Patent Publication Number: US-2012038706-A1

Title: Line Head Wiping Method

Description:
RELATED APPLICATIONS 
     This application claims priority of Japanese application no. 2010-179462 filed Aug. 10, 2010, the entire content of which is hereby incorporated by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a line head wiping method for wiping nozzle faces of a line head that constitutes a printing head in an ink jet recording apparatus. 
     BACKGROUND OF THE INVENTION 
     A wiping method of this sort has been known as shown in  FIG. 1  for a plurality of nozzle heads a, b, c and d having nozzle faces at their end portions that protrude from a lower surface of a carriage e. When the carriage e is moved from a printing region over to a wiping region along a guide rail f, a blade g under the carriage e is moved up to a position at which its end portion can interfere with the protruding end portions of the nozzle heads a to d. As the carriage e is moved, nozzle faces that are constituted by the end faces of the protruding end portions of the nozzle heads a to d are rubbed and wiped by the blade g along the lower surface of the carriage e (see JP H04-371851 A). 
     In the abovementioned wiping method in the prior art, the end portion of the wiping blade g before the nozzle heads moving with the carriage e arrive reaches the position where it comes into flexural contact with a portion of the lower surface of the carriage e on the near side of the nozzle head a most downstream in the direction of movement of the carriage. Thereafter, the end portion of the blade g comes to interfere with the end portions of the nozzle heads a to d successively to wipe them. 
     Thus, since the end portion of the wiping blade g while being elastically deformed against and getting over the end portion of each nozzle head a, b, c, d is to wipe the nozzle face, a large shear force acts on the end portion of the blade g while getting over the end portion of the nozzle head a, b, c, d, giving rise to the problem that a premature wear or break tends to occur there. 
     Also, foreign matter that may have been attached to the end portion of the blade g when starting to wipe tends to be attached to a corner of the end portion of the most downstream nozzle head a. And, in ending the wiping, when the end portion of the blade g comes off the end portion of the nozzle head d most upstream in the direction of movement of the carriage, instantaneous release of the end portion of the blade g from its elastic deformation may cause the foreign matter attached to the blade g to be scattered into its surroundings, presenting the problem that an ambient component and the recording medium may be soiled thereby. 
     The printing head may include a line head that has a plurality of nozzle heads which are arranged in a direction of printing width and carried by a carriage and each of which is formed at its end with a head bottom face including a nozzle face and flush with a lower surface of the carriage. The line head in this case is wiped over a full length in a direction of printing width by a blade that is wider in width than the head bottom face in the state that its end is brought into flexural contact with the lower surface of the carriage. 
     Attaching such nozzle heads to the carriage so that each head bottom face is flush with the lower surface of the carriage allows a groove to become created between the periphery of the head bottom face and its surrounding surface of the carriage where the end corner of the nozzle head is usually chamfered. 
     Thus, wiping then over the entire lower surface of the carriage allows ink as attached to the blade end while wiping the head bottom face to become entering the groove, with the result that the lower surface of the line head may not be wiped neatly. 
     Also if such nozzle heads are attached to the carriage so that each head bottom face is flush with the lower surface of the carriage, each head bottom face may be recessed slightly from the lower surface of the carriage due to a dimensional error or the like. Then, wiping with the blade end in flexural contact with the lower surface of the carriage may leave ink around a region of the head bottom face. Here again, the lower surface of the line head cannot be wiped neatly. 
     SUMMARY OF THE INVENTION 
     One object of the present invention is to provide a method of wiping a line head having a plurality of nozzle heads arranged in a direction of printing width and carried by a carriage wherein a head bottom face of each of the nozzle heads is wiped with a blade, the method preventing premature wear and break of the blade and preventing soiling of the environment by its elastic deformation even where a line head having the head bottom face of a nozzle head protruding from a lower surface of the carriage is wiped, the method making it possible to wipe a lower surface of a line head neatly for in which the head bottom face of a nozzle head is made flush with the lower surface of the carriage or in which the head bottom face is slightly recessed from the lower surface of the carriage, and the method furthermore ensuring an elongated useful life of the blade by wiping the minimum requisite area of the line head. 
