Abstract:
A variable resistor including a resistive element and a conductive element supported by a plate. Contacting terminals are provided on one or more ends of each element. A carriage is slidably supported above the elements and a conductive roller is supported from the carriage by a suspension member that biases the conductive roller against the elements. The effective length of the current path through the resistive element is varied by using the conductive roller to electrically connect the two elements to one another along different portions of their length. In a preferred embodiment, the carriage moves under the guidance of at least one guide bar and the conductive roller is suspended from the carriage by a coiled spring.

Description:
This application is a Continuation-in-Part of U.S. Ser. No. 159,831, filed Feb. 24, 1988, now issued at U.S. Pat. No. 4,878,040. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to variable resistors and, more specifically, to an improved guided variable resistor that minimizes noise and wear resulting from use. 
     2. Description of the Related Art 
     Variable resistors have typically utilized a sliding element resembling a brush wherein the brush slides across a surface of a resistive element and a conductive element to vary resistance. However, noise is generated as a result of the brush element lifting from the resistor element as it slides across the resistor element and the conductive element. Obviously, noise generation becomes more of a problem as the need for steady resistance increases. 
     There is an additional problem in that the sliding brush element makes it difficult to achieve a smooth sliding motion. The rough sliding motion, caused by the large amount of friction that typically exists between the sliding element and the resistive and conductive elements, adversely affects the degree to which the variance of resistance can be controlled. 
     Another problem has been performance deterioration over time. This results from the constant frictional wear caused by the sliding of the brush element across the resistor and conductive elements each time the resistance is changed. 
     At least one prior art variable resistor has used a rolling contact member that is biased against the resistive and conductive elements by a spring. Such devices, however, are complicated, requiring a large number of components and a lengthy assembly time. 
     A need therefore still exists in the art to provide an improved sliding type variable resistor which minimizes wear and noise and which is simple in construction. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an improved strip-shaped variable resistor; 
     Another object of the present invention is to provide a variable resistor that minimizes the amount of wear and noise generated from use; 
     Another object of the present invention is to provide a variable resistor that is simple to construct; and 
     Another object of the present invention is to provide a sliding type variable resistor that can be used in various orientations. 
     The objects of the present invention are achieved by providing a strip-shaped conductive element, a strip-shaped resistive element, and a support element or plate for supporting the conductive element and the resistive element. A contact element is also provided for electrically connecting the conductive element and the resistive element. A slider or carriage moves the contact element under the guidance of guide bars located above the resistive and conductive elements. The slider is provided with a hook and a pair of protrusions. A spring suspension member having a pair of coiled sections is installed on the protrusion and locked in place with the hook. The coiled spring further has two arms which extend from each of the coiled sections, the far end of each of the extending arms being bent back in a hairpin-like fashion in order to accommodate the shaft of a conductive roller. When installed, the conductive roller supported by the extending arms of the coiled spring and is biased against the resistive element and the conductive element under pressure from the coiled spring. The effective length of the resistive element is changed as the conductive roller moves along. As a result, the resistance between the terminals connected to the resistive and conductive elements will change. Upon activation, the conductive element remains in rolling contact with the resistive element while eliminating substantially all sliding contact. 
     These and other objects of the present invention can be best understood from an examination of the accompanying specification, the claims, and the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side, cross-sectional view of the present invention; 
     FIG. 2 is a bottom view of the slider according to the present invention; 
     FIG. 3 is a side view of the present invention; 
     FIG. 4 is a partial perspective view of the present invention; 
     FIG. 5 is a top view of a spring in the slider according to the present invention; and 
     FIG. 6 is a side view of the spring in FIG. 5. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The following description is provided to enable any person skilled in the art to which the present invention pertains, or with which is most nearly connected, to make and use the same and sets forth the best mode contemplated by the inventors of carrying out their invention. Various modifications, however, will remain readily apparent to those skilled in the art since the generic principles of the present invention have been defined herein specifically to provide a guided variable resistor. 
