Abstract:
A distortion correcting device is accommodated at a concave portion of the neck of a stringed instrument, and comprises: a bar  10  including a bottom plate portion  11  and a pair of opposing side plate portions  12  erected at both sides of the bottom plate portion  11 ; and an adjusting rod  20  whose one end portion is secured to one end portion of the bar  10  and whose other end portion engages with an adjusting nut  30  which is rotatably supported by the other end portion of the bar  10 , and in which the distance between the one end portion of the adjusting rod  20  and the adjusting nut  30  can be changed by turning the adjusting nut  30 . A first support member  40  and a second support member  50  are secured to the side plate portions  12  at both end portions of the bar  10 , and one end portion of the adjusting rod  20  is supported such that movement in an axial direction is blocked by the first support member  40 , and the adjusting nut  30  is rotatably supported by the second support member  50.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Technical Field  
           [0002]    The present invention relates to a distortion correcting device for use at the neck of a stringed instrument such as a guitar, and more particularly, relates to a distortion correcting device in which the downward bow when the neck is distorted so as to be concave with respect to the strings and the upward bow when the neck is distorted so as to be convex with respect to the strings, is corrected.  
           [0003]    2. Background Art  
           [0004]    In a stringed instrument such as a guitar, strings are wound between a bridge mounted on the body, and a tuner mounted on the head which is at the front end of the neck. As a result, if the stringed instrument is stored with the strings being tensioned, the neck may distort into a concave configuration. When the neck bows downward, the length of the string is increased and playing of the instrument becomes difficult, and also when a string is depressed, the string tension is increased, thus causing the fret to be out of tune. In the past, various distortion correcting devices for correcting the downward bow of the neck have been proposed. For example, Japanese Utility Model Application Laid-Open No. 62-146195 discloses a distortion correcting device which includes an adjusting rod disposed inside a bar whose central portion has a U-shaped cross section, and the bar is nipped between one end portion of the adjusting rod which extends from the bar and an adjusting nut which screws together with the other end portion of the adjusting rod at the other end portion side of the bar. In this type of distortion correcting device, a closed space is accommodated between the groove and the finger plate formed in the neck. Also, when the neck bows downward, by the adjusting nut being tightened, the bar bends in the direction for upward bowing, and the downward bow in the neck is thereby corrected.  
           [0005]    Also, there are guitars in which the neck is formed beforehand so as to have an upward bow and thus has a slightly convex portion, and when the strings are tensioned, the neck is distorted due to the string tension and the strings becomes parallel to the neck. As a result, the upward bow of the neck may become larger due to the quality of the seasoning of the material used for forming the neck, or due to changes in the environment subsequent to the manufacturing of the guitar. Thus, distortion of the convex configuration may still remain after the string has been tensioned. This distortion is an upward bow, and when this upward bow is formed, the string which is pressed during performance contacts the fret causing chattering and making performance impossible.  
           [0006]    In the distortion correcting device disclosed by the applicant of the present invention in Japanese Patent No. 2,736,860, the downward bow and the upward bow of the neck can be corrected. In this distortion correcting device, one end portion of an adjusting rod is secured to a bottom portion of one end of a bar having a U-shaped cross-section, and an adjusting nut, which is screwed together with the other end portion of the adjusting rod, is rotatably supported by the other end portion of the bar. In this distortion correcting device, when the adjusting nut is tightened, the secured ends of the adjusting nut and the adjusting rod approach each other, and the bar bends back in the direction opposite to that of the downward bow of the neck. As a result, the downward bow of the neck is corrected. In addition, if the adjusting nut is turned in the direction for slackening, the distance between the secured ends of the adjusting nut and the adjusting rod is increased, and the bar bends back in the direction opposite to that of the upward bow of the neck, and as a result, the upward bow of the neck is corrected.  
           [0007]    It should be noted that in Japanese Patent No. 2,736,860, a pressing element is provided at the adjusting rod so as to be positioned at the center of the distortion of the neck, and the distortion of the neck is effectively corrected by the bar being pressed by the pressing element.  
