JPH08335118A - Flow rate control method - Google Patents

Abstract

PURPOSE: To provide a flow rate control method with which control into a prescribed flow rate can be speedily performed without generating overshoot. CONSTITUTION: Concerning the flow rate control method with which the flow rate of fluid is controlled by controlling a flow rate control valve 10 interposed at a fluid passage 4 for letting the fluid flow corresponding to a valve driving signal from a flow rate control part 22, this method is provided with a process for tabulating and storing the valve driving signals corresponding to plural flow rate set value as learning values in advance, process for finding and storing relearning values corresponding to the plural flow rate set values based on the real valve driving signal and the learning value of the table corresponding to the prescribed set value while letting the fluid flow to the flow rate control valve 10 after the flow rate control valve 10 is really assembled with a using system, and process for finding and outputting the valve driving signal based on the relearning value. Thus, the valve driving signal based on the relearning value suited to real use conditions can be outputted and speedy flow rate control is enabled without overshoot.

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 accurately within a stroke range of, for example, several tens of μm. A laminated piezoelectric element is generally used because it has a thrust force and can generate a minute displacement.This allows the valve element consisting of a diaphragm to be operated based on the gas flow rate set value, and the desired valve to be operated. The opening is controlled.

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]

The control equation of the velocity type PID control generally used for the flow rate control is generally expressed by the following equation 1 in a digital system.

[0005]

[Equation 1]

Here, Δm _n represents a correction amount from the current valve opening degree, and gives a formula for recognizing the current 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 There is a problem that the response speed at the time of response is considerably poor. FIG. 12 shows this state, and when the set value suddenly changes from 0 V to 5 V in a stepwise manner, the valve opening (operation amount) gradually rises as shown by the dotted line, and therefore However, the flow rate does not overshoot, but the flow rate slowly increases toward the set value, and there is a problem that the response speed is poor.

In particular, the actual flow rate characteristic of the valve portion is 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.

Therefore, the inventor of the present invention filed an earlier application (Japanese Patent Application No.
No. 339737), in order to solve the above-mentioned problem, when the flow rate setting value is changed, an initial operation amount lower than the steady operation amount is obtained based on a table created in advance. The value is output to the flow control valve, and then
A flow rate control method is disclosed in which the speed type PID control is immediately started. According to this control method, the desired flow rate can be set to some extent quickly, but it has been found that flow rate overshoot occurs in some cases.

The cause of such an overshoot is that the valve drive voltage of the initial manipulated variable is first output in a step-like manner on and off as described above. Therefore, a sudden change in the gas flow rate due to the step-like displacement causes a PID. It acts as a disturbance to the control system, which causes overshoot and hunting. There is also a mass flow controller of some kind in which a differentiating circuit is provided in the subsequent stage of the sensor section in order to speed up the response speed of the sensor. The circuit responded excessively, which also caused overshoot. Further, in the above-mentioned example of the method of the previous application, since the table is created in consideration of the hysteresis characteristic of the flow control valve, there is a drawback that this creation becomes very complicated.

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 controlling the flow rate to a predetermined flow rate quickly without causing overshoot.

[0011]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention controls a flow control valve provided in a fluid passage through which a fluid flows by controlling a valve drive signal from a flow control unit. In a flow rate control method for controlling the flow rate of a fluid, a step of storing a valve drive signal corresponding to a plurality of flow rate set values in advance as a learning value in a table,
After actually assembling the flow control valve into the system for use, the plurality of the plurality of flow control valves based on the actual valve drive signal and the learned value of the table corresponding to the predetermined set value while flowing the fluid through the flow control valve are used. It is configured to include a step of obtaining and storing a relearning value corresponding to the flow rate set value, and a step of obtaining and outputting a valve drive signal based on the relearning value.

