Abstract:
Methods and apparatus for twisting rectangular rotor and stator conductor ends whereby most if not all conductor ends are bent at once, radially adjacent ends being bent in opposite directions. A lost motion member may be used to bend selected conductors through lesser angles for such purposes as phase interconnection and power leads. The rectangular conductors are retained against twisting so that flat conductors will bend about an axis perpendicular to the larger dimension of the conductor cross section. Various features of the methods and apparatus are disclosed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the field of electric motors. 
     2. Prior Art 
     Tecnomatic S.p.A., assignee of the present invention, has in the past made a limited number of motor stators and D.C. motor rotors using flat or square wire for the windings. In that regard, it is to be noted that as used herein, “flat” or “square” wire means wire having four substantially flat sides, each joined to adjacent sides, typically by a rounded edge. In the case of square wire, the wire may be formed in the square shape and then coated with typical winding insulation, or in some cases, pre-coated round wire has been rolled into the square shape. Rolling of round wire to a square shape has definite limits if the insulation is not to be damaged, though smaller rounded edges may be achieved if the wire is first formed by drawing or otherwise formed into the square shape and then coated. Even if the wire is first formed in the desired shape and then coated, some degree of rounding on the edges is desired for various reasons, including prevention of surface tension from pulling the coating away from the sharp edges during coating, preventing the sharp edges from cutting through the coating afterward, and preventing electric field concentration on the sharp edges to induce early breakdown. Thus, as used herein, the words “square” or “flat” or equivalent words used to describe the cross-section of an insulated copper wire are used in the general sense and are not to be construed as excluding significant or substantial rounded corners joining the substantially flat sides. “Flat” as used herein and in the claims means having two opposite sides having a greater separation than the other two opposite sides, its width being greater than its thickness. “Straight” as used herein and in the claims means substantially free of bends. Accordingly, either a flat or a square conductor may or may not be straight. “Rectangular” as used herein is a more general term meaning flat or square, square being a special case of rectangular wherein the dimension between two opposite sides is equal to the dimension between the other two opposite sides. 
     In the prior art stators, the wire has been cut to the desired length and stripped, then bent into a hairpin shape by hand on a one at a time basis, then the two legs of the hairpin separated one hairpin at a time and hand inserted into one end of a stator, with the stripped ends of the wires sticking out of the other end of the stator being all bent all in one row uniformly in one direction and all in the adjacent row uniformly bent in the opposite direction so interconnection of wires in the two rows forming a given phase could be welded, one at a time, to provide the stator windings. However, to bring out the connections to the phases, and to interconnect phases, the corresponding wires needed to be re-bent to isolate them from the connections within each phase, something again previously done by hand. 
     The use of the flat or square wire for the windings produces very efficient and high power to weight ratio motors because of the greater cross-section of copper that can be put into a winding slot. However, the procedure described above is slow and highly labor intensive, and not suitable for a mass produced motor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows three motor stators, one insulated but unpopulated with stator conductors, one populated with stator conductors with stator conductor ends not yet bent, and one populated with stator conductors with stator conductor ends bent using the methods and apparatus of the present invention. 
         FIGS. 2 and 3  are cross sections of an exemplary bending fixture in accordance with the present invention. 
         FIG. 4  is a view of part of an exemplary ring assembly used in the method and apparatus of  FIGS. 2 and 3 . 
         FIG. 5  is a side view of an exemplary bending station for carrying out the methods of the present invention. 
         FIG. 6  is a cross section of part of the bending station illustrating part of the drive system therefor. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First referring to  FIG. 1 , three motor stators  20 ,  22  and  24  may be seen. Stator  20  is an insulated motor stator not yet populated with stator conductors. Stator  22 , on the other hand, is populated with rectangular stator conductors  26 . The lower ends of these stator conductors are bent so that an individual stator conductor spans a fixed number of stator slots, specifically, six stator slots in an exemplary embodiment. In atypical motor stator of the type described, certain stator conductors have one side thereof longer than the other conductors to provide terminal connections for the completed stator winding. In a three phase motor, three such longer stator conductors  28  are used, all three being visible in stator  24  of  FIG. 1 . 
