JPH11326512A - Ultrasonic range finder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic range finder which excludes an external noise causing an erroneous distance measurement, other disturbing waves and an influence by a change in a receiving signal due to an interference and which can measure a distance precisely. SOLUTION: In an ultrasonic range finder, a transmitting signal by reference pulses and by ultrasonic carrier waves is radiated from a transmitter 13 to an object to be measured, a receiving signal which is reflected by the object to be measured is received by a receiver 14, receiving pulses are created on the basis of the receiving signal, the time difference between the reference pulses and the receiving pulses is measured, and a distance is measured. In the ultrasonic range finder, the receiving signal is received by two receivers 14a, 14b, respective receiving signals are changed into a correction receiving signal via an OR coupled circuit 15, the receiving pulses are created so as to be used as the transmitting signal, and a negative-logic (L-active) signal which transmits the ultrasonic carrier waves is used during a period excluding the generation period of the reference pulses.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic range finder for measuring a distance to a target by using an ultrasonic signal, and more particularly to a function of reducing the probability of erroneous distance measurement being performed due to external noise and improving the measurement accuracy. The present invention relates to an ultrasonic distance meter to which is added.

[0002]

2. Description of the Related Art As shown in FIG. 1, this type of ultrasonic range finder is equipped with a pair of a transmitter 3 and a receiver 4 in a range finder main body A, and the transmitter 3 normally receives a carrier frequency. A reference pulse, which is an ultrasonic signal of about 40 KHz, is emitted to a target object to be measured B, and the time until the reference pulse returns after the reflected wave from the measured object B is received by the receiver 4 and measured. It is used in various fields such as detection of an object being transported on a conveyor, determination of the height of an object, or detection of a human body in an automatic door or an intrusion alarm, for example. Is the block diagram shown in FIG. 2 and FIG.
Are configured as shown in the waveform diagram of each part.

In FIGS. 2 and 3, a pulse generation circuit 1 generates a reference pulse 101 at predetermined time intervals, and a carrier wave generation circuit 2 uses the reference pulse 101 as a gate signal every time the reference pulse 101 is input. The carrier wave of the ultrasonic wave is output intermittently to the transmitter 3 only during the width period, and the transmitter 3 emits the transmission signal 103 toward the DUT B. In this case, the transmission logic is based on the reference. Positive logic (H) that generates the transmission signal 103 only during the generation period of the pulse 101
Active).

The transmitted transmission signal 103 is reflected by the DUT B and returns to the receiver 4 as a reception signal 104. After the reception signal 104 is amplified to a sufficient level by the amplifier circuit 5, the detection circuit Detected at 6 and its envelope (envelope)
Is detected, the signal detection pulse 105 having a predetermined level h1 or higher is detected from the output of the detection circuit 6 when the signal detection pulse 105 is detected.
With the leading edge (leading edge) of 5 as a trigger pulse, the signal level determination circuit 7 shapes the waveform into a rectangular wave and sends the received pulse 107 to the counting circuit 9.

The counting circuit 9 receives a reference pulse 101 from the pulse generation circuit 1 and a clock pulse 108 from the clock generation circuit 8 in addition to the reception pulse 107 from the signal level determination circuit 7. The counting of the clock pulse 108 is started at the rising edge of the pulse 101, and the counting is stopped at the rising edge of the receiving pulse 107. The counting circuit 9 outputs the distance signal 109 based on these input pulses.

The reference pulse 101 and the reception pulse 107
Since the rising time interval T is proportional to the distance to the device under test B, the distance is measured by the distance signal 109 (the count value of the clock pulse 108 at the time interval T) output from the counting circuit 9 at the end of counting. The counting circuit 9 resets the previous count value at the next rising edge of the reference pulse 101 and starts a new counting at the same time, and stops counting at the next rising edge of the receiving pulse 107 and latches the count value at the same time. Output continuously until counting stops.

In the case of the conventional ultrasonic range finder having the above-described configuration, extraneous ultrasonic noise containing an ultrasonic component of 40 KHz used as a carrier wave, for example, noise due to frictional sound of metal, clapping or air brake sound. When these ultrasonic noises arrive between the reference pulse 101 and the reception pulse 107 in a time-series manner, an erroneous distance measurement that measures the distance short by mistake as the reception pulse 107 is performed. The transmission signal 103
Was transmitted with H active, it was susceptible to external noise.

