The present application claims the benefit of foreign priority to Japanese Patent Application No. 2013-229151 filed on Nov. 5, 2013, the contents of which are incorporated herein by reference.
1. Technical Field
The technical field relates to a method and a device for measuring an inside of a measured object by using ultrasonic waves propagating through the air.
2. Description of Related Art
As shown in
However, the difference of acoustic impedances between the measured object and the air is generally 1000 times or more, therefore, the transmittance of ultrasonic waves is low in the above related art example, which causes problems that a SN ratio (signal to noise ratio) is lowered and measurement accuracy is low.
Accordingly, this disclosure has been made for solving the above problems and a measured object thereof is to provide a highly-accurate ultrasonic measuring method and device by increasing the transmittance of ultrasonic waves.
In order to achieve the above object, this disclosure provides an ultrasonic measuring method for measuring an inside of a measured object by using ultrasonic waves propagating through the air, which includes attaching a sheet having an acoustic impedance higher than the air as well as lower than the measured object to the measured object and measuring the inside of the measured object to which the sheet is attached by using a sensor.
This disclosure also provides an ultrasonic measuring device measuring the inside of a measured object by using ultrasonic waves propagating through the air, which includes a sheet having an acoustic impedance higher than the air as well as lower than the measured object, an attaching mechanism configured to attach the sheet to the measured object and a sensor configured to measure the inside of the measured object to which the sheet is attached.
As described above, according to this disclosure, highly accurate ultrasonic measuring method and device can be realized by performing ultrasonic measurement of the measured object through the sheet.
Hereinafter, embodiments will be explained with reference to the drawings.
In
Here, the transmittance of the ultrasonic wave 2 is compared between the embodiment and the related art example. Acoustic impedances of the air, the measured object 3, the sheet 101 and the sheet 102 are respectively set to Z1, Z2 and Z3. In this case, the ultrasonic wave propagates through the air, the measured object 3 and the air in this order in the related art example shown in
T
conv.=4·Z1·Z2/(Z1+Z2)2 (Equation 1)
On the other hand, the ultrasonic wave propagates through the air, the sheet 101, the measured object 3, the sheet 102 and the air in this order in the present embodiment shown in
T
exe1=16·Z1·Z2·Z32/{(Z1+Z3)2·(Z3+Z2)2} (Equation 2)
When the measured object 3 is copper and the sheet 101 as well as the sheet 102 are cis-butadiene rubber, respective acoustic impedances are Z1=408 Ns/m, Z2=4.49×107 Ns/m and Z3=1.5×106 Ns/m. In this case, the transmittance Tconv. equals to 3.63×10−5 based on Equation 1. Then, the transmittance Texe1 in the embodiment shown in
In this case, it is desirable to set a thickness “t” of the sheet 101 and the sheet 102 to a value defined by Equation 3 in the embodiment. The transmittance of the ultrasonic wave can be improved more by satisfying a condition of Equation 3.
t=Vs/(4×fo) (Equation 3)
Here, “Vs” denotes an acoustic velocity of a longitudinal wave of the sheet 101 and the sheet 102, and “fo” denotes the center frequency of the ultrasonic sensor 1 and the ultrasonic sensor 4. Respective components are set so as to satisfy Equation 3, thereby minimizing reflection at respective interfaces of the sheet 101, the sheet 102, the measured object 3 and the air as well as maximizing the transmittance of the ultrasonic wave 2. As the sheet 101 and the sheet 102 having an acoustic velocity of a longitudinal wave Vs=1590 m/s and the ultrasonic sensors 1 and 4 having the center frequency fo=800 kHz are applied in the embodiment, the thickness of the sheet 101 and the sheet 102 is set to 0.5 mm based on Equation 3.
Next, preferable acoustic impedances in the sheet 101 and the sheet 102 will be explained.
Accordingly, materials satisfying a condition in which the acoustic impedance is higher than the air as well as lower than the measured object 3 are applied for the sheet 101 and the sheet 102 of
Here,
The measuring device 301 includes a position “B” where sheet attaching mechanisms 302 and 303 are disposed, a position “C” where ultrasonic sensors 1 and 4 are disposed and a position “D” where sheet detaching mechanisms 304 and 305 are disposed. The measuring device 301 attaches the sheets to obverse and reverse surfaces of the measured object 3 at the same time. The measuring device 301 also detaches the sheets from the obverse and reverse surfaces of the measured object 3 at the same time.
