Abstract:
A metering pump device capable of performing a fixed amount of discharge with a high accuracy even if a pressure difference occurs between outflow side valves. In the metering pump device, two reciprocating pump devices are used. The end and start of the discharge period of one reciprocating pump device are overlapped with the start and end of the discharge period of the other reciprocating pump device. After the inhalation operation and before the discharge period, both the inflow side valves and the outflow side valves are closed to perform a correction operation for eliminating the pressure difference by increasing or decreasing the internal volumes of the pump chambers.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a U.S. national stage application of PCT International application No. PCT/JP2007/058484, filed on Apr. 19, 2007. Priority under 35 U.S.C. §119(a) and 35 U.S.C. §365(b) is claimed from Japanese Application No. 2006-117194, filed Apr. 20, 2006, the disclosures of which are also incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a metering pump device which is provided with a plurality of reciprocating pump devices. 
       BACKGROUND 
       [0003]    There is a metering pump device which utilizes a reciprocating pump device. In a reciprocating pump, there always exists a point where a discharge amount becomes zero at a top dead point or a bottom dead point and thus accuracy of a constant-quantity discharge is not satisfactory. Therefore, a structure has been proposed in which two reciprocating pump devices are connected in parallel to each other and, at the time when discharge of one of the reciprocating pump devices has finished, the other of the reciprocating pump devices starts to discharge so that the whole discharge flow rate becomes constant (see Patent Reference 1). 
         [0004]    [Patent Reference 1] Japanese Patent Laid-Open No. 2001-207951. 
       SUMMARY 
       [0005]    However, even when two reciprocating pump devices are phased each other like reciprocating pump devices disclosed in Patent Reference 1, in a case when there is a difference in pressure between an inside of a pump chamber and a common discharge port side, immediately after an outflow side valve has been changed to an open state, outflow of fluid from the pump chamber to the common discharge port side may occur, or inflow of fluid from the common discharge port side to the inside of the pump chamber may occur, which incurs a problem that discharge amount is varied. In the metering pump device disclosed in Patent Reference 1, an inflow side valve is set in an open state to contract the pump chamber in order to discharge air bubbles from the pump chamber after fluid is sucked into the pump chamber. However, in this operation, dispersion of discharge amount per unit of time cannot be prevented when there is a difference in pressure between the inside of the pump chamber and the common discharge port side. 
         [0006]    In view of the problems described above,the present invention may provide a metering pump device which is capable of discharging quantitatively or discharging at a constant rate with a high degree of accuracy even when a difference in pressure is generated on both sides of an outflow side valve. 
         [0007]    In order to achieve the above, there may be provided a metering pump device including a plurality of reciprocating pump devices each of which is connected with an inflow side valve and an outflow side valve on an inflow side and an outflow side, a common discharge port which is connected with the plurality of the reciprocating pump devices through the outflow side valves, and a control part for controlling the inflow side valves, the outflow side valves and the reciprocating pump devices. The control part sets a discharge period and a waiting period for each of the plurality of the reciprocating pump devices so as to shift timings of the discharge period and the waiting period each other, and a starting time and an ending time of the discharge period of one of the reciprocating pump devices are superposed on an ending time and a starting time of the discharge period of another reciprocating pump device and, after a suction operation into a pump chamber has been performed in the waiting period and before the discharge period, a correcting operation is performed in which both of the inflow side valve and the outflow side valve are closed and a volume within the pump chamber is expanded or contracted to eliminate a difference in pressure between a pressure within the pump chamber and a common discharge port side. 
         [0008]    According to at least an embodiment of the present invention, a plurality of reciprocating pump devices is used and a starting time and an ending time of the discharge period of one of the reciprocating pump devices are superposed on an ending time and a starting time of the discharge period of another reciprocating pump device. Therefore, even when there is a point where a discharge amount becomes zero at a top dead point or a bottom dead point in the reciprocating pump device, the entire amount of discharge flow becomes always constant. Further, after a suction operation and before a discharge period, a correcting operation is performed in which both of the inflow side valve and the outflow side valve are closed and a volume within the pump chamber is expanded or contracted to eliminate a difference in pressure. Therefore, even when there is a difference in pressure on both sides of the outflow side valve, discharging quantitatively or discharging at a constant rate can be performed with a high degree of accuracy. 
         [0009]    In accordance with at least an embodiment of the present invention, a plurality of reciprocating pump devices may be structured so that they are connected to separate suction ports through separate inflow side valves. However, a structure may be used in which a common suction port is connected with the plurality of the reciprocating pump devices through the inflow side valves. 
         [0010]    In at least an embodiment of the present invention, it is preferable that a drive source for the reciprocating pump device is a stepping motor or an AC synchronous motor. In such a motor, even when energization is stopped, position holding for the rotor can be attained by holding power. Therefore, even when position holding for a valve element is to be performed, continuous energization is not required which is different from a case where a solenoid or the like is used, and thus power consumption can be reduced. Further, when a drive source for the reciprocating pump device is a stepping motor, it is preferable that a variation amount of an internal volume of the pump chamber corresponding to one (1) step of the stepping motor is set to be 1/100 or less with respect to an entire internal volume of the pump chamber. According to this structure, a metering pump device with a high degree of resolving power can be realized. 
         [0011]    In at least an embodiment of the present invention, a structure may be used in which a monitoring device is provided for directly or indirectly monitoring a difference in pressure between a pressure in an inside of the pump chamber in the reciprocating pump device and a pressure on the common discharge port side, and the control part performs the correcting operation on a basis of a monitoring result in the monitoring device when there is a difference in pressure between a pressure in the inside of the pump chamber and the pressure on the common discharge port side. 
         [0012]    In at least an embodiment of the present invention, a structure may be used in which the monitoring device is provided with a plurality of first pressure sensors for monitoring respective pressures within the pump chambers of the plurality of the reciprocating pump devices, and a second pressure sensor for monitoring a pressure on the common discharge port side, and the difference in pressure is monitored by comparing a detection result of the first pressure sensor with a detection result of the second pressure sensor. 
         [0013]    In at least an embodiment of the present invention, a structure may be used in which the monitoring device is provided with a plurality of pressure sensors for monitoring respective pressures within the pump chambers of the plurality of the reciprocating pump devices, and the difference in pressure is monitored by comparing a detection result of a pressure sensor, which is disposed in the pump chamber of the reciprocating pump device in which the suction operation is performed, with a detection result of a pressure sensor which is disposed in the pump chamber of the reciprocating pump device whose output side valve is opened. 
         [0014]    Thus, a metering pump device, which is capable of realizing the above-mentioned control, may be provided with a plurality of reciprocating pump devices each of which is connected with an inflow side valve and an outflow side valve on an inflow side and an outflow side, a common discharge port which is connected with the plurality of the reciprocating pump devices through the outflow side valves, and pressure sensors for monitoring respective pressures within the pump chamber of the plurality of the reciprocating pump devices. 
         [0015]    In at least an embodiment of the present invention, when a number of the reciprocating pump device is two, the control device may set an expanding speed of the pump chamber at the time of the suction operation higher than a contracting speed of the pump chamber in the discharge period. 
