JP3417391B2 - Flow control method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow rate control method for controlling the flow rate of a fluid having a relatively small flow rate such as gas.

[0002]

2. Description of the Related Art Generally, in order to manufacture semiconductor products and the like, for example, CVD film formation and etching operations are repeatedly performed on semiconductor wafers and the like, but in this case, it is necessary to accurately control a small amount of processing gas. For example, a precision gas flow rate control device is used. This type of gas flow rate control device is mainly configured by a sensor unit that detects the mass flow rate of a trace amount of gas, a valve unit, and a control circuit unit that controls this. The sensor portion has a sensor in which an electrothermal coil is wound around a sensor tube through which a small amount of the total gas amount passes, and most of the gas flows through the bypass. Then, the control circuit unit controls the valve opening of the valve unit based on the detection value of the sensor unit to flow the gas flow rate of the set value. Further, in order to control the valve opening, since the entire gas flow rate itself is very small, it is necessary to control the valve opening with high accuracy within a stroke range of, for example, several tens of μm. Since a large thrust change can be produced within the stroke range, a laminated piezoelectric element body is generally used, which allows the valve opening of the valve body consisting of a diaphragm to be operated based on the set value. It has become.

By the way, as a method for controlling the gas flow rate by controlling the valve opening of the valve, that is, the operation amount,
Position PID control method and speed type PID control method are known, and when controlling the gas flow rate, particles that cause product defects do not wind up in the semiconductor processing chamber due to a sudden gas flow. Need to control. Therefore, it is necessary to suppress the occurrence of overshoot, which causes particles, as much as possible.

[0004]

By the way, the control equation of the above-described position PID control is generally expressed by the following equation 1 in a digital system.

[0005]

[Equation 1]

Where m _n is the operation amount of the n-th valve,
k is a proportional constant, Ts is the sampling time, Ti is the integration time (constant concept has entered time), e _n is the actual amount of operation of the deviation with respect to the set value, Td is determined by differentiation time constant, m ₀ is required Bias amounts added according to Accordingly, Ts / TiΣe _n term is accumulation of the deviation is determined represents the integral term, Td / Ts (e _n -e
The term _n-1 ) represents the differential term, and the gradient of the deviation is obtained.

According to this integral term, for example, even if there is a slight deviation in the temperature control of the processing furnace where strictness is required, this deviation is accumulated and corrected, but the response is slow as a whole. In addition, when the set value is changed, the value of the integral term may act in the direction of preventing the change.Therefore, in the actual control, the value of the integral term should be set to zero by software when the set value is changed. Has become.

Further, since the differential term takes the difference between the deviations, it does not work very well when the change in the manipulated variable is small, but it acts suppressively when the deviation changes abruptly. Then, in the actual flow rate control device, if the valve is set to the fully closed state at the initial stage, for example, the flow rate will be 50%.
Since a large deviation occurs when the set value of% is input, in order to prevent this, m ₀ is set to an operation amount of 50%, for example, and the valve is opened.

However, in general, the response speed of the sensor is not so fast. Therefore, for example, when the set value is sharply lowered, the sensor output which is feeding back shows the previous state for a short time and deviates. Becomes zero, then m
There was a problem that the valve opened to 50% due to _0, and as a result, gas rapidly flowed and overshoot occurred. On the other hand, the control formula of the speed type PID control is generally expressed by the following equation 2 in a digital system.

[0010]

[Equation 2]

Here, Δm _n represents the difference in valve opening,
This is an equation for recognizing the present valve opening degree m _n and what kind of change is given to it. According to this control, as is clear from the equation, only the change in the valve opening is calculated, and the sum of the output and the previous position is performed by the output processing unit. Therefore, the internally calculated output value exceeds the output signal range. It has the advantages that it does not change excessively, the calculated output value does not easily change excessively, and that there is no problem due to saturation in the internal calculation of the integrated value, but on the other hand, the step when the set value changes abruptly The response speed at the time of response is the above position PID
There is a problem that it is considerably inferior to the case of control. FIG. 6 shows this state. For example, when the set value is rapidly changed stepwise from 0 V to 5 V in a digital system, the valve opening (operation amount) gradually rises as shown by the dotted line, Therefore, the actual flow rate does not overshoot, but the flow rate slowly rises toward the set value, which causes a problem of poor response speed.

