Patent Publication Number: US-11391278-B2

Title: Fluid control device

Description:
This is a continuation of International Application No. PCT/JP2019/002922 filed on Jan. 29, 2019 which claims priority from Japanese Patent Application No. 2018-075104 filed on Apr. 10, 2018. The contents of these applications are incorporated herein by reference in their entireties. 
    
    
     BACKGROUND 
     Technical Field 
     The present disclosure relates to a fluid control device that uses a piezoelectric pump to move fluids to a predetermined direction. 
     Patent Document 1 describes a fluid control device including a piezoelectric pump and a driver circuit. The driver circuit is connected to the piezoelectric pump and supplies a drive voltage to the piezoelectric pump. The piezoelectric pump sucks fluids from a suction inlet and discharges from a discharge outlet in response to the drive voltage. This moves fluids in a predetermined direction. 
     Patent Document 1: Japanese Patent No. 6160800 specification 
     BRIEF SUMMARY 
     As a way to use a fluid control device, it is conceivable to use a fluid control device in which capability, for example, pressure is improved. Because of this, in the related art, it is conceivable to use a fluid control device in which piezoelectric pumps are connected in series. The term “connected in series” means that for example, in the case where two piezoelectric pumps (first piezoelectric pump and second piezoelectric pump) are being used, a discharge outlet of the first piezoelectric pump is communicating with a suction inlet of the second piezoelectric pump. 
     In this configuration, the pressure is improved by simultaneously driving the first piezoelectric pump and the second piezoelectric pump. 
     However, such configuration and control develop a problem in that the amount of power consumption increases more than necessary. 
     The present disclosure provides a fluid control device that suppresses unnecessary power consumption. 
     A fluid control device of the present disclosure includes a first pump, a second pump, a container, a first communicating path, a second communicating path, a valve, a first control unit, and a second control unit. The first pump includes a first hole and a second hole and moves a fluid between the first hole and the second hole. The second pump includes a third hole and a fourth hole and moves a fluid between the third hole and the fourth hole. The first communicating path communicates with the second hole and the third hole. The second communicating path communicates with the fourth hole and the container. The valve is installed in the second communicating path and switches between opening the second communicating path to outside and closing the second communicating path from the outside. 
     The first control unit controls driving of the first pump and the second pump. Specifically, the first control unit generates a drive signal for the first pump and a drive signal for the second pump, and the first pump and the second pump repeat a start of operation and a stop of operation in accordance with a drive control cycle. The second control unit controls opening and closing of the valve. Specifically, the second control unit generates a control signal to start a control to close the valve at start timing of one cycle of the drive control cycle and to start a control to open the valve at time of stopping the first pump and the second pump. Time from the start timing of one cycle of the drive control cycle to time at which, of the first pump and the second pump, an upstream side pump with respect to a flow of the fluid reaches a normal operation drive voltage is longer than time from the start timing to time at which, of the first pump and the second pump, a downstream side pump with respect to the flow of the fluid reaches a normal operation drive voltage. The normal operation is a state where the pump is operating at a constant voltage that is the maximum value of the drive voltage within one cycle of the drive control cycle. Note that meanings of the terms “maximum value” and “constant” are within the range of control errors. 
     This configuration shortens the application time of the drive voltage to the upstream side pump without necessarily significantly decreasing the pressure of the fluid control device. 
     Further, in the fluid control device of the present disclosure, the normal operation drive voltage of the upstream side pump can be lower than the normal operation drive voltage of the downstream side pump. 
     This configuration suppresses the power consumption of the upstream side pump at the time of normal operation without necessarily significantly decreasing the pressure. 
     Further, in the fluid control device of the present disclosure, a drive voltage to be applied to the upstream side pump can be equal to or less than a drive voltage to be applied to the downstream side pump. 
     This configuration constantly suppresses the power consumption of the upstream side pump without necessarily significantly decreasing the pressure. 
     Further, in the fluid control device of the present disclosure, the drive voltage may be applied to the upstream side pump after stopping the upstream side pump for a predetermined time period from the start timing. 
     This configuration facilitates the control of the drive voltage for the upstream side pump. 
     Further, the fluid control device of the present disclosure can have the following configuration. The drive voltage is applied simultaneously to the upstream side pump and the downstream side pump at the start timing. A change rate of the drive voltage for the upstream side pump during a period of transition is lower than a change rate of the drive voltage for the downstream side pump during a period of transition. 
     This configuration improves drive efficiency while suppressing the power consumption. 
     Further, in the fluid control device of the present disclosure, the first control unit and the second control unit may be formed into a single control device. 
     This configuration facilitates synchronization of controls of the first control unit and the second control unit, that is, synchronization of operations of the first pump, the second pump, and the valve. 
     Further, in the fluid control device of the present disclosure, the stop timing of the downstream side pump may be later than the stop timing of the upstream side pump. 
     This configuration allows the upstream side pump to be cooled, thereby ensuring more stable operation. 
     The present disclosure enables to suppress unnecessary power consumption. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating the configuration of a fluid control device  10  according to a first embodiment of the present disclosure. 
         FIG. 2  is a flowchart of a control process performed at the fluid control device  10  according to the first embodiment of the present disclosure. 
         FIG. 3A  and  FIG. 3B  are diagrams illustrating waveforms of drive voltages for a piezoelectric pump  21  and a piezoelectric pump  22 . 
         FIG. 4  is a diagram illustrating change patterns of pressure in the fluid control device  10  of the present application and a comparison configuration. 
         FIG. 5  is a diagram illustrating change patterns of temperature in the fluid control device  10  of the present application and a comparison configuration. 
         FIG. 6  is a diagram illustrating change patterns of battery voltage (power supply voltage) in the fluid control device  10  of the present application and a comparison configuration. 
         FIG. 7  is a diagram illustrating change patterns of pressure decrease in the fluid control device  10  of the present application and a comparison configuration. 
         FIG. 8  is a diagram illustrating waveforms of drive voltages for the piezoelectric pump  21  and the piezoelectric pump  22  in a different mode. 
         FIG. 9  is a block diagram illustrating the configuration of a fluid control device  10 A according to a second embodiment of the present disclosure. 
         FIG. 10  is a diagram illustrating waveforms of drive voltages for the piezoelectric pump  21  and the piezoelectric pump  22 . 
         FIG. 11  is a diagram illustrating a change pattern of pressure in the case where the fluid control device  10 A of the present application is used. 
         FIG. 12  is a diagram illustrating waveforms of drive voltages for the piezoelectric pump  21  and the piezoelectric pump  22  in a different mode. 
         FIG. 13  is a block diagram illustrating the configuration of a fluid control device  10 B according to a third embodiment of the present disclosure. 
         FIG. 14  is a chart illustrating transition states of control in two cycles. 
         FIG. 15  is a diagram illustrating waveforms of drive voltages for the piezoelectric pump  21  and the piezoelectric pump  22 . 
         FIG. 16  is a diagram illustrating waveforms of drive voltages for the piezoelectric pump  21  and the piezoelectric pump  22 . 
         FIG. 17  is a diagram illustrating waveforms of drive voltages for the piezoelectric pump  21  and the piezoelectric pump  22 . 
         FIG. 18A ,  FIG. 18B ,  FIG. 18C , and  FIG. 18D  are charts illustrating transition of states in derived patterns of control. 
         FIG. 19  is a functional block diagram of a control unit of the fluid control device. 
         FIG. 20  is a first example of circuit configuration of the control unit. 
         FIG. 21  is a circuit diagram illustrating a first example of a self-excited oscillation type drive voltage generation circuit. 
