Flow rate control apparatus, flow rate control method, and program recording medium in which program for flow rate control apparatus is recorded

Abstract

This invention provides a flow control device, a flow control method, and a program storage medium that can obtain the flow rate of fluid flowing through a downstream side valve with virtually no time delay and significantly reduced noise, and improves responsiveness compared to the past. The flow control device includes: a downstream side valve flow meter (VFS) for measuring the flow rate of fluid flowing through a downstream side valve (V2); and an observer (3) including a downstream side valve flow estimation model (31) for estimating the flow rate of the downstream side valve based on input parameters that change the opening of the downstream side valve (V2), wherein the deviation between the measured value of the downstream side valve flow rate output by the downstream side valve flow meter (VFS) and the estimated value of the downstream side valve flow rate output by the downstream side valve flow estimation model is fed back to the observer (3).

Description

Technical Field

[0001] This invention relates to, for example, a flow control device for controlling the flow rate of fluids in a semiconductor manufacturing process. Prior Technology

[0002] For example, in order to control the flow rate of various gases introduced into the processing chamber, a flow control device is used, which is a component of various fluid devices and control mechanisms known as mass flow controllers.

[0003] A typical flow control device includes: a flow sensor installed in the flow channel; a downstream valve installed downstream of the flow sensor; and a downstream valve controller that controls the opening of the downstream valve so that the measured flow rate measured by the flow sensor is consistent with the user-set time-varying set flow rate.

[0004] However, because the fluid measurement point of the flow sensor and the fluid control point of the downstream valve are offset by a predetermined distance in the flow direction, there is a time delay between the flow rate measured by the flow sensor and the flow rate flowing through the downstream valve. This time delay included in the measured flow rate poses a problem in achieving the responsiveness of flow control sought in semiconductor manufacturing processes.

[0005] To address this issue, an attempt was made to apply a downstream valve flow meter, capable of measuring the actual flow rate (hereinafter referred to as downstream valve flow) through the downstream valve, to flow control devices. For example, the downstream valve flow meter incorporates an existing pressure flow sensor and a downstream valve flow calculator to calculate the downstream valve flow. The downstream valve flow calculator uses the flow rate of the fluid flowing through the laminar flow element (hereinafter referred to as resistance flow) measured by the pressure flow sensor and the pressure in the volume between the pressure flow sensor and the downstream valve (hereinafter referred to as downstream pressure) to calculate the downstream valve flow. Specifically, the downstream valve flow calculator calculates the downstream valve flow by subtracting the time derivative of the downstream pressure from the resistance flow and multiplying it by a predetermined coefficient.

[0006] However, the downstream valve flow measured using this method sometimes contains significant noise that can affect the degree of flow control. This is because if the downstream pressure contains, for example, electrical noise, the noise is amplified due to the time derivative of the downstream pressure.

[0007] In this case, it is also possible to pass the downstream pressure or downstream valve flow through a low-pass filter to remove noise. However, this will cause a time delay due to the filter, so the actual downstream valve flow without time delay cannot be obtained.

[0008] Existing technical documents

[0009] Patent Document 1: Japanese Patent Publication No. 2004-280688 Summary of the Invention

[0010] In view of the problems described above, the present invention aims to provide a flow control device that can obtain the flow rate of fluid flowing through the downstream side valve with virtually no time delay and significantly reduced noise, and with improved responsiveness than before.

[0011] The flow control device of the present invention includes: a fluid resistance disposed on a flow channel; a downstream valve disposed on the downstream side of the fluid resistance; a downstream valve flow meter that measures the downstream valve flow rate as the flow rate of fluid flowing through the downstream valve based on a time change in the downstream pressure, which is the pressure within the internal volume between the fluid resistance and the downstream valve, and a resistance flow rate, which is the flow rate of fluid flowing through the fluid resistance; and an observer that includes a downstream valve flow rate estimation model that estimates the downstream valve flow rate based on an input parameter that changes the opening degree of the downstream valve, wherein the deviation between the measured value of the downstream valve flow rate output by the downstream valve flow meter and the estimated value of the downstream valve flow rate output by the downstream valve flow rate estimation model is fed back to the observer.

[0012] Furthermore, the flow control method of the present invention employs a flow control device, which includes a fluid resistance disposed on a flow channel and a downstream valve disposed on the downstream side of the fluid resistance. The flow control method is characterized by comprising: measuring a downstream valve flow rate, which is the flow rate of fluid flowing through the downstream valve, based on the time change of the downstream pressure, which is the pressure within the internal volume between the fluid resistance and the downstream valve, and the resistance flow rate, which is the flow rate of fluid flowing through the fluid resistance; and estimating the downstream valve flow rate using an observer, the observer comprising a downstream valve flow rate estimation model that estimates the downstream valve flow rate based on an input parameter that changes the opening degree of the downstream valve, wherein the deviation between the measured value of the downstream valve flow rate and the estimated value of the downstream valve flow rate output by the downstream valve flow rate estimation model is fed back to the observer.

[0013] With this configuration, the observer can estimate the downstream valve flow rate based on the downstream valve flow rate estimation model, in a form free from time delay and, for example, electrical noise. Furthermore, since the deviation between the measured and estimated downstream valve flow rates is fed back to the observer, in cases where the measured and estimated values ​​deviate from each other in initial values, this deviation is quickly eliminated, resulting in an estimated value representing the actual state of the flow control device. Therefore, based on the estimated downstream valve flow rate output by the observer, the responsiveness of flow control can be improved compared to previous methods.

[0014] To fully simulate the control characteristics of the flow control device and accurately estimate the flow rate of the downstream valve, a first voltage generation circuit is preferably included, which outputs a voltage corresponding to the input opening command to the downstream valve. The downstream valve flow estimation model is a model of the characteristics of the first voltage generation circuit, the downstream valve, and the downstream valve flow meter. The opening command, which is input as the input parameter, is input to the observer to estimate the flow rate of the downstream valve.

[0015] As a specific structural example for improving the accuracy of the estimated value of the downstream valve flow rate, the downstream valve flow rate estimation model can be used to simulate the time delay in the first voltage generation circuit.

[0016] In order for the observer to eliminate the error of the estimated value caused by the difference between the estimated value and the initial value as early as possible, the observer preferably further includes an observer gain section, which multiplies the deviation between the measured value of the downstream valve flow and the estimated value of the downstream valve flow by the observer gain.

[0017] In order to eliminate the deviation as early as possible when the estimated value of the downstream valve flow rate deviates significantly from the measured value and the observer cannot reflect the actual state, and in order to make the observer robust against sudden noise from outside the system when the observer can estimate the downstream valve flow rate with sufficient accuracy, the observer gain unit preferably includes: a first observer gain, used when the flow rate of the fluid flowing through the flow channel is stable at a predetermined value; and a second observer gain, which is greater than the first observer gain, used when the flow rate of the fluid flowing through the flow channel changes.