     In order to achieve the object mentioned above there is provided in accordance with one aspect of the present invention a method of wiping a line head comprising a plurality of nozzle heads each of which has a head bottom face and a nozzle face in which a number of open ink nozzles are formed, the nozzle face lying centrally of the head bottom face in a direction of printing width and being flush with the head bottom face, the nozzle heads being arranged in a direction of printing width and supported by a carriage wherein the head bottom face of each of the nozzle heads of the line head is wiped with a blade moved relative thereto in a direction of printing width, characterized in that wiping is effected with an end of the said blade brought into contact with the said head bottom face from a position between one end of the said head bottom face in the direction of printing width and the corresponding one end of the said nozzle face to a position between the other end of the said head bottom face in the direction of printing width and the corresponding other end of the said nozzle face. 
     Further, in the line head wiping method mentioned above, the plurality of nozzle heads of the line head may be arranged zigzag (staggered) so that their nozzle faces are linked together in a direction of printing width, the head bottom faces of the plurality of nozzle heads being wiped successively in the direction of printing width. Also, the plurality of nozzle heads of the line head are each preferably in the form of a rectangle (reed-shape) and may be arranged in a direction of printing width with an inclination, the head bottom faces of the plurality of nozzle heads being wiped as a whole in the direction of printing width. 
     And, in the line head wiping method mentioned above, wiping with said blade may be effected over a width in a direction orthogonal to the direction of printing width of the nozzle head, the width being narrower than the corresponding one of the head bottom face and wider than the corresponding one of the nozzle face. 
     Further, the blade may be adapted to be inclined fore and aft with an angle of inclination of −30 to +30 degrees to a direction orthogonal to the direction of printing width. 
     According to an embodiment of the method of the present invention, it can be seen that if it is applied to a line head in which the head bottom face of the end portion of each of a plurality of nozzle heads protrudes from a lower surface of the carriage, the blade for wiping the head bottom face is allowed to wipe only the head bottom face (planar section) of the nozzle head. Thus, the blade is freed from contacting a corner of the end portion of the nozzle head, making it possible to prevent its premature wear and break. 
     Also, according to an embodiment of the present method, freeing the blade from flexurally contacting a corner of the end portion of the nozzle head protruding from the lower surface of the carriage keeps foreign matter that may have be attached to the end of the blade from attaching to such a corner of the end portion of the nozzle head. Also, when the wiping is ended at which time the blade end portion is released from its sliding (elastic deformation) on the head bottom face, there is no foreign matter scattered by rebounding from the elastic deformation due to the flexural contact. This prevents the wiping action from soiling the environment. 
     Further, according to an embodiment of the present invention, since wiping with the blade is effected over a width in a direction orthogonal to the direction of printing width of the nozzle head, the width being narrower than the corresponding one of the head bottom face and wider than the corresponding one of the nozzle face, wiping with the blade can be effected over on an area slightly larger than the nozzle face of each nozzle head and thus with a minimized wiping area, making it possible to ensure an elongated useful life of the blade. And, even if the head bottom face of each nozzle head is made flush with or recessed slightly from the lower surface of the carriage, there is no ink that can be left in a groove as formed on a lower surface of the line head or in a corner of the recess, making it possible to wipe the lower surface of the line head in that state. 
     Also, with a blade inclined in a range of −30 to +30 degrees to a direction orthogonal to the direction of printing width, the wiping action for the lower surface of a line head is bettered. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an explanatory view illustrating a method in the prior art; 
         FIG. 2  is an explanatory view illustrating an essential part of an ink jet recording apparatus for carrying out a method according to an embodiment of the present invention; 
         FIGS. 3A and 3B  are a front and a bottom view, respectively, of an essential part of a line head which are used as explanatory views to illustrate a wiping operation on the line head; 
         FIGS. 4A and 4B  are each a cross sectional view illustrating the makeup and operation of a wiping unit provided with a cleaning function; and 
         FIGS. 5A and 5B  are a front and a bottom view, respectively, of an essential part of an alternative form of the line head which are used as explanatory views to illustrate a wiping operation thereon. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
       FIG. 2  is an explanatory view that diagrammatically shows an ink jet recording apparatus for carrying out the present invention. The apparatus includes a conveyor (platen)  1  by which a recording medium (continuous sheet of recording paper) can be conveyed to pass orthogonally to the sheet of drawing and a printing head  2  positioned at an upper side of the conveyor  1  for printing over an entire width of the recording medium conveyed by the conveyor  1 . At a lower surface of the printing head  2  there is a line head  3  supported by a carriage  4  so as to be opposite to the continuous sheet of paper entirely its widthwise. 
