CN108832842B - Frequency-raising type piezoelectric generator for collecting horizontal direction ultralow frequency vibration energy - Google Patents
Frequency-raising type piezoelectric generator for collecting horizontal direction ultralow frequency vibration energy Download PDFInfo
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Abstract
The embodiment of the invention discloses an up-conversion piezoelectric generator for collecting horizontal ultralow-frequency vibration energy, relates to the technical field of renewable energy sources and micro-power generation, can automatically collect vibration energy in a horizontal plane, can stably and reliably operate, and is low in processing and use cost. The invention comprises the following steps: the mass block 1 used for swinging, the cycloid 2 used for drawing the mass block 1, the first cantilever beam 3, the second cantilever beam 4, the piezoelectric element 5 used for electromechanical coupling conversion, the first permanent magnet 6 and the second permanent magnet 7; the mass block 1 forms a pendulum ball in an oscillating structure; the rigidity of the first cantilever beam 3 is smaller than that of the second cantilever beam 4, and the first cantilever beam 3, the mass block 1 and the swinging ball 2 jointly form an oscillating structure; the second cantilever beam 4 and the piezoelectric element 5 form a piezoelectric cantilever beam for generating an oscillating structure; the first permanent magnet 6 and the second permanent magnet 7 are disposed in parallel and constitute a pair of nonlinear mutual repulsive forces. The invention is suitable for automatically collecting the vibration energy in any direction in the horizontal plane.
Description
Technical Field
The invention relates to the technical field of renewable energy sources and micro-power generation, in particular to an up-conversion piezoelectric generator for collecting horizontal ultralow-frequency vibration energy.
Background
The environmental energy collection technology is a technology for converting one or more energy sources in the surrounding environment into electric energy in a certain mode. At present, the intelligent lock is applied to shared equipment such as a shared bicycle and a shopping cart in a large quantity and is used for supplying power to intelligent lock equipment, and huge maintenance cost caused by the fact that an operator needs to replace batteries in a large quantity every day is avoided. Among them, a piezoelectric power generator that converts mechanical energy of environmental vibration into electric energy by using a positive piezoelectric effect of a piezoelectric material is favored by most scholars.
In order to maximize the electromechanical coupling efficiency, it is often required that the natural frequency of the collector itself be matched to the frequency of the ambient vibration source. In practical applications, the problem of low generated power is particularly present in piezoelectric and electromagnetic generators. In addition, since the power generation power of the piezoelectric electromagnetic generator is increased along with the increase of the vibration frequency, taking the electromagnetic generator as an example, in order to increase the vibration frequency, a complicated gear speed increasing device (such as a planetary gear) is often required to be designed to increase the rotation frequency so as to increase the electric power, which causes a problem of high cost and is difficult to rapidly form industrialization. Therefore, how to design a piezoelectric generator scheme with a relatively simple structure and simpler and cheaper processing compared with a gear speed increasing design becomes a problem to be solved urgently in the field.
Disclosure of Invention
The embodiment of the invention provides an up-conversion piezoelectric generator for collecting ultralow frequency vibration energy in the horizontal direction, which can stably and reliably operate, has low processing and use cost and can automatically collect vibration energy in any direction in the horizontal plane.
In order to achieve the above purpose, the embodiment of the invention adopts the following technical scheme:
an upconverting piezoelectric generator for collecting ultra low frequency vibration energy in a horizontal direction, comprising: the device comprises a mass block (1) used for swinging, a cycloid (2) used for drawing the mass block (1), a first cantilever beam (3), a second cantilever beam (4), a piezoelectric element (5) used for electromechanical coupling conversion, a first permanent magnet (6) and a second permanent magnet (7); the mass block (1) forms a pendulum ball in an oscillating structure, a cycloid (2) is tied at the free end of the cantilever beam (3), and the cycloid (2) is an inextensible cycloid; the rigidity of the first cantilever beam (3) is smaller than that of the second cantilever beam (4), the first cantilever beam (3), the mass block (1) and the swing ball (2) jointly form an oscillation structure, and the first cantilever beam (3) forms an equivalent spring in the oscillation structure; the second cantilever beam (4) and the piezoelectric element (5) form a piezoelectric cantilever beam with an oscillation structure, and the piezoelectric cantilever beam is used for converting the mechanical energy of vibration into electric energy; the first permanent magnet (6) and the second permanent magnet (7) are arranged in parallel and form a pair of nonlinear mutual repulsion forces.
