Manufacturing method of electromagnetic self-powered strain sensor

Abstract

The invention discloses a manufacturing method of an electromagnetic self-powered strain sensor, and relates to the technical field of sensors, and the method is based on an electromagnetic induction principle to design an energy collection device which comprises a sleeve whose outer wall is wound with a coil, and a fixed magnet and a suspension magnet which are arranged in the sleeve. Structural parameters meeting power supply requirements are determined by combining energy conversion analysis on the energy collection device, and then the energy collection device is manufactured according to the design structure and the structural parameters. The energy collection device is excited by external vibration to generate alternating-current electric energy in the moving process of the moving object to be monitored and supplies power to the sensing monitoring device through the rectification energy storage circuit, so that the sensing monitoring device can continuously and stably sense the strain of the position to be detected of the moving object to be monitored without being externally connected with other power supplies.

Description

Technical Field

[0001] The present application relates to the field of sensor technology, and in particular to a method for manufacturing an electromagnetic self-powered strain sensor. Background Art

[0002] Human motion recognition technology is a very important research topic. After monitoring and collecting human posture data, human motion data can be identified. These human motion data can provide a data basis for subsequent analysis and control, and are widely used in medical rehabilitation, human-computer interaction, sports science and other fields.

[0003] Traditional human posture data monitoring mainly relies on various specialized wearable devices, which have complex structures and will restrict and affect human movement, resulting in limited use scenarios and affecting data collection accuracy. With the development of sensor technology, various types of flexible strain sensors have gradually been developed. These strain sensors have a higher degree of integration, and their flexibility allows them to be well attached to the human body to collect posture data, thus having higher sensitivity and better application effects than wearable devices. However, since strain sensors require electric drive, if the strain sensor is connected to an external power supply during use, it will still affect human movement due to cable restrictions, and if an independent power supply is used, the working time of the strain sensor will be limited. Summary of the invention

[0004] In view of the above problems and technical requirements, this application proposes a method for manufacturing an electromagnetic self-powered strain sensor. The technical solution of this application is as follows:

[0005] A method for manufacturing an electromagnetic self-powered strain sensor, the method comprising:

[0006] Determine the design structure of the energy collection device, the energy collection device includes a sleeve with a coil wound around the outer wall, and a fixed magnet and a suspension magnet arranged in the sleeve, the suspension magnet and the fixed magnet are arranged opposite to each other at one end with the same polarity, the fixed magnet is fixed in the sleeve, the suspension magnet is movably arranged in the sleeve and can move along the axial direction of the sleeve under the action of external vibration excitation, and the magnetic flux of the coil changes with the movement of the suspension magnet;

[0007] Under the constraint that the output voltage of the energy collection device reaches the minimum voltage required for the diode in the rectifier energy storage circuit to be turned on, the structural parameters of the energy collection device are determined, and the structural parameters of the energy collection device include the structural parameters of the sleeve, the structural parameters of the coil, the structural parameters of the fixed magnet, and the structural parameters of the suspension magnet;

[0008] An energy collection device is manufactured according to the design structure and structural parameters of the energy collection device, and a sensor monitoring device is manufactured according to the design structure and structural parameters of the sensor monitoring device. The coil of the energy collection device is connected to the power supply end of the sensor monitoring device through a rectifier energy storage circuit to manufacture an electromagnetic self-powered strain sensor. The sensor monitoring device is used to sense the strain at a position to be detected of a moving object to be monitored, and the energy collection device is used to be arranged on the moving object to be monitored and generate AC power when stimulated by external vibration during the movement of the moving object to be monitored.

[0009] A further technical solution is that the energy collection device and the sensor monitoring device are manufactured including:

[0010] The sleeve is printed and manufactured using the fused deposition modeling printing technology according to the structural parameters of the sleeve, the coil is printed and manufactured on the outer wall of the sleeve using the straight writing printing wire technology according to the structural parameters of the coil, a fixed magnet with corresponding structural parameters is fixed inside the sleeve, and a suspended magnet with corresponding structural parameters is placed inside the sleeve to manufacture an energy collection device;

[0011] A sensing layer is formed by printing conductive carbon paste on an insulating base layer using direct writing printing technology, and electrodes are formed by printing conductive silver paste on the sensing layer using direct writing printing technology and connected with conductive wires to produce a resistive strain sensing unit. A resistance meter is connected with the conductive wires of the resistive strain sensing unit to produce a sensing monitoring device. The resistive strain sensing unit is used to be arranged at a position to be detected of a moving object to be monitored.

[0012] A further technical solution is that the structural parameters of the coil include the specification parameters of the metal wire wound to form the coil and the number of turns of the coil, and the coil is printed on the outer wall of the sleeve to obtain:

[0013] After a double-sided adhesive polyimide film is attached to the outer wall of a sleeve, the sleeve with the polyimide film attached is placed on the rotating shaft of a printer and fixed, and a syringe is fixed on the horizontal axis of the printer; the rotating shaft of the printer is controlled to drive the sleeve to rotate, and the syringe is controlled to move along the horizontal axis, and a metal wire with corresponding specification parameters is guided out of the syringe during the sleeve rotation and syringe movement process, and the metal wire is attached to the outer wall of the sleeve under the action of the polyimide film to form a spiral coil with a corresponding number of turns.

