Ink jet printing apparatus and method for filling ink into ink tank in ink jet printing apparatus

An ink jet printing apparatus having reduced manufacture costs is provided. The ink jet manufacturing apparatus includes a diaphragm section configured to be able to change the volume of a subtank, and an atmosphere communication port configured to allow the interior of the subtank to communicate with the atmosphere. The ink jet printing apparatus further includes an atmosphere communication valve configured to be able to close the atmosphere communication port, and a driving mechanism configured to drive the diaphragm section and the atmosphere communication valve. The driving mechanism opens the atmosphere communication port and then reduces the volume of the diaphragm section. The driving mechanism subsequently allows the atmosphere communication valve to close the atmosphere communication port and then increases the volume of the diaphragm section. The driving mechanism thus supplies the ink accommodated in a main tank to the subtank.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an ink jet printing apparatus configured to perform printing by ejecting ink to a print medium and a method for filling ink into an ink tank mounted in the ink jet printing apparatus.

2. Description of the Related Art

According to Japanese Patent Laid-Open No. 2001-113716, to eliminate the possible need to replace an ink tank during an operation of printing a print medium, a structure of an ink jet printing apparatus that uses a subtank separately from a main tank is described. In the ink jet printing apparatus disclosed in the specification, ink is supplied from the main tank, which is replaceable and has a large capacity, to the subtank, which has a relatively small capacity. The ink stored in the subtank is supplied to the print head.

Hence, even if the ink in the main tank is exhausted during printing of one print medium, a certain amount of ink still remains in the subtank. The ink stored in the subtank can be used to continue printing. Then, the printing operation can be achieved without interruption by completing replacement of the main tank while printing is being performed with ink supplied from the subtank. As a result, the quality of print images can be kept high.

In the printing apparatus disclosed in Japanese Patent Laid-Open No. 2001-113716, the print head and the subtank are mounted in a carriage. The main tank is located separately from the carriage, with an ink channel extending from the main tank to the subtank. The ink channel extending from the main tank to the subtank is allowed to contact and leave the subtank. A pump is located in the ink channel extending from the main tank, to supply ink from the main tank to the subtank.

However, the pump configured to supply ink from the main tank to the subtank is often expensive. In general, the pump requires arrangements such as a driving source, a transmission mechanism configured to transmit a driving force generated by the driving source, and the ink channel, and so on. Thus, the pump requires relatively high costs compared to the other components forming the printing apparatus. Moreover, the printing apparatus configured to supply ink from the main tank to the subtank requires an exhaust air mechanism. The exhaust air mechanism requires, for example, a valve configured to allow the subtank to communicate with the atmosphere and to break the communication between the subtank and the atmosphere and a driving mechanism for the valve, or the pump. The exhaust air mechanism may thus have a complicated and expensive configuration.

SUMMARY OF THE INVENTION

Thus, in view of the above-described circumstances, an object of the present invention is to provide an ink jet printing apparatus configured to perform printing by ejecting ink stored in a subtank from a print head, ink being supplied from a main tank to a subtank, the ink jet printing apparatus achieved reducing manufacture costs.

According to a first aspect of the present invention, there is provided an ink jet printing apparatus comprising: a print head configured to perform printing by ejecting ink supplied from a first ink tank removably mounted in a printing apparatus main body; a second ink tank configured to be able to temporarily store, between the first ink tank and the print head, ink supplied from the first ink tank to the print head; a volume changing member configured to be able to change volume of the second ink tank; an atmosphere communication port configured to enable an interior of the second ink tank to communicate with atmosphere; and a driving mechanism configured to control changing of the volume of the volume changing member and opening and closing of the atmosphere communication port, wherein, the driving mechanism opens the atmosphere communication port and then the volume changing member reduces the volume of the second ink tank, and subsequently closes the atmosphere communication port and then the volume changing member increases the volume of the second ink tank, thus the ink accommodated in the first ink tank is supplied to the second ink tank.

According to a second aspect of the present invention, there is provided a method for filling ink into a second ink tank in an ink jet printing apparatus, the ink jet printing apparatus comprising a print head configured to perform printing by ejecting ink supplied from a first ink tank removably mounted in a printing apparatus main body and the second ink tank configured to be able to temporarily store ink supplied from the first ink tank to the print head between the first ink tank and the print head, said method comprising: a step of opening an atmosphere communication port configured to allow interior of the second ink tank to communicate with atmosphere and then reducing volume of a volume changing member configured to be able to change volume of the second ink tank; and a step of closing the atmosphere communication port and then increasing the volume of the volume changing member.

The present invention provides an ink jet printing apparatus configured to perform printing by ejecting ink stored in a subtank from a print head, ink being supplied from a main tank to a subtank, the ink jet printing apparatus achieved reducing manufacture costs.

DESCRIPTION OF THE EMBODIMENTS

First Embodiment

FIG. 1is a schematic plan view illustrating the general configuration of an ink jet printing apparatus to which a present invention is applied. The ink jet printing apparatus shown herein is of what is called a serial type in which a print head capable of ejecting ink droplets is moved in a direction crossing a direction in which a print medium is conveyed to perform printing.

InFIG. 1, the print head1is an ink jet print head capable of ejecting supplied ink through a plurality of ejection ports, and is removably mounted in a carriage102. The carriage102includes a connector holder (electric connection section) configured to transmit driving signals and the like to the print head1via a connector (not shown in the drawings). The carriage102is supported by a guide shaft103installed in the apparatus main body, so as to be able to reciprocate in a main scanning direction shown by arrow A. A timing belt107connected to the carriage102is passed between a motor pulley105and a driven pulley106both rotationally driven by a main scanning motor104. The carriage102is moved in the main scanning direction by a driving mechanism comprising the motor104, the pulleys105and106, and the timing belt107.

