JP2758654B2 - Ultrasonic surface roughness measurement method for solids - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for measuring surface roughness of a solid, a step on a surface of a solid, and the like by using ultrasonic waves.

[Prior art] The conventional method for measuring the surface roughness of a solid is a method for determining the surface roughness based on the definition and display of the surface roughness defined in JISB0601, or manufactured based on JISB0601. In addition to the method of comparing and measuring the specimen using a standard specimen of surface roughness, the optical method shown in FIG. 8 described below, the method using ultrasonic waves shown in FIG. 9, and the like are generally used. It had been.

FIG. 8 shows an example of an optical method, showing the principle thereof. When the surface of the subject 1 is displaced in the direction A or B shown by the arrow in the figure, the reflected light of the spot irradiated from the semiconductor laser 3 in the head 2 via the light projecting lens is changed to the light position detecting element 4 in the head 2. Is moved through the light receiving lens and moves on the light position detecting element 4 in the direction of arrow A 'or B'. The movement of this spot is converted to a digital signal,
After data processing such as linear correction and averaging is performed by three CPUs (CPU1, CPU2, and CPU3 in the figure), a numerical value of the surface roughness is output as a measurement result.

FIG. 9 shows an example of a method using ultrasonic waves, in which the surface roughness is measured by a water immersion method. FIG. 9 (a) shows water 6
The subject 1 immersed in the same water 6 from the probe 5 immersed in
FIG. 9 is a diagram in which an ultrasonic wave is radiated on the smooth plane 1a of FIG. 1, a reflected wave from the subject surface 1a is received by the probe 5, and an echo 7 of the received reflected wave is displayed on an A scope. b)
When ultrasonic waves are radiated to the minute irregularities 1b present on the surface 1a of the subject, the ultrasonic waves are scattered on the irregularities 1b, the scattered reflected waves are received by the probe 5, and the received scattered reflected waves This is an A scope display of the echo 8. Since the level of the echo 8 is displayed lower than that of the echo 7, the correlation between the level of the unevenness 1b, that is, the roughness and the level of the echo 8 is previously obtained on the test piece, and the measured level 8 is compared with the measured level 8. To measure the roughness.

As another method of using ultrasonic waves, ultrasonic waves are obliquely incident on the surface of the subject by a water immersion method, and backscattered waves from surface roughness are detected. A method for measuring the height has been proposed. (For example, Non-Destructive Inspection, Vol. 37, No. 5, May 1988, pp. 411 to 412) [Problems to be Solved by the Invention] Among the above conventional methods, the method specified in JISB0601 Approximately 10 to 20 mm square, it is necessary to appropriately cut off the test piece from the test subject in order to insert the test piece into the roughness tester, and measure the surface roughness at an arbitrary position of the large-sized structure It is not possible. In addition, since a hard stylus (for example, a diamond needle) comes into contact with the surface of the test piece, it cannot be applied to a soft resin material, a rubber product, or the like in which a streak is formed by the contact. Next, the method of using a standard test piece of surface roughness is simple but difficult to display quantitatively, and it is difficult to measure in places where visual inspection is not possible, for example, in a space such as a pipe where an inspector cannot enter. is there.

The optical method shown in FIG.
It is a high-precision measurement method that can measure steps of about m, but the scanning accuracy directly affects the measurement accuracy due to the principle of this method, so it is necessary to perform scanning with a position accuracy several times higher than the surface step of the subject. In addition, it is not possible to measure materials that are altered by light.

In the method using the ultrasonic waves shown in FIG. 9, it is necessary that the ultrasonic beam radiated from the probe 5 always be incident perpendicularly to the subject surface 1a. There is a problem that scanning must be performed with a scanner having positioning means. And, in reality, it is possible to measure the irregularities 1b present on the subject surface 1a only when the smooth subject surface 1a is scanned by the high-precision scanner, but the roughness micro shape Therefore, the measurement accuracy is low, for example, the scattering echo direction is different, and even if the roughness is almost the same, a difference occurs in the received echo level.

Further, in another method using ultrasonic waves described in the above document, since the probe emits ultrasonic waves at an angle to a certain angle, the ultrasonic beam having a circular cross section emitted from the probe is The object surface is irradiated in an elliptical shape. Here, the minor axis of the ellipse is equal to the diameter D of the vibrator, and the major axis is equal to Dtanφ when the inclination angle is φ. From this, as described in the literature, the change in the echo level based on the roughness or unevenness of the surface of the object hardly occurs in the minor axis direction of the ellipse, and the ultrasonic wave incident on the surface of the object Most change in the vector of the major axis, which is the direction of travel. Also, depending on the angle of inclination of the probe, the roughness of the surface of the object or the shadow of the ultrasonic beam may be generated on the uneven portion, so that accurate measurement cannot be performed unless the object is scanned from various directions. Had a point.

