JPH03167055A - Drive unit for vibrator and waterdrop eliminator using the same - Google Patents

Abstract

PURPOSE:To enable a strong vibration to be generated at once through resonance in a vibrator by constituting an ac power supply, which supplies ac power to the vibrator being attached to a platelike member such as a mirror or the like, so that it can to output resonance frequency and semiresonance frequency of this vibrator alternately. CONSTITUTION:Only the peripheral edge of a spacer 30 made of an epoxy plate is stuck to a convex mirror 11 made by binders 32, 33, making a clearance 31 to be formed between the spacer 30 and the mirror 11, and a piezoelectric vibrator 20 is fixed to the almost central part of this spacer 30 by a bonding agent. This piezoelectric vibrator 20 is composed by conducting and bonding electrodes 22, 23, using respective flexible substrates to both ends of a platelike electrostrictive element 21. Then, ac power is fed to this piezoelectric vibrator 20 from an alternating current power supply AC whereby the spacer 30, namely, the mirror 11 is vibrated. In this case, this AC power supply is constituted so as to output resonance frequency and antiresonance frequency of the vibrator 20 alternately, thus a strong vibration can be generated by means of the resonance of the vibrator 20.

Description

[Detailed Description of the Invention] (1) (2) [Objective of the Invention] (Field of Industrial Application) The present invention relates to a driving device for a vibrator used in various devices using ultrasonic vibration. In particular, it can be applied to a water droplet removing device for removing water droplets adhering to a plate-like member such as a rearview mirror for an automobile.

(Prior Art) Conventionally, as this type of device, techniques disclosed in Japanese Patent Application Laid-open No. 56-89881, Japanese Patent Application Laid-Open No. 56-102977, etc. are known.

These publications disclose that by changing the output frequency of an AC power source, a vibrator is vibrated at different resonant frequencies, and the antinodes and nodes of ultrasonic vibration are moved. By moving the antinode and node of the ultrasonic vibration, the energy of the vibration can be uniformly distributed inside the ultrasonic cleaning device.

In addition, in Japanese Utility Model Application Publication No. 63-69646, etc., by vibrating an automobile rearview mirror with a vibrator,
An apparatus for removing water droplets attached to the mirror is disclosed.

(Problem that the invention sought to solve) However, in conventional devices, when the vibrator starts vibrating at a certain resonant frequency and starts vibrating at another resonant frequency, part of the energy supplied from the AC power source is There was a problem in that the frequency was consumed to damp the vibration of the previous resonant frequency. This has caused a problem in that it takes time for the vibrator to begin strong resonance.

The present invention 1 was made in order to solve the problems of such conventional devices, and its technical problem is to reduce as much as possible the energy consumed to damp the vibration of the previous resonant frequency. .

(Means for solving the problem) The technical means taken to achieve the above-mentioned technical problem is to alternately output the resonant frequency and anti-resonant frequency of the resonator from the AC power source to the resonator. That's what I did.

(Function) According to the above-mentioned technique (Hotel's method), the vibration of the vibrator is (3
) (4) Before moving from one resonant frequency to another, an anti-resonant frequency is supplied from the AC power source to the vibrator.

The vibrations occurring in the vibrator while the anti-resonant frequency is being supplied are attenuated. As a result, when another resonant frequency is supplied from the AC power source to the vibrator, strong vibrations are immediately generated due to the resonance of the vibrator, since the vibration of the previous resonant frequency has been attenuated.

(Embodiment) Hereinafter, a preferred embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a plan view of a water droplet removing device to which the present invention is applied, seen from the back side. Further, FIG. 2 is a sectional view taken along the line AA in FIG. 1.

A spacer 30 made of a glass epoxy plate is attached to a convex mirror 11 having a predetermined curvature. Spacer 30 is fixed to the outer periphery of mirror 11 by adhesive 32,33.

As shown in FIG. 2, spacer 30 and mirror 1
1, a gap 31 is formed between them.

The piezoelectric vibrator 20 is fixed approximately at the center of the spacer 30 with an adhesive. The piezoelectric vibrator 20 is constructed by conductively bonding electrodes 22 and 23 using a flexible printed circuit board to both end surfaces of a flat electrostrictive element 21. In the first embodiment, piezoelectric ceramic is used as the electrostrictive element 21.

An alternating current power supply AC is connected between the electrode 22 and the electrode 23.

When electric power is applied between the electrodes 22 and 23, the piezoelectric vibrator 20 expands or contracts in the thickness direction (vertical direction in the second figure) and length direction (horizontal direction in the second figure).

This will be explained with reference to FIG. 3a. When the (+) terminal of the DC power source E is connected to the electrode 22 and the (-) terminal of the DC power source E is connected to the electrode 23, the piezoelectric vibrator 20 contracts in the length direction due to a transverse effect. At this time, a strong contraction force acts on one surface of the spacer 30, causing the spacer 30 to bend.

This will be explained with reference to FIG. 3b. Contrary to the case in Fig. 3a, when the (-) terminal of the DC power supply E is connected to the electrode 22 and the (+) terminal of the DC type #E is connected to the electrode 23, (5) (6) the piezoelectric vibrator 20 is horizontally The effect is to stretch in the length direction.

