Abstract:
A relative linear motion apparatus comprising: a first structure having at least a pair of inner wall surfaces opposing to each other; a second structure arranged between the pair of inner wall surfaces, the second structure being movable in linear motion relative to the first structure; at least two rectilinear guides arranged between the first structure and the second structure; and a displacement absorbing device arranged on at least one of the first structure and the second structure so as to allow at least one of the two rectilinear guides to move in a intersecting direction against the wall surfaces.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a relative linear motion apparatus in which a second structure is movable in linear motion relative to a first structure, for example in which the second structure formed like a plate is put in the first structure formed like a frame, plurality of rectilinear guides are arranged between the first structure and the second structure so that the second structure is movable relative to the first structure. 
     In a known art, the Japanese Patent Laid-open Publication No. HEI 7-190053 discloses a mounting plate for a rectilinear guide in order to allow misalignment such as an installation error caused when rectilinear guide is installed. FIG. 15 shows this mounting plate. The mounting plate  1  is put between the rectilinear guide  5  and a fixed member  2 , and allows the rectilinear guide  5  to move in a perpendicular direction {circle around ( 1 )} against the fixed member  2 . The mounting plate  1  consists of fixed portion  6  mounted to the fixed member  2 , attached portion  4  mounted to a movable block  3  of the rectilinear guide  5 , and thin board portion  7  which connect the fixed portion  6  with the attached portion  4 . 
     Since the misalignment such as the installation error deforms the thin board portion  7 , the attached portion  4  moves relative to the fixed portion  6  in the perpendicular direction {circle around ( 1 )} and the mounting plate  1  absorbs the misalignment. 
     SUMMARY OF THE INVENTION 
     In some cases, a relative linear motion apparatus comprises a fixed member (first structure) having at least a pair of inner wall surfaces opposing to each other, a movable member (second structure) arranged between the pair of inner wall surfaces, two rectilinear guides arranged between the fixed member and the movable member. The movable member guided by the rectilinear guides slides relative to the fixed member in linear motion to a direction parallel to the inner wall surfaces of the fixed member. 
     In such a relative linear motion apparatus, when the parallelism of one rectilinear guide to the other rectilinear guide is spoiled by an installation error, or when installing position for the rectilinear guide is under slight error, the movable member can not slide smoothly. Therefore it is necessary to install the rectilinear guides with high accuracy. Also, even if the rectilinear guides are installed with high accuracy, since the rectilinear guides are applied a load caused by thermal expansion and contraction difference between the fixed member and the movable member in a perpendicular direction to the wall, the movable member sometimes can not slide smoothly 
     In case the conventional mounting plate  1  is used for the relative linear motion apparatus described above, deformation of the thin board portion  7  is small and the mounting plate  1  can not absorb a large error. Therefore, though the mounting plate  1  can absorb small misalignment, the mounting plate  1  can not sufficiently absorb thermal expansion and contraction difference between the fixed member and the movable member. 
     Also the conventional mounting plate  1  allows the movable member to move slightly not only in the perpendicular direction {circle around ( 1 )} but also in a horizontal direction {circle around ( 2 )} (which is parallel to the inner wall surface and perpendicular to a sliding direction of the movable member). So the movable member can not be guided with good rigidity. Further, it is difficult to process the thin board portion  7  on the mounting plate  1 . 
     An object of the present invention is to provide a relative linear motion apparatus which can sufficiently absorb the installing error of rectilinear guides or thermal expansion and contraction difference between the fixed member and the movable member, and guide the movable member with good rigidity. 
     In order to achieve the above-mentioned object, the relative linear motion apparatus according to the present invention is constructed so as to comprise: a first structure having at least a pair of inner wall surfaces opposing to each other; a second structure arranged between the pair of inner wall surfaces, the second structure being movable in linear motion relative to the first structure; at least two rectilinear guides arranged between the first structure and the second structure; and a displacement absorbing device arranged on at least one of the first structure and the second structure so as to allow at least one of the two rectilinear guides to move in a intersecting direction against the wall surfaces. The two rectilinear guides make the second structure to be movable in linear motion relative to the first structure. 
     When the second structure is arranged between the pair of inner wall surfaces of the first structure through the rectilinear guides, and a processing error including an installation error or thermal expansion and contraction difference between the first structure and the second structure occurs, the second structure could not smoothly slide relative to the first structure. 
     According to the invention described above, even if the processing error including the installation error occurs, or even if the thermal expansion and contraction difference occurs, the displacement absorbing device can absorb the displacement of the rectilinear guide in the intersecting direction against the wall surfaces. Therefore the rectilinear guides are not applied an excessive load and work smoothly, and the second structure smoothly slide relative to the first structure. If the displacement absorbing device allows at least one of the two rectilinear guides to move only in the intersecting direction against the wall surfaces (for example only in the perpendicular direction to the wall surfaces), and restricts the rectilinear guide to move in a horizontal direction (which is parallel to the inner wall surface and perpendicular to a sliding direction of the second structure), it is possible to guide the second structure with good rigidity. 
     In the relative linear motion apparatus to which the present invention is applied, at least one of the two rectilinear guides moves in the intersecting direction against the wall surfaces due to a processing error including an installation error caused when said at least one of the two rectilinear guides is installed or thermal expansion or thermal contraction difference between the first structure and the second structure. 
     The relative linear motion apparatus of the invention is effective in absorbing such large displacement. 
     In a preferred embodiment of the present invention, the displacement absorbing device is arranged between (i) one of said first structure and said second structure and (ii) one of said two rectilinear guides, said displacement absorbing device having an elastic beam which can deflect toward the intersecting direction against the wall surfaces. 
     According to this embodiment, an elastic beam can deflect and absorb the processing error or the thermal expansion and contraction difference between the first structure and the second structure. 
     In a further embodiment, said elastic beam has span which is capable of deflection, and the span is longer than width of said one of the two rectilinear guides. 
     According to this embodiment, the span of the elastic beam become longer, and the deflection of the elastic beam become larger. Therefore the elastic beam can absorb the large processing error or the large thermal expansion and contraction difference. 
     In a further embodiment, a spacer is arranged between said elastic beam and said one of the two rectilinear guides so that said elastic beam deflects larger, the spacer having width less than the width of said one of the two rectilinear guides. 
     According to this embodiment, since the load placed on the elastic beam approaches to concentrated load from distributed load, the elastic beam deflects larger. 
     In a further embodiment, said elastic beam has both longitudinal end portions fixed to said first structure or said second structure, and said one of the two rectilinear guides is arranged in the middle of said elastic beam in a longitudinal direction thereof. 
     According to this embodiment, the elastic beam deflects with easy construction. 
     In a further embodiment, said first structure or said second structure has guide surfaces which guide said one of the two rectilinear guides to move in the intersecting direction against the wall surfaces. 
     According to this embodiment, since the rectilinear guide is guided to move in the intersecting direction against the wall surfaces, the rectilinear guide is prevented from moving in another direction except the intersecting direction. For example it is possible for the rectilinear guide to move only in the perpendicular direction to the wall surfaces so as to absorb the error and not to move in the horizontal direction. Therefore the second structure can be guided with good rigidity. 
     In a further embodiment, said guide surfaces allows said one of the two rectilinear guides to move only in a perpendicular direction to the wall surfaces without occurrence of change in posture thereof. 
     According to this embodiment, the rectilinear guide is allowed to move only in the perpendicular direction to the wall surfaces, and is restricted to move in the horizontal direction. 
     In a further embodiment, each of said rectilinear guides comprises: 
     a track member formed with a rolling member rolling surface along a longitudinal direction; 
     a movable block mounted to be relatively movable to the track member formed with a rolling member circulation passage including a loaded rolling member rolling surface opposing to the rolling member rolling surface of the track member when mounted; 
     and a number of rolling members arranged in the rolling member circulation passage so as to circulate therein in conformity with the relative motion of the movable block with respect to the track rail. 
     In a further embodiment, each of movable blocks is fixed to said each of said inner wall surfaces of said first structure, and each of track members is fixed to each of edges of said second structure. 
