U.S. patent application number 15/941810 was filed with the patent office on 2018-08-09 for single-step manufacturing of flux-directed permanent magnet assemblies.
This patent application is currently assigned to Advanced Magnet Lab, Inc.. The applicant listed for this patent is Advanced Magnet Lab, Inc.. Invention is credited to Sasha Ishmael, Rainer Meinke.
Application Number | 20180226190 15/941810 |
Document ID | / |
Family ID | 59966477 |
Filed Date | 2018-08-09 |
United States Patent
Application |
20180226190 |
Kind Code |
A1 |
Meinke; Rainer ; et
al. |
August 9, 2018 |
Single-step Manufacturing of Flux-Directed Permanent Magnet
Assemblies
Abstract
A flux directed magnet and a method of manufacturing a
flux-directed magnet in a reduced number of process steps is
described and claimed. The present invention is, in an embodiment,
a single-step manufacturing of flux directed magnet assemblies such
as, but not limited to, Halbach arrays of arbitrary multipole
order. Even tube-shaped flux directed magnet assemblies such as
Halbach arrays with large aspect ratio, i.e. length to diameter,
can be produced in single steps using the method of the invention.
Alternatively, the present invention may be one step of a plurality
of steps in a process for manufacturing of flux directed magnet
assemblies.
Inventors: |
Meinke; Rainer; (Melbourne,
FL) ; Ishmael; Sasha; (Raleigh, NC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Advanced Magnet Lab, Inc. |
Palm Bay |
FL |
US |
|
|
Assignee: |
Advanced Magnet Lab, Inc.
Palm Bay
FL
|
Family ID: |
59966477 |
Appl. No.: |
15/941810 |
Filed: |
March 30, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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PCT/US17/25212 |
Mar 30, 2017 |
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15941810 |
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62478941 |
Mar 30, 2017 |
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62315622 |
Mar 30, 2016 |
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62314991 |
Mar 30, 2016 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02K 2201/03 20130101;
H01F 41/0266 20130101; H02K 3/42 20130101; H02K 21/12 20130101;
H01F 1/0576 20130101; H01F 41/0273 20130101; H02K 1/278 20130101;
H02K 1/2786 20130101; H02K 16/02 20130101; B60K 7/00 20130101; H02K
3/28 20130101; H02K 16/025 20130101; H02K 1/27 20130101; H02K 15/03
20130101; B22F 9/04 20130101 |
International
Class: |
H01F 41/02 20060101
H01F041/02; H01F 1/057 20060101 H01F001/057 |
Claims
1. A method for producing a flux-directed magnet assembly,
comprising the steps of: a. Providing an assembly having a first
region, second region and a third region in cross section, wherein
said second region is disposed between said first and said third
regions, and wherein said second region comprises permanent magnet
material; and b. Wherein, in said cross section of said flux
directed magnet assembly, said first region, said second region,
and said third region form concentric circles, said second region
being defined as having a radius; and c. Wherein, for
inside-directed flux, said first region contains an enhanced
magnetic flux and said third region is quasi flux-free, and wherein
for outside-directed flux said first region is quasi flux-free said
third region contains an enhanced magnetic flux; d. Wherein the
magnetization of any point in said second region is defined as
being continuously variable, substantially independent for the
point along the radius due to the operation of the magnetization
field as being above the saturation magnetization of the permanent
magnetic material, and is given by the equations:
M_r(.phi.)=B_rem*cos(n.phi.) M_.phi.(.phi.)=B_rem*sin(n.phi.) where
.phi. is the azimuthal direction, Brem is the remanent flux density
of the magnetic material and n is the multipole order; and e.
wherein the absolute value of the magnetization is substantially
constant throughout said second region. f. using amplitudes
B.sub.rem of different size in front of the cosine and sine
functions above enables flux-directed assemblies with elliptical
cross section.
2. The method for producing a flux directed magnet assembly of
claim 1, wherein said magnetic flux directed magnet assembly is
defined as a Halbach array.
3. The method of claim 1, wherein the equations for the magnetic
flux density in said first region and said second region for
inside-directed flux, multipole order greater than 1 in cylindrical
coordinates are: for said first region, (n>1): B_r
|=(B_rem*n)/(n-1)*(1-(R_i/R_o) (n-1))*(r/R_i)(n-1)*cos(n.phi.)
B_.phi. |=-(B_rem*n)/(n-1)*(1-(R_i/R_o)
(n-1))*(r/R_i)(n-1)*sin(n.phi.) For said second region, (n>1):
B_r .parallel.=(B_rem*n)/(n-1)*(1-(r/R_o) (n-1))*cos(n.phi.)
B_.phi. .parallel.=-B_rem/(n-1)*(1-n(r/R_o) (n-1))*sin(n.phi.)
4. The method of claim 1, wherein the equations for the magnetic
flux density in said second region and said third region for
outside-directed flux, multipole order greater than 1 in
cylindrical coordinates are: For said third region, (n<-1): B_r
|.parallel.=(B_rem*n)/(n-1)*(1-(R_i/R_o) (1-n))*(R_o/r)
(1-n)*cos(n.phi.) B_.phi. |.parallel.=-(B_rem*n)/(n-1)*(1-(R_i/R_o)
(1-n))*(R_o/r) (1-n)*sin(m.phi.) For said second region, (n<-1):
B_r .parallel.=(B_rem*n)/(n-1)*(1-(R_i/r)(1-n))*cos (n.phi.)
B_.phi..parallel.=-B_rem/(n-1)*(1-n(R_i/r) (1-n))*sin(n.phi.)
5. The method of any of claims 1-4, wherein said magnetic flux is
produced by at least one double-helix magnet configurations.
6. The method of claims 1-4, wherein said magnetic flux is produced
by at least one direct double-helix magnet configurations.
7. The method of any of claims 1-6, wherein the magnetic material
is further defined as being manufactured from a powdered metal,
produced by the steps of: a. Preparing the powdered metal by
providing the appropriate amounts of neodymium, iron, and boron; b.
Heating the powdered to a melting point under vacuum. c. Cooling
said powdered metal; d. Crushing and then grinding said powdered
metal into a fine powder. e. Placing said powdered metal into a die
that has the approximate shape of the finished magnet; f. Applying
a magnetic field to the powdered material to line up the powder
particles; g. While the magnetic force is being applied, pressing
the powder from the top and bottom with hydraulic or mechanical
rams to compress it to within about 0.125 inches (0.32 cm) of its
final intended dimensions; h. Sintering the compressed powdered
metal, which fuses the powder into a solid piece; i. Annealing the
compressed powdered metal the sintered material in a second
controlled heating and cooling process to remove residual stresses
within the material and strengthen it; j. Machining the annealed
material to produce a smooth surface; and k. Applying a protective
coating to the annealed material.
Description
CROSS REFERENCE TO RELATED APPLICATIONS AND INCORPORATION BY
REFERENCE
[0001] This non provisional patent application is a non-provisional
of and claims the benefit of U.S. provisional patent application
62/478,941, filed in the United States Patent Office (USPTO) on
Mar. 30, 2017 titled SINGLE-STEP MANUFACTURING OF FLUX-DIRECTED
PERMANENT MAGNET ASSEMBLIES which is hereby incorporated by
reference in its entirety; this application is also a
continuation-in-part of international application PCT/US17/25212
filed in the USPTO on Mar. 30, 2017 which is incorporated herein by
reference and which was a non-provisional of U.S. provisional
applications 62/315,622 and 62/314,991 both of which were filed in
the USPTO on Mar. 30, 2016 and which are also incorporated herein
by reference. This application also incorporates by reference in
its entirety international application PCT/US17/25212 filed in the
USPTO on Mar. 30, 2017.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not applicable.
INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT
DISK
[0003] Not applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0004] The field of the invention relates generally to improvements
in flux-directed magnet assemblies such as, for example, Halbach
arrays and to methods of manufacturing in flux-directed magnet
assemblies such as, for example, Halbach arrays.
2. Background Art
[0005] Halbach arrays, as the best-known example of flux-directed
magnet assemblies, reinforce the flux density on one side of the
magnet assembly, while almost completely canceling the flux density
on the opposing side of the magnet assembly. These quasi one-sided
flux structures are achieved by successively rotating the
magnetization direction of adjacent permanent magnet segments that
form the assembly.
[0006] Flux-directed assemblies can be arranged as straight, linear
structures, as originally invented by John Mallison, or as
doughnut-shaped arrangements with various multipole orders,
invented by Klaus Halbach. The latter class, now known as Halbach
arrays, was originally intended for charged particle beam optics,
and therefore channel the magnetic flux to the inside of the
dough-nut shaped assembly. It has become a generally accepted
nomenclature to refer to all flux-directed magnet assemblies as
Halbach arrays.
[0007] Due to the one-sided flux density enhancement, Halbach
arrays have found important applications as rotors in electrical
machines. A recent AML patent application (U.S. patent application
Ser. No. 63/314,991) uses a dual-rotor systems consisting of two
concentric flux-directed assemblies, where the flux of the inner
one points outwards, and the flux of the outer one points inwards.
This arrangement enables very high flux densities at the stator
winding, does not require iron teeth for the stator nor backiron,
and therefore yields unprecedented torque and power densities.
[0008] Despite a clear performance advantage, the rather complex
and costly manufacturing process, has prevented Halbach arrays from
being widely used in electrical machines. The typical manufacturing
process of Halbach arrays demonstrates its complexity: A
doughnut-shaped Halbach array requires pie-shaped segments of
permanent magnet material, with each segment having a different
magnetization direction with the same absolute value. This is
achieved by machining pie-shaped segments out of rectangular blocks
in such a way that the resulting pieces have the required
orientation of flux direction. After these segments have been
manufactured, they are glued together, forming the final circular
shape. Since the individual segments repel each other, the array
requires special tooling to overcome substantial repulsion forces
during assembly and a support structure that holds the final
assembly together. If Halbach arrays are needed for long,
tube-shaped assemblies, several shorter, dough-shaped assemblies
are attached to each other which again requires overcoming large
opposing forces. It is important to point out that arrays assembled
out of pie-shaped segments constitute only approximations to ideal
Halbach arrays. Ideal arrays would require a continuous change in
magnetization direction or at least a very large number of
pie-shaped pieces.
[0009] For synchronous electrical machines the alternating
arrangement of north and south poles constitutes the main
requirement, and assemblies are sometimes manufactured in which the
flux direction is reversed between adjacent segments. Such
assemblies neither show one-sided flux enhancement as in Halbach
arrays nor vanishing flux on the opposite side, but are much
simpler in manufacturing.
BRIEF SUMMARY OF THE INVENTION
[0010] The present invention is, in an embodiment, a single-step
manufacturing of flux directed magnet assemblies such as, but not
limited to, Halbach arrays of arbitrary multipole order. Even
tube-shaped flux directed magnet assemblies such as Halbach arrays
with large aspect ratio, i.e. length to diameter, can be produced
in single steps using the method of the invention. Alternatively,
the present invention may be one step of a plurality of steps in a
process for manufacturing of flux directed magnet assemblies.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The accompanying drawings, which are incorporated into and
form a part of the specification, illustrate one or more
embodiments of the present invention and, together with the
description, serve to explain the principles of the invention. The
drawings are only for the purpose of illustrating the preferred
embodiments of the invention and are not to be construed as
limiting the invention. In the drawings:
[0012] FIG. 1 depicts three concentric regions with unique flux
density distributions for a doughnut shaped Halbach array.
[0013] FIG. 2 depicts a flux density distribution of Halbach array
for Region I and Region III with quadrupole configuration. The
color coding shows the total flux density in Tesla, the arrows show
the field direction. The dashed lines indicate the radial
boundaries of the permanent magnet material.
[0014] FIG. 3 depicts a radial dependence of a radial field
component (left), azimuthal field component (middle) and total
field (right) for an azimuth of Phi=22.5 degree. An angle of 22.5
degree is chosen, where both field components, B.sub.r and
B.sub.phi are relatively large.
[0015] FIG. 4 depicts a flux density distribution of a Halbach
array for Region-I, -II and -III with quadrupole configuration. The
color coding shows the total flux density in Tesla, the arrows show
the field direction. The dashed lines indicate the radial
boundaries of the permanent magnet material.
[0016] FIG. 5 depicts a radial dependence of a radial field
component (left), azimuthal field component (middle) and total
field (right) for an azimuth of Phi=22.5 degree. An angle of 22.5
degree is chosen, where both field components, B.sub.r and
B.sub.phi are relatively large.
[0017] FIG. 6 depicts a 2-D coil configuration for the magnetizer
comprising of two inner and two outer DH/DDH coils placed
concentrically to magnet ring with center radius R.sub.h. Coils at
R1 &R4 are coupled to generate angular field at R.sub.h. Coils
at R.sub.2&R.sub.3 are coupled to generate radial field at
R.sub.h.
[0018] FIG. 7 depicts steps of: step 1--forming
die/tooling/rotor-housing; step 2--filing, compressing and
annealing process; step 3--flux-directed magnetizing; step
4--finished rotor.
[0019] FIG. 8 depicts a example of a four coil, flux-directed
magnetizing coil system (Step 3 of FIG. 7).
[0020] FIG. 9 depicts a 2-D analysis of the magnetized rotor having
a flux directed field configuration.
DETAILED DESCRIPTION OF THE INVENTION
[0021] The claimed single-step manufacturing process of Halbach
arrays, requires a detailed understanding of the magnetization
distribution of the permanent magnet material. For circular Halbach
arrays three concentric regions can be identified, as shown in FIG.
1. The grey ring array 002 represents the permanent magnet
material, the inner 001 and outer 002 regions contain either the
enhanced magnetic flux or are quasi flux-free, depending on the
type of Halbach array. For inside-directed flux, 001 contains the
enhanced magnetic flux, and 003 is flux free. For the opposite case
of outside-directed flux, 001 is flux free, and the enhanced flux
is directed into 003 Region-III.
[0022] The magnetization of the magnetic material at any point
inside of Region-II is described by the following equations.sup.1,
.sup.1 Analysis of the magnetic field, force, and torque for
two-dimensional Halbach cylinders, R. Bjork et al., published in
Journal of Magnetism and Magnetic Materials, Vol. 322(1), 133-141,
2014
M.sub.r(.PHI.)=B.sub.rem*cos(n.PHI.)
M.sub..PHI.(.PHI.)=B.sub.rem*sin(n.PHI.) Equation 1:
where .phi. is the azimuthal direction, B.sub.rem is the remanent
flux density of the magnetic material and n is the multipole order.
For a positive value of n the resulting flux is directed towards
the inside and for negative values of n the flux is
outward-directed. As can be seen from these equations the absolute
value of the magnetization is constant throughout Region-II, the
radial and azimuthal components vary in a sinusoidal fashion.
[0023] If the amplitudes, B.sub.rem, in front of the cosine and
sinus functions of Equation 1 are different the equations describe
a Halbach array with elliptical instead of circular cross section;
in all other aspects the features of the resulting magnet array
remains unchanged. Such magnet assemblies have applications in
charged particle beam optics.
[0024] The resulting distribution of the local flux density in 001
Region-I and 002 Region-II with a multipole order greater than 1,
for inside-directed flux, and in cylindrical coordinates are
described by the equations in Table 1.sup.1. The equations for the
flux density in Region-II and Region-III for outside-directed flux,
multipole order greater than 1 in cylindrical coordinates are
presented in Table 2. The special case for a dipole Halbach array
with inside-directed flux are presented in Table 3. In the three
sets of equations R.sub.i and R.sub.o are the inner and outer radii
of the permanent magnet material, n is the multipole order, and
B.sub.rem is the remanent field strength of the permanent magnet
material.
TABLE-US-00001 TABLE 1 Equations for Halbach array for
inside-directed flux. Region-I (n > 1): B r I = B rem * n n - 1
* ( 1 - ( R t R o ) n - 1 ) * ( r R t ) n - 1 * cos ( n .phi. )
##EQU00001## B .phi. I = B rem * n n - 1 * ( 1 ( R t R o ) n - 1 )
* ( r R t ) n - 1 * sin ( n .phi. ) ##EQU00002## Region-II (n >
1): B r II = B rem * n n - 1 * ( 1 - ( r R o ) n - 1 ) * cos ( n
.phi. ) ##EQU00003## B .phi. II = B rem n - 1 * ( 1 n ( r R o ) n -
1 ) * sin ( n .phi. ) ##EQU00004## The flux density in Region-III
is zero.
TABLE-US-00002 TABLE 2 Equations for Halbach array for outer flux.
Region-III (n < -1): B r III = B rem * n n - 1 * ( 1 - ( R t R o
) 1 - n ) * ( R o r ) 1 - n * cos ( n .phi. ) ##EQU00005## B .phi.
III = - B rem * n n - 1 * ( 1 - ( R t R o ) 1 - n ) * ( R o r ) 1 -
n * sin ( n .phi. ) ##EQU00006## Region-II (n < -1): B r II = B
rem * n n - 1 * ( 1 - ( R t r ) 1 - n ) * cos ( n .phi. )
##EQU00007## B .phi. II = - B rem n - 1 * ( 1 - n ( R t r ) 1 - n )
* sin ( n .phi. ) ##EQU00008## The flux density in Region-I is
zero.
TABLE-US-00003 TABLE 3 Equations for a dipole Halbach array for
inner flux. Region-I: B r I = B rem * ln ( R o R t ) * cos ( .phi.
) ##EQU00009## B .phi. I = - B rem * ln ( R o R t ) * sin ( .phi. )
##EQU00010## Region-II: B r II = B rem * ln ( R o r ) * cos ( .phi.
) ##EQU00011## B .phi. II -- B rem * ( ln ( R o r ) - 1 ) * sin (
.phi. ) ##EQU00012## The flux density in Region-III is zero.
[0025] The resulting flux density distribution given by these
equations for the case of a quadrupole (n=2) for inside-directed
flux are shown in FIG. 2. The inner and outer radii (R.sub.i 004
and R.sub.o 005) of the permanent magnet material are arbitrarily
chosen as 100 mm and 150 mm, respectively, as an example.
[0026] The flux density distribution in the inner circle, i.e. the
inside of the Halbach array shows a "standard" 2-D quadrupole
field, given by: B.sub.r=const*r*cos(.PHI.) and
B.sub..PHI.=-const*r*sin(.PHI.) with 0.ltoreq.r.ltoreq.R.sub.i. As
can be seen from the equations in Table 1, the flux density inside
of the permanent magnet material itself is more complicated. The
complete radial dependence of the radial and azimuthal field
component for Regions-I, -II and -III are shown in FIG. 3.
[0027] The flux density in Region-I is a precise quadrupole field,
represented by a linear increase of B.sub.r and linear decrease of
B.sub..PHI. from the center to the inner boundary of the permanent
magnet material (see FIG. 4 left and middle). The total field in
this region shows a linear rise. In the adjacent Region-II, B.sub.r
is decreasing from its maximum value at the start of Region-II to
zero; the azimuthal component shows a linear rise from a pedestal
value to a maximum at the border to Region-III. The total field
shows a complex dependence on radius, first falling than
increasing, given by the opposite radial dependence of B.sub.r and
Bo in this region.
[0028] The resulting flux density distribution described by the
equations in Table 2 for the case of a quadrupole (n=2) for
outside-directed flux are shown in FIG. 5. As can be seen in that
figure, the flux density in Region-I is zero and the flux from
Region-II extends towards the outside into Region-III.
[0029] For both cases, the inside-directed and outside-directed
Halbach array, the radial distributions further depend on the
radial thickness of the permanent magnet material. As can be seen
by the equations in Tables 1 to 3, all flux densities obey the same
multipole order as given by the magnetization (Equation 1), and no
terms of a different multipole order are present. Although, the
resulting flux density distributions, shown in FIG. 2 and FIG. 3
are rather complex, they result from the simple sinusoidal
magnetization given be equation 1.
Manufacturing of Permanent Magnets:
[0030] Permanent magnets with high energy products like
neodymium-iron-boron magnets are produced with a modified powdered
metallurgical process which requires the following manufacturing
steps. See FIG. 7 for an exemplary process.
Preparing the Powdered Metal
[0031] The appropriate amounts of neodymium, iron, and boron are
heated to the melting point under vacuum. The vacuum prevents any
chemical reaction between air and the melting materials that might
contaminate the final metal alloy. Once the metal has cooled and
solidified, it is broken up and crushed into small pieces, which
are then ground into a fine powder.
Pressing
[0032] The powdered metal is placed in a die that has the
approximate shape of the finished magnet. A magnetic field is
applied to the powdered material to line up the powder particles.
While the magnetic force is being applied, the powder is pressed
from the top and bottom with hydraulic or mechanical rams to
compress it to within about 0.125 inches (0.32 cm) of its final
intended dimensions.
Heating
[0033] The compressed, powdered metal is removed from the die and
placed in an oven for sintering which fuses the powder into a solid
piece. The process usually consists of three stages. In the first
stage, the compressed material is heated at a low temperature to
slowly drive off any moisture or other contaminants that may have
become entrapped during the pressing process. In the second stage,
the temperature is raised to about 70-90% of the melting point of
the metal alloy and held there for a period of several hours or
several days to allow the small particles to fuse together.
Finally, the material is slowly cooled down in controlled,
step-by-step temperature decrements.
Annealing
[0034] The sintered material undergoes a second controlled heating
and cooling process known as annealing. This process removes
residual stresses within the material and strengthens it.
Finishing
[0035] The annealed material is very close to the finished shape
and required dimensions. A final machining process removes any
excess material and produces a smooth surface. The material is then
given a protective coating to seal the surfaces.
Magnetizing
[0036] Up to this point, the material is just a piece of compressed
and fused metal powder. Even though it was subjected to a magnetic
force during pressing, that force didn't magnetize the material, it
simply lined up the loose powder particles. To turn it into a
magnet, the piece is placed between the poles of a powerful
electromagnet and oriented in the desired direction of
magnetization. The electromagnet is then pulsed, typically for a
few milli-seconds to several Tesla. The resulting magnetic force
aligns the magnetic domains within the material and transforms the
piece into a permanent magnet. The remanent flux density,
B.sub.rem, achieved in the magnetization process depends on the
field strength of the magnetizer. For neodymium-iron-boron field
strengths of more then 60 kOersted are needed to achieve the
highest possible values of B.sub.rem. A 2D coil configuration for
an embodiment of a magnetizer is shown in FIG. 6 which depicts a
coil configuration for the magnetizer comprising of two inner and
two outer DH/DDH coils placed concentrically to magnet ring with
center radius R.sub.h. Coils at R1&R4 are coupled to generate
angular field at R.sub.h. Coils at R2&R3 are coupled to
generate radial field at R.sub.h.
Quality Control
[0037] Each step of the manufacturing process is monitored and
controlled. The sintering and annealing processes are especially
critical to the final mechanical and magnetic properties of the
magnet, and the variables of time and temperature are therefore
closely controlled.
Single Step Manufacturing of Halbach Arrays:
[0038] As has been pointed out herein, manufacturing Halbach arrays
out of pie-shaped pieces with appropriate magnetization direction
requires machining of permanent magnet material. The required
machining process is complex and expensive due to the hardness and
brittleness of the sintered permanent magnet material and the
presence of strong magnetic forces.
[0039] A recently disclosed manufacturing process of manufacturing
so-called permanent magnet wire disclosed in patent application
PCT/US17/25212 filed Mar. 30, 2017, herein incorporated by
reference, enables manufacturing of pie-shaped permanent magnets of
any length with arbitrary magnetization direction. In case of
neodymium-iron-boron, the prepared fine powder is inserted into
tubes of a non-magnetic metal, e.g. stainless steel or titanium,
which allows unhampered penetration of magnetic flux of the final
magnet wire. Using a swaging process the tubes are shaped and
reduced in size to the required cross section. The swaging process
compresses the powder under an external magnetic field that aligns
the crystals. The final resulting cross section of the tubes can be
circular, rectangular, pie-shaped or other. The tubes are then
sintered with the appropriate temperature profile. After cooldown,
the tubes are magnetized with the required orientation of the field
direction. For the application in Halbach arrays the disclosed
process eliminates the costly machining process of permanent magnet
material and significantly facilitates the assembly of tube-shaped,
long Halbach arrays.
[0040] With the powder-in-tube process no annealing and machining
of the sintered magnets is needed, and no further surface coating,
as required for conventional permanent magnets, is required.
[0041] The powder-in-tube process described here can be modified to
enable single-step manufacturing of flux-directed assemblies
(Halbach arrays) of such as, for example, doughnut shape or in the
form of linear structures. For dough-nut shape assemblies the
magnetic powder, e.g. neodymium-iron-boron, is filled into the
radial gap of two concentric tubes of appropriate diameter and
length. As for the permanent magnet wire the tube must be
non-magnetic to allow unhampered penetration of magnetic flux of
the final product. The powder is compressed while exposed to a
magnetic field that aligns the magnetic particles in the direction
needed in the final flux direction. The field direction as a
function of azimuth is determined by Equation 1. After sintering
and cool-down the dough-nut shaped structures are magnetized. The
magnetizer, described in the following, imprints the correct field
directions as needed for the flux-directed assembly. The resulting
Halbach arrays for inside- or outside-directed flux have the ideal
continuous magnetization directions which cannot be achieved with
arrays assembled out of a given number of pie-shaped segments. The
described manufacturing process significantly reduces manufacturing
cost of Halbach arrays. Given by the mechanical strength of the
concentric tubes being used, the resulting assemblies can be highly
robust as needed for example for electrical machines operating at
high RPM. Due to the continuous variation of the magnetization
direction, which is not possible with an assembly of separate pie
shaped segments, the performance of the single-step Halbach arrays
is superior to that available in the prior art.
[0042] The disclosed manufacturing process of flux-directed
assemblies is applicable to any magnetic powder material and not
limited to neodymium-iron-boron. Novel, non-rare-earth materials
currently under development are directly applicable. As shown in
equation 1, the field of the magnetizers should not have any
dependence on the radius. While any multiple field with order n
greater than 1 has a radial dependence, this is overcome by using a
magnetization filed that is higher than the saturation
magnetization of the material being magnetized. For NdFeB this can
be as high as 7 Tesla. However, using pulsed magnetic fields this
can be achieved.
Magnetizer Coil Design:
[0043] The 2-D field generated inside and outside of an ideal cos
n.PHI. coil of radius R is given by Beth's current sheet
theorem.sup.2,
B i n ( z ) = - .mu. 0 J n 2 ( z R ) n - 1 ##EQU00013## B out ( z )
= .mu. 0 J n 2 ( R 2 ) n + 1 ##EQU00013.2##
where .pi. represents the multipole order, z=re.sup.-.PHI. the
complex coordinate and J.sub.n the current density in the current
sheet. The current density J.sub.n can be expressed as number of
ampere-turns I in the
.pi. 2 n ##EQU00014##
section of the coil and is given by J.sub.n=nI/R. Replacing current
density with ampere-turns in above relation gives,
B i n ( z ) = - .mu. 0 nI 2 z n - 1 R n ##EQU00015## B out ( z ) =
.mu. 0 nI 2 R n z n + 1 ##EQU00015.2##
The 2-D magnetic field in a region between two concentrically
placed cos n .PHI. coils with radius R.sub.a and R.sub.b
(R.sub.b>R.sub.a) and currents I.sub.a and I.sub.b is given
by,
B ( z ) = .mu. 0 n 2 ( I a R a n z n + 1 - I b z n - 1 R b n )
##EQU00016##
Noting z=re.sup.-.PHI. and B(z)=B.sub.y(r,.PHI.)+iB.sub.x(r,
.PHI.)=e.sup.-i.PHI.(B.sub.r(r, .PHI.)-iB.sub..theta.(r, .PHI.)),
the radial and angular component of the resulting magnetic field
are given by,
B r ( r , .phi. ) = .mu. 0 n 2 ( I a R a n r n + 1 - I b r n - 1 R
b n ) cos n .phi. ##EQU00017## B .phi. ( r , .phi. ) = .mu. 0 n 2 (
I a R a n r n + 1 + I b r n 1 R b n ) sin n .phi.
##EQU00017.2##
[0044] At any given radius r a purely radial field with cos n.PHI.
variation is generated, if relations R.sub.aR.sub.b=r.sup.2 and
I.sub.a=-I.sub.b are simultaneously satisfied. In that case the
resulting B.sub..PHI.(r, .PHI.)=0 everywhere on a circle of radius
r. On the other hand, a purely angular field with sin n.PHI.
variation is generated on circle of radius r if relations
R.sub.aR.sub.b=r.sup.2 and I.sub.a=I.sub.b are simultaneously
satisfied.
[0045] Design for single step magnetization fixture is based on cos
n.PHI. coils. The actual implementation of such coils can be based
on AML patent technologies including Double-Helix (DH),
Direct-Double-helix (DDH) or Constant-cosine-theta (CCT) coil
configurations. The single step magnetization process requires four
cos n.PHI. coils to independently control radial and angular
magnetization of a ring magnet. Such a system can produce both
internal and external Halbach field configurations.
[0046] A 2-D coil configuration for the magnetizer comprising of
two inner and two outer DH/DDH coils placed concentrically to
magnet ring with center radius R.sub.h as show in FIG. 6. Coils at
R.sub.1 & R.sub.4 are coupled to generate purely angular field
with sin n.PHI. variation at R.sub.h. They have same number of
Amp-turns I.sub.14. Coils at R.sub.2 & R.sub.3 are coupled to
generate radial field with cos n.PHI. variation at R.sub.h and have
number of same number of Amp-turns I.sub.23. The field at center
radius R.sub.h of magnet ring is given by,
B r ( .phi. ) = + .mu. 0 nI 23 R 2 n r h n + 1 cos n .phi.
##EQU00018## B .phi. ( .phi. ) = .+-. .mu. 0 nI 14 R 1 n r h n + 1
sin n .phi. ##EQU00018.2##
[0047] The amplitude of the radial and angular field components can
be made identical by satisfying relation
I.sub.14R.sub.1.sup.n=I.sub.23R.sub.2.sup.n, as required for
Halbach magnet ring configuration. Further all four coils can be
coupled to have same current amplitude I.sub.0 by adjusting number
of turns in coil 1 & 4 N.sub.14, and coils 2 &3 N.sub.23
such that the relation
I 23 N 23 = I 14 N 14 = I 0 ##EQU00019##
is satisfied. The current direction in each magnetizer coil will
depend on the remanent magnetization required for the ring
magnet.
[0048] Direct Helix (DH), Direct Double Helix (DDH) and Canted
Cosine Theta (CCT) coil configurations offer highest field
uniformity, i.e. for a sufficiently long coil higher-order
components are highly suppressed. DDH coils can sustain very high
current densities and therefore enable coils with very low
inductance, which is needed to achieve the required high field
strength in the magnetizer. Since the remanent field achieved in
the magnetization process depends on the magnetizer field strength,
this field strength should be uniform throughout the permanent
magnet material. This can be realized by choosing the magnetizer
field strength in the saturation region.
Other Materials:
[0049] The manufacturing processes of flux-directed magnet
assemblies, described above, are not limited to the use of magnetic
powders like neodymium-iron-boron or samarium-cobalt, but any other
magnetic powder. Also, the recently disclosed manufacturing of
permanent magnet wire described in international application
PCT/US17/25212, filed in the United States Receiving Office on Mar.
30, 2017, which is herein incorporated by reference in its
entirety, would benefit from the magnetizer described in this
disclosure. Un-magnetized pie-shaped permanent magnet wires can be
assembled to Halbach arrays and the then magnetized as a complete
assembly. In this case, no magnetic forces must be overcome in the
assembly process, and the individual wires can be welded together
before magnetization. Welding already magnetized wires could
destroy the existing magnetization by exceeding the Curie
temperature of the magnetic material. Likewise the present method
would benefit the manufacture of dual rotor synchronous machines as
described in international application PCT/US17/25214, filed in the
United States Receiving Office on Mar. 30, 2017, which is herein
incorporated by reference in its entirety,
Example Process and Magnetizer for a Motor Rotor:
[0050] FIG. 7 provides photos of example configuration for a motor
rotor including the resultant flux-directed magnetic field of using
two, magnetizer coils (FIG. 8). FIG. 9 provides the 2D D analysis
of the magnetized rotor having a flux-directed field
configuration.
* * * * *