JP7535469B2 - Flow control device, flow control method, and program for flow control device - Google Patents

Description

The present invention relates to a flow control device that controls the flow rate of a fluid, for example, in a semiconductor manufacturing process.

For example, mass flow controllers, which are flow control devices that package various fluid devices and control mechanisms, are used to control the flow rates of various gases introduced into a process chamber.

A typical flow control device includes a flow sensor provided in the flow path, a downstream valve provided 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 matches a time-varying set flow rate set by the user.

However, since the point at which the fluid is measured by the flow sensor and the point at which the fluid is controlled by the downstream valve are offset by a certain distance in the flow direction, there is a time delay in the measured flow rate by the flow sensor compared to the flow rate passing through the downstream valve. This time delay contained in the measured flow rate poses a problem when trying to achieve the responsiveness of flow control required in semiconductor manufacturing processes.

In order to solve these problems, attempts have been made to apply a downstream valve flow measuring device capable of measuring the actual flow rate passing through the downstream valve (hereinafter also referred to as the downstream valve flow rate) to a flow control device. For example, a downstream valve flow measuring device includes a conventional pressure type flow sensor and a downstream valve flow rate calculator that calculates the downstream valve flow rate. The downstream valve flow rate calculator calculates the downstream valve flow rate using the flow rate of the fluid passing through the laminar flow element that is being measured by the pressure type flow sensor (hereinafter also referred to as the resistance flow rate) and the pressure in the volume between the pressure type flow sensor and the downstream valve (hereinafter also referred to as the downstream pressure). Specifically, the downstream valve flow rate calculator calculates the downstream valve flow rate by subtracting a value obtained by multiplying the time derivative of the downstream pressure by a predetermined coefficient from the resistance flow rate.

However, the downstream valve flow measured using this method may contain noise large enough to cause problems in flow control. This is because if the downstream pressure contains, for example, electrical noise, the noise is amplified by the time derivative of the downstream pressure.

In such cases, it may be possible to remove noise by passing the downstream pressure or downstream valve flow through a low-pass filter, but doing so would cause a time delay due to the filter, making it impossible to obtain the actual downstream valve flow without time delay.

JP 2004-280688 A

The present invention was made in consideration of the above-mentioned problems, and aims to provide a flow control device that can obtain the flow rate of fluid passing through a downstream valve with almost no time delay and with significantly reduced noise, and that can improve responsiveness compared to conventional devices.

The flow control device according to the present invention comprises a fluid resistance provided in a flow path, a downstream valve provided downstream of the fluid resistance, a downstream valve flow measuring device that measures the downstream valve flow rate, which is the flow rate of fluid passing through the downstream valve, based on a resistance flow rate, which is the flow rate of fluid flowing through the fluid resistance, and a time change in downstream pressure, which is the pressure in the internal volume between the fluid resistance and the downstream valve, and an observer having a downstream valve flow rate estimation model that estimates the downstream valve flow rate based on input parameters that change the opening of the downstream valve, and is characterized in that the observer is configured to feed back the deviation between the measured value of the downstream valve flow rate output by the downstream valve flow measuring device and the estimated value of the downstream valve flow rate output by the downstream valve flow rate estimation model.

The flow control method according to the present invention is a flow control method using a flow control device equipped with a fluid resistance provided in a flow path and a downstream valve provided downstream of the fluid resistance, and includes measuring a downstream valve flow rate, which is the flow rate of fluid passing through the downstream valve, based on a resistance flow rate, which is the flow rate of fluid flowing through the fluid resistance, and a time change in downstream pressure, which is the pressure in the internal volume between the fluid resistance and the downstream valve, and estimating the downstream valve flow rate using an observer having a downstream valve flow rate estimation model that estimates the downstream valve flow rate based on input parameters that change the opening of the downstream valve, and is characterized in that 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.

In this way, the observer can estimate the downstream valve flow rate based on the downstream valve flow rate estimation model without including time delays and, for example, electrical noise. In addition, the deviation between the measured and estimated values of the downstream valve flow rate is fed back to the observer, so that if there is a discrepancy between the measured and estimated values at the initial values, etc., such a discrepancy is quickly eliminated and an estimated value indicating the actual state of the flow control device can be obtained. As a result, the responsiveness of flow control can be improved compared to conventional methods based on the estimated value of the downstream valve flow rate output by the observer.

In order to be able to accurately estimate the downstream valve flow rate by fully simulating the control characteristics of the flow control device, the device may further include a first voltage generation circuit that outputs a voltage to the downstream valve according to an input opening command, the downstream valve flow rate estimation model is a model of the characteristics of the first voltage generation circuit, the downstream valve, and the downstream valve flow rate measuring device, and the observer receives the opening command as the input parameter and estimates the downstream valve flow rate.

A specific example of a configuration for increasing the accuracy of the downstream valve flow rate estimate is one in which the downstream valve flow rate estimation model simulates a time delay in the first voltage generation circuit.

In order for the observer to be able to quickly eliminate errors in the estimated value due to the difference between the estimated value and the initial value, the observer may further include an observer gain section that multiplies the deviation between the measured value of the downstream valve flow rate and the estimated value of the downstream valve flow rate by an observer gain.

When the estimated value of the downstream valve flow rate deviates significantly from the measured value and the observer is unable to reflect the actual state, it is possible to quickly eliminate such deviation, and when the observer can estimate the downstream valve flow rate with sufficient accuracy, to make the observer robust against sudden noise not originating from the system, the observer gain section may include a first observer gain that is used when the flow rate of the fluid flowing through the flow path is stable at a predetermined value, and a second observer gain that is used when the flow rate of the fluid flowing through the flow path is changing and has a value greater than the first observer gain.

To improve the responsiveness of the control of the downstream valve flow rate compared to the conventional system, a downstream valve controller that controls the opening of the downstream valve may be further provided, and the downstream valve controller may be configured to generate the opening command based on the deviation between a target value of the set flow rate and an estimated value of the downstream valve flow rate output by the observer.

A specific example of the feedback control based on the downstream valve flow rate estimated by the observer is one in which the downstream valve controller includes a PID controller that performs PID calculations based on the deviation between a target value for 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 from the PID controller according to the PID calculation results.

