Abstract:
A sealing head for an inductive cap sealing apparatus includes a outer housing containing a coil bobbin supporting a wire coil wound about a magnetic isolator. The coil bobbin and the magnetic isolator can be axially repositioned independently to vary the magnetic field with respect to a container being sealed placed below the sealing head. The housing has a pair of axial apertures containing spring and push rod assemblies connected to a cap plate. The cap plate is spring loaded away from the outer housing so as to clamp the cap and/or seal against the container being sealed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit to U.S. provisional application serial No. 60/186,181 filed Mar. 1, 2000. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH/DEVELOPMENT 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     The invention relates to the field of heat sealing caps to containers. In particular, the invention is an adjustable sealing head for an inductive cap sealing apparatus. 
     Inductive sealing is a well-known method for hermetically sealing the openings of containers. Inductive sealing requires an electromagnetic-field-producing apparatus and a foil-polymer seal. Typically, the apparatus includes at least one coil of wire wound to produce an electromagnetic field when electric current is supplied to the coil. It is well-known in the art that electromagnetic fields induce eddy currents within metal, which in turn heat the metal. The seal comprises a thin layer of aluminum foil onto which is laminated a polymer layer that is molecularly compatible with the container to be sealed. When the seal is placed onto the container and the container is placed within an electromagnetic field, the eddy currents in the foil give off energy in the form of heat, which melts the polymer layer. Removing the seal from the electromagnetic field allows the polymer to cool and molecularly fuse with the container to create an airtight seal. U.S. Pat. No. 6,153,864, assigned to the assignee of the present invention and hereby incorporated by reference, discloses an example of an inductive sealing apparatus using this technique. 
     Typically, containers to be sealed ride along on conveyers beneath one or more sealing heads. The sealing heads can be fixed in place or indexed in a rotary carriage. Multi-headed cap sealers typically provide higher sealing rates than single-headed cap sealers. In both cases, however, it is important for the sealing head to provide an appropriate magnitude of magnetic flux in the area of the container top. Too much flux can melt the container or weld the foil seal to the container such that it is difficult to remove. Too little flux will not adequately seal the container. 
     Typical inductive sealing apparatuses have an adjustable mounting frame to properly position the sealing head with respect to containers being sealed. Such an adjustment is usually adequate for cap seals with a single sealing head. However, slight differences in the coil winding and loop isolation of multiple sealing heads can cause variances in the magnetic flux at the container top. Thus, adjusting the head mounting frame does not correct for magnetic flux variations between the heads of a multi-headed cap sealer, which can result in inconsistent sealing of the containers. 
     Accordingly, there is a need in the art for an adjustable sealing head that can be used in a multi-headed cap sealer to compensate for magnetic flux variations between multiple sealing heads. 
     SUMMARY OF THE INVENTION 
     The present invention provides an adjustable sealing head for use with an inductive sealing apparatus. The sealing head includes a housing defining a cavity that is disposed about and extends along a central axis. A coil bobbin disposed in the housing cavity has a cylindrical support extending along the central axis about which a wire coil capable of producing a magnetic field when energized is wound. An adjustment mechanism attaches the coil bobbin to the housing and enables manual adjustment of the coil bobbin in the axial direction with respect to the housing. 
     In one preferred form, the coil bobbin is adjustably fastened to a cap plate fixed at one of the housing. Rotating the fasteners allows the coil bobbin to be axially repositioned with respect to the housing. 
     In one preferred form, the inner housing is adjustably mounted at its top to a radial member fixed to the housing in the central cavity. Rotating fasteners threaded into the radial member moves the coil bobbin axially with respect to the housing. Preferably, the cylindrical wall of the housing includes a pair of axial apertures housing a pair of spring and push rod assemblies mounting a lower cap plate. The spring and rod assemblies bias the cap plate away from housing so that the cap plate can clamp the cap and/or seal against a container being sealed placed beneath the sealing head. 
