Abstract:
A droplet discharge apparatus includes a droplet discharge head which discharges droplets; a liquid retention unit which is configured such that a liquid surface of a liquid retained in the liquid retention unit is located below the droplet discharge head, the liquid retention unit including an atmosphere open port; a liquid channel which couples the droplet discharge head and the liquid retention unit; a liquid tank in which the liquid is retained, the liquid tank being sealed; a liquid inflow channel which couples the liquid retention unit and the liquid tank, an inflow port of the liquid inflow channel in the liquid retention unit being located below the atmosphere open port; a liquid sending channel which couples the liquid tank and the droplet discharge head; and a pump which sending the liquid in the liquid tank to the droplet discharge head.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a division of U.S. patent application Ser. No. 11/592,601 filed Nov. 3, 2006, now U.S. Pat. No. 7,658,481. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present invention relates to a droplet discharge apparatus which discharges droplets. 
     2. Related Art 
     In the droplet discharge apparatus such as an inkjet recording apparatus, bubbles in a droplet discharge head or a liquid channel cause discharge failure and an increase in channel resistance. Therefore, conventionally liquid is circulated between the droplet discharge head and a liquid tank opened to atmosphere, bubbles are recovered to the liquid tank or to a sub-liquid tank coupled to the liquid tank, and the bubbles are discharged to the atmosphere from the liquid tank or the sub-liquid tank. 
     SUMMARY 
     A droplet discharge apparatus according to one aspect of the invention is a droplet discharge apparatus including: a droplet discharge head that discharges droplets; a liquid retention unit that is provided below the droplet discharge head, the liquid retention unit including an atmosphere open port; a liquid channel that couples the droplet discharge head and the liquid retention unit; a liquid tank that retains liquid therein, the liquid tank being sealed; a liquid inflow channel that couples the liquid retention unit and the liquid tank, an inflow port of the liquid inflow channel in the liquid retention unit being located below the atmosphere open port; a liquid sending channel that couples the liquid tank and the droplet discharge head; and a pump that is provided at the liquid sending channel, the pump sending the liquid in the liquid tank to the droplet discharge head. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  is a schematic view showing an inkjet recording apparatus according to a first exemplary embodiment of the invention; 
         FIG. 2  is a schematic view showing the inkjet recording apparatus according to the first exemplary embodiment of the invention; 
         FIG. 3  is a schematic view showing a maintenance unit of the inkjet recording apparatus according to the first exemplary embodiment of the invention; 
         FIG. 4  is a partially schematic view showing the inkjet recording apparatus according to the first exemplary embodiment; 
         FIG. 5  is a schematic view showing an operation of the inkjet recording apparatus according to the first exemplary embodiment; 
         FIG. 6  is a perspective view showing a positional relationship among a main tank, a reservoir tank, and a recording head of the inkjet recording apparatus according to the first exemplary embodiment; 
         FIG. 7  is a side view showing the positional relationship among the main tank, the reservoir tank, and the recording head; 
         FIG. 8  is a sectional side view of the reservoir tank; 
         FIG. 9  is a flowchart showing operations of ink filling and ink circulation; 
         FIG. 10  is a side view showing a positional relationship among the main tank, the reservoir tank, and the recording head of an inkjet recording apparatus according to a second exemplary embodiment; 
         FIG. 11  is a side view showing a positional relationship among the main tank, the reservoir tank, and the recording head of an inkjet recording apparatus according to a third exemplary embodiment; 
         FIG. 12  is a sectional side view of the reservoir tank; 
         FIG. 13  is a side view showing a positional relationship among the main tank, the reservoir tank, and the recording head of an inkjet recording apparatus according to a fourth exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A first exemplary embodiment of the invention will be described below with reference to the drawings. 
       FIG. 1  shows an inkjet recording apparatus  12  according to the first exemplary embodiment. A sheet feed tray  16  is provided in a lower portion of a chassis  14  of the inkjet recording apparatus  12 , and sheets P stacked in the sheet feed tray  16  can be drawn one by one by a pickup roller  18 . The drawn sheet P is conveyed by plural pairs of conveyance rollers  20  constituting a predetermined conveyance path  22 . 
