JPH0569474B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a pulse-type ultrasonic detector that detects the presence of an object using ultrasonic pulses.

[Background technology] Conventional ultrasonic detectors detect the presence of an object based on the presence or absence of reflected waves of ultrasonic pulses from an object, and the time delay from the time the ultrasonic pulse is transmitted until the reflected waves from the object are received. There are things that can detect this.

FIG. 3 is a schematic diagram showing the change over time in the voltage between the terminals of the ultrasonic vibrator of the ultrasonic detector.
A transmitting signal is applied to the ultrasonic transducer used for both transmitting and receiving waves during the transmitting wave application period indicated by _t1 in the figure, and the ultrasonic pulse is transmitted from the ultrasonic transducer. In this type of ultrasonic detector, the ultrasonic transducer continues to vibrate even after a transmission signal is applied to the ultrasonic transducer, producing a so-called reverberant signal that attenuates over time as shown by A in the figure. Note that the straight line B in the figure indicates a reflected wave from an object, and the peak value of this reflected wave indicates that the level increases as it approaches the ultrasonic transducer (the less time passes). Since the above reverberant signal attenuates over time, if this reverberant signal attenuates below the threshold value V _th that is the object detection level, the received signal due to the reflected wave from the object will
If the presence of an object can be detected, but the reverberant signal has not attenuated below the threshold value V _th , and the ultrasound transducer receives a reflected wave from an object that exists in a short distance, the reverberant signal The presence of an object cannot be detected because it cannot be distinguished from the received signal due to the reflected wave from the object. In other words, conventional ultrasonic detectors have a problem of poor detection ability for objects at close range.

FIG. 4 shows the circuit configuration of such a conventional ultrasonic detector. This ultrasonic detector includes a transmitting means that drives an ultrasonic transducer 1 to transmit ultrasonic pulses, a transmitting signal generating circuit 2 that generates a transmitting signal,
It consists of a transmitting amplifier circuit 3 that amplifies the output of the transmitting signal generating circuit 2 to the driving level of the ultrasonic transducer 1, and receives the reflected waves of the ultrasonic pulses transmitted from the ultrasonic transducer 1 by objects. The wave receiving means for generating waves is constituted by a wave receiving circuit 4 that amplifies and detects the output of the ultrasonic transducer 1. The object detection means for detecting an object from the output of the wave receiving circuit 4 sets the output of the wave receiving circuit 4 to a threshold value.
A level detection circuit 5 that shapes the waveform of a digital signal that becomes high level when it is equal to or higher than a threshold value V _th when compared with V _th , and a gate signal creation circuit 6 that creates a gate signal based on the output of the transmission signal creation circuit 2 and a gate circuit 7 that extracts only the signal corresponding to the received signal due to the reflected wave by performing an AND process between the gate signal that is the output of this gate signal generation circuit 6 and the output of the level detection circuit 5, and this gate circuit 7. From the output, check whether there is a reflected wave of the ultrasonic pulse from an object,
Alternatively, it is configured with a detection circuit 8 that detects the presence of an object based on the time delay from the time when the ultrasonic pulse is transmitted until the reflected wave from the object is received.

In this conventional circuit, an ultrasonic transducer 1 is driven by a drive signal obtained by amplifying a transmitting signal, which is an output of a transmitting signal generating circuit 2, by a transmitting amplifier circuit 3. Transmit the ultrasonic pulse shown in c of a. Now, if there is an object in the detection area,
The amplified output of the wave receiving circuit 4 has a waveform shown in FIG. 5b. Note that d in Fig. 5 is a received signal due to a reflected wave from an object, and the output after amplification of this receiving circuit 4 includes the signal when an ultrasonic pulse is being transmitted from the ultrasonic transducer 1. Ultrasonic transducer 1 output E and reverberation signal H are included. The output of this wave receiving circuit 4 is compared with a threshold value V _th by a level detection circuit 5,
The fifth level becomes high level when the threshold value V _th or more.
The waveform is shaped into the digital signal shown in Figure c. The output of this level detection circuit 5 is AND-processed in the gate circuit 7 with the gate signal created by the gate creation circuit 6 shown in FIG. 5d, and only the signal corresponding to the received signal d in FIG. taken out. When an output is generated in the gate circuit 7 in this way, a high-level signal, which is a detection output indicating the presence of an object, is output from the detection circuit 8 as shown in FIG. 5e.