Print media108such as print sheets or thin plastic plates or the like are separately fed one by one from an auto sheet feeder (ASF)114by rotation of a pickup roller113driven by a sheet feeding motor115. Moreover, the print medium108is conveyed in a sub-scanning direction shown by arrow B, by rotation of a conveying roller109. The print medium108thus passes through a position (printing section) located opposite a surface (ejection port surface) of the print head1in which ejection ports are formed. The conveying roller109is drivingly rotated by the conveying motor116. The following are performed based on sensing signals from a paper end sensor112located upstream of the conveying roller109: determination of whether or not the print medium108has been supplied and setting the front end of the print medium during supplying. The back surface of the print medium108is supported by a platen (not shown in the drawings) so that the print medium forms a flat print surface in the printing section.

The ink jet printing apparatus configured as described above forms an image on the print medium by repeating a print scan in which the print head1ejects ink while performing a scan in the direction of arrow A together with the carriage102and a conveying operation performed between scans by the print head.

FIG. 2is a schematic diagram of an ink supply system in the ink jet printing apparatus100according to the first embodiment of the present invention. For simplification, only a path for ink as a liquid in one color is shown.FIG. 2particularly shows that a sufficient amount of ink is accommodated inside a main tank5and that printing is performed using the ink in the main tank5.

First, the configuration of the ink supply system according to the present embodiment will be described. The ink supply system according to the first embodiment includes the print head1, the main tank5, a subtank4, and a buffer chamber6. The print head1comprises an element substrate including print elements provided thereon to allow ink to be ejected, and an orifice plate joined to the element substrate. The orifice plate includes a plurality of ejection ports through which ink droplets are ejected, a bubbling chamber configured to communicate with the ejection ports when the bubbling chamber is joined to the element substrate, the bubbling chamber serving as an energy generation chamber, and an ink channel configured to communicate with the bubbling chamber. The print elements are driven to eject ink through the ejection ports.

The main tank (first ink tank)5is removably mounted in the printing apparatus main body. In the present embodiment, the main tank5is formed to be able to accommodate a relatively large amount of ink. The ink accommodated in the main tank5is supplied to the subtank4mounted in the printing apparatus main body. Moreover, ink in the subtank is supplied to the print head1mounted in the carriage. The print head1ejects the supplied ink through the ejection ports to print an image. As the printing operation progresses, ink is supplied from the main tank5to the subtank4, with the amount of ink in the main tank decreasing. When the ink in the main tank5is exhausted or the amount of ink in the main tank5is insufficient to print one print medium, the main tank5is replaced with a new main tank with ink filled therein.

The subtank (second ink tank)4can store ink temporarily, between the main tank5and the print head1, ink supplied from the main tank5to the print head1. An amount of ink sufficient to enable a printing operation during a replacement operation for the main tank5is accommodated in the subtank4so as to avoid interrupting the printing operation. Thus, the capacity of the subtank4is set to be relatively smaller than that of the main tank5. Separation of the subtank4from the main tank5enables image quality to be prevented from being degraded by the interruption of the printing operation during the replacement of the main tank5. The main tank5and the subtank4are allowed to communicate through a first hollow pipe11projected from the top surface of a liquid chamber in the subtank4. The first hollow pipe11is formed of a conductive member such as metal, and ink can flow through the pipe11.

Here, the first hollow pipe11is formed to have a sufficiently small inner diameter so as to allow the channel through which ink flows to offer sufficient channel resistance to the ink. Thus, even if the main tank5is located above the subtank4, the ink accommodated in the main tank5is prevented from being supplied into the subtank4only by gravity. When the print head1ejects ink to reduce the amount of ink in the subtank4, thus allowing generation of a negative pressure of at least a predetermined value in the subtank4, then the ink is supplied from the main tank5to the subtank4.

Furthermore, a supply tube2is located between the print head1and the subtank4to connect the print head1and the subtank4together. The supply tube2enables ink to flow through therein and allow the ink inside the subtank4to be supplied to the print head1. The supply tube2is formed of a flexible material and enables ink to be supplied to the print head1during scanning.

An atmosphere communication path8is coupled to the subtank4so as to allow air to flow between the subtank4and the exterior so that the interior and the atmosphere can communicate. The atmosphere communication path8comprises an entry section81, a space section82, and a discharge section83. The entry section81is formed to extend upward from the highest position41in the subtank4. The space section82is coupled to an outlet81bformed at the upper end of the entry section81. The discharge section83is formed to extend downward from the space section82to below the bottom surface of the subtank4. The atmosphere communication path8is shaped generally like an inverted letter U. An inlet81aformed at the lower end of the entry section81is disposed at the same height position as the highest position in the subtank4. Furthermore, an atmosphere communication valve9is provided in the discharge section83of the atmosphere communication path8so as to be slidable along the outer peripheral surface of the discharge section83. Moving the atmosphere communication valve9enables the atmosphere communication port8a, the outlet of the atmosphere communication path8, to be opened and closed. Hence, when the atmosphere communication port8ais open, the air inside the subtank4can be emitted to the exterior via the entry section81, the space section82, and the discharge section83.

Furthermore, a solid pipe13formed of a conductive material such as metal or the like is attached to the subtank4so as to contact the ink in the subtank4when the liquid surface of the ink is at least at a predetermined height. The solid pipe13and the hollow pipe11are electrically connected together by a wiring section (not shown in the drawings). Thus, when the solid pipe13and the hollow pipe11come into contact with the ink stored in the subtank, a closed circuit is formed to allow outputting of an electric signal indicating that ink has been filled into the subtank.

