JPH11142516A - Ultrasonic wave range finder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce possibility of erroneous range-finding for higher measurement precision by, when external noise is detected during noise measurement period, not performing next range finding, nor outputting previous range-finding data. SOLUTION: In addition to a conventional ultrasonic wave range finder, a pulse generating circuit 1 for generating a series of pulse train, a noise measurement period setting circuit 10 wherein pulses of the output pulse train are divided and a noise measurement period is set after range finding, a level judging circuit 11 for detecting noise, a flip flop 12 where occurrence of noise is temporarily stored, and an AND circuit 13 which, based on the result, temporarily cuts off an output pulse of the pulse generating circuit 1 are provided to a noise measurement circuit A. A data holding circuit may be added to stop the output of a previous range-finding data.

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 measured as a short distance due to the reception pulse 107. Therefore, in the present invention, the probability of erroneous distance measurement due to extraneous ultrasonic noise is reduced. It is another object of the present invention to provide an ultrasonic distance meter having a function of improving measurement accuracy.

[0009]

In order to solve the above problems and achieve the object, a first ultrasonic range finder according to the present invention comprises a noise measuring circuit in addition to the conventional ultrasonic range finder described above. In addition, if extraneous noise is detected during the noise measurement period while alternately repeating distance measurement and noise measurement by this noise measurement circuit, the next distance measurement will not be performed. Is reduced to increase the measurement accuracy.

As a concrete means for implementing this, for example, as in the embodiment shown in FIGS. 3 and 4, a pulse generating circuit 1 for generating a series of pulse trains, And a noise measurement period setting circuit 10 for providing a noise measurement period after the distance measurement,
A noise measurement circuit A including a level determination circuit 11 for detecting noise, a flip-flop 12 for temporarily storing the presence of noise, and an AND circuit 13 for temporarily interrupting an output pulse of the pulse generation circuit 1 based on the result is used. When noise arrives during the noise measurement period, this can be achieved by interrupting the output pulse immediately after that and temporarily suspending the distance measurement.

In the second ultrasonic distance meter according to the present invention, a data holding circuit is provided in addition to the noise measuring circuit, and the distance signal measured immediately before the external noise is detected by the data holding circuit is not output. By maintaining the distance signal measured before that, the measurement error due to noise contamination during the distance measurement period before and after the noise is detected is eliminated, and the measurement accuracy is further improved.

As concrete means for implementing this, for example, as in the embodiments shown in FIGS. 5 and 6, a synchronous pulse generating circuit replacing the pulse generating circuit 1, a flip-flop 15, an AND circuit 16, and a latch circuit 17 and the like, when noise arrives during the noise measurement period, the output pulse immediately thereafter is cut off to temporarily suspend the distance measurement, and the distance measurement data immediately before is measured by the operation of the AND circuit and the latch circuit. Can be achieved by not outputting.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the ultrasonic distance meter 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 generator 1, a carrier generator 2, a transmitter 3, a receiver 4, an amplifier 5, a detector 6,
A signal level determining circuit 7, a clock generating circuit 8, and a counting circuit 9 are provided. In addition, a noise measuring period setting circuit 10, a noise level determining circuit 11, a flip-flop, and a flip-flop are provided between the pulse generating circuit 1 and the carrier generating circuit 2. 12 and A
When the noise measurement circuit A including the ND circuit 13 is provided, and the distance measurement and the noise measurement are alternately repeated and the noise is detected during the noise measurement period, the distance measurement is not performed during the immediately following distance measurement period. Like that.

The noise measurement period setting circuit 10 generates a period setting pulse 110 having a predetermined width in synchronization with the reference pulse 101 output from the pulse generation circuit 1, and the period of this pulse width is set as the distance measurement period t1. While the distance measurement based on the received pulse 105 is performed,
The subsequent period is a noise measurement period t2 for performing noise measurement. For example, a monostable multivibrator using the reference pulse 101 as a trigger sets a period setting pulse 110 of about half the period of the reference pulse 101.
Set the pulse width to obtain

The noise level determination circuit 11 operates only during the noise measurement period t2 in which the period setting pulse 110 sent from the noise measurement period setting circuit 10 is at a low level,
During the noise measurement period t2, the noise detection pulse 106 having a predetermined level h2 or higher is set from the output of the detection circuit 6 in advance.
Is detected, the noise pulse 111 shaped into a rectangular wave is sent to the flip-flop 12.

