WO2016173151A1

WO2016173151A1 - Piezoelectric oscillator structure for vibration energy recovery

Info

Publication number: WO2016173151A1
Application number: PCT/CN2015/087213
Authority: WO
Inventors: 吴义鹏; 季宏丽; 裘进浩
Original assignee: 南京航空航天大学
Priority date: 2015-04-28
Filing date: 2015-08-17
Publication date: 2016-11-03
Also published as: CN104868784A

Abstract

A piezoelectric oscillator structure for vibration energy recovery, comprising a base structure and a piezoelectric electromechanical coupling power generation unit fixed onto the base structure, wherein the unit comprises at least one pair of piezoelectric electromechanical coupling power generators comprising variable cross-section beams (1, 1'), permanent magnet mass blocks (3, 3') and piezoelectric elements (2, 2') integrated on surfaces of the variable cross-section beams, the permanent magnet mass blocks are fixed onto free ends of the variable cross-section beams, a root portion is fixed onto the base structure, and the thickness of the free ends of the variable cross-section beams is less than the thickness of the other ends; and opposed faces of each of the permanent magnet mass blocks have the same polarity, and a gap is left therebetween. An amplitude limiting structure is added to the piezoelectric oscillator structure for recovering impact vibration energy, which can protect an internal cantilever beam structure; and each of the variable cross-section beams adopts a variable cross-section design to enable the piezoelectric elements to have equal strain in a beam length direction, which improves the electromechanical coupling coefficient of the structure.

Description

Piezoelectric oscillator structure for vibration energy recovery

Technical field

The invention relates to an energy recovery device, in particular to an energy recovery structure based on a piezoelectric material, belonging to the field of vibration energy collection, and is suitable for multi-directional, low-frequency, wide-frequency or shock vibration energy collection.

Background technique

With the rapid development of technologies such as sensors, microprocessors, and wireless communications, wireless sensor networks have also developed rapidly. It can directly learn the physical information of the objective world, and connect them with the remote control terminal through network transmission, providing people with the most direct, most effective and true objective information. However, as one of the basic technologies of wireless sensor networks, independent power supply technology still severely restricts its further application. At present, most network nodes still use battery-powered technology. Once the number of nodes is large, or where it is not convenient for people to contact, the maintenance cost of regular battery replacement will be very expensive. In addition, the discarded batteries have also placed a serious burden on the environment.

For the above reasons, recycling energy in the environment and replacing traditional battery-powered technology is attracting the attention of a large number of scholars. In general, the average power consumption of wireless sensor nodes is extremely low, and there are many types of energy in the external environment to meet the normal working consumption of the nodes, such as solar energy, vibration energy, wind energy, and the like. Among them, the vibration energy has the advantage of being ubiquitous and always present, and has received a lot of attention from scholars at home and abroad. The conversion of vibration energy into electrical energy currently has several conversion principles such as electromagnetic, electrostatic, and piezoelectric. The invention relates to piezoelectric vibration energy collection, and the main consideration is that the piezoelectric material has a high energy density, is convenient to integrate with the oscillating structure, and is advantageous for miniaturization and the like.

The piezoelectric vibration energy collecting device mainly comprises an electromechanical coupling generator (ie, a piezoelectric coupling structure) with a piezoelectric material, and the charge extraction circuit is also called an interface circuit, and an electric energy storage and a voltage stabilizing circuit. Among them, the electromechanical coupling generator is a key component of the whole device, which basically determines the maximum energy conversion efficiency of the device. The cantilever beam structure with the piezoelectric element attached is a typical electromechanical coupling generator. When the external excitation frequency is consistent with the resonance frequency of the cantilever beam, the cantilever beam will generate a great amplitude, which will result in a higher piezoelectric element. AC voltage. However, in practical applications, the external excitation frequency is often randomly changed. Once the excitation frequency deviates from the resonant frequency of the cantilever beam structure, the electrical energy generated by the coupling structure will drastically decrease. Therefore, many scholars have proposed many improved devices based on the structure of the cantilever beam generator. For example, Wu Xiaoming of Tsinghua University (Wu Xiaoming transliteration) et al. proposed an energy recovery structure with adjustable cantilever beam resonance frequency: an axially adjustable thick bolt is fixed on the end mass of the cantilever beam, and the quality is changed by adjusting the position of the bolt in the axial direction of the beam. The position of the center of gravity of the block, which in turn changes the equivalent beam length of the cantilever beam, ultimately changes the resonant frequency of the structure to match the excitation frequency. However, this method requires manual adjustment. So far, the practicality is not strong. For example, Liu Jingquan of Shanghai Jiaotong University and others have integrated piezoelectric cantilever structures with different parameters on a basic structure. The resonant frequencies of the cantilever beams are sequentially shifted, ensuring that the entire generator is in a wide range. High voltage output is available in the frequency band. However, the energy density of the structure is obviously small, and the subsequent interface circuit will be very complicated due to the phase difference of the output voltage. The proposed structure of the nonlinear coupled generator theoretically solves the shortcomings of the above two methods. A typical nonlinear structure is a permanent magnet mass at the end of a piezoelectric cantilever beam, and a fixed permanent magnet is arranged on the base structure near the end. When the cantilever beam structure vibrates, the surrounding magnetic field is attached to the end of the cantilever beam. The non-linear "elastic" forces cause hardening, softening, or bistable phenomena in the structure. Many scholars at home and abroad have conducted in-depth research on such structures, and theoretical modeling and related experimental research have obtained very good expected results. Designing nonlinear electromechanical coupling structures to recover wide and low frequency vibrational energy has also become a mainstream research trend in academia.

