JPH11202050A - Ultrasonic distance meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic distance meter that reduces the probability of an erroneous distance measurement due to external noise and has an added function of improving measurement accuracy. SOLUTION: In an ultrasonic distance meter for measuring distance by emitting an ultrasonic signal 103 to a target and then measuring time until a reflection wave 104 from the target returns, a noise detection means B1 is provided for detecting a reception pulse 107, based on the reflection signal 104 from the target, and discriminates the reception pulse 107 whose pulse width differs from a reference pulse width which is preset as an external noise the output of a new distance signal being measured immediately before is stopped by a latch means 16 when the noise detection means B1 detect the external noise, and at the same time a distance signal being measured previously is maintained.

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 An ultrasonic distance meter of this type measures a distance by emitting an ultrasonic signal to a target and measuring a time until a reflected wave from the target returns. It is used in various fields such as detection of an object being transported, determination of the height of an object, and detection of a human body in an automatic door or an intrusion alarm, as an example of which is shown in the block diagram of FIG. 1 and FIG. It is configured as shown in the waveform diagram of each part in FIG.

In FIGS. 1 and 2, 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.
Is driven to emit the transmission signal 103 into the air. This carrier frequency is about 40 KHz when the signal is emitted into the air.

The transmitted transmission signal 103 is reflected from a target object 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 6 The detection is performed to detect the signal detection pulse 105 formed by the envelope. When the signal detection pulse 105 having a predetermined level h1 or more is detected as the output of the detection circuit 6, the signal level determination circuit 7 detects this. The reception pulse 107 shaped into a rectangular wave is sent 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.

That is, since the time interval T between the rise of the reference pulse 101 and the reception pulse 107 is proportional to the distance to the target, the distance signal 109 (the clock pulse at the time interval T) output from the counting circuit 9 at the end of counting. 108, the distance to the target can be measured, and the counting circuit 9 outputs the next reference pulse 1
At the rising edge of 01, the previous count value is reset and a new count is started at the same time.
The count value is latched at the same time as the counting is stopped at the rising edge of 07, and is continuously output until the next counting is stopped.

Note that the output of the distance signal 109 in FIG. 2 is actually reset each time measurement is performed. However, in order to clearly indicate the timing, the output is displayed in a state where the target is gradually changed away from the target. ing.

[0008]

However, in the case of the conventional ultrasonic range finder having the above-described structure, external ultrasonic noise including ultrasonic waves used as a carrier wave, for example, mechanical noise of rotating gears. Such as the air brake sound of a large vehicle or a large car, etc., it is easily affected by a noise source that generates an ultrasonic wave containing a 40 KHz component.
7, the distance may be erroneously recognized as the received pulse 107 and the distance may be measured to be shorter.

Therefore, the applicant of the present application has previously filed Japanese Patent Application No. 9-30.
According to No. 7461, a distance measurement period and a noise measurement period are provided on the time axis, distance measurement and noise measurement are alternately repeated, and when noise is detected during the noise measurement period, the distance measurement for the next distance measurement period is performed. An ultrasonic range finder having a noise measuring circuit for stopping the measurement, and a data holding circuit for stopping the output of the distance measurement data immediately before the noise is detected during the noise measurement period and maintaining the previous distance measurement data We proposed an ultrasonic rangefinder equipped with.

In the ultrasonic range finder according to this proposal, the noise measurement circuit detects extraneous ultrasonic noise, thereby eliminating distance measurement data that is not based on a correct reflected wave. By removing the distance measurement data immediately before the detection of the ultrasonic noise as unreliable, the probability that an erroneous distance measurement is performed is reduced and the measurement accuracy is increased.

However, 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 the tempo is delayed by one tempo. It is an object of the present invention to provide an ultrasonic range finder having a function of improving the measurement accuracy by reducing the probability of erroneous distance measurement due to extraneous ultrasonic noise in a state where this point is improved.

In the ultrasonic range finder according to the present invention which achieves this object, a special noise measurement period is not provided for distinguishing a correct distance measurement signal from extraneous ultrasonic noise as in the above-mentioned proposal. The duration of the reception pulse during the period, that is, the magnitude of the pulse width is used to distinguish between the two, and the noise detection unit determines that the reception pulse outside the range of the preset duration (set pulse width) is ultrasonic noise. This is reflected in the distance signal output.

