Design method of two-degree-of-freedom configuration miniature vibration generator based on stop block magnetic coupling

Abstract

The invention discloses a two-degree-of-freedom configuration miniature vibration generator design method based on check block magnetic coupling. Non-contact magnetic repulsive force is used for replacing collision force in an external coupling configuration structure, and the energy collection capacity of the generator under the broadband is remarkably improved. A two-degree-of-freedom configuration miniature vibration generator based on stop block magnetic coupling is characterized in that firstly, a theoretical analysis model of a two-degree-of-freedom configuration based on stop block magnetic coupling is established, theoretical analysis is carried out on dynamics of a system, and the theoretical analysis is compared with a traditional fixed stop block structure and a stop block self-coupling structure; on the basis of configuration design, the specific structure of the generator is optimized, the generator adopts a two-dimensional plane zigzag beam structure, and a mass block and a magnetic stop block are respectively mounted at different positions of a beam, so that a wider working frequency band is realized, and mechanical energy loss caused by collision of the stop block is avoided.

Description

Technical Field

[0001] This invention relates to energy-saving generator and generator set technology, specifically to a design method for a two-degree-of-freedom micro vibration generator based on stop magnetic coupling. Background Technology

[0002] In recent years, with the continuous advancement of low-power integrated circuit technology and the widespread application of small electronic devices such as wireless sensor network (WSN) nodes and wearable devices, vibration energy harvesting technology has received increasing attention. Research focus has gradually shifted from theoretical exploration to improving the efficiency and applicability of vibration generators in practical applications. Traditional vibration generators typically employ a linear resonant design, whose operating principle relies on matching the external vibration frequency with the generator's natural frequency. However, this design is limited by its narrow operating bandwidth, restricting the generator's applicability. Therefore, recent research has increasingly focused on how to broaden the generator's operating bandwidth to improve its adaptability and energy conversion efficiency in real-world environments.

[0003] To broaden the operating frequency band of piezoelectric generators, one common method is to adjust their natural frequency, thereby improving their adaptability to vibrations at different frequencies. While this control system-dependent approach allows for precise frequency adjustment, it has limitations in practical applications, especially in environments where manual intervention is impossible. Furthermore, the use of actuators consumes additional energy, impacting the overall generator efficiency. Another common method for broadening the frequency band is to array energy harvesters with different natural frequencies. This method can cover a wider frequency range, but its drawbacks include increased generator size and greater challenges in designing the energy harvesting circuitry.

[0004] In recent years, expanding the operating bandwidth and increasing the power output of piezoelectric generators using nonlinear vibration systems has become a research hotspot. Common nonlinear design methods include introducing nonlinear restoring forces and employing bistable structures. Bistable structures, by designing vibration systems capable of crossing the potential well, expand the operating bandwidth and achieve higher energy output under specific excitations.

[0005] Traditional bistable generators require strong external excitation to overcome the system potential well and generate significant power, which limits their ability to harvest weak vibrational energy. To address this, a novel dual-magnet tristable piezoelectric energy harvester (TPEH) has been proposed. This TPEH consists of rectangular magnets, a piezoelectric cantilever beam, a ring magnet, and a base. Due to variations in magnetic force, the system degenerates from tristable to bistable, and then to monostable, with increasing magnetic moment. The results show that the output performance of this structure is superior to that of the bistable configuration.

[0006] Another common nonlinear approach is to add baffles to the structure to limit the generator's displacement range, thereby making the system's restoring force nonlinear. This design can effectively alter vibration modes and broaden the operating frequency band. Simultaneously, the baffles, by limiting the displacement, can effectively reduce material fatigue caused by excessive material fatigue. However, while the use of baffles helps improve system stability, it may also limit the generator's maximum output power because it restricts the magnitude of displacement. Although nonlinear designs can broaden the generator's operating frequency band, further optimization and validation are still needed.

