Abstract:
A microprocessor-controlled tuning apparatus for a stringed instrument, wherein the tension of a string is detected by a sensor, compared with a reference value, and readjusted if necessary until the detected value conforms with the reference value, thereby achieving a corresponding musical pitch.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an apparatus for tuning stringed instruments. 
     BACKGROUND OF THE INVENTION 
     In a stringed instrument, each string is extended with a predetermined tension between two critical contact points that primarily define the effective length of the string. The first critical contact point is generally at the bridge, which is provided on the body of the instrument. The second critical contact point is generally at the nut which, depending on the instrument, is usually positioned on the head or at a point of the neck distant from the body of the instrument. Both the tension and the effective length of the string determine its musical tone. 
     The distance between the bridge and the nut is the primary determinant of the effective length of a string. However, an instrumentalist can shorten the effective length during a musical performance, by depressing the string with a finger until it contacts any one of a plurality of frets that are positioned along the neck of the instrument between the nut and the bridge. 
     Vibrating the string generates a musical tone. In an instrument such as a guitar, a musical tone is conventionally obtained by plucking the string with a finger; in an instrument such as a violin, the musical tone is obtained by drawing a bow back and forth across the string. 
     A string that is extended with an improper tension and is extended for a distance of an improper string length may result in a generation of a musical tone of an incorrect sound frequency. Accordingly, each of the strings specially needs to be extended under a proper tuning state. 
     SUMMARY OF THE INVENTION 
     The present invention relates to an apparatus for tuning stringed instruments in which each of a plurality of strings is operably connected to a corresponding sensor and a tensioning driver. The sensor provides to a microprocessor controller a real time value of the tension in the corresponding string. A computer receives the real time tension value from the microprocessor and compares it with a predetermined reference value stored in the computer memory. Feedback information is provided to the microprocessor, which commands the driver to adjust the string tension accordingly. 
     In a preferred embodiment, the sensor that measures the string tension is a strain gauge. The operative component of a strain gauge is an electrically conductive element that is connected to the system whose tension is to be measured, and is thereby subjected to the same tension. The electrical conductivity of the element varies with tension in a known manner; it is determined by imposing a known voltage across the element, and measuring the resultant current. Since the musical pitch of a musical instrument is directly related to its tension, other factors being unchanged, the strain gauge therefore provides a simple means of tuning the instrument. The measurement of string tension may also be done using the conductivity of the strings themselves, if electrically conductive strings are used. 
     When, after time and repeated use, the string stretches and becomes looser, the microprocessor may compare the present value of the tension to the value in memory and command the driver to tighten the string back to the tension it possessed upon first being tuned. 
     The stored reference tuning values set by the user may be changed as desired. Further, multiple settings may be stored in the computer to allow a user to alter the tuning of the instrument as it is played. 
     A computer may be used having a wireless connection to the adjusting drivers on the instrument. In addition, plurality of instruments may be operably connected by the wireless communication to the operator, wherein each stringed instrument has its own channel of communication. The computer would coordinate actions among multiple instruments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic showing a tuning apparatus for a stringed instrument. 
     FIG. 2 is a schematic plan view of the stringed instrument, omitting the tuning apparatus. 
     FIG. 3 is a schematic side elevation of the instrument of FIG.  2 . 
     FIG. 4 is a schematic plan view of the strings of a stringed instrument, including elements of the tuning apparatus. 
     FIG. 5 is a schematic plan view of part of the instrument with elements of the tuning apparatus. 
     FIG. 6 is a schematic plan view of a driver including a motor and a worm drive. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, FIG. 1 shows schematically a tuning apparatus  10  for a musical instrument  20  which, as shown in FIGS. 2 and 3, has a body  22 , a neck  24 , a head  26  and a plurality of strings  28 . Each string  28  is affixed to the body  22  by an anchor  30 , then passes over a bridge  32 , and extends without contact along the length of the neck  24  until it passes over a nut  34 . The bridge  32  and the nut  34  provide critical contact points which define the effective length of the string  28  when it is set into vibration. As best seen in FIGS. 4 and 5, the string terminates (after changing direction if necessary at a point such as  36 ) at a tension-sensing device  40 , which has on one side  42  an attachment point whereto the string  28  is fixedly but removably connected. The tension-sensing device  40  is preferably a strain gauge. An opposite side  44  of the tension-sensing device  40  has a second attachment point, whereto is fixedly attached a tuning string  46 . This extends to a driver  50 , where it is wound around a rotatable spindle  52 . 