Specifically, in the oscillating structure: the second permanent magnet (7) is fixed at the free end of the first cantilever beam (3), and the second permanent magnet (6) is fixed at the free end of the second cantilever beam (4). The second cantilever beam (4) is in a sheet shape, the first cantilever beam (3) is in a sheet U-shaped frame, the first cantilever beam (3) and the second cantilever beam (4) are placed on the same horizontal plane, and the first cantilever beam (3) and the second cantilever beam (4) are not in contact with each other; the second cantilever beam (4) is embedded in the structure of the first cantilever beam (3).
Optionally, in the oscillating structure: the first cantilever beam (3) and the second cantilever beam (4) are distributed at one end of the fixed foundation in parallel, and the geometric center points of the second permanent magnet (6) and the second permanent magnet (7) are in the same horizontal plane in an initial state. In the oscillating structure: the first cantilever beam (3) and the second cantilever beam (4) are both in a sheet shape, the first cantilever beam (3) and the second cantilever beam (4) are placed on the same horizontal plane, and the first cantilever beam (3) and the second cantilever beam (4) are not in contact with each other; the first cantilever beam (3) and the second cantilever beam (4) are arranged in parallel.
According to the frequency-boosting piezoelectric generator for collecting the ultralow-frequency energy in the horizontal direction, firstly, a nonlinear spring pendulum principle is utilized, a low-frequency vibration source matched with a pendulum natural frequency is boosted by 2 times, namely, a first cantilever beam (3) greatly oscillates at the natural frequency; and then, the vibration source frequency is further increased to 6 times by utilizing a two-degree-of-freedom cubic nonlinear principle and through nonlinear magnetic force, namely the second cantilever beam (4) greatly oscillates at the natural frequency. Because the root of the second cantilever beam (4) is integrated with the piezoelectric element, the frequency of the finally output voltage is equal to the oscillation frequency of the second cantilever beam (4), namely 6 times of the frequency of the original environment vibration source. Therefore, the piezoelectric oscillator structure capable of matching the ultra-low frequency environment vibration source is realized, the operation is stable and reliable, the processing and use cost is low, and meanwhile, the output frequency can be effectively improved, and the power generation power is improved; and the vibration energy in any direction in the horizontal plane can be automatically collected without external intervention.
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In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic diagram of a possible structure provided by an embodiment of the present invention;
FIG. 2 is a schematic diagram of another possible structure provided by an embodiment of the present invention;
fig. 3 is a schematic diagram of an equivalent model of the structure of the frequency-up piezoelectric generator;
fig. 4 is a schematic diagram of the simplified equivalent structure operation process of the up-conversion piezoelectric generator;
FIG. 5 is a schematic diagram of a wobble natural frequency adjustment provided by an embodiment of the present invention;
FIG. 6 is a schematic view of a pendulum ball mass adjustable design provided by an embodiment of the present invention;
fig. 7 is a diagram illustrating a system oscillation waveform with various degrees of freedom and its power spectral density obtained through theoretical calculation according to an embodiment of the present invention.
Detailed Description
In order to make the technical solutions of the present invention better understood, the present invention will be described in further detail with reference to the accompanying drawings and specific embodiments. Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the same or similar parts throughout, or parts having the same or similar functions. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention. It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
The embodiment specifically provides an up-conversion piezoelectric generator for collecting ultra-low frequency vibration energy in the horizontal direction, which includes:
the device comprises a mass block (1) for swinging, a cycloid (2) for drawing the mass block (1), a first cantilever beam (3), a second cantilever beam (4), a piezoelectric element (5) for electromechanical coupling conversion, and a first permanent magnet (6) and a second permanent magnet (7) for providing nonlinear coupling force. Specifically, the method comprises the following steps:
the mass block (1) forms a pendulum ball in an oscillating structure, a cycloid (2) is tied at the free end of the cantilever beam (3), and the cycloid (2) is an inextensible cycloid.
The first cantilever beam (3), the mass block (1) and the pendulum ball (2) jointly form an oscillating structure, and are placed on the same horizontal plane in an initial state, so that the size of the device is greatly reduced by the design.
The stiffness of the first cantilever beam (3) is less than that of the second cantilever beam (4), and in the practical application of the embodiment, the first cantilever beam (3) can also be called a low-stiffness cantilever beam (3), and the second cantilever beam (4) can be called a high-stiffness cantilever beam (4).
