Patent Publication Number: US-2006013703-A1

Title: Multi-channel pump and its control method

Description:
CROSS REFERENCE TO RELATED APPLICATION  
      The present invention claims priority under 35 U.S.C. §119 to Japanese Application No. 2004-208551 filed Jul. 15, 2004, which is incorporated herein by reference.  
     FIELD OF THE INVENTION  
      The present invention relates to a multi-channel pump which is used in a direct methanol type fuel cell or the like and a control method for the multi-channel pump.  
      In the present specification, the “multi-channel pump” means a pump which is provided with a plurality of outflow passages for discharging fluid.  
     BACKGROUND OF THE INVENTION  
      Expectation for a fuel cell has been elevated as a power supply for a portable electronic device used in information society in recent years or as a power supply for coping with air pollution or global warning. Among the fuel cells, a direct methanol type fuel cell hereinafter, referred to as DMFC: Direct Methanol Fuel Cell) in which power generation is performed by directly taking out protons from methanol provides characteristics that a reformer is not required and the volume energy density is high, and thus application to a portable electronic device has been increasingly expected  
      Various DMFC&#39;s have been proposed which are provided with a power generating device having a power generating part (cell), an accommodating vessel for accommodating methanol or methanol aqueous solution (hereinafter, referred to as methanol), and a liquid feed pump for feeding methanol forcibly from the accommodating vessel (see, for example, Japanese Patent Laid-Open No. 2004-71262, Japanese Patent Laid-Open No. 2004-127618, and Japanese Patent Laid-Open No. 2004-152741).  
      The cell includes an anode electrode (fuel electrode) having an anode collector and an anode catalyst layer, a cathode electrode (air electrode) having a cathode collector and a cathode catalyst layer, and an electrolyte membrane disposed between the anode electrode and the cathode electrode. Methanol is supplied to the anode electrode by a liquid feed pump and air is supplied to the cathode electrode by an air supply pump.  
      The activity of methanol oxidation is low in the anode electrode of the cell which is the power generating part of an above-mentioned DMFC and thus a voltage loss occurs. Further, a voltage loss occurs in the cathode electrode. Therefore, an output capable of being obtained from one cell becomes extremely low. Accordingly, a plurality of cells is used in the DMFC to obtain a prescribed output  
      When methanol is excessively supplied to the anode electrode, a so-called crossover occurs which means that a part of the methanol transmits through the electrolyte membrane in an unreacted state and leaks to the cathode electrode. Since the crossover causes the electric potential of the cathode electrode to decrease, the voltage loss occurs in the cathode electrode. Further, unreacted methanol that is reaches the cathode electrode is not related to power generation but reacts with oxygen to generate heat, and thus the power-generating efficiency in the cell is significantly reduced by the crossover. Accordingly, it is preferable not to supply excessive methanol to the anode electrode.  
      As described above, as a liquid feed pump for supplying methanol to the anode electrode of a cell, it has been desired which is provided with characteristics that discharge to a plurality of cells is possible and an appropriate amount of methanol can be accurately discharged. However, the liquid feed pump having such characteristics has not been proposed.  
     SUMMARY OF INVENTION  
      In view of the problems descried above, the present invention may advantageously provide a multi-channel pump which is provided with a plurality of outflow passages for discharging fluid and capable of accurately discharging an appropriate amount of fluid and provide a control method for the multi-channel pump.  
      Further, the present invention may advantageously provide a multi-channel pump which is capable of being mounted in a small-sized DMFC or the like that is used in a portable electronic device or the like.  
      Thus, according to the present invention, there may be provided a multi-channel pump including a pump chamber, an inflow passage for fluid which is connected to the pump chamber, two or more outflow passages which are connected to the pump chamber, outflow side active valves which are provided in the outflow passages so as to correspond to the outflow passages, and a movable body which is reciprocated to change the volumetric capacity of the pump chamber.  
      In accordance with an embodiment of the present invention, the multi-channel pump is provided with two or more outflow passages which are connected to a pump chamber through outflow side active valves. Accordingly, the reverse flow of the fluid can be surely prevented when the outflow side active valve is closed. Further, the discharge destination of the fluid discharged from the outflow passage can be controlled by the outflow side active valve. In addition, the multi-channel pump is provided with one movable body which is reciprocated to change the volume of the pump chamber. Therefore, since the fluid is discharged from the respective outflow passages by using one movable body, the discharging performance becomes uniform and thus the variation of the discharge amount from the respective outflow passages is restrained and an appropriate amount of fluid can be accurately discharged.  
      Further, in accordance with an embodiment of the present invention, an inflow passage is connected to the pump chamber to which a plurality of outflow passages are connected. Therefore, the inflow passage can be provided in common for the plurality of outflow passages and thus the structure of the pump can be simplified. In addition, since only one movable body is provided, the structure of the pump is also simplified. Accordingly, the downsizing of the pump can be attained and the pump can be mounted in a small-sized device such as a DMFC that is used in a portable electronic device.  
      In accordance with an embodiment of the present invention, the movable body is preferably a piston which is reciprocated within a cylinder that is connected to the pump chamber. When the movable body is a piston, the moving quantity of the piston is relatively easy to control and thus a minute flow rate can be accurately discharged.  
