Abstract:
An apparatus and method for extending and retracting frets of stringed musical instruments such as a guitar or bass guitar. Each of a plurality of frets is an integral part of a fret-cylinder having an axis oriented approximately perpendicular to the direction of the strings when positioned in a neck of the instrument. Each fret-cylinder has integral cylinder-adjusting teeth that engage rod-adjusting teeth of a rod enclosed within a cavity in the neck of the instrument. Moving the rod in an axial direction by a rod actuating mechanism causes the fret-cylinders to rotate about their axis, extending the frets above a fingerboard attached to the instrument neck for fretted play and retracting the frets flush with the fingerboard for unfretted play. The rod actuating mechanism may be positioned on a neck of an instrument or a body of an instrument, and may be manually or electric motor actuated.

Description:
BACKGROUND OF INVENTION 
   The invention relates generally to the field of stringed musical instruments having frets, and particularly to stringed musical instruments that may be played using frets and without using frets. More particularly, the invention provides for frets on a fingerboard or neck of a stringed musical instrument that can be raised or lowered in unison, allowing a musician to play the instrument as fretted and unfretted. 
   Most stringed musical instruments, and particularly guitars and bass guitars, comprise a body fixed to a neck having a fingerboard, and a headstock having tuning pegs and tuning knobs connected to the neck opposite the body. Strings are fixed to the body at one end and adjustably connected to the tuning pegs at the other end for adjusting the string tension and corresponding string pitch. The strings are tensioned between a bridge positioned on the body and a nut positioned on the far end of the neck. A musician plays the instrument by strumming or plucking the strings with one hand while selecting a pitch by pressing the strings down against the fingerboard at suitably selected positions with the other hand. The fingerboard may have frets below the strings and positionally fixed along the fingerboard, oriented substantially perpendicular to the direction of the strings. The fingerboard may be also be unfretted. 
   For instruments with frets, a musician presses the strings against the fingerboard behind selected frets opposite the body, to produce a pitch from each string that is precisely determined by the distance between the fret and the bridge, and the characteristics of the particular string. The sounds from a fretted instrument tend to be sharp and clearly defined. For instruments without frets a performer presses the strings against the fingerboard to produce a pitch that is determined by the distance between the point where the string is pressed against the fingerboard and the bridge, as well as the characteristics of the particular string. Unfretted instruments usually produce a softer sound and provide a wider range of selectable pitches available to a musician due to the wider range of points where a string may be pressed against a fingerboard. They also enable a musician to produce certain sound characteristics that cannot be produced with an equivalent fretted instrument. 
   Because of the different sounds produced by fretted and unfretted instruments, musicians sometimes rely on two different instruments, a fretted and an unfretted instrument. It is desirable to have a single instrument that is capable of both fretted and unfretted play, which may be quickly and easily switched between the two modes of play. 
   SUMMARY OF INVENTION 
   The present invention provides an apparatus and method for adjusting a stringed musical instrument between fretted and unfretted play, wherein each fret has a cylindrical shape that may be extended above the surface of the fingerboard for fret play or retracted flush with the surface of the fingerboard for fretless play. When extended, the cylindrical shaped frets form surfaces against which the strings of the instrument are pressed in order to change the effective string lengths and thereby change the acoustic pitches of the vibrating strings. Typical instruments that may benefit from this invention include guitars and bass guitars. 
   The individual fret-cylinders are mounted in recessions formed in the fingerboard/neck and are supported at each end by a dowel and bushing arrangement such that the fret-cylinders may be made to rotate. Because of the cross-sectional shape of the fret-cylinders, the rotating motion causes the frets to be lowered from an extended fretted position to a fully retracted unfretted position. In the following description, that portion of the fret-cylinders against which the strings press when being played in a fretted position are called frets. The parts of the fret-cylinders that do not come in contact with the strings are referred to as cylinders. 
