Magnetic field generator and position sensing assembly

Abstract

A magnetic field generator having at least one magnet extending along a longitudinal axis, wherein the magnetic material of the at least one magnet is arranged such that the at least one magnet produces a magnetic field with a magnetic flux density that changes substantially continuously in magnitude in the axial direction substantially along the length of the at least one magnet in the axial direction and a position sensing assembly comprising the magnetic field generator.

1 . A magnetic field generator comprising a magnet extending along a longitudinal axis, wherein the magnetic material of the magnet is arranged such that the magnet produces a magnetic field with a magnetic flux density that changes substantially continuously in magnitude in the axial direction substantially along a length of the magnetic field generator;
 wherein the magnet extends in the axial direction from a first end, that forms a first pole, to a second end, that forms a second pole, wherein the outer diameter of the magnet changes substantially continuously from the first and/or second ends of the magnet towards the midpoint between the first and second ends such that the amount of magnetic material in a plane substantially perpendicular to the axis changes substantially continuously from the first and/or second ends of the magnet towards the midpoint between the first and second ends.   
     
     
         2 . A magnetic field generator according to  claim 1  wherein the amount of magnetic material is varied by at least one continuous change in the amount of magnetic material in said plane as the axial position of the plane varies, along at least a section of the entire length of the magnet in the axial direction. 
     
     
         3 . A magnetic field generator according to  claim 1  wherein the magnet is disposed within a wall of a housing of magnetically insulating material. 
     
     
         4 . A magnetic field generator according to  claim 1  wherein the magnet is received within a bore in the wall of the housing. 
     
     
         5 . A magnetic field generator according to  claim 1  wherein the magnet is substantially enclosed by the magnetically insulating material. 
     
     
         6 . A magnetic field generator according to  claim 1  wherein the magnetic field generator comprises one or more sets of magnets, each set comprising at least a pair of said magnets. 
     
     
         7 . A magnetic field generator according to  claim 1 , wherein the amount of magnetic material in the plane increases linearly from the first and/or second ends towards the midpoint. 
     
     
         8 . A magnetic field generator according to  claim 1 , wherein the amount of magnetic material in the plane increases non-linearly from the first and/or second ends towards the midpoint. 
     
     
         9 . A magnetic field generator according to  claim 1 , wherein the amount of magnetic material in the plane increases from the first and/or second ends to the midpoint. 
     
     
         10 . A magnetic field generator according to  claim 1 , wherein the magnet is solid. 
     
     
         11 . A magnetic field generator according to  claim 1 , wherein a diameter of the magnet is greatest at the midpoint. 
     
     
         12 . A magnetic field generator according to  claim 11 , wherein the diameter is greatest in a flat central section comprising the midpoint. 
     
     
         13 . A position sensing assembly comprising a movable member arranged to move along an axis, wherein a magnetic field generator according to  claim 1  is coupled to the movable member, to move with the movable member, and a magnetic sensor arrangement comprising at least one magnetic sensor arranged to determine the axial position of the magnetic field generator. 
     
     
         14 . A position sensing assembly according to  claim 13 , wherein the axis of the moveable member is parallel to, and offset from, an axis of the magnetic sensor.