In particular, the actual flow rate characteristics of the valve section are such that the flow rate change is small when the valve opening degree is small, and the flow rate change becomes large when the valve opening degree exceeds a certain level. There was a problem that the responsiveness when the set value changed stepwise from zero in the fully closed state was considerably poor.

The present invention focuses on the above problems,
It was created to solve this effectively. An object of the present invention is to provide a flow rate control method capable of performing flow rate control quickly and without overshoot by switching the flow rate control method in the middle.

[0014]

In order to solve the above problems, the present invention controls the flow rate of the fluid by controlling a flow rate control valve provided in a fluid passage through which the fluid flows from a flow rate control section. In the flow rate control method, when the flow rate is suddenly changed from the zero flow state to the predetermined flow rate setting value,
The flow rate control unit outputs to the flow rate control valve an initial voltage value that is smaller than the outflow drive voltage at which the fluid starts to flow out by a small voltage value as a small initial operation amount, and thereafter,
Immediately, the initial operation amount is used as a reference to shift to speed type PID control.

[0015]

Since the present invention is configured as described above, when the flow rate is suddenly changed from the zero flow rate state to the predetermined flow rate setting value, the outflow drive voltage at which the fluid starts to flow out regardless of the flow rate setting value. An initial voltage value that is smaller by a smaller voltage value than that is immediately applied to the flow rate control valve, and then, immediately after, for example, a short time until the sensor unit becomes stable, the speed type PID control is performed. As a result, the driving voltage is suddenly applied in a step-like pattern immediately before the flow control valve is opened, and then immediately after that, the speed type PID is immediately applied.
By shifting to control, the flow control valve is a speed type PID
Under control, the valve opening gradually increases toward the steady operation amount, and finally the flow rate corresponding to the flow rate set value flows. In this way, it is possible to control the flow rate to quickly change to the desired set flow rate without causing overshoot or the like even when the set flow rate changes rapidly from the state of zero flow rate. Become.

In this case, when the fluid shown in the flow rate set value is actually flowing due to changes in the environment in which it is used, such as gas differential pressure in the piping system to which the fluid passages are connected and changes over time in the fluid passages. There may be a difference between the actual operation amount and the steady operation amount at this time, but it is preferable to always keep the update state when the deviation becomes excessively large.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a flow rate control method according to the present invention will be described in detail below with reference to the accompanying drawings. 1 is a schematic configuration diagram showing a gas mass flow rate control device for carrying out the flow rate control method according to the present invention, FIG. 2 is a block diagram showing the configuration of a flow rate control unit of the control device shown in FIG. 1, and FIG. 5 is a graph showing changes in the flow rate set value, flow rate and manipulated variable when the control method of the invention is carried out, FIG. 4 is a graph showing the relationship between the manipulated variable and flow rate of the flow rate control valve when the differential pressure is changed, FIG. 4 is a graph showing a part of characteristic curves extracted from FIG. 4.

First, a gas mass flow rate control device for carrying out the flow rate control method according to the present invention will be described. As shown in the figure, the gas mass flow rate control device 2 has a fluid passage 4 formed of, for example, stainless steel, and most of the flow rate is provided upstream of the fluid passage 4 in the flow direction of the gas fluid. A flow bypass 6 is provided, and a flow rate control valve 10 having a diaphragm 8 as a valve body is provided on the downstream side for controlling the flow rate of the gas fluid.

