  We study in detail the recent suggestions by Tshiprut et al. [Phys. Rev.
Lett. 95, 016101 (2005)] to tune tribological properties at the nanoscale by
subjecting a substrate to periodic mechanical oscillations. We show that both
in stick-slip and sliding regimes of motion friction can be tuned and reduced
by controlling the frequency and amplitude of the imposed substrate lateral
excitations. We demonstrate that the mechanisms of oscillation-induced
reduction of friction are different for stick-slip and sliding dynamics. In the
first regime the effect results from a giant enhancement of surface diffusion,
while in the second regime it is due to the interplay between washboard and
oscillation frequencies that leads to the occurrence of parametric resonances.
Moreover we show that for particular set of parameters it is possible to
sustain the motion with the only oscillations.