         FIG. 22  is a circuit diagram illustrating a second example of a self-excited oscillation type drive voltage generation circuit. 
     
    
    
     DETAILED DESCRIPTION 
     A fluid control device according to a first embodiment of the present disclosure is now described with reference to the drawings.  FIG. 1  is a block diagram illustrating the configuration of a fluid control device  10  according to a first embodiment of the present disclosure. 
     As illustrated in  FIG. 1 , a fluid control device  10  includes a piezoelectric pump  21 , a piezoelectric pump  22 , a valve  30 , a container  40 , a communicating path  51 , a communicating path  52 , and a control unit  60 . The fluid control device  10  is a device that sucks a fluid from the container  40  side, and is used in a milking machine, for example. 
     The piezoelectric pump  21  includes a hole  211  and a hole  212  provided on a housing. The piezoelectric pump  21  includes a piezoelectric element. The housing includes a pump chamber. The pump chamber communicates with the hole  211  and the hole  212 . Note that the housing, the pump chamber, and the piezoelectric element are not illustrated in the drawings. 
     The piezoelectric pump  21  moves a fluid between the hole  211  and the hole  212  by varying the volume or pressure of the pump chamber using displacement of the piezoelectric element caused by a drive voltage. In the present embodiment, the hole  211  is the suction inlet, and the hole  212  is the discharge outlet. The piezoelectric pump  21  corresponds to “first pump” of the present disclosure. The hole  212  corresponds to “first hole” of the present disclosure, and the hole  211  corresponds to “second hole” of the present disclosure. 
     The piezoelectric pump  22  includes a hole  221  and a hole  222  provided on a housing. The piezoelectric pump  22  includes a piezoelectric element. The housing includes a pump chamber. The pump chamber communicates with the hole  221  and the hole  222 . Note that the housing, the pump chamber, and the piezoelectric element are not illustrated in the drawings. 
     The piezoelectric pump  22  moves a fluid between the hole  221  and the hole  222  by varying the volume or pressure of the pump chamber using displacement of the piezoelectric element caused by a drive voltage. In the present embodiment, the hole  221  is the suction inlet, and the hole  222  is the discharge outlet. The piezoelectric pump  22  corresponds to “second pump” of the present disclosure. The hole  222  corresponds to “third hole” of the present disclosure, and the hole  221  corresponds to “fourth hole” of the present disclosure. 
     The communicating path  51  is tubular. The hole  211  of the piezoelectric pump  21  and the hole  222  of the piezoelectric pump  22  are communicating with each other via the communicating path  51 . The communicating path  51  corresponds to “first communicating path” of the present disclosure. 
     The communicating path  52  is tubular. The hole  221  of the piezoelectric pump  22  and the container  40  are communicating with each other via the communicating path  52 . The communicating path  52  corresponds to “second communicating path” of the present disclosure. 
     The valve  30  is installed in the communicating path  52 . The valve  30  opens the inside of the communicating path  52  to the outside (valve open state) or closes the inside of the communicating path  52  from the outside (valve close state) in response to the valve control signal. 
     The control unit  60  generates drive voltages for the piezoelectric pump  21  and the piezoelectric pump  22  and respectively supplies these drive voltages to the piezoelectric pump  21  and the piezoelectric pump  22 . Further, the control unit  60  generates the valve control signal and supplies to the valve  30 . The control unit  60  performs a drive control of the piezoelectric pump  21  and the piezoelectric pump  22  and an opening/closing control of the valve  30  in synchronization with each other. The control unit  60  repeats the drive control of the piezoelectric pump  21  and the piezoelectric pump  22  and the opening/closing control of the valve  30  based on a drive control cycle. The drive control cycle is set in advance. 
     In outline, the fluid control device  10  starts the operation of the piezoelectric pump  21  and the piezoelectric pump  22  at the time of performing the closing control of the valve  30 , moves a fluid from the container  40  to the communicating path  52  to the piezoelectric pump  22  to the communicating path  51  to the piezoelectric pump  21  in this order, and discharges the fluid from the hole  212  of the piezoelectric pump  21 . That is to say, the piezoelectric pump  22  corresponds to “upstream side pump” of the present disclosure, and the piezoelectric pump  21  corresponds to “downstream side pump” of the present disclosure. Further, the fluid control device  10  stops the piezoelectric pump  21  and the piezoelectric pump  22  and performs the opening control of the valve  30 . Further, the fluid control device  10  repeats these operations in line with the drive control cycle. 
       FIG. 2  is a flowchart of a control process performed at the fluid control device according to the first embodiment of the present disclosure. 
     As illustrated in  FIG. 2 , the fluid control device  10  starts the downstream side pump (piezoelectric pump  21  in the first embodiment) at the start timing of one cycle of the drive control cycle (S 101 ). The fluid control device  10  performs the closing control of the valve  30  (S 102 ). The fluid control device  10  starts a time measurement or resets the time measurement when the control is in progress (S 103 ). The step S 101 , the step S 102 , and the step S 103  are performed at substantially the same time. Note that the step S 101 , the step S 102 , and the step S 103  may be performed with some time differences or the order of these steps may be replaced, within the range where functionalities of the fluid control device  10  can be actualized. Particularly, in a mode where the order of the steps is replaced, the power consumption can be suppressed. 
     The fluid control device  10  refers to the measured time and continues the time measurement until a delay start time (S 104 : NO). Upon reaching the delay start time (S 104 : YES), the fluid control device  10  starts the upstream side pump (piezoelectric pump  22  in the first embodiment) (S 105 ). 
     The fluid control device  10  causes the upstream side pump and the downstream side pump to continue their operations until a pump stop time (S 106 : NO). 
     Upon reaching the pump stop time (S 106 : YES), the fluid control device  10  stops the upstream side pump and the downstream side pump (S 107 ). The fluid control device  10  performs the opening control of the valve  30  (S 108 ). The step S 107  and the step S 108  are performed at substantially the same time. The step S 108  may be performed with some time differences within the range where functionalities of the fluid control device  10  can be actualized. 
     Note that in the step S 107 , the stop timing of the downstream side pump (piezoelectric pump  21 ) may be delayed from the stop timing of the upstream side pump (piezoelectric pump  22 ). This allows the upstream side pump to be cooled, thereby ensuring more stable operation. 
     Further, in the configuration described above, the configuration in which the upstream side pump is started after starting the downstream side pump is illustrated. Alternatively, the downstream side pump may be started after starting the upstream side pump. At this time, the stop timing of the upstream side pump may be delayed from the stop timing of the downstream side pump. 
     The fluid control device  10  stops the upstream side pump and the downstream side pump, waits for a predetermined time period in the state where the opening control of the valve  30  is performed (S 109 ), ends the one cycle of the drive control cycle, and returns to the step S 101 . 
     With such control, the driving time of the upstream side pump is shorter than that of the downstream side pump. That is to say, the application time of drive voltage to the upstream side pump becomes shorter than the application time of drive voltage to the downstream side pump. Because of this, compared with a prior art configuration in which the upstream side pump and the downstream side pump are driven at the same time, the fluid control device  10  can suppress the amount of power consumption. 
       FIG. 3A  and  FIG. 3B  are diagrams illustrating waveforms of drive voltages for the piezoelectric pump  21  and the piezoelectric pump  22 . In  FIG. 3A  and  FIG. 3B , t 0  is the start timing of one cycle. t 1  is the first timing at which the drive voltage of the piezoelectric pump  21  (downstream side pump) reaches a normal operation drive voltage. t 2  is the first timing at which the drive voltage of the piezoelectric pump  22  (upstream side pump) reaches the normal operation drive voltage. Tc is the drive control cycle. Ts 1  is a drive time. Ts 2  is a non-drive time and corresponds to a waiting time of the step S 109  described above. The drive control cycle Tc is an added time of the drive time Ts 1  and the non-drive time Ts 2 . 
