Abstract:
An image forming apparatus includes a printing head having an ink nozzle configured to discharge ink droplets onto a recording medium in order to form an image on the recording medium in a recording operation; a carriage on which the printing head is mounted and being moved in a main-scan direction during the recording operation; a linear encoder sheet having a counter for detecting a position of the carriage; an encoder sensor mounted on the carriage and detecting the position of the carriage by optically reading the counter of the linear encoder sheet; an carriage unit enclosure in which at least the carriage, the linear encoder sheet, and the encoder sensor are disposed; and an internal pressure adjusting unit adjusting an internal pressure of the carriage unit enclosure to be other than a negative pressure.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to image forming apparatuses having ink-mist blocking mechanisms. 
         [0003]    2. Description of the Related Art 
         [0004]    Image forming apparatuses include printers, facsimile machines, copy apparatuses, plotters, and multifunction peripherals, an inkjet recording apparatus is known. An inkjet apparatus is an image forming apparatus of a fluid-discharging type, which discharges ink droplets onto a sheet of recording material (“recording medium”) from a recording head in a printing operation. In a serial type of an inkjet recording apparatus, the printing operation is performed while the printing head is moved in a direction (“main-scan direction”) perpendicular to the direction of transport of the sheet (“sub-scan direction”). 
         [0005]    In the serial type of an inkjet recording apparatus, a mechanism for detecting the position of a carriage carrying the printing head and the amount of its movement is required for an accurate printing operation. In one example, the detection mechanism includes a linear encoder sheet. An inkjet recording apparatus of the serial type having such a detection mechanism using a linear encoder sheet is described below. 
         [0006]      FIG. 13  is a plan view of a conventional inkjet recording apparatus of the serial type. The inkjet recording apparatus includes a carriage  1  on which plural printing heads  2  for discharging ink droplets are mounted. The carriage  1  is configured to be moved in the main-scan direction along a guide rod  5  by an endless timing belt  4  rotated by a motor  3 . A linear encoder sheet  6  having a counter is disposed at least in a scanning area of the carriage  1  in the main-scan direction. The linear encoder sheet  6  is read by an encoder sensor  7  mounted on the carriage  1 , and the scan position of the carriage  1  is detected by determining a count value read from the linear encoder sheet  6 . 
         [0007]    Each time the sheet  8  is transported by a transport mechanism  9  in the sub-scan direction by a predetermined distance, the carriage  1  is moved (or “scanned”) while the printing head  2  discharges ink droplets onto the sheet  8 , forming an image thereon. Thus, the linear encoder sheet  6  is installed near the carriage  1  such that it can be reliably read by the encoder sensor  7 . More specifically, the linear encoder sheet  6  is exposed along the scanning area of the carriage  1 . 
         [0008]    In the serial type of an inkjet recording apparatus, as the ink droplets are discharged via the printing head nozzle, a mist of fine ink droplets is produced. The ink mist may become attached to various portions of the apparatus due to the flow of air caused by the scanning movement of the carriage or by an electrostatic attractive force, thus contaminating the apparatus. Particularly, the ink mist may become attached to the exposed surface of the linear encoder sheet over a long period. As a result, the encoder sensor may fail to read the linear encoder sheet accurately. Such a failure to detect the carriage position affects not only the resultant image formed on the recording medium, but may also prevent an appropriate control of the carriage  1 . The failure to control the carriage  1  may result in the carriage  1 , which may be moved at high speed, colliding with other components within the image forming apparatus, potentially breaking them and adversely affecting the reliability or durability of the apparatus. 
         [0009]    In order to overcome such problems, various proposals have been made. For example, Patent Document 1 discusses installing the linear encoder sheet and the encoder sensor within a cylindrical carriage unit enclosure in order to prevent the ink mist from attaching onto the linear encoder sheet. Specifically, a magnet is provided to the encoder sensor and another magnet is also provided to the carriage facing the magnet on the encoder sensor. As the two magnets are magnetically coupled to each other via the cylindrical carriage unit enclosure member, the encoder sensor can be moved along with the carriage, thus enabling the detection of the carriage position. 
