JP6211329B2 - Ultrasonic thickness measurement method and ultrasonic thickness measurement system - Google Patents

Description

The present invention relates to an ultrasonic thickness measuring method and an ultrasonic thickness measuring system.

  Various methods have been conventionally known for measuring the thickness of a material layer by ultrasonic waves. In particular, in the method of measuring the thickness of the second and subsequent layers of a multilayer structure material, the method depends on the previous layer. We encounter the problem of multiple reflections of ultrasound. As means for solving the problem of multiple reflection, for example, there is a technique as disclosed in Patent Document 1.

In patent document 1, in order to avoid the overlap with the ultrasonic echo of a steel pipe with respect to the multiple reflection by a coating layer, the method of detecting the multiple reflection in a steel pipe in the time when the multiple reflection of the coating layer fully attenuate | damped. I'm taking it.
The method of Patent Document 1 is particularly effective if there is a material that easily attenuates ultrasonic waves in the previous stage and there is little ultrasonic attenuation in the measurement target layer.

JP 2007-64904 A

However, for example, when there is a resin layer between metal layers and it is desired to measure the thickness of the resin layer with ultrasound, if the multiple reflection echo due to the metal layer overlaps the echo of the resin layer, the ultrasonic echo due to the resin layer It is not easy to separate multiple reflection echoes with metal layers.
FIG. 9 is a diagram showing a conventional method for measuring the ultrasonic thickness, and shows a method for measuring the thickness by applying the ultrasonic thickness gauge 1 to the multilayer structure material 10.

  Since the ultrasonic waves are reflected at the interface between materials having different acoustic impedances, multiple reflections occur in each layer as shown in FIG. At this time, if the sound velocity of each layer i is Vi and the thickness of each layer is Li, when the Li / Vi is equal in each layer, the second multiple reflection echo of the first layer 101 is the second layer 102. The third multiple reflection echo of the first layer 101 overlaps with the second multiple reflection echo of the second layer 102 and the first echo of the third layer 103. End up. When the spectrum of all echoes is almost the same, it is difficult to separate the information of each layer folded in the waveform.

In such a case, due to the uncertain analogy that the echo of the second layer 102 will overlap the multiple reflection of the first layer 101, the time of the multiple reflection echo of the first layer 101 is Although the thickness will be determined as the same as the time, it is not known from the waveform itself whether or not it is actually overlapping. Such a trial is necessary.
However, if the measurable range is narrow or the thickness is uniform, the overlapping waveforms are not separated.

  The present invention has been made in view of such circumstances, and even when the ultrasonic echo of the measurement target layer overlaps the multiple reflection echo by the previous layer, the thickness of the second and subsequent layers of the multilayer structure material can be easily reduced. It is an object of the present invention to provide an ultrasonic thickness measurement method and an ultrasonic thickness measurement system that can be used for measurement.

In order to solve the above-described problem, the first invention of the present application is an ultrasonic thickness measurement method for measuring the thickness of each layer of a multilayer structure material in which a plurality of at least two different materials are laminated by an ultrasonic echo method, ultra said multilayer structural material positively changing the temperature of, by utilizing the fact that the difference by ultrasonic wave propagation time is temperature change of the previous layer as measured layer occurs, to measure the thickness of the second layer after It is a sonic thickness measurement method.

  Further, the second invention of the present application is the ultrasonic thickness measurement method according to claim 1, wherein the spectrum of the result of attenuation from the transmission waveform and the fact that the temperature characteristics of ultrasonic attenuation are different in each layer and This is an ultrasonic thickness measurement method in which the reflection position is simultaneously detected by wavelet conversion and the thickness of each layer is measured.

The third invention of the present application is an ultrasonic thickness measurement system for measuring the thickness of each layer of a multilayer structure material in which a plurality of at least two different materials are laminated by an ultrasonic echo method, the multilayer structure An ultrasonic thickness measuring system comprising means for changing the temperature of a material and using the method according to claim 1.

  The fourth invention of the present application is the ultrasonic thickness measurement system according to claim 3, wherein at least one display device capable of performing wavelet display and a waveform is manually selected from the displayed waveforms. An ultrasonic thickness measurement system comprising: at least one input device capable of:

  According to the first invention of this application, even when multiple reflections overlap each other and the echo of the next layer is unclear, the mechanical characteristics of each layer can be obtained by positively changing the temperature of the multilayer structure material. Is changed according to the temperature, the propagation characteristic of the ultrasonic wave in each layer is changed, and the reflected echo from the entire multilayer structure material at each temperature is obtained, so that the overlap of the reflected echo is separated in time, and 2 The thickness after the layer can be measured.

  For example, L1 is the thickness of the first layer, L2 is the thickness of the second layer, V1 is the sound velocity of the first layer, and V2 is the sound velocity of the second layer. Is f (t), the first reflection of the first layer can be expressed as αf (t−2 · L1 / V1), and the second reflection can be expressed as βf (t−4 · L1 / V1), The first reflection from the second layer is γf (t−2 · L1 / V1-2 · L2 / V2).