That is, in this type of ultrasonic distance meter, the shorter the pulse width of the reference pulse 101, that is, the shorter the duration of the transmission signal 103, the less the influence of extraneous ultrasonic noise and the higher the distance measurement accuracy. However, since it is limited by the time response characteristics of the transmitter and the receiver, it is usually selected to be about 0.5 millisecond,
Further, since the directivity of the transmitter and the receiver is several degrees to several tens degrees, the reception signal 10
4 is slightly longer than 0.5 milliseconds, while the ultrasonic noise source is a continuous sound such as the mechanical sound of the gears described above, as well as the ignition sound of an electronic lighter and metal tools on a concrete floor. The duration of these ultrasonic waves is often on the order of several milliseconds and is longer than the duration of the signal. It is possible to determine right or wrong.

[0014]

In the ultrasonic range finder according to the present invention, a reception pulse based on a reflection signal from a target is detected by the conventional ultrasonic range finder described above, and the reception pulse is detected in the reception pulse. If a received pulse different from the preset standard pulse width is mixed, noise detection means for determining this as external noise is provided, and the distance signal measured at the time when the external noise is detected by the noise detection unit is The proposed method is to maintain the previously measured distance signal without outputting it by the latch means, thereby reducing the probability of erroneous distance measurement and increasing the measurement accuracy, and alternately performing distance measurement and noise measurement. The measurement is performed more quickly than in the case of.

The noise detecting means in the ultrasonic range finder includes a noise detecting means for discriminating a received pulse which continues for a longer time than a preset standard pulse width as an external noise outside the range of the set pulse width; In some cases, a reception pulse that continues for a short time is added to the noise to generate external noise.Moreover, a signal indicating the authenticity of the distance signal is output from the noise detection means as an authenticity determination output, so that a measurement error due to noise contamination can be reduced. It can improve the reliability of data.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the ultrasonic range finder of the present invention will be described with reference to the accompanying drawings.
3 is a block diagram of the ultrasonic range finder according to the first embodiment, FIG. 4 is a waveform diagram of each part in FIG. 3, FIG. 5 is a block diagram of the ultrasonic range finder according to the second embodiment, and FIG. 5 shows waveform diagrams of respective parts in FIG. 5. In these embodiments, the same reference numerals are given to the same parts as those in the above-described conventional structure, and the detailed description is omitted.

The ultrasonic range finder according to the first embodiment has a pulse generation circuit 1, a carrier generation circuit 2, a transmitter 3, a receiver 4, an amplification circuit 5, an detection circuit 6,
A distance measuring unit A comprising a signal level determining circuit 7, a clock generating circuit 8, and a counting circuit 9 is provided. In addition, the pulse generating circuit 1, the signal level determining circuit 7, and the counting circuit 9 are provided.
A noise detection unit B1, a control pulse generation unit C, and a signal output unit D are provided, and when noise is detected, distance measurement data due to noise is not output, and true data indicating that the data is false. A fake signal can be output.

The noise detecting section B1 comprises an integrating circuit 10, an integrating level judging circuit 11 and a flip-flop 12. The control pulse generating section C comprises a delay circuit 13 and a waveform shaping circuit 14, and a signal output section. D is an AND circuit 1
5 and 17 and a latch circuit 16.

In the integration circuit 10, the signal level determination circuit 7
Is integrated, and outputs an integrated output 110 of a voltage proportional to the pulse width to the integration level determination circuit 11 at the next stage.
In order to prevent accumulation of a plurality of reception pulses having a short pulse width, an integration circuit having a function of resetting immediately at the falling edge of each reception pulse is used.

In the integration level determination circuit 11, the integration circuit 1
It is determined whether or not the integrated output 110 sent from 0 is equal to or higher than a predetermined fixed level ha (corresponding to the time ta). Shape and alarm pulse 1
11 is sent to the flip-flop 12.

The flip-flop 12 receives the reference pulse 10
1 is reset to a high level at the rising edge of the signal, and is set to a low level at the rising edge of the alarm pulse 111 output from the integration level judging circuit 11. / F output pulse 112 is always at a high level, and when an alarm pulse 111 is input, A
A low-level F / F output pulse 112 is sent to the ND circuit 15.

