A skin pressure measurement system and method based on human body surface capacitance

Abstract

The present application relates to the technical field of pressure sensor, in particular to a skin pressure measurement system and method based on human body surface capacitance, the system comprises: a metal electrode, the metal electrode as the contact surface with the skin, the contact capacitance between the metal electrode and the skin is measured to measure the pressure, wherein the metal electrode is used to make the pressure and the contact area in a mapping increasing relationship.The flexible strain unit of the present application adopts the human skin, and the capacitance is changed as the strain unit by changing the contact area of the electrode through the pressure change.

Description

Technical Field

[0001] This invention relates to the field of pressure sensor technology, and in particular to a skin pressure measurement system and method based on the capacitance of the human body surface. Background Technology

[0002] Hand pressure sensing technology relies on core principles such as flexible electronics, magnetic induction, and piezoelectric effect. Through high sensitivity, real-time monitoring, and flexible wearable characteristics, it achieves precise perception of pressure distribution. This technology can be used in medical rehabilitation to improve the accuracy of patient muscle strength assessment and tactile feedback, in industrial robotics to test grasping safety, in VR / AR scenarios to optimize immersive interactive experiences, and to provide data support for smart homes and human-computer interaction, driving the upgrade of intelligent services. However, current pressure sensor testing circuits are complex, and flexible sensitive units face challenges in balancing lifespan and manufacturing cost. To address this issue, this invention provides a skin pressure measurement system and method based on the capacitance of the human body surface. Summary of the Invention

[0003] The purpose of this invention is to provide a skin pressure measurement system and method based on the capacitance of the human body surface. The flexible strain unit uses human skin, and the capacitance is changed by changing the pressure and the contact area of ​​the electrodes, thus serving as the strain unit.

[0004] To achieve the above objectives, the present invention provides the following solution:

[0005] A skin pressure measurement system based on human surface capacitance includes: a metal electrode, which serves as a contact surface with the skin; pressure is measured by measuring the contact capacitance between the metal electrode and the skin; wherein the metal electrode is configured to create a mapping relationship between pressure and contact area.

[0006] Optionally, measuring the contact capacitance between the metal electrode and the skin includes: obtaining a measurement capacitance matrix by means of a self-capacitance measurement method, wherein the self-capacitance measurement method uses the electrode in contact with the skin and not subject to external pressure as the ground electrode;

[0007] According to the mutual capacitance measurement method, the mutual capacitance matrix is ​​obtained, wherein the measurement frequency of the self-capacitance measurement method and the mutual capacitance measurement method is 1kHz~2MHz;

[0008] Remove the mutual capacitance matrix from the measured capacitance matrix to obtain the true capacitance matrix after removing the mutual capacitance.

[0009] The contact capacitance is obtained from the true value matrix of the capacitance after removing mutual capacitance.

[0010] Optionally, the mutual capacitance matrix C M for:

[0011] ;

[0012] The measured capacitance matrix C T for:

[0013] ;

[0014] The true value matrix of capacitance after removing mutual capacitance, C R for:

[0015] ;

[0016] Among them, C1~C j Let C be the capacitance value measured by j sensors. M1j For capacitive sensor C1 and capacitive sensor C j The mutual capacitance parameters between them.

[0017] Optionally, the mutual capacitance matrix can be obtained by individually pressing each of the metal electrodes or by using the least squares method iteratively based on the measured capacitance values.

[0018] Optionally, pressure and contact area may exhibit a mapping relationship of increasing, including:

[0019] F=F MAX *(C'-C0) / (C MAX -C0) or F=f(ΔC);

[0020] Where F is the applied pressure, F MAX C is the maximum pressure value, C0 is the capacitance value at the initial contact, C' is the capacitance value after applying pressure, and C... MAX Let ΔC be the maximum capacitance value, ΔC be the capacitance change, and f be the function of the applied pressure and the capacitance change.