However, in this type of ultrasonic detector, if the ultrasonic transducer receives a reflected wave from a nearby object at a time when the reverberant signal has not attenuated below the threshold value V _th , the reverberation will occur. Since it becomes impossible to distinguish between the signal and the received signal due to the reflected wave from the object, the gate circuit 7 is opened later than the time _t2 when the reverberant signal becomes less than the threshold value _Vth . Therefore, even if a reflected wave from a nearby object is received during a period in which the reverberant signal has not attenuated below the threshold value V _th , the presence of the object cannot be detected. It was hot. In other words, conventional ultrasonic detectors have poor ability to detect objects at close range.

[Object of the Invention] The present invention has been made in view of the above-mentioned points, and its object is to provide an ultrasonic detector with improved ability to detect objects at close range.

[Disclosure of the Invention] (Structure) The present invention is a pulse-type ultrasonic detector that detects the presence of an object by transmitting ultrasonic pulses and receiving reflected waves from the object. a waveform shaping means for shaping and outputting the output after amplification and detection into a plurality of rectangular waveforms that become high level when the level is higher than the threshold value using a plurality of threshold values each having a different level; It has a rising edge detection means for detecting the rising edge of the rectangular wave signal output from the shaping means, and when the rising edge of the rectangular wave output from any of the waveform shaping means is detected after the ultrasonic pulse is transmitted, the presence of an object is detected. The waveform shaping means shapes the output after amplifying and detecting the received wave output into a rectangular waveform using a plurality of threshold values of different levels, and detects the object. By detecting that one of the rectangular wave outputs rises after transmitting the ultrasonic pulse with the detection means,
The received wave output contained in the reverberant signal can be detected as long as it is not completely hidden by the reverberant signal, and the presence of a nearby object that cannot normally be detected by the reverberant signal can also be detected.

(Example) An embodiment of the present invention is shown in FIGS. 1 and 2. FIG.

First, the reason why the present invention can detect the presence of a close object will be explained. The reverberant signal monotonically decreases and usually does not show an increasing trend. However, if there is an object at a close distance,
This reverberation signal shows an increasing tendency. Therefore, in the present invention, the tendency of the reverberation signal to increase is detected, thereby making it possible to detect the presence of a nearby object.

The ultrasonic detector of this embodiment also uses an ultrasonic transducer 1 for both transmitting and receiving waves, as shown in FIG. The transmitting means for driving the ultrasonic transducer 1 to transmit ultrasonic pulses is composed of a transmitting signal generating circuit 2 for generating a transmitting signal and an output of the transmitting signal generating circuit 2, as in the conventional example. A wave transmitting amplifier circuit 3 that amplifies the ultrasonic pulse to the driving level of the ultrasonic transducer 1, and a receiving means that receives the reflected wave of the ultrasonic pulse transmitted from the ultrasonic transducer 1 by an object, Vibrator 1
It consists of a wave receiving circuit 4 that amplifies and detects the output.
In this embodiment, a waveform shaping means is provided for shaping the waveform of the output of the wave receiving circuit 4 into a digital signal that becomes high level when the level is equal to or higher than the threshold value of each different level.
This waveform shaping means is composed of a plurality of level detection circuits 9 each having a threshold value of a different level (in this embodiment, a plurality of level detection circuits are shown as one block). . An object detecting means 12 that detects the presence of an object from the time delay from the time when the output of the level detecting circuit 9 rises after transmitting the ultrasonic pulse differentiates the output of each of the level detecting circuits 9. A differentiating circuit 10 (the number of differentiating circuits is provided in accordance with the number of level detecting circuits 9) 10, an OR circuit 11 which takes the logical sum of the respective outputs of the differentiating circuit 10, and an OR circuit 11 which calculates the value of the object from the output of the OR circuit 11. The output of this object detection means 12 is input to an output circuit 13, and this output circuit 13 drives a display, an alarm, etc.