[0018] To improve the responsiveness of the control of the downstream valve flow rate compared to the past, it is preferable to further include a downstream valve controller that controls the opening degree of the downstream valve, the downstream valve controller generating the opening command based on the deviation between the target value of the set flow rate and the estimated value of the downstream valve flow rate output by the observer.

[0019] As a specific structure for feedback control based on the downstream valve flow estimated by the observer, the downstream valve controller can include: a PID controller that performs PID calculation based on the deviation between the target value of the set flow and the estimated value of the downstream valve flow output by the observer; and an opening command generator that generates the opening command corresponding to the PID calculation result from the PID controller.

[0020] To construct the downstream valve flow meter using hardware such as flow sensors used in existing flow control devices, the downstream valve flow meter may include: an upstream pressure sensor disposed upstream of the fluid resistance to measure the upstream pressure; a downstream pressure sensor disposed between the fluid resistance and the downstream valve to measure the downstream pressure; a resistance flow calculator to calculate the resistance flow based on the upstream and downstream pressures; and a downstream valve flow calculator to calculate the downstream valve flow by subtracting a value obtained by multiplying the time change of the downstream pressure by a predetermined coefficient from the resistance flow.

[0021] To further improve responsiveness by increasing the control margin of the downstream valve or suppressing fluctuations in the fluid supply pressure, the preferred flow control device further includes: an upstream valve disposed upstream of the upstream pressure sensor; and an upstream valve controller for controlling the opening of the upstream valve.

[0022] When the set flow rate increases or decreases, the opening directions of the upstream valve and the downstream valve change in opposite directions. In order to achieve the desired flow rate by rapidly changing the pressure before and after the fluid resistance, and to keep the average pressure before and after the fluid resistance at a low pressure so as to maintain the high sensitivity of the pressure-type flow sensor, it is preferable to further include an upstream valve flow calculator. The upstream valve flow calculator adds a value to the resistance flow rate by multiplying the time change of the upstream pressure by a predetermined coefficient, and calculates the upstream valve flow rate through the upstream valve. The upstream valve controller controls the opening of the upstream valve in a manner that reduces the deviation between the set flow rate and the upstream valve flow rate.

[0023] To further reduce noise impact on the upstream valve flow rate and thus improve control performance, the system preferably includes: an upstream valve flow rate calculator that adds a value equal to the time variation of the upstream pressure multiplied by a predetermined coefficient to the resistance flow rate to calculate the upstream valve flow rate through the upstream valve; and a secondary observer that includes an upstream valve flow rate estimation model that estimates the upstream valve flow rate based on input parameters that change the opening of the upstream valve, wherein the upstream valve controller controls the opening of the upstream valve in a manner that reduces the deviation between the target value of the set flow rate and the estimated value of the upstream valve flow rate output by the secondary observer.

[0024] As a specific example of a structure that can maintain a constant supply pressure of the fluid supplied to the flow control device, the upstream valve controller can be cited as an example to control the opening of the upstream valve in a way that reduces the deviation between the set pressure and the upstream pressure.

[0025] By maintaining the downstream valve opening at a predetermined opening even when the target flow rate changes, the absolute value of the pressure before and after the fluid resistance is kept low. Preferably, the upstream valve controller controls the opening of the upstream valve in a manner that reduces the deviation between the set voltage corresponding to the opening maintained by the downstream valve and the voltage applied to the downstream valve. With this configuration, the sensitivity of the downstream valve flow meter performing pressure-based flow measurement can be improved. For example, simply keeping the downstream valve opening fully open or near its opening maintains the pressure before and after the fluid resistance at a low pressure. Thus, when using a pressure-based flow detection method, the control responsiveness can be improved by increasing the measurement sensitivity.

[0026] As a prerequisite for the downstream valve flow meter to measure the flow rate of the downstream valve, in order to clearly separate the fluid resistance from the downstream valve and obtain an accurate volume value to improve the accuracy of the downstream valve flow rate measurement, the fluid resistance is preferably a laminar flow element, a flow splitting element, or a throttling orifice.

[0027] Traditionally, in flow control devices used in semiconductor manufacturing processes, when an anomaly occurs in the flow sensor or similar device, the abnormality is notified by sending an alarm to the user's or controller's control device or by setting the flow rate displayed externally to a negative value. Furthermore, in the event of an anomaly, the process is interrupted even during operation by changing the control valve to a safe state such as complete closure. Even after restarting, interrupted processes rarely achieve the same results and effects as before the interruption. Therefore, especially in batch processing systems, the damage caused by interruptions to wafer scrap increases; for example, the yield may be zero or essentially zero during an interruption.

[0028] In order to reduce the losses caused by the interruption of the process as described above, for example, even if an anomaly occurs in the various sensors used to measure the flow rate, the process can continue to ensure a certain level of yield. It is preferable to also include an anomaly mode switching unit. The anomaly mode switching unit causes the observer to operate in an anomaly mode at least when the downstream valve flow meter malfunctions. In the anomaly mode, the measured value of the downstream valve flow rate output by the downstream valve flow meter is not fed back to the observer.

[0029] With this configuration, in abnormal modes, the output of the downstream valve flow meter, whose values ​​may be unreliable due to malfunctions, can be disregarded, and flow control can continue using only the estimated value of the downstream valve flow rate output by the observer. Therefore, since flow control can continue based on a value that approximates the actual flow rate, for example, the wafer yield in the process can be maintained at a predetermined value.

[0030] In order to maintain a high wafer yield and other values ​​by using parameters that are close to the estimated flow rate at a normal time point when the downstream valve flow meter malfunctions, the observer preferably further includes: an observer gain unit that, at least when the downstream valve flow meter is operating normally, multiplies the deviation between the measured value of the downstream valve flow rate and the estimated value of the downstream valve flow rate by the observer gain; a normal value storage unit that, at least when the downstream valve flow meter is operating normally, stores the deviation between the measured value of the downstream valve flow rate and the estimated value of the downstream valve flow rate, or a value calculated based on the deviation, as a normal value; and a recovery unit that, in the abnormal mode, inputs the value based on the normal value into the downstream valve flow estimation model.

[0031] In order to enable flow control to continue using only the estimated value of the observer in the event of an anomaly in the downstream valve flow meter with a simple structure, without using the measured value of the downstream valve flow meter, the observer may include an observer gain unit that multiplies the deviation between the measured value and the estimated value of the downstream valve flow by the observer gain, and the observer gain unit uses zero as the observer gain in the anomaly mode.

[0032] As a specific method of the abnormal mode switching unit, it can be listed that the downstream valve flow meter is operating normally or has generated an abnormality based on the measured value of the downstream valve flow output by the downstream valve flow meter or the internal parameters used in the downstream valve flow meter.