[0007] In summary, recent research on vibration energy harvesters has increasingly focused on improving their adaptability to broadband vibration excitations in the environment, thereby enhancing their output characteristics. Common optimization schemes include array generators, multimodal structural design, and nonlinear structures. However, each of these methods has its limitations. How to fully exploit the potential of nonlinear structures to achieve efficient and low-loss energy harvesting remains a significant challenge requiring further research and solutions. Summary of the Invention

[0008] This invention addresses the problems of narrow operating frequency band and low energy harvesting efficiency of traditional piezoelectric vibration generators by proposing a micro vibration generator based on a two-degree-of-freedom stop block magnetic coupling power generation mechanism.

[0009] First, a two-degree-of-freedom vibration generator with magnetic coupling was designed. By replacing traditional mechanical coupling with magnetic force, the generator's adaptability to broadband vibrations is improved. Second, a theoretical analysis model of the generator was established, and its dynamic characteristics were analyzed in detail. Furthermore, through optimized design, the generator's natural frequency was better matched with the center frequency of the environment, thereby improving its energy harvesting efficiency. The structure was also optimized to ensure the generator's reliability during long-term operation. Finally, the energy output performance of the generator under different vibration environments was evaluated, demonstrating its higher energy harvesting efficiency and operational stability compared to traditional vibration generators.

[0010] A micro vibration generator based on a two-degree-of-freedom stop block magnetic coupling power generation mechanism includes the following steps:

[0011] Step 1: Design a two-degree-of-freedom vibration power generation mechanism with magnetic coupling, namely, a stop block magnetic coupling power generation mechanism;

[0012] Step 2: Based on the block magnetic coupling generator configuration, establish a theoretical analysis model of the generator and analyze its dynamic characteristics to determine the theoretical output power exceeding that of the external coupling configuration or the block self-coupling configuration generator.

[0013] Step 3: Based on the theoretical analysis model of the generator, design the basic structure of the block magnetic coupling generator, and then obtain the electromechanical coupling model of the block magnetic coupling generator.

[0014] Step 4: Based on the optimized configuration of the stop block magnetic coupling generator, design the piezoelectric generator parameters.

[0015] Compared with the prior art, the significant advantages of this invention are:

[0016] (1) Compared with the nonlinear generators based on the self-coupling configuration of the baffle in the existing research, the baffle magnetic coupling configuration generator proposed in this invention has a more obvious bandwidth expansion effect and can output higher power.

[0017] (2) The generator with the block magnetic coupling configuration is expected to be applied to low-frequency vibration energy harvesting in real environment and can be applied to real working conditions with variable amplitude excitation. Attached Figure Description

[0018] Figure 1 It is a two-degree-of-freedom power generation mechanism, where (a) is a stop block at position 1, (b) is a stop block at position 2, (c) is a stop block self-coupling, and (d) is a stop block magnetic coupling.

[0019] Figure 2 This is a schematic diagram of interacting magnets.

[0020] Figure 3 These are different generator structures, of which (a) is an externally coupled configuration, (b) is a self-coupling structure of the baffle, and (c) is a magnetically coupled structure of the baffle.

[0021] Figure 4 This is a flowchart for the parameter design of a piezoelectric generator.

[0022] Figure 5 It refers to the dimensions of a piezoelectric generator.

[0023] Figure 6 The acceleration obtained from the simulation is 0.5 m / s². 2 The output characteristics of the generator are given, where (a) is an externally coupled generator, (b) is a self-coupled generator with a stop block, (c) is a magnetically coupled generator with a stop block, and (d) is the maximum output voltage.

[0024] Figure 7 The acceleration obtained from the simulation is 3.0 m / s². 2 The output characteristics of the generator are given, where (a) is an externally coupled generator, (b) is a self-coupled generator with a stop block, (c) is a magnetically coupled generator with a stop block, and (d) is the maximum output voltage.

[0025] Figure 8This is a flowchart of the design method for a two-degree-of-freedom micro vibration generator based on block magnetic coupling according to the present invention. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0027] Combination Figures 1-3 as well as Figure 8 The present invention discloses a design method for a two-degree-of-freedom micro vibration generator based on stop magnetic coupling, comprising the following steps:

[0028] Step 1: Design a two-degree-of-freedom vibration power generation mechanism with magnetic coupling, namely, a stop block magnetic coupling power generation mechanism.

