JPH03165286A - Ultrasonic detector - Google Patents

Abstract

PURPOSE:To improve detecting ability for an object in a short distance by changing the gain of a received wave amplifying circuit for next cycle to a lower gain, when a received wave signal right after the start of detecting gate cycle is detected with a detecting means. CONSTITUTION:When an object detecting operation is started, an ultrasonic pulse is transmitted from a transmitter-receiver 3. Succeedingly, a reverberating signal and the received wave signals related to a reflecting wave from the object are ampli fied by the received wave amplifying circuit 4, and an envelope detection is made thereto by a detecting circuit 5, then among the detected signal, those higher than the threshold are inputted to a signal processing circuit 1 from a comparator 6 as the received wave signal. Then the decision is made whether the received wave signal at the time right after the start of detecting gate is in existence or not, and when the received wave signal is detected right after the start of detecting gate, a gain changing signal is outputted to the received wave amplifying circuit 4 from the signal processing circuit 1 to change the gain of the circuit 4 to a specified low gain. By this procedure, the reverberating signal and the received wave signal related to the object can be easily discriminated and the detecting ability for the object in a short distance is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ultrasonic detector, and particularly to an ultrasonic detector that detects objects at close range.

[Conventional technology]

Conventionally, an ultrasonic detector detects an object by transmitting ultrasonic pulses of a predetermined frequency at a predetermined period and receiving return reflected waves from the object. That is, as shown in the block diagram of FIG. 6 and the flowchart of FIG. The transducer 3 is excited by the oscillation output signal and an ultrasonic pulse is transmitted (step 511 in FIG. 7).

When this ultrasonic pulse is reflected by an object and the return reflected wave is received by the transducer 3, this received signal is transmitted to the receiving amplifier circuit 4.
1 and subjected to envelope detection by a detection circuit 5. This detected signal is pulse-shaped by a comparator 6 for signals higher than a predetermined level, and is sent to a signal processing circuit 1 as a received signal.
2 is input.

Then, the signal processing circuit 12 determines whether or not the received signal is input within a predetermined detection gate period T1 (FIG. 8, waveform a) (step S in FIG. 7). When the received signal is input within T□ (YES in step S12), a detection signal is output to the output circuit 7 (step S□3 in FIG. 7). After this, the ultrasonic pulse is transmitted again from the transducer 3, and the object detection operation continues to be repeated.

On the other hand, if the received signal is not input within the detection gate period T The object detection operation continues to be repeated.

[Problem to be solved by the invention]

By the way, conventional ultrasonic detectors have a receiving amplifier circuit 41 in order to detect weak reflected wave signals from relatively distant objects.
The gain is set high. Therefore, as shown in the waveform b to in FIG. do.

In addition, the reverberation signal B generated after the end of transmission of the ultrasonic pulse
1 also exceeds the dynamic range of the wave receiving amplification circuit 41 and becomes saturated.

Therefore, as shown in waveform b 20 in FIG. 8, for example, when a received signal B 21 due to a reflected wave from a nearby object is received following the reverberant signal B, the receiving amplification circuit 4
1, the reverberant signal Bll and the received signal B21 are output as continuous waveforms. On the other hand, as shown in waveform b30 in FIG. 8, when the reverberation time is extended due to an external cause such as adhesion of water droplets, the latter half of the reverberation signal B3□ also becomes saturated as described above. That is, the waveform b 20 and the waveform b 30 become the same waveform.

Therefore, as shown in waveform C in FIG.
If a received signal is obtained immediately after the start of the process, it will not be possible to determine whether the received signal is due to a reflected wave from a nearby object or due to reverberation.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an ultrasonic detector that can distinguish and detect reverberation and objects at a short distance.

[Means to solve the problem]

In order to achieve the above object, the present invention repeatedly transmits ultrasonic pulses, receives and amplifies the return reflected waves, and
In an ultrasonic detector that extracts and detects a received signal within a detection gate period from a received signal of a predetermined detection level or higher, the ultrasonic detector includes a detection means for detecting the presence or absence of a received signal immediately after the start of the detection gate period, and a receiving signal amplification. and gain changing means for changing the gain of the circuit to a low gain such that the reverberant signal becomes below the detection level, and when the receiving signal is detected by the detecting means, the gain of the receiving amplifying circuit for the next cycle is changed. The gain is changed to low.

