Patent Publication Number: US-7594712-B2

Title: Ink-jet printer

Description:
The present application is based on Japanese Patent Application No. 2004-336091 filed on Nov. 19, 2004, the contents of which are incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates in general to an ink-jet printer. 
   2. Discussion of Related Art 
   Generally, in an ink-jet printer wherein a carriage which carries a recording head reciprocates, it is known that an accuracy with which ink droplets ejected from the recording head attach to target or intended positions on a recording medium such as a sheet of paper is largely influenced by not only ejection-related conditions such as an accuracy with which nozzle holes are formed and a water-repellent property of a nozzle surface of the recording head in which the nozzle holes are formed, but also flying conditions under which the ink droplets fly from the recording head to the recording medium. Namely, it is known that the ink droplets ejected from the recording head are subjected, during flying toward the recording medium, to air flows (cross winds) caused as a result of the reciprocating movement of the carriage on which the recording head is mounted. 
   Where there is a variation in the degree of influence of the air flows among the ink droplets ejected from the respective nozzle holes, actual attaching positions on the recording medium to which the respective ink droplets actually attach deviate from target attaching positions on the recording medium to which the respective ink droplets should attach. In bi-directional printing, this causes bi-directional deviation in the attaching position of the ink droplet, resulting in a deterioration in the printing quality. 
   Particularly, in the light of the recent trend toward high-speed operation of the carriage as well as downsizing of the ink-jet printer, the moving speed of the carriage is increased to a level ranging from about 75 cm/s to about 100 cm/s. Therefore, the air flows generated by the reciprocating movement of the carriage give a significantly large influence on the flying of the ink droplets from the recording head toward the recording medium. 
   Described more specifically, the ink-jet printer has a structure shown in  FIGS. 3-5 , for instance. The ink-jet printer generally indicated at  101  includes a casing  102  consisting of an upper casing member  102 A and a lower casing member  102 B. The casing  102  defines a closed interior space which is inhibited from communicating with an outside. In the interior space of the casing  102 , a head unit  103  is disposed so as to be reciprocally movable, relative to a recording medium P, by driving means (not shown) in a rightward and leftward (transverse) direction of the printer indicated by an arrow A in  FIG. 3  along a guide portion  104 A supported by a frame  104 , so that images, characters, and the like are recorded on the recording medium P. The head unit  103  includes a carriage  103 A and a recording head  103 B mounted on the carriage  103 A. Ink droplets are ejected from a plurality of nozzle holes of the recording head  103 B for performing printing on the recording medium P placed on a platen  105 . The frame  104  also supports a sheet feed roller  106  and a sheet-discharge roller  107  such that these rollers  106 ,  107  are rotatable. In the following description, the direction in which the head unit  103 , accordingly the carriage  103 A moves may be referred to as a “carriage-moving direction”. 
   In the thus constructed ink-jet printer  101 , for the purpose of downsizing the printer  101 , a clearance S 1  ( FIG. 3 ) between a spatial region defined by the movement of the head unit  103  and an upper portion of the casing  102 , in other words, between an upper surface of the carriage  103 A and the upper portion of the casing  102 , is made as small as a clearance S 2  ( FIG. 3 ) between a nozzle surface of the recording head  103 B in which the nozzle holes are formed and the recording medium P. In this arrangement, the above-described air flows caused as a result of the movement of the carriage  103 A and entered the clearance S 1  are not likely to pass through the clearance S 1 . 
   In the meantime, clearances S 3 , S 4  ( FIG. 4 ) between respective side surfaces of the carriage  103 A which are opposed to each other in a perpendicular direction that is perpendicular to the carriage-moving direction in plan view and portions of the casing  102  which are respectively opposed to the respective side surfaces of the carriage  103 A are larger than the above-described clearance S 1  between the upper surface of the carriage  103 A and the upper portion of the casing  102 . Therefore, the air flows generated by the movement of the carriage  103 A and entered the clearance S 1  are likely to flow toward the clearances S 3 , S 4  as shown in  FIG. 6A . Accordingly, the ink droplets ejected from the nozzle holes in the neighborhood of the clearances S 3 , S 4  are influenced by the air flows more largely than the ink droplets ejected from the other nozzle holes, causing deviation (disturbance) in the attaching positions of the respective ink droplets ejected from the nozzle holes in the neighborhood of the clearances S 3 , S 4 . In other words, the deviation of the attaching positions of the ink droplets ejected from the opposite end portions of the recording head  103 B as seen in the perpendicular direction (in the neighborhood of the clearances S 3 , S 4 ) becomes larger than the deviation of the attaching positions of the ink droplets ejected from a middle portion of the recording head  103 B as seen in the perpendicular direction. 
