Patent Publication Number: US-2004042833-A1

Title: Wire dot printer head

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to a wire dot printer head provided in a wire dot printer and more particularly to a wire dot printer head having armatures with printing wires connected to the armatures respectively, the armatures being each adapted to pivot about a pivot shaft and between a printing position and a stand-by position.  
       [0003] 2. Description of the Background Art  
       [0004] Heretofore there has been known a wire dot printer head wherein an armature with printing wire connected thereto is moved pivotally between a printing position and a stand-by position and a tip of the wire is caused to strike against printing paper when the armature is pivoted to the printing position, to effect printing.  
       [0005] In such a wire dot printer head it is necessary that the tip position of the wire be kept constant when the armature pivots to the printing position, thereby maintaining the printing pressure constant. To meet this requirement it has been proposed to provide a pivot shaft in the armature, allowing the armature to pivot stably about the pivot shaft.  
       [0006] In this case it is necessary that the pivot shaft be supported in a positionally fixed state by some suitable means. An example of a method for supporting the pivot shaft is pinching the pivot shaft between two opposed support members from both sides in the pivoting direction of the armature. In case of thus pinching the pivot shaft between two opposed support members, the pivot shaft comes into linear contact with the two support members.  
       [0007] Once the pivot shaft is pinched in linear contact with the two support members, a strong force is concentrated on the linear contact portions between the support members and the pivot shaft as the armature moves pivotally in printing, so that wear is apt to occur in the linear contact portions of the pivot shaft or the support members and the wear causes wobbling of the support shaft.  
       [0008] Once there occurs wobbling of the pivot shaft in printing due to such wear of the pivot shaft or the support members, there occur variations in the wire tip position during printing and there also occur variations in printing pressure, with consequent deterioration of the print quality.  
       [0009] Moreover, if wear dust resulting from the wear adheres to the armature, the pivotal motion of the armature may be obstructed.  
       [0010] Further, upon wobbling of the pivot shaft, the opposition area between members which constitute magnetic circuits for pivoting the armature varies, and when the opposition area becomes small, there increases a magnetic resistance, causing deterioration of the armature pivoting performance.  
       SUMMARY OF THE INVENTION  
       [0011] Accordingly, it is an object of the present invention to prevent the occurrence of wear of a pivot shaft serving as a fulcrum of an armature or wear of support members which pinch and support the pivot shaft and further prevent the occurrence of various inconveniences caused by wear of the pivot shaft or support members such as variations in printing pressure and consequent deterioration of the print quality, obstruction of a pivotal motion of the armature caused by the adhesion of resulting wear dust to the armature, and an increase of a magnetic resistance between members which constitute magnetic circuits and consequent obstruction of a pivotal motion of the armature.  
       [0012] The above object of the present invention is achieved by a novel wire dot printer head of the present invention.  
       [0013] According to the novel wire dot printer head of the present invention, a support groove having a concave shape is formed in at least one of support members which pinch and support a pivot shaft of an armature, and an outer periphery surface of the armature pivot shaft is allowed to get into the support groove in a state of surface contact with the groove, to increase the area of contact between the pivot shaft and the support members and prevent a local concentration of a strong force on the contact portions of the pivot shaft or the support members, thereby diminishing wear of the contact portions of the pivot shaft or the support members. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0014] A more complete understanding of the present invention and many associated advantages will be obtained from a reading and better understanding of the following detailed description when the same is read in connection with the accompanying drawings.  
     [0015]FIG. 1 is a front view in central vertical section of a wire dot printer head according to the present invention;  
     [0016]FIG. 2 is a sectional view taken on line A-A in FIG. 1 for explaining an armature support structure;  
     [0017]FIG. 3 is a sectional view taken on line B-B in FIG. 2 for explaining a pivot shaft support structure;  
     [0018]FIG. 4 is a partially cut-away exploded perspective view of a yoke and an armature spacer for explaining the armature support structure;  
     [0019]FIG. 5 is a front view in central vertical section of another wire dot printer head;  
     [0020]FIG. 6 is a sectional view taken on line a-a in FIG. 5 for explaining an armature support structure;  
     [0021]FIG. 7 is a sectional view taken on line b-b in FIG. 6 for explaining a pivot shaft support structure; and  
     [0022]FIG. 8 is a partially cut-away exploded perspective view of a yoke, an armature spacer, and a resin film for explaining the armature support structure. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0023] An embodiment of the present invention will be described hereinunder with reference to FIGS.  1  to  4 .  
