Flow rate control device, flow rate control method, and control program for flow rate control device

Abstract

[Problem] To obtain a flow rate control device with a high response accuracy. [Solution] A flow rate control device 1 including a flow rate sensor 102 for measuring a flow rate of fluid and a control unit 104 for adjusting the flow rate of the fluid to be a flow rate set value, wherein the control unit includes: a control valve 105 for changing the flow rate; a driver circuit 41 for driving the control valve; a sensor response adjustment circuit 43 for correcting frequency characteristics of a measurement value of the flow rate sensor; and a first filter 44 for attenuating a predetermined frequency band of an output of the sensor response adjustment circuit, a feedback loop that includes the driver circuit, the flow rate sensor, the sensor response adjustment circuit, and a first filter is configured, and the driver circuit receives a difference between the flow rate set value and an output value of the first filter.

Description

[Technical Field]

[0001] The present invention relates to a flow rate control device, a flow rate control method, and a control program for a flow rate control device. [Background technology]

[0002] There are known flow control devices and mass flow controllers (hereinafter also referred to as "MFCs") that adjust the flow rate of a fluid flowing downstream to a set value by adjusting a control valve based on the flow rate measured by a flow sensor.

[0003] Patent document 1 discloses a method for controlling the flow rate of a fluid in a flow control device including a flow sensor coupled to a fluid flow path having an inlet side and an outlet side, the flow sensor being adapted to provide a sensor output signal indicative of a sensed fluid flow through the flow path, the method including measuring at least one pressure in the flow path and adjusting the sensor output signal based on measuring the at least one pressure.

[0004] Patent Document 2 discloses a flow control device in which control constants corresponding to multiple flow rate setting values ​​and multiple fluid pressure values ​​are stored in advance in a control unit, and the control constant is selected based on the flow rate setting value and the detection value of a pressure sensor to control the flow rate. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2005-534110 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-090405 Summary of the Invention [Problem to be solved by the invention]

[0006] In order to achieve fast feedback control in an MFC, the response characteristics of the sensor that provides the control input are one of the important factors. In a thermal MFC, the sensor is, for example, a thermal flow sensor. However, in actual measurements, the response characteristics of a thermal MFC are slower than the theoretical value predicted from the response characteristics of a thermal flow sensor, and only a slow response with a time constant of about 10 seconds can be obtained. This is because the rate at which heat is transported by a fluid such as gas flowing through the flow path is small compared to the heat capacity of the sensor tube or heating resistor.

[0007] The flow rate control devices disclosed in Patent Documents 1 and 2 are both pressure-type MFCs. Neither device achieves feedback control with a fast response speed in the MFC.

[0008] Therefore, one of the objects of the present invention is to provide a flow rate control device with high response accuracy. [Means for solving the problem]

[0009] In order to achieve the above object, a flow control device according to one aspect of the present invention comprises a flow sensor that measures the flow rate of a fluid, and a control unit that adjusts the flow rate so that the flow rate of the fluid becomes a flow rate set value, the control unit comprising a control valve that changes the flow rate, a drive circuit that drives the control valve, a sensor response adjustment circuit that corrects the frequency characteristics of the measurement value of the flow rate sensor, and a first filter that attenuates a predetermined frequency band of the output of the sensor response adjustment circuit, a feedback loop including at least the drive circuit, the flow sensor, the sensor response adjustment circuit, and the first filter is formed, and the deviation between the flow rate set value and the output value of the first filter is input to the drive circuit.

[0010] The control unit may further include a second filter outside the feedback loop that amplifies a predetermined frequency band of the output of the sensor response adjustment circuit and does not change the gain of frequencies different from the predetermined frequency band.

[0011] The sensor response conditioning circuit and the first filter may be analog filters that process analog signals.

[0012] The flow sensor may be a thermal flow sensor.

[0013] In order to achieve the above object, a flow control method according to another aspect of the present invention is a flow control method using a flow control device comprising a flow sensor that measures the flow rate of a fluid, a control unit that adjusts the flow rate so that the flow rate of the fluid becomes a flow rate set value, and a control valve that changes the flow rate, and includes a drive step that drives the control valve, a measurement step that measures the flow rate, a sensor response adjustment step that corrects the frequency characteristics of the measurement value of the flow sensor, and a attenuation step that attenuates a predetermined frequency band of the output of the sensor response adjustment step, wherein a feedback loop is formed that includes at least the drive step, the measurement step, the sensor response adjustment step, and the attenuation step, and the deviation between the flow rate set value and the value obtained in the attenuation step becomes the input to the drive step.

