Motion transducer for motion related to the direction of the axis of an eddy-current displacement sensor

Abstract

A motion transducer comprising one or more electromagnetic coils provided on a first element, each of the coils having a magnetic axis of symmetry.

Description

DRAWING DESCRIPTION

FIG. 1 shows the basic magnetic elements of an eddy-current displacement detector;

FIG. 2 a and FIG. 2b show two different simple embodiments of electronic circuits that can provide a measure of distance between an electromagnetic coil and a conducting surface;

FIG. 3 a shows a simple structure that has been used to form a linear motion transducer, for motion of a conducting surface normal to the magnetic axis of the electromagnetic coil;

FIG. 3 b shows details of an electromagnetic coil used with the apparatus of FIG. 3a; and includes view A taken in section and view B taken on lines B-B of view A;

FIG. 4 is a graph that shows a sample of data measured with the apparatus of FIGS. 3aand 3bwhen connected to an electronic circuit of the type shown in FIG. 2;

FIGS. 5 a, 5b, 5cand 5d show alternative forms for a conducting surface for an extended range linear motion transducer of the present invention type;

FIG. 6 shows another alternative configuration having a conical conducting surface surrounded by an electromagnetic coil;

FIG. 7 shows an example of a motion transducer for angular motion based on the current invention.

Claims

1. A motion transducer comprising: a) one or more electromagnetic coils provided on a first element, each of said coils having a magnetic axis of symmetry,b) a conducting surface provided on a second element moveable with respect to said first element, said surface oriented so as not to be normal to the said magnetic axis or axes of symmetry of said electromagnetic coil or coils,c) first means to excite said coil with an alternating voltage or current,d) second means to detect the impedance of said coil or coils using said first means to excite said coil, ande) third means to interpret detected impedance of said coil in terms of relative displacement of said conducting surface with respect to said coil.

2. The apparatus of claim 1 wherein one of said electromagnetic coils is provided, the said conducting surface defines a single plane inclined at an angle to a linear axis defined by said second element.

3. The apparatus of claim 1 wherein one of said electromagnetic coils is provided and the said conducting surface defines a sequence of single planes inclined at an angle to a linear axis defined by said second element.

4. The apparatus of claim 1 wherein the said conducting surface is a single plane inclined at an angle to a linear axis defined by said second element, and a selected number of said electromagnetic coils is or are provided in a sequence on said first element.

5. Apparatus as defined in any of claims 1 through 4, wherein an auxiliary electromagnetic coil, not exposed to said conducting element, is used to provide a compensating signal that may be subtracted from all of said electromagnetic coils in said claims.

6. A linear motion transducer comprising: a) two electromagnetic coils provided on a first element, each of said coils having a magnetic axis of symmetry, said coils being spaced apart along an axis defined by said first element,b) a conducting surface on a second element and configured to be generally sinusoidal along a dimension of the second element, said sinusoidal surface having a wavelength of about four times the spacing between said two coils,c) first means operating to excite said two coils with an alternating voltage or current,d) a second means to detect changes in the impedances of said coils in response to said operation of the first means,e) third means to interpret said detected impedance changes of said coils as a function of distance of said coils from said conducting surface, andf) fourth means to determine linear motion of said conducting surface with respect to said coils along a line generally normal to the magnetic axis or axes of symmetry of said coils in terms of the arctangent of the ratio of the measurements obtained from each of said two coils.

7. A linear motion transducer comprising: a) two pairs of electromagnetic coils provided on a first element, each of said coils having a magnetic axis of symmetry, said coils being spaced apart along an axis defined by said first element,b) two conducting surfaces on a second element and configured such that each surface is generally sinusoidal along a dimension or dimensions of the second element, both sinusoidal surfaces being in generally the same phase relation along said dimension or dimensions, each of said sinusoidal surfaces having a wavelength of four times the spaced apart separation distance of said two coils,c) first means operating to excite said two pairs of coils with an alternating voltage or current,d) second means to detect changes in the impedances of said coils in response to said operation of the first means,e) third means to interpret said detected impedance changes of said coils as a function of distance of said coils from said conducting surface said observed impedance changes and of the difference of the impedances of the two coils in each said pair of coils, andf) fourth means to determine linear motion of said conducting surface with respect to said coils along a line generally normal to the magnetic axis or axes of symmetry of said coils in terms of the arctangent of the ratio of the measurements obtained from each of said two coils.

8. A rotary angular motion transducer comprising: a) an electromagnetic coil provided on a first element, said coil having a magnetic axis of symmetry,b) a second element, a conducting surface having a spiral-shape, said spiral-shaped surface having an axis of rotation defined on the second element and moveable in an angular sense with respect to said first element,c) first means to excite said coil with an alternating voltage or current,d) second means to detect the impedance change of said coil as said second element is rotated about said rotation axis of symmetry using said first means to excite said coil, ande) third means to interpret detection impedance of said coil as a function of angular rotary motion of said conducting surface with respect to said coil.

9. The method of operating a motion transducer having coil means having impedance, and conducting surface means, that includes a) electrically energizing said coil means in alternating sense,b) relatively displacing said coil means and said conducting surface means, while maintaining said surface means out of perpendicularity relation to an axis defined by the coil means, thereby to produce changes in the coil means impedance,c) and detecting said changes in impedance as a function of said relative displacement.

10. The method of operating a rotary angular motion transducer that includes a) an electromagnetic coil provided on a first element, said coil having a magnetic axis of symmetry,b) providing a second element, a conducting surface having a spiral-shape, said spiral-shaped surface having an axis of rotation defined on the second element and moveable in an angular sense with respect to said first element,c) providing first means operating to excite said coil with an alternating voltage or current,d) providing second means to detect the impedance change of said coil as said second element is rotated about said rotation axis of symmetry using said first means to excite said coil, ande) providing third means operating to interpret detection impedance of said coil as a function of angular rotary motion of said conducting surface with respect to said coil.

11. A motion transducer comprising: a) one or more electromagnetic coils provided on a first element, each of said coils having a magnetic axis of symmetry,b) a conducting surface provided on a second element moveable with respect to said first element, said surface oriented so as not to be normal to the said magnetic axis or axes of symmetry of said electromagnetic coil or coils,c) first means to excite said coil with an alternating voltage or current,d) second means to detect the impedance of said coil or coils using said first means to excite said coil, ande) third means to interpret detected impedance of said coil in terms of relative displacement of said conducting surface with respect to said coil.

12. A motion transducer comprising: a) two electromagnetic coils provided on a first element, each of said coils having a magnetic axis of symmetry, said coils being spaced apart along an axis defined by said first element,b) a conducting surface on a second element and configured to be generally sinusoidal along a dimension of the second element, said sinusoidal surface having a wavelength of about four times the spacing between said two coils,c) first means operating to excite said two coils with an alternating voltage or current,d) second means to detect changes in the impedances of said coils in response to said operation of the first means,e) third means to interpret said detected impedance changes of said coils as a function of distance of said coils from said conducting surface, andf) fourth means to determine motion of said conducting surface with respect to said coils along a line related to the magnetic axis or axes of symmetry of said coils in terms of the arctangent of the ratio of the measurements obtained from each of said two coils.