CN112701956B - Magnetostrictive bistable vibration collecting device with amplifying mechanism and design method - Google Patents
Magnetostrictive bistable vibration collecting device with amplifying mechanism and design method Download PDFInfo
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- CN112701956B CN112701956B CN202011533798.8A CN202011533798A CN112701956B CN 112701956 B CN112701956 B CN 112701956B CN 202011533798 A CN202011533798 A CN 202011533798A CN 112701956 B CN112701956 B CN 112701956B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
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- H02N2/00—Electric machines in general using piezoelectric effect, electrostriction or magnetostriction
- H02N2/18—Electric machines in general using piezoelectric effect, electrostriction or magnetostriction producing electrical output from mechanical input, e.g. generators
- H02N2/186—Vibration harvesters
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- H—ELECTRICITY
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Abstract
The invention discloses a magnetostriction bistable vibration collection device with an amplifying mechanism, which comprises a platform, wherein a pair of first full-thread screws are arranged on the left side of the platform, an upper clamping plate and a lower clamping plate are arranged on the pair of first full-thread screws, one end of a cantilever beam is fixed between the upper clamping plate and the lower clamping plate, a permanent magnet A is arranged at the other end of the cantilever beam, and a pickup coil is arranged on the cantilever Liang Waishe; the right side of platform is equipped with a pair of slide, is equipped with the full screw thread screw rod of second in a pair of slide, a pair of be equipped with right splint on the full screw thread screw rod of second, installs permanent magnet B on the right splint. The invention relates to a magnetostrictive vibration collecting and utilizing device with a displacement amplifying mechanism and nonlinear bistable state, which has reasonable structure, simple operation, stronger vibration collecting capability, reduced working frequency and widened frequency band width, and can effectively convert vibration energy into electric energy for collecting and utilizing the energy.
Description
Technical Field
The invention relates to the technical field of vibration collection and utilization, in particular to a magnetostrictive nonlinear bistable vibration collection and utilization device which takes a magnetostrictive sheet material as a core element and generates electric energy through absorbing vibration.
Background
Magnetostrictive materials are smart materials that have the inverse effect of magnetostriction and are capable of electromechanical-magneto-electrical energy conversion. When the magnetostrictive material is subjected to deformation and external force, the magnetization state of the material is changed. If coils are arranged around the magnetic field generator, the changed magnetization state can be further converted into electric energy through Faraday electromagnetic induction effect, and finally the conversion from mechanical energy to electric energy is realized. Therefore, by utilizing the magnetostrictive material, the waste vibration energy in the environment can be collected and reused, for example, the power is supplied to a low-power electronic element such as a wireless sensor, and the aim of reusing the waste vibration energy is fulfilled. The magnetostrictive material has good thermal stability and better mechanical processing performance, is not easy to age, has no depolarization problem, and can work under severe environmental conditions.
In 2019 Tianjin university of industry, it has been proposed to vertically place an L-beam, fix a permanent magnet near the free end of the L-beam, and place a permanent magnet opposite the permanent magnet, and the pair of permanent magnets repel each other, so that the system forms a bistable structure, thereby reducing the resonant frequency of the whole device. Permanent magnets are respectively arranged on two sides of a piezoelectric cantilever beam which is vertically arranged in the Shanghai transportation university in 2020, so that the system forms a bistable structure, the resonance frequency band of the whole device is effectively widened, and the system has a good power generation effect in a wider frequency band range.
The magnetostrictive material has good characteristics, so that the magnetostrictive material has good application prospect in the field of collecting waste vibration energy in the environment. Therefore, intensive research on magnetostrictive vibration collection technology is necessary to improve the vibration collection capability and convert the vibration energy to the maximum extent into electric energy which can be used by us.
Disclosure of Invention
The invention aims to provide a magnetostrictive bistable vibration collecting device with an amplifying mechanism, which comprises a displacement amplifying mechanism and a bistable structure, can improve the vibration collecting energy of a system and can also adjust the working frequency range.
In order to achieve the above purpose, the present invention provides the following technical solutions: the magnetostrictive bistable vibration collecting device with the amplifying mechanism comprises a platform, wherein a pair of first full-thread screws are arranged on the left side of the platform, an upper clamping plate and a lower clamping plate are arranged on the pair of first full-thread screws, one end of a cantilever beam is fixed between the upper clamping plate and the lower clamping plate, a permanent magnet A is arranged at the other end of the cantilever beam, and a pickup coil is arranged on the cantilever Liang Waishe; the right side of the platform is provided with a pair of slide ways, a second full-thread screw rod is arranged in the pair of slide ways, a right clamping plate is arranged on the pair of second full-thread screw rods, a permanent magnet B is arranged on the right clamping plate, and the permanent magnet B and the permanent magnet A repel each other;
The platform is provided with a permanent magnet fixing frame, the cantilever beam penetrates through the permanent magnet fixing frame, and the upper side and the lower side of the permanent magnet fixing frame are respectively provided with a third permanent magnet; the lower side wall of the platform is provided with a spring upper clamp, and the spring upper clamp is connected with the spring lower clamp through a spring displacement amplifying mechanism.