Since the first reflection of the first layer does not overlap with other reflections in time, the thickness of the first layer can be easily determined as long as the sound speed is calibrated with a reference sample or the like.
Considering only the second reflection of the first layer and the first reflection of the second layer, and considering the superposition F (t), F (t) = βf (t−4 · L1 / V1) + γf (T-2 · L1 / V1-2 · L2 / V2), but if L2 / V2 = L1 / V1 at this time, F (t) = βf (t−4 · L1 / V1) + Γf (t−4 · L1 / V1) = (β + γ) · f (t−4 · L1 / V1), and information on L2 cannot be obtained from F (t).

  Therefore, in the present invention, a thickness measurement error due to a temperature change, which has been regarded as a problem, is actively used. That is, by changing the temperature of the multilayer structure material, the propagation time is changed by changing the temperature of the thickness and the speed of sound. For example, in the above-described example, L2 / V2 ≠ L1 / V1 is set, and information on L2 can be obtained by shifting the overlap of two waveforms at F (t).

  Furthermore, according to the second invention of the present application, even when multiple reflections overlap in each layer and the echo of the next layer is unclear, the ultrasonic attenuation is different in each layer, so The spectrum and reflection position as a result of attenuation can be detected simultaneously by wavelet transform, and the thickness of each layer can be measured. That is, it is possible to measure the thickness of each layer by separating the overlap of reflected echoes in frequency within a local time and detecting the difference in spectrum that is the result of passing ultrasonic waves in each layer.

  Further, according to the ultrasonic thickness measurement system of the third invention of the present application, when the first invention of the present application is carried out, the thickness measurement can be easily performed by reducing the problem of multiple reflection without providing a separate temperature control device. It becomes possible.

  Furthermore, according to the fourth invention of the present application, the wavelet transformation of the third invention of the present application can be visually recognized, and even when it is difficult to detect with an automatic algorithm, by manually selecting the waveform, Thickness can be measured.

It is a figure which shows the structure of embodiment of this invention. It is the figure which showed the ultrasonic waveform at room temperature in embodiment of this invention. It is a figure which shows an ultrasonic waveform when temperature is raised in embodiment of this invention. It is a figure which shows the waveform which processed the waveform of FIG. It is a figure which shows the waveform which processed the waveform of FIG. It is the figure which compared the waveform of FIG. 4 and FIG. It is a wavelet display of the waveform of FIG. 6 is a wavelet display of the waveform of FIG. It is a figure which shows the method of the conventional ultrasonic thickness measurement.

FIG. 1 is a diagram showing an embodiment of the present invention. In measuring the thickness of a multilayer structure material 30, an ultrasonic thickness measurement system 201 according to the second invention of the present application is applied.
The first layer 301 of the multilayer structural material 30 is a metal material, the second layer 302 is a resin material, and the third layer 303 is a metal material. The thickness of each layer is different, but ultrasonic waves are applied from the front to the back of the first layer 301. The time for the ultrasonic wave to pass from the front to the back of the second layer 302 is almost the same in calculation, and the reflected echo of the second layer 302 overlaps the multiple reflection of the first layer 301 It is in a state.

  The ultrasonic thickness measurement system 201 includes an ultrasonic transmission / reception element 202 and is held by a support 206. The ultrasonic transmitting / receiving element 202 can be divided into a transmitting element and a receiving element for the purpose of increasing sensitivity. However, if there is no problem in sensitivity, it is easy to use one element for both transmitting and receiving. Further, the ultrasonic transmission / reception element 202 preferably has a high frequency band as much as possible so that the ultrasonic attenuation due to the multilayer structure material does not become a problem for the purpose of clearly raising the difference in propagation speed of each layer depending on the temperature. Furthermore, in order to detect a difference in ultrasonic attenuation of each layer due to a difference in temperature, a wide band is preferable.

Furthermore, the ultrasonic thickness measurement system 201 includes a temperature control element 203 and includes means for transferring heat to the multilayer structure material 30 via the heat conduction element 204. Further, a heat insulating material 205 is provided so that the temperature is not directly transmitted to the ultrasonic transmitting / receiving element 202 from these temperature control structures. In order to more effectively use the temperature control structure, a temperature measuring means can be provided.

  Furthermore, the ultrasonic thickness measurement system 201 has a space 208 for holding an ultrasonic medium such as water, and can supply the ultrasonic medium to the space 208 through the medium supply path 207.

  FIG. 2 is a diagram showing an ultrasonic waveform at room temperature, and is an output waveform from the ultrasonic thickness measurement system 201 while keeping the multilayer structure material 30 at room temperature in FIG. However, the reflection from the surface of the first layer 301 is excluded from the waveform, and the first waveform in time in FIG. 2 is the reflection waveform from the back surface of the first layer 301. The second waveform is mostly the second waveform of the multiple reflection of the first layer 301, but it can be inferred that the reflection from the bottom surface of the second layer 302 is superimposed.

  FIG. 3 is a diagram showing an ultrasonic waveform when the temperature is raised. Compared with FIG. 2, since the difference from FIG. 2 is unclear as it is, the time difference between the first waveform and the second waveform is shifted, and the intensity of the first waveform is changed to the intensity of the second waveform. The difference is taken after adjusting. The result of each of the processes is shown in FIGS.

