METHOD AND FIXTURE FOR EVALUATING
STATOR CORE QUALITY IN PRODUCTION
FIELD OF THE INVENTION
This invention relates generally to the field of stator core
production, and more particularly to quality testing of stator cores
during production.
BACKGROUND OF THE INVENTION
In the manufacture of high efficiency motors and precision
resolvers, for example, it is necessary to be able to evaluate the effects
of processing steps on the quality of the magnetic core material in a
timely and cost efficient manner. Heretofore, this issue has been
addressed by winding a multitum coil, laboriously by hand, through the
bore and around the yoke of the magnetic circuit to provide the
capability to excite and evaluate the state of the material.
It is therefore desirable to provide a fixture for quickly placing a
multiturn coil, having a precisely fixed and repeatable geometry, around
the yoke of a typical magnetic machine in order to make measurements
of and trend magnetic properties. It is also desirable to be able to
remove this fixture quickly without damaging or stressing the core.
SUMMARY OF THE INVENTION
A two part fixture, with conductors embedded, is mated on a
motor core to complete a multiturn winding in order to evaluate core
permeability and losses. The fixture includes an inner annulus with a
plurality of inner axial conductors thereon, an outer annulus with a
plurality of outer axial conductors thereon, a bottom plate with a
plurality of bottom plate conductors thereon, and a top plate with a
plurality of top plate conductors thereon. The inner conductors and
outer conductors are electrically connected to one another at lower
ends thereof through the bottom plate conductors and at upper ends
thereof through the top plate conductors, so as to form a complete,
continuous electrical winding.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a plan view of a conventional stator core lamination.
FIG. 2 is a perspective view of a conventional stator core
assembled by stacking a large number of the laminations shown in FIG.
1 and inserting wire.
FIG. 3 is a front schematic view of a typical (prior art) toroidal
winding about a stator core, used to test production quality of the core.
FIG. 4 is a perspective view of a representative stator core
quality evaluation fixture in accordance with the invention.
FIG. 5 is a top plan view of a set of representative electrical
connections for a bottom plate of the fixture shown in FIG. 4.
FIG. 6 is a bottom (upside down) plan view of a set of
representative electrical connections for a top plate that is attached to
the top portion of the fixture shown in FIG. 4, to complete the electrical
connections of that fixture.
FIGS. 7 and 8, respectively, are top and bottom plan views of
(illustrative) bottom and top plates for a multilayer fixture.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 illustrates a lamination 10 typical of electromechanical
energy converters and transducers such as precision resolvers. As
shown in FIG. 2, core 11 of the device is formed by stacking a large
number of laminations 10 in registration, and inserting wires 12 into the
slots. The efficiency of energy converters and the accuracy and
precision of transducers depends on maintaining the quality of the core
magnetic material. The quality is manifest in the principal properties of
the core, which are the permeability and the specific losses. These
properties are severely affected by mechanical stresses, coating
integrity, contaminants, bonding or impregnating compounds, dull tools,
and other quality-compromising factors commonly encountered in
manufacturing processes.
FIG. 3 illustrates the usual (prior art) method of checking these
properties of an assembled magnetic core, such as that shown in FIG.
2, which is to wind a toroidal coil with testing leads 21 and 22 around
core (yoke) 11 to create a winding 20. Although automatic winding
machines are available for winding multitum inductors of this general
form with large numbers of turns, they are inappropriate for test
windings of this nature because they are expensive and difficult to use,
and introduce more defects. Consequently, windings are laboriously
wound by hand with hookup wire. In addition, windings must be
removed when testing is complete, which adds more time and labor.
Naturally the windings do not always go on in exactly the same
configuration, and so the test results from one stator core to the next
are not uniform.
