A pressure control method for a plug valve

Abstract

The present application relates to the technical field of valve control, and discloses a pressure control method of a plug valve, which comprises the following steps: opening the plug valve, pre-extracting the cavity pressure of a cavity to the working pressure range of a molecular pump, opening the molecular pump, and then performing the next step after the molecular pump reaches a set stable rotating speed and the cavity pressure is stable; closing the plug valve, gradually opening the plug valve after the molecular pump raises the cavity pressure to a preset pressure, until the cavity pressure no longer rises, and recording data; establishing a model of the opening degree and the valve flow guide; establishing a model of the opening degree, the cavity pressure, and the cavity pressure change value; and based on the current opening degree of the plug valve, the cavity pressure, and the adjusted cavity pressure, the adjusted opening degree of the valve is obtained by backstepping, and the valve is controlled to operate to the opening degree. The present application can effectively cope with the nonlinear characteristics of the chamber gas leakage and the plug valve pumping, and improve the accuracy and the response speed of the plug valve pressure control.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of valve control, in particular to a pressure control method of a flapper valve. BACKGROUND

[0002] In the fields of semiconductor manufacturing, thin film deposition, surface science experiment and precision instrument processing, precise high vacuum pressure control is crucial. The current control method of the flapper valve is usually based on simple PID or set value regulation method using traditional PID control or empirical parameter open loop regulation, ignoring the nonlinear pumping characteristics of the system and the influence of leakage on control, failing to effectively cope with the nonlinear characteristics of chamber gas leakage and flapper valve pumping, resulting in limited pressure control accuracy, slow response, large overshoot and significant steady-state error. SUMMARY

[0003] To solve the above problems, the technical scheme adopted by the present application is:

[0004] A pressure control method of a flapper valve, comprising the following steps:

[0005] S1, open the flapper valve, pre-pump the chamber pressure of the chamber to the working pressure range of the molecular pump, open the molecular pump, and after the molecular pump reaches the set stable speed and the chamber pressure is stable, proceed to the next step;

[0006] S2, close the flapper valve, gradually open the flapper valve after the molecular pump raises the chamber pressure to the preset pressure, until the chamber pressure no longer rises, record the opening X of the flapper valve at this time min and the corresponding chamber pressure P max ;

[0007] S3, open the flapper valve from opening X min to X max and record the opening time, split the opening time into N unit times , and record the opening X of the flapper valve in each unit time, record the time chamber pressure P, valve flow conductance , molecular pump gas intake Q in and effective pumping amount Q out of N opening X;

[0008] S4, establish a flapper valve opening X and valve flow conductance model:

[0009]

[0010] Wherein, is the maximum flow conductance when the flapper valve is fully open X max , a is the geometric correction coefficient, and b is the nonlinear index;

[0011] S5, establish the model of the change of the valve opening degree X of the plug-in valve and the cavity pressure and the cavity pressure change value:

[0012]

[0013] wherein V is the volume of the cavity, is the Boltzmann constant, T is the temperature, is the gas inlet amount of the molecular pump, is the effective pumping amount of the molecular pump; is the cavity pressure change value, is the opening x change corresponding to the unit time;

[0014] The effective pumping rate of the molecular pump satisfies

[0015]

[0016] The effective pumping speed of the molecular pump and the valve flow rate The relationship is:

[0017]

[0018] wherein is the nominal pumping speed of the molecular pump, since in the molecular flow state is greater than , , ;

[0019] Let then get

[0020] wherein , r=Q in ;

[0021] S6, when adjusting the valve opening degree of the plug-in valve, based on the current opening degree of the plug-in valve, the cavity pressure and the adjusted cavity pressure, substitute it into the model of step S5, back calculate the adjusted opening degree of the valve and control the valve to run to the calculated opening degree, complete the pressure control.

[0022] Further, in the step S2, the preset pressure is 80%-90% of the highest working pressure of the molecular pump.

[0023] Further, in the step S3, N is a positive integer, and N≥5.