     The printing head  2  can be guided by a guide rail  5  between a printing region above the conveyor  1  for printing with the line head  3  on the recording medium over a given width and a maintenance region established shifted from the printing region in a direction of printing width. The printing head  2  can be moved by a feed screw  7  driven to rotate by a motor  6 . A movement of the printing head  2  is proportional to a number of revolutions of the feed screw  7  which is proportional to a number of revolutions of the motor  6 . The movement of the printing head  2  can thus be detected by an encoder  8  for detecting the number of revolutions of the motor  6 . 
     In the maintenance region, there is arranged a purging unit  9  for purging the line head  3  of the printing head  2 . The purging unit  9  is movable vertically. In a purging operation, it is moved up so that its upper end is made in contact with a lower surface of the carriage  4  for the printing head  2 . Note further that the purging unit  9  is here of suction type to recover the line head  3  and if there is arranged a recovery means of pressure type to recover the line head  3 , the purging unit  9  is used as a cap receiving ink blown off from the line head  3 . 
     Between the printing and maintenance regions, there is arranged a wiping unit  10  that can be made in rubbing contact with a lower surface of the line head  3  for the printing head  2  moving from the printing region to the maintenance region. The wiping unit  10  is constituted of a blade  11  that can be brought into contact with the head bottom face, a blade support cylinder  12  for supporting the blade  11  and a lifting means  13  for moving the cylinder  12  together with the blade  11  up and down to bring an end of the blade  11  into and out of contact with the lower surface of the line head  3 . 
     Between the printing and maintenance regions, there is also arranged a printing head detector  14  between the wiping unit  10  and the printing region for detecting a point P of the printing head  2  moving from the printing region to the maintenance region, e.g., as an end point of the carriage  4  on the side of the maintenance region. 
     A controller  15  is provided to receive detected values respectively by the encoder  8  and the printing head detector  14 . In response to these detected values, the controller  15  can furnish a signal to operate the lifting means  13  of the wiping unit  10  in automatic sequences. In this form of implementation of the invention, the operation is such that when the point P of the carriage  4  detected by the printing head detector  14  for the printing head  2  moving towards the maintenance region has then moved a given distance, the lifting means  13  of the wiping unit  10  is operated to move the blade  11  up and down as in steps to be described. 
       FIGS. 3A and 3B  shows an embodiment of the line head  3 . In this form of implementation, five (5) nozzle heads  3   a ,  3   b ,  3   c ,  3   d  and  3   e  are configured and arranged zigzag (staggered) in two lines. With this line head, the continuous sheet of paper can be printed on with a single color over an entire width thereof except for a given area at each of its both sides. 
     The nozzle heads  3   a - 3   e  as shown in  FIG. 3A  have their end head bottom faces evenly protruded slightly from the carriage  4 . Each nozzle head  3   a - 3   e  as shown in  FIG. 3B  has, centrally of its bottom face, a nozzle face A of a given area which is flush with the head bottom face and in which a given number of ink nozzles are formed, wherein the width of the nozzle face A in the direction of printing width constitutes an effective printing width W of each nozzle head. An end of the nozzle face A in the direction of printing width lies inside by a given dimension a from an end of the head bottom face in the direction of printing width, and the effective printing width W is of (L- 2   a ) with respect to the total width L of the head bottom face in the direction of printing width. In this connection, the width of the nozzle face A and the width of the head bottom face in the direction orthogonal to the direction of printing width are assumed to be S 1  and S 2 , respectively. 
     Of the five (5) nozzle heads  3   a - 3   e  in two lines that make up the line head  3 , the three (3) nozzle heads  3   a ,  3   b  and  3   c  in the first line as shown in  FIG. 3  are arranged in a direction of printing width so that the spacing between the adjacent nozzle faces A becomes the effective printing width W. And, the two (2) nozzle heads  3   d  and  3   e  in the second line are arranged so that their effective printing width W is coincident with the effective printing width W between the adjacent nozzle heads in the first line. In this line head  3  in which the effective printing widths W of the five nozzles heads  3   a - 3   e  are continuously linked together in a direction of printing width, it follows, therefore, that printing with a printing width that is five times of the effective printing width W is effected on the recording medium. 