The solution to this problem, in accordance with the invention, is
to construct a rigid winding fixture in two pieces which, when
assembled, form a toroidal winding around the core. A representative
embodiment of such a fixture is shown in FIGS. 4, 5 and 6. FIG. 4
shows a first fixture piece 301 comprised of a non-conductive, non-
magnetic bottom plate 302 on which two annuli - inner annulus 303
and outer annulus 304 -- are mounted. Inner annulus 303 is sized to fit
within the inside diameter 23 of core 11, shown in FIG. 3, for example,
and is fitted with a plurality of inner annulus axial conductors 305. The
twelve inner conductors 305 illustrated in FIG. 4 each contain an
associated reference label A' through L\ Outer annulus 304 is sized to
fit around outside diameter 24 of core 11 shown in FIG. 3, for example,
and is similarly fitted with a plurality of outer annulus axial conductors
306 equal in number to the number of inner conductors 305. Each of
the outer conductors 306 corresponds to an inner conductor 305, and
so is illustrated with an associated reference label A through L
corresponding to the labels A' through L'. Although twelve inner and
outer conductors 305 and 306 are illustrated, there may be any number
of conductors allowed by the space available on the annuli. Annuli 303
and 304 are fabricated of non-conductive, non-magnetic materials, so
that the only electric current on the annuli will be that in conductors 305
and 306.
FIG. 5 shows how electrical connections between inner and
outer axial conductors 305 and 306 (FIG. 4) are made on bottom plate
302 via a plurality of bottom plate conductors 307 equal in number to
one less than the number of inner and outer conductors 305 and 306,
shown in FIG. 4. Each inner conductor 305 is connected to an outer
conductor 306 that is displaced by one unit from the directly
corresponding outer conductor (connection displacement). Thus, for
example, a contact for inner conductor A' is connected to a contact for
outer conductor B; a contact for inner conductor B' is connected to a
contact for outer conductor C; etc. The first outer conductor contact A
and the last inner conductor contact L' are not connected to one
another, but are connected to testing leads 21 and 22 for external
connection. This accounts for the number of bottom plate conductors
307 being one less than the number of inner and outer conductors 305
and 306. Bottom plate 302 is, of course, also non-conductive and non-
magnetic. Test leads 21 and 22 are connected to contacts for inner
conductor L' and outer conductor A.
FIG.6 illustrates a second fixture piece 308 which comprises a
top plate 309 designed to mate with the first fixture piece 301 (FIG. 4).
Top plate 309 is shown from a bottom (upside down) view, and has
points for contacting both sets of inner and outer axial conductors 305
and 306 (FIG. 4) and connecting them together via a plurality of top
plate conductors 310 equal in number to the number of inner and outer
conductors 305 and 306 (FIG. 4). Top plate 309 is also non-conductive
and non-magnetic.
When second piece 308 is turned over and properly mated with
first piece 301 (FIG.4) each inner conductor 305 makes electrical
contact with, and is connected directly, to its directly corresponding
outer conductor 306. Thus, for example, inner conductor A* is
connected to outer conductor A; inner conductor B' is connected to
outer conductor B; etc. Consequently, when second piece 308 is
joined with first piece 301 and stator core 11 (FIG. 2) is contained
between the inner and outer annuli 303 and 304 (FIG. 4), a complete
winding similar to that shown in FIG. 3 is formed about core 11. The
connection displacement illustrated in FIG. 5 is ultimately responsible
for achieving the necessary continuity of the winding. Test leads 21
and 22 may then be externally connected for stator quality testing, as
shown in FIG. 3.
Although a single layer cf turns is shown in FIG. 3, multiple
layers may be implemented by adding axial conductors and contact
points similarly connected on the top and bottom plates. Known
methods of keying may be used to assure proper alignment of the
elements. If the core is small enough, the axial leads and/or their
connections may be plated in a manner similar to that for printed circuit
boards and the connections may either be a simple metal-to-metal
contact or actual circuit board type connectors. For large cores the
leads need to be more substantial and comprise insulated wires glued
or similarly attached to the annuli and fitted with connectors suitable for
larger currents. The instant technique may be applied to cores ranging
from resolvers where the typical dimensions may be in fractions of an
inch, to locomotive traction motors where the typical dimensions may
be in feet. FIGS. 7 and 8 depict use of this technique for large cores,
illustrating a two-layer configuration which can readily be extended to
multiple layers, as required. Where there is not enough physical space
for all of the axial conductors (which would in reality be a problem
primarily with inner annulus 303 (FIG. 4) due to its limited
circumference), a second inner annulus can be introduced just inside
the original inner annulus 303, with a second set of inner contact points
as shown in FIGS. 7 and 8. Of course, a corresponding set of changes
would have to be made on top and bottom plates 309 and 302,
respectively. If layering were required on outer annulus 304 (FIG. 4), a
second outer annulus just outside original outer annulus 304 would be
introduced, and appropriate realignment of other contacts as well would
have to be done. The net result would be a multilayer, rather than
single layer, winding.
