Abstract:
A liquid ejecting apparatus includes a liquid ejecting head having a nozzle from which a liquid is ejected, a capping unit sealing the liquid ejecting head, a tube pump applying a negative pressure to the capping unit by rotating operation to suck a fluid, and a controller varying a rotation speed of the tube pump. The controller rotates the tube pump at a first rotation speed for a first predetermined time. The controller rotates the tube pump at a second rotation speed lower than the first rotation speed for a second predetermined time after rotating the tube pump at the first rotation speed for the first predetermined time.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a liquid ejecting apparatus for varying the rotation speed of a tube pump during cleaning and a method for controlling the liquid ejecting apparatus.  
           [0002]    Recently, one of liquid ejecting apparatus which eject a liquid from a liquid ejecting head is an ink-jet printer. The ink-jet printer performs printing by carrying paper while traveling a recording head as a liquid ejecting head mounted on a carriage and discharging ink droplets as a liquid from the recording head. A recording head has a nozzle group which formed on the bottom of the recording head. Ink droplets are discharged from the nozzle group. The ink-jet printer may suffer from ink thickening or clogging due to evaporation of ink solvent in a nozzle or nozzle blocking due to deposition of dust while printing is halted. Also, air bubbles may invade from the opening of a nozzle to invite improper printing such as dot dropouts. In order to prevent such nozzle blocking and dot dropouts, the inkjet printer performs cleaning to suck ink in the recording head when specified by the user. To perform the cleaning, the ink-jet printer is equipped with a capping unit for sealing a nozzle forming face of the recording head and a pump unit having a tube pump for applying a negative pressure on the capping unit.  
           [0003]    The tube pump has a pump wheel rotating in the forward and backward directions and a roller. The pump wheel is connected to a drive motor. By applying a pressure onto and deforming the tube connected to the capping unit by way of the roller moving in accordance with the rotation of the pump wheel, a negative pressure is applied to the capping unit. A plurality of values are set as the rotation speed and the ink suction speed may be varied by varying the rotation speed of the tube pump. A cleaning has a regular suction where high speed rotation is performed to enhance the discharge performance of air bubbles and a micro-suction where low speed rotation is performed to suck bubbled ink (for example, refer to the JP-A-11-138859). In the regular suction, the ink suction speed must be high enough to obtain sufficient discharge performance of the air bubbles.  
           [0004]    In case a tube pump is continuously rotated at a high speed in order to provide a sufficiently high ink suction speed during the regular suction, the consumption power could be increased. On the other hand, in case a tube pump is rotated at a low speed so as to gradually increase the suction speed of the ink or the rotation speed of the tube pump is gradually increased, the tube pump operating time is prolonged, which may increase the power consumption and ink consumption volume.  
         SUMMARY OF THE INVENTION  
         [0005]    It is therefore an object of the present invention to provide a liquid ejecting apparatus capable of suppressing the power consumption for cleaning and minimizing the degradation of a tube pump.  
           [0006]    In order to achieve the above object, as set forth in the present invention, there is provided a liquid ejecting apparatus comprising:  
           [0007]    a liquid ejecting head, having a nozzle from which a liquid is ejected;  
           [0008]    a capping unit, sealing the liquid ejecting head;  
           [0009]    a tube pump, applying a negative pressure to the capping unit by rotating operation to suck a fluid; and  
           [0010]    a controller, varying a rotation speed of the tube pump,  
           [0011]    wherein the controller rotates the tube pump at a first rotation speed for a first predetermined time; and  
           [0012]    wherein the controller rotates the tube pump at a second rotation speed lower than the first rotation speed for a second predetermined time after rotating the tube pump at the first rotation speed for the first predetermined time.  
           [0013]    In the configuration, the tube pump is rotated at the first rotation speed for the first predetermined time so that it is possible to increase the suction speed of the fluid from the capping unit in a relatively short time. It is thus possible to shorten the time required to increase the suction speed as well as suppress the liquid volume consumed until the suction speed is increased. It is possible, when the suction speed is increased, to drive the tube pump at the second speed as a relatively low rotation speed. It is thus possible to reduce the power required to drive the tube pump while maintaining the suction speed of a fluid from the capping unit to a high speed.  
           [0014]    Preferably, the first predetermined time is a time from a start of the rotating operation of the tube pump to when a suction speed at which the tube pump sucks the fluid reaches a predetermined value.  
           [0015]    In the configuration, it is possible to rotate a tube pump at a high speed until the suction speed at which the tube pump sucks a fluid reaches a predetermined value. Thus, it is possible to shorten the time required until the suction speed reaches a predetermined value.  
           [0016]    Preferably, a plurality of rotation speeds of the tube pump capable of increasing a suction speed of the fluid to a predetermined value are set to the controller. The controller rotates the tube pump at one rotation speed of the set rotation speeds of the tube pump for a predetermined time. The controller rotates the tube pump at another rotation speed of the set rotation speeds of the tube pump lower than the one rotation speed for a predetermined time after rotating the tube pump at the one rotation speed.  
           [0017]    In the configuration, it is possible to rotate the tube pump at a high speed until the suction speed at which the tube pump sucks a fluid reaches the predetermined value. Thus, it is possible to shorten the time required until the suction speed reaches the predetermined value as well as suppress the liquid volume consumed until the suction speed reaches the predetermined value. It is possible, when the suction speed is increased, to drive the tube pump at a relatively low rotation speed. It is thus possible to reduce the power required to drive the tube pump while maintaining the suction speed of a fluid from the capping unit to a high speed.  
           [0018]    According to the present invention, there is also provided a method for controlling a liquid ejecting apparatus, comprising the steps of:  
           [0019]    providing a liquid ejecting head which has a nozzle from which a liquid is ejected;  
           [0020]    providing a capping unit which seals the liquid ejecting head;  
           [0021]    providing a tube pump which applies a negative pressure to the capping unit by rotating operation to suck a fluid;  
           [0022]    setting a plurality of rotation speeds of the tube pump capable of increasing a suction speed of a fluid to a predetermined value;  
           [0023]    rotating the tube pump at one rotation speed of the rotation speeds of the tube pump for a predetermined time in a high speed rotation stage; and  
           [0024]    rotating the tube pump at another rotation speed of the rotation speeds lower than the one rotation speed for a predetermined time in a low speed rotation stage after the step of rotating the tube pump in the high speed rotation stage.  
           [0025]    In the method, it is possible, in the high speed rotation stage, to increase the suction speed of the fluid from the capping unit. Thus, it is possible to shorten the time required until the suction speed reaches a predetermined value as well as suppress the liquid volume consumed until the suction speed reaches the predetermined value. It is possible, when the suction speed is increased, to drive the tube pump at a speed lower than that in the high speed rotation stage. It is thus possible to reduce the power required to drive the tube pump while maintaining the suction speed of the fluid from the capping unit to a high speed.  
           [0026]    Preferably, the rotating of the tube pump in the low speed rotation stage is performed when the suction speed of the fluid is reached the predetermined value in the high speed rotation stage.  
           [0027]    In the method, in the high speed rotation stage, it is possible to drive the tube pump at a high speed until the suction speed of the fluid from the capping unit reaches the predetermined value. Thus, it is possible to shorten the time required until the suction speed reaches a predetermined value as well as suppress the liquid volume consumed until the suction speed reaches the predetermined value. It is possible, when the suction speed has reached the predetermined value, to drive the tube pump at a rotation speed lower than that in the high speed rotation stage. It is thus possible to reduce the power consumption while maintaining the suction speed of the fluid from the capping unit to a predetermined value.  
           [0028]    Preferably, the rotating of the tube pump in the low speed rotation stage is performed when a time predicted that the suction speed of the fluid is reached the predetermined value is elapsed in the high speed rotation stage.  
