Fluid control device

Abstract

To cool a plurality of piezoelectric pumps connected to each other in series while continuously ejecting fluid.SOLUTION: A fluid control device 10 comprises: a first piezoelectric pump 41 and a second piezoelectric pump 42 connected sequentially from the upstream of a flow path where fluid flows, to the downstream; a drive circuit 30 supplying a first drive signal to the first piezoelectric pump 41 and a second drive signal to the second piezoelectric pump 42; and a control circuit 20 controlling the operation of the drive circuit 30. The control circuit 20 acquires a control command value which depends on the temperature of the second piezoelectric pump 42. The control circuit 20 controls the drive circuit in such a manner that the drive circuit stops the supply of the first drive signal while continuing the supply of the second drive signal when detecting that the control command value falls within a stop determination range.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a fluid control device in which a plurality of piezoelectric pumps are connected in series.

Background Art

[0002] Patent Document 1 describes a fluid control device. The fluid control device of Patent Document 1 includes two piezoelectric pumps. The two piezoelectric pumps are connected in series to the flow path. The piezoelectric pump on the upstream side in the flow path is referred to as the upstream pump, and the piezoelectric pump on the downstream side is referred to as the downstream pump.

[0003] The fluid control device of Patent Document 1 includes a control circuit. The control circuit performs specific pattern control of a plurality of modes on the upstream pump and the downstream pump. The control circuit controls the on (operation) / off (stop) of the upstream pump and the downstream pump based on the measured current of the upstream pump or the downstream pump.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Piezoelectric pumps generate heat during operation. The temperature of the piezoelectric pump rises by continuous operation. Then, when the temperature exceeds a predetermined temperature, the performance (fluid conveyance performance) as a pump deteriorates.

[0006] In the fluid control device of Patent Document 1, as a type of specific pattern control, both the upstream pump and the downstream pump are turned off (stopped). By using such control, the conventional fluid control device cools the upstream pump and the downstream pump and reduces the temperatures of the upstream pump and the downstream pump.

[0007] However, when both piezoelectric pumps stop, during this stop period, fluid (e.g., gas) cannot be discharged.

[0008] Therefore, an object of the present invention is to provide a technique for cooling a plurality of piezoelectric pumps connected in series while continuously discharging fluid.

Means for Solving the Problems

[0009] A fluid control device according to an embodiment of the present invention includes a first piezoelectric pump and a second piezoelectric pump connected in order from upstream to downstream in a flow path through which fluid flows, a drive circuit that supplies a first drive signal to the first piezoelectric pump and a second drive signal to the second piezoelectric pump, and a control circuit that controls the operation of the drive circuit.

[0010] The control circuit acquires a control command value that depends on the temperature of the second piezoelectric pump. When the control circuit detects that the control command value has fallen within a stop determination range, the control circuit causes the drive circuit to stop supplying the first drive signal while continuing to supply the second drive signal.

[0011] In this configuration, when the temperature of the second piezoelectric pump reaches the reference temperature for stop determination, the first piezoelectric pump stops. When the first piezoelectric pump stops, the heat generation of the first piezoelectric pump stops. Since the second piezoelectric pump continues to operate, a fluid flow with a low temperature from the outside is applied to the first piezoelectric pump, and the first piezoelectric pump is cooled. Then, as the first piezoelectric pump is cooled, the temperature of the fluid sucked into the second piezoelectric pump decreases. Therefore, the second piezoelectric pump is cooled.

Effects of the Invention

[0012] According to the present invention, a plurality of piezoelectric pumps connected in series can be cooled while continuously discharging fluid.

Brief Description of the Drawings

[0013]

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BEST MODE FOR CARRYING OUT THE INVENTION

[0014] [First Embodiment] The fluid control device according to the first embodiment of the present invention will be described with reference to the drawings. In the following embodiments, gas is taken as an example of the fluid, but the configuration of the fluid control device of the present application can also be applied to fluids other than gas.

[0015] FIG. 1 is a functional block diagram showing the main configuration of the fluid control device according to the first embodiment. A specific configuration example of the fluid control device will be described later. In FIG. 1, the acquisition configuration of the control command value (drive voltage, drive current, impedance, temperature) is omitted from the figure.

[0016] As shown in FIG. 1, the fluid control device 10 includes a control circuit 20, a drive circuit 30, a first piezoelectric pump 41, and a second piezoelectric pump 42. The drive circuit 30 includes a first drive circuit 31 and a second drive circuit 32.

[0017] The first piezoelectric pump 41 and the second piezoelectric pump 42 have the same configuration. The first piezoelectric pump 41 and the second piezoelectric pump 42 include a diaphragm on which a piezoelectric element is disposed. The first piezoelectric pump 41 and the second piezoelectric pump 42 are configured to support the diaphragm so as to be vibratable by a spring member. The first piezoelectric pump 41 and the second piezoelectric pump 42 convey fluid in a predetermined direction by the vibration of the diaphragm.

[0018] The first piezoelectric pump 41 includes a suction port P41i and a discharge port P41o. The first piezoelectric pump 41 is configured such that the suction port P41i and the discharge port P41o communicate with each other in a stopped state (non-driven state).

[0019] The first piezoelectric pump 41 vibrates the diaphragm when a first drive signal having a predetermined frequency is supplied from the first drive circuit 31. The first piezoelectric pump 41 inhales gas from the suction port P41i by the vibration of the diaphragm and discharges this gas from the discharge port P41o.

[0020] The second piezoelectric pump 42 includes a suction port P42i and a discharge port P42o. The second piezoelectric pump 42 is configured such that the suction port P42i and the discharge port P42o communicate with each other in a stopped state (non-driven state).

[0021] The second piezoelectric pump 42 vibrates the diaphragm when a second drive signal having a predetermined frequency is supplied from the second drive circuit 32. The second piezoelectric pump 42 inhales gas from the suction port P42i by the vibration of the diaphragm and discharges this gas from the discharge port P42o.

[0022] The first piezoelectric pump 41 and the second piezoelectric pump 42 are connected in series in order from upstream to downstream of the flow path 100 through which gas flows. More specifically, the discharge port P41o of the first piezoelectric pump 41 and the suction port P42i of the second piezoelectric pump 42 communicate with each other. When at least one of the first piezoelectric pump 41 and the second piezoelectric pump 42 is driven, gas is drawn into the flow path 100 and supplied to a load 90 connected to the most downstream of the flow path 100 through the suction port P41i, the discharge port P41o of the first piezoelectric pump 41, the suction port P42i of the second piezoelectric pump 42, and the discharge port P42o in order.

[0023] The control circuit 20 controls the first drive circuit 31 to generate and output a first drive signal. The control circuit 20 controls the second drive circuit 32 to generate and output a second drive signal. At this time, the control circuit 20 performs constant current control for each of the first piezoelectric pump 41 and the second piezoelectric pump 42 so that a predetermined flow rate can be obtained constantly. The control circuit 20 generates and outputs the first drive signal and the second drive signal based on this constant current control.

[0024] Furthermore, the control circuit 20 acquires a control command value that depends on the temperature of the second piezoelectric pump 42.

[0025] The control circuit 20 stores in advance a stop determination range for the control command value. The stop determination range represents the range of the control command value for which it is necessary to cool the second piezoelectric pump 42. The control circuit 20 sets the stop determination range based on the change characteristics of the gas flow rate with respect to the temperature in the second piezoelectric pump 42. Specifically, the control circuit 20 sets the range in which the gas flow rate with respect to the temperature in the second piezoelectric pump 42 becomes significantly low as the stop determination range.

[0026] If the control command value is not within the stop determination range, the control circuit 20 performs normal operation control. In normal operation control, the control circuit 20 controls the first drive circuit 31 to continue supplying the first drive signal. The control circuit 20 controls the second drive circuit 32 to continue supplying the second drive signal.

[0027] Upon receiving the control to continue supplying the first drive signal, the first drive circuit 31 continues to generate the first drive signal. Thereby, the supply of the first drive signal to the first piezoelectric pump 41 continues.

[0028] Upon receiving the control to continue supplying the second drive signal, the second drive circuit 32 continues to generate the second drive signal. Thereby, the supply of the second drive signal to the second piezoelectric pump 42 continues.

[0029] When the control command value is within the stop determination range, the control circuit 20 performs cooling. During cooling, the control circuit 20 controls the first drive circuit 31 to stop supplying the first drive signal. The control circuit 20 controls the second drive circuit 32 to continue supplying the second drive signal.

