JPH0432994B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an ultrasonic distance measuring device that measures the distance to a target object using ultrasonic waves, an ultrasonic object detection device that detects the presence or absence of an object, etc. The present invention relates to an ultrasonic receiving device used in the field, and particularly relates to an ultrasonic transmitting/receiving device using a single piezoelectric ceramic (hereinafter referred to as a piezoelectric sensor) as an ultrasonic transmitting/receiving device.

Configuration of conventional examples and their problems In recent years, various object detection devices that utilize ultrasonic transmission and reception operations, such as distance measuring devices such as cameras, have been put into practical use. Devices that can perform detection are also emerging.

This device uses an electrostatic sensor as an ultrasonic transmitter/receiver, and makes effective use of its low mechanical Q. In other words, even at short distances as described above, even after stopping the supply of transmitted signals, This makes full use of the advantage that the falling characteristic of the transmitting operation can be made steep, in that the vibrational operation of the ultrasonic transceiver quickly attenuates.

On the other hand, a piezoelectric sensor is recognized as an ultrasonic transmitter/receiver along with the above-mentioned electrostatic sensor, but this piezoelectric sensor has various advantages over the electrostatic sensor, such as high sensitivity, low cost, and good humidity characteristics. However, due to its high mechanical Q, the falling characteristic during transmission operation is extremely poor, and when connected to a signal amplification section, a so-called tailing phenomenon occurs.
It is known that it is extremely difficult to identify the received signal due to the reflected wave from a short distance of about 30 cm, which is described above, and there is a problem that object detection cannot be performed at a short distance.

To further explain this point, as mentioned above, piezoelectric sensors usually have a high mechanical Q, so once they are vibrated by electrical energy, they do not release the applied energy even if the electrical energy is removed. The vibration operation will continue until it is completely removed.

In other words, the piezoelectric sensor continues to vibrate even after the supply of the transmission signal is stopped due to its inherent characteristic of having a high mechanical Q. As a result,
This means that the falling characteristic in the transmission operation was not a steep characteristic.

On the other hand, the device using ultrasonic waves as described above cannot achieve its function unless it detects whether or not it has received a reflected wave from a target object.

Therefore, if the falling characteristic of the transmitting operation is not steep and the vibration operation is continued even after the transmitting operation is finished, if there is a target object at a short distance of about 30 cm, the reflected wave will not be reflected after the ultrasonic wave is transmitted. Since the time it takes for the ultrasonic wave to return is extremely short, there are cases where the vibration operation does not end within the extremely short period of time. Therefore, when transmitting and receiving ultrasonic waves using a single piezoelectric sensor, It is no longer possible to distinguish between the vibratory motion inherent to the element and the vibratory motion due to the reception of reflected waves after completion of the process.

As a result, as mentioned earlier, an ultrasonic transmitting/receiving device that uses a single piezoelectric sensor cannot perform ranging operations for target objects that are at a very close distance of less than about 1 m. This recognition had become common.

Incidentally, the relationship as described above will be briefly explained using the drawings as follows.

FIG. 1 is a schematic electrical circuit diagram of an ultrasonic transmitting/receiving device using a conventionally well-known single piezoelectric sensor. 1 shows an amplification section 3 consisting of first and second diodes 6, 7 and an amplifier 8.

FIG. 2 shows a signal waveform diagram at an arbitrary point in the configuration shown in FIG. 1, and of course, such a waveform diagram itself is well known.

In FIG. 1, when a transmission signal as shown in FIG. 2A is formed by a transmission circuit 1 and is supplied to a piezoelectric sensor 2 to transmit an ultrasonic wave, a transmission signal is generated at a point a at the input/output end of the piezoelectric sensor 2. A signal as shown in FIG. 2B appears.

That is, at point a, there are diodes 6, which are connected in antiparallel, indicating that the vibration operation of the piezoelectric sensor 2 continues even after the supply of the transmission signal shown in FIG.
An alternating current signal having a peak value of less than 7 conduction voltages will result.

