Abstract:
Method and apparatus for insertion of preformed rotor and stator conductors into a twisting machine for forming hairpin shaped conductors of rectangular wire into stator conductors. The method comprises providing a forming fixture having a plurality of pockets distributed in equal number in an even number of adjacent circles concentric with a center of the forming fixture, receiving hairpin conductors positioned side by side from a feeder and feeding the hairpins, one by one, into a hairpin insertion assembly oriented above the forming fixture so that the legs are side by side along a line passing through the center and disposed adjacent a pair of pockets in first and second adjacent circles, and with the forming fixture angularly indexed relative to the hairpin insertion assembly, pushing a hairpin conductor down so that the legs thereof extend into a respective pair of pockets, and indexing the forming fixture about the center to align an additional pair of pockets with a hairpin in the hairpin insertion assembly and repeating until the forming fixture is substantially populated with hairpin conductors.

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 rotors and 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 rotor or 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 rotor pr stator windings. However in the case of stators, 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 
         FIGS. 1   a ,  1   b  and  1   c  illustrate exemplary hairpin conductors used in the present invention method and apparatus. 
         FIGS. 2 and 3  show an exemplary fixture into which the hairpin conductors are to be automatically inserted. 
         FIG. 4  illustrates the fixture of the preferred embodiment having two rows of hairpin conductors with the inner diameter of hairpin conductors standing higher than the outer diameter thereof. 
         FIG. 5  shows an exemplary embodiment of an overall system in which the present invention is used. 
         FIG. 6  illustrates the support of the insertion assembly in a preferred embodiment to feed the hairpin conductors to the insertion assembly when the insertion assembly is in either of the required two radial positions. 
         FIGS. 7   a  and  7   b  show a face view of part of the hairpin insertion assembly and a local portion thereof taken on an expanded scale. 
         FIG. 8  is a side cutaway view of part of the hairpin insertion assembly. 
         FIG. 9  illustrates a stop to prevent the hairpin conductor from falling out of the insertion assembly when the hairpin conductor is released. 
         FIGS. 10 ,  11  and  12  show perspective views of the hairpin conductor insertion assembly and parts thereof. 
         FIG. 13  shows the push bar and the cam bar used in the insertion assembly of a preferred embodiment. 
         FIG. 14  shows more details of the drive for the forming fixture. 
         FIG. 15  shows a pneumatic actuator to drive pins from below the forming fixture to assure that each hairpin conductor is at the proper elevation once inserted into the fixture. 
         FIG. 16  is a cross-section of a forming fixture of a preferred embodiment. 
         FIG. 17  shows the drive system for the forming fixture. 
         FIG. 18  shows two servo gear motors which controllably drive gear sectors in opposite directions to power the forming fixture. 
         FIG. 19  illustrates a populated forming fixture after twisting. 
         FIG. 20  shows an individual winding conductor as formed as shown in  FIG. 19 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the description of preferred embodiments of the present invention to follow, the terms “flat”, “square”, “rectangular” and “straight” will be used. Unless otherwise apparent, such terms are used in accordance with the definitions thereof set forth in the prior art section above. 
     The purpose of the present invention is to automatically receive hairpin shaped conductors of rectangular wire as may be used, by way of example, as part of a process for automatically manufacturing motor rotors and stators of the type described above, and to automatically place the same in a fixture so that they may be twisted to form motor winding conductors. An exemplary hairpin conductor may be seen in  FIG. 1   a  and is characterized by an overall length L 0 , formed by bending a rectangular insulated conductor with the ends thereof being stripped of insulation over the length L S . The typical insulation on the hairpin conductors is a typical motor or solenoid winding insulation well known in the motor art. In a preferred embodiment of the invention, one side  20  of the hairpin conductor as formed is substantially flat up to the loop  22 , with the upper portion  24  of the other side of the hairpin being bent initially to touch or almost touch the opposite leg of the hairpin, resulting in a slight outward bend in region  26 , which together with spring back after bending, results in the lower ends of the hairpin shape being somewhat separated, but elastically deformable into contact with each other. In the preferred embodiment this is desired, as this separation, coupled with the elasticity of the bent conductor, is used in a subsequent process for forming motor rotors and stators. The rectangular wire in one stator embodiment has a cross-section having a width of 4.4 millimeters and a thickness of 3.0 millimeters measured over the insulation, and is used for the fabrication of a 65 kilowatt three-phase AC motor. Obviously these dimensions are representative of one motor only, as the dimensions will vary depending on the motor design and power. In the exemplary stator, the dimension L S  for the particular hairpin conductor illustrated is approximately 18.1 cm, though as shall subsequently be seen, the exemplary stator uses hairpin conductors of two similar but slightly different overall lengths. The stripped length L S  in the exemplary stator is approximately 7.5 millimeters across the width (larger dimension) of the hairpin conductors, though the stripped length across the thickness of the exemplary hairpin conductors is slightly less. During formation of the hairpin conductors, preferably the free ends thereof are tapered inward in both planes, as shown in  FIGS. 1   b  and  1   c.    
