Patent Publication Number: US-6989482-B2

Title: Stringed instrument string winder and method of manufacturing the chord winder

Description:
BACKGROUND OF THE INVENTION 
   1. Technical Field 
   The present invention relates to a winding device for a stringed instrument such as a guitar, and relates to a manufacturing method therefore, and more particularly, the present invention relates to a technique for decreasing backlash of gears by preventing the generation of play in a worm gear and a bearing. 
   2. Background Art 
     FIG. 9  shows an example of a peg for a conventional classical guitar. As shown in this figure, a worm gear  3  having a knob  2 , fixed to one end thereof, is rotatably supported on a main body  1  which is mounted to the guitar head. A worm wheel  4  meshing with the worm gear  3  is rotatably supported on the main body  1 , and a winding shaft  5  which is coaxial with respect to the worm wheel  4  is mounted to the worm wheel  4  by a screw  6 . 
   An ordinary steel plate is press molded and a plurality of bearings  7  are formed so as to be bent at an angle substantially equal to 90 degrees and is erected on the main body  1 . The side of the shaft receiving portion is open so as to have a U-shaped recessed portion  7   a . Grooves  3   a  which are formed in both end portions of the worm gear  3  engage with the recessed portion  7   a  and thereby support both end portions of the worm gear  3 . 
   In addition, the wall portion of the worm gear  3  is nipped from both sides by two bearings  7  and  7 , and hence resistance is given to the rotation of the worm gear  3  and this thus prevents rotation in the reverse direction (rotation causing loosening of the string). In the PEG, a string is wound on the winding surface  5   a  of the winding shaft  5 , and the tuning of the stringed instrument is performed by rotating the knob  2  so that the string is wound or unwound. 
   However, in the PEG described in the foregoing, the backlash of the worm gear  3  and the worm wheel  4  is large. Furthermore, because the backlash gradually increases as the instrument is used, tuning becomes more difficult, and this may cause decreased performance. 
   That is to say, the side of the bearing  7  of the peg described in the foregoing is open, and thus its assembly is simple. However, in order to achieve this simple assembly, a large clearance must be provided between the worm gear  3  and the worm wheel  4 , and the worm gear  3  is movable with respect to the worm wheel  4  according to the size of the clearance. As a result, the backlash between the worm gear  3  and the worm wheel  4  is large. Therefore, when the knob  2  is rotated by a small amount, the winding shaft does not rotate, and therefore fine tuning is difficult. 
   Furthermore, when the worm gear  3  as viewed from the side shown in  FIG. 9  is rotated in a clockwise direction, the moment of the clockwise rotation having a center at the point P shown in  FIG. 3  is added to the worm gear  3 , and thus the worm gear  3  moves to the worm wheel  4  side. As a result, the seizure of teeth surfaces of both the worm gear  3  and the worm wheel  4  cause the teeth surfaces to wear and the backlash of the gears is even larger. Furthermore, in the peg described above, since the bearing  7  is formed of a ordinary steel plate which is low in strength, and also since the side of the bearing  7  is open, less of the wall portions can be supported than in comparison with the bearing of a round hole. 
   On the other hand, in consideration of bearing manufacturing error and ease of assembly, the grooves  3   a  of the worm gear  3  are made wider than the thickness of the bearing  7 . As a result, due to the thrust load received from the worm gear  3 , the bearings  7  and  7  which initially nipped the grooves  3   a  and  3   a  of the worm gear  3  from both sides, are deformed and open up. Consequently, the worm gear  3  also becomes movable in the thrust direction (axial direction). In a case in which a play is formed in the thrust direction, even when the worm gear  3  is rotated, it continues to idle until the groove  3   a  comes into contact with the bearing  7 . Thus, the play in rotating the knob  2  is large, and tuning is extremely difficult. 
   Furthermore, when there is play at the worm gear  3  and the bearing  7  and the worm gear  3  is in a free state, the vibrations of the string may be transmitted to the worm gear  3 , thereby causing an unusual noise during performance. The worm gear  3  rotates in the opposite direction due to the vibrations, and thus the notes become out of tune. 
   If the bearing is made so as to have a round hole, the worm gear  3  is prevented from moving in the direction of the worm wheel  4 , and the problem of the large backlash as well as the problem that the backlash is increased due to the wear of the teeth surfaces are solved. However, although the strength of the bearing is increased because it is made to have a round hole, this alone does not sufficiently prevent transformation caused when the worm gear receives the thrust load. Accordingly, the problems of the generation of play due to the deformation of the bearing and the generation of unusual noises caused by this deformation, and of reverse rotation of the worm gear, remain unsolved. 