     [0024] First, with reference to FIG. 1, a description will be given about the entire construction of a wire dot printer head  1  embodying the invention. The wire dot printer head  1  comprises a front case  2 , a circuit board  3 , a yoke  4  as a support member, an armature spacer  5  as a support member, a rear case  6 , plural armatures  7 , and a wire guide  8 . The front case  2  and the rear case  6  are coupled together with use of mounting screws (not shown), and the circuit board  3 , yoke  4 , armature spacer  5 , armatures  7 , and wire guide are held grippingly between the front case  2  and the rear case  6 . The plural armatures  7  are arranged radially.  
     [0025] The armatures  7  are each made up of an arm  9 , a wire  10  soldered to one end side of the arm  9 , magnetic circuit forming members  11  welded to both side faces of the arm  9 , and a cylindrical pivot shaft  12  provided on an opposite end side of the arm  9 . Each armature  7  is supported pivotably between a printing position and a stand-by position with the pivot  12  being as a center. With this pivotal motion of the armature, the wire  10 , which is guided by the wire guide  8 , performs a sliding motion. When the armature  7  pivotally reaches the printing position, a tip of the wire  10  strikes against printing paper to effect printing. At a front end portion of the front case  2  there is provided a tip guide  13  for holding the tip of each slidable wire  10  in a line in accordance with a predetermined pattern.  
     [0026] The yoke  4 , which is formed of a magnetic material, has a cylindrical portion  14  on an outer periphery side and a cylindrical portion  15  on an inner periphery side, with plural cores  16  being formed between the cylindrical portions  14  and  15 . Coils  18  are mounted on outer peripheries of the cores  16 . Plural recesses  19  are formed in an upper surface of the cylindrical portion  14 . The number of the cores  16 , that of the recesses  19 , and that of the armatures  7  are the same. The recesses  19  are formed on virtual straight lines L joining the center of the yoke  4  and the centers of pole faces  17  of the cores  16 , and the armatures  7  are arranged on the virtual straight lines L.  
     [0027] On one end side of each magnetic circuit forming member  11  is formed a supported member  20 , while on an opposite end side thereof is formed a attracted face  21 . When the armatures  7  are arranged on the virtual straight lines L, the supported portions  20  of the magnetic circuit forming members  12  get into the recesses  19  formed in the cylindrical portion  14  and the attracted faces  21  become opposed to the pole faces  17  of the cores  16 .  
     [0028] On both sides of each recess  19  and at positions orthogonal to the associated virtual straight line L there are formed support grooves for insertion therein of the pivot shaft  12 . An inner periphery surface of each support groove  22  is formed in a concave shape with a radius of curvature equal to that of an outer periphery surface of the pivot shaft  12 . The depth of each support groove  22  is set approximately equal to the radius of the pivot shaft  12 . As a result, when the armatures  7  are arranged on the virtual straight lines L, an approximately half in sectional area of each pivot shaft  12  gets into the associated support grooves  22  and the outer periphery surface of the pivot shaft  12  and the inner periphery surface of the support grooves  22  come into surface contact with each other.  
     [0029] The armature spacer  5  is made up of a ring-shaped portion  5   a  opposed to the cylindrical portion  14  of the yoke  4  and plural guide portions  5   b  which are radially arranged inside the ring-shaped portion  5   a.  Guide grooves  23 , in which the armatures  7  are arranged respectively, are formed in such a manner that each guide groove  23  is positioned between adjacent guide portions  5   b.  Support grooves  24  for insertion therein of the pivot shafts  12  of the armatures  7  are formed in a surface of the ring-shaped portion  5   a  which surface is opposed to the cylindrical portion  14 . The support grooves  24  are each formed in a concave shape with a radius of curvature equal to or a little larger than that of the outer periphery surface of each pivot shaft  12 . The depth of each of the support grooves  24  is set to be approximately equal to the radius of the pivot shaft  12 .  
     [0030] The armatures  7  are arranged on the virtual straight lines L and the armature spacer  5  is disposed at a predetermined position so that its ring-shaped portion  5   a  is opposed to the cylindrical portion  14 , further, the circuit board  3  and the wire guide  8  are disposed at predetermined positions and the front and rear cases  2 ,  6  are coupled together with use of mounting screws, whereby the pivot shafts  12  are sandwiched in between the support grooves  22  and  24  and the outer periphery surfaces thereof come into surface contact with the inner periphery surfaces of the support grooves  22 ,  24 .  
     [0031] A metallic annular armature stopper  25  is mounted at a center of the rear case  6 . The mounting of the armature stopper  25  to the rear case  6  is performed by fitting the armature stopper  25  into a mounting recess  26  formed in the rear case  6 . When an armature  7  pivots from the printing position to the stand-by position, the arm  9  as part of the armature  7  comes into abutment against the armature stopper  25  and thus the armature stopper defines the stand-by position of the armature  7 .  