Compared with the prior art, the beneficial effects are that: the invention relates to a magnetostrictive vibration collecting and utilizing device with a displacement amplifying mechanism and nonlinear bistable state, which has reasonable structure, simple operation, stronger vibration collecting capability, reduced working frequency and widened frequency band width, and can effectively convert vibration energy into electric energy for collecting and utilizing the energy.
By taking the magnetostrictive material sheet as a core element, under the low excitation level, the vibration of the magnetostrictive material is effectively enhanced through the nonlinear repulsive magnetic force between the permanent magnet fixed at the free end of the cantilever beam and the permanent magnet fixed on the right clamping plate and the amplification effect of the spring displacement amplification mechanism on the external excitation amplitude, the generated electric energy is picked up by the pickup coil, and the whole system has higher vibration collecting and converting capability under the low excitation level and in a wider frequency band range.
By selecting a horizontally placed cantilever beam, fixing a permanent magnet near the free end of the cantilever beam, placing the permanent magnet opposite to the permanent magnet, and making the two pairs of permanent magnets repel each other, the system forms a bistable structure, and the resonance frequency of the device is reduced. The spring mechanism is added below the device, so that the vibration level of the cantilever beam can be effectively improved under the same external excitation level, and the power generation effect is better. Permanent magnets are placed on the cantilever beam vertically twice, so that a bias magnetic field is provided for the cantilever beam, and the power generation effect is better improved.
Drawings
Fig. 1 is a schematic general structure of the present invention.
Fig. 2 is a front view of the platform of the present invention.
Fig. 3 is a top view of the platform of the present invention.
Fig. 4 is a left side view of the platform of the present invention.
Fig. 5 is a schematic structural view of the full flight screw of the present invention.
Fig. 6 is a front view of the up/down/right clamping plate of the present invention.
Fig. 7 is a top view of the up/down/right clamping plate of the present invention.
Fig. 8 is a left side view of the up/down/right clamping plate of the present invention.
Fig. 9 is a schematic structural view of the cantilever beam of the present invention.
Fig. 10 is a schematic structural view of the permanent magnet of the present invention.
Fig. 11 is a front view of the permanent magnet holder of the present invention.
Fig. 12 is a top view of the permanent magnet holder of the present invention.
Fig. 13 is a left side view of the permanent magnet holder of the present invention.
FIG. 14 is a schematic view of the structure of the spring clip of the present invention.
Fig. 15 is a front view of the sprung jaws of the present invention.
Fig. 16 is a top view of the sprung jaws of the present invention.
Fig. 17 is a schematic view of the structure of the unsprung clamp of the present invention.
Fig. 18 is a front view of the unsprung clip of the present invention.
Fig. 19 is a top view of the unsprung clip of the present invention.
FIG. 20 is a schematic view of a spring displacement amplifying mechanism of the present invention.
FIG. 21 is a voltage versus frequency plot with or without a bistable structure at 6.272m/s 2.
FIG. 22 is a voltage versus frequency plot with or without a spring displacement amplifying mechanism at 4.704m/s 2.
FIG. 23 is a voltage versus frequency plot at 4.704m/s 2 with or without permanent magnets on the upper and lower sides of the cantilever beam.
1. A platform; 2. a first full-flight screw; 2-1, a second full-thread screw; 3. an upper clamping plate; 4. a lower clamping plate; 5. a cantilever beam; 6. picking up the coil; 7-1, permanent magnet A;7-2, permanent magnet B;7-3, a third permanent magnet; 8. permanent magnet fixing frame; 9. a right clamping plate; 10. a spring-loaded clamp; 11. a spring displacement amplifying mechanism; 12. and (5) a spring-loaded clamp.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Referring to fig. 1-20, the present invention provides a technical solution: the magnetostrictive bistable vibration collecting device with the amplifying mechanism comprises a platform 1, wherein a pair of first full-thread screws 2 are arranged on the left side of the platform 1, an upper clamping plate 3 and a lower clamping plate 4 are arranged on the pair of first full-thread screws 2, one end of a cantilever beam 5 is fixed between the upper clamping plate 3 and the lower clamping plate 4, a permanent magnet A7-1 is arranged at the other end of the cantilever beam 5, a pickup coil 6 is arranged outside the cantilever beam 5, and the cantilever beam 5 is a magnetostrictive material sheet; the right side of the platform 1 is provided with a pair of slide ways, a second full-thread screw rod 2-1 is arranged in the pair of slide ways, a right clamping plate 9 is arranged on the pair of second full-thread screw rods 2-1, a permanent magnet B7-2 is arranged on the right clamping plate 9, and the permanent magnet B7-2 and the permanent magnet A7-1 repel each other.
