JP5277027B2 - Micro flow liquid pump controller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a minute flow rate liquid pump control device inhibiting increase of cost and accurately controlling minute flow rate. <P>SOLUTION: This minute flow rate liquid pump control device 1 changes a liquid feed flow rate by controlling a drive pulse width and drive frequency of a drive coil of an electromagnetic drive type pump, and controls the drive frequency and the pulse width based on a pressure of liquid phase. Accurate control is possible even in a minute flow rate by controlling the drive pulse width and the drive frequency of the drive coil 6 of the electromagnetic drive type pump 2 based on the pressure of the liquid phase in such a manner. Cost can be reduced by applying the electromagnetic drive type pump 2. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a micro flow rate liquid pump control device for controlling an electromagnetically driven pump.

  In recent years, it has been demanded worldwide to reduce the use of fossil fuels from the viewpoint of saving resources and suppressing global warming, and fuel cells have been developed as one solution. Moreover, in order to take advantage of the characteristics of fuel cells, small-sized home-installed types are the mainstream. Here, in a fuel cell system with a small amount of power generation compared to a medium-sized fuel cell system, the amount of fuel or water delivered per hour is very small. In addition, the effect of the cost of a single component of the components used on the entire system is very large in the case of a small fuel cell, and even if it is highly accurate, expensive components can be used in the process of popularization. Therefore, the development of an inexpensive and highly accurate liquid pump has been demanded. And as a conventional pump, what applied a diaphragm type and a Hycera type pump to a fuel cell system was known (for example, refer to patent documents 1).

JP 2007-18893 A

  However, the diaphragm type and hysera type pumps as described above have a relatively large liquid feeding amount, and sufficient accuracy can be obtained when a minute flow rate (for example, 1 g / min or less) suitable as a pump applied to the fuel cell system is controlled. There was a problem that I could not. In addition, double plunger type pumps (used in high-speed liquid chromatograms, etc.) used in chemical analysis equipment, etc. are used to send minute flow rates in the laboratory, but they are very expensive and are fuel cells. When applied to a system, there is a problem that the cost becomes high. Furthermore, in order to improve the flow rate accuracy, a flow rate measuring device was connected to the pumping side of the pump and control was performed based on the measured flow rate of the pumped fluid. However, the flow rate measuring device measures a minute flow rate. However, there is a problem that sufficient accuracy for application to a fuel cell system cannot be obtained.

  The present invention has been made to solve such a problem, and an object of the present invention is to provide a micro flow rate liquid pump control apparatus capable of controlling the micro flow rate with high accuracy while reducing the cost.

  Here, as a result of earnest research, the inventors of the present invention are most effective to use an electromagnetically driven pump in order to reduce the cost of the liquid feed pump, and the mechanism of the change in the flow rate characteristic according to the pressure. In order to control a minute flow rate with an electromagnetically driven pump, it is preferable to perform control based on the pressure of the pump rather than performing control based on the measurement result of the flow meter. It has been found that precise flow rate control can be performed.

  Therefore, a micro flow rate liquid pump control device according to the present invention is a micro flow rate liquid pump control device that changes a liquid feed flow rate by controlling a drive frequency and a drive pulse width of a drive coil of an electromagnetically driven pump. The driving frequency and the pulse width are controlled based on the phase pressure.

  In this minute flow rate liquid pump control device, even with a minute flow rate, control can be performed with high accuracy by controlling the drive frequency and drive pulse width of the drive coil of the electromagnetically driven pump based on the liquid phase pressure. it can. In addition, the cost can be reduced by applying an electromagnetically driven pump. As described above, the cost can be reduced and the minute flow rate can be controlled with high accuracy.

  Moreover, in the micro flow rate liquid pump control device according to the present invention, it is preferable that the liquid flow rate includes 1 g / min or less, and when such a small range of flow rate is controlled, it is more particularly than other types of pumps. The flow rate can be controlled with high accuracy.

  Moreover, in the micro flow rate liquid pump control device according to the present invention, it is preferable to acquire the pressure with a pressure sensor. By detecting the pressure of the pump directly with a pressure sensor, an accurate pressure can be obtained.

