Collarless circularly magnetized torque transducer and method for measuring torque using the same

A method of sensing a torque applied to a torqued member extending in an axial direction, comprising the steps of:

• (a) providing 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;
• (b) providing 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 a magnetic field;
• 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 a magnetic field sensing means;
• (c) producing a magnetic field as a consequence of the application of torque to said member;
• and
• (d) sensing a characteristic of the magnetic field at a position proximate to said active region which is indicative of the torque applied to said member.

A method of producing a magnetoelastic torque transducer from a member to which an axial torque is applied for producing a magnetic field varying with said torque, the magnitude of said magnetic field being sensed by magnetic field sensors for providing an output signal indicative of the applied torque, comprising the steps of:

• (a) providing a magnetostrictive member having a first magnetostrictive, magnetoelastically active region in said member;
• (b) providing a first inactive region in said member proximate to said first 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 a magnetic field;
• (c) polarizing a finite axial extent of said active region in a magnetizing field in a single circumferential direction, said active region possessing sufficient magnetic anisotropy to return the magnetization in said region to said single circumferential direction when the applied torque is reduced to zero and possessing sufficient remanent magnetization;
• and
• (d) whereby the field arising from said first 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 sensors.