Patent Publication Number: US-2007107580-A1

Title: Friction torque capo

Description:
BACKGROUND  
      The present invention relates to a capo. The capo is configured with a friction torque hinge for controlling opening and closing.  
      A capo is a well-known movable bar attached to the fingerboard or fret board of a fretted instrument to uniformly raise the pitch of all the strings. Capos are typically used by musicians who play guitars and other stringed instruments to easily change music keys. In effect, a capo will simultaneously finger all the strings at a single fret as long as the capo is secured in place. This sets the half-notes sounded when the open strings are strummed. In this way, playing the guitar at a half-note increase is simplified without compromising the original string composition. Capos are in widespread use as a result, and there are many screw-down and clamp-down versions being sold commercially.  
      One particular type of capo is a levered clamp with separate rubber linings on the inside of the two jaws, commonly called a “C-clamp” capo. In such a C-clamp design, a frame with a straight rubber facing is clamped down tight over the strings of a guitar and pulls them against the fret board. An idler clamp with a concave curve and a short rubber facing presses from behind the fret board. Typically, a hinge or locking lever couples the two in order to hold the strings down tightly.  
      Typically, in its closed position on the fret board, the capo must exert enough force such that the strings are held sufficiently firmly against the fret board. Then, the capo is typically configured to be disengaged so that it can be removed from the guitar so that its strings return to normal pitch. Consequently, many capos include some sort of locking mechanism with some sort of associated release mechanism.  
      For these and other reasons, there is a need for the present invention.  
     SUMMARY  
      The present invention is a friction capo. The friction capo includes a first hinged arm and a second hinged arm coupled together by a friction hinge. The friction hinge includes a rotatable shaft and a friction element mounted on the shaft. The first hinged arm is coupled to the shaft and the second hinged arm is coupled to the friction element. The friction element is placed over the shaft such that the shaft frictionally engages the friction element. The capo has a holding torque configured to hold strings of an instrument firmly against a fret board.  
      In one embodiment, the torque of the capo increases as an increased number of friction elements are mounted on the shaft. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  illustrates a perspective view of one embodiment of a friction capo in accordance with the present invention.  
       FIG. 2  illustrates an exploded view of one embodiment of a friction capo in accordance with the present invention.  
       FIG. 3  illustrates a cross-sectional end view of one embodiment of a friction capo in accordance with the present invention.  
       FIG. 4  illustrates a partial side view, with a portion ghosted, of one embodiment of a friction capo in accordance with the present invention.  
       FIG. 5  illustrates an alternative embodiment of a friction hinge for a friction capo in accordance with the present invention.  
       FIG. 6  illustrates an alternative embodiment of a friction hinge for a friction capo in accordance with the present invention.  
       FIG. 7  illustrates an alternative embodiment of a friction hinge for a friction capo in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION  
      In the following Detailed Description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology, such as “top,” “bottom,” “front,” “back,” “leading,” “trailing,” etc., is used with reference to the orientation of the Figure(s) being described. Because components of embodiments of the present invention can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.  
       FIG. 1  illustrates a perspective view of friction capo  10  in accordance with one embodiment of the present invention. In  FIG. 1 , capo  10  is illustrated placed over an exemplary stringed instrument  11 . Strings  11   a  and fret board  11   b  are also illustrated. Capo  10  includes barre  12 , back arm  14 , and friction hinge  16 . In one embodiment, capo  10  is configured to be attachable to the neck of a guitar or other stringed instrument  11  in order to firmly hold strings  11   a  of the instrument  11  against a fret board  11   b . No lock or release mechanism is needed to engage or disengage capo  10  from the instrument.  
      In operation of one embodiment, capo  10  is attached to the neck of stringed instrument  11  by applying a closing force relative to barre  12  and back arm  14  such that they are forced toward each other. In this way, the closing force is applied in the direction of arrows  17   a  and  17   b  to barre  12  and back arm  14 , respectively. This closing force is applied until the strings  11   a  of instrument  11  are firmly held against fret board  11   b . A holding torque within friction hinge  16  then holds capo  10  in this closed position such that strings  11   a  continue to be firmly held against fret board  11   b , even after the closing force is removed.  