   Described more specifically, under ink-ejection conditions in which, upon ejection of the ink droplets, small-sized ink particles (hereinafter may be referred to as “satellite particles”) are ejected together with main ink particles, there are recorded, on the recording medium, dots U 2  formed by attachment of the satellite particles, in addition to dots U 1  formed by attachment of the main particles, as shown in  FIG. 6B . In this instance, because the satellite particles are lightweight, the satellite particles ejected from the opposite end portions of the recording head (in the neighborhood of the clearances S 3 , S 4 ) as seen in the perpendicular direction are largely influenced by the air flows flowing from the clearance S 1  toward the clearances S 3 , S 4 , so that the attaching positions of those satellite particles largely deviate from the target attaching positions. In other words, since air flows flowing on the recording medium in the vicinity of the clearances S 3 , S 4  flow or escape outwards and upwards through the clearances S 3 , S 4 , the lightweight satellite particles are influenced by such air flows and undesirably fly in directions inclined with respect to a direction in which the main particles fly. The dots U 2  formed by attachment of the satellite particles nearer to the clearances S 3 , S 4  tend to largely deviate in directions inclined with respect to the dots U 1  formed by attachment of the corresponding main particles. 
   Where the casing  102  has the closed structure which inhibits communication with the outside, the above-indicated air flows generated by the reciprocating movement of the carriage  103 A hardly escape or leak from the casing  102 . Therefore, it is conceivable that the above-indicated tendency becomes larger, namely, the influence of the above-indicated air flows on the flying of the ink droplets becomes larger. 
   In an attempt to prevent the deterioration in the print quality due to the air flows generated as a result of the reciprocating movement of the head unit (the carriage), it is proposed in U.S. Pat. No. 6,561,620 corresponding to JP-A-2002-361858, for instance, to provide a skirt member which extends from the carriage in the carriage-moving direction so as to be substantially parallel with the nozzle surface of the recording head. 
   SUMMARY OF THE INVENTION 
   The provision of such a skirt member, however, results in an increase in the weight of the carriage and raises an obstacle to an increase in the moving speed of the carriage. 
   Accordingly, it is desired to reduce the influence of the air flows generated as a consequence of the reciprocating movement of the carriage by increasing or extending the nozzle surface in the carriage-moving direction while minimizing the weight of the carriage, for thereby making deviation of the attaching positions of the ink droplets uniform among the respective ink droplets or eliminating the deviation. If the deviation of the attaching positions is made uniform among the respective ink droplets, it is conceivable that formation of undesirable interference patterns due to mutually different deviation amounts of the attaching positions of the respective ink droplets can be avoidable, even if ordinary interlace printing is performed. 
   The inventor of the present invention made an extensive study on the above-indicated air flows arising from the reciprocating movement of the carriage while considering a reduction in the weight of the carriage. As a result of the sturdy, the inventor has noticed the following: It is estimated that the air flows flowing on the recording medium flow outwards through the above-indicated clearances S 3 , S 4 , causing the deviation in the attaching positions of the ink droplets on the recording medium. Accordingly, the inventor conceived an idea of restraining the influence of the air flows flowing outwards through the clearances S 3 , S 4  by forming a skirt member to have a shape in plan view in which portions of the skirt member in the vicinity of the clearances S 3 , S 4  largely protrude in the carriage-moving direction. In view of this, the present invention has been developed in which an improvement in the attaching accuracy of the ink droplets on the recording medium is assured while reducing the weight of the carriage to meet the demand for an increase in its moving speed. It is therefore an object of the invention to provide an ink-jet printer which is capable of preventing the air flows flowing on the recording medium from influencing on the flying of the ink droplets owing to a provision of a lightweight skirt member. 