A permanent magnet fixing frame 8 is arranged on the platform 1, the cantilever beam 5 penetrates through the permanent magnet fixing frame 8, and the upper side and the lower side of the permanent magnet fixing frame 8 are respectively provided with a third permanent magnet 7-3; the lower side wall of the platform 1 is provided with a spring upper clamp 10, and the spring upper clamp 10 is connected with a spring lower clamp 12 through a spring displacement amplifying mechanism 11. The device takes the cantilever beam 5 as a core element, adopts the pickup coil 6 to convert the magnetic flux change into voltage, and realizes the process of converting the vibration energy generated in the motion process into electric energy for output.
The cantilever beam 5 is fixed on the platform through the full-thread screw rod, the upper clamping plate 3 and the lower clamping plate 4, wherein the cantilever beam 5 is formed by three layers of sheets, the upper layer and the lower layer are magnetostrictive material sheets, the middle layer is a substrate sheet, and the middle layer can be beryllium copper, stainless steel, aluminum alloy and other materials. The cantilever beam 5 with the upper and lower layers of magnetostrictive material sheets has a higher level of conversion of mechanical energy into magnetic energy. The pick-up coil 6 is wound on the cantilever beam 5. The permanent magnet A7-1 is fixed at the free end of the cantilever beam 5, the same permanent magnet B7-2 is fixed on the right clamping plate, the two pairs of permanent magnets repel each other, and the group of permanent magnets enables the system to form a bistable structure. A slideway mechanism is designed on the platform, the distance between the two pairs of permanent magnets is adjusted through the slideway mechanism, and the right clamping plate 9 is fixedly connected with the platform through a full-thread screw rod. And a permanent magnet fixing frame 8 is arranged at the position of the cantilever beam close to the free end and is fixed with the platform 1, a third permanent magnet 7-3 is arranged on the permanent magnet fixing frame 8, the upper side and the lower side of the cantilever beam are ensured to be provided with permanent magnets, a certain distance is reserved between the permanent magnets and the cantilever beam 5, and the permanent magnets are bias permanent magnets to provide a bias magnetic field for the magnetostrictive material sheet. A spring is placed between the spring lower clamp 12 and the platform 1, and the spring is fixed by the spring upper clamp 10 and the spring lower clamp 12, which forms a displacement amplifying mechanism for amplifying vibration displacement from a vibration source and improving the vibration collecting capability of the system.
Five through holes and two slide ways are arranged on the platform 1 with the cuboid structure along the height direction. The platform and the upper clamping plate 3 and the lower clamping plate 4 on the left side are fixed through two full-thread screws and hexagonal nuts. The cantilever beam 5 wound with the coil 6 is fixed between the upper clamping plate 3 and the lower clamping plate 4, and is fastened by a hexagonal nut. And then the right clamping plate is assembled on the slideway through two full-thread screws and a hexagonal nut.
Two permanent magnets A7-1 are fixed at the free end of the cantilever beam 5 wound with the pick-up coil 6, two permanent magnets B7-2 are fixed on a right clamping plate fixed on a slideway in the same way, the two pairs of permanent magnets repel each other, the repulsive magnetic force generated between the two pairs of permanent magnets is nonlinear, the distance between the two pairs of permanent magnets is controlled through the slideway, the magnitude of the nonlinear repulsive magnetic force between the two pairs of permanent magnets is controlled, when the two pairs of permanent magnets are at a proper distance, the whole system has optimal bistable characteristic, so that the resonance frequency of the cantilever beam 5 is reduced, and the working frequency range of the system is regulated, so that the working frequency of the magnetostrictive vibration collecting and utilizing device accords with the characteristic of lower waste vibration frequency in the environment.
A permanent magnet fixing frame 8 is arranged near the free end close to the cantilever beam 5, through holes are respectively formed in the left side and the right side of the permanent magnet fixing frame 8 and are respectively aligned with the through holes in the two sides of the platform 1, and the permanent magnet fixing frame 8 and the platform 1 are fixed together through screws and hexagonal nuts. The third permanent magnets 7-3 are respectively placed in the middle of the upper surface and the middle of the lower surface of the inner side of the permanent magnet fixing frame 8, a certain distance is ensured between the third permanent magnets 7-3 and the cantilever beam 5, and the group of permanent magnets are used for providing a bias magnetic field for the magnetostrictive thin sheet, so that the power generation performance of the whole system is further improved.
