High-temperature fatigue testing machine self-compensation clamp based on temperature compensation algorithm and control method

Abstract

The invention discloses a high-temperature fatigue testing machine self-compensation clamp based on a temperature compensation algorithm and a control method thereof, and relates to the technical field of high-temperature fatigue testing machines, a temperature sensor and a force sensor are adopted to collect intelligent sensing data, and the control method is high in compensation precision and wide in application range. An original thermal expansion-creep-rigidity temperature drift-gradient learning four-in-one temperature compensation algorithm is adopted, the nonlinear effects of thermal expansion, high-temperature creep and system rigidity changing along with temperature are comprehensively considered, the error source of the whole temperature range can be covered, the strict requirement for verifying the fatigue life under the extreme working condition is met, and the fatigue life is verified. Through a'temperature-clamping force 'closed-loop control algorithm and a unique feedforward-feedback displacement compensation mechanism of a PID controller, the clamping force is dynamically and accurately adjusted.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-temperature fatigue testing machines, in particular to a high-temperature fatigue testing machine self-compensation clamp based on a temperature compensation algorithm and a control method. BACKGROUND

[0002] With the continuous improvement of the performance requirements of materials in extreme environments in high-precision fields such as aerospace and nuclear power, high-temperature fatigue testing has become one of the core means for evaluating material reliability. In the process of high-temperature fatigue testing, the sample needs to be tested for a long time under constant alternating load and high-temperature environment, therefore, whether the clamping force of the testing machine clamp can remain stable directly affects the accuracy and reliability of the test data.

[0003] However, there is a key technical problem in the existing high-temperature fatigue testing system: the clamp body, the clamping block and the sample itself are usually made of different materials, and their thermal expansion coefficients differ significantly. When the test environment temperature rises, this difference will cause a "thermal expansion effect", which will cause the initial set clamping force of the clamp to change significantly, usually uncontrollably increasing. This will cause the clamp clamping force to relax or overload, which may cause the sample to fail prematurely or be crushed, leading to distorted test data, or may damage the clamp itself and interrupt the test process.

[0004] Currently, in order to solve this problem, two technical solutions are mainly used in the industry: one is a spring pre-tightening heat insulation structure and other mechanical compensation methods, and the other is a hydraulic compensation method. However, both of these two traditional solutions have obvious defects: they are usually designed for specific temperature points or specific material combinations, and the compensation accuracy is limited, making it difficult to adapt to complex testing conditions of a wide temperature range (such as from room temperature to 1000℃) and different material combinations (such as metal, ceramic, composite materials, etc.). More importantly, conventional clamps generally lack real-time, accurate monitoring and response means for the actual clamping force, and cannot sense and actively compensate for the clamping force drift caused by temperature changes in time, which has become a bottleneck for obtaining high-precision high-temperature fatigue test data.

[0005] Therefore, it is of great significance to develop a system that can monitor, accurately calculate and actively compensate for the clamping force changes caused by temperature in real time, in order to improve the accuracy and reliability of high-temperature fatigue testing. SUMMARY

[0006] The present application provides a high-temperature fatigue testing machine self-compensation clamp based on a temperature compensation algorithm and a corresponding control method, aiming to solve the problems of unstable clamping force and distorted test data caused by the thermal expansion effect in the prior art.

[0007] The control method according to the first aspect of the embodiments of the present application for controlling a high-temperature fatigue testing machine self-compensation clamp based on a temperature compensation algorithm comprises the following steps:

[0008] S1: Real-time data acquisition, the current working temperature of the clamp is acquired in real time through the temperature sensor arranged on the clamp, and the actual clamping force acting on the test sample is acquired in real time through the force sensor arranged on the clamp;

[0009] S2: Feedforward compensation displacement calculation, the thermal expansion compensation force caused by the difference in thermal expansion coefficients between the clamp and the test sample is calculated based on the difference between the working temperature and the initial set temperature, the creep compensation force caused by the high-temperature creep of the test sample is calculated when the working temperature exceeds the preset creep activation temperature, the thermal expansion compensation force and the creep compensation force are combined to obtain the total feedforward compensation force, and the feedforward compensation displacement is calculated according to the total feedforward compensation force and the equivalent stiffness of the clamp-test sample system;

[0010] S3: Feedback compensation displacement calculation, the actual clamping force is compared with the target clamping force to calculate the clamping force deviation, and the feedback compensation displacement is calculated according to the clamping force deviation by using the PID control algorithm;

[0011] S4: Total displacement compensation, the feedforward compensation displacement and the feedback compensation displacement are added to obtain the total compensation displacement, and the actuator connected to the clamp is controlled to adjust the displacement of the clamp according to the total compensation displacement, so as to dynamically compensate the clamping force drift caused by temperature change.

