Abstract:
A linear motor includes a movable element and a stator. The stator includes a pair of back yokes provided opposing each other such as to flank the movable element along a direction perpendicular to the movable element&#39;s axis of travel, a plurality of main pole magnets provided spaced apart from each other and paralleling the axis of travel, on respective inside lateral surfaces of the pair of back yokes, and first and second interpole magnets provided, adjoining along said axis of travel, in each of intervals between adjoining couples of the main pole magnets.

Description:
RELATED APPLICATIONS 
       [0001]    Priority is claimed to Japanese Patent Application No. 2015-028193, filed Feb. 17, 2015, the entire content of which is incorporated herein by reference. 
       BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    Certain embodiments of the invention relate to linear motors. 
         [0004]    2. Description of Related Art 
         [0005]    A linear motor is used to convert electrical energy into linear motion.  FIG. 1  is a perspective view of a linear motor in the related art.  FIG. 2  is a plan view showing the arrangement of field magnets of the linear motor in the related art. 
         [0006]    A linear motor  2   r  as represented in  FIG. 1  is furnished with a movable element  10  and a stator  20   r . The stator  20   r  is furnished with a pair of yokes (back yokes)  22   a  and  22   b  disposed in opposition with the movable element  10  interposed between them, and pluralities of field magnets  24  provided along the way that the movable element  10  travels (along the x-axis) on respective inside lateral surfaces S 1   a  and S 1   b  of the back yokes  22   a  and  22   b.    
         [0007]    As shown in  FIG. 2 , the pluralities of field magnets  24  include main pole magnets  24   a  and interpole magnets  24   b . The main pole magnets  24   a   1 ,  24   a   2 ,  24   a   3  . . . are bonded in place according to a magnetic pole pitch and such that the N poles and S poles appear in alternation. Interpole magnets  24   b   i , which have magnetic poles oriented along the magnetic field generated by two adjoining main pole magnets  24   a   i  and  24   a   i+1 , are provided in between the adjoining main pole magnet pairs. (Here, i=1, 2, 3 . . . . ) The configuration of such a magnetic circuit is called a Halbach array, employed in various linear motors. 
       SUMMARY 
       [0008]    In one aspect the present invention affords a linear motor. The linear motor includes a movable element and a stator. The stator includes a pair of back yokes provided opposing each other such as to flank the movable element along a direction perpendicular to the movable element&#39;s axis of travel, a plurality of main pole magnets provided spaced apart from each other and paralleling the axis of travel, on respective inside lateral surfaces of the pair of back yokes, and first and second interpole magnets provided, adjoining along said axis of travel, in each of intervals between adjoining couples of the main pole magnets. 
         [0009]    In another aspect, the present invention affords a stage device. The stage device includes a linear motor as set forth above. 
         [0010]    In still another aspect, the present invention affords a magnet unit. The magnet unit is used in a linear motor that includes a movable element and a stator. The stator includes a pair of back yokes provided opposing each other such as to flank the movable element along a direction perpendicular the movable element&#39;s axis of travel, and pluralities of magnet units disposed paralleling said axis of travel on respective inside lateral surfaces of the pair of back yokes. The magnet unit includes main pole magnets and interpole magnets snugly affixed to either of ends of the main pole magnets. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a perspective view of a linear motor in the related art. 
           [0012]      FIG. 2  is a plan view showing the arrangement of field magnets of the linear motor in the related art. 
           [0013]      FIG. 3  is a perspective view of a linear motor according to an embodiment. 
           [0014]      FIG. 4  is a plan view showing the arrangement of field magnets of  FIG. 3 . 
           [0015]      FIGS. 5A to 5C  are views showing steps of manufacturing a stator. 
           [0016]      FIG. 6  is a plan view of a stage device that uses the linear motor according to the embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    The inventor has found out the following problems as a result of the examination of the Halbach array of  FIG. 2 . In a magnetic circuit that does not include the interpole magnet  24   b , a magnetic field generated by the main pole magnet  24   a  passes through the yoke  22 . However, in the Halbach array structure including the interpole magnet  24   b , the interpole magnets  24   b  serves as an alternative magnetic path, that is, a magnetic field generated by the main pole magnet  24   a  passes through the interpole magnet  24   b.    
         [0018]    Attention is paid to the i th  main pole magnet  24   a   i . The N pole of the main pole magnet  24   a   i  and the S pole of an interpole magnet  24   b   i , which is adjacent to the main pole magnet  24   a   i , generate an attractive force F i . Likewise, the N pole of the main pole magnet  24   a   i  and the S pole of an interpole magnet  24   b   i−1 , which is adjacent to the main pole magnet  24   a   i , also generate an attractive force F i−1 . Since the other main pole magnets  24   a  are also the same as described above, a force is applied in a direction, in which the main pole magnet  24   a  is separated from the yoke  22 , by the interpole magnet  24   b.    
         [0019]    In order to resist a force F that separates the main pole magnet  24   a  from the yoke  22 , the main pole magnet  24   a  needs to be bonded to the yoke  22  by a strong adhesive, or the side surface of the main pole magnet  24   a  and the interpole magnet  24   b  need to be bonded to each other. For this reason, an assembling step may be complicated. 
         [0020]    Further, even though such a countermeasure is prepared, bonding strength varies due to the dimensional variations and the non-flatness of the main pole magnets  24   a  or the interpole magnets  24   b . For this reason, it is difficult to completely prevent some of the field magnets  24  from being separated from the yoke  22 . 
         [0021]    The invention provides a linear motor of which reliability is high in an assembling step and/or after assembly. 
         [0022]    In this aspect, one interpole magnet, which has been provided between adjacent main pole magnets in the Halbach array in the related art, is divided into two magnets. Accordingly, it is possible to inhibit a force, which separates a certain main pole magnet from the back yoke, from being generated so as to be concentrated on the main pole magnet in an assembling step. Eventually, it is possible to improve reliability in the assembling step and/or after assembly. 
         [0023]    When a magnetic pole pitch is denoted by Wp, a width Wa of the main pole magnet, a width Wc of the first interpole magnet, and a width Wd of the second interpole magnet may satisfy 
         [0000]    
       