         [0016]    In the metering pump device in accordance with at least an embodiment of the present invention, a plurality of reciprocating pump devices is used and a starting time and an ending time of the discharge period of one of the reciprocating pump devices are superposed on an ending time and a starting time of the discharge period of another reciprocating pump device. Therefore, even when there is a point where a discharge amount becomes zero at a top dead point or a bottom dead point in the reciprocating pump device, the entire amount of discharge flow becomes always constant. Further, after a suction operation and before a discharge period, a correcting operation is performed in which both of the inflow side valve and the outflow side valve are closed and a volume within the pump chamber is expanded or contracted to eliminate a difference in pressure. Therefore, when there is a difference in pressure between an inflow side of an inflow side valve and a discharge side of a discharge side valve, as a result, even when there is a difference in pressure on both sides of the outflow side valve, discharging quantitatively or discharging at a constant rate can be performed with a high degree of accuracy. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    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: 
           [0018]      FIG. 1  is a schematic view showing a basic structure of a metering pump device in accordance with a first embodiment of the present invention. 
           [0019]      FIG. 2  is a perspective view showing a structural example of the metering pump device shown in  FIG. 1 . 
           [0020]      FIG. 3  is a longitudinal sectional view showing a main body portion of the metering pump device shown in  FIG. 2 . 
           [0021]      FIGS. 4(   a ) through  4 ( h ) are timing charts showing an operation of a metering pump device to which at least an embodiment of the present invention is applied. 
           [0022]      FIGS. 5(   a ) through  5 ( h ) are timing charts showing an operation of a metering pump device to which at least an embodiment of the present invention is applied. 
           [0023]      FIG. 6  is a schematic view showing a basic structure of a metering pump device in accordance with a second embodiment of the present invention. 
           [0024]      FIG. 7  is a schematic view showing a basic structure of a metering pump device in accordance with a third embodiment of the present invention. 
           [0025]      FIG. 8  is an exploded perspective view showing a reciprocating pump device which is longitudinally divided and is used in a metering pump device to which at least an embodiment of the present invention is applied. 
           [0026]      FIG. 9  is an explanatory longitudinal sectional view showing an active valve which is used as an inflow side valve and an outflow side valve in a metering pump device to which at least an embodiment of the present invention is applied. 
           [0027]      FIG. 10  is an explanatory longitudinal sectional view showing another active valve which is viewed from obliquely above and is used as an inflow side valve and an outflow side valve in a metering pump device to which at least an embodiment of the present invention is applied. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0028]    Embodiments of the present invention will be described below with reference to the accompanying drawings. 
       First Embodiment 
     (Device Structure) 
       [0029]      FIG. 1  is a schematic view showing a basic structure of a metering pump device to which at least an embodiment of the present invention is applied.  FIG. 2  is a perspective view showing a structural example of a metering pump device to which at least an embodiment of the present invention is applied.  FIG. 3  is a longitudinal sectional view showing a main body portion of the metering pump device shown in  FIG. 2 . 
         [0030]    As shown in  FIG. 1 , a metering pump device  1  in this embodiment is a pump device for discharging liquid or gas quantitatively or at a constant rate. The metering pump device  1  is provided with two reciprocating pump devices  10 A and  10 B in which inflow side valves  11 Ai and  11 Bi and outflow side valves  11 Ao and  11 Bo are respectively connected to inflow passages  12 Ai and  12 Bi and outflow passages  12 Ao and  12 Bo. A common discharge port  13   o  is structured in a common outflow passage  12   o  which is connected to the two reciprocating pump devices  10 A and  10 B through the outflow side valves  11 Ao and  11 Bo. Further, in the metering pump device  1  in this embodiment, a common suction port  13   i  is structured in a common inflow passage  12   i  which is connected to the two reciprocating pump devices  10 A and  10 B through the inflow side valves  11 Ai and  11 Bi. In this embodiment, the reciprocating pump devices  10 A and  10 B are provided with the same structure as each other and all of the inflow side valves  11 Ai and  11 Bi and the outflow side valves  11 Ao and  11 Bo are provided with the same structure as each other. Further, the inflow passages  12 Ai and  12 Bi are provided with the same structure as each other and the outflow passages  12 Ao and  12 Bo are provided with the same structure as each other. 
         [0031]    The metering pump device  1  in this embodiment is, for example, as shown in  FIG. 2 , provided with a main body portion  2  in a rectangular parallelepiped shape in which plural pieces of plate are laminated and a control device  3  (control part) which is connected with the main body portion  2  through a connector and a cable. The main body portion  2  is structured so that a bottom plate  75 , a base plate  76 , a flow passage structure plate  77 , and a top plate  78  for closing an upper face of the flow passage by covering an upper face of the flow passage structure plate  77  are laminated in this order. A pipe  781  structuring the common discharge port  13   o  and a pipe  782  structuring the common suction port  13   i  are connected to the top plate  78 . 
         [0032]    As shown in  FIG. 3 , each of the reciprocating pump devices  10 A and  10 B is provided with a valve element comprised of a diaphragm valve  170 , which is disposed in a pump chamber  20 , and a drive device  105  including a stepping motor (drive source) for driving the valve element to contract or expand an internal volume of the pump chamber  20 . When the stepping motor is rotated in one direction, the diaphragm valve  170  is driven in a direction to expand the internal volume of the pump chamber  20  and, when the stepping motor is rotated in the opposite direction, the diaphragm valve  170  is driven in the direction where the internal volume of the pump chamber  20  is contracted. In this embodiment, an amount of change of the internal volume of the pump chamber  20  corresponding to one step of the stepping motor is set to be 1/100 or less to the entire internal volume of the pump chamber  20 . 
         [0033]    The inflow side valves  11 Ai and  11 Bi and the outflow side valves  11 Ao and  11 Bo are respectively an active valve which is provided with a valve element (diaphragm valve  260 ) and a linear actuator  201  and they perform an opening/closing operation independently. 
       (Operation) 
       [0034]      FIGS. 4(   a )- 4 ( h ) are timing charts showing an operation of a metering pump device in this embodiment and its control is performed by the control device  3  shown in  FIG. 2 . 
         [0035]      FIG. 4(   a ) shows a state where a valve element is driven by a stepping motor in the first reciprocating pump device  10 A. In  FIG. 4(   a ), an upward period in the waveform shows a state where the pump chamber  20  is contracted to discharge fluid and a downward period in the waveform shows a state where the pump chamber  20  is expanded to suck liquid.  FIGS. 4(   b ) and  4 ( c ) show states where the inflow side valve  11 Ai and the outflow side valve  11 Ao are driven for the first reciprocating pump device  10 A. When an upward signal in the waveform is inputted, after that, the valve is maintained in an open state until a downward signal in the waveform is inputted. When a downward signal in the waveform is inputted, after that, the valve is maintained in a close state until an upward signal in the waveform is inputted.  FIG. 4(   d ) shows a state where a valve element is driven by a stepping motor in the second reciprocating pump device  10 B. In  FIG. 4(   d ), during an upward period in the waveform, the pump chamber  20  is contracted to discharge liquid and, during a downward period in the waveform, the pump chamber  20  is expanded to suck liquid.  FIGS. 4(   e ) and  4 ( f ) show states where the inflow side valve  11 Bi and the outflow side valve  11 Bo are driven for the second reciprocating pump device  10 B. When an upward signal in the waveform is inputted, after that, the valve is maintained in an open state until a downward signal in the waveform is inputted. When a downward signal in the waveform is inputted, after that, the valve is maintained in a close state until an upward signal in the waveform is inputted.  FIG. 4(   g ) shows a synthesized result of discharge amounts of liquids (discharge amount from the common discharge port  13   o ) which are discharged from the first reciprocating pump device  10 A and the second reciprocating pump device  10 B.  FIG. 4(   h ) shows a synthesized result of suction amounts of liquids (suction amount from the common suction port  13   i ) which are sucked into the first reciprocating pump device  10 A and the second reciprocating pump device  10 B. 
