JP6818357B2 - Piezoelectric valve and flow control device - Google Patents

Description

The present invention relates to a piezoelectrically driven valve and a flow rate control device including the same, and more particularly to a piezoelectrically driven valve provided in a flow rate control device used in a semiconductor manufacturing device, a chemical plant, or the like.

Since the pressure type flow rate control device can control the flow rate of various fluids with high accuracy by a relatively simple mechanism that combines a pressure control valve driven by a piezo (piezoelectric) element and a throttle portion (for example, an orifice plate). , Widely used in semiconductor manufacturing equipment and chemical plants (for example, Patent Document 1).

In Patent Documents 2 and 3, a piezoelectric drive type control valve (for example, a piezoelectric drive type control valve) configured to open and close a valve body (for example, a metal diaphragm) by an actuator using a piezoelectric element (hereinafter, may be referred to as “piezoelectric actuator”). Hereinafter, it may be referred to as "control valve"). There are two types of piezoelectric drive type control valves, a normally open type and a normally closed type, and a mechanism for converting the extension of the piezoelectric actuator into the opening / closing operation of the valve body is provided corresponding to each type.

Japanese Unexamined Patent Publication No. 2004-138425 JP-A-2003-120832 JP-A-2007-192269 Patent No. 5054904

However, in recent years, the flow rate control device has been required to be applied to, for example, ALD (Atomic layer deposition), and in such an application, a control valve is provided by a high-speed (very short period) pulsed control signal. It is required to open and close. In this case, the opening / closing speed, displacement amount, and opening / closing frequency of the piezoelectrically driven control valve increase remarkably.

As a result, the piezoelectric actuator tends to deteriorate over time due to a decrease in insulation resistance or the like, and there is a problem that high-precision flow rate / pressure control cannot be performed (for example, Patent Document 4).

That is, in the above-mentioned applications, a defect may occur at a stage earlier than the durability of the piezoelectrically driven valve that has been assumed in the past. In this case, when a predetermined drive voltage is applied to the piezoelectric actuator, there is a possibility that the fluid will flow at a flow rate that greatly deviates from the accuracy, which is different from the previous one.

Further, when a flow rate control device equipped with a conventional piezoelectrically driven control valve having such a problem is used in a semiconductor manufacturing process, it is possible to quickly determine whether or not the cause of malfunction is caused by the piezoelectrically driven control valve. And it may be difficult to make a reliable judgment. Therefore, the semiconductor manufacturing process may be continued under the malfunctioning state, and a large loss may be incurred.

Further, conventionally, in the pressure type flow rate control device, the drive voltage of the control valve is feedback-controlled from the output of the pressure sensor, and the absolute value of the drive voltage is not so problematic for the flow rate control. That is, even if the relationship between the actual opening / closing degree of the valve and the drive voltage fluctuates due to aged deterioration or the like, no major problem has occurred from the viewpoint of flow rate control.

Therefore, it was not particularly necessary to detect the opening degree of the control valve, but if the inventor of the present application refers only to the drive voltage, it is appropriate to discover and predict when a malfunction occurs. I found that there are cases where it cannot be done.

The present invention has been made to solve the above problems, and a main object of the present invention is to provide a piezoelectrically driven valve having improved performance in finding and predicting malfunctions, and a flow rate control device including the same. ..

The piezoelectric drive type valve according to the embodiment of the present invention is for moving the valve body provided with the flow path, the valve seat provided on the flow path, the valve body detached from and seated on the valve seat, and the valve body. A piezoelectric drive type valve including a support cylinder for accommodating the piezoelectric element, the support cylinder is moved by the extension of the piezoelectric element, and the valve body is moved by the support cylinder. A gap sensor including a flat surface sensor and an opposing member having a surface facing the flat surface sensor is provided, and one of the flat surface sensor and the opposing member of the gap sensor is immovable with respect to the valve body. It is fixed at the position, and the other is fixed to the support cylinder, and the change in the distance between the plane sensor and the facing member is detected as the movement amount of the support cylinder.

In certain embodiments, the opposing surfaces of the opposing member are formed of a conductor.

In a certain embodiment, a temperature compensation sensor having the same configuration as the plane sensor is provided on the surface of the facing member opposite to the surface facing the plane sensor.

In certain embodiments, the planar sensor has an oscillating circuit, and the gap sensor detects a change in the distance between the planar sensor and the facing surface as a change in oscillation frequency.