[0021] Optionally, measuring pressure by measuring the contact capacitance between the metal electrodes and the skin includes: connecting the metal electrodes located in the same row or column in parallel, obtaining the sum of the capacitances in the same row or column by scanning the rows and columns as the contact capacitance, and obtaining the pressure.

[0022] This invention also provides a method for measuring skin pressure based on the capacitance of the human body surface, comprising:

[0023] The contact capacitance between the metal electrode and the skin is measured by pressing the metal electrode onto the surface of human skin.

[0024] Skin pressure is obtained based on the contact capacitance.

[0025] Optionally, measuring the contact capacitance between the metal electrode and the skin includes: obtaining a measurement capacitance matrix by means of a self-capacitance measurement method, wherein the self-capacitance measurement method uses the electrode in contact with the skin and not subject to external pressure as the ground electrode;

[0026] According to the mutual capacitance measurement method, the mutual capacitance matrix is ​​obtained, wherein the measurement frequency of the self-capacitance measurement method and the mutual capacitance measurement method is 1kHz~2MHz;

[0027] Remove the mutual capacitance matrix from the measured capacitance matrix to obtain the true capacitance matrix after removing the mutual capacitance.

[0028] The contact capacitance is obtained from the true value matrix of the capacitance after removing mutual capacitance.

[0029] Optionally, the mutual capacitance matrix can be obtained by individually pressing each of the metal electrodes or by using the least squares method iteratively based on the measured capacitance values.

[0030] Optionally, measuring pressure by measuring the contact capacitance between the metal electrodes and the skin includes: connecting metal electrodes located in the same row or column in parallel, obtaining the sum of the capacitances in the same row or column by scanning rows and columns as the contact capacitance, and obtaining the pressure.

[0031] The beneficial effects of this invention are as follows: The method of this invention uses a simple metal electrode and skin to form a sensor unit. By detecting the change in capacitance on the surface of human skin, the degree of pressure is confirmed by fitting the obtained data. This is used to judge the grip posture and as a basis for the magnitude of force exerted. It saves costs, increases the lifespan of the pressure sensor, and reduces the difficulty of arranging multiple pressure sensors. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a schematic diagram of the capacitance testing circuit according to an embodiment of the present invention;

[0034] Figure 2 This is a schematic diagram of a skin pressure measurement system based on human surface capacitance according to an embodiment of the present invention;

[0035] Figure 3 This is a schematic diagram illustrating the measurement of self-capacitance according to an embodiment of the present invention;

[0036] Figure 4 This is a schematic diagram of multiple pressure sensors combined into a tactile sensor according to an embodiment of the present invention. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0039] Example 1:

[0040] This embodiment provides a skin pressure measurement system based on the capacitance of the human body surface, including: a metal electrode, which serves as the contact surface with the skin. The pressure is measured by measuring the contact capacitance between the metal electrode and the skin, wherein the metal electrode is used to make the pressure and the contact area have a mapping relationship of increasing.

[0041] Specifically, a sensor unit is constructed using a simple flexible substrate (e.g., TPU, which serves only as mechanical support and does not participate in the test circuit), metal electrodes (e.g., copper foil), and human skin. This unit can detect pressure on the skin surface of, for example, the hands or feet. The metal electrodes are disposed on the substrate. The capacitance test circuit of this embodiment is as follows: Figure 1 As shown, the test interface connects to the sensor end on the skin, and the ground electrode is connected to the end of the skin that is not under pressure. The sensor end is connected to the ground electrode through the skin's own conductivity. The system composition diagram is shown below. Figure 2 As shown, the TPU deforms during pressing, increasing the contact area and thus the capacitance between the skin and the metal electrode. The degree of pressure can be determined by measuring the capacitance. The flexible substrate used here can be eliminated; by shaping the metal itself, the skin's bending during contact will naturally increase the contact area.

