JPH0447788B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a so-called ultrasonic distance measuring device that measures the distance to a target object using the transmission and reception of ultrasonic waves,
The present invention relates to an ultrasonic transceiver used in a so-called ultrasonic object detection device that detects the presence or absence of an object, and particularly relates to an ultrasonic transceiver having a single piezoelectric ceramic sensor as an ultrasonic transducer. .

BACKGROUND ART In recent years, with the advancement of measurement technology, various types of ultrasonic distance measuring devices and ultrasonic object detection devices such as those mentioned above have been proposed and put into practical use, for example, for use in automatic focusing devices of cameras and back sensors of automobiles. has been made into

Furthermore, in the ultrasonic transmitter/receiver of the above device, a capacitor type sensor or a piezoelectric ceramic sensor is well known as an ultrasonic wave transmitter/receiver that transmits and receives ultrasonic waves in the same part.

Problems to be Solved by the Invention As mentioned above, two types of ultrasonic transducers are well known as ultrasonic transducers that both transmit and receive ultrasonic waves. It has been recognized that capacitor type sensors are disadvantageous in terms of sensitivity, cost, and temperature characteristics compared to piezoelectric ceramic sensors.

However, it is well known that when considering distance measurement or object detection operations for a target object located at a very short distance of about 30 cm, for example, a capacitor type sensor is more advantageous than a piezoelectric type ceramic sensor.

This means that capacitor-type sensors can utilize a relatively low mechanical Q, making it possible, for example, to have steep ultrasonic transmission operating characteristics over a predetermined period of time, whereas piezoelectric-type ceramic sensors It is clear that since the Q is high and the vibration operation continues even if the transmission operation is stopped, the transmission operation cannot be made steep.

In general, a distance measuring device or an object detecting device using ultrasonic waves cannot basically achieve its functions unless it performs an operation of detecting whether or not a reflected wave from a target object is received.

Therefore, when there is a target object at a short distance of about 30cm as mentioned above, the time from when the ultrasound is transmitted until the reflected wave returns is extremely short, so the transmission operation characteristics are steep. If the vibration operation is performed even after the predetermined transmission operation ends, when transmitting and receiving ultrasonic waves at the same part, if the vibration operation does not end within the above short time, the reflected wave from the target object will not be received. It becomes impossible to distinguish it from the movement of time.

From this point of view, a capacitor type sensor is more advantageous in distance measuring operations and object detection operations for a target object at a short distance, as it rapidly stops vibrating after the transmission operation is completed.

By the way, among the devices actually used,
When we investigated the short-range operation of ultrasonic distance measurement devices used in camera automatic focusing devices, we found that when using a capacitor-type sensor, it can be used from a distance of about 27 cm. However, when using a piezoelectric ceramic sensor, it is only possible to measure distances from a distance of about 1 meter, and when it comes to distance measurement only at short distances, capacitor type sensors are far more effective. It was confirmed that the sensor was superior.

However, the advantages of piezoelectric ceramic sensors over capacitor-type sensors, such as their price, cannot be ignored when considering practical application.
At present, there is a strong desire to improve the short-range operation limit of piezoelectric ceramic sensors.

The present invention has been made in consideration of the above-mentioned points, and its purpose is to create an ultrasonic transducer using a piezoelectric ceramic sensor that can reliably receive reflected waves from a short distance of about 25 cm. An object of the present invention is to provide an ultrasonic transmitting/receiving device used as an ultrasonic transceiver.

Means for Solving the Problems An ultrasonic transmitter/receiver according to the present invention includes a single piezoelectric ceramic sensor that is an ultrasonic transducer, and a transmitter that supplies an alternating current signal having a transmission frequency as a transmission signal to the sensor for a predetermined period of time. a signal amplifying section including a circuit section, an amplifier for amplifying a signal received by the sensor, and a plurality of coupling capacitors coupling the amplifier and the sensor; It is configured to include a DC voltage supply means for supplying a falling DC voltage via the signal amplification section for a predetermined period arbitrarily determined by the short distance limit to the target object to be detected.

Function Since the ultrasonic transmitting/receiving device according to the present invention is configured as described above, a single piezoelectric ceramic sensor receives a voltage that decreases over time via a signal amplifying section until an arbitrary period has elapsed from the end of the transmitting operation. is applied, and at the same time, the energy accumulated in the piezoelectric ceramic sensor during the transmission operation is released via the signal amplification section. Therefore, it is possible to rapidly attenuate the vibration operation after the transmission operation due to the characteristics unique to the element.

Embodiment Hereinafter, an ultrasonic transmitter/receiver according to the present invention will be described.

FIG. 1 is an electric circuit diagram showing an embodiment of an ultrasonic transmitting/receiving device according to the present invention, and in the figure, a transistor 1 and a transformer 2 constitute a conventionally well-known transmitting circuit section. That is, transistor 1 is A
The transformer 2 amplifies the transmit operating signal having the transmit frequency supplied to the base indicated by the dots, and the transformer 2
By supplying a voltage V at a predetermined level to the input terminal indicated by a dot for a predetermined period, for example, 500 μs, a transmission signal is outputted to the secondary side together with the transmission operation signal.

The DC voltage supply means 3, which is a feature of the present invention, includes a diode 4 and a transformer 2 for rectifying the transmission signal.
, a capacitor 5 forming a vibration system, and a discharging resistor 6 connected in parallel to each of the diode 4 and capacitor 5 via a signal amplifying section 8 to be described later.

The signal amplifying section 8 is a circuit section that amplifies the received signal received by the single piezoelectric ceramic sensor 7, and includes an amplifier 9, and first and second coupling capacitors 10 that couple the amplifier 9 and the sensor 7. ,11
It also includes two protection diodes 12 and 13 connected in antiparallel to protect the amplifier 9, which is connected between the connection point of the coupling capacitors 10 and 11 and the ground.