[0014] A further technical solution is that the structural parameters of the sleeve include the radial parameters of the sleeve and the length of the sleeve, the structural parameters of the two magnets are the same, and the structural parameters of each magnet include the size parameters, weight and magnetic induction intensity of the magnet; the structural parameters of the energy collection device include:

[0015] Determine the diameter of the sleeve, the structural parameters of the coil, the size parameters of the magnet and the weight of the magnet;

[0016] Based on the design structure of the energy harvesting device, a finite element model is established according to the diameter of the sleeve, the structural parameters of the coil, and the size parameters of the two magnets;

[0017] Under different magnetic induction intensities of the magnet, the finite element model is used to perform finite element analysis on the movement process of the suspended magnet from the fixed magnet to the direction away from the fixed magnet, and the voltage distance curve of the energy collection device under the current magnetic induction intensity is obtained. The voltage distance curve indicates the curve of the output voltage of the energy collection device changing with the distance between the two magnets;

[0018] According to the voltage-distance curve of the energy collection device under different magnetic induction intensities, determine the magnetic induction intensity that makes the output voltage of the energy collection device reach the minimum voltage required for the diode in the rectifier energy storage circuit to be turned on;

[0019] The length of the sleeve is determined according to the determined magnetic induction intensity.

[0020] A further technical solution is to use a finite element model to perform a finite element analysis on the movement of the suspension magnet from the fixed magnet to the direction away from the fixed magnet, including:

[0021] Finite element analysis is performed based on the system balance equation of the suspended magnet during movement combined with Faraday's law of electromagnetic induction to determine the change in magnetic flux and the corresponding output voltage generated during the movement of the suspended magnet from the fixed magnet to the direction away from the fixed magnet, and obtain a voltage-distance curve.

[0022] The system balance equation of the suspended magnet during motion is:

[0023]

[0024] Among them, m f is the mass of the suspension magnet, g is the gravitational acceleration; x1(t) represents the displacement of the energy collection device along the axial direction of the sleeve caused by the external vibration excitation at time t, and x2(t) represents the magnet displacement along the axial direction of the sleeve relative to the initial static equilibrium position of the suspension magnet at time t; F M (x2(t)) is the repulsive force between the suspended magnet and the fixed magnet at time t, and F M (x2(t)) is related to x2(t); c e (x2(t)) is the electromagnetic damping at time t and is related to x2(t); f is the sum of the air viscosity and the inner wall contact friction, and the sign factor sgn(x2(t)) is used to adjust the direction of f to be opposite to the direction of x2(t).

[0025] A further technical solution is that the method for manufacturing the electromagnetic self-powered strain sensor further includes:

[0026] The bottom fixture is used to clamp the fixed magnet, and the top fixture is used to clamp the fixed suspension magnet through the pressure sensor. The top fixture is controlled to drive the suspension magnet and the fixed magnet to move relative to each other, and the repulsive force of the pressure sensor at different distances between the suspension magnet and the fixed magnet is read. The repulsive force F between the suspension magnet and the fixed magnet at any time t is obtained by fitting. M (x2(t)) is:

[0027]

[0028] Among them, a, b, and c are correction coefficients obtained by fitting, H1 is the magnetic induction intensity of the suspension magnet, H2 is the magnetic induction intensity of the fixed magnet, and R M (t) is the distance between the suspended magnet and the fixed magnet at time t, and μ0 is the magnetic permeability of vacuum.

[0029] A further technical solution is that determining the magnetic induction intensity that makes the output voltage of the energy collection device reach the minimum voltage required for the diode in the rectifier tank circuit to conduct includes:

[0030] The relationship between the device displacement x1(t) and the magnet displacement x2(t) is determined based on the system balance equation, and the magnet displacement range is determined based on the unique range of the device generated by the external vibration excitation generated by the moving object to be monitored;

[0031] For any magnetic induction intensity, when the output voltage of the voltage-distance curve of the energy collection device under the magnetic induction intensity within the magnet displacement range reaches the minimum voltage required for the diode in the rectifier energy storage circuit to be turned on, the magnetic induction intensity is determined so that the output voltage of the energy collection device reaches the minimum voltage required for the diode in the rectifier energy storage circuit to be turned on.

[0032] A further technical solution is that determining the length of the sleeve according to the determined magnetic induction intensity includes:

[0033] Based on the characteristic that the repulsive force between the suspension magnet and the fixed magnet in a static state is equal to the gravity of the suspension magnet, the distance d between the suspension magnet and the fixed magnet when the energy collection device is in a static state is calculated, and the length of the sleeve is determined to be 2d.

[0034] A further technical solution is that the coil is wound and fixed on the outer wall of the sleeve in a segmented structure.

[0035] A further technical solution is that the surface of the suspension magnet is coated with a lubricant.

[0036] The beneficial technical effects of this application are:

[0037] The present application discloses a method for manufacturing an electromagnetic self-powered strain sensor. The method designs a design structure of an energy collection device with a cylindrical structure based on the principle of electromagnetic induction, and determines the structural parameters that meet the power supply requirements in combination with the energy conversion analysis of the energy collection device. Then, after the energy collection device is manufactured according to the design structure and structural parameters, it is connected to the manufactured sensor monitoring device through a rectifier energy storage circuit to manufacture an electromagnetic self-powered strain sensor. Each component of the manufactured electromagnetic self-powered strain sensor is arranged on the moving object to be monitored. During the movement of the moving object to be monitored, the energy collection device is stimulated by external vibration to generate AC power and supplies power to the sensor monitoring device through a rectifier energy storage circuit, so that the sensor monitoring device can continuously and stably sense the strain at the position to be detected of the moving object to be monitored without the need for other external power supplies. The manufactured electromagnetic self-powered strain sensor has good performance especially in human motion recognition technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a schematic diagram of the circuit structure of an electromagnetic self-powered strain sensor according to an embodiment of the present application.

