JP5402033B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus provided with a recording head for discharging droplets.

  As an image forming apparatus such as a printer, a facsimile machine, a copying apparatus, a plotter, and a complex machine of these, for example, an ink jet recording apparatus is known as an image forming apparatus of a liquid discharge recording method using a recording head for discharging ink droplets. . This liquid discharge recording type image forming apparatus means that ink droplets are transported from a recording head (not limited to paper, including OHP, and can be attached to ink droplets and other liquids). Yes, it is also ejected onto a recording medium or a recording medium, recording paper, recording paper, etc.) to form an image (recording, printing, printing, and printing are also used synonymously). And a serial type image forming apparatus that forms an image by ejecting liquid droplets while the recording head moves in the main scanning direction, and a line type head that forms images by ejecting liquid droplets without moving the recording head There are line type image forming apparatuses using

  In the present application, the “image forming apparatus” of the liquid ejection method is an apparatus that forms an image by ejecting liquid onto a medium such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, ceramics, or the like. In addition, “image formation” means not only that an image having a meaning such as a character or a figure is imparted to the medium but also an image having no meaning such as a pattern is imparted to the medium (simply liquid. It also means that a droplet hits the medium). “Ink” is not limited to ink, but is used as a general term for all liquids capable of image formation, such as recording liquid, fixing processing liquid, and liquid. DNA samples, resists, pattern materials and the like are also included.

  In particular, in a line type image forming apparatus (hereinafter also simply referred to as “inkjet recording apparatus”), a recording head configured by arranging a plurality of heads, a main tank for storing ink, and an ink supplied from the main tank are stored. An ink supply system that can handle deaerated ink including a sealed sub-tank formed of a flexible member (for example, a flexible film) that is supplied to the recording head, and a branch member that branches the ink to a plurality of heads of the recording head ( Distributor tanks) and means for discharging air bubbles accumulated in the distributor tank from the ink supply path are known.

  For example, Patent Documents 1 and 2 describe an ink tank and a pump for pumping ink to the head for the purpose of preventing air from entering the ink supply path or discharging dust or bubbles present in the ink flow path or the head. An intermediate tank having a flexible bag for storing ink provided between the pump and the head, an ink flow path bypassing the intermediate tank, a plurality of valves disposed on the upstream and downstream sides of the intermediate tank, and a valve A configuration is disclosed in which ink is supplied through an intermediate tank or a bypass ink flow path by opening and closing.

  In Patent Documents 3 to 5, for the purpose of discharging bubbles in the buffer tank, an ink tank, a sub-tank of a type open to the atmosphere storing ink in the ink tank, and a buffer tank (distributor tank) above the head are used. And a configuration having an ink flow path for sucking bubbles in the buffer tank with an ink circulation pump and circulating them in the sub tank.

  In Patent Document 6, for the purpose of discharging air bubbles from the ink supply path and improving ejection reliability, the ink tank and a flexible sub tank that is not open to the atmosphere, and air bubbles in the sub tank are discharged. And a configuration including negative pressure and pressurizing means for controlling the negative pressure means of the sub-tank is disclosed.

JP 2007-245451 A JP 2007-223278 A Japanese Patent No. 3901718 JP 2004-114611 A JP 2004-114335 A JP 2004-216797 A

  Conventionally, an ink supply system that can handle deaerated ink including a sealed sub-tank formed of a flexible member that stores ink supplied from the main tank as described above and supplies the recording head, and a plurality of recording heads In an image forming apparatus having a branching member (distributor tank) for branching ink to the head and means for discharging air bubbles accumulated in the distributor tank from the ink supply path, the air bubbles accumulated in the distributor tank are sucked. A configuration in which a pump for discharging is attached to the upstream side of the bubble reservoir in the distributor tank, or a configuration in which the pump is arranged on the upstream side of the sealed sub-tank when the ink in the distributor tank is pressurized and discharged. It has been adopted.

  However, in the case of a configuration in which the air bubbles in the distributor tank are sucked and discharged, the air bubbles accumulated in the upper part of the distributor tank must first be sucked with a pump, and when the air bubbles (air) are sucked with the pump, the ink ( Since a large suction force is required compared with the case of sucking (liquid), there is a problem that the pump is enlarged and the cost is increased.

  Also, in the case of a configuration in which air is discharged by pressurizing the ink in the distributor tank, the pump is arranged in the supply path between the sub tank and the ink tank on the upstream side of the sealed sub tank, or the ink tank is pressurized. However, when the pump is arranged upstream of the sealed sub-tank to pressurize the ink, the sealed sub-tank part is formed by a pack-like flexible member. The pressure is not transmitted to the distributor tank and the loss increases. In this case, in order to prevent pressure loss due to the sealed sub-tank as in Patent Documents 1 and 2, an ink path bypass that avoids the sub-tank is also provided. In this case, a valve for switching the flow path is provided. There is a problem that the configuration becomes complicated as well as the cost becomes necessary.

  The present invention has been made in view of the above problems, and has an object of reducing the amount of ink that becomes waste liquid that flows out together with bubbles when the bubbles stay in the branch member with a simple configuration. .

