CN108398962B

CN108398962B - Maintenance timing prediction device, flow rate control device, and maintenance timing prediction method

Info

Publication number: CN108398962B
Application number: CN201810123202.3A
Authority: CN
Inventors: 田中雅人; 原田贤吾
Original assignee: Azbil Corp
Current assignee: Azbil Corp
Priority date: 2017-02-07
Filing date: 2018-02-07
Publication date: 2021-04-09
Anticipated expiration: 2038-02-07
Also published as: CN108398962A; JP2018128757A; JP6753791B2; KR102003156B1; KR20180091764A

Abstract

The invention predicts the maintenance period of the flow control device and the related equipment. A maintenance timing prediction device according to the present invention includes: a valve opening degree acquisition unit (3) that acquires the opening degree of the valve when the flow rate of the fluid is maintained at a predetermined target flow rate in flow rate control that controls the flow rate of the fluid using the valve; and an uncontrollable time estimating unit (4) for estimating a time until the fluid flow rate becomes uncontrollable, wherein the time is obtained by approximating a relationship between the valve opening and the fluid flow rate, and the change in the valve opening acquired at predetermined time intervals.

Description

Maintenance timing prediction device, flow rate control device, and maintenance timing prediction method

Technical Field

The present invention relates to a technique for predicting a time period required for maintenance of a flow rate control device such as a mass flow controller and related equipment such as a filter.

Background

In a semiconductor manufacturing apparatus or the like, a flow rate control device such as a mass flow controller as shown in fig. 7 is used to introduce a material gas or the like into a vacuum chamber at a constant flow rate (see patent document 1). In fig. 7, 100 denotes a main body block, 101 denotes a sensor module, 102 denotes a head of the sensor module 101, 103 denotes a fluid sensor mounted on the

head

102, 104 denotes a valve, 105 denotes a flow path formed inside the

main body block

100, 106 denotes an opening on an inlet side of the

flow path

105, and 107 denotes an opening on an outlet side of the flow path 105.

Fluid flows from the opening 106 into the flow path 105 and is discharged from the opening 107 through the valve 104. The fluid sensor 103 measures the flow rate of the fluid flowing in the flow path 105. A control circuit, not shown, of the mass flow controller drives the valve 104 so that the flow rate of the fluid measured by the fluid sensor 103 matches a set value.

When the flow rate of the material gas is continuously controlled by the mass flow controller, contaminants may adhere to the mass flow controller itself or a relevant device such as a filter provided in a flow path of the material gas due to the influence of components contained in the material gas, and the like, thereby causing a failure.

Therefore, a device has been proposed which operates and corrects the valve opening degree so that a flow rate error and a pressure error occur only within an allowable accuracy range in the entire measurement range of a fluid sensor incorporated in a mass flow controller (see patent document 2).

However, the diagnostic mechanism disclosed in patent document 2 can diagnose whether or not the error between the measurement value of the fluid sensor and the actual flow rate is tolerable with respect to accuracy, but has a problem that it is impossible to predict when maintenance such as correction is necessary. In semiconductor manufacturing apparatuses and the like, operation management is easy by predicting maintenance timing, and therefore improvement is demanded in the industry.

[ Prior art documents ]

[ patent document ]

[ patent document 1 ] Japanese patent application laid-open No. 2008-039588

[ patent document 2 ] Japanese patent No. 5931668

Disclosure of Invention

[ problem to be solved by the invention ]

The present invention has been made to solve the above-described problems, and an object thereof is to provide a maintenance timing prediction device, a flow rate control device, and a maintenance timing prediction method that can predict the timing at which the flow rate control device and its related equipment need to be maintained.

[ MEANS FOR SOLVING PROBLEMS ] A method for producing a semiconductor device

The maintenance timing prediction device of the present invention is characterized by comprising: a valve opening degree acquisition unit configured to acquire an opening degree of a valve when a flow rate of a fluid is maintained at a predetermined target flow rate in a flow rate control for controlling the flow rate of the fluid using the valve; and an uncontrollable time estimating unit configured to estimate a time until the flow rate of the fluid becomes an uncontrollable state in which the flow rate of the fluid cannot be maintained at the target flow rate, based on a function obtained by approximating a relationship between the opening degree of the valve and the flow rate of the fluid and a change in the opening degree of the valve acquired at predetermined time intervals.