[0024] Further, in the step S4, based on the valve flow rate in the N opening degrees X of step S3 The parameters a and b are obtained using a non-linear least squares method.

[0025] Advantages of the present application:

[0026] The present application collects pressure data in real time, can effectively deal with the nonlinear characteristics of chamber gas leakage and plate valve pumping, dynamically learns the plate valve pumping model in real time, updates the a and b values in real time, and improves the accuracy and response speed of plate valve pressure control. BRIEF DESCRIPTION OF DRAWINGS

[0027] The accompanying drawings, which are incorporated into and form part of the specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the application.

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, for those skilled in the art, other drawings can also be obtained without creative labor based on these drawings.

[0029] Figure 1 Flowchart of the present application. DETAILED DESCRIPTION

[0030] In order to make the objects, technical solutions and advantages of the embodiments of the present disclosure clearer, the technical solutions of the embodiments of the present disclosure will be described clearly and completely below with reference to the drawings of the embodiments of the present disclosure. Obviously, the described embodiments are part of the embodiments of the present disclosure, rather than all the embodiments. Based on the described embodiments of the present disclosure, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present disclosure.

[0031] Unless otherwise defined, the technical terms or scientific terms used in the present disclosure should be understood as the usual meaning understood by those skilled in the art to which the present disclosure belongs. The terms "first", "second" and similar words used in the present disclosure do not represent any order, number or importance, but are only used to distinguish different components. The terms "include" or "contain" and similar words mean that the elements or objects before the words cover the elements or objects listed after the words and their equivalents, without excluding other elements or objects. "Up", "down", "left", "right" and the like are only used to represent relative positional relationships, which may also change accordingly when the absolute position of the described object changes.

[0032] A pressure control method of a plate valve, comprising the following steps:

[0033] S1, open the plug valve, pre-pump the chamber pressure (vacuum chamber) to the working pressure range of the molecular pump, open the molecular pump, and after the molecular pump reaches the set stable speed and the chamber pressure is stable, proceed to the next step;

[0034] In the present application, the working pressure range of the molecular pump is 10 -9 Pa~1Pa, and the pumping rate is generally below 5000 L / s. When the plug valve is just opened, the chamber is in an atmospheric state. If the molecular pump is started directly to pump the air in the chamber, the working intensity of the molecular pump will be significantly increased, causing the molecular pump to be overloaded and damaging the internal high-speed rotating blades. In addition, when the chamber pressure is lower than the lower limit of the working range of the molecular pump, serious cavitation will occur in the pump cavity of the molecular pump. When the negative pressure in the pump cavity of the molecular pump is reduced to below the saturated vapor pressure of the working medium (usually oil vapor), the medium will suddenly vaporize to form a large number of bubbles. When these bubbles enter the high-pressure area of the pump along with the medium flow, they will rapidly break due to the increase in pressure. The bubbles will produce a local high-pressure shock wave with a pressure of up to tens of megapascals. This high-frequency (600-25000 Hz) impact will repeatedly act on the inner wall of the pump cavity and the surface of the blades. The continuous cavitation impact will cause the metal surface to appear pitting and honeycomb erosion. In severe cases, it can even cause the blades to break. At the same time, the local high temperature (200-300℃) generated by the bubble rupture will also accelerate the electrochemical corrosion of the material. Therefore, the molecular pump needs to be used in conjunction with a front-stage pump (such as a rotary vane pump) to pre-pump the chamber negative pressure to the working range of the molecular pump and maintain sufficient front-stage pressure.

