure as the pressure (e.g., -<NUM> kPa) in pressure reduction tank <NUM> accordingly with time after the pressure fluctuation in pressure reduction tank <NUM> is started.

Further, in atmosphere communication path <NUM>, second fluid resistance section <NUM> is provided to give resistance, that is, to generate a pressure loss, to a fluid (e.g., air) flowing through atmosphere communication path <NUM> so that the internal pressure of first supply tank <NUM> becomes a predetermined pressure (e.g., -<NUM>. 5kPa) different from the pressure (e.g., -<NUM> kPa) in pressure reduction tank <NUM>.

Thus, when the amount of air in the atmosphere suctioned into first supply tank <NUM> through atmosphere communication path <NUM> is adjusted by the opening and closing of opening/closing valve <NUM>, the pressure fluctuation caused by the adjustment in first supply tank <NUM> can be easily reduced, and thus the pressure in first supply tank <NUM> can be easily adjusted. When opening/closing valve <NUM> is not provided and it is difficult to adjust the internal pressure of first supply tank <NUM> to a predetermined pressure only by first fluid resistance section <NUM> (e.g., when the pressure value in pressure reduction tank <NUM>, consequently, the negative pressure value applied to first supply tank <NUM>, is very large), providing second fluid resistance section <NUM> allows the adjustment of the amount of air in the atmosphere suctioned into first supply tank <NUM> through atmosphere communication path <NUM> and the adjustment of the pressure in first supply tank <NUM> to a predetermined pressure.

Further, in atmosphere communication path <NUM>, second fluid resistance section <NUM> is provided to give resistance, that is, to generate a pressure loss, to a fluid (e.g., air) flowing through atmosphere communication path <NUM> so that the internal pressure of first collection tank <NUM> becomes a predetermined pressure (e.g., -<NUM>. 5kPa) different from the pressure (e.g., -<NUM> kPa) in pressure reduction tank <NUM>.

Thus, when the amount of air in the atmosphere suctioned into first collection tank <NUM> through atmosphere communication path <NUM> is adjusted by the opening and closing of opening/closing valve <NUM>, the pressure fluctuation caused by the adjustment in first collection tank <NUM> can be easily reduced, and thus the pressure in first collection tank <NUM> can be easily adjusted. When opening/closing valve <NUM> is not provided and it is difficult to adjust the internal pressure of first collection tank <NUM> to a predetermined pressure only by first fluid resistance section <NUM> (e.g., when the pressure value in pressure reduction tank <NUM>, consequently, the negative pressure value applied to first collection tank <NUM>, is very large), providing second fluid resistance section <NUM> allows the adjustment of the amount of air in the atmosphere suctioned into first collection tank <NUM> through atmosphere communication path <NUM> and the adjustment of the pressure in first collection tank <NUM> to a predetermined pressure.

Further, in atmosphere communication path <NUM>, second fluid resistance section <NUM> is provided to give resistance, that is, to generate a pressure loss, to a fluid (e.g., air) flowing through atmosphere communication path <NUM> so that the internal pressure of second supply tank <NUM> becomes a predetermined pressure (e.g., -<NUM>. 5kPa) different from the pressure (e.g., -<NUM> kPa) in pressure reduction tank <NUM>.

Thus, when the amount of air in the atmosphere suctioned into second supply tank <NUM> through atmosphere communication path <NUM> is adjusted by the opening and closing of opening/closing valve <NUM>, the pressure fluctuation caused by the adjustment in second supply tank <NUM> can be easily reduced, and thus the pressure in second supply tank <NUM> can be easily adjusted. When opening/closing valve <NUM> is not provided and it is difficult to adjust the internal pressure of second supply tank <NUM> to a predetermined pressure only by first fluid resistance section <NUM> (e.g., when the pressure value in pressure reduction tank <NUM>, consequently, the negative pressure value applied to second supply tank <NUM>, is very large), providing second fluid resistance section <NUM> allows the adjustment of the amount of air in the atmosphere suctioned into second supply tank <NUM> through atmosphere communication path <NUM> and the adjustment of the pressure in second supply tank <NUM> to a predetermined pressure.