For example, as shown in FIG.
When the noise signal 104n is mixed between the noise detection pulses 4a and 104a, a noise detection pulse 105n is detected by the noise signal 104n. Based on the noise detection pulse 105n, a false reception pulse 107n having a narrower pulse width than the normal reception pulse 107a is generated. Since it is made, it is erroneously regarded as a received pulse based on the received signal 104a to be reached next, and an erroneous distance measurement is performed in which the distance is measured as a distance signal t2 shorter than the normal distance signal t1.

In order to solve this problem, the applicant of the present application proposes that a noise measuring circuit detects extraneous ultrasonic noise, thereby eliminating distance measurement data not based on a correct reflected wave, and a noise measuring circuit in a data holding circuit. Ultrasonic rangefinders that reduce the probability of erroneous distance measurement by increasing the measurement accuracy by eliminating the distance measurement data immediately before the detection of extraneous ultrasonic noise as unreliable, In Japanese Patent Application No. 9-307461.

In the case of the ultrasonic range finder according to the above proposal, since the distance measurement and the noise measurement are performed alternately, there is a disadvantage that the distance measurement result is not output immediately and is delayed by one tempo. As a means to identify the correct distance measurement signal and extraneous ultrasonic noise,
The duration of the received pulse during the distance measurement period, that is, the magnitude of the pulse width is used to distinguish between the two, and the noise detection unit determines that the received pulse outside the range of the preset duration (set pulse width) is ultrasonic noise, An ultrasonic range finder in which this is reflected in the distance signal output has been separately proposed in Japanese Patent Application No. 10-6375.

[0011]

However, the cause of the erroneous distance measurement is not only the above-mentioned external noise generated from the external noise source, but also a peripheral object other than the reflected wave from the object to be measured. In some cases, the pseudo-reflected wave from the object returns as an echo, and sometimes the double-reflected wave returns as an interference wave from the DUT via the surrounding object, and accurate distance measurement is performed accordingly. This is difficult with the conventional ultrasonic range finder described above, and the ultrasonic range finder according to the above-described concept of the present applicant was also insufficient.

That is, in addition to a true received signal which is a reflected wave from the object to be measured, there is also a false received signal which is a pseudo reflected wave from a peripheral object which is farther away from the object to be measured. If the received signal returns later as an echo between the reference pulse 101 and the received pulse 107 in the next measurement period, it can be determined whether the transmitted signal is H-active or not. Therefore, there is a possibility that an erroneous distance measurement for measuring the distance to be shorter by mistake in regarding the echo as the reception pulse 107 may be performed.

[0013] Further, since the transmitted signal has a spread, not only the reflected wave directly reflected by the object to be measured but returned directly,
There are also double reflected waves that return to the object under measurement after they have hit the surrounding object and then return.These reflected waves cause interference at the receiver, and the phases of the reflected waves are reversed. When combined in a state where it is combined, especially in the case of a configuration using a pair of transducers, the received signal decreases, so if the reception level required for measurement becomes less than the distance measurement becomes impossible,
The influence of this interference cannot be avoided by a configuration using a pair of transducers 3 and 4 as shown in FIG.

Therefore, in the ultrasonic range finder according to the present invention, not only the case of the above-mentioned external noise, which is the cause of the erroneous distance measurement, but also the case where the pseudo reflected wave returns as an echo and the case where the double reflected wave is the interference wave It is another object of the present invention to provide an ultrasonic range finder capable of performing accurate distance measurement by correcting the strength of a received signal and responding to the case of returning.

[0015]

SUMMARY OF THE INVENTION According to the present invention, a transmission signal based on a reference pulse and an ultrasonic carrier is emitted from a transmitter to an object to be measured, and a received signal reflected from the object is received by a receiver. An ultrasonic range finder that generates a reception pulse based on the received signal, measures a time difference between the reference pulse (start signal) and the received pulse (stop signal), and measures the distance. Are received by two receivers arranged at positions for receiving under different input conditions, each received signal is taken out as a corrected received signal via an OR circuit, and the received pulse is formed from the corrected received signal. I did it.

According to this ultrasonic range finder, even if the received signal is weak due to interference of reflected waves or other causes, one of the two receivers receives a signal suitable for accurate distance measurement. If a wave signal is received, accurate distance measurement can be performed in a state in which the influence of interference or the like is reduced, and this concept is excluded as a transmission signal during a period during which the reference pulse described later is generated. Not only when a negative logic (L active) signal for transmitting the ultrasonic carrier is used during the period, but also for a positive logic (H) for transmitting the ultrasonic carrier only during the generation period of the reference pulse as in the related art. The present invention can also be applied to a case where an (active) signal is used.

