JPH0346586A - Ultrasonic distance measuring device - Google Patents

Abstract

PURPOSE:To eliminate the generation of an error caused by an interference from other reflected pulse by measuring the time extending from the transmitting time of an ultrasonic transmitting intermittent pulse to the receiving time of a reflected receiving intermittent pulse signal. CONSTITUTION:A frequency signal from an AC voltage generator 4 is supplied to an ultrasonic transmitter/receiver 8, an ultrasonic transmitting intermittent pulse whose frequency is varied with a prescribed frequency range in a prescribed period is generated with a prescribed continued time at every prescribed time, and an ultra sonic reflected receiving intermittent pulse reflected by a measuring object is received by the transmitter/receiver 8, amplified 9 and detected 10. Subsequently, among the reflected receiving intermittent pulse signals, the pulse signal whose continued time is within a prescribed time range is extracted by an under-pulse comparator 11, an over-pulse comparator 12 and a gate circuit 14, and by using the extracted reflected receiving intermittent pulse signal, the time extending from the transmitting time of the ultrasonic transmitting intermittent pulse to the receiving time of the reflected receiving intermittent pulse is measured. In such a way, an error of a measuring distance caused by an interference from other reflected pulse of the ultrasonic reflected receiving pulse can be eliminated.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides an ultrasonic distance measuring device suitable for use in measuring the height of a surface exclusively for powder or liquid contained in a container. Regarding improvements.

[Conventional technology]

A conventional ultrasonic distance measuring device will be described below with reference to FIG. (8) indicates an ultrasonic transceiver. (
18) shows the frequency oscillator, which is the reference timer (1)
for a predetermined period (e.g. 150m5e
An intermittent transmission pulse signal of a predetermined frequency (for example, 33 kHz) is generated with a predetermined duration (for example, 1.2 mSeC) every 333 m5ec (in this case), and this is transmitted through the power amplifier (7) to the handset (8). [However, an elastic body provided in the transmitter of the transceiver (8) that is fixed to the piezoelectric vibrator and whose mechanical impedance is between the air and the piezoelectric element] Due to the presence of the layer, its duration is e.g. 1°1
5m5ec) is transmitted from the handset (8).

Further, this ultrasonic transmission pulse is reflected by the measurement target, and the ultrasonic reflected reception intermittent pulse is received by the transceiver (8), and after the reception intermittent pulse signal is amplified by the amplifier (9), it is sent to the detector. (10) and detected.

Incidentally, as shown in FIG. 7, the attenuation characteristics of a sound wave depend on its frequency, and the higher the frequency, the easier it is to attenuate, and the lower the frequency, the more difficult it is to attenuate.

On the other hand, as shown in FIGS. 8A and 8B, the directional characteristics of the transmitted sound waves become duller as the frequency is lower and sharper as the frequency is higher. Therefore, several ultrasonic transceivers (8) with different ultrasonic transmission frequencies are prepared, and when measuring a relatively long distance in a relatively wide space, a transceiver with a relatively low ultrasonic frequency is used. For measurements over relatively short distances in relatively narrow spaces, a transceiver with a relatively high ultrasonic frequency is selected.

The detector (10) is equipped with a frequency/voltage converter using a PLL circuit, and as shown in FIG. The lower the voltage, the smaller the received voltage pulse signal (B in the same figure)
Convert to In this case, the frequency of the received pulse signal should be equal to the frequency of the transmitted pulse signal from the frequency oscillator (18), so as shown in Figure 10, the voltage corresponding to the frequency of the transmitted pulse signal is detected. The detector (10) is provided with a circuit that extracts, as the voltage Vd, a voltage pulse signal having a voltage within a predetermined range before and after the detected voltage Vd, and outputs it as a rectangular wave signal.
The voltage pulse signals corresponding to noise at 28 kHz and 30 kHz are excluded.

The received voltage pulse signal from this detector (10) is supplied to an amplification controller (13) and a time/voltage converter (15).

