In a method p for controlling translocation of a target polymer molecule through a nanopore, a clamp is reversibly bound to a sequential plurality of polymer subunits along the target polymer molecule length and the molecule and clamp are disposed in an ionic solution that is in fluidic communication with the nanopore. A constant translocation force is applied across the nanopore to induce travel of the target polymer molecule into the nanopore, until the clamp abuts the nanopore aperture and stops further travel of the target polymer molecule into the nanopore. Then a voltage control pulse is applied across the nanopore and/or a thermal control pulse is applied at the nanopore, with a pulse duration that steps the clamp along the target polymer molecule by no more than one polymer subunit in a direction opposite that of travel into the nanopore. No fuel is provided to the clamp.