The fixture of this invention is easily placed around a stator core
and easily removed. The fixture provides uniformity that cannot be
achieved by hand winding. As the fixture does not directly contact the
core, its use is non-destructive of stator quality. The invention has
application to resdver testing, and generally, for controlling the quality
of high efficiency motors.
Many variations can be made of this invention, all of which fall
within the scope of this disclosure and its associated claims. For
example, while axial conductors 305 and 306 (FIG. 4) are depicted as
being substantially vertical, top plate conductors 310 (FIG. 6) are
depicted as being substantially radial, and the connection displacement
is achieved by the configuration of bottom plate connectors 307 as
illustrated in FIG. 5, the overall winding effect of this invention can be
achieved by a wide range of geometric variations to this configuration,
all of which would be obvious in light of this disclosure. Thus, for
example, axial conductors 305 and 306 can be mostly vertical, with a
slight horizontal displacement, so that the connection displacement is
achieved along the annuli rather than along the bottom plate. Or, the
roles of the upper and lower plates can be reversed, with lower plate
302 providing a directly-corresponding inner-to-outer connection and
upper plate 309 providing the connection displacement as well as leads
21 and 22 for external connection. Alternatively, the configuration of
axial conductors 305 and 306 in combination with bottom and top plate
conductors 307 and 310 can be such that all of the conductors are
mildly graded to produce the necessary connection displacement. In
short, there are a wide variety of configurations encompassed by the
invention that can achieve the same net effect as the configurations
illustrated herein.
While only certain preferred features of the invention have been
illustrated and described, many modifications, changes and
substitutions will occur to those skilled in the art. It is, therefore, to be
understood that the appended claims are intended to cover all such
modifications and changes as fall within the true spirit of the invention.
What is claimed is:
1. A fixture for evaluating production quality of a stator
core (11), comprising:
an inner annulus having a plurality of inner axial
conductors thereon;
an outer annulus having a plurality of outer axial
conductors thereon;
a bottom plate having a plurality of bottom plate
conductors (307) thereon; and
a top plate having a plurality of top plate conductors
(310) thereon; wherein
the inner conductors and outer conductors are
electrically connected to one another at lower ends thereof through
said bottom plate conductors and at upper ends thereof through said
top plate conductors, so as to form a complete, continuous electrical
winding.
2. The fixture of claim 1, wherein:
said inner annulus, said outer annulus and said bottom
plate together comprise a unitary first fixture piece to electrically
connect the inner conductors and the outer conductors to one another
at said lower ends thereof through said bottom plate conductors; and
wherein
said top plate comprises a unitary second fixture piece
which is mated to said first fixture piece to electrically connect the inner
conductors and the outer conductors to one another at said upper ends
thereof through said top plate conductors, to complete said continuous
electrical winding.
3. The fixture of claim 1, wherein:
said inner annulus, said outer annulus and said top plate
together comprise a unitary first fixture piece to electrically connect the
inner conductors and the outer conductors to one another at said upper
ends thereof through said top plate conductors; and wherein
said bottom plate comprises a unitary second fixture
piece which is mated to said first fixture piece to electrically connect the
inner conductors and the outer conductors to one another at said lower
ends thereof through said bottom plate conductors, to complete said
continuous electrical winding.
