Abstract:
A tunable bridge for a string musical instrument is provided to enable a user to rapidly switch between two pre-selected string tunings simply by movement of an actuator arm. The actuator arm controls the position of a cam roller assembly, which in turn controls the pivotal movement of a rocker arm between a lower position and an upper position. A multiplicity of string fingers are mounted for pivotable movement between respective first and second tuning positions. A plurality of manually-adjustable tuning screws with engagement tips are threadedly disposed in the rocker arm. Each engagement tip is configured to press against a respective string finger when the rocker arm is placed in its upper position, thereby further stretching the strings attached to the respective string fingers and increasing their pitch in accordance with the second pre-selected tuning. Mounting of the tunable bridge does not require permanent modification of the string instrument.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 61/983,431 filed Apr. 23, 2014, the content of which is incorporated by this reference in its entirety for all purposes as if fully set forth herein. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to string musical instruments. More particularly, the invention relates to devices which support and facilitate the tuning of the strings of such instruments. 
     BACKGROUND 
     The use of the Resophonic Guitar has increased in popularity in many genres of music including Bluegrass, Folk, Country, Country Rock, and Rock and Roll. A popular style of resophonic guitar playing uses a bar, usually made of steel or brass and raised strings. The bar (or slide as it is commonly referred to) is held against the strings producing a slurring sound. The strings do not contact the fret board as is the case in traditional guitar playing. Also the instrument is generally held in a horizontal position as opposed to the usual vertical position that is popular in traditional guitar playing. This style of playing is similar to Hawaiian Steel Guitar or Lap Steel Guitar. 
     The resophonic guitar is usually tuned to an open chord, the popular tunings being Open D (DADF#AD) and Open G (GBDGBD). It would be a tremendous advantage if an instrument could be instantly retuned to either of these tunings with a single flip of a toggle lever during a song. Of course in doing so, many factors would have to be addressed. For convenience, the example of tuning between Open D and Open G tunings will be used for this patent application. It must be noted that there are many other tunings that lie within the scope of this invention. It must also be noted that although the resophonic guitar is highlighted in this application, the invention will work on many other types of acoustic and electric guitars as well as many other types of string musical instruments. 
     Manually retuning the guitar from one open tuning to another during a performance would not be practical. It would take many minutes to tune and retune the instrument. So if a performer would like to be able to switch from one tuning to another, traditionally two guitars would have to be used. 
     The open D tuning consists of the strings tuned to these specific notes: The 6 th  string is D (which is stretched to about 21 pounds in tension), the 5 th  is A (36 pounds), 4 th  string is D (32 pounds), 3rd is F# (32 pounds), 2 nd  is A (18 pounds) and 1 st  is D (24 pounds). The total tension of all string applied to the guitar when tuned to open D is about 163 pounds. 
     The open G tuning consists of the strings tuned to the following notes; 6 th  string is G (38 pounds), 5 th  string is B (44 pounds), 4 th  string is D (32 pounds), 3 rd  string is G (36 pounds), 2 nd  string is B (22 pounds) and the 1 st  string is D (24 pounds). The total pounds applied to the guitar when tuned to an open G chord are about 196 pounds. The change of tension of the strings between Open D and Open G tuning totals approximately 33 pounds. A mechanical device would have to be developed to accurately and simultaneously retune this tension differential. 
     The following tuning charts are helpful in visualizing and comparing the Open D tuning with the Open G tuning 
     
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 OPEN D TUNING 
               
             
          
           
               
                   
                 STRING 
                 LBS 
               
               
                   
                   
               
               
                   
                 1 ST  STRING D 
                 24 
               
               
                   
                 2 ND  STRING A 
                 18 
               
               
                   
                 3 RD  STRING F# 
                 32 
               
               
                   
                 4 TH  STRING D 
                 32 
               
               
                   
                 5 TH  STRING A 
                 36 
               
               
                   
                 6 TH  STRING D 
                 21 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 OPEN G TUNING 
               
             
          
           
               
                   
                 STRING 
                 LBS 
               
               
                   
                   
               
               
                   
                 1 ST  STRING D 
                 24 
               
               
                   
                 2 ND  STRING B 
                 22 
               
               
                   
                 3 RD  STRING G 
                 36 
               
               
                   
