Flexible strain sensor for hand posture monitoring and its preparation method and application

Abstract

The present invention belongs to the technical field of flexible strain sensors, and specifically relates to a preparation method and application of a flexible strain sensor for hand posture monitoring. MWNTs are attached to the surface of AgNFs silver nanoflowers. The ultra-high conductivity of AgNFs increases the sensitivity of the conductive film. MWNTs can connect each AgNF under large stretching to ensure the connectivity of the conductive network on the conductive film. AgNFs / MWNTs are deposited on the surface of PDMS by spraying to produce a flexible strain sensor with a sandwich structure. The flexible strain sensor is applied to a portable data acquisition system. The present invention realizes online precise monitoring of human motion signals and physiological signals and realizes human-computer interaction. A flexible pressure sensor based on a puncture microstructure and a strain sensor based on a sandwich structure are designed. In view of the needs of portability and wearability, a wearable intelligent detection system is built to realize human-computer interaction and online detection of health signals.

Description

Technical Field

[0001] The present invention belongs to the technical field of flexible strain sensors, and in particular relates to a flexible strain sensor for hand posture monitoring and a preparation method and application thereof. Background Art

[0002] As the core component of wearable electronic devices, flexible sensors have attracted more and more attention. The flexible and changeable shape of flexible sensors breaks the limitations of traditional sensors, and the ability to synchronize movement with objects such as the human body and equipment is becoming a hot research direction. Traditional strain electronic sensors are mostly limited by materials and have a rigid substrate. Their flexibility and sensitivity are difficult to break through and it is difficult to meet the requirements of wearability. Flexible multifunctional wearable sensors overcome the shortcomings of rigidity and brittleness, and have obvious advantages in flexibility, stretchability, and wearability.

[0003] At present, some high-performance and stable flexible sensors have been developed, and have made certain progress in sensitivity, detection limit, self-power supply, etc., but they still face huge challenges in practical application. Specifically: flexible sensors need to adapt to complex and harsh environments, be small, multifunctional, low power, biocompatible and dynamically tolerant, the equipment must be bendable and stretchable, there is no feeling when worn on the body or arm, and it can present data about human body information.

[0004] Flexible sensors have many practical and potential applications, mainly focusing on health monitoring, human motion detection, human-computer interaction and electronic skin. They can be connected to clothing or the surface of human skin to measure human strain, and through wireless transmission technology, combined with mobile terminals, a unified cloud service is established to achieve real-time data transmission, analysis and feedback. In addition, after broadening the functions of wearable sensors, they have broad application prospects in health monitoring, drug release, prosthesis technology and other aspects in the medical field. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a preparation method and application of a flexible strain sensor for hand posture monitoring, so as to realize online precise monitoring of human motion signals and physiological signals and realize human-computer interaction. The present invention selects PDMS as a flexible substrate, prepares AgNFs / MWNTs as conductive films, designs a flexible pressure sensor based on a puncture microstructure and a strain sensor based on a sandwich structure, and builds a wearable intelligent detection system to realize human-computer interaction and online detection of health signals in response to the needs of portability and wearability.

[0006] In order to achieve the above objectives, the present invention adopts the following technical solution: a conductive film, MWNTs are attached to the surface of AgNFs silver nanoflowers, the ultra-high conductivity of AgNFs increases the sensitivity of the conductive film, and MWNTs can connect each AgNF under large stretching to ensure the connectivity of the conductive network on the conductive film.

[0007] The present invention also includes a method for preparing the conductive film, the preparation steps comprising:

[0008] (1) Mixing and stirring the AgNO3 solution and the diamine hydrogen citrate solution in a water bath to obtain a white precipitate;

[0009] (2) adding aqueous ammonia dropwise into the mixed solution until the solution becomes colorless;

[0010] (3) adding the boric acid solution into the colorless solution and stirring to maintain the pH value of the mixed solution;

[0011] (4) adding L-ascorbic acid solution to promote the spontaneous anisotropic growth of AgNFs, and the colorless solution turns brown. After heating and stirring in a water bath, the AgNFs solution is prepared. The prepared AgNFs solution is washed and dried to obtain silver nanoflower particles.

[0012] (5) mixing silver nanoflower particles with a multi-walled carbon nanotube solution and subjecting the mixture to ultrasonic vibration to obtain a AgNFs / MWNTs composite sensing material;

[0013] (6) Spraying the AgNFs / MWNTs composite sensing material onto the substrate surface and obtaining a conductive film after drying.

[0014] Furthermore, in the step (5), the concentration of the multi-walled carbon nanotube solution is 4 mg / mL, and the mass ratio of the silver nanoflowers to the multi-walled carbon nanotubes is 1:1.

[0015] The present invention also includes a flexible strain sensor, which is manufactured by depositing AgNFs / MWNTs on the surface of PDMS by a spraying method to obtain a flexible strain sensor with a sandwich structure.

[0016] Furthermore, the sensing principle of the sensor is:

[0017] The strain sensor belongs to the adsorption type strain sensor. The sensing material is adsorbed on the surface of PDMS. When the sensor is stretched, cracks appear in the sensing layer, causing the resistance to increase. When the stretching is restored, the cracks disappear and the resistance of the strain sensor returns to its original state.

[0018] The MWNTs attached to the surface of AgNFs play a good connecting role. Under the state of small strain, the small separation between AgNFs will cause a significant change in the resistance of the sensing layer, resulting in the strain sensor based on AgNFs / MWNTs to maintain high sensitivity under small strain. Under large strain, AgNFs will be completely separated from each other, but MWNTs act as a bridge to connect each AgNF to ensure the passage of the sensing layer, greatly extending the sensing range of the strain sensor; AgNFs / MWNTs composite material as a sensing layer film can ensure that the strain sensor has excellent sensitivity and a large strain range.

[0019] The present invention also includes a method for preparing a flexible strain sensor, the preparation steps comprising:

[0020] (1) Mix reagent A and reagent B of PDMS in a ratio of 1:1 and place them in a vacuum hood for 30 min to remove bubbles;

[0021] (2) The mixed reagents were evenly coated on a smooth wooden board with polyimide tape and placed in a vacuum hood;

[0022] (3) After the bubbles inside the PDMS are completely dissipated and evenly and smoothly distributed on the surface of the wooden board, the wooden board coated with PDMS is placed in an oven for heating and curing to obtain a PDMS film;

[0023] (4) The AgNFs / MWNTs composite sensing material was sprayed on the surface of the PDMS film by a spray brush, and the spraying was performed 10 times to form a conductive film;

[0024] (5) removing the polyimide tape and the wooden board and cutting to obtain a PMDS film covered with a conductive film;

[0025] (6) Attaching the conductive copper foil to both ends of the conductive film and leading them out;

[0026] (7) A layer of liquid PDMS reagent is further covered on the PDMS surface with the conductive film and placed in an oven for curing to obtain a flexible strain sensor with a sandwich structure.

[0027] The present invention also includes an application of a flexible strain sensor,

[0028] The flexible strain sensor is applied to a portable data acquisition system.

[0029] The data acquisition system also includes a signal conditioning circuit, an STM32 processor, a wireless communication module, a power module, an alarm circuit, a key circuit and a protection circuit.

[0030] Furthermore,

[0031] The data acquisition system is used for human health monitoring, detecting blinking, swallowing, voice recognition, breathing and joint bending signals;

[0032] Alternatively, the data acquisition system is used to be applied to smart wearable gloves to realize human-computer interaction function with a Labview host computer, and the smart wearable gloves can monitor the bending state and bending amplitude of the fingers in real time.

[0033] Furthermore,

[0034] The sensor converts external tactile pressure and bending strain into a resistance signal, which is then converted into a voltage signal through a signal conditioning circuit. The voltage signal is collected by the ADC of the STM32 processor. The received voltage data information is processed in the program. The resistance value of the sensor can be inferred under the condition of a known voltage value through the conversion formula. After further formula conversion, the current response value of the sensor can be obtained, which reflects the stress changes of the sensor in real time. The wireless transmission module transmits the data of the detection system to the host computer.

[0035] Furthermore,

[0036] The smart wearable glove is a device that places five flexible strain sensors on the knuckles of the back of a leather sports glove; an industrial-strength elastomer adhesive is used to bond the sensor to the glove, and a soft, ultra-fine, high-temperature-resistant wire is used to connect the copper foils at both ends of the strain sensor for signal transmission. The outside of the wire is wrapped with an insulating material to ensure that each strain sensor will not be short-circuited. The elastomer adhesive is also used to stick the wire to the surface of the glove to ensure the cleanliness of the surface of the smart glove; finally, the wire connecting each strain device is welded together with a DuPont wire and connected to a customized PCB. The data acquisition circuit board is powered by a mobile power supply, which can realize the portability and mobility of the hardware device. The hardware circuit acquisition system obtains and sends the signal of the flexible device to realize real-time display and human-computer interaction on the upper computer interface.

