JP2012117964A - Ultrasonic wave measurement system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic wave measurement system capable of highly accurately measuring a distance with low power consumption.SOLUTION: The system is constructed in such a manner that a transmission transducer transmits a plurality of continuous waves by changing its frequency, a reception transducer calculates the amplitude and phase of a reception wave relative to a transmission wave, discrete Fourier transformation is executed based on these values to acquire an impulse response waveform, and a distance from the transmission/reception to a reflective object is specified based on this waveform. High measurement accuracy is obtained by subtracting transducer phase characteristics from measurement data beforehand. The distance can be measured with extremely high accuracy by using the waveform itself rather than the envelope of a discrete Fourier transform waveform. Further, the movement of the object is specified from a difference between the discrete Fourier transform waveforms at two points different in time.

Description

  The present invention relates to a measurement system using ultrasonic waves, and more particularly to a system capable of measuring a distance with high accuracy even with low power consumption that can be introduced into a future sensor network or the like and dynamically measuring the movement of a moving object.

  Conventionally, a method called a pulse echo method has been used for distance measurement using ultrasonic waves. The pulse echo method cuts out ultrasonic waves of a certain frequency (for example, 40 kHz in the case of air use) into a very narrow pulse shape, measures the time it takes to transmit it and return from the object, The distance is calculated. This technique is often used for backside sonar of passenger cars (see Non-Patent Document 1).

JP 2009-276118 A

Junsuke Kuroki, “Electronic suspension of an automobile using ultrasonic road sonar,” October 1998, Ultrasonic TECHNO (Nikkan Kogyo Publishing), paragraphs 62-66.

  There is a new concept called sensor network that has begun to attract attention recently in the medical and nursing care environment as well as in the home or office. Assuming that a safe, healthy and comfortable living environment will be realized, it is also considered to introduce a monitor function to understand the dynamic state of the resident along with various sensors in the sensor nodes of the sensor network. It is being advanced. The most common device for such a monitor is a CCD camera, but the sensor node needs characteristics with very low power consumption, for example, a single battery is required to operate for several years. Therefore, it is almost impossible to introduce a CCD camera into the sensor node.

  In a conventional pulse echo method, a sensor using ultrasonic waves transmits pulsed ultrasonic waves and monitors reflected waves from an object. By combining a plurality of transmitting transducers and a plurality of receiving transducers, some information about the position of the reflecting object can be obtained. However, in the conventional pulse echo method, when introduced into a general house or the like, it is necessary to narrow the pulse width in order to increase the distance resolution with respect to the reflecting object. When the pulse width is narrowed, the transmission power decreases. Therefore, the transmission power is kept constant by increasing the amplitude of the pulse. For this reason, the pulse voltage of the final transmission stage for driving the transmission transducer reaches several to several tens of volts (V). Such a circuit is difficult to introduce into a low power consumption device that needs to operate for several years with a single battery, such as a sensor node of a sensor network. In general, in the ultrasonic sensor of the pulse echo method, since all information is extracted from the envelope of the received pulse on the receiving side, many operations such as amplification of the received ultrasonic wave, envelope detection, and differentiation processing are required. There is a drawback that the amount of processing at the node is too large to be adopted in the sensor network. In addition, the information obtained is related to the envelope of the pulse, and when many reflective objects are present in close proximity, the envelopes of multiple reflected waves are superimposed, so obtaining the motion of the object from the envelope information It is extremely difficult. Considering these points, it is considered impossible to apply the pulse echo method to the sensor network.

As described above, since the conventional ultrasonic pulse echo method is difficult to apply to the sensor node, the present inventor has proposed a method obtained by further developing the previously applied method (Patent Document 1). reference). This method does not use ultrasonic pulses as in the past, but by using ultrasonic continuous waves (ie, CW waves: Continuous Wave), the increase in power consumption due to handling large amplitude pulses Don't make it happen. That is, the frequency from the transmitting transducer, the frequency components f (1) that n divides the period from f ₁ to _{f 2, f (2),} ..., and transmits the CW wave with f (n + 1) Similarly, the receiving transducer receives a CW wave having these frequency components. The relative amplitude and phase of the received CW wave with respect to the transmitted CW wave are stored as data for each frequency component. The impulse response waveform between the transmission transducer and the reception transducer is derived by performing discrete Fourier transform using these data. Since the time delay between transmission and reception is known from the impulse response waveform, distance information is obtained by multiplying the time delay by the ultrasonic velocity.

  In this method, it is possible to measure the distance to the reflective object with high power and low power consumption, but it is desirable to increase the distance resolution.

  Therefore, a main object of the present invention is to provide an ultrasonic measurement system that can measure with a higher distance resolution with low power consumption.