For the fixing problem of the spring, the spring upper clamp 10 is designed to fix the upper end of the spring and the lower surface of the platform 1, the spring upper clamp 10 is a thin disc with a through hole, a thin cylinder is attached on the disc, and the spring is sleeved in the spring upper clamp 10 in the fixing process, and the spring upper clamp 10 and the platform 1 are fixed through screws and hexagonal nuts. The spring lower clamp 12 is designed to fix the lower end of the spring, the spring lower clamp 12 is a thin disc with five through holes, a thin cylinder is attached on the disc, and the spring is embedded into the spring lower clamp mechanism in the fixing process, and the spring lower clamp 12 is fixed through a screw and a hexagonal nut. The above structure is a displacement amplifying mechanism in a magnetostrictive vibration collecting and utilizing system.
The spring has good elastic performance, so that the vibration excitation level of the vibration source can be effectively amplified. Compared with a vibration collecting device without a spring mechanism, the vibration collecting device can effectively transmit amplified vibration excitation to the cantilever beam 5 above the platform by using the spring displacement amplifying mechanism 11, so that the whole system can provide higher excitation for the cantilever beam 5 under a lower vibration excitation level, and the cantilever beam 5 can generate larger vibration amplitude, so that the whole system still has better vibration effect under the lower excitation level.
The working principle of the magnetostrictive nonlinear bistable energy collecting device is as follows: the main power provided by the vibration exciter is applied to the spring displacement amplifying mechanism 11, the amplified excitation is applied to the platform 1 through the amplifying action of the spring displacement amplifying mechanism 11 on the amplitude, so that the cantilever beam 5 structure wound with the pickup coil 6 is vibrated due to the exciting action, the repulsive magnetic force in the vertical direction between the permanent magnet A7-1 fixed at the free end of the cantilever beam 5 structure and the permanent magnet B7-2 fixed on the right clamping plate is changed, and the internal magnetization state of the cantilever beam 5 structure is changed, namely, the internal magnetic flux is changed due to the vibration, and the changed magnetic field generates an electric field according to Faraday electromagnetic induction law, so that induced electromotive force is generated in the pickup coil. Simultaneously, external excitation is transmitted to the platform 1 for fixing the cantilever beam 5 structure through the spring displacement amplifying mechanism 11, and the cantilever beam 5 structure is longitudinally bent and deformed due to the action of force, so that the internal magnetization states of the upper and lower magnetostrictive material sheets in the cantilever beam 5 structure are changed, namely magnetic fluxes are changed, and the changed magnetic fluxes generate induced voltages through the pickup coil 6 wound on the cantilever beam 5 structure.
As shown in fig. 2-4, five through holes and two slide ways are drilled on the platform 1. The left two through holes are used for fixing the upper clamping plate 3 and the lower clamping plate 4, the front and rear two through holes are used for fixing the permanent magnet fixing frame 8, the middle through hole is used for fixing the spring upper clamp 10, and the right two slide ways are used for installing the right clamping plate 9.
As shown in fig. 5, a full-thread screw is schematically shown, and the upper clamping plate 3, the lower clamping plate 4 and the right clamping plate 9 are fixed by the full-thread screw.
As shown in fig. 6-8, the upper clamping plate 3, the lower clamping plate 4 and the right clamping plate 9 are all of cuboid structures, and two through holes are formed in the upper side of the upper clamping plate, so that the upper clamping plate is convenient to connect with a full-thread screw rod.
As shown in fig. 9, the cantilever beam 5 is formed by three layers of thin sheets, an upper layer and a lower layer are magnetostrictive thin sheets, a middle layer is a basal layer, and a pickup coil 6 is wound on the outer surface of the whole structure. One end of the cantilever beam 5 is fixed between the upper clamping plate 3 and the lower clamping plate 4.
As shown in fig. 10, the permanent magnet has a rectangular parallelepiped structure and is fixed to the free end of the magnetostrictive material sheet 5, the right clamping plate 9, and the permanent magnet fixing frame 8, respectively.
As shown in fig. 11-13, a through hole is respectively drilled on the left side and the right side of the permanent magnet fixing frame 8, and the permanent magnet fixing frame is fixed with the platform 1 through screws.
As shown in fig. 14, a schematic structural view of the spring clip 10 is provided for fixing the upper end portion of the spring displacement amplifying mechanism 11 and the lower surface of the platform 1.
As shown in fig. 15-16, the spring loaded fixture 10 is a thin disc with a through hole, a thin cylinder is attached to the disc, and during the fixing process, the spring displacement amplifying mechanism 11 is sleeved into the spring loaded fixture 10, and the spring loaded fixture 10 and the platform 1 are fixed by screws and hexagonal nuts.
As shown in fig. 17, a schematic structure of the spring clip 12 is provided for fixing the lower end portion of the spring displacement amplifying mechanism 11.