[0035] S2, close the plug valve, raise the chamber pressure (vacuum chamber) to the preset pressure, and then gradually open the plug valve until the chamber pressure no longer rises. Record the opening X min of the plug valve at this time and the corresponding chamber pressure P max ;

[0036] The preset pressure is 80%-90% of the highest working negative pressure of the molecular pump. In the present application, the turbine molecular pump transmits momentum to gas molecules through a high-speed rotating impeller (rotating speed of 10000-60000 rpm) to achieve directional flow of the gas. The peripheral speed of the rotor of the branch pump can reach 150-400 m / s. Therefore, the molecular pump must work in a molecular flow state, i.e., the mean free path of the gas molecules is greater than the blade spacing (1 mm). The chamber pressure of 80%-90% ensures that the molecular pump can be completely in a molecular flow state, and the working efficiency of the molecular pump is the highest, which can effectively pump the gas and will not cause excessive compression. In addition, the chamber pressure of 80%-90% also provides a buffer interval for the molecular pump to protect the molecular pump from being overloaded.

[0037] In addition, the valve is gradually opened in a uniform rotation mode, so that the vacuum chamber has sufficient time to reach a new equilibrium state, avoid pressure oscillation, achieve smooth transition of pressure, prevent sudden change of pressure, and protect the molecular pump from pressure impact.

[0038] S3, opening the gate valve from X min to X max , and recording the opening time, and dividing the opening time into N unit time , and recording the opening degree X of the gate valve in each unit time, recording the time chamber pressure P, valve flow conductance , molecular pump gas intake Q in , and effective pumping capacity Q out of N opening degrees X

[0039] In the present application, in order to ensure the accuracy of data acquisition, N is a positive integer, and N≥5, that is, the opening time is divided into at least 5 unit time points, at least 5 effective data of time chamber pressure P, valve flow conductance , molecular pump gas intake Q in , and effective pumping capacity Q out can be obtained, 0.1% opening degree resolution can be realized, and the dynamic response relationship between valve opening degree and various parameters can be accurately captured. This high sampling rate can record the transient change characteristics of pressure, flow conductance and other parameters, and can accurately identify the inflection point characteristics of the flow conductance curve. Of course, according to actual needs, the larger N is, the more complete and accurate the data obtained is.

[0040] S4, establish a gate valve opening degree X and valve flow conductance model:

[0041]

[0042] Wherein, is the maximum flow conductance of the gate valve when fully open X max , a is the geometric correction coefficient, and b is the nonlinear index;

[0043] Based on the valve flow conductance of N opening degrees X in step S3, the parameters a and b are obtained by using nonlinear least squares method. A group of data of the present application is shown in Table 1

[0044]

[0045] Table 1

[0046] The optimal parameters a and b are solved by nonlinear least squares method, so that the residual sum of squares of the model prediction value and the experimental data is minimized:

[0047]

[0048] Set initial guess: a(0)=0.5 (initial value of geometric correction factor), b(0)=1.0 (initial value of nonlinear exponent); set boundary constraints: a∈[0.1, 5.0], b∈[0.1, 5.0]; the residual of each data point (xi, Ci) is

[0049]

[0050] The partial derivative of the residual function with respect to parameters a and b, the partial derivative with respect to a:

[0051]

[0052] The partial derivative with respect to b:

[0053]

[0054] The residual sum of squares objective function is:

[0055]

[0056] The vector gradient is:

[0057]

[0058] Use damped least squares method for iteration, iteration k=1, calculate the current residual:

[0059]

[0060] Calculate the Jacobian matrix:

[0061]

[0062] Calculate the parameter increment:

[0063]

[0064] where, is the initial damping factor;

[0065] Update the parameters:

[0066] Calculate the new residual sum of squares S(1), compare S(1) and S(0), if S(1)<S(0), accept the update, reduce the damping factor λ to 1 / 10 of the original λ; if S(1)>S(0), increase the damping factor λ to 10 times of the original λ, recalculate;

[0067] Iteration k=2, 3,..., repeat the above process until the convergence condition is met

[0068] S5, establish the model of the change of the valve opening degree X of the plug-in valve and the cavity pressure and the cavity pressure change value:

[0069]

[0070] wherein V is the volume of the cavity, is the Boltzmann constant, T is the temperature, is the gas inlet amount of the molecular pump, is the effective pumping amount of the molecular pump; is the cavity pressure change value, is the unit time corresponding to the change of the opening x;