In order to solve the above problems, an image forming apparatus according to the present invention provides:
A recording head in which a plurality of heads for discharging droplets are arranged side by side;
A main tank for storing ink;
A sub tank that is supplied with ink from the main tank and supplies ink to the recording head;
A branch member that branches and supplies ink from the sub-tank to each head of the recording head,
The sub tank has a sealed structure in which at least a part of the ink storage portion is formed of a flexible member,
The recording head and the sub tank are arranged with a water head difference,
The branch member is formed such that the inner top surface is inclined in the height direction,
One end portion of the branch member is a position where the inner top surface is the highest, and the other end portion of the branch member is a position where the inner top surface is the lowest,
On the upper part of the one end of the branch member , there is a bubble discharge port and an opening / closing valve that opens and closes the bubble discharge port,
The lower part of the one end of the branch member has a supply port for supplying ink from the sub tank,
The bubble discharge port and the supply port of the branch member are arranged at positions facing vertically at the one end of the branch member,
A pump that sucks or pressurizes ink in the sub-tank and sends the ink to the branch member ;
The pump is directly below the supply port of the branch member, and is disposed between the sub tank and the branch member,
In the state where the on-off valve of the branch member is open, the pump supplies the ink from the sub tank to the supply port of the branch member, thereby discharging the air in the branch member from the bubble discharge port.

According to the onset bright, it can discharge the bubbles staying in the branch member with a simple structure, yet it is possible to reduce the amount of ink to be the waste liquid flowing along at bubble discharging.

1 is a schematic front view illustrating the overall configuration of an example of an image forming apparatus according to the present invention. Similarly it is principal part plane explanatory drawing. FIG. 2 is an explanatory plan view of a recording head. It is a plane explanatory view of a head. FIG. 2 is a schematic explanatory diagram of an ink supply system according to the first embodiment of the present invention. It is typical explanatory drawing with which it uses for description of the supply pump of the ink supply system. It is a functional block diagram explaining the outline | summary of a control part. It is typical explanatory drawing which shows the state in which the bubble of the branch member was mixed. It is a timing chart with which it uses for description of the bubble discharge | emission operation | movement in the same embodiment. 6 is a timing chart for explaining the head cleaning operation. It is a typical explanatory view of an ink supply system in a second embodiment of the present invention. It is a timing chart with which it uses for description of the bubble discharge | emission operation | movement in the same embodiment. 6 is a timing chart for explaining the head cleaning operation. 6 is a schematic explanatory diagram for explaining an ink supply system of Comparative Example 1. FIG. 10 is a schematic explanatory diagram for explaining an ink supply system of Comparative Example 2. FIG. 12 is a schematic explanatory diagram for explaining an ink supply system of Comparative Example 3. FIG. 10 is a schematic explanatory diagram for explaining an ink supply system of Comparative Example 4. FIG. It is a typical explanatory view of an ink supply system in a third embodiment of the present invention. 6 is a timing chart for explaining ink circulation control in the embodiment. It is a typical explanatory view of the ink supply system in a 4th embodiment of the present invention. 6 is a timing chart for explaining ink circulation control in the embodiment.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. First, an example of an image forming apparatus according to the present invention will be described with reference to FIGS. 1 is a schematic configuration diagram for explaining the overall configuration of the image forming apparatus, and FIG. 2 is a schematic plan explanatory diagram of the apparatus.

  This image forming apparatus is a line type image forming apparatus, and includes an apparatus main body 1, a paper feed tray 2 on which paper P is stacked and fed, a paper discharge tray 3 on which printed paper P is discharged and stacked, and paper P An image forming unit 5 that includes a head module 51 that constitutes a recording head that discharges and prints droplets on a sheet P that is transported by the transport unit 4. The head cleaning device 6 that is a maintenance / recovery mechanism that performs maintenance / recovery of each recording head of the image forming unit 5 after printing is completed or at a required timing, a conveyance guide portion 7 that opens and closes the head cleaning device 6, and the image forming unit 5 An ink tank unit 8 composed of sub-tanks that supply ink to the head module 51, and a main tank that supplies ink to the ink tank unit 8. And a tank unit 9.

  The apparatus main body 1 includes front and rear side plates and stays (not shown), and the sheets P stacked on the sheet feed tray 2 are fed one by one to the transport unit 4 by the separation roller 21 and the sheet feed roller 22. Is done.

  The transport unit 4 includes a transport driving roller 41A, a transport driven roller 41B, and an endless transport belt 43 wound around these rollers 41A and 41B. A plurality of holes (not shown) are formed on the surface of the transport belt 43, and a suction fan 44 that sucks the paper P is disposed below the transport belt 43. Further, conveyance guide rollers 42A and 42B are respectively held on guides (not shown) on the conveyance driving roller 41A and conveyance driven roller 41B and are in contact with the belt 43 by their own weight.

  The conveyance belt 43 rotates around when the conveyance driving roller 41A is rotated by a motor (not shown), and the paper P is sucked onto the conveyance belt 43 by the suction fan 44 and is conveyed by the rotation movement of the conveyance belt 43. The transport driven roller 41 </ b> B and the transport guide rollers 42 </ b> A and 42 </ b> B rotate following the transport belt 43.

  An image forming unit 5 composed of a plurality of head modules 51 for discharging droplets to be printed on the paper P is disposed above the transport unit 4 so as to be movable in the arrow A direction (and the reverse direction). The image forming unit 5 is moved to above the cleaning device 6 during the maintenance and recovery operation (during cleaning), and is returned to the position shown in FIG. 1 during image formation.

  As shown in FIGS. 3 and 4, the image forming unit 5 arranges a plurality of heads 101 in which a plurality of nozzles 102 for ejecting liquid droplets are arranged in two rows on the nozzle surface 104, and ink is applied to each head 101. Head modules (recording head units) 51A, 51B, 51C, 51D integrated with a branching member 54, which is a distributor for distribution and supply, are arranged along the sheet conveying direction and attached to the line base member 52.

