System for optically examining plastic card surfaces

Details System for optically examining plastic card surfaces System for optically examining plastic card surfaces

1999-07-16

2001-06-05

Font, Frank G. (Department: 2877)

Optics: measuring and testing

Inspection of flaws or impurities

Reexamination Certificate

active

06243162

ABSTRACT:

The invention relates to a method for examining plastic cards having the features named in the preamble of claim
1
. The invention can also be applied in the case of other flat objects in which detection of surface defects is to be undertaken.
In the fabrication of plastic cards such as identity cards, chip cards, credit cards and the like, stringent requirements are placed on maintaining narrow quality tolerances. Thus, in particular, the surfaces are to be free from scratches; for example, signature strips envisaged may not be lacking or be impressed askew or otherwise be defective, impressed holograms must be free from defects and be positioned at the correct point, etc. Known methods use a video camera with downstream image processing for monitoring the surface, a specimen under examination being illuminated with diffuse light so that the card surfaces can be effectively detected. An operator is then responsible for fixing the limits between “free from defects” (good) and “defective” (rejects).
The cards under discussion here frequently consist of a plurality of layers which are laminated together and of which at least one is generally printed. A desired alignment and quality of the overprinted image is naturally a part of the surface examination. Consequently, the cards are illuminated during examination with diffuse light such that the video camera picks up an image reflected from the surface of the specimen under examination. Such an optical examining method is certainly largely insensitive with respect to slight sagging of the flat specimens under examination, but it has the great disadvantage that scratches and grooves are imaged only with poor contrast.
It is therefore the object of the invention to develop a method according to the preamble of claim
1
in such a way that even relatively slight surface defects can be detected and the examination cannot be falsified by overprinted images.
This object is achieved by means of the features of patent claim
1
. Claims
5
and
7
name important applications of the method. Claims
8
to
17
relate to an illuminating device with which the method according to the invention can be carried out.
The result is to create a method which by reflection supplies a light/dark image of a card surface with an adequate contrast for simultaneously detecting a glossy card surface and an intentional two-dimensional change, achieved by embossing, in the card surface such as, for example, a hologram, signature field, etc. In addition to surface defects such as scratches and grooves, it is, in particular, the contours and thus the position of the intentional two-dimensional changes in the card surface which can be reliably detected. A further substantial advantage consists in that, to mirror the card surface, the position of the latter relative to the beam path is no longer quite so critical, with the result that even should the card possibly sag the reflection is still sufficiently good. The diffuse light component supplies a scattered reflection component which leads to a lesser situational sensitivity of the reflection. The loss in contrast occurring to this extent is slight. The viewing possibilities are consequently substantially enhanced according to the invention.
Further embodiments and advantages of the invention are to be gathered from the dependent claims and the following description.


REFERENCES:
patent: 4202626 (1980-05-01), Mayer, Jr. et al.
patent: 4501439 (1985-02-01), Antes
patent: 5155558 (1992-10-01), Tannenbaum et al.
patent: 5436716 (1995-07-01), Stein
patent: 5640237 (1997-06-01), Esrig et al.
patent: 0 735 361A2 (1996-02-01), None
patent: 0 735 361 (1996-10-01), None

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