According to another aspect of the present invention, a transmitter transmits a transmission signal based on a reference pulse and an ultrasonic carrier to an object to be measured, and receives a received signal reflected from the object to be measured by the receiver.
In an ultrasonic range finder that generates a reception pulse based on the received signal and measures a time difference between the reference pulse (start signal) and the received pulse (stop signal) to measure a distance, the transmission signal is Negative logic (L) for transmitting the ultrasonic carrier during a period except during the generation period of the reference pulse
Active) signal.

According to this ultrasonic range finder, since L-active is used as the transmission logic, an extraneous noise signal is added to the ultrasonic carrier, which is the high (H) portion of the received signal, when the measurement is performed. Even in the case of mixing, there is no influence on the reference pulse for generating the reception pulse serving as the stop signal. That is, since the reception pulse is not generated by the external noise signal, the conventional method using the H active is used. As described above, erroneous measurement by erroneously recognizing an external noise signal as a received signal is avoided.

Further, when an external noise signal is mixed in a reference pulse which is a low (L) part in a received signal,
If the pulse width of the extraneous noise signal is longer than the reference pulse, the extraneous noise signal fills the low (L) portion. At that time, no reception pulse is generated and measurement is not performed. False distance measurements due to extraneous noise signals are avoided.

When an external noise signal is mixed in a reference pulse which is a low (L) portion in a received signal,
If the pulse width of this extraneous noise signal is short and mixed immediately before the reference pulse, even if a spurious reception pulse is generated by the extraneous noise signal, the reception pulse is generated by the regular reception signal. And the timing difference between them is very small, and when the deviation is extremely short (for example, 1/30) as compared with the measurement time T, the measurement result is hardly affected.

When an external noise signal is mixed in a reference pulse which is a low (L) portion in a received signal,
When this extraneous noise signal is mixed immediately after generating a reception pulse in a regular reception signal, even if a pseudo reception pulse is generated by the extraneous noise signal, the distance is already set by the regular reception pulse. Since the measurement has been completed, no erroneous measurement is performed.

When echo noise due to a pseudo-reflected wave from a surrounding object mixes between a reference pulse and a received pulse in the next measurement period, this echo noise signal is a high (long) signal even in a received signal. H), that is, the probability of being buried by mixing into the ultrasonic carrier wave is high, and in that case, no reception pulse is generated by the echo noise signal. Therefore, erroneous measurement is performed as compared with the conventional method using H active. Is extremely low.

According to still another aspect of the present invention, a negative logic (L active) signal is used as a transmission signal, and a reception signal is received by two receivers arranged at positions for receiving reception signals under different input conditions. Each received signal is an ultrasonic range finder that takes out a corrected received signal via an OR circuit to form a reception pulse, and this ultrasonic range finder can obtain both effects of the present invention already described. Can be.

In the case of the above ultrasonic range finder using a negative logic (L active) signal as a transmission signal, an ultrasonic carrier component is removed from a received signal or a corrected received signal by a detection circuit. It is preferable that a reference pulse component having a certain level or more obtained by removing a pulsating portion of the envelope by a limit circuit is used as a signal detection pulse, and a reception pulse shaped by using the signal detection pulse as a trigger pulse is generated. The effect of extraneous noise mixed in the wave signal, a pseudo-reflected wave, and other interfering waves that lower the measurement accuracy is reduced, and the effect using the negative logic (L active) signal is easily and more reliably achieved.

[0025]

FIG. 5 is a block diagram of an ultrasonic range finder according to a first embodiment of the present invention. FIG. 6 is a block diagram of the ultrasonic range finder according to the first embodiment. FIG. 7 is a schematic diagram illustrating a transmitting / receiving state by a meter, FIG. 7 is a plan view illustrating an arrangement of a transmitter / receiver mounted on the distance meter in FIG. 5,
8 to 11 are waveform diagrams of respective parts in the range finder of FIG. 5. In particular, FIG. 8 shows a case where external noise is mixed in a high portion of a received signal, and FIG. 9 shows an external noise in a low portion of the received signal. FIG. 10 shows a case where a pseudo reflected wave is mixed in a received signal, FIG. 11 shows a case where a double reflected wave is mixed in a received signal, and FIG. 12 shows a detailed main part of FIG. The waveform diagram is shown in FIG.
3 is a block diagram of the ultrasonic range finder according to the second embodiment, and FIG. 14 is a waveform diagram of each part in the range finder of FIG.

As shown in the block diagram of FIG. 5, the ultrasonic range finder according to the first embodiment has a pulse generation circuit 11, a carrier generation circuit 12, an ORing circuit 15, a detection circuit 16, a limit circuit 17, a polarity inversion circuit. 18, a distance meter main body C1 composed of a signal level determination circuit 19, a clock generation circuit 20, and a counting circuit 21.
Two transmitters 13 and two receivers 14 are provided.

When the above configuration is compared with the conventional configuration shown in FIG. 2, two receivers, ie, a first receiver 14a and a second receiver 14b, are provided. Vessel 1
The difference is that the 4a and the second receiver 14b are connected to the ORing circuit 15 and the limit circuit 17 and the polarity inversion circuit 18 are provided between the detection circuit 16 and the signal level determination circuit 19. Although the details will be described later based on the waveform diagrams 8 to 11, the negative logic (L active) in which the transmission signal 103 is generated from the transmitter 3 during a period excluding the generation period of the reference pulse 201 is used. The configuration of the carrier generation circuit 12 is different from that in FIG.

For one transmitter 13 and two receivers 1
The configuration using 4a and 14b is a means for preventing erroneous distance measurement due to the reception level of a received signal being weakened by interference of a reflected wave or the like. As shown in FIG. When the transmitting signal 203 is emitted from the detector 13 to the device under test B, the reflected wave 204 reaches the first receiver 14a and the second receiver 14b via different paths.
Distance measurement is performed using one of the received signals suitable for accurate distance measurement.

For example, even when reflected waves having phases opposite to each other arrive at the first receiver 14a and are canceled out, only a received signal having a low reception level can be obtained. When the reflected wave arrives and a superimposed received signal with a high reception level is obtained, the received signals from the receivers 14a and 14b are taken out as a logical sum (OR output) via the OR coupling circuit 15. Thus, accurate distance measurement with reduced influence of interference becomes possible.

Receivers 14a, 14b for transmitter 13
In the arrangement, the two receivers can receive reflected waves under different input conditions (particularly, phase relations), and can receive with high sensitivity, taking into account the sensitivity directivity of the receivers. It is desirable to select and arrange the positions. As shown in an example shown in FIG. 7, a mode in which the receivers 14a and 14b are arranged on both sides of the transmitter 13 (a), one of the transmitters 13 There is a mode (b) or the like in which the receiver 14a and the receiver 14b are arranged side by side, and the arrangement interval L and the displacement angle θ between the receiver 14a and the receiver 14b are set as desired in conformity with the above purpose. Is done.

In the example of FIG. 7A, the displacement angle θ is 0 to 1
At 5 degrees, the arrangement interval L1 is set to 20 to 50 mm, and FIG.
In the example, the displacement angle θ is 0 to 15 degrees and the arrangement interval L1 is 1
However, when the displacement angle θ becomes 15 degrees or more, the sensitivity directivity of the receivers 14a and 14b rapidly decreases.
It is better to be as small as possible, but since the outer diameter of each element used as a transducer is approximately 10 mm, the lower limit is the state where these elements are arranged adjacent to each other, and each element is attached. The outer diameter of the rangefinder body C was set as the upper limit.

The pulse generation circuit 11 generates a reference pulse 201 at predetermined time intervals as shown in FIG. 8, and this reference pulse 201 is output to the carrier generation circuit 12 and the counting circuit 21 as a start signal for distance measurement. The carrier generation circuit 12 always generates an ultrasonic carrier 202 of about 40 KHz, but every time the reference pulse 201 is input, the carrier is intermittently used only during the pulse width period using the reference pulse 201 as a gate signal. The generation of the signal 202 is stopped, and the signal from which the carrier 202 is removed intermittently is output to the transmitter 13 as a transmission signal 203, and the transmission signal from the transmitter 13 is transmitted to the DUT B by L-active. Fire.

The reception signal 204a output from the first receiver 14a and the reception signal 204b output from the second receiver 14b are combined with an operational amplifier (OP) for performing an analog addition operation.
Amplifier) or the like, and the corrected received signal whose waveform is shaped as an OR-coupled output by a logical sum (OR output) from the OR-coupled circuit 15 to reduce the influence of interference. 204c is extracted, and the corrected reception signal 204c is amplified to a desired level by providing an amplifier (not shown) as necessary.

From the corrected received signal 204c, the carrier wave 202 is removed by the detection circuit 16 and the envelope (envelope) portion is taken out as a detection output. The limit circuit 17 clips it at a constant level to remove the pulsation component of the envelope. The cut limit signal 205 is produced, and the polarity of the limit signal 205 is inverted by the polarity inversion circuit 18 to generate the signal detection pulse 20.
6 is input to the signal level determination circuit 19, and when the signal level determination circuit 19 detects a signal detection pulse 206 of a predetermined level h1 or more, the predetermined level h1 on the leading edge (leading edge) side of the signal detection pulse 206. Is used as a trigger point to form a reception pulse 207 shaped into a rectangular wave, and the reception pulse 207 is sent to the counting circuit 21 as a distance measurement stop signal.

The counting circuit 21 includes a signal level determination circuit 1
9, the pulse generation circuit 11
, And a clock pulse 208 from the clock generation circuit 20 are input.
The counting of the clock pulse 208 is started at the rise of the received pulse 207, and the counting is stopped at the rise of the received pulse 207. The number of clock pulses during the measurement time T from the reference pulse 201 to the received pulse 207 is counted. Counting circuit 2 at the end of counting
1 is output as a distance signal 209.

Since the number of clock pulses output as the distance signal 209 is proportional to the distance to the device under test B, the distance can be measured, and the counting circuit 21 counts the previous count at the next rise of the reference pulse 201. , A new count is started at the same time as resetting, the count is stopped at the next rising edge of the reception pulse 207, the count is latched at the same time, and the latched count is continuously output until the next count is stopped.

When the above measurement is performed, as shown in FIG. 8, for example, even if the external noise signal N1 is mixed in the high (H) portion of the received signals 204a and 204b, L active is set as the transmission logic. Since it is used, there is no effect on the generation of the reception pulse 207 serving as a stop signal, that is, the reception pulse 207 is generated by the external noise signal N1.
Is not generated, so that there is no possibility of erroneous measurement by erroneously recognizing the received signal as in the case of the conventional method using H active.

When the above measurement was performed, as shown in FIG.
When the external noise signal N2 is mixed in the low (L) portion of the received signals 204a and 204b, the situation differs depending on the length of the pulse width of the external noise signal N2 and the difference in the generation position. Is long, the low (L) portion is filled with the extraneous noise signal N2 and the signal detection pulse 206 is not detected, so that the reception pulse 207 is not generated and the counting circuit 21 overflows. The latched count number is output as the distance signal 209.

In the case of FIG. 9, when the pulse width of the external noise signal T2 is short, for example, as shown in FIG. When the noise signal N2 is mixed, a slight deviation may occur in the timing at which the reception pulse 207 serving as the stop signal is generated, but the deviation is extremely short as compared with the measurement time T (for example, 1/30). Has little effect on the measurement results.

As shown in FIG. 12B, the external noise signal N2
Is mixed immediately after the rising trigger level of the signal detection pulse 206, or the external noise signal N2 is mixed between the rising side and falling trigger level of the signal detection pulse 206 as shown in FIG. In this case, the noise detection pulse 206 due to the external noise signal N2
Although a pseudo reception pulse may be generated at n, the measurement has already been completed by the normal reception pulse 207, so that erroneous measurement is not performed.

When the above measurement is performed, as shown in FIG. 10, when an echo noise signal N3 due to a pseudo reflection wave from a surrounding object is mixed between the reference pulse 201 and the reception pulse 207 in the next measurement period. In this case, the echo noise signal N3 has a high probability of being mixed and buried in the high (H) portion having a long period in the reception signals 204a and 204b. This has no effect on the generation of the received pulse 207, that is, the received pulse 207 is not generated by the external noise signal N1, so that it is erroneously recognized as a received signal as in the case of the conventional method using H active. There is no wrong measurement.

With respect to the mutual interference of the received signals, for example, as shown in FIG. 11, a part of the received signal 204a received by the first receiver 14a is attenuated, and the received signal 204a is received by the second receiver 14b. When the received signal 204b is normal, the corrected received signal 204c from which the logical sum output is extracted through the OR combination circuit 15 is output.
Has a sufficient level and waveform to generate a reception pulse 207 serving as a measurement stop signal, so that accurate distance measurement can be performed in a state where the influence of a decrease in reception level due to interference is reduced.

Next, an ultrasonic range finder according to a second embodiment of the present invention will be described with reference to FIGS. 13 and 14. This range finder uses a transmission logic based on H active as in the prior art. It has two receivers 4 and an OR-coupling circuit 10 to enable accurate distance measurement in a state in which the influence of interference such as a decrease in reception level is reduced. Except for this point, it is the same as the conventional configuration shown in FIG.