[0012]

As described above, according to the present invention, for example, at the time of shipment from a factory, a plurality of flow rate set values are given while a certain pressure is applied to the fluid passage 4 of FIG.
The finally settled valve drive signal value is stored as a learning value table. When this flow control valve is actually used, initially, a valve drive signal is output according to a learning value created in advance corresponding to a plurality of flow rate setting values. Then, based on the valve drive signal at the time when the deviation between the flow rate and the set value becomes less than or equal to a predetermined range, that value is stored as a re-learning value. At this time, relearning values are calculated for each of the learned values corresponding to the plurality of flow rate setting values, and are stored as a relearning value table. The re-learned value table reflects the pressure condition actually used. Or later,
The valve drive signal for each set value is determined based on the relearning value table. The output of the valve drive signal is
It is not output in steps, but for a very short time, some time, for example 50 msec to 70
The voltage value of the valve drive signal thus obtained is increased over a time period of about msec. And the voltage value is 100%
When it reaches to, PID control is performed.

As a result, it becomes possible to quickly change the flow rate to a predetermined value without causing overshoot. The re-learned value is updated as needed due to changes in operating pressure conditions. In practice, the set value of the flow rate does not change for a certain period of time, and the deviation between the flow rate and the set value is within a predetermined range, for example ± Frequently it is desirable to do it at 1.0% or less.

[0014]

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. 3 is a sensor. FIG. 4 is a schematic block diagram showing a general control state from the output of the control circuit to the output of the valve drive signal. FIG. 4 shows the flow rate setting value and the learning value and the re-learning value when the control method of the present invention is carried out. FIG. 5 is a graph showing the change, and FIG. 5 is a graph showing the relationship between the flow rate set value and the valve drive signal when the method of the present invention is carried out.

First, a gas mass flow controller for carrying out the flow control method according to the present invention will be described. As shown in the figure, the gas mass flow rate control device 2 is detachably provided in an actual usage system, for example, a gas piping system PA of a semiconductor manufacturing apparatus. The control device 2 has a fluid passage 4 formed of, for example, stainless steel or the like, and a bypass 6 that allows most of the flow rate to flow is provided upstream of the fluid passage 4 in the flow direction of the gas fluid. On the downstream side, a flow rate control valve 10 having a diaphragm 8 as a valve body is provided for controlling the flow rate of the gas fluid.

Sensor pipes 14 of the mass flow rate detection sensor unit 12 are connected to both ends of the bypass 6 so that a small amount of gas fluid can flow through the sensor pipes 14 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 input to a flow rate control unit 22 including, for example, a microcomputer via the A / D converter 20 of two channels. Further, a setting signal indicating a flow rate setting value input from the outside is also input to the flow rate control unit 22 via the A / D 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.

The flow control valve 10 has a large thrust as an actuator for driving the diaphragm 8 up and down, and has, for example, a laminated piezoelectric element 24 that produces a minute displacement. Is controlled by the drive signal. The digital drive signal from the flow rate control unit 22 is input to the drive unit 26 after being converted into an analog signal by the D / A converter 28, and the flow rate control valve is controlled so that the flow rate corresponding to the flow rate set value flows. The operation amount of 10, that is, the valve opening is controlled.

In the present invention, for example, a valve drive signal (voltage) corresponding to a plurality of flow rate setting values is preset at the factory shipment stage.
Is stored as a learning value in a table, and after this device is attached to an actual usage system, the above learning on the table corresponding to the actual valve drive signal (voltage) and each set value while flowing a fluid The re-learning value corresponding to the plurality of flow rate setting values is obtained based on the value and the table, and the table is stored. Then, it is programmed so as to obtain and output the valve drive signal based on the re-learned value. In addition, this re-learning value is updated as necessary, for example, when the flow rate set value is stable and the deviation between this set value and the actual flow rate is below a certain level and the flow is settled. Programmed to correct.

A functional representation of the contents of this program is shown in FIG. 2, and roughly, a valve characteristic learning block 28 for learning valve characteristics in a factory or the like and re-learning and flow rate control by an actually used system are performed. The re-learning block 30 is included, and each block includes a valve characteristic learning calculation control unit 36 and a re-learning calculation control unit 38. Each of the control units 36 and 38 has the above table.
Is connected in common to a storage unit 32 for storing the number and a table counter 34 for counting the permutation of each set value in the table. The valve characteristic learning calculation control unit 36 includes a flow rate setting value generation unit 40 that electrically generates various flow rate setting values during learning.
Is also connected to each of the control units 36 and 38, and the outputs of comparison units 42 and 44 for comparing the sensor output with the flow rate setting value at that time to obtain the deviation are connected.

