Patent ID: 7521922

Claim:
A linear position sensor comprising: a magnetic field strength sensor positioned on substantially an axis; a first magnet extending parallel to the axis, and spaced from the axis, the first magnet having a pole of a first polarity arranged facing the axis; a second magnet arranged as a mirror image of the first magnet about the axis with respect to the first magnet, the second magnet facing the axis and the first magnet, the second magnet having a pole of a second polarity that is opposite to the first polarity of the first magnet; a third magnet extending parallel to the axis, and spaced from the axis, the third magnet having a pole of the second polarity arranged facing the axis; a fourth magnet arranged as a mirror image about the axis with respect to the third magnet, the fourth magnet having a pole of the first polarity opposite the second polarity of the third magnet; wherein the third magnet and the fourth magnet are arranged spaced from the first magnet and second magnet arranged as a mirror images of the first magnet and second magnet about a plane perpendicular to the axis; wherein the first magnet, the second magnet, the third magnet, and the fourth magnet, are fixedly mounted with respect to each other; wherein at least one of the magnetic field strength sensor or the magnets are mounted for movement with respect to the other along the axis; and wherein each of the four spaced apart magnets has portion facing the axis which form a first planar step spaced from the axis, and a second planar step spaced further from the axis than the first step, wherein the second steps are closer to the plane pernendicular to the axis than the first steps.