[0033] In order to obtain the same flow control characteristics as the flow control device of the present invention by updating the existing flow control device, such as the one that includes a fluid resistance provided on the flow channel and a downstream valve provided on the downstream side of the fluid resistance, it is preferable to use a flow control device program. The computer performs the following functions by executing the flow control device program: a downstream valve flow meter, which measures the downstream valve flow rate as the flow rate of the fluid flowing through the downstream valve based on the time change of the downstream pressure, which is the pressure in the internal volume between the fluid resistance and the downstream valve, and the resistance flow rate, which is the flow rate of the fluid flowing through the fluid resistance; and an observer, which includes a downstream valve flow estimation model that estimates the downstream valve flow rate based on the input parameter of changing the opening of the downstream valve, and the deviation between the measured value of the downstream valve flow rate output by the downstream valve flow meter and the estimated value of the downstream valve flow rate output by the downstream valve flow estimation model is fed back to the observer.

[0034] In addition, the program for the flow control device can be sent electronically or stored on program storage media such as CDs, DVDs, and USB flash drives.

[0035] Thus, the flow control device of the present invention, by having an observer for estimating the downstream valve flow rate as the flow rate of fluid flowing through the downstream valve, can obtain a downstream valve flow rate with reduced time delay and noise. Therefore, according to the present invention, responsiveness and accuracy in flow control can be improved compared to the past. Simple Explanation of the Diagram

[0036] Figure 1 is a schematic diagram of the flow control device in the first embodiment of the present invention. Figure 2 is a simplified schematic block diagram of the control system of the downstream valve of the flow control device according to the first embodiment. Figure 3 is a detailed block diagram of the observer and downstream valve controller of the first embodiment. Figure 4 is a structural block diagram of a first modified example of the flow control device in the first embodiment. Figure 5 is a schematic diagram of a second variation of the flow control device in the first embodiment. Figure 6 is a schematic diagram of the flow control device in the second embodiment of the present invention. Figure 7 is a schematic diagram of the flow control device in the third embodiment of the present invention. Figure 8 is a schematic diagram of the flow control device in the fourth embodiment of the present invention. Figure 9 is a schematic diagram of the flow control device in the normal mode according to the fifth embodiment of the present invention. Figure 10 is a schematic diagram of the flow control device in the abnormal mode of the fifth embodiment. Figure 11 is a schematic diagram of the operation of the flow control device in normal mode and abnormal mode in the fifth embodiment. Implementation

[0037] The flow control device 100 of the first embodiment will be described with reference to Figures 1 to 3.

[0038] The flow control device 100 of the first embodiment is used to supply a process gas, a rare gas, or a dilution gas to a chamber at a set flow rate, for example, in a semiconductor manufacturing process. Here, the set flow rate includes, for example, a step-like time change that increases or decreases from one target value to another. The flow control device 100 is configured to follow this step flow command of the set flow rate within a predetermined time. Furthermore, the predetermined time can be set to a time that satisfies the quality requirements of the manufactured semiconductor.

[0039] As shown in Figure 1, the flow control device 100 includes a fluid device consisting of a sensor and a valve disposed on the flow channel, and a control device COM responsible for controlling the fluid device. Furthermore, the flow channel is formed, for example, as a plurality of internal flow channels formed within a module (not shown), each internal flow channel having an opening at at least one end on the mounting surface of the component on which the fluid device is mounted.

[0040] The flow channel is configured sequentially from the upstream side with a supply pressure sensor (not shown), an upstream valve V1, an upstream pressure sensor P1, a fluid resistance R, a downstream pressure sensor P2, and a downstream valve V2. Here, the fluid resistance R is, for example, a laminar flow element, which generates a pressure difference before and after it corresponding to the flow rate of the gas passing through it.

[0041] The upstream pressure sensor P1 measures the pressure of the gas introduced into the upstream volume VL1, which is the volume between the upstream valve V1 and the fluid resistance R in the flow channel. In the following description, the pressure measured by the upstream pressure sensor P1 is also referred to as the upstream pressure.

[0042] Downstream pressure sensor P2 measures the pressure of the gas entering downstream volume VL2, which is the volume between the fluid resistance R in the flow channel and downstream valve V2. In the following description, the pressure measured by downstream pressure sensor P2 is also referred to as downstream pressure.

[0043] In the first embodiment, the upstream pressure sensor P1 and the downstream pressure sensor P2 are, for example, identical in type, and the gas is guided from the flow channel to the pressure-sensitive surface formed by the thin film. For example, the displacement of the pressure-sensitive surface is measured using a capacitive displacement sensor, and the pressure is measured based on this displacement. In this way, the upstream pressure sensor P1 and the downstream pressure sensor P2 respectively measure the pressure of the two volumes formed by the upstream valve V1, the fluid resistance R, and the downstream valve V2.

[0044] In the first embodiment, the upstream valve V1 and the downstream valve V2 are identical, for example, piezoelectric valves that drive the valve body relative to the valve member via a piezoelectric element. In the first embodiment, the upstream valve V1 controls the pressure within the upstream volume based on the upstream pressure measured by the upstream pressure sensor P1. On the other hand, the downstream valve V2, which is provided at the most downstream side in the fluid device, controls the overall gas flow rate exiting the fluid device.

[0045] Next, the control device COM will be explained in detail.

[0046] The control device COM is, for example, a computer equipped with a CPU, memory, A / D converter, D / A converter, and input / output means. Its functions are implemented using a microcomputer board, or a general-purpose computer. The control device COM uses programs stored in memory to coordinate the operation of various devices, functioning at least as a resistance flow calculator 1, downstream valve flow calculator 2, observer 3, downstream valve controller 4, first voltage generation circuit 5, upstream valve flow calculator 6, upstream valve controller 7, and second voltage generation circuit 8.

[0047] The resistance flow calculator 1, together with the upstream pressure sensor P1, the fluid resistance R, and the downstream pressure sensor P2, constitutes a so-called pressure-type flow sensor. That is, the resistance flow calculator 1 takes the upstream pressure measured by the upstream pressure sensor P1 and the downstream pressure measured by the downstream pressure sensor P2 as inputs, calculates the resistance flow as the gas flow rate through the fluid resistance R, and outputs the result to the downstream valve flow calculator 2.

[0048] Here, the flow rate calculation formula used in the resistance flow rate calculator 1 can be the one employed by existing pressure flow sensors. The resistance flow rate calculated by the resistance flow rate calculator 1 changes continuously, but with a specified time delay relative to the actual flow rate flowing through the downstream side valve V2, which is controlled by the downstream side valve V2.

[0049] The flow rate through the downstream valve V2 will henceforth also be referred to as the downstream valve flow rate. Furthermore, in the first embodiment, the value calculated based on the outputs of the upstream pressure sensor P1 and the downstream pressure sensor P2 is defined as the measured value of the downstream valve flow rate. On the other hand, the downstream valve flow rate calculated based on the internal output of the downstream valve controller 4 and a mathematical model, without directly using the outputs of the upstream pressure sensor P1 and the downstream pressure sensor P2, is defined as the estimated value.

[0050] The downstream valve flow calculator 2 calculates the downstream valve flow rate, which is the gas flow rate exiting the downstream valve V2, based on the resistance flow rate calculated by the resistance flow calculator 1 and the downstream pressure measured by the downstream pressure sensor P2, and outputs the result to the observer 3. More specifically, the downstream valve flow calculator 2 calculates the downstream valve flow rate based on the fact that the difference between the resistance flow rate and the downstream valve flow rate is equal to the time change of the downstream pressure. The resistance flow rate is the gas flow rate in the downstream volume VL2 between the inflow fluid resistance R and the downstream valve V2, and the downstream valve flow rate is the gas flow rate exiting the downstream volume VL2. Specifically, assuming the downstream pressure is P2, the size of the downstream volume VL2 is V2, the gas temperature is T, the gas constant is RG, and the mass is n2, if the equation of state for the gas is applied with the downstream volume VL2 as the object, then P2 = n2RGT / V2 is derived. Furthermore, since the resistance flow rate QR flowing into the downstream volume VL2 is proportional to the difference between the downstream valve flow rate QV2 flowing out of the downstream volume VL2 and the time derivative of the mass n2, the downstream valve flow rate QV2 can ultimately be calculated using the following formula: QV2 = QRA·d / dt (P2): where d / dt is the time derivative operator, and A is a constant determined by the gas temperature T, gas constant RG, etc.

[0051] In the first embodiment, the upstream pressure sensor P1, the fluid resistance R, the downstream pressure sensor P2, and the resistance flow calculator 1 constitute a so-called pressure-type flow sensor. Furthermore, by adding the downstream valve flow calculator 2 to the pressure-type flow sensor, a downstream valve flow meter VFS is constructed.

[0052] Observer 3 estimates the downstream valve flow rate based on the mathematical control system model and the input parameters that change the opening degree of downstream valve V2. The downstream valve flow rate estimated by observer 3 is then output to downstream valve controller 4.

[0053] The downstream valve controller 4 controls the opening of the downstream valve V2 in a manner that reduces the deviation between the user-set flow rate and the downstream valve flow rate estimated by the observer 3. In the first embodiment, the downstream valve controller 4 generates an opening command corresponding to the deviation and outputs it to the first voltage generation circuit 5.

[0054] The first voltage generation circuit 5 applies a voltage corresponding to the opening command to the downstream valve V2. A time delay, for example a major delay, is generated in the first voltage generation circuit 5 relative to the opening command.

[0055] The upstream valve flow calculator 6 calculates the upstream valve flow rate, which is the gas flow rate flowing from the upstream valve V1 into the upstream volume VL1, based on the resistance flow rate calculated by the resistance flow calculator 1 and the upstream pressure measured by the upstream pressure sensor P1, and outputs the result to the upstream valve controller 7. More specifically, the upstream valve flow calculator 6 calculates the upstream valve flow rate based on the fact that the difference between the upstream valve flow rate and the resistance flow rate is equal to the time change of the upstream pressure. The upstream valve flow rate is the gas flow rate flowing into the upstream volume VL1 between the upstream valve V1 and the fluid resistance R, and the resistance flow rate is the gas flow rate flowing out of the upstream volume VL1. Specifically, assuming the upstream pressure is P1, the size of the upstream volume VL1 is V1, the gas temperature is T, the gas constant is RG, and the mass is n1, if the equation of state for the gas is applied to the upstream volume VL1, then P1 = n1RGT / V1 is derived. Furthermore, since the difference between the upstream valve flow rate QV1 flowing into the upstream volume VL1 and the resistance flow rate QR flowing out of the upstream volume VL1 is proportional to the time differential value of the mass n1, the upstream valve flow rate QV1 can ultimately be calculated using the following formula: QV1 = QR + A·d / dt (P1): where d / dt is the time differential operator, and A is a constant determined by the gas temperature T, gas constant RG, etc.

[0056] Furthermore, the upstream valve flow calculator 6 shares the upstream pressure sensor P1, fluid resistance R, downstream pressure sensor P2, and resistance flow calculator 1, which constitute a pressure-type flow sensor in the downstream valve flow meter VFS. That is, the upstream valve flow calculator 6 functions as an upstream valve flow meter by sharing a pressure-type flow sensor with the downstream valve flow meter VFS.

[0057] The upstream valve controller 7 controls the upstream valve V1 based on the user-set flow rate and the upstream valve flow rate calculated by the upstream valve flow calculator 6. That is, the upstream valve controller 7 controls the upstream valve V1 in a manner that reduces the deviation between the target value of the user-set flow rate and the measured value of the upstream valve flow rate. More specifically, the upstream valve controller 7 uses PID calculation based on the deviation between the set flow rate and the upstream valve flow rate to generate an opening command representing the opening degree that the upstream valve V1 should achieve, and inputs this opening command to the second voltage generation circuit. The second voltage generation circuit applies a voltage corresponding to the opening command to the upstream valve V1. That is, unlike the downstream valve V2, the upstream valve V1 is controlled based on the measured value, not the estimated value from the observer. Furthermore, the set flow rates input to the upstream valve controller 7 and the downstream valve controller 4 are the same and are input synchronously.

[0058] Next, referring to the block diagrams in Figures 2 and 3, we will specifically describe the control system, observer 3, and downstream valve controller 4 related to the downstream valve V2.

[0059] As shown in the block diagram of Figure 2, the control system of the downstream valve V2 includes: a real system that measures the downstream valve flow rate based on the hardware output and affects the actual downstream valve flow rate; and a hypothetical system that estimates the downstream valve flow rate based on a mathematical model. The real system consists of the downstream valve controller 4, the first voltage generation circuit 5, the downstream valve V2, and the downstream valve flow meter VFS. On the other hand, the hypothetical system consists of the observer 3.

[0060] The downstream valve flow rate estimated by observer 3 is fed back to downstream valve controller 4. That is, the deviation between the target flow rate and the estimated downstream valve flow rate is input to downstream valve controller 4. Furthermore, the deviation between the downstream valve flow rate estimated by observer 3 and the downstream valve flow rate measured by the downstream valve flow meter is fed back to observer 3. The same opening command input from downstream valve controller 4 to the actual system is input to observer 3, and the estimated downstream valve flow rate corresponding to the opening command is output.