The present invention has been made in view of the above-mentioned problems of the prior art, and is capable of easily and accurately measuring the surface roughness of a solid or a step on the surface of a solid, and a soft solid having a low hardness such as resin or rubber. It is an object of the present invention to provide a method for measuring the surface roughness of a solid by using an ultrasonic wave, which can be applied and measured.

[Means for solving the problem]

In order to achieve the above object, a method for measuring the surface roughness of a solid using ultrasonic waves according to the present invention is a point-focus type probe in which the center of a concave curved surface that emits ultrasonic waves blocks direct reflection echoes from the surface of the subject. The probe is positioned almost perpendicular to the surface of the subject, and is located farther than the focal length to emit ultrasonic waves, and the probe receives backscattered waves due to the roughness of the surface of the subject, and receives the backscattered waves. The echo level of the backscattered wave is measured by comparing it with a correlation value between the surface roughness obtained by measuring a test piece in advance and the echo level of the backscattered wave.

[Action]

Ultrasonic waves radiated from a point-focus type probe that is substantially perpendicularly opposed to the subject are focused before reaching the subject surface, and then reach the subject surface. At this time, the ultrasonic beam incident on the surface of the subject becomes a hollow circular donut because the center of the concave curved surface of the probe blocks the direct reflection echo from the subject, and the vector of the incident ultrasonic wave is equal. Become one-sided. Therefore, if the surface of the object on which the ultrasonic wave is incident is smooth without any irregularities or steps, the ultrasonic wave is specularly reflected on the surface of the object, and the specularly reflected wave has a donut shape. Not received by the tentacles.

However, for example, in the case of an object surface having roughness such as unevenness or a step on a part of a smooth surface, the ultrasonic wave incident on the object surface is specularly reflected on the surface of the smooth part as described above. Then, the reflected wave is not received, but on the rough surface, it is backscattered due to the roughness of the surface, and the backscattered wave is received by the probe. The received echo level of the backscattered wave is compared with a correlation value between the surface roughness previously measured by the test piece and the echo level of the backscattered wave, and the surface roughness of the subject is measured. Then, in this measurement, since the vector of the incident ultrasonic wave is isotropic as described above, the roughness can be measured by scanning in one direction irrespective of the shape or direction of the unevenness or the step, and the like. Because of the configuration for receiving backscattered waves, the relative position between the surface of the subject and the probe does not need to be maintained with high accuracy and a slight inclination is allowed.

〔Example〕

An embodiment of the present invention will be described with reference to FIGS. In the figure, the same reference numerals as those in FIG. 9 indicate the same parts.
In FIG. 4, reference numeral 9 denotes a cylindrical case, 10 denotes a disc-shaped vibrator provided in the case 9, 11 denotes a plano-concave acoustic lens mounted on the front surface of the vibration 10, and has a concave curved surface curvature. Is R. Reference numeral 12 denotes a masking material that is attached to the center of the concave curved surface of the acoustic lens 11 and masks the center of the acoustic lens 11. SN by directly blocking the reflected echo
Improve the ratio. 13 is a damper attached to the rear surface of the vibrator 10, and P is a point focus type probe having the above configuration.
FIG. 5 is a view taken in the direction of arrows V-V in FIG.

FIG. 1 is a view showing a state in which the surface roughness of the surface 1a of a subject is measured in water using the probe P, and the probe P is almost perpendicular to the surface 1a of the subject (strictly (It is not necessary to be vertical and a slight inclination is allowed.) In water 6, it is positioned farther than focal length 1 determined by the sound speed ratio between acoustic lens 11 and water 6. When an ultrasonic wave is emitted in this state, the ultrasonic wave shielded by the masking material 12 propagates with a beam indicated by oblique lines in the figure, and focuses at a focal length 1 before reaching the subject surface 1a, Further, the light propagates through the water 6 and reaches the subject surface 1a. The ultrasonic wave incident on the surface 1a of the subject is a hollow beam,
Since the beam propagates while expanding the beam diameter until 1a, the vector of the incident ultrasonic wave becomes the third on the subject surface 1a.
As shown in the figure, the beam becomes isotropic in the direction of the arrow from the center of the beam toward the outer circumference of the beam. Here, when the object surface 1a is smooth without irregularities or steps, the incident ultrasonic wave is specularly reflected on the object surface 1a as shown in FIG. Is not received by the probe P because it is reflected to