   The above-indicated object of the invention may be achieved according to a principle of the invention, which provides an ink-jet printer, comprising: a casing; a head unit which is disposed in the casing and which includes (a) a carriage that moves reciprocally relative to a recording medium and (b) a recording head mounted on the carriage for ejecting ink droplets from a plurality of nozzle holes; and a pair of skirt members which are provided respectively on opposite sides of the carriage as seen in a carriage-moving direction in which the carriage moves, so as to protrude outwardly from respective first side surfaces of the carriage that are opposed to each other in the carriage-moving direction and which are flush with a nozzle surface of the recording head in which the plurality of nozzles are open, for rectifying air flows which are generated as a result of the movement of the carriage and which flow on the recording medium, each of the pair of skirt members protruding, in the carriage-moving direction, at opposite end portions thereof as seen in a perpendicular direction that is perpendicular to the carriage-moving direction in plan view, by an amount larger than at a middle portion thereof as seen in the perpendicular direction. 
   In the ink-jet printer constructed as described above, the pair of skirt members provided respectively on the opposite sides of the carriage as seen in the carriage-moving direction so as to protrude outwardly from the respective first side surfaces of the carriage exhibit an effective air-flow rectifying function so as to effectively rectify or control the air flows which are generated as a result of the reciprocating movement of the carriage and which flow on the recording medium. 
   Here, there are clearances between respective second side surfaces of the carriage which are opposed to each other in the perpendicular direction that is perpendicular to the carriage-moving direction and portions of the casing which respectively face the respective second side surfaces of the carriage, i.e., clearances between respective front and back parts of the head unit that are opposed to each other in the perpendicular direction and respective front and back parts of the casing which are opposed to each other in the perpendicular direction and between which the head unit is interposed. Therefore, the air flows flowing on the recording medium (on an underside of the nozzle surface) tend to flow outwards through those clearances. In this respect, each of the pair of skirt members protrudes, in the carriage-moving direction, at opposite end portions thereof in the perpendicular direction that is perpendicular to the carriage-moving direction in plan view, by an amount larger than at a middle portion thereof as seen in the perpendicular direction. Therefore, the air-flow rectifying effect provided by the pair of skirt members can be enhanced, whereby the air flows are prevented from flowing outwards at the opposite end portions of the recording head. Consequently, the attaching positions of the ink droplets are less likely to be deviated, resulting in an improvement in the printing accuracy. 
   Described more specifically, the air-flow rectifying effect is enhanced owing to the configuration of the skirt member in which the opposite end portions thereof as seen in the perpendicular direction protrude in the carriage-moving direction by a larger amount than the middle portion thereof as seen in the perpendicular direction, so that the air flows are prevented from being disturbed due to the existence of the clearances explained above. On the other hand, the air flows flowing on the recording medium at the middle portion of the recording head are allowed to flow without being influenced by the existence of the clearances. Therefore, the air flows flowing on the recording medium at the middle portion of the recording head need not be rectified by the skirt member. Thus, in the present arrangement, the air-flow rectifying function of the skirt member is tuned in the perpendicular direction depending upon the degree of necessity of rectifying the air flows. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features, advantages and technical and industrial significance of the present invention will be better understood by reading a following detailed description of a preferred embodiment of the invention, when considered in connection with the accompanying drawings, in which: 
       FIGS. 1A-1C  are views showing a head unit according to the invention, wherein  FIG. 1A  is a plan view,  FIG. 1B  is a front view, and  FIG. 1C  is a view for explaining an air-flow rectifying effect by skirt members; 
       FIG. 2  is a view for explaining an attached state of ink droplets on a recording medium according to the head unit of the invention; 
       FIG. 3  is a front elevational view in cross section showing an ink-jet printer based on which an ink-jet printer of the invention has been developed; 
       FIG. 4  is a side elevational view in cross section showing the ink-jet printer of  FIG. 3 ; 
       FIG. 5  is a plan view showing an internal structure of the ink-jet printer of  FIG. 3 ; 
       FIGS. 6A-6B  are views showing a conventional head unit, wherein  FIG. 6A  is a view for showing air flows and  FIG. 6B  is a view for explaining an attached state of ink droplets on a recording medium according to the conventional head unit. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to the drawings, there will be described a preferred embodiment of the present invention. Because an ink-jet printer according to the present invention is identical in construction with the ink-jet printer shown in  FIGS. 3-5 , except for a structure of skirt members  1 A,  1 B (which will be explained), the same reference numerals are used to identify the corresponding components and a detailed explanation of which is dispensed with. 