[0039] Figure 2 The diagram is a schematic diagram of a partial explosion structure of a resistive strain sensing unit of an embodiment.

[0040] Figure 3 is a schematic structural diagram of an energy collection device according to an embodiment.

[0041] Figure 4 yes Figure 3 Schematic diagram of the motion force analysis of the energy harvesting device.

[0042] Figure 5 This is a schematic diagram of an application scenario in which an electromagnetic self-powered strain sensor according to an embodiment of the present application is used for human motion recognition. DETAILED DESCRIPTION

[0043] The specific implementation of the present application is further described below in conjunction with the accompanying drawings.

[0044] The present application discloses a method for manufacturing an electromagnetic self-powered strain sensor. The electromagnetic self-powered strain sensor of the present application mainly includes three parts: an energy collection device, a rectifier energy storage circuit and a sensor monitoring device. When the electromagnetic self-powered strain sensor is used: the energy collection device is used to be arranged on the moving object to be monitored and is stimulated by external vibration to generate alternating current during the movement of the moving object to be monitored. The rectifier energy storage circuit is also arranged on the moving object to be monitored to rectify the alternating current output by the energy collection device into direct current energy, and store it to power the sensor monitoring device. Please refer to Figure 1In the circuit structure shown, the rectifier energy storage circuit includes a bridge rectifier composed of four diodes, a capacitor C, a voltage regulator diode D and a resistor R1. In practice, an inductive coupling amplification structure is also connected between the energy collection device and the rectifier energy storage circuit. The sensor monitoring device is used to sense the strain data at the position to be detected of the moving object to be monitored. The moving object to be monitored here can theoretically be any moving object that needs to be strain monitored, and when applied in human motion recognition technology, it is the human body.

[0045] The rectifier energy storage circuit is a commonly used circuit structure. Therefore, the focus of the electromagnetic self-powered strain sensor manufacturing method is to manufacture the energy collection device and the sensor monitoring device, which are introduced as follows:

[0046] 1. Make a sensor monitoring device

[0047] First, the design structure and structural parameters of the sensor monitoring device must be determined. The sensor monitoring device of this embodiment includes two parts, such as Figure 1 The resistance meter 1 and the resistive strain sensing unit 2, wherein the resistance meter 1 uses a finished small portable resistance meter, and its volume is also very small.

[0048] The resistive strain sensing unit 2 is used to be arranged at the position to be detected of the moving object to be monitored. As the position to be detected of the moving object to be monitored moves, the resistance value of the resistive strain sensing unit 2 will change under the action of the strain at the position to be detected, and the resistance meter 1 can collect the resistance value change of the resistive strain sensing unit 2, thereby realizing strain data monitoring. The specific size of the resistive strain sensing unit 2 can be designed according to actual needs such as the shape and area of ​​the position to be detected.

[0049] Then, the sensor monitoring device is manufactured according to the design structure and structural parameters of the sensor monitoring device. This application uses direct writing printing technology to manufacture the resistive strain sensor unit 2, so that it has the ability to accurately monitor high strain and good wearability. Please refer to Figure 2 The schematic diagram of the partial explosion structure of the resistive strain sensor unit 2 is shown. The method for manufacturing the resistive strain sensor unit 2 includes:

[0050] First, the insulating base layer 21 is selected, and then the direct writing printing technology is used to print the conductive carbon paste on the insulating base layer to form the sensing layer. The carbon paste line is printed on the base surface to form the sensing layer 22. The conductive carbon paste has strong plasticity and good stretchability, and is very suitable as a sensitive unit. It should be noted that although Figure 2The schematic diagram shows that the sensing layer 22 is a straight line structure, but in actual application, it is generally printed into the most widely used serpentine structure. Finally, the electrode 23 is printed on the sensing layer 22 using conductive silver paste using direct writing printing technology and connected with the conductive wire 24, and then the resistive strain sensing unit 2 is manufactured after packaging. Then the conductive wire of the manufactured resistive strain sensing unit 2 is connected to the resistance meter 1, and the sensing monitoring device can be manufactured. The conductive wire of the resistive strain sensing unit 2 is also used to connect the rectifier energy storage circuit.

[0051] Specifically, when printing the sensing layer 22, first prepare the conductive carbon slurry: use a planetary mixer to stir the carbon slurry material (CH-8 / MOD2, JELCON) at 2000rpm for 2 minutes and then load it into the printing syringe, then centrifuge it at 3000rpm for 3 minutes to remove the bubbles in the carbon slurry material, and prepare the required conductive carbon slurry. After preparing the conductive carbon slurry, load the conductive carbon slurry into the opaque printing syringe of the direct writing printing device. After debugging, for the conductive carbon slurry with a viscosity of 30000cP, the inner diameter of the printing needle of the printing syringe is 1mm, the printing line spacing is 1.5mm, the printing speed is 5mm / s, the printing time is about 20s, and the extrusion pressure is 0.25Mpa. At this time, better printing quality can be achieved. After printing the conductive carbon slurry, use an oven to dry it at 120°C for 120 minutes to complete the curing to form a carbon slurry capacitor.

