JP2003156561A - Method and device for ultrasonic wave distance measurement - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic wave distance measuring method and a device thereof, capable of accurately measuring a distance from a target only by judging the level of a received echo, with no AGC required. SOLUTION: The received echo is discriminated for three different threshold levels (TH). Based on both a time T1 starting from the time point of transmission through the time point which exceeds a first TH and a time T2 starting from the time point of transmission through the time point which exceeds a second TH, a time T0 starting from the time point of transmission through the time point of rising of the received echo is calculated by linear approximation, for measuring a distance. If the received echo exceeds a third TH, distance measurement result is assumed to be varid while it is assumed to be invalid if the received echo does not exceed the third TH.

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 method and apparatus for measuring a distance from a time until ultrasonic waves are transmitted and reflected waves from a target are received.

[0002]

2. Description of the Related Art Conventionally, a distance measuring device utilizing ultrasonic waves has been widely used to measure a distance to a target.

FIG. 7 is a diagram showing a block configuration of an ultrasonic distance measuring device generally used conventionally, and FIG. 8 is a diagram for explaining a distance measuring operation.

In FIG. 7, a central processing unit (hereinafter,
The CPU 71 operates based on the reference clock signal from the oscillator 72. When measuring the distance to the target, first, a transmission trigger is given from the CPU 71 to the drive signal generation circuit 73, and a burst signal of a predetermined frequency formed based on this is amplified by the power amplification circuit 74 and transmitted via the transmission / reception switch 75. It is supplied to the ultrasonic sensor 76. In addition,
The drive signal generation circuit 73 and the power amplification circuit 74 constitute a transmission circuit.

The ultrasonic sensor 76 is driven by a burst signal, and the ultrasonic sensor 76 transmits a transmission pulse toward a target. The transmission pulse is reflected by the target, the ultrasonic echo is received by the ultrasonic sensor 76, converted into an electric signal, and the received echo is supplied to the reception circuit via the transmission / reception switch 75.

The received echo has a bandpass filter 77 of the receiving circuit to remove noise outside the band, is amplified by an amplifying circuit 78, is detected by a detecting circuit 79, and is compared with the level comparing circuit 8
Supplied to zero. The level comparison circuit 80 is set with a threshold level TH, the detection output from the detection circuit 79 is compared with the threshold level TH, and supplies a level comparison signal to the CPU 71 when the detection output exceeds the threshold level TH. The CPU 71 measures the distance from the distance measuring device to the target based on the time T from the generation of the transmission trigger to the reception of the level comparison signal, and displays the measured distance on the display 81.

[0007]

In this distance measurement, the level of the received echo may vary greatly depending on the shape (concavities and convexities), material and distance of the target. In particular, with a short-range target (for example, vehicle height measurement on a road surface with severe unevenness), when the echo level is not stable, it causes a large error in the distance measurement result.

This state will be described with reference to FIG. The distance to the target is obtained from the time T until the echo received after transmitting the ultrasonic pulse exceeds the threshold level TH in the level comparison circuit 80.
The received echo waveform generally has a delay in its rising and falling due to the characteristics of the ultrasonic sensor 76 and the characteristics of the receiving circuit including a bandpass filter. For this reason, the time when the received echo exceeds the threshold level TH is greatly different between the case of the waveform B indicated by the solid line having a high echo level and the case of the waveform B indicated by the broken line having a low echo level. The distance measurement value changes greatly depending on the level. In particular, when measuring a target at a short distance, a large error will be included.

In order to solve this problem, as shown in FIG. 7, a bandpass filter 77, an amplifier circuit 78, a detection circuit 79, and a AGC detection circuit 82 which form a reception circuit.
Is provided so that the amplification degree of the amplifier circuit 78 can be controlled. Then, the echo level (peak value) of the detection circuit 79
The automatic gain control (to be referred to as AGC hereinafter) is performed so that is a constant value. That is, the AGC circuit configuration reduces the gain of the amplification circuit 78 by feeding back when the received echo level is high, and conversely increases the gain of the amplification circuit 78 when the echo level is low. That is, it operates so as to automatically control the amplification degree of the amplifier circuit 78 and keep the output level constant. However, since the output is fed back, there is a problem that it is difficult to keep the output level constant when the echo level (peak value) fluctuates significantly.

