JPH03282386A - Ultrasonic range finder - Google Patents

Abstract

PURPOSE:To reduce residual vibration and to expand the measurable range by inverting the phase of the detection signal of a residual vibration detecting vibrator fitted to part of a vibrator at need and impressing the phase-inverted signal to signal electrodes. CONSTITUTION:When electric driving pulses are impressed from an oscillator 25 to the signal electrodes 11 and 12 of the ultrasonic vibrator 1, an ultrasonic wave generated by respiratory vibration caused by the vibrator 1 travel as a beam. During this period, a switch 31 is ON and switches 32 and 33 are OFF. When external pressure is applied to the vibrator 1, on the other hand, the vibrator expands and contracts to develop a voltage between the electrodes 11 and 12. The switch 31 is turned OFF and the switches 32 and 33 are turned ON right after the impression of the driving pulses, and the detection signal of the residual signal of the vibrator 1 detected by the detecting vibrator 21 is amplified 41 and inverted 42 in phase; and its voltage is applied to the electrodes 11 and 12 and then cancel the residual vibration, which is, therefore, reduced securely and speedily.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an ultrasonic distance meter that can expand the measurable range.

<Prior Art> FIG. 5 is a diagram illustrating the configuration of a conventional example that has been commonly used.

In the figure, 1 is a cylindrical pressure KG mover made of ceramics, 11
．． Reference numeral 12 denotes electrodes provided on the inner and outer peripheral surfaces of the piezoelectric vibrator 1.

2 is a plastic case that also serves as an acoustic matching layer.

3 is a damping material for damping the piezoelectric vibrator 1, and 4 is a reflective umbrella for changing the direction of transmitted and received ultrasonic waves from the piezoelectric vibrator 1 to provide directivity.

In the above configuration, (1) In the case of ultrasonic transmission, when an electric pulse is applied to the piezoelectric vibrator 1, the piezoelectric vibrator 1
causes breathing vibrations in the radial direction and generates ultrasonic waves in the normal direction of the outer periphery.

The direction of travel of this ultrasonic wave is changed by reflection i#4,
The beam becomes a donut-shaped beam as shown in FIG. 6 and travels downward in FIG.

(2) In the case of receiving ultrasonic waves The ultrasonic waves incident from below in FIG. The piezoelectric vibrator 1 generates an electric field between electrodes in response to applied stress.

<Problems to be Solved by the Invention> Based on this principle, an ultrasonic distance meter is required to have the following characteristics.

☆ High damping characteristic Ultrasonic distance meter is an instrument that determines the distance liL to the target by emitting ultrasonic waves towards the target and measuring the time t until it is reflected and returned.

Here, L= (1/2)Ct (
1) C: Sound velocity in the propagation medium However, since the ceramic piezoelectric vibrator 1 generally has a large inertia, even after the electric drive pulse shown in FIG. As shown in Fig. 7 (C), if the damping vibration continues and this is called residual vibration, if the distance to the measurement object is short,
), the reflected wave C may arrive while some residual vibration remains, making it impossible to separate and distinguish between the two. In other words, it becomes difficult to measure at close range.

On the other hand, if the distance to the measurement target is long, Figure 7 (D
As shown in >, since the reflected wave amplitude becomes extremely small, it becomes necessary to electrically amplify the received voltage to a large extent. At this time, the electromotive force caused by the residual vibration is also amplified, so
In order to avoid erroneously detecting the residual vibration, the detection prohibited area (dead zone) e of the reflected wave C must be set as shown in Fig. 7 (E) until the amplitude of the residual vibration becomes smaller than the amplitude of the reflected wave C.
), it is necessary to provide the following.

From the above, if you try to measure long distances, it becomes impossible to measure short distances.On the other hand, if you try to measure short distances (shorten the dead zone), you can measure long distances with small reflections. The problem arises that it becomes difficult.

In order to avoid this situation, a method is generally used to apply a brake to the pressure S @ mover 1 using a damping material 3 as shown in Fig. 5, but this method has the following two problems. are doing.

