JP2018021810A - Ultrasonic displacement measuring device and ultrasonic displacement measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic displacement measuring device that facilitates generation of a beat signal at a receiver, restrains costs, and is accurate and energy saving even in the case of measuring distance from a small target at a high frequency.SOLUTION: An ultrasonic displacement measuring device includes: a first transmitter 3 for transmitting an ultrasonic wave at a first frequency as a consecutive wave; a second transmitter 2 for transmitting an ultrasonic burst wave continuing only for a prescribed time at a second frequency different from the first frequency; a receiver 1 located at a position where ultrasonic beams transmitted by the first transmitter 3 and the second transmitter 2 overlap; and an analyzer for finding a reception time reference point from phases of signals obtained by the receiver 1 and finding distance between the first transmitter 3 or second transmitter 2 and the receiver 1 on the basis of time at which the second transmitter 2 started transmission and the reception time reference point.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an apparatus and method for high-accuracy position measurement using ultrasonic waves, and more particularly to an ultrasonic displacement measurement apparatus and an ultrasonic displacement measurement method for measuring a relative distance between devices using ultrasonic propagation time. .

  2. Description of the Related Art Conventionally, a technique for measuring the displacement of an object to be measured in air at a position away from a reference point by using an ultrasonic wave is known. Ultrasonic distance measurement is useful in places where it is dangerous for people to enter, and when managing distance measurement continuously, etc. If it is an environment where sound can be transmitted in the air, liquid or metal Distance measurement is possible.

  An ultrasonic element is used for transmission and reception of ultrasonic waves. The ultrasonic element is also an ultrasonic transmitter and serves as a receiver. The selection of the ultrasonic frequency for distance measurement is such that the lower the frequency (the longer the wavelength), the smaller the attenuation, the farther the distance, the higher the frequency (the shorter the wavelength), the higher the distance resolution, It is determined by the directivity and range.

  In addition to ultrasonic waves, light waves, electromagnetic waves, etc. are used as distance measurements by waves. However, ultrasonic wave distance measurements are much slower than electromagnetic waves and light waves, so they are used for measurement. Long time axis, easy processing, accurate measurement, short wavelength, high resolution, accurate measurement, high human safety, environmental friendliness, relatively low cost, etc. There are advantages.

  In technology that uses ultrasonic waves to measure the displacement of a measurement object in the air at a certain distance from the reference point, the object is irradiated with ultrasonic waves, and its transmission time and reception time at the object What measures the displacement of a target object based on the difference with is known. In such a displacement measuring apparatus, a method for determining a voltage threshold for detecting reception of ultrasonic waves is important in displacement measurement accuracy, and an error increases in determination of arrival time as the received intensity decreases. Furthermore, due to the influence of attenuation and dispersion of ultrasonic waves in the air, the waveform changes in the path to reach the object, and the waveform change becomes an obstacle in determining the reception time.

  Therefore, a displacement measurement method based on the phase difference between the transmission signal and the reception signal using the frequency sweep wave ultrasonic wave is not used to detect the reception time of the ultrasonic wave but using the ultrasonic reception voltage threshold. Yes. However, the range of displacement that can be measured is limited to within one wavelength of the ultrasonic wave.

  Therefore, in order to measure the displacement that changes over a wider range than the wavelength with high resolution with a resolution that is sufficiently finer than the wavelength, the phase delay measurement using two different frequencies f1 and f2 is performed twice while switching. It is known to measure the phase using a frequency of “f1−f2”, and is described in Patent Document 1.

  In addition, it is known to transmit an ultrasonic burst in order to accurately transmit timing information from the waveform generator to the waveform receiver, but the ultrasonic burst has an infinite spread in the frequency spectrum. In contrast, existing waveform generators, wave propagation media and waveform receivers have somewhat uneven amplitude frequency characteristics and phase frequency characteristics. Therefore, rectangular electric signal pulses and rectangular ultrasonic bursts are deformed at the receiving end, and it is difficult to strictly transmit timing information.

  In particular, since the piezoelectric ceramic element used in the ultrasonic displacement measuring apparatus has a narrow band frequency characteristic, the received waveform is subjected to strong distortion. In addition, if a region such as the leading edge of an ultrasonic burst that has a strong influence on the transient response characteristic in terms of signal is used, variations in the characteristics of the transmitting and receiving elements tend to affect the measurement accuracy and the transmission accuracy of timing information. Furthermore, since the envelope of the waveform is affected by both the amplitude frequency characteristic and the phase frequency characteristic of the transmission line, when using a transmission line having these characteristics, the shape of the envelope is likely to change, and as a result The transmission accuracy of timing information is reduced.

