JP5090559B2 - Mass flow controller - Google Patents

Description

  The present invention relates to a mass flow controller that controls the flow rate of a fluid such as gas or liquid.

  For example, when various gases used for semiconductor manufacturing are supplied to a semiconductor manufacturing apparatus, mass flow controllers are provided in the supply flow paths, thereby adjusting the gas flow rates. In the past, each mass flow controller was accompanied by a pressure regulator in series, and flow control was facilitated by preventing extreme fluctuations in the flow passage pressure of each mass flow controller.

  As a flow rate control method in the mass flow controller, PID control is fundamental, but for example, as shown in Patent Document 1, feedback control is performed by switching the PID coefficient between a transient response state and a stable state. Things are known.

  Specifically, Patent Document 1 uses a value obtained by substituting a flow rate setting value into a predetermined function as a gain value to be multiplied by a deviation in proportional calculation. For example, the predetermined value used in a stable state is used. The function is such that a smaller value is calculated if the assigned flow rate setting value becomes smaller. That is, the conventional mass flow controller shown in Patent Document 1 only changes the proportional coefficient, integral coefficient and differential coefficient (hereinafter also referred to as PID coefficient) in a stable state in proportion to only the flow rate setting value.

  However, the inventor of the present application shows that the optimum value of the PID coefficient is different between when the primary side pressure rises and when the primary side pressure rises in a stable state, and even if the amount of time change of the primary side pressure is the same, An experimental result was obtained that the PID coefficient was different if the side pressure was different, and that the flow rate set value and the PID coefficient optimum value were not in a linear relationship. Then, it has been found that there is a limit to improving the PI (Pressure Insensitive) performance only by making the PID coefficient proportional to the flow rate set value in a stable state.

JP 2007-34550 A

  Accordingly, the present invention has been made to solve the above-mentioned problems all at once, and its main intended task is to further improve the PI performance in the mass flow controller.

  That is, the mass flow controller according to the present invention is provided on the upstream side or the downstream side of the flow rate sensor unit that measures the flow rate of the fluid flowing in the flow path and outputs a flow rate measurement signal indicating the measured value. A flow rate control valve, a calculation unit for calculating a feedback control value to the flow rate control valve by performing a PID operation on a deviation between a flow rate measurement value indicated by the flow rate measurement signal and a flow rate set value that is a target value, and the feedback control value And an opening degree control signal output unit that generates an opening degree control signal and outputs the opening degree control signal to the flow rate control valve, and the calculation unit calculates a proportional coefficient, an integral coefficient, and a differential coefficient used for PID calculation in a stable state, It is changed based on at least one of the primary side pressure or the flow rate set value and the time change amount of the primary side pressure.

  If it is such, the proportionality coefficient, integral coefficient, and differential coefficient used for the PID calculation in the stable state are based on at least two of the primary side pressure, the temporal change amount of the primary side pressure, and the flow rate setting value. Compared to the conventional method of changing the proportionality coefficient, integral coefficient, and derivative coefficient in proportion to the flow rate setting value, more optimal proportionality coefficient, integral coefficient, and derivative coefficient can be obtained. Therefore, it is difficult to be affected by the pressure fluctuation of the primary side pressure, and stable flow rate control can be performed.

  In particular, since the optimum values of the proportional coefficient, integral coefficient, and differential coefficient differ between when the primary side pressure rises and when the primary side pressure rises in a stable state, the calculation unit determines the proportionality coefficient depending on whether the time change amount of the primary side pressure is positive or negative. It is desirable to change the integral coefficient and the differential coefficient.

  In order to set the proportionality coefficient, integral coefficient, and derivative coefficient to the most optimal values and are not easily affected by pressure fluctuations of the primary side pressure, and to perform stable flow rate control, the calculation unit changes the amount of time variation of the primary side pressure. The proportional coefficient, integral coefficient, and differential coefficient are changed according to the positive / negative of the value, and a predetermined calculation is performed using the value obtained by substituting the flow rate setting value into the predetermined function for the changed proportional coefficient, integral coefficient, and differential coefficient. It is desirable that the change is made by performing a predetermined calculation using a value obtained by substituting the primary side pressure into a predetermined function for the proportional coefficient, the integral coefficient, and the differential coefficient that are changed accordingly.

  According to the present invention configured as described above, the PI performance in the mass flow controller can be improved.

1 is an overall schematic diagram of a mass flow controller according to an embodiment of the present invention. The structural example of the flow control system using the mass flow controller which concerns on the same embodiment. The functional block diagram of the control part in the embodiment. The flowchart which shows the PID coefficient change procedure in the embodiment. The schematic diagram which shows the function used for a PID coefficient change.

