JP2009156694A - Measurement method and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology capable of heightening accuracy of ultrasonic sensor measurement. <P>SOLUTION: The first acquisition part 52 acquires as a reference signal 206, a pulsed chirp signal to be transmitted from a transmission sensor 14. The second acquisition part 54 acquires as a reception signal 204, the pulsed chirp signal received by a reception sensor 18 via a measuring object 16 installed between the transmission sensor 14 and the reception sensor 18 after being transmitted from the transmission sensor 14. A measuring part 56 measures a distance of the measuring object 16 from the transmission sensor 14 to the reception sensor 18 based on a difference between a peak position of the pulsed chirp signal acquired by the first acquisition part 52 and a peak position of the pulsed chirp signal acquired by the second acquisition part 54. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a measurement technique, and more particularly to a measurement method and apparatus for measuring a distance of a measurement object.

  In recent years, ultrasonic sensors have been used in various fields represented by industrial products that have been automated. For example, the detection of transparent objects such as glass, monitoring and diagnosis equipment such as pumps, ultrasonic distance meters, pre-detection of damage to bite drills by detecting AE (Acoustic Emission) energy, and its applications are active, The range is also wide (for example, refer nonpatent literatures 1 and 2). As described above, the ultrasonic sensor measurement technology in a broad sense including AE is expected to be further developed and further expanded in application range. In particular, thickness measurement for structures and the like is an extremely important item both during manufacturing and during maintenance inspection (see, for example, Non-Patent Document 1). In addition, the need for life prediction and maintenance inspection for many structures constructed during the period of high economic growth is increasing, and thickness measurement technology is expected to become increasingly important in the future (for example, Non-Patent Document 3).

  Under such circumstances, thickness measurement using an ultrasonic sensor is currently based on the principle of transmitting a rectangular pulse wave and receiving its echo and measuring the propagation delay time between transmitted and received signals. A measurement method based on this (hereinafter referred to as a general method) is used as a mainstream (see, for example, Non-Patent Documents 4 and 5). However, it is pointed out that in general methods, high measurement accuracy cannot be obtained due to errors such as noise and threshold setting due to the small amount of information obtained from transmission / reception signals used for measurement. (For example, see Non-Patent Documents 1 and 5). On the other hand, the ultrasonic distance measurement method based on the phase detection of the two received signals corresponding to the two transmitted burst waves with different frequencies has been proposed and its effectiveness has been reported. (See Patent Document 5).

  By the way, when focusing on the field of precision measurement radar technology, the chirp pulse method has been widely used for the purpose of improving the accuracy of target distance measurement in radar measurement (for example, see Non-Patent Document 6). The chirp pulse method is a method of transmitting and receiving a chirp wave, that is, a pulse signal characterized as a frequency sweep wave, and improving measurement resolution by applying a pulse compression process to each of the transmitted and received signals (for example, Non-patent document 6). Furthermore, some attempts to further improve the distance measurement accuracy by applying the time domain MUSIC method have been studied at the actual machine level (see, for example, Non-Patent Document 7).

Koji Tanikoshi, Ultrasound and its usage, Nikkan Kogyo Shimbun, 92-102, 1995 Kenji Ozaki, Yukio Watanabe, Shigeru Kanemoto, Koji Hinokawa, Katsumi Arakawa, Masuhisa Yamada, Research on practical application of seawater pump monitoring and diagnostic equipment, Proc. Shimakawa Masanori, Ultrasonic Engineering -Theory and Practice-, Industrial Research Committee, 1-6, 12-19, 1975 JIS Z 2355, thickness measurement method by ultrasonic pulse reflection method Tomonori Kimura, Shuzo Wakako, Koichiro Misu, Tsutomu Nagatsuka, Yone Toru Taji, Mitsuhiro Koike, High-resolution ultrasonic distance measurement method using two-frequency phase detection, Journal of the Acoustical Society of Japan, 52, 3, 179-185, 1996 Takashi Yoshida, Revised radar technology, IEICE, 19, 274-279, 1996 Michio UNEDA, Hirokazu HOKAZONO: DOA Estimation Characteristics of the MUSIC Algorithm for the Actual Extended Targets of the Tracking Radar, Proceedings of IEEE RadarConference 2002, CD-ROM, (2002)

  High accuracy is required for ultrasonic sensor measurement as described above. In particular, it is required to apply a measurement technique based on transmission and reception of chirp burst waves to ultrasonic sensor measurement. This invention is made | formed in view of such a condition, The objective is to provide the technique which raises the precision of ultrasonic sensor measurement.