[0012] The control method according to the embodiments of the present application has at least the following beneficial effects:

[0013] 1. High compensation accuracy and wide application range: The unique "thermal expansion-creep-stiffness temperature drift-gradient learning" four-in-one temperature compensation algorithm is adopted, the nonlinear effects of thermal expansion, high-temperature creep and system stiffness change with temperature are comprehensively considered, the error sources in the full temperature range (20℃-1000℃) can be covered, and the stringent requirements for verifying fatigue life under extreme working conditions can be met.

[0014] 2. The stability of clamping force is significantly improved: Through the "temperature-clamping force" closed-loop control algorithm and the unique feedforward-feedback displacement compensation mechanism of the PID controller, the dynamic and accurate adjustment of the clamping force is realized. In the long-term fatigue test of 1000℃ / 100h, the clamping force fluctuation can be accurately controlled within ±1.8%, while the fluctuation range of the traditional mechanical compensation scheme is as high as ±15%-20%, which greatly improves the stability of the clamping force in high-temperature environment.

[0015] 3. High intelligence and adaptability: The innovative gradient learning algorithm is used to identify and update the equivalent expansion coefficient β of different sample materials to the fixture system online, enabling it to adapt to any new material sample such as metal, ceramic, and CMC composite material. It eliminates the need for tedious calibration and downtime after changing to different material samples, reducing the amount of manual calibration work by more than 90% and realizing automated and intelligent nonlinear correction.

[0016] A self-compensating fixture for a high-temperature fatigue testing machine based on a temperature compensation algorithm, according to a second aspect of the present invention, comprises:

[0017] The fixture body is used to hold the sample.

[0018] A temperature sensor is installed on the fixture body to monitor the working temperature of the fixture body in real time.

[0019] A force sensor, linked to the fixture body, is used to monitor the actual clamping force acting on the sample in real time.

[0020] A piezoelectric actuator, integrated on the fixture body, is used to drive the fixture to generate compensating displacement according to a control signal;

[0021] The control unit is electrically connected to the temperature sensor, force sensor and piezoelectric actuator, and is configured to perform the control method described in the first aspect embodiment.

[0022] According to the embodiments of the present invention, since the control method described in the first aspect embodiment is performed, at least the above-mentioned beneficial effects are achieved, which will not be repeated here.

[0023] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0024] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0025] Figure 1 This is a flowchart of a control method for a self-compensating fixture of a high-temperature fatigue testing machine based on a temperature compensation algorithm, according to some embodiments of the present invention.

[0026] Figure 2 This is a general logic diagram of the control method for a self-compensating fixture of a high-temperature fatigue testing machine based on a temperature compensation algorithm, according to some embodiments of the present invention.

[0027] Figure 3 This is a flowchart illustrating the driving voltage output to the piezoelectric actuator in some embodiments of the present invention.

[0028] Figure 4PID parameter temperature zone adjustment logic diagram of the control method of some embodiments of the present application. DETAILED DESCRIPTION

[0029] The present application provides a high-temperature fatigue testing machine self-compensation clamp based on temperature compensation algorithm and a corresponding control method, aiming at solving the problems of unstable clamping force, distorted test data and other problems caused by thermal expansion effect in the prior art.

[0030] The self-compensation clamp provided by the present application mainly comprises a clamp body, a core algorithm module, a PID feedforward-feedback compensation control system, a clamping mechanism, a temperature sensor, a force sensor, a piezoelectric actuator and a control unit. The core idea is: by real-time monitoring of the temperature and actual clamping force of the clamp, collecting intelligent sensing data, using a "thermal expansion-creep-rigidity temperature drift-gradient learning" composite algorithm to accurately calculate the feedforward compensation amount caused by temperature change, and using a PID controller to calculate the feedback compensation amount according to the deviation of the actual clamping force from the target value, the two are combined to form a total compensation signal, which drives the high-precision piezoelectric actuator to adjust the micro-displacement, so as to realize dynamic, closed-loop and accurate control of the clamping force.