     The head bottom face of each of the nozzle heads  3   a  to  3   e  of the line head  3  so configured as mentioned above is wiped while the printing head  2  is being moved from the printing region to the maintenance region and when the end of the blade  11  at the upper position in the wiping unit  10  is brought into rubbing contact with the head bottom face. In this form of implementation, two wiping units  10 A and  10 B as shown in  FIG. 3B  are provided so as to confront two lines, respectively, of the line head  3  into which a plurality of nozzle heads  3   a  to  3   e  are grouped in the printing direction. In these wiping units  10 A and  10 B, blades  11   a  and  11 B are made individually movable up and movable down in accordance with timings of movement to the maintenance region of the nozzle head  3   a ,  3   b  and  3   c  in the first line and the nozzle heads  3   d  and  3   e  in the second line. 
     In the first line in which three nozzle heads  3   a ,  3   b  and  3   c  are arranged, each of positions of blade contact (i), (ii), (iii), (iv), (v), (vi) is established corresponding to one half of each of distances a between both ends of each nozzle head  3   a ,  3   b ,  3   c  in the direction of printing width and both ends of each nozzle face A therein in the direction of printing width. Then, each width or spacing W 1  between these positions of blade contact (i)-(ii), (iii)-(iv), (v)-(vi) with the nozzle heads  3   a ,  3   b ,  3   c  becomes (W+a). Also, each width r spacing W 3  between the positions of blade contact (ii)-(iii), (vi)-(v) with the nozzle heads  3   a ,  3   b ,  3   c  becomes (W-a). And, a width or distance between the position of blade contact (i) at which the nozzle head  3   a  begins to be contacted by the blade  11   a  in the maintenance region and point P at the end of the carriage  4  on the side of the maintenance region is established as W 2 . 
     In the second line in which two nozzle heads  3   d  and  3   e  are arranged, each position of blade contact (vii), (viii), (ix), (x) with each nozzle head  3   d ,  3   e  is established as in the first line. And, a width or distance between the position of blade contact (vii) with the nozzle head  3   d  and the point P mentioned above is established as W 2 ′. 
     The controller  15  is provided with a first and a second control unit  15   a  and  15   b  for operating the blades  11   a  and  11   b  in the wiping units  10   a  and  10   b  for the first and second lines of the line head  3 , respectively, which are shown in  FIGS. 3A and 3B . Mention is made below of an operation of the wiping units  10   a  and  10   b  by these control units. 
     With the wiping units  10   a  and  10   b  deactivated, the ends of the blades  11   a  and  11   b  are positioned on standby below a level of the head bottom faces of the nozzle heads  3   a - 3   e  of the line head in the printing head  2 . Now in movement of the printing head  2  towards the maintenance region, when the point P of the carriage  4  is detected by the printing head detector  14 , the printing head  2  is moved from this position P by W 2  to a position (i), at which it is brought to a halt and stands still for a time. While the printing head  2  stands still, the blade  11   a  in the wiping unit  10   a  for the first line is moved up, reaching the position of blade contact (i) with the first nozzle head  3   a . At this position, the end of the blade  11   a  which is made in contact with the bottom face of the nozzle head  3   a  may be somewhat deformed to come into flexural contact therewith. 
     In this state, by moving the printing head  2  towards the maintenance region, the lower surface (namely, head bottom face) of the nozzle head  3   a  is wiped by the blade  11   b . And, the printing head  2  is moved by a distance W 1  to a position (ii) at which it is temporarily stopped. This position of blade contact (ii) with the first nozzle head  3   a  has then been reached by the blade  11   a . The blade  11   a  is then moved by the wiping unit  10   a  down to stay on standby, separated from the head bottom face of the nozzle head  2 . Thence, the printing head  2  is moved by a distance W 3 . 
