Abstract:
A strap-drive system that provides smooth, reliable potentiometer adjustment, particularly in devices used in conjunction with musical instruments.

Description:
PRIORITY 
     This application is related to and claims priority under 35 USC 119(e) to U.S. Provisional Patent Application No. 61/232,423 filed on Aug. 8, 2009, the complete contents of which is hereby incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     The present disclosure relates to the field of drive systems for potentiometer adjustment mechanisms, particularly those used in effects pedals that are used in conjunction with musical instruments. 
     2. Background 
     Potentiometers are widely used in applications where smooth control of an electrical device is desired, such as in controlling the volume of an audio device. In some devices, a potentiometer is connected to a knob to allow direct rotational adjustment, but in other devices it needs to be able to respond to forces in other directions, such as a linear force. In such devices, linear motion can be translated into rotational motion via a rack-and-pinion or cable-winding mechanism. 
     Effects pedals are one such device that controls a potentiometer via motion of a pivoting pedal. These pedals are connected between a musical instrument, such as a guitar, and an amplifier. A user rocks a pedal up and down to vary the volume of the guitar through the amplifier and achieve many interesting sound effects. Currently, these pedals use either a rack-and-pinion mechanism or a string to mechanically link the pedal to the potentiometer. Although commonly used in effects pedals, these mechanisms present several drawbacks. 
     In rack-and-pinion systems, the mechanism requires maintenance, such as lubrication and cleaning, to keep it running smoothly and avoid excessive wear. However, even sufficient maintenance cannot prevent gear lash, or slop, in the drive train to the potentiometer shaft. Further, a rack-and-pinion system can damage a potentiometer. A side load on the rack gear is required to maintain sufficient contact with the pinion gear, which can put a stress on the potentiometer shaft and shorten its life. In addition, a rack-and-pinion drive can skip a tooth and misalign the pedal position and damage the potentiometer. Finally, rack-and-pinion systems can create excessive noise, which could interfere with playing music. 
     String-drive systems eliminate some of the problems found in rack-and-pinion systems, but also have their own problems. String-drive systems can overlap their windings during use, which can cause excessive string wear, fraying, and eventual failure. When the string or cable breaks, it is difficult to repair. Further, string-drive systems can have tensioning errors during the full travel of the pedal, which requires springs in the drive train. 
     What is needed is a drive mechanism that can smoothly and quietly adjust a potentiometer, while operating with low friction, low wear, and high reliability. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a side view of one embodiment of the present device. 
         FIG. 1   a  depicts a detail perspective view of a cam bracket component of one embodiment of the present device. 
         FIG. 1   b  depicts a detail perspective view of a cam component of one embodiment of the present device. 
         FIG. 1   c  depicts a detail perspective view of a capstan assembly component of one embodiment of the present device. 
         FIG. 1   d  depicts a detail perspective view of a strap component of one embodiment of the present device. 
         FIG. 1   e  depicts a detail perspective view of a strap bracket component of one embodiment of the present device. 
         FIG. 2  depicts a perspective view of one embodiment of a strap configuration of the present device. 
         FIG. 3  depicts a front view of one embodiment of the present device. 
         FIG. 4  depicts a top view of one embodiment of the present device. 
         FIG. 5  depicts a perspective view of one embodiment of the present device. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  depicts a side view of one embodiment of the present device. In some embodiments, as shown in  FIG. 1 , a pedal device  102  can have a pedal  104  and a base  106 . A pedal  104  can be connected to a base  106  at a fulcrum point  108 , where a pivot pin  110  running perpendicular to the longitudinal axis of a pedal  104  can allow a pedal  104  to pivot up and down relative to a base  106 . 
     A cam  112  can be connected at one end to a pedal  104  via a cam bracket  114  and a connector pin  116 . In some embodiments, as shown in  FIG. 1 , a cam bracket  114  can be positioned approximately one-third of the length of a pedal  104  at a position forward of a fulcrum point  108 , but in other embodiments can be positioned in any known and/or convenient location. A cam  112  can be connected at the other end to a base  106 . As shown in  FIG. 1 , both ends of a cam  112  can be connected such that they can each pivot about an axis parallel to a pivot pin  110 . 