[0037] The advantages of the preparation method and application of a flexible strain sensor for hand posture monitoring of the present invention are as follows:

[0038] (1) The flexible strain sensor prepared by the present invention is stretchable (100% strain) and highly sensitive (GF=1187.071). The AgNFs / MWNTs strain sensor based on the sandwich structure shows a fast response time (60ms) and a qualified durability of more than 2000 stretching cycles. It can identify strains ranging from tiny deformations to a wide range, such as pulse signals, voice recognition, respiratory monitoring, and joint bending.

[0039] (2) The present invention designs a signal conditioning circuit, an STM32 microprocessor module, a wireless communication module, a power module, an alarm circuit, a button circuit and a protection circuit. The data acquisition board can realize real-time data acquisition, processing and sending. At the same time, the software design of the data acquisition system is introduced, and matching lower computer programs are written for the mobile health monitoring system and the smart glove human-computer interaction system respectively.

[0040] (3) The health monitoring system constructed by the present invention realizes the real-time display of coughing, breathing and joint bending signals on the mobile phone. An intelligent wearable glove is manufactured based on the strain sensor, and the human-computer interaction function is realized with the Labview host computer. The wearable intelligent glove can monitor the bending state and bending amplitude of the fingers in real time. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a preparation process diagram of the AgNFs / MWNTs composite sensing material according to an embodiment of the present invention;

[0042] Figure 2 X-ray diffraction (XRD) patterns of AgNFs, MWNTs and AgNFs / MWNTs (Rigaku D / Max 2500PC) of the embodiments of the present invention.

[0043] Figure 3 a, b are SEM images of AgNFs of the present invention;

[0044] c is a SEM image of MWNTs of an embodiment of the present invention;

[0045] d is the SEM image of AgNFs / MWNTs of the embodiment of the present invention;

[0046] Figure 4 This is a flow chart of the structural design of the flexible strain sensor device according to an embodiment of the present invention;

[0047] Figure 5 a is a schematic diagram of the change of microcracks during the stretching process of the AgNFs / MWNTs strain sensor according to an embodiment of the present invention; b is a schematic diagram of the strain behavior mechanism of the AgNFs / MWNTs film;

[0048] Figure 6 a is a strain-response curve of a sensor device based on a single conductive material and composite materials of different proportions according to an embodiment of the present invention;

[0049] b is Ag2-CNT of the present invention 0.5 Strain response curve of the sensor;

[0050] Figure 7 a is the step response of the strain sensor in the strain range of 0.3% to 5% according to the embodiment of the present invention;

[0051] b is the step response of the strain sensor in the embodiment of the present invention within the strain range of 10% to 80%;

[0052] c is the step response of the strain sensor of the embodiment of the present invention at different stretching speeds;

[0053] d is the resistance response of the strain sensor of the embodiment of the present invention from 0.1 Hz to 1.2 Hz;

[0054] e is the response and recovery time of the embodiment of the present invention;

[0055] f is the resistance response of the strain sensor of the embodiment of the present invention during more than two thousand loading and unloading processes;

[0056] Figure 8 a is a pulse signal recorded by the strain sensor of an embodiment of the present invention;

[0057] b is an enlarged view of a single pulse signal within the dotted frame of embodiment a of the present invention;

[0058] c is the response curve recorded when “silver”, “carbon” and “sensor” are said respectively in the embodiment of the present invention;

[0059] de is the relative resistance response of the sensor of the embodiment of the present invention when detecting human swallowing and blinking;

[0060] f is the breathing state before and after exercise in the embodiment of the present invention;

[0061] Fig. 9 ad is the relative resistance response of the finger, wrist, elbow and knee of the sensor of the embodiment of the present invention when detecting the bending of human joints;

[0062] Fig.10 a is a schematic diagram of a flexible interdigitated electrode array according to an embodiment of the present invention;

[0063] b is a PCB of a flexible interdigital electrode array according to an embodiment of the present invention;

[0064] c is a steel mesh of an interdigitated electrode array according to an embodiment of the present invention;

[0065] Fig.11 a is a 4×4 array pressure sensor of an embodiment of the present invention connected to the skin;

[0066] b is a photo of the PDMS membrane on top of the sensor array of an embodiment of the present invention;

[0067] c is a photo and schematic diagram of the bottom panel of the sensor array according to an embodiment of the present invention;

[0068] df is the resistance response of the sensor array when the letter weights "T", "4" and "U" are applied according to the embodiment of the present invention;

[0069] Fig.12 The overall structure diagram of the system of the embodiment of the present invention;

[0070] Fig.13 This is a resistance-to-voltage circuit diagram of an embodiment of the present invention;

[0071] Fig.14 A voltage source low-pass filter according to an embodiment of the present invention;

[0072] Fig.15 It is a schematic diagram of an integrated resistance-to-voltage circuit and a filter circuit on a data acquisition board according to an embodiment of the present invention;

[0073] Fig.16 This is a circuit diagram of a power module according to an embodiment of the present invention;

[0074] Fig.17 This is a schematic diagram of the minimum system of a single-chip microcomputer according to an embodiment of the present invention;

[0075] Fig.18 This is a SWD interface circuit diagram of an embodiment of the present invention;

[0076] Fig.19 The key circuit principle diagram and LED light alarm circuit of the embodiment of the present invention;

[0077] Fig. 20 This is a schematic diagram of a protection circuit according to an embodiment of the present invention;

[0078] Fig.21 a is the ESP8266-01 module of the embodiment of the present invention;

[0079] b is a Wifi interface circuit according to an embodiment of the present invention;

[0080] c is the HC-05 module of the embodiment of the present invention;

[0081] d is a Bluetooth interface circuit according to an embodiment of the present invention;

[0082] Fig. 22 The PCB design diagram of the data acquisition board according to the embodiment of the present invention;

[0083] Fig.23 This is a flowchart of the lower computer program of the mobile terminal health monitoring system according to an embodiment of the present invention;

[0084] Fig.24 This is a physical picture of the PCB of the mobile health monitoring system according to an embodiment of the present invention;

[0085] Fig.25 The health monitoring system APP display interface of the embodiment of the present invention;

[0086] Fig.26 a is a respiratory monitoring in an embodiment of the present invention;

[0087] b is the cough monitoring of the embodiment of the present invention;

[0088] c is the finger bending monitoring in the embodiment of the present invention;

[0089] Fig. 27 The smart glove system according to an embodiment of the present invention;

[0090] Fig.28 Design of serial communication, sampling rate and sampling time software for the embodiments of the present invention;

[0091] Fig.29 Identification and data verification of the string frame header of the embodiment of the present invention;

[0092] Fig.30 It is the data curve display and storage function of the embodiment of the present invention;

[0093] Fig.31 The front panel design of the finger bending response curve interface of the embodiment of the present invention;

[0094] Fig.32 A three-dimensional manipulator model according to an embodiment of the present invention;

[0095] Fig.33 Design of the main function program of the manipulator model according to the embodiment of the present invention;

[0096] Fig.34 It is the human-machine interaction interface of the robot according to the embodiment of the present invention;

[0097] Fig.35 a is a schematic diagram of a wearable gesture recognition device system according to an embodiment of the present invention;

[0098] b is a wearable smart glove device according to an embodiment of the present invention;

[0099] c is the monitoring of the resistance response changes of the five strain sensors of the smart glove according to the embodiment of the present invention;

[0100] d is a human-computer interaction interface for gesture recognition according to an embodiment of the present invention. DETAILED DESCRIPTION

[0101] The specific implementation manner will be further described below in conjunction with the accompanying drawings.

[0102] Embodiment 1:

[0103] A conductive film, silver nanoflowers (AgNFs) were prepared by water heating method, and AgNFs / MWNTs composite nanomaterials were prepared by mixing with MWNTs in different proportions. AgNFs have a large specific surface area, which allows MWNTs to adhere well to its surface, and the ultra-high conductivity allows the conductive film to have ultra-high sensitivity under low strain, while MWNTs can connect each AgNF under large stretching to ensure the connectivity of the conductive network, thereby extending the sensing range of the conductive film.

