JPS5968685A - Ultrasonic object detector - Google Patents

Abstract

PURPOSE:To mask sneak waves, by connecting the constitution of a waveform shaping circuit provided with a waveform shaping circuit and a voltage comparing circuit with a diode, a capacitor, and a resistance. CONSTITUTION:Ultrasonic pulses having a certain period are impressed to a cable transmitter 3 from a timing circuit 1 and are transmitted, and a reflected signal 16 of an detection object 15 and a sneak wave 17 are mixed and received by a receiver 6. Pulses having a certain period are supplied to a waveform shaping circuit 5, which is constituted by connection of a diode 18, a capacitor 19, and a resistance 20, through a timer circuit 4, and the output voltage which is reduced exponential-functionally with time is inputted to a voltage comparing circuit 9. The reflected signal 16 including the sneak wave 17 which is attained by the receiver 6 is inputted to the circuit 9 through an amplifier 7 and a detector 8. The output voltage of the circuit and the reflected signal 16 including the sneak wave 17 are compared with each other in the circuit 9 to output only the reflected signal 16. Thus, the sneak wave 17 is masked to detect easily the position of the object 15.

Description

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

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, a problem with the conventional system is that the pulse emitted from the transmitter is directly received by the receiver, a so-called direct wave loop-in phenomenon, which causes 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 make the device 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 is directly transmitted from the transmitter 5 to the receiver 6 as a reflected wave 17. There is.

This amount is very small compared to the total energy emitted from the transmitter 5, but since the transmitter 3 and receiver 6 are close, it is quite large as a detected hypochondrium signal and compared to the normal reflected signal voltage. I can't ignore it. Therefore, it is necessary to create a structure that reduces the amount of the wrap-around waves 17, and also to eliminate the wrap-around waves 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 that can detect cloth at extremely short distances. In other words, it includes a waveform shaping circuit whose voltage decreases exponentially over the course of two hours, and a voltage comparison circuit that compares its output voltage with the reflected signal voltage, and the waveform shaping circuit is composed of diodes, resistors, and capacitors. It is.

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. 2 is an amplifier circuit which amplifies the power so as to sufficiently drive the transmitter 3. 4 is a timer circuit that operates only for a predetermined time according to a signal from the timing circuit 1;

A signal is supplied to the waveform shaping circuit 5 and gate circuit 11. The waveform shaping circuit 5 is a circuit whose voltage decreases exponentially over time. Reference numerals 6, 7.8 denote respective wave receivers, amplifier circuits, and detection circuits, which convert ultrasonic signals into voltages, amplify them, and then detect them. Reference numeral 9 represents a voltage comparison circuit, which compares the ultrasonic signal voltage with the output voltage of the waveform shaping circuit 5 to determine the magnitude relationship. Reference numeral 10 represents a flip-flop circuit.

The output of the timing circuit 1 is converted to voltage comparator circuit 9.
is reset by the output of 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 3 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 sending and receiving devices changes. There are some differences depending on the shape of the object, but
In both cases, as the distance increases, the voltage received by the receiver 6 decreases in inverse proportion, and this relationship shows a similar 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, 21 is a battery with voltage VTH, and capacitor 1
9 and the resistor 20 are connected in parallel, and the others are connected in series.

FIG. 5 illustrates voltage waveforms at various parts when the circuits shown in FIGS. 1 and 4 are operated. In the figure, fa) is the output waveform of the timing circuit 1.

(C) is the output waveform of the timer circuit 4, and (A) is the output waveform of the waveform shaping circuit 5. l
) VTR is a DC voltage. fe) is an output waveform after the signal received by the wave receiver 6 is amplified by the amplifier circuit 7, and is a reflected signal voltage. (The phantom is the output waveform of the detection circuit 8. In Figure 2, (a) is due to the wrap-around wave 17 in Figure 2. (b) is due to the reflected signal 16 reflected from the object 15.
C) is caused by a smaller object located further away, to)
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 ff+ in FIG.
state. (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 is generated by the timing circuit 1, the amplified waveform is applied to the transmitter 3 and is emitted into space as an ultrasonic pulse. The emitted ultrasonic pulse is the result of a wrap-around wave 17 that directly enters the receiver 6, and the resulting output voltage appears as (a) in Fig. 5 fe) (fl. Therefore, this is judged to be a reflected signal from an object. To prevent the circuit from malfunctioning.

