JP2668122B2 - Micro flow controller - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a micro flow control device of the type that performs opening / closing control of a valve by a piezoelectric element, and mainly relates to fine gas control in a vacuum device or the like. It is used for flow rate adjustment.

[Conventional technology]

In vacuum equipment and gas purification equipment for semiconductors, 100
It is often necessary to control the flow rate of a very small flow rate gas of about 500 cc / min. A so-called piezo valve as shown in FIG. 4 is usually used for controlling such a minute flow rate gas. By changing the input voltage applied to the piezoelectric element (piezoelectric ceramic) 1 to control the extension amount, The valve body 4 is moved up and down via the diaphragm 2 and the valve body presser 3 to adjust the gap between the valve body 4 and the valve seat 5.

4, 6 is a valve box, 7 is a fluid inlet, 8
Denotes a fluid outlet, 9 denotes a manual handle with a ratchet, and 10 denotes a piezoelectric element case.

In the piezo valve, the input voltage to the piezoelectric element 1 is adjusted so that a driving force of about
The vertical movement of the valve element 4 can be finely adjusted over a stroke range of 0 μm, and a fine flow control valve with low power consumption and high resolution can be obtained.

For example, in the piezo valve having the structure shown in FIG. 4, the elongation rate of the piezoelectric element 1 and the flow rate per unit stroke are about 0.15 to 0.2 μm / v and 500 to 600 cc / μm, respectively.
Extremely precise fine flow control can be performed.

However, the conventional piezo valve still has many problems to be improved. Among them, the biggest problem is a decrease in flow controllability due to a temperature change.

That is, when the ambient temperature fluctuates, the extension amount of the piezoelectric element 1 and the piezoelectric element storage case 10 naturally changes. In this case, there is no problem if both have the same coefficient of thermal expansion,
There is a considerable difference in the coefficient of thermal expansion between the piezoelectric element 1 and the storage case 10, which causes various problems in control accuracy and the like.

For example, when the piezoelectric element 1 is a ceramic piezoelectric element and the storage case 10 is made of stainless steel (SUS304), the coefficient of thermal expansion of the former is about 1.2 × 10 ⁻⁶ , while the coefficient of thermal expansion of the latter is It is about 17.3 × 10 ^-6 , and there is an order of magnitude difference between the two. Therefore, when the ambient temperature increases, the extension of the storage case 10 exceeds the extension of the piezoelectric element 1. As a result, the downward pressing force applied to the valve body retainer 3 decreases, and the valve body 4 is pressed upward by the spring 11 to reduce the gap between the valve body 4 and the valve seat 5,
Even if the input value to the piezoelectric element 1 is the same, the flow value will decrease.

[Problems to be solved by the invention]

The present invention aims to solve the above-mentioned problem in a conventional piezo valve for controlling a minute flow rate, that is, the problem of deterioration in control accuracy due to a difference in thermal expansion coefficient between a piezoelectric element and a piezoelectric element housing case. The present invention provides a micro flow control device capable of maintaining stable flow control accuracy over a predetermined temperature range by automatically compensating for a difference in elongation due to a difference in thermal expansion coefficient between the two. Is what you do.

[Means for solving the problem]

The present invention includes a control valve body A for driving a valve body 4 by a piezoelectric element 1 supported in a storage case 10; and strain detection elements 12, 13 fixed to the piezoelectric element 1 and the storage case 10, respectively. An elongation amount detection device B that outputs a compensation signal proportional to the difference in elongation amount; an input signal is corrected by a compensation signal from the elongation amount detection device B, and the corrected signal is output to the piezoelectric element 1 The drive control device C is a basic configuration of the present invention.

[Action]

When the amount of extension of the piezoelectric element 1 and the housing case 10 changes due to a temperature change, the resistance values of the respective extension amount detection elements 12 and 13 fixed to each other change, and a compensation signal proportional to the difference between the amounts of extension is output. .

The input signal to the drive control device C is modified by the compensation signal, and the modified signal is applied to the piezoelectric element 1.

That is, when the temperature rises, the input voltage to the piezoelectric element 1 is corrected in the increasing direction by the compensation signal, and the extension of the piezoelectric element 1 becomes substantially equal to the extension of the storage case 10. As a result, the driving force acting on the valve element 4 is always kept at a constant value, and the fluctuation of the valve opening due to the temperature change is prevented.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. It should be noted that in FIG. 1 to FIG.
The same reference numerals are used for the same parts as in the drawings.

FIG. 1 is a block diagram showing the overall configuration of the present invention. In the micro flow control device according to the present invention, a control valve main body A, an extension detecting device B for detecting the extension of a piezoelectric element and a piezoelectric element housing case are shown. And a drive control device C for the piezoelectric element.

Further, in the present invention, the extension amount of the piezoelectric element 1 for driving the valve body and the
A compensation signal proportional to the difference in the extension of
The signal corrected by the compensation signal is applied to the drive control device C.
Is output to the piezoelectric element 1 and the piezoelectric element 1 and the storage case 10
Is always maintained at a constant value regardless of the temperature change.

FIG. 2 is a longitudinal sectional view of a control valve body A used in the present invention. In the figure, 1 is a piezoelectric element, 2 is a diaphragm,
Is a valve body retainer, 4 is a valve body, 5 is a valve seat, 6 is a valve box, 7 is a fluid inlet, 8 is a fluid outlet, 9 is a manual handle with a ratchet,
Reference numeral 10 denotes a piezoelectric element storage case, 11 denotes a spring, 12 denotes a strain detection element fixed to the piezoelectric element 1, and 13 denotes a strain detection element fixed to the piezoelectric element storage case 10.

A so-called piezoelectric ceramic is used for the piezoelectric element 1, and an input voltage of 12 to 150 V, a maximum stroke of 22 μm, an elongation rate of 0.16 μm / v, and a thermal expansion coefficient of 1.2 × 10 ⁻⁶ are selected. The piezoelectric element 1 is located above the diaphragm 2 and is disposed in a storage case 10 made of stainless steel (SUS304) (coefficient of thermal expansion 17.3 × 10 ^-6 ), and its upper end portion is provided by a manual handle 9 with a ratchet. Are pressed downward at a constant pressure. That is, the piezoelectric element 1 in the storage case 10 is sandwiched and held between the handle 9 and the diaphragm 2 without causing rattling in the axial direction, and the piezoelectric element 1 is expanded by receiving a valve driving signal. As a result, the valve element 4 is pressed downward via the diaphragm 2 and the valve element retainer 3, and the valve is opened according to the amount of extension. Further, as the valve driving signal decreases, the length of the piezoelectric element 1 itself decreases, and the valve element 4 moves in the valve closing direction by the elastic force of the spring 11.

FIG. 3 is a circuit configuration diagram of the extension amount detection device B and the drive control device C. The extension amount detecting device B includes a strain detecting element 12 fixed to the piezoelectric element 1, a strain detecting element 13 fixed to the housing case 10, a bridge circuit 14 for taking out the difference between the strain amounts of both, and a difference from the bridge circuit 14. It is composed of a differential amplifier 15 that outputs a compensation signal P proportional to the signal, and the resistance of both distortion detection elements 12 and 13 changes, causing the bridge circuit 14 to lose its balance, resulting in an unbalanced differential current. A compensation signal P amplified by the amplifier 15 and proportional to the difference in the amount of distortion is output.

The drive control device C includes an amplifier 1 for the reference operation signal S.
6 ', the operation signal S and the compensation signal P from the distortion detecting device B are inputted, the operation amplifier 16 which corrects the reference operation signal S by the compensation signal P, and the distortion amount after correction (temperature compensation) The signal S ′, which is composed of a signal amplifier 17 and an output transformer 18, is applied to the piezoelectric element 1 after the reference operation signal S is corrected by the compensation signal P in proportion to the amount of distortion. .

For example, in the present embodiment, when the extension amount on the storage case 10 side increases due to a rise in temperature, the operation signal S is corrected by the compensation signal P and increases by a predetermined amount. As a result, the input signal S 'to the piezoelectric element 1 increases, and the piezoelectric element 1 expands by the amount of extension of both, thereby canceling out the effect of the temperature change.

〔The invention's effect〕

In the present invention, the piezoelectric element 1 for driving the valve element 4, the housing case 10 for housing and supporting the piezoelectric element 1 and the strain detecting elements 12 and 13 are respectively arranged, and a difference in extension amount between them due to temperature change. Is output from the elongation amount detection device B to the drive control device C, and the drive control device C modifies the reference operation signal with the compensation signal,
The length of extension of the storage case 10 is always kept substantially equal.

As a result, the pressing force acting on the valve body 4 changes according to the ambient temperature, so that the valve opening does not fluctuate, so that a high-precision fine flow control can always be performed.

The present invention has excellent practical utility as described above.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing the overall configuration of the present invention. FIG. 2 is a longitudinal sectional view showing an example of a control valve main body used in the present invention. FIG. 3 is a circuit configuration diagram of a distortion amount detection device and a drive control device which constitute a part of the present invention. FIG. 4 is a longitudinal sectional view showing an example of a conventional piezo valve. 1 ... Piezoelectric element, 11 ... Spring, 2 ... Diaphragm, 12/13 ... Strain detection element 4 ... Valve body, A ... Control valve body 5 ... Valve seat, B ... Extension amount detection device 10 ... ... Storage case, C ... Drive control device

Claims (1)

(57) [Claims] A control valve body (A) for driving a valve body (4) by a piezoelectric element (1) supported in a storage case (10).
And an extension amount detection device which includes strain detection elements (12) and (13) fixed to the piezoelectric element (1) and the housing case (10), respectively, and outputs a compensation signal proportional to the difference between the extension amounts of the two. B) and a drive control device (C) that corrects an input signal with a compensation signal from the elongation amount detection device (B) and outputs the corrected signal to the piezoelectric element (1). Flow control device.