  Hereinafter, an embodiment of a mass flow meter 100 according to the present invention will be described with reference to the drawings. 1 is an overall schematic diagram of a mass flow controller according to the present embodiment, FIG. 2 is a configuration example of a flow rate control system using the mass flow controller, FIG. 3 is a functional block diagram of a control unit, and FIG. FIG. 5 is a flowchart showing a procedure for changing the PID coefficient, and FIG. 5 is a schematic diagram showing a function used for changing the PID coefficient.

<Device configuration>
As shown in a schematic diagram in FIG. 1, the mass flow controller 100 according to the present embodiment includes an internal flow channel 1, a flow rate sensor unit 2 that measures the flow rate of the fluid F that flows in the internal flow channel 1, and the flow rate sensor unit. 2, for example, a flow rate control valve 3 provided on the downstream side, a pressure sensor unit 4 provided on the upstream side of the flow rate sensor unit 2 and the flow rate control valve 3, and a control unit 5. As shown in FIG. 2, the gas supply system is used for a gas supply system to a chamber in a semiconductor process.

  Explaining each part, the internal flow path 1 is opened with an upstream end as an introduction port P1 and a downstream end as a lead-out port P2. For example, the introduction port P1 has a fluid supply source such as a cylinder via an external pipe. B is connected, and a chamber (not shown) for semiconductor manufacturing is connected to the lead-out port P2 via an external pipe. In this embodiment, as shown in the figure, a plurality of pipes are branched from one fluid supply source B, and a mass flow controller 100 is provided for each pipe. Further, the pressure regulator PR is provided only at the outlet of the fluid supply source B, and the pressure regulator for the mass flow controller 100 is not provided for each pipe. Reference sign FV is a pneumatic valve.

  Although the flow rate sensor unit 2 is not shown in detail, for example, the flow rate sensor unit 2 includes a pair of thermal sensors (thermal sensors) provided in the flow path 1, and the instantaneous flow rate of the fluid F is converted into an electrical signal by the thermal sensor. The electric signal is detected and amplified by an internal electric circuit, and output as a flow rate measurement signal having a value corresponding to the detected flow rate.

  Although the flow control valve 3 is not shown in detail in detail, for example, the valve opening degree is configured to be changed by an actuator made of a piezo element, and an opening degree control signal that is an electric signal from the outside is provided. When given, the actuator is driven, and the flow rate of the fluid F is controlled by adjusting the valve opening according to the value of the opening control signal.

  Although not shown in detail, the pressure sensor unit 4 includes, for example, a diaphragm (such as a stainless steel diaphragm or a silicon diaphragm) and a pressure sensitive element that measures the displacement of the diaphragm, and the displacement of the diaphragm is the pressure sensitive element. Is detected as an electric signal, and the electric signal is amplified by an internal electric circuit and output as a pressure measurement signal having a value corresponding to the detected flow rate.

  The control unit 5 is composed of a digital or analog electric circuit having a CPU, a memory, an A / D converter, a D / A converter, and the like, and may be dedicated or partly or wholly. Alternatively, a general-purpose computer such as a personal computer may be used. Further, it may be configured such that the functions of the respective units are achieved by using only an analog circuit without using a CPU, and need not be physically integrated, but includes a plurality of devices connected to each other by wire or wirelessly. It may be a thing.

  Then, by storing a predetermined program in the memory and operating the CPU and peripheral devices in cooperation with each other according to the program, the control unit 5 has a signal receiving unit 6, a calculating unit 7, The opening control signal output unit 8 and the flow rate output unit 9 are configured to exhibit at least the functions.

  The signal receiving unit 6 receives the flow rate measurement signal transmitted from the flow rate sensor unit 2, the flow rate setting signal input from another computer or the like, and the pressure measurement signal transmitted from the pressure sensor unit 4, For example, the value is stored in a predetermined area in the memory.

  The calculation unit 7 acquires a flow rate measurement value indicated by the flow rate measurement signal, and calculates a deviation between the flow rate measurement value and a target value, that is, a flow rate setting value indicated by the flow rate setting signal, And a control value calculation unit 72 that calculates a feedback control value to the flow control valve 3 by performing PID calculation on the deviation.

  The opening control signal output unit 8 generates an opening control signal having a value based on the feedback control value and outputs the opening control signal to the flow control valve 3.

  The flow rate output unit 9 performs a predetermined calculation on the flow rate measurement value to calculate a flow rate display value, and a flow rate display signal (analog or digital signal) having the flow rate display value as a value can be used externally. Is output as follows.

