Image analysis – Applications – Manufacturing or product inspection
Reexamination Certificate
2001-05-15
2004-12-28
Metha, Bhavesh M. (Department: 2625)
Image analysis
Applications
Manufacturing or product inspection
C702S034000
Reexamination Certificate
active
06836561
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods and apparatuses for detecting defects in an object having projected portions formed in the same shape with a predetermined pitch along an arc, the object including, for example, an external gear, an internal gear, a sprocket, or a mechanical element having projected portions equivalent to those modules along part of an arc. More particularly, the present invention relates to a method and apparatus preferably used for detecting a chipped portion in an object such as castings or sintered products, on the tip of the projected portion of which a defect or flaw may be easily formed.
2. Description of the Related Art
Known as a defect detection method and apparatus of this type is such that the reference image data of a good object is predetermined and then the image data of an inspected object is compared with the reference data to thereby determine if a rejectable defect exists on the object.
Now, a conventional defect detection method and apparatus of this type will be briefly explained below with reference to the conceptual view of a processing procedure shown in FIG.
8
and the view of the processing principle shown in FIG.
9
.
In the conventional defect detection method and apparatus, first, as the pre-processing for the actual inspection of a defect, an object having a proper shape with no defect is positioned in place and then the image data of the object is obtained as shown in FIG.
9
(
a
) (step a
1
of FIG.
8
).
Subsequently, the image data is stored in an image processing apparatus or the like as the reference image data for determining if a defect exists on an inspected object (step a
2
of FIG.
8
). As shown in FIG.
9
(
a
), the frame of image data contains information on the position of the object, that is, information as to where the object is placed in the view field of the camera. More specifically, this positional information represents addresses in a frame memory.
In addition, in this pre-processing step, an operator manually inputs criteria such as allowable errors in dimension or shape of the object for determining that the object is acceptable, considering the properties of the object such as the shape, size or the like (step a
3
of FIG.
8
). Excessively exacting tolerances would provide excessively tightened GO/NO-GO criteria, whereas loosely determined tolerances would provide inaccurate GO/NO-GO criteria.
Upon inspection of a newly manufactured object, the object to be inspected is placed in the same position as that of the good object placed to prepare the reference image data mentioned above (step a
4
of FIG.
8
). Then, a frame of image data of the inspected object is obtained in the same manner as described above as shown in FIG.
9
(
b
) (step a
5
of FIG.
8
). Incidentally, as shown in FIG.
9
(
b
), it should be understood that the inspected object is supposed to have a defect on its circumference portion in its image frame, with a portion corresponding to the defect being indicated qualitatively with a hollow circle.
Then, the image data registered beforehand as described above, or the reference for a determination of whether the object is acceptable, is read into the image processing apparatus, and thereafter the reference image data and the currently captured image data of the inspected object are compared with each other to output the difference therebetween (step a
6
of FIG.
8
). In practice, the two frames of image data are compared bit by bit with each other in the frame memory of the image processing apparatus to output the portions having inconsistencies in density. Accordingly, the difference between the reference data of FIG.
9
(
a
) and the inspection data of FIG.
9
(
b
) can be outputted qualitatively in the form of a hollow circle as shown in FIG.
9
(
c
).
In other words, the size of the area of the circle indicates the degree of inconsistency in density between the two, with a smaller area indicating a less degree of inconsistency and a larger area indicating a higher degree of inconsistency.
Thus, it is finally determined that the inspected object is acceptable if the degree of inconsistency or the output level of difference does not exceed the aforementioned criteria but determined that the object is rejectable if the output level of difference exceeds the criteria (step a
7
of FIG.
8
).
However, as described above, the frames of image data of FIGS.
9
(
a
) and
9
(
b
) contain information regarding the position of the object in s frame. If the object is not properly positioned in place upon preparation of reference image data or inspection of the object, this would provide an increased output level of difference due to a shift in position and thereby result in determining that the object is rejectable even if the object is actually acceptable.
On the other hand, if the object has a generally round outer diametric contour such as an external gear, an internal gear, or a sprocket and has been positioned in place exactly in the same way, even when the outer periphery of the object abuts a jig or the like and the object is thereby positioned precisely in place, a shift in orientation caused by the rotation of the object in the place cannot be controlled. Thus, the shift in rotational orientation of the object would lead to an inconsistency in position of the projected portions on the outer periphery even when the outer diametric portion of the object is pushed against the jig or the like to position the center of the object with accuracy. This inconsistency would cause the aforementioned output level of difference to increase, thereby making it rather difficult to properly determine whether a defect exists on the object.
As described above, the conventional defect detection method and apparatus of this type had a drawback of making it extremely difficult to determine whether a defect exists on the object, due to a shift in position of the placement or in rotational orientation of the object.
In addition, as is obvious from the aforementioned operation principle, it is necessary to prepare individual reference data and criteria for each size and shape of an inspected object of a different type in order to determine whether the object is acceptable. Thus, this raises such problems that the preparation is laborious and requires storage means having an increased capacity for storing a plurality of types of reference data and criteria.
The GO/NO-GO criteria are also affected by a shift in position of the placement and in rotational orientation of the object, and thus no reasonable guidance is available for determining the magnitude of the criteria. This raises a problem of making it difficult to provide criteria which allow a precise determination of whether the object is acceptable.
Furthermore, with the conventional apparatus of this type, it is commonly practiced that an inspected object is illuminated with light and then the reflected light is used for imaging the object to generate image data thereof. Thus, in some cases, depending on the relationship between the color of the inspected object and a background color, the apparatus would have a drawback of making it impossible to provide a sufficient contrast required for generating a binary image from the image information of the object.
Furthermore, shades or the like caused by ambient light have an effect on a determination of whether the object is acceptable. Thus, it is very difficult to always provide an optimum inspection environment.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a defect detection method and system which eliminate the aforementioned drawbacks of the prior art, which always provides a correct determination of whether an object such as a gear or a sprocket is acceptable even with a shift in position of placement or in rotational orientation of the object, and which require no laborious preparation and facilitate the setting of GO/NO-GO criteria.
The present invention provides a method for detecting a defect on an
Miyahara Yutaka
Murota Naoya
Nakajima Tsuyoshi
Takeshi Masami
Greenblum & Bernstein P.L.C.
Hung Yubin
Metha Bhavesh M.
Suzuki Motor Corporation
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