     In a further embodiment, said track member is integrally formed with said second structure by an inserting mold. 
     In case the second structure is arranged between the pair of the inner wall surfaces of the first structure through the rectilinear guides, it is necessary to reduce the processing error including the installation error so that the second structure smoothly slides relative to the first structure. 
     According to this embodiment, since the track rail is inserted in second structure and is integrally molded with the second structure, the processing error is reduced as small as possible. Also, since component parts are reduced too, a relative linear motion apparatus of the invention can be fitted for mass production. On the contrary, if the track rail and the second structure are separately made and the track rail and the second structure are joined together with bolts and so on, the occurrence of the installing error caused by the operator&#39;s degree of aging can not be avoided. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
     FIG. 1 is a perspective view showing a relative linear motion apparatus according to a first embodiment of the present invention. 
     FIG. 2 is a cross sectional view of the apparatus shown in FIG. 1, the cross section being taken in a direction parallel to a movable member of the device. 
     FIG. 3 is a side view of the apparatus of FIG. 2 taken along the line III—III therein. 
     FIG. 4 is a plan view of the apparatus of FIG. 2 taken along the line IV—IV therein, partially in section. 
     FIG. 5 is a cross sectional view showing the deflection of the elastic beam. 
     FIG. 6 is perspective view showing a rectilinear guide put in the apparatus. 
     FIG. 7 is a cross sectional view showing the rectilinear guide, the cross section being taken in a direction normal to a track rail of the guide. 
     FIG. 8 is a cross sectional view showing a movable block of the rectilinear guide, the cross section being taken in a direction parallel to a track rail of the guide. 
     FIG. 9 is a cross sectional view showing a relative linear motion apparatus according to a second embodiment of the present invention, the cross section being taken in a direction normal to a movable member. 
     FIG. 10 is a cross sectional view showing another crossing portion of the apparatus in FIG.  9 . 
     FIG. 11 is a perspective view showing a relative linear motion apparatus according to a third embodiment of the present invention. 
     FIG. 12 is a plan view of the apparatus in FIG. 11, partially in section. 
     FIG. 13 is a cross sectional view showing a combination of a movable member and a track rail of the apparatus in FIG.  11 . 
     FIG. 14 is a cross sectional view showing another variations of the point of apparatus in FIG. 11, and includes FIG. 14A showing a first variation, FIG. 14B showing a second variation, FIG.  14 (C) showing a third variation. 
     FIG. 15 is a plan view, partially in section, of a mounting plate having a conventional structure. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 to  4  respectively show a relative linear motion apparatus according to a first embodiment of the present invention. 
     As shown in FIG. 1, This relative linear motion apparatus comprises a fixed member  11  formed like a quadrilateral frame as first structure, movable member  12  (a second structure) arranged between a pair of inner wall surfaces  11   a ,  11   b  in short sides of the quadrilateral frame, movable member  12  being formed like a plate, and a pair of rectilinear guides  13   a ,  13   b  arranged between each of the inner wall surfaces  11   a ,  11   b  and each of both edges of the movable member  12 . The inner wall surfaces  11   a ,  11   b  are parallel to each other. The movable member  12  arranged between the pair of inner wall surfaces  11   a ,  11   b  is perpendicular to the pair of inner wall surfaces  11   a ,  11   b . Also the movable member  12  slides relative to the inner wall surfaces  11   a    11   b  in a direction parallel to the inner wall surfaces  11   a    11   b.    
     This relative linear motion apparatus is used for a linear motor for example. In this case, as shown in FIG. 4 a permanent magnet  14  as a magnetic material is disposed in a frame of the movable member  12 . And a pair of coils  8 ,  8  are disposed on a pair of inner wall surfaces  11   c    11   d  in long sides of the fixed member  11 . And the movable member  12  is put between the pair of coils  8 ,  8 . Producing a magnetic field of the coils  8 ,  8  slides the movable member  12 . 