To configure the downstream valve flow measuring device using hardware such as a flow sensor used in conventional flow control devices, the downstream valve flow measuring device may include an upstream pressure sensor that is provided upstream of the fluid resistance and measures the upstream pressure, a downstream pressure sensor that is provided between the fluid resistance and the downstream valve and measures the downstream pressure, a resistance flow calculator that calculates the resistance flow rate based on the upstream pressure and the downstream pressure, and a downstream valve flow calculator that calculates the downstream valve flow rate by subtracting from the resistance flow rate a value obtained by multiplying the amount of change in the downstream pressure over time by a predetermined coefficient.

To increase the control margin of the downstream valve and suppress fluctuations in the fluid supply pressure to further improve responsiveness, the flow control device may further include an upstream valve provided upstream of the upstream pressure sensor and an upstream valve controller that controls the opening of the upstream valve.

When the set flow rate rises or falls, the upstream valve and the downstream valve change their openings in opposite directions, and the pressure before and after the fluid resistance is changed at high speed to obtain the desired flow rate at high speed, while the average pressure before and after the fluid resistance is kept low to maintain high sensitivity as a pressure-type flow sensor. To this end, an upstream valve flow rate calculator is further provided that calculates the upstream valve flow rate passing through the upstream valve by adding a value obtained by multiplying the amount of change in the upstream pressure over time by a predetermined coefficient from the resistance flow rate, and the upstream valve controller controls the opening of the upstream valve so as to reduce the deviation between the set flow rate and the upstream valve flow rate.

To further improve control performance by reducing the effect of noise on the upstream valve flow rate, an upstream valve flow rate calculator that calculates the upstream valve flow rate passing through the upstream valve by adding a value obtained by multiplying the amount of change in the upstream pressure over time by a predetermined coefficient to the resistance flow rate, and a sub-observer having 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, may be further provided, and the upstream valve controller may control the opening of the upstream valve so as to reduce 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.

A specific example of a configuration that can keep the supply pressure of the fluid supplied to the flow control device constant is one in which the upstream valve controller controls the opening of the upstream valve so that the deviation between the set pressure and the upstream pressure is small.

In order to maintain the opening of the downstream valve at a predetermined opening even when the target value of the set flow rate changes, and to maintain the absolute value of the pressure before and after the fluid resistance at a low pressure, the upstream valve controller only needs to control the opening of the upstream valve so that the deviation between the set voltage corresponding to the opening maintained by the downstream valve and the voltage applied to the downstream valve is small. In this way, the sensitivity of the downstream valve flow meter that performs flow measurement based on pressure can be improved. For example, the opening of the downstream valve can be maintained at or near a fully open state, and the pressure before and after the fluid resistance can be maintained at a low pressure. In this way, when a pressure-based flow detection method is used, the measurement sensitivity can be increased and the control responsiveness can be improved.

The prerequisite for the downstream valve flow measurement by the downstream valve flow measurement device is that the volume between the fluid resistance and the downstream valve can be clearly separated, allowing an accurate volume value to be obtained and improving the measurement accuracy of the downstream valve flow rate. In order to do this, the fluid resistance may be a laminar flow element, a dividing element, or an orifice.

Conventionally, when an abnormality occurs in a flow sensor or the like in a flow control device used in a semiconductor manufacturing process, the abnormality is notified to the user or the master control device by outputting an alarm, or by changing the flow rate displayed externally to an impossible value such as a negative value. Furthermore, when an abnormality occurs, even if the process is in progress, the control valve is changed to a safe state such as fully closed and the process is interrupted. When a process is interrupted, restarting it often does not produce the same results or effects as before the interruption. For this reason, especially in batch processing type process equipment, the damage to wafer scrap caused by interruptions is large, and for example, the yield when interrupted is zero or almost zero.

In order to reduce losses due to interruptions to the process as described above, and to ensure a certain degree of yield by continuing the process even if an abnormality occurs in the various sensors used to measure flow rates, it is sufficient to further include an abnormality mode switching unit that operates the observer in an abnormality mode in which the observer does not provide feedback of the measured value of the downstream valve flow rate output by the downstream valve flow rate measuring device when an abnormality occurs in the downstream valve flow rate measuring device.

In this way, in abnormal mode, flow control can be continued using only the estimated value of the downstream valve flow rate output from the observer, without using the output of the downstream valve flow rate measuring device whose value is unreliable due to a malfunction or the like. Therefore, flow control can be continued based on a value that is relatively close to the actual flow rate, making it possible, for example, to maintain the yield of wafers during processing at a predetermined value.

In order to enable the observer to output an estimated value close to the flow rate at that time by using the parameters used when the downstream valve flow measuring device was normal when an abnormality occurs and to maintain a high wafer yield, etc., the observer may further include an observer gain unit that multiplies the deviation between the measured downstream valve flow rate and the estimated downstream valve flow rate by an observer gain when at least the downstream valve flow measuring device is operating normally, a normal value storage unit that stores the deviation between the measured downstream valve flow rate and the estimated downstream valve flow rate, or a value obtained by performing a predetermined calculation on the deviation, as a normal value when at least the downstream valve flow measuring device is operating normally, and a rollback unit that inputs a value based on the normal value to the downstream valve flow rate estimation model in the abnormal mode.

In a simple configuration, in the event of an abnormality occurring in the downstream valve flow measuring instrument, flow control can be continued using only the estimate of the observer without using the measurement value of the downstream valve flow measuring instrument for flow control. The flow control observer can include an observer gain unit that multiplies the deviation between the measurement value of the downstream valve flow rate and the estimate value of the downstream valve flow rate by an observer gain, and the observer gain unit is configured to use a value of zero as the observer gain in the abnormality mode.

Specific examples of the abnormality mode switching unit include a unit configured to determine whether the downstream valve flow measuring device is operating normally or whether an abnormality has occurred based on the measurement value of the downstream valve flow rate output by the downstream valve flow measuring device or on internal parameters used in the downstream valve flow measuring device.