■ It is extremely difficult to select a damping material that has a satisfactory or appropriate damping effect over a wide temperature range.In other words, the physical properties of many viscous substances change greatly depending on temperature, and in reality, damping materials that have a satisfactory or appropriate damping effect It is difficult to find a damping material that provides sufficient braking characteristics up to high temperatures.

■ Applying damping with damping material means suppressing vibrations, which leads to a reduction in the sound pressure generated during transmission.

The present invention solves this problem.

An object of the present invention is to provide an ultrasonic distance meter that can expand the measurable range.

<Means for Solving the Problems> In order to achieve this object, the present invention provides an ultrasonic transducer that includes an ultrasonic transducer that transmits and receives ultrasonic waves, and electrodes provided on both sides of the ultrasonic transducer. In the sonic distance meter, a residual vibration detection vibrator is attached to a part of the vibrator, and a detection signal of the residual vibration detection vibrator is phase-inverted when necessary and applied to the signal electrode to generate the ultrasonic vibration. The ultrasonic distance meter is characterized in that it is equipped with a phase inversion circuit that reduces residual vibration of the child.

Effect> In the above configuration, when an electric drive pulse is applied to the signal electrode of the ultrasonic vibrator by the oscillation circuit, the ultrasonic vibrator causes respiratory vibration, and the ultrasonic waves generated by this respiratory vibration are as follows: Proceeds as a beam.

On the other hand, if external pressure is applied to the ultrasonic vibrator, the ultrasonic vibrator expands and contracts, generating a voltage between the electrodes.

Therefore, the detection signal of the residual vibration detection vibrator can be transmitted at the required time.
The phase is inverted by a phase inversion circuit and applied to the signal electrode to reduce the residual vibration of the ultrasonic transducer.

Hereinafter, a detailed explanation will be given based on examples.

<Example> FIG. 1 is an explanatory diagram of the main part configuration of an embodiment of the present invention.

In the figure, structures with the same symbols as in FIG. 5 represent the same functions.

Hereinafter, only the differences from FIG. 5 will be explained.

In the figure, 21 is a vibrator for detecting residual vibration provided in a part of the vibrator 1. In this case, it is made of a polymer piezoelectric film and has a shape that is a part of a cylinder.

22 and 23 are electrodes provided on both sides of the detection vibrator 21, respectively.

25 is an oscillator provided between the signal electrodes 11 and 12, and a switch 31 is provided in the middle.

A switch 32 and an amplifier 4 are connected between the till and the electrode 22.
11 Phase inversion circuit 42. The switch 33 is connected in its original state.

The phase inversion circuit 42 inverts the phase of the output signal when necessary and applies it to the signal electrodes 11 and 12 to reduce the residual vibration of the ultrasonic transducer 1.

A signal processing circuit 43 that processes measurement signals is connected to the electrode 11.

Thus, electrodes 12.23 are connected to the circuit common.

Figure 2 shows a detailed diagram of the vibrator section.

Pressure! A detection vibrator 21 made of a polymer piezoelectric film is connected to a part of the vibrator 1 with an adhesive 51.

In the above configuration, the signal electrode 11 of the ultrasonic transducer 1
．． 12, when an electric drive pulse a is applied by the oscillation circuit 25 as shown in FIG. 3(A), the ultrasonic vibrator 1 causes respiratory vibration. and proceed. During this time, switch 3
1 is on, and switches 32 and 33 are off.

On the other hand, when external pressure is applied to the ultrasonic transducer 1, the ultrasonic transducer 1 expands and contracts, generating a voltage between the electrodes 11 and 12.

Immediately after the application of the drive pulse a ends, the switch 31
is off, and the swifts 32 and 33 are on.

The residual vibration of the ultrasonic transducer 1 is detected by the detection transducer 21, the detection signal C is amplified by the amplifier 41, and the voltage d inverted by the phase inversion circuit 42 is converted to the voltage d shown in FIG. D
) is added to the signal electrodes 11 and 12 as shown in FIG. Since this voltage d acts to cancel the residual vibrations of the ultrasonic transducer 1, the residual vibrations are significantly reduced compared to the residual vibrations, as shown in FIG. 3(E).