     The movable member  12  is composed of a frame  12   a , the permanent magnet  14  disposed in the frame  12   a , and rail holding portions  12   b ,  12   b  which are fixed to both edges of the frame  12   a . Track rails  16   a ,  16   b  are attached to the rail holding portions  12   b ,  12   b . This movable member  12  slides in a direction parallel to the inner wall surfaces  11   a    11   b  (in FIG. 1 vertical direction) with the track rails  16   a ,  16   b.    
     Each of the rectilinear guides  13   a ,  13   b  comprises the track rail  16   a  ( 16   b ) as a track member, and the movable block  17   a  ( 17   b ) as slide member. In this embodiment, two movable blocks  17   a ,  17   a  ( 17   b ,  17   b ) are put side by side on the track rail  16   a  ( 16   b ). Each of the track rails  16   a ,  16   b  is arranged on each of both edges of the movable member  12 . And the movable blocks  17   a ,  17   a ,  17   b ,  17   b  are arranged on the inner wall surfaces  11   a ,  11   b  of fixed member  11 . The track rails  16   a ,  16   b  slide along the movable blocks  17   a ,  17   a ,  17   b ,  17   b  without changing the position of the movable blocks  17   a ,  17   a ,  17   b ,  17   b.    
     In this embodiment, although the backs of the movable blocks  17   a ,  17   a ,  17   b ,  17   b  are attached to the inner wall surfaces  11   a ,  11   b  and the movable member  12  is arranged between the track rails  16   a ,  16   b  opposing to each other, the arrangement of the rectilinear guides  13   a ,  13   b  is not restricted to these. For example, it may be possible to turn the rectilinear guides  13   a ,  13   b  over so that the backs of the movable blocks  17   a ,  17   b  are attached to the both edges of the movable member  12  and the track rails  16   a ,  16   b  are attached to the inner wall surfaces  11   a ,  11   b . Also it may be possible to turn only one of the rectilinear guides  13   a ,  13   b  over. In this case, the track rail  16   b  is attached to the inner wall surface  11   b  in one rectilinear guide  13   b  and the back of movable block  17   a  is attached to the inner wall surface  11   a  in other rectilinear guide  13   a.    
     As shown in FIGS. 2 to  4 , the fixed member  11  is formed like a quadrilateral frame. And the movable blocks  17   a ,  17   a ,  17   b ,  17   b  are attached to the inner wall surfaces  11   a ,  11   b  in short sides of the quadrilateral frame. The movable blocks  17   a ,  17   a  attached to the inner wall surface  11   a  does not change the position. And the movable blocks  17   b ,  17   b  attached to the inner wall surface  11   b  are allowed to be movable in a perpendicular direction to the inner wall surface  11   b  so as to absorb an installation error caused when said the pair of rectilinear guides  13   a ,  13   b  are installed, or thermal expansion and contraction difference between the fixed member  11  and the movable member  12 . 
     In the inner wall surface  11   a , a fitting groove  21   a  which has a width equal to the width of the movable blocks  17   a ,  17   a  are formed so as to locate the movable blocks  17   a ,  17   a . The movable blocks  17   a ,  17   b  are fitted in the fitting groove  21   a  and fixed to the inner wall surface  11   a . In the inner wall surface  11   b , fitting groove  21   b  is formed by which the rectilinear guide  13   b  is guided to move in the direction perpendicular to the inner wall surface  11   b . The width of the fitting groove  21   b  is equal to the width of the movable blocks  17   b ,  17   b  of the rectilinear guide  13   b . The fitting groove  21   b  has a pair of wall guide surfaces opposing to each other. Being guided by a pair of wall guide surfaces of the fitting groove  21   b , movable blocks  17   b ,  17   b  move in the perpendicular direction. 
     The movable blocks  17   b ,  17   b  are attached to the inner wall surface  11   b  of the fixed member  11  through elastic beams  19 ,  19  as a displacement absorbing device. 
