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.