  In order to compensate for this defect and improve accuracy, an ultrasonic burst that is a beat signal consisting of two frequencies is transmitted as a transmission signal with only one phase matching point, and this phase matching point is received at the reception time. A measuring means called a phase matching method using a reference point is known, and is described in Patent Document 2, for example.

JP 2004-191145 A Japanese Patent No. 4621924

  In the phase matching method, which is the conventional technique, it is important to generate and receive a high-quality beat. For this reason, in Patent Document 2, a plurality of frequency signals are generated by the transmitter, the phase is adjusted, and then the plurality of frequency signals are synthesized. Then, the generated composite waveform is stored, D / A converted and converted into an analog signal. Further, the amplification unit amplifies the analog signal to drive the piezoelectric ceramic vibrating body, which is an ultrasonic element, and transmits a plurality of synthesized frequency signals to the receiver using ultrasonic waves.

  Therefore, not only is complicated processing necessary for generating a synthesized waveform and the cost is high, but also the amplification unit handles analog signals, so it requires wasteful power consumption and requires high quality beats with less distortion. In addition, driving the ultrasonic element requires a large amplitude and a high output, and driving at a high frequency has to drive the ultrasonic wave at a relatively low frequency of 40 kHz.

  In addition, although the low-frequency ultrasonic element can generate vibration with low energy, the beam diameter increases when transmitted to a distant place, and the one described in Patent Document 2 is not suitable for position measurement of a small target. . Furthermore, a high-frequency element having a small beam diameter requires higher energy for driving, and it is extremely difficult to generate a beat as a high-quality composite waveform by synthesizing in an electric circuit.

  The object of the present invention is to solve the above-described problems of the prior art, simplify the generation of a composite waveform at the receiver, reduce costs, and perform distance measurement of a small target at high frequency with high accuracy. The purpose is to save energy and reduce distortion.

  In order to achieve the above object, the present invention transmits an ultrasonic beam from a transmitter to a receiver and obtains a propagation time from transmission to reception to measure the distance between the transmitter and the receiver. In the acoustic displacement measuring apparatus, a first transmitter that transmits an ultrasonic wave as a continuous wave at a first frequency, and a second transmission that transmits an ultrasonic burst wave continuous for a predetermined time at a second frequency different from the first frequency. A reception time reference point from the receiver, the receiver arranged at the position where the ultrasonic beams transmitted from the first transmitter and the second transmitter overlap, and the phase of the signal obtained by the receiver An analysis device for obtaining a distance between the first transmitter or the second transmitter and the receiver based on a time when transmission is started by the second transmitter and the reception time reference point It is.

  Thereby, the receiver is arranged at a position where the ultrasonic beams transmitted from the transmitter overlap, and the reception time reference point is obtained from the phase of the signal obtained by the receiver, so that the generation process of the composite waveform is easier, High-power, high-frequency ultrasonic waves can be used, and distance measurement of a small target can be performed with high accuracy.

In the above configuration, it is preferable that the first transmitter and the second transmitter include a switch circuit that drives the ultrasonic element with an on / off signal.
As a result, the power consumption of the drive circuit is reduced, and high-frequency ultrasonic waves can be transmitted.

Further, in the above, the first transmitter is disposed on the central axis of the receiver so as to face the receiver, and the second transmitter is in a direction that forms a predetermined angle with the central axis. It is desirable that it is arranged.
Thereby, the distance between the second transmitter and the receiver can be accurately measured.

Furthermore, in the above, the second transmitter is disposed on the central axis of the receiver so as to face the receiver, and the first transmitter is in a direction that forms a predetermined angle with the central axis. It is desirable that it is arranged.
Thereby, the distance along the central axis of the receiver can be measured more accurately.

Furthermore, in the above, it is desirable that a plurality of the second transmitters are arranged.
This enables more accurate and reliable distance measurement.

Further, in the above, it is preferable that the first transmitter and the second transmitter are arranged on a vertical plane separated from the receiver by a predetermined distance.
This enables distance measurement from the receiver to the vertical plane with higher accuracy and higher reliability.

Furthermore, in the above, it is desirable that the analysis device samples a signal obtained by the receiver by a trigger signal that determines a time when transmission is started by the second transmitter.
Thereby, the calculation of the propagation time from transmission to reception becomes more accurate.

Further, in the above, the first transmitter is disposed on a vertical plane perpendicular to the central axis and separated from the receiver by a predetermined distance, and the second transmitter is disposed on the vertical plane. It is desirable that the central axis is arranged in a direction that forms a predetermined angle.
This enables distance measurement from the receiver to the vertical plane with higher accuracy and higher reliability.