[0052] When printing the electrode 23, the conductive silver paste (EN-06B8, ENSON) is loaded into the opaque printing syringe of the direct writing printing device. After the printing syringe is connected to the air pressure control valve, it is clamped on the CNC three-axis motion platform and printed using the 3D printing direct writing method.

[0053] 2. Make an energy harvesting device

[0054] The purpose of the energy collection device is to capture the mechanical vibration energy of the moving object to be monitored during its movement, and then convert it into usable AC electrical energy. Considering the simplicity of the structure, manufacturability and miniaturization, this application sets up a cylindrical energy collection device based on the principle of electromagnetic induction. The energy collection device is designed based on the electromagnetic principle and uses a changing magnetic field to generate current in the conductor to achieve energy collection and conversion. The most basic principle of the energy collection device is Faraday's law of electromagnetic induction, that is, in a changing magnetic field, an induced electromotive force will be generated in a closed conductor loop, thereby generating current. According to this principle, the energy collection device generates electrical energy by changing the strength or direction of the magnetic field.

[0055] The cross-sectional schematic diagram of the energy collection device determined in this application is as follows Figure 3As shown, the design structure of the energy collection device includes a sleeve 3 and a fixed magnet 4 and a suspension magnet 5 arranged in the sleeve 3. The fixed magnet 4 is fixed in the sleeve 3, and the suspension magnet 5 is movably arranged in the sleeve 3. The ends of the suspension magnet 5 and the fixed magnet 4 with the same polarity are arranged opposite to each other. In order to simplify the design, the fixed magnet 4 and the suspension magnet 5 have the same specifications. In another embodiment, in order to minimize the friction between the suspension magnet 5 and the inner wall of the sleeve, the surface of the suspension magnet 5 is coated with a lubricant. The outer wall of the sleeve 3 is wound with a coil 6.

[0056] Under the action of external vibration excitation, the suspension magnet 5 moves axially along the sleeve 3, and the magnetic flux of the coil 6 changes with the movement of the suspension magnet 5, thereby generating current. This cylindrical structure design can not only improve the space utilization efficiency of the energy collection device, but also more effectively capture the magnetic field changes in all directions, which is very important for improving the energy conversion efficiency.

[0057] In another embodiment, the coil 6 is wound and fixed to the outer wall of the sleeve 3 in a segmented structure. The segmented coil 6 is used to convert energy to minimize eddy current loss and improve the magnetic field distribution inside the energy collection device. In actual use, in order to reduce the number of connection points and miniaturize the structure, the coil 6 is fixed to the outer wall of the sleeve 3 in two sections, such as Figure 3 As shown, the AC voltage output from the coil 6 is more stable and the voltage ripple is reduced.

[0058] In determining the energy harvesting device Figure 3 After the design structure shown, it is necessary to further determine the structural parameters of the energy collection device. The power generation effect of the energy collection device is different when different structural parameters are used. In order to ensure that the energy collection device can continuously and stably achieve the self-powered effect, the structural parameters of the energy collection device must be determined under the constraint that the output voltage of the energy collection device reaches the minimum voltage required for the diode in the rectifier energy storage circuit to turn on, so as to ensure that the output voltage of the energy collection device is sufficient to turn on the rectifier energy storage circuit. The minimum voltage required for the diode to turn on in a typical rectifier energy storage circuit is 1.4V.

[0059] The structural parameters of the energy collection device include the structural parameters of the sleeve, the structural parameters of the coil, the structural parameters of the fixed magnet and the structural parameters of the suspension magnet. The structural parameters of the sleeve include the radial parameters of the sleeve and the length of the sleeve. The structural parameters of the coil include the specification parameters of the metal wire wound to form the coil and the number of turns of the coil. The structural parameters of the two magnets are the same, and the structural parameters of each magnet include the size parameters, weight and magnetic induction intensity of the magnet.

[0060] The applicant has found through research that the magnetic induction intensity of the magnet has a major influence on the output voltage of the energy collection device, while other structural parameters have a smaller influence on the output voltage of the energy collection device. Therefore, when determining the structural parameters of the energy collection device, the focus needs to be on determining the magnetic induction intensity of the magnet, while other parameters can be set according to actual needs to reduce the complexity of the design. The method for determining the structural parameters includes the following steps:

[0061] 1. Determine the diameter of the sleeve, the structural parameters of the coil, the size parameters of the magnet and the weight of the magnet. These structural parameters can be customized according to actual needs.

[0062] The size parameters and weight of the magnet can be customized. After determining the size parameters of the magnet, set the diameter of the sleeve to be consistent with the diameter of the magnet as much as possible, so as to increase the magnetic flux size of the outer coil of the sleeve in the horizontal cross section. Considering the processing error and assembly problems, the inner diameter of the sleeve can be slightly larger than the magnet.

[0063] The wire diameter of the metal wire used in the coil should be as large as possible to reduce the internal resistance of the coil. The more turns the coil has, the greater the output voltage will be, but at the same time the internal resistance of the coil will also increase. Therefore, a suitable number of turns can be selected according to actual needs, rather than using the number of turns as the main adjustment parameter of the output voltage.

[0064] 2. Based on the design structure of the energy collection device, a finite element model is established according to the diameter of the sleeve, the structural parameters of the coil, and the size parameters of the two magnets. This step can be implemented using existing modeling software. During modeling, the length of the sleeve can be as large as possible.