In the maintenance timing prediction device 1 according to the present invention, the uncontrollable time estimating unit estimates a time until the opening degree of the valve obtained by the valve opening degree obtaining unit reaches an upper limit as a time until the uncontrollable state is achieved.

In addition, the maintenance timing prediction device 1 of the present invention is characterized in that the function is defined by at least a term relating to the opening degree of the valve and a gain which is a numerical value multiplied by the term, and the uncontrollable time estimating unit estimates the time until the uncontrollable state is reached, based on a numerical expression obtained from the function when it is assumed that the gain decreases with the passage of time and a change in the opening degree of the valve acquired by the valve opening degree acquiring unit.

In addition, in the example configuration 1 of the maintenance timing prediction apparatus according to the present invention, the function is a function that approximates a nonlinear relationship between the opening degree of the valve and the flow rate of the fluid, and the term relating to the opening degree of the valve is expressed by an exponential function.

In addition, in the example configuration 1 of the maintenance timing prediction apparatus according to the present invention, the function is a function that approximates a nonlinear relationship between the opening degree of the valve and the flow rate of the fluid, and the term relating to the opening degree of the valve is expressed by a fractional function.

In addition, the maintenance timing prediction device 1 according to the present invention is characterized in that the uncontrollable time estimating unit includes a 1 st gain calculating unit, a 2 nd gain calculating unit, a 3 rd gain calculating unit, and a time calculating unit, the 1 st gain calculating unit calculates the gain at a past time point from the opening degree of the valve acquired by the valve opening degree acquiring unit at a past time point that is a time point before a current time point at which a time to change to the uncontrollable state is estimated, the 2 nd gain calculating unit calculates the gain at the current time point from the opening degree of the valve acquired by the valve opening degree acquiring unit at the current time point, the 3 rd gain calculating unit calculates the gain when the opening degree of the valve acquired by the valve opening degree acquiring unit at a time point after the current time point reaches an upper limit from the target flow rate, the time calculation unit calculates the time until the state becomes uncontrollable based on the gains calculated by the 1 st gain calculation unit, the 2 nd gain calculation unit, and the 3 rd gain calculation unit and the time from the past time point to the present time point.

In addition, the maintenance timing prediction device 1 according to the present invention further includes an estimation result output unit that numerically displays the time estimated by the uncontrollable time estimating unit.

In addition, the maintenance timing prediction device 1 according to the present invention further includes an estimation result output unit that issues an alarm when the time estimated by the uncontrollable time estimating unit is less than a predetermined threshold time.

Further, a flow rate control device according to the present invention includes: a flow rate measurement unit that measures a flow rate of a fluid flowing through the flow path; a valve disposed on the flow path; a flow rate control unit that operates the valve so that the flow rate measured by the flow rate measurement unit matches a predetermined target flow rate; and a maintenance timing prediction device, wherein the valve opening degree acquisition unit of the maintenance timing prediction device acquires an opening degree of the valve provided in the flow path.

Further, a maintenance timing prediction method according to the present invention includes: a step 1 of acquiring an opening degree of a valve when a flow rate of a fluid is maintained at a predetermined target flow rate in a flow rate control for controlling the flow rate of the fluid using the valve; and a 2 nd step of estimating a time until the flow rate of the fluid becomes uncontrollable state in which the flow rate of the fluid cannot be maintained at the target flow rate, based on a predetermined function obtained by approximating a relationship between the opening degree of the valve and the flow rate of the fluid and a change in the opening degree of the valve acquired at predetermined time intervals.

[ Effect of the invention ]

According to the present invention, it is possible to predict the timing (time until the flow rate control device and the related equipment become uncontrollable) at which maintenance is required. As a result, it is easy for the operator to perform operation management of the semiconductor manufacturing apparatus and the like provided with the flow rate control device.