     As illustrated in  FIG. 3A , the fluid control device  10  starts applying the drive voltage to the piezoelectric pump  21  at the start timing t 0 . At this time, the fluid control device  10  gradually increases the drive voltage at a predetermined voltage change rate. At the timing (time) t 1 , the fluid control device  10  sets the drive voltage being applied to the piezoelectric pump  21  at a normal operation drive voltage Vdd 1  and keeps the drive voltage constant thereafter. 
     The fluid control device  10  starts applying the drive voltage to the piezoelectric pump  22  after a lapse of a delay time τ from the start timing t 0 . At this time, the fluid control device  10  gradually increases the drive voltage at a predetermined voltage change rate. The delay time τ can be shorter than, for example, the timing at which transition from a flow volume mode to a pressure mode is made. The flow volume mode is a mode where the pressure is relatively low and difficult to increase, and the flow volume is large. The pressure mode is a mode where the pressure is relatively high, and the flow volume is difficult to increase. Further, the delay time τ can be shorter than, for example, the time to reach about ⅓ of a pressure whose absolute value is the largest, that is, the pressure immediately before performing the opening control of the valve  30 . 
     At the timing (time) t 2 , the fluid control device  10  sets the drive voltage being applied to the piezoelectric pump  22  at a normal operation drive voltage Vdd 2  and keeps this drive voltage constant thereafter. The drive voltage Vdd 2  for the piezoelectric pump  22  is lower than the drive voltage Vdd 1  for the piezoelectric pump  21 . 
     Note that the ratio of the drive voltage Vdd 2  to the drive voltage Vdd 1  can be within 30% or less given individual variation of piezoelectric pumps. 
     The fluid control device  10  stops driving the piezoelectric pump  21  and the piezoelectric pump  22  after a lapse of the drive time Ts 1  from the start timing t 0 . 
     With such control, as described above, the application time of drive voltage to the piezoelectric pump  22  becomes shorter than the application time of drive voltage to the piezoelectric pump  21 . Because of this, the power consumption of the piezoelectric pump  22  becomes lower than the power consumption of the piezoelectric pump  21 . That is to say, the power consumption of the upstream side pump becomes lower than the power consumption of the downstream side pump. 
     Further, the application time of the normal operation drive voltage Vdd 2  to the piezoelectric pump  22 , which is the upstream side pump, becomes shorter than the application time of the normal operation drive voltage Vdd 1  to the piezoelectric pump  21 , which is the downstream side pump. Because of this, the power consumption of the piezoelectric pump  22  becomes additionally lower than the power consumption of the piezoelectric pump  21 . That is to say, the power consumption of the upstream side pump becomes additionally lower than the power consumption of the downstream side pump. 
     Furthermore, as illustrated in  FIG. 3A , the normal operation drive voltage Vdd 2  for the piezoelectric pump  22  is lower than the normal operation drive voltage Vdd 1  for the piezoelectric pump  21 . Because of this, the power consumption of the piezoelectric pump  22  becomes additionally lower than the power consumption of the piezoelectric pump  21 . That is to say, the power consumption of the upstream side pump becomes additionally lower than the power consumption of the downstream side pump. 
     As with  FIG. 3A ,  FIG. 3B  is a diagram illustrating the waveforms of drive voltages for the piezoelectric pump  21  and the piezoelectric pump  22 . 
       FIG. 3B  is different from  FIG. 3A  in the stop timing of the piezoelectric pump  22 . Specifically, the fluid control device  10  stops driving the piezoelectric pump  22  after a lapse of a drive time Ts 3  from the start timing t 0  and stops driving the piezoelectric pump  21  after a lapse of the drive time Ts 1  from the start timing t 0 . That is to say, the stop timing of the piezoelectric pump  21  is later than the stop timing of the piezoelectric pump  22 . 
     Even with such control, the application time of drive voltage to the piezoelectric pump  22  becomes shorter than the application time of drive voltage to the piezoelectric pump  21 . Because of this, the power consumption of the piezoelectric pump  22  becomes lower than the power consumption of the piezoelectric pump  21 . That is to say, the power consumption of the upstream side pump becomes lower than the power consumption of the downstream side pump. 
     Further, the application time of the normal operation drive voltage Vdd 2  to the piezoelectric pump  22 , which is the upstream side pump, becomes shorter than the application time of the normal operation drive voltage Vdd 1  to the piezoelectric pump  21 , which is the downstream side pump. Because of this, the power consumption of the piezoelectric pump  22  becomes additionally lower than the power consumption of the piezoelectric pump  21 . That is to say, the power consumption of the upstream side pump becomes additionally lower than the power consumption of the downstream side pump. 
     Further, by performing the control described above, the piezoelectric pump  22  is cooled. That is to say, the piezoelectric pump  22  operates more stably. Further, the configuration may be such that the stop timing of the piezoelectric pump  21  is later than the stop timing of the piezoelectric pump  22 . 
       FIG. 4  is a diagram illustrating change patterns of pressure in the fluid control device  10  of the present application and a comparison configuration. In  FIG. 4 , the horizontal axis is the time, and the vertical axis is the pressure (discharge pressure). In the comparison configuration, the upstream side pump and the downstream side pump operate at the same time, and the normal operation drive voltage of the upstream side pump and the normal operation drive voltage of the downstream side pump are the same. 
     As illustrated in  FIG. 4 , with the configuration and the control of the fluid control device  10 , the pressure changes in line with the drive control cycle. That is to say, the pressure gradually decreases from the start timing of one cycle of the drive control cycle, reaches the lowest at the end timing of the one cycle of the drive control cycle, and returns to the original pressure. 
     Although there is some time difference, a pressure similar to that of comparison configuration can be provided even using the configuration of the present application. That is to say, the fluid control device  10  enables to suppress the power consumption without necessarily significantly decreasing pressure capability. In other words, the fluid control device  10  can efficiently provide a desired discharge pressure while suppressing unnecessary power consumption. 
     Further, the fluid control device  10  enables to produce the following advantageous effects.  FIG. 5  is a diagram illustrating change patterns of temperature in the fluid control device  10  of the present application and a comparison configuration. In  FIG. 5 , the horizontal axis is the time, and the vertical axis is the surface temperature of the downstream side pump. In the comparison configuration, the upstream side pump and the downstream side pump operate at the same time, and the normal operation drive voltage of the upstream side pump and the normal operation drive voltage of the downstream side pump are the same. 
     As illustrated in  FIG. 5 , with the configuration and the control of the fluid control device  10 , the temperature increase of the downstream side pump is suppressed. Further, although it is not illustrated in the drawing, the temperature increase of the upstream side pump is also suppressed. This is due to the following reasons. Because of a decrease in the drive voltage of the upstream side pump, a temperature increase at the upstream side pump is suppressed. This suppresses the temperature of a fluid flowing into the downstream side pump. Because the temperature of a fluid flowing into the downstream side pump is suppressed, the temperature increase of the downstream side pump is suppressed. 
     Further, as illustrated in  FIG. 6 , the fluid control device  10  enables to suppress the power consumption.  FIG. 6  is a diagram illustrating change patterns of battery voltage (power supply voltage) in the fluid control device of the present application and a comparison configuration. In  FIG. 6 , the horizontal axis is the time, and the vertical axis is the battery voltage. In the comparison configuration, the upstream side pump and the downstream side pump operate at the same time, and the normal operation drive voltage of the upstream side pump and the normal operation drive voltage of the downstream side pump are the same. 
