Optics: measuring and testing – Inspection of flaws or impurities – Surface condition
Reexamination Certificate
2000-01-13
2001-11-20
Font, Frank G. (Department: 2877)
Optics: measuring and testing
Inspection of flaws or impurities
Surface condition
Reexamination Certificate
active
06320654
ABSTRACT:
The invention relates to a process for automatic recognition of surface defects in body shells and a device for application of the process.
BACKGROUND OF THE INVENTION
In the manufacture of vehicles, body shells which are conveyed from a body shell construction line to an enameling line painting station generally have surface defects which are regarded by a customer as quality- lowering defects unless subjected to finishing operations. Consequently, such surface defects in body shells are to be detected and reworked.
In the past, relevant surface defects in series production have been recognized and evaluated subjectively by an inspector, especially by probing while wearing gloves, by display from different viewing directions and, if desired, by stripping with a whetstone if the inspector's experience has been that surface defects often occur at specific points on a body shell type.
Surface defects such as this may be dents/bulges, collapses, injection point/solder voids, uneven areas/hairline cracks, etc. The geometric parameters in evaluation are depth, extent, gradients, surface curvature, local frequencies of undulations, and positions of surface defects. Determination of whether a surface defect is relevant for a reworking operation normally depends on evaluation of a combination of the parameters indicated. For example, a dent 20 &mgr;m deep and 50 mm long can easily be recognized and must be reworked, while a dent of the same depth and 200 mm long normally is not recognized as a surface defect impairing quality and accordingly no reworking is required. Such combinations and relationships of parameters are of necessity made by an inspector in subjective evaluation, no clear-cut boundaries existing between the various relevant surface defects present resulting from such combinations.
In view of the complex and variable defect patterns indicated, automated computer recognition of such relevant surface defects has not been possible in the past.
In addition, the surface of body shells from body shell operations is often coated with a film of oil which is dull, diffused and dirty. This situation makes both subjective detection of surface defects by an inspector and automated recognition difficult. Relevant surface defects not recognized in the body shell are not recognized until after base enameling, when additional inspection is required. It is apparent that the cost of reworking surface defects is the higher the farther the body has advanced in the manufacturing process, and especially in the enameling process.
In order to reduce the high cost of recognizing relevant surface defects and of regular late reworking after base enameling, a number of attempts have already been made and experiments conducted to automate recognition of surface defects requiring reworking by measurement systems and machines, with the aim of recognizing as large a number of relevant surface defects as possible before enameling.
State-of-the-art systems, for example, involve operation by a strip projection process or on the basis of moire interferometry, in which adequate measurement accuracies of about 10 &mgr;m can be achieved by means of phase-shift processes. These processes do, however, require a time of approximately 1 minute for recognition and evaluation of an area measuring approximately 250 mm×250 mm. Such measurement processes are accordingly much too long for series production, in which a normal conveyor belt speed for body shells is about 4 meters per minute.
An alternative state-of-the-art process, called retroreflex process, has also been tested for recognition of surface defects in body shells. In this process the surface of a body shell is irradiated with a light beam. The radiation is reflected at the angle of incidence of a retroflector which is positioned perpendicularly to the surface examined. Display of surface defects is markedly intensified by multiple reflection of the light beam and so can be recognized by means of relatively simple image processing operations. A disadvantage of this process is, of course, that it is feasible only if a brightening agent is used. This brightening agent is to be applied to the surface before detection and recognition and rinsed off again after recognition. This represents a costly additional process step involving expenditure for the brightening agent. In addition, the brightening agent is a chemical harmful to the environment which creates the problem of disposal. Consequently, this process as well is to be rejected for use in series production.
The object of the invention is creation of a process for automatic recognition of surface defects requiring reworking, one suitable for series production, and of a device for application of this process.
SUMMARY OF THE INVENTION
In accordance with the present invention, a body shell is carried on a conveyor belt controlled by an optical measuring device. This optical measuring device comprises a projection device which generates a disk-shaped light tunnel as a light curtain extending more or less transversely to the direction of conveyance, through which light curtain a body shell is conveyed. A test strip of the surface positioned in a transverse plane of the body shell is irradiated.
The projection device emits a grid structure so that the test strip is correspondingly irradiated with a specific grid image made up of light and dark grid points, preferably in black and white.
The test device also comprises a camera device which records light reflected from the test strip as a representation of the grid image points at a specific angle. The position and shape of the representation of the reflected grid image of the grid points recognized by the camera device, which points regularly depict displacement and distortion relative to the grid emitted, is sent to a computer system as a test signal.
State-of-the-art triangulation methods are employed, or three-dimensional phase shifts are taken into account, in the computer system to recognize surface unevenness on the basis of the test signal.
Such surface defects are recognized as relevant ones requiring reworking through comparison with defect patterns stored in the computer.
This process is used to advantage for complete three- dimensional scanning of the surfaces of a body shell as this body shell is conveyed through the optical measuring device. The strip projection applied and evaluation of the test strip, in conjunction with a CCD camera, allow online scanning of the three-dimensional surface under operating conditions and at the conveyor speeds used in series production. A laser sweep projection process, in which a laser beam is projected onto the surface and recorded by a CCD camera (area camera or video camera), may also be used in place of normal light. A line scan camera may also be employed in a more costly solution.
This yields the advantage of making complete and accurate surface recognition before enameling possible. Such defects are preferably recognized by the proposed measuring process in body shells coming directly from body shell production, where the body surfaces to be examined are normally diffuse, of different dull colors, and often fouled. Complete and accurate recognition of surface defects before enameling greatly reduces costly reworking operations during or after the enameling process, so that on the whole higher quality is achieved at lower cost. The large volumes of data accumulated can be processed at higher body conveying speeds of up to 5 meters per minute by use of strip projection and CCD cameras.
The projection device consists preferably of a plurality of adjacent radiation emitters irradiating the continuous test strips, and the camera device of a plurality of adjacent CCD cameras recording the test strip. The radiation emitters and the CCD cameras are controlled at a distance from and at an angle to the test strip just acquired such that each of them is positioned in an interval window relative to the body outline and/or a suitable reflection angle is formed.
Such control is advantageously made possible by
Alders Klaus
Lehe Martina
Wan Gang
Audi AG
Font Frank G.
Lalos & Keegan
Nguyen Tu T
LandOfFree
Method for the automatic recognition of surface defects in... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for the automatic recognition of surface defects in..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for the automatic recognition of surface defects in... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2598034