An adaptive multi-element calibration method for wind tunnel balances

Abstract

The present application belongs to the technical field of wind tunnel test, and discloses a self-adaptive multi-element calibration method for a wind tunnel balance. The calibration method is based on a multi-point force application body shafting balance calibration system, and the loaded load is divided into a basic group load, an improved group load and a comprehensive group load. After the basic group load is loaded, a calibration formula with low precision is initially fitted, then the comprehensive group load is applied, the measurement value is calculated according to the calibration formula, the units with poor inspection precision of the balance are analyzed item by item, the interference term with larger error is obtained, then the corresponding improved group load is recompiled for the interference term, the calibration value range of the improved group load is wider and the ladder is denser, the improved group load is loaded again, the calibration formula is continuously fitted, and the automatic iterative loading is repeatedly carried out, so that the precision of the calibration formula is continuously improved, until the precision error of the calibration formula is less than the pre-set accuracy error value, the balance calibration formula with high precision is obtained, and the method has engineering practical value.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of wind tunnel test, and particularly relates to a self-adaptive multi-element calibration method for a wind tunnel balance. BACKGROUND

[0002] The wind tunnel balance is essentially a multi-dimensional force sensor. Balance calibration refers to applying a load to the balance on a ground static calibration device, collecting the corresponding voltage output value, fitting the balance calibration formula matrix of the load and the corresponding voltage output value, and inversely calculating the force and torque exerted by the airflow on the model during the wind tunnel test. The conventional force balance generally has six components, measuring three forces and three torques.

[0003] The balance calibration process generally involves first preparing a load table, then applying a load according to the load table, and finally performing curve fitting on the load and the corresponding voltage value to obtain the balance calibration formula matrix. According to the loading method, balance calibration can be divided into single-element calibration method and multi-element calibration method. When the single-element calibration method is used, the balance calibration coefficients are generally calculated using the least squares method. When the multi-element calibration method is used, multi-element linear regression calculation is performed after all items (the number of items is greater than the number of components) in the load group are loaded, and the corresponding balance calibration formula matrix is obtained through the relationship between the load and the corresponding voltage output value. In addition, when the loading data is large and the number of iterations is large, a neural network algorithm can also be used.

[0004] Specifically, the balance calibration process generally involves first loading the balance according to the load table, collecting the corresponding voltage value, and then fitting a balance formula for the load-voltage relationship. The conventional six-component balance calibration formula should include 96 coefficients, including: 1 main item coefficient, 5 first-order interference coefficients, 6 second-order square interference coefficients, 6 cubic interference coefficients, 15 second-order cross interference coefficients, 6 first-order asymmetric interference coefficients, 51 second-order asymmetric interference coefficients, and 6 third-order asymmetric interference coefficients. Currently, in the balance calibration formula matrix, the asymmetry and cubic term interference coefficients are generally not considered, so each component has 27 coefficients. The conventional six-component balance forms a 6x27 matrix as the final balance calibration formula matrix. The calculation of the calibration coefficients generally uses the least squares method for fitting. When the single-element calibration method is used, one item can be calculated for each calibration, and after the single-element and cross-element loading calibration is completed, the coefficients are combined to obtain the balance calibration formula matrix. When the single-element calibration method is used, multi-element linear regression calculation is performed after all items (the number of items is greater than the number of components) in the load group are completed, and the corresponding balance calibration formula matrix is obtained.

[0005] The wind tunnel balance calibration system can be divided into a body axis system wind tunnel balance calibration system and a ground axis system wind tunnel balance calibration system according to a loaded coordinate axis system. The body axis system balance calibration system has a reset mechanism, and is complex in structure and high in cost. However, the body axis system wind tunnel balance calibration system has the advantages that the number of interference terms in the balance calibration formula matrix is significantly reduced, the interference value is obviously reduced, and the balance measurement accuracy is higher. Therefore, the body axis system calibration system is usually used. However, the body axis system calibration system needs to be reset for each loaded step value when performing unit or multi-element calibration, so the overall efficiency is not high. Moreover, all calibration items need to be loaded before the formula can be fitted, and the time cost is high.

[0006] At present, it is urgent to develop a wind tunnel balance self-adaptive multi-element calibration method for a body axis system balance calibration system. SUMMARY

[0007] The technical problem to be solved by the present application is to provide a wind tunnel balance self-adaptive multi-element calibration method to overcome the defects of the prior art.

