JP2015012762A - Piezoelectric power generation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently generate power while controlling vibration by using a piezoelectric element.SOLUTION: In a power generation element 10 comprising a piezoelectric element 20, a serial circuit of an inductor 30 and a switch 40 is connected. A control part 50 detects timing Tin which an absolute value of a voltage generated by the power generation element 10 becomes a maximum value. The control part 50 detects timing Tin which a phase of a voltage waveform is advanced by +45° from the timing Tin which the voltage absolute value becomes the maximum value, and performs control to conduct the switch 40. The control part 50 performs control to turn off the switch 40 by counting a time length of a 1/2 resonance cycle determined by inductance of the inductor 30 and capacitance of an element capacitor 200.

Description

  The present invention relates to a piezoelectric power generation device including a piezoelectric element that converts vibrations into electricity and outputs the electricity.

  Conventionally, various piezoelectric power generation devices using piezoelectric elements have been devised. The piezoelectric power generation device has a structure as shown in Patent Document 1, for example. One end of the flat beam is fixed, the other end is a free end, and a weight is attached to the other end. A flat piezoelectric element is mounted on the beam. When receiving vibration from the outside, the beam is bent and the piezoelectric element is displaced in a direction perpendicular to the flat plate surface. Due to this displacement, the piezoelectric element is polarized and generates electric charges. That is, in the conventional piezoelectric power generation device, power generation is performed by bending displacement of the piezoelectric element.

  The piezoelectric power generation device described in Patent Document 1 includes a circuit configuration in which a series circuit of an inductor and a switch is connected in parallel to a piezoelectric element. In the piezoelectric power generation device described in Patent Document 1, the switch is turned on at the timing when the displacement of the piezoelectric element becomes maximum. When a time that is half the resonance period of the piezoelectric element and the inductor has elapsed from the timing when the switch is turned on, the switch is disconnected. By this switching control, charges generated by displacements of the piezoelectric elements in different directions are added and boosted.

JP 2012-105518 A

  However, the piezoelectric element is deteriorated by repeated bending displacement. And when deterioration progresses, it may be damaged. In this case, the piezoelectric element and the beam must be replaced. In addition, since resonance between the piezoelectric element and the vibration source is used, when a large vibration is applied from the vibration source, the piezoelectric element may be excessively deformed and the piezoelectric element or the beam may be damaged.

  In order to suppress damage to the piezoelectric element and the beam and to slow down the deterioration rate, vibration suppression may be performed. However, if vibration is completely suppressed, power generation cannot be performed.

  Accordingly, an object of the present invention is to provide a piezoelectric power generator that efficiently generates power while suppressing vibration.

  The present invention includes a piezoelectric element that generates an electric charge by vibration, a vibration transmission member that transmits the vibration to the piezoelectric element, a series circuit of an inductor and a switch, and a control unit that controls conduction / disconnection of the switch. And a piezoelectric power generation apparatus in which a piezoelectric element and a series circuit are connected in parallel, and has the following characteristics. The control unit controls the conduction of the switch at a timing at which the phase of the voltage waveform is advanced by 45 ° from the timing at which the absolute value of the voltage due to the charge generated by the piezoelectric element is maximized. The control unit controls the disconnection of the switch at the timing when a half of the resonance period of the piezoelectric element and the inductor has elapsed from the timing at which the switch is controlled to conduct.

  In this configuration, in a state where the piezoelectric element is deformed by the vibration of the vibrating body on which the piezoelectric power generation device is mounted, a stress that deforms the piezoelectric element in a direction opposite to the deformation direction of the piezoelectric element due to the vibration of the vibrating body is generated. ing. Accordingly, the two stresses cancel each other, and the vibration of the vibrating body and the vibration transmitting member can be suppressed. At this time, by using the above-described switching conditions, vibrations continue without being completely damped, and power generation can be continued.

  In the piezoelectric power generation device of the present invention, it is preferable that a plurality of pairs of piezoelectric elements and vibration transmission members are provided. In the piezoelectric power generation device of the present invention, the combination of the piezoelectric element and the vibration transmitting member may have different vibration frequencies.