[0061] As shown in the block diagram of Figure 3, the observer 3 has a downstream valve flow estimation model 31 for simulating the first voltage generation circuit 5, the downstream valve V2, and the downstream valve flow meter VFS, which are the controlled objects in the real system. That is, the downstream valve flow estimation model 31 consists of a first voltage generation circuit simulation unit 5M, a downstream valve simulation unit V2M, and a downstream valve flow meter simulation unit VFM, which correspond to the first voltage generation circuit 5, the downstream valve V2, and the downstream valve flow meter VFS, respectively.

[0062] The first voltage generation circuit simulation unit 5M simulates the time delay of the voltage actually output by the first voltage generation circuit 5 relative to the opening command. Furthermore, the downstream valve simulation unit V2M simulates the control characteristics of the downstream valve V2 (i.e., the piezoelectric valve) by referring to theoretical formulas, and outputs the downstream valve flow rate corresponding to the voltage applied to the downstream valve V2. Additionally, the downstream valve simulation unit V2M can simulate the valve characteristics by referring to a lookup table storing relationships between flow rate, valve pressures, temperature, and voltage equivalent to the opening degree. Furthermore, the downstream valve flow meter simulation unit VFM simulates the time delay in the measured value relative to the actual downstream valve flow rate. Here, the time delay simulated by the downstream valve flow meter simulation unit VFM is not caused by the misalignment of the control point and the measurement point, but by internal circuit calculations. Since the downstream valve flow estimation model 31 is a mathematical model, the estimated value of the downstream valve flow rate output according to the input opening command does not contain overlapping electrical noise, but only reflects the change in the downstream valve flow rate.

[0063] Furthermore, the observer 3 also includes an observer gain unit 32, which multiplies the deviation between the measured and estimated downstream valve flow rate by a predetermined observer gain OG. An integrator is provided corresponding to the observer gain OG, and the output of the integrator is applied to the voltage output by the analog unit 5M of the first voltage generation circuit.

[0064] Finally, the downstream valve controller 4 is described. The downstream valve controller 4 includes: a PID controller 41, into which the deviation between the set flow rate and the downstream valve flow rate estimated by the observer 3 is input; and an opening command generator 42, which outputs an opening command corresponding to the PID calculation result output by the PID controller 41. That is, the downstream valve flow rate measured by the downstream valve flow meter VFS is only used for feedback to the observer 3, and is not directly used to determine the voltage applied to the downstream valve V2. The downstream valve V2 is controlled based on the deviation between the target value of the set flow rate (free of electrical noise) and the estimated value of the flow rate by the observer 3.

[0065] The flow control device 100 with this structure can estimate the downstream flow rate of the fluid flowing through the downstream valve V2 through the observer 3 in a manner that is substantially free of time delay and electrical noise. Since the downstream valve controller 4 controls the opening of the downstream valve V2 based on this estimated value, flow control with better responsiveness than before can be achieved.

[0066] Furthermore, since the upstream valve V1 is controlled to reduce the deviation between the measured upstream valve flow rate and the set flow rate, and the downstream valve V2 is controlled to reduce the deviation between the estimated flow rate estimated by the observer 3 and the set flow rate, the pressure difference across the fluid resistance R can be changed rapidly. For example, when the set flow rate is increased compared to the current situation, the upstream valve controller 7 controls the upstream valve V1 to increase the upstream pressure, and the downstream valve controller 4 controls the downstream valve V2 to decrease the downstream pressure. When the set flow rate is decreased compared to the current situation, the opposite action is achieved. Therefore, since the upstream and downstream pressures can be changed in opposite directions using two valves, the increase or decrease of flow rate can be adjusted rapidly. Moreover, the average pressure of the upstream and downstream pressures can be kept at a relatively constant level. Furthermore, by adjusting this average pressure to a low pressure suitable for calculating the resistance flow rate, the sensitivity of the pressure-type flow sensor can be maintained at a high level. As a result, the sensitivity of the measured upstream valve flow rate and the estimated downstream valve flow rate can be improved, further enhancing the responsiveness in flow control.

[0067] Next, a first variation of the flow control device 100 according to the first embodiment will be described with reference to FIG4. In the first variation, the structure of the observer gain unit 32 of the observer 3 is different from that in the aforementioned embodiment. Specifically, the observer gain unit 32 includes: a first observer gain OG1 used when the flow rate of the fluid flowing in the flow channel is stable; a second observer gain OG2 with a value greater than the first observer gain OG1 used when the flow rate of the fluid flowing in the flow channel changes by a predetermined amount or more; and a switch SW that determines which observer gain to use based on the state of the flow. An integrator is provided corresponding to each observer gain OG1, OG2, and the output of the integrator is applied to the voltage output by the analog unit 5M of the first voltage generation circuit.

[0068] For example, when the target value of the set flow rate is kept within a certain range, the switch SW multiplies the first observer gain OG1 by the deviation between the measured value and the estimated value of the downstream valve flow rate. When the target value of the set flow rate rises or falls from one value to another, the switch SW multiplies the second observer gain OG2 by the aforementioned deviation.

[0069] Due to the above configuration, the voltage output of the analog section 5M of the first voltage generation circuit is significantly corrected using the second observer gain OG2 when the flow rate changes drastically. As a result, deviations from the estimated value of observer 3 are corrected in a short time. On the other hand, when the target flow rate is set within a certain range and the flow rate is stable, the first observer gain OG1 is used to suppress the correction sensitivity relative to the deviation. That is, when there is essentially no difference between the estimated value and the measured value, observer 3 is less susceptible to sudden disturbances and becomes highly robust.

[0070] Next, a second variation of the flow control device 100 of the first embodiment will be described with reference to FIG5. In the second variation, the observer estimates not only the flow rate of the downstream valve but also the flow rate of the upstream valve, further realizing highly responsive flow control. Specifically, a sub-observer 9 is provided, which has an upstream valve flow rate estimation model that estimates the flow rate of the upstream valve based on the input parameter of changing the opening degree of the upstream valve V1. The upstream valve controller 7 controls the opening degree of the upstream valve V1 in a manner that reduces the deviation between the target value of the set flow rate and the estimated value of the upstream valve flow rate output by the sub-observer 9. In addition, the specific structure of the sub-observer 9 corresponds to the observer 3 for estimating the downstream valve flow rate shown in FIGS. 2 and 3. That is, the sub-observer 9 estimates the upstream valve flow rate based on the opening command output by the upstream valve controller 7, and multiplies the deviation between the estimated value and the measured value calculated by the upstream valve flow rate calculator 6 by a predetermined observer gain, and feeds it back into the upstream valve flow rate estimation model.

[0071] According to this second variation, it is possible to obtain estimated values ​​for both the upstream and downstream valve flow rates from an observer based on a mathematical model, thereby achieving flow control with further improved responsiveness and control stability.

[0072] Next, the flow control device 100 of the second embodiment of the present invention will be described with reference to FIG6. Furthermore, in the following descriptions of each embodiment, the same reference numerals are used for parts corresponding to those described in the first embodiment.