Furthermore, in the above, it is preferable that the ultrasonic beam size by the first transmitter is larger than that of the second transmitter.
As a result, the measurable area in the measurement axis direction can be expanded, and influences other than the measurement axis direction can be avoided.

  The present invention also provides an ultrasonic burst wave that is transmitted for a predetermined time at a second frequency different from the first frequency by the second transmitter, wherein the first transmitter transmits an ultrasonic wave that is a continuous wave of the first frequency. The reception time reference point is obtained from the phase of the signal obtained by the receiver arranged at a position where the ultrasonic beams transmitted from the first transmitter and the second transmitter overlap with each other, and the second The distance between the first transmitter or the second transmitter and the receiver is obtained based on the time when transmission is started by the transmitter and the reception time reference point.

  According to the present invention, the receiver is arranged at a spatial position where the ultrasonic beams transmitted from a plurality of transmitters having different frequencies overlap, and the reception time reference point is obtained from the phase of the signal obtained by the receiver. This makes it possible to easily generate a beat signal in the machine, reduce costs, and achieve high accuracy and energy saving even when measuring the distance of a small target at a high frequency.

1 is a basic configuration diagram of an ultrasonic displacement measuring apparatus according to an embodiment of the present invention. Basic configuration diagram of an ultrasonic displacement measuring apparatus according to another embodiment The figure which shows the measurable area at the time of setting as FIG. The block diagram which shows the drive circuit of the ultrasonic element in one Embodiment The block diagram which shows the whole signal processing in one Embodiment Block diagram showing details of transmitter signal processing in one embodiment The block diagram which shows the detail of the signal processing of the receiver in one Embodiment Explanatory diagram showing relationship between beat signal and phase match point Explanatory diagram showing the measurement principle using ultrasonic waves according to the prior art Explanatory drawing showing how to synthesize beat waves in the phase matching method according to the prior art Graph showing the relationship between beam size, transmission frequency and distance of ultrasonic displacement measuring device Graph showing relationship between energy density, transmission frequency and distance of ultrasonic displacement measuring device A graph showing the actual measurement value of the beam size when the transmission frequency is 40 kHz and 300 kHz A graph that records the received waveform when transmitting an ultrasonic burst according to the prior art The graph which recorded the received waveform in one Embodiment The figure which showed the layout of the transmitter and receiver in other embodiment

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  Ultrasonic distance measurement enables distance measurement in an environment where sound can be transmitted in the air, in liquid, or in metal, and the measurement distance is as long as 60 to 10 m. Thereby, as various positioning, height control before robot adsorption, positioning of robot arm, detection of misalignment of steel plate, positioning of machine tool, etc., scanning control of welding position, positioning of liquid crystal glass, stop of transportation of solar cell substrate Widely used for position measurement.

  The ultrasonic displacement measuring device detects the presence / absence of an object and the distance to the object by transmitting ultrasonic waves with a transmitter and receiving them with a receiver. Ultrasonic elements are used to transmit and receive ultrasonic waves. Ultrasonic elements are elements that generate ultrasonic waves by applying electrical energy or convert ultrasonic vibration energy into electrical signals. A barium titanate vibrator using a piezoelectric phenomenon is used.

  A piezoelectric element vibrates efficiently when an AC voltage is applied, the element vibrates and has a specific frequency, and an AC voltage having the same frequency as that frequency is applied. Generally, a frequency of 40 kHz is often used. A low frequency is used to measure a long distance, and a high frequency is used to accurately measure a short distance.

  FIG. 1 is a basic configuration diagram of an ultrasonic displacement measuring apparatus according to an embodiment of the present invention, and FIG. 2 is a basic configuration diagram of an ultrasonic displacement measuring apparatus according to another embodiment.

  As shown in FIGS. 1 and 2, three high-frequency (about 300 kHz) ultrasonic elements are used, one of which can be used as a receiver 1 and two as a transmitter 2 and a transmitter 3. . The transmitter 2 and the transmitter 3 transmit ultrasonic waves having different frequencies (for example, the transmitter 2 is 296 kHz, and the transmitter 3 is 304 kHz). The transmitter 2 (second transmitter) transmits an ultrasonic burst wave continuous for a predetermined time, that is, an ultrasonic pulse burst wave, and the transmitter 3 (first transmitter) converts the ultrasonic burst wave of the transmitter 2 into an ultrasonic burst wave. Ultrasonic waves are transmitted as a continuous wave for a sufficiently long time.