      In accordance with an embodiment of the present invention, the multi-channel pump preferably includes a piston rod to which the piston is fixed, a male screw formed on the outer peripheral part of the piston rod, a rotation body which is formed with a female screw threadedly engaging with the male screw to make the piston reciprocate, and a piston drive motor which drives the rotation body to rotate. In this case, the moving quantity of the piston can be controlled by the pitch of the screw and the rotation quantity of the piston drive motor and thus a minute flow rate can be accurately discharged with a simple structure.  
      In accordance with an embodiment of the present invention, the piston drive motor is preferably a stepping motor. In this case, the moving quantity of the piston can be further accurately controlled.  
      In accordance with an embodiment of the present invention, the multi-channel pump is preferably provided with two or more inflow passages. According to the construction described above, for example, when fluid accommodating vessels are respectively connected to the respective inflow passages, the fluid accommodating vessel can be easily replaced.  
      In accordance with an embodiment of the present invention, the inflow passage is preferably connected to the pump chamber through an inflow side active valve. In this case, the reverse flow from the pump chamber to the inflow passage can be surely prevented in comparison with the case where the inflow passage is connected to the pump chamber through a passive valve.  
      In accordance with an embodiment of the present invention, the multi-channel pump may include a first flow passage provided in the inflow passage and having a passive valve which is capable of opening in an inflow direction to the pump chamber, and a second flow passage provided in the inflow passage and having a passive valve which is capable of opening in an outflow direction from the pump chamber. In this case, the inflow side active valve is preferably provided between the first flow passage, the second flow passage and the pump chamber.  
      In accordance with an embodiment of the present invention, the fluid is liquid and a detector for detecting presence of bubbles may be provided in the pump chamber.  
      In accordance with an embodiment of the present invention, the inflow passage is connected to the pump chamber through an inflow side active valve which is opened and closed by a drive actuator for inflow side active valve, the outflow side active valves which are provided so as to correspond to the two or more outflow passages are individually opened and closed by a drive actuator for outflow side active valve, and the movable body is a piston which is reciprocated within a cylinder that is connected to the pump chamber.  
      In accordance with an embodiment of the present invention, the drive actuator for outflow side active valve is a valve opening/closing drive motor, a cam is provided which is moved by the valve opening/closing drive motor, and the outflow side active valves provided so as to correspond to the outflow passages are individually opened and closed by the cam. Therefore, a plurality of outflow side active valves are successively opened and closed by the cam which is moved by the valve opening/closing drive motor.  
      Further, according to the present invention, there may be provided a control method for a multi-channel pump including a suction step in which the inflow side active valve is opened and the fluid is sucked into the pump chamber by a suction operation of the movable body and then the inflow side active valve is closed, an initial discharge step after the suction step in which one of the outflow side active valves is opened and the fluid is discharged from the pump chamber by the discharge operation of the movable body to eliminate backlash of the pump, and a discharge step after the initial discharge step in which an outflow side active valve is successively opened and a prescribed amount of the fluid is discharged by the discharge operation of the movable body.  
      Alternatively, according to the present invention, there may be provided a control method for a multi-channel pump including a suction step in which the inflow side active valve is opened and the fluid is sucked into the pump chamber from a first flow passage by a suction operation of the movable body, an initial discharge step after the suction step in which the backlash of the pump is eliminated by means of that the fluid is discharged from the pump chamber to a second flow passage by the discharge operation of the movable body and then the inflow side active valve is closed, and a discharge step after the initial discharge step in which an outflow side active valve is successively opened and a prescribed amount of the fluid is discharged by the discharge operation of the movable body.  
      According to the control method of the present invention, the initial discharge step for eliminating the backlash of the pump is provided between the suction step and the discharge step. Therefore, the relationship between the moving quantity of the movable body and the discharge amount from the outflow passage can be maintained in a linear manner from the beginning of the discharge step. Accordingly, when the moving quantity of the movable body is appropriately controlled, the discharge amount from the outflow passage where the fluid is firstly discharged in the discharge step can be accurately controlled and thus the variation of the discharge amounts from the respective outflow passages can be reduced.  
      Further, in the control method for the multi-channel pump in accordance with an embodiment of the present invention, fluid is collectively sucked in the suction step which is required to discharge from the outflow passages by a plurality of times in the discharge step. Therefore, even when the discharge amount of the fluid which is discharged from the respective outflow passages is a significantly small amount, the suction amount can be ensured to some extent Accordingly, the capacity of the multi-channel pump can be increased and the self-feeding performance can be easily attained.  
      In the present specification, “backlash of a pump” means a phenomenon that, when the operation of the movable body is changed from suction to discharge, a linear relationship is not obtained between the moving quantity of the movable body and the discharge amount from the outflow passage. This is a phenomenon occurred by the backlash of a mechanism for driving the movable body.  