         [0010]    Patent Document 2 discusses an inkjet recording apparatus that includes plural inlets disposed within an area of movement of the carriage, plural valves for individually opening or closing the inlets, and fans producing an airflow for guiding the ink mist toward the inlets. By activating the fans and opening the inlets by the valves, an airflow is produced between the fans and the inlets, by which the ink mist is guided and eventually collected, thus preventing the attaching of the ink mist onto the linear encoder sheet. 
         [0011]    Patent Document 3 discusses a technology for preventing the flow of ink mist from the printing head to the linear encoder sheet. The technology involves producing an airflow from the linear encoder sheet toward the carriage by using an airflow producing unit. 
         [0012]    In the technology of Patent Document 1, the carriage and the encoder sensor are separately installed. Thus, the technology cannot be applied to the typical structure illustrated in  FIG. 15  where the encoder sensor is installed on the carriage. Further, the magnetic force of the magnets by which the encoder sensor and the carriage are magnetically coupled to each other may decrease over time to such an extent that the encoder sensor and the carriage cannot be accurately positioned with respect to each other. If that happens, the carriage position cannot be accurately detected. 
         [0013]    In the case of Patent Document 2, the linear encoder sheet is installed near the airflow produced by the fans. As a result, the ink mist may become attached to the linear encoder sheet during the ink mist collecting operation. Thus, the problem of contamination of the linear encoder sheet is not overcome. 
         [0014]    In the case of Patent Document 3, because the airflow produced by the airflow producing unit flows from where the linear encoder sheet is installed toward the carriage, the airflow produces an external force which is directly applied to the linear encoder sheet. As a result, the linear encoder sheet may be warped or distorted, thus preventing an accurate carriage position detection. 
         [0015]    Patent Document 1: Japanese Laid-open Patent Publication No. 2007-326257 
         [0016]    Patent Document 2: Japanese Laid-open Patent Publication No. 2008-260154 
         [0017]    Patent Document 3: Japanese Laid-open Patent Publication No. 2001-191604 
       SUMMARY OF THE INVENTION 
       [0018]    According to an embodiment, an image forming apparatus includes a printing head having an ink nozzle configured to discharge ink droplets onto a recording medium in order to form an image on the recording medium in a recording operation; a carriage on which the printing head is mounted and configured to be moved in a main-scan direction during the recording operation; a linear encoder sheet having a counter for detecting a position of the carriage; an encoder sensor mounted on the carriage and detecting the position of the carriage by optically reading the counter of the linear encoder sheet; an carriage unit enclosure in which at least the carriage, the linear encoder sheet, and the encoder sensor are disposed; and an internal pressure adjusting unit adjusting an internal pressure of the carriage unit enclosure to be other than a negative pressure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIGS. 1A and 1B  are a perspective view and a front view, respectively, of an image forming apparatus according to an embodiment of the present invention; 
           [0020]      FIG. 2  is a cross section of a carriage unit enclosure of the image forming apparatus, illustrating the internal pressure of the carriage unit enclosure; 
           [0021]      FIG. 3  is a flowchart of a fan operation control process according to an embodiment; 
           [0022]      FIG. 4  is a flowchart of a fan operation control process according to another embodiment; 
           [0023]      FIGS. 5A and 5B  are a perspective view and a cross section, respectively, of an image forming apparatus according to an embodiment; 
           [0024]      FIGS. 6A and 6B  are a perspective view and a cross section, respectively, of an image forming apparatus according to an embodiment; 
           [0025]      FIGS. 7A and 7B  are perspective views of an image forming apparatus according to an embodiment; 
           [0026]      FIGS. 8A and 8B  are perspective views of an image forming apparatus according to an embodiment; 
           [0027]      FIGS. 9A and 9B  are perspective views of an image forming apparatus according to an embodiment; 
           [0028]      FIGS. 10A ,  10 B, and  10 C illustrate an image forming apparatus according to an embodiment; 
           [0029]      FIGS. 11A through 11F  illustrate steps of an assembly process of an image forming apparatus according to an embodiment; 
           [0030]      FIG. 12  illustrates an image forming apparatus to which a harness and an ink tube are connected from the outside of the apparatus main body; and 
           [0031]      FIG. 13  is a plan view of a conventional serial type inkjet printer. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0032]    In accordance with the embodiments of the present invention, the “image forming apparatus of the fluid discharging type” refers to an apparatus that performs an image forming operation by discharging a recording fluid onto a recording medium, such as an inkjet recording apparatus. The “recording medium” may include a sheet of various material, such as paper, thread, fiber, cloth, leather, metal, plastic, glass, wood, and ceramics. “Image formation (or recording)” may refer to the process of forming (or recording) not just an image with some apparent meaning, such as characters and figures, but also an image with apparently no meaning, such as a random pattern, on the recording medium. The “recording fluid” is not limited to ink but may include a DNA sample, a resist, and a patterning material. The “image” is not limited to two-dimensional images but may refer to an image formed on a three-dimensional object, or even a three-dimensional image. 