In order to obtain flow control characteristics equivalent to those of the flow control device of the present invention by updating the program of an existing flow control device equipped with a fluid resistance provided in a flow path and a downstream valve provided downstream of the fluid resistance, a downstream valve flow rate, which is the flow rate of the fluid passing through the downstream valve, based on the resistance flow rate, which is the flow rate of the fluid flowing through the fluid resistance, and the time change in the downstream pressure, which is the pressure in the internal volume between the fluid resistance and the downstream valve, and an observer having a downstream valve flow rate estimation model that estimates the downstream valve flow rate based on input parameters that change the opening of the downstream valve, a flow control device program configured to cause a computer to function as such may be used, in which the observer feeds back the deviation between the measured value of the downstream valve flow rate output by the downstream valve flow rate measurement device and the estimated value of the downstream valve flow rate output by the downstream valve flow rate estimation model.

The program for the flow control device may be distributed electronically or may be recorded on a program recording medium such as a CD, DVD, or flash memory.

In this way, the flow control device according to the present invention is equipped with the observer that estimates the downstream valve flow rate, which is the flow rate of the flow passing through the downstream valve, so that it is possible to obtain a downstream valve flow rate with reduced time delay and noise. Therefore, with the present invention, it is possible to improve the responsiveness and accuracy of flow control compared to the conventional art.

1 is a schematic diagram showing a configuration of a flow rate control device according to a first embodiment of the present invention; FIG. 2 is a block diagram showing an outline of a control system for a downstream valve of the flow rate control device of the first embodiment. FIG. 4 is a block diagram showing details of an observer and a downstream valve controller according to the first embodiment. FIG. 4 is a block diagram showing a configuration of a first modified example of the flow rate control device in the first embodiment. FIG. 4 is a schematic diagram showing a configuration of a second modified example of the flow rate control device in the first embodiment. FIG. 5 is a schematic diagram showing the configuration of a flow rate control device according to a second embodiment of the present invention. FIG. 11 is a schematic diagram showing the configuration of a flow rate control device according to a third embodiment of the present invention. FIG. 13 is a schematic diagram showing the configuration of a flow rate control device according to a fourth embodiment of the present invention. FIG. 13 is a schematic diagram showing a configuration of a flow control device in a normal mode according to a fifth embodiment of the present invention. FIG. 13 is a schematic diagram showing the configuration of a flow rate control device in an abnormal mode according to the fifth embodiment. 13A and 13B are schematic diagrams showing an operation image of the flow rate control device in a normal mode and an abnormal mode in the fifth embodiment.

The flow control device 100 according to the first embodiment will be described with reference to Figures 1 to 3.

The flow control device 100 of the first embodiment is used, for example, in a semiconductor manufacturing process to supply a process gas or a dilution gas such as a noble gas to a chamber at a set flow rate. Here, the set flow rate includes, for example, a step-like time change that rises or falls in a step-like manner from one target value to another target value. The flow control device 100 is configured to follow such a step flow rate command for the set flow rate within a specified time. The specified time can be set as a time that can satisfy the quality of the semiconductor being manufactured.

Specifically, as shown in FIG. 1, the flow control device 100 includes a fluid device consisting of a sensor and a valve provided in a flow path, and a control device COM that controls the fluid device. The flow paths are formed as multiple internal flow paths formed in a block (not shown), for example, and at least one end of the internal flow paths opens to a component mounting surface of the block to which the fluid device is attached.

In order from the upstream side, the flow path is provided 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, and generates a differential pressure according to the gas flow rate flowing before and after it.

The upstream pressure sensor P1 measures the pressure of the gas charged in the upstream volume VL1, which is the volume in the flow path between the upstream valve V1 and the fluid resistance R. In the following explanation, the pressure measured by the upstream pressure sensor P1 is also referred to as the upstream pressure.

The downstream pressure sensor P2 measures the pressure of the gas charged in the downstream volume VL2, which is the volume between the fluid resistance R and the downstream valve V2 in the flow path. In the following explanation, the pressure measured by the downstream pressure sensor P2 is also referred to as the downstream pressure.

In the first embodiment, the upstream pressure sensor P1 and the downstream pressure sensor P2 are, for example, of the same type, and gas is guided from a flow path to a pressure-sensitive surface formed, for example, by a diaphragm. The displacement of the pressure-sensitive surface is measured, for example, by a capacitance-type displacement sensor, and each pressure is measured from that displacement. In this way, the upstream pressure sensor P1 and the downstream pressure sensor P2 respectively measure the pressures of the two volumes formed by the upstream valve V1, the fluid resistance R, and the downstream valve V2.

In the first embodiment, the upstream valve V1 and the downstream valve V2 are of the same type, e.g., a piezo valve in which a valve body is driven relative to a valve material by a piezo element. In the first embodiment, the upstream valve V1 controls the pressure in 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 flowing out of the fluid device.

Next, we will explain the control device COM in detail.

The control device COM is a so-called computer equipped with, for example, a CPU, memory, A/D converter, D/A converter, and input/output means. Specifically, its functions are realized using a microcomputer board, but a general computer may also be used. The control device COM executes a flow control device program stored in the memory and various devices work together to perform the functions of at least the resistance flow rate calculator 1, downstream valve flow rate calculator 2, observer 3, downstream valve controller 4, first voltage generation circuit 5, upstream valve flow rate calculator 6, upstream valve controller 7, and second voltage generation circuit 8.

The resistance flow rate 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 rate sensor. In other words, the resistance flow rate 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 rate, which is the gas flow rate flowing through the fluid resistance R, and outputs the result to the downstream valve flow rate calculator 2.

The flow rate calculation formula used in the resistance flow rate calculator 1 can be the same as that used in existing pressure-type flow rate sensors. The resistance flow rate calculated by the resistance flow rate calculator 1 changes continuously, but there is a certain time delay with respect to the actual flow rate passing through the downstream valve V2, which is realized by controlling the downstream valve V2.

Hereinafter, the flow rate passing through the downstream valve V2 is also referred to as the downstream valve flow rate. In addition, in the first embodiment, the downstream valve flow rate is defined as a measured value calculated based on the outputs of the upstream pressure sensor P1 and the downstream pressure sensor P2. 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 an estimated value.

