Abstract:
A variable electronic component in the nature of a trimmed capacitor has a very low cost and simple design. A dielectric housing has an open end that a plug may be press fit into. The plug grips an upper region of the dielectric housing with at least one projection. A conductive body acts as a variable electrode, moving axially within the dielectric housing. A stator, acting as a fixed electrode, is securely affixed to an outer portion of the dielectric housing opposite the open end by crimping the top of the stator over a protrusion on an outer surface of the dielectric housing. The total press fit design reduces the number of steps normally required to make a trimmed capacitor, thereby reducing the cost of manufacture.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates in general to variable electronic components, and more particularly, to a variable trimmed capacitor having a design that reduces manufacturing time and cost while providing a high level of quality. 
     Capacitors are critical components used in a vast array of electronic devices, from simple circuit boards to entire computer systems. Capacitors have two main types, fixed and variable. A fixed capacitor has a pre-defined capacitance that is fixed during manufacturing. Variable or trimmed capacitors do not have their capacitance fixed during manufacturing. Instead, these capacitors are designed so that they afford a range of capacitance values. Adjusting along this range allows a user, for example, to fine-tune a circuit. Thus, variable capacitors are often employed in transmitter and receiver circuitry. Variable capacitors are known from U.S. Pat. Nos. 5,229,911; 5,155,654; 4,876,627; 4,764,843; and 4,575,779, all assigned to the assignee of this application, the disclosures of which are incorporated herein by reference. 
     Variable capacitors come in many different designs. One method of varying capacitance is to interleave several variable electrodes among fixed electrodes. See U.S. Pat. Nos. 4,002,957; 3,624,469; and Re. 30,406. Adjusting the position of the variable electrodes relative to the fixed electrodes increases or decreases the capacitance. One drawback to this kind of variable capacitor is the number of electrodes. Multiple fixed and variable electrodes necessitate a housing large enough to accommodate them. This may make these devices unsuitable for many small-scale applications. And if the fixed and variable electrodes are not carefully situated, or if the structure is not rugged enough, the capacitor may not operate properly. 
     Other drawbacks to variable capacitors are that the outer housing is often formed of multiple parts, and the entire structure is held together with a combination of screws, clips, soldering and other connection mechanisms. As components are added, manufacturing time and expense rise. Likewise, certain processes such as soldering or welding sections of the capacitor together also increase the cost and time of manufacturing. Furthermore, each additional step in the manufacturing process increases the chance for error, so the percentage of device failures may rise. In turn, this also drives up the cost of manufacturing. 
     Accordingly, there is a need for improvements in variable capacitors, and in particular, to provide a simple variable capacitor design having a minimum number of components, and for the variable capacitor to be quickly and easily assembled at a low cost. 
     SUMMARY OF THE INVENTION 
     In one embodiment of the present invention, a variable electronic component is provided. The variable electronic component comprises a dielectric housing, a conductive stator and an actuator assembly. The dielectric housing includes a hollow tubular body having an open end. The conductive stator surrounds a portion of the dielectric housing. The actuator assembly is secured within the dielectric housing. The actuator assembly includes a conductive body moveable within the hollow tubular body. The conductive body is in operative relationship with the conductive stator upon operation of the actuator assembly. The actuator assembly also has at least one projection adapted to secure the actuator assembly within the hollow tubular body at the open end. 
     In another embodiment of the present invention, the at least one projection includes a plurality of teeth. Preferably, the plurality of teeth circumscribe an outer surface of the actuator assembly, whereby the plurality of teeth grab into an inner surface of the hollow tubular body at the open end. 
     In another embodiment of the present invention, the at least one projection includes an annular ring. The annular ring surrounds an outer surface of the actuator assembly, whereby the annular ring grabs into an inner surface of the open end. 
     In another embodiment of the present invention, the actuator assembly is friction fit into the dielectric housing. The at least one projection digs into an inner surface of the dielectric housing. 
     In another embodiment of the present invention, the dielectric housing, conductive stator and the actuator assembly form a capacitor. Adjusting the actuator assembly in operative relation to the conductive stator varies a capacitance of the capacitor. 
