Abstract:
An image forming apparatus includes a sub tank that supplies a liquid to a head that ejects liquid droplets, the sub tank including a generating unit that generates a negative pressure inside the sub tank by expanding and contracting as the liquid is supplied to and ejected from the sub tank, and an opening mechanism that performs an opening operation of opening the sub tank to atmospheric air; a supply mechanism that supplies the liquid in a main tank to the sub tank; a carriage that moves in a main scanning direction above a sheet, the head being disposed in the carriage; a moving mechanism that changes a distance between the sheet and the head; and a control unit that causes the opening mechanism to perform the opening operation in conjunction with the moving mechanism changing the distance between the sheet and the ejecting head.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a liquid droplet ejecting type image forming apparatus and an atmospheric air opening method of a sub tank of a liquid droplet ejecting type recording head. 
     2. Description of the Related Art 
     In a liquid droplet ejecting type image forming apparatus, for example, an inkjet type image forming apparatus, a head unit is provided with a sub tank, and an amount of ink that has been consumed at a recording head is supplied to the sub tank from a main tank. For example, as described in patent document 1, when air enters a supply path to the sub tank, a failure may occur in the negative pressure in the sub tank for a certain time period. Therefore, a negative pressure recovery operation involving an atmospheric air opening operation is performed. The negative pressure recovery operation involving an atmospheric air opening operation is preferably performed only when air enters the supply path, because ink is consumed by performing these operations. However, in order to perform the negative pressure recovery operation involving an atmospheric air opening operation only when air enters the supply path, it would be necessary to determine whether air has entered the supply path. Thus, in consideration of ink consumption, there are two types of negative pressure recovery operations. One type is a negative pressure recovery operation involving an atmospheric air opening operation, and another type is a negative pressure recovery operation that does not involve an atmospheric air opening operation. 
       FIG. 9  is an exploded perspective view of a conventional inkjet head unit. As shown in  FIG. 9 , a head unit  1  includes heads  3  on which sub tanks  4  are mounted, an ink supply mechanism  2  for supplying ink to the sub tanks  4 , a carriage  5  carrying the heads  3  corresponding to four colors that moves in a main scanning direction, and a support shaft  6  that supports the carriage  5  such that the carriage  5  is movable in the main scanning direction. The ink supply mechanism  2  is used to supply ink from ink cartridges  2 Y,  2 M,  2 C, and  2 K corresponding to the respective colors of YMCK, to the sub tanks  4  corresponding to the respective colors provided above the heads  3 . The sub tank  4  maintains a negative pressure required for ejecting ink, and constantly maintains a fixed negative pressure for preventing the ink inside the sub tank  4  from dripping out. A flexible film is adhered to the side surfaces of the sub tank  4 . The flexible film expands and contracts in accordance with the pressure inside the sub tank  4 , so that the internal volume changes. Accordingly, the ink in the sub tank  4  is consumed. The sub tank  4  has negative pressure until a predetermined amount of ink is consumed, and the sub tank  4  may continue to maintain the negative pressure. 
     The negative pressure is attained by opening the sub tank  4  to atmospheric air so that atmospheric pressure is attained, and ejecting a predetermined amount of ink. For this purpose, the sub tank  4  is provided with an atmospheric air opening mechanism  7 . The atmospheric air opening mechanism  7  of the sub tank  4  mounted on the carriage  5  is activated by pressing a pin  8  with a lever  10  of a solenoid  9 . The pin  8  contacts the atmospheric air opening mechanism  7  via a pin hole (through hole)  11  provided in the carriage  5 , from a direction perpendicular to the carriage moving direction, to activate the atmospheric air opening mechanism  7 . 
     The negative pressure in the sub tank  4  may not be maintained if gas enters the sub tank  4  as time passes or when the ink cartridges  2 Y,  2 M,  2 C, and  2 K are replaced. When the negative pressure is no longer maintained, the negative pressure needs to be attained once again. To attain the negative pressure, a predetermined amount of ink is ejected as described above, and therefore ink is wasted. Therefore, the atmospheric air opening operation is preferably not performed under regular circumstances; the atmospheric air opening operation is preferably performed only when necessary. Accordingly, a separate driving mechanism such as a solenoid shown in  FIG. 9  is typically provided. Examples are disclosed in patent document 2 and patent document 3. 
     Meanwhile, in recent years and continuing, printers are being used by users for versatile purposes. Accordingly, there is a wide variety of paper types being used. Particularly, there is a wide variety of paper types with different thicknesses (plain paper, post cards, cardboard, envelopes, etc.). In order to address the wide variety of paper types, patent document 4 discloses a mechanism for adjusting the gap between the paper sheet and the image forming mechanism (head gap). 
