Linear variable differential transformers for high precision position measurements

• US 20020175677A1
• Filed: 11/30/2001
• Published: 11/28/2002
• Est. Priority Date: 11/30/2000
• Status: Abandoned Application

• Current Assignee: Asylum Research Corporation (Oxford Instruments PLC)
• Original Assignee: Oxford Instruments Asylum Research Inc (Oxford Instruments PLC)
• Inventors: Proksch, Roger, Bocek, Dan, Cleveland, Jason
• Application Number:
  US10/016,475
• Publication Number:
  US 20020175677A1
• Time in Patent Office: Days
• US Class Current: 324/207.18
• CPC Class Codes: B82Y 35/00 Methods or apparatus for measurement or analysis of nanostructures
• CPC Class Codes: G01D 5/2066 by movement of a single coil with respect to a single other coil
• CPC Class Codes: G01D 5/2291 Linear or rotary variable differential transformers (LVDTs/RVDTs) having a single primary coil and two secondary coils
• CPC Class Codes: G01Q 10/04 Fine scanning or positioning
• CPC Class Codes: H01F 21/04 by relative movement of turns or parts of windings

Abstract

A transducer that reduces noise, increases sensitivity, and improves the time response of a linear variable differential transformer (LVDT). The device replaces the primary coil and the high permeability ferromagnetic core of conventional LVDTs with a primary wound around a moving non-ferromagnetic core. In addition to reducing or eliminating Barkhausen noise, this approach reduced or eliminated a number of other undesirable effects in conventional LVDTs including excessive eddy current heating in the core, non-linearities associated with high permeability materials and the length scale of the flux circuit. These improvements are coupled with improved LVDT signal conditioning circuitry. The device is also an actuator and may be used to convert differential voltages into force. Devices with these improvements have numerous applications, including molecular force measurements, atomic force microscopy and manipulation technology, lithographic manufacturing, nanometer scale surface profiling and other aspects of nanotechnology.

Claims

1. A displacement transducer comprising:

first and second non-ferromagnetic coil forms with a common axis, each wound with at least one winding;

the outside diameter of the first form with its winding or windings being smaller than the inside diameter of the second form so that each may be displaced relative to the other with the first form inside the second form;

one of the coil forms being movable and the other coil form being stationary;

the winding or windings on the movable form magnetically coupled to the winding or windings on the stationary form in the absence of any ferromagnetic element inductively coupling the windings; and

electronic circuitry generating a signal responsive to relative displacements between the coil forms in the range of microns or less.

2. The transducer of claim 1, in which the sensor comprises;

the coil form with the smaller outside diameter wound with two or more windings and the other coil form wound with a single winding.

3. The transducer of claim 1, in which the sensor comprises;

the coil form with the larger inside diameter wound with two or more windings and the other coil form wound with a single winding. ¹ Urbach defect paper on Barkhausen noise.