     As shown in FIG. 4, the elastic beam  19  has both longitudinal end portions fixed to the fixed member  11 , the movable block  17   b  is substantially arranged in the middle of the elastic beam  19  in the longitudinal direction thereof. A hollow  23  which has the same area as the elastic beam  19  is formed on an outer wall surface  22 , and the elastic beam  19  is fitted in the hollow  23 . The hollow  23  is extended to the fitting groove  21   b . A wall is penetrated by the hollow  23  and the fitting groove  21   b . The elastic beam  19  has span which is capable of deflection, and the span is longer than the width W of the movable block  17   b . And a spacer  20  is arranged between the elastic beam  19  and the movable block  17   b  so that the elastic beam  19  deflects larger. The spacer  20  has width less than the width of the movable block  17   b.    
     As shown FIG. 5, when a processing error including an installation error caused by the installation of the two rectilinear guides  13   a ,  13   b  occurs, or when thermal expansion and contraction difference between the fixed member  11  and the movable member  12  occurs, or when a deformation of the relative linear motion apparatus caused by a load from the inside or the outside of the apparatus occurs, the elastic beam  19  is deflected by a load applied from the spacer  20  to the elastic beam  19 . The elastic beam  19  is deflected by the load, as if a fixed beam is deflected by a concentrated load applied to the middle of the fixed beam. Deflecting the elastic beam  19  to the perpendicular direction allows the movable block  17   b  to move in the perpendicular direction {circle around ( 1 )} and absorbs the installing error or the thermal expansion and contraction difference or the deformation of the relative linear motion apparatus caused by the load. Since the movable block  17   b  is allowed to move only in the direction {circle around ( 1 )} perpendicular to the inner wall surface  11   b  and restricted to move in the horizontal direction {circle around ( 2 )}, it is possible to guide the movable member  12  in good rigidity. Further, In this embodiment, since elastic beam  19  is disposed only on the movable block  17   b  and is not disposed on the movable block  17   a , the movable member  12  is stably supported by the rectilinear guides  13   a ,  13   b  in the perpendicular direction {circle around ( 1 )}. 
     In order to absorb the expansion and contraction difference, it is expected that the elastic beam  19  deflect largely. Disposing the spacer between the movable member  17   b  and the elastic beam  19  the load placed on the elastic beam  19  approaches to the concentrated load from the distributed load, and deflects the elastic beam  19  larger. Furthermore, since the span of the elastic beam  19  is longer than the width W of the movable block  17   b , the deflection of the elastic beam  19  becomes all the more larger. 
     FIG.  6 . Shows the rectilinear guide  13   a  ( 13   b ). The rectilinear guides  13   a  ( 13   b ) comprises, a track rail  16   a  ( 16   b ) as a track member formed with rolling member rolling grooves  31 , 31  as rolling member rolling surfaces along a longitudinal direction thereof, a movable block  17   a  ( 17   b ) mounted to be relatively movable to the track rail  16   a  ( 16   b ), the movable block  17   a  ( 17   b ) being formed with rolling member circulation passages including loaded rolling member rolling grooves as loaded rolling member rolling surfaces opposing to the rolling member rolling grooves  31 , 31  of the track rail  16   a  ( 16   b ) when mounted, and a number of balls  33 , - - - ,  33  as rolling members arranged in the rolling member circulation passages so as to circulate therein in conformity with the relative motion of the movable block  17   a  ( 17   b ) with respect to the track rail  16   a  ( 16   b ). This rectilinear guides  13   a  ( 13   b ) is constructed so as to bear a load not only in the perpendicular direction but also in the horizontal direction. 
     The track rail  16   a  ( 16   b ) has a rectangular shape in section. Each of the right and left side surfaces of the track rail  16   a  ( 16   b ) is formed with two lines of loaded ball rolling grooves  31 , 31 . And the total of ball rolling grooves  31 , 31  is four. 