An amplification controller (13) receives the output from the detector (10), and when the received voltage pulse signal is not obtained from the detector (10) or its level is quite low, the amplification controller (13) adjusts the level to a certain level or higher. The amplifier (9) increases the amplification degree of the amplifier (9) so that a received pulse signal of
The degree of amplification is controlled. As a result, as shown in FIG. 11, the received pulse signal with a small peak value is amplified and then supplied to the detector (10), so that the received pulse signal at the detector (10) is increased from the start of the transmitted pulse signal. The error Δt of the time t2 to the leading edge of the rectangular wave signal obtained by comparing the pulse signal with the detection voltage Vd relative to the correct time t1 can be made zero.

Furthermore, as shown in FIG. 12, the detector (10) converts the pulse width Pi of the received voltage pulse signal (input pulse) shown in B and D in the same figure to the reference pulse width of the reference pulse shown in A to C in the same figure. Compared with PO, as shown in Figure B, when the pulse width Pi of the input pulse is narrower than the pulse width Po of the reference pulse,
This is determined to be noise and is not output, but as shown in the figure, when it is wider than the reference pulse width Po, it is output.

In the time/voltage converter (15), based on the timing signal from the reference timer (1), the timing of the leading edge of the received voltage pulse signal (rectangular wave signal) from the detector (10) is determined by the reference timer (1). ) The time from the timing of the leading edge of the transmitted pulse signal, the generation of which is controlled by Outputs a distance voltage output of voltage (for example, OV at 10 m, 5 V at 2 m),
This is supplied to an indicator (17) through an output circuit (16), and a number indicating the distance is displayed along with a unit.

(2) is a temperature sensing element, and a temperature sensing signal from this element is supplied to a temperature converter (3) and converted into a predetermined temperature detection signal, and this temperature detection signal is sent to a frequency oscillator (18) and a time/time/temperature detection signal. It is supplied to a voltage converter (15).

In the frequency oscillator (18), the ultrasonic transceiver (8)
) of the wavelength of the ultrasonic transmission pulse emitted from the transmitter
The frequency oscillator (18) oscillates according to the temperature so that the length of the transmitter 74 is always equal to the thickness of the elastic layer provided in the transmitter, so that the radiation efficiency of the ultrasonic wave is high. I try to control the frequency.

Further, in the time/voltage converter (15), since the speed of sound changes depending on the temperature, the value of the speed of sound is changed depending on the temperature.

[Problem to be solved by the invention]

Such conventional ultrasonic distance measuring devices have the following drawbacks. That is, since the ultrasonic transmission pulses transmitted from the ultrasonic transceiver are diffusely reflected by the measurement object and the shape of the container in which the measurement object is housed, the ultrasonic reception pulses reflected from the measurement object are reflected by other objects. The envelope waveform of the reflected and received intermittent pulse signal obtained from the transceiver (8) is interfered with by the ultrasonic reflected pulse, (1) split into two, (2) partially missing, (3) Some levels may be deformed such that some levels become extremely small, or (3) some levels become excessively large.

The reason for this is that the directional characteristics of the ultrasonic radiation from the ultrasonic transceiver (8) exhibit characteristics consisting of a blunt main lobe and sublobes on both sides, as shown in Figure 13. Radiation is emitted from the radiation surface of the vessel (8) not only in the perpendicular direction but also in the diagonal direction. Therefore, when the object to be measured is the surface of powder contained in a tank as shown in FIG. 14, if there is a step on the powder surface, the following phenomenon occurs.

That is, the ultrasonic transmission pulse vertically radiated from the radiation surface of the transceiver (8) is reflected vertically at the flat part The reflected pulse Ry reflected at
As shown in FIGS. 15A and 15B, when the phase difference between the re-reflected pulses Rx and R at the intersection point is λ/2 (where λ is the wavelength of the ultrasonic transmission pulse), as shown in FIG. As shown in FIG. 6, the reflected received pulse shown in FIG. 6 is interfered with by the reflected pulse shown in FIG. .

Furthermore, as shown in Fig. 17, when the object to be measured is the surface of a powder layer on a layer of granules, and the thickness of the powder layer is λ/2, Also, the reflected received pulse Ra from the surface of the powder layer is the reflected pulse R from the surface of the granular layer.
b, the envelope waveform is significantly disrupted and the peak value is significantly lowered, as described above.