On the other hand, the ultrasonic waves transmitted from the piezoelectric sensor 2 are
For example, the signal is reflected by a target object at a sufficiently distant distance and is received again by the piezoelectric sensor 2, so that a reception signal indicated by X in FIG. 2B appears at the point a. become.

The signal at point a is supplied to the amplifier 8 of the amplification section 3 via the first and second coupling capacitors 4 and 5, and as a result, the amplification section 3 is transferred to the point b in the figure as shown in Fig. 2C. _A signal containing the received signal
Distance information, etc. is obtained by detecting the point in time when X ₁ occurs.

Now, if we look at the waveform at the time of reverse signal among the output waveforms shown in _FIG . The alternating current signal based on the vibrational motion inherent to the element of the piezoelectric sensor 2 continues to exist for a period up to time _t2 .

Therefore, for example, if we consider a case where the amplified waveform of the received signal occurs as shown by the broken line X ₂ from time t ₁ to t ₂ above, the waveform
X ₂ It is included in the signal due to the vibration operation inherent to the element of the piezoelectric sensor 2 between the above time points t ₁ and t ₂ and cannot be distinguished as a received signal, so naturally the point of occurrence must be detected. will not be possible.

That is, in the case of a conventional ultrasonic transmitter/receiver using a single piezoelectric sensor, a target object located within the distance from which the reflected wave returns between the above time points t ₁ and t ₂ is detected as described above. That's why I couldn't do it.

By the way, in recent years, as a piezoelectric sensor that takes the above-mentioned problems into account, the vibration movement in the piezoelectric sensor is mechanically suppressed, that is, the piezoelectric element and aluminum diaphragm that constitute the piezoelectric sensor are held down with silicone rubber, etc., so-called. Various sensors subjected to Q-dumping have been proposed.

However, the above-mentioned Q-dump method also has the problem that when trying to detect a received signal at a short distance of about 30 cm as described above, an extremely strong Q-dump is required, resulting in a significant decrease in sensitivity. have. In other words, it is difficult to sufficiently suppress the tailing phenomenon while maintaining sensitivity to a certain level.On the other hand, if we ignore the decrease in sensitivity in order to detect objects at a short distance, then the reflected waves from the target object at a long distance will be This results in the problem that the signal cannot be output as a received signal.

Purpose of the Invention The purpose of the present invention is to reduce the circuit impedance seen from the piezoelectric sensor from the time when the supply of the transmission signal is stopped to an arbitrary time after the supply is stopped, to rapidly release the energy stored in the piezoelectric sensor, and to rapidly release the energy stored in the piezoelectric sensor. An object of the present invention is to provide an ultrasonic transmitter/receiver that can greatly improve falling characteristics in transmission operation due to characteristics.

Configuration of the Invention The ultrasonic transmitting/receiving device according to the present invention includes a single piezoelectric sensor, a transmitting circuit that supplies a transmitting signal to the piezoelectric sensor, and a circuit impedance seen from the piezoelectric sensor by operating in parallel connection with the piezoelectric sensor. and a signal amplifying section that amplifies the signal appearing at both ends of the piezoelectric sensor.

DESCRIPTION OF THE EMBODIMENTS FIG. 3 is an electrical circuit diagram showing an embodiment of the ultrasonic transmitter/receiver according to the present invention. In the figure, the same numbers as those in FIG. 1 indicate the same functional members.

In FIG. 3, reference numeral 9 includes an impedance variable means 10 made of a photoconductor 11, a light source 13, and a lighting circuit 14 for this light source 13. By controlling the lighting state of the light source 13, the impedance variable means 10 operates. That is, the operation control means 12 controls the operation of varying the resistance value of the photoconductor 11 and reducing the circuit impedance seen from the piezoelectric sensor 2.
It shows an impedance control means consisting of.

Hereinafter, the operation of an embodiment of the ultrasonic transmitter/receiver according to the present invention having the impedance control means 9 as described above will be explained with reference to a signal waveform diagram at an arbitrary point in the embodiment shown in FIG.

