JPH0449077B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a technique for preventing malfunction of an ultrasonic detector due to noise.

[Background Art] Generally, in an ultrasonic detector, most of the noise received is ultrasonic pulses emitted by rotating machines such as engines, and the period is relatively close to the operating period of the ultrasonic detector. There is a problem in that malfunctions are likely to occur due to noise. Therefore, by making use of the periodicity of this noise and measuring the repetition period and duration, or pulse width, from the detected noise, we can predict the next point in time when there will be no noise, and output a transmission pulse at that point. A method has been proposed in which detection processing is performed using

Figure 3 shows the method. Figure a shows the tone burst-like noise waveform generated from the rotating machine, Figure b shows the timing of the operation of the ultrasonic detector, and P in the figure shows In the transmission pulse, _T1 is the reception period of the reflected wave pulse from the object, _T2 is the noise monitoring period, and _T3 is the detection processing period. In this noise monitoring section T ₂ , the object is outside the detection area and there is no possibility that the reflected wave from the object will be received due to attenuation in the air, so the signal received in this section T ₂ is is an interval that can be determined to be noise, and if a noise pulse is detected in this interval, measure its repetition period τ ₁ and pulse width τ ₂ , predict the next time when no noise will occur, and The next detection process is delayed until that point.

If there is no noise now, the detector operates as shown in figure b, repeating the detection process in section T ₃ and the noise monitoring in section T _2. However, when noise as shown in figure a arrives, the detector operates as shown in figure b. Due to two or more noise pulses N detected in the monitoring interval _T2 , the repetition period _τ1
and the pulse width τ ₂ and determine the next point A when the detection process is possible, as shown in figure c.
The detection process is postponed until that point A. At this point A
Usually comes immediately after the end of the noise monitoring period T ₂ or immediately after the first noise N after the noise monitoring period T ₂ (in the case shown), but when the repetition period of the noise is small, the detection is continued until the noise disappears. In some cases, processing may not be possible.

By the way, in the above conventional method, in order to measure the noise repetition period τ ₁ , it is necessary to detect at least two noises, and therefore the noise monitoring interval
It is necessary to set the length of T ₂ to at least twice τ ₁ , but if T ₂ is made too large and a large number of noise pulses N are detected, the interval between detection processing will become longer. The response of the detector deteriorates, and conversely,
If T ₂ is made small, there is a problem that the detector cannot cope with large noise with a repetition period τ ₁ and becomes unpredictable, reducing the reliability of the detector. Furthermore, this repetition period τ ₁ is determined by the rotational speed of the rotating machine that is the source of noise, and for example, the repetition period τ ₁ differs several times between a motorcycle that has just started and a motorcycle that is running at high speed. It was extremely difficult to set the noise monitoring section _T2 without sacrificing either responsiveness or reliability.

[Object of the Invention] The present invention has been made in view of the above-mentioned problems, and its purpose is to provide a wide range of repetition periods without sacrificing either the responsiveness or reliability of the detector. The goal is to provide an ultrasonic detector that can deal with noise.

[Disclosure of the Invention] The present invention provides an ultrasonic detector that transmits ultrasonic pulses intermittently and receives reflected waves from an object to detect the presence of an object or the distance to the object. A noise monitoring period is provided after the end of the detection processing period including wave transmission and reception, and when a noise pulse is detected in the noise monitoring period, the noise monitoring period is extended until a second noise pulse is detected, When the second noise pulse is detected within the extended noise monitoring interval, it is assumed that the noise pulse has periodicity,
The next detection processing point is determined by measuring the pulse width and repetition period of the noise pulse, and the detection processing is performed by expanding and contracting the noise monitoring interval according to the repetition period of the detected noise. This device is characterized in that it improves responsiveness by minimizing the interval, and that even when noise with a long repetition period arrives, it can be reliably dealt with and prevent malfunctions.

[Embodiment] FIG. 1 shows an embodiment of the present invention, in which an ultrasonic transducer 1 for transmitting and receiving waves is driven by a wave transmitting circuit 2 to intermittently transmit ultrasonic pulses, It receives reflected wave pulses from an object, and this received signal is amplified by a wave receiving circuit 3, further amplified and detected by an amplification/detection circuit 4, and inputted to an object detection circuit 5. As shown in FIG. 2b, the object detection circuit 5 detects the presence of an object when a signal is received within the receiving section _T1 , and also detects the presence of an object from the transmitted pulse P of the received pulse. The distance to the object is calculated from the time delay, and the output is displayed on the display 6.

The output of the wave receiving circuit 3 is also input to the noise detection circuit 7, and in this noise detection circuit 7, the second
When a signal is received within the noise monitoring section _T2 in FIG. b, it is detected as noise. Noise pulse N ₁
is detected, the signal processing circuit 8 immediately controls the noise monitoring gate of the noise detection circuit 7 to control the noise monitoring period until the second noise pulse _N2 is detected.
T ₂ is extended, during which time the repetition period τ ₁ of the noise and its duration, that is, the pulse width τ ₂ are measured, thereby determining the possible time point A of the next detection process, and based on the result, the wave transmission The circuit 2 is controlled to send out a transmission pulse P. Also, at this time, the length of the next noise monitoring section _T2 is the initial setting value, that is, b
Return to T ₂ in the figure.

Figure 2b shows the operation of the detector in a noise-free state, in which a detection processing section _T3 consisting of a transmission pulse P and a reception section _T1 immediately after it is repeated at regular intervals; A noise monitoring section T ₂ of a predetermined length is provided within. Now, when a noise pulse N ₁ as shown in figure a arrives and it is detected within the noise monitoring interval T ₂ , this noise monitoring interval T ₂ becomes the second noise pulse N ₂ as shown in figure c. The repetition frequency τ ₁ and pulse width τ ₂ of the noise pulse are measured, and the transmission time point A of the next transmission pulse P is determined from the values of τ ₁ and τ ₂ . Calculated. In the figure, the transmission time point A is the time when the reverberation time α has elapsed from the fall of the second noise pulse N ₂ , and in reality N ₂
It is calculated after (τ ₂ +α) has elapsed from the rising point of . Furthermore, if the noise repetition period τ ₁ is very short and the detection processing period T ₃ including the transmission and reception periods does not fall within the period (τ ₁ − _{τ 2} − α),
The detection processing enable point A will be postponed until the noise disappears. The purpose of the present invention is to prevent malfunctions caused by noise in an ultrasonic detector used mainly in an environment where a rotating machine such as an engine emits ultrasonic pulses. Therefore, it is safe to assume that normal noise pulses have periodicity.

According to the above configuration, even if noise with a large repetition period arrives, the noise monitoring period is extended to follow it, and two noise pulses are always detected.
Since the period and pulse width can be measured, there is no need to set the noise monitoring interval to a sufficiently large value, and even if noise with a large period arrives on rare occasions, it will not become unpredictable. do not have. In addition,
Since the purpose of the present invention is to prevent malfunctions due to periodic noise pulses, if it is necessary to prevent malfunctions due to single noise pulses, it is necessary to separately set the maximum value of the noise monitoring interval. A combination of these methods should be used.

[Effects of the Invention] As described above, the present invention provides noise monitoring in an ultrasonic detector that detects objects by detecting noise by detecting its repetition period and duration and predicting the point in time when noise does not occur. When a noise pulse is detected in the period, the noise monitoring period is extended until a second noise pulse is detected, and when the second noise pulse is detected within the extended noise monitoring period, the period of the noise pulse is Since the pulse width and repetition period of the noise pulse are measured, the time required for detection processing can be extended or shortened depending on the size of the noise repetition period, and the time required for detection processing can be predicted. The required time can be minimized, thereby improving the responsiveness of the detector, and even when noise with a long repetition period arrives, it can be handled reliably without becoming unpredictable. ,
This has the advantage of preventing malfunctions.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention;
FIG. 2 is a timing diagram showing the same operation as above, and FIG. 3 is a timing diagram showing the operation of the conventional example. P...Transmission pulse, _T1 ...Reception section, _T2 ...
Noise monitoring section, T ₃ ... Detection processing section, N ₁ , N ₂ ...
...Noise pulse, τ ₁ ...Noise repetition period, τ ₂ ...
...Pulse width of noise, A...Detectable point.

Claims (1)

[Claims] 1 In an ultrasonic detector that transmits ultrasonic pulses intermittently and receives reflected waves from an object to detect the presence of an object or the distance to the object, a detection processing section that includes wave transmission and wave reception. A noise monitoring period is provided after the end of the noise monitoring period, and when a noise pulse is detected in the noise monitoring period, the noise monitoring period is extended until a second noise pulse is detected, and a second noise monitoring period is set within the extended noise monitoring period. When a noise pulse is detected, it is assumed that the noise pulse has periodicity, and the next detection processing point is determined by measuring the pulse width and repetition period of the noise pulse. Sonic detector.