Abstract:
A linear motor ( 15 ) comprising a stator ( 16 ) having an opening ( 18 ), a mover ( 19 ) disposed in the opening and configured and arranged to reciprocate linearly in an axial direction (x-x) relative to the stator, the stator comprising a first pole section and a second pole section ( 22 ) stacked in the axial direction and forming a recess ( 26 ) between them for receiving annular windings, the first pole section comprising a first laminate ( 17   a ) having a first cross-sectional geometry ( 29 ) and a second laminate ( 17   b ) having a second cross-sectional geometry ( 30 ) different from the first cross-sectional geometry, and the first laminate and the second laminate stacked in the axial direction.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates generally to linear motors, and more particularly to a laminated stator and method of assembly for a linear motor. 
       BACKGROUND ART 
       [0002]    Linear motors are known in the prior art. Conventional linear motors generally comprise a mover that reciprocates through the field of a stator due to magnetic forces generated by energized coils in the stator. Normally the stator is stationary and drives the mover in an axial direction. However, it is possible to make the mover stationary and have the stator drive itself in an axial direction. Accordingly, the axial direction is the linear direction of movement for either the mover or stator, depending on which of them is to move in relation to the other. The stator conventionally includes at least one coil wound in at least one stator core. The stator coil may be a single winding connected to an electrical supply unit or a distributive winding. The purpose of the stator coils is to generate magnetic flux that interacts with permanent magnets on the mover. Thus, a conventional linear motor includes a generally cylindrical outer stator core, stator coils wound within the stator core, and an inner mover having permanent magnets and that moves linearly in an axial direction relative to the stator core so as to provide linear motion by means of interaction with the magnetic field of the stator. 
         [0003]    Various stator assembly configurations are known. For example, U.S. Pat. No. 6,603,224, entitled “Linear Motor Stator Assembly Piece,” discloses a stator for a linear motor that is built by stacking module parts. U.S. Pat. No. 6,289,575, entitled “Method of Manufacturing a Stacked Stator Assembly for a Linear Motor,” discloses a method of manufacturing a stator from individual pieces assembled around a removable form. U.S. Pat. No. 7,378,763, entitled “Linear Motor,” discloses a stator core divided into two parts with each of the parts being made of a soft magnetic powder. U.S. Pat. No. 7,884,508, entitled “Linear Motor”, also discloses a stator core divided into two parts formed of a soft magnetic powder and a mover that has at least one section also formed of a soft magnetic material. U.S. Pat. No. 6,060,810, entitled “Stator for Linear Motor by Staggered Core Lamination,” discloses a stator for a linear motor formed from radially-extending laminates. Each of these U.S. patents is incorporated herein by reference. 
       BRIEF SUMMARY OF THE INVENTION 
       [0004]    With parenthetical reference to corresponding parts, portions or surfaces of the disclosed embodiment, merely for the purposes of illustration and not by way of limitation, the present invention provides a linear motor ( 15 ) comprising a stator ( 16 ) having an opening ( 18 ), a mover ( 19 ) disposed in the opening and configured and arranged to reciprocate linearly in an axial direction (x-x) relative to the stator, the stator comprising a first pole section ( 21 ) and a second pole section ( 22 ) stacked in the axial direction and forming a recess ( 26 ) between them for receiving annular windings, the first pole section comprising a first laminate ( 17   a ) having a first, cross-sectional geometry ( 29 ) and a second laminate ( 17   b ) having a second cross-sectional geometry ( 30 ) different from the first cross-sectional geometry, and the first laminate and the second laminate stacked in the axial direction. 
         [0005]    The first pole section may further comprise a third laminate ( 17   c ) having a third cross-sectional geometry ( 33 ) different from the first cross-sectional geometry and the second cross-sectional geometry and stacked in the axial direction with the first laminate and the second laminate. The first pole section may further comprise a fourth laminate ( 17   d ) having the first cross-sectional geometry ( 29 ) and stacked in the axial direction with the first, second and third laminates. 
         [0006]    The first pole section may comprise multiple laminates having the first cross-sectional geometry and multiple laminates having the second cross-sectional geometry and stacked in the axial direction. The first cross-sectional geometry ( 29 ) of the first laminate may comprise an annular ring ( 35 ) having an outer perimeter ( 36 ) and an inner perimeter ( 37 ). The annular ring may comprise an opening ( 38 ) between the outer perimeter and the inner perimeter. The second cross-sectional geometry ( 30 ,  33 ) of the second laminate may comprise an annular ring ( 39 ,  55 ) having an outer perimeter ( 40 ,  56 ) and an inner perimeter ( 41 ,  57 ) and a radial thickness ( 42 ,  58 ) between them greater than a radial thickness ( 60 ) of the annular ring of the first cross-sectional geometry. The annular ring ( 55 ) of the second cross-sectional geometry ( 33 ) of the second laminate may comprise a shaped opening ( 59 ) between the outer perimeter ( 56 ) and the inner perimeter ( 57 ). The annular ring ( 39 ) of the second cross-sectional geometry ( 30 ) of the second laminate may comprise a first face ( 39   a ) and a second face and an opening ( 44 ) between the first face and the second face. The annular ring of the second cross-sectional geometry ( 30 ) of the second laminate may further comprise a notch ( 43 ) extending towards the inner perimeter ( 41 ) from the outer perimeter ( 40 ). 