      As described above, in the multi-channel pump in accordance with the present invention, since two or more outflow passages are connected to the pump chamber through the outflow side active valves, the reverse flow of fluid can be surely prevented when the outflow side active valves are closed and the discharge destination of the fluid discharged from the outflow passage can be controlled by using the outflow side active valve. In addition, the multi-channel pump is provided with one movable body that is reciprocated to change the volume of the pump chamber. Therefore, the discharging performance becomes uniform and thus the variation of discharge amount from the respective outflow passages can be restrained and an appropriate amount of fluid can be accurately discharged.  
      Further, in the multi-channel pump in accordance with the present invention, an inflow passage is connected to the pump chamber to which a plurality of outflow passages are connected Therefore, the inflow passage can be provided in common for the plurality of outflow passages and thus the structure of the pump can be simplified. In addition, since only one movable body is provided, the structure of the pump is also simplified. As a result, the downsizing of the pump can be attained.  
      Further, in the control method for the multi-channel pump of the present invention, the initial discharge step for eliminating the backlash of the pump is provided between the suction step and the discharge step. Therefore, the relationship between the moving quantity of the movable body and the discharge amounts from the outflow passages can be maintained in a linear manner from the beginning of the discharge step. Accordingly, the discharge amount from the outflow passage where the fluid is firstly discharged in the discharge step can be also accurately controlled and thus the variation of the discharge amounts from the respective outflow passages can be reduced. As a result, an appropriate amount of fluid can be accurately discharged from the respective outflow passages.  
      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  is a schematic view showing a basic structure of a multi-channel pump in accordance with an embodiment of the present invention  
       FIG. 2  is a perspective view showing a concrete structure of the multi-channel pump shown in  FIG. 1  which is viewed from the discharge side of methanol.  
       FIG. 3  is a perspective view showing the multi-channel pump shown in  FIG. 2  which is viewed from the “X” direction.  
       FIG. 4  is a perspective view showing the multi-channel pump shown in  FIG. 2  which is cut in the “Y” cross section.  
       FIG. 5  is an exploded perspective view showing an opening/closing mechanism of active valves of the multi-channel pump shown in  FIG. 2 .  
       FIG. 6  is a plan view showing a structure of inflow passages and outflow passages of the multi-channel pump shown in  FIG. 2 .  
       FIG. 7  is a timing chart showing a control method of the multi-channel pump shown in  FIG. 2 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      An embodiment of the present invention will be described below with reference to the accompanying drawings.  
       FIG. 1  is a schematic view showing a basic structure of a multi-channel pump in accordance with an embodiment of the present invention.  
      A multi-channel pump  1  (pump  1 ) in accordance with an embodiment of the present invention is used as a liquid feed pump for feeding methanol forcibly in a DMFC used, for example, in a portable electronic device. The multi-channel pump  1  includes a pump chamber  2 , inflow passages  3  connected to the pump chamber  2 , two or more outflow passages  4  connected to the pump chamber  2  through outflow side active valves  6 , and a movable body  13  which is reciprocated to change the volumetric capacity of the pump chamber  2 . More concretely, two inflow passages  3   a,    3   b  are connected to a pump chamber  2  and eight outflow passages  4   a  through  4   h  are connected to the pump chamber  2  through eight outflow side active valves  6   a  through  6   h.    
      One end sides of the inflow passages  3   a,    3   b  (upper end side in the drawing) are connected to the pump chamber  2  through inflow side active valves  5   a,    5   b.  The other end sides of the inflow passages  3   a,    3   b  are connected to first flow passages  8   a,    8   b  (first flow passage  8 ) provided with passive valves  10   a,    10   b  (passive valve  10 ) which respectively open in an inflow direction to the pump chamber and connected to second flow passages  9   a,    9   b  (second flow passage  9 ) provided with passive valves  11   a,    11   b  (passive valve  11 ) which respectively open in an outflow direction from the pump chamber  2 .  
      The first flow passage  8  and the second flow passage  9  are arranged so as to be capable of connecting to a methanol accommodating vessel (not shown in the drawing and, hereinafter, refereed to as an accommodating vessel). Concretely, the first flow passage  8  is arranged so as to be capable of connecting to the under side of the accommodating vessel and the second flow passage  9  is arranged so as to be capable of connecting to the upper side of the accommodating vessel. The passive valve  10  is a normal valve, which is, for example, made of rubber and opens in only one direction by fluid pressure. The passive valve  10  is provided in the first flow passage  8  which is the inflow passage and thus the passive valve  10  opens when a pressure is applied in a suction direction of methanol directing to the pump chamber  2  but does not open even when a pressure is applied in a discharge direction of methanol directing to the accommodating vessel. On the other hand, the passive valve  11  is also a normal valve, which is, for example, made of rubber and the passive valve  11  is provided in the second flow passage  9 , which is the outflow passage. The passive valve  11  opens when a pressure is applied in a discharge direction of methanol directing to the accommodating vessel but does not open even when a pressure is applied in a suction direction of methanol directing to the pump chamber  2 . Therefore, methanol is sucked to the pump chamber  2  from the accommodating vessel through the first flow passage  8  and the inflow passage  3 , and is discharged from the pump chamber  2  to the accommodating vessel through the inflow passage  3  and the second flow passage  9 . In the embodiment of the present invention, the first flow passage  8   a  and the second flow passage  9   a,  and the first flow passage  8   b  and the second flow passage  9   b  are respectively connected to different accommodating vessels.  