[0029] The mass-spring-damping model of a two-degree-of-freedom power generation mechanism is as follows: Figure 1 As shown. In a traditional two-degree-of-freedom generator, i.e., an externally coupled configuration, to extend the operating frequency band, external blocks are typically added to limit the displacement of the first mass block m1 or the second mass block m2, such as... Figure 1 (a) and Figure 1 As shown in (b), the stiffness of the stop is represented by k. s Indicates that damping is represented by c. s This indicates. However, in Figure 1 In (a), while the stop block widens the generator's operating frequency band, its displacement restriction effect on the first mass block m1 also limits the generator's maximum output voltage. Figure 1 In (b), when the two mass blocks vibrate in phase, the displacement limiting effect of the stop on the second mass block m2 will also be transmitted to the first mass block m1, thereby affecting the output performance of the generator.

[0030] To address the limiting effect of the stop block on the maximum displacement and maximum output voltage under the aforementioned external coupling configuration, a self-coupling generator configuration with the stop block is proposed (see...). Figure 1 (c) The stop is a U-shaped component, with one end of the second mass block m2 inserted into the U-shaped groove of the stop to limit the relative displacement of the first mass block m1 and the second mass block m2. When the second mass block m2 collides with the inner wall of the stop, some kinetic energy is transferred to the first mass block m1, and this kinetic energy transfer can still effectively increase the displacement of the first mass block m1. The self-coupling generator mechanism of the stop theoretically changes the absolute displacement constraint to the relative displacement constraint, thus resolving the contradiction between a wide operating frequency band and high output power. However, a large amount of energy is still lost during the mechanical collision between the stop and the mass block.

[0031] To address the non-ideal collision energy loss in the self-coupling block power generation mechanism, a magnetic coupling block power generation mechanism is proposed, such as... Figure 1 As shown in (d), the block magnetic coupling power generation mechanism sets magnets with opposite polarities on the surfaces of the self-coupling block and the second mass block m2. It uses the non-contact repulsive force between the magnets to replace mechanical collisions to constrain the relative displacement of the first mass block m1 and the second mass block m2. Thus, while retaining all the advantages of the block self-coupling configuration, it further eliminates the energy loss caused by block collisions. The magnets installed on the inner wall of the block have the same polarity, and the magnets installed on the second mass block m2 also have the same polarity, but opposite polarity to the magnets on the inner wall of the block.

[0032] Step 2: Based on the block magnetic coupling generator configuration, establish a theoretical analysis model of the generator and analyze its dynamic characteristics to determine the theoretical output power exceeding that of the external coupling configuration or the block self-coupling configuration generator.

[0033] The characteristic of the block-coupled power generation mechanism in terms of system dynamics lies in the use of non-contact repulsive forces between permanent magnets to constrain the relative displacement of the mass blocks, thereby achieving nonlinear modulation of the system dynamic equations. In previous studies, the evaluation of the magnetic force of permanent magnets is usually quite complex, as it is nonlinearly related to many variables (such as the shape of the magnet, the physical properties of the magnetization vector, and the spatial orientation of the magnet). This invention is based on the interaction energy between two cubic magnets with parallel magnetization vectors, and then derives the magnetic force through a gradient operator.

[0034] The general component of force in three-dimensional space F i As shown below:

[0035]

[0036] Where J and J′ are both magnetization vectors in Tesla, and μ0 is the permeability of vacuum, μ0 = 4π·10 -7 The unit is Henry per meter. Parameters m, n, p, q, r, and s are related to the magnetic angular states of the two magnets (i.e., the magnets on the self-coupling block and the second mass block); the magnetic angular state is equal to 0 or 1. The combination of m, p, and r represents the magnetic angular state of one magnet, q, r, and s represents the magnetic angular state of the other magnet, and φ... i U mn V pq W rs R

[0037] All represent coefficients.

