Vibration power generation device

Abstract

This invention provides a vibration power generation device that can maximize output by automatically adjusting the resonant frequency of the vibration power generation element to follow changes in the frequency of environmental vibrations. [Solution] A vibration power generation device (100) comprising a vibration power generation element (10) having a fixed electrode (12) which is a first electrode, a movable electrode (11) which is a second electrode facing the fixed electrode (12), and an elastic support part (14) which elastically supports the movable electrode (11) with respect to the fixed electrode (12) so that it can move relative to it, and a frequency tracking means that makes the resonance frequency of the vibration power generation element (10) follow the environmental vibration frequency (fe).

Description

Technical Field

[0001] The present disclosure relates to a vibration power generation device.

Background Art

[0002] Conventionally, as one of the energy harvesting technologies for harvesting energy from environmental vibrations, a vibration power generation device including a vibration power generation element is known. When the resonance frequency of the vibration power generation element is synchronized with the environmental vibration, a large output can be obtained. However, if the environmental vibration deviates from the resonance frequency, the output will significantly decrease.

[0003] Patent Document 1 (see paragraphs

[0034] to

[0048] , FIG. 3) discloses a vibration power generation device including a frequency detection circuit for detecting a vibration frequency. In the device, feedback is performed on an output control circuit while monitoring the vibration frequency, and the impedance of the output control circuit is controlled based on the detected frequency so that the output power becomes maximum. With such a configuration, the vibration power generation device of Patent Document 1 enables efficient extraction of power even when the vibration frequency changes.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the impedance control based on the vibration frequency detected by the frequency detection circuit in the vibration power generation device described in Patent Document 1, it is difficult to appropriately respond to the change in the frequency of the environmental vibration and maximize the output.

[0006] This disclosure has been made in view of the above issues and aims to provide a vibration power generation device that can automatically track changes in the frequency of environmental vibrations and maximize output. [Means for solving the problem]

[0007] A vibration power generation device according to one aspect of the present disclosure is characterized by comprising a vibration power generation element having a first electrode, a second electrode facing the first electrode, and an elastic support portion that elastically supports the second electrode with respect to the first electrode so that it can move relative to the first electrode, and a frequency tracking means for causing the resonance frequency of the vibration power generation element to follow the ambient vibration frequency.

[0008] Furthermore, according to one aspect of the present disclosure, the frequency tracking means is characterized by comprising: a rectifier circuit for rectifying the AC power input from the vibration power generation element; a first capacitor connected to the rectifier circuit and charged by the power generated by the vibration power generation element; and a feedback circuit for feeding back the charging voltage of the first capacitor to the vibration power generation element.

[0009] Furthermore, according to one aspect of this disclosure, the feedback circuit is characterized by having a resistor.

[0010] Furthermore, according to one aspect of this disclosure, the rectifier circuit is characterized in that it is a half-wave rectifier circuit.

[0011] Furthermore, according to one aspect of this disclosure, the rectifier circuit is characterized in that it further includes a second capacitor.

[0012] Furthermore, according to one aspect of the present disclosure, an electret is formed on at least one of the first electrode or the second electrode. [Effects of the Invention]

[0013] According to this disclosure, it is possible to provide a vibration power generation device that can maximize output by having the resonant frequency of the vibration power generation element automatically follow the frequency changes of the environmental vibration. [Brief explanation of the drawing]

[0014] [Figure 1] This is a schematic diagram of a vibration power generation device according to one embodiment of the present invention. [Figure 2] This graph shows how the resonant frequency of the vibration power generation element of a vibration power generation device according to one embodiment of the present invention tracks the frequency change of the environmental vibration. [Figure 3] This graph shows the frequency characteristics of the change in vibration velocity when the charging voltage is changed in a vibration power generation device according to one embodiment of the present invention. [Modes for carrying out the invention]

[0015] Embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. The same elements are denoted by the same reference numerals throughout this specification and the accompanying drawings, and redundant descriptions are omitted.