  As shown in FIG. 1, the transmitter 3 (first transmitter) is arranged to face the receiver 1 on the central axis of the receiver 1, and the transmitter 2 (second transmitter) is the central axis. Are arranged in a direction forming a predetermined angle. In the receiver 1, the ultrasonic beams of the transmitter 3 and the transmitter 2 are overlapped and spatially synthesized at the position of the receiver 1 to be a reception waveform of the receiver 1. Further, since the transmitter 2 and the transmitter 3 transmit ultrasonic waves having different frequencies, they are synthesized as beat signals at the position of the receiver 1, that is, for a predetermined time transmitted by the transmitter 2. The transmitter 3 (first transmitter) that transmits a continuous wave only needs to be a position that can transmit ultrasonic waves to the position of the receiver 1, and the arrangement of the transmitter 3 and the transmitter 2 is reversed as shown in FIG. Anyway.

In either arrangement of FIG. 1 and FIG. 2, the distance from the transmitter 2 (second transmitter) that transmits the ultrasonic pulse burst wave to the receiver 1 is obtained. In FIG. 1, the distance between the transmitter 2 (second transmitter) and the transmitter 3 (first transmitter) is known at the time of setting, and from the transmitter 2 (second transmitter) to the receiver 1. If the distance is obtained and converted, the distance from the transmitter 3 (first transmitter) to the receiver 1 can be obtained. In addition, since the ultrasonic beams from the transmitter 2 (second transmitter) and the transmitter 3 (first transmitter) overlap at the position of the receiver 1 and are spatially synthesized, only the operating distance from the receiver 1 is required. A plurality of three or more transmitters may be three-dimensionally arranged on a separated vertical plane.
FIG. 3 is a diagram showing a measurable area when the transmitter 2 (second transmitter) and the transmitter 3 (first transmitter) are arranged as shown in FIG. The upper diagram of FIG. 3 shows the case where the size of the ultrasonic beam 51 of the transmitter 2 (second transmitter) is small, and the lower diagram shows the case where the size of the ultrasonic beam 52 of the transmitter 2 (second transmitter) is large. Yes, the size of the ultrasonic beam 50 of the transmitter 3 (first transmitter) is the same.

  In distance measurement, an area where the ultrasonic beam 51 of the transmitter 2 (second transmitter) and the ultrasonic beam 50 of the transmitter 3 (first transmitter) overlap is an area that can be measured in the measurement axis direction. . Therefore, the measurable area in the measurement axis direction can be expanded by increasing the size of the ultrasonic beam 50 of the transmitter 3 (first transmitter) that transmits continuous waves.

  On the other hand, when the size of the ultrasonic beam 51 of the transmitter 2 (second transmitter) that transmits the ultrasonic burst wave is increased like the ultrasonic beam 52, the measurable area is expanded in directions other than the measurement axis. Therefore, an error occurs with respect to the measurement direction, and the size of the ultrasonic beam 50 of the transmitter 3 (first transmitter) that transmits a continuous wave is made larger than the size of the ultrasonic beam 51 as shown in the above diagram, thereby expanding the measurable area. It is preferable.

  The position of the receiver 1 is installed at a position where the ultrasonic beams from the transmitter 2 and the transmitter 3 overlap, and the transmitter 2 and the transmitter 3 transmit ultrasonic waves having different frequencies in synchronization with each other. It is synthesized at the position of the machine 1, that is, spatially as a beat signal. Since the transmitter 2 transmits high-frequency ultrasonic waves to the air, the ultrasonic element is turned on and off as a high voltage, that is, as an ultrasonic pulse burst wave continuous for a predetermined time by a switch circuit that drives in a pulse manner with a rectangular wave. Send. The transmitter 3 transmits the ultrasonic element as a continuous wave of ultrasonic pulses by a switch circuit that drives the ultrasonic element in a pulse manner with a rectangular wave.

  The signal obtained by the receiver 1 is sampled and A / D converted by the analyzer and recorded in the memory. Then, a reception time reference point is obtained by a phase matching method for detecting a point where the phase difference is 0 from the received waveform. A propagation delay time is obtained based on the time when a transmission trigger is applied to start transmission to the transmitter 2 and the obtained reception time reference point, and the distance from the transmitter 2 to the receiver 1 is determined.

  FIG. 4 is a block diagram showing a driving circuit for ultrasonic elements in the transmitter 2 and the transmitter 3, and the CPU 4 generates a pulse signal that is a rectangular wave. The transmitter 2 generates a pulse signal of 296 kHz, and the transmitter 3 generates a pulse signal of 304 kHz. Since the circuit that drives the ultrasonic element 6 does not handle an analog signal such as an electrically synthesized beat signal, the drive circuit itself may be a switch circuit 5 that does not require wasteful power consumption and that simply turns on and off. . Therefore, the ultrasonic element 6 can be driven with a large amplitude and a high output up to about 300 kHz, which is a high frequency, without distortion, and the measurement accuracy can be increased by an order of magnitude. Actually, since the transmitter 2 and the transmitter 3 each transmit an ultrasonic pulse wave that is continuous for a predetermined time and a continuous wave of ultrasonic pulses, the CPU 4 sends the respective pulse signals to the transmitter 2 and the transmitter 3. Is generated and applied to the switch circuit 5.