[0031] The control method of the present application comprises the following steps:

[0032] S1: Real-time data acquisition, the current working temperature of the clamp is acquired in real time through the temperature sensor arranged on the clamp, and the actual clamping force acting on the sample is acquired in real time through the force sensor arranged on the clamp;

[0033] S2: Feedforward compensation displacement calculation, based on the difference between the working temperature and the initial set temperature, the thermal expansion compensation force caused by the difference in thermal expansion coefficients between the clamp and the sample is calculated, when the working temperature exceeds the preset creep activation temperature, the creep compensation force caused by the high-temperature creep of the sample is calculated, the thermal expansion compensation force and the creep compensation force are combined to obtain the total feedforward compensation force, and the feedforward compensation displacement is calculated according to the total feedforward compensation force and the equivalent stiffness of the clamp-sample system;

[0034] S3: Feedback compensation displacement calculation, the actual clamping force is compared with the target clamping force to calculate the clamping force deviation, and the feedback compensation displacement is calculated according to the clamping force deviation by using a PID control algorithm;

[0035] S4: Total displacement compensation, the feedforward compensation displacement and the feedback compensation displacement are added to obtain the total compensation displacement, and the actuator connected with the clamp is controlled to adjust the displacement of the clamp according to the total compensation displacement, so as to dynamically compensate the clamping force drift caused by temperature change.

[0036] REFERENCE Figure 2As shown, the following explains the feedforward compensation link calculation and the feedback compensation link calculation.

[0037] (1) 1.1 Feedforward compensation link: temperature compensation algorithm based on "thermal expansion-creep-stiffness temperature drift-gradient learning": ΔF comp = f(ΔT, α, β, K, C, Q, γ).

[0038] This algorithm module runs in the control unit, and its function is to predict and compensate in advance the clamping force change caused by temperature change. Its calculation process is as follows:

[0039] First step: calculate the thermal expansion compensation force ΔF thermal (including stiffness temperature correction)

[0040] This part mainly compensates the force change caused by the difference in thermal expansion coefficients between the fixture and the sample material, and considers the nonlinear change of system stiffness with temperature.

[0041] ΔF thermal = K system · L0· ΔT· (α fixture - β new );

[0042] Where:

[0043] ΔT is the change of the current temperature (T current ) relative to the initial set temperature (T0), measured by the temperature sensor.

[0044] L0 is the relevant characteristic length of the fixture when clamping the sample at the initial set temperature to generate clamping force, such as the distance from the effective contact point of the clamping block to the support point.

[0045] α fixture is the average thermal expansion coefficient of the fixture body (this is the key component).

[0046] K system is the equivalent stiffness of the fixture-sample system in the clamping force direction, which changes with temperature, and is calculated through the nonlinear correction formula K system (T) = K0· [1- γ[(T-T0)]]. Where K0 is the initial stiffness calibrated by load-curve (S-N), and γ is the stiffness temperature coefficient, which is usually 0.3×10-3 / ℃ for high-temperature alloys. β new is the equivalent influence coefficient of the sample thermal expansion on the fixture system. To adapt to samples of different materials, the invention introduces a gradient learning algorithm for online identification and update, and the gradient learning algorithm is as follows:

[0047] β new = β old + η· (Factual -F predicted )·K0·[1-γ(T-T0)]·L0·ΔT;

[0048] where β old is the initial value, which can be calibrated manually or taken from experience; F actual is the real-time measurement value of the force sensor, F predicted is the initial measurement value; η is the step reduction coefficient of gradient learning, to ensure that the algorithm converges as soon as possible, η adopts an adaptive rule: when |F actual |>50N, take η=0.05; when |F predicted |≤50N, take η=0.01. actual -F predicted

[0049] The activation condition of the above gradient learning algorithm is: the temperature change amount |ΔT| = |T current -T0|≥20℃, and the creep compensation is not activated (i.e. T current <600℃). To avoid out-of-control caused by outliers, the value range of β new is restricted (for example, 5e-6≤β new ≤25e-6), when the continuous 10 times of updating satisfy |Δβ| = |βnew-β old |<0.1×10 -6 , then stop learning, and count into the next cycle.

[0050] Second step: calculate the high-temperature creep compensation force (ΔF creep )

[0051] When the temperature of the test sample exceeds the preset creep activation temperature (for example, 600℃), the difference in creep characteristics between the test sample and the fixture needs to be considered, and the creep compensation calculation is activated.

[0052] ΔF creep =-K system ·[1-γ(T-T0)]·L0·C·σ·t·exp(-Q / RT);

[0053] where C is the creep constant, Q is the activation energy, σ is the current stress of the material, R is the gas constant, T is the real-time measured temperature (Kelvin), and t is the time. This formula is used to calculate the change in clamping force caused by creep relaxation.