  In this configuration, a higher voltage can be output if all the piezoelectric elements and the vibration transmitting members have the same vibration frequency. Further, if the vibration frequency of the set of the piezoelectric element and the vibration transmitting member is different, vibration can be generated corresponding to a plurality of vibration frequencies, and power can be efficiently generated with respect to the vibration.

  In the piezoelectric power generator of the present invention, a rectifier circuit may be connected to the output terminal of the parallel circuit of the piezoelectric element and the series circuit.

  In this configuration, a DC voltage can be output.

  According to the present invention, it is possible to suppress breakage and suppress the deterioration rate while efficiently generating power by the applied vibration.

1 is a circuit block diagram of a piezoelectric power generator according to a first embodiment of the present invention. It is a side view of the mechanism part of the piezoelectric power generator concerning the 1st embodiment of the present invention. It is the top view which looked at the power generating element concerning a 1st embodiment of the present invention from the vibration source side. It is a graph which shows the characteristic of the piezoelectric power generator concerning the 1st Embodiment of the present invention. It is a graph for demonstrating the effect of the piezoelectric electric power generating apparatus which concerns on the 1st Embodiment of this invention. It is an external appearance perspective view of the piezoelectric electric power generating apparatus which concerns on the 2nd Embodiment of this invention. It is a graph showing the output electric power characteristic of the piezoelectric power generator which concerns on the 2nd Embodiment of this invention.

  A piezoelectric power generator according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit block diagram of the piezoelectric power generation apparatus according to the first embodiment of the present invention.

  The piezoelectric power generation apparatus 1 includes a power generation element 10, an inductor 30, a switch 40, a control unit 50, and a rectifier circuit 60.

  The power generation element 10 includes a piezoelectric element 20 and includes an element capacitance 200. FIG. 2 is a side view of the mechanism portion of the piezoelectric power generation apparatus according to the first embodiment of the present invention. FIG. 3 is a plan view of the power generation element according to the first embodiment of the present invention as viewed from the vibration source side.

  As shown in FIGS. 2 and 3, the power generation element 10 includes a long and flat plate beam 11. The beam 11 is made of a material that bends in a direction orthogonal to the flat plate surface due to external vibration. For example, the beam 11 uses nickel (Ni42). The dimensions are, for example, a width of 8 mm, a thickness of 0.4 mm, and a length of about 60 mm.

  One end of the beam 11 in the longitudinal direction is fixed to the vibration source 900 via the support column 12. A weight 13 is attached to the other end of the beam 11 in the longitudinal direction. For the weight 13, for example, copper (Cu) is used. The dimensions are, for example, length × width 15 mm × 20 mm and thickness 4.5 mm.

  The piezoelectric element 20 is long and flat like the beam 11. The piezoelectric element 20 is mounted on one flat surface of the beam 11. At this time, the piezoelectric element 20 is disposed on one end of the beam 11 in the longitudinal direction, that is, on the end side connected to the support column 12.

  The piezoelectric element 20 uses, for example, lead zirconate titanate (PZT). The dimensions are, for example, a width of 8 mm, a thickness of 0.2 mm, and a length of 35 mm. The piezoelectric element 20 is polarized. For example, the polarization treatment is performed in advance at 3 kV / mm.

  A detection control electrode 21 and a charge extraction electrode 22 are provided on the surface of the piezoelectric element 20 opposite to the surface with which the beam 11 contacts. The detection control electrode 21 is an electrode that monitors the output in order to measure the switching timing of the switch 40. The charge extraction electrode 22 is an electrode for extracting charge generated in the piezoelectric element 20. The detection control electrode 21 and the charge extraction electrode 22 are electrically separated.

  With such a structure, when the vibration source 900 vibrates in the thickness direction (in the direction of the thick arrow in FIG. 2), the beam 11 has the end portion side where the weight 13 is mounted as the maximum vibration portion. Vibrates in a direction perpendicular to the flat plate surface. This beam 11 corresponds to the vibration transmitting member of the present invention.

  As the beam 11 vibrates, the piezoelectric element 20 is bent and stress is applied. The piezoelectric element 20 generates a charge having a magnitude corresponding to the stress. This charge can be output to the outside as a voltage using the charge extracting electrode 22.

