Three-stable-state electromagnetic energy harvesting device suitable for low-frequency vibration excitation

Abstract

The invention discloses a three-stable-state electromagnetic energy harvesting device suitable for low-frequency vibration excitation, and belongs to the field of energy harvesters. The device comprises a mass block, a spring, a rack, a magnet, an energy conversion device and a laser displacement sensor. The upper surface of the mass block is vertically connected with the inner side wall of the top end through a spring, and the lower surface is vertically connected with the energy conversion device through a spring. The energy conversion device and the vertical spring are coaxially arranged on the lower end face of the inner side of the rack. The laser displacement sensor is arranged at the upper end of the inner side of the rack. According to the invention, on the basis of fixedly mounting structures such as a rack, the vertical distance 2b between hinge points on the same side of the inclined pull spring and the horizontal distance a between the inclined pull spring and the mass block are adjusted to realize the tri-stable potential energy of the tri-stable electromagnetic energy harvesting device. Under the tri-stable potential energy working condition of the tri-stable electromagnetic energy harvesting device, the energy harvesting efficiency of the tri-stable electromagnetic energy harvesting device is high, and the acquisition voltage peak value is improved by more than 10%; the energy harvesting frequency band is reduced, the collection frequency band moves leftwards by 16 Hz, and the comprehensive energy harvesting effect is good.

Description

TECHNICAL FIELD

[0001] The present application relates to a vibration energy harvesting device, in particular to a three-stable-state electromagnetic energy harvesting device suitable for low-frequency vibration excitation. BACKGROUND

[0002] With the rapid development of modern science and technology, the number of wireless sensor devices has increased rapidly, and the contradiction between the increasing demand for electric energy and the limited battery endurance has become increasingly prominent. The traditional battery power supply method has been difficult to meet the actual application requirements. As a device that can collect energy from environmental vibrations, the energy harvester is considered as an effective solution to replace traditional chemical batteries and achieve continuous power supply, which is of great significance to promote the progress of wireless sensor networks and other fields. Therefore, it has received widespread attention in recent years.

[0003] Notably, under the impetus of the continuous progress of microelectronics technology and microfabrication processes, wireless sensor networks and portable electronic devices have developed rapidly and have been widely used in remote control, national defense and military, environmental monitoring, emergency rescue and other important fields. However, the limitations of traditional chemical batteries in terms of life, weight, volume and environmental performance have brought many difficulties to the application of microelectronic devices, and this defect is particularly prominent in the rapidly developing field of wireless sensor networks and embedded systems. Although researchers have developed a variety of micro energy devices such as micro solar cells, micro lithium batteries and fuel cells using MEMS technology, the application of micro solar cells is subject to weather conditions and installation environment, while micro lithium batteries and fuel cells have problems such as insufficient energy density and limited service life. Therefore, developing an independent energy supply system with long service life has become a key technical problem to be solved.

[0004] Vibration as a ubiquitous natural phenomenon, due to its wide distribution and high energy density, the research on vibration energy conversion and harvesting has gradually risen and developed in recent decades. The early linear energy harvester has a narrow frequency band, which seriously limits its practicality and cannot be efficiently applied to wideband vibration sources. To break through the limitations of the traditional energy harvester, the design of nonlinear structure has gradually become a research hotspot, which has derived various nonlinear energy harvester configurations, including single-stable, double-stable and triple-stable nonlinear oscillators. Compared with linear systems, this nonlinear electromechanical coupling characteristic can not only improve the energy output efficiency, but also reduce the sensitivity of the system to external conditions. However, it should be noted that under the condition of weak nonlinearity or small excitation amplitude, the performance of single-stable energy harvester is similar to that of linear system. In contrast, double-stable energy harvester effectively solves this limitation by exciting large-amplitude inter-well motion, and can achieve higher average output power in a wider frequency range. The paper "Human motion energy harvesting backpack using quasi-zero stiffness mechanism, Energy Conversion and Management, 2023, 288: 117158" proposes a quasi-zero stiffness energy harvesting backpack (QZS-EHB), which constructs a double-stable quasi-zero stiffness mechanism by connecting a pair of positive stiffness springs and a pair of negative stiffness springs in parallel, so that the vibration system is more easily excited by low-frequency human motion to produce rapid action, and the bidirectional mechanical vibration is modulated into unidirectional high-speed rotation, and then harvested by an electromagnetic coil. The theoretical model of the double-stable system is established by using the Lagrangian functional method, and the double-stable mechanism is verified. Through experiments, the advantages of the design are verified. However, due to the use of more gear pairs in the process of modulating bidirectional mechanical vibration into unidirectional mechanical motion, the energy transmission efficiency is reduced, and the lubrication problem derived from the gear pairs leads to poor applicability of the structure. At the same time, the two vertical guide rods absorb part of the oblique spring tension, affecting the motion state of the system.

