Method of moving head to correct for hysteresis

Abstract

First and second portions having different magnetizable properties are alternately disposed on a stator. A head movable relative to the stator has first and second poles each having a pair of magnetizable legs contiguous to the stator and displaced from each other, and from the other pole legs, along a first axis relative to the stator portions. The poles introduce magnetic flux in the same direction to the legs. First and second windings, each respectively associated with the legs on an individual pole, produce in one leg a flux aiding the pole flux and in another a flux opposing the pole flux. Alternating currents flow through each winding at each instant at a frequency dependent upon the head speed to the produced along the first axis at that instant. The windings are programmed to provide signals for producing a movement of the head to a plurality of different destinations along the first axis. The windings are further programmed to produce a movement of the head to an intermediate position along the first axis before each movement of the head to a related destination along that axis. Each intermediate portion is displaced from the related destination by a particular distance, preferably short, in a particular direction from the related destination. This causes the head to move slowly from each intermediate position precisely to the related destination. This eliminates the effects of magnetic hysteresis in the movement of the head to the desired positions relative to the stator.