   The fret-cylinders are made to rotate by means of a rod of suitable material positioned in and extending the length of the neck of the instrument. The rod is movable in the axial direction approximately perpendicular to the axis of the fret-cylinders. The axes of the fret-cylinders are positioned approximately perpendicular to the extended length of the neck of the instrument. The fret-cylinders are provided with a small number of teeth or cogs that run parallel to the axis of the fret-cylinders. These teeth or cogs engage a matching set of teeth or cogs provided along the length of the rod and perpendicular to the axis of the rod. By sliding the rod in its axial direction, the interconnecting teeth or cogs of the rod and the fret-cylinders cause the fret-cylinders to rotate, which causes the frets to be extended or retracted into the fingerboard/neck of the instrument. There are several different embodiments that enable a musician to cause the rod to slide in an axial direction for determining fretted or unfretted play. 
   An embodiment of the present invention is a method for adjusting a stringed musical instrument for fretted and unfretted play that comprises the steps of slideably moving in an axial direction a rod having an actuating end in a rod hole extending the length of a neck of the instrument, fixing a positional relationship of the actuating end of the rod with respect to multiple instances of rod-adjusting teeth positioned on a circumference and perpendicular to the axis of the rod, engaging each instance of rod-adjusting teeth with a corresponding instance of cylinder-adjusting teeth positioned on a circumference and parallel to an axis of a fret-cylinder, and rotating all fret-cylinders by moving the rod for positioning all frets in an extended fretted position above a fingerboard of the instrument and positioning all frets in a retracted unfretted position flush with the fingerboard of the instrument. The method may further comprise positioning a means for moving the rod on a head stock of the instrument near the actuating end of the rod. The method may further comprise positioning a means for moving the rod on a body of the instrument near the actuating end of the rod. The step of slideably moving may further comprise rotationally adjusting a handle for rotating a gear fixed to the handle by a gear shaft, and engaging the gear with rod teeth positioned at the actuating end of the rod on a circumference and perpendicular to an axis of the rod for moving the rod in an axial direction. The step of slideably moving may further comprise rotationally adjusting a handle for rotating a wheel fixed to the handle by a gear shaft, and engaging a linkage lever for connecting between a linkage lug eccentrically positioned on the wheel and a rotatable saddle positioned on the actuating end of the rod for moving the rod in an axial direction. The step of slideably moving may further comprise rotating a first end of a lever about an axle for rotating a second end of the lever having a lever slot, and positioning a rod arm fixed to the actuating end of the rod into the lever slot for moving the rod in an axial direction. The step of slideably moving may further comprise actuating a reversible electric motor connected to an instrument&#39;s electric system for rotating a worm gear fixed to a motor shaft, and engaging the worm gear with rod teeth positioned at the actuating end of the rod on a circumference and perpendicular to an axis of the rod for moving the rod in an axial direction. The method may further comprise activating limit switches by a rod lug fixed to the rod for interrupting a current to the motor for stopping rod movement when the frets are in an extended fretted position above a fingerboard of the instrument and when the frets are in a retracted unfretted position flush with the fingerboard of the instrument. 
   Another embodiment of the present invention may be an apparatus for adjusting a stringed musical instrument for fretted and unfretted play that comprises means for slideably moving in an axial direction a rod having an actuating end in a rod hole extending the length of a neck of the instrument, the rod having an actuating end fixed in a positional relationship with respect to multiple instances of rod-adjusting teeth positioned on a circumference and perpendicular to the axis of the rod, each instance of rod-adjusting teeth for engaging with a corresponding instance of cylinder-adjusting teeth positioned on a circumference and parallel to an axis of a fret-cylinder, and each fret-cylinder being rotated by moving the rod for positioning a fret in an extended fretted position above a fingerboard of