Polar coordinate sensor driven by a poly-phase stator core

Poly-phase induction motor-stator rotating magnetic fields are utilized as driving cores coupled to polar coordinate sensors for higher driving flux utilization and size reduction. External internal and combinational driving core structures are disclosed. An unsegmented stator having an extended longitudinal coupling portion is also disclosed.

The basic polar coordinate sensor comprises a driving core wound with 
poly-phase (previously referred to as sine-cosine) excitation coils and a 
pick-up core having one or more pick-up coils wound around a central pole 
or a hexagonal array of poles. 
The present invention utilizes rotating field stator structure concepts 
originating with Tesla, e.g. all poly-phase induction motor stator 
designs. All present and future developed magnetic core materials are 
suitable and deemed covered, presently ferrite is the preferred magnetic 
material. 
The primary objectives of the invention are to increase sensing pattern 
flux density, simplify construction, and size reduction. The Logue patent 
application Ser. Nos. 07/842,244, 08/142,933, 08/187,072, 08/217,738, 
08/267,511, 08/388,825, 08/685,854 and 08/599,775 utilized several 
variations-of hollow toroid driving cores. The Logue patent application 
Ser. No. 08/685,854 disclosed cross arm driving core ideas. The motor 
stator types disclosed have a higher net flux utilization than the earlier 
hollow toroid driving core embodiments.

BASIC PRINCIPLES 
Research to date indicates a synergism of basic electromagnetic principles 
embodied in the following key words. 
Key I) Parametric Coupling/Coplanar Driven pick-up coil. 
The driving flux natural direction is orthogonal to the pick-up core axis 
i.e. the pick-up coil turns are disposed in the plane of the driving flux 
therefore inherently nulled. 
Key II) A Coupling Coefficient (longitudinal/tangential). 
This flux gap allows the pick-up core inductance to ring as a true 
reflection of a flaw imbalance. 
Key III) An Oscillatory Tank Circuit. 
Key IV) Swept Angular Velocity (SAV), formerly called Variable Angular 
Velocity (VAV). 
Key V) A Precessing Elliptical sensing pattern. 
These key words will be further defined as dispersed throughout the 
detailed description of the invention. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The External Field Stator Driving Core 
FIGS. 1-5 are illustrative of an eddy current (not limited to eddy current 
effects) probe utilizing a driving stator of this invention (an external 
field). The generic polar coordinates sensor (FIGS. 4 and 5) comprises a 
pick-up core 88 formed of a high permeability material, such as ferrite (a 
slotless pot core half) and a pick-up coil 90 having many turns. Pick-up 
core 88, also has a cylindrical outer pole 84, a cylindrical central pole 
86 and a base portion 85. Pick-up coil 90 has an inner diameter 93, an 
outer diameter 92, and a longitudinal length 91. Pick-up coil 90 is 
disposed concentrically within toroidal space 89. Driving core 55a is 
formed of a high permeability material, such as laminated steel or 
ferrite, depending on the excitation frequency range. FIG. 1 is a 
perspective view of driving core 55a similar to a two phase induction 
motor stator with orthogonal field coils 58a, 58b (x-axis) 62a, 62b 
(y-axis) wound through slots 39a. Driving core 55a may be divided into any 
number of pole segments, odd or even, and all sinusoidal winding methods 
may be utilized. Semi-circle 70 represents the rotating driving field 
(example direction). As induction motor stators utilize external and 
internal stator fields, the disclosed eddy current probes make use of both 
external, internal, and a combinational arrangement. Driving stator 55a 
has an outside diameter 40, an inside driving diameter (bore 41) and an 
axial length 42. FIG. 2 is a radial view of driving core 55a showing a 
polar sensor PS (pick-up assembly proper) mounted concentric in bore 41 
(rotor location if this were a motor). 
FIG. 3 is a cross-section longitudinal view taken along lines BB showing 
polar sensor PS mounted partially within bore 41 leaving an extending 
portion 83 to form an annular sensing face 79. The driving flux lines 80 
couple orthogonally to the axis of pick-up core 88, thus the winding turns 
of pick-up coil 90 are said to be coplanar driven (key I). Also, there is 
an annular coupling gap (key II) in the driving flux circuit of pick-up 
core 88 within bore 41 i.e. there being a small difference in the bore 
I.D. and the pick-up core O.D. to form a concentric magnetic gap 96a in 
the driving flux path. A primary signal nulling requirement is the 
concentricity of the pick-up core axis within bore 41. Constancy of 
annular gap 96a width is one of the chief factors affecting the tuning of 
a perfect null. The experimential gap width being &lt;0.001", rigidity being 
the prime requisite. The pick-up coil turns must also be concentric to the 
annular space 89. The external field driving core embodiments (PSa, PSc) 
of this disclosure also have special application as driving cores for the 
angular resolver and proximity sensor of the Logue U.S. Pat. No. 5,404,101 
and including the joystick invention disclosed in the Logue U.S. Pat. No. 
