Stringed instrument capo
BACKGROUND OF THE INVENTION 
     This invention relates to a capo for use with a stringed musical instrument, such as a guitar or banjo, having a neck and a set of strings extending along the length of the neck, the capo serving to hold the strings against the fingerboard surface of the neck to make the strings of shorter than normal open length. More particularly, the invention relates to a capo which is an improvement over previous capo designs especially with regard to the case with which it may be attached to or removed from an instrument neck or moved from one position to another along the neck. 
     When a capo is in use on an instrument neck, it is desirable that its string engaging portion securely and tightly press the strings against the surface of the fingerboard regardless of whether or not the fingerboard includes frets. This requires that the capo be clamped to the neck with a considerable clamping force, and in previous capo constructions this force has been obtained through the use of relatively cumbersome clamping utilizing screws, toggle levers, springs, elastic bands etc. which were difficult to handle or time consuming to manipulate. In particular, the constructions of previous capos have generally been such that the acts of attaching one to an istrument neck, removing it from the neck or shifting it from one position to a another along the neck have required the use of two hands and have further required the performer to shift the instrument from its normal playing position. 
     The general object of this invention is, therfore, to provide an improved capo which includes a simple rapid application and rapid release clamping mechanism allowing it to be rapidly applied, released or shifted relative to an instrument neck by a simple one-handed manual operation without moving the instrument from its normal playing position thereby allowing the capo to be quickly applied, released or shifted, and enabling such changes to be made during a performance, if need be, without substantial interruption of the performance. 
     A further object of this invention is to provide a capo of the foregoing character which is of a rugged construction and which when operatively in place serves to hold the strings tightly against the fingerboard surface. 
     A still further object of this invention is to provide a capo of the foregoing character which is capable of being clamped to neck sections of a wide range of different sizes thereby permitting it be used with various different sized necks and/or with a single neck having a cross section which varies substantially in sized in going from one end to the other. 
     Other objects and advantages of the invention will be apparent from the following description and from the drawings forming a part hereof. 
     SUMMARY OF THE INVENTION 
     The invention resides n a stringed instrument capo having a body providing a top or string engaging arm adapted to extend transversely across the strings and the fingerboard surface of the neck of the instrument with which it is used. A side arm is integrally connected with one end of the top arm and extends rearwardly therefrom. A clamping jaw, pivotally connected to the side arm, extends from its pivot axis generally parallel to the top arm and is movable about its pivot axis into and out of engagement with the rear surface of an instrument neck received between it and the tip arm. The clamping jaw is movable by an operating lever also pivotally connected to the side arm through coengageable cam areas on the jaw and lever, the cam area of the lever comprising a plurality of rise and dwell surfaces arranged as a stair with the result that as the operating lever is moved in one direction about its pivot axis the clamping jaw is moved in step-wise fashion toward clamping engagement with the rear surface of the instrument neck and with the result that when the desired clamping relationship is reached the jaw and lever hold their last positions until released by further manual operation of the lever. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a capo embodying this invention. 
     FIG. 2 is a side elevational view of the capo of FIG. 1 showing it attached to a neck at a point where the neck has substantially the minimum cross sectional size with which the capo may be used. 
     FIG. 3 is a view similar to FIG. 2 but shows the capo attached to a neck at a point where it has a cross sectional size substantially equal to the maximum with which the capo may be used. 
     FIG. 4 is an enlarged fragmentary view showing the cam areas of the jaw and of the operating lever of the capo of FIG. 1. 
     FIG. 5 is a view similar to FIG. 4 but shows an alternative embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 1 to 4, a capo embodying the invention is shown generally at 10. It includes a one-piece body 12 shaped somewhat like the letter &#34;C&#34; and having a top arm 14 and a side arm 16. As shown in FIGS. 2 and 3, the top arm 14 is intended to extend across the strings 18, 18 and the fingerboard surface 20 of the instrument neck 22 with which the capo is used. The arm 14 has one free end and the side arm 16 is integrally connected to it at its opposite end. The side arm 16, n turn, extends rearwardly from the top arm 14 and in doing so curves inwardly towards the free end of the top arm so as to terminate in a free end 24 located rearwardly of the top arm and between its two ends. 
     A clamping jaw 26 is pivotally connected to the side arm 16 for pivotal movement relative to the side arm about a first pivot axis 28. To make this connection, the side arm 16 is divided into two spaced cheeks by a slot 30 which receives an ear portion of the jaw, and a roll pin 32 is inserted through the side arm cheeks and through the ear of the jaw. 