         [0036]    Although an operation for each time will be described below, in this embodiment, as shown in an upper side of  FIGS. 4(   a )- 4 ( h ), the control device  3  sets discharge periods T 1 A and T 1 B and waiting periods T 2 A and T 2 B at shifted timings for two reciprocating pump devices  10 A and  10 B. In addition, a starting time and an ending time of a discharge period (for example, discharge period T 1 A) of one of the reciprocating pump devices (for example, the first reciprocating pump device  10 A) are superposed on an ending time and a starting time of a discharge period (for example, discharge period T 1 B) of the other of the reciprocating pump devices (for example, the second reciprocating pump device  10 B). 
         [0037]    Further, after a suction operation to the pump chamber  20  has been performed during the waiting periods T 2 A and T 2 B and, before the discharge periods T 1 A and T 1 B, the control device  3  performs a correcting operation in which both the inflow side valves  11 Ai and  11 Bi and the outflow side valves  11 Ao and  11 Bo are set in close states and a volume within the pump chamber  20  is contracted to eliminate a difference in pressure. 
         [0038]    In  FIGS. 4(   a )- 4 ( h ), first, up to the time “t 0 ”, the reciprocating pump devices  10 A and  10 B are in a stop state in which liquid (fluid) has been sucked to the respective pump chambers  20 . Further, all of the valves are in a close state. In this state, as shown in  FIGS. 4(   a ),  4 ( b ) and  4 ( c ), after the outflow side valve  11 Ao for the first reciprocating pump device  10 A is opened at the time “t 0 ”, at the time “t 1 ”, the valve element in the first reciprocating pump device  10 A is driven in a direction so that the pump chamber  20  is contracted and, as a result, a liquid discharge is started. This discharge continues during the discharge period T 1 A (i.e., from time “t 1 ” up to the time “t 8 ”) and, during this time period, the first reciprocating pump device  10 A discharges liquid in a fixed quantity. 
         [0039]    Then, at the time “t 8 ”, the outflow side valve  11 Ao for the first reciprocating pump device  10 A is set in a close state and the liquid discharge is stopped. This stopped state is continued during the waiting period T 2 A up to the time “t 13 ”. In this waiting period T 2 A, at the time “t 9 ”, the inflow side valve  11 Ai for the first reciprocating pump device  10 A is set in an open state and, after that, from the time “t 10 ” to the time “t 11 ”, the valve element in the first reciprocating pump device  10 A is driven in a direction to expand the pump chamber  20  to perform a suction operation of liquid. 
         [0040]    Next, at the time “t 13 ”, the outflow side valve  11 Ao for the first reciprocating pump device  10 A is set in an open state again and, after that, at the time “t 14 ”, the valve element in the first reciprocating pump device  10 A is driven in a direction to contract the pump chamber  20  again and liquid discharge is started. This discharge is continued during the discharge period T 1 A up to the time “t 22 ” and, during that time period, the first reciprocating pump device  10 A discharges liquid at a constant rate. 
         [0041]    At the time “t 22 ”, the outflow side valve  11 Ao for the first reciprocating pump device  10 A is set in the close state and the liquid discharge is stopped. This stop state is continued during the waiting period T 2 A (i.e., from time “t 22 ” up to the time “t 27 ”). In this waiting period T 2 A, at the time “t 23 ”, the inflow side valve  11 Ai for the first reciprocating pump device  10 A is set in the open state and, after that, from the time “t 24 ” to the time “t 25 ”, the valve element in the first reciprocating pump device  10 A is driven in a direction to expand the pump chamber  20  and a liquid suction operation is performed. Afterwards, the above-mentioned serial operations are repeated with the valve element in the first reciprocating pump device  10 A driven in a direction between time “t 28 ” through “t 29 ” to contract the pump chamber  20  again and liquid discharge started again. 
         [0042]    On the other hand, as shown in  FIGS. 4(   d ),  4 ( e ) and  4 ( f ), the same operations are performed in the second reciprocating pump device  10 B but their timings are shifted. Therefore, at the time “t 6 ”, the outflow side valve  11 Bo for the second reciprocating pump device  10 B is set in an open state and, after that, at the time “t 7 ”, the valve element in the second reciprocating pump device  10 B is driven in a direction to contract the pump chamber  20  and a liquid discharge is started. The discharge is continued during the discharge period “T 1 B” up to the time “t 15 ” and, during that time period, the second reciprocating pump device  10 B discharges the liquid at a constant rate. Next, at the time “t 15 ”, the outflow side valve  11 Bo for the second reciprocating pump device  10 B is set in a close state and the liquid discharge is stopped. This stop state is continued during the waiting period T 2 B up to the time “t 20 ”. In the waiting period T 2 B, at the time “t 16 ”, the inflow side valve  11 Bi for the second reciprocating pump device  10 B is set in an open state and, after that, from the time “t 17 ” to the time “t 18 ”, the valve element in the second reciprocating pump device  10 B is driven in a direction to expand the pump chamber  20  and a liquid suction operation is performed. Afterwards, the above-mentioned serial operations are repeated. 
         [0043]    In this embodiment, in the time period “t 7 ” through “t 8 ” and the time period “t 21 ” through “t 22 ”, the ending time of the discharge period T 1 A of the first reciprocating pump device  10 A is overlapped with the starting time of the discharge period T 1 B of the second reciprocating pump device  10 B. Further, in the time period “t 14 ” through “t 15 ”, the ending time of the discharge period T 1 B of the second reciprocating pump device  10 B is overlapped with the starting time of the discharge period T 1 A of the first reciprocating pump device  10 A. Therefore, as shown in  FIG. 4(   h ), liquid suction is intermittently performed but, as shown in  FIG. 4(   g ), a discharge rate (discharge amount per unit time) is always constant which is a synthesized liquid discharge amount (discharge amount from a common discharge port), which is synthesized of amounts that are discharged from the first reciprocating pump device  10 A and the second reciprocating pump device  10 B. 
       (Correcting Operation for Pressure Difference) 
       [0044]    In the metering pump device  1  in this embodiment, in a case that there is a difference in pressure between the inside of the pump chamber  20  and the common discharge port  13   o  side, immediately after the outflow side valves  11 Ao and  11 Bo have been changed into the open state, outflow of liquid occurs from the pump chamber  20  to the common discharge port  13   o  side or inflow of liquid occurs from the common discharge port  13   o  side to the pump chamber  20  to vary the discharge amount. 