[0008] The wind tunnel balance self-adaptive multi-element calibration method of the present application comprises the following steps:

[0009] A. Compiling a calibration load of the balance;

[0010] B. Loading a basic group load;

[0011] C. Linear fitting;

[0012] D. Tare calculation;

[0013] E. Nonlinear fitting;

[0014] F. Iterative calculation;

[0015] G. Accuracy calculation;

[0016] H. Error analysis;

[0017] I. Repeating the loading of an improved group load, error analysis and iteration.

[0018] Further, the step A comprises the following steps:

[0019] A1. Compiling a basic group load;

[0020] A1.1 Compiling a unit item in the basic group load;

[0021] According to the design load of the balance, calibration loads of six components X, Y, Z, Mx, My and Mz of the balance are determined, X is a drag component, Y is a lift component, Z is a side force component, Mz is a roll moment component, My is a yaw moment component and Mz is a pitch moment component; the calibration loads are taken as 80% to 120% of the design range value, and are loaded according to nine steps of 0%, 25%, 50%, 75%, 100%, 75%, 50%, 25% and 0%, and after each component is loaded with positive and negative values respectively, 12 unit items of loading arrays are obtained;

[0022] A1.2, compiling combination items in the basic group load;

[0023] According to the calibration load of the balance, six components of the balance are selected according to 15 positive combination items of YMz+, YX+, YMx+, YZ+, YMy+, MzX+, MzMx+, MzZ+, MzMy+, XMx+, XZ+, XMy+, MxZ+, MxMy+ and ZMy+, and 15 negative combination items YMz-, YX-, YMx-, YZ-, YMy-, MzX-, MzMx-, MzZ-, MzMy-, XMx-, XZ-, XMy-, MxZ-, MxMy- and ZMy- are selected;

[0024] A2, compiling the improved group load;

[0025] A2.1, compiling unit items in the improved group load;

[0026] The loading steps in A1.1 are encrypted and the calibration range is improved at the same time, so that the calibration loads are loaded according to nineteen steps of 0%, 12.5%, 25%, 37.5%, 50%, 62.5%, 75%, 87.5%, 100%, 125%, 100%, 87.5%, 75%, 62.5%, 50%, 37.5%, 25%, 12.5% and 0%;

[0027] A2.2, compiling combination items in the improved group load;

[0028] The loading steps in A1.2 are encrypted, and the five steps of 0%, 50%, 100%, 50% and 0% of the basic group load are expanded to nine steps of 0%, 25%, 50%, 75%, 100%, 75%, 50%, 25% and 0%, and at the same time, 2 positive and negative direction combination items of one unit item are expanded to 4 combination items;

[0029] A3, compiling the comprehensive group load;

[0030] According to the requirements of full range coverage, uniform distribution, and positive-negative symmetry, a comprehensive group load is prepared, which is used to check the accuracy error of the balance calibration formula.

[0031] Further, the step B comprises the following steps:

[0032] B1. Determine the reference reading: collect the voltage value arrays of the six components in the four states of the balance roll angle being 0°, 90°, 180° and 270°, respectively, and obtain an average voltage value array by averaging the four voltage value arrays, which is the reference voltage of the balance calibration , , respectively representing the voltage readings of X, Y, Z, Mx, My and Mz elements;

[0033] B2. Complete the loading of the unit items and combined items of the basic group load according to the balance calibration specification, and obtain the calibration array including the load value and the corresponding voltage value , , ; and represent the six components of the balance X, Y, Z, Mx, My and Mz elements.

[0034] Further, the step C comprises the following steps:

[0035] C1. Data preprocessing; subtract the zero load value from the balance loading step value in the positive and negative 12 unit items and the positive and negative 30 combined items to obtain the net increase value;

[0036] C2. Perform multiple regression calculation to obtain the corresponding calibration coefficients, and the calculation formula is:

[0037] ;

[0038] wherein, is the component of the applied load value, is the component of the applied load value; is the loading step voltage value of each unit of the balance, is the initial value of each unit of the balance; is the first-order coefficient, which is the main coefficient when , and is the first-order interference coefficient of the component to the component when ; is the second-order interference coefficient of the component and the component to the component; , , ; , and represent six components of X, Y, Z, Mx, My and Mz elements of the balance;

[0039] C3. Formula conversion is performed; after 27 coefficients corresponding to each element of the balance are calculated respectively, a 27x6 matrix is formed, first, the main coefficient of each element is converted, second, the first-order interference coefficient and the second-order interference coefficient are multiplied by the new main coefficient, and finally, the whole is transposed to obtain a 6x27 matrix.

