JP3510137B2 - Ultrasonic thickness measurement method and device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic wall thickness measuring method and apparatus, and particularly to meat such as cast iron and cast steel in which the front and back surfaces of an object to be measured have roughness and unevenness due to coating and corrosion. The present invention relates to a thickness measuring method and its device.

[0002]

2. Description of the Related Art When an ultrasonic probe having a natural frequency is brought into contact with the surface of an object to be measured and an ultrasonic wave is oscillated as a transmission wave 15 as shown in FIG. The bottom reflected wave 16 can be received. When the bottom surface reflected wave 16 is received using this principle to measure the wall thickness value D of the measurement object, the wall thickness value D is the sound velocity C of the measurement object and the time it takes to travel back and forth inside the measurement object (path length). ) T is calculated using the following formula.

D = C · t / 2 (1) In the conventional measurement method, the time t in the equation (1) is the time when the transmission wave 15 from the ultrasonic probe first exceeds the threshold value 18. Is the rising time T1 of the transmitted wave as the transmission time, and the rising time T2 of the bottom surface reflected wave 16 is the reflected wave reception time and the time when the bottom surface reflected wave 16 first exceeds the threshold value 18 is the time at these times T1 and T2. (Interval) tp was used.

The threshold 18 has been arbitrarily set to a value that allows a measurer to remove noise based on experience by looking at the waveform. The echo height is the intensity of the transmitted wave or reflected wave.

[0005]

When the thickness of the object to be measured is measured by ultrasonic waves and the front and back surfaces of the object to be measured are smooth, FIG.
6, the bottom surface reflected wave 16 is obtained (hereinafter, such a waveform of the bottom surface reflected wave 16 is referred to as a basic pattern). When ultrasonic waves are scattered due to the roughness or unevenness of the front and back surfaces of the measurement object, and forest echoes that are reflected waves from many minute boundary surfaces (boundary surfaces of metal crystal grains) inside the measurement object occur, A bottom reflected wave 17 (shown by a broken line) having a smaller rise than the basic pattern of the bottom reflected wave 16 may be obtained under the influence of scattered waves or forest echoes (waveform interference).

In this case, the time Tb when the bottom surface reflected wave 17 first exceeds the threshold value 18 is detected as the rising time. However, this time Tb is not the original rising time, and the original rising is the time Ta as shown in FIG. As a result, an accurate road distance cannot be obtained because the time tg, which is the interval between the rising time Tb obtained by the measurement and the original rising time Ta, is delayed. On the contrary, in some cases, a bottom reflected wave (not shown) for early detection of rising may be generated due to the influence of scattered waves or forest echoes, and an accurate path may not be obtained.

Further, in the conventional measuring method, since the rising of the bottom reflected wave is detected by the threshold value 18 without being influenced by the scattered wave or the forest echo, for example, the bottom reflected wave 16
In the above case, the actual rise time Ta and the rise time Tc detected by the threshold value 18 have a time difference of th, and thus an accurate road distance cannot be obtained.

On the other hand, there is also a method of calculating the rising time from the waveform using the time indicating the maximum echo height of the bottom reflected wave 17, but the bottom reflected wave is affected by scattered waves and forest echoes, It is not possible to obtain an accurate path length even if the time at which the maximum echo height is used is used, because the waveform at which the maximum echo height is displayed is deviated without a beautiful waveform such as a pattern.

Therefore, for these reasons, there is a problem that the conventional measuring method cannot accurately measure the wall thickness.

Therefore, it is an object of the present invention to provide an ultrasonic wall thickness measuring method and apparatus capable of accurately measuring the wall thickness even under the influence of forest echoes and scattered waves.

[0011]

To achieve the above object, the present invention is characterized in that the transmission time of ultrasonic waves from the surface of an object to be measured and the reception of reflected waves of ultrasonic waves from the back surface of the object to be measured. In the wall thickness measurement method using ultrasonic waves to obtain the time and measure the wall thickness of the measurement object from the interval between the two times, use a test piece with smooth front and back surfaces to determine the rising direction of the reflected wave of the ultrasonic probe. Obtained in advance, obtain the maximum echo height of the reflected wave in the measurement object by the ultrasonic probe, and based on the maximum echo height in the direction opposite to the reflected wave rising direction with respect to the reflected wave. The threshold value is set, the time at which the maximum value in the waveform of the reflected wave that first exceeds this threshold value is obtained, and the time that is 3/4 cycle back from this time is set as the reflected wave reception time.