[0042] Furthermore, measuring the contact capacitance between the metal electrode and the skin includes: obtaining a measurement capacitance matrix using a self-capacitance measurement method, wherein the self-capacitance measurement method uses the electrode in contact with the skin and not subject to external pressure as the ground electrode; obtaining a mutual capacitance matrix using a mutual capacitance measurement method, wherein the measurement frequencies of the self-capacitance measurement method and the mutual capacitance measurement method are 1kHz~2MHz; removing the mutual capacitance matrix from the measurement capacitance matrix to obtain a true capacitance matrix after removing the mutual capacitance; and obtaining the contact capacitance based on the true capacitance matrix after removing the mutual capacitance.

[0043] Specifically, there are two methods for measuring capacitance: self-capacitance (which requires grounding) and mutual capacitance. This scheme is compatible with both methods. For self-capacitance, the electrode that is in constant contact with the skin and not subjected to external pressure (e.g., the wrist) is used as the ground electrode. The ground electrode is connected to the GND port of the capacitance test chip via a lead, and the metal electrode is connected to the test port of the capacitance test chip via a lead. The principle is as follows: Figure 3 As shown:

[0044] This connection method can be compatible with a large number of metal electrodes while using a single ground electrode, saving test interfaces and simplifying the overall circuit design. The disadvantage is that there is mutual capacitance between different metal electrodes, which needs to be removed through testing in the subsequent process.

[0045] In addition, multiple pressure sensors can be combined for use as a tactile sensor, such as... Figure 4 As shown, capacitor C11 is connected to both vertical column S1 and row H1, and so on for each metal electrode. At this time, the circuit quickly detects the capacitance of S1-S3 and H1-H3. The capacitance of S1 is the sum of capacitances C11, C21, and C31, and the capacitance of H1 is the sum of capacitances C11, C12, and C13. In practical applications, the corresponding pressure distribution can be generated according to the degree of change of the values ​​of the vertical column and row, and then the corresponding lateral force and tangential force distribution can be generated according to the position distribution of each point.

[0046] Furthermore, the mutual capacitance matrix C M for:

[0047] ;

[0048] The measured capacitance matrix C T for:

[0049] ;

[0050] The true value matrix of capacitance after removing mutual capacitance, C R for:

[0051] ;

[0052] Among them, C1~C j Let C be the capacitance value measured by j sensors. M1j For capacitive sensor C1 and capacitive sensor C j The mutual capacitance parameters between them.

[0053] Specifically, when multiple metal electrodes are arranged and self-capacitance is used for testing, mutual capacitance may exist between the electrodes, which can easily interfere with the test results. The traditional method of subtracting mutual capacitance from chips generally treats mutual capacitance as a constant value.

[0054] C can be obtained by pressing each metal electrode individually. M The value, or using C during dynamic processes. M The invariant characteristic is that the capacitance value measured multiple times during the test is used to apply the least squares method to C. M Perform iterations, where C M Corresponding parameters in the matrix The iterative formula is:

[0055] ;

[0056] In the formula, i is the iteration number, and C q,t Let C be the measured value of capacitance q in the t-th measurement. k,t Let be the measured value of capacitance k in the t-th measurement. This represents the true value of capacitance q after deducting mutual capacitance at the (t-1)th iteration. Let q be the true value of capacitance k after deducting mutual capacitance at the (t-1)th iteration, where k is a natural number between 1 and j and q < k.

[0057] Furthermore, the linear relationship between pressure and contact area includes:

[0058] F=F MAX *(C'-C0) / (C MAX -C0);

[0059] Where F is the applied pressure, F MAX Where C is the maximum pressure, C0 is the capacitance at the initial contact, and C' is the capacitance after pressure is applied. MAX This represents the maximum capacitance value.

[0060] Furthermore, the mapping relationship between pressure and contact area includes:

[0061] F = f(ΔC);

[0062] Where F is the applied pressure and ΔC is the change in capacitance.

[0063] Specifically, the pressure acquisition method during the working process. Initially, there are two scenarios: one where the metal electrode is not in contact with the skin, and the other where the metal electrode is in contact with the skin.