[0038] coefficient φ i The component coefficients φ in the x, y, and z directions are respectively. x φ y φ z :

[0039]

[0040] according to Figure 2 Let two rectangular coordinate reference frames be located at the centers of two magnets respectively; α, β and γ are the vector components of the distance between the centers O and O' of the reference frames, a, b and c are the half lengths of the side of one magnet, and A, B and C are the half lengths of the side of the other magnet.

[0041] coefficient U mn V pq W rs The definitions of R and R are as follows:

[0042] U mn =α + A(-1) m -a(-1) n (5),

[0043] V pq =β + B(-1) q -b(-1) p (6),

[0044] W rs =γ + C(-1) s -c(-1) r (7),

[0045]

[0046] Without considering piezoelectric elements, the dynamic equations of the above-mentioned block magnetic coupling generator mechanism, i.e., the theoretical analysis model of the generator, are expressed as follows:

[0047]

[0048] Where m1 is the mass of the first mass block, m2 is the mass of the second mass block, and y0, y1, and y2 are the displacements of the substrate, position 1, and position 2, respectively. Figure 1 c1 and c2 are damping coefficients, k1 is the stiffness coefficient of the first spring, k2 is the stiffness coefficient of the second spring, F1 is the force exerted by the stop on the first mass block, and F2 is the force exerted by the stop on the second mass block. The first derivative of y0 The first derivative of y1 The first derivative of y2 The second derivative of y0 The second derivative of y1 It is the second derivative of y2.

[0049] When the force of the stop F1 = F2 = 0, formula (9) is the dynamic equation of the linear generator without the stop.

[0050] For the generator type with a stop installed outside position 1, F2 = 0, and F1 is as follows:

[0051]

[0052] Where, k s c s are the stiffness coefficient and damping coefficient of the stop, respectively, and d represents the initial distance between the first mass block and the stop when no external force is applied.

[0053] Similarly, for the generator type with a stop installed outside position 2, F1 = 0, and F2 is as follows:

[0054]

[0055] For the self-coupling generator mechanism with a stop block, the force acting on the stop block is as follows:

[0056]

[0057] For the stop-type magnetic coupling power generation mechanism, the magnetic force needs to be taken into account. Therefore, the force exerted by the stop is as follows:

[0058]

[0059] Among them, F z1 express Figure 1 The magnetic force between the two magnets at the bottom of (d) is F. z2 This represents the magnetic force between the two top magnets. Since the stop block can be approximated as being fixed to the first mass block, and the two pairs of magnets in the stop block are symmetrically positioned in equilibrium, the distances between two adjacent magnets can be expressed as d-(y1-y2) and d+(y1-y2), respectively.

[0060] Analyze the elastic potential energy of a two-degree-of-freedom system with no stopper and three different stopper designs. Set the spring constant as k1 = 1 × 10⁻⁶. 3 N / m, k2=2×10 2 N / m. Stiffness coefficient k of the stop. s =1×10 4N / m. In the block-coupled magnetic generator configuration, the rectangular magnets are all 3mm × 3mm × 1mm in size and are parallel in space, with a distance of 1.1mm between them. Assuming an external force is applied at position 2 to achieve static equilibrium, the displacement and corresponding elastic potential energy at position 1 are calculated. It is found that, without block collision, the elastic potential energy of the configurations without blocks, with blocks at positions 1 and 2, and with self-coupled blocks exhibits consistent characteristics. Meanwhile, the proposed block-coupled magnetic configuration has a slightly lower elastic potential energy than the others. This is because a magnetic force exists even when the block is not in contact with the substrate, requiring less energy to overcome the same displacement. When the external force is large enough that the blocks begin to contact, the elastic potential energy curves of the two configurations with blocks show significant similarity, and the potential energy rises rapidly with the increase of displacement at position 1. This indicates that once the blocks contact, the system needs to overcome a greater potential energy to achieve a small displacement change, which will negatively impact the energy harvesting of the generator. This also explains from another perspective why traditional stop designs limit the maximum output power of generators. Therefore, a generator based on a stop magnetically coupled two-degree-of-freedom configuration can theoretically output more power than generators with external coupling or stop self-coupling configurations.