  Moreover, in the micro flow rate liquid pump control device according to the present invention, the pressure can be acquired by prediction. For example, the pressure can be predicted from the use environment at the time of control by measuring the relationship between the use environment and the pressure in advance and creating a data table. This makes it possible to control the electromagnetically driven pump without newly attaching a pressure sensor and increasing the number of parts.

  Here, the present inventors have found that the liquid flow rate changes nonlinearly according to the pressure, but can be approximated by a straight line within each section by dividing the liquid flow rate for each pressure range. . Therefore, in the micro flow rate liquid pump control device according to the present invention, the liquid flow rate is divided into a plurality of sections for each pressure range, and the control is performed on the assumption that the liquid flow rate varies linearly according to the pressure in each section. Preferably it is done. Thereby, the calculation of the arithmetic processing at the time of control can be made easy.

  In the micro flow rate liquid pump control device according to the present invention, it is preferable to perform control using a function in which the liquid flow rate is expressed as a drive frequency and the drive pulse width as a variable. By using the function of the liquid supply flow rate expressed by simple four arithmetic operations with the driving frequency and the driving pulse width as variables, calculation of arithmetic processing at the time of control can be facilitated.

  In the micro flow rate liquid pump control device according to the present invention, it is preferable to perform control by further using a function in which the liquid flow rate is expressed with the pressure as a variable. The function that expresses the liquid flow rate as the drive frequency and the drive pulse width as a variable is valid when the pressure is constant, but it can be used even when the pressure fluctuates by further using the function with the pressure as a variable. Control can be performed using a function in which the flow rate is represented by a drive frequency and the drive pulse width is represented by a variable.

  According to the present invention, it is possible to reduce costs and control a minute flow rate with high accuracy.

It is a figure which shows the structure of the pump system to which the micro flow rate liquid pump control apparatus which concerns on embodiment of this invention is applied. It is a diagram for demonstrating the approximation of the relationship between a pressure and a liquid feeding flow volume. It is a flowchart which shows the control processing of the micro flow volume liquid pump control apparatus which concerns on this embodiment. It is a figure which shows the structure of the evaluation apparatus for measuring the liquid feeding flow volume of an electromagnetic drive pump. It is a diagram which shows the measurement result in an Example.

  DESCRIPTION OF EMBODIMENTS Hereinafter, a preferred embodiment of a micro flow rate liquid pump control device according to the present invention will be described in detail with reference to the drawings.

  First, the configuration of the micro flow rate liquid pump control device 1 according to the embodiment of the present invention will be described. FIG. 1 is a diagram showing a configuration of a pump system 100 to which a micro flow rate liquid pump control device 1 according to an embodiment of the present invention is applied. As shown in FIG. 1, the pump system 100 includes a minute flow rate liquid pump control device 1, an electromagnetically driven pump 2, and a pressure sensor 3. The pump system 100 has a function of feeding a liquid by a desired flow rate by controlling the electromagnetically driven pump 2 in accordance with the input target flow rate. The pump system 100 cannot be used with a highly volatile liquid such as gasoline, but can be applied to various liquids including water. Here, the pump system 100 is most suitable for a fuel cell system using a fossil fuel such as liquid carbon hydrogen fuel or synthetic fuel, and a hydrocarbon fuel having a carbon content of 80 mass% or more and 90 mass% or less. It is desirable to use

When the density of the pump system 100 changes, the volumetric flow rate can be controlled. However, the density flow rate is difficult to control due to the density change, and the density at 15 ° C. is 0.7 g / cm ³ or more. It is desirable to use a hydrocarbon fuel of 0.9 g / cm ³ or less. Further, it is known that the kinematic viscosity of the liquid feeding affects the liquid feeding performance of all kinds of pumps. In the pump system 100, the kinematic viscosity of the liquid feeding at 30 ° C. is considered based on the characteristics of the electromagnetically driven pump 2. It is desirable to use a hydrocarbon-based liquid having a thickness of 1.0 mm ² / s to 5.0 mm ² / s.