   In an effort to solve these problems, a peg is provided in which the main body and the bearing are formed separately and both parts are joined together by a welding or calking process. In this type of peg, each of the bearings is completely nipped at both sides using the flange, the washer, and the screw formed on the worm gear. In this type of peg, the thrust load in all directions is supported on a pair of bearings, and thus the resistance of transformation of the bearing is high. However, in this bearing, it is necessary to provide many parts in order to nip the respective bearings, and it is also necessary to carry out a calking process for preventing disengagement of the worm gear. Thus, there is a problem in that the number of processes to be carried out in assembly is increased. 
   In addition, examples of the peg which has been integrally formed by press molding the main body and the bearing, include those in which a ring is rotatably supported at one end of the worm gear, and a screw which is formed at the outer periphery of the ring is screwed together with a screw formed at the inner periphery of the bearing. In the peg having this type of structure, the ring is moved and the worm end surface of the worm gear is pressed with force, and thus the bearing can be secured to the worm gear so as to open to the outer side, and the play of the bearing and the worm gear in the thrust direction is eliminated. In addition, there is also an example in which a screw is formed on a shaft of a worm gear and a bearing is secured to the worm gear with a ring which engages with the screw. However, in this type of peg as well, the number of complicated parts is increased, and the manufacturing cost is relatively high. 
   An object of the invention is to provide, without significantly increasing the manufacturing cost, a peg in which the deformation of the bearing in the thrust direction is controlled, the play of the worm gear and the bearing in the thrust direction is eliminated, and accordingly, tuning is carried out easily, and problems of the generation of unusual noises and reverse rotation of the worm gear do not occur. 
   SUMMARY OF THE INVENTION 
   The present invention provides a peg, for a stringed instrument, having a main body for mounting to a head portion of the stringed instrument; a pair of bearings integrally formed with the main body and erected at both sides of the main body so as to oppose each other; a worm gear having two ends which are rotatably supported in round holes disposed so as to oppose each other on the pair of bearings, a knob provided at an end portion of the worm gear, and a winding shaft connected to the worm gear via a worm wheel, the bearing being formed of a material having spring properties (elastic properties). 
   In the peg having the above-described structure, the bearing is formed of a material having spring properties and has a round hole, so that even when a thrust load is applied from the worm gear, the bearing is not deformed easily. Accordingly, formation of play between the worm gear and the bearing can be inhibited, and thus the problems of increased backlash and unusual noises, and problems in tuning resulting from reverse rotation of the worm gear, can be inhibited. 
   Examples of the spring material used here of course include a stainless steel plate for forming springs, spring steels (SUP) and phosphor bronze for forming springs. Also, ordinary materials which have been subjected to heat processing and the like in order to increase the elastic limit may be used. For example, by using a ordinary steel plate such as a cold rolled soft steel plate (SPC) material which has been subjected to a carburizing process to a depth of preferably 0.05 to 0.3 mm from its surface and more preferably 0.1 to 0.15 mm from its surface, so that the tension is increased and the elastic limit is also increased, thus imparting a spring properties to the steel plate. Alternatively, a ordinary steel plate which has been subjected to nitration or carbonitration may be used. However in cases in which these materials are used, the elastic limit (spring properties) is insufficient, and plating processes become difficult. Therefore, it is preferable to carry out a carburizing process. It should be noted that it is sufficient for only the bearing (including those portions that border the main body) to be subjected to the carburizing process. 
   The bearings are inclined with respect to the base portion so as to open slightly outwards in a direction in which they are erected, and a tightening device for tightening the bearing to the worm gear from both sides thereof are provided at both ends of the worm gear. 
   In this embodiment, by the bearing being secured to the worm gear with the tightening device, the bearing deforms elastically, and due to the counter force caused by the spring properties of the bearing, frictional resistance is given between the bearing and the worm gear. As a result, play in the thrust direction of the bearing and the worm gear is eliminated, and when the knob is turned, a suitable amount of resistance is generated, and tuning can be easily performed. 
   Furthermore, even if vibrations are transmitted to the worm gear, problems such as unusual noises and reverse rotation of the winding shaft can be inhibited. In addition, by securing the outward opening bearings to the worm gear in advance, the bearings are parallel, or substantially parallel, to each other, and thus the counter force due to the spring property acts directly in the axial direction, and the frictional resistance with respect to the worm gear is efficiently generated. Furthermore, the worm gear is fit into the round hole of the bearing when the hole is completely round, and thus the characteristics of the bearing can be favorably maintained. It should be noted that the angle of inclination of the bearing with respect to the plane perpendicular to the main body is preferably in a range of 0 to 6° for obtaining a suitable securing force. 