[0054] Third step: calculate the total feedforward compensation force (ΔF comp ) and feedforward compensation displacement (ΔF comp )

[0055] Add the above two compensation forces to obtain the total feedforward compensation force (ΔF comp ): ΔF​comp =ΔF thermal+ ΔF creep .

[0056] Then, this force is converted into the feedforward compensation displacement that needs to be performed, the feedforward compensation displacement (Δd). comp ) and feedforward compensation force (ΔF) comp The following relationship exists: Δd comp ==ΔF comp / K system (T), this displacement is the output of the feedforward compensation circuit.

[0057] 1.2 Feedback Compensation Component: Feedback Displacement Compensation Based on PID Controller

[0058] Feedforward compensation addresses most of the deterministic drift caused by temperature, while feedback compensation is used to eliminate residual errors and unmodeled perturbations.

[0059] First, calculate the clamping force deviation: e(t) = F target -F actual , where F target The preset target clamping force.

[0060] Then, the feedback compensation displacement (Δd) is calculated using a standard PID controller. fb ):

[0061] Δd fb =K p ·e(t)+K i ·∫e(t)dt+K d ·de(t) / dt.

[0062] Reference Figure 4 As shown, to adapt to high-temperature environments, the PID parameters are dynamically adjusted: when T current At temperatures above 600℃, considering the increased integral characteristics of the system due to material creep, and to reduce high-frequency noise pollution, the integral gain K is... i Increase the differential gain K by 50%. d Reduced by 30%.

[0063] 1.3 Total Displacement Compensation Execution

[0064] The feedforward compensation displacement (Δd) comp ) and feedback compensation displacement (Δd) fb Adding these together, we get the total compensated displacement: Δd total =Δd comp +Δd fb .

[0065] The control unit is based on Δd totalThe driving signal is generated to drive the piezoelectric actuator to produce precise displacement, so as to dynamically adjust the position of the clamping block, and the actual clamping force F actual is always stabilized at the target value F target , and the self-compensation closed-loop control of the clamping force is realized. The final compensation accuracy requires that the total displacement error Δd total <0.5 μm, which can be referred to Figure 3 .

[0066] In order to perfectly execute the above-mentioned advanced control algorithm, the application is carefully integrated in the hardware structure, adopts an innovative structure of "deep hole embedded temperature measurement + piezoelectric direct drive + circuit hysteresis compensation", and ensures that each link from signal sensing, control execution to error elimination has high precision and high reliability.

[0067] Firstly, in order to obtain the core temperature closest to the real heating state of the sample, so as to ensure the accuracy of the temperature compensation algorithm, a deep hole with a diameter of 1.5 to 2.0 millimeters and a hole wall roughness less than Ra 0.8 microns is opened in the clamping block, which is a key component of the clamp. The probe of an optical fiber temperature sensor is completely embedded in the bottom of the deep hole, so that the temperature measurement point is infinitely close to the contact interface between the clamping block and the sample, so that the most real and timely temperature change can be captured. In order to ensure that the sensor works stably for a long time in a high-temperature and vibrating environment, the opening of the deep hole is precisely filled with high-temperature resistant epoxy resin, which plays a dual role of firm fixation and reliable sealing.

[0068] Secondly, in order to realize the physical execution of the compensation action, the application adopts a multi-layer PZT piezoelectric ceramic stack as a direct driving source, which is highly integrated on the back of the clamping block. This actuator has the advantages of fast response, high resolution and large output force, and is an ideal choice for realizing micro-displacement precise compensation. In order to cope with the test environment of up to 1000℃, the surface of the PZT stack is specially treated and sprayed with a 100-micron-thick alumina ceramic coating, which effectively enhances its high-temperature resistance, oxidation resistance and electrical insulation performance. In order to constitute a complete "force-position" closed-loop control, the system also integrates multi-dimensional sensing devices. A high-precision pressure sensor is connected in series with the output shaft of the actuator for real-time measurement of the actual clamping force on the sample; at the same time, in order to accurately monitor the output displacement of the actuator, a 5-millimeter-diameter observation window is provided on the side surface of the clamping block for non-contact laser displacement sensor measurement.