      
       Wa+Wc+Wd=Wp,  
      
     
         [0000]      0.5× Wp≦Wa≦ 0.9× Wp , and
 
         [0000]      0.1× Wp≦Wc+Wd≦ 0.5× Wp.  
 
         [0024]    Wc may be equal to Wd. 
         [0025]    The main pole magnet and two interpole magnets, which are provided on both ends of the main pole magnet, may be integrated as a magnet unit and may then be bonded to the back yoke. 
         [0026]    Since every magnet unit is bonded to the back yoke, an attractive force acts between the back yoke and the magnet unit as a whole, and a force, which separates the main pole magnet from the yoke, can be reduced. Further, since an attractive force acts between adjacent magnet units, the assembling of the stator becomes easy. 
         [0027]    Meanwhile, arbitrary combinations of the above-mentioned components, and aspects in which the components or expressions of the invention are replaced between methods, devices, systems, and the like are also effective as aspects of the invention. 
         [0028]    According to the invention, it is possible to improve the reliability of the linear motor in an assembling step and/or after assembly. 
         [0029]    The invention will be described below on the basis of a preferred embodiment thereof with reference to the drawings. Hereinafter, the same or equivalent components, members, and processing, which are shown in the respective drawings, are denoted by the same reference numerals, and the repeated description thereof will be appropriately omitted. Further, the embodiment is illustrative without limiting the invention, and all characteristics, which are described in the embodiment, or the combinations thereof do not necessarily need to be essential in the invention. 
         [0030]      FIG. 3  is a perspective view of a linear motor  2  according to an embodiment.  FIG. 4  is a plan view showing the arrangement of field magnets of  FIG. 3 . In the drawings, arrows indicate the orientations of magnetic poles, the tip of the arrow corresponds to an N pole, and the base of the arrow corresponds to an S pole. 
         [0031]    As shown in  FIG. 3 , the linear motor  2  includes a movable element  10  and a stator  20 . The stator  20  includes a pair of back yokes (simply referred to as yokes)  22   a  and  22   b  and a plurality of field magnets  24 . The pair of yokes  22   a  and  22   b  are provided so as to face each other with the movable element  10  interposed therebetween in a direction (y direction) perpendicular to a movable direction of the movable element  10  (x direction). 
         [0032]    The plurality of field magnets  24  include a plurality of main pole magnets  24   a  and a plurality of interpole magnets  24   c  and  24   d . The plurality of main pole magnets  24   a   1 ,  24   a   2 ,  24   a   3  . . . are provided along the movable direction (the x direction) on inner surfaces S 1   a  and S 1   b  of the pair of back yokes  22   a  and  22   b.    
         [0033]    As shown in  FIG. 4 , two interpole magnets  24   c  and  24   d  are provided between two adjacent main pole magnets  24   a  so as to be adjacent to each other in the movable direction (the x direction). Specifically, a first interpole magnet  24   c   i  and a second interpole magnet  24   d   i+1  are inserted between the i th  main pole magnet  24   a   i  and the (i+1) th  main pole magnet  24   a   i+1  so as to be adjacent to each other. 
         [0034]    The width Wc of the first interpole magnet  24   c   i+1  and the width Wd of the second interpole magnet  24   d   i  may be designed so that the sum of the width Wc of the first interpole magnet  24   c   i+1  and the width Wd of the second interpole magnet  24   d   i  is substantially equal to the width of the interpole magnet  24   b  of a magnetic circuit having the Halbach array structure in the related art. 
         [0035]    When a distance between the centers of adjacent main pole magnets  24   a  is defined as a magnetic pole pitch Wp, it is preferable that the width Wa of the main pole magnet  24   a  satisfies Wa≧0.5×Wp. In this case, the sum Wc+Wd of the widths of the two interpole magnets  24   c  and  24   d  satisfies Wc+Wd≦0.5×Wp≦Wa. Meanwhile, in order to obtain the effects of the interpole magnets  24   c  and  24   d , it is preferable that the sum Wc+Wd of the widths of the interpole magnets  24   c  and  24   d  is larger than 1/10 of the magnetic pole pitch Wp. 
         [0036]    Considering these conditions, the widths of the main pole magnet  24   a  and the interpole magnets  24   c  and  24   d  may be determined so as to satisfy the following expressions. 
         [0000]    
       