Summary of the invention

technical problem

The technical problem to be solved by the present invention is to provide a piezoelectric oscillator structure based on a practical electromechanical coupling generator structure for piezoelectric energy recovery, which can be used for environmental vibration energy recovery of wide, low frequency and impact loads, or It can be used for environmental vibration energy recovery in multiple directions by simple changes.

Technical solutions

In order to solve the above technical problem, the piezoelectric oscillator structure for vibration energy recovery of the present invention includes a structural base and a piezoelectric electromechanical coupling power generation unit fixed on the structure, and the piezoelectric electromechanical coupling power generation unit includes At least one pair of piezoelectric electromechanical coupling generators, wherein the first electromechanical coupling generator includes a first variable section beam, a first permanent magnet mass, and a first piezoelectric element disposed on a surface of the first variable section beam, The first permanent magnet mass is fixed at the free end of the first variable section beam, and the root of the first variable section beam is fixed on the structural foundation, and the thickness of the free end of the first variable section beam is smaller than the thickness of the root; the second electromechanical coupling generator includes a second variable section beam, a second permanent magnet mass, and a second piezoelectric element disposed on a surface of the second variable section beam The second permanent magnet mass is fixed to the free end of the second variable section beam, and the second variable section root beam is fixed on the structural foundation, and the thickness of the free end of the second variable section beam is less than the thickness of the root The first permanent magnet mass and the second permanent magnet mass are arranged opposite each other with a gap between opposite faces and the same polarity. Among them, the first piezoelectric element and the second piezoelectric element are used to recover wide and low frequency vibration energy.

Further, the piezoelectric oscillator structure of the present invention further includes a limiting structure made of a non-magnetic material having a large coefficient of rigidity; and a third piezoelectric element is disposed on a surface of the piezoelectric electromechanical coupling power generating unit. . The limiting structure can not only protect the internal variable cross section cantilever beam structure from being damaged due to excessive amplitude, but also effectively recover the impact vibration energy. Wherein, the third piezoelectric element is used for recovering impact vibration energy. When the permanent magnet mass hits the limiting structure, part of the energy is dissipated in the form of sound, heat, etc., and most of the impact energy remains inside the variable section beam and the limiting structure. After the collision, the limiting structure will have a damped free oscillation at its first-order resonant frequency, and because of its large stiffness coefficient, the first-order oscillation frequency will be higher. This design subtly transforms the low-frequency large shock vibration energy that is difficult to collect in practical applications into the high-frequency vibration energy that is easy to collect. Another function of the limiting structure is that when the amplitude of the inner cantilever beam is too large, the limiting structure additionally adds a piece of elastic restoring force, and the additional elastic restoring force can further widen the working frequency band of the inner cantilever beam structure.

Further, in the technical solution of the present invention, the first variable section beam, the second variable section beam and the structural foundation are all made of a non-magnetic material.

Further, the first permanent magnet mass and the second permanent magnet mass have different masses, and the first variable cross-section beam and the second variable-section beam have different axial lengths, that is, the two The variable section beam is fixed on the same structure as a set of asymmetric structures; in the structural design, the resonant frequencies of the two variable section beams are close but offset from each other to ensure that the external excitation frequency changes between the two resonance frequencies. The entire device has a high voltage output. In addition, the repulsive force is generated between the permanent magnets, so that the change of the repulsive force is nonlinear during the vibration of the cantilever beam. Since the repulsive force does not consume energy, it can be equivalent to the "elastic" force in the structure. . If the structure is properly designed, the device will have two lowest potential energy points, regardless of the influence of gravity. When the variable section beam does not have bending strain, the variable section beam structure is under stress equilibrium, but there exists between the permanent magnet masses. The repulsive force adds an additional amount of potential to the entire electromechanical coupling device. Such a structure is a typical bistable structure. When the external acceleration is relatively large, the mass at the end of the variable-section beam can easily switch back and forth between the two lowest potential points, thereby increasing the amplitude and improving the piezoelectric element. Output voltage.