That is, as shown in FIG. 13, a first wave receiver 4a and a second wave receiver 4
b is received and the received signal 104 received by the first receiver 4a
By outputting the logical sum of “a” and the received signal 104b received by the first receiver 4b from the OR combination circuit 10 as a corrected received signal 104c, as shown in FIG.
Even if the reception level of one of the signals a and 104b is low, the reception pulse 107 which is covered by the other and functions as a stop signal of the clock pulse 108 is secured, so that the influence such as a decrease in the reception level due to interference is reduced. Accurate distance measurement is possible in the state.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a transmitting / receiving state of an ultrasonic range finder according to a conventional technique.

FIG. 2 is a block diagram showing a configuration of an ultrasonic distance meter according to a conventional technique.

FIG. 3 is a waveform chart of each part for explaining the operation of the ultrasonic range finder of FIG. 2;

FIG. 4 is a waveform chart of each unit for explaining an operation when external noise is mixed in the ultrasonic distance meter of FIG. 2;

FIG. 5 is a block diagram showing a configuration of a first embodiment of an ultrasonic range finder according to the present invention.

FIG. 6 is a schematic diagram showing a state of transmission and reception by the ultrasonic distance meter of the present invention.

FIG. 7 is a plan view showing an arrangement state of a transducer in the ultrasonic range finder of the present invention.

8 is a waveform diagram of each section for explaining the operation of the ultrasonic range finder of FIG. 5, particularly showing a case where external noise is mixed in a high portion of a received signal.

9 is a waveform diagram of each part for explaining the operation of the ultrasonic range finder of FIG. 5, particularly showing a case where external noise is mixed in a low portion of a received signal.

10 is a waveform diagram of each part for explaining the operation of the ultrasonic range finder of FIG. 5, particularly showing a case where a pseudo reflected wave is mixed in a received signal.

11 is a waveform diagram of each unit for explaining the operation of the ultrasonic range finder of FIG. 5, particularly showing a case where a double reflected wave is mixed into a received signal.

FIG. 12 is a detailed waveform diagram of a main part of FIG. 9;

FIG. 13 is a block diagram showing the configuration of a second embodiment of the ultrasonic range finder according to the present invention.

14 is a waveform chart of each part for explaining the operation of the ultrasonic range finder of FIG.

[Explanation of symbols]

 1,1 pulse generating circuit 2,12 carrier generating circuit 3,13 transmitting device 4,14 receiving device 5 amplifying circuit 6,16 detecting circuit 7,19 signal level judging circuit 8,20 clock generating circuit 9,21 counting circuit 10, 15 OR connection circuit 17 Limit circuit 18 Polarity inversion circuit A Distance meter body B DUT C1, C2 Distance meter body

Claims (4)

[Claims] A transmitter transmits a transmission signal based on a reference pulse and an ultrasonic carrier wave from a transmitter to an object to be measured, receives a received signal reflected from the object to be measured by the receiver, and generates a signal corresponding to the received signal. An ultrasonic range finder that generates a reception pulse based on the reference pulse (start signal) and a time difference between the reference pulse (start signal) and the reception pulse (stop signal) to measure a distance receives the reception signal under different input conditions. The ultrasonic wave distance is received by two receivers arranged at positions, each received signal is taken out as a corrected received signal via an OR circuit, and the received pulse is formed from the corrected received signal. Total. 2. A transmission signal based on a reference pulse and an ultrasonic carrier is emitted from a transmitter to an object to be measured, a received signal reflected from the object to be measured is received by a receiver, and the received signal is An ultrasonic range finder that generates a reception pulse based on the reference pulse, and measures a time difference between the reference pulse (start signal) and the reception pulse (stop signal) to measure a distance. Negative logic (L active) for transmitting the above ultrasonic carrier during the period except for the inside
An ultrasonic rangefinder using a signal. 3. The ultrasonic range finder according to claim 1, wherein a negative logic (L active) signal for transmitting said ultrasonic carrier during a period excluding a period during which said reference pulse is generated is used as said transmission signal. Ultrasonic rangefinder characterized by the fact that 4. The reception pulse removes an ultrasonic carrier component from a reception signal according to claim 2 or a correction reception signal according to claim 3 by a detection circuit, and removes a pulsating component of an envelope by a limit circuit. 4. The ultrasonic distance meter according to claim 2, wherein a reference pulse component having a predetermined level or higher obtained as a result is used as a signal detection pulse, and the signal detection pulse is used as a trigger pulse to shape the waveform.