      The inflow side active valves  5   a,    5   b  are capable of being individually opened or closed by a drive actuator (not shown in  FIG. 1 ).  
      Eight outflow passages  4   a  through  4   h  are respectively connectable to eight cells (not shown in the drawing) as power generating parts of the DMFC. The methanol discharged from the outflow passages  4   a  through  4   h  are capable of being supplied to the anode electrodes of the cells.  
      The outflow side active valves  6   a  through  6   h  are individually openable/closable by a drive actuator (not shown in  FIG. 1 ) similarly to the inflow side active valves  5   a,    5   b.    
      The movable body  13  in this embodiment of the present invention is a piston (hereinafter, referred to as a piston  13 ) which is reciprocated within a cylinder  14  connected to the pump chamber  2 . The piston  13  is fixed on the upper end of a piston rod  15  in the drawing. The piston rod  15  is connected to a drive actuator (not shown in  FIG. 1 ) and is reciprocated within the cylinder  14  by the drive actuator.  
      In this pump  1  constructed as described above, when the outflow side active valves  6   a  through  6   h  are in a closed state and at least one of the inflow side active valves  5   a,    5   b  is in an open state, the piston  13  moves downward in the drawing and methanol is sucked into the pump chamber  2 . On the other hand, when the inflow side active valves  5   a,    5   b  are in a closed state and at least one of the outflow side active valves  6   a  through  6   h  is in an open state, the piston  13  moves upward in the drawing and the methanol is discharged to a cell from the pump chamber  2 . When the outflow side active valves  6   a  through  6   h  are in a closed state and at least one of the inflow side active valves  5   a,    5   b  is in an open state and, in this state, when the piston  13  moves upward in the drawing, the methanol is discharged to the accommodating vessel. A concrete control method for the pump  1  will be described in detail below.  
      The concrete structure of the multi-channel pump  1  provided with the above-mentioned basic structure will be described below.  FIG. 2  is a perspective view showing the concrete structure of the multi-channel pump shown in  FIG. 1  that is viewed from the discharge side of methanol.  FIG. 3  is a perspective view showing the multi-channel pump shown in  FIG. 2  that is viewed from the “X” direction.  FIG. 4  is a perspective view showing the multi-channel pump shown in  FIG. 2  which is cut in the “Y” cross section  FIG. 5  is an exploded perspective view showing an opening/closing mechanism of active valves of the multi-channel pump shown in  FIG. 2 .  FIG. 6  is a plan view showing the structure of inflow passages and outflow passages of the multi-channel pump shown in  FIG. 2 .  
      In the pump  1  shown in  FIGS. 2 through 4 , a base part  24  and a bracket  31  are connected to each other with screws through four pole braces  32  to construct a main body frame. On a base plate  25  and a bracket  31  constructing the base part  24  are fixed and held a driving mechanism for the piston  13  and an opening/closing mechanism for the inflow side active valves  5   a,    5   b  and the outflow side active valves  6   a  through  6   h.  The arrows in  FIG. 4  show an example of the flowing of methanol in the pump  1 .  
      The bracket  31  is provided with a semi-cylindrical extended part  31   a  which is extended downward in  FIG. 2 . On the inner peripheral side of the extended part  31   a  are formed concave grooves  31   b,    31   b  at two positions by a pitch of approximately 180° which construct the detent portion of the piston  13  along with protruded parts  18   a  of a slide plate  18  described below.  
      The base part  24  includes a base plate  25 , in which the pump chamber  2 , the inflow passages  3 , the outflow passages  4 , the first flow passages  8  and the second flow passages  9  are formed, an active valve plate  29  integrally provided with the inflow side active valves  5  and the outflow side active valves  6 , a valve presser plate  26  pressing the active valve plate  29 , a port  27  formed with outflow ports  40  ( 40   a  through  40   h ) which are aperture ends of the outflow passages  4 , suction ports  80  ( 80   a,    80   b ) which are aperture ends of the first flow passages  8 , and discharge ports  90  ( 90   a,    90   b ) which are aperture ends of the second flow passages  9 , and a port presser plate  28  pressing the port  27 . The valve presser plate  26 , the active valve plate  29 , the base plate  25 , the port  27 , and the port presser plate  28  are laminated in this order.  
      The piston  13  is moved so as to be reciprocated in the inside of the cylinder  14  by a piston drive motor  51 . The cylinder  14  is integrally formed with the base plate  25  so as to be connected to the pump chamber  2  (see  FIG. 4 ). The structure of the driving mechanism for the piston  13  will be described below.  
      The piston drive motor  51  is concretely a stepping motor and fixed to the bracket  31  with a screw. In this embodiment of the present invention, the piston drive motor  51  rotates in forward and reverse directions. A small gear  53  is fixed on the tip end of the output shaft of the piston drive motor  51 . An idle gear  19  is rotatably supported by a fixed shaft  20  which is fixed to the bracket  31  so as to be engaged with the small gear  53 . A gear  17  is rotatably held by a bearing  61  which is fixed on the outer peripheral part of the cylinder  14  so as to be engaged with the idle gear  19 .  
