Patent Publication Number: US-2009226233-A1

Title: Print head of printer and gap spacer used for print head

Description:
TECHNICAL FIELD 
     The present invention relates to a print head for a printer, and a gap spacer used for the print head. 
     BACKGROUND ART 
     A dot-impact type printer is known as a conventional printer, and a clapper type print head is also known. The print head is a type that a plurality of print levers are electromagnetically driven (see, for example, Unexamined Patent Application KOKAI Publication No. H2-39947 (p. 2 and 3, and FIG. 1)). 
       FIG. 10  shows the mechanism of a conventional clapper type print head. As shown in  FIG. 10 , in the conventional print head, a plurality of print wires  52  are slidably held by a yoke presser frame  51 . The rear end portion of each print wire  52  is fixed to the leading end of a print lever  53 . 
     A core  54  is formed of a soft magnetic material, and has iron cores  54   a.  The end face of the iron core  54   a  faces the end face of the print lever  53 . As a current is supplied to a drive coil  55 , the iron core  54   a  becomes magnetized. 
     As the iron core  54   a  is magnetized, the iron core  54   a,  the print lever  53  and a yoke plate  56  form a magnetic path. The print lever  53  is attracted to the respective iron core  54   a,  and the print wire  52  is urged toward a print surface direction (downward side in  FIG. 10 ). The print wire  52  protrudes from the print head, and the leading end of the wire is hit against the print surface. 
     Yoke plates  57 ,  58  are stacked above the yoke plate  56 . As shown in  FIG. 11 , the yoke plate  57  has a plurality of notches  57   a.  The print levers  53  are inserted into the respective notches  57   a.    
     As shown in  FIG. 12 , the yoke plate  58  has plural holes  58   a,  plural long holes  58   b,  and a stopper portion  58   c.    
     The rear end portion of a print lever  53  is inserted into a hole  58   a,  and this position becomes a support point for the print lever  53 . The middle portion of the print lever  53  is inserted into a long hole  58   b,  thereby fixing the position of the print lever  53 . The stopper portion  58   c  abuts the print lever  53  when the print lever  53  is attracted to the iron core  54   a,  and suppresses the print lever from hitting the iron core  54   a.    
     DISCLOSURE OF INVENTION 
     Problems to be Solved by the Invention 
     The print lever  53  repeatedly hits the stopper portion  58   c.  The yoke plate  58  is formed of a thin tabular metal. Therefore, as the print lever  53  repeatedly hits, the yoke plate  58  gradually deforms. 
     Wrinkles are formed in the yoke plate  58  due to the deformation of the yoke plate  58 . Namely, the stopper portion  58   c  of the yoke plate  58  is misaligned, thereby forming an overlapped part. Due to the wrinkles, it becomes difficult to maintain an appropriate gap between the yoke plate  58  and the print lever  53 , resulting in a difficulty of obtaining appropriate print pressure. 
     The present invention has been made in view of the foregoing conventional problems, and it is an object of the invention to provide a print head of a printer which can continuously maintain an appropriate gap between a yoke plate and a print lever. 
     Means for Solving the Problems 
     To achieve the object, a print head of a printer according to the first aspect of the invention comprises:
         a plurality of print wires each hitting a leading end portion against a print surface to do printing:   a plurality of return springs which urge the respective print wires in a direction opposite to the print surface;   a plurality of print lever mechanism each of which comprises a print lever and a moving yoke, and which is provided for each print wire, the print lever having a leading end portion that abuts a rear end portion of a corresponding print wire, the moving yoke formed of a magnetic material and attached to a rear end portion of the print lever, and the print lever pressing the print wire in a direction of the print surface;   a yoke which is formed of a soft magnetic material, has a plurality of iron cores each having an end face that faces an end face of the respective moving yoke, the magnetized iron core attracting the moving yoke, thereby causing the print lever to urge a corresponding print wire in the direction of the print surface against urging force of the return spring;   a yoke plate which is formed of a soft magnetic material, and forms a magnetic path between the yoke and the moving yoke of each print lever mechanism; and   a gap spacer which is inserted between the plurality of print levers and the yoke plate to set a clearance between the print lever and the yoke plate, and has a plurality of print-lever abutting portion each allowing the attracted print lever to abut, thereby absorbing impact from each print lever to the yoke plate, and wherein   the gap spacer has notches each formed between adjoining ones of the plurality of print-lever abutting portions, and the individual print-lever abutting portions are separated and independent from one another.       

