CN116345951A - Piezoelectric energy harvester capable of automatically adjusting natural frequency - Google Patents
Piezoelectric energy harvester capable of automatically adjusting natural frequency Download PDFInfo
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- CN116345951A CN116345951A CN202310270429.1A CN202310270429A CN116345951A CN 116345951 A CN116345951 A CN 116345951A CN 202310270429 A CN202310270429 A CN 202310270429A CN 116345951 A CN116345951 A CN 116345951A
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- H—ELECTRICITY
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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
- H02N2/188—Vibration harvesters adapted for resonant operation
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
Abstract
The invention discloses a piezoelectric energy harvester capable of automatically adjusting natural frequency, which comprises the steps that a mathematical mapping relation between the natural frequency of a cantilever beam and the rotation angle of a steering engine rotating shaft is pre-stored in a controller, a circular turntable and the steering engine are arranged, when the cantilever beam generates forced vibration under the excitation of environmental vibration to output piezoelectric alternating voltage to the controller, the piezoelectric alternating voltage is rectified on one hand by the controller and then is charged into a rechargeable battery, on the other hand, the current environmental vibration frequency is calculated, then the current environmental vibration frequency is taken as the natural frequency of the cantilever beam, the corresponding rotation angle of the steering engine rotating shaft is obtained according to the mathematical mapping relation between the natural frequency of the cantilever beam and the rotation angle of the steering engine rotating shaft, the rotation angle of the steering engine rotating shaft is a target value of the natural frequency adjustment of the cantilever beam, the steering engine is controlled to rotate to a corresponding angle according to the target value, and the position of a counterweight mass block is changed; the method has the advantages of low hardware cost, wide application range and high reliability.
Description
Technical Field
The invention relates to a piezoelectric energy harvester, in particular to a piezoelectric energy harvester capable of automatically adjusting natural frequency.
Background
Piezoelectric energy harvesting technology can capture and convert vibration energy in an environment into electrical energy, thereby powering low-power microelectronic devices. Compared with other energy harvesting modes such as magnetoelectric mode and electrostatic mode, the piezoelectric energy harvesting device has the advantages of high energy density, high electromechanical conversion efficiency, easiness in micro-electromechanical integration and the like, and therefore the piezoelectric energy harvesting device is widely focused. The cantilever beam type piezoelectric energy harvester is a resonant mechanical structure based on rectangular cantilever beam design and manufacture. In the cantilever beam type piezoelectric energy harvester, one end of the cantilever beam is fixed, the end is a fixed end of the cantilever beam, the other end of the cantilever beam is suspended, the end is a free end of the cantilever beam, the piezoelectric sheet is adhered to the cantilever beam at a position close to the fixed end of the cantilever beam, and meanwhile, a counterweight is added to the free end of the cantilever beam to increase the amplitude of the cantilever beam. The cantilever type piezoelectric energy harvester has a specific natural frequency, and when the environmental vibration frequency is consistent with the natural frequency, the cantilever type piezoelectric energy harvester enters a mechanical resonance state, so that the optimal energy harvesting effect can be exerted; and when the environmental vibration frequency deviates from the natural frequency, the cantilever type piezoelectric energy harvester exits from the mechanical resonance state, and the energy harvesting effect is attenuated sharply along with the expansion of the deviation degree of the environmental vibration frequency relative to the natural frequency.
Therefore, the natural frequency of the cantilever type piezoelectric energy harvester is adjusted to be close to the environmental vibration frequency, and the cantilever type piezoelectric energy harvester is an important means for improving the performance of the cantilever type piezoelectric energy harvester. A self-tuning piezoelectric energy harvester is disclosed in chinese patent application No. CN2 02111288785.3. Based on a reasonable comprehensive optimization design method of materials, structures, mechanics and the like, the self-tuning piezoelectric energy harvesting device can change the matching of the natural frequency of the self-tuning piezoelectric energy harvesting device and the environmental vibration frequency under the preset external excitation condition so as to improve the piezoelectric energy harvesting effect. The natural frequency adjusting mode of the environment vibration frequency is passive, does not need to rely on an additional active adjusting mechanism or consume external energy, so that the hardware cost of the environment vibration frequency is lower; however, the passive adjustment mode needs to be activated under a preset external excitation condition, so that the application range of the environmental vibration frequency is limited, and the reliability is low.