Drawings

Fig. 1 is a diagram showing an example 1 of a relationship between an opening degree of a valve provided in a mass flow controller and a flow rate of a fluid.

Fig. 2 is a diagram showing a change with time of a valve opening for maintaining a target flow rate.

Fig. 3 is a diagram showing another example of the relationship between the opening degree of a valve provided in a mass flow controller and the flow rate of a fluid.

Fig. 4 is a block diagram showing a configuration of a flow rate control device according to an embodiment of the present invention.

Fig. 5 is a flowchart illustrating a flow rate control operation of the flow rate control device according to the embodiment of the present invention.

Fig. 6 is a flowchart illustrating a maintenance timing prediction operation of the flow rate control device according to the embodiment of the present invention.

Fig. 7 is a cross-sectional view of a mass flow controller.

Detailed Description

[ principles of the invention ]

In most cases, the purpose of a mass flow controller is to maintain the flow rate of a fluid stably at a target flow rate that is determined in a predefined manner. Therefore, assuming such an application, the influence of clogging of the filter and the like can be estimated under highly reliable detection conditions. Specifically, a state in which a predetermined target flow rate (in the case where there are a plurality of target flow rates, the maximum target flow rate is set as a reference) is stably maintained is detected at substantially constant intervals (for example, at 24-hour intervals), and the valve opening degree instruction signal under the condition is acquired.

Considering the deterioration of clogging of a filter provided upstream of the mass flow controller, the time during which the valve opening degree is saturated and reaches the upper limit (for example, 100%) is theoretically determined as the time during which the valve becomes uncontrollable and cannot be maintained at the target flow rate, and the time when the valve becomes uncontrollable is predicted to determine that maintenance is efficient.

Therefore, the inventors have considered that it is appropriate to acquire information on the valve opening degree with high reliability based on the use conditions specific to the mass flow controller, and predict the time when the valve opening degree reaches the upper limit (for example, 100%) when the temporal change in the valve opening degree is continuously performed, as the time when maintenance is necessary.

[ examples ]

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Patent document 2 shows the following: when the opening degree of a valve provided in a mass flow controller is changed linearly in time, the higher the opening degree, the less the change in the flow volume of the fluid flowing through the flow path. From this, it is understood that the valve opening MV and the flow rate PV are nonlinear, and the amount of change in the flow rate PV decreases as the opening degree becomes higher. The outline of the characteristics of such a mass flow controller is shown in fig. 1. In the example of FIG. 1, the flow rate PV is normalized to a value of 0 to 100%. Since the characteristic shown in fig. 1 is a nonlinear convergence phenomenon, it can be expressed by an exponential function of the following formula.

PV＝K{1.0－exp(-MV/A)}···(1)

As described above, the function approximating the relationship between the valve opening MV and the flow rate PV is defined by the constant term (1.0), the term relating to the valve opening MV, and the gain K which is a numerical value multiplied by these terms. A in the formula (1) is a coefficient for giving a nonlinear convergence state. Curve cur1 of fig. 1 represents the initial characteristic of a mass flow controller. The curve cur1 can be expressed as an exponential function of a coefficient value such as the following equation, in combination with a normal nonlinear image, with the flow rate PV reaching the maximum value 100% when the valve opening MV is set to 100%, based on the supply pressure which can be grasped in advance.

PV＝104.0{1.0－exp(-MV/30.0)}···(2)

In formula (2), K ═ 104.0 and a ═ 30.0 represent 1 example of these values. In the clogging phenomenon of a filter or the like provided in a flow path, it can be estimated that the nonlinearity, which is the characteristic of the valve itself of a mass flow controller located downstream of the filter, does not change, and therefore the coefficient a can be regarded as fixed. Therefore, it is assumed that only the gain K is reduced by a clogging phenomenon of the filter or the like.

In the prediction of the maintenance period of the mass flow controller or the equipment related to the mass flow controller, although it is assumed that several factors affect the operation time of the mass flow controller, it is not certain whether the gain K is changed in an acceleration or deceleration manner, and therefore it is appropriate to assume that the gain K is decreased at a fixed rate in proportion to the operation time of the mass flow controller.