      The gear  17  is formed in an approximately bottomed cylindrical shape. On the center portion of the bottom part of the gear  17  is fixed a nut  16  as a rotation body on which a female screw  16   a  is formed. On the other hand, a male screw  15   a  is formed on the outer peripheral part of the piston rod  15  to which the piston  13  is fixed on one end and the male screw  15   a  is threadedly engaged with the female screw  16   a.  Further, on the other end of the piston rod  15  is fixed a slide plate  18  in which there are protruded parts  18   a,    18   a  engaging with the concave grooves  31   b  formed in the extended part  31   a  of the bracket  31  are formed at two positions by a pitch of approximately 180° (see  FIG. 3 ). The rotation of the piston  13  is prevented by the protruded parts  18   a  and the concave grooves  31   b.    
      On the outer peripheral side of the piston  13  are fixed sealing members (oil-seal)  63 ,  63  for preventing the leakage of methanol which is sucked in the pump chamber  2 .  
      In the driving mechanism for the piston  13  constructed as described above, when the piston drive motor  51  is rotated, the driving force is transmitted to the gear  17  through the small gear  53  and the idle gear  19 . When the driving force of the piston drive motor  51  is transmitted to the gear  17 , the nut  16  is rotated together with the gear  17 . The rotation preventing or detent mechanism for the piston  13  is structured on the other end side of the piston rod  15  on which the male screw  15   a  is formed to engage threadedly with the female screw  16   a  of the nut  16 . Therefore, the rotary motion of the nut  16  is converted into the straight motion of the piston  13 . The piston  13  is reciprocated in the inside of the cylinder  14  by the piston drive motor  51  that rotates in the both directions.  
      The inflow side active valves  5  and the outflow side active valves  6  are capable of being individually opened or closed by a valve opening/closing drive motor  52 . The opening/closing mechanism of the inflow side active valves  5  and the outflow side active valves  6  includes a cam  36  and a plate spring  37  in addition to the valve opening/closing drive motor  52  as principal components (see  FIG. 5 ). The structure of the opening/closing mechanism for the inflow side active valves  5  and the outflow side active valves  6  will be described below.  
      The valve opening/closing drive motor  52  is concretely a stepping motor which is fixed to the bracket  31  with a screw. In this embodiment of the present invention, the valve opening/closing drive motor  52  rotates in one direction (counter clockwise direction in  FIG. 5 ). A small gear  54  is fixed at the tip end of the output shaft of the valve opening/closing drive motor  52 . A cam  36  is provided with a gear  36   a  engaging with the small gear  54  and rotatably supported by a bearing  62  that is fixed on the outer peripheral part of the cylinder  14 . In the embodiment of the present invention, the cam  36  is rotated by the valve opening/closing drive motor  52  in the clockwise direction in  FIG. 5 . The bearing  61  and the bearing  62  are fixed on the outer peripheral part of the cylinder  14  such that they overlap each other in the moving direction of the piston  13 . The cam  36  and the gear  17  are disposed so as to overlap each other in the moving direction of the piston  13  (see  FIG. 4 ).  
      The cam  36  is formed in a cylindrical shape and provided with a flange part. The gear  36   a  is formed on the outer peripheral face of the flange part of the cam  36 . On the outer peripheral face of the cam  36  is fixed a pin  38  protruding in the radial direction for causing the inflow side active valves  5  and the outflow side active valves  6  to open and close.  
      The plate spring  37  includes, as shown in  FIG. 5 , a ring-shaped center part  37   a,  ten arm parts  37   b  extended from the center part  37   a  outward in the radial direction in a spiral manner, valve holding parts  37   c  respectively formed at the tip end of the arm part  37   b,  and a tip end part  37   d  which is formed so as to be bent upward in the drawing from the outer end of the valve holding part  37   c  in the radial direction and then bent toward the center part  37   a.  The tip end part  37   d  is provided with a sliding part  37   d   1  capable of contacting with the pin  38  and a guide part  37   d   2  which is bent from the sliding part  37   d   1  obliquely upward in the drawing to guide the pin  38  to the sliding part  37   d   1 . The notational symbols are shown for some of the arm parts  37   b,  the valve holding parts  37   c,  and the tip end parts  37   d  of the plate spring  37  for convenience.  
      The plate spring  37  is fixed to the outer peripheral face of the cylinder  14  through its center part  37   a.  In the state that the plate spring  37  is fixed to the outer peripheral face of the cylinder  14  and the cam  36  is supported by the bearing  62  fixed on the outer peripheral part of the cylinder  14 , the pin  38  is positioned on the upper side of the under face of the sliding part  37   d   1  and on the under side of the upper end portion of the guide part  37   d   2  in the vertical direction in  FIG. 5 . Therefore, when the cam  36  is rotated, the pin  38  is guided to the under face of the sliding part  37   d   1  through the guide part  37   d   2 , and the arm part  37   b  is deflected and thus the valve holding part  37   c  and the tip end part  37   d  are lift upward in  FIG. 5 .  