     The movable block  17   a  ( 17   b ) comprises a body portion  34  and end covers (plates)  35 ,  35  disposed on both longitudinal end sides of the body portion  34 , the body portion  34  and the end covers  35 ,  35  being secured together by means of bolts. The movable block  17   a  ( 17   b ) straddles the track rail  16   a  ( 16   b ). The movable block  17   a  ( 17   b ) is formed with the loaded ball rolling grooves  32 , 32  and the ball escape bores, while each of the end plates  35 , 35  is formed with the direction changing passages. Each of the ball escape bores linearly passes through the movable block  17   a  ( 17   b ). A fixing surface  36  attached to the inner wall surface  11   a  ( 11   b  ) or the spacer  20  is formed on the upper surface of the body portion  34 . Four screw holes  37   a , - - - ,  37   a  for fixing the inner wall surface  11   a  ( 11   b ) are formed around the fixing surface  36 , and two screw holes  37   b ,  37   b  for fixing the spacer  20  are formed inside the screw holes  37   a , - - - ,  37   a.    
     The loaded rolling member rolling grooves  32 ,  32  are opposing to the rolling member rolling grooves  31 ,  31  of the track rail  16   a  ( 16   b ), and the loaded rolling member rolling grooves  32 ,  32  and the rolling member rolling grooves  31 ,  31  compose loaded ball rolling passages. A number of balls (rolling members)  33 , - - - ,  33  are arranged in the ball circulation passages and are put between the loaded rolling member rolling grooves  32 ,  32  and the rolling member rolling grooves  31 , 31 . According to the movement of the movable blocks  17   a  ( 17   b ) along the track rail  16   a  ( 16   b ), the balls  33 , - - - ,  33  are moved (rolled) from one end to the other end of the loaded ball rolling passages and scooped by the direction changing passages of the end plates  35 ,  35  and guided by the ball escape bores, and then returned to the one end of the loaded ball rolling passages through the other one of the direction changing passages. The balls circulate in conformity with the relative motion of the movable block  17   a  ( 17   b ) with respect to the guide rail  16   a  ( 16   b ). 
     As shown in FIGS. 7 to  8 , a chain of balls are held capable of rotation and slide by retainer  44 . This retainer  44  is composed of a plurality of spacers  40 , - - - ,  40  interposed alternately between a plurality of balls  33 , - - - ,  33 , and a thin belt  41  connecting the each of the spacers  40 , - - - ,  40 . 
     A seal member  42  is disposed between the movable block  17   a  ( 17   b ) and a upper surface of track rail  16   a  ( 16   b ). Seal members  43 ,  43  are disposed between the movable block  17   a  ( 17   b ) and side surfaces of the track rail  16   a  ( 16   b ). This seal members  42 ,  43 ,  43  seal lubricating oil filled between the ball rolling grooves  31 ,  31  and the loaded ball rolling grooves  32 ,  32 . 
     FIG. 9 shows a relative linear motion apparatus according to a second embodiment of the present invention. In this embodiment, a fixed member  51  has a octagonal frame in section, a movable member  52  is cross-shaped in section. Four rectilinear guides  53   a ,  53   a ,  53   b ,  53   b  are disposed between tips of a cross and inner wall surfaces opposing to the tips. Four permanent magnets  54 , - - - ,  54  are fitted in four plate members  52   a ,  52   b ,  52   c ,  52   d  composing the cross. And four coils  55 , - - - ,  55  are attached to the fixed member so that the each of permanent magnets  54 , - - - ,  54  are put between each of the coils  55 , - - - ,  55 . The movable member  52  is moved by producing a magnetic field of the coils  55 , - - - ,  55 . 
     In one direction and in other direction crossing to one direction, rectilinear guides  53   a ,  53   a  and rectilinear guides  53   b ,  53   b  are arranged between the fixed member  51  and the plate members  52   a ,  52   b ,  52   c ,  52   d  of the movable member  52 . As the relative linear motion apparatus according to the first embodiment, movable blocks  56   b ,  56   b  are attached to the fixed member  51  through elastic beams  57 ,  57 , and are capable of moving in a direction perpendicular to the inner wall surfaces. Also, these movable blocks  56   b ,  56   b  are guided to move only in the direction perpendicular to the inner wall surfaces and restricted to move in a horizontal direction by guide surfaces. 