The downstream valve flow rate calculator 2 calculates the downstream valve flow rate, which is the gas flow rate flowing out from the downstream valve V2, based on the resistance flow rate calculated by the resistance flow rate 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 rate calculator 2 calculates the downstream valve flow rate based on the fact that a constant multiple of the difference between the resistance flow rate, which is the gas flow rate flowing into the downstream volume VL2 between the fluid resistance R and the downstream valve V2, and the downstream valve flow rate, which is the gas flow rate flowing out from the downstream volume VL2, is equal to the time change amount of the downstream pressure. Specifically, when the downstream pressure is _P2 , the size of the downstream volume VL2 is _V2 , the gas temperature is T, the gas constant is R _G , and the mass is _n2 , _P2 = _n2 R _G T/ _V2 is derived by applying the gas state equation to the downstream volume VL2. Furthermore, since the time differential value of mass _n2 is proportional to the difference between the resistance flow rate _QR flowing into the downstream volume VL2 and the downstream valve flow rate _QV2 flowing out from the downstream volume VL2, the downstream valve flow rate _QV2 can ultimately be calculated using the following formula: _QV2 = _QR - A d/dt ( _P2 ): Here, d/dt is the time differential operator, and A is a constant determined by the gas temperature T, gas constant _RG , etc.

In the first embodiment, the upstream pressure sensor P1, the fluid resistance R, the downstream pressure sensor P2, and the resistance flow rate calculator 1 constitute a so-called pressure-type flow rate sensor. In addition, the downstream valve flow rate calculator 2 is added to the pressure-type flow rate sensor to constitute a downstream valve flow rate measuring device VFS.

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

The downstream valve controller 4 controls the opening of the downstream valve V2 so that the deviation between the set flow rate set by the user and the downstream valve flow rate estimated by the observer 3 is reduced. In the first embodiment, the downstream valve controller 4 generates an opening command according to the deviation and outputs it to the first voltage generating circuit 5.

The first voltage generating circuit 5 applies a voltage corresponding to the opening command to the downstream valve V2. In this first voltage generating circuit 5, a time delay, for example a first-order delay, occurs with respect to the opening command.

The upstream valve flow rate calculator 6 calculates an upstream valve flow rate, which is the gas flow rate flowing from the upstream valve V1 to the upstream volume VL1, based on the resistance flow rate calculated by the resistance flow rate 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 rate calculator 6 calculates the upstream valve flow rate based on the fact that a constant multiple of the difference between the upstream valve flow rate, which 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, which is the gas flow rate flowing out of the upstream volume VL1, is equal to the amount of change in the upstream pressure over time. Specifically, when the upstream pressure is _P1 , the size of the upstream volume VL1 is _V1 , the gas temperature is T, the gas constant is R _G , and the mass is _n1 , applying the gas state equation to the upstream volume VL1 results in P1= _{n1R G} T/ _V1 . Furthermore, since the time differential value of mass _n1 is proportional to the difference between the upstream valve flow rate _QV1 flowing into the upstream volume VL1 and the resistance flow rate _QR flowing out from the upstream volume VL1, the upstream valve flow rate _QV1 can ultimately be calculated using the following formula: _QV1 = _QR + A·d/dt( _P1 ): Here, d/dt is the time differential operator, and A is a constant determined by the gas temperature T, gas constant _RG , etc.

The upstream valve flow calculator 6 shares the upstream pressure sensor P1, fluid resistance R, downstream pressure sensor P2, and resistance flow calculator 1 that constitute the pressure-type flow sensor in the downstream valve flow measuring device VFS. In other words, the upstream valve flow calculator 6 is configured to share the pressure-type flow sensor with the downstream valve flow measuring device VFS and function as an upstream valve flow measuring device.

The upstream valve controller 7 controls the upstream valve V1 based on the set flow rate set by the user and the upstream valve flow rate calculated by the upstream valve flow rate calculator 6. That is, the upstream valve controller 7 controls the upstream valve V1 so that the deviation between the target value of the set flow rate set by the user and the measured value of the upstream valve flow rate is small. More specifically, the upstream valve controller 7 generates an opening command indicating the opening degree to be achieved by the upstream valve V1 by PID calculation based on the deviation between the set flow rate and the upstream valve flow rate, and inputs the opening command to the second voltage generation circuit. The second voltage generation circuit applies a voltage according 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 on an estimate by an observer. In addition, the set flow rates input to the upstream valve controller 7 and the downstream valve controller 4 are the same and are input in synchronization.

Next, the details of the control system related to the downstream valve V2, the observer 3, and the downstream valve controller 4 will be described with reference to the block diagrams in Figures 2 and 3.

As shown in the block diagram of Figure 2, the control system of the downstream valve V2 is composed of a real system that measures the downstream valve flow rate based on the output of the hardware and affects the actual downstream valve flow rate, and an imaginary system that estimates the downstream valve flow rate based on a mathematical model. The real system is composed of the downstream valve controller 4, the first voltage generating circuit 5, the downstream valve V2, and the downstream valve flow rate measuring device VFS. On the other hand, the imaginary system is composed of the observer 3.

The downstream valve flow rate estimated by the observer 3 is fed back to the downstream valve controller 4. That is, the deviation between the target value of the set flow rate and the estimated value of the downstream valve flow rate is input to the downstream valve controller 4. In addition, the deviation between the downstream valve flow rate estimated by the observer 3 and the downstream valve flow rate measured by the downstream valve flow rate measuring device is fed back to the observer 3. The observer 3 receives the same opening command as that input to the real system from the downstream valve controller 4, and outputs an estimated value of the downstream valve flow rate according to the opening command.

As shown in the detailed block diagram of FIG. 3, the observer 3 has a downstream valve flow estimation model 31 that simulates the first voltage generation circuit 5, downstream valve V2, and downstream valve flow meter VFS, which are the control targets in the real system. That is, the downstream valve flow estimation model 31 is composed 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, downstream valve V2, and downstream valve flow meter VFS, respectively.