     As shown in  FIG. 1   a , a cam bracket  114  can have an elongated base member  115  that can have a substantially quadrilateral geometry or any other known and/or convenient geometry. A base member  115  can have a plurality of holes  118  to allow said base member  115  to be connected to another surface, such as the underside of a pedal  104 . A pair of tabs  120  can extend substantially perpendicularly from substantially parallel edges of a base member  115 . In some embodiments, tabs  120  can have a substantially rectangular geometry, but in other embodiments can have any other known and/or convenient geometry. As shown in  FIG. 1   a , in some embodiments, tabs  120  can be located substantially along the midline of a base member  115 , or in any other known and/or convenient location. Tabs  120  can have holes  122  oriented perpendicularly to the face of and substantially through the center of said tabs  120  to accommodate a pin  116 . In other embodiments, holes  122  can be located in any known and/or convenient position on tabs  120 . In some embodiments, a cam bracket  114  can be made from metal, alloy, polymer, composite, polyoxymethylene, glass-filled polyoxymethylene, or any other known and/or convenient material. 
     As shown in  FIG. 1   b , a cam  112  can have a substantially rounded face  124 . As shown in  FIG. 1 , the radius of curvature of a cam face  124  can correspond to the distance measured from the fulcrum point  108 , but in other embodiments can be any other known and/or convenient radius. In other embodiments, a cam face  124  can have an ellipsoid profile or any other known and/or convenient geometry. In some embodiments, the back surface  128  of a cam  112  can be substantially flat, but I other embodiments can include at least one indentation  130 . As shown in  FIG. 1   b , an indentation  130  can be a substantially rounded groove that can be oriented perpendicularly across the back surface  128  of a cam  112 . In the embodiment shown in  FIG. 1   b , two grooved indentations  130  are located at approximately one-third of the length of a cam  112 , but in other embodiments can be any other known and/or convenient geometry and be positioned at any other known and/or convenient location on the back surface  128  of a cam  112 . In the embodiment shown in  FIG. 1   b , the back surface  128  of a cam  112  can have a hole  132  positioned substantially at the midpoint between two indentations  130  or an any other known and/or convenient location on the back surface  128  of a cam  112 . In some embodiments, a hole  132  can be tapped to accommodate a tensioning screw  166 . In some embodiments, a cam  112  can be made from metal, alloy, polymer, composite, polyoxymethylene, glass-filled polyoxymethylene, or any other known and/or convenient material. 
     At either one or both ends of a cam  112 , which, in some embodiments can be substantially rounded, but in other embodiments can be any other known and/or convenient geometry, protrusions  134  can extend perpendicularly from the lateral faces of a cam  112 . In some embodiments, protrusions  134  can extend from the lateral faces of a cam  112  at substantially one end of a cam  112 . However, in other embodiments, such protrusions can be present at both ends of a cam  112 . Although shown in  FIG. 1   b  as substantially cylindrical, in other embodiments, protrusions  134  can have any other known and/or convenient geometry. At least one end of a cam  112  can have holes  136  oriented transversely, and said holes  136  can be substantially concentric with protrusions  134  or in oriented in any other known and/or convenient geometry. In some embodiments, holes  136  can be configured to accommodate an expansion pin  116  of any known and/or convenient geometry. 
     As shown in  FIG. 1   c , in some embodiments a capstan assembly  138  can be substantially cylindrical, but in other embodiments can be any other known and/or convenient geometry. In some embodiments, a capstan assembly  138  can be divided into at least two parts along a longitudinal plane located substantially three-fourths along a cross-section, or any other known and/or convenient location, to produce two complementary pieces. In other embodiments, two parts of a capstan assembly  138  can be integrated. In such embodiments, a cut of a substantially linear or any other known and/or convenient geometry can partially separate two parts of a capstan assembly  138 . In some embodiments, as shown in  FIG. 1   c , each part can have at least one substantially flat surface, but in other embodiments can have at least one surface that can be curved or any other known and/or convenient geometry. In such embodiments, a plurality of holes  142  can be oriented perpendicularly to a substantially flat surface of a larger piece  140 . A smaller piece  144  can have a plurality of pins  146  extending substantially perpendicularly from a flat surface of a smaller piece  144  that can selectively engage with a plurality of holes  142  in a larger piece  140 . In other embodiments, holes  142  can be located on a substantially flat surface of a smaller piece  144  and pins  146  can extend substantially perpendicularly from a substantially flat surface of a larger piece  140 . As shown in  FIG. 1   c , a capstan assembly  138  can have three pairs of substantially parallel pins  146  and three pairs of corresponding holes  142  aligned on either side of the longitudinal axis of a capstan assembly  138 . In some embodiments, a capstan assembly  138  can be made from metal, alloy, polymer, composite, polyoxymethylene, glass-filled polyoxymethylene, or any other known and/or convenient material. 