         [0007]    The linear motor may further comprise a center ring ( 70   b ) within the first pole section ( 21 ) and defining the opening of the stator. The center ring element may comprise an inner perimeter ( 76 ) configured to define at least in part the stator opening and an outer perimeter ( 74 ) configured to fit at least in part within the inner perimeter ( 41 ,  57 ) of the first pole section ( 21 ), a first facing surface ( 71 ) and a second facing surface ( 75 ), and the first facing surface skewed relative to an imaginary plane (y-y) oriented generally perpendicular to the axial direction (x-x) of the mover such that the first facing surface is not parallel to the plane oriented generally perpendicular to the axial direction of the mover. The second facing surface ( 75 ) may be skewed relative to the plane (y-y) perpendicular to the axial direction and may be parallel to the first facing surface ( 71 ). The first pole section ( 21 ) may comprise a first facing surface ( 39   b ) orientated in a plane (y-y) generally perpendicular to the axial direction (x-x) of the mover and the outer perimeter of the center ring element may comprise an axial alignment projection ( 79   b ) configured and arranged to extend radially outward at least in part beyond the inner perimeter ( 41 ,  57 ) of the first pole section ( 21 ) and to abut against the first facing surface ( 39   b ) of the first pole section ( 21 ). The axial alignment projection may comprise an annular contact surface ( 73 ) oriented in a plane (y-y) generally perpendicular to the axial direction of the mover. The center ring element may comprise a solid unitary steel tube. 
         [0008]    The second pole section ( 22 ) may comprise a first laminate ( 17   e ) having a first cross-sectional geometry ( 29 ) and a second laminate ( 17   f ) having a second cross-sectional geometry ( 31 ) different from the first cross-sectional geometry, and the first laminate and the second laminate stacked in the axial direction. The second pole section may further comprise a third laminate ( 17   g ) having a third cross-sectional geometry ( 32 ) different from the first cross-sectional geometry and the second cross-sectional geometry and stacked in the axial direction with the first laminate and the second laminate. The second pole section may further comprise a fourth laminate ( 17   h ) having the first cross-sectional geometry ( 29 ) and stacked in the axial direction with the first, second and third laminates. 
         [0009]    The second pole section may comprise multiple laminates having the first cross-sectional geometry and multiple laminates having the second cross-sectional geometry and stacked in the axial direction. The first cross-sectional geometry ( 29 ) of the first laminate may comprise an annular ring ( 35 ) having an outer perimeter ( 36 ) and an inner perimeter ( 37 ). The annular ring may comprise an opening ( 38 ) between the outer perimeter and the inner perimeter. The second cross-sectional geometry ( 31 ,  32 ) of the second laminate may comprise an annular ring ( 45 ,  50 ) having an outer perimeter ( 46 ,  51 ) and an inner perimeter ( 47 ,  52 ) and a radial thickness ( 48 ,  53 ) between them greater than a radial thickness ( 60 ) of the annular ring of the first cross-sectional geometry. The annular ring ( 50 ) of the second cross-sectional ( 32 ) of the second laminate may comprise a shaped opening ( 54 ) between the outer perimeter ( 51 ) and the inner perimeter ( 52 ). The annular ring of the second cross-sectional geometry ( 31 ) of the second laminate may comprise a notch ( 49 ) extending towards the inner perimeter ( 447 ) from the outer perimeter ( 46 ). 
         [0010]    The linear motor may further comprise a center ring ( 70   c ) within the second pole section ( 22 ) and defining the opening of the stator. The center ring element may comprise an inner perimeter ( 76 ) configured to define at least in part the stator opening and an outer perimeter ( 74 ) configured to fit at least in part within the inner perimeter ( 47 ,  52 ) of the second pole section ( 21 ), a first facing surface ( 71 ) and a second facing surface ( 75 ), and the first facing surface skewed relative to an imaginary plane (y-y) oriented generally perpendicular to the axial direction (x-x) of the mover such that the first facing surface is not parallel to the plane oriented generally perpendicular to the axial direction of the mover. The second facing surface ( 75 ) may be skewed relative to the plane (y-y) perpendicular to the axial direction and may be parallel to the first facing surface ( 71 ). The second pole section ( 22 ) may comprise a first facing surface ( 45   b ) orientated in a plane (y-y) generally perpendicular to the axial direction (x-x) of the mover and the outer perimeter of the center ring element may comprise an axial alignment projection ( 79   c ) configured and arranged to extend radially outward at least in part beyond the inner perimeter ( 47 ,  52 ) of the first pole section and to abut against the first facing surface ( 45   b ) of the second pole section ( 22 ). The axial alignment projection may comprise an annular contact surface ( 73 ) oriented in a plane (y-y) generally perpendicular to the axial direction of the mover. 
         [0011]    The first pole section ( 21 ) may comprise a first center ring element ( 70   b ) and the second pole section ( 22 ) may comprise a second center ring element ( 70   c ), wherein each of the first center ring element and the second center ring element comprise an inner perimeter ( 76 ) configured to define at least in part the stator opening and an outer perimeter ( 74 ) configured to fit at least in part within the inner perimeter of the respective pole section ( 41 ,  57  and  47 ,  52 ), a first facing surface ( 71 ) and a second facing surface ( 75 ), and the first and second facing surface skewed relative to an imaginary plane (y-y) orientated generally perpendicular to the axial direction (x-x) of the mover such that the first and second facing surface are not parallel to the plane oriented generally perpendicular to the axial direction of the mover, wherein the skew of the second facing surface of the first center ring element of the first pole section is substantially equal to the skew of the first facing surface of the second center ring element of the second pole section, and wherein the first center ring element and the second center ring element are stacked in the axial direction to form at least in part the opening of the stator. The skew may be configured and arranged to reduce cogging forces in the motor. 