A learning flag 46 is provided to selectively switch between the two blocks 28 and 30. Although this flag 46 is described as a switch in the illustrated example for easy understanding, it is actually selected depending on whether or not a specific bit is set in a program. The re-learning calculation control unit 38 also includes a set value displacement detection unit 4 for detecting whether or not the flow rate set value has changed.
8 is connected to detect the displacement of the set value. In the drive of the flow control valve described above, PID control is performed during normal operation except for a short time after the set value is changed. The outline of the control block diagram at this time is shown in FIG.
It is expressed as shown in. That is, the sensor control circuit 18
The phase of the sensor output from is advanced in the differentiating circuit 48, and its output is compared with the flow rate setting value in the comparing section 50 to obtain the deviation. Then, a valve drive signal indicating a predetermined voltage is output from the valve drive signal output section 52 according to this deviation. This output is fed back via the PID control unit 54.

Further, on the output side of the valve drive signal output section 52, an addition section 56 is provided which outputs a re-learning value for a short time after the set value changes, and
A switch unit 58 is provided for stopping the PID control while the relearning value is being output. Incidentally, in FIG. 1, 60
Is a D / A converter that converts a flow rate output into an analog signal of 0 to 5 V, for example, and 62 is an interface of RS232C standard for communicating with the outside.

Next, an example of the method of the present invention which is carried out by using the gas mass flow rate controller constructed as described above will be specifically described. For example, the fluid passage 4 with a differential pressure of 3 kgf / cm ²
When the gas fluid flows into the sensor unit 12, a part thereof flows through the sensor pipe 14 of the sensor unit 12, and most of the gas flows through the bypass 6. The fluid control valve 10 controls the flow rate of the gas fluid toward the semiconductor manufacturing apparatus, for example.

The flow rate of the gas fluid flowing through the sensor pipe 14 is detected by the sensor control circuit 18, 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 performed so that the detected value becomes the same as 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 perform PID control of the valve opening degree. become.

In the present invention, the flow rate control device 2
There is a learning mode that is performed in the assembly factory before attaching to the user's actual usage system, and a re-learning mode (normal operation mode) that is performed after mounting in the user's actual usage system. It is performed by switching 46. First, the overall flow will be described. The storage unit 32 is configured by a table as shown in Table 1.

[0026]

[Table 1]

The table counter value n in Table 1 is 0 to 1
It is divided into 11 stages up to 0, and this value is counted by the table counter 34. The counter value does not have to be limited to 11 levels, and may be more finely divided into multiple levels.
The flow rate setting value is 2% to 100% corresponding to the counter value.
Up to the above, the intervals are appropriately set. Further, the learned value is a value that is a base for calculating the re-learned value, and is a voltage value of the valve drive signal measured and stored at the factory level. On the other hand, the re-learning value is the voltage value of the valve drive signal measured and stored after the flow rate control device is mounted in the actual usage system. Therefore, the column of the re-learning value is not stored at the time of factory shipment. As will be described later, this re-learned value is updated at an appropriate time and is constantly corrected.

The reason why the learning value and the re-learning value are set in this way is that the test pressure condition performed in the factory and the operating pressure condition in the actual operating system are usually different, and the actual evaluation is performed as it is in the factory. This is because it cannot be applied to the usage system. This is because, for example, even if the valve opening degree is the same, the flow rate of the gas varies depending on the pressure of the flowing gas, and it is necessary to re-evaluate. The contents of Table 1 are shown in the graph shown in FIG. 4, and when the learning value is obtained, the table counter 3
The flow rate setting value is increased by 2% by increasing the value n of 4 sequentially.
The value is sequentially changed in 11 steps from 100% to 100%, and the voltage value of the valve drive signal at that time is read. As for the relearning value, as will be described later, the voltage of the actual valve drive signal at a certain predetermined flow rate setting value sp (generally, it is different from the learning value because it is an actual usage system) is read. Then, the learning value is calculated by shifting the learning value in proportion to the learning value at this time.