   More specifically, the tightening means preferably comprises a flange portion disposed at a base end portion side of the worm gear and a push nut which is press-inserted into a leading end of the worm gear, the leading end of the worm gear and the groove extending along a peripheral direction thereof, the groove engages with an inner periphery of the push nut. 
   It is more preferable that plural grooves of this type be provided. The push nut generally has a washer member whose center is concave in the thickness direction thereof, and has slits formed radially from the center. The shaft can be inserted through the center of the push nut in the direction in which the slits open, but in the opposite direction, the slits are closed and the push nut engages with the shaft and cannot come out therefrom. 
   On the other hand, the worm gear is generally used after being subjected to a plating process, and thus the coefficient of friction is usually low and there is a possibility that the push nut may be disengaged from the worm gear. Thus, as described above, it is preferable that the leading end of the worm gear be formed so as to be engaged with the inner periphery of the push nut. As a result, the worm gear is prevented from becoming disengaged from the bearing, and the setting of the securing force in the thrust direction can be carried out in a single operation, thus reducing the number of steps in the assembly process. 
   In addition, by serially disposing a plurality of grooves, the securing force can be suitably adjusted in the thrust direction, and the groove positions and the interval between the respective grooves (for example, 0.1 mm) can be severely controlled. By standardizing such that the push nut which will be engaged with a particular groove has predetermined characteristics, the securing force in the thrust direction of the bearing can be made uniform, thereby stabilizing the quality of the product. Furthermore, even if the bearing deforms towards the inner side, the push nut can be tightened even further, thereby eliminating play of the worm gear and the bearing. 
   The bearing side surface of the flange portion provided at the base end side of the worm gear may be at right angles with respect to the shaft, or may be tapered so as to correspond to the incline of the bearing. In addition, it is desirable that a synthetic resin washer or a metal washer having a lubricating coating on a surface thereof, be placed between the flange portion and the bearing, and between the push nut and the bearing. As a result, contact of the metal surfaces is prevented, and the worm gear is not heated due to surface seizure when rotated. Consequently, a soft and smooth feel can be obtained when tuning is being carried out. 
   The material for the washer may be can a synthetic resin including a polyacetal resin having 10% or more by weight of polytetrafluoroethylene, a metal washer having a solid lubricant such as molybdenum disulfide or the like coated on the surface thereof, or a metal washer whose surface was plated and subsequently coated with a Teflon (trademark) mixture film. 
   The peg is preferably manufactured by a method having the steps of press forming a plate metal composed of an ordinary steel plate so as to from a main body in which bearings having round holes are erected from both sides thereof so as to oppose each other, subjecting the main body to carburization, and a finishing process such as plating, and rotatably mounting to the bearing having the round holes, a worm gear having a knob at one end thereof, mounting a winding shaft including a worm wheel meshing with the worm gear to the main body. In this manufacturing method, since an ordinary steel plate is molded, material cost is considerably lower than in the case in which material for forming springs is used. In addition, since the material used is not an ordinary steel plate which has been formed into a spring or is carburized, the processing cost also is considerably lower. 

   
     BRIEF EXPLANATION OF THE DRAWINGS 
       FIG. 1  is an assembly view of a peg of an embodiment of the present invention. 
       FIG. 2  is a plan view of the main body of the embodiment. 
       FIG. 3A  is a side view of the main body of the embodiment, and  FIG. 3B  is a cross-sectional view taken along line B—B in  FIG. 2 . 
       FIG. 4A  is side view of a main body which corresponds to that of  FIG. 3 , and  FIG. 4B  is a cross sectional view thereof. 
       FIG. 5  is a side view of the worm gear of the embodiment. 
       FIG. 6  is a lateral partial cross-sectional view of the peg of the embodiment. 
       FIG. 7  is a lateral partial cross-sectional view of the peg of another embodiment of the present invention. 
       FIG. 8  is a side view of the worm gear of the embodiment. 
       FIG. 9  is a perspective view of a conventional peg. 
   

   BEST MODE FOR CARRYING OUT THE INVENTION 
   The following is a description of embodiments of the present invention with reference to  FIGS. 1 to 6 . 
