Patent Publication Number: US-2006008367-A1

Title: Actuator and pump device

Description:
CROSS REFERENCE TO RELATED APPLICATION  
      The present invention claims priority under 35 U.S.C. §119 to Japanese Application No. 2004-201966 filed Jul. 8, 2004, which is incorporated herein by reference.  
     FIELD OF THE INVENTION  
      The present invention relates to an electromagnetic actuator and to a pump device which is structured to perform a pumping operation by utilizing the reciprocating movement of a movable body in the actuator.  
     BACKGROUND OF THE INVENTION  
      A pump device provided with an electromagnetic actuator has been proposed in which a pumping operation is performed by means of a movable body disposed in a cylinder that is reciprocated by electromagnetic force (see, for example, Japanese Patent Laid-open No. Hei 5-240163, Japanese Patent Laid-open No. 2004-124724, and Japanese Patent Laid-Open No. 2004-60641).  
      In a pump device as described in Japanese Patent Laid-Open No. Hei 5-240163, a movable body provided with a drive coil is disposed in a cylinder and a ring-shaped magnet is disposed outside the cylinder. Further, a cylindrical yoke is extended to an inner side of the drive coil from the magnet and a ferrite core is disposed on the outer side of the coil such that the coil is interposed between the cylindrical portion of the yoke and the ferrite core. In a pump device described in Japanese Patent Laid-open No. 2004-124724, a movable body provided with a drive magnet is slidably disposed in the axial direction of a cylinder and a drive coil is disposed on the outer peripheral side of the cylinder. In a pump device in Japanese Patent Laid-open No. 2004-60641, a movable body provided with a drive magnet is supported in the axial direction of a cylinder by an elastic member in a movable manner and a drive coil is disposed on the outer side of the cylinder.  
      However, in the pump device described in Japanese Patent Laid-Open No. 2004-124724 or Japanese Patent Laid-open No. 2004-60641, since the drive magnet is disposed on the movable body, a space is required between the drive magnet and its peripheral magnetic member in consideration of the moving range of the drive magnet so that the drive magnet is not attracted by the peripheral magnetic member. Further, when the magnetic field is shielded so that surrounding objects are not attracted by the drive magnet or malfunctions are not induced in peripheral devices, it is necessary to provide clearance for the full range of motion of the drive magnet. Thus, the outer dimension of the actuator is quite large.  
      Further, in the pump device described in Japanese Patent Laid-Open No. Hei 5-240163, only one magnet can be disposed due to the restriction on a layout, for example, that the yoke cannot be disposed on the movable body. Therefore, since the magnetic flux density interlining with the coil is lower, thrust acting on the movable body becomes smaller.  
     SUMMARY OF THE INVENTION  
      In view of the problems described above, the present invention may advantageously provide a small-sized actuator capable of applying a large thrust to a movable body, and provide a pump device with the actuator.  
      Thus, according to the present invention, there may be provided an actuator including a fixed body having a first yoke, a pair of drive magnets which are overlapped so as to interpose the first yoke therebetween with their same polarities being directed to the first yoke, and a second yoke which faces an outer peripheral end face of the first yoke and is superposed on the respective end faces positioned on outer sides of the pair of drive magnets, and a movable body having a coil which is disposed so as to surround around the outer peripheral end face of the first yoke between the first yoke and the second yoke and the coil is displaced in an axial direction by energization of the coil.  
      In an actuator in accordance with an embodiment of the present invention, a pair of drive magnets are overlapped so as to interpose the first yoke therebetween with their same polarities being directed to the first yoke and a second yoke is disposed so as to face the outer peripheral end face of the first yoke in a fixed body. Therefore, the magnetic flux from the pair of the drive magnets can be efficiently guided from the outer peripheral end face of the first yoke in the direction perpendicular to the axial direction. Accordingly, the density of magnetic flux interliking with the coil is high which is disposed to surround around the outer peripheral end face of the first yoke, and thus a large thrust can be applied to the movable body. Further, the same polarities of the two drive magnets are directed so as to face each other but, since the first yoke is sandwiched between the two drive magnets, assembling operations can easily be performed without being affected by the repulsion of the two drive magnets. In addition, since the drive magnets are disposed on the fixed body, the drive magnets are not attracted to peripheral members even when the drive magnets and the peripheral members are placed in a close relation. Moreover, even when a shield is applied to the magnetic field such that the peripheral members are not attracted to the drive magnets or such that malfunctions are not induced in the peripheral devices, the periphery of the drive magnets can be covered in a compact manner because the drive magnets are fixed. Consequently, the outer dimension of the actuator can be made smaller. In addition, since the second yoke is disposed to cover the drive magnets and the coil, the shield is efficiently attained with the second yoke. Accordingly, since another shield member is not required, the outer dimension of the actuator is not required to be made larger.  