         [0033]    Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views,  FIGS. 1A and 1B  are a perspective view and a side view, respectively, of an image forming apparatus according to an embodiment. The image forming apparatus includes a carriage unit enclosure  11  in which a carriage unit is disposed. The carriage unit includes a carriage  1  on which printing heads  2  are mounted, a guide rod  5 , a linear encoder sheet  6 , and an encoder sensor  7 . 
         [0034]    The carriage unit enclosure  11  has an opening portion  12  in an area corresponding to the area of movement of the printing head  2 . The size of the opening portion  12  may correspond to at least a printed area of a sheet  8  and the size of an upper surface of a maintenance/recovery unit  13  that performs a maintenance or recovery operation on the printing head  2 . On top of the carriage unit enclosure  11 , fans  14 - 1  and  14 - 2  (either of which may be referred to as “the fan  14 ”) for supplying the outside air into the carriage unit enclosure  11  are installed. By supplying the outside air, the fans  14 - 1  and  14 - 2  adjust the internal pressure of the carriage unit enclosure  11  so that the internal pressure of the carriage unit enclosure  11  does not reach a negative pressure state. 
         [0035]    Other than the opening portion  12  in the area of movement of the printing heads  2 , the carriage unit enclosure  11  has no opening via which a large amount of pressure may leak from within the carriage unit enclosure  11 . Smaller openings may be present as long as they do not produce a significant pressure leak, such as openings for the mounting of the guide axle or the linear encoder sheet  6 . 
         [0036]    While the carriage unit enclosure  11  is described as an independent component in accordance with the present embodiment, the carriage unit enclosure  11  may be formed by a part of an exterior of the image forming apparatus or a frame member as long as the carriage unit can be hermetically sealed therein. Further, the fans  14 - 1  and  14 - 2  may be mounted on the sides of the image forming apparatus  100  instead of on the upper surface of the carriage unit enclosure  11  as illustrated in  FIG. 1 . 
         [0037]    Thus, in the image forming apparatus, the internal pressure of the carriage unit enclosure  11  is increased compared to the outside by the operation of the fans  14 - 1  and  14 - 2 . Thus, the ink mist produced by the printing heads  2  is prevented from entering the carriage unit enclosure  11 . In this way, the contamination of the linear encoder sheet  6  disposed within the carriage unit enclosure  11  can be prevented. 
         [0038]    Because the contamination by ink mist is prevented within the space of the carriage unit enclosure  11 , the encoder sheet  6  and other components may be disposed in the same layout as that of a conventional apparatus. Further, because the contamination by ink mist is prevented not by blowing the mist using airflow but simply by creating the pressure difference between the inside and outside of the hermetically enclosed space, the number of fans or their capacity may be smaller than in the case of using an airflow. There is also no need for applying the airflow against the linear encoder sheet. 
         [0039]    Next, an operation of the fans  14 - 1  and  14 - 2  is described.  FIG. 2  is a schematic cross section of the carriage unit enclosure  11 , illustrating the development of internal pressure. When the carriage  1  is moved at high speed in the main-scan direction as illustrated in  FIG. 2 , the internal pressure is reduced in an area “b” behind the carriage  1 . The reduced pressure in the area b causes the ink mist to move up as illustrated by arrows A, thus increasing the probability of attachment of the ink mist within the carriage unit enclosure  11 . 