Sensor pipes 14 of the mass flow rate detecting sensor unit 12 are connected to both ends of the bypass 6 so that a small amount of gas fluid can be made to flow therethrough as compared with the bypass 4. A pair of electric heating coils 16 for control are wound around the sensor tube 14, and a sensor control circuit 18 connected to the electric coil 16 detects the mass flow rate of the gas fluid.

The detected value here is the A / D of 2 channels.
It is input to the flow rate control unit 22 including a microcomputer or the like via the converter 20. In addition, the setting signal indicating the flow rate setting value input from the outside is also the A / D
It is input to the flow rate control unit 22 via the converter 20. This setting signal is usually an analog signal of 0 to 5 V, and is input to the flow rate control unit 22 after being converted into a digital signal by the A / D converter 20.

Further, the flow control valve 10 has, for example, a laminated piezoelectric element 24 that produces a large thrust change within a small stroke range as an actuator for vertically driving the diaphragm 8, and the piezoelectric element drive section 26 Is controlled by the driving signal (driving voltage). The drive unit 2
6, the digital drive signal from the flow rate controller 22 is D /
It is input after being converted into an analog signal by the A converter 28, and the operation amount of the flow rate control valve 10, that is, the valve opening degree is controlled so that the flow rate corresponding to the flow rate set value flows.

In this embodiment, the steady operation amount of the flow rate control valve corresponding to a plurality of flow rate setting values is measured in advance and stored in a table, and when the set flow rate value suddenly changes, a new value is newly set. The steady operation amount corresponding to the flow rate set value set to is calculated based on the table, and an initial operation amount smaller than the obtained steady operation amount by a predetermined ratio is first output to the flow control valve 10 and then The flow rate control unit 22 is programmed so as to immediately shift to the velocity type PID control (represented by the above-mentioned equation 2) with the initial operation amount as a reference.

In other words, when the flow rate setting value is changed, the valve opening degree (initial operation amount) slightly smaller than the valve opening degree (operation amount) corresponding to the newly set flow rate setting value is first set. It is opened or closed all at once, and then immediately shifts to the speed type PID control which is characterized by stable control, and as a result, it quickly shifts to the set flow rate without causing overshoot.

The functional contents of the program are represented as shown in FIG. 2, for example, and the arithmetic unit 3 for performing various arithmetic operations.
0 and a measurement result of the flow rate control valve measured in advance are rewritably stored, for example, in an EEPROM (electric)
al erasable programmable R
OM), a memory unit 31, a sensor stability confirmation unit 34 that indicates whether or not the sensor 12 is stable, and a rewrite command unit 33 that notifies the timing of rewriting the table.

The sensor stability confirmation unit 32 is a speed type PI.
It informs the timing to switch to D control,
When a sudden decrease or increase in the gas flow rate is detected, the sensor is recognized as stable and the arithmetic unit 30 is notified that the sensor is stable. The time until the sensor is stabilized (response time) is very short, for example, on the order of μmsec, whereas the response time of the actuator that operates the diaphragm 8 is relatively long, for example, on the order of msec.

Further, the rewrite command section 33 operates in the table of the actual operation amount output as a drive signal and the flow rate set value at that time when the input flow rate value is stable (constant). A certain amount between the amount and, for example, 10%
If the above difference occurs, a rewriting signal for rewriting the flow rate setting value in the table is output, and the arithmetic unit 30 receiving this rewriting signal performs a predetermined calculation to perform rewriting. . All the above operations are processed by the program. Here, the contents shown in Table 1 stored in the storage unit 32 will be described.

