Abstract:
A linear motor assembly includes two stators extending in parallel and having salient poles arranged at a predetermined interval on opposing surfaces and a mover having three types of mover blocks. The mover blocks are made up of three-phase alternating current coils configuring magnetic poles of three phases and permanent magnets arranged in alternating polarities on two surfaces of the mover blocks opposing each of the two stators. The mover blocks are movable between the two stators along a direction in which the stators extend. A plurality of linear motors are arranged in parallel with respect to a travel direction of the movers, and the stators provided between adjacent movers are integrally formed such that they have said salient poles on the two surfaces opposing these movers.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Japanese Patent Application No. 2009-53518, filed on Mar. 6, 2009, which is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to linear motors used in industrial machines such as machine tools. 
     2. Description of the Related Art 
     Linear motors have conventionally been used in industrial machines such as machine tools for realizing high-speed and high-accuracy. Among such linear motors, there are some that have realized low cost particularly in long-stroked machines by disposing expensive permanent magnets on the mover side and thus allowing the use of fewer permanent magnets. (For example, see Japanese Patent Laid-Open Publication No. 2007-318839 below.) An example of a conventional linear motor will be explained with reference to  FIGS. 7 through 9 .  FIG. 7A  is a diagram showing a schematic structure of a conventional linear motor, and  FIG. 7B  and C show arrangements of permanent magnets.  FIG. 8  is a sectional diagram of the linear motor in  FIG. 7A  taken along a line C-C.  FIG. 9  is a connecting diagram of coils wound in a linear motor. 
     A linear motor has two stators  52   a ,  52   b  extending in parallel and a mover  51  movable between the stators  52   a ,  52   b  along a direction in which the stators  52   a ,  52   b  extend. 
     The stators  52   a ,  52   b  are formed by laminating magnetic steel sheets. The stators  52   a ,  52   b  have salient poles  50  on surfaces opposing each other at a predetermined pitch, at pitch P, for example. Further, the stators  52   a ,  52   b  are prepared in a predetermined length Las shown in  FIG. 7A . A plurality of stators  52   a ,  52   b  are disposed along the stroke of the mover  51  in a traveling direction of the mover  51 . The stators  52   a ,  52   b  are fixed, for example, on a base  72  of a machine tool (shown in  FIG. 8 ). Specifically, as shown in  FIG. 8 , the stators  52   a ,  52   b  are fixed by a bolt  71  such that a bottom face  74  of the stator contacts the base  72 . 
     On the other hand, the mover  51  is movably supported in the X-axis direction in  FIG. 7  by a rolling guide or the like provided between the base  72  and a table (now shown) and fixed to the table. The mover  51  has mover blocks  53 ,  54 ,  55  formed by laminating magnetic steel sheets. The mover block  53  is a mover block for the U-phase, the mover block  54  is a mover block for the W-phase, and the mover block  55  is a mover block for the V-phase. The mover blocks  53 ,  54 ,  55  are arranged such that they are relatively displaced by 120°, that is, by one third of the pole pitch P of the stators  52   a ,  52   b , in the X-axis direction which is the direction of travel of the mover  51 . A part of the mover blocks  53 ,  54 ,  55  are in some cases mechanically connected to each other in order to maintain dimensional accuracy between the blocks. 
     Three-phase alternating current coils are wound around each of the mover blocks  53 ,  54 ,  55 . That is, a three-phase alternating current coil  56  for the U-phase is wound around the mover block  53 , a three-phase alternating current coil  57  for the W-phase is wound around the mover block  54 , and a three-phase alternating current coil  58  for the V-phase is wound around the mover block  55 , respectively. The mover blocks  53 ,  54 ,  55  around which the three-phase alternating current coils  56 ,  57 ,  58  are wound are integrally formed by a mold resin  76 . 