     As illustrated in  FIG. 6 , with the configuration and the control of the fluid control device  10 , a decrease of the battery voltage can be delayed. That is to say, with the configuration and the control of the fluid control device  10 , the battery life can be prolonged while suppressing the power consumption. For example, in the case of  FIG. 6 , the battery life can be extended to about 1.5 times. 
     Further, as illustrated in  FIG. 7 , the fluid control device  10  enables to delay degradation of reliability.  FIG. 7  is a diagram illustrating change patterns of pressure decrease in the fluid control device  10  of the present application and a comparison configuration. In  FIG. 7 , the horizontal axis is the time, and the vertical axis is the pressure. In the comparison configuration, the upstream side pump and the downstream side pump operate at the same time, and the normal operation drive voltage of the upstream side pump and the normal operation drive voltage of the downstream side pump are the same. 
     As illustrated in  FIG. 7 , with the configuration and the control of the fluid control device  10 , a decrease of the pressure can be substantially delayed. That is to say, with the configuration and the control of the fluid control device  10 , a decrease of reliability can be delayed, and a product life can be prolonged. 
     Note that in the control described above, the mode is described in which the drive start timing of the piezoelectric pump  22  is delayed for the delay time τ from the drive start timing of the piezoelectric pump  21 . However, even in the case where the drive start timing of the piezoelectric pump  22  is set equal to the drive start timing of the piezoelectric pump  21 , similar functions and effects can be achieved by performing the following control. 
       FIG. 8  is a diagram illustrating waveforms of drive voltages for the piezoelectric pump  21  and the piezoelectric pump  22  in a different mode. As illustrated in  FIG. 8 , the fluid control device  10  sets the application start timing of drive voltage to the piezoelectric pump  21  and the application start timing of drive voltage to the piezoelectric pump  22  equal to each other. The fluid control device  10  sets the change rate of the drive voltage for the piezoelectric pump  22  during a period of transition lower than the change rate of the drive voltage for the piezoelectric pump  21 . That is to say, the application start timing of the normal operation drive voltage Vdd 2  for the piezoelectric pump  22  is delayed from the application start timing of the normal operation drive voltage Vdd 1  for the piezoelectric pump  21 . 
     Because of this, the fluid control device  10  can suppress the power consumption. Further, by using this control, the application of the drive voltage for the piezoelectric pump  22  can be performed from the start timing of one cycle of the drive control cycle, and the suction of fluid from the container  40  can be performed more efficiently. 
     Next, a fluid control device according to a second embodiment is described with reference to the drawings.  FIG. 9  is a block diagram illustrating the configuration of a fluid control device  10 A according to the second embodiment of the present disclosure. 
     As illustrated in  FIG. 9 , compared with the fluid control device  10  according to the first embodiment, the fluid control device  10 A according to the second embodiment is a device in which the flow of a fluid is reversed. With regard to parts of the fluid control device  10 A similar to those of the fluid control device  10 , the description is omitted. The fluid control device  10 A is used in, for example, a blood pressure meter and the like. 
     In the fluid control device  10 A, the hole  212  of the piezoelectric pump  21  and the hole  221  of the piezoelectric pump  22  are communicating with each other via the communicating path  51 . The hole  222  of the piezoelectric pump  22  and the container  40 A are communicating with each other via the communicating path  52 . Accordingly, in the fluid control device  10 A, the piezoelectric pump  21  is the upstream side pump, and the piezoelectric pump  22  is the downstream side pump. 
       FIG. 10  is a diagram illustrating waveforms of drive voltages for the piezoelectric pump  21  and the piezoelectric pump  22 . As illustrated in  FIG. 10 , the fluid control device  10 A applies the drive voltage to the piezoelectric pump  22 , which is the downstream side pump, at the start timing of one cycle of the drive control cycle. At this time, the fluid control device  10 A increases the drive voltage for the piezoelectric pump  22  in a stepwise fashion and sets the drive voltage at the normal operation drive voltage. Subsequently, the fluid control device  10 A maintains the normal operation drive voltage for a predetermined time period. 
     In this state, the fluid control device  10 A applies the normal operation drive voltage to the piezoelectric pump  21 , which is the upstream side pump, at the drive start timing t 20  of the piezoelectric pump  21 . At this time, the normal operation drive voltage of the piezoelectric pump  21  (upstream side pump) is lower than the normal operation drive voltage of the piezoelectric pump  22  (downstream side pump). Further, the drive voltage of the piezoelectric pump  22  is decreased temporarily. However, the decreased drive voltage for the piezoelectric pump  22  can be higher than the drive voltage for the piezoelectric pump  21 . 
     Note that the drive start timing t 20  is set at, for example, the timing at which the pressure of the container  40 A reaches a predetermined pressure.  FIG. 11  is a diagram illustrating a change pattern of pressure in the case where the fluid control device  10 A of the present application is used. As illustrated in  FIG. 11 , the timing at which the pressure becomes equal to a threshold value Pa is defined as the drive start timing t 20  of the piezoelectric pump  21  described above. 
     Subsequently, the fluid control device  10 A gradually increases both the normal operation drive voltage for the piezoelectric pump  21  and the normal operation drive voltage for the piezoelectric pump  22 . Further, although it is not illustrated in the drawing, upon reaching a predetermined pressure, the fluid control device  10 A stops applying the drive voltage and performs the opening control of the valve  30 . 
     As described above, as is the case with the fluid control device  10 , the fluid control device  10 A that moves a fluid to the container  40 A can suppress unnecessary power consumption and suppress an increase in temperature and a decrease in reliability by implementing the control described above. 
     Note that in the control described above, the mode is described in which the drive start timing of the piezoelectric pump  21  is delayed from the drive start timing of the piezoelectric pump  22 . However, as with the first embodiment, even in the case where the drive start timing of the piezoelectric pump  21  is set equal to the drive start timing of the piezoelectric pump  22 , similar functions and effects can be achieved by performing the following control. 
       FIG. 12  is a diagram illustrating waveforms of drive voltages for the piezoelectric pump  21  and the piezoelectric pump  22  in another mode. As illustrated in  FIG. 12 , the fluid control device  10 A sets the application start timing of drive voltage to the piezoelectric pump  22  and the application start timing of drive voltage to the piezoelectric pump  21  equal to each other. The fluid control device  10 A sets the change rate of the drive voltage for the piezoelectric pump  21  during a period of transition lower than the change rate of the drive voltage for the piezoelectric pump  22 . That is to say, the application start timing of the normal operation drive voltage for the piezoelectric pump  21  is delayed from the application start timing of the normal operation drive voltage for the piezoelectric pump  22 . 
     Because of this, the fluid control device  10 A can suppress the power consumption. Further, with this control, the drive voltage can be applied to the piezoelectric pump  21  from the start timing of one cycle of the drive control cycle, and discharge of fluid to the container  40 A and an increase of pressure in the container  40 A can be achieved more efficiently. 
     Next, a fluid control device according to a third embodiment of the present disclosure is described with reference to the drawings.  FIG. 13  is a block diagram illustrating the configuration of a fluid control device  10 B according to a third embodiment of the present disclosure. 
     As illustrated in  FIG. 13 , a fluid control device  10 B according to the third embodiment is different from the fluid control device  10 A according to the second embodiment in that the fluid control device  10 B further includes a piezoelectric pump  23 , a piezoelectric pump  24 , a communicating path  53 , a communicating path  54 , a communicating path  55 , and a communicating path  56 . The other configuration of the fluid control device  10 B is similar to that of the fluid control device  10 A, and the description regarding the similar part is omitted. 
