A kind of pneumatic amplifier diaphragm micro-displacement nonlinear testing device and method

Abstract

The application relates to the technical field of fluid transmission and control, and discloses a kind of gas amplifier diaphragm micro-displacement nonlinear testing device and method, testing device includes precision displacement driving mechanism, diaphragm profiling mechanism, pre-tightening force exerting and measuring mechanism, force transmission baffle, micro-displacement measuring mechanism, air pressure control and collection mechanism, data acquisition and processing system.The application can accurately simulate the physical boundary of the original back pressure cavity of the gas amplifier, exert controllable initial pre-tightening force of millinewton level, and capture the small deformation of the diaphragm in non-contact mode with 0.01mm resolution, and then accurately extract the nonlinear stiffness coefficient of the diaphragm through physical measurement data.

Description

Technical Field

[0001] This invention relates to the field of fluid transmission and control technology, specifically to the testing technology of the mechanical properties of the diaphragm of the pneumatic amplifier, a core component of industrial automated pneumatic valve positioners, and more specifically, to a device and method for testing the micro-displacement nonlinearity of the pneumatic amplifier diaphragm. Background Technology

[0002] The pneumatic amplifier is the core power amplification unit of the pneumatic valve positioner. Its internal flexible diaphragm undergoes micro-displacement under the pressure of the back pressure chamber, driving the valve core to amplify the pressure signal. Currently, the industry commonly uses the classical equivalent area method for calculating diaphragm stress, employing the linear formula F=P×A (where P is the back pressure chamber pressure and A is the effective pressure-bearing area of ​​the diaphragm). This method is applicable to pneumatic control valves operating under large displacement and high pressure conditions. For diaphragm mechanical performance testing, existing testing schemes mostly use general-purpose material testing machines or dedicated testing devices designed for large-stroke control valve diaphragms.

[0003] The existing calculation methods and testing techniques described above have significant drawbacks when applied to the testing of pneumatic amplifier diaphragms, as detailed below: 1. Linear models have large errors and cannot meet the requirements for high-precision modeling. The diaphragm of a pneumatic amplifier actually operates under sub-millimeter displacement of 0-0.5 mm and low pressure of 0-0.2 MPa. The bending deformation and tensile tension of the diaphragm contain high-order nonlinear terms accounting for more than 10%. The existing linear equivalent area method completely ignores this nonlinear effect, which directly leads to a dynamic simulation error of more than 15% for the pneumatic amplifier, making it difficult to meet the modeling and simulation requirements of high-precision pneumatic valve positioners.

[0004] 2. The testing equipment lacks precision and has a low degree of matching with actual working conditions. The displacement resolution of general-purpose material testing machines is insufficient (≥0.01mm), making it impossible to accurately capture sub-millimeter-level micro-deformations or achieve precise loading of millinew-level micro-forces. Existing diaphragm testing devices are all designed for large-stroke regulating valves and cannot reproduce the actual assembly and working conditions of the original back pressure chamber of the pneumatic amplifier in a 1:1 manner, such as the clamping boundary and internal volume. This results in a large deviation between the test data and the actual working state of the diaphragm, making it unsuitable for direct use in product modeling.

[0005] 3. Inability to accurately extract nonlinear parameters Existing testing methods cannot decouple the nonlinear restoring force of the diaphragm itself from the linear elastic force of the loading mechanism. The measured stiffness data contains a large number of interference terms and cannot quantify the geometric and material nonlinearity of the diaphragm. At the same time, they cannot eliminate the initial dead zone caused by the diaphragm installation gap, resulting in serious distortion of the diaphragm opening threshold prediction.

[0006] 4. Simulation methods have strong limitations and are difficult to use as a basis for product finalization. Finite element simulation relies heavily on the viscoelastic parameters of materials, which are difficult to measure precisely, and cannot take into account actual engineering factors such as processing errors and assembly gaps. The simulation results deviate significantly from the measured data, and cannot be directly used as a reliable basis for the finalization and design optimization of pneumatic amplifier products. Summary of the Invention