[0005] Meanwhile, the document "Theoretical and experimental studies on the characteristics of a tri-stable piezoelectric harvester Arch. Appl. Mech. 2017, 87: 1541-1554" discloses a tri-stable energy harvester composed of a cantilever beam and a magnetic mass oscillating between two fixed magnets, and studies its harvesting performance under external periodic excitation from the perspective of numerical simulation and experiment, and the study finds that compared with a bistable energy harvester, the tri-stable energy harvester has a smaller energy motion threshold and can effectively harvest energy in a wider low-frequency range. However, the energy harvesting frequency band of the cantilever beam type tri-stable piezoelectric energy harvesting device is biased towards the high-frequency region, and it is difficult to appear in the actual life activities of human beings, and therefore a vibration energy harvesting device more suitable for low-frequency conditions is needed. SUMMARY

[0006] In order to solve the problem of low harvesting efficiency of the vibration energy harvesting device under low-frequency conditions, the purpose of the present application is to provide a tri-stable electromagnetic energy harvesting device suitable for low-frequency vibration excitation, which realizes the tri-stable potential energy of the tri-stable electromagnetic energy harvesting device by adjusting the vertical distance 2b of the same side hinge point of the inclined pull spring and the horizontal distance a of the mass block based on the structure of the fixed installation rack. Under the working condition of the tri-stable potential energy of the tri-stable electromagnetic energy harvesting device, the tri-stable electromagnetic energy harvesting device has higher energy harvesting efficiency than similar structures, and the peak harvesting voltage is increased by more than 10%; at the same time, the system energy harvesting frequency band is reduced, and the harvesting frequency band of similar structures is shifted to the left by 16Hz, and the comprehensive energy harvesting effect is better.

[0007] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0008] The tri-stable electromagnetic energy harvesting device suitable for low-frequency vibration excitation disclosed by the present application comprises a mass block, a spring, a rack, a magnet, an energy conversion device and a laser displacement sensor.

[0009] The mass block is located in the center of the rack, and the upper surface is connected to the inner side wall of the top end through the spring, and the lower surface is connected to the energy conversion device through the spring. The energy conversion device is coaxially arranged with the vertical spring on the inner side lower end surface of the rack, and the laser displacement sensor is arranged on the inner side upper end of the rack. The left and right sides of the mass block are respectively hinged to the rack through two pairs of left-right symmetrical inclined pull springs. The vertical distance of the same side hinge point is 2b, and the horizontal distance from the mass block is a. The magnet is arranged on the lower surface of the mass block and is symmetrically parallel to the vertical spring.

[0010] After fixing the installation rack, the mass block, the vertical spring and the energy conversion device, the method for realizing tri-stable motion by adjusting a and b is as follows:

[0011] F = 2F v + 2F h1 sinθ1+ 2F h2 sinθ2 (1)

[0012] In the formula, F is the force that the bottom excitation band brings to the mass block, F v is the elastic restoring force of the vertical spring, F h1 and F h2 are the elastic restoring forces of the inclined pull springs, where X is the vertical relative displacement of the mass block, L is the initial length of the inclined pull spring, K h and K v are the stiffness of the inclined pull spring and the vertical spring respectively, and the spring restoring force is specifically

[0013]

[0014] The inclination angles of the inclined pull springs are respectively

[0015]

[0016] Bring (2) and (3) into (1), and the formula (1) is transformed into

[0017]

[0018] Integrate formula (4) to obtain the system potential energy U(x):

[0019]

[0020] According to the α and β when the U(x) is in the three-stable state potential energy, a and b are obtained, and then the three-stable state motion is realized.