The flip-flop 12 is reset to a high level at the falling edge of a period setting pulse 110 output from the noise measurement period setting circuit 10 and goes to a low level at the rising edge of a noise pulse 111 output from the noise level determination circuit 11. Therefore, if the noise pulse 111 is not input during the noise measurement period t2, the F / F output pulse 112 of the flip-flop 12 is always at the high level, and if the noise pulse 111 is input, the F / F output pulse 112 is set to the low level to the AND circuit 13. Level F / F output pulse 11
Send 2

The AND circuit receives the reference pulse 101 from the pulse generation circuit 1 and the F / F output pulse 112 from the flip-flop 12, and outputs the logical product of the AND signal to the carrier generation circuit 2 and the counting circuit 9 as a corrected reference pulse 113. Sent.

Therefore, during the noise measurement period t2 of the period setting pulse 110 by the noise measurement period setting circuit 10, the noise pulse 111 is not detected by the noise level determination circuit 11 and the F / F output pulse 112 of the flip-flop 12 is not detected.
Is a high level, the reference pulse 101 of the pulse generation circuit 1 is passed as it is and the corrected reference pulse 11
3, which is sent to the carrier wave generating circuit 2 and the counting circuit 9, so that the subsequent operation is the same as in the case of the conventional structure described with reference to FIGS.

When noise is detected during the noise measurement period t2, the flip-flop 12 is set to low level, and the F / F output pulse 112 is reset to high level at the fall of the output 110 of the noise measurement period setting circuit 10. Therefore, the reference pulse 101 of the pulse generation circuit 1 cannot pass through the AND circuit 13, and no correction reference pulse 113 for driving is sent to the carrier generation circuit 2 and the counting circuit 9. Since the transmitter 3 does not generate the transmission signal 103, the distance is not measured.

In the ultrasonic distance meter according to the first embodiment to which the noise measurement circuit A is added, the noise detection pulse 106 is detected during the noise measurement period t2 while alternately repeating distance measurement and noise measurement at a fixed cycle. In this case, the driving of the carrier generation circuit 2 and the counting circuit 9 necessary for distance measurement is stopped by preventing the generation of the correction reference pulse 113 immediately after that. Since the signal detection pulse 105 and the noise detection pulse 106 do not appear as outputs and neither the start pulse nor the stop pulse is applied to the counting circuit 9, the previous measurement value is continuously output to the distance signal output 109 of the counting circuit 9 as it is. Will be done.

The waveforms shown by solid lines in FIG. 4 indicate the operation when there is noise, and the broken lines indicate the operation when there is no noise. The output of the distance signal 109 in FIG. Although reset, it is displayed in a state where the target has been changed so as to gradually move away in order to clearly indicate the timing.

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 pulse generation circuit 1 in the first embodiment shown in FIG. Instead of using another pulse generation circuit 14,
The other constituent blocks except for the pulse generating circuit 1 are the same as those of the first embodiment including the noise measuring circuit A shown in FIG.
6 and a data holding circuit B composed of a latch circuit 17. When noise is detected during the noise measurement period, the distance measurement measured by the data holding circuit B during the immediately preceding distance measurement period is performed. The data is held so as not to be output.

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.
The common circuit section C shown in FIG. 5 has the same configuration as that of the first embodiment shown in FIG. 3 except for the pulse generation circuit 1, and has a reference pulse 101 and a period setting pulse 11 shown in FIG.
0, the F / F output pulse 112, and the distance signal 109 are all the same as those in the first embodiment shown in FIG. 4, and FIG. 6 particularly shows a case where noise is present during the noise measurement period t2. I have.