According to the present invention,
It is composed of a plurality of waves with different transmission times, and each wave is a continuous wave whose frequency does not change with time, and the frequency of each wave is excited by different excitation signals at a certain frequency interval to generate ultrasonic waves. A transmission unit comprising a transmission transducer for transmitting to an object;
A receiving unit comprising a receiving transducer for receiving ultrasonic waves reflected from the object;
Using the relative amplitude and phase data of the excitation signal and the output signal from the receiving transducer, and performing arithmetic processing determined by the frequency interval on them, the distance between the transmitting transducer and the object and the object And a calculation unit that calculates a sum of the distances between the receiving transducers and the receiving transducers, wherein the calculation processing is performed by the excitation signal and the receiving transducers when the distance between the transmitting and receiving transducers is substantially zero. Using the fixed relative amplitude and phase data of the output signal, at least one of the excitation signal and the relative amplitude and phase data of the output signal from the receiving transducer when the ultrasonic wave is transmitted to the object The processing unit including a process of correcting
An ultrasonic measurement system comprising: is provided.

  Preferably, the arithmetic processing determined by the frequency interval is a discrete Fourier transform, and each frequency determined by the frequency interval corresponds to each discrete frequency of the discrete Fourier transform.

  Preferably, the calculation process includes a process of correcting by subtracting only a fixed relative phase component.

  Preferably, the calculation process includes a step of correcting both the relative amplitude and phase data of the excitation signal and the output signal from the receiving transducer when the ultrasonic wave is transmitted to the object. Yes.

  Preferably, the sum of the distances is measured in the vicinity of the peak value of the envelope of the waveform obtained by performing the discrete Fourier transform on the basis of the zero point of the waveform obtained by performing the discrete Fourier transform.

  Preferably, the movement of the object is measured from a difference between results obtained by performing the arithmetic processing at least twice.

  Preferably, the former and the latter are two times before and after the arithmetic processing of at least two times, and a value representing the relative amplitude and phase data of the former excitation signal and the output signal from the receiving transducer in complex numbers From the result obtained by subtracting the value representing the relative amplitude and phase data of the latter excitation signal and the output signal from the receiving transducer in a complex number, a value obtained by performing a discrete Fourier transform determined by the frequency interval Measure movement based on

  Preferably, when the receiving transducer moves together with the object, the frequency interval of the discrete Fourier transform is larger than the value obtained by dividing the distance between the transmitting and receiving transducers by the speed of sound, that is, the reciprocal of time, and twice that. Smaller than.

  Preferably, the transmission unit and the reception unit are driven by a battery.

  Preferably, the transmitting transducer and the receiving transducer are different transducers.

  The transmitting transducer and the receiving transducer may be the same transducer.

  Preferably, the receiving unit and the processing unit are arranged at different positions.

  Preferably, the receiving unit and the processing unit move together.

  ADVANTAGE OF THE INVENTION According to this invention, the ultrasonic measurement system which can be measured with low power consumption and higher distance resolution is provided.

Sensor network configuration Illustration of the principle of the measurement method according to the present invention Illustration of the principle of the measurement method according to the present invention Illustration of the principle of the measurement method according to the present invention An example of a distance measurement result according to the present invention Illustration of the principle of the measurement method according to the present invention Example of measurement results of transducer transfer characteristics Illustration of the principle of high-precision measurement method according to the present invention Illustration of measurement by conventional method Example results according to the present invention when there are two reflective objects Illustration of the principle of the measurement method according to the present invention Example of measurement results by conventional method Examples of measurement results according to the present invention Examples of measurement results according to the present invention Examples of measurement results according to the present invention Application example of the measurement method according to the present invention Illustration of the principle of the measurement method according to the present invention

As a result of various studies by the present inventor, it has been found that correction of the frequency characteristics of the transmission / reception transducer is indispensable in order to obtain high distance resolution by a method using a continuous wave of ultrasonic waves. The correction of the frequency characteristic, the frequency components f the frequency is divided into n between from f ₁ to _{f 2 (1), f (} 2), ..., with respect to CW wave with f (n + 1) The distance resolution with very high accuracy can be realized by directly performing the relative amplitude and phase of the received CW wave to the transmitted CW wave. In addition to the high-accuracy impulse response obtained in this way, it is possible to distinguish moving objects from stationary objects by taking the difference between impulse response waveforms over multiple times, and to accurately move the moving objects. Can be detected. The important point here is different from the conventional method in that, unlike the pulse echo method, the difference does not take the envelope, but is the difference in the impulse response waveform itself. These detection methods respond to the demands of sensors and networks.