           [0029]    In the method, it is possible to drive the tube pump at a high speed until the time predicted that the suction speed of the fluid is reached the predetermined value. It is thus possible to shorten the time required to reach the predetermined value as well as suppress the liquid volume consumed until the predetermined value is reached. It is possible, when it is expected that the predetermined time is reached, drive the tube pump at a speed lower than that in the high speed rotation stage. It is thus possible to reduce the power consumption while maintaining the suction speed of the fluid from the capping unit to the predetermined value.  
           [0030]    Preferably, the rotating of the tube pump in the high speed rotation stage and the rotating of the tube pump in the low speed rotation stage are successively performed.  
           [0031]    In the method, in a shift from the high speed rotation stage to the low speed rotation stage, attenuation of the suction speed of the fluid which has reached the predetermined value is minimized. It is thus possible to maintain section of the fluid to the predetermined value.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0032]    The above objects and advantages of the present invention will become more apparent by describing in detail preferred exemplary embodiments thereof with reference to the accompanying drawings, wherein:  
         [0033]    [0033]FIG. 1 is a perspective view of the main section of an ink-jet printer main unit according to an embodiment of the present invention;  
         [0034]    [0034]FIG. 2 is a conceptual drawing of capping unit and a tube pump according to the embodiment;  
         [0035]    [0035]FIG. 3 is a block diagram of a control circuit according to the embodiment;  
         [0036]    [0036]FIG. 4 is a graph illustrating the ink suction speed according to the embodiment; and  
         [0037]    [0037]FIG. 5 is a graph illustrating the ink suction speed according to the embodiment. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0038]    The embodiment of the invention will be described referring to FIGS. 1 through 5.  
         [0039]    [0039]FIG. 1 is a perspective view of the main section of an ink-jet printer main unit (hereinafter referred to as a printer main unit) as a liquid ejecting apparatus. The printer main unit  11  has a frame  12  and a platen  13  inside the frame  12 . A guide member  14  is arranged in parallel with the platen  13 . A carriage  15  is slidably supported along the guide member  14 . The carriage  15  is reciprocated in the main scan direction by a carriage motor  16  provided outside the frame  12  via a timing belt  17  looped in parallel with the guide member  14 . On the carriage  15  is provided a recording head  20  having a nozzle group for discharging a black ink and various color inks as opposed to recording paper P. The nozzles of the recording head  20  is supplied ink from each ink cartridge  21  mounted on the carriage  15  and discharge the ink onto the recording paper P to print characters and images. The recording paper P is fed in the sub-scan direction by a paper feed mechanism (not shown) in accordance with the travel of the carriage  15 .  
         [0040]    In the non-print area to the right of the frame  12  are provided capping unit for sealing the opening portion of the nozzles of the recording head  20  and a pump unit  24  having a tube pump  26  (see FIG. 2). The capping unit  23  includes a cap  25  and an elevating unit (not shown) for traveling the cap  25  upward and downward. In the capping unit  23 , when the carriage  15  travels to the non-print area, the elevating unit lifts the cap  25  to seal the recording head  20 .  
         [0041]    When cleaning is performed to suck the ink in the recording head  20 , the nozzle forming face of the recording head  20  is sealed by the cap  25  and a negative pressure is applied in the cap  25  by the pump unit  24  connected to the cap  25  so that the ink in the recording head is sucked. The sucked ink is stored in a waste ink tank  28  (see FIG. 2).  
         [0042]    [0042]FIG. 2 is a schematic view showing the tube pump  26  and the cap  25  which seals the recording head  20 . For convenience, only the sectional view is provided only with regard to the main part. The cap  25  includes a cap holder  25   a  and a cap member  25   b  of a flexible material such as elastomer in the shape of a rectangle arranged at the upper end of the cap holder  25   a . A bottom of the cap  25  has an outlet  15   c  to which one end of a tube  27  is connected. The other end of the tube  27  is connected to the waste ink tank  28 . The tube pump  26  is arranged between the outlet  15   c  and the waste tank  28 . A waste ink absorber  28   a  of a porous material which absorbs the recovered ink, is provided in the waste ink tank  28 .  