[0040] Further, the step D includes the following steps:

[0041] D1. The tare is the sum of the loading load of the loading device and the weight load when loaded, and the corresponding voltage value is the difference between the loading zero point and the reference reading;

[0042] D2. The loading zero points of 42 groups of unit items and combined items are combined to form a loading zero point group , wherein the reference reading is taken as the first row initial reading, then iteration is performed according to the implicit formula of the balance to obtain a tare load group corresponding to 42 loading zero points , and the calculation formula is:

[0043] ;

[0044] In the formula, is the balance component load calculation value, and are the load values of the remaining five components of the balance when calculating ; is the initial load value, is the main coefficient, is the component to component first-order interference coefficient; is the component to component first-order asymmetric interference coefficient; is the component to component second-order interference coefficient, when it is a second-order square term interference coefficient; when it is a second-order cross term interference coefficient; , , ​​​​, ; 、 and represent six components of X, Y, Z, Mx, My and Mz elements of the balance.

[0045] Further, the step E includes the following steps:

[0046] E1. restore the values in the loading zero point group in D2 to the corresponding unit item or the combined item loading group respectively, to obtain the actual load value based on the reference reading , the actual load value including the loading value and the tare, and the actual load value and the corresponding voltage value are combined into a new calibration array;

[0047] E2. repeat steps C2~C3 to obtain a new round of balance calculation formula matrix ;

[0048] E3. perform a new round of tare calculation according to the D2 calculation method for the new round of balance calculation formula matrix and the loading zero point group of D2, to obtain a new round of tare load group, and perform corresponding difference calculation with the tare load group of the previous round.

[0049] Further, the step F includes the following steps:

[0050] If the difference value of the new round of tare load group and the tare load group of the previous round is greater than the pre-set iteration convergence standard, the balance calibration formula matrix does not converge, and steps D~E are repeated until the difference value meets the iteration convergence standard, the iteration calculation is ended, and the obtained balance calculation formula matrix is stable in performance and meets the calibration specification.

[0051] Further, the step G includes the following steps:

[0052] G1. perform loading of the comprehensive group load of the balance;

[0053] G2. utilize the calibration coefficients in the matrix to perform calculation according to the implicit formula of the balance, to obtain the measurement value of the balance, and calculate the test standard deviation value :

[0054] ;

[0055] wherein, is the difference value of the measurement value and the theoretical value; is the number of comprehensive group load loading items;

[0056] G3. calculate the test standard deviation value of each unit Divide by the calibration maximum value to obtain a calibration accuracy value, and if the accuracy error of each unit is less than the preset accuracy error value, the balance calibration ends; otherwise, error analysis is performed.

[0057] Further, the step H includes the following steps:

[0058] H1. Calculate the relative error amount; take the calibration maximum value of each unit as input and bring it into the balance calculation formula matrix in E3 , perform coefficient multiplication, wherein, for the coefficient of the first-order interference term of Mz to Y , the maximum value of the first-order interference of Mz to Y :

[0059] ;

[0060] Obtain the relative error of Y elements :

[0061] ;

[0062] H2. According to H1, calculate the 27 coefficients of each unit of the 6 units of the balance in turn to obtain a relative error group ;

[0063] H3. Screen to obtain the relatively large error term; select the maximum coefficient in all the 27 coefficients of the relative error group that is greater than the preset accuracy error value.

[0064] Further, the step I includes the following steps:

[0065] I1. Select the load group corresponding to the maximum coefficient in the improved load group, if YMz interferes with X the most, select the 4 cross terms +Y+Mz, +Y-Mz, -Y+Mz, -Y-Mz in the improved load group for loading calibration;

[0066] I2. Replace the corresponding items in the original calibration array with the collected data of the 4 cross terms, repeat D~H to obtain a new formula matrix and the corresponding test standard deviation value ;

[0067] I3. Perform error analysis again, if the accuracy error of the relatively large error term is less than the preset accuracy error value, stop calibration, and obtain the final balance calibration formula of the relatively large error term;

[0068] I4. If the accuracy error of the error relative large item is greater than the pre-set accuracy error value, return H, continue to screen the error relative large item, and increase the group load again. If the accuracy error is still greater than the pre-set accuracy error value, the corresponding unit item or combined item is encrypted again according to 2 n mode, return to step D until the accuracy error is less than the pre-set accuracy error value.

