Abstract:
The objectives of the present invention are to provide an image forming apparatus and an image forming method which can solve problems such that a large amount of pre-ejected ink is consumed for preventing a mix color phenomenon and the like. A recording head having the following constitution can solve the above-mentioned problem.  
     A cap for attaching to/detaching from liquid eject portion of the recording head is arranged. The recording head ejects liquid while the cap is moving from a attached state to the liquid eject portion to a detached state. Alternatively, a recording head for recording, the cap for capping liquid eject portion of the recording head and a sucking means for sucking via the cap may be arranged. The recording head ejects liquid while the cap is moving from an attached state to the liquid eject portion to a detached state, after a sucking operation by the sucking means is executed.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a liquid eject apparatus equipped with a liquid eject head for ejecting liquid and relates to an eject recovery method of the liquid eject head.  
           [0003]    2. Brief Description of the Related Art  
           [0004]    An ink-jet printer, a typical example of liquid eject apparatuses, widely known as an image forming apparatus, is generally equipped with an eject recovery device for removing thickened ink, foreign particles and the like stuck to a liquid eject portion of its recording head so as to keep a stable ejecting performance of the ink-jet printer. As shown in FIG. 8 for example, the eject recovery device comprises one or a plurality of caps  2  for covering a liquid eject portion  5   a  of a recording head  5  during non-printing operations to prevent ink as a liquid for recording from drying or evaporating and a pump  4  for sucking the thickened ink from and around the liquid eject portion  5   a  via the cap  2 .  
           [0005]    The above-mentioned eject recovery device is for example, arranged at a pre-determined standby position apart from a recording movement area of the recording head  5  of the ink-jet printer so as to face the recording head  5 . The recording head  5 , for example, is arranged below an ink cartridge  1  detachably mounted on a carriage (not shown in FIG. 8).  
           [0006]    The pump  4 , for example as also shown in the Japanese laid open patent No. 10-67121, comprises a cylinder connected to the inside of the cap  2  via a connecting tube  11  and a piston (not shown in FIG. 8) which reciprocally moves along an inner circular surface of the cylinder in a direction depicted by a bilateral horizontal arrow in FIG. 8 so as to generate a pre-determined negative pressure in the cap  2 . Ink is sucked from and around the liquid eject portion  5   a  of the recording head  5 , when the pump  4  is operated as the cap  2  is kept contacting closely to the liquid eject portion  5   a  of the recording head  5 .  
           [0007]    The cap  2  is held by a cap holder  3  rotatably supported by a cam surface formed on a cap cam  9  so as to move in directions depicted by a arched bi-directional arrows in FIG. 8, so that cap  2  selectively can be attached closely to the liquid eject portion  5   a  of the recording head  5  as depicted in two-dot chain lines in the figure, or can be detached from the liquid eject portion  5   a  of the recording head  5  as depicted respectively in solid lines in the figure.  
           [0008]    The rotating movement of the cap holder  3  is controlled in accordance with a shape of the cam surface formed on the cap cam  9  which transmits a driving force from a driving power source to a supporting mechanism of the cap holder  3  at predetermined timings. The reciprocating movement of a piston rod  6  is controlled in accordance with a shape of the cam surface formed on a pump cam  7  which transmits the driving force from the driving power source to the piston rod  6  at predetermined timings.  
           [0009]    The eject recovery treatment is executed according to the following operating procedures. The cap cam  9  is driven so that the cap  2  held in the cap holder  3  is moved from a pre-determined position and attached closely to the recording head  5 . From a pre-determined initial position, the piston (not shown in FIG. 8) is moved reciprocally in accordance with synchronous movements of the piston rod  6  driven by the synchronously moving pump cam  7  so that a predetermined amount of ink is sucked from the recording head. Then the cap  2  is detached from the liquid eject portion  5   a  of the recording head  5  and returned to the initial position. Simultaneously the piston is moved to a predetermined position and is moved reciprocally for discharging ink filled in the inside of the cap  2  and the pump  4 . Finally the piston is returned to the initial position. Thus a series of operations are executed continuously.  