Compared with a natural frequency passive adjustment mode, the piezoelectric energy harvester adopting the natural frequency active adjustment mode has wider application range and higher reliability. A piezoelectric energy harvester capable of self-adapting to variable frequency is disclosed in the chinese patent application No. cn201710169222. The piezoelectric energy harvesting device detects the environmental vibration frequency by using a special vibration sensor, then controls a voice coil motor to drive a clamping device arranged on the cantilever beam to move along the length direction of the cantilever beam, and changes the effective length of the cantilever beam to adjust the natural frequency of the piezoelectric energy harvesting device to approach the environmental vibration frequency. Although the piezoelectric energy harvesting device has a wide application range and high reliability, the piezoelectric energy harvesting device needs to be provided with an additional vibration sensor and an expensive voice coil motor, and high hardware cost is caused.
As another example, in chinese patent with application number CN201811490567.6, a piezoelectric energy harvesting device capable of automatically adjusting resonance frequency and bandwidth is disclosed, where the piezoelectric energy harvesting device determines the working state of the cantilever beam by detecting the open-circuit voltage and the short-circuit current of the piezoelectric sheet, and uses a motor to rotate the screw rod positively and negatively to drive the mass block to make linear displacement motion on the cantilever beam to adjust the natural frequency, thereby improving the piezoelectric energy harvesting effect. Because the short-circuit current of the piezoelectric sheet is usually only hundreds of microamps and is in an alternating current form, the accuracy and the signal-to-noise ratio of a current detection circuit for detecting the short-circuit current of the piezoelectric sheet are extremely high. The high-performance hardware circuit is adopted to realize the current detection circuit, so that the reliability can be improved, but the hardware cost of the piezoelectric energy harvesting device can be greatly increased; the low-performance hardware circuit is adopted to realize the current detection circuit, so that the hardware cost can be reduced, but the reliability of the piezoelectric energy harvesting device is also reduced. Therefore, the piezoelectric energy harvester has a wide application range, but the reliability and the hardware cost are in great contradiction.
Disclosure of Invention
The invention aims to solve the technical problem of providing the piezoelectric energy harvesting device which has low hardware cost, wide application range and high reliability and can automatically regulate the natural frequency.
The technical scheme adopted for solving the technical problems is as follows: the piezoelectric energy harvesting device comprises a cantilever beam with a fixed end and a free end, a piezoelectric sheet and a counterweight mass block, wherein the direction from the fixed end to the free end of the cantilever beam is the length direction of the cantilever beam, the piezoelectric sheet is adhered to the upper surface of the cantilever beam and is close to the fixed end of the cantilever beam, the piezoelectric energy harvesting device further comprises a controller, a circular turntable and a steering engine, the controller is pre-stored with a mathematical mapping relation between the natural frequency of the cantilever beam and the rotation angle of a steering engine rotating shaft, the steering engine is arranged at the free end of the cantilever beam, the rotating shaft of the steering engine vertically penetrates through the cantilever beam from bottom to top, the circular turntable is positioned above the cantilever beam, the circular turntable is coaxially arranged on the rotating shaft of the steering engine, the counterweight mass block is positioned above the circular turntable and is arranged on the circular turntable, the installation position of the counterweight mass block is close to the outer circumference of the circular turntable, and the counterweight mass block is smaller than the radial dimension of the circular turntable and the piezoelectric sheet is respectively connected with the piezoelectric sheet; when the cantilever beam is forced to vibrate under the excitation of environmental vibration, the piezoelectric sheet is periodically deformed so as to output piezoelectric alternating voltage to the controller; the controller rectifies the piezoelectric alternating voltage input into the controller and then charges the piezoelectric alternating voltage into the rechargeable battery for electric energy storage, calculates the current environment vibration frequency according to the piezoelectric alternating voltage input into the controller, then uses the current environment vibration frequency as the natural frequency of the cantilever beam, obtains the corresponding rotation angle of the steering engine rotating shaft according to the mathematical mapping relation between the natural frequency of the cantilever beam and the rotation angle of the steering engine rotating shaft prestored in the controller, the rotation angle of the steering engine rotating shaft is the target value of the natural frequency adjustment of the cantilever beam, controls the steering engine to rotate to the corresponding angle according to the target value, changes the position of the counterweight block, and adjusts the natural frequency of the cantilever beam to approach the environment vibration frequency, thereby improving the piezoelectric energy harvesting effect.