                 4 TH  STRING D 
                 32 
               
               
                   
                 5 TH  STRING B 
                 44 
               
               
                   
                 6 TH  STRING G 
                 38 
               
               
                   
                   
               
             
          
         
       
     
     In reviewing the charts, it is apparent that the 4 th  string D and 1 st  string D are common between the G and D tunings One might think that this would facilitate the rapid transition tuning between D and G tunings. However, as the 6 th  string D tension is increased to G, the 5 th  string A tension is increased to B, the 3 rd  string F# tension is increased to G and the 2 nd  string A tension is increased to B, a slight flexing or bending motion takes place in the instrument. This bending motion is much like how a bow deforms as an archer pulls the bow string back. Unlike the archer and bow, the deformation of the instrument is not as visually apparent. However it does affect the pitch of the common notes of the 1 st  and 4 th  strings. As the instrument bends inward (switching from D to G), the common strings slacken slightly which audibly lowers their pitch. Therefore it would be highly desirable that the device be able to automatically compensate for this drop of pitch incurred on the common strings. 
     As Resophonic guitars can be very expensive, it would be preferable that the invention mount to the instrument in such a manner as to not degrade or permanently alter the instrument. 
     It would be highly desirable that the invention also fit into the guitar case. 
     It would be important that the invention not detract from the aesthetic of the instrument. 
     It would be desirable that the invention be quickly tunable without the use of tools such as tuning wrenches. 
     Because the instrument is generally played acoustically, it is highly desirable that no electric power or any other alternative power be required to perform the tuning function. 
     Smooth, musical transition between tunings should be accomplished. 
     Because the instrument is acoustic and is very often amplified or recorded by the use of sensitive microphones, it is essential that the invention operate quietly and smoothly. 
     By the use of descriptions and figures, the following pages will show how embodiments of the present invention accomplish these objectives. 
     SUMMARY 
     Certain deficiencies of the prior art may be overcome by the provision of one or more embodiments of a self-compensating tunable bridge for string musical instrument. 
     An exemplary embodiment of a tunable bridge for a string musical instrument may comprise a base plate, a rocker arm, a cam roller fork, a cam roller, an actuator arm, a multiplicity of string fingers and a corresponding plurality of tuning screws. 
     The base plate is typically securable to the instrument without permanently modifying the instrument. The rocker arm may have a proximal portion, a distal portion and a rocker axis therebetween. The rocker arm is mounted for pivoting movement with respect to the base plate about the rocker axis between a lower position and an upper position. The rocker arm may include one or more noise attenuation pads configured to prevent direct contact between the rocker arm and the base plate when the rocker arm is in its lower position; 
     The cam roller fork is mounted for rotational movement with respect to the distal portion about a cam axis between a lock position and a release position. The cam roller is mounted to the cam roller fork and configured to contact the base plate for translational movement relative thereto when the cam roller fork is moved between its lock and unlock positions. The cam roller is preferably rotatably mounted to the cam roller fork for rotation about a roller axis such that the translational movement causes rolling contact between the cam roller and base plate. The cam roller may comprise one or more elastomeric rings disposed thereabout. The actuator arm is actuatable about the cam axis between a first arm position and a second arm position. 
     Each of the string fingers preferably has a tuning interface portion, a ball detent portion and a finger axis therebetween. Each ball detent portion is adapted to receive a string having a string ball, and to prevent the string ball from passing through the ball detent portion. Each string finger is mounted for pivotable movement with respect to the base plate about its finger axis between a first tuning position and a second tuning position. Each string finger preferably includes a foot on its ball detent portion. The foot is adapted to rest against the base plate when its respective string finger is in its first tuning position, thereby restraining the string finger from pivotal movement past its first tuning position in a direction away from its second tuning position. 