     An endless conveyance belt  28  is arranged above the sheet feed tray  16 , and the conveyance belt  28  is tensioned between a driving roller  24  and a driven roller  26 . A recording head array  30  is arranged above the conveyance belt  28 , and the recording head array  30  faces a flat portion  28 F of the conveyance belt  28 . The area where the recording head array  30  faces a flat portion  28 F becomes a discharge area SE where the ink droplet is discharged from the recording head array  30 . The sheet P conveyed through the conveyance path  22  reaches the discharge area SE while retained by the conveyance belt  28 , and the ink droplet is caused to adhere onto the sheet P from the recording head array  30  according to image information with the sheet P facing the recording head array  30 . 
     In the first exemplary embodiment, the recording head array  30  is formed in a long shape in which an effective recording area is larger than a width (length in a direction orthogonal to a conveyance direction) of the sheet P. In the recording head array  30 , four inkjet recording heads (hereinafter referred to as recording head)  32  corresponding to four colors of yellow (Y), magenta (M), cyan (C), and black (K) are arranged along the conveyance direction to enable a full-color image to be recorded. 
     A head controller  52  (see  FIG. 5 ) controls each recording head  32 . The head controller  52  determines discharge timing of the ink droplet and an ink discharge port (nozzle) to be used according to the image information, and the head controller  52  transmits a drive signal to the recording head  32 . 
     The recording head array  30  may be fixed in the direction orthogonal to the conveyance direction. However, when the recording head array  30  is formed to be able to be moved in the direction orthogonal to the conveyance direction if needed, the image having higher resolution can be recorded or a trouble with the recording head  32  cannot be reflected on recording result by the multi-pass image recording. 
     Four maintenance units  34  corresponding to the recording heads  32  are arranged on both sides of the recording head array  30 . As shown in  FIG. 2 , in the case where maintenance is performed to the recording head  32 , the recording head array  30  is moved upward, and the maintenance unit  34  is moved and intrudes into a gap formed between the conveyance belt  28  and the recording head array  30 . The maintenance unit  34  performs a predetermined maintenance operation (such as suction, wiping, and capping) while facing the nozzle surface  32 N (see  FIG. 8 ). 
     As shown in  FIG. 3 , the maintenance unit  34  includes a cap  56  and a drain line  58 . The cap  56  receives the ink from a nozzle surface  33 N in a recovery operation of the inkjet recording apparatus  12 . The ink received by the cap  56  is drained through the drain line  58 . A waste ink tank  62  is provided at a downstream end in the drain direction of the drain line  58  while a valve  60  is located in the middle of the drain line  58 . The inkjet recording apparatus  12  also includes a pump  63  which imparts ink sending force (ink sucking force) to the cap  56 . The ink sending force is one with which the ink is sent from the cap  56  to the drain line  58 . The pump  63  is controlled by a controller  48  (see  FIG. 5 ) which controls the whole of the inkjet recording apparatus  12 . 
     In the first exemplary embodiment, the four maintenance units  34  are divided into two sets of two maintenance units  34 , and the two sets are respectively arranged in the upstream side and down stream side in the conveyance direction of the recording head array  30  during the image recording. 
     As shown in  FIG. 4 , a charging roller  36  connected to a power supply  38  is arranged on the upstream side of the recording head array  30 . The charging roller  36  is driven while nipping the conveyance belt  28  and sheet P along with the driven roller  26 , and the charging roller  36  is formed so as to be movable between a pressing position where the charging roller  36  presses the sheet P against the conveyance belt  28  and a distance position where the charging roller  36  is distanced from the conveyance belt  28 . Because a predetermined potential difference between the charging roller  36  and the driven roller  26  is generated at the pressing position, an electric charge can be imparted to the sheet P to electrostatically suck the sheet P to the conveyance belt  28 . A separation plate  40  is arranged on the downstream side of the recording head array  30 , and the sheet P is separated from the conveyance belt  28  by the separation plate  40 . 