As shown in fig. 18 to 19, the mechanism of the under-spring clamp 12 is a thin disc with five through holes, a thin cylinder is attached to the disc, and during the fixing process, the spring displacement amplifying mechanism 11 is embedded in the mechanism of the under-spring clamp 12, and the under-spring clamp 12 is fixed by screws and hexagonal nuts.
As shown in fig. 20, a schematic structural view of the spring displacement amplifying mechanism 11 is shown, and the spring displacement amplifying mechanism 11 is used for amplifying an external excitation source.
Referring to fig. 21-23, the present invention further provides a design method: the bistable characteristic of the system is utilized to improve the electromechanical coupling efficiency, reduce the working frequency of the system and widen the frequency bandwidth of the system; bistable state is a phenomenon that uses nonlinear repulsive magnetic force generated between a permanent magnet fixed at the free end of a cantilever beam and a permanent magnet fixed on a right clamping plate, thereby causing the cantilever beam to vibrate back and forth between two stable equilibrium states.
When the distance between the two permanent magnets is large, the nonlinear repulsive magnetic force between the two pairs of permanent magnets is zero, the whole system is a linear system, the equivalent stiffness coefficient is positive, and the system has only one stable equilibrium state, and at the moment, the system has monostable characteristic; when the distance between the two permanent magnets is further reduced and exceeds a critical value, the whole system is a nonlinear system, the equivalent stiffness coefficient becomes negative, and at this time the system has two stable equilibrium states, and the system thereby exhibits bistable properties.
The nonlinear repulsive magnetic force between the two pairs of permanent magnets is analyzed through a magnetic dipole model, so that the permanent magnet fixed at the free end of the cantilever beam is A, the permanent magnet fixed on the right clamping plate is B, and the magnetic dipole moment m A、mB of the permanent magnet A, B is represented by formulas (1) and (2) respectively:
mA＝MAVA cosα·i+MAVA sinα·j (1)
mB＝-MBVB·i (2)
Wherein M A、MB is the magnetization of permanent magnet A, B, respectively; v A、VB is the volume of permanent magnet A, B; i. j is a vector coordinate; alpha is the deflection angle of the permanent magnet A;
Assuming that the horizontal distance between the permanent magnets A, B is e and the deflection of the free end of the cantilever beam is w (l, t), the direction vector r BA from the permanent magnet B to the permanent magnet a is represented by formula (3):
rBA＝-e·i+w(l，t)·j (3)
The magnetic flux density B BA generated at a by the permanent magnet B is represented by formula (4):
the potential energy U m between the permanent magnets is:
Um＝-BBA·mA (5)
Wherein mu 0 is vacuum permeability, mu 0＝4π×10-7 H/m; is a vector gradient operator, and there is the following relationship between deflection angle α and deflection w (l, t):
from the above formula, the potential energy of the magnetic field generated by the repulsive force of the permanent magnet can be obtained as follows:
the elastic potential energy of the spring is expressed by formula (8):
The total potential energy U of the whole system is expressed by formula (9):
wherein the first term is the magnetic field potential energy generated by the repulsive force of the permanent magnets, and the second term is the elastic potential energy of the springs.
From the potential energy perspective, when the distance between the two pairs of permanent magnets is smaller, the generated nonlinear repulsive magnetic force is larger, the deflection of the free end of the cantilever beam is larger, and the potential energy of the magnetic field is larger, so that two potential wells appear in the total potential energy curve, and one potential barrier is a typical bistable structure; the system with bistable characteristic has two stable states, and as known from the principle of minimum potential energy, if and only if the potential energy of the system is minimum, the system is in a stable equilibrium state, so that the two stable equilibrium states of the bistable system are both present at the position where the potential energy is minimum; when the system does not have enough energy to escape from the potential well, the system can only generate monostable vibration in monostable state at the moment; when the energy of the system reaches a threshold value required for escaping from the potential well, the system is in a critical state, and the system reaches another steady-state position from one steady-state position; when the system has sufficient energy to escape from the potential well, the system vibrates between two steady states.
From the aspect of dynamic characteristics of the system, when the external excitation frequency is gradually increased, the system can show different motion phenomena, including a small-amplitude periodic motion phenomenon, a chaotic motion phenomenon, a large-amplitude periodic motion phenomenon and the like, and the different motion phenomena have different dynamic characteristics; when the system shows a large-amplitude periodic motion phenomenon, the system can show a bistable state phenomenon and keep oscillating on a high-energy track, so that the system has higher and stable electric energy output; when the system shows the chaotic motion phenomenon, the system has unstable electric energy output; when the system shows a small-amplitude periodic motion phenomenon, the system can oscillate on a low-energy track, and has lower and stable electric energy output; due to the introduction of the nonlinear repulsive magnetic force and the spring mechanism, when the system performs small-amplitude periodic motion or chaotic motion, the system can still enter the next stable position through the potential barrier under a certain excitation level, so that the system vibrates between the two stable positions to display bistable characteristics, and the system has the bistable characteristics in a larger frequency range. Therefore, the complex dynamic behavior greatly improves the power generation efficiency and effectively widens the frequency bandwidth of the system.