The target value of natural frequency adjustment of the cantilever beam is recorded as theta, the value range is 0-180 degrees, when the rotation angle of the steering engine rotating shaft is 0 degrees, the counterweight mass block is positioned at the outermost end of the cantilever beam in the length direction, and the cantilever beam has the minimum natural frequency and is recorded as f min The method comprises the steps of carrying out a first treatment on the surface of the When the rotation angle of the steering engine rotating shaft is 180 degrees, the counterweight block is positioned at the innermost end of the cantilever beam in the length direction, and the cantilever beam has the largest natural frequency, and is marked as f max The method comprises the steps of carrying out a first treatment on the surface of the In the process that the rotation angle of the steering engine rotating shaft is increased from 0 degree to 180 degrees, the counterweight mass block moves from the outermost end to the innermost end in the length direction of the cantilever beam, so that the natural frequency of the cantilever beam is increased from f min Increase to f max The method comprises the steps of carrying out a first treatment on the surface of the The current environmental vibration frequency is denoted as f e When f e F is less than or equal to min When the natural frequency of the cantilever beam is regulated, the target value theta is 0 DEG, the controller controls the steering engine rotating shaft to rotate to the position of 0 DEG, and the natural frequency of the cantilever beam is regulated to be f min The method comprises the steps of carrying out a first treatment on the surface of the When f e F is greater than or equal to f max When the natural frequency of the cantilever beam is adjusted, the target value theta is 180 degrees, the controller controls the steering engine rotating shaft to rotate to the 180-degree position, and the natural frequency of the cantilever beam is adjusted to be f max The method comprises the steps of carrying out a first treatment on the surface of the When f e At f min And f max When the rotation angle of the steering engine rotating shaft is equal to the preset rotation angle of the steering engine rotating shaft, the controller determines the target value of the rotation angle of the steering engine rotating shaft according to the mathematical mapping relation between the natural frequency of the cantilever beam and the rotation angle of the steering engine rotating shaft, and finally drives the steering engine to rotate by the corresponding target value angle, so that the natural frequency of the cantilever beam is adjusted to be f e 。
The controller outputs square wave signals with the amplitude of 3.3V, the period of 20ms and the pulse width of (theta/90+0.5) ms to the steering engine, and the steering engine drives the circular turntable and the counterweight mass block to rotate together to a position corresponding to the target value theta under the action of the square wave signals input into the steering engine.
The piezoelectric sheet is provided with a positive output end and a negative output end, the positive output end and the negative output end of the piezoelectric sheet respectively generate an alternating voltage signal to be output, the alternating voltage signal output by the positive output end of the piezoelectric sheet is called a positive alternating voltage signal, the alternating voltage signal output by the negative output end of the piezoelectric sheet is called a negative alternating voltage signal, and the piezoelectric alternating voltage comprises the positive alternating voltage signal and the negative alternating voltage signal; the controller comprises a synchronous charge extraction circuit, a voltage stabilizing circuit, a common-frequency square wave generating circuit and a singlechip, wherein the synchronous charge extraction circuit is used for extracting piezoelectric alternating voltage output by the piezoelectric sheet, rectifying the piezoelectric alternating voltage and outputting the piezoelectric alternating voltage to the rechargeable battery, and charging the rechargeable battery to increase the electric quantity of the rechargeable battery; the same-frequency square wave generating circuit is used for acquiring the positive-end alternating-current voltage signal, comparing the positive-end alternating-current voltage signal, outputting the same-frequency square wave signal to the singlechip, and calculating the frequency of the same-frequency square wave signal by counting the pulse rising edge of the same-frequency square wave signal input into the singlechip, wherein the frequency is the current environmental vibration frequency; the singlechip determines the target value of natural frequency adjustment of the cantilever beam according to the calculated current environment vibration frequency.