The first voltage generating circuit simulation unit 5M simulates the time delay of the voltage actually output by the first voltage generating circuit 5 in response to the opening command. The downstream valve simulation unit V2M simulates the control characteristics of the downstream valve V2, i.e., the piezo valve, for example, by referring to a theoretical formula, and outputs the downstream valve flow rate corresponding to the voltage applied to the downstream valve V2. The downstream valve simulation unit V2M may simulate the valve characteristics by referring to a lookup table that stores the relationship between the flow rate, the pressure before and after the valve, the temperature, the voltage corresponding to the opening, etc. In addition, the downstream valve flow rate measurement device simulation unit VFM simulates the time delay that appears in the measured value with respect to the actual downstream valve flow rate. Here, the time delay simulated by the downstream valve flow rate measurement device simulation unit VFM is not due to the difference between the control point and the measurement point, but is due to the electric circuit or calculation. Because the downstream valve flow rate estimation model 31 is a mathematical model, the estimated value of the downstream valve flow rate that is output when an opening command is input is not superimposed with electrical noise, and only the change in the downstream valve flow rate is reflected.

The observer 3 further includes an observer gain section 32 that multiplies the deviation between the measured value and the estimated value of the 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 added to the voltage output by the first voltage generation circuit simulation section 5M.

Finally, the downstream valve controller 4 will be described. The downstream valve controller 4 is equipped with a PID controller 41 to 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 that outputs an opening command according to the PID calculation result output by the PID controller 41. In other words, the downstream valve flow rate measured by the downstream valve flow rate meter VFS is used only for feedback to the observer 3, and is not used directly 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, which does not include electrical noise, and the flow rate estimated by the observer 3.

With the flow control device 100 configured in this way, the observer 3 can estimate the downstream valve flow rate of the fluid passing through the downstream valve V2 with almost no time delay or electrical noise. The downstream valve controller 4 controls the opening of the downstream valve V2 based on this estimated value, achieving flow control with better responsiveness than before.

In addition, the upstream valve V1 is controlled so that the deviation between the measured upstream valve flow rate and the set flow rate is small, and the downstream valve V2 is controlled so that the deviation between the estimated flow rate estimated by the observer 3 and the set flow rate is small, so that the differential pressure before and after the fluid resistance R can be changed at high speed. For example, when the set flow rate is to be increased from the current state, the upstream valve controller 7 controls the upstream valve V1 so that the upstream pressure increases, and the downstream valve controller 4 controls the downstream valve V2 so that the downstream pressure decreases. When the set flow rate becomes smaller than the current state, the reverse operation described above is realized. Therefore, the upstream pressure and the downstream pressure can be changed in the opposite directions by the two valves, so that the increase or decrease in the flow rate can be adjusted at high speed. Furthermore, the average pressure of the upstream pressure and the front downstream pressure can be kept at a nearly constant pressure. In addition, by adjusting this average pressure to a low pressure suitable for calculating the resistance flow rate, the sensitivity as a pressure-type flow sensor can also be kept high. As a result, the sensitivity of the measured value of the upstream valve flow rate and the estimated value of the downstream valve flow rate can be increased, further improving the responsiveness in flow rate control.

Next, a first modified example of the flow control device 100 of the first embodiment will be described with reference to FIG. 4. In this first modified example, the configuration of the observer gain unit 32 of the observer 3 is different from that of the above-mentioned embodiment. Specifically, the observer gain unit 32 includes a first observer gain OG1 that is used when the flow rate of the fluid flowing through the flow path is stable, a second observer gain OG2 that is used when the flow rate of the fluid flowing through the flow path changes by a predetermined amount or more and has a value larger than the first observer gain OG1, and a switch SW that determines which observer gain to use depending on the state of the flow rate. An integrator is provided corresponding to each observer gain OG1, OG2, and the output of the integrator is added to the voltage output by the first voltage generation circuit simulation unit 5M.

The switch SW, for example, multiplies the first observer gain OG1 by the deviation between the measured and estimated downstream valve flow rates in the section where the target value of the set flow rate is maintained at a constant value, and multiplies the second observer gain OG2 by the deviation when the target value of the set flow rate rises from one value to another or falls.

Because of this configuration, when the flow rate changes significantly, the second observer gain OG2 is used and the voltage value output by the first voltage generation circuit simulation unit 5M is significantly corrected. As a result, the deviation from the value estimated by the observer 3 is corrected in a short time. On the other hand, when the target value of the set flow rate is in a constant value range and the flow rate is stable, the first observer gain OG1 is used and the correction sensitivity to the deviation is suppressed. In other words, when there is almost no difference between the estimated value and the measured value, the observer 3 is less susceptible to sudden disturbances and is in a state of high robustness.

Next, a second modified example of the flow control device 100 of the first embodiment will be described with reference to FIG. 5. In the second modified example, not only the downstream valve flow rate but also the upstream valve flow rate is estimated by the observer, realizing flow control with better response. Specifically, a sub-observer 9 having an upstream valve flow rate estimation model that estimates the upstream valve flow rate based on an input parameter that changes the opening of the upstream valve V1 is further provided, and the upstream valve controller 7 controls the opening of the upstream valve V1 so that 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 becomes small. Note that the specific configuration of the sub-observer 9 corresponds to the configuration of the observer 3 that estimates the downstream valve flow rate shown in FIG. 2 and FIG. 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 the deviation between the estimated value and the measured value calculated by the upstream valve flow rate calculator 6 is multiplied by a predetermined observer gain and fed back into the upstream valve flow rate estimation model.

In this way, with the second variant, both the upstream valve flow rate and the downstream valve flow rate can be obtained as estimates by an observer based on a mathematical model, making it possible to achieve flow rate control with improved responsiveness and control stability.

Next, a flow control device 100 according to a second embodiment of the present invention will be described with reference to FIG. 6. In the following description of each embodiment, parts corresponding to those described in the first embodiment will be given the same reference numerals.

The flow control device of the second embodiment has the same control configuration for the downstream valve V2 as the first embodiment, but differs in that the upstream valve V1 is controlled based on pressure rather than flow rate.

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, the set pressure is set based on the pressure difference that should be maintained across the fluid resistance R when the downstream valve flow rate is stable at the set flow rate.

