Abstract:
A method and apparatus for assembling permanent magnet segments and a back ring wherein a fixture holds segments in circumaxially spaced relationship, adhesive is applied to the segments, externally from pressure sensitive adhesive tape and the fixture then expands to urge the segments into firm bonding engagement with the back ring.

Description:
BACKGROUND OF INVENTION  
       [0001]     In the manufacture of permanent magnet motors, magnet segments are conventionally secured in circumaxially spaced relationship on the interior surfaces of cylindrical back rings in a manual operation employing a two-part epoxy. The assembled magnet segments and rings are then conventionally encapsulated in an injection molding operation.  
         [0002]     While generally satisfactory, the procedure is a slow and tedious step in the manufacturing process and the epoxy is both expensive and difficult to apply.  
         [0003]     Accordingly, it is a general object of the present invention to provide an efficient and more expeditious method and apparatus for assembling magnet segments on a back ring.  
         [0004]     A further object of the invention is to provide an assembly method and apparatus which requires minimal manual intervention and which exhibits a high degree of consistency and repeatability in the results achieved.  
       SUMMARY OF THE INVENTION  
       [0005]     In fulfillment of the aforementioned objects and in accordance with the present invention, a rotatable expandable and contractible fixture is provided and the magnet segments are releasably secured on and about the fixture in circumaxially spaced relationship with their exterior surfaces outwardly exposed and provided with an arcuate configuration substantially conforming to that of the interior surface of the back ring. Preferably, a liner backed pressure sensitive adhesive tape known as an “adhesive transfer tape” is then employed with a means for applying the adhesive sequentially to the magnet segments during fixture rotation. The liner is separated during application of the adhesive to the segments. Relative axial movement is then effected between the fixture carrying the segments and the back ring to enter the former within the latter. Expansion of the fixture follows urging the magnet segments firmly into engagement with the interior surface of the back ring and bonding them in position thereon. The fixture is thereafter contracted and relative axial movement is again effected between the fixture and the back ring to remove the former from the interior of the ring assembly.  
         [0006]     Apparatus employed in the practice of the foregoing method in addition to the fixture and adhesive applying means which preferably comprises an application roller includes a vacuum source for releasably securing the magnet segments on the fixture, a rotary drive means preferably in the form of a step motor for the fixture, locating surfaces on the fixture and an opposing device resiliently urging the segments against the surfaces to precisely locate the same, a liner take-up roll, and other auxiliary devices.  
     
    
     DRAWINGS  
       [0007]      FIG. 1  is a top view of an assembled back ring and six (6) magnet segments.  
         [0008]      FIG. 2  is a cross sectional view taken generally as indicated at  2 - 2  in  FIG. 1   
         [0009]      FIG. 3  is a somewhat schematic exploded perspective showing a rotatable fixture, a drive motor and vacuum pump therefore, and a collet-like expander associated therewith.  
         [0010]      FIG. 4  is a side view showing the fixture of  FIG. 3  with a single magnet segment mounted thereon.  
         [0011]      FIG. 5  is a somewhat schematic perspective view showing the fixture with a single magnet segment thereon and a device which operates to precisely locate the segments axially on the fixture.  
         [0012]      FIG. 6  is a somewhat schematic perspective view showing the majority of the major components of the apparatus of the invention.  
         [0013]      FIG. 7  is a perspective view showing a rotatable turret carrying a “bumper” for axially locating the segments and a gripper for placing back rings about fixtures carrying adhesive bearing segments. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENT  
       [0014]     Referring particularly to  FIGS. 1 and 2 , it will be observed that six (6) permanent magnet segments  10 , 10  are provided in the preferred embodiment of the invention shown. The magnet segments  10 , 10  are equally spaced circumaxially as shown and are mounted on the interior surface of a cylindrical back ring  12 . The segments may be metallic or ceramic and the back ring is conventionally of iron. Exterior surfaces  14 , 14  of the magnet segments are arcuate to conform substantially with the interior surface of the back ring  12 . The interior surfaces of the segments are flat as shown and presently preferred for engagement with similar flat surfaces  16 , 16  on a fixture  18  best illustrated in  FIG. 3 .  