         [0012]    In another aspect, a linear motor is provided comprising a stator ( 16 ) having an opening ( 18 ), a mover ( 19 ) disposed in the opening and configured and arranged to reciprocate the linearly in an axial direction (x-x) relative to the stator, the stator comprising a first pole section ( 21 ) and a second pole section ( 22 ) stacked in the axial direction and forming a recess ( 26 ) between them for receiving annular windings, the first pole section having an outer perimeter ( 36 ,  40 ,  56 ) and an inner perimeter ( 41 ,  57 ), a center ring element ( 70   b ) having an inner perimeter ( 76 ) configured to define at least in part the stator opening and an outer perimeter ( 74 ) configured to fit at least in part within the inner perimeter of the first pole section, the center ring element further comprising a first facing surface ( 71 ) and a second facing surface ( 75 ), and the first facing surface skewed relative to an imaginary plane (y-y) orientated generally perpendicular to the axial direction (x-x) of the mover such that the first facing surface is not parallel to the plane orientated generally perpendicular to the axial direction of the mover. 
         [0013]    The second facing surface may be skewed relative to the plane (y-y) perpendicular to the axial direction (x-x) and may be parallel to the first facing surface. The first pole section ( 21 ) may comprise a first facing surface ( 39   b ) orientated in a plane (y-y) generally perpendicular to the axial direction of the mover and the outer perimeter of the center ring element may comprise an axial alignment projection ( 79   b ) configured and arranged to extend radially outward at least in part beyond the inner perimeter ( 41 ,  57 ) of the first pole section and to butt against the first facing surface ( 39   b ) of the first pole section ( 21 ). The axial alignment projection may comprise an annular contact surface ( 73 ) orientated in a plane (y-y) generally perpendicular to the axial direction of the mover. The center ring element may comprise a solid unitary steel tube. 
         [0014]    The first pole section and the second pole section may be provided with a rotational alignment contour ( 87 ) and the rotational alignment contour may comprise an axial notch. 
         [0015]    The first stator pole section ( 21 ) may comprise a pole section rotational alignment contour ( 87 ) corresponding to a first rotational alignment key ( 82 ) of a ring rotational alignment fixture ( 81 ) and the center ring element ( 70 ) may comprise a ring rotational alignment contour ( 80 ) corresponding to a second rotational alignment key ( 83 ) of the ring rotational alignment fixture. The pole section rotational alignment contour may comprise an axial notch ( 38 ), the first rotational alignment key may comprise a tab ( 82 ) corresponding to the notch, the ring rotational alignment contour may comprise an axial notch ( 80 ), and the second rotational alignment key may comprise a protrusion ( 83 ) corresponding to the notch of the ring rotational alignment contour. 
         [0016]    In another aspect, a method of forming a stator core of a linear motor is provided comprising the steps of forming a plurality of first laminates ( 17   a ) having a first cross-sectional geometry ( 29 ), forming a plurality of second laminates ( 17   b,    17   c,    17   f,    17   g ) having a second cross-sectional geometry ( 30 ,  31 ,  32 ,  33 ) different from the first cross-sectional geometry, stacking the plurality of first laminates and the plurality of second laminates in an axial direction (x-x) to form at least in part a first stator pole ( 21 ) section having an inner perimeter ( 41 ,  57 ), stacking the plurality of the first laminates and the plurality of the second laminates in an axial direction to form at least in part a second stator pole section ( 22 ) having an inner perimeter ( 47 ,  52 ), forming a first skewed center ring element ( 17   b ), forming a second skewed center ring element ( 17   c ), pressing at least a portion ( 74 ) of the first skewed center ring element into the inner perimeter of the first stator pole section, pressing at least a portion of the second skewed center ring element ( 74 ) into the inner perimeter of the second stator pole section, and stacking the first pole section and the second pole section in the axial direction so as to form a recess ( 26 ) between them for receiving annular windings, and so that the first skewed center ring element and the second skewed center ring element form at least in part an opening ( 18 ) for receiving a mover ( 19 ) configured and arranged to reciprocate linearly in the axial direction (x-x) relative to the first and second stacked stator pole sections. 
         [0017]    Each of the first skewed center ring element and the second skewed center ring element may comprise an inner perimeter ( 76 ) configured to define at least in part the stator opening and an outer perimeter ( 74 ) configured to fit at least in part within the inner perimeter of the respective pole section, a first facing surface ( 71 ) and a second facing surface ( 75 ), and the first and second facing surfaces skewed relative to an imaginary plane (y-y) orientated generally perpendicular to the axial direction of the mover such that the first and second facing surfaces are not parallel to the plane orientated generally perpendicular to the axial direction of the mover, and the steps of pressing at least a portion of the first skewed center ring element into the inner perimeter of the first stator pole section and pressing at least a portion of the second skewed center ring element into the inner perimeter of the second stator pole section may comprise rotationally aligning the first skewed center ring element and the second skewed center ring element such that the first facing surface and the second facing surface of the first skewed center ring element and the first facing surface and the second facing surface of the second skewed center ring element are all substantially parallel. 