[0016] In this specification, frequency tracking means refers to a means for causing the resonant frequency of a vibration power generation element to track the environmental vibration frequency, comprising: a rectifier circuit for rectifying the AC power input from the vibration power generation element; a capacitor connected to the rectifier circuit and charged by the power generated by the vibration power generation element; and a feedback circuit for feeding back the charging voltage of the capacitor to the vibration power generation element. The environmental vibration frequency refers to the frequency of vibration from an environmental vibration source.

[0017] Figure 1 is a schematic diagram of a vibration power generation device 100 according to one embodiment. The vibration power generation device 100 comprises a vibration power generation element 10 and a feedback circuit 30. This vibration power generation device 100 is connected to an environmental vibration source (not shown), such as a bridge or an electric motor, and vibrations transmitted when an automobile passes over the bridge are transmitted to it. The vibration power generation device 100 is also electrically connected to an external load device (not shown), such as a bridge inspection device, to supply power generated by vibration. As a result, the inspection device can perform the necessary inspections and reports related to the bridge using the supplied power.

[0018] (First Embodiment) The vibration power generation element 10 is a capacitive vibration power generation element equipped with an electret electrode. In response to vibrations from an environmental vibration source, the movable electrode 11, which is the second electrode, vibrates relative to the fixed electrode 12, which is the first electrode, thereby generating electricity. An electret is formed on at least one of the movable electrode 11 and the fixed electrode 12 near the surface 25 of the face of the movable electrode 11 and the fixed electrode 12. In this embodiment, a negative electret is formed near the surface 25 of the fixed electrode 12 facing the movable electrode 11. The movable electrode 11 is, for example, a comb-shaped electrode having two comb-tooth portions 21, and the fixed electrode 12 is, for example, a comb-shaped electrode having three comb-tooth portions 22.

[0019] The comb-tooth portion 21 of the movable electrode 11 and the comb-tooth portion 22 of the fixed electrode 12 have a predetermined thickness in the Z direction in the figure, and face each other at the portion where they interlock. The movable electrode 11 and the fixed electrode 12 can be manufactured, for example, as MEMS structures with silicon as the base material.

[0020] The fixed electrode 12 is fixedly held by an insulating support frame 13. On the other hand, the movable electrode 11 is elastically supported by an elastic support portion 14 (electrode holding portion 14a, connecting portion 14b, fixing portion 14c) so as to vibrate in the vertical direction (X direction) in the drawing with respect to the support frame 13. The elastic support portion 14 is composed of an electrode holding portion 14a that holds the movable electrode 11, a fixing portion 14c fixed to the support frame 13, and a flexible connecting portion 14b that connects the electrode holding portion 14a and the fixing portion 14c.

[0021] The connecting portion 14b is a portion that is thin in the X direction and thick in the Z direction in FIG. 1. When the connecting portion 14b is manufactured as a separate part, the flexible material constituting the connecting portion 14b may be metal or the like. When vibration is applied to the support frame 13 from an environmental vibration source, the two connecting portions 14b provided on the left and right of the electrode holding portion 14a in the drawing are bent, so that the electrode holding portion 14a vibrates in the X direction with respect to the support frame 13. As a result, the movable electrode 11 held by the electrode holding portion 14a is relatively movable with respect to the fixed electrode 12 fixed to the support frame 13 and vibrates in the X direction.

[0022] Note that the configurations of the movable electrode 11 and the fixed electrode 12 are not limited to the illustrated configurations. In this embodiment, a two-terminal structure is adopted. However, for example, a three-terminal structure having an axisymmetric shape in which the movable electrode 11 and the fixed electrode 12 in FIG. 1 are inverted up and down with the connecting portion 14b as an axis in a plan view may be used. Further, in this embodiment, the two connecting portions 14b provided on the left and right of the electrode holding portion 14a are bent, so that the movable electrode 11 vibrates in the X direction with respect to the support frame 13. However, the present invention is not limited to this. As a capacitive vibration power generation element, a cantilever-type vibration power generation element in which the movable electrode has a cantilever-type elastic support structure may be used.