The measured object 3 is conveyed from a position “A” to the position “B” of the measuring device 301 by a conveying means 306, then, sequentially conveyed in the order of the positions “B”, “C” and “D” in the measuring device 301, and finally, conveyed to a position “E” which is the outside of the measuring device 301. As the measured object 3 is sequentially supplied to the position “A”, plural measured objects 3 are fed into the measuring device 301, and work is performed in the positions “B”, “C” and “D” in parallel. The conveying means 306 is, for example, a belt conveyer conveying the measured object 3 by supporting two edges at both ends of the measured object 3 by two belts, which has an opening at the center so that measurement by the ultrasonic sensors 1 and 4 in the position “C” can be performed on the belt conveyor.
The sheet attaching mechanisms 302 and 303 include, for example, a robot which can perform triaxial drive and a suction nozzle. Plural sheets 101 and 102 previously prepared in a sheet supply means 307 are sequentially conveyed to obverse and reverse surfaces of the measured object 3 by the suction nozzle, and the sheets 101 and 102 are pressed onto the obverse and reverse surfaces of the measured object 3 with a pressurizing force of approximately 10N. Accordingly, the sheet attaching mechanisms 302 and 303 configured to attach the sheets 101 and 102 to both surfaces as principal surfaces of the measured object 3. The sheet detaching mechanisms 304 and 305 also include the robot which can perform triaxial drive and the suction nozzle, sucking the sheet 101 and the sheet 102 stuck to both surfaces of the measured object 3 respectively by the suction nozzle to peel off (detach) the sheets. The sheet 101 and the sheet 102 which have been peeled off are conveyed to a sheet collecting means 308. The sheet 101 and the sheet 102 which have been collected by the sheet collecting means 308 are disposed on the sheet supply means 307 and used again. The above sheet attaching mechanisms 302, 303, the sheet detaching mechanisms 304, 305, the ultrasonic sensors 1, 4, the conveying means 306, the sheet supply means 307 and the sheet collecting means 308 are arranged on a frame 309 of the measuring device 301.
Next, the flow of the ultrasonic measuring method according to the embodiment will be explained in accordance with a flowchart of
Next, Step S102 of
Lastly, Step S103 of
These steps of S101 to S103 can be executed in parallel when plural measured objects 3 are sequentially measured. Accordingly, even when the attaching/detaching steps of the sheets are performed as in the embodiment, the sensitivity of ultrasonic waves which can be received can be improved without extending the measurement time per one measured object as compared with the related art example.
Although the sheet 101 and the sheet 102 of
In the present embodiment, other mechanism can be applied in addition to the sheet attaching mechanisms 302, 303 and the sheet detaching mechanisms 304, 305. For example, it is preferable to apply a mechanism as the sheet attaching mechanism 302 and 303, in which the sheet 101 and the sheet 102 are arranged at ends of a mechanism which holds the measured object 3 by sandwiching the measured object 3, holding the measured object 3 and allowing the sheet 101 and the sheet 102 to closely contact measured surfaces of the measured object 3 in the position “B”. In this case, the sheet detaching mechanisms 304 and 305 may nave a structure in which the holding of the measured object 3 is released as well as the sheet 101 and the sheet 102 are detached from the measured object 3 in the position “D”. Such mechanism is preferable when a turn-table system is applied as the conveying means.
Although the sheet 101 and the sheet 102 are attached to both surfaces of the measured object 3 in the embodiment, it is also preferable that the sheet is attached only to one side of the measured object 3. For example, when only the sheet 102 is provided without the sheet 101, the ultrasonic wave 2 propagates through a path of the air, the measured object 3, the sheet 102 and the air in this order, and a transmittance Texe2 in this case is represented by Equation 4.
T
exe2=8·Z1·Z2·Z3/{(Z1+Z2)·(Z2+Z3)·(Z3·Z1)} (Equation 4)
The transmittance Texe2 is 7.03×10−5 from Equation 4 in this case, and a ratio with respect to the transmittance Tconv. in the related art example (Texe2/Tconv.) is 1.93. That is, the transmittance of ultrasonic waves is improved 1.93 times also when the sheet is attached only to one side. In this case, it is more effective that the sheet 102 is attached only to the surface facing the ultrasonic sensor 4 for reception in principal surfaces of the measured object 3. The sheet 102 is set to a size necessary for measurement, thereby relatively reducing effects of ultrasonic waves 2 propagating through paths not necessary for measurement and improving the S/N ratio. More specifically, the ultrasonic wave 2 is scattered inside and is emitted from the measured object 3 to the air also including reflection waves (noise) in portions which are not measured. The effects of noise can be alleviated by the sheet 102. In the case where the sheet 101 is not provided, for example, a pulse laser which directly introduces ultrasonic waves to the surface of the measured object 3 can be used instead of using the ultrasonic sensor for transmission 1.