  In order to solve the above problems, a measurement device according to an aspect of the present invention includes a first acquisition unit that acquires a pulsed chirp signal to be transmitted from a transmission sensor, a transmission sensor, and a reception unit that are transmitted from the transmission sensor. A second acquisition unit that acquires a pulsed chirp signal received by the reception sensor via a measurement object installed between the sensor and a peak position of the pulsed chirp signal acquired by the first acquisition unit; And a measurement unit that measures the distance of the measurement object from the transmission sensor to the reception sensor based on the difference from the peak position of the pulsed chirp signal acquired by the second acquisition unit.

  According to this aspect, the transmission sensor and the reception sensor are separately installed so that the measurement object is installed between the transmission sensor and the reception sensor, and the pulsed chirp signal is transmitted from the transmission sensor to the reception sensor. The thickness of the measurement object can be measured with high accuracy.

  The pulse-shaped chirp signal acquired by the first acquisition unit may be amplitude-modulated. In this case, since the amplitude modulation is performed on the pulsed chirp signal, the rising and falling of the waveform can be stabilized.

  Another aspect of the present invention is a measurement method. This method includes a step of obtaining a pulsed chirp signal to be transmitted from a transmission sensor, and a transmission sensor after being transmitted from the transmission sensor and passing through a measurement object installed between the transmission sensor and the reception sensor. A step of acquiring the pulsed chirp signal received in step, and a step of measuring the distance of the measured object from the transmitting sensor to the receiving sensor based on the difference between the peak positions of the two acquired pulsed chirp signals. And comprising.

  It should be noted that any combination of the above-described constituent elements and a conversion of the expression of the present invention between a method, an apparatus, a system, a recording medium, a computer program, etc. are also effective as an aspect of the present invention.

1. 1. Outline of Experiment and Pulse Compression Process 1.1 Outline of Experiment FIG. 1 shows a configuration of a thickness measurement experiment system 100 according to the embodiment. The thickness measurement experimental system 100 includes a PC 10, a signal generator 12, a transmission sensor 14, a measurement object 16, a reception sensor 18, and a digital oscilloscope 20. The thickness measurement experimental system 100 includes a modulation signal 200, a transmission signal 202, a reception signal 204, and a reference signal 206 as signals. That is, this is a method in which two AE sensors are used to transmit ultrasonic waves from the transmission sensor 14 which is one of the sensors, and the reception sensor 18 which is the other sensor receives the ultrasonic waves.

  For the purpose of preventing the presence of air due to the influence of the surface roughness between the transmission sensor 14 or the reception sensor 18 and the measurement object 16 or between the sensors when the transmission sensor 14 and the reception sensor 18 are in direct contact with each other. Vaseline was applied. Note that the surface roughness Rz of the measurement object 16 used in this example is about 2.1 mm, which is determined by the standard for ultrasonic measurement. Further, when transmitting ultrasonic waves, a chirp burst waveform or a rectangular pulse waveform is created as a modulation signal 200 according to experimental conditions by dedicated software installed in the PC 10, and the signal generator 12 is connected to the transmission sensor 14. I went there.

  At this time, the output from the signal generator 12 was branched, one was connected to the transmission sensor 14 as the transmission signal 202, and the other was input to the digital oscilloscope 20 as the reference signal 206. Then, a signal was received by the receiving sensor 18 opposed across the measurement object 16, and the received signal 204 was also input to the same digital oscilloscope 20, thereby comparing with the reference signal 206. Unless otherwise specified in this embodiment, the measured objects 16 were all the same, and SS400 steel disks having a diameter of 300 mm and a thickness of 10 mm were used.