  5 is a general signal processing, FIG. 6 is a block diagram showing details of the transmitter signal processing, FIG. 7 is a block diagram showing details of the signal processing of the receiver, and FIG. 8 shows the relationship between the beat signal and the phase matching point. It is explanatory drawing shown. In FIG. 5, the transmitter 2 and the transmitter 3 are the same as those shown in FIG. 4, but transmit the pulse signal output from the switch circuit 5 to the analyzer 9 as a trigger signal. The influence of the delay time from the CPU 4 on the input side of the switch circuit 5 to the switch circuit 5 can be avoided.

  In FIG. 5, the receiver 1 uses an ultrasonic element 7 to transmit an ultrasonic pulse burst wave transmitted from the transmitter 2 and a continuous wave of ultrasonic pulses having a frequency different from that of the transmitter 2 transmitted from the transmitter 3. And a combined burst-like beat signal is received. The ultrasonic element 7 is connected to the analysis device 9 via a filter 8 that removes out-of-band noise and improves the signal-to-noise ratio of the system.

  In FIG. 6, the preparation for measurement is started by turning on the external switch 10, and the signal is input to the CPU 4-1 that controls the transmitter 3. The CPU 4-1 generates a pulse signal that is a rectangular wave. A pulse signal having a frequency f1 (304 kHz) is input to the switch circuit 5-1, and the ultrasonic element 6-1 is driven. Since the switch circuit 5-1 does not amplify an analog signal in which amplitude distortion becomes a problem, even if it is a continuous wave, the drive circuit itself is merely turned on and off without requiring unnecessary power consumption.

  Measurement is started by turning on the external switch 11, and the signal is input to the CPU 4-2 that controls the transmitter 2. The CPU 4-2 generates a pulse burst signal that is a rectangular wave. A pulse burst signal having a frequency f2 (296 kHz) is input to the switch circuit 5-2, and the ultrasonic element 6-2 is driven for a predetermined time.

  In FIG. 7, the ultrasonic pulse burst wave transmitted by the transmitter 2 and the ultrasonic pulse wave that is a continuous wave transmitted by the transmitter 3 are at the position of the receiver 1, that is, as spatial beat signals. The synthesized beat signal is received by the ultrasonic element 7. The signal received by the ultrasonic element 7 is sent to the analysis device 9 through the filter 8 and analyzed through removal of noise outside the band, amplification, and the like. The analysis device 9 obtains the reception time reference point by the phase matching method. Then, the propagation delay time is obtained based on the time when the transmission trigger is applied by the external switch 11 to start transmission to the transmitter 2 and the obtained reception time reference point, and the distance from the transmitter 2 to the receiver 1 is obtained. To decide.

  As shown in FIG. 8, the beat signal is a combination of a signal of frequency f1 and phase φ1 and a signal of frequency f2 and phase φ2. The two phases change rapidly at each frequency, but the difference only changes between -π and π. Therefore, there is always only one point where the phase difference becomes 0 in one packet of the beat signal.

  In the receiver 1, since the signals transmitted by the transmitter 2 and the transmitter 3 are combined, the phase of the combined signal only changes between −π and π. Since there is one phase coincidence point in this, the analysis device 9 extracts it from the synthesized waveform as a reception time reference point. Thereby, the detection of the reception time reference point can be detected with an accuracy of several μs.

  5 and 7, the analysis device 9 samples the received signal at the receiver 1 with reference to the trigger signal input from the transmitter 2, performs A / D conversion, and performs FFT processing. Next, the phase of the carrier at the time origin of each of the transmitter 2 and the transmitter 3 is obtained, and a phase coincidence point is obtained from the difference between them to be a reception time reference point. If the reception time reference point can be detected, the propagation delay time can be known as the difference between the time when the trigger is applied and the reception time reference point, and the distance from the transmitter 2 to the receiver 1 can be determined.

  Since the address of the memory at the time of A / D conversion corresponds to the reception time, the propagation delay time is recorded by the analyzer 9 at the time when the transmitter 2 is triggered, and the received signal is sampled. It can be obtained from the recording address.

