Abstract:
A linear actuator, comprising: a base; a fixed part support mechanism attached to the base; a fixed part elastically supported by the fixed part support mechanism; and a movable part driven to reciprocate in a predetermined drive direction with respect to the fixed part, wherein the fixed part support mechanism comprises: a movable block attached to the fixed part; a linear guide that couples the movable block with the base to be slidable in the predetermined drive direction; and an elastic member that is disposed between the base and the movable block and prevents transmission of a high frequency component of vibration in the predetermined drive direction.

Description:
[0001]    This is a Continuation-in-Part of International Application No. PCT/JP2012/060581 filed Apr. 19, 2012, which claims priority from Japanese Patent Applications Nos. 2011-098775 filed Apr. 26, 2011 and 2011-238849 filed Oct. 31, 2011. The entire disclosure of the prior applications is hereby incorporated by reference herein its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to an electrodynamic actuator and an electrodynamic excitation device employing the electrodynamic actuator. 
       BACKGROUND 
       [0003]    An electrodynamic excitation device employing a so-called voice coil motor as a driving device is known. In PCT International Publication No. WO2009/130953 (hereafter, referred to as patent document 1), a triaxial excitation device  1  in which three electrodynamic actuators  200 ,  300  and  400  whose drive axes are oriented to perpendicularly intersect with each other are coupled to a vibration table  100  is disclosed. In the excitation device  1  described in the patent document 1, a drive shaft of each electrodynamic actuator is coupled to the vibration table  100  via a biaxial slider (joint parts  240 ,  340  and  440 ) which is slidable in two axes directions which are perpendicular to the drive axis. The biaxial slider  240  ( 340 ,  440 ) is configured by coupling a pair of linear guides disposed such that movable axes thereof are perpendicular to each other, via an intermediate stage  245  ( 345 ,  445 ). With this configuration, one electrodynamic actuator is able to drive the excitation table  100  without being strongly affected by driving of the excitation table  100  by the other electrodynamic actuators. 
       SUMMARY 
       [0004]    However, in the electrodynamic actuator used in the excitation device  1  of the patent document 1, a movable part  230  is supported by a fixed part  222  only at a tip portion of a slender bar  234  protruding in a drive direction from one end off a body part  232 . Therefore, the body part  232  of the movable part  230  is not supported at a high degree of rigidity in regard to the direction perpendicular to the drive direction, and therefore is easily vibrated in non-drive directions. For this reason, there is a case where crosstalk is caused between the drive axes due to vibrations of the movable part  230  in the non-drive directions and thereby the accuracy of excitation deteriorates. 
         [0005]    The present invention is advantageous in that it provides an electrodynamic actuator whose movable part is hard to vibrate in the non-derive directions, and an electrodynamic excitation device configured to have an excellent accuracy of excitation by using such an electrodynamic actuator. 
         [0006]    According an aspect of the invention, there is provided a linear actuator, comprising: a base; a fixed part support mechanism attached to the base; a fixed part elastically supported by the fixed part support mechanism; and a movable part driven to reciprocate in a predetermined drive direction with respect to the fixed part. The fixed part support mechanism comprises: a movable block attached to the fixed part; a linear guide that couples the movable block with the base to be slidable in the predetermined drive direction; and an elastic member that is disposed between the base and the movable block and prevents transmission of a high frequency component of vibration in the predetermined drive direction. 
         [0007]    Since the fixed part is fixed to the base via the fixed part support mechanism, transmission of vibration in the axial direction to the fixed part can be prevented. 
         [0008]    The elastic member may comprise an air spring. 
         [0009]    The linear actuator may further comprise a fixing block fixed to the base. In this case, at least one of the linear guide and the elastic member may be attached to the base via the fixing block. 
         [0010]    The movable block may be provided as a pair of movable blocks. In this case, the pair of movable blocks may be attached to both side surfaces of the fixed part to sandwich an axis of the fixed part therebetween. 
         [0011]    At least a part of the movable part may be accommodated in a cylindrical hollow part of the fixed part, thereby forming the linear actuator as an electrodynamic actuator. The linear actuator may further comprise a plurality of movable part support mechanisms that support the movable part from a lateral side to enable the movable part to reciprocate in an axial direction of the fixed part. In this configuration, each of the plurality of movable part support mechanisms may comprise: a rail attached to a side surface of the movable part to extend in the predetermined drive direction; and a runner block attached to the fixed part to engage with the rail. The plurality of movable part support mechanisms may be arranged to have approximately constant intervals therebetween around an axis of the fixed part. 
         [0012]    The plurality of movable part support mechanisms may be two pairs of movable part support mechanisms. In this case, the movable part may be disposed to be sandwiched between the two pairs of movable part support mechanisms in two directions which are perpendicular to each other. 
         [0013]    The linear actuator may be horizontally disposed in a state where the axis of the fixed part is oriented in a horizontal direction. In this case, one of the plurality of movable part support mechanisms may be disposed under the axis of the fixed part. 