           [0008]    However, in the above-described distortion correcting device, despite the fact that the pressing element is being used, when the bar is caused to bend back, it is difficult for the bar to achieve a suitable curvature, and it has become apparent that at the front end portion which secures the adjusting rod, the bar is not sufficiently bent back. In addition, there are some guitars in which the adjusting nut is accommodated at the head, and some in which the adjusting nut is accommodated at the base portion of the body side of the neck, and the type which is used is different depending on the guitar manufacturer or the type of guitar. In particular, in the guitar in which the adjusting nut is accommodated at the base portion of the neck, in order to ensure that the neck is sufficiently hard, the bar is sometimes not extended to the front end portion of the neck, and in this case, it is difficult for the correction of the distortion of the front end portion of the neck to be suitably carried out, and this problem needs to be solved.  
           [0009]    An object of the present invention is to provide a distortion correcting device in which the curve of the bar is suitable after distortion is corrected, and the correction of the distortion can be accurately carried out.  
         SUMMARY OF THE INVENTION  
         [0010]    A distortion correcting device for a neck of a stringed instrument comprising, a bar accommodated at a concave portion of the neck, the bar having a bottom plate portion and a pair of opposing side plate portions erected from both sides of the bottom plate portion, an adjusting rod whose one end portion is secured to one end portion of the bar and whose other end portion engages with an adjusting nut which is rotatably supported at the other end portion of the bar, a first support member and a second support member which are secured to the side plate portions at both end portions of the bar, wherein the distance between the one end portion of the adjusting rod and the adjusting nut can be changed by turning the adjusting nut, and one end portion of the adjusting rod is supported such that movement in an axial direction is blocked by the first support member, and the adjusting nut is rotatably supported by the second support member.  
           [0011]    In the distortion correcting device for the neck of a stringed instrument (simply referred to as “distortion correcting device” hereinafter), by turning the adjusting nuts, the distance between a first and second support member is changed, and the side plate portion which is secured by first and second support members extend or contract in the longitudinal direction. On the other hand, since the length of the bottom plate portion does not change, a bend moment is generated at both end portions of the bottom plate portion by the length of the side plate portion being changed. The entire bar including the bottom plate portion is bent back by this bend moment. In this case, the bend moment which is generated at both end portions of the bottom plate portion acts on the support end portions of the adjusting rod and the adjusting nut which are at both the first and second support members. As a result, the size of bend moment of both is approximately the same. Accordingly, the bottom plate portion can be bent substantially uniformly and the distortion can be accurately corrected.  
           [0012]    The side plate portions of the first and second support members are closely fitted into each other and may be fixed by being welded. However, if the first and second support members are fixed only by the welding the strength by which they are secured together and this is insufficient, it is thus preferable that the first and second support members be provided with convex portions which closely fitted into a concave portion formed in the side plate portions. Also, it is preferable that the concave portion and the convex portion be welded in a state in which they are fit into each other. In addition, the first support member is engaged in an axial direction with a peripheral edge groove formed in an outer periphery of one end portion of the adjusting rod, and the second support member is engaged in an axial direction with a peripheral edge groove formed in an outer periphery of the adjusting nut. Thus, the adjusting rod and the adjusting nut are firmly supported by the first support member and the second support member. Furthermore, the distances of the concave portions from the bottom plate portion are approximately equal, and thus the bend moment which acts on the respective end portions of the adjusting rod is approximately equal.  
           [0013]    In the present invention, the adjusting nut is turned and caused to move relative to the adjusting rod, and thus it is necessary for the adjusting rod to be secured so that it does not rotate. In this case, the adjusting rod may be welded to the first supporting tool; however, by applying the structure described in the following, anti-rotation can be simplified and can be carried out at a low cost.  
           [0014]    That is to say, at the front end surface of the adjusting rod, an anti-rotation concave portion which has a non-circular cross-section is provided, and the bottom plate portion is bent with respect to the front end edge of the bottom plate portion, thereby providing an anti-rotation plate portion which is equipped with a concave anti-rotation portion into which the convex anti-rotation portion fits. The cross section of the convex anti-rotation portion may have any suitably selected configuration, as long as it is not circular, and these include that of a circle having one or both sides cut out, or a polygonal configuration. In addition, since the anti-rotation plate portion is bent by sheet metal working, if the bottom plate portion and the side plate portion of the bar is formed integrally by a metal sheet being subjected to sheet metal working, the manufacturing cost is further reduced.  