      Then, capo  10  is released from the neck of instrument  11  by applying an opening force relative to barre  12  and back arm  14  such that they are forced away from each other. In this way, the opening force is applied in the direction opposite arrows  17   a  and  17   b  to barre  12  and back arm  14 , respectively. In one case, the opening force is at least slightly more than the holding torque within friction hinge  16 . Thus, the opening force overcomes the holding torque such that capo  10  opens and releases the neck of the stringed instrument  11 .  
       FIG. 2  illustrates an exploded view of friction capo  10  in accordance with one embodiment of the present invention. Capo  10  includes barre  12 , back arm  14 , and friction hinge  16 . Friction hinge  16  is illustrated in exploded view so that further components of friction hinge  16  are visible. In one embodiment, friction hinge  16  includes washer  18 , shaft  20  and a plurality of friction elements  22 . Shaft  20  has a first end  20   a  and a middle portion  20   b . In one embodiment, friction hinge  16  and its components establish the holding torque for capo  10 .  
      In one embodiment, each of the plurality of friction elements  22  is placed over shaft  20  at its middle portion  20   b  when capo  10  is fully assembled. In one case, the plurality of friction elements  22  are each configured such that they have an inner opening for receiving shaft  20  in such a way that they frictionally engage shaft  20 . In one example, the plurality of friction elements  22  each have an inner opening with a relaxed diameter that is less than the diameter of shaft  20  at its middle portion  20   b  where friction elements  22  are each placed. In this way, when friction elements  22  are placed over the larger diameter of shaft  20 , they are frictionally engaged therewith. In one case, it is this frictional engagement that contributes to the holding torque within friction hinge  16 .  
      In one embodiment, shaft  20  is further provided with a groove in the shaft proximate to an edge of middle portion  20   b . In this way, one of the plurality of clips  22  can be placed within the groove when capo  10  is fully assembled. Washer  18  is then press fit on an opposite edge of middle portion  20   b  of shaft  20 . Washer  18  is then configured to be press fit to, or otherwise held within, barre  12 . In this way, capo  10  is held together in the axial direction, that is, the direction in which shaft  20  extends. In this way, it will not tend to pull apart axially with use. As an alternative to the groove in shaft  20 , a washer can be press fit on either side of friction elements  22 . Various other known methods for axial containment can be used as well.  
       FIGS. 3 and 4  respectively illustrate cross-sectional end and partial side views of capo  10  in accordance with one embodiment of the present invention. In  FIGS. 3 and 4 , capo  10  is illustrated fully assembled. In  FIG. 4 , a portion of friction hinge  16  of capo  10  is ghosted so that its internal components are visible.  
      In one embodiment, shaft  20  has an end portion  20   a  with raised tangs. End portion  20   a  is then coupled within hole  14   a  of back arm  14 . In this way, shaft  20  is fixed to back arm  14  such that shaft  20  does not rotate relative to back arm  14 . In the same way, rotation of back arm  14  also rotates shaft  20 . Also in one embodiment, the plurality of friction elements  22  are each contained within a slot  12   a  of barre  12 . In one case, the friction elements  22  have an outer profile that engages the shape of slot  12   a  such that the plurality of friction elements  22  do not rotate relative to barre  12 . In the same way, rotation of barre  12  also rotates the plurality of friction elements  22 .  
      Consequently, the rotation of barre  12  relative to back arm  14  causes the rotation of shaft  20  within friction elements  22 . Since the friction elements  22  are pressed on to shaft  20 , when they are rotated relative to each other the interference between the friction elements  22  and shaft  20  provides, in one case, a constant static and dynamic torque.  
      In one embodiment, the number of friction elements  22  that are placed over shaft  20  can be varied, thereby varying the amount of torque produced by the relative rotation of friction elements  22  and shaft  20  and varying the holding torque of capo  10 . The holding toque of capo  10  is increased by the addition of friction elements  22 , and decreased by their subtraction. In this way, the number of friction elements  22  placed over shaft  20  can be selected based on the desired holding torque for the application.  