[0061] Step 3: Based on the theoretical analysis model of the generator, design the basic structure of the block magnetic coupling generator, and then obtain the electromechanical coupling model of the block magnetic coupling generator.

[0062] The aforementioned block-coupled magnetic generator design provides an optimal theoretical framework for designing a wide-bandwidth, high-output vibration generator. Based on this theoretical support, and considering specific operating conditions and dimensional constraints, a detailed design of a micro piezoelectric generator with this block-coupled magnetic generator design was carried out. The basic structure of the generator is as follows: Figure 3 As shown. First, for both the externally coupled and the self-coupled configuration with stoppers, the vibration generator can use a two-dimensional "zigzag" planar beam as its base structure. The advantage of this beam structure is its small size and compact structure, which can reduce the generator's natural frequency within a limited space and effectively collect more energy. Based on this, to increase the deformation of the beam structure, mass blocks can be arranged on both sides of the second beam away from the fixed support end; to increase the stress and charge of the piezoelectric material, piezoelectric sheets can be arranged at the root of the first beam near the fixed support end. For the self-coupled configuration with stoppers, to constrain the relative displacement between the first and second beams, the stoppers are fixed to the end of the first beam by epoxy resin bonding, such as... Figure 3 As shown in (b).

[0063] To address the energy loss caused by the mechanical collision between the stop and the mass block in the stop self-coupling configuration, based on the design concept of a stop magnetic coupling power generation mechanism, magnets of opposite polarity are placed on the surfaces of the stop and the substrate facing each other. The non-contact magnetic repulsion between the two magnets constrains the relative displacement of the first and second beams. Thus, as... Figure 3 The novel piezoelectric vibration generator structure shown in (c) can achieve the theoretical advantages of a block magnetic coupling generator structure, while maximizing the operating frequency band and output power.

[0064] Based on the system vibration equation of formula (9), and considering the influence of piezoelectric elements and magnets, the electromechanical coupling dynamic equation of the block magnetic coupling structure generator can be obtained as follows:

[0065]

[0066] Where Θ is the piezoelectric generator coupling coefficient, and V is the voltage of the piezoelectric generator. Let V be the first derivative, F1 and F2 be the forces exerted on the first and second mass blocks by the stop block, respectively, R0 be the load resistance, and C be the first derivative of V. p This refers to the piezoelectric generator's own capacitance. 11 c 12 c 21 c 22 k is the damping coefficient. 11 k 21 The stiffness coefficient of the first spring in the magnetic coupling structure of the stop block, k 12 k 22 denoted as the stiffness coefficient of the second spring in the magnetic coupling structure of the stop block.

[0067] The system's mass matrix [M], stiffness matrix [K], and damping matrix [C] are as follows:

[0068]

[0069] Assuming the system satisfies the Rayleigh damping assumption, the damping matrix of the model can be expressed by the following formula:

[0070] [C]=α0[M]+β0[K] (18),

[0071] Where α0 and β0 are proportionality coefficients.

[0072] For an externally coupled generator, F1 = 0, and F2 is as follows:

[0073]

[0074] d t k is the limiting displacement of the stop block in the external coupling configuration. sc is the stiffness coefficient of the stop. s Damping coefficient of the stop.

[0075] F1 = -F2, where F2 is shown below:

[0076]

[0077] For a stop-type magnetic coupling generator, F1 = -F2, and F2 is shown below:

[0078]

[0079] d s The stop limit displacement is for the stop self-coupling configuration.

[0080] Given state variables u1 = y1, u2 = y2, u5=V, formula (14) can be transformed into the following first-order form, namely the electromechanical coupling model of the block magnetic coupling generator:

[0081]

[0082] In the above formula, F z1 and F z2 All of these can be represented by state variables. The above differential equations can be solved numerically in MATLAB to obtain the generator's vibration output characteristics y1, y2 and voltage output characteristics V.

[0083] Step 4: Based on the electromechanical coupling model of the stop block magnetic coupling generator, design the piezoelectric generator parameters.

[0084] S4.1 Based on the optimized configuration of the stop-type magnetic coupling generator and the space occupation limit of the piezoelectric generator, the maximum length L of the generator is initially determined. max Maximum width W max The mass of the mass block is determined, and the center frequency of the environmental vibration is also determined.