[0064] Taking the initial state where the metal electrode and skin are not in contact as an example, the initial capacitance value is 0, and the capacitance value at the initial contact is C0. After applying pressure F, the contact area between the skin and the metal electrode increases due to the pressure, and the capacitance value rises to C'. Continuing to apply pressure until the maximum pressure F is reached... MAX Then the capacitance value rises to C. MAXIf the increase in the contact area between the skin and the metal electrode caused by pressure is proportional to the pressure, then the change in capacitance and the force F satisfy a linear relationship:

[0065] F=F MAX *(C'-C0) / (C MAX -C0);

[0066] If initial contact has occurred, the capacitance value at initial contact is C0, and so on. It's important to note that because each person's skin electrical properties are different, the capacitance value is a process-dependent sampling value. If the initially measured pressure is a known standard pressure, the specific pressure value can be calculated subsequently based on the measured capacitance value; otherwise, it serves more as a value reflecting the degree of pressure during the test. During the process, C... Max It may refresh continuously. For convenience, an initial sample can be taken at the beginning, obtained by clenching a fist or pressing the metal electrode firmly to get an initial approximate value. C0 and C Max It can also be dynamically updated by recording sensor data in subsequent processes. Furthermore, if the increase in the contact area between the skin and the metal electrode caused by pressure is not directly proportional to the pressure, then the change in capacitance and the force F have a point-to-point mapping relationship:

[0067] F = f(ΔC);

[0068] The specific mapping formula can be hypothesized based on the deep learning model and data to obtain the optimal result.

[0069] Furthermore, measuring pressure by measuring the contact capacitance between the metal electrodes and the skin includes: connecting metal electrodes located in the same row or column in parallel, obtaining the sum of the capacitances in the same row or column by scanning the rows and columns as the contact capacitance, and obtaining the pressure.

[0070] Example 2:

[0071] A skin pressure measurement method based on human surface capacitance, implemented according to the system provided in Embodiment 1, includes:

[0072] The contact capacitance between the metal electrode and the skin is measured by pressing the metal electrode onto the surface of the human skin.

[0073] Skin pressure is obtained based on contact capacitance.

[0074] Furthermore, measuring the contact capacitance between the metal electrode and the skin includes: obtaining a measurement capacitance matrix by means of a self-capacitance measurement method, wherein the self-capacitance measurement method uses the electrode in contact with the skin and not subject to external pressure as the ground electrode;

[0075] The mutual capacitance matrix is ​​obtained according to the mutual capacitance measurement method, wherein the measurement frequency of the self-capacitance measurement method and the mutual capacitance measurement method is 1kHz~2MHz;

[0076] Remove the mutual capacitance matrix from the measured capacitance matrix to obtain the true capacitance matrix after removing the mutual capacitance.

[0077] The contact capacitance is obtained from the true capacitance matrix after removing mutual capacitance.

[0078] Furthermore, the mutual capacitance matrix can be obtained by pressing each metal electrode individually or by using the least squares method iteratively based on the measured capacitance values.

[0079] The parameters of the mutual capacitance matrix obtained by iterative fitting using the least squares method include:

[0080] ;

[0081] In the formula, i is the iteration number, and C q,t Let C be the measured value of capacitance q in the t-th measurement. k,t Let be the measured value of capacitance k in the t-th measurement. This represents the true value of capacitance q after deducting mutual capacitance at the (t-1)th iteration. Let q be the true value of capacitance k after deducting mutual capacitance at the (t-1)th iteration, where q and k are natural numbers between 1 and j and q < k.

[0082] Furthermore, measuring pressure by measuring the contact capacitance between the metal electrodes and the skin includes: connecting metal electrodes located in the same row or column in parallel, obtaining the sum of the capacitances in the same row or column by scanning the rows and columns as the contact capacitance, and obtaining the pressure.