In the delay circuit 13, the reception pulse 107 is delayed by a predetermined time td. The reception pulse 107 is longer than the maximum pulse width ta within a range of a pulse width that can be regarded as a reflection pulse from a target. The delay time td is thus set, and the waveform shaping circuit 14 shapes the waveform so that this pulse has a constant pulse width, and sends a high-level delayed reception pulse as a control pulse 114 to the AND circuit 15.

The AND circuit 15 includes a flip-flop 12
The output of the F / F output pulse 112 from the F / F output pulse 11 and the control pulse 114 from the waveform shaping circuit 14 are input.
2 is high level, that is, when the noise is not detected by the noise detection unit B, the latch pulse 115 is output to the latch circuit 16 with the control pulse 114 passed as it is,
When the F / F output pulse 112 is at a low level, that is, when noise is detected, the latch pulse 115 is not output.

When the distance signal 109 is input from the counting circuit 9, the latch circuit 16 outputs the distance signal
The correction distance signal 116 is output under the control of the latch pulse 115 from the circuit 15, but the noise detection unit B1 detects no noise and the latch pulse 1 is output from the AND circuit 15.
15 is input, the distance signal 109 measured each time is maintained until the next distance measurement without correction, but when noise is detected and the latch pulse 115 is not input, the immediately preceding distance signal 109 is input. Is not output, the distance signal measured before that is maintained and output.

As signals representing the authenticity of the distance signal, a control pulse 114 from the waveform shaping circuit 14 and a latch pulse 115 from the AND circuit 15 are input to the AND circuit 17, and when both pulses are at the high level. Is true, and the distance signal when only the latch pulse 114 is at the high level is determined to be false.
The alarm lamp (not shown) is turned on by the true / false judgment output 117 to call attention to the measurer.

Although the output of the distance signal 109 in FIG. 4 is actually reset every time the measurement is performed, the output is displayed in a state where the target is gradually moved away to clearly indicate the timing. ing.

Next, an ultrasonic range finder according to a second embodiment of the present invention will be described with reference to FIGS. 5 and 6. In this embodiment, the noise detector B1 in the first embodiment shown in FIG. And a noise detection unit B2 in which the two-input AND circuit 15 is replaced with a three-input AND circuit 20. In addition to the received signal that lasts longer than the reflected signal, the received signal that lasts shorter than the target reflected signal is regarded as extraneous noise.

In the description of this embodiment, the same parts as those in the first embodiment described above are denoted by the same reference numerals, and will not be described in detail because they are duplicated. When the pulse width to is within a range (tb <to <ta) that can be regarded as a target reflected signal, when the pulse width is larger (to> ta), and when it is smaller (to <tb), Are shown for each part.

The judgment level hb of the integration level judgment circuit 18
Is set to a value (hb <ha) corresponding to the time tb, and while the integrated value of the received pulse 107 is equal to or greater than hb, the alarm pulse 118 obtained by shaping the received pulse 107 into a rectangular wave is used as a flip-flop 19 The alarm pulse 118 is not generated when the pulse width of the reception pulse 107 is equal to or less than tb.

The flip-flop 19 is connected to the reference pulse 10
At the rise of 1, contrary to the flip-flop 12, the level is reset to the low level, and the integration level determination circuit 1 is reset.
8 is set to a high level at the rising edge of the alarm pulse 118, which is the output of the flip-flop 19 when the alarm pulse 118 is not input.
The F / F output pulse 119 is always at the low level, and when the alarm pulse 118 is input, the F / F output pulse 119 at the high level is sent to the AND circuit 20.

The integration circuit 10, the integration level determination circuit 11, the flip-flop 12, the delay circuit 13, and the waveform shaping circuit 1
Operation 4 is as described in the first embodiment.

The AND circuit 20 includes a flip-flop 12
Output pulse 112 from flip-flop and flip-flop 19
The F / F output pulse 119 from the F / F and the control pulse 114 from the waveform shaping circuit 14 are input, and the F / F output pulse 11
2 and the F / F output pulse 119 are both at a high level, that is, when the noise is not detected by the noise detection unit B2, the control pulse 114 is passed and the latch pulse 12 is passed.
0 is output to the latch circuit 16 and the F / F output pulse 11
If one of the signals 2 and 119 is at a low level, that is, if noise is detected, the latch pulse 120 is not output, and the next operation of the latch circuit 16 is as described in the first embodiment.

