Optics: measuring and testing – Inspection of flaws or impurities – Transparent or translucent material
Reexamination Certificate
2000-06-21
2001-12-18
Pham, Hoa Q. (Department: 2877)
Optics: measuring and testing
Inspection of flaws or impurities
Transparent or translucent material
Reexamination Certificate
active
06331889
ABSTRACT:
FIELD OF THE INVENTION
The invention pertains to a method for inspecting an essentially large-area article which consists of at least two opposing, partially-transparent, outer layers and at least one intermediate layer located between the outer layers. In particular, the invention pertains to the optical inspection of an optical data media, for example, a DVD, which has the above described three-layer structure. Therefore, hereinafter the discussion of the present invention pertains primarily to a DVD. However, it should be readily apparent that the method of the present invention is not necessarily restricted to use on that specific article.
BACKGROUND OF THE INVENTION
As is known, an optical data medium, such as a CD, DVD, CD-R or similar item, can be sensed optically and the data of the recorded image points can be evaluated in order to detect any potential flaws. In general, light is applied to the data side and is reflected from the reflecting layer of the optical data medium and shines on an optical receiver, for example, a CCD-camera. The light is often shaped as line light which extends across a radius of the data side of the optical data medium. The optical data medium is rotated about its rotational axis perpendicular to its flat sides so that, to check one entire side, at least one complete rotation of the data medium is required.
Only one data side is used on a CD so that this kind of sensing need be performed only from one side. However, in the case of a DVD, both opposing, flat sides are designed as data sides. In this case, checking of both sides is necessary. Basically, a DVD is configured such that it has two outer, transparent, plastic layers coated with a reflective layer and an adhesive layer provided as an intermediate layer which joins the two outer plastic layers together. Thus, a data medium is created which can be read on both sides.
In addition to checking the finished products for potential flaws, it is also necessary to classify the flaws, on the one hand, to handle certain flaws with more strict inspection criteria, and on the other hand, to allow a specific intervention in the on-going production process. This prevents additional flaws from occurring during production. The essential factor in this case, among others, is to recognize potential flaws in the intermediate layer, since these flaws will have an effect on both data sides.
The flaws in the intermediate layer are detectable from both sides. However, each optical receiver sees only the side of the intermediate layer which it faces. Thus, as a rule, a flaw in the intermediate layer cannot be classified as such solely due to its pattern.
OBJECT OF THE INVENTION
The invention is based on the problem of defining a method of the kind described above, so that a flaw in the intermediate layer will be reliably and dependably recognized as such.
SUMMARY OF THE INVENTION
According to this invention, the problem is solved by a method in which the opposing sides of the article are optically sensed with at least two optical receivers. The data of the recorded image points of the one optical receiver are allocated to the data of the recorded image points of the other optical receiver in such a manner that the data of the opposing points of the article are allocated to each other and can be evaluated. The identification of a potential error in the intermediate layer takes place when the data of the opposing image points indicate an error in the case of both optical receivers. This has the advantage that the opposing image points will be handled as such, and their data can be evaluated accordingly. If both data sets of the mutually opposing points have values that correspond to a flaw, then it has to be assumed that this flaw is located in the intermediate layer. Thus, the flaw will be identified immediately as a flaw in the intermediate layer and can be further evaluated accordingly.
In particular, it is possible, in the case of a potential detected flaw in the intermediate layer, to specify another, in particular a smaller fault tolerance in the course of the evaluation, than for other flaws. Thus, the inspection method can operate more precisely. The entire test method thus has a better effectiveness (yield), since the other flaws need not be handled with the same, more stringent test conditions.
In accordance with one design format of the invention, it is possible that the optical receivers or the recorded images have a predefined, relative alignment to each other or to a reference position, where the allocation of the data of the recorded image points takes place by a transformation of the geometric data with respect to the relative alignment to each other or to the reference position. Accordingly, the allocation can be a coordinate transformation which can be carried out quickly and easily. Typically, the coordinate transformation will be restricted to an offset. In this regard, it can be expedient to use the alignment of an optical receiver as a reference position so that only the data of the image points of the other optical receiver is required to be transformed.
Basically, the optical sensing can be carried out by both optical receivers simultaneously. In this case, the article is located on only one test station so that for a simultaneous sensing of the one or of the other side, a geometric allocation of the image points of both sides is readily possible. Thus the article to be tested cannot undergo any additional movements or rotations which will not be reliably ascertained and which would render an allocation of the opposing points impossible. Thus, the image points located on opposing sides always have an unambiguous geometric relation.
It is also useful to configure the optical receivers synchronously in such a manner that opposing points of the article are sensed simultaneously. The data of the image points of the opposing points of the article can then be compared at the same time, and any potential flaw in the intermediate layer can then be marked as such, possibly before its actual evaluation, so that the evaluation can be carried out with greater precision there, or the evaluation can be conducted with other criteria.
It is also possible to sense opposing sides in a chronological or geometric sequence or in partial optical offset, where the recorded image data of the one side or of a region of this one side, are saved at least until the other side or the region of the opposing side corresponding to the sensed side or region has been sensed. Then, the image data of the mutually opposing points are allocated to each other and evaluated. A storage of the data of the image points, as a rule, is necessary anyway, so that little or no time will be lost by the transformation.
Optical receivers can be provided by electronic cameras with, for instance, a CD chip. CMOS sensors or similar sensors, can also be utilized. These light-sensitive chips feature a number of pixels. According to the invention, it is possible to have a design such that the optical receivers each have at least one light-sensitive element with a number of pixels, and are aligned so that opposing image points of the article are imaged on the same or mirror-imaged pixels of the light-sensitive elements of the optical receivers. Thus, the allocation of the data of the mutually opposing points can be simplified.
It may be expedient for at least one optical receiver to have a line-like, light-sensitive element. Here the determination of the relative alignment to each other, or to a reference position, can take place very easily. The transformation of the data can thus be implemented very easily. It is also possible that at least one optical receiver will have one matrix-like, light-sensitive element.
The allocation of the optical receivers with respect to the article is essentially random, as long as an unambiguous allocation is possible to each other and to the article. Therefore, it is helpful for the optical receivers to be located on opposing sides of the article. It is also possible to use mirror elements which guide the tw
Basler AG
Howson and Howson
Pham Hoa Q.
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