The second cantilever beam (4) and the piezoelectric element (5) form the piezoelectric cantilever beam of the oscillation structure, and the piezoelectric cantilever beam is used for converting the vibration mechanical energy into electric energy.
The first permanent magnet (6) and the second permanent magnet (7) are arranged in parallel and form a pair of nonlinear mutual repulsion forces.
Wherein the first cantilever beam (3) constitutes an equivalent spring in the oscillating structure, but the spring expansion changes only in the vertical direction, and the oscillation of the equivalent spring is equivalent to the expansion of the spring. In practical application, the frequency matching adjustment can be realized only by changing the equivalent gravity acceleration around the pendulum ball, and compared with the traditional method for changing the pendulum length, the method is more suitable for the vibration energy collecting device.
In the embodiment, the oscillating structure consisting of the mass block (1) for oscillating, the cycloid (2) and the first cantilever beam (3) has the oscillating natural frequency only related to the oscillating length and the gravitational acceleration so as to realize ultra-low frequency matching without reducing the structural rigidity or adding the equivalent mass. The vibration energy in any direction in the horizontal plane can be collected in a self-adaptive mode, and any external operation is not needed. The cantilever beam (3) is equivalent to a spring in a spring pendulum system, and is slightly different from a strictly defined spring pendulum because: in the spring pendulum in a strict sense, there is an acceleration varying along the pendulum length direction, and in the present embodiment, the acceleration varying along the pendulum length only varies along the vertical direction.
In the embodiment, the free ends of the first cantilever beam (3) and the second cantilever beam (4) are fixed with permanent magnets which are mutually repulsive, and the frequency-up conversion is finally realized through the coupling of nonlinear magnet force. In addition, the spacing between the permanent magnets can be manually adjusted during assembly. The nonlinear mutual repulsion force coupling between the first permanent magnet (6) and the second permanent magnet (7) influences the dynamic characteristics of the first cantilever beam (3) and the second cantilever beam (4). As long as the mechanical effect is satisfied, the specific installation manner of the second cantilever beam (4) and the first cantilever beam (3) is not completely limited in this embodiment. Two possible approaches are listed below.
One is as follows: as shown in fig. 1, in the oscillation structure: the second permanent magnet (7) is fixed at the free end of the first cantilever beam (3), and the second permanent magnet (6) is fixed at the free end of the second cantilever beam (4). The second cantilever beam (4) is in a sheet shape, the first cantilever beam (3) is in a sheet U-shaped frame, the first cantilever beam (3) and the second cantilever beam (4) are placed on the same horizontal plane, and the first cantilever beam (3) and the second cantilever beam (4) are not in contact with each other; the second cantilever beam (4) is embedded in the structure of the first cantilever beam (3). In the initial state, the neutral surfaces of the two cantilever beams are positioned on the same plane, and the design greatly reduces the volume of the device. Therefore, the size of the device is greatly reduced on the basis of meeting the performance requirement.
The second step is as follows: as shown in fig. 2, considering that the embedded design will increase the difficulty of structure processing and assembly, and further improve a simpler assembly implementation, the cantilever beams (4) and the cantilever beams (3) can be distributed at one end of the fixed foundation in parallel, and in the initial state, the geometric center points of the permanent magnets should be on the same horizontal plane, and the design can also reduce the volume of the device. Specifically, in the oscillating structure:
the first cantilever beam (3) and the second cantilever beam (4) are distributed at one end of the fixed foundation in parallel, and the geometric center points of the second permanent magnet (6) and the second permanent magnet (7) are in the same horizontal plane in an initial state. The first cantilever beam (3) and the second cantilever beam (4) are both in a sheet shape, the first cantilever beam (3) and the second cantilever beam (4) are placed on the same horizontal plane, and the first cantilever beam (3) and the second cantilever beam (4) are not in contact with each other; the first cantilever beam (3) and the second cantilever beam (4) are arranged in parallel, so that the assembly difficulty is reduced on the basis of meeting the performance requirement and reducing the size of the device.
Furthermore, in the embodiment, the action point of the cycloid (2) is fixed at the middle position in the width direction of the first cantilever beam (3), so that the torsional vibration of the cantilever beam (3) is avoided. Wherein, the cycloid (2) is fixedly connected or hinged with the free end of the cantilever beam (3). If the free end of the cycloid (2) and the free end of the cantilever beam (3) are hinged through a universal coupling, so that the free end can collect vibration energy in any direction in a horizontal plane.