[0007] In view of this, the present invention proposes a nonlinear testing device and method for micro-displacement of a pneumatic amplifier diaphragm. Specifically, it is a testing device and method that can accurately simulate the physical boundary of the original back pressure cavity of a pneumatic amplifier, apply a controllable initial preload at the millinewton level, and capture the micro-deformation of the diaphragm non-contactly with a resolution of 0.01 mm, and then accurately extract the nonlinear stiffness coefficient of the diaphragm through physical measurement data.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: First, this invention provides a nonlinear testing device for the micro-displacement of a pneumatic amplifier diaphragm, comprising: A precision displacement drive mechanism includes a base, a fixed slide table fixedly mounted on the base, and a movable slide table slidably mounted on the base and coaxially arranged with the fixed slide table; the movable slide table is driven to achieve submicron-level axial linear feed and position locking. The diaphragm conforming mechanism, fixed on the fixed slide, includes a diaphragm inflation chamber and a diaphragm pressure plate; the internal structure and volume parameters of the diaphragm inflation chamber are replicated 1:1 with the original back pressure chamber of the pneumatic amplifier under test; the open end face of the diaphragm inflation chamber cooperates with the diaphragm pressure plate to seal and clamp the edge of the diaphragm under test. The preload application and measurement mechanism is fixed on the movable slide to simulate the initial compression state of the spring inside the pneumatic amplifier, eliminate the initial dead zone caused by the diaphragm installation gap, and monitor the preload and loading force applied to the diaphragm in real time. A force transmission baffle is disposed between the pre-tightening force application and measuring mechanism and the diaphragm conforming mechanism. One end of the force transmission baffle is connected to the diaphragm pressure plate, and the other end serves as a reflective target for micro-displacement measurement and is used to transmit axial force to the diaphragm to be measured. A micro-displacement measuring mechanism is fixed on the moving slide table and is used to perform non-contact measurement of the axial displacement of the force transmission baffle. The air pressure control and acquisition mechanism is connected to the inner cavity of the diaphragm conforming mechanism and is used to apply controllable air pressure to the diaphragm and monitor the real-time pressure value of the inner cavity of the diaphragm inflation cavity. The data acquisition and processing system is electrically connected to the air pressure control and acquisition mechanism, the micro-displacement measurement mechanism, and the pre-tightening force application and measurement mechanism, respectively, and is used to synchronously acquire displacement, pressure, and force signal data.

[0009] Preferably, the precision displacement driving mechanism further includes a stepper motor and a high-precision lead screw. The stepper motor is mounted on the outer wall of the axial end of the base. The high-precision lead screw is axially rotatably mounted on the base and passes through the fixed slide. The movable slide has a threaded hole that mates with the high-precision lead screw. The base is also provided with a high-precision linear ball guide that slides with the movable slide. The stepper motor drives the high-precision lead screw to rotate, thereby causing the movable slide to reciprocate linearly along the high-precision linear ball guide to move closer to or away from the fixed slide.

[0010] Preferably, the stepper motor has a step angle of 1.8° and is paired with a driver with a step size of not less than 32 microsteps; the high-precision lead screw has a lead accuracy grade of C3 or higher.

[0011] Preferably, the central pressure-bearing area of ​​the diaphragm to be tested is opposite to the inner cavity of the diaphragm inflation chamber, forming a closed pressure-bearing air chamber.

[0012] Preferably, the force transmission baffle is a centrally symmetrical double-wing structure, which includes a central circular area, a first extension plate and a second extension plate. The central circular area is coaxial with the diaphragm to be tested. The first extension plate and the second extension plate extend outward from the central circular area and are centrally symmetrically distributed about the center of the central circular area. The first extension plate and the second extension plate have the same mass, and the end face of the first extension plate facing the micro-displacement measuring mechanism is provided with an optical reflective surface.

[0013] Preferably, the preload application and measurement mechanism includes a pressure sensor bracket fixed to the movable slide, and a high-precision pressure sensor is fixed on the side of the pressure sensor bracket facing the force transmission baffle for real-time monitoring of preload and loading force; a low-stiffness elastic preload member is coaxially connected to the force measuring end of the high-stiffness pressure sensor, and the low-stiffness elastic preload member is directly opposite the central circular area of ​​the force transmission baffle.

[0014] Preferably, the micro-displacement measuring mechanism includes a displacement sensor bracket fixed to the movable slide and a laser displacement sensor mounted on the displacement sensor bracket; the measuring optical axis of the laser displacement sensor is parallel to the axial movement direction of the force transmission baffle, and the measuring spot of the laser displacement sensor is perpendicularly aligned with the optical reflecting surface of the first extension plate.

[0015] Preferably, the pressure control and acquisition mechanism consists of a pressure acquisition mechanism and a pressure control mechanism; the pressure acquisition mechanism includes a pressure transmitter for monitoring the real-time pressure value of the diaphragm inflation cavity, and the accuracy of the pressure transmitter is not less than 0.05%FS; the pressure control mechanism includes a gas source connected to the diaphragm inflation cavity and a pressure reducing valve for controlling the output pressure of the gas source; the diaphragm inflation cavity is provided with a control gas inlet and a pressure transmitter mounting port.