      In accordance with an embodiment of the present invention, the second yoke is preferably provided with a ring-shaped protruding part which protrudes toward and faces the outer peripheral end face of the first yoke. According to the construction described above, the magnetic flux density to the coil can be enhanced which is disposed between the first yoke and the second yoke. Therefore, since thrust acting on the movable body can be increased, the response speed and the output characteristics of the movable body can be improved. Further, the second yoke may include a pair of yoke members which are formed in a bottomed cylinder shape and capable of being divided in the axial direction. The pair of the yoke members may be disposed such that the respective end faces of respective cylindrical body parts of the pair of the yoke members are butted with each other and that the bottom plate portions of the pair of the yoke members are overlapped on the respective end faces of the pair of drive magnets. According to the construction described above, a space that is formed by the second yoke and the first yoke and the pair of the drive magnets can be utilized as the space within which the movable body is moved in the axial direction. Further, since the coil may be wound around the coil bobbin, the coil bobbin may be preferably provided with a guide part which engages with a guide member, which is disposed in a space formed by the second yoke and the first yoke and the pair of drive magnets, for performing a guide operation to the movement of the movable body. Further, the coil may be supported by a sheet-shaped elastic member such that the coil is capable of moving in the axial direction between the first yoke and the second yoke.  
      The actuator in accordance with the present invention may be applied to a pump device. In the pump device, the actuator may be used to perform the suction of fluid to a pump chamber and the discharge of the fluid from the pump chamber by the movement of the movable body.  
      In this case, the movable body may be structured as a piston, which serves to form a first pump chamber disposed on one side of the piston in the axial direction in a space which is formed with the second yoke and form a second pump chamber disposed on the other side of the piston in the axial direction in the space.  
      Further, the movable body may be structured as a diaphragm, which serves to form a first pump chamber disposed on one side of the diaphragm in the axial direction in a space which is formed with the second yoke and form a second pump chamber disposed on the other side of the diaphragm in the axial direction in the space. The diaphragm may include the coil and a sheet-shaped elastic member which supports the coil between the first yoke and the second yoke such that the coil is capable of moving in the axial direction.  
      In accordance with an embodiment of the present invention, the pump device may be structured such that the first pump chamber and the second pump chamber are in communication with a common fluid inlet port and a common fluid outlet port. According to the construction described above, fluid can be sent out alternately from the first pump chamber and die second pump chamber, and thus the flow rate of the fluid becomes large and the occurrence of pulsating flow can be restrained.  
      Further, in accordance with an embodiment of the present invention, the pump device may be provided with a first fluid inlet port which is in communication with the first pump chamber, a second fluid inlet port which is in communication with the second pump chamber, a first fluid outlet port which is in communication with the first pump chamber, and a second fluid outlet port which is in communication with the second pump chamber. According to the construction described above, different fluids can be respectively sent out from the first pump chamber and the second pump chamber in one pump device.  
      As described above, in the actuator of the present invention, a pair of drive magnets are overlapped so as to interpose the first yoke therebetween with their same polarities being directed to the first yoke and a second yoke is disposed so as to face the outer peripheral end face of the first yoke in the fixed body. Therefore, the magnetic flux from the pair of the drive magnets can be efficiently guided from the outer peripheral end face of the first yoke in the direction perpendicular to the axial direction. Accordingly, since the density of magnetic flux interliking with the coil is high which is disposed to surround around the outer peripheral end face of the first yoke, a large thrust can be applied to the movable body. Further, the same polarities of the two drive magnets face each other but, since the first yoke is sandwiched between the two drive magnets, assembling operations can easily be performed without being affected by the repulsion of the two drive magnets. In addition, since the drive magnets are disposed on the fixed body, the drive magnets are not attracted by peripheral members even when the drive magnets and the peripheral members are placed in a close relation. Moreover, even when a shield is applied to the magnetic field such that the peripheral members are not attracted to the drive magnets or such that malfunctions are not induced in the peripheral devices, the periphery of the drive magnets can be covered in a compact manner because the drive magnets are fixed. Consequently, the outer dimension of the actuator can be made smaller. In addition, since the second yoke is disposed to cover the drive magnets and the coil, the shield is efficiently attained by the second yoke. Accordingly, since another shield member is not required, the outer dimension of the actuator is not required to be larger.  