In the present embodiment, the solid pipe13is located in an inclined surface formed in the top surface of the subtank4. This avoids the collection, around the solid tube13, of bubbles generated in the ink in the subtank4. Hence, possible misdetection can be avoided in which even though the liquid surface has reached the position where the ink comes into contact with the solid tube13, bubbles collected around the solid tube13prevent the contact of the ink with the solid tube13and thus the detection of the position of the liquid surface.

Furthermore, the diaphragm section3is provided on a part of a wall surface forming the subtank4to enable the volume of the subtank4to be varied. In the present embodiment, the subtank4comprises a liquid chamber section4aand a channel section4bconfigured to communicate with the liquid chamber section4a. The diaphragm section3is provided on the channel section4b. The diaphragm section3is formed of a flexible rubber.FIG. 2shows an initial condition in which the diaphragm section3bulges outward from the wall surface of the channel section4b; the volume of the subtank4has been increased. On the other hand,FIG. 3shows that a central portion of the diaphragm section3has been pressed to a position where the central portion comes into contact with the wall surface of the channel section4b. In this condition, the volume of the subtank4is smaller than that in the above-described expanded condition. A communication port4b1configured to be opened and closed by the diaphragm section3is formed in the channel section4baccording to the present embodiment. Furthermore, the lower end of the above-described supply tube2is coupled to a portion of the channel section4blocated downstream of the communication port4b1(downstream in the direction in which ink is supplied from the subtank to the print head). Hence, with the diaphragm section3pressed as shown inFIG. 3, the communication port4b1is closed by the diaphragm section3to break the communication between the liquid chamber section4aand the print head1. That is, the diaphragm section3also functions as an on-off valve configured to allow the print head and the liquid chamber section4ato communicate and to break the communication between the print head and the liquid chamber section4a.

Furthermore, the channel section4bwith the diaphragm section3provided therein is located below the liquid chamber section4aof the subtank4. A communication port between the channel section4band the liquid chamber section4ais formed at a relatively low position in the subtank4. This prevents air from flowing into the channel section4band the diaphragm section3until the ink is consumed to reduce the amount of ink remaining in the subtank to a very small value.

The buffer chamber6is formed as a container inside which ink can be accommodated and to communicate with the main tank5. An atmosphere communication path7that is open to the atmosphere is located inside the buffer chamber6. The main tank5and the buffer chamber6are connected together by a second hollow pipe12. The second hollow pipe12is formed of a conductive member such as metal so that ink can flow through the second hollow pipe12. Since the main tank5and the buffer chamber6are in communication, even if an increase in temperature causes the ink inside the main tank5to be expanded to increase the pressure inside the main tank5, the ink inside the main tank5can be allowed to flow into the buffer chamber6. This inhibits the pressure inside the main tank5from increasing excessively. Furthermore, the main tanks is formed to communicate with the atmosphere via the buffer chamber6. Consequently, the buffer chamber6serves to balance the pressure inside the main tank5with the atmospheric pressure.

Now, a mechanism configured to press and open the diaphragm section3and to perform open and close operation of the atmosphere communication port will be described. In the present embodiment, a driving mechanism30with the same motor14presses and opens the diaphragm section3to reduce and increase operation of the volume of the subtank4and open and close operation of the atmosphere communication port. The driving mechanism30comprises the motor14and a driving force transmitting mechanism composed of a driving gear14afixed to an output shaft of the motor14, an idle gear15, and a planetary gear16. The driving mechanism30also includes a first gear19and a second gear24selectively rotationally driven by the driving force transmitting mechanism, a first cam20rotated integrally with the first gear, and a second cam25rotated integrally with the second gear24atmosphere valve lever.

More specifically, the driving gear14afixed to the output shaft of the motor14is located so as to mesh with the idle gear15. Furthermore, the idle gear15and the planetary gear16mesh with each other and each transmit the driving force of the motor14. The planetary gear16is connected to the idle gear15via the arm17. The planetary gear16can move in a direction R1or R2depending on the rotating direction of the motor14shown inFIG. 2, with keeping a distance between the planetary gear16and the center shaft of the idle gear15. Upon moving in the direction R1, the planetary gear16can mesh with the second gear24. Upon moving in the direction R2, the planetary gear16can mesh with the first gear19.

Moreover, the driving mechanism30further includes an atmosphere valve lever21configured to rotate using a supporting point22as a center shaft and a diaphragm lever27configured to rotate using a supporting point26as a center shaft. One end of the atmosphere valve lever21is coupled to the atmosphere communication valve9configured to open and close the above-described atmosphere communication port8a. The atmosphere valve lever21is biased by the bias force of a compression spring23to the position where the atmosphere communication port8ais opened. A pressing section20aprojecting outward is provided on apart of the outer periphery of the first cam20. The first cam20rotates to a predetermined phase position to allow the pressing section20ato press one end of the atmosphere valve lever21against the bias force of the compression spring23. Furthermore, the second cam25rotates to a predetermined phase position to allow the pressing section25ato press the diaphragm lever27against the force of the compression spring28. Atmosphere valve sensor43and Diaphragm section sensor42are arranged close to the first gear19and the second gear24, respectively to sense the phases of the first cam20and the second cam25, which rotate in conjunction with the first gear19and the second gear24, respectively. The diaphragm section sensor42senses the phases of the second cam25, which allows the pressing section25ato press the diaphragm lever27, which operates the diaphragm section3. Furthermore, the atmosphere valve sensor43senses the phases of the first cam20, which allows the pressing section20ato press the atmosphere valve lever21, which operates the atmosphere communication path9. The atmosphere valve sensor43and the diaphragm section sensors42accurately detect the phases of the first gear19and the second gear24to reliably enable the operation of opening and closing the atmosphere communication port and the operation of moving the diaphragm section3to increase and reduce the volume of the subtank4. In the present embodiment, the diaphragm section sensor42and atmosphere valve sensor43are optical photo sensors including a light emitting element and a light receiving element. In the present embodiment, flags are provided at predetermined positions on the first gears19and the second gear24. When the flag is positioned at a predetermined phase, light from the light emitting element is blocked. Thus, the phase of the first gear19and the second gear24is sensed. The aspect of the diaphragm section sensor42and the atmosphere valve sensor43is not limited to the one described above. Magnetic sensors may be used which detect a change in magnetic field caused by the passage of the gear by the sensor.

FIG. 9is a block diagram of a control system of the ink jet printing apparatus according to the present embodiment. InFIG. 9, the operations of the sections of the ink jet printing apparatus are controlled by a CPU120based on control programs stored in a ROM121and various data stored in a RAM122. That is, the CPU120connects to a head driving circuit123to drive electrothermal conversion elements provided in the print head1, a main scanning motor driving circuit124configured to drive a main scanning motor104, a conveying motor driving circuit125configured to drive a conveying motor116, and the like. The above-described motor4is also connected to the CPU120; the motor4is a driving source configured, for example, to open and close the atmosphere valve9and to move the diaphragm section3. The CPU120further connects to, for example, a display section52configured to display the operating status of the ink jet printing apparatus, and an ASF114configured to supply print media. The CPU120further connects to, for example, the above-described atmosphere valve sensor43, diaphragm section sensor42, and paper end sensor112. The CPU120further connects to a liquid detecting circuit50configured to output a signal indicating whether or not the amount of ink accommodated in the main tank5and in the subtank4has reached a predetermined value or smaller. The liquid detecting circuit50applies predetermined voltages to between the above-described first hollow pipe11and second hollow pipe12and to between the above-described first solid pipe11and solid pipe13. The liquid detecting circuit50determines whether or not a current has flowed between the first hollow pipe11and the second hollow pipe12and between the first hollow pipe11and the solid pipe13. If a current has flowed between the first hollow pipe11and the second hollow pipe12and between the first hollow pipe11and the solid pipe13, the liquid detecting circuit50outputs a detection signal to the CPU120. The liquid detecting circuit50, the hollow pipes11and12, and the solid pipe13form liquid detecting means for determining whether or not ink is present in the main tank and the subtank.

Furthermore, in the above-described control system, in response to signals output by the liquid detecting circuit50and the sensors for the respective sections, the CPU120controls various operations such as a printing operation and an operation of filling ink into the subtank in accordance with the control programs stored in the ROM121. For example, in the operation of filling ink into the subtank after replacement of the main tank5, signal indicative of the phases of the first cam20detected by the atmosphere valve sensor43is input to the CPU120. Further, signal indicative of the phases of the second cam25detected by the diaphragm section sensor42is input to the CPU120. Based on the phases and a signal from the liquid detecting circuit50, the CPU120controls the rotating direction and rotation amount of the motor14.

When the print head1of the ink jet printing apparatus100configured as described above ejects ink, and ink is consumed as a result of ejection of ink, a negative pressure is generated in the print head1. At this time, since the atmosphere communication valve9is closed, the negative pressure propagates into the subtank4without escaping to the exterior. Then, since the main tank5and the subtank4are in communication via the first hollow pipe11as described above, the negative pressure formed in the subtank4allows the ink to be supplied from the main tank5to the subtank4. Furthermore, in the present embodiment, the main tank5and the buffer chamber6are in communication via the second hollow pipe12as described above. The air inside the buffer chamber6, which is in communication with the exterior through the atmosphere communication path7, can flow into the main tank5. Hence, even if the amount of ink inside the main tank5decreases as a result of the above-described printing, the pressure in the main tank5is prevented from decreasing excessively.

In the present embodiment, since the interior of the first hollow pipe11has sufficiently high resistance, only an amount of ink corresponding to the consumption in the print head is supplied from the interior of the main tank5to the subtank4. Thus, the level of the ink in the subtank4is adjusted to within a given range. In the present embodiment, with ink accommodated in the main tank5, the level of the ink inside the subtank4is adjusted to between the lower end of the solid pipe13and the top surface of the subtank4.

When the ink inside the main tank5is exhausted, air is supplied from the main tank5to the subtank4. Hence, as shown inFIG. 4, as the ink continues to be ejected from the print head1after the main tank5has become empty, air is supplied into a supply path10in the subtank4. The air flows into the supply path10in the subtank4via the first hollow tube11, which couples the main tank5and the subtank4together.