  Here, one of the two nozzle rows of the head modules 51A and 51B ejects yellow (Y) droplets and the other of the magenta (M) droplets, and the two nozzle rows of the head modules 51C and 51D. On the other hand, cyan (C) droplets are discharged, and on the other hand, black (K) droplets are discharged. That is, in the image forming unit 5, two head modules 51 that discharge droplets of the same color are arranged side by side in the paper transport direction, and the two head modules 51 form a nozzle row corresponding to the paper width. It has a configuration.

  In addition, as shown in FIG. 3, the branch member 54 is an inclined surface in which the inner top surface 54a is inclined in the height direction, and bubbles generated inside move to the highest position on the top surface 54a. become.

  On the upstream side of the image forming unit 5, a sub tank (ink tank) 81 of the ink tank unit 8 (only one ink tank is indicated for convenience in the drawing) is disposed, and the sub tank is connected via a supply tube 82. Ink is supplied from 81 to the branching member 54 of each head module 51, and a negative pressure with respect to each head of the head module 51 is formed by a water head difference between the ink tank 81 and the head module 51. The ink tank unit 8 is arranged so as to be movable in the direction of arrow A together with the image forming unit 5. Note that the supply tube 82 from the ink tank 81 to the head module 51 is shown as being connected from above the head module 51 for easy understanding, but in reality, the longitudinal direction of the head module 51 (the direction orthogonal to the paper transport direction). ) Is connected to the end.

  Further, the main tank unit 9 is arranged on the upstream side of the ink tank 81, and ink is supplied from the main tank (ink cartridge) 91 to the sub tank 81 through the supply tube 92.

  On the downstream side of the transport unit 4, a transport guide portion 7 that discharges the paper P to the paper discharge tray 3 is provided. The paper P guided and conveyed by the conveyance guide unit 7 is discharged to the paper discharge tray 3. The paper discharge tray 3 includes a pair of side fences 31 that regulate the width direction of the paper P and an end fence 32 that regulates the front end of the paper P.

  The maintenance / recovery mechanism (head cleaning device) 6 includes four rows of cleaning means 61 </ b> A to 61 </ b> D corresponding to each head module 51 of the image forming unit 5, and one cleaning means 61 corresponds to each head of the head module 51. The cap member 62 and the wiper member (not shown) are provided. The cap member 62 of each cleaning means 61 can be moved up and down independently for each row. Furthermore, suction pumps 63 </ b> A to 63 </ b> D for sucking ink from the nozzles with the cap member 62 capping the nozzle surface of the head module 51 are disposed below the cleaning unit 61.

  Further, in this image forming apparatus, after the printing is finished, when the nozzle surface of each head of the head module 51 that discharges droplets is capped by the cleaning unit 61, or ink is sucked from the nozzle, or the head module 51 When the ink adhering to the nozzle surface of each head is cleaned with a wiping member, as shown in FIG. 1, after the printing is stopped, the entire transport unit 4 rotates in the direction of arrow B with the transport driven roller 41B as a fulcrum, A space for moving the image forming unit 5 is ensured by making the space between the image forming unit 5 larger than that at the time of image formation. At this time, the conveyance guide plate 71 of the conveyance guide portion 7 disposed on the upper portion of the head cleaning device 6 is also rotated upward in the direction of arrow C at the fulcrum 72, and the upper portion of the head cleaning device 6 is opened.

  Then, after the transport unit 4 and the transport guide portion 7 are released (released), the image forming unit 5 moves in the paper passing direction (arrow A direction), is stopped above the head cleaning device 6, and is cleaned. 61 rises and shifts to the cleaning operation (maintenance recovery operation) of each head module 51.

Next, a first embodiment of the present invention will be described with reference to FIG. FIG. 5 is a schematic explanatory view showing an ink supply system in the embodiment.
A sub tank (ink tank) 81 that stores ink to be supplied to each head 101 of the head module 51 is configured as a sealed structure in which at least a part is formed of a flexible member, for example, a flexible film (this is referred to as “sealed”). It is referred to as “type sub-tank”), and the head module 51 is arranged with a required water head difference between each head 101. The sub tank 81 is replenished with ink from a main tank (ink cartridge) 91 that is replaceably mounted via a supply path (supply tube) 91. A supply control electromagnetic valve 93 is interposed between the supply path 91 and the sub tank 81.

  A supply path 83 (supply tube) 82 from the sub tank 81 to the branching member 54 is provided with a supply pump 83 as a bubble discharging means. The supply pump 83 is not used for normal ink supply, and is used to pressurize and supply ink when the air bubbles are discharged from the branching member 54 or when maintenance of the nozzle down (discharge failure) of each head 101 of the head module 51 is performed. Also, it is used when ink is filled into the initial supply path (ink initial filling).

  The supply pump 83 is a known tube pump. As shown in FIG. 6, the supply pump 83 serving as a tube pump squeezes the tube 130 with a roller 131 and feeds it. The drive shaft 132 is rotated counterclockwise as shown in FIG. In this case, the roller 131 is pressed against the tube 130, and the tube 130 is squeezed by the roller 131. However, when the drive shaft 132 is rotated clockwise as shown in FIG. Leaves the tube 130 and releases the pressing of the tube 130. When the normal head difference of ink supply is used, the latter state is established, and the roller 131 is not pressed against the tube 130.

  Further, in order to detect the amount of ink in the sub tank 81, an ink amount detection filler 85 that is urged to come into contact with the sub tank 81 and is swingably disposed, and an ink amount that is detected by the ink amount detection filler 85. An upper limit detection sensor 86 and an ink amount lower limit detection sensor 87 are provided. When the ink amount upper limit detection sensor 86 detects the filler 85, the ink amount is the upper limit value (the state of the sensor 86 at this time is “ON”), and the ink amount upper limit detection sensor 86 does not detect the filler 85. Therefore, when the ink amount lower limit detection sensor 87 detects the filler 85, the ink amount is the lower limit value (the state of the sensor 87 at this time is set to “ON”).