1.2 Outline of pulse compression process In thickness measurement using ultrasonic waves, it is considered possible to improve measurement resolution by narrowing the pulse width. However, it is assumed that reducing the pulse width will reduce the pulse energy and as a result, the signal may not be propagated to the receiving sensor 18. Therefore, it is considered effective to transmit / receive a relatively long pulsed chirp burst waveform and to perform signal amplification processing based on the pulse compression processing on the transmission / reception signals obtained there. That is, it can be said that by performing transmission / reception with a wide pulse width and compressing the obtained signal, the pulse width is equivalently narrowed and the measurement resolution can be improved.

と仮定すると、周波数帯域幅をB[Hz]とすれば、リニアアップチャープにおけるゲインkは

として与えられる。 Here, the theoretical outline of the pulse compression processing is briefly described as follows. Assume that the base signal in the chirp burst waveform is given by sinφ (t). Also, assuming that the minimum frequency is f _min [Hz], the chirp gain is k [rad / s ² ], and the pulse width is T (t = 0 to T) [s], the chirp waveform is generated by ultrasonic waves. In the meantime, it is assumed that the transmission frequency is changed in a linear function (linear up chirp). At this time, φ (t) [rad] giving the phase change in the chirp burst waveform is

Assuming that the frequency bandwidth is B [Hz], the gain k in linear up chirp is

As given.

となる。したがって、ベース信号sinφ（ｔ）に対して、チャープバースト波の送受信によって得られる受信信号２０４をR(t)とすれば、これらの相関演算から得られる係数P(t)は、サンプリング数をN_smpとすると

として与えられる。このことから、パルス圧縮処理は式(4)で与えられるデジタル信号処理であると言える。すなわち、式(4)はベース信号と送受信信号の相関が高いほど、大きな値が得られることを示すものである。 From this, assuming that the maximum frequency is f _max [Hz] (that is, bandwidth B = f _max −f _min ), the phase modulation φ (t) in the chirp burst wave is

It becomes. Therefore, if the received signal 204 obtained by transmitting and receiving the chirped burst wave with respect to the base signal sinφ (t) is R (t), the coefficient P (t) obtained from these correlation operations has the number of samplings N _smp

As given. From this, it can be said that the pulse compression processing is digital signal processing given by Equation (4). That is, Equation (4) indicates that a larger value is obtained as the correlation between the base signal and the transmission / reception signal is higher.

として与えられるものと考える。なお、Ampは送信信号２０２の振幅である。また、位相差j(f)は、伝搬遅延時間τ(f)[s]をラジアンで表したものであり、

として与えられる。 In the AE sensor, the passing amplitude and the phase characteristic change depending on the oscillation frequency. In other words, when the chirp burst waveform to be transmitted is sinφ (t), the passing amplitude ratio of each signal is A (f), and the passing phase difference is j (f) [rad], the received signal considering the characteristics of the sensor 204 is

As given. Amp is the amplitude of the transmission signal 202. The phase difference j (f) is the propagation delay time τ (f) [s] expressed in radians,

As given.

として求めることができる。ここで、縦弾性係数をE[Pa]、密度をρ[kg/m³]とすると、測定物１６の伝播音速V[m/s]は

として与えられる。本実施例においては、既述のとおりSS400鋼製円板を測定物１６に用いたことから、E = 206GPa、ρ= 7.86×103kg/m³として、式（８）から測定物１６の伝播音速Vを5120m/sとして求め、厚さ計測を行った。 1.3 Principle and method of thickness measurement This section briefly describes the principle and method of thickness measurement in ultrasonic sensor measurement. When the propagation sound velocity of the measurement object 16 is V [m / s] and the time difference between signals obtained between the transmitting and receiving sensors is Δt [s], the thickness L [m] of the measurement object 16 is

Can be obtained as Here, when the longitudinal elastic modulus is E [Pa] and the density is ρ [kg / m ³ ], the propagation sound velocity V [m / s] of the measurement object 16 is

As given. In this example, since the SS400 steel disk was used for the measurement object 16 as described above, E = 206 GPa, ρ = 7.86 × 103 kg / m ³ , and the propagation sound velocity of the measurement object 16 from the equation (8). V was determined as 5120 m / s, and the thickness was measured.

