Measuring and testing – Vibration – By mechanical waves
Patent
1990-05-01
1992-06-02
Chapman, John E.
Measuring and testing
Vibration
By mechanical waves
G01N 2904
Patent
active
051176971
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an ultrasonic flaw detector for inspecting the surface condition of a specimen or the existence or non-existence of one or more internal defects in the specimen by radiating ultrasonic waves to scan the specimen and then analyzing waves reflected by the specimen.
BACKGROUND ART
Ultrasonic flaw detectors can detect internal defects of specimens without destruction of the specimens and are employed in many fields. The existence or non-existence of a defect inside a specimen is checked over a predetermined area of the specimen in many instances. In this case, the inspection is conducted by scanning the above-described area of the specimen with ultrasonic waves radiated from a probe. Actually employed as such a probe includes an array probe constructed of many piezoelectric elements arranged in a line. An ultrasonic flaw detector making use of such an array probe will hereinafter be described.
FIG. 1 is a perspective view of a scanner unit of the conventional ultrasonic flaw detector. FIGS. 2(a) and 2(b) are plan and side views of an array probe, respectively. In each of the drawings, there are shown a water tank 1 for inspection, water 2 charged in the water tank 1, and a specimen 3 placed on the bottom wall of the water tank 1. Designated at numeral 4 is a scanner, which is constructed of the following members: a scanner table 5 on which the water tank 1 is mounted, frames 6 fixed on the scanner table 5, an arm 7 extending between the frames 6, a holder 8 mounted on the arm 7, a pole 9 pendant from the holder 8, and an array probe 10. The frames 6 can move the arm 7 in the direction of Y-axis by an unillustrated mechanism, while the arm 7 can move the holder 8 in the direction of Y-axis by a mechanism which is free of illustration. Further, the holder 8 can move the array probe 10 in the direction of Z-axis (the direction perpendicular to X-axis and also to Y-axis) in association with the pole 9 by means of a mechanism (not shown).
The array probe 10 is constructed of a number of minute piezoelectric elements (hereinafter called "array elements") arranged in a line. The direction of arrangement of the array elements is in conformance with the direction of X-axis. Whenever a pulse is applied, each array element radiates an ultrasonic wave and then converts a reflected wave of the ultrasonic wave by the specimen 3 to a corresponding electrical signal. The individual array elements are indicated by numerals 10.sub.1 -10.sub.n in FIGS. 2(a) and 2(b), in which dots indicate points of sampling. Symbol YP indicates the sampling pitch in the direction of Y-axis, while symbol XP represents the sampling pitch in the direction of X-axis. In addition, symbol AP shows the pitch between the adjacent array elements 10.sub.1 -10.sub.n. Designated at numeral 11 is a casing in which the array probe 10, etc. are accommodated.
Here, the function of the array probe 10 shown in each of the above drawings is described in brief with reference to FIGS. 3(a) and 3(b). In FIG. 3(a), there are illustrated array elements T.sub.1 -T.sub.9 arranged in a line, delay elements D.sub.1 -D.sub.9 connected to the respective array elements T.sub.1 -T.sub.9, and pulses p to be inputted to the respective array elements T.sub.1 -T.sub.9. The delay elements D.sub.1,D.sub.9 have been set at the same delay time (t.sub.19). Likewise, the delay elements D.sub.2,D.sub.8 at the same delay time (t.sub.28), the delay elements D.sub.3,D.sub.7 at the same delay time (t.sub.37), and the delay elements D.sub.4,D.sub.6 at the same delay time (t.sub.46). The relationship among the delay times thus set can be expressed by the following inequality:
Now, the delay times of the individual delay elements D.sub.1 -.sub.9 are set at desired values while maintaining the relationship of the inequality (1), and the pulses p are inputted. From the array elements T.sub.1 -T.sub.9, ultrasonic waves are then radiated in accordance with the delay times so set, i.e., first from the array elements T.sub.1,T.sub.9 and last from
REFERENCES:
patent: 4135140 (1979-01-01), Buchner
patent: 4589284 (1986-05-01), Breimesser et al.
Patent Abstract of Japan, vol. 8, No. 242 (p. 311)(1697) Nov. 7, 1984 & JP-A-59 116542 (Kobe Seikosho K.K.) Jul. 5, 1984.
Patent Abstracts of Japan, vol. 7, No. 260 (p. 237)(1405) Nov. 18, 1983, & JP-A-58 143265 (Nihon Denpa Kogyo K.K.) Aug. 25, 1983.
Patent Abstracts of Japan, vol. 7, No. 98 (p. 664) Aug. 22, 1987 & JP-A-62 191757 (Nippon Steel Corp.) Aug. 22, 1987.
Sasaki Souji
Takishita Yoshihiko
Chapman John E.
Hitachi Construction Machinery Co. Ltd.
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