     In yet another preferred form, the sealing head is includes a magnetic isolator disposed within the cylindrical support about which the wire coil is wound. The magnetic isolator is contained in an isolator housing have an externally threaded end that engages a threaded bore in a radial member fixed to the housing or part of the movable coil bobbin. Rotating the isolator housing changes its axial position with respect to the coil bobbin so as to alter the magnetic flux lines produced by the wire coil when energized 
     The invention thus provides a sealing head for an inductive cap sealer that can be adjusted with respect to its mounting frame. The magnetic flux at the opening of the container being sealed can be adjusted by changing the position of the coil with respect to the container. The magnetic flux can also be adjusted by changing the position of the coil with respect to a loop isolation element. The sealing head is particularly suitable for use with multi-headed cap sealers because each sealing head can be independently adjusted to provide consistent magnetic flux of the all the sealing heads despite slight variation in mounting location and sealing characteristics of each sealing head. Proper sealing is further ensured by the spring loading the cap plate to clamp the cap and/or the inner seal against the container being sealed. 
     The foregoing and other objects and advantages of the present invention will appear from the following description. In the description, reference is made to the accompanying drawings which form a part hereof and in which there is shown by way of illustration a preferred embodiment of the invention. Such an embodiment does not necessarily represent the full scope of the invention, however, a reference must be made therefore to the claims for interpreting the scope of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side cross-sectional view of an adjustable sealing head according to the present invention, showing a moveable sealing head housing in a retracted position; 
     FIG. 2 is a side cross-sectional view of the sealing head of FIG. 1, showing the moveable sealing head housing in a fully lowered position; 
     FIG. 3 is a side cross-sectional view of an alternate embodiment of the invention with a spring loaded container clamp shown in an extended position; and 
     FIG. 4 is a side cross-sectional view of the alternate embodiment of FIG. 3 with the container clamp shown in a retracted position. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The sealing head of the present invention is illustrated in the drawings and referred to generally by reference  10 . Referring to FIG. 1, the sealing head  10  is preferably used with a multi-headed inductive cap sealer (not shown) having an in-line or rotary lift mechanism (not shown) suitable for holding two or more such sealing heads. It should be noted, however, that the sealing head of the present invention may also be used with a single-headed cap sealer. 
     The sealing head  10  includes a housing  12  fixed to the lift mechanism by fasteners (not shown) disposed in bores  16  at the top of the housing  12 . The housing  12  is generally cylindrical in shape defining a cylindrical cavity  14  along a central axis  15 . A cap plate  18  at the bottom of the housing has a circular recess  19  concentric with the axis  15 . The recess  19  has an inwardly tapered circumference  13 , which helps center a container to be sealed with the sealing head  10 . 
     A coil bobbin  20  is disposed in the cavity  14  of the housing  12  and has a cylindrical wall  17  with an open top and a radially extending bottom  22  defining an opening  23  concentric with the axis  15 . A cylindrical wire support  26  extends along the axis  15  within the coil bobbin  20  from the opening  23 . The coil bobbin  20  thus defines an annular chamber  28  in which a wire coil  30  is disposed. The coil  30  is comprised of suitable wire, such as litz wire, wrapped in a loop around the wire support  26 . The ends of the coil  30  are preferably connected to a single power supply through suitable openings at the top of the housing  12 . 
     The coil bobbin is attached to the housing  12  by an adjustment mechanism including adjustment fasteners  54  having a threaded end  56  disposed through recesses  52  in the cap plate  18  and threaded into threaded bores  58  in coil bobbin  20 . The heads of the adjustment fasteners  54  are secured within the recesses  52  by a retaining plate  60  having bores  62  through which the adjustment fasteners  54  pass. Bores  64  extend from the bottom of the housing  12  into the recesses  52  so that the adjustment fasteners  54  can be accessed easily for adjustment. Referring to FIG. 2, by rotating the adjustment fasteners  54 , the coil bobbin  20  can be positioned axially (up and down) within the housing  12 . 
     The coil bobbin  20  is capped by an end cap  32  held in place with threaded fasteners  34 . The end cap  32  has a threaded bore  36  concentric with the axis  15  for engagement with an externally threaded end  38  of an isolator housing  40  disposed within the wire support  26  of the coil bobbin  20 . 
     The isolator housing  40  is a cylinder in which is disposed a triangular arrangement of magnetically isolating blocks  42 , preferably made of a ferromagnetic compound having ferric oxide. A top end  44  of the isolator housing  40  is solid and forms a hexagonal head  46  for rotating the isolator housing  40  with a standard wrench. The isolator housing  40 , as well as the coil bobbin  20 , is filled with an epoxy resin, which secures the isolator blocks  42  and wire coil  30  in place. 