         [0043]    When the cap  25  is elevated by the elevating unit and the cap member  25   b  comes into contact with the recording head  20 , the space enclosed by the nozzle forming face and the cap  25  is almost sealed. When the tube pump  26  is driven in this state, the air and ink as fluids in this space are sucked to generate a negative pressure which is applied to a nozzle. The ink in the nozzle is discharged from the outlet  25   c  formed on the bottom of the cap holder  25   a.    
         [0044]    A sheet-shaped ink absorber  25   d  is provided in the cap holder  25   a . The ink absorber  25   d  receives ink discharged from a nozzle and temporarily stores the ink. When the nozzle forming face is sealed with the cap  25 , the humidity in the cap  25  is maintained high so as to prevent drying of the ink in the nozzle.  
         [0045]    The tube pump  26  provided at a midpoint of the tube  27  is fixed to a frame  12 . The tube pump  26  includes a pump frame  26   a , a pump wheel  26   b  and rollers  26   c ,  26   d  traveling along roller supporting grooves  26   c ,  26   d  formed on the pump wheel  26   b . The pump frame  26   a  restricts the travel of the tube  27  in the outer direction in the shape of an arc. The tube  27  including an overlapping section (section the tube  27  is arranged over the pump frame  26   a ) is arranged between the pump frame  26   a  and the pump wheel  26   b.    
         [0046]    The pump wheel  26   b  rotates as driven by a paper feed motor  29  (see FIG. 1). When the pump wheel  26   b  is rotated in the forward direction (arrow direction in FIG. 2), the rollers  26   e ,  26   f  move out along the radius of the wheel in the roller supporting grooves  26   c ,  26   d  and rotates while sequentially crushing the tube  27 . This reduces the pressure inside the tube  27  upstream of the tube pump  26 . The air or ink inside the cap  25  sealing the nozzle forming face is gradually discharged in the direction of the waste ink tank  28  by way of the rotation of the pump wheel  26   b , thus accumulating a negative pressure inside the cap  25 .  
         [0047]    When the pump wheel  26   b  is rotated in the backward direction (direction opposite to the arrow direction in FIG. 2), the rollers  26   e ,  26   f  move in along the radius of the wheel in the roller supporting grooves  26   c ,  26   d . This brings the rollers  26   e ,  26   f  into the release state where they come in slight contact with the tube  27 . As a result, the internal pressure of the tube pump  26  becomes uniform.  
         [0048]    [0048]FIG. 3 is a block diagram showing the control circuit of a printer thus configured. A print controller  30  generates bitmap data as droplet injection data based on print data from the host computer of the printer. Based on the data, the print controller  30  instructs a head driver  31  to generate a drive signal to discharge ink from the recording head  20 .  
         [0049]    A cleaning controller  32  as a controller accesses data concerning the suction time and suction intensity stored in a storage (not shown) at power on or in response to a signal from a cleaning (CL) command detector  33  and a suction timer  34 . The cleaning command detector  33  detects ON/OFF of the cleaning command switch SW provided on the printer case. The cleaning controller  32  controls the tube pump  26  via a pump driver  35 . The pump driver  35  in this example is a paper feed motor  29  which rotates in steps of a predetermined angle. Thus the rotation speed of the tube pump  26  is variable in accordance with the frequency of the input pulse signal of the pump driver  35 .  