  By the way, the method of obtaining the value of the time difference Δt used for thickness measurement is naturally different between the pulse compression method studied in this embodiment and the general method. In the pulse compression method, pulse compression processing is performed on each acquired transmission / reception signal of the chirp burst wave, and the time difference value of the peak position of the pulse compression waveform obtained from each of the transmission signal 202 and the reception signal 204 is used as Δt. In the general method, a rectangular pulse wave having a pulse width of 10 ms is transmitted, and a time difference value between rising points of the transmission signal 202 and the reception signal 204 is used as Δt. In this embodiment, the rising point of the signal obtained by the general method is the received signal 204 in consideration that the digital oscilloscope 20 used for measurement includes noise with a standard deviation value of 0.003 mV. A rising threshold was determined by setting a threshold of 0.08 mV for the output voltage waveform.

2. Basic study using AE sensor In order to consider the sensor characteristics in the measurement and signal processing of this embodiment and to determine the frequency band to be used for the chirp burst wave, the experiment to investigate the passing amplitude and phase characteristics of the sensor Went. FIG. 2 shows experimental conditions for confirming the characteristics of the transmission sensor 14 and the reception sensor 18 in the thickness measurement experimental system 100. Since the oscillation frequency band is defined as 70 kHz to 200 kHz as the specification of the AE sensor used in this embodiment, the experiment was performed within this range. At this time, without passing through the measurement object 16 between the sensors, the sensors are brought into direct contact with each other to transmit / receive a continuous sine wave (CW), and the obtained transmission / reception signals are compared to obtain a passing amplitude ratio and a delay time. It was.

  FIGS. 3A and 3B show the result of the characteristic confirmation experiment of the transmission sensor 14 and the reception sensor 18 in the thickness measurement experimental system 100. FIG. 3A shows the pass amplitude ratio, and FIG. 3B shows the delay time. From this result, it was possible to know the characteristics of the passage amplitude and the delay time due to the frequency change. Therefore, a base theoretical signal for use in pulse compression processing is created based on these sensor characteristics and applied to the correlation processing given by equation (4). Further, from the results of FIGS. 3A to 3C, it is understood that the amplitude ratio and the delay time are stable values with little sudden change in the frequency band of 160 kHz to 180 kHz. When transmitting and receiving a chirp wave, it is considered that a stable waveform can be transmitted and received by selecting a frequency band in which sensor characteristics are stable. On the other hand, it is known that the measurement resolution improves as the bandwidth increases, so it is preferable to increase the bandwidth as much as possible. Based on these facts, it was determined that it was desirable to conduct the experiment with the bandwidth set from 160 kHz to 180 kHz, and this was used for the subsequent experiments.

として与えられる振幅変調を加えたものを用いることとした。 In this example, a waveform shape confirmation experiment was performed in order to confirm the correlation between the experimental waveform and the theoretical waveform when a chirp burst wave was transmitted and received. FIG. 4 shows the conditions of the chirp burst waveform shape confirmation experiment in the thickness measurement experimental system 100. The center frequency f _center of the chirp burst waveform to be transmitted and received was kept constant at 170 kHz, the bandwidth was changed, and the experiment was performed, and each was compared with the theoretical waveform. Note that the AE sensor used has a feature that it cannot oscillate or stop a signal suddenly. Therefore, to stabilize the rise and fall of the waveform, the transmission waveform S (t) is

As a result, a signal to which amplitude modulation given as follows is added is used.