         [0040]    Thus, in this case, the fan  14 - 1  disposed behind the carriage  1  is activated to supply air into the area b, thus preventing the decrease in pressure in the area b and the entry of ink mist into the carriage unit enclosure  11 . Such an upward airflow tends to occur more frequently at the point of change in operation of the carriage, such as at the point of reversal of scan direction or at the ends of the internal space of the carriage unit enclosure  11 . Thus, the fans  14 - 1  and  14 - 2  may preferably be disposed at the ends of the area of movement of the carriage  1 . Preferably, the fans  14 - 1  and  14 - 2  (either of which may be referred to as “the fan  14 ” hereafter) may be installed on the sides of the carriage unit enclosure  11 . 
         [0041]    Next, the operation of the fans  14 - 1  and  14 - 2  is described with reference to  FIGS. 1 and 3 . As illustrated in  FIG. 1 , the position and direction of movement of the carriage  1  are constantly detected by the encoder sensor  7  in combination with the linear encoder sheet  6 . Referring to a flowchart of  FIG. 3 , after the position of the fan  14  is defined, it is determined whether the scanning position of the carriage  1  is near the fan  14  (step S 101 ). When the scanning position of the carriage  1  is near the fan (“Yes” in S 101 ), the fan  14  is activated (step S 102 ). It is then determined whether the carriage  1  is to be further moved (step  103 ). If the carriage  1  is not to be moved further (“No” in step  103 ), the process ends. If the carriage  1  is to be moved further (“Yes” in step  103 ), the routine goes back to step S 101 . 
         [0042]    When the position of the carriage  1  is not near the fan  14  (“No” in step S 101 ), it is determined whether the direction of movement of the carriage  1  is toward or away from the fan  14  (step S 104 ). When the direction of movement of the carriage  1  is not toward the fan  14  (“No” in step S 104 ), the fan  14  is activated (step S 102 ). When the direction of movement of the carriage  1  is toward the fan  14  (“Yes” in step S 104 ), the fan  14  is turned off (step S 105 ). 
         [0043]    By this operation, the generation of negative pressure within the carriage unit enclosure  11  by the movement of the carriage  1  can be prevented, thus preventing the entry of ink mist into the carriage unit enclosure  11 . Because there is no need to activate plural fans at all times, an efficient fan operation can be realized. The ink mist may remain floating within the image forming apparatus even after the printing operation and the carriage  1  is stopped. Thus, preferably, the fan  14  may be continuously activated for a certain period of time even after the printing operation, as illustrated in step S 207  of an operation flow of  FIG. 4 . 
         [0044]      FIGS. 5A and 5B  are a perspective view and a front view, respectively, of the image forming apparatus according to another embodiment. In accordance with the present embodiment, the sides of the carriage  1  are connected with the corresponding internal sides of the carriage unit enclosure  11  via a bellows member  21  as an example of a flexible shielding member installed on or above the opening portion  12 . The bellows member  21  is capable of being expanded or contracted in accordance with the movement of the carriage  1  in the main-scan direction. Thus, the opening portion  12  of the carriage unit enclosure  11  can be covered at all times even when the carriage  1  is moved, so that the entry of ink mist into the carriage unit enclosure  11  via the opening portion  12  can be prevented. The bellows member  21  may be installed on an existing apparatus with only a minimum modification, thus providing a high degree of versatility. Preferably, the bellows member  21  may be made of a highly flexible material, such as rubber. 
         [0045]      FIGS. 6A and 6B  are a perspective view and a front view, respectively, of an image forming apparatus according to another embodiment. According to the present embodiment, a rotatable sheet member  31  as an example of the flexible shielding member is extended above the carriage  1 , with the ends of the sheet member  31  attached to the corresponding sides of the carriage  1  via two rollers  32  attached on each internal side of the carriage unit enclosure  11 . Thus, the carriage  1  is encircled by the sheet member  31  when seen from the sub-scan direction, as illustrated in  FIG. 6B . Because the sheet member  31  is attached to the carriage  1 , the sheet member  31  can be rotated as the carriage  1  is moved back and forth in the main-scan direction. Thus, the opening portion  12  of the carriage unit enclosure  11  can be covered at all times even when the carriage  1  is moved, thus effectively preventing the entry of ink mist into the carriage unit enclosure  11  via the opening portion  12 . 