At this time, a strong stretching force acts on one side of the spacer 30,
The spacer 30 is bent in the opposite direction to that in FIG. 3a.

This will be explained with reference to FIG. 3c. When an AC power source AC is connected to the piezoelectric vibrator 20 and AC power is supplied to the piezoelectric vibrator 20, the spacer 30 is repeatedly bent in the opposite direction, causing the spacer 30 to vibrate. Since the spacer 30 is bonded to the mirror 11, vibrations generated in the spacer 30 are absorbed by the mirror 11.
1 and causes the mirror 11 to vibrate.

If the frequency of AC power is selected to an appropriate value, mirror 1
1 resonates, and a standing wave that is uniform and large in amplitude is generated throughout the mirror 11. This standing wave causes the surface of the mirror 11 to move at high speed. At this time, the water droplets adhering to the mirror 11 are given high kinetic energy by the mirror 11 and are removed from the mirror 11 by being dropped or atomized by gravity.

According to the device of this embodiment, a gap 31 that does not contact the mirror 11 is formed in the center of the spacer 30 . mirror 1
Compared to the case where the piezoelectric vibrator 20 is directly bonded to the piezoelectric vibrator 1, the mirror 11 is easily bent because a gap 31 is formed between the mirror 11 and the piezoelectric vibrator 20. Hence,
The vibration excited on the mirror 11 is not weakened by the piezoelectric vibrator 20 and propagates throughout the mirror 11 with a large amplitude.

The resonance frequency and anti-resonance frequency will be explained below with reference to FIGS. 4a and 4b.

FIG. 4a is a graph depicting the results of measuring the impedance of the piezoelectric vibrator 20 alone at various frequencies. When an electrical signal of about 54 kHz is supplied from the alternating current power source AC to the piezoelectric vibrator 20, the piezoelectric vibrator 20 enters a resonant state and the electrical impedance becomes extremely small. Also,
When an electrical signal of about 56 kilohertz is supplied to the piezoelectric vibrator 20 from the alternating current power supply AC, the piezoelectric vibrator 20 enters an anti-resonance state, and its electrical impedance becomes extremely large.

(7) (8) If the piezoelectric vibrator 20 is bonded to the spacer 30 or the like, the system that vibrates together with the piezoelectric vibrator 20 becomes complicated, so the impedance of the piezoelectric vibrator 20 exhibits a complicated waveform. FIG. 4a is a graph depicting the results of measuring the impedance of the piezoelectric vibrator 20 in the state shown in FIG. When the impedance of the piezoelectric vibrator 20 is locally minimum, the system vibrating together with the piezoelectric vibrator 20 is in a resonant state, and when the impedance of the piezoelectric vibrator 20 is locally maximum, the liquid system is in a resonant state. It is in an anti-resonant state. Resonant states and anti-resonant states appear alternately from low frequencies to high frequencies.

Furthermore, the magnitude of the impedance of the piezoelectric vibrator 20 is related to the amplitude of the standing wave generated on the mirror 11. That is, the smaller the impedance of the piezoelectric vibrator 20, the more
Since a large amount of power is supplied from C to the piezoelectric vibrator 20, the amplitude of the standing wave generated on the mirror 11 increases.

Therefore, in the characteristics depicted in Figure 4b, the frequencies f2 and f
At 6, a standing wave with a large amplitude is generated on mirror 11, and water droplets adhering to mirror 11 can be quickly removed.

Therefore, the alternating current power supply AC of the device of the first embodiment oscillates in a frequency range including frequencies 12 and f6.

Hereinafter, with reference to FIG.
Let me explain about two things. The alternating current power supply AC includes a triangular wave generator 41, a voltage controlled oscillator 42, and a drive circuit 43.

When the switch 45 is closed and the battery 44 and constant voltage power supply circuit 46 are connected, the triangular wave generator 41 starts oscillating.

FIG. 6 shows the waveform of the electrical signal output from the triangular wave generator 41. As shown in the figure, the triangular wave generator 41 outputs a triangular wave that sweeps a predetermined voltage range every predetermined period T. The electrical signal output from the triangular wave generator 41 is input to the voltage controlled oscillator 42.

The frequency of the electrical signal output from the voltage controlled oscillator 42 is shown in FIG. As shown in the figure, the voltage controlled oscillator 42 outputs an electrical signal that sweeps a predetermined frequency range fw according to the voltage level of the electrical signal output from the triangular wave generator 41. be done. The electrical signal output from the voltage controlled oscillator 42 is boosted by the drive circuit 43 and then supplied to the piezoelectric vibrator 20 .

In the example shown in FIG. 4b, within the frequency range fw swept by the voltage controlled oscillator 43, there are four resonant frequencies f2.
f4. f6. f8 and five antiresonant frequencies fl, [3, f
5. f7. Contains f9. Therefore, when the voltage controlled oscillator 43 sweeps the predetermined frequency range fw, a standing wave is generated on the mirror 11 at each resonance frequency f2° (4, [6, 18), and a standing wave generated on the mirror ll is It is attenuated each time it passes through each anti-resonant frequency.