Here, the predetermined target flow rate PVx is assumed to be PVx — 60.0%. That is, the most basic value given as the flow rate set value SP of the mass flow controller is SPx 60.0%. When the valve opening degree in the initial state of the mass flow controller for setting the flow rate of the fluid to PVx-60.0% is MV1, MV 1-25.8% is obtained from curve cur 1. Since the coefficient a of the nonlinear characteristic can be grasped in advance at 30.0%, the gain K1 in the initial state can be inversely calculated from PVx at 60.0% and MV1 at 25.8% as in the following equation.

K1＝PVx/{1.0－exp(-MV1/A)}

＝60.0/{1.0－exp(-25.8/30.0)}＝104.0

···(3)

Next, during the continuous operation of the mass flow controller, the valve opening MV for maintaining the target flow rate PVx at 60.0% is acquired at regular intervals (for example, at intervals of Δ T24 hours). It is assumed that a significant difference from the initial state is grasped at a time point when 3 times (n-3) have passed, that is, 72 hours. Specifically, at the time point when 72 hours have elapsed from the start of operation, the valve opening MV increases to 29.4% from MV 2.

The rise of the valve opening MV is the following phenomenon: the clogging phenomenon of the filter causes a pressure drop at the point of inflow to the mass flow controller, and thus the valve opening MV for maintaining the target flow rate PVx at 60.0% must be made larger than the initial state. The gain K2 at the time point when 72 hours have elapsed from the start of operation can be inversely calculated from PVx ═ 60.0% and MV2 ═ 29.4% as in the following equation.

K2＝PVx/{1.0－exp(-MV2/A)}

＝60.0/{1.0－exp(-29.4/30.0)}＝96.0

···(4)

Therefore, it is inferred that the gain K is reduced from the initial state of K1 ═ 104.0 to the initial state of K2 ═ 96.0 within 72 hours, and is reduced in value by 8.0. In this case, the characteristic of the mass flow controller is as shown by curve cur2 in fig. 1.

Since it is assumed that the gain K decreases at a fixed rate in proportion to the operating time of the mass flow controller, it can be concluded that when 72 hours have elapsed from the state cur2, the gain K decreases by 8.0 again and the characteristic of the mass flow controller changes to the same state as curve cur3 of fig. 1 (K3 ═ 88.0). The valve opening MV3 at this time point may be calculated in reverse as follows.

MV3＝-Aln{1.0－(PVx/K3)}

＝-30.0ln{1.0－(60.0/88.0)}＝34.4

···(5)

The above contents are organized as follows. In the initial state (cur1), the performance was MV1 ═ 25.8%. In a state (cur2) after 72 hours from the start of operation, the performance was MV2 — 29.4%. In a state (cur3) after 72 hours, MV3 can be estimated to be 34.4%. That is, the valve opening MV does not change at a fixed rate, but rises in an accelerated manner under the influence of the nonlinearity of the exponential function. This is also a reason why the change in the valve opening degree cannot be simply assumed to be a fixed speed.

There may be a problem in how many hours later the valve opening MV for maintaining the target flow rate PVx at 60.0% becomes uncontrollable by reaching MV at 100.0% (curve cur4 in fig. 1). When the gain K in the uncontrollable state is set to Kh, the gain Kh can be calculated by the following equation.

Kh＝PVx/{1.0－exp(-MV/A)}

＝60.0/{1.0－exp(-100.0/30.0)}＝62.2

···(6)

Since the gain K changes by 8.0 every 72 hours (n Δ T is 3 × 24), the time Th from when the gain K2 is 96.0 to when Kh is 62.2 in a state (cur2) after 72 hours from the start of operation can be calculated by the following equation.

Th＝nΔT(Kh－K2)/(K2－K1)

＝3×24.0(62.2－96.0)/(96.0-104.0)＝304.0

···(7)

That is, starting from the state of curve cur2 in fig. 1, Kh becomes 62.2 after 304 hours. When the gain K3 of the state (cur3) after 144 hours from the start of operation is obtained as a result, the time Th can be calculated by the following equation.