     In another embodiment of the present invention, the dielectric housing includes a closed end opposing the open end. The conductive stator surrounds the portion of the dielectric housing having the closed end. 
     In another embodiment of the present invention, the hollow tubular body includes an outer surface. The hollow tubular body is at least partly exposed along a portion of the outer surface to the surrounding environment. 
     In another embodiment of the present invention, the hollow tubular body further includes an opposing closed end opposite the open end. The hollow tubular body includes an outer protrusion between the open end and the opposing closed end. The conductive stator has a portion that is attached about the outer protrusion. 
     In another embodiment of the present invention, the variable electronic component further includes a ring. The ring surrounds a portion of the hollow tubular body about the open end. The ring prevents the hollow tubular body from disengaging from the at least one projection. 
     In yet another embodiment of the present invention, a variable capacitor is provided. The variable capacitor comprises a housing of dielectric material, a plug, a metal body, a stator and an actuator. The housing of dielectric material has a closed end and an open end having an inner surface. The closed end and the open end form a bore therebetween. The plug has an outer surface and an inner opening. The outer surface includes at least one projection embedded into the inner surface, thereby securing the plug within the bore of the housing adjacent to the open end of the housing. The metal body is moveably received within the bore of the housing between the closed end and the plug. The stator surrounds an outer portion of the closed end of the housing. The actuator is received within the inner opening of the plug and is attached to the metal body. The actuator is operable to axially move the metal body within the bore of the housing in operative relationship to the stator, whereby the capacitance of the variable capacitor is altered. 
     In another embodiment of the present invention, the at least one projection includes a plurality of teeth. Preferably, the plurality of teeth circumscribes the outer surface of the plug, whereby the plurality of teeth digs into the inner surface of the bore. 
     In another embodiment of the present invention, the at least one projection includes at least one annular ring. The at least one annular ring digs into the inner surface of the bore. 
     In another embodiment of the present invention, the plug is press fit into the housing. Preferably, the dielectric material is polytetrafluoroethylene. 
     In another embodiment of the present invention, the actuator is threaded. The inner opening of the plug is reciprocally threaded to engage the actuator. 
     In another embodiment, the variable capacitor further includes a ring surrounding a portion of the open end. The ring prevents the inner surface from disengaging from the at least one projection. 
     In yet another embodiment of the present invention, a variable electronic component is provided. The variable electronic component comprises a dielectric housing, a conductive stator and an actuator assembly. The dielectric housing includes a hollow tubular body having an open end and an opposing end. The hollow tubular body includes an outer surface whereby the hollow tubular body is partly exposed along a portion of the outer surface to the surrounding environment. The conductive stator surrounds a portion of the dielectric housing at the opposing end. The actuator assembly includes a conductive body. The conductive body is moveable within the hollow tubular body in operative relationship with the conductive stator upon operation of the actuator assembly. 
     In another embodiment of the present invention, the dielectric housing, the conductive stator and the actuator assembly form a capacitor. Adjusting the actuator assembly in operative relationship to the conductive stator varies a capacitance of the capacitor. 
     In another embodiment of the present invention, the dielectric housing is a plastic material. The plastic material is preferably polytetrafluoroethylene. 
     In another embodiment of the present invention, the hollow tubular body is partly exposed along the portion of the outer surface adjacent the open end. 
     In another embodiment of the present invention, the actuator assembly further includes at least one projection. The at least one projection is adapted to secure the actuator assembly to the hollow tubular body adjacent the open end. 
     In another embodiment of the present invention, the variable electronic component further includes a ring surrounding a portion of the hollow tubular body about the open end. The ring prevents the hollow tubular body from disengaging from the at least one projection. 
     In another embodiment of the present invention, the outer surface of the dielectric housing includes an outer protrusion. The conductive stator is operable to attach to the dielectric housing about the outer protrusion. 