5,559,432 providing an overall size reduction. Further by longitudinal 
lengthening of the stator two pick-up cores may be driven (base portions 
disposed adjacently) as in the the cross arm version disclosed in patent 
application Ser. No. 08/685,854. 
The theory of operation is as follows, however, it is not intended that the 
invention in any way be restricted by this explanation. Analysis 
indicates, flux linkage through pick-up coil 90 is the result of a type of 
parametric coupling found in equation: E=Ri+L(di/dt)+i(dL/dt), the 
parametric term being i (dL/dt). In the preferred embodiments of the 
invention pick-up coil 90 (190, 290a) is shunted by a capacitor 75 in FIG. 
5A, forming a series resonant-tank circuit 74. Tank circuit oscillatory 
action in magnetically balanced coils and cores is known in prior art, 
e.g. Wiegand U.S. Pat. No. 2,910,654, col. 3 lines 5-75, the Paraformer 
(Wanlass Electric Co. patent assignee). 
To continue this anslysis, refer now to FIG. 14, being an axial view of 
pick-up core 88 and driving core 55 (excitation windings and slots are not 
shown for clarity). Cylindrical outer pole 84 is magnetized diametrically 
by the driving flux flow. Rotating vector 70 may be seen as a rotating bar 
permanent magnet i.e. the effective portion of the driving flux path 
instantaneously in time. The coupling coefficient is effectively reduced 
to two arcuate portions (ap0 and ap180) of the annular gap 96 in FIG. 14 
(annular gap 96 is drawn oversized for illustration). Tests have shown, if 
there is even a small irregularity in the width of annular gap 96, the 
tangential motion of ap0 and ap180 will produce a rotating incremental 
permeability effect generating an off-null signal. This effect is much 
more pronounced when the driving core is excited by the precessing 
elliptical waveforms as disclosed in pending patent application Ser. No. 
08/599,775. 
The Internal Field Stator Driving Core 
FIGS. 6-9 are illustrative of a further embodiment of this invention, (an 
internal field driving stator). 
Driving stator core 155a in FIG. 6 has an outside driving diameter 140, an 
inside diameter 141 (also used as a mounting bore for a central pole 186 
in FIG. 9). Stator 155a is formed of a high permeability magnetic material 
such as ferrite, powered iron or laminated steel. For illustration 
simplicity, driving stator 155a is orthogonally divided into only four 
wound poles i.e. 158a-158b on the x-axis and 162a-162b on the y-axis. 
Winding slots 139a permit conventional winding insertion. FIG. 7, is a 
radial view of stator 155a showing a basic sine-cosine x-y winding 
structure 158a-158b, 162a-162b wound through slots 139a to form an 
external radiating rotating magnetic field. 
FIG. 8, is an isometric view of assembled probe PSb with the driven element 
(cylindrical outer pole 184) mounted around driving stator 155a. Pick-up 
coil 190 is shown wound around cylindrical pole 186. The coplanar driving 
principle is symbolized by the S-N dipole action of rotating vector 70 
across the annular sensing face 179. Other conventional poly-phase pole 
combinations (odd or even) are deemed covered by this disclosure. 
A greater number of pole segments provide more perfect circularity to the 
rotating driving field 70. Well known motor stator sinusoidal winding 
patterns are utilized for optimum poly-phase distributions. The integrated 
pick-up elements of polar coordinates sensor PSb are disposed both inside 
and outside the driving core 155a (FIGS. 8 and 9.), comprising a central 
cylindrical pole 186 and a cylindrical outer pole 184, both being formed 
of a high permeability low conductivity material/materials such as 
ferrite. FIG. 9 is a cross-sectional view taken along lines CC. The 
expanding internal driving flux is coupled from driving core 155a to the 
lower longitudinal portion of the cylindrical outer pole 184, and thence 
to the fringing sensing pattern. An axial portion of central cylindrical 
pole 186 is concentrically positioned within bore 141 (also called the 
I.D. of driving core 155a). In this embodiment there are two annular 
locations for incorporating the mentioned coupling coefficient (synergism 
term II): (a) an annular gap between driving core 155a and the cylindrical 
outer pole 184. (b) an annular gap 141a between central pole 186 and 
driving core 155a. Around central pole 186 is wound pick-up coil 190a. A 
nonferrous washer 199 encircles central pole 186 between the excitation 
windings and the pick-up coil windings as a high reluctance barrier to 
stray flux leakage from the excitation coils 158a, 158b, 162a, 162b. 