[Effect]

According to the ultrasonic detector with the above configuration, when a received signal is detected immediately after the start of the detection gate period, the gain of the received wave amplification circuit is changed to a low gain that reduces the reverberant signal below the detection level, and this low gain The reception signal of the next cycle is amplified by the reception amplification circuit, and only the reception signal related to the reflected wave from the object is extracted and detected.

〔Example〕

FIG. 1 is a block diagram of a first embodiment of an ultrasonic detector according to the present invention.

The signal processing circuit 1 controls the transmission timing of ultrasonic pulses,
As will be described later, it performs various signal processing on the received signal. The transmitting amplifier circuit 2 amplifies the power of the oscillation output signal of a predetermined width from the signal processing circuit 1 to excite the transducer 3. The transducer 3 is composed of an ultrasonic transducer, etc., and converts the excitation signal from the wave transmitting amplifier circuit 2 into an ultrasonic pulse and transmits the wave, and also receives reflected waves from an object and transmits the wave to the receiving amplifier circuit 4. This is what is output to.

The wave receiving amplification circuit 4 amplifies the return reflected wave signal from an object, which is received by the wave transmitter/receiver 3, to a level that can be processed by the detection circuit 5. In addition, when the gain change signal is input from the signal processing circuit 1, the receiving amplification circuit 4 detects the reverberation signal of the next cycle by setting the detection level (threshold value) of the comparator 6, which will be described later.
The gain is changed to a predetermined low gain in order to make it 1 or less. The detection circuit 5 performs envelope detection of the reception signal amplified by the reception amplification circuit 4. The comparator 6 forms, for example, a pulse of the detected signal from the detection circuit 5, which is equal to or greater than the threshold value v1, and outputs it to the signal processing circuit 1 as a received signal. The signal processing circuit 1 generates a detection gate for a period T (waveform a in FIG. 3), and determines that a received signal input within this period T1 is a reflected wave from an object. Further, when the signal processing circuit 1 receives a reception signal immediately after the detection gate a starts, it outputs a gain change signal to the reception amplification circuit 4. The output circuit 7 sends out a signal indicating the presence or absence of an object or a distance to the object in response to a signal from the signal processing circuit 1.

Next, the operation of the first embodiment will be explained using the flowchart of FIG. 2 and the waveform diagram of FIG. 3. In addition, the third
Waveforms b□ to b3 in the figure each indicate the output signal of the receiving amplification circuit 4, and waveform b2 is the receiving signal B2 from a nearby object.
is received following the reverberant signal B□, and the waveform b
3 shows a case where the reverberation signal B3 is mixed into the detection gate period T due to an external cause or the like.

When the object detection operation is started, ultrasonic pulses are transmitted from the transducer 3 (step Sl).

Subsequently, the received signal related to the reverberation signal and the reflected wave from the object is amplified by the receiving amplifier circuit 4 (Fig. 3, saturated waveform b1), envelope detected by the detection circuit 5, and the threshold value V is determined from this detected signal. □The above signals are sent to comparator 6 as received signals.
The signal is input to the signal processing circuit 1 from the signal processing circuit 1.

Then, the signal processing circuit 1 determines the presence or absence of the received signal immediately after the start of the detection gate a (step S2), and as shown in the waveform C□ in FIG. When □ is detected (YES in step S2),
A gain change signal is output from the signal processing circuit 1 to the receiving amplifier circuit 4, and the gain of the receiving amplifier circuit 4 is changed to the predetermined low gain mentioned above. After this, the ultrasonic pulse is transmitted again from the transducer 3 (step S4), and the waveform b in FIG.
2 and waveform b3, the reception signal of the next period is amplified by the reception amplification circuit 4 with a low gain after the gain change. Then, a signal equal to or greater than the threshold value ■1 is outputted from the comparator 6 to the signal processing circuit 1 as a received signal.

