Detection of Magnetic Object Movements by Flux Density Tracking Control

In this paper, a motion trajectory detecting method that permits tracking of magnetic objects is investigated by the magnetic flux density of a 3-D Hall probe. Inaccurate motion trajectory information may be produced physically due to the measured magnetic field signal altering as the distance between the Hall probe and the object changes. A magnetic flux feedback control is proposed such that the motion command of the control system is generated in real time by the coordinated geometry of the Hall probe and the magnetic object. The magnetic tracking control system consists of an inner position/velocity control loop and an outer magnetic control loop that employs a position vector expressed in terms of the magnetic flux density to detect the relative distance between a magnetic object and the Hall probe. The measurement of the Hall probe can, hence, be kept within an effective distance such that the motion trajectory of the measured magnetic object can be detected accurately for the case of large movements. An experimental setup with a five-axis servo mechanism is constructed for the validation study, in which the three-axis moving table is utilized to control the motion of the Hall probe, and the other two-axis moving table facilitates the movement of the magnetic object. A circular motion and a rhomboidal path are given to verify the improvement of the proposed detecting method.