  Since the propagation delay time includes the response time of the ultrasonic element, in the actual distance measurement, it is necessary to convert the propagation delay time into a distance, and it is necessary to cancel the response time. Therefore, the transmitter 2, the transmitter 3 and the receiver 1 are set apart by a predetermined distance, and the relative displacement is measured based on the distance. Usually, it is often measured not the distance between the transmitter and the receiver, but the displacement that the receiver or transmitter has moved. At this time, for example, the position of the receiver is moved according to the reference gauge, and a change in the distance between the transmitter and the receiver is set as a calibration value. In this calibration, it is preferable to obtain a calibration value by changing the one corresponding to the reference gauge and measuring at several points. In addition, since the measurement result of the ultrasonic displacement measuring device is affected by atmospheric changes, it is desirable to record the temperature with the analyzing device 9 and calibrate the distance measurement.

  The transmitter 2 and the transmitter 3 have the same configuration, and ultrasonic waves are transmitted in synchronization with the clock signal generated by the CPU 4. Thereby, even if measurement is repeated many times, the transmission timing of ultrasonic waves does not shift.

  Further, since the phase of the signal is used for measurement, a measurement error due to multipath due to surrounding reflected waves is received. However, since a short burst wave is used, the signal processing in the analysis device 9 is compared with the duration of the burst. If done fast enough, the measurement time can be brought close to the duration of the burst. Therefore, if the path difference between the multipath wave and the direct wave is equal to or greater than the measurement distance, the influence of the multipath can be avoided.

  FIG. 9 is an explanatory diagram of conventional position measurement using ultrasonic waves, and FIG. 10 is an explanatory diagram illustrating a method of synthesizing a beat wave in the conventional phase matching method. Will be described in detail.

  In FIG. 9, the transmitter 20 transmits an ultrasonic burst at about 40 kHz. The signal is received by the receiver 21 installed at a position separated by a distance L. Since the transmission waveform 22 has a rectangular envelope, the starting position should be uniquely determined, but the reception waveform 23 is deformed by the attenuation and response characteristics of the receiving side element. Also, providing frequency selectivity with a filter is indispensable for removing out-of-band noise, improving the signal-to-noise ratio of the system, and extending the measurement distance. Therefore, as shown in FIG. 9, it is difficult to accurately determine the propagation time by simply setting a threshold from the received waveform 23 from the received signal envelope 24 and obtaining the reception time.

  The prior art shown in FIG. 10 eliminates the drawbacks shown in FIG. 9 and synthesizes the waveforms of the frequency f1 of 30 and the frequency f2 of 31 to calculate the beat signal 32 of f1 + f2, and stores it in the memory 34. In the ultrasonic transmitter 33 serving as a transmitter, the data stored in the memory 34 is D / A converted into an analog signal whose amplitude and phase change, and is transmitted to the drive circuit 35 (analog amplifier circuit). In the drive circuit 35, it converts into electric power required in order to drive the piezoelectric ceramic which is an ultrasonic element. The ultrasonic element 36 transmits an ultrasonic burst 37.

  The synthesized waveform is generated according to the measurement distance, the characteristics of the ultrasonic element, the size of the target, and the like, and data stored in the memory 34 is required each time. The drive circuit 35 requires wasteful power consumption because the amplification unit handles analog signals. In addition, driving the ultrasonic element requires a large amplitude and a high output, and driving at a high frequency has to drive the ultrasonic wave at a relatively low frequency of 40 kHz.

  In addition, the low-frequency ultrasonic element can generate vibration with low energy, but when transmitted to a far distance, the beam diameter becomes large, and driving at about 40 kHz is not suitable for position measurement of a small target. Furthermore, high-frequency devices with a small beam diameter require higher energy to drive, and it is difficult to synthesize a high-frequency signal of about 300 kHz in an electric circuit and to drive without distortion at a high output. there were.

  In general, ultrasonic waves tend to have a wide beam size as well as a measurement value that is affected by temperature. As a result, the area of the measurement target must be increased, and is affected by the surface shape, the roughness, and the like. Therefore, it is desirable to utilize the fact that the ultrasonic wave can increase in linearity in proportion to the frequency and can reduce the beam size.

  Also, when the vibrators have the same frequency and different dimensions, the directivity becomes sharp when the vibrator dimensions are large, and the beam width is large at a short distance, but the ultrasonic beam is not so wide at a long distance. On the other hand, if the size of the vibrator is small, the directivity becomes dull and the beam width becomes small at a short distance.

