Brunel University School of Engineering and Design PhD Theses
Abstract
This thesis was submitted for the degree of Doctor of Philosophy and was awarded by Brunel University.In the modem automotive industry, more and more manufacturers recognise that
vehicle paint appearance makes an important contribution to customer satisfaction.
Attractive appearance has become one of the important factors for customers in
making a decision to purchase a car. Objective measurement of the quality of
autobody paint appearance, as perceived by the customer, in a repeatable,
reproducible, continuous scale manner is an important requirement for improving the
paint appearance. It can provide car manufacturers a standard reference to evaluate
the quality of the paint appearance.
This thesis mainly deals with the measurement of paint appearance quality in the
automotive industry by investigating, identifying and developing measurement methods in
this area. First of all, the 'state of the art' in the area of paint appearance measurement
was presented, which summarised the concept of appearance, models, attributes and
definitions. To further identify the parameters and instruments used in the automotive
industry, a round robin test was launched to perform visual assessment and instrument
measurements on a set of panels in some European car manufacturers. A summary of
the correlation found between measurable parameters and visual assessment provided
the basis of the further work. Based on the literature survey and round robin test
results, the next work is mainly concentrated on the two most important parameters,
'orange peel' and 'metal texture effect', how to separate and evaluate them. Digital
signal processing technique, FFT and Filtering, have been employed to separate them
and a set of measures have been provided for evaluation. At the same time, the
technique for texture pattern recognition was introduced to evaluate the texture effect
when a fine texture comparison was needed. A set of computable textural parameters
based on grey-tone spatial-dependence matrices gives good correlation directly
corresponding to visual perception.
To resolve the overall appearance modelling problem, two novel and more powerful
modelling tools, artificial neural networks and fuzzy logic, are introduced to model the
overall appearance. The test results showed that both of them are able to reflect the
correlation between overall appearance and the major parameters measured from a
painted surface.
Finally, an integrated measurement system, 'Smart Appearance', was developed using
the image processing techniques and the artificial neural network model. The
implement results show that this system can measure the major attributes of paint
appearance and provide an overall appearance index corresponding to human visual
perception. This system is helpful to product quality control on car body paint. It also
could be used on the paint production line for dynamic measurement.European Union BRITE EURAM Projec
