Abstract:
A self-contained tuning stabilizer for a stringed instrument consists of a body which is attachable to the stringed instrument like a capo, the stabilizer containing mechanical members for increasing or decreasing the tension on each of the strings to keep them in tune as the instrument is played. The device contains sensors for each string, an analyzer for determining if the frequency produced by each string is correct, and a driver for each of the mechanical members for applying micro-tuning corrections to the strings. The device must first be zeroed, and the instrument tuned by hand. Thereafter, the device will maintain the original tuning.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Many stringed instruments, and guitars in particular, require periodic tuning to remain playable. Due to the stresses on the strings and the tuning mechanisms imposed during the normal course of use of the instrument, constant tuning may be required, even during the course of a single performance. The need for constant tuning may disrupt the flow of a performance and is a distraction for the musician. 
         [0002]    Automatic tuners for guitars are well known in the art. Most are built into a guitar or require major modification to retrofit into a guitar and consist of a sensor for sensing the pitch of a string and a means for tensioning the string to achieve the proper tension. 
         [0003]    Such a system is described in U.S. Pat. No. 6,437,226, issued Aug. 20, 2002 to Oudshoorn, et al. The patent describes system wherein a signal is induced onto a string under tension by a linear displacement motor. The resonance signal generated by the string is picked up by a transducer, converted to a digital signal and analyzed by a microprocessor. The motors then tension or slacken the string in response to the analysis to achieve the proper tuning. 
         [0004]    Another such system is sold by Tronical, GmbH of Hamburg, Germany. The Tronical system requires that the musician strum the strings of the instrument to generate a test frequency, which is then analyzed by a microprocessor. The strings are tensioned or slackened by machine heads which are driven by servo motors. 
         [0005]    Both the Oudshoorn system and the Tronical system are capable of tuning a guitar, regardless of how far out of tune. Such systems, however, not only are expensive, but have the drawback of requiring permanent installation in a guitar. Therefore, it would be desirable to have a device for keeping a stringed instrument in tune that could be used with any instrument, without the requirement of major modification to the guitar for permanent installation. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention is a retro-fit device that may be used with any stringed instrument having a neck, such as a guitar, banjo, bass or violin. The device is not meant to perform the function of tuning the instrument from scratch, but instead is designed to maintain the instrument in tune after it has been hand-tuned, such as during the course of a performance. 
         [0007]    The device consists of a mechanical portion that is attached to the neck of the instrument, much like a capo. The device has built-in sensors to pick up the frequency of a string and a microprocessor to determine when the strings have drifted from their tuned frequencies. The strings may then be “micro-tuned” by a series of cams which may be rotated to further tension or slacken each of the strings. 
         [0008]    The device is completely self-contained and battery-powered, and has the advantages over the prior art systems of relatively low cost and portability. The device may quickly be attached and removed from the neck of the instrument. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1(   a ) is a top view of a guitar having the device attached thereto. 
           [0010]      FIG. 1(   b ) is a side view of a guitar having the device attached thereto. 
           [0011]      FIG. 2  shows a side view of a first embodiment of the invention mounted on a guitar. 
           [0012]      FIG. 3  shows a side view of a second embodiment of the invention mounted on a guitar. 
           [0013]      FIG. 4(   a ) shows a to view of a sub-assembly of the device 
           [0014]      FIG. 4(   b ) shows a side view of a sub-assembly of the device. 
           [0015]      FIG. 5  shows a side view of a third embodiment of the device mounted on a guitar, 
           [0016]      FIG. 6  shows the detail of the pin and gear assembly of the third embodiment. 
           [0017]      FIG. 7  shows the pin/string interaction of the third embodiment 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    The invention herein described may be used with any stringed instrument having a neck defining a fretboard. The example used to show the embodiments of the invention utilize a guitar for explanation purposes only. This is not meant to limit the invention in any way. In addition, the device is meant to be compatible with guitars of all configurations, including 6 and 12 string varieties, as well as those guitars having all machine heads on one side of the headstock or divided between both sides of the headstock. 
         [0019]    The device is preferably attached to the guitar like a capo, via a hinged clasp mechanism secured by a latch. The bottom brace of the clasp engages the rear of the headstock  52  or fretboard  50  of the guitar opposite the strings, while the top brace consists of the main body of the device. Preferably, the bottom brace is lined with a scratch-resistant material, such as rubber, neoprene or felt to prevent scratching the guitar, while still providing enough gripping power to keep the device securely fastened in place. 
         [0020]      FIGS. 1(   a ) and  1 ( b ) show top and side views respectively of the tuning device  100  mounted on a guitar in the preferred position. Tuning device  100  preferably sits between nut  107  and the first machine head  70  on headstock  52  of the guitar, with felt pad  106  resting on nut  107 . 
         [0021]    The body of tuning device  100  consists of a subassembly, shown in  FIG. 4 , which consists of top portion  102 , heel portion  104  and felt pad  106 . Defined in top portion  102  are a plurality of peg holes  108   a  through which pegs  108  are disposed. Heel  104  has defined therein a plurality of cam holes  110   a  which are the mounting points for cams  110 . The subassembly of tuning device  100  can be composed of any material suited for the purpose, such as wood or plastic, as can cams  110  and pins or pistons  108 . The invention is not meant to be limited to any particular material. 