      Other features and advantages of the invention will be apparent from the following detailed description, taken in conjunction with the accompanying drawings that illustrate, by way of example, various features of embodiments of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Embodiments will now be described, by way of example only, with reference to the accompanying drawings which are meant to be exemplary, not limiting, and wherein like elements are numbered alike in several Figures, in which:  
       FIG. 1 ( a ) is a schematic cross-sectional view showing an entire structure of an actuator in accordance with an embodiment of the present invention, and  FIG. 1 ( b ) is an explanatory view showing the lines of magnetic force in the actuator.  
       FIG. 2  is a plan view showing a pump device in accordance with an embodiment of the present invention.  
       FIG. 3 ( a ) is a cross-sectional view showing the pump device which is cut by the line of “A-A” in  FIG. 2  and  FIG. 3 ( b ) is a cross-sectional view showing the pump device which is cut by the line of “B-B” in  FIG. 2 .  
       FIG. 4  is an exploded perspective view showing the pump device shown in FIGS.  2  and FIGS.  3 ( a ) and  3 ( b ).  
      FIGS.  5 ( a ) through  5 ( c ) are cross-sectional views showing another pump device in accordance with an embodiment of the present invention.  FIG. 5 ( a ) is a cross-sectional view showing the pump device that is cut at a position corresponding to the line of “A-A” in  FIG. 2 ,  FIG. 5 ( b ) is a cross-sectional view showing the pump device which is cut at a position corresponding to the line of “B-B” in  FIG. 2 , and  FIG. 5 ( c ) is an enlarged view showing a portion of the pump device encircled by the line “C” in  FIG. 5 ( a ). 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      An actuator and a pump device in accordance with embodiments of the present invention are described below with reference to the accompanying drawings.  
     Embodiment of Actuator  
       FIG. 1 ( a ) is a schematic cross-sectional view showing the entire structure of an actuator in accordance with an embodiment of the present invention and  FIG. 1 ( b ) is an explanatory view showing the lines of magnetic force in the actuator.  
      As shown in  FIG. 1 ( a ), an actuator  1  in accordance with the embodiment of the present invention includes a fixed body  3  and a movable body  2  provided with a coil  8  for constructing a magnetic-drive circuit between the fixed body  3  and the movable body  2 .  
      The fixed body  3  includes a first yoke  4 , a pair of drive magnets  5 ,  6  disposed in an axial direction “L” so as to sandwich the first yoke  4 , and a second yoke  7 .  
      The first yoke  4  and the pair of drive magnets  5 ,  6  are respectively formed in a disk-like shape with the same diameter. Each of the drive magnets  5 ,  6  is a permanent magnet which is magnetized in a thickness direction such that one of its faces is magnetized at an N-pole and the other at an S-pole. The respective drive magnets  5 ,  6  are disposed such that their same polarities (N-pole in this embodiment) are directed to the first yoke  4 .  
      The second yoke  7  includes a pair of yoke members  71 ,  72  shaped in a bottomed cylinder which are capable of being divided in the axial direction “L”. The yoke members  71 ,  72  are disposed in the state where respective annular end faces  71   a ,  72   a  of respective cylindrical body parts  711 ,  721  of the yoke members  71 ,  72  are butted with each other. In this state, the cylindrical body parts  711 ,  721  of the second yoke  7  are disposed so as to face the outer peripheral end face  40  of the first yoke  4  and the outer peripheral end faces of the pair of drive magnets  5 ,  6 . The bottom plate portions  712 ,  722  of the second yoke  7  are overlapped on the respective end faces  51 ,  61  which are located on the outer side of the drive magnets  5 ,  6  in the axial direction “L”.  