The synchronizing pulse generating circuit 14 replaces the pulse generating circuit 1 of the first embodiment, and operates the noise measuring period setting circuit 10 in the common circuit section C to generate the period setting pulse 110 and , A reference pulse 101 for activating the AND circuit 13 to generate the correction reference pulse 113, and a latch activation pulse 114 for activating the AND circuit 16 immediately before the reference pulse 101.
Although the type is generated, the reference pulse 101 is generated at the falling edge of the latch activation pulse 114 so that the two pulses 101 and 114 are synchronized with each other.

The flip-flop 15 is connected to the noise measurement period setting circuit 10 and the flip-flop 12 in the common circuit section C.
Receive the period setting pulse 110 and the F / F output pulse 112, respectively, and reset to the high level at the falling edge of the period setting pulse 110.
When the noise measurement circuit A detects the noise signal and returns to the high level after the noise pulse 112 from the flip-flop 12 goes to the low level, it is set at that moment. The F / F output pulse 115 of the flip-flop 15 becomes low level.

The AND circuit 16 is a synchronous pulse generator 1
4 and the flip-flop 1
5 and a noise pulse 112 from the flip-flop 12 are input, respectively.
When both the F / F output pulses 112 and 115 are at a high level, that is, when noise is not detected by the noise measurement circuit A, a latch pulse 116 is output to the latch circuit 17 with the latch start pulse 114 passed as it is, and the F / F When at least one of the output pulses 112 and 115 is at a low level, that is, when noise is detected, the latch pulse 116 is not output.

When the distance signal 109 is input from the counting circuit 9 in the common circuit section C, the latch circuit 17 controls the distance signal 109 by the latch pulse 16 from the AND circuit 16 and outputs a corrected distance signal 117. However, when the latch pulse 116 is input from the AND circuit 16 without noise being detected by the noise measurement circuit A, the distance measured each time without correction is performed in the same manner as in the first embodiment. The signal 117 is maintained until the next distance measurement, but when noise is detected and the latch pulse 116 is not input, a new distance signal measured immediately before that is not output and the distance signal measured before that is maintained. And the next distance measurement is not performed as in the first embodiment.

As described above, when external noise is detected, the first
In the embodiment of the present invention, a new distance measurement is temporarily stopped, and in the second embodiment, the distance signal measured immediately before the new distance measurement is not output, and the distance signal measured previously is maintained. The distance measurement is restarted again when the influence of the noise is eliminated. This makes it possible to reduce the probability of erroneous distance measurement due to extraneous noise and increase the measurement accuracy. In particular, in the case of the second embodiment, Is effective when there is a measurement error due to the contamination of the noise during the distance measurement period before and after the noise is detected.

[0030]

As is apparent from the embodiments described above, in the ultrasonic range finder of the present invention, a noise measurement circuit is added to the conventional configuration, and distance measurement and noise measurement are alternately repeated. When the external noise is detected, the next distance measurement is not performed, so that the probability of erroneous distance measurement can be reduced and the measurement accuracy can be improved.

Further, by providing a data holding circuit in addition to the noise measuring circuit, the distance signal measured immediately before the detection of the external noise is not output, and the previously measured distance signal is maintained. In addition to the first embodiment, when the external noise is detected, the immediately preceding distance data is not output, so that a measurement error due to noise contamination during the distance measurement period before and after the noise is detected is eliminated, and the measurement is further performed. Accuracy can be increased.

[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 noise measurement period setting circuit 11 noise level determination circuit 12 flip-flop 13 AND Circuit 14 Synchronous pulse generation circuit 15 Flip-flop 16 AND circuit 17 Latch circuit

Claims (2)

[Claims] 1. A distance measurement period and a noise measurement period are provided on a time axis, distance measurement and noise measurement are alternately repeated, and when noise is detected during the noise measurement period, the distance measurement in the next distance measurement period is performed. An ultrasonic distance meter comprising a noise measuring circuit for stopping the measurement. 2. A distance measurement period and a noise measurement period are provided on a time axis, and distance measurement and noise measurement are repeated alternately. When noise is detected during the noise measurement period, the distance measurement period of the next distance measurement period is measured. And a data holding circuit for stopping the output of the immediately preceding distance measurement data when noise is detected during the noise measurement period and maintaining the previous distance measurement data. Ultrasonic rangefinder.