   As described above in the BACKGROUND OF THE INVENTION with respect to  FIGS. 3-5 , an ink-jet printer  101  includes a casing  102  in which is disposed a head unit  103  including a carriage  103 A and a recording head  103 B mounted on the carriage  103 A. The head unit  103 , namely, the carriage  103 A reciprocally moves in the casing  102 , and the recording head  103 B ejects droplets of ink from a plurality of nozzle holes so that images, characters, etc., are printed on a recording medium P. In the present embodiment, there are provided skirt members  1 A,  1 B (as shown in  FIGS. 1A-1C  and  FIG. 2 ) each as an air-flow rectifying or adjusting member which rectifies or adjusts air flows flowing on the recording medium P and which is formed so as to be co-planar with a nozzle surface of the printing head  103 B outwardly of the carriage  103 A. As described below, the skirt members  1 A,  1 B according to the present invention differ in configuration from a carriage skirt disclosed in the above-indicated U.S. Pat. No. 6,561,620. 
   The carriage  103 A is a rectangular shape in plan view. On opposite sides of the carriage  103 A as seen in a direction in which the carriage  103 A reciprocally moves (i.e., in a carriage-moving direction), the skirt members  1 A,  1 B are respectively provided so as to protrude outwardly from respective first side surfaces of the carriage  103 A that are opposed to each other in the carriage-moving direction. Each skirt member  1 A,  1 B extends over an entire length of the carriage  103 A as seen in a perpendicular direction that is perpendicular to the carriage-moving direction in plan view. In each skirt member  1 A,  1 B, its opposite end portions  1 Aa,  1 Bb protrude in the carriage-moving direction by an amount larger than its middle portion  1 Ab,  1 Bb. Each skirt member  1 A,  1 B is flush, at its lower surface, with the nozzle surface as if the skirt member  1 A,  1 B extends from the nozzle surface, and is disposed so as to be parallel with the recording medium to which each skirt member  1 A,  1 B is opposed. 
   Described more specifically, in each of the skirt members  1 A,  1 B, the amount of protrusion in the carriage-moving direction gradually and smoothly decreases from its opposite end portions  1 Aa,  1 Ba toward its middle portion  1 Ab,  1 Bb, such that each skirt member  1 A,  1 B has a curved profile and such that its middle portion  1 Ab,  1 Bb is substantially flush with a corresponding one of the first side surfaces of the carriage  103 A, i.e., such that the middle portion  1 Ab,  1 Bb hardly protrudes. The thus constructed skirt members  1 A,  1 B in which the amount of protrusion in the carriage-moving direction gradually, continuously, and smoothly decreases advantageously has a reduced weight without deteriorating its air-flow rectifying function (that will be explained below in detail). 
   It is noted that the curved profile of each skirt member  1 A,  1 B and the maximum amount of protrusion are suitably determined depending upon a result of measurement in which deviation of dots formed by attachment of ink droplets on the recording medium is obtained in actual printing. For instance, a distance L 1  ( FIG. 1A ), as measured in the carriage-moving direction, between each end of the recording head  103 B as seen in the perpendicular direction and a corresponding one of the opposite end portions of each skirt member  1 A,  1 B may be made larger than 1.5 times a distance L 2  ( FIG. 1A ), as measured in the carriage-moving direction, between the each end of the recording head  103 B and a portion of each skirt member  1 A,  1 B at which the amount of protrusion is the smallest. Preferably, the distance L 1  may be made larger than twice the distance L 2 . Further, for instance, a distance L 3  ( FIG. 1A ), as measured in the carriage-moving direction, between each of the opposite end portions of each skirt member  1 A,  1 B and the portion of each skirt member  1 A,  1 B at which the amount of protrusion is the smallest made be larger than 10% of a dimension or length W ( FIG. 1A ) of each skirt member  1 A,  1 B as measured in the perpendicular direction. Preferably, the distance L 3  may be made larger than 15% of the dimension W. 