     At the crossing part of the movable member  52 , notches  58 , - - - ,  58  are made to reduce a rigidity of the movable member  52  slightly. Since there is a reduction in the rigidity of the crossing part, the crossing part absorbs the displacement caused by the thermal expansion and contraction of the plate members  52   a ,  52   c  in one direction or the plate members  52   b ,  52   d  in other direction. And a load which is caused by the thermal expansion and contraction of the plate members  52   a ,  52   c  is not transmitted to the plate members  52   b ,  52   d . Also, a load which is caused by the thermal expansion and contraction of the plate members  52   b ,  52   d  is not transmitted to the plate members  52   a ,  52   c  in the same way. 
     FIG. 10 shows another variation of the crossing part. In this variation, four plate members  52   a ,  52   b ,  52   c ,  52   d  which compose the cross are connected with gussets  59 , - - - ,  59 . The rigidity of gussets  59 , - - -,  59  are reduced. In this case, the gussets  59 , - - - ,  59  absorb the displacement caused by the thermal expansion and contraction of the plate members  52   a ,  52   c  in one direction or the plate members  52   b ,  52   d  in other direction. And a load which is caused by the thermal expansion and contraction of the plate members  52   a ,  52   c  is not transmitted to the plate members  52   b ,  52   d . Also, a load which is caused by the thermal expansion and contraction of the plate members  52   b ,  52   d  is not transmitted to the plate members  52   a ,  52   c  in the same way. 
     In this embodiment, making the movable member in the shape of the cross give good rigidity to the movable member  52  itself. Also, since an area of the coils  55 , - - - ,  55  and the permanent magnets  54 , - - - ,  54  become larger, an output of the primary drive become larger. 
     Further, in the described embodiment of the relative linear motion apparatus, the elastic beam  57  is arranged on only one side of the rectilinear guides  53   a ,  53   b  opposing to each other so that only one side of the rectilinear guides  53   a ,  53   b  moves in the perpendicular direction. However, in an alternation, it may be adopted that the elastic beams  57 ,  57  are arranged on both rectilinear guides  53   a ,  53   b  so that both sides of the rectilinear guides  53   a ,  53   b  move in the perpendicular direction. 
     Further, in the described embodiment of the relative linear motion apparatus, the elastic beams (plate)  57  are attached to the fixed member  51 . However, in an alternation, it may be adopted that the elastic beam  57 ,  57  are attached to the movable member  52 . 
     Still furthermore, the shape of the fixed member  51  in cross section is not restricted to a quadrilateral or an octagon, and alternations and many other changes such as a polygon or a circle or a substantially -shaped cross section of which one side is opened may be adopted. As to the movable member  52 , the shape of the movable member  52  in cross section is not restricted to a plate or an crossing which miniaturize the relative linear motion apparatus, and alternations and many other changes such as a cylinder may be adopted. 
     FIGS. 11 to  13  show a relative linear motion apparatus according to a third embodiment of the present invention. In this embodiment, the relative linear motion apparatus comprises a fixed member  11  formed like a quadrilateral frame as first structure, movable member  12  arranged between a pair of inner wall surfaces  11   a    11   b  in short sides of the quadrilateral frame as second structure, the movable member  12  being formed like a plate as a second structure, and a pair of rectilinear guides  13   a ,  13   b  arranged between each of the inner wall surfaces  11   a ,  11   b  and each of both edges of the movable member  12 . The movable member  12  slides relative to the inner wall surfaces  11   a ,  11   b  in a direction parallel to the inner wall surfaces  11   a ,  11   b.    
     Each of the rectilinear guides  13   a ,  13   b  comprises the track rail  16   a  ( 16   b ) as a track member, and the movable block  17   a  ( 17   b ) as slide member. Each of the track rails  16   a ,  16   b  is arranged on each of both edges of the movable member  12 . And the movable blocks  17   a ,  17   a ,  17   b ,  17   b  are arranged on the inner wall surfaces  11   a ,  11   b  of fixed member  11 . The movable blocks  17   a ,  17   a  are attached to the inner wall surface  11   a , and the movable blocks  17   b ,  17   b  are attached to the inner wall surface  11   b . And the movable blocks  17   b ,  17   b  are set to be movable only in the direction perpendicular to the inner wall surface  11   b  so as to absorb the installing error of the rectilinear guides  13   a ,  13   b  or the thermal expansion and construction difference between fixed member  11  and movable member  12 . 