In the present embodiment, a predetermined voltage is applied to between the hollow pipe11and the solid pipe13. Then, depending on whether or not electric continuity is established between the hollow pipe11and the solid pipe13, the apparatus determines whether or not ink remains in the supply path10. At this time, if ink is present in the supply path10entirely, electric continuity is established between the hollow pipe11and the solid pipe13. If ink is not present in any area of the supply path10, electric continuity is not established between the hollow pipe11and the solid pipe13. The electric continuity allows the apparatus to determine whether or not ink is accommodated in the supply path10and thus whether or not ink is present in the main tank5. For example, when the hollow pipe11and the solid pipe13are electrically disconnected from each other, the apparatus determines that the ink inside the subtank4has started to be consumed. At this time, it is expected that no ink is present inside the main tank5, which is thus empty, and that the air in the main tank5has been flowed into the supply path10in the subtank4. The hollow pipe11has an inner diameter of φ1.6 mm, and the supply path10has an inner diameter of φ2 mm to φ3 mm, in order to allow the apparatus to more accurately determine whether or not ink is present in the main tank5. Since the wall surface forming the supply path10is shaped like a cylinder with a small inner diameter, when air is supplied into the subtank4to lower the liquid surface of the ink, the liquid surface is relatively significantly displaced. Hence, when air is supplied into subtank4, amount of the moving of liquid surface of the ink is large. Thus, even when only a small amount of air flows from the main tank5into the subtank4, the electric conduction between the hollow pipe11and the solid pipe13can be reliably interrupted. Since the ink jet printing apparatus has such construction, the exhaustion of the ink in the main tank5can be reliably detected based on the displacement of the liquid surface of the ink. Thus, an ink presence sensor (liquid presence sensor) is attached to the inside of the subtank4at a position close to a supply port through which the ink from the main tank5is supplied. The ink presence sensor determines whether or not ink is present to sense when the supplying of ink from the main tank5is stopped. In the present embodiment, since the hollow pipe11functions both as the supply port for the ink from the main tank5and as the ink presence sensor, the position of the supply port for the ink from the main tank5aligns substantially with the position where whether or not ink is present is sensed.

Once the exhaustion of the ink in the main tank5is detected as a result of detection of whether or not ink is present in the supply path10in the subtank4, the amount of ink consumed by the print head1is calculated based on the number of times that the ink has been ejected. Then, based on the amount of ink consumed, the amount of ink remaining in the subtank4is calculated. Thereafter, if printing is continued with the main tank5not replaced, when the subtank4becomes empty, the printing is interrupted. Then, an alarm operation is performed to urge a user to replace the main tank5with a new one.

When the exhaustion of the ink inside the main tank5is sensed, this is indicated on a display of the host computer or the display section of the printing apparatus to let the user know the exhaustion.

To replace the main tank5, the user pulls the main tank5upward and out from the first hollow pipe11and the second hollow pipe12. Then, a new main tank5is installed so that the first hollow pipe11and the second hollow pipe12penetrate the wall surface of the main tank5. The subtank4and the buffer chamber6are connected to the main tank5.

In the present embodiment, a predetermined voltage is applied to between the first hollow pipe11and the second hollow pipe12. Then, depending on whether or not electric continuity is established between the first hollow pipe11and the second hollow pipe12, the apparatus can determine whether or not the main tank5is installed, in which the main tank5is filled with ink. Thus, in the present embodiment, a main tank installation sensor (first main tank installation sensor) is mounted in the apparatus to sense that the main tank5filled with ink has been installed.

FIG. 5is a diagram showing that in the state shown inFIG. 4, the printing operation further progresses to consume and reduce the ink in the subtank4. While the printing operation is being performed, the apparatus is in the initial state in which the atmosphere communication valve9is closed, with the diaphragm section3bulging outward. At this time, the internal volume of the subtank4is kept larger.

The main tank5is located above the subtank4. However, even when the main tank5with ink accommodated therein is mounted in the apparatus, the ink is not immediately supplied into the subtank4. Normally, when the main tank5is replaced new one, this main tank5has been empty. Thus, as shown inFIG. 6, when the main tank5is replaced, air has been flowed into the supply path10in the subtank4from the empty main tank5. Hence, normally, when the main tank5is replaced, the air is present in the supply path10in the subtank4.

Furthermore, when the main tank5is replaced, the atmosphere communication valve9is closed. Furthermore, air is accommodated above the ink in the subtank4. Thus, even when the main tank5is replaced to allow the main tank5with ink accommodated therein to communicate with the subtank4, the air is prevented from being discharged from the subtank4. Consequently, almost no ink flows into the subtank4. Thus, even when the main tank5is replaced, no ink is supplied from the main tank5unless a negative pressure is generated in the subtank4.

Thus, to supply ink to the subtank4, it is necessary to generate a negative pressure in the subtank4to substitute the air in the subtank4with the ink in the newly replaced main tank5, thus filling the ink into the subtank4.

The operation of filling ink into the subtank will be described in brief with reference toFIGS. 7A to 7Cand8.FIGS. 7A to 7Care diagrams illustrating the operations of the subtank and the surrounding sections which operations are performed to fill ink into the subtank.FIG. 8is a flowchart showing control steps for the operation of filling ink into the subtank as shown inFIGS. 7A to 7C.

FIG. 7Ashows that with the main tank5replaced with a new one, the amount of ink in the subtank has decreased to a very small value.FIG. 7Bshows that the diaphragm section3has been moved inward to discharge the air in the subtank4to the exterior of the subtank4.FIG. 7Cshows that the diaphragm section3has been moved outward to supply the ink from the main tank5into the subtank4.

As shown inFIG. 7A, immediately after replacement of the main tank5, the diaphragm section3is bulged outward with the volume of the subtank4increased. At this time, the atmosphere communication valve9is closed. Then, as shown inFIG. 7B, the closed atmosphere communication valve9is opened (S201) from closed state. The diaphragm section3is then positioned inward to reduce the volume of the subtank4(S202). The movement of the diaphragm section3changes the volume of the subtank4by about 0.5 cc.