     Each tuning screw preferably has an engagement tip and is threadedly disposed in the proximal portion for adjustable placement of the engagement tip at a respective axial distance therefrom. Each of the engagement tips is configured to pressingly engage a respective tuning interface portion. 
     Actuation of the actuator arm to the second arm position forces the cam roller fork into its lock position. This in turn forces the rocker arm toward its upper position. Movement of the rocker arm to its upper position causes one or more of the tuning screw engagement tips to come into pressing engagement with their respective string finger tuning interface portion so as to impose a pivoting force on the respective string finger about its finger axis toward its second tuning position. This in turn causes respective strings to tighten to a pre-selected degree, thereby causing the instrument to almost instantaneously achieve a second tuning Actuation of the actuator arm from its second arm position toward its first arm position forces the cam roller fork out of its lock position, thereby allowing the instrument to rapidly return to its first tuning 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages of the present invention may become apparent to those skilled in the art with the benefit of the following detailed description of the preferred embodiments and upon reference to the accompanying drawings in which: 
         FIG. 1  is a diagrammatic plan view of a resophonic guitar featuring one example embodiment of a tunable bridge in accordance with the present invention; 
         FIG. 2  is a diagrammatic partial perspective view of the guitar and tunable bridge of  FIG. 1 , wherein the actuator arm is in its first arm position and the rocker arm is resultingly in its lower position; 
         FIG. 3  is a diagrammatic partial perspective view similar to that of  FIG. 2 , but wherein the actuator arm is in its second arm position, the cam roller fork is rotated into its lock position and the rocker arm is resultingly maintained in its upper position; 
         FIG. 4  is a diagrammatic plan view showing an example of a tunable bridge in accordance with the present invention, wherein the actuator arm is in its first arm position and the cam roller fork is rotated therewith to its unlock positon; 
         FIG. 5  is a diagrammatic plan view similar to that of  FIG. 4 , but wherein the actuator arm is in its second arm position and the cam roller fork is rotated therewith to its lock positon; 
         FIG. 6  is a diagrammatic side view of components of a tunable bridge, illustrating an example of the mechanical interaction between the cam roller assembly, including the actuator arm, cam roller fork, cam roller and rocker arm; 
         FIG. 7  is a further diagrammatic side view of components of a tunable bridge, illustrating an example of the mechanical interaction between a base plate, rocker arm, tuning screw, string finger and string; 
         FIG. 8  is a diagrammatic partial perspective view of one embodiment of a tunable bridge, illustrating the ability to set the second tuning position of each individual string finger independently by way of respective manually-adjustable tuning screws; 
         FIG. 9  is a diagrammatic side view of components of one embodiment of a tunable bridge, illustrating the potential mechanical advantage provided by a first lever system involving the interaction between a rocker arm, tuning screws, string fingers and strings; 
         FIG. 10  is a further diagrammatic side view of components of one embodiment of a tunable bridge, illustrating the potential mechanical advantage provided by a second lever system involving the interaction between an actuator arm, cam roller fork, cam roller and rocker arm; 
         FIG. 11  is a further diagrammatic side view of components of one embodiment of a tunable bridge, illustrating the cam roller fork moving into its lock position as a result of the actuator arm being moved into its second arm position; 
         FIG. 12  is a diagrammatic perspective view of an embodiment of a tunable bridge in accordance with the present invention, wherein the actuator arm is shown in its second arm positon, the cam roller fork is shown in its lock position and the rocker arm is shown in its upper position; 
         FIG. 13  is an exploded view of the embodiment of a tunable bridge shown in  FIG. 12 ; 
         FIG. 14  is a diagrammatic plan view of one embodiment of a rocker arm; 
         FIG. 15  is a diagrammatic side view of the rocker arm shown in  FIG. 14 ; and 
         FIG. 16  is a diagrammatic side view of one embodiment of a string finger. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, like reference numerals designate identical or corresponding features throughout the several views. 