the instrument and positioning the fret in a retracted unfretted position flush with the fingerboard of the instrument. The apparatus may further comprise means for moving the rod being positioned on a head stock of the instrument near the actuating end of the rod. The apparatus may further comprise means for moving the rod being positioned on a body of the instrument near the actuating end of the rod. The means for slideably moving may further comprise a handle for rotating a gear fixed to the handle by a gear shaft and the gear for engaging rod teeth positioned at the actuating end of the rod on a circumference and perpendicular to an axis of the rod for moving the rod in an axial direction. The means for slideably moving may further comprise a handle for rotating a wheel fixed to the handle by a gear shaft, and a linkage lever for connecting between a linkage lug eccentrically positioned on the wheel and a rotatable saddle positioned on the actuating end of the rod for moving the rod in an axial direction. The means for slideably moving may further comprise a lever for rotating about an axle for rotating a second end of the lever having a lever slot, and a rod arm fixed to the actuating end of the rod and positioned into the lever slot for moving the rod in an axial direction. The means for slideably moving may further comprise a reversible electric motor connected to an instrument&#39;s electric system for rotating a worm gear fixed to a motor shaft, and the worm gear for engaging rod teeth positioned at the actuating end of the rod on a circumference and perpendicular to an axis of the rod for moving the rod in an axial direction. The apparatus may further comprise limit switches activated by a rod lug fixed to the rod for interrupting a current to the motor for stopping rod movement when the frets are in an extended fretted position above a fingerboard of the instrument and when the frets are in a retracted unfretted position flush with the fingerboard of the instrument. 
   Yet another embodiment of the present invention includes a kit for adjusting a stringed musical instrument for fretted and unfretted play, capable of being assembled in the field, that comprises means for slideably moving in an axial direction a rod having an actuating end, the rod having an actuating end fixed in a positional relationship with respect to multiple instances of rod-adjusting teeth positioned on a circumference and perpendicular to the axis of the rod, each instance of rod-adjusting teeth for engaging with a corresponding instance of cylinder-adjusting teeth positioned on a circumference and parallel to an axis of a fret-cylinder, each fret-cylinder being rotated by moving the rod for positioning a fret in an extended fretted position above a fingerboard of the instrument and positioning the fret in a retracted unfretted position flush with the fingerboard of the instrument, and a neck for the stringed musical instrument for positioning the moving means, the rod, the fret-cylinders, and the fingerboard. The means for slideably moving may further comprise a handle for rotating a gear fixed to the handle by a gear shaft positioned on the neck, and the gear for engaging rod teeth positioned at the actuating end of the rod on a circumference and perpendicular to an axis of the rod for moving the rod in an axial direction. The means for slideably moving may further comprise a handle for rotating a wheel fixed to the handle by a gear shaft positioned on the neck, and a linkage lever for connecting between a linkage lug eccentrically positioned on the wheel and a rotatable saddle positioned on the actuating end of the rod for moving the rod in an axial direction. The means for slideably moving may further comprise a lever for rotating about an axle for rotating a second end of the lever having a lever slot positioned on the neck, and a rod arm fixed to the actuating end of the rod and positioned into the lever slot for moving the rod in an axial direction. The means for slideably moving may further comprises a reversible electric motor positioned on the neck and connected to an instrument&#39;s electric system for rotating a worm gear fixed to a motor shaft, and the worm gear for engaging rod teeth positioned at the actuating end of the rod on a circumference and perpendicular to an axis of the rod for moving the rod in an axial direction. The kit may further comprise limit switches positioned on the neck and activated by a rod lug fixed to the rod for interrupting a current to the motor for stopping rod movement when the frets are in an extended fretted position above a fingerboard of the instrument and when the frets are in a retracted unfretted position flush with the fingerboard of the instrument. 
   DESCRIPTION OF NUMERIC REFERENCES OF INVENTION EMBODIMENTS 
   