[0014] In order to achieve the above object, a control program for a flow control device according to yet another aspect of the present invention is a control program for a flow control device comprising a flow sensor that measures the flow rate of a fluid, a control unit that adjusts the flow rate so that the flow rate of the fluid becomes a flow rate set value, and a control valve that changes the flow rate, and causes a computer to execute a drive command that drives the control valve, a measurement command that measures the flow rate, a sensor response adjustment command that corrects the frequency characteristics of the measurement value of the flow sensor, and an attenuation command that attenuates a predetermined frequency band of the output of the sensor response adjustment command, and a feedback loop that includes at least the drive command, the measurement command, the sensor response adjustment command, and the attenuation command, and the deviation between the flow rate set value and the acquired value of the attenuation command becomes the input to the drive command. The computer program can be provided by downloading it via a network such as the Internet, or by recording it on various computer-readable recording media such as a CD-ROM. [Effects of the Invention]

[0015] According to the present invention, a flow rate control device with high response accuracy can be obtained. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is an overall schematic diagram showing an embodiment of a flow rate control device according to the present invention; [Figure 2] FIG. 2 is a control block diagram of the flow rate control device. [Figure 3] 4 is an example of a Bode diagram of a first filter, a second filter, and a sensor response adjustment circuit included in the flow rate control device. [Figure 4] FIG. 1 is a control block diagram of a flow rate control device according to a related art. DETAILED DESCRIPTION OF THE INVENTION

[0017] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a flow rate control device, a control method, and a control program according to the present invention will be described with reference to the drawings.

[0018] Overview of flow control devices 1, the flow rate control device 1 includes a valve body 101, a flow rate sensor 102, a conversion unit 103, a control unit 104, and a control valve 105. The flow rate control device 1 is a device also called a mass flow controller (also called an "MFC").

[0019] The valve body 101 is a substantially cylindrical member that defines an upstream flow path 101a and a downstream flow path 101b. The upstream side of the upstream flow path 101a and the downstream side of the downstream flow path 101b are connected to pipes or flow path blocks through which the fluid to be controlled flows.

[0020] The upstream flow path 101a is a flow path into which fluid flows from the upstream side. The upstream flow path 101a branches into a flow path that passes through the flow sensor 102 and a bypass flow path 101c, and then these two flow paths merge and flow out to the control valve 105. The control valve 105 has a diaphragm 110 and a valve seat 112 facing the diaphragm 110. The space between the diaphragm 110 and the valve seat 112 is a space that communicates between the upstream flow path 101a and the downstream flow path 101b. The flow rate of the fluid can be adjusted by deforming the diaphragm 110 with an actuator 111, thereby opening and closing the diaphragm 110 relative to the valve seat 112. Although the internal structure of the actuator 111 is not shown in FIG. 1, the control valve 105 is a piezoelectric element-driven control valve that opens and closes, for example, a metal diaphragm using a piezoelectric element (piezo actuator) inside the actuator 111.

[0021] The downstream flow path 101b is configured so that a fluid whose flow rate is controlled by a control valve 105 flows in from the upstream side and flows out to the downstream side of the flow control device 1. The bypass flow path 101c is a flow path having a laminar flow element with a structure in which many thin flow paths are arranged in parallel so that the fluid becomes a laminar flow. In this embodiment, the laminar flow element is formed by stacking multiple plates (bypass sheets) with grooves carved by etching.

[0022] The flow sensor 102 is a sensor that measures the flow rate of a fluid flowing through a sensor tube 102a. The flow sensor 102 has, for example, heating resistors 102b and 102c upstream and downstream of the sensor tube 102a, and converts the flow rate of the fluid flowing through the sensor tube 102a into a voltage based on the difference in temperature between the heating resistors 102b and 102c. Because the ratio of the flow rate flowing through the bypass flow path 101c to the flow rate flowing through the sensor tube 102a is known, the flow rate of the upstream flow path 101a can be calculated by measuring the flow rate flowing through the sensor tube 102a. The output value of the flow sensor 102 saturates as the flow rate increases, so the measurable range of flow rates is limited. However, by adjusting the bypass flow path 101c, the flow rate of the upstream flow path 101a, i.e., the range of flow rates measurable by the flow control device 1, can be adjusted.