As signals representing the authenticity of the distance signal, a control pulse 114 from the waveform shaping circuit 14 and a latch pulse 120 from the AND circuit 20 are input to the AND circuit 17, and when both pulses are at a high level. Is true, and the distance signal when only the latch pulse 114 is at the high level is determined to be false.
The alarm lamp (not shown) is turned on by the true / false judgment output 117 to call attention to the measurer.

As described above, in the first embodiment for detecting extraneous noise, noise having a longer duration than a reflection signal of a target which is frequently occurring as extraneous noise is detected, and when the extraneous noise is detected. The output of the previously measured distance signal is maintained without outputting the measured distance signal, and a signal indicating the authenticity of this distance signal can be output. In the second embodiment, the first signal is output. In addition to the embodiment described above, noise having a shorter duration than the reflected signal of the target is also detected, so that the probability of erroneous distance measurement due to extraneous noise can be reduced, and the measurement accuracy can be further increased.

In these embodiments, the reception pulse 10
As means for performing noise detection based on the pulse width of 7, an analog circuit including the integration circuit 10 and the integration level determination circuits 11 and 18 has been described because of its simple configuration. This can be achieved by using an integration function by a digital circuit similar to the case of the generation circuit 8 and the counting circuit 9, and the function of the integration level determination circuit can be achieved by a magnitude comparator that compares the count values. It goes without saying that circuit variations are included in this patent.

[0036]

As is apparent from the embodiments described above, in the ultrasonic range finder of the present invention, a reception pulse having an unusual duration is mixed in a reception pulse due to a reflected signal from a target. Noise is detected by judging whether or not the received signal has a pulse width different from the normal one, and the received pulse is regarded as extraneous noise, and the distance signal measured at the time when the noise detection means detects the noise is output by the latch means. By keeping the distance signal measured before that, and outputting a signal indicating the authenticity of the distance signal from the noise detection circuit as necessary, measurement errors due to noise contamination are eliminated, and measurement accuracy is improved. Can be enhanced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an ultrasonic distance meter according to a conventional technique.

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

FIG. 3 is a block diagram showing a configuration of a first embodiment of the ultrasonic range finder according to the present invention.

FIG. 4 is a waveform chart of each part for explaining the operation of the ultrasonic range finder of FIG. 3;

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

FIG. 6 is a waveform chart of each part for explaining the operation of the ultrasonic range finder of FIG. 5;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 pulse generation circuit 2 carrier generation circuit 3 transmitter 4 receiver 5 amplification circuit 6 detection circuit 7 signal level determination circuit 8 clock generation circuit 9 counting circuit 10 integration circuit 11, 18 integration level determination circuit 12, 19 flip-flop 13 Delay circuit 14 Waveform shaping circuit 15, 17, 20 AND circuit 16 Latch circuit A Distance measuring unit B Noise detecting unit C Control pulse generating unit D Signal output unit

Claims (4)

[Claims] An ultrasonic range finder for measuring a distance by emitting an ultrasonic signal to a target and returning a reflected wave from the target to measure a distance based on the reflected signal from the target. A noise detecting means for detecting a pulse and determining a received pulse whose pulse width is different from a preset reference pulse width as an external noise, and immediately before the noise detecting means detects the external noise, An ultrasonic rangefinder characterized in that the output of a newly measured distance signal is stopped by a latch means and the previously measured distance signal is maintained. 2. The ultrasonic range finder according to claim 1, wherein said noise detecting means determines a received pulse that lasts longer than a predetermined reference pulse width as an external noise. 3. The noise detection device according to claim 1, wherein the noise detection unit determines a reception pulse that lasts longer than a preset reference pulse width and a reception pulse that lasts shorter than the reference pulse width as external noise. Item 7. An ultrasonic distance meter according to Item 1. 4. The ultrasonic range finder according to claim 1, wherein a signal representing true / false of the distance signal is output from said noise detecting section.