[0023] The vibration power generation element 10 converts the vibration energy of the environmental vibration source on which the vibration power generation device 100 is installed into electrical energy, generating AC power. The vibration power generation element 10 is electrically connected to the rectifier circuit 20, which rectifies the AC power input from the vibration power generation element. The fixed electrode 12 is electrically connected to the anode of diode D1, which is the first rectifier element of the rectifier circuit 20, and also to the cathode of diode D2, which is the second rectifier element of the rectifier circuit 20. More specifically, the cathode of diode D2, the second rectifier element, is connected to the fixed electrode 12 via capacitor C1, which will be described later. On the other hand, the cathode of diode D1 and the anode of diode D2 are electrically connected to the movable electrode 11. Capacitor C1 is electrically connected to the cathode of diode D2, the second rectifier element of the rectifier circuit 20. The potential of the fixed electrode 12 is at ground potential.

[0024] As a result, when the movable electrode 11 is at a positive potential and the fixed electrode 12 is at a negative potential in the AC power generated by the vibration power generation element 10, the diode D2 is forward-biased, and the current flowing from the movable electrode 11 to the fixed electrode 12 passes through the diode D2 and charges the capacitor C1.

[0025] When the movable electrode 11 is at a negative potential and the fixed electrode 12 is at a positive potential, the diode D2 is reverse-biased, so no current flows through the diode D2 to the fixed electrode 12. In other words, no current flows from the movable electrode 11 to the fixed electrode 12 through the capacitor C1.

[0026] On the other hand, since diode D1 is forward-biased, the current flowing from the fixed electrode 12 to the movable electrode 11 passes through diode D1. Diodes D1 and D2 and capacitor C1 constitute a half-wave rectifier circuit for rectifying the alternating current generated by the vibration power generation element 10. Note that the rectifier circuit 20 is not limited to a half-wave rectifier circuit, but may also be a full-wave rectifier circuit.

[0027] This embodiment includes a feedback circuit (path) 30 containing a resistor R1 in addition to the rectifier circuit 20. The feedback circuit 30 feeds back the DC component of the charging voltage of the capacitor C1 connected to the rectifier circuit to the movable electrode 11 side of the vibration power generation element 10. As a result, the spring constant due to the action of the electrostatic spring becomes variable, as will be described in detail later.

[0028] In this specification, the property of the electrostatic force that behaves like a spring, resulting from the potential difference between the fixed electrode 12 (its comb teeth) and the movable electrode 11 (its comb teeth) when the movable electrode 11 moves relative to the fixed electrode 12, is referred to as an "electrostatic spring." In this embodiment, the initial potential difference is generated by an electret formed on the fixed electrode 12.

[0029] The output power of the vibration power generation element 10 is greatest when the vibration frequency of the environmental vibration source matches the resonant frequency of the vibration power generation element 10, which is determined by the spring constant due to the elasticity of the vibration power generation element 10 (the connecting part 14b in the vibration power generation element) and the spring constant due to the electrostatic spring. The output power decreases when the vibration frequency of the environmental vibration source deviates from the resonant frequency. The rectifier circuit 20 and the feedback circuit 30 can be configured with two diodes D1 and D2, a resistor R1, and a first capacitor C1, but are not limited to this configuration. As shown in Figure 1, a second capacitor C2 (not shown) may be provided between the input section 31 and the output section 32 of the feedback circuit 30, or more specifically, between the input section 31 and diode D2. In this case, leakage current to the vibration power generation element side when the charging voltage is high can be suppressed. As a result, the power stored in capacitor C1 does not escape to the vibration power generation element 10, and the charging efficiency can be increased.

[0030] The feedback circuit 30 may include a resistor R1. This prevents the power generated by the vibration power generation element 10 from leaking from the feedback circuit 30 to the capacitor C1, thereby efficiently charging the capacitor C1. However, since the feedback circuit 30 feeds back the charging voltage of the capacitor C1 to the vibration power generation element 10, it is preferable not to include a capacitor within the feedback circuit 30.

