Flexible pressure sensor system and strain interference detection method and calibration method thereof

Abstract

The invention provides a flexible pressure sensor system and a strain interference detection method and calibration method thereof, and the system comprises a flexible pressure sensor array which comprises a plurality of composite films, and each composite film comprises a positive draw-resistance effect film and a negative draw-resistance effect film; a positive effect electrode pair; a negative effect electrode pair; the row electrode array comprises a plurality of parallel row electrodes which are arranged along the length direction of the composite film; the column electrode array comprises a plurality of parallel column electrodes which are arranged along the width direction of the composite film; the row electrodes, the column electrodes and the composite film form pressure sensing units, and a plurality of pressure sensing units form a row-column crossed pressure sensing array; the plurality of composite films are arranged along the length direction of the row electrode array and / or the column electrode array to form a flexible pressure sensor array; and the rear-end circuit is connected with the flexible pressure sensor array and is used for detecting voltage data of the flexible pressure sensor array. According to the invention, strain interference can be detected, and calibration can be realized after quantitative evaluation.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible sensors, and in particular, to a flexible pressure sensor system, a strain interference detection method and a calibration method thereof. Background Art

[0002] With the development of flexible electronics technology, flexible high-density pressure sensor arrays have been widely used in the fields of human-computer interaction, health monitoring, electronic skin, smart home, and robot touch. However, current flexible high-density pressure sensor arrays do not have the high adaptability to the surrounding environment like human touch, and there is an easily overlooked problem: due to the deformability of the flexible pressure sensor, when it interacts with a flexible object, a conformal contact will be formed on the contact surface, which may cause the flexible pressure sensor itself to generate minute strains during stretching, bending, and other actions. These strain interferences may lead to mechanical property fluctuations, electrical property crosstalk, or attenuation of some functions. Some researchers believe that when two soft objects are squeezed, the normal force cannot be measured independently of the mechanical stress. In other words, the influence of strain on the measurement result of the normal force must be considered. Therefore, when designing, manufacturing, and applying a flexible pressure sensor, it is necessary to evaluate its resistance to strain interference, and propose an effective solution to resist strain interference to improve the accuracy of the flexible pressure sensor's perception of force.

[0003] In the prior art, the strain interference suppression strategies of flexible sensors can be mainly divided into three categories: symmetric structure, stress-absorbing material, and multi-layer stacked structure. First, the symmetric structure means that sensitive units vulnerable to strain interference, such as stretchable electrodes, are designed into a symmetric structure of multiple concentric circles, or an origami-like symmetric structure. These symmetric structures themselves also have structural stretchability. Therefore, when strained, the stress will be redistributed on this kind of structure. Due to the overall symmetry, the stress can cancel each other out, so finally no local stress concentration is shown, and thus it will not affect other sensitive layers of the sensor; the second strategy is to develop stress-absorbing materials. This kind of material generally has microcracks or micropores, or irregular pores formed by electrospinning. When strain acts on the sensor material layer, these microstructures can dispersedly bear the shape change caused by the strain and absorb the stress and convert it into the change of other forces inside the material. In addition, this kind of material also has good elasticity and can return to its original morphology when the strain is removed, so it also has the ability to resist strain interference; the last category is the most common multi-layer stacked structure. Different structural layers are prepared with materials having different tensile moduli. The structure vulnerable to strain interference usually has a large tensile modulus, and a material with a small tensile modulus is used in the core functional area of the sensor. Therefore, when subjected to strain interference, due to the large difference in tensile moduli, the core functional area will basically remain unchanged, so that the output performance of the sensor is not affected by strain interference.

[0004] However, the above three suppression strategies for strain interference still have the following deficiencies: (1) It is impossible to quantitatively evaluate the magnitude of the strain interference suffered; (2) The structure preparation process is complex, the cost is high, the structure is fragile, and it is not suitable for application scenarios with large loads; (3) The microstructure of the stress-absorbing material is easily irreversibly damaged, has a limited lifespan, and is not suitable for long-term use; (4) The interface matching problem existing in the multi-layer stacked structure easily causes packaging failure. Summary of the Invention

[0005] Aiming at the defects in the prior art, the purpose of the present invention is to provide a flexible pressure sensor system and its strain interference detection method and calibration method. The flexible pressure sensor system has the advantages of easy processing, low cost, long lifespan, etc., can detect strain interference, quantitatively evaluate it and then achieve calibration, which is beneficial to improving the mechanical detection accuracy of the pressure sensor system in flexible interaction scenarios, so as to provide reliable sensing data for subsequent applications.

[0006] According to the first aspect of the present invention, a flexible pressure sensor system is provided, and the system includes a flexible pressure sensor array and a backend circuit;

[0007] The flexible pressure sensor array includes:

[0008] Multiple assembled composite films, each of the assembled composite films includes a positive piezoresistive effect film and a negative piezoresistive effect film stacked in sequence from bottom to top, and the assembled composite film has a positive and negative piezoresistance cancellation effect;

[0009] Positive effect electrode pairs are arranged at both ends of the positive piezoresistive effect film, and the positive effect electrode pairs collect the resistance value change of the positive piezoresistive effect film when it is strained;

[0010] Negative effect electrode pairs are arranged at both ends of the negative piezoresistive effect film, and the negative effect electrode pairs collect the resistance value change of the negative piezoresistive effect film when it is strained; the assembled composite film, the positive effect electrode pairs and the negative effect electrode pairs form a strain detection unit;

[0011] A row electrode array includes multiple parallel row electrodes arranged along the length direction of the assembled composite film, and the row electrodes are cross-arranged on the assembled composite film;

[0012] A column electrode array includes multiple parallel column electrodes arranged along the width direction of the assembled composite film, the column electrodes are perpendicular to the row electrodes, and the column electrodes are cross-arranged on the assembled composite film;

[0013] The row electrodes and the column electrodes form a pressure sensing unit with the assembled composite film, and a plurality of the pressure sensing units constitute a row-column cross-type pressure sensing array; a plurality of the assembled composite films are arranged along the length direction of the row electrode array and / or the column electrode array to form a flexible pressure sensor array;

[0014] The backend circuit is connected to the flexible pressure sensor array. The input ends of the backend circuit are respectively connected to the positive negative differential resistance effect film and the negative negative differential resistance effect film. The backend circuit is used to collect the voltage data caused by the strain on the assembled composite film and the voltage data of the flexible pressure sensor array after being stressed, and send the voltage data to the host computer.