  Therefore, in this embodiment, the control value calculation unit 72 uses the proportional coefficient (P), integral coefficient (I), and differential coefficient (D) used for PID calculation in a state where the flow rate is stable (stable state). In other words, the PID coefficient used for PID control in a stable state is changed based on the primary side pressure (supply pressure), the temporal change amount of the primary side pressure, and the flow rate setting value. Here, the stable state is a state in a period other than a change period (for example, about 2 seconds), which is a predetermined period from the time when the flow rate set value is changed by a predetermined amount or more per unit time, and the flow rate set value changes almost. do not do. The predetermined amount is a percentage value with respect to full scale of about 0 to 10%, preferably 0.3 to 5%. Further, the predetermined period means about several seconds, specifically about 0 to 10 seconds, preferably 0.3 to 5 seconds.

  More specifically, the control value calculation unit 72 changes a proportional coefficient, an integral coefficient, and a differential coefficient (hereinafter also referred to as a PID coefficient) depending on whether the primary pressure (the pressure on the upstream side of the mass flow controller) changes with time. Thus, the changed PID coefficient is changed by calculating using a value obtained by substituting the flow rate setting value into a predetermined function, and the changed PID coefficient is changed to a predetermined primary pressure. Change by calculating using the value obtained by assigning to the function. In addition, the control value calculation unit 72 determines the function and the primary side pressure that are specific to the flow rate setting value depending on whether the primary side pressure changes with time, that is, when dp / dt> 0 and dp / dt ≦ 0. The functions specific to are different.

  Hereinafter, a specific change method in the control value calculation unit 72 will be described with reference to FIG.

  First, the control value calculation unit 72 acquires the pressure measurement signal of the primary pressure obtained by the pressure sensor unit 4 and calculates the primary pressure and the temporal change amount of the primary pressure.

  And the control value calculation part 72 judges the positive / negative of the time variation | change_quantity of a primary side pressure (step S1). When it is determined that the time variation of the primary pressure is positive (dp / dt> 0), that is, when the primary pressure rises, the control value calculation unit 72 uses the following formula to calculate the PID coefficient based on the flow rate setting value. Is changed (step S2).

P ′ = P × Fu (set) (1)
I ′ = I × Fu (set) (2)
D ′ = D × Fu (set) (3)

  Here, Fu () is a setting coefficient function that is a function specific to the flow rate setting value, and set indicates the flow rate setting value. As shown in FIG. 5A, the setting coefficient function Fu of the present embodiment is a polygonal line function with different proportional constants of 0-50% and proportional constants of 50-100%. The polygonal line shape is not limited to this and can be set as appropriate. The setting coefficient function Fu can be a curve function, but there are problems that the amount of calculation processing increases and the adjustment of the PID coefficient becomes difficult.

  Next, the control value calculation unit 72 changes the P′I′D ′ coefficient obtained by the above (1) to (3) based on the primary pressure by the following formula (step S3).

P ″ = P ′ × Gu (p) (4)
I ″ = I ′ × Gu (p) (5)
D ″ = D ′ × Gu (p) (6)

  Here, Gu () is a pressure coefficient function that is a function inherent to the primary pressure, and p indicates the primary pressure value. As shown in FIG. 5A, the pressure coefficient function of the present embodiment is a proportional function for calculating a value proportional to the input primary pressure. The pressure coefficient function Gu can be a line function or a curve function. When the curve function is used, there is a problem that the amount of calculation processing increases and adjustment of the PID coefficient becomes difficult.

  As described above, the control value calculation unit 72 changes P, I, and D to P ″, I ″, and D ″ based on the flow rate setting value and the primary side pressure when the temporal change amount of the primary pressure is positive. Then, using the PID coefficient (proportional coefficient P ″, integral coefficient I ″, and differential coefficient D ″), a PID calculation is performed on the deviation to calculate a feedback control value (step S4).

  On the other hand, when the control value calculation unit 72 determines that the change amount of the primary pressure is negative, that is, when the primary pressure is decreasing, the control value calculation unit 72 changes the PID coefficient based on the flow rate setting value by the following equation (step S5). ).

P ′ = P × Fd (set) (7)
I ′ = I × Fd (set) (8)
D ′ = D × Fd (set) (9)

  Here, Fd () is a setting coefficient function that is a function specific to the flow rate setting value, and set indicates the flow rate setting value. As shown in FIG. 5B, the setting coefficient function Fd is a line function similar to the setting coefficient function Fu, but the bending point and the proportionality constant are different. The set coefficient function Fd can be a curve function, but there are problems that the amount of calculation processing increases and the adjustment of the PID coefficient becomes difficult.

  Next, the control value calculation unit 72 changes the P′I′D ′ coefficient obtained by the above (7) to (9) based on the primary pressure by the following equation (step S6).