     FIG. 4 shows a component assembly of the present invention including an insulator plate 1 which, in this particular embodiment, is planar and rectangular shaped. The insulator plate 1 is made of any appropriate conventional material that has a high insulating property and is preferably made of bakelite paper. The insulator plate 1 also has a sufficiently rigid character to prevent bending or flexing when in use. 
     A strip-shaped resistive element 3 is affixed to a top, planar side 1a of the insulator plate 1. For example, the resistive element 3 may be adhered to or may be silk screened on the insulator plate 1. In this particular embodiment, the resistive element 3 is rectangular shaped and approximately less than one-half of the dimensions of the insulator plate 1. The resistive element 3 is constructed of any appropriate conventional high-resistive element, and is preferably made of a carbon coating. A pair of connecting terminals 3a, 3b are connecting terminal is located at each opposite end along the longitudinal length of the resistive element 3. As further described below, the connecting terminals 3a, 3b provide an electrical connection between either of them and a conductive element 4. 
     A strip-shaped conductive element 4 is affixed to the insulator plate 1 by means similar to that of the resistive element 3 such that the conductive element 4 and the resistive element 3 are positioned substantially parallel to one another on the top planar side la of the insulator plate 1. The conductive element 4 is configured and dimensioned like the resistive element 3. The conductive element 4 is made of any appropriate material having a high conductive property, and is preferably made of a silver coating. A connecting terminal 4a is provided on an upper planar surface 4c of the conductive element 4 at one end thereof so as to be positioned adjacent the connecting terminal 3a, in this particular embodiment. 
     A cylindrical-shaped roller element 10 is positioned above and in contact with the top planar surfaces of the resistive element 3 and the conductive element 4 in order to provide electrical conduction between those two elements. The roller element 10 has a smooth, rolling contact surface 10a that remains in rolling contact with the resistive and conductive elements during variance of resistance. The roller element 10 may be made of a conductive silicon rubber. 
     FIG. 3 is an end view of the present invention. As shown in FIG. 3, there are two pairs of adjacent open-ended slots 2c and 2e extending downward from the top of each of the two vertical end-walls 2b of the case 2. Each of the slots 2f is adjacent to each of the slots 2c in order to allow the narrow wall section between each slot pair 2c,2f to slightly bend during installation of guide bars 5. As shown in FIGS. 1 and 3, each guide bar downward into the slot 2c. Protrusions 2e are present in order to secure the guide bars 5 in the slots 2c. 
     FIG. 2 illustrates the relationship between a slider 7 and the two guide bars 5. The slider 7 is equipped with two guide holes 7a and 7b which accommodate the two guide bars 5. One end of guide hole 7a and both ends of guide hole 7b are fitted with a low friction bushing 8a, 8b and 8c, respectively. A first pair of identical rectangular cavities 7d and 7e, and a second pair of identical rectangular cavities 7f and 7g are cutout of the bottom 7c of the slider 7. Hooks 7h and 7i are respectively located between cavities 7d,7f and 7e,7g. In the preferred embodiment, each cavity 7f and 7g contains a pair of inwardly extending protrusions 7j and 7k. As shown in FIGS. 1 and 2, coiled sections 8b of a coiled spring 8 are fitted over the inwardly extending protrusions 7j and the spring 8 is secured in place by engaging the mid-section 8a with hook 7h. A coiled spring, although not shown for clarity, is also be attached to protrusions 7k and hook 7i in like fashion. 
     The coiled spring serves as a suspension member between the slider or carriage 7 and the roller element 10. The coiled spring 8 will be further explained with reference to FIGS. 5 and 6. The coiled spring 8 consists of a mid-section 8a which is to be secured to the hook 7h, two coils 8b which fit over the inwardly extending protrusions 7j, and two legs 8c that are each bent into a hair pin shape 8d for receiving the roller shaft 9. 