[0027]

[Table 1]

In Table 1, the flow rate setting value Q represents a target flow rate input from the outside. For convenience, the maximum flow rate is divided into 10 steps of 10% from Q _{1 to} Q ₁₀ . It may be further subdivided. The manipulated variable indicates the valve opening degree of the control valve, and indicates the valve opening degree required when the flow rate represented by the flow rate setting value is allowed to flow stably. Here, in general, the characteristic of the operation amount (valve opening) of the flow control valve and the flow rate has a hysteresis characteristic as shown in FIG. 4, and the operation amount is increased or decreased. It has a complicated characteristic that the flow rate is different even when the valve opening is the same, and the flow rate is different even when the differential pressure is different.
For example, assuming that the valve openings are the same, the flow rate increases as the differential pressure increases, and the entire characteristic curve shows a similar shape. Therefore, as shown in Table 1, for the same flow rate setting value Q, there are an operation amount mA when the valve opening is increasing and an operation amount mB when the valve opening is decreasing, both of which are measured. Also, when the flow rate is zero, the valve is pressed down with a strong force to prevent leakage, so that the drive voltage is 5
In a region lower than V, the valve is not open and the flow rate is zero. When the driving voltage becomes higher than approximately 5V, the valve starts to open and the gas flows out.

Incidentally, compensation for the point that the flow rate changes even if the valve opening is the same due to the difference in the differential pressure will be described later. These manipulated variables mA and mB are measured after the gas flow rate control device 2 is actually incorporated in, for example, a piping system of a semiconductor manufacturing apparatus, and the flow rate is increased or decreased by 10%, for example, and the flow rate is changed each time. Reading the valve opening (equivalent to the drive voltage of the actuator) when the valve is stable, and manipulated variables mA and mB
Is stored in the storage unit 32.

Then, the respective manipulated variables mA and mB
Then, a predetermined ratio α (1 <0) is added to obtain the corresponding initial manipulated variables mAo and mBo, which are similarly stored. Therefore, the initial manipulated variables mAo and mBo are obtained by calculation as follows. mAo = α · mA mBo = α · mB Here, α is set to a value such that the flow rate does not overshoot even if the valve opening degree corresponding to the initial operation amount is established at once, and normally 0.6 to 0. It is set within the range of 7.

The differential pressure when forming Table 1 is set to the largest differential pressure expected in the environment in which this flow rate control device is installed. For example, the gas pressure of the processing gas piping system in a semiconductor manufacturing apparatus is usually 3 kgf / cm ^{2 at} maximum.
Therefore, when preparing Table 1, data should be taken under the pressure difference of 3 kgf / cm ² . As a result, even if the flow rate control device is installed in any piping system having a maximum differential pressure of 3 kgf / cm ² , no overshoot will occur.
Further, the differential pressure of the piping system in which the flow rate control device is arranged is smaller than, for example, 3 kgf / cm ² , for example, 2 kgf / c.
When that m ^2, and each of the operation amount corresponding to the flow rate set value Q represented in Table 1 and the initial operation amount are all increased (see FIG. 4).

Therefore, in order to ensure the quickness of the control speed, the learning function rewrites all the flow rate setting values Q in Table 1 so as to correspond. Specifically, the flow rate control valve 10 when the flow rate specified by the flow rate set value is flowing stably
Of the actual flow rate (corresponding to the voltage of the drive signal) is monitored, and based on the ratio between this flow rate set value and the flow rate set value in Table 1 corresponding to the above manipulated variable, the flow rate set value in Table 1 To be rewritten. The rewritten state is shown in Table 2.

[0033]

[Table 2]

In this case, since it is considered that the manipulated variable actually changes microscopically due to the hysteresis characteristic, the rewrite command section 34 rewrites when there is a difference in manipulated variables of 10% or more, for example. The replacement signal is output. Further, the flow rate set value Q not stored in Table 1, for example, the flow rate set value Q
₁ and it is between for example 15% when the flow rate set value is inputted Q _2, to seek a corresponding value by interpolation from the operation amount and initial operation amount corresponding to the flow rate set value Q _1, Q ₂ To Further, the steady operation amount and the initial operation amount in Tables 1 and 2 respectively correspond to the drive voltage, and this drive voltage is directly applied to the laminated voltage element 24.
In FIG. 1, 34 is a D / A converter for converting the flow rate output into an analog signal of 0 to 5 V, and 36 is an interface of RS232C standard for communicating with the outside.