[0073] In the flow control device of the second embodiment, the control structure of the downstream valve V2 is the same as that of the first embodiment, but the difference is that the upstream valve V1 is controlled based on pressure rather than flow rate.

[0074] Specifically, the upstream valve controller controls the upstream valve V1 based on the deviation between the set pressure set by the user and the upstream pressure measured by the upstream pressure sensor P1. Here, when the downstream valve flow rate is stable at the set flow rate, the set pressure is set based on the pressure difference that should be maintained before and after the fluid resistance R.

[0075] According to this flow control device 100, the flow rate through the downstream valve V2 can be controlled while maintaining a constant supply pressure and being less susceptible to interference from pressure fluctuations from the upstream side. In other words, the pressure difference across the fluid resistance R is less prone to rapid changes as in the first embodiment, but instead, the stability of flow control is improved. For example, if the supplied fluid is a gaseous product obtained by vaporizing liquid raw materials, it is easy to maintain a constant flow rate even when the production rate is unstable. Furthermore, since the downstream valve flow rate is estimated using the observer 3 and controlled based on its estimated value, the responsiveness of flow control can be improved compared to the existing simple combination of pressure feedback control and flow feedback control.

[0076] Next, the flow control device 100 of the third embodiment of the present invention will be described with reference to FIG7. Furthermore, in the following descriptions of each embodiment, the same reference numerals are used for parts corresponding to those described in the first embodiment.

[0077] Compared to the first embodiment, the upstream valve controller 7 in the flow control device 100 of the third embodiment has a different structure. Specifically, the voltage applied to the downstream valve V2 from the first voltage generation circuit 5 is fed back to the upstream valve controller 7, controlling the opening of the upstream valve V1 based on the deviation from the user-set voltage. The set voltage is, for example, a voltage equivalent to the opening maintained in the downstream valve V2. In pressure-based flow measurement using the upstream pressure sensor P1, fluid resistance R, and downstream pressure sensor P2, lower pressure results in higher sensitivity. Therefore, the user-set voltage is a voltage equivalent to the opening at a low pressure that achieves the desired flow sensitivity. The downstream valve controller 4 controls the voltage applied to the downstream valve V2 based on the upstream pressure, ensuring that the estimated downstream valve flow rate of the observer 3 matches the set flow rate. In this state, the upstream valve controller 7 closes the opening of the upstream valve V1 by reducing the absolute value of the pressure before and after the fluid resistance R, thereby reducing the gas supply. As a result, the pressure of the gas inside the flow control device 100 is reduced while achieving the desired flow rate, thereby improving the sensitivity of flow rate measurement.

[0078] Next, the flow control device 100 of the fourth embodiment of the present invention will be described with reference to FIG8.

[0079] The flow control device 100 of the fourth embodiment is shown in FIG8. Compared with the first embodiment, the difference is that the upstream valve V1 and the upstream valve controller 7 are omitted.

[0080] Even this third embodiment of the flow control device 100, compared with the existing flow control device 100 with a single valve, can perform responsive flow control based on the time delay estimated by the observer 3 and the downstream valve flow with less noise.

[0081] Next, the flow control device 100 of the fifth embodiment of the present invention will be described with reference to Figures 9 to 11.

[0082] In the fifth embodiment, the flow control device 100, for example, in the event of an anomaly in the downstream valve flow meter VFS or the sensor constituting the downstream valve flow meter VFS, does not use the measured value of the downstream valve flow meter VFS in flow control, but continues flow control only with the estimated value output from the observer 3. Specifically, the flow control device 100 of the fifth embodiment is shown in Figures 9 and 10, and differs from the first embodiment in that it includes an abnormal mode switcher AMS, a normal value storage unit, and a recovery unit RB. Each part will be described in detail below.

[0083] In the event of an anomaly, at least in the case of an anomaly occurring in the downstream valve flow meter (VFS), the abnormal mode switcher (AMS) switches the control structure of the flow control device 100 from the normal mode shown in FIG9 to the abnormal mode shown in FIG10. More specifically, the abnormal mode switcher (AMS) monitors the measured value of the flow rate output by the downstream valve flow meter (VFS) or the internal parameters used within the downstream valve flow meter (VFS), and determines whether an anomaly has occurred in the downstream valve flow meter (VFS) based on the monitored values. Furthermore, if the abnormal mode switcher (AMS) determines that an anomaly has occurred in the downstream valve flow meter (VFS), it cuts off the loop in the control structure of the flow control device 100 as shown in FIG10, so that the measured value of the flow rate output by the downstream valve flow meter (VFS) is not used in the flow control loop. Instead, the abnormal mode switcher (AMS) switches the control structure to form a flow control loop based solely on the flow rate estimated by the observer 3.

[0084] The abnormal mode determination performed by the Abnormal Mode Switcher (AMS) is, for example, performed when the flow rate remains relatively stable at a constant value. In other words, if the target flow rate changes abruptly or the flow rate is in a transitional state, the AMS will not perform anomaly determination based on the aforementioned deviation. That is, while the target flow rate remains constant, the AMS monitors, for example, the deviation between the flow rate measured by the downstream valve flow meter (VFS) and the target flow rate. If the absolute value of the deviation exceeds a predetermined abnormal mode switching determination threshold, it determines that an anomaly has occurred in the downstream valve flow meter (VFS). Furthermore, after anomaly determination, the AMS continues to display an alarm to notify the user that an anomaly has occurred.

[0085] When the flow control device 100 is operating in normal mode, the normal value storage unit NM stores the value where the deviation (innovation) between the flow rate measured by the downstream valve flow meter VFS and the flow rate estimated by the observer 3 meets a predetermined benchmark. Specifically, when the target value of the set flow rate remains stable at a certain value, the normal value storage unit NM stores the aforementioned refresh as a normal value if the absolute value of the difference between the target value of the set flow rate and the flow rate output by the downstream valve flow meter VFS is less than the normal value determination threshold. The normal value storage unit NM may, for example, store only the latest normal value, or it may store multiple normal values ​​along with the date and time.

[0086] When the control structure of the flow control device 100 is switched to abnormal mode by the abnormal mode switcher AMS, the recovery unit RB inputs a fixed value calculated by multiplying the normal value stored in the normal value storage unit NM by a predetermined value into the downstream valve flow estimation model 31. That is, in abnormal mode, the outputs of the downstream valve flow meter VFS and the downstream valve flow meter simulation unit VFM are not input into the recovery unit RB, which constitutes the observer gain unit 32. Instead, the recovery unit RB uses the normal value input when operating in normal mode to calculate the output of the observer gain unit 32. Therefore, the value output from the observer gain unit 32 in abnormal mode is based on the assumption that the modeling error of the downstream valve flow estimation model 31 is the same as in normal mode.