FIG. 5 shows the result of the chirp burst waveform shape confirmation experiment in the thickness measurement experimental system 100. Here, as an example, an experimental result of the waveform shape confirmation in the case of 160 kHz to 180 kHz where the bandwidth is 20 kHz is shown. In FIG. 5, the theoretical waveform and the received waveform are both shown by solid lines. From the result of FIG. 5, it can be seen that the theoretical waveform and the received waveform are almost overlapped. FIG. 6 shows the correlation between the received waveform and the theoretical waveform. That is, FIG. 6 shows the result of calculating the correlation value between the theoretical waveform and the received waveform in each bandwidth. That is, FIG. 6 shows the result of changing only the bandwidth while keeping the center frequency f _center constant at 170 kHz as in FIG. From this result, it can be seen that high correlation is obtained as a whole, and that the correlation value decreases as the bandwidth increases. The reason why the correlation decreases as the bandwidth increases is considered to be due to the sensor characteristics. It has been found that the used AE sensor changes its pass amplitude and phase characteristics with respect to the transmission frequency. That is, since a chirp wave is used in the present embodiment, it is assumed that the wider the frequency bandwidth used, the stronger the influence of the sensor characteristics. Therefore, in consideration of this result, the following investigation will be conducted with a bandwidth of 20 kHz at which the highest correlation value is obtained among the chirp burst waves.

3. Thickness measurement experiment using AE sensor 3.1 Experimental method It was confirmed by the examination up to the previous chapter that the received signal 204 has a waveform having a high correlation with the theoretical waveform. Therefore, in this chapter, the thickness measurement experiment on the measurement object 16 was performed by both the pulse compression method and the general method. At this time, in order to conduct a more accurate comparative study, first, the experiment was performed with the sampling period unified by both methods. FIG. 7 shows experimental conditions for measuring the thickness of the measurement object 16 in the thickness measurement experimental system 100. In addition, thickness measurement was performed based on Formula (7), and the value calculated using Formula (8) was used for the propagation sound speed.

  FIGS. 8A to 8C show an example of a result obtained by performing pulse compression processing on a signal obtained by transmitting and receiving a chirp burst wave in the thickness measurement experimental system 100. FIG. FIG. 8A shows the result of pulse compression processing of the transmission signal 202, and FIG. 8B shows the result of pulse compression processing of the reception signal 204. FIG. 8C shows a theoretical result of the pulse compression process. In these figures, normalization is performed with a maximum value of 1. Thus, by performing the pulse compression process, it can be seen that a waveform having a convex shape, which is a feature of the pulse compression process, is obtained for both transmission and reception signals, and there is a peak value. Further, since the pulse compression result close to the theoretical result is obtained for both the transmission and reception signals, it is considered that the processing can be performed accurately in the experiment. And as described above, Δt required in the thickness measurement is obtained as a peak time difference in the pulse compression result of each transmission / reception signal.

  Next, a general thickness measuring method will be described. An experiment was performed under the conditions of FIG. 7, and adjacent averaging processing was applied to the acquired received signal 204. The adjacent average process means a smoothing process that averages n pieces of data in total before and after the target data for all data. In this example, the adjacent average range n is 30 as shown in FIG. 7, which corresponds to 750 ns when the sampling period is 25 ns and 37.5 ns when the frequency is 1.25 ns.

3.2 Experimental Results 3.2.1 Study on Measurement Value Distribution FIGS. 9A to 9C show measurement results in the thickness measurement experimental system 100. FIG. Here, the distribution of measurement results obtained when the thickness measurement is repeated 50 times under each condition is shown. It should be noted that the class width of the histogram in FIGS. 9A to 9C is obtained with reference to the Sturges formula. 9A shows the distribution of results in the pulse compression method, and FIG. 9B shows the distribution in the general method when the pulse compression method and the sampling period are unified (25 ns). FIG. 9 (c) shows the result of the general method when the sampling period is very small as 1.25 ns. In any result, the probability density function obtained from the average value and the standard deviation is shown by a solid line. Comparing FIGS. 9A and 9B, the distribution of the general method is scattered over a wide range of data, whereas the result of the pulse compression method is concentrated in data.