      Further, annular protruding parts  715 ,  725  which are protruded toward the outer peripheral end face  40  of the first yoke  4  are formed near the butting portion of the yoke members  71 ,  72  of the second yoke  7 . Therefore, as shown in  FIG. 1 ( b ), the magnetic flux which is to be guided to the first yoke  4  from the pair of drive magnets  5 ,  6  can be efficiently guided to the protruding parts  715 ,  725  of the second yoke  7  and the magnetic flux is radially radiated from the outer peripheral end face  40  of the first yoke  4  in the direction perpendicular to the axial direction “L”. The magnetic flux guided to the protruding parts  715 ,  725  forms a loop where the flux is guided to the cylindrical body part  711 ,  721  through the bottom plate portions  712 ,  722  and reaches the S-poles of the magnets  5 ,  6 .  
      The movable body  2  is provided with the coil  8  which is disposed to surround around the outer peripheral end face  40  of the first yoke  4  between the first yoke  4  and the protruding parts  715 ,  725  of the second yoke  7 . The coil  8  is wound around a coil bobbin  9  which is made of an electrically insulative resin and formed in a U-shape in cross-section. The coil  8  is supported by an elastic support member or the like (not shown).  
      In the actuator  1  as structured above, the movable body  2  is located at a stand-by position shown in FIGS.  1 ( a ) and  1 ( b ) when the coil  8  is not energized. In this state as shown in  Fig. 1 ( b ), when an electric current directed up from the paper surface is applied to the coil  8 , the movable body  2  is displaced or moved in the direction shown by the arrow “F 1 ”. On the other hand, when an electric current directed down into the paper surface is applied to the coil  8 , the movable body  2  is displaced or moved in the direction shown by the arrow “F 2 ”. Therefore, when an alternating current is applied to the coil  8 , the movable body  2  is alternately displaced or moved in the direction shown by the arrow “F 1 ” and in the direction shown by the arrow “F 2 ”. Consequently, the movement of the movable body  2  can be utilized in the driving of various types of members.  
      As described above, in the fixed body  3  of the actuator  1  in accordance with an embodiment of the present invention, a pair of the drive magnets  5 ,  6  are superposed in the axial direction “L” such that the respective N-poles of the drive magnets  5 ,  6  face the first yoke  4 . Further, the second yoke  7  is disposed so as to face the outer peripheral end face  40  of the first yoke  4 . Therefore, the magnetic flux from the pair of the drive magnets  5 ,  6  can be efficiently guided to the direction perpendicular to the axial direction “L” from the outer peripheral end face  40  of the first yoke  4 . Accordingly, the density of the magnetic flux is high, which interlinks with the coil  8  disposed so as to surround the outer peripheral end face  40  of the first yoke  4 , and thus a large thrust can be acted on the movable body  2 .  
      The first yoke  4  is sandwiched between common poles of the drive magnets  5 ,  6 . Therefore, the drive magnets  5 ,  6  are not attracted to each other simplifying the assembly operation.  
      In addition, since the drive magnets  5 ,  6  are disposed in the fixed body  3 , the moving range of the drive magnets  5 ,  6  is not required to be considered which is different from the case in which the drive magnets  5 ,  6  are disposed in the movable body. Accordingly, even when the drive magnets  5 ,  6  are disposed close to peripheral members, the movement of the movable body is not disturbed because the drive magnets  5 ,  6  are not magnetically attracted by the peripheral members. In addition, even when a shield is applied to the magnetic field such that the peripheral members are not attracted by the drive magnet  5 ,  6 , or such that malfunction is not induced in peripheral devices, the drive magnets  5 ,  6  can be compactly covered because the drive magnets  5 ,  6  are fixed. In addition, in an embodiment of the present invention, since the second yoke  7  is disposed to cover the drive magnets  5 ,  6  and the coil  8 , the shield is efficiently performed by the second yoke  7 . Accordingly, since another shield member is not required, the outer dimension of the actuator  1  can be made small. As a result, the actuator  1  in the embodiment of the present invention is suitable for mounting on a small-sized device such as a lens drive device, which is mounted on a portable telephone with a camera, and a pump device described later.  
     Embodiment of Pump Device  
      The actuator  1  described with reference to FIGS.  1 ( a ) and  1 ( b ) can be used in a pump device that is constructed so that the reciprocating movement of the movable body  2  performs a pumping operation  FIG. 2  is a plan view showing a pump device to which the present invention is applied.  FIG. 3 ( a ) is a cross-sectional view showing the pump device that is cut by the line of “3-3A-A” in  FIG. 2  and  FIG. 3 ( b ) is a cross-sectional view showing the pump device that is cut by the line of “B-B” in  FIG. 2 .  FIG. 4  is an exploded perspective view showing the pump device shown in FIGS.  2  and FIGS.  3 ( a ) and  3 ( b ). Respective component members shown in  FIG. 4  are vertically symmetrically disposed with the movable body as a center and the respective corresponding component parts structured in a vertically symmetrical manner.  
      As shown in  FIG. 2 , FIGS.  3 ( a ) and  3 ( b ) and  FIG. 4 , a pump device  10  in accordance with an embodiment of the present invention is provided with an electromagnetic actuator on the inside of a sealing case  50 . The structure of the actuator is basically the same as that of the above-mentioned actuator  1  and thus the same notational symbol is used for the corresponding structural element  
      In the pump device  10  in accordance with the embodiment of the present invention, the movable body  2  is disposed in the space formed by the second yoke  7  such that a first pump chamber  11  is formed on one side of the movable body  2  in the axial direction “L” and a second pump chamber  12  is formed on the other side of the movable body  2  in the axial direction “L”. In this embodiment, the movable body  2  is used as a piston which is reciprocated in the axial direction “L”.  
      More concretely, the fixed body  3  includes two plates of the first yoke  4 , a pair of drive magnets  5 ,  6  overlapped so as to interpose the first yoke  4  therebetween, and the second yoke  7 . The two plates of the first yoke  4  are superposed in the axial direction “L” and formed with the same diameter as that of the drive magnets  5 ,  6 . Each of the drive magnets  5 ,  6  is a permanent magnet that is magnetized in a thickness direction such that one of its faces is magnetized at an N-pole and the other at an S-pole. The respective drive magnets  5 ,  6  are disposed such that their same polarities (N-pole in this embodiment) are directed to the first yoke  4 .  
      In this embodiment of the present invention, the second yoke  7  includes a pair of yoke members  15 ,  16  shaped in a bottomed cylinder and a pair of ring-shaped yoke members  17 ,  18 . In the state that these yoke members are superposed each other, the bottom plate portions  712 ,  722  of the yoke members  15 ,  16  are overlapped on the respective end faces  51 ,  61  of the drive magnets  5 ,  6  in the axial direction “L”. The inner peripheral edge portions of the ring-shaped yoke members  17 ,  18  are protruded in the inside of the space that is formed by the second yoke  7 . Annular protruding parts  715 ,  725  protruded toward the outer peripheral end face  40  of the first yoke  4  are formed by the inner peripheral edge portions of the ring-shaped yoke members  17 ,  18 . Flange portions are formed in the yoke members  15 ,  16  at the butting portions with the yoke members  17 ,  18 . Sealing is applied between the flange portions of the yoke members  15 ,  16  and the outer peripheral edge portions of the yoke members  17 ,  18 . The inner peripheral edge portions of the sealing members  19 ,  20  are pinched between the yoke members  17 ,  18 .  
      The movable body  2  is provided with the coil  8  which is disposed to surround around the outer peripheral end face  40  of the first yoke  4  between the first yoke  4  and the second yoke  7 . The coil  8  is wound around a coil bobbin  9  which is made of an electrically insulative resin and formed in a U-shape in cross-section. Ring-shaped guide members  22 ,  23  are disposed within the space which is formed by the second yoke  7  for performing the guide operation at the time of the movement of the movable body  2 . The movable body  2  can be moved in the axial direction “L” while sliding on the inner peripheral face of the guide members  22 ,  23 , the outer peripheral end face  40  of the first yoke  4 , and the outer peripheral end faces of a pair of the drive magnets  5 ,  6 . Therefore, the movable body  2  serves as a piston of the first pump chamber  11  and the second pump chamber  12 .  
