JPS6123983A - Ultrasonic wave transmitting and receiving device - Google Patents

Abstract

PURPOSE:To end the oscillating operation of a piezoelectric sensor speedily and to receive a reflected wave from a short-distance target, and measuring its range by discharging energy accumulated in the piezoelectric sensor during transmission within a specific time after the end of transmitting operation. CONSTITUTION:The gate signal of a means 15 is supplied to the gate of a thyristor 14 at the end of transmitting operation associatively with the stop of the supply of the transmit signal of a circuit 1, and the thyristor 14 is held on until a capacitor for a power source is discharged. Therefore, the energy accumulated in the sensor 2 durin the transmitting operation is consumed by a resistance 13 speedily to reduce a trailing phenomenon after the transmitting operation, thereby lowering the signal at a point (b) of an amplification part 3 to the zero level in a short time. Consequently, the received signal of a reflected wave from the short-distance body is detected and the short distance is measured.

Description

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

Conventional configurations and their problems In recent years, various object detection devices that utilize ultrasonic transmission and reception, such as distance measuring devices such as cameras, have been put into practical use. Devices that can detect this have also appeared.

Such a device uses an electrostatic sensor as an ultrasonic transmitter/receiver, and makes effective use of its low mechanical Q, i.e.,
Even at short distances as mentioned above, the advantage that the vibration operation of the ultrasonic transmitter/receiver is attenuated as soon as the supply of the transmission signal is stopped, and the falling edge of the transmission operation can be made steep, can be fully utilized. That's why there is.

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. Although the mechanical Q
Due to the high value, the falling characteristic during transmission operation is extremely poor, and when connected to a signal amplification section, a so-called tailing phenomenon occurs, making it extremely difficult to identify the received signal due to the reflected wave from a short distance of about 3 o. It is known that there is a problem in that object detection cannot be performed at short distances.

To further explain this point, as mentioned above, piezoelectric sensors usually have a high mechanical Q, so once they are vibrated with electrical energy, they will release the applied energy even if the electrical energy is removed. The vibration operation will continue until the end.

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 high mechanical Q, and as a result, the falling characteristic of the transmission operation is steep. So it didn't happen.

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

Therefore, if the falling characteristic in the 2nd transmission operation is not steep and the vibration operation is performed even after the transmission operation is completed, the previous approximately 30c
If there is a target object at a short distance of m, the time from when the ultrasonic wave is transmitted until the reflected wave returns is extremely short, so if the vibration operation does not end within the extremely short time. Therefore, when transmitting and receiving ultrasonic waves using a single piezoelectric sensor, it becomes impossible to distinguish between the vibrational motion inherent to the element after the transmission operation is completed and the vibrational motion due to reception of reflected waves.

As a result, as mentioned earlier, in an ultrasonic transmitter/receiver using a single piezoelectric sensor, approximately 1'm j
It was generally recognized that distance measuring operations, etc., could not be performed on a target object that was too close to the target object.

The relationship as described above will be briefly explained below using the drawings.

FIG. 1 is a schematic electrical circuit diagram of an ultrasonic transmitting/receiving device using a conventionally known single piezoelectric sensor, including a transmitting circuit 1, a piezoelectric sensor 2, a first . Second coupling capacitor 4,5. The first one is connected in anti-parallel. 2nd diode 6.7% - and amplifier 8
This shows an amplifying section 3 consisting of.

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

In FIG. 1, when a transmission signal as shown in FIG. 2(A) is formed by a transmission circuit 1 and supplied to a piezoelectric sensor 2 to transmit ultrasonic waves, a A signal as shown in FIG. 2 (b) appears at the point.

That is, at point a, there is a voltage lower than the conduction voltage of the diode 6.7 connected in antiparallel, which indicates 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 with a peak value will result.

On the other hand, the ultrasonic waves transmitted from the piezoelectric sensor 2 are received again by the piezoelectric sensor 2 by being reflected by, for example, a target object located at a sufficiently distant distance. (b) A received signal indicated by an X will appear in (b).

The signal at point a is the first signal. Second coupling capacitor 4, 5
As a result, the amplifying section 3 outputs a signal containing the received signal X1 as shown in FIG. 2 (C) at point b in the figure, and the following , distance information and the like are obtained by detecting the point in time when the received signal X1 is generated by the amplifying section 3.