  The branch member 54 is provided with a bubble discharge port 56 and a bubble discharge electromagnetic valve 57 that is an open / close valve for opening and closing the bubble discharge port 56. The bubble discharge port 56 includes an opening (discharge port 56a) provided in the branching member 54 and a discharge path connected to the discharge port 56a. However, the bubble discharge port 56 may be a simple discharge port (opening). The branch member 54 is provided with a liquid level detection sensor 58 composed of two detection electrodes in order to detect the ink height inside. The bubble discharge port 56 is disposed in the vicinity of the supply port 59 to which ink is supplied from the sub tank 81, in this example, above the supply port 59.

  Detection signals of the ink amount upper limit detection sensor 86, the ink amount lower limit detection sensor 87, and the liquid level detection sensor 58 are input to the control unit 500, and the control unit 500 controls the supply electromagnetic control valve 93 and the bubble discharge electromagnetic wave based on these detection signals. Open / close control of the valve 57 and drive control of the pump 83 are performed.

  In the ink supply system configured as described above, ink is supplied from the main tank 91 to the sealed sub-tank 81 using the water head difference. The ink amount in the sealed sub tank 81 is detected by the ink amount detection filler 85 that moves up and down following a flexible film (flexible member) provided on the upper surface side of the sealed sub tank 81, and the ink amount detection filler. When 85 blocks the ink amount upper limit detection sensor 86, the supply control electromagnetic valve 93 is closed by the control unit 500 and the ink supply from the main tank 91 to the sub tank 81 is stopped.

  When ink is consumed by the ink ejection by the head module 51 and the sealed sub-tank 81 is deflated (the ink amount is decreased), the ink amount detection filler 85 is lowered and detected by the ink amount lower limit sensor 87, and is controlled thereby. The supply control electromagnetic valve 93 is opened by the unit 500, and ink is supplied from the main tank 91 to the sub tank 81.

  Ink supply from the sealed sub tank 81 to each head 101 of the head module 51 is performed by a natural supply method using a water head difference between the nozzle surface of the head 101 and the upper surface of the sealed sub tank 81.

Next, an outline of the control unit will be described with reference to the block explanatory diagram of FIG.
The control unit 500 includes a main control unit (system controller) 501 including a microcomputer that also serves as a control unit according to the present invention that controls the entire image forming apparatus, an image memory, a communication interface, and the like. The main control unit 501 sends print data to the print control unit 502 in order to form an image on a sheet based on image data transferred from an external information processing apparatus (host side) and various command information.

  Based on the print data signal received from the main control unit 501, the print control unit 502 generates data for driving pressure generating means for ejecting droplets from the head module 51, and transfers the data. Various signals necessary for confirmation of transfer and the like are transferred to the head driver 503, and a storage unit as drive waveform data storage means, a D / A converter, a voltage amplifier and a current amplifier for D / A conversion of drive waveform data Drive waveform generation unit configured by the above and selection means for selecting a drive waveform to be given to the head driver 503, and generates a drive waveform configured by one drive pulse (drive signal) or a plurality of drive pulses (drive signal) Then, the head module 51 is output to the head driver 503 to drive and control the head module 51.

  The main control unit 501 also drives and controls the paper feed motor 505 that rotates the transport belt 43 and the supply pump 84 via the motor driver 504, and also opens and closes the supply control electromagnetic valve 93 and the bubble discharge electromagnetic valve 57. Control.

  Further, the main control unit 501 receives detection signals from the sensor group 506 including the ink amount upper limit detection sensor 86, the ink amount lower limit detection sensor 87, and the liquid level detection sensor 58 described above. Input / output various information and exchange display information.

Next, the bubble discharging operation in this embodiment will be described with reference to the schematic explanatory view of FIG. 8 and the timing chart of FIG.
First, as shown in FIG. 8, when bubbles 300 accumulate in the branch member 54, the ink level disappears between the two detection electrodes constituting the liquid level detection sensor 58 attached to the top of the branch member 54. Based on the detection signal of the detection sensor 58, it is detected that the bubble 300 is mixed in the branching member 54, and operation control of bubble discharge by the control unit 500 is started.

  As shown in FIG. 9 (f), the operation sequence at the time of discharging the bubbles is as shown in FIG. 9 (b) when the ink amount lower limit detection sensor 87 is ON in the confirmation of the ink remaining amount in the sealed sub-tank 81. As shown in the figure, the supply control electromagnetic valve 93 is opened to replenish ink from the main tank 91 to the sub tank 81, and the supply control electromagnetic valve 93 is closed when the ink amount upper limit detection sensor 86 is turned on as shown in FIG. Stop supplying ink.

  Next, as shown in FIG. 6C, the bubble discharge electromagnetic valve 57 is opened to discharge the bubbles in the branching member 54, and at the same time, the supply pump 83 is driven as shown in FIG. The ink is sent from the sub-tank 81 to the branching member 54 side. At this time, since the bubble discharge electromagnetic valve 57 is opened, the ink is not discharged from the nozzles of the head 101, and only the bubble 300 is discharged from the bubble discharge port (bubble discharge port) 56 to the atmosphere, and the ink is branched by the ink. 54 is satisfied. In this case, since the branching member 54 has the bubble discharge port 56 mounting position for discharging bubbles almost directly above the mounting position of the tube (supply path) 82 for supplying ink, the bubbles are discharged. It is easy to come out from the exit 56.