[0085] S4.2, Based on the maximum length L of the generator max Maximum width W max The size of the piezoelectric element is selected based on the mass of the mass block.

[0086] S4.3. Combining the center frequency of environmental vibration, finite element simulation is performed using Comsol to obtain the stiffness matrix and mass matrix of the piezoelectric generator, so as to calculate its natural frequency and finally determine the thickness of the generator substrate.

[0087] S4.4 Under ideal conditions, generators should avoid fatigue failure. Therefore, when designing the stop distance, it is necessary to ensure that the maximum stress on the generator base plate does not exceed its fatigue strength. To this end, a finite element simulation model of the generator was established using Comsol to perform stress analysis and determine the maximum displacement without fatigue failure.

[0088] S4.5 Analyze the output characteristics of the optimized configuration of the block-based magnetic coupling generator to obtain its operating bandwidth and maximum output voltage.

[0089] Example 1

[0090] In practical applications, the space occupied by piezoelectric generators is usually strictly limited, and there are also specific requirements for the size of the mass block. Therefore, the generator parameters must be designed reasonably to ensure that its natural frequency matches the frequency range of the environmental excitation. In addition, to extend the service life of the generator, the distance between the stop block and the base plate must at least meet the requirement that the piezoelectric generator does not experience fatigue strength under ultimate displacement. Therefore, the present invention has made the following design.

[0091] First, the beam base plate of the piezoelectric generator is made of H62 brass, and the piezoelectric sheet is made of PZT5-H, which is attached to the base of the generator. The two are bonded together using modified acrylic structural adhesive, and neodymium iron boron permanent magnets are used as the mass block. Because cutting the piezoelectric sheet after processing is difficult, a suitable model of piezoelectric sheet manufactured by APC International was selected. A piezoelectric generator parameter design method is proposed, such as... Figure 4 As shown. Before parameter design, the maximum length, width, and mass of the generator are set, and the center frequency of the environmental vibration is determined. Assume the maximum length is L. max =38mm, maximum width is W max =38mm. Based on these parameters, an appropriate piezoelectric element was selected, using the Item1778 model from APC, with dimensions: length l = 15mm, width w = 5mm, and thickness b0 = 0.5mm. In the design, the width of each beam on the generator base plate is the same as the piezoelectric element, and the total length is the maximum allowable length. The mass of the mass block was set to m0 = 8.78g, and the center frequency of the environmental vibration was f0 = 28Hz. Finite element simulation was performed using Comsol to obtain the stiffness matrix and mass matrix of the piezoelectric generator, and its natural frequency was calculated. After calculation, the final thickness of the generator base plate was determined to be B0 = 0.40mm, at which point the first natural frequency of the generator was f = 27.6Hz. The final dimensions of the designed piezoelectric generator are as follows. Figure 5As shown. In practical applications, generators should ideally avoid fatigue failure. Therefore, when designing the stop distance, it is necessary to ensure that the maximum stress on the generator base plate does not exceed its fatigue strength (the fatigue strength of brass material H62 is 154 MPa). To this end, a finite element simulation model of the generator was established using Comsol to perform stress analysis to determine the maximum displacement without fatigue failure.

[0092] The output characteristics of the optimized configuration of the block-based magnetic coupling generator are analyzed to obtain its operating bandwidth and maximum output voltage.

[0093] The output characteristics of the two generators are simulated, analyzed, and compared below. First, the case under sinusoidal sweep excitation is analyzed. The excitation frequency is changed at different amplitudes to obtain the generator's output voltage. When the external excitation acceleration increases to 0.5 m / s²... 2 At that time, the generator end displacement 2 remained within 1.50mm, the stop block did not collide with the base plate, and the maximum output voltage of the externally coupled generator was approximately 7.48V. Figure 6 As shown in the diagram, at this point, for the self-coupled generator with the stop block, the maximum displacement at position 2 is also less than 1.50 mm, and its maximum output voltage is 7.46 V. The maximum voltage output capability of the self-coupled generator with the stop block is very close to that of the externally coupled generator, because their structures are almost identical before the stop block collides. However, compared with the externally coupled and self-coupled generators with the stop block, the magnetically coupled generator with the stop block, although its displacement is reduced, performs better in terms of output voltage, reaching 9.15 V, which is about 23% higher than the other two. This indicates that before the collision occurs, the mutual repulsion of the magnets has already taken effect. The mutual repulsion between the magnets replaces the mechanical collision to constrain the relative displacement between the stop block and the base plate, making the system response more efficient.

