Optics: measuring and testing – Surface roughness
Reexamination Certificate
2000-03-03
2003-04-01
Pham, Hoa Q. (Department: 2877)
Optics: measuring and testing
Surface roughness
C356S446000, C356S630000
Reexamination Certificate
active
06542248
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device and method for determining the quality of structured surfaces.
The quality of a surface, or of a structured surface, is to be understood as those physical characteristics which determine the appearance of the surface for a human observer. The characteristics which in particular distinguish a structured surface include structure. color, color brightness, gloss, distinction of image (DOI), haze, surface textures and surface ripples (orange peel), etc.
2. Description of the Related Art
The nature of visible surface properties is an essential constituent of objects in daily life as, for example, all manner of furnishings and consumer objects such as cars, etc.
Within the realm of automobile technology, considerable value is placed on the visual impression created by the visible surfaces. In the following, the technical problems which arise in devising surfaces within the realm of automobile technology will be explained in greater detail without, however, in any way restricting the present invention as regards its scope of application.
Automobile bodies are customarily provided with a high gloss or metallic finish which has far superior reflective or glossy characteristics than the corresponding values of other surfaces such as, for example, furniture. The high gloss to the finish to be applied and the relatively large even surface it will be applied upon necessitate an extraordinarily precise preparation of the surfaces to be finished and an especially high degree of carefulness when applying the finish
Various methods, devices and apparatus for determining the visual characteristics and especially the reflective behavior of surfaces are known in the state of the art such as is described in DE 44 34 203 A1.
The automobile industry furthermore also makes use of a plurality of processed structured surfaces in the interior of their cars which are derived from natural materials like, for example, wood or from plastic.
The visual appearance of structured surfaces depends fundamentally on the distinctiveness of the surface structure, although it is also determined by the other afore-mentioned visual parameters.
Automobile manufacturers today employ a large number of inspectors and make use of many high-priced industrial-sized measuring apparatuses to visually or automatically inspect surface quality in order to distinguish surface quality deficiencies while still at the production stage. This method, however, entails a whole set of disadvantages.
The job of a visual inspector is very exhausting and necessitates work bays having precisely defined lighting conditions at all times. Nevertheless, it has still been determined that large discrepancies exist among different inspectors when evaluating the same surface since, for one thing, the respective physiological impressions differ from one inspector to the next and, for another, an individual inspectors' eyesight is also dependant upon his own respective physical constitution.
Thereby, huge difficulties arise in the defining of lower quality thresholds for which a specimen falling short of would be rejected.
Furthermore, it is quite difficult even for experienced inspectors to ascertain the causes of inadequate visual appearance. Especially with regard to structured surfaces, visual appearance is determined by a combination of various parameters so that it becomes difficult, due to the observations and measurements which are carried out, to, for example, modify the control values of an automatic finishing device for the purpose of improving quality.
Structured plastic surfaces are frequently manufactured by means of a stamping procedure in which the molds, embossing rolls respectively, etc., utilized are subjected to abrasive wear-and-tear. With an increasing number of surfaces cast, the structure of the molds employed and consequently also the structure of the plastic surfaces continues to deteriorate. Production quality and quantity can be optimized with a regular replacement of the casting instruments used, although because the lifespan of these tools varies due to fluctuations in their material composition or fluctuations in environmental conditions, they are generally replaced on a regular basis, even before they lose sufficient quality to manufacture finished structured surfaces.
Structured surfaces are increasingly being utilized wherein not only those structured surfaces having a surface structure exhibiting a surface profile in cross section are employed, but also structured surfaces which consistently or in statistical distribution exhibit different visual properties in addition to, respectively instead of, a surface profile.
Such surfaces comprise, for example, a proportion of said surface being of high gloss and another proportion of said surface being of low gloss. Even when these surfaces exhibit no or very little surface profile, an observer will see a distinctive surface structure to said surface. The visual impression on an observer depends upon the relationship between the proportion of the surface which has a high gloss (or respectively has a high reflective proportion) and the proportion of the surface which has a low gloss (or high absorption or scattering respectively). The same applies analogously to the other characteristic visual parameters.
In cases where, for example, the structured surface consists of high gloss sections and low gloss sections, the individual proportional sections can be considered as gloss domains in contrast to the integral gloss relative the entire surface. A characteristic of this is the gloss cover which can be determined as a proportional ratio, respectively difference. Introducing or defining the concept of “gloss domain” allows for a much more unambiguous description of such surfaces in that a gloss parameter can be determined for each respective surface proportion (high gloss, low gloss) which relates to said respective corresponding gloss domain.
Visual testing is very difficult for assessing such surfaces characterized by two, three or multiple gloss effect surfaces since, due to the size of the individual surface elements, the examiner will mainly perceive the overall total impression of the structured surface, making it consequently difficult to render a detailed assessment of the individual surface elements and thus the total surface.
Examples of such multiple gloss effect surfaces include double gloss foils, or also sintered skins having leather or synthetic leather structures.
In addition to the surface's gloss parameter, haze, distinction of image (DOI) and ripples, respectively the individual sections of the surfaces (the “domains”), are also of significance when assessing such structured surfaces.
When automatic devices are used to inspect structured surface quality to determine, for example, surface gloss or distinction of image (DOI), a quantitative numerical scale value can be attained. A decisive disadvantage with visual and also automatic inspections, however, is that although values for the visual characteristics to be tested can be ascertained, the user receives no information as to their basis or cause.
A further disadvantage of conventional measuring apparatuses is that they necessitate considerable space requirements and thereby cannot be portably taken with the user.
BRIEF SUMMARY OF THE INVENTION
It is therefore the task of the present invention to provide a method and a device of the type as identified in the introduction to enable a reproducible assessment of surface quality, and in particular structured surfaces, and that such surface physical variables to be measured can be determined such that a representative characteristic of said surface, contingent upon its structure, can be determined.
Another aspect of the task of the present invention is to provide a device which is smaller and simpler in its construction such that a user can effortlessly take it with him and manipulate it to evaluate a surface without the need to utilize any other aids.
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BYK-Gardner GmbH
Ohlandt Greeley Ruggiero & Perle L.L.P.
Pham Hoa Q.
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