  Then, after the ink level in the branching member 54 rises and the liquid level detection sensor 58 is turned on (detects the liquid level) as shown in FIG. 4D, the bubble discharge electromagnetic valve 57 is closed after a predetermined time. At the same time, the drive of the supply pump 83 is also stopped.

  Here, when the ink amount lower limit detection sensor 87 of the sealed sub-tank 81 is ON, the ink supply operation from the main tank 91 is performed until the ink amount upper limit detection sensor 86 is turned ON as described above. Finally, the supply pump 83 is rotated in the reverse direction to release the state where the roller 131 inside the pump 83 presses the tube 130, thereby making the ink supply path 82 free. That is, since a tube pump is used as the supply pump 83, the inner roller 131 is in a state of pressing the tube 130 in a state where it is stopped, so that it rotates slightly in the reverse direction (for example, clockwise). The pressing state of the tube 130 by the roller 131 is released.

  Further, since the branching member 54 has the bubble discharge port 56 mounting position for discharging bubbles almost directly above the mounting position (supply port 59) of the supply tube (supply path) 82 for supplying ink. , Bubbles are likely to escape from the bubble outlet 56.

Next, the operation at the time of cleaning the head nozzle in this embodiment will be described with reference to the timing chart of FIG.
As described above, the image forming unit 5 is moved to the cleaning device 6 side so that the nozzle surface 104 of the head 101 of the head module 51 is capped with the cap 61.

  Similarly to the bubble discharging operation, as shown in FIG. 10D, when the ink amount lower limit detection sensor 87 is ON in the ink remaining amount confirmation in the sealed sub tank 81, FIG. The supply control electromagnetic valve 93 is opened to supply ink from the main tank 91 to the sub tank 81, and the supply control electromagnetic valve 93 is turned on when the ink amount upper limit detection sensor 86 is turned on as shown in FIG. Close to stop ink supply.

  Next, the suction pump (suction means) 63 of the cleaning device 6 is driven as shown in FIG. 5E, and the supply pump 83 is driven as shown in FIG. Thus, when the ink is sucked from the nozzles of the head 101 by the suction pump 63 to recover the non-ejection nozzles, the supply pump 83 is driven simultaneously with the operation of the suction pump 63 to pressurize and supply the ink. The recovery of the non-ejection nozzle can be assisted.

  Thereafter, the driving of the supply pump 83 is stopped simultaneously with the stop of the suction pump 63 of the cleaning device 6, and the cleaning operation is finished. Finally, the state in which the supply pump 83 rotates reversely and the roller in the pump 83 presses the tube is released, and the ink supply path 82 is made free.

  As described above, the branch member has a bubble discharge port and an opening / closing valve that opens and closes the bubble discharge port, and is provided with a bubble discharge unit that sucks or pressurizes the ink in the sub tank and sends the ink to the branch member. The air in the branch member is discharged from the bubble discharge port by sending ink from the sub tank to the branch member by the bubble discharge means with the opening / closing valve of the member open, so that the air stays in the branch member with a simple configuration. Bubbles can be discharged, and the amount of ink that becomes waste liquid that flows together when bubbles are discharged can be reduced.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 11 is a schematic explanatory view showing an ink supply system in the embodiment.
Here, the sealed sub tank 81 is accommodated in a hard case 181 having a sealed structure made of, for example, resin. A compression pump 182 configured with a tube pump or the like as a means (pressure means) for supplying air into the hard case 181 to pressurize the sub-tank 81 is provided. In addition, a pressure sensor 183 that detects the pressure in the case 181 is provided, and when the pressure in the case 181 reaches a predetermined pressure, the pressure sensor 183 controls to stop the rotation of the compression pump 182. In this embodiment, the supply pump 83 of the first embodiment is not provided. Although not shown for the control unit, the detection signal of the pressure sensor 183 is input to the control unit 500 of the first embodiment, and the control unit 500 controls the driving of the compression pump 182 instead of the supply pump 83. It is configured to do.

Next, the bubble discharging operation in this embodiment will be described with reference to the timing chart of FIG.
First, as in the first embodiment (see FIG. 8), when the bubbles 300 are accumulated in the branch member 54, the two detection electrodes constituting the liquid level detection sensor 58 attached to the upper part of the branch member 54 are used. Since the ink runs out, it is detected by the detection signal of the liquid level detection sensor 58 that the bubbles 300 are mixed in the branch member 54, and the control of the bubble discharge operation by the control unit 500 is started.

  As shown in FIG. 12 (f), the operation sequence at the time of discharging the bubbles is as shown in FIG. 12 (b) when the ink amount lower limit detection sensor 87 is ON in the confirmation of the ink remaining amount in the sealed sub-tank 81. As shown in the figure, the supply control electromagnetic valve 93 is opened to replenish ink from the main tank 91 to the sub tank 81, and the supply control electromagnetic valve 93 is closed when the ink amount upper limit detection sensor 86 is turned on as shown in FIG. Stop supplying ink.

  Next, as shown in FIG. 6A, the compression pump 182 is driven to supply air into the case 181 and the bubble discharge electromagnetic valve 57 is opened as shown in FIG. The flexible member is pressurized and ink is supplied to the branching member 54. At this time, since the bubble discharge electromagnetic valve 57 is opened, the ink is not discharged from the nozzles of the head 101, and only the bubble 300 is discharged from the bubble discharge port (bubble discharge port) 56 to the atmosphere, and the ink is branched by the ink. 54 is satisfied.

  When the pressure sensor 183 detects that the inside of the case 181 has reached a predetermined pressure, the compression pump 182 is closed.

  Further, after the ink liquid level in the branching member 54 rises and the liquid level detection sensor 58 is turned ON (the liquid level is detected) as shown in FIG. At the same time, the drive of the supply pump 83 is also stopped.