     As shown in the embodiment in  FIG. 1   c , a larger piece  140  of a capstan assembly  138  can have a substantially cylindrical hole  148  oriented substantially along the central longitudinal axis of a capstan assembly  138 . In some embodiments, a substantially cylindrical hole  148  can have at least one substantially flat side to selectively couple with a potentiometer shaft. In some embodiments, a capstan assembly  138  can have a radius having any known and/or convenient ratio to the radius of curvature of a cam face  124  to produce a desired range of rotation of a capstan assembly  138 . In some embodiments, this range of rotation of a capstan assembly  138  can be approximately 210 degrees, but in other embodiments, can be any other known and/or convenient quantity. 
     As shown in  FIG. 1 , a strap  152  can connect a capstan assembly  138  to a cam  112  such that when a cam  112  is moved perpendicularly to the longitudinal axis of a capstan assembly  138 , a capstan assembly  138  can rotate about its longitudinal axis. In the embodiment shown in  FIG. 1   d , a strap  152  can have one end that can be divided into a pair of substantially parallel extensions  154  that can each have a length less than one half of the total length of a strap  152  and can each have a width approximately one third of the total width of a strap  152  or any other known and/or convenient dimensions. A pair of substantially parallel extensions  154  can be separated by a distance of approximately one third of the total width of a strap  152  or any other known and/or convenient dimension and or elastomeric relation. The other end of a strap  152  can have an extension  156  that can have a length less than one half of the total length of a strap  152  and can have a width approximately one third of the total width of a strap  152  or any other known and/or convenient dimensions and or geometric relations. As shown in  FIG. 1   d , an extension  156  can be located substantially along the longitudinal midline of a strap  152  or at any other known and/or convenient location. 
     Extensions  154  and  156  can have at least one hole  158  located substantially at the end of each extension or at any other known and/or convenient location. In some embodiments, as shown in  FIG. 1   d , pairs of holes  158  can be located at each end of extensions  154  and  156 . The spacing of each pair of holes  158  can correspond to the configuration of pins  146  and their corresponding holes  142  in a capstan assembly  138  such that a strap  152  can be attached to a capstan assembly  138 . Another hole  160  can be positioned at substantially the center of a strap  152 . In some embodiments, this hole  160  can be dimensioned to accommodate a tensioning screw  166 , or can have any other known and/or convenient dimensions. In some embodiments, a strap  152  can be made from stainless steel, other metal, alloy, polymer, or any other known and/or convenient flexible, durable, thermally-stable, corrosion-resistant material. 
     As shown in the embodiment in  FIG. 1 , a strap bracket  162  can secure a strap  152  to the back surface  128  of a cam  112 . As shown in  FIG. 1   e , in some embodiments, a strap bracket  162  can have a substantially quadrilateral planar geometry, but in other embodiments can have any other known and/or convenient geometry. In some embodiments, a strap bracket  162  can have substantially curved ends  164  that can have a geometry corresponding to indentations  130  in the back surface  128  of a cam  112 . In such embodiments, a strap bracket  162  can selectively couple with the back surface  128  of a cam  112  and can be adjustably attached with a tensioning screw  166 . As shown in  FIG. 1   e , a strap bracket  162  can have a hole  168  located substantially through the center of a strap bracket  162 , and in some embodiments, a hole  168  can be tapped to engage a screw or any other known and/or convenient fastener. In other embodiments, curved ends  164  can have any other known and/or convenient geometry. In some embodiments, a strap bracket  162  can be made from metal, alloy, polymer, composite, polyoxymethylene, glass-filled polyoxymethylene, or any other known and/or convenient material. 