     In yet another embodiment of the present invention, a variable capacitor is provided. The variable capacitor comprises a housing of dielectric material, a stator and an actuator assembly. The housing of dielectric material has a lower region including a closed end and an upper region including an open end. The housing between the closed end and the open end have a bore therebetween. The upper region is exposed to the surrounding environment along an external surface. The stator is affixed to an outer portion of the closed end of the housing. The actuator assembly is received within the bore of the housing. Adjusting the actuator assembly alters the capacitance of the variable capacitor. 
     In another embodiment of the present invention, the housing is a plastic material. The housing is preferably polytetrafluoroethylene. In another embodiment of the present invention, the housing is generally cylindrical. 
     In yet another embodiment of the present invention, a variable electronic component is provided. The variable electronic component comprises a dielectric housing, a conductive stator and an actuator assembly. The dielectric housing includes a hollow tubular body having an open end and an opposing end. The hollow tubular body has an outer protrusion between the open end and the opposing end. The conductive stator surrounds a portion of the dielectric housing, and is attached about the outer protrusion. The actuator assembly includes a conductive body moveable within the hollow tubular body in operative relationship with the conductive stator upon operation of the actuator assembly. 
     In another embodiment of the present invention, the conductive stator is crimped around the outer protrusion. Preferably, the conductive stator surrounds a portion of the dielectric housing including the opposing end. 
     In another embodiment of the present invention, the conductive stator is attached about the outer protrusion at an area of reduced diameter. 
     In another embodiment of the present invention, the conductive stator is attached about the outer protrusion along a ledge of the outer protrusion. 
     In another embodiment of the present invention, the dielectric housing, conductive stator and the actuator assembly form a capacitor. Adjusting the actuator assembly in operative relation to the conductive stator varies a capacitance of the capacitor. 
     In another embodiment of the present invention, the hollow tubular body includes an outer surface. The hollow tubular body is partly exposed along a portion of the outer surface. 
     In another embodiment of the present invention, the actuator assembly further includes at least one projection. The at least one projection is adapted to secure the actuator assembly to the hollow tubular body adjacent the open end. 
     In another embodiment of the present invention, the variable electronic component further includes a ring surrounding a portion of the hollow tubular body about the open end. The ring prevents the hollow tubular body from disengaging from the at least one projection. 
     In yet another embodiment of the present invention, a variable capacitor is provided. The variable capacitor comprises a housing of dielectric material, a stator and an actuator assembly. The housing has a closed end and an open end forming a bore therebetween. The stator has a top and a bottom. The bottom of the stator receives the closed end of the housing. The top of the stator is affixed around an outer portion of the bore. The actuator assembly is received within the bore of the housing. Adjusting the actuator assembly alters the capacitance of the variable capacitor. 
     In another embodiment of the present invention, the top of the stator is crimped to the outer portion of the bore. 
     In another embodiment of the present invention, the top of the stator is crimped to a protrusion on the outer portion of the bore. 
     In another embodiment of the present invention, the top of the stator is crimped to a recess on the outer portion of the bore. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional illustration of a variable capacitor in accordance with an embodiment of the present invention; 
     FIG. 2 a  is a cross-sectional illustration of a portion of the variable capacitor shown in FIG. 1 having a projection in accordance with one embodiment gripping the housing; 
     FIG. 2 b  is a cross-sectional illustration of a portion of the variable capacitor shown in FIG. 1 having a projection in accordance with one embodiment gripping the housing; 
     FIG. 2 c  is a top plan illustration of a plug for a variable capacitor, wherein a projection in accordance with one embodiment circumscribes the plug; 
     FIG. 2 d  is a top plan illustration of a plug for a variable capacitor, wherein projections in accordance with one embodiment do not circumscribe the plug; 
     FIG. 3 is a top plan illustration of a portion of the variable capacitor shown in FIG. 1; and 
     FIG. 4 is a cross-sectional illustration of a variable capacitor in accordance with a preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     In describing the preferred embodiments of the subject matter illustrated and to be described with respect to the drawings, specific terminology will be resorted to for the sake of clarity. However, the invention is not intended to be limited to the specific terms so selected, and is to be understood that each specific term includes all technical equivalence which operate in a similar manner to accomplish a similar purpose. 