      The active valve plate  29  is made, for example, of rubber and integrally provided with the inflow side active valves  5   a,    5   b  and the outflow side active valves  6   a  through  6   h  which are concentrically formed with a pitch of equal angle. The inflow side active valves  5   a,    5   b  and the outflow side active valves  6   a  through  6   h  are normally urged to be in a closed state by the elasticity of rubber of the active valve plate  29 . Concretely, they are urged downward in  FIG. 5 . In addition, the upper ends of the inflow side active valves  5   a,    5   b  and the outflow side active valves  6   a  through  6   h  are respectively held by the valve holding parts  37   c  of the plate spring  37 .  
      In the opening/closing mechanism of the inflow side active valves  5  and the outflow side active valves  6  constructed as described above, the driving force of the valve opening/closing drive motor  52  is transmitted to the gear  36   a  through the small gear  54 . When the driving force is transmitted to the gear  36   a,  the cam  36  is rotated and the pin  38  is also rotated together with the cam  36 . The pin  38  is guided to the under face side of the sliding part  37   d   1  through the guide part  37   d   2 , which causes the arm part  37   b  to be deflected, and the valve holding part  37   c  is lifted upward in  FIG. 5 . In other words, either one of the inflow side active valves  5   a,    5   b  or the outflow side active valves  6   a  through  6   h  which are held in the valve holding parts  37   c  is lifted upward to be in an open state. When the pin  38  is further rotated and disengaged from the under face of the sliding part  37   d   1 , the active valve in the open state becomes to be in a closed state by the urging force. When the pin  38  is further rotated, the pin  38  is guided by the succeeding guide part  37   d   2  to the under face side of the sliding part  37   d   1  and the succeeding active valve becomes in an open state similarly to the above-mentioned case. These operations are repeated and the inflow side active valves  5   a,    5   b  and the outflow side active valves  6   a  through  6   h  which are respectively held in the valve holding parts  37   c  are successively opened and closed.  
      The pump chamber  2 , the inflow passages  3 , the outflow passages  4 , the first flow passages  8  and the second flow passages  9  are formed in the base plate  25  as described above.  
      The pump chamber  2  is formed in an approximately central part of the base plate  25  and provided with ten passages which radially extend toward the inflow side active valves  5   a,    5   b  and the outflow side active valves  6   a  through  6   h  (see  FIG. 6 ). A detector (not shown) for detecting the presence of bubbles may be provided in the pump chamber  2 .  
      The outflow passages  4   a  through  4   h  are formed so as to direct from the outflow side active valves  6   a  through  6   b  toward the outer side of the base plate  25 . The inflow passages  3   a,    3   b  are respectively formed between the inflow side active valves  5   a,    5   b  and the passive valves  10   a  and  11   a,    10   b  and  11   b  formed in an umbrella-shape (see  FIGS. 4 and 6 ). In addition, the first passages  8   a,    8   b  are respectively formed on the outer side of the passive valves  10   a,    10   b  and the second passages  9   a,    9   b  are formed on the outer side of the passive valves  11   a,    11   b.    
       FIG. 7  is a timing chart showing the control method of the multi-channel pump in  FIG. 2 .  
      In the embodiment of the present invention, the pump  1  is controlled by a control method including a suction step “S 1 ” in which the inflow side active valve  5  is opened and methanol is sucked into the pump chamber  2  from the first flow passage  8  by a suction operation of the piston  13 , an initial discharge step “S 2 ” after the suction step “S 1 ” in which the backlash of the pump  1  is eliminated by means of that methanol is discharged from the pump chamber  2  to the second flow passage  9  by the discharge operation of the piston  13  and then the inflow side active valve  5  is closed, and a discharge step “S 3 ” after the initial discharge step “S 2 ” in which an outflow side active valve  6  is successively opened and a prescribed amount of methanol is discharged by the discharge operation of the piston  13 . The control method will be described in detail below.  
      In the timing chart for the piston drive motor  51  in  FIG. 7 , the portions on the under side of the center horizontal line where the hatching is applied indicate states of a discharge operation in which the piston  13  is operated in the discharge direction (left direction in  FIG. 4 ). The portion on the upper side of the center horizontal line where the hatching is applied indicates the state of a suction operation in which the piston  13  is operated in the suction direction (right direction in  FIG. 4 ). In the timing chart for the valve opening/closing drive motor  52 , the portions where the hatching is applied indicate states in which the respective active valves are opened.  
      In the initial state, all of the inflow side active valves  5  and the outflow side active valves  6  are in the closed state. First, the valve opening/closing drive motor  52  is driven to make the inflow side active valve  5   b  to be in an open state. After that, the piston  13  is moved in the discharge direction of methanol by the piston drive motor  51 . The discharge operation by the piston  13  is performed to the top dead point (home position) and the origin-reset of the piston  13  is performed (origin-reset step “S 0 ”). In this case, methanol is discharged to the second flow passage  9   b  from the pump chamber  2  through the passive valve  11   b  which is capable of being in an open state.  