         [0018]    The plurality of first laminates and the plurality of second laminates may be provided with a rotational alignment contour ( 38 ,  43 ,  49 ,  54 ,  59 ) and the step of stacking the plurality of the first laminates and the plurality of the second laminates in an axial direction may comprise the steps of providing a stator laminate assembly fixture ( 100 ,  103 ), rotationally aligning the stator laminate assembly fixture with the rotational alignment contours of the laminates, and stacking the laminates with the stator laminate assembly fixture such that the stator laminate assembly fixture corresponds with the alignment contour of each of the laminates so as to provide a desired rotational alignment of the laminates relative to each other. The rotational alignment contour may comprise an axial notch ( 38 ,  43 ,  49 ,  54 ,  59 ) having a first edge ( 85   a ) and a second edge ( 85   b ) spaced apart from the first edge, and the stator laminate assembly fixture may comprise a first axial rod ( 86   a ) and a second axial rod ( 86   b ) spaced apart from the first rod. 
         [0019]    The first stator pole section may be provided with a pole section alignment contour ( 87 ), the first skewed center ring element and the second skewed center ring element may be each provided with a ring alignment contour ( 80 ), and the step of pressing at least a portion of the first skewed center ring element into the inner perimeter of the first stator pole section may comprise the steps of providing a ring alignment fixture ( 81 ) having a first rotational alignment key ( 82 ) corresponding to the pole section alignment contour and a second rotational alignment key ( 83 ) corresponding to the ring alignment contour, rotationally aligning the first rotational alignment key with the pole section alignment contour and the second rotational alignment key with the ring alignment contour, and pressing at least a portion of the first skewed center ring element into the inner perimeter of the first stator pole section such that the first rotational alignment key corresponds with the pole section alignment contour and the second rotational alignment key corresponds with the ring alignment contour, so as to provide a desired rotational alignment of the first pole section and the first skewed center ring element relative to each other. 
         [0020]    The first pole section alignment contour may comprise an axial notch ( 38 ), the first rotational alignment key may comprise a tab ( 82 ) corresponding to the notch, the ring alignment contour may comprise an axial notch ( 80 ), and the second rotational alignment key may comprise a protrusion ( 83 ) corresponding to the notch of the ring alignment contour. 
         [0021]    The second stator pole section ( 22 ) may be provided with a pole section alignment contour ( 87 ) and the step of pressing at least a portion of the second skewed center ring element into the inner perimeter of the second stator pole section may comprise the steps of providing an ring alignment fixture having a first rotational alignment key ( 82 ) corresponding to the pole section alignment contour and a second rotational alignment key ( 83 ) corresponding to the ring alignment contour, rotationally aligning the first rotational alignment key with the pole section alignment contour and the second rotational alignment key with the ring alignment contour, and pressing at least a portion of the second skewed center ring element into the inner perimeter of the second stator pole section such that the first rotational alignment key corresponds with the pole section alignment contour and the second rotational alignment key corresponds with the ring alignment contour so as to provide a desired rotational alignment of the second pole section and the second skewed center ring element relative to each other. The second pole section alignment contour may comprise an axial notch ( 38 ), the first rotational alignment key may comprise a tab ( 82 ) corresponding to the notch, the ring alignment contour may comprise an axial notch ( 80 ), and the second rotational alignment key may comprise a protrusion ( 83 ) corresponding to the notch of the ring alignment contour. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is a longitudinal vertical cross-sectional view of the first embodiment of the linear motor assembly. 
           [0023]      FIG. 2  is a right perspective view of a first pole section shown in  FIG. 1 . 
           [0024]      FIG. 3  is an exploded view of the pole section shown in  FIG. 2 . 
           [0025]      FIG. 4  is a right plan view of the pole section shown in  FIG. 2 . 
           [0026]      FIG. 5  is a vertical cross-sectional view of the pole section shown in  FIG. 4 , taken generally on line B-B of  FIG. 4 . 
           [0027]      FIG. 6  is a right perspective view of a second pole section shown in  FIG. 1 . 
           [0028]      FIG. 7  is an exploded view of the pole section shown in  FIG. 6 . 
           [0029]      FIG. 8  is a right plan view of the pole section shown in  FIG. 6 . 
           [0030]      FIG. 9  is a vertical cross-sectional view of the pole section shown in  FIG. 8 , taken generally on line B-B of  FIG. 8 . 
           [0031]      FIG. 10  is a side view of a first laminate geometry. 
           [0032]      FIG. 11  is a side view of a second laminate geometry. 
           [0033]      FIG. 12  is a side view of a third laminate geometry. 
           [0034]      FIG. 13  is a side view of a forth laminate geometry. 
           [0035]      FIG. 14  is a side view of a fifth laminate geometry. 
           [0036]      FIG. 15  is a right side view of the center ring shown in  FIG. 2 . 
           [0037]      FIG. 16  is a right side view of the center ring shown in  FIG. 15 . 
           [0038]      FIG. 17  is an enlarged detailed view of the center ring shown in  FIG. 12 , taken within the indicated circle of  FIG. 12 . 
           [0039]      FIG. 18  is an exploded perspective view of the fixtures used to assemble the laminated pole section shown in  FIG. 2 . 
           [0040]      FIG. 19  is an exploded perspective view of the fixture used to assemble a center ring and laminated pole section shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0041]    At the outset, it should be clearly understood that like reference numerals are intended to identify the same structural elements, portions or surfaces consistently throughout the several drawing figures, as such elements, portions or surfaces may be further described or explained by the entire written specification, of which this detailed description is an integral part. Unless otherwise indicated, the drawings are intended to be read (e.g., cross-hatching, arrangement of parts, proportion, degree, etc.) together with the specification, and are to be considered a portion of the entire written description of this invention. As used in the following description, the terms “horizontal”, “vertical”, “left”, “right”, “up” and “down”, as well as adjectival and adverbial derivatives thereof (e.g., “horizontally”, “rightwardly”, “upwardly”, etc.), simply refer to the orientation of the illustrated structure as the particular drawing figure faces the reader. Similarly, the terms “inwardly” and “outwardly” generally refer to the orientation of a surface relative to its axis of elongation, or axis of rotation, as appropriate. 