     The basic configuration of the piezoelectric pump  23  and the piezoelectric pump  24  is the same as the basic configuration of the piezoelectric pump  21  and the piezoelectric pump  22 . The piezoelectric pump  23  includes a hole  231  that is a suction inlet and a hole  232  that is a discharge outlet. The piezoelectric pump  24  includes a hole  241  that is a suction inlet and a hole  242  that is a discharge outlet. 
     The hole  232  of the piezoelectric pump  23  and the hole  241  of the piezoelectric pump  24  are communicating with each other via the communicating path  53 . The hole  242  of the piezoelectric pump  24  and the valve  30  are communicating with each other via the communicating path  54 . The communicating path  51  and the communicating path  53  are communicating with each other via the communicating path  55 , and the communicating path  52  and the communicating path  54  are communicating with each other via the communicating path  56 . 
     In this configuration, the piezoelectric pump  21  and the piezoelectric pump  23  are upstream side pumps, and the piezoelectric pump  22  and the piezoelectric pump  24  are downstream side pumps. That is to say, the fluid control device  10 B has the configuration in which two pairs of piezoelectric pumps are connected in series, and the piezoelectric pumps of each pair are connected in parallel with respect to fluid flow paths. 
     For such configuration, the fluid control device  10 B performs the following control using the control unit  60 .  FIG. 14  is a chart illustrating transition states of control in two cycles.  FIG. 15  and  FIG. 16  are diagrams, each illustrating waveforms of drive voltages for the respective piezoelectric pumps. 
     (State ST 1 ) 
     As illustrated in  FIG. 14 , the fluid control device  10 B performs the closing control (CL) of the valve  30 . This closing control continues from the state ST 1  to the state ST 4 . Further, at the start timing t 30  of the drive control cycle, the fluid control device  10 B applies the drive voltage Vdd 2  to the piezoelectric pump  22  and the piezoelectric pump  24 , and the state ST 1  extends to the timing t 31 . At this time, as illustrated in  FIG. 15  and  FIG. 16 , during a period of transition, the fluid control device  10 B increases the drive voltage in a stepwise fashion in such a manner as to include a stage where the drive voltage is set equal to a drive voltage Vdd 2   t . This enables the fluid control device  10 B to drive two pumps installed in parallel on the downstream side. This enables the fluid control device  10 B to gain a large flow volume. 
     (State ST 2 ) 
     Next, as illustrated in  FIG. 14 , assuming the state ST 2  extends from the timing t 31  to the timing t 32 , the fluid control device  10 B continues applying the drive voltage Vdd 2  to the piezoelectric pump  22  and the piezoelectric pump  24 . Further, in the state ST 2 , the fluid control device  10 B applies the drive voltage Vdd 1  to the piezoelectric pump  21  and the piezoelectric pump  23 . The drive voltage Vdd 1  is lower than the drive voltage Vdd 2 . At this time, as illustrated in  FIG. 15  and  FIG. 16 , during a period of transition, the fluid control device  10 B increases the drive voltage in a stepwise fashion in such a manner as to include a stage where the drive voltage is set equal to a drive voltage Vdd 1   t . This enables the fluid control device  10 B to drive all the pumps. This enables the fluid control device  10 B to gain a large flow volume. 
     Further, these state ST 1  and state ST 2  is a period corresponding to the flow volume mode described above, and thus the fluid control device  10 B enables to actualize efficient operations for the flow volume mode. Further, in the state ST 1 , only the downstream side pumps are driven. Therefore, unnecessary power consumption can be suppressed. 
     (State ST 3 ) 
     Next, as illustrated in  FIG. 14 , assuming the state ST 3  extends from the timing t 32  to the timing t 33 , the fluid control device  10 B continues applying the drive voltage Vdd 1  to the piezoelectric pump  21  and the drive voltage Vdd 2  to the piezoelectric pump  22 . Further, at the timing t 33  which is the start of the state ST 3 , the fluid control device  10 B stops applying the drive voltages to the piezoelectric pump  23  and the piezoelectric pump  24 . This enables the fluid control device  10 B to drive only one pair of pumps connected in series. This state is a period corresponding to the pressure mode described above, and thus the fluid control device  10 B enables to actualize efficient operations for the pressure mode. Further, the state ST 4  becomes a state where the flow volume hardly increases, and in this state, only two pumps connected in series are driven. Therefore, unnecessary power consumption can be suppressed. 
     (State ST 4 ) 
     Next, as illustrated in  FIG. 14 , assuming the state ST 4  extends from the timing t 33  to the timing t 34 , the fluid control device  10 B continues applying the drive voltage Vdd 1  to the piezoelectric pump  21  and the drive voltage Vdd 2  to the piezoelectric pump  22 . Further, the fluid control device  10 B applies an auxiliary drive voltage to the piezoelectric pump  23  and the piezoelectric pump  24 . Further, at the timing t 34  which is the end of the state ST 4 , the fluid control device  10 B stops applying the drive voltages to the piezoelectric pump  21 , the piezoelectric pump  22 , the piezoelectric pump  23 , and the piezoelectric pump  24 . As described above, by stopping the application of the drive voltages after applying the drive voltages to all the piezoelectric pumps, it becomes possible to ensure that all the piezoelectric pumps are brought back to a normal default state. 
     (State ST 5 ) 
     Next, as illustrated in  FIG. 14 , the fluid control device  10 B performs the opening control (OP) of the valve  30 . Assuming the state ST 5  extends from the timing t 34  to the timing t 40 , the fluid control device  10 B continues stopping the application of the drive voltages to the piezoelectric pump  21 , the piezoelectric pump  22 , the piezoelectric pump  23 , and the piezoelectric pump  24 . 
     With these controls, the control for one cycle of the drive control cycle ends. 
     (State ST 6 ) 
     As illustrated in  FIG. 14 , in the state ST 6 , the fluid control device  10 B performs a control similar to that in the state ST 1 . 
     (State ST 7 ) 
     As illustrated in  FIG. 14 , in the state ST 7 , the fluid control device  10 B performs a control similar to that in the state ST 2 . 
     (State ST 8 ) 
     As illustrated in  FIG. 14 , in the state ST 8 , the fluid control device  10 B applies the drive voltage to the piezoelectric pump  23  and the piezoelectric pump  24 , instead of the piezoelectric pump  21  and piezoelectric pump  22  in the state ST 3 . 
     (State ST 9 ) 
     As illustrated in  FIG. 14 , in the state ST 9 , the fluid control device  10 B performs a control similar to that in the state ST 4 . 
     (State ST 10 ) 
     As illustrated in  FIG. 14 , in the state ST 10 , the fluid control device  10 B performs a control similar to that in the state ST 5 . 
     With these controls, the control for one cycle of the drive control cycle ends. 
     As described above, in the control illustrated in  FIG. 14 ,  FIG. 15 , and  FIG. 16 , the fluid control device  10 B repeats the same control in increments of one cycle of the drive control cycle. Further, both the pressure and the flow volume can be improved by using the configuration of the fluid control device  10 B. Further, the fluid control device  10 B can suppress unnecessary power consumption. 
     Further, the life of piezoelectric pump can be prolonged by switching the series-connected piezoelectric pumps to be driven at each cycle, like the state ST 3  and the state ST 8 . 
     Note that in the description described above, the mode is illustrated in which the drive voltage is applied to the piezoelectric pump in a stepwise fashion. However, a mode in which the drive voltage is applied as illustrated in  FIG. 17  may also be used.  FIG. 17  is a diagram illustrating waveforms of drive voltages for the piezoelectric pump  21  and the piezoelectric pump  22 . 