     As shown in  FIG. 5 , the controller  48  controls the whole of the inkjet recording apparatus  12 , and the controller  48  controls the operations including the feed of the sheet P, the image recording, discharge of the sheet P, and the maintenance. Various kinds of data concerning the image to be recorded are transmitted from an image controller  50  to the controller  48 . A head controller  52  controls a later-mentioned inkjet recording head  32  (see  FIG. 6 , hereinafter referred to as recording head), and the controller  48  transmits a signal to the head controller  52 . The power supply  38  supplies the electric power to the controller  48 , the head controller  52 , and the charging roller  36 . 
     In the inkjet recording apparatus  12  having the above configuration, the sheet P drawn from the sheet feed tray  16  reaches the conveyance belt  28  as described above. While the sheet P is pressed against the conveyance belt  28  by the charging roller  36 , the sheet P is attracted to and retained on the conveyance belt  28  by the applied voltage from the charging roller  36 . In this state, the ink droplet is discharged from the recording head array  30  while the sheet P passes through the discharge area SE by the rotation of the conveyance belt  28 , which allows the image to be recorded on the sheet P. Then, the sheet P is separated from the conveyance belt  28  by the separation plate  40 , the sheet P is conveyed by plural pair of discharge rollers  42  constituting a discharge path  44  on the downstream side of the separation plate  40 , and the sheet P is discharged to a sheet discharge tray  46  provided in an upper portion of the chassis  14 . 
     As shown in  FIGS. 6 and 7 , a reservoir tank  64  is arranged obliquely below the recording head  32 . The recording head  32  and the reservoir tank  64  are coupled to each other with an ink channel  68 , and a back pressure is generated in a channel of the recording head  32  such that the ink does not leak from the nozzle. When the ink is discharged from the nozzle of the recording head  32 , the inside of the recording head  32  becomes a negative pressure and the ink is supplied from the reservoir tank  64  to the recording head  32  in the negative pressure state. 
     A sealed main tank  66  (ink tank) is arranged obliquely below the reservoir tank  64 . The reservoir tank  64  and the main tank  66  are coupled to each other with a return channel  74  and, as described later, the reservoir tank  64  is filled with the ink from the main tank  66  as required. 
     As shown in  FIG. 8 , an atmosphere communicating port  70  is provided in an upper wall (top wall) of the reservoir tank  64 . The atmosphere communicating port  70  is always opened to atmospheric pressure, and the atmospheric pressure is applied to a liquid surface of the ink in the reservoir tank  64 . 
     A pipe  71  pierces through the upper wall (top wall) of the reservoir tank  64 . An ink inlet port  72  at one end portion of the pipe  71  is located below the atmosphere communicating port  70 . A return channel  74  coupled to the main tank  66  (see  FIG. 7 ) is attached to an outflow port  73  at the other end of the pipe  71 . 
     Therefore, when the ink in the reservoir tank  64  rises up to the ink inlet port  72 , because the main tank  66  becomes a negative pressure state as described later, the ink flows into the main tank  66  through the return channel  74 . 
     As shown in  FIGS. 6 and 7 , the main tank  66  and the recording head  32  are coupled to each other with an ink channel  76 . A filling pump  78  is provided in the ink channel  76 , and the ink flows from the main tank  66  into the recording head  32  by driving the filling pump  78 . 
     The main tank  66  is molded by a rigid member. Therefore, the negative pressure state is maintained while the main tank  66  is not deformed, even if the ink flows out from the sealed main tank  66  to generate the negative pressure inside the main tank  66 . 
     An optical sensor  80  which is of ink amount detection means is provided in the main tank  66 . The optical sensor  80  includes a light emitting device (not shown) and a light acceptance device (not shown). When the liquid surface of the ink rises above the optical sensor  80 , light emitted from the light emitting device is blocked by the ink and the light is not received by the light acceptance device. 