[0015] Optionally, the positive negative differential resistance effect film and the negative negative differential resistance effect film have the same size and are both prepared from the same type of nano-conductive material and the same type of stretchable polymer. Among them, the content of the nano-conductive material in the positive negative differential resistance effect film is lower than that in the negative negative differential resistance effect film.

[0016] Optionally, the positive effect electrode pair is insulated from the negative negative differential resistance effect film, and the negative effect electrode pair is insulated from the positive negative differential resistance effect film.

[0017] Optionally, the positive effect electrode pair is connected to both ends of the positive negative differential resistance effect film based on the full-woven lead process, and the negative effect electrode pair is connected to both ends of the negative negative differential resistance effect film based on the full-woven lead process.

[0018] Optionally, the row electrode is made of conductive fabric, and the row electrode is cross-sewn on the assembled composite film by flat stitching based on the full-woven lead process.

[0019] Optionally, the column electrode is made of conductive fabric, and the column electrode is cross-sewn on the assembled composite film by flat stitching based on the full-woven lead process.

[0020] Optionally, the backend circuit includes:

[0021] A multi-channel acquisition circuit, including a row scanning control module, a plurality of voltage signal amplification modules with adjustable gains, and a plurality of analog-to-digital conversion chips. The row scanning control module collects the resistance values of the assembled composite film at the intersections of different columns and the scanned row by row scanning. The voltage signal amplification module and the analog-to-digital conversion chip convert the resistance values into voltage data;

[0022] A strain interference detection circuit for monitoring the strain resistance values of the positive negative differential resistance effect film and the negative negative differential resistance effect film in the strain detection unit;

[0023] The processing circuit packs and uniformly sends the voltage data of the collected flexible pressure sensor array to the host computer through a wired data transmission protocol.

[0024] According to a second aspect of the present invention, there is provided a method for detecting strain interference of the above flexible pressure sensor system, the method comprising:

[0025] Monitoring the strain detection unit through the strain interference detection circuit unit to obtain the real-time output voltage signal of the strain interference detection circuit unit;

[0026] Judging whether there is a rising edge and a warning signal in the output voltage signal of the strain interference detection circuit unit according to the real-time output voltage signal, so as to realize the detection of strain interference.

[0027] According to a third aspect of the present invention, there is provided a method for calibrating strain interference of the above flexible pressure sensor system, the method comprising:

[0028] When the flexible pressure sensor system is subjected to strain interference, determining the magnitude of the strain interference suffered by the flexible pressure sensor system according to the relative resistance change of the negative effect electrode pairs on the negative piezoresistive effect film;

[0029] Calibrating the output voltage - force relationship curve of the flexible pressure sensor array under strain interference to obtain the mechanical output response curve under strain interference;

[0030] Determining the estimated force value after calibration through voltage according to the mechanical output response curve.

[0031] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0032] 1. The flexible pressure sensor system of the present invention is realized based on an assembled composite film with positive and negative piezoresistance cancellation effects. It can not only be used as a strain sensor to monitor the strain interference suffered, but also be used as a multi - channel flexible pressure sensing array for normal force sensing, and has the advantages of simple structure, low processing cost, good flexibility, expandable as needed, and large - scale production.

[0033] 2. The flexible pressure sensor system of the present invention combines the positive and negative piezoresistance cancellation effects with the backend detection circuit to amplify weak strain interference, has a low lower limit of quantitatively detectable strain interference, is overall more sensitive, ensures the accuracy of the flexible pressure sensor system when interacting with flexible objects, and is of great significance for improving the stability and reliability of the human - machine interaction interface. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] By reading the following detailed description of non - restrictive embodiments with reference to the accompanying drawings, other features, objects, and advantages of the present invention will become more apparent:

[0035] Figure 1 It is a schematic structural diagram of a flexible pressure sensor array in an embodiment of the present invention;

[0036] Figure 2 (A) is a process flow diagram of the full-woven lead of the flexible pressure sensor array in an embodiment of the present invention;

[0037] Figure 2 (B) is a schematic diagram of the position of the pressure sensing unit in an embodiment of the present invention;

[0038] Figure 3 It is a connection schematic diagram of a shared row electrode and a shared column electrode for multiple assembled composite films in an embodiment of the present invention;

[0039] Figure 4 It is a relationship diagram of the relationship between the output voltage and the force of the flexible pressure sensor array in an embodiment of the present invention under different strain interferences;

[0040] Figure 5 It is a schematic diagram of the connection method of the strain detection unit and the strain interference detection circuit unit in an embodiment of the present invention;

[0041] Figure 6 (A) is a flowchart of the strain interference detection and calibration method of the flexible pressure sensor system in an embodiment of the present invention;

[0042] Figure 6 (B) is the relationship between the relative resistance change rate of the positive piezoresistive effect film and the negative piezoresistive effect film and the strain interference received in an embodiment of the present invention;

[0043] Figure 6 (C) is a comparison diagram of the relationship curve between the output voltage and the force of the flexible pressure sensor before and after calibration in an embodiment of the present invention;

[0044] Figure 7 It is a schematic diagram of three types of flexible adapter plates of the flexible pressure sensor system in an embodiment of the present invention;

[0045] Figure 8 It is a packaging method of the conductive woven wire and the flexible adapter plate in an embodiment of the present invention;

[0046] Figure 9 It is a distribution schematic diagram of multiple assembled composite films on the tactile glove in an embodiment of the present invention;

[0047] Figure 10 It is a schematic structural diagram of each part of the high-density tactile glove in an embodiment of the present invention;

[0048] Figure 11Schematic diagram of the signal flow of the high-density tactile glove in an embodiment of the present invention;

[0049] Figure 12 Wired data transmission protocol of the flexible pressure sensor system in an embodiment of the present invention;

[0050] Figure 13 Schematic diagram for calibrating the relationship curve between the output voltage of the pressure sensing unit and the applied load force in an embodiment of the present invention;

[0051] Figure 14 Relationship diagram between the estimated force on the sensor and the actual force when the flexible pressure sensor system is interfered by 30% strain, 25% strain, 20% strain, 15% strain, 10% strain, 5% strain and calibration strain respectively in an embodiment of the present invention.