[0065] 3. Under different magnetic induction intensities of the magnet, the finite element model is used to perform finite element analysis on the movement process of the suspended magnet from the fixed magnet to the direction away from the fixed magnet, and the voltage distance curve of the energy collection device under the current magnetic induction intensity is obtained. The obtained voltage distance curve indicates the curve of the output voltage of the energy collection device changing with the distance between the two magnets.

[0066] When performing finite element analysis, the system balance equation of the suspended magnet during movement is combined with Faraday's law of electromagnetic induction to determine the change in magnetic flux and the corresponding output voltage generated during the movement of the suspended magnet from the fixed magnet to the direction away from the fixed magnet, so that the voltage-distance curve can be obtained.

[0067] The energy harvesting device can be described as a damped vibration model. The suspended magnet 5 moves axially under external vibration excitation. Figure 4Schematic diagram of force analysis: When the energy collection device is subjected to external vibration excitation, the energy collection device will generate a device displacement x1 along the axial direction of the sleeve, and the device displacement of the energy collection device at time t is recorded as x1(t). The device displacement generated by the energy collection device will cause the suspension magnet 5 to also generate a displacement in the same direction along the axial direction of the sleeve. However, the movement of the suspension magnet 5 is affected by the combined action of multiple forces. Therefore, the displacement of the suspension magnet 5 along the axial direction of the sleeve is not equal to the device displacement x1. The magnet displacement of the static equilibrium position of the suspension magnet relative to the initial static equilibrium position along the axial direction of the sleeve is recorded as x2, and the magnet displacement of the suspension magnet at time t is recorded as x2(t). This application defines x1(t) and x2(t) as positive in the direction away from the fixed magnet 4 and negative in the direction toward the fixed magnet 4. The entire system is in a state of equilibrium. Based on the motion force of the suspension magnet under external vibration excitation combined with Newton's second law, the system equilibrium equation of the energy collection device can be constructed as follows:

[0068]

[0069] Among them, m f is the mass of the suspended magnet, g is the gravitational acceleration, f is the sum of the air viscosity force and the inner wall contact friction, and the sign factor sgn(x2(t) is used to adjust the direction of f to be opposite to the direction of x2(t).

[0070] F M (D(t)) is the repulsive force between the suspended magnet 5 and the fixed magnet 4 at time t, F M (D(t)) is related to the distance D(t) between the suspension magnet 5 and the fixed magnet 4 at time t, and the distance D(t) between the suspension magnet 5 and the fixed magnet 4 at time t is D(t)=d+x2(t), where d refers to the axial distance between the suspension magnet 5 and the fixed magnet 4 when the suspension magnet 5 is not subjected to external vibration excitation and is in the initial static equilibrium position, and is a known quantity after the structural design of the energy collection device is completed.

[0071] For the study of the force between two magnets, there is still a lack of a specific and accurate calculation model to quantitatively describe it. The Coulomb model is used as an approximate magnetic analysis model in mainstream theory, but the Coulomb model cannot accurately calculate the magnetic force within a small distance, and the size of the energy collection device of the present application is relatively small. The actual height of the entire energy collection device is only about 160 mm. Therefore, the distance between the two magnets is small, so the Coulomb model cannot be used directly to calculate the repulsive force between the two magnets. In order to accurately characterize the relationship between the repulsive force between the suspended magnet 5 and the fixed magnet 4 and the distance between the two magnets, the electromagnetic self-powered strain sensor manufacturing method also includes:

[0072] The experimental scene is built using the first magnet and the second magnet with known magnetic induction intensity: the first magnet is clamped by the bottom fixture, and the second magnet is clamped and fixed by the top fixture through the pressure sensor. In the initial state, the second magnet and the first magnet are arranged opposite to each other and separated by a known distance. Then the top fixture is controlled to drive the second magnet to move toward the first magnet, and the repulsive force of the pressure sensor at different distances between the second magnet and the first magnet is read. The repulsive force F between the two magnets at any time t is fitted according to the following function form: M (R M (t)) and the distance R between the two magnets M (t) Relationship:

[0073]

[0074] Among them, a, b, and c are correction coefficients obtained by fitting, H1 is the magnetic induction intensity of the first magnet, H2 is the magnetic induction intensity of the second magnet, and R M (t) is the distance between the first magnet and the second magnet at time t, and μ0 is the magnetic permeability of vacuum.

[0075] c e (x2(t)) is the electromagnetic damping at time t and is related to x2(t). When the suspension magnet 5 is excited and moves by external vibration, it will cause the change of magnetic flux in the coil 6. The kinetic energy is converted into electrical energy through the magnetic field. At this time, the output voltage U obtained by Faraday's law of electromagnetic induction is:

[0076]

[0077] in is the magnetic flux in the coil, which varies with the displacement of the magnet. e is the electromagnetic coupling coefficient, through which the electromagnetic damping c can be obtained e (x2(t)) expression. For the axial magnetic induction B inside a single coil x , the single coil internal flux is obtained by dividing it by the area, and the N coil internal fluxes are summed to give the total flux:

[0078]

[0079] When the load is connected to the circuit, current is generated in the circuit, and the coil in the circuit can be equivalent to the inductance L. Therefore, the electromechanical coupling equation of the entire circuit is:

[0080] L·dI / dt+(r+R)·I=ke·dx2 / dt

[0081] Where I is the time-varying current in the circuit, r is the coil resistance, and R is the resistance of the load part of the energy harvesting device. In this model, considering that the frequency of the external vibration excitation of the moving object to be monitored in the application scenario of this application is often low, the inductance L can be ignored in the low-frequency excitation scenario. After introducing the load into the system, we need to find the electromagnetic damping c in the equation e (x2(t)). Since electrical energy is obtained by converting mechanical energy into electromagnetic damping, according to the law of conservation of energy, the formula is as follows:

[0082] F e ·dx1 / dt=c e (x2)·(dx2 / dt) 2 =U 2 / (R+r)

[0083] where F e is the force due to electromagnetic damping and can be derived from the above equation:

[0084]

[0085] When the finite element analysis is actually performed, the magnetic flux equation and electromagnetic field simulation in the Comsol software are used to perform the finite element analysis. First, a finite element model is established in the Comsol software. In view of the two-dimensional symmetrical configuration of the energy collection device, the space on which the modeling is based is defined in a rectangular area bounded by a magnetic insulation boundary condition, which simulates the effect of metal shielding. In this finite element model, the magnet and the multi-turn coil are characterized in the geometric form of a matrix to simplify the grid construction and thus reduce the complexity of the solution. Since the purpose of the finite element simulation of this application is to determine the output voltage induced in the coil, and the output voltage is obtained by regional integration of the field, the simulation calculation of the output voltage shows extremely high robustness to the singularity in the field. Therefore, although the sharp corner design of the rectangle introduces local singularity in the magnetic field, the impact on the simulation process of this application can be ignored. In order to define the displacement of the magnet and the surrounding air domain, the dynamic mesh function is used in Comsol. Since the coil and the air domain around it do not deform, the dynamic mesh can be used to describe the displacement of the magnet and the air domain above and below it. When conducting field motion analysis, if the motion phenomenon is significant, it is necessary to use sliding grid technology.

[0086] During the finite element analysis, the magnetic induction intensity of the two magnets is configured, and the suspended magnet is controlled to move sinusoidally at a set frequency starting from the initial position (that is, in contact with the fixed magnet). The analysis and solution of the finite element model is divided into two steps. First, a steady-state analysis of the magnetic field is performed to calculate the magnetic field generated by the suspended magnet in the initial position (that is, in contact with the fixed magnet). This analysis step provides accurate initial conditions, and then a transient analysis of the magnetic field and dynamic grid is performed to obtain the voltage-distance curve under the current magnetic induction intensity. The magnetic induction intensity of the magnet is changed and the above process is repeated for finite element analysis to obtain the voltage-distance curve under different magnetic induction intensities.

[0087] 4. According to the voltage-distance curve of the energy collection device under different magnetic induction intensities, determine the magnetic induction intensity that makes the output voltage of the energy collection device reach the minimum voltage required for the diode in the rectifier energy storage circuit to conduct. Including:

[0088] According to the above system balance equation, the relationship between the device displacement x1(t) and the magnet displacement x2(t) can be determined. The external vibration excitation of the moving object to be monitored has an amplitude range, and the amplitude range can be determined by pre-statistics and analysis. Therefore, the device displacement range generated by the external vibration excitation generated by the moving object to be monitored is known. According to the value range of the device displacement x1(t) indicated by the device displacement range, combined with the relationship between the device displacement x1(t) and the magnet displacement x2(t), the magnet displacement range of the magnet displacement x2(t) can be determined, thereby determining the range of displacement of the suspended magnet under the external vibration excitation.

[0089] Then, for any magnetic induction intensity, when the output voltage of the voltage-distance curve of the energy collection device under this magnetic induction intensity reaches the minimum voltage required for the diode to be turned on in the rectifier energy storage circuit within the above-determined magnet displacement range, it means that the output voltage during the movement of the suspended magnet meets the requirements, and it can be determined that the current magnetic induction intensity can make the output voltage of the energy collection device reach the minimum voltage required for the diode to be turned on in the rectifier energy storage circuit, and the current magnetic induction intensity can be selected as the magnetic induction intensity of the two magnets in the energy collection device.

[0090] 5. Determine the length of the sleeve according to the determined magnetic induction intensity

[0091] In the static state, the suspended magnet 5 is subjected to a downward gravity m f g and the upward repulsive force between the fixed magnet 4 and the fixed magnet 4 to remain stationary at the initial static equilibrium position. The mass m of the suspended magnet 5 fIt is known that the repulsive force exerted on the suspension magnet 5 can be calculated according to the calculation formula of the repulsive force determined above. In the calculation formula of the repulsive force, the magnetic induction intensity of the magnet has been determined through the above steps. Based on the characteristic that the repulsive force between the suspension magnet 5 and the fixed magnet 4 in a static state is equal to the gravity of the suspension magnet, the distance d between the suspension magnet and the fixed magnet when the energy collection device is in a static state can be calculated, thereby determining the length of the sleeve to be 2d, to ensure that the coil can effectively sense the change of magnetic flux during the up and down vibration of the magnet, thereby generating an induced current.