     Permanent magnets  59 ,  64  are arranged on the surface of the mover blocks  53 ,  54 ,  55  such that N and S poles alternate. Specifically, as shown in  FIGS. 7B , C, three pairs of permanent magnets, a pair comprising an N and an S, are arranged at a pitch P. Here, as shown in  FIG. 7A , supposing that the stator  52   a  side is SIDE-A and the stator  52   b  side is SIDE-B, the permanent magnets  59  on the SIDE-A and the permanent magnets  64  on the SIDE-B are arranged such that the polarity as seen from the SIDE-A is opposite to the polarity as seen from the SIDE-B. 
     The three-phase alternating coils  56 ,  57 ,  58  are connected in a star connection as shown in  FIG. 9 . As shown in  FIG. 7A , for example, when a current is applied to the three-phase alternating current coils  56 ,  57 ,  58  from U in the directions of V and W, a magnetic flux  62  is excited in the linear motor. 
     Now, the operation of the linear motor will be described. When current is applied to the three-phase alternating current coils  56 ,  57 ,  58 , the mover blocks  53 ,  54 ,  55  are excited in the positive direction or in the negative direction on the Y-axis (refer to  FIG. 7A ). At that time, out of the permanent magnets  59 ,  64 , magnetic flux of the permanent magnets arranged in the same magnetization direction as the direction in which the alternating current coils is excited will be strengthened. On the other hand, magnetic flux of the permanent magnets arranged in the opposite direction of the direction in which the alternating coils is excited will be weakened. Accordingly, the permanent magnets  59  and  64  will be excited such that the polarities will be opposite to each other, that is, one will serve as the N pole and the other will serve as the S pole. Magnetic fluxes having passed through the respective mover blocks  53 ,  54 ,  55  and the stator  52   a ,  52   b  sides form a flux path as shown by reference numeral  62  in  FIG. 7A . At this time, magnetic attractive force is generated depending on the positions of the mover  51  and the stators  52   a ,  52   b , generating thrust in the mover  51 , resulting in a movement of the mover  51 . 
     The magnetic flux flow will now be explained in further detail. Suppose that current is directed from the U-phase to the V and W-phases, that is, in the winding direction shown in  FIG. 7A  in the case of three-phase alternating current coil  56  and in the opposite direction of the winding direction shown in  FIG. 7A  in the case of three-phase alternating current coils  57 ,  58 . As a result, the SIDE-A becomes the S-pole and the SIDE-B becomes the N-pole in the case of the mover block  53 . In contrast, in the case of mover blocks  54 ,  55 , the SIDE-A becomes the N-pole and the SIDE-B becomes the S-pole. Consequently, as shown in  FIG. 7A , a magnetic path  62  is formed such that the magnetic flux from the mover block  53  passes through the stator  52   b  to the mover blocks  54 ,  55 , then through the stator  52   a  and back to the mover block  53 . As a result, magnetic attractive force in the X-axis direction acts on the mover  51  and therefore thrust is generated. 
     SUMMARY OF THE INVENTION 
     However, the above-mentioned conventional linear motors had drawbacks as described below. 
     Heavy workpieces need to be driven when driving a table of a large machine tool. A large thrust is often obtained by using a plurality of movers  51 . In that case, it may be possible to arrange a plurality of linear motors in parallel in the travel direction of the mover  51 , that is, in the Y-axis direction in  FIG. 7A  so as to increase thrust. However, the installation area of the linear motors in the Y-axis direction becomes large as a result of arranging a plurality of linear motors in parallel in the Y-axis direction. This causes a problem that the linear motors do not fit into a machine space. 
     Further, as is disclosed in Japanese Patent Publication No. 2007-31 8839, the stators are prepared in a predetermined length L and a plurality of stators are disposed along the stroke of the mover in the direction of travel thereof. At this time, adjacent stators are arranged such that a slight clearance is formed in a boundary portion formed therebetween. This is to allow removal of only a target stator for replacement in the case where chips from cutting enter an air gap between a mover and a stator, for example, and the stator located at the center of the stroke breaks. However, since magnetic flux passes through the clearance in the boundary portion while the linear motor is in operation, magnetic resistance increases in that clearance. In the case where a mover is located between two adjacent boundary portions, that is, when a mover is located on the inside of both ends of a stator, there is no increase of magnetic resistance due to a magnetic flux passing through a clearance in the boundary portion, since a magnetic flux does not pass through the boundary portion. However, when the mover  51  passes through the boundary portion  101  as shown in  FIG. 7A , the magnetic flux  62  passes through the boundary portion  101 , and magnetic resistance increases due to the clearance in the boundary portion  101 . There is a problem that thrust ripple is generated, since the magnetic flux intensity of the magnetic flux  62  varies depending on the position of the mover  51 . 