[0104] A method for preparing a conductive film,

[0105] First, 50 mL AgNO3 (0.3 M) solution and 50 mL diamine hydrogen citrate (0.15 M) solution were mixed and stirred in a 50 ° C water bath for 2-3 minutes. The white precipitate can be clearly seen. Then, ammonia water (14.8 M) was added dropwise to the mixed solution using a rubber-tipped dropper until the solution became colorless. The third step was to add the prepared boric acid solution (50 mL, 0.5 M) to the colorless solution and stir to maintain the pH of the mixed solution. Finally, L-ascorbic acid solution (50 mL, 0.3 M) was added as a reducing agent to promote the spontaneous anisotropic growth of AgNFs, and the colorless solution turned brown. After 15 minutes of water bath heating and stirring, the AgNFs solution was prepared. The prepared AgNFs solution was washed and dried to obtain silver nanoflower particles. Finally, 20 mg of silver nanoflowers were mixed with 5 mL of multi-walled carbon nanotube solution (4 mg / mL) and ultrasonically vibrated to obtain AgNFs / MWNTs composite sensing material. The AgNFs / MWNTs composite sensing material is sprayed on the surface of the substrate and a conductive film is obtained after drying. Figure 1 This is the preparation process diagram of AgNFs / MWNTs composite sensing material.

[0106] Conductive film characterization analysis:

[0107] The microstructure of AgNFs / MWNTs nanocomposite films was analyzed using SEM and XRD characterization methods.

[0108] Figure 2 X-ray diffraction (XRD) patterns of AgNFs, MWNTs and AgNFs / MWNTs (Rigaku D / Max 2500PC).

[0109] The main diffraction peaks of AgNFs are at 38.1°, 44.09°, 64.36°, 77.29° and 81.31°, which are attributed to the (111), (200), (220), (311) and (222) crystal planes of Ag. The diffraction peaks of MWNTs at 28° and 47° are attributed to the (002) and (100) crystal planes of MWNTs (JCPDS card number 29-0914). The XRD of AgNFs / MWNTs composite film shows the characteristic peaks of AgNFs, and also shows a small broad peak at 28°. This indicates that the composite film contains MWNTs. The diffraction peak at 47° generated by MWNTs is masked by the diffraction peak of AgNFs at 44.09°, which results in only one peak of MWNTs being shown in the composite material.

[0110] The surface morphology of the sensing materials was characterized by scanning electron microscopy.

[0111] Figure 3 a and b are SEM images of AgNFs; c is the SEM image of MWNTs; d is the SEM image of AgNFs / MWNTs.

[0112] like Figure 3 As shown in a and b, AgNFs have a flower-like structure and a large surface area, and their diameters range from 200 to 400 nm. Figure 3 c shows the morphology of carbon nanotubes with a mesh structure. The composite material makes up for the shortcomings of the small sensing range of single AgNFs and the low sensitivity of single MWNTs, while maintaining the advantages of each material. AgNFs enhance the conductivity of the sensing layer, thereby improving the sensitivity, and MWNTs ensure that the sensor device will not undergo irreversible deformation under large strain, thereby expanding the sensing range of the strain sensor.

[0113] The present invention designs a simple, time-saving, cost-effective and scalable method based on spray coating to prepare stretchable (100% strain) and highly sensitive (GF=1187.071) flexible strain sensors. The microstructure and elemental composition of AgNFs and MWNTs were studied by XRD and SEM characterization techniques.

[0114] Embodiment 2:

[0115] A flexible strain sensor is prepared by depositing AgNFs / MWNTs on a PDMS surface by a spraying method to obtain a flexible strain sensor with a sandwich structure.

[0116] A method for preparing a flexible strain sensor, wherein reagent A and reagent B of PDMS are uniformly mixed in a ratio of 1:1 and placed in a vacuum hood for 30 minutes to remove bubbles. Then the mixed reagent is uniformly coated on a smooth wooden board with a polyimide (PI) tape and the board is also placed in a vacuum hood. After the bubbles inside the PDMS are completely dissipated and evenly and smoothly distributed on the surface of the wooden board, the wooden board coated with PDMS is placed in an oven and heated at 80°C for 30 minutes to cure, and finally a PDMS film with a thickness of about 200 microns is obtained. The wooden board, the PDMS film and the PI tape with rectangular holes are closely stacked together, and then the AgNFs / MWNTs solution is sprayed on its surface by a spray brush, and the spraying distance is always kept unchanged during the spraying process, and the spraying time is kept the same each time, and a total of 10 sprayings are performed to form a conductive film. The PI tape and the wooden board are removed and cut to obtain a PMDS film (3 cm long and 1.2 cm wide) covered with a conductive sensing material, wherein the size of the coated conductive material is 2 cm long and 0.9 cm wide. In the third step, conductive copper foil is attached to both ends of the conductive nanopattern and led out. Finally, a layer of liquid PDMS reagent is continued to be covered on the prepared PDMS surface with conductive rectangular patterns and placed in an oven to cure at 80°C for 30 minutes to obtain a flexible strain sensor device with a sandwich structure. Figure 4 Structural design flow chart for flexible strain sensor devices.

[0117] The sandwich packaging method allows the sensing conductive film and sensing electrodes to be encapsulated inside the flexible PDMS. During the stretching process, the resistance change of the sensing layer will not be disturbed by the external environment, such as humidity, thus ensuring that the strain sensor has excellent stability.

[0118] The sensing principle of the sandwich structure AgNFs / MWNTs flexible strain sensor is:

[0119] AgNFs / MWNTs strain sensor is an adsorption strain sensor, and the sensing material is adsorbed on the surface of PDMS. Figure 5 a is a schematic diagram of the change of microcracks in the AgNFs / MWNTs strain sensor during stretching; b is a schematic diagram of the strain behavior mechanism of the AgNFs / MWNTs film; Figure 5 As shown in a, macroscopically, when the sensor device is stretched, cracks appear in the sensing layer, causing an increase in resistance. When the stretching is restored, the cracks disappear and the resistance of the strain sensor returns to its original state. Figure 5b shows the structural changes of the strain sensor at the microscopic level under tension. The MWNTs attached to the surface of AgNFs play a good connecting role. Under small strain conditions, a small separation between AgNFs causes a significant change in the resistance of the sensing layer, which results in the strain sensor based on AgNFs / MWNTs to maintain high sensitivity under small strains. Under larger strains, the AgNFs will be completely separated from each other, but the MWNTs act as a bridge to connect each AgNF to ensure the passage of the sensing layer, which greatly extends the sensing range of the strain sensor. Therefore, choosing a suitable mixing ratio of AgNFs / MWNTs composite materials as the sensing layer film can ensure that the strain sensor has excellent sensitivity and a large strain range.

[0120] Comparison of sensitivity of sandwich structure AgNFs / MWNTs flexible strain sensors:

[0121] According to the method of expressing the sensitivity of the pressure sensor, the sensitivity of the strain sensor can be evaluated by the gauge factor, which is referred to as GF. GF is defined as:

[0122]

[0123] where R0 is the resistance in the initial state, R is the resistance in the stretched state, and ε is the mechanical strain applied to the sensor.

[0124] In order to prove that composite materials have more advantages than single materials, sensors based on AgNFs, MWNTs and AgNFs / MWNTs were developed. The concentration of AgNFs solution in the experiment was 30 mg / mL. The strain sensor prepared by diluting 1g MWNTs solution (MWNTs 2wt%) into 5mL solution as a conductive material is marked as CNT1. Take 2mL of AgNFs solution (30mg / mL) and mix it with 1g, 0.5g and 0.2g of MWNTs solution (MWNTs 2wt%) respectively and dilute it into 5mL solution to prepare a composite sensing layer material. The strain sensors prepared based on the above composite materials are named Ag2-CNT1, Ag2-CNT 0.5 , Ag2-CNT2. The strain sensor prepared by diluting 2 mL AgNFs solution (30 mg / mL) into 5 mL solution as the conductive material is marked as Ag2. All sensors were sprayed 10 times during the fabrication process. Figure 6 a is the strain-response curve of the sensor device based on a single conductive material and a composite material with different proportions. The response value is defined as:

[0125]

[0126] It can be found that the strain sensor based on pure AgNFs has the highest sensitivity, which is much higher than the strain sensor device based on pure MWNTs. Although the introduction of AgNFs ensures that the sensing material has extremely high conductivity and sensitivity, the sensing material breaks significantly when the strain is only higher than 25%, which makes the strain sensor unable to detect large strains. In order to ensure that the strain sensor can meet the requirements of human motion monitoring, MWNTs and AgNFs are compounded to increase the sensing range of the strain sensor. Figure 6 It can be seen from a that the addition of MWNTs significantly increases the sensing range of the strain sensor. After comparing five different sensor devices, Ag2-CNT was selected. 0.5 The device of this model is used for subsequent tests because this model of strain sensor device has both high sensitivity and a large detection range, which can fully meet the detection of physiological signals and large strain body movement signals. Figure 6 b is Ag2-CNT 0.5 The strain response curve of the sensor is divided into three linear regions. The GF value reaches 43.406 at relatively low strain, 126.863 in the second linear range, and 1187.071 when the strain is greater than 80%, which is significantly better than most flexible strain sensors.