     Therefore, a liquid surface level of the ink is detected in the main tank  66  by the optical sensor  80 . When ink runout is detected in the main tank  66 , the ink runout is displayed on a display panel (not shown) of the inkjet recording apparatus  12  (see  FIG. 1 ) through the controller  48  connected to the optical sensor  80 , and a user is encouraged to exchange the main tanks  66 . 
     A method of filling the reservoir tank  64  with the ink from the main tank  66  and a method of circulating the ink among the main tank  66 , the reservoir tank  64 , and the recording head  32  will be described with reference to a flow chart of  FIG. 9 . 
     When an instruction for filling the reservoir tank  64  with the ink from the main tank  66  or an instruction for circulating the ink among the main tank  66 , the reservoir tank  64 , and the recording head  32  is outputted, the optical sensor  80  detects the liquid surface level of the ink in the main tank  66  in Step  120 . 
     When a residual ink amount in the main tank  66  is lower than a predetermined amount, the flow goes to Step  122 , and the ink runout is displayed on the display panel (not shown) of the inkjet recording apparatus  12 . Therefore, a user is notified of the ink runout in the main tank  66  and the user exchanges the main tanks  66 . 
     On the other hand, in Step  120 , when the residual ink amount in the main tank  66  is not lower than the predetermined amount, the flow goes to Step  124 . In Step  124 , the maintenance unit  34  (see  FIG. 1 ) is moved beneath the recording head  32  to perform the capping of the nozzle surface. 
     In Step  126 , the drive operation of the filling pump  78  is started to cause the ink in the main tank  66  to flow into the reservoir tank  64  through the ink channel  76 , the recording head  32 , and the ink channel  68 . 
     At this point, when the liquid surface of the ink flowing into the reservoir tank  64  reaches the ink inlet port  72 , the ink flows into the main tank  66  from the reservoir tank  64  through the return channel  74 . 
     In Step  128 , it is determined whether or not a predetermined time elapses since the drive operation of the filling pump  78  is started. For example, in the ink filling, it is determined whether or not a time necessary to fill the reservoir tank  64  with a predetermined amount of ink elapses. For example, in the ink circulation, it is determined whether or not a time necessary to circulate the ink among the reservoir tank  64 , the main tank  66 , and the recording head  32  elapses. 
     The ink circulation among the reservoir tank  64 , the main tank  66 , and the recording head  32  transports the bubble (gas dissolved in the ink and the bubble generated from a component having permeability to the gas) generated in the recording head  32  to the reservoir tank  64 , and the bubble is exhausted from the atmosphere communicating port  70  into the atmosphere. Because the ink circulation stirs the ink, settling of pigment can also be prevented. 
     When the predetermined time elapses since the drive operation of the filling pump  78  is started, the flow goes to Step  130 , and the drive operation of the filling pump  78  is stopped. In Step  132 , the capping of the nozzle surface is released to retract the maintenance unit  34  from beneath the recording head  32 , and the operation of the ink filling or ink circulation is ended. 
     The residual ink amount in the reservoir tank  64  is estimated from print information. That is, the ink amount discharged from the nozzle of the reservoir tank  64  is computed by summing the number of pixels of the print, and thereby the residual ink amount in the reservoir tank  64  is computed. The operation in which the reservoir tank  64  is filled with the ink from the main tank  66  is started when it is determined that residual ink amount in the reservoir tank  64  is lower than the predetermined amount (for example, the ink amount necessary for the print of one sheet). 
     Not only the residual ink amount in the reservoir tank  64  is estimated from the print information, but also the residual ink amount may be detected by a sensor provided in the reservoir tank  64 . Because the reservoir tank  64  is sufficiently filled with ink by the ink circulation, the operation in which the reservoir tank  64  is filled with the ink from the main tank  66  is not generated in the case of the small print amount. 