     As shown in  FIG. 8 , the stators  52   a ,  52   b  of the linear motor are fixed to a base  72 . Specifically, a stator bottom face  74  corresponding to the lower surfaces of the stators  52   a ,  52   b  is fixed so as to be in contact with a base  72 . However, there is a problem that the rigidity of the stators  52   a ,  52   b  is low since a stator top face  73  corresponding to the upper surfaces of the stators  52   a ,  52   b  is not fixed. Particularly, in the case of conventional linear motors having stators  52   a ,  52   b  that are constructed by laminating magnetic steel sheets, the magnetic steel sheets are laminated in a direction perpendicular to a magnetic attractive force. As a result, a force working in the direction to cause lateral displacement acts on the magnetic steel sheets, making rigidity of the stators  52   a ,  52   b  particularly low. 
     Further, in such stators  52   a ,  52   b , since only the stator top face  73  is bent by the magnetic attractive force, the air gap between the mover  51  and the stators  52   a ,  52   b  becomes narrow only at the stator top face  73 . Further, pieces of the stators  52   a ,  52   b  are arranged in the travel direction of the mover  51 , and the rigidity of each of the stators  52   a ,  52   b  varies depending on the lamination states of the magnetic steel sheets. Accordingly, the air gap between the mover  51  and the stators  52   a ,  52   b  varies depending on the position of the stator  52   a ,  52   b . As a result, there is a drawback that the motor thrust varies depending on the positions of the stators  52   a ,  52   b.    
     Yet further, in a conventional linear motor, electricity is applied to three-phase alternating current coils  56 ,  57 ,  58  disposed on the mover  51  side to excite the stators  52   a ,  52   b  via the air gap. Since the magnetic resistance of the air gap is high, the smaller the air gap, the higher the thrust. However, since stators  52   a ,  52   b  bend as mentioned above, the air gap needs to be predetermined taking into consideration the amount of bending. Consequently, the air gap must be made wider than desired, resulting in a problem that the motor thrust is reduced. Still further, from the aspect of motor control, gain must be increased to improve feedback controllability. However, increased gain causes the stators with low rigidity to vibrate. This leads to a problem that positional error becomes large due to the fact that the gain cannot be increased up to a desired level, resulting in a deteriorated level of machine tool accuracy and machined surface quality 
     The present invention aims to solve at least one of the drawbacks, and one purpose of the present invention is to provide a linear motor capable of attaining as small an installation area as possible when a multiple number of linear motors are disposed in parallel with respect to the travel direction of a mover. 
     Another purpose of the invention is to provide a linear motor capable of reducing thrust ripple generated depending on the position of a mover in the case where a plurality of linear motors are disposed in parallel with respect to the travel direction of a mover. 
     Yet another purpose of the present invention is to provide a linear motor capable of preventing variation in motor thrust that occurs depending on the position of a stator. 
     Still another purpose of the present invention is to provide a linear motor capable of improving motor thrust. 
     Another purpose of the present invention is to provide a linear motor capable of improving accuracy of machining tools and machined surface quality. 
     SUMMARY OF THE INVENTION 
     A linear motor of the present invention comprises two stators extending in parallel and having salient poles arranged at a predetermined interval on opposing surfaces, a mover having three types of mover blocks made up of three-phase alternating current coils configuring magnetic poles of three phases and permanent magnets arranged in alternating polarities on two surfaces of the mover blocks opposing each of the two stators, and movable between the two stators along a direction in which the stators extend, wherein a plurality of linear motors are arranged in parallel with respect to a travel direction of the mover, and the two stators provided between adjacent movers are integrally formed such that they have the salient poles on the two surfaces opposing these movers. 