Similar to the conventional device shown in FIG. 2, when transmitting ultrasonic waves, the transmitting circuit 1 generates a transmitting signal as shown from time t ₀ to t ₁ in FIG. supply

Therefore, the piezoelectric sensor 2 starts transmitting ultrasonic waves, and the point a, which is the input/output end, has the above-mentioned time t ₀ ~
At _t1 , a signal waveform as shown in FIG. 4B appears.

Incidentally, since the light source 13 of the operation control means 12 is not yet turned on between the time points _t0 and _t1 as described above, the resistance value of the photoconductor 11, which is the variable impedance means 10, is extremely large, that is, It can be considered to be in an electrically open state, and therefore, the operation at the above-mentioned time points t ₀ to t ₁ is exactly the same as that of the conventional device shown in FIG.

However, in the embodiment of the ultrasonic transmitter/receiver according to the present invention shown in _FIG . A sawtooth panel voltage signal that rises instantaneously and gradually falls as shown in FIG. 4C is supplied from the lighting circuit 14 to the light source 13.

Therefore, the light source 13 is first turned on at time _t1 ,
Thereafter, a characteristic lighting state is formed in which the emission intensity decreases.

On the other hand, as mentioned above, the light from the light source 13 is supplied to the photoconductor 11, and therefore the resistance value of the photoconductor 11, which had been considered infinite until then, becomes smaller at time _t1 . First, there will be a steep decline.

By the way, it is well known that the resistance value of the photoconductor 11 responds to the intensity of the light it receives, and therefore, after the above-mentioned time _t1 , the resistance value of the photoconductor 11 is determined by the gradual decrease of the emission intensity of the light source 13. As the price increases, the price will gradually increase. That is, the fluctuation characteristics of the resistance value are as shown in FIG. 4D.

Now, if we consider the fluctuation state of the resistance value of the photoconductor 11 mentioned above, that is, the operating state of the impedance variable means 10, the circuit impedance seen from the piezoelectric sensor 2 first decreases rapidly, and then It is nothing but a gradual recovery.

That is, the characteristics of the circuit impedance seen from the piezoelectric sensor 2 are the same as the resistance value fluctuation characteristics of the photoconductor 11 shown in FIG. 4D.

Now, if we consider the trailing phenomenon of the piezoelectric sensor 2, which was a problem in the conventional device mentioned at the beginning, it is caused by the energy stored during the transmission operation being released via the piezoelectric sensor 2. Needless to say, this is a phenomenon in which an alternating current signal waveform is generated at point a, albeit minutely.

However, in the ultrasonic transmitter/receiver according to the present invention, as described above, the circuit impedance seen from the piezoelectric sensor 2 is reduced in conjunction with the end of the transmitting operation. Therefore, in the present invention, the energy stored in the piezoelectric sensor 2 during the transmission operation, which conventionally caused a tailing phenomenon, is rapidly released through the photoconductor 11 of the variable impedance means 10 whose resistance value has been reduced. It turns out.

That is, the energy that was conventionally released through the piezoelectric sensor 2 is released through the variable impedance means 10 in the present invention, and needless to be described in detail, the vibration operation of the piezoelectric sensor 2 is rapidly attenuated after the time t ₁ when the supply of the transmitted signal is stopped, and the tailing phenomenon that appears due to its oscillation also rapidly converges to the zero level, as shown after time t ₁ in Figure 4 (b). .

In other words, the falling characteristic in the transmission operation is greatly improved compared to the conventional device.

Therefore, as shown in FIG. 4E, the signal at point b of the amplifying section 3 also becomes zero level in a much shorter time than in the conventional device after the transmission operation is completed, and as a result, in the ultrasonic transmitting and receiving device according to the present invention, For example, the broken line in Fig. 2 (c) cannot be detected with conventional equipment.
The received signal as indicated by X ₂ can also be reliably detected as indicated by the solid line X ₂ ' in FIG. 4E.

Incidentally, if the circuit impedance decreases during the operation of the impedance variable means 10 after the above-mentioned time point _t1 , if the circuit impedance continues to decrease for too long, the received signal will also be emitted.