Here, FIG. 3(B) shows the case where no reversal voltage d is applied to the ultrasonic transducer 1. FIG. 3(E) shows the case where a reversal voltage d is applied.

The on/off chart of the switch 31 is shown in Figure 3 (
In FIG. 3(G), a chart showing the on/off state of the switches 32 and 33 is shown in FIG.

As a result, the residual vibrations that continue after the ultrasonic transducer 1 is driven are detected, and this is fed back to control the residual vibrations, so that the residual vibrations can be reliably and Residual vibration can be rapidly reduced.

FIG. 4 is an explanatory diagram of the main part configuration of another embodiment of the present invention.

In this embodiment, a polymer piezoelectric film protected by a protective film 52 via an adhesive 51 is used as the signal transducer 1a, and a lead derconate titanate (trade name: PZT) is used as the detection transducer 21a. ) and a non-piezoelectric polymer such as rubber.

In the embodiment shown in FIG. 1, the ultrasonic transducer 1 is described as a ceramic piezoelectric element, but it is not limited to this, and may be made of a piezoelectric material such as polyvinylidene fluoride (P), which is a polymeric piezoelectric film. ■DE), copolymer of vinylidene fluoride and trifluoroethylene (P (VDF-
TrFE)), a copolymer of vinylidene fluoride and tetrafluoroethylene (P(VDF-TeFE)), or an alternating copolymer of cyanovinylidene and vinyl acetate (P(VCN-VAC)), or The composite piezoelectric element described in the embodiment of FIG. 4 may be used, as long as it exhibits good piezoelectricity.

Further, in the embodiment shown in FIG. 1, the detection vibrator 21 has been described as a polymer piezoelectric film, but is not limited to this, and may be a ceramic piezoelectric element or a composite piezoelectric element.

In short, the ultrasonic transducer 1 and the detection transducer 21 may be any combination of a ceramic piezoelectric element, a polymer piezoelectric film, or a composite piezoelectric element.

<Effects of the Invention> As explained above, the present invention provides an ultrasonic distance meter that includes an ultrasonic transducer that transmits and receives ultrasonic waves, and electrodes provided on both sides of the ultrasonic transducer. A residual vibration detection transducer is attached to a part of the transducer, and the detection signal of the residual vibration detection transducer is phase inverted when necessary and applied to the signal electrode to reduce the residual vibration of the ultrasonic transducer. An ultrasonic range finder is constructed, which is characterized by being equipped with a phase inversion circuit that allows

As a result, the residual vibration that continues after the ultrasonic transducer ends is detected, and this is fed back to control the residual vibration, so the residual vibration can be reliably and rapidly removed without using damping material. Vibration can be reduced.

Therefore, according to the present invention, it is possible to realize an ultrasonic distance meter that can expand the measurable range.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the main part configuration of an embodiment of the present invention, FIG. 2 is a detailed diagram of the essential part of FIG. 1, FIG. 3 is an explanatory diagram of the operation of FIG. 1, and FIG. FIG. 5 is a diagram illustrating the configuration of a conventional example that has been generally used, and FIGS. 6 and 7 are diagrams illustrating the operation of FIG. 5. 1... Ultrasonic transducer, 11.12... as pole, 21.
...Detection vibrator, 22.23...@pole, 25...
Oscillator, 31, 32. 33... switch, 41...
Amplifier, 42... Phase inversion circuit, 43... Signal processing circuit, 51... Adhesive side, 52... Protective film. Fig. 3 between u4 (Cr) off - → Fig. /22 electrode

Claims (1)

[Scope of Claims] An ultrasonic distance meter comprising an ultrasonic transducer that transmits and receives ultrasonic waves, and electrodes provided on both sides of the ultrasonic transducer, wherein comprising a residual vibration detection vibrator and a phase inversion circuit that inverts the phase of a detection signal of the residual vibration detection vibrator when necessary and applies it to the signal electrode to reduce residual vibration of the ultrasonic vibrator. An ultrasonic distance meter featuring