The spring displacement amplifying mechanism is arranged, the vibration displacement amplitude of the cantilever beam structure is amplified by utilizing the good elastic characteristic of the spring, the frequency bandwidth of the system is further widened by adjusting the mass ratio r m and the stiffness ratio r k between the bistable energy collecting system and the spring on the platform, and the mass ratio r m and the stiffness ratio r k between the bistable energy collecting system and the spring are respectively represented by formulas (10) and (11):
Wherein M eq and K eq are respectively equivalent mass and equivalent stiffness of the bistable energy-harvesting system, and M b and K b are respectively equivalent mass and stiffness of the spring.
By adjusting the mass ratio r m and the stiffness ratio r k between the bistable energy collection system and the spring system, the whole system can realize two formants with stronger nonlinear response and has good dynamic characteristics and energy characteristics; due to the nonlinear repulsive magnetic force between the two permanent magnets, the two formants are bent rightwards, as the mass ratio r m and the stiffness ratio r k of the bistable energy collection system and the spring are further increased, the formants move rightwards, the movement speed of the left peak is faster than that of the right peak, and the distance between the two formants is narrowed, so that a wider frequency band is formed.
Compared with the traditional bistable energy collection system without a spring structure, the whole system has substantial advantages on a plurality of excitation frequencies and excitation levels after the spring mechanism is added, and particularly under some low excitation levels, when the mass ratio r m and the stiffness ratio r k of the bistable energy collection system and the spring are increased, the whole system can oscillate on a high-energy track greatly and continuously generate higher output response. And at low excitation levels, the spring mechanism amplifies the external excitation amplitude imparted to the cantilever beam, thereby providing the system with energy high enough to overcome the potential barrier, making the system more likely to exhibit bistable behavior and oscillate on high energy tracks, ultimately producing a wider frequency band and a larger dynamic output response.
By adding a spring displacement amplifying mechanism between the bistable energy collecting system and an external excitation source, the external excitation is greatly amplified by adjusting the mass ratio r m and the stiffness ratio r k between the bistable energy collecting system and the spring, and a higher excitation level is provided for the bistable energy collecting system, so that the bistable energy collecting system forms large-amplitude interwell motion, and the system has higher dynamic response and energy characteristics in a wider frequency band range.
Through placing the permanent magnet on the permanent magnet fixing frame near the free end of the cantilever beam structure, the permanent magnet is respectively arranged on the upper side and the lower side of the cantilever beam structure and is positioned at a certain distance from the cantilever beam structure, so that the magnetostrictive material sheet is ensured to generate larger magnetic induction intensity change in the cantilever beam direction in the vibration process, and a proper bias magnetic field is provided for the cantilever beam, and is represented by a formula (12):
H＝Hb+Ni(t)/l (12)
Wherein l is the length of the pick-up coil, and N is the number of turns of the coil;
From the electromagnetic principle, the relation expression (13) between the magnetic field intensity H l along the length center line direction and the total magnetization M in the magnetostrictive material sheet is as follows:
Wherein mu 0 is vacuum magnetic permeability, mu 0＝4π×10-7H/m;μσ is magnetic permeability coefficient; h l represents the magnetic field strength along the length centerline in the magnetostrictive material; m represents the total magnetic field strength; h i denotes the total applied magnetic field, including the sum of the applied bias magnetic field H and the magnetic field H g generated by the induced current in the coil;
the magnetic induction intensity expression of the finally obtained magnetostrictive material sheet is as follows:
wherein sigma is the stress to which the magnetostrictive material is subjected; Is the reverse piezomagnetic coefficient;
When the cantilever beam is subjected to external excitation and an externally applied bias magnetic field, the magnetic domains in the magnetostrictive material sheet can be greatly deflected and expanded, so that the internal magnetization intensity of the magnetostrictive material sheet is changed, and the magnetostrictive material sheet externally shows magnetism; according to the magnetostriction inverse effect, the magnetism of the magnetostriction material sheet is greatly changed, the surrounding magnetic field is changed, and according to Faraday electromagnetic induction law, the magnetic flux in a pickup coil wound outside the cantilever structure is correspondingly changed, so that electromotive force with a certain magnitude is generated inside the pickup coil; therefore, by arranging the permanent magnets on the upper side and the lower side of the cantilever structure close to the free end, the externally applied bias magnetic field H i can be increased, and the induced current in the coil is very small, so that the magnetic field H g generated from the coil is ignored, the externally applied total magnetic field H i is increased, and the magnetic induction intensity B of the magnetic induction material sheet is increased; therefore, the whole system can work in a working area with better electromechanical coupling relation, and has the strongest promotion effect on energy conversion capability.