[0087] The control operation of the flow control device 100 of the fifth embodiment of this structure in normal mode and abnormal mode will be described with reference to FIG11.

[0088] The operation in normal mode is basically the same as the control operation in the first embodiment. In a stable state, when the absolute value of the deviation between the flow value measured by the downstream valve flow meter VFS and the flow value estimated by the analog unit VFM of the downstream valve flow meter is less than the normal value judgment threshold, the value is stored as a normal value in the normal value storage unit NM.

[0089] Furthermore, if an anomaly occurs in the downstream valve flow meter VFS, and under stable conditions, the absolute value of the difference between the measured value output by the downstream valve flow meter VFS and the set flow rate exceeds the anomaly mode switching threshold, the anomaly mode switching unit determines that an anomaly has occurred. The anomaly mode switching unit switches the control structure of the flow control device 100 to an anomaly mode, preventing the output of the downstream valve flow meter VFS from being used by the observer 3, while outputting the output from the observer gain unit 32 from the recovery unit RB. That is, the recovery unit RB outputs the fixed value obtained by multiplying the normal value stored in the normal value storage unit NM by a predetermined value to the downstream valve flow estimation model 31. As a result, the state of the observer 3 is restored to the state before the anomaly occurred, and from this state, the flow feedback control in the flow control device 100 continues only with the estimated value of the observer 3.

[0090] The flow control device 100 according to this fifth embodiment can continue flow control without interruption, even if the sensor or other components constituting the downstream valve flow meter VFS malfunction, based solely on the estimated flow rate output by the observer 3. Furthermore, since the flow rate estimated by the observer 3 is a value calculated based on a refresh in normal mode and corrected for modeling errors, deviations from the actual flow rate can be reduced. Therefore, the flow rate supplied from the flow control device 100 can have only an acceptable error relative to the set flow rate, maintaining a higher wafer yield compared to process interruptions.

[0091] A variation of the flow control device 100 according to the fifth embodiment will be described.

[0092] The normal value stored in the normal value storage unit NM may not be the aforementioned refresh value, but rather the value output by the observer gain unit 32 in normal mode. In this case, the recovery unit RB only needs to input the normal value as is into the downstream valve flow estimation model 31.

[0093] The anomaly detection algorithm in the AMS (Abnormal Mode Switch) is not limited to those described above. For example, an anomaly can be determined when the output of the downstream valve flow meter (VFS) is out of range. Furthermore, an anomaly can be determined based on the outputs of the various sensors and circuits constituting the downstream valve flow meter (VFS).

[0094] For example, in order to use the original structure of the flow control device 100 of the first embodiment and to continue to perform flow control with a specified control accuracy even in abnormal mode, the abnormal mode switcher AMS can be configured to change the observer gain of the observer gain unit 32 to zero in abnormal mode.

[0095] Other implementation methods will be described.

[0096] The upstream and downstream valves are not limited to piezoelectric valves; they can be driven by other actuators. For example, each valve can be a solenoid valve, and the valves do not necessarily have to be the same model.

[0097] Fluid resistance is not limited to laminar flow elements; for example, it can be a flow divider element used to construct throttling orifices and thermal flow sensors. In short, fluid resistance is a resistance body located in the flow channel, which can be achieved by separating the fluid resistance from the downstream valve, causing it to change to present a different pressure than other parts.

[0098] The flow rate over the fluid resistance is not limited to being measured by a pressure-type flow sensor. For example, a flow divider element can be used as the fluid resistance, and the flow rate can be measured by a thermal flow sensor with a pair of temperature-measuring elements installed on the branch flow path formed by a thin tube bypassing the flow divider element. In this case, a separate downstream pressure sensor is installed to measure the pressure in the downstream volume between the flow divider element and the downstream valve, thereby enabling control equivalent to that of the flow control device in the first embodiment.

[0099] The input parameters input to the observer to estimate the downstream valve flow rate are not limited to opening commands. Input parameters can be, for example, a set flow rate or a voltage input to the downstream valve. The elements included in the downstream valve flow rate estimation model can be added or removed from the components of the actual system, depending on the type of input parameters. Furthermore, elements that provide an ideal response in each component with negligible time delay can be removed from the elements constituting the downstream valve flow rate estimation model. That is, the flow rate estimation model is not limited to the components shown in each embodiment. The downstream valve flow rate estimation model can be, for example, a mathematical equation established based on the physical laws satisfied by the various components of the control system, or it can be experimentally established based on a step response, etc.

[0100] Furthermore, variations of various embodiments and elements of each embodiment can be combined with each other without departing from the spirit of the present invention.

[0101] 100: Flow control device P1: Upstream pressure sensor P2: Downstream pressure sensor V1: Upstream side valve V2: Downstream valve VL1: Upstream side volume VL2: Downstream volume COM: Control device 1: Resistance Flow Calculator 2: Downstream valve flow calculator 3: Observer 31: Downstream valve flow estimation model V2M: Downstream side valve simulation unit 5M: Analog Section of First Voltage Generation Circuit VFM: Downstream side valve flow meter simulation unit 32: Observer Gain Section OG1: First Observer Gain OG2: Second Observer Gain SW: Switcher 4: Downstream side valve controller 41: PID controller 42: Opening Instruction Generator 5: First voltage generation circuit 6: Upstream side valve flow calculator 7: Upstream side valve controller 8: Second voltage generation circuit 9: Secondary Observer AMS: Abnormal Mode Switcher NM: Normal value storage unit RB: Recovery Department

Claims

1. A flow control device, comprising: Fluid resistance set on the flow channel; A downstream valve located on the downstream side of the fluid resistance; The downstream valve flow meter measures the downstream valve flow rate as the flow rate of the fluid flowing through the downstream valve, based on the time change of the downstream pressure, which is the pressure in the internal volume between the fluid resistance and the downstream valve, and the resistance flow rate, which is the flow rate of the fluid flowing through the fluid resistance. The observer includes a downstream valve flow estimation model that estimates the flow rate of the downstream valve based on an input parameter that changes the opening degree of the downstream valve; and a first voltage generation circuit that outputs a voltage corresponding to the input opening degree command to the downstream valve. The deviation between the measured value of the downstream valve flow rate output by the downstream valve flow meter and the estimated value of the downstream valve flow rate output by the downstream valve flow estimation model is fed back to the observer. The downstream valve flow estimation model includes a first voltage generation circuit simulation unit configured to simulate the characteristics of the first voltage generation circuit.

2. The flow control device as claimed in claim 1, wherein, The downstream valve flow estimation model is a model of the characteristics of the first voltage generation circuit, the downstream valve, and the downstream valve flow meter. The opening command, which is input as the input parameter, is given to the observer to estimate the downstream valve flow.

3. The flow control device as claimed in claim 2, wherein, The downstream valve flow estimation model simulates the time delay in the first voltage generation circuit.