Furthermore, the permanent magnet mass used in the technical solution of the present invention should be as large as possible as compared with the entire energy recovery device, so that the resonance frequency of the variable section beam structure can be effectively reduced, and the strain of the structure at the same amplitude can be increased. To increase the energy density of the device. In addition, the mutual repulsion between the magnets can further reduce the structural resonance frequency and improve the low-frequency vibration energy recovery efficiency of the structure.

Further, the neutral planes of the first variable section beam and the second variable section beam may be arranged at any angle, and the entire power generating device may collect vibration energy in multiple directions in a two-dimensional plane.

Beneficial effect

The piezoelectric oscillator structure for vibration energy recovery of the present invention has the following beneficial effects:

(1) The limiting structure is added to recover the impact vibration energy, and the internal cantilever beam structure can be protected from damage due to excessive amplitude, thereby improving the vibration energy recovery efficiency;

(2) The first and second variable cross-section beams are asymmetric structures. After ensuring that the neutral line (ie, the symmetry line of the neutral plane of the cantilever beam) is on the same line, the neutral plane of the beam can be designed at any angle. At this time, the vibration directions of the two variable-section beams will no longer be the same, and the entire generator structure can recover the multi-directional vibration energy in a two-dimensional plane perpendicular to the neutral line;

(3) Each variable-section beam is an asymmetric nonlinear cantilever beam structure, which is arranged in pairs, which is much more effective than increasing the working frequency band by a single increase of the cantilever beam structure;

(4) Each variable-section beam adopts a variable-section design. On the basis of not changing the shape of the piezoelectric element, the piezoelectric element is made to have equal strain in the beam length direction as much as possible, and the electromechanical coupling coefficient of the structure is improved.

DRAWINGS

1 is a schematic structural view of a piezoelectric oscillator structure of the present invention;

2 is a cross-sectional structural view showing the structure of a piezoelectric oscillator according to an embodiment of the present invention;

Fig. 3 is a partial structural view showing the structure of a piezoelectric oscillator of an embodiment of the present invention.

The mark in the figure shows:

1: first variable section beam; 2: first piezoelectric element; 3: first permanent magnet mass; 4: first limiting structure; 5: threaded hole; 6: round hole;

1': second variable-section beam; 2': second piezoelectric element; 3': second permanent magnet mass; 4': second limiting structure; 5': second threaded hole

2": third piezoelectric element; 2"': fourth piezoelectric element

detailed description

The technical solution of the present invention will be specifically described below with reference to the accompanying drawings.

As shown in FIG. 1, the piezoelectric oscillator structure for vibration energy recovery of the present embodiment includes a base structure and a piezoelectric electromechanical coupling power generation unit fixed on the base structure, and the piezoelectric electromechanical coupling power generation unit includes At least one pair of piezoelectric electromechanical coupling generators: a first variable section beam 1 and a first piezoelectric element 2 integrated on a surface thereof, the first permanent magnet mass 3 being fixed at a free end of the first variable section beam 1, first The root of the variable section beam 1 is fixed on the base structure, the thickness of the free end of the first variable section beam 1 is smaller than the thickness of the root; the second variable section beam 1' and the second piezoelectric element 2' integrated on the surface thereof, The second permanent magnet mass 3' is fixed at the free end of the second variable section beam 1', and the root of the second variable section beam 1' is fixed on the base structure, and the thickness of the free end of the second variable section beam 1' is smaller than the thickness of the root; The first permanent magnet mass 3 and the second permanent magnet mass 3' are opposite in polarity and have a gap. Since the cantilever beam adopts a variable cross-section design, the strain in the longitudinal direction of the beam is basically the same, so that the piezoelectric element can cover the entire beam length and be effectively utilized, and the design can greatly improve the electromechanical coupling coefficient of the structure. As shown in FIG. 2, the first piezoelectric element 2 and the second piezoelectric element 2' are disposed only on the upper surface of the variable-section beam. In a specific implementation, a suitable arrangement may be selected according to requirements, and the variable-section beam is correspondingly The permanent magnet mass at the end should be as large as possible within a reasonable range.

As shown in FIG. 1 and FIG. 2, the piezoelectric energy recovery device of the present embodiment further includes a first limiting structure 4 and a second limiting structure 4' made of a non-magnetic material, which are electrically coupled to the piezoelectric electromechanical coupling. The surface of the unit is integrated with a third piezoelectric element 2" and a fourth piezoelectric element 2'".

The first variable section beam 1, the second variable section beam 1' and the base structure are made of a non-magnetic material.

The first permanent magnet mass 3 and the second permanent magnet mass 3' have different masses, and the first variable section beam 1 and the second variable section beam 1' have different axial lengths.