Further, FIG. 5 is a diagram showing an actual output method of the relearning value in the operating system, that is, an output state of the valve drive signal (voltage) during the normal operation.
The output is increased substantially linearly to the re-learning value Vm over a predetermined time T, and then the PID control is performed. In this way, the valve drive signal (voltage) is not changed abruptly but brought to the peak over a certain period of time T. Therefore, after the learning value is output, the transitional PID control acts excessively. Therefore, it is possible to reach the predetermined flow rate quickly without causing overshoot. If the length of this time T is made excessively long, it is not swift, so normally, for example, 50 to 70 ms.
Set to about ec. Here, the valve characteristic learning operation performed in order to obtain the learning value shown in Table 1 at the factory stage will be described with reference to the flow shown in FIG.

The valve characteristic is a characteristic peculiar to each flow rate control device, and is learned under a gas pressure of a constant pressure (for example, 1.5 kgf / cm ² ) at the time of assembling and adjusting the device in a factory. Is automatically started by setting the learning flag. In this case, as described above, each of the 11 flow rate setting values shown in Table 1 is set to the table counter 34.
Is generated from the flow rate setting value generation unit 40 by incrementing the contents of 1 by 1. In FIG. 6, first, it is checked whether the learning flag 46 is set (S1). In FIG. 2, as the learning flag 46,
For convenience, it is shown as a switch, but it is actually a CP.
The setting is performed by writing [1] in a predetermined memory of U. Subsequent operations are performed under the control of the valve characteristic learning calculation control unit 36.

When the learning flag 46 is set to the valve characteristic learning side, the flow rate setting value is set to 0% (S2), and the value n of the table counter 34 is cleared (S3). Next, the flow rate setting value is set according to the count value n of the table counter (S4). In this case, the count value n is 0
So, for example, for 5 seconds, set the flow rate to 0% (valve fully closed)
After that, the flow rate setting value is set to 2%. Accordingly, the flow rate control valve 10 operates so that the actual gas flow rate matches the sensor output (flow rate) in the PID control (S).
5). Then, after 5 seconds, for example, the sensor output indicating the actual flow rate and the current flow rate setting value (2%) are compared with each other by the comparison unit 42.
Then, these deviations are compared to determine the deviations, and it is judged whether or not the deviations are within a predetermined range, for example, within ± 1.0% (S6). This operation is performed until the deviation value falls within the predetermined range.

Here, if the deviation value is within the predetermined range (YES), it indicates that the flow rate is stable and in the settling state. Therefore, the voltage of the valve drive signal at that time is read. Then, the read value is stored in the corresponding learning value column of the table (S7). Here, the learning value C0 is stored while the flow rate setting value is 2%. Next, it is determined whether or not the value n of the table counter 34 has reached 10 (S8), and in the case of NO, the table counter 34 increments the value n by 1 (S9), and the above S4 to S8. Repeat the above steps. As a result, the flow rate setting value is gradually increased to 10 to 100%, and C10 in Table 1 is filled. And
When the value n of the counter 34 reaches 10, YE is performed in S8.
Then, the learning flag 46 is cleared (S10), and the valve characteristic learning operation ends.

In this way, the flow rate control device 2 is shipped from the factory with the learning values C0 to C10 in Table 1 being filled.
It is connected to the piping system of the user's actual usage system. Next, the re-learning operation and the actual flow rate control operation performed in the state of being connected to the piping system of the actual use system will be described with reference to FIGS. 7 and 8.
This will be described with reference to the flow shown in. This re-learning operation is
This is an operation mainly for adapting to the actual use condition determined by the pressure condition of the gas flow. For example, re-learning is performed when the following conditions are satisfied. There is no change in the flow rate setting value. The deviation between the flow rate setting value and the sensor output (flow rate) must be within a predetermined range, for example, within ± 1.0% for a fixed time, for example, 5 seconds. In this re-learning operation, when the above conditions are satisfied, the current flow rate setting value sp and the learning value in Table 1 above
A tentative learning value (valve driving voltage) Vc is obtained from the two learning values sandwiching sp by Equation 2, and then relearning of each flow rate setting value is performed based on the ratio between the actual valve driving voltage Vm and the tentative learning value Vc. The value m _n is calculated by the equation 3. Therefore, as shown in FIG. 4, the re-learning value graph has a form in which the learning value graph is shifted by a predetermined amount.