         [0042]    This invention provides an improved linear motor, an embodiment of which is generally indicated at  15 . As shown in  FIG. 1 , linear motor  15  generally includes specifically configured stator  16  and mover  19 . Mover  19  is a cylindrical member elongated about axis x-x and formed of a plurality of annular permanent magnets, severally indicated at  65 , spaced axially along its outer circumference. Mover  19  is coincident with stator  16  and moves linearly along axis x-x relative to stator  16 . Movement along axis x-x is referred to herein as movement in the axial direction. 
         [0043]    As shown in  FIGS. 1 and 2 , stator  16  is a generally cylindrical member elongated about axis x-x and having inner opening  18  through which mover  19  moves. As shown in  FIG. 1 , stator  16  is primarily formed from four pole sections  20 - 24  that are stacked in the axial direction to form recesses  25 - 28  therebetween. Individual stator pole sections  20 - 24  are glued or bolted together, with coils therebetween, to form stator core  16 . Stator  16  also includes end pieces, also formed of laminates, which are fixed by glue, bolts or other means to either end of the stacked pole sections  20 - 24  to form stator core  16 . Recess  25 - 28  house conventional coils, which are energized as desired to magnetically interact with mover  19  to cause axial movement of mover  19  relative to stator  16 . The interior of stator  16  is a cylindrical hollow  18  of constant diameter along the length thereof. 
         [0044]    As shown in  FIGS. 1-14 , each individual pole section  20 - 24  is in turn formed from multiple laminates  17  that are stacked and glued together axially. Thus, the laminates are orientated in a plane that is generally perpendicular to axis x-x of mover  19 . As shown in  FIGS. 1-17 , each of pole sections  20 - 24  also includes inner, specially configured cylindrical center ring  70   a - 70   e,  respectively, the inner cylindrical surfaces of which define opening  18  through which mover  19  reciprocates. 
         [0045]    In this embodiment, laminates  17  are formed of a magnetic steel lamination material, such as M-15 type, that is either laser-cut or punched into the desired cross-sectional geometry. The thickness of each laminated layer  17  is generally the same. However, the cross-sectional geometry of each laminate  17  varies depending on its axial spaced location in the subject pole section. The cross-sectional geometry of laminates  17  are configured so as to form, when stacked and held together with a lamination adhesive, the shape of the respective stator pole section  20 - 24 . 
         [0046]    Pole section  21  is shown in more detail in  FIGS. 2-5 . As shown in  FIG. 3 , pole section  21  is formed by stacking multiple laminates  17   a,  having cross-sectional geometry  29  shown in  FIG. 12 , together with multiple laminates  17   b,  having cross-sectional geometry  30  shown in  FIG. 11 , together with multiple laminates  17   c,  having cross-sectional geometry  33  shown in  FIG. 14 , together with multiple laminates  17   d,  having cross-sectional geometry  29  shown in  FIG. 12 . In this embodiment, pole section  21  comprises about  25  individual laminates  17   a  having geometry  29 , about 14 individual laminates  17   b  having cross-sectional geometry  30 , about 25 individual laminates  17   c  having cross-sectional geometry  33 , and about 25 individual laminates  17   d  again having cross-sectional geometry  29 , moving left-to-right along axis x-x with reference to  FIG. 3 . When stacked and glued together, the outer portion of pole section  21  is formed. Thereafter, center ring  70   b  is pressed into the center opening of laminated section  21 , as further described below. 
         [0047]    Pole section  22  is shown in more detail in  FIGS. 6-9 . As shown in  FIG. 7 , pole section  22  is formed by stacking multiple laminates  17   e,  having cross-sectional geometry  29  shown in  FIG. 12 , together with multiple laminates  17   f,  having cross-sectional geometry  31  shown in  FIG. 10 , together with multiple laminates  17   g,  having cross-sectional geometry  32  shown in  FIG. 13 , together with multiple laminates  17   h,  having cross-sectional geometry  29  shown in  FIG. 12 . Thus, pole section  22  may be varied from pole section  21  by using alternatively-configured cross-sectional geometry laminates. Whereas the center portion of pole section  21  is formed of multiple laminates  17   b  and  17   c  having cross-sectional geometries  31  and  32 , respectively, the center portion of pole section  22  is formed of laminates  17   f  and  17   g  having alternative cross-sectional geometries  31  and  32 , respectively. In this embodiment, pole section  22  comprises about  25  individual laminates  17   e  having geometry  29 , about 14 individual laminates  17   f  having cross-sectional geometry  31 , about 25 individual laminates  17   g  having cross-sectional geometry  32 , and about 25 individual laminates  17   h  having cross-sectional geometry  29 , moving left-to-right along axis x-x with reference to  FIG. 7 . When stacked and laminated together, the outer portion of pole section  22  is formed. Thereafter, center ring  70   c  is pressed into the center opening of laminated section  22 , as further described below. 
         [0048]    It is contemplated that pole sections may be formed with multiple laminates having various alternative combinations of cross-sectional geometries. Thus, while a number of cross-sectional geometries for the laminates are shown and described, it is contemplated that other alternative geometries may be employed by one skilled in the art. Having laminations that are oriented in planes perpendicular to axis x-x has been unexpectedly found to reduce undesired stator heating and to avoid eddy currents. 