  At this time, the resonance phenomenon occurs by matching the natural frequency of the vibration source 900 with the natural frequency of the power generation element 10. In the resonance state, the power generation element 10 amplifies the vibration energy propagating from the vibration source 900, and the power generation element 10 vibrates. For this reason, power generation efficiency can be increased.

  The inductor 30 and the switch 40 are connected in series. This series circuit is connected to the power generation element 10. More specifically, the electric power generation element 10 is composed of a series circuit of a piezoelectric element 20 and an element capacitance 200 as shown in FIG. Therefore, the series circuit of the inductor 30 and the switch 40 is connected in parallel to the series circuit of the piezoelectric element 20 and the element capacitor 200.

  A full-wave rectifier circuit 60 is connected to two connection points of the inductor 30 and the series circuit of the switch 40 and the power generation element 10. The full-wave rectifier circuit 60 is connected to a load 800 that uses the generated voltage. The load 800 may be a secondary battery such as a capacitor, or may be other various loads (light source or power unit). A connection terminal to the load 800 is a voltage output terminal of the piezoelectric power generator 1.

  In the present embodiment, the full-wave rectifier circuit 60 is provided to output a DC voltage. However, a rectifier circuit different from the full-wave rectifier circuit may be used, and further, no rectifier circuit may be provided. Also good.

  The control unit 50 detects the voltage generated by the power generation element 10 and controls conduction / disconnection of the switch 40. FIG. 4 is a graph showing characteristics of the piezoelectric power generation device according to the first embodiment of the present invention. FIG. 4A is a waveform diagram of a switch control signal generated by the control unit 50. FIG. 4B shows output voltage waveforms of the power generation element 10 when the switch control is performed and when the switch control is not performed. FIG. 4C shows the vibration displacement amount of the vibration source 900 when the switch control is performed and when the switch control is not performed. 4B and 4C, a solid line indicates a waveform when the switch control is performed, and a broken line indicates a waveform when the switch control is not performed.

The control unit 50 observes the voltage generated by the power generation element 10. The control unit 50 detects the maximum voltage value. At this time, the control unit 50 uses the absolute value of the voltage. That is, the maximum value of the voltage absolute value in the positive voltage region is detected. A timing T _{ON1 in} which the phase of the voltage waveform is advanced by + 45 ° from the timing T _{M1 at} which the voltage absolute value becomes the maximum value is detected. For example, since the resonance frequency of the power generating element 10 is known in advance as described above, the control unit 50 may calculate the timing T _ON1 at which the phase of the voltage waveform has advanced by + 45 ° from the resonance frequency.

The control unit 50 controls the switch 40 to be conductive at the timing _TON1 . The control unit 50 _measures the time length of 1/2 of the resonance period determined by the inductance of the inductor 30 and the capacitance of the element capacitor 200, with the timing T _ON1 as the timing start timing. When detecting that the time length of ½ of the resonance period has elapsed, that is, when detecting that the timing T _OFF1 is reached, the control unit 50 controls the switch 40 to be disconnected.

As shown in FIG. 4B, at the timing _TON1 , the power generation element 10 is curved so as to generate a positive voltage. Here, when the switch 40 is turned on, a resonance circuit is formed by the inductor 30 and the element capacitance 200, and resonance occurs. The resonance voltage has the same polarity as the voltage generated by the power generation element 10 during the period from the start of the resonance to the time half the resonance period. However, the resonance voltage has a polarity opposite to that of the voltage generated by the power generation element 10 in a state in which a time of ½ or more and less than 1 of the resonance period has elapsed since the resonance started. When such a reverse polarity voltage is applied to the power generation element 10, a stress that bends in a direction opposite to the bending direction at that time is applied to the piezoelectric element 20. As a result, stress is applied to the power generation element 10 in a direction to suppress bending due to vibration at that time, and vibration is suppressed. That is, the power generation element 10 is damped. In particular, the above-described effect is significant in a state in which a half of the resonance period has elapsed since the start of resonance.

  As a result, as shown in FIG. 4C, the amount of displacement due to vibration of the vibration source 900 can be reduced in the positive voltage region.

