U.S. patent application number 11/326487 was filed with the patent office on 2006-06-08 for electrodynamic apparatus and method of manufacture.
This patent application is currently assigned to Petersen Technology Corporation. Invention is credited to Christian C. Petersen.
Application Number | 20060119192 11/326487 |
Document ID | / |
Family ID | 34700763 |
Filed Date | 2006-06-08 |
United States Patent
Application |
20060119192 |
Kind Code |
A1 |
Petersen; Christian C. |
June 8, 2006 |
Electrodynamic apparatus and method of manufacture
Abstract
Electrodynamic apparatus such as a motor, generator or
alternator is configured having a stator core assembly formed of
pressure shaped processed ferromagnetic particles which are
pressure molded in the form of stator modules. These generally
identical stator modules are paired with or without intermediate
modules to provide the stator core structure for receiving field
winding components. In one embodiment, two sets of the paired
stator modules are combined in tandem to enhance operational
functions without substantial diametric increases in the overall
apparatus.
Inventors: |
Petersen; Christian C.;
(Sandwich, MA) |
Correspondence
Address: |
Diane E. Burke;Mueller and Smith, LPA
7700 Rivers Edge Drive
Columbus
OH
43235
US
|
Assignee: |
Petersen Technology
Corporation
|
Family ID: |
34700763 |
Appl. No.: |
11/326487 |
Filed: |
January 6, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10747538 |
Dec 29, 2003 |
7005764 |
|
|
11326487 |
Jan 6, 2006 |
|
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Current U.S.
Class: |
310/44 ; 310/112;
310/179; 310/216.067; 310/216.114 |
Current CPC
Class: |
H02K 21/16 20130101;
Y10T 29/49009 20150115; H02K 16/04 20130101 |
Class at
Publication: |
310/044 ;
310/112; 310/259; 310/179; 310/216 |
International
Class: |
H02K 15/12 20060101
H02K015/12; H02K 47/00 20060101 H02K047/00; H02K 3/00 20060101
H02K003/00 |
Claims
1-39. (canceled)
40. A method for manufacturing a stator assembly for a multiphase
electrodynamic apparatus having an axis, comprising the steps of:
(a) providing a powdered metal pressing facility for producing by
compressive molding a stator core module, said facility being
configured to provide said stator core module as being formed of
ferromagnetic particles which are generally mutually insulatively
associated, and said stator core module comprising a back iron
portion and a plurality of stator pole core members each formed
integrally with said back iron portion said said back iron portion
having a back iron widthwise extent and back iron length extending
from a bottom surface to a top surface, said core members having a
winding core portion with core widthwise extent and extending a
core length between bottom and top winding core surfaces, and a
flux interaction portion having an interaction widthwise extent,
integrally formed with said winding core portion and extending an
interaction length from a top surface to a bottom surface, said
back iron widthwise extent and corresponding said back iron length,
said winding core widthwise extent and corresponding said winding
core length, and said interaction widthwise extent and
corresponding said interaction length being selected to derive a
said stator core module by said compressive molding wherein said
particles of said stator core modules exhibit a density effective
to achieve adequate operational permeability and avoidance of
magnetic saturation under operating conditions; (b) molding at
least a first and a second stator core module in a said powdered
metal pressing facility; (c) symmetrically disposing said first and
second stator core modules about said axis in a manner wherein said
back iron portions are circumferentially aligned and said stator
pole core members are axially aligned to an extent permitting
stator pole winding to be applied over said axially aligned stator
pole core members said winding core portion of said first and
second stator core modules; (d) fixing said stator pole core
members of said first and second stator core modules in such
axially aligned orientation; and (e) providing a sequence of field
windings each extending over and supported by the mutually
outwardly disposed top surfaces of said winding core portions of
said first and second stator core modules.
41. The method of claim 40 wherein: said back iron widthwise extent
and corresponding back iron length are selected in step (a) to
respectively exhibit a ratio equal to or less than about 1 to
5.
42. The method of claim 40 wherein: said winding core widthwise
extent and corresponding winding core length are selected in step
(a) to respectively exhibit a ratio equal to or less than about 1
to 5.
43. The method of claim 40 wherein: said interaction widthwise
extent and corresponding interaction length are selected in step
(a) to respectively exhibit a ratio equal to or less than about 1
to 5.
44. The method of claim 40 wherein: at least a third said stator
core module is placed and aligned intermediate said first and
second stator core modules; said field winding surmounting said
winding core portions between said winding core portions of said
first and second stator modules.
45. The method of claim 40 wherein: said step (b) further comprises
molding at least a third and a forth stator core module in a said
powdered metal pressing facility; said step (c) further comprises
symmetrically disposing said first, second, third and fourth stator
core modules about said axis in a manner wherein said back iron
portions are circumferentially aligned and said third and fourth
stator core modules' stator pole core members are axially aligned
to an extent permitting stator pole winding to be applied over said
axially aligned stator pole core members said winding core portion
of said third and fourth stator core modules; said step (d) further
comprises fixing said stator pole core members of said third and
fourth stator core modules in such axially aligned orientation; and
said step (e) further comprises providing a sequence of field
windings each extending over and supported by the mutually
outwardly disposed top surfaces of said winding core portions of
said third and fourth stator core modules, said first and second
stator core modules being connected in series or parallel
electrical interconnection with said third and fourth stator core
modules.
46. A method of enclosing a stator core module assembly comprising
of two or more stator core modules each formed of pressure shaped
ferromagnetic particles which are generally mutually insulatively
associated comprising the steps of: (a) placing a rotor assembly
central to said stator core modules; (b) affixing a first motor end
cap over one end of the shaft of said rotor assembly and adjacent
with an end surface of said stator core module assembly; (c)
affixing a second motor end cap over the opposite end of said rotor
shaft and adjacent with the other end of said stator core module
assembly; and (d) installing two or more fastening devices through
said rotor assembly from said first motor end cap to said second
motor end cap and tightening said fastening devices such that the
components of said stator core module assembly are firmly held in
place and aligned.
47. The method of claim 46 further comprising the step of: (e)
installing a sleeve over the outside surface of said stator core
module assembly intermediate said first motor end cap and said
second motor end cap, said sleeve aligning and enclosing said
stator core module assembly.
48. The method of claim 46 wherein said step (d) further comprises
installing said fastening devices as screws.