The operation of this embodiment will be explained below with reference to FIG. As explained in the conventional example, the ultrasonic transducer 1 is driven by a drive signal obtained by amplifying the transmitting signal, which is the output of the transmitting signal generating circuit 2, by the transmitting amplifier circuit 3. An ultrasonic pulse shown in FIG. 1 is transmitted from the ultrasonic transducer 1. When an object exists in the detection area, the amplified output of the wave receiving circuit 4 has a waveform shown in FIG. 2b. Note that the amplified output of the wave receiving circuit 4 includes the received signal as well as the ultrasonic transducer 1 output E and the reverberant signal A when the ultrasonic transducer 1 is transmitting ultrasonic pulses. It is. Further, the gain of the amplification stage of this wave receiving circuit 4 is set so that the output will not be saturated even if the reverberant signal 1 and the received signal 2 are at the same level. The output of the wave receiving circuit 4 is compared with the respective threshold values V _a to V _d by the level detection circuit 9, and is waveform-shaped into a digital signal that becomes high level when the output is equal to or higher than the threshold value. The outputs of the level detection circuit 9 which performed level detection at the respective threshold values V _a to V _d are shown in FIGS. 2 c to f. The output of this level detection circuit 9 is the differential circuit 10.
The outputs of the differentiating circuit 10 shown in FIG. 2 g to j are obtained. By taking the logical sum of the outputs of the differentiating circuit 10 using the OR circuit 11, the negative pulse indicating the fall of the output of the level detection circuit 9 is removed, and the positive pulse indicating the rise of the output of the level detection circuit 9 is removed. Get only the output that was specified. This OR circuit 1
1 output is shown in Figure 2k. The occurrence of this output from the OR circuit 11 indicates that the received wave signal D exists, so when this output is input to the detection circuit 8, the detection circuit 8 outputs a detection signal shown in FIG. Output. Note that this OR circuit 11
Since a rising output occurs at the start of transmission of the ultrasonic pulse wave, the gate signal shown in FIG. Then, the output of the OR circuit 11 during the period when this gate signal is at a low level is not accepted. As described above, according to this embodiment, the level detection circuit 9 detects the level of the output of the ultrasonic transducer 1 using a plurality of threshold values having different levels, so that the received signal is not included in the reverberant signal. As long as the object is not completely hidden, the received signal can be detected. Therefore, by detecting the rising edge of the ultrasonic pulse output from the level detection circuit 9 after transmission, the object detection means 8 detects the object. can detect the presence of

[Effects of the Invention] As described above, in the pulse-type ultrasonic detector that detects the presence of an object by transmitting ultrasonic pulses and receiving reflected waves from the object,
Waveform shaping that uses multiple thresholds, each with a different level, to shape the output after amplifying and detecting the received output into multiple rectangular waveforms that become high level when the thresholds are exceeded. and a rising edge detection means for detecting a rising edge of a rectangular wave signal output from the waveform shaping means, and when a rising edge of the rectangular wave output of any of the waveform shaping means is detected after transmitting the ultrasonic pulse. The device is equipped with object detection means that determines that an object exists in By detecting when any rectangular wave output rises after transmitting the ultrasonic pulse using the object detection means, the received wave output included in the reverberant signal is detected unless it is completely hidden by the reverberant signal. I can,
Therefore, it is possible to detect the presence of a close object that cannot normally be detected by a reverberant signal, and it is possible to improve the detection ability of the ultrasonic detector for close objects.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the circuit configuration of an embodiment of the present invention, Fig. 2 is an explanatory diagram of the same operation as above, and Fig. 3 shows the change in voltage between the terminals of a conventional ultrasonic transducer used for both transmitting and receiving waves. FIG. 4 is a block diagram showing the circuit configuration of the same as above, and FIG. 5 is an explanatory diagram of the same as above. 1 is an ultrasonic vibrator, 5 is a level detection circuit, 12
is an object detection means.

Claims (1)

[Claims] 1. In a pulse-type ultrasonic detector that detects the presence of an object by transmitting ultrasonic pulses and receiving reflected waves from the object, Waveform shaping means for shaping and outputting the output into a plurality of rectangular waveforms that become high level when the level is higher than the threshold value using a plurality of threshold values each having a different level, and an output of the waveform shaping means. It has a rising edge detection means for detecting the rising edge of a certain rectangular wave signal, and determines that an object exists when the rising edge of the rectangular wave output of any of the waveform shaping means is detected after transmitting the ultrasonic pulse. An ultrasonic object detector comprising: object detection means. 2 The rising edge detection means includes a differentiating circuit that differentiates each output, which is a rectangular wave signal, of the waveform shaping means, and detects that a differential output corresponding to the rising edge of the rectangular wave signal is obtained by any of these differential outputs. 2. The ultrasonic object detector according to claim 1, wherein the ultrasonic object detector comprises an OR circuit.