     FIG. 1  is an assembly view of a peg of an embodiment. In  FIG. 1 , reference numeral  10  indicates a main body, reference numeral  20  indicates a worm gear assembly, reference numeral  30  indicates a winding shaft, and reference numeral  40  indicates a worm wheel. These structures will be described in order.  FIG. 2  is a plan view of the main body  10 . As shown in this figure, the main body  10  in plan view has a substantially rectangular shape and is basically formed of a flat base portion  11 , and bearings  12  are erected at both sides of the base  11 . A support hole  13  is formed in the base  11  for rotatably supporting the winding shaft  30 . Also holes  14  are formed in the base  11  for mounting the peg to the head of a classical guitar with screws. 
   A large diameter hole  15  is formed in one bearing  12  for rotatably supporting the base portion of the worm gear assembly  20 , a small diameter hole  16  is formed in the other bearing  12  for rotatably supporting a leading end of the worm gear assembly  20 . As shown in  FIG. 3B , the bearings  12  are respectively inclined outwards with respect to the base  11 . The angle of inclination is a maximum of 6° with respect to the vertical direction of  FIG. 3B . 
   It should be noted that the main body shown in  FIGS. 2 ,  3 A, and  3 B is to be mounted to one side of the guitar head and that shown in  FIGS. 4A and 4B  is to be mounted to the other side and corresponds to that of  FIGS. 2 ,  3 A and  3 B. The main body  10  having the structure described in the foregoing is formed as one body by pressing an ordinary SPC steel plate and the like, and is subsequently carburized to thereby impart spring-like properties. 
     FIG. 5  is a side view of the worm gear  21 . The worm gear  21  is basically composed of the worm  22  and the worm shaft  23 . A flange  24  is formed between the worm  22  and the worm shaft  23 . The end surface of the flange  24  at the worm  22  side is tapered, and the taper angle θ is 6° or less. At one end portion of the worm  22 , a small diameter hole  16  of the bearing  12  and a small diameter shaft  25  which fits therein so as to be rotatable are formed. At the leading end portion of the small diameter shaft  25 , an engagement portion  26  with an even smaller diameter is formed. Plural grooves  27  are formed so as to be spaced apart and extend along the entire outer periphery of the engagement portion  26 . In addition, at the other end portion of the worm  23 , a mounting portion  28  which has a smaller diameter than the worm  23  is formed, and flat notches  28   a  are formed at both side surfaces of the mounting portion  28 . In addition, as shown in  FIG. 1 , knobs  29  are mounted at the mounting portion  28  in a state in which they are engaged to the rotation direction with the notches  28   a,  and they are fixed by an appropriate means such as bonding. 
   As shown in  FIG. 1 , at one end portion of the winding shaft  30 , a winding surface  31  is formed whose center has a reduced diameter and is thus shaped like an hourglass. A through hole  32  is formed in the center of the winding surface  31 , and one end portion of the string is passed through the through hole  32  and the string is then wound onto the winding shaft  30  therefrom. Also, the support hole  13  for the main body  10  and the small diameter shaft  33  which fits therein so as to be rotatable, is formed at the other end portion of the winding shaft  30 . A mounting shaft  34  with an even smaller diameter is formed at the leading end portion of the small diameter shaft  33 , and in addition, flat notches  35  are formed at both side surfaces of the mounting shaft  34 . 
   The worm wheel  40  meshes with the worm  22 . A hole  41 , into which the mounting shaft  34  of the winding shaft  30  fits, is formed in the center of one end portion of the worm wheel  40  (see  FIG. 6 ), and the hole  41  engages with the notch  35  of the mounting shaft  34  in the direction of rotation. Also, a counter-bore  42  which has a larger diameter than that of the hole  41 , is formed at the center of the other end portion of the worm wheel  40 . The worm wheel  40  is accommodated in the hole  42  which seats the head portion  43   a , and is mounted to the winding shaft  30  so as to nip the base  11 , using screws  43  which are engaged in screw holes  34   a  of the mounting shaft  34 . In  FIGS. 1 and 6 , reference numerals  50  and  51  indicate washers and reference numeral  52  indicates a push nut. The washers  50  and  51  are formed of a synthetic resin. 