     As illustrated in  FIG. 17 , the fluid control device  10 B gradually increases the drive voltage during a period of transition for the piezoelectric pump  21  and the piezoelectric pump  22 . Note that the drive voltage for the piezoelectric pump  23  is similar to that of the piezoelectric pump  21 , and the drive voltage for the piezoelectric pump  24  is similar to that of the piezoelectric pump  22 . 
     Even by using such control of the drive voltage, the pressure and the flow volume can be improved, and unnecessary power consumption can be suppressed. Further, performing such control of the drive voltage enables to drive the piezoelectric pumps more efficiently. 
     Further, the control for the third embodiment described above enables to provide various derived controls, such as illustrated in  FIG. 18A ,  FIG. 18B ,  FIG. 18C , and  FIG. 18D .  FIG. 18A ,  FIG. 18B ,  FIG. 18C , and  FIG. 18D  are charts illustrating transition of states in derived patterns of control. 
     The controls illustrated in  FIG. 18A ,  FIG. 18B , FIG.  18 C, and  FIG. 18D  are basically similar to the control illustrated in  FIG. 14 , and only different states are illustrated by hatching. Timings of the closing control and the opening control of the valve in the controls illustrated in  FIG. 18A ,  FIG. 18B ,  FIG. 18C , and  FIG. 18D  are the same as those in the control illustrated in  FIG. 14 . 
     In the control illustrated in  FIG. 18A , compared with the control illustrated in  FIG. 14 , the same control as that in the state ST 3  is performed in the state ST 8 . 
     In the control illustrated in  FIG. 18B , compared with the control illustrated in  FIG. 14 , in the state ST 3 , the drive voltage is applied to the piezoelectric pump  23  and the piezoelectric pump  24 , instead of the piezoelectric pump  21  and piezoelectric pump  22 . 
     In the control illustrated in  FIG. 18C , compared with the control illustrated in  FIG. 14 , in the state ST 6 , the drive voltage is applied to the piezoelectric pump  21  and the piezoelectric pump  23 , instead of the piezoelectric pump  22  and piezoelectric pump  24 . 
     In the control illustrated in  FIG. 18D , compared with the control illustrated in  FIG. 14 , in the state ST 4 , the application of the drive voltage to the piezoelectric pump  21  and the piezoelectric pump  22  continues while no drive voltage is applied to the piezoelectric pump  23  and piezoelectric pump  24 . Further, in the state ST 9 , the application of the drive voltage to the piezoelectric pump  23  and the piezoelectric pump  24  continues while no drive voltage is applied to the piezoelectric pump  21  and piezoelectric pump  22 . 
     The control patterns are not limited to those described above, and those control patterns may be combined as needed. 
     Note that the control units  60  according to the first and second embodiments described above may be actualized using the following configuration, for example.  FIG. 19  is a functional block diagram of the control unit of the fluid control device. 
     As illustrated in  FIG. 19 , the control unit  60  includes an MCU  61 , a power supply circuit  621 , a power supply circuit  622 , a drive voltage generation circuit  631 , a drive voltage generation circuit  632 , and a valve control signal generation circuit  64 . The control unit  60  is a device that actualizes “first control unit” and “second control unit” of the present disclosure using a single IC. 
     The MCU  61  is connected to the power supply circuit  621 , the power supply circuit  622 , the drive voltage generation circuit  631 , the drive voltage generation circuit  632 , and the valve control signal generation circuit  64 . Power supply voltages are being supplied from a battery  70  to the MCU  61 , the power supply circuit  621 , and the power supply circuit  622 . The MCU  61  performs drive controls for the power supply circuit  621 , the power supply circuit  622 , the drive voltage generation circuit  631 , the drive voltage generation circuit  632 , and the valve control signal generation circuit  64 . For example, the control of the drive voltage value, the control of output timing of the drive voltage, the control of output timing of the valve control signal, and the like are performed. 
     The power supply circuit  621  converts the power supply voltage into a voltage to be applied to the piezoelectric pump  21  and outputs to the drive voltage generation circuit  631 . The power supply circuit  622  converts the power supply voltage into a voltage to be applied to the piezoelectric pump  22  and outputs to the drive voltage generation circuit  632 . 
     The drive voltage generation circuit  631  converts the voltage from the power supply circuit  621  into a waveform for driving the piezoelectric pump  21  and outputs to the piezoelectric pump  21 . 
     The drive voltage generation circuit  632  converts the voltage from the power supply circuit  622  into a waveform for driving the piezoelectric pump  22  and outputs to the piezoelectric pump  22 . 
     The valve control signal generation circuit  64  generates a valve control signal for the closing control and a valve control signal for the opening control and outputs to the valve  30 . 
     Note that the control unit  60  according to the third embodiment can be actualized by adding two more pairs of the power supply circuit and the drive voltage generation circuit illustrated in  FIG. 19 . 
     Further, the control unit  60  may have a configuration in which a first control unit for applying the drive voltage to the piezoelectric pump and a second control unit for outputting the control signal to the valve are provided separately. In this case, in the configuration of  FIG. 19 , the first control unit includes a device in which a control unit at least performing the drive controls of the piezoelectric pumps using the drive voltage generation circuit  631 , the drive voltage generation circuit  632 , and the MCU  61  are packaged into a single unit. Further, the second control unit includes a device in which functionalities for performing the valve control in the valve control signal generation circuit  64  and the MCU  61  are packaged into a single unit. Note that the actualization of the first control unit and the second control unit using the singly packaged devices facilitates synchronization of the drive voltage and the valve control signal. 
     Further, the control unit  60  can be actualized using the following various circuit configurations. 
     (Separately Excited Oscillation Type) 
       FIG. 20  is a first example of the circuit configuration of the control unit. 
       FIG. 20  includes the MCU  61  and a drive voltage generation circuit  630 . This circuit is a circuit that drives and controls a single piezoelectric pump (piezoelectric element  200 ). Therefore, in a mode where a plurality of piezoelectric pumps is controlled and driven, such as the ones described above, the same number of the drive voltage generation circuits  630  as the piezoelectric pumps is included. 
     The drive voltage generation circuit  630  is a full bridge circuit including FET 1 , FET 2 , FET 3 , and FET 4 . The gate of FET 1 , the gate of FET 2 , the gate of FET 3 , and the gate of FET 4  are connected to the MCU  61 . 
     The drain of FET 1  and the drain of FET 3  are connected to each other. A voltage Vc obtained from the power supply voltage is supplied to the drain of FET 1  and the drain of FET 3 . 
     The source of FET 1  is connected to the drain of FET 2 , and the source of FET 2  is connected to a reference potential. The source of FET 3  is connected to the drain of FET 4 , and the source of FET 4  is connected to the reference potential via a resistive element Rs. 
     A connection point of the source of FET 1  and the drain of FET 2  is connected to one terminal of the piezoelectric element  200 , and a connection point of the source of FET 3  and the drain of FET 4  is connected to the other terminal of the piezoelectric element  200 . 
     The MCU  61  performs, as a first control state, a turn-on control (conduction control) of FET 1  and FET 4  and a turn-off control (open control) of FET 2  and FET 3 . Further, the MCU  61  performs, as a second control state, the turn-off control (open control) of FET 1  and FET 4  and the turn-on control (conduction control) of FET 2  and FET 3 . The MCU  61  performs the first control state and the second control state in this order. At this time, the MCU  61  performs the control in such a way that the time during which the first control state and the second control state are sequentially performed becomes equal to the period (inverse of resonant frequency) of the piezoelectric pump (piezoelectric element  200 ). This allows to apply the drive voltage to the piezoelectric element  200 , thereby driving the piezoelectric pump. 