     The bridge  32  and the nut  34  are grooved at their points of contact with all the strings to preclude unintentional displacement of the strings. For clarity, the grooves are omitted from the drawings. 
     The schematic of FIG. 1 shows a microprocessor  70  that is electrically linked to the tension-sensing devices  40  by connector wires  72 . Similar connector wires  74  link the microprocessor  70  to the drivers  50 . FIG. 1 also shows connector wires  76  and  78  extending, respectively, from the microprocessor  70  to a computer  80 , and from the computer  80  to a keyboard  82  or other input device. 
     FIG. 5 shows an embodiment that has a wireless connection  84  between the microprocessor  70  and the computer  80 . As FIG. 5 shows, the microprocessor  70  can be conveniently positioned at some point on the surface of the head  24  of the instrument  20 . For clarity, FIG. 5 shows only one of the connector wires  72  that link the microprocessor  70  with the tension-sensing devices  40 . 
     As pointed out earlier, the bridge  32  and the nut  34  constitute critical contact points. Their distance apart determines the effective length of the string in determining the pitch. However, during a musical performance an instrumentalist can depress any of the strings with a finger until it contacts any of several frets  90  along the neck  24 . This changes the effective length of the string and therefore its pitch. However, the pitch of the string is still subject to its tension as well as to its effective length. 
     The tuning apparatus operates as follows. The microprocessor  70  is commanded to activate by a signal from the computer  80  in response to user input at the keyboard  82 . A signal from the tension-sensing device  40  is received as input by the microprocessor  70  and passed to the computer  80 . The information from the tension-sensing device  40  is compared with a reference value stored in the computer  80  and if any difference is detected, an appropriate command is fed back to the microprocessor  70 , which then causes the driver  50  to activate and change the tension in the string accordingly. As shown in FIG. 6, the driver  50  includes an electric motor  54  with a driveshaft  56  and a worm drive  58 , which consists of a worm  60  which engages with a gear wheel  62 . In turn, the gear wheel  62  is axially connected with the spindle  52  around which the tuning string  46  is wound. 
     Worm drives of the type described have two well-known attributes. First, they are an extremely effective reduction mechanism, being capable of providing a great reduction in speed and a correspondingly great mechanical advantage. Secondly, they are irreversible in the sense that while the worm can easily drive the gear, the gear cannot drive the worm. Both attributes are important to the present invention. 
     In particular, it can be seen that the motor  54  can easily adjust the tension of the instrument string  28  and the tuning string  46 , but that the tension, once set, cannot be transmitted back to the motor  54 . When the worm  60  is stationary, it precludes the gear  62  from rotating. Therefore, the pitch of the instrument string  28  is set until it either degrades from continued use or aging, or until it is intentionally readjusted. 
     In another embodiment, the strings themselves may be used as the tension-sensing devices. This would depend on the strings having an electrical conductivity that changes with tension. A voltage would be imposed across an element of each string between two unchanging reference points to produce an electrical current depending on the resistance, providing a measure of the resistance and thus of the tension. The current would be much smaller than would be obtained from a strain gauge and would likely have to be electrically amplified to be readily detectable; an electrical amplifier coupled to a current detector coupled to the string would be connected to the microprocessor in the same manner as the strain gauges. 
     The tuning apparatus may be used on an intermittent basis, between musical performances, or it may be used during a performance to vary the pitch of one or more strings on demand when required to produce special effects. Furthermore, the tuning apparatus may be use on multiple instruments; each instrument would be independently tunable, with its own wired or wireless channel of communication to the computer. 
     Obviously, some source of power must be provided for the drive motors  54  and for the tension-sensing devices. For clarity, no power source is shown in the drawings. An external power lead may be provided. Alternatively, a power source may be provided on board the instrument in the form of one or more batteries or power packs. 
     The tuning apparatus described above may also find use in other applications. For example, on interaction with suitable software, the signal received by the computer can be used to transcribe to a different musical key a piece of music performed on the instrument. 
     While the foregoing description and figures are directed toward preferred embodiments of the present invention, it should be appreciated that numerous modifications can be made to the structure and orientation of the various components of the present tuning system without departing from the spirit and scope of the present invention. Accordingly, the foregoing description should be taken by way of illustration rather than by way of limitation as the present invention is defined by the claims set forth below.