In a certain embodiment, a storage device for storing a table showing the relationship between the output value of the plane sensor and the movement amount of the support cylinder is provided, and the movement amount of the support cylinder is detected using the table.

In a certain embodiment, the distance between the plane sensor and the facing surface of the facing member is 30 μm or more and 300 μm or less in a state where no voltage is applied to the piezoelectric element.

In certain embodiments, the valve body has a guide member fixed to the valve body and provided to cover the lower portion of the support cylinder, the planar sensor is fixed to the guide member, and the opposing member is the support cylinder. It is fixed to.

In certain embodiments, the piezoelectric driven valve is a normally closed type control valve.

In one embodiment, the piezoelectric driven valve is used as a variable orifice device and is configured to detect the orifice opening degree by the gap sensor and control the opening degree position.

In a certain embodiment, the amount of movement by the gap sensor is monitored and compared with a normal state to determine whether or not there is an abnormality in the piezoelectric actuator including the piezoelectric element and the support cylinder.

The flow control device according to the embodiment of the present invention includes a throttle portion, any of the above-mentioned piezoelectric driven valves provided on the upstream side of the throttle portion, and a gas pressure between the throttle portion and the piezoelectric driven valve. It is provided with a pressure sensor for measuring the pressure sensor and a calculation control unit for determining the drive voltage of the piezoelectric drive valve based on the output of the pressure sensor.

According to the embodiment of the present invention, it is possible to more reliably find and predict a malfunction in the piezoelectrically driven valve.

It is a schematic diagram which shows the structure of the flow rate control apparatus provided with the piezoelectric drive type valve (control valve) by embodiment of this invention. It is sectional drawing which shows the piezoelectric drive type valve by embodiment of this invention. 2 is a view showing a support cylinder of the valve shown in FIG. 2, where FIG. 2A is a side sectional view and FIG. 2B is a sectional view taken along the line AA of FIG. 2A. It is a figure which shows the split base of the valve shown in FIG. 2, (a) is a plan view, (b) is a side view along line BB of (a). It is a schematic side view which shows the piezoelectric drive type valve by embodiment of this invention. It is a graph which shows the relationship between the drive voltage of a piezoelectric element, and the output value (count value) of a plane sensor. It is a graph which shows the relationship between the drive voltage of a piezoelectric element and the movement amount (stroke) of a piezoelectric actuator. It is a graph showing the relationship between the gap measured by the gap sensor and the output value (count value) of the plane sensor, the solid line shows the actual graph, and the broken line shows the graph after linear correction.

Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments.

FIG. 1 is a diagram showing a configuration of a pressure type flow rate control device 8 (hereinafter, may be simply referred to as a flow rate control device 8) according to an embodiment of the present invention. The flow control device 8 includes a throttle portion 2 (for example, an orifice plate) interposed in a flow path (gas supply path) 1 through which the fluid G passes, and a first pressure sensor 3 and a temperature sensor provided on the upstream side of the throttle portion 2. 5, a second pressure sensor 4 provided on the downstream side of the throttle portion 2, and a control valve 6 which is a piezoelectric drive type valve provided on the upstream side of the first pressure sensor 3 are provided.

The first pressure sensor 3 can measure the upstream pressure P ₁ , which is the pressure in the flow path between the control valve 6 and the throttle portion 2, and the second pressure sensor 4 has the throttle portion 2 and the downstream valve 9. The downstream pressure P ₂ , which is the pressure of the flow path between the _two , can be measured.

The flow rate control device 8 also includes an arithmetic processing circuit 7 that controls the opening / closing operation of the control valve 6 based on the outputs of the first pressure sensor 3 and the second pressure sensor 4. The arithmetic processing circuit 7 compares the set flow rate received from the external control device 12 with the flow rate calculated from the outputs of the first and second pressure sensors 3 and 4, and controls the control valve 6 so that the calculated flow rate approaches the set flow rate. Drives the drive mechanism 6B and the valve mechanism 6A.

Unlike the illustrated embodiment, the flow rate control device 8 does not have to include the second pressure sensor 4. In this case, the arithmetic processing circuit 7 calculates the flow rate based on the output of the first pressure sensor 3. Further, in a preferred embodiment, the arithmetic processing circuit 7 is configured to correct the arithmetic flow rate based on the fluid temperature detected by the temperature sensor 5.