       FIG. 1  depicts the plan view of a resophonic guitar  102  with the invention  100  installed at the tail piece area  170  of the instrument. Note that each string (strings 1-6) has a corresponding tuning machine mounted at the instrument&#39;s peg head  162  as is customary in the art. The first string is depicted at  148 ′, and the sixth string is depicted at  148 ″. Correspondingly, the first string tuning machine is shown at  164 , whereas the sixth string tuning machine is shown at  166 . Also note that the invention possesses an alternate set of 6 tuning screws, (one tuning screw for each string). The sixth tuning screw is depicts at  130 ″.  FIG. 1  depicts the tuning actuator arm  120  which is in position “ 2 ”, (parallel to the strings). This may also be referred to herein as the second arm position. For the example illustrated herein, position  2  will correspond to the Open G chord position. Also depicted in  FIG. 1  are other various components including the rocker arm  106  and cam roller fork  114  which will be depicted in more detail in the following figures. 
       FIG. 2  is a perspective drawing of the rear area of the guitar and an embodiment of the invention showing a method of fastening the invention to the guitar. The embodiments of the invention may preferably use the same mounting method as the original tailpiece  170 ; a single screw  172  which secures the base plate  104  to the guitar and also secures the strap button  168  in place. In preferred embodiments, because no other fastening points are required, there is no modification or alteration to the original instrument necessary. By using the same screw mounting point, installation of preferred embodiments of the invention is greatly simplified. The base plate  104  may provide the platform for which all other components are mounted. A rocker arm  106  may be pivotally connected to the base plate  104  around center line “C” (otherwise referred to herein as a rocker axis  112 ). The actuator arm  120 , cam roller fork  114  and cam roller assembly is also preferably pivotally mounted to the rocker arm  106  at center line “B” (otherwise referred to herein as the cam axis  116 ). The tuning screws  130  are also preferably threaded into the rocker arm  106 . Also pivotally attached to the base plate  104  are the string fingers  122 . Each string  148  may be attached at its corresponding string finger  122  as shown, for example, in  FIGS. 4 and 5 . Note that the actuator arm  120  is in position  1  (rotated approximately 90 degrees to the arm depicted in  FIG. 1 ). This may also be referred to herein as the first arm position. For the example shown herein, the Actuator Arm is in position  1  which will correspond to the Open “D” chord position. Also note that the Rocker Arm  106  is in contact with the base plate  104  in the embodiments shown. 
       FIG. 3  is another perspective drawing showing the rear view of the guitar and a preferred embodiment of the invention. It depicts the actuator arm  120  in position  2  (Open G chord Position), or second arm position. Note that the rocker arm  106  is lifted away from the base plate  104  by the cam roller  118 . Also note that a pair of cork, rubber or soft plastic pads may be fastened to the underside of the rocker arm  106 . These pads  140  eliminate any noise caused by contact between the rocker arm  106  and base plate  104  during use. 
     The cam roller  118  is preferably equipped with rubber or neoprene “O” rings  138 . These “O” rings cushion and help eliminate the noise created by its contact to the base plate  104  as it is rotated to lift the rocker arm  106  up away from the base plate  104 . 
       FIG. 4  is close up plan view of an embodiment of the invention showing an actuator arm  120 , cam roller fork  114  and cam roller  118  in the 1st or “D” position. The first string ball is shown at  150 ′, and the sixth string ball is shown at  150 ″. The detail of the cam roller fork  114  and cam roller  118  can more easily be seen. While the actuator arm  120  is pivotally mounted to the rocker arm at center line “B”, the actuator arm and cam roller fork are preferably rigidly connected at approximately 90 degrees. The cam roller  118  is preferably pivotally connected to the cam roller fork  114  at center line “A” (which may also be refereed to herein as the roller axis  136 ). Note that the “O” rings  138  may preferably extend out from the surface of the cam roller  118  so that they contact the base plate  104  to cushion and muffle the contact noise created during the actuation process. 
       FIG. 5  is the same view as  FIG. 4  except that the actuator arm  120  is shown in position  2  (in this case an Open G position), or second arm position. Note that the cam roller fork  114  and cam roller  118  have rotated approximately 90 degrees as it then rotates about the cam axis  116 . In doing so, it lifts the rocker arm  106  to its upper position as depicted in  FIG. 3 . A soft rubber bumper  146  is preferably also mounted to the pivot axel  142  which acts as a stop for the actuator arm  120 . This rubber bumper acts to eliminate any noise caused by the actuation of the bridge  100 . 