           [0015]    By carrying out anti-rotation in the manner described above without welding the adjusting rod to the first support member, the adjusting rod is movable in the direction which is perpendicular to the axial direction by the amount of the space between the convex anti-rotation portion and the convex anti-rotation portion. This is very important in order for the direction in which the bar is bent back to be secured and for the bending of the bar to be uniform. That is to say, when the adjusting rod is welded to the first support member, the center of the adjusting rod is sometimes mispositioned with respect to the center of the adjusting nut, due to error in manufacturing, or error in assembling or the like. If the adjusting nut is turned in this state, the bend moment acts on the adjusting rod, and this bend moment in turn acts on the bar.  
           [0016]    Thus, it is not desirable for the front end portion of the adjusting rod to be firmly fixed by welding and the like, and it is desirable that a space be provided such that the adjusting rod is movable with respect to the bar in the direction which is perpendicular to the axial direction thereof. This space is suitably provided at both sides in the direction in which the adjusting rod moves toward or separates from the bottom plate portion (vertical direction) so as have sizes of 0.2 to 0.4 mm respectively, and to have sizes of 0.1 to 0.3 mm respectively in the direction which crosses that direction (lateral direction). The space which allows and also restricts movement of the adjusting rod in the above-mentioned direction is provided between the anti-rotation concave portion and the anti-rotation convex portion, and between the adjusting rod and the first support member and members, such as the bottom plate portion of the bar. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    [0017]FIG. 1 is an assembly perspective view of the distortion correcting device of an embodiment of the present invention;  
         [0018]    [0018]FIG. 2 is a perspective view of a guitar for installing the distortion correcting device of the embodiment of the present invention;  
         [0019]    [0019]FIG. 3 is a side sectional view of the neck of the guitar;  
         [0020]    [0020]FIG. 4A is side view of the distortion correcting device of the embodiment, and FIG. 4B is bottom surface view thereof;  
         [0021]    [0021]FIG. 5A is a side sectional view of the distortion correcting device showing a state in which a concave distortion of the neck is corrected; and  
         [0022]    [0022]FIG. 5B is a side sectional view of the distortion correcting device showing a state in which a convex distortion of the neck is corrected. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]    A. Structure of the Embodiment  
         [0024]    The following is a description of the embodiment of the present invention with reference to FIGS.  1  to  5 . It should be noted that in the following description, the left side of the FIG. 1 is considered the top end side, and this direction is taken as a reference when expressions such as “longitudinal direction” and “lateral direction” are used.  
         [0025]    [0025]FIG. 1 is an assembly perspective view of the distortion correcting device A of the embodiment of the present invention. In the figures, reference numeral  10  is the bar. The bar  10  comprises: the bottom plate portion  11 ; the side plates  12  which are erected at both sides of the bottom plate portion  11  so as to be at perpendiculars with respect thereto; and the anti-rotation plate portion  13  which is erected at the edge of the front end of base plate portion so as to be at perpendiculars with respect thereto.  
         [0026]    Concave portions  14  which are rectangular in shape are provided so as to penetrate the side plate portion  12  at both ends thereof. The distance of each of the concave portions  14  from the bottom plate portion  11  is secured. It should be noted that the concave portion  14  may also be circular. Also, a concave anti-rotation portion  15  which is rectangular in shape is provided so as to penetrate the center of the anti-rotation plate portion  13 . A thin joint  16  is formed by press molding at the border of the anti-rotation plate portion  13  and the bottom plate portion  11 , and the anti-rotation plate portion  13  can be easily folded along the joint  16 .  
         [0027]    In the figures, reference numeral  20  is the adjusting bar. The adjusting bar  20  is a steel rod which has a circular cross section, and at the front end portion thereof, two large diameter portions  21  having a larger diameter than the back end portion, are formed, and between these two large diameter portion, a peripheral edge groove portion is formed. At the front end face of the adjusting bar  20 , a convex anti-rotation portion  23  having a rectangular cross-section is formed. This convex anti-rotation portion  23  engages with the concave anti-rotation portion  15  leaving a predetermined space between the two. Also, a screw  24  is formed in the outer periphery of the back end portion of the adjusting screw  20 , and the screw  24  is screwed together with the adjusting nut  30 .  