     The present invention will now be described in relation to the drawings, wherein like reference numbers represent like elements. FIG. 1 illustrates an embodiment of a variable capacitor according to the present invention, which has been designated generally by reference number  100 . As shown in FIG. 1, the structure of the variable capacitor  100  includes a dielectric housing  102 , a stator  114  and an actuator assembly  103 . The housing  102  is constructed in the nature of a hollow tubular body  130  having an open end  116  and a closed end  117 . The interior  132  of housing  102 , defined by its inner surface  134 , is substantially cylindrical. Preferably, the interior  132  will have a uniform cross-section or diameter from the open end  116  to the closed end  117  of the housing  102 . The hollow tubular body  130  has an exterior surface  118 , which may be cylindrical, but other shapes such as rectangular, polygonal, and the like are contemplated. The dielectric housing  102  is preferably a polymer material, such as polytetrafluoroethylene (PTFE-commonly known as Teflon®), polycarbonate, polypropylene, or polyethylene. As shown by FIG. 1, dielectric housing  102  is preferably a one-piece design formed, for instance by molding the polymer material, which in the preferred embodiment is PTFE. 
     Dielectric housing  102  may vary in thickness between the inner surface  134  and exterior surface  118  along the region from closed end  117  to the open end  116 . For instance, the dielectric housing  102  may be thin in the region adjacent to the closed end  117 , which is surrounded by the relatively thick walled stator  114 , in order to vary the capacitance of the variable capacitor  100 . Varying the thickness also serves to provide a protrusion  136  along a portion of exterior surface  118 . Preferably, the protrusion  136  is provided along exterior surface  118  so that stator  114  can be attached thereto. Additionally, a portion of exterior surface  118  can be uncovered and exposed to the surrounding environment. 
     The polymer material should be rigid enough tomaintain its shape without deforming yet malleable enough to securely receive the actuator assembly  103  in a compression fit as to be described. The actuator assembly  103  is secured within the open end  116  of dielectric housing  102  and is operable to vary the capacitance of the variable capacitor  100 , as will be explained below. 
     The actuator assembly  103  is constructed from plug  104 , conductive body  124 , and actuator  126 . Plug  104  has a cylindrical outer surface  128 , a cylindrical inner opening  120 , a circumscribing lip  112  and bottom edge  113 . Lip  112  acts to secure conductive lead  110  to the capacitor  100 . Bottom edge  113  assists in constraining the movement of conductive body  124  within interior  132  of dielectric housing  102 . Outer surface  128  grips a portion of the inner surface  134  of dielectric housing  102  by the presence of at least one projection  106 . Various embodiments of projection  106  are illustrated in FIGS. 2A-D. 
     FIG. 2A illustrates a cross-sectional blown-up view of plug  104  engaging housing  102 . In the example of FIG. 2A, the projections  106  are in the nature of a plurality of teeth-like structures formed by continuous rings about the plug  104 . The projections preferably are provided with a sharp edge  200 . 
     As plug  104  is inserted into dielectric housing  102 , the teeth grip by digging into the inner surface  134  of the housing  102 . This conveniently secures the plug  104  in the housing. The plug is preferably sized to be force fit into the dielectric housing  102 , thereby eliminating the need if desired for soldering, screws or other expensive and time-consuming connection methods. 
     Preferably, the projections  106  circumscribe the outer surface  128  of plug  104  in one or more circumscribing rings to provide adequate gripping with a portion of inner surface  134  near open end  116 . Projections  106  are not limited to a plurality of teeth-like rings. Alternatively, projection  106  can be at least one annular ring, as shown in FIG.  2 B. As plug  104  is inserted into housing  102 , the annular ring(s) grips into the polymer material which is softer than the housing  102 . As shown in the bottom plan view of FIG. 2C, the projections  106  such as the annular ring can completely circumscribe the outer surface  128  of plug  104 . Alternatively, as shown in FIG. 2D, the projections  106  such as the teeth-like rings of FIG. 2A need not completely circumscribe outer surface  128  thus forming individual teeth-like projections. Other types, quantity and placement of projection  106  may be employed, and it should be understood that the invention is not limited to those specifically illustrated as described. Rather, it is contemplated that any type of projection in the plug  104  which will cooperate with the housing  102  to secure the two components together can be incorporated in accordance with the present invention. Further, it is contemplated that a groove may be formed in the inner surface  14  of the housing  102  to receive the projection  106  in a locking arrangement. 