     The wiping unit  10   a  is maintained on standby while the printing head  2  is moved by the distance W 3 . Thereafter, when the printing head  2  has been moved by the distance W 3  and is temporarily stopped, the blade  11   a  is again moved up, reaching a position (iii). The end of the blade  11   a  in the wiping unit  10   a  is thus brought into contact with the second nozzle head  3   b  at the position of blade contact (iii). The subsequent movement of the second printing head  2  by the distance W 1  allows the lower surface of the second nozzle head  3   b  to be wiped by the blade  11   a  over the width W 1 . And, when the blade  11   a  reaches a position of blade contact (iv) and the printing head  2  is temporarily halted, the blade  11   a  is moved down by the wiping unit  10   a  to stay on standby, separated from the lower surface of the nozzle head  3   b.    
     The abovementioned cycle of operation is effected as well for the blade  11   a  to be positioned relatively to confront the third nozzle head  3   c  wherein at the position of blade contact (v) with the third nozzle head  3   c  the blade  11   a  is moved up to start wiping the lower surface of the nozzle head  3   c  and at the position of blade contact (vi) the blade  11   a  is moved down by the wiping unit  10   a  for standby. 
     In the mean time, the wiping unit  10   b  for the second line is operated interlocked with operation of the wiping unit  10   a  for the first line. Starting from the state that the printing head  2  has been moved by a distance W 2 ′ after detection of the point P, the wiping unit  10   b  for the second line is operated as the wiping unit  10   a  for the first line 
     In wiping operation, there is an overlap between the first and second lines. During wiping of a nozzle head on the first line, there is a temporary stop of movement of the printing head  2  by wiping operation for a nozzle head in the second line. Also, during wiping of a nozzle head on the second nozzle head in the second line, there is a temporary stop of movement of the printing head  2  by wiping operation for a nozzle head in the first line. With the printing head  2  temporarily stopped to move in wiping each of all the nozzle heads  3   a  to  3   d , the nozzle faces of the nozzle heads  3   a  to  3   e  are wiped over defined extents of (i)-(ii) (iii)-(iv), (v)-(vi), (vii)-(viii) and (ix)-(x), respectively. 
     For each of the line for the nozzle heads  3   a  to  3   c  and the line for the nozzle heads  3   d  and  3   e , it should be noted here that the printing head  2  may be reciprocated twice, and wiping operation for the second line may be performed after the wiping operation for the first line is terminated. In this case, there is no temporary stop of wiping by a blade due to temporary stop of movement of the printing head  2  in wiping each nozzle head, and wiping of an entire wiping length for each nozzle head is done in a single action. 
     By the wiping operation mentioned above, the head bottom surface of each of the nozzle heads  3   a  to  3   e  is wiped over a blade contact point spacing W 1 . The head bottom face of an effective printing width W of the nozzle face A inside of the blade contact point spacing W 1  is wiped. 
     In this way, the blade  11   a ,  11   b  in the wiping unit  10   a ,  10   b  is brought into contact with the head bottom face in a spacing from one end, on the side of the maintenance region, of each nozzle head  3   a ,  3   b ,  3   c ,  3   d ,  3   e  to one end of the nozzle face A to initiate acting to wipe the nozzle face A. After acting to wipe the nozzle face A, the blade  11   a ,  11   b  in the wiping unit  10   a ,  10   b  continuing to wipe and having acted to wipe a planar portion of the head bottom face of each nozzle head  3   a ,  3   b ,  3   c ,  3   d ,  3   e  is separated from the head bottom face in a spacing from the other end of the nozzle face A to the other end of the nozzle head on the side of the printing region. 
     While the blade  11   a ,  11   b  in the wiping unit  10   a ,  10   b  is wiping a nozzle head in each line, a problem arises that ink as adhered on the nozzle face may be transferred onto the blade. In continuing to wipe with the blade, it is feared that ink as transferred to the blade may be transferred to a next nozzle head. 
     In order to resolve the problem, there has been proposed an arrangement in which in an interval between successive cycles of wiping as mentioned above, each time a blade finishes wiping a nozzle head or wiping a plurality of nozzle heads in each line, the blade is cleaned (see JP 2008-119,836 A).  FIGS. 4A and 4B  are each a cross sectional view that illustrates the makeup and operation of a wiping unit equipped with a self-cleaning function. 
     Mention is made of a first wiping unit  1  for wiping nozzle heads  3   a  to  3   b  in a first line. In the description of this form of implementation, the lifting means for moving up and down the blade support cylinder  12  is omitted from illustration. 
