CN110174213B - Calibration method of flexible pressure sensing array - Google Patents

Abstract

The invention relates to the technical field of pressure sensing, in particular to a calibration method of a flexible pressure sensing array. The method for calibrating the flexible pressure sensing array includes the following steps: sequentially applying a plurality of pressures of different magnitudes to the entire flexible pressure sensing array, and acquiring the response characteristic value of each pixel point under each pressure ; Obtain the basic calibration formula of each of the pixel points; provide a compensation calibration function: obtain the compensation calibration formula of each of the pixel points; calculate the product of the basic calibration formula and the compensation calibration formula of each of the pixel points, so that The above product is used as the calibration formula for the pixel. The invention improves the calibration accuracy of a single pixel point, ensures the accuracy of the measurement result of the flexible pressure sensing array, and improves the performance of the flexible pressure sensing array.

Description

Calibration Method of Flexible Pressure Sensing Array

technical field

The invention relates to the technical field of pressure sensing, in particular to a calibration method of a flexible pressure sensing array.

Background technique

Flexible pressure sensing arrays can detect the location distribution of pressure and the pressure in each area, and can be applied to wearable electronic devices, environmental monitoring, human-computer interaction interfaces, electronic skin and other fields, and have broad application prospects.

However, since the flexible pressure sensing array itself has defects such as creep, inconsistency, attenuation, etc., its detection accuracy during use cannot be maintained for a long time. However, detection accuracy is a key factor to measure the performance of flexible pressure sensing arrays. Therefore, at present, periodic calibration of flexible pressure sensing arrays is mainly used to ensure its measurement accuracy.

The traditional calibration method is to fit the characteristic curve of each sensor in the array according to the response characteristics of the entire sensing area of the flexible pressure sensing array after multiple pressure applications. However, in actual use, a part of the flexible pressure sensing array is often subjected to force, rather than the entire sensing area. The change of the force area will cause the change of the crosstalk characteristics in the mechanical and electrical aspects of the sensor, resulting in different conditions during calibration and in the actual use process, which will lead to deviations in the final measurement results.

Therefore, how to improve the calibration method of the flexible pressure sensing array and improve the calibration accuracy to ensure the accuracy of the measurement results of the flexible pressure sensing array is a technical problem that needs to be solved urgently.

SUMMARY OF THE INVENTION

The invention provides a calibration method for a flexible pressure sensing array, which is used to solve the problem of low calibration accuracy of the existing calibration method, so as to ensure the accuracy of the measurement result of the flexible pressure sensing array and improve the performance of the flexible pressure sensing array .

In order to solve the above problems, the present invention provides a method for calibrating a flexible pressure sensing array, wherein the flexible pressure sensing array includes a plurality of sensors arranged in an array, and each of the sensors is used as a pixel, including the following steps :

successively applying a plurality of pressures of different magnitudes to the entire flexible pressure sensing array to obtain the response characteristic value of each of the pixels under each of the pressures;

Fitting a response characteristic curve of each pixel point according to a plurality of the response characteristic values of the pixel point under a plurality of the pressures to obtain a basic calibration formula of each pixel point;

Provides a compensation calibration function as shown below:

In the formula, Y ₁ represents the function value of the compensation calibration function, a _i and b are function coefficients, X ₀ represents the response characteristic value of a pixel point, and X _i represents the same pressure, corresponding to X ₀ The response eigenvalues of the pixels adjacent to the pixel point;

Substitute the response characteristic value of a pixel point and the response characteristic value of the pixel point adjacent to the pixel point into the compensation calibration function, and set the value Y ₁ of the compensation calibration function to be 1, Obtain the compensation calibration formula for each of the pixel points;

Calculate the product of the basic calibration formula and the compensation calibration formula for each pixel, and use the product as the calibration formula for the pixel.

Preferably, the response characteristic value type is capacitance type, current type, resistance type or voltage type.

Preferably, the specific steps of sequentially applying multiple pressures to the entire flexible pressure sensing array include:

placing the flexible pressure sensing array on the surface of a rigid water platform;

providing a rigid pressure plate, the area of the rigid pressure plate is greater than or equal to the area of the flexible pressure sensing array;

The pressure is applied to the entire flexible pressure sensing array through the rigid pressure plate.

Preferably, the specific step of applying the pressure to the entire flexible pressure sensing array through the rigid pressure plate includes:

The rigid pressure plate applies the same pressure to the entire flexible pressure sensing array multiple times, and for each pixel point, the average value of the response characteristic values under the same pressure multiple times is used as the pixel point in the Response eigenvalues under pressure.