[0030] Upon receiving the control to stop supplying the first drive signal, the first drive circuit 31 stops generating the first drive signal. As a result, the supply of the first drive signal to the first piezoelectric pump 41 stops.

[0031] Upon receiving the control to continue supplying the second drive signal, the second drive circuit 32 continues generating the second drive signal. As a result, the supply of the second drive signal to the second piezoelectric pump 42 continues.

[0032] With such a configuration, the fluid control device 10 assumes the following states during normal operation control and cooling.

[0033] FIG. 2(A) is a diagram showing the gas flow and the temperature of each part during normal operation control, and FIG. 2(B) is a diagram showing the gas flow and the temperature of each part during cooling.

[0034] As shown in FIG. 2(A), during normal operation control, the first piezoelectric pump 41 is in an operating state (ON state), and the second piezoelectric pump 42 is in an operating state (ON state). As a result, the fluid control device 10 conveys gas at a predetermined flow rate from the upstream to the downstream of the flow path 100.

[0035] Since the first piezoelectric pump 41 is operating, it generates heat. As a result, for example, the first piezoelectric pump 41 reaches a temperature T41N. The temperature T41N is higher than the outside air temperature To (To < T41N).

[0036] Since the temperature of the first piezoelectric pump 41 is T41N, the temperature T1N of the gas discharged from the discharge port P41o of the first piezoelectric pump 41 and inhaled into the suction port P42i of the second piezoelectric pump 42 before being inhaled is higher than the outside air temperature To (To < T1N). Therefore, the second piezoelectric pump 42 inhales gas at a temperature T1N higher than the outside air temperature To.

[0037] Since the second piezoelectric pump 42 is operating, it generates heat. As a result, for example, the second piezoelectric pump 42 reaches a temperature T42N. Here, since the temperature T1N of the gas inhaled by the second piezoelectric pump 42 is higher than the outside air temperature To, the temperature T42N of the second piezoelectric pump 42 becomes higher than when it inhales gas at the outside air temperature To. That is, in normal operation control, the temperature T42N of the second piezoelectric pump 42 tends to rise.

[0038] Since the temperature of the second piezoelectric pump 42 is T42N, the temperature T2N of the gas discharged from the discharge port P42o of the second piezoelectric pump 42 becomes even higher than the temperature T1N of the gas inhaled by the second piezoelectric pump 42 (T1N < T2N). Therefore, the temperature of the gas supplied to the load 90 tends to be high.

[0039] If such normal operation control continues, the temperature T41N of the first piezoelectric pump 41 rises, and the temperature T42N of the second piezoelectric pump 42 rises further. And the temperature T42N of the second piezoelectric pump 42 enters the stop determination range earlier than the first piezoelectric pump 41.

[0040] When the temperature T42N of the second piezoelectric pump 42 enters the stop determination range, the pump characteristics of the second piezoelectric pump 42 rapidly deteriorate, and the flow rate decreases. And when the temperature T42N of the second piezoelectric pump 42 rises further, adverse effects on reliability such as damage to the second piezoelectric pump 42 are likely to occur.

[0041] Therefore, the fluid control device 10 performs cooling as shown in Fig. 2(B).

[0042] As shown in FIG. 2(B), during cooling, the first piezoelectric pump 41 is in a stopped state (OFF state), and the second piezoelectric pump 42 is in an operating state (ON state). Since the second piezoelectric pump 42 is continuously operating, the fluid control device 10 conveys gas, which has a lower flow rate than in the normal state, from the upstream to the downstream of the flow path 100. That is, the fluid control device 10 can continuously supply gas to the load 90.

[0043] Since the first piezoelectric pump 41 is stopped, it does not generate heat. As a result, for example, the temperature of the first piezoelectric pump 41 becomes the outside air temperature To. When the first piezoelectric pump 41 stops from an operating state, the temperature of the first piezoelectric pump 41 decreases with a predetermined time constant according to the outside air temperature To and the gas flow rate, and becomes the outside air temperature To as the steady state of cooling.

[0044] Since the temperature of the first piezoelectric pump 41 is the outside air temperature To, the temperature of the gas discharged from the discharge port P41o of the first piezoelectric pump 41 and before being sucked into the suction port P42i of the second piezoelectric pump 42 becomes the outside air temperature To in the steady state of cooling. For this reason, gas at the outside air temperature To is sucked into the second piezoelectric pump 42 in the steady state of cooling.

[0045] Since the second piezoelectric pump 42 is operating, it generates heat. As a result, for example, the temperature of the second piezoelectric pump 42 becomes the temperature T42C. However, since the gas sucked by the second piezoelectric pump 42 is at the outside air temperature To, the temperature T42C of the second piezoelectric pump 42 is lower than the temperature T42N in the normal state (T42C < T42N). Thereby, the fluid control device 10 can cool the second piezoelectric pump 42 while conveying gas and continuously supplying it to the load 90.

[0046] Since the temperature of the second piezoelectric pump 42 is the temperature T42C (< T42N), the temperature T2C of the gas discharged from the discharge port P42o of the second piezoelectric pump 42 is lower than the temperature T2N of the gas discharged from the discharge port P42o of the second piezoelectric pump 42 in the normal state (T2C < T2N). For this reason, the fluid control device 10 can lower the temperature of the gas supplied to the load 90.

[0047] FIG. 3(A) is a diagram showing an example of the temperature change of the first piezoelectric pump and the second piezoelectric pump, and FIG. 3(B) is a diagram showing an example of the change in the flow rate of the fluid control device. Note that FIGS. 3(A) and 3(B) show the case where the temperature of the second piezoelectric pump 42 is directly used as the control command value.

[0048] In FIGS. 3(A) and 3(B), timec indicates the timing at which the control switches from normal operation control to cooling control. This timing corresponds to the timing at which the control circuit 20 detects that the control command value has entered the stop determination range. In FIG. 3(A), the solid line indicates the temperature change of the second piezoelectric pump 42, and the dotted line indicates the temperature change of the first piezoelectric pump 41. Also, in FIG. 3(A), To is the outside air temperature, and Thc is the temperature (threshold temperature) for determining the stop determination range.

[0049] When the fluid control device 10 starts up, it performs normal operation control. As a result, the temperature T41 of the first piezoelectric pump 41 and the temperature T42 of the second piezoelectric pump 42 increase. At this time, as described above, the temperature T42 of the second piezoelectric pump 42 disposed downstream of the first piezoelectric pump 41 in the flow path 100 becomes higher than the temperature T41 of the first piezoelectric pump 41.

[0050] When the control circuit 20 detects that the control command value has entered the stop determination range, that is, when it detects that the temperature T42 of the second piezoelectric pump 42 has reached the threshold temperature Thc, it switches from normal operation control to cooling control. Specifically, the control circuit 20 stops the supply of the first drive signal and continues to supply the second drive signal. As a result, the first piezoelectric pump 41 stops, and the second piezoelectric pump 42 continues to operate.

[0051] Since the first piezoelectric pump 41 has stopped, it does not generate heat and is cooled by the passage of outside air. As a result, the temperature T41 of the first piezoelectric pump 41 gradually decreases to the outside air temperature To.

[0052] The second piezoelectric pump 42 continuously operates, but since the temperature of the gas being inhaled decreases, it is gradually cooled.

[0053] In this way, the fluid control device 10 can cool the first piezoelectric pump 41 and the second piezoelectric pump 42 while continuously supplying gas to the load 90. That is, the fluid control device 10 can cool a plurality of piezoelectric pumps connected in series while continuously discharging gas (fluid).

[0054] Thereby, as shown in FIG. 3(B), the pressure of the second piezoelectric pump 42 (the discharge pressure of the fluid control device), which gradually decreased over time during the normal operation control period, can be recovered during the cooling control period.

[0055] Furthermore, the fluid control device 10 can cool not only the second piezoelectric pump 42 (downstream pump) but also the first piezoelectric pump 41 (upstream pump) by stopping the first piezoelectric pump 41 (upstream pump) for cooling the second piezoelectric pump 42 (downstream pump).

[0056] Here, in order to cool the second piezoelectric pump 42 (downstream pump), it is also possible to stop the second piezoelectric pump 42 (downstream pump) and continue to operate the first piezoelectric pump 41 (upstream pump). In this case, although the temperature T42 of the second piezoelectric pump 42 (downstream pump) decreases, the temperature T41 of the first piezoelectric pump 41 (upstream pump) cannot be decreased.

