Correlation to human perception

As a low correlation to the human perception was identified as one of the drawbacks of existing devices for surface measurement, it is important to evidence an improvement of this situation with the application of the new algorithm. To achieve this, the measurement data was compared to the results of a sensory assessment of the high gloss surfaces carried out by a panel of trained assessors [3]. For this comparison a set of nine samples from one production series was taken. The best and the worst one were defined as threshold samples. In an investigation of profiles the assessors were asked to choose a rank from 1 to 9 for each sample, where 1 equals the best threshold sample and 9 equals the worst threshold sample. Each sample could be compared to both threshold samples, but not to the other ones. The average and the standard deviation of the ranking from all assessors was calculated and compared to the measured ratio hill height/area. Figure 4 shows the result of this comparison.

Figure 4: Correlation between measurement results and Investigation of profiles.

For six out of seven samples the measurement results correspond to the sensory evaluation. Only for sample 88980132 a discrepancy can be observed. This may be caused by a directional character of the surface structure, which strongly influences the evaluation. While the results of the sensory assessment do not allow a sharp differentiation due to overlapping range of variation, the measurement results show a clearer difference between the samples. This indicates a higher resolution of the measurement system compared to human perception.

In a next step structures of the different attributes orange peel and lacquer sinking were analyzed. Tests for the analysis of the attribute orange peel

Development of an Algorithm for Measuring the Quality of High Gloss Surfaces Correlated to Human Perception

were applied on a set of orange peel standards, used in automotive industry.

This are ACT Orange Peel Standards by ACT Test Panel Technologies.

Different samples of black liquid coatings on wood-based panel were used for the evaluation of the attribute lacquer sinking. The results of the correlation analyses are presented in figure 5.

Figure 5: Relationship between ratio hill height/area and ranking

These analyses show a strong correlation between the ratio hill height/area and the ranking based on sensory assessment for both evaluated attributes.

For the attribute orange peel an exponential correlation with a correlation coefficient of R = 0.98 can be determined. In contrast for the attribute lacquer sinking the results show a linear correlation with a correlation coefficient of R = 0.95. For interpreting these results it has to be taken into account that the extent of orange peel represented by the ACT Standards is usually not found on furniture high gloss surfaces.

Based on the results of the correlation analyses the calculated ratio hill height/area proves to be applicable evaltuating the extent of a single attribute. Nevertheless further comparison of the results shows that the absolute values of hill heigt/area do not differ between the two different attributes. Thus the ratio is innapropriate for distinguishing one attribute from an other. First approaches based on the contur length of topografic elements or the ratio of their expanse in x- and y-direction did not enable a sharp differentiation of attributes.

4 CONCLUSION

The ratio hill height/area can be applied as a specific value for evaluation of furniture high gloss surfaces. The algorithm developed for the calculation of the value delivers consistent results and – together with the measurement device – enables a measurement with sufficient repeatability and uncertainty for the estimated application.

As the ratio hill height/area enables a measurement of the extent of single attributes as well as an assessment of the overall quality concerning surface structures, it can be applied in quality control and its changes indicate variations in the production process. Nevertheless the value does not enable the identification of the root cause of a process variation. At the current state this still requires the knowledge of a well-trained expert for differentiation of various attributes.

Further benefits for the process control could be achieved by developing a more complex interpretation of the three-dimensional surface data that enables the separation of attributes. This can probably not be achieved by analyzing a single attribute and will require a set of specific values and some kind of fuzzy logic for a differentiation.

REFERENCES

[1] Herzberg, K., Dekomien, K., Huxol, A., Riegel, A (2013) High gloss surfaces: valid quality evaluation, 3rd International Conference on Production Engineering and Management for Furniture Industry, 207-218, Universita degli studi di Trieste, Trieste.

Development of an Algorithm for Measuring the Quality of High Gloss Surfaces Correlated to Human Perception

[2] Dekomien, K., Huxol, A., Riegel, A. (2014) Beitrag zur sensorischen Gütebestimmung von rohen und beschichteten Holz- und Holzwerkstoffoberflächen, 76-89,

Tagungsband des 16. Holztechnologischen Kolloquiums, Dresden.

[3] Dekomien, K., Huxol, A., Riegel, A. (2015) Entwicklung eines umfassenden Qualitätskonzeptes zur Bewertung von Hochglanzoberflächen, Abschlussbericht zum Forschungsvorhaben, Förderkennzeichen 17007X11, Lemgo. the 4th International Conference, Production Engineering and Management, 155-166, Lemgo.

[6] DIN EN ISO 25178-2 (2012) Geometrische Produktspezifikationen (GPS), Oberflächenbeschaffenheit: Flächenhaft – Teil 2: Begriffe und Oberflächen-Kenngrößen, Beuth Verlag, Berlin.

[7] Huxol, A., Dekomien, K., Schulz, S., Riegel, A. (2014) Subjektiv wahrnehmen – objektiv messen, Hochglanzbeschichtungen, Qualitätsprüfung der Anmutungsleistung von Hochglanzoberflächen, Vincentz Verlag, Hannover, FARBEUNDLACK 8/2014.

[8] DIN EN ISO 12085 (1998) Geometrische Produktspezifikationen (GPS), Oberflächenbeschaffenheit: Tastschnittverfahren, Motifkenngrößen, Beuth Verlag, Berlin.

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[11] DIN EN ISO 16610-21 (2013) Geometrische Produktspezifikation (GPS) - Filterung - Teil 21: Lineare Profilfilter: Gauß-Filter, Beuth-Verlag, Berlin.

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Beuth-Verlag.

LARGE-SCALE 3D PRINTERS: THE CHALLENGE OF