  FIG. 10 shows another measurement result in the thickness measurement experimental system 100. Here, the result of comparing the standard deviation values is shown. As can be seen from FIG. 10, when the sampling period is the same, the value of the standard deviation is clearly smaller in the pulse compression method. Note that the ratio of the standard deviation between the pulse compression method and the general method was 12.5%. In addition, in the case of 1.25 ns in the general method, the result is almost the same as the pulse compression processing, so when trying to obtain the same level of measurement accuracy as the pulse compression processing in general measurement, the sampling period Needs to be reduced to about 1/20. From these facts, it is considered that the pulse compression method is capable of very precise measurement compared to the general method.

  Furthermore, when the average values of the measurement data are compared from the results of FIGS. 9 and 10, it can be considered that accurate measurement can be performed because the result of the pulse compression method is closer to the true value. As described above, the reason why the pulse compression method can be measured more accurately and accurately than the general method is considered as follows. That is, it is considered that the general method measures only at one rising point, whereas the pulse compression method uses multi-point measurement using the entire pulse signal, and the amount of information used for measurement is large.

3.2.2 Effect of signal-to-noise ratio When performing ultrasonic sensor measurement, the measurement accuracy is considered to be reduced due to the effect of noise. Therefore, an experimental study was conducted on the plate thickness measurement accuracy in a state where the amplitude of the transmission signal 202 was decreased and the signal-to-noise ratio was lowered. FIG. 11 shows experimental conditions for considering the influence of the transmission signal amplitude in the thickness measurement experimental system 100. In this study, in order to clarify the degree of accuracy reduction accompanying the decrease in transmission signal amplitude, the sampling period in the general method is the same as the condition shown in FIG. 1/20 is set to be significantly smaller.

  FIG. 12 shows the experimental results of changing the transmission signal amplitude in the thickness measurement experimental system 100. This is a result obtained in an experiment in which the transmission signal amplitude is changed, and shows a change in the standard deviation in the distribution of the plate thickness measurement result with respect to a change in the transmission signal amplitude. In FIG. 12, the horizontal axis represents the transmission signal amplitude, but it is added that the reception signal amplitude is about 1/20 of the transmission signal amplitude. From the result of FIG. 12, it can be seen that the value of the standard deviation increases as the transmission signal amplitude decreases in the general measurement. In particular, it can be seen that the value of the standard deviation is particularly large when the transmission signal amplitude is 0.05V. From this, it can be said that in the general method, the measurement accuracy is greatly lowered with the decrease of the transmission signal amplitude, and the influence appears remarkably when the transmission signal amplitude is particularly small. On the other hand, in the pulse compression method, the standard deviation value tends to increase slightly as the transmission signal amplitude decreases, but it can be seen that the tendency to decrease accuracy is weaker than in the general method. From these facts, it can be said that the effectiveness of the pulse compression method can be confirmed particularly remarkably when the transmission signal amplitude is particularly small.

3.2.3 Influence of measured object thickness When measuring thickness using an ultrasonic sensor, it is considered that the measurement accuracy decreases as the measured object 16 becomes thicker. Therefore, an experimental study was conducted on the plate thickness measurement accuracy when the measurement object 16 was made of the same material and the thickness was changed. FIG. 13 shows experimental conditions for considering the influence of the thickness of the measurement object 16 in the thickness measurement experimental system 100. This shows the condition of the experiment in which the thickness of the measurement object 16 is changed. In the experiment, both the pulse compression method and the general method were performed on the measurement objects 16 of each thickness.

  FIG. 14 shows experimental results in which the thickness of the measurement object 16 in the thickness measurement experimental system 100 is changed. This shows the change of the standard deviation in the distribution of the measurement result with respect to the change of the thickness. As can be seen from FIG. 14, the pulse compression method is more accurate at any thickness compared to the general method. From this, even when the thickness changes, it is considered that the pulse compression method can obtain higher measurement accuracy than the general method. That is, it is assumed that the pulse compression method can be measured with higher accuracy than the general method for any thickness.