     When a magnet valve or a solenoid is provided for selecting the atmospheric air opening operation as described above, the number of components increases, the control operation becomes complex, and the apparatus size becomes large. Meanwhile, as described in patent document 4, there is known a mechanism for adjusting the gap between the paper sheet and the image forming mechanism. This mechanism is only used for adjusting the gap.
     Patent Document 1: Japanese Laid-Open Patent Publication No. 2007-15153   Patent Document 2: Japanese Patent No. 4155879   Patent Document 3: Japanese Laid-Open Patent Publication No. 2007-125825   Patent Document 4: Japanese Laid-Open Patent Publication No. 2008-179103   

     SUMMARY OF THE INVENTION 
     The present invention provides an image forming apparatus and an atmospheric air opening method, in which one or more of the above-described disadvantages are eliminated. 
     A preferred embodiment of the present invention provides an image forming apparatus and an atmospheric air opening method, in which a function that is intrinsically provided in a head unit such as a gap adjustment mechanism is used for performing an atmospheric air opening operation, so that the number of components is reduced and the apparatus is simplified. 
     According to an aspect of the present invention, there is provided an image forming apparatus including a sub tank that supplies a liquid to an ejecting head that ejects liquid droplets, the sub tank including a negative pressure generating unit that generates a negative pressure inside the sub tank by expanding and contracting as the liquid is supplied to and ejected from the sub tank, and an atmospheric air opening mechanism that performs an atmospheric air opening operation of opening the sub tank to atmospheric air; a supply mechanism that supplies the liquid in a main tank to the sub tank; a carriage that moves in a main scanning direction above a sheet, the ejecting head being disposed in the carriage; a moving mechanism that changes a distance between the sheet and the ejecting head; and an atmospheric air opening control unit that causes the atmospheric air opening mechanism to perform the atmospheric air opening operation in conjunction with the moving mechanism changing the distance between the sheet and the ejecting head. 
     According to an aspect of the present invention, there is provided an atmospheric air opening method of opening a sub tank to atmospheric air, the sub tank supplying a liquid to an ejecting head that ejects liquid droplets, the sub tank including a negative pressure generating unit that generates a negative pressure inside the sub tank by expanding and contracting as the liquid is supplied to and ejected from the sub tank, and an atmospheric air opening mechanism that performs an atmospheric air opening operation of opening the sub tank to atmospheric air, the liquid being supplied to the sub tank from a main tank, the atmospheric air opening method including moving a carriage in a main scanning direction above a sheet, the ejecting head being disposed in the carriage; changing a distance between the sheet and the ejecting head, the changing being performed before or after the moving; and causing a protruding member provided separately from the atmospheric air opening mechanism to come in contact with the atmospheric air opening mechanism of the sub tank at a predetermined position in conjunction with the moving or the changing, to open the sub tank to the atmospheric air. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings, in which: 
         FIG. 1  is an exploded perspective view of an atmospheric air opening device according to a first embodiment of the present invention; 
         FIG. 2  is for describing the operation of the atmospheric air opening device shown in  FIG. 1 ; 
         FIG. 3  is an exploded perspective view of an atmospheric air opening device according to a second embodiment of the present invention; 
         FIG. 4  is for describing the operation of the atmospheric air opening device shown in  FIG. 3 ; 
         FIG. 5  is an exploded perspective view of an atmospheric air opening device according to a third embodiment of the present invention; 
         FIG. 6  is for describing the operation of the atmospheric air opening device shown in  FIG. 5 ; 
         FIG. 7  is an exploded perspective view of an atmospheric air opening device according to a fourth embodiment of the present invention; 
         FIG. 8  is for describing the operation of the atmospheric air opening device shown in  FIG. 7 ; and 
         FIG. 9  is an exploded perspective view of a conventional atmospheric air opening device. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of the present invention includes a feature of performing an atmospheric air opening operation with the use of functions that are intrinsically provided in a head unit, such as operations of moving a carriage and adjusting a gap. 
     A description is given, with reference to the accompanying drawings, of embodiments of the present invention. Elements corresponding to those of the conventional example described with reference to  FIG. 9  are denoted by the same reference numerals and are not further described. 
     First Embodiment 
       FIG. 1  is an exploded perspective view of an atmospheric air opening device according to a first embodiment of the present invention.  FIG. 2  is for describing the operation of the atmospheric air opening device according to the first embodiment of the present invention. 
     As shown in  FIG. 1 , the atmospheric air opening device according to the present embodiment does not have the solenoid  9  provided for the atmospheric air opening device of the conventional example described with reference to  FIG. 9 . In the present embodiment, the pin hole  11  is formed in the side surface of the carriage  5 , i.e., in the side surface perpendicular to the support shaft  6  of the carriage  5 . The pin hole  11  is formed at a position such that the pin  8  can contact the atmospheric air opening mechanism  7  in the sub tank  4 . The atmospheric air opening mechanism  7  is disposed in a direction such that an operation part  7 A of the atmospheric air opening mechanism  7  faces the pin hole  11 , i.e., in a direction parallel to the support shaft  6 . The other elements are configured similarly to the conventional example described with reference to  FIG. 9 . The operation part  7 A is for opening the valve of the atmospheric air opening mechanism  7  so that the inside of the sub tank  4  is open to the atmospheric air (atmospheric air opening operation). The mechanism of the atmospheric air opening mechanism  7  is known in the art and not directly related to the mechanism according to an embodiment of the present invention, and is thus not further described in detail. 
     The pin  8  is positioned above the carriage  5  under regular circumstances as shown in  FIG. 2  ( a ). The carriage  5  moves back and forth along the support shaft  6 , at a position at which the head  3  is spaced away from a sheet P by a gap G 1  during printing. When an atmospheric air opening operation needs to be performed, the carriage  5  is raised (in a direction indicated by an arrow A 1  in  FIG. 2  ( b )), so that the operation part  7 A of the atmospheric air opening mechanism  7  is pushed up to a position facing the pin  8 , i.e., to a position such that the head  3  is spaced away from the sheet P by a gap G 2 . Next, a carriage scanning mechanism moves the carriage  5  toward the pin  8  (in a direction indicated by an arrow A 2  in  FIG. 2  ( b )). Accordingly, the operation part  7 A of the atmospheric air opening mechanism  7  is pushed by the pin  8 , so that the sub tank  4  is subjected to an atmospheric air opening operation. 
     According to the present embodiment, a carriage raising/lowering mechanism and a carriage scanning mechanism are used for performing the atmospheric air opening operation. Therefore, the apparatus can have a simple configuration and a compact size. Under regular circumstances, a regular printing operation can be performed without performing the atmospheric air opening operation. 
     Second Embodiment 
       FIG. 3  is an exploded perspective view of an atmospheric air opening device according to a second embodiment of the present invention.  FIG. 4  is for describing the operation of the atmospheric air opening device according to the second embodiment of the present invention. 
     As shown in  FIG. 3 , the atmospheric air opening device according to the present embodiment does not have the solenoid  9  provided for the atmospheric air opening device of the conventional example described with reference to  FIG. 9 . Furthermore, the pin  8  is provided above the carriage  5 , and the pin hole  11  is not provided. The other elements are configured similarly to the conventional example described with reference to  FIG. 9 . 
     In the present embodiment, as shown in  FIG. 4 , the pin  8  is provided at a predetermined position at an upper part of a path along which the operation part  7 A of the atmospheric air opening mechanism  7  of the sub tank  4  moves. When the atmospheric air opening operation is to be performed, as shown in  FIG. 4  ( a ), the carriage  5  is moved such that the sub tank  4  to be subjected to the atmospheric air opening operation carried by the carriage  5 , comes to a position immediately under the pin  8 . Then, the carriage  5  is raised (in a direction indicated by an arrow A 1  in  FIG. 4  ( b )) from this position to a position where the gap G 1  between the sheet P and the head  3  becomes the gap G 2  as shown in  FIG. 3  ( b ). Accordingly, the operation part  7 A of the atmospheric air opening mechanism  7  contacts the tip of the pin  8 , so that the atmospheric air opening operation is performed. 
     According to the present embodiment, a carriage raising/lowering mechanism and a carriage scanning mechanism are used for performing the atmospheric air opening operation. Therefore, the apparatus can have a simple configuration and a compact size. Under regular circumstances, a regular printing operation can be performed without performing the atmospheric air opening operation. 
     The second embodiment is different from the first embodiment in that one head  3  can be selected from among plural heads  3  carried by a single carriage  5 , as the head  3  to be subjected to an atmospheric air opening operation. When the atmospheric air opening operation is performed, the negative pressure becomes zero, and ink may drip out. Therefore, the head  3  is preferably capped while performing the atmospheric air opening operation. In this respect, the second embodiment is advantageous over the first embodiment because the atmospheric air opening operation may be performed on only a single head. 