     
       
             
           
             
             
           
         
             
                 
             
             
               Description of Numeric References of Invention Embodiments 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               1. 
               Head Stock 
             
             
               2. 
               Neck 
             
             
               3. 
               Fingerboard 
             
             
               4. 
               Fret-Cylinder 
             
             
               5. 
               Slidable Rod 
             
             
               6. 
               Strings 
             
             
               7. 
               Tuning Pegs 
             
             
               8. 
               Tuning Knobs 
             
             
               9. 
               Gear 
             
             
               10. 
               Gear Shaft 
             
             
               11. 
               Handle 
             
             
               12. 
               Bushing/Cover Plate 
             
             
               13. 
               Rod Hole 
             
             
               14. 
               Fret 
             
             
               15. 
               Fret-Cylinder 
             
             
               16. 
               Side Plate 
             
             
               17. 
               Pinion 
             
             
               18. 
               Side Plate Hole 
             
             
               19. 
               Instrument Body 
             
             
               20. 
               Electric Motor 
             
             
               21. 
               Worm Gear 
             
             
               22. 
               Motor Shaft 
             
             
               23. 
               Switch 
             
             
               24. 
               Wires 
             
             
               25. 
               Limit Switches 
             
             
               26. 
               Rod Teeth 
             
             
               27. 
               Rod Lug 
             
             
               28. 
               Lever 
             
             
               29. 
               Axle 
             
             
               30. 
               Lever Slot 
             
             
               31. 
               Rod Arm 
             
             
               32. 
               Wheel 
             
             
               33. 
               Linkage Lug 
             
             
               34. 
               Linkage Lever 
             
             
               35. 
               Rotatable Saddle 
             
             
               36. 
               Fret-Cylinder Bushing 
             
             
               37. 
               Slot in Head Stock 
             
             
               38. 
               Rod-Adjusting Teeth 
             
             
               39. 
               Cylinder-Adjusting Teeth 
             
             
                 
             
           
        
       
     
   

   
     BRIEF DESCRIPTION OF DRAWINGS 
     These and other features, aspects and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings wherein: 
       FIG. 1  shows a partial sectional view of a head stock and fingerboard of a stringed musical instrument having all tuning knobs on the same side of the head stock; 
       FIG. 2  shows an embodiment of a means for adjusting a position of a rod; 
       FIG. 3  shows a top view of the  FIG. 2  embodiment of a gear engaging means for actuating the rod; 
       FIG. 4  shows a bottom view of the  FIG. 2  embodiment of the handle actuating means for actuating the rod; 
       FIG. 5  shows a section view of the head stock and upper neck area of the  FIG. 2  embodiment for actuating the rod; 
       FIG. 6  shows a portion of the neck and fingerboard showing several frets; 
       FIG. 7  shows an embodiment of rotatably mounting a fret-cylinder to a side plate; 
       FIG. 8  shows an alternative embodiment of rotatably mounting a fret-cylinder to a side plate; 
       FIG. 9  shows a top view of a fret-cylinder installed in a fingerboard; 
       FIG. 10  shows sectional views of the fingerboard and neck assembly, including a rod and a fret-cylinder in an extended position and in a retracted position; 
       FIG. 11  shows a partial sectional view of a head stock and fingerboard of a stringed musical instrument having tuning knobs equally located on both sides of the head stock; 
       FIG. 12  shows an alternative embodiment of a means for actuating the rod with an electric motor in an instrument body; 
       FIG. 13  shows a detailed implementation of the embodiment of  FIG. 12 ; 
       FIG. 14  shows an alternative embodiment of a method for actuating the rod by manual means in an instrument body; 
       FIG. 15  shows a detailed implementation of the embodiment of  FIG. 14 ; 
       FIG. 16  shows another embodiment of a means for actuating the rod by manual means at the instrument head stock; and 
       FIG. 17  shows yet another embodiment of a means for actuating the rod by manual means at the instrument head stock. 
   