[0016] Secondly, the present invention further provides a method for testing the nonlinear micro-displacement of a pneumatic amplifier diaphragm, which utilizes the aforementioned apparatus and includes the following steps: S1. Installation and Mechanical Zeroing: Seal the diaphragm to be tested between the diaphragm inflation chamber and the diaphragm pressure plate; control the moving slide in the precision displacement drive mechanism to feed towards the fixed slide. During this process, the diaphragm to be tested approaches and contacts the force transmission baffle. After they contact each other, apply a preload to the measuring mechanism and pressurize it until the reading of the preload applied to the measuring mechanism reaches the preset initial preload threshold F0. Then stop feeding and lock the moving slide; clear the reading of the micro-displacement measuring mechanism to zero and define it as the displacement zero point. S2. Nonlinear air pressure loading and synchronous acquisition: Air pressure is input into the inner cavity of the diaphragm inflation chamber through the air pressure control and acquisition mechanism, so that the air pressure increases instantaneously from 0MPa to 0.4MPa or increases in increments of 0.05MPa; during the loading process, the air pressure value Pᵢ and the axial displacement change Xᵢ in the cavity are synchronously latched by the data acquisition and processing system to form a discrete data point set (Pᵢ, Xᵢ); S3. Decoupling and Fitting of Diaphragm Nonlinear Elastic Restoring Force Characteristics: Perform polynomial fitting on the discrete data point set to establish the functional relationship between equilibrium air pressure P and displacement X, P=f(X); Based on the known effective area A of the diaphragm to be measured, calculate the elastic restoring force Fd=P·A of the diaphragm to obtain the nonlinear relationship between the elastic restoring force of the diaphragm and the displacement.

[0017] Preferably, the polynomial fitting in step S3 adopts a quadratic polynomial fitting, with the functional relationship being: P=aX²+bX+c, where a, b, and c are fitting coefficients used to characterize the geometric and material nonlinear properties of the diaphragm.

[0018] Compared with the prior art, the present invention provides a nonlinear testing device and method for micro-displacement of a pneumatic amplifier diaphragm, which has the following advantages: 1) Improved testing accuracy: Through submicron-level drive mechanism, non-contact laser displacement measurement, and symmetrical anti-deflection force transmission baffle structure, high-precision measurement of nonlinear stiffness coefficient of pneumatic amplifier diaphragm under 0-0.5mm submillimeter displacement is achieved. The displacement measurement accuracy reaches 0.01mm, the force measurement accuracy reaches 0.001N, and the measurement signal-to-noise ratio is much higher than that of traditional contact measurement schemes.

[0019] 2) 100% accuracy in replicating working conditions and strong engineering applicability: The diaphragm inflation chamber is a 1:1 replica of the original back pressure chamber structure, completely reproducing the actual working boundary conditions of the diaphragm. The nonlinear coefficients obtained from the test can be directly used as input parameters for the whole simulation model of the pneumatic amplifier, eliminating the equivalent parameter correction process and shortening the product development cycle of the positioner.

[0020] 3) Accurate extraction of nonlinear parameters: By using low-stiffness elastic preload, the interference of linear elastic force in the loading mechanism is effectively eliminated.

[0021] 4) Strong versatility and scalability, enabling platform-based applications: The device supports quick replacement of inflation chambers of different specifications and diaphragms of different materials. It can not only perform batch calibration of diaphragms of different models of pneumatic amplifiers, but also carry out scientific experiments such as diaphragm material selection, back pressure cavity volume optimization, and fluid-structure interaction characteristic research, thus having the dual functions of product testing and mechanism research.

[0022] 5) Easy to operate and good data reproducibility: The device is equipped with automated testing and data processing programs, which can realize the full automation of loading, acquisition and fitting. The test data reproducibility error does not exceed 2%, and it can be widely used in the R&D, quality inspection and factory calibration of pneumatic component manufacturing enterprises. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the overall structure of the testing device of the present invention.

[0025] Figure 2 This is a schematic diagram of the precision displacement drive mechanism in the testing device of the present invention.

[0026] Figure 3 This is a schematic diagram of the diaphragm conformal mechanism in the testing device of the present invention.

[0027] Figure 4 This is a schematic diagram of the force transmission baffle in the testing device of the present invention.

[0028] Figure 5 This is a schematic diagram of the preload application and measurement mechanism in the testing device of the present invention.

[0029] Figure 6 This is a schematic diagram of the micro-displacement measurement mechanism in the testing device of the present invention.