[0069] The wind tunnel balance self-adapting multi-element calibration method of the application is based on a multi-point force applying body shaft system balance calibration system capable of simultaneous loading, and divides the loading load into three groups: a basic group load, an improved group load and a comprehensive group load. After the basic group load is loaded, a calibration formula with low precision is initially fitted, then the comprehensive group load is applied, the measurement value is calculated according to the calibration formula, the units with poor test precision are analyzed item by item, the interference items with greater error are obtained, the corresponding improved group load of the interference items is recompiled, the calibration value range of the improved group load is wider and the step is more dense, the improved group load is loaded again, the data is processed again after the improved group load is loaded, the error of the calibration process is known at any time, the calibration formula is continuously fitted, and the automatic iterative loading is repeatedly performed, so that the precision of the calibration formula is continuously improved. When the precision of the calibration formula reaches the advanced index of the industry specification, the calibration is ended, and finally the balance calibration formula with high precision is obtained.

[0070] The wind tunnel balance self-adapting multi-element calibration method of the application can adapt to various balances with different interference coefficients without human intervention, the calculation mode is based on the traditional multi-element regression classic framework, the mathematical model is robust, the calculation method is mature, the calibration efficiency can be improved under the premise of ensuring the calibration quality, and the method has engineering practical value. BRIEF DESCRIPTION OF DRAWINGS

[0071] Figure 1 The flowchart of the wind tunnel balance self-adapting multi-element calibration method of the application is shown. DETAILED DESCRIPTION

[0072] The application will be described in detail below with reference to the drawings and examples.

[0073] The wind tunnel balance of the embodiment is a rod type six-component balance. The rod type six-component balance is essentially a six-dimensional force sensor used to measure forces and corresponding moments in three directions in space. The measurement principle is to paste a resistance strain gauge on the balance body. The resistance strain gauge changes in resistance due to the small deformation caused by the load on the balance. The resistance change is converted into voltage change by a Wheatstone bridge. The balance calibration is to apply a standard force (moment) to the balance, measure the corresponding voltage change value, and fit the load-voltage relationship formula matrix. In the embodiment, six-component loads are applied to the balance (see Table 1), and then the final relationship matrix is calculated by multivariate linear regression (see Table 2). The experimental standard deviation of the relationship matrix is calculated by comprehensive group loading data, and the accuracy error value of the balance calibration is 0.129% (see Table 3).

[0074] As shown in Figure 1 The wind tunnel balance self-adaptive multivariate calibration method of the embodiment includes the following steps:

[0075] A. Compiling the calibration load of the balance;

[0076] B. Performing basic group load loading;

[0077] C. Linear fitting;

[0078] D. Tare weight calculation;

[0079] E. Nonlinear fitting;

[0080] F. Iterative calculation;

[0081] G. Accuracy calculation;

[0082] H. Error analysis;

[0083] I. Repeat the improved group load loading, error analysis and iteration.

[0084] Further, the step A includes the following steps:

[0085] A1. Compiling the basic group load;

[0086] A1.1 Compiling the unit item in the basic group load;

[0087] According to the design load of the balance, the calibration load of the six components X, Y, Z, Mx, My and Mz of the balance is determined, X is the resistance component, Y is the lift component, Z is the side force component, Mz is the roll moment component, My is the yaw moment component, and Mz is the pitch moment component; the calibration load is 80%~120% of the design range value, and is loaded according to 0%, 25%, 50%, 75%, 100%, 75%, 50%, 25%, 0% nine steps, and after each component is loaded with positive and negative values respectively, 12 unit items of loading array are obtained;

[0088] A1.2 Compiling the combination items in the basic group load;

[0089] According to the calibration load of the balance, the six components of the balance are selected according to the combination mode of 15 positive combination items YMz+, YX+, YMx+, YZ+, YMy+, MzX+, MzMx+, MzZ+, MzMy+, XMx+, XZ+, XMy+, MxZ+, MxMy+ and ZMy+, and 15 negative combination items YMz-, YX-, YMx-, YZ-, YMy-, MzX-, MzMx-, MzZ-, MzMy-, XMx-, XZ-, XMy-, MxZ-, MxMy- and ZMy- are selected; for example: for YMz+ combination: the combination item Y takes 50%~80% of the calibration load value, and when calibrating YMz+, Y remains constant, and the combined item Mz is loaded according to 0%, 50%, 100%, 50%, 0% five steps;