[0094] When the amplitude of the acceleration excitation increases to 3 m / s 2 At that time, the result was as follows Figure 7As shown, the maximum displacement at position 2 of the externally coupled generator does not exceed 2.4 mm, which is basically equivalent to the stop limit displacement. Similarly, it can be seen from the end displacement that the maximum displacement of the other two types of generators does not exceed the fatigue limit. In terms of output characteristics, the maximum output voltage of the traditional generator does not exceed 12.0V, and the operating frequency bandwidth is 4.5Hz. For the stop self-coupled generator, its operating frequency bandwidth reaches 7Hz, which shows that it plays a significant role in broadening the operating frequency, and the maximum output voltage reaches 18.09V. For the stop magnetic coupling generator, the operating frequency bandwidth is significantly broadened to 8.5Hz at the same output voltage, and the maximum output voltage is increased to 2.37 times and 1.56 times that of the externally coupled generator and the stop self-coupled generator, respectively. It can be seen that the proposed stop magnetic coupling generator type piezoelectric generator has a significantly improved operating frequency bandwidth and maximum output voltage performance under the action of repulsive magnetic force.

[0095] In summary, a micro piezoelectric vibration generator was designed based on a two-degree-of-freedom stop-and-magnetically-coupled generator structure. Compared with existing nonlinear generators based on stop-and-magnetically-coupled structures, the novel generator exhibits a more significant bandwidth broadening effect and can output higher power. A theoretical analysis model of the two-degree-of-freedom configuration based on stop-and-magnetic coupling was established, and its dynamic equations and output characteristics were analyzed. Based on the configuration theory, the generator structure was optimized and parameters were designed to match the generator's natural frequency with the ambient center frequency. Simulation analysis of its output characteristics verified that the effective operating frequency range of the stop-and-magnetically-coupled generator was broadened, even at an excitation acceleration of 10 m / s². 2 At the same time, the effective operating frequency range of the generator is 1.74 times higher than that of the externally coupled generator, while its output voltage is 2.11 times and 1.46 times that of the externally coupled generator and the self-coupled generator with a stop block, respectively. Therefore, the stop block magnetic coupling generator is expected to be applied to low-frequency vibration energy harvesting in real-world environments and can be suitable for real-world operating conditions with variable amplitude excitation.

Claims

1. A micro vibration generator based on a two-degree-of-freedom stop block magnetic coupling power generation mechanism, characterized in that, Includes the following steps: Step 1: Design a two-degree-of-freedom vibration power generation mechanism with magnetic coupling, namely, a stop block magnetic coupling power generation mechanism; Step 2: Based on the block magnetic coupling generator mechanism, establish a theoretical analysis model of the generator and analyze its dynamic characteristics; Step 3: Optimize the configuration of the block-based magnetic coupling generator to obtain the optimized configuration of the block-based magnetic coupling generator; Step 4: Based on the optimized configuration of the stop block magnetic coupling generator, design the piezoelectric generator parameters.

2. The micro vibration generator based on a two-degree-of-freedom stop block magnetic coupling power generation mechanism according to claim 1, characterized in that, In step 1, the two-degree-of-freedom vibration power generation mechanism with magnetic coupling is designed, namely the stop block magnetic coupling power generation mechanism, as follows: The block magnetic coupling power generation mechanism sets magnets with opposite polarities on the surfaces of the self-coupling block and the second mass block m2. It uses the non-contact repulsive force between the magnets to replace mechanical collisions to constrain the relative displacement of the first mass block m1 and the second mass block m2. Thus, while retaining all the advantages of the block self-coupling configuration, it further eliminates the energy loss caused by block collisions. The magnets installed on the inner wall of the block have the same polarity, and the magnets installed on the second mass block m2 also have the same polarity, but opposite polarity to the magnets on the inner wall of the block.