[0127] Dynamic performance test of sandwich structure AgNFs / MWNTs flexible strain sensor:

[0128] In order to verify whether the sandwich structure AgNFs / MWNTs strain sensor can be used in the field of human motion detection in a long-term and stable manner, it is necessary to test the dynamic performance of the sensor device, such as response time, hysteresis characteristics, and repeatability. 0.5 The response and recovery time, repeatability, stretching at different speeds, stretching at different frequencies, and long-term stability of the strain sensor were tested.

[0129] AgNFs / MWNTs-based strain sensors can maintain excellent repeatability in the range from small to large strains. Figure 7 a is the step response of the strain sensor in the strain range of 0.3% to 5%; b is the step response of the strain sensor in the strain range of 10% to 80%; c is the step response of the strain sensor at different stretching speeds; d is the resistance response of the strain sensor from 0.1Hz to 1.2Hz; e is the response and recovery time; f is the resistance response of the strain sensor during more than two thousand loading and unloading processes.

[0130] Figure 7a and b show that when stretched to a maximum strain of 0.3%, 0.6%, 1%, 5%, 10%, 20%, 50%, and 80%, the relative resistance changes are 0.036, 0.096, 0.229, 0.652, 2.327, 6.120, 28.58, and 121.946, respectively. These peak signals show obvious changes under different strains, which is consistent with Figure 7 The fitted curve in b is in good agreement. Figure 7 c shows the relative resistance change curves obtained by stretching the strain sensor at 10mm / min, 20mm / min, 40mm / min, and 80mm / min in the same time. The sensor device remains stable and has good repeatability under different stretching speeds, which shows that the strain sensor can adapt to fast and slow strain changes in practical applications. Figure 7 d shows Ag2-CNT 0.5 The output signals of the strain sensor at different frequencies show that the response signal of the strain sensor maintains regular periodic changes in the frequency range of 0.1 Hz to 1.2 Hz.

[0131] Figure 7 e shows the response and recovery time of the strain sensor tested by a tensile tester, which is 60ms and 75ms respectively, which is significantly better than most reported strain sensors and can well meet the frequency of human motion. To further study the long-term stability of the strain sensor, the Ag2-CNT was repeatedly loaded / unloaded with a 10% strain. 0.5 Relative resistance change of a strain sensor. Figure 7 f shows the real-time response-cycle curve of the sensing device. In two thousand repeated stretching / releasing tests, the change in its response value is almost constant. The resistance value of the strain sensor at the beginning and end of the experimental test has hardly changed, which is due to the close bonding between the sensor material and the PDMS surface and the excellent sandwich structure design.

[0132] Considering that the AgNFs / MWNTs strain sensor has high sensitivity, short response time and ultra-wide sensing range, it is compared with the reported flexible strain sensors in terms of strain range, GF value, response time and other aspects, as shown in Table 1. Its comprehensive performance is very outstanding compared with many current research works listed in Table 1, thus expanding its application range in detecting the full range of human body movements.

[0133] Table 1 Comparison of maximum strain, specification factor and response time of various strain sensors

[0134]

[0135] The sandwich-structured AgNFs / MWNTs strain sensor of the present invention shows a fast response time (60ms) and a qualified durability of more than 2000 stretches. The AgNFs / MWNTs strain sensor can identify strains ranging from small deformations to a wide range, such as pulse signals, voice recognition, respiratory monitoring, and joint bending. A flexible sensing array that can be closely attached to human skin is made by spraying to identify the distribution of pressure.

[0136] Embodiment 3:

[0137] An application of a flexible strain sensor, the flexible strain sensor can be applied to human health signal monitoring.

[0138] Figure 8 The sensor is shown attached to the skin to detect weak signals and physiological signals generated by the body. Strain sensors can be installed on the wrist, face, throat and abdomen to identify small-scale strain.

[0139] Figure 8 a is the pulse signal recorded by the strain sensor. Obviously, the strain sensor is sensitive enough to detect the typical pulse waveform (88 / min), which is expected to help users adjust their exercise intensity. Figure 8 b is an enlarged view of a single pulse signal within the dotted box in a. It can be seen that every beat of the pulse can be clearly captured as a knock wave, a tidal wave, and a diastolic wave, which provides an important reference for human health monitoring.

[0140] In addition to pulse monitoring, strain sensors can also be installed in the throat to detect voice recognition and swallowing status.

[0141] Figure 8 c is the response curve recorded when saying "silver", "carbon" and "sensor" respectively. The strain sensor can identify the complex skin stretching on the throat associated with repeating "Sliver", "Carbon" and "Sensor". Since different words are pronounced differently, the vibration frequency and amplitude caused in the throat are also different, so the detected curve peaks are also different, which can be used to distinguish different words. Therefore, the excellent sound recognition ability of the strain sensor makes the sensor have great potential in voice rehabilitation exercises and human-computer interaction.

[0142] Figure 8 de is the relative resistance response of the sensor when detecting human swallowing and blinking. Each swallowing causes the throat to move, squeezing the strain sensor to generate a pulse, with a pulse response value of up to 300%. In addition, attaching the strain device to the corner of the eye can be used to detect the state of blinking ( Figure 8e). When the eyes are open, the skin at the corners of the eyes is slightly stretched, and the strain sensor deforms with the stretching of the skin, which results in a relative resistance change of about 10%. When the eyes are closed, the strain device also returns to its original state, and multiple blinks can be accurately detected. At present, traffic accidents caused by driver fatigue are common. Therefore, the strain sensor device is expected to be used to monitor the driver's blinking state. When the driver closes his eyes for a long time due to fatigue, the detected signal will be different from the previous signal, thereby triggering the alarm device to remind the driver, which will greatly reduce the frequency of traffic accidents.

[0143] Figure 8 f is the breathing state before and after exercise. The flexible device is attached to the abdomen of the volunteer. Each breath causes the abdomen to float slightly, and the frequency of the floating of the abdomen is different before and after exercise. The strain device attached to the abdomen will change its resistance regularly with the change of breathing frequency. The breathing frequency before and after exercise reached 14 times / min and 26 times / min respectively, which were accurately captured by the strain device.

[0144] Embodiment 4:

[0145] The invention discloses an application of a flexible strain sensor, wherein the flexible strain sensor can be applied to the detection of body motion signals in a wide range.

[0146] The strain sensor greatly improves the strain range due to the presence of MWNTs, so it is fully capable of monitoring a wide range of body movement signals, such as finger bending, wrist bending, elbow and knee bending.

[0147] Fig. 9 ad is the relative resistance response of the sensor when detecting the bending of the fingers, wrists, elbows and knees of the human body.

[0148] Fig. 9 a shows that the strain sensor is used to monitor the bending state of the finger. When the finger is bent, the strain device is stretched and the resistance increases. As the bending angle of the finger gradually increases, the response value of the strain device also increases in a step-by-step manner, which shows that the strain sensor can accurately identify the bending angle of the finger as the finger bends. Therefore, the strain sensor can be integrated into the glove to make a smart glove for real-time monitoring of the joint movement of the finger, which will be specifically applied below.

[0149] Fig. 9 b shows that the strain sensor is installed on the wrist to detect the bending state of the wrist. From a small bend to a large bend of 90 degrees, the resistance of the strain sensor shows a clear step-by-step increase, which helps to clearly distinguish the bending angle of the wrist. At a large bend of 90 degrees, its response value is as high as 700%.

[0150] Fig. 9 The CD shows that the strain sensor device is attached to the knee and elbow to monitor the joint bending. The response curve is smooth and stable, and the bending and recovery states of the joints can be clearly captured. From the response curve, it can be seen that the encapsulated strain sensor shows a fast and smooth response change under each large strain, and the response signal does not show obvious fluctuations, which is suitable for real-time monitoring of walking and running. Therefore, through circuit design, the resistance signal of the strain sensor can be converted into a voltage signal and collected, and then transmitted to the smartphone through the WiFi module to monitor the bending state of the human joints during exercise in real time.

[0151] Embodiment 5:

[0152] Flexible sensor array based on AgNFs / MWNTs,

[0153] A 4×4 sensing array is deposited on the PDMS film by spraying, and the bottom layer uses a flexible PCB with an integrated 4×4 interdigital electrode array. The top layer of the PDMS film deposited with conductive material and the bottom layer of the flexible PCB constitute the entire pressure sensing array, which can be used to measure external stimuli and identify the distribution area of ​​pressure.