Th＝nΔT(Kh－K3)/(K3－K2)

＝3×24.0(62.2－88.0)/(88.0－96.0)＝232.0

···(8)

In this way, the time Th until the MV becomes 100.0% can be estimated from the current time and the latest valve opening.

According to the calculation of equations (1) to (8), the valve opening degree for maintaining the target flow rate PVx at 60.0% changes as shown in fig. 2 with the passage of time.

From the above, the prediction order of the maintenance timing of the mass flow controller and the related devices can be organized as the following (I) to (IV). In the following steps, the time point at which the gain K1 is calculated does not necessarily mean the time point in the initial state, but means the time point in an arbitrary past state. Therefore, the influence of whether the change in gain K due to clogging of the filter or the like is acceleration or deceleration can be solved only by the error amount from the nearest speed.

(I) Before n Δ T hours, a valve opening MV1 for maintaining at the target flow rate PVx is acquired. From this, a gain K1(n is an integer of 1 or more) before n Δ T hours is calculated. However, the nonlinear coefficient a is predetermined.

K1＝PVx/{1.0－exp(-MV1/A)}···(9)

(II) at the present time point, valve opening MV2 for maintaining at target flow PVx is acquired. From this, the gain K2 at the current time point is calculated. However, the nonlinear coefficient a is unchanged.

K2＝PVx/{1.0－exp(-MV2/A)}···(10)

(III) a gain Kh is calculated when the valve opening MV to maintain the target flow rate PVx reaches 100%.

Kh＝PVx/{1.0－exp(-100.0/A)}···(11)

(IV) finally, the time Th until the gain K reaches Kh is calculated.

Th＝nΔT(Kh－K2)/(K2－K1)···(12)

The same method can be applied to a function that can approximate the nonlinearity of fig. 1, but is not an exponential function. For example, if the following fractional function is used, nonlinearity between the valve opening and the flow rate can be described by only four arithmetic operations.

PV＝K[{-A/(MV+B)}+C]

＝1.0[{-3130.0/(MV+25.0)}+125.2]

···(13)

K1＝PVx/[{-A/(MV1+B)}+C]···(14)

K2＝PVx/[{-A/(MV2+B)}+C]···(15)

Kh＝PVx/[{-A/(100.0+B)}+C]···(16)

Like equation (1), the function of equation (13) is defined by a constant term (C ═ 125.2), a term relating to the valve opening MV, and a gain K multiplied by these terms. From equations (13) to (16), the characteristics of the mass flow controller can be shown in fig. 3 as in fig. 1. Gain K1 in the state of curve cur1 in fig. 3 is 1.0, gain K2 in the state of curve cur2 is 0.923, gain K3 in the state of curve cur3 is 0.846, and gain Kh in the case where valve opening MV reaches 100% (cur4) is 0.596. That is, as with the example of fig. 1, the gain K decreases at a fixed rate in proportion to the operating time.

Next, the structure of the flow rate control device (mass flow controller) of the present embodiment will be described. As shown in fig. 4, the flow rate control device of the present embodiment includes: a flow rate measurement unit 1 that measures a flow rate of a fluid flowing through a flow path; a flow rate control unit 2 that operates the valve so that the flow rate measured by the flow rate measurement unit 1 matches the target flow rate PVx; a valve opening acquiring unit 3 that acquires a valve opening MV when the flow rate of the fluid is maintained at a predetermined target flow rate PVx during flow rate control; an uncontrollable time estimating unit 4 for estimating a time Th until the flow rate of the fluid becomes uncontrollable where the flow rate of the fluid cannot be maintained at the target flow rate PVx; and an estimation result output unit 5 that outputs information on the estimation result of the uncontrollable time estimation unit 4.

Next, the operation of the flow rate control device according to the present embodiment will be described with reference to fig. 5 and 6. Fig. 5 is a flowchart illustrating the flow rate control operation, and fig. 6 is a flowchart illustrating the maintenance timing prediction operation.