[0083] For tactile sensors that use row and column scanning (measuring pressure at each point and converting it into lateral and tangential forces), the following is how to convert a 3x3 pressure signal into a lateral force F. normal and tangential force F friction Method:

[0084] ;

[0085] ;

[0086] Where a and b represent that the sensor is located in row a and column b, respectively, and F ab This indicates the magnitude of the pressure experienced by the column b in row a. This represents the unit area and the angle of the force applied in the a-th row and b-th column.

[0087] The capacitance measurement method is the RC capacitance coupling method, which determines the capacitance value by measuring the frequency. The frequency of the response signal used should be as low as possible, in the range of 1k~2MHz.

[0088] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A skin pressure measurement system based on human surface capacitance, characterized in that, include: A metal electrode serves as a contact surface with the skin. Pressure is measured by measuring the contact capacitance between the metal electrode and the skin, wherein the metal electrode is configured to create a mapping relationship between pressure and contact area. Measuring the contact capacitance between the metal electrode and the skin includes obtaining a capacitance matrix using a self-capacitance measurement method, wherein the self-capacitance measurement method uses the electrode in contact with the skin and not subject to external pressure as the ground electrode. According to the mutual capacitance measurement method, the mutual capacitance matrix is ​​obtained, wherein the measurement frequency of the self-capacitance measurement method and the mutual capacitance measurement method is 1kHz~2MHz; Remove the mutual capacitance matrix from the measured capacitance matrix to obtain the true capacitance matrix after removing the mutual capacitance. The contact capacitance is obtained from the capacitance truth matrix after removing mutual capacitance; The relationship between pressure and contact area showing a mapping increase includes: F=F MAX ( C’-C0) / ( C MAX -C0); Where F is the applied pressure, F MAX C is the maximum pressure value, C0 is the capacitance value at the initial contact, C' is the capacitance value after applying pressure, and C... MAX This represents the maximum capacitance value.

2. The skin pressure measurement system based on human surface capacitance according to claim 1, characterized in that, The mutual capacitance matrix is ​​obtained by individually pressing each of the metal electrodes or by using the least squares method iteratively based on the measured capacitance values.

3. The skin pressure measurement system based on human surface capacitance according to claim 1, characterized in that, Measuring pressure by measuring the contact capacitance between the metal electrodes and the skin includes: connecting the metal electrodes located in the same row or column in parallel, obtaining the sum of the capacitances in the same row or column by scanning the rows and columns as the contact capacitance, and obtaining the pressure.

4. The skin pressure measurement method based on human surface capacitance implemented according to claim 1, characterized in that, include: The contact capacitance between the metal electrode and the skin is measured by pressing the metal electrode onto the surface of human skin. Skin pressure is obtained based on the contact capacitance; The measurement of the contact capacitance between the metal electrode and the skin includes: obtaining a measurement capacitance matrix by means of a self-capacitance measurement method, wherein the self-capacitance measurement method uses the electrode in contact with the skin and not subject to external pressure as the ground electrode; According to the mutual capacitance measurement method, the mutual capacitance matrix is ​​obtained, wherein the measurement frequency of the self-capacitance measurement method and the mutual capacitance measurement method is 1kHz~2MHz; Remove the mutual capacitance matrix from the measured capacitance matrix to obtain the true capacitance matrix after removing the mutual capacitance. The contact capacitance is obtained from the true value matrix of the capacitance after removing mutual capacitance.

5. The skin pressure measurement method based on human surface capacitance according to claim 4, characterized in that, The mutual capacitance matrix is ​​obtained by individually pressing each of the metal electrodes or by using the least squares method iteratively based on the measured capacitance values.

6. The skin pressure measurement method based on human surface capacitance according to claim 4, characterized in that, Measuring pressure by measuring the contact capacitance between the metal electrodes and the skin includes: connecting metal electrodes located in the same row or column in parallel, obtaining the sum of the capacitances in the same row or column by scanning the rows and columns as the contact capacitance, and obtaining the pressure.

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