[0052] The markings in the figure are respectively represented as: 101 - assembled composite film, 102 - strain detection electrode pair, 103 - row electrode array, 104 - column electrode array, 105 - negative magnetoresistive effect film, 106 - positive magnetoresistive effect film, 107 - negative effect electrode pair, 108 - positive effect electrode pair; 201 - lead-out of strain detection electrode pair, 202 - sewn row electrode array, 203 - sewn column electrode array, 204 - pressure sensing unit; 301 - shared column electrode, 302 - shared row electrode; 501 - resistance value of positive or negative magnetoresistive effect film, 502 - strain interference received, 503 - ground terminal of negative effect electrode pair, 504 - lead terminal of negative effect electrode pair, 505 - ground terminal of positive effect electrode pair, 506 - lead terminal of positive effect electrode pair, 507 - output voltage of negative effect circuit arm, 508 - output voltage of positive effect circuit arm, 509 - total output voltage; 601 - relationship between relative resistance change rate of positive magnetoresistive effect film and strain interference received; 602 - relationship between relative resistance change rate of negative magnetoresistive effect film and strain interference received, 603 - mechanical output response curve corresponding to strain less than and closest to strain interference received, 604 - mechanical output response curve corresponding to strain greater than and closest to strain interference received, 605 - mechanical output response curve of strain interference received; 701 - finger area flexible adapter board, 702 - palm area flexible adapter board, 703 - general adapter board, 704 - fixing hole, 705 - pad, 706 - row electrode, 707 - column electrode, 708 - ordinary electrode wire; 801 - flexible base layer, 802 - pad metal through hole, 803 - conductive woven wire, 804 - silver paste fixing layer, 805 - ultraviolet curing glue layer; 901 - thumb pressure detection area, 902 - index finger pressure detection area, 903 - middle finger pressure detection area, 904 - ring finger pressure detection area, 905 - little finger pressure detection area, 906 - palm pressure detection area; 1001 - composite film, 1002 - glove base, 1003 - first flexible adapter board, 1003’ - second flexible adapter board, 1004 - multi-channel acquisition circuit, 1005 - processing circuit, 1006 - bracelet. Detailed implementation manners

[0053] The present invention will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made. These all belong to the protection scope of the present invention.

[0054] Refer to Figures 1 - 3, a flexible pressure sensor system provided by an embodiment of the present invention includes a flexible pressure sensor array and a backend circuit; the flexible pressure sensor array includes a plurality of assembled composite films 101, a positive effect electrode pair 108, a negative effect electrode pair 107, a row electrode array 103, and a column electrode array 104. Each assembled composite film 101 includes a positive piezoresistive effect film 106 and a negative piezoresistive effect film 105 stacked sequentially from bottom to top to form an assembled composite film. The positive piezoresistive effect film 106 has the characteristic that its resistance increases with the increase of strain when subjected to strain, and the negative piezoresistive effect film 105 has the characteristic that its resistance decreases with the increase of strain when subjected to strain. The assembled composite film 101 has a positive and negative piezoresistance cancellation effect; the positive effect electrode pair 108 and the negative effect electrode pair 107 constitute a strain detection electrode pair 102. The positive effect electrode pair 108 is disposed at both ends of the positive piezoresistive effect film 106, and the positive effect electrode pair 108 collects the resistance change of the positive piezoresistive effect film 106 when subjected to strain; the negative effect electrode pair 107 is disposed at both ends of the negative piezoresistive effect film 105, and the negative effect electrode pair 107 collects the resistance change of the negative piezoresistive effect film 105 when subjected to strain; the assembled composite film 101, the positive effect electrode pair 108, and the negative effect electrode pair 107 form a strain detection unit; the row electrode array 103 includes a plurality of parallel row electrodes arranged along the length direction of the assembled composite film 101. The row electrodes are cross - arranged on the assembled composite film 101, that is, the cross - arrangement is located on the upper and lower surfaces of the assembled composite film 101; the column electrode array 104 includes a plurality of parallel column electrodes arranged along the width direction of the assembled composite film 101. The column electrodes are perpendicular to the row electrodes, and the column electrodes are cross - arranged on the assembled composite film 101, that is, the cross - arrangement is located on the upper and lower surfaces of the assembled composite film 101; the row electrodes and the column electrodes form a pressure sensing unit 204 with the assembled composite film 101, and a plurality of pressure sensing units 204 constitute a row - column cross - type pressure sensing array; a plurality of assembled composite films 101 are arranged along the length direction of the row electrode array 103 and / or the column electrode array 104, that is, a plurality of assembled composite films 101 share row electrodes and / or column electrodes to constitute a flexible pressure sensor array; the backend circuit is connected to the flexible pressure sensor array through a flexible adapter board. The input ends of the backend circuit are respectively connected to the positive piezoresistive effect film 106 and the negative piezoresistive effect film 105. The backend circuit is used to collect the voltage data caused by the strain of the assembled composite film and the voltage data of the flexible pressure sensor array after being stressed, and send the voltage data to the host computer.

[0055] In the embodiment of the present invention, the positive effect electrode pair 108 and the negative effect electrode pair 107 form two pairs of strain detection electrode pairs 102 in the strain detection unit. Refer to Figure 2The extraction of the strain detection electrode pairs in step 201 of (A), the positive effect electrode pair 108 is connected to both sides of the longest side of the positive piezoresistive effect film 106, and the negative effect electrode pair 107 is connected to both sides of the longest side of the negative piezoresistive effect film 105. The negative effect electrode pair 107 and the positive effect electrode pair 108 are isolated from each other, that is, the positive effect electrode pair 108 is insulated from the negative piezoresistive effect film 105, and the negative effect electrode pair 107 is insulated from the positive piezoresistive effect film 106. Two pairs of strain detection electrodes 102 of each assembled composite film 101 simultaneously collect the resistance changes of the positive piezoresistive effect film 106 and the negative piezoresistive effect film 105 when they are strained. The relative resistance change rate of the positive piezoresistive effect film 106 and the relative resistance change rate of the negative piezoresistive effect film 105 show the characteristics of the same absolute value but opposite signs, that is, the sum of the relative resistance change rate of the positive piezoresistive effect film 106 and the relative resistance change rate of the negative piezoresistive effect film 105 is approximately zero. This characteristic exhibited by the assembled composite film 101 when strained is called the positive and negative piezoresistance cancellation effect.