         [0015]     The fixture  18  has six (6) flat surfaces  16 , 16  respectively for receiving the six (6) magnet segments  10 , 10 . Each of the flat surfaces has a pair of vacuum ports  20 , 20  connected by suitable conduits (not shown) to a vacuum source which may comprise a conventional vacuum pump at  22 . An appropriate computer controlled valve system (not shown) provides for the establishment and removal of a vacuum at the ports  20 , 20  suitably timed respectively to secure and release magnet segments from the surfaces  16 , 16 . A step motor  24  rotates the fixture also in timed relationship with other elements of the apparatus under computer control.  
         [0016]     Disposed within and forming a part of the fixture  18  is an axially movable collet-like member indicated generally at  26  and which has six (6) flexible fingers  28 , 28 . The fingers co-operate with radially inwardly biased pins  30 , 30  which project through openings  32 , 32  in the fixture  18  to engage magnet segments and urge the same outwardly for engagement with and bonding to an associated back ring. A pneumatic cylinder  34  operates the collet axially under computer control, to expand and contract the pins as required.  
         [0017]     A locating device best illustrated in  FIGS. 3 and 7  includes radially extending locating surfaces  36 , 36  on six (6) small projections  38 , 38  on the fixture  18 , one for each magnet segment  10 , 10 . At an opposite end of the fixture six (6) resiliently mounted “bumpers”  40 , 40  are moveable axially toward and away from the segments to urge them into engagement with the locating surfaces  36 , 36  and precisely position the same axially. The bumpers may also be pneumatically operated under computer control.  
         [0018]      FIG. 4  shows a single magnet segment  10  mounted on a fixture  18  and engaged by a pair of “grippers”  42 , 42  which have long narrow fingers  43 , 43  operable to locate and hold the segment. The “grippers” may also be pneumatically operated under computer control.  
         [0019]     In  FIGS. 6 , and  7  components of the apparatus of the invention are illustrated. A fixture  18  with six (6) magnet segments mounted thereon is positioned adjacent an adhesive applying means indicated generally at  44  and comprising an application roller  46  about which an adhesive liner tape  48  is directed from an adhesive storage reel  50 . An intermediate roller  52  directs the tape from the storage reel  50  to the application roller  46  where it is resiliently urged against the magnet segments by pneumatic means indicated generally at  53 . Friction created at the interface between the adhesive bearing tape and the rotating magnet segments serves to drive the apparatus with the tape being thus drawn from its storage reel  50  and about the rolls  46  and  52 . A take-up reel  54  receives the liner  48   a  which separates from the adhesive at the interface between the magnet segments and tape at the application roll  46  and is over driven by a timing belt  56  extending from the friction driven application roller. A small friction clutch  58  accommodates the variation in speed as the tape reel  50  becomes smaller and the liner take-up reel  54  becomes larger.  
         [0020]     In operation, the fixture is rotated through 345° and then stopped. A pneumatically operated brake  60  stops the tape dispensing reel  50  and the fixture  18  is then rotated an additional fifteen degrees (15°) to break the adhesive. The application roller  46  then backs off. At this point, it should be noted that a blank area is thus created on the liner  48   a.  This of course results in a loss of the necessary friction to rotate the application roller  46 , supply reel  50  etc. Accordingly, an index arm over with a needle-roller clutch is provided to advance the tape as the application roller moves forward for a succeeding adhesive applying sequence.  
         [0021]     Once the adhesive has been applied, the back ring and the fixture carrying the segments are moved relatively in an axial direction to assemble the elements as best illustrated in  FIG. 7 . Turret  54  is rotatable and movable vertically to alternately present the “bumpers”  40 , 40  and a back ring gripper  56  to the fixture  18 . As shown, the “bumpers”  40 , 40  are elevated prior to a segment loading operation. They are subsequently lowered to precisely locate the segments and then raised prior to turret rotation. When the turret has been rotated, the back ring  12  is placed about the adhesive carrying segments and the collet  26  urges the pins  32 , 32  outwardly and the segments against the back ring to bond the same in the desired positions thereon.  
         [0022]     As indicated above, the assembly may then be over molded in an injection molding operation.  
         [0023]     In practicing the method of the invention with the afore described apparatus, the segments are mounted on the fixture, adhesive is applied to the segments, the fixture carrying the segments is assembled with the back ring, and the segments are urged into firm bonding engagement with the ring.