Now, while a transmitting operation signal having a transmitting frequency as shown in Figure 2A is being supplied to point A in Figure 1, one end of the primary winding of the transformer 2, which is indicated by point B in the figure, is being supplied to point A in Figure 1. , a predetermined voltage V having a period T is applied at a time
If the signal is supplied from T1 to T2, transistor 1 will operate in synchronization with the previous transmission frequency.

Therefore, the transformer 2 transmits an AC signal, which is conventionally used as a transmission signal having a transmission frequency, at point C, which is the output end of the secondary winding, at time T1 in FIG. 2B.
The output will be as shown in T2.

However, in the illustrated embodiment of the present invention, the AC signal at the point C is controlled by the DC voltage supply means 3 consisting of the diode 4, etc., so that one end D of the sensor 7 is , an oscillating voltage as shown from time T1 to T2 in FIG. 2C is output.

That is, a transmission signal in the form of a DC biased alternating current signal as shown in FIG.

Next, consider the time after time T2 when the AC signal at point C disappears.

When the energy supply to the primary side of the transformer 2 is stopped and the AC signal disappears at time T2, the transformer 2, the DC voltage supply means 3, and the piezoelectric ceramic sensor 7 in the illustrated circuit need not be described in detail. A vibrational movement will occur between the two.

When the vibration operation is performed, the capacitor 5 of the DC voltage supply means 3 is instantly charged with the voltage obtained by rectifying the vibration voltage generated by the vibration operation with the diode 4.

However, as is clear from FIG. 1, the charge in the capacitor 5 is stored in a parallel relationship with the capacitor 5 through the signal amplifying section 8, since the resistor 6 is connected across the first coupling capacitor 10. Since the resistor 6 is connected to
It will be released through etc.

As a result, in the present invention, the state of one end D after time T2 is controlled by the DC voltage supply means 3, piezoelectric ceramic sensor 7, and signal amplifying section 8, for example, as shown in FIG. 2C after time T2. A DC oscillating voltage appears whose peak decreases over time.

In other words, the capacitor 5 is first charged to an arbitrary predetermined level by the vibration operation as described above, and then the charged charge is discharged according to a time constant determined between the capacitor 5 and the resistor 6, etc., and at this time, At the same time, the energy stored in the piezoelectric ceramic sensor 7 that had been stored during the transmission operation is also released, and therefore, a DC oscillating voltage appears at one end D in the figure, which gradually decreases over time from the above arbitrary level. So it becomes.

Now, if we look at the generation period of the DC oscillating voltage after the above-mentioned time T2, it will follow the time constant determined by the above-mentioned capacitor 5 and resistor 6. As described above, control can be performed in an extremely short time, within about 1 ms. That is, according to the present invention, for example
The DC oscillating voltage can be converged within 1.3 ms, which is sufficiently shorter than the time required to detect reflected waves from a short distance of about 25 cm.

Although not mentioned in the previous explanation, the vibration waveform at one end D is generated by the piezoelectric ceramic sensor 7 electrically as a component in which the conductor C is connected in parallel to a series body of an inductor L, a resistor R, and a conductor C. In order to function, the signal waveform output to point C has a slightly gentler waveform.

Effects of the Invention In the ultrasonic transmitting/receiving device according to the present invention, as described above, the DC voltage supply means operates via the signal amplifying section in synchronization with the stop of the transmitting operation, so that the piezoelectric ceramic sensor is not affected during the transmitting operation. The accumulated energy is released through the signal amplification section when the DC voltage supply means is operated, and the vibration operation after the transmission operation due to the inherent characteristics of the piezoelectric ceramic sensor element can be rapidly damped. As a result, the time from transmitting ultrasonic waves to the return of reflected waves is extremely short, approximately 30 cm.
This has the effect of being able to reliably receive the reflected waves from target objects located at close distances in front and behind.

[Brief explanation of the drawing]

FIG. 1 is an electric circuit diagram showing an embodiment of an ultrasonic transmitter/receiver according to the present invention, and FIG. 2 is a signal waveform diagram at a predetermined point in FIG. DESCRIPTION OF SYMBOLS 1...Transistor, 2...Transformer, 3...DC voltage supply means, 4...Diode, 5...Capacitor,
6... Resistor, 7... Piezoelectric ceramic sensor, 8... Signal amplification section, 9... Amplifier, 10, 11... Coupling capacitor, 12, 13... Protection diode.

Claims (1)

[Scope of Claims] 1. A single piezoelectric ceramic sensor that is an ultrasonic transducer, a transmission circuit section that supplies an alternating current signal having a transmission frequency to the piezoelectric ceramic sensor as a transmission signal for a predetermined period of time, and the piezoelectric a signal amplifying section including an amplifier for amplifying a received signal received by the piezoelectric ceramic sensor; a signal amplifying section including a plurality of coupling capacitors coupling the amplifier and the piezoelectric ceramic sensor; DC voltage supply means for supplying a DC voltage that decreases over time to the ceramic sensor via the signal amplification section for a predetermined period arbitrarily determined by the short distance limit to the target object to be detected. Ultrasonic transceiver device. 2. The DC voltage supply means includes a capacitor inserted in series in the power supply loop to the piezoelectric ceramic sensor of the transmitting circuit section, a diode connected in parallel with the sensor, and a diode connected in parallel with the capacitor and a signal source. The ultrasonic transmitting/receiving device according to claim 1, comprising a resistor connected to both ends of one of the plurality of coupling capacitors of the amplifying section and forming a discharge loop of the capacitor via the signal amplifying section. .