Further, there is a drawback that the circuit scale becomes large due to the AGC, the circuit mounting area increases, and the cost increases.

The present invention has been made in view of the above problems.
An object of the present invention is to provide an ultrasonic distance measuring method and an apparatus therefor, which can accurately measure the distance to a target by eliminating the need for GC and only by judging the level of the received echo.

[0012]

An ultrasonic distance measuring method according to a first aspect of the present invention is a method for measuring a distance to a target by a time from a transmission time point of an ultrasonic pulse to a reception time point of a reception echo reflected by the ultrasonic pulse at the target. In the ultrasonic distance measuring method for measuring, the reception echo is determined at at least three different first threshold levels to third threshold levels, and the reception echo has a time from a transmission time point to a time point exceeding the first threshold level, and The time from the transmission time to the rising edge of the reception echo is calculated by linear approximation from the time from the transmission time to the time when the second threshold level which is higher than the first threshold level is exceeded, and the reception echo changes to the second threshold. Calculated when the 3rd threshold level, which is higher than the level, is exceeded While more the obtained the rising time and the reception time of the received echo, when said received echo does not exceed said third threshold level, characterized by a disabling said rise time.

According to the ultrasonic distance measuring method of claim 1,
Since the rising time of the reception echo is calculated from the time when the first threshold level is exceeded and the time when the second threshold level is exceeded, the reception echo level constantly fluctuates without using a complicated circuit such as AGC. Even under the time, the time from the transmission time to the reception time can be accurately obtained. Therefore, it is possible to accurately measure the distance of the short-range target in which the echo level varies greatly. Further, since the rising time of the received echo is acquired as the received time only when the received echo exceeds the third threshold level, the reliability of distance measurement can be ensured.

An ultrasonic distance measuring apparatus according to a second aspect of the present invention is a transmission means for generating a transmission pulse, a transmission pulse from the transmission means is transmitted as an ultrasonic pulse, and a reflected wave reflected by a target is received to receive echo. An ultrasonic sensor means for outputting, a detecting means for detecting a reception echo from the ultrasonic sensor means, and a detected reception echo for at least 3
The first threshold level to the third threshold level, which have a large sequential level, are compared with each other, and a level comparison means for outputting a comparison result and a transmission trigger are given to the transmission circuit to measure a time, and at the same time, a judgment and control function is provided. And a time from the time when the transmission echo exceeds the first threshold level to the time when the reception echo exceeds the first threshold level, and a time from the time when the transmission trigger exceeds the second threshold level to the time when the transmission echo exceeds the second threshold level. From the above, the time from the transmission trigger time to the rising time of the reception echo is calculated by linear approximation, and when the reception echo exceeds the third threshold level, the rising time is taken as the reception time of the reception echo to the target. While measuring the distance of the received echo, the received echo is equal to the third threshold level. If not exceeded, characterized in that it does not perform a distance measurement to the target.

According to the ultrasonic distance measuring device of claim 2,
The level comparison means compares the received echo with the first to third threshold levels, and the control means calculates the rising time of the received echo based on the comparison result to measure the distance. Therefore, a complicated circuit such as AGC is used. Without using
The distance to the target can be accurately obtained even in a situation where the received echo level constantly fluctuates. In particular, it is suitable for distance measurement of a short-range target in which the echo level varies greatly. Further, since the rising time of the received echo is acquired as the received time only when the received echo exceeds the third threshold level, the reliability of distance measurement can be ensured.

An ultrasonic distance measuring apparatus according to a third aspect is the ultrasonic distance measuring apparatus according to the second aspect, wherein the level comparing means is any one of the first threshold level to the third threshold level for each received echo. Can be set as a threshold level, the control means,
It is characterized in that any one of the first to third threshold levels is set as the threshold level in the level comparing means.

According to the ultrasonic distance measuring device of claim 3,
Each time an ultrasonic pulse is transmitted, the threshold level of the comparing means is sequentially changed and set to the first, second and third threshold levels, and one level judgment is made for each reception of each received echo. Also, the time measuring means can have a simple structure such as a single comparator and a counter, and the device structure can be reduced.

An ultrasonic distance measuring apparatus according to a fourth aspect is the ultrasonic distance measuring apparatus according to the second aspect, wherein the level comparing means has a first comparator set to the first threshold level, and the second comparator. It is characterized by having a second comparator set to a threshold level and a third comparator set to the third threshold level.

According to the ultrasonic distance measuring device of claim 4,
By providing a comparator for each threshold level in the level comparing means, and performing multi-step level comparison for each received echo,
The distance measurement result can be obtained in a short time.

An ultrasonic distance measuring apparatus according to claim 5 is the ultrasonic distance measuring apparatus according to any one of claims 2, 3 and 4, wherein the control means starts time counting by the transmission trigger, It is characterized in that it has a counter means for stopping the time counting by the comparison result output of the level comparing means, and measures the time by the count value of the counter means.

According to the ultrasonic distance measuring device of claim 5,
Since the time counting is started by the transmission trigger, and the time counting is stopped by the comparison result output of the level comparing means, the time is measured by the counter means. It is possible to measure the time accurately by simply counting the clock signals with the resolution of. Further, the control means does not require an expensive CPU that operates at high speed, and can be configured by a control device such as an inexpensive CPU that operates at a relatively low speed.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

The basic concept of the ultrasonic distance measuring method and apparatus of the present invention will be described with reference to FIG. The reception echo E for the ultrasonic transmission pulse is determined at at least three different first threshold levels TH1 to TH3. In addition, TH1 <TH2
<TH3 is set.

First, the reception echo E has a time T1 from the transmission time ts to the time t1 when it exceeds the first threshold level TH1 and a time T2 from the transmission time ts to the time t2 when it exceeds the second threshold level TH2. Ask.

Next, a triangle similarity is applied to the rising of the reception echo E, and the time T0 from the transmission time ts to the rising time t0 of the reception echo E is calculated by linear approximation. That is, TH2: TH1 = (T2-T0) :( T
The time T0 is calculated from (1-T0). This time T0
This is the time required to make a round trip of the ultrasonic pulse to the target.

Next, when the received echo E exceeds the third threshold level TH3, the magnitude of which is appropriately determined, it is assumed that the linear approximation is valid, and the rising time point t0 (that is, calculated) is calculated. The distance is measured with the time T0) as the reception time of the reception echo E.

However, as shown by the broken line in the figure, when the received echo E does not reach the third threshold level TH3, the linear approximation is not appropriate and the rising time t.
A lot of errors are included in 0 '. That is, the rising time point t when the echo level is normal indicated by the solid line
As apparent from comparison with 0, the time T1 ′ from the transmission time ts to the time t1 ′ when the reception echo E exceeds the first threshold level TH1 and the time T1 ′ from the transmission time ts to the second threshold level TH2. The rising time point t0 'calculated based on the time T2' up to t2 'is deviated from the true rising time point, which causes a large error in the distance measurement. Therefore, the obtained rising time t0 '(that is, the time T0') is invalidated. That is, in this case, the distance to the target is not obtained or even if it is obtained, it is invalid.

In this way, according to the present invention, the distance from the ultrasonic pulse transmission time ts to the reception time t0 of the reception echo E is measured accurately and highly reliably to measure the distance to the target.

FIG. 2 is a diagram showing an overall block configuration of the ultrasonic distance measuring apparatus according to the first embodiment of the present invention, and FIG. 3 is a diagram for explaining the procedure of its measuring operation.

In FIG. 2, the CPU 11 has an oscillator 12
Receives the reference clock signal from the
Threshold level TH (TH1, TH2 or TH
In addition to outputting 3), it controls the judgment and control functions of this device.
The counter 13 is composed of, for example, a 16-bit binary counter, receives a measurement clock signal from the oscillator 12, and starts a counting operation by a transmission trigger. Then, the count operation is terminated by the comparison output from the comparator 21, the count value is latched and supplied to the CPU 11 as 16-bit count data. The CPU 11, the oscillator 12, and the counter 13 constitute control means.

The drive signal generation circuit 14 receives a transmission trigger to generate a drive signal having a predetermined frequency and a predetermined pulse width, and the power amplification circuit 15 amplifies the drive signal. The drive signal generation circuit 14 and the power amplification circuit 15 form a transmission circuit.
The transmission / reception switch 16 gives the transmission pulse from the power amplification circuit 15 to the ultrasonic sensor 17, the ultrasonic sensor 17 sends out the ultrasonic pulse toward the target, receives the reflected wave reflected by the target, and receives it as a reception echo. It is supplied to the receiving circuit via the transmission / reception switch 16.

The receiving circuit is composed of a bandpass filter 18, an amplifying circuit 19 and a detecting circuit 20, and the reception echo E detected by the detecting circuit 20 is output to a comparator 21 which is a comparing means. The amplifier circuit 19 amplifies the signal at the set amplification degree, but does not perform the AGC operation.

A procedure for measuring the distance to the target with the distance measuring device shown in FIG. 2 will be described. In the first embodiment, the distance measurement is performed once by setting transmission and reception three times.

First, at the time of the first transmission, the CPU 1
1 to the comparator 21 to the first threshold level TH1
To set. Then, the CPU 11 generates a transmission trigger to drive the transmission circuit, and the ultrasonic sensor 17 sends an ultrasonic pulse toward the target. The transmission trigger is given to the counter 13, resets the count value, and then starts the counting operation from the initial value.

The reflected wave reflected by the target is received by the ultrasonic sensor 17, detected by the receiving circuit, becomes a reception echo E, and is supplied to the comparator 21. The threshold level of the comparator 21 is the first threshold level T
It is set to H1.

Referring to FIG. 3 (a), at time t1 when the received echo E reaches the first threshold level TH1, the comparator 21 supplies the signal of the comparison result to the counter 13 to stop the counting operation. Then, the count value at that time is latched. This count value is input to the CPU 11 as 16-bit count data. This count value corresponds to the time T1 from the transmission trigger ts to the time point t1. TR is a transmission wave (including a reverberation wave).

Next, the second transmission is performed. At the time of the second transmission, the CPU 111 sets the second threshold level TH2 in the comparator 21. This second
The second transmission and reception are performed in the same manner as the first transmission, and as a result, as shown in FIG. 3B, at the time t2 when the reception echo E reaches the second threshold level TH2, the comparison result from the comparator 21 is output. A signal is supplied to the counter 13, the counting operation is stopped, the count value is latched, and the count value is input to the CPU 11. This count value corresponds to the time T2 from the transmission trigger ts to the time point t2.

These times T1, T2, the first threshold level TH1 and the second threshold level TH
Based on 2, the time T0 until the rising time t0 of the reception echo E is obtained by linear approximation.

Furthermore, the third transmission is performed. At the time of this third transmission, the CPU 11 makes the comparator 21
Set the threshold level TH3. This third transmission and reception is performed in the same manner, and as a result, as shown in FIG.
As shown in (c), it is determined whether the received echo E has exceeded the third threshold level TH3. This determination is made by the CPU 11 by stopping the counting operation of the counter 13 when the reception echo E exceeds the third threshold level TH3 and inputting the count value.

When the received echo E exceeds the third threshold level TH3, the linear approximation is valid, so that the rising time t0 (that is, the time T
0) is the reception time of the reception echo E, and the distance to the target is immediately obtained from this time T0.

However, when the received echo E does not reach the third threshold level TH3, the linear approximation is not appropriate and the rising time includes many errors.
0) is invalid. That is, in this case, the distance to the target is not obtained or even if it is obtained, it is invalid.

The fact that the received echo E does not reach the third threshold level TH3 can be determined by the fact that the count value is not input from the counter 13 to the CPU 11.
Alternatively, the output of the comparator 21 may be monitored to make the determination.

As each threshold level, TH1
Setting x2 = TH2 facilitates calculation. Further, the larger the third threshold level TH3 is than the second threshold level TH2, the smaller the error included in the rising time point, which is preferable. However, from the viewpoint of stably detecting the first threshold level TH1 and the second threshold level TH2, for example, T
It is preferable to set H3 = 3 · TH1 and TH2 = 2 · TH1. It should be noted that the first threshold level TH1 may be set so that a margin of about 5 times the noise level can be obtained so that noise other than the received echo from the target is not detected.

The threshold levels need not necessarily be set in the order of TH1, TH2, TH3, but the order can be reversed.

As described above, after the distance measurement has been completed by transmitting and receiving the ultrasonic pulse three times, the measurement is continuously performed, and the measurement results of the plurality of times are averaged to obtain the measured distance. Is good. In this case, it is not strictly real-time measurement, but the transmission / reception cycle is short (cycle:
10 ms), no substantial change occurs in the level of each received echo during the averaging.

As a concrete example of this embodiment, the characteristics of the transmission / reception circuit can be set as follows. Further, the characteristic of the received echo is such that the actually measured waveform is shown in FIG. Transmission frequency / voltage: 800 kHz, 10 waves, 3
8Vp-p band pass filter characteristic: 740 to 860 kHz (-
3 dB) Gain of amplifier circuit: 70 dB (Fig. 4 (a)),
74 dB (Fig. 4 (b)) Transducer characteristics of sensor: resonance frequency 790 kHz,
Q = 13.2 (-3 dB),
Cd = 116 pF (at 1 kHz)

In particular, in this embodiment, the transducer of the ultrasonic sensor is not saturated so as to be suitable for the measurement of the distance to the short-range target, and the transmission pulse is 800 kH.
z, 10 burst waves. As a result, the waveform of the received echo can be made substantially triangular.

FIG. 4A shows that the gain of the amplifier circuit is 70 dB.
The echo waveform E in the case of is shown. Since the amplifier circuit is not saturated, the output echo waveform E has a triangular shape.

FIG. 4B shows a gain of the amplifier circuit of 74 dB.
The echo waveform E in the case of is shown, and the upper portion of the echo waveform is cut because the amplification circuit is saturated,
The rising edge of the waveform is sharp.

In FIG. 4, since the echo waveform in the receiving circuit is actually measured, the transmission pulse TR looks small and conversely a large reverberation wave TR 'is observed. Further, in FIGS. 4A and 4B, the position of the target is different.

In the first embodiment, the distance to the target can be obtained accurately even in a situation where the level of the received echo E constantly fluctuates without using a complicated circuit such as AGC. In particular, it is suitable for distance measurement of a short-range target in which the echo level varies greatly. Further, since the rising time t0 of the reception echo is acquired as the reception time only when the reception echo E exceeds the third threshold level TH3, the reliability of the distance measurement can be ensured.

Further, every time the ultrasonic pulse is transmitted, the comparator 2
The threshold level TH of 1 is sequentially changed and set to the first, second, and third threshold levels, and one level judgment is performed for each reception of each received echo, so that a simple comparator, counter, etc. can be used. Therefore, it is possible to reduce the size of the device.

FIG. 5 is a diagram showing the overall block configuration of an ultrasonic distance measuring apparatus according to the second embodiment of the present invention, and FIG. 6 is a diagram for explaining its measuring operation.

In the second embodiment shown in FIG. 5, the distance is measured by transmitting and receiving the ultrasonic pulse once. For that purpose, the comparison means has a first comparator 21-1 set to the first threshold level and a second comparator 21-2 set to the second threshold level.
And a third comparator 21-3 set to the third threshold level.

Further, as a counter in the control means,
A first counter 13-1 that counts the comparison result of the first comparator 21-1, a second counter 13-2 that counts the comparison result of the second comparator 21-2, and a third comparator 21-3.
And a third counter 13-3 that counts the comparison result of. Other configurations are the same as those in the first embodiment shown in FIG.

In FIG. 5, first to third comparators 21-1
21-3 are preset to the first to third threshold levels TH1 to TH3, respectively. When the transmission trigger is output from the CPU 11, the first to third counters 13
After the count value is reset, -1 to 13-3 simultaneously start the count operation from the initial value.

At this time, the transmission circuit is driven by the transmission trigger and the ultrasonic transmission pulse is sent from the ultrasonic sensor 17 toward the target. The reflected wave reflected by the target is received by the ultrasonic sensor 17, detected by the receiving circuit, and becomes the received echo E, which is the first to third comparators 21-.
1 to 21-3 are supplied in parallel.

Referring to FIG. 6, at the time t1 when the reception echo E reaches the first threshold level TH1, the signal of the comparison result from the first comparator 21-1 is the first counter 13-1.
To stop the counting operation and latch the count value at that time. This count value is input to the CPU 11 as 16-bit count data. This count value corresponds to the time T1 from the transmission trigger ts to the time point t1.

Subsequently, at the time t2 when the received echo E reaches the second threshold level TH2, the second comparator 2
The signal of the comparison result is supplied to the second counter 13-2 from 1-2, the counting operation is stopped, and the count value at that time is latched. This count value is input to the CPU 11 as 16-bit count data. This count value is the time T from the transmission trigger ts to the time point t2.
Corresponds to 2.

Further, when the reception echo E exceeds the third threshold level TH3, the signal of the comparison result is supplied from the third comparator 21-3 to the third counter 13-3,
The counting operation stops, and the count value at that time is C
It is input to PU11. As a result, the CPU 11 detects that the third threshold level TH3 has been exceeded. The third counter 13-3 can be omitted. In this case, the output level of the third comparator 21-3 may be directly recognized by the CPU 11.

When the received echo E exceeds the third threshold level TH3, the linear approximation is valid, so that the time T1, the time T2, and the first threshold level T are obtained.
Based on H1 and the second threshold level TH2,
The time T0 until the rising time t0 of the reception echo E is obtained by linear approximation. From this time T0, the distance to the target is immediately obtained.

However, when the received echo E does not reach the third threshold level TH3, the linear approximation is not appropriate and the rising time point contains many errors.
That is, compared with the rising time point t0 in the case of a normal echo level, the calculated rising time point is deviated from the true rising time point, which causes a large error in the distance measurement. Therefore, the obtained rising time t0 (that is, the time T0) is invalidated. That is, in this case, the distance to the target is not obtained or even if it is obtained, it is invalid.

In the second embodiment, the level comparing means further includes the first to third threshold levels.
Since the third comparators 21-1 to 21-3 are provided to perform multi-step level comparison for each received echo, the distance measurement result can be obtained in a short time.

[0064]

According to the ultrasonic distance measuring method of the first aspect, since the rising time of the reception echo is calculated from the time when the first threshold level is exceeded and the time when the second threshold level is exceeded, the AGC is performed. It is possible to accurately obtain the time from the transmission time point to the reception time point even in a situation where the reception echo level constantly fluctuates without using such a complicated circuit. Therefore, it is possible to accurately measure the distance of the short-range target in which the echo level varies greatly. Further, since the rising time of the received echo is acquired as the received time only when the received echo exceeds the third threshold level, the reliability of distance measurement can be ensured.

According to the ultrasonic distance measuring device of claim 2,
The level comparison means compares the received echo with the first to third threshold levels, and the control means calculates the rising time of the received echo based on the comparison result to measure the distance. Therefore, a complicated circuit such as AGC is used. Without using
The distance to the target can be accurately obtained even in a situation where the received echo level constantly fluctuates. In particular, it is suitable for distance measurement of a short-range target in which the echo level varies greatly. Further, since the rising time of the received echo is acquired as the received time only when the received echo exceeds the third threshold level, the reliability of distance measurement can be ensured.

According to the ultrasonic distance measuring device of claim 3,
Each time an ultrasonic pulse is transmitted, the threshold level of the comparing means is sequentially changed and set to the first, second and third threshold levels, and one level judgment is made for each reception of each received echo. Also, the time measuring means can have a simple structure such as a single comparator and a counter, and the device structure can be reduced.