3.2.4 Influence of frequency band In order to confirm how the change of the frequency bandwidth used affects the measurement accuracy in the thickness measurement by chirp burst wave using an ultrasonic sensor, the frequency bandwidth We compared the measurement accuracy when changing. FIG. 15 shows experimental conditions for considering the influence of the bandwidth in the thickness measurement experimental system 100. FIG. 15 shows experimental conditions in which the frequency bandwidth is changed. In the experiment, the center frequency f _center was kept constant at 170 kHz, and only the frequency bandwidth was changed.

  FIG. 16 shows the experimental results of changing the bandwidth in the thickness measurement experimental system 100. In addition, the dotted line in FIG. 16 is a result by a general system. In FIG. 16, the experiment with a bandwidth of 0 kHz is a sine wave burst with only amplitude modulation, not a chirp wave, so the plot is changed. From the results of FIG. 16, it can be seen that the standard deviation value is larger than the other results when the frequency bandwidth is 0 kHz, and the values are almost the same for each of 20 kHz, 40 kHz, and 60 kHz. From this result, it can be seen that the measurement accuracy can be improved somewhat by widening the frequency bandwidth.

4). Device Configuration FIG. 17 shows a detailed configuration of the thickness measurement experimental system 100. The thickness measurement experimental system 100 includes an oscillation unit 50, a first acquisition unit 52, a second acquisition unit 54, a measurement unit 56, a transmission sensor 14, a measurement object 16, and a reception sensor 18. Here, the oscillation unit 50 is included in the signal generator 12 of FIG. 1, and the first acquisition unit 52, the second acquisition unit 54, and the measurement unit 56 are included in the digital oscilloscope 20 of FIG.

  The oscillation unit 50 outputs a pulsed chirp signal that has been amplitude-modulated. Here, the pulsed chirp signal corresponds to the above-described chirp burst waveform, and is represented by equation (9). The chirp burst waveform from the oscillation unit 50 is output as the transmission signal 202 to the transmission sensor 14 and is output as the reference signal 206 to the first acquisition unit 52. The first acquisition unit 52 acquires a reference signal 206, that is, a chirp burst waveform to be transmitted from the transmission sensor 14. As described above, the reference signal 206 received by the first acquisition unit 52 is also amplitude-modulated. In addition, the transmission sensor 14 outputs a chirp burst waveform to the reception sensor 18 via the measurement object 16.

  The reception sensor 18 outputs the chirp burst waveform received from the transmission sensor 14 as a reception signal 204. The second acquisition unit 54 acquires the reception signal 204 from the transmission sensor 14. The reception signal 204 is transmitted from the transmission sensor 14, and then the chirp burst waveform received by the reception sensor 18 via the measurement object 16 installed between the transmission sensor 14 and the reception sensor 18. It can be said.

  The measurement unit 56 receives the reference signal 206 from the first acquisition unit 52 and the reception signal 204 from the second acquisition unit 54. The measuring unit 56 detects the difference between the peak position of the chirp burst waveform that is the reference signal 206 and the peak position of the chirp burst waveform that is the received signal 204. That is, the measurement unit 56 detects a time difference Δt of signals. The measurement unit 56 measures the thickness L of the measurement object 16 according to the equation (7). Here, the thickness of the measurement object 16 corresponds to the distance of the measurement object 16 from the transmission sensor 14 to the reception sensor 18.

  This configuration can be realized in terms of hardware by a CPU, memory, or other LSI of any computer, and in terms of software, it can be realized by a program loaded in the memory, but here it is realized by their cooperation. Draw functional blocks. Accordingly, those skilled in the art will understand that these functional blocks can be realized in various forms by hardware only, software only, or a combination thereof.