The radial dimension of the counterweight mass block along the circular turntable is smaller than 1/10 of the radius of the circular turntable.
The cantilever beam fixing end is fixed through the fixing base and the cover plate, the fixing base is located below the cantilever beam fixing end, and the cover plate is located above the cantilever beam fixing end.
Compared with the prior art, the invention has the advantages that the controller, the circular turntable and the steering engine are arranged, the mathematical mapping relation between the natural frequency of the cantilever beam and the rotation angle of the rotating shaft of the steering engine is prestored in the controller, the steering engine is arranged at the free end of the cantilever beam, the rotating shaft of the steering engine vertically passes through the cantilever beam from bottom to top, the circular turntable is positioned above the cantilever beam, the circular turntable is arranged on the rotating shaft of the steering engine in a coaxial manner, the counterweight mass block is positioned above the circular turntable and is arranged on the circular turntable, the installation position of the counterweight mass block is close to the outer circumference of the circular turntable, the radial dimension of the counterweight mass block along the circular turntable is smaller than the radius of the circular turntable, and the piezoelectric sheet and the steering engine are respectively connected with the controller; when the cantilever beam is forced to vibrate under the excitation of environmental vibration, the piezoelectric sheet is periodically deformed so as to output piezoelectric alternating voltage to the controller; the invention can autonomously sense the environmental vibration frequency, adaptively adjust the natural frequency, has higher frequency measurement accuracy, does not need to use an additional vibration sensor or adopt a high-performance current detection circuit, reduces hardware cost, and has wide application range and high reliability.
Drawings
FIG. 1 is a schematic diagram of a piezoelectric energy harvester capable of autonomously adjusting natural frequency according to the present invention;
FIG. 2 is a schematic diagram of a mathematical mapping relationship between the natural frequency of a cantilever beam of the piezoelectric energy harvester capable of autonomously adjusting the natural frequency and the rotation angle of a steering engine rotating shaft;
FIG. 3 is a block diagram of circuitry of a controller of a piezoelectric energy harvesting device capable of autonomously adjusting natural frequencies in accordance with the present invention;
fig. 4 is a waveform diagram of the vibration speed, the working voltage of the piezoelectric plate and the output signal of the same-frequency square wave generating circuit module of the piezoelectric energy harvesting device capable of automatically adjusting the natural frequency.
Detailed Description
The invention is described in further detail below with reference to the embodiments of the drawings.
Examples: as shown in FIG. 1, the piezoelectric energy harvesting device capable of automatically adjusting the natural frequency comprises a fixed base P1, a cover plate P2, a cantilever beam P5 with a fixed end and a free end, a piezoelectric sheet P4 and a counterweight mass block P7, wherein the direction from the fixed end of the cantilever beam P5 to the free end of the cantilever beam P5 is the length direction of the cantilever beam P5, the fixed end of the cantilever beam P5 is fixed through the fixed base P1 and the cover plate P2, the fixed base P1 is positioned below the fixed end of the cantilever beam P5, the cover plate P2 is positioned above the fixed end of the cantilever beam P5, the piezoelectric sheet P4 is adhered to the upper surface of the cantilever beam P5 and is close to the fixed end of the cantilever beam P5, the piezoelectric sheet P4 also comprises a controller P3, a circular turntable P6 and a steering engine P8, the mathematical mapping relation between the natural frequency of the cantilever beam and the rotating angle of the steering engine is arranged in the controller P3, the steering engine P8 is arranged at the free end of the cantilever beam P5, a rotating shaft of the steering engine P8 vertically penetrates through the cantilever beam P5 from bottom to top, the circular turntable P6 is positioned above the cantilever beam P5, the circular turntable P6 is positioned above the rotating block P6, the circular turntable P6 is arranged on the circular turntable P6 and is arranged on the circular turntable P6 in a radial direction and is arranged on the circular turntable P6 and is close to the rotating disk 7, and is in a radial direction of the circular turntable P6 and is arranged on the circular turntable P6, and is in a radial diameter of the circular turntable P6 is in the circular turntable P6, and is in the circular turntable is positioned on the circular turntable P6; when the cantilever beam P5 is forced to vibrate under the excitation of environmental vibration, the piezoelectric sheet P4 is periodically deformed so as to output piezoelectric alternating voltage to the controller P3; the controller P3 rectifies the piezoelectric alternating voltage input into the piezoelectric alternating voltage storage device and then charges the piezoelectric alternating voltage input into the rechargeable battery A2 for electric energy storage, on the other hand, calculates the current environment vibration frequency according to the piezoelectric alternating voltage input into the piezoelectric alternating voltage storage device to obtain the current environment vibration frequency, then uses the current environment vibration frequency as the natural frequency of the cantilever beam, obtains the corresponding rotation angle of the steering engine rotating shaft according to the mathematical mapping relation between the natural frequency of the cantilever beam and the rotation angle of the steering engine rotating shaft pre-stored in the cantilever beam, the rotation angle of the steering engine rotating shaft is the target value of the natural frequency adjustment of the cantilever beam P5, controls the steering engine P8 to rotate to the corresponding angle according to the target value, changes the position of the counterweight mass block P7, and adjusts the natural frequency of the cantilever beam P5 to approach the current environment vibration frequency, and improves the piezoelectric energy harvesting effect.