     (Self-Excited Oscillation Type) 
       FIG. 21  is a circuit diagram illustrating a first example of a self-excited oscillation type drive voltage generation circuit  650 . 
     As illustrated in  FIG. 21 , the drive voltage generation circuit  650  includes a H-bridge IC (Integrated Circuit)  651 , a differential circuit  652 , an amplifier circuit  653 , a phase reversing circuit  654 , and an intermediate voltage generation circuit  655 . 
     In outline, the drive voltage generation circuit  650  operates in the following manner. 
     The H-bridge IC  651  receives supply of the voltage Vc, receives an output of the amplifier circuit  653  and an output of the phase reversing circuit  654 , and outputs drive voltages having the same absolute value and opposite phases to each other from a first output terminal and a second output terminal to the piezoelectric element  200 . The piezoelectric element  200  is excited by receiving these drive voltages, thereby driving the piezoelectric pump. 
     The differential circuit  652  differentially amplifies voltages at both ends of a resistive element R 12  caused by a current flowing through the piezoelectric element  200  and outputs to the amplifier circuit  653 . The amplifier circuit  653  amplifies an output voltage of the differential circuit  652  and outputs to the H-bridge IC  651  and the phase reversing circuit  654 . The phase reversing circuit  654  reverses the phase of an output voltage of the amplifier circuit  653  and outputs to the H-bridge IC  651 . 
     By performing such feedback control, the piezoelectric element  200  is driven at an optimum frequency based on the impedances of respective circuit elements that constitute the drive voltage generation circuit  650  and the piezoelectric element  200 . 
     As illustrated in  FIG. 21 , a specific circuit configuration of the drive voltage generation circuit  650  is, for example, the following circuit configuration. 
     The intermediate voltage generation circuit  655  includes an operational amplifier U 10 , a resistive element R 13 , a resistive element R 14 , a resistive element R 15 , a capacitor C 3 , and a capacitor C 4 . 
     The resistive element R 14  and the resistive element R 13  are connected in series in this order in between a supply point of the voltage Vc and the reference potential. The capacitor C 3  is connected in parallel to the resistive element R 13 . The capacitor C 4  is connected in parallel to a series circuit of the resistive element R 14  and the resistive element R 13 . A non-inverting input terminal of the operational amplifier U 10  is connected to a connection point of the resistive element R 13  and the resistive element R 14 . An output terminal of the operational amplifier U 10  is connected to an inverting input terminal of the operational amplifier U 10  via a resistive element R 15 . The intermediate voltage generation circuit  655  outputs, as an intermediate voltage Vm, a voltage of a terminal of the resistive element R 15  opposite to a terminal connected to the output terminal of the operational amplifier U 10 . 
     A first output terminal of the H-bridge IC  651  is connected to one of terminals of the piezoelectric element  200  via a resistive element R 11 . A second output terminal of the H-bridge IC  651  is connected to the other terminal of the piezoelectric element  200  via a resistive element R 12 . 
     The differential circuit  652  includes an operational amplifier U 3 , a resistive element R 1 , a resistive element R 2 , a resistive element R 3 , a resistive element R 4 , a capacitor C 5 , a capacitor C 6 , a capacitor C 7 , and a capacitor C 8 . 
     A drive voltage V+ is supplied to the operational amplifier U 3 . An inverting input terminal of the operational amplifier U 3  is connected to the piezoelectric element  200  side of the resistive element R 12  for current detection via a parallel circuit of the resistive element R 2  and the capacitor C 5 . A non-inverting input terminal of the operational amplifier U 3  is connected to the H-bridge IC  651  side of the resistive element R 12  via a parallel circuit of the resistive element R 1  and the capacitor C 6 . The intermediate voltage Vm is supplied to the non-inverting input terminal of the operational amplifier U 3  via a parallel circuit of the resistive element R 4  and the capacitor C 7 . An output terminal of the operational amplifier U 3  is connected to an inverting input terminal of the operational amplifier U 3  via a parallel circuit of the resistive element R 3  and the capacitor C 8 . 
     The amplifier circuit  653  includes an operational amplifier U 2 , a resistive element R 5 , a resistive element R 6 , a resistive element R 7 , a capacitor C 1 , and a capacitor C 2 . 
     The drive voltage V+ is supplied to the operational amplifier U 2 . An inverting input terminal of the operational amplifier U 2  is connected to the output terminal of the operational amplifier U 3  of the differential circuit  652  via the capacitor C 1  and the resistive element R 5 . A connection point of the capacitor C 1  and the resistive element R 5  is connected to the reference potential via the resistive element R 7 . One terminal of the capacitor C 2  is connected to a connection point of the capacitor C 1  and the resistive element R 5 , and the other terminal of the capacitor C 2  is connected to one terminal of the resistive element R 6 . The other terminal of the resistive element R 6  is connected to an inverting input terminal of the operational amplifier U 2 . The intermediate voltage Vm is supplied to a non-inverting input terminal of the operational amplifier U 2 . An output terminal of the operational amplifier U 2  is connected to the one terminal of the resistive element R 6 . Further, the output terminal of the operational amplifier U 2  is connected to the H-bridge IC  651 . 
     The phase reversing circuit  654  includes an operational amplifier U 1 , a resistive element R 8 , a resistive element R 9 , and a resistive element R 10 . 
     The drive voltage V+ is supplied to the operational amplifier U 1 . An inverting input terminal of the operational amplifier U 1  is connected to the output terminal of the operational amplifier U 2  of the amplifier circuit  653  via the resistive element R 8 . The intermediate voltage Vm is supplied to a non-inverting input terminal of the operational amplifier U 1  via the resistive element R 10 . An output terminal of the operational amplifier U 1  is connected to the inverting input terminal of the operational amplifier U 1  via the resistive element R 9 . Further, the output terminal of the operational amplifier U 1  is connected to the H-bridge IC  651 . 
       FIG. 22  is a circuit diagram illustrating a second example of a self-excited oscillation type drive voltage generation circuit  660 . 
     As illustrated in  FIG. 22 , the drive voltage generation circuit  660  includes an amplifier circuit  661 , a phase reversing circuit  662 , a differential circuit  663 , a filter circuit  664 , and an intermediate voltage generation circuit  665 . 
     In outline, the drive voltage generation circuit  660  operates in the following manner. 
     The amplifier circuit  661  supplies a first drive voltage to the one terminal of the piezoelectric element  200  via a resistive element R 100 . The phase reversing circuit  662  supplies a second drive voltage to the other terminal of the piezoelectric element  200 . The first drive voltage and the second drive voltage are opposite phase voltages having the same absolute value. The piezoelectric element  200  is excited by receiving these drive voltages, thereby driving the piezoelectric pump. 
     The differential circuit  663  differentially amplifies voltages at both ends of the resistive element R 100  caused by a current flowing through the piezoelectric element  200  and outputs to the filter circuit  664 . The filter circuit  664  filters an output voltage of the differential circuit  663  and outputs to the amplifier circuit  661 . The amplifier circuit  661  receives an output voltage of the filter circuit  664  and outputs the first drive voltage. The phase reversing circuit  662  receives the first drive voltage, reverses the phase thereof, and outputs the second drive voltage. 
     By performing such feedback control, the piezoelectric element  200  is driven at an optimum frequency based on impedances of respective circuit elements that constitute the drive voltage generation circuit  660  and the piezoelectric element  200 . 
     As illustrated in  FIG. 22 , a specific circuit configuration of the drive voltage generation circuit  660  is, for example, the following circuit configuration. 
     The intermediate voltage generation circuit  665  includes a resistive element R 35 , a resistive element R 36 , a capacitor C 23 , and a capacitor C 24 . 