[0154] Flexible interdigitated electrode array design:

[0155] The bottom layer of the flexible sensor array is a flexible PCB, and the schematic diagram and PCB wiring of the flexible interdigital electrodes are designed using Altium Designer. Fig.10 a is the schematic diagram of the flexible interdigital electrode array. The design schematic diagram includes 16 interdigital electrode structures and 20 pins. These pins are the lead-out terminals of the 16 interdigital electrode signals and 4 ground terminals (all the ground terminals are already shared inside the PCB). Fig.10 b is a PCB of a flexible interdigital electrode array, the whole board is 75 mm long and 57 mm wide. The material of the flexible interdigital electrode array is polyimide, which has good bending properties and can fit perfectly with the top PDMS film.

[0156] Flexible film array design:

[0157] The entire sensor array is divided into two layers, the top layer is a PDMS film deposited with AgNFs / MWNTs sensing materials, and the bottom layer is a customized flexible PCB board with 16 interdigital electrodes. The top layer of the PDMS film with conductive materials is prepared by spraying. A steel mesh with 16 square holes is customized in advance and a PDMS film with a length and width of 41 mm is prepared. Fig.10c is a steel mesh of an interdigitated electrode array. The steel mesh and the PDMS film are tightly combined and the conductive material is sprayed on the PDMS surface by a spray brush. After removing the steel mesh, a PDMS sensor array with 16 square conductive areas is obtained. The PDMS film covered with conductive material is attached to the flexible PCB board by polyimide tape. During the entire production process, it is necessary to ensure that the upper and lower layers are tightly combined and that there are no bubbles, so as to ensure that the sensor array can achieve stable signal transmission.

[0158] Flexible sensor array testing:

[0159] Flexible sensor arrays are used to measure external stimuli and identify the distribution area of ​​pressure. Fig.11 a is a 4×4 array pressure sensor connected to the skin; b is a photo of the PDMS membrane on the top of the sensor array; c is a photo and schematic diagram of the bottom panel of the sensor array; df are the resistance responses of the sensor array when letter weights "T", "4" and "U" are applied.

[0160] like Fig.11 As shown in a, the flexible sensor array can be attached to the human skin and used as electronic skin. Fig.11 b and c show the top PDMS film and bottom PCB film of the flexible interdigital electrode array. In addition, the pressure sensing array needs to be subjected to pressure testing. In the experiment, the letter weights "U", "T" and "4" are placed on the 4×4 pressure sensing array respectively. The pressure is applied to the sensor through the letter weights placed on the surface of the device, as shown in Figure 2. Fig.11 df. The corresponding electrical signal changes are also recorded in the figure. Different letter weights placed on the pressure sensing array can be accurately identified, which shows that the pressure sensing array has great potential in identifying pressure distribution.

[0161] Embodiment 6:

[0162] Based on the AgNFs / MWNTs flexible strain sensor, a portable data acquisition system was built. The system includes multiple modules such as signal conditioning circuit, STM32 processor module, power module, protection circuit and communication circuit, etc. The acquisition and transmission of sensor signals are realized.

[0163] Based on the developed AgNFs / MWNTs flexible strain sensor, a data acquisition system is built. The entire acquisition system can convert the resistance signal of the sensor into a voltage signal. The voltage signal is collected by ADC, and then the response value change of the sensor can be obtained through program processing.

[0164] The main functions and parameter requirements of the system are as follows:

[0165] (1) The data acquisition board integrates five signal conditioning circuits and can connect five sensor devices at the same time;

[0166] (2) Equipped with 5 ADC acquisition channels, it can simultaneously collect signal changes of five sensor devices and accurately measure the stress changes of each sensor device;

[0167] (3) Design protection circuit to ensure stable operation of acquisition board;

[0168] (4) The lower computer communicates with the mobile phone APP and PC through the ESP8266 wifi module and HC-05 Bluetooth module respectively;

[0169] (5) The power supply is 5V mobile power supply.

[0170] Fig.12 The overall structure diagram of the system is shown in the figure. The data acquisition system consists of flexible sensors, signal conditioning circuits, STM32 processors, wireless communication modules, power modules, alarm circuits, button circuits, and protection circuits. The sensor converts external tactile pressure and bending strain into resistance signals, which are then converted into voltage signals through signal conditioning circuits. The voltage signal is collected by the ADC of STM32. The received voltage data information is processed in the program. The resistance value of the sensor can be inferred under the condition of known voltage value through the conversion formula. After further formula conversion, the current response value of the sensor can be obtained, which can reflect the stress changes of the sensor in real time. The wireless transmission module refers to the device that transmits the data of the detection system to the host computer. The ESP8266-01 module is used to communicate with the mobile terminal, and the HC-05 Bluetooth module and USB to TTL module are used to communicate with the Labview host computer. Two Bluetooth modules are used in the experiment, one is connected to the serial port of the STM32 microcontroller, and the other HC-05 is connected to the PC through the USB to TTL module.

[0171] In the constructed data acquisition system, the STM32 chip is the main controller of the detection system and the core of the entire data acquisition system. The entire process of the detection system is completed under the control of STM32. In addition, STM32 provides external interfaces for other modules. The central processing unit of the STM32 microcontroller can process the collected voltage signals, and then transmit the processed signals to the mobile terminal through wireless transmission for digital / graphic display, or transmit them to the Labview interface on the PC to realize human-computer interaction. In addition, the system can switch the data to be sent by pressing buttons, and can also judge whether the acquisition system is running normally by LED detection lights. The entire acquisition system adopts a modular design, which can make the system design simpler, smaller in size, reduce system consumption, and facilitate packaging and portable carrying.

[0172] Signal conditioning circuit:

[0173] The signal conditioning circuit includes a resistance-to-voltage circuit and a low-pass filter circuit. Because the self-developed sensors selected are all resistance-type sensors, the signal conditioning circuit mainly has two functions: one is to convert the sensor resistance signal into a voltage signal that is easier to collect, and the other is to filter the collected voltage signal to reduce high-frequency interference.

[0174] The resistance of the sensor will change with the change of pressure and strain. There is a certain relationship between the resistance of the sensor and the stress. The magnitude of the force applied to the sensor can be inverted from the resistance of the sensor. To achieve resistance measurement, the resistance needs to be converted into an easily measurable voltage signal. The circuit is based on the same-direction amplifier design. The feedback resistor Rg in the circuit represents the resistance of the flexible sensor. When the sensor is subjected to different pressures or strains, the sensor resistance Rg will increase or decrease accordingly, which will cause the output voltage Uo to change. The change of Uo can feedback the magnitude of the current strain. Since the ADC acquisition range of STM32 is 0-3.3V, 3.3V is connected to the R1 terminal.

[0175] Fig.13 This is the resistance to voltage circuit diagram;

[0176] According to the principle of voltage divider circuit and unidirectional amplifier, the relationship between the circuit output voltage Uo and the sensor resistance Rg can be obtained:

[0177]

[0178] R g with U o It is a linear relationship, that is, this circuit does not change the linearity. Considering the change of the resistance value of the connected sensor, different R1, R2 and R3 can be selected to make U o More accurately reflects changes in sensor resistance.

[0179] AD8629 (including two op amps) is used as the op amp of the signal conditioning circuit, which uses a single power supply (2.7 ~ 5V) or a dual power supply (±1.35 ~ ±2.5V). AD8629 has the advantages of ultra-low drift, high impedance input, low offset voltage and low cost, and can achieve rail-to-rail input and output.

[0180] Since the frequency of changes in human motion signals and physiological health signals is low, a low-pass filter is needed to filter out high-frequency noise to ensure the stability of the output signal. Fig.14 is a voltage source low-pass filter, such as Fig.14 As shown, it has few components and low output impedance. In addition, it is necessary to calculate the parameters of the filter based on the Butterworth characteristic, as shown in the following formula:

[0181]

[0182] Let R4=R5=R, C2=C and C1=2C to simplify the calculation and get the cutoff frequency as:

[0183]

[0184] Let the cut-off frequency f0 = 100 Hz, and calculate the circuit parameters according to the above formula, and obtain R = 11.3k, C = 0.1μF.

[0185] Since the AD8629 integrates two operational amplifiers, a resistance-to-voltage circuit and a filtering circuit can be built simultaneously based on one AD8629. Fig.15 The schematic diagram of the integrated resistance-to-voltage circuit and filter circuit on the data acquisition board. Sensor1+ and Sensor1- are connected to the two ends of the flexible sensor, and ADC1 is connected to the ADC function pin of STM32, that is, PA0. The data acquisition board integrates five Fig.15 The circuit module shown can simultaneously connect five sensor devices for data collection and send them one by one through the wireless module.