4. The fixture of claim 1, wherein:
quantities of said plurality of inner axial conductors, said
plurality of outer axial conductors, and said plurality of top plate
conductors are equal to one another, and are greater by one than a
quantity of said plurality of bottom plate conductors; and wherein '
each one of said inner axial conductors corresponds with
and is connected to one of said outer axial conductors at said upper
ends thereof, via a further corresponding one of said top plate
conductors; and
further including first and second test leads situated upon
said bottom plate;
a first one of said outer axial conductors being connected
to said first test lead and a last one of said inner annulus axial
conductors being connected to said second test lead;
each remaining one of said inner axial conductors being
connected to a respective remaining one of said outer axial conductors
that is displaced by one unit from its corresponding outer axial
conductor at said lower ends thereof through a respective one of said
bottom plate conductors.
5. The fixture of claim 1, wherein at least one of the inner
annulus and the outer annulus comprises a plurality of annulus layers
with a plurality of axial conductor layers, such that said complete,
continuous electrical winding is a multilayer winding.
6. A method for testing a stator core, comprising the
steps of:
containing said stator core between an inner annulus
fitted within an inside diameter of the core and an outer annulus fitted
around an outside diameter of the core, and further containing said
stator core between a bottom plate proximate lower ends of the annuli
and a top plate proximate upper ends of the annuli;
electrically connecting a plurality of inner axial
conductors on said inner annulus and a plurality of outer axial
conductors on said outer annulus to one another at lower ends of the
axial conductors through bottom plate conductors on said bottom plate
and at upper ends of the axial conductors through top plate conductors
on said top plate, so as to form a complete, continuous electrical
winding about said stator core; and
connecting first and second ones of said conductors on
said bottom plate to an external testing device.
7. The method of claim 6, wherein the step of containing
the stator core between the inner annulus and outer annulus, and
between the bottom plate and the top plate, comprises:
mating a unitary first fixture piece to a unitary second
fixture piece;
said unitary first fixture piece comprising said inner
annulus (303), said outer annulus and said bottom plate electrically
connecting the inner axial conductors and the outer axial conductors to
one another at said lower ends thereof through said bottom plate
conductors, said unitary second fixture piece comprising said top plate
electrically connecting the inner axial conductors and the outer axial
conductors to one another at said upper ends thereof through said top
plate conductors.
8. The method of claim 6, wherein the steps of
containing the stator core between the inner annulus and the outer
annulus, and between the bottom plate and the top plate, comprises:
mating a unitary first fixture piece to a unitary second
fixture piece;
said unitary first fixture piece comprising said inner
annulus, said outer annulus and said top plate electrically connecting
the inner axial conductors and the outer axial conductors to one
another at said upper ends thereof through said top plate conductors,
said unitary second fixture piece comprising said bottom plate
electrically connecting the inner axial conductors and the outer axial
conductors to one another at said lower ends thereof through said
bottom plate conductors.
9. The method of claim 6. wherein:
quantities of said plurality of inner axial conductors, said
plurality of outer axial conductors, and said plurality of top plate
conductors are equal to one another, and greater by one than a
quantity of said plurality of bottom plate conductors; and further
comprising the steps of:
connecting each one of said inner axial conductors to a
corresponding one of said outer axial conductors at said upper ends
thereof, via a further corresponding one of said top plate conductors;
connecting a first one of said outer axial conductors to
said first one of said conductors on said bottom plate and a last one of
said inner axial conductors to said second one of said conductors on
said bottom plate; and
connecting each remaining one of said inner axial
conductors to a respective remaining one of said outer axial
conductors that is displaced by one unit from its corresponding outer
axial conductor at said lower ends thereof, through a respective
remaining one of said bottom plate conductors.
10. The method of claim 6, wherein at least one of the
inner annuius and the outer annulus comprises a plurality of annulus
layers with a plurality of axial conductor layers, such that said complete,
continuous electrical winding is a multilayer winding.

A fixture to evaluate stator production quality is placed about a
stator core so as to introduce a test winding about the stator without
need for hand winding. The fixture includes an inner annulus and an
outer annulus each with axial conductors thereon, and top and bottom
plates each with conductors thereon. The core is fitted between the
inner and outer annuli, and between the top and bottom plates. The
inner axial conductors and outer axial conductors are connected to one
another at their lower ends through the bottom plate conductors and at
their upper ends through the top plate conductors. Once testing is
complete, the fixture is easily removed.