  In the fuel cell system, the elution of sulfur from the pump and piping members may be a problem in the liquid feeding of the fuel cell system. However, in the present invention, by appropriately selecting the material of the wetted part of the electromagnetically driven pump 2 It is possible to use a hydrocarbon-based liquid having a sulfur compound of 10 mass ppm or less based on the total sulfur compounds in the liquid.

  In the pump system 100, the upper limit value of the applicable flow rate range is not particularly limited. However, in consideration of the flow rate accuracy within ± 5% on the basis of the flow rate value in the use flow range, 10 g / min is more preferable for a single pump. It is preferable to set it as 5 g / min. And in the range below 1 g / min which is a micro flow rate range as an applicable flow rate range, a flow rate can be controlled with the especially outstanding precision compared with the conventional pump system. In this case, the lower limit value of the applicable flow rate range is preferably 0.2 g / min, more preferably 0.3 g / min.

  The electromagnetically driven pump 2 is configured by arranging a plunger 8 in a casing 7 having a drive coil 6 attached to the periphery thereof so as to be able to reciprocate. The casing 7 is provided with an inlet channel 11 for taking the liquid into the casing 7 and an outlet channel 12 for supplying the liquid to the outside under pressure. The electromagnetically driven pump 2 takes in liquid from the inlet channel 11 side by reciprocating the plunger 8 in the casing 7 when a control signal having a predetermined drive frequency and drive pulse width is input to the drive coil 6. At the same time, the liquid can be supplied from the outlet channel 12 under pressure. A pressure sensor 3 is attached to the outlet channel 12, and the pressure sensor 3 detects the pressure of the liquid supplied from the electromagnetically driven pump 2 and outputs the detected pressure to the minute flow rate liquid pump control device 1. In the electromagnetically driven pump 2, the moving speed of the plunger 8 changes when the driving frequency of the control signal changes, and the moving width of the plunger 8 changes when the driving pulse width changes. That is, the plunger 8 not only reciprocates in the casing 7 with a full stroke, but also the stroke can be shortened depending on the drive pulse width of the control signal, so that the flow rate can be reduced as compared with the full stroke. Therefore, it is possible to control the flow rate of the liquid according to the drive frequency and drive pulse width of the control signal. In the present embodiment, the range of the driving frequency and the driving pulse width to be used is not particularly limited, but it is preferable that the driving frequency is 50 Hz or less and the driving pulse width is within 50 m · sec. At that time, the drive pulse width is preferably shorter than the non-energization time.

  The micro flow rate liquid pump control device 1 includes a target flow rate setting unit 21 that sets a target flow rate by receiving a signal or an input signal from an external device, and a drive frequency and a drive pulse width so that the set target flow rate can be obtained. And a control unit 22 for outputting a control signal to the drive coil 6 of the electromagnetically driven pump 2 and a storage unit 23 for storing various data tables acquired in advance for setting the drive frequency and the drive pulse width. And is configured.

  The control unit 22 has a function of setting a drive frequency and a drive pulse width based on the target flow rate set by the target flow rate setting unit 21 and the pressure detected by the pressure sensor 3 and outputting a control signal. . At this time, the control unit 22 appropriately reads the data table from the storage unit 23, and sets the drive frequency and the drive pulse width using each data table, the target flow rate, and the acquired pressure.

  In addition, the control unit 22 has a function of performing control on the assumption that the liquid supply flow rate linearly changes in accordance with the drive frequency in the range of the drive frequency used in order to reduce the calculation load. It has a function of performing control on the assumption that the flow rate of liquid feed varies linearly according to the drive pulse width in the range.

  The control unit 22 has a function of performing control using a function expressing the drive frequency and the drive pulse width as variables under the condition where the pressure is constant. As described above, by using the function of the liquid supply flow rate expressed by simple four arithmetic operations with the driving frequency and the driving pulse width as variables, it is possible to facilitate calculation of arithmetic processing at the time of control. For example, an equation as shown in equation (1) can be used as an example of a function of the liquid feeding flow rate expressed with the driving frequency and the driving pulse width as variables. Note that the function is not limited to that shown in Expression (1).