[0186] Power module:

[0187] In order to meet the needs of portability and wearability, the power supply is powered by a power bank with an output voltage of 5V, while the STM32 minimum system requires 3.3V power supply. Fig.16 The power module circuit diagram is as follows: Fig.16 As shown in the figure, the linear regulator LP5907MFX3.3 module is selected here to realize the conversion from 5V voltage to 3.3V voltage. LP5907 is a linear regulator that can provide 250mA output current. This device is specially designed for analog circuits and can meet its many requirements such as low noise, low quiescent current and low line. This device is designed to be used with 1uf input and 1uf output ceramic capacitors. The 5V voltage enters through the USB port and outputs a stable 3.3V after passing through the LP5907 module, which can be used by subsequent microcontrollers, signal conditioning circuits, ESP8266 and HC-05 Bluetooth modules.

[0188] STM32 microprocessor module:

[0189] The data acquisition system has high requirements for portability, acquisition accuracy, size, and battery life. After comparing different parameters and performance, the STM32 series microcontroller developed by STMicroelectronics was selected. This series of microcontrollers has high cost performance, rich and relatively simple peripheral interfaces, low power consumption, low cost, and is suitable for low-power detection systems. The STM32F103RCT6 model microcontroller is used.

[0190] STM32F103RCT6 is an embedded microcontroller integrated circuit (IC) with a core size of 32 bits, a speed of 72MHz, a program memory capacity of 256KB, a program memory type of FLASH, and a RAM capacity of 48K. The operating temperature is -40℃~85℃, and the operating voltage is 2V~3.6V.

[0191] The data acquisition system uses the STM32F103RCT6 microcontroller to build the minimum system of the single-chip microcomputer. The minimum system requires at least five parts, namely the power supply circuit, clock circuit, BOOT startup circuit, debug interface circuit and reset circuit. Fig.17 This is the minimum system schematic diagram of the microcontroller. The power supply is 3.3V, and the clock circuit uses a crystal oscillator + oscillator capacitor. BOOT0 is grounded through a 10K resistor. Because the program is burned into the flash register using ST-Link, the startup circuit should be started from the flash register.

[0192] SWD interface circuit:

[0193] To burn the written lower computer program to the STM32 microcontroller, the corresponding port needs to be debugged. Currently, there are two debugging interfaces: JTAG and SWD. The JTAG debugging interface requires the use of six lines, namely VCC, GND power supply signals and four clock and data transmission signals of TCK, TMS, TDO, and TDI. TRST, RESET (reset signal) and RTCK (synchronous clock) are optional signals. Compared with the JTAG burning method, the other SWD interface can use fewer signal lines and only needs four lines to complete the connection. In addition, the SWD interface is more reliable at high speeds and has a lower probability of failure when the program memory is large. SWD burning can use fewer pins, which can save board space, better meet the requirements of small and portable size, and solve the problem of insufficient GPIO. Fig.18 This is the SWD interface circuit diagram.

[0194] Detection light and button module:

[0195] In order to enrich the functions of the data acquisition system and ensure the stable operation of the data acquisition board, it is also necessary to design detection light alarm circuit and button circuit. Fig.19 For the key circuit schematic and LED light alarm circuit, such as Fig.19 As shown, the detection lights D18 and D19 can provide real-time feedback on whether the 5V power supply and 3.3V power supply in the circuit are normal, while D20 and D21 detect the correctness of the STM32 program. When the program runs normally, the green light of D20 is on, otherwise the red light of D21 is on to remind you that there is an error in the program.

[0196] The detection lamp uses a 0603-type SMD LED lamp, which saves space and meets the requirements of portability and wearability. Because the data acquisition system can access five sensor devices at the same time, the data acquisition board integrates five buttons. In the mobile health monitoring system, each button controls the output of a sensor signal. By pressing different buttons, the sensor response signals of different lines can be switched.

[0197] Protection circuit module:

[0198] In order to ensure the long-term stable operation of the data acquisition system, protection circuits are essential. Fig. 20 To protect the circuit schematic, such as Fig. 20 As shown in the figure, magnetic beads are used in the protection circuit. Magnetic beads are specially used to suppress high-frequency noise and spike interference on signal lines and power lines, and also have the ability to absorb electrostatic pulses. The data acquisition board will be used for human motion detection and must meet the requirements of wearability. When worn on the human body, the friction between clothes will often generate electrostatic pulses. Connecting magnetic beads in parallel at each input end of the acquisition board can absorb these electrostatic pulses well, and also prevent the circuit from short-circuiting and damaging components. At the same time, it can also suppress the noise on the power line and signal line, playing a role in protecting the circuit.

[0199] Communication module:

[0200] The present invention builds a mobile health monitoring system and a smart glove human-computer interaction system, wherein the communication method with the mobile phone APP adopts the ESP8266-01 module, and the communication method with the PC Labview interface adopts the HC-05 module and the USB to TTL module. Fig.21 a is the ESP8266-01 module; b is the Wifi interface circuit; c is the HC-05 module; d is the Bluetooth interface circuit.

[0201] Fig.21 Figures a and b show the schematic diagram of ESP8266 and the interface circuit on the data acquisition board. ESP8266 is integrated on a small board of 2.5cm×1.5cm and leads to ESP_TXD, ESP_RXD, ESP_VDD, WGND, CH_PD, GPIO0, GPIO2 and RST pins, as shown in Figure 1. Fig.21 a. The 8 pins are connected to Fig.21 The eight pins of the b interface circuit are connected to complete the WiFi communication. The ESP8266-01 module is inserted into the data acquisition board. The operation is flexible and convenient, and it greatly saves the space of the data acquisition circuit, making it easy to wear.

[0202] The human-computer interaction system of the smart gloves uses Bluetooth module communication. Fig.21The cd shows the schematic diagram of HC-05 and the interface circuit on the data acquisition circuit. The HC-05 module is a high-performance master-slave integrated Bluetooth serial port module with the advantages of low cost, small size and low power consumption. HC-05 is integrated on a small board of 3.6cm×1.6cm, such as Fig.21 c, where the six pins STATE, RXD, TXD, GND, VCC and EN are brought out through the pin header. Fig.21 d interface circuit to complete Bluetooth communication, and the same operation mode as ESP8266, plugged into the data acquisition board to realize Bluetooth transmission of signals. Two HC-05s are used in the human-computer interaction system. Before use, the two HC-05s are paired through AT commands. After successful configuration, the two HC-05s will automatically pair when powered on. One HC-05 is plugged into the data acquisition circuit board, and the other is connected to the PC through a USB to TTL module to realize signal reception on the Labview side.

[0203] Data acquisition system PCB design:

[0204] Connect the modules together in Altium Designer to form the schematic diagram of the data acquisition system and generate the PCB file to complete the wiring and copper laying. Fig. 22 PCB design for data acquisition board. The data acquisition board is 6.5cm long and 5cm wide, making it easy to carry around.

[0205] Lower computer program design:

[0206] Two sets of lower computer programs were designed for the mobile health system and the smart glove system. The lower computer programs were designed in C language and compiled in Keil UVision5 software. The programs were burned into the STM32 microcontroller through ST-Link.

[0207] Lower computer program design of mobile health monitoring system:

[0208] The mobile health monitoring system uses ESP8266-01 communication, and the data display can be switched by pressing buttons. Fig.23 This is the lower computer program flow chart of the mobile health monitoring system. The design idea of ​​the STM32 main program is as follows Fig.23 As shown. First, clarify the functional requirements. The real-time changing voltage value is obtained through the data acquisition board, and then the relationship between the voltage value and the resistance of the sensor is analyzed, and the normalized response of the sensor device is obtained through formula processing. The normalized response value is transmitted to the mobile terminal through the wifi module, and the sensor detection signal is displayed in real time, so that the wearer can understand his or her own physiological health status in real time.

[0209] After the system is powered on, it is reset, and then the initialization configuration of related functions is performed. The data acquisition system can collect five sensor signals at the same time, so in the actual operation process, five buttons are used to switch data transmission. Each button press will trigger an external interrupt of a line, and the global variable a is assigned in the interrupt. The value of a is determined to determine which sensor signal to send. For example, when button 1 is pressed, an external interrupt will be triggered. In the interrupt event, a is assigned to 1, and the instruction to send Sensor1 data will be executed in the main program. When other buttons are pressed, an interrupt will also be triggered, the value of a will change, and the execution instruction in the main program will also change.

[0210] The lower computer program design of the intelligent glove human-computer interaction system:

[0211] The lower computer program design of the smart glove system needs to collect five sensor signals (each signal feeds back the bending condition of a finger) and transmit them to the Labview interface on the PC through the serial port and Bluetooth module. The protocol of the Labview interface has been written, and the lower computer needs to send the collected data according to the serial port protocol of Labview. Fig.24 Flow chart of the lower computer program of the human-computer interaction system.