[0030] Figure 7 This is a schematic diagram of the air path of the air pressure control and acquisition mechanism in the testing device of the present invention.

[0031] Figure 8 This is a measured air pressure-displacement curve from Embodiment 1 of the present invention.

[0032] In the diagram: 1-Precision displacement drive mechanism, 11-Base, 12-Fixed slide, 13-Moving slide, 14-Stepper motor, 15-High-precision lead screw; 2-Diaphragm contouring mechanism, 21-Diaphragm inflation chamber, 22-Diaphragm pressure plate, 23-Diaphragm to be tested; 3-Force transmission baffle, 31-Central circular area, 32-First extension plate, 33-Second extension plate; 4-Pressure application and measurement mechanism, 41-Pressure sensor bracket, 42-High-precision pressure sensor, 43-Low-stiffness elastic pre-tensioning component; 5-Micro-displacement measurement mechanism, 51-Displacement sensor bracket, 52-Laser displacement sensor; 6-Air pressure acquisition mechanism, 61-Pressure transmitter; 7-Air pressure control mechanism, 71-Pressure reducing valve; 8-Data acquisition and processing system. Detailed Implementation

[0033] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0034] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0035] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0036] First, embodiments of the present invention provide a nonlinear testing device for the micro-displacement of a pneumatic amplifier diaphragm, such as... Figure 1As shown, it includes a precision displacement drive mechanism 1, a diaphragm contouring mechanism 2, a preload application and measurement mechanism 4, a force transmission baffle 3, a micro-displacement measurement mechanism 5, a pneumatic pressure control and acquisition mechanism, and a data acquisition and processing system 8.

[0037] See Figure 2 In this embodiment, the precision displacement drive mechanism 1 includes a base 11, a fixed slide 12 fixedly mounted on the base 11, and a movable slide 13 slidably mounted on the base 11 and coaxially arranged with the fixed slide 12; the movable slide 13 is driven to achieve submicron-level axial linear feed and position locking.

[0038] In a further specific embodiment, the precision displacement drive mechanism 1 also includes a stepper motor 14 and a high-precision lead screw 15. The stepper motor 14 is mounted on the outer wall of the axial end of the base. The high-precision lead screw 15 is axially rotatably mounted on the base 11 and passes through the fixed slide table 12. The movable slide table 13 has a high-precision threaded hole that mates with the high-precision lead screw 15. The base 11 is also provided with a high-precision linear ball guide that slides with the movable slide table 13. The stepper motor 14 drives the high-precision lead screw 15 to rotate, thereby driving the movable slide table 13 to make linear reciprocating motion along the high-precision linear ball guide to move closer to or away from the fixed slide table 12, effectively ensuring the axial movement accuracy of the movable slide table.

[0039] Furthermore, in the above embodiments, the stepper motor 14 has a step angle of 1.8°, and is equipped with a driver with a microstepping of no less than 32 micrometers; the lead screw 15 has a lead accuracy of C3 or above, thereby driving the movable slide 13 to achieve submicron-level axial linear feed and position locking along the guide rail.

[0040] See Figure 3 In this embodiment, the diaphragm conforming mechanism 2 is fixed on the fixed slide 12 and includes a diaphragm inflation chamber 21 and a diaphragm pressure plate 22. The internal structure and volume parameters of the diaphragm inflation chamber 21 are replicated 1:1 with the original back pressure chamber of the pneumatic amplifier under test. The open end face of the diaphragm inflation chamber 21 cooperates with the diaphragm pressure plate 22 to seal and clamp the edge of the diaphragm 23 under test.

[0041] The diaphragm inflation chamber 21 is the core of the diaphragm conforming mechanism 2. In a further specific embodiment, the diaphragm inflation chamber 21 is made so that its internal structure and volume parameters are completely consistent with the original back pressure chamber of the pneumatic amplifier under test through three-dimensional reverse mapping and precision machining.

[0042] Meanwhile, the central pressure-bearing area of ​​the diaphragm 23 under test is opposite to the inner cavity of the diaphragm inflation chamber 21, forming a closed pressure-bearing air chamber, which 100% reproduces the actual working boundary of the diaphragm under test.

[0043] In this embodiment, the preload application and measurement mechanism 4 is fixed on the movable slide 13 to simulate the initial compression state of the spring inside the pneumatic amplifier, eliminate the initial dead zone caused by the diaphragm installation gap, and monitor the preload and subsequent loading force applied to the diaphragm in real time. The force transmission baffle 3 is disposed between the preload application and measurement mechanism 4 and the diaphragm conforming mechanism 2. One end of the force transmission baffle 3 is connected to the diaphragm pressure plate 22, and the other end serves as a reflective target surface for micro-displacement measurement and is used to transmit the axial force to the diaphragm 23 to be measured.