     The resistive element R 35  and the resistive element R 36  are connected in series in this order in between the supply point of the voltage Vc and the reference potential. The capacitor C 23  is connected in parallel to the resistive element R 35 . The capacitor C 24  is connected in parallel to the resistive element R 36 . The intermediate voltage generation circuit  665  outputs, as the intermediate voltage Vm, a divided voltage obtained by the resistive element R 35  and the resistive element R 36 . 
     The amplifier circuit  661  includes an operational amplifier U 21 , a transistor Q 21 , a transistor Q 22 , a resistive element R 24 , and a resistive element R 25 . 
     One end portion of the resistive element R 24  is an input port of the amplifier circuit  661  and is connected to an output terminal of an operational amplifier U 24  of the filter circuit  664 . 
     The other end portion of the resistive element R 24  is connected to an inverting input terminal of the operational amplifier U 21 . The intermediate voltage Vm is supplied to a non-inverting input terminal of the operational amplifier U 21 . The drive voltage V+ is supplied to the operational amplifier U 21 . An output terminal of the operational amplifier U 21  is connected to a base terminal of the transistor Q 21  and a base terminal of the transistor Q 22 . 
     The transistor Q 21  is a n-type transistor. The transistor Q 22  is a p-type transistor. The voltage Vc is supplied to a collector terminal of the transistor Q 21 . An emitter terminal of the transistor Q 21  and an emitter terminal of the transistor Q 22  are connected. A collector terminal of the transistor Q 22  is connected to ground. A resistive element R 33  is connected between a connecting part of the base terminals of the transistor Q 21  and the transistor Q 22  and a connecting part of the emitter terminal of the transistor Q 21  and the emitter terminal of the transistor Q 22 . 
     The connecting part of the emitter terminal of the transistor Q 21  and the emitter terminal of the transistor Q 22  is an output port of the amplifier circuit  661  and is connected to one end portion of the resistive element R 100 . The other end portion of the resistive element R 100  is connected to the one terminal of the piezoelectric element  200 . 
     The phase reversing circuit  662  includes an operational amplifier U 23 , a transistor Q 23 , a transistor Q 24 , a resistive element R 26 , a resistive element R 32 , and a resistive element R 34 . 
     One end portion of the resistive element R 26  is an input port of the phase reversing circuit  662  and is connected to a connecting part of the emitter terminal of the transistor Q 21  and the emitter terminal of the transistor Q 22 . The other end portion of the resistive element R 26  is connected to an inverting input terminal of the operational amplifier U 23 . The intermediate voltage Vm is supplied to a non-inverting input terminal of the operational amplifier U 23 . The drive voltage V+ is supplied to the operational amplifier U 23 . An output terminal of the operational amplifier U 23  is connected to a base terminal of the transistor Q 23  and a base terminal of the transistor Q 24 . 
     The transistor Q 23  is a n-type transistor. The transistor Q 24  is a p-type transistor. The voltage Vc is supplied to a collector terminal of the transistor Q 23 . An emitter terminal of the transistor Q 23  and an emitter terminal of the transistor Q 24  are connected. A collector terminal of the transistor Q 24  is connected to the ground. A resistive element R 34  is connected between a connecting part of the base terminals of the transistor Q 23  and the transistor Q 24  and a connecting part of the emitter terminal of the transistor Q 23  and the emitter terminal of the transistor Q 24 . 
     The resistive element R 32  is connected between a connecting part of the emitter terminal of the transistor Q 23  and the emitter terminal of the transistor Q 24  and the inverting input terminal of the operational amplifier U 23 . 
     The connecting part of the emitter terminal of the transistor Q 23  and the emitter terminal of the transistor Q 24  is an output port of the phase reversing circuit  662  and is connected to the other terminal of the piezoelectric element  200 . 
     The differential circuit  663  includes an operational amplifier U 24 , a resistive element R 27 , a resistive element R 28 , a resistive element R 29 , and a resistive element R 30 . 
     The drive voltage V+ is supplied to the operational amplifier U 24 . A non-inverting input terminal of the operational amplifier U 24  is connected to an output port of the amplifier circuit  661  (one end portion of the resistive element R 100 ) via the resistive element R 27 . Further, the intermediate voltage Vm is supplied to the non-inverting input terminal of the operational amplifier U 24  via the resistive element R 30 . An inverting input terminal of the operational amplifier U 24  is connected to the other end portion of the resistive element R 100  via the resistive element R 28 . The resistive element R 29  is connected between an output terminal and the inverting input terminal of the operational amplifier U 24 . The output port of the operational amplifier U 24  is an output port of the differential circuit  663 . 
     The filter circuit  664  includes an operational amplifier U 22 , a resistive element R 21 , a resistive element R 22 , a resistive element R 23 , a capacitor C 21 , and a capacitor C 22 . 
     One end portion of the resistive element R 21  is an input port of the filter circuit  664 . The other end portion of the resistive element R 21  is connected to one end portion of the capacitor C 21 . A connecting part of the resistive element R 21  and the capacitor C 21  is connected to the ground via the resistive element R 22 . The other end portion of the capacitor C 21  is connected to an inverting input terminal of the operational amplifier U 22 . The drive voltage V+ is supplied to the operational amplifier U 22 . The intermediate voltage Vm is supplied to a non-inverting input terminal of the operational amplifier U 22 . 
     The resistive element R 23  is connected between an output port of the operational amplifier U 22  and the inverting input terminal of the operational amplifier U 22 . The capacitor C 22  is connected between a connecting part of the resistive element R 21  and the capacitor C 21  and the resistive element R 23  on the output port side of the operational amplifier U 22 . 
     In the case where these self-excited oscillation type drive voltage generation circuits are used, the valve control signal generation circuit  64  may, for example, monitor the drive voltage and output a valve control signal in such a manner as to synchronize with the drive voltage. 
     Further, in the description described above, the following is set as conditions: The time it takes for the upstream side pump to reach the normal operation drive voltage is longer than the time it takes for the downstream side pump to reach the normal operation drive voltage, and the drive voltage of the upstream side pump is lower than the drive voltages of a plurality of downstream side pumps. Further, in the description described above, both the conditions are satisfied. However, in the fluid control devices, only at least one of these conditions needs to be set. 
     Further, in the description described above, the number of piezoelectric pumps to be connected in series is two and may alternatively be three or more. In this case, the time it takes for at least the most upstream side pump to reach the normal operation drive voltage may only need to be longer than the time it takes for any of a plurality of downstream side pumps to reach their normal operation drive voltages. 
     Further, the drive voltage of at least the most upstream side pump may only need to be lower than the drive voltage of any of the plurality of downstream side pumps. 
     Further, the number of the piezoelectric pumps to be connected in parallel is not limited to two and may alternatively be three or more. 
     REFERENCE SIGNS LIST 
     
         
         
           
               10 ,  10 A,  10 B: Fluid control device 
               21 ,  22 ,  23 ,  24 : Piezoelectric pump 
               30 : Valve 
               40 ,  40 A: Container 
               51 ,  52 ,  53 ,  54 ,  55 ,  56 : Communicating path 
               60 : Control unit 
               61 : MCU 
               64 : Valve control signal generation circuit 
               70 : Battery 
               211 ,  212 ,  221 ,  222 ,  231 ,  232 ,  241 ,  242 : Hole 
               621 ,  622 : Power supply circuit 
               631 ,  632 ,  650 ,  660 : Drive voltage generation circuit 
               651 : H-bridge IC 
               652 ,  663 : Differential circuit 
               653 ,  661 : Amplifier circuit 
               654 ,  662 : Phase reversing circuit 
               655 ,  665 : Intermediate voltage generation circuit 
               664 : Filter circuit