           [0010]    When a plurality of color ink tanks are mounted on the recording head  5  equipped with a color cartridge where a plurality of nozzle rows for respective colors or a plurality nozzle groups for respective colors arranged on one nozzle row, usually caps for respective colors are not arranged, but one or smaller number of caps than color number to cover a plurality nozzle rows or nozzle groups are arranged so as to simplify a sucking mechanism and reduce a production cost of the liquid eject apparatus.  
           [0011]    However, in the above-mentioned conventional examples, a plurality of inks mix each other and form a turbid ink which fill the inside of the cap, when the sucking operation is executed. Even after the cap is detached from the liquid eject portion of the recording head, the remaining turbid ink stuck to the liquid eject portion is mixed with ink inside nozzles. Which causes a problem the so called “mixed color phenomenon” such that light colors such as yellow and the like are contaminated by the remaining turbid ink, when information is recorded on a recording medium.  
           [0012]    As a measure trying to prevent the mixed color phenomenon, the turbid ink is ejected from the nozzles by executing pre-ejection, after a series of operations and a succeeding detaching operation of the cap from the recording head are finished, but before a recording operation is started.  
           [0013]    However owing to ink properties and other various conditions a problem that the pre-determined amount of pre-ejection is not enough to eject mixed ink completely, is remained unsolved, consequently a fairly amount of ink has to be wasted for the pre-ejection in the following cases: (1) A large amount of ink remains in the recording head after detaching the cap from the recording head; (2) A large negative pressure (holding pressure) inside of the ink tank mounted on the recording head causes the more aggravated “mixed color phenomenon” due to a large amount of mixed ink flowing into nozzles.  
         SUMMARY OF THE INVENTION  
         [0014]    The present invention is carried out in view of the problems mentioned above so as to provide an image forming apparatus and an image forming method which can solve problems such that a large amount of pre-ejected ink is consumed for preventing the mix color phenomenon and the like.  
           [0015]    The following constitutions according to the present invention can solve the above-mentioned problems.  
           [0016]    (1) A liquid eject apparatus comprising: a cap for capping a liquid eject portion for ejecting liquid, where: liquid is ejected from the liquid eject portion while the cap and the liquid eject portion are relatively moving from a closely attached state to a detached state.  
           [0017]    (2) A liquid eject apparatus comprising: a liquid eject portion for ejecting liquid; a cap for capping the liquid eject portion; and a sucking means for sucking liquid from the liquid eject portion via the cap, where: after sucking by the sucking means is finished, liquid is ejected from the liquid eject portion while the cap and the liquid eject portion are relatively moving from a closely attached state to a detached state.  
           [0018]    (3) The liquid eject apparatus according to (2), where: after sucking by the sucking means is executed, ejecting liquid from the liquid eject portion is started while the relative movement is started when a pressure inside the cap returns to almost atmospheric pressure.  
           [0019]    (4) The liquid eject apparatus according to (2), where: after sucking by the sucking means is executed, ejecting liquid from the liquid eject portion is started before a pressure inside the cap returns to almost atmospheric pressure; and then the relative movement is started.  
           [0020]    (5) The liquid eject apparatus according to (2) or (3), where: sucking by said sucking means is executed again as said cap and the liquid eject portion are mutually being detached.  
           [0021]    (6) The liquid eject apparatus according to (5), where: a gap formed between the cap and the liquid eject portion during the detached state is set between 0.1 mm and 1.5 mm.  
           [0022]    (7) The liquid eject apparatus according to (5), where: sucking by the sucking means is executed again before ejecting liquid from the liquid eject portion is finished.  
           [0023]    (8) The liquid eject apparatus according to (1) or (2), where: ejecting liquid from the liquid eject portion during the relative movement is executed against the cap.  
           [0024]    (9) The liquid eject apparatus according to (1) or (2), where: the cap is capping a plurality of the liquid eject portion, which respectively eject different liquids, altogether.  