[Flow rate] = Coefficient 1 x [Drive frequency] x [Drive pulse width]
+ Coefficient 2 × [driving frequency] + coefficient 3 × [driving pulse width] + coefficient 4 (1)

  It is known that when the pressure changes, the liquid flow rate changes due to the pressure characteristics of the electromagnetically driven pump 2. In general, this appears because the flow rate of the liquid decreases as the pressure increases. Here, the present inventors have found that the liquid flow rate changes nonlinearly according to the pressure, but can be approximated by a straight line within each section by dividing the liquid flow rate for each pressure range. . Therefore, when control is performed with a combination of the same drive frequency and drive pulse width, the micro flow rate liquid pump control device divides the liquid feed flow rate into a plurality of sections for each pressure range, and the liquid feed flow rate in each section. Has a function of performing control assuming that the pressure linearly changes according to pressure. Thereby, the calculation of the arithmetic processing at the time of control can be made easy. For example, as shown in FIG. 2, when the actual flow rate is represented by a flow rate curve Q, it is divided into a section between pressure P1 and pressure P2 and a section between pressure P3 and pressure P1, and the flow rate in each section is It can be assumed that it changes according to the straight line L1 and the straight line L2.

  The control unit 22 performs the assumption as described above, and in the section of the pressure P1 and the pressure P2 that can be expressed by a straight line, by using the equation (1), the liquid supply flow rate at the pressure P1 and the pressure P2 The liquid flow rate at a predetermined pressure PA in the section can be approximated to the straight line L1, and can be expressed by, for example, Expression (2).

[Flow rate] = [Flow rate at pressure P1]
+ {([Flow rate at pressure P2] − [flow rate at pressure P1]) / ([pressure P2] − [pressure P1])}
× ([pressure PA] − [pressure P1]) (2)

  When the liquid flow rate to be obtained is not in the section between the pressure P1 and the pressure P2, it can be obtained by the same method by setting a new section. For example, it can be obtained by setting an interval between the pressure P3 and the pressure P1 and approximating the straight line L2.

  Next, control processing by the micro flow rate liquid pump control device 1 of the present invention will be described in detail with reference to FIG. FIG. 3 is a flowchart showing a control process of the micro flow rate liquid pump control device 1 according to the present embodiment. This process is executed at a predetermined timing in the control unit 22 of the minute flow rate liquid pump control device 1 while the electromagnetically driven pump 2 is in operation. The control processing described below is merely an example of a method for setting the drive frequency and the drive pulse width, and may be set by another method.

  First, before describing the control process, a data table used during the control process will be described. This data table is created in advance by performing measurement and calculation by the evaluation device, stored in the storage unit 23, and read out at a desired timing. Note that the data tables shown below are merely examples, and other data tables may be used.

  The creation of a data table for setting each coefficient of the equation (1) used for the calculation during processing will be described. First, as shown in FIG. 4, using a common kerosene, a supply tank 31 in which kerosene is stored, an electromagnetically driven pump 32 that sends kerosene from the supply tank 31, and an output flow of the electromagnetically driven pump 32 Using an evaluation device 30 configured to include a pressure sensor 34 provided in the passage 33 and a measurement tank 35 for storing the supplied kerosene and measuring the flow rate of the electromagnetically driven pump 32, the pump The relationship between each of the pressure, the driving frequency, the driving pulse width, and the liquid feeding flow rate is measured. For example, at each pressure of 0, 10, 20, and 50 kPa as measurement conditions, the drive frequency and the drive pulse width are set so as to be appropriately distributed in the used drive frequency range and the drive pulse width range. Measure the flow rate. As a representative example, the measurement results at a pressure of 20 kPa are shown in Table 1.

  Using the measurement results represented by Table 1 and the measurement results at other pressures, coefficient 1, coefficient 2, coefficient 3, and coefficient 4 in equation (1) are obtained by regression analysis. At this time, a technique is usually used to obtain a minimum deviation in the regression equation. Here, in order to improve the accuracy at a minute flow rate, the error (ratio of the deviation to the target value) is minimized. calculate. The calculation results at this time are shown in Table 2. Table 2 is a data table used when setting the coefficient of the expression (1) in the control process. Note that the number of data in the data table may be increased by increasing the pressure to be measured.