         [0045]    In order to prevent this problem, in this embodiment, conditions are set in the control device  3  based on operating conditions of the metering pump device  1  so that a pressure in the common discharge port  13   o  side is higher than a pressure within the pump chamber  20 . In other words, the control device  3  performs a correcting operation according to a previously set condition such that, in the waiting periods T 2 A and T 2 B, after a suction operation to the pump chamber  20  has been performed and before the discharge periods T 1 A and T 1 B, during the time periods “t 5 ” through “t 6 ”, “t 12 ” through “t 13 ” and “t 19 ” through “t 20 ”, both of the inflow side valve  11 Ai and the outflow side valve  11 Ao are closed, or both of the inflow side valve  11 Bi and the outflow side valve  11 Bo are closed, the valve element is driven in a direction contracting a volume of the inside of the pump chamber  20  in the first reciprocating pump device  10 A or the second reciprocating pump device  10 B. For example, in the waiting period T 2 A, after a suction operation to the pump chamber  20  has been performed and before the discharge period T 1 A, during the time periods “t 5 ” through “t 6 ” and “t 19 ” through “t 20 ”, both of the inflow side valve  11 Ai and the outflow side valve  11 Ao for the first reciprocating pump device  10 A are closed and the valve element is driven in a direction contracting the volume of the inside of the pump chamber  20  in the first reciprocating pump device  10 A to increase a pressure in the pump chamber  20  to eliminate a difference in pressure with respect to the common discharge port  13   o  side. Further, in the waiting period T 2 B, after a suction operation to the pump chamber  20  has been performed and before the discharge period T 1 B, during the time period “t 12 ” through “t 13 ”, both of the inflow side valve  11 Bi and the outflow side valve  11 Bo for the second reciprocating pump device  10 B are closed and the valve element is driven in a direction contracting the volume of the inside of the pump chamber  20  of the second reciprocating pump device  10 B to increase a pressure in the pump chamber  20  to eliminate a difference in pressure with respect to the common discharge port  13   o  side. 
         [0046]    In the embodiment described above, since the pressure on the common discharge port  13   o  side is higher than the pressure in the inside of the pump chamber  20 , the pressure within the pump chamber  20  before being discharged is increased. However, in a case that a pressure on the common discharge port  13   o  side is lower than a pressure in the inside of the pump chamber  20 , as shown in  FIGS. 5(   a )- 5 ( h ), a correcting operation may be performed in which, in the waiting periods T 2 A and T 2 B, after a suction operation to the pump chamber  20  has been performed and before the discharge periods T 1 A and T 1 B, during the time periods “t 5 ” through “t 6 ”, “t 12 ” through “t 13 ” and “t 19 ” through “t 20 ”, both of the inflow side valve and the outflow side valve are closed and a valve element is driven in a direction expanding a volume in the inside of the pump chamber  20 . 
         [0000]    (Principal Effects of this Embodiment) 
         [0047]    As described above, in the metering pump device  1  in this embodiment, two reciprocating pump devices  10 A and  10 B are used and a starting time and an ending time of a discharge time period of one of the reciprocating pump devices are overlapped with an ending time and a starting time of a discharge time period of the other of the reciprocating pump devices. Therefore, in the reciprocating pump devices  10 A and  10 B, even when a discharge amount becomes zero at a top dead point or a bottom dead point, the entire discharge flow rate becomes always constant. 
         [0048]    Further, after the suction operation and before the discharge periods T 1 A and T 1 B, the correcting operations T 3 A and T 3 B are performed in which both of the inflow side valve and the outflow side valve are closed and the volume of the inside of the pump chamber  20  is expanded or contracted to eliminate a difference in pressure. Therefore, even when there is a difference in pressure on both sides of the outflow side valves  11 Ao and  11 Bo, discharging at a constant rate can be performed with a high degree of accuracy. Further, in a case that a diaphragm valve is used as a valve element, unnecessary deformation may occur in the diaphragm valve due to a difference in pressure between an internal-pressure of the pump chamber  20  and atmospheric pressure. However, in this embodiment, suction and discharge can be performed while the above-mentioned deformation is corrected and thus high degree of accuracy for suction amount and discharge amount is obtained. 
         [0049]    Further, in the reciprocating pump devices  10 A and  10 B, an operation is controlled by a signal pattern which is supplied to a stepping motor used in the drive device  105 . Therefore, different from a structure in which an operation of a reciprocating pump device is controlled by a cam mechanism, a moving speed of a valve element (diaphragm valve  170 ) can be easily changed only by changing a signal pattern which is supplied to the stepping motor. Accordingly, the reciprocating pump devices  10 A and  10 B can stably deal with a condition from a little discharge amount to a large discharge amount per unit time. Further, even in a case of condition that a discharge amount per unit time is large, reciprocating number of times of the diaphragm valve  170  is small and thus service life time of the metering pump device  1  is increased. 
         [0050]    Further, each of the inflow side valves  11 Ai and  11 Bi and the outflow side valves  11 Ao and  11 Bo is an active valve which independently performs an opening/closing operation and thus both of the inflow side and the outflow side can be prevented from being opened. Therefore, even when a pressure in the valve suction port  13   i  side is higher than that in the discharge opening  13   o  side, a forward flow does not occur and thus the metering pump device  1  is capable of discharging at a constant rate all the time. Further, when all of the inflow side valves  11 Ai and  11 Bi and the outflow side valves  11 Ao and  11 Bo are set in the open state and the reciprocating pump devices  10 A and  10 B are operated, liquid can be drawn from the insides of the reciprocating pump devices  10 A and  10 B. As a result, freeze proofing can be easily performed. 
         [0051]    In addition, in the metering pump device  1  in this embodiment, the suction side and the discharge side are provided with the same structure and thus the suction side and the discharge side can be replaced with each other to be operated. Therefore, liquid recovery can be performed from the discharge side to the suction side. 
         [0052]    In addition, a stepping motor is used as a drive source in the drive device  105  of the reciprocating pump devices  10 A and  10 B and a variation amount of the internal volume of the pump chamber  20  corresponding to one (1) step of the stepping motor is set to be 1/100 or less with respect to the entire internal volume of the pump chamber  20 . Therefore, the resolving power of the metering pump device  1  in this embodiment is high. Further, when energization is stopped, a stepping motor can hold the position of the rotor by holding power. Therefore, even when a position holding of the diaphragm valve  170  is performed, continuous energization is not required which is different from a case when a solenoid or the like is used and thus low power consumption can be attained. According to this viewpoint, an AC synchronous motor may be used instead of the stepping motor. 
       Second Embodiment 
       [0053]    In the first embodiment, it is set in advance that the correcting operations shown in  FIG. 4  or  5  are performed. However, in the second embodiment, a monitoring device is provided which directly or indirectly monitors a difference in pressure between pressures in the insides of the pump chambers  20  in the reciprocating pump devices  10 A and  10 B and that of the common discharge port  13   o  side. The control device  3  performs a correcting operation which is described with reference to  FIGS. 4(   a )- 4 ( h ) or  FIGS. 5(   a )- 5 ( h ) on the basis of a monitoring result in the monitoring device when there is a difference in pressure between a pressure in the inside of the pump chamber  20  and the common discharge port side. 