Moving the diaphragm section3inward allows about 0.5 cc of ink to be pushed out from the diaphragm section3toward the main tank side of the subtank4. At this time, the channel resistance ΔPHbetween the diaphragm section3and the print head1(the channel resistance in the supply tube2) is overwhelmingly higher than that ΔPSbetween the diaphragm section3and the subtank4(main tank5). Consequently, at this time, almost no ink is pushed out toward the print head1.

The channel resistance in the pipe can be expressed in terms of a pressure loss in the flow in the pipe as follows.

The pressure loss ΔP can be expressed by:
ΔP=Q×(128μΔL)/πd4(1)

where Q denotes the flow rate of the ink, μ denotes the viscosity of the ink, ΔL denotes the length of the channel, and d denotes the inner diameter of the channel.

In the present embodiment, the supply tube2has an inner diameter of φ2.4 mm and a length of about 1.9 m. On the other hand, when the subtank4is divided into the liquid chamber section4aand a portion of the channel section4bwhich extends from the diaphragm section3to the liquid chamber section4a, the portion extending from the diaphragm section3to the liquid chamber section has an inner diameter of φ5 mm and a length of about 10 mm. In this case, the ratio of the resistance ΔPHin the channel from the diaphragm section3to the print head1to the channel resistance ΔPSin the channel section4bin the subtank4which extends from the diaphragm section3is:
ΔPH:ΔPS=3580:1  (2).

Thus, the resistance in the channel from the diaphragm section3to the print head1is overwhelmingly higher than that in the channel section4bin the subtank4which extends from the diaphragm section3.

Hence, even when the diaphragm section3moves to push the ink inside the subtank4, almost none of the ink accommodated in the subtank4is pushed out toward the print head1. As a result, the ink compressed and pushed out from the diaphragm section3as a result of the inward movement of the diaphragm section3moves toward the subtank4.

Then, the resistance value ΔPH2obtained when the ink flows into the main tank5via the supply path10in the subtank and the first hollow pipe11is compared with the resistance value ΔPAobtained when the air in the subtank4is discharged to the atmosphere via the atmosphere communication path8in the subtank4. In the present embodiment, the viscosity of the ink is about one hundredfold higher than that of air. Furthermore, the supply path10has an inner diameter of φ2 mm to φ3 mm and a length of about 20 mm. The first hollow pipe11has an inner diameter of φ1.6 mm and a length of about 30 mm. On the other hand, the atmosphere communication path8has an inner diameter of φ2.7 mm and a length of about 74 mm. Thus, the ratio of the resistance ΔPH2in the channel from the subtank4to the main tank5to the resistance ΔPAin the channel from the subtank4to the atmosphere via the atmosphere communication path8is:
ΔPH2:ΔPA=27.5:1  (3).

As described above, the resistance ΔPAin the channel from the subtank4to the atmosphere formed when the atmosphere communication valve9is open is overwhelmingly lower than that ΔPH2in the channel from the subtank4to the main tank5. Thus, when the diaphragm section3moves inward to reduce the volume of the subtank4to push the ink and air inside the subtank4, the air in the subtank4is discharged to the atmosphere through the atmosphere communication valve9. Consequently, the pressure in the subtank4is prevented from increasing, and almost no ink flows to the main tank5.

Then, as shown inFIG. 7C, the open atmosphere communication valve9is closed (S203). The inwardly pressed diaphragm section3is moved to the initial state in which the diaphragm section3is bulged outward (S204). The movement of the diaphragm section3increases the volume of the subtank4. Hence, a negative pressure is generated in the subtank4to allow about 0.5 cc of ink to flow into the diaphragm section3. Furthermore, the ink flows from the main tank5to the subtank4. At this time, since the resistance in the channel from the diaphragm section3to the print head1is considerably higher than that in the channel from the diaphragm section3to the main tank5, almost no ink flows from the print head1into the diaphragm section3. In the present embodiment, the supply path10has an inner diameter of φ2 mm to φ3 mm and a length of about 20 mm. The first hollow pipe11has an inner diameter of φ1.6 mm and a length of about 30 mm. Consequently, the ratio of the resistance ΔPHin the channel from the diaphragm section3to the print head1to the resistance ΔPTin the channel from the diaphragm section3to the main tank5is:
ΔPH:ΔPT=11:1  (4).

Thus, the resistance in the channel from the diaphragm section3to the print head1is considerably higher. As a result, almost none of the ink present closer to the print head1flows into the diaphragm section3. At this time, since the atmosphere communication valve9is closed, almost no air flows from the exterior of the printing apparatus into the subtank4via the atmosphere communication path8. Then, a negative pressure is generated in the main tank5. However, since air is introduced from the buffer chamber6into the main tank5via the atmosphere communication path7, the negative pressure in the main tank5is eliminated. As a result, a given amount of ink is introduced from the main tank5into the subtank4.

Now, description will be given of the operations of the components of the driving mechanism30performed when ink is supplied from the main tank5into the subtank4after replacement of the main tank5in the ink supply system according to the present embodiment.

As described above, the following are repeated to supply ink from the main tank5to the subtank4while removing air from the subtank4after replacement of the main tank5: the operation of expanding and contracting the diaphragm section3(moving the diaphragm) and the operation of closing and opening the atmosphere communication valve9. At this time, the diaphragm section3and atmosphere communication valve9in the printing apparatus may be in one of roughly two possible states. First, in one of the states, as shown inFIG. 2, the diaphragm section3is bulged outward of the subtank4to increase the volume of the diaphragm section3(this state is hereinafter referred to as a diaphragm section expanded state). Furthermore, the atmosphere communication valve9is closed. In the other state, as shown inFIG. 3, the diaphragm section3is pressed to reduce the internal volume thereof (this state is hereinafter referred to as a diaphragm section contracted state). Furthermore, the atmosphere communication valve9is open.