Now, if we look at the waveforms during communication among the output waveforms shown in FIG. 2(C) of the amplifying section 3, we can see that after the time t1 when the supply of the transmission signal shown in FIG. 2(B) is stopped. Also, the alternating current signal based on the vibrational motion inherent to the element of the piezoelectric sensor 2 described above 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 X2 between the above time t1 and t2, the waveform X2 will be the same as the above time t1.
Since it is included in the signal due to the vibrational operation inherent to the element of the piezoelectric sensor 2 between t2 and t2, it cannot be distinguished as a received signal, and it is naturally impossible to detect the point in time when it occurs.

That is, the target object located within the distance from which the reflected wave returns between the above-mentioned time points t1 and t2 cannot be detected by the conventional ultrasonic transceiver device using a single piezoelectric sensor, as described above. That's why.

By the way, in recent years, as a piezoelectric sensor that takes the above-mentioned problems into consideration, vibration motion in the piezoelectric sensor is mechanically suppressed. In other words, by pressing the piezoelectric element and aluminum diaphragm that make up the piezoelectric sensor with silicone rubber, etc., the so-called Q
Various types of sensors with stamps have been proposed.

However, the above-mentioned Q-dump method also requires a Q-dump with extremely strong suppressing power when trying to detect a received signal at a short distance of about 30α as described above.
The problem is that the sensitivity is significantly reduced. In other words, it is difficult to sufficiently suppress the trailing 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 short distances, we will receive reflected waves from target objects at far distances. This results in a problem in that it cannot be output as a signal.

OBJECTS OF THE INVENTION An object of the present invention was to take into consideration the problems of the conventional devices as described above, and to greatly improve the falling characteristic in the transmitting operation due to the inherent characteristics of the piezoelectric sensor element.
An object of the present invention is to provide an ultrasonic transmitting/receiving device using a single piezoelectric sensor capable of detecting a target object around 0α.

Another object of the present invention is to reduce the circuit impedance seen from the piezoelectric sensor by using the charging or discharging operation of the capacitor until an arbitrary point after the supply of the transmission signal is stopped without applying a DC signal to the piezoelectric sensor. An object of the present invention is to provide an ultrasonic transmitting/receiving device that can rapidly release the kinetic energy stored in a sensor and can significantly reduce the trailing phenomenon caused by the inherent characteristics of the device.

Structure 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, an impedance variable means connected in parallel with the piezoelectric sensor, and a transmitting signal that connects the impedance variable means to the piezoelectric sensor. The piezoelectric sensor is composed of an impedance control means consisting of a power supply capacitor that is kept in an operating state by charging or discharging until an arbitrary point after the supply of the piezoelectric sensor is stopped, and a signal amplification section that amplifies the signal appearing at both ends of the piezoelectric sensor.

DESCRIPTION OF THE EMBODIMENT 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 parts.

Reference numeral 9 denotes impedance control means that significantly reduces the circuit impedance for AC signals seen from both ends of the piezoelectric sensor 2 in conjunction with the end of the transmission operation, and as is clear from FIG. a first series body consisting of a power supply capacitor 1Q and a rectifier diode 11; a diode 12 and a resistor 13 connected to both ends of the rectifier diode 11 to form a discharge loop for the charge of the power supply capacitor 10; and a second series body which is an impedance variable means consisting of a thyristor 14 and a thyristor 14. Portrait 5 is a gate circuit that supplies a gate signal to the gate of thyristor 14 in conjunction with the stop of supply of the transmission signal from transmission circuit 1.

Hereinafter, the operation 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 the signal waveform diagram at an arbitrary point in the above embodiment shown in FIG.

The transmitting circuit 1 is similar to the conventional device shown in FIG.
When transmitting ultrasonic waves, at time t0 to t1, the fourth
A transmission signal as shown in figure (a) is generated.

This transmission signal is supplied to the piezoelectric sensor 2, the impedance control means 9, etc., and therefore the piezoelectric sensor 2 transmits ultrasonic waves, and the eight points that are the input and output terminals of the ultrasonic wave are supplied to the piezoelectric sensor 2, the impedance control means 9, etc. A signal waveform as shown in FIG. Thus, nine charging operations are performed. That is, a signal as shown at time t0 to t1 in FIG. 4(c) appears at point C at one end of the power supply capacitor 1°.

By the way, in one embodiment of the ultrasonic transmitter/receiver of the present invention shown in FIG. 3, at time t when the transmission operation in which the transmission signal is supplied as described above is completed, that is, the supply of the transmission signal is stopped. In conjunction, a gate signal as shown in FIG. 4) is supplied from the gate means 15 to the gate of the thyristor 14.

Therefore, the cyrisk 14 becomes conductive at the above-mentioned time point t1, and needless to say, the conductive state is maintained until the charge in the power supply capacitor 1o is discharged. That is, since the potential of the point C at one end of the power supply capacitor 10 is a DC potential due to charging, the impedance variable means is activated by the conduction of the thyristor 14, and the charged charge is discharged via the diode 12, the resistor 13, and the thyristor 14. become.