[0056] In some embodiments, the positive piezoresistive effect film 106 and the negative piezoresistive effect film 105 have the same size and are stacked and integrated along two largest cross-sections through a non-conductive adhesive to form an assembled composite film. Both the positive piezoresistive effect film 106 and the negative piezoresistive effect film 105 are prepared from the same type of nano-conductive material and the same type of stretchable polymer. Among them, the content of the nano-conductive material in the positive piezoresistive effect film 106 is lower than that in the negative piezoresistive effect film 105. Specifically, the nano-conductive material is multi-walled carbon nanotubes, and the stretchable polymer is low-ammonia natural latex. When the concentration of multi-walled carbon nanotubes in low-ammonia natural latex is 3.3 - 10 wt%, it exhibits a negative piezoresistive effect; when the concentration of multi-walled carbon nanotubes in low-ammonia natural latex is 0.5 - 3.299 wt%, it exhibits a positive piezoresistive effect. The assembled composite film 101 realizes the positive piezoresistive effect film 106 and the negative piezoresistive effect film 105 respectively by regulating the concentration of the doped nano-conductive material therein, and then forms an assembled composite film with positive and negative piezoresistance cancellation effect through assembly.

[0057] In some embodiments, the positive effect electrode pair 108 is connected to both ends of the positive piezoresistive effect film 106 based on the all-woven lead process, and the negative effect electrode pair 107 is connected to both ends of the negative piezoresistive effect film 105 based on the all-woven lead process.

[0058] In some embodiments, the row electrodes are made of conductive fabric. One conductive thread is one row electrode, and multiple parallel conductive threads form a conductive fabric row electrode array, and the spacing between multiple parallel conductive threads is adjustable. Refer to Figure 2 (A) Step 202, based on the all-woven lead process, the row electrodes are cross-sewn on the assembled composite film 101 by the flat stitch method.

[0059] In some embodiments, the column electrodes are made of conductive fabric. One conductive wire is one column electrode, and multiple parallel conductive wires form a conductive fabric column electrode array. The spacing between multiple parallel conductive wires is adjustable, and the row electrodes and column electrodes are perpendicularly wired and distributed on both sides of the assembled composite film without being directly connected. Refer to Figure 2 (Steps 201-203 of (A)), based on the full knitting lead process, the row electrode array and the column electrode array are cross-sewn on the assembled composite film 101 on which the strain detection electrode pair 102 has been sewn by the flat stitch method.

[0060] Exemplarily, refer to Figure 2 (As shown in (B)), it is a schematic diagram of the position of each pressure sensing unit in the flexible pressure sensor array. A pressure sensing unit 204 is formed between the fourth row electrode, the assembled composite film, and the first column electrode; refer to Figure 3 As shown, multiple assembled composite films 101 are arranged through the shared column electrode 301 and the shared row electrode 302, thereby forming a flexible pressure sensor array. The density of this array is obtained by multiplying the number of row electrodes on a single assembled composite film 101 by the number of column electrodes, and then multiplying by the number of assembled composite films.

[0061] In the embodiments of the present invention, the electrode materials of the strain detection electrode pair 102, the row electrode array 103, and the column electrode array 104 are flexible, low-impedance, and sewable conductive wires. The strain detection electrode pair 102, the row electrode array 103, and the column electrode array 104 are processed by the full knitting lead process and are tightly connected to the assembled composite film 101. Different from the traditional method of using adhesives to separately fix the row electrode layer and the column electrode layer on both sides of the sensitive layer, the full knitting lead process in the embodiments of the present invention avoids the hidden danger of electrode layer delamination and is more suitable for long-term and repetitive application scenarios.

[0062] In the above embodiments, when the assembled composite film is subjected to a load, its resistance value will decrease. The assembled composite film 101, the row electrode array 103, and the column electrode array 104 form a row-column cross-type flexible pressure sensing array. Refer to Figure 4 , Curves A, B, C, D, E, F, and G are the relationship curves between the output voltage and the force under no strain interference, 5% strain, 10% strain, 15% strain, 20% strain, 25% strain, and 30% strain interference respectively. When the flexible pressure sensing array is subjected to gradually increasing strain interference, the relationship curve between the output voltage of the pressure sensing unit 204 and the force will have premature saturation of the output voltage, and the greater the strain interference, the earlier the output voltage of the pressure sensing unit 204 will saturate.

[0063] In some embodiments, the backend circuit includes a multi-channel acquisition circuit, a strain interference detection circuit, and a processing circuit. Preferably, the strain interference detection circuit unit and the multi-channel acquisition circuit in the backend circuit are integrated into an integrated microcircuit. The multi-channel acquisition circuit includes a row scanning control module, a plurality of voltage signal amplification modules with adjustable gains, and a plurality of analog-to-digital conversion chips (ADCs). The row scanning control module acquires the resistance values of the assembled composite film at the intersections of different columns and the scanned rows through progressive scanning. The voltage signal amplification modules and the analog-to-digital conversion chips convert the resistance values into voltage data. The strain interference detection circuit unit monitors the strain resistance values of the positive magnetoresistive effect film and the negative magnetoresistive effect film in the strain detection unit. The processing circuit packs and uniformly sends the acquired voltage data of the flexible pressure sensor array to the host computer through a wired data transmission protocol.

