Apparatus for controlling motion of an invasive proberelative to a sheath enclosing the probe. The apparatusincludes an outer casing, configured for connection to thesheath. The apparatus further includes a drive mechanism,fixedly connected to the outer casing. The drive mechanismhas a first set of components, configured to translate theprobe along a direction parallel to an axis of the probe,in order to advance and retract the probe with respect tothe sheath in a translational stepwise manner. The drivemechanism also includes a second set of components,configured to rotate the probe around the axis of theprobe, in order to rotate the probe clockwise andcounter-clockwise, with respect to the sheath, in a rotationalstepwise manner.