   In each of the skirt members  1 A,  1 B, a point at which the amount of protrusion is the smallest, as seen in the perpendicular direction, and a center point of a nozzle region in which the plurality of nozzle holes are distributed, as seen in the perpendicular direction, are situated at the same position in the carriage-moving direction. In this arrangement, the configuration of each skirt member  1 A,  1 B is determined so as to be in accord with the distribution of the nozzle holes in the nozzle region, so that the influence of the air flows generated by the movement of the carriage  103 A on the ink droplets ejected from the nozzle holes can be effectively reduced. In this embodiment, the point of each skirt member  1 A,  1 B at which the amount of protrusion is the smallest is located at a midpoint of the opposite end portions  1 Aa,  1 Bb thereof. The dimension (length) W of each skirt member  1 A,  1 B as measured in the perpendicular direction may be determined depending upon the distribution of the nozzle holes in the nozzle region. In the present embodiment wherein a length of the recording head  103 B as measured in the perpendicular direction is smaller than the length of the carriage  103 A as measured in the perpendicular direction, the dimension W of the skirt member  1 A,  1 B is made substantially equal to the length of the carriage  103 A. In any case, the dimension W of the skirt member  1 A,  1 B should be determined to be larger than a dimension of the nozzle region as measured in the perpendicular direction. 
   On the opposite end portions of the recording head  103 B which are opposed to each other in the perpendicular direction, the air flows flowing over the recording medium tend to flow outwards and upwards through the aforementioned clearances S 3 , S 4 , whereby the attaching positions of the ink droplets on the recording medium tend to deviate from the target attaching positions. In the present embodiment, however, the opposite end portions  1 Aa,  1 Bb of each skirt member  1 A,  1 B corresponding to the opposite end portions of the recording head  103 B protrude largely in the carriage-moving direction, so that the air flows which tend to flow outwards can be rectified by the opposite end portions  1 Aa,  1 Bb of each skirt member  1 A,  1 B, as shown in  FIG. 1C . In other words, a component of the air flows which tends to flow outwards can be reduced owing to the skirt members  1 A,  1   b  constructed as described above. Consequently, the amount and direction of the air flows flowing between the nozzle surface and the recording medium are made comparatively uniform, irrespective of the locations of the nozzle holes, thereby reducing the deviation of the actual attaching positions of the ink droplets from the target attaching positions. 
   Accordingly, even if the moving speed of the carriage  103 A (the head unit  103 ) in the casing  102  becomes high, the deviation of the attaching positions of the ink droplets can be reduced. Thus, the accuracy with which the ink droplets attach to the target positions on the recording medium can be improved while decreasing the weight of the head unit  103  (the carriage  103 A). 
   In the present embodiment, the amount of protrusion of each skirt member  1 A,  1 B in the carriage-moving direction is decreased to an extent that the skirt member  1 A,  1 B is substantially flush, at its middle portion  1 Ab,  1 Bb, with the corresponding first side surface of the carriage  103 A. In other words, each skirt member  1 A,  1 B hardly protrudes in the carriage-moving direction at its middle portion  1 Ab,  1 Bb. Accordingly, this arrangement is effective to reduce the weight of the carriage  103 A as compared with a case in which each skirt member protrudes throughout its length as measured in the perpendicular direction that is perpendicular to the carriage-moving direction. 
   Accordingly, this arrangement improves the accuracy with which the ink droplets are attached to the target positions on the recording medium while reducing the weight of the head unit  103 . 
