Patent ID: 6433536
Filing Date: 2002-08-13
Classification: G01D

Abstract:
An apparatus for providing an output indicative of the instantaneous position of a movable member along a range of motion with respect to a reference position, comprising: a magnetic body being fixedly attached to said movable member, said body having a contoured surface and producing a magnetic field, wherein said movable member includes a shaft rotatable about a rotation axis, and a disc having an outer periphery defined by a non-uniform radius, said disc being fixedly attached to said shaft at a disc center such that said disc rotates within a plane substantially normal to said rotation axis, said magnetic body being fixedly attached to said disc;at least two magnetic field sensors, each of said sensors being (i) disposed adjacent to said contoured surface of said magnetic body, (ii) fixed with respect to said reference position, and (iii) positioned apart from said other sensor, so as to form a non-uniform gap between said contoured surface and each of said magnetic field sensors, wherein each of said sensors produces a position dependent signal corresponding to a value of said magnetic field, said at least two magnetic field sensors including two sets of three magnetic field sensors disposed at angular intervals substantially equal to 120 electrical degrees; and, a decoding circuit electrically coupled to each of said magnetic field sensors so as to receive each of said position dependent signals, said decoding circuit producing an output position dependent signal being a predetermined function of said position dependent signals, wherein said magnetic field sensors are disposed about said outer periphery at substantially equal radii with respect to said rotational axis; wherein said predetermined function of said position dependent signals includes a difference between two said sensors in either of said sets of three magnetic field sensors, so as to substantially cancel a 3N harmonic distortion term, N being an integer greater than or equal to one.