Image analysis – Applications – Manufacturing or product inspection
Reexamination Certificate
1994-02-14
2001-11-06
Chang, Jon (Department: 2623)
Image analysis
Applications
Manufacturing or product inspection
C356S239200
Reexamination Certificate
active
06314199
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a process and an apparatus for examining optical components, in which an image of the particular component to be examined is produced and flaws in the imaged article are detected by image analysis, and furthermore to an illuminating device for illuminating clear-transparent test objects.
In the manufacture and quality control of optical components, especially optical components for the eye, such as contact lenses, examination is still carried out visually. Attention may be drawn in this connection, for example, to DIN specification 58 223. Visual quality control is a subjective examination only, which depends on the person concerned and is likely to vary depending on the time of day. Consequently there are inevitably shifts in the quality standards of the quality control and it is not possible to achieve adequate reproducibility of the quality of the products. In addition, the possibilities of automation, especially where such components are mass-produced, are considerably handicapped.
Detection of the presence or absence of scratches and the like on the curved surface of lenses in contact lens manufacture by means of an optical projector device and an image-processing device is known from EP O359 084 A2. The said specification does not, however, disclose how the projector device and the image-processing device are designed so that they can be used for a reproducible quality control, especially in the automatic production of optical components.
Referring to illumination of test objects, the illumination of objects in a microscope by means of “dark field illumination” is known. Such a dark field illumination comprises illuminating an object by means of a light source and an illuminating lens (condenser) in such a manner that the illuminating light beam does not itself enter the ray path of the microscope. Consequently, only the light that is scattered into the ray path by the object is observed.
Illuminating lenses for dark field illumination are known in which there is arranged in the ray path a central diaphragm plate which covers the central portion of the illuminating light beam. It is thus an annular illuminating light beam which strikes a condenser lens and which is collected by the edge parts of the condenser lens in the plane of the object and then directed to the side past the ray path of the microscope lens.
Also known is a so-called “cardioid condenser” in which an annular illuminating light beam is fully reflected at a concave surface at the object side of a first lens. The light beam deflected outwards in this manner strikes an essentially cylindrical generated surface of a second lens. The light beam is again fully reflected by this generated surface. The second lens collects again in the plane of the object the light beam reflected inwards from the edge. From there the light beam, in the shape of a cone, again passes by the ray path of the microscope (Grimsehls Lehrbuch der Physik, 11th edition (1943), vol. 2, published by B. G. Teubner, pages 707-708). These known arrangements are concerned with the illumination of objects in a microscope having an invariable illuminating lens.
SUMMARY OF THE INVENTION
Starting from this state of the art it is an object of the invention to create a process and an apparatus for examining optical components that promote the automation of the examining steps and the manufacture of the optical components. Furthermore, it is another object of the invention to provide an illuminating device for illuminating clear-transparent test objects in order to examine the test objects for flaws, which device permits the flaws to be made clearly detectable. Test objects for such a device may be optical elements, such as lenses, or also spectacle lenses, contact lenses etc. Another problem underlying the invention is especially so to design such an illuminating device that it permits automatic flaw evaluation by observing the test objects using an electronic image-recording device and image-processing.
The problem is solved in the invention as far as the process is concerned by a process in which a two-dimensional high-contrast image of the particular component to be examined is produced and the image area of the flaws which have been made visible is determined, for the purpose of quality control, by comparison with one or more threshold values.
With respect to apparatus, this problem is solved in the invention by providing an optical image-producing device that has a high-contrast-image producing device, and also an image-processing device which comprises an image-recording means with an image sensor that can carry out an area determination of the flaws detected in the high-contrast image.
In the invention an illuminating means is used that renders possible the simultaneous high-contrast representation, in two-dimensional form, of all structures that are of interest on the component to be examined. There is used in combination with this illuminating means an image-recording means with an optical image sensor. The image-recording means may also optionally be provided with a focussing lens with which the high-contrast image can be recorded. The high-contrast image is transmitted to an image-processing device. For that purpose it is advantageous to divide the high-contrast image into image elements (pixels). When a CCD is used as image sensor, this division into image elements is already provided by the design or construction of the CCD. The image elements are converted by means of a converter into digital image signals which can be stored and processed. In this manner an analysis of the structural features of the optical component to be examined (an area determination), and consequently of the flaws detected in the high-contrast image, is possible. For the conversion, advantageously a binary image is first of all produced.
In order to produce the high-contrast image, preferably a dark field illumination of the component to be examined is carried out. With the aid of appropriately scattered light, the component to be examined is illuminated against a dark background, using a camera that optionally contains the image sensor. The image sensor is preferably in the form of a CCD. In this manner a dark field illumination image is taken of the illuminated test specimen. Such an image gives a high-contrast representation of flaws, these flaws appearing as areas on the high-contrast image representation. For example, the flaws in a dark field illumination are represented as light flecks with well-defined areas against a dark (black or grey) background that has no flaws. The flaws may be scratches, holes, air bubbles, fissures, adhering fragments and accumulations of dirt or shrunken areas and the like. The flaws present themselves as areas in the image area. It is also possible, however, to detect errors at the perimeter of the test specimen, which can be represented as two-dimensional shapes. These may be gaps in the perimeter, flash, fissures, fragments adhering to the perimeter, accumulations of dirt and shrunken areas at the perimeter, and perimeter inhomogeneities.
The image areas of the detected flaws can be divided into pixels (image area elements). By means of the number of image area elements (pixels) it is possible to ascertain the extent of a particular flaw or of all the flaws. For this purpose a scanning/counting means may be provided by means of which the pixels can be counted. The number of pixels ascertained for the individual image areas of the detected flaws is compared with a predetermined number of pixels. This predetermined number of pixels is a quality standard which the test specimen has to meet.
For the examination the test specimen can also be divided into different zones for which different threshold values are preset as quality standards. For the examination of a contact lens, for example, different quality standards in the form of preset image areas may be stipulated for the optical zone and the lenticular zone. The quality of the perimeter of the lens can also be determined o
Geissler Wolfgang
Hagmann Peter
Hauck Roland
Hofer Peter
Lutz Hubert
Chang Jon
Gorman Jr. Robert J.
Meece R. Scott
Novartis AG
LandOfFree
Process and apparatus for examining optical components,... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process and apparatus for examining optical components,..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process and apparatus for examining optical components,... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2609956