         [0054]    In this embodiment, as shown in  FIG. 6 , first pressure sensors  14 A and  14 B which monitor pressures in the respective pump chambers  20  in the reciprocating pump devices  10 A and  10 B and a second pressure sensor  14 o which monitors a pressure in the common discharge port  13   o  side are used as the monitoring device. In the monitoring device structured as described above, for example, after a suction operation to the inside of the pump chamber  20  has finished, detection results of the first pressure sensors  14 A and  14 B and a detection result of the second pressure sensor  14   o  are compared with each other and a difference in pressure is monitored. The control device  3  determines on the basis of the monitoring result which condition of the correcting operations is performed, in other words, which condition is performed whether the condition shown in  FIGS. 4(   a )- 4 ( h ) or the condition shown in  FIGS. 5(   a )- 5 ( h ). On the other hand, when there is no difference in pressure between the inside of the pump chamber  20  and the common discharge port side, the correcting operation is not performed. 
       Third Embodiment 
       [0055]    In the first embodiment, it is set in advance that the correcting operations shown in  FIG. 4  or  5  are performed. However, in the third embodiment, similarly to the second embodiment, a monitoring device is provided which directly or indirectly monitors a difference in pressure between pressures in the insides of the pump chambers  20  in the reciprocating pump devices  10 A and  10 B and that of the common discharge port  13   o  side. The control device  3  performs the correcting operation which is described with reference to  FIGS. 4(   a )- 4 ( h ) or  FIGS. 5(   a )- 5 ( h ) on the basis of a monitoring result in the monitoring device when there is a difference in pressure between a pressure in the inside of the pump chamber  20  and the common discharge port side. 
         [0056]    In this embodiment, as shown in  FIG. 7 , pressure sensors  14 A and  14 B for monitoring pressures in the respective insides of the pump chambers  20  in the reciprocating pump devices  10 A and  10 B are used as the monitoring device. In the monitoring device structured as described above, for example, at the time “t 19 ”, a detection result of the pressure sensor  14 B which is disposed in the pump chamber  20  in the reciprocating pump device  10 B where a suction operation to the inside of the pump chamber  20  has been finished and a detection result of the pressure sensor  14 A which is disposed in the pump chamber  20  in the reciprocating pump device  10 A are compared with each other and a difference in pressure between the inside of the pump chamber  20  and the common discharge port side is monitored. This is because that, at the time “t 14 ”, a detection result of the pressure sensor  14 A in the reciprocating pump device  10 A is equal to a pressure of the common discharge port side. The control device  3  determines on the basis of the monitoring result the condition where the correcting operation is performed during the time period “t 19 ” through “t 20 ”, in other words, which of the condition shown in  FIGS. 4(   a )- 4 ( h ) or the condition shown in  FIGS. 5(   a )- 5 ( h ) is performed. On the other hand, when there is no difference in pressure between the inside of the pump chamber  20  and the common discharge port side, the correcting operation is not performed. 
       (Specific Structural Example of Reciprocating Pump Device) 
       [0057]    A specific structural example of the reciprocating pump devices  10 A and  10 B which are used in the metering pump device in this embodiment will be described with reference to  FIGS. 3 and 8 . 
         [0058]      FIG. 8  is an exploded perspective view showing the reciprocating pump device which is longitudinally divided and is used in a metering pump device to which at least an embodiment of the present invention is applied. As shown in  FIGS. 3 and 8 , the main body portion  2  of the metering pump device  1  in this embodiment is structured so that the bottom plate  75 , the base plate  76 , the flow passage structuring plate  77  and the top plate  78  are laminated in this order. The reciprocating pump devices  10 A and  10 B are structured within holes formed in the base plate  76 . In this embodiment, each of the reciprocating pump devices  10 A and  10 B include the pump chamber  20 , the diaphragm valve  170  (valve element) for expanding and contracting an internal volume of the pump chamber  20  to perform suction and discharge of liquid, and the drive device  105  for driving the diaphragm valve  170 . 
         [0059]    The drive device  105  includes a ring-shaped stator  120 , a rotation body  103  coaxially disposed on an inner side of the stator  120 , a movable body  160  coaxially disposed on an inner side of the rotation body  103 , and a conversion mechanism  140  for converting rotation of the rotation body  103  into a force for moving the movable body  160  in an axial direction to transmit to the movable body  160 . In this embodiment, the drive device  105  is mounted between a foundation plate  79  and the base plate  76  in a space formed in the base plate  76 . 
         [0060]    In the drive device  105 , the stator  120  is structured so that a unit including a coil  121  which is wound around a bobbin  123  and two pieces of yoke  125  which are disposed to cover the coil  121  is stacked in two layers in an axial direction. In this state, in both of the up-and-down two layers, pole teeth protruded in the axial direction from inner circumferential edges of two pieces of the yoke  125  are alternately juxtaposed in a circumferential direction to function as a stator of the stepping motor. 
         [0061]    The rotation body  103  is provided with a cup-shaped member  130  which opens upward and a ring-shaped rotor magnet  150  which is fixed on an outer peripheral face of a cylindrical drum part  131  of the cup-shaped member  130 . A center of a bottom wall  133  of the cup-shaped member  130  is formed with a recessed part  135  which is recessed upward in the axial direction. The foundation plate  79  is formed with a bearing part  751  which receives a ball  118  disposed in the recessed part  135 . Further, an inside surface on an upper end side of the base plate  76  is formed with a ring-shaped stepped part  766  and an upper end portion of the cup-shaped member  130  is formed with a ring-shaped stepped part, which faces the ring-shaped stepped part  766  of the base plate  76 , comprised of an upper end portion of the drum part  131  and the ring-shaped flange part  134 . A bearing  180  comprised of a ring-shaped retainer  181  and bearing balls  182  which are held by the retainer  181  at separated positions in a circumferential direction is disposed in an annular space which is formed by these ring-shaped stepped parts. In this manner, the rotation body  103  is supported by the main body portion  2  in the state that the rotation body  103  is capable of rotating around an axial line. 
         [0062]    An outer peripheral face of the rotor magnet  150  in the rotation body  103  faces the pole teeth which are juxtaposed in the circumferential direction along an inner peripheral face of the stator  120 . In this embodiment, an “S”-pole and an “N”-pole are alternately arranged in the circumferential direction on the outer peripheral face of the rotor magnet  150 , and the stator  120  and the cup-shaped member  130  structures the stepping motor. 
         [0063]    The movable body  160  is provided with a bottom wall  161 , a cylindrical part  163  which is protruded in the axial direction from a center of the bottom wall  161 , and a drum part  165  which is formed in a cylindrical shape so as to surround the cylindrical part  163 . A male screw  167  is formed on an outer periphery of the drum part  165 . 
