JPS5968691A - Ultrasonic object detector - Google Patents

Abstract

PURPOSE:To detect an object up to the closest distance by providing a waveform shaping circuit and a voltage comparing circuit for an ultrasonic wave and masking voltage of a sneak wave by the waveform shaping circuit and taking out only the voltage of a reflected signal. CONSTITUTION:A pulse is generated by a timing circuit 1, and the waveform obtained by amplifying it is impressed to a transmitter 3 and is radiated as ultrasonic pulse to the space. A voltage comparing circuit 9 which compares the output voltage of the waveform shaping circuit 5 and the voltage of the reflected signal 16, which is received when said ultrasonic pulse is radiated to the object 15 to output is provided not to make malfunction the voltage of the reflected signal 16 and the output voltage of a sneak wave 17 inputted directly to a receiver 6, and the voltage of the sneak wave 17 is masked with the output voltage of the circuit 5 to take out only the voltage of the reflected signal. Thus, the object 15 is detected surely even if the object 15 exists near transmitter and receiver 3 and 6, and the non-detection range is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an object detection device using ultrasonic waves, and for example, to a detection device for a rear object such as a vehicle.

Conventionally, many ultrasonic object detection devices have been proposed that aim to detect objects existing in a specific space by emitting ultrasonic pulses into space. In this method, an ultrasonic pulse emitted from a transmitter hits an object, and the reflected wave is received by a receiver, converted into an electrical signal, and the time delay from the time of ultrasonic emission is measured. There are many methods that measure the distance between. However, the problem with the conventional method is that the pulses emitted from the transmitter are directly received by the receiver.

There was a so-called direct wave feed-in phenomenon, which caused the receiving circuit to malfunction. That is, in general, a transmitter and a receiver are often placed close to each other, and furthermore, it is extremely difficult to configure the device to be compact.

Conventionally, a method to solve this problem was to interrupt the operation of the receiving circuit only during the time when the wraparound wave was present, and cut that period. That is, to explain this using FIG. 2, the transmitter 3
The ultrasonic wave emitted from the object 15 is reflected by the object 15 and returns to the receiver 6 as a reflected wave 16, but a small amount of the ultrasonic wave 17 is directly transmitted from the transmitter 3 to the receiver 6. be.

This amount is very small compared to the total energy emitted from the transmitter 3, but since the transmitter 3 and receiver 6 are close, the detected electrical signal is quite large, and compared to the normal reflected signal voltage. I can't ignore it. Therefore, it is necessary to create a structure that reduces this wrap-around wave 17 as much as possible, and also to eliminate the wrap-around wave 17 electrically.

The present invention solves the above-mentioned problems, and an object of the present invention is to provide an ultrasonic object detection device capable of detecting objects at extremely short distances. That is, it includes a waveform shaping circuit whose voltage changes toward another predetermined voltage as two hours pass, and a voltage comparison circuit which compares its output voltage with the reflected signal voltage.

Next, one embodiment of the present invention will be described with reference to the drawings below. 1st
The figure is a block diagram of the present invention, and 1 is a timing circuit which generates a pulse voltage of a constant period. Reference numeral 2 denotes an amplifier circuit which amplifies power so as to sufficiently drive the transmitter 5. 4 is a timer circuit that operates only for a predetermined time based on the signal from the timing circuit 1; the waveform shaping circuit 5 and the gate circuit 11
supply the signal to. The waveform shaping circuit 5 is a circuit whose voltage changes toward another predetermined voltage over time.

6-. 7. B is each receiver, amplifier circuit, and detection circuit,
The ultrasonic signal is converted to voltage, amplified, and then detected. 9 is a voltage comparator circuit, which processes the ultrasonic signal voltage and waveform shaping;
a circuit that compares the output voltages of the circuit 5 and determines the magnitude relationship;
10 is a flip-flop circuit, and timing circuit 1
It is set by the output of the voltage comparator circuit 9, and reset by the output of the voltage comparator circuit 9.