[0057] Therefore, by stopping the first piezoelectric pump 41 (upstream pump) and continuously operating the second piezoelectric pump 42 (downstream pump) like the fluid control device 10, both the second piezoelectric pump 42 (downstream pump) and the first piezoelectric pump 41 (upstream pump) can be cooled while realizing continuous supply of gas.

[0058] Thereby, the fluid control device 10 can recover the flow rate of the first piezoelectric pump 41 (upstream pump) during the cooling control period.

[0059] Therefore, as a whole, the fluid control device 10 can recover the flow rate.

[0060] In the above configuration, the stop determination range is set based on the change characteristics of the gas flow rate with respect to the temperature in the second piezoelectric pump 42. However, the stop determination range may be set based on at least one of the deterioration of the electromechanical coupling coefficient of the piezoelectric element (piezoelectric body) constituting the second piezoelectric pump 42, the fatigue failure of the spring material, and the fatigue failure of the joint portion between the diaphragm on which the piezoelectric element is disposed and the spring member. In this case, the stop determination range is set within a range according to the temperature at which the piezoelectric element of the second piezoelectric pump 42 is damaged or broken. Further, in this case, it is preferable to set the stop determination range with a predetermined margin with respect to the temperature at which damage or breakage occurs.

[0061] (First control switching method) The first control switching method uses the voltage of the second drive signal of the second piezoelectric pump 42 (second drive voltage) as the control command value. When driving the piezoelectric pump with a constant current, the drive voltage decreases as the temperature of the piezoelectric pump increases. The first control switching method utilizes this phenomenon.

[0062] FIG. 4 is a control flowchart when using the drive voltage as the control command value.

[0063] The control circuit 20 acquires the second drive voltage (S11). The control circuit 20 determines whether or not the second drive voltage falls within the stop determination range. More specifically, the control circuit 20 determines whether or not the second drive voltage is less than or equal to the stop determination voltage (S12).

[0064] If the second drive voltage is not less than or equal to the stop determination voltage (S12: NO), the control circuit 20 performs normal operation control (S14). The normal operation control is control to continue the operation of the first piezoelectric pump 41 and continue the operation of the second piezoelectric pump 42.

[0065] If the second driving voltage is less than or equal to the stop determination voltage (S12: YES), the control circuit 20 performs cooling control (S13). The cooling control is control to stop the operation of the first piezoelectric pump 41 and continue the operation of the second piezoelectric pump 42.

[0066] In the above-described first control switching method, an embodiment in which the driving voltage is used as the control command value is shown. However, the control circuit 20 may have a function of storing the driving voltage, calculate the amount of change in the driving voltage over time, and use the amount of change in the driving voltage as the control command value. In this case, if the amount of change is not greater than or equal to the determination threshold value, the control circuit 20 may perform normal operation control, and if the amount of change is greater than or equal to the determination threshold value, the control circuit 20 may perform cooling control.

[0067] (Second control switching method) The second control switching method uses the impedance of the second piezoelectric pump 42 as the control command value. When the piezoelectric pump is driven with a constant current, the driving voltage decreases as the temperature of the piezoelectric pump rises. Since it is constant voltage control, when the driving voltage decreases, the impedance of the piezoelectric pump decreases. The second control switching method utilizes this phenomenon.

[0068] FIG. 5 is a control flowchart when impedance is used as the control command value.

[0069] The control circuit 20 acquires the second driving voltage (S11). The control circuit 20 acquires the current of the second piezoelectric pump 42. The control circuit 20 calculates the impedance of the second piezoelectric pump 42 from the acquired current of the second piezoelectric pump 42 and the second driving voltage (S21). The control circuit 20 determines whether or not the impedance falls within the stop determination range. More specifically, the control circuit 20 determines whether or not the impedance is less than or equal to the stop determination impedance (S22).

[0070] If the impedance is not less than or equal to the stop determination impedance (S22: NO), the control circuit 20 performs normal operation control (S14). If the impedance is less than or equal to the stop determination impedance (S22: YES), the control circuit 20 performs cooling control (S13).

[0071] In the above-described second control switching method, an aspect of using impedance as the control command value has been shown. However, the control circuit 20 has an impedance storage function, calculates the amount of change in impedance over time, and may use the amount of change in impedance as the control command value. In this case, if the amount of change is less than the determination threshold value, the control circuit 20 may perform normal operation control, and if the amount of change is equal to or greater than the determination threshold value, the control circuit 20 may perform cooling control.

[0072] (Third control switching method) The third control switching method uses the frequency of the second drive signal (second drive frequency) of the second piezoelectric pump 42 as the control command value. The piezoelectric pump (piezoelectric body) has a predetermined resonance frequency. By matching the frequency of the drive signal supplied to the piezoelectric pump with the resonance frequency of the piezoelectric pump, highly efficient vibration can be realized. Therefore, when driving the piezoelectric pump, the frequency of the drive signal is matched with the resonance frequency. And the resonance frequency decreases as the temperature of the piezoelectric pump (piezoelectric body) rises. The third control switching method utilizes this phenomenon.

[0073] FIG. 6 is a control flowchart when the drive frequency is used as the control command value.

[0074] The control circuit 20 acquires the frequency of the second drive signal (second drive frequency) (S31). The control circuit 20 determines whether or not the second drive frequency falls within the stop determination range. More specifically, the control circuit 20 determines whether or not the second drive frequency is less than or equal to the stop determination frequency (S32).

[0075] If the second drive frequency is not less than or equal to the stop determination frequency (S32: NO), the control circuit 20 performs normal operation control (S14). The normal operation control is control to continue the operation of the first piezoelectric pump 41 and continue the operation of the second piezoelectric pump 42.

[0076] If the second drive frequency is less than or equal to the stop determination frequency (S32: YES), the control circuit 20 performs cooling control (S13).

[0077] In the above-described second control switching method, an embodiment in which the drive frequency is used as the control command value has been shown. However, the control circuit 20 has a function of storing the drive frequency, calculates the amount of change in the drive frequency over time, and may use the amount of change in the drive frequency as the control command value. In this case, if the amount of change is less than the determination threshold value, the control circuit 20 may perform normal operation control, and if the amount of change is equal to or greater than the determination threshold value, the control circuit 20 may perform cooling control.

[0078] (Fourth control switching method) In the fourth control switching method, the temperature of the second piezoelectric pump 42 is used as the control command value. For example, by arranging a temperature sensor near the second piezoelectric pump 42, the temperature of the second piezoelectric pump 42 can be measured.

[0079] FIG. 7 is a control flowchart when the temperature is used as the control command value.

[0080] The control circuit 20 acquires the temperature of the second piezoelectric pump 42 (S41). The control circuit 20 determines whether or not the temperature falls within the stop determination range. More specifically, the control circuit 20 determines whether or not the temperature is equal to or higher than the stop determination temperature (S42).

[0081] If the temperature is not equal to or higher than the stop determination temperature (S42: NO), the control circuit 20 performs normal operation control (S14). If the temperature is equal to or higher than the stop determination temperature (S42: YES), the control circuit 20 performs cooling control (S13).

[0082] In the above-described first control switching method, an embodiment in which the drive voltage is used as the control command value has been shown. However, the control circuit 20 has a function of storing the drive voltage, calculates the amount of change in the drive voltage over time, and may use the amount of change in the drive voltage as the control command value. In this case, if the amount of change is less than the determination threshold value, the control circuit 20 may perform normal operation control, and if the amount of change is equal to or greater than the determination threshold value, the control circuit 20 may perform cooling control.

[0083] (With return control) Although each of the above control methods shows the state until the transition to the cooling control, if the temperature of the second piezoelectric pump 42 decreases due to the cooling control, the fluid control device 10 can return to the normal operation control. In the following, the case where the return control is added to the first control switching method is shown, but the return control can be similarly added to the second, third, and fourth control switching methods.

[0084] FIG. 8 is a control flowchart in the case including the return control using the drive voltage as the control command value. Note that steps S11 to S14 are the same as those in FIG. 4, and the description thereof is omitted.

[0085] The control circuit 20 stores a return determination voltage corresponding to the return determination range to the normal operation control. The return determination range (return determination voltage) is set based on the temperature at which the second piezoelectric pump 42 operates while suppressing the decrease in the flow rate when returning to the normal operation control (when the operation of the first piezoelectric pump 41 resumes).

[0086] During the cooling control, the control circuit 20 acquires the second drive voltage (S41). When the second drive voltage becomes equal to or higher than the return determination voltage (S42: YES), the control circuit 20 returns from the cooling control to the normal operation control (S14).