     [0032] As to the construction of the wire dot printer using the wire dot printer head  1 , it is already known, so only the principle thereof will here be described briefly. As to the other components that the wire dot printer head  1  which constitute the wire dot printer, explanations will be given with drawings thereof omitted. The wire dot printer head  1  is mounted on a carriage which is reciprocated along a platen. Printing paper is fed between the platen and the wire dot printer head  1  by conveying rollers. In case of using a pressure-sensitive color-developing paper as the printing paper, the paper develops color under the pressure of wire  10  which is driven, to effect printing. In case of using plain paper as the printing paper, the plain paper undergoes the pressure of wire  16  through an ink ribbon, whereby the ink of the ink ribbon is transferred onto the plain paper to effect printing.  
     [0033] When a certain coil  18  is energized during a printing operation by the wire dot printer, a magnetic circuit is formed among the core  16  on which the coil  18  is mounted, the magnetic circuit forming members  11  of the armature  7  opposed to the core  16 , and the outer- and inner-periphery side cylindrical portions  14 ,  15  of the yoke  4 . As a result, the armature  7  moves pivotally about the pivot shaft  12  in a direction in which the attracted faces  21  of the magnetic circuit forming members  11  are attracted to the pole face of the core  16 . The pivoted position of the armature  7  at this time is the printing position shown in FIG. 1, and as a result of a pivotal movement of the armature to the printing position the tip of wire  10  projects to the printing paper side to effect printing.  
     [0034] When the coil  18  is de-energized, the magnetism so far developed becomes extinct and the armature  7  moves pivotally about the pivot shaft  12  toward the stand-by position with an urging force of an urging member (not shown). When the armature  7  pivotally reaches the stand-by position, its arm  9  is put in abutment against the armature stopper  25 , whereby the armature  7  is stopped at the standby position.  
     [0035] When the armature  7  pivots between the printing position and the stand-by position, the pivot shaft  12  is supported while being sandwiched between the associated support grooves  22  formed in the yoke  4  and the associated support grooves  24  formed in the armature spacer  5 , and the outer periphery surface of the pivot shaft  12  is put in surface contact with the inner periphery surfaces of the support grooves  22  and  24 . As a result, the area of contact between the pivot shaft  12  and the support grooves  22 ,  24  formed in the yoke  4  and the armature spacer  4  as support members for pinching and supporting the pivot shaft becomes larger. For this reason, when the armature  7  pivots between the printing position and the stand-by position, centered on the pivot shaft  12 , a locally strong force is not concentrated on the contact portions of the pivot shaft  12  or the support grooves  22 ,  24 , whereby the wear of the pivot shaft and the support grooves is diminished and wobbling of the support shaft does not occur.  
     [0036] Consequently, the wires  10  do not undergo variations in their tip positions during printing and the printing pressure can be kept constant over a long period, whereby a high printing quality can be ensured over a long period.  
     [0037] Besides, since the wear of the pivot shafts  12  and support grooves  22 ,  24  is diminished, the formation of wear dust is suppressed and the obstruction of the armature pivoting motion caused by the adhesion of wear dust to the armature  7  is prevented.  
     [0038] Moreover, since wobbling of the support shafts  12  does not occur, it is possible to keep maximum the area of the opposed portions between the supported portions  20  of the magnetic circuit forming members  11  and side faces of the recesses  19 . As a result, the magnetic resistance of the magnetic circuits can be kept low and the attractive force acting on each armature  7  can be kept high, whereby a satisfactory performance can be ensured for moving the armature  7  to the printing position.  
     [0039] Another embodiment of the present invention will now be described with reference to FIGS.  5  to  8 . The same portions as in FIGS.  1  to  4  will be identified by like reference numerals and explanations thereof will be omitted.  
     [0040] First, with reference to FIG. 5, a description will be given about the entire construction of a wire dot printer head  30 . A basic structure of the wire dot printer head  30  is the same as that of the wire dot printer head  1  shown in FIG. 1. The wire dot printer head  30  comprises a front case  2 , a circuit board  3 , a yoke  4  as a support member, an armature spacer  31 , a resin film  32 , a rear case  6  as a support member, plural armatures  7 , and a wire guide  8 . The front case  2  and the rear case  6  are coupled together with use of mounting screws (not shown), and the circuit board  3 , yoke  4 , armature spacer  31 , resin film  32 , armatures  7 , and wire guide  8  are held grippingly between the front case  2  and the rear case  6 . The plural armatures  7  are arranged radially.  