Further, another feature of the present invention is to obtain an ultrasonic wave transmission time from the front surface of the object to be measured and a reflected wave reception time of the ultrasonic wave from the rear surface of the object to be measured, and calculate from the interval between the both times. In measuring the wall thickness of the measuring object, the rising direction of the reflected wave of the ultrasonic probe that receives the ultrasonic wave on the surface of the measuring object and receives the reflected wave from the back surface of the measuring object is stored. Means for setting, a means for setting a threshold value in a direction opposite to the rising direction of the reflected wave with respect to the reflected wave based on the maximum echo height of the reflected wave in the object to be measured, reflection that first exceeds the threshold value Get the time that shows the maximum value of the waveform of the wave,
There is provided a means for setting the time, which is 3/4 cycle from this time, as the reception time of the reflected wave.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of an ultrasonic wall thickness measuring apparatus according to a first embodiment of the present invention. 1 is an object for measuring wall thickness, 2 is an ultrasonic probe, 3 is a transmitter, 4 is a receiver,
5 is a measurement unit, 6 is a calculation unit, 7 is a storage unit, 8 is an input unit, 9
Is a display unit. Further, 10 indicates a transmitted wave and 11 indicates a bottom reflected wave.

The ultrasonic wave is generated by applying a voltage from the transmitting unit 3 to the ultrasonic probe 2, and propagates by being reflected and transmitted inside the measuring object 1. After that, the bottom surface reflected wave 11 from the measuring object 1 is received by the ultrasonic probe 2 and converted into a voltage value proportional to the intensity of the ultrasonic wave by the receiving unit 4. The measuring unit 5 measures the reflection time of the bottom surface reflected wave 11 and the voltage value for that time. From the measured reflection time and voltage value and the bottom surface reflected wave stored in the storage unit 7, the calculation unit 6 calculates the road length, and the measurement target stored in the storage unit 7 in advance from the road length and the input unit 8 The wall thickness value is calculated from the sound velocity value of, and the result is displayed on the display unit 9 and also stored in the storage unit 7. The input unit 8 is necessary for inputting the material, the number of times of measurement, etc., in addition to the sound velocity value of the measurement object.

Next, the operation of the first embodiment of the present invention having the above configuration will be described. FIG. 2 is a flow chart of the wall thickness measuring method in the present invention, and FIG. 3 is a bottom surface reflected wave generated by ultrasonic measurement. FIG. 4 is an enlarged view of the bottom surface reflected wave shown in the part A in FIG.

In the method of measuring wall thickness by ultrasonic waves according to the present invention, first, a bottom surface as shown in FIG. 5 which is generated when ultrasonic waves are incident on a test piece whose front and back surfaces are smooth and which has a small internal attenuation factor. Input the data necessary for calculating the wall thickness value such as the reflected wave 16, the sound velocity C in the material of the measurement object, the frequency of the ultrasonic wave, the threshold coefficient α, the rising direction of the bottom reflected wave from the input unit 8. It is stored in the storage unit 7 (FIG. 1) (step (S) 1 in FIG. 2).

The rising direction of the bottom reflected wave is a characteristic peculiar to the ultrasonic probe 2. That is, when the ultrasonic probe 2 is replaced, the bottom surface reflected wave 11 shown in FIG. 4 on the display unit 9 may have its waveform rising direction inverted. Therefore, the rising direction of the waveform of the bottom surface reflected wave in the ultrasonic probe 2 to be used is measured with a test piece in which the waveform appears neatly and used for setting the threshold value described later.

The threshold coefficient α is the bottom reflected wave when the maximum echo height of the bottom reflected wave of the test piece shown in FIG. 6 is Ep1, and the echo height at the 3 / 4th cycle from the rising of the bottom reflected wave is Et. And the empirical formula established by the experiment shown in the following formula (Formula (2)). The concept of setting the threshold coefficient α will be described later.

Α = (Et / Ep1) −0.1 (2) The ultrasonic probe 2 is moved to the measurement position of the measuring object 1 in S2, and the measuring object is measured by the ultrasonic probe 2 in S3. The ultrasonic wave is incident on the first ultrasonic wave 1, and the transmission wave 10 obtained by the ultrasonic wave on S4 and the bottom surface reflected wave 11 as shown in FIG. In S5, the peak value (maximum echo height) Ep of the echo height is detected from the bottom reflected wave 11 captured as shown in FIG. 4, and in S6, the threshold coefficient α and the bottom reflection previously stored in S1 are stored. The wave rising direction and the like are called from the storage unit 7. In step S7, the threshold value E1 is calculated from the peak value (maximum echo height) Ep and the threshold coefficient α input from the input unit 8 by the following equation. In addition, after S6, the calculation unit 6 of FIG.

E1 = α · Ep (3) At S8, the threshold value E1 is set in the direction opposite to the rising direction of the bottom surface reflected wave 16 (FIG. 6), that is, in the negative direction in this case. In S9, the first intersection point u between the threshold value E1 and the bottom surface reflected wave 11 is detected. In S10, the gate 14 for one cycle is set on the time axis with the intersection u as the starting point of time as an arbitrary time (gate) on the time axis for waveform determination.
At 1, the peak value Es of the echo height between the gates 14 and its time Tv are detected.

At S12, the peak value Es of the bottom reflected wave 11 is obtained.
From the time Tv at which 3 /
The time point traced back to the time tm up to four cycles is defined as the rising time point (reflected wave reception time point) Ts of the bottom surface reflected wave 11.

In S13, the rising time T1 is obtained from the threshold value of the transmission wave (not shown) as shown in FIG. At S14, the rising time T1 of the transmission wave obtained at S13
Is the transmission time, and the rising time Ts of the bottom surface reflected wave obtained in S12 is the reflected wave reception time, and the time (road length) t of the ultrasonic measurement object is calculated.

In step S15, the wall thickness D is calculated from the time t and the sound velocity C from the above equation (1). If measurement is continued in S16, S
Returning to step 3, the measurement position is moved and measurement is performed.

Now, according to the experiments by the present inventors, in FIG. 4, the peak value of the echo height (maximum echo height) Ep
Although it is easy to obtain a waveform that shows,
The times at which the peak value Ep is displayed appear at different places, and the rise of the reflected wave becomes small under the influence of the forest echo. However, the waveforms between the ½th cycle and the first cycle from the rise of the reflected wave are not affected by the scattered wave and the forest echo, and the time Tv at which the waveform shows the peak value Es is extremely uniform. I found it.

Therefore, in order to obtain the waveform having the time Tv, the threshold value E1 is obtained from the maximum echo height Ep to obtain the gate 14
By setting, the waveform of the peak value Es can be easily obtained from the waveform and the time Tv can be obtained.

The threshold coefficient α obtained by the equation (2) is the equation (3), which is the idea determined by the equation (2).
This is because the threshold value E1 obtained from this takes a value of 0 <E1 <Es (4), and the waveform of the peak value Es can be easily obtained.

That is, since the rising time of the reflected wave itself is not known, the threshold value E1 is set in the opposite direction based on the rising direction (characteristic) peculiar to the ultrasonic probe 2 obtained in the test piece. The first waveform exceeding this threshold value E1 is the waveform of the 1/2 cycle and the 1st cycle from the rise of the reflected wave,
That is, it is possible to obtain a waveform in which the time Tv of the peak value Es is uniform without being affected by the scattered wave or the forest echo described above.

As the ultrasonic probe, there are a high-sensitivity type in which the reflected wave reflected on the display unit 9 lasts for a relatively long time and a high-resolution type in which the reflected wave is attenuated early. Thing 1
Depending on the degree of absorption of ultrasonic waves in, the ultrasonic probes of any of the above types show the same tendency in the rising condition of the bottom surface reflected wave. Therefore, according to the present invention, it is possible to obtain the waveform having the peak value Es by using the threshold value E1 to obtain the rising time Ts of the bottom surface reflected wave and to calculate the wall thickness D.

Further, if the 3/4 cycle is traced back from the time Tv based on the oscillation frequency peculiar to the ultrasonic probe 2, the rising time Ts of the reflected wave can be easily obtained as the reflected wave receiving time. Is.

A high resolution ultrasonic probe was used to measure the wall thickness of the object to be measured with rough front and back surfaces where scattered waves and forest echoes are likely to occur.
The number of times was 19.99 mm, and the average value of wall thickness measurement (30 times) measured by the conventional method was 17.32 mm, but the average value of wall thickness measurement (30 times) measured by the method of the present invention was 30.
The number of turns is 19.76 mm, and when the time of measurement with a caliper is used as a guide, a result with even smaller error was obtained compared to the conventional method.

