A tristable electromagnetic energy harvesting device suitable for low-frequency vibration excitation

Abstract

A tristable electromagnetic energy harvesting device suitable for low-frequency vibration excitation belongs to the field of energy harvesters. This invention includes a mass block, springs, a frame, magnets, an energy conversion device, and a laser displacement sensor. The mass block is located in the center of the frame, its upper surface is vertically connected to the inner wall of the top via a spring, and its lower surface is vertically connected to the energy conversion device via a spring. The energy conversion device and the vertical spring are coaxially arranged on the lower inner end face of the frame, and the laser displacement sensor is arranged on the upper inner end of the frame. Based on a fixed frame and other structures, this invention achieves tristable potential energy of the tristable electromagnetic energy harvesting device by adjusting the vertical distance 2b between the hinge points on the same side of the inclined springs and its horizontal distance a between the springs and the mass block. Under the tristable potential energy operating conditions, the tristable electromagnetic energy harvesting device exhibits high energy harvesting efficiency, increasing the peak acquisition voltage by more than 10%; the energy harvesting frequency band is reduced, shifting the acquisition frequency band to the left by 16Hz, resulting in good overall energy harvesting performance.

Description

Technical Field

[0001] This invention relates to a vibration energy harvesting device, and more particularly to a tristable electromagnetic energy harvesting device suitable for low-frequency vibration excitation. Background Technology

[0002] With the rapid development of modern technology, the number of wireless sensor devices has surged, highlighting the growing contradiction between their increasing power demands and limited battery life. Traditional battery-powered methods are no longer sufficient to meet practical application needs. As a device capable of harvesting energy from environmental vibrations, energy harvesters are considered an effective solution to replace traditional chemical batteries and achieve continuous power supply. They are of great significance for promoting progress in fields such as wireless sensor networks and have therefore received widespread attention in recent years.

[0003] It is worth noting that, driven by continuous advancements in microelectronics technology and microfabrication processes, wireless sensor networks and portable electronic devices have developed rapidly and are widely used in many important fields such as remote control, national defense, environmental monitoring, and emergency rescue. However, the limitations of traditional chemical batteries in terms of lifespan, weight, size, and environmental performance have brought many challenges to the application of microelectronic devices, a deficiency that is particularly prominent in the rapidly developing fields of wireless sensor networks and embedded systems. Although researchers have developed various miniature energy devices using MEMS processes, such as miniature solar cells, miniature lithium batteries, and fuel cells, the application of miniature solar cells is limited by weather conditions and installation environment, while miniature lithium batteries and fuel cells suffer from insufficient energy density and limited lifespan. Therefore, developing independent power supply systems with long lifespan characteristics has become a key technical challenge that urgently needs to be solved.

[0004] Vibration, as a ubiquitous natural phenomenon, has seen a surge in research on vibration energy conversion, harvesting, and utilization in recent decades due to its wide distribution and high energy density. Early linear energy harvesters, with their narrow bandwidth, severely limited their practicality and hindered efficient application to wide-frequency vibration sources. To overcome the bandwidth limitations of traditional energy harvesters, nonlinear structural design has become a research hotspot, leading to various nonlinear energy harvester configurations, including monostable, bistable, and tristable nonlinear oscillators. Compared to linear systems, this nonlinear electromechanical coupling characteristic not only improves energy output efficiency but also reduces the system's sensitivity to external conditions. However, it's important to note that under weak nonlinearity or small excitation amplitude conditions, the performance of monostable energy harvesters is relatively close to that of linear systems. In contrast, bistable energy harvesters, by exciting large-amplitude inter-well motion, effectively overcome this limitation, achieving higher average output power over 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). It constructs a bistable quasi-zero stiffness mechanism by connecting a pair of positive stiffness springs and a pair of negative stiffness springs in parallel. This makes the vibration system more susceptible to excitation by low-frequency human motion, generating rapid action and modulating bidirectional mechanical vibration into unidirectional high-speed rotation, with energy harvested through electromagnetic coils. A theoretical model of the bistable system was established using the Lagrange functional method, and the bistable mechanism was verified. Experiments confirmed the design's advantages. However, the use of numerous gear pairs in modulating bidirectional mechanical vibration into unidirectional mechanical motion reduces energy transmission efficiency, and the lubrication problems arising from these gear pairs lead to poor structural applicability. Furthermore, the two vertical guide rods absorb some of the oblique spring tension, affecting the system's motion state.

[0005] Meanwhile, the paper "Theoretical and experimental studies on the characteristics of a tri-stable piezoelectric harvester Arch. Appl. Mech. 2017, 87: 1541–1554" discloses a tristable energy harvester consisting of a cantilever beam and a magnetic mass oscillating between two fixed magnets. The paper studies its harvesting performance under external periodic excitation from both numerical simulation and experimental perspectives. The study found that compared to a bistable energy harvester, the tristable energy harvester has a smaller energy movement threshold and can effectively harvest energy over a wider low-frequency range. However, the energy harvesting frequency band of the cantilever beam tristable piezoelectric energy harvester is biased towards the high-frequency region, which is difficult to observe in actual human life. Therefore, a vibration energy harvesting device more suitable for low-frequency conditions is needed. Summary of the Invention

[0006] To address the issue of low energy harvesting efficiency in vibration-induced energy harvesting devices under low-frequency conditions, this invention aims to provide a tristable electromagnetic energy harvesting device suitable for low-frequency vibration excitation. Based on a fixed mounting frame and other structures, this device achieves tristable potential energy by adjusting the vertical distance 2b between the hinge points on the same side of the inclined spring and its horizontal distance a from the mass block. Under the tristable potential energy operating conditions, the tristable electromagnetic energy harvesting device exhibits higher energy harvesting efficiency than similar structures, with a peak harvesting voltage increase of over 10%. Simultaneously, the system's energy harvesting frequency band is reduced, shifting the acquisition frequency band 16Hz to the left compared to similar structures, resulting in better overall energy harvesting performance.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] The present invention discloses a tristable electromagnetic energy harvesting device suitable for low-frequency vibration excitation, comprising a mass block, a spring, a frame, a magnet, an energy conversion device, and a laser displacement sensor.

[0009] The mass block is located in the center of the frame. Its upper surface is vertically connected to the inner top wall via springs, and its lower surface is vertically connected to the energy conversion device via springs. The energy conversion device is coaxially arranged with the vertical springs on the lower inner surface of the frame, and the laser displacement sensor is located on the upper inner surface of the frame. The left and right sides of the mass block are hinged to the frame by two pairs of symmetrical diagonal tension springs. The vertical distance between the hinge points on the same side is 2b, and the horizontal distance from the mass block is a. Magnets are placed on the lower surface of the mass block, parallel and symmetrical to the vertical springs.

[0010] After fixing the frame, mass block, vertical spring, and energy conversion device, the method for achieving tristable 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 exerted on the mass block by the bottom excitation. v F is the elastic restoring force of the vertical spring. h1 and F h2 All are elastic restoring forces of tension springs. Where X is the vertical relative displacement of the mass block, L is the initial length of the cable spring, and K h With K v These are the stiffnesses of the inclined spring and the vertical spring, respectively, and the spring restoring force is specifically...

[0013]

[0014] The inclination angles of the tension springs are respectively

[0015]

[0016] Substituting (2) and (3) into (1), equation (1) transforms into:

[0017]

[0018] Integrating equation (4) yields the system potential energy U(x):

[0019]

[0020] Based on α and β when U(x) is in a tristable state, we can obtain a and b, and thus achieve tristable motion.

[0021] The energy conversion device is mainly composed of coils, which act as the energy conversion carriers. During the vertical movement of the magnet, the mechanical energy of the tristable electromagnetic energy trapping device is converted into electrical energy.

[0022] Furthermore, when α = 0.4 and 0 < β < 0.4, the tristable electromagnetic energy harvesting device has tristable potential energy.

[0023] Furthermore, the lower end of the frame is fixed to the exciter with bolts, and the exciter simulates low-frequency vibration excitation and transmits it to the tristable electromagnetic energy harvesting device.

[0024] Furthermore, the stiffness ratio of the inclined spring to the vertical spring... At that time, the tristable electromagnetic energy harvesting device has tristable potential energy.

[0025] Furthermore, the low-frequency vibration excitation is harmonic excitation, with an excitation frequency of less than 2Hz.

[0026] The energy harvesting method disclosed in this invention employs a tristable electromagnetic energy harvesting device suitable for low-frequency vibration excitation. Specifically, the method involves: harmonic excitation output from a signal generator, amplified by a power amplifier, and then input to an exciter that acts on the tristable electromagnetic energy harvesting device. Under vertical excitation, a mass block drives a magnet to move vertically and cuts the coil, achieving energy conversion. The energy harvesting device, in its tristable motion state, ensures both anti-interference capability and wideband energy harvesting.