           [0025]    (10) The liquid eject apparatus according to (1) or (2), where: the liquid eject portion is equipped with electro-thermal conversion modules to generate thermal energy utilized for ejecting liquid.  
           [0026]    (11) An eject recovery method comprising steps of: relatively moving a liquid eject portion for ejecting liquid and a cap for capping the liquid eject portion from a closely attached state to a detached sate; and ejecting liquid from the liquid eject portion; where: both moving and ejecting steps are executed concurrently.  
           [0027]    (12) An eject recovery method comprising steps of: sucking liquid from a liquid eject portion for ejecting liquid while a cap for capping the liquid eject portion caps the liquid eject portion; relatively moving the liquid eject portion and the cap from a attached state to a detached sate; and ejecting liquid from the liquid eject portion; where: both moving and ejecting steps are executed concurrently.  
           [0028]    (13) The eject recovery method according to (11), where: after sucking liquid from the liquid eject portion, ejecting liquid from the liquid eject portion is started when a pressure inside the cap returns to almost atmospheric pressure.  
           [0029]    (14) The eject recovery method according to (11), where: after sucking by the sucking means, ejecting liquid from the liquid eject portion is started before a pressure inside the cap return to almost atmospheric pressure; and then the relative movement is started.  
           [0030]    (15) The eject recovery method according to (11) or (12), where: sucking by the sucking means is executed again as the cap and the liquid eject portion are mutually being detached.  
           [0031]    (16) The eject recovery method according to (15), where: a gap formed between the cap and the liquid eject portion during the detached state is set between 0.1 mm and 1.5 mm.  
           [0032]    (17) The eject recovery method according to (15), where: sucking by the sucking means is started again before ejecting liquid from the liquid eject portion is finished.  
           [0033]    (18) The eject recovery method according to (11) or (12), where: ejecting liquid from the liquid eject portion during the relative movement is executed against the cap.  
           [0034]    (19) The eject recovery method according to (11) or (12), where: the cap is capping a plurality of the liquid eject portion, which respectively ejecting different liquids, altogether. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0035]    [0035]FIG. 1 is a perspective view showing an ink-jet printer as an example of image forming apparatuses according to the present invention.  
         [0036]    [0036]FIG. 2 is a partial perspective view schematically depicting a structure of eject portion of the recording head.  
         [0037]    [0037]FIG. 3 is a perspective view showing an eject recovery unit of the ink-jet printer and a driving power source from which a driving power is transmitted to the eject recovery unit.  
         [0038]    [0038]FIG. 4 is a sectional view for explaining a series of movements of a recording head during the eject recovery operation (where a cap, a blade and the recording head are in detached states).  
         [0039]    [0039]FIG. 5 is a sectional view for explaining a series of movements of the recording head during the eject recovery operation (where the cap is attached to the recording head).  
         [0040]    [0040]FIG. 6 is a sectional view for explaining a series of movements of the recording head during the eject recovery operation (ready for a wiping operation).  
         [0041]    [0041]FIG. 7 is a time chart for explaining eject recovery movements of the recording head.  
         [0042]    [0042]FIG. 8 is a schematic figure showing the conventional eject recovery device. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0043]    Hereinafter embodiments according to the present invention are explained by referring to drawings.  
         [0044]    [0044]FIG. 1 is the perspective view showing the ink-jet printer with the upper cover removed, as an example of image forming apparatuses according to the present invention.  
         [0045]    A sheet (a medium to be recorded) mounted on a paper supply tray  101  is supplied by revolving paper supply rollers (not shown in FIG. 1) and fed onto a platen  301  by feeding rollers (not shown in FIG. 1). While the sheet is being fed, a recording (forming) an image and the like is executed by ejecting ink from the recording head mounted on a carriage  203  onto the sheet in accordance with scanning movements of the recording head.  