  In a preferred embodiment of the present invention, a pulse having a large amplitude as described above is not used. Further, in the case of a sensor network, the receiving transducer does not process the received CW signal, but only sends the raw data of relative amplitude and relative phase to the center node via the network. Based on the data sent from each sensor node, the center node performs batch signal processing. That is, by performing discrete Fourier transform or the like, the distance of the measurement object with respect to each node can be obtained from the impulse response. Moreover, a stationary object map, a moving object map, etc. can be formed based on such information over a plurality of times. In general, the center node is operated by a separate power source unlike the sensor node, and the power consumed by various processes does not become a problem. Further, each sensor node transmits or receives a CW ultrasonic wave having a small amplitude, and only sends data related to the amplitude and phase of the received signal to the center node, and can operate with extremely low power consumption.

  As described above, according to a preferred embodiment of the present invention, in a future sensor network or the like, a distance measuring sensor or an animal body using ultrasonic waves to a sensor node that requires particularly low power consumption characteristics. It becomes possible to introduce a monitor sensor. For example, it can be applied to collecting dynamic information of elderly residents, monitoring behaviors of people in public facilities such as hospitals, and crime prevention.

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

  In sensor networks, standardized 2.4 GHz band ZigBee (registered trademark) is often used as a wireless medium. One form of sensor network is to arrange a large number of sensor nodes in the living environment, mainly sensing environmental parameters related to life such as temperature, humidity, and brightness, and comforting based on such data Control to realize a comfortable living environment. As one of the functions of such a sensor network, it is required to incorporate functions such as a patient behavior monitor in a public facility such as a hospital, a remote monitor of a resident in an elderly house, and a crime prevention function.

  The proposed ultrasonic high-precision distance measurement and motion detection system meets the above requirements by including an ultrasonic transmission / reception transducer as a part of the sensor node as shown in FIG. The distance from each sensor node to the object is measured from the impulse response, and a two-dimensional or three-dimensional object map is created based on these data. In addition, it is possible to distinguish moving objects and stationary objects by taking differences between impulse responses over a plurality of times, and to infer changes in human movement and environment from temporal changes in the map. It also guarantees the most important low power consumption required by the sensor node. The measurement data is collected to the center node via a wireless medium network such as ZigBee (registered trademark). At the center node, necessary signal processing and the like are performed collectively. This achieves both low power consumption and aggregation of necessary data to the center node. It is possible to construct a sensor network system capable of various controls based on data at every place.

(First embodiment)
FIG. 1 is a configuration showing a specific first embodiment of ultrasonic measurement according to the present invention. In the sensor network, in addition to information on the temperature, humidity, illuminance, etc. in the house, a large number of sensor nodes installed in the house, etc. will collect dynamic information on the residents in the future. That is, many sensor nodes are also equipped with transducers that transmit and receive ultrasonic waves, sequentially transmit ultrasonic waves from the transmitting transducers of the nodes, and receive reflected ultrasonic waves from the object by the receiving transducers of its own node or other nodes. Is. If the distance between the object and the transmitting transducer of the transmitting node and the receiving transducer of the receiving node can be accurately measured, a two-dimensional or three-dimensional map can be formed by associating these values across multiple nodes. I can do it. Dynamic information such as human movements can also be obtained from changes in the map over time. Such a measurement system is highly expected for future monitoring of elderly homes and hospitals, or for applications such as crime prevention. In particular, the Sense Network is a new concept that has been proposed with the advance of mobile communications, and will become widespread in the future. Introducing an ultrasonic position measurement system as part of such a network is also a very natural requirement. In general, ZigBee (registered trademark) using a frequency in the 2.4 GHz band is the most promising wireless medium for sensor networks. Therefore, as shown in FIG. 1, the data measured at each sensor node can be aggregated to the center node via ZigBee (registered trademark), and signal processing or the like can be performed collectively. As a matter of course, Bluetooth (registered trademark), wireless LAN, WiMAX, cellular phone, and the like can also be used as a wireless medium.

The basics of the present invention will be described in the case where there is one reflective object shown in FIG. In the measurement method of the present invention, the transmitted wave is not an ultrasonic pulse or a code-spread ultrasonic wave but a continuous wave having a constant frequency. As a transmission frequency, as shown in FIG. 2B, a frequency band between f ₁ and f ₂ is considered. f ₂ −f ₁ is divided into n, and the frequency f (i) = f ₁ + (f ₂ −f ₁ ) / n × (i−1), i = 1 from the lowest frequency in the band to n + 1 , ..., define n + 1. FIG. 3 (a) schematically shows an actual ultrasonic waveform in the case of f (1) = f ₁ and f (n + 1) = f ₂ . As compared to the transmitted ultrasound of f (1), ..., f (n + 1) frequency, the received ultrasound has a smaller amplitude due to attenuation due to propagation and reflection, as schematically shown in Fig. 3 (b). Become. The phase increases in proportion to the distance between the transmitting / receiving transducer and the object, but repeats with 2π as the period. Therefore, the phase delay of the received wave with respect to the transmitted wave is a value between 0 and 2π. When the above relationship is shown in the figure, the frequency and phase of the received wave are represented in FIG. 2 (c). Here, as shown in FIG. 2B, the phase of the transmission wave is assumed to be uniform with respect to the frequency because it is a reference phase. FIG. 2 (c) is actually expressed by taking the horizontal axis as a discrete frequency obtained by dividing the frequency band of f ₂ −f ₁ by n, but in general, since n is a sufficiently large value, FIG. ), The horizontal axis is treated as an approximately continuous frequency. From FIG. 2 (c), it can be seen that the amplitude of the received wave is smaller than that of the transmitted wave of FIG. Here, the relative value of each amplitude and phase of the received wave in FIG. 2 (c) with respect to the transmitted wave in FIG. 2 (b) is normalized in amplitude, but the phase is interpreted as FIG. 2 (c) itself. I know it ’s good.

