Linear variable differential transformers for high precision position measurements

Abstract

A linear variable transformer (LVDT) for use in a transducer. The LVDT has a non-ferromagnetic core which may eliminate Barkhausen noise and thereby improve the sensitivity of the resulting measurements. In one aspect, this system may be used in an atomic force microscope.

1 . A position sensor, comprising: 
 a moving coil part, having a first coil form formed of a non ferromagnetic material, and a coil element having an electrical connection part, formed around said first coil form, said moving coil part constrained to move in a linear direction, and said moving coil part including a connection element adapted for connection to a moving object of interest;    a stationary coil part, having a second coil form also formed of a non ferromagnetic material, and a second coil element wound on said second coil form, with said second coil element having at least first and second electrical connections which produce an output signal indicative of a moving relationship between said moving coil part and said stationary coil part, said stationary coil part sufficiently close to said moving coil part such that magnetic flux from said moving coil part is induced into said stationary coil part; and    a shell material, surrounding at least a part of said moving coil part and stationary coil part, said shell material supporting an external magnetic field therein.    
     
     
         2 . A position sensor assembly, comprising: 
 a primary non ferromagnetic coil assembly including all non ferromagnetic material, coupled to a movable object of interest, and being movable according to movement of the movable object of interest;    at least first and second stationary coil assemblies, each including all non ferromagnetic materials, said first and second stationary coil assemblies being located adjacent to said primary non ferromagnetic coil assembly; and    an electronics portion, producing electrical current to one of said coil assemblies, and receiving an induced signal from the other of said coil assemblies, and determining a position of said primary non ferromagnetic coil assembly relative to said first and second stationary coil assemblies from said induced signal, said electronics portion including a synchronizing element which synchronizes a detection of a signal from said receiver circuit with a desired time of detection based on said drive signal.    
     
     
         3 . A method, comprising: 
 driving a primary coil with a voltage;    sensing voltages induced into a plurality of secondary coils, from movement of the primary coil relative to the secondary coils, in a way that avoids parts of the signal being effected by Barkhausen noise.    
     
     
         4 . A method, comprising: 
 using a molecular force probe to cause deflection of a cantilever; and    using movements of said cantilever to drive a plurality of coils which detects said movements substantially without being effected by Barkhausen noise.    
     
     
         5 . A method, comprising: 
 using a surface profiling instrument to cause a deflection; and    moving using movements caused by the deflection to drive a plurality of coils to detect said movements substantially without being effected by Barkhausen noise.    
     
     
         6 . A method, comprising: 
 using an atomic force microscope to cause a deflection; and    moving using movements caused by the deflection to drive a plurality of coils to detect said movements substantially without being effected by Barkhausen noise.    
     
     
         7 . A system, comprising: 
 an atomic force microscope having an optical detection system, said atomic force microscope defining a frame of reference, said atomic force microscope having a cantilever, with a flexure that constrains the cantilever to move in a specified axis relative to said frame of reference, and with a moving coil part which detects movement of the cantilever in the direction of the specified axis, said moving coil being formed without ferromagnetic materials.    
     
     
         8 . A system as in  claim 7 , wherein said moving coil includes a coil mounted on a solid form.  
     
     
         9 . A system as in  claim 7 , wherein the specified axis is a z axis relative to the frame of reference.  
     
     
         10 . A system as in  claim 7 , wherein the specified axis is the x and/or y axis relative to the frame of reference.