         [0049]    Laminates  17   a,    17   d,    17   e  and  17   h  each have cross-sectional geometry  29 . As shown in  FIG. 12 , geometry  29  comprises thin ring  35  having outer perimeter  36 , inner perimeter  37 , thickness  60  between outer perimeter  36  and inner perimeter  37 , front face  35   a  and rear face  35   b.  Opening or radial gap  38  is provided between inner perimeter  37  and outer perimeter  36 . 
         [0050]    Cross-sectional geometry  30  of laminates  17   b  is shown in  FIG. 11 . As shown, geometry  30  comprises thickened ring  39 , having outer perimeter  40  and inner perimeter  41 . Thickness  42  between outer perimeter  40  and inner perimeter  41  is significantly larger than thickness  60  of cross-sectional geometry  29 . Ring  39  includes front face  39   a  and opening  44  between face  39   a  and its rear face  39   b.  In addition, notch  43  is provided at the top extending in from outer perimeter  40 . Opening  44  is provided so that when multiple laminates  17   b  of cross-sectional geometry  30  are stacked together, a cylindrical space is provided for housing a temperature sensor. 
         [0051]    Cross-sectional geometry  33  of laminates  17   c  is shown in  FIG. 14 . Cross-sectional geometry  33  comprise ring  55  of the same thickness  58  as thickness  42  of cross-sectional geometry  30 . Ring  55  is defined by outer perimeter  56 , inner perimeter  57 , front face  55   a  and a rear face. Cross-sectional geometry  33  includes a specially configured contoured opening  59  between outer perimeter  56  and inner perimeter  57 . Opening  59  is a relief that provides clearance to allow the last turn of the windings in respective recesses  25 - 28  to exit. 
         [0052]    Cross-sectional geometer  31 , shown in  FIG. 10 , comprises ring  45  having front face  45   a,  rear face  45   b,  outer perimeter  46 , inner perimeter  47  and thickness  48  between outer perimeter  46  and an inner perimeter  47 , which is the same as thickness  42  of cross-sectional geometry  30  and thickness  48  of cross-sectional geometry  33 . This lamination geometry is essentially the same as cross-sectional geometry  30 , except that it only has notch  49  and does not include opening  44 . 
         [0053]    Cross-sectional geometry  32  is shown in  FIG. 13 , and is similar to cross-sectional geometry  33 , shown in  FIG. 14 . It is formed of ring  50  having outer perimeter  51 , inner perimeter  52 , front face  50   a  and a corresponding rear face. It has thickness  53  between outer perimeter  51  and inner perimeter  52 , which is the same as thicknesses  58 ,  48  and  42  of cross-sectional geometries  33 ,  31  and  30 , respectively. However, the inner portion of relief  54  between inner perimeter  52  and outer perimeter  51  of cross-sectional geometry  32  varies slightly from the inner portion of relief  59  of cross-sectional geometry  33 , as shown. 
         [0054]      FIGS. 15-17  show inner rings  70   a - 70   e.  These inner rings are all specially machined unitary tubular members. As shown in  FIG. 16 , ring  70  is a cylindrical ring-shaped annular structure elongated along axis x-x and generally bounded by rightwardly and downwardly-facing annular angled off-vertical surface  71 , rightwardly-facing annular vertical surface  77 , outwardly-facing horizontal cylindrical surface  72 , leftwardly-facing annular vertical surface  73 , outwardly-facing cylindrical horizontal surface  74 , leftwardly and upwardly-facing angled off-vertical annular surface  75 , and inwardly-facing horizontal cylindrical surface  76 . Surfaces  73 ,  72  and  77  define alignment protrusion  79 . As described below, the small edge  79  machined into ring  70  creates a stop such that the pressing of ring  70  into the inner opening of the laminated pole section is repeatable with precision and such that axial alignment of the ring is correct. In particular, surface  73  of alignment protrusion  79  acts as a stop so that center ring  70  extends into the inner perimeter of the subject laminated pole section the desired amount. 
         [0055]    As shown in  FIG. 17 , alignment protrusion  79  includes alignment notch  80  extending inwards from surface  72 . Alignment notch  80  is used to rotationally align ring  70  with the laminated pole section into which it is inserted. 
         [0056]    As shown in  FIGS. 1 ,  5 ,  9  and  16 , center ring  70  is machined as a solid steel ring that is pressed into the center of an assembled laminated pole section in order to create skew in stator  16  and reduce cogging forces in motor  15 . As shown in  FIG. 16 , surfaces  71  and  75  are parallel annular surfaces and are angled off-vertical by skew angle  88 . In this embodiment, skew angle  88  is about 3.2 degrees. Because of the positioning of center ring  70  within the subject laminated pole section, center ring  70  forms the inner tooth of the pole piece. It has been found that the skew of ring  70  and its placement helps to reduce torque ripple and provides unexpected and improved performance characteristics. As shown in  FIG. 1 , pole sections  20 - 24 , together with the end sections are stackable at axial spaced locations along axis x-x. Also as shown, each of the laminated pole sections  20 - 24  includes skewed center rings  70   a - 70   e,  respectively, which are pressed into the inner opening of the laminated portion of the pole section until projections  79   a - 70   e,  respectively, abut against the leftwardly-facing surface of the subject stator pole section. Thus, ring  70   b  is pressed into the center opening of the laminated portion of pole section  21  until surface  73  of projection  79   b  abuts against and is stopped by leftwardly-facing surface  39   b  of pole section  21 . Similarly, ring  70   c  is pressed into the center opening of the laminated portion of pole section  22  until annular surface  73  of projection  79   c  abuts against and is stopped by leftwardly-facing surface  45   b  of pole section  22 . 