      A small projecting part  91  in a pillar shape is formed on each of the end faces of the coil bobbin  9  and small holes  221 ,  231  are formed in the guide members  22 ,  23  into which the small projecting parts  91  in the pillar shape are slidably fitted. The small projecting parts  91  are sidably guided by the small holes  221 ,  231 . Therefore, the movable body  2  does not incline because the small pillar shaped projecting parts  91  are fitted into and guided by the small holes  221 ,  231  when the movable body  2  is moved in the axial direction “L”. Further, thin plate-like projecting parts  92  are protruded from the respective outer peripheral edge portions of both the end faces of the coil bobbin  9 . On the other hand, grooves  222 ,  232  to which the plate-like projecting parts  92  are fitted are formed in the guide members  22 ,  23 . Therefore, since the projecting parts  92  of the coil bobbin  9  are guided by the grooves  222 ,  232  of the guide members  22 ,  23 , the movable body  2  does not move around the axial direction “L”. Further, the plate-like projecting parts  92  of the coil bobbin  9  are guided by the inner peripheral faces of the guide members  22 ,  23 , and thus the movable body  2  does not incline. In addition, thin plate-like projecting parts  93  are protruded from the inner peripheral edge portions of both the end faces of the coil bobbin  9  and the plate-like projecting parts  93  slide on the outer peripheral end face  40  of the first yoke  4  and on the outer peripheral end faces of a pair of the drive magnets  5 ,  6 . Therefore, the movable body  2  does not incline.  
      The actuator  1  is housed in the sealing case  50  and a common fluid inlet port  28  and a common fluid outlet port  29  are formed in the sealing case  50 , which are in communication with both the first pump chamber  11  and the second pump chamber  12 . The sealing case  50  includes rectangular and tubular main case bodies  58 ,  59 , which are formed with circular aperture parts  58   a ,  59   a  for accommodating the actuator  1  and rectangular case covers  53 ,  54  for closing the circular aperture parts  58   a ,  59   a  of the main case bodies  58 ,  59  from the outside. A discharge pipe  31  in communication with the common fluid outlet port  29  is connected with the main case body  58  and a suction pipe  30  in communication with the common fluid inlet port  28  is connected with the main case body  59 . The case covers  53 ,  54  are fixed to the main case bodies  58 ,  59  with screws  55  or the like. When the sealing case  50  is assembled, the outer peripheral edge portions of the sealing members  19 ,  20  are pinched by the main case bodies  58 ,  59 .  
      In the state when the pump device is disassembled, in other words, the assembling is on the way as shown in  FIG. 4 , the common fluid inlet port  28  and the common fluid outlet port  29  are exposed to the outside, and thus the valves  111 ,  121  for suction and the valves  112 ,  122  for discharge can be mounted. The valve  111  for suction prevents fluid from flowing backward from the first pump chamber  11  to the suction pipe  30 . The valve  112  for suction prevents the fluid from flowing backward from the second pump chamber  12  to the suction pipe  30 . The valve  112  for discharge prevents the fluid from flowing backward from the discharge pipe  31  to the first pump chamber  11 . The valve  122  for discharge prevents the fluid from flowing backward from the discharge pipe  31  to the second pump chamber  12 .  
      In the actuator  1  for the pump device  10  structure described above, when an alternating current is applied to the coil  8 , the movable body  2  is alternately moved with a stroke length of about 1 mm in the direction shown by the arrow “F 1 ” and the direction shown by the arrow “F 2 ”. At this time, when the movable body  2  moves to the upper side as shown by the arrow “F 1 ” in  FIG. 1 ( b ), the fluid is sent out from the first pump chamber  11  through the common fluid outlet port  29  and the discharge pipe  31 . On the other hand, the fluid is introduced into the second pump chamber  12  through the suction pipe  30  and the common fluid inlet port  28 . On the contrary, when the movable body  2  moves to the under side as shown by the arrow “F 2 ”, the fluid is introduced into the first pump chamber  11  through the suction pipe  30  and the common fluid inlet port  28 , and the fluid is sent out from the second pump chamber  12  through the common fluid outlet port  29  and the discharge pipe  31 .  
      As described above, the pump device  10  in accordance with this embodiment of the present invention includes the actuator  1  provided with the fixed body  3  in which a pair of the drive magnets  5 ,  6  are overlapped on the first yoke  4  in the axial direction “L” with the N-poles of the drive magnets  5 ,  6  directing to the first yoke  4 . In this actuator  1 , the second yoke  7  is disposed so as to face the outer peripheral end face  40  of the first yoke  4 . Moreover, the second yoke  7  is provided with the protruding parts  715 ,  725  that are protruded toward the outer peripheral end faces  40  of the first yoke  4 . Therefore, the magnetic flux from the pair of the drive magnets  5 ,  6  can be effectively guided from the outer peripheral end face  40  of the first yoke  4  to the direction perpendicular to the axial direction “L”. Accordingly, since the density of the magnetic flux is high which interlinks with the coil  8  disposed so as to surround around the outer peripheral end face  40  of the first yoke  4 , a large thrust can be acted on the movable body  2 . As a result, the movable body  2  can effectively perform as a piston the suction of fluid to the first pump chamber  11  and the second pump chamber  12  and the discharge of the fluid from the pump chambers  11 ,  12 .  