         [0028]    At the front end portion of the adjusting nut  30 , a female screw  31  which screws together with the screw  24 , is formed. Also, at the back end portion of the adjusting nut  30 , a wrench hole  33  having, for example, a hexagonal cross-section is formed. At the middle portion of the adjusting nut  30  in the axial direction thereof (in the middle of the female screw  31  and the wrench hole  33 ), a peripheral edge groove  32 , whose diameter is smaller than that of the other portions, is formed.  
         [0029]    The first support member  40  and the second support member  50  are engaged with the peripheral edge portions  22  and  32  of the adjusting bar  20  and the adjusting nut  30 , respectively. The first support member  40  is U-shaped, and at both side faces thereof, convex portions  41  which extend laterally are formed. This convex portion  41  closely fitted with the concave portion  14  which is formed in the side plate portion  12  of the bar  10 . In addition, the inner peripheral face  42  of the first support member  40  is U-shaped and the space between the inner peripheral face  42  and the inner face which faces the inner peripheral face  42  is slightly larger than the distance across from the adjusting rod  20  to the peripheral edge portion  22 . Also, the curve radius of the arc-shaped inner face is set so as to be slightly larger than the outer diameter (radius) of the peripheral edge portion  22 . It should be noted that the second support member  50  has the same shape and same size as the first support member  40 , and includes the convex portion  51  and the inner peripheral face  52 . In the first and second support members  40  and  50  having the structure described above, the convex portions  41  and  51  are closely fitted with the concave portion  14 , and these portions are fixed by being welded.  
         [0030]    In FIG. 1, reference numeral  60  is a pressing element, and when the pressing element  60  is turned in the tightening direction of the adjusting nut  30  and the adjusting rod  20  shortens, the bottom plate portion of the bar  10  is effectively pressed and then bent back. In addition, reference numeral  70  is a block, and the block  70  prevents the side plate  12  from deforming when the bar  10  bends backs. FIG. 4A is side view of the distortion correcting device of the embodiment, and FIG. 4B is bottom surface view thereof.  
         [0031]    Next, FIGS. 2 and 3 show a distortion correcting device A having the structure described above and a guitar in which is installed this distortion correcting device. In the drawings, reference numeral  80  is the body and reference numeral  81  is the neck. At the center of the surface of the neck  81 , the groove  84  which extends from the base portion  82  to the head  83  is formed. Also, the distortion correcting device A is accommodated in a state in which the adjusting nut  30  contacts the head  83  and the bottom plate portion  11  is in the direction toward the neck  81 , and the finger plate  85  is attached to the surface of neck  81 , and the distortion correcting device A is thereby mounted. It should be noted that in FIG. 2, reference numeral  86  represents the guitar strings.  
         [0032]    B. Application of the Present Embodiment  
         [0033]    Next, the application of the distortion correcting device having the above structure will be described. First, the correction process for downward bow generated in the case where the neck  81  has concave distortion caused by tensioning of the string  86  will be described. In the guitar neck  81  described above, as can be seen from FIG. 3 which shows the neck in detail, the adjusting nut  30  extends to the head  83  portion of the groove  84 . A wrench is inserted into the wrench hole  33  and the adjusting nut  30  is twisted in the direction for tightening. As a result, the adjusting nut  30  is moved relative to the base plate  82  side of the neck  81  along the screw  24  of the adjusting rod  20 . Thus since the length along the adjusting rod  20  between the first and second support members  40  and  50  is shorter that the length along the bar  10 , as shown in FIG. 5, and the distortion correcting device causes the first and second support members  40  and  50  to bend back in the upward direction to form a convexity along with the bar  10 . At this time, the pressing element  60  is pressed onto the bottom plate portion  11  of the bar  10 , and therefore the bending back of the bar  10  can be ensured. Also, since the distortion correcting device A which is restricted by the groove  84  and the finger plate  85  of the neck causes bending back in the upward direction so as to form a convexity, and the downward bow which was generated at the neck is corrected.  
         [0034]    Next, in the case where an upward bow is generated by concave distortion of the neck  81 , the nut  30  is twisted in the direction for loosening which is opposite to the direction for tightening in which it was turned above. Thus, the adjusting nut  30  is moved relative to the head  83  side along the screw  24  of the adjusting rod  20 . Therefore, since the length of the adjusting rod  20 , which is between the first and second support members  40  and  50 , is longer than the length along the bar  10 , as shown in FIG. 5B, the distortion correcting device A bends back the first and second support members  40  and  50  along with the bar  10  in the downward direction to form a concavity. Also, because the distortion correcting device is bent back in a concave configuration, the neck  81  having an upward bow is corrected.  
         [0035]    In the distortion correcting device A having the structure described above, the distance between the first support members  40  and  50  changes by the adjusting nut  30  being turned. As a result, the side plate  12  extends or shortens in the longitudinal direction. Therefore, the bend moment acts upon both end portions of the bottom plate portion  11 , and the bottom plate portion is bent backward due to this bend moment. In this case, since the bend moment generated at the both end portions of the act on portions of the support members  40  and  50  which support the adjustment rod  20  and the adjustment nut  30 , the size of the bend moment is substantially equal. As a result, the curve of the bottom plate portion  11  is imparted in a substantially uniform manner, and correction of the distortion is thereby carried out.  
         [0036]    In particular, in the embodiment described above, the concave portion  14  formed in the side plate portion  12  closely fitted together with the convex portions  41  and  51  formed in the first and second support members  40  and  50 , and due to stress in the axial direction, the first and second support members  40  and  50  never separate from the side plate portion  12 . Furthermore, the concave portion  14  and the convex portions  41  and  51  are welded together, and thus, when compression stress acts in the axial direction, outward opening of the side plates  12  is controlled.  
         [0037]    Also, in this embodiment, the first support member  40  is engaged in the axial direction with the peripheral edge groove  22  of the adjusting rod  20 , and the second support member  50  is engaged in the axial direction with the peripheral edge groove  32  of the adjusting nut  30 . Therefore, the adjusting rod  20  and the adjusting nut  30  are firmly supported by the first and second support members  40  and  50 . Furthermore, the distance between the bottom plate portion  11  and the concave portions  14  at both end portions of the adjustment rod from each other is approximately equal, and thus the bend moment which acts on the respective end portions of the adjusting rod  20  is approximately equal, and the curvature of the bar  10  can be made even more uniform.  
         [0038]    Furthermore, in this embodiment, at the front end face of the adjusting rod  20 , an anti-rotation concave portion  23  which has a non-circular cross-section is provided, and an anti-rotation plate portion  13  with a concave anti-rotation portion  15  is provided at the top end edge of the bottom plate portion. Thus, by the anti-rotation bottom plate portion  13  being simply bent, anti-rotation of the adjusting rod  20  is carried out. In addition, since the anti-rotation plate bending working of the portion  13  can be carried out at the same time as the bending working of the side plate portion  12 , the manufacturing cost is further reduced.  
         [0039]    In addition, in this embodiment space is provided between the anti-rotation convex portion  23  and the peripheral edge groove  22 , and between the concave anti-rotation portion  15  and the inner peripheral face of the first support member  40 , and thus the adjustment rod is movable in the axial direction as well as in the direction perpendicular thereto. As a result, when the adjusting nut  30  is turned and stress is applied to the adjusting rod  20 , the centers of both the adjusting nut  30  and the adjusting rod  20  are automatically aligned, and stress is prevented from being unintentionally generated. Thus, the curvature of the bar can be made even more uniform.  
         [0040]    It should be noted that, in this embodiment, the anti-rotation plate portion  13  folds with respect to the bottom plate portion  11 , but they may be formed separately and secured together by welding or some other means. Also, flat surfaces which are parallel to each other are formed in the peripheral edge groove  22  of the adjusting rod  20 , and anti-rotation is achieved by the inner peripheral face  42  of the first support member  40  being nipped in between these flat surfaces. In that case, the positioning of the adjusting rod  20  in the vertical direction may be carried out by the distance away from the large diameter portion  21  being set, or by shaving the lower surface of the large diameter portion. In addition, the adjusting nut  30  is disposed at the head  83  side, but opposite to the present embodiment, the adjusting nut  30  may be disposed at the base portion  82  side of the neck  81 , and the adjusting nut  30  may be turned by inserting a wrench in the sound hole  87  formed in the body.