     To achieve the object, a gap spacer for a print mechanism according to the second aspect of the invention comprises a plurality of print lever mechanisms which have a plurality of print levers pressing respective print wires in a direction of a print surface and moving yokes attached to respective print levers, a yoke which allows iron cores to attract respective moving yokes to urge the print wires in the direction of the print surface, and a yoke plate which forms a magnetic path between the yoke and the moving yoke, the gap spacer is inserted between the plurality of print levers and the yoke plate, and has a plurality of print-lever abutting portions where the respective print levers, attracted to the yoke plate by the moving yokes attracted to the iron cores, abut and wherein
         the plurality of print-lever abutting portions of the gap spacer have notches each formed between adjoining print-lever abutting portions, and are separated from one another.       

     The gap spacer may be formed of a material having smaller coercive force than coercive force of the yoke plate. 
     It is desirable that the gap spacer should have coercive force formed by a material having a higher strength and flexibility than those of the yoke plate. 
     For example, a leading end portion of each print-lever abutting portion of the gap spacer is separated from a leading end portion of the adjoining abutting portion by the notch, and the base portion thereof is formed integral with a base portion of the adjoining abutting portion. 
     For example, each print-lever abutting portion of the gap spacer is formed in a shape having a narrow leading end portion and a wide base portion. 
     The notch is formed in, for example, a triangular shape which becomes wide at the leading end portion of the print-lever abutting portion, and becomes narrow at the base portion of the print-lever abutting portion. 
     For example, each print-lever abutting portion of the gap spacer is formed as to be wider than the print lever. 
     It is desirable that the notch should be formed as to extend to a position near the moving yoke or to a position beyond that position. 
     The gap spacer comprises, for example, a ring-like member and the plurality of finger-like abutting portions extending from the ring-like member toward a center of the ring. 
     EFFECT OF THE INVENTION 
     According to the invention, because the abutting portion of a print lever is separated away from the abutting portion of an adjoining print lever by a notch, it is possible to continuously maintain an appropriate gap between a yoke plate and a print lever. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       [ FIG. 1 ] A cross-sectional view showing the structure of a print head of a printer according to an embodiment of the invention. 
       [ FIG. 2 ] A partial enlarged view of  FIG. 1 . 
       [ FIG. 3 ] (a) is a plan view and (b) is a side view of a print lever mechanism shown in  FIG. 1 . 
       [ FIG. 4 ] (a) is a plan view and (b) is a cross-sectional view of a lever guide shown in  FIG. 1 . 
       [ FIG. 5 ] (a) is a plan view and (b) is a cross-sectional view of a lever spring shown in  FIG. 1 . 
       [ FIG. 6 ] (a) is a plan view and (b) is a cross-sectional view of a yoke case shown in  FIG. 1 . 
       [ FIG. 7 ] (a) is a plan view and (b) is a cross-sectional view of a yoke plate shown in  FIG. 1 . 
       [ FIG. 8 ] A plan view of a gap spacer shown in  FIG. 1   
       [ FIG. 9 ] Both (a) and (b) are plan views showing modified examples of the gap spacer shown in  FIG. 8 . 
       [ FIG. 10 ] A relevant-part cross-sectional view showing a conventional print head for a printer. 
       [ FIG. 11 ] A plan view of a yoke plate ( 1 ) shown in  FIG. 10 . 
       [ FIG. 12 ] A plan view of a yoke plate ( 2 ) shown in  FIG. 10   
     
    
    
     DESCRIPTION OF REFERENCE NUMERALS 
       1  Print head 
       11  Wire case 
       12  Print wire 
       14  Print lever mechanism 
       14   a  Print lever 
       14   b  Moving yoke 
       20  Yoke case 
       21  Yoke plate 
       24  Gap spacer 
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, an explanation will be given of a print head for a printer according to an embodiment of the invention with reference to the drawings. 