     The linear motor may further include a base contacting a bottom face of the stator for fixing the stator, two stator installation members provided outside of outermost stators located on the outer side in a perpendicular direction with respect to the travel direction of the mover, the outermost stators being stators of two linear motors on an outermost side of the plurality of linear motors arranged in parallel, the two stator installation members extending up to a height substantially matching a height from the base to a top face of the outermost stators, and two plate-like supporting members connected and fixed to a top face of the outermost stators and a top face of the two stator installation members. The outermost stator may be fixed to the base on a bottom face thereof, and may be fixed to the stator installation member via the plate-like supporting member on a top face thereof. 
     Further, the stators of two linear motors on the outermost side of the plurality of linear motors arranged in parallel and located on the outer side in a perpendicular direction with respect to the travel direction of the mover may have the same shape as the integrally formed stators. 
     Yet further, the integrally formed stators are stators of two linear motors located on the outermost side of a plurality of linear motors arranged in parallel, and may be formed such that a width thereof in the direction perpendicular to the travel direction of the mover is made smaller than the outermost stator located on the outer side with respect to the travel direction of the mover. 
     According to the linear motor of the present invention, it is possible to attain as small an installation area as possible and it is also possible to reduce thrust ripple generated depending on the position of a mover in the case where a plurality of linear motors are disposed in parallel with respect to the travel direction of a mover. Also, it is possible to prevent the motor thrust from varying depending on the position of the stator. Further, since it is possible to install the air gap between the stator and the mover at a predetermined pitch, it is possible to improve motor thrust. Still further, with regard to the aspect of motor control, improvement in rigidity will allow increase in gain which leads to improvement of controllability of feedback control, thereby reducing positional error, which will then lead to improvement in precision of machine tools and machined surface quality. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing a schematic construction of a linear motor according to the present embodiment. 
         FIG. 2  is a diagram showing an installation structure of a linear motor according to the present embodiment. 
         FIG. 3  is a perspective view of a stator. 
         FIG. 4  is a diagram of two linear motors disposed in parallel with respect to the travel direction of a mover. 
         FIG. 5  is a diagram showing another installation structure of a linear motor according to another embodiment. 
         FIG. 6A  is a diagram showing an example of a construction of a linear motor with different salient pole positions to which the present invention has been applied. 
         FIG. 6B  shows arrangements of the permanent magnets. 
         FIG. 6C  shows arrangements of the permanent magnets. 
         FIG. 7A  is a diagram showing a schematic construction of a conventional linear motor. 
         FIG. 7B  is a diagram showing arrangements of the permanent magnets. 
         FIG. 7C  is a diagram showing arrangements of the permanent magnets. 
         FIG. 8  is a sectional view taken along a line C-C in  FIG. 7A . 
         FIG. 9  is a connecting diagram of coils wound in a linear motor. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Hereinafter, embodiments of a linear motor according to the present invention will be explained with reference to the drawings. Explanation will now be given of linear motors arranged in two rows parallel to the travel direction of a mover, as an example. The present invention is not limited to linear motors arranged in two rows but is also applicable to linear motors arranged in multiple rows. 
       FIG. 1  is a diagram showing a schematic construction of a linear motor according to the present embodiment.  FIG. 2  is a drawing showing an installation structure of a linear motor according to the present embodiment.  FIG. 3  is a perspective view of a stator. Here, construction that is similar to the linear motor explained as a related art will be denoted by similar reference numerals, and detailed description thereof will be omitted. 