In the fields of renewable energy sources and micro-power generation, solar energy, wind energy, temperature difference energy, vibration energy and the like are common environmental energy sources. Each energy source has its advantages and disadvantages, and the specific selection of which energy source should be selected takes into consideration various factors in the actual application. The invention mainly relates to the field of environmental vibration energy collection, and basically meets the application requirements of most low-power consumption intelligent equipment because vibration energy is ubiquitous and has considerable energy density in natural environment. And because the piezoelectric material has the advantages of good electromechanical coupling characteristic, convenience in integration with a collector structure and the like, the piezoelectric material converts the environmental vibration mechanical energy into electric energy by utilizing the positive piezoelectric effect of the piezoelectric material, and is favored by most students.
The peak frequency of the power spectrum of most environmental vibration energy is extremely low, such as vibration energy introduced by human/animal activities, and the frequency is about 1 Hz; vibration of large mechanical equipment and civil engineering structures, the frequency is within 5Hz, and the like. In order to maximize the electromechanical coupling efficiency, the natural frequency of the collector is often required to be matched with the frequency of the environmental vibration source, and the design idea brings a series of new problems. Firstly, the structure is fragile, the fatigue life is low, most of the existing oscillation structures are designed by adopting a mass-spring-damping second-order oscillation model, and in order to obtain lower inherent frequency, the structure equivalent stiffness is particularly low, and the equivalent mass is particularly large; secondly, the generated power is particularly low, and for piezoelectric and electromagnetic generators, the generated power is improved along with the increase of vibration frequency, for example, the power density of the piezoelectric ceramic PZT is 80mW/cm3 under the working condition of 20Hz, and the power density can reach 150W/cm3 under the working condition of high frequency (10kHz), the frequency is increased by 500 times, and the power density is improved by nearly 2000 times. For example, a complicated gear increasing device is specially designed inside a typical wind power generator, and is used for increasing the rotation frequency to increase the generated power. At present, for piezoelectric engines, some scholars also start to design an ascending frequency type structure, such as a mechanical collision type, a mechanical stirring type, an inertial impact type, a magnetic ascending frequency type and the like, and the ascending frequency ratio of the design is high, but the new problems of high required excitation acceleration threshold, energy dissipation, large impact force and the like exist.
In order to maximize the electromechanical coupling efficiency, it is often required that the natural frequency of the oscillating structure of the piezoelectric generator is matched with the frequency of the environmental vibration source. In practical application, both piezoelectric and electromagnetic generators have the problem of generating extremely low power once the vibration source frequency is extremely low. And as the generated power is increased along with the increase of the vibration frequency, in order to increase the vibration frequency, the generated power is often realized by designing a complicated mechanical structure. For example, a large-scale wind driven generator is internally provided with an expensive planetary gear speed increasing device to increase the frequency of a coil cutting magnetic induction line so as to increase the generating power, so that the problem of high maintenance and use cost is caused; such mechanical structures are also not suitable for use in some micro-power generation applications. Therefore, how to design a piezoelectric generator scheme with a relatively simple structure and lower maintenance cost in the field of low-frequency vibration energy collection becomes a problem to be solved urgently in the field.
The technical problem to be solved by the embodiment is how to design a piezoelectric oscillator structure capable of matching an ultralow frequency environment vibration source, the piezoelectric oscillator structure is stable and reliable in operation and low in processing and use cost, and meanwhile, the output frequency can be effectively improved, and the power generation power is improved. In addition, it is also desirable to be able to automatically collect vibration energy in any direction within the horizontal plane without external intervention.
Therefore, the invention provides a piezoelectric oscillator structure for realizing frequency-up conversion based on resonance phenomenon in a multi-degree-of-freedom nonlinear system, which is formed by combining a typical two-degree-of-freedom oscillation structure and a two-degree-of-freedom cubic nonlinear structure based on nonlinear magnetic coupling. The frequency matching adjustment is realized only by changing the equivalent gravity acceleration around the pendulum ball, and compared with the traditional method for changing the pendulum length, the method is more suitable for the vibration energy collecting device. The spring pendulum ball can be designed into a combined assembly structure of a polished rod bolt and a mass block with a threaded through hole, the mass of the pendulum ball is adjusted by selecting the number of the mass blocks, and then the natural frequency of the second degree of freedom is adjusted, so that the structure can further adapt to an environmental vibration source.