         [0014]    The movable part may comprise a rod extending along the axis of the fixed part to protrude from one end of the movable part. In this case, the fixed part may comprise a bearing which supports the rod to be movable in the axial direction of the fixed part. 
         [0015]    According to another aspect of the invention, there is provided an excitation device, comprising: at least one linear actuator described above; and a vibration table coupled to the movable part of the at least one linear actuator. 
         [0016]    The at least one linear actuator may comprise two linear actuators. In this case, one of the two linear actuators may be a first actuator having a driving axis in a first direction, and the other of the two linear actuators may be a second actuator having a driving axis in a second direction perpendicular to the first direction. The excitation device may further comprise: a first slider that couples the vibration table with the first actuator to be slidable in the second direction; and a second slider that couples the vibration table with the second actuator to be slidable in the first direction. 
         [0017]    The excitation device may further comprise: a third actuator having a driving axis in a third direction which is perpendicular to the first direction and the second direction; and a third slider that couples the vibration table with the third actuator to be slidable in the first direction and the second direction. In this configuration, the first slider may couple the vibration table with the first actuator to be slidable in the second direction and the third direction, and the second slider may couple the vibration table with the second actuator to be slidable in the first direction and the third direction. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a front view of an electrodynamic excitation device according to a first embodiment of the invention. 
           [0019]      FIG. 2  is a plan view of the electrodynamic excitation device according to the first embodiment of the invention. 
           [0020]      FIG. 3  is a block diagram of a drive system of the electrodynamic excitation device according to the first embodiment of the invention. 
           [0021]      FIG. 4  is a front view of a main body of a Z-axis actuator according to the first embodiment of the invention. 
           [0022]      FIG. 5  is a plan view of the main body of the Z-axis actuator according to the first embodiment of the invention. 
           [0023]      FIG. 6  is a vertical cross section of the main body of the Z-axis actuator according to the first embodiment of the invention. 
           [0024]      FIG. 7  is an enlarged plan view illustrating a portion around a vibration table of the Z-axis actuator according to the first embodiment of the invention. 
           [0025]      FIG. 8  is a cross section of a linear guide used in the electrodynamic excitation device according to the first embodiment of the invention. 
           [0026]      FIG. 9  is a cross section taken by a line I-I in  FIG. 8 . 
           [0027]      FIG. 10  is a front view of an electrodynamic excitation device according to a second embodiment of the invention. 
           [0028]      FIG. 11  is a plan view of the electrodynamic excitation device according to the second embodiment of the invention. 
           [0029]      FIG. 12  is a side view of the electrodynamic excitation device according to the second embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0030]    Hereafter, embodiments of the invention are described with reference to the accompanying drawings. 
       First Embodiment  
       [0031]    Hereafter, an electrodynamic triaxial excitation device  1  (hereafter, simply referred to as an excitation device  1 ) according to a first embodiment of the invention is described with reference to  FIGS. 1 to 9 .  FIGS. 1 and 2  are a front view and a plan view of the excitation device  1 , respectively.  FIG. 3  is a block diagram illustrating a general configuration of a drive system of the excitation device  1 . In the following explanation of the first embodiment, the left and right direction in  FIG. 1  is defined as a X-axis direction (the rightward direction is a positive direction of X-axis), a direction perpendicular to the paper face of  FIG. 1  is defined as a Y-axis direction (the direction from the front side to the back side of the paper face of  FIG. 1  is a positive direction of Y-axis), and an up and down direction in  FIG. 1  is defined as a Z-axis direction (the upward direction is a positive direction of Z-axis). The Z-axis direction is a vertical direction, and each of the X-axis direction and the Y-axis direction is a horizontal direction. 
         [0032]    As shown in  FIGS. 1 and 2 , the excitation device  1  includes a vibration table  400  to which a test piece (not shown) is attached, three actuators (an X-axis actuator  100 , a Y-axis actuator  200  and a Z-axis actuator  300 ) which vibrate the vibration table  400  in X-axis, Y-axis and Z-axis directions, respectively, and a device base  50  which supports the actuators  100 ,  200  and  300 . The actuators  100 ,  200  and  300  are electrodynamic linear motion actuators each having a voice coil motor, and respectively include main bodies  101 ,  201  and  301 , and covers  103 ,  203  and  303  covering movable parts (described later) protruding from the respective main bodies  101 ,  201  and  301 . The vibration table  400  is coupled to the actuators  100 ,  200  and  300  via respective biaxial sliders (a YZ slider  160 , a ZX slider  260  and a XY slider  360 ). The excitation device  1  is able to vibrate the test piece attached to the vibration table  400  in the three axes directions which are perpendicular to each other, by driving the vibration table  400  with the actuators  100 ,  200  and  300 . 
         [0033]    The device base  50  is formed such that horizontally arranged bottom and top plates and  56  are coupled to each other with a plurality of wall plates  58 . The actuators  100 ,  200  and  300  are fixed to the top plate  56  of the device base  50  with a pair of fixing blocks  110 , a pair of fixing blocks  210  and a pair of fixing blocks  310 , respectively. An opening  57  is formed in the top plate  56 , and the lower portion of the Z-axis actuator  300  is accommodated in the device base  50  via the opening  57 . With this configuration, the excitation device  1  is formed to have a low height. In order to suppress transmission of the vibration from the device base  50  to an installation floor F, a plurality of antivibration mounts  52  are attached to the lower surface of the bottom plate  54 . 