     Also carried by the side arm 16 is an operating lever 34 pivotally connected to the side arm by another roll pin 36 inserted through the side arm cheeks and a portion of the operating lever received in the slot 30. The pivot axis of the operating lever relative to the side arm is indicated at 38 and is located between the pivot axis 28 and the free end 24 of the side arm. 
     The clamping jaw 26 extends from its pivot axis 28 in a generally parallel relationship to the top arm 14 and is therefore, as a result of pivotal movement about its axis 28, movable toward and away from the rear surface 40 of the neck 22 positioned between it and the top arm. Such movement of the jaw 26 is effected by movement of the operating lever 34 through coengaging cam areas on the jaw and lever. As shown best in FIG. 4, the cam area of the lever 34 is comprised of a plurality of dwell surfaces 42, 42 which alternate with a plurality of rise surfaces 43, 43 so that the dwell and rise surfaces are arranged in a stair fashion. That is, in going from one circumferential end to the other circumferential end of the lever&#39;s cam area, the dwell surfaces 42, 42 are at progressively larger or smaller (depending on the direction of movement) radial levels from the pivot axis 28. For example, of the three radiuses shown in FIG. 4 R 1  &lt;R 2  &lt;R 3 . 
     The dwell surfaces 42, 42 and rise surfaces 43, 43 of the lever 34 cooperate with two rest surfaces 44, 44 and two cam surfaces 45, 45 on the jaw 26. From FIGS. 2 and 4, it will therefore be evident that as the lever 34 is moved clockwise from its illustrated full line position toward the illustrated broken line position, the jaw 26 will be allowed to move clockwise to bring it out of clamping relationship with the instrument neck. On the other hand, when the operating lever 34 is in the broken line position of FIG. 2 and then moved counterclockwise toward the full line position, the surfaces 42, 42 and 43, 43 will cause the jaw 26 to be moved in step-wise fashion toward the rear surface 40 of the instrument neck and into eventual clamping relationship with it. That is, as the rise surfaces 43, 43 of the lever engage and move over the cam surfaces 45, 45 of the jaw, the jaw will be cammed incrementally toward the neck, and as the dwell surfaces 42, 42 move over the rest surfaces 44, 44 the jaw 26 will momentarily retain its present position. The dwell surfaces 42, 42 are slightly curved and have their centers of curvature substantially coincident with the pivot axis 28. Therefore, when the rest surfaces 44, 44 engage a pair of dwell surfaces 42, 42 the lines of action of the forces imposed by the rest surfaces on the operating lever pass through the pivot axis 28 and produce no torque on the operating lever. When manual movement of the operating lever in the clamping direction is stopped, this causes the lever to hold its last position. That is, after the clamping jaw has reached clamping relationship with the neck, it will be held there by the lever until it is released by the lever being manually moved in the releasing or clockwise direction. 
     As shown by comparison of FIG. 2 with FIG. 3, the arrangement of the cam areas of the operating lever and jaw, and the arrangement of other parts, allows the capo to be used with neck cross sections of various different sizes, FIG. 2 showing the capo in clamped engagement with a small section neck and FIG. 3 showing it in clamped engagement with a large neck section. 
     Preferably, and as shown, the top arm 14 includes a resilient pad 46 of rubber or the like for engaging the strings 18, 18 and likewise the clamping jaw 26 includes a resilient pad 48 of rubber or the like for engaging the rear surface of the neck. The remaining parts of the capo may be made of various suitable materials. In particular, the body 16, jaw 26 and lever 34 may be made of metal or plastic, a preferred material for all three of these parts being powdered stainless steel. 
     The dwell and rise surfaces of the cam area of the operating lever and the rest and cam surfaces of the jaw may take various different shapes without departing from the broader aspects of the invention. Also, the number of rest and cam surfaces on the jaw may vary. As a limit, only one rest surface and one cam surface may suffice, and these may blend with one another and be provided by a simple bump or protrusion on the jaw. In any event, however, the shape and arrangement of the dwell surfaces should always be such that the line of action of a force imposed on the lever by the jaw will either pass substantially through the lever&#39;s pivot axis 28 or to such side of such pivot axis that the torque exerted on the operating lever urges it in the counterclockwise direction. 
     By way of example, FIG. 5 shows a lever 34 with an alternative form of dwell surfaces. Referring to this figure, the cam area of the illustrated operating lever 34 includes dwell surfaces 50, 50 and rise surfaces 52, 52. Each dwell surface 50 is curved and has its center of curvature displaced slightly from the line 54 passing through the pivot axis. Therefore, the line of action 56 has a moment arm d with respect to the pivot axis, producing a torque tending to rotate the lever 34 in the counterclockwise direction in FIG. 5 and thereby causing the lever to hold the illustrated position until moved from it by a manually applied force.