       FIG. 1  shows the structure of a print head  1  for a printer according to the embodiment.  FIG. 2  is a partial enlarged view of  FIG. 1 . 
     The print head  1  for a printer of the embodiment has a wire case  11 , print wires  12 , return springs  13 , print lever mechanisms  14 , a lever guide  15 , a stopper  16 , a lever spring  17 , spacers  18 ,  19 , a yoke case  20 , a yoke plate  21 , a drive coil  22 , a bobbin  23 , a gap spacer  24 , a head cover  25 , and a latch spring  26 . 
     The wire case  11  is for setting the components of the print head like the print wires  12 , and is formed of, for example, a plastic. The wire case  11  has a lateral cross-section formed in a circular shape with respect to a central axis  110 .  FIG. 1  shows the cross-section of the wire case  11  in an axial direction. The wire case  11  has a stepped portion  11   a  for holding individual components, such as the spacers  18 ,  19 , and the yoke case  20 . 
     Formed in the wire case  11  are nine holes  11   b  for print wires  12  and nine grooves  11   c  for latching the return springs  13 . The nine holes  11   b  are disposed substantially evenly for each 40° around the central axis  110  of the wire case  11 . Each hole  11   b  is formed in an inclined direction to a print surface, and passes through the wire case  11 . 
     The print wires  12  are for printing and allows the leading end portions thereof to hit against the print surface like a piece of paper for printing. Nine print wires  12  are provided, and inserted into the respective holes  11   b  formed in the wire case  11 . The rear end portion of the print wire  12  is thicker than the leading end portion to efficiently transmit force from the print lever mechanism  14 . 
     The return springs  13  are for urging the respective print wires  12  in a direction opposite to the print surface. Nine return springs  13  are provided for respective nine print wires  12 . The return spring  13  comprises a coil spring into which a print wire  12  is inserted. The bottom end portion of the return spring  13  is inserted into a groove  11   c  of the wire case  11 , and held by the wire case  11 . 
     The print lever mechanisms  14  are for hitting the respective print wires  12  against the print surface. The print lever mechanism  14  is formed in, for example, a shape shown in  FIGS. 3(   a ) and ( b ).  FIG. 3(   a ) is a plan view of the print lever mechanism  14 , and  FIG. 3(   b ) is a side view thereof. As shown in  FIGS. 3(   a ) and ( b ), the print lever mechanism  14  comprises a print lever  14   a  and a moving yoke  14   b . The leading end portion of the print lever  14   a  abuts the print wire  12 . The rear end portion of the print lever  14   a  protrudes from both sides. 
     The moving yoke  14   b  is formed of a soft magnetic material, and is formed in a cylindrical shape. The moving yoke  14   b  is fixed to the rear end portion of the print lever  14   a  by, for example, caulking. 
     The lever guide  15  is for fixing the rear end portion of the print lever  14   a.  It is formed as to have, for example, a planer shape shown in  FIG. 4(   a ) and a side face shown in  FIG. 4(   b ).  FIG. 4(   b ) is a cross-sectional view along a line A-A in  FIG. 4(   a ). As shown in  FIGS. 4(   a ) and ( b ), the lever guide  15  is provided with fitting portions  15   a.  As the fitting portion  15   a  and the protrusions of the rear end portion of the print lever  14   a  fit together, the lever guide  15  supports the print lever  14   a  movable in the vertical direction. The print lever  14   a  moves in the vertical direction with the fitting portion  15   a  taken as a support point. 
     The stopper  16  is for latching the leading end portion of the print lever  14   a  when the print wires  12  are housed in the wire case  11 , and is disposed around an axial portion  11   d  of the wire case  11 . 