      Next methanol is sucked into the pump chamber  2  (suction step “S 1 ”). Concretely, under the open state of the inflow side active valve  5   b,  the piston drive motor  51  is driven to move the piston  13  in the suction direction of methanol. The suction operation of the piston  13  is performed, for example, to the bottom dead point of the piston  13 . Methanol is sucked into the pump chamber  2  from the first flow passage  8   b  through the passive valve  10   b  which is capable of being in an open state by the suction operation of the piston  13 ,  
      Next, after the backlash of the pump  1  is eliminated by means of that methanol is discharged from the pump chamber  2  by the discharge operation of the piston  13 , the inflow side active valve  5   b  is closed (initial discharge step “S 2 ”). Concretely, under the open state of the inflow side active valve  5   b,  the piston  13  is moved in the discharge direction of methanol by the piston drive motor  51  until the backlash of pump  1  is eliminated. Methanol is discharged to the second flow passage  9   b  by the discharge operation of the piston  13  through the passive valve  11   b  which comes to be in an open state, and after that the inflow side active valve  5   b  is closed by the valve opening/closing drive motor  52 .  
      Next, a prescribed outflow side active valve  6  is successively opened and a predetermined amount of methanol is discharged by the discharge operation of the piston  13  (discharge step “S 3 ”). Concretely, firs, the outflow side active valve  6   f  is set to be in an open state by the valve opening/closing drive motor  52 , and the discharge operation of the piston  13  is performed by the piston drive motor  51  to discharge a predetermined amount of methanol to the outflow passage  4   f  After that, the outflow side active valve  6   f  is set to be in a closed state and the outflow side active valve  6   g  is set to be in an open state by the valve opening/closing drive motor  52  and the discharge operation of the piston  13  is performed to discharge a predetermined amount of methanol from the outflow passage  4   g.  In this manner, while the opening/closing operations of the outflow side active valves  6   f,    6   g,    6   h,    6   a,    6   b,    6   c,    6   d,    6   e  are successively performed by the valve opening/closing drive motor  52  in this order, a prescribed amount of methanol is discharged from the outflow passages  4   f,    4   g,    4   h,    4   a,    4   b,    4   c,    4   d,    4   e  by the discharge operation of the piston  13  in this order.  
      In the case that a detector for detecting the presence of bubbles is provided in the pump chamber  2 , when the detector detects bubbles, the discharge operation of the piston  13  is, for example, performed under the state that the inflow side active valve  5   b  is set to be in an open state. The bubbles can be discharged to the second flow passage  9   b  through the passive valve  11   b  capable of being in an open state. Further, at the starting time of the pump  1  or after the exchange of the accommodating vessel, bubbles can be discharged by performing similar operations.  
      When the structure of the multi-channel pump  1  shown in  FIGS. 2 through 6  is employed, the opening/closing operation of the inflow side active valve  5   a,  is performed by the valve opening/closing drive motor  52  even though a series of the above-mentioned operations are not used. However, a series of the above-mentioned operations are not affected even when the inflow side active valve  5   a  is set to be in an open state as long as the piston  13  is not moved.  
      As described above, the multi-channel pump  1  in accordance with the embodiment of the present invention is provided with the outflow side active valves  6   a  through  6   b.  Therefore, the reverse flow of methanol from the outflow passages  4   a  through  4   h  to the pump chamber  2  can be surely prevented. Further, the discharge destinations of methanol which is discharged from the outflow passages  4   a  through  4   h  can be controlled by the outflow side active valves  6   a  through  6   h.  In addition, in the multi-channel pump  1 , methanol is discharged from the respective outflow passages  4   a  through  4   h  by the discharge operation of one piston  13 . Therefore, discharging performance is uniform in comparison with the case when separate pistons are provided for the respective outflow passages  4   a  through  4   h  and thus the variation of discharge amount from the respective outflow passages  4   a  through  4   h  can be restrained Accordingly, an appropriate amount of methanol can be accurately discharged in the multi-channel pump  1 .  
      In this embodiment of the present invention, two inflow passages  3   a,    3   b  are connected to the pump chamber  2  to which eight outflow passages  4   a  through  4   h  are connected. Therefore, the inflow passages  3   a,    3   b  can be commonly used for a plurality of outflow passages  4   a  through  4   h  and thus the structure of the pump  1  can be simplified. Further, since only one piston  13  is used and thus the structure of the pump  1  can be further simplified. Accordingly, the downsizing of the pump  1  can be attained and thus the pump  1  can be mounted in a small-sized device such as, for example, a DMFC used in a portable electronic device.  
      In this embodiment of the present invention, the drive mechanism for the piston  13  includes a piston rod  15  on which a male screw  15   a  is formed on its outer peripheral part, a nut  16  on which a female screw  16   a  for threadedly engaging with the male screw  15   a  is formed, and a piston drive motor  51  which rotationally drives the nut  16  through a gear  17  and the like. Therefore, the moving quantity of the piston  13  can be controlled with the pitch of the screw and the quantity of rotation of the piston drive motor  51 . Accordingly, a minute flow rate can be discharged from the outflow passages  4   a  through  4   h . Further, the accuracy of a discharge flow rate can be enhanced. Especially, in this embodiment of the present invention, since the piston drive motor  51  is a stepping motor, the moving quantity of the piston  13  can be further accurately controlled. For example, in the pump  1  in accordance with these embodiment of the present invention, a minute flow rate such as, for example, 0.01 cc can be accurately discharged from the respective outflow passages  4   a  through  4   h.  Further, a minute flow rate can be intermittently discharged.  