[0069] On the mechanical connection structure, the application also carries out exquisite design to give consideration to force transmission, heat insulation and centering. The output shaft of the actuator is connected through a pre-tightening disc spring group to provide stable axial pre-tightening force and eliminate transmission gap. In order to achieve effective heat insulation between the high-temperature end and the normal-temperature end, high-strength, low-thermal-conductivity zirconia ceramic heat-insulating force transmission rods are used in the structure. Further, taper surface matching design is used between the force transmission rods and the titanium alloy interfaces to cleverly use the difference in thermal expansion coefficients of different materials to compensate for thermal deformation, so as to ensure that the force transmission components always maintain good centering state in the full temperature range. In addition, a flexible beryllium copper transition block is arranged between the pressure sensor and the upper clamping block to compensate for small assembly misalignment errors and protect the sensor from damage by eccentric load.

[0070] Another key technology of the application lies in the design of the driving circuit, which aims to overcome the inherent hysteresis nonlinearity problem of the piezoelectric actuator. For this purpose, the driving circuit of the control unit not only contains a high-power operational amplifier (such as ADA4870) for signal amplification, but more importantly, a Preisach hysteresis compensation module based on a model is integrated. The module can compensate in a feedforward manner according to the mathematical model of the hysteresis of the piezoelectric actuator before outputting the driving signal, and actively eliminate the nonlinearity error. In this way, the driving circuit can ensure that the displacement command issued by the PID controller can be converted into the actual displacement output of the actuator with high fidelity, and ultimately realize that the displacement output error is less than 1%, which provides the final guarantee for the high precision of the entire self-compensation system.

[0071] Overall, the application adopts an integrated structure of "deep hole embedded temperature measurement + piezoelectric direct drive + circuit hysteresis compensation", realizes accurate temperature measurement of the core working area of the clamp through the embedded optical fiber thermometer, solves the heat conduction problem, adopts a piezoelectric ceramic actuator with high stiffness and high response speed for direct driving, and effectively eliminates the hysteresis effect of the piezoelectric actuator through the integrated Preisach hysteresis compensation module, realizes high-precision displacement compensation with a PID displacement output error of less than 1%. The structure realizes excellent performance of clamp force fluctuation ≤±1.8%, service life > 10^7 cycles, and displacement attenuation <3% after cycling in the temperature range of 20-1000℃.

[0072] Examples of the embodiments described above are shown in the accompanying drawings, in which the same or similar reference numerals represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described above by referring to the drawings are exemplary and are only used to explain the application and cannot be understood as a limitation of the application.

[0073] In the description of the present application, it should be understood that the orientation description, such as the orientation or position relationship indicated by up, down, front, back, left, right and the like, is based on the orientation or position relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0074] In the description of the present application, the meaning of several is one or more, the meaning of multiple is more than two, greater than, less than, more than and the like are understood as not including the number, above, below, within and the like are understood as including the number. If the first, second is described, it is only for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance of the indicated technical features or implying the number of the indicated technical features or the order of the indicated technical features.

[0075] In the description of the present application, unless otherwise explicitly limited, the words such as setting, installing, connecting and the like should be broadly understood, and the person skilled in the art can reasonably determine the specific meaning of the above words in the present application in combination with the specific content of the technical scheme.

[0076] The embodiments of the present application are described in detail above in combination with the drawings, but the present application is not limited to the above embodiments, and various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the purpose of the present application.

Claims

1. A control method, characterized in that, The control method for controlling a self-compensating fixture of a high-temperature fatigue testing machine based on a temperature compensation algorithm includes the following steps: S1: Real-time data acquisition. The current working temperature of the fixture is obtained in real time through a temperature sensor installed on the fixture, and the actual clamping force acting on the sample is obtained in real time through a force sensor installed on the fixture. S2: Feedforward compensation displacement calculation: Based on the difference between the working temperature and the initial set temperature, calculate the thermal expansion compensation force caused by the difference in thermal expansion coefficients between the fixture and the sample. When the working temperature exceeds the preset creep activation temperature, calculate the creep compensation force caused by high-temperature creep of the sample. Combine the thermal expansion compensation force and the creep compensation force to obtain the total feedforward compensation force. Calculate the feedforward compensation displacement based on the total feedforward compensation force and the equivalent stiffness of the fixture-sample system. S3: Feedback compensation displacement calculation: The actual clamping force is compared with the target clamping force to calculate the clamping force deviation. The PID control algorithm is used to calculate the feedback compensation displacement based on the clamping force deviation. S4: Perform total displacement compensation, add the feedforward compensation displacement and the feedback compensation displacement to obtain the total compensation displacement, and control the actuator connected to the fixture to adjust the displacement of the fixture according to the total compensation displacement in order to dynamically compensate for the clamping force drift caused by temperature changes.