The technical problem to be solved by the embodiment of the invention is to design a simple vibration energy collecting structure on the basis of meeting the performance requirement, so that the vibration energy collecting structure is stable and reliable in operation and low in processing and using cost, and mainly solves the problem of how to collect ultralow frequency vibration energy in the horizontal direction and output higher power generation power. In the prior art, the research on multi-direction vibration energy collectors is less, the embodiment of the invention creatively applies excitation in any direction in a horizontal plane by virtue of an oscillating structure, and a spring in the structure can realize telescopic deformation, namely, a cantilever beam (3) oscillates; simultaneously creatively and respectively utilizing the 1:2 and 1:3 internal resonance phenomena of the multi-degree-of-freedom nonlinear system to realize the 1:6 frequency-up conversion; in addition, the swing natural frequency of the oscillating structure is only related to the gravity acceleration and the swing length and is unrelated to the equivalent rigidity and the mass of the structure, so that the embodiment of the invention creatively realizes the ultra-low vibration frequency matching and simultaneously avoids the structural vulnerability problem.
According to the frequency-boosting piezoelectric generator for collecting the ultralow-frequency energy in the horizontal direction, firstly, a nonlinear spring pendulum principle is utilized, a low-frequency vibration source matched with a pendulum natural frequency is boosted by 2 times, namely, a first cantilever beam (3) greatly oscillates at the natural frequency; and then, the vibration source frequency is further increased to 6 times by utilizing a two-degree-of-freedom cubic nonlinear principle and through nonlinear magnetic force, namely the second cantilever beam (4) greatly oscillates at the natural frequency. Because the root of the second cantilever beam (4) is integrated with the piezoelectric element, the frequency of the finally output voltage is equal to the oscillation frequency of the second cantilever beam (4), namely 6 times of the frequency of the original environment vibration source.
The frequency-raising type design is realized through a nonlinear vibration theory, and from the theoretical point of view, no energy loss exists in the frequency-raising conversion process, and meanwhile, the required external acceleration threshold is low, so that the theoretical advantage is obvious. From the viewpoint of a dynamic system, due to the inherent characteristic of damping of the oscillator structure, the total energy loss of the system should be increased as the frequency up-conversion times are increased. On the other hand, however, as the vibration frequency increases, the electromechanical conversion efficiency of the piezoelectric element increases, the output power increases, and therefore the energy loss by the up-conversion is acceptable. Compared with the wind driven generators widely applied nowadays, the transmission gear box with high installation cost must be designed in the engine room, and although energy loss exists in the operation process of the transmission gear, the transmission gear can increase the extremely low blade rotation frequency (about 19-30 rpm) to about 1500 rpm, so that the frequency of the coil cutting magnetic induction lines is greatly increased, and the power generation power is further increased.
In summary, for the low-frequency large energy generated by the spring pendulum under the external excitation, the frequency-up design provided by the embodiment of the invention can effectively convert the large energy into the electric energy with higher output power. In addition, the piezoelectric generator structure provided by the invention has the advantages of simple structure, easiness in processing and assembling, stability and reliability in working and the like.
The specific implementation principle of this embodiment can be understood as follows: the three-degree-of-freedom nonlinear system can be regarded as a two-degree-of-freedom square nonlinear system and a two-degree-of-freedom cubic nonlinear system which are combined, and finally, the three-degree-of-freedom cubic nonlinear system can be equivalent to a complex nonlinear system. The second degree of freedom is respectively attached to the square nonlinear system and the cubic nonlinear system, plays a role of an intermediate bridge, and effectively connects the first degree of freedom and the third degree of freedom together. According to the nonlinear dynamics theory, assuming that the ratio of the natural frequencies of the first, second and third degrees of freedom is ω 1, ω 2 and ω 3, respectively, when the ratio of the natural frequencies is 1:2:6, the system will generate internal resonance. The first degree of freedom of the structure belongs to pendulum ball swing, and the natural frequency omega 1 is only related to the pendulum length l and the pendulum ball mass m, so that the structure can be matched with the external ultra-low excitation frequency (generally lower than 5Hz) under the condition of ensuring the structural strength. Meanwhile, due to the occurrence of the internal resonance phenomenon, the output voltage frequency of the final generator is 6 times of the excitation frequency, so that the power generation power of the electromechanical coupling structure is improved, and the recovery efficiency of a subsequent energy extraction circuit is also improved.