     The exemplary fixture into which the hairpin conductors are to be automatically inserted may be seen in  FIGS. 2  and  3 . This exemplary fixture is configured for forming motor stator conductors for a 65 kilowatt three phase AC motor having four conductors per stator slot. It is to be understood, however, that fixtures of different sizes, etc. may be used for forming rectangular winding conductors for rotors or stators of various size motors having the same or different number of rectangular conductors per rotor or stator slot. In the case of the exemplary stator, there are sixty stator slots. Accordingly, in the fixture of  FIGS. 2 and 3 , sixty individual pockets  28 , sixty individual pockets  30 , sixty individual pockets  32  and sixty individual pockets  34  are provided, equally spaced around different diameter circumferences, though closely spaced radially, with pockets  28  and  30  as well as pockets  32  and  34  being radially aligned with each other, at least when the fixture is in the position shown. In the embodiment shown, there is a thin divider between each pair of pockets. It should be noted however, that the word pockets is used herein and in the claims in the general sense, and includes slots in the fixture parts that confine each of the hairpin conductor legs when the fixture is energized. The different diameters on which the pockets are located are approximately the same as the diameters of the respective locations of the legs of the stator conductors in the stator in which the stator conductors will be used. 
     An object of the present invention is to automatically place hairpin conductors of the type shown in  FIG. 1   a  into a respective pair of pockets  28  and  30  or  32  and  34 , with the straight side  20  of the exemplary hairpin conductor of  FIG. 1   a  facing radially inward in the fixture. The different diameters on which the pockets are located are approximately the same as the diameters of the respective locations of the legs of the stator conductors in the stator in which the stator conductors will be used also, while the legs of the hairpin conductors do not fit tightly in the pockets, but rather slide in easily, the pockets do restrict the rotation of the rectangular conductors relative to the respective pocket. Further, as shall subsequently be seen, because the stator slot openings at a smaller diameter are not as far between as the stator slot openings on the larger diameter, but the end turns at each end of the stator are the same, the hairpin conductors to be inserted into pockets  32  and  34  are intentionally made a predetermined amount shorter than the hairpin conductors to be inserted into the outer pockets  28  and  30 . 
     When substantially all of the pockets  28 ,  30 ,  32  and  34  of the fixture  36  are filled with hairpin conductors  20 , the fixture will appear as shown in  FIG. 4 , with the inner diameter of hairpin conductors standing higher than the outer diameter thereof because of the step in the fixture. Preferably the hairpin conductors in the outer diameter are slightly longer than those in the inner diameter and stand slightly higher relative to the adjacent surface of the forming fixture than the hairpin conductors in the inner diameter. This accounts for the diameter difference, so that once the conductors are formed, the part forming the end turns will extend the same distance from the motor stator or rotor, regardless of which diameter within the slots they are placed. The object of the present invention is to achieve the loading of the fixture as shown in  FIG. 4  in an automated manner to avoid what otherwise would be a very labor intensive operation. 