The processing using the data of FIG. 2 (c) will be described. The data of FIG. 2 (c) is assumed to be a relative value normalized by each value of the transmission wave of FIG. 2 (b). Fourier transform is performed using the relative amplitude and relative phase corresponding to the n + 1 frequencies in FIG. Strictly speaking, the Fourier transform is a transform for a continuous function, and therefore, when the frequency is n + 1, as shown in FIG. However, it is well known mathematically that an almost accurate conversion value can be obtained by setting the value of n + 1 to a sufficiently large value. Here, further consider the case where f ₁ is zero and f ₂ is infinite. In this case, the Fourier transform of FIG. 2 (c) becomes an approximate delta function as shown in FIG. 4 (a). This can also be seen from the fact that a signal distributed with uniform amplitude on all frequency axes is a delta function as a function on the time axis that is related to the Fourier transform. In this case, the phase of FIG. 2 (c) corresponds to the shift amount on the time axis of the approximate delta function of FIG. 4 (a), that is, the time delay (l ₁ + l ₁ ′) / v. The same can be derived from FIG. 2 (c). If the phase in FIG. 2 (c) is Φ, the group delay is given by τ _g = −δΦ / δω (“δΦ / δω” means a partial differentiation with respect to Φ by ω). In the ultrasonic wave propagation as discussed here, the propagation speed is not dispersive depending on the frequency, and the group velocity and the phase velocity are equal. Therefore, the group delay τ _g is the wave delay, that is, the time delay of FIG. Equivalent to (l ₁ + l ₁ ') / v. Therefore, if the phase characteristic of FIG. 2 (c) is given, the time delay of FIG. 4 (a) is also uniquely determined. In other words, in Fig. 2 (a), assuming that the transmitting transducer is input and the receiving transducer is output, Fig. 2 (c) is the amplitude and phase characteristics of the transfer function between input and output, and Fig. 4 (a) is the impulse response. I can do it. When the time delay of the impulse response is known, the distance to the reflecting object is derived by multiplying the value by the speed v.

Next, let us consider a case where f ₁ to f ₂ in FIG. 2 (c) are sufficiently large but finite. In this case, as shown in FIG. 4B, the Fourier response subjected to Fourier transform spreads slightly on the time axis and has a function form close to a sinc function (hence sinx / x). However, the time delay to the maximum value of the approximate sinc function (the center of the main lobe) is given by (l ₁ + l ₁ ') / v, which is the same as the approximate delta function in Fig. 4 (a). . That is, if f ₂ −f ₁ is finite but sufficiently large, the time delay (l ₁ + l ₁ ′) / v can be determined with high accuracy. Further, by multiplying the value by the velocity v, the distance to the reflecting object can be measured with high distance resolution.

  The above is the basic principle of the present invention. That is, as shown in FIG. 3 (a), for each transmitted wave, a continuous wave whose frequency does not change with time is used, and relative values of amplitude and phase between transmission and reception for these continuous waves are obtained, and those waves are obtained. Fourier transform is performed using the above data. Thus, an impulse response between transmission and reception is obtained, and the distance to the reflecting object is measured from the time delay. The important point here is not to transmit a pulse with a short time width as in the conventional pulse echo method, but to transmit a wave whose phase reverses with time as in the code diffusion method. However, it is a point that transmits a continuous wave having a constant frequency with respect to time. Therefore, the power consumption of the transmission side (transmission unit) including the transmission transducer can be extremely reduced. In order to transmit such a wave from the transmission transducer, the transmission transducer is composed of a plurality of waves having different transmission times, and each wave is a continuous wave whose frequency does not change with time. Different excitation signals are applied at regular frequency intervals. On the receiving side, a relative value between the received wave and the transmitted wave, that is, a relative amplitude and a relative phase are obtained. When each sensor node is connected via a sensor network, etc., the reference amplitude and phase of the transmitted wave can be transmitted to other sensor nodes related to the transmission of ultrasonic waves, such as ZigBee (registered trademark) The information is sent by wireless means (in the case of a wired network, it may be sent by wire). Each sensor node obtains the relative amplitude and relative phase of the received wave and the transmitted wave, and sends the information to the center node via the sensor network or the like. For this reason, the power consumption of the receiving side (receiving unit) including the receiving transducer can be extremely reduced. Thus, since the power consumption of each sensor node is small, each sensor node can be driven by a battery. Since the center node is generally operated by a separate power source such as a commercial power source, power consumption does not become a problem. Based on the relative amplitude and relative phase from each sensor node, Fourier transform is performed collectively. As a result, an impulse response between the sensor and the node is obtained. That is, the distance between each sensor node and the reflecting object is calculated. Note that arithmetic processing such as Fourier transformation at the center node, calculation of distance, and the like are performed by a computer functioning as a processing unit, and arithmetic processing of each embodiment described below is also performed by this computer.