Subsequently, the control unit 50 observes the voltage generated by the power generation element 10. The control unit 50 detects the minimum voltage value. At this time, the control unit 50 uses the absolute value of the voltage. That is, the maximum value of the voltage absolute value in the negative voltage region is detected. The timing T _{ON2 in} which the phase of the voltage waveform is advanced by + 45 ° from the timing T _M2 at which the voltage absolute value is obtained is detected. Timing T _ON2 that phase + 45 ° proceeds of the voltage waveform, similar to the timing T _ON1, for example, the resonance frequency of the power generating element 10 as described above is known in advance, the control unit 50, from the resonant frequency What is necessary is just to calculate.

The control unit 50 controls the switch 40 to be conductive at the timing _TON2 . The control unit 50 _measures a time length that is ½ of the resonance period determined by the inductance of the inductor 30 and the capacitance of the element capacitor 200, with the timing T _ON2 as a timing start timing. In the example of this embodiment, as an example, an inductance of 5.6 [mH] is used, and an element capacitance of 40 [nF] is used. When detecting that the time length of ½ of the resonance period has elapsed, that is, when detecting that the timing T _OFF2 is reached, the control unit 50 controls the switch 40 to be disconnected.

As shown in FIG. 4B, at the timing _TON2 , the power generation element 10 is curved so as to generate a negative voltage. Here, when the switch 40 is turned on, a resonance circuit is formed by the inductor 30 and the element capacitance 200, and resonance occurs. The resonance voltage has the same polarity as the voltage generated by the power generation element 10 during the period from the start of the resonance to the time half the resonance period. However, the resonance voltage has a polarity opposite to that of the voltage generated by the power generation element 10 in a state in which a time of ½ or more and less than 1 of the resonance period has elapsed since the resonance started. When such a reverse polarity voltage is applied to the power generation element 10, a stress that bends in a direction opposite to the bending direction at that time is applied to the piezoelectric element 20. As a result, stress is applied to the power generation element 10 in a direction to suppress bending due to vibration at that time, and vibration is suppressed. That is, the power generation element 10 is damped. In particular, the above-described effect is significant in a state where a time of 1/2 of the resonance period has elapsed since the start of resonance.

  As a result, as shown in FIG. 4C, the amount of displacement due to vibration of the vibration source 900 can be reduced even in the negative voltage region.

  The control unit 50 continuously executes the above processing. Thereby, the power generation element 10 can control the vibration source 900, the piezoelectric element 20, and the beam 11.

  FIG. 5 is a graph for explaining the operational effects of the piezoelectric power generation apparatus according to the first embodiment of the present invention. FIG. 5A is a graph showing a change in the maximum displacement amount of the power generation element 10 with respect to the phase change amount from the timing of the maximum value of the voltage absolute value until the switch 40 is turned on. FIG. 5B is a graph showing a change in the voltage generated by the power generation element 10 with respect to the phase change amount from the timing of the maximum value of the voltage absolute value until the switch 40 is turned on.

  As shown in FIG. 5A, vibration can be minimized by using the configuration of this embodiment. Specifically, in the example of this embodiment, vibration can be suppressed by about 80%. That is, vibration can be suppressed most effectively.

  At this time, as shown in FIG. 5B, the voltage output from the power generation element 10 is not significantly reduced as compared with the case where the vibration is most suppressed. Specifically, in the example of this embodiment, the voltage is reduced only by about 30%. That is, a voltage of about 70% can be secured.

  Therefore, by using the configuration of this embodiment, it is possible to continue power generation more efficiently while effectively suppressing vibration.

  Next, a piezoelectric power generator according to a second embodiment will be described with reference to the drawings. FIG. 6 is an external perspective view of the piezoelectric power generation apparatus according to the second embodiment of the present invention.

  The piezoelectric power generating apparatus 1A according to the present embodiment generally includes a plurality of power generating elements having the above-described configuration. The piezoelectric power generation apparatus 1A includes a vibration source 900A and a plurality of power generation elements 10A, 10B, 10C, 10D, and 10E.

  The vibration source 900A includes a bottom wall 910A and side walls 911A and 912A. A recess 901A is provided by the bottom wall 910A and the side walls 911A and 912A.

  Each of the power generating elements 10A, 10B, 10C, 10D, and 10E is the same as the power generating element 10 shown in the first embodiment, except that the beam width is narrower as it approaches the weight.