Now, considering the conduction of the thyristor 14 due to the release of the charge charged in the power supply capacitor 10, that is, the operation of the impedance variable means, a circuit for an AC signal whose potential width between peaks is within the range of the potential at the 0 point. This is nothing more than an extremely low impedance.

In other words, if the thyristor 14 can maintain conduction while the AC voltage signal is superimposed on the DC voltage at the 0 point, the AC voltage signal will be consumed by the resistor 13 and the like.

Now, if we look at the tailing phenomenon of the piezoelectric sensor 2, which was a problem in the conventional device mentioned at the beginning, and the DC potential at the zero point in the illustrated embodiment, firstly, the two tailing phenomena are accumulated during the transmission operation. This is a phenomenon in which an alternating current voltage signal waveform is generated at point a due to the vibration operation based on the energy generated.As mentioned above, the potential width is not large and is less than the conduction voltage of the diode 6.7 connected in antiparallel. This is a phenomenon that takes a long time.

Furthermore, regarding the DC potential at point C, the voltage level of the transmission signal is quite high, so by appropriately setting the capacity of the power supply capacitor 1o, etc., the AC voltage signal generated at the piezoelectric sensor 2 can be superimposed very easily. Thyristor 1 is enough
Of course, in the ultrasonic transmitter/receiver according to the present invention, the potential at point C is set to a certain high potential as described above.

Therefore, in the present invention, the energy stored in the piezoelectric sensor 2 during the transmission operation can be rapidly consumed by the resistor 13 and the like.

That is, in the ultrasonic transmitting/receiving device of the present invention, the vibration operation after the time t1 when the supply of the transmission signal to the piezoelectric sensor 2 is stopped is rapidly attenuated, and the signal waveform that appears due to the vibration is also as shown in FIG. After time t1, it rapidly converges to the zero level as shown at tit.

In other words, the trailing phenomenon after the transmission operation is significantly reduced,
This means that the falling characteristics in the transmission operation have been greatly improved.

Therefore, as shown in FIG. 4(e), the signal at point b of the amplifying section 3 is also naturally transmitted from time t1 to t1 after the transmission operation is completed.
As a result, the ultrasonic transmitter/receiver according to the present invention can detect the ultrasonic waves that cannot be detected by the conventional device, for example, as shown by the broken line X2 in FIG. 2 (c). Even such received signals can be reliably detected as shown by the solid line X' in FIG. 4(E).

Incidentally, the state of point C at one end of the power supply capacitor 10 during operation after time t1 as described above is as follows:
If the piezoelectric sensor 4 is maintained in a conductive state, the received signal based on the reception of the reflected wave will also be consumed by the resistor 13, etc. Therefore, as shown in FIG. Control is performed by appropriately setting the discharge time constant of the power supply capacitor 10 so that the AC voltage signal rapidly converges to zero level after passing through a state in which the AC voltage signal is superimposed due to vibrations based on the characteristics inherent to the element.

Furthermore, although the supply of the gate signal shown in FIG.
If the charged charge is released and its discharge current becomes less than the above-mentioned holding current, it will naturally become non-conductive.In addition, if the supply is forcibly stopped, it will have an adverse effect on the circuit including the piezoelectric sensor 2. Therefore, it is not necessary to perform the supply stop operation in a hurry. In other words, it is necessary to stop the supply immediately after the reception signal detection operation has been completed, without causing any inconvenience to the circuit system, for example, immediately before the next ultrasonic wave transmission operation. Needless to say, it's a good thing.

Furthermore, although it is not necessary to describe in detail, the above-mentioned power supply capacitor 1o after the above-mentioned transmission operation in the present invention is
Most of the energy that can be consumed due to the decrease in circuit impedance during the period based on the discharge time constant is the energy of the piezoelectric element of the piezoelectric element of the appropriate diaphragm constituting the piezoelectric sensor 2; Although the energy stored in the plate is smaller than that of the conventional device due to the above operation, there is a risk that the energy stored in the plate may cause the piezoelectric element to vibrate. More preferable transmission operation characteristics can be obtained by using the so-called Q-dump method, which mechanically suppresses vibration operation, as described above.

FIG. 5 is an electric circuit diagram showing another embodiment of the ultrasonic transmitting/receiving device according to the present invention, and FIG.

Figures with the same numbers as those in FIG. 3 indicate the same functional members.