[0044] In a further specific embodiment, see [link to relevant documentation]. Figure 4 The force transmission baffle 3 is a centrally symmetrical double-wing structure, which includes a central circular area 31, a first extension plate 32 and a second extension plate 33. The central circular area 31 is coaxial with the diaphragm 23 to be tested. The first extension plate 32 and the second extension plate 33 extend outward from the central circular area 31 and are centrally symmetrical about the center of the central circular area. The first extension plate 32 and the second extension plate 33 have the same mass, and the end face of the first extension plate facing the micro-displacement measuring mechanism is provided with an optical reflective surface.

[0045] In this embodiment, by making the masses of the first extension plate 32 and the second extension plate 33 completely consistent, the mass dynamic balance of the force transmission baffle 3 is achieved, the deflection torque during axial movement is eliminated, and the force transmission baffle 3 is guaranteed to only produce axial translation without angular deflection, thus eliminating the yaw error of micro-displacement measurement.

[0046] See Figure 5 The preload application and measurement mechanism 4 includes a pressure sensor bracket 41 fixed on the movable slide table 13. A high-precision pressure sensor 42 is fixed on the side of the pressure sensor bracket facing the force transmission baffle. The high-precision pressure sensor 42 has a range of 0~10N and a measurement accuracy of not less than 0.01N. It can monitor the preload and loading force applied to the diaphragm in real time. A low-stiffness elastic preload member 43 is coaxially connected to the force measuring end of the high-precision pressure sensor 42, and the low-stiffness elastic preload member 43 is directly facing the central circular area 31 of the force transmission baffle 3.

[0047] In this embodiment, the low-stiffness elastic preload 43 is specifically a cylindrical helical compression spring with a stiffness coefficient of 0.1~1.0 N / mm. This cylindrical helical compression spring ensures consistent operating conditions by simulating the actual preload state of the spring inside the pneumatic amplifier. On the other hand, it eliminates the diaphragm installation gap through preload force, completely eliminating the initial dead zone and ensuring that the diaphragm opening threshold and micro-displacement test are accurate.

[0048] In this embodiment, the micro-displacement measuring mechanism 5 is fixed on the moving slide table 13 and is used to perform non-contact measurement of the axial displacement of the force transmission baffle 3.

[0049] In a further specific embodiment, see [link to relevant documentation]. Figure 6The micro-displacement measuring mechanism 5 includes a displacement sensor bracket 51 fixed on the movable slide 13 and a laser displacement sensor 52 mounted on the displacement sensor bracket 51; the measuring optical axis of the laser displacement sensor 52 is parallel to the axial movement direction of the force transmission baffle 3, and the measuring spot of the laser displacement sensor 52 is vertically aligned with the optical reflecting surface of the first extension plate 32. Figure 6 The part at point A in the middle refers to the laser.

[0050] In this embodiment, the linear measurement accuracy of the laser displacement sensor 52 is not less than 0.01 mm, and the sampling frequency is not less than 1 kHz. It is used to measure the axial micro-displacement of the diaphragm without contact, thus eliminating the force interference of contact measurement.

[0051] In this embodiment, the air pressure control and acquisition mechanism is connected to the inner cavity of the diaphragm conforming mechanism 2, and is used to apply controllable air pressure to the diaphragm and monitor the real-time pressure value of the inner cavity of the diaphragm inflation chamber.

[0052] In a further specific embodiment, see [link to relevant documentation]. Figure 7 The pressure control and acquisition mechanism consists of a pressure acquisition mechanism 6 and a pressure control mechanism 7. The pressure acquisition mechanism 6 includes a pressure transmitter 61 for monitoring the real-time pressure value of the diaphragm inflation cavity, and the accuracy of the pressure transmitter 61 is not less than 0.05%FS. The pressure control mechanism 7 includes a gas source connected to the diaphragm inflation cavity and a pressure reducing valve 71 for controlling the output pressure of the gas source. The diaphragm inflation cavity 21 is provided with a control gas inlet and a pressure transmitter mounting port. Figure 7 The red pipe in the diagram is the gas pressure delivery pipe, and point B indicates the gas inlet of the pipe.

[0053] In this embodiment, the data acquisition and processing system 8 is electrically connected to the air pressure control and acquisition mechanism, the micro-displacement measurement mechanism 5, and the pre-tightening force application and measurement mechanism 4, respectively, and is used to synchronously acquire displacement, pressure, and force signal data.