Furthermore, as shown in Figure 18, even when the object to be measured is the surface of water contained in a small pipe, the ultrasonic transceiver (
The ultrasonic transmission pulse radiated vertically from the radiation surface in 8) is reflected vertically on the water surface, and the reflected reception pulse Ra is
Even when the obliquely emitted ultrasonic transmission pulse intersects with the reflected pulse Rb that has been repeatedly reflected on the inner surface of the pipe, and the phase difference between the two reflected waves at the intersection point is λ/2, reflected reception is possible. The pulse Ra is interfered with by the reflected pulse Rh,
As described above, the envelope waveform is significantly distorted and the peak value thereof is significantly reduced.

(Then, if the reflected received pulse is not interfered with by other reflected pulses and its envelope waveform is not significantly disrupted or its peak value is not significantly reduced, the detector (10)
The waveforms of the received voltage pulse signal and its rectangular wave signal are as shown in FIGS. 5A and 5B, respectively, and the time t from the leading edge of the transmitted voltage pulse signal to the leading edge of the rectangular wave signal is measured correctly. .

However, the phase difference between the reflected received pulse and this pulse is λ/2.
If the envelope waveform is significantly distorted or the peak value is significantly lowered due to interference by other reflected pulses with a value very close to the received voltage pulse signal at the detector (10) and its rectangle. The wave signal waveforms are shown in Figure 5C.
, D, the time from the leading edge of the transmission voltage pulse signal to the leading edge of the rectangular wave signal is not tl, but the error Δt.
I warn that t2 includes 0.

In view of this, the present invention proposes an ultrasonic distance measuring device that can eliminate errors in measurement distance due to interference of ultrasonic reflected received pulses from other reflected pulses.

[Means to solve the problem]

The present invention transmits intermittent ultrasonic transmission pulses emitted from an ultrasonic transceiver (8) for a predetermined duration at predetermined intervals toward a measurement object, and receives intermittent ultrasonic reception pulses reflected from the measurement object. The ultrasound transmitter/receiver (8) receives the reflected reception intermittent pulse signal and measures the time from the transmission of the ultrasound transmission intermittent pulse signal to the reception of the reflected reception intermittent pulse signal. In an ultrasonic distance measuring device that measures the distance from a device (8) to a measurement target, a frequency signal generating means (4) whose frequency changes within a predetermined frequency range at a predetermined period is provided, and the frequency signal generation means (4) is provided. The frequency signal from the means (4) is supplied to the ultrasonic transmitter/receiver (8) to transmit intermittent ultrasonic transmission pulses whose frequency changes within a predetermined frequency range at a predetermined period with a predetermined duration at predetermined intervals. At the same time, an extraction means (1112, 14) is provided for extracting a reflected reception intermittent pulse signal whose duration is within a predetermined time range from among the reflected reception intermittent pulse signals. The reflected reception intermittent pulse signal from 12, 14) is used to measure the time from the transmission of the ultrasonic transmission intermittent pulse to the reception of the reflected reception intermittent pulse signal.

[Effect]

According to the present invention, the frequency signal from the frequency signal generating means (4) is supplied to the ultrasonic transmitter/receiver (8) to generate a frequency within a predetermined frequency range at a predetermined period with a predetermined duration every predetermined time. Generates intermittent pulses of ultrasonic transmission that vary. Then, among the reflected reception intermittent pulse signals, a reflected reception intermittent pulse signal whose duration is within a predetermined time range is extracted by the extraction means <LL 12.14),
Using the extracted reflected reception intermittent pulse signal, the time from the transmission of the ultrasonic transmission intermittent pulse signal to the reception of the reflected reception intermittent pulse signal is measured.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail with reference to FIG. 1, but parts that overlap with the conventional example shown in FIG. do.

(4) is an AC voltage generator, which has a period of, for example, 60
In seconds, an alternating voltage is generated that varies between +IV and -IV. This AC voltage is supplied to an adder (5) and added to the temperature detection signal (voltage) from the temperature converter (3),
The added voltage is supplied to a voltage/frequency converter (6). Then, from this voltage/frequency converter (6), it is controlled by the reference timer (1) for a predetermined period (for example, 15
0 m5ec~1sec, here 333m5ec)
Each time, a predetermined duration (for example, 1, 2 m5ec
＞, as shown in FIG.
An intermittent pulse signal varying in the range ~35kHz is generated, which is transmitted through a power amplifier (7) to an ultrasound transceiver (8).
supplied to

As a result, intermittent ultrasonic pulses are transmitted from the transceiver (8) [However, the transmitter is fixed to a piezoelectric vibrator provided in the transmitter of the transceiver (8), and the mechanical impedance is between the air and the piezoelectric element. Due to the presence of the elastic layer, a duration of, for example, 1.15 m5ec) is transmitted from the handset (8). Further, this ultrasonic transmission pulse is reflected by the measurement target, and the ultrasonic reflected reception intermittent pulse is received by the transceiver (8), and the reception intermittent pulse signal is transmitted to the amplifier (9).
) and then supplied to the detector (10) where it is detected in the same way as in the conventional example.

The reflected received voltage pulse signal (rectangular wave signal) from the detector (10) is supplied to an under pulse width comparator (11), an over pulse width comparator (12), and a gate circuit (14), respectively. Then, the pulse width of the rectangular waveform received voltage pulse signal (input pulse) (Figure 3) supplied from the wave detector (10) to the pulse width comparators (11) and (12) is equal to the under pulse width. The under pulse shown in FIG. 3B of the comparator (11) (its pulse width is, for example, 1 m5ec)
reference pulse), and the overpulse width comparator (1
2), the gate circuit (■4) is opened only when the overpulse shown in FIG. 3C (its pulse width is, for example, 1.3 m5ec reference pulse) is The pulse) (Figure 3) is output from the gate circuit (14) and is sent to the time/voltage converter (15).
).

Note that the amplification controller (13) is also controlled by the comparison output of the under pulse width comparator (11), and is controlled by the comparison output of the under pulse width comparator (11).
Rectangular waveform received voltage pulse signal (input pulse) from )
The pulse width of the person (Figure 3) is under pulse (Figure 3B).
), the amplification increase control of the amplifier (9) by the amplification controller (13) is stopped.

Now, as shown in Figure 4, there is a layer of soft powder on a hard surface, and the distance from the ultrasonic transceiver (8) to the surface of the powder layer is L+ (-3400 mm), and the distance to the hard surface is L+ (-3400 mm). Let the distance be L2 (=3417mm). Further, the frequency of the ultrasonic transmission pulse emitted from the ultrasonic transceiver (8) is assumed to be 10 kHz. Thus, the handset (8)
The wavelength λ of the ultrasonic wave emitted from the
Therefore, in this case, when the ultrasonic transmission pulse from the transceiver (8) is reflected from the surface of the powder layer and the hard surface, the reflected reception pulse reflected from the powder surface is equal to the hard surface. Interfering with the reflected pulses reflected from the surface, the envelope waveform is significantly disrupted and the peak value is significantly lowered.

However, if the frequency of the ultrasonic transmission pulse emitted from the handset (8) changes to, for example, 15kHz, then the wavelength λ is: λ-340 (m/5ec) x 15kHz-22,667
Therefore, L2-Ll = 17mm-(3/4
)×λ. In this case, the reflected received pulse reflected from the powder surface is not interfered with by the reflected pulse reflected from the hard surface, and its envelope waveform is not significantly distorted or its peak value is not significantly reduced.

(Then, the reflected received pulse has a phase difference of λ/2
Or, if it is interfered with by another reflected pulse with a value very close to this, and its envelope waveform is significantly disrupted or its peak value is significantly lowered, the received voltage pulse signal at the detector (10) will be As shown in Figure 5C, the waveform collapses,
From the leading edge of the transmitted voltage pulse signal of the inverted square wave signal shown in FIG. 5C, which is obtained by detecting that the voltage of the received voltage pulse signal is within the upper and lower detection levels. The time is not tl, but t2, which includes the error Δt. However, in such a case, the rectangular waveform received voltage pulse signal from the detector (10) is transmitted to the gate circuit (10).
4) and is not supplied to the time/voltage converter (15).

However, the frequency of the ultrasonic transmission 7 pulse transmitted from the transceiver (8) changes, and the reflected wave reception pulse from the measurement target is interfered with by other reflected pulses, causing its envelope waveform to be significantly distorted. , when the peak value no longer decreases significantly, the detector (10) detects the
As shown in Figure 5, a received voltage pulse signal with a normal waveform was obtained, and it was detected that the voltage of the received voltage pulse signal was within the upper and lower detection levels.
The inverted rectangular wave signal shown in FIG. Time t1 is correctly measured.

Thus, the correct distance between the ultrasonic transceiver (8) and the object to be measured is measured and displayed on the indicator (17).

In addition, in the wave detector (10), an envelope detection circuit may be provided instead of the frequency/voltage converter.

However, in the case of a frequency/voltage converter, particles such as powder fly in between the transceiver (8) and the object to be measured, and the ultrasonic transmission pulse is reflected by this, causing the frequency to change due to the Doppler effect. It is possible to avoid erroneous measurements when an ultrasonic reflected pulse with a changed value occurs.

〔Effect of the invention〕

According to the present invention described above, it is possible to obtain an ultrasonic distance measuring device that can eliminate errors in measurement distance due to interference of ultrasonic reflected received pulses from other reflected pulses.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is an explanatory diagram of frequency change of the voltage/frequency converter, Fig. 3 is an explanatory diagram of pulse width comparison, and Fig. 4 is an illustration of reflected wave interference. An explanatory diagram of
Figure 5 is an explanatory diagram of measurement time in the case of normal waves and interference waves,
Fig. 6 is a block diagram showing a conventional example, Fig. 7 is a sound wave attenuation characteristic diagram, Fig. 8 is a directional characteristic diagram, Fig. 9 is an explanatory diagram of frequency/voltage conversion, and Fig. 10 is reflected wave detection. Explanatory diagram, 1st
Figure 1 is an explanatory diagram of the amplification factor control, Figure 12 is an explanatory diagram of the pulse width check, Figure 13 is a directional characteristic diagram of the radiated ultrasound from the ultrasonic transceiver 9, and Figure 14 is the interference of reflected waves. FIG. 15 is an explanatory diagram of the relative phase of reflected waves, and FIGS. 16, 17, and 18 are explanatory diagrams of interference of reflected waves, respectively. (1) is a reference timer, (2) is a temperature sensing element, (3) is a temperature converter, (4) is an AC voltage generator, (5) is an adder, (6) is a voltage/frequency converter, ( 7) is a power amplifier,
(8) is the ultrasonic transceiver, (9) is the amplifier, (10) is the detector, (11) is the under pulse width comparator, (12) is the over pulse width comparator, and (13) is the amplification controller. ,(
14) is a gate circuit, (15) is a time/voltage converter, (
16) is an output circuit, and (17) is an indicator. Agent Hidemori Matsukuma 0 JP-A-3 46586 (7) Tanuki yo g! 'Crab (J beak9ko-b'qi - ■ Medium

Claims (1)

[Claims] Intermittent ultrasonic transmission pulses emitted from an ultrasonic transceiver at predetermined intervals with a predetermined duration are transmitted toward a measurement target, and intermittent ultrasonic reception pulses reflected from the measurement target are transmitted over a predetermined period of time. Receive it with a sonic transceiver to obtain a reflected reception intermittent pulse signal,
An ultrasonic type that measures the distance from the ultrasonic transceiver to the measurement target by measuring the time from the transmission of the ultrasonic transmission intermittent pulse to the reception of the reflected reception intermittent pulse signal. In the distance measuring device, a frequency signal generating means whose frequency changes within a predetermined frequency range with a predetermined period is provided, and the frequency signal from the frequency signal generating means is supplied to the ultrasonic transceiver, and the frequency signal is supplied to the ultrasonic transceiver at the predetermined time intervals. An intermittent ultrasonic transmission pulse whose frequency changes within the predetermined frequency range with the predetermined cycle is generated for the predetermined duration, and the duration of the reflected reception intermittent pulse signal is within the predetermined time range. an extraction means for extracting the intermittent reflected reception pulse signal from the extraction means, and using the intermittent reflected reception pulse signal from the extraction means, from the time of transmission of the intermittent ultrasonic transmission pulse to the time of reception of the intermittent reflected reception pulse signal. An ultrasonic distance measuring device characterized by measuring the time taken to reach the destination.