  The above is the basic part of the present invention, which is further developed in the present application.

Fig. 5 (a) shows the case where l ₁ + l ₁ '= 150cm in Fig. 2 (a) and actually measured the distance by the above method using a transducer with a center frequency of about 40kHz and BW = 5%. is there. The measurement distance was 160.86 cm, resulting in an error of about 11 cm. The cause is considered as follows. The ultrasonic transducer emits ultrasonic waves into the air using a mechanical piezoelectric vibrator such as ceramic. The vibrator has inertia, which causes a phase difference in the ultrasonic wave radiated with respect to the electrical excitation signal. This will be described in detail with reference to block diagrams and transfer functions often used in control theory. The measurement system used in the experiment of FIG. 5 (a) is represented by a block diagram in FIG. 6 (a). I (f) is a signal (input signal) for exciting the transmission transducer having the frequency f. O (f) is an output signal from the receiving transducer of frequency f. Between the I (f) and O (f), transmission transducer transfer function H ₁ (f), the receiving transducer space propagation part of the transfer function H ₂ (f), a transfer function H ₃ (f) There is. The measurement result in Fig. 5 (a) is the Fourier transform from the transfer function H ₁ (f), H ₂ (f), H ₃ (f) between I (f) and O (f) in Fig. 6 (a). This corresponds to the impulse response waveform obtained by. Therefore, the characteristics (transfer function) H ₁ (f) · H ₃ (f) of the transmission / reception transducer are included, and a measurement error occurs due to the influence of this characteristic.

7 (a) and 7 (b) show the relative amplitude characteristics of the excitation signal (input signal) and the output signal from the receiving transducer when the distance between the transmitting and receiving transducers is substantially zero ((a) ) And phase characteristics ((b) diagram) are shown. As is well known, the amplitude characteristics were obtained with a center frequency of about 40 kHz and BW = 5%. The phase characteristic is a characteristic in which the phase is substantially zero in the resonance state of the center frequency, the phase is advanced at a low frequency, and the phase is delayed at a high frequency. The results of FIGS. 7 (a) and (b) are the results of the measurement system represented by the block diagram of FIG. 6 (b). The transfer function is given by H ₁ (f) · H ₃ (f). That is, when the transfer function of FIG. 6 (a) is divided by the transfer function of FIG. 6 (b), a transfer function H ₂ (f) corresponding to only spatial propagation is obtained. From the Fourier transform of H ₂ (f), an impulse response waveform with only spatial propagation is obtained. This is equivalent to correcting or removing the influence of the transmission / reception transducer equivalently, whereby the distance between the transmission / reception transducers can be accurately obtained.

Here, there are two correction methods. The amplitude of H ₂ (f) is iH ₁ (f) ・ H ₂ (f) ・ H ₃ (f) i / iH ₁ (f) ・ H ₃ ( f) is given by i. The phase is a value obtained by subtracting the phase characteristic between the transmission / reception signals in FIG. 6 (b) from the phase characteristic between the transmission / reception signals in FIG. 6 (a). In the first correction method, the amplitude is iH ₁ (f) ・ H ₂ (f) ・ H ₃ (f) i / iH ₁ (f) ・ H ₃ (f) i = iH ₁ (f) ・ H ₂ ( Put f) ・ H ₃ (f) i. That is, the amplitude is a method of correcting only the phase using the value of FIG. 6 (a). The second correction method uses iH ₁ (f), H ₂ (f), H ₃ (f) i / iH ₁ (f), H ₃ (f) i, and both amplitude and phase are used. This is a correction method. When both methods are compared, when the bandwidth of f ₂ −f ₁ is widened to some extent, the first correction method is accurate. Experiments have shown that the second correction method is excellent in accuracy when f ₂ −f ₁ is a narrow bandwidth.

