The evaluation is also influenced by the spirit of the times
When it comes to the testers’ evaluation of the texture of a leather
surface - that is, its natural grain - it becomes evident that tastes
change over time. In previous years, testers tended to prefer, in terms
of both visual and tactile criteria, an irregular, “natural” grain in leather,
artificial leather or hard plastic surfaces. In a recent series of tests,
though, a different set of priorities emerged.
The Mercedes-Benz designers had a very specific assignment: They
asked their colleagues in Berlin to test customer acceptance of various
plastic surfaces for the instrument panel of the new A-Class. “These
days the testers are giving higher marks to a regular, ‘technical’ grain
than to an irregular grain,” Rosenberg concludes.

The Universal Surface Tester is used to precisely measure the topography of
material surfaces. A button creates a “deformation profile pattern” of a piece of leather

The researchers at the haptics laboratory receive vital support from
their colleagues in the Materials Testing units in Ulm and Sindelfingen.
The engineers subject the materials they investigate to every kind of
physical stress, and in the process they gather information about all of
the material parameters that have an impact on the materials’ tactile
properties. These parameters include performance criteria such as
static deformation, roughness, shock absorption and coefficient of
friction. The results arising from these standard physical tests are then
compared with the various rankings that the testers assigned to the
materials on the basis of their subjective evaluations.
These comparisons have shown, for example, that softer types of
leather are unanimously given higher marks than hard leather surfaces.
“That means we don’t have to reinvent the wheel every time we run a
test. Instead, we can utilize the general patterns that have already been
discovered as we go about our work. In turn, we can provide the
developers with some clear conclusions about the material
characteristics that are definiy in demand, so that the leather they
use will feel like genuine leather and the metal will feel like metal,”
explains Enigk.

DaimlerChrysler material researchers are refining their testing methods in
close cooperation with Innowep, a manufacturer specializing in measuring
instruments. One result of this cooperation is the papillary button - an artificial
“fingertip” that takes measurements with unprecedented precision.

A second focus of the haptics laboratory team is its testing program to
determine the interplay between an automotive component’s “feel” and
its perceived function. Two years ago, for example, Enigk’s team
examined a series of pushbuttons, asking themselves questions such
as: How easy or how hard should it be to push such buttons? Should
the buttons themselves be hard or soft? And what kind of sound or
feeling will give the user the clearest feedback indicating the
pushbutton has done its job?