     The lever spring  17  is for holding and latching the rear end portion of the print lever  14   a  to prevent the rear end portion of the print lever  14   a  from coming apart from the lever guide  15 . The lever spring  17  is formed in, for example, a shape shown in  FIGS. 5(   a ) and ( b ).  FIG. 5(   a ) is a plan view of the lever spring, and  FIG. 5(   b ) is a cross-sectional view along a line B-B in  FIG. 5(   a ). The lever spring  17  has nine nail portions  17   a.  The nail portions  17   a  are respectively disposed around the central axis for each 40° or so. The leading end of each nail portion  17   a  holds down the rear end portion of the print lever  14   a.    
     The yoke case  20  is for attracting the moving yoke  14   b  of the print lever mechanism  14  to drive the print lever  14   a.  The yoke case  20  is formed of, for example, a soft magnetic material, such as electromagnetic soft iron or silicon steel. The yoke case  20  is held on the stepped portion  11  a of the wire case  11  via the spacers  18 ,  19 . 
     The yoke case  20  is formed in, for example, a shape shown in  FIG. 6 .  FIG. 6(   a ) is a plan view of the yoke case  20 , and  FIG. 6(   b ) is a cross-sectional view along a line C-C in  FIG. 6(   a ). As shown in  FIGS. 6(   a ) and ( b ), the yoke case  20  has nine iron cores  20   a.  The iron cores  20   a  are formed on the yoke case  20  in such a way that the end faces thereof face respective end faces of nine moving yokes  14   b  of the print lever mechanisms  14 . As the yoke case  20  is magnetized, the iron core  20   a  attracts the moving yoke  14   b.    
     The yoke plate  21  is for forming a closed magnetic path, and is formed of, for example, a soft magnetic material, such as electromagnetic soft iron or silicon steel. For example, the yoke plate  21  is formed in a shape shown in  FIGS. 7(   a ) and ( b ). FIG.  7 ( a ) is a plan view of the yoke plate  21 , and  FIG. 7(   b ) is a cross-sectional view along a line D-D. As shown in  FIGS. 7(   a ) and ( b ), the yoke plate is provided with nine holes  21   a  through which the respective moving yokes  14   b  of the print lever mechanisms  14  pass. The nine holes  21  are formed in the yoke plate  21  around a central axis  110  for each 40° or so. 
     The drive coil  22  is for magnetizing the yoke case  20  and the yoke plate  21  as a current is supplied thereto. The drive coil  22  is wound on the bobbin  23 . The bobbin  23  is formed in such a shape as to surround the circumference of the iron cores  20   a  of the yoke case  20 . 
     The gap spacer  24  is for maintaining a gap between the yoke plate  21  and the print lever  14   a  appropriately. A gap spacer  24  having a thickness in accordance with the heights of the yoke case  20  and the yoke plate  21  is used to eliminate the variability in heights between the yoke case  20  and the yoke plate  21 . 
     The gap spacer  24  has following functions. 
     First, the gap spacer  24  enables the print head  1  to do high speed operation. More specifically, in a case where the print lever  14   a  is directly disposed on the yoke plate  21 , the print lever  14   a  sticks to the yoke plate  21  because of the remaining magnetism of the yoke plate  21 , and is not quickly released from the yoke plate  21 . The larger the coercive force is, the larger the remaining magnetism becomes. When such a phenomenon occurs, the operation of the print head  1  becomes slow. As the gap spacer  24  is inserted between the yoke plate  21  and the print lever  14   a,  the gap spacer  24  reduces the effect of the coercive force of the yoke plate  21 , thereby suppressing the occurrence of such a phenomenon. 
     Second, the gap spacer  24  maintains an appropriate gap between the print lever  14   a  and the yoke plate  21 . When the gaps between the individual print levers  14   a  and the yoke plate  21  vary, the delays in the operations of the respective print levers  14   a  due to the remaining magnetism vary. By maintaining the appropriate gap between the print lever  14   a  and the yoke plate  21 , the responsiveness of the print levers  14   a  are equalized. Further, when the gaps between the individual print levers  14   a  and the yoke plate  21  vary, the strokes of the print wires also vary, thus causing variability in the print quality. The gap spacer  24  maintains the appropriate gap between the print lever  14   a  and the yoke plate  21 , thereby equalizing the print qualities. 
