Abstract:
An inductive device comprises a coil having a winding and extending along and spaced from an axis, and a pair of lead wires extending internally between the ends of the coil. The lead wires extend externally from one of said ends for connection to an electrical circuit, and form start and finish posts at the other of said ends. The respective ends of the winding are wound on and electrically connected to the posts, for which purposes the posts extend axially away from the coil in spaced relationship.

Description:
RELATED APPLICATION 
     This application is a continuation-in-part of Ser. No. 10/057,248, filed Jan. 25, 2002 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to inductive devices, and more particularly to coils of fine wire and of very small dimensions suitable for use in hearing aids and other devices employing miniature circuitry. 
     In certain applications, such devices are referred to as telecoils and are installed in a hearing aid to sense the magnetic field of a telephone or other assistive listening system for the hearing impaired. The detection of such fields controls the operation of the electronic circuit of the hearing aid. In current practice, a telecoil typically consists of several thousand turns of fine insulated coil wire, typically on the order of one thousandth inch in diameter, wound on a ferrous or other core of magnetic material. In manufacture, the winding wire may be wound directly on a bobbin of magnetic material which forms a part of the telecoil, or the wire may be wound on a mandrel which is removed after winding, leaving a hollow core into which a ferrous rod is later inserted. The ultrafine coil wire is very fragile and is typically unsuited for connection to external circuit components for that reason. Therefore, it is typically necessary to provide heavier connection or lead wires that extend to such external circuit elements, the lead wires having, for example, five or six times greater diameter and being soldered or otherwise electrically connected to the ends of the fine winding wire. In these miniature devices terminal pads may be provided at one or both ends of the coil or cemented to the exterior body of the coil, and the fine wire may be wrapped around the lead wires which are in turn attached by adhesive or otherwise to the outside of the coil after winding. 
     One of the objects of the invention is to provide improved coils of minimized diameter and overall coil length. 
     Another object is to provide an improved structure whereby the lead wires are pre-mounted on the bobbin (or mandrel) prior to winding, thus providing to the winding equipment integral posts for coil wire terminations. 
     Another object is to provide an improved structure in which neither solder connections nor bare lead wires come into contact with the ultrafine coil wire of the winding. 
     Another object is to provide an improved construction that eliminates mechanical stress on the solder connections and increases the pull strength of the lead wires when connecting them to external circuit elements. 
     Another object is to provide a construction in which the lead or connection wires will only be subjected to bending in an area remote from the soldered area during connection of the coil to external circuit elements, as the soldered area typically becomes embrittled and weakened during soldering. 
     Another object is to provide the foregoing advantages to the coil using conventional winding methods but at reduced costs for parts, tooling and assembly. 
     Other objects of the invention will be understood from the following detailed description with reference to the appended drawings. 
     BRIEF SUMMARY OF THE INVENTION 
     With the foregoing objects in view, this invention features lead wires that extend inwardly of the coil winding from end to end thereof, forming start and finish connection posts at one end of the coil around which the respective ends of the winding wire are wound. Advantageously, the lead wires are preformed and the coil winding is wound over the lead wires, the ends of the winding being extended out to the posts for winding on and electrical connection to the posts. 
     Another feature is that the foregoing construction can be achieved either by winding the fine coil wire on a bobbin of magnetic material that forms a part of the completed coil, or the fine wire may be wound on a removable mandrel which, after winding, is replaced by a ferrous or other magnetic core or rod. 
     Another feature is that the improved coil may be formed on any of several presently available winding machines in which the bobbin or mandrel is either rotating or non-rotating. 
     Other features of the invention and the achievement of other objects hereinabove referred to will be evident from the following description. 
    
    
     DRAWING 
     FIG. 1 is a side elevation of a first embodiment of coil bobbin for winding the coil of the invention. 
     FIG. 2 is a view in plan of the bobbin of FIG.  1 . 
     FIG. 3 is a right end elevation on line  3 — 3  of FIG.  1 . 
     FIG. 4 is an end elevation corresponding to FIG.  3  and illustrating an alternative embodiment of the bobbin. 
     FIG. 5 is an axial elevation of an assembly having a coil wound on the bobbin of FIGS. 1 to  3 . 
     FIG. 6 is an elevation taken on line  6 — 6  of FIG.  5 . 
     FIG. 7 is an end elevation on line  7 — 7  of FIG.  5 . 
     FIG. 8 is an elevation corresponding to FIG.  7  and illustrating the alternative embodiment of FIG.  4 . 
     FIG. 9 is a schematic drawing of a conventional flying head multi-axis coil winding machine suitable for forming coils according to the invention. 
     FIG. 10 is a schematic drawing of a rotating chuck winding machine suitable for winding coils according to the invention. 
     FIG. 11 is a view in perspective of a second embodiment of coil bobbin for winding the coil of the invention. 
     FIG. 12 is a front elevation of the embodiment of FIG.  11 . 
     FIG. 13 is a right side elevation taken on line  13 — 13  of FIG.  12 . 
     FIG. 14 is an end elevation taken on line  14 — 14  of FIG.  12 . 
    
    
     DETAILED DESCRIPTION 
     Referring to FIGS. 5-7, a coil  10  comprises a winding  12  of several thousand turns of ultrafine wire closely compacted and extending between ends  14  and  16  of the coil. The turns of the winding are spaced from a longitudinal axis a—a of the coil, and a pair of lead wires  18  and  20  extend axially from end to end of the coil through the space so provided. 
     At the end  14  of the coil the lead wires  18  and  20  extend a sufficient distance for connection to the external circuitry of a hearing aid or other device (not shown). At the end  16  of the coil the lead wires are formed and separated to extend axially away from the coil, forming a start post  22  and a finish post  24 . Ends  26  and  28  of the wire of the winding  12  are respectively wrapped on the posts  22  and  24 , and soldered or welded thereto. 
     FIGS. 1 to  3  illustrate a first alternative form of bobbin  30  over which the turns of the winding  12  may be formed. The bobbin  30  is formed of two identical pieces  32  of ferrous or other magnetic material blanked from a flat sheet. Each of the pieces  32  is formed with dimples  34 , then cut into elongate strips and formed with ends  36  extending normal to the axis a—a. Two of the pieces so formed are placed with their dimples  34  in mutual contact, providing a space  38  between the pieces  32  extending longitudinally of the bobbin  30 . The dimples  34  are then welded to form a rigid structure. Other conventional steps of fabrication such as tumbling, annealing and coating may also be performed on the bobbin in preparation for winding the fine wire thereon. 
     The lead wires  18  and  20 , preferably preformed to provide the terminal posts  22  and  24 , are extended through the space  38  from end to end of the bobbin  30  in preparation for forming the winding  12  thereon between the ends  36  of the bobbin. 
     If desired, the ends  36  of the bobbin may be replaced by ends  40  of more extended area as illustrated by the alternative embodiment of FIGS. 4 and 8. The bobbin ends  40  are preferably shaped to extend only minimally or not at all beyond the diameter of the winding  12  of the coil  10 . The ends  40  serve for further confinement of the ends  14  and  16  of the coil  10  during and after the winding operation. 
     FIG. 9 illustrates the winding of the coil of the invention on a conventional flying head multi-axis winding machine. The fine wire  42  is drawn from a supply spool  44  over an adjustable tensioning device  46 , through a hollow tube wire guide  48 , and downwardly through a depending tubular portion  50  thereof. The bobbin  30  is fastened to a chuck  32 . The wire guide  48  is the so-called flying head type, being adapted for rotation as indicated by an arrow b about an axis c to form the turns of the winding  12  around the stationery bobbin  30 , or alternatively for rotation around either of the respective axes of the start and finish posts  22  and  24  to wrap the ends of the winding wire  12  thereon. 
     The winding operation begins with the winding of the wire  42  on the start post  22 , after which the wire is directed to the space between the ends  14  and  16  of the spool, the axis of rotation of the guide  48  reverting to the axis c—c. Rotation about the axis c—c then begins. As the rotation continues, the wire guide  48  reciprocates vertically as indicated by arrows  52  to distribute the turns of the winding uniformly between the ends  14  and  16  of the coil. Finally, the rotational axis is again shifted to wrap the end of the wire  42  on the finish post  24 . 
     FIG. 10 illustrates a conventional rotating chuck winding machine having a chuck  54  rotated by a motor  56 . Winding wire  58  is fed from a supply spool  60  over an adjustable tensioning device  62  to a traversing wire guide  64  which moves reciprocally between limits  66  and  68  to distribute the turns of the winding uniformly between the ends  14  and  16  of the coil  10 . 
     In operation, an end of the wire  58  is first wrapped on the start post  22  either manually or in any other convenient manner, then fed to the space between the ends  14  and  16  of the bobbin for winding the body of the coil. Finally, the wire is led to the finish post  24  and manually or otherwise wrapped thereon. In accordance with conventional practice, a controller  70  coordinates the speed of rotation of the motor  56  and the reciprocal movement of the guide  64  for controlling the formation of the coil  10 . 
     In either of the winding machines of FIGS. 9 and 10, in place of the bobbin  30  a removable mandrel of suitable form may be placed in the chuck  20  or  54 . The mandrel can be formed to accept the lead wires  18  and  20  with the start and finish posts  20  preformed thereon prior to formation of the winding  12 . In that case, the mandrel is provided with longitudinally extending slots to accept the lead wires. After completion of the winding including attachment of an end thereof to the finish post  24 , the mandrel  28  is removed from the chuck and withdrawn from the coil. A core of ferrous or other magnetic material is then inserted through the coil to complete the inductive device. Alternatively, the lead wires can be mounted in longitudinal slots of a suitable core and the assembly inserted into the coil after forming the winding and withdrawing the mandrel. 
     In the illustrated embodiments, both of the lead wires  18  and  20  are preformed at the end  16  of the coil  10  with two right angle bends to form radially extending portions thereof for mutually spacing the posts  22  and  24 . Alternatively, only one of the lead wires may be bent in this fashion. In either case, the posts  22  and  24  extend in the axial direction of the coil  10  for wrapping the ends of the winding  12  thereon. In a subsequent operation the posts  22  and  24  are advantageously located for automated dip-soldering of the connections to the wires  26  and  28  of the winding without refixturing of the coil. After the soldering operation the posts  22  and  24  are trimmed to a suitable length if necessary and then preferably bent back against the ends  14  and  16  of the coil to minimize its overall length. 
     Other embodiments may be substituted for that of the bobbin  30 , if desired. Advantageously, the one-piece alternative bobbin  72  of FIGS. 11 to  14  may be employed. The bobbin  72  is blanked from a flat sheet of ferrous or other magnetic material to form integral elongate portions  74  and  76  joined by an integral elongate connecting portion  78 . Each of the portions  74  and  76  is formed with ends  80  similar in form and function to the bobbin ends  36  in FIGS. 1 to  8 . The blank so formed is then folded by bending the connecting portion  78  longitudinally to create an elongate space  82  between the portions  74  and  76 , similar in function to the space  38  of FIGS. 1 to  8 . 
     The foregoing description with reference to the winding of the bobbin  30  is fully applicable to the bobbin  72 . In addition, the bobbin  72  provides other advantages. Its fabrication, employing fewer parts and fewer steps of fabrication, may be easier and less costly to produce, particularly with regard to alignment of parts and the elimination of welding time and equipment. The bobbin  72  is strong and durable in the form illustrated. With the connecting portion  78  extending the full length of the coil winding between the ends  80 , it increases the core cross-section and thereby improves the magnetic performance of the coil. The longitudinal opening on one side of the space  82  allows for faster insertion of both lead wires into this space, and cementing of the wires in this space, from the same side of the bobbin. The connecting portion more fully encloses and contains the cement and leads, making it feasible to use bifilar rather than individual lead wires in some applications.