JPH08201514A - Ultrasonic distance measuring instrument - Google Patents

Abstract

PURPOSE: To optimally set a threshold signal by measuring a time until a detection signal exceeds a threshold signal from transmission trigger output and changing the threshold signal according to the speed of a traveling body when distance is calculated from sound speed. CONSTITUTION: A signal processing circuit 6 gives a transmission trigger 101 to a transmission circuit 3, the circuit 3 gives a drive signal 102 to a transmitter 2, and an ultrasonic wave 103 is applied to a distance measurement target 7. A reflection ultrasonic wave 104 enters a receiver 4, a reception signal 105 is amplified and detected by a reception circuit 5, and a detection signal 106 is sent to the signal processing circuit 6. A threshold signal 107 is set in the inside of the circuit 6 as a function of time after a trigger 101 is outputted, a time when the signal 106 after the output of the trigger 101 exceeds the signal 107 is judged as a reception time, the time is measured, and the time is multiplied by sound speed to obtain a distance. At this time, the signal 107 is set to small and large values depending on whether a traveling body is fast or slow, respectively, thus preventing usage environmental noise and positively detecting a close object.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic distance measuring device which transmits ultrasonic pulses, receives reflected waves from an object, and detects the distance to the object.

[0002]

2. Description of the Related Art Conventionally, various measuring devices using a distance sensor using ultrasonic waves, a sensor attached to a moving body to detect the distance from the periphery of the moving body, or an ultrasonic detector for detecting irregularities on a road surface have been used. It has been commercialized.

In the case of measuring a distance using ultrasonic waves, a burst-type constant output drive signal is applied to a transmitter composed of a piezoelectric element or the like to transmit an ultrasonic wave, which is emitted to a distance measurement target and reflected from the target. A general method is to receive a wave, measure its propagation time, and measure a distance.

To detect the propagation time, the time from the transmission time to the time when the received wave exceeds the threshold signal is measured. The threshold signal may be a constant value, but it is more effective to change it with the passage of time from the transmission time in order to prevent erroneous detection of distance due to noise noise. There is no general method for determining this threshold signal.

[0005]

[Problems to be Solved by the Invention]

(1) In the signal processing circuit, having a threshold signal to be compared with the detection signal after the transmission trigger signal, comparing the detection signal and the threshold signal, from the transmission trigger output, the detection signal is The time until the threshold signal is exceeded is measured, and the distance is calculated from the speed of sound.
This threshold signal is given as a function of the time from the transmission trigger.The lower this signal is, the smaller the reflected wave can be detected, and the distance that can be measured extends to a long distance. There is a trade-off relationship between noise resistance and reflected wave detection capability because false detection becomes easier. It is an object to change this threshold signal according to the moving speed of the moving body and set it optimally according to the usage situation.

(2) Further, in the detection signal of the received wave, noise noise in the ultrasonic region received by the receiver and electrical noise generated in the receiving circuit are mixed. In order to detect small reflections from distant objects, it is desirable to bring the threshold signal close to the noise level within a range not lower than the noise level. A second object is to automatically set the threshold signal according to noise, prevent erroneous detection due to noise, and extend the measurable distance according to the usage environment.

[0007]

[Means for Solving the Problems]

(1) A mobile body ultrasonic distance measuring device that is mounted on a mobile body, transmits ultrasonic pulses, receives a reflected wave from an object, and detects the distance to the object. A speed detection device for detecting a moving speed, a transmitter for transmitting ultrasonic waves to a distance measurement target, a transmission circuit for outputting a burst drive signal to the transmitter in response to a transmission trigger, and a reflection from the distance measurement target. A receiver that receives a wave, a receiving circuit that amplifies the signal and amplitude-detects it, outputs a transmission trigger signal to the transmission circuit, and inputs the amplitude-detection signal of the reflected wave and the moving speed of a mobile body to be mounted. A signal processing circuit, wherein the signal processing circuit has a threshold signal to be compared with the detection signal after the transmission trigger signal, compares the detection signal with the threshold signal, and transmits the transmission trigger. From the output, the detection signal There, depending on the speed of the moving body when calculating the distance from the sound velocity by measuring the time until beyond the thread and hold signal, to vary the thread and hold signal.

(2) An ultrasonic distance measuring device for a moving body, which transmits an ultrasonic pulse, receives a reflected wave from an object, and detects the distance to the object. And a transmitter circuit that receives a transmission trigger and outputs a burst drive signal to the transmitter, a receiver that receives a reflected wave from the target object, and amplifies and amplitude-detects the signal. A signal processing circuit that outputs a trigger signal for transmission to the transmission circuit, and that receives the amplitude detection signal of the reflected wave and the moving speed of the mounted mobile object as inputs is provided in the signal processing circuit. It has a threshold signal to be compared with the detection signal after the trigger signal, compares the detection signal with the threshold signal, and the time from the transmission trigger output until the detection signal exceeds the threshold signal. Measure The distance is calculated from the sound velocity, and the detection signal is read for a predetermined time that does not issue the transmission trigger every time the distance is measured a predetermined number of times, and the minimum value of the threshold signal is recreated inside the signal processing circuit based on the signal. .

(3) The minimum value of the threshold signal to be recreated inside the signal processing circuit is the sum of the detection signal and the detection signal at a predetermined time during which the transmission trigger is not issued.

(4) The minimum value of the threshold signal generated inside the signal processing circuit is obtained by multiplying the detection signal at a predetermined time when the transmission trigger is not issued by a predetermined value.

[0011]

The operation of the above-described structure of the present invention is as follows.

(1) The signal processing circuit has a threshold signal to be compared with the detection signal after the transmission trigger signal, compares the detection signal with the threshold signal, and outputs the transmission trigger output to The time until the detection signal exceeds the threshold signal is measured, and the distance is calculated from the speed of sound. This threshold signal is given as a function of the time from the transmission trigger.The lower this signal is, the smaller the reflected wave can be detected, and the distance that can be measured extends to a long distance. There is a trade-off relationship between noise resistance and reflected wave detection capability because false detection becomes easier.

In order to use the detected distance signal as a control or alarm for the moving body, when the moving body has a high speed, it is necessary to detect a far distance detection target, but when the moving body has a slow speed, It is necessary to reliably measure an object at a relatively short distance. Therefore, the speed of the moving body is detected, and the threshold signal is changed according to the speed. In particular,
When the speed is relatively low, an object at a short distance is surely detected. Therefore, the threshold signal is set high, noise resistance is enhanced, and an object at a short distance is surely detected. On the other hand, when the speed of the moving body is high, set the threshold signal low,
It can detect even small received signals and increase the measurable distance.

(2) Further, in the detection signal of the received wave, noise noise in the ultrasonic range received by the receiver and electrical noise generated in the receiving circuit are mixed. In order to detect small reflections from distant objects, it is desirable to bring the threshold signal close to the noise level within a range not lower than the noise level. Therefore, observe the noise level received by the receiver when it is not transmitting from the transmitter, and add a certain value to the noise level, or multiply it by a value slightly larger than 1 and use that value as the minimum threshold value. The threshold signal is newly updated so that

[0015]

EXAMPLES Details of the present invention will be described below with reference to examples. FIG. 1 shows the configuration of the first embodiment of the present invention.
1 is a speed detecting device for a moving body, 2 is a transmitter, 3 is a transmitting circuit, 4 is a receiver, 5 is a receiving circuit, 6 is a signal processing circuit, 7
It is an object to be measured.

At the time of measuring the distance, the signal processing circuit 6 gives a transmission trigger 101 to the transmission circuit 3, and the transmission circuit 3 outputs a burst-shaped drive signal 102 to the transmitter 2. When the ultrasonic wave 103 is emitted from the transmitter 2 and the ultrasonic wave is applied to the distance measurement target 7, the ultrasonic wave 103 is reflected by the distance measurement target 7 and reflected ultrasonic wave 10
4, and the reflected wave 104 is received by the receiver 4. The receiving circuit 5 detects the amplification and amplitude of the received signal 105 and detects the detected signal 106.
Is output to the signal processing circuit 6.

FIG. 2 is a diagram for explaining the process of calculating the distance inside the signal processing circuit 6. Inside the signal processing circuit 6,
It has a threshold signal 107 as a function of time after the transmission trigger output. It is better to decrease the threshold signal with time, considering that the closer the target signal is, the larger the received wave is.

Detection signal 1 after the transmission trigger 101 is output
First, the detected signal is compared with 06 and the threshold signal.
The point where 106 exceeds the threshold signal 107 is determined to be the reception time, and the time Δt from the transmission trigger output time to the reception time is measured. Using this Δt and sound velocity C, (1 formula)
Calculate the distance based on.

Distance from transmitter to target = C × Δt / 2 (Equation 1) In this processing, the lower the threshold signal, the smaller the reflected wave that can be detected, and the distance that can be measured increases, but the operating environment Since noise noise in the ultrasonic region in 3) is likely to be erroneously detected, there is a trade-off relationship between the noise resistance and the reflected wave detection ability.

When the speed of the moving body is high, it is necessary to detect a distance measurement target which is relatively far, but when the speed is low, a distance measurement target relatively close may be detected.

Therefore, as shown in FIG. 2, when the speed of the moving body is high, the threshold signal is set small so that a small received signal can be detected, and when the speed is low, the threshold signal is set large. Depending on the matter
Prevents false detection due to noise and noise in the operating environment, and reliably detects objects in a short distance.

Next, a second embodiment will be described. The configuration is the same as in FIG. 1 except for the signal processing part. Further, the distance measuring method is basically the same as that of the first embodiment, and therefore its explanation is omitted. Other components are the same as those in FIG. 1 except that the variable gain power amplifier is a power amplifier with a constant gain. The distance measuring method is basically the same as that of the first embodiment except for the method of setting the threshold signal.

FIG. 3 shows a flowchart of processing performed by the signal processing circuit. First, before starting measurement, step 20
Measure the noise level received by the receiver from 1 to 203, and add the value at that noise level, or multiply by a value slightly larger than 1, and set that value to the minimum threshold value. Set a new hold signal.

Next, in step 204, a transmission trigger is output and an ultrasonic wave is emitted from the transmitter 2. In step 205, the detection signal 1 from the receiving circuit is output for a certain period of time from the transmission trigger
06 is read, and the detected signal is compared with the threshold signal in step 206, and the time when the detected signal exceeds the threshold signal is regarded as the time when the reflected wave from the distance measurement target 7 arrives from the transmission trigger output. Time to reach the reflected wave Δ
t is measured, and in step 207, the distance to the distance measurement target 7 is calculated based on (1 expression).

Thereafter, if the number of times of continuous measurement is less than or equal to a predetermined number of times, a transmission trigger is continuously output, and the step
Repeat the distance measurement operation from 204 to 207. When the number of times of continuous measurement reaches the predetermined number of times, the process returns to step 202, and the threshold signal is updated as described above by measuring the noise level.

FIG. 4 is a diagram for explaining the updating of the threshold signal. The threshold signal is updated so that the minimum value of the threshold signal approaches the measured noise level. In this embodiment, the software processing is assumed as the means for realizing the signal processing, but it may be realized only by hardware.

Although the amplification gain for amplifying the received wave in the receiving circuit has been described as constant, it is still more effective if it is increased with time after the output of the transmission trigger.

[0028]

【The invention's effect】

(1) As described above, in the first invention, the threshold signal is changed according to the speed of the moving object, and when the speed is relatively low, the object at a short distance is reliably detected. , Threshold signal is set high, noise resistance is enhanced, and target in short distance can be detected reliably. On the other hand, when the speed of the moving body is high, the threshold signal is set low, and even a small reception signal can be detected, and the measurable distance becomes large.

(2) In the second aspect of the invention, the noise level of the use environment is measured during the time when no ultrasonic wave is transmitted, and the minimum value of the threshold signal is set according to the noise level. It is possible to prevent erroneous detection of the distance when there is noise in the ultrasonic region in the environment, and it is possible to increase the measurable distance according to the usage environment.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a first embodiment of the present invention.

FIG. 2 is an operation explanatory diagram of the first embodiment of the present invention.

FIG. 3 is a flow chart for explaining signal processing contents in the second embodiment of the present invention.

FIG. 4 is an operation explanatory diagram of the second embodiment of the present invention.

[Explanation of symbols]

 1 speed detection device 2 transmitter 3 transmission circuit 4 receiver 5 reception circuit 6 signal processing circuit 7 distance measurement target 101 transmission trigger 102 transmitter drive signal 103 ultrasonic wave 104 reflected wave 105 reception signal 106 detection signal 107 threshold signal 108 Reflected wave from the target object

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location G01S 15/93

Claims (4)

[Claims] 1. Mounted on a moving body to transmit ultrasonic pulses,
An ultrasonic distance measuring device for a moving body, which receives a reflected wave from an object and detects a distance to the object, a velocity detecting device for detecting a moving speed of the moving body, and an ultrasonic wave for a distance measuring object. A transmitter for transmitting and a transmission circuit for receiving a transmission trigger to output a burst drive signal to the transmitter, a receiver for receiving a reflected wave from the object to be measured, and amplifying the signal,
In the signal processing circuit, a reception circuit that detects an amplitude, a signal processing circuit that outputs a transmission trigger signal to the transmission circuit, and receives an amplitude detection signal of the reflected wave and a moving speed of a moving body to be mounted are provided. , Having a threshold signal to be compared with the detection signal after the transmission trigger signal, comparing the detection signal with the threshold signal, and the detection signal exceeds the threshold signal from the transmission trigger output. An ultrasonic distance measuring device characterized in that a threshold signal is changed according to the speed of a moving body when the time until is calculated and the distance is calculated from the speed of sound. 2. An ultrasonic distance measuring device for a mobile body, which transmits an ultrasonic pulse, receives a reflected wave from an object, and detects a distance to the object, wherein the ultrasonic wave is applied to an object to be measured. A transmitter for transmitting and a transmitter circuit for receiving a transmission trigger to output a burst drive signal to the transmitter, a receiver for receiving a reflected wave from the target object, and a receiver for amplifying and amplitude-detecting the signal. Circuit, and a signal processing circuit that outputs a transmission trigger signal to the transmission circuit, and inputs the amplitude detection signal of the reflected wave and the moving speed of a moving body to be mounted, in the signal processing circuit, the transmission trigger A threshold signal to be compared with the detection signal after the signal, comparing the detection signal and the threshold signal, the time from the transmission trigger output until the detection signal exceeds the threshold signal Measured , Calculates the distance from the speed of sound, reads the detection signal for a predetermined time that does not issue the transmission trigger for each predetermined number of distance measurements, and recreates the minimum value of the threshold signal in the signal processing circuit based on the signal. An ultrasonic distance measuring device characterized by the above. 3. The minimum value of the threshold signal produced in the signal processing circuit is the sum of the detection signal and a predetermined value at a predetermined time when the transmission trigger is not issued. Ultrasonic distance measuring device. 4. The minimum value of the threshold signal produced in the signal processing circuit is obtained by multiplying the detection signal at a predetermined time when the transmission trigger is not issued by a predetermined value. Ultrasonic distance measuring device.