[0064] In the embodiments of the present invention, the positive effect electrode acquires the resistance value change when the positive magnetoresistive effect film is strained, and the negative effect electrode acquires the resistance value change when the negative magnetoresistive effect film is strained. The strain interference detection circuit unit monitors the resistance value changes obtained by the positive and negative effect electrode pairs. The change in the strain resistance value will cause a change in the voltage signal output by the circuit arm where it is located. Specifically, when the strain resistance value of the positive magnetoresistive effect film becomes larger, the voltage signal output by the circuit arm where the positive magnetoresistive effect film is located decreases; when the strain resistance value of the negative magnetoresistive effect film becomes smaller, the voltage signal output by the circuit arm where the negative magnetoresistive effect film is located increases.

[0065] Exemplarily, Figure 5 a structural design of the strain interference detection circuit unit is provided. Referring to Figure 5 as shown, the grounding end 503 of the negative effect electrode pair on the negative magnetoresistive effect film 105 is connected to the ground, and the lead end 504 of the negative effect electrode pair on the negative magnetoresistive effect film 105 is connected to the negative effect circuit arm; the grounding end 505 of the positive effect electrode pair on the positive magnetoresistive effect film 106 is connected to the ground, and the lead end 506 of the positive effect electrode pair on the positive magnetoresistive effect film 106 is connected to the positive effect circuit arm. 501 represents the resistance value of the positive magnetoresistive effect film or the negative magnetoresistive effect film. The negative magnetoresistive effect film 105 and the positive magnetoresistive effect film 106 respectively connected to the negative effect circuit arm and the positive effect circuit arm serve as two variable input terminals of the strain interference detection circuit unit, and simultaneously monitor the received strain interference 502. The output voltage 507 (denoted as V1) of the negative effect circuit arm and the output voltage 508 (denoted as V2) of the positive effect circuit arm are amplified by a backend adjustable proportional coefficient differential amplifier to generate a total output voltage 509 (denoted as V out ). In some embodiments, let Figure 5 R1 = R3 and R2 = R4 in out , then V

[0066] In some embodiments, the processing circuit includes: a central processing unit, a power supply module, and a data transmission module. The central processing unit receives voltage data from the multi-channel acquisition circuit and the strain interference detection circuit unit. The power supply module provides electrical energy for the central processing unit. The data transmission module packs the data received by the central processing unit according to the wired transmission protocol and then sends it to the host computer.

[0067] In some embodiments, in the wired data transmission protocol, each frame of voltage data transmitted each time consists of the following four parts: a start bit, a data length bit, data to be transmitted, and a check bit; wherein, the start bit occupies two bytes, and the content is a number represented in hexadecimal that does not repeat the data to be transmitted; the data length bit occupies two bytes, the unit of the data length is bytes, and it is represented in hexadecimal; each data to be transmitted occupies two bytes, and multiple data can be transmitted at a time; the check bit occupies two bytes and is obtained by performing an exclusive OR operation on 0x0000, the start bit, the data length bit, and each data to be transmitted one by one; the pressure sensing data is sent frame by frame to the host computer, and the host computer cuts the received data by detecting the start bit and verifying the check bit, so as to obtain each frame of pressure sensing data.

[0068] Based on the same inventive concept, an embodiment of the present invention provides a method for detecting strain interference of the above flexible pressure sensor system, referring to Figure 6 (A), the method includes:

[0069] S1. The strain interference detection circuit unit continuously, dynamically, and real-time monitors the strain detection unit;

[0070] S2. When the strain interference increases, the output voltage 507 (V1) of the negative effect circuit arm will have a large-amplitude rise, and the output voltage 508 (V2) of the positive effect circuit arm will have a small-amplitude drop. V1 and V2 are amplified by the adjustable proportional coefficient differential amplifier at the back end, and finally a rising edge will be generated on the output voltage signal 509 of the strain interference detection circuit unit. This rising edge indicates that the strain detection unit is affected by strain interference and will cause the host computer to issue a warning signal. By continuously monitoring whether there is a rising edge and a warning signal in the output voltage signal of the strain interference detection circuit unit, the detection of strain interference is realized. If there is no rising edge in the output voltage signal 509, it means that the strain detection unit is not affected by strain interference at this time.

[0071] Based on the same inventive concept, an embodiment of the present invention provides a method for calibrating strain interference of the above flexible pressure sensor system, continuing to refer to Figure 6 (A), the method includes:

[0072] S1. When the flexible pressure sensor system is affected by strain interference, measure the magnitude of the strain received. Refer to Figure 6(B), 601 is the relationship between the relative resistance change rate of the positive piezoresistive effect film and the strain interference it receives, and 602 is the relationship between the relative resistance change rate of the negative piezoresistive effect film and the strain interference it receives. Since the magnitude of the strain interference deduced from the relative resistance change of the positive effect electrode pair and the relative resistance change of the negative effect electrode pair is the same, the magnitude of the strain interference received by the flexible pressure sensor system can be determined only based on the relative resistance change of the negative effect electrode pair on the negative piezoresistive effect film;

[0073] S2. Start the calibration module of the host computer to calibrate the relationship curve between the output voltage and the force of the flexible pressure sensor array under strain interference (denoted as the mechanical output response curve). Refer to Figure 6 (C). According to the magnitude of the strain interference σ deduced in S1 0 , in the existing mechanical output response curve, find the strain (i.e., σ 0 ) that is less than and closest to the received strain interference (i.e., σ A ), and find the corresponding mechanical output response curve 603. Find the strain (i.e., σ 0 ) that is greater than and closest to the received strain interference (i.e., σ B ), and find the corresponding mechanical output response curve 604. According to the differences between σ 0 and σ A and σ B respectively, interpolate and fit between the two mechanical output response curves to obtain the mechanical output response curve 605 of the received strain interference (i.e., σ 0 ), that is, the correction of the mechanical output response curve measured under the strain interference σ 0 is realized;

[0074] S3. Use the mechanical output response curve 605 as the mechanical output response curve under the current strain interference, and the calibrated estimated force value can be deduced through the voltage. If the strain detection unit is not affected by strain interference, the mechanical output response curve measured without strain interference is used for force estimation.