[0087] If the second drive voltage is not equal to or higher than the return determination voltage (S42: NO), the control circuit 20 continues the cooling control (S13).

[0088] Note that the return determination voltage may be the same as the stop determination voltage, but it is preferably higher than the stop determination voltage. Thereby, the fluid control device 10 can suppress becoming the cooling control immediately after returning to the normal operation control. Further, the fluid control device 10 can suppress the undesired frequent switching between the normal operation control and the cooling control, and can stabilize the operation.

[0089] (Specific circuit configuration examples of various types) Next, an example of a specific circuit configuration of the fluid control device will be described with reference to FIGS. 9 to 16. Note that FIGS. 9 to 16 show only the circuit for the second piezoelectric pump 42, but the fluid control device includes a circuit similar to the circuit for the second piezoelectric pump 42 also for the first piezoelectric pump 41.

[0090] (Specific Circuit Configuration Example 1) FIG. 9 is a functional block diagram showing a first example of the circuit configuration of the fluid control device according to the first embodiment. The fluid control device 10 shown in FIG. 9 has a configuration of a self-excited oscillation circuit.

[0091] As shown in FIG. 9, the fluid control device 10 includes a control circuit 20, a second drive circuit 32, a second piezoelectric pump 42, a differential amplifier circuit 51, a filter 52, an operational amplifier circuit 53, a current sense circuit 61, a filter 62, a voltage dividing circuit 70, a current detection resistor R51, and a current detection resistor R61.

[0092] The control circuit 20 is constituted by an NCU or the like. The control circuit 20 is a common circuit element not only for the circuit for the second piezoelectric pump 42 but also for the circuit for the first piezoelectric pump 41.

[0093] The second drive circuit 32 includes a DCDC converter 321 and an H-bridge circuit 322.

[0094] The control circuit 20 outputs a voltage control signal to the DCDC converter 321. The DCDC converter 321 is driven based on the voltage control signal, converts the voltage from the power supply voltage to the second drive voltage, and supplies it to the H-bridge circuit 322.

[0095] Switch control signals that are in opposite phases to each other are input to the H-bridge circuit 322 from the operational amplifier circuit 53. The H-bridge circuit 322 generates a second drive signal having a predetermined frequency from the DC second drive voltage based on the switch control signal, and supplies it to the second piezoelectric pump 42.

[0096] The current detection resistor R51 is inserted in the connection line between the H-bridge circuit 322 and the second piezoelectric pump 42.

[0097] One terminal of the current detection resistor R51 is connected to the first input terminal of the differential amplifier circuit 51, and the other terminal of the current detection resistor R51 is connected to the second input terminal. The differential amplifier circuit 51 outputs a differential signal corresponding to the voltage across the current detection resistor R51. In other words, the differential amplifier circuit 51 outputs a differential signal corresponding to the current flowing through the current detection resistor R51, that is, the drive current of the second piezoelectric pump 42.

[0098] The filter 52 suppresses the noise included in the differential signal and outputs it to the operational amplifier circuit 53.

[0099] The operational amplifier circuit 53 amplifies the differential signal, generates a switch control signal, and outputs it to the H-bridge circuit 322.

[0100] With this circuit configuration, the fluid control device 10 constitutes a self-excited oscillation circuit for the second piezoelectric pump 42.

[0101] The current sense circuit 61 is connected to the H-bridge circuit 322. The current sense circuit 61 inputs a voltage corresponding to the current flowing through the H-bridge circuit 322 through the current detection resistor R61. The current sense circuit 61 outputs a current sense signal corresponding to the input voltage. Since the current sense signal is based on the current flowing through the H-bridge circuit 322, it reflects the drive current of the second piezoelectric pump 42. That is, the current sense signal is a signal corresponding to the drive current (the current of the second drive signal) of the second piezoelectric pump 42.

[0102] The filter 62 suppresses the noise included in the current sense signal and outputs it to the control circuit 20.

[0103] Based on the current sense signal, the control circuit 20 adjusts the voltage control signal to the DCDC converter 321. Thereby, the control circuit 20 realizes constant current control of the second piezoelectric pump 42 using feedback control.

[0104] The voltage dividing circuit 70 includes a series circuit of a voltage dividing resistor R71 and a voltage dividing resistor R72. One end of the voltage dividing circuit 70 is connected to the node between the DC-DC converter 321 and the H-bridge circuit 322. The other end of the voltage dividing circuit 70 is connected to the reference potential. The node between the voltage dividing resistor R71 and the voltage dividing resistor R72 is connected to the control circuit 20. Thereby, the control circuit 20 can acquire the second driving voltage.

[0105] Based on the second driving voltage acquired using the voltage dividing circuit 70, the control circuit 20 performs the above-described control switching.

[0106] (Specific circuit configuration example 2) FIG. 10 is a functional block diagram showing a second example of the circuit configuration of the fluid control device according to the first embodiment. The fluid control device 10A shown in FIG. 10 has a circuit configuration in which the voltage dividing circuit 70 is omitted with respect to the fluid control device 10 shown in FIG. 9. Other configurations of the fluid control device 10A are the same as those of the fluid control device 10 except for the method of acquiring the second driving voltage in the control circuit 20A, and the description of the same parts will be omitted.

[0107] When performing constant current control, the control circuit 20A adjusts the voltage control signal to the DC-DC converter 321. This voltage control signal is a signal for controlling the output voltage of the DC-DC converter 321. Therefore, the control circuit 20A can acquire the second driving voltage based on the voltage control signal.

[0108] Based on the second driving voltage thus acquired from the voltage control signal, the control circuit 20A performs the above-described control switching.

[0109] (Specific circuit configuration example 3) FIG. 11 is a functional block diagram showing a third example of the circuit configuration of the fluid control device according to the first embodiment. The fluid control device 10B shown in FIG. 11 has a configuration of a separately excited circuit.

[0110] As shown in FIG. 11, the fluid control device 10B includes a control circuit 20B, a second drive circuit 32, a second piezoelectric pump 42, an operational amplifier circuit 53B, a current sense circuit 61, a filter 62, a voltage dividing circuit 70, and a current detection resistor R61.

[0111] The control circuit 20 is constituted by an NCU or the like. The control circuit 20 is a common circuit element not only for the circuit for the second piezoelectric pump 42 but also for the circuit for the first piezoelectric pump 41.

[0112] The second drive circuit 32 includes a DC-DC converter 321 and an H-bridge circuit 322.

[0113] The control circuit 20B outputs a voltage control signal to the DC-DC converter 321. The DC-DC converter 321 is driven based on the voltage control signal, converts the voltage from the power supply voltage to the second drive voltage, and supplies it to the H-bridge circuit 322.

[0114] The control circuit 20B generates switch control signals having a predetermined frequency and opposite phases to each other, and outputs them to the operational amplifier circuit 53B. The operational amplifier circuit 53B amplifies the switch control signals and outputs them to the H-bridge circuit 322.

[0115] Switch control signals having opposite phases to each other are input from the operational amplifier circuit 53B to the H-bridge circuit 322. The H-bridge circuit 322 generates a second drive signal having a predetermined frequency from the DC second drive voltage based on the switch control signals, and supplies it to the second piezoelectric pump 42.

[0116] The current sense circuit 61 is connected to the H-bridge circuit 322. The current sense circuit 61 inputs a voltage corresponding to the current flowing through the H-bridge circuit 322 through the current detection resistor R61. The current sense circuit 61 outputs a current sense signal corresponding to the input voltage. Since the current sense signal is based on the current flowing through the H-bridge circuit 322, it reflects the drive current of the second piezoelectric pump 42. That is, the current sense signal is a signal corresponding to the drive current (the current of the second drive signal) of the second piezoelectric pump 42.

[0117] The filter 62 suppresses the noise contained in the current sense signal and outputs it to the control circuit 20B.

[0118] Based on the current sense signal, the control circuit 20B adjusts the voltage control signal to the DCDC converter 321 and adjusts the frequency of the switch control signal output to the H-bridge circuit 322 through the operational amplifier circuit 53B. Thereby, the control circuit 20B realizes the constant current control of the second piezoelectric pump 42 using feedback control.

[0119] With this circuit configuration, the fluid control device 10B constitutes a separately excited circuit for the second piezoelectric pump 42.