     The arrangements and functions of elements or parts of the relative linear motion apparatus the same as the relative linear motion apparatus shown in FIGS. 1 to  6  are not described herein by adding the same reference numerals to the corresponding elements or parts. 
     The frame  12   a  and rail holding portions  12   b ,  12   b  fixed to the both edges of the frame  12   a  are integrally formed by a die casting using metal such as aluminum. Further, the track rails  16   a ,  16   b  are inserted in rail holding portions  12   b ,  12   b  of the movable member  12 , and are integrally molded with movable member  12 . In different words, the movable member  12  is integrally formed with the track rails  16   a ,  16   b  by injecting metal such as aluminum into a metal mold in which the track rails  16   a ,  16   b  are placed, i.e. through a so-called insert molding method. Since the track rails  16   a ,  16   b  are affected by heat when the track rails  16   a ,  16   b  are molded, the ball rolling grooves  31 , 31  are formed by machining or grinder after molding the track rails  16   a ,  16   b . Also, it may be possible to arrange a means for preventing the track rails  16   a ,  16   b  from slipping out of the rail holding portions  12   b ,  12   b  to the axial direction of the track rails  16   a    16   b . And forming a difference in level on the track rails  16   a    16   b  prevents the track rails  16   a ,  16   b  from slipping out of the rail holding portions  12   b ,  12   b.    
     When movable member  12  are arranged between the pair of inner wall surfaces  11   a ,  11   b  opposing to each other of the fixed member  11  through the rectilinear guides  13   a ,  13   b , it is necessary to reduce the processing error including the installing error of the rectilinear guides  13   a ,  13   b . According to this embodiment, since the track rails  16   a ,  16   b  are inserted in the movable member  12  and are integrally molded with the movable member  12 , it is possible to reduce the processing error as much as possible. Also it is possible to reduce the number of articles. 
     FIG. 14 shows a variation of the point in the third embodiment. As shown in FIG.  14 ( a ), the rail holding portion  12   b  of the movable member  12  is extended from a base of the track rail  16   a  ( 16   b ) to hollows  16   f ,  16   f  formed on side surfaces of the track rail  16   a  ( 16   b ). A lower part of the track rail  16   a  ( 16   b ) is wrapped by the rail holding portion  12   b . According to this construction, since combination of the track rail  16   a  ( 16   b ) and the rail holding portion  12   b  becomes firmer, both are not separated by added vibration or shock. 
     In a second variation shown in FIG.  14 ( b ), a dovetail groove  16   g  is formed on the base of the track rail  16   a  ( 16   b ), a part  12   e  of the rail holding portion  12   b  is injected into the dovetail groove  16   g . According to this structure, combination of the track rail  16   a  ( 16   b ) and the rail holding portion  12   b  becomes firmer as much as the variation shown in FIG.  14 ( a ). Also, it is possible to narrow down the width of the rail holding portion  12   b  to the width of the track rail  16   a  ( 16   b ) and to miniaturize the relative linear motion apparatus. 
     In a third variation shown in FIG.  14 ( c ), a part  12   f  of the rail holding portion  12   b  is injected into bore  16  for inserting bolt. According to this structure, combination of the track rail  16   a  ( 16   b ) and the rail holding portion  12   b  becomes firmer as much as the variations shown in FIG.  14 ( a ) and FIG.  14 ( b ). And it is possible to narrow down the width of the rail holding portion to the width of the track rail  16   a  ( 16   b ). Furthermore since the existing bore  16   h  for inserting bolt is used for casting, it is not necessary to form the dovetail groove  16   g  shown in FIG.  14 ( b ) on the track rail  16   a  ( 16   b ), and as a result costs fall. 
     It is further to be noted that the present invention is not limited to the described embodiments and alternations and many other changes and modifications may be made without departing from the scopes of the appended claims.