[0090] A2. Compiling the improved group load;

[0091] A2.1 Compiling the unit items in the improved group load;

[0092] The loading steps in A1.1 are encrypted and the calibration range is improved at the same time, so that the calibration load is loaded according to 0%, 12.5%, 25%, 37.5%, 50%, 62.5%, 75%, 87.5%, 100%, 125%, 100%, 87.5%, 75%, 62.5%, 50%, 37.5%, 25%, 12.5%, 0% nineteen steps;

[0093] A2.2 Compiling the combination items in the improved group load;

[0094] The loading steps in A1.2 are Encryption, five steps of 0%, 50%, 100%, 50%, 0% of the basic group load are expanded to nine steps of 0%, 25%, 50%, 75%, 100%, 75%, 50%, 25%, 0%, and at the same time, two positive and negative combinations of a single unit item are expanded to four combinations; for example, YMz+ and YMz- are expanded to YMz+, YMz-, Y-Mz+, and Y-Mz- four combination values respectively loaded;

[0095] A3. Compile comprehensive group load;

[0096] According to the requirements of full range coverage, uniform distribution and positive and negative symmetry, compile the comprehensive group load, and the comprehensive group load is used to check the accuracy error of the balance calibration formula.

[0097] Further, the step B comprises the following steps:

[0098] B1. Determine the reference reading: respectively collect the voltage value arrays of six components under the conditions that the balance roll angle is 0°, 90°, 180° and 270°, and obtain an average voltage value array by averaging the four voltage value arrays, which is the reference voltage of the balance calibration , , respectively representing the voltage readings of X, Y, Z, Mx, My and Mz elements;

[0099] B2. Complete the loading of the unit items and combination items of the basic group load according to the balance calibration specification, and obtain the calibration array including the load value and the corresponding voltage value , , ; and represent the six components of the balance X, Y, Z, Mx, My and Mz.

[0100] Further, the step C comprises the following steps:

[0101] C1. Data preprocessing; subtract the zero load value from the balance loading step value in the positive and negative 12 unit items and the positive and negative 30 combination items to obtain the net increase value;

[0102] C2. Perform multiple regression calculation to obtain the corresponding calibration coefficient, and the calculation formula is:

[0103] ;

[0104] wherein, is the component of the applied load value, is the component of the applied load value; is the loading step voltage value of each unit of the balance, is the initial value of each unit of the balance; is the coefficient of the first order term, when is the main coefficient, is the component to the first order interference coefficient of the component; is the component and the second order interference coefficient of the component to the component; , , ; , and represent the six components of the balance X, Y, Z, Mx, My and Mz;

[0105] C3. Formula conversion; after calculating the 27 coefficients of each unit of the balance, a 27x6 matrix is formed. First, the main coefficient of each unit is multiplied by the new main coefficient , then the first order interference coefficient and the second order interference coefficient are multiplied by the new main coefficient , and finally the whole is transposed to obtain a 6x27 matrix.

[0106] Further, the step D includes the following steps:

[0107] D1. The tare is the sum of the load of the loading device and the load of the counterweight when loaded, and the corresponding voltage value is the difference between the loading zero point and the reference reading;

[0108] D2. The loading zero points of the 42 groups of unit terms and combined terms are combined to form a loading zero point group , wherein the reference reading is taken as the first row initial reading, and then the balance implicit formula is iterated to obtain the tare load group corresponding to the 42 loading zero points , and the calculation formula is:

[0109] ;

[0110] In the formula, is the balance component load calculation value, and are the load values of the remaining five components of the balance when calculating ; is the initial load value, is the main coefficient, is the component to ​The first order interference coefficient of the component; For The component pair The first order asymmetric interference coefficient of the component; For The component and The component pair The second order interference term coefficient of the component, When it is a second square term interference coefficient; When it is a second cross term interference coefficient; , , ; , And The six components of the X, Y, Z, Mx, My and Mz elements of the balance represent.

