Optics: measuring and testing – Inspection of flaws or impurities – Surface condition
Reexamination Certificate
1999-08-17
2003-12-23
Nguyen, Tu T. (Department: 2877)
Optics: measuring and testing
Inspection of flaws or impurities
Surface condition
Reexamination Certificate
active
06667800
ABSTRACT:
DESCRIPTION
Technical Field
The present invention relates to a method and a device for measuring and quantifying surface defects, such as defects on polished surfaces, by means of optical registration with subsequent image analysis and image processing.
The method and the device according to the invention are primarily applicable for measuring and quantifying surface defects in the form of so-called polishing roses, which may arise in connection with polishing of, for example, painted sheet metal details within the motor car industry. The method and the device according to the present invention may also be utilized, however, for other similar applications, for example in connection with quality control of rubbing or grinding processes.
In this context, the expression “polishing roses” refers to a certain type of surface defects which have arisen during polishing or other similar surface finishing, such as rubbing or grinding. The polishing roses may adopt several different shapes, depending on the circumstances under which they have arisen.
The method practiced by means of the device according to the present invention may replace the manual, visual examination process which has been previously used for quality testing and assessment of surface defects, such as polishing roses, within applications where a painted surface with a smooth and glossy surface finish is required.
BACKGROUND OF THE INVENTION
Within the vehicle manufacturing industry (motor car. industry), ever increasing demands are made today on the quality of the end product, something which has resulted in the use of more and more advanced systems for quality testing and control.
As is well-known to persons skilled in the art, a modern passenger car or truck consists of a plurality of components which originate from different production lines, or from different manufacturers, and which are assembled in a step-by-step process into a vehicle.
Some of these components have painted sheet metal components which, in the case of visible body components, generally are polished in order to achieve a smooth and glossy surface finish. In certain cases, it may also happen that components made at least partially of polymeric materials (different plastics) are polished for the same reason.
Independent of the stage one has reached in the assembly process, the need sometimes arises for testing of the polishing result of a component which has been polished in an earlier step.
Also in connection with product or process development, there is a need to be able to test or evaluate surface finishing results. Such an evaluation may serve as a guide in the choice of, for example, surface finishing equipment, polishing equipment or polishing technique.
Also when developing new paints and car enamels, it is of great importance to be able to identify and eliminate those paints and enamels in which polishing roses frequently arise.
Before the present invention, such quality testing of polished surfaces has in principle been done by means of manual, visual assessment of polished test specimens or finished polished components or vehicles.
One great disadvantage with such manual, visual assessment of the polishing result has been that it is dependent on the individual, i.e. only experienced staff with many years of experience from practicing such assessment are been able to accurately perform such evaluation.
Another disadvantage has been that the assessment results have not been reproducible or quantifiable. Furthermore, such results to a great extent have been dependent on the light conditions at the testing station. The manual, visual assessment of the polishing result has until this time been most advantageously accomplished outdoors and in brilliant sunshine.
A frequently occurring surface defect which may arise in connection with surface finishing of different components is so-called polishing roses. As mentioned earlier, in this context polishing roses refer to certain types of surface defects which have arisen during polishing or other similar surface finishing such as rubbing or grinding processes. The polishing roses may adopt several different forms, depending on conditions under which they have arisen.
Accordingly, a typical form of polishing rose manifests itself as a so-called holographic image. In this case, the holographic image may be described as a situation in which an image or pattern appears to be situated below the plane of a polished surface when it is observed from one direction, and the same image appears to be situated above the plane of the polished surface when that surface is observed from an opposite direction.
Another frequently occurring form of polishing rose manifests itself as a blurred polishing pattern in the surface when the surface is observed from above. Such a blurred polishing pattern usually appears together with polishing roses of the earlier-mentioned type, i.e. holographic images.
A third form in which polishing roses occur is sharp, thin scratches, which are clearly visible when the angle of observation is perpendicular to the scratches. This form of polishing rose may appear alone, or together with polishing roses of the two above-mentioned types.
Common to all different forms of polishing roses is that they are practically invisible during normal lighting conditions, something which renders detection difficult.
One reason that polishing roses arise is uneven pressure application which occurs in different movements when a rotating polishing drum or a polishing cloth is moved across the surface which is to be polished by the movement. Grinding, rubbing, and other forms of rotating or oscillating finishing processes may also cause polishing roses.
Unsatisfactorily often, polishing roses are not discovered until the finished vehicle is subjected to bright sunlight, and the roses are then visible only when the polished surface is observed at a certain angle. The problem is more evident for vehicles which have been painted in dark shades than for light-color painted vehicles since the polishing roses are more prominent on dark surfaces than on light surfaces. Since the majority of stations in a production process are indoors, and that is where testing for such surface defects would be best accomplished, it has been difficult to determine the presence of polishing roses before the vehicle has been fully assembled and able to be driven outside for ocular inspection. Accordingly, it is very difficult to continuously check the polishing result of individual sheet metal components before assembly.
Therefore, it is evident that there has long been a need for a reproducible and quantifiable measurement method for evaluating the presence of polishing roses or other similar surface defects of polished, or in otherwise finished components. Such a measurement method should further be insensitive to the light conditions which prevail at the testing station, and should be able to distinguish polishing roses from surface defects of other types which do not originate from the surface finishing.
In view of the above described deficiencies associated with methods and devices for inspecting, analyzing and identifying defects in polished surfaces, the present invention has been developed to alleviate these drawbacks and provide further benefits to the user. These enhancements and benefits are described in greater detail hereinbelow with respect to several alternative embodiments of the present invention.
DISCLOSURE OF THE INVENTION
The present invention in its several disclosed embodiments alleviates the drawbacks described above with respect to conventional methods and devices for inspecting, analyzing and identifying defects in polished surfaces and incorporates several additionally beneficial features.
Accordingly, an object of the present invention is to provide a method and a device for measuring and quantifying surface defects on a test or finished surface by means of optical registration with subsequent image analysis and/or image processing. This object may be achieved by and through methods and devices that are c
Larsson Anders
Larsson Peter
Max Erland
Howrey Simon Arnold & White , LLP
Nguyen Tu T.
Volvo Car Corporation
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