4. The flow control device as claimed in claim 1, wherein, The observer also includes an observer gain unit, which multiplies the deviation between the measured value of the downstream valve flow and the estimated value of the downstream valve flow by the observer gain.

5. The flow control device as claimed in claim 4, wherein, The observer gain unit includes: a first observer gain, used when the flow rate of the fluid flowing through the channel is stable at a predetermined value; and a second observer gain, which is greater than the first observer gain, used when the flow rate of the fluid flowing through the channel changes.

6. The flow control device as claimed in claim 2, wherein, The flow control device further includes a downstream valve controller that controls the opening degree of the downstream valve. The downstream valve controller generates the opening command based on the deviation between the target value of the set flow rate and the estimated value of the downstream valve flow rate output by the observer.

7. The flow control device as claimed in claim 6, wherein, The downstream valve controller includes: a PID controller that performs PID calculation based on the deviation between the target value of the set flow rate and the estimated value of the downstream valve flow rate output by the observer; and an opening command generator that generates the opening command corresponding to the PID calculation result from the PID controller.

8. The flow control device as claimed in claim 1, wherein, The downstream valve flow meter includes: an upstream pressure sensor disposed upstream of the fluid resistance to measure the upstream pressure; a downstream pressure sensor disposed between the fluid resistance and the downstream valve to measure the downstream pressure; a resistance flow calculator to calculate the resistance flow based on the upstream and downstream pressures; and a downstream valve flow calculator to calculate the downstream valve flow by subtracting a value obtained by multiplying the time change of the downstream pressure by a predetermined coefficient from the resistance flow.

9. The flow control device as claimed in claim 8, wherein, The flow control device further includes: an upstream valve disposed on the upstream side of the upstream pressure sensor; and an upstream valve controller for controlling the opening degree of the upstream valve.

10. The flow control device as claimed in claim 9, wherein, The flow control device further includes an upstream valve flow calculator, which adds a value equal to the time change of the upstream pressure multiplied by a predetermined coefficient to the resistance flow to calculate the upstream valve flow. The upstream valve controller controls the opening of the upstream valve in a manner that reduces the deviation between the set flow and the upstream valve flow.

11. The flow control device as claimed in claim 9, wherein, The flow control device further includes: an upstream valve flow calculator, which adds a value equal to the time change of the upstream pressure multiplied by a predetermined coefficient to the resistance flow to calculate the upstream valve flow rate through the upstream valve; and a secondary observer, including an upstream valve flow estimation model that estimates the upstream valve flow rate based on an input parameter that changes the opening of the upstream valve, wherein the upstream valve controller controls the opening of the upstream valve in a manner that reduces the deviation between the target value of the set flow rate and the estimated value of the upstream valve flow rate output by the secondary observer.

12. The flow control device as claimed in claim 9, wherein, The upstream valve controller controls the opening of the upstream valve in a manner that reduces the deviation between the set pressure and the upstream pressure.

13. The flow control device as claimed in claim 9, wherein, The upstream valve controller controls the opening of the upstream valve in such a way that the deviation between the set voltage, which is equivalent to the opening maintained by the downstream valve, and the voltage applied to the downstream valve is reduced.

14. The flow control device as claimed in claim 1, wherein, The fluid resistance is a laminar flow element, a flow splitting element, or a throttling orifice.

15. The flow control device as claimed in claim 1, wherein, The flow control device further includes an abnormal mode switching unit, which, at least in the event of an abnormality in the downstream valve flow meter, causes the observer to operate in an abnormal mode, in which the measured value of the downstream valve flow output by the downstream valve flow meter is not fed back to the observer.

16. The flow control device as claimed in claim 15, wherein, The observer further includes: an observer gain unit, which, at least when the downstream valve flow meter is operating normally, multiplies the deviation between the measured value of the downstream valve flow and the estimated value of the downstream valve flow by the observer gain; a normal value storage unit, which, at least when the downstream valve flow meter is operating normally, stores the deviation between the measured value of the downstream valve flow and the estimated value of the downstream valve flow, or a value calculated according to a specified method for the deviation, as a normal value; and a recovery unit, which, in the abnormal mode, inputs the value based on the normal value into the downstream valve flow estimation model.

17. The flow control device as claimed in claim 15, wherein, The observer includes an observer gain unit, which multiplies the deviation between the measured value of the downstream valve flow and the estimated value of the downstream valve flow by the observer gain. The observer gain unit uses zero as the observer gain in the abnormal mode.

18. The flow control device as claimed in claim 15, wherein, The abnormal mode switching unit determines whether the downstream valve flow meter is operating normally or has malfunctioned based on the measured value of the downstream valve flow meter output by the downstream valve flow meter or the internal parameters used in the downstream valve flow meter.

19. A flow control method employing a flow control device, the flow control device comprising a fluid resistance disposed on a flow channel and a downstream valve disposed downstream of the fluid resistance, the flow control method comprising: The downstream valve flow rate, which is the flow rate of the fluid flowing through the downstream valve, is determined by the time change of the downstream pressure, which is the pressure in the internal volume between the fluid resistance and the downstream valve, and the resistance flow rate, which is the flow rate of the fluid flowing through the fluid resistance. The downstream valve flow rate is estimated using an observer, the observer including a downstream valve flow rate estimation model that estimates the downstream valve flow rate based on input parameters that change the opening degree of the downstream valve; and a first voltage generation circuit that outputs a voltage corresponding to the input opening degree command to the downstream valve, the deviation between the measured value of the downstream valve flow rate and the estimated value of the downstream valve flow rate output by the downstream valve flow rate estimation model being fed back to the observer, the downstream valve flow rate estimation model including a first voltage generation circuit simulation unit configured to simulate the characteristics of the first voltage generation circuit.

20. A program storage medium for storing a program for use in a flow control device, the flow control device comprising a fluid resistance disposed on a flow channel and a downstream valve disposed downstream of the fluid resistance, wherein, The computer performs the following function by executing the program: downstream valve flow meter, which measures the downstream valve flow rate as the flow rate of the fluid flowing through the downstream valve based on the time change of the downstream pressure, which is the pressure in the internal volume between the fluid resistance and the downstream valve, and the resistance flow rate, which is the flow rate of the fluid flowing through the fluid resistance. The observer includes a downstream valve flow estimation model that estimates the flow rate of the downstream valve based on an input parameter that changes the opening degree of the downstream valve; and a first voltage generation circuit that outputs a voltage corresponding to the input opening degree command to the downstream valve. The deviation between the measured value of the downstream valve flow rate output by the downstream valve flow meter and the estimated value of the downstream valve flow rate output by the downstream valve flow estimation model is fed back to the observer. The downstream valve flow estimation model includes a first voltage generation circuit simulation unit configured to simulate the characteristics of the first voltage generation circuit.

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