[0075] In the embodiments of the present invention, once the flexible pressure sensor array is strained, a rising edge signal is generated in the output voltage of the strain interference detection circuit unit, and a warning signal is sent. By detecting whether there is a warning signal, it is judged whether the flexible pressure sensor array is affected by strain interference, and the magnitude of the strain interference is speculated through the relative change amount of the resistance. Then, according to the quantified strain interference, the calibration module is started. The above embodiments of the present invention can realize the real-time quantitative detection of the strain interference received by the flexible pressure sensor system, and calibrate the force of the flexible pressure sensor array under strain interference, improving its accuracy.

[0076] The technical solutions of the present application are further described below with embodiments and application examples.

[0077] Example

[0078] In this example, the nano-conductive material for preparing the positive piezoresistive effect film 106 and the negative piezoresistive effect film 105 is a one-dimensional conductive nano-material with tensile orientation, which can be selected but not limited to multi-walled carbon nanotubes with a length less than 10 microns. The stretchable polymer for preparing the positive piezoresistive effect film 106 and the negative piezoresistive effect film 105 can be selected but not limited to natural or synthetic low-ammonia latex materials. And the one-dimensional conductive nano-material can be uniformly dispersed in the stretchable polymer, and there should be a high-strength connection between the one-dimensional conductive nano-material and the stretchable polymer, such as but not limited to chemical bonds and / or van der Waals forces. The mass fraction of the conductive nano-material in the positive piezoresistive effect film 106 is 5-9 wt%, and the mass fraction of the conductive nano-material in the negative piezoresistive effect film 105 is 1-2.9 wt%.

[0079] Specifically, the above positive piezoresistive effect film 106 and negative piezoresistive effect film 105 are obtained by the following preparation method:

[0080] First, weigh 40 g of multi-walled carbon nanotube aqueous solution (mass fraction 10 wt%) and 10 g of multi-walled carbon nanotube aqueous solution (mass fraction 10 wt%) into two beakers respectively, and ultrasonicate for 15 minutes under ice bath, with an ultrasonic power of 1200 W. Secondly, weigh two portions of 40 g of low-ammonia natural latex solution into two beakers. Then pour 40 g of multi-walled carbon nanotube aqueous solution into 40 g of low-ammonia natural latex solution to obtain a negative piezoresistive effect mixture; pour 10 g of multi-walled carbon nanotube aqueous solution into 40 g of low-ammonia natural latex solution to obtain a positive piezoresistive effect mixture. Then add an aqueous dispersant with a mass fraction not higher than 1 wt% to the negative piezoresistive effect mixture and the positive piezoresistive effect mixture respectively. Next, place the negative piezoresistive effect mixture and the positive piezoresistive effect mixture in an ice bath, control the environmental temperature not higher than 15 °C, add a magnetic stirring rotor to each of the negative piezoresistive effect mixture and the positive piezoresistive effect mixture, and stir rapidly at a speed of 1200-1800 rpm. The magnetic stirring time of the negative piezoresistive effect mixture is 6 hours, and the magnetic stirring time of the positive piezoresistive effect mixture is 9 hours. After that, use a syringe to suck the negative piezoresistive effect mixture and the positive piezoresistive effect mixture respectively, and drop them into the groove with a size of 2 cm×1 cm×0.4 cm (length×width×depth) on a polytetrafluoroethylene mold. Then place it in an oven at 85 °C for curing, and the curing time is 15 hours. Finally, release the cured positive piezoresistive effect film 106 and negative piezoresistive effect film 105 from the mold.

[0081] Use silver / silver chloride conductive wire with a resistivity of 2 Ω·cm as the electrode material for the strain detection electrode pair, the conductive fabric row electrode array and the conductive fabric column electrode array. The silver / silver chloride conductive wire is usedFigure 2 For the all-woven lead process shown in (A), the strain detection electrode pair 102 is sewn, and then the negative effect electrode pair 107 and the positive effect electrode pair 108 are insulated using a flexible self-adhesive polyurethane film. Next, the negative piezoresistive effect film 105 with the sewn negative effect electrode pair 107 and the positive piezoresistive effect film 106 with the sewn positive effect electrode pair 108 are assembled along the maximum cross-section using glue.

[0082] According to Figure 5 Connect the flexible pressure sensor array and the backend circuit. Referring to Figure 4 shown, for the flexible pressure sensor array under different strain interferences, the relationship curve between its output voltage and the applied force changes. Specifically, curves A, B, C, D, E, F, and G are the relationship curves between the output voltage and the applied force under no strain interference, 5% strain, 10% strain, 15% strain, 20% strain, 25% strain, and 30% strain interferences respectively. It can be seen that when under different degrees of strain interference, compared with the output voltage under no strain interference, the performance of its output range decays significantly. Therefore, strain interference suppression for the flexible pressure sensor array is required.

[0083] Application Example

[0084] In this application example, the flexible pressure sensor system is integrated into a high-density tactile glove with strain interference suppression ability.

[0085] Referring to Figure 7 shown, the flexible pressure sensor array is connected to the backend circuit through the finger area flexible adapter board 701, the palm area flexible adapter board 702, and the general adapter board 703. Ordinary sewing thread passes through the fixing holes 704 to fix the flexible adapter board and the glove base together. The conductive woven wire is fixed on the pad 705 and is electrically connected to the row electrode 706 or the column electrode 707. The ordinary electrode wire 708 is a metal wire on the flexible adapter board.

[0086] Figure 8 It is a cross-sectional view and encapsulation method of the flexible adapter board with the pad 705. As Figure 8 shown, the flexible base layer 801 is a base made of three layers of polyimide material, on which there are pad metal through-holes 802, and the surface of the pad metal through-holes is exposed. The single conductive woven wire 803 first passes through the pad metal through-hole 802 and is fixed on its upper surface by tying a knot. Then, a low-temperature quick-drying conductive silver paste is used to evenly and completely wrap the fixing knot of the conductive woven wire 803 on the pad metal through-hole 802 to form a silver paste fixing layer 804, so as to form a reliable electrical connection with the metal pad surface. Finally, a quick-drying ultraviolet curing glue is used to completely wrap the silver paste fixing layer 804 again to form an ultraviolet glue fixing layer 805, so as to form a reliable connection with the flexible base layer 801.