         [0064]    In this embodiment, in order to structure the conversion mechanism  140  for reciprocatedly moving the movable body  160  in the axial direction by using rotation of the rotation body  103 , a female screw  137  is formed on an inner peripheral face of the drum part  131  of the cup-shaped member  130  at four portions away from each other in the circumferential direction. In addition, the male screw  167  which is engaged with the female screw  137  in the cup-shaped member  130  to structure the power transmission mechanism  141  is formed on the outer peripheral face of the drum part  165  of the movable body  160 . Therefore, when the movable body  160  is disposed on the inner side of the cup-shaped member  130  so as to make the male screw  167  engage with the female screw  137 , the movable body  160  is supported on the inner side of the cup-shaped member  130 . Further, the bottom wall  161  of the movable body  160  is formed with six elongated holes  169  as a through hole in the circumferential direction, and six projections  769  are extended from the base plate  76  so that lower end parts of the projections are  769  are fitted into the elongated holes  169  to structure a co-rotation preventive mechanism  149 . In other words, when the cup-shaped member  130  is rotated, rotation of the movable body  160  is prevented by the co-rotation preventive mechanism  149  which is structured of the projections  769  and the elongated holes  169 . Therefore, the rotation of the cup-shaped member  130  is transmitted to the movable body  160  through the power transmission mechanism  141  comprised of the female screw  137  and the male screw  167  of the movable body  160  and, as a result, the movable body  160  is linearly moved between one side and the other side in the axial direction depending on rotating direction of the rotation body  103 . 
         [0065]    The diaphragm valve  170  is directly connected with the movable body  160 . The diaphragm valve  170  is formed in a cup shape which is provided with a bottom wall  171 , a cylindrical drum part  173  which is formed upright in the axial direction from an outer peripheral edge of the bottom wall  171 , and a flange part  175  which is widened on an outer peripheral side from an upper end of the drum part  173 . A center portion of the bottom wall  171  is fixed with a fixing screw  178  and a cap  179  in a vertical direction in a state that the center portion of the bottom wall  171  is covered over the cylindrical part  163  of the movable body  160 . Further, an outer peripheral edge of the flange part  175  of the diaphragm valve  170  is formed with a thick wall part functioning as a liquid-tightness and positioning portion. The thick wall part is fixed between the base plate  76  and the flow passage structuring plate  77  around the through hole  21  of the flow passage structuring plate  77 . In this manner, the diaphragm  170  defines a bottom face of the pump chamber  20  and liquid-tightness between the base plate  76  and the flow passage structuring plate  77  is secured around the pump chamber  20 . 
         [0066]    In this state, the drum part  173  of the diaphragm valve  170  is turned around in a “U”-shape in cross section and a shape of a turn-around portion  172  varies depending on a position of the movable body  160 . However, in this embodiment, the turn-around portion  172  of the diaphragm valve  170  which is formed in a “U”-shape in cross section is disposed in an annular space structured between a first wall face  168  formed of an outer peripheral face of the cylindrical part  163  of the movable body  160  and a second wall face  768  formed of inner peripheral faces of the projections  769  extended from the base plate  76 . Therefore, the diaphragm valve  170  deforms to be developed or wound up along the first wall face  168  and the second wall face  768  under the state that the turn-around portion  172  is held in the annular space in every state. 
         [0067]    Further, the bottom wall  133  of the cup-shaped member  130  is formed with one groove  136  over an angular range of 270° in the circumferential direction, and a bottom face of the movable body  160  is formed with a downward projection (not shown). In this embodiment, the movable body  160  does not rotate around the axial line but moves in the axial direction and, on the other hand, the rotation body  103  rotates around the axial line but does not move in the axial direction. Therefore, the projection and the groove  136  function as a stopper which determines a stop position of the rotation body  103  and the movable body  160 . In other words, a depth of the groove  136  varies in the circumferential direction and, when the movable body  160  is moved downward in the axial direction, the projection is fitted into the groove  136  and the end part of the groove  136  is abutted with the projection by rotation of the rotation body  103 . As a result, the rotation of the rotation body  103  is prevented and the stop position of the rotation body  103  with the movable body  160 , i.e., the maximum expanded position of the internal volume of the diaphragm valve  170  is determined. 
         [0068]    In the reciprocating pump devices  10 A and  10 B structured as described above, when the stepping motor in the drive device  105  is rotated in one direction, the diaphragm valve  170  is driven in the direction so that the internal volume of the pump chamber  20  is enlarged and, when the stepping motor is rotated in the other direction, the diaphragm valve  170  is driven in the direction so that the internal volume of the pump chamber  20  is reduced. In other words, when an electrical power is applied to the coil  121  of the stator  120 , the cup-shaped member  130  is rotated and the rotation is transmitted to the movable body  160  through the conversion mechanism  140 . Therefore, the movable body  160  performs a reciprocating linear-motion in the axial direction. As a result, the diaphragm valve  170  deforms in conformity to movement of the movable body  160  to expand or contract the internal volume of the pump chamber  20  and thus, in the pump chamber  20 , inflow of liquid from the inflow passages  12 Ai and  12 Bi is performed and outflow of liquid to the outflow passages  12 Ao and  12 Bo is performed. 
         [0069]    As described above, in the reciprocating pump devices  10 A and  10 B in accordance with this embodiment, rotation of the rotation body  103  by the stepping motor mechanism is transmitted to the movable body  160  through the conversion mechanism  140 , in which the power transmission mechanism  141  comprised of the male screw  167  and the female screw  137  is utilized, to perform a reciprocating linear-motion in the movable body  160  to which the diaphragm valve  170  is fixed. Therefore, power is transmitted from the drive device  105  to the diaphragm valve  170  with the minimum necessary members and thus the size, thickness and cost of the reciprocating pump devices  10 A and  10 B can be reduced. Further, when lead angles of the male screw  167  and the female screw  137  in the power transmission mechanism  141  are set to be smaller or, when the number of the pole teeth of the stator on the driving side is increased, a minute feeding of the movable body  160  can be performed. Therefore, the volume of the pump chamber  20  can be controlled strictly and thus discharging in a fixed amount can be performed with a high degree of accuracy. 
         [0070]    Further, in this embodiment, the diaphragm valve  170  is used and the turn-around portion  172  of the diaphragm valve  170  is deformed to develop or wind up along the first wall face  168  and the second wall face  768  under the state that the turn-around portion  172  is held in the annular space and thus excessive sliding does not occur. Therefore, a useless load does not occur and service life time of the diaphragm valve  170  becomes longer. Further, the diaphragm valve  170  does not deform even when a pressure is applied by liquid in the pump chamber  20 . Therefore, according to the reciprocating pump devices  10 A and  10 B in this embodiment, discharging with a fixed amount can be performed with a high degree of accuracy and reliability is also high. 
         [0071]    In addition, the rotation body  103  is rotatably supported around the axial line by the main body portion  2  through the bearing balls  182 . Therefore, sliding loss is small and, since the rotation body  103  is stably held in the axial direction, a thrust force in the axial direction is stable. Accordingly, the size of the drive device  105  can be reduced and improvement of the durability and discharging performance can be obtained. 