As described in detail above, inkjet image forming apparatus <NUM> (image forming apparatus) includes: inkjet heads 242A and 242B; first supply tank <NUM>, first collection tank <NUM>, second supply tank <NUM>, and second supply tank <NUM> (ink storage section) that each store ink supplied and collected (communicated) between inkjet head 242A and the ink storage section and between inkjet head 242B and the ink storage section; a pressure generating section (control section <NUM>, pressure reduction tank <NUM>, vacuum pump <NUM>, opening/closing valve <NUM>, and pressure detection section <NUM>) that communicates with the inkjet head and generates a first pressure so that an internal pressure of the ink storage section becomes the first pressure; and first fluid resistance sections <NUM>, <NUM> and <NUM> that each give resistance to a fluid flowing through a communication path between the ink storage section and the pressure generating section so that the internal pressure of the ink storage section becomes a second pressure different from the first pressure.

According to the present embodiment configured as described above, providing first fluid resistance sections <NUM>, <NUM>, and <NUM> and adjusting the resistance value of the fluid allows free adjustment of each internal pressure of first supply tank <NUM>, first collection tank <NUM>, and second supply tank <NUM> to a predetermined pressure different from the pressure generated from one negative pressure generating source (the pressure in pressure reduction tank <NUM>). Therefore, when a plurality of supply tanks (first supply tank <NUM> and second supply tank <NUM>) and a plurality of collection tanks (first collection tank <NUM> and second collection tank <NUM>) are provided respectively to the plurality of inkjet heads (inkjet heads 242A and 242B), it is not necessary to prepare negative pressure generating sources (pressure reduction tank and vacuum pump) for the number of the plurality of inkjet heads. Thus, the flow rate of ink flowing to each of the plurality of inkjet heads can be adjusted without involving any increase in the apparatus cost.

Note that, in the present embodiment, an exemplary configuration of ink supply mechanism <NUM> has been described in which the internal pressure difference (<NUM> kPa = -<NUM> - (-<NUM>)) between first supply tank <NUM> and first collection tank <NUM> is different from the internal pressure difference (<NUM> kPa = -<NUM> - (-<NUM>)) between second supply tank <NUM> and second collection tank <NUM>, that is, a plurality of inkjet heads 242A and 242B are driven under a plurality of types of pressure difference conditions between the supply tanks and the collection tanks, but the present invention is not limited thereto. For example, ink supply mechanism <NUM> may adopt a configuration in which the internal pressure difference between first supply tank <NUM> and first collection tank <NUM> is the same as the internal pressure difference between second supply tank <NUM> and second collection tank <NUM>, that is, the plurality of inkjet heads 242A and 242B are driven under one type of pressure difference condition between the supply tanks and the collection tanks.

Further, in the above-described embodiment, an example has been described in which a first fluid resistance section is provided to ink supply mechanism <NUM> that supplies ink to the inkjet head while circulating ink between a supply tank supplying ink, an inkjet head, and a collection tank collecting ink, but the present invention is not limited thereto. For example, a first fluid resistance section may be provided to an ink supplying mechanism that supplies ink from the supply tank to the inkjet head without circulating ink between the supply tank, inkjet head, and the collection tank, in order to adjust the internal pressure of the supply tank to a predetermined pressure different from the pressure of the one negative pressure generating source.

Claim 1:
An image forming apparatus comprising:
an inkjet head (<NUM>);
an ink storage section (<NUM>, <NUM>, <NUM>, <NUM>) that stores ink circulating between the inkjet head (<NUM>) and the ink storage section (<NUM>, <NUM>, <NUM>, <NUM>);
a pressure generating section (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) that communicates with the inkjet head (<NUM>) and generates a first pressure so that an internal pressure of the ink storage section (<NUM>, <NUM>, <NUM>, <NUM>) becomes the first pressure; and
a first fluid resistance section (<NUM>, <NUM>, <NUM>) that gives resistance to a fluid flowing through a communication path (<NUM>) between the ink storage section (<NUM>, <NUM>, <NUM>, <NUM>) and the pressure generating section (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) so that the internal pressure of the ink storage section becomes a second pressure different from the first pressure,
an atmosphere communication path (<NUM>, <NUM>, <NUM>) that is connected to the ink storage section (<NUM>, <NUM>, <NUM>, <NUM>) and is communicable with an atmosphere; and
an opening/closing section (<NUM>, <NUM>, <NUM>) that opens and closes the atmosphere communication path (<NUM>, <NUM>, <NUM>).