JPH0413670B2 - - 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 this method. Figure a shows the tone burst noise waveform generated from the rotating machine, Figure b shows the operation timing of the ultrasonic detector, and P in the figure shows the transmitting wave. pulse, T ₁ is the reception period of the reflected wave pulse from the object, T ₂ is the noise monitoring period,
T ₃ is the detection processing period. This noise monitoring section T ₂
If the object is outside the detection area, there is no possibility that the reflected wave from the object will be received due to attenuation in the air, and therefore the signal received in this interval _T2 is an interval that can be distinguished as noise. If a noise pulse is detected in this interval, the repetition period τ ₁ and pulse width τ ₂ are measured, the next time when no noise occurs is predicted, and the next detection process is continued until that point. It is something that delays the

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 T _2. However, when noise as shown in figure a arrives, the detector operates as shown in figure b. The repetition period τ ₁ and pulse width τ ₂ of two or more noise pulses N detected in the interval T ₂ are measured, and the next point in time A at which detection processing is possible is determined. The detection process is postponed until that point A, as shown in FIG. This point A usually comes immediately after the end of the noise monitoring interval T ₂ or immediately after the first noise N after the noise monitoring interval T ₂ (in the case shown), but when the repetition period of the noise is small, the noise In some cases, detection processing cannot be performed until it disappears.

By the way, in the above conventional method, in order to measure the noise repetition period τ ₁ , it is necessary to set the length of the noise monitoring interval T ₂ to at least twice the length _of τ ₁ . If T2 is increased so that a large number of noise pulses N are detected, the detection processing interval becomes longer and the responsiveness of the detector deteriorates.On the other hand, if _T2 is decreased, large noise with a repetition period _τ1 is generated. There is a problem in that the detector becomes unable to respond and becomes unpredictable, reducing the reliability of the detector. Moreover, 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. Noise monitoring section T ₂ so as not to sacrifice responsiveness or reliability
It was extremely difficult to set the

[Object of the Invention] The present invention has been made in view of the above-mentioned problems, and its purpose is to cope with noise having a wider range of repetition periods than before without sacrificing the responsiveness of the detector. We aim to provide ultrasonic detectors that can

[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 section is provided after the detection section including transmission and reception, and when a noise pulse is detected in this section, the repetition period and pulse width of the noise pulse are measured and stored in a storage circuit. , the next detection processing time point is determined from the measurement result, and if the above measurement cannot be performed during the noise monitoring section, the next detection processing time point is determined using the previously stored measurement result. and
Since prediction is now possible without necessarily detecting two noise pulses in the noise monitoring interval, the range of detectable noise repetition periods has been almost doubled without reducing responsiveness compared to before. The feature is that it can be expanded.

[Embodiment] FIG. 1 shows an embodiment of the present invention, in which an ultrasonic transducer 1 for both transmitting and receiving waves is driven by a wave transmitting circuit 2 to intermittently transmit ultrasonic pulses, It is intended to receive a reflected wave pulse from an object, and this received signal is amplified by a wave receiving circuit 3, further 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 reception period _T1 , and also detects the presence of an object from the transmission pulse P of the reception pulse. The distance to the object is calculated from the time delay, and the output is displayed on the display 6.
will be displayed.

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
As shown in FIG. b, when a signal is received within a noise monitoring period T ₂ of a fixed time set after the reception period T ₁ , this is detected as noise. This section T ₂
When two noise pulses N ₁ and N ₂ are detected within
Measure the repetition period τ ₁ of the noise and its duration, or pulse width τ ₂ , determine the possible time point A ₁ for the next detection process, and control the transmitter circuit 2 based on the results. do.

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, and each detection After each processing interval T ₃ ends, a noise monitoring interval T ₂ of a certain length is provided. At this point, the noise shown in figure a has arrived,
When two of them, noise pulses N ₁ and N ₂ , are detected within the noise monitoring section T ₂ , the repetition frequency τ ₁ and pulse width τ ₂ of the noise pulses are measured, and from this measurement result, as shown in figure c, The transmission time point _A1 of the next transmission pulse P is calculated at . In the figure, this time _A1 is the time when the reverberation time α has elapsed since the fall of the second noise pulse _N2 , and in reality
It is calculated after (τ ₂ −α) has elapsed since the rise of N ₂ .

In figure c, when the next detection process is completed and the third noise pulse N ₃ is detected in the subsequent noise monitoring interval T ₂ , two noise pulses can now be detected within the same noise monitoring interval ₂ . It disappears. This may occur if the repetition period τ ₁ is larger than 1/2 of the noise audit interval T ₂ , but in that case, the values of τ ₁ and ₂ are stored in the storage circuit 9. Use the previous measurement results.

Time point _A2 in figure c is calculated in this way, and the arrival time point of _N4 is calculated from one noise pulse _N3 and the previous result, and the transmitted wave P is calculated at the previous time point _A2. It is predicted that a reception T ₁ will be possible.

By predicting the generation period of noise pulses in this way and setting the detection processing period T ₃ to a period in which it is estimated that no noise pulses exist, the detection processing period T ₃ can be adjusted to match the generation period of noise pulses. It can be set irregularly and can be measured while eliminating the influence of noise pulses that have periodicity in their generation intervals.

According to the above configuration, _one
As long as the noise is detected even if the noise is detected, the next noise arrival point can be predicted almost accurately _.
For example, by setting the length to be about twice the repetition period of the noise of a motorbike running at normal speed, it will be sufficient to deal with the case where a low-speed motorbike passes by, which rarely happens. It is something that can be done.

Note that if the repetition period τ ₁ of the noise pulse is very short and the detection processing period T ₃ including the wave transmission and reception period does not fall within the period (τ ₁ − _{τ 2} − α), the detection processing Possible point A ₁ will be postponed until the noise disappears.

[Effects of the Invention] As described above, the present invention provides noise monitoring in an ultrasonic detector that detects an object by detecting the repetition period and duration of noise and predicting the point at which no noise occurs. If two noise pulses are not detected in an interval and the repetition period cannot be measured, the previous measurement result is used, so as long as at least one noise pulse is detected in this interval, predictions can be made correctly. Therefore, there is an advantage that malfunctions can be reliably prevented even with noise of approximately twice the repetition period without impairing responsiveness compared to the conventional method.

[Brief explanation of drawings]

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 ,
N ₃ ... Noise pulse, τ ₁ ... Noise repetition period,
τ ₂ ...Pulse width of noise, A ₁ , A ₂ ...Detectable time 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. After the end of the noise monitoring period, a noise monitoring period is provided, and when a noise pulse is detected in the noise monitoring period, the repetition period and pulse width of the noise pulse are measured and stored in a storage circuit,
The next detection processing time point is determined from the measurement result, and if the above measurement cannot be performed in the noise monitoring section, the next detection processing time point is determined using the previously stored measurement result. Ultrasonic detector.