FIG. 5 (b) shows the result of discrete Fourier transform using data obtained by correcting the phase characteristics of the transducer by subtracting the phase characteristics of the transducer of FIG. 7 (b) from the actually measured data. The measured distance was l ₁ + l ₁ '= 150.66 cm, which was extremely accurate. Moreover, the impulse response waveform has a shape very close to the sinc function, and it can be seen that very ideal measurement is possible. From the above, the feature of this embodiment is that, first, as shown in FIG. 2, the relative amplitude and the relative phase between the transmitting and receiving ultrasonic transducers are measured, and the amplitude or phase of only the transmitting and receiving transducers obtained from FIG. By subtracting or correcting the characteristic, an ultrasonic transfer function that is purely related only to air propagation is obtained. Next, an impulse response is obtained by performing a discrete Fourier transform on the transfer function. Furthermore, the equivalent distance can be measured very accurately by multiplying the time delay of the impulse response by the sound velocity v. Further, such a method for improving the distance measurement accuracy by correcting the frequency characteristics of the transducer cannot be applied to the conventional pulse echo method, and is effective only with a series of measurement methods proposed by the present invention.

(Second Embodiment)
In relation to the first embodiment, another embodiment of the present invention will be described. In FIG. 5 (b), the distance was obtained using the peak value of the impulse response waveform (envelope) as the information source for distance measurement. However, the impulse response waveform is a waveform whose time or distance is on the horizontal axis, and corresponds to the transfer function in a one-to-one relationship with the discrete Fourier transform. Therefore, for determining the distance, it is possible to use the waveform itself with higher accuracy than the envelope information as an information source. For example, FIG. 8 (a) shows an example of an impulse response waveform when the distance between the transducers is 2.5 m. The peak value of the envelope can be identified from the waveform of FIG. 8 (a), and the distance can be obtained based on that point. However, as can be seen from the figure, the peak value itself is very vague, and high distance accuracy cannot be expected. FIG. 8 (b) shows an enlarged view of the vicinity of the peak value of the envelope in FIG. 8 (a). In the vicinity of the peak value of the envelope of the impulse response waveform in FIG. 8 (b), attention is paid to the point where the waveform itself crosses the horizontal axis, that is, zero, and the distance is always obtained using this point as a measurement point. Thereby, the point of interest can be specified with an extremely high accuracy compared to the center point specified from the peak value of the envelope, and the distance measurement accuracy is also greatly improved. On the other hand, in the conventional pulse echo method, the pulsed ultrasonic wave is a wave propagating along the horizontal axis when time is expressed on the horizontal axis, and its instantaneous waveform has no meaning, and only the envelope is the distance. Give information. Therefore, unlike the method of the present invention, the distance measurement accuracy inevitably yields only a low result.

(Third embodiment)
Another embodiment of the present invention will be described with reference to FIG. Assuming that sensor nodes (1) and (2) are on the ceiling, ultrasonic waves are transmitted from sensor node (1) and received by sensor node (2). There are reflective objects from (1) to (5), and the sum of the distance from the sensor node (1) to the reflective object and the distance from the sensor node (2) to the reflective object is 5.5 for the reflective object (1). m, reflective object (2) is 5.35 m, reflective object (3) is 5.2 m, reflective object (4) is 5.05 m, reflective object (5) is 4.9 m (each distance is also entered in Figure 11) ) Reflective object (1) is a small object, the reflection coefficient is 1/2 compared to other reflective objects, and the initial value is from the point (1) to the point (1) '(corresponding distance is , 4.8m).

In order to consider the state in which the conventional pulse echo method is applied to the model in FIG. 11, first consider a model in which there are two reflecting objects in FIG. 9 (a). As shown in FIG. 9 (b), the received pulse is observed with a time delay of (l ₁ + l ₁ ') / v and (l ₂ + l ₂ ') / v from the transmitted pulse. On the receiver side, since envelope detection is performed, the actual receiver output has the waveform shown in FIG. 9 (c). That is, only two pulses are observed with a time delay of (l ₁ + l ₁ ′) / v and (l ₂ + l ₂ ′) / v. Next, consider the case of applying this method. The waveform of FIG. 10 is obtained as a result of the discrete Fourier transform. In other words, it is an impulse response waveform with the horizontal axis as time or equivalent distance, which corresponds to the transfer function between the transmitting and receiving transducers, and does not change with time unlike the received waveform of the pulse echo method.