Embodiment two: this embodiment is substantially the same as embodiment one, except that:
as shown in fig. 2, in this embodiment, the target value of the natural frequency adjustment of the cantilever beam P5 is denoted as θ, the value range is 0-180 degrees, when the rotation angle of the steering engine shaft is 0 degrees, the counterweight mass block P7 is located at the outermost end of the cantilever beam P5 in the length direction, and the cantilever beam P5 has the minimum natural frequency, which is denoted as f min The method comprises the steps of carrying out a first treatment on the surface of the When the rotation angle of the steering engine rotating shaft is 180 degrees, the counterweight mass block P7 is positioned at the innermost end of the cantilever beam P5 in the length direction, and the cantilever beam P5 has the largest natural frequency, and is marked as f max The method comprises the steps of carrying out a first treatment on the surface of the In the process that the rotation angle of the steering engine rotating shaft is increased from 0 degree to 180 degrees, the counterweight mass block P7 moves from the outermost end to the innermost end in the length direction of the cantilever beam P5, so that the natural frequency of the cantilever beam P5 is increased from f min Increase to f max The method comprises the steps of carrying out a first treatment on the surface of the The current environmental vibration frequency is denoted as f e When f e F is less than or equal to min At this time, the target value θ of the natural frequency adjustment of the cantilever beam P5 is 0 degrees, the controller P3 controls the steering engine P8 to rotate to a position of 0 degrees, and adjusts the natural frequency of the cantilever beam P5 to be f min The method comprises the steps of carrying out a first treatment on the surface of the When f e F is greater than or equal to f max At this time, the target value θ of the natural frequency adjustment of the cantilever beam P5 is 180 degrees, the controller P3 controls the steering engine P8 to rotate to a position 180 degrees, and adjusts the natural frequency of the cantilever beam P5 to be f max The method comprises the steps of carrying out a first treatment on the surface of the When f e At f min And f max In the process, the controller P3 determines a target value of the rotation angle of the steering engine rotating shaft according to a mathematical mapping relation between the natural frequency of the cantilever beam and the rotation angle of the steering engine rotating shaft pre-stored in the controller P3, and finally drives the steering engine P8 to rotate by an angle corresponding to the target value, so that the natural frequency of the cantilever beam P5 is adjusted to be f e The method comprises the steps of carrying out a first treatment on the surface of the Frequency interval f min ,f max ]Namely the adjustable range of the natural frequency of the piezoelectric energy harvesting device, and the piezoelectric energy harvesting deviceSetting a minimum value f of an adjustable range of natural frequency min Maximum f max The width of the frequency interval is determined by the geometric dimensions and the mass distribution relation of the cantilever beam P5, the circular turntable P6 and the counterweight mass block P7 in the piezoelectric energy harvesting device, and the frequency interval is customized according to design requirements; the mathematical mapping relation between the natural frequency of the cantilever beam and the rotation angle of the steering engine rotating shaft is calibrated through currently known resonance experiment tests and data fitting.