[0092] After determining the design structure and structural parameters of the energy collection device, the energy collection device can be manufactured according to the design structure and structural parameters of the energy collection device, including:

[0093] First, the sleeve 3 is printed using a thermoplastic material using the fused deposition modeling printing technology according to the structural parameters of the sleeve. Then, the coil 6 is printed on the outer wall of the sleeve using the straight writing printing wire technology according to the structural parameters of the coil. Finally, the fixed magnet 4 is fixed inside the sleeve, and the suspension magnet 5 is placed inside the sleeve to obtain an energy collection device.

[0094] In order to make the coil 6 more quickly and easily, this embodiment uses a five-axis surface conformal printing technology to print and make the coil 6. The printing method includes: after a polyimide film (PI film) with double-sided adhesiveness is attached to the outer wall of the sleeve 3, the sleeve 3 attached with the polyimide film is mounted on the rotating shaft of the printer for fixing, and a syringe is fixed on the horizontal axis of the printer. Then, according to the structural parameters of the coil, the rotating shaft of the printer is controlled to drive the sleeve to rotate, and the syringe is controlled to move along the horizontal axis, and a metal wire is guided out of the syringe during the sleeve rotation and syringe movement process. The metal wire is attached to the outer wall of the sleeve under the action of the polyimide film to form a spiral coil.

[0095] Finally, the coil of the energy collection device is connected to the conductive wire of the sensor monitoring device through a rectifier energy storage circuit to produce the electromagnetic self-powered strain sensor of the present application. When the electromagnetic self-powered strain sensor is applied to human motion recognition technology, one application is as follows: Figure 5 As shown, the resistive strain sensor unit 2 is attached to the human leg to sense strain, and the energy collection device 100 and the monitoring board 200 integrated with the rectifier energy storage circuit and the resistance meter are fixed on the human leg. In the process of human movement, energy conversion and strain monitoring can be continuously realized, and no external power supply is required, and continuous and stable operation can be maintained. Figure 5 In addition to detecting leg movements in the example, the entire sensor has a high degree of integration in size, so it can also be used to monitor human hand movements and even finger movements, which has high application value.

[0096] The above is only a preferred embodiment of the present application, and the present application is not limited to the above embodiments. It is understood that other improvements and changes directly derived or associated by those skilled in the art without departing from the spirit and concept of the present application should be considered to be included in the protection scope of the present application.

Claims

1. A method for manufacturing an electromagnetic self-powered strain sensor, characterized in that: The method for manufacturing the electromagnetic self-powered strain sensor comprises: Determine the design structure of the energy collection device, the energy collection device includes a sleeve with a coil wound around the outer wall, and a fixed magnet and a suspension magnet arranged in the sleeve, the suspension magnet and the fixed magnet are arranged opposite to each other at one end with the same polarity, the fixed magnet is fixed in the sleeve, the suspension magnet is movably arranged in the sleeve and can move along the axial direction of the sleeve under the action of external vibration excitation, and the magnetic flux of the coil changes with the movement of the suspension magnet; Under the constraint that the output voltage of the energy collection device reaches the minimum voltage required for the diode in the rectifier energy storage circuit to be turned on, determining the structural parameters of the energy collection device, the structural parameters of the energy collection device including the structural parameters of the sleeve, the structural parameters of the coil, the structural parameters of the fixed magnet and the structural parameters of the suspension magnet; An energy collection device is manufactured according to the design structure and structural parameters of the energy collection device, and a sensor monitoring device is manufactured according to the design structure and structural parameters of the sensor monitoring device. The coil of the energy collection device is connected to the power supply end of the sensor monitoring device through a rectifier energy storage circuit to manufacture an electromagnetic self-powered strain sensor. The sensor monitoring device is used to sense the strain at a position to be detected of the moving object to be monitored, and the energy collection device is used to be arranged on the moving object to be monitored and generate AC power when it is excited by external vibration during the movement of the moving object to be monitored.

2. The method for manufacturing an electromagnetic self-powered strain sensor according to claim 1, characterized in that: Making energy harvesting devices and sensor monitoring devices includes: The sleeve is printed and manufactured using the fused deposition modeling printing technology according to the structural parameters of the sleeve, the coil is printed and manufactured on the outer wall of the sleeve using the straight writing printing wire technology according to the structural parameters of the coil, a fixed magnet with corresponding structural parameters is fixed inside the sleeve, and a suspended magnet with corresponding structural parameters is placed inside the sleeve to manufacture the energy collection device; A sensing layer is formed by printing conductive carbon paste on an insulating base layer using direct writing printing technology, and electrodes are formed by printing conductive silver paste on the sensing layer using direct writing printing technology and connected with conductive wires to produce a resistive strain sensing unit, and a resistance meter is connected with the conductive wires of the resistive strain sensing unit to produce the sensing monitoring device, and the resistive strain sensing unit is used to be arranged at a position to be detected of a moving object to be monitored.

3. The method for manufacturing an electromagnetic self-powered strain sensor according to claim 2, characterized in that: The structural parameters of the coil include the specification parameters of the metal wire wound to form the coil and the number of turns of the coil. The coil is printed on the outer wall of the sleeve and includes: After a double-sided adhesive polyimide film is attached to the outer wall of the sleeve, the sleeve with the polyimide film attached is placed on the rotating shaft of the printer for fixing, and a syringe is fixed on the horizontal axis of the printer; the rotating shaft of the printer is controlled to drive the sleeve to rotate, and the syringe is controlled to move along the horizontal axis, and during the rotation of the sleeve and the movement of the syringe, a metal wire with corresponding specification parameters is guided out of the syringe, and the metal wire is attached to the outer wall of the sleeve under the action of the polyimide film to form a spiral coil with a corresponding number of turns.