[0071] The effective pumping rate of the molecular pump satisfies

[0072]

[0073] The effective pumping speed of the molecular pump and the valve flow guide are related as follows:

[0074]

[0075] wherein is the nominal pumping speed of the molecular pump, since in the molecular flow state is much greater than , , ;

[0076] Let then obtain

[0077] wherein , r=Q in ;

[0078] S6, when adjusting the valve opening degree of the plug-in valve, based on the current opening degree of the plug-in valve, the cavity pressure and the adjusted cavity pressure, the model in step S5 is substituted, the adjusted opening degree of the valve is calculated by back calculation, and the valve is controlled to run to the calculated opening degree, to complete the pressure control.

[0079] Unless otherwise defined, the same reference numbers in the embodiments of the disclosure and the drawings represent the same meaning.

[0080] In the drawings of the embodiments of the disclosure, only the structures related to the embodiments of the disclosure are involved, and other structures can be referred to the general design.

[0081] For clarity, components or regions are exaggerated in the drawings used to describe embodiments of the present disclosure. It can be understood that when an element is referred to as being "on" or "under" another element, it can be "directly" on or under the other element, or an intermediate element can be present.

[0082] The above description is merely that of a specific implementation of the present disclosure, but the scope of protection of the present disclosure is not limited thereto. Any person skilled in the art can easily think of changes or replacements within the technical scope disclosed by the present disclosure, and all such changes or replacements should be encompassed within the scope of protection of the present disclosure. Therefore, the scope of protection of the present disclosure should be subject to the scope of protection of the claims.

Claims

1. A pressure control method for a slide gate valve, characterized in that: Includes the following steps: S1. Open the slide gate valve to pre-pump the chamber pressure to the working pressure range of the molecular pump, turn on the molecular pump, and wait for the molecular pump to reach the set stable speed and the chamber pressure to stabilize before proceeding to the next step. S2. Close the slide gate valve. After the molecular pump raises the chamber pressure to the preset pressure, gradually open the slide gate valve until the chamber pressure stops rising. Record the opening degree X of the slide gate valve at this point. min and the corresponding cavity pressure P max ; S3. Adjust the gate valve opening from X degree. min Fully open to X max It also records the opening time and breaks it down into N time units. Record the valve opening degree X of the slide gate valve in each unit of time, and record the real-time cavity pressure P and valve conductance within N opening degrees X. The inlet flow rate Q of the molecular pump in and the effective pumping capacity Q of the molecular pump out N is a positive integer, and N≥5; S4. Establish a model for the valve opening degree X and valve flow conductance of the slide gate valve: ； in, X is the fully open gate valve. max The maximum conductance at time t, where a is the geometric correction factor and b is the nonlinear exponent; S5. Establish a model for the relationship between the valve opening degree X of the slide gate valve and the cavity pressure, as well as the change in cavity pressure: ； Where V is the volume of the cavity. Where is Boltzmann's constant, and T is temperature. This refers to the intake air volume of the molecular pump. This is the effective pumping capacity of the molecular pump. for Cavity pressure change value, for The unit time corresponding to the change in opening degree x; Effective pumping rate of molecular pump satisfy ; Effective pumping speed of molecular pump With valve flow guide The relationship is: ； in This refers to the nominal pumping speed of the molecular pump, expressed in L / s. This is because it operates under molecular flow conditions. Greater than , , ; let but get ; in r=Q in ; S6. When adjusting the valve opening of the slide gate valve, based on the current valve opening, cavity pressure and adjusted cavity pressure, substitute them into the model of step S5, calculate the adjusted valve opening, and control the valve to run to the calculated opening to complete the pressure control.

2. The pressure control method for a slide gate valve according to claim 1, characterized in that: In step S2, the preset pressure is 80%-90% of the maximum working pressure of the molecular pump.

3. The pressure control method for a slide gate valve according to claim 1, characterized in that: In step S4, the valve flow guide within the N opening degrees X in step S3 is... The parameters a and b are obtained using the nonlinear least squares method.

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