Preferably, the number of multiple pressures with different magnitudes is 5 or more.

Preferably, the specific steps of obtaining the basic calibration formula for each of the pixel points include:

Perform the response characteristic curve fitting on each of the pixel points by using a variety of different data fitting methods, to obtain a plurality of fitting curves for each of the pixel points;

The fitting curve with the largest coefficient of determination is selected as the basic calibration formula for this pixel.

Preferably, a variety of different data fitting methods include linear fitting and curve fitting; the curve fitting includes exponential function fitting, polynomial function fitting, logarithmic function fitting, power exponential function fitting, and trigonometric function fitting Fitting and inverse trigonometric function fitting.

Preferably, the data fitting algorithm is a least squares method or a maximum likelihood estimation method.

Preferably, the maximum pressure among the multiple different pressures is the maximum pressure that can be detected by the flexible pressure sensing array; the minimum pressure among the multiple different pressures is the maximum pressure detected by the flexible pressure sensing array The minimum pressure that can be detected.

Preferably, the flexible pressure sensing array is a thin film pressure sensing array or a fiber braided pressure sensing array.

For the calibration method of the flexible pressure sensing array provided by the present invention, for the calibration of each pixel point, on the basis of the basic calibration formula, the influence of other pixel points adjacent to each pixel point on the pixel point is comprehensively considered, The product of the compensation calibration formula and the basic calibration formula is used as the final calibration formula for a pixel, which avoids the stress on the entire sensing area of the flexible pressure sensing array during calibration in the prior art and the local part of the sensing area during actual detection. The crosstalk error caused by different forces improves the calibration accuracy of a single pixel point, ensures the accuracy of the measurement results of the flexible pressure sensing array, and improves the performance of the flexible pressure sensing array.

Description of drawings

1 is a flowchart of a calibration method for a flexible pressure sensing array in a specific embodiment of the present invention;

2 is a schematic structural diagram of a flexible pressure sensing array when calibrating in a specific embodiment of the present invention;

FIG. 3 is a fitting curve diagram of a specific embodiment of the present invention when fitting a basic calibration formula of a pixel.

Detailed ways

The specific embodiments of the calibration method of the flexible pressure sensing array provided by the present invention will be described in detail below with reference to the accompanying drawings.

This specific embodiment provides a method for calibrating a flexible pressure sensing array. FIG. 1 is a flow chart of the calibration method of the flexible pressure sensing array in the specific embodiment of the present invention. Schematic diagram of the structure of the flexible pressure sensing array during calibration. As shown in FIG. 1 and FIG. 2 , the flexible pressure sensing array 21 includes a plurality of sensors arranged in an array, and each of the sensors serves as a pixel 22 . The calibration method of the flexible pressure sensing array provided by this specific embodiment includes the following steps:

Step S11 , sequentially applying a plurality of pressures of different magnitudes to the entire flexible pressure sensing array 21 to acquire the response characteristic value of each of the pixels 22 under each of the pressures.

The "plurality" as used in the present embodiment refers to two or more.

Preferably, the specific steps of sequentially applying multiple pressures to the entire flexible pressure sensing array 21 include:

placing the flexible pressure sensing array 21 on the surface of a rigid water platform 20;

providing a rigid pressure plate 23, the area of the rigid pressure plate 23 is greater than or equal to the area of the flexible pressure sensing array 21;

The pressure is applied to the entire flexible pressure sensing array 21 through the rigid pressure plate 23 .

The dotted lines in Figure 2 represent pixels that are not visible at this angle. The specific embodiment does not limit the specific type of the flexible pressure sensing array 21, for example, the flexible pressure sensing array 21 is a thin film pressure sensing array or a fiber braided pressure sensing array. The type of the sensors in the flexible pressure sensing array 21 may be capacitive, resistive, piezoelectric, triboelectric or thin film transistor type. Correspondingly, the response characteristic value type is capacitance type, current type, resistance type or voltage type. The flexible pressure sensing array 21 has a sensing area, and all the pixel points 22 are arranged in the sensing area in an array.