Therefore, in the illustrated embodiment, the light emission intensity of the light source 13 in the operation control means 12 that controls the operation of the variable impedance means 10 is determined by the lighting circuit 1.
The circuit impedance is set to be gradually weakened by the voltage signal as shown in FIG.

Further, although it is unnecessary to describe it in detail, the energy that can be released due to the reduction in circuit impedance by the impedance control means 9 described above in the present invention is stored in the piezoelectric element of the piezoelectric element and the diaphragm etc. that constitute the piezoelectric sensor 2. Although most of the energy is stored in the diaphragm, for example, the energy stored in the diaphragm is smaller than in conventional devices due to the above-mentioned operation, there is a risk that it may cause development that causes the piezoelectric element to vibrate. It is also clear that the ultrasonic transmitter/receiver according to the present invention can obtain more preferable transmitting operation characteristics when used in combination with the so-called Q-dump method that mechanically suppresses the vibration operation described at the beginning.

FIG. 5 is an electric circuit diagram showing another embodiment of the ultrasonic transmitter/receiver according to the present invention. The same numbers as those in FIG. A DC current is generated and supplied to diode 6, and approximately 0.6 to 0.8V is applied to point c in the figure.
An external power supply device is shown that generates a DC voltage that drops from .

As is clear from FIG. 5, in this embodiment, the function of the photodynamic body 11 forming the variable impedance means 10 in the embodiment shown in FIG. This is achieved by using one diode 6 of the diodes 6 and 7 connected in antiparallel, and has an external power supply 15 as the operation control means 12. Needless to say, the structure is simpler than that of the previous embodiment. It's summery.

Now, the operation of the embodiment shown in FIG. 5 will be explained below.

First, the operation of the transmitting circuit 1 is exactly the same as that of conventional devices, and for example, when transmitting ultrasonic waves from _t0 to _t1 , a transmitting signal as shown in FIG. 6A is generated.

Therefore, at point a, which is the input/output end of the piezoelectric sensor 2, a signal as shown at time _t0 to _t1 in FIG. 6B appears.

Next, in this embodiment, after the time point _t1 when the supply of the transmission signal is stopped, the external power supply device 15 outputs a direct current as shown in FIG. 6C.

Therefore, after the above time point _t1 , the diode 6 becomes conductive, and the potential at point c in the figure becomes approximately
After the DC potential is set to 0.6V to 0.8V, it gradually decreases as the DC current decreases, and this state is due to the fact that the circuit impedance seen from the piezoelectric sensor 2 has significantly decreased. It won't happen.

On the other hand, the tailing phenomenon that has been a problem in conventional devices is caused by the energy stored in the piezoelectric sensor 2 during the transmission operation.
This was a development in which a minute alternating current signal lower than the conduction potential of the anti-parallel diodes 6 and 7 was generated at point a in the figure due to its emission through the diodes 6 and 7.

That is, in the case of the conventional device, since neither of the diodes 6 and 7 is conductive, the AC signal below the conduction level of the diode due to the energy stored in the piezoelectric sensor 2 is generated after time t ₁ in FIG. It appeared for a long time.

However, in the embodiment shown in FIG. 5, the external power supply 15 makes the diode 6 conductive at time _t1 , so the above-mentioned minute AC signal does not flow as a current through the diode 6. That is, it is consumed in the diode 6 while being superimposed on the DC potential at point c in the figure.

In other words, the energy stored in the piezoelectric sensor 2 is released through the diode 6 because the circuit impedance seen from the piezoelectric sensor 2 is greatly reduced due to the conduction of the diode 6. be.

Therefore, the same effect as the above-mentioned embodiment, namely,
This means that the falling characteristics in the transmission operation can be greatly improved.

It goes without saying that the signal waveform at point a, which is the input/output terminal of the piezoelectric sensor 2 after the supply of the transmission signal is stopped, becomes as shown in FIG. It will converge to the same level.

Although not shown, the circuit impedance fluctuation characteristics due to conduction of the diode 6 and the signal characteristics appearing at point D of the amplifying section 3 are the same as those of the photoconductor shown in FIG. It goes without saying that this characteristic is similar to the resistance value change characteristic, and is the same as the signal characteristic at point b of the amplifying section 3 in FIG. 4C.