[0087] Referring toFigure 9 As shown, multiple assembled composite films 101 are arranged on the thumb pressure detection area 901, index finger pressure detection area 902, middle finger pressure detection area 903, ring finger pressure detection area 904, little finger pressure detection area 905, and palm pressure detection area 906 of the high-density tactile glove by sharing row electrodes or column electrodes. Among them, there are two assembled composite films 101 on the thumb pressure detection area 901, three assembled composite films 101 on each of the index finger pressure detection area 902, middle finger pressure detection area 903, ring finger pressure detection area 904, and little finger pressure detection area 905, and a total of twenty-four assembled composite films 101 arranged in four rows and six columns on the palm pressure detection area 906.

[0088] Refer to Figure 10 As shown, the high-density tactile glove has the following structure: The composite film 1001 is an assembled structure formed by a positive piezoresistive effect film 106 and a negative piezoresistive effect film 105. Multiple composite films 1001 are arranged on the palm side of the glove base 1002 according to the Figure 9 rule shown, fixed by non-conductive sewing threads. The multi-channel acquisition circuit 1004 is arranged on the back side of the glove base 1002. The bracelet 1006 is wound around the lower part of the glove base 1002. The processing circuit 1005 is fixed at the middle position on the side of the bracelet 1006 facing the back of the hand; The flexible adapter board includes three types: finger area flexible adapter board 701, palm area flexible adapter board 702, and general adapter board 703. As shown in Figure 10 The first adapter board 1003 corresponds to the palm area flexible adapter board 702, and the second flexible adapter board 1003' corresponds to the finger area flexible adapter board 701. Among them, the five finger area flexible adapter boards 701 connect the thumb pressure detection area 901, index finger pressure detection area 902, middle finger pressure detection area 903, ring finger pressure detection area 904, and little finger pressure detection area 905 to the multi-channel acquisition circuit 1004 respectively; The palm area flexible adapter board 702 connects the column electrode array of the palm pressure detection area 906 to the processing circuit 1005, and the general adapter board 703 connects the multi-channel acquisition circuit 1004 and the processing circuit 1005.

[0089] When the flexible pressure sensor system is integrated into the high-density tactile glove, the signal flow is as shown in Figure 11As shown, on the one hand, the central processing unit controls the line scanning module to scan each row of the row electrode array of the conductive fabric in the tactile glove row by row. When a certain row electrode is selected, that row is grounded, and the remaining unselected row electrodes are all kept connected to the reference voltage. The voltage signals of the sensing units on each column electrode cross-connected to the selected row electrode are led out through the pressure sensor input module, amplified by the voltage signal amplification module, and then transmitted to the input ends of multiple analog-to-digital conversion chips (ADC modules). Then, the ADC modules transmit the converted digital voltage signals to the central processing unit through the SPI communication mode. The central processing unit then packs the received multiple pressure sensing data through the wired or wireless data transmission module and sends it to the host computer module. After decoding by the host computer module, the data will finally correspond one by one to its position on the tactile glove. Without strain interference, the high-density estimated force on the tactile glove will be directly presented on the tactile glove in the virtual reality interface. The power supply module supplies power to the central processing unit, the multi-channel acquisition circuit, and the strain interference detection circuit; on the other hand, the strain interference detection circuit judges whether the strain detection unit is affected by strain interference. If it is affected by strain interference, the central processing unit sends an alarm signal to the host computer module through the data transmission module, and then calibrates the multiple pressure sensing data received by the host computer through the calibration module, so as to realize the suppression of strain interference.

[0090] Referring to Figure 12 shown, the wired data transmission protocol in this application example is that each frame of voltage data transmitted consists of four parts combined:

[0091] (1) Start bit: Occupies two bytes, and the content is a number represented in hexadecimal that does not repeat the data to be transmitted, which can be, but is not limited to, 0xFFFF;

[0092] (2) Data length bit: Occupies two bytes, and the unit of data length is bytes, represented in hexadecimal; for example, in this embodiment, there are 24 rows multiplied by 48 columns, a total of 1152 data to be transmitted, and each data occupies two bytes, so the number of bytes to be transmitted is 2304. 2304 is represented in hexadecimal as 0x0900, so the content of this data length bit is 0x0900;

[0093] (3) Data to be transmitted: In this embodiment, there are a total of 1152 collected voltage data to be transmitted;

[0094] (4) Check bit: Occupies two bytes. In this embodiment, the check bit is obtained by performing an exclusive OR operation on the start bit 0xFFFF, the data length bit 0x0900, and each data to be transmitted one by one;

[0095] Voltage data is sent frame by frame to the host computer. The host computer detects the start bit and verifies the check bit, and cuts the received data to obtain each frame of pressure sensing data. Setting the check bit can determine the integrity and correctness of the data transmission process by confirming whether the check bit is the same as the check bit before data transmission after the host computer receives a frame of data and decodes it. Figure 13 This is an example method for calibrating the relationship curve (denoted as the mechanical output response curve) between the output voltage of the pressure sensing unit and the applied load force when the flexible pressure sensor is subjected to a strain interference σ less than 10%. Since it is impossible to enumerate all the relationship curves between the output voltage and the applied load force under different strain interferences, the calibration unit of the host computer will first find the closest existing ones, that is, the mechanical output response curve B under 10% strain interference and the mechanical output response curve A under no strain interference. According to the difference between σ x and 0% and 10% respectively, interpolation fitting is performed between the mechanical output response curve B and the mechanical output response curve A to obtain the mechanical output response curve C under the strain interference σ x which is the calibrated mechanical output response curve. Based on this calibrated curve, the accurate force at this time is calculated. Through the above calibration, the deviation between the mechanical estimated value and the true value of the flexible pressure sensor caused by strain interference can be eliminated, thus improving the mechanical perception accuracy of the tactile glove when interacting with flexible objects. x Figure

[0096] Figure 14 shows the relationship diagram between the force estimation value and the true force of the flexible pressure sensor system on the tactile glove after being subjected to 30% strain interference, 25% strain interference, 20% strain interference, 15% strain interference, 10% strain interference, 5% strain interference and calibration strain interference respectively. It can be seen that after calibration, the error between the force estimation value and the true force decreases.