In this embodiment, the controller P3 outputs a square wave signal with an amplitude of 3.3V, a period of 20ms and a pulse width of (θ/90+0.5) ms to the steering engine P8, and the steering engine P8 drives the circular turntable P6 and the counterweight block P7 to rotate together to a position corresponding to the target value θ under the action of the square wave signal input into the steering engine P8.
As shown in fig. 3, in the present embodiment, the piezoelectric sheet P4 has a positive output end and a negative output end, the positive output end and the negative output end of the piezoelectric sheet P4 respectively generate an ac voltage signal output, the ac voltage signal output by the positive output end of the piezoelectric sheet P4 is referred to as a positive ac voltage signal Vp, the ac voltage signal output by the negative output end of the piezoelectric sheet P4 is referred to as a negative ac voltage signal Vn, and the piezoelectric ac voltage includes the positive ac voltage signal Vp and the negative ac voltage signal Vn; the controller P3 includes a synchronous charge extraction circuit A1, a voltage stabilizing circuit A3, a common-frequency square wave generating circuit A4 and a singlechip A5, where the synchronous charge extraction circuit A1 is used to extract a piezoelectric ac voltage output by the piezoelectric sheet P4, rectify the piezoelectric ac voltage, output a voltage Vr to the rechargeable battery A2, and charge the rechargeable battery A2 to increase its electric quantity; the common-frequency square wave generating circuit A4 is used for obtaining a positive end alternating voltage signal Vp, comparing the positive end alternating voltage signal Vp and outputting a common-frequency square wave signal V frep For the singlechip A5, the singlechip A5 inputs the same-frequency square wave signal V into the singlechip A5 frep Counting the rising edges of the pulses to calculate the common-frequency square wave signal V frep The frequency is the current environmental vibration frequency; the singlechip A5 determines a target value of natural frequency adjustment of the cantilever beam P5 according to the calculated current environment vibration frequency. The rechargeable battery A2 supplies power for the steering engine P8 and the singlechip A5 through the voltage stabilizing circuit A3. Synchronous charge extractionThe circuit A1, the voltage stabilizing circuit A3, the same-frequency square wave generating circuit A4 and the singlechip A5 are mature products in the technical field.
In this embodiment, the dimension of the counterweight block P7 along the radial direction of the circular turntable P6 is less than 1/10 of the radius of the circular turntable P6.
In this embodiment, the specific implementation steps of frequency adjustment of the piezoelectric energy harvesting device capable of autonomously adjusting the natural frequency are as follows:
step S100: when the singlechip A5 is electrified, the internal timer is started, and the timing period is recorded as T 1 The value range is 20 ms-100 ms, and the singlechip A5 inputs the same-frequency square wave signal V into the singlechip through an internal timer freq Performing rising edge counting;
step S110: the timing reaches a timing period T 1 Closing the timer and stopping timing;
step S120: read timing period T 1 Is recorded as N, and the environmental vibration frequency is set as f e Then calculate the environmental vibration frequency f e ＝N/T 1 F currently calculated e The natural frequency of the cantilever beam is the adjusting value;
step S130: according to a mathematical mapping relation between the natural frequency of the cantilever beam and the rotation angle of the steering engine rotating shaft pre-stored in the singlechip A5, calculating to obtain an angle target value to be rotated by the steering engine rotating shaft, and recording the angle target value as theta;
step S140: according to the target value theta of the angle to be rotated of the steering engine rotating shaft, calculating the pulse width value of the square wave signal for driving the steering engine to rotate, wherein the pulse width value is (theta/90+0.5) ms;
step S150: generating a square wave signal with the amplitude of 3.3V, the period of 20ms and the pulse width of (theta/90+0.5) ms, outputting the square wave signal to the steering engine P8, driving the steering engine P8 to rotate to the position corresponding to the angle theta, and changing the position of the counterweight mass block P7 on the cantilever beam P5 so as to adjust the natural frequency of the cantilever beam to be f e ；
Step S160: starting the internal timer of the singlechip A5 again, and recording the timing period as T 2 The value range is 60 s-300 s, and the low-power-consumption sleep state is entered;
step S170: the timing reaches a timing period T 2 Closing a timer, stopping timing, and exiting the low-power-consumption sleep state;
thus, a timer period (T 1 +T 2 ) The method comprises the following steps of environmental frequency sensing, steering engine rotating shaft angle adjustment, cantilever beam natural frequency adjustment and singlechip low-power-consumption dormancy, and then entering the next timing period, and repeating the steps and the reciprocating steps.
