JPH01237483A - Ultrasonic detector of invader - Google Patents

Abstract

PURPOSE:To improve reliability by detecting a time point whereat a change in a peak value of an envelope of an averaged waveform made by superposing reflection signals of ultrasonic signals transmitted repeatedly, is larger than that due to natural phenomenon. CONSTITUTION:A converter 1 for transmission is connected to a transmission circuit 10 and a reference signal generating device 11, and it transmits a burst-form electric signal sent from the reference signal generating device 11, as a burst-form ultrasonic signal. A converter 2 for reception receives a reflection wave and converts it into an electric signal. The electric signal amplified by an amplifier circuit 12 is turned to be of an envelope waveform by an envelope detector 13. From a digital value obtained through conversion by an A/D converter 14 a peak detecting circuit 15 takes out a peak value and memories it together with a time required from the transmission. A peak value change computing circuit 17 repeats comparison between a repetition average value obtained in a peak value averaging circuit 16 and a previous average value, and when a comparison value thus obtained exceeds a fluctuation due to natural phenomenon, a next comparison judgement circuit 18 judges that there occurs an abnormality, such as the presence of an invader, and outputs a detection signal.

Description

[Detailed Description of the Invention] (Field of Industrial Application) The present invention relates to an ultrasonic intruder detector that uses ultrasonic waves to detect an intruder into a space such as a room or the inside of a car. .

(Prior Art) Conventionally, this type of ultrasonic intruder detector is equipped with a circuit that integrates the electrical signal of the reflected waves, and monitors the reflected waves of the ultrasonic waves that are repeatedly emitted in bursts at an integral level. A method that detects when the reflected wave is disturbed by an intruder and the integrated value level exceeds a threshold, a method that simply detects disturbance of the envelope, or a method that detects the level fluctuation of the reflected wave as in the above method. In addition to detection methods using amplitude-modulated signals, methods that utilize the Doppler effect of ultrasound reflected signals from moving objects are also used.

(Problem to be Solved by the Invention) However, in the method using amplitude modulation described above, since the signal reflected by the intruder is primarily monitored, the signal reflected by the air turbulence caused by heat or the movement of air such as wind There was a problem in that it was difficult to separate noise caused by signal disturbances, resulting in malfunctions. As a countermeasure for this, a method takes advantage of the fact that reflected waves from fixed objects are constant, and a fixed position detection circuit is installed in the processing circuit to remove the reflected components from fixed objects and detect only the reflected components from moving objects. However, this also has the problem that when the air is fluctuated by wind etc., a reflected signal appears as if a fixed object has moved, making it impossible to completely eliminate malfunctions.

In addition, in the method using the Doppler effect described above, since the polarity of the frequency shift is monitored, it is possible to create an intruder detector with a high S/N ratio. For a moving object of 1/6
Since the change is less than 80, the circuit becomes complicated and signal processing becomes difficult.

The present invention solves the above problems and provides an intruder detection device that uses simple signal processing and is less likely to malfunction.

(Means for Solving the Problems) In order to solve the above problems, the present invention calculates an average waveform by superimposing reflected signals of ultrasonic signals that are repeatedly transmitted several times per second multiple times. This method detects the point in time when the change in the peak value of the envelope changes more greatly than the change caused by natural phenomena.

(Function) With the above configuration, since the judgment criterion is the point immediately before the intruder appears, changes in the peak value due to changes in the environment, fluctuations in the air, etc. are eliminated, and malfunctions are prevented.

(Example) An example of the present invention will be described with reference to FIGS. 1 to 4.

Figure 4 is a structural model diagram of a passenger car equipped with an ultrasonic intruder detector, in which there is a transmission ultrasonic transducer (hereinafter referred to as the transmission transducer) 1 on the front panel of the driver's seat and a reception transducer on the front panel. Ultrasonic transducers (hereinafter referred to as reception transducers) 2 are arranged next to each other.

The ultrasonic waves repeatedly emitted in bursts from the transmitting transducer 1 at several times per second spread in all directions as indicated by the dashed arrows, and are transmitted to the shoulder rests 3 and 4 of the driver's seat and the passenger seat. Alternatively, it is reflected by the ceiling 5, rear window glass 6, etc., and is received by the reception converter 2 as a reflected wave.

Figure 2 is a picture of the input signal of the receiving converter 2 shown on the screen of a cathode ray tube oscilloscope with the camera shutter open for a few seconds.The reflected waves are superimposed over 10 times, and the outline is the average. It is shown as envelope waveform 7.

FIG. 3 shows the waveform of a reflected wave of one burst-like ultrasonic wave, with the solid line showing the ultrasonic waveform 8 of the reflected wave, and the broken line showing the envelope waveform 9 of the reflected wave. Peak value 9a of envelope waveform 9
, 9b, 9c, and 9d each include a plurality of ultrasound waveforms 8.

Returning to FIG. 2, in the average envelope waveform 7, peak values 7b, 7c, 7d, 7e, 7f and 7g appear in decreasing order from the direct wave waveform 7a showing the maximum value.

The interval from the direct wave waveform 7a to each of the peak values 7b to 7g is the time from transmission to reception, and corresponds to the round trip distance of the reflected wave.

In addition, in Fig. 2, one scale on the horizontal axis is 0.2ms/div,
Therefore, it corresponds to a propagation distance of 64 square meters per div, that is, 32 square meters one way.

When the oscilloscope screen is continuously observed, it can be seen that the peak values 9a to 9c always fluctuate between 0.1'Hz and several sevens. This fluctuation in the peak value is thought to be caused by slight movement of air within the closed interior space of the vehicle, vibration of the vehicle body due to unevenness of the ground, or other causes. Moreover, the magnitude of this fluctuation changes depending on changes in the environment.

This can be said to be the cause of malfunction of conventional ultrasonic intruder detectors.

An embodiment of the present invention will be explained with reference to the circuit block diagram of FIG. The transmitting transducer 1 and the receiving transducer 2 use ceramic ultrasonic microphones in order to ensure reliability in places where indoor and outdoor environments are subject to rapid changes, and to obtain stable transmission and reception and sufficient sensitivity. The transmitting converter 1 includes a transmitting circuit 1
0 and the reference signal generator 11, and is sent from the reference signal generator]1, for example, 100m5.
A burst-like electrical signal of 32 ms is transmitted as a burst-like ultrasound signal.

The receiving converter 2 includes an amplifier circuit 12. Envelope detection circuit 13. A/D converter 14. peak value detection circuit 15,
Peak value averaging circuit 16. It is connected to a peak value change calculation circuit 17 and a comparison judgment circuit 18 in this order.

The receiving converter 2 receives the reflected wave and converts it into an electrical signal. The electrical signal amplified by the amplifier circuit 12 becomes an envelope waveform 9 by the envelope detector 13. A/D
A peak value detection circuit 15 extracts peak values 9a to 9d from the digital values converted by the converter 14 and stores them together with the time from transmission.

The time and level from the transmission of each of the peak values 9a to 9d are reflected waves from fixed objects, so they do not vary greatly with the elapsed time, but they do fluctuate little by little due to changes in the environment.

The peak value averaging circuit 16 is provided for the purpose of increasing the SN ratio, and averages the time and level of the peak value every several transmissions. The peak value change calculation circuit 17 is
The repeated average value obtained by the above peak value averaging circuit 16 is constantly compared with the previous average value, and when this comparison value exceeds the fluctuation due to natural phenomena, the next comparison judgment circuit 18 detects an intruder. It determines that there is an abnormality such as, and outputs a detection signal.

The fluctuations of natural phenomena are 0.1 Hz to 0.5 Hz, while the fluctuations of intruders are 2 Hz to 5 Hz. Furthermore, since the fluctuations of natural phenomena do not change suddenly even if they become large, the system judges the fluctuations of the intruder by comparing them with the state immediately before, so there is no possibility of malfunction.

(Effects of the Invention) As explained above, according to the present invention, fluctuations caused by an intruder are always determined by comparing with the state immediately before, so the reliability can be improved regardless of the installation location or environment. A highly efficient ultrasonic intruder detector can be obtained. Further, since there is no need for sensitivity adjustment, handling becomes easy.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the circuit configuration of an ultrasonic intruder detector according to the present invention, Fig. 2 is a photograph of an oscilloscope screen showing the envelope waveform of the reflected wave, Fig. 3 is a waveform diagram of the reflected wave, and Fig. 4 The figure is a model diagram of the device installed in a passenger car. 1... Ultrasonic transducer for transmission, 2... Ultrasonic transducer for reception, 3, 4... Shoulder rest, 5... Ceiling,
6... Window glass, 7... Average envelope waveform,
7a... Direct wave waveform, 7b. 7c, 7d, 7e, 7f, 7g, 9a, 9
b, 9c. 9d...Peak value, 8...Ultrasonic waveform, 9
... Envelope waveform, 10... Transmission circuit, 11
...Reference signal generator, 1z...Amplification circuit, 13
...Envelope detection circuit, 14.A/D converter,
15...Peak value detection circuit, 16...Peak value averaging circuit, 17...Peak value change calculation circuit, 1
8...Comparative judgment circuit.

Claims (3)

[Claims] (1) A transmitter that repeatedly transmits an electrical signal at regular intervals, a transmitting ultrasonic converter that converts the electrical signal into an ultrasonic wave, a receiving ultrasonic converter that converts reflected waves into an electrical signal, and a receiving signal. In an ultrasonic intruder detector consisting of an amplifier circuit that amplifies the signal, a circuit that stores the peak value of the envelope of the amplified signal, and a judgment circuit, the peak value that is compared at regular intervals by the judgment circuit is An ultrasonic intruder detector that outputs a detection signal when the frequency of level fluctuation is doubled or more. (2) The ultrasonic intruder detector according to claim 1, wherein the peak value of the envelope is an average value of at least three consecutive received signals. (3) The ultrasonic method according to claim (1), wherein the average peak value is stored by amplifying it, converting it into a digital value, and further averaging it in a shift register within one reflected wave time. Intruder detector.