A bale opener for removing fiber tufts from top surfaces of fiber bales assembled in a series includes a carriage for travelling back-and-forth along a generally horizontal, first path of travel along the fiber bale series; a tower mounted on the carriage for travel therewith; a fiber tuft detaching device extending from the tower and movable relative to the tower along a generally vertical, second path of travel; and an incremental rotary displacement signalling device including a shaft; a toothed rotary element mounted on the shaft; a counter element meshing with the rotary element which is movable relative to the counter element; and a signal generator coupled to the toothed element for generating signals as a function of rotary displacements of the toothed element. One of the elements is mounted on the detaching device (or other cotravelling component) and the other element is mounted along one of the first and second paths of travel for generating signals as a function of displacement of the detaching device along at least one of the first and second paths of travel.