In order to ensure the same pressure value applied to each pixel point in the flexible pressure sensing array 21 and further ensure the calibration accuracy, the flexible pressure sensing array 21 is placed in a The surface of the rigid water platform 20 as shown in FIG. 2 . The rigid water platform 20 is also provided with a height regulator 25 and a pressure indicator 24, and the pressure indicator 24 is arranged on the flexible pressure sensing array 21 along the direction perpendicular to the rigid water platform 20. The upper part is used to adjust and display the value of the pressure applied by the rigid pressure plate 23 to the entire flexible pressure sensing array 21 . The rigid pressure plate 23 is fixedly connected below the pressure indicator 24 . The height adjuster 25 is connected to the pressure indicator 24 for driving the pressure indicator 24 to move up and down in the vertical direction (ie, the direction perpendicular to the rigid water platform 20 ) to adjust the rigidity The height of the pressure plate 23. The specific structure of the height adjuster 25 can be set by those skilled in the art according to actual needs, as long as the height adjustment of the rigid pressure plate 23 can be achieved. In order to simplify the structure of the calibration device, preferably, the height adjuster 25 includes a lifting column and a connecting rod, one end of the connecting rod is connected to the lifting column, and the other end is connected to the pressure indicator 24 . The vertical lifting movement of the lifting column drives the rigid pressure plate 23 to move vertically, thereby adjusting the distance between the rigid pressure plate 23 and the flexible pressure sensing array 21 .

Preferably, the specific steps of applying the pressure to the entire flexible pressure sensing array 21 through the rigid pressure plate 23 include:

The rigid pressure plate 23 applies the same pressure to the entire flexible pressure sensing array 21 multiple times, and for each pixel 22, the average value of the response characteristic values under the same pressure is used as the pixel The characteristic value of the response of point 22 at this pressure.

The specific number of different pressures applied to the entire flexible pressure sensing array 21 can be selected by those skilled in the art according to actual needs. In order to further improve the calibration accuracy, preferably, the number of pressures with different magnitudes is 5 or more.

Preferably, the maximum pressure among the multiple different pressures is the maximum pressure that can be detected by the flexible pressure sensing array 21; the minimum pressure among the multiple different pressures is the flexible pressure sensing array 21 The minimum pressure that can be detected. The other said pressures are distributed between said maximum pressure and said minimum pressure.

For example, five pressure values of P1, P2, P3, P4, and P5 are provided in ascending order, where P1 is the minimum pressure that can be detected by the flexible pressure sensing array 21, and P5 is the The maximum pressure that can be detected by the flexible pressure sensing array. By adjusting the height adjuster 25 and the pressure indicator 24, the pressure of the magnitude P1 is applied to the entire sensing area of the flexible pressure sensing array 21 for multiple times (ie, more than twice). For each of the pixel points 22, each time the P1 pressure is applied, a response characteristic value will be obtained. The average value method is adopted, and the average value of the response eigenvalues obtained for a pixel point multiple times is taken as the response eigenvalue of the pixel point under the P1 pressure. Using the same method, the response characteristic values of each of the pixel points under the pressures of P2, P3, P4 and P5 can be obtained. In this specific embodiment, the response characteristic value of a pixel point under a pressure is obtained by the method of multiple measurements and averaging, which reduces the measurement error and further improves the calibration accuracy.

Step S12, fitting a response characteristic curve of each pixel point 22 according to a plurality of the response characteristic values under a plurality of the pressures to obtain a basic calibration formula of each pixel point.

Preferably, the specific steps of obtaining the basic calibration formula of each of the pixel points include:

The response characteristic curve fitting is performed on each of the pixel points 22 by using a variety of different data fitting methods to obtain a plurality of fitting curves for each of the pixel points 22;

The fitting curve with the largest coefficient of determination is selected as the basic calibration formula for the pixel point 22 .

Preferably, a variety of different data fitting methods include linear fitting and curve fitting; the curve fitting includes exponential function fitting, polynomial function fitting, logarithmic function fitting, power exponential function fitting, and trigonometric function fitting Fitting and inverse trigonometric function fitting.

Preferably, the data fitting algorithm is a least squares method or a maximum likelihood estimation method.

Specifically, for each of the pixel points, a variety of different fitting curves can be used, and the least squares method or the maximum likelihood estimation method is used to fit the response characteristic curve, so as to obtain multiple fitting curves; Compare the coefficients of determination of multiple fitting curves, select the fitting curve that is closest to each response characteristic value of the pixel point as the final fitting curve of the pixel point, and use the function formula corresponding to the fitting curve as the pixel point. Point-based calibration formula.

The process of data fitting in this specific embodiment is to change the coefficients in the function (that is, the fitting curve), so that the function curve is as close as possible to all the test data points of the pixel point (that is, the multiple responses corresponding to multiple different pressures one-to-one). Eigenvalue), the degree of approximation can be judged by the coefficient of determination after fitting (the higher the coefficient of determination, the higher the degree of approximation, the better the fitting effect), from which the best fitting function (including the specific coefficients in the function) can be obtained. .