      In this embodiment of the present invention, the multi-channel pump  1  is provided with two inflow passages  3   a,    3   b.  Therefore, when accommodating vessels are connected to the respective inflow passages  3   a,    3   b,  the exchanging work of the accommodating vessel becomes easy.  
      In this embodiment of the present invention, the one end sides of the inflow passages  3   a,    3   b  are connected to the pump chamber  2  through the inflow side active valves  5   a,    5   b.  Therefore, the reverse flow from the pump chamber  2  to the inflow passages  3   a,    3   b  can be surely prevented  
      In the control method for the multi-channel pump  1  in this embodiment of the present invention, the initial discharge step “S 2 ” for eliminating the backlash of the pump  1  is provided between the suction step “S 1 ” and the discharge step “S 3 ”. Therefore, in the discharge step “S 3 ”, the relationship between the moving quantity of the piston  13  and the discharge amounts from the outflow passages  4   a  through  4   h  can be maintained in a linear manner from the beginning. Accordingly, when the moving quantity of the piston  13  is appropriately controlled, the discharge amount of the fluid from the outflow passage  4   f  which is firstly discharged in the discharge step “S 3 ” can be accurately controlled and thus the variation of the discharge amounts from the respective outflow passages  4   a  through  4   h  can be reduced.  
      In addition, in the control method for the multi-channel pump  1  in accordance with this embodiment of the present invention, methanol is sucked in the suction step “S 1 ” which is required to discharge from the outflow passages  4   a  through  4   h  by a plurality of times in the discharge step “S 3 ”. Therefore, even when the discharge amount of methanol which is discharged from the respective outflow passages  4   a  through  4   h  is a significantly small amount, the suction amount can be ensured to some extent. For example, even when each of the discharge amounts from the respective outflow passages  4   a  through  4   h  is 1 (μl), the suction amount can be totally 8 (μl). Accordingly, the capacity of the pump  1  can be increased and the self-feeding performance can be easily attained.  
      Although the present invention has been shown and described with reference to specific embodiments, various changes and modifications will be apparent to those skilled in the art from the teachings herein.  
      For example, the multi-channel pump  1  in accordance with an embodiment of the present invention is a piston type pump in which the piston  13  is used as a movable body. However, the present invention is not limited to a piston type pump and a diaphragm type pump provided with only one movable body may be used. Further, the present invention may be applied to other types of pumps.  
      Further, in the embodiment of the present invention, the inflow side active valves  5  and the outflow side active valves  6  are driven so as to be opened or closed by the valve opening/closing drive motor  52  which is a common drive actuator. However, drive actuators may be provided for each of the respective active valves or a plurality of drive actuators may be provided each of which opens and closes some of the active valves.  
      In addition, the piston drive motor  51  is not limited to a stepping motor and may utilize other types of a motors. Further, the drive actuator for the piston  13  is not limited to a motor and various types of a drive actuators may be used.  
      In addition, in the embodiment shown of the present invention, two inflow passages  3   a,    3   b  are provided, but only one inflow passage may be provided. On the other hand, three or more inflow passages may be provided  
      Further, the control method for the multi-channel pump  1  is not limited to the above mentioned control method. For example, the pump  1  may be controlled by a control method which includes a suction step in which the inflow side active valve  5  is opened and methanol is sucked into the pump chamber  2  by the suction operation of the piston  13  and then the inflow side active valve  5  is closed, an initial discharge step after the suction step in which one of the outflow side active valves  6  is opened and the methanol is discharged from the pump chamber  2  by the discharge operation of the piston  13  to eliminate the backlash of the pump  1 , and a discharge step after the initial discharge step in which an outflow side active valve  6  is successively opened and a prescribed amount of methanol is discharged by the discharge operation of the piston  13 .  
      Also in this case, the initial discharge step for eliminating the backlash of the pump  1  is provided between the suction step and the discharge step. Therefore, in the discharge step, the relationship between the moving quantity of the piston  13  and the discharge amount from the outflow passage  4  can be maintained in a linear manner from the beginning. Thus, the variation of the discharge amounts from the respective outflow passages  4  can be reduced In addition, methanol is collectively sucked in the suction step which is required to discharge from the outflow passage  4  by a plurality of times. Therefore, even when the discharge amount of methanol which is discharged from the respective outflow passages  4  is a significantly small amount, the suction amount can be ensured to some extent Accordingly, the capacity of the pump  1  can be increased and the self-feeding performance can be easily attained  
      The fluid used is not limited to methanol and methanol aqueous solution. Ethanol (ethyl-alcohol) and its aqueous solution or another liquid may be used.  
      The application of the multi-channel pump in accordance with the embodiment of the present invention is not limited to a fuel cell. For example, the multi-channel pump may be used in the field of an analyzing device for chemical substance and may be used in substitution for a plurality of cylinder pump which is used in a dropping device of trace reagent  
      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.