         [0022]    With reference now to  FIG. 2 , showing a preferred embodiment of the invention, pegs  108  are disposed through peg holes  108   a  and are positioned one each in close proximity to each string  60  of the guitar. In the preferred embodiment of the invention, pegs  108  will rotate cams  110  which are mounted via connectors  112  through cam holes  110   a  by exerting a force on the lobe of cam  110 . Cams  110  are positioned such that pressure in direction  109  as shown in  FIG. 2  will cause pin  108  to rotate cam  110  to deflect against string  60 , thus providing additional tension on string  60 . Likewise, when pin  108  is moved in a direction opposite direction  109  cam  110  will be allowed to rotate in such as manner as to lessen the tension on string  60 . Cams  110  may be rotationally driven by springs (not shown) which will drive them in a rotational direction to insure that they are always providing a resistive force against pin  108 , such that the cams will return to their neutral position when the force exerted by pin  108  is lessened. It should be noted that cam holes  110   a  are not horizontally aligned but extend in a sloped direction dependant upon the slope and contour of headstock  52  of the guitar. 
         [0023]    Cams  110  may be driven by a driving device (not shown), such as a motor, a solenoid, or a servo, that may generate a mechanical, electromechanical, pneumatic or hydraulic force upon the pins to drive them in direction  109 . Any means of performing this function well known in the art may be used for this purpose. 
         [0024]    In an alternate embodiment of the invention, cams  110  may be eliminated and pins  108  may be caused to press directly upon strings  60  of the guitar. In such a case, pins  108  may be spring loaded such as to be forced in the direction opposite direction  109 . 
         [0025]      FIG. 3  shows a second embodiment of the invention utilizing a different type of cam  111 . Cams  111  are center mounted in cam holes  110   a  and define a worm gear on the outer edge thereof such as to be driven by a worm  113  defined on the end of shaft  112 . A driver or servo to rotate shaft  112  (not shown) is also provided and may be of any standard means of providing a rotational force well known in the art. Note that in this embodiment of the invention, cams  111  need not be spring loaded, however the driver that rotates shaft  112  needs to be capable of providing a rotational force in both directions, such that cams  111  may also be rotated in both directions. 
         [0026]    With respect to both embodiments shown in  FIGS. 2 and 3 , the rotating cam will preferably be able to provide at least a 0.04 inch deflection of each string  60  on the guitar. 
         [0027]    A third embodiment of the invention is shown in  FIGS. 5-7 . In this embodiment, as shown in  FIG. 5 , pins  108  define notch  107  at the bottom end thereof, with notch  107  of each pin engaging one of strings  60 . Pins  108  may then be rotated clockwise or counterclockwise to increase or lessen the tension on string  60 . 
         [0028]    Preferably, as shown in  FIG. 6 , pins  108  will define a pinion gear  105   b  around the outer circumference thereof. Pin  108  may then be rotationally driven by engagement with rack  105   a  or a circular gear (not shown). As with the first two embodiments of the invention, the linear motion of rack  105   a  may be driven by any means known in the art, such as by a geared motor, a solenoid, or a servo, that may generate a mechanical, electromechanical, pneumatic or hydraulic force on rack  105   a.    
         [0029]      FIG. 7  shows the engagement of pin  108  with string  60 . Preferably, the inner contours of notch  107  will be rounded to reduce the possibility of breaking string  60 . 
         [0030]    In an alternate to embodiment 3, strings  60  could be wound multiple times around pins  108 , such as to eliminate the need for machine heads  70 . In some cases, entire headstock  52  could be eliminated. In this embodiment, pins  108  may take on a concave outer profile, such as to provide room for multiple windings of string  60  around pin  108 . In addition, pins  108  may define a hole therein to accept the end of string  60 . In this alternate embodiment, the guitar could become a completely self-tuning instrument, being able to tune to different pre-programmed ranges. 
         [0031]    Also included as part of the invention, but not shown in the drawings, is a means of detecting the frequency of strings  60  as they are strummed by the musician. This means will likely consist of a plurality of audio input transducers which will pick up an analog signal from each of the strings. The analog signal would likely be converted to a digital signal via an analog to digital converter and then analyzed by either a programmed microprocessor or a specialized circuit capable of analyzing the received audio input and determining if the string needs to be retensioned to bring it back into tune. 
         [0032]    In another aspect of the invention, the device cold be outfitted with a wireless transceiver such that a signal picked up by sensors from one or more of the strings could be sent wirelessly to a base station for amplification or processing, or may be supplied to a computer as a MIDI signal. 
         [0033]    In operation, tuning device  100  would be initialized by zeroing the cams, such that the cams are deflected half way against the strings, or, as in the third embodiment, partially twisted around each of the pins. The guitar is then manually tuned utilizing machine heads  70  for each string in the normal manner. After a period of use, the guitar may have drifted out of tune. To have tuning device  100  perform the micro tuning adjustments to the strings to bring the instrument back into tune, the strings may be strummed either one at a time or in series while alerting tuning device  100  that a tuning operation has begun by, for example, depressing a button on the device. 
         [0034]    It is also contemplated that tuning device  100  may assist the musician in the manual tuning of the guitar by providing an indication that each of the strings is sharp, flat or tuned to the correct frequency by providing some form of feedback to the musician, such as a light or series of lights which indicate if the string is sharp, flat or properly tuned. 
         [0035]    Although the invention is shown having pins pushing against the cams to rotate them, it is contemplated that other means of rotating the cams could be used such as a direct drive of the cams with a servo providing a rotational force or a force exerted through a series of gears such as to provide rotational movement in both directions of the cams, thus allowing the pins to be eliminated. In addition, it is possible that the driver or servo mechanism could sit higher on the headstock than the rest of the device, such as between the machine heads, and be connected to the cams via a linkage. 
         [0036]    The device is contemplated to be battery powered, with the batteries likely resident in the bottom brace of the device. It is also contemplated that the frequency detection circuitry and mechanical driver portions be located within the top portion  102  of the device, but in certain configurations, could also be located in the bottom brace, and thus be resident on the underside of fretboard  52  of the guitar and be linked via mechanical linkage to the cams.