  Creation of a data table for setting the drive frequency during processing will be described. This data table is created by setting an optimum drive frequency in the flow range and pressure of the liquid flow rate to be used. Various methods are conceivable for setting the optimum driving frequency. Here, the setting is made so that a region where the linearity of the driving pulse width of the electromagnetic driving pump is high can be used. Table 3 shows a data table created by such a method. A data table in which the flow rate range is divided more finely may be created.

  Next, the control process of FIG. 3 will be described. As shown in FIG. 3, the target flow rate is first input from the target flow rate setting unit 21 (step S100). Next, the pressure measured by the pressure sensor 34 is input (step S110). After the target flow rate and pressure are input, the data table shown in Table 3 is read from the storage unit 23, the target flow rate is inquired against the data table, and the measured pressure is inquired to set the drive frequency ( Step S120).

  Next, coefficients 1 to 4 of the equation (1) applied at the pressure input in S110 are set (step S130). In S130, the data table shown in Table 1 is read from the storage unit 23 to inquire which range the measured pressure belongs to 0 to 10, 10 to 20, 20 to 50 kPa, and 0, 10, 20, 50 kPa. Among these, the values of the coefficients 1 to 4 corresponding to the pressures before and after the measured pressure are acquired from the data table, and the coefficients 1 to 4 at the measured pressure are calculated by linear interpolation using the acquired data. As described above, the coefficients 1 to 4 can be obtained immediately by linear interpolation. The liquid supply flow rate is divided into a plurality of sections for each pressure range, and the liquid supply flow rate changes linearly according to the pressure in each section. This is because it is assumed that the relationship represented by Equation (2) is established. In this way, it is possible to reduce the calculation load in the control unit 22 and incorporate the pump control in the control device that controls the entire system.

  Next, the drive pulse width is set using equation (1) (step S140). In S140, Formula (1) is transformed as shown in Formula (3), and the target flow rate input in S100, the drive frequency set in S120, and the coefficients 1 to 4 set in S130 are converted into Formula (3). By substituting, the drive pulse width is calculated.

[Drive pulse width] = ([Flow rate] − [Drive frequency] × Coefficient 2−Coefficient 4)
/ (Coefficient 1 × [driving frequency] + coefficient 3) (3)

  After setting the drive pulse width in S140, a control signal is output to the drive coil 6 of the electromagnetically driven pump 2 in accordance with the set drive frequency and drive pulse width (step S150). When the process of S150 ends, the control process shown in FIG. 3 ends, and the process starts again from S100.

  By the above, according to the micro flow rate liquid pump control device 1 according to the embodiment of the present invention, by controlling the drive frequency and the drive pulse width of the drive coil 6 of the electromagnetically driven pump 2 based on the pressure of the liquid phase, Control can be performed with high accuracy even at a minute flow rate. In addition, the cost can be reduced by applying the electromagnetically driven pump 2. As described above, the cost can be reduced and the minute flow rate can be controlled with high accuracy.

  Here, an embodiment when the electromagnetically driven pump is controlled by the control method according to the example shown in FIG. 3 will be described. In the present embodiment, the driving frequency and the driving pulse width for obtaining the target flow rate shown in Table 4 are set by the control method shown in FIG. 3, and the electromagnetic drive pump is driven and the evaluation device 30 shown in FIG. The measurement result will be described. In actual operation, the pressure fluctuates during driving of the electromagnetically driven pump, but in this measurement, the pressure valve was adjusted to verify the appropriateness of the drive frequency and drive pulse width set based on the pressure. The flow rate was measured while maintaining the pressure at a predetermined value. In Table 4, the “driving frequency” and “driving pulse width” columns describe set values when the values shown in the “target flow” and “pressure” columns are calculated as input values, respectively. In addition, the measurement related to the condition group 1 is mainly performed in order to verify the accuracy of the flow rate control at a minute flow rate, and the measurement related to the condition group 2 has a larger flow rate than the condition group 1 and the pressure fluctuation range. This is done in order to verify that the flow rate can be accurately controlled by the control method of the present invention even if the pressure fluctuates in the increasing flow rate range. In condition group 2, each of the lowest pressure and the highest pressure assumed for each target flow rate is measured. In the embodiment, taking into account manufacturing errors for each pump, measurement is performed for the four electromagnetically driven pumps under the same conditions, and each data is measured in the first, second, third, and fourth embodiments. And