[0027] Beneficial effects:

[0028] 1. The present invention discloses a tristable electromagnetic energy harvesting device suitable for low-frequency vibration excitation. It uses harmonic excitation with a frequency lower than 2Hz to simulate human walking behavior, which satisfies the low frequency of human behavior and successfully simulates the periodicity of walking, thus better reflecting the energy harvesting effect of the tristable energy harvesting device under low-frequency conditions.

[0029] 2. The present invention discloses a tristable electromagnetic energy harvesting device suitable for low-frequency vibration excitation. It adopts a multi-spring structure to achieve tristable motion energy harvesting. Compared with bistable motion energy harvesting, it ensures the anti-interference capability of the energy harvesting device. At the same time, due to the strong nonlinear force of the inclined spring, the energy harvesting frequency band of the energy harvesting device is broadened.

[0030] 3. The present invention discloses a tristable electromagnetic energy harvesting device suitable for low-frequency vibration excitation. It uses an electromagnetic coil and a permanent magnet to harvest energy. Compared with piezoelectric energy harvesting, it is more sensitive to the motion of the central mass block, reduces the acquisition frequency band, and improves the energy harvesting efficiency under low-frequency vibration. Attached Figure Description

[0031] Figure 1 This is a forward schematic diagram of a tristable electromagnetic energy harvesting device under low-frequency vibration excitation.

[0032] Figure 2 This is a schematic diagram of some parameters of a tristable electromagnetic energy harvesting device under low-frequency vibration excitation.

[0033] Figure 3 This is a force analysis diagram of the mass block of a tristable electromagnetic energy harvesting device under low-frequency vibration excitation.

[0034] Figure 4 This is a diagram showing the system potential energy of a tristable electromagnetic energy harvesting device under low-frequency vibration excitation as a function of α.

[0035] Figure 5 This is a potential energy diagram of the system potential energy of a tristable electromagnetic energy harvesting device under low-frequency vibration excitation as a function of β.

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

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

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

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

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

[0041] Among them, 1—mass block, 2—spring, 3—frame, 4—magnet, 5—energy conversion device, and 6—laser displacement sensor. Detailed Implementation

[0042] The specific implementation method is described below 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. Its upper surface is vertically connected to the inner top wall via springs, and its lower surface is vertically connected to the energy conversion device via springs. The energy conversion device is coaxially arranged with the vertical springs on the lower inner surface of the frame, and a laser displacement sensor is located on the upper inner surface of the frame. The left and right sides of the mass block are hinged to the frame by two pairs of symmetrical diagonal springs. Magnets are placed on the lower surface of the mass block, parallel and symmetrical to the vertical springs. Figure 2 As shown, the stiffness of the vertical spring is K. v The stiffness of the cable spring is K. h The vertical distance between the hinge points on the same side of the tension spring is 2b, and the horizontal distance between it and the mass block is a. After being subjected to a 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 tension spring change; for example... 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 the F generated by the inclined spring h1 F h2 Integrating the elastic restoring force yields the potential energy function U(x) shown in equation (5) of the claim. Figure 4As shown, the influence of α on the shape of the system's 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 tristable. Figure 5 As shown, the influence of β on the shape of the system's 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 tristable. 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. At this time, the energy harvesting device has tristable characteristics and is a tristable energy harvesting system.

[0045] like Figure 7 As shown, the frame, energy conversion device, and laser displacement sensor are fixedly installed, and the vertical spring mass block is connected, according to... Figure 6 The given ratio of α = 0.4 and β = 0.35 is used to install the inclined spring, so that the potential energy of the energy harvesting device exhibits tristable characteristics.