As the throttle portion 2, a critical nozzle or a sound velocity nozzle may be used in addition to an orifice member such as an orifice plate. The diameter of the orifice or nozzle is set to, for example, 10 μm to 500 μm. As the downstream valve 9, for example, a known fluid operating valve whose supply of compressed air is controlled by a solenoid valve can be used. A valve with a built-in orifice in which the orifice member is arranged in the vicinity of the on-off valve is known, and this may be incorporated into the flow control device 8 as a configuration in which the throttle portion 2 and the downstream valve 9 are integrated.

The flow path 1 of the flow rate control device 8 may be formed of a pipe or a flow path hole formed in a metal block. The first and second pressure sensors 3 and 4 may include, for example, a silicon single crystal sensor chip and a diaphragm.

In the present embodiment, the control valve 6 is a piezoelectric drive type control valve that opens and closes, for example, a valve mechanism 6A including a metal diaphragm by using a drive mechanism 6B composed of a piezoelectric actuator. The detailed configuration of the control valve 6 will be described later.

In the fluid supply system including the flow rate control device 8 configured in this way, the upstream side of the control valve 6 is connected to a gas supply source such as a raw material gas, an etching gas, or a carrier gas, and is a downstream side of the second pressure sensor 4. Is connected to the process chamber 10 of the semiconductor manufacturing apparatus via the downstream valve 9. A vacuum pump 11 for performing a vacuum process is connected to the process chamber 10, and the inside of the process chamber 10 is evacuated when gas is supplied.

The flow control device 8 of the present embodiment is a pressure type flow control device, and the critical expansion condition P ₁ / P ₂ ≧ about 2 (P ₁ : gas pressure (upstream pressure) on the upstream side of the throttle portion, P ₂ : throttle. When the gas pressure (downstream pressure) on the downstream side of the section is satisfied, the flow velocity of the gas passing through the throttle section is fixed at the sound velocity, and the flow rate is determined by the upstream pressure P ₁ regardless of the downstream pressure P _2. The flow rate is controlled. When the critical expansion condition is satisfied, the flow rate Q on the downstream side of the throttle is given by Q = K ₁ · P ₁ (K ₁ is a constant that depends on the type of fluid and the fluid temperature), and the flow rate Q becomes the upstream pressure P ₁ . Proportional. Further, when the second pressure sensor 4 is provided, the difference between the upstream pressure P ₁ and the downstream pressure P ₂ is small, and the flow rate can be calculated even when the critical expansion condition is not satisfied, and the pressure is measured by each pressure sensor. Based on the upstream pressure P ₁ and the downstream pressure P ₂ , the predetermined formula Q = K ₂ · P ₂ ^m (P _{1 −} P ₂ ) ⁿ (where K ₂ depends on the type of fluid and the fluid temperature. The flow rate Q can be calculated from the constants, m, and n that are derived from the actual flow rate.

In order to control the flow rate, the set flow rate set in the external control device 12 is sent from the external control device 12 to the arithmetic processing circuit 7. The arithmetic processing circuit 7 is based on the output of the first pressure sensor 3 (upstream pressure P ₁ ), the output of the second pressure sensor 4 (downstream pressure P ₂ ), the output of the temperature sensor 5 (gas temperature T ₁ ), and the like. Then, using the flow rate calculation formula under the critical expansion condition or the non-critical expansion condition, the flow rate is calculated from the above Q = K ₁ · P ₁ or Q = K ₂ · P ₂ ^m (P ₁ −P ₂ ) ^n. .. Then, the control valve 6 is controlled so that the flow rate of the fluid passing through the throttle portion 2 approaches the set flow rate. Further, the calculated flow rate may be output to the external control device 12 and displayed as a flow rate output value.

Hereinafter, the control valve 6 in this embodiment will be described in detail.

FIG. 2 is a cross-sectional view showing the configuration of the control valve 6. The control valve 6 is a normally closed type piezoelectrically driven valve that opens and closes the valve body 22 by using the piezoelectric element 20.

As shown in FIG. 2, the control valve 6 includes a valve body 21 provided with the flow path 1, a valve seat 21a provided on the flow path, and a valve body 22 arranged in close proximity to the valve seat 21a so as to be able to take off and seat. A valve body retainer 25 in contact with the valve body 22, a piezoelectric element 20, and a support cylinder 23 for accommodating the piezoelectric element 20 are provided. The piezoelectric element 20 and the support cylinder 23 are arranged in the protective case 16 together with the control circuit board 7'. In the present embodiment, the valve body retainer 25 is fixed to the tip of the support cylinder 23 and moves integrally with the support cylinder 23. The take-off seat means that the valve body comes into contact with and separates from the valve seat.

In the control valve 6, a drive voltage controlled by an arithmetic processing circuit 7 (see FIG. 1) provided on the control circuit board 7'is applied to the piezoelectric element 20 via the connector 15, and the magnitude of the drive voltage is large. The piezoelectric element 20 extends accordingly. As the piezoelectric element 20, a plurality of laminated piezoelectric elements (also referred to as piezo stacks) can be used. A piezoelectric actuator in which one or a plurality of piezoelectric elements 20 are sealed in a metal case is known as a piezoelectric actuator, and as the piezoelectric actuator, for example, one sold by NTK Ceratech Co., Ltd. or the like can be used. Hereinafter, an actuator configured by using the piezoelectric element 20 may be referred to as a piezoelectric actuator 20.

The valve body 21 is made of stainless steel and includes a hole forming a part of the valve chamber, a fluid inlet, a fluid outlet, a flow path, a valve chamber, a valve seat 21a, and the like. In the present embodiment, the inlet joint and the outlet joint are connected to both sides of the valve body 21 via the primary connection portion 21b and the orifice mounting portion 21c. The primary connection portion 21b may be composed of, for example, a connection guide or a gasket, and the orifice mounting portion 21c may be composed of an orifice plate, an orifice guide, a gasket or the like as the throttle portion 2 shown in FIG.

Further, in the embodiment shown in FIG. 2, the first pressure sensor 3 shown in FIG. 1 is attached to the lower surface side of the valve body 21. However, the present invention is not limited to this, and the first pressure sensor 3 may be attached to the upper surface side of the valve body. Further, although not shown in FIG. 2, it goes without saying that the second pressure sensor 4 (see FIG. 1) may be provided on the downstream side of the orifice mounting portion 21c.

The valve body 22 in the present embodiment is a self-elastic return type metal diaphragm. The metal diaphragm is formed of a thin plate such as nickel-chromium alloy steel, and is formed in an inverted dish shape in which the central portion slightly bulges upward. The shape of the metal diaphragm may be flat, and the material may be stainless steel, Inconel alloy, or other alloy steel. Further, the metal diaphragm 22 may use one diaphragm, or may be a diaphragm valve body in which two or three diaphragms are laminated.

The metal diaphragm 22 is arranged in the valve chamber so as to face the valve seat 21a. The outer peripheral edge of the metal diaphragm 22 is hermetically held and fixed to the valve body 21 side by tightening the mounting bolts to the valve body 21 via the presser adapter 25a, the split base 26 and the guide member 24. The presser foot adapter 25a, the guide member 24, the split base 26, and the like may be made of metal such as stainless steel. The guide member 24 is a hollow member provided so as to cover the lower portion of the support cylinder 23, and is fixed to the valve body 21 by a fixing member such as a screw. Further, an O-ring 27 is provided between the guide member 24 and the support cylinder 23.

The support cylinder 23 is formed in a cylindrical shape by, for example, an Invar material having a small coefficient of thermal expansion, and as shown in FIG. 3A, the support cylinder 23 has a large diameter portion 23c for accommodating the piezoelectric actuator 20, a lower pedestal 29, and elasticity. It has a reduced diameter portion 23d for accommodating the member 28 and the like. Further, a fitting portion 23e for fitting the valve body retainer 25 is formed at the lowermost end portion of the support cylinder 23. In the present embodiment, the fitting portion 23e is a recess in which the valve body retainer 25 is inserted and fixed, but the fitting portion 23e is not limited to this, and may have various modes as long as the valve body retainer 25 can be fixed. Further, the support cylinder 23 and the valve body retainer 25 may be provided integrally.

FIG. 3A is a vertical sectional view of the support cylinder 23, and FIG. 3B is a sectional view taken along line AA of FIG. 3A. A pair of holes 23a arranged so as to face each other with the central axis of the support cylinder 23 interposed therebetween are provided near the boundary between the large diameter portion 23c and the reduced diameter portion 23d of the support cylinder 23. A pair of split base pieces 26a shown in FIG. 4 are inserted into the holes 23a facing each other from both sides, and the inserted split base pieces 26a are combined. The combined split base piece 26a is integrally held and fixed as the split base 26 by the guide member 24. Before assembling the split base piece 26a, the elastic member 28 shown in FIG. 2 is previously inserted into the bottom portion 23b of the reduced diameter portion 23d.

