Abstract:
Methods of fabricating electromagnet assemblies are disclosed. In one embodiment, a includes forming a first helix and a second helix, each helix having a first end and a second end and a substantially oval cross-section, the cross-section having a major axis, each helix being configured to concentrate electromagnetic flux at a midpoint on the major axis. Each helix is bent at an angle and offset from the major axis, resulting in a first planar surface including the major axis and a second planar surface. The first and second helixes are oriented such that the outer edges of the respective second planar surfaces coincide and the outer edges of the respective first planar surfaces are in diametric opposition. The first and second helixes are affixed by their respective second planar surfaces, and electrically connected by their respective second ends.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This patent application is a divisional application of co-pending, commonly-owned U.S. patent application Ser. No. 11/192,783 entitled “Layered Wing Coil for an Electromagnetic Dent Remover” filed on Jul. 29, 2005, which is a divisional application of commonly-owned U.S. patent application Ser. No. 10/377,487 entitled “Layered Wing Coil for an Electromagnetic Dent Remover” filed on Feb. 28, 2003, issued as U.S. Pat. No. 6,954,127 on Oct. 11, 2005, which applications and issued patent are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates generally to electromagnetism and, more specifically, to electromagnets.  
       BACKGROUND OF THE INVENTION  
       [0003]     Dents may occur in metal surfaces, and removal of the dents may be desirable for aesthetic or performance reasons. For example, airplane wings may become dented during operational service. Dents in airplane wings may decrease lift and may increase drag. As a result, it would be desirable to remove dents from airplane wings.  
         [0004]     It is currently known to remove dents in metal surfaces by “pulling” the dents in the surface of the metal with a magnetic field generated by a coil of an electromagnet. Examples of known coils are disclosed in U.S. Pat. Nos. 4,061,007 and 4,123,933, the contents of which are hereby incorporated by reference.  
         [0005]     Referring to  FIG. 1 , a prior art electromagnetic coil  10  includes an annular wrap of layers  12  of a conductor  14 . These coils are visible through the head  13  of the coil  10 . The coil  10  defines notches in the annular wrap that serve as foot  18 . The foot  18  and is the locus on the electromagnetic coil  10  used for pulling dents.  
         [0006]     However, present coils have presented some shortcomings. For example, known coils are expensive to fabricate and have reached their maximum power level. Further, current coils are subject to a high failure rate. Current coils may fail if the coil moves excessively in its housing while the coil is energized to pull a dent. Further, dielectric material within the coil may become damaged from high heat and stresses generated during the firing process. Also, current coils may experience reduced performance. For example, current coils may generate excessive amounts of heat and may generate a reduced magnetic field due to mechanical property changes at elevated temperatures.  
         [0007]     Referring now to  FIG. 2 , a failure  20  of the prior art electromagnetic coil  10  is illustrated. The annular wrap of the layers  12  of the conductor  14  is a principal feature allowing susceptibility to the failure  20 . The failure  20  occurs when an applied electromagnetic force pulls one of the layers  12  of the conductor  20  from the electromagnetic coil  10 .  
         [0008]     Therefore, there is an unmet need in the art for a coil for an electromagnetic dent remover that is less expensive to fabricate and has a lower failure rate than currently known coils, and has increased performance over currently known coils.  
       SUMMARY OF THE INVENTION  
       [0009]     The present invention provides an electromagnet assembly for supplying a region of concentrated electromagnetic flux, and methods of fabricating such assemblies. In one embodiment, a method for making an electromagnetic coil assembly includes forming a first helix and a second helix, each helix having a first end and a second end and a substantially oval cross-section, the cross-section having a major axis, each helix being configured to concentrate electromagnetic flux at a midpoint on the major axis. Each helix is bent at an angle along a line in the plane of the cross-section parallel to and offset from the major axis resulting in a first planar surface including the major axis and a second planar surface, each planar surface having an outer edge opposite the offset line. The first and second helixes are oriented such that the outer edges of the respective second planar surfaces coincide and the outer edges of the respective first planar surfaces are in diametric opposition. The first and second helixes are affixed by their respective second planar surfaces, and electrically connected by their respective second ends. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     Embodiments of the present invention are described in detail below with reference to the following drawings.  