  FIG. 11 shows the relationship between the beam size, the transmission frequency, and the distance of the ultrasonic displacement measuring apparatus, where the alternate long and short dash line is 40 kHz, the broken line is 100 kHz, and the solid line is 300 kHz. On the other hand, FIG. 12 shows the relationship between the energy density of the ultrasonic displacement measuring device, the transmission frequency, and the distance. The energy density related to the output intensity is attenuated as the transmission frequency is higher as shown in the figure. As in FIG. 11, the alternate long and short dash line is 40 kHz, the broken line is 100 kHz, and the solid line is 300 kHz.

  FIG. 13 shows the actual measurement values of the beam size when the transmission frequency is 40 kHz and 300 kHz. In the figure, if the transmission frequency is 300 kHz, it can be 20 mm corresponding to the measurement area. If the transmission frequency is 200 to 400 kHz, the beam size can be 15 to 25 mm. When the transmission frequency is 40 kHz and the beam size is about 60 to 80 mm as in the conventional ultrasonic displacement sensor, the resolution is about 1 mm. When the transmission frequency is 200 to 400 kHz, the resolution is improved to about 0.1 mm at an operating distance of 500 mm. be able to.

  FIG. 14 shows a recording of an actual received waveform when an ultrasonic burst is transmitted from the transmitter 20 in the conventional ultrasonic position measurement shown in FIG. 9 at about 40 kHz, with the horizontal axis representing time and the vertical axis Is the strength. As shown in FIG. 9, the envelope of the received waveform is deformed by decreasing or decreasing the strength of the transmitted waveform. It is difficult to accurately determine the propagation time by simply obtaining the reception time from the time exceeding the threshold from this waveform.

  FIG. 15 shows the result of spatial synthesis at one point separated by an operating distance, with one being transmitted as a continuous wave and the other being transmitted as an ultrasonic pulse burst wave. Compared with FIG. 14, the shape of the envelope is almost the same in consideration of the scale, but the ultrasonic element is driven at a high frequency of about 300 kHz. Nevertheless, a beat signal similar to that obtained by electrically synthesizing at a low frequency of 40 kHz and driving the ultrasonic element is obtained. If the phase of the beat signal is detected, the reception time can be determined more accurately. Further, it becomes easy to generate a composite waveform at the receiver, and the cost can be suppressed. Further, even when the position of a small target at high frequency is measured with high accuracy, distortion is reduced, and higher accuracy can be achieved with energy saving.

  In order to reduce the variation in measured values, repeat the number of measurements even in the cases shown in FIGS. 1 and 2 to exclude measurement errors, calculation of average values, or calculation of median values of measurement values and extruding values. The reliability can be improved. Further, the reliability can be further improved by using three or more transmitters.

  FIG. 16 is a diagram showing a layout of a transmitter and a receiver when three or more transmitters are used. Since it is only necessary that the ultrasonic beams overlap and be spatially synthesized at the receiver 1, a plurality of transmitters 2, 4, 4, 41, and 42 in the figure are arranged on the vertical plane separated from the receiver 1 by an operating distance. 1 is three-dimensionally arranged. That is, the transmitters 2, 3, 41, and 42 are arranged so as to form a cone with the receiver 1 as a vertex.

  The transmitter 3 transmits ultrasonic waves with a continuous wave of frequency f1, and the transmitters 2, 41, and 42 transmit ultrasonic waves with different frequencies as ultrasonic pulse burst waves of frequencies f2, f3, and f4, respectively. . The ultrasonic beams from the transmitters 2, 41, and 42 are transmitted to the receiver 1 along the cone bus, and the ultrasonic beams from the transmitter 3 are transmitted to the receiver 1 from the height direction of the cone.

  Since the ultrasonic beam has a width, the range in which the ultrasonic beam from the transmitters 2, 41, and 42 and the continuous wave from the transmitter 3 overlap can be measured within a range in which a beat signal can be synthesized. It becomes a certain measurable area. If the transmitters 2, 41, 42 are arranged so as to reduce the apex angle of the cone, the overlapping range extends in the height direction of the cone, that is, in the measurement axis direction, and the measurement range becomes large.

  When the transmitter 2, 41, 42 transmits an ultrasonic beam at the same time, a signal for each frequency of each transmitter can be obtained by performing a Fourier transform process on the signal received by the receiver 1, The arrival time of the ultrasonic beam for each transmitter can be obtained, and the distance for each transmitter can also be obtained.