  Here, when the ink amount lower limit detection sensor 87 of the sealed sub-tank 81 is ON, the ink supply operation from the main tank 91 is performed until the ink amount upper limit detection sensor 86 is turned ON as described above. Finally, the supply pump 83 is reversely rotated to release the state in which the roller inside the pump presses the tube, and the ink supply path 82 is made free. That is, since a tube pump is used as the supply pump 83, the inner roller is in a state of pressing the tube in a stopped state, so that the roller rotates slightly in the reverse direction (for example, clockwise), Release the pressed state of the tube.

  As described above, the sealed sub tank 81 is pressurized from the outside to supply ink to the branch member 54 side, and the supply pump as in the first embodiment is not disposed between the sub tank 81 and the branch member 54. With this configuration, the supply path is complicated by attaching the supply pump, and there is no possibility that the fluid resistance increases.

Next, the operation at the time of cleaning the head nozzle in this embodiment will be described with reference to the timing chart of FIG.
As described above, the image forming unit 5 is moved to the cleaning device 6 side so that the head 101 of the head module 51 is capped with the cap 62.

  Similarly to the bubble discharging operation, as shown in FIG. 13 (d), when the ink amount lower limit detection sensor 87 is ON in the confirmation of the ink remaining amount in the sealed sub tank 81, FIG. 13 (b). The supply control electromagnetic valve 93 is opened to supply ink from the main tank 91 to the sub tank 81, and the supply control electromagnetic valve 93 is turned on when the ink amount upper limit detection sensor 86 is turned on as shown in FIG. Close to stop ink supply.

  Next, the suction pump (suction means) 63 of the cleaning device 6 is driven as shown in FIG. 5E, and the compression pump 182 is driven as shown in FIG. Then, the sub tank 81 is pressurized to supply ink to the head 101 side. As described above, when the suction pump 63 sucks ink from the nozzles of the head 101 and recovers the non-ejection nozzles, the ink is pressurized and supplied by driving the compression pump 182 simultaneously with the operation of the suction pump 63. The recovery of the non-ejection nozzle can be assisted.

  Thereafter, when a predetermined pressure is detected by the pressure sensor 183, the driving of the compression pump 182 is stopped, and the cleaning operation is finished. Finally, as the suction pump 63 stops driving, the state in which the compression pump 182 rotates reversely and the roller in the pump 182 presses the tube is released to make the ink supply path 82 free.

Next, a comparative example for the embodiment of the present invention will be described with reference to FIG.
In Comparative Example 1 shown in FIG. 14, a supply pump 83 is disposed in the supply path 92 between the main tank 91 and the sub tank 81. In such a configuration, when the ink is pressurized by the supply pump 83 when the bubbles in the branching member 54 are discharged, the pressure is absorbed by the sealed sub-tank 81 made of a flexible film and the pressure is increased to the branching member 54. Has the disadvantage of not being transmitted efficiently. In order to compensate for this drawback, in the case of ink pressure supply by the supply pump 83, the upper surface of the flexible film closed sub-tank 81 is regulated by a member that is difficult to deform, such as a steel plate, to suppress deformation of the flexible film. However, an effect that greatly increases the transmission efficiency of the ink supply pressure cannot be obtained.

  A comparative example 2 shown in FIG. 15 is provided with a bypass channel 401 that bypasses the sealed sub tank 81 in the configuration of the comparative example 1. The solenoid valves 402 and 403 are attached to the upstream side and the downstream side of the sealed sub tank 81, and the solenoid valves 404 and 405 are also attached to the bypass channel 401. When ink is supplied during normal printing, the solenoid valves 402 and 403 are open and the solenoid valves 404 and 405 are closed. When pressurized ink is supplied by the supply pump 83, such as discharge of bubbles in the branch member 54 or recovery operation of the nozzles of the head 101, the electromagnetic valves 404 and 405 are opened and the electromagnetic valves 402 and 403 are closed. By providing the bypass flow path 401 in this way, the drawbacks described in the description of the configuration of the comparative example 1 are eliminated, but not only the supply path is complicated, but the number of used solenoid valves 402 to 405 is also increased. This increases the cost of the device.

  In Comparative Example 3 shown in FIG. 16, the bubbles 300 are sucked out from the bubble discharge port 56 of the branching member 54 using the suction pump 483. When sucking out air (bubbles) with a pump, it requires a larger suction force than when sucking out or pushing out liquid (ink), so a large pump is required and the device becomes expensive. .

  In Comparative Example 4 shown in FIG. 17, the main tank 91 is pressurized by a compression pump 490 to supply ink. Also in this configuration, since the pump 490 is arranged on the upstream side of the sealed sub-tank 81, when the ink is pressurized and supplied by the compression pump 490 when the bubbles accumulated in the branching member 54 are discharged, the pump 490 is flexible. There is a problem similar to that of Comparative Example 1 in which the pressure is absorbed by the sealed sub-tank 81 portion of the conductive film and the pressure is not efficiently transmitted to the branching member 54.

Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 18 is a schematic explanatory diagram of an ink supply system in the embodiment.
In this embodiment, a circulation path for circulating the ink in the branch member 54 is provided. That is, as described above, the branch member 54 is an inclined surface in which the inner top surface 54a is inclined in the height direction, and is provided with the ink circulation path 150 that passes through the highest position and the lowest position. In the middle of the circulation path 150, a bubble discharge electromagnetic valve 58, a circulation pump 151, a deaeration device 152, and a deaeration device decompression pump 153 controlled by the control unit 500 are arranged. The circulation pump 151, the deaeration device 152, and the deaeration device decompression pump 153 constitute a means for degassing and circulating the ink.