         [0034]    As shown in  FIG. 3 , the drive system of the excitation device  1  includes a control unit  10  which totally controls operation of the excitation device  1 , a measurement unit  20  which measures vibration of the vibration table  400 , a power source unit  30  which supplies electric power to the control unit  10 , and an input unit  40  which receives a data input from a user or an external device. The measurement unit  20  includes a triaxial vibration pickup  21  attached to the vibration table  400 . The measurement unit  20  amplifies a signal (e.g., a speed signal) outputted by the triaxial vibration pickup  21  to convert the signal to a digital signal, and transmits the digital signal to the control unit  10 . The triaxial vibration pickup  21  detects the vibrations in the X-axis, Y-axis and Z-axis directions of the vibration table  400  independently. Based on an excitation waveform inputted from the input unit  40  and the signal from the measurement unit  20 , the control unit  10  is able to vibrate the vibration table  400  at desired amplitude and frequency by controlling the magnitude and the frequency of AC currents to be inputted to drive coils (described later) of the actuators  100 ,  200  and  300 . Furthermore, based on the signal of the triaxial vibration pickup  21 , the measurement unit  20  calculates various parameters (e.g., speed, acceleration, amplitude, power spectrum) indicating a vibrating state of the vibration table  40 , and transmits the parameters to the control unit  10 . 
         [0035]    Next, configurations of the actuators  100 ,  200  and  300  are explained. Since each of the X-axis actuator  100  and the Y-axis actuator  200  has the same configuration as that of the Z-axis actuator  300 , except that an air spring is not provided in the Z-axis actuator  300 , the Z-axis actuator  300  is explained in detail as a representative example of the actuators. 
         [0036]      FIGS. 4 ,  5  and  6  are a front view, a plan view and a vertical cross section of the main body  301  of the Z-axis actuator  300 . The main body  301  includes a fixed part  320  having a cylindrical body  322 , and a movable part  350  accommodated in a cylinder of the cylindrical body  322 . The movable part  350  is provided to be movable in the Z-axis direction (the up and down direction in  FIGS. 4 and 6 ) with respect to the fixed part  320 . The movable part  350  includes a cylindrical movable frame  356 , and a drive coil  352  disposed to be substantially coaxial with the movable frame  356 . The drive coil  352  is attached to a lower end of the movable frame  356  via a drive coil holding member  351 . The movable frame  356  is configured such that an upper portion thereof is formed in a shape of a cylinder and a lower portion thereof is formed in a shape of a frustum cone whose side face is gently inclined so that the outer diameter becomes larger toward the lower side. Furthermore, as shown in  FIG. 6 , the movable frame  356  includes a rod  356   a  extending along the center axis, a top plate  356   b  disposed to be perpendicular to the center axis, an intermediate plate  356   c  and a bottom plate  356   d . The top plate  356   b , the intermediate plate  356   c  and the bottom plate  356   d  are coupled to each other by the rod  356   a . The rod  356   a  is formed to further extend downward from the bottom plate  356   d . Furthermore, the vibration table  400  is attached to the top plate  356   b  via the XY slider  360 . 
         [0037]    In the cylindrical body  322  of the fixed part  320 , a cylindrical inner magnet  326  is fixed to be coaxial with the cylindrical body  322 . The inner magnet  326  has an outer diameter smaller than the inner diameter of the drive coil  352 , and the drive coil  352  is disposed in a gap sandwiched between the outer circumferential surface of the inner magnet  326  and the inner circumferential surface of the cylindrical body  322 . Each of the cylindrical body  322  and the inner magnet  326  is made of magnetic material. In the cylinder of the inner magnet  326 , a bearing  328  which slidably supports the rod  356   a  in the Z-axis direction is fixed. 
         [0038]    On the inner circumferential surface  322   a  of the cylindrical body  322 , a plurality of recessed parts  322   b  are formed, and, in each recessed part  322   b , an excitation coil  324  is accommodated. When a DC current (the excitation current) flows through the excitation coil  324 , a magnetic field indicated by an arrow A is produced in the radial direction of the cylindrical body  322  in a portion where the inner circumferential surface  322   a  of the cylindrical body  322  is situated to closely face the outer circumferential surface of the inner magnet  326 . When the current is supplied in this state, a Lorentz force is caused in the axial direction of the drive coil  352 , i.e., in the Z-axis direction, and the movable part  350  is driven in the Z-axis direction. 