[0031] The vibration power generation device 100 according to this embodiment, by including a feedback circuit 30, can automatically follow changes in the vibration frequency of the environmental vibration source, thereby maximizing the output. The operation of the feedback circuit 30 of the vibration power generation device 100 according to this embodiment will be described below.

[0032] Figures 2(a) to 2(d) are graphs illustrating how the resonance frequency of the vibration power generation element 10 of a vibration power generation device 100 according to one embodiment of the present invention tracks the frequency change of the environmental vibration. The vertical axis of the graph shows the power generated by the vibration power generation element 10, the horizontal axis shows the vibration frequency, and fe shows the environmental vibration frequency. Of these, Figures 2(a) and (b) show the case where the vibration frequency of the environmental vibration source is greater than the resonance frequency of the vibration power generation element 10, while Figures 2(c) and 2(d) show the case where the vibration frequency of the environmental vibration source is less than the resonance frequency of the vibration power generation element 10. In this embodiment, the resonance frequency of the vibration power generation element 10 is set to be lower than the vibration frequency of the environmental vibration source during manufacturing.

[0033] In this embodiment, as described above, the vibration power generation element 10 is manufactured with a resonant frequency set lower than the vibration frequency of the environmental vibration source. Therefore, as shown in Figure 2(a), the initial state is when the vibration frequency fe of the environmental vibration source is greater than the resonant frequency of the vibration power generation element 10. In this state, the vibration power generation element 10 generates electricity due to the vibration of the environmental vibration source, and the capacitor C1 connected to the rectifier circuit 20 is charged. The charging voltage of the charged capacitor C1 is then fed back to the movable electrode 11 of the vibration power generation element 10 by the feedback circuit 30. Since a negative electret is formed on the fixed electrode 12 facing the movable electrode 11, the potential difference between the comb teeth of the movable electrode 11 and the comb teeth of the fixed electrode 12 of the vibration power generation element 10 becomes large.

[0034] When the potential difference between the comb teeth of the movable electrode 11 and the fixed electrode 12 of the vibration power generation element 10 increases, the spring constant due to the electrostatic spring between the movable electrode 11 and the fixed electrode 12 increases. As a result, the resonant frequency of the vibration power generation element 10 increases and comes to match the vibration frequency fe of the environmental vibration source, as shown in Figure 2(b). Consequently, the amount of power generated increases, and the maximum amount of power can be obtained.

[0035] If the charging voltage increases further from the state shown in Figure 2(b), and the resonant frequency of the vibration power generation element 10 becomes greater than the vibration frequency fe of the environmental vibration source, as shown in Figure 2(c), the resonant frequency of the vibration power generation element 10 will no longer match the vibration frequency fe of the environmental vibration source. As a result, the amount of power generated will decrease, and the charging voltage of the capacitor C1 will also decrease. When the charging voltage decreases, the feedback to the movable electrode 11 also decreases, so the potential difference between the comb teeth of the movable electrode 11 of the vibration power generation element 10 and the comb teeth of the fixed electrode 12 decreases.

[0036] When the potential difference between the comb teeth of the movable electrode 11 and the fixed electrode 12 of the vibration power generation element 10 decreases, the spring constant due to the electrostatic spring between the movable electrode 11 and the fixed electrode 12 decreases. As a result, the resonant frequency of the vibration power generation element 10 decreases and, as shown in Figure 2(d), it again matches the ambient vibration frequency. Consequently, the amount of power generated increases, and the maximum power generation can be obtained again.

[0037] As described above, the electrostatic spring generated between the comb teeth of the movable electrode 11 and the comb teeth of the fixed electrode 12 due to the potential difference acts similarly to an elastic spring, and its spring constant ke contributes to the resonant frequency of the vibration power generation element 10. That is, in this embodiment, if the spring constant due to the elastic support part 14 is kn, the resonant frequency of the vibration power generation element 10 is determined by the spring constant K, which is determined by the elastic spring constant kn and the electrostatic spring constant ke. In the cases of Figures 2(a) and 2(b), as the electrostatic spring constant ke increases, the overall spring constant K increases, and the resonant frequency of the entire vibration power generation element 10 increases, approaching the vibration frequency fe of the environmental vibration source.