In a first aspect, an embodiment of the present invention provides an up-conversion piezoelectric generator for collecting ultra-low frequency vibration energy in a horizontal direction, which has a structure as shown in fig. 1 and fig. 2, and includes: the device comprises a swinging mass block (1), a cycloid (2), a low-rigidity cantilever beam (3), a high-rigidity cantilever beam (4), a piezoelectric element (5) for electromechanical coupling conversion and permanent magnets (6) and (7) for providing nonlinear coupling force. The mass block (1) forms a pendulum ball in a spring pendulum system, and a non-telescopic pendulum line is tied at the free end of the cantilever beam (3); the cantilever beam (3) forms an equivalent spring in the spring pendulum system, and the oscillation of the equivalent spring is equivalent to the extension and contraction of the spring; the cantilever beam (4) and the piezoelectric element (5) form a piezoelectric cantilever beam for converting the vibration mechanical energy into electric energy; the permanent magnets (6) and (7) form a pair of nonlinear mutual repulsive forces, and the dynamic characteristics of the cantilever beams (3) and (4) are influenced by coupling.
The structural equivalent model of the frequency-up piezoelectric generator for collecting ultra-low frequency vibration energy in the horizontal direction provided by the embodiment of the invention is shown in fig. 3, and the frequency-up piezoelectric generator comprises: the degree of freedom of the pendulum system is marked as x1, and the natural frequency of the pendulum is omega 1; a mass-spring-damped oscillatory system with a natural frequency of ω 2, the degree of freedom of which is denoted as x 2; the natural frequency is omega 3, and the degree of freedom is recorded as x 3. When the excitation in any direction in the horizontal plane is carried out, if the frequency is near the swing natural frequency omega 1, the large-amplitude oscillation of the simple pendulum can be caused, and then the mass-spring-damping oscillation system is driven to generate the large-amplitude oscillation, and finally the mass-spring-damping-piezoelectric oscillation system also generates the large-amplitude oscillation due to the existence of the nonlinear magnet force, so that the piezoelectric element is driven to generate electricity efficiently.
The working principle and the operation process of the embodiment of the invention are schematically shown in fig. 4, which shows the oscillation states of the single pendulum system in a half cycle (ω 1/2) corresponding to each part. When the pendulum ball is located at the highest point on the left side shown in fig. 3, the spring in the spring pendulum is in a 'compressed' state, namely the cantilever beam (3) is at the highest point. When the cantilever beam (3) is in the horizontal state shown in fig. 3, the cantilever beam (4) is also in the horizontal state generally; but now the cantilever beam (3) vibrates for 1/4 cycles and the cantilever beam (4) vibrates for 3/4 cycles. When the pendulum ball is at the lowest point shown in fig. 3, the spring in the spring pendulum is in an "extended" state, i.e., the cantilever beam (3) is at the lowest point. When the cantilever beam (3) is in the horizontal state shown in fig. 3, the cantilever beam (4) is also in the horizontal state in general. Finally, when the ball is located at the highest point on the right and left sides as shown in fig. 3, the spring in the spring pendulum is in a "compressed" state, that is, the cantilever beam (3) is at the highest point, 1 oscillation cycle is completed, and at this time, the pendulum ball only completes 1/2 oscillation cycles, and the cantilever beam (4) completes 3 oscillation cycles.
For the structure of the frequency-raising piezoelectric generator, the pendulum ball can be made of materials with higher density and lower cost, such as metal materials of lead, steel and the like; the cycloid is made of inextensible flexible materials, such as nylon wires, steel wire wires, polyethylene fiber wires and the like; the cantilever beam structures (3) and (4) are made of stainless steel, spring steel and other materials generally; the permanent magnets (6) and (7) are generally made of neodymium iron boron materials.
Because the high-rigidity cantilever beam (4) is embedded in the low-rigidity cantilever beam (3) structure, the length of the device is reduced by half, and neutral surfaces of the two cantilever beams are in the same plane during initial assembly.
In consideration of the difficulty of the embedded design in the aspects of assembly and processing, the invention also provides a parallel assembly scheme, namely the cantilever beams (3) and (4) are arranged on one side of the basic device in parallel, the length of the whole device can be reduced by half, and the geometric centers of the permanent magnets are in the same horizontal plane during initial assembly.
