Patent ID: 6553847
Filing Date: 2003-04-29
Classification: G01L

Abstract:
A magnetoelastic torque sensor for providing an output signal indicative of the torque applied to a member about an axially extending axis of said member, comprising:a first magnetostrictive, magnetoelastically active region in said member, said active region having magnetic domains magnetically polarized in a single circumferential direction and possessing sufficient magnetic anisotropy to return the magnetization in said active region to said single circumferential direction when the applied torque is reduced to zero, and possessing sufficient remanent magnetization whereby said active region produces a magnetic field varying with said torque; a first inactive region in said member proximate to said active region, said inactive region being sufficiently weakly magnetostrictive and having magnetic domains with substantially less remanent magnetization compared to said active region when said active region is magnetically polarized or when said active region produces the magnetic field; and magnetic field sensor means mounted proximate to said active region for sensing a characteristic of the magnetic field at said sensor means which is indicative of said applied torque and providing said output signal in response thereto; whereby the field arising from said active region does not magnetize said inactive region to give rise to parasitic magnetic fields from said inactive region which are of sufficient strength to destroy the usefulness, for torque sensing purposes, of the net magnetic field seen by said magnetic field sensor means.