     The ink circulation is performed at predetermined intervals irrespective of print frequency. For example, the ink circulation timing is performed, when the power of the inkjet recording apparatus  12  is turned on, when a standby state is released, or when a predetermined time elapses since the previous ink circulation (or ink filling) is performed. 
     Then, the operation of the inkjet recording apparatus  12  during the ink discharge will be described. 
     During the ink discharge, the operation of the filling pump  78  is stopped, so that the ink does not flow into the recording head  32  from the main tank  66  through the ink channel  76 . Therefore, when the ink discharged from the nozzle of the recording head  32 , the negative pressure is generated in the recording head  32 , and the ink in the reservoir tank  64  is supplied through the ink channel  68  to the recording head  32  which is in the negative pressure state. 
     The negative back pressure is applied to the ink supplied to the recording head  32  by a water head difference between the recording head  32  and the reservoir tank  64  communicated with the atmosphere, which allows a meniscus suitable to the print to be formed in the nozzle. 
     Then, action of the first exemplary embodiment of the invention will be described. 
     When the filling pump  78  is driven to fill the reservoir tank  64  with the ink, the ink flows into the recording head  32  from the main tank  66  through the ink channel  76 . The ink flowing into the recording head  32  flows into the reservoir tank  64 , and the reservoir tank  64  is filled with the ink. 
     That is, when the filling pump  78  is driven to send the ink from the main tank  66  to the recording head  32 , the ink in the main tank  66  flows into the recording head  32 , the ink is supplied to the reservoir tank  64 , and the reservoir tank  64  is filled with the ink. 
     When the liquid surface of the ink with which the reservoir tank  64  is filled reaches the ink inlet port  72  of the pipe  71  coupled to the return channel  74 , the ink is sucked into the main tank  66  which is in the negative pressure state. That is, the ink is circulated among the recording head  32 , the reservoir tank  64 , and the main tank  66 . 
     On the other hand, when the ink is discharged from the recording head  32 , the negative pressure is generated in the recording head  32 , and the ink in the reservoir tank  64  is supplied to the recording head  32  which is in the negative pressure state. 
     Thus, the ink filling and the ink circulation can be performed by driving the one filling pump  78 . Because it is not necessary that an airtight state be generated in the reservoir tank  64  when the ink is discharged from the recording head  32 , it is not necessary to provide an on-off valve which opens and closes the reservoir tank  64  to and from the atmospheric pressure. Accordingly, the whole configuration of the apparatus becomes simple to lead to the cost reduction. 
     The filling pump  78  is provided in the ink channel  76  which couples the main tank  66  and the recording head  32 . That is, in the ink circulation and ink filling, the filling pump  78  is provided on the downstream side in the ink flowing direction of the main tank  66 . Therefore, the ink flows out from the main tank  66  to generate the negative pressure in the main tank  66  by the operation of the filling pump  78 . However, the breakage of the main tank  66  is never generated because the main tank  66  is not pressurized. As described above, the main tank  66  is formed by the rigid member such that the main tank  66  is not broken even if the main tank  66  becomes the negative pressure state. 
     In the first exemplary embodiment, the main tank  66  is arranged below the reservoir tank  64 . However, because the negative pressure is generated in the main tank  66  when the filling pump  78  is driven, the main tank  66  is not always arranged below the reservoir tank  64 , but the main tank  66  may be provided above the reservoir tank  64 . 
     An inkjet recording apparatus according to a second exemplary embodiment of the invention will be described below. The description of the same component as the first exemplary embodiment will be omitted. 
     As shown in  FIG. 10 , a filling pump  84  is provided in the return channel  74  which couples the reservoir tank  64  and the main tank  66 . 
     When the filling pump  84  is operated in the ink filling and in the ink circulation, the air or the ink flows into the main tank  66 , the main tank  66  is pressurized, the ink in the main tank  66  flows into the ink channel  76 , and the ink flows into the reservoir tank  64  through the recording head  32  and the ink channel  68 . The ink flows into the main tank  66  through the return channel  74 , when the liquid surface of the ink flowing into the reservoir tank  64  reaches the ink inlet port  72  of the pipe  71 . 