The flow rate measurement unit 1 continuously measures the flow rate of the fluid flowing through the flow path (flow path 105 in fig. 7) (step S100 in fig. 5). The flow rate measuring unit 1 corresponds to the fluid sensor 103 shown in fig. 7, and is a known structure provided in a mass flow controller.

The flow rate control unit 2 continuously operates the valve (the valve 104 in fig. 7) so that the flow rate of the fluid measured by the flow rate measurement unit 1 matches a target flow rate PVx set by an operator, for example (step S101 in fig. 5). The flow rate control unit 2 is also a known structure provided in a mass flow controller.

In this manner, the processing in steps S100 and S101 is repeatedly executed for each predetermined cycle (for example, 50msec.) until the operator instructs the termination of the operation of the apparatus (yes in step S102 in fig. 5).

On the other hand, the valve opening acquiring unit 3 acquires the valve opening MV (target maintaining valve opening) when the flow rate of the fluid is maintained at the target flow rate PVx (step S200 in fig. 6). Specifically, when the absolute value of the deviation between the flow rate measured by the flow rate measurement unit 1 and the target flow rate PVx is continuously within the predetermined value during a period from a certain time onward to the current time, the valve opening degree acquisition unit 3 determines that the flow rate of the fluid is maintained at the target flow rate PVx, and acquires the valve opening degree MV at the current time. The value of the fixed time T (T < Δ T) is set to a predetermined value in the valve opening degree acquisition unit 3.

Although the valve opening degree itself may be detected, the valve opening degree itself may not be detected strictly at the time of implementation, and a signal (for example, a valve opening degree instruction signal or a valve driving current) output from the flow rate control portion 2 to the valve may be acquired and the valve opening degree may be determined based on the signal.

Next, the uncontrollable time estimating unit 4 estimates a time Th until the valve opening MV reaches an upper limit (for example, 100%) and becomes an uncontrollable state in which the flow rate of the fluid cannot be maintained at the target flow rate PVx, based on a change in the valve opening MV acquired at predetermined time intervals. As shown in fig. 4, the uncontrollable time estimating unit 4 includes a 1 st gain calculating unit 40 for calculating a gain K1, a 2 nd gain calculating unit 41 for calculating a gain K2, a 3 rd gain calculating unit 42 for calculating a gain Kh, and a time calculating unit 43 for calculating a time Th.

The 1 st gain calculation unit 40 of the uncontrollable time estimation unit 4 calculates the gain K1 before n Δ T hours at the current time of the just-to-be-estimated time Th by using equation (9) (step S201 in fig. 6). As described above, MV1 in equation (9) is the valve opening MV acquired by valve opening acquiring unit 3 n Δ T hours ago. The coefficient a of equation (9) is set to a predetermined value in the uncontrollable time estimating unit 4. In order to grasp the coefficient a, for example, a flow rate test of the flow rate control device is performed in advance, and the value of the coefficient a may be investigated.

Then, the 2 nd gain calculation unit 41 of the uncontrollable time estimation unit 4 calculates the gain K2 at the current time point of the just-to-be-estimated time Th by using equation (10) (step S202 in fig. 6). As described above, MV2 in equation (10) is the latest valve opening MV acquired by valve opening acquiring unit 3 at the current time point.

Further, the 3 rd gain calculation unit 42 of the uncontrollable time estimation unit 4 calculates the gain Kh when the valve opening MV reaches the upper limit at the time point subsequent to the current time point, using equation (11), based on the target flow rate PVx (step S203 in fig. 6).

Then, the time calculation unit 43 of the uncontrollable time estimation unit 4 calculates a time Th from the current time point to the uncontrollable state by equation (12) based on the gains K1, K2, Kh and the time n Δ T (step S204 in fig. 6). As described above, the processing of the uncontrollable time estimating unit 4 is ended.