       FIG. 2  depicts a perspective view of the configuration of a strap  152  as it can be wrapped around a capstan assembly  138  and a cam  112 . For clarity, a capstan assembly  138  has been cut away to show how a strap  152  can be wrapped around it. When assembled, a capstan assembly  138  can be positioned proximal to a cam face  124 . A strap  152  can be oriented substantially perpendicularly to the longitudinal axis of a capstan assembly  138  such that the ends of parallel extensions  154  can be proximal to a capstan assembly  138  and a strap  152  extends away from a cam  112 . Holes  158  can align with the outer pairs of pins  146  and holes  142  on a capstan assembly  138  such that the ends of parallel extensions  154  can be held in place. Two complementary parts  140 ,  144  of a capstan assembly  138  can be joined together with the ends of parallel extensions  154  held between them. Extensions  154  can be wrapped “back” around the outer surface of a capstan assembly  138  such that extensions  154  can be situated between a capstan assembly  138  and a cam face  124 . Extensions  154  can travel along a cam face  124 , around one end of a cam  112 , and wrap around to a back surface  128  such that a central portion of a strap  152  can be positioned on a back surface  128  of a cam  112 . Substantially near the opposite end of a cam  112 , extension  156  can wrap around a cam  112  to a cam face  124  such that an extension  156  can be situated between a cam face  124  and a capstan assembly  138 . An extension  156  can wrap around the outer surface of a capstan assembly  138 , opposite extensions  154 , such that the holes  158  at the terminal end of an extension  156  can align with an inner pair of pins  146  and holes  142  on a capstan assembly  138  such that the end of parallel extension  156  can be held in place. 
     In some embodiments, a strap  152  can be wrapped in opposite directions, or in any other known and/or convenient configuration, so that when a strap  152  is pulled taut, it secures a cam  112  to a capstan assembly  138 . As shown in  FIG. 1 , a strap bracket  162  can be aligned with indentations  130  in the back surface  128  of a cam  112  with a strap  152  positioned between a strap bracket  162  and a back surface  128  of a cam  112 . A tensioning screw  166  can be adjusted to push a strap bracket  162  against the back surface  128  of a cam  112 , such that curved ends  164  of strap bracket  162  can push a strap  152  into indentations  130  to tension a strap  152 . 
     A strap  152  can be wrapped around a cam  112  and a capstan assembly  138  such that when a cam  112  is moved perpendicularly to the longitudinal axis of a capstan assembly  138 , a capstan assembly  138  can rotate about its longitudinal axis. 
       FIG. 3  depicts a front view of the exterior of one embodiment of the present device, showing a pedal  104  and a base  106 .  FIG. 4  depicts a top view of the exterior of one embodiment of the present device.  FIG. 5  depicts a perspective view of the exterior of one embodiment of the present device. 
     In use, a user applies a force, usually via a foot, to a pedal  104 , thereby rotating a pedal  104  about a fulcrum  108 . This motion can be translated to a motion of a cam  112 . As a cam  112  moves, a strap  152  can wind onto a cam  112 , while unwinding the same length of a strap  152  from a capstan assembly  138 . This can maintain equilibrium in the length of a strap  152  around a cam  112 . In some embodiments, the radius of a cam face  124  can be calculated to be the distance from a fulcrum point  108  of a pedal device  102 , so that the cam face  124  can remain tangent to the surface of a capstan assembly  138 . In such embodiments, the amount of capstan assembly  138  rotation can be less than 210 degrees, but in other embodiments can be any other known and/or convenient amount of rotation. Further, in such embodiments there can be a fixed first-order relationship between the number of degrees of pedal  104  movement about a fulcrum point  108  and the eventual rotation of a potentiometer shaft. 
     As a result, a potentiometer can be adjusted smoothly and quietly with a direct relationship between the pedal  104  movement and potentiometer adjustment. Further, no side loading is required to maintain control, which decreased wear on a potentiometer. The force required to change a cam&#39;s  112  position need only be applied to one end of a cam  112 . 
     Although the method has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the method as described and hereinafter claimed is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.