As a result, when the mirror 11 pulsates at a certain resonant frequency (e.g. resonant frequency f2) and then another resonant frequency (e.g. resonant frequency f4) is supplied from the AC power source AC to the piezoelectric vibrator 20, the previous resonant frequency (e.g. Resonant frequency f2
) vibrations are damped and weakened. Therefore, when another resonance frequency (for example, resonance frequency f4) is supplied from the AC power source AC to the piezoelectric vibrator 20, the standing wave generated at the previous resonance frequency (for example, resonance frequency f2) is not canceled. energy becomes less. Therefore, another resonant frequency (
For example, when the resonance frequency f4) is supplied, a standing wave with a large amplitude is immediately generated on the mirror 11.

In the device of this embodiment, the resonance frequency f2. which is generated by a standing wave of large amplitude. Since the predetermined frequency range fw is set to include all of f6, the predetermined frequency range fw includes five anti-resonant frequencies fl, f3°f5f1, and 19. However, the anti-resonant frequency is within a predetermined frequency range f
It is sufficient if one or three are included in wO.

As shown in FIG. 8, even if only one anti-resonant frequency fa is included in the predetermined frequency range fw, when changing from the resonant frequency frl to the resonant frequency fr2 or from the resonant frequency fr2 to the resonant frequency frl, Since the standing wave on the mirror 11 is attenuated during the transition, the resonance frequency frl
, fr2, a standing wave with a thick amplitude immediately begins to be generated on mirror ll.

In exactly the same way, there are three anti-resonant frequencies fa1 . fa2. Even if fa3 is included (
(see FIG. 9), resonant frequency frl.

When fr2 is supplied, a standing wave with a large amplitude begins to be generated on the mirror 11 immediately.

In this way, in the device of this embodiment, the energy consumed to damp the vibration of the previous resonant frequency can be minimized, so the energy of the standing wave generated on the mirror 11 can be increased. Therefore, water droplets attached to the mirror 11' can be removed more quickly and uniformly.

〔Effect of the invention〕

According to the present invention, vibrations occurring in the vibrator while the anti-resonant frequency is being supplied to the vibrator are attenuated. As a result, when another resonant frequency is supplied from the AC power source to the vibrator, the vibration of the previous resonant frequency has already been attenuated, so strong vibrations are immediately generated due to the resonance of the vibrator.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a water droplet removing device to which the present invention is applied, seen from the back side. FIG. 2 is a sectional view taken along the line AA in FIG. 1. FIGS. 3a and 3b FIG. 3c is an explanatory diagram showing the operation of the apparatus according to the embodiment of the present invention. FIG. 4a is a graph depicting the results of measuring the impedance of a single piezoelectric vibrator at various frequencies. FIG. 4b is a graph depicting the results of measuring the impedance of the piezoelectric vibrator in the state shown in FIG. FIG. 5 is a circuit diagram depicting the AC power source of the device of this embodiment. FIG. 6 is a waveform diagram showing the waveform of the electrical signal output from the triangular wave generator. FIG. 7 is a graph depicting the frequency of the electrical signal output from the voltage controlled oscillator. FIG. 8 is a graph showing another way of determining the predetermined frequency range. (13) (14) FIG. 9 is a graph showing another way of determining the predetermined frequency range. 11...Mirror (plate-shaped member), 20...Piezoelectric vibrator (vibrator) AC...Alternating current power source.

Claims (6)

[Claims] (1) A vibrator drive device comprising a vibratingly supported vibrator and an AC power source supplying AC power to the vibrator, wherein the AC power source alternately changes the resonant frequency and anti-resonance frequency of the vibrator. A vibrator drive device characterized by outputting. (2) Claim (1) characterized in that the AC power supply further includes an oscillation circuit that repeatedly sweeps oscillation in a frequency range between the first anti-resonance frequency and the second anti-resonance frequency at a predetermined period. A drive device for the vibrator described. (3) The vibrator driving device according to claim 1, wherein the AC power source further includes an oscillation circuit that repeatedly oscillates in a predetermined period in a frequency range that includes at least three anti-resonance frequencies. (4) A water droplet removal device for a vibrator, which includes a plate-shaped member that is supported so as to be able to freely vibrate, a vibrator fixed to the plate-shaped member, and an AC power source that supplies AC power to the vibrator, the alternating current A water droplet removing device characterized in that a power source alternately outputs a resonant frequency and an anti-resonant frequency of a vibrator. (5) The AC power source further includes an oscillation circuit that repeatedly sweeps and oscillates a frequency range between a first anti-resonant frequency and a second anti-resonant frequency of a system including the plate member and the vibrator at a predetermined period. The water droplet removing device according to claim 4, further comprising: (6) The AC power source further comprises an oscillation circuit that repeatedly sweeps and oscillates a frequency range including at least three anti-resonance frequencies of a system including the plate member and the vibrator at a predetermined period. The water droplet removing device according to item (4).