Next, an example of an embodiment which is carried out by using the gas mass flow rate control device constructed as described above will be specifically described. For example, when the gas fluid flows through the fluid passage 4 having a differential pressure of 3 kgf / cm ^2, a part of the gas fluid flows through the sensor pipe 14 of the sensor portion 12 and most of the gas flows through the bypass 6, and the flow rate is controlled by the fluid control valve 10. Heading to the gas usage system while being controlled.

The flow rate of the gas fluid flowing through the sensor tube 14 is detected by the sensor 12 of the constant temperature difference type, the mass flow rate flowing through the entire fluid passage 4 is obtained, and the mass flow rate is input to the flow rate control unit 22. Then, feedback control is applied so that the detected value becomes equal to the flow rate set value input from the outside, and the laminated piezoelectric element 24 of the flow rate control valve 10 is driven to control the valve opening degree. Become.

Now, in the present embodiment, a case where the flow rate set value changes drastically, for example, a case where the flow rate set value Q abruptly changes to Q _{3 in} Table 1 from the state of zero flow rate will be described. As shown in 3, time t
When the flow rate setting value Q ₃ is input as the setting signal in, the calculating unit 30 obtains the steady operation amount mA ₃ at the time of increasing the flow amount from Table 1 stored in the storage unit 31, and adds a predetermined ratio α to this value. The initial manipulated variable mAO ₃ at the time of increase is obtained by performing the calculation. If the initial manipulated variable is calculated in advance and tabulated in Table 1, the initial manipulated variable mAO ₃ (<mA ₃ ) may be directly read as a value corresponding to the flow rate setting value Q _3. Good. This initial manipulated variable mAO ₃ is immediately transmitted as a drive signal from the flow rate control unit 22 to the flow rate control valve 10 side, and the diaphragm 8 is opened all at once up to the initial manipulated variable mAO ₃ .

As a result, the gas suddenly flows out, and this gas flow is detected by the sensor 12 having a high response sensitivity. Then, the sensor stability confirmation unit 32 (see FIG. 2) informs the arithmetic unit 30 that the sensor is stable. . Then, the arithmetic unit 30
At the point A, the control method is switched to the speed type PID control as shown in the above-mentioned mathematical expression 2. As described above, this control method recognizes the current valve opening degree and adjusts the valve opening degree stably and slowly toward the set value based on this, so that the valve operation amount is set at point A. At the boundary, that is, the initial manipulated variable mAO ₃ rises steadily and slowly. During this period, the gas flow rate sharply increases toward the flow rate setting value Q ₃ , but the initial operation amount mAO ₃ is set smaller than the steady operation amount mA ₃ so that overshoot does not occur, so that the overshoot occurs. It is possible to rapidly increase the gas flow rate up to the flow rate set value Q ₃ without generating a chute. Therefore, since no overshoot occurs, in a semiconductor manufacturing apparatus, for example, it is possible to prevent the particles from being swirled up due to a sudden entrainment of gas.

Such an operation is the same not only when the flow rate set value increases stepwise from zero flow rate, but also when the flow rate set value increases stepwise from the state where the gas fluid is flowing to some extent. Conversely, when the flow rate set value decreases stepwise from the state where the gas fluid flows to some extent, the same operation is performed. However, in this case, since the gas flow rate decreases, a value is selected or calculated from the fields of the steady operation amount mB at the time of decrease and the initial operation amount mBO at the time of decrease. In this case, when the flow rate set value Q is very low, for example, when the set flow rate is about 0.5% of the maximum flow rate, the voltage value of the initial operation amount mAO at this time is In some cases, the drive signal (drive voltage) immediately before is slightly smaller than the drive signal (drive voltage) to be started. This point will be described with reference to FIG.
For example, assuming that the steady operation amount at the set flow rate of 0.5% of the maximum flow rate is 7 V and α = 0.6, the initial operation amount mAO is 4.2 V (= 7 V × 0.6), The voltage becomes smaller than the voltage at which the valve starts to open and gas flows out, that is, 5 volts.