  FIG. 4 is a diagram showing a waveform obtained by differential processing of the waveform of FIG. 2, but the second reflection waveform of the first layer 301 and the first reflection position of the second layer 302 are almost completely the same. It is superimposed because it is in position. However, the weak waveform is observed at the position of the second waveform because the first waveform and the second waveform are not completely similar to each other. It is unclear whether echoes from the target second layer 302 are superimposed on each other.

  FIG. 5 is a diagram showing a waveform obtained by processing the waveform of FIG. 3. As in the case of FIG. 4, the echo from the target second layer 302 is superimposed on the second waveform only with the waveform of FIG. Whether it is unclear.

  FIG. 6 is a diagram comparing the waveform of FIG. 4 with the waveform of FIG. 5, in which the waveform of FIG. 4 is indicated by a solid line and the waveform of FIG. The dotted waveform, which is a waveform when the temperature is high, is not substantially shifted from the reflection time of the first layer 301, whereas the reflection time of the second layer 302 is delayed.

  Due to the temperature dependence of the ultrasonic wave propagation time between the metal layer and the resin layer, the propagation time of each layer varies depending on the temperature change. The thickness can be calculated based on this time.

  It is unlikely that errors in thickness measurement due to temperature will be a problem, but even in such a case, by preparing a reference sample with a known thickness and measuring it in the same process, It is also possible to reduce the error.

  FIG. 7 is a wavelet display of the waveform of FIG. 3, where the vertical axis is the frequency parameter and the horizontal axis is the time parameter. For clarity, the original waveform has the sign reversed. In FIG. 7, the position of the intensity peak of the wavelet of each multiple reflection waveform is indicated by a cross. The peak position shows almost the same frequency position in any waveform. From this, it can be seen that there is almost no ultrasonic attenuation of the first layer 301.

  On the other hand, FIG. 8 is a wavelet display of the waveform of FIG. 5, where the vertical axis is the frequency parameter and the horizontal axis is the time parameter. Similarly, although the sign of the original waveform is inverted, the scale of the wavelet intensity is changed from the middle of the time axis for easier understanding. FIG. 8 also shows the position of the wavelet intensity peak with a cross, but the frequency of the second waveform processed as the echo waveform from the second layer 302 is compared with the frequency of the echo waveform of the first layer 301. It can be seen that the frequency shifts to the low frequency side.

  Thus, by utilizing the fact that the ultrasonic attenuation in the resin layer is larger than the ultrasonic attenuation in the metal layer, it is possible to separate the waveform overlap in terms of frequency. If the principle of performing frequency analysis with the time information, which is the greatest advantage of the conversion, is used, time information corresponding to the thickness of each layer can be obtained at the same time, and the thickness of each layer can be calculated.

  In the fourth invention of the present application, at least one display device for displaying the wavelet transform is provided. Since the attenuation of the frequency can be visually recognized on the display device, even if there is an exception in the algorithm for automatic measurement, the thickness can be calculated from the temporal position of the selected waveform by the input device that manually selects the waveform. Can be calculated.

  INDUSTRIAL APPLICABILITY The ultrasonic thickness measuring method and ultrasonic thickness measuring system according to the present invention can be used for measuring the film thickness of each layer of a multilayer structure material, and the temperature change rate of mechanical properties is particularly remarkable between the constituent layers of the multilayer structure material. It is suitable in some cases.

DESCRIPTION OF SYMBOLS 1 Conventional ultrasonic thickness meter 10, 30 Multilayer structure material 101, 301 First layer of multilayer structure material 102, 302 Second layer of multilayer structure material 103, 303 Third layer of multilayer structure material 201 Ultrasonic thickness measurement system 202 Ultrasonic transmitting / receiving element 203 Temperature control element 204 Thermal conduction element 205 Heat insulation material 206 Support body 207 Medium supply path 208 Space

Claims (4)

An ultrasonic thickness measurement method for measuring the thickness of each layer of a multilayer structure material in which a plurality of at least two different materials are laminated by an ultrasonic echo method, wherein the temperature of the multilayer structure material is actively changed, layer and by using the fact that difference by the ultrasonic wave propagation time is temperature change of the measurement target layer occurs, ultrasonic thickness measuring method for measuring the thickness of the second layer after the. 2. The ultrasonic thickness measurement method according to claim 1, wherein the spectrum and reflection position of the attenuation result from the transmission waveform are simultaneously detected by wavelet transform by utilizing the fact that the temperature characteristics of ultrasonic attenuation are different in each layer. Then, an ultrasonic thickness measurement method for measuring the thickness of each layer. An ultrasonic thickness measurement system for measuring the thickness of each layer of a multilayer structure material in which a plurality of at least two or more different materials are laminated by an ultrasonic echo method, comprising means for changing the temperature of the multilayer structure material An ultrasonic thickness measurement system using the method according to claim 1. The ultrasonic thickness measurement system according to claim 3, comprising: at least one display device capable of performing wavelet display; and at least one input device capable of manually selecting a waveform from the displayed waveforms. An ultrasonic thickness measurement system comprising: