JPH09257931A - Ultrasonic sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure speedy measurement of a distance and relative speed by providing a high speed counter capable of counting at least one wave of reception waves. SOLUTION: The maximum and minimum values of the count values of reception waves obtained by a high speed counter 12 are detected by a maximum and minimum value detection unit 14. An average value calculation circuit 15 performs average calculation per one wave with respect to the count values operated by the counter 12, in terms of the rest values obtained by reducing the maximum value and the minimum value from the count values. According to the average count value per one wave, a frequency-voltage conversion unit 16 calculates the frequency of the reception wave, and on reception of the determination result of determination unit 13 determining the data of the frequency of the wave from an oscillator 2 and approaching/separating, outputs the relative speed of substance with the speed converted into the voltage. The distance of substance can be measured with the time of delay of the reception wave form the transmission time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic sensor for measuring a distance to an object and a relative speed of the object by utilizing ultrasonic waves.

[0002]

2. Description of the Related Art Conventionally, as an ultrasonic sensor of this type, there is one having a structure disclosed in Japanese Patent Application No. 7-223084 filed by the applicant of the present application. As shown in FIG. 6, this one has a shorter first transmission time Ts and a longer second transmission time compared to a predetermined time Tf (not shown) for the transmission time of the ultrasonic wave transmission. Alternating to two types of Tl in a cycle of tr / 2, the transmission wave W ₀ s (frequency f ₀ ) is transmitted at the first transmission time Ts, and then the reflected wave from the object is received. The distance to the object with the delay time Td until it is detected as the wave Ws (frequency f) is the transmission wave W ₀ l (frequency
The relative velocity of the object is switched and measured by the frequency difference Δf = ff ₀ between f ₀ ) and the received wave Wl (frequency f).

[0003]

In the above-mentioned conventional example, even when the object is at a short distance, when the relative speed is measured, the relative speed is small, that is, the transmitted wave W ₀ l (frequency f ₀ ) is received. When trying to measure up to a small frequency difference Δf = ff _{0 from the} wave Wl (frequency f), the wavelength of the waveform with that frequency difference Δf becomes longer, but at least one wavelength longer than the predetermined continuous time Tf Transmission W ₀ l with long second transmission time Tl
Is transmitted, the wave number difference Δf = ff ₀ can be detected in the duration of the second transmission time Tl, and when measuring the distance, the first transmission time Ts shorter than the predetermined time Tf and The transmitted wave W ₀ s is transmitted so that the transmitted wave W ₀ s and the received wave Ws can be distinguished from each other without being continuous, so that the transmitted wave W ₀ s is transmitted and then the received wave Ws is detected. It is possible to reliably detect the delay time Td up to and to measure both the distance and the relative velocity without widening the short-range dead zone by making the first transmission time Ts as small as possible at this time.

However, two types of transmission waves, W ₀ s having a first transmission time Ts and a transmission wave W ₀ l having a second transmission time Tl, for measuring the distance and the relative velocity, respectively, are set as tr. Since it is necessary to alternately change and transmit the data at the cycle of / 2, it takes at least twice the response time tr of the cycle tr / 2 to complete the measurement of both the distance and the relative speed. The measurement speed will be slow.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an ultrasonic sensor capable of measuring both a distance to an object and a relative speed more quickly. .

[0006]

In order to solve the above-mentioned problems, according to a first aspect of the present invention, from transmitting an ultrasonic pulse as a transmitted wave to detecting a reflected wave from an object as a received wave. The distance to the object is measured with a delay time, in an ultrasonic sensor for measuring the relative velocity of the object with the difference between the frequency of the transmitted wave and the frequency of the received wave detected, for detecting the frequency of the received wave, A high-speed counter capable of counting the time of at least one wave of the received wave is provided.

According to a second aspect of the present invention, in the first aspect of the present invention, a wave number check unit for checking that the received wave is present at a predetermined wave number or more is provided, and when the signal of the wave number check unit is received, The high-speed counter counts at least one time of the predetermined wave number,
An average value calculation circuit for calculating the average of the count values of the high-speed counter per wave is provided.

According to a third aspect of the present invention, in the second aspect, the maximum and minimum values among the count values of the plurality of high-speed counters each having one unit of the predetermined wave number as one unit. Is provided with a maximum / minimum detection unit for detecting
Except for the maximum and minimum values, the average value calculation circuit performs the calculation.

According to a fourth aspect of the present invention, in the second aspect, a predetermined upper limit value and a lower limit value among the count values of the plurality of high-speed counters each having one unit of the predetermined wave number as one unit. An upper limit / lower limit determination unit for determining a deviation is provided, and the average value calculation circuit is configured to exclude the deviation.

According to a fifth aspect of the present invention, in the first aspect, the wave number counting section for counting all the wave numbers of the received waves and the total count value of the received waves by the high speed counter are counted by the wave number counting section. An average value calculation circuit for calculating an average per wave number is provided.

According to a sixth aspect of the present invention, in the fifth aspect, the maximum / minimum detection for detecting the maximum and minimum values among the count values by the high-speed counter for each one wave of the count wave number. A unit is provided, and the average value calculation circuit is configured to perform calculations except for the maximum and minimum values.

According to a seventh aspect of the present invention, in the fifth aspect, it is determined whether or not the count value by the high-speed counter per each wave of the count wave number deviates from a predetermined upper and lower limit value. An upper / lower limit determination unit is provided, and the average value calculation circuit is configured to perform calculations excluding those that are outside the upper / lower limit determination unit.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIGS. In FIG. 1, the transmission pulse generator 1 generates a transmission pulse oscillated at the frequency f ₀ of the oscillator 2, and the transmission pulse passes through the booster 3 and the anti-parallel connection diode 4 to generate the transmission pulse shown in FIG. ) The wave transmitter / receiver (specifically, the ultrasonic transducer) 5 is vibrated as a wave W ₀ shown in), and the ultrasonic wave is transmitted from the wave transmitter / receiver 5 toward the object by the vibration. Then, the transmitting / receiving section 5 receives and oscillates the reflected wave reaching the object and reflected, and the amplifying section 6 amplifies the oscillating wave. As shown in FIG. 2 (a), the received wave W is Detected.
At this time, the mechanical vibration of the wave transmitter / receiver 5 due to the wave W ₀ remains as reverberation, and the reverberant wave is amplified by the amplifier 6 and is shown in FIG.
It is detected as the transmitted wave W ₀ .

Then, each signal of the transmitted wave (reverberation wave) W ₀ and the received wave W is cut by a detection waveform shaping section 7 by a threshold value K and converted into a digital signal, and then passed through a reverberation wave removal section 8. As shown in FIG. 2 (b), the digital signal Wp of only the received wave W is obtained. Specifically, the received wave W shown in Fig. 3 (a) is the threshold value K.
As shown in (b) of the figure, when the received wave W is larger than the threshold value K, it becomes a high level voltage, and when it is smaller than the threshold value K, it becomes a low level voltage. Thus, the waveform is shaped and converted into the digital signal Wp, and therefore, the time t for one wave of the received wave W 1 is from the rising time point to the high level voltage to the next rising time point.

This digital signal Wp is sent to the delay time detector 9
2b, the delay time Td of the received wave W from the time of transmission of the transmitted wave W ₀ is detected, and the time-voltage conversion unit 10 is detected.
Is converted into a voltage and the distance L is output as a voltage. Here, the distance L is a relational expression of L = C * Td / 2 where C is the speed of sound.
Calculated by (A).

The digital signal Wp is also sent to the wave number check unit 11 to check whether the received wave W exists at a predetermined wave number or more. For example, when the 8 waves of predetermined wave number, as shown in FIG. 4, reception W is t ₁₁ ~ as 1 Namibun time t
If there are eight or more waves of t ₁₈ , the signal of the wave number check unit 11 is sent to the high speed counter 12, and the received wave is received as described later.
The frequency f of W is detected.

By the way, when the object is moving at the relative velocity V, the frequency f of the received wave W is transmitted by the Doppler effect.
There is a frequency difference Δf = ff ₀ because it is different from the frequency f _{0 of} W ₀ . Then, when the object is approaching, f = f ₀ * (C
+ V) / (C-V ) by modifying the _{V = C * (f -f 0} ) /
It is calculated by the relational expression (B) of {2f ₀ + (f −f ₀ )}, and when the object is separated, f = f ₀ * (C−V) /
(C + V) by transforming the _{V = C * (f 0 -f} ) / {2f +
It is calculated by the relational expression (C) of (f ₀ −f)}.

The high-speed counter 12 operates at a frequency fc capable of counting the time t of at least one wave of the received wave W, and is actually a number with respect to the frequency f ₀ of the transmitted wave W _0. Those operating at a frequency fc that is ten to several hundred times higher are used. For example, the frequency f ₀ of the transmitted wave W ₀ is 40 kHz, and the frequency fc is 10 MHz.
When using high-speed counter 12 which operates in z, if when the object is not the Doppler effect occurs at rest, the frequency f of the received wave W equal to the frequency f ₀ of the transmit W ₀ 40 kHz
Therefore, the time for one wave shown in Fig. 3 (b) is t = 250 * 10 ^-4 ms, while the high-speed counter 12 counts at 1 count time tc = 10 ^-4 ms shown in Fig. 3 (c). Therefore, the count value for one wave of the received wave W is 250.

Therefore, when the object is approaching at the relative velocity V, the count value for one wave of the received wave W is obtained from the relational expression (B).
When it is smaller than 250 and is separated, the relational expression
From (C), the count value becomes larger than 250, and the determination is performed by the approach / separation determination unit 13.

By the way, the transmission time of one transmission W ₀ is set to 2 ms.
Then, in one received wave W, as shown in Fig. 4,
The above-mentioned predetermined wave number, that is, 8 waves is 2 ms / 250 * 8 * 10 ^-4 ms = 10
Therefore, 10 pieces of T _{1 to} T ₁₀ can be counted, and the ideal count value of 8 waves is 2000 when the Doppler effect does not occur. But actually the received W
The count value is small due to the low level or noise.
It may be 2010 or 1990. Further, even if the ideal count value of 8 waves is 2300 due to the Doppler effect, the count value is 2310 or 2290.

Therefore, among the count values by the high-speed counter 12 of ₁₀ of T _{1 to} T ₁₀ with one of the eight waves of the received wave W as one unit, the maximum and minimum detection unit has the maximum and minimum values. 14, the average value calculation circuit 15 detects the maximum and minimum values of the two high-speed counters for the two
The count value of 12 is calculated for each wave.

Then, the frequency-voltage converter 16 calculates the frequency f of the received wave W based on the averaged count value of the received wave W per wave, and at the same time transmits the wave from the oscillator 2. Data of frequency f ₀ of W ₀ and approach / separation determination unit 13
The relative speed V of the object is converted into a voltage and output by either the relational expression (B) or the relational expression (C).

In the ultrasonic sensor of the first embodiment, as described above, the distance L is determined by the delay time Td from the transmission W _{0 of the} received wave W regardless of the distance to the object. The time t of one wave of the received wave W itself can be measured by the high-speed counter 12 and the frequency f of the received wave W can be measured.
By detecting the frequency of the detected received wave W
The relative velocity V of the object is calculated by the difference between f and the frequency f ₀ of the transmitted wave W _0.
Since it is also possible to measure the distance L and the relative velocity V, two types of transmission waves with different transmission times are measured.
The W ₀ s and the transmitted wave W ₀ l can be measured faster than in the conventional example in which it is necessary to alternately vary the constant period tr / 2 and to transmit.

The high-speed counter that receives the signal from the wave number check unit 11 only when the wave number check unit 11 checks that the received wave W has eight or more waves of a predetermined wave number.
12 counts the time of one of the eight waves as one unit, and the maximum / minimum detection unit 14 detects the maximum and minimum values among the count values of the ten waves existing as the received wave W. However, since the average value calculation circuit 15 averages the count values for eight waves excluding the two of the maximum and minimum values per wave, the error of each wave of the received wave W is reduced. In this state, the averaged frequency f can be detected, so that the relative velocity V of the object can be measured with higher accuracy.

It should be noted that, instead of the maximum / minimum detection unit 14 provided in the first embodiment, the maximum / minimum detection unit 14 deviates from the predetermined upper and lower limit values set as values that cannot actually occur, such as noise. It is also possible to provide an upper / lower limit determination unit for determining, and in that case, the frequency f of the received wave W averaged by the average value calculation circuit 15 only for those actually generated excluding the error affected by noise etc. Therefore, the relative velocity V of the object can be measured with higher accuracy.

Further, without using the maximum / minimum detector 14 provided in the first embodiment, when it is checked by the wave number checker 11 that the received wave W has 8 or more waves of a predetermined wave number, the high speed counter The 12 may be configured to count only the time corresponding to one of the eight waves. In that case, the measurement accuracy is lower than that when the time corresponding to ten is counted, but the measurement can be performed correspondingly faster.

Furthermore, if at least one wave is present without using the wave number check unit 11 provided in the first embodiment, that is, regardless of whether the received wave W is equal to or more than a predetermined wave number such as eight waves, The time may be counted by the high-speed counter 12, and in that case, the measurement accuracy is lower than that when the wave number check unit 11 is used, but the measurement can be performed correspondingly faster.

Next, a second embodiment of the present invention will be described below with reference to FIG. In addition, the same reference numerals are given to those having substantially the same functions as those in the first embodiment.

This one does not use the wave number check unit 11 provided in the first embodiment to check that the received wave W has eight or more waves of a predetermined wave number, and counts all the wave numbers of the received wave W. The wave number counting unit 17 is used.

Therefore, even when the receiving time of the receiving wave W is shorter than the transmitting time of the transmitting wave W ₀ due to the difference in the type of the detected object and the detecting distance, and the wave number of the receiving wave W cannot be predicted in advance, The wave number counting unit 17 can count and obtain all wave numbers of the received wave W, and the high-speed counter 12
Counts the time of all the waves of the received wave W, and the maximum / minimum detection unit 14 detects the maximum and minimum values among the count values of the high-speed counter 12 for each wave, and the average value calculation circuit 15 Except for the maximum and minimum values, the total count value by the high speed counter 12 is averaged for each wave number of the wave number counted by the wave number counting section 17.

In the ultrasonic sensor of the second embodiment, as in the first embodiment, the distance L and the relative speed V are measured faster than the conventional example regardless of the distance to the object. In addition, the wave number counting unit 17 counts all the wave numbers of the received wave W, and the maximum / minimum detecting unit 14 detects the maximum and minimum values among the count values of the high-speed counter 12 for each wave. Since the average value calculation circuit 15 calculates the average per one wave except for the maximum and minimum values, all the received waves W except the maximum and minimum values are calculated by the error of each wave. It becomes possible to detect the averaged frequency f with a reduced number of captured signals,
Therefore, the relative velocity V of the object can be measured with higher accuracy.

In place of the maximum / minimum detection section 14 provided in the second embodiment, the maximum / minimum detection section 14 deviates from the predetermined upper and lower limit values set as values that cannot actually occur, such as noise. It is also possible to provide an upper / lower limit determination unit for determining, and in that case, the frequency f of the received wave W averaged by the average value calculation circuit 15 only for those actually generated excluding the error affected by noise etc. Therefore, the relative velocity V of the object can be measured with higher accuracy.

Further, without using the maximum / minimum detection unit 14 provided in the first embodiment, that is, without removing the maximum and minimum values, all the received waves W which have been generated are averaged in a state of being taken in. May be, in that case, it is not necessary to compare the count values of each wave to obtain the maximum and minimum values,
The high-speed counter 12 does not need to count the time of all the waves of the received wave W and has only to output the total count value of the received wave W, so that the measurement accuracy decreases but the measurement can be performed correspondingly faster.

[0034]

According to the first aspect of the present invention, regardless of the distance to the object, if there is at least one received wave, the received object will be delayed with a delay time from the transmitted wave. The distance can be measured, and the frequency of at least one wave of the received wave is counted by the high-speed counter to detect the frequency of the received wave, so that the difference between the detected frequency of the received wave and the frequency of the transmitted wave can be obtained. Since the relative velocity of the object can also be measured, in order to measure the distance and the relative velocity respectively, two types of transmission waves with different transmission times need to be alternately varied at a constant cycle and transmitted. Can be measured even faster.

In addition to the effect of the first aspect, the second aspect receives the signal from the wave number check section only when the wave number check section checks that the received wave is equal to or more than a predetermined wave number. The high-speed counter counts at least one time of the predetermined wave number,
Since the average value calculation circuit averages the count value by the high-speed counter for each wave, it becomes possible to detect the frequency obtained by averaging the error of each wave of the received wave, and thus the relative speed of the object can be more accurately determined. It can measure high.

According to a third aspect of the present invention, in addition to the effect of the second aspect, the maximum / minimum detecting section has a plurality of high-speed counters each having a predetermined wave number as one unit. The maximum and minimum values are detected, and the average value calculation circuit excludes the maximum and minimum values and averages for each wave, so the average of the received waves is reduced Since the converted frequency can be detected, the relative velocity of the object can be measured with higher accuracy.

According to a fourth aspect of the present invention, in addition to the effect of the second aspect, the upper and lower limit determination unit has a plurality of high-speed counters each having a predetermined wave number as one unit. Since the average value calculation circuit calculates an average per one wave except for those that deviate from the predetermined upper and lower limits, the predetermined upper and lower limits are generated, for example, due to noise or the like. By setting a value that does not actually occur like this, it becomes possible to detect the frequency of the received wave that averages only what actually occurred excluding the error affected by noise etc. The relative velocity of the object can be measured with higher accuracy.

According to a fifth aspect of the invention, in addition to the effect of the first aspect, the wave number counting section counts all the wave numbers of the received waves, and the average value calculation circuit calculates the total count value by the high-speed counter of the received waves. Since the average is calculated for each wave number of the wave number counted by the wave number counting unit, it becomes possible to detect the frequency that averages the error of each wave in the state that all the received waves that have been generated are captured, and therefore the relative velocity of the object Can be measured with higher accuracy.

According to a sixth aspect of the present invention, in addition to the effect of the fifth aspect, the maximum / minimum detection unit has the maximum and minimum values among the count values of the high-speed counter for each one of the count wave numbers. In addition to detecting the average value, the average value calculating circuit calculates the average value for each wave excluding the maximum and minimum values, so that it is possible to detect the averaged frequency with a smaller error of each received wave. Therefore, the relative velocity of the object can be measured with higher accuracy.

According to a seventh aspect of the present invention, in addition to the effect of the fifth aspect, the upper and lower limit determination unit has predetermined upper and lower limit values among the count values by the high-speed counter for each one wave of the count wave number. Since the average value calculation circuit calculates the average per one wave except for the ones that are out of the range, the average upper limit value and the lower limit value may be the actual values such as those generated by noise. By setting a value that does not exist, it becomes possible to detect the frequency that averaged only the actually generated error without being affected by the noise of each received wave, so the relative velocity of the object Can be measured with higher accuracy.

[Brief description of drawings]

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

FIG. 2 is a diagram showing signal waveforms of the same.

FIG. 3 is a partially enlarged view showing only one wave portion of the above signal waveform.

FIG. 4 is an enlarged view showing a digital signal after waveform shaping in the same as above.

FIG. 5 is a block circuit configuration diagram showing a second embodiment of the present invention.

FIG. 6 is a diagram showing a signal waveform of a conventional example.

[Explanation of symbols]

11 Wave number check unit 12 High-speed counter 14 Maximum / minimum detection unit 15 Average value calculation circuit 17 Wave number counting unit W ₀ Transmission frequency ₀ Transmission frequency W Reception f Reception frequency t Reception time of one wave Td Delay Time Δf Frequency difference L Distance (not shown) V Relative velocity (not shown)

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Toshiaki Yoshiyasu 1048, Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Works Co., Ltd. (72) Inventor, Koji Ohno, 1048, Kadoma, Kadoma City, Osaka Matsushita Electric Works, Ltd.

Claims (7)

[Claims] 1. A distance to an object is measured with a delay time from the transmission of an ultrasonic pulse as a transmission wave to the detection of a reflected wave from an object as a reception wave, and the frequency of the transmission wave and the detected reception wave. In an ultrasonic sensor for measuring the relative velocity of an object by the difference from the frequency of the received wave, a high-speed counter capable of counting the time of at least one wave of the received wave is provided for detecting the frequency of the received wave. Ultrasonic sensor characterized by. 2. A wave number check unit is provided for checking that the number of received waves is greater than or equal to a predetermined wave number, and when the high-speed counter receives a signal from the wave number check unit, the high-speed counter waits at least one time corresponding to the predetermined wave number. The ultrasonic sensor according to claim 1, further comprising: an average value calculation circuit that counts and averages the count value of the high-speed counter per wave component. 3. A maximum / minimum detection unit is provided for detecting the maximum and minimum values of the count values of the plurality of high-speed counters in which one unit of the predetermined wave number is one unit, and the maximum and minimum detection units are provided. The ultrasonic sensor according to claim 2, wherein the calculation of the average value calculation circuit is performed except for the minimum value. 4. An upper / lower limit determination unit is provided for determining a count value from a plurality of high-speed counters each having one unit of the predetermined wave number as a unit, and deviating from a predetermined upper and lower limit value. 3. The ultrasonic sensor according to claim 2, wherein the average value calculation circuit is calculated excluding the deviation. 5. A wave number counting unit that counts all wave numbers of the received waves, and an average value calculation circuit that averages a total count value of the received waves by the high-speed counter for each wave number of the wave numbers counted by the wave number counting unit. The ultrasonic sensor according to claim 1, further comprising: 6. A maximum / minimum detection unit is provided for detecting the maximum and minimum values of the count values by the high-speed counter for each one wave of the count wave number, and the maximum and minimum values are excluded. The ultrasonic sensor according to claim 5, wherein the calculation of the average value calculation circuit is performed. 7. An upper / lower limit determination unit is provided for determining a count value of each of the count wave counts by the high-speed counter that deviates from a predetermined upper limit and a lower limit value, and excludes those that do not fall. The ultrasonic sensor according to claim 5, wherein the calculation of the average value calculation circuit is performed.