That is, for example, if the received signal B2 from a nearby object is received following the reverberant signal B1 (waveform b in FIG.
2) Even if the received signal B2 of the next cycle is amplified with the low gain mentioned above, it does not become less than the threshold value ■1, and therefore, as shown in the waveform C2 of FIG. Signal C
2 is output from the comparator 6.

On the other hand, if reverberation is mixed into the gate period T1 due to external factors (waveform b3 in Figure 3), the level of the latter half of the reverberant signal B3 will be suppressed after changing the receiving amplifier circuit 4 to a low gain. Immediately after the start of the gate period a, the voltage is lowered to below the threshold value V4. Therefore, the received signal related to the reverberant signal B3 is not output from the comparator 6.

Then, it is determined whether the received signal is input within the detection gate period Tl of the signal processing circuit 1 (step S
5) If no received signal is input within the detection gate period T□ as shown in waveform b3 in FIG.
(NO), the process returns to step S1 again, and the ultrasonic pulse is transmitted from the transducer 3.

On the other hand, as shown in waveform b2 in FIG. 3, if the received signal C2 is input within the detection gate period Tl (YES in step S5), this detection output is sent out from the output circuit 7 ( Step S6).

Thereafter, the process returns to step S again, the ultrasonic pulse is transmitted from the transducer 3, and the object detection operation continues to be repeated.

On the other hand, if the received signal is not inputted immediately after the start of the detection gate a in step S2 (NO in step S2),
It is determined whether another received signal is input within the detection gate period T□ (step S7). If no other received signal is input within the detection gate period T (NO in step S7), the process returns to step Sl again, and the ultrasonic pulse is transmitted from the transducer 3. On the other hand, if another received signal is input within the detection gate period Tl (YES in step S7), the process moves to step S6, and a detection output is sent out from the output circuit 7.

Next, a second embodiment will be described using FIG. 4. In the second embodiment, a signal processing circuit 11 and a comparator 61 are provided in place of the signal processing circuit 1 and comparator 6 of the first embodiment.

In addition, in the figure, parts given the same numbers as in FIG. 1 perform the same functions.

In addition to the functions of the signal processing circuit 1 of the first embodiment, the signal processing circuit 11 is configured to output a threshold value change signal to the comparator 61. That is, when the signal processing circuit 11 receives the reception signal from the comparator 61 immediately after the start of the detection gate a, it outputs a gain change signal to the reception amplifier circuit 4 and a threshold change signal to the comparator 61. It is done like this. Furthermore, when the above-mentioned threshold value change signal is inputted, the comparator 61 changes the threshold value vl to a predetermined threshold value V2 (>Vl).

Next, the operation of the second embodiment will be explained. Note that the low gain after the gain change of the receiving amplification circuit 4 and the threshold value v2 after changing the threshold value of the comparator 61 are such that if the received signal is related to an object, the threshold value v2 is equal to or higher than the threshold value 72; For example, they are each set to be equal to or less than the threshold value ■2.

That is, when the signal processing circuit 11 receives the reception signal from the comparator 61 immediately after the start of the detection gate a, it changes the reception amplifier circuit 4 to a low gain and changes the threshold value v1 of the comparator 61 to the threshold value v2. do. After this, for example, if a received signal from a nearby object is received following the reverberation signal in the next cycle, the received signal from the nearby object will exceed the threshold ■2, and this received wave A signal is output from the comparator 61 to the signal processing circuit 11, and a detection output is sent from the output circuit 7.

On the other hand, for example, if a reverberation signal is mixed in the detection gate period, the receiving amplifier circuit 4 is set to a low gain, and the comparator 6 is set to a low gain.
After changing the threshold value 1 to 2, the level of the latter half of the reverberation signal is suppressed, and immediately after the start of the gate period T1, the level is reduced to the threshold value v
It can be lowered to 2 or less. Therefore, the reverberation signal of the next cycle is not output from the comparator 61.

