JPS5968690A - Ultrasonic object detector - Google Patents

Abstract

PURPOSE:To mask a sneak wave by outputting only a reflected signal by the output voltage of a waveform shaping circuit provided with a waveform shaping circuit and a voltage comparing circuit. CONSTITUTION:An ultrasonic pulse having certain period of a timing circuit 1 is impressed to a transmitter 3 to transmit, and the mixed signal of a reflected signal 16 of a detection object 15 and a sneak wave 17 is received by a receiver 6. The pulse having a certain period of the circuit 1 is supplied to a waveform shaping circuit 5 through a timer circuit 4, and a reference voltage which changes exponential-functionally with time is inputted to a voltage comparing circuit 9. The reflected signal 16 including the sneak wave 17 attained by the receiver 6 is inputted to the circuit 9 through an amplifeir 7 and a detector 8. The output voltage of the circuit 5 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 more particularly, 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, 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 with reference to FIG. 2, the ultrasonic wave emitted from the transmitter 3 is reflected by the object 15 and returns to the receiver 6 as a reflected wave 16. There is a wraparound wave 17 from the transmitter 6 to the receiver 6. This dragon is very small compared to the total energy emitted from the transmitter 3, but since the transmitter 5 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 is intended to solve the above-mentioned problems, and the object of the present invention is to provide an ultrasonic object detection device capable of detecting objects at extremely short distances. That is, it is equipped with a circuit whose reference voltage changes exponentially over time and a voltage comparison circuit which compares its output voltage with a 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. 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 timing circuit j, and waveform shaping circuit 5 and gate circuit 1
1. The waveform shaping circuit 5 is a circuit in which the reference voltage changes exponentially over time after the ultrasonic wave is emitted. Reference numerals 6, 7, and 8 denote respective wave receivers, amplifier circuits, and detection circuits, which convert ultrasonic signals into voltages, amplify them, and then detect the waves. Reference numeral 9 denotes a voltage comparison circuit, which compares the voltage of the reflected ultrasonic signal with the output voltage of the waveform shaping circuit 5 to determine the magnitude relationship; is 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 3 hits the object 15
17 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.
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 represents a resistor in parallel therewith, and 21 represents a battery of voltage VTH, which are 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, fal is the output waveform of the timing circuit 1.

(G) is the output waveform of the amplifier circuit 2, (C) is the output waveform of the timer circuit 4, and (A) is the output waveform of the waveform shaping circuit 5. The VTR is a DC voltage. (θ) is the output waveform after the signal received by the receiver 6 is amplified by the amplifier circuit 7, and is the reflected signal voltage. (f+ is the output waveform of the detection circuit 8, (a) in Figure 5 is due to the wrap-around wave 17 in Figure 2, -) is due to the reflected signal 16 reflected from the object 15, (
C) is caused by a smaller object located further away than N).
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 in (a) and (f) in FIG. is the output waveform of the slip-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 6 and is emitted into space as an ultrasonic pulse. The output voltage caused by the wrap-around wave 17 that directly enters the receiver A appears as (a) in Figure 5 (θ) (f).Therefore, this is judged to be a reflected signal from an object and the circuit malfunctions. To prevent.

Conventionally, the receiving circuit system was killed only during the time (T1) until this voltage disappeared, and it was not possible to detect nearby objects that reflected back during this period.In the present invention, this has been improved. Even objects can be detected without any problem. That is, as shown in FIG. 5, as the distance between the detection device and the object becomes short, 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 as an input voltage reference to the input terminal of the voltage comparison circuit 90, and an output waveform of the detection circuit 8 is applied to the other input terminals. A circuit that generates a waveform like the one shown in FIG. and a diode 18 in the waveform shaping circuit 5.
The capacitor 19 is instantaneously charged through the capacitor 19. On the other hand, since the resistor 20 is connected in parallel with the capacitor 19,
The voltage across capacitor 19 decreases exponentially. Since the DC voltage VTH 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. 3 depending on the distance, the reference voltage of the voltage comparison 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.

Also, as shown in Figure 5 (f+), reflected signals from small objects that do not need to be detected will not be detected if the voltage is small and the DC voltage VTR is adjusted appropriately. This 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 is shown in FIG.
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 ultrasonic path is also very narrow, as shown in 17 in Figure 2. It is short and therefore appears immediately after the ultrasonic emission. On the other hand, the circular waveform is higher immediately after the ultrasonic wave is emitted because the voltage of the capacitor 19 is immediately after discharge, and the two-port waveform is larger than the (a) waveform of (f+), and the voltage comparator circuit 9
As an output, the wrap-around wave 17 is masked and is not output.

This relationship is shown in more detail in FIG. 6, in which the (mountain waveform and +f) waveform in FIG. 5 are combined in peak value and time series. The waveform shown by the dotted line (E) in the figure shows how the reflected signal (B) from the object 15 approaches the device further in the waveform f in Figure 5.
The wave height value is increasing. At this time, (f) What) the waveform is smaller than the mountain waveform, so the voltage comparison circuit 9 is masked and does not detect it, but (e) The waveform is larger than the waveform, so the voltage comparison circuit 9 operates and E "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.

Depending on the magnitude of the wrap-around wave 17, the capacitor 19,
Alternatively, if the value of the resistor 20 is made continuously variable, it is possible to operate as described above.

On the other hand, although the reflected signal from a distant object is detected as shown in FIG. is not output.

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 not masked, and only the reflected signal from the object can be detected. , whether the object is far or near, since the reference voltage changes exponentially over time, and that change is similar to the situation in which the magnitude of the reflected signal changes with distance.

It has industrially excellent effects such as being able to extract reflected signals of the same magnitude.

[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... Surrounding waves. Applicant: Hitachi Thermal Equipment Co., Ltd. Figure 1 Figure 2 Figure 3 θ 20 40 6θ 60 /ll) /20 1
40 161) /IF) Distance (cnl) Fig. 4

Claims (1)

[Claims] A waveform shaping circuit (5) whose reference voltage changes exponentially over time after ultrasonic emission;
A voltage comparison circuit (
9), and is specially modified to mask the voltage of the wrap-around wave (17) by the output voltage of the circuit (5) and extract only the reflected signal voltage.