  In actual measurement, it is not necessary to simultaneously transmit ultrasonic beams by the transmitters 2, 41, and 42, and a beat signal is first synthesized by the receiver 1 using the transmitter 3 and the transmitter 2. The distance between the receiver 1 and the transmitter 2 is measured by the synthesized beat signal. Next, the transmitter 3 and the transmitter 41 sequentially repeat the second measurement, and the transmitter 3 and the transmitter 42 repeat the third measurement. Thereby, the distance from the transmitters 2, 41, 42 to the receiver 1 is obtained. Furthermore, by measuring the three distances with the transmitters 2, 41 and 42, the distance from the transmitter 3 as the position of one point in space or the receiver 1 which is the base of the cone to the vertical plane can be accurately determined. It can be obtained.

  Further, by repeating the measurement, the reliability can be improved by calculating the average value or calculating the median value of the measurement values and excluding the protruding values. Also, place a reference gauge within the measurement range and measure it to obtain a calibration value. The transmitters 2, 41, and 42 may be three or more, and may be measured in combination with the transmitter 3 sequentially in the same manner.

1, 21 Receiver 2, 3, 20, 41, 42 Transmitter 2 Second transmitter, 3 First transmitter 4, 4-1, 4-2 CPU
5, 5-1, 5-2 Switch circuit 6, 6-1, 6-2 Ultrasonic element (transmission side)
7 Ultrasonic element (receiving side)
8 Filter 9 Analyzing device 10, 11 External switch 22 Transmission waveform 23 Reception waveform 24 Envelope 30 Frequency f1
31 frequency f2
32 Beat signal 33 Ultrasonic transmitter 34 Memory 35 Drive circuit 36 Ultrasonic element 37 Ultrasonic burst 50, 51, 52 Ultrasonic beam

Claims (10)

In the ultrasonic displacement measuring device for measuring the distance between the transmitter and the receiver by transmitting an ultrasonic beam from the transmitter to the receiver and obtaining a propagation time from transmission to reception,
A first transmitter for transmitting ultrasonic waves as a continuous wave at a first frequency;
A second transmitter for transmitting an ultrasonic burst wave continuous for a predetermined time at a second frequency different from the first frequency;
The receiver disposed at a position where the ultrasonic beams transmitted from the first transmitter and the second transmitter overlap; and
A reception time reference point is obtained from the phase of the signal obtained by the receiver, and the first transmitter or the second transmitter is determined based on the time when transmission is started by the second transmitter and the reception time reference point. And an analysis device for obtaining a distance between the receiver and the receiver,
An ultrasonic displacement measuring apparatus comprising:   The ultrasonic displacement measuring apparatus according to claim 1, wherein the first transmitter and the second transmitter include a switch circuit that drives an ultrasonic element with an on / off signal.   The first transmitter is disposed on the central axis of the receiver so as to face the receiver, and the second transmitter is disposed in a direction that forms a predetermined angle with the central axis. The ultrasonic displacement measuring device according to claim 1 or 2.   The second transmitter is disposed on the central axis of the receiver so as to face the receiver, and the first transmitter is disposed in a direction that forms a predetermined angle with the central axis. The ultrasonic displacement measuring device according to claim 1 or 2.   The ultrasonic displacement measuring device according to any one of claims 1 to 3, wherein a plurality of the second transmitters are arranged.   The ultrasonic displacement according to any one of claims 1 to 5, wherein the first transmitter and the second transmitter are arranged on a vertical plane separated from the receiver by a predetermined distance. Measuring device.   The said analysis apparatus samples the signal obtained by the said receiver with the trigger signal which determines the time which started transmission with the said 2nd transmitter, The any one of Claim 1 to 6 characterized by the above-mentioned. Ultrasonic displacement measuring device.   The first transmitter is disposed on a vertical plane perpendicular to the central axis that is separated from the receiver by a predetermined distance, and the second transmitter is at a predetermined angle with respect to the central axis on the vertical plane. The ultrasonic displacement measuring device according to claim 3, wherein the ultrasonic displacement measuring device is arranged in a direction in which   The ultrasonic displacement measuring apparatus according to any one of claims 1 to 8, wherein an ultrasonic beam size by the first transmitter is larger than an ultrasonic beam size by the second transmitter. An ultrasonic displacement measurement method for measuring a distance between the transmitter and the receiver by transmitting an ultrasonic beam from a transmitter to a receiver and obtaining a propagation time from transmission to reception,
The first transmitter transmits ultrasonic waves that are continuous waves of the first frequency, the second transmitter transmits ultrasonic burst waves that are continuous for a predetermined time at a second frequency different from the first frequency, and the first transmitter A reception time reference point is obtained from the phase of the signal obtained by the receiver arranged at a position where the ultrasonic beams transmitted from the first transmitter and the second transmitter overlap, and transmission is started by the second transmitter. An ultrasonic displacement measuring method, comprising: obtaining a distance between the first transmitter or the second transmitter and the receiver based on the received time and the reception time reference point.