     The isolator housing  40  can be rotated by applying a rotational force to the head  46  so that the threads of the isolator housing  40  engage with the threaded bore  36  of the top plate  32  so that the isolator housing  40  moves axially with respect to the coil bobbin  20 . Repositioning the isolator housing  40  with respect to the coil  30  alters the flux lines of the coil  30  and affects the magnitude of magnetic flux at the bottom of the sealing head  10  wherein containers are sealed. A locking nut  50  can be threaded onto the isolator housing  40  for fixing the relative position of the isolator housing  40  and the coil bobbin  20 . The locking nut  50  would need to be loosened before adjusting the axial position of the coil bobbin  20  so that the isolator housing  40  is free to rotate. 
     The housing  12 , coil bobbin  20  and isolator housing  40  are preferably constructed from acrylonitrile butadiene styrene (“ABS”) plastic, as are the end cap  32  and retaining plate  60 . A deformable pad, preferably made of silicon  70 , can be disposed in the recess  19  in the cap plate  18 , which compensates for irregularities in the height of a container or the surface of a container lid to ensure a proper seal. 
     Thus, the coil bobbin  20  can be adjusted with respect to the housing  12  and the isolator housing  40  can be adjusted with respect to the coil bobbin  20 . Either or both of these adjustments alter the magnitude of the magnetic flux below the sealing head  10  where a container for sealing (not shown) would be disposed. By suitable calculation or empirical study, sealing heads  10  can be calibrated for a given container size to provide the appropriate magnetic flux and to ensure a proper seal of the container consistently. 
     For a multi-headed cap sealer, each sealing head  10  can be calibrated by a trial and error process wherein each coil bobbin  20  is set in the fully retracted position by rotating the adjustment fasteners  54  counterclockwise (after loosening the locking nut  50  on the isolator housing  40 ), then energizing the coil  30  to seal a container of a prescribed sized. If the container is found to be properly sealed, the same is done for the next sealing head  10 . If the seal is unsatisfactory, however, the coil bobbin  20  can be incrementally lowered by tightening the adjustment fasteners  54  until a satisfactory seal is achieved. 
     Additionally, or alternatively, the isolator housing  40  can be incrementally repositioned as needed between energizing the sealing heads  10  being calibrated. The isolator housing  40  is repositioned by loosening the locking nut  50  and rotating the isolator housing  40  by applying a rotational force at the head  46 , preferably using a standard sized wrench. When the isolator housing  40  is in the desired position, the locking nut  50  is re-tightened. 
     Another preferred embodiment of the invention is shown in FIGS. 3 and 4. Elements similar to the those of the above embodiment are referred to with like numerals albeit with the suffix “A”. In this embodiment, the sealing head  10 A includes a housing  12 A secured to the cap sealer lift mechanism at its top end. The housing  12 A is generally cylindrical in shape defining a cylindrical cavity  14 A therethrough opening to the bottom of the sealing head  10 A and extending along a central axis  15 A. 
     The housing  12 A includes two axial through bores  80  and  82  closed at the top end by a ring  83  bolted to the top of the housing  12 A. Each bore  80  and  82  contains a compression spring  84  and  86  and a push rod  88  and  90 , respectively. The springs  84  and  86  are disposed in enlarged sections of the bores  80  and  82 . The push rods  88  and  90  engage the springs  84  and  86  through washers  91  and  93  connected to the top ends of the push rods  88  and  90  by threaded fasteners  92  and  94 , respectively. The washers  91  and  93  also engage the shoulders of the bores  80  and  82  at the bottom of the enlarge sections to retain the push rods  88  and  90  in the bores  80  and  82 , respectively. A cap plate  18 A is fastened to the bottom of the push rods  88  and  90  by threaded fasteners  96  and  98  disposed in bores  100  and  102 , respectively. The cap plate  18 A defines an opening  19 A having an inwardly tapered circumference  13 A, which aids in centering the container being sealed. 