         [0039]    In the cylinder of the inner magnet  326 , an air spring  330  is accommodated. The lower end of the air spring  330  is fixed to the fixed part  320 , and the rod  356   a  is fixed to the upper end of the air spring  330 . The air spring  330  supports the movable frame  356  via the rod  356   a  from the lower side. That is, the weight (the static load) of the movable part  350 , the XY slider  360  supported by the movable part  350 , the vibration table  400  and the test piece is supported by the air spring  330 . Therefore, by providing the air spring  330  for the Z-axis actuator  300 , it becomes unnecessary to support the weight (the static load) of the movable part  350 , the vibration table  400  and etc. by the driving force (Lorentz force) of the Z-axis actuator  300 . Since it is only required to provide the dynamic load to vibrate the movable part  350 , the driving current to be supplied to the Z-axis actuator  300  (i.e., power consumption) is reduced considerably. Furthermore, since the drive coil  352  can be downsized thanks to the reduction of the required driving force, it becomes possible to drive the Z-axis actuator  300  at a high frequency. Furthermore, it becomes unnecessary to supply a large DC component to the drive coil for supporting the weight of the movable part  350 , the vibration table  400  and etc. Therefore, it becomes possible to employ a simple and compact circuit as the power source unit  30 . 
         [0040]    When the movable part  350  of the Z-axis actuator  300  is driven, the fixed part  320  also receives a reaction force (the excitation force) in the drive axis (Z-axis) direction. By providing the air spring  330  between the movable part  350  and the fixed part  320 , the exciting force transmitted from the movable part  350  to the fixed part  320  is reduced. As a result, for example, the vibration of the movable part  350  is prevented from being transmitted, as noise, to the vibration table  400  via the fixed part  320 , the device base  50  and the actuators  100  and  200 . 
         [0041]    Next, a configuration of a movable part support mechanism  340  which supports the upper portion of the movable part  350  to be slidable in the axis direction is explained. The movable part support mechanism  340  includes guide frames  342 , Z-axis runner blocks  344  and Z-axis rails  346 . To a side surface of a cylindrical upper portion of the movable part  350  (the movable frame  356 ), four Z-axis rails  346  extending in the Z-axis direction are attached. On the upper surface of the fixed part  320  (the cylindrical body  322 ), four guide frames  342  are fixed to have constant intervals (of 90°) along the outer circumferential surface of the cylindrical body  322 . The guide frame  342  is a fixing member having a cross section formed in a shape of a letter L enforced by a rib. To an upright part  342   u  of each guide frame  342 , the Z-axis runner block  344  engaging with the Z-rail  346  is attached. The Z-axis runner block  344  has a plurality of rotatable balls  344   b  (described later), and constitutes a Z-axis linear guide  345  of a ball bearing type, together with the Z-axis rail  346 . That is, the movable part  350  is supported, from the lateral side, by the four pairs of supporting mechanisms each of which is formed of the guide frame  342  and the Z-axis linear guide  345 , so that the movable part  350  is not able to move in the X-axis and Y-axis directions. As a result, occurrence of crosstalk by the vibration of the movable part  350  in the X-axis and Y-axis directions can be prevented. Furthermore, through use of the Z-axis linear guide  345 , the movable part  350  is able to smoothly move in the Z-axis direction. Furthermore, since the movable part  350  is supported to be movable only in the Z-axis direction by the bearing  328  also in the lower portion as described above, the movable part  350  is not able to move in the X-axis and Y-axis directions. As a result, the vibration of the movable part  350  in the X-axis and Y-axis directions becomes hard to occur. 
         [0042]    In the case where the movable frame  356  and the guide frame  342  are coupled to each other with the Z-axis linear guide  345 , it is also possible to employ a configuration where the Z-axis rail  346  is attached to the guide frame  342  fixed to the fixed part  320  and the Z-axis runner block  344  is attached to the movable frame  356 . However, in this embodiment, the Z-axis rail  346  is attached to the movable frame  356  and the Z-axis runner block  344  is attached to the guide frame  342 , in contrast to the above described configuration. By employing such a configuration in this embodiment, unnecessary vibration can be suppressed. This is because the Z-axis rail  346  is lighter than the Z-axis runner block  344 , the Z-axis rail  346  is longer than the Z-axis runner block  344  in the drive direction (Z-axis direction) (therefore, mass per a unit of length is small), the mass distribution in the drive direction is uniform, and therefore the fluctuation of the mass distribution caused when the Z-axis actuator  300  is driven is smaller in the case where the Z-axis rail  346  is attached to the movable side and as a result the vibration caused in accordance with the fluctuation of the mass distribution can be suppressed to a low level. Furthermore, since the barycenter of the Z-axis rail  346  is lower (i.e., the distance from the installation surface to the barycenter is shorter) than the barycenter of the Z-axis runner block  344 , the moment of inertia becomes smaller in the case where the Z-axis rail  346  is fixed to the movable side. Accordingly, with this configuration, it becomes possible to set the resonance frequency to be higher than the excitation frequency (e.g., 0 to 100 Hz), and thereby it becomes possible to prevent deterioration of the accuracy of excitation by resonance. 
