TECHNICAL FIELD

The present invention relates to a flow rate control method and a flow rate control device, and more particularly, to a flow rate control method and a flow rate control device suitably used in a semiconductor manufacturing equipment, a chemical plant, or the like.

BACKGROUND OF INVENTION

In semiconductor manufacturing equipment and chemical plants, various types of flowmeters and flow rate control devices are used to control the flow of fluids such as material gas and etching gas. Among them, the pressure-type flow rate control device is widely used because it is possible to control the flow rate of various fluids with high accuracy by a relatively simple mechanism, which is a combination of a control valve and a restriction part (for example, an orifice plate). Further, the pressure-type flow rate control device has an excellent flow rate control characteristic that stable flow rate control can be achieved even if the primary supply pressure fluctuates greatly.

As the control valve used in the pressure-type flow rate control device, a piezoelectric element driven valve for opening/closing a metal diaphragm valve element by a piezoelectric element driven device (hereinafter, sometimes referred to as a piezo actuator) is used. Patent Document 1 discloses a pressure type flow rate control device, and Patent Document 2 discloses a normally open type piezoelectric element driven valve used as the control valve.

PRIOR ART LITERATURE

Patent Literature

Patent Document 1: Japanese Laid-Open Patent Publication No. 2007-192269

Patent Document 2: Japanese Patent No. 4933936

Patent Document 3: International Publication No. 2018/021277

Patent Document 4: International Publication No. 2018/008420

Patent Document 5: International Publication No. 2013/179550

SUMMARY OF INVENTION

Problems to be Solved by Invention

A pressure-type flow rate control device is configured to adjust the flow rate by controlling a fluid pressure upstream of the restriction part (hereinafter, sometimes referred to as upstream pressure). The upstream pressure can be controlled by adjusting the opening degree of a control valve provided upstream of the restriction part, and the fluid can be flowed at a desired flow rate by matching the upstream pressure to a pressure corresponding to the desired flow rate using the control valve.

However, there is a problem that in the pressure-type flow rate control device, since the restriction part such as an orifice plate having a fine opening is used, it is difficult to increase the responsiveness when shifting from a high set flow rate to a low set flow rate, i.e. the flow rate step down. The main reason why it cannot improve the responsiveness at the time of step-down is that, it is difficult to rapidly reduce the upstream pressure and flow rate even if the control valve closes, because the gas between the control valve and the restriction part is continued to flow out through the restriction part.

As a countermeasure to the responsiveness in such a flow rate step-down, it is conceivable to reduce the flow path volume between the control valve and the restriction part as much as possible. However, since the pressure-type flow rate control device controls the fluid pressure between the control valve and the restriction part based on the output of a pressure sensor or the like, there is also a limit to reduce the volume of the flow path described above. Therefore, particularly when performing the flow rate control in a small flow rate range, in which the aperture diameter of the restriction part is small, also sufficient step-down responsiveness cannot be obtained, using a conventional control method, it may take more than 2 seconds when reducing from 100% flow rate to 5% flow rate.

The present invention has been made in view of the above-mentioned problems, and its main object is to provide a flow rate control method and a flow rate control device capable of improving the responsiveness particularly at the time of flow rate step-down.

Means for Solving Problem

The flow rate control method according to an embodiment of the present invention is performed by using a flow rate control device comprising: a first control valve provided in a flow path, a second control valve provided downstream of the first control valve, and a pressure sensor for measuring the fluid pressure downstream of the first control valve and upstream of the second control valve, the flow rate control device being configured to control the flow rate of a fluid flowing to the downstream of the second control valve, based on a signal output by the pressure sensor, and including the steps of (a) while controlling the opening degree of the first control valve so that the flow rate become a first flow rate based on the output of the pressure sensor, keeping the second control valve open, flowing a fluid at the first flow rate, then closing the first control valve from this state; (b) on the basis of the output of the pressure sensor, controlling the pressure remaining downstream of the first control valve by adjusting the opening degree of the second control valve, and flowing the fluid at a second flow rate downstream of the second control valve.

In an embodiment, in the step (b), when α is the proportional constant, ΔP/Δt is the pressure change rate, i.e. the ratio of the change ΔP of the upstream pressure output from the pressure sensor and the time Δt is time required for the change ΔP of the upstream pressure, V is the internal volume between the first control valve and the second control valve, in order to match the builddown flow rate Q represented by Q=α·(ΔP/Δt)·V to the second flow rate, based on the signal output from the pressure sensor, the opening of the second control valve is feedback controlled.

In an embodiment, the flow rate control method further includes a step (c) of flowing fluid downstream at the second flow rate by controlling the opening of the first control valve based on the output of the pressure sensor, at a time point when the output of the pressure sensor falling to a predetermined value, after performing the step (b).

In an embodiment, the second control valve is fully opened when the fluid is flowing at the first flow rate in the step (a), and when the fluid is flowing at the second flow rate by controlling the opening degree of the first control valve in the step (c).

In an embodiment, in the step (a), the first control valve is closed at an opening that is smaller than the opening when the opening of the first control valve is controlled to be the second flow rate, based on the output of the pressure sensor.

In an embodiment, the timing of closing the first control valve in the step (a) and the timing of starting the adjustment of the opening degree of the second control valve in the step (b) are synchronized.