11 is a gate circuit, 12 is an output circuit, and 13 is a speaker.

FIG. 2 illustrates the state of object detection by ultrasonic waves, and the same parts as in FIG. 1 are given the same numbers. 14
is a horn that serves as transmitter, receiver directivity, and protection, 1
5 is the object to be detected.

16, the ultrasonic pulse emitted from the transmitter 6 hits the object 15
The reflected signal 17 that hits and reflects from the object 15 is a wrap-around wave that directly enters the receiver 6 from the transmitter 3, regardless of the object 15.

Figure 3 shows the actual measurement of the relationship between the intensity of the reflected signal voltage when the distance between the object 15 to be detected and the transmitter and receiver changes. (2) 50mm x IIJ 1000m
m pipe is used. There are some differences depending on the shape of the object, but in all cases the voltage received by the receiver 6 decreases inversely as the distance increases, and this relationship shows the same tendency even if the size of the object changes.

FIG. 4 shows a specific example of a circuit according to the present invention.

Items with the same numbers as above indicate the same items.

In the figure, 18 is a diode and 19 is a capacitor.

20 is a resistor in parallel with it, and 21 is a battery with a voltage of TH.

Each connected in series.

FIG. 5 shows voltage waveforms at various parts when the circuits shown in FIGS. 1 and 4 are operated. In the figure (al is the output waveform of the timing circuit 1.

(C) is the output waveform of the amplifier circuit 2, and (C) is the output waveform of the timer circuit 4.
The output waveform 1il is the output waveform of the waveform shaping circuit 5, and VTH is a DC voltage. (el is the output waveform after the signal received by the wave receiver 6 is amplified by the amplifier circuit 7, and is the reflected signal voltage. b) is the output waveform of the detection circuit 8, and (
A) is due to the wraparound wave 17 in Figure 2, (B) is due to the reflected signal 16 reflected from the object 15, and (C) is due to a small object located further away than (B).
is due to an object located further away, but is an unnecessary signal. (B) is the output waveform of the voltage comparator circuit 9, which determines the magnitude relationship between the voltages of (A) and +fl in FIG. . (Company) is the output waveform of the flip-flop circuit 10.

Next, the operation according to the present invention will be explained. When a pulse as shown in Fig. 5 (al) is generated by the timing circuit 1, the amplified waveform is applied to the transmitter O and is emitted into space as an ultrasonic pulse. Because of the wrap-around wave 17 that directly enters the receiver A, the resulting output voltage appears as (a) in Figure @5 (el (f5). Therefore, it is assumed that this is a reflected signal from an object and the circuit malfunctions. To prevent.

Conventionally, the receiving circuit system was killed for the time (TL) until this voltage disappeared, so it was impossible to detect a nearby object reflected back during this period.

The present invention improves this so that even nearby objects can be detected without any problem. That is, as shown in FIG.
As the distance between the object and the object becomes shorter, the output of the reflected signal 15 reflected from the object increases rapidly. Therefore, even if the object is small, its reflected signal becomes considerably large when it approaches. Here, a waveform as shown in FIG. 5(a) is applied to the input terminal of the voltage comparator circuit 9 as a voltage reference for the voltage comparison circuit 9, and an output waveform of the detection circuit 8 is applied to the other input terminal. A circuit for creating a waveform as shown in FIG. 5(a) can be realized, for example, by a circuit configuration like 5 shown in FIG. 4. That is, when the output of the timer circuit 4 is applied to the waveform shaping circuit 5, the capacitor 19 is instantaneously charged through the diode 18 in the waveform shaping circuit 5. On the other hand, since the resistor 20 is connected in parallel with the capacitor 19, the voltage across the capacitor 19 decreases exponentially. Since the DC voltage VTR is connected as shown in the figure, the output waveform of the waveform shaping circuit becomes as shown in FIG. 5(a).

On the other hand, since the reflected signal obtained as the output of the detection circuit 8 also has a tendency as shown in FIG. 5 depending on the distance, the base voltage of the voltage comparator circuit 9 is changed as shown in FIG. 5(a).

Even if the sensitivity of the receiving circuit system is made worse as the distance approaches.

There is no relative relationship, and objects can be detected to the same degree whether they are far or close.

In addition, the voltage of the reflected signal from an object so small that it does not need to be detected is small, as shown in (c) of FIG. 5 (fl).

If the DC voltage v'ru is adjusted appropriately, it will not be detected. This DC voltage VTR is extremely important because it does not operate due to malfunctions due to minute input voltages such as noise or minute fluctuations due to voltage fluctuations.

On the other hand, the signal voltage due to the wrap-around wave 17 has a waveform like that shown in B) of Fig. 5ff+, but the waveform (A) shows that the distance between the transmitter 3 and the receiver 6 is generally close to each other. Therefore, the path of the ultrasonic wave is extremely short as shown at 17 in FIG. 2, and therefore appears immediately after the ultrasonic wave is emitted. On the other hand, the waveform of the company is high immediately after the ultrasonic wave is emitted because the voltage of the capacitor 19 is after the first discharge, and (
The mountain waveform is larger than the (a) waveform of fl, and the wraparound wave 17 is not output as a masked form as the output of the voltage comparison circuit 9.This relationship is shown in more detail in the sixth section. It is a diagram.

The waveform marked in Fig. 5 and the waveform ")" are shown together in terms of peak value and time series. In the figure, the waveform ")" indicated by the dotted line is shown.
0→ shows a state in which the reflected signal (b) from the object 15 approaches the device further in the waveform f in FIG. 5, and the wave height value becomes larger. At this time.

Since the (f) (a) waveform is smaller than the (a) waveform, the voltage comparison circuit 9 is masked and does not detect it, but since the ff+ (e) waveform is larger than the (f) waveform, the voltage comparison circuit 9 is activated.
"High" output. Therefore, the presence of the object 15 can be detected. Here, the discharge curve of capacitor 19 is as follows.

This is determined by the values of capacitor 19 and resistor 20.

If the value of the capacitor 19° or the resistor 20 can be continuously varied depending on the magnitude of the wrap-around wave 17, the above-described operation can be achieved.

On the other hand, in the +f+ waveform in FIG. 0 As stated above, according to the present invention, even if there is a reflected signal from an object close to the wraparound wave, the wraparound wave is masked, so only the reflected signal from the object can be detected. In addition, since the voltage changes over time toward another predetermined voltage, the sensitivity of the receiving circuit system does not change suddenly, and reflected signals below other predetermined voltages can be detected. It has excellent industrial effects, such as being able to reliably detect objects near the transmitter and receiver without having to take out the signal, and eliminating non-detection ranges.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an ultrasonic object detection device according to an embodiment of the present invention, Fig. 2 is an explanatory diagram of the ultrasonic transmission path between the transmitter, receiver, and an object, and Fig. 3 is a block diagram of the ultrasonic object detection device according to an embodiment of the present invention. A diagram showing the relationship between the distance between objects and the ultrasonic intensity. Figure 4 is a specific circuit diagram of the same main part. Figure 5
The figure is a voltage waveform diagram of each part of the device, and FIG. 6 is a detailed diagram of the voltage waveform diagram. 5... Waveform shaping circuit, 9... Voltage comparison circuit. 17... Recirculating wave J" TH... Other predetermined voltage. Applicant: Hitachi Thermal Appliances Co., Ltd. Figure 1 Figure 2 Figure 3 θ 20 , m i!6 Protection 〃η Iρ I
θ 〃θ βU distance (Cffl) Figure 4

Claims (1)

[Claims] A waveform shaping circuit (5) whose voltage changes over time toward another predetermined suppression VTR, and a voltage comparison circuit (9) which compares and outputs the output voltage of the circuit (5) and the reflected signal voltage. An ultrasonic object detection device comprising: masking the voltage of the wraparound wave (17) by the output voltage of the circuit (5) and extracting only the reflected signal voltage.