The connection between the permanent magnet mass and the end of the variable section beam can be mainly carried out in two ways: the first method is directly fixed to the end of the variable section beam by welding, but the spot temperature should be reduced in time by using spot welding and cooling liquid. The second method is to reserve a frame of magnets at the end of the variable section beam, and then assemble the permanent magnet mass into the frame and fix it by interference fit. When assembling a coupled power unit, it is generally It is said that the distance between the two permanent magnet masses is calculated in advance by the specific application. For the dynamic analysis of a pair of asymmetric cantilever beam structures, two potential energy points will appear. Thus, once the outside has a large exciting force acting on the structure, the permanent magnet mass will oscillate back and forth between the two lowest potential points, increasing the voltage output of the piezoelectric element.

FIG. 3 is a schematic view showing the components of the partial structure of the present embodiment. The electromechanical coupling power generation unit is composed of two similar components as shown in FIG. 3, and only differs in the dimensions of the variable section beam and the permanent magnet mass. When designing a miniature generator, this part should be a whole, except for the permanent magnet and the piezoelectric element, and be formed on the same piece of metal material. If you consider the processing cost, you can consider separately processing the base structure and the variable section beam, and then fixing them together by means of countersunk screws. The two components are secured together by bolts 5 and threaded holes 5' to form a cartridge device in the form of a six-sided shield. In the actual design, it should be considered that the repulsive force between the permanent magnets during assembly needs to be fine-tuned, and the circular hole 6 can be processed into a micro-elliptic shape on the side shield of the structural foundation, so that fine adjustment can be made according to actual conditions during assembly. .

In the schematic diagram of the component shown in Fig. 3, the shield below the variable-section beam is the limiting structure 4, which can be equivalent to a cantilever beam structure with a relatively large stiffness coefficient, and the thickness is thicker relative to the inner cantilever beam, and There is no mass at the end, so during the vibration caused by the impact, the stress at the root of the limiting structure is much smaller and it is less prone to damage. This limiting structure eliminates the need for additional protection. In addition, the limiting structure does not have a variable cross-section design, and the piezoelectric element only needs to be attached to a section of the root of the structure. On the one hand, the position of the impact point of the permanent magnet mass can be reserved, and on the other hand, the strain has been attenuated relatively small in the middle of the structure, and it is not necessary to stick the piezoelectric element. In view of the fact that the piezoelectric element is generally made of a piezoelectric ceramic material, the material is fragile and fearful of impact, so that the piezoelectric element is generally not disposed on the other side surface of the limiting structure.

The specific embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but this embodiment only shows the simplest structure, that is, a pair of asymmetric nonlinear piezoelectric coupling power generation structures, and the cantilever beam neutral face clamp The angle is 0. In fact, the technical solution of the present invention is not limited to the above embodiment, and the practical application performance of the device can be improved by adding a plurality of pairs of asymmetric structures or changing the angle of the neutral faces. Various other changes can be made within the scope of the invention as claimed within the scope of the invention.

Claims

A piezoelectric oscillator structure for vibration energy recovery, comprising a base structure and a piezoelectric electromechanical coupling power generation unit fixed on the base structure, wherein the piezoelectric electromechanical coupling power generation unit comprises at least one pair A piezoelectric electromechanical coupling generator, wherein the first electromechanical coupling generator comprises a first variable section beam (1), a first permanent magnet mass (3), and a first pressure integrated on a surface of the first variable section beam (1) An electric component (2), the first permanent magnet mass (3) is fixed at a free end of the first variable section beam (1), and the root of the first variable section beam (1) is fixed on the base structure, The thickness of the free end of the first variable section beam (1) is smaller than the thickness of the other end; the second electromechanical coupling generator comprises a second variable section beam (1 '), a second permanent magnet mass (3') and integrated in the second variation a second piezoelectric element (2') of the surface of the section beam (1'), the second permanent magnet mass (3') is fixed to the free end of the second variable section beam (1'), and the second variable section beam (1') the root is fixed to the base structure, and the thickness of the free end of the second variable section beam (1') is smaller than the thickness of the other end; A first permanent magnet mass (3) and a second permanent magnet mass (3 ') of the same relative polarity and a clearance surface.
A piezoelectric oscillator structure for vibration energy recovery according to claim 1, further comprising two first and second limiting structures (4, 4') made of a non-magnetic material, The surface of the piezoelectric electromechanical coupling power generating unit is provided with third and fourth piezoelectric elements (2", 2"').
A piezoelectric oscillator structure for vibration energy recovery according to claim 1 or 2, wherein said first variable section beam (1), second variable section beam (1') and basic structure are Made of non-magnetic material.
A piezoelectric oscillator structure for vibration energy recovery according to claim 1, wherein a pair of piezoelectric coupling generators are of an asymmetrical structure, that is, said first permanent magnet mass (3) and second permanent The magnet mass (3') has different masses, and the first variable section beam (1) and the second variable section beam (1 ') have different axial lengths.