         [0046]      FIGS. 7A and 7B  illustrate an image forming apparatus according to another embodiment.  FIG. 7A  is an overall perspective view of the image forming apparatus.  FIG. 7B  is a perspective view of the image forming apparatus with an open/close cover  41  of the carriage unit enclosure  11  opened. During the scanning operation of the carriage  1  in the printed area, a sheet with a bend or warping may cause a jam, requiring access to the carriage  1 . Also, it is preferable to be able to easily access the carriage  1  for replacement of the printing head or ink cartridges mounted on the carriage  1 . The open/close cover  41  of the carriage unit enclosure  11  provides easy access to the carriage  1  for replacement or maintenance, as illustrated in  FIG. 7B . 
         [0047]      FIGS. 8A and 8B  are perspective views of an image forming apparatus according to another embodiment, which includes an exterior cover  51  which may be openable. The exterior cover  51  has vent openings  52  for enabling the effective supply of outside air into the carriage unit enclosure  11  by the fans, as better illustrated in  FIG. 8B  where the exterior cover  51  is in an open status. 
         [0048]      FIGS. 9A and 9B  are perspective views of an image forming apparatus according to another embodiment, which includes the exterior cover  51  and in which the carriage unit enclosure  11  includes the open/close cover  41  as according to the embodiment of  FIGS. 7A and 7B . 
         [0049]      FIGS. 10A ,  10 B, and  100  illustrate an image forming apparatus according to another embodiment.  FIG. 10A  is a perspective view, and  FIGS. 10B and 10C  are lateral cross sections. In accordance with the present embodiment, the carriage unit enclosure  11  includes an opening portion  61  in its top surface, which may be used for maintenance purposes. The opening portion  61  is closed by a casing cover  62  attached to the apparatus main body. When the casing cover  62  is closed as illustrated in  FIG. 10C , the opening portion  61  is hermetically closed by a resilient member  63  provided on a back surface of the casing cover  62 , thus hermetically sealing the carriage unit enclosure  11 . Thus, in accordance with the present embodiment, the carriage unit enclosure  11  may not have an open/close cover of its own, thus reducing the total number of components of the image forming apparatus. 
         [0050]    Next, an assembly process of the image forming apparatus according to an embodiment is described with reference to  FIGS. 11A through 11F . As illustrated in  FIGS. 11A and 11B , a transport unit  9  is attached to a base portion  71 . On top of the transport unit  9 , a lower main-scan-unit casing member  72  is attached to the base portion  71  with a fastening device, such as screws or glues. The lower main-scan-unit casing member  72  has the opening portion  12  corresponding to the area of movement of the printing head. 
         [0051]    Then, as illustrated in  FIG. 11C , a frame member  73  is attached. Alternatively, the frame member  73  may be attached prior to the mounting of the transport mechanism  9 . Thereafter, the carriage unit is attached to the left and right sides of the frame member  73 , as illustrated in  FIG. 11D , and a top main-scan-unit casing member  74  is mounted, as illustrated in  FIG. 11E . 
         [0052]    During this assembly process, the distance between the transport mechanism  9  and the carriage unit is important. Thus, in accordance with the present embodiment, the position of the carriage unit relative to the transport mechanism  9  may be made adjustable. The main-scan-unit casing ( 72 ,  74 ) may be preferably mounted with a certain degree of freedom in order to minimize the amount of modification in the existing system. For this purpose, the main-scan-unit casing is divided into the lower main-scan-unit casing member  72  and the main-scan-unit casing upper member  74 , and the main-scan unit lower member  72  is positioned first with respect to the transport mechanism  9 . 
         [0053]    The top main-scan-unit casing member  74  includes a clearance portion to clear the area of connection of the carriage unit and the frame member  73 . After the position of the carriage  1  is determined, the top main-scan-unit casing member  74  is mounted. Because the position of the main-scan-unit casing and that of the carriage  1  are separately determined, the position of the carriage  1  may be adjusted by adjusting the location of mounting of the carriage unit to the frame member  73 . In accordance with the present embodiment, the main-scan-unit casing is attached with its sides in intimate contact with the left and right sides of the frame members  73 , so that the clearance portion can be covered by the frame member  73 . Thus, the hermetically sealed state of the carriage unit enclosure  11  can be maintained in spite of the clearance portions of the top main-scan-unit casing member  74 . 