         [0046]    The above-mentioned recording head  201  and an ink tank  202  where ink is stored for supplying ink to the recording head are detachably mounted on the carriage  203 . The carriage  203  is slidably connected to a scanning rail  360  supported by a chassis  350  so as to scan the above-mentioned recording head by transmitting a driving force from a carriage motor (not shown in FIG. 1) via a transmitting mechanism such as a belt. At the one end of scanning region of the carriage  203 , a recovery unit  500  for executing eject recovery treatments so as to maintain a ejecting performance of the recording head  201  in a good state.  
         [0047]    Some functions of the recovery unit  500 , which is explained later by referring to FIG. 3, shares a driving power source with the supply rollers so that a switching mechanism to switch the driving power is equipped in the recovery unit. In the same way, other function of the recovery unit  500  shares other driving power source with feeding rollers so that other switching mechanism to switch the other driving power is equipped in the recovery unit.  
         [0048]    As mentioned above the recording head  201  and the ink tank  202  are detachably mounted on the carriage  203 . In the present embodiment, however, a tank holder equipped with the ink tank is mounted on a holder monolithically formed with the recording head  201 , which is integrally mounted on the carriage  203 . The above-mentioned recording head  201  and ink tank  202  are constituted so as to meet requirements of respective inks i.e. black, cyan, magenta and yellow inks for recording. Further the recording head  201  of the present embodiment employs the so-called bubble jet method, where a pressure caused by bubbles generated in ink by utilizing thermal energy so as to eject ink. In order to supply thermal energy for generating bubbles to eject ink, the above-mentioned recording head  201  is equipped with electro-thermal energy conversion modules (not shown in FIG. 1).  
         [0049]    [0049]FIG. 2 is the partial perspective view schematically depicting a structure of eject portion of the recording head. A plurality of eject ports  82  are formed by a predetermined pitch on eject port surface  81  facing against the medium to be recorded by a predetermined gap (for example, ca. 0.2 to ca. 0.3 mm). Electro-thermal energy conversion modules (exothermic resistance modules, heaters)  85  for generating energy to eject ink are arranged along walls of respective liquid paths  84  communicating a common liquid chamber  83  and respective eject ports  82  together. The recording head  201  is mounted on the carriage  203  in a way where a row of eject ports is positioned so as to cross a main scanning direction (a moving direction of the recording head and carriage). When electro-thermal energy conversion modules are driven (applied electricity), inks in liquid paths  84  are brought to a film boiling and are ejected from eject ports  82  by generated pressure from the film boiling.  
         [0050]    [0050]FIG. 3 is the perspective view showing the recovery unit  500  of the ink-jet printer shown in FIG. 1 and the driving power source transmitting the driving power to the recovery unit  500 .  
         [0051]    Reference numeral “ 305 ” is an LF motor as a first driving power source and reference numeral “ 501 ” is an AP motor as a second driving power source.  
         [0052]    The driving force generated in the LF motor  305  functioning as the first driving power, is transmitted to a pump driving gears (not shown in FIG. 3) arranged in the recovery unit  500  via an LF reduction gear  306 , an LF gear  303 , a feeding roller  302  and an LF transmission switching mechanism  304 . And finally a driving cam  510  is driven by the above-explained transmitted driving power.  
         [0053]    A paper supplying mechanism (not shown in FIG. 3) is driven by the transmitted driving power, when the driving power generated in the AP motor functioning as the second driving power source, is transmitted to a paper supplying output gear  512  via an AP reduction gear  511  and an AP transmission switching mechanism  502 . A cap holder  504  and a wiping means  508  are driven by the transmitted power, when the driving power is transmitted to a cap cam (not shown in FIG. 3) via the AP transmission switching mechanism  502 . In the above-mentioned arrangement, the AP transmission switching mechanism  502  can transmit the driving force to either one of ways mentioned above in accordance with revolving directions of the AP motor  501 .  
         [0054]    The recovery unit  500  has a cap  503  for covering the liquid eject portion of the recording head during non-printing operations to prevent ink from drying and evaporating, and also has the cap holder  504  which supports the cap  503 . The cap arrangement mentioned above can execute capping movements, namely the cap  503  can be attached closely to or detached from the liquid eject portion of the recording head  201  by the AP motor functioning as the second driving power source.  
