U.S. patent application number 16/891489 was filed with the patent office on 2020-09-17 for pole-piece structure for a magnetic gear.
The applicant listed for this patent is Goodrich Actuation Systems Limited. Invention is credited to Andrew HAWKSWORTH, Paul PROVERBS.
Application Number | 20200295648 16/891489 |
Document ID | / |
Family ID | 1000004870139 |
Filed Date | 2020-09-17 |
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United States Patent
Application |
20200295648 |
Kind Code |
A1 |
HAWKSWORTH; Andrew ; et
al. |
September 17, 2020 |
POLE-PIECE STRUCTURE FOR A MAGNETIC GEAR
Abstract
The disclosure provides a pole-piece structure for a magnetic
gear, comprising a plurality of laminate plates, wherein each plate
comprises one or more apertures and an aperture in each plate
aligns with an aperture in an adjacent plate to form one or more
channels extending from a first end of the laminate plates to a
second, opposite end of the laminate plates, wherein a resin cast
is provided within each channel to hold the plurality of laminate
plates together.
Inventors: |
HAWKSWORTH; Andrew;
(Newport, GB) ; PROVERBS; Paul; (Wolverhampton,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Goodrich Actuation Systems Limited |
Solihull West Mdilands |
|
GB |
|
|
Family ID: |
1000004870139 |
Appl. No.: |
16/891489 |
Filed: |
June 3, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
15622575 |
Jun 14, 2017 |
10707742 |
|
|
16891489 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01F 7/0205 20130101;
H02K 49/102 20130101; H01F 41/0266 20130101; H02K 51/00
20130101 |
International
Class: |
H02K 49/10 20060101
H02K049/10; H01F 7/02 20060101 H01F007/02; H01F 41/02 20060101
H01F041/02; H02K 51/00 20060101 H02K051/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 23, 2016 |
EP |
16275085.5 |
Claims
1. A pole-piece assembly comprising: a pole-piece structure
comprising a longitudinal axis and one or more channels extending
from a first end to a second, opposite end of the pole-piece
structure; a first rotating component; and a second rotating
component; wherein said pole-piece structure is located between the
first and second rotating components; wherein a solid,
substantially non-magnetic material is provided throughout each
channel; and wherein the solid, substantially non-magnetic material
comprises cavities at each first and second end, and each of