     Third Embodiment 
       FIG. 5  is an exploded perspective view of an atmospheric air opening device according to a third embodiment of the present invention.  FIG. 6  is for describing the operation of the atmospheric air opening device according to the third embodiment of the present invention. 
     As shown in  FIG. 5 , the atmospheric air opening device according to the present embodiment is different from the atmospheric air opening device according to the second embodiment of  FIG. 3  in that the carriage  5  is lowered to perform the atmospheric air opening operation. The carriage  5  is lowered with the use of a mechanism for adjusting the head gap (hereinafter, a gap adjustment mechanism)  12 . Specifically, the pin  8  is positioned below the carriage  5  ( FIG. 6  ( a )). When the gap adjustment mechanism  12  lowers the carriage  5 , the tip of the pin  8  located below the carriage  5  presses the operation part  7 A of the atmospheric air opening mechanism  7  of the sub tank  4  ( FIG. 6  ( b )), so that the atmospheric air opening operation is performed. Accordingly, the atmospheric air opening mechanism  7  is positioned at the bottom part of the sub tank  4 , as shown in  FIG. 6 . 
     Furthermore, as shown in  FIG. 5 , the atmospheric air opening mechanism  7  is protruding out from the side wall of the sub tank  4 , and the operation part  7 A is positioned above the head  3  and below the below the top edge of the sub tank  4 . The pin  8  is disposed at a position corresponding to the operation part  7 A, i.e., at a position where the pin  8  contacts the operation part  7 A when the carriage  5  is lowered by a predetermined amount so that the valve is opened. 
     The gap adjustment mechanism  12  is originally provided for the purpose of adjusting the gap between the head  3  and the sheet P, i.e., the gap through which the paper sheet passes, so that printing is performed with an appropriate gap. Thus, the gap adjustment mechanism  12  has a function of moving the head  3  up and down. 
     Other elements of the third embodiment that are not particularly described are the same as those of the second embodiment. 
     In the present embodiment, as shown in  FIG. 6  ( a ), under regular operations, the gap between the head  3  and the sheet P is G 1 , and the tip (top tip) of the pin  8  is positioned below the head  3 . When an atmospheric air opening operation is to be performed, the operation part  7 A of the sub tank  4  in the carriage  5  to be subjected to the atmospheric air opening operation is moved along the support shaft  6  to the position above the pin  8 . Then, from this position, the operation part  7 A is lowered (in the direction indicated by an arrow A 3 ) as shown in  FIG. 6  ( b ). According to this lowering movement, the tip of the pin  8  pushes the operation part  7 A to open the valve, and the atmospheric air opening operation is performed. 
     According to the present embodiment, a gap adjusting mechanism and a carriage scanning mechanism are used for performing the atmospheric air opening operation. Therefore, the apparatus can have a simple configuration and a compact size. Under regular circumstances, a regular printing operation can be performed without performing the atmospheric air opening operation. 
     The third embodiment is different from the first embodiment in that one head  3  can be selected from among plural heads  3  carried by a single carriage  5 , as the head  3  to be subjected to an atmospheric air opening operation. When the atmospheric air opening operation is performed, the negative pressure becomes zero, and ink may drip out. Therefore, the head  3  is preferably capped while performing the atmospheric air opening operation. In this respect, the third embodiment is advantageous over the first embodiment because the atmospheric air opening operation may be performed on only a single head. Furthermore, in the present embodiment, the elements used for the atmospheric air opening operation can be integrally combined with a cap holder, and therefore the present embodiment may have an even simpler configuration than that of the second embodiment. 
     Fourth Embodiment 
       FIG. 7  is an exploded perspective view of an atmospheric air opening device according to a fourth embodiment of the present invention.  FIG. 8  is for describing the operation of the atmospheric air opening device according to the fourth embodiment of the present invention. 
     As shown in  FIG. 7 , the atmospheric air opening device according to the present embodiment is configured to perform the atmospheric air opening operation with the use of a link cam  14  driven by a maintenance unit (not shown), instead of the solenoid  9  provided for the atmospheric air opening device according to the conventional example described with reference to  FIG. 9 . Specifically, the maintenance unit includes a unit housing (not shown) and a cap  16  (see  FIG. 8 ) for sealing the head  3 . During the printing operation, the cap  16  is opened ( FIG. 8  ( a )), and during a maintenance operation, the cap  16  seals the head  3  ( FIG. 8  ( b )). The other elements that are not particularly described in the present embodiment have the same configurations as those of the conventional example described above. The maintenance head functions as a maintenance recovery mechanism for maintaining or recovering the ink ejecting state of the head  3 . Such a mechanism is indispensable in this type of device and known in the art, and is thus not further described in detail. 