[0023] The conversion unit 103 is a functional unit that converts the flow rate setting value into a state that can be compared with the output value of the flow rate sensor 102, and then outputs it to the control unit 104 together with the output value of the flow rate sensor 102. The conversion unit 103 may rectify and amplify the output value of the flow rate sensor 102, or apply a low-pass filter to the output value to remove noise. The conversion unit 103 corrects for measurement errors that occur due to differences depending on the type of fluid and individual differences in the flow control device 1, and then outputs the flow rate setting value to the control unit 104 as a sensor output target value.

[0024] The control unit 104 is a functional unit that compares the output value of the flow rate sensor 102 with a sensor output target value, and controls the control valve 105 based on the comparison result.

[0025] The control unit 104 performs feedback control to control the opening of the control valve 105 so that the flow rate discharged from the downstream flow path 101b becomes a flow rate set value. The control unit 104 has a built-in CPU, memory M, A / D converter, etc. The control unit 104 may include a computer program configured to execute the operations described below, and may be realized by a combination of hardware and software.

[0026] ● Control block diagram of a flow rate control device of related technology As shown in FIG. 4, the flow rate control device of the related art has a drive circuit 141, a flow rate sensor 102, and a sensor response adjustment circuit 143 as control blocks.

[0027] The drive circuit 141 is a circuit that applies a drive current to the control valve 105. The drive circuit 141 opens and closes the control valve 105 based on an input flow rate set value, thereby changing the actual flow rate Q. The actual flow rate Q is the flow rate of the fluid that is physically flowing through the flow control device 1.

[0028] The flow rate sensor 102 measures the actual flow rate Q, and inputs a voltage value corresponding to the actual flow rate Q to the sensor response adjustment circuit 143 .

[0029] The sensor response adjustment circuit 143 is a circuit that corrects the frequency characteristics of the measurement value of the flow sensor 102. The sensor response adjustment circuit 143 is, for example, a band amplification filter that has a large gain in a predetermined band and a gain of 0 dB at DC.

[0030] The drive circuit 141, flow sensor 102, and sensor response adjustment circuit 143 are connected in this order to form a feedback loop. The deviation between the flow rate set value and the output value of the sensor response adjustment circuit 143 is input to the drive circuit 141. The drive circuit 141 drives the control valve 105 based on the deviation between the flow rate set value and the output value of the sensor response adjustment circuit 143. The output of the sensor response adjustment circuit 143 is also input to a display unit (not shown) and displayed as a flow rate display value indicating the current flow rate.

[0031] The guaranteed response speed in the flow rate control device of the related art is, for example, about one second.

[0032] ●Control block diagram of flow control device 1 and frequency characteristics of each filter 2, the flow control device 1 has, as control blocks, a drive circuit 41, a flow sensor 102, a sensor response adjustment circuit 43, a first filter 44, and a second filter 45. The drive circuit 41, the flow sensor 102, the sensor response adjustment circuit 43, and the first filter 44 form a feedback loop that receives a flow rate set value as an input and outputs an actual flow rate Q. The deviation between the flow rate set value and the output value of the first filter 44 is input to the drive circuit 41.

[0033] The drive circuit 41 is a circuit that applies a drive current to the control valve 105. The drive circuit 41 opens and closes the control valve 105 based on an input flow rate set value, thereby changing the actual flow rate Q. The actual flow rate Q is the flow rate of the fluid that is physically flowing through the flow control device 1.

[0034] The flow rate sensor 102 measures the actual flow rate Q, and inputs a voltage value corresponding to the actual flow rate Q to the sensor response adjustment circuit 43 .

[0035] The sensor response adjustment circuit 43 is a circuit that corrects the frequency characteristics of the measurement value of the flow sensor 102. In the thermal flow sensor 102, if the heat transport rate of a fluid such as a gas flowing through the flow path is small compared to the thermal capacity of the sensor tube 102a or the heating resistor, the heat transport rate of the fluid will be lower than the theoretical value, and the measurement value will be broad. In other words, the measurement value of the flow sensor 102 is a value obtained by applying a powerful low-pass filter (hereinafter also referred to as "LPF") to the actual flow rate Q. Therefore, as shown in FIG. 3, the sensor response adjustment circuit 43 is a band amplification filter that has gain in the cutoff band of the LPF to cancel out the attenuation of the LPF caused by the flow sensor 102. The sensor response adjustment circuit 43 may also have the properties of a low-pass / high-cut filter that attenuates frequencies higher than the amplified frequency band.