       FIG. 6  is a side view of an embodiment of the invention specifically depicting the motion of the actuator arm  120 , cam roller fork  114 , cam roller  118  and rocker arm  106 . For clarity, the string finger  122  has been omitted in this drawing. As the cam roller assembly is actuated by rotating the actuator arm  120  from position  1  (first arm position) to position  2  (second arm position), the rocker arm  106  pivots about center line C (rocker axis  112 ) in a counter clockwise direction. This action forces the tuning screws  130  downward against the string fingers as shown in  FIG. 7 . 
       FIG. 7  shows the preferred relationship between the rocker arm tuning screws, the string fingers and the strings. As the tuning screws are adjusted downward, the string finger&#39;s rotation is increased; therefore the strings are stretched farther. The farther the strings are stretched, the more their pitch is increased. Notice that when the tuning screws  130  are not in contact with the string fingers (as may be the case when the actuator arm is in position  1 ), the string tension pulls the string finger  122  in a clock wise direction so that the foot  152  of the string finger  122  comes to rest against the base plate  104 . 
     The pitches of all strings  148  can be adjusted individually to attain an exact specific pitch for each string as shown in  FIG. 8 . Notice the different heights of the string fingers from the base plate  104 . The tuning screws  130  are shown adjusted to retune the instrument to the open G tuning. Also notice that strings 1 and 4 string fingers are hardly displaced. This is because the pitches of string 1 (D) and string 4 (D) are common between the Open D tuning and the Open G tuning Only a very slight tuning is necessary to slightly sharpen their pitches to compensate for the flattening effect which occurs do to the bending of the instrument. 
       FIGS. 9 and 10  show the mechanical advantage designed into preferred embodiments of the invention. The maximum string tension is typically 196 pounds. Because embodiments of the invention must operate smoothly and easily within the normal and comfortable range of hand pressure, embodiments are preferably comprised of two lever systems. 
       FIG. 9  illustrates a first lever system which is comprised of the strings which represent the load of 196 pounds. The string finger/rocker arm assembly which rotates about Center line “C” is the lever arm. The attachment point of the actuator arm/cam roller fork/cam roller (Center line “B”) is the point at which effort is exerted. By way of example, the calculations for determining the amount of effort needed to move 196 pounds of string force applied at Point “B” is as follows: 2.30/0.4=5.75:1 (mechanical advantage). Therefore 196 pounds/5.75=34.1 pounds of effort needed at center line “B’. 
       FIG. 10  illustrates a second lever needed to reduce the load of 34.1 pounds further. The contact point of the cam roller  118  to the base plate  104  is the fulcrum. Note that the fulcrum point does shift as the roller moves along the base plate  104 . However for the purpose of this example, the average distance of 0.55 inches is used. The point of pressure exerted at the Actuator Arm is approximately 5.5 inches from the fulcrum point. Therefore the calculation is as follows: 5.5/0.55=10:1. Therefore the amount of force needed to move the load of 34.1 pounds at center line “B” is 3.4 pounds. Such embodiment of the invention successfully reduces the force of 196 pounds to a very manageable force of 3.4 pounds. 
       FIG. 11  illustrates the locking mechanism used to secure the actuator arm/roller cam mechanism into the G (or high tension) position. By moving the roller cam just past center line (or locking axis)  158 , string pressure forces the cam roller “back up”. However its movement is halted by the contact between the actuator arm  120  and rubber bumper  146  of the axle  142  at center point “C”. 
     An exemplary embodiment of a tunable bridge  100  for a string musical instrument  102  may preferably comprise a base plate  104 , a rocker arm  106 , a cam roller fork  114 , a cam roller  118 , an actuator arm  120 , a multiplicity of string fingers  122  and a plurality of tuning screws  130 . As illustrated in  FIG. 2 , the base plate  104  may be securable to the tailpiece section  170  of the musical instrument  102  by way of a single conventional mount screw. Such a mount screw may be provided without modifying the instrument, as it may, for example, already serve the purpose of mounting the original tailpiece and pre-existing strap button  168  to the instrument. 
     Referring to  FIGS. 14 and 15 , a rocker arm  106  may have a proximal portion  108 , a distal portion  110  and a rocker axis  112  therebetween. The rocker arm  106  may be mounted for pivoting movement with respect to the base plate  104  about the rocker axis  112  between a lower position (see, for example,  FIG. 2 ) and an upper position (see, for example,  FIGS. 3 and 12 ). 