  According to the embodiment of the present invention, a chirp burst wave can be applied to the ultrasonic sensor measurement technique. In addition, the thickness measurement result by the pulse compression method can be measured more accurately than the result by the general method. Further, even in a situation where the amplitude of the transmission signal is small, it is possible to suppress a tendency of decreasing accuracy in the measurement using the chirp burst wave as compared with the general method. In addition, when it is intended to obtain measurement accuracy equivalent to that of the general method using chirp burst waves, the sampling period can be delayed. Moreover, the cost of the measuring instrument can be reduced by delaying the sampling cycle.

  In the above, this invention was demonstrated based on the Example. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to the combination of each component and each processing process, and such modifications are also within the scope of the present invention. .

It is a figure which shows the structure of the thickness measurement experiment system which concerns on an Example. It is a figure which shows the experimental conditions for confirming the characteristic of the sensor for transmission in the thickness measurement experiment system of FIG. 1, and the sensor for reception. FIGS. 3A and 3B are diagrams showing the results of a characteristic confirmation experiment of the transmission sensor and the reception sensor in the thickness measurement experimental system of FIG. It is a figure which shows the conditions of the shape confirmation experiment of a chirp burst waveform in the thickness measurement experiment system of FIG. It is a figure which shows the result of the shape confirmation experiment of the chirp burst waveform in the thickness measurement experiment system of FIG. FIG. 6 is a diagram illustrating a correlation between a reception waveform and a theoretical waveform in FIG. 5. It is a figure which shows the experimental condition of the thickness measurement of the measured object in the thickness measurement experimental system of FIG. FIGS. 8A to 8C are diagrams illustrating an example of a result of performing pulse compression processing on a signal obtained by transmitting and receiving a chirp burst wave in the thickness measurement experimental system of FIG. FIGS. 9A to 9C are diagrams showing measurement results in the thickness measurement experimental system of FIG. It is a figure which shows another measurement result in the thickness measurement experiment system of FIG. It is a figure which shows the experimental condition for considering the influence of the transmission signal amplitude in the thickness measurement experimental system of FIG. It is a figure which shows the experimental result which changed the transmission signal amplitude in the thickness measurement experimental system of FIG. It is a figure which shows the experimental condition for considering the influence of the thickness of the to-be-measured object in the thickness measurement experiment system of FIG. It is a figure which shows the experimental result which changed the thickness of the to-be-measured object in the thickness measurement experiment system of FIG. It is a figure which shows the experimental condition for considering the influence of the bandwidth in the thickness measurement experimental system of FIG. It is a figure which shows the experimental result which changed the bandwidth in the thickness measurement experiment system of FIG. It is a figure which shows the detailed structure of the thickness measurement experiment system of FIG.

Explanation of symbols

  10 PC, 12 signal generator, 14 transmission sensor, 16 measurement object, 18 reception sensor, 20 digital oscilloscope, 50 oscillation unit, 52 first acquisition unit, 54 second acquisition unit, 56 measurement unit, 100 thickness measurement Experimental system.

Claims (3)

A first acquisition unit that acquires a pulsed chirp signal to be transmitted from the transmission sensor;
A second acquisition unit that acquires a pulsed chirp signal received at the reception sensor via a measurement object installed between the transmission sensor and the reception sensor after being transmitted from the transmission sensor;
Based on the difference between the peak position of the pulsed chirp signal acquired in the first acquisition unit and the peak position of the pulsed chirp signal acquired in the second acquisition unit, from the transmission sensor to the reception sensor A measuring unit that measures the distance of the object to be measured,
A measuring device comprising:   The measurement apparatus according to claim 1, wherein the pulse-shaped chirp signal acquired by the first acquisition unit is amplitude-modulated. Obtaining a pulsed chirp signal to be transmitted from the transmission sensor;
Obtaining a pulsed chirp signal received at the reception sensor after being transmitted from the transmission sensor via a measurement object installed between the transmission sensor and the reception sensor;
Measuring the distance of the measured object from the transmitting sensor to the receiving sensor based on the difference between the peak positions of the two obtained pulsed chirp signals;
A measurement method comprising:

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