However, as shown in FIG.
If there are minute irregularities 1b in a part of the
The ultrasonic wave incident on the surface is specularly reflected on the smooth surface as described above, and the reflected wave is not received, but the unevenness 1b portion is backscattered due to its roughness, and the backscattered wave 14 is a probe. Received by P. The received echo level of the backscattered wave 14 is compared with a correlation value between the surface roughness previously measured by a test piece and the echo level of the backscattered wave, and the surface roughness of the subject 1 is measured. Subsequently, scanning is performed to move the position to be measured. At this time, since the vector of the ultrasonic wave incident on the surface 1a of the subject is isotropic as shown in FIG. It is possible to measure the surface roughness by scanning in one direction irrespective of the orientation and the like. In addition, since the backscattered wave 14 is received and measured, the subject surface 1a and the probe P may be almost vertically opposed using a normal precision scanner, which facilitates the measurement.

FIG. 6 shows a probe P 'having another configuration in place of the probe P.
A case 15 includes a hollow disk-shaped donut-shaped vibrator 16 having a concave curved surface with a curvature R and lacking the center of the concave curved surface, and a damper 17 attached to the rear surface of the vibrator 16. This is a point-focus type probe. Since the probe P 'has a donut shape by removing the center of the concave curved surface of the transducer 16 that emits ultrasonic waves, the probe P' is masked so as to block direct reflection echoes from the subject surface 1a. The same operation as the probe P shown in FIG. 4 is performed, and the measurement can be performed in the same manner as the probe P.

FIG. 7 shows an example of measuring the surface roughness of a solid using the method of the present invention. The horizontal axis is a step (unit: μm) on the surface of the object, and the vertical axis is a backscattered wave due to the step. Is the echo height (in dB). The figure shows a correlation in which the echo height increases with respect to the same step as the frequency of the probe used increases, and shows that a minute step can be measured as the frequency is increased. From the figure, it can be seen that at a frequency generally used in the prior art, a step of about 30 μm can be measured with high accuracy. By selecting a frequency, it is possible to measure a surface roughness of about 1 μm to several mm.

As can be understood from the above description, since the measurement of the present invention is performed in a non-contact state with the subject by the water immersion method (including the local water immersion method), the measurement is performed on a low-hardness soft solid such as resin or rubber. The present invention is also applicable to measurement of a large subject or a narrow part. Further, in the case where the condition of the inner peripheral surface of the pipe is measured by using a robot, a device that can use the method of the present invention at a tip portion or the like of the robot can be used to measure a dangerous height that the robot can reach. It becomes possible to measure the surface roughness such as the position.

〔The invention's effect〕

Since the present invention is measured by the method described above, the surface roughness of a solid or a step on the surface of a solid can be easily and accurately measured, and the method can be applied to a soft solid having a low hardness such as a resin. This also has an effect that can be applied and measured.

[Brief description of the drawings]

1 to 7 are explanatory views of an embodiment of the present invention. FIG. 1 is an explanatory view of a measurement state of the method of the present invention when the surface of the subject is smooth, and FIG. 2 is a part of the surface of the subject. FIG. 3 is an explanatory view of a measurement state in the case where minute irregularities are present in FIG.
FIG. 4 is an explanatory view of the vector of the ultrasonic wave on the surface of the subject in the view from the arrow I-III, FIG. 4 is a view showing an example of the probe used in the method of the present invention, and FIG. FIG. 6 is a view showing another example of the probe used in the method of the present invention.
The figure shows the relationship between the surface roughness measured using the method of the present invention and the echo height. FIG. 8 is a diagram showing an example of measuring the surface roughness by a conventional optical method, and FIG. 9 is a diagram showing an example of a method of measuring the surface roughness using a conventional ultrasonic wave. FIG. 9A is a diagram for a smooth subject, and FIG. 9B is a diagram for a case where minute irregularities exist on the subject surface.

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Yoshiaki Suzuki 650, Kandamachi, Tsuchiura-shi, Ibaraki Hitachi Construction Machinery Co., Ltd. (56) References JP-A-62-251609 (JP, A) JP-A-64-26145 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01B 17/00 -17/04 G01N 29/10

Claims (1)

(57) [Claims] 1. A point-focus type probe whose central part of a concave curved surface that emits ultrasonic waves blocks direct reflection echoes from the surface of an object, is arranged substantially perpendicular to the surface of the object and at a focal length. An ultrasonic wave was emitted at a farther position, a backscattered wave due to the roughness of the surface of the subject was received by the probe, and the echo level of the received backscattered wave was determined by previously measuring a test piece. A method for measuring the surface roughness of a solid by ultrasonic waves, which is measured by comparing the surface roughness with the correlation value between the echo level of the backscattered wave.