         [0055]    The cap  503  is communicated to a pump  506  via the cap holder  504  and a joint tube  505 . In this way the sucking operation can be executed by the driving force from the LF motor  305  functioning as the above-mentioned first driving power source.  
         [0056]    A blade  507  and a blade holder  508  which holds the blade  507 , can execute wiping operations to remove stuck ink and the like to the recording head  201  through the driving force from the AP motor  501  functioning as the second driving power.  
         [0057]    Hereinafter respective operations of a series of recovering operations in the arrangement mentioned above are explained.  
         [0058]    FIGS.  4  to  6  are sectional views illustrating a series of recovering operations of the recording head.  
         [0059]    In FIG. 4 both the cap  503  and the blade  507  are detached from the recording head  201 , namely, they are positioned in an inactive status against movements of the carriage  203 . The recovery unit  500  is placed in the position shown in FIG. 4 in ordinary printing operations. Consequently, since a starting point of the main scanning operation of the carriage  203  is kept at a position where the recording head  201  and the cap  503  are facing each other as shown in FIG. 4, other carriage positions beyond the starting position for switching operation and the like, are not required.  
         [0060]    [0060]FIG. 5 shows the so-called capping status, namely a contacting status of the cap  503  to the recording head  201  mounted on the carriage  203 , which is moved to a facing position against the cap  503 .  
         [0061]    When a cap cam (not shown in FIG. 5) revolves, the cap  503  is contacted to the facing recording head  201  by an applied pressure on the cap holder  504  generated by a cap spring  518 . As mentioned above, ink and the like can be sucked from the recording head  201  by driving the pump (see FIG. 3). In ordinary standby statuses (non-printing statuses) the recording head  201  is kept the status shown in FIG. 5 to prevent eject portion of the recording head from drying.  
         [0062]    [0062]FIG. 6 shows a status where the cap  503  is detached from the recording head  201  and the blade  507  is advanced to a position so as to contact to the recording head  201  by a pressure from a blade spring  519  so that the wiping can be executed, when the cap cam (not shown in FIG. 6) revolves further from the position in FIG. 5.  
         [0063]    Ink is sucked as keeping the status shown in FIG. 5. Then ink remaining in the cap  503  and the pump is discharged from the recovery unit, namely the so-called dummy sucking operation can be executed by driving pump (see FIG. 3) as the cap  503  is kept being detached from the recording head  201  as shown in FIG. 6.  
         [0064]    A plurality of color inks are mixed when the sucking operation is executed, as a result a turbid ink is formed and filled in the cap. When the cap is detached after the sucking operation, the turbid ink is mixed with ink in nozzles, as a result the so-called mixed color phenomenon such that a light color such as yellow mixed with a dark color is recorded on the sheet, might occur. Particularly immediately after detaching the cap  503  from the recording head  201 , mixed turbid ink is apt to flow reversely from nozzles owing to a negative pressure in the ink tank  202  behind the recording head  201  due to a fluctuation of the pressure balance against ink.  
         [0065]    In order to prevent the above-mentioned mixed color phenomenon, ink is ejected from the recording head  201  as the cap  503  is kept being detached from the contacting position on the liquid eject portion of the recording head  201  to the standby position after the above-mentioned sucking operation is finished. Since the turbid ink, which tends to flow into the nozzles, is pushed out of nozzles by the above-mentioned ejected ink during detaching operation of the cap  503 , the mixed color phenomenon can be prevented.  
         [0066]    As mentioned above, since the driving source power for the cap  503  is the AP motor  501  and that of the pump  506  is the LF motor, both can be driven independently on desired timings. Therefore, the pump can be driven while adjusting a detaching distance of the cap  503  from the recording head  201 . More specifically, it is known fact that the stuck ink to liquid eject portion of the recording head  201  is rather easily removed when the sucking is executed by maintaining a small gap formed between the recording head  201  and the cap  503 . For that purpose, the cap  503  is moved to a position detached a little bit from the recording head  201  while ink is being ejected from the recording head, in other words, the first dummy sucking is executed by driving the pump  506 . Then the second dummy sucking is executed after the cap  503  is detached from the recording head completely. Thus, ink including stuck ink to the recording head  201  can be effectively removed and discharged, and at the same time ink is kept from flowing into nozzles of the recording head  201 .  