  When there are a plurality of reflecting objects as shown in FIG. 11, the conventional pulse echo method can obtain an envelope detection waveform as shown in FIG. 12 (a) as an output. Here, the numerical value in each figure represents the sum of the distances from each node to the reflecting object (1). It can be seen that the envelope detection waveform slightly changes as the reflecting object (1) moves. The difference in change is shown in FIG. 12 (b). The upper arrow in each figure indicates that the figure is a waveform difference corresponding to the distance given by the left and right numerical values. From Fig. 12 (b), even the slight movement of the reflecting object (1) (about 2 to 3 mm in distance) causes fluctuations in the difference in the envelope detection waveform, including the sign of +/-, and quantitative analysis of the movement. You can see that no information is available.

  The results when the method of the present invention is applied to the same model in FIG. 11 are shown in FIGS. FIG. 13 (a) corresponds to FIG. 12 (a), and FIG. 13 (b) corresponds to FIG. 12 (b). From FIG. 13 (a), it can be seen that the impulse response waveform between the sensor nodes (1) and (2) is represented by the sum of the impulse responses for the respective reflecting objects. FIG.13 (b) represents the movement of the reflective object (1), and the upper arrow in each figure represents the difference in waveform corresponding to the distance given by the left and right numerical values. . In the method of the present invention, it can be seen that the movement distance is accurately expressed even for a slight movement (distance is about 1 mm). As a practical condition in FIGS. 14 (a), 14 (b) and 15 (a), 15 (b), the reflective object (1) moved from 5.5 m to 4.8 m, and the distance information was acquired with a 10 cm dent. Indicates the situation. Each figure (a) shows an impulse response waveform according to the present technique, and each figure (b) shows the difference between them and the movement of the reflecting object (1). From these figures, it can be seen that only the movement of the moving object (1) can be expressed with respect to the stationary objects (2), (3), (4), and (5).

  This characteristic is very important when, for example, an ultrasonic wave transmission / reception function is actually introduced to a sensor node of a sensor network to collect resident dynamic information. FIG. 16 schematically shows an actual embodiment of the present invention. For example, a plurality of sensor nodes having an ultrasonic transmission / reception function are arranged on the ceiling. There are many reflective objects in the room, and the impulse response waveform between the two sensor nodes is given by superimposing the impulse response waveforms from these multiple reflective objects, so the waveform becomes quite complex. In this method, information about moving objects can be extracted accurately by taking the difference between impulse response waveforms with different measurement times. It is a very useful technique for crime prevention purposes and for collecting dynamic information at residents or hospitals.

(Fourth embodiment)
In the third embodiment, it is necessary to obtain a difference between impulse response waveforms having different measurement times. The impulse response waveform can be obtained by performing discrete Fourier transform on the transmitted ultrasonic waves with frequencies f (1), ..., f (n + 1) using the relative amplitude and relative phase of the received ultrasonic waves. . Therefore, the same result can be obtained for derivation of the difference in the impulse response waveform even if the order of the operation for performing the discrete Fourier transform and the operation for taking the difference are interchanged. Rather, it is advantageous in terms of time and processor load to perform the operation of taking the difference first and then perform the discrete Fourier transform, since the number of operations of the discrete Fourier transform is halved.

  The actual calculation operation is performed as follows. The measurement data of the relative amplitude and the relative phase of the reception ultrasonic wave with respect to the series of transmission ultrasonic waves at least two times before and after are set as the former data and the latter data. Each data is represented by a complex number using the amplitude and phase of the former data and the latter data. Next, a value obtained by subtracting these data is obtained. By using this subtracted value and performing a discrete Fourier transform determined by the frequency interval, the same result as the difference in impulse responses with different measurement times can be obtained.

(Fifth embodiment)
Another embodiment of the present invention will be described with reference to FIG. As described in the first to fourth embodiments, the present invention obtains an impulse response waveform between the transmitting and receiving transducers, and performs high-precision distance measurement, motion identification, and the like based on the data. . A discrete Fourier transform is used to derive the impulse response waveform. This embodiment will be described with a simple structure in which the transmission / reception transducers in FIG. 17 (a) face each other. If the distance between the transmitting and receiving transducers is l ₁ and the sound velocity is v, the delay time between the transmitting and receiving transducers is t ₁ = l ₁ / v. Discrete Fourier transform is performed using the relative amplitude and relative phase between transmission and reception corresponding to the n + 1 frequencies described in the above embodiment. Here, when the frequency interval Df of the discrete Fourier transform is Df <1 / t ₁ as shown in FIG. 17 (b), the impulse response has a sinc function centered at t ₁ = l ₁ / v. A typical waveform is obtained. As shown in FIG. 17C, when Df> 1 / t ₁ , a sinc function-like waveform centered at t ₁ −1 / Df is obtained. In this case, if another reflecting object exists in the vicinity of t ₁ -1 / Df in the actual model, the reflected waveform from another reflecting object and the waveform in FIG. .