3. The micro vibration generator based on a two-degree-of-freedom stop block magnetic coupling power generation mechanism according to claim 1, characterized in that, In step 2, based on the block magnetic coupling generator mechanism, a theoretical analysis model of the generator is established, and its dynamic characteristics are analyzed, as follows: The magnetic force is derived from the interaction energy between two parallel magnetization vectors of a cubic magnet, and then through the gradient operator. Without considering piezoelectric elements, the dynamic equations of the stop-block magnetic coupling generator mechanism, i.e., the theoretical analysis model of the generator, are expressed as follows: Where m1 is the mass of the first mass block, m2 is the mass of the second mass block, y0, y1, and y2 are the displacements of the base plate, position 1, and position 2, respectively, c1 and c2 are the damping coefficients, k1 is the stiffness coefficient of the first spring, k2 is the stiffness coefficient of the second spring, F1 is the force exerted by the stop on the first mass block, and F2 is the force exerted by the stop on the second mass block. The first derivative of y0 The first derivative of y1 The first derivative of y2 The second derivative of y0 The second derivative of y1 y is the second derivative of y²; For the stop-type magnetic coupling power generation mechanism, the magnetic force needs to be taken into account; therefore, the force exerted by the stop is as follows: Among them, F z1 F represents the magnetic force between the two magnets at the bottom of the magnetic coupling generator mechanism. z2 The magnetic force between the two top magnets is represented by d-(y1-y2) and d+(y1-y2), respectively. Since the stop is approximately fixed to the first mass block and the two pairs of magnets in the stop are symmetrical in the equilibrium state, the distance between two adjacent magnets can be represented by d-(y1-y2) and d+(y1-y2), respectively.

4. The micro vibration generator based on a two-degree-of-freedom stop block magnetic coupling power generation mechanism according to claim 1, characterized in that, In step 3, based on the theoretical analysis model of the generator, the basic structure of the stop-type magnetic coupling generator is designed, thereby obtaining the electromechanical coupling model of the stop-type magnetic coupling generator, as follows: For a stop-type magnetic coupling generator, F1 = -F2, and F2 is shown below: Given state variables u1 = y1, u2 = y2, u5=V ， The electromechanical coupling model of the stop-type magnetic coupling generator is as follows: In the above formula, F z1 and F z2 Both can be represented by state variables; The differential equations above are solved using numerical methods in MATLAB, thereby obtaining the vibration output characteristics y1, y2 and voltage output characteristics V of the generator.

5. The micro vibration generator based on a two-degree-of-freedom stop block magnetic coupling power generation mechanism according to claim 1, characterized in that, In step 4, based on the optimized configuration of the stop-block magnetic coupling generator, the piezoelectric generator parameters are designed as follows: S4.1 Based on the optimized configuration of the stop-type magnetic coupling generator and the space occupation limit of the piezoelectric generator, the maximum length L of the generator is initially determined. max Maximum width W max And the mass of the mass block, while determining the center frequency of the environmental vibration; S4.2, Based on the maximum length L of the generator max Maximum width W max The size of the piezoelectric element is selected based on the mass of the mass block. S4.

3. Combining the center frequency of environmental vibration, finite element simulation is performed using Comsol to obtain the stiffness matrix and mass matrix of the piezoelectric generator, so as to calculate its natural frequency and finally determine the thickness B of the generator substrate. S4.

4. Ideally, generators should avoid fatigue failure; therefore, when designing the distance between the stops, it is necessary to ensure that the maximum stress on the generator base plate does not exceed its fatigue strength. Therefore, a finite element simulation model of the generator was established using Comsol to perform stress analysis in order to determine the maximum displacement without fatigue failure. S4.5 Analyze the output characteristics of the optimized configuration of the block-based magnetic coupling generator to obtain its operating bandwidth and maximum output voltage.

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