Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Patent
1988-06-20
1990-04-03
Eisenzopf, Reinhard J.
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
324263, 324691, G01R 2714, G01R 2726, G01N 2782
Patent
active
049143786
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an apparatus for finding defects such as cracks that are initiated in metal materials and to a method thereof, and more specifically to an apparatus for precisely detecting the shape of crack and to a method thereof.
BACKGROUND ART
A potential method has heretofore been employed for detecting defects such as cracks were initiated in the metal materials. The potential drop method has been described, for example, in Japanese Patent Publication No. 2593/1975 and Japanese Patent Laid-Open No. 160054/1982.
The conventional apparatus for detecting defects on the surfaces of materials based upon the potential drop method employs a so-called four-terminal method. According to the four-terminal method which employs a probe in which are arranged in alignment a pair of power supplying electrodes and a pair of potential difference-measuring electrodes on the inside thereof, the surfaces of metallic structural members are scanned to measure the change in the potential distribution thereby to detect surface defects such as cracks. That is, the potential difference in a flawless region is used as a reference potential, and it is determined that a defect exists in a place if the potential difference there is greater than the reference potential.
In a large metal structure, initiation of surface cracks does not mean that its life has expired; i.e., the structure in many cases can be used for considerably extended periods of time even after defects have been initiated. The life after the surface defects have been initiated may often be longer than the period before the defects are initiated. It is therefore important to monitor the progress of surface defects from the standpoint of using the structure effectively for extended periods of time maintaining safety.
According to the conventional apparatus having a pair of power supplying electrodes, however, the electric current is not uniformly distributed due to a change in the shape of a member in a measuring region and makes it difficult to determine the reference potential for measurement. Furthermore, determination of the shapes of surface defects lacks precision which makes it difficult to precisely monitor the growth of surface defects. Due to the spread of current, furthermore, inspection is affected by the change of shapes near the measuring regions and by the neighboring defects.
DISCLOSURE OF INVENTION
The object of the present invention is to provide a novel method of and apparatus for detecting surface defects, which is capable of monitoring defects in the surface of a metal material maintaining high precision.
It is a further object of the invention to provide a novel method and apparatus for inspecting surface defects wherein power supplying electrodes are formed in a plural pairs maintaining a freedom of displacement, and a electrode position control unit is provided which causes said power supplying electrode pairs to undergo displacement to determine their positions based upon the current distribution on the inside of said pairs of power supply electrodes, and wherein a non-uniformity signal of current distribution due to a change of shape of the measuring region is received by said electrodes position control unit which produces control signals to change the positions of each of the pairs of power supplying electrodes to offset the non-uniformity, in order to uniformalize the current distribution.
Another object of the invention is to provide a novel method and apparatus for inspecting surface defects wherein power supplying electrodes are formed in a plurality of pairs, and a current control unit is provided to change currents that will be supplied to each of the pairs of power supplying electrodes depending upon the current distribution on the inside of said pairs of power supplying electrodes, and wherein a non-uniformity signal of current distribution is received by the current control unit which produces control signals to change currents that will be supplied to the pairs of power supply electrodes
REFERENCES:
patent: 4656595 (1987-04-01), Hognestad
patent: 4683419 (1987-07-01), Neuelman
patent: 4764970 (1988-08-01), Hayashi et al.
patent: 4789829 (1988-12-01), Stribling
IBM Technical Disclosure, H. Hova, Measuring Thickness and Resistance of Semiconductor Layers, vol. 6, No. 2, Jul. 1963.
Hayashi Makoto
Naruse Akisuke
Ootaka Masahiro
Takaku Kazuo
Eisenzopf Reinhard J.
Hitachi , Ltd.
Solis Jose M.
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