[0054] Since the data acquisition and processing system 8 belongs to the acquisition and post-processing part of the data and is not part of the hardware structure, it is not shown in the diagram. Only some data transmission lines are shown.

[0055] In a further specific embodiment, the data acquisition and processing system 8 synchronously receives the pressure signal from the pressure transmitter 61, the displacement signal from the laser displacement sensor 52, and the force signal from the high-precision pressure sensor 42 through a synchronous data acquisition card, and realizes synchronous data storage and polynomial fitting based on the Matlab platform.

[0056] Secondly, this invention also provides a method for testing the nonlinear micro-displacement of a pneumatic amplifier diaphragm, utilizing the aforementioned apparatus and comprising the following steps: S1. Installation and Mechanical Zeroing: Seal the diaphragm to be tested between the diaphragm inflation chamber and the diaphragm pressure plate; control the stepper motor in the precision displacement drive mechanism to drive the moving slide towards the fixed slide. During this process, the diaphragm to be tested approaches and contacts the force transmission baffle. After they contact each other, the preload is applied and coaxially compressed with the low-stiffness elastic preload in the measuring mechanism until the preload is applied and the reading of the high-precision pressure sensor in the measuring mechanism reaches the preset initial preload threshold F0. Then, stop the feed and lock the moving slide; clear the reading of the laser displacement sensor in the micro-displacement measuring mechanism to zero, which is defined as the displacement zero point. S2. Nonlinear air pressure loading and synchronous acquisition: By controlling the pressure reducing valve in the air pressure control and acquisition mechanism, air pressure is input into the inner cavity of the diaphragm inflation chamber, causing the air pressure to increase instantaneously from 0MPa to 0.4MPa or increase in increments of 0.05MPa; during the loading process, the synchronous data acquisition card of the data acquisition and processing system synchronously latches the air pressure value Pᵢ and the axial displacement change Xᵢ in the cavity at a frequency of not less than 100Hz, forming a discrete data point set (Pᵢ, Xᵢ); More specifically, the air pressure loading method starts from 0 MPa and increases in steps of 0.05 MPa. At each air pressure level, the system is allowed to reach quasi-static equilibrium before data acquisition is performed. That is, the intracavitary air pressure value p and the corresponding displacement value Xi are recorded in the equilibrium state. S3. Decoupling and Fitting of Diaphragm Nonlinear Elastic Restoring Force Characteristics: Perform polynomial fitting on the discrete data point set to establish the functional relationship between equilibrium air pressure P and displacement X, P=f(X); calculate the elastic restoring force Fd=P·A of the diaphragm based on the known effective area A of the diaphragm to be measured, thereby obtaining the nonlinear relationship between the elastic restoring force of the diaphragm and the displacement. More specifically, the above polynomial fitting adopts a quadratic polynomial fitting, and the functional relationship is: P=aX²+bX+c, where a, b, and c are fitting coefficients used to characterize the geometric and material nonlinear properties of the diaphragm.

[0057] In the above method, by replacing the test diaphragm with a different material and repeating steps S1 to S3, the pressure-displacement relationship and elastic restoring force expression corresponding to the diaphragm with different materials can be obtained respectively, so as to compare mechanical properties. Specific Implementation Example 1

[0058] The following describes the accurate testing of the nonlinear elastic restoring force characteristics of the back pressure diaphragm of a pneumatic amplifier in a certain positioner using the device and method of this invention: A stepper motor drives a high-precision lead screw to rotate, causing the movable slide to move along a high-precision linear ball bearing guide towards the fixed slide. The low-stiffness elastic preload is compressed, which in turn pushes the force transmission baffle and diaphragm pressure plate to apply an initial preload to the diaphragm under test. When the reading of the high-precision pressure sensor reaches the preset initial preload threshold, the stepper motor stops and the movable slide is locked in position. At this time, the laser displacement sensor reading returns to zero.

[0059] Next, compressed air is introduced into the inner cavity of the diaphragm inflation chamber from an external air source. The operator adjusts the air pressure and observes the real-time reading of the laser displacement sensor. When the air pressure thrust and the diaphragm's elastic restoring force reach a quasi-static equilibrium, the laser displacement sensor reading stabilizes again at the target displacement X. The cavity air pressure value p and the current displacement X are recorded in this equilibrium state.

[0060] Repeat the above displacement increment and air pressure balance adjustment process to obtain a series of data points from 0 to 2.2 mm. Perform a quadratic polynomial fitting on the experimental data to obtain the relationship between the equilibrium air pressure p and the displacement X: P = 0.0047·X² + 0.0374·X + 0.0022. Given the known effective diaphragm area A = 1565.5 mm², the elastic restoring force Fd of the diaphragm in equilibrium is equal to the air pressure thrust, i.e., Fd = P·A = P × 1565.5.