     First, the installation structure of a linear motor will be explained. The cross-sectional shape of a base  72  is U-shaped. In  FIG. 2 , reference numerals of the respective parts of the base  72  represent the following. That is,  85  represents a U-shaped groove formed in the base  72 ,  82  represents a U-shaped groove surface wall formed in a side wall of the base  72 , and  84  represents a U-shaped end portion, in other words, a base top face corresponding to the top face of the base  72 . The base top face  84  is formed such that the height thereof is substantially the same as the height of the stator top face  73 . A plate-like supporting member  81  in the form of a flat plate is disposed so as to form a bridge over the base top face  84  and the stator top face  73  of the stators  52   a ,  52   b  located on the outside of the linear motor in the Y-direction (refer to  FIG. 1 ) (hereinafter simply referred to as the outermost stator). A plurality of bolt holes  77  are formed in the plate-like supporting member  81  as shown in  FIG. 3 . The plate-like supporting member  81  is fixed to the base top face  84  by a bolt  83 , and the plate-like supporting member  81  is fixed to the stator top face  73  of the outermost stators  52   a ,  52   b  by a bolt  71 . Consequently, the outermost stators  52   a ,  52   b  are fixed to the bottom of the U-shaped groove  85  of the base  72  via a bolt  71 , while it is fixed to the base top face  84  of the base  72  via the plate-like supporting member  81  fixed to the stator top face  73 . While the present embodiment had been described with reference to the case where the outermost stators are the stators located on the outside of the linear motor in the Y-direction (refer to  FIG. 1 ), in the case of two or more rows of linear motors arranged in parallel, the outermost stator refers to the stators of the two linear motors located on the outermost side of the plurality of linear motors arranged in parallel and located on the outside in the Y-direction, respectively. 
     As described above, since the stator top face  73  of the outermost stators  52   a ,  52   b  is supported by the base top face  84  via the plate-like supporting member  81 , magnetic attractive force acting between the mover  51   a  and the outermost stator  52   a  and between the mover  51   b  and the outermost stator  52   b  prevents the outermost stators  52   a ,  52   b  from bending toward the movers  51   a ,  52   b , respectively. Accordingly, the air gap formed between the mover  51   a  and the outermost stator  52   a , and that formed between the mover  51   b  and the outermost stator  52   b , may be maintained constant between the stator top face  73  to the stator bottom face  74 . Also, since the stator top face  73  of the outermost stators  52   a ,  52   b  is fixed to the base  72  by the plate-like supporting member  81 , rigidity of the outermost stators  52   a ,  52   b  increases. As a result, it will be possible to prevent the motor thrust from varying depending on the positions of the outermost stators  52   a ,  52   b . Further, since it is possible to provide the air gap formed between the mover  51   a  and the outermost stator  52   a , and that formed between the mover  51   b  and the outermost stator  52   b , at a predetermined clearance, it will no longer be necessary to set a wider air gap in consideration of bending of the outermost stators  52   a ,  52   b , and the motor thrust will thereby improve. Also, in terms of motor control, increased rigidity will increase gain, which will in turn improve feedback controllability, which will then reduce positional error, leading to improved accuracy of machine tools and machined surface quality. 
     In the case of arranging a plurality of linear motors of the prior art in parallel with respect to the travel direction of the mover by using such a configuration, it would be necessary to provide a U-shaped groove side surface wall  107  between adjacent linear motors, as shown in  FIG. 4 , for fixing the stator top face  73  via the plate-like supporting member  81 . By doing so, however, the installation area of the linear motors may become too large such that the linear motors do not fit into the space for the machine. Also, the base top face  108  shown in  FIG. 4  requires a wide machining range in the case of a machine with a longer stroke, which would require numerous tapping for fixing more bolts  83 , resulting in high machining cost, which is a problem. 
     In order to solve such a problem, the linear motor of the present embodiment is characterized in that two stators provided between adjacent movers  51   a ,  51   b  are integrally formed. Integrally formed integral stators will be hereinafter referred to as the integral stator  52   c . The integral stator  52   c  is characterized by having salient poles  50  on the respective two surfaces opposing the movers  51   a ,  51   b . The integral stator  52   c  is fixed to the base  72  by the bolts  71 , as shown in  FIG. 2 . 