     Thus, when the filling pump  84  is provided in the return channel  74  which couples the reservoir tank  64  and the main tank  66 , the main tank  66  molded by a flexible member can be used because the negative pressure is not generated in the main tank  66  during the operation of the filling pump  84 . 
     An inkjet recording apparatus according to a third exemplary embodiment of the invention will be described below. The description of the same component as the first exemplary embodiment will be omitted. 
     As shown in  FIG. 11 , the ink channel  76  and the reservoir tank  64  are coupled to each other with a connecting channel  86 . 
     As shown in  FIG. 12 , a check valve  88  is provided in a connecting port of the connecting channel  86 . Not only the check valve  88  enables the ink to flow into the connecting channel  86  from the reservoir tank  64 , but also the check valve  88  causes the ink not to flow into the reservoir tank  64  from the connecting channel  86 . 
     When the filling pump  78  is operated in the ink filling and in the ink circulation, the ink in the main tank  66  flows into the reservoir tank  64  through the ink channel  76 , the recording head  32 , and the ink channel  68 . The ink flows into the main tank  66  through the return channel  74 , when the liquid surface of the ink flowing into the reservoir tank  64  reaches the ink inlet port  72  of the pipe  71 . 
     On the other hand, when the ink is discharged from the nozzle of the recording head  32 , the negative pressure is generated in the recording head  32 , and the ink in the reservoir tank  64  is supplied to the recording head  32  through the ink channel  68 . Because the ink flows in the direction in which the check valve  88  provided in the connecting port of the connecting channel  86  is opened, the ink in the reservoir tank  64  flows into the ink channel  76  from the connecting channel  86 , and the ink is supplied to the recording head  32 . 
     The operation of the filling pump  78  is stopped in discharging the ink, so that the ink does not flow into the recording head  32  from the main tank  66  through the ink channel  76 . 
     Thus, because the ink in the reservoir tank  64  is supplied to the recording head  32  through the two ink channels  68  and  76 , pressure loss generated in the ink channels  68  and  76  during the discharge of the ink can be decreased to hardly generate the defective print caused by shortage of ink supply. 
     An inkjet recording apparatus according to a fourth exemplary embodiment of the invention will be described below. The description of the same component as the first exemplary embodiment will be omitted. 
     As shown in  FIG. 13 , the filling pump  84  is provided in the return channel  74  which couples the reservoir tank  64  and the main tank  66 . 
     When the filling pump  84  is operated in the ink filling and in the ink circulation, the air or the ink flows into the main tank  66 , the main tank  66  is pressurized, the ink in the main tank  66  flows into the ink channel  76 , and the ink flows into the reservoir tank  64  through the recording head  32  and the ink channel  68 . The ink flows into the main tank  66  through the return channel  74 , when the liquid surface of the ink flowing into the reservoir tank  64  reaches the ink inlet port  72  of the pipe  71 . 
     Thus, when the filling pump  84  is provided in the return channel  74  which couples the reservoir tank  64  and the main tank  66 , the main tank  66  molded by the flexible member can be used because the negative pressure is not generated in the main tank  66  during the operation of the filling pump  84 . 
     On the other hand, when the ink is discharged from the nozzle of the recording head  32 , the negative pressure is generated in the recording head  32 , and the ink in the reservoir tank  64  is supplied to the recording head  32  through the ink channel  68 . The check valve  88  provided in the connecting port of the connecting channel  86  is opened, the ink in the reservoir tank  64  flows into the ink channel  76  from the connecting channel  86 , and the ink is supplied to the recording head  32 . 
     Therefore, because the ink in the reservoir tank  64  is supplied to the recording head  32  through the two ink channels  68  and  76 , the pressure loss generated in the ink channels  68  and  76  during the discharge of the ink can be decreased to hardly generate the defective print caused by the shortage of ink supply. 
     The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The exemplary embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.