P ″ = P ′ × Gd (p) (10)
I ″ = I ′ × Gd (p) (11)
D ″ = D ′ × Gd (p) (12)

  Here, Gd () is a pressure coefficient function that is a function inherent to the primary pressure, and p indicates the primary pressure value. As shown in FIG. 5B, the pressure coefficient function Gd is a proportional function similar to the pressure coefficient function Fd, but is a proportional constant different from the proportional constant of the pressure coefficient Fd. The pressure coefficient function Gd can be a line function or a curve function. When the curve function is used, there is a problem that the amount of calculation processing increases and adjustment of the PID coefficient becomes difficult.

  As described above, the control value calculation unit 72 changes P, I, and D to P ″, I ″, and D ″ based on the flow rate setting value and the primary side pressure when the temporal change amount of the primary pressure is negative. Then, using the PID coefficient (proportional coefficient P ″, integral coefficient I ″, and differential coefficient D ″), a PID calculation is performed on the deviation to calculate a feedback control value (step S4).

<Effect of this embodiment>
According to the mass flow controller 100 according to the present embodiment configured as described above, the proportional coefficient, the integral coefficient, and the differential coefficient used for the PID calculation in the stable state are set to the primary pressure, the temporal change amount of the primary pressure, and the flow rate. Since it is changed based on the set value, the optimal proportional coefficient, integral coefficient, and differential coefficient can be obtained compared to the conventional method in which the proportional coefficient, integral coefficient, and derivative coefficient are changed in proportion to the flow rate set value. As a result, it is difficult to be affected by the pressure fluctuation of the primary side pressure, and stable flow rate control can be performed.

<Other modified embodiments>
The present invention is not limited to the above embodiment. In the following description, the same reference numerals are given to members corresponding to the above-described embodiment.

  For example, in the above-described embodiment, the PID coefficient is changed based on all of the primary pressure, the temporal change amount of the primary pressure, and the flow rate setting value. Further, the primary side pressure may be changed using a combination of a temporal change amount of the primary side pressure, a primary side pressure and a flow rate set value, and the like.

  Further, in the above embodiment, the PID coefficient changing procedure was in the order of “change by the amount of change in the primary pressure with time” → “change by the flow rate set value” → “change by the primary pressure”. However, other combinations may be used.

  Furthermore, the control valve may be provided on the upstream side of the flow rate sensor unit, and the flow rate sensor unit is not limited to the thermal sensor, and may be of another flow rate measurement method such as a differential pressure type sensor.

  In addition, some or all of the above-described embodiments and modified embodiments may be combined as appropriate, and the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. .

DESCRIPTION OF SYMBOLS 100 ... Mass flow controller 1 ... Flow path 2 ... Flow rate sensor part 3 ... Flow rate control valve 7 ... Calculation part 8 ... Opening degree control signal output part

Claims (4)

A flow rate sensor unit for measuring a flow rate of the fluid flowing in the flow path and outputting a flow rate measurement signal indicating the measured value;
A flow control valve provided on the upstream side or downstream side of the flow rate sensor unit;
A calculation unit that calculates a feedback control value to the flow control valve by performing a PID calculation on a deviation between the flow rate measurement value indicated by the flow rate measurement signal and a flow rate setting value that is a target value;
An opening degree control signal output unit that generates an opening degree control signal based on the feedback control value and outputs the opening degree control signal to the flow rate control valve;
The calculation unit changes a proportional coefficient, an integral coefficient, and a differential coefficient used for PID calculation in a stable state based on at least one of a primary side pressure or a flow rate set value and a temporal change amount of the primary side pressure. A mass flow controller characterized by   2. The mass flow controller according to claim 1, wherein, when a predetermined primary pressure is given, the calculation unit varies a proportional coefficient, an integral coefficient, and a differential coefficient depending on whether the primary pressure changes with time.   3. The mass flow according to claim 1, wherein, when a predetermined flow rate setting value is given, the calculation unit varies the proportional coefficient, the integral coefficient, and the differential coefficient depending on whether the time change amount of the primary pressure is changed over time. controller.   The calculation unit changes the values of the proportional coefficient, the integral coefficient, and the derivative coefficient itself according to the positive / negative of the temporal change amount of the primary pressure, and sets the flow rate setting value to the changed proportional coefficient, the integral coefficient, and the derivative coefficient. The value obtained by substituting the value obtained by substituting into the function specific to the flow rate setting value is changed, and the primary pressure is changed to the proportional coefficient, the integral coefficient and the differential coefficient, which are changed by the predetermined calculation. 4. The mass flow controller according to claim 1, wherein the mass flow controller is changed by performing a predetermined calculation using a value obtained by substituting it into a function.