Optics: measuring and testing – Inspection of flaws or impurities – Surface condition
Reexamination Certificate
2000-01-10
2002-09-10
Font, Frank G. (Department: 2877)
Optics: measuring and testing
Inspection of flaws or impurities
Surface condition
C356S601000, C356S629000, C356S237100, C359S216100, C359S219200, C359S211200
Reexamination Certificate
active
06449036
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention concerns a device and a process for the inspection of the surface of an object.
With respect to the surface inspection of materials, it is known to scan the respective surface with charge-coupled device (CCD), line, or matrix cameras as well as with laser scanners. It is also known in the art to analyze the gray-scale value or color pictures with image processing means.
In the case of the processing of wood, for example in door and window manufacture, or in the fabrication of veneer sheets, it is necessary to investigate and determine the quality of the wood to be processed. In doing so, it should be determined whether the wood has shakes, fissures, knot holes, protrusions or indentations. It should also be determined whether the wood has blue stain or red ring rot, which makes them unsuitable for the foreseen purpose.
Prior to the present invention, wood surfaces have normally been manually inspected. It is up to now practically impossible to automatically identify wood which is affected by blue stain or red ring rot. There are a number of technical problems, which generally are associated with the great depth of focus and the simultaneously high resolution called for by the process as well as with the transportation speed of the wood. For this, relatively elaborate illumination equipment with a very high performance is necessary.
When illuminating wood by means of a laser beam, the so-called scatter effect occurs, which means that a part of the light is dispersed into the wood fibers. The light scatters in the vicinity of the surface in a function of the local density distribution. In the case of an undisturbed fiber orientation, a characteristic dipole distribution in the spatial intensity distribution of the diffusely reflected light is manifest, whereby the (1/e) drop, the integral intensity, as well as the actual structure of the maxima of the emissions are dependent on the type of material and on the structure of the defect. Through SE-A-7500465-5, a process and a device utilizing a helium-neon laser has become known, where the scatter effect is indirectly exploited for the evaluation.
Through EP-0 198 037 B1, a process for measuring the fiber angles in a fibrous material, such as wood, has become known. In the EP '037 process, an area on the surface of the material is illuminated with an impinging ray of light and photo-sensitive devices are spatially arranged in such that they measure the light reflected by the illuminated area. The fiber angle is measured relative to three reference axes perpendicular to one another (x, y, z) and any point on the surface of the material is defined as the point of origin of the axes. The illuminated area encompasses the point of origin and has a diameter, which is at least ten times the size of the average fiber diameter of the substance to be measured. A majority of the photo-sensitive devices are positioned so as to be able to assess the azimuthal angular positions around the point of origin of the intensity maximum of the reflected light. Furthermore, a number of arbitrary points in transverse and longitudinal direction of an area on the surface of the material are staked out, in order to be in a position to assess the azimuthal angular positions of the intensity maxima at each of the points. By means of the relationship between the azimuthal angular position of the reflected light maxima and the fiber angle, for every measuring point the corresponding fiber angle is calculated relative to all three axes in order to indicate the complete pattern of the fiber angles within the measured area of the fibrous material. For carrying out this process, a highly elaborate installation is necessary in order to, on the one hand, measure the radiated beam proportion of the reflected light and, on the other hand, measure the proportion of the diffusely reflected light.
DE-A-196 04 076.0 proposes a device for the inspection of the surface of wood for the purpose of determining surface characteristics. The DE '076 device includes an opto-electronic sensor, an electronic and/or optical processing unit, a computer capable of real-time operation. With the De '076 device, the wood can be moved relative to the sensor, as well as an incremental position transducer, which synchronizes the sensor with the speed of the wood. The sensor consists of a color laser scanner with at least two beam bundles of differing wave lengths and a receiver with two channels with one opto-electrical receiving element each. The channels are formed by beam splitting of the reflected beam bundle. A lens for creating an intermediate image plane is located in at least one of the channels. After the lens, within one of the channels there is an optical graduated filter, which is capable of modulating the passing light current to the opto-electrical receiving element belonging to it independent of the position. The signals of the receiving element of the channel without the graduated filter are converted into a color image in the computer. The signals of the other channel, the light current of which has been modulated independent of the position, are converted into a profile image of the surface.
It is, for example, known from U.S. Pat. No. 4,286,880 and JP 59 040 149 A that wood surfaces can be investigated by scanning with a light beam. These two documents divulge a rotating mirror, which is located in the focal point of a parabolic mirror. Light is emitted onto the rotating mirror from a light source and from there distributed by reflection on the parabolic mirror along a scanning line on the wood surface. In U.S. Pat. No. 4,286,880, the subject is an improvement of work stations for the localization of wood defects, wherein an operating person has to find the defects. The operating person marks the defects and the marks are detected by an optical sensor with a binary output signal. The object of JP 59 040 149 A is the detection of live knots by means of asymmetrically scattered light. For the solution of this problem, a wood surface is scanned by a light beam and light scattered from the wood surface is directly detected by two detectors arranged symmetrically with respect to the scanning beam.
From the state of the technology, optical distance sensors are also known. The distance sensor divulged in EP-0 387 521 A2 is based on a triangulation process. A beam of light is focused on the surface to be measured by means of a lens. Light scattered by the surface is collected by the same lens and focused on position-sensitive detectors by a concave mirror. The components are positioned relative to an optical axis such that a high light sensitivity is assured by a small angle of incidence. Another distance sensor, divulged in WO 93/11403, contains a rotating polygonal mirror, which distributes light emitted from a light source onto a scanning line on the surface to be measured. A scanning lens projects the point-shaped light source onto the surface. The light reflected by the surface is projected onto a point-shaped detector by means of the same scanning lens and a further lens. A maximum light intensity impinges on the detector only when the object is in the focal plane of the scanning lens and when the detector is simultaneously in the focal plane of the further lens. The detected light intensity is therefore a measure for the distance of the object from the scanning lens. The construction can be refined by utilizing several detectors, each of which supply maximum signals at differing object distances.
SUMMARY OF THE INVENTION
The present invention is directed toward a device and a process for the dynamic inspection of the surfaces of objects such as wood, tile, textile, and glass. The present invention is further directed toward a device and process for the identification of surface characteristics. With the present invention an automatic inspection of the surface can be carried out continuously and with a high speed. The continuous, high speed inspection provided by the present invention permits characteristics such as sha
Grieser Ralf
Ihlefeld Joachim
Wenert Lutz
Wollmann Christian
Baumer Optronic GmbH
Font Frank G.
Nguyen Sang H.
Rankin, Hill Porter & Clark LLP
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