         [0011]      FIG. 1  is a perspective view of the prior art electromagnetic coil;  
         [0012]      FIG. 2  is a perspective view of the failure of the prior art electromagnetic coil;  
         [0013]      FIG. 3  is an upper perspective view of the encased layered wing coil;  
         [0014]      FIG. 4  is a lower perspective view of the encased layered wing coil;  
         [0015]      FIG. 5  is an exploded perspective view of the components of the layered wing coil;  
         [0016]      FIG. 6  is the support for the layered wing coil;  
         [0017]      FIG. 7  is a cut-away diagram of the layered wing coil along the major axis of symmetry;  
         [0018]      FIG. 8  is a cut-away diagram of the layered wing coil along the minor axis of symmetry;  
         [0019]      FIG. 9  is a perspective view of the layered wing coil;  
         [0020]      FIG. 10  is a close-up perspective view of the layered wing coil;  
         [0021]      FIG. 11  is a flux diagram of the layered wing coil;  
         [0022]      FIG. 12  is a block diagram of the principal components of the electronic dent puller;  
         [0023]      FIG. 13  is a flow chart of the formation of the layered wing coil; and  
         [0024]      FIG. 14  is a flow chart of the formation of the component helices of the layered wing coil. 
     
    
     DETAILED DESCRIPTION  
       [0025]     By way of overview, an electromagnet assembly for supplying a region of concentrated electromagnetic flux is provided. The assembly includes a flat strip of an electrically conductive metal. The strip has a first and a second opposite planar surfaces at least one of which is covered by a dielectric material. The strip has first and second end portions. The strip is wound in a coil including at least one first loop and one second loop and disposing the second opposite planar surface in the first loop substantially adjacent the first opposite planar surface in the second loop. The coil is disposed about an axis of symmetry configured to concentrate electromagnetic flux at a midpoint on the axis of symmetry. First and second electrical terminals are connected at the first and second end portions, respectively.  
         [0026]     Referring now to  FIG. 3 , a layered wing coil assembly  25  according to an embodiment of the invention includes a fastening point  29  and an encasement  30 . The fastening point  29  provides a suitable holding spot when the assembly  25  is energized. Advantageously, the fastening point  29  allows the assembly  25  to be used in a working head (not shown) of currently known electromagnetic dent removers. Two conductors  26  and  28  extend from the fastening point  29  through the encasement  30 . The encasement  30  provides electromechanical integrity to the whole of the packaged assembly  25 .  
         [0027]     Referring now to  FIG. 4 , a lower surface  32  of the encasement  30  defines a foot portal  34  that exposes a coil&#39;s keel  48  at its point of concentrated flux. Advantageously, the lower surface  32  of the encasement is the mechanical support for the assembly  25  allowing the lifting of the assembly  25  from a dented surface and for maintaining alignment between the assembly  25  and the dented surface (not shown). The features evident in  FIG. 3  are present here as well. The fastening point  29 , the conductors  26 ,  28 , and the encasement  30  each are visible.  
         [0028]      FIG. 5  is an exploded perspective view of components of the layered wing coil assembly  25 . In the presently preferred embodiment, the components fixedly position and encase a layered wing coil  40 . The encasement  30  and its lower surface  32  form an outer shell. Within the shell, a spacer  36  receives and holds separate the two conductors  26  and  28 . The conductors  26  and  28  pass to either side of a stabilizing mount  38  to feed current to the layered wing coil  40 .  
         [0029]     Referring now to  FIG. 6 , shelf support  31  for the layered wing coil (not shown) is molded into the inner surface of the lower case  32 . The foot portal  34  defined by the lower case  32  also maintains the appropriate alignment between the workpiece (not shown) and the layered wing coil  40 . Additionally, the walls  33  of the lower case  32  in connection with the upper encasement (not shown) provide the mechanical integrity of the electromagnetic coil (not shown).  
         [0030]      FIG. 7  is a cut-away diagram of the layered wing coil  40  along a major axis of symmetry. The conductors  26  and  28  extend from the top of the encasement (not shown) to the bottom of the layered wing coil  40  where they provide a current path. Layers of conductive, substantially oval-shaped sheets  44  are stacked to either side of a midline. A jumper  46  completes the current path from the conductor  26  through the layers of the sheets  44  to the conductor  28 . The sheets  44  are bent to form a keel  48  that concentrates the magnetic flux produced when current flows through the layered wing coil  40 .  