     Third, the gap spacer  24  reduces the impact of the print lever  14   a  to the yoke plate  21 . That is to say, when the moving yoke  14   b  is attracted to the iron core  20   a  of the yoke case  20 , the print lever  14   a  abuts the gap spacer  24 . The yoke plate  21  is formed of, for example, electromagnetic soft iron or silicon steel, and is frangible, so that the gap spacer  24  absorbs the impact force of the print lever  14   a  to reduce the impact of the print lever  14   a  to the yoke plate  21 , thereby protecting the yoke plate  21 . 
     To make the gap spacer  24  having such functions, used for the gap spacer  24  is a material which has weaker coercive force than that of the yoke plate  21  and has a strength and a flexibility to make the gap spacer to sufficiently withstand even if impact is applied from the print lever  14   a.  As such a material, austenitic stainless steel is used for the gap spacer  24 . 
     As shown in  FIG. 8 , the gap spacer  24  has nine print-lever abutting portions  24   b  where respective print levers  14   a  abut. The print-lever abutting portion  24   b  is a part which allows the print lever  14   a  urged by the yoke case  20  and the yoke plate  21  to abut, and as the print lever  14   a  abuts the print-lever abutting portion  24   b,  the impact of the print lever  14   a  to the yoke plate  21  is absorbed. 
     The gap spacer  24  is provided with notches  24   a  between adjoining print-lever abutting portions  24   b  so as not to have a wrinkle even when impact is applied from the print lever  14   a,  and is constituted in such a way that the nine print-lever abutting portions  24   b  where respective print levers  14 , one of which is shown in the figure by dashed lines, are separated and independent from one another. More specifically, as shown in  FIG. 8 , the gap spacer  24  comprises a ring-like rim portion, and the nine finger-like print-lever abutting portions  24   b  protruding toward the center of the ring from the rim portion. Each print-lever abutting portion  24   b  is formed in a trapezoidal shape having a narrow leading end and a wide base portion. The leading end portion of each print-lever abutting portion  24   b  is separated from an adjoining print-lever abutting portion  24   b  by a notch  24   a,  and the base portion is formed integral with the base portion of an adjoining print-lever abutting portion  24   b.  The notch  24   a  is formed in an approximately triangular shape which becomes wide adjacent to the leading end portion of the print-lever abutting portion  24   b,  and becomes narrow as the notch becomes deep. Each print-lever abutting portion  24   b  is so formed as to have a wider width than that of the print lever  14   a.    
     The head cover  25  is for fixing the lever spring  17 . The latch spring  26  is for fixing individual components of the print head  1  by pressing down the head cover  25 . 
     The following is an explanation of the operation of the print head  1  for a printer. To cause the print wires  12  to protrude, a current is supplied to the drive coil  22 . The iron cores  20   a  of the yoke case  20  attract the respective moving yokes  14   b.  As the end face of the moving yoke  14   b  contacts the end face of the iron core  20   a  tightly, the yoke case  20 , the iron cores  20   a,  the moving yokes  14   b,  and the yoke plate  21  form a closed magnetic path. 
     As the end faces of the moving yokes  14   b  contact respective end faces of the iron cores  20   a  tightly, the print levers  14   a  press the respective print wires  12  against the urging forces of the respective return springs  13 . The print wire  12  is pressed by the print lever  14   a,  and the leading end of the print wire  12  protrudes from the wire case  11 , and hits the print surface to do printing. 
     To return the print wire  12 , the current supplied to the drive coil  22  is shut off. As the supplied current is shut off, the magnetic force of the iron core  20   a  disappears. The return spring  13  urges the print wire  12  in a direction opposite to the print surface. This urging force releases the moving yoke  14   b  from the iron core  20   a,  and the leading end portion of the print lever  14   a  moves to a side opposite to the print surface. The stopper  16  latches the leading end of the print lever  14   a.    