The internal measurement is realized by using the ultrasonic wave 2 which has been transmitted through the measured object 3 in
As it is necessary to separate the ultrasonic wave 2 reflected on the surface of the measured object 3 and the ultrasonic wave reflected on the gap defect 503 inside the measured object 3 in the case of the structure shown in
The structure of
As described above, the sensitivity of ultrasonic waves can be improved also in the ultrasonic measuring method by a pulse reflection method which performs measurement only from one side surface of the measured object 3 by using the ultrasonic sensor 501 for transmission/reception.
In the ultrasonic measuring method by the transmission method as shown in
When the sheet 101 and the sheet 102 do not affect the measured object 3, it is not always necessary to perform the process of Step S103. In this case, it is not always necessary that the measuring device 301 of
Here, when the distance between the sheet 601 and the ultrasonic sensor 4 for reception is “L”, the shape of the concave portion on the surface of the sheet 601 is preferably a curved shape with a curvature of a radius “L”. That is, it is preferable that the ultrasonic sensor 4 is disposed in the center of the curvature in the concave portion having the curved surface provided on the surface of the sheet 601. The structure of
As described above, the sensitivity of ultrasonic waves to be received can be improved more according to the embodiment.
When the acoustic impedances of the air, the measured object 3, the first layer 801a (802a) and the second layer 801b (802b) are respectively set to Z1, Z2, Z3 and Z4, a transmittance Texe4 of the ultrasonic wave transmitting through the air, the second layer 801b, the first layer 801a, the measured object 3 and the first layer 802a, the second layer 802b and the air in this order can be represented by Equation 5.
T
exe4=64·Z1·Z2·Z32·Z42/{(Z1+Z4)2·(Z3+Z4)2·(Z2+Z3)2} (Equation 5)
The acoustic impedances of respective components are set based on Equation 5 as described above, the transmittance of the ultrasonic wave 2 can be improved. Specifically, when the acoustic impedances of the first layer 801a (802a) and the second layer 801b (802b) are respectively set to 1.5×106 Ns/m and 9×105 Ns/m, the transmittance Texe4 is 2.13×10−4 based on Equation 5, and a ratio of the transmittance Texe4 of the present embodiment with respect to the transmittance Tconv. in the related art example (Texe4/Tconv.) is 5.85. Consequently, according to the embodiment, approximately 5.85 times improvement of transmittance can be expected as compared with the related art example, and the sensitivity of ultrasonic waves to be received can be improved more.
In the present embodiment, cis-butadiene rubber is applied for the first layers 801a and 802a. A resin obtained by mixing plural hollow glasses having approximately 10 μm in diameter to reduce the density and thereby lower an apparent acoustic impedance is used for the second layers 801b and 802b. The flexible rubber material is used for the first layers 801a and 802a which contact the measured object 3, thereby increasing adhesion with respect to the measured object 3 and securing work efficiency. Additionally, the layer closer to the acoustic impedance of the air is applied for the second layers 801b and 802b, the transmittance of the ultrasonic wave 2 can be improved more.
It is possible to realize highly accurate measurement by allowing the sheet 801 to include the first layer 801a and the second layer 801b having a lower acoustic impedance than the first layer 801a as described above. The highly accurate measurement can be also realized by allowing the sheet 802 to include the first layer 802a and the second layer 802b having a lower acoustic impedance than the first layer 802a.
It is desirable to set a thickness “t” of the sheets 801 and 802 to be a value defined by Equation 3. The transmittance of ultrasonic waves can be improved more by satisfying the condition of Equation 3.
Among the above-mentioned various embodiments and modified examples, arbitrary embodiments or modified examples can be appropriately selected and combined to achieve their respective effects. For example, the concave portion having the curved surface applied in Embodiment 2 may be applied to the second layer 802b in
The embodiments can be also applied to applications such as ultrasonic inspection with respect to the inside of electronic devices and structures such as vehicle bodies.
Number | Date | Country | Kind |
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2013-229151 | Nov 2013 | JP | national |