     The purpose of the present invention is to provide a method for twisting the upper ends (referenced to the orientation of  FIG. 1 ) of the stator conductors  26  as shown in stator  22  so that the ends of most of these conductors may be welded to the end of another stator conductor a fixed number of slots away, again in the exemplary embodiment spaced six slots away. In so bending, it is to be noted that the leads  28  must be bent through a different angle so as to not interfere with the welded connection of stator conductors with adjacent stator conductors. Similarly, phase connections need to be made separate and apart from the interconnection of individual stator connectors, and accordingly, it is desired to also bend the ends of each stator conductor that is to be used for phase interconnections through a different angle than adjacent stator conductors. In the exemplary embodiment sixty stator slots are used, 6 degrees apart. Since each turn of the stator winding spans six motor slots, the ends of conductors  26  on stator  22  must each be bent to span 3 degrees. In that regard, in the exemplary embodiment there are four layers of flat stator conductors lying on top of each other in each slot with the wide portion of the rectangular conductor being circumferentially oriented. Consequently, to bend the conductors as shown in stator  24 , the conductors must be held against twisting, as otherwise they will tend to twist to bend around the thinner dimension. Further, as may be seen in  FIG. 1 , the upper ends of the conductors  26  as well as conductors  28  are stripped of insulation, with the stripped ends of conductors  26  being maintained in a substantially vertical orientation, as viewed in  FIG. 1 . The terminal leads  28  as well as one end of each stator conductor that is to be used for phase connections are bent through a lesser angle so as to be positioned between locations at which the ends of most stator conductors are welded together. 
     In accordance with the present invention, the ends of all stator conductors shown in the stator  22  of  FIG. 1  are simultaneously bent to the position shown on stator  24 . As shown in that Figure, the outer layer of stator conductor ends is bent in a counterclockwise direction, the next layer (the other end of the stator conductors in the outer layer) in a clockwise direction, followed by a third layer bent in a counterclockwise direction, and the fourth layer (the other end of the stator conductors in the third layer) bent in a clockwise direction. 
     Now referring to  FIGS. 2 and 3 , a cross-section of a bending fixture in accordance with the present invention may be seen. As may be best seen in  FIG. 2 , the fixture includes four concentric ring-like members  30 ,  32 ,  34  and  36 , each having either pockets or slots  38  therein, each for receiving the end of a stator conductor as shown on stator  22  of  FIG. 1 . In general the slots or pockets  38  shown in  FIGS. 2 and 3  are of limited depth, though those for the input leads  28  of  FIG. 1  extend along the entire height of the fixture with clearance provided as may be required for proper operation of the fixture. As used herein and in the claims to follow, a pocket may be defined by a depression or hole in a member surrounded by part of that member, and further includes a pocket defined by a slot in one member effectively closed by a surface or wall of an adjacent member. 
     Now referring to  FIG. 4 , an exemplary one of the rings  30 ,  32 ,  34  and  36  of  FIG. 2  may be seen. While the rings are of slightly different configuration and obviously of different diameters as may be seen in  FIGS. 2 and 3 , the general structure of the rings or most of them is the same. In particular, pockets or slots  38  are equally spaced around most of the periphery of the ring. However in a typical ring, one or more slots or pockets  38 ′ is mounted not rigidly to the structure of the main part of the ring, but rather is supported on a separate ring integral with, or at least attached to, protrusions  40  within slots of the main ring structure. Coil springs  44  force the protrusions  40  to the position shown after removing one stator with bent stator lead ends, with pocket or slot  38 ′ being located against the side of the main circular structure. With this general structural organization with the ends of the stator conductors in the pockets  38  and  38 ′, rotation of the base  46  of the main ring structure in the counterclockwise direction will initiate the bending of most of the ends of the stator conductors. However, pockets  38 ′ will at least initially not be positively driven, with the resistance of the ends of the stator conductors in those pockets preventing the rotation of the member holding pockets  38 ′ with the main ring against the springs  44 . Pins  42 , which are fastened to the same structure as pockets  38 , rotate therewith in slots  48  in the main ring structure until reaching the ends of the slots, after which the structure supporting pockets  38 ′ begins to rotate with the main structure supporting pockets  38 . Thus there is a lost motion between the rotation of the main ring structure holding pockets  38  and the structure holding pockets  38 ′ before the two rotate together. The angle of rotation of the lost motion before the two sets of pockets are driven in unison is the difference in angle of the bending of the regular stator conductor ends and the stator conductor ends for the phase connections and the terminal conductors. Of course, for rings rotating in the opposite direction, lost motion structure is changed to reverse the lost motion direction. Also while all rings in the exemplary embodiment include the lost motion structure, this is not a limitation of the invention. 
     Now referring to  FIG. 5 , an exemplary bending station may be seen. The bending fixture  50  shown in  FIGS. 2 and 3  is located in the upper region of the bending station. At the top of the bending station is a stripper  52  on which the stator will be positioned. The stripper  52  is mounted for vertical motion, being in its lowermost position during bending and then raised to extract the ends of the stator conductors, except for the entire leads, from the bending fixture  50 . The various rings  30 ,  32 ,  34  and  36  ( FIG. 2 ) are driven in rotation by pneumatic actuators  54 ,  56 ,  58  and  60 , respectively. The actuators, as well as bending fixture  50 , are supported by a table  62  structure of conventional design, the details of which are not shown. It will be noted from the Figure that the actuators alternate in direction of actuation, as of course the rings themselves alternate in direction of rotation. Each actuator in the exemplary embodiment is actually a pair of diametrically disposed actuators to provide the desired torque on the respective drive member without significant side force. 
       FIG. 6  shows a cross-section of part of the bending station shown in  FIG. 5 , generally illustrating the drive mechanism for the various rings. In particular, a central shaft  64 , configured for vertical motion, supports the stripper  52 . Concentric therewith is a tubular member  68 , driven in rotation by pneumatic actuator  60  ( FIG. 5 ). Concentric therewith is a larger tubular member  70  driven in rotation in the opposition direction by pneumatic actuator  58 . A third concentric tubular member  72  driven by actuator  56 , and finally a fourth tubular member  73  driven by actuator  54 . Thus these concentric drive members are coupled to the pneumatic actuator pairs  54  through  60 , with the innermost ring being driven by the lowermost actuator, etc. 
     Referring again to  FIG. 1 , it will be noted that as the stator conductors are bent, they bend in an arc. That arc is greatest for the ends of the stator conductors in the outermost circle and reduces to the innermost circle. Accordingly in the preferred system, as may be seen in  FIG. 5 , in order for the four rings of the fixture to follow the arc of the respective circle of stator conductor ends, four cam assemblies  74 ,  76 ,  78  and  80  are provided. The lowest cam assembly  74  controls the drive member for the innermost ring  36  ( FIG. 2 ), with each additional cam assembly thereabove driving the next outer respective ring  34 ,  32  and  30 , respectively. These cams raise the respective drive members and in turn raise the respective ring in a controlled manner so that the pockets in the bending fixture follow the arc of the bend, retaining the tip ends of the stator conductors in the vertical orientation without longitudinal sliding or longitudinal stressing of the stator conductors. Because the arc is somewhat different for each ring, four cam assemblies are used rather than merely one. Of course one could use a single cam assembly, or alternatively, similarly control the elevation of the stripper  52  to approximately follow the arcs, though this is not preferred because of the lack of precision in so doing. One could also simply rotate one of each pair of rings ( 30  or  32 , and  34  or  36 ) in the appropriate direction, raising all rings equally or unequally as the bending proceeds or lowering the stripper supporting the stator (or both), though this would also require the rotation of the rings through twice the angle of the preferred embodiment, and rotation of the stripper supporting the stator through half the ring rotation angle. 
     After the ends of the stator conductors are bent as described, the actuators are depressurized or even slightly driven in the opposition direction to relieve spring-back before the extractor  52  is raised for extraction purposes. 
     While the invention has been described with respect to an exemplary embodiment for bending the ends of rectangular stator conductors, it is to be noted that the invention is also applicable to the bending of rectangular rotor conductors. Thus there has been described herein motor stator conductor bending methods and apparatus which bends all or substantially all, or at least a majority of the free ends of motor stator conductors for interconnection with associated stator conductors, which further may include the bending of stator conductors to a different angle for phase interconnections as well as longer stator conductors for input terminals. Thus while certain preferred embodiments of the present invention have been disclosed and described herein for purposes of illustration and not for purposes of limitation, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.