Measurement of experimental results: the following were measured by connecting the end of a pick-up coil wound outside the cantilever structure to an oscilloscope
(1) The voltage-frequency plot of a system with bistable structure, i.e. permanent magnets fixed to the right clamp plate near the free end of the cantilever structure and making the pair of permanent magnets mutually exclusive to a conventional system without bistable structure, was measured under vibration excitation of 6.272m/s 2, and as shown in fig. 21, it was found that the resonance frequency was 60Hz when the system had no bistable structure, and 22Hz when the permanent magnets were fixed to the right clamp plate near the free end of the cantilever structure and making the pair of permanent magnets mutually exclusive. And the peak voltage of the system with the bistable structure is increased by more than 4 times compared with that of the system without the bistable structure, and the design theory is met.
(2) The voltage-frequency plot was measured at 4.704m/s 2 for a bistable energy harvesting system without the addition of a spring displacement amplifying mechanism and with the addition of a spring displacement amplifying mechanism under the bistable energy harvesting system, as shown in fig. 22, it can be seen that only one formant appears for a conventional bistable energy harvesting system without a spring displacement amplifying mechanism, whereas two formants appear when the bistable energy harvesting system incorporates a spring displacement amplifying mechanism, with both peak voltages being higher than the peak voltage without a spring displacement amplifying mechanism. Therefore, after the bistable energy collection system is introduced into the spring displacement amplifying mechanism, the resonance frequency band is widened, higher output voltage is obtained, and the design theory is met.
(3) The voltage-frequency plot was measured at vibration excitation of 4.704m/s 2 when no permanent magnets were added to and from the upper and lower sides of the cantilever structure in the bistable energy harvesting system, as shown in fig. 23, it can be seen that the voltage obtained at the resonant frequency was increased by a factor of 2, in accordance with the design theory, when the permanent magnets were added to and from the upper and lower sides of the cantilever structure in the bistable energy harvesting system, compared to the upper and lower sides of the cantilever structure in the bistable energy harvesting system.
Claims (3)
1. Magnetostrictive bistable vibration collecting device with amplifying mechanism, characterized in that: the device comprises a platform (1), wherein a pair of first full-thread screws (2) are arranged on the left side of the platform (1), an upper clamping plate (3) and a lower clamping plate (4) are arranged on the pair of first full-thread screws (2), one end of a cantilever beam (5) is fixed between the upper clamping plate (3) and the lower clamping plate (4), the cantilever beam (5) is formed by three layers of thin sheets, the upper layer and the lower layer are magnetostrictive thin sheets, the middle layer is a base thin sheet, a permanent magnet A (7-1) is arranged at the other end of the cantilever beam (5), and a pickup coil (6) is arranged outside the cantilever beam (5); the right side of the platform (1) is provided with a pair of slideways, a second full-thread screw rod (2-1) is arranged in the pair of slideways, a right clamping plate (9) is arranged on the pair of second full-thread screw rods (2-1), a permanent magnet B (7-2) is arranged on the right clamping plate (9), and the permanent magnet B (7-2) and the permanent magnet A (7-1) repel each other;
A permanent magnet fixing frame (8) is arranged on the platform (1), the cantilever beam (5) penetrates through the permanent magnet fixing frame (8), and third permanent magnets (7-3) are arranged on the upper side and the lower side of the permanent magnet fixing frame (8); the lower side wall of the platform (1) is provided with a spring upper clamp (10), and the spring upper clamp (10) is connected with a spring lower clamp (12) through a spring displacement amplifying mechanism (11);
The main power provided by the vibration exciter is applied to the spring displacement amplifying mechanism (11), the amplified excitation is applied to the platform (1) through the amplification action of the spring displacement amplifying mechanism (11) on the amplitude, so that the amplified excitation is applied to the cantilever beam (5) structure, the cantilever beam (5) structure wound with the pick-up coil (6) vibrates due to the excitation action, the repulsive magnetic force in the vertical direction between the permanent magnet A (7-1) fixed at the free end of the cantilever beam (5) structure and the permanent magnet B (7-2) fixed on the right clamping plate changes, the internal magnetization state of the cantilever beam (5) structure changes, namely the internal magnetic flux changes, an electric field is generated according to Faraday electromagnetic induction law, induced electromotive force is generated in the pick-up coil, meanwhile, the external excitation is transmitted to the platform (1) fixed with the cantilever beam (5) structure through the spring displacement amplifying mechanism (11), the longitudinal bending magnetostriction is generated due to the action of the force, and the internal magnetization states of two layers of material sheets under the cantilever beam (5) structure are changed, namely the induced magnetic flux changes on the cantilever beam (5) through winding coil (6).