2. The method as described in claim 1, characterized in that, In step S2, the calculation of the total feedforward compensation force includes the calculation of the thermal expansion compensation force, and the calculation formula is as follows: ΔF thermal =K system ·L0·ΔT·(α fixture -b new ); Among them, K system Let L0 be the equivalent stiffness of the system as a function of temperature, L0 be the characteristic length of the fixture, ΔT be the difference between the current operating temperature of the fixture and the initial set temperature, and α be the equivalent stiffness of the system as a function of temperature. fixture β is the average coefficient of thermal expansion of the fixture material. new The effective thermal expansion coefficient of the sample on the fixture system is denoted as .

3. The control method as described in claim 2, characterized in that, The equivalent thermal expansion coefficient β of the sample on the clamping system new The algorithm for online updating via gradient learning has the following update formula: b new =b old +η·(F actual -F predicted )·K0·[1-γ(T-T0)]·L0·ΔT; Where, β old The coefficients are the values ​​before the update, η is the gradient learning reduction coefficient, and F is the coefficient value before the update. predicted For the initial clamping force value, K0 is the initial stiffness of the system, γ is the stiffness temperature coefficient, L0 is the characteristic length of the fixture, and T0 is the initial set temperature.

4. The method as described in claim 3, characterized in that, The activation condition for the gradient learning algorithm is: temperature change |T current -T0| is not less than 20℃, and the current operating temperature T current Below the preset creep activation temperature.

5. The control method as described in claim 2, characterized in that, The equivalent stiffness of the system as a function of temperature is calculated using the following nonlinear correction formula: K system (T)=K0·[1-γ[(T-T0)]; Where K0 is the initial stiffness of the system and γ is the stiffness temperature coefficient.

6. The control method as described in claim 2, characterized in that, In S2, when the operating temperature T current When the preset creep activation temperature is exceeded, the calculation of the total feedforward compensation force also includes calculating the high-temperature creep compensation force, the formula of which is: ΔF creep =-K system ·[1-γ(T-T0)]·L0·C·σ·t·exp(-Q / RT); ΔF comp =ΔF thermal+ ΔF creep ; Where C is the creep constant, Q is the activation energy, σ is the current stress of the material, R is the gas constant, T is the Kelvin temperature, t is time, and ΔF is the current stress of the material. comp This is the total feedforward compensation force.

7. The control method as described in claim 6, characterized in that, In step S3, the calculation formula for the feedback compensation displacement is as follows: Δd fb =K p ·e(t)+K i ·∫e(t)dt+K d ·de(t) / dt; e(t)=F target -F actual ; Among them, K p Proportional gain, F target For the target clamping force, F actual The actual clamping force, Δd fb For the feedback compensation displacement, K p For proportional gain, K i For integral gain, K d This is the differential gain; In step S4, the formula for calculating the total compensation displacement is: Δd total =Δd comp +Δd fb 。 8. The control method as described in claim 1, characterized in that, In step S3, when the operating temperature exceeds 600°C, the parameters of the PID control algorithm are adjusted: The integral gain K i Increase the differential gain K by 50%. d Reduced by 30%.

9. A self-compensating fixture for a high-temperature fatigue testing machine based on a temperature compensation algorithm, characterized in that, include: The fixture body is used to hold the sample. A temperature sensor is installed on the fixture body to monitor the working temperature of the fixture body in real time. A force sensor, linked to the fixture body, is used to monitor the actual clamping force acting on the sample in real time. A piezoelectric actuator, integrated on the fixture body, is used to drive the fixture to generate compensating displacement according to a control signal; A control unit, electrically connected to the temperature sensor, force sensor and piezoelectric actuator, is configured to perform the control method as described in any one of claims 1 to 8.

10. The clamp as described in claim 9, characterized in that, The temperature sensor is a fiber optic temperature sensor, which is embedded in a deep hole inside the clamping block of the fixture body. The opening of the deep hole is encapsulated with high-temperature resistant epoxy resin. The piezoelectric actuator includes a high-temperature resistant multilayer PZT piezoelectric ceramic stack, and the control unit includes a drive circuit for driving the piezoelectric actuator. The drive circuit integrates a Preisach hysteresis compensation module to eliminate the output hysteresis error of the piezoelectric actuator.

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