Furthermore, the permanent magnets (6) and (7) are respectively and correspondingly fixed at the free ends of the cantilever beams (3) and (4), mutual repulsion is formed between the two permanent magnets, and the distance between the permanent magnets can be conveniently adjusted and set during assembly.
The cantilever beams (3) and (4) are designed into an asymmetric form, so that the repulsive force formed between the permanent magnets in the theoretical model is prevented from being 0 all the time, and the asymmetry is mainly embodied as the equivalent beam length or the rigidity of the cantilever beams.
As an embodiment, the ratio of the natural frequencies of the respective degrees of freedom of the up-conversion piezoelectric generator system should be 1:2:6 or close to this value under linear conditions. When magnetic coupling occurs in the system, the natural frequency of the cantilever beams (3) and (4) is shifted, and the shift degree is related to the distance between the permanent magnets, so that the equivalent beam length of the cantilever beams (3) and (4) can be further adjusted in a micro-adjustment mode in practical design.
Furthermore, the modes of micro-adjustment of the natural frequency of the cantilever beams (3) and (4) can be realized through two modes respectively. For the cantilever beam (3), the position of the fixed cycloid at the free end of the cantilever beam can be properly adjusted along the beam length direction, which is equivalent to the fine adjustment of the equivalent beam length of the cantilever beam (3) and the proper change of the natural frequency. For the cantilever beam (4), the fixed end can be properly extended or retracted into the basic device, and the natural frequency of the cantilever beam can be changed directly by means of fine adjustment of the length of the cantilever beam. It is noted that when the equivalent beam length of the cantilever beam changes, the permanent magnets should be properly positioned to be as opposite as possible for the side-by-side assembly system.
Furthermore, once the assembly of the up-conversion piezoelectric generator system is completed, the natural frequency ω 1 of the oscillation is also shifted. According to the nonlinear vibration mechanics theory, the amplitude-frequency characteristic curve of the swing system shifts to two sides to obtain two peak frequencies. In order to match the frequency of the environmental vibration source, when designing the piezoelectric generator, the natural frequency ω 1 of the oscillation under the linear condition should slightly deviate from the frequency of the environmental vibration source to be collected. Aiming at the application occasions where the frequency of the environmental vibration source changes frequently, the inherent frequency deviation characteristic widens the working frequency band of the device, is more beneficial to environmental vibration energy collection, and enhances the environmental viability of the piezoelectric generator device.
Furthermore, the frequency-increasing piezoelectric generator can also adjust the swing natural frequency in a self-adaptive manner, so that the frequency of the environment vibration source is matched to the maximum extent, and higher generated power output is always realized. For the adjustment of the natural frequency of the swing, the adjustment can be realized by changing the swing length l and the gravity acceleration g in theory, and the gravity acceleration g is generally considered to be a constant, and the adjustment can be realized only by changing the swing length l. The embodiment of the invention innovatively realizes frequency matching adjustment by changing the equivalent gravity acceleration g, and the method is most effective and feasible in practical application.
According to the principle, the permanent magnet material can be fixed below the pendulum ball in the embodiment of the invention, as shown in fig. 5. At the moment, the pendulum ball is made of a magnetic conductive material, the attraction force generated by the permanent magnet to the pendulum ball (1) equivalently increases the value of the gravity acceleration g, and the smaller the distance d is, the higher the swing natural frequency of the pendulum ball is. Compared with the method for adjusting the frequency by changing the pendulum length l, the method has the advantages of easiness in implementation, simplicity in adjustment and the like.
Furthermore, considering that the natural frequency of the second-degree-of-freedom mass-spring oscillation system is adjustable, the embodiment of the invention adds a pendulum ball mass adjustable design, as shown in fig. 6. The pendulum ball structure can be composed of a polished rod bolt and a plurality of mass blocks with threaded through holes, and the manual adjustment of equivalent mass is realized by selecting a combination mode of different mass blocks. The pendulum ball mass is positively correlated with the equivalent mass in the second degree-of-freedom mass-spring oscillation system, so that the natural frequency of the degree of freedom can be conveniently adjusted, the pendulum ball mass is further suitable for an environmental vibration source, and the survival capability of the device is enhanced.