[0021] The energy conversion device is mainly composed of a coil, which serves as an energy conversion carrier and converts the mechanical energy of the three-stable state electromagnetic energy trapping device into electrical energy during the vertical movement of the magnet.

[0022] Further, when α = 0.4 and 0 < β < 0.4, the three-stable state electromagnetic energy trapping device has three-stable state potential energy.

[0023] Further, the lower end of the rack is fixed on the exciter through bolts, and the low-frequency vibration excitation is simulated through the exciter and transmitted to the three-stable state electromagnetic energy trapping device.

[0024] Further, when the stiffness ratio of the inclined pull spring to the vertical spring is , the three-stable state electromagnetic energy trapping device has three-stable state potential energy.

[0025] Further, the low-frequency vibration excitation is a harmonic excitation, and the excitation frequency is less than 2Hz.

[0026] The method for collecting electric energy disclosed by the application is realized by using a three-stable-state electromagnetic energy trapping device suitable for low-frequency vibration excitation.

[0027] Advantages:

[0028] 1. The three-stable-state electromagnetic energy trapping device suitable for low-frequency vibration excitation disclosed by the application uses harmonic excitation with a frequency lower than 2 Hz to simulate human walking behavior, which not only meets the low-frequency nature of human behavior but also successfully simulates the periodicity during walking, thereby better reflecting the energy collection effect of the three-stable-state energy trapping device under low-frequency conditions.

[0029] 2. The three-stable-state electromagnetic energy trapping device suitable for low-frequency vibration excitation disclosed by the application uses a multi-spring structure to realize three-stable-state motion energy trapping, which ensures the anti-interference ability of the energy trapping device compared with double-stable-state motion energy trapping, and simultaneously widens the energy collection frequency band of the energy trapping device due to the strong nonlinear force of the inclined spring.

[0030] 3. The three-stable-state electromagnetic energy trapping device suitable for low-frequency vibration excitation disclosed by the application uses an electromagnetic coil plus a permanent magnet to trap energy, which is more sensitive to the motion of the central mass block compared with piezoelectric energy trapping, reduces the collection frequency band, and improves the energy trapping efficiency under low-frequency vibration. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is a forward schematic view of the three-stable-state electromagnetic energy trapping device under low-frequency vibration excitation;

[0032] Figure 2 is a partial parameter schematic view of the three-stable-state electromagnetic energy trapping device under low-frequency vibration excitation;

[0033] Figure 3 is a force analysis diagram of the mass block of the three-stable-state electromagnetic energy trapping device under low-frequency vibration excitation;

[0034] Figure 4 is a potential energy diagram of the system potential energy of the three-stable-state electromagnetic energy trapping device under low-frequency vibration excitation with respect to α;

[0035] Figure 5 is a potential energy diagram of the system potential energy of the three-stable-state electromagnetic energy trapping device under low-frequency vibration excitation with respect to β;

[0036] Figure 6It is the system tristable cross-sectional potential energy diagram of the tristable electromagnetic energy harvesting device under low-frequency vibration excitation;

[0037] Figure 7 This is a physical picture of a tristable electromagnetic energy harvesting device under low-frequency vibration excitation;

[0038] Figure 8 This is the frequency sweep result diagram of the tristable electromagnetic energy harvesting device under low-frequency vibration excitation;

[0039] Figure 9 This is the collected voltage diagram of the tristable electromagnetic energy harvesting device under low-frequency vibration excitation;

[0040] Figure 10 It is the system phase diagram of the tristable electromagnetic energy harvesting device under low-frequency vibration excitation.