[0097] In the above embodiments of the present invention, when the assembled composite film is subjected to strain interference, the positive-effect electrode pair and the negative-effect electrode pair can collect two relative resistance change rates with the same amplitude and opposite change trends, so as to achieve addition and cancellation, that is, the positive and negative piezoresistive cancellation effect; each layer of the film of the assembled composite film is respectively connected to two input ends of the strain interference detection circuit unit. Then, once strain interference occurs, the total output voltage of the strain interference detection circuit unit will generate a rising-edge signal. By detecting the rising-edge signal, it can be determined whether strain interference exists. Then, the magnitude of the strain interference suffered at this time is deduced from the relative resistance change rate of the negative piezoresistive effect film, and the calibration module is enabled to correct the output mechanical response curve of the flexible pressure sensor array at this time. According to the corrected curve, the force value is estimated, and the error between the estimated force value and the true force can be reduced. The flexible pressure sensor array has the functions of automatically, continuously and quantitatively monitoring strain interference, and can calibrate the mechanical output response of the sensor under strain interference, thereby improving the accuracy of mechanical estimation.

[0098] The flexible pressure sensor array provided by the above embodiments of the present invention has the characteristics of anti-strain interference, wearable, high density, scalable and stable output, and can perform normal force estimation in a variety of flexible, curved and stretching application scenarios, and has important application values in the fields of human-computer interaction, health monitoring and robot touch, etc.

[0099] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various deformations or modifications within the scope of the claims, which do not affect the essence of the present invention. The above preferred features can be used in any combination without conflict.

Claims

1. A flexible pressure sensor system, characterized in that, it includes a flexible pressure sensor array and a backend circuit; The flexible pressure sensor array includes: a plurality of assembled composite films, each of the assembled composite films includes a positive piezoresistive effect film and a negative piezoresistive effect film stacked in sequence from bottom to top, and the assembled composite film has a positive and negative piezoresistance cancellation effect; a positive effect electrode pair, arranged at both ends of the positive piezoresistive effect film, and the positive effect electrode pair collects the resistance change of the positive piezoresistive effect film when it is strained; a negative effect electrode pair, arranged at both ends of the negative piezoresistive effect film, and the negative effect electrode pair collects the resistance change of the negative piezoresistive effect film when it is strained; the assembled composite film, the positive effect electrode pair and the negative effect electrode pair form a strain detection unit; a row electrode array, including a plurality of parallel row electrodes arranged along the length direction of the assembled composite film, and the row electrodes are cross - arranged on the assembled composite film; a column electrode array, including a plurality of parallel column electrodes arranged along the width direction of the assembled composite film, the column electrodes are perpendicular to the row electrodes, and the column electrodes are cross - arranged on the assembled composite film; the row electrodes and the column electrodes form a pressure sensing unit with the assembled composite film, and a plurality of the pressure sensing units constitute a row - column cross - type pressure sensing array; a plurality of the assembled composite films are arranged along the length direction of the row electrode array and / or the column electrode array to constitute a flexible pressure sensor array; the backend circuit is connected to the flexible pressure sensor array, the input ends of the backend circuit are respectively connected to the positive piezoresistive effect film and the negative piezoresistive effect film, and the backend circuit is used to collect the voltage data caused by the strain of the assembled composite film and the voltage data of the flexible pressure sensor array after being stressed, and send the voltage data to the host computer.

2. The flexible pressure sensor system according to claim 1, characterized in that, the positive piezoresistive effect film and the negative piezoresistive effect film have the same size and are both made of the same kind of nano - conductive material and the same kind of stretchable polymer, wherein the content of the nano - conductive material in the positive piezoresistive effect film is lower than that in the negative piezoresistive effect film.

3. The flexible pressure sensor system according to claim 1, characterized in that, the positive effect electrode pair is insulated from the negative piezoresistive effect film, and the negative effect electrode pair is insulated from the positive piezoresistive effect film.

4. The flexible pressure sensor system according to claim 1, characterized in that, the positive effect electrode pair is connected to both ends of the positive piezoresistive effect film based on a full - woven lead process, and the negative effect electrode pair is connected to both ends of the negative piezoresistive effect film based on a full - woven lead process.

5. The flexible pressure sensor system according to claim 1, characterized in that, the row electrodes are made of conductive fabric, and the row electrodes are cross - sewn on the assembled composite film in a flat - stitch method based on a full - woven lead process.

6. The flexible pressure sensor system according to claim 1, characterized in that, The column electrodes are made of conductive fabric, and the column electrodes are cross-sewn on the assembled composite film by flat stitching based on the full-woven lead process.

7. The flexible pressure sensor system according to claim 1, wherein, the backend circuit includes: a multi-channel acquisition circuit, including a row scanning control module, a plurality of voltage signal amplification modules with adjustable gains, and a plurality of analog-to-digital conversion chips. The row scanning control module collects the resistance values of the assembled composite film at the intersections of different columns and the scanned row by row scanning. The voltage signal amplification module and the analog-to-digital conversion chip convert the resistance values into voltage data; a strain interference detection circuit for monitoring the strain resistance values of the positive piezoresistive effect film and the negative piezoresistive effect film in the strain detection unit; a processing circuit that packs and uniformly sends the collected voltage data of the flexible pressure sensor array to the host computer through a wired data transmission protocol.

8. A strain interference detection method for the flexible pressure sensor system according to any one of claims 1-7, wherein, it includes: monitoring the strain detection unit through the strain interference detection circuit unit to obtain the real-time output voltage signal of the strain interference detection circuit unit; judging whether there is a rising edge and a warning signal in the output voltage signal of the strain interference detection circuit unit according to the real-time output voltage signal to realize the detection of strain interference.

9. A strain interference calibration method for the flexible pressure sensor system according to any one of claims 1-7, wherein, it includes: when the flexible pressure sensor system is subjected to strain interference, determining the magnitude of the strain interference received by the flexible pressure sensor system according to the relative resistance change of the negative effect electrode pairs on the negative piezoresistive effect film; calibrating the output voltage vs. force relationship curve of the flexible pressure sensor array under strain interference to obtain the mechanical output response curve under strain interference; determining the estimated force value after calibration through voltage according to the mechanical output response curve.

Images