     A cam roller fork  114  may be mounted for rotational movement with respect to the distal portion  110  of the rocker arm  106  about a cam axis  116  between a lock position (see, for example,  FIGS. 3 ,  11  and  12 ) and a release position (see, for example,  FIGS. 2 and 4 ). Referring to  FIG. 6 , a cam roller  118  may be mounted to the cam roller fork  114  and configured to contact the base plate  104  for translational movement relative thereto when the cam roller fork  114  is moved between its lock and unlock positions. An actuator arm  120  may be actuatable about the cam axis  116  between a first arm positions (see, for example,  FIG. 4 ) and a second arm position (see, for example,  FIG. 5 ). In certain preferred embodiments, the actuator arm  120  and cam roller fork  114  are rigidly connected to one another. 
     Referring to  FIG. 16 , each string finger  122  may have a tuning interface portion  124 , a ball detent portion  126  and a finger axis therebetween 128. Each string finger  122  may be mounted for pivotable movement with respect to the base plate  104  about its finger axis  128  between a first tuning position (see, for example,  FIG. 9 ) and a second tuning position (see, for example,  FIG. 11 ). Referring to  FIGS. 3 ,  4  and  10 , each ball detent portion  126  is preferably adapted to receive a string  148  having a string ball  150 , and to prevent the string ball  150  from passing through the ball detent portion  126 . Each of the string fingers may include a foot  152  on its ball detent portion  126 . Referring to  FIG. 7 , such a foot  152  may be adapted to rest against the base plate  104  when its respective string finger  122  is in its first tuning position, thereby restraining the string finger  122  from pivotal movement past its first tuning position in a direction away from its second tuning position. 
     Referring to  FIGS. 6 and 10 , each tuning screw  130  may have an engagement tip  132  and be threadedly disposed in the proximal portion  108  of the rocker arm  106  for adjustable placement of the engagement tip  132  at a respective axial distance  134  therefrom. Each of the engagement tips may preferably be configured to pressingly engage a respective tuning interface portion  124 . Referring to  FIG. 13 , in certain embodiments, inserts  174  may be disposed between the tuning screws  130  and the proximal portion  108  of the rocker arm  106 . 
     Referring to  FIGS. 10 and 11 , in certain preferred embodiment of a tunable bridge, actuation of the actuator arm  120  to the second arm position is adapted to force the cam roller fork into its lock position (see, for example,  FIG. 11 ). Moreover, movement of the cam roller fork  114  toward its lock position is typically adapted to force the rocker arm  106  toward its upper position. Referring to  FIGS. 6 and 7 , movement of the rocker arm  106  to its upper position is adapted to cause one or more engagement tips  132  to each come into pressing engagement with the respective tuning interface portion  124  so as to impose a pivoting force on the respective string finger  122  about its finger axis  128  toward its second tuning position. Further, referring to  FIGS. 2 and 4 , actuation of the actuator arm  120  from its second arm position toward its first arm position is preferably adapted to force the cam roller fork  114  out of its lock position. 
     In particular preferred embodiments, the cam roller  118  may be rotatably mounted to the cam roller fork  114  for rotation about a roller axis  136  such that the translational movement causes rolling contact between the cam roller  118  and the base plate  104 . A cam axle  154  may be provided to facilitate this rotatable mounting. Moreover, the cam roller  118  may comprise one or more elastomeric (e.g., rubber) O-rings  138  disposed thereabout. 
     Referring to  FIG. 3 , in certain preferred embodiments, the rocker arm  106  may include one or more noise attenuation pads  140  on the distal portion  110 . Such noise attenuation pads may be configured, for example, to prevent direct contact between the rocker arm  106  and the base plate  104  when the rocker arm  106  is in its upper position. Such noise attenuation pads  140  may be adhered to the rocker arm  106 , and may be made of a material such as cork, rubber, plastic or the like. 
     Referring to  FIGS. 4 ,  12  and  13 , in particular preferred embodiments, the rocker arm  106  and string fingers  122  may be mounted to the base plate  104  for their respective pivotal movement by way of an axle  142 . This axle  142  may also include an arm detent  144  configured to engage the actuator arm  120  when in its second arm position, and limit further movement of the actuator arm toward the base plate  104 . In embodiments, the arm detent may include an elastomeric bumper element  146  to dampen or eliminate noise which may otherwise result from the contact between the actuator arm  120  and the arm detent  144 . As illustrated in  FIGS. 4 and 5 , the axle may be held in place with respect the base plate  104  by way of, for example, snap rings  160 . 
     While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.