[0120] The voltage dividing circuit 70 includes a series circuit of a voltage dividing resistor R71 and a voltage dividing resistor R72. One end of the voltage dividing circuit 70 is connected to the node between the DCDC converter 321 and the H-bridge circuit 322. The other end of the voltage dividing circuit 70 is connected to the reference potential. The node between the voltage dividing resistor R71 and the voltage dividing resistor R72 is connected to the control circuit 20B. Thereby, the control circuit 20B can acquire the second drive voltage.

[0121] When the control circuit 20B performs control switching using the drive voltage, the control circuit 20B performs the above-described control switching based on the second drive voltage acquired using the voltage dividing circuit 70.

[0122] When the control circuit 20B performs switching control using the drive frequency, since the frequency of the switching control signal generated by the control circuit 20B corresponds to the drive frequency, the control circuit 20B performs the above-described control switching based on the frequency of the switching control signal (second drive frequency).

[0123] (Specific Circuit Configuration Example 4) FIG. 12 is a functional block diagram showing a fourth example of the circuit configuration of the fluid control device according to the first embodiment. The fluid control device 10C shown in FIG. 12 has a circuit configuration in which the voltage dividing circuit 70 is omitted with respect to the fluid control device 10B shown in FIG. 11. Other configurations of the fluid control device 10C are the same as those of the fluid control device 10B except for the switching control of the control circuit 20C, and the description of the same parts will be omitted.

[0124] The control circuit 20C performs the above-described control switching based on the frequency (second driving frequency) of the switching control signal generated by the control circuit 20C.

[0125] (Specific Circuit Configuration Example 5) FIG. 13 is a functional block diagram showing a fifth example of the circuit configuration of the fluid control device according to the first embodiment. The fluid control device 10D shown in FIG. 13 has a circuit configuration in which a temperature sensor 80 is added to the fluid control device 10 shown in FIG. 9. Other configurations of the fluid control device 10D are the same as those of the fluid control device 10 except for the method of obtaining the temperature of the second piezoelectric pump 42 in the control circuit 20D, and the description of the same parts will be omitted.

[0126] The temperature sensor 80 measures the temperature of the second piezoelectric pump 42. The temperature sensor 80 is disposed, for example, on the outer surface of the housing of the second piezoelectric pump 42. The temperature sensor 80 outputs the measured temperature to the control circuit 20D.

[0127] The control circuit 20D performs the above-described control switching based on the temperature input (acquired) from the temperature sensor 80.

[0128] Note that, in this configuration, strictly speaking, the temperature sensor 80 measures the temperature of the outer surface of the housing of the second piezoelectric pump 42. However, the relationship between the temperature of the outer surface of the second piezoelectric pump 42 and the temperature of the piezoelectric body inside the second piezoelectric pump 42 can be grasped in advance by experiments, simulations, or the like.

[0129] The control circuit 20D stores the relationship between the temperature on the outer surface of the second piezoelectric pump 42 and the temperature of the piezoelectric element inside the second piezoelectric pump 42. The control circuit 20D can calculate the temperature of the piezoelectric element of the second piezoelectric pump 42 from the input (acquired) temperature, and based on the temperature of this piezoelectric element, perform the above-described control switching.

[0130] At this time, an outside air temperature sensor for measuring the outside air temperature To may be provided, and the control circuit 20D may acquire the outside air temperature To and set a threshold temperature Thc for defining the stop determination range according to the outside air temperature To. Thereby, the control circuit 20D can perform the above-described control switching in consideration of the influence of the outside air temperature To, and can perform appropriate control switching according to the outside air temperature To.

[0131] (Specific circuit configuration example 6) FIG. 14 is a functional block diagram showing a sixth example of the circuit configuration of the fluid control device according to the first embodiment. The fluid control device 10E shown in FIG. 14 has a circuit configuration in which the voltage dividing circuit 70 is omitted with respect to the fluid control device 10D shown in FIG. 13. That is, the fluid control device 10E has a configuration combining the fluid control device 10D and the fluid control device 10B.

[0132] With this configuration, the control circuit 20E performs the above-described control switching.

[0133] (Specific circuit configuration example 7) FIG. 15 is a functional block diagram showing a seventh example of the circuit configuration of the fluid control device according to the first embodiment. The fluid control device 10F shown in FIG. 15 has a circuit configuration in which the self-excited oscillation circuit is replaced with a separately-excited oscillation circuit with respect to the fluid control device 10D shown in FIG. 13. That is, the fluid control device 10F has a configuration combining the fluid control device 10D and the fluid control device 10C.

[0134] With this configuration, the control circuit 20F performs the above-described control switching.

[0135] (Specific circuit configuration example 8) FIG. 16 is a functional block diagram showing an eighth example of the circuit configuration of the fluid control device according to the first embodiment. The fluid control device 10G shown in FIG. 16 has a circuit configuration in which the voltage dividing circuit 70 is omitted with respect to the fluid control device 10F shown in FIG. 15. That is, the fluid control device 10G has a configuration in which the voltage dividing circuit 70 of the fluid control device 10B is omitted with respect to the fluid control device 10F and combined.

[0136] With this configuration, the control circuit 20G performs the above-described control switching.

[0137] [Second Embodiment] The fluid control device according to the second embodiment of the present invention will be described with reference to the drawings. FIG. 17 is a functional block diagram showing the main configuration of the fluid control device according to the second embodiment.

[0138] As shown in FIG. 17, the fluid control device 10X according to the second embodiment is different from the fluid control device 10 according to the first embodiment in the number of piezoelectric pumps connected in series and the method of control switching. Other configurations and methods of the fluid control device 10X are the same as those of the fluid control device 10 according to the first embodiment, and the description of the same parts is omitted.

[0139] As shown in FIG. 17, the fluid control device 10X includes a control circuit 20X, a drive circuit 30X, a first piezoelectric pump 41, a second piezoelectric pump 42, and a third piezoelectric pump 43. The drive circuit 30X includes a first drive circuit 31, a second drive circuit 32, and a third drive circuit 33.

[0140] The first piezoelectric pump 41, the second piezoelectric pump 42, and the third piezoelectric pump 43 have the same configuration.

[0141] The first piezoelectric pump 41 includes a suction port P41i and a discharge port P41o. The second piezoelectric pump 42 includes a suction port P42i and a discharge port P42o. The third piezoelectric pump 43 includes a suction port P43i and a discharge port P43o.

[0142] The first piezoelectric pump 41, the second piezoelectric pump 42, and the third piezoelectric pump 43 are connected in series in order from the upstream to the downstream of the flow path 100 through which gas flows. More specifically, the discharge port P41o of the first piezoelectric pump 41 and the suction port P42i of the second piezoelectric pump 42 communicate with each other. The discharge port P42o of the second piezoelectric pump 42 and the suction port P43i of the third piezoelectric pump 43 communicate with each other.

[0143] The control circuit 20X performs control to generate and output a first drive signal to the first drive circuit 31. The control circuit 20X performs control to generate and output a second drive signal to the second drive circuit 32. The control circuit 20X performs control to generate and output a third drive signal to the third drive circuit 33.

[0144] More specifically, the control circuit 20X acquires a first control command value that depends on the temperature of the third piezoelectric pump 43 and a second control command value that depends on the temperature of the second piezoelectric pump 42.

[0145] The control circuit 20X stores in advance a first stop determination range for the first control command value. The first stop determination range represents a range of control command values for which it is necessary to cool the third piezoelectric pump 43. The control circuit 20X sets the first stop determination range based on the change characteristics of the gas flow rate with respect to the temperature in the third piezoelectric pump 43. Specifically, the control circuit 20X sets, as the first stop determination range, a range in which the gas flow rate with respect to the temperature in the third piezoelectric pump 43 significantly decreases.

[0146] The control circuit 20X stores in advance a second stop determination range for the second control command value. The second stop determination range represents a range of control command values for which it is necessary to cool the second piezoelectric pump 42. The control circuit 20X sets the second stop determination range based on the change characteristics of the gas flow rate with respect to the temperature in the second piezoelectric pump 42. Specifically, the control circuit 20X sets, as the second stop determination range, a range in which the gas flow rate with respect to the temperature in the second piezoelectric pump 42 significantly decreases.

[0147] If the first control command value is not within the first stop determination range and the second control command value is not within the second stop determination range, the control circuit 20X performs normal operation control. In normal operation control, the control circuit 20X controls the first drive circuit 31 to continue supplying the first drive signal. The control circuit 20X controls the second drive circuit 32 to continue supplying the second drive signal. The control circuit 20X controls the third drive circuit 33 to continue supplying the third drive signal.