[0036] The first filter 44 shown in Fig. 2 is a frequency filter to which the output of the sensor response adjustment circuit 43 is input. As shown in Fig. 3, the first filter 44 attenuates a predetermined frequency band of the output of the sensor response adjustment circuit 43. The first filter 44 does not change the gain of frequencies other than the frequency band to be attenuated. In other words, the gain of frequency bands other than the attenuated frequency band is approximately 1. The center frequency of the attenuation band in the first filter 44 is higher than the center frequency of the pass band in the sensor response adjustment circuit 43.

[0037] The first filter 44 attenuates signals in a predetermined frequency band and passes signals in a low-frequency band. Therefore, when the signal changes monotonically, the input signal is output with a delay. Therefore, in this feedback loop, a signal delayed from the actual flow rate Q is detected, which is the deviation between the flow rate set value and the actual flow rate Q. Considering a transient response in which the actual flow rate Q gradually approaches the flow rate set value, the delayed signal deviates more from the flow rate set value than the actual flow rate Q. This allows for greater drive of the control valve 105 compared to when the first filter 44 is not used. This allows for faster feedback control and a faster response speed. The response speed of the flow control device 1 is, for example, approximately 0.5 seconds, which is approximately twice as fast as that of a flow control device of a related art that does not have the first filter 44. This configuration allows for fast response, especially to transient responses when the flow rate set value is significantly changed.

[0038] The second filter 45 is a frequency filter to which the output of the sensor response adjustment circuit 43 is input, and is arranged outside the feedback loop. The output of the second filter 45 is input to a display unit (not shown). The display unit displays the current flow rate calculated based on the output of the second filter 45 as a flow rate display value. The display unit may be included in the flow control device 1, or may be provided in an external device connected to the flow control device 1.

[0039] 3, second filter 45 amplifies a predetermined frequency band of the output of sensor response adjustment circuit 143, and does not change the gain of frequencies other than the predetermined frequency band. First filter 44 and second filter 45 have approximately the same center frequency.

[0040] Since the second filter 45 amplifies frequencies in a predetermined band, it emphasizes signal changes in the time domain, and in a situation where the input value is changing monotonically, the value is corrected in the direction of the change, so it can also be said that the signal is accelerated by passing through this filter. According to the configuration in which the flow rate display value is calculated based on the output value of the second filter 45, by accelerating the output signal of the sensor response adjustment circuit 43, it is possible to display a value that more accurately reflects the actual flow rate Q as the flow rate display value.

[0041] Sensor response adjustment circuit 43, first filter 44, and second filter 45 may be analog filters that process analog signals. This configuration can be implemented at low cost and can perform high-speed processing with low power consumption, compared to a configuration using a digital circuit such as a microcomputer.

[0042] Both the sensor response adjustment circuit 43 and the second filter 45 are BPFs that amplify a predetermined band. If the frequency characteristics obtained by combining the characteristics of the sensor response adjustment circuit 43 and the second filter 45 were to be realized by a single circuit, the frequency characteristics would become too steep, which could result in noise. If the output value of the flow sensor 102 is passed through the sensor response adjustment circuit 43 and the second filter 45 before being used to calculate the flow rate display value, the signal-to-noise ratio can be ensured.

[0043] The first filter 44 and the second filter 45 have opposite frequency characteristics, meaning that their gains are positive and negative. The sensor response adjustment circuit 43 and the first filter 44 also have substantially opposite frequency characteristics, although their center frequencies are different. Applying filters with opposite frequency characteristics to the same signal would attenuate the signal that is amplified once, which is undesirable in terms of maintaining the S / N ratio. By branching the output from the sensor response adjustment circuit 43 and arranging the first filter 44 and the second filter 45 on their respective paths, the use of filters with opposite frequency characteristics can be minimized, ensuring a good S / N ratio.

[0044] Furthermore, by configuring the sensor response adjustment circuit 43, the first filter 44, and the second filter 45 as separate control blocks, even if the sensor response adjustment circuit 43, the first filter 44, and the second filter 45 are configured as analog circuits, the signal can be controlled by the voltage width applied to each analog element.

[0045] In this way, according to the flow rate control device of the present invention, a flow rate control device with high response accuracy can be obtained.

[0046] Furthermore, according to the flow control device of the present invention, by calculating the flow rate display value based on the output value of the second filter, it is possible to display a value that more accurately reflects the actual flow rate as the flow rate display value.