When a flow rate set value Q which is not stored in Table 1 is input (actually, there are many cases of this kind), this flow rate set value Q is shown in Table 1. From the steady state operation amount corresponding to the flow rate setting values on both sides of the position located at the position and the initial operation amount at that time, the corresponding steady state operation amount and initial operation amount are obtained by an interpolation method such as proportional division. The time Δt from the time t to the point A is very small, and depends on the responsiveness of the sensor, for example, several μs
It is set to about c.

In addition, in the above operation, when preparing Table 1, actual measurement was performed based on a differential pressure of 3 kgf / cm ² , and the differential pressure of the piping system equipped with the flow control valve was 3 kgf / cm 2.
Since it is the case of the piping system of ² , there will be almost no problem if the values shown in Table 1 are used as they are, but in reality, due to the nature of the gas used, it will be used in an environment with a differential pressure below 3 kgf / cm ^2. There are also cases where

In this case, as described above with reference to FIG. 4, when the differential pressure is different, the flow rate characteristics are different even at the same valve opening, so that it becomes necessary to correct Table 1. As shown in FIG. 5, Table 1 measured at a differential pressure of 3 kgf / cm ² (corresponding to Table 1) corresponds to, for example, when the flow rate control device is used at a differential pressure of 0.5 kgf / cm ^2. Differential pressure 0.5k
Although it becomes necessary to create a flow rate characteristic of gf / cm ^2, a learning function is provided in this embodiment, and Table 1 is automatically set.
Is rewritten into Table 2 corresponding to a differential pressure of 0.5 kgf / cm ² .

Specifically, for example, in the case of increasing the gas flow rate, initially, the initial operation amount is selected or calculated based on Table 1, and the valve opening is controlled by this initial operation amount. However, when the flow rate of the flow rate setting value Ql is stable, the actual manipulated variable mAk at that time is different from the steady-state manipulated variable mA1 in Table 1 at the time of increase. Therefore,
The flow rate set value Qk in Table 1 corresponding to the actual manipulated variable mAk at this time is obtained, and all the flow rate set values Q in Table 1 are rewritten by Ql and Qk to obtain the flow rate set value Q'shown in Table 2. create. This formula is given as follows. Q '= Q · Ql / Qk

In the actual control, as shown in FIG. 2, the rewrite command section 33 constantly monitors the actual operation amount indicated by the flow rate set value and the drive signal, and in the state where the flow rate set value does not change, When the difference between the actual manipulated variable and the steady manipulated variable in Table 1 corresponding to the flow rate setting value at that time exceeds a predetermined range, for example, 10% or more, a rewrite signal is output and Rewriting operation was done,
A new table as shown in Table 2 is created and stored. After that, the above-mentioned control is performed based on Table 2.

By providing a learning function in this way and performing a table rewriting operation when necessary, not only can it be applied to a piping system having any pressure difference, but also a gas cylinder can be used. Even if the differential pressure changes due to a change in the source pressure, it can be dealt with. In the above embodiment, the control switching timing is set by the operation of the sensor stability confirmation unit 32, but this is only an example, and the speed type PID control is performed immediately after the output of the initial operation amount. Any switching function may be provided as long as it can be moved to.