     Returning to FIGS. 1 and 2, it can be seen that each end of the roller shaft 9 has an annular groove which fits the hairpin-like section 8d of the coiled spring 8 in order to allow free rotation of the roller shaft 9 and the conductive roller 10. 
     In FIG. 6, the bold lines represent the coiled spring 8 in its uncompressed state. When the coiled spring 8 is installed on slider 7, the spring mid-section 8a, as shown by the broken line, will be compressed between the slider 7 and the roller 10 inside of the case 2 (see FIG. 1). Thus, the coiled spring 8 operates to bias the conductive roller 10 towards the conductive and resistive elements 3 and 4. 
     As shown by FIG. 1, a preferred embodiment of a variable resistor according to the present invention includes an open rectangular case 2 that is covered with a lid 12. Slider arm 11 is mounted on the upper section 7u of the slider 7. An elongated slit 2d is present in a wall 2c of case 2 so that the slider arm 11 may extend therethrough and be moved by the operator. Cushion rings 13 are installed at both ends of each of the two guide bars 5 near the vertical end-walls 2b of the case 2. The cushion rings 13 are present to dampen the shock from the slider 7 hitting the vertical end-wall 2b of the case. 
     The operation of the variable resistor of FIGS. 1 to 6 will now be explained. When the slider arm 11 is moved along the slit 2d, the conductive roller 10 will roll while being biased against the resistive element 3 and conductive element 4. A desired resistance can be obtained because, as the slider arm 11 is moved, the conductive roller 10 will change position so as to change the effective resistor length between terminals 3a and 4a (or between 3b and 4a). 
     If the above composition is employed, the construction will be simple and the components few as the only component supporting the conductive roller 10 and shaft 9 is the coiled spring 8. 
     The assembly of the conductive roller 10 and the shaft onto the slider 7 is as follows: the shaft 9 is first fit in the bent hairpin-like section 8d of the coiled spring 8; then the two coiled sections 8b of the spring are fitted onto the two protrusions 7j (or 7k); and finally the spring mid-section 8a is secured to the hook 7h (or 7i). The steps for installing the guide bars 5 include: inserting the annular groove 5a of the guide bar 5 into slot 2c and pressing guide bar 5 down in order to bend the wall between slot 2c and slot 2f so as to force and firmly secure the annular groove 5a below retaining protrusion 2e. 
     The variable resistor according to the present invention is less prone to noise generation when resistance is varied because the conductive roller 10 is biased against the resistive element 3 and conductive element 4 by coiled spring 8 and therefore is less apt to lift up from the resistive element 3 and the conductive element 4 as it rolls in contact over the two elements 3 and 4. Note that the motion is extremely smooth because the conductive roller 10 rolls as it moves. Hence, friction between the roller 10 and the resistive and conductive elements 3 and 4 is only rolling friction. Moreover, even after the roller element 10, the resistive element 3, and the conductive element 4 have been worn from excessive use, performance is less apt to deteriorate because the conductive roller 10 continues to roll over the elements 3 and 4 under pressure from coiled spring 8. Finally, the variable resistor according to the present invention can be installed and used at any angle of attitude. 
     While the above disclosed features of the present invention teach an improved variable resistor, it can be readily appreciated that it would be possible to deviate from the above embodiments of the present invention, for instance, in the above embodiment, conductive silicon rubber is used in the conductive roller 10, but it need not be limited to this material. For example, a normal synthetic rubber roller can be used with a conductive coating. The resistive element 3 and the conductive element 4 could be made of elastic material and the roller 10 of rigid material. Three terminals are provided but it could be only two (e.g. 3a and 4a or 3b and 4a) or could be four in order to provide many different connections. It is also possible that the either resistive terminals 3a and/or 3b could be used in conjunction with a terminal that is connected directly to the conductive roller 10 of the slider 7. Needless to say, the above actual example can be converted into a motor driven variable resistor. Also, in the above example, only one conductive roller 10 was used but is possible to use two. Accordingly, it will be understood that the invention is not to be limited by the specific embodiments but only by the spirit and scope of the appended claims.