  We describe a surface force apparatus designed to probe the rheology of a
nanoconfined medium under large shear amplitudes (up to 500 $\mu$m). The
instrument can be operated in closed-loop, controlling either the applied
normal load or the thickness of the medium during shear experiments. Feedback
control allows to greatly extend the range of confinement/shear strain
attainable with the surface force apparatus. The performances of the instrument
are illustrated using hexadecane as the confined medium.