     [0041] The armature spacer  31  is made up of a ring-shaped portion  31   a  opposed to a cylindrical portion  14  of the yoke  4  and plural guide portions  31   b  which are radially arranged inside the ring-shaped portion  31   a.  Guide grooves  23  for insertion therein of the armatures  7  are formed in such a manner that each guide groove  23  is positioned between adjacent guide portions  31   b.  Grooves  33  for insertion therein of the pivot shafts  12  are formed in the ring-shaped portion  31   a  at positions opposed to support grooves  15 . The thickness of the ring-shaped portion  31   a,  i.e., the depth of each groove  33 , is set approximately equal to the radius of each pivot shaft  12 .  
     [0042] The resin film  32  is formed of a polyimide resin, possessing resistance to both wear and heat. The resin film  32  is formed in a ring shape to cover the ring-shaped portion  31   a  of the armature spacer  31  and is held in a sandwiched state between the ring-shaped portion  31   a  and the rear case  6 . Instead of the resin film  32  there may be used a metal such as stainless steel having been subjected to a rust preventing treatment.  
     [0043] The armatures  7  are arranged on virtual straight lines L, the armature spacer  31  is disposed in a predetermined position in which the ring-shaped portion  31   a  is opposed to the cylindrical portion  14 , the resin film  32  is disposed on the ring-shaped portion  31   a,  the circuit board  3  and the wire guide  8  are arranged at predetermined positions, and the front and rear cases  2 ,  6  are coupled together with use of mounting screws, whereby a semicircle portion of an outer periphery surface of each pivot shaft  12  comes into surface contact with inner periphery surfaces of the associated support grooves  22  and the outer periphery surface of the pivot shaft  12  comes into linear contact with the resin film  32 .  
     [0044] At the time of printing operation by the wire dot printer using the wire dot printer head  30  described above, an armature  7  pivots to the printing position upon energization of the associated coil  18 . When the coil  18  is de-energized, the armature pivots to the stand-by position and printing is performed with the pivotal motion.  
     [0045] When an armature  7  pivots between the printing position and the stand-by position, its pivot shaft  12  is pinched and supported between the associated support grooves  22  formed in the yoke  4  and the resin film  32 , and the outer periphery surface of the pivot shaft  12  comes into surface contact with the inner periphery surfaces of the support grooves  22  and comes into linear contact with the resin film  32 . Thus the pivot shaft  12  and the support grooves  22  are in surface contact with each other and the area of the contact is large, so when the armature  7  pivots between the printing position and the stand-by position, centered on the pivot shaft  12 , there does not occurs a local concentration of a strong force on the contact portions of the pivot shaft  12  and the support grooves  22  and hence the wear of the pivot shaft  12  and that of the support grooves  22  are diminished. On the other hand, the pivot shaft  12  and the resin film  32  are in linear contact with each other, but approximately a semicircle portion of the outer peripheral surface of the pivot shaft  12  is in surface contact with the support grooves  22  and its movement is restricted thereby, so such a movement as being rubbed is restricted also in the contact portion of the pivot shaft  12  with the resin film  32  and the occurrence of wear is suppressed despite of the linear contact. Further, since the pivot shaft  12  is in linear contact with the resin film  32  which is difficult to undergo wear, the wear of the pivot shaft is diminished in comparison with the case where the pivot shaft is brought into linear contact with the metallic rear case  6  directly.  
     [0046] Therefore, even if the armature  7  repeats a pivotal movement between the printing position and the stand-by position, the wear of the pivot shaft  12 , support grooves  22  and resin film  32  are diminished and wobbling of the pivot shaft  12  does not occur during printing. Consequently, variations in the tip positions of wires  10  do not occur during printing and hence the printing pressure can be kept constant and the print quality can be kept high both over a long period.  
     [0047] Moreover, since the wear of the pivot shafts  12 , support grooves  22  and resin film  32  is diminished, the occurrence of wear dust is suppressed and the obstruction of the pivotal motion of each armature  7  caused by the adhesion of wear dust thereto is prevented.  
     [0048] Further, since wobbling of the pivot shafts  12  does not occur, it is possible to keep maximum the area of the opposed portions between the supported portions  20  of the magnetic circuit forming members  11  and side faces of the recesses  19 . As a result, not only the magnetic circuits can be kept low in magnetic resistance, but also the attractive force acting on each armature  7  can be kept high and hence the performance of causing the armature  7  to move pivotally to the printing position can be maintained in a satisfactory condition.  
     [0049] In the light of the above description it is obvious that many modifications and changes of the present invention may be made. Accordingly, it is understood that within the scope of the appended claims the present invention can be practiced in other modes than those described above concretely.