[0212] Similar to the lower computer programming of the mobile health monitoring system, the system is reset after power is turned on, and then the initialization configuration of related functions is performed. The data acquisition board collects five sensor signals in turn, and saves them in an array after data processing. The key can be used to control whether to start data transmission. When the key is pressed, the lower computer sends the processed data through the serial port and Bluetooth module according to the serial port protocol of Labview. The Labview end receives the sent data and can provide real-time feedback on the bending state of the finger.

[0213] Embodiment 7:

[0214] An application of a flexible strain sensor in wearable intelligent systems.

[0215] 1. Application of mobile health monitoring system

[0216] Hardware circuit:

[0217] Fig.24This is a physical picture of the mobile health monitoring system PCB. The wearable health monitoring system composed of flexible sensor devices, portable data acquisition boards and smart phones transmits data to the mobile phone through the wifi module. In the sensor data acquisition system, the sensor devices are connected to the circuit board through soft and ultra-fine wires. The ADC port of the STM32 microcontroller (MCU) in the circuit board collects and converts data, and sends the data to the wifi module through the universal asynchronous serial interface (Universal Asynchronous Receiver / Transmitter, UART). The wifi module acts as a relay station to send the data to the user's mobile phone.

[0218] Mobile APP:

[0219] The health monitoring system APP can realize basic data reception and transmission, has the function of switching between data / waveform, and can clear data and view historical records at any time. Fig.25 It is the display interface of the health monitoring system APP.

[0220] The specific operation process can be divided into several steps: (1) Initialization of mobile software. After opening the APP, the interface will prompt the user to connect to the sensor device. At this time, only "IP" and "Port" are available in the interface. Other button functions are unavailable and there is no output waveform of the sensor signal. (2) Wifi hotspot connection. The domain name and port of ESP8266 have been configured in the lower computer program, so the input in the interface can match the content configured in the lower computer. Click the "IP" position, enter 192.168.4.1, enter the port value 8080 and click Connect. If the pairing is successful, the interface will prompt the user to prepare to receive data and start receiving data sent by the lower computer. (3) Receiving numerical information and displaying waveforms. After the connection is successful, click the "START" button to start the data receiving mode, click the "DATA / WAVE" button to switch to the sensor response value display interface, and click again to return to the data display interface. The user can switch at will. In addition, click the "HISTORY" button to view the previous test data and waveform; click the "CLEAR" button to clear the data in the black area; click the "STOP" button to stop receiving data.

[0221] The mobile terminal detection system constructed by the present invention can be used for a variety of health monitoring, such as breathing detection, cough detection and joint bending monitoring. Actual test results are as follows Fig.26 As shown, Fig.26a is breathing monitoring; b is cough monitoring; c is finger bending monitoring. The microstructure flexible pressure sensor can be attached to the throat to detect the user's cough signal. Each cough will cause the pressure sensor to generate a signal pulse, which can be captured by the data acquisition system and displayed in real time on the mobile terminal. Attach it to the abdomen to detect breathing signals, and the ups and downs of each breath can also be observed in real time on the mobile terminal. In addition, it can be attached to the joints, such as fingers, and the amplitude of each joint bending can also be fed back on the mobile phone APP. The data acquisition circuit board is portable, compact, can be carried with the speaker, and meets the requirements of wearable.

[0222] 2. Smart Glove System Design:

[0223] Fig. 27 For the smart glove system, five flexible strain sensors are placed on the knuckles of the back of a leather sports glove. Industrial-strength elastomer adhesive E6000 is used to bond the sensor to the glove. Soft, ultra-fine, high-temperature-resistant wires are used to connect the copper foils at both ends of the strain sensor for signal transmission. The outside of the wires is wrapped with insulating material to ensure that each strain sensor will not be short-circuited. E6000 is also used to stick the wires on the surface of the glove to ensure the cleanliness of the surface of the smart glove. Finally, the wires connecting each strain device are welded together with DuPont wires and connected to a customized PCB. The data acquisition circuit board is powered by a mobile power supply, which can realize the portability and mobility of the hardware equipment. The hardware circuit acquisition system obtains and sends the signals of the flexible device to achieve real-time display and human-computer interaction on the host computer interface.

[0224] 3. Application of human-computer interaction system based on Labview:

[0225] Labview finger bending response curve interface design:

[0226] The host computer software design of the Labview finger bending response curve interface is divided into two parts: the front panel and the program flowchart. The program functions include serial port communication configuration and sampling time configuration, start, stop and refresh of the host computer software system, recognition of string frame header and data verification function, real-time display and storage of data waveform, real-time display of acquisition time and acquisition points, and sampling rate configuration.

[0227] Fig.28Design of software for serial communication, sampling rate and sampling time. Use VISA module in Labview to configure serial port parameters, mainly setting serial port number, baud rate, data bit, parity bit, using 9600b / s, 8 data bits, no parity bit data frame format, matching with the lower computer. The program also includes system start, stop and refresh, and the sampling rate can be set according to user needs. In addition, the sampling time can also be freely configured. Once the sampling time is reached, the system will stop collecting. During the sampling period, the system's collection time and number of collection points can be displayed in real time on the front panel.

[0228] Fig.29 For the identification of the string frame header and data verification, the communication between the host computer and the slave computer is sent in the form of a string. The system host computer needs to identify the frame header of the string to receive the data sent by the slave computer. According to the frame header, it can determine whether a new string has arrived, so as to parse and perform other operations. After identifying the frame header, it starts to process the new string of data. In addition, a verification function is added to the program to ensure that the sent data is accurate before subsequent data processing and real-time display can be performed. The frame header is set to AACC in the communication protocol, followed by the collected data, and finally the verification data. Therefore, each string of characters consists of a frame header, collected data, and verification data.

[0229] The sensor device outputs an analog voltage signal, which is converted into a digital signal by the lower computer ADC. The lower computer sends the data signal to the upper computer in the form of a string. The string includes a frame header, the digital signals of five sensors, and verification data. After receiving the string data, the upper computer determines the starting position of the data according to the frame header, and then extracts the digital signal of each sensor and displays it in five interfaces respectively. Each interface can display the signal change of one sensor, and then can feedback the bending state of the five fingers. A data saving function is added to the program. By setting the path, the collected five digital signals can be saved in a folder on the PC. Fig.30 It is the function of displaying and saving data curve.

[0230] Fig.31 The front panel design for the finger bending response curve interface contains five display interfaces, which respectively display the bending status of the thumb, index finger, middle finger, ring finger and pinky finger. The baud rate is set to 9600, and the sampling rate can be freely configured from 0 to 1000Hz. The interface is equipped with start and stop buttons to control the start and stop of the monitoring system, and the refresh button can clear historical data and refresh the interface.

[0231] 3D robot model construction:

[0232] The present invention designs a robot model. By importing the three-dimensional model into Labview, human-computer interaction based on the intelligent glove system can be realized. 3D Studio Max, often referred to as 3dMax, is a three-dimensional animation rendering and production software based on PC system developed by Discreet (later merged by Autodesk), which is widely used in various fields

[92] . The three-dimensional model of the robot is drawn based on 3D max software. Fig.32 For a three-dimensional robot model, Fig.32 As shown in the figure, the 3D robot model is composed of multiple finger joints and palms, and the thumb and other four fingers are divided into three sections: upper, middle and lower. The assembly process of the robot model will be completed in Labview.

[0233] Human-computer interaction interface of robot model based on Labview:

[0234] The present invention uses the 3D picture control function of Labview to convert the 3D model previously designed in 3D max into WRL format, and then imports the various parts of the manipulator model into Labview to splice them into a complete palm. Fig.33 Design the main function program for the robot model.

[0235] The data is received by serial communication, and the communication protocol is 3333+15 bytes of data (every 3 bytes control one finger, and each byte controls one joint of the finger, that is, from the root of the finger to the fingertip, the received 15 bytes of data just control the bending of the five fingers, and the control order is from the thumb to the little finger). After importing the 3D model into Labview, the coordinate system is established and spliced ​​to assemble the complete robot model. Fig.34 It is the human-computer interaction interface of the robot.

[0236] Human-computer interaction system testing and result analysis:

[0237] In order to verify the application potential of sandwich-structured flexible strain sensors in human-computer interaction and medical health, a strain force signal detection and feedback system was built.

[0238] Fig.35 a is a schematic diagram of the wearable gesture recognition device system; b is a wearable smart glove device; c is the resistance response change monitoring of the five strain sensors of the smart glove; d is the human-computer interaction interface for gesture recognition.

[0239] Fig.35ab demonstrated the overall sensor detection system, which is mainly composed of smart gloves with sensor components, lower computer hardware acquisition circuit, upper computer data processing display interface and upper computer 3D manipulator model. The hardware circuit acquisition system can convert the sensor's resistance signal into a voltage signal and collect it through ADC. The data collected by the lower computer is sent to the PC port through the Bluetooth wireless transmission module, and the real-time display is realized on the upper computer interface. Fig.35 c shows the response curves of five sensors attached to five fingers. The response value of the sensor caused by the bending of each finger can be detected in real time. The greater the degree of bending, the greater the response value. This can help the observer analyze the current bending state and bending angle of each finger.