4. The method for manufacturing an electromagnetic self-powered strain sensor according to claim 1, characterized in that: The structural parameters of the sleeve include radial parameters of the sleeve and the length of the sleeve. The structural parameters of the two magnets are the same. The structural parameters of each magnet include size parameters, weight and magnetic induction intensity of the magnet. Determining the structural parameters of the energy harvesting device includes: Determine the diameter of the sleeve, the structural parameters of the coil, the size parameters of the magnet and the weight of the magnet; Based on the design structure of the energy harvesting device, a finite element model is established according to the diameter of the sleeve, the structural parameters of the coil, and the size parameters of the two magnets; Under different magnetic induction intensities of the magnet, a finite element model is used to perform finite element analysis on the movement process of the suspended magnet from the fixed magnet to the direction away from the fixed magnet, and a voltage distance curve of the energy collection device under the current magnetic induction intensity is obtained, and the voltage distance curve indicates a curve of the output voltage of the energy collection device changing with the distance between the two magnets; According to the voltage-distance curve of the energy collection device under different magnetic induction intensities, determine the magnetic induction intensity that makes the output voltage of the energy collection device reach the minimum voltage required for the diode in the rectifier tank circuit to be turned on; The length of the sleeve is determined according to the determined magnetic induction intensity.

5. The method for manufacturing an electromagnetic self-powered strain sensor according to claim 4, characterized in that: The finite element analysis of the movement of the suspension magnet from the fixed magnet to the direction away from the fixed magnet using the finite element model includes: Finite element analysis is performed based on the system balance equation of the suspended magnet during movement in combination with Faraday's law of electromagnetic induction to determine the change in magnetic flux and the corresponding output voltage generated during the movement of the suspended magnet from the fixed magnet to a direction away from the fixed magnet, thereby obtaining the voltage-distance curve; The system balance equation of the suspended magnet during motion is: Among them, m f is the mass of the suspension magnet, g is the gravitational acceleration; x1(t) represents the device displacement along the axial direction of the sleeve caused by the external vibration excitation of the energy collection device at time t, and x2(t) represents the magnet displacement along the axial direction of the sleeve relative to the initial static equilibrium position of the suspension magnet at time t; F M (D(t)) is the repulsive force between the levitation magnet and the fixed magnet at time t, and F M (x2(t)) is related to the distance D(t)=d+x2(t) between the suspension magnet and the fixed magnet at time t, where d is the axial distance between the suspension magnet and the fixed magnet when the suspension magnet is not subjected to external vibration excitation and is in the initial static equilibrium position; c e (x2(t)) is the electromagnetic damping at time t and is related to x2(t); f is the sum of the air viscosity and the inner wall contact friction, and the sign factor sgn(x2(t)) is used to adjust the direction of f to be opposite to the direction of x2(t).

6. The method for manufacturing an electromagnetic self-powered strain sensor according to claim 5, characterized in that: The method for manufacturing the electromagnetic self-powered strain sensor also includes: The first magnet is clamped by the bottom fixture, and the second magnet is clamped and fixed by the top fixture through the pressure sensor. The top fixture is controlled to drive the second magnet to move toward the first magnet, and the repulsive force of the pressure sensor at different distances between the second magnet and the first magnet is read. The repulsive force F between the two magnets at any time t is obtained by fitting. M (R M (t)) and the distance R between the two magnets M The relationship between (t) is: Among them, a, b, and c are correction coefficients obtained by fitting, H1 is the magnetic induction intensity of the first magnet, H2 is the magnetic induction intensity of the second magnet, and R M (t) is the distance between the first magnet and the second magnet at time t, and μ0 is the magnetic permeability of vacuum.

7. The method for manufacturing an electromagnetic self-powered strain sensor according to claim 5, characterized in that: Determining the magnetic induction intensity that enables the output voltage of the energy collection device to reach the minimum voltage required for the diode in the rectifier tank circuit to conduct includes: Determine the relationship between the device displacement x1(t) and the magnet displacement x2(t) according to the system balance equation, and determine the magnet displacement range in combination with the device displacement range generated by the external vibration excitation of the moving object to be monitored; For any magnetic induction intensity, when the output voltage of the voltage-distance curve of the energy collection device under the magnetic induction intensity within the magnet displacement range reaches the minimum voltage required for the diode in the rectifier energy storage circuit to be turned on, the magnetic induction intensity is determined so that the output voltage of the energy collection device reaches the minimum voltage required for the diode in the rectifier energy storage circuit to be turned on.

8. The method for manufacturing an electromagnetic self-powered strain sensor according to claim 6, characterized in that: Determining the length of the sleeve according to the determined magnetic induction intensity comprises: Based on the characteristic that the repulsive force between the suspension magnet and the fixed magnet in a static state is equal to the gravity of the suspension magnet, the distance d between the suspension magnet and the fixed magnet when the energy collection device is in a static state is calculated, and the length of the sleeve is determined to be 2d.

9. The method for manufacturing an electromagnetic self-powered strain sensor according to claim 1, characterized in that: The coil is wound and fixed on the outer wall of the sleeve in a segmented structure.

10. The method for manufacturing an electromagnetic self-powered strain sensor according to claim 1, characterized in that: The surface of the suspension magnet is coated with a lubricant.

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