[0111] Further, the step E includes the following steps:

[0112] E1. The loading zero point group in D2 The values in the group are respectively restored to the corresponding unit item or combined item load group, to obtain the actual load value based on the reference reading The actual load value includes the load value and the tare weight, and the actual load value is combined with the corresponding voltage value to form a new calibration array;

[0113] E2. Repeat steps C2~C3 to obtain a new round of balance calculation formula matrix ;

[0114] E3. The new round of balance calculation formula matrix And the loading zero point group D2 According to the D2 calculation method, a new round of tare weight calculation is performed to obtain a new round of tare load group, and the corresponding difference calculation is performed with the last round of tare load group.

[0115] Further, the iterative calculation of F includes the following steps:

[0116] If the difference between the new round of tare load group and the last round of tare load group is greater than the pre-set iteration convergence standard, the balance calibration formula matrix does not converge, and steps D~E are repeated until the difference meets the iteration convergence standard, the iteration calculation is ended, and the obtained balance calculation formula matrix The performance is stable and meets the calibration specification.

[0117] Further, the step G includes the following steps:

[0118] G1. Perform comprehensive group load of the balance;

[0119] G2. Use the matrix The calibration coefficient in the formula is calculated according to the balance implicit formula, the measurement value of the balance is obtained, and the test standard deviation value is calculated by the measurement value and the theoretical value :

[0120] ;

[0121] Wherein, is the difference between the measurement value and the theoretical value; is the number of comprehensive group load loading items;

[0122] G3. Divide the test standard deviation value of each unit by the calibration maximum value to obtain the calibration accuracy value, if the accuracy error of each unit is less than the pre-set accuracy error value, the balance calibration is completed; otherwise, error analysis is performed.

[0123] Further, the step H comprises the following steps:

[0124] H1. Calculate the relative error amount; take the calibration maximum value of each unit as input and bring it into the balance calculation formula matrix in E3 , perform coefficient multiplication, wherein, for the coefficient of the first-order interference term of Mz to Y , the maximum value of the first-order interference of Mz to Y :

[0125] ;

[0126] , the relative error of Y elements is :

[0127] ;

[0128] H2. According to H1, calculate the 27 coefficients of each unit of the 6 units of the balance in turn to obtain the relative error group ;

[0129] H3. Screen to obtain the relatively large error term; select the maximum coefficient in all the 27 coefficients of the relative error group .

[0130] Further, the step I comprises the following steps:

[0131] I1. Select the load group corresponding to the maximum coefficient in the improved group load, if YMz interferes with X the most, select the 4 cross terms +Y+Mz, +Y-Mz, -Y+Mz, -Y-Mz in the improved group load for loading calibration;

[0132] ​​I2. Replace the collected data of the four cross terms with the corresponding items in the original calibration array, repeat D-H to obtain a new formula matrix and the corresponding test standard deviation value ; ;

[0133] I3. Perform error analysis again, if the accuracy error of the error relatively large item is less than the pre-set accuracy error value, stop calibration, and obtain the final balance calibration formula of the error relatively large item;

[0134] I4. If the accuracy error of the error relatively large item is greater than the pre-set accuracy error value, return to H, continue to screen the error relatively large item, and again perform the step of increasing the group load. If the accuracy error is still greater than the pre-set accuracy error value, the corresponding unit item or combined item step value is again encrypted in a manner of , return to step D until the accuracy error is less than the pre-set accuracy error value.

[0135] Table 1: Original data of bar type six-component balance calibration

[0136] ,

[0137]

[0138] Table 2: Coefficients of bar type six-component balance calibration formula matrix

[0139]

[0140] Table 3: Accuracy calculation of bar type six-component balance calibration

[0141] ,

[0142]

[0143] (Note: The odd-numbered rows in the table are zero point readings, and the even-numbered rows are readings after loading).

[0144] Although the embodiments of the present application have been disclosed as above, they are not limited to the application listed in the specification and the embodiments, and all the features disclosed in the present application, or the steps in all the methods or processes disclosed in the present application, except for mutually exclusive features and / or steps, can be combined in any manner, and the present application is not limited to specific details and the figures shown and described herein.