[0061] Figure 8 The figure shown is the measured air pressure-displacement curve in this embodiment.

[0062] This device and method can accurately extract the second-order nonlinear stiffness coefficient of the diaphragm under sub-millimeter displacement, quantitatively revealing the significant contribution of the nonlinear term to the restoring force under small displacement conditions, thus providing key mechanical parameters for the accurate modeling of the positioner pneumatic amplifier and the prediction of the valve core opening threshold. Specific Implementation Example 2

[0063] The following is a comparative test of the nonlinear mechanical properties of diaphragms made of different materials using the device and method of this invention: Based on the apparatus of Example 1, the diaphragm to be tested was successively replaced with a nitrile rubber diaphragm, a fluororubber diaphragm, and a polyurethane-reinforced rubber diaphragm. The operation steps in Example 1 were repeated—an initial preload was applied and then returned to zero by a stepper motor, followed by increasing the compression displacement X in preset steps, introducing compressed air into the diaphragm inflation chamber and adjusting the air pressure to a balanced state, and recording the balanced air pressure value P of each diaphragm material at different displacements.

[0064] By performing quadratic polynomial fitting on each group of data, the pressure-displacement relationship P=f and the elastic restoring force expression Fd=A·f corresponding to each diaphragm material were obtained.

[0065] By comparing the differences in the fitting coefficients of each group, the linear stiffness, nonlinear strength, and magnitude of zero displacement bias force of different diaphragm materials under small displacement conditions can be directly evaluated.

[0066] The device and method of this invention provide a quantitative basis for comparing the mechanical properties of diaphragm materials during the design phase of a positioner pneumatic amplifier.

[0067] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0068] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A nonlinear testing device for micro-displacement of a pneumatic amplifier diaphragm, characterized in that, include: A precision displacement drive mechanism includes a base, a fixed slide table fixedly mounted on the base, and a movable slide table slidably mounted on the base and coaxially arranged with the fixed slide table; the movable slide table is driven to achieve submicron-level axial linear feed and position locking. The diaphragm conforming mechanism, fixed on the fixed slide, includes a diaphragm inflation chamber and a diaphragm pressure plate; the internal structure and volume parameters of the diaphragm inflation chamber are replicated 1:1 with the original back pressure chamber of the pneumatic amplifier under test; the open end face of the diaphragm inflation chamber cooperates with the diaphragm pressure plate to seal and clamp the edge of the diaphragm under test. The preload application and measurement mechanism is fixed on the movable slide to simulate the initial compression state of the spring inside the pneumatic amplifier, eliminate the initial dead zone caused by the diaphragm installation gap, and monitor the preload and loading force applied to the diaphragm in real time. A force transmission baffle is disposed between the pre-tightening force application and measuring mechanism and the diaphragm conforming mechanism. One end of the force transmission baffle is connected to the diaphragm pressure plate, and the other end serves as a reflective target for micro-displacement measurement and is used to transmit axial force to the diaphragm to be measured. A micro-displacement measuring mechanism is fixed on the moving slide table and is used to perform non-contact measurement of the axial displacement of the force transmission baffle. The air pressure control and acquisition mechanism is connected to the inner cavity of the diaphragm conforming mechanism and is used to apply controllable air pressure to the diaphragm and monitor the real-time pressure value of the inner cavity of the diaphragm inflation cavity. The data acquisition and processing system is electrically connected to the air pressure control and acquisition mechanism, the micro-displacement measurement mechanism, and the pre-tightening force application and measurement mechanism, respectively, and is used to synchronously acquire displacement, pressure, and force signal data.

2. The nonlinear testing device for micro-displacement of a pneumatic amplifier diaphragm according to claim 1, characterized in that, The precision displacement drive mechanism also includes a stepper motor and a high-precision lead screw. The stepper motor is mounted on the outer wall of the axial end of the base. The high-precision lead screw is axially rotatably mounted on the base and passes through the fixed slide. The movable slide has a threaded hole inside that mates with the high-precision lead screw. The base is also provided with a high-precision linear ball guide that slides with the movable slide. The stepper motor drives the high-precision lead screw to rotate, thereby causing the movable slide to reciprocate linearly along the high-precision linear ball guide to move closer to or further away from the fixed slide.

3. The nonlinear testing device for micro-displacement of a pneumatic amplifier diaphragm according to claim 2, characterized in that, The stepper motor has a step angle of 1.8° and is paired with a driver with a step size of no less than 32 microsteps; the high-precision lead screw has a lead accuracy grade of C3 or above.