With such a flow control device 100, the downstream valve flow rate passing through the downstream valve V2 can be controlled while maintaining a constant supply pressure and being less susceptible to disturbances due to pressure fluctuations from the upstream side. In other words, the differential pressure before and after the fluid resistance R is less likely to change as quickly as in the first embodiment, but the stability of the flow rate control is improved. For example, when the fluid being supplied is a raw material gas obtained by vaporizing a liquid raw material, it becomes easier to continue supplying a constant flow rate even if the amount generated is unstable. In addition, since the downstream valve flow rate is estimated by the observer 3 and control is performed based on the estimated value, the responsiveness of the flow rate control can be improved compared to the conventional combination of a simple pressure feedback control and a flow rate feedback control.

Next, a flow control device 100 according to a third embodiment of the present invention will be described with reference to FIG. 7. In the following description of each embodiment, parts corresponding to those described in the first embodiment will be given the same reference numerals.

The flow control device 100 of the third embodiment has a different configuration of the upstream valve controller 7 compared to the first embodiment. That is, the voltage applied to the downstream valve V2 from the first voltage generating circuit 5 is fed back to the upstream valve controller 7, and the opening of the upstream valve V1 is controlled based on the deviation from the set voltage set by the user. For example, a voltage equivalent to the opening maintained in the downstream valve V2 is input as the set voltage. The lower the pressure, the higher the sensitivity of the pressure-based flow measurement using the upstream pressure sensor P1, the fluid resistance R, and the downstream pressure sensor P2. Therefore, the set voltage is set by the user to a voltage equivalent to the opening at which the pressure is reduced to a low pressure at which the desired flow sensitivity can be achieved. The downstream valve controller 4 controls the voltage applied to the downstream valve V2 according to the upstream pressure, and controls so that the estimated value of the downstream valve flow rate by the observer 3 matches the set flow rate. In this state, the upstream valve controller 7 closes the opening of the upstream valve V1 so that the absolute value of the pressure before and after the fluid resistance R becomes smaller, and throttles the supply of gas. As a result, the gas pressure inside the flow control device 100 can be reduced while achieving the desired flow rate, thereby increasing the sensitivity of the flow rate measurement.

Next, a flow control device 100 according to a fourth embodiment of the present invention will be described with reference to FIG.

The flow control device 100 of the fourth embodiment differs from the first embodiment in that the upstream valve V1 and the upstream valve controller 7 are omitted, as shown in FIG. 8.

Even with the flow control device 100 of the third embodiment, compared to a conventional flow control device 100 equipped with a single valve, it is possible to achieve flow control with good response based on the time delay and downstream valve flow rate estimated by the observer 3 with less noise.

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

The flow control device 100 of the fifth embodiment is configured so that, for example, when an abnormality occurs in the downstream valve flow measuring device VFS or a sensor constituting the downstream valve flow measuring device VFS, the measurement value of the downstream valve flow measuring device VFS is not used for flow control, and flow control is continued using only the estimated value output from the observer 3. Specifically, as shown in Figures 9 and 10, the flow control device 100 of the fifth embodiment differs from the first embodiment in that it is equipped with an abnormality mode switcher AMS, a normal value memory unit, and a rollback unit RB. Each unit will be described in detail below.

When an abnormality occurs at least in the downstream valve flow measuring device VFS, the abnormality mode switch AMS switches the control configuration of the flow control device 100 from the normal mode shown in FIG. 9 to the abnormal mode shown in FIG. 10. More specifically, the abnormality mode switch AMS monitors the flow measurement value output by the downstream valve flow measuring device VFS or the internal parameters used in the downstream valve flow measuring device VFS, and determines whether an abnormality has occurred in the downstream valve flow measuring device VFS based on the monitored value. In addition, when the abnormality mode switch AMS determines that an abnormality has occurred in the downstream valve flow measuring device VFS, the control configuration of the flow control device 100 is disconnected so that the flow measurement value output by the downstream valve flow measuring device VFS is not used in the flow control loop as shown in FIG. 10. Instead, the abnormality mode switch AMS switches the control configuration so that the flow control loop is configured only with the flow rate estimated by the observer 3.

The abnormality mode switch AMS judges the abnormality mode, for example, in a steady state where the flow rate is kept at a nearly constant value. In other words, when the target value of the set flow rate changes stepwise and the flow rate is in a transient state, the abnormality mode switch AMS does not judge the abnormality based on the deviation described above. In other words, during the period when the target value of the set flow rate is kept constant, the abnormality mode switch AMS monitors, for example, the deviation between the flow rate value measured by the downstream valve flow meter VFS and the target value of the set flow rate, and judges that an abnormality has occurred in the downstream valve flow meter VFS if the absolute value of the deviation exceeds a predetermined abnormality mode switching judgment threshold. After judging the abnormality, the abnormality mode switch AMS also continues to display an alarm to notify the user that an abnormality has occurred.

The normal value memory unit NM stores as a normal value a value when the deviation (innovation) between the flow rate measured by the downstream valve flow measuring device VFS and the flow rate estimated by the observer 3 meets a predetermined standard when the flow control device 100 is operating in normal mode. Specifically, in a steady state in which the target value of the set flow rate is maintained at a constant value, the normal value memory unit NM stores the above-mentioned innovation as a normal value when the absolute value of the difference between the target value of the set flow rate and the flow rate value output by the downstream valve flow measuring device VFS is smaller than the normal value adoption determination threshold. The normal value memory unit NM may, for example, store only the most recent normal value, or may store multiple normal values along with the date and time.

When the control configuration of the flow control device 100 is switched to abnormal mode by the abnormal mode switch AMS, the rollback unit RB inputs a fixed value calculated by multiplying the normal value stored in the normal value memory unit NM by a predetermined value to 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 to the rollback unit RB constituting the observer gain unit 32. Instead, the rollback unit RB uses the normal value that was input when operating in normal mode to calculate the output as the observer gain unit 32. For this reason, the value output from the observer gain unit 32 in abnormal mode is output under the assumption that the modeling error of the downstream valve flow estimation model 31 is the same as in normal mode.

The control operations in normal and abnormal modes of the flow control device 100 of the fifth embodiment configured in this manner will be described with reference to FIG. 11.

Operation in normal mode is almost the same as the control operation in the first embodiment, and if the absolute value of the innovation, which is the deviation between the flow rate value measured by the downstream valve flow rate measuring device VFS in a steady state and the flow rate value estimated by the downstream valve flow rate measuring device simulation unit VFM, is smaller than the normal value adoption determination threshold, the value is stored in the normal value memory unit NM as a normal value.