     The blade support cylinder  12  is here in the form of a bottomed rectangular cylinder, in whose upper part a rotating shaft  16  is journaled extending in a direction orthogonal to that in which the printing head  2  is moved. The rotating shaft  16  has a blade supporting member  17  fastened thereto, to which the blade  11   a  is in turn fastened with an inclination so that its upper part is oriented towards the maintenance region in the direction in which the printing head  2  is moved. The blade  11   a  is composed of hard rubber or any other suitable material that is suitable in its elasticity. 
     The blade supporting member  17  is of a length such that its both ends are in contact with inner surface of the blade support cylinder  12 . The blade supporting member  17  also has, at both sides of its axis of rotation, supporting pieces  17   a  and  17   b  fastened thereto as shown in  FIG. 4A . The supporting pieces  17   a  and  17   b  in turn have rectangular leakproof plates  18   a  and  18   b  fastened thereto, respectively. 
     When the rotating shaft  16  is rotated, the blade supporting member  17  is designed to rotate by about 180 degrees between a wiping state in which the blade  11   a  is oriented upwards as shown in  FIG. 4A. 4A  and a storing state in which the blade  11   a  is oriented downwards as shown in  FIG. 4B . The leakproof plate  18   a  and  18   b  are made horizontal at least when the blade supporting member  17  is in the storing state so that their ends and both side ends may be closely in contact with the inner surface of the blade support cylinder  12 . It should be noted further that the leakproof plate  18   a  and  18   b  may be composed of an elastic material such as rubber plate so that their ends and both side ends can be closely in elastic contact with the inner surface of the blade support cylinder  12 . 
     In the lower part of the blade support cylinder  12 , there is provided a cleaning liquid spray nozzle  19  oriented towards the blade  11   a  in the storing state. Also, the blade support cylinder  12  has an air nozzle  20  formed in its side wall such that it laterally confronts the end portion of the blade  11   a  in a storing position such as mentioned above. The blade support cylinder has a drain hole  21   a  formed in its bottom plate. 
     In wiping operation by the wiping unit  10   a , the rotary shaft  16  is driven by a rotary actuator (not shown) to bring the blade  11   a  into the wiping state in which it is oriented upwards and the lifting means  13  is driven to move the blade support cylinder  12  up to a position at which it is restrained by a stopper (not shown). 
     By moving the printing head  2  towards the maintenance region in this state, the head bottom face of the nozzle head of the printing head  2  is wiped with the blade  11   a , thereby ink adhered to the nozzle face is wiped and scraped off. Ink scraped off is adhered to the blade  11   a  which after wiping operation is cleaned in a cleaning operation. 
     The cleaning operation for the blade  11   a  is carried out as mentioned below. 
     The rotary actuator is driven to bring the blade  11   a  into the storing state in which it is oriented downwards as shown in  FIG. 4B . In this state, the leakproof plate  18   a  and  18   b  are oriented horizontally to bring and hold their ends and side ends in elastic contact with the inner surface of the blade support cylinder  12 . A space of the upper part within the blade support cylinder  12  is closed liquid-tight with these leakproof plates  18   a  and  18   b  and both sides of the blade supporting member  17 . 
     In this state, a cleaning liquid is sprayed from the cleaning liquid spray nozzle  19 . The cleaning liquid is then sprayed from the cleaning liquid spray nozzle  19  directly towards the blade  11   a  to flush ink adhered on the blade  11   a . Here, the cleaning liquid is kept from leaking into above the blade support cylinder  12  and drained through the drain hole  21 . After spraying the blade  11   a  with the cleaning liquid, the air nozzle  20  sprays the blade  11   a  with air to dry the blade  11   a.    
     The cleaning operation mentioned above is effected in the state that the blade support cylinder  12  in the wiping means  10  is moved down, each time each of the nozzles  3   a ,  3   b  and  3   c  arranged in a line has been wiped. 