[0047] Furthermore, according to the flow control device of the present invention, by configuring each frequency filter as an analog filter, it can be configured more inexpensively and can perform processing at high speed with less power consumption than when it is configured with a digital circuit such as a microcomputer.

[0048] Furthermore, according to the flow control device of the present invention, even when the flow sensor is a thermal flow sensor, high response accuracy can be achieved.

[0049] 1 Flow control device 41 Drive circuit 43 Sensor response adjustment circuit 44 First Filter 45 Second filter 102 Flow sensor 104 Control Unit 105 Control valve

Claims

1. a flow rate sensor that measures the flow rate of the fluid; a control unit that adjusts the flow rate of the fluid so that the flow rate becomes a flow rate setting value; Equipped with The control unit a control valve for varying the flow rate; a drive circuit for driving the control valve; a sensor response adjustment circuit that corrects the frequency characteristics of the measurement value of the flow rate sensor; a first filter for attenuating a predetermined frequency band of the output of the sensor response adjustment circuit; Equipped with The measurement value of the flow rate sensor is a value obtained by applying a low-pass filter to the actual flow rate, the correction of the frequency characteristics of the measurement value of the flow rate sensor in the sensor response adjustment circuit includes a correction to cancel out attenuation of a low-pass filter caused by the flow rate sensor; a center frequency of an attenuation band in the first filter is higher than a center frequency of a pass band in the sensor response adjustment circuit; a feedback loop including the drive circuit, the flow sensor, the sensor response adjustment circuit, and the first filter is configured; a deviation between the flow rate setting value and the output value of the first filter is input to the drive circuit; Flow control device.

2. the control unit further includes a second filter outside the feedback loop that amplifies a predetermined frequency band of the output of the sensor response adjustment circuit and does not change a gain of a frequency different from the predetermined frequency band. The flow control device according to claim 1 .

3. the sensor response adjustment circuit and the first filter are analog filters that process analog signals; The flow rate control device according to claim 1 or 2.

4. The flow rate sensor is a thermal flow rate sensor. The flow rate control device according to any one of claims 1 to 3.

5. a flow rate sensor that measures the flow rate of the fluid; a control unit that adjusts the flow rate of the fluid so that the flow rate becomes a flow rate setting value; a control valve for varying the flow rate; A flow rate control method using a flow rate control device comprising: a driving step of driving the control valve; a measuring step of measuring the flow rate; a sensor response adjustment step of correcting the frequency characteristics of the measurement value of the flow rate sensor by a sensor response adjustment circuit; an attenuation step of attenuating a predetermined frequency band of the output of the sensor response adjustment step by a first filter; Including, The measurement value of the flow rate sensor is a value obtained by applying a low-pass filter to the actual flow rate, the correction of the frequency characteristics of the measurement value of the flow rate sensor in the sensor response adjustment step includes a correction to cancel out attenuation of a low-pass filter caused by the flow rate sensor; a center frequency of an attenuation band in the first filter is higher than a center frequency of a pass band in the sensor response adjustment circuit; a feedback loop is configured including the driving step, the measuring step, the sensor response adjusting step, and the attenuation step; The deviation between the flow rate setting value and the acquired value of the attenuation step is the input of the drive step. Flow control method.

6. a flow rate sensor that measures the flow rate of the fluid; a control unit that adjusts the flow rate of the fluid so that the flow rate becomes a flow rate setting value; a control valve for varying the flow rate; A control program for a flow rate control device comprising: a drive command for driving the control valve; a measurement command to measure the flow rate; a sensor response adjustment command for correcting the frequency characteristics of the measurement value of the flow sensor by a sensor response adjustment circuit; an attenuation command for attenuating a predetermined frequency band of the output of the sensor response adjustment command by a first filter; on the computer, The measurement value of the flow rate sensor is a value obtained by applying a low-pass filter to the actual flow rate, the correction of the frequency characteristics of the measurement value of the flow sensor in the sensor response adjustment command includes a correction to cancel out attenuation of a low-pass filter caused by the flow sensor; a center frequency of an attenuation band in the first filter is higher than a center frequency of a pass band in the sensor response adjustment circuit, and a feedback loop is formed including the drive command, the measurement command, the sensor response adjustment command, and the attenuation command; The deviation between the flow rate setpoint and the acquired value of the attenuation command is the input of the drive command. Control program for flow control device.

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