   DETAILED DESCRIPTION 
   Turning now to  FIG. 1 ,  FIG. 1  shows a partial sectional view  110  of a head stock  1  and fingerboard  3  connected to the neck  2  of a stringed musical instrument such as a guitar or bass guitar having all tuning knobs  8  on the same side of the head stock  1 . The view  110  also shows strings  6  wrapped around tuning pegs  7 , that are rotatably connected to tuning knobs  8 , as conventionally configured on a guitar or bass guitar, whereby the tuning knobs  8  are turned to adjust tension on the strings  6  to determine acoustic pitch. An embodiment of the present invention is also shown in the view  110  that includes a fret-cylinder  4  that connectively engages a slidable rod  5 , and a rod adjusting mechanism comprising a handle  11 , a gear shaft  10  and a gear  9 . The slidable rod  5  extends from the head stock  1  through an aperture in the neck  2  to the instrument body. 
   Turning to  FIG. 2 ,  FIG. 2  shows an embodiment of a means for adjusting a position of the rod. A rod adjusting mechanism  120  shown in  FIG. 2  is an isometric view of the rod adjusting mechanism  120  comprising a handle  11 , a gear shaft  10  and a gear  9 , as describe in  FIG. 1 .  FIG. 3  is a top view  130  and  FIG. 4  is a bottom view of the rod adjusting mechanism  120  shown in  FIG. 2 . The handle  11  is fixed to the gear shaft  10 , which is fixed to the gear  9 . The gear  9  engages rod teeth  26  on the rod  5  such that when a musician turns the handle  11 , the gear  9  is caused to rotate, causing the rod  5  to move in an axial direction. 
   Turning to  FIG. 5 ,  FIG. 5  shows a section view  150  of the head stock  1  and upper neck area  2  of the  FIG. 2  embodiment for actuating the rod  5 . As shown in  FIG. 5 , the handle  11  is connected to the gear shaft  10 , which is rotatably positioned in the head stock  1  by bushing/cover plates  12 . The gear  9  engages the teeth  26  on the rod  5  causing it move within a rod hole  13  in the neck  2 . The rod hole  13  extends the length of the neck  2 . The fit of the rod  5  within the rod hole  13  is such that the hole diameter is no more than necessary to permit slidable axial movement of the rod  5  within the hole  13  with minimal restriction. 
   Turning to  FIG. 6 ,  FIG. 6  shows a portion  160  of the neck  1  and fingerboard  3  showing several frets  14 . The frets  14  form a part of the fret-cylinders  15  in an extended position.  FIG. 6  also show one fret-cylinder  15  with a portion of a side plate  16  cut away to reveal the general shape of the fret-cylinders  15 . Located at both ends of each fret-cylinder  15  is a pinion  17  for positioning the fret-cylinders  15 .  FIG. 7  shows an embodiment  170  of rotatably mounting a fret-cylinder  15  to a side plate  16  using a pinion  17  that is located on the fret-cylinder  15  to fit within a hole  18  in a side plate.  FIG. 8  shows an alternative embodiment  180  of rotatably mounting a fret-cylinder  15  to a side plate  16  using a pinion  17  that fits into a fret-cylinder bushing  36  located in a fret-cylinder  15 , and fits into a hole  18  in a side plate  16 . 
   Turning to  FIG. 9 ,  FIG. 9  shows a top view  190  of a fret-cylinder  15  installed in a fingerboard  3 .  FIG. 10A  shows a sectional view  200  of the section A—A shown in  FIG. 9 , showing the fingerboard  3  and neck  2 , including a rod  5  and a fret-cylinder  15  in a retracted position. The rod  5  has rod-adjusting teeth  38  that engage cylinder-adjusting teeth  39  on the fret-cylinder  15 . When the rod  5  is caused to move in an axial direction by the rod adjusting mechanism  120  shown in  FIG. 2 , the rod-adjusting teeth  38  engage the cylinder-adjusting teeth  38 , causing the fret-cylinder  15  to rotate about an axis determined by the pinion  17 .  FIG. 10B  shows a sectional view  205  of the section A—A shown in  FIG. 9  showing the fingerboard  3  and neck  2 , including a rod  5  and a fret-cylinder  15  in an extended position with a fret  4  extending above a surface of the fingerboard  3 . The fret  4  may be retracted in an unfretted position shown in  FIG. 10A  or extended in a fretted position shown in  FIG. 10B  by axial movement of the rod  5 . 
   Turning now to  FIG. 11 ,  FIG. 11  shows a partial sectional view  210  of a head stock  1  and fingerboard  3  connected to the neck  2  of a stringed musical instrument such as a guitar or bass guitar having tuning knobs  8  equally located on both sides of the head stock  1 . The view  210  also shows strings  6  wrapped around tuning pegs  7 , that are rotatably connected to tuning knobs  8 , as conventionally configured on a guitar or bass guitar, whereby the tuning knobs  8  are turned to adjust tension on the strings  6  to determine acoustic pitch. An embodiment of the present invention is also shown in the view  210  that includes a fret-cylinder  4  that connectively engages a slidable rod  5 , and a rod adjusting mechanism comprising a handle  11 , a gear shaft  10  and a gear  9 . The slidable rod  5  extends from the head stock  1  through an aperture in the neck  2  to the instrument body. The description of the embodiment of the present invention shown in  FIG. 11  is the same as that described with reference to  FIG. 1  through  FIG. 5 , and will not be repeated here for brevity. 