The flow rate control device according to an embodiment of the present invention includes a first control valve provided in a flow path, a second control valve provided downstream of the first control valve, a pressure sensor for measuring the fluid pressure downstream of the first control valve and upstream of the second control valve, and a control circuit for controlling the operation of the first control valve and the second control valve, the control circuit being configured to control the flow rate by controlling the first control valve based on a signal output from the pressure sensor, and to perform the steps of: (a) while controlling the opening of the first control valve so that the flow rate become a first flow rate based on the output of the pressure sensor, and keeping the second control valve open, flowing a fluid at the first flow rate, then closing the first control valve from this state; (b) on the basis of the output of the pressure sensor, controlling the pressure remaining downstream of the first control valve by adjusting the opening degree of the second control valve, and flowing the fluid at a second flow rate downstream of the second control valve.

In an embodiment, the second control valve is a normally open type valve.

In an embodiment, the flow rate control device further comprises another pressure sensor provided downstream of the second control valve.

The flow rate control device according to an embodiment of the present invention includes a first control valve provided in a flow path, a second control valve provided downstream of the first control valve, and a pressure sensor for measuring the fluid pressure downstream of the first control valve and upstream of the second control valve, the flow rate control device controls the flow rate of the downstream side based on a signal output from the pressure sensor, when controlling the flow rate from the first flow rate to a second flow rate smaller than the first flow rate, while closing the first control valve, controls the opening degree of the second control valve based on the output of the pressure sensor, the opening degree of the second control valve is controlled to match the rate of change of the pressure remaining downstream of the first control valve to the rate of change of the flow rate when flowing out from the second control valve becomes the second flow rate.

In an embodiment, when controlling the flow rate from the first flow rate to the second flow rate, the first control valve is controlled to an opening degree smaller than the opening degree corresponding to the second flow rate.

In an embodiment, when α is a proportional constant, ΔP/Δt is the pressure change rate of the ratio between the change ΔP of the upstream pressure output by the pressure sensor and the time Δt required for the pressure change ΔP, V is an internal volume between the first control valve and the second control valve, the opening of the second control valve is controlled to an opening degree capable of maintaining ΔP/Δt when the flow rate Q represented by Q=α·(ΔP/Δt)·V reaches the second flow rate.

In an embodiment, the flow rate control device further comprises another pressure sensor provided downstream of the second control valve.

The flow rate control device according to an embodiment of the present invention is a flow rate control device comprising a first control valve provided in a flow path, a second control valve provided downstream of the first control valve, and a first pressure sensor measuring a fluid pressure downstream of the first control valve and upstream of the second control valve, the flow rate control device controlling the downstream flow rate based on a signal output from the pressure sensor, when controlling the flow rate from a first flow rate to a second flow rate that is smaller than the first flow rate, changing the flow rate controlled by Q=K1·P1 to a flow rate controlled by Q=α·(ΔP/Δt). V, and when the pressure of the first pressure sensor reaches a predetermined pressure, returning to the flow rate controlled by Q=K1·P1, here, Q is a flow rate, K1is a constant depending on the type and temperature of the fluid, P1 is a constant depending on the type and temperature of the fluid, and P1 is an upstream pressure sensor output by the first pressure sensor, α is a proportional constant, ΔP/Δt is a pressure change rate of the upstream pressure, V is an internal volume between the first control valve and the second control valve.

In an embodiment, when the pressure of the first pressure sensor reaches the pressure corresponding to the second flow rate controlled by Q=K1·P1, the control by Q=α·(ΔP/Δt). V is returned to the control by Q=K1·P1.

The flow rate control device according to an embodiment of the present invention includes a first control valve provided in a flow path, a second control valve provided downstream of the first control valve, a first pressure sensor for measuring the fluid pressure downstream of the first control valve and upstream of the second control valve, and a second pressure sensor for measuring the fluid pressure downstream of the second control valve, the flow rate control device controls the downstream flow rate based on signals output by the first and second pressure sensors, when controlling the flow rate from the first flow rate to the second flow rate smaller than the first flow rate, changes the flow rate control from the control by Q=K2·P2m(P1−P2)nto the control by Q=α·(ΔP/Δt)·V, and when the pressures of the first pressure sensor and second pressure sensor reach to predetermined pressures, returns to the control by Q=K2·P2m(P1−P2)n, where Q is the flow rate, K2is a constant depending on the type and temperature of the fluid, P1 is the upstream pressure output by the first pressure sensor, P2 is the downstream pressure output by the second pressure sensor, m and n are indexes derived based on the actual flow rate, α is a proportional constant, ΔP/Δt is the pressure change rate of the upstream pressure, V is the internal volume between the first control valve and the second control valve.

In an embodiment, when pressures of the first and second pressure sensor reach the pressure corresponding to the second flow rate in the control by Q=K2·P2m(P1−P2)n, the control is returned from the control of Q=α·(ΔP/Δt)·V to the control by Q=K2·P2m(P1−P2)n.

Further, in an embodiment, the flow rate control device may be provided with both the first control valve and the second control valve having adjustable opening degrees, and the restriction part provided downstream of the first control valve having a fixed opening degree. The restriction part and the second control valve may be provided integrally, and may constitute a valve with a built-in orifice. Further, when reducing the flow rate from the first flow rate to the second flow rate smaller than the first flow rate, in the above step (a), while closing the first control valve to an opening smaller than the opening corresponding to the second flow rate, in step (b), in conjunction with the operation of closing the first control valve, while maintaining the opening of the first control valve in a closed state, the opening of the second control valve may be controlled based on the output of the pressure sensor.

Effect of Invention

According to the embodiments of the present invention, a flow rate control method and a flow rate control device capable of improving responsiveness when reducing flow rate is provided.