Conventionally, the receiving circuit system was killed only during the time (TI) until this voltage disappeared, and it was not possible 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. 3, as the distance between the detection device and the object becomes short, the output of the reflected signal 15 reflected from the object suddenly increases. Therefore, even if the object is small, its reflected signal becomes considerably large when it approaches. Here, a fifth voltage is applied to the input terminal of the voltage comparator circuit 9 as an input voltage reference.
Figure (Add a waveform like J, and add the output waveform of the detection circuit 8 to the other input terminal. Figure 5 (Add a waveform like J). This can be realized by a circuit configuration. 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, the capacitor 19 and Since the resistor 20 is connected in parallel, 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 will eventually change. is shown in Figure 5 (like a mountain 1).

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. 3 depending on the distance, the reference voltage of the voltage comparison circuit 9 is changed as shown in FIG.

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.

Also, 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 Figure 5+f).

If the DC voltage VTR 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 17K is shown in Figure 5 (Rino(
The waveform shown in (a) is as shown in (a), but since the transmitter 3 and receiver 6 are generally installed close to each other, the path of the ultrasonic wave is also as shown in 17 in Figure 2. It is very short and therefore appears immediately after the ultrasound is emitted. On the other hand, the fil waveform shows that immediately after the ultrasonic wave is emitted, the voltage of the capacitor 19 is as high as 7.
The waveform (b) is larger than the (a) waveform of (f+), and the wrap-around wave 17 is masked as an output of the voltage comparator circuit 9 and is not output.

This relationship is shown in more detail in FIG. 6, which shows the (mountain waveform and (f) waveform in FIG. 5 together in peak value and time series. waveform ω
) and (e) show how the reflected signal (b) from the object 15 approaches the device further in the waveform of FIG. 5, and the wave height value becomes sharper. At this time, the waveforms (f) and (a) are smaller than the J waveform (the voltage comparator circuit 9 is masked and does not detect it), but the +fl (e) waveform is larger than the ■ waveform, and the voltage comparator circuit 9 operates and becomes "high". Therefore, the presence of the object 15 can be detected.Here, the discharge curve of the capacitor 19 is the same as that of the capacitor 19 and the resistor 20.
Since the value of the capacitor 19. is determined by the magnitude of the wrap-around wave 17. Alternatively, if the value of the resistor 20 is made continuously variable, it is possible to operate as described above. Since they are composed of the minimum units of capacitors and resistors, they can be implemented extremely easily.

On the other hand, in the waveform of FIG. 5(f), the reflected signal from a distant object is detected as 2), but since it is outside the desired detection distance, it is masked by the output waveform of the timer circuit 4 and the voltage is compared. It is not output to circuit 9.0 As described above, according to the present invention, even if there is a reflected signal from an object that is close to the wraparound wave, the wraparound wave is masked, so the reflected signal from the object can be detected. In addition, the voltage changes exponentially over time, and this change is similar to the change in the reflected signal size depending on the distance, so when the object is far away, However, the reflected signal can be extracted as the same magnitude even if it is nearby, and the circuit that changes it is a diode.

Since it has a simple circuit configuration with the minimum unit of resistors and capacitors, it is possible to easily adjust the state of change, and it has practical effects.

[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. 18...Diode, 19...Capacitor. 20--Resistance. Applicant: Hitachi Thermal Equipment Co., Ltd. Figure 1 Figure 2 Figure 3 0 20 40 60 δθ /lD /20
/47) /60 /367 distance (crn) Figure 4

Claims (1)

[Claims] It is equipped with a waveform shaping circuit (5) whose voltage decreases exponentially with the passage of 9 hours after ultrasonic emission, and a voltage comparison circuit (9) which compares the output voltage of the circuit (5) and the reflected signal voltage. , an ultrasonic object detection device characterized in that the circuit (5) is composed of a diode (1B), one resistor (20), and one capacitor (19).