         [0057]      FIG. 18  shows the use of fixtures  100  and  103  to properly align laminates  17   a - 17   e  about axis x-x relative to each other when forming pole section  21 . As shown, fixture  100  is a generally cylindrical member having an outer perimeter and an inner perimeter. Two outer positioning rods  86   a  and  86   b  extend from the left face of fixture  100  parallel to axis x-x. In addition, three inner positional rods  90   a - 90   c  extend from the left face of fixture  100  parallel to axis x-x. Also, three shorter positional rods  91   a - 91   c  extend from the left face of fixture  100  parallel to axis x-x. Inner rods  90   a - 90   c  are positioned on fixture  100  such that an imaginary circle drawn about all three rods has a diameter that is substantially equal to the diameter of inner perimeter  41 ,  57  of geometry  30 ,  33  of laminates  17   b  and  17   c,  respectively. Rods  91   a - 91   c  are positioned on fixture  100  such that an imaginary circle drawn about all three rods has a diameter that is substantially equal to the diameter of inner perimeter  37  of geometry  29  of laminates  17   a  and  17   d.  Rods  86   a  and  86   b  are in turn positioned on fixture  100  separated from each other a distance approximately equal to the distance between edges  85   a  and  85   b  of notches  38 ,  43 ,  49 ,  54  and  59 . As shown, fixture  103  is a generally cylindrical member having an outer perimeter and an inner perimeter. Three shorter positional rods  92   a - 92   c  extend from the right face of fixture  100  parallel to axis x-x. Inner rods  90   a,    92   b  (not shown) and  92   c  (not shown) are positioned on fixture  100  to match the location of rods  91   a - 91   c  on fixture  100 , such that an imaginary circle drawn about all three rods has a diameter that is substantially equal to the diameter of inner perimeter  37  of geometry  29  of laminates  17   a  and  17   d.  Thus, all of the required laminates may be slipped over the rods and stacked on fixtures  100  and  103  so that they are all properly rotationally aligned relative to each other. 
         [0058]    In particular, spacer  101  is first aligned and positioned on fixture  100  with rods  86   a - 86   b  and  91   a - 91   c  extending through the respective corresponding openings in spacer  101  and rods  90   a - c  extending through the center opening of spacer  101 . Next, laminates  17   a  having cross-sectional geometry  29  are positioned and slipped over the rods of fixture  100  such that rods  86   a  and  86   b  extend between the opposed sides of gap  38  of cross-sectional geometry  29  of laminates  17   a,  and rods  91   a - 91   c  fit within and support inner perimeter  37  of cross-sectional geometry  29  of laminates  17   a.  Next, laminates  17   b  having cross-section geometry  30  are positioned and slipped over the rods of fixture  100  such that arms  86   a  and  86   b  extend between the outer opposed sides of notch  43  of cross-sectional geometry  30  of laminates  17   b,  and rods  90   a - 90   c  fit within and support inner perimeter  41  of cross-sectional geometry  30  of laminates  70   b.  Next, laminates  17   c  having cross-sectional geometry  33  are positioned and slipped over the rods of fixture  100  such that arms  86   a  and  86   b  extend between the outer opposed sides of opening  59  of cross-sectional geometry  33  of laminates  17   c,  and arms  90   a - 90   c  fit within and support inner perimeter  57  of cross-sectional geometry  33  of laminates  17   c.  Next, laminates  17   d  having cross-sectional geometry  29  are positioned and slipped over the rods of fixture  100  such that rods  86   a  and  86   b  extend between the opposed sides of gap  38  of cross-sectional geometry  29  of laminates  17   d.  Next, spacer  102  is aligned and positioned on fixture  100  with rods  86   a - 86   b  extending through the respective corresponding openings in spacer  102  and rods  90   a - 90   c  extending through the center opening of spacer  102 . End fixture  103  is then aligned and positioned in fixture  100  such that rods  86   a  and  86   b  of fixture  100  extend through the corresponding openings in end fixture  103  and such that rightward-extending rods  92   a - 92   c  of fixture  103  extending through the respective corresponding openings in spacer  102  and then in turn fit within and inner perimeter  37  of cross-sectional geometry  29  of laminates  17   d.  With laminate adhesive between laminate layers  17   a - 17   d,  fixture  100  and fixture  103  are then pressed against each other while the adhesive of the assembly cures. In this manner, the stator pole section laminations are assembled in a fixture which aligns each of the lamination pieces in the proper orientation while the adhesive cures so that a fully assembled laminated pole section is provided. 