         [0054]    Harnesses and ink tubes from the apparatus main body may be connected to the carriage  1  for controlling the printing head.  FIG. 12  illustrates an example in which an ink tube  81  connected to the ink head on the carriage  1  and a harness  82  connected to the printing head  2  of the carriage  1  are connected, via a rear portion of the frame member  73 , to a control substrate and an ink supply unit, respectively (both of which not illustrated) disposed outside the frame portion  73 . By installing the main-scan-unit casing in intimate contact with the rear surface and the left and right side surfaces of the frame member  73 , the opening portion  12  is enclosed by the frame member  73 . Thus, the ink tube  81  and the harness  82  can be connected to the carriage  1  while the sheet transport area in which ink mist may be present is separated from the inside of the main-scan-unit casing. 
         [0055]    Thus, in accordance with the embodiment illustrated in  FIG. 1 , at least the carriage  1 , the linear encoder sheet  6 , and the encoder sensor  7  are disposed within the carriage unit enclosure  11 . The internal pressure of the carriage unit enclosure  11  may become negative in some areas due to the scan operation of the carriage  1 , causing the entry of ink mist. Thus, the fans  14 - 1  and  14 - 2  (internal pressure adjusting unit) are configured to forcibly supply air into the carriage unit enclosure  11  to prevent the negative pressure within the carriage unit enclosure  11 . In this way, the entry of ink mist into the carriage unit enclosure  11  is prevented, thus preventing the contamination of the linear encoder sheet  6  by the ink mist. Further, in accordance with the present embodiment, because the encoder sensor  7  is mounted on the carriage  1  that is scanned along and near the linear encoder sheet  6 , the position of the carriage  1  can be accurately detected. 
         [0056]    In accordance with another embodiment, the opening portion  12  of the carriage unit enclosure  11  is covered by the flexible shielding member, such as the bellows member  21  illustrated in  FIG. 5  or the rotatable sheet member  31  illustrated in  FIG. 6 . The flexible shielding member is configured to be moved in accordance with the scanning movement of the carriage  1 . Thus, the opening portion  12  of the carriage unit enclosure  11  can be hermetically sealed at all times even during the scanning operation of the carriage  1 , thus preventing the entry of ink mist into the carriage unit enclosure  11  and preventing the contamination of the linear encoder sheet  6 . 
         [0057]    As illustrated in  FIG. 2 , when a negative pressure state develops in the area behind the carriage  1  in the carriage unit enclosure  11 , the ink mist may enter into the negative pressure state area. Thus, the fans  14 - 1  and  14 - 2  (internal pressure adjusting unit) are provided at the lateral ends of the carriage unit enclosure  11 , and one of the fans  14 - 1  and  14 - 2  that is located in the rear of the carriage  1  in a direction of scan operation is activated in order to supply air into the rear area, thereby eliminating the negative pressure state in the carriage unit enclosure  11 . Thus, the entry of ink mist into the carriage unit enclosure  11  and the resultant contamination of the linear encoder sheet  6  can be prevented. 
         [0058]    Within the image forming apparatus, the ink mist may remain floating even after the printing operation. Thus, in accordance with an embodiment, the fans  14 - 1  and  14 - 2  may be continuously operated for a period of time after the printing operation in order to prevent the entry of the floating ink mist into the carriage unit enclosure  11 . 
         [0059]    Preferably, the carriage unit enclosure  11  may be provided with an open/close cover for the purpose of replacement or maintenance of the printing head and the like. The open/close cover may be provided by a part of the exterior member of the image forming apparatus. In this case, the number of components of the image forming apparatus may be reduced. 
         [0060]    Although this invention has been described in detail with reference to certain embodiments, variations and modifications exist within the scope and spirit of the invention as described and defined in the following claims. 
         [0061]    The present application is based on Japanese Priority Application No. 2010-059798 filed Mar. 16, 2010, the entire contents of which are hereby incorporated by reference.