     In a linear motor thus constructed, the integral stator  52   c  has formed thereon salient poles  50  on the two surfaces opposing the movers  51   a ,  51   b  such that the magnetic attractive force acting between the mover  51   a  and the integral stator  52   c  and that acting between the mover  51   b  and the integral stator  52   c  are equivalent but act in opposite directions, therefore cancelling out the magnetic attractive forces. Accordingly, it is possible to prevent the integral stator  52   c  from bending toward the movers  51   a ,  51   b , respectively, and therefore it is possible to attain the advantage mentioned in the foregoing paragraph. Further, since magnetic attractive force does not act on the integral stator  52   c  only in one direction toward the movers  51   a ,  51   b  as in the case with the outermost stators  52   a ,  52   c , it would be unnecessary to fix the integral stators  52   c  to the U-shaped groove side surface wall  107  via the plate-like supporting member  81 , as shown in  FIG. 4 . Consequently, it would be unnecessary to provide a U-shaped groove side surface wall  107  between adjacent linear motors, whereby installation area of plural linear motors arranged in parallel with respect to the travel direction of the mover  51  may be made small. 
     Further, the installation area of the linear motor according to the present embodiment may be made even smaller when arranging plural linear motors in parallel with respect to the travel direction of the mover  51 . Specific description will be given hereafter. 
     As shown in  FIG. 1 , the linear motor will be excited by a magnetic flux  110  when electrical current is applied to the three-phase alternating current coils  56 ,  57 ,  58  of the movers  51   a ,  51   b  from U to the directions of V and W. At this time, the magnetic flux  110  is generated at a stator yoke  61  of the outermost stators  52   a ,  52   b  from mover blocks  54 ,  55  to the mover block  53 . Accordingly, the width of the stator yoke  61  or the length of the stator yoke  61  in the Y-direction needs to be selected such that magnetic flux saturation does not occur. 
     However, in the case of the integral stator  52   c , as shown in  FIG. 1 , the magnetic flux  110  is generated in the Y-direction perpendicular to the travel direction of the movers  51   a ,  51   b . The width of the stator yoke  102  having a length corresponding to the length in the travel direction of the movers  51   a ,  51   b  will be ensured. Accordingly, magnetic saturation will not occur at the stator yoke  102 , and therefore it will be possible to make the width of the stator yoke  102  smaller than the total length obtained by adding the width of the stator yoke  61  of the outermost stator  52   a  and the width of the stator yoke  61  of the outermost stator  52   b . Consequently, a smaller width of the stator yoke  102  can be obtained with the integral stator  52   c  than in the case of simply integrating two stators provided between adjacent movers  51   a ,  51   b , thereby further reducing the installation area of the linear motor. 
     In the linear motor of the prior art, as shown in  FIG. 7A , the stators  52   a ,  52   b  are made in a predetermined length L and a plurality of such stators  52   a ,  52   b  are disposed along the stroke of the mover  51  in the travel direction of the mover  51 . At this time, if a clearance is provided in the boundary portion  101  between the adjacent stator  52   a  and the adjacent stator  52   b , the magnetic flux  62  will pass through this clearance, thereby increasing the magnetic resistance. When the mover  51  passes the position where the boundary potion  101  is located in the X-axis direction, the magnetic flux  62  passes the boundary portion  10 , whereby the magnetic resistance is increased. On the other hand, in the case where the mover  51  does not pass the position where the boundary  101  is located in the X-axis direction, the magnetic flux  62  does not pass the boundary portion  10 , which results in low magnetic resistance. In this way, there had been a drawback that thrust ripple becomes large due to variation of the magnetic flux  62  generated inside the stators  52   a ,  52   b  depending on the position of the mover  51 . 
     In a linear motor configured as described above, the direction of generation of the magnetic flux  110  generated inside the integral stator  52   c  is in the Y-direction which is perpendicular to the travel direction of the movers  51   a ,  51   b . Consequently, the magnetic flux  110  generated at the stator yoke  102  of the integral stators  52   c  does not pass the boundary portion  101  of the integral stator  52   c . Accordingly, variation in the magnetic resistance of the stator yoke is reduced and the thrust ripple is reduced compared to the case where a plurality of prior art linear motors are arranged in parallel with respect to the travel direction of the mover. For example, in the case where two linear motors are arranged in two rows with respect to the travel direction of the mover  51 , variation of magnetic resistance of the stator yoke  61 ,  102  in the linear motor of the present invention becomes one half compared to a prior art linear motor, whereby thrust ripple is reduced. Further, the more linear motors are disposed with respect to the travel direction of the mover  51 , the more integral stators  52   c  are disposed between the movers  51 , the integral stators  52   c  generating magnetic flux  110  in the direction perpendicular to the travel direction of the mover  51 , thus resulting in higher thrust ripple reduction effect. 