         [0072]    In this embodiment, a screw is utilized for the power transmission mechanism  141  of the conversion mechanism  140  but a cam groove may be utilized. In addition, in the embodiment described above, a cup-shaped diaphragm valve is used as a valve element. However, a diaphragm valve having another shape or a piston provided with an O-ring may be used. 
       [Specific Structural Example of Active Valve] 
       [0073]    With reference to  FIG. 3  and  FIG. 9 , in a metering pump device in this embodiment, a specific structural example of the active valve will be described below which is used as the inflow side valves  11 Ai and  11 Bi and the outflow side valves  11 Ao and  11 Bo.  FIG. 9  is an explanatory longitudinal sectional view showing an active valve which is used as the inflow side valves  11 Ai and  11 Bi and the outflow side valves  11 Ao and  11 Bo in the metering pump device  1  to which at least an embodiment of the present invention is applied. 
         [0074]    In  FIG. 3  and  FIG. 9 , the active valve is provided with a stepping motor  301  that is a drive source, an inflow port  308   a  and an outflow port  308   b.  A lead screw  302  comprised of, for example, a right-hand screw is press-fitted and fixed to the rotation shaft  301   a  of the stepping motor  301 . The lead screw  302  rotates in a direction which is the same as that of the stepping motor  301 . A female screw  303   a  of the valve holding member  303  is threadedly fitted to the lead screw  302 . Therefore, when the stepping motor  301  is rotated in a CCW direction (counterclockwise direction) which is viewed from the lead screw  302  side, the valve holding member  303  approaches to the stepping motor  301  and, when the stepping motor  301  is rotated in a CW direction (clockwise direction) which is viewed from the lead screw  302  side, the valve holding member  303  goes away from the stepping motor  301 . In other words, rotation of the lead screw  302  is converted into a linear-motion because the lead screw  302  and the valve holding member  303  are engaged with each other through screw engagement and turning of the valve holding member  303  is prevented. 
         [0075]    A spring receiving part  303   b  is concentrically formed on an outer peripheral side of the valve holding member  303  and a spring  304  is held by the spring receiving part  303   b  and the stepping motor  301 . The spring  304  is comprised of a compression coil spring, which urges the valve holding member  303  in a direction separating from the stepping motor  301 . In this embodiment, a compression coil spring is utilized but, for example, a tension coil spring may be utilized. In this case, a tension coil spring is held on an opposite face of the spring receiving part  303   b  of the valve holding member  303 . 
         [0076]    A center portion of the valve holding member  303  is formed with a convex-shaped diaphragm holding part  303   c,  which is fitted to an undercut part  260   a  of the diaphragm valve  260 . In this embodiment, the diaphragm valve  260  is fixed by means of that its outer peripheral portion  260   b  is pinched by the base plate  76  and the flow passage structuring plate  77  and a bead  260   e  on its outer peripheral side is also pinched and fixed. The bead  260   e  prevents fluid from leaking from a gap space between the base plate  76  and the flow passage structuring plate  77  to improve sealing property. Further, since a film part  260   c  of the diaphragm valve  260  is easily deformed, the film part  260   c  is formed in a circular arc shape so that stress is not concentrated. In this embodiment, the diaphragm valve  260  is formed with a bead part  260   d  in a concentric manner on an opposite side to the undercut part  260   a  and on an abutting portion with the flow passage structuring plate  77 . 
         [0077]    In the active valve structured as described above, the valve holding member  303  is urged in a direction separating from the stepping motor  301  by the spring  304 . Therefore, when the valve holding member  303  is linearly moved, a state is maintained in which a slant face on the stepping motor  301  side of the screw part of the lead screw  302  is contacted with a slant face on an opposite side to the stepping motor  301  side of the female screw  303   a  of the valve holding member  303 . In other words, a state that the lead screw  302  and the valve holding member  303  are engaged with each other is maintained. On the other hand, when the hole  277  is closed by the diaphragm valve  260 , the urging force of the spring  304  is balanced with a force of counteraction which is applied to the diaphragm valve  260  by the flow passage structuring plate  77 , and a state is maintained in which a slant face, which is on an opposite side of the stepping motor  301  side, of the screw part of the lead screw  202  is not contacted with a slant face on the stepping motor  301  side of the female screw  303   a  of the valve holding member  303 . In other words, the lead screw  302  and the valve holding member  303  are maintained in a non-engaging state with each other through a play (backlash), and the diaphragm valve  260  is urged by the spring  304  in a direction closing the hole  277 . Therefore, the hole  277  can be closed securely. 
       [Another Specific Structural Example of Active Valve] 
       [0078]    With reference to  FIGS. 3 and 10 , in a metering pump device in this embodiment, another specific structural example of an active valve which is used as inflow side valves  11 Ai and  11 Bi and outflow side valves  11 Ao and  11 Bo will be described below. 
         [0079]      FIG. 10  is an explanatory longitudinal sectional view showing an active valve which is used as inflow side valves  11 Ai and  11 Bi and outflow side valves  11 Ao and  11 Bo in the metering pump device  1  to which at least an embodiment of the present invention is applied and which is viewed from obliquely below. As shown in  FIGS. 3 and 10 , an active valve which is used as the inflow side valves  11 Ai and  11 Bi and the outflow side valves  11 Ao and  11 Bo is provided with a linear actuator  201  within a hole  765  of the base plate  76 . The linear actuator  201  includes a cylindrical fixed body  203  and a roughly cylindrical movable body  205  which is disposed on an inner side of the fixed body  203 . The fixed body  203  is provided with a coil  233  circumferentially wound around a bobbin  231 , and a fixed body side yoke  235  which surrounds the coil  233  from an outer peripheral face of the coil  233  to an inner side through both sides in an axial direction of the coil  233  and whose one tip end part  236   a  and the other tip end part  236   b  are faced each other in the axial direction on an inner peripheral side of the coil  233  through a slit  237 . The movable body  205  includes a first movable body side yoke  251  formed in a circular plate shape and a pair of magnets  253   a  and  253   b  which are laminated on both sides in the axial direction of the first movable body side yoke  251 . Rare earth magnet of Nd—Fe—B system or Sm—Co system, or resin magnet may be used for the pair of the magnets  253   a  and  253   b.  Further, in the movable body  205 , second movable body side yokes  255   a  and  255   b  are respectively laminated on end faces on an opposite side to the first movable body side yoke  251  of the pair of the magnets  253   a  and  253   b.    
         [0080]    Each of the pair of the magnets  253   a  and  253   b  is magnetized in the axial direction, and the same poles are directed to the first movable body side yoke  251 . In this embodiment, each of the pair of the magnets  253   a  and  253   b  is disposed so that an “N”-pole is directed to the first movable body side yoke  251  and an “S”-pole is directed to an outer side in the axial direction. However, the magnetizing direction may be reversed. 
         [0081]    In this embodiment, the outer peripheral face of the first movable body side yoke  251  is protruded on an outer peripheral side from the outer peripheral faces of the pair of the magnets  253   a  and  253   b.  Further, the outer peripheral faces of the second movable body side yokes  255   a  and  255   b  are protruded on an outer peripheral side from the outer peripheral faces of the pair of the magnets  253   a  and  253   b.    
