Measurement of extremely low pre-rolling resistance in dry and lubricating conditions

This paper aims to experimentally determine the pre-rolling resistance coefficient based on a theoretical model for various contact material interfaces e.g. Al2O3 and silica balls on aluminum nanometer coated and non-coated single crystal Si wafers. The pre-rolling is the initial transient phase before complete rolling. This is of great interest to many applications e.g. nano-positioning using rolling actuators. The experiments are carried out using a precision designed pendulum securing pure pre-rolling without any external effect nor any slippage that may occur at the contact patch. With a design objective to quantify and minimize this resistance, the experiments under the conditions described in this paper, have revealed for the first time, extremely low values of pre-rolling resistance coefficients in the order of 10-7 for various combinations of materials depending on the interface of contact and type of material. The experimental results have shown that as the surface roughness increases the time of the pendulum oscillation decreases, and hence the coefficient of pre-rolling friction increases. The lubrication of the contact has exhibited a slight effect showing little decrease of the pre-rolling friction coefficient by 30% in average under similar conditions and less than 5% decrease of the oscillations period of the pendulum.