         [0043]    Hereafter, a configuration of the XY slider  360  which couples the Z-axis actuator  300  to the vibration table  400  is explained.  FIG. 7  is a plan view enlarging a portion around the vibration table  400 . As shown in  FIGS. 6 and 7 , the XY slider  360  includes two Y-axis rails  362   a , four Y-axis runner blocks  362   b , four joint plates  364 , four X-axis runner blocks  366   b  and two X-axis rails  366   b . The two Y-axis rails  362   a  extending in the Y-axis direction are attached to the upper surface of the top plate  356   b . To the Y-axis rails  362   a , the two Y-axis runner blocks  362  engaging with the Y-axis rail  362  are attached to be slidable along the Y-axis rails  362   a . The two X-axis rails  366   a  extending in the X-axis direction are attached to the lower surface of the vibration table  400 . To the X-axis rails  366   a , the two X-axis runner blocks  366   b  engaging with the X-rail  366   a  are attached to be slidable along the X-axis rails  366   a . The X-axis runner blocks  366   b  are coupled to respective ones of the Y-axis runner blocks  362   b  via the respective joint plates  364 . Specifically, one of the X-axis runner blocks  366   b  engaging with one X-axis rail  366   a  is coupled to one of the Y-axis runner blocks  362   b  engaging with one Y-axis rails  362   a , and the other X-axis runner block  366   b  is coupled to one of the Y-axis runner blocks  362   b  engaging with the other Y-axis rail  362   a . That is, each X-axis rail  366   a  is coupled to the Y-axis rail  362   a  via the X-axis runner block  366   b  and the Y-axis runner block  362   b  coupled with the joint plate  364 . With this configuration, the vibration table  400  is coupled to the movable part  350  of the Z-axis actuator  300  to be slidable in the X-axis and Y-axis directions. 
         [0044]    As described above, by coupling the Z-axis actuator  300  to the vibration table  400  via the XY slider  360  to be slidable in the X-axis and Y-axis directions by a very small force, the vibration components of the vibration table  40  in the X-axis and Y-axis directions are not transmitted to the Z-axis actuator  300  even when the vibration table  400  is vibrated in the X-axis and Y-axis directions by the X-axis actuator  100  and the Y-axis actuator  200 . Furthermore, even when the vibration table  400  is vibrated in the Z-axis direction by the Z-axis actuator  300 , the vibration component of the vibration table  400  in the Z-axis direction is not transmitted to the X-axis actuator  100  and the Y-axis actuator  200 . Accordingly, excitation in a low degree of crosstalk can be realized. 
         [0045]    Hereafter, a configuration of the YZ slider  160  which couples the X-axis actuator  100  to the vibration table  400  is explained. The YZ slider  160  includes two Z-axis rails  162   a , two Z-axis runner blocks  162   b , two joint plates  164 , two Y-axis runner blocks  166   b  and one Y-axis rail  166   a . The two Z-axis rail  162   a  extending in the Z-axis direction are attached to a top plate  156   b  of the movable frame of the X-axis actuator  100 . To the Z-axis rail  162   a , the Z-axis runner block  162   b  engaging with the Z-axis rail  162   a  is attached to be slidable along the Z-axis rail  162   a . Furthermore, to a side surface of the vibration table  400  facing the X-axis actuator  100 , the Y-axis rail  166   a  extending in the Y-axis direction is attached. The Y-axis runner block  166   b  is coupled to one of the Z-axis runner blocks  162   b  via one of the Z-axis runner blocks  162   b . That is, the Y-axis rail  166   a  is coupled to the Z-axis rail  162   a  via the Y-axis runner block  166   b  and the Z-axis runner block  162   b  coupled by the joint plate  164 . With this configuration, the vibration table  400  is coupled to the movable part  150  of the X-axis actuator  100  to be slidable in the Y-axis and Z-axis directions. 
         [0046]    As described above, by coupling the X-axis actuator  100  to the vibration table  400  via the YZ slider  160  to be slidable in the Y-axis and Z-axis directions at a small degree of frictional force, the vibration components of the vibration table  400  in the Y-axis and Z-axis directions are not transmitted to the X-axis actuator  100  even when the vibration table  400  is vibrated by the Y-axis actuator  200  and the Z-axis actuator in the Y-axis and Z-axis directions. Furthermore, even when the vibration table  400  is vibrated in the X-axis direction by the X-axis actuator  100 , the vibration component of the vibration table  400  in the X-axis direction is not transmitted to the Y-axis actuator  200  and the Z-axis actuator  300 . As a result, excitation in a low degree of crosstalk can be realized. 
         [0047]    The ZX slider  260  which couples the Y-axis actuator  200  to the vibration table  400  also has the same configuration as that of the YZ slider  160 , and the vibration table  400  is coupled to the movable part of the Y-axis actuator  200  to be slidable in the Z-axis and X-axis directions. Therefore, even when the vibration table  400  is vibrated by the Z-axis actuator  300  and the X-axis actuator  100  in the Z-axis and X-axis directions, the vibration components of the vibration table  400  in the Z-axis and X-axis directions are not transmitted to the Y-axis actuator  200 . Furthermore, even when the vibration table  400  is vibrated in the Y-axis direction by the Y-axis actuator  200 , the vibration component of the vibration table  400  in the Y-axis direction is not transmitted to the Z-axis actuator  300  and the X-axis actuator  100 . As a result, excitation in a low degree of crosstalk can be realized. 
         [0048]    As described above, the actuators  100 ,  200  and  300  are able to accurately excite the vibration table  400  in the drive axis directions without interfering with each other. Furthermore, since each of the actuators  100 ,  200  and  300  is supported by the guide frame and the linear guide such that the movable part thereof is slidable only in the drive direction, vibration in the non-drive direction is hard to occur. Therefore, vibration in the non-drive direction which is not being controlled is not applied to the vibration table  400 . As a result, the vibration of the vibration table  400  in each drive axis direction can be accurately controlled by driving of the corresponding one of the actuators  100 ,  200  and  300 . 
         [0049]    Next, a configuration of a liner guide mechanism (a rail and a runner block) used in each of the movable part support mechanism  340 , the YZ slider  160 , the ZX slider  260  and the XY slider  360  is explained, taking the Z-axis linear guide mechanism  345  (the Z-axis runner block  344  and the Z-axis rail  346 ) used in the movable part support mechanism  340  as an example. The other rails and the runner blocks are also configured to have the same configurations as those of the Z-axis runner block  344  and the Z-axis rail  346 , respectively. 
         [0050]      FIG. 8  is a cross-sectional view of the Z-axis rail  346  and the Z-axis runner block  344  of the movable part support mechanism  340 , viewed by cutting along a plane (i.e., an XY plane) perpendicular to the longer axis of the Z-axis rail  346 .  FIG. 9  is an I-I cross section of the  FIG. 8 . As shown in  FIGS. 8 and 9 , a recessed part is formed on the Z-axis runner block  344  to surround the Z-axis rail  346 , and two pairs of grooves  344   a  and  344 ′ a  are formed on the recessed part to extend in the axial direction of the Z-axis rail  346 . In each of the grooves  344   a  and  344   a ′, a plurality of stainless steel balls  344   b  and a resin retainer  344   r  are accommodated. The retainer  344   r  has a plurality of spacers  344   rs  disposed between the balls  344   b , and a pair of bands  344   rb  coupling the plurality of spaces  344   rs . The balls  344   b  are held in spaces surrounded by the plurality of spacers  344   rs  and the band  344   rb . Grooves  346   a  and  346   a ′ are formed on the Z-axis rail  346  at positions facing the grooves  344   a  and the  344   a ′ of the Z-axis runner block  344 , respectively, and the balls  344   b  and the retainer  344   r  are sandwiched between the groove  344   a  and the groove  346   a  or between the groove  344   a ′ and the groove  346   a ′. Each of the grooves  344   a ,  344   a ′,  346   a  and  346   a ′ has a cross section formed in a shape of an arc, and the curvature radius of the arc is the same as the radius of the ball  344   b . Therefore, the ball  344   b  closely contacts each of the grooves  344   a ,  344   a ′,  346   a  and  346   a ′ with almost no play. 
         [0051]    In the Z-axis runner block  344 , two pairs of ball saving paths  344   c  and  344   c ′ are provided to extend in substantially parallel with the grooves  344   a  and  344   a ′. As shown in  FIG. 9 , the groove  344   a ′ and the saving path  344   c ′ are connected by U-shaped paths  344   d ′ at both ends, and a circular path for circulating the balls  344   b  and the retainer  344   r  is formed by the groove  344   a ′, the groove  346   a ′, the saving path  344   c ′ and the U-shaped paths  344   d . Similarly, a circular path is also formed by the groove  344   a , the groove  346   a  and the saving path  344   c.    
         [0052]    Therefore, when the Z-axis runner block  344  moves with respect to the Z-axis rail  346 , the plurality of balls  344   b  circulate, together with the retainer  344   r , while rotating along the grooves  344   a  and  346   a  and the grooves  344   a ′ and  346   a ′. Therefore, even when a large load is applied in a direction other than the axial direction of the rail, the Z-axis runner block  344  can be smoothly moved along the Z-axis rail  346  because the Z-axis runner block  344  can be supported by the plurality of balls  344   b  and resistance in the axial direction of the rail can be kept at a low level due to rotations of the balls  344   b . An inner diameter of each of the saving paths  344   c  and  344   c ′ and the U-shaped paths  344   d  and  344   d ′ is slightly larger than the diameter of the ball  344   b . For this reason, the frictional force caused between the ball  344   b  and each of the saving paths  344   c  and  344   c ′ and the U-shaped paths  344   d  and  344   d ′ is very small, and the circulating motion of the balls  344   b  are not hampered by the frictional force. 
         [0053]    By providing the spacers  344   rs  of the retainer  344   r  having a low degree of rigidity between the balls  344   b , wearing and loss of oil film which would be caused by direct contact of the balls at one point can be avoided, the frictional resistance is lowered, and as a result the lifetime can be increased considerably. 
         [0054]    Each of the X-axis actuator  100  and the Y-axis actuator  200  also has a movable part support mechanism (not shown). The movable part of the X-axis actuator  100  is supported by a guide frame from the both sides in the two directions (Y-axis and Z-axis directions) which are perpendicular to the drive direction (X-axis). Similarly, the movable part of the Y-axis actuator  200  is supported by a guide frame from the both sides in the two directions (Z-axis and X-axis directions) which are perpendicular to the drive direction (Y-axis). Each of the X-axis actuator  100  and the Y-axis actuator  200  is placed such that the longer side direction of the movable part is oriented horizontally. Therefore, in a conventional actuator not provided with a movable part support mechanism, a movable part is supported only by a rod in a state of a cantilever type, and therefore a tip side (the vibration table  400  side) of the movable part falls downward due to its own weight and this causes factors of friction and undesired vibration during the driving. By contrast, in this embodiment, the movable part of each of the X-axis actuator  100  and the Y-axis actuator  200  is supported from the lower side by the guide frame, such a problem is solved. 
       Second Embodiment  
       [0055]    Hereafter, an electrodynamic biaxial excitation device  1000  (hereafter, simply referred to as an “excitation device  1000 ”) according to a second embodiment of the invention is explained with reference to  FIGS. 10 to 12 . In the excitation device  1  according to the above described first embodiment, the main bodies  101 ,  201  and  301  (specifically, the fixed part) of the actuators are firmly supported by the device base  50  via the fixing blocks  110 ,  210  and  310 , respectively. Therefore, vibration of the fixed part of one actuator may be transmitted to the vibration table  400  via the device base  50  and the other of the actuators  100 ,  200  and  300 , and may becomes a noise component of the vibration. As described later, the excitation device  1000  according to the second embodiment is configured such that a fixed part of each actuator is supported by a device base via an air spring in the drive direction in which strong vibration is caused. Therefore, according to the second embodiment, excitation with a still higher degree of accuracy can be realized. 
         [0056]      FIGS. 10 ,  11  and  12  are a front view, a plan view and a side view (showing a left side in  FIG. 10 ) of the excitation device  1000 , respectively. In the following explanation about the second embodiment, the rightward direction in  FIG. 10  is defined as a positive direction of the X-axis, the direction pointing from the front side to the back side of the paper face of  FIG. 10  is defined as the positive direction of the Y-axis, and the upward direction in  FIG. 10  is defined as the positive direction of the Z-axis. The Z-axis direction is a vertical direction, and each of the X-axis and Y-axis directions is a horizontal direction. To elements which are the same or substantially the same as those of the first embodiment, the similar reference numbers are assigned, and detailed explanations thereof are omitted. 
         [0057]    The excitation device  1000  is configured to be able to vibrate a test piece (not shown) in the two directions, i.e., the X-axis direction and the Z-axis direction, and includes a vibration table  1400  to which the test piece is attached, two actuators (an X-axis actuator  1100  and a Z-axis actuator  1300 ) which vibrate the vibration table  1400  in the X-axis and Z-axis directions, respectively, a device base  1050  which supports the actuators  1100  and  1300 . One side surface of the vibration table  1400  is coupled to the X-axis actuator  1100  via a Z-axis slider  1160 , and the lower surface of the vibration table  1400  is coupled to the Z-axis actuator  1300  via an X-axis slider  1360 . As in the case of the excitation device  1  of the first embodiment, the excitation device  1000  also includes a biaxial vibration pickup, a measurement unit, a control unit, an input unit and a power source unit (not shown). The inner configuration of the actuators  1100  and  1300  and the configuration of the device base  1050  are the same as those of the excitation device  1  of the first embodiment. 
         [0058]    The X-axis actuator  1100  is fixed to a top plate  1056  of the device base  1050  by a support unit  1110 . The support unit  1110  includes a pair of fixing blocks  1112  each having an inverted T-shape attached to the top plate  1056 , a pair of movable blocks  1118  each having a rectangular plate shape respectively attached to the both side faces of a fixed part  1120  of the X-axis actuator  1100 , and a pair of linear guides  1114  which slidably couple the fixing block  1112  and the movable block  1118  in the X-axis direction. Each linear guide  1114  includes a rail  1114   a  which is attached to the upper surface of a foot part  1112   b  of the inverted T-shape fixed block  1112  to extend in the X-axis direction, and a pair of runner blocks  1114   b  which is attached to the lower surface of the movable block  1118  to engage with the rail  1114   a . On a side surface of the foot part  1112   b  of the fixed block  1112  on the positive side of the X-axis, a branch part  1112   a  extending upward is fixed. The side surface of the movable block  1118  on the positive side of the X-axis is coupled to the branch part  1112   a  of the fixed block  1112  via a pair of air springs  1116  arranged in the up and down direction. Thus, the fixed part  1120  of the X-axis actuator  1100  is flexibly supported, by the fixed part support mechanism including the linear guide  1114  and the air springs  1116 , in the drive direction (X-axis direction), with respect to the fixed block  1112  (i.e., the device base  1050 ). Therefore, the strong reaction force (the excitation force) applied to the fixed part  1120  in the X-axis direction during driving of the X-axis actuator  1100  is not directly transmitted to the device base  1050 , and is transmitted to the device base  1050  after the high frequency component thereof is largely reduced by the air springs  1116 . Therefore, the vibration noise transmitted to the vibration table  1400  is reduced considerably. 
         [0059]    The Z-axis actuator  1300  is fixed to the top plate  1056  of the device base  1050  by a pair of support units  1310  arranged on the both sides thereof in the Y-axis direction. The lower portion of the Z-axis actuator  1300  is accommodated in the device base  1050  through an opening  1057  provided in the top plate  1056  of the device base  1050 . Each support unit  1310  includes a movable block  1318 , a pair of angles  1312  and a pair of linear guides  1314 . The movable block  1318  is a support member attached to the side surface of a fixed part  1320  of the Z-axis actuator  1300 . The pair of angles  1312  is disposed to face the both sides of the movable block  1318  in the X-axis direction, and is attached to the upper surface of the top plate  1056 . The both sides of the movable block  1318  in the X-axis direction are coupled to the respective angles  1312  to be slidable in the Z-axis direction by the pair of linear guides  1314 . The movable block  1318  includes an angle block  1318   a , a flat plate block  1318   b  and a pair of T-shaped blocks  1318   c . One attachment surface of the L-shaped angle block  1318   a  is fixed to the side surface of the fixed part  1320  of the Z-axis actuator  1300 . On the other attached surface of the angle block  1318   a  oriented upward, the flat plate block  1318   b  having a rectangular flat shape extending in the X-axis direction is fixed at the central portion in the longer side direction of the flat plate block  1318   b . To the upper surfaces at the both ends in the X-axis direction of the flat plate block  1318   b , foot parts  1318   d  of the T-shaped blocks  1318   c  are attached. To the attachment surfaces of the T-shaped blocks  1318   c  (the both side surfaces in the X-axis direction of the movable block  1318 ), the rails  1314   a  of the linear guides  1314  extending in the Z-axis direction are attached, respectively. The runner block  1314   b  which faces and engages with the rail  1314   a  is attached to each angle  1312 . At the both ends in the X-axis direction of the angle block  1318   a , a pair of air springs  1316  is disposed to be sandwiched between the flat plate block  1318   b  and the top plate  1056  of the device base  1050 , and the movable block  1318  is supported by the top plate  1056  via the pair of air springs  1316 . Thus, as in the case of the X-axis actuator  1100 , the Z-axis actuator  1300  is also flexibly supported, in the drive direction (Z-axis direction), with respect to the device base  1050  via the fixed part support mechanism including the liner guide  1314  and the air springs  1316 . Therefore, the strong reaction force (the excitation force) applied to the fixed part  1320  during driving of the Z-axis actuator  1300  is not directly transmitted to the device base  1050 , and the high frequency component thereof is largely reduced by the air springs  1316 . As a result, the vibration noise transmitted to the vibration table  1400  is reduced largely. 
         [0060]    The forgoing is the explanations about the embodiments of the invention. It is understood that embodiments of the present invention are not limited to the above described embodiments, and can be varied within the scope of the invention. 
         [0061]    For example, the excitation device  1  of the first embodiment is an example in which the invention is applied to an actuator of an electrodynamic triaxial excitation device, and the excitation device  1000  of the second embodiment is an example in which the invention is applied to an actuator of an electrodynamic biaxial excitation device; however, the invention may also be applied to an electrodynamic single-axis excitation device. 
         [0062]    In the above described first embodiment, the movable part  350  of the electrodynamic actuator  300  is supported, from the lateral side, by the four movable part support mechanism  340  disposed to have approximately constant intervals around the axis of the cylindrical body  322 . However, the invention is not limited to such a configuration. In another embodiment, the movable part may be supported, from the lateral side, by two or more (preferably more than three) movable part support mechanisms arranged to have approximately constant intervals around the axis of the cylindrical body. 
         [0063]    In the above described first embodiment, the runner block is fixed to the upper surface of the cylindrical body  322  via the fixed guide frame  342 ; however, the runner block may be directly fixed to the inner circumferential surface of the cylindrical body  322 . 
         [0064]    In the above described second embodiment, the air springs  1116  and  1316  are used as buffering members for reducing the vibration of the fixed part support mechanism; however, various members, such as another type of spring or an elastic body (a rubber cushion) having the vibration absorption function, or a damper device using an electromagnetic reaction force, may be used. 
         [0065]    The linear actuator according to the embodiment of the invention may be used for a device other than the excitation device. For example, the actuator according to the embodiment may be used for a universal test device (material test device) for performing a tension and compression test, an accurate positioning device or a jack device. 
         [0066]    In the above described embodiment, the actuator is controlled using the speed of the vibration table as a control variable; however, control may be performed by using the displacement or the acceleration of the vibration table as a control variable. In place of the vibration table, the displacement, the speed or the acceleration of the test piece or the movable part of the actuator may be used as a control variable to drive and control the actuator.