Finally, fig. 7 shows the dynamic response time domain diagram and its power spectrum diagram of each degree of freedom of the system under a typical ultra-low frequency excitation source. The frequency of the excitation source is 3.36Hz, which is close to the swing natural frequency, and the vibration frequency of the cantilever beam (3) is 6.71Hz which is 2 times of the excitation frequency due to the internal resonance effect of 1: 2; and due to the internal resonance effect of the cubic nonlinear system 1:3, the main vibration frequency of the cantilever beam (4) is 20.29 Hz which is 3 times of the vibration frequency of the cantilever beam (3). In conclusion, as the piezoelectric conversion element is integrated on the cantilever beam (4), the final output voltage frequency is equal to the vibration frequency of the cantilever beam (4), namely 6 times of the excitation frequency, and the frequency-up conversion rate is greatly improved.
The embodiment of the invention has simple and reliable structure and great application prospect. Considering the problems of the service life, the stability and the like of the device, a protection device can be simply added during the specific implementation, such as the encapsulation protection of a cuboid structure, and the influence of extreme conditions such as impact, inversion and the like can be prevented.
The embodiments in the present specification are described in a progressive manner, and the same and similar parts among the embodiments are referred to each other, and each embodiment focuses on the differences from the other embodiments. In particular, for the apparatus embodiment, since it is substantially similar to the method embodiment, it is relatively simple to describe, and reference may be made to some descriptions of the method embodiment for relevant points. The above description is only for the specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (2)
1. An upconverting piezoelectric generator for collecting ultra low frequency vibration energy in a horizontal direction, comprising:
the device comprises a mass block (1) for swinging, a cycloid (2) for drawing the mass block (1), a first cantilever beam (3), a second cantilever beam (4), a piezoelectric element (5) for electromechanical coupling conversion, a first permanent magnet (6) and a second permanent magnet (7);
the mass block (1) forms a pendulum ball in an oscillating structure, a cycloid (2) is tied at the free end of the cantilever beam (3), and the cycloid (2) is an inextensible cycloid;
the rigidity of the first cantilever beam (3) is smaller than that of the second cantilever beam (4), the first cantilever beam (3), the mass block (1) and the swing ball (2) jointly form an oscillation structure, and the first cantilever beam (3) forms an equivalent spring in the oscillation structure;
the second cantilever beam (4) and the piezoelectric element (5) form a piezoelectric cantilever beam of an oscillation structure, and the piezoelectric cantilever beam is used for converting the vibration mechanical energy into electric energy;
the first permanent magnet (6) and the second permanent magnet (7) are arranged in parallel and form a pair of nonlinear mutual repulsion forces;
the cycloid (2) is hinged with the free end of the cantilever beam (3) through a universal coupling;
the action point of the cycloid (2) is fixed at the middle position of the first cantilever beam (3) in the width direction;
the cycloid (2) is fixedly connected or hinged with the free end of the cantilever beam (3);
the cycloid (2) is made of a non-stretchable flexible material; in the oscillating structure: the second permanent magnet (7) is fixed at the free end of the first cantilever beam (3), and the second permanent magnet (6) is fixed at the free end of the second cantilever beam (4);
in the oscillating structure:
the second cantilever beam (4) is in a sheet shape, the first cantilever beam (3) is in a sheet U-shaped frame, the first cantilever beam (3) and the second cantilever beam (4) are placed on the same horizontal plane, and the first cantilever beam (3) and the second cantilever beam (4) are not in contact with each other; the second cantilever beam (4) is embedded in the structure of the first cantilever beam (3);
in the oscillating structure:
the first cantilever beam (3) and the second cantilever beam (4) are distributed at one end of the fixed foundation in parallel, and the geometric center points of the second permanent magnet (6) and the second permanent magnet (7) are in the same horizontal plane in an initial state.
2. The booster piezoelectric generator for collecting ultra low frequency vibration energy in the horizontal direction according to claim 1, wherein in the oscillation structure:
the first cantilever beam (3) and the second cantilever beam (4) are both in a sheet shape, the first cantilever beam (3) and the second cantilever beam (4) are placed on the same horizontal plane, and the first cantilever beam (3) and the second cantilever beam (4) are not in contact with each other;
the first cantilever beam (3) and the second cantilever beam (4) are arranged in parallel.
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| CN112910312B (en) * | 2021-03-18 | 2023-03-10 | 重庆大学 | Wind-induced vibration piezoelectric wind power generation device and piezoelectric wind power generation device group |
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