In the state shown inFIG. 2, the pressing section20aof the first cam20presses the right end of the atmosphere valve lever21against the bias force of the compression spring23. Thus, the atmosphere communication valve9, provided at the left end of the atmosphere valve lever21, closes the atmosphere communication port8a. Furthermore, the pressing section25aof the second cam25is separated from the diaphragm lever27which is in abutting contact with the circular outer peripheral surface of the cam25owing to the bias force of the spring28. At this time, the left end of the diaphragm lever27is prevented from pressing the diaphragm section3(open state). The diaphragm section3is thus kept expanded.

First, the motor14is driven to rotate the driving gear14ain a direction S2. The rotational force of the driving gear14ais transmitted to the planetary gear16via the idle gear15. The planetary gear16rotates around a pivotal-movement center shaft. At a fixed position, the idle gear15rotates around a shaft (not shown in the drawings) held at a fixed position. Rotation of the planetary gear16allows the first cam20to rotate together with the first gear19meshed with the planetary gear16. Then, the pressing section20ais separated from the right end of the atmosphere valve lever21. As a result, the atmosphere valve lever21rotates counterclockwise inFIG. 2around the supporting point22owing to the elastic force of the compression spring23. The atmosphere communication valve9is moved from the position where the atmosphere communication valve9closes the atmosphere communication port8a. This makes the atmosphere communication port8aopen to the atmosphere.

Then, when the motor14rotates the driving gear14ain the direction S2, the idle gear15meshed with the driving gear14arotates. The rotation of the idle gear15moves the planetary gear16meshed with the idle gear15in the direction R1. The planetary gear16then comes into mesh with the second gear24as shown inFIG. 3. Thereafter, the motor14is continuously driven to rotate the planetary gear16around the pivotal-movement center thereof. The pressing section25athen moves to a position where the pressing section25asits opposite the diaphragm lever27. The pressing section25apresses the right end of the diaphragm lever27against the force of a compression spring28. Thus, left end of the diaphragm lever27presses the diaphragm section3and the diaphragm section3is contracted (seeFIG. 3). Thus, the contracted diaphragm section3allows the ink in the diaphragm section3to be supplied toward the liquid chamber4aof the subtank4. As a result, the liquid surface of the ink of the liquid chamber4rises. At this time, since the atmosphere communication port8ais open owing to the open state of the atmosphere communication valve9, the air collected in the upper portion of the subtank4is discharged to the atmosphere through the atmosphere communication port8awith rising of the liquid surface of ink in the subtank4.

As described above, the positional relationship between the diaphragm section3and the atmosphere communication valve9can be changed from the one shown inFIG. 2to the one shown inFIG. 3.

The operations of the sections of the printing apparatus will be described, which operations are performed to shift the state in which the diaphragm section3is contracted with the atmosphere communication valve9open as shown inFIG. 3to the state in which the diaphragm section3is expanded with the atmosphere communication valve9closed as shown inFIG. 2.

When the diaphragm is contracted as shown inFIG. 3, the motor14is driven to rotate the driving gear14ain the direction S1. Thus, the idle gear15rotates to move the planetary gear16in the direction R2. The planetary gear16then comes into mesh with the first gear19. Thereafter, the motor14is continuously driven to rotate the planetary gear16via the idle gear15. In conjunction with the rotation of the planetary gear16, the first gear19and the first cam20rotate. The rotation of the first cam20allows the pressing section20ato press the end of the atmosphere valve lever21against the force of the compression spring23. The atmosphere valve lever21then rotates around the supporting point thereof. In conjunction with the movement of the atmosphere valve lever21, the atmosphere communication valve9moves to close the atmosphere communication port8ahaving been opened until then. At this time, the rotation of the motor14is temporarily stopped. Furthermore, the diaphragm section3keeps contracted as shown inFIG. 3.

After the atmosphere communication port8ais closed by the atmosphere communication valve9as described above, the motor14is driven to rotate the driving gear14ain the direction S2. In conjunction with the rotation of the driving gear14a, the idle gear15rotates to move the planetary gear16in the direction R1. The planetary gear16thus comes into mesh with the second gear24. Even after the planetary gear16engages with the second gear24, the driving gear14acontinues to rotate under the driving force of the motor14. The planetary gear16then rotates around the pivotal-movement center thereof to rotate the second gear24. Thus, the pressing section25aof the second cam25is separated from the diaphragm lever27. The diaphragm lever27rotates clockwise inFIG. 3around the supporting point26by the bias force of the compression spring28. As a result, the diaphragm lever27releases the pressing force exerted on the diaphragm section3, which then returns to the expanded state shown inFIG. 2, by the restoring force of the diaphragm section3. At this time, since the atmosphere communication port8ais closed, the diaphragm section3returns to the expanded state. Thus, a negative pressure is generated in the subtank4to allow the ink in the main tank5to flow into the subtank4through the hollow pipe11.

By repeating the contraction and expansion of the diaphragm and opening and closing of the atmosphere communication port8aas described above, a given amount (in the present embodiment, 0.5 cc) of ink in the main tank5is supplied to the subtank4. In the above-described operation, when the first gear19is rotated, the atmosphere valve sensor43accurately senses the phases of the first cam20. Further, when the second gear24is rotated, the diaphragm section sensor42accurately senses the phases of the second cam25. Thus, it is accurately recognized whether the atmosphere communication valve9is open or closed and a condition of the diaphragm section3.