Claims

1. An adaptive multi-element calibration method for a wind tunnel balance, characterized by, It comprises the following steps: A. Compiling calibration load of the balance; The loading load is divided into three groups: basic group load, improved group load and comprehensive group load; it comprises the following steps: A1. Compiling basic group load; A1.1 Compiling unit items in the basic group load; According to the design load of the balance, the calibration load of the six components X, Y, Z, Mx, My and Mz of the balance is determined, X is the resistance component, Y is the lift component, Z is the side force component, Mz is the roll moment component, My is the yaw moment component and Mz is the pitch moment component; the calibration load is taken as 80%~120% of the design range value, and is loaded according to nine steps of 0%, 25%, 50%, 75%, 100%, 75%, 50%, 25% and 0%; after taking positive and negative values for loading of each component, 12 unit items of loading array are obtained; A1.2 Compiling combined items in the basic group load; According to the calibration load of the balance, 15 positive combination terms YMz+, YX+, YMx+, YZ+, YMy+, MzX+, MzMx+, MzZ+, MzMy+, XMx+, XZ+, XMy+, MxZ+, MxMy+ and ZMy+ and 15 negative combination terms YMz-, YX-, YMx-, YZ-, YMy-, MzX-, MzMx-, MzZ-, MzMy-, XMx-, XZ-, XMy-, MxZ-, MxMy- and ZMy- are selected from the 6 components of the balance according to the combination mode ​ A2. Compiling improved group load; A2.1 Compiling unit items in the improved group load; The loading steps in A1.1 are performed The calibration range is increased by encrypting and simultaneously increasing the calibration load in 19 steps of 0%, 12.5%, 25%, 37.5%, 50%, 62.5%, 75%, 87.5%, 100%, 125%, 100%, 87.5%, 75%, 62.5%, 50%, 37.5%, 25%, 12.5%, 0%. A2.2 Compiling combined items in the improved group load; The loading steps in A1.2 are performed Encryption, five steps of 0%, 50%, 100%, 50%, 0% of the basic group load are expanded to nine steps of 0%, 25%, 50%, 75%, 100%, 75%, 50%, 25%, 0%, and at the same time, 2 positive and negative combination items of a unit item are expanded to 4 combination items; A3. Compiling comprehensive group load; According to the requirements of full-range coverage, uniform distribution and positive-negative symmetry, the comprehensive group load is compiled, which is used to check the accuracy error of the balance calibration formula; B. Loading the basic group load; C. Linear fitting; D. Tare calculation; It comprises the following steps: D1. The tare weight is the sum of the load tool load and the weight load at the loading, and the voltage value corresponding to the tare weight is the difference between the loading zero point and the reference reading D2. The load weight is the weight of the load tool and the weight load at the loading, and the voltage value corresponding to the load weight is the difference between the loading zero point and the reference reading D2. The loading zero point set of 42 groups of unit items and combination items are combined to form a loading zero point group , wherein the reference reading is taken as the first row initial reading, and then the iteration is carried out according to the balance implicit formula to obtain the tare load group corresponding to the 42 loading zero points , and the calculation formula is: ； In the formula, For balance Calculated values ​​of component loads and For calculation At that time, the load values ​​of the remaining 5 components of the balance; This is the initial load value. Main coefficient, for Component pairs The interference coefficient of the first-order term of the component; for Component pairs The first-order asymmetric interference coefficient of the component; for Quantity and Component pairs The coefficient of the second-order interference term of the component. When is the quadratic interference coefficient, The time is the interference coefficient of the quadratic cross term; , , ; , and The six components representing the X, Y, Z, Mx, My, and Mz elements of the balance scale; E. Nonlinear fitting; F. Iterative calculation; G. Accuracy calculation; H. Error analysis; I. Repeating improved group load loading, error analysis and iteration.

2. The method for wind tunnel balance self-adapting multi-element calibration of claim 1, wherein, The step B comprises the following steps: B1. Determine the reference reading: Collect the voltage value array of the six components in the four states of the balance roll angle being 0°, 90°, 180° and 270° respectively, and obtain an average voltage value array by averaging the four voltage value arrays. The average voltage value array is the reference voltage of the balance calibration , , respectively represent the voltage readings of X, Y, Z, Mx, My and Mz elements. B2. Complete the loading of the unit items and combined items of the basic group load according to the balance calibration specification, and obtain the calibration array including the load value and the corresponding voltage value , , ; and represent the six components of the X, Y, Z, Mx, My and Mz elements of the balance.