Further, in the above-mentioned method, when the flow rate set value Q is extremely small as described above, for example, the flow rate set value Q
Is about 0.5 to 1% of the maximum flow rate value, the drive voltage corresponding to the initial manipulated variable mAO when a predetermined ratio α (for example, 0.6 to 0.7) is added is In some cases, the voltage value becomes lower than the outflow drive voltage at which the fluid starts to flow out. The initial manipulated variable at this time is, of course, zero flow rate. This point will be described with reference to FIG. FIG. 6 is a graph showing an example of the relationship between the drive voltage and the flow rate (corresponding to the valve opening). The drive voltage is different from the characteristic shown in FIG. 4, but the characteristic is similar. As shown in FIG. 6, the relationship between the drive voltage and the flow rate has no linearity, and when the voltage is gradually increased from the fully closed state (0 V), the flow rate does not change even if the voltage is increased and the state is zero. There is an area shown. In FIG. 6, almost no gas flows up to 50V. Incidentally, in the case shown in FIG. 4, almost no gas flows up to 5V. The reason is that when the drive voltage is increased, a force is generated in the direction of opening the valve body (diaphragm 10), but the force does not immediately displace, and the force (contact pressure) by which the valve body presses the valve seat is reduced. Used to do. Then, the voltage increase after the surface pressure becomes zero appears as a displacement.

For the valve actuator of the mass flow controller, a solenoid, thermal expansion, etc. are used in addition to the above-mentioned laminated piezoelectric element. However, since leakage prevention performance when fully closed is required, any actuator will have a certain degree. It is designed to apply surface pressure. In addition, the mechanical displacement of the valve and the displacement due to the difference in thermal expansion of the components due to changes in the ambient temperature are absorbed, and leakage does not occur even with a small displacement, so such design and adjustment is necessary. is necessary. Thus, in the case shown in FIG.
0V is the outflow drive voltage. Under such characteristics, for example, when the maximum flow rate is 2000 cc / minute and the flow rate setting value is 10 cc / minute, which is 0.5% of the maximum flow rate value, for example, the drive voltage for the constant operation amount mA at that time. Is approximately 75V, and therefore, this initial manipulated variable mAO is 45V (= 75V ×) when α = 0.6.
0.6). This drive voltage 45V is slightly lower than the flow-out drive voltage of 50V, and gas does not flow out at this point. After the initial manipulated variable is set to this drive voltage 45V, the speed-type PID control is performed as described above. Immediately after the transition, the gas starts to flow out when the driving voltage exceeds approximately 50V.

As described above, when the driving voltage (initial voltage value) of the initial manipulated variable flows out slightly lower or less than the driving voltage, for example, 50 V, the speed type PID is immediately thereafter.
Since the control shifts to the control, it is possible to surely eliminate the occurrence of overshoot, and it is possible to quickly and stably set a desired flow rate. Therefore, here, when the flow rate is rapidly changed from the state of zero flow rate to the predetermined flow rate setting value, regardless of the value of the flow rate setting value Q at that time, a voltage smaller than the flow-out drive voltage, for example, about 50V. value,
For example, a voltage reduced by 5V is output as an initial voltage value (initial operation amount), for example, 45V, as a drive voltage to the flow control valve 10. Then, immediately thereafter, similarly to the above, the high-speed PID control is performed. Therefore, in the case of this embodiment, the flow rate from zero to the maximum flow rate (flow rate 100%)
Even when the flow rate is drastically changed to, the drive voltage of 45 V is output as the initial voltage value.

In the case of this embodiment, the control speed is slightly slower than the method described in Table 1, but the occurrence of overshoot is suppressed more reliably than in the method shown in Table 1. In addition, the desired flow rate can be quickly and stably set. In this case, when obtaining the initial voltage value, for example, the maximum flow rate of 0.5 is used as described above.
%, Or a drive voltage corresponding to a predetermined flow rate setting value with a small flow rate, for example, a voltage value smaller than 75 V by a predetermined ratio, for example, 45 V (= 75 V × 0.6), or may be obtained. Alternatively, a predetermined ratio of the outflow drive voltage, for example, 50V, for example, 90% is 45V (= 50).
V × 0.9), or a voltage value that is smaller than the outflow drive voltage, for example, 50 V by a predetermined amount, for example, 5 V, may be calculated as the initial voltage value. Needless to say, these calculations and the like are performed by the flow rate control unit 22.