  When the ink is circulated through the circulation path 150, the circulation pump 151 and the supply pump 83 are simultaneously rotated with the bubble discharge electromagnetic valve 57 opened, so that the ink in the branch member 54 is sucked and removed. Into the air device 152. The inside of the deaeration device 152 has a structure in which a hollow fiber that is generally used is incorporated. By depressurizing the inside of the deaeration device 152 with a decompression pump 153, bubbles (air) in the ink are removed. Then, it is again fed into the branching member 54.

  Here, the bubbles in the branch member 54 accumulate from the highest position of the inclined top surface 54a, and the suction port 150a of the circulation path 150 sucked by the circulation pump 151 is the highest on the inclined top surface 54a inside the branch member 54. Since the ink is opened at the position, ink containing bubbles can be efficiently sucked into the circulation path 150.

Next, ink circulation control in this embodiment will be described with reference to the timing chart of FIG.
First, when bubbles accumulate in the branching member 54, ink disappears between the two detection electrodes constituting the liquid level detection sensor 58 attached to the upper part of the branching member 54, so that branching occurs according to the detection signal of the liquid level detection sensor 58. When it is detected that bubbles are mixed in the member 54, the control of the ink circulation by the control unit 500 is started.

  First, as shown in FIG. 19 (f), when the ink amount lower limit detection sensor 87 is ON in the ink remaining amount confirmation in the sealed sub tank 81, as shown in FIG. The valve 93 is opened to replenish ink from the main tank 91 to the sub tank 81, and when the ink amount upper limit detection sensor 86 is turned on as shown in FIG. .

  Next, as shown in FIG. 6C, the bubble discharge electromagnetic valve 57 is opened for ink circulation (bubble discharge) in the branching member 54, and at the same time, as shown in FIGS. 83 and the ink circulation pump 151 are driven to supply the ink into the branching member 54 and suck the ink from the branching member 54 to discharge the bubbles to the ink circulation path 150.

  Then, after the ink liquid level in the branching member 54 rises and the liquid level detection sensor 58 is turned on as shown in FIG. 4D, the drive of the supply pump 83 is stopped as shown in FIG. However, the ink circulation pump 151 is driven as it is and the ink circulation in the branch member 54 is continued as shown in FIG. The ink circulation pump 151 stops after being driven for a predetermined time. At this time, the bubble discharge electromagnetic valve 57 is simultaneously closed.

  Here, when the ink amount lower limit detection sensor 87 of the sealed sub-tank 81 is ON, the ink supply operation from the main tank 91 is performed until the ink amount upper limit detection sensor 86 is turned ON as described above.

  Further, as shown in FIG. 9H, the deaeration device decompression pump 153 is driven in advance before the ink circulation pump 151 is driven, and the inside of the deaeration device 152 is decompressed. The degassing device 152 is stopped after the ink circulation pump 151 is stopped.

  Finally, the supply pump 83 is rotated in the reverse direction to release the state where the roller 131 inside the pump 83 presses the tube 130, thereby making the ink supply path 82 free.

  In this way, the branch member is formed with the inner top surface inclined in the height direction, and has a circulation path that connects a position relatively lower than the highest position of the inner top surface to the position, By providing a means for degassing and circulating the ink in the circulation path, the amount of ink that becomes waste liquid can be reduced with a simple structure, and bubbles remaining in the branch member can be degassed.

Next, a fourth embodiment of the present invention will be described with reference to FIG. FIG. 20 is a schematic explanatory diagram of an ink supply system in the embodiment.
In this embodiment, a circulation path for circulating the ink in the branching member 54 back to the upstream side of the sub tank 81 is provided. In other words, as described above, the branch member 54 is an inclined surface in which the top surface 54 a inside is inclined in the height direction, and the ink circulation through the highest position of the branch member 54 and the upstream side of the sub tank 81. A path 150 is provided. The upstream side of the sub tank 81 in the ink circulation path 150 is connected to the supply path 92 via a flow path switching three-way valve 154.

  In the middle of the circulation path 150, a bubble discharge electromagnetic valve 58, a circulation pump 151, a deaeration device 152, and a deaeration device decompression pump 153 controlled by the control unit 500 are arranged. The circulation pump 151, the deaeration device 152, and the deaeration device decompression pump 153 constitute a means for degassing and circulating the ink.

  When the ink is circulated through the circulation path 150, the circulation pump 151 and the supply pump 83 are simultaneously rotated with the bubble discharge electromagnetic valve 57 opened, so that the ink in the branch member 54 is sucked and removed. Into the air device 152. By depressurizing the inside of the deaeration device 152 with the decompression pump 153, bubbles (air) in the ink are removed and sent to the supply path 92 via the flow path switching three-way valve 154. The flow path switching three-way valve 154 is normally in a state where the flow path connecting the ink cartridge 91 and the sub tank 81 is opened, and the flow path connecting the ink circulation path 150 and the sub tank 81 is opened during ink circulation. become.

  Here, the bubbles in the branch member 54 accumulate from the highest position of the inclined top surface 54a, and the suction port 150a of the circulation path 150 sucked by the circulation pump 151 is the highest on the inclined top surface 54a inside the branch member 54. Since the ink is opened at the position, ink containing bubbles can be efficiently sucked into the circulation path 150.

Next, ink circulation control in this embodiment will be described with reference to the timing chart of FIG.
First, when bubbles accumulate in the branching member 54, ink disappears between the two detection electrodes constituting the liquid level detection sensor 58 attached to the upper part of the branching member 54, so that branching occurs according to the detection signal of the liquid level detection sensor 58. When it is detected that bubbles are mixed in the member 54, the control of the ink circulation by the control unit 500 is started.