[0041] Among them, 1 is a mass block, 2 is a spring, 3 is a frame, 4 is a magnet, 5 is an energy conversion device, and 6 is a laser displacement sensor. DETAILED DESCRIPTION

[0042] The specific implementation is described as follows with reference to the accompanying drawings:

[0043] This embodiment discloses a tristable electromagnetic energy harvesting device suitable for low-frequency vibration excitation, including a mass block 1, a spring 2, a frame 3, a magnet 4, an energy conversion device 5 and a laser displacement sensor 6.

[0044] like Figure 1 As shown, the mass block is located in the center of the frame, with its upper surface vertically connected to the inner wall of the top through a spring, and its lower surface vertically connected to the energy conversion device through a spring; the energy conversion device and the vertical spring are coaxially arranged on the lower end surface of the inner side of the frame, and the laser displacement sensor is arranged at the upper end of the inner side of the frame; the left and right sides of the mass block are respectively hinged to the frame through two pairs of left-right symmetrical inclined springs, and the magnet is placed on the lower surface of the mass block, parallel and symmetrical to the vertical spring; as shown Figure 2 As shown, the vertical spring stiffness is K v , the stiffness of the inclined spring is K h , the vertical distance between the hinge points on the same side of the inclined spring is 2b, and the horizontal distance between the hinge points and the mass block is a. After being acted upon by the vertical external excitation force F, the mass block undergoes vertical displacement, and at the same time, the horizontal inclination angles θ1 and θ2 of the inclined spring change; Figure 3 As shown, the elastic restoring force on the central mass block at this time includes F generated by the vertical spring v , and F generated by the inclined spring h1 、F h2 Integrating the elastic restoring force yields the potential energy function U(x) shown in formula (5) in the claims. Figure 4As shown, the effect of α on the shape of the system potential energy is analyzed, and it is found that when α = 0.4, the cross-sectional shape of the potential energy function U(x) is tri-stable. As shown in Figure 5 As shown, the effect of β on the shape of the system potential energy is analyzed, and it is found that when β < 0.4, the cross-sectional shape of the potential energy function U(x) is tri-stable. As shown in Figure 6 As shown, when α = 0.4 and β = 0.35, the potential energy function U(x) exhibits three stable solutions and two unstable solutions, and the energy trapping device has a tri-stable characteristic, which is a tri-stable energy trapping system.

[0045] As shown in Figure 7 As shown, the frame, energy conversion device and laser displacement sensor are fixedly installed, the vertical spring mass block is connected, and the Figure 6 As shown in

[0046] The embodiment discloses a method for implementing a tri-stable electromagnetic energy trapping device suitable for low-frequency vibration excitation, and the specific implementation method is as follows:

[0047] The harmonic excitation is generated by a signal generator and transmitted to an exciter after being amplified by a signal amplifier, and the vertical displacement of the central mass block and the real-time acquisition voltage of the energy conversion device are collected and recorded by a laser displacement sensor and an oscilloscope, respectively; the dynamic response and energy harvesting effect of the system at different frequencies are tested by changing the harmonic excitation frequency.

[0048] As shown in Figure 8 As shown, the system acquisition voltage amplitude reaches 5.6V, which is 10% higher than the peak voltage 5.12V in the literature "Human motion energy harvesting backpack using quasi-zero stiffness mechanism, Energy Conversion and Management, 2023, 288: 117158", and the acquisition voltage presents a harmonic shape, and the acquisition voltage is more stable. As shown in Figure 9As shown, the voltage peak collection frequency band of the system in the voltage sweep result is concentrated on the 0.3Hz-0.8Hz frequency band, compared with the system peak collection frequency band of 16.8Hz-17.5Hz in the device system peak collection frequency band in the literature "Theoretical and experimental studies on the characteristics of a tri-stable piezoelectric harvester Arch. Appl. Mech. 2017, 87: 1541-1554", the system peak collection frequency band is left shifted by 16Hz, has a lower frequency collection effect, and is conducive to realizing the collection of low-frequency vibration energy more in line with actual life. As shown in Figure 10 As shown, the motion represented by the phase diagram of the system is a large-amplitude tri-stable periodic motion, which has good dynamic performance, and the motion amplitude is larger than that in the literature "Human motion energy harvesting backpack using quasi-zero stiffness mechanism, Energy Conversion and Management, 2023, 288: 117158", which is more conducive to vibration energy harvesting.