FIG. 4A is a plan view showing the split base 26, and FIG. 4B is a sectional view taken along line BB of FIG. 4A. As can be seen from FIGS. 4A and 4B, the split base 26 has a shape in which a collar portion 26c is formed on the outer periphery of the lower end of a short cylinder provided with an upper wall 26b when the split base pieces 26a are combined. Have. The upper wall 26b is provided with an insertion hole 26d through which the reduced diameter portion 23d of the support cylinder 23 penetrates. Further, a fitting portion 26e for supporting the lower pedestal 29 is formed in the central portion of the upper wall 26b.

As shown in FIG. 2, the flange portion 26c of the split base 26 presses the pressing adapter 25a by receiving pressing pressure from the lower end of the guide member 24. Further, the insertion hole 26d can be inserted through the wall body (the portion between the pair of holes 23a) of the reduced diameter portion 23d of the support cylinder 23, and the split base 26 is assembled from the outside of the support cylinder 23. Is possible.

To explain the procedure for assembling the control valve 6, first, the metal diaphragm 22, the presser foot adapter 25a, and the valve body retainer 25 are placed in the mounting recess provided in the valve body 21 (the mounting recess in which the valve seat 21a is formed). The fixed support cylinder 23, the elastic member 28, and the split base 26 are assembled in this order, and the support cylinder 23 is inserted into the valve body 21 via the guide member 24. Next, the lower pedestal 29, the ball, the hemisphere, the piezoelectric actuator 20, and the like are inserted into the support cylinder 23, and the tightening amount of the bag nut forming the positioning member 17 is adjusted to adjust the piezoelectric actuator 20. The operating stroke of the metal diaphragm 22 is finely adjusted to the set value.

In the control valve 6 described above, a hemisphere in contact with the lower surface of the piezoelectric actuator (piezoelectric element) 20 is provided, and this hemisphere is supported by the lower pedestal 29. Further, the lower pedestal 29 is supported by the split base 26 shown in FIGS. 4A and 4B, and the split base 26 is fixed to the valve body 21 by the guide member 24. In the example shown in FIG. 2, a hemisphere separately formed is inserted between the lower pedestal 9 and the piezoelectric actuator 20, but the tip is spherical at the center of the lower end surface of the piezoelectric actuator 20. In some cases, the shaped protrusions are integrally formed and the hemispheres are brought into contact with the lower pedestal 9.

In this configuration, when a valve opening signal is input (for example, input voltage 0 to 120v) from the arithmetic control circuit 7 via the connector 15 provided on the upper part, the piezoelectric actuator 20 has only a set value (for example, 0 to 45 μm). Stretch. As a result, for example, a pushing force of about 40 to 80 kgf acts on the support cylinder 23, and the support cylinder 23 resists the elastic force of the elastic member 28 while the shaft core is held by the O-ring 27 of the guide member 24. It increases by the above set value. As a result, the pressing force from the valve body retainer 25 to the metal diaphragm 22 is reduced, and the metal diaphragm 22 is separated from the valve seat 21a by the elastic force and the valve is opened. As the elastic member 28, for example, a stack of disc springs can be used.

Further, when the valve opening input is turned off, the piezoelectric actuator 20 returns to the state of the original length dimension, and as a result, the bottom portion of the support cylinder 23 of the piezoelectric actuator 20 is pushed downward by the elastic force of the elastic member 28. Then, the metal diaphragm 22 is seated on the valve seat 21a by the valve body retainer 25, and the valve is closed.

As can be seen from the above description, in the control valve 6, the support cylinder 23 moves when a voltage is applied to the piezoelectric element 20, and the valve body (metal diaphragm) is connected to the valve body retainer 25 connected to the support cylinder 23. The force applied to 22 is configured to change. Therefore, in the control valve 6 of the present embodiment, a gap sensor 30 for measuring the movement amount of the support cylinder 23 is provided, and the opening degree of the valve body 22 is detected from the measured movement amount of the support cylinder 23. I have to.

Hereinafter, the gap sensor 30 provided in the control valve 6 will be described.

As shown in FIGS. 2 and 5, the gap sensor 30 is configured by using a flat surface sensor 31 and an opposing member 32 arranged to face the flat surface sensor 31. The plane sensor 31 and the facing member 32 are preferably arranged so as to overlap with the valve body 21, thereby preventing the size of the flow rate control device 8 from increasing in the width direction. In the flow rate control device 8 shown in FIG. 5, an inflow pressure sensor 13 for measuring the gas supply pressure is provided on the upstream side of the control valve 6. The inflow pressure sensor 13 can measure the pressure of the gas supplied from the connected gas supply device (for example, the raw material vaporizer), and can be used to control the gas supply amount or the supply pressure.