[0148] Upon receiving the control to continue supplying the first drive signal, the first drive circuit 31 continues to generate the first drive signal. As a result, the supply of the first drive signal to the first piezoelectric pump 41 continues.

[0149] Upon receiving the control to continue supplying the second drive signal, the second drive circuit 32 continues to generate the second drive signal. As a result, the supply of the second drive signal to the second piezoelectric pump 42 continues.

[0150] Upon receiving the control to continue supplying the third drive signal, the third drive circuit 33 continues to generate the third drive signal. As a result, the supply of the third drive signal to the third piezoelectric pump 43 continues.

[0151] If the first control command value is within the first stop determination range and the second control command value is not within the second stop determination range, the control circuit 20X performs first cooling. In first cooling, the control circuit 20X controls the first drive circuit 31 to stop supplying the first drive signal. The control circuit 20X controls the second drive circuit 32 to stop supplying the second drive signal. The control circuit 20X controls the third drive circuit 33 to continue supplying the third drive signal.

[0152] Upon receiving the control to stop supplying the first drive signal, the first drive circuit 31 stops generating the first drive signal. As a result, the supply of the first drive signal to the first piezoelectric pump 41 stops.

[0153] Upon receiving the control to stop supplying the second drive signal, the second drive circuit 32 stops generating the second drive signal. As a result, the supply of the second drive signal to the second piezoelectric pump 42 stops.

[0154] Upon receiving control to continue supplying the third drive signal, the third drive circuit 33 continues to generate the third drive signal. As a result, the supply of the third drive signal to the third piezoelectric pump 43 continues.

[0155] If the first control command value is within the first stop determination range and the second control command value is within the second stop determination range, the control circuit 20X performs the second cooling. In the second cooling, the control circuit 20X controls the first drive circuit 31 to stop supplying the first drive signal. The control circuit 20X controls the second drive circuit 32 to continue supplying the second drive signal. The control circuit 20X controls the third drive circuit 33 to continue supplying the third drive signal.

[0156] Upon receiving control to stop supplying the first drive signal, the first drive circuit 31 stops generating the first drive signal. As a result, the supply of the first drive signal to the first piezoelectric pump 41 stops.

[0157] Upon receiving control to continue supplying the second drive signal, the second drive circuit 32 continues to generate the second drive signal. As a result, the supply of the second drive signal to the second piezoelectric pump 42 continues.

[0158] Upon receiving control to continue supplying the third drive signal, the third drive circuit 33 continues to generate the third drive signal. As a result, the supply of the third drive signal to the third piezoelectric pump 43 continues.

[0159] With such a configuration, the fluid control device 10X assumes the following states during normal operation control, first cooling, and second cooling.

[0160] FIG. 18(A) is a diagram showing the gas flow and the temperature of each part during normal operation control, FIG. 18(B) is a diagram showing the gas flow and the temperature of each part during first cooling, and FIG. 18(C) is a diagram showing the gas flow and the temperature of each part during second cooling.

[0161] As shown in FIG. 18(A), during normal operation control, the first piezoelectric pump 41 is in an operating state (ON state), the second piezoelectric pump 42 is in an operating state (ON state), and the third piezoelectric pump 43 is in an operating state (ON state). Thereby, the fluid control device 10 conveys gas at a predetermined flow rate from the upstream to the downstream of the flow path 100.

[0162] Since the first piezoelectric pump 41 is operating, it generates heat. As a result, for example, the first piezoelectric pump 41 reaches a temperature T41N. The temperature T41N is higher than the outside air temperature To (To < T41N).

[0163] Since the first piezoelectric pump 41 is at the temperature T41N, the temperature T1N of the gas before being discharged from the discharge port P41o of the first piezoelectric pump 41 and inhaled into the suction port P42i of the second piezoelectric pump 42 becomes higher than the outside air temperature To (To < T1N). Therefore, the second piezoelectric pump 42 inhales gas at a temperature T1N that is higher than the outside air temperature To.

[0164] Since the second piezoelectric pump 42 is operating, it generates heat. As a result, for example, the second piezoelectric pump 42 reaches a temperature T42N. Here, since the temperature T1N of the gas inhaled by the second piezoelectric pump 42 is higher than the outside air temperature To, the temperature T42N of the second piezoelectric pump 42 becomes higher than when it inhales gas at the outside air temperature To. That is, during normal operation control, the temperature T42N of the second piezoelectric pump 42 tends to rise.

[0165] Since the second piezoelectric pump 42 is at the temperature T42N, the temperature T2N of the gas before being discharged from the discharge port P42o of the second piezoelectric pump 42 and inhaled into the suction port P43i of the third piezoelectric pump 43 becomes higher than the outside air temperature To and the temperature T1N (To < T1N < T2N). Therefore, the third piezoelectric pump 43 inhales gas at an even higher temperature T2N.

[0166] Since the third piezoelectric pump 43 is operating, it generates heat. As a result, for example, the third piezoelectric pump 43 reaches a temperature T43N. Here, since the temperature T2N of the gas inhaled by the third piezoelectric pump 43 is higher than the outside air temperature To and the temperature T1N, the temperature T43N of the third piezoelectric pump 43 becomes higher than when it inhales the gas at the outside air temperature To. That is, in normal operation control, the temperature T43N of the third piezoelectric pump 43 tends to rise.

[0167] Since the third piezoelectric pump 43 is at the temperature T43N, the temperature T3N of the gas discharged from the discharge port P43o of the third piezoelectric pump 43 becomes even higher than the temperature T2N of the gas inhaled by the third piezoelectric pump 43 (T2N < T3N). For this reason, the temperature of the gas supplied to the load 90 tends to become even higher.

[0168] Therefore, in the fluid control device 10X, as shown in FIG. 18(B), the first cooling is performed.

[0169] As shown in FIG. 18(B), during the first cooling, the first piezoelectric pump 41 is in a stopped state (OFF state), the second piezoelectric pump 42 is in a stopped state (OFF state), and the third piezoelectric pump 43 is in an operating state (ON state). Since the third piezoelectric pump 43 is continuously operating, the fluid control device 10X conveys gas at a lower flow rate than in the normal state from the upstream to the downstream of the flow path 100. That is, the fluid control device 10X can continuously supply gas to the load 90.

[0170] Since the first piezoelectric pump 41 and the second piezoelectric pump 42 are stopped, they do not generate heat. As a result, for example, the temperatures of the first piezoelectric pump 41 and the second piezoelectric pump 42 become the outside air temperature To.

[0171] Since the temperatures of the first piezoelectric pump 41 and the second piezoelectric pump 42 are the outside air temperature To, the gas discharged from the discharge port P42o of the second piezoelectric pump 42 and inhaled into the suction port P43i of the third piezoelectric pump 43 becomes the outside air temperature To in the steady state of the first cooling. For this reason, the gas at the outside air temperature To is inhaled into the third piezoelectric pump 43 in the steady state of the first cooling.

[0172] Since the third piezoelectric pump 43 is operating, it generates heat. As a result, for example, the temperature of the third piezoelectric pump 43 becomes the temperature T43C. However, since the gas inhaled by the third piezoelectric pump 43 is the outside air temperature To, the temperature T43C of the third piezoelectric pump 43 is lower than the normal state temperature T43N (T43C < T43N). Thus, the fluid control device 10X can cool the third piezoelectric pump 43 while transporting the gas and continuously supplying it to the load 90.

[0173] Since the temperature of the third piezoelectric pump 43 is the temperature T43C (< T43N), the temperature T3C of the gas discharged from the discharge port P43o of the third piezoelectric pump 43 is lower than the temperature T3N of the gas discharged from the discharge port P43o of the third piezoelectric pump 43 in the normal state (T3C < T3N). Therefore, the fluid control device 10X can lower the temperature of the gas supplied to the load 90.

[0174] Also, in the fluid control device 10X, as shown in FIG. 18(C), second cooling is performed.

[0175] As shown in FIG. 18(C), during the second cooling, the first piezoelectric pump 41 is in a stopped state (OFF state), and the second piezoelectric pump 42 and the third piezoelectric pump 43 are in an operating state (ON state). Since the second piezoelectric pump 42 and the third piezoelectric pump 43 are continuously operating, the fluid control device 10X transports gas at a lower flow rate than in the normal state from the upstream to the downstream of the flow path 100. That is, the fluid control device 10X can continuously supply gas to the load 90.