FIG. 10Ashows a condition in which the liquid surface of the ink has come into contact with the solid pipe13in the subtank4.FIG. 10Bshows a condition in which the operation of filling ink into the subtank4has been finished.

In the operation of filling ink into the subtank4, a judgment can be performed by sensing whether or not electric continuity is established in a space between the solid pipe13and the hollow pipe11.FIG. 10Ashows a state observed immediately after the space has been filled with ink to allow electric continuity to be established (S205). In the present embodiment, the subtank4is configured such that the top surface of the subtank4is inclined and that the discharge port through which air is discharged to the atmosphere is positioned above the inclined surface. The subtank4is further configured such that the inlet through which ink is introduced from the main tank5into the subtank4is positioned below the inclined surface and that the solid pipe13, which allows sensing of the presence or absence of ink, is positioned in the middle of the inclined surface. Thus, the air collected in the subtank4is smoothly removed via the atmosphere communication path8. The subtank4thus formed serves to prevent generation of possible erroneous in which the presence of ink fails to be sensed in spite of the filled ink because of a failure to remove air from the interior of the subtank4. In the state shown inFIG. 10A, a given amount of ink has been filled into the subtank4. In the present embodiment, the filling operation is thereafter finished by carrying out 10 sets each involving one control operation for the first step and one control operation for the second step (S206). The number of times that the first and second steps are repeated is not limited to 10. Alternatively, the first and second steps may be repeated until the presence of ink is sensed based on determination of whether or not ink is present between the solid pipe13and the hollow pipe11. Alternatively, the amount of ink may be adjusted in accordance with the purpose of the printing.

Furthermore, in the present embodiment, the ratio of the resistance ΔPHin the channel from the diaphragm section3to the print head1to the resistance ΔPTin the channel from the diaphragm section3to the main tank5is:
ΔPH:ΔPT=11:1  (5).

However, the supply tube used in the present invention is not limited to this aspect. A supply tube having a different length and a different inner diameter may be used. In a printing apparatus according to another embodiment in which the supply tube has an inner diameter of φ2.4 mm and a length of about 1 m and in which the other arrangements are the same as those of the above-described embodiment, ΔPH:ΔPT=6:1. Here, the resistance in the channel from the diaphragm section3to the print head1is defined as ΔPH. The resistance in the channel from the diaphragm section3to the main tank5is defined as ΔPT. The subtank4is similar to the one in the above-described embodiment; the supply path10has an inner diameter of φ2 mm to φ3 mm and a length of about 20 mm, and the first hollow pipe11has an inner diameter of φ1.6 mm and a length of about 30 mm. This embodiment exerts almost the same effects as those of the above-described embodiment.

With the above-described magnitude relation in channel resistance, substantially the same effects as those of the embodiments of the present invention can be exerted by controlling the speed at which the diaphragm section is opened and closed, or the like.

Furthermore, in the configuration of the printing apparatus according to the present embodiment, the means for forming a negative pressure required to supply ink into the subtank4and the driving mechanism configured to remove air from the interior of the subtank4can use same driving source in common. In the present embodiment, the operation of varying the volume of the diaphragm section3and the operation of opening and closing the atmosphere communication valve9are selectively performed. Hence, the single driving source is used both to form a negative pressure in the subtank4and to remove air from the subtank4.

Here, the method for filling ink into the subtank4according to the present embodiment includes a step of reducing the volume of the diaphragm section3(S202) which enables the volume of the subtank4to be changed after the atmosphere communication port8ahas been opened. The method for filling ink into the subtank4according to the present embodiment includes a step of expanding the volume of the diaphragm section3(S201) after the atmosphere communication port8ahas been closed. In this case, to allow ink to be quickly supplied to the subtank4, in a step of reducing the volume of the diaphragm section3, the time from the start of opening of the atmosphere communication port8atill the start of reduction of the volume of the diaphragm section3is preferably set to a smaller value. In the present embodiment, the time from the start of opening of the atmosphere communication port8atill the start of reduction of the volume of the diaphragm section3is set to within five seconds. Furthermore, similarly, also in a step of the expanding volume of the diaphragm section3after the atmosphere communication port8ahas been closed, the time from the start of closing of the atmosphere communication port8atill the start of increase of the volume of the diaphragm section3is preferably set to a smaller value. In the present embodiment, the time from the start of closing of the atmosphere communication port8atill the start of increase of the volume of the diaphragm section3is set to within five seconds.

Moreover, the time between the step of reducing the volume of the diaphragm section3after the atmosphere communication port8ahas been opened and the step of expanding the volume of the diaphragm section3after the atmosphere communication port8ahas been closed is preferably set to a smaller value. In the present embodiment, when the step of reducing the volume of the diaphragm section3and the step of expanding the volume of the diaphragm section3are repeated, each step requires finishing within five seconds.

In the present embodiment, a construction such that the operation of the diaphragm section3and the opening and closing of the atmosphere communication valve9are performed by using the springs to bias the atmosphere valve lever21and the diaphragm lever27and changing the rotating direction of the motor14and thus the gear to mesh with the planetary gear16is applied. However, the present invention is not limited to the present embodiment, motors may be installed so as to drive the first gear19and the second gear24separately to drive the first gear19and the second gear24respectively.

Furthermore, the printing apparatus according to the present embodiment is not limited to the tube supply type and the serial scan type. The present invention is applicable to a full-line printing apparatus that uses a print head extending all along the width of the print medium.

This application claims the benefit of Japanese Patent Application No. 2009-056899, filed Mar. 10, 2009, which is hereby incorporated by reference herein in its entirety.