   When the peg having the above-described structure is assembled, the washer  50  of the peg in the state shown in  FIG. 1  is inserted through the worm gear assembly  20 , and the worm gear assembly  20  is inserted through the large diameter hole  15  of the bearing  12 . Then, the small diameter shaft  25  of the worm gear  21  is fit into the small diameter hole  16  of the bearing, and the washer  51  is fit into the small diameter shaft  25  and the push nut  52  is pressure inserted into the engagement portion  26 . As a result, the inner periphery of the push nut  52  is engaged with the groove  27 , and the push nut  52  is in a state in which it cannot become disengaged therefrom. Next, the small diameter shaft  33  of the winding shaft  30  is engaged with the support hole  13  of the main body  10 , and the mounting shaft  34  of the winding shaft  30  is fit into the hole  41  of the worm wheel  40 . Then, the screw  43  is screwed into the screw hole  34   a  of the mounting shaft  34 , thus completing the assembly of the peg. 
   A peg which has been assembled as described in the foregoing is shown in  FIG. 6 . As shown in  FIG. 6 , by the push nut  52  being pressure-inserted into the engagement portion  26 , the bearings  12  and  12  are secured between the flange  24  of the worm gear  21  and the push nut  52 , and are substantially parallel to each other due to elastic deformation. In this state, when the thrust load acts upon the worm gear  21 , the thrust load is applied to the bearing  12  via the flange  24  or the push nut  52 . In the peg having the above structure, the bearing  12  is formed of a spring material (an elastic material), and furthermore the large diameter hole  15  and the small diameter hole  16  which supports the worm gear  21 , are formed as round holes. As a result, it is difficult for the bearing  12  to be deformed. Accordingly, it is difficult for the worm gear  21  and the bearing  12  to have play, and thus it is unlikely that problems will arise such as increased backlash and unusual noises or for the notes to become out of tune due to rotation of the worm gear  21  in the wrong direction. 
   In particular, in the embodiment described above, by the push nut  52  being pressure-inserted, the bearings  12  and  12  are caused to elastically deform towards the inside, and thus frictional resistance with the worm gear  21  is caused by the repulsive force due to the spring-like property of the bearing  12 . As a result, the play of the bearing  12  and the worm gear  21  in the direction of thrust is eliminated, and also when the knob  29  is rotated, a suitable amount of resistance is generated, and thus tuning is made easy. In addition, even if vibrations are transmitted to the worm gear  21 , problems such as unusual noises and rotation of the winding shaft  30  in the wrong direction are controlled. Furthermore, since synthetic resin washers  50  and  51  are placed between the flange  24  and the bearing  12 , as well as between the push nut  52  and the bearing  12 , surface contact of the metal portions with each other is prevented, and seizing due to sliding contact of the surfaces when the worm gear rotates is prevented, and also a soft and smooth feel can be obtained when the stringed instrument is being tuned. 
   Furthermore, in this embodiment, the bearings  12  are inclined so as to extend outwards with respect to the base portion  11 , and they are disposed so as to be substantially parallel to each other by the push nut  52  being pressure inserted. As a result, the repulsive force due to the spring-like properties of the bearing  12  acts directly in the axial direction, thus efficiently generating frictional resistance with the worm gear  21 . Also, the worm gear  21  is fit into the large diameter hole  15  and the small diameter hole  16  of the bearing  12  when the holes are in a state of being perfectly round, and thus the characteristics of the bearing can be favorably maintained. 
   Furthermore, in this embodiment, because the push nut  52  engages with the grooves  27  on the worm gear  21 , the worm gear  21  is prevented from becoming disengaged from the bearing  12 , and the setting of the securing force in the thrust direction can be carried out in a single operation, thus reducing the number of steps in the assembly process. In addition, as shown in  FIGS. 1 to 6 , by serially providing a plurality of grooves  27 , the securing force can be suitably adjusted in the direction of thrust, and thus the positions and also the interval between the grooves can be precisely controlled, and by carrying out standardization such that a particular push nut  52  will be engaged with a particular groove  27 , the securing force in the thrust direction of the bearing can be made uniform, thus improving the uniformity of the product. 
     FIGS. 7 and 8  show another embodiment of the present invention. The only difference between this embodiment and the previous embodiment is that one groove  27  is formed at the outer periphery of the engagement portion  26  of the worm gear  21 . The parts which are the same as those of the previous embodiment are assigned the same reference numerals. The same operation and effects obtained in the previous embodiment are obtained in this embodiment as well, except for those caused by the plural grooves  27  being provided. 
   In the inventions described above, because the bearing is formed of a material having a spring-like properties, the following can be achieved without increasing the manufacturing cost: the transformation of the bearing in the direction of thrust is controlled, and play between the worm gear and the bearing in the direction of thrust is eliminated, and accordingly tuning is facilitated and problems of the generation of unusual noises and reverse rotation of the worm gear do not occur.