[0046] This embodiment discloses a method for implementing a tristable electromagnetic energy harvesting device suitable for low-frequency vibration excitation. The specific implementation method is as follows:

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

[0048] like Figure 8 As shown, the system's acquired voltage amplitude reached 5.6V, a 10% improvement over the peak voltage of 5.12V reported in the literature "Human motion energy harvesting backpack using quasi-zero stiffness mechanism, Energy Conversion and Management, 2023, 288:117158". Furthermore, the acquired voltage exhibited a harmonic pattern, indicating greater stability. Figure 9As shown, the voltage peak acquisition frequency band in the system's voltage frequency sweep results is concentrated in the 0.3Hz-0.8Hz band. Compared to the system in the literature "Theoretical and experimental studies on the characteristics of a tri-stable piezoelectric harvester Arch. Appl. Mech. 2017, 87: 1541–1554" where the peak acquisition frequency band is 16.8Hz-17.5Hz, the peak acquisition frequency band is shifted to the left by 16Hz, resulting in a lower frequency acquisition effect. This is beneficial for achieving the acquisition of low-frequency vibration energy that is more consistent with real-life situations. Figure 10 As shown, the phase diagram of the system exhibits a large-amplitude tristable periodic motion, which has good dynamic performance. The motion amplitude is larger than that in the literature "Human motion energy harvesting backpack using quasi-zerostiffness mechanism, Energy Conversion and Management, 2023, 288:117158", which is more conducive to vibrational energy harvesting.

[0049] In summary, this embodiment has higher acquisition performance in low-frequency vibration environments, has a simple structure, and is more suitable for acquiring vibration energy during daily human activities.

[0050] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A tristable electromagnetic energy harvesting device suitable for low-frequency vibration excitation, characterized in that: It includes a mass block, springs, frame, magnets, energy conversion device, and laser displacement sensor; The mass block is located in the center of the frame. Its upper surface is vertically connected to the inner wall of the top via a spring, and its lower surface is vertically connected to the energy conversion device via a spring. The energy conversion device is coaxially arranged with the vertical spring on the lower inner surface of the frame, and the laser displacement sensor is arranged on the upper inner surface of the frame. The left and right sides of the mass block are hinged to the frame by two pairs of symmetrical inclined tension springs. The vertical distance between the hinge points on the same side is 2b, and the horizontal distance from the mass block is a. The magnet is placed on the lower surface of the mass block, parallel and symmetrical with the vertical spring. Under the combined action of the vertical and inclined tension springs, the mass block exhibits a tristable motion law. After fixing the frame, mass block, vertical spring, and energy conversion device, the method for achieving tristable motion by adjusting a and b is as follows: (1) In the formula, The force exerted on the mass block by the bottom excitation. The elastic restoring force of the vertical spring. and All are tension springs with elastic restoring force, and the spring restoring force is: (2) The horizontal distance between the hinge points on the same side of the tension spring is 2b, and the horizontal distance between it and the mass block is a. and These are the stiffnesses of the inclined spring and the vertical spring, respectively. The vertical relative displacement of the mass block. This is the initial length of the tension spring; The inclination angles of the tension springs are respectively (3) Substitute (2) and (3) into (1), and combine with the dimensionless algebraic expression. Equation (1) can be transformed into, (4) Integrating equation (4) yields the system potential energy. : (5) according to When in a state of three-stability and We obtain a and b, and then realize the tristable motion of the tristable electromagnetic energy harvesting device.

2. The tristable electromagnetic energy harvesting device as described in claim 1, characterized in that: The energy conversion device is mainly composed of coils, which act as the energy conversion carriers. During the vertical movement of the magnet, the mechanical energy of the tristable electromagnetic energy trapping device is converted into electrical energy.

3. The tristable electromagnetic energy harvesting device as described in claim 1, characterized in that: =0.4, 0< When the energy level is less than 0.4, the tristable electromagnetic energy harvesting device has tristable potential energy.

4. The tristable electromagnetic energy harvesting device as described in claim 1, characterized in that: The lower end of the frame is fixed to the exciter with bolts. The exciter simulates low-frequency vibration excitation and transmits it to the tristable electromagnetic energy harvesting device.

5. The tristable electromagnetic energy harvesting device as described in claim 1, characterized in that: Stiffness ratio of inclined spring to vertical spring At that time, the tristable electromagnetic energy harvesting device has tristable potential energy.

6. The tristable electromagnetic energy harvesting device as described in claim 4, characterized in that: The low-frequency vibration excitation is a harmonic excitation with an excitation frequency of less than 2Hz.

7. A method for collecting electrical energy using a tristable electromagnetic energy harvesting device as described in claim 1 or 2, characterized in that: The harmonic excitation is output by the signal generator, amplified by the power amplifier, and then input to 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, realizing energy conversion. The energy harvesting device can ensure anti-interference capability and realize broadband energy harvesting in the tristable motion state.

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