         [0059]    Pole section  22  is formed in a similar manner. In particular, spacer  101  is first aligned and positioned on fixture  100  with rods  86   a - 86   b  and  91   a - 91   c  extending through the respective corresponding openings in spacer  101  and rods  90   a - 90   c  extending through the center opening of spacer  101 . Next, laminates  17   e  having cross-sectional geometry  29  are positioned and slipped over the rods of fixture  100  such that rods  86   a  and  86   b  extend between the opposed sides of gap  38  of cross-sectional geometry  29  of laminates  17   e,  and rods  91   a - 91   c  fit within and support inner perimeter  37  of cross-sectional geometry  29  of laminates  17   e.  Next, laminates  17   f  having cross-section geometry  31  are positioned and slipped over the rods of fixture  100  such that arms  86   a  and  86   b  extend between the outer opposed sides of notch  49  of cross-sectional geometry  31  of laminates  17   f,  and rods  90   a - 90   c  fit within and support inner perimeter  47  of cross-sectional geometry  31  of laminates  70   f . Next, laminates  17   g  having cross-sectional geometry  32  are positioned and slipped over the rods of fixture  100  such that arms  86   a  and  86   b  extend between the outer opposed sides of opening  54  of cross-sectional geometry  32  of laminates  17   g,  and arms  90   a - 90   c  fit within and support inner perimeter  52  of cross-sectional geometry  32  of laminates  17   g.  Next, laminates  17   h  having cross-sectional geometry  29  are positioned and slipped over the rods of fixture  100  such that rods  86   a  and  86   b  extend between the opposed sides of gap  38  of cross-sectional geometry  29  of laminates  17   h.  Next, spacer  102  is aligned and positioned on fixture  100  with rods  86   a - 86   b  extending through the respective corresponding openings in spacer  102  and rods  90   a - c  extending through the center opening of spacer  102 . End fixture  103  is then aligned and positioned in fixture  100  such that rods  86   a  and  86   b  of fixture  100  extend through the corresponding openings in end fixture  103  and such that rightward-extending rods  92   a - 92   c  of fixture  103  extending through the respective corresponding openings in spacer  102  and then in turn fit within and inner perimeter  37  of cross-sectional geometry  29  of laminates  17   h.  With laminate adhesive between laminate layers  17   e - 17   h,  fixture  100  and fixture  103  are then pressed against each other while the adhesive of the assembly cures. 
         [0060]      FIG. 19  is a representative view showing the use of fixture  81  and press  84  to combine ring  70  with the laminated portion of each pole section formed as described above. In particular, fixture  81  is provided to properly align ring  70  in the center opening of the laminated portion of pole section  20 - 24 . As shown, fixture  81  is a specially configured cylindrical member having an outer perimeter and an inner perimeter defining a center opening. Alignment key  82  extends from the outer perimeter of fixture  81 . The outer perimeter of fixture  81  has a diameter that is substantially equal to the diameter of inner perimeter  37  of geometry  29  of laminates  17   a.  Alignment key  82  extends beyond that perimeter and has a width that is to the width of gap  38  of cross-sectional geometry  29  of laminates  17   a.  Thus, if aligned properly about axis x-x, fixture  81  should fit within the recess of pole section  21  formed by laminates  17   a  such that its outer perimeter is encompassed within inner perimeter  37  of geometry  29  of laminates  17   a  and alignment key projection  82  fits through opening  38  of geometry  29  of laminates  17   a.    
         [0061]    The inner perimeter of fixture  81  has a diameter that is substantially equal to the diameter of surface  72  of projection  79   b  of ring  70   b.  Thus, ring  70   b  slides within the inner perimeter of fixture  81  if and when ring  70   b  is properly rotationally aligned such that inner projection  83  slides axially into notch  80  in projection  79   b  of ring  70   b.  Thus, to properly align ring  70   b  in the laminated portion of pole section  21 , ring  70   b  is rotationally aligned with fixture  81  such that projection  83  axially slides into notch  80  and the outer perimeter of alignment projection  79   b  is within the inner perimeter of fixture  81 . 
         [0062]    So first ring  70   b  is rotationally aligned with fixture  81  such that projection  83  axially slides into notch  80  and the outer perimeter of alignment projection  79   b  is within the inner perimeter of fixture  81 . Once ring  70   b  is rotationally aligned within the inner perimeter of fixture  81 , fixture  81  is aligned with the laminated portion of pole section  21  such that outer alignment key  82  slides within the gap formed by opening  38  of geometry  29  in laminates  17   a.  This assures that fixture  81  is rotationally aligned properly with the laminated portion of pole section  21 . Press  89  is then used to force ring  70  into the center opening of the laminated portion of pole section  21 . Ring  70  is pressed into the center opening of the laminated portion of pole section  21  until annular surface  73  of alignment projection  79   b  abuts and is stopped by leftward-facing surface  39   b  of pole section  21 . In this manner, ring  70  is rotationally aligned about axis x-x relative to pole section  21  and is axially aligned along axis x-x relative to laminate pole section  21 . This method of both rotationally and axially aligning ring  70   b  into the center opening of laminated pole section  21  provides for repeatability, precision and accurate ring positioning so that a proper skew is provided. The same process is employed with respect to the other pole sections. 
         [0063]    Once each of the pole sections, with its respective center ring, are formed, they are in turn stacked axially in the desired configuration to form stator core  16  with windings as required in recesses  25 ,  26 ,  27  and  28 . In addition, temperature gages and the like may be positioned in the specially configured openings, for example opening  44 , when the pole sections are stacked together. In this manner, any combination or configuration of laminates, laminated pole sections or pole core may be formed as desired. 
         [0064]    The present invention contemplates that many changes and modifications may be made. For example, the assembled stator core may be fitted inside a magnetic tube which adds an additional magnetic flux path, thereby improving the force generated by the motor. Such pipe may be ordinary or magnetic stainless steel for improved corrosion resistance. The magnetic lamination material of laminates  17  may be of various grades or have various magnetic properties, depending on the performance versus cost desired. The diameter size of the stator components are scalable, depending on the performance desired from the final motor. The length of the assembled stator, the axial thickness of the pole sections, and the number of pole sections are scalable, again depending on the performance desired and the practical manufacturing limits of the components. The cross-sectional geometries of the individual laminates may be varied as desired. The number and geometries of the pole sections may be varied as desired. Therefore, while the presently preferred form of the linear motor has been shown and described, those persons skilled in this art will readily appreciate the various additional changes and modification may be made without departing from the spirit of the invention, as defined and differentiated by the following claims.