     A coil bobbin  20 A is disposed in the cavity  14 A of the housing  12 A and has a cylindrical wall  17 A with a bottom  22 A and a top end cap  32 A. The bottom  22 A has a through opening  23 A and the end cap  32 A has a threaded opening  36 A, both concentric with the axis  15 A. A cylindrical wire support  26 A extends along the axis  15 A within the coil bobbin  20 A from the bottom opening  23 A. The coil bobbin  20  thus defines an annular chamber  28 A in which a wire coil  30 A (as described above) is disposed. 
     The coil bobbin  20 A is mounted to the housing  12 A at a radial support plate  101  bolted radially to the cylindrical wall  17 A of the housing  12 A. Adjustment fasteners  34 A extend through bores in the support plate  101  and thread into set collars  35 A disposed in recesses in the end cap  32 A of the coil bobbin  20 A. The adjustment fasteners  34 A also thread into threaded bores beneath the recesses extending through the end cap  32 A of the coil bobbin  20 A. This arrangement allows the axial position of the coil bobbin  20 A to be changed by rotating the adjustment fasteners  34 A to engage the threaded bores in the end cap  32 A of the coil bobbin  20 A. 
     The support plate  101  has a threaded bore  92 , which engages (along with bore  36 A in the end cap  32 A) a threaded top end  38 A of an isolator housing  40 A disposed within the wire support  26 A of the coil bobbin  20 A. The isolator housing  40 A is a cylinder containing magnetically isolating blocks  42 A held in place with an epoxy. A top end  44 A of the isolator housing  40 A is solid and forms a slot  48  at the top for receiving the blade of a screwdriver. The isolator housing  40 A can be rotated with a screwdriver so as to move axially with respect to the coil  30 A in the coil bobbin  20 A (as described above). A locking nut  50 A can be threaded onto the isolator housing  40 A for fixing the relative position of the isolator housing  40 A and the coil bobbin  20 A. As with the first described embodiment, the locking nut  50 A would need to be loosened or removed before adjusting the position of the coil bobbin  20 A with respect to the housing  12 A. 
     Thus, like the above described embodiment, the magnetic field can be varied with respect to the container being sealed by axially adjusting the coil bobbin  20 A with respect to the outer housing  12 A and by adjusting the axial position of the isolator housing  40 A in the wire coil  30 A. Either or both of these adjustments alter the magnitude of the magnetic flux below the sealing head  10 A where a container for sealing would be disposed. 
     Moreover, in this embodiment, the spring loaded cap plate  18 A is biased away from the outer housing  12 A by the springs  84  and  86 , as shown in FIG.  4 . When sealing a container with a rotary type cap sealer, for example, the cap plate  18 A will engage a container placed or conveyed beneath the cap sealer. As the carriage mechanism rotates the sealing head  10 A over the container, the tapered circumference  13 A of the recess  19 A will engage the cap of the container and center the container with the sealing head  10 A. As the sealing head continues to rotate and engage the container cap, the cap plate  18 A will be forced upward and the compression of the springs  84  and  86  will provide a downward clamp force on the cap to seat the cap and inner seal against the sealing surface (rim) of the container to ensure proper seating of the seal on the lip of the container. It should be noted that the cap plate  18 A will engage the seal directly if the container does not include a cap. As the sealing head  10 A continues to rotate, the cap plate  18 A disengages from the cap (or seal) and extends outward due to the spring force until the washers  91  and  93  seat against the shoulders in the bores  80  and  82 . 
     As in the first embodiment, the housing  12 A, coil bobbin  20 A, isolator housing  40 A and end cap  32 A are preferably constructed of ABS plastic. The cap plate  18 A is preferably a suitable phenolic or glass fiber reinforced epoxy and the push rods are preferably a suitable metal. A deformable silicon pad  70 A can be placed in the recess  19 A in the cap plate  18 A. Additionally, as above, the magnetic flux of the sealing head can be set by calculation or empirical study and incremental adjustment of the coil  20 A and isolator  40 A housings until proper sealing is achieved. 
     Preferred embodiments of the invention have been described in detail for the purpose of disclosing practical, operative structures whereby the invention may be practiced advantageously. The design described is intended to be illustrative only. The novel characteristics of the invention may be incorporated in other structural forms without departing from the scope of the invention.