   In improving the attaching accuracy of the ink droplets, it is effective to minimize a clearance between the nozzle holes (the nozzle surface) and the recording medium. At the same time, the air existing ahead of the carriage when the carriage moves in its moving direction need to be escaped. If such air is not effectively escaped, there may be caused strong, complex air flows on the underside of the nozzle surface, so that the attaching positions of the ink droplets are undesirably deviated as a whole. 
   It is particularly important to effectively escape the air in a case where the downsizing (i.e., the reduction in height) is attained as in the ink-jet printer  101  of  FIGS. 3-5 . In detail, in the ink-jet printer  101  wherein the casing  102  defines the closed interior space which is inhibited from communicating with the outside, where the clearance S 1  between the upper surface of the carriage  103 A and the upper portion of the casing  102  is made substantially as small as the clearance S 2  (1-3 mm) between the nozzle surface of the recording head  103 B and the recording medium, it is important to effectively escape the air described above. More specifically described, in the ink-jet printer  101 , the clearances S 3 , S 4  between the respective second side surfaces of the carriage  103 A that are opposed to each other in the perpendicular direction and the portions of the casing  102  which respectively face the respective second side surfaces of the carriage  103 A are both made larger than the above-indicated clearance S 1 , that is, the clearance S 3  is equal to about 20 mm and the clearance S 4  is equal to about 5 mm. Where there is a large difference between the clearance S 1  and the clearances S 3 , S 4 , the attaching positions of the ink droplets are less likely to be influenced by the air flows generated as a result of the reciprocating movement of the carriage  103 A. On the other hand, where the difference between the clearances S 1  and the clearances S 2 , S 3  is not sufficiently large, the air flows flowing on the recording medium tend to flow outwards through the clearances S 3 , S 4 . 
   Where the casing  102  is configured to define the closed interior space and the clearance S 1  between the upper surface of the carriage  103 A and the upper portion of the casing  102  is made substantially equal to the clearance S 2  between the nozzle surface of the recording head  103 B and the recording medium as described above, a spatial region within the casing  102  is comparatively small, so that it may be considered that the influence of the air flows on the ink droplets ejected from the nozzle holes is large. In the present embodiment, however, the skirt members  1 A,  1 B configured as described above exhibit the air-flow rectifying function so as to effectively reduce the influence of the air flows on the ink droplets. Because the influence of the air flows on the ink droplets increases with an increase in the moving speed of the carriage  103 A, this arrangement is advantageous particularly where the carriage  103 A is moved at a high speed. Further, where the clearances S 3 , S 4  between the respective second side surfaces of the carriage  103 A that are opposed to each other in the perpendicular direction and the portions of the casing  102  which respectively face the respective second side surfaces of the carriage  103 A are both made larger than the above-indicated clearance S 1  as described above, it may be considered that the air flows are likely to flow through the clearances S 3 , S 4 . In the present embodiment, however, the air flows are prevented from flowing through the clearances S 3 , S 4  owing to the air-flow rectifying function of the skirt members  1 A,  1 B. 
   Thus, the skirt members  1 A,  1 B constructed according to the present embodiment is effective for rectifying the air flows. In the ink-jet printer  101  having the thus constructed skirt members  1 A,  1 B, therefore, the dots U 1  formed on the recording medium by attachment of the main particles and the dots U 2  formed on the recording medium by attachment of the satellite particles hardly deviate from the respective target positions, as shown in  FIG. 2 . Accordingly, the skirt members  1 A,  1 B assure improved accuracy with which the ink droplets attach to the target positions on the recording medium while reducing the weight of the head unit  103  (the carriage  103 A). 
   In the illustrated embodiment, the casing  102  is configured to define the closed interior space that is inhibited from communicating with the outside. The casing  102  may be configured otherwise. Even in an instance wherein the casing does not have such a closed structure, if the above-indicated clearances S 1 -S 4  are formed in the casing around the head unit as a consequence of the reduction in the size (the height) of the casing, the same advantages mentioned with respect to the illustrated embodiment are assured by employing the present skirt members. 
   It is to be understood that the invention is not limited to the details of the illustrated embodiment, but may be embodied with various changes and modifications, which may occur to those skilled in the art, without departing from the spirit and scope of the invention defined in the attached claims.