     Returning to FIG. 1, conductive body  124  is disposed within the interior  132  of hollow tubular body  130 . Conductive body  124  is moveable within the hollow tubular body  130 , and acts as a variable electrode. Conductive body  124  is preferably adjustable between the bottom edge  113  of plug  104  and the closed end  117  of the hollow tubular body  130 . Preferably, conductive body  124  is a metal, such as of copper-based alloys, brass-beryllium-copper, phosphor bronze, zinc-plated metal, metal coated plastic and the like. 
     The conductive body  124  is attached at one end to the actuator  126 . Alternatively, conductive body  124  and actuator  126  may comprise a one-piece structure. Actuator  126  is formed of a conductive material, preferably the same type of metal as conductive body  124 . Actuator  126  is adjustable within inner opening  120  of plug  104 . For example, actuator  126  may be threadedly engaged with inner opening  120 . Preferably, actuator  126  has a groove  200  at the end opposite conductive body  124  such that the actuator  126  can be rotated through the threading with a screwdriver. As will be apparent to those skilled in the art, other means to adjust the actuator  126  within dielectric housing  102  may be employed. 
     FIG. 1 shows a lead  110  disposed between the top of open end  116  and the lip  112  of plug  104 . The lead  110  provides an electrical contact to conductive body  124  through plug  104  and actuator  126 . FIG. 3 illustrates a top view of lead  110 . Inner opening  122  preferably has the same shape as outer surface  128  of plug  104 . Preferably, lead  110  is placed on top of open end  116  and is secured between the top of open end  116  and lip  112  of plug  104  as plug  104  is pressed into open end  116 . Because projection  106  secures plug  104  into dielectric housing  102 , soldering or additional components are unnecessary to secure lead  110 . 
     Returning to FIG. 1, stator  114 , having a cup shape, receives a bottom portion of dielectric housing  102  including closed end  117 . The bottom of the cup shape is preferably closed, with the bottom substantially encompassing closed end  117 . The sides of stator  114  can vary in thickness. The sides may be thicker near the region adjacent to the closed end  117  in order to support the correspondingly thinner portion of dielectric housing  102  in the same region. The top of stator  114  is attached about protrusion  136  of exterior surface  118 . Stator  114  is preferably affixed by crimping the top of the stator around the protrusion  136 . Crimping, as used herein, means to press or pinch an object into small regular folds or ridges. Crimping acts to secure the stator  114  to the dielectric housing  102  without resorting to soldering the two units together or joining them with additional components. Thus it is evident that crimping stator  114  to dielectric housing  102  can reduce the cost of manufacturing capacitor  100 . 
     Stator  114  is formed of a conductive material, preferably a metal, which can be similar to that of the conductive body  124 . Stator  114  preferably acts as a fixed electrode or electrical contact. For instance, capacitor  100  can be affixed to a circuit board by soldering stator  114  to the circuit board. 
     The capacitor  100  can be fabricated in the following manner by way of one example. First, conductive body  124  is secured to actuator  126 . Next, actuator  126  is threaded into inner opening  120  of plug  104 . Then, lead  110  is placed over open end  116  of dielectric housing  102 . Next, plug  104  is press fit into open end  116  with projection  106  gripping into the polymer material of dielectric housing  102 . Lead  110  is secured to dielectric housing  102  by lip  112  of plug  104  as the plug  104  is press fit into open end  116 . Then, stator  114  receives a portion of dielectric housing  102 , preferably including closed end  117 . The top of stator  114  is crimped around recess or protrusion  136  of exterior surface  118 , securing the dielectric housing  102  and the stator  114  together. This method of fabrication illustrates that a variable capacitor of the present invention may be easily and rapidly constructed using a few components without the need for soldering, welding or other time-consuming and/or expensive processes. Other methods of fabrication and variations on this method of fabrication will be apparent to those skilled in the art. 