4. The nonlinear testing device for micro-displacement of a pneumatic amplifier diaphragm according to claim 1, characterized in that, The central pressure-bearing area of ​​the diaphragm under test is opposite to the inner cavity of the diaphragm inflation chamber, forming a closed pressure-bearing air chamber.

5. The nonlinear testing device for micro-displacement of a pneumatic amplifier diaphragm according to claim 1, characterized in that, The force transmission baffle is a centrally symmetrical double-wing structure, which includes a central circular area, a first extension plate and a second extension plate. The central circular area is coaxial with the diaphragm to be tested. The first extension plate and the second extension plate extend outward from the central circular area and are centrally symmetrically distributed about the center of the central circular area. The first extension plate and the second extension plate have the same mass, and the end face of the first extension plate facing the micro-displacement measuring mechanism is provided with an optical reflective surface.

6. The nonlinear testing device for micro-displacement of a pneumatic amplifier diaphragm according to claim 5, characterized in that, The preload application and measurement mechanism includes a pressure sensor bracket fixed to the movable slide. A high-precision pressure sensor is fixed to the side of the pressure sensor bracket facing the force transmission baffle for real-time monitoring of preload and loading force. A low-stiffness elastic preload member is coaxially connected to the force measuring end of the high-stiffness pressure sensor, and the low-stiffness elastic preload member is directly opposite the central circular area of ​​the force transmission baffle.

7. The nonlinear testing device for micro-displacement of a pneumatic amplifier diaphragm according to claim 5, characterized in that, The micro-displacement measuring mechanism includes a displacement sensor bracket fixed to the moving slide and a laser displacement sensor mounted on the displacement sensor bracket; the measuring optical axis of the laser displacement sensor is parallel to the axial movement direction of the force transmission baffle, and the measuring spot of the laser displacement sensor is perpendicularly aligned with the optical reflecting surface of the first extension plate.

8. The nonlinear testing device for micro-displacement of a pneumatic amplifier diaphragm according to claim 1, characterized in that, The pressure control and acquisition mechanism consists of a pressure acquisition mechanism and a pressure control mechanism. The pressure acquisition mechanism includes a pressure transmitter for monitoring the real-time pressure value of the diaphragm inflation cavity, and the accuracy of the pressure transmitter is not less than 0.05%FS. The pressure control mechanism includes a gas source connected to the diaphragm inflation cavity and a pressure reducing valve for controlling the output pressure of the gas source. The diaphragm inflation cavity is provided with a control gas inlet and a pressure transmitter mounting port.

9. A method for testing the nonlinear micro-displacement of a pneumatic amplifier diaphragm, using the apparatus described in any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Installation and Mechanical Zeroing: Seal the diaphragm to be tested between the diaphragm inflation chamber and the diaphragm pressure plate; control the moving slide in the precision displacement drive mechanism to feed towards the fixed slide. During this process, the diaphragm to be tested approaches and contacts the force transmission baffle. After they contact each other, apply a preload to the measuring mechanism and pressurize it until the reading of the preload applied to the measuring mechanism reaches the preset initial preload threshold F0. Then stop feeding and lock the moving slide; clear the reading of the micro-displacement measuring mechanism to zero and define it as the displacement zero point. S2. Nonlinear air pressure loading and synchronous acquisition: Air pressure is input into the inner cavity of the diaphragm inflation chamber through the air pressure control and acquisition mechanism, so that the air pressure increases instantaneously from 0MPa to 0.4MPa or increases in increments of 0.05MPa; during the loading process, the air pressure value Pᵢ and the axial displacement change Xᵢ in the cavity are synchronously latched by the data acquisition and processing system to form a discrete data point set (Pᵢ, Xᵢ); S3. Decoupling and Fitting of Diaphragm Nonlinear Elastic Restoring Force Characteristics: Perform polynomial fitting on the discrete data point set to establish the functional relationship between equilibrium air pressure P and displacement X, P=f(X); Based on the known effective area A of the diaphragm to be measured, calculate the elastic restoring force Fd=P·A of the diaphragm to obtain the nonlinear relationship between the elastic restoring force of the diaphragm and the displacement.

10. The method for testing the nonlinear micro-displacement of a pneumatic amplifier diaphragm according to claim 9, characterized in that, The polynomial fitting in step S3 uses a quadratic polynomial fitting, with the functional relationship being: P=aX²+bX+c, where a, b, and c are fitting coefficients used to characterize the geometric and material nonlinear properties of the diaphragm.

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