As is clear from FIG. 6, this embodiment
The function of the diode 12 and thyristor 14 forming the impedance variable means in the embodiment shown in the figure is attempted to be achieved by one diode 6 connected in anti-parallel and forming a part of the amplifier section 3. Needless to say, this embodiment has a simpler configuration than the previous embodiment.

Now, regarding the operation of the embodiment shown in FIG. 6, first, the charging operation of the power supply capacitor 10 during transmission is exactly the same as in the previous embodiment.

Therefore, when the charging voltage value becomes high, the diode 6 becomes always conductive even during transmission, and the transmission signal that was not transmitted at point a also tries to escape through the capacitor 4 and diode 6. , the voltage level of the transmitted signal during transmission is extremely high, and the AC signal that is not supplied to the piezoelectric sensor 2 and leaves the piezoelectric sensor 2 ends up being the same as the conventional device shown in FIG. The signal remains at a potential of approximately ±0.6V, and all of the signal is not lost, so there is no particular effect on the transmission operation.

Next, as in the previous embodiment, when the supply of the transmission signal is stopped, the diode 6 is maintained in a conductive state by the charge of the power supply capacitor 1Q, so that the AC voltage generated by the characteristics inherent to the element of the piezoelectric sensor 2 is reduced. The signal is superimposed on the discharge of the charged charge, that is, the level of the AC voltage signal is not large, less than ±○, eV, and therefore it is superimposed on the DC component of the power supply capacitor 10 and is applied to the capacitor 4 or the resistor 13. , will be emitted via the diode 6.

That is, the energy stored during transmission by the piezoelectric sensor 2 can be rapidly released due to the conduction of the diode 6, as in the previous embodiment, and of course the signal waveforms at points a and b can be rapidly released, although not shown. It will converge to zero level.

Therefore, it is possible to reliably detect a received signal by receiving a reflected wave from a target object at a very close distance, which could not be detected by the conventional device.

FIG. 6 is an electric circuit diagram showing another embodiment of the ultrasonic transmitting/receiving device according to the present invention, and FIG.

Figures with the same numbers as in Figures 3 and 5 indicate the same functional components;
Reference numeral 16 indicates a transistor which is turned on at the end of the transmission operation, and reference numerals 17, 18, and 19 each indicate a resistor.

The operation of the embodiment shown in FIG. 7 will be described below with reference to a signal waveform diagram at an arbitrary point in the diagram shown in FIG.

Now, when the transmission circuit 1 generates a transmission signal as shown in FIG. 7(a) at time t0 to t1 and supplies it to the piezoelectric sensor 2, as in the conventional device and the embodiment described above, as shown in FIG. 7(b). A signal from time t0 to t1 appears at point a in the figure.

At this time, the transistor 16 is still held in a non-conductive state, so that the power supply capacitor 10 is not charged by the arbitrary power supply Vc.

In this embodiment, a conductive signal as shown in FIG. 7e is supplied from the gate means 15 to the base of the transistor 16 via the base resistor 17 at time t1 when the supply of the transmission signal is stopped. ing.

Therefore, at time t1, transistor 16 is conductive;
As a result, the time t1 when the power supply capacitor 1o is charged
In other words, a charging current flows through the resistor 18 and the diode 6.

Now, if we consider the state in which the charging current of the power supply capacitor 10 flows through the diode 6, although the operation of the power supply capacitor 10 is different from the discharging operation in the previous embodiment, the diode 6 itself is conductive. The state is the same as that of the previous embodiment.

Therefore, the 0 point in Figure 6 is the DC potential, for example about 0.6
Therefore, as in the previous embodiment, an AC signal due to the release of the energy stored in the piezoelectric sensor 2 can be released in a form superimposed on the DC potential.

It should be noted that the fact that the voltage signal waveform at the above point is as shown in FIG. 7 is beyond the scope of detailed description.

Therefore, even in the embodiment shown in FIG.
Similar to the embodiment shown in the figure, the trailing phenomenon after the transmitting operation of the piezoelectric sensor 2 can be made extremely short as shown after time t1 in FIG. This means that the characteristics can be significantly improved.

Furthermore, in the embodiment shown in FIG. 6, the charging operation, which is the operation of the power supply condenser 1Q to bring the diode 6 into a conductive state, is made such that it does not affect the power supply state to the piezoelectric sensor 2. That is, this is done without using the transmission signal for charging, and therefore the rise characteristics in the transmission operation can be improved compared to the previously described embodiments.