[0031]

Further, in the above embodiment, the path length is obtained using the transmitted wave and the bottom reflected wave of the measurement object at the first time (first order). For example, the path length may be obtained by utilizing the bottom surface reflected waves of the measurement object between the first time (first order) and the second time (secondary).

It should be noted that the ultrasonic probe 2 is replaced by the transmitter 3, receiver 4, and measuring section 5 of the device configuration section shown in the above embodiment.
The computer unit may be used as the calculation unit 6 and the storage unit 7, the input unit 8 may be a keyboard, and the display unit 9 may be a display.

[0034]

As described above, according to the present invention,
Accurate wall thickness measurement is possible even when affected by forest echo and scattered waves in wall thickness measurement by ultrasonic waves.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an ultrasonic wall thickness measuring apparatus according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a first embodiment of the present invention.

FIG. 3 is a diagram showing bottom surface reflected waves generated by ultrasonic measurement.

FIG. 4 is an enlarged view of a bottom surface reflected wave shown in a part shown in FIG.

FIG. 5 is a diagram showing a transmitted wave and a bottom surface reflected wave generated by ultrasonic measurement.

FIG. 6 is an enlarged view of a bottom surface reflected wave shown in a portion B shown in FIG.

[Explanation of symbols]

1 ... Object to be measured 2 ... Ultrasonic probe 3 ... Transmitter 4 ... Receiver 5 ... Measuring unit 6 ... Calculation unit 7 ... Storage 8 ... Input section 9 ... Display 11, 16, 17 ... Bottom reflected wave 14 ... Gate 15 ... transmitted wave 18 ... Threshold

Front Page Continuation (72) Inventor Tetsuya Tominaga 2-28-4 Shinto Higashi, Tsuchiura-shi, Ibaraki Hirate Techno Engineering Co., Ltd. Tsuchiura Works (72) Toshiyuki Yamaguchi 2-28 Shinto Higashi, Tsuchiura, Ibaraki Prefecture No. 4 Nitrate Techno Engineering Co., Ltd. Tsuchiura Works (56) References JP 10-132927 (JP, A) JP 2-134511 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01B 17/00-17/08 G01N 29/00-29/28 G01S 1/72-1/82 G01S 3/80-3/86 G01S 5/18-5/30 G01S 7/52- 7/64 G01S 15/00-15/96

Claims (3)

(57) [Claims] 1. Obtaining the transmission time of ultrasonic waves from the front surface of an object to be measured and the reception time of reflected waves of ultrasonic waves from the back surface of the object to be measured, the wall thickness of the object to be measured is calculated from the interval between both times. In the thickness measurement method using ultrasonic waves to be measured, the rising direction of the reflected wave of the ultrasonic probe is obtained using a test piece with smooth front and back surfaces, and the reflected wave of the reflected wave on the measurement object is measured by the ultrasonic probe. The maximum echo height is obtained, a threshold value is set based on the maximum echo height in the direction opposite to the reflected wave rising direction with respect to the reflected wave, and the waveform of the reflected wave that first exceeds this threshold value. In the method of measuring wall thickness by ultrasonic wave, the time at which the maximum value is obtained is obtained, and the time that is 3/4 cycle back from this time is set as the reflected wave reception time. 2. An ultrasonic wave transmission time from the front surface of the measurement object and a reflected wave reception time of the ultrasonic wave from the back surface of the measurement object are obtained, and the wall thickness of the measurement object is calculated from the interval between the both times. In the measurement, a means for storing the rising direction of the reflected wave of the ultrasonic probe that receives ultrasonic waves from the back surface of the measurement object and that receives ultrasonic waves on the surface of the measurement object, the measurement object Means for setting a threshold value in the direction opposite to the rising direction of the reflected wave with respect to the reflected wave based on the maximum echo height of the reflected wave, and showing the maximum value of the waveform of the reflected wave that first exceeds the threshold value An ultrasonic wall thickness measuring device comprising means for obtaining a time and setting a time obtained by tracing back a 3/4 cycle from this time as a reception time of the reflected wave. 3. The ultrasonic wave according to claim 2, wherein the rising direction of the reflected wave of the ultrasonic probe is obtained by using a test piece having smooth front and back surfaces. Wall thickness measuring device.