As the planar sensor 31, for example, the ultra-compact displacement sensor DS2001 series manufactured by Nippon System Development Co., Ltd. can be used. This ultra-compact displacement sensor has a configuration in which an oscillation circuit or the like is formed on a substrate having a coil, and the oscillation (resonance) frequency changes according to a change in distance from an opposing conductor, and the integrated value thereof. (Count value) can be output digitally. Here, the count value is specifically given by the oscillation frequency × the measurement time, and the oscillation frequency f is f = 1 / 2π (LC) ^1/2 (L is inductance, C is capacitance). It is given.

Further, the facing member 32 is typically a flat metal member having a conductor surface 32s facing the plane sensor 31. In the present embodiment, the entire facing member 32 is formed of a conductor (aluminum plate in the embodiment), but the present invention is not limited to this, and a conductor film formed on the surface of the facing member 32 may be used. Good. The conductor surface 32s of the facing member 32 may be formed of any conductor (for example, aluminum, copper, iron, gold, silver, stainless steel, etc.) regardless of whether it is a magnetic material or a non-magnetic material.

As shown in the fixing example in FIG. 5, in the control valve 6, the plane sensor 31 is fixed to the guide member 24 fixed to the valve body 21 by screwing. In this configuration, since the guide member 24 is in an immovable state with respect to the valve body 21, the flat surface sensor 31 fixed to the guide member 24 is fixed at a position immovable with respect to the valve body 21. Become. On the other hand, the facing member 32 is fixed to the support cylinder 23 by screwing.

However, in another embodiment, the flat surface sensor 31 may be attached to the support cylinder 23, and the opposing member 32 may be attached to the guide member 24. The planar sensor 31 and the facing member 32 are various as long as one is directly or indirectly fixed to the valve body 21 and the other is directly or indirectly fixed to the support cylinder 23. It goes without saying that it may be attached in a mode.

Further, as shown in FIG. 5, in the control valve 6 of the present embodiment, the surface of the opposing member 32 opposite to the surface facing the flat surface sensor 31 has the same configuration as the flat surface sensor 31 for temperature compensation. A reference plane sensor 33 is provided. The reference plane sensor 33 is provided to compensate for the output of the plane sensor 31, which may fluctuate due to a temperature change or the like. Specifically, by reading the change in the output of the reference plane sensor 33 as a change in the background and subtracting the change from the output of the plane sensor 31, it is possible to compensate for the change due to a temperature change or the like.

In the gap sensor 30, the change in the distance between the flat surface sensor 31 and the facing member 32 is detected as the amount of movement of the support cylinder 23. More specifically, as described above, the planar sensor 31 of the present embodiment has an oscillating circuit, and changes in the distance between the planar sensor 31 and the conductor surface (opposing member 32) facing the oscillating frequency (here). Then, it is detected as a change in the count value). By using such a plane displacement sensor, it is possible to accurately read a change in a distance of, for example, 10 μm to 100 μm. Therefore, it is possible to accurately detect the movement amount and the valve open / close degree of the piezoelectric actuator 20 whose displacement amount is, for example, about 0 to 50 μm. In the normally closed type control valve 6 of the present embodiment, the distance between the plane sensor 31 and the facing member 32 in the initial state (voltage-free state) is, for example, 30 to 300 μm, more specifically, It may be set to about 30 to 70 μm, and the distance increases (oscillation frequency decreases) according to the magnitude of the applied drive voltage.

FIG. 6 is a graph showing the relationship between the drive voltage (piezo voltage) of the piezoelectric element and the count value which is the output of the plane sensor 31. When the drive voltage is 0, the normally closed type control valve 6 is in the closed state, and at this time, the gap between the plane sensor 31 and the facing member 32 is the smallest. Correspondingly, the count value detected by the plane sensor 31 takes the largest value. As shown by the arrows in the figure, when the drive voltage to the piezoelectric element is increased from 0V to 150V, the opening degree of the control valve 6 increases and the gap between the plane sensor 31 and the facing member 32 increases. The count value decreases. Further, as shown by the reverse arrow in the figure, when the drive voltage is reduced from 150 V to 0 V, the opening degree of the control valve 6 is reduced and the gap between the plane sensor 31 and the facing member 32 is reduced. And the count value increases.

