  The ratchet effect is demonstrated theoretically for the simple model of a
vortex in a thin superconducting film interacting with a periodic array of
magnetic dipoles placed in the vicinity of the film . The pinning potential for
the vortex is calculated in the London limit and found to break spatial
inversion symmetry and to depend on the orientation of the magnetic dipole
moments. The motion of the vortex at zero temperature driven by a force
oscillating periodically in time is investigated numerically. Drift vortex
motion consisting of displacements by a translation vector of the dipole array
during each period of oscillation is obtained and studied in detail. The
direction of drift differs in general from that of the driving force, except if
the driving force oscillates in a direction of high symmetry of the dipole
array. The vortex drift velocity depends on the orientation of the magnetic
moments, and can be tuned by rotating the dipoles. It is pointed out that if
the magnetic moments are free to rotate, the ratchet effect can be produced and
tuned by a magnetic field applied parallel to the film surfaces