In any case, since the characteristics of the flow control valve 10 are peculiar to each control valve, the outflow drive voltage is obtained in advance at the factory shipping stage or the like. Further, in consideration of the quickness of control, it is preferable that the difference between the outflow drive voltage and the initial voltage value is set as small as possible within a range in which the initial voltage value does not exceed the outflow drive voltage. Is preferably in the range of 5 to 10 V, for example, in the range of 10 to 20% with respect to the outflow drive voltage. Further, in this case, the flow-out drive voltage may change due to aging of the flow control valve 10, or the like.
Of course, this is constantly monitored and updated. Furthermore, when changing from a state in which the gas having a predetermined flow rate is already flowing to another flow rate, it goes without saying that the method described in Table 1 is used.

The numerical example shown in FIG. 6 is merely an example in order to facilitate understanding of the contents, and it goes without saying that the numerical example is not limited to this. FIG. 7 is a graph showing the relationship between the gas flow rate, the drive voltage, and the set value when controlled by the above method. As shown in the graph of FIG. 7, it is found that the gas flow rate stably reaches the predetermined flow rate in about 2 seconds without causing overshoot.

[0052]

As described above, according to the flow rate control method of the present invention, the following excellent operational effects can be exhibited. When the flow rate is suddenly changed from the zero flow rate state to the predetermined flow rate setting value, it is possible to set the desired flow rate rapidly without causing almost certain overshoot. Therefore, when applied to the gas supply system of the semiconductor manufacturing apparatus, it is possible to prevent the particles from being wound up due to the overshoot and contribute to the improvement of the yield.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a gas mass flow rate control device for carrying out a flow rate control method according to the present invention.

FIG. 2 is a block diagram showing a configuration of a flow rate control unit of the control device shown in FIG.

FIG. 3 is a graph showing changes in flow rate set value, flow rate, and manipulated variable when the control method of the present invention is performed.

FIG. 4 is a graph showing the relationship between the operation amount of the flow control valve and the flow rate when the differential pressure is changed.

FIG. 5 is a graph showing a part of characteristic curves extracted from FIG.

FIG. 6 is a graph showing an example of the relationship between drive voltage and flow rate (corresponding to valve opening).

FIG. 7 is a graph showing the relationship among gas flow rate, drive voltage, and set value.

FIG. 8 is a graph showing changes in a flow rate set value, a flow rate, and a manipulated variable when speed type PID control is performed from the beginning.

[Explanation of symbols]

2 Gas mass flow controller 4 fluid passages 6 bypass 8 diaphragm 10 Flow control valve 12 Mass flow sensor 14 sensor tubes 22 Flow rate control unit 24 Multilayer piezoelectric element 26 Piezoelectric element driver 30 operation unit 31 storage 32 Sensor stability confirmation unit 33 Rewrite command section

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-7-160338 (JP, A) JP-A-9-114502 (JP, A) JP-A-9-217898 (JP, A) JP-A-8- 335118 (JP, A) JP-A 6-187046 (JP, A) JP-A 4-296270 (JP, A) JP-A 4-47416 (JP, A) JP-A 1-158501 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G05D 7/06 G05B 7/02 F16K 31/02

Claims (3)

(57) [Claims] 1. A flow rate control method for controlling the flow rate of a fluid by controlling a flow rate control valve interposed in a fluid passage through which a fluid flows, from a state of zero flow rate to a predetermined flow rate set value. When the flow rate is suddenly changed, the flow rate control unit outputs an initial voltage value, which is smaller than the outflow drive voltage at which the fluid starts to flow out, by a small voltage value to the flow rate control valve as a small initial operation amount, and immediately thereafter. A flow rate control method, characterized in that a transition is made to speed type PID control based on the initial operation amount. 2. The flow rate according to claim 1, wherein the initial voltage value is a voltage value that is smaller than a drive voltage of a steady operation amount corresponding to a predetermined flow rate set value with a small flow rate by a predetermined ratio. Control method. 3. The flow rate control method according to claim 1, wherein the initial voltage value is a voltage value that is smaller than the outflow drive voltage by a predetermined amount.