2. A method of designing a magnetostrictive bistable vibration harvesting device having an amplifying mechanism according to claim 1, wherein: the bistable characteristic of the system is utilized to improve the electromechanical coupling efficiency, reduce the working frequency of the system and widen the frequency bandwidth of the system;
When the distance between the two permanent magnets is large, the nonlinear repulsive magnetic force between the two pairs of permanent magnets is zero, the whole system is a linear system, the equivalent stiffness coefficient is positive, and the system has only one stable equilibrium state, and at the moment, the system has monostable characteristic; when the distance between the two permanent magnets is further reduced and exceeds a critical value, the whole system is a nonlinear system, the equivalent stiffness coefficient becomes negative, and the system has two stable equilibrium states at the moment, so that the system shows bistable property;
The nonlinear repulsive magnetic force between the two pairs of permanent magnets is analyzed through a magnetic dipole model, so that the permanent magnet fixed at the free end of the cantilever beam is A, the permanent magnet fixed on the right clamping plate is B, and the magnetic dipole moment m A、mB of the permanent magnet A, B is represented by formulas (1) and (2) respectively:
mA＝MAVAcosα·i+MAVAsinα·j (1)
mB＝-MBVB·i (2)
Wherein M A、MB is the magnetization of permanent magnet A, B, respectively; v A、VB is the volume of permanent magnet A, B; i. j is a vector coordinate; alpha is the deflection angle of the permanent magnet A;
Assuming that the horizontal distance between the permanent magnets A, B is e and the deflection of the free end of the cantilever beam is w (l, t), the direction vector r BA from the permanent magnet B to the permanent magnet a is represented by formula (3):
rBA＝-e·i+w(l,t)·j (3)
The magnetic flux density B BA generated at a by the permanent magnet B is represented by formula (4):
the potential energy U m between the permanent magnets is:
Um＝-BBA·mA (5)
Wherein mu 0 is vacuum permeability, mu 0＝4π×10-7 H/m; Is a vector gradient operator, and there is the following relationship between deflection angle α and deflection w (l, t):
from the above formula, the potential energy of the magnetic field generated by the repulsive force of the permanent magnet can be obtained as follows:
the elastic potential energy of the spring is expressed by formula (8):
wherein K b is the equivalent stiffness of the spring:
The total potential energy U of the whole system is expressed by formula (9):
wherein the first term is magnetic field potential energy generated by the repulsive force of the permanent magnet, and the second term is elastic potential energy of the spring;
Through placing the permanent magnet on the permanent magnet fixing frame near the free end of the cantilever beam structure, the permanent magnet is respectively arranged on the upper side and the lower side of the cantilever beam structure and is positioned at a certain distance from the cantilever beam structure, so that the magnetostrictive material sheet is ensured to generate larger magnetic induction intensity change in the cantilever beam direction in the vibration process, and a proper bias magnetic field is provided for the cantilever beam, and is represented by a formula (12):
H＝Hb+Ni(t)/l (12)
Wherein l is the length of the pick-up coil, and N is the number of turns of the coil;
From the electromagnetic principle, the relation expression (13) between the magnetic field intensity H l along the length center line direction and the total magnetization M in the magnetostrictive material sheet is as follows:
Wherein mu 0 is vacuum magnetic permeability, mu 0＝4π×10-7H/m;μσ is magnetic permeability coefficient; h l represents the magnetic field strength along the length centerline in the magnetostrictive material; m represents the total magnetic field strength; h i denotes the total applied magnetic field, including the sum of the applied bias magnetic field H and the magnetic field H g generated by the induced current in the coil;
the magnetic induction intensity expression of the finally obtained magnetostrictive material sheet is as follows:
wherein sigma is the stress to which the magnetostrictive material is subjected; Is the reverse piezomagnetic coefficient.
3. The method of designing a magnetostrictive bistable vibration collecting device with amplifying mechanism according to claim 2, wherein: in the introduction of the spring mechanism, the spring mechanism is a spring displacement amplifying mechanism, the vibration displacement amplitude of the cantilever beam structure is amplified by utilizing the good elastic characteristic of the spring, the frequency bandwidth of the system is further widened by adjusting the mass ratio r m and the stiffness ratio r k between the bistable energy collecting system and the spring on the platform, and the mass ratio r m and the stiffness ratio r k between the bistable energy collecting system and the spring are respectively represented by formulas (10) and (11):
Wherein M eq and K eq are respectively equivalent mass and equivalent stiffness of the bistable energy-harvesting system, and M b and K b are respectively equivalent mass and stiffness of the spring.
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