  First, as shown in FIG. 21 (f), when the ink amount lower limit detection sensor 87 is ON in the ink remaining amount confirmation in the sealed sub tank 81, as shown in FIG. The valve 93 is opened to replenish ink from the main tank 91 to the sub tank 81, and when the ink amount upper limit detection sensor 86 is turned on as shown in FIG. .

  Next, as shown in FIG. 6C, the bubble discharge electromagnetic valve 57 is opened for ink circulation (bubble discharge) in the branching member 54, and at the same time, as shown in FIGS. 83, the ink circulation pump 151 is driven, and the flow path switching three-way valve 154 is supplied from the normal supply (supply from the ink cartridge 91 to the sub tank 81) to the ink circulation (the ink circulation path 150 and the sub tank 81) as shown in FIG. The air bubbles are discharged into the ink circulation path 150 by sucking ink from the branch member 54 while supplying ink into the branch member 54.

  Then, after the ink liquid level in the branching member 54 rises and the liquid level detection sensor 58 is turned on as shown in FIG. 4D, the drive of the supply pump 83 is stopped as shown in FIG. However, the ink circulation pump 151 is driven as it is and the ink circulation in the branch member 54 is continued as shown in FIG. The ink circulation pump 151 stops after being driven for a predetermined time. At this time, the bubble discharge electromagnetic valve 57 is simultaneously closed and the flow path switching three-way valve 154 is switched to the normal supply side.

  Here, when the ink amount lower limit detection sensor 87 of the sealed sub-tank 81 is ON, the ink supply operation from the main tank 91 is performed until the ink amount upper limit detection sensor 86 is turned ON as described above.

  Further, as shown in FIG. 9H, the deaeration device decompression pump 153 is driven in advance before the ink circulation pump 151 is driven, and the inside of the deaeration device 152 is decompressed. The degassing device 152 is stopped after the ink circulation pump 151 is stopped.

  Finally, the supply pump 83 is rotated in the reverse direction to release the state where the roller 131 inside the pump 83 presses the tube 130, thereby making the ink supply path 82 free.

  As described above, the branch member is formed such that the top surface of the branch member is inclined in the height direction, and has a circulation path that connects the highest position of the top surface of the branch member to the upstream side of the sub tank. Since the apparatus is provided with a means for degassing and circulating the ink, it is possible to degas bubbles remaining in the branch member by reducing the amount of ink used as waste liquid with a simple structure.

  In the above-described embodiment, an example in which the present invention is applied to a line type image forming apparatus has been described. However, the present invention can be similarly applied to a serial type image forming apparatus.

DESCRIPTION OF SYMBOLS 1 ... Apparatus main body 4 ... Conveyance unit (conveyance part)
5. Image forming unit 6. Cleaning device (maintenance and recovery mechanism)
7: Transport guide 8: Ink tank unit (sub tank unit)
9 ... Main tank unit 51 ... Head module (recording head unit)
54. Branch member (distributor)
56 ... Bubble discharge port 57 ... Open / close valve 81 ... Sub tank (ink tank)
83 ... Supply pump (bubble discharging means)
91 ... Main tank (ink cartridge)
DESCRIPTION OF SYMBOLS 101 ... Head 150 ... Ink circulation path 151 ... Ink circulation pump 152 ... Deaeration device 153 ... Deaeration device decompression pump 154 ... Three-way valve for flow path switching

Claims (5)

A recording head in which a plurality of heads for discharging droplets are arranged side by side;
A main tank for storing ink;
A sub tank that is supplied with ink from the main tank and supplies ink to the recording head;
A branch member that branches and supplies ink from the sub-tank to each head of the recording head,
The sub tank has a sealed structure in which at least a part of the ink storage portion is formed of a flexible member,
The recording head and the sub tank are arranged with a water head difference,
The branch member is formed such that the inner top surface is inclined in the height direction,
One end portion of the branch member is a position where the inner top surface is the highest, and the other end portion of the branch member is a position where the inner top surface is the lowest,
On the upper part of the one end of the branch member , there is a bubble discharge port and an opening / closing valve that opens and closes the bubble discharge port,
The lower part of the one end of the branch member has a supply port for supplying ink from the sub tank,
The bubble discharge port and the supply port of the branch member are arranged at positions facing vertically at the one end of the branch member,
A pump that sucks or pressurizes ink in the sub-tank and sends the ink to the branch member ;
The pump is directly below the supply port of the branch member, and is disposed between the sub tank and the branch member,
The air in the branch member is discharged from the bubble discharge port by sending ink from the sub tank to the supply port of the branch member with the pump in a state where the on-off valve of the branch member is open. Image forming apparatus. The sub tank is disposed substantially horizontally in the longitudinal direction, one end in the horizontal direction is connected to the main tank, the other end in the horizontal direction is connected to the branch member at the same height as the one end,
  A flexible member is provided on the upper surface side of the sub tank,
  The ink amount in the sub tank is detected by an ink amount detecting means that moves up and down following the flexible member of the sub tank.
The image forming apparatus according to claim 1. A circulation path connecting the other end of the branch member and the supply port ;
The image forming apparatus according to claim 1, wherein the circulation path is provided with a means for degassing and circulating the ink. Claims, characterized in that a circulation path connecting the upstream side of the sub-tank and the other end of the branch member, said the circulation path means for circulating degassed the ink is provided The image forming apparatus according to 1. 5. The image forming apparatus according to claim 3 , further comprising a unit that detects air bubbles in the branch member, wherein the ink is circulated through the circulation path when the air bubbles are detected.

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