      
       Wa+Wc+Wd=Wp  
      
     
         [0000]      0.5× Wp≦Wa≦ 0.9× Wp  
 
         [0000]      1.0× Wp≦Wc+Wd≦ 0.5× Wp  
 
         [0000]    Wc=Wd may also be satisfied in terms of the simplification of design and manufacture. 
         [0037]    The structure, which has been described until now, is the structure of the stator  20 . Subsequently, a method of manufacturing the stator  20  will be described. After the i th  main pole magnet  24   a   i  and the first and second interpole magnets  24   c   i  and  24   d   i , which are provided on both ends of the i th  main pole magnet  24   a   i , are integrated as a magnet unit  26   i , the stator  20  can be assembled while the magnet unit  26   i  is used as a unit. As shown in  FIG. 5A to 5C , the directions of the interpole magnets  24   c  and  24   d  of an even-numbered magnet unit are opposite to those of an odd-numbered magnet unit. Accordingly, two kinds of magnet units  26   x  and  26   y  are prepared. 
         [0038]      FIGS. 5A to 5C  are views showing steps of manufacturing the stator  20 . 
         [0039]    The second interpole magnet  24   d  and the first interpole magnet  24   c  are fixed to both side surfaces of the main pole magnet  24   a  by an adhesive as shown in  FIG. 5A , so that two kinds of magnet units  26   x  and  26   y  are formed as shown in  FIG. 5B . Then, the magnet units  26   x  and  26   y  are alternately bonded to a surface  51  of the yoke  22  by an adhesive. An adhesive may also be applied between the adjacent magnet units  26   x  and  26   y . The method, which has been described until now, is the method of manufacturing the stator  20 . 
         [0040]    Subsequently, the advantages of the linear motor  2  according to the embodiment will be described. One interpole magnet, which has been provided between the adjacent main pole magnets in the Halbach array in the related art, is divided into two magnets in this embodiment. 
         [0041]    Accordingly, when the plurality of field magnets  24 , specifically, the plurality of main pole magnets  24   a , the plurality of first interpole magnets  24   c , and the plurality of second interpole magnets  24   d  are bonded to the yoke  22 , the field magnets can be assembled in an order that is not mentioned in the Halbach array in the related art. Accordingly, it is possible to inhibit a force, which separates the main pole magnet  24   a  from the back yoke  22 , from being generated so as to be concentrated on the main pole magnet  24   a . In other words, the field magnets  24  can be bonded to the yoke  22  in an order where the separation of the main pole magnet  24   a  from the back yoke  22  is suppressed. Accordingly, it is possible to improve reliability in an assembling step and/or after assembly. 
         [0042]    Specifically, in the embodiment, particularly, every magnet unit  26  is bonded to the yoke  22  as shown in  FIGS. 5A to 5C . Accordingly, a force, which attracts the back yoke  22 , acts on the magnet unit  26  as a whole, and a force, which separates the main pole magnet  24   a  from the yoke  22 , is reduced. In addition, an attractive force acts between the adjacent magnet units  26 . Accordingly, work for bonding the plurality of field magnets  24  to the yoke  22  becomes easy, so that the assembling of the stator  20  becomes easy. 
         [0043]    The advantages, which have been described until now, are the advantages of the linear motor  2 . Subsequently, the use of the linear motor  2  will be described. 
         [0044]      FIG. 6  is a plan view of a stage device  100  that uses the linear motor  2  according to the embodiment. The stage device  100  is called an XY stage, and positions an object in the x direction and the y direction. 
         [0045]    The stage device  100  mainly includes a Y stage  120 , an X stage  130 , and a surface plate  140 . 