  The measurement results in condition group 1 in Table 4 are shown in FIG. 5 (a), and the measurement results in condition group 2 are shown in FIG. 5 (b). In FIG. 5, the horizontal axis represents the measured flow rate, and the vertical axis represents the error of each measured flow rate with respect to the target flow rate. As shown in FIG. 5 (a), in any of the first to fourth embodiments, the error from the target flow rate is within ± 5% for all the flow rates, and high-precision flow rate control can be performed even in a minute flow rate range. Is understood. In addition, as shown in FIG. 5 (b), even when the minimum pressure and the maximum pressure at a predetermined target flow rate are set and measured, the error with respect to the target flow rate is within ± 7% for all flow rates. It is understood that the flow rate can be controlled with high accuracy even if the pressure fluctuates. Therefore, even when the pressure fluctuation during operation becomes large, it is understood that the flow rate can be accurately controlled by newly setting the drive frequency and the drive pulse width according to the measurement value of the pressure sensor.

  Next, a comparative example will be described. Table 5 shows the guaranteed accuracy of the flow rate measuring device B generally used in the fuel cell system and the guaranteed accuracy of the flow rate measuring device A that is more accurate than the flow rate measuring device B.

  As shown in Table 5, even with a high-precision flow rate measuring device A, the accuracy at low flow rate is guaranteed only ± 10% RD (± 10% of the measured value), and is particularly small at 1 g / min or less. The flow rate is not guaranteed. Furthermore, with respect to the flow rate measuring device A, the accuracy in the flow rate range outside the measurement guarantee is verified, and the result is shown in Table 6.

  As can be seen from Table 6, it is understood that the error is greatly increased at a low flow rate of 0.5 g / min. Therefore, it is apparent that the flow rate cannot be accurately controlled in the minute flow rate range using the measurement result of the flow rate measuring device in which the error becomes large.

  The present invention is not limited to the above-described embodiment.

  In the present embodiment, the pressure of the liquid phase is acquired by the pressure sensor, but instead of this, the pressure may be acquired by prediction. Specifically, a data table is created by measuring the relationship between the usage environment such as temperature and pressure in advance, and when operating the electromagnetically driven pump, the pressure is determined by referring the usage environment to the data table. It is possible to predict and input the pressure value. This makes it possible to control the electromagnetically driven pump without newly attaching a pressure sensor and increasing the number of parts. Note that both acquisition by the pressure sensor and acquisition by prediction may be performed. For example, in a state where the use environment is stable, only prediction is performed, and in a situation where the use environment changes rapidly and prediction is difficult, the pressure sensor You may switch to.

  DESCRIPTION OF SYMBOLS 1 ... Micro flow rate liquid pump control apparatus, 2 ... Electromagnetic drive pump, 3 ... Pressure sensor, 6 ... Drive coil.

Claims (6)

A micro flow rate liquid pump control device that changes a flow rate by controlling a drive frequency and a drive pulse width of a drive coil of an electromagnetically driven pump,
Controlling the driving frequency and the pulse width based on the pressure of the liquid phase ;
The liquid flow rate is divided into a plurality of sections for each pressure range, and the control is performed on the assumption that the liquid flow rate varies linearly according to the pressure in each of the sections. Pump control device.   2. The micro flow rate liquid pump control device according to claim 1, wherein the liquid flow rate is 1 g / min or less.   3. The micro flow rate liquid pump control device according to claim 1, wherein the pressure is acquired by a pressure sensor.   The pressure is acquired by predicting from the use environment at the time of control by measuring the relationship between the use environment and the pressure in advance and creating a data table. Micro flow rate liquid pump control device. The micro flow rate liquid pump control device according to any one of claims 1 to 4 , wherein the liquid flow rate is controlled by using a function that represents the drive frequency and the drive pulse width as variables. 6. The micro flow rate liquid pump control device according to claim 5, wherein the liquid flow rate is further controlled using a function expressing the pressure as a variable.

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