In addition, if some abnormality occurs in the downstream valve flow measuring device VFS and the absolute value of the difference between the measured value output by the downstream valve flow measuring device VFS and the set flow rate in a steady state becomes larger than the abnormality mode switching threshold, the abnormality mode switching unit determines that an abnormality has occurred. The abnormality mode switching unit switches the control configuration of the flow control device 100 to abnormal mode, and while preventing the output of the downstream valve flow measuring device VFS from being used by the observer 3, the output from the observer gain unit 32 is output from the rollback unit RB. In other words, the rollback unit RB outputs a fixed value obtained by multiplying the normal value stored in the normal value memory unit NM by a predetermined value to the downstream valve flow estimation model 31. As a result, the state of the observer 3 is rolled back to the state before the abnormality occurred, and from that state, the flow feedback control in the flow control device 100 will continue using only the estimated value of the observer 3.

With the flow control device 100 of the fifth embodiment configured in this manner, even if an abnormality occurs in a sensor or the like that constitutes the downstream valve flow meter VFS, the flow control can be continued based only on the estimated flow value output by the observer 3 without interrupting the flow control. Furthermore, since the flow rate estimated by the observer 3 is a value calculated based on innovation in normal mode and has had modeling errors corrected, the deviation from the actual flow rate can be reduced. Therefore, the flow rate supplied from the flow control device 100 can be made to have only an acceptable error from the set flow rate, making it possible to maintain a higher wafer yield than if the process was interrupted.

A modification of the flow rate control device 100 of the fifth embodiment will be described.
The normal value stored in the normal value storage unit NM may not be the innovation described above, but may be the value itself that was output by the observer gain unit 32 in the normal mode. In such a case, the rollback unit RB may be configured to input the normal value directly to the downstream valve flow rate estimation model 31.

The abnormality determination algorithm in the abnormality mode switch AMS is not limited to the one described above. For example, it may be determined that an abnormality has occurred if the output of the downstream valve flow meter VFS is over-range. It may also be determined whether an abnormality has occurred based on the output of various sensors and electrical circuits that make up the downstream valve flow meter VFS.

For example, in order to be able to continue flow control with a predetermined control accuracy even in abnormal mode while using the configuration of the flow control device 100 of the first embodiment as is, the abnormal mode switcher AMS may be configured to change the observer gain of the observer gain section 32 to zero in abnormal mode.

Other embodiments will be described.

The upstream valve and downstream valve are not limited to piezo valves, and may be driven by other actuators. Each valve may be, for example, a solenoid valve, and each valve does not have to be the same type.

The fluid resistance is not limited to a laminar flow element, but may be, for example, an orifice or a flow dividing element for forming a thermal flow sensor. In short, the fluid resistance is a resistor provided in the flow path, and it is sufficient that the volume between the flow path resistance and the downstream valve is partitioned and changed to a pressure different from that of other parts.

The resistance flow rate through the fluid resistance is not limited to that measured by a pressure-type flow rate sensor. For example, a flow dividing element may be used as the fluid resistance, and the resistance flow rate may be measured by a thermal flow rate sensor having a pair of temperature measuring elements in a bypass flow path formed by a thin tube that bypasses the flow dividing element. In this case, by providing a separate downstream pressure sensor to measure the pressure of the downstream volume between the flow dividing element and the downstream valve, it becomes possible to achieve control equivalent to that of the flow control device of the first embodiment.

The input parameters input to the observer for estimating the downstream valve flow rate are not limited to the opening command. The input parameters may be, for example, a set flow rate or a voltage input to the downstream valve. The number of elements in the real system included in the downstream valve flow rate estimation model may be increased or decreased depending on the type of input parameter. In addition, elements that have an ideal response in which time delays and the like can be ignored may be removed from the elements that make up the downstream valve flow rate estimation model. In other words, the flow rate estimation model is not limited to those shown in each embodiment. The downstream valve flow rate estimation model may be, for example, a mathematical equation based on the physical laws satisfied by each element of the control system, or may be experimentally determined from step responses, etc.

In addition, various modifications of the embodiments and combinations of elements of each embodiment are possible as long as they do not go against the spirit of the present invention.

100: Flow control device P1: Upstream pressure sensor P2: Downstream pressure sensor V1: Upstream valve V2: Downstream valve VL1: Upstream volume VL2: Downstream volume COM: Control device 1: Resistance flow rate calculator 2: Downstream valve flow rate calculator 3: Observer 31: Downstream valve flow rate estimation model V2M: Downstream valve simulation unit 5M: First voltage generation circuit simulation unit VFM: Downstream valve flow rate measurement device simulation unit 32: Observer gain unit OG1: First observer gain OG2: Second observer gain SW: Switcher 4: Downstream valve controller 41: PID controller 42: Opening command generator 5: First voltage generation circuit 6: Upstream valve flow rate calculator 7: Upstream valve controller 8: Second voltage generation circuit 9: Sub-observer AMS: Abnormality mode switcher NM : Normal value storage section RB: Rollback section

Claims (20)