   Turning now to  FIG. 12 ,  FIG. 12  shows an alternative embodiment  220  of a means for actuating the rod  5  with a small reversible electric motor  20  connected to a worm gear  21  located within an instrument body  19 . Turning to  FIG. 13 ,  FIG. 13  shows a detailed implementation  230  of the embodiment of  FIG. 12 . The small reversible electric motor  20  is connected to a worm gear  21  by a motor shaft  22 , causing the worm gear  21  to rotatably engage rod teeth  26  on the rod  5 , moving the rod  5  in an axial direction. A switch  23  connected by wires  24  to an electric system associated with the stringed musical instrument actuates the motor  20 . Motion limit switches  25  are activated by a rod lug  27  attached to the rod  5  to interrupt the current to the motor  20 , causing the motor  20  to stop when travel of the rod  5  reaches a position where the frets ( 4  in  FIG. 10B ) are either completely extended in a fretted position (shown in  FIG. 10B ) or completely retracted in an unfretted position (shown in  FIG. 10A ). 
   Turning to  FIG. 14 ,  FIG. 14  shows an alternative embodiment  240  of a method for actuating the rod  5  by manual means comprising an adjusting mechanism that includes a handle  11 , a bushing/cover plate  12 , a gear shaft  10 , a gear  9 , a rod  5 , and rod teeth  26 , all located in an instrument body  19 . Turning to  FIG. 15 ,  FIG. 15  shows a detailed implementation of the embodiment of  FIG. 14 .  FIG. 15  is similar to the adjusting mechanism shown in  FIG. 2 . A rod adjusting mechanism  250  shown in  FIG. 15  is an isometric view of the rod adjusting mechanism  250  comprising a handle  11 , a bushing/cover plate  12 , a gear shaft  10 , a gear  9 , a rod  5 , and rod teeth  26 . The handle  11  is fixed to the gear shaft  10 , which is fixed to the gear  9 . The gear  9  engages rod teeth  26  on the rod  5  such that when a musician turns the handle  11 , the gear  9  is caused to rotate, causing the rod  5  to move in an axial direction. This movement of the rod  5  causes the frets shown in  FIG. 10  to be extended or retracted. The bushing  12  positions the gear shaft  10 , allowing the gear shaft  10  to freely rotate within the bushing  12 . 
   Turning to  FIG. 16 ,  FIG. 16  shows another embodiment of a means  260  for adjusting a rod  5  by manual means at the instrument head stock  1 . The adjusting means  260  shown in  FIG. 16  comprises a slot  37  in the head stock  1  to receive a lever  28  that may pivot about an axle  29 . A lever slot  30  is provided in the upper part of the lever  28  to receive a rod arm  31  fixed to the rod  5 , and extending from the rod  5  through the lever slot  30 . Movement of the lever  29  by a musician imparts movement in an axial direction to the rod  5 , which causes the frets shown in  FIG. 10  to be extended or retracted. Although this adjusting means  260  is shown positioned in the head stock  1  of a stringed musical instrument, it may also be located in a body of a stringed musical instrument to accomplish the same axial movement of a rod  5 . 
   Turning now to  FIG. 17 ,  FIG. 17  shows yet another embodiment of a means  270  for adjusting a rod  5  by manual means at the instrument head stock  1 . The adjusting means  270  shown in  FIG. 17  comprises a handle  11  attached to a gear shaft  10 , which passes through the head stock  1 . Fixed to gear shaft  10  at the opposite end from the handle  11  is a wheel  32  having a linkage lug  33  that is radially offset from center of the wheel  32 . The linkage lug  33  is rotatably attached near an end of a linkage lever  34  that is rotatably attached to a saddle  35  near an opposite end of the linkage lever  34 . The saddle  35  is fixed to an end of the rod  5 . The wheel  32  and the linkage lug  33  function as a cam to transfer rotational motion of the shaft  10  to linear motion of the rod  5  in an axial direction. Movement of the lever  11  by a musician imparts movement in an axial direction to the rod  5 , which causes the frets shown in  FIG. 10  to be extended or retracted. Although this adjusting means  270  is shown positioned in the head stock  1  of a stringed musical instrument, it may also be located in a body of a stringed musical instrument to accomplish the same axial movement of a rod  5 . 
   Although the present invention has been described in detail with reference to certain preferred embodiments, it should be apparent that modifications and adaptations to those embodiments might occur to persons skilled in the art without departing from the spirit and scope of the present invention.