Step S13, providing a compensation calibration function as shown below:

In the formula, Y ₁ represents the function value of the compensation calibration function, a _i and b are function coefficients, X ₀ represents the response characteristic value of a pixel point, and X _i represents the same pressure, corresponding to X ₀ The response eigenvalues of the pixels adjacent to the pixel point.

Step S14: Substitute the response characteristic value of a pixel point 22 and the response characteristic value of the pixel point 22 adjacent to the pixel point 22 into the compensation calibration function, and make the compensation calibration function The value Y ₁ is 1, and the compensation calibration formula for each of the pixel points 22 is obtained.

将该像素点在一压力下测得的响应特征值、以及在相同压力下与该像素点相邻的周围像素点测得的响应特征值作为一组补偿校准数据，则总共得到多组补偿校准数据。将上述多组补偿校准数据依次代入上述补偿校准函数，经计算或者逼近得到所述补偿函数中的函数系数a_i和b的值，即得到该像素点的补偿校准公式。Specifically, for each of the pixel points 22, let Y ₁ =1, that is,

The response characteristic value measured by the pixel point under a pressure and the response characteristic value measured by the surrounding pixel points adjacent to the pixel point under the same pressure are used as a set of compensation calibration data, then a total of multiple sets of compensation calibration are obtained. data. Substitute the above multiple sets of compensation calibration data into the above compensation calibration function in turn, and obtain the values of the function coefficients a _i and b in the compensation function through calculation or approximation, that is, the compensation calibration formula of the pixel point is obtained.

In this specific embodiment, for a pixel located in the middle of the flexible sensing array 21, the pixels adjacent to the pixel include four pixels located on the upper side, the lower side, the left side and the right side of the pixel point. pixel point (that is, X _i represents the response characteristic values of four pixel points located on the upper side, lower side, left side and right side of the pixel point corresponding to X ₀ under the same pressure); The pixel point at the boundary of the sensing array 21, the pixel point adjacent to the pixel point includes the pixel point located at two or three positions in the upper side, the lower side, the left side and the right side of the pixel point (that is, X _i Represents the response characteristic values of two or three pixel points located on the upper side, lower side, left side and right side of the pixel point corresponding to X ₀ under the same pressure), for example, for the flexible transmission If the pixel at the lower right corner of the sensor array 21 is located, the adjacent pixel includes two pixels located on the left and the upper side of the pixel.

Step S15: Calculate the product of the basic calibration formula and the compensation calibration formula for each pixel 22, and use the product as the calibration formula for the pixel.

FIG. 3 is a fitting curve diagram of a specific embodiment of the present invention when fitting a basic calibration formula of a pixel. For example, if the number of the pressures is 5, then each pixel point obtains 5 response characteristic values through the test. The response characteristic value is a capacitance difference, and the fitting curve is an exponential function Y ₀ =A*exp(-X/B)+C, where A, B, and C are function coefficients. The capacitance difference refers to the difference between the capacitance value detected by the pixel point and the initial capacitance value of the pixel point after the pressure is applied. The abscissa in FIG. 3 represents the capacitance difference, the test point 30 represents the response characteristic value of a pixel point under a pressure during the calibration process, and the surface of the curve 31 is the best fitting curve obtained by fitting the above exponential function. . After fitting, the values of the function coefficients A, B, and C in the exponential function are: 72.645, -248.3, and -73.94, respectively. Thus, the basic calibration formula of the pixel is obtained as: Y ₀ =72.645*exp(X/248.3)-73.94.

其中，X1、X2、X3、X4分别表示位于该像素点上侧、下侧、左侧和右侧的像素点的响应特征值。Substitute the response characteristic values of the pixel points measured under different pressures into the compensation calibration function in turn, and set the function value Y ₁ of the compensation calibration function to be 1, and the value of b obtained by calculation or approximation is − 1.6234, the values of a ₁ , a ₂ , a ₃ , and a ₄ are 0.369872, 0.149765, 1.075986, and 1.007117, respectively. Among them, a ₁ , a ₂ , a ₃ , and a ₄ respectively represent the function coefficients corresponding to the pixel points located on the upper side, the lower side, the left side and the right side of the pixel point. Then the final calibration formula of the pixel is:

Among them, X1, X2, X3, and X4 respectively represent the response feature values of the pixel points located on the upper side, the lower side, the left side and the right side of the pixel point.