The estimation result output unit 5 outputs the estimation result of the uncontrollable time estimation unit 4 (step S205 in fig. 6). Examples of the method of outputting the estimation result include a numerical value display with time Th, an alarm output based on time Th, and transmission of information of the estimation result to the outside. In the case of alarm output, when the time Th is less than a predetermined threshold time (for example, less than 48 hours), the LED for notifying an alarm may be turned on.

The valve opening degree acquisition unit 3, the uncontrollable time estimation unit 4 and the estimation result output unit 5 repeatedly execute the processing of steps S200 to S205 for a predetermined period Δ T (for example, 24 hours) until the operator instructs the termination of the operation of the apparatus (yes in step S206 of fig. 6).

As described above, in the present embodiment, it is possible to predict the timing (time Th until the flow rate control device and its related equipment (such as a filter provided in the flow path) require maintenance. Since the operator can predict when maintenance such as calibration is necessary from the estimated result of the flow rate control device, the operation management of the semiconductor manufacturing apparatus and the like is easy.

While the uncontrollable time estimating unit 4 calculates the gain K1 before n Δ T hours (n is an integer equal to or greater than 1), the valve opening acquiring unit 3 acquires the valve opening MV at each cycle Δ T, and therefore the integer n may take various values. If the flow rate of the fluid is not maintained at the target flow rate PVx, the valve opening MV cannot be acquired at the time determined by the valve opening acquiring unit 3, and the data of the valve opening MV at that time is missing. Further, in order to appropriately estimate the time Th until the state becomes uncontrollable, the time n Δ T is preferably within an appropriate range that is not excessively long but is excessively short.

Therefore, the uncontrollable time estimating unit 4 may calculate the expressions (9) and (12) for n Δ T, which is the latest time point within a predetermined range and at which the valve opening degree MV can be acquired by the valve opening degree acquiring unit 3, among the time points just before n Δ T of the current time point of the estimated time Th is small.

The uncontrollable time estimating unit 4 may calculate the gains K1, K2, and Kh using the expressions (14), (15), and (16) instead of the expressions (9), (10), and (11). The coefficient A, B, C of the expressions (14), (15), and (16) is set as a predetermined value in the uncontrollable time estimating unit 4. To grasp this coefficient A, B, C, for example, a flow rate test of the flow rate control device may be performed in advance.

In the present embodiment, the target flow rate PVx is assumed to be fixed, but the target flow rate PVx may be changed halfway. The process in fig. 6 is a process in which the target flow rate PVx is always maintained at a constant value, and therefore, when the target flow rate PVx is changed in the middle, the process in fig. 6 may be executed for each target flow rate PVx. For example, when the target flow rate is changed from PVx ═ 60.0% to PVx ═ 50.0%, the processing of fig. 6 is executed using the data of the valve opening MV acquired when PVx is 60.0%, instead of using the data of the valve opening MV acquired when PVx is 50.0%.

In the present embodiment, the entire configuration shown in fig. 4 is provided in the flow rate control device (mass flow controller), but the present invention is not limited to this. The valve opening degree acquisition unit 3, the uncontrollable time estimation unit 4, and the estimation result output unit 5 may be provided in a higher-level device (for example, a programmable logic controller PLC) as a maintenance timing prediction device, and may be used in combination with a general micro-flow controller including the flow rate measurement unit 1 and the flow rate control unit 2.

The flow rate control device described in this embodiment can be realized by a computer having a cpu (central Processing unit), a storage device, and an interface, and a program for controlling these hardware resources. Similarly, the maintenance timing prediction device including the valve opening degree acquisition unit 3, the uncontrollable time estimation unit 4, and the estimation result output unit 5 can be realized by a computer and a program. The CPU of each device executes the processing described in the present embodiment in accordance with the program stored in each storage device. Thus, the maintenance timing prediction method of the present embodiment can be realized.

[ industrial applicability ]

The present invention can be applied to a technique for predicting the period of time required for maintenance of a flow control device and its related equipment.

Description of the symbols

1 flow rate measuring section

2 flow rate control part

3-valve opening degree acquisition unit

4 uncontrollable time estimating part

5 output part of estimation result

40 to 42 gain calculating part

43 time calculating part.