     After fabrication, capacitor  100  is, for example, placed on a circuit board for use in an electrical circuit. Lead  110  and stator  114  are preferably soldered to the circuit board. Once affixed to the circuit board, variable capacitor  100  is operable to effectuate a variable capacitance. For example, a voltage may be applied to one or both of conductive body  124  and stator  114  such that a voltage difference is created between the two components. The voltage difference gives rise to a capacitance that can be used in operation of the electrical circuit. Adjusting conductive body  124  with actuator  126  moves conductive body  124  within interior  132 . Moving conductive body  124  closer to closed end  117  increases the relative area of conductive body  124  in overlapping relationship with the stator  114  in the region spanned by the thinner portion of dielectric housing  102 , which may alter the capacitance of variable capacitor  100 . For example, the variable capacitor of FIG. 1 may have an adjustable capacitance of between about 0.6 to 3.0 pF. 
     FIG. 4 illustrates a preferred embodiment of capacitor  100 . This preferred embodiment includes a dielectric housing  102 , a stator  114 , an actuator assembly  103 , lead  110  and ring  140 . As described above in relation to FIG. 1, dielectric housing  102  is formed of hollow tubular body  130  having open end  116  and closed end  117 . Interior  132  of housing  102 , having inner surface  134 , is substantially cylindrical. 
     As with the embodiment of FIG. 1, dielectric housing  102  preferably varies in thickness between the inner surface  134  and exterior surface  118  along the region from closed end  117  to open end  116 . In addition to the protrusion  136  that stator  114  can attach about, exterior surface  118  may include a shelf  138  to support ring  140 . Ring  140  rests upon the shelf, which prevents the ring  140  from sliding down exterior surface  118  while aligning the ring opposing the projection  106 . 
     Ring  140  encompasses a top portion of exterior surface  118 . Ring  140  has a bottom  142 , a top  144 , an interior  146  and an exterior  148 . Bottom  142  rests on the shelf  138  of exterior surface  118 . Top  144  supports lead  110  and compresses the lead into contact with the lip  112  of the plug  104 . Because polymer materials may tend to flow, it is possible for the polymer material to disengage from projection  106 . Ring  140  exerts a compressive or restraining force on the polymer material, preventing it from flowing and disengaging from projection  106 . Ring  140  is preferably a metal, such as brass. Preferably, interior  146  is shaped to securely fit about the top portion of exterior surface  118  between shelf  138  and open end  116 . Exterior  148  may be cylindrical, but other shapes such as rectangular, polygonal and the like are contemplated. 
     The stator  114 , actuator assembly  103  and lead  110  of the preferred embodiment have the same form and function as described in the embodiment of FIG.  1 . The capacitor illustrated in the preferred embodiment of FIG. 4 can be fabricated in the following manner. First, ring  140  is placed over open end  116  of dielectric housing  102 . The ring  140  is slid down exterior surface  118  until the bottom  142  of ring  140  contacts the shelf  138  of exterior surface  118 . Next, lead  110  is placed onto ring  140  so that lead  110  contacts top  144 . Then actuator assembly  103  is pressed into open end  116 . Ring  140  and lead  110  are secured to capacitor  100  by lip  112  as the projection  106  of the actuator assembly  103  grips into the polymer material of dielectric housing  102 . Lip  112  of plug  104  covers a portion of lead  110 , preventing the lead  110  from coming off of the capacitor  100 . Next, the dielectric housing  102  inserted into stator  114 . Alternatively, stator  114  is placed about the closed end  117  of dielectric housing  102 . Then the top of stator  114  is secured about the protrusion  136  of exterior surface  118  of dielectric housing  102 . Stator  114  is preferably secured by crimping its top about the recess or protrusion  136 . After the capacitor  100  has been fabricated, it may be employed in an electrical circuit, for example, by soldering the lead  110  and stator  114  to the appropriate connections of the circuit. 
     Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.