       FIG. 5  shows an installation structure of a linear motor of another embodiment. While the U-shaped groove side surface wall  82  in  FIG. 1  had been formed by cutting into a part of the base  72 , in  FIG. 5 , a U-shaped cross-section is formed by fixing a stator installation member  90  to the base  72  by a bolt. As a result, the outermost stators  52   a ,  52   b  are installed on the top face of the stator installation member  90  via the plate-like supporting member  81 , whereby similar effects to those obtained by the linear motor of the aforementioned embodiment can be obtained. 
     Further, although not shown, it would be possible to reduce the costs of jigs such as a die for making the stator  52 , by making the shapes of the outermost stators  52   a ,  52   b  in  FIG. 1  the same as that of the integral stator  52   c . However, in this case, the size of the width of the stator yoke  102  of the integral stator  52   c  needs to be made the same as that of the stator yoke  61  of the outermost stators  52   a ,  52   b , which slightly increases the installation area of the linear motor. 
     While the salient poles  50  of the stators  52   a ,  52   b ,  52   c  shown in  FIG. 1  are all in the same positions in the X-axis direction, it is possible to obtain the same effect as that with the present invention even if not all the salient poles  50  are in the same positions. The reason for this will be described below. 
       FIG. 6  shows an example of a configuration adopting a structure of a linear motor of the present invention with different positions of the salient poles. The outermost stator  52   a  has a salient pole  50   a  on the surface opposing the mover  51   a . The outermost stator  52   b  has a salient pole  50   b  on the surface opposing the mover  51   b . The integral stator  52   c  has a salient pole  50   cb  on the surface opposing the mover  51   a , and a salient pole  50   ca  on the surface opposing the mover  51   b . The salient poles  50   ca ,  50   cb  are displaced by one half the pitch P in the travel direction of the mover  51  with respect to the salient poles  50   a ,  50   b . On the other hand, magnets  64  and  59  placed on the SIDE-A, SIDE-B of the mover blocks  53 ,  54 ,  55  are arranged as shown in  FIG. 6B  and  FIG. 6C . In other words, only the magnets on the SIDE-B shown in  FIG. 7C  are arranged such that the N-poles and S-poles are reversed with respect to the arrangement of magnets of an embodiment of a linear motor according to the present invention shown in  FIG. 7B  and  FIG. 7C . It also means that the magnetic poles of the magnets are displaced by one half the pitch P. Consequently, a magnetic attractive force the same as that in  FIG. 1  is generated around the mover  51 , and therefore the same thrust is generated even with the structure of a linear motor shown in  FIG. 6 . 
     As described above, since the same performance of a linear motor may be obtained by a linear motor structure shown in  FIG. 6 , and the width of the integral stator  52   c  and the magnetic flux  110  generated inside the integral stator  52   c  are the same as those in  FIG. 1 , it is possible to obtain similar effects to those obtained by the present invention. 
     The same is true with a structure where the salient poles  50   a ,  50   ca ,  50   cb  are at the same positions and only the salient pole  50   b  is displaced by one half the pitch P, or where the salient poles  50   b ,  50   ca ,  50   cb  are at the same positions and only the salient pole  50   a  is displaced by one half the pitch P. As described hereinabove, structures where the salient poles  50  of the respective stators  52  are displaced in the travel direction of the mover  51  yield similar effects to those obtained by the present invention, and therefore such structures are included in the present invention. 
     While explanation had been given for linear motors having a mover  51  constructed as shown in  FIG. 1  and  FIG. 6  in all of the foregoing embodiments, the structure of the mover  51  is not limited thereto. The present invention is applicable to a linear motor having a different type of mover  51  structure to those shown in  FIG. 1  and  FIG. 6  as long as the shape of the stator  52  is the same.