      For example, for a variety of stringed instruments, there will be a certain amount of force required to push and hold strings  11   a  of instrument  11  firmly against fret board  11   b  of instrument  11 . This “spring back force” from strings  11   a  being stretched above fret board  11   b  will tend to move strings  11   a  away from the fret board  11   b  (in the direction opposite  17   a  in  FIG. 1 ) as they are pushed toward it by barre  12 . In one case, the number of the friction elements  22  used is such that that holding torque of capo  10  is sufficiently high to overcome the spring back force of the stringed instrument  11 . In this way, when the user applies a closing force on barre  12  and back arm  14  in order to close capo  10  on a stringed instrument  11 , the holding torque of capo  10  is sufficiently high to overcome the spring back force of strings  11   a , thereby allowing barre  12  to hold strings  11   a  firmly against the fret board  11   b , even after the closing force is removed from capo  10 . In order to remove capo  10 , an opening force greater than the holding torque of capo  10  is applied to barre  12  and back arm  14 , thereby opening capo  10  off the stringed instrument  11 . No independent release mechanism is needed to allow barre  12  and back arm  14  to be separated.  
      In one embodiment, capo  10  exhibits a different amount of torque in opening than it does in closing. In such case, relatively low torque is needed in closing capo  10  and pressing the strings  11   a  of the instrument  11  against the fret board  11   b . A relatively higher torque is needed to remove capo  10 . In such an embodiment, capo  10  also has a relatively high holding torque that will firmly hold the strings  11   a  down and counteract the spring back force of the strings  11   a , which tends to push back.  
      In one embodiment, this differing torque is achieved by providing a friction element  22  configured with first and second toes  22   a  and  22   b , as illustrated in  FIG. 4 . Then, rather than have the profile of the friction elements  22  engage the entire slot  12   a  in order to prevent relative rotation of friction elements  22  and slot  12   a , only first toe  22   a  is configured to engage a recessed portion of slot  12   a , such a groove as illustrated in  FIG. 4 . In this way, when barre  12  and back arm  14  are pressed closed, first toe  22   a , which engages the recessed portion of slot  12   a , will tend to “wrap open” or tend to pull away from shaft  20  such that torque is slightly decreased. Conversely, when barre  12  and back arm  14  are pressed open, toe  22   a  will tend to “wrap down” or slightly push down on shaft  20  such that torque is slightly increase. One skilled in the art will understand that various other techniques and configurations of friction elements  22  can be used to produce different torque in rotation directions, or symmetrical torque in both rotation directions.  
      In one embodiment, friction elements  22  are each configured to be relatively flat members. In other words, the dimension of friction elements  22  in an axial direction, that is, the direction in which shaft  20  extends, is significantly less than the dimension of friction elements  22  in the direction perpendicular to the axial direction. In this way, the outer profile of each of the friction elements  22  is substantially larger than the radial thickness of each of the friction elements  22 . As a result, friction elements  22  are easily added or subtracted from the design of capo  10  in order to achieve the desired torque properties without substantially changing the overall package design.  
       FIG. 5  illustrates an alternative embodiment of a friction hinge  26  for a friction capo, such as friction capo  10 , in accordance with the present invention. For example, friction hinge  26  can be coupled between barre  12  and back arm  14 , in place of friction hinge  16 , in order to provide the holding torque that holds capo  10  in its closed position. In the illustrated example, friction hinge  26  is a roll pin. Barre  12  is then provided with first and second barre flanges  27  and  28 , and back arm  14  is provided with arm flange  29 . In this way, when the capo is assembled, arm flange  29  is placed between first and second barre flanges  27  and  28 , and friction hinge  26  is inserted in slot provided in each of the flanges  27 ,  28  and  29  of barre  12  and back arm  14 . One or both ends can be configured to be frictionally engaged in the slot so that it can slip as force is applied relative to barre  12  and back arm  14 , thereby providing the holding torque.  
      In this alternative embodiment, friction capo  10  operates as described above. In this way, capo  10  is attached to the neck of stringed instrument  11  by applying the closing force relative to barre  12  and back arm  14  such that they are forced toward each other in the direction of arrows  17   a  and  17   b , until strings  11   a  are firmly held against fret board  11   b . The holding torque of friction hinge  26  holds capo  10  in this closed position such that strings  11   a  continue to be firmly held against fret board  11   b , even after the closing force is removed. Capo  10  is released from the neck of instrument  11  by applying the opening force relative to barre  12  and back arm  14  such that they are forced away from each other.  
      In this alternative embodiment using friction hinge  26 , the holding torque can be varied by adjusting the size of the holes within flanges  27 ,  28 , and  29  of barre  12  and back arm  14  into which friction hinge  26  is received, adjusting the thickness of the roll pin, as well as various other modifications. As long as the holding torque is greater than the spring back force of strings  11   a , and is overcome by the opening and closing forces, capo  10  will operate properly. In this alternative embodiment, placing arm flange  29  between first and second barre flanges  27  and  28  provides axial containment, but other methods, such as those discussed above and others, can be used for axial containment as well.  