      In addition, since the coil  8  is constructed as the movable body  2 , the weight of the movable body  2  can be reduced. Therefore, when the movable body  2  is used as a piston, a large thrust is capable of acting on the movable body  2 . Further, since the movable body  2  can be light-weight, the pump device  10  in accordance with the embodiment of the present invention can feed liquid as well as gas.  
      The first pump chamber  11  and the second pump chamber  12  are in communication with the common fluid inlet port  28  and in communication with the common fluid outlet port  29 . Therefore, fluid can be alternately sent out from the first pump chamber  11  and the second pump chamber  12 . Accordingly, the Flow rate can be large in comparison with the size of the pump device  10  and the occurrence of pulsating flow can be restrained.  
      In this embodiment of the present invention, two drive magnets  5 ,  6  are disposed such that the same polarities are directed to each other. However, since two plates of the first yoke  4  are sandwiched between the drive magnets  5 ,  6 , assembly against the repulsive forces of the drive magnets  5 ,  6  is simplified.  
      In addition, since the drive magnets  5 ,  6  are disposed in the fixed body  3 , the drive magnets  5 ,  6  are not attracted to peripheral magnetic members even when the drive magnets  5 ,  6  and the peripheral members are positioned in a close relation. Moreover, even when a shield is applied to the magnetic field such that the peripheral members are not attracted to the drive magnets  5 ,  6  or such that malfunctions are not induced in the peripheral devices, the periphery of the drive magnets  5 ,  6  can be covered in a compact manner because the drive magnets  5 ,  6  are fixed.  
      In addition, since the second yoke  7  is disposed so as to cover the drive magnets  5 ,  6  and the coil  8 , a shield is efficiently executed by the second yoke  7 . Therefore, since another shield member is not required, the outer dimension of the actuator  1  can be made smaller. As a result, the pump device  10  in this embodiment of the present invention can be made thinner to the extent of the thickness of 10 mm or less, and thus the pump device  10  can be used as a cooling pump for a CPU and the like in a notebook type personal computer.  
     Another Embodiment of Pump Device  
      FIGS.  5 ( a ) through  5 ( c ) are cross-sectional views showing another pump device in accordance with an embodiment of the present invention  FIG. 5 ( a ) is a cross-sectional view showing the pump device that is cut at a position corresponding to the line of “A-A” in  FIG. 2 ,  FIG. 5 ( b ) is a cross-sectional view showing the pump device which is cut at a position corresponding to the line of “B-B” in  FIG. 2 , and  FIG. 5 ( c ) is an enlarged view showing a portion of the pump device encircled by the line “C” in  FIG. 5 ( a ). The structure of the pump device in this embodiment is basically the same as that of the above-mentioned pump device  10  and thus the same notational symbol is used for the corresponding structural element.  
      In the pump device  10  of this embodiment shown in FIGS.  5 ( a ) through  5 ( c ), similarly to the pump device described with reference to  FIG. 2 , FIGS.  3 ( a ) and  3 ( b ) and  FIG. 4 , the actuator  1  described with reference to FIGS.  1 ( a ) and  1 ( b ) is provided on the inside of the sealing case  50 . In other words, in the actuator  1 , the fixed body  3  includes two plates of the first yoke  4 , a pair of the drive magnets  5 ,  6  overlapped so as to interpose the first yoke  4  therebetween, and the second yoke  7 . The respective drive magnets  5 ,  6  are disposed such that their same polarities are directed to the first yoke  4 . The second yoke  7  is superposed on the respective end faces  51 ,  61  of the drive magnets  5 ,  6  positioned on the outer side in the axial direction “L”. The second yoke  7  is provided with ring-shaped protruding parts  715 ,  725  which are protruded to the outer peripheral end face  40  of the first yoke  4 .  