The application of pressure, data fitting, and calculation of calibration formulas described in this specific embodiment can be realized by numerical control and computer.

For the calibration method of the flexible pressure sensing array provided by this specific embodiment, for the calibration of each pixel point, on the basis of the basic calibration formula, comprehensively consider the influence of other pixel points adjacent to each pixel point on the pixel point. The product of the compensation calibration formula and the basic calibration formula is used as the final calibration formula for one pixel point, which avoids the stress on the entire sensing area of the flexible pressure sensing array during calibration in the prior art and the sensing area during actual detection. The crosstalk error caused by different local forces improves the calibration accuracy of a single pixel point, ensures the accuracy of the measurement results of the flexible pressure sensing array, and improves the performance of the flexible pressure sensing array.

The above are only the preferred embodiments of the present invention. It should be pointed out that for those skilled in the art, without departing from the principles of the present invention, several improvements and modifications can also be made, and these improvements and modifications should also be regarded as It is the protection scope of the present invention.

Claims (10)

1. A calibration method of a flexible pressure sensing array comprises a plurality of sensors which are arranged in an array, and each sensor is used as a pixel point, and is characterized by comprising the following steps:

sequentially applying a plurality of pressures with different sizes to the whole flexible pressure sensing array to obtain a response characteristic value of each pixel point under each pressure;

fitting a response characteristic curve of each pixel point according to a plurality of response characteristic values of each pixel point under a plurality of pressures to obtain a basic calibration formula of each pixel point;

providing a compensating calibration function as follows:

in the formula, Y₁A function value representing the compensation calibration function, a_iB are all function coefficients, X₀Representing a response characteristic value, X, of a pixel_iIs at the same said pressure as X₀Pixel point adjacent to corresponding pixel pointThe response characteristic value of (1);

substituting the response characteristic value of one pixel point and the response characteristic value of a pixel point adjacent to the pixel point into the compensation calibration function, and enabling the value Y of the compensation calibration function₁Obtaining a compensation calibration formula of each pixel point as 1;

and calculating the product of the basic calibration formula and the compensation calibration formula of each pixel point, and taking the product as the calibration formula of the pixel point.

2. The method of calibrating a flexible pressure sensing array of claim 1, wherein said response characteristic value type is capacitive, current, resistive, or voltage.

3. The method of calibrating a flexible pressure sensing array of claim 1, wherein the step of sequentially applying a plurality of pressures throughout the flexible pressure sensing array comprises:

placing the flexible pressure sensing array on the surface of a rigid horizontal table;

providing a rigid pressure plate having an area greater than or equal to an area of the flexible pressure sensing array;

applying the pressure to the entire flexible pressure sensing array through the rigid pressure plate.

4. The method of calibrating a flexible pressure sensing array of claim 3, wherein said step of applying said pressure to the entire flexible pressure sensing array via said rigid pressure plate comprises:

the rigid pressure plate applies the same pressure to the whole flexible pressure sensing array for multiple times, and for each pixel point, the average value of response characteristic values under the same pressure for multiple times is used as the response characteristic value of the pixel point under the pressure.

5. The method of calibrating a flexible pressure sensing array of claim 1, wherein the number of the plurality of pressures of different magnitudes is greater than 5.

6. The method of calibrating a flexible pressure sensing array of claim 1, wherein the step of obtaining a base calibration equation for each pixel comprises:

performing the response characteristic curve fitting on each pixel point by adopting a plurality of different data fitting modes to obtain a plurality of fitting curves aiming at each pixel point;

and selecting the fitting curve with the maximum decision coefficient as a basic calibration formula of the pixel point.

7. The method of calibrating a flexible pressure sensing array of claim 6, wherein the plurality of different data fitting modalities includes linear fitting and curve fitting; the curve fitting includes exponential function fitting, polynomial function fitting, logarithmic function fitting, power exponential function fitting, trigonometric function fitting, and inverse trigonometric function fitting.

8. The method of calibrating a flexible pressure sensing array of claim 7, wherein the algorithm of the data fitting is a least squares method or a maximum likelihood estimation method.

9. The method of calibrating a flexible pressure sensing array of claim 1, wherein a maximum pressure of a plurality of different said pressures is a maximum pressure detectable by said flexible pressure sensing array; the minimum pressure of the plurality of different pressures is the minimum pressure detectable by the flexible pressure sensing array.

10. The method of calibrating a flexible pressure sensing array of claim 1, wherein said flexible pressure sensing array is a thin film type pressure sensing array or a fiber weave type pressure sensing array.

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