[0176] Since the first piezoelectric pump 41 is stopped, it does not generate heat. As a result, for example, the temperature of the first piezoelectric pump 41 becomes the outside air temperature To.

[0177] Since the temperature of the first piezoelectric pump 41 is the outside air temperature To, the gas discharged from the discharge port P41o of the first piezoelectric pump 41 and inhaled into the suction port P42i of the second piezoelectric pump 42 becomes the outside air temperature To in the steady state of the second cooling. Therefore, the second piezoelectric pump 42 inhales the gas at the outside air temperature To in the steady state of the second cooling.

[0178] Since the second piezoelectric pump 42 is operating, it generates heat. As a result, for example, the temperature of the second piezoelectric pump 42 becomes the temperature T42C. However, since the gas inhaled by the second piezoelectric pump 42 is the outside air temperature To, the temperature T42C of the second piezoelectric pump 42 is lower than the normal state temperature T42N (T42C < T42N). Thereby, the fluid control device 10X can cool the second piezoelectric pump 42 while transporting the gas and continuously supplying it to the load 90.

[0179] Furthermore, since the temperature of the second piezoelectric pump 42 is the temperature T42C (< T42N), the temperature T2C of the gas discharged from the discharge port P42o of the second piezoelectric pump 42 and inhaled into the suction port P42i of the second piezoelectric pump 42 before being inhaled is lower than the normal temperature T2N (T2C < T2N). Therefore, the third piezoelectric pump 43 inhales the gas at a lower temperature than during normal operation in the steady state of the second cooling. Thereby, the third piezoelectric pump 43 can be cooled.

[0180] Therefore, by keeping the temperature T43C of the third piezoelectric pump 43 low, the temperature T3C of the gas discharged from the discharge port P43o of the third piezoelectric pump 43 can be kept low. As a result, the fluid control device 10X can lower the temperature of the gas supplied to the load 90.

[0181] (Control switching method) The control switching method of the fluid control device 10X uses the voltage of the third drive signal of the third piezoelectric pump 43 (third drive voltage) as the first control command value, and uses the voltage of the second drive signal of the second piezoelectric pump 42 (second drive voltage) as the second control command value. Hereinafter, the case where the drive voltage is used as the first control command value and the second control command value is shown, but similar to the first embodiment, the impedance and the drive frequency can be used as the first control command value and the second control command value.

[0182] FIG. 19 is a diagram showing an example of a control flowchart in the fluid control device according to the second embodiment.

[0183] The control circuit 20X acquires the second drive voltage and the third drive voltage (S51). The control circuit 20X determines whether the third drive voltage falls within the stop determination range. More specifically, the control circuit 20X determines whether the third drive voltage is equal to or lower than the first stop determination voltage (S52).

[0184] If the third drive voltage is not equal to or lower than the first stop determination voltage (S52: NO), the control circuit 20X performs normal operation control (S56). The normal operation control is control to continue the operation of the first piezoelectric pump 41, continue the operation of the second piezoelectric pump 42, and continue the operation of the third piezoelectric pump 43.

[0185] If the third drive voltage is equal to or lower than the first stop determination voltage (S52: YES) and the second drive voltage is not equal to or lower than the second stop determination voltage (S53: NO), the control circuit 20X performs first cooling control (S55). The first cooling control is control to stop the operation of the first piezoelectric pump 41 and the second piezoelectric pump 42 and continue the operation of the third piezoelectric pump 43.

[0186] If the third drive voltage is equal to or lower than the first stop determination voltage (S52: YES) and the second drive voltage is equal to or lower than the second stop determination voltage (S53: YES), the control circuit 20X performs second cooling control (S54). The second cooling control is control to stop the operation of the first piezoelectric pump 41 and continue the operation of the second piezoelectric pump 42 and the third piezoelectric pump 43.

[0187] With such a configuration, even if the fluid control device 10X has a configuration in which the first piezoelectric pump 41, the second piezoelectric pump 42, and the third piezoelectric pump 43 are connected in series, it can appropriately cool a plurality of piezoelectric pumps connected in series while continuously discharging gas (fluid) according to the temperatures of the second piezoelectric pump 42 and the third piezoelectric pump 43.

[0188] Note that the number of piezoelectric pumps connected in series is not limited to two or three, and may be four or more. When four or more piezoelectric pumps are connected in series, the control in the configuration where three piezoelectric pumps are connected in series may be appropriately applied according to the number of piezoelectric pumps.

[0189] <1> A first piezoelectric pump and a second piezoelectric pump connected in order from upstream to downstream of a flow path through which a fluid flows, A drive circuit that supplies a first drive signal to the first piezoelectric pump and a second drive signal to the second piezoelectric pump, A control circuit that controls the operation of the drive circuit, Comprising, The control circuit, Obtains a control command value that depends on the temperature of the second piezoelectric pump, If the control command value is within the stop determination range, the drive circuit is made to perform control to stop the supply of the first drive signal while continuing the supply of the second drive signal. Fluid control device.

[0190] <2> The stop determination range is set based on the change characteristics of the flow rate of the fluid with respect to the temperature in the second piezoelectric pump, and the fluid control device according to <1>.

[0191] <3> The stop determination range is set based on the deterioration of the electromechanical coupling coefficient of the piezoelectric element constituting the second piezoelectric pump, the fatigue failure of the spring material, and the fatigue failure of the joint portion between the piezoelectric element and the spring material, and the fluid control device according to <1> or <2>.

[0192] <4> The drive circuit and the second piezoelectric pump constitute a self-excited oscillation circuit, The control command value is at least one of the voltage value of the second drive signal and the impedance of the second piezoelectric pump, and the fluid control device according to any one of <1> to <3>.

[0193] <5> The drive circuit and the second piezoelectric pump constitute a separately excited circuit that operates in response to a drive control signal of a predetermined frequency from the control circuit. The control command value is the frequency of the drive control signal corresponding to the second drive signal, and the fluid control device according to any one of <1> to <3>.

[0194] <6> A temperature sensor for measuring the temperature of the second piezoelectric pump is provided. The control command value is the temperature measured by the temperature sensor, and the fluid control device according to any one of <1> to <3>.

[0195] <7> An outside air temperature measurement sensor for measuring the outside air temperature around the fluid control device is provided. The stop determination range is set based on the outside air temperature, and the fluid control device according to any one of <1> to <6>.

[0196] <8> The control circuit When detecting that the control command value has fallen within the return determination range, the control circuit performs control to resume the supply of the first drive signal to the drive circuit, and the fluid control device according to any one of <1> to <7>.

[0197] <9> A first piezoelectric pump, a second piezoelectric pump, and a third piezoelectric pump connected in sequence from upstream to downstream of a flow path through which fluid flows, A drive circuit that supplies a first drive signal to the first piezoelectric pump, a second drive signal to the second piezoelectric pump, and a third drive signal to the third piezoelectric pump, A control circuit that controls the operation of the drive circuit, is provided. The control circuit obtains a first control command value that depends on the temperature of the third piezoelectric pump. If the first control command value is within the first stop determination range, control is performed on the drive circuit to stop the supply of at least the first drive signal while continuing the supply of the third drive signal. Fluid control device.

[0198] <10>The control circuit is The fluid control device according to <9>, wherein if the first control command value is within the first stop determination range, control is performed on the drive circuit to stop the supply of the first drive signal and the second drive signal.

[0199] <11>The control circuit is acquires a second control command value that depends on the temperature of the second piezoelectric pump, The fluid control device according to <10>, wherein if the second control command value is within the second stop determination range, control is performed on the drive circuit to continue the supply of the second drive signal and stop the supply of the first drive signal.

[0200] <12>The first stop determination range is set based on the change characteristics of the flow rate of the fluid with respect to the temperature in the third piezoelectric pump, and the fluid control device according to any one of <9> to <11>.

[0201] <13>The first stop determination range is set based on the deterioration of the electromechanical coupling coefficient of the piezoelectric element constituting the third piezoelectric pump, the fatigue failure of the spring material, and the fatigue failure of the joint portion between the piezoelectric element and the spring material, and the fluid control device according to any one of <9> to <11>.

[0202] <14>The second stop determination range is set based on the change characteristics of the flow rate of the fluid with respect to the temperature in the second piezoelectric pump, and the fluid control device according to <11>.

[0203] <15>The second stop determination range is set based on the deterioration of the electromechanical coupling coefficient of the piezoelectric element constituting the second piezoelectric pump, the fatigue failure of the spring material, and the fatigue failure of the joint portion between the piezoelectric body and the spring material, and the fluid control device according to <11>.