      The movable body  2  is provided with the coil  8  which is disposed to surround around the outer peripheral end face of the first yoke  4  between the first yoke  4  and the ring-shaped plate members  17 ,  18  of the second yoke  7 .  
      In this embodiment the movable body  2  is supported in the state that the coil  8  is wrapped with two sheet-shaped elastic members  60  from both sides in the axial direction “L”. The two overlapped inner peripheral edge parts of the elastic members  60  are held between the two plates of the first yoke  4  and the two overlapped outer peripheral edge parts are held between the protruding parts  715 ,  725 . Therefore, the first pump chamber  11  is formed by the movable body  2  on one side of the movable body  2  in the axial direction “L” in the space which is formed by the second yoke  7 , and the second pump chamber  12  is formed in the other side of the movable body  2  in the axial direction “L”. In other words, the movable body  2  serves as a diaphragm for the first pump chamber  11  and the second pump chamber  12 . The elastic member  60  may be formed of a film-like member basically made of rubber and fiber, or a film-like member that is formed of resin in a film-like shape.  
      Annular recessed parts  401 ,  750  in a rectangular cross section are resctively formed on the outer peripheral end faces  40  of two plates of yokes  4  and the inner peripheral end faces of the protruding parts  715 ,  725  to accommodate elastic deforming parts  601 ,  602  which permit the elastic member  60  to elastically deform in the axial direction “L”.  
      Also in this embodiment of the present invention, the first pump chamber  11  and the second pump chamber  12  are connected to the discharge pipe  31  through the common fluid outlet port  29  and connected to the suction pipe  30  through the common fluid inlet port  28 . Further, the valves  112 ,  122  for discharge are disposed between the first pump chamber  11  and the common fluid outlet port  29 , and the valves  111 ,  121  for suction are disposed between the second pump chamber  12  and the common fluid inlet port  28 .  
      The pump device  10  structured as described above includes the actuator  1  provided with the fixed body  3  in which a pair of the drive magnets  5 ,  6  are overlapped on the first yoke  4  in the axial direction “L” with the N-poles of the drive magnets  5 ,  6  directing to the first yoke  4  similarly to the pump device described with reference to  FIG. 2 , FIGS.  3 ( a ) and  3 ( b ) and  FIG. 4 . In this actuator  1 , the second yoke  7  is disposed so as to face the outer peripheral end face  40  of the first yoke  4 . Moreover, the second yoke  7  is provided with the protruding parts  715 ,  725  which are protruded toward the outer peripheral end faces  40  of the first yoke  4 . Therefore, the magnetic flux from the pair of the drive magnets  5 ,  6  can be effectively guided from the outer peripheral end face  40  of the first yoke  4  to the direction perpendicular to the axial line direction “L”. Accordingly, since the density of the magnetic flux is high which interlinks with the coil  8  disposed so as to surround the outer peripheral end face  40  of the first yoke  4 , a large thrust can be acted on the movable body  2 . As a result, the movable body  2  can effectively perform as a diaphragm the suction of fluid to the first pump chamber  11  and the second pump chamber  12  and the discharge of the fluid from the pump chambers  11 ,  12 , and thus has similar effects as the pump device described with reference to  FIG. 2 , FIGS.  3 ( a ) and  3 ( b ) and  FIG. 4  can be obtained.  
     Other Embodiments  
      In the embodiments of the present invention, the first pump chamber  11  and the second pump chamber  12  are connected to the common fluid outlet port  29  and the common fluid inlet port  28 . However, when the pump device is provided with a first fluid inlet port which is in communication with the first pump chamber  11 , a second fluid inlet port which is in communication with the second pump chamber  12 , a first fluid outlet port which is in communication with the first pump chamber  11 , and a second fluid outlet port which is in communication with the second pump chamber  12 , different fluids can be respectively sent out from the first pump chamber  11  and the second pump chamber  12  by using only one pump device. Therefore, for example, the feeding of water and alcohol can be performed by using one pump device in a fuel cell system.  
      When the number of turns of the coil  8  is small, a flexible printed circuit board (FPC) may be used as the movable body  2  instead of the coil  8 .  
      While the description above refers to particular embodiments of the present invention, it will be understood that many modifications may be made without departing from the spirit thereof. The accompanying claims are intended to cover such modifications as would fall within the true scope and spirit of the present invention.  
      The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.