         [0031]      FIG. 8  is a cut-away diagram of the layered wing coil  40  along a minor axis of symmetry. The conductors  26  and  28  conduct transient current to the lowest layer of the sheets  44 . Interruptions  50  in each of the sheets  44 , in concert with dielectric sheets  45  between conductive sheets  44 , force the flow of current around each of the sheets  44  rather than through the height of the stack of sheets  44 . A foot  52  is formed at the bottom of the keel  48 . The magnetic flux is connected to the foot  52 .  
         [0032]     Referring now to  FIG. 9 , the conductors  26  and  28  conduct current to the bottom of the sheets  44 . The jumper  46  provides a conductive path between a second end  44   b  of one sheet  44  to a second end (not shown) of another sheet  44 . First ends  44   a  of one sheet  44  are electrically joined to second ends of a sheet  44  directly beneath it to form substantially helical current paths (not shown). This maintains the current flow direction in foot  52 .  
         [0033]     Referring now to  FIG. 10 , details are shown of the helical coil structure of the sheets  44 . The jumper  46  carries current from the second end  44   b  of a top sheet  44 . The interruptions  50  in each sheet  44  allow a current path around the sheet  44 . Fusion points  56  join second ends of a first sheet  44   b  to first ends of a second sheet  44   a.  The resulting helical current path propagates a magnetic field when a transient current is applied.  
         [0034]     Referring now to  FIG. 11 , a diagram  71  shows flux generated by the layered wing coil  25 . The Finite Element Method Magnetics® chart shows the sums of the flux contribution of each element in the layered wing coil  40  as isolines. An isoline is a line on a map or chart along which there is a constant value, in this case, magnetic flux. The flux concentrated at a workpiece surface  60  and flux concentrating features of the keel  48 , and the layered wing coil  40  appear through an orthogonal slice through the coil assembly  25 . The concentrations of isolines  76  and  78 , for example, show the superior magnetic flux concentration at the workpiece surface  60  in the layered wing coil  40 .  
         [0035]     Referring now to  FIG. 12 , a block diagram of the functional portions of an electronic dent remover  90  according to another embodiment of the invention is shown. The working coil  95  including the layered wing coil is connected to the power supply  93 . As shown, the power supply  30  has both fast and slow capacitor banks to provide fast and slow rise current. A controller  91  is connected to and governs the power supply  93  to the working coil  95 .  
         [0036]     Referring now to  FIG. 13 , a method  100  for forming the layered wing coil assembly  25  according to another embodiment of the invention is shown. The method  100  starts at a block  101 . At the block  101 , forming the first helix occurs; at a block  103 , forming the second helix occurs. These helices are formed of a flat strip of conductive metal coiled and interleaved with an insulating coating. In the presently preferred embodiment, the coils are roughly oval in section.  
         [0037]     At a block  105 , each of the helices is bent along a line parallel and offset from the major axis. The resulting helix has an “L”-shaped (appearing) profile. The major axis remains in the unbent section of coil. At a block  107 , the second helix is oriented towards the first helix such that each shorter leg of each “L” is placed in contact with the other. The resulting joined helices appear to be a mirror image one of the other. In toto, the bent helices give an impression of an opened book bound with the coils of the helix as pages. At a block  109 , the helices are electrically joined for electromagnetic effect. As a result, the magnetic coil has its most efficient concentration of flux.  
         [0038]     Referring now to  FIG. 14 , a non-limiting presently preferred method  120  for forming the component helices of the layered wing coil  40  starts at a block  121 . At the block  121 , fabricate an interrupted substantially oval-shaped ring. Such rings can be easily milled and stamped from copper sheeting. At a block  123 , a second ring can be easily fabricated with an identical profile to the first ring but interrupted at a place slightly displaced from the location of the first interruption. At a block  125 , the first ring is fused to the second ring at the slight overlap. As a result of the fusion, a two-turn helix is manufactured.  
         [0039]     Where another ring is necessary, it is fabricated at a block  127 . Like the second ring, the interruption of the oval is offset slightly from that in the second ring. At a block  129 , it is fused to the helix to extend it by another coil. At a block  131 , the length of the resulting coil is compared to the desired coil length. If the coil length is long enough, the method terminates, otherwise, the method returns to the block  127  to fabricate another ring.  
         [0040]     While preferred and alternate embodiments of the invention have been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is not limited by the disclosure of these preferred and alternate embodiments. Instead, the invention should be determined entirely by reference to the claims that follow.