     Now referring to  FIG. 5 , an exemplary embodiment of an overall system in which the present invention is used may be seen. Of particular relevance to the present invention is the hairpin forming apparatus, generally indicated by the numeral  38 , and fixture  36  positioned to receive the hairpin conductors from the hairpin  38 . In that regard, it will be noted that the hairpin conductors  20  slide down a vertically oriented sheet metal guide  42 , positioned as may be seen in  FIG. 5  to deliver the hairpin conductor substantially tangentially to the circumference on which the pockets  28  through  34  reside. The hairpin conductors  20  ejected by the hairpin forming apparatus  38  slide under the influence of gravity along sheet metal member  42  to the hairpin insertion assembly, generally indicated by the numeral  44 . 
     A face view of part of the hairpin insertion assembly and a local portion thereof taken on an expanded scale may be seen in  FIGS. 7   a  and  7   b , with a side cutaway view of part thereof being shown in  FIG. 8 . The hairpin conductors  20  are delivered to the insertion assembly from the lower end of member  42  and initially are held there by a finger  46  on a pivoting member  48 , normally held in the extended position by spring  50 . The hairpin conductor  20  will freely hang vertically in this position, being sensed that it is in the proper vertical position by photo-optical detectors  52 . Once in that position, pneumatic actuator  51  may be energized to swing finger  46  down and out of the way, generally allowing hairpin conductor  20  to fall within the confines of the opening in the face of the insertion assembly. In that regard, as may be noted in  FIG. 9 , when the hairpin conductor  20  is released, because of the spread in the legs thereof, the right-hand leg as shown in that Figure will be caught by stop  54 , thereby preventing the hairpin conductor from falling out of the insertion assembly. 
     In the exemplary method the fixture  36 , ( FIGS. 2 through 5 ) is mounted for accurate angular indexing in six degree increments (360° divided by sixty slots) between hairpin insertions. In the preferred process, first the hairpin conductors  20  each are placed with a respective leg thereof in a respective one of pockets  28  and  30  until these pockets are substantially fully populated. The word “substantially” is added here, however, as in one embodiment three predetermined pair of pockets  28  and  30  of the outer pockets are automatically left empty because the corresponding positions in the final stator uses conductors with one lead having a substantially greater length to provide external connection to the various phases of the motor. In the preferred embodiment, fifty-seven pairs of pockets  28  and  30  automatically become populated with hairpin conductors, with all sixty of the pockets  32  and  34  of the inner diameter getting populated. One unpopulated pocket may be seen in  FIG. 19 . 
     Now referring to  FIGS. 10 ,  11  and  12 , perspective views of the hairpin conductor insertion assembly  44  and parts thereof may be seen.  FIG. 10  shows the entire assembly, which is mounted on a support  56  in a manner to provide horizontal and vertical motion of the insertion assembly. For horizontal motion, the assembly is mounted on rails  58  ( FIG. 12 ) as controlled by actuator  60  and on vertical rails  62  (only one of which is visible in  FIG. 11 ) for vertical motion as controlled by actuator  64 . To properly feed the hairpin conductor to the insertion assembly  44  when the insertion assembly is in either of the required two radial positions in fixture  36 , the feeder is coupled to the insertion assembly  44  and supported on a combination of a bearing  66  ( FIG. 6 ), allowing the feeder assembly to pivot at the hairpin forming assembly  38  ( FIG. 5 ), with the center of the feeder assembly being supported on bearings or wheels  68  to provide a second support allowing the desired motion. In addition, the final path of travel of the hairpin conductors  20  into the insertion assembly  44  is defined by a pivoted section seen in part as section  70  in  FIG. 6 , thereby accommodating the required vertical motion of the insertion assembly. 
     To actually insert a hairpin conductor once the fixture  36  is properly position and a hairpin conductor is sensed as being in the proper position, actuator  51  ( FIG. 8 ) is actuated, causing member  48  to rotate about axis  72 , swinging finger  46  down and away from the support of the hairpin  20 . Also, actuator  74  ( FIG. 10 ) is actuated, which has two primary functions. First, it moves push bar  76 , visible in  FIGS. 6 and 7 , though best illustrated in  FIG. 12 , downward and at the same time and as part of the same motion, moves cam bar  78  downward. The function of the cam bar  78  is best illustrated in  FIG. 9 , namely, to force assembly  80  as a result of the force of cam bar  78  on cam follower  82  to sufficiently close the legs of the hairpin conductor so that the same will fit through opening  84  as pushed there through and into an associated pair of a pocket in the fixture  36  ( FIGS. 2 and 3 ). Thus by sequentially inserting hairpin conductors into the fixtures  36 , the fixture may be populated as required for the particular motor or stator, except for a very limited number of hairpin conductors of extraordinary length for phase connections in a stator assembly. In that regard, it should be noted that the feeding of each hairpin conductor into the fixture may be assisted in part by the ends thereof shaped as shown in  FIGS. 1   b  and  1   c.    
     Now referring to  FIG. 14 , more details of the drive for the fixture  36  ( FIGS. 2 and 3 ) may be seen. In the preferred embodiment, the indexing of the fixture is done through gear servomotor  86 , driving coupler  88  coupled from underneath to the fixture. Also in a preferred embodiment a pneumatic actuator  90  drives pins generally indicated by the numeral  92  (see also  FIG. 15 ) from below the fixture to assure that each hairpin conductor is at the proper elevation once inserted into the fixture. This may or may not be necessary, as the insertion operation itself may assure the proper and repeatable elevation. In that regard, note from  FIGS. 2 and 3  that on the fixture the pockets  32  and  34  are elevated with respect to pockets  28  and  30 . This is to provide clearance over the hairpin conductors inserted into the outer pockets  28  and  30  while inserting hairpin conductors into pockets  32  and  34 . In the preferred embodiment, the fixture is sufficiently deep to hold the hairpin conductors at the proper elevation for the twisting operation without having the ends of the hairpin conductor legs extending out of the bottom of the fixture. 
       FIG. 16  is a cross-section of the fixture  36  of a preferred embodiment of  FIGS. 2 ,  3  and  4 . Of particular importance to this embodiment is the fact that the outer member  94  containing pockets  28  ( FIGS. 2 ,  3 ,  4  and  16 ) is mounted for rotation, as is inner member  96  containing pockets  34 . The region between these two, however, containing pockets  30  and  32  ( FIG. 3 ) is rigidly attached to the base  98  ( FIG. 16 ). The equally spaced three holes in the inner member  96  and the three equally spaced holes in the outer member  94  ( FIGS. 2 and 4 ) are to receive a drive system from above, supported to be lowered so as to engage these holes with drive pins without contact with the hairpin conductors. The drive system, generally indicated by the numeral  100  ( FIG. 17 ), includes two servo gear motors  102  which controllably drive gear sectors  104  ( FIG. 18 ) in opposite directions. The net result of this motion is that pockets  28  ( FIG. 3 ) move clockwise with respect to pockets  30 , and pockets  34  move counterclockwise with respect to pockets  32 . This is equivalent to moving both pockets  30  and  34  counterclockwise with respect to pockets  28  and  32 , but transmits less torque to the base  98  ( FIG. 16 ). In that regard, obviously different types of drive systems could be used, with either one of each pair of pockets being driven, or as a further alternative, retaining the member containing either pockets  34  or  28 , rotating the other set of pockets through twice the desired angle, with the intermediate pockets  30  and  32  having a limitation on their rotation equal to half the total drive. In any event, the net result of the twisting is shown in  FIG. 19 , twisting each winding conductor as shown in  FIG. 20 . Each of the hairpin conductors  20  is now formed with the legs separated and joined at one end thereof by part of the insulated conductor which part will become part of the end turns of the finished motor stator or rotor. The open loop of the hairpin conductors before twisting helps avoid an excessive concentration of bending of the insulated conductor at one location, thereby somewhat distributing the bending and avoiding damage to the insulation layer. After forming the hairpin conductors as described, the rotatable parts of the fixture are controllably rotated a small amount in the opposite direction to relieve the spring-back of the formed conductors. In a preferred stator or rotor fabrication process incorporating the present invention, the fixtures are advanced to the next station in the system of  FIG. 5  for removal and placement in a rotor or stator, after which the fixture is rotated back to its initial state of  FIGS. 2 and 3 . 
     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.