49. The method of claim 46 wherein said step (d) further comprises
installing said fastening devices as fastening rods.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
[0001] Not applicable.
BACKGROUND OF THE INVENTION
[0002] Investigators in the electric motor arts have been called
upon to significantly expand motor technology from its somewhat
static status of many decades. Improved motor performance
particularly has been called for in such technical venues as
computer design and secondary motorized systems carried by
vehicles, for example, in the automotive and aircraft fields. With
progress in these fields, classically designed electric motors, for
example, utilizing brush-based commutation, have been found to be
unacceptable or, at best, marginal performers.
[0003] From the time of its early formation, the computer industry
has employed brushless d.c. motors for its magnetic memory systems.
The electric motors initially utilized for these drives were
relatively expensive and incorporated a variety of refinements, for
instance as necessitated with the introduction of rotating disc
memory. Over the recent past, the computer industry has called for
very low profile motors capable of performing in conjunction with
very small disc systems and at substantially elevated speeds.
[0004] Petersen, in U.S. Pat. No. 4,745,345, entitled "D.C. Motor
with Axially Disposed Working Flux Gap", issued May 17, 1988,
describes a PM d.c. motor of a brushless variety employing a
rotor-stator pole architecture wherein the working flux gap is
disposed "axially" with the transfer of flux being in parallel with
the axis of rotation of the motor. This "axial" architecture
further employs the use of field windings which are simply
structured, being supported from stator pole core members, which,
in turn, are mounted upon a magnetically permeable base. The
windings positioned over the stator pole core members
advantageously may be developed upon simple bobbins insertable over
the upstanding pole core members. Such axial type motors have
exhibited excellent dynamic performance and efficiency and,
ideally, may be designed to assume very small and desirably
variable configurations.
[0005] Petersen in U.S. Pat. No. 4,949,000, entitled "D.C. Motor",
issued Aug. 14, 1990 describes a d.c. motor for computer
applications with an axial magnetic architecture wherein the axial
forces which are induced by the permanent magnet based rotor are
substantially eliminated through the employment of axially
polarized rotor magnets in a shear form of flux transfer
relationship with the steel core components of the stator poles.
The dynamic tangentially directed vector force output (torque) of
the resultant motor is highly regular or smooth lending such motor
designs to numerous high level technological applications such as
computer disc drives which require both design flexibility,
volumetric efficiency, low audible noise, and a very smooth torque
output.
[0006] Petersen et al, in U.S. Pat. No. 4,837,474 entitled "D.C.
Motor", issued Jun. 6, 1989, describes a brushless PM d.c. motor in
which the permanent magnets thereof are provided as arcuate
segments which rotate about a circular locus of core component
defining pole assemblies. The paired permanent magnets are
magnetized in a radial polar sense and interact without back iron
in radial fashion with three core components of each pole assembly
which include a centrally disposed core component extending within
a channel between the magnet pairs and to adjacently inwardly and
outwardly disposed core components also interacting with the
permanent magnet radially disposed surface. With the arrangement,
localized rotor balancing is achieved and, additionally, discrete
or localized magnetic circuits are developed with respect to the
association of each permanent magnet pair with the pole
assembly.
[0007] Petersen in U.S. Pat. No. 5,659,217, issued Aug. 19, 1997
and entitled "Permanent Magnet D.C. Motor Having Radially-Disposed
Working Flux-Gap" describes a PM d.c. brushless motor which is
producible at practical cost levels commensurate with the
incorporation of the motors into products intended for the consumer
marketplace. These motors exhibit a highly desirable heat
dissipation characteristic and provide improved torque output in
consequence of a relatively high ratio of the radius from the motor
axis to its working gap with respect to the corresponding radius to
the motors' outer periphery. The torque performance is achieved
with the design even though lower cost or, lower energy product
permanent magnets may be employed with the motors. See also:
Petersen, U.S. Pat. No. 5,874,796, issued Feb. 23, 1999.
[0008] The above-discussed PM d,c, motors achieve their quite
efficient and desirable performance in conjunction with a
multiphase-based rotational control. This term "multiphase" is
intended to mean at least three phases in conjunction with either a
unipolar or bipolar stator coil excitation. Identification of these
phases in conjunction with rotor position to derive a necessary
controlling sequence of phase transitions traditionally has been
carried out with two or more rotor position sensors. By contrast,
simple, time domain-based multiphase switching has been considered
to be unreliable and impractical since the rotation of the rotor
varies in terms of speed under load as well as in consequence of a
variety of environ mental conditions.
[0009] Petersen in application for U.S. patent Ser. No. 10/706,412,
filed Nov. 12, 2003, entitled "Multiphase Motors With Single Point
Sensing Based Commutation" describes a simplified method and system
for control of multiphase motors wherein a single sensor is
employed with an associated sensible system to establish reliable
phase commutation sequencing.
[0010] Over the years of development of what may be referred to as
the Petersen motor technology, greatly improved motor design
flexibility has been realized. Designers of a broad variety of
motor driven products including household implements and
appliances, tools, pumps, fans and the like as well as more complex
systems such as disc drives now are afforded an expanded
configuration flexibility utilizing the new brushless motor
systems. No longer are such designers limited to the essentially
"off-the-shelf" motor varieties as listed in the catalogues of
motor manufacturers. Now, motor designs may become components of
and compliment the product itself in an expanded system design
approach.
[0011] During the recent past, considerable interest has been
manifested by motor designers in the utilization of magnetically
"soft" processed ferromagnetic particles in conjunction with
pressed powder technology as a substitute for the conventional
laminar steel core components of motors. So structured, when
utilized as a motor stator core component, the product can exhibit
very low eddy current loss which represents a highly desirable
feature, particularly as higher motor speeds and resultant core
switching speeds are called for. As a further advantage, for
example, in the control of cost, the pressed powder assemblies may
be net shaped wherein many intermediate manufacturing steps and
quality considerations are avoided. Also, tooling costs associated
with this pressed powder fabrication are substantially lower as
compared with the corresponding tooling required for typical
laminated steel fabrication. The desirable net shaping pressing
approach provides a resultant magnetic particle structure that is
3-dimensional magnetically (isotropic) and avoids the difficulties
encountered in the somewhat two-dimensional magnetic structure
world of laminations. See generally U.S. Pat. No. 5,874,796
(supra).
[0012] The high promise of pressed powder components for motors and
generators initially was considered compromised by a characteristic
of the material wherein it exhibits relatively low permeability.
However, Petersen, in U.S. Pat. No. 6,441,530, issued Aug. 27, 2000
entitled "D.C. PM Motor With A Stator Core Assembly Formed Of
Pressure Shaped Processed Ferromagnetic Particles", describes an
improved architecture for pressed powder formed stators which
accommodates for the above-noted lower permeability characteristics
by maximizing field coupling efficiencies.
[0013] As the development of pressed powder stator structures for
electrodynamic devices such as motors and generators has
progressed, investigators have undertaken the design of larger,
higher power systems. This necessarily has lead to a concomitant
call for larger press molded structures. The associated molding
process calls for press pressures adequate to evolve requite
material densities to gain adequate electrical properties. To
achieve those densities, press pressures are needed in the 40 tons
per square inch to 50 tons per square inch range. As a consequence
the powdered metal pressing industry suggest that the design of
molded parts exhibit aspect ratios (width or thickness to length in
the direction of pressing) equal to or less than about 1:5. Thus as
the length of stator core component structures increase, their
thickness must increase to an extent that a resultant shape becomes
so enlarged in widthwise cross section as to defeat the design
goal, with attendant loss of both the economies of cost and
enhanced performance associated with this emerging pressed powder
technology.
BRIEF SUMMARY OF THE INVENTION
[0014] The present invention is addressed to electrodynamic
apparatus and a method of manufacturing the stator core assemblies
thereof utilizing press powder technologies wherein requisite
stator core material densities are achieved while part thicknesses
and volumes are retained within desirable dimensional limits.
Requisite ratios of component widths or thicknesses to
corresponding lengths are maintained in proper combinations while
minimizing thicknesses of core structures through the employment of
two or more stator core modules or components which, following
their press forming, are selectively combined to define a sequence
of module core components over which field windings are positioned.
Because the stator core modules may be geometrically identical,
tooling costs may be conserved through employment, in effect, of a
single mold to produce them.
[0015] In one embodiment of the invention, paired stator core
modules are combined in tandem along the axis of the electrodynamic
apparatus to achieve an enhanced functional capacity while
minimizing the diametric extent of the device within which they
perform. With this arrangement, two or more sets of phase defining
field windings are utilized with wire diameters of smaller extent.
These phase defining windings advantageously then may be combined
for simultaneous excitation through employment of a series or
parallel electrical interconnection.
[0016] Where stator assembly sizes are called for which are large,
the stator core modules may be press formed in segmented fashion.
The resulting segments then may be combined in mutually abutting
fashion to form the stator modules. Further, the configuration of
these segments may be selected such that segments otherwise aligned
within paired stator modules can be pre-wound with field winding
elements prior to being abuttably joined together.
[0017] A convenient feature of the stator assemblies resides in the
utilization of electrically insulative shields positioned over the
mutually outwardly disposed winding support surfaces of field
winding core portions of the stator pole core member. In general,
the pole core members are formed with wire receiver troughs within
which field windings are retained. To facilitate the circuit
association of the windings from pole-to-pole within the stator
assembly, the insulative shield may be configured to extend
outwardly to define an outwardly open wire receiving channel
adjacent the inner surface of an associated back iron region of the
stator structure. The stator structures revealed in the embodiments
presented herein are all shown in the classical inward facing
salient stator pole configuration. This should not be considered a
limitation as U.S. Pat. No. 6,441,530 (supra) illustrates both
inward and outward facing stators and is incorporated by reference
herewith.
[0018] Other objects of the invention will, in part, be obvious and
will, in part, appear hereinafter.
[0019] The invention, accordingly, comprises the apparatus and
method possessing the construction, combination of elements,
arrangement of parts and steps which are exemplified in the
following detailed description.
[0020] For a fuller understanding of the nature and objects of the
invention, reference should be made to the following detailed
description taken in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a perspective view of electrodynamic apparatus
incorporating the features of the invention;
[0022] FIG. 2 is a sectional view taken through the plane 2-2 shown
in FIG. 1;
[0023] FIG. 3 is a sectional view taken through the plane 3-3 shown
in FIG. 2;
[0024] FIG. 3A is a partial top view of an alternate configuration
for a core member flux interaction region;
[0025] FIG. 4 is a perspective view of a core component configured
in accordance with the invention;
[0026] FIG. 5 is an exploded view showing a combination of four of
the components shown in FIG. 4;
[0027] FIG. 6 is an electrical schematic diagram showing the
parallel association of two "Y" winding configurations employed
with the stator structure of FIG. 5;
[0028] FIG. 7 is a schematic representation of a phase winding
configuration;
[0029] FIG. 8 is a partial sectional view of electrodynamic
apparatus according to the invention showing interpole winding
geometry;
[0030] FIG. 9 is a sectional view of another electrodynamic
apparatus structuring according to the invention;
[0031] FIG. 10 is a sectional view of another electrodynamic
apparatus stator component structuring according to the
invention;
[0032] FIG. 11 is a sectional view of a electrodynamic apparatus
structure having a segmented stator core architecture;
[0033] FIG. 12 is a perspective view of a stator core component
architecture shown in FIG. 11;
[0034] FIG. 13 is a sectional view of apparatus according to the
invention showing a multi-segmented stator core component
architecture; and
[0035] FIG. 14 is a perspective view of a stator core component as
depicted in connection with FIG. 13.
DETAILED DESCRIPTION OF THE INVENTION
[0036] In the discourse to follow radially salient pole stator
structures and the techniques of their formation and assembly are
described in conjunction with d.c. PM motors having an architecture
for deriving relatively higher power outputs, for example, about
250 watts and above. The structuring and techniques apply
additionally to other forms of motors such as doubly salient pole
motors and to electricity generators. Thus, the term
"electrodynamic apparatus" is utilized with the meaning that it
incorporates motors and generators employing the noted techniques
of stator formation. In developing such electrodynamic devices
utilizing magnetically soft composite pressed powder technology for
stator construction the developer will establish a variety of
dimensional parameters for electrical reasons establishing, for
instance, appropriate material thicknesses to achieve flux transfer
and avoidance of saturation. These electrical criteria are
generated by calculation. When those requisite thicknesses are so
established with judicious safety factors, the utilization of
pressed powder material above and beyond those thicknesses will
contribute only to weight and cost without improvement in device
performance. Once these dimensional parameters are established,
then the developer is confronted with the mandates of the powder
metal pressing industry requiring molded part aspect ratios calling
for structural thicknesses well beyond those necessary for
electrical performance criteria.
[0037] Looking to FIG. 1, a d.c. PM motor configured according to
the precepts of the invention is represented generally at 10. Motor
10 is formed with a cylindrical outer sleeve 12 formed, for
example, of aluminum or plastic to which is connected cylindrical
end caps 14 and 16. These caps 14 and 16 are retained in place by
three hex head machine screws 18-20. Extending from an opening 22
within end cap 14 is a rotor shaft 24.
[0038] Referring to FIG. 2, device 10 is revealed in section. Rotor
shaft 24 is seen disposed symmetrically about a rotor axis 26. The
shaft 24 is necked down to define an annular shoulder 28 which
engages the inner race of a ball bearing 30, which in turn, is
seated within a cylindrical bearing cavity 32 formed within end cap
14. In similar fashion, the opposite end of shaft 24 is necked down
to define an annular shoulder 34 which abuttably engages the inner
race of a ball bearing 36. The outer race of ball bearing 36, in
turn, is biased inwardly by a wavy washer 40 interposed between
bearing 36 and bearing cavity surface 42.
[0039] Shaft 24 supports a rotor represented generally at 44 which
is formed having a cylindrical core 46 formed of aluminum extending
to an outer cylindrical surface 48. Coupled with that surface 48 is
a cylindrical back iron 50 formed of ferrous material and extending
to a cylindrical back iron surface 52. Surface 52, in turn,
supports a cylindrical radially magnetized permanent magnet 54
which extends to flux confronting surfaces 56. Those flux
confronting surfaces provide, in this embodiment, a sequence of six
magnetic regions of alternating polarity generally extending in
parallel with the rotor axis 26.
[0040] Additionally supported for rotation upon shaft 24 is a
polymeric annular disc 58 which rotationally supports an
annularly-shaped sequence of sensible system permanent magnets
shown in cross section at 60. The annular magnets sequence 60 is
shown mounted within an annular steel back iron 62 supported, in
turn, upon an annular shoulder 64 formed within disc 58. Mounted
internally upon end cap 16 is a printed circuit board 66 which
functions to carry an integrated circuit 68 along with appropriate
driver transistors and one or more Hall effect sensors as shown at
70. Sensor 70 is positioned for magnetic field response to the
magnetic regions of sensible system magnet 60.
[0041] An annular stator assembly is represented generally at 80.
Assembly 80 is formed using a material composed of magnetically
soft pressure shaped processed ferromagnetic particles which are
generally mutually insulatively associated. These materials such as
Somaloy 500, are sometimes referred to as involving soft magnetic
composite technology and are marketed, inter alia, by North
American Hoganas, Inc. of Hollsopple, Pa. Assembly 80 is configured
as a radial salient pole stator having nine, angularly spaced apart
identical stator pole core members. Looking additionally to FIG. 3,
these core members are represented in general at 82a-82i. Core
members 82a-82i are formed integrally with and extend radially
inwardly from a portion of a cylindrically shaped back iron 84
having a widthwise extent identified by paired arrows 86. Extending
radially inwardly from back iron 84 are nine winding core portions
88a-88i of the stator pole core members. The widthwise dimension or
thickness of these winding core portions 88a-88i are identified at
paired arrows 90. Winding core portions 88a-88i extend radially
inwardly to respective integrally formed flux interaction portions
92a-92i. The widthwise extent or thickness of these flux
interaction portions is represented at paired arrows 94. Depending
on the arc length of the flux interaction portions relative to the
widthwise extent of the winding core portions the flux interaction
portions on 92a-i on either side of the widthwise extent of the
winding core portions may be tapered to a lesser widthwise extent
at the extremes of its arcuate extent as shown in FIG. 3A. These
flux interaction portions extend to respective arcuate flux
interaction surfaces 96a-96i which are spaced from flux confronting
surface 56 of rotor 44 to define a functioning or working gap 98.
Regions as at 92'' are more typical when the air gap between
adjacent stator pole tips is less than twice the distance from the
flux interaction surface to the magnet back iron. FIG. 3 reveals
that the permanent magnet feature of rotor 44 is formed with six
magnetic regions extending along the motor axis. These regions are
identified at 100a-100f.
[0042] Core members 82a-82i and back iron 84 are not formed as a
unitary part in their axial plane. Were they to be so formed, the
widthwise dimensions required to meet the pressing criteria for
pressure shaped processed ferromagnetic particles would increase
significantly causing the resulting structure to be less desirable
for its intended electrodynamic function. In accordance with the
precepts of the invention, the back iron and core members are
constructed, for the instant embodiment, as four identically
structured modules, each of which is formed meeting press forming
criteria and optimum electrical criteria. In this regard, the ratio
of each of the noted predetermined widthwise or thickness
dimensions with respect to their length in the direction of
pressing is equal to or less than a ratio of about 1 to 5. Looking
to FIG. 4, a perspective view of the uppermost one of these modules
is represented in general at 110. In the following descriptions top
and bottom surfaces of a stator module or component such as seen in
perspective in FIG. 4 are defined as the axial end surfaces of each
component. In an assembly of components these surfaces form outward
facing and inward facing surfaces of an electrodynamic device. In
general, the term "bottom is used in an inward sense, and the term
"top" is used in an outward sense. The terms "component" or
"module" as used herein are intended to mean not only identical
components but components having different configurations, for
instance, with stator core portions made from different molds.
Module 110 is formed with a back iron portion 84' which extends
from a back iron top surface region 116' a predetermined length
l.sub.1 (press direction), to a back iron bottom surface region
118'. That length, l.sub.1, is determined with respect to the wall
thickness regions 86, 90 and 94 and noted high pressure pressing
criteria. In similar fashion, the flux interaction portions, which
are now identified generally at 92', for module 110 extend from
flux interaction top surface regions certain of which are
identified at 120' and extend the same length, l.sub.1, to a flux
interaction bottom surface region is which identified at 122'. As
revealed in FIGS. 2 and 4, back iron top surface region 116' and
flux interaction top surface region 120' reside in a common plane
which is perpendicular to the axis 26. In similar fashion, back
iron bottom surface region 118' and flux interaction bottom surface
region 122' reside in a common plane which is parallel with the top
surface region common plane. FIG. 4 also reveals the presence of
top and bottom alignment notches shown respectively at 124' and
126'.
[0043] Certain of the winding core portions of module 110 are
identified in general in FIG. 4 at 88'. Looking additionally to
FIG. 2, these winding core portions 88' extend from a winding core
top surface region certain of which are identified at 128' a length
l.sub.2 to a winding core bottom surface region certain of which
are revealed at 130'. FIG. 4 reveals that the winding core top
surface regions 128' reside in a common plane and that the edges
thereof are chamfered to facilitate the mounting of field winding
wire thereover. In contrast, the winding core bottom surface
regions 130' need not be chamfered inasmuch as they will be seen
not to receive or support field winding wire. FIGS. 2 and 4 further
reveal that the winding core top surface regions 128' are recessed
inwardly from the back iron top surface regions 116' and flux
interaction top surface regions 120' to define receiver troughs
certain of which are identified at 132'. Receiver troughs 132'
further are defined by a radially inwardly slopping surface 134'
formed within the module back iron portion 84'. In similar fashion,
a radially outward slopping surface, certain of which are
identified at 136' is formed in each of the stator pole core member
flux interaction portions.
[0044] Looking additionally to FIG. 5, it may be observed that
stator assembly 80 is configured with four modules which are shown
as being identified for illustrative purposes and thus are
configured as described in conjunction with FIG. 4. Accordingly,
not only do the modules have dimensional aspect ratios which permit
their compression molding and practical shapes, but also they are
economically fabricable inasmuch as for the present embodiment a
singular molding tool is employed. The four modules are revealed in
FIGS. 2 and 5 at 110-113. To facilitate the identification of the
identical portions of these modules, such elements are numerically
identified in the same fashion as provided in FIG. 4 but with
priming provided for modules 110 through 113 respectively extending
from a single prime to four primes. Modules 111 and 112 may be
referred to as medial modules with medial stator pole core members
of medial dimensions. Note in FIG. 5 that modules 110 and 111 are
paired such that, for example, the back iron top surface regions
116' and 116'' as well as the corresponding flux interaction top
surface regions 120' and 120'' face mutually outwardly. The same
mutual orientation is provided in conjunction with components 112
and 113. Mutual angular alignment or slight misalignment of all of
the modules 110-113 is provided by three alignment pins 138-140. In
this regard, alignment pin 138 engages notches 126' and 126''.
Aligning pin 139 engages notches 124'' and 124''', and alignment
pin 140 engages notches 126''' and 126''''.
[0045] Returning to FIG. 2, modules 110-113 are retained in mutual
abutment and alignment by combination of cylindrical sleeve 12, end
caps 14 and 16 and their mutual coupling by machine screws 18-20.
For the device design at hand, a mutual contacting abutment between
paired modules as at 110 and 111 or 112 and 113 is not a requisite
arrangement. In this regard, the paired components will perform
appropriately if slightly separated in an axial sense with shock
absorbing materials or the like.
[0046] FIG. 2 illustrates, inter alia, stator pole core member 82g
in section as well as a non-sectional view of core member 82c.
These core members, as described above, are configured with modules
110-113 in paired and stacked relationship. Note in FIG. 2 that the
winding core portions of these core members support two as opposed
to a single field winding. In this regard, core member 82g is seen
supporting field windings 150g and 152g. Field winding 150g is
wound about the receiver troughs 132' and 132'' of respective
modules 110 and 111, while field winding 152g is wound about
receiver troughs 132''' and 132'''' of respective modules 112 and
113. Similarly, field winding 150c is seen wound about receiver
troughs 132' and 132'' at core member 82c and additionally the
field winding 152c is shown wound about receiver troughs 132''' and
132'''' of that core member. Conventional brushless motor
architecture will incorporate a single winding for each core member
as at 82a-82i. Where the core members are formed, for example,
utilizing conventional thin laminations, larger gage field winding
wire is necessitated because of the single winding per stator pole
member and the accumulated winding bundle will protrude above and
below the core members. By virtue of the utilization of net shaped
modules 110-113, receiver troughs as at 132'-132'''' can be
employed which fully incorporate the field winding wire bundles,
i.e., the outermost level of field winding wire is spaced inwardly
from back iron and flux interaction outer tip or top surface
regions as shown respectively at 116'-116'''' and 120'-120''''.
Because two windings are incorporated with each core member 82a-82i
and if the windings are connected in parallel the current carried
by each field winding is, in effect, reduced by 50% and, thus, the
gauge thickness of the wire may be reduced proportionally. Also the
machine winding time is greatly reduced because the axial length
over which the winder must reach is cut in half in this
embodiment.
[0047] FIGS. 2 and 3 reveal that an electrically insulative,
polymeric shield is positioned within each of the receiver troughs
132'-132'''' intermediate the winding core and an associated field
winding. In this regard, shields are shown in section in FIG. 3 at
154a-154i. Shield 154g is revealed in position over receiving
trough 132' in FIG. 2. Similarly, shield 154c also is shown
associated with module 110. FIG. 2 reveals shields 156c and 156g
located within receiver trough 132'' in conjunction with module
111. Shields 158c and 158g are revealed as installed within
receiver troughs 132'''; and shields 160c and 160g are shown
installed within receiver troughs 132''''. FIG. 2 further reveals
that that portion of the shield adjacent the back iron portion of
the stator core member extends to an outer tip or top surface
region and defines an outwardly open channel configured to carry
lead out and lead in components of field winding wire. For a
multiphase architecture, it is necessary to interconnect these
windings and thus a non-interfering intercommunicating arrangement
be developed. Note, that channels 162c and 162g are formed within
respective shields 154c and 154g. Similarly, outwardly open
channels are shown at 164c within shield 156c and at 164g in shield
156g. An outwardly open channel is seen at 166c in shield 158c and
at 166g in shield 158g. Finally, an outwardly open channel 168c is
formed within shield 160c and an outwardly open channel 168g is
seen formed within shield 160g.
[0048] The receiving troughs and associated shields are configured
to carry windings below the noted tip or top surface regions of the
back iron portions and flux interaction portions and thus permit
module stackability. Additionally, FIGS. 2 and 5 reveal another
feature of the device architecture, note that the winding core
bottom surface regions identified at 130'-130'''' are recessed
inwardly from the associated flux interaction bottom surface
regions 122'-122'''' and back iron bottom surface regions
118'-118''''. These recesses are provided to achieve the desired
amount of winding core cross-section area. It may be recalled that
the design of the motors calls for utilizing thicknesses and
lengths for the modules 110-113 which are appropriate to avoid flux
saturation phenomena and to incorporate a suitable safety factor.
However, beyond those criteria no additional materials are
utilized. Therefore, recesses may not be necessary and should not
be considered limiting. Accordingly, the modular stacking design at
hand within modules 110-113 is one permitting a highly efficient
utilization of the pressure shaped processed ferromagnetic
particles.
[0049] Turning now to the configuration of the windings 150a-150i
provided with modules 110 and 111, reference is made to FIG. 6. In
the figure, the windings at modules 110-111 are represented in
general at 150 and the windings associated with modules 112 and 113
are represented in general at 152. The three phases of these
windings further are identified at branches A, B, and C and the
winding positions are identified by the numeration 1, 2, and 3.
These "Y" windings are connected in parallel. In this regard, note
that phase A of windings 150 and 152 are commonly connected to line
180 which additionally is labeled as a phase "A". Phase B of
windings 150 is coupled to line 182, while the corresponding phase
B of windings 152 are coupled via line 184 to line 182. Finally,
phase C of windings 150 is coupled to line 186 while the
corresponding phase C of windings 152 is coupled to line 186 via
line 188. Thus, phases A, B, and C at respective lines 180, 182 and
186 extend to the printed circuit board 66 as shown in FIG. 2.
[0050] Referring to FIG. 7, the geometric aspect for the winding of
one of these Y structures, for example, at 152 is schematically
revealed. In the figure, the nine windings are identified in the
manner of FIG. 6, i.e., being shown as C1, C2, C3, A1, A2, A3, and
B1, B2, and B3. Lines 180, 182, and 186 are reproduced in FIG. 7
and the windings are represented showing clockwise rotation of the
wire from the start lead to the center tap where the windings join
in common as the center of the Y architecture. Now looking to the
partial sectional end view of the motor 10 in FIG. 8, windings A2
and B2 are represented. The figure represents these windings from a
schematic standpoint in the direction represented by the viewing
directional arrow 190 in FIG. 7. Referring additionally to that
figure, the start of the winding B2 and, correspondingly the finish
of winding B1 is represented at 182' in both figures. Note that the
winding is within outwardly open channel 168e. Correspondingly, the
start of winding A2 and correspondingly the finish of winding A1 is
represented at 180' extending from channel 168e. The finish of
winding A2 is represented in both figures at 180'' while the start
of winding B2 again is identified at 182' exiting from channel
168f. Finally, the finish of winding B2 is represented in FIGS. 7
and 8 at 182''. The manufacturing procedures for carrying out these
windings are substantially simplified and improved by virtue of the
reduced axial winding length for each "Y" winding 152 and 150 as
provided by the combination of modules 112 and 113 and 110 and
111.
[0051] This approach of achieving higher power motors through the
combining of components or modules to form the field wound stator
is uniquely suited to powder metal technology. Since the module
design is optimized for uniting the requirements of the powder
metal pressing industry and the electrical requirements of the
motor design under consideration the total number of modules may
vary. Also, the stacking ability of the modules yields a
versatility to the motor design unavailable with a typical steel
lamination motor design. Referring to FIG. 9, a version of the
motor or electrodynamic apparatus limited to two modules is
represented in general at 200. The similarity of the architecture
of device 200 with that of electrodynamic apparatus or motor 10
becomes immediately apparent. In this regard, the motor is
configured with an aluminum cylindrical sleeve 202, the ends of
which are joined to cylindrical end caps 204 and 206. A bearing 208
is mounted within end cap 204 adjacent a shaft opening 210.
Similarly, a bearing 212 is installed within end cap 206 adjacent
opening 214. Bearings 208 and 212 support motor shaft 213, their
inner raceways being rotatably engaged with respective shoulders
216 and 218 of the shaft. Shaft 213 is disposed about axis 280. A
wavy washer 220 loads the outer race of bearing 212 into
appropriate position. Shaft 213 supports a rotor represented
generally at 222 formed having an aluminum inner core 224, a
cylindrical back iron 226 and cylindrical permanent magnet or rotor
pole region 228 extending outwardly to a cylindrical flux
confronting surface 230. The assemblage of end caps 204 and 206,
sleeve 202 and the shaft 213 is retained together, as before, by a
sequence of machine screws, one of which is revealed at 232.
[0052] Motor 200 is configured with an annular stator assembly
represented generally at 234, the stator portion of which is formed
of two annular modules formed of pressure shaped processed
ferromagnetic particles and here represented in general at 236 and
237. Note that the profiles of components 236 and 237 are identical
to those described earlier at 110 and 111 or 112 and 113. Using the
identifying convention of the earlier figures, for a nine stator
pole embodiment, stator pole core members 240c and 240g of module
236 are revealed. In similar fashion, core members 242c and 242g
are illustrated in connection with module 237. As before, each of
these modules is net shaped with back iron portions as shown
respectively at 244c, 244g and 246c, 246g. The back iron portions
are integrally formed with the winding core portions of the stator
pole core members as seen at 248g and 250g. Those winding core
portions are, in turn, integrally formed with flux interaction
portions as at 252c, 252g and 254c, 254g. These flux interaction
portions extend to arcuate flux interaction surfaces as at 256c,
256g in the case of module 236 and at 258c, 258g for the case of
module 237. The surfaces define, with the flux confronting surface
230 of rotor 222 a functioning or working air gap 260. Note that as
in the case of earlier embodiments, both the back iron portions and
flux interaction portions of the core components extend to coplanar
top and bottom surface regions. The bottom surface disposed tip
regions are located in mutual adjacency and alignment while the top
surface regions extend to define receiver troughs as represented at
262c, 262g for module 236 and at 264c, 264g as illustrated in
connection with module 237. In each receiver trough, the winding
core portions support a polymeric electrically insulative shield,
each configured in the manner described above in connection with
motor 10. Note that polymeric shields 266c, 266g are positioned
within respective receiver troughs 262c and 262g while polymeric
shields 268c, 268g are located within respective receiver troughs
264c, 264g. Field windings are shown, as before, at 270c, 270g, the
winding starts and finishes thereof being carried about the motor
via outwardly open channels formed within the shields 266c, 266g
and 268c, 268g. Those open channels are represented, for instant
illustration at 272c, 272g and 274c, 274g. As before, motor 200
incorporates a sensible system having a disc form and represented
generally at 276 which performs in conjunction with printed circuit
board mounted control circuit sensors. Such a printed circuit board
is represented in general at 278. A preferred sensible system and
sensor implementation for the motor as disclosed herein is
described in a co-pending application for United States patent by
Petersen entitled "Multi-Phase Motors With Single Point Sensing
Based Commutation" (supra).
[0053] As in the previous embodiment, winding core regions 284g and
286g are recessed to help achieve the desired electrical
characteristics while retaining a suitable safety factor in overall
winding core area. Additionally, some material and weight economies
are also achieved. It should be noted that the recess 284g and 286g
as well as recesses in the winding core bottom surface;
130'-130'''' in the previous equipment are not required for proper
or efficient motor assembly and may not be a necessary feature when
designing for the optimum electrical characteristics, but are shown
as an optional design feature available with pressed powder
technology and suitable for many applications.
[0054] Referring to FIG. 10, a motor or electrodynamic device
represented generally at 300 is shown having an elongated
architecture extending along its motor axis 302. Device 300
represents a design wherein a stator assembly and associated rotor
are of greater lengthwise extent along axis 302 as compared with
the lengthwise extent of motor 200 along axis 280 (FIG. 9). To
achieve this desired extra length without excessive widthwise
extents of the stator core components mandated by the above
discussed pressed molding procedures, the stator is formed with
three free-form components with lengths along axis 302 suited to
achieve appropriate net shaping without excess thickness. As in the
case of motors or electrodynamic devices 10 and 200, motor 300 is
formed with a aluminum cylindrical sleeve 304 the axially
oppositely disposed ends of which are coupled with identical end
caps 306 and 308. End cap 306 is configured to support a bearing
310 at a shaft opening 312 and, correspondingly, a bearing 314 is
mounted within end cap 308 adjacent opening 316. Bearings 310 and
314 support a rotor shaft 318, the shoulders of which at 320 and
322 are engageable with the bearing internal raceways. A wavy
washer 324 functions to load the external race of bearing 314
inwardly. Shaft 318 supports a rotor represented generally at 326
having a cylindrical aluminum inner core 328, the outer cylindrical
surface of which supports a cylindrical rotor back iron 330. Rotor
back iron 330, in turn, supports cylindrical permanent magnet 332
defining a sequence of, for example, six rotor poles and providing
a flux confronting surface 334. As before, the device assemblage is
interconnected utilizing a sequence of machine screws, one of which
is revealed at 336.
[0055] The stator assembly for motor or device 300 is represented
generally at 338 and is seen to be structured having three
pre-formed stator core module components 340-342. Again utilizing
the descriptive approach employed with motor or device 10 in FIG.
2, stator pole core members 344c, 344g are shown in conjunction
with module component 340. Stator pole core members 346c, 346g are
shown associated with module component 341, and stator pole core
members 348c, 348g are shown associated with module component 342.
Core members 344c, 344g are shown formed integrally with respective
back iron portions 350c, 350g. Core members 346c, 346g are shown
formed integrally with respective back iron portions 352c, 352g,
and core members 348c, 348g are shown formed integrally with
respective back iron portions 354c, 354g. These back iron portions
are integrally formed with winding core portions extending
therefrom. In this regard, core member 344g is shown having a
winding core portion 356g. Core member 346g is shown having a
winding core portion 358g and core member 348g is shown having an
integrally formed winding core portion 360g. These winding core
regions are formed integrally with flux interaction portions. In
this regard, core members 344c, 344g incorporate respective flux
interaction portions 362c, 362g. Core members 346c, 346g
incorporate respective flux interaction portions 364c, 364g, and
core members 348c, 348g incorporate respective flux interaction
portions 366c, 366g. The flux interaction portions extend to define
arcuate flux interactions surfaces. In this regard, flux
interaction portions 362c, 362g define respective flux interaction
surfaces 368c, 368g. Flux interaction portions 364c, 364g extend to
form respective arcuate flux interaction surfaces 370c, 370g and
flux interaction portions 366c, 366g extend to form respective flux
interaction surfaces 372c, 372g. These flux interaction surfaces
cooperate with the corresponding rotor flux confronting surface 334
to define a functional or working gap 374.
[0056] Each of the stator pole core members of each module 340-342
is configured with an inwardly depending receiver trough from each
axial surface. For example, receiver troughs 376c, 376g and 388g
are formed within respective core members 344c, 344g of module 340.
Centrally disposed core members as at 346g also are formed having
an identical receiver trough as represented at 378g and 389g, and
core members 348c, 348g are seen to have respective receiver
troughs 380c, 380g and 390g. For the present embodiment
electrically insulative polymeric shields are inserted over the
winding core portion in the outboard or outwardly opening receiver
troughs of the module assembly. In this regard, shields 382c, 382g
are inserted within respective receiver troughs 376c, 376g and
shields 384c, 384g are inserted within respective receiver troughs
380c, 380g. Shields 382c and 384c are seen to support a more
elongate field winding 386c. Similarly, shields 382g and 384g are
seen to support field winding 386g.
[0057] As illustrated on the C numerated side of FIG. 10 the field
winding encompasses all three stator pole core members 344c, 346c
and 348c coupling them together magnetically. The figure also
reveals the formation of recesses on the bottom surfaces of each of
the end module stator pole core members and on both surfaces of the
center module. For example, such recesses are revealed at 378g,
388g, 389g and 390g. As before, the recesses function to permit
fabrication of the winding core regions to satisfy the electrical
design requirements of the motor and to an extent sufficient to
avoid saturation and provide a reasonable factor of safety. Note
that the recesses formed on the top and bottom surface regions of
the winding core portion of each core member of each stator module
are identical in this embodiment.
[0058] Motor 300 also contains a sensible system represented as a
disc at 392 which cooperates with a sensor arrangement and control
circuit at a printed circuit board 394.
[0059] In the embodiment presented herein the individual stator
core modules can be purposely slightly angularly misaligned or
skewed within the cylindrical outer sleeve resulting in an offset
between adjacent stator pole core members of adjacently stacked
core modules yet still permitting the winding operation to occur in
the same manner as if each individual stator core module was
perfectly angularly aligned. This misalignment can be used in
certain motor designs to reduce the effects of cogging or detent
torque where desirable or required.
[0060] As the instant electrodynamic apparatus structures reach
larger sizes the module components forming the stator structure may
themselves be segmented, again to accommodate for the severe
molding requirements at hand as well as to facilitate the winding
of field coils about the winding core regions. One such
segmentation approach is illustrated in connection with FIGS. 11
and 12. Looking to FIG. 11, a motor represented generally at 400 is
shown in a sectional portrayal similar to that seen in FIG. 3. In
this regard, the section is taken through a module component
represented generally at 402 and seen additionally in perspective
fashion in FIG. 12. Component 402 is formed with nine stator pole
core member assemblies represented generally at 404a-404i. Stator
pole assemblies 404a-404i are formed with corresponding pressed
powder net shaped stator pole core members represented generally at
406a-406i as seen additionally in FIG. 12. Each of the core members
406a-406i is formed, as before, integrally with back iron portions
408a-408i from which emanate the winding core portions shown
respectively at 410a-410i which, in turn, are integrally formed
with respective flux interaction portions 412a-412i. The flux
interaction portions 412a-412i extend respectively to arcuate flux
interaction surfaces 414a-414i. A rotor is represented generally at
416 structured in the same manner as rotor 44 described in
connection with FIGS. 1-3. This rotor extends to a flux confronting
surface and is spaced from flux interaction portions 412a-412i to
define a working or functional gap 420. Component retention is
provided by a sequence of machine screws in the same manner as
described in connection with motor 10. In this regard, sectional
representations of three such machine screws are provided at
421-423.
[0061] Note that component 402 is not net shaped as a unit but is
pre-formed in three arc shaped segments which are joined together
in mutual abutment at edge locations 426-428. This form of abutment
is intimate and touching inasmuch as the resultant three segments
reside in flux transfer communication. Three segments are
maintained in their arch-like structural orientation by the outer
cylindrical sleeve 430 seen in FIG. 11. The three segments,
identified in general at 432-434 are seen in FIG. 11 to be
associated with insulating sleeve and field winding combinations
436a-436i. Preferably, the field windings are mounted upon the
stator pole core members 406a-406i as they exist in the segments
432-434. In certain rotor pole, stator pole, pair arrangements such
as a nine pole stator and an eight pole rotor the three windings of
each phase are wound on adjacent poles meaning A1, A2, A3, B1, B2,
B3 and C1, C2, C3 as one proceeds around the stator. This winding
form could be enhanced with the stator arrangement of FIGS. 11 and
12 since the multiple stacked core components or modules of a
single phase could be pre-wound prior to assembly into sleeve
430.
[0062] Note additionally in FIG. 12 that alignment notches are
provided, for example as shown at 438 and 440 in segment 433. The
figure further reveals the provision of receiver troughs 442a-442i
at respective winding core portions 410a-410i.
[0063] Looking to FIGS. 13 and 14, an architecture is presented
wherein a single component is formed of nine segments in a nine
stator pole assembly configuration. This form of construction would
only be applicable on larger motor types since assembly of multiple
segments is first required prior to assembly of the stacked modules
to complete a single stator assembly such as shown in FIGS. 9 and
10. In FIG. 13, motor or device 500 is represented in sectional
format in the manner of FIGS. 3 and 11. Correspondingly, FIG. 14
shows in perspective a multi-segmented module which is provided in
conjunction with the sectional locations on the motor 500 shown in
FIG. 13. Looking to that figure, motor or device 500 is seen to be
comprised of nine distinct stator pole assemblies 504a-504i. As
represented additionally in FIG. 14, these stator pole assemblies
504a-504i are configured with corresponding and respective stator
pole core members 506a-506i. As before, each of the stator pole
core members 506a-506i is formed integrally with a back iron
portion as represented in FIG. 13 respectively at 508a-508i.
Integrally formed therewith and extending radially inwardly from
the back iron portions 508a-508i are respective winding core
portions 510a-510i. These winding core portions which are recessed
as seen in FIG. 14, extend radially inwardly to and are formed
integrally with flux interaction portions shown respectively at
512a-512i. The flux interaction portions 512a-512i extend radially
inwardly to define arcuate flux interaction surfaces shown
respectively at 514a-514i.
[0064] The rotor of motor or device 500 is represented in general
at 516 and is configured in the same manner as rotor 44 described
in connection with FIGS. 2 and 3. The rotor extends radially
outwardly to provide a flux confronting surface 518 which in turn,
cooperates with flux interaction surfaces 514a-514i to define a
working or functional gap 520. Each of the stator pole core members
506a-506i is provided with a polymeric electrically insulative
shield over the winding core portion interfacing with the
associated winding combination as shown in general at 522a-522i
within respective stator pole assemblies 504a-504i.
[0065] FIGS. 13 and 14 reveal that the module 502 is formed of nine
discrete segments, the edges of the back iron portions of which are
abutted together in flux transfer relationship at nine locations
shown at 524-532. Thus, each segment is configured with a singular
component stator core assembly. In this regard, it may be recalled
that at least two axially stacked modules are called for in this
axially modular form of optimized large motor construction. As in
the case of component 402 described in connection with FIGS. 11 and
12, the segments are assembled in compression along their back iron
portions to evolve an arch form of structure exhibiting desirable
structural integrity. The back iron components are retained in
their appropriate orientation by cylindrical sleeve 544 seen in
FIG. 13. As described in connection with motor 10, motor 400 module
components, end caps and cylindrical sleeve are retained in
position by a sequence of three machine screws, sectional
representation of which are shown in FIG. 13 at 534-536. It should
be noted that there are other suitable means of securing the final
assembly of the end caps and the stator module assemblies other
than the aforementioned machine screws and therefore their use in
the embodiments presented herein should not be considered in a
limiting sense. One segment, for example, that representing a back
iron portion and a stator pole core member 506e is configured
having alignment notches as at 538 and 540 to aid in assembly of
the entire stator core as described in connection with FIG. 5. Note
additionally in FIG. 14 that the motor axial length of the winding
core portions 510a-510i is diminished, inter alia, to define
receiver troughs shown respectively at 542a-542i.
[0066] Since certain changes may be made in the above-described
apparatus and method without departing from the scope of the
invention herein involved, it is intended that all matter contained
in the description thereof or shown in the accompanying drawings
shall be interpreted as illustrative and not in a limiting
sense.
* * * * *