  In order to examine the influence of system dynamics on sliding friction, we
introduce the so-called micro-walking machine. This model consists of a rigid
body with a number of elastic contact spots that is pulled by a constantly
moving base. The system slides with dry friction on a rigid substrate. The
kinematic coupling of the rotation and the translation of the rigid body
results in varying normal and tangential forces at the contact spots. For
certain parameter ranges this leads to self-excited oscillations in the
vertical direction. A particular dynamic mode occurs which is characterized by
a strong correlation between low or even zero normal forces and a fast forward
motion. This effect is referred to as micro-walking. In addition to an
experimental rig we use numerical integration and an extensive parameter study
for the analysis. In theory, the reduction of the frictional resistance reaches
up to 98%. These results are confirmed by the experiments where the maximal
reduction was 73%. Our model shows that micro-vibrations play an important role
for the dynamic influences on the frictional resistance of systems that exhibit
apparently smooth sliding. The identification of the critical parameter range
enables the systematic control of frictional resistance through the adjustment
of attributes such as geometry and stiffness. In addition, it is possible to
deduce guidelines for how tribological test rigs should be designed in order to
get reliable results.