[0240] In order to realize real-time monitoring more intuitively, a 3D model of the manipulator was developed on the Labview interface. Fig.35 As shown in Figure d, the robot model on the computer can be connected to the smart glove to realize human-computer interaction. Due to the excellent sensitivity of the sensor, the 3D model of the robot on the computer can change rapidly with the wearer's fingers with less delay. During the experiment, the wearer completed a variety of gestures, such as fisting, scissors hand, etc., and these gestures can be accurately recognized. Therefore, the flexible strain sensor with a sandwich structure has great application potential in the field of human-computer interaction due to its excellent sensitivity and high stability. In addition, combining smart gloves with manipulators in the industrial field is expected to achieve precise control of the manipulator. By wearing the smart gloves, the manipulator can be controlled to grasp objects, which has good application value in complex industrial environments. Therefore, the smart glove system based on flexible wearable sensors provides a new method for the fields of robot precision control, intelligent prosthetic palms, human-computer interaction, etc., and has broad application prospects.

[0241] For the sandwich-structured AgNFs / MWNTs flexible strain sensor, the unique sandwich structure helps to improve the stability of the strain sensor. AgNFs, due to its ultra-high conductivity, can make the strain sensor have ultra-high sensitivity under low strain, while MWNTs can extend the sensing range of the strain sensor and improve the overall performance of the sensor.

[0242] The flexible PCB based on PI substrate is bendable, easy to cut, transparent and beautiful. The flexible sensor array based on flexible PCB and PDMS film is easy to package, easy to carry, and has the advantage of wearability, and can be used for pressure distribution testing.

[0243] It is proved that the signal conditioning circuit can be used for the signal conditioning of the self-developed sensor, and can effectively convert the resistance signal into a voltage signal. The health monitoring system and smart glove system developed based on STM32, mobile phone APP and Labview realize the monitoring of human health signals and human-computer interaction functions.

[0244] A unique sensor structure and a new type of nanosensing material were developed. Using sandpaper as a template to make a PDMS film with a rough surface structure can improve the sensitivity of the pressure sensor. The sandwich structure can improve the stability of the strain sensor. By introducing the conductive network of the composite material into the flexible sensor, the synergistic effect between the conductive materials will make up for the shortcomings of a single material while maintaining the advantages of each material.

[0245] The wearable flexible sensor is combined with a mobile terminal and a Labview host computer to build a detection system, which can be applied in medical health, human-computer interaction, virtual electronics, etc.

[0246] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable ordinary technicians in the field to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made based on the essence of the content of the present invention should be included in the protection scope of the present invention.

Claims

1. A conductive film, characterized in that: MWNTs are attached to the surface of AgNFs silver nanoflowers. The ultra-high conductivity of AgNFs increases the sensitivity of the conductive film. MWNTs can connect each AgNFs under large stretching to ensure the connectivity of the conductive network on the conductive film. The preparation steps include: (1) Mixing and stirring the AgNO3 solution and the diamine hydrogen citrate solution in a water bath to obtain a white precipitate; (2) adding aqueous ammonia dropwise into the mixed solution until the solution becomes colorless; (3) adding the boric acid solution into the colorless solution and stirring to maintain the pH value of the mixed solution; (4) adding L-ascorbic acid solution to promote the spontaneous anisotropic growth of AgNFs, and the colorless solution turns brown. After heating and stirring in a water bath, the AgNFs solution is prepared. The prepared AgNFs solution is washed and dried to obtain silver nanoflower particles. (5) mixing silver nanoflower particles with a multi-walled carbon nanotube solution and subjecting the mixture to ultrasonic vibration to obtain a AgNFs / MWNTs composite sensing material; (6) Spraying the AgNFs / MWNTs composite sensing material onto the substrate surface and obtaining a conductive film after drying.

2. The method for preparing a conductive film according to claim 1, wherein: In the step (5), the concentration of the multi-walled carbon nanotube solution is 4 mg / mL, and the mass ratio of the silver nanoflowers to the multi-walled carbon nanotubes is 1:

1.

3. A flexible strain sensor for hand posture monitoring, the sensor comprising the conductive film according to claim 1, or the conductive film in the sensor is prepared according to the method of claim 2, characterized in that: AgNFs / MWNTs were deposited on the PDMS surface by spraying to produce a flexible strain sensor with a sandwich structure.

4. The flexible strain sensor for hand posture monitoring according to claim 3 is characterized in that: The sensing principle of the sensor is: The strain sensor belongs to the adsorption type strain sensor. The sensing material is adsorbed on the surface of PDMS. When the sensor is stretched, cracks appear in the sensing layer, causing the resistance to increase. When the stretching is restored, the cracks disappear and the resistance of the strain sensor returns to its original state. The MWNTs attached to the surface of AgNFs play a good connecting role. Under small strain conditions, a small separation occurs between the AgNFs, resulting in a significant change in the resistance of the sensing layer, causing the strain sensor based on AgNFs / MWNTs to maintain a high sensitivity under small strain. Under strain, the AgNFs will be completely separated from each other, but the MWNTs act as a bridge to connect each AgNF to ensure the path of the sensing layer, greatly extending the sensing range of the strain sensor; the AgNFs / MWNTs composite material as a sensing layer film can ensure that the strain sensor has excellent sensitivity and a large strain range.

5. A method for preparing a flexible strain sensor for hand posture monitoring according to any one of claims 3 to 4, characterized in that: The preparation steps include: (1) Mix reagent A and reagent B of PDMS in a ratio of 1:1 and place them in a vacuum hood for 30 min to remove bubbles; (2) The mixed reagents were evenly coated on a smooth wooden board with polyimide tape and placed in a vacuum hood; (3) After the bubbles inside the PDMS are completely dissipated and evenly and smoothly distributed on the surface of the wooden board, the wooden board coated with PDMS is placed in an oven for heating and curing to obtain a PDMS film; (4) The AgNFs / MWNTs composite sensing material was sprayed on the surface of the PDMS film by a spray brush, and the spraying was performed 10 times to form a conductive film; (5) removing the polyimide tape and the wooden board and cutting to obtain a PMDS film covered with a conductive film; (6) Attaching the conductive copper foil to both ends of the conductive film and leading them out; (7) A layer of liquid PDMS reagent is further covered on the PDMS surface with the conductive film and placed in an oven for curing to obtain a flexible strain sensor with a sandwich structure.

6. A portable data acquisition system, comprising the flexible strain sensor for hand posture monitoring according to any one of claims 3-4, characterized in that: The data acquisition system also includes a signal conditioning circuit, an STM32 processor, a wireless communication module, a power module, an alarm circuit, a key circuit and a protection circuit.

7. The portable data acquisition system according to claim 6, characterized in that: The data acquisition system is used for human health monitoring, detecting blinking, swallowing, voice recognition, breathing and joint bending signals; The data acquisition system is used to be applied to smart wearable gloves and realizes human-computer interaction function with a Labview host computer. The smart wearable gloves can monitor the bending state and bending amplitude of fingers in real time.

8. The portable data acquisition system according to any one of claims 6 or 7, characterized in that: The sensor converts external tactile pressure and bending strain into a resistance signal, which is then converted into a voltage signal through a signal conditioning circuit. The voltage signal is collected by the ADC of the STM32 processor. The received voltage data information is processed in the program, and the resistance value of the sensor is inferred through the conversion formula under the condition of a known voltage value. After further formula conversion, the current response value of the sensor can be obtained, which reflects the stress changes of the sensor in real time. The wireless transmission module transmits the data of the detection system to the host computer.

9. The portable data acquisition system according to claim 7, characterized in that: The smart wearable glove is a device that places five flexible strain sensors on the knuckles of the back of a leather sports glove; an industrial-strength elastomer adhesive is used to bond the sensor to the glove, and a soft, ultra-fine, high-temperature-resistant wire is used to connect the copper foils at both ends of the strain sensor for signal transmission. The outside of the wire is wrapped with an insulating material to ensure that each strain sensor will not be short-circuited. The elastomer adhesive is also used to stick the wire to the surface of the glove to ensure the cleanliness of the surface of the smart glove; finally, the wire connecting each strain device is welded together with a DuPont wire and connected to a customized PCB. The data acquisition circuit board is powered by a mobile power supply to realize the portability and mobility of the hardware device. The hardware circuit acquisition system obtains and sends the signal of the flexible device to realize real-time display and human-computer interaction on the upper computer interface.

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