That is, the second embodiment also provides the same effects as the first embodiment.

Next, a third example will be described. Note that the block configuration of the third embodiment is similar to that of the first embodiment.

In the third embodiment, when a received signal is inputted immediately after the detection gate a of the signal processing circuit 1 starts, the gain of the received wave amplification circuit 4 is changed in stages. That is, the level of the received signal varies depending on the shape and size of the reflecting object, the distance to the reflecting object, or the reverberation level. Therefore, by changing the gain of the receiving amplification circuit 4 in stages, the reverberation signal and the receiving signal related to the object can be distinguished.

Next, the operation of the third embodiment will be explained using FIG. 5. In addition, in the following description, a case will be described in which a received signal from a nearby object is received following a reverberant signal.

The received wave signal shown in the waveform b1 in FIG. A gain change signal is output to the receiving amplifier circuit 4, and the gain of the receiving amplifier circuit 4 is slightly lowered. Then, as shown by waveform b2 in FIG. 5, the width of the received signal from the transfer amplifier circuit 4 in the next cycle becomes slightly narrower.

Thereafter, when the received signal is input to the signal processing circuit 1 again immediately after the start of the detection gate period a of the next cycle, the gain of the received wave amplification circuit 4 is further lowered, as shown in the waveform b3 in FIG. Furthermore, the width of the received signal from the transfer amplifier circuit 4 also becomes narrower. Furthermore, when the received signal is input to the signal processing circuit 1 again immediately after the start of the detection gate period a of the next cycle, the gain of the received wave amplifier circuit 4 is further reduced, and the received signal from the received wave amplifier circuit 4 is width becomes even narrower.

At this time, as shown by waveform b4 in FIG. 5, the received signal immediately after the start of the detection gate period a becomes equal to or less than the threshold value vl, and the gain reduction of the received wave amplification circuit 4 is stopped. After this, the fifth
As shown in waveform C in the figure, a received signal C3 related to an object in the work during the detection gate period T of the next cycle is outputted from the comparator 6 to the signal processing circuit 1, and this detection output is sent out from the output circuit 7.

In this third embodiment, the reduction in the gain of the reception amplifier circuit 4 is stopped when the reception signal immediately after the start of the detection gate period a becomes equal to or less than the threshold value v1. The impact of this can be minimized.

〔Effect of the invention〕

In the present invention, when a received signal is detected immediately after the start of the detection gate period, the gain of the received wave amplification circuit is reduced until the reverberant signal is below the detection level, so that the reverberant signal and the received signal related to the object are They can be easily identified and can improve the ability to detect objects at close range.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a first embodiment of the ultrasonic detector according to the present invention, FIG. 2 is a flowchart showing the operation of the first embodiment, and FIG. 3 is a waveform diagram showing the operation of the first embodiment. , 4th
The figure is a block diagram of the second embodiment of the operation of this ultrasonic detector, Figure 5 is a waveform diagram showing the operation of the third embodiment of this ultrasonic detector, and Figure 6 is a conventional ultrasonic detector. FIG. 7 is a flowchart showing the conventional operation, and FIG. 8 is a waveform diagram for explaining the problems of the conventional ultrasonic detector. 1.11... Signal processing circuit, 2... Transmission amplifier circuit,
3... Transmitter/receiver, 4... Wave receiving amplification circuit, 5... Detection circuit, 6.61... Comparator, 7... Output circuit.

Claims (1)

[Claims] 1. In an ultrasonic detector that repeatedly transmits ultrasonic pulses, receives and amplifies the returned reflected waves, and extracts and detects received signals within a detection gate period from received signals exceeding a predetermined detection level, the above-mentioned The detection means includes a detection means for detecting the presence or absence of a reception signal immediately after the start of the detection gate period, and a gain change means for changing the gain of the reception amplification circuit to a low gain such that the reverberation signal becomes below the detection level. An ultrasonic detector characterized in that when a reception signal is detected by the means, the gain of the reception amplification circuit in the next cycle is changed to a low gain.