         [0046]    The Y stage  120  includes a pair of sliders  124  and a horizontal member  122  that is horizontally provided between the pair of sliders  124 . An X linear motor  2 X, which moves the X stage  130  in the x direction, is provided on the horizontal member  122 . The X linear motor  2 X includes the stator  20  that is fixed to the horizontal member  122  and extends in the x direction, and the movable element (coil)  10  that is provided on the lower surface of the X stage  130 . Accordingly, the X stage  130  is positioned in the x direction by the control of the movable element  10  of the X linear motor  2 X. 
         [0047]    A pair of Y linear motors  2 Y are provided on both ends of the surface plate  140 . Each of the Y linear motors  2 Y includes the movable element  10  and the stator  20 . The above-mentioned sliders  124  are fixed to the stators  20  of the Y linear motors  2 Y. The Y stage  120  is positioned in they direction by the control of the movable elements  10  of the Y linear motors  2 Y. 
         [0048]    The structure, which has been described until now, is the structure of the stage device  100 . The linear motor  2  according to the embodiment can be suitably used as the X linear motor  2 X or the Y linear motor  2 Y of the stage device  100 . The stage device  100  can be used to position a wafer or a glass substrate in an exposure apparatus, or can also be used for an actuator, which is used in a scanning electron microscope (SEM), or the like. 
         [0049]    The invention has been described above on the basis of the embodiment. The embodiment is illustrative, and it is understood by those skilled in the art that combinations of the respective components or various kinds of processing of the embodiment can have various modifications and the modifications are also included in the scope of the invention. These modifications will be described below. 
       Modification 1 
       [0050]    In the embodiment, as shown in  FIGS. 5A to 5C , the main pole magnet  24   a  and the first and second interpole magnets  24   c  and  24   d , which are provided on both ends of the main pole magnet  24   a , have been integrated as one magnet unit  26  and the magnet unit then has been bonded to the yoke  22 . However, the invention is not limited thereto. For example, the magnet unit  26   x  and the magnet unit  26   y  may be bonded to each other to form one magnet unit, and may be bonded to the yoke  22  while the magnet unit is used as a unit. 
       Modification 2 
       [0051]    Alternatively, after the plurality of main pole magnets  24   a  are bonded to the stator  20  at predetermined intervals in a horizontal direction, the first interpole magnets  24   c  and the second interpole magnets  24   d  may be bonded so as to fill the intervals. That is, an order in which the field magnets  24  are bonded to the yoke  22  is not particularly limited, and the field magnets  24  may be assembled in an arbitrary order as long as the separation of the field magnets  24  from the yoke  22  is prevented. 
       Modification 3 
       [0052]    A case in which each of the first and second interpole magnets  24   c  and  24   d  is magnetized in a direction perpendicular to the direction of the magnetic pole of the main pole magnet  24   a  has been described in the embodiment, but the invention is not limited thereto. The first and second interpole magnets  24   c  and  24   d  may be magnetized so as to have a gradient with respect to the direction perpendicular to the direction of the magnetic pole of the main pole magnet  24   a.    
       Modification 4 
       [0053]    A case in which the width Wc of the first interpole magnet  24   c  and the width Wd of the second interpole magnet  24   d  are equal to each other has been described in the embodiment, but the width Wc and the width Wd may be different from each other under a condition in which the magnetic pole pitch Wp is constant. 
         [0054]    The invention has been described using specific words and phrases on the basis of the embodiment, but the embodiment merely shows the principle and application of the invention and allows various modifications and the changes of disposition without departing from the scope of the invention that is defined in claims.