[0204] <16> The drive circuit and the third piezoelectric pump constitute a first self-excited oscillation circuit, The first control command value is at least one of the voltage value of the third drive signal and the impedance of the third piezoelectric pump, and is the fluid control device according to any one of <9> to <15>.

[0205] <17> The drive circuit and the third piezoelectric pump constitute a first externally-excited oscillation circuit that operates upon receiving a drive control signal of a predetermined frequency from the control circuit, The first control command value is the frequency of the drive control signal corresponding to the third drive signal, and is the fluid control device according to any one of <9> to <16>.

[0206] <18> A temperature sensor for measuring the temperature of the third piezoelectric pump is provided, The first control command value is the temperature measured by the temperature sensor, and is the fluid control device according to any one of <9> to <17>.

[0207] <19> An outside air temperature measurement sensor for measuring the outside air temperature around the fluid control device is provided, The first stop determination range is set based on the outside air temperature, and is the fluid control device according to any one of <9> to <18>.

[0208] <20> The drive circuit and the second piezoelectric pump constitute a second self-excited oscillation circuit, The second control command value is at least one of the voltage value of the second drive signal and the impedance of the second piezoelectric pump, and is the fluid control device according to <11>.

[0209] <21> The drive circuit and the second piezoelectric pump constitute a second externally-excited oscillation circuit that operates upon receiving a drive control signal of a predetermined frequency from the control circuit, The second control command value is the frequency of the drive control signal corresponding to the second drive signal, and is the fluid control device according to <11>.

[0210] <22> A temperature sensor for measuring the temperature of the second piezoelectric pump is provided, The fluid control device according to <11>, wherein the second control command value is the temperature measured by the temperature sensor.

[0211] <23> The fluid control device includes an outside air temperature sensor that measures the outside air temperature around the fluid control device. The fluid control device according to any one of <11>, <20>, <21>, <22>, wherein the second stop determination range is set based on the outside air temperature.

[0212] <24> The control circuit The fluid control device according to any one of <9> to <23>, wherein when the first control command value is within the return determination range, the drive circuit is controlled to resume supplying the first drive signal.

Explanation of Signs

[0213] 10, 10A, 10B, 10C, 10D, 10E, 10F, 10G, 10X: Fluid control device 20, 20A, 20B, 20C, 20D, 20E, 20F, 20G, 20X: Control circuit 30, 30X: Drive circuit 31: First drive circuit 32: Second drive circuit 33: Third drive circuit 41: First piezoelectric pump 42: Second piezoelectric pump 43: Third piezoelectric pump 51: Differential amplifier circuit 52: Filter 53, 53B: Operational amplifier circuit 61: Current sense circuit 62: Filter 70: Voltage division circuit 80: Temperature sensor 90: Load 100: Flow path 321: DC-DC converter 322: H-bridge circuit

Claims

1. A first piezoelectric pump and a second piezoelectric pump connected in sequence from upstream to downstream of a flow path through which a fluid flows, A drive circuit that supplies a first drive signal to the first piezoelectric pump and a second drive signal to the second piezoelectric pump, A control circuit that controls the operation of the drive circuit, comprising: The control circuit obtains a control command value that depends on the temperature of the second piezoelectric pump, and if the control command value is within a stop determination range, performs control on the drive circuit to stop supplying the first drive signal while continuing to supply the second drive signal. A fluid control device.

2. The stop determination range is set based on the change characteristics of the flow rate of the fluid with respect to the temperature in the second piezoelectric pump. The fluid control device according to claim 1.

3. The stop determination range is set based on deterioration of the electromechanical coupling coefficient of the piezoelectric element constituting the second piezoelectric pump, fatigue failure of the spring material, and fatigue failure of the joint portion between the piezoelectric element and the spring material. The fluid control device according to claim 1.

4. The drive circuit and the second piezoelectric pump constitute a self-excited oscillation circuit, and the control command value is at least one of the voltage value of the second drive signal and the impedance of the second piezoelectric pump. The fluid control device according to claim 1.

5. The drive circuit and the second piezoelectric pump constitute a separately excited oscillation circuit that operates in response to a drive control signal of a predetermined frequency from the control circuit, and the control command value is the frequency of the drive control signal corresponding to the second drive signal. The fluid control device according to claim 1.

6. It is provided with a temperature sensor for measuring the temperature of the second piezoelectric pump, The control command value is the temperature measured by the temperature sensor, The fluid control device according to claim 1.

7. It is provided with an outside air temperature measurement sensor for measuring the outside air temperature around the fluid control device, The stop determination range is set based on the outside air temperature, The fluid control device according to claim 1.

8. The control circuit, When detecting that the control command value has fallen within the return determination range, it performs control on the drive circuit to resume the supply of the first drive signal, The fluid control device according to claim 1.

9. A first piezoelectric pump, a second piezoelectric pump, and a third piezoelectric pump connected in order from the upstream to the downstream of the flow path through which the fluid flows, A drive circuit that supplies a first drive signal to the first piezoelectric pump, a second drive signal to the second piezoelectric pump, and a third drive signal to the third piezoelectric pump, A control circuit that controls the operation of the drive circuit, provided with, The control circuit, obtains a first control command value that depends on the temperature of the third piezoelectric pump, If the first control command value is within the first stop determination range, it performs control on the drive circuit to stop the supply of at least the first drive signal while continuing the supply of the third drive signal, Fluid control device.

10. The control circuit, If the first control command value is within the first stop determination range, it performs control on the drive circuit to stop the supply of the first drive signal and the second drive signal, The fluid control device according to claim 9.

11. The control circuit, Obtain a second control command value that depends on the temperature of the second piezoelectric pump, If the second control command value is within the second stop determination range, perform control on the drive circuit to continue supplying the second drive signal and stop supplying the first drive signal, The fluid control device according to claim 10.

12. The first stop determination range is set based on the change characteristic of the flow rate of the fluid with respect to the temperature in the third piezoelectric pump, The fluid control device according to claim 9.

13. The first stop determination range is set based on the deterioration of the electromechanical coupling coefficient of the piezoelectric element constituting the third piezoelectric pump, the fatigue failure of the spring material, and the fatigue failure of the joint portion between the piezoelectric element and the spring material, The fluid control device according to claim 9.

14. The second stop determination range is set based on the change characteristic of the flow rate of the fluid with respect to the temperature in the second piezoelectric pump, The fluid control device according to claim 11.

15. The second stop determination range is set based on the deterioration of the electromechanical coupling coefficient of the piezoelectric element constituting the second piezoelectric pump, the fatigue failure of the spring material, and the fatigue failure of the joint portion between the piezoelectric element and the spring material, The fluid control device according to claim 11.

16. The drive circuit and the third piezoelectric pump constitute a first self-excited oscillation circuit, The first control command value is at least one of the voltage value of the third drive signal and the impedance of the third piezoelectric pump, The fluid control device according to claim 9.

17. The drive circuit and the third piezoelectric pump constitute a first externally excited oscillation circuit that operates in response to a drive control signal of a predetermined frequency from the control circuit, The first control command value is the frequency of the drive control signal corresponding to the third drive signal, The fluid control device according to claim 9.

18. It includes a temperature sensor for measuring the temperature of the third piezoelectric pump, The first control command value is the temperature measured by the temperature sensor, The fluid control device according to claim 9.

19. It includes an outside air temperature measurement sensor for measuring the outside air temperature around the fluid control device, The first stop determination range is set based on the outside air temperature, The fluid control device according to claim 9.

20. The drive circuit and the second piezoelectric pump constitute a second self-excited oscillation circuit, The second control command value is at least one of the voltage value of the second drive signal and the impedance of the second piezoelectric pump, The fluid control device according to claim 11.

21. The drive circuit and the second piezoelectric pump constitute a second externally excited oscillation circuit that operates in response to a drive control signal of a predetermined frequency from the control circuit, The second control command value is the frequency of the drive control signal corresponding to the second drive signal, The fluid control device according to claim 11.

22. It includes a temperature sensor for measuring the temperature of the second piezoelectric pump, The second control command value is the temperature measured by the temperature sensor, The fluid control device according to claim 11.

23. It includes an outside air temperature measurement sensor for measuring the outside air temperature around the fluid control device, The second stop determination range is set based on the outside air temperature, The fluid control device according to claim 11.

24. The control circuit, If the first control command value is within the return determination range, the drive circuit is controlled to resume the supply of the first drive signal. The fluid control device according to claim 9.

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