     By repeating such operations, impacts from the print lever  14   a  is continuously applied to the gap spacer  24 . Because the nine print-lever abutting portions  24   b  of the gap spacer  24  are separated and independent from one another by the notches  24   a  arranged between adjoining print-lever abutting portions  24   b,  each print-lever abutting portion is not affected by another print-lever abutting portion  24   b . Therefore, no wrinkle is formed in the gap spacer  24 , and the gap between the yoke plate  21  and the print lever  14   a  is maintained appropriately. 
     As explained above, according to the embodiment, the gap spacer  24  is provided with the notches  24   a,  so that the nine print-lever abutting portions  24   b  are structured in such a manner as to be separated and independent from one another. 
     Accordingly, because the holding positions of individual print levers  14   a  are ensured independently, even if impact is applied from the print lever  14   a  to the gap spacer  24  and the print-lever abutting portion  24   b  is deformed, the individual print-lever abutting portions  24   b  is not affected by one another. Therefore, no wrinkle is formed in the gap spacer  24 , and an appropriate gap between the yoke plate  21  and the print lever  14   a  is continuously maintained, thereby maintaining the stable performance. 
     Note that various embodiments can be thinkable to embody the invention, and the invention is not limited to the foregoing embodiment. 
     For example, the print lever mechanism  14  may have the print lever  14   a  and the moving yoke  14   b  formed integral with each other, like the conventional ones. In this case, a yoke plate  58  corresponding to the gap spacer  24  is structured in such a way that stopper portions  58   c  are separated and independent from one another. 
     The shapes of the notch  24   a  and the print-lever abutting portion  24   b  of the gap spacer  24  shown in  FIG. 8  are not limited to ones shown in the figure as long as it prevents the formation of a wrinkle. For example, as shown in  FIG. 9(   a ), the depth of the notch  24   a  may be deeper than that shown in  FIG. 8 , and for example, may extend beyond the position of the moving yoke  14   b.  Note that it is desirable that the notch  24   a  should be formed near the connection portion of the moving yoke  14   b  and the print lever  14   a,  or should be formed deeper than that. 
     Further, the shape of the innermost end portion of the notch  24   a  is not limited to an arc-like shape, but may be a rectangular shape as shown in  FIG. 9(   b ). The width of the notch  24   a  may be uniform as shown in  FIG. 9(   b ). 
     The shape of the print-lever abutting portion  24   b  is not limited to a tapered shape, and may be an arbitral shape. 
     It is desirable that all print-lever abutting portions  24   b  should be separated and independent from one another, but the notch  24   a  may be formed for each two or three print-lever abutting portions  24   b.    
     The leading end of the print-lever abutting portion  24   b  may be also formed in an arc-like shape, or may be formed in a rectangular shape shown in  FIG. 9(   b ). The clearance between the leading ends of the print-lever abutting portions  24   b  may be smaller than that shown in  FIG. 8 . The plate thickness at the leading end portion side of the print-lever abutting portion  24   b  may be thicker or thinner than that at the rear end portion side. By employing such a structure, formation of a wrinkle in the gap spacer  24  is suppressed, and an appropriate gap can be maintained. The material of the gap spacer  24  is not limited to austenitic stainless steel, and may be a metal other than stainless if it has durability. The gap spacer  24  may be formed of a material other than metal. 
     The structures of the components other than the gap spacer  24  can be changed and modified arbitrarily. For example, in  FIG. 1 , the print wire  12  is urged by the return spring  13  to urge the print wire  12  in a direction opposite to the print surface, but like the conventional example shown in  FIG. 10 , the print lever  14   a  itself may be urged. 
     It is to be noted that the disclosed embodiment is just for exemplification and is not for limitation. The scope of the invention is indicated not by the foregoing explanation but by the appended claims, and it is intended that equivalences and all changes within the scope of the invention should be included. 
     This application is based on Japanese Patent Application No. 2005-231410 filed on Aug. 9, 2005. The entire specification, claims, and drawing of Japanese Patent Application No. 2005-23410 should be incorporated in this specification by reference. 
     INDUSTRIAL APPLICABILITY 
     According to the invention, it is possible to continuously maintain an appropriate gap between a yoke plate and a print lever. The frequency of replacing a component is reduced, thereby extending the Mean Time Between Failure (MTBF).