[0034]

[Equation 2]

[0035]

(Equation 3)

C _n and C _n-1 are flow rate set values (n: 1 to 10) on both sides of the flow rate set value corresponding to sp in Table 1. Then, after the relearning value is calculated, the valve drive voltage is output based on this relearning value. Here, a case where the current flow rate value sp is 65% will be described as an example. In FIG. 7, first, the learning flag 46 is reset to perform a re-learning operation (normal operation) (S1), and the set value displacement detection unit 4
At 8 it is judged whether or not the flow rate setting value has changed (S
2). Here, if it is determined that the flow rate set value has not changed, the comparison unit 44 causes the current flow rate set value (65
%) And the sensor output indicating the actual flow rate to obtain a deviation, and it is determined whether or not the deviation is within a predetermined range, for example, ± 1.0% for a certain period of time, for example, 5 seconds. (S3).

If the result of the above determination is YES, the current voltage Vm of the valve drive signal is read (S
4). Next, based on the valve voltage Vm and the learning value in Table 1, each re-learning value is obtained based on the equations 2 and 3 (S
5). Here, since the flow rate set value sp is set to 65%, the learning values on both sides of the set value are C6 and C7. First, from Equation 2, the provisional learning value Vc is as shown in Equation 4 below.

[0038]

[Equation 4]

Substituting this tentative learning value Vc into Equation 3, C
By changing _n from 0 to 10, all re-learning m0 to m10 in Table 1 can be obtained. Incidentally, sp
If the value is the flow rate setting value shown in Table 1, the learning value corresponding to the temporary learning value Vc may be used. Also, when the re-learning value has little change from the previous re-learning value (for example,
2%), only the re-learning values on both sides of the flow rate setting value may be rewritten.

In this way, once the relearning value is set, the actual flow rate control operation is started. In this control process, for example, when the flow rate setting value does not change, the relearning value is repeatedly updated ( Is updated) and corrections are always made. Next, a method of outputting a relearning value in this actual flow rate control operation will be described. In this case, the re-learning value Vm for the flow rate setting value sp may be obtained from Table 1 by the complementary method, and the value may be output (see FIG. 4). When the valve drive voltage Vm is output, the valve drive voltage Vm is not output stepwise, but has a multi-step up to 100% of the re-learning value so that it becomes linear in a fixed time, for example, 50 msec to 70 msec. To go. For example, when the flow rate setting value changes from 0% to 85% (sp value), the learning value (valve driving voltage) Vm to be output by the complementary method is obtained as shown in Expression 5.

[0041]

(Equation 5)

Here, when the control cycle of the flow control valve is t, the output change ΔVm of the valve voltage per step is
Is as in the following Equation 6. Incidentally, t is usually 10 msec.
It is set to some extent but variable.

[0043]

(Equation 6)

Here, the control cycle t also corresponds to the output time of the relearning value. Therefore, as shown in FIG. 5, the change in valve drive voltage should be 2
% Valve drive voltage is output, then (t × 10) ms
Gradually increase the valve drive voltage over ec,
When (t × 10) msec has elapsed, the valve drive voltage reaches Vm, which is the calculated re-learning value. Then, after the output of the re-learning value is completed in this way, the PID control is performed. Here, in order to avoid a gentle overshoot due to a delay in the sensor output, the sensitivity of the PID control constant is low for a short period of time (for example, 1 second) after the transition to PID control, that is, in the equation 1, K, Td Smaller,
A method of increasing Ti and then shifting to a normal control constant may be adopted. In this case, the proportional constant may be set to zero only during the short time. Note that in FIG. 5, the rise of the valve drive voltage is slightly delayed from the rise of the flow rate setting value due to the stabilization of the flow rate setting value. Further, initially, the valve driving voltage of 2% is suddenly stepped. The reason is that the slight play of the valve is absorbed to prevent a delay in valve operation, and the sensor output change is obtained as soon as possible. Also, FIG.
In the above, the valve drive voltage linearly increases, but it is needless to say that microscopically it increases stepwise in multiple steps every 10 msec as described above.