According to the ultrasonic distance measuring device of claim 4,
By providing a comparator for each threshold level in the level comparing means, and performing multi-step level comparison for each received echo,
The distance measurement result can be obtained in a short time.

According to the ultrasonic distance measuring device of claim 5,
Since the time counting is started by the transmission trigger, and the time counting is stopped by the comparison result output of the level comparing means, the time is measured by the counter means. It is possible to measure the time accurately by simply counting the clock signals with the resolution of. Further, the control means does not require an expensive CPU that operates at high speed, and can be configured by a control device such as an inexpensive CPU that operates at a relatively low speed.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the concept of an ultrasonic distance measuring method and device according to the present invention.

FIG. 2 is a diagram showing an overall block configuration according to the first embodiment.

FIG. 3 is a diagram illustrating the procedure of the measurement operation.

FIG. 4 is a diagram showing characteristics of a received echo in the embodiment.

FIG. 5 is a diagram showing an overall block configuration according to a second embodiment.

FIG. 6 is a diagram for explaining the measurement operation.

FIG. 7 is a diagram showing a block configuration of a conventional ultrasonic distance measuring device.

FIG. 8 is a diagram for explaining the distance measurement operation of FIG. 7.

[Explanation of symbols]

11 CPU 12 oscillators 13, 13-1 to 13-3 counter 14 Drive signal generation circuit 15 Power amplifier circuit 16 transmission / reception switch 17 Ultrasonic sensor 18 bandpass filter 19 Amplifier circuit 20 Detection circuit 21, 21-1 to 21-3 Comparator

Claims (5)

[Claims] 1. An ultrasonic distance measuring method for measuring a distance to a target according to a time from a transmission time point of an ultrasonic pulse to a reception time point of a reception echo reflected by the ultrasonic pulse at the target. Judgment is made from three different first to third threshold levels, and the time from the time when the reception echo exceeds the first threshold level to the time when the reception echo is exceeded, and the second threshold level higher than the first threshold level from the time of transmission. The time from the point of transmission to the point of rise of the received echo is calculated by linear approximation from the time until the point of time when the received echo exceeds the third threshold level which is higher than the second threshold level. The obtained rising time is set to the reception The ultrasonic distance measuring method is characterized in that the rising time is invalidated when the reception echo does not exceed the third threshold level while the reception time of the code is set. 2. A transmitting means for generating a transmitting pulse, an ultrasonic sensor means for transmitting the transmitting pulse from the transmitting means as an ultrasonic pulse, receiving a reflected wave reflected by a target and outputting a reception echo. The detection means for detecting the reception echo from the ultrasonic sensor means and the detected reception echo are compared with at least three first threshold levels to third threshold levels having large levels, and a level for outputting a comparison result. Comparing means, and a control means having a function of judging and controlling while giving a transmission trigger to the transmission circuit to measure a time, the control means is configured such that a reception echo changes the first threshold level from a transmission trigger time point. Time until the time exceeds the time, and time from the time of the transmission trigger to the time when the second threshold level is exceeded From the time interval, the time from the transmission trigger time to the rising time of the reception echo is calculated by linear approximation, and when the reception echo exceeds the third threshold level, the rising time is taken as the reception time of the reception echo and the target The ultrasonic distance measuring device is characterized in that the distance to the target is not measured when the received echo does not exceed the third threshold level while the distance to the target is measured. 3. The level comparing means can set any one of the first threshold level to the third threshold level as a threshold level for each received echo, and the control means includes the level comparing means in the level comparing means. The ultrasonic distance measuring device according to claim 2, wherein any one of the first threshold level to the third threshold level is set as the threshold level. 4. The level comparing means sets a first comparator set to the first threshold level, a second comparator set to the second threshold level, and the third threshold level. The ultrasonic distance measuring device according to claim 2, further comprising a third comparator which is provided. 5. The control means has counter means for starting time counting by the transmission trigger and stopping time counting by the comparison result output of the level comparing means, and measuring time by the count value of the counter means. It carries out, The ultrasonic distance measuring device in any one of Claim 2, 3 or 4 characterized by the above-mentioned.