  The power generation elements 10A, 10C, and 10E are fixed to the side wall 911A so that the respective weights are arranged in the vicinity of the side wall 912A in the recess 910A. The power generating elements 10B and 10D are fixed to the side wall 912A so that the respective weights are arranged in the vicinity of the side wall 911A of the recess 910A. The power generating elements 10A, 10B, 10C, 10D, and 10E are arranged in this order in parallel with the inner wall surfaces of the side walls 911A and 912A. By setting it as such a structure, even if it has arrange | positioned several electric power generation element 10A, 10B, 10C, 10D, 10E, the piezoelectric power generator 1A can be reduced in size.

  In addition, in the configuration of the piezoelectric power generating apparatus 1A according to the present embodiment, since a plurality of power generating elements are arranged, power generation can be performed efficiently. Specifically, the shapes of the power generating elements 10A, 10B, 10C, 10D, and 10E are determined so that the resonance frequencies are different. FIG. 7 is a graph showing the output power characteristics of the piezoelectric power generator according to the second embodiment of the present invention.

  With such a configuration, as shown in FIG. 7, output power can be obtained at a plurality of vibration frequencies. That is, an output voltage can be generated in a wide frequency range. Thereby, electric power generation can be performed efficiently.

  Note that the resonance frequencies of the plurality of power generating elements may be matched. In this case, if the voltage generated from the power generation element having the same resonance frequency is added so as not to cancel, the magnitude of the output voltage against vibration can be increased. Thereby, electric power generation can be performed efficiently.

  Further, by using the beam shape shown in the present embodiment, the reliability can be increased, and the vibration can be efficiently propagated to the piezoelectric element. This beam shape may be applied to the power generation element 10 of the first embodiment.

  In each of the above-described embodiments, an example in which the beam is formed of a conductor has been described. However, the beam may be formed of an insulator. In this case, charge extraction electrodes are provided on both opposing surfaces of the piezoelectric element.

  In addition, the material and shape of the above-described piezoelectric element and the material and shape of each member constituting the power generation element are examples, and if the switch timing is set as described above, the mechanical constituent material has other configurations. May be.

  In the above description, the switch 40 is turned on when the phase has advanced by + 45 °. However, the switch 40 is not limited to when the phase has advanced by + 45 °. For example, any phase range in which the phase has advanced from + 30 ° to + 60 °. Even in this phase, the same effect can be obtained. However, as shown in FIG. 5 described above, when the phase advances by + 45 ° is set as the conduction timing of the switch 40, the vibration suppressing effect is most obtained and is suitable for extending the life.

1, 1A: Piezoelectric generators 10, 10A, 10B, 10C, 10D, 10E: Power generation element 11: Beam 12: Support column 13: Weight 20: Piezoelectric element 21: Detection control electrode 22: Charge extraction electrode 30: Inductor 40: Switch 50: Control unit 60: Rectifier circuit 900, 900A: Vibration source 910A: Bottom wall 911A, 912A: Side wall

Claims (4)

A piezoelectric element that generates electric charge by vibration;
A vibration transmitting member that transmits the vibration to the piezoelectric element;
A series circuit of an inductor and a switch;
A control unit for controlling conduction / disconnection of the switch;
With
A piezoelectric power generator in which the piezoelectric element and the series circuit are connected in parallel,
The controller is
From the timing at which the absolute value of the voltage due to the electric charge generated by the piezoelectric element is maximized, at a timing at which the phase of the voltage waveform advances by 45 °, the switch is conductively controlled,
The switch is controlled to be cut off at a timing at which a half of the resonance period of the piezoelectric element and the inductor has elapsed from the timing at which the switch is conductively controlled.
Piezoelectric generator. A plurality of sets of the piezoelectric element and the vibration transmitting member are provided.
The piezoelectric power generation device according to claim 1. The set of the piezoelectric element and the vibration transmitting member has different vibration frequencies.
The piezoelectric power generation device according to claim 1 or 2. A rectifier circuit is connected to an output terminal of a parallel circuit of the piezoelectric element and the series circuit.
The piezoelectric power generation device according to any one of claims 1 to 3.

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