       FIGS. 5A and 5B  shows another embodiment of the printing head to be wiped. In this alternative embodiment, the printing head  2 ′ has a line head  3 ′ comprising a plurality of rectangular (reed-shaped) nozzle heads  3   a ′,  3   b ′,  3   c ′, . . . arranged in a direction of printing width with an angle of inclination thereto. In this line head  3 ′, the lower surface of all the nozzle heads  3   a ′,  3   b ′,  3   c ′, . . . as a whole corresponds to a head bottom face of a nozzle head  3   a ,  3   b ,  3   c ,  3   d ,  3   e , and the lower surface of all portions as a whole of the nozzle heads  3   a ′,  3   b ′,  3   c ′, . . . in which ink nozzles are open corresponds to a nozzle face of the nozzle head,  3   a ,  3   b ,  3   c ,  3   d ,  3   e , in the embodiment shown in  FIGS. 3A and 3B . And, an effective printing width W 1 ′ in this embodiment is equal to a dimension between, outmost nozzles N 1  and N 2  of the nozzle heads positioned at both ends of the line head. 
     On the other hand, a blade  11 ′ in a wiping unit  10 ′ for wiping the nozzle face of the line head  3 ′ is made somewhat longer than a width of the line head  3 ′ in the printing direction (the direction in which the recording medium is moved). And, when printing head  2 ′ is moved towards the maintenance region and its point P′ is detected by the printing head detector  14  whereby the line head  3 ′ is moved by a distance W 2  to a position (i′) at which the printing  2 ′ head is temporarily stopped, the blade  11 ′ is moved up in the wiping unit  10 ′ to bring its end into contact with the head face (head bottom face) of the nozzle head  3   a ′ slightly outside of the nozzle at an end of the line head on the side of the maintenance region. A subsequent movement of the printing head  2 ′ towards the maintenance region causes wiping the head bottom face of the line head  3 ′. And, at the position (ii′) to which the printing head  2 ′ is moved by the distance W 1 , the blade  11 ′ lies outside of the nozzle of the nozzle head at an end of the line head on the side of the printing region. When the printing head  2 ′ is temporarily halted there, the blade  11 ′ in the wiping unit  10 ′ is moved down, leaving the head face of the nozzle head at the end of the line head on the side of the printing region without passing beyond the end of the head face of that nozzle head. 
     In this alternative embodiment of printing head, the end of the blade  11 ′ comes in contact with the head bottom face at the position (i) which is entered by a distance a′ into the upstream side from the downstream end of the head bottom face of the most downstream side nozzle head  3   a ′ in the direction of movement of the printing head  2 ′ and which is near side of the nozzle face of the nozzle head  3   a ′, the blade  11 ′ starting to wipe at this position and acting to wipe over the effective printing width W 1  of the line head  3 ′. The blade  11 ′ comes out of contact with the head bottom face at a position (ii′) which is past the nozzle face of the most upstream side nozzle head and which is downstream by the distance a′ from the most upstream end of the head bottom face of the nozzle head. 
     In each of the forms of implementation mentioned above,  11   a ,  11   b ,  11 ′ in the wiping unit  10   a ,  10   b ,  10 ′ may not necessarily be oriented orthogonally to the direction of movement of the printing head  2 ,  2 ′ as shown in  FIG. 3B  and  FIG. 5B  but may possibly be inclined fore and aft to a direction orthogonal to the direction of movement of the printing head  2 ,  2 ′, as shown by at an angle in the range of ±30°, for example an angle of +15 or −15 degrees, thereby bettering the wiping action. 
     While in the embodiments of the wiping unit, a wiping operation is illustrated as effected such that a printing head is moved for each line or while intermittently halting and in conjunction therewith a wiping blade in the wiping unit is moved up and down, it should be noted that with respect to a lower surface of the printing head moved to a maintenance position the wiping unit may be moved over an entire length of the printing head in a direction of printing width while moving the blade up and down in accordance with a layout of head bottom faces of nozzle heads of the printing head. 
     Also, while in the embodiments mentioned above, the end portion of each nozzle head of the line head is illustrated as protruding from the lower surface of a carriage, note that the end portion (head bottom face) of the nozzle head may be made flush with the lower surface of the carriage to achieve a like function. 
     In this case, the wiping width of the blade  11  in the wiping unit  10  should preferably be made narrower than a width S 2  orthogonal to the direction of printing width and wider than a width S 1  of the nozzle face A as shown in  FIG. 3B . 
     By making so, it is possible to wipe each nozzle head over a minimum area. In this case, it is possible to wipe the nozzle head  3   a ,  3   b ,  3   c ,  3   d ,  3   e  without hindrance if its head bottom face is recessed from the lower surface of the carriage  4 .