Now, the actual flow of valve control performed by combining the above-described operations will be described based on the flow shown in FIG. First, it is determined whether or not the learning flag 46 is set (S1). When the learning flag is set (YES), the valve characteristic learning operation shown in FIG. 6 is performed (S2), and the flag is set. If is not set (NO), the set value displacement detection unit 48 determines whether or not the flow rate set value has changed (S).
3). If the set value has not changed (NO), the process proceeds to the re-learning operation (S4), and the re-learned value is recalculated and updated according to the flow shown in FIG. In this way, when the flow rate set value has not changed and the deviation is within the standard, the relearning value is updated regularly to cope with the change in the valve characteristics. On the other hand, when the flow rate setting value has changed in S3 (YES), the process proceeds to the relearning value output operation (S
5), the re-learning value obtained based on the above equations 6 and 7 is output as the valve drive voltage.

As described above, the valve characteristic learning operation is carried out at the factory stage, but after the flow rate control device is installed in the actual use system, the actual flow rate control is performed and the learning is re-learned under specific conditions. The operation is performed. Therefore, even if the valve characteristic changes due to aging or fluctuation of gas pressure, the relearning operation is always performed to update the relearning value, so that appropriate control can be performed according to the valve characteristic. . Further, when outputting the relearning value (valve driving voltage), a very short time T, for example, 50 msec.
Since it gradually increases over 70 msec to bring it to 100% output, the PID control system does not react excessively unlike the case where the PID control system changes abruptly. It is possible to quickly set the predetermined flow rate without causing any occurrence.

The time T until the valve drive voltage reaches 100% is preferably set in the vicinity of the shortest time during which the valve control differentiating circuit does not react excessively. Naturally, this time T is excessively large. If set, an operation delay will occur. In the control method according to the conventional method, it takes about 2 seconds until the flow rate is settled, but by adopting the control method according to the present invention, the flow rate can be settled in about 0.5 seconds. It is possible to control the speed approximately four times faster.
Further, in the case of the control method according to the earlier application of the present inventor,
Since the flow rate hysteresis effect was taken into consideration, the calculation was very complicated, but according to the present invention, since the control method incorporates the hysteresis effect, it is possible to perform the simple arithmetic processing as described above. Also, it becomes easy to create a table.

Next, the simulation results of the conventional method and the method of the present invention will be compared and examined. FIG. 9 shows a control graph when the control method according to the applicant's earlier application (Japanese Patent Application No. 5-339737) is performed, and FIG. 10 shows that the relearning value is not updated in the control method of the present invention. 11 is a control graph when the re-learned value is updated under the latest actual use condition in the control method of the present invention. As is clear from FIG. 9, in the control method of the previous application, when the valve drive voltage is rapidly increased stepwise with a change in the flow rate setting value,
Although the sensor output (flow rate) is slight, overshoot occurs, which is not preferable.

Further, as is apparent from FIG. 10, when the relearning value is not updated even in the control method of the present invention,
That is, in this example, if the gas pressure is changed and the usage conditions are not updated, the valve drive voltage is output by the method according to the present invention.
Since the re-learned value is not updated so as to meet the usage conditions, the sensor output (flow rate) overshoots greatly, which is not preferable. On the other hand, in the case of the control method of the present invention shown in FIG. 11 and when the re-learning value is updated, the sensor output (flow rate) does not overshoot and quickly reaches the target flow rate. It has been reached and proved to be preferable.

Each numerical example in the above embodiment is merely an example, and it goes without saying that it is not limited to these values. Further, in the present embodiment, the piezoelectric element is used as the actuator that drives the diaphragm 8, but the present invention is not limited to this, and an electromagnetic actuator may be used, for example. The valve drive voltage is in the range of about 0 to 120 V in the case of a piezoelectric element, whereas it is in the range of about 0 to 15 V in the case of an electromagnetic actuator.