     In the present embodiment, the link cam  14  is configured to sway about a support shaft  14 A. The pin  8  is attached to the tip of an operating end of a lever  14 B of the link cam  14 . A driven end of the link cam  14  is driven by a driving source  13  via a cam mechanism  15 . The L-shaped lever  14 B of the link cam  14  sways in accordance with the rotation of a cam surface  15 A of the cam mechanism  15  that drives the maintenance unit. As shown in  FIG. 8  ( a ), during the printing operation, the carriage  5  is lowered to maintain a gap G 1  for printing between the head  3  and the sheet P. Accordingly, even if the lever  14 B is driven, the pin  8  is positioned above the operation part  7 A of the atmospheric air opening mechanism  7 , and therefore the pin  8  does not contact the operation part  7 A so that the atmospheric air opening operation is not performed. 
     Meanwhile, when the carriage  5  moves to a maintenance position and switches to a maintenance state, the carriage  5  rises, and the operation part  7 A of the atmospheric air opening mechanism  7  reaches a position facing the pin  8  that is attached to the tip of the lever  14 B. At the same time, the cap  16  is fixed to the head  3  to seal the ink eject outlet of the head  3 . The pressure applied to the cap  16  is adjusted by a spring. In this state, the cam mechanism  15  is driven to cause the link cam  14  to contact the operation part  7 A of the atmospheric air opening mechanism  7  to open the valve, so that the inside of the sub tank  3  is open to the atmospheric air. In the present embodiment, the carriage  5  is raised so that the operation part  7 A to open the valve reaches a position level with the pin  8 . However, in another embodiment, the same function may be implemented by lowering the carriage  5 . 
     According to the present embodiment, a carriage raising/lowering mechanism and a carriage scanning mechanism are used for performing the atmospheric air opening operation. Therefore, the apparatus can have a simple configuration and a compact size. Under regular circumstances, a regular printing operation can be performed without performing the atmospheric air opening operation. 
     The fourth embodiment is different from the first embodiment in that one head  3  can be selected from among plural heads  3  carried by a single carriage  5 , as the head  3  to be subjected to an atmospheric air opening operation. When the atmospheric air opening operation is performed, the negative pressure becomes zero, and ink may drip out. Therefore, the head  3  is preferably capped while performing the atmospheric air opening operation. In this respect, the fourth embodiment is advantageous over the first embodiment because the atmospheric air opening operation may be performed on only a single head. Furthermore, the present embodiment is advantageous when the size of the device in the width direction is restricted, or when the gap G 1  between the head and the paper sheet cannot be made narrower than that under regular conditions. 
     As described above, according to an embodiment of the present invention, the following effects can be achieved.
     (1) It is possible to select whether to perform the atmospheric air opening operation by adjusting the gap between the carriage and the sheet. Therefore, there is no need to provide a lever driving mechanism or to control the lever driving mechanism, so that the apparatus can have a simple configuration.   (2) When the gap between the carriage and the sheet is adjusted for performing a printing operation, the atmospheric air opening operation is not performed, and therefore the atmospheric air opening operation can be performed without affecting regular operations.   (3) The atmospheric air opening operation is not performed at the initial stage of a printing operation, and therefore the time taken for printing out the first sheet can be prevented from increasing, and there is no need to take time to transfer to an atmospheric air opening operation after the printing operation.   (4) The atmospheric air opening operation is performed by driving relevant elements such as the carriage and the maintenance unit, and therefore configurations and operations for driving the atmospheric air opening device can be further simplified.   

     According to one embodiment of the present invention, an image forming apparatus and an atmospheric air opening method are provided, in which the distance between a paper sheet being passed through and an ejecting head is changed by a changing mechanism, and the atmospheric air opening operation is performed in conjunction with the changing operation, and therefore a function that is intrinsically provided in a head unit is used for performing the atmospheric air opening operation, so that the number of components is reduced and the apparatus is simplified. 
     The present invention is not limited to the specific embodiments described herein, and variations and modifications may be made without departing from the scope of the present invention. 
     The present application is based on Japanese Priority Patent Application No. 2010-060757, filed on Mar. 17, 2010, the entire contents of which are hereby incorporated herein by reference.