In order to verify the sensing capability of the piezoelectric energy harvesting device capable of autonomously adjusting the natural frequency to the environmental vibration frequency, circuit simulation is performed on the synchronous charge extraction circuit A1 and the same-frequency square wave generation circuit A4 in the controller P3, wherein simulation parameters are configured as follows: the vibration frequency is 50Hz, the internal capacitance of the piezoelectric sheet P4 is 200nF, the open-circuit output voltage of the piezoelectric sheet P4 is 3.6V, and the comparison threshold value of the comparator in the same-frequency square wave generating circuit A4 is 0.2V; the piezoelectric energy harvester can autonomously adjust the input vibration speed of the natural frequency and output voltage (V) of the piezoelectric plate P4 connected with the synchronous charge extraction circuit A1 p -V n ) And the same-frequency square wave generating circuit A4 outputs a signal V freq Is shown in fig. 4; as can be seen from an analysis of fig. 4, the synchronous charge extraction circuit A1 can perform synchronous charge extraction operation near the peak point of the output voltage of the piezoelectric plate P4, and extract the charge in the internal capacitor of the piezoelectric plate P4 to the rechargeable battery A2 for storage, so that the voltage of the piezoelectric plate P4 is rapidly reduced to zero, and then the charge accumulation is restarted, and the cycle is repeated. Meanwhile, the same-frequency square wave generating circuit A4 can output a high-level signal when the output voltage of the piezoelectric sheet P4 is more than or equal to 0.2V, and output a low-level signal when the output voltage of the piezoelectric sheet P4 is less than 0.2V, so that the same frequency of the output square wave signal, the output voltage of the piezoelectric sheet P4 and the vibration speed signal is realized, and the frequency of the same-frequency square wave signal can be measured by a counter in the singlechip A5; therefore, the piezoelectric energy harvester capable of automatically adjusting the natural frequency can automatically sense the environmental vibration frequency, the frequency measurement precision is high, an additional vibration sensor is not needed in the measurement process, and the hardware cost is reduced.
Claims (6)
1. The piezoelectric energy harvesting device capable of automatically adjusting the natural frequency comprises a cantilever beam with a fixed end and a free end, a piezoelectric sheet and a counterweight block, wherein the direction from the fixed end to the free end of the cantilever beam is the length direction of the cantilever beam, the piezoelectric sheet is adhered to the upper surface of the cantilever beam and is close to the fixed end of the cantilever beam; when the cantilever beam is forced to vibrate under the excitation of environmental vibration, the piezoelectric sheet is periodically deformed so as to output piezoelectric alternating voltage to the controller; the controller rectifies the piezoelectric alternating voltage input into the controller and then charges the piezoelectric alternating voltage into the rechargeable battery for electric energy storage, calculates the current environment vibration frequency according to the piezoelectric alternating voltage input into the controller, then uses the current environment vibration frequency as the natural frequency of the cantilever beam, obtains the corresponding rotation angle of the steering engine rotating shaft according to the mathematical mapping relation between the natural frequency of the cantilever beam and the rotation angle of the steering engine rotating shaft prestored in the controller, the rotation angle of the steering engine rotating shaft is the target value of the natural frequency adjustment of the cantilever beam, controls the steering engine to rotate to the corresponding angle according to the target value, changes the position of the counterweight block, and adjusts the natural frequency of the cantilever beam to approach the environment vibration frequency, thereby improving the piezoelectric energy harvesting effect.