A fluid resistance provided in the flow path;
A downstream valve provided downstream of the fluid resistance;
a downstream valve flow rate measuring device that measures a downstream valve flow rate, which is the flow rate of a fluid passing through the downstream valve, based on a resistance flow rate, which is the flow rate of a fluid flowing through the fluid resistance, and a time change in a downstream pressure, which is the pressure in an internal volume between the fluid resistance and the downstream valve;
an observer including 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;
A flow control device configured such that the observer feeds back a deviation between the measurement value of the downstream valve flow rate output by the downstream valve flow measuring device and the estimated value of the downstream valve flow rate output by the downstream valve flow rate estimation model. a first voltage generating circuit that outputs a voltage corresponding to an input opening command to the downstream valve;
the downstream valve flow rate estimation model is a model of characteristics of the first voltage generating circuit, the downstream valve, and the downstream valve flow rate measuring device,
2. The flow control device according to claim 1, wherein the observer receives the opening command as the input parameter and estimates the downstream valve flow rate. The flow control device according to claim 2, wherein the downstream valve flow estimation model simulates a time delay in the first voltage generation circuit. A flow control device according to any one of claims 1 to 3, wherein the observer further comprises an observer gain section that multiplies the deviation between the measured value of the downstream valve flow rate and the estimated value of the downstream valve flow rate by an observer gain. The observer gain unit,
a first observer gain that is used when a flow rate of the fluid flowing through the flow path is stable at a predetermined value;
5. The flow rate control device according to claim 4, further comprising: a second observer gain that is used when a flow rate of the fluid flowing through the flow path is changing and has a value larger than that of the first observer gain. A downstream valve controller for controlling an opening degree of the downstream valve is further provided.
4. The flow control device according to claim 2, wherein the downstream valve controller is configured to generate the opening command based on a deviation between a target value of a set flow rate and an estimated value of the downstream valve flow rate output by the observer. The downstream valve controller,
a PID controller that performs a PID calculation based on a deviation between a target value of a set flow rate and the estimated value of the downstream valve flow rate output by the observer;
7. The flow control device according to claim 6, further comprising: an opening command generator that generates the opening command according to a PID calculation result from the PID controller. The downstream valve flow meter includes:
an upstream pressure sensor provided upstream of the fluid resistance for measuring an upstream pressure;
a downstream pressure sensor provided between the fluid resistance and the downstream valve and configured to measure the downstream pressure;
a resistance flow rate calculator that calculates the resistance flow rate based on the upstream pressure and the downstream pressure;
8. The flow control device according to claim 1, further comprising: a downstream valve flow rate calculator that calculates the downstream valve flow rate by subtracting a value obtained by multiplying a time change in the downstream pressure by a predetermined coefficient from the resistance flow rate. an upstream valve provided upstream of the upstream pressure sensor;
The flow rate control device according to claim 8 , further comprising an upstream valve controller that controls an opening degree of the upstream valve. an upstream valve flow rate calculator that calculates an upstream valve flow rate passing through the upstream valve by adding a value obtained by multiplying a time change amount of the upstream pressure by a predetermined coefficient to the resistance flow rate,
10. The flow control device according to claim 9, wherein the upstream valve controller controls the opening of the upstream valve so that a deviation between a set flow rate and the upstream valve flow rate becomes small. an upstream valve flow rate calculator that calculates an upstream valve flow rate passing through the upstream valve by adding a value obtained by multiplying a time change amount of the upstream pressure by a predetermined coefficient to the resistance flow rate;
a sub-observer having an upstream valve flow rate estimation model that estimates the upstream valve flow rate based on an input parameter that changes the opening degree of the upstream valve,
10. The flow control device according to claim 9, wherein the upstream valve controller controls the opening of the upstream valve so as to reduce a deviation between a target value of a set flow rate and an estimated value of the upstream valve flow rate output by the sub-observer. The flow control device according to claim 9, wherein the upstream valve controller controls the opening of the upstream valve so that the deviation between the set pressure and the upstream pressure is small. A flow control device according to claim 9, wherein the upstream valve controller controls the opening of the upstream valve so that the deviation between a set voltage corresponding to the opening maintained by the downstream valve and the voltage applied to the downstream valve is reduced. A flow control device according to any one of claims 1 to 13, wherein the fluid resistance is a laminar flow element, a flow dividing element, or an orifice. The flow control device according to claim 1, further comprising an abnormality mode switching unit that operates the observer in an abnormality mode in which the observer does not provide feedback of the measured value of the downstream valve flow rate output by the downstream valve flow rate measuring device when an abnormality occurs at least in the downstream valve flow rate measuring device. The observer,
an observer gain unit that multiplies a deviation between the measured value of the downstream valve flow rate and the estimated value of the downstream valve flow rate by an observer gain at least when the downstream valve flow rate measuring device is operating normally;
a normal value storage unit that stores, as a normal value, a deviation between the measured value of the downstream valve flow rate and the estimated value of the downstream valve flow rate, or a value obtained by performing a predetermined calculation on the deviation, at least when the downstream valve flow rate measuring device is operating normally;
The flow control device according to claim 15, further comprising: a rollback unit that, in the abnormal mode, inputs a value based on the normal value into the downstream valve flow rate estimation model. the observer includes an observer gain unit that multiplies a deviation between the measurement value of the downstream valve flow rate and the estimation value of the downstream valve flow rate by an observer gain,
The flow control device of claim 15 , wherein the observer gain unit is configured to use a value of zero as the observer gain in the abnormal mode. A flow control device according to any one of claims 15 to 17, wherein the abnormality mode switching unit is configured to determine whether the downstream valve flow measuring device is operating normally or whether an abnormality has occurred based on the measurement value of the downstream valve flow rate output by the downstream valve flow measuring device or on internal parameters used in the downstream valve flow measuring device. A flow rate control method using a flow rate control device including a fluid resistance provided in a flow path and a downstream valve provided downstream of the fluid resistance,
Measuring a downstream valve flow rate, which is the flow rate of fluid passing through the downstream valve, based on a resistance flow rate, which is the flow rate of fluid flowing through the fluid resistance, and a time change in a downstream pressure, which is the pressure in an internal volume between the fluid resistance and the downstream valve;
estimating the downstream valve flow rate using an observer having a downstream valve flow rate estimation model that estimates the downstream valve flow rate based on an input parameter that changes an opening degree of the downstream valve;
A flow rate control method comprising: feeding back to the observer a 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. A program used in a flow control device including a fluid resistance provided in a flow path and a downstream valve provided downstream of the fluid resistance,
a downstream valve flow rate measuring device that measures a downstream valve flow rate, which is the flow rate of a fluid passing through the downstream valve, based on a resistance flow rate, which is the flow rate of a fluid flowing through the fluid resistance, and a time change in a downstream pressure, which is the pressure in an internal volume between the fluid resistance and the downstream valve;
an observer having a downstream valve flow rate estimation model that estimates the downstream valve flow rate based on an input parameter that changes the aperture of the downstream valve,
A program for a flow control device, wherein the observer is configured to feed back a deviation between the measurement value of the downstream valve flow rate output by the downstream valve flow measuring device and the estimated value of the downstream valve flow rate output by the downstream valve flow rate estimation model.