Further, FIG. 7 shows the relationship between the drive voltage of the piezoelectric element (when the voltage is increased or decreased in the direction of the arrow in the figure) and the actual movement amount (stroke) of the piezoelectric actuator measured by the laser displacement meter. Is shown. The amount of movement of the piezoelectric actuator by the laser displacement meter is optically measured by irradiating the reflector fixed to the upper end of the piezoelectric actuator with laser light and detecting the laser light from the reflector with a CMOS image sensor or the like. There is.

As can be seen from FIG. 6, the output of the planar sensor has a substantially linear relationship with the drive voltage. Similarly, as can be seen from FIG. 7, the relationship between the drive voltage and the amount of movement of the piezoelectric actuator also has a substantially linear relationship.

However, as shown by the solid line in FIG. 8, the output (count value) of the plane sensor and the actual displacement amount of the gap sensor may have some curvilinear characteristics. Therefore, the displacement output of the piezoelectric actuator measured by the laser displacement meter and the displacement output measured by the plane sensor are linearly corrected (that is, the linear relationship as shown by the broken line in FIG. 8 is obtained. ), Finally, a conversion table between the output of the plane sensor and the displacement of the piezoelectric actuator may be created and stored in the storage device.

By using the conversion table created in advance in this way, the opening degree of the valve body can be detected more accurately from the output value of the flat surface sensor. The conversion table is stored in advance in a storage device such as a memory provided in the arithmetic processing circuit 7, for example, and when a gap is detected, the conversion table is read out and used to obtain the output value of the planar sensor of the support cylinder. The amount of movement, and thus the opening degree of the valve, can be detected.

As described above, in the control valve 6 of the present embodiment, since the movement amount of the support cylinder 23 or the piezoelectric actuator 20 is directly measured by using the gap sensor 30, it is compared with the case of estimating from the drive voltage or the like. Therefore, it is possible to detect the opening / closing degree of the valve body 22 more accurately. If the opening / closing degree of the valve body 22 can be detected accurately in this way, the control valve 6 can be used like a variable orifice device as described later.

Since the opening / closing degree of the valve body 22 is directly detected by using the gap sensor 30, it is possible to detect the opening / closing degree with high accuracy even when the gas pressure on the upstream side fluctuates. Then, the measured movement amount of the piezoelectric actuator 20 is monitored, and compared with the normal state, for example, when the movement amount in the fully open state falls below a preset threshold value, or when the drive voltage is supplied to the piezoelectric actuator. When a tendency of abnormality is observed, such as when the movement amount does not reach the planned value even though the movement amount has been increased, it is determined that an abnormality has occurred in the piezoelectric actuator 20 (the usage limit has been reached), and the control valve 6 or replace the internal piezoelectric actuator 20. As a result, the piezoelectric actuator 20 can be replaced before it completely fails, and a large loss can be prevented without using a valve in a failed state.

Further, since the movement amount of the piezoelectric actuator 20 can be accurately measured, the control valve 6 configured as described above can be used not only as a flow rate control valve but also as, for example, a variable orifice device. In the present specification, the variable orifice device is a device that provides an opening narrowed in a flow path through which a fluid passes, such as an orifice member, and is configured such that the opening degree (flow path cross-sectional area) in the opening can be changed. It means various devices made. The variable orifice device may include a valve mechanism with adjustable opening instead of the orifice member.

When a piezoelectric drive type valve having the same configuration as the control valve 6 is used as a variable orifice device, the orifice opening (valve opening) is detected by the gap sensor 30 and the drive voltage to the piezoelectric element 20 is controlled. , The opening position can be controlled. Further, the cross-sectional area of the flow path can be obtained from the opening / closing degree of the valve body 22 detected by the gap sensor 30. Therefore, the piezoelectrically driven valve can be suitably used as a variable orifice device having a desired flow path cross-sectional area.

For example, the throttle portion 2 of the flow rate control device 8 can be configured by a piezoelectrically driven valve. In the flow rate control device 8 configured in this way, the control valve on the upstream side of the throttle portion 2 is controlled so that the upstream pressure P ₁ detected by the pressure sensor 3 becomes constant, and the piezoelectric provided as the throttle portion 2 is provided. The flow rate can be controlled by adjusting the valve opening degree of the driven valve (variable orifice device). Further, the opening degree of the piezoelectric-type valve provided as a throttle portion 2 while constant, it is possible to control the flow rate by controlling by the control valve of the upstream pressure P ₁ as well. Also in this case, it is advantageous because the flow rate control range can be changed by switching the opening degree of the piezoelectric drive type valve provided as the variable orifice device. Needless to say, the above two flow rate control operations may be combined.