         [0050]    The data such as the suction time stored in the storage (not shown) is a fixed value, so that the frequency of a pulse signal supplied to the pump driver  35  is fixed to for example 4100 Hz, 3600 Hz, 2400 Hz, or 1200 Hz. FIG. 4 shows the suction speed of the tube pump  26  relative to the elapsed time assumed when these pulse signals are continuously supplied to the pump driver  35 . The curves a through c represent the suction speed corresponding to the elapsed time obtained from the rotation speeds a through c of the tube pump  26 . The rotation speed a is a rotation speed obtained when the frequency of the pulse signal supplied to the pump driver  35  is 4100 Hz. The rotation speed b is a rotation speed obtained when the frequency of the pulse signal supplied to the pump driver  35  is 3600 Hz. The rotation speed c is a rotation speed obtained when the frequency of the pulse signal supplied to the pump driver  35  is 2400 Hz.  
         [0051]    When the tube pump is rotated at one of the rotation speeds a through c, the rotation speed finally reaches a predetermined suction speed. Thus, the curves a through c in FIG. 4 converge to the maximum suction speed Vm as a predetermined value such as 0.2 cc/sec as the time elapses. This is due to the fact that the nozzle diameter of the recording head  20  is small and the channel resistance is large, thus the speed of the ink discharged from the nozzle is limited even when a greater negative pressure is applied by the tube pump  26  and the suction speed of the tube pump  26  is limited.  
         [0052]    In addition to these rotation speeds, a pulse signal having a relatively low frequency such as 1200 Hz may be supplied to the pump driver  35 . The suction speed obtained by the rotation speed of the tube pump  26  assumed in case the pulse signal is supplied does not reach the maximum suction speed Vm. The pulse signal is used to drive the pump driver  35  in the bubbled ink in the cap  25  is to be sucked. The pulse signal is not transmitted in case air bubbles or thickened ink in a nozzle is to be sucked.  
         [0053]    In order to discharge air bubbles or thickened ink in a nozzle of the recording head  20 , a negative pressure applied to the air bubbles or thickened ink must be increased. It is thus desirable to increase the suction speed. Cleaning for discharging air bubbles is set to maintain for a predetermined time a state where the ink suction speed has reached the maximum suction speed Vm. To attain the maximum suction speed Vm, it is necessary to perform preliminary suction where the tube pump  26  is previously driven and the negative pressure in the tube  27  upstream of the tube pump  26  or in the cap  25  is gradually increased. The preliminary suction is a suction operation from when the tube pump  26  started rotation at one speed to when the suction speed has reached the maximum suction speed Vm. The time required for preliminary suction as a predetermined time depends on the rotation speed of the tube pump  26 . The time required for the preliminary suction when the tube pump  26  is rotated at a highest rotation speed a is shorter than that required when the tube pump is rotated at a rotation speed b, c. Thus, in case the tube pump is rotated at the rotation speed a, the time required for preliminary suction is shortened and the ink volume consumed by preliminary suction can be suppressed.  
         [0054]    When the tube pump  26  is constantly rotated at the rotation speed a during cleaning, the power consumption is increased. Once the suction speed has reached the maximum suction speed Vm and is kept constant, the maximum suction speed Vm is maintained due to the negative pressure accumulated in the cap  25  and the inertial force of ink, irrespective of which speed of the rotation speeds a through c is used to rotate the tube pump  26 . Note that rotation speeds where the maximum suction speed Vm can be maintained do not include a relatively small rotation speed which will not allow the suction speed to reach the maximum suction speed Vm.  
         [0055]    Next, the rotation speed of the tube pump  26  assumed when cleaning is performed to discharge air bubbles or thickened ink is described below referring to FIG. 5. FIG. 5 is a graph showing the ink suction speed relative to the elapsed time during a cleaning process. When the cleaning controller  32  receives a cleaning execution command from the cleaning command detector  33 , the cleaning controller  32  drives the tube pump  26  at the rotation speed a for preliminary suction as a high speed rotation stage via the pump driver  35 . A negative pressure is applied in the tube  27  upstream of the tube pump  26  and in the cap  25  to gradually increase the ink suction speed. The tube pump  26  is rotated at the rotation speed a, so that the maximum suction speed Vm is attained in the shortest time among the set rotation speeds.  