Consider the case where the transmitting transducer is fixed and the receiving transducer accurately measures the distance to the moving object, such as in an industrial machine moving with the moving object. In many cases, there is no reflecting object between the transmitting transducer and the moving object. In such an application, Df> 1 / t ₁ can be set as shown in FIG. In this case, an accurate time t ₁ can be obtained by adding the inverse of the frequency interval Df of the discrete Fourier transform to the pseudo time t ₁ -1 / Df obtained from the impulse response waveform. Since this method can set Df to some extent, n + 1 corresponding to the number of measurements can be reduced as a result. This is very effective for shortening the measurement time. However, as can be seen from FIG. 17 (c), t ₁ −1 / Df cannot overlap 1 / Df. That is, t ₁ −1 / Df <1 / Df needs to be satisfied. From this, it can be seen that the effect is large when Df is used with 2 / t ₁ >Df> 1 / t ₁ . In the case of an industrial machine in which the receiving transducer moves with a moving object, a receiving unit including the receiving transducer and a computer functioning as a processing unit that performs processing such as discrete Fourier transform are incorporated in the moving object. The processing unit and the processing unit often move together.

  While various typical embodiments of the present invention have been described above, the present invention is not limited to these embodiments. Accordingly, the scope of the invention is limited only by the following claims.

DESCRIPTION OF SYMBOLS 1 ... Sensor node of sensor network 2 ... Center node of sensor network 3 ... Data transmission path by ZigBee (registered trademark) 4 ... Ultrasonic transmission / reception path 5 ... Reflective object 6 ... Transmitting transducer 7 ... Receiving transducer

Claims (13)

It is composed of a plurality of waves with different transmission times, and each wave is a continuous wave whose frequency does not change with time, and the frequency of each wave is excited by different excitation signals at a certain frequency interval to generate ultrasonic waves. A transmission unit comprising a transmission transducer for transmitting to an object;
A receiving unit comprising a receiving transducer for receiving ultrasonic waves reflected from the object;
Using the relative amplitude and phase data of the excitation signal and the output signal from the receiving transducer, and performing arithmetic processing determined by the frequency interval on them, the distance between the transmitting transducer and the object and the object And a calculation unit that calculates a sum of the distances between the receiving transducers and the receiving transducers, wherein the calculation processing is performed by the excitation signal and the receiving transducers when the distance between the transmitting and receiving transducers is substantially zero. Using the fixed relative amplitude and phase data of the output signal, at least one of the excitation signal and the relative amplitude and phase data of the output signal from the receiving transducer when the ultrasonic wave is transmitted to the object The processing unit including a process of correcting
An ultrasonic measurement system comprising:   2. The ultrasonic measurement system according to claim 1, wherein the arithmetic processing determined by the frequency interval is a discrete Fourier transform, and each frequency determined by the frequency interval corresponds to each discrete frequency of the discrete Fourier transform.   The ultrasonic measurement system according to claim 2, wherein the arithmetic processing includes a process of correcting by subtracting only a fixed relative phase component.   The arithmetic processing includes a step of correcting both the relative amplitude and phase data of the excitation signal and the output signal from the receiving transducer when the ultrasonic wave is transmitted to the object. The ultrasonic measurement system according to claim 2.   3. The sum of the distances is measured in the vicinity of a peak value of an envelope of a waveform obtained by performing a discrete Fourier transform on the basis of a zero point of the waveform obtained by performing a discrete Fourier transform. The ultrasonic measurement system of any one of -4.   The ultrasonic measurement system according to claim 2, wherein the movement of the object is measured from a difference between results obtained by performing the arithmetic processing at least twice.   From the value representing the relative amplitude and phase data of the former excitation signal and the output signal from the receiving transducer in complex numbers, the former and the latter two times before and after the arithmetic processing of at least two times, the latter Using the result obtained by subtracting the value representing the relative amplitude and phase data of the excitation signal and the output signal from the receiving transducer in a complex number, the movement is performed based on the value subjected to the discrete Fourier transform determined by the frequency interval. The ultrasonic measurement system according to claim 6, wherein measurement is performed.   The receiving transducer moves with the object, and a frequency interval of the discrete Fourier transform is larger than a value obtained by dividing a distance between the transmitting and receiving transducers by a sound speed, that is, a reciprocal of time and smaller than twice. Item 6. The ultrasonic measurement system according to any one of Items 2 to 5.   The ultrasonic measurement system according to claim 1, wherein the transmission unit and the reception unit are driven by a battery.   The ultrasonic measurement system according to claim 1, wherein the transmission transducer and the reception transducer are different transducers.   The ultrasonic measurement system according to claim 1, wherein the transmission transducer and the reception transducer are the same transducer.   The ultrasonic measurement system according to claim 1, wherein the receiving unit and the processing unit are arranged at different positions.   The ultrasonic measurement system according to claim 1, wherein the receiving unit and the processing unit move together.