2. The piezoelectric energy harvester capable of automatically adjusting natural frequency as in claim 1, wherein the target value of natural frequency adjustment of the cantilever beam is designated as θ and ranges from 0 degrees to 180 degrees, and when the rotation angle of the steering engine rotating shaft is 0 degrees, the weight mass block is located at the outermost end of the cantilever beam in the length direction, and the cantilever beam has the minimum natural frequency and is designated as f min The method comprises the steps of carrying out a first treatment on the surface of the When the rotation angle of the steering engine rotating shaft is 180 degrees, the counterweight block is positioned at the innermost end of the cantilever beam in the length direction, and the cantilever beam has the largest natural frequency, and is marked as f max The method comprises the steps of carrying out a first treatment on the surface of the In the process that the rotation angle of the steering engine rotating shaft is increased from 0 degree to 180 degrees, the counterweight mass block moves from the outermost end to the innermost end in the length direction of the cantilever beam, so that the natural frequency of the cantilever beam is increased from f min Increase to f max The method comprises the steps of carrying out a first treatment on the surface of the The current environmental vibration frequency is denoted as f e When f e F is less than or equal to min When the natural frequency of the cantilever beam is regulated, the target value theta is 0 DEG, the controller controls the steering engine rotating shaft to rotate to the position of 0 DEG, and the natural frequency of the cantilever beam is regulated to be f min The method comprises the steps of carrying out a first treatment on the surface of the When f e F is greater than or equal to f max When the natural frequency of the cantilever beam is adjusted, the target value theta is 180 degrees, the controller controls the steering engine rotating shaft to rotate to the 180-degree position, and the natural frequency of the cantilever beam is adjusted to be f max The method comprises the steps of carrying out a first treatment on the surface of the When f e At f min And f max When the rotation angle of the steering engine rotating shaft is equal to the preset rotation angle of the steering engine rotating shaft, the controller determines the target value of the rotation angle of the steering engine rotating shaft according to the mathematical mapping relation between the natural frequency of the cantilever beam and the rotation angle of the steering engine rotating shaft, and finally drives the steering engine to rotate by the corresponding target value angle, so that the natural frequency of the cantilever beam is adjusted to be f e 。
3. The piezoelectric energy harvester capable of automatically adjusting natural frequency according to claim 2, wherein the controller outputs square wave signals with amplitude of 3.3V, period of 20ms and pulse width of (theta/90+0.5) ms to the steering engine, and the steering engine drives the circular turntable and the counterweight mass block to rotate together to a position corresponding to a target value theta under the action of the square wave signals input into the steering engine.
4. The piezoelectric energy harvester capable of automatically adjusting natural frequency according to claim 2, wherein the piezoelectric plate is provided with a positive output end and a negative output end, the positive output end and the negative output end of the piezoelectric plate respectively generate an alternating voltage signal output, the alternating voltage signal output by the positive output end of the piezoelectric plate is called a positive alternating voltage signal, the alternating voltage signal output by the negative output end of the piezoelectric plate is called a negative alternating voltage signal, and the piezoelectric alternating voltage comprises the positive alternating voltage signal and the negative alternating voltage signal; the controller comprises a synchronous charge extraction circuit, a voltage stabilizing circuit, a common-frequency square wave generating circuit and a singlechip, wherein the synchronous charge extraction circuit is used for extracting piezoelectric alternating voltage output by the piezoelectric sheet, rectifying the piezoelectric alternating voltage and outputting the piezoelectric alternating voltage to the rechargeable battery, and charging the rechargeable battery to increase the electric quantity of the rechargeable battery; the same-frequency square wave generating circuit is used for acquiring the positive-end alternating-current voltage signal, comparing the positive-end alternating-current voltage signal, outputting the same-frequency square wave signal to the singlechip, and calculating the frequency of the same-frequency square wave signal by counting the pulse rising edge of the same-frequency square wave signal input into the singlechip, wherein the frequency is the current environmental vibration frequency; the singlechip determines the target value of natural frequency adjustment of the cantilever beam according to the calculated current environment vibration frequency.
5. The piezoelectric energy harvester of claim 2, wherein the dimension of the counter weight along the radial direction of the circular turntable is less than 1/10 of the radius of the circular turntable.
6. The piezoelectric energy harvester of claim 2, wherein the fixed end of the cantilever beam is fixed by a fixing base and a cover plate, the fixing base is located below the fixed end of the cantilever beam, and the cover plate is located above the fixed end of the cantilever beam.
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