         [0056]    When the tube pump  26  is rotated at the rotation speed a and the time set for preliminary suction at the rotation speed a as predetermined time has elapsed, the tube pump  26  is rotated at the rotation speed c to perform main suction as a low speed rotation stage. The ink suction speed is maintained to the maximum suction speed Vm even when the tube pump  26  is rotated at the rotation speed c since the ink suction speed has reached the maximum suction speed Vm after the preliminary suction is performed. The main suction is a suction operation to apply a negative pressure to air bubbles and thickened ink in a nozzle to discharge the air bubbles and thickened ink. When the time set for the main suction as a predetermined time has elapsed from the main suction started, the main suction is complete. Thus the main suction can suppress power consumption when compared with the case where the tube pump  26  is driven at the rotation speed a.  
         [0057]    The above-mentioned embodiment provides the following advantages:  
         [0058]    (1) In this embodiment, the cleaning controller  32  supplies pulse signals having different frequencies. A plurality of frequencies which allow the ink suction speed to reach the maximum suction speed Vm can be set as these frequencies. One of the pulse signals is supplied to the pump driver  35  so that the pump driver  35  rotates the tube pump  26  in accordance with the frequency of the input pulse signal. During cleaning to suck air bubbles and thickened ink, preliminary suction is performed at the rotation speed a as the maximum speed and main suction is performed at the rotation speed c which is lower than the rotation speed a.  
         [0059]    Thus, in the preliminary suction, the time required to attain the maximum suction speed Vm is shortened and the ink consumption volume in the preliminary suction is suppressed. Once the maximum suction speed Vm is attained, the tube pump  26  is driven at a rotation speed lower than the rotation speed a. This makes it possible to reduce power consumption while maintaining the ink suction speed to the maximum suction speed Vm to assure discharge performance of air bubbles. Reduction of power consumption reduces the heating volume of a motor for driving the pump, thereby suppressing noise. Reduced time for the preliminary suction and lower rotation speed in the main suction minimize degradation of the tube pump such as wear of the tube  27 .  
         [0060]    (2) In this embodiment, the preliminary suction where the tube pump  26  is rotated at a relatively high speed and the main suction where the tube pump  26  is rotated at a relatively low speed are performed in succession. Thus, the attenuation of the ink suction speed after reaching the maximum suction speed Vm is minimized in the switchover from the preliminary suction to the main suction. It is thus possible to efficiently maintain the ink suction speed to the maximum suction speed Vm.  
         [0061]    The above embodiment may be modified as follows:  
         [0062]    While cleaning is executed when the user has pressed the cleaning command switch SW in the embodiment, cleaning may be executed after a long-hour printing pause or every predetermined period.  
         [0063]    Cleaning to such air bubbles and thickened ink includes a stage where the tube pump  26  is rotated at a rotation speed a and a stage where the tube pump  26  is rotated at a rotation speed c in the embodiment. In the stage where the tube pump  26  is rotated at a rotation speed c, the tube pump  26  may be rotated at a rotation speed b or another speed which is lower than the rotation speed a. Note that the rotation speeds are those which maintain the maximum suction speed Vm and do not include a rotation speed which will not allow the suction speed to reach the maximum suction speed Vm after a predetermined time.  
         [0064]    While the tube pump  26  includes two rollers  26   e ,  26   f  in the embodiment, the tube pump  26  may be otherwise configured. For example, the tube pump  26  may include a single roller alone or include a tube so as not to form an overlapping section.  
         [0065]    While the liquid ejecting apparatus is an ink-jet printer in the embodiment, the invention may be applied to a liquid ejecting apparatus which ejects a liquid other than ink. Such a liquid ejecting apparatus may be a liquid ejecting apparatus which ejects a liquid such as an electrode material or color material used for fabrication of a liquid crystal display, EL display or FED (field emission display), a liquid ejecting apparatus which ejects a biological organic substance used for bio-chip fabrication, or a sample ejecting apparatus as a micro-pipet.