3. The method for wind tunnel balance self-adapting multi-element calibration of claim 2, wherein, The step C comprises the following steps: C1. Data preprocessing; the balance loading step values in the 12 unit items and 30 combined items are all subtracted by zero load value to obtain net increase value; C2. Multiple regression calculation is performed to obtain corresponding calibration coefficients, and the calculation formula is: ； wherein, is a component of the applied load value is a component of the applied load value ; is a load step voltage value for each cell of the balance, is an initial value for each cell of the balance; is a primary term coefficient when is a main coefficient, is a component to component first order interference coefficient; is a component and component to component second order interference coefficient; , , ; , and represent the six components of the X, Y, Z, Mx, My and Mz elements of the balance;​ C3. Formula conversion; after calculating 27 coefficients corresponding to each unit of the balance, a 27x6 matrix is formed. First, the main coefficient of each unit is converted Converting , secondly, the first interference coefficient and the second interference coefficient are multiplied by the new main coefficient , and finally, the whole is transposed to obtain a 6x27 matrix.

4. The method for wind tunnel balance self-adapting multi-element calibration of claim 3, wherein, The step E comprises the following steps: E1. Load the zero-point group in D2 The values ​​in the data are respectively restored to the load groups of the corresponding element items or combination items to obtain the reference readings. The actual load value, which includes the load value and tare weight, is combined with the corresponding voltage value to form a new calibration array; E2. Repeat steps C2~C3 to get a new round of balance calculation formula matrix ; E3. A new round of balance calculation formula matrix and the loading zero point group of D2 According to the D2 calculation method, a new round of tare calculation is performed to obtain a new round of tare load group, and a corresponding difference calculation is performed with the last round of tare load group.

5. The method for wind tunnel balance self-adapting multi-element calibration of claim 4, wherein, The step F comprises the following steps: If the difference between the new round of tare load group and the last round of tare load group is greater than the preset iteration convergence standard, the balance calibration formula matrix does not converge, steps D~E are repeated until the difference meets the iteration convergence standard, the iteration calculation is ended, and the balance calculation formula matrix obtained The performance is stable, and the calibration specification is met.

6. The method for wind tunnel balance self-adapting multi-element calibration of claim 5, wherein, The step G comprises the following steps: G1. Loading the comprehensive group load of the balance; G2. Utilizing the calibration coefficients in the matrix , the measured value of the balance is calculated according to the balance implicit formula, and the test standard deviation value is calculated by the measured value and the theoretical value : ； wherein is the difference between the measured value and the theoretical value; is the integrated group load loading term number; G3. Calculate the test standard deviation value of each unit Divide by the calibration maximum value to obtain the calibration accuracy value. If the accuracy error of each unit is less than the pre-set accuracy error value, the balance calibration is completed; otherwise, error analysis is performed.

7. The method for wind tunnel balance self-adapting multi-element calibration of claim 6, wherein, The step H comprises the following steps: H1. Calculate the relative error amount; take the calibration maximum value of each cell as input into the balance calculation formula matrix in E3 , carry out coefficient multiplication, where the coefficient of the first-order interference term of Mz to Y is : the maximum value of the first-order interference of Mz to Y ； Obtained The relative error for Y elements is : ； H2. According to H1, sequentially calculate the 6 units of the balance, 27 coefficients of each unit, and obtain the relative error group ; H3. Screen for the relatively large error item; in the relative error group of 27 coefficients, select the maximum one of all coefficients greater than the pre-set accuracy error value.

8. The method for wind tunnel balance self-adapting multi-element calibration of claim 7, wherein, The step I comprises the following steps: I1. In the improved group load, the load group corresponding to the maximum coefficient of the largest item is selected, if YMz interferes with X most, then the four cross items +Y+Mz, +Y-Mz, -Y+Mz and -Y-Mz in the improved group load are selected for loading calibration; I2. Replace the original calibration array with the collected data of the 4 cross terms in the corresponding items, repeat D-H to get a new formula matrix and the corresponding test standard deviation value ;​ I3. Error analysis is performed again, if the accuracy error of the relatively large item is less than the pre-set accuracy error value, then the calibration is stopped, and the final balance calibration formula of the relatively large item is obtained; I4. If the accuracy error of the error relatively large item is greater than the pre-set accuracy error value, return H, continue to screen the error relatively large item, and again increase the group load loading. If the accuracy error is still greater than the pre-set accuracy error value, the corresponding unit item or combined item step value is encrypted again according to the manner, return to step D until the accuracy error is less than the pre-set accuracy error value.

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