Further, for example, Japanese Patent Application Laid-Open No. 11-265217 discloses a variable orifice device that controls a needle valve with a piezoelectric element. The piezoelectrically driven valve according to the embodiment of the present invention can be applied to such a variable orifice device, and the opening degree of the needle valve can be detected by providing the gap sensor 30. Specifically, one of the flat surface sensor and the opposing member is fixed to a movable part such as a piezoelectric actuator connected to a valve body retainer in contact with the needle valve, and a predetermined gap is provided in the fixed part such as the valve body to provide the other. By fixing the valve, the valve opening degree can be detected with high accuracy.

Although the embodiment of the present invention has been described above, various modifications can be made. For example, although the pressure control type flow rate control device has been described in the above embodiment, the present invention also applies to a control method other than the pressure control type, for example, a thermal flow rate control device that controls the flow rate using a thermal sensor. Applicable. Further, in the above embodiment, a piezoelectrically driven valve including a self-elastic return type metal diaphragm valve body has been described, but it is obvious to those skilled in the art that it can be applied to valve bodies other than the metal diaphragm. is there.

Further, the piezoelectric drive type valve according to the embodiment of the present invention may be a normally open type, and in this case as well, a flat surface sensor or a facing cylinder in a support cylinder that moves downward with respect to the valve body due to extension of the piezoelectric element By attaching the member and measuring the gap, the opening degree of the valve can be detected accurately.

The piezoelectrically driven valve according to the embodiment of the present invention is particularly used in a flow rate control device, and can be suitably used for detecting the actual opening / closing degree of the valve body.

1 Flow path 2 Squeezing part 3 1st pressure sensor 4 2nd pressure sensor 5 Temperature sensor 6 Control valve (piezoelectric drive type valve)
7 Arithmetic processing circuit 8 Flow control device 9 Downstream valve 10 Process chamber 11 Vacuum pump 12 External control device 20 Piezoelectric element (piezoelectric actuator)
21 Valve body 21a Valve seat 22 Valve body 23 Support cylinder 24 Guide member 25 Valve body retainer 26 Split base 27 O-ring 28 Elastic member 29 Lower cradle 30 Gap sensor 31 Plane sensor 32 Opposing member 33 Reference plane sensor

Claims (6)

Based on the output of the throttle portion, the piezoelectric drive valve provided on the upstream side of the throttle portion, the pressure sensor for measuring the gas pressure between the throttle portion and the piezoelectric drive valve, and the output of the pressure sensor. A flow control device including an arithmetic control unit that determines the drive voltage of the piezoelectric drive valve.
The piezoelectric driven valve is
A valve body provided with a flow path, a valve seat provided on the flow path, a valve body that takes off and seats on the valve seat, a support cylinder containing a piezoelectric element for moving the valve body, and the above. It is provided with a guide member fixed to the valve body and provided so as to cover the lower portion of the support cylinder, so that the support cylinder moves due to the extension of the piezoelectric element, and the valve body moves by the support cylinder. Made up to,
The piezoelectric drive type valve includes a gap sensor including a flat surface sensor and an opposing member having a surface facing the flat surface sensor, and the flat surface sensor of the gap sensor is the guide member that is immovable with respect to the valve body. The facing member is fixed to the support cylinder, and a change in the distance between the plane sensor and the facing member is detected as the amount of movement of the support cylinder .
A flow rate control device configured to monitor the amount of movement by the gap sensor and compare it with a normal state to determine whether or not there is an abnormality in the piezoelectric element and the piezoelectric actuator including the support cylinder. The flow rate control device according to claim 1, wherein the facing surfaces of the facing members are formed of a conductor. The flow rate control device according to claim 1 or 2, wherein a temperature compensation sensor having the same configuration as the plane sensor is provided on a surface of the facing member opposite to the surface facing the plane sensor. The flow rate according to any one of claims 1 to 3, wherein the planar sensor has an oscillation circuit, and the gap sensor detects a change in the distance between the planar sensor and the facing surface as a change in oscillation frequency. Control device . Claims 1 to 4 include a storage device for storing a table showing the relationship between the output value of the plane sensor and the movement amount of the support cylinder, and the movement amount of the support cylinder is detected using the table. The flow rate control device according to any one of. The piezoelectric drive type valve is a normally closed type control valve, and the distance between the plane sensor and the facing surface of the facing member is 30 μm or more and 300 μm in a state where no voltage is applied to the piezoelectric element. The flow rate control device according to any one of claims 1 to 5, which is as follows.