Effects of the Invention The ultrasonic transmitting/receiving device according to the present invention has an impedance control means that lowers the circuit impedance seen from the piezoelectric sensor in order to release the energy stored in the piezoelectric sensor during the transmitting operation until an arbitrary period has elapsed from the end of the transmitting operation. Because of this, it can be expected that the vibration motion due to the inherent characteristics of the piezoelectric sensor element after the end of the transmission operation can be rapidly attenuated. This has the effect of being able to reliably detect a received signal resulting from reception of a radiation wave from a target object at a very close distance, which otherwise could not be detected.

Therefore, when applied to a distance measuring device, for example, it can be expected to have a practical effect of being able to measure extremely close distances of about 20 cm, which was impossible in the past.

[Brief explanation of drawings]

Fig. 1 is an electric circuit diagram of an ultrasonic transmitting/receiving device using a single piezoelectric sensor which is conventionally known, Fig. 2 is a signal waveform diagram at an arbitrary point in the conventional example of Fig. 1, and Fig. 3 is a diagram according to the present invention. An electric circuit diagram showing one embodiment of the ultrasonic transmitting/receiving device, FIG. 4 is a signal waveform diagram at an arbitrary point in the embodiment of FIG. 3, and FIG. 5 shows another embodiment of the ultrasonic transmitting/receiving device according to the present invention. The electric circuit diagram, FIG. 6, shows signal waveform diagrams at arbitrary points in the embodiment of FIG. 5, respectively. DESCRIPTION OF SYMBOLS 1... Transmission circuit, 2... Piezoelectric ceramic sensor, 3... Amplifying section, 9... Impedance control means, 10... Impedance variable means, 11...
Photoconductor, 12...Operation control means, 13...Light source, 14...Lighting circuit.

Claims (1)

[Claims] 1. A single piezoelectric ceramic sensor that is an ultrasonic transmitter/receiver, a transmission circuit that supplies an alternating current signal at a transmission frequency to the piezoelectric ceramic sensor as a transmission signal, and a transmission circuit that is connected in parallel with the piezoelectric ceramic sensor. an impedance control means comprising a connected impedance reduction means and an operation control means for controlling the operation timing of the impedance reduction means in conjunction with the supply state of the transmission signal; and amplification of the signal appearing at both ends of the piezoelectric ceramic sensor. The impedance lowering means changes its own electrical characteristics by operating to lower the circuit impedance seen from the piezoelectric ceramic sensor, and the operation control means lowers the circuit impedance seen from the piezoelectric ceramic sensor. An ultrasonic transmitting/receiving device that starts the operation of the impedance reducing means in conjunction with stopping the supply of the signal, and stops the operation of the impedance reducing means at an appropriate time after the supply of the transmission signal stops. 2. The impedance control means includes an impedance lowering means made of a photoconductor connected in parallel to a piezoelectric ceramic sensor, a light source that supplies emitted light to the photoconductor, and a sawtooth that changes the intensity of the emitted light from strong to weak. 2. The ultrasonic transmitting/receiving device according to claim 1, wherein the ultrasonic transmitting/receiving device is controlled by operation control means comprising a lighting circuit that supplies a pulse voltage to the light source in conjunction with stopping the supply of the transmission signal. 3. The amplification section includes a series body consisting of a first coupling capacitor connected to both ends of the piezoelectric ceramic sensor and a pair of protection diodes connected in antiparallel, and the first coupling capacitor and the protection diode. and an amplifier connected to the other end of the second coupling capacitor, and the impedance control means has an output end connected to the connection point. At the same time, a sawtooth pulse signal is generated from the output end, which reaches a conduction level sufficient to instantaneously make one of the protection diodes conductive in conjunction with the stoppage of the supply of the transmission signal, and thereafter gradually reaches a non-conduction level; comprising an operation control means consisting of an external power supply device which makes one of the protection diodes conductive by outputting an output;
The ultrasonic transmitting/receiving device according to claim 1, which uses one as an impedance variable means.