         [0067]    When the detached gap between the recording head  201  and the cap  503  during the first dummy sucking is set too large, ink removal effects around the liquid eject portion are reduced. Therefore, the detached gap should be kept preferably between 0.1 mm to 1.5 mm, which might be different depend on characteristics of ink and shapes of the recording heads.  
         [0068]    [0068]FIG. 7 is the timing chart illustrating a series of recovering operations mentioned above.  
         [0069]    Reference characters “T 101 ” shows a negative pressure curve generated in the cap (in the recording head), “T 102 ” shows a driving status of the cap, “T 103 ” shows a driving status of the pump and “T 104 ” shows a driving status of ink ejection (pre-ejection) from the recording head.  
         [0070]    As shown in FIG. 7, at first the cap  503  is driven so as to attach closely to the recording head  201  and the negative pressure is caused in the cap  503  by driving the pump. Ink is sucked from the recording head  201  and the cap  503  by the above-mentioned negative pressure, but the negative pressure in the cap  503  is gradually reaching to atmospheric pressure as the sucked ink fills the cap  503  and the inside of the pump. Finally a sucked volume reaches maximum amount when the negative pressure returns to almost the atmospheric pressure.  
         [0071]    Even the cap  503  is detached from the recording head a little bit, the turbid ink is prevented from flowing from the nozzles by ejecting ink (pre-ejection) simultaneously from the recording head  201  as the driving status T 104  in FIG. 7 depicts.  
         [0072]    Then the ink in the cap  503  and around the liquid eject portion of the recording head  210  is removed by driving the pump again as the driving status T 103  in FIG. 7 depicts as the cap  503  is kept being detached a little bit. Further the discharging ink in the pump (dummy sucking) is executed by driving the pump again as the cap is kept being in a completely detached state from the recording head. Thus a series of recovering operations are finished.  
         [0073]    The recovering operations according to the present invention are not limited in the way as described in the above-mentioned embodiment such that the dummy sucking is started after the detaching operation is finished followed by a series of the operations; namely, sucking operation, recovering the pressure in the cap  503  nearly to the atmospheric pressure and the pre-ejection from the recording head  201  as the cap is kept being detached from the recording head. For example, ink ejection from the recording head  201  can be started after the detaching movement of the cap is started.  
         [0074]    In accordance with properties of ink or recording head, the pre-ejection from the recording head may be started before the pressure in the cap returns to the atmospheric pressure and the cap may be detached from the recording head as the pre-ejection is being continued. In this case, ink and the air is kept from flowing into nozzles when and after the cap is opened.  
         [0075]    In accordance with properties of ink or recording head as the cap is kept being detached, the dummy ejection may be started after the pre-ejection from the recording head is started, but before the pre-ejection is finished. In this case, ink stuck to the liquid eject portion and ejected ink during the detaching operation can be removed together.  
         [0076]    Further the pre-ejection can be executed not only during the detaching operation of the cap after the sucking operation, but also during moving the cap from the standby state to open the cap.  
         [0077]    In the above-described embodiment, the recovery unit comprising the cap movable up/downwards for attaching to/detaching from the liquid eject portion of the recording head is explained. However, the recovery unit is not limited to the above-mentioned arrangement, the present application is applicable to any arrangements where the moving operations of the cap and pre-ejection of the recording head can be executed at any timings.  
         [0078]    As explained above, the present invention attains recordings with high quality by ejecting liquids from the liquid eject head during detaching the cap relatively from the recording head so as to eliminate or reduce adverse effects caused due to mixing different liquids, represented by the so-called mix color phenomenon immediately after the adverse effects are caused. In addition, since the time for eject recovery is diminished according to the present invention, an overall processing rate of the liquid eject apparatus can be kept at a higher level.