Claims

1. A maintenance timing prediction device is characterized by comprising:

a valve opening degree acquisition unit configured to: acquiring an opening degree of a valve when a flow rate of a fluid is maintained at a predetermined target flow rate in a flow rate control for controlling the flow rate of the fluid using the valve; and

an uncontrollable time estimating unit configured to: the time until the flow rate of the fluid becomes uncontrollable, which cannot be maintained at the target flow rate, is estimated based on a function obtained by approximating a relationship between the opening degree of the valve and the flow rate of the fluid and a change in the opening degree of the valve acquired at predetermined time intervals.

2. The maintenance period prediction device according to claim 1,

the uncontrollable time estimating unit estimates a time until the opening degree of the valve acquired by the valve opening degree acquiring unit reaches an upper limit as a time until the uncontrollable state is achieved.

3. The maintenance period prediction device according to claim 1 or 2,

the function is defined by at least a term relating to the opening degree of the valve and a gain which is a numerical value multiplied by the term,

the uncontrollable time estimating unit estimates the time until the uncontrollable state is achieved, based on the numerical expression obtained from the function when the gain is assumed to decrease with the passage of time and the change in the opening degree of the valve acquired by the valve opening degree acquiring unit.

4. The maintenance period prediction device according to claim 3,

the function is a function obtained by approximating a nonlinear relationship between the opening degree of the valve and the flow rate of the fluid, and the term relating to the opening degree of the valve is expressed by an exponential function.

5. The maintenance period prediction device according to claim 3,

the function is a function obtained by approximating a nonlinear relationship between the opening degree of the valve and the flow rate of the fluid, and the term relating to the opening degree of the valve is expressed by a fractional function.

6. The maintenance period prediction device according to claim 3,

the uncontrollable time estimating unit comprises a 1 st gain calculating unit, a 2 nd gain calculating unit, a 3 rd gain calculating unit and a time calculating unit,

the 1 st gain calculation unit calculates the gain at a past time point that is a time point before a current time point at which a time until the state is changed to the uncontrollable state is estimated, based on the opening degree of the valve acquired by the valve opening degree acquisition unit at the past time point,

the 2 nd gain calculating unit calculates the gain at the current time point based on the opening degree of the valve acquired by the valve opening degree acquiring unit at the current time point,

the 3 rd gain calculating unit calculates the gain when the opening degree of the valve acquired by the valve opening degree acquiring unit reaches an upper limit at a time point subsequent to a current time point, based on the target flow rate,

the time calculation unit calculates the time until the state becomes uncontrollable based on the gains calculated by the 1 st gain calculation unit, the 2 nd gain calculation unit, and the 3 rd gain calculation unit and the time from the past time point to the present time point.

7. The maintenance period prediction device according to claim 1 or 2, characterized by further comprising:

and an estimation result output unit that numerically displays the time estimated by the uncontrollable time estimating unit.

8. The maintenance period prediction device according to claim 1 or 2, characterized by further comprising:

and an estimation result output unit that issues an alarm when the time estimated by the uncontrollable time estimating unit is less than a predetermined threshold time.

9. A flow rate control device is characterized by comprising:

a flow rate measurement unit that measures a flow rate of a fluid flowing through the flow path;

a valve disposed on the flow path;

a flow rate control unit that operates the valve so that the flow rate measured by the flow rate measurement unit matches a predetermined target flow rate; and

the maintenance timing prediction device according to claim 1 or 2, wherein the valve opening degree acquisition unit of the maintenance timing prediction device acquires an opening degree of the valve provided in the flow passage.

10. A method for predicting a maintenance period, comprising:

a step 1 of acquiring an opening degree of a valve when a flow rate of a fluid is maintained at a predetermined target flow rate in a flow rate control for controlling the flow rate of the fluid using the valve; and

and a step 2 of estimating a time until the flow rate of the fluid becomes uncontrollable at the target flow rate based on a function obtained by approximating a relationship between the opening degree of the valve and the flow rate of the fluid and a change in the opening degree of the valve acquired at predetermined time intervals.