[0051]

As described above, according to the flow rate control method of the present invention, the following excellent operational effects can be exhibited. Since the re-learning value corresponding to the flow rate set value is obtained in the actual use system and the valve drive signal is output based on this, an appropriate flow rate control can be performed. In addition, when outputting the valve drive signal corresponding to the calculated re-learning value, it takes a very short period of time to bring the valve up to 100% output, so that the differential circuit of the control system The flow rate can be rapidly increased or decreased to a predetermined flow rate without causing excessive reaction and without causing flow rate overshoot. Further, since the relearning value is constantly updated under a predetermined condition, it can be followed even if the valve characteristic changes due to aging of the valve or change of the fluid pressure.

[Brief description of drawings]

FIG. 1 is a 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 configuration diagram showing a configuration of a flow rate control unit of the control device shown in FIG.

FIG. 3 is a schematic block diagram showing a general control state from the output of the sensor control circuit to the output of a valve drive signal.

FIG. 4 is a graph showing changes in a flow rate set value, a learned value, and a relearning value when the control method of the present invention is carried out.

FIG. 5 is a graph showing a relationship between a flow rate setting value and a valve driving signal when the method of the present invention is carried out.

FIG. 6 is a diagram showing a flow of a valve characteristic learning operation.

FIG. 7 is a diagram showing a flow of a re-learning operation.

FIG. 8 is a diagram showing a flow of valve control.

FIG. 9 is a graph showing a simulation result of the method of the previous application (Japanese Patent Application No. 5-339737).

FIG. 10 is a graph showing a simulation result before updating the relearning value in the method of the present invention.

FIG. 11 is a graph showing a simulation result after updating the relearning value in the method of the present invention.

FIG. 12 is a graph showing a change in flow rate according to a conventional flow rate control method.

[Explanation of symbols]

 2 Gas mass flow rate control device 4 Fluid passage 6 Bypass 8 Diaphragm (valve body) 10 Flow control valve 12 Mass flow rate detection sensor section 18 Sensor control circuit 22 Flow rate control section 24 Multilayer pressure element 26 Piezoelectric element drive section 28 Valve characteristic learning block 30 re-learning block 32 storage unit 34 table counter 36 valve characteristic learning calculation unit 38 re-learning calculation control unit 40 flow rate set value generation unit 42, 44 comparison unit 46 learning flag PA gas piping system

Claims (9)

[Claims] 1. A flow rate control method for controlling the flow rate of a fluid by controlling a flow rate control valve provided in a fluid passage for flowing a fluid by a valve drive signal from a flow rate control unit. A step of storing a valve drive signal corresponding to the above as a learned value in a table and storing the flow control valve in an actual operating system, and then flowing the fluid through the flow control valve to obtain an actual valve drive signal. Obtaining and storing relearning values corresponding to the plurality of flow rate set values based on the learned values of the table corresponding to the predetermined set values, and obtaining a valve drive signal based on the relearned values. A flow rate control method, comprising: a step of outputting. 2. The flow rate control method according to claim 1, wherein the re-learning value is updated as needed. 3. The flow rate control method according to claim 1, wherein the flow rate control valve is controlled under PID control when the learning value is obtained. 4. The valve drive signal of the re-learned value is output so as to gradually increase to the obtained drive signal over a predetermined time. Flow control method. 5. The flow control method according to claim 4, wherein the flow control valve is controlled under PID control after the valve drive signal of the relearning value is output. 6. The configuration is such that, after the shift to the PID control, the proportional constant K is lowered or set to zero for a short time, and then the normal proportional constant K is set. 5. The flow rate control method described in 5. 7. The flow rate control method according to claim 1, wherein the valve drive voltage value is read when the deviation between the set value and the flow rate of the fluid falls within a predetermined range during the learning. 8. The flow control method according to claim 1, wherein the valve drive voltage value is read when the deviation between the set value and the flow rate of the fluid falls within a predetermined range in the re-learning value. . 9. The flow control method according to claim 7, wherein the deviation is within ± 0.1%.