       FIG. 6  illustrates an alternative embodiment of a friction hinge  36  for a friction capo, such as friction capo  10  in  FIGS. 1-4 , in accordance with the present invention. For example, friction hinge  36  can be coupled between barre  12  and back arm  14 , in place of friction hinge  16 , in order to provide the holding torque that holds capo  10  in its closed position. In the illustrated example, friction hinge  36  is an elongated friction element  38  that is fitted over a shaft  39 . Barre  12  is then provided with first and second barre flanges  40  and  41 , and back arm  14  is provided with arm flange  42 . In this way, when the capo is assembled, arm flange  42  is placed between first and second barre flanges  40  and  41 , and friction hinge  36  is inserted in slot provided in each of the flanges  40 ,  41  and  42  of barre  12  and back arm  14 .  
      Shaft  39  has an end with raised tangs that is inserted into a slot within flange  41  of back arm  14 , and elongated friction element  38  is inserted within a slot and adjacent slit in arm flange  42  of back arm  14 . In this way, shaft  39  is fixed to barre  12  via the raised tangs such that shaft  39  does not rotate relative to barre  12 . Similarly, elongated friction element  38  is configured to engage back arm  14  such that elongated friction element  38  does not rotate relative to back arm  14 . Finally, elongated friction element  38  is configured to contain and frictionally engage shaft  39 .  
      Consequently, the rotation of barre  12  relative to back arm  14  causes the rotation of shaft  39  within elongated friction element  38 . Since elongated friction element  38  frictionally engages shaft  39 , when they are rotated relative to each other the interference between them provides the holding torque.  
      In this alternative embodiment using friction hinge  36 , the holding torque can be varied by adjusting the inner diameter of elongated friction element  38  and/or the outer diameter of shaft  39 , thereby adjusting the amount of interference between them. Various other modifications can be used as well to adjust the holding torque. As with the other designs above, as long as the holding torque is greater than the spring back force of strings  11   a , and is overcome by the opening and closing forces, capo  10  will operate properly. In this alternative embodiment, placing arm flange  42  between first and second barre flanges  40  and  41  provides axial containment, but other methods, such as those discussed above and others, can be used for axial containment as well.  
       FIG. 7  illustrates an alternative embodiment of a friction hinge  46  for a friction capo, such as friction capo  10 , in accordance with the present invention. For example, friction hinge  46  can be coupled between barre  12  and back arm  14 , in place of friction hinge  16  in  FIGS. 1-4 , in order to provide the holding torque that holds capo  10  in its closed position. In the illustrated example, friction hinge  46  is a Bellville washer  50 , a first flat washer  52  and a second flat washer  54 , which are all placed over a shaft  56 . First flat washer  52  is press fit over shaft  56  such that they rotate together. Shaft  56  has an end with raised tangs that is inserted into a slot within back arm  14 . In this way, shaft  56  is fixed to back arm  14  such that shaft  56  does not rotate relative to back arm  14 .  
      Second flat washer  54  is press fit, or otherwise coupled within, barre  12  in such a way that all three washers  50 ,  52  and  54  are axially compressed. In this way, Bellville washer  50  and second flat washer  54  are configured to be fixed to barre  12  such that they do not rotate relative to barre  12 . With the axial compression, Bellville washer  50  pushes against first and second flat washers  52  and  54  in the axial direction such that they frictionally engage each other.  
      Consequently, the rotation of barre  12  relative to back arm  14  causes the surfaces of first and second flat washers  52  and  54  to engage their respective surfaces. Since washers  50 ,  52 , and  54  are all axially compressed, and thus, frictionally engaged, when they are rotated relative to each other the interference between them provides the holding torque.  
      In this alternative embodiment using friction hinge  46 , the holding torque can be varied by adjusting the amount of axial compression, and the overall size and/or rigidity of the washers, thereby adjusting the amount of interference between them. Various other modifications can be used as well. As with the other designs above, as long as the holding torque is greater than the spring back force of strings  11   a , and is overcome by the opening and closing forces, capo  10  will operate properly.  
      Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof.