Measurement device

Abstract

A measurement device according to the present invention comprises: a piezoelectric micropump that forms a flow of a fluid by an expansion / contraction operation of a piezoelectric element; a capacitive bridge circuit that includes the piezoelectric element as a first capacitor and that further includes a second capacitor which adjusts an equilibrium state of the bridge circuit, a third capacitor which is connected in series with the first capacitor, and a fourth capacitor which is connected in series with the second capacitor; and a measurement circuit that measures a potential difference between a connection point between the first and third capacitors and a connection point between the second and fourth capacitors.

Description

Measuring device

[0001] The present invention relates to a measuring device that measures displacement of a piezoelectric element provided in a piezoelectric micropump.

[0002] Conventionally, piezoelectric micropumps that form a fluid flow through the expansion and contraction operation of a piezoelectric element have been used to cause fluid such as gas and liquid sucked from a body cavity such as the thoracic cavity, or a medical solution injected into a patient to flow. Further, there is known a technology of measuring displacement occurring during the expansion and contraction operation of a piezoelectric element, and detecting an abnormality in a fluid state caused by bending of a tube, blockage in the tube, or the like based on the measurement result.

[0003] For example, Patent Document 1 discloses a microfluidic component including a membrane actuator (piezoelectric micropump) having a membrane element and an actuator element (piezoelectric element) for deflecting the membrane element. It also discloses a technology that, during operation of the microfluidic component, detects the influence of external influencing factors on the temporal signal curve of the control signal that actuates the actuator element, and identifies and / or classifies the external influencing factors based on the result.

[0004] Conventionally, in the technology as disclosed in Patent Document 1, a current-voltage conversion circuit 91 and an amplifier circuit 92 as shown in FIG. 15 have been used to measure displacement occurring during the expansion and contraction operation of a piezoelectric element. For this reason, as shown in a graph G91 of FIG. 16, when a driving voltage Vdrive including noise generated by a power supply circuit that easily generates noise such as a switching power supply circuit is applied to a piezoelectric element Cpzt, the current flowing through the piezoelectric element Cpzt is input to the current-voltage conversion circuit 91. As a result, the signal indicating the voltage at the output terminal P11 of the current-voltage conversion circuit 91 becomes a waveform with amplified noise as shown in a graph G92 of FIG. 16. Furthermore, when this signal is amplified by the amplifier circuit 92, the signal indicating the voltage at the output terminal P12 of the amplifier circuit 92 becomes a waveform with further amplified noise as shown in a graph G93 of FIG. 16. This signal is then measured as the signal indicating the displacement of the piezoelectric element.

[0005] Thus, when using the current-voltage conversion circuit 91 and the amplification circuit 92, if noise is present in the driving voltage of the piezoelectric element, there was a risk that the voltage representing the displacement of the piezoelectric element in the piezoelectric micropump could not be measured with high accuracy.

[0006] Special Publication No. 2024-544240

[0007] The object of the present invention is to provide a measuring device that can accurately measure the voltage representing the displacement of a piezoelectric element, even when noise is present in the driving voltage of the piezoelectric element of a piezoelectric micropump.

[0008] A measuring device according to one aspect of the present invention comprises a piezoelectric micropump that forms a fluid flow by the expansion and contraction of a piezoelectric element; a capacitive bridge circuit that further includes a second capacitor that adjusts the equilibrium state of the bridge circuit and includes the piezoelectric element as a first capacitor, a third capacitor connected in series with the first capacitor, and a fourth capacitor connected in series with the second capacitor; and a measuring circuit that measures the potential difference between the connection point of the first capacitor and the third capacitor and the connection point of the second capacitor and the fourth capacitor.

[0009] According to the present invention, it is possible to provide a measuring device that can accurately measure the voltage representing the displacement of a piezoelectric element, even when noise is present in the driving voltage of the piezoelectric element of a piezoelectric micropump.

[0010] The object, features, and advantages of the present invention will become more apparent from the following detailed description and accompanying drawings.

[0011] Figure 1 shows the overall configuration of a drug injection system according to an embodiment of the present invention. Figure 2 is a cross-sectional view illustrating the operation of a piezoelectric micropump. Figure 3 is a schematic configuration diagram of a drug injection device. Figure 4 shows an example of a first feature extracted from the temporal transition of the potential difference measured by the measurement circuit. Figure 5 shows an example of a second feature extracted from the temporal transition of the potential difference measured by the measurement circuit. Figure 6 shows the characteristics of the first and second feature in accordance with the back pressure applied to the drug solution. Figure 7 shows the characteristics of the first and second feature in the case where bubbles are present in the drug solution and when they are not. Figure 8 shows the temporal transition of the back pressure applied to the drug solution. Figure 9 shows the temporal transition of a 10-point moving average value based on the average values ​​of the first and second feature values ​​obtained in multiple experiments. Figure 10 shows the temporal transitions of the first feature, second feature, back pressure feature, and bubble feature when the back pressure applied to the drug solution is 0 kPa in the second experiment. Figure 11 shows the temporal changes of the first feature, second feature, back pressure feature, and bubble feature when the back pressure applied to the chemical solution in the second experiment was 20 kPa. Figure 12 shows the temporal changes of the first feature, second feature, back pressure feature, and bubble feature when the back pressure applied to the chemical solution in the second experiment was 40 kPa. Figure 13 shows an example of a linear function. Figure 14 is a flowchart of the chemical solution injection process. Figure 15 shows an example of a measurement circuit for measuring the displacement of a conventional piezoelectric element. Figure 16 shows an example of a waveform of a voltage signal in the measurement circuit shown in Figure 15.

[0012] The embodiments of the present invention will be described below with reference to the drawings. Note that the following embodiments are merely examples of the present invention and do not limit the technical scope of the present invention.

[0013] [Medication Infusion System] Figure 1 shows the overall configuration of a medication infusion system 1 according to an embodiment of the present invention. The medication infusion system 1 is used to inject medications appropriate to the patient's condition, etc., at pre-set values. The medication infusion system 1 can be used to inject various medications into a patient, such as anticoagulants, circulatory agonists, anesthetics, anticancer drugs, and antibiotics. However, the medications used in the medication infusion system 1 are not limited to these.

[0014] As shown in Figure 1, the drug injection system 1 comprises a drug container 6, a drug tube 60, and a drug injection device 2 (measuring device).

[0015] The drug solution container 6 contains a drug solution appropriate to the patient's condition. A drug solution tube 60 is connected to the drug solution container 6. The drug solution in the drug solution container 6 is delivered through the drug solution tube 60 by a piezoelectric micropump 10 provided in the drug solution injection device 2 and injected into the patient.

[0016] The drug injection device 2 has functions such as sending drug solution to inject it into the patient according to a set value, detecting the state of the drug solution, and outputting the detection result of the state of the drug solution via the input / output device 70.

[0017] [Piezoelectric Micropump] The configuration of the piezoelectric micropump 10 provided in the chemical injection device 2 will be described below with reference to Figure 2. Figure 2 is a cross-sectional view illustrating the operation of the piezoelectric micropump 10. The upper part of Figure 2 shows a state in which no driving voltage is supplied to the piezoelectric element 14 of the piezoelectric micropump 10. The lower left part of Figure 2 shows a state in which the pump chamber 12a is expanded. The lower right part of Figure 2 shows a state in which the pump chamber 12a is contracted.

[0018] The piezoelectric micropump 10 has the function of discharging the drug solution contained in the drug solution container 6 from the drug solution container 6 and delivering it to the patient through the drug solution tube 60. The piezoelectric micropump 10 comprises a housing 12 having a bottom and side walls erected on the periphery of the bottom, a diaphragm 13, a piezoelectric element 14, a connecting conductor 15 for supplying a driving voltage to the piezoelectric element 14, an inlet-side one-way valve 16, and an outlet-side one-way valve 17.

[0019] The diaphragm 13 is attached to the side wall of the housing 12 such that a pump chamber 12a is formed between it and the bottom of the housing 12. The piezoelectric element 14 is provided on the side of the diaphragm 13 opposite to the pump chamber 12a. The inlet-side one-way valve 16 is provided on the connecting conductor 15 and on the inlet 12b formed at the bottom of the housing 12. The outlet-side one-way valve 17 is provided on the outlet 12c formed at the bottom of the housing 12.

[0020] The inlet-side one-way valve 16 opens when the pressure of the chemical solution in the inlet 12b exceeds the pressure of the chemical solution in the pump chamber 12a, allowing the chemical solution to flow from the inlet 12b towards the pump chamber 12a. The outlet-side one-way valve 17 opens when the pressure of the chemical solution in the pump chamber 12a exceeds the pressure of the chemical solution in the outlet 12c, allowing the chemical solution to flow from the pump chamber 12a towards the outlet 12c.

[0021] The piezoelectric element 14 repeatedly expands and contracts when supplied with a drive voltage generated by the switching power supply circuit 30. This expansion and contraction of the piezoelectric element 14 causes the diaphragm 13 to vibrate.

[0022] The upper part of Figure 2 shows the state when no drive voltage is supplied from the switching power supply circuit 30. As shown in the lower left part of Figure 2, when a drive voltage is supplied from the switching power supply circuit 30 and the pump chamber 12a begins to expand, the discharge valve 17 closes and the inlet valve 16 opens as the pressure in the pump chamber 12a decreases, and the chemical solution is introduced into the pump chamber 12a.

[0023] Next, as shown in the lower right diagram of Figure 2, when the pump chamber 12a attempts to contract due to the drive voltage from the switching power supply circuit 30, the inlet valve 16 closes and the outlet valve 17 opens as the pressure inside the pump chamber 12a increases, and the chemical solution inside the pump chamber 12a is discharged.

[0024] As described above, the inlet 12b and outlet 12c of the piezoelectric micropump 10 are in communication with the drug solution tube 60 (Figure 1). Therefore, when the piezoelectric micropump 10 is driven, the drug solution in the drug solution container 6 is guided into the pump chamber 12a via the drug solution tube 60, and the drug solution in the pump chamber 12a is pushed toward the patient via the drug solution tube 60.

[0025] [Medicinal Solution Injection Device] The configuration of the medicinal solution injection device 2 will be described below with reference to Figure 3. Figure 3 is a schematic diagram of the medicinal solution injection device 2. The medicinal solution injection device 2 includes the piezoelectric micropump 10 described above, a capacitive bridge circuit 20, a switching power supply circuit 30, a measurement circuit 40, an input / output device 70, a storage device 80, a communication device 90, and a control device 50.

[0026] The capacitive bridge circuit 20 includes the piezoelectric element 14 (Figure 2) of the piezoelectric micropump 10 as the first capacitor 21, and further includes the second capacitor 22, the third capacitor 23, and the fourth capacitor 24.

[0027] The first capacitor 21 is an equivalent representation of the piezoelectric element 14 (Figure 2) provided in the piezoelectric micropump 10. The second capacitor 22 is a capacitor that adjusts the equilibrium state of the bridge circuit and is connected in parallel with the first capacitor 21. The third capacitor 23 and the fourth capacitor 24 are capacitors that appropriately adjust the capacitance ratio between each capacitor in the capacitive bridge circuit 20. The third capacitor 23 is connected in series with the first capacitor 21, and the fourth capacitor 24 is connected in series with the second capacitor 22.

[0028] The switching power supply circuit 30 is a power supply circuit that generates a drive voltage for the piezoelectric element 14 by a switching operation that repeatedly switches on and off using a switching element such as an FET. The drive voltage for the piezoelectric element 14 is an AC voltage that switches between a high voltage of several hundred volts (hereinafter referred to as the first voltage) and a low voltage of several tens of volts minus (hereinafter referred to as the second voltage) at a predetermined period. The first voltage, the second voltage, and the period are set by the control device 50. The switching power supply circuit 30 is configured, for example, by a step-up / step-down chopper circuit. In this case, it is possible to miniaturize the switching power supply circuit 30 and simplify the circuit configuration.

[0029] The measurement circuit 40 is a circuit that measures the potential difference between the connection point P1 of the first capacitor 21 and the third capacitor 23, and the connection point P2 of the second capacitor 22 and the fourth capacitor 24 in the capacitive bridge circuit 20. Specifically, the measurement circuit 40 is configured with a differential amplifier and periodically detects the potential difference between connection point P1 and connection point P2, and outputs a signal obtained by inverting and amplifying that potential difference.

[0030] The input / output device 70 includes a display device such as a liquid crystal display and an operating device such as a touch button or touch panel. The input / output device 70 outputs information input using the operating device to the control device 50, and under the control of the control device 50, displays various information on the display device.

[0031] The storage device 80 includes a storage medium such as flash memory, a hard disk, an SSD (Solid State Drive), or an HDD (Hard Disk Drive). The storage device 80 stores various information used by the control device 50 for control purposes in the storage medium.

[0032] The communication device 90 consists of communication equipment such as a wireless communication module and a network interface. The communication device 90 outputs information received from external devices to the control device 50. Furthermore, under the control of the control device 50, the communication device 90 transmits various information to external devices.

[0033] The control device 50 consists of a computer such as a microcontroller (MPC) which includes a processor such as a Central Processing Unit and memory such as RAM and ROM. The control device 50 performs processing such as detecting the state of the drug solution based on the potential difference measured by the measurement circuit 40 and controls the overall operation of the drug solution injection device 2.

[0034] The control device 50 functions as an extraction unit 51, a detection unit 52, a setting unit 53, an output unit 54, and a main control unit 55 by having the processor execute a program stored in memory. However, this is just one example, and the extraction unit 51, the detection unit 52, the setting unit 53, the output unit 54, and the main control unit 55 may be composed of dedicated integrated circuits.

[0035] The extraction unit 51 extracts characteristic quantities of the potential difference from the time progression of the potential difference between connection point P1 and connection point P2, which is measured by the measurement circuit 40.

[0036] Specifically, the extraction unit 51 extracts a first feature quantity and a second feature quantity from the temporal change of the potential difference between connection point P1 and connection point P2, as measured by the measurement circuit 40.

[0037] The first feature is the difference between the potential difference at the time when the driving voltage of the piezoelectric element 14 switches from the first voltage to the second voltage (hereinafter referred to as the first time point) and the potential difference when it switches from the second voltage to the first voltage immediately after the first time point.

[0038] The second feature is the difference between the potential difference at the point when the driving voltage of the piezoelectric element 14 stabilizes at the first voltage (hereafter referred to as the second time point) and the potential difference at the point immediately after the second time point when it stabilizes at the second voltage.

[0039] Figure 4 shows an example of a first feature quantity extracted from the temporal transition of the potential difference measured by the measurement circuit 40. In Figure 4, the horizontal axis represents time, and the vertical axis represents the voltage value of the potential difference measured by the measurement circuit 40. Waveform W30 shows the temporal transition of the driving voltage of the piezoelectric element 14 over one cycle. Waveform W31 shows the differential value of the temporal transition of the driving voltage of the piezoelectric element 14 over one cycle. Waveform W41a shows the temporal transition of the potential difference measured by the measurement circuit 40 when there is no back pressure applied to the chemical solution in the pump chamber 12a. Waveform W41b shows the temporal transition of the potential difference measured by the measurement circuit 40 when there is back pressure applied to the chemical solution in the pump chamber 12a.

[0040] In the example of FIG. 4, from the temporal transition of the potential difference shown in the waveform W41a, a difference F1a between the potential difference V11a at a first time point t11 when the drive voltage of the piezoelectric element 14 is switched from a first voltage to a second voltage, and the potential difference V12a at a time point t12 when the voltage is switched from the second voltage back to the first voltage immediately after the first time point t11, is extracted as a first feature quantity. Similarly, from the waveform W41b, a difference F1b between the potential difference V11b and the potential difference V12b is extracted as the first feature quantity.

[0041] Furthermore, the extraction unit 51 recognizes, as the first time point t11, the time point at which the potential difference measured by the measurement circuit 40 reaches a maximum (peak). The extraction unit 51 also recognizes, based on the cycle of the drive voltage of the piezoelectric element 14, the time point at which the time period during which the drive voltage is set (maintained) at the second voltage has elapsed from the first time point t11, as the time point t12 at which the voltage is switched from the second voltage to the first voltage immediately after the first time point t11.

[0042] FIG. 5 is a diagram showing an example of a second feature quantity extracted from the temporal transition of the potential difference measured by the measurement circuit 40. In FIG. 5, the horizontal axis represents time, and the vertical axis represents the voltage value of the potential difference measured by the measurement circuit 40. Waveforms W30, W31, W41a, and W41b are the same as those in FIG. 4.

[0043] For example, in the example of FIG. 5, from the temporal transition of the potential difference shown in the waveform W41a, a difference F2a between the potential difference V21a at a second time point t21 when the drive voltage of the piezoelectric element 14 stabilizes at the second voltage, and the potential difference V22a at a time point t22 when the drive voltage stabilizes at the first voltage immediately after the second time point t21, is extracted as a second feature quantity. Similarly, from the waveform W41b, a difference F2b between the potential difference V21b and the potential difference V22b is extracted as the second feature quantity.

[0044] Furthermore, the extraction unit 51 recognizes, as the second time point t21, the time point at which the amount of change in the potential difference measured by the measurement circuit 40 becomes equal to or less than a predetermined value immediately after the first time point t11. The extraction unit 51 also recognizes, based on the cycle of the drive voltage of the piezoelectric element 14, the time point at which the amount of change in the potential difference measured by the measurement circuit 40 becomes equal to or less than a predetermined value immediately after the time point t12 (FIG. 4) when the time period during which the drive voltage is set (maintained) at the second voltage has elapsed from the first time point t11, as the time point t22 when the drive voltage stabilizes at the first voltage immediately after the second time point t21.

[0045] As shown in FIG. 4, the first feature value (difference F1b) obtained when back pressure is applied to the chemical liquid in the pump chamber 12a is larger than the first feature value (difference F1a) obtained when no back pressure is applied to the chemical liquid in the pump chamber 12a. Further, as shown in FIG. 5, the second feature value (difference F2b) obtained when back pressure is applied to the chemical liquid in the pump chamber 12a is also larger than the second feature value (difference F2a) obtained when no back pressure is applied to the chemical liquid in the pump chamber 12a.

[0046] [Characteristics of First Feature Value and Second Feature Value] The characteristics of the first feature value and the second feature value depending on the back pressure applied to the chemical liquid will be described with reference to FIG. 6. FIG. 6 is a diagram showing the characteristics of the first feature value and the second feature value depending on the back pressure applied to the chemical liquid.

[0047] The upper diagram in FIG. 6 is a cross-sectional view of the piezoelectric micropump 10 when back pressure is applied to the chemical liquid, and the lower diagram shows the temporal transition of the level of the original signal of the measurement circuit 40. The original signal of the measurement circuit 40 is a signal before being inverted and amplified by a differential amplifier included in the measurement circuit 40. In the lower diagram of FIG. 6, the dotted line shows the temporal transition of the level of the original signal when the back pressure applied to the chemical liquid is small, and the solid line shows the temporal transition when the back pressure is large. Further, the left arrow indicates the first time point t11 (FIG. 4), and the right arrow indicates the second time point t21 (FIG. 5).

[0048] The greater the back pressure applied to the chemical liquid, the more the vibration of the diaphragm 13 is suppressed, and the smaller the vibration amplitude becomes. As a result, the level of the original signal of the measurement circuit 40 decreases overall, and the level of the subsequently inverted output signal of the measurement circuit 40 increases. Therefore, both the first feature value and the second feature value exhibit a characteristic that they increase as the back pressure increases.

[0049] Next, the characteristics of the first feature value and the second feature value in the case where air bubbles exist in the chemical liquid and the case where no air bubbles exist in the chemical liquid will be described with reference to FIG. 7. FIG. 7 is a diagram showing the characteristics of the first feature value and the second feature value in the case where air bubbles exist in the chemical liquid and the case where no air bubbles exist in the chemical liquid.

[0050] The upper part of Figure 7 is a cross-sectional view of the piezoelectric micropump 10 when air bubbles are present in the chemical solution, and the lower part, similar to the lower part of Figure 6, shows the temporal change in the level of the original signal from the measurement circuit 40. In the lower part of Figure 7, the dotted line shows the temporal change in the level of the original signal when air bubbles are present in the chemical solution, and the solid line shows the temporal change in the level of the original signal when air bubbles are not present in the chemical solution. The arrows on the left and right indicate the first time point t11 ​​(Figure 4) and the second time point t21 (Figure 5), similar to the lower part of Figure 6.

[0051] When air bubbles are present in the chemical solution, the density of the solution decreases and its fluidity increases, causing the diaphragm 13 to vibrate faster. As a result, the level of the original signal in the measurement circuit 40 at the first time point t11 ​​is higher than when no air bubbles are present. Also, when air bubbles are present, the decay rate of the original signal level in the measurement circuit 40 is faster (the time constant is smaller), so the level of the original signal at the second time point t21 is lower than when no air bubbles are present.

[0052] Therefore, when air bubbles are present in the drug solution, the level of the output signal of the measurement circuit 40, obtained by inverting the original signal of the measurement circuit 40 at the first time point t11, will be lower than when air bubbles are absent. As a result, the first feature quantity will be smaller than when air bubbles are absent. On the other hand, when air bubbles are present, the rate at which the level of the output signal of the measurement circuit 40 rises is faster, so the level of the output signal of the measurement circuit 40 at the second time point t21 will be higher than when air bubbles are absent. As a result, the second feature quantity will be larger than when air bubbles are absent. Thus, when air bubbles are present in the drug solution, the first feature quantity becomes smaller and the second feature quantity becomes larger, exhibiting the opposite characteristics compared to when air bubbles are absent.

[0053] [Verification of the characteristics of the first and second feature quantities] In order to verify the characteristics of the first and second feature quantities in response to the back pressure applied to the above-mentioned chemical solution, and the characteristics of the first and second feature quantities in response to the presence or absence of air bubbles in the chemical solution, the inventors repeated several experiments in which, after priming, back pressure was applied to the chemical solution in a predetermined pattern, and the temporal changes of the first and second feature quantities were obtained. Priming refers to, for example, temporarily setting the flow rate of the chemical solution to a value greater than the normal operating setting value in order to discharge air bubbles present in the chemical solution tube 60, and driving the piezoelectric micropump 10.

[0054] The results of this experiment will be explained with reference to Figures 8 and 9. Figure 8 shows the temporal change in back pressure applied to the drug solution. Figure 9 shows the temporal change in the 10-point moving average value based on the average values ​​of the first and second features obtained from multiple experiments. The 10-point moving average value based on the average values ​​of the first and second features is the average value calculated using the average values ​​of the first and second features from the most recent 10 experiments.

[0055] Graph G61 in Figure 9 shows the waveform W41ave, which represents the temporal evolution of a 10-point moving average value based on the average value of the first feature obtained from multiple experiments. Graph G62 shows the waveform W42ave, which represents the temporal evolution of a 10-point moving average value based on the average value of the second feature obtained from multiple experiments. The plots shown in graphs G61 and G62 represent the data for the first and second features obtained from multiple experiments.

[0056] In Figure 9, the period from time t61 to time t62 is the period during which priming is performed, and during this period, air bubbles are present in the chemical solution. The period from time t61 to time t63 corresponds to the period from time 0 sec to time 60 sec shown in Figure 8, and is the period after priming during which no back pressure is applied to the chemical solution filled in the pump chamber 12a. The period from time t63 to time t64 corresponds to the period from time 60 sec to time 110 sec shown in Figure 8, and is the period during which the back pressure applied to the chemical solution increases in increments of 40 kPa. The period from time t64 onward corresponds to the period from time 110 sec onward shown in Figure 8, and is the period during which the back pressure applied to the chemical solution decreases in increments of 40 kPa.

[0057] As shown in graph G61, during the period from time t61 to time t62 when bubbles are present in the chemical solution in the pump chamber 12a, the first feature is smaller than during the period from time t62 to time t63 when no back pressure is applied to the chemical solution. In contrast, as shown in graph G62, during the period from time t61 to time t62, the second feature is larger than during the period from time t62 to time t63.

[0058] These results confirmed that the first and second feature quantities exhibit a temporal change in the opposite direction to the presence or absence of bubbles in the pump chamber 12a (reverse bubble change). In other words, it was confirmed that when bubbles are present in the chemical solution, the first feature quantity becomes smaller than when bubbles are absent, and the second feature quantity becomes larger than when bubbles are absent, indicating that they have reverse characteristics.

[0059] On the other hand, as shown in graph G61, during the period from time t63 onwards when back pressure is applied to the drug solution, the first feature shows a temporal change similar to that of the back pressure shown in Figure 8. Also, as shown in graph G62, during the period from time t63 onwards, the second feature also shows a temporal change similar to that of the back pressure shown in Figure 8.

[0060] These results confirmed that the first and second feature quantities exhibit a temporal change in the same direction in response to increases and decreases in back pressure applied to the drug solution (co-directional change in back pressure). In other words, it was confirmed that the first and second feature quantities have the characteristic of increasing in the same direction as the back pressure applied to the drug solution increases.

[0061] Refer back to Figure 3. Based on the first and second feature quantities extracted by the extraction unit 51, the detection unit 52 detects the magnitude of the back pressure acting on the chemical solution in the pump chamber 12a (Figure 2) and whether or not air bubbles are present in the chemical solution.

[0062] Specifically, the detection unit 52 detects the magnitude of the back pressure acting on the chemical solution in the pump chamber 12a (Figure 2) based on the back pressure feature (= first feature + second feature), which is the sum of the first feature and the second feature. The detection unit 52 also detects whether or not bubbles are present in the chemical solution in the pump chamber 12a (Figure 2) based on the bubble feature (= first feature - second feature) obtained by subtracting the second feature from the first feature.

[0063] [Method for detecting the magnitude of back pressure and the presence or absence of bubbles] The method by which the detection unit 52 detects the magnitude of the back pressure acting on the chemical solution in the pump chamber 12a (Figure 2) based on back pressure characteristics, and the method for detecting whether or not bubbles are present in the chemical solution in the pump chamber 12a (Figure 2) based on bubble characteristics, will be explained below based on the results of the experiment shown.

[0064] In the above experiment (hereafter referred to as Experiment 1), the period during which air bubbles were present in the drug solution (times t61-t62 (Figure 9)) and the period during which no back pressure was applied to the drug solution (time t63 onwards (Figure 9)) did not overlap. However, in the actual operating environment of the drug solution injection device 2, it is possible that air bubbles may be present in the drug solution and that back pressure may be applied to the drug solution.

[0065] Therefore, in order to appropriately detect the presence of air bubbles in the chemical solution and the presence of back pressure on the chemical solution, the inventors conducted an experiment (hereinafter referred to as the second experiment) in which, after priming, a predetermined back pressure was applied to the chemical solution filled in the pump chamber 12a (Figure 2), and air bubbles were mixed into the chemical solution multiple times while the chemical solution was under back pressure.

[0066] Figures 10 to 12 show the temporal changes of the first feature, second feature, back pressure feature, and bubble feature in the second experiment when the back pressure applied to the chemical solution was 0 kPa, 20 kPa, and 40 kPa, respectively. On the left side of each figure, the waveforms W411, W412, W413 of the temporal change of the first feature and W421, W422, W423 of the temporal change of the second feature are shown. On the right side of each figure, the waveforms WP1, WP2, WP3 of the temporal change of the back pressure feature and WB1, WB2, WB3 of the temporal change of the bubble feature are shown. The arrows indicate the period during which bubbles were mixed into the chemical solution.

[0067] In the first experiment, it was confirmed that the first and second feature quantities exhibited a similar characteristic, increasing as the back pressure on the drug solution increased. Furthermore, it was confirmed that when air bubbles were present in the drug solution, the first feature quantity decreased and the second feature quantity increased, exhibiting a reverse characteristic.

[0068] The results of the second experiment revealed why it is difficult to accurately determine the presence or absence of back pressure and air bubbles using only the first and second feature quantities. Specifically, when back pressure is applied to the drug solution, both the first and second feature quantities increase, but when air bubbles are present in the drug solution, the first feature quantity decreases and the second feature quantity increases. Therefore, when the drug solution contains air bubbles and is also subjected to back pressure, the characteristics of the first and second feature quantities overlap, making it impossible to clearly separate the effects of back pressure and air bubbles using a single feature quantity.

[0069] This can be confirmed from the experimental results shown in Figures 10 to 12. Figures 11 and 12 show the state in which air bubbles are contained in the drug solution under different back pressure conditions (20 kPa and 40 kPa), and the waveforms W412 to W413 of the temporal transition of the first feature and W422 to W423 of the temporal transition of the second feature are displayed superimposed.

[0070] Specifically, in these figures, even when the back pressure on the drug solution is high, the first feature quantity does not increase in proportion to the magnitude of the back pressure when air bubbles are present; rather, it decreases. On the other hand, the second feature quantity increases in both cases: when the back pressure on the drug solution is high and when air bubbles are present. Therefore, it is not possible to accurately determine whether the increase in the second feature quantity is due to the magnitude of the back pressure or the presence of air bubbles. Thus, it was confirmed that when the effects of back pressure and air bubbles overlap, it is difficult to separate the effects of back pressure and air bubbles from the first and second feature quantities alone.

[0071] However, it was confirmed that the state of the drug solution can be detected more accurately by using back pressure features and bubble features.

[0072] Specifically, the magnitude of the back pressure can be determined by substituting the back pressure feature, which is the sum of the first and second feature quantities extracted by the extraction unit 51, into the linear function (correlation function) F shown in Figure 13.

[0073] The linear function F can be derived by performing an experiment similar to the second experiment using multiple piezoelectric micropumps 10 of the same type, and then performing a regression analysis on the relationship between the representative value C (Figure 13) of the average value of the back pressure features obtained in this experiment and the magnitude of the back pressure applied to the drug solution in the same experiment. The linear function F derived in this way can be stored in advance in the memory device 80.

[0074] After priming, the back pressure feature obtained when no air bubbles are present in the chemical solution and no back pressure is applied may be set as the back pressure feature when the magnitude of the back pressure in the linear function F is 0 (i.e., the intercept b of the linear function F (Figure 13)). In this case, individual errors of the piezoelectric element 14 in the piezoelectric micropump 10 can be corrected, and the magnitude of the back pressure applied to the chemical solution can be detected with higher accuracy.

[0075] On the other hand, if the bubble feature quantity obtained by subtracting the second feature quantity from the first feature quantity extracted by the extraction unit 51 exceeds a predetermined threshold, it is determined that bubbles are present in the drug solution; if it is below the threshold, it is determined that bubbles are not present.

[0076] The threshold can be derived, for example, by performing an experiment similar to the second experiment using multiple identical piezoelectric micropumps 10, and using the representative value of the average value of the bubble feature quantities obtained when bubbles are present in this experiment as the threshold. The threshold derived in this way can be stored in the memory device 80 beforehand. Alternatively, the bubble feature quantities obtained after priming, when no bubbles are present in the chemical solution and no back pressure is applied, may be set as the threshold. In this case, individual errors of the piezoelectric elements 14 in the piezoelectric micropump 10 can be corrected, and whether or not bubbles are present in the chemical solution can be detected with higher accuracy.

[0077] In other words, the detection unit 52 obtains a linear function F from the storage device 80 and detects the magnitude of the back pressure obtained by substituting the back pressure feature quantity into the linear function F. Alternatively, the detection unit 52 may detect that back pressure is acting on the drug solution when it detects that the magnitude of the back pressure is greater than 0, and detect that no back pressure is acting on the drug solution when the magnitude of the back pressure is 0 or less.

[0078] Furthermore, similar to the linear function F, the same experiment as in the second experiment may be performed using multiple piezoelectric micropumps 10 of the same type, and a correlation function such as a polynomial function showing the relationship between the back pressure feature and the magnitude of back pressure may be derived by performing regression analysis on the relationship between the representative value C (Figure 13) of the average value of the back pressure feature obtained in this experiment and the magnitude of the back pressure applied to the drug solution in the same experiment. This correlation function may be stored in the memory device 80 in advance, and the detection unit 52 may detect the magnitude of back pressure obtained by substituting the back pressure feature into the correlation function. In this case as well, the back pressure feature obtained after priming, when there are no bubbles in the drug solution and no back pressure is applied, may be set as the back pressure feature when the magnitude of back pressure in the correlation function is 0.

[0079] Furthermore, the detection unit 52 obtains a threshold from the storage device 80, detects that bubbles are present in the drug solution if the bubble feature quantity exceeds the threshold (a predetermined value), and detects that bubbles are not present in the drug solution if the bubble feature quantity is less than or equal to the threshold.

[0080] The setting unit 53 sets the back pressure feature when the magnitude of the back pressure in the linear function F (Figure 13) is 0, when the chemical solution in the pump chamber 12a does not contain air bubbles and there is no back pressure on the chemical solution. Specifically, the setting unit 53 sets the back pressure feature when the magnitude of the back pressure in the linear function F (Figure 13) is 0, immediately after the completion of priming, when the chemical solution in the pump chamber 12a does not contain air bubbles and there is no back pressure on the chemical solution.

[0081] Furthermore, if the detection unit 52 performs detection using the correlation function described above instead of the linear function F, the setting unit 53 may, in the same manner as above, set the back pressure feature quantity when the magnitude of back pressure in the correlation function is 0, which is when the chemical solution in the pump chamber 12a does not contain air bubbles and there is no back pressure on the chemical solution.

[0082] The output unit 54 displays (outputs) the magnitude of the back pressure detected by the detection unit 52 on the display device provided in the input / output device 70. Furthermore, if the detection unit 52 detects the presence of air bubbles in the chemical solution in the pump chamber 12a, the output unit 54 may control the communication device 90 to transmit (output) warning information indicating the result of the detection to an external device.

[0083] The main control unit 55 controls the overall operation of the drug injection device 2. The main control unit 55 is configured to execute the drug injection process when the communication device 90 receives a drug injection instruction.

[0084] [Medicinal Solution Injection Process] The medicinal solution injection process will be explained below with reference to Figure 14. Figure 14 is a flowchart of the medicinal solution injection process.

[0085] When the communication device 90 receives an injection instruction for the drug solution, the main control unit 55 accepts the injection instruction (step S10) and starts the drug solution injection process.

[0086] When the chemical injection process is started, the main control unit 55 starts priming (step S11) and causes the measurement circuit 40 to start measuring the potential difference between connection point P1 (Figure 3) and connection point P2 (Figure 3) (step S12).

[0087] The extraction unit 51 determines whether one cycle of the driving voltage of the piezoelectric element 14 has finished during the process of measuring the potential difference by the measurement circuit 40 (step S13). If the extraction unit 51 determines that one cycle of the driving voltage has finished (YES in step S13), it extracts a first feature quantity and a second feature quantity based on the temporal change of the potential difference measured by the measurement circuit 40 during that cycle (step S14).

[0088] The detection unit 52 calculates the bubble feature quantity by subtracting the second feature quantity extracted in step S14 (step S15), and detects whether or not bubbles are present in the chemical solution in the pump chamber 12a based on the calculated bubble feature quantity (step S16). If the detection unit 52 detects that bubbles are present (YES in step S16), it returns to step S13.

[0089] On the other hand, if the detection unit 52 detects that no bubbles are present (NO in step S16), it calculates the sum of the first and second feature quantities extracted in step S14 as the back pressure feature quantity (step S17). The setting unit 53 sets the back pressure feature quantity calculated in step S17 as the back pressure feature quantity when the magnitude of the back pressure is 0 in the linear function F (Figure 13) stored in the memory device 80 (intercept b of the linear function F (Figure 13)) (step S18).

[0090] The main control unit 55 determines whether priming is complete or not (step S19). If it is not complete (NO in step S19), it continues priming. On the other hand, if priming is complete (YES in step S19), the main control unit 55 sets the flow rate of the chemical solution to the set value for normal operation and starts driving the piezoelectric micropump 10 to inject the chemical solution (step S20).

[0091] The extraction unit 51 determines whether one cycle of the driving voltage of the piezoelectric element 14 has finished during the injection of the drug solution (step S21). If the extraction unit 51 determines that one cycle of the driving voltage has finished (YES in step S21), it extracts a first feature quantity and a second feature quantity based on the temporal change of the potential difference measured by the measurement circuit 40 during that cycle (step S22).

[0092] The detection unit 52 calculates the sum of the first and second feature quantities extracted in step S22 as the back pressure feature quantity (step S23), and detects the magnitude of the back pressure acting on the drug solution based on the calculated back pressure feature quantity. The output unit 54 displays the detected magnitude of the back pressure on the display device provided in the input / output device 70 (step S24).

[0093] Furthermore, the detection unit 52 calculates the bubble feature quantity by subtracting the second feature quantity extracted in step S22 (step S25), and detects whether or not bubbles are present in the drug solution based on the calculated bubble feature quantity (step S26). If it is detected that bubbles are present in the drug solution (YES in step S26), the output unit 54 displays warning information indicating that bubbles are present in the drug solution on the display device provided by the input / output device 70 (step S27).

[0094] On the other hand, if it is detected that the drug solution does not contain air bubbles (NO in step S26), the main control unit 55 determines whether the injection of the drug solution has been completed (step S28). If the injection of the drug solution has not been completed (NO in step S28), the main control unit 55 returns to step S21 and continues the drug solution injection process. If the injection of the drug solution has been completed (YES in step S28), the main control unit 55 terminates the drug solution injection process.

[0095] In this embodiment, the potential difference between the connection point P1 of the first capacitor 21 and the third capacitor 23, and the connection point P2 of the second capacitor 22 and the fourth capacitor 24, which are equivalent to the piezoelectric element 14 of the piezoelectric micropump 10 in the capacitive bridge circuit 20, is measured. As a result, even if the driving voltage of the piezoelectric element 14 generated by the switching power supply circuit 30 contains noise, the noise propagated to the two connection points P1 and P2 via the piezoelectric element 14 is canceled out, and the potential difference between the two connection points P1 and P2 can be measured with high accuracy as a voltage representing the displacement of the piezoelectric element 14.

[0096] Furthermore, the control device 50 can detect with high accuracy the state of the chemical solution corresponding to the displacement of the piezoelectric element 14, based on the potential difference measured with high accuracy by the measurement circuit 40. Specifically, a first feature quantity and a second feature quantity are extracted from the temporal change of the potential difference measured with high accuracy by the measurement circuit 40, and based on the back pressure feature quantity and bubble feature quantity obtained from the first feature quantity and the second feature quantity, the magnitude of the back pressure acting on the chemical solution and whether or not bubbles are present in the chemical solution can be detected with high accuracy.

[0097] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than by the description of the embodiments above, and further includes all modifications in the sense and scope equivalent to the claims.

[0098] (1) The detection unit 52 may be configured to detect whether or not back pressure is applied to the drug solution or whether or not air bubbles are present, based on the first characteristic quantity. This configuration can be realized, for example, as follows.

[0099] The detection unit 52 detects that back pressure is being applied to the drug solution if the first feature quantity exceeds a predetermined voltage value, and detects that there is no back pressure being applied to the drug solution if the first feature quantity is less than or equal to the predetermined voltage value. The predetermined voltage value can be set to, for example, the first feature quantity obtained in an experiment similar to the first experiment described above when there is no back pressure being applied to the drug solution in the pump chamber 12a and no air bubbles are present.

[0100] Furthermore, in the drug injection process shown in Figure 14, steps S13 to S18 and steps S23 to S25 are omitted. In step S26, the detection unit 52 detects whether or not back pressure is being applied to the drug solution based on the first feature quantity extracted in step S22. If back pressure is detected, in step S27, the output unit 54 displays warning information indicating that back pressure is being applied to the drug solution on the display device provided in the input / output device 70.

[0101] Alternatively, the detection unit 52 detects that the drug solution contains air bubbles if the first feature quantity is less than or equal to a predetermined voltage value, and detects that the drug solution does not contain air bubbles if the first feature quantity exceeds a predetermined voltage value. The predetermined voltage value can be set, for example, to the first feature quantity obtained in an experiment similar to the first experiment described above, when there is no back pressure on the drug solution in the pump chamber 12a and no air bubbles are present.

[0102] Furthermore, in the drug injection process shown in Figure 14, steps S15 and S21 to S27 are omitted. In step S16, the detection unit 52 detects whether or not the drug solution contains air bubbles based on the first characteristic quantity extracted in step S14.

[0103] (2) The detection unit 52 may be configured to detect whether or not back pressure is applied to the drug solution or whether or not air bubbles are present, based on the second characteristic quantity. This configuration can be realized, for example, as follows.

[0104] The detection unit 52 detects that back pressure is being applied to the drug solution when the second feature quantity exceeds a predetermined voltage value, and detects that there is no back pressure being applied to the drug solution when the second feature quantity is less than or equal to the predetermined voltage value. The predetermined voltage value can be set, for example, to the second feature quantity obtained when air bubbles are present in the drug solution in the pump chamber 12a in an experiment similar to the first experiment described above.

[0105] Furthermore, in the drug injection process shown in Figure 14, steps S13 to S18 and steps S23 to S25 are omitted. In step S26, the detection unit 52 detects whether or not back pressure is being applied to the drug solution based on the second characteristic quantity extracted in step S22. If back pressure is detected, in step S27, the output unit 54 displays warning information indicating that back pressure is being applied to the drug solution on the display device provided in the input / output device 70.

[0106] Alternatively, the detection unit 52 detects that the drug solution contains air bubbles if the second feature quantity exceeds a predetermined voltage value, and detects that the drug solution does not contain air bubbles if the second feature quantity is less than or equal to the predetermined voltage value. The predetermined voltage value can be set, for example, to the second feature quantity obtained when the drug solution in the pump chamber 12a contained air bubbles in an experiment similar to the first experiment described above.

[0107] Furthermore, in the drug injection process shown in Figure 14, steps S13 to S18 and steps S23 to S25 are omitted. In step S26, the detection unit 52 detects whether or not the drug solution contains air bubbles based on the second characteristic quantity extracted in step S22.

[0108] (3) In the above embodiment, an example was described in which the detection unit 52 determines that bubbles are present in the drug solution if the bubble feature amount obtained by subtracting the second feature amount extracted by the extraction unit 51 exceeds a predetermined threshold, and determines that bubbles are not present if it is below the threshold.

[0109] However, conversely, the detection unit 52 may calculate the bubble feature quantity by subtracting the first feature quantity from the second feature quantity extracted by the extraction unit 51. The detection unit 52 may then determine that bubbles are present in the drug solution if the bubble feature quantity is below a predetermined threshold, and determine that bubbles are not present if it exceeds the threshold.

[0110] In this case, the threshold can be derived as a representative value of the average value of the bubble feature obtained by performing an experiment similar to the second experiment using multiple piezoelectric micropumps 10 of the same type, and subtracting the first feature from the second feature when bubbles are present in this experiment.

[0111] In other words, the detection unit 52 detects whether or not bubbles are present in the drug solution based on a bubble feature quantity that represents the difference between the first feature quantity and the second feature quantity. Specifically, the detection unit 52 detects whether or not bubbles are present in the drug solution according to the relationship between the bubble feature quantity, which represents the difference between the first feature quantity and the second feature quantity, and a predetermined threshold.

[0112] (4) The same configuration as the drug injection device 2 in the above embodiment may be applied to a suction device that drives a piezoelectric micropump 10 to flow gas and liquid aspirated from a body cavity such as the pleural cavity. This may enable the detection of the magnitude of the back pressure acting on the gas and liquid, whether or not back pressure is acting on the gas and liquid, and whether or not the liquid contains air bubbles.

[0113] The specific embodiments described above mainly include inventions having the following configurations.

[0114] A measuring device according to one aspect of the present invention comprises a piezoelectric micropump that forms a fluid flow by the expansion and contraction of a piezoelectric element; a capacitive bridge circuit that further includes a second capacitor that adjusts the equilibrium state of the bridge circuit and includes the piezoelectric element as a first capacitor, a third capacitor connected in series with the first capacitor, and a fourth capacitor connected in series with the second capacitor; and a measuring circuit that measures the potential difference between the connection point of the first capacitor and the third capacitor and the connection point of the second capacitor and the fourth capacitor.

[0115] In this measurement device, the potential difference between the connection point of the piezoelectric element (acting as the first capacitor) and the third capacitor, and the connection point of the second capacitor and the fourth capacitor, in a capacitive bridge circuit, is measured. This allows for the cancellation of noise propagated to the two connection points via the piezoelectric element, even when noise is present in the driving voltage of the piezoelectric element, and enables high-precision measurement of the potential difference between the two connection points as a voltage representing the displacement of the piezoelectric element.

[0116] The measuring device may further include a switching power supply circuit that generates the driving voltage for the piezoelectric element.

[0117] This configuration allows for the cancellation of noise generated by the switching operation when generating the drive voltage in a switching power supply circuit, and enables high-precision measurement of the voltage representing the displacement of the piezoelectric element.

[0118] In the measuring device, the switching power supply circuit may be a step-up / step-down chopper circuit.

[0119] This configuration allows for miniaturization and simplification of the power supply circuit that generates the driving voltage for the piezoelectric element.

[0120] The measuring device may further include a control device that detects the state of the fluid based on the potential difference.

[0121] According to this configuration, the control device can detect the fluid state corresponding to the displacement of the piezoelectric element with high precision based on the potential difference measured with high precision by the measurement circuit.

[0122] In the measuring device, the measuring circuit periodically measures the potential difference, and the control device may include an extraction unit that extracts characteristic quantities of the potential difference from the temporal changes in the potential difference, and a detection unit that detects the state of the fluid based on the characteristic quantities.

[0123] According to this configuration, the fluid state corresponding to the displacement of the piezoelectric element can be detected with high accuracy based on feature quantities extracted from the temporal changes of the potential difference measured periodically by the measurement circuit.

[0124] In the measuring device, the feature quantity includes a first feature quantity which is the difference between the potential difference at a first time point when the driving voltage of the piezoelectric element switches from a first voltage to a second voltage, and the potential difference when it switches from the second voltage to the first voltage immediately after the first time point, and the detection unit may detect whether or not back pressure is applied to the fluid or whether or not bubbles are present based on the first feature quantity.

[0125] According to this configuration, based on the first feature quantity, it is possible to detect with high accuracy whether back pressure is being applied to the fluid or whether or not bubbles are present.

[0126] In the measuring device, the feature quantity includes a second feature quantity which is the difference between the potential difference at a second time point when the driving voltage of the piezoelectric element stabilizes at a first voltage and the potential difference at a second voltage different from the first voltage immediately after the second time point, and the detection unit may detect whether or not back pressure is applied to the fluid or whether or not bubbles are present based on the second feature quantity.

[0127] According to this configuration, based on the second feature quantity, it is possible to detect with high accuracy whether or not back pressure is being applied to the fluid or whether or not bubbles are present.

[0128] In the measuring device, the feature quantity includes a first feature quantity which is the difference between the potential difference at a first time point when the driving voltage of the piezoelectric element switches from a first voltage to a second voltage and the potential difference when it switches from the second voltage to the first voltage immediately after the first time point, and a second feature quantity which is the difference between the potential difference at a second time point when the driving voltage of the piezoelectric element stabilizes at the first voltage and the potential difference when it stabilizes at the second voltage immediately after the second time point, and the detection unit may detect the magnitude of the back pressure acting on the fluid and whether or not bubbles are contained in the fluid based on the first feature quantity and the second feature quantity.

[0129] According to this configuration, based on the first and second feature quantities, the magnitude of the back pressure acting on the fluid and whether or not the fluid contains bubbles can be detected with high accuracy.

[0130] In the measuring device, the detection unit may detect the magnitude of the back pressure based on a back pressure feature, which is the sum of the first feature and the second feature.

[0131] According to this configuration, the magnitude of the back pressure acting on the fluid can be detected with high accuracy based on the back pressure feature.

[0132] The measuring device further includes a storage device that stores a correlation function showing the relationship between the magnitude of the back pressure and the back pressure feature, and the detection unit may detect the magnitude of the back pressure obtained by substituting the back pressure feature into the correlation function.

[0133] According to this configuration, the magnitude of the back pressure acting on the fluid can be detected regularly and with high accuracy by using the correlation function stored in the memory device.

[0134] In the measuring device, the control device may further include a setting unit that sets the back pressure feature quantity when the fluid does not contain bubbles and there is no back pressure on the fluid as the back pressure feature quantity when the magnitude of the back pressure in the correlation function is 0.

[0135] In this configuration, the back pressure feature when the fluid does not contain bubbles and there is no back pressure acting on the fluid is set as the back pressure feature when the back pressure is 0 in the correlation function stored in the memory. Therefore, by using the correlation function after this setting, individual errors of the piezoelectric element can be corrected and the magnitude of the back pressure acting on the fluid can be detected with higher accuracy.

[0136] In the measuring device, the detection unit may detect whether or not bubbles are present in the fluid based on a bubble feature quantity that represents the difference between the first feature quantity and the second feature quantity.

[0137] According to this configuration, it is possible to detect with high accuracy whether or not bubbles are present in the fluid based on the bubble characteristics.

[0138] In the measuring device, the detection unit may detect whether or not bubbles are present in the fluid according to the relationship between the bubble characteristic quantity and a predetermined value.

[0139] According to this configuration, it is possible to detect with high accuracy whether or not bubbles are present in the fluid, based on the relationship between the bubble characteristic quantity and a predetermined value.

[0140] In the measuring device, the control device may further include a setting unit that sets the bubble characteristic quantity when the fluid does not contain bubbles and there is no back pressure on the fluid as the predetermined value.

[0141] In this configuration, the bubble characteristic quantity when the fluid does not contain bubbles and there is no back pressure on the fluid is set as the predetermined value. Therefore, individual errors of the piezoelectric element can be corrected, and whether or not bubbles are present in the fluid can be detected with higher accuracy.

[0142] As described above, the present invention provides a measuring device that can accurately measure the voltage representing the displacement of a piezoelectric element, even when noise is present in the driving voltage of the piezoelectric element of a piezoelectric micropump.

Claims

1. A measuring device comprising: a piezoelectric micropump that forms a fluid flow by the expansion and contraction of a piezoelectric element; a capacitive bridge circuit that further includes the piezoelectric element as a first capacitor and a second capacitor that adjusts the equilibrium state of the bridge circuit, a third capacitor connected in series with the first capacitor, and a fourth capacitor connected in series with the second capacitor; and a measuring circuit that measures the potential difference between the connection point of the first capacitor and the third capacitor and the connection point of the second capacitor and the fourth capacitor.

2. The measuring device according to claim 1, further comprising a switching power supply circuit for generating the driving voltage of the piezoelectric element.

3. The measuring device according to claim 2, wherein the switching power supply circuit is a step-up / step-down chopper circuit.

4. The measuring device according to any one of claims 1 to 3, further comprising a control device for detecting the state of the fluid based on the potential difference.

5. The measuring device according to claim 4, wherein the measuring circuit periodically measures the potential difference, and the control device includes an extraction unit that extracts characteristic quantities of the potential difference from the temporal changes of the potential difference, and a detection unit that detects the state of the fluid based on the characteristic quantities.

6. The measuring device according to claim 5, wherein the feature quantity includes a first feature quantity which is the difference between the potential difference at a first time point when the driving voltage of the piezoelectric element switches from a first voltage to a second voltage and the potential difference when it switches from the second voltage to the first voltage immediately after the first time point, and the detection unit detects whether or not back pressure is applied to the fluid or whether or not bubbles are present based on the first feature quantity.

7. The measuring device according to claim 5, wherein the feature quantity includes a second feature quantity which is the difference between the potential difference at a second time point when the driving voltage of the piezoelectric element stabilizes at a first voltage and the potential difference at a second voltage different from the first voltage immediately after the second time point, and the detection unit detects whether or not back pressure is applied to the fluid or whether or not bubbles are present based on the second feature quantity.

8. The measuring device according to claim 5, wherein the feature quantities include: a first feature quantity which is the difference between the potential difference at a first time point when the driving voltage of the piezoelectric element switches from a first voltage to a second voltage and the potential difference when it switches from the second voltage to the first voltage immediately after the first time point; and a second feature quantity which is the difference between the potential difference at a second time point when the driving voltage of the piezoelectric element stabilizes at the first voltage and the potential difference when it stabilizes at the second voltage immediately after the second time point, and the detection unit detects the magnitude of the back pressure acting on the fluid and whether or not bubbles are contained in the fluid based on the first feature quantity and the second feature quantity.

9. The measuring device according to claim 8, wherein the detection unit detects the magnitude of the back pressure based on a back pressure feature which is the sum of the first feature and the second feature.

10. The measuring device according to claim 9, further comprising a storage device for storing a correlation function showing the relationship between the magnitude of the back pressure and the back pressure feature quantity, wherein the detection unit detects the magnitude of the back pressure obtained by substituting the back pressure feature quantity into the correlation function.

11. The measuring device according to claim 10, further comprising: a setting unit that sets the back pressure feature quantity when the fluid does not contain bubbles and there is no back pressure on the fluid as the back pressure feature quantity when the magnitude of the back pressure in the correlation function is 0.

12. The measuring device according to claim 8, wherein the detection unit detects whether or not bubbles are present in the fluid based on a bubble feature quantity that shows the difference between the first feature quantity and the second feature quantity.

13. The measuring device according to claim 12, wherein the detection unit detects whether or not bubbles are present in the fluid according to the relationship between the bubble characteristic quantity and a predetermined value.

14. The measuring device according to claim 13, further comprising: a setting unit for setting the bubble characteristic quantity when the fluid does not contain bubbles and there is no back pressure on the fluid as the predetermined value.

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