[0038] In this way, by using the feedback circuit 30, the resonant frequency of the vibration power generation element 10 can be increased from a state where the resonant frequency is small relative to the ambient vibration frequency, allowing it to automatically track the ambient vibration frequency. Furthermore, if the resonant frequency of the vibration power generation element 10 becomes even larger than the ambient vibration frequency, the resonant frequency can be reduced by using the feedback circuit 30, allowing it to automatically track the ambient vibration frequency.

[0039] Figure 3 is a graph showing the frequency characteristics of the change in vibration velocity when the charging voltage is changed in a vibration power generation device 100 according to one embodiment of the present invention.

[0040] The frequency characteristics of the vibration velocity were measured using a laser Doppler vibrometer when a DC voltage was applied to capacitor C1 from an external power supply, forcibly changing the charging voltage from 0V to 10V. Figure 3 shows the measurement results when the charging voltage was applied in a direction that enhances the electret of the vibration power generation element 10.

[0041] Figure 3 shows that when the charging voltage is fed back in a direction that enhances the electret, the resonant frequency shifts to a higher direction even with a voltage of a few volts. Furthermore, the peak of the generated voltage decreases as the voltage increases, which is thought to be because the restraining force between the comb teeth has increased due to the enhancement of the electret. Thus, by using the vibration power generation device 100 of this embodiment, the resonant frequency of the vibration power generation element 10 can be changed in a direction that follows the value of the environmental vibration frequency.

[0042] (Second embodiment) In the embodiments described above, the resonant frequency of the vibration power generation element 10 was set to be lower than the vibration frequency of the environmental vibration source during manufacturing. However, the invention is not limited to this, and the resonant frequency of the vibration power generation element 10 may be set to be higher than the vibration frequency of the environmental vibration source during manufacturing. Below, we will explain using the case in which a negative electret is formed on the fixed electrode 12, similar to the embodiments described above, as an example.

[0043] In this case, the circuit in Figure 1 is connected in reverse. That is, the anode (and input section 31) of diode D2 is connected to the fixed electrode 12 on which the negative electret is formed, and the anode of diode D1 is connected to the movable electrode 11. As a result, each part is connected so that the charging voltage of capacitor C1 is fed back to the fixed electrode 12 on which the negative electret is formed.

[0044] As described above, the resonant frequency of the vibration power generation element 10 is set to be higher than the vibration frequency of the environmental vibration source. Therefore, in this embodiment, the initial state is as shown in Figure 2(c), where the resonant frequency of the vibration power generation element 10 is higher than the vibration frequency of the environmental vibration source. In this state, the vibration power generation element 10 generates electricity due to the vibration of the environmental vibration source, and the DC voltage from the charged capacitor C1 is fed back to the fixed electrode 12 of the vibration power generation element 10 by the feedback circuit 30. Since a negative electret is formed on this fixed electrode 12, the potential difference between the comb teeth of the movable electrode 11 and the comb teeth of the fixed electrode 12 decreases due to the feedback to the fixed electrode 12. In other words, as the charging voltage of the capacitor C1 increases, the feedback acts in such a way that the potential difference between the comb teeth of the movable electrode 11 and the comb teeth of the fixed electrode 12 decreases.

[0045] When the potential difference between the comb teeth of the movable electrode 11 and the comb teeth of the fixed electrode 12 of the vibration power generation element 10 decreases, the spring constant due to the electrostatic spring between the movable electrode 11 and the fixed electrode 12 decreases. As a result, the resonance frequency of the vibration power generation element 10 decreases and matches the ambient vibration frequency, as shown in Figure 2(d). Consequently, the amount of power generated increases, and the maximum amount of power can be obtained.

[0046] If the charging voltage increases further from the state shown in Figure 2(d), and the vibration frequency fe of the environmental vibration source becomes greater than the resonant frequency of the vibration power generation element 10, as shown in Figure 2(a), the resonant frequency of the vibration power generation element 10 will no longer match the vibration frequency fe of the environmental vibration source. As a result, the amount of power generated will decrease, and the charging voltage of capacitor C1 will also decrease. When the charging voltage decreases, the feedback to the fixed electrode 12 also decreases, so the potential difference between the comb teeth of the movable electrode 11 of the vibration power generation element 10 and the comb teeth of the fixed electrode 12 increases.