Washer 199 may be alternately utilized as a shorted pick-up coil turn or 
formed as multiple turns of thin flat stock wound in a tight longitudinal 
spiral (insulation between adjacent turns). The shorted turn version has a 
Lenz reflective flux interaction with the afore described coplanar 
disposed driving flux in the plane of the pick-up coil. 
Surplus driving flux generated in the rear of driving core 155b may be 
repelled toward the sensing face for greater efficiency by means of a 
copper repulsion ring 167, as seen in FIGS. 8, 9. Repulsion ring 167 is 
isometrically illustrated in FIG. 9A, comprising an outer diameter 168, an 
inner diameter 169 and a longitudinal length 181. Excitation and pick-up 
coil connecting leads are not shown in any drawing figures for clarity. 
External-Internal Field Stator Driving Core 
FIG. 9, also illustrates an internal-external field driving combination 
PSx, by addition of stator 155b concentrically around a cylindrical outer 
pole 184, having a conducting thickness 184a. Stator 155b has excitation 
windings 158c. Although mechanically obvious, the vectorial sum of dual 
excitation possibilities are not readily apparent. The resultant 
excitation of cylindrical outer pole 184 by driving cores 155a and 155b 
may have the same frequency and in phase for greater driving flux, or e.g. 
different frequencies (two excitation sources) for harmonic generation 
(odd/even) in the resultant sensing pattern. The two driving fields may 
even counter-revolve at same/different angular velocities to provide a 
steerable beacon-like sensing pattern as disclosed in patent application 
Ser. No. 08/685,854. A disadvantage of the driving core embodiments of 
FIGS. 1-9 is the longitudinal winding slots 39a, 139a which are widened 
areas in the coupling coefficient gap between the driving and pick-up 
core. FIGS. 8, 9, also show a non-ferrous repulsion ring 167 around the 
rear portion of driving core 155a for driving field enhancement. This 
enhancement means serves a dual purpose: (1) repelling the driving flux 
toward the sensing end, (2) the I.D. of ring 167 may be made slightly 
larger than the O.D. of core 155a, as a flux concentricity adjustment 
means to compensate for manufacturing flaws. FIG. 10 is an isometric view 
(including a cut-away section) of probe PSc, which embodies elements of 
probes PSa, PSb, plus further utilization of high and low reluctance 
elements to enhance the resultant sensing pattern. 
A nonferrous (copper) sensing end cap 271 is a dual utilization of the 
previously disclosed non-ferrous washer magnetic shield idea. The primary 
purpose of sensing end cap 271 is to concentrically support the outer pole 
84, 184, 284 (pick-up core element) partially within the driving core 55a, 
155b, 255a. The second purpose of copper sensing end cap 271 is to block 
away from the sensing pattern any stray flux leaking from the driving core 
255a and the excitation windings. The disadvantage of the winding slot 
39a, 139a openings breaking into the coupling coefficient gap (96a in FIG. 
3) is eliminated in FIGS. 10, 11, by locating winding bores 239 away from 
the mounting bore 241 (stator I.D.) forming an integrate portion 241a. 
Longitudinally adjoining integrate portion 241a is coupling flange 276 for 
utilization of excitation winding 258a, 258b, 258c, 258d, clearance space 
at the top in FIG. 11. Annular space 279 is provided for pick-up coils 
290a, 290b. Driving stator core 255 may be made separable for winding 
facility by a cone separation means 202, a cone being the least flux 
leakage separation means. FIG. 11 is a cross-section longitudinal view 
taken along lines FF in FIG. 10 of probe PSc, showing the concentric 
construction of flux concentricity slug 205. Slug 205 is further shown 
isometrically in FIG. 11, comprising a ferromagnetic portion 267 having a 
greater diameter 267b and a lesser diameter 267a. Concentrically fitted 
around lesser diameter 267a is a copper ring 303 producing an annular high 
reluctance area at the base portion 285 of pick-up core 288. Slug 303 is 
adjustably mounted to rear end cap 272 by means of slug screw 273, and 
made eccentrically adjustable by nuts 273b, 273d. Sensing end cap 271 and 
rear end cap 272 are joined around driving core 255 at 203 forming a 
casing. This nonferrous casing form may also be used with probes PSa, PSb, 
PSx. FIG. 13 illustrates an alternate coupling coefficient annular gap 
296a within the base 285 of pick-up core 288 i.e central pole 286 is 
coupled to the base portion 285 by a coefficient. There are two pick-up 
coils 290a, 290b, wound around a central cylindrical pole 286 in a 
longitudinal arrangement.