         [0082]    Recessed parts are formed on both end faces in the axial direction of the first movable body side yoke  251 , and the pair of the magnets  253   a  and  253   b  are respectively fitted to the recessed parts and fixed with an adhesive or the like. The first movable body side yoke  251 , the pair of the magnets  253   a  and  253   b  and the second movable body side yokes  255   a  and  255   b  may be fixed to each other by adhesion, press fitting or their combination to be integrated. 
         [0083]    Further, bearing plates  271   a  and  271   b  (bearing member) are fixed to opening parts on both sides in the axial direction of the fixed body  203 . Support shafts  257   a  and  257   b  which are projected on both sides in the axial direction from the second movable body side yokes  255   a  and  255   b  are slidably inserted into the holes of the bearing plates  271   a  and  271   b.  In this manner, the movable body  205  is supported by the fixed body  203  in the state that it is capable of reciprocating in the axial direction. In this state, the outer peripheral face of the movable body  205  faces the inner peripheral face of the fixed body  203  through a predetermined gap space, and the tip end parts  236   a  and  236   b  of the fixed body side yoke  235  face each other in the axial direction in a gap space between the outer peripheral face of the first movable body side yoke  251  and the inner peripheral face of the coil  233 . Further, a space is secured between the movable body  205  and the fixed body side yoke  235 . The second movable body side yokes  255   a  and  255   b  and the support shafts  257   a  and  257   b  may be fixed by adhesion, press fitting or their combination to be integrated. 
         [0084]    In the linear actuator  201  structured as described above, in this embodiment, a shaft body  259  is connected with a tip end part the support shaft  257   b,  and a center portion of the diaphragm valve  260  disposed in a valve chamber  270  is connected with the shaft body  259 . A ring-shaped thick wall part  261  which functions as liquid-tightness and positioning is formed on an outer peripheral side of the diaphragm valve  260 . The outer peripheral side including the ring-shaped thick wall part  261  of the diaphragm valve  260  is sandwiched between the base plate  76  and the flow passage structuring plate  77  to secure liquid-tightness. 
         [0085]    In the linear actuator  201  structured as described above, during a period when an electric current flows through the coil  233  from a rear side to a front side on the right side in the paper and, the electric current flows through the coil  33  from the front side to the rear side on the left side in the paper, the movable body  205  is received with a thrust force in the axial direction by a Lorentz force as shown by the arrow “B” to be moved. As a result, a hole  277  structuring a middle portion of the flow passage is closed and the flow passage is shut off. On the other hand, when the energization direction to the coil  233  is reversed, the movable body  205  is moved downward along the axial direction as shown by the arrow “A” to open the hole  277  structuring the middle portion of the flow passage. 
         [0086]    In the linear actuator  201  in this embodiment, the movable body  205  is advanced by a magnetic force and, in addition, a coil spring  291  in a truncated-cone shape is disposed between the bearing plate  271   a  and the second movable body side yoke  255   a  as an urging member on one side in the axial direction. Therefore, when the movable body  205  is moved down, the movable body  205  is moved while the compression spring is deformed and, when the movable body  205  is moved upward, a returning force of the compression spring to its original shape assists to move it at a high speed. 
         [0087]    In this embodiment, the valve element is not limited to the diaphragm valve  260  and a bellows valve or another valve element may be used. Further, the support shafts  257   a  and  257   b  and the valve element may be structured of separated members which are to be integrated, or one piece of member may be used which is integrally structured of the support shafts  257   a  and  257   b  and the valve element. 
         [0088]    As described above, in this embodiment, the pair of the magnets  253   a  and  253   b  in the movable body  205  is disposed so that the same pole are faced each other and thus magnetic repulsive forces are acted on each other. However, since the first movable body side yoke  251  is disposed between the magnets  253   a  and  253   b,  the pair of the magnets  253   a  and  253   b  can be fixed in the state that the same poles are directed to each other. 
         [0089]    Further, the pair of the magnets  253   a  and  253   b  in the movable body  205  is disposed so that the same poles are directed to the first movable body side yoke  251 . Therefore, a strong magnetic flux is generated from the first movable body side yoke  251  in the radial direction. As a result, when the first movable body side yoke  251  and the peripheral face of the coil  233  are faced each other, a large thrust force can be applied to the movable body  205 . 
         [0090]    In addition, magnetizing is performed on the magnets  253   a  and  253   b  in the axial direction and thus, different from a case that magnetizing is performed on the magnets  253   a  and  253   b  in the radial direction, the magnetizing is easy even when they are miniaturized and suitable for mass production. 
         [0091]    Moreover, in this embodiment, the outer peripheral face of the first movable body side yoke  251  is protruded on the outer peripheral side from the outer peripheral faces of the pair of the magnets  253   a  and  253   b.  Therefore, even when the fixed body side yoke  235  is provided, a magnetic attractive force acting on the movable body  205  in the direction perpendicular to the axial direction can be made smaller. Similarly, the outer peripheral faces of the second movable body side yokes  255   a  and  255   b  are protruded on the outer peripheral side from the outer peripheral faces of the pair of the magnets  253   a  and  253   b.  Therefore, even when the fixed body side yoke  235  is provided, magnetic attractive forces acting on the movable body  205  in the direction perpendicular to the axial direction can be made smaller. As a result, assembling work is easily performed and the movable body  205  is hardly inclined. 
         [0092]    Further, in this embodiment, the magnets  253   a  and  253   b  are disposed on the inner peripheral side of the coil  33  and thus, in comparison with a case that the magnets  253   a  and  253   b  are disposed on the outer side of the coil  233 , the magnets  253   a  and  253   b  can be made smaller and the active valve can be structured at a low cost. Further, since the coil  233  is disposed on the outer side, a magnetic path can be closed only with the fixed side yoke. 
         [0093]    In addition, the bearing plates  271   a  and  271   b  which movably support the support shafts  257   a  and  257   b  in the axial direction are held by the opening parts in the fixed body  203  which open in the axial direction. Therefore, bearing members are not required to be disposed separately. Further, since the bearing plates  271   a  and  271   b  can be fixed with the fixed body  203  as a reference, the support shafts  257   a  and  257   b  are not inclined. 
       [Application of Metering Pump Device] 
       [0094]    The metering pump device  1  to which at least an embodiment of the present invention is applied is used, for example, to quantitatively supply water to a reformer of various fuel cells. Further, the metering pump device  1  to which at least an embodiment of the present invention is applied may be used for quantitatively supplying urea aqueous solution to a reformer for resolving and removing nitrogen oxides from exhaust gas of a diesel engine or used for feeding infusion liquid. Especially, the metering pump device  1  is suitable to discharge at a constant rate or quantitatively in a field where a difference in pressure is large between a suction side and a discharge side. 
       Anther Embodiment 
       [0095]    In the embodiment described above, two reciprocating pump devices  10 A and  10 B are used. However, at least an embodiment of the present invention may be applied to a metering pump device which is provided with three or more reciprocating pump devices. 
         [0096]    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. 
         [0097]    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 charges which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.