[0049] In summary, the embodiment has higher collection performance in a low-frequency vibration environment, and the structure is simple, and is more suitable for vibration energy collection in human daily activities.

[0050] The above specific description further details the purpose, technical solutions and beneficial effects of the application. It should be understood that the above description is only a specific embodiment of the application and is not used to limit the protection scope of the application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the application should be included in the protection scope of the application.

Claims

1. A tristable electromagnetic energy harvesting device suitable for low-frequency vibration excitation, characterized by: It includes a mass block, a spring, a frame, a magnet, an energy conversion device and a laser displacement sensor; The mass block is located in the center of the frame, with its upper surface vertically connected to the inner wall of the top via a spring, and its lower surface vertically connected to the energy conversion device via a spring. The energy conversion device and the vertical spring are arranged coaxially on the lower inner end surface of the frame, and the laser displacement sensor is arranged at the upper inner end of the frame. The left and right sides of the mass block are hinged to the frame via two pairs of symmetrical oblique tension springs. The vertical spacing between the hinge points on the same side is 2b, and the horizontal spacing with the mass block is a. The magnet is placed on the lower surface of the mass block, parallel and symmetrical to the vertical spring. Under the combined action of the vertical and oblique tension springs, the mass block exhibits a tristable motion law.

2. The tristable electromagnetic energy harvesting device according to claim 1, wherein: After the frame, mass, vertical spring, and energy conversion device are fixed and installed, the method of achieving tristable motion by adjusting a and b is as follows: F=2F v +2F h1 sinθ1+2F h2 sinθ2 (1) Where F is the force exerted by the bottom excitation on the mass block, F v is the elastic restoring force of the vertical spring, F h1 and F h2 The elastic restoring force of the inclined spring is: The horizontal distance between the hinge points on the same side of the inclined spring is 2b, and the horizontal distance between the hinge points and the mass block is a; K h With K v are the stiffness of the inclined spring and the vertical spring respectively; X is the vertical relative displacement of the mass block, and L is the initial length of the inclined spring; The inclination angles of the inclined springs are Substitute (2) and (3) into (1) and combine the dimensionless substitution Formula (1) can be transformed into, Integrating equation (4) yields the system potential energy U(x): According to α and β when U(x) is in the tristable potential energy, a and b are obtained, thereby realizing the tristable motion of the tristable electromagnetic energy harvesting device.

3. The tristable electromagnetic energy harvesting device according to claim 1, wherein: The energy conversion device is mainly composed of a coil, which serves as an energy conversion carrier and converts the mechanical energy of the tristable electromagnetic energy harvesting device into electrical energy during the vertical movement of the magnet.

4. The tristable electromagnetic energy harvesting device according to claim 2, wherein: When α=0.4 and 0<β<0.4, the tristable electromagnetic energy harvesting device has tristable potential energy.

5. The tristable electromagnetic energy harvesting device according to claim 2, wherein: The lower end of the frame is fixed to the exciter by bolts, and the exciter simulates low-frequency vibration excitation and transmits it to the tristable electromagnetic energy capture device.

6. The tristable electromagnetic energy harvesting device according to claim 2, wherein: Ratio of the stiffness of the inclined spring to the vertical spring When , the tristable electromagnetic energy harvesting device has tristable potential energy.

7. The low-frequency vibration excitation according to claim 5, characterized in that: Low-frequency vibration excitation is harmonic excitation, and the excitation frequency is less than 2Hz.

8. A method for collecting electrical energy using the tristable electromagnetic energy harvesting device according to claim 1, 2 or 3, characterized in that: The harmonic excitation is output from the signal generator, amplified by the power amplifier, and then input into the exciter to act on the tristable electromagnetic energy harvesting device. Under the vertical excitation, the mass block drives the magnet to move vertically and cuts the coil to realize energy conversion. In the tristable motion state, the energy harvesting device can not only ensure anti-interference ability but also realize broadband energy collection.

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