That is, in the embodiment described above, the power supply capacitor 1 that makes the thyristor 14 or the diode 6 conductive is
Since the charging operation, which is one of the operations of 0, is performed using the transmission signal, the power supply state of the piezoelectric sensor 2, especially the state at the start of power supply, is inevitably affected, and the rise characteristic in the transmission operation is As shown in Figure (B), the characteristics were gradual, but as shown in Figure 6 ((In the illustrated embodiment, the charging of the power supply capacitor 10 was performed without using the transmission signal, and the transmission operation Since it is started from the end point, unlike the previous embodiment, it does not affect the power supply state of the piezoelectric sensor 2, and the rise characteristic can be improved as shown in FIG. 7(b).

Such an improvement in the rise characteristic contributes to improving the accuracy of the ultrasonic transmitter/receiver, since it is desired that the rise characteristic be steeper in an ultrasonic transmitter/receiver whose main operation is to detect the generation point of a received signal. Becoming something is not a good thing.

Although not shown in the figure, the connection position of the power supply capacitor 10 is replaced with the resistor 19, and the gate signal supplied to the base of the transistor 16 is made into a signal having an inverse relationship to that shown in FIG. 7(c). It is not impossible to say that the impedance variable operation can be performed by the discharging operation of the power supply capacitor 10 as in the embodiment described above.

Effects of the Invention The ultrasonic transmitting/receiving device according to the present invention has impedance control means for releasing the energy stored in the piezoelectric sensor during transmission before a predetermined period of time has elapsed from the end of the transmission operation, so the transmission operation ends. It can be expected that the subsequent vibration action due to the inherent characteristics of the piezoelectric sensor element can be quickly terminated, and this action allows for the detection of extremely close target objects that were conventionally impossible to detect with a single piezoelectric sensor. This has the effect of being able to detect a received signal by receiving a reflected wave from.

For this reason, when applied to a distance measuring device, for example, it is possible to expect a practical effect of being able to measure short 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 well 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 of the present invention. FIG. 4 is a signal waveform diagram at an arbitrary point in the embodiment of FIG. 3, and FIGS. 1... Transmission circuit, 2... Piezoelectric ceramic sensor, 3... Amplifying section, 4, 5...
Coupling capacitor, 6.7... (anti-parallel) diode, 9... impedance control means, 1o...
...Power supply capacitor, 11... Rectifier diode, 12... Diode, 13... Resistor, 14... Thyristor, 15... Gate means , 16...transistor. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 3 Figure 5 Figure 6 Figure 7

Claims (4)

[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 at least two diodes. The variable impedance means connected in parallel with the piezoelectric ceramic sensor may perform a charging or discharging operation via the variable impedance means from any time after the supply of the transmission signal is started to any time after the supply is stopped. impedance control means consisting of a power supply capacitor that puts the impedance variable means into an operating state by performing the adjustment for a period of time; and an amplification section that amplifies the signal appearing at both ends of the piezoelectric ceramic sensor, An ultrasonic transmitting/receiving device characterized in that circuit impedance with respect to an alternating current signal is lowered during the arbitrary period in which the power supply capacitor is charged or discharged. (2) The impedance control means includes a first series body consisting of a power supply capacitor and a rectifying diode connected to both ends of the piezoelectric ceramic sensor, and a diode, a resistor, and a thyristor connected to both ends of the rectifying diode. and a gate means for outputting a gate signal that makes the thyristor conductive in conjunction with stopping the supply of the transmission signal. The ultrasonic transceiver device described in . (3) The amplifying section includes a first series body including a first coupling capacitor connected to both ends of the piezoelectric ceramic sensor and a pair of protection diodes connected in anti-parallel;
The impedance control means includes a second coupling capacitor having one end connected to a connection point between the coupling capacitor and the protection diode, and an amplifier connected to the other end of the second coupling capacitor. a second series body consisting of a power supply capacitor and a rectifying diode connected to both ends of the piezoelectric ceramic sensor; a second series body consisting of a resistor connected to both ends of the rectifying diode and one of the pair of protection diodes; 2. The ultrasonic transmitting/receiving device according to claim 1, comprising impedance variable means formed by three impedance units in series. (4) The amplification section includes a first series body including a first coupling capacitor connected to both ends of the piezoelectric ceramic sensor, a pair of protection diodes connected in antiparallel, and the first coupling capacitor. a second coupling capacitor, one end of which is connected to a connection point between the protection diode and the second coupling capacitor;
and an amplifier connected to the other end of the coupling capacitor. Consisting of a power supply capacitor connected to a connection point between the first coupling capacitor and the protection diode, and a gate means for outputting a gate signal that makes the switch element conductive in conjunction with stopping the supply of the transmission signal. An ultrasonic transmitting/receiving device according to claim 1.