[0047] When the potential difference between the comb teeth of the movable electrode 11 and the fixed electrode 12 of the vibration power generation element 10 increases, the spring constant due to the electrostatic spring between the movable electrode 11 and the fixed electrode 12 increases. As a result, the resonant frequency of the vibration power generation element 10 increases and comes to match the vibration frequency fe of the environmental vibration source, as shown in Figure 2(b). Consequently, the amount of power generated increases, and the maximum power generation can be obtained again.

[0048] In the embodiments described so far, a negative electret is formed on the side of the fixed electrode 12, but the invention is not limited to this, and a negative electret may also be formed on the side of the movable electrode 11.

[0049] In this configuration, a negative electret is formed on the movable electrode 11 side, and the resonant frequency of the vibration power generation element 10 is set to be lower than the vibration frequency of the environmental vibration source. In this configuration, the circuit is connected so that the charging voltage of the capacitor C1 is fed back to the fixed electrode 12, where no negative electret is formed. This results in behavior similar to that of the first embodiment described above. Similarly, in this configuration, a negative electret is formed on the movable electrode 11 side, and the resonant frequency of the vibration power generation element 10 is set to be higher than the vibration frequency of the environmental vibration source. In this configuration, the circuit is connected so that the charging voltage of the capacitor C1 is fed back to the movable electrode 11 where the negative electret is formed. This results in behavior similar to that of the second embodiment described above.

[0050] In the embodiments described above, a negative electret was formed on either the movable electrode 11 or the fixed electrode 12. However, if a potential difference is generated between the comb teeth of the movable electrode 11 and the comb teeth of the fixed electrode 12 in the initial state, electrets may be formed on both the movable electrode 11 and the fixed electrode 12.

[0051] In the embodiments described above, the vibration power generation element is made from an SOI (Silicon On Insulator) wafer, but it is not limited to this and may be manufactured by any method.

[0052] According to the embodiments described above, the following effects and advantages are achieved.

[0053] (1) Even if the environmental vibration frequency changes, the resonance state can be automatically maintained, thus maximizing the output of the vibration power generation device.

[0054] (2) Furthermore, since a significant decrease in power output due to resonance shifts can be avoided, a larger amount of power can be obtained when compared with conventional vibration power generation devices over the same period. In other words, the power generation efficiency of vibration power generation devices can be improved. [Explanation of symbols]

[0055] 10. Vibration power generation element 11 Movable electrode (second electrode) 12 Fixed electrode (1st electrode) 13 support slots 14 Elastic support section 20 Rectifier circuit 21 Comb teeth part 22 Comb teeth part 30 Feedback Circuit 100 Vibration power generation device D1 diode D2 Diode R1 Resistor C1 Capacitor

Claims

1. A first electrode and a second electrode facing the first electrode, A vibration power generation element comprising: an elastic support portion that elastically supports the second electrode relative to the first electrode, allowing for relative movement; A vibration power generation device characterized by comprising a frequency tracking means for causing the resonant frequency of the vibration power generation element to follow the environmental vibration frequency.

2. The frequency tracking means is A rectifier circuit for rectifying the AC power input from the vibration power generation element, A capacitor connected to the rectifier circuit, which is charged by the power generated by the vibration power generation element, The vibration power generation device according to claim 1, further comprising a feedback circuit that feeds back the charging voltage of the first capacitor to the vibration power generation element.

3. The vibration power generation device according to claim 2, characterized in that the feedback circuit has a resistor.

4. The vibration power generation device according to claim 2, characterized in that the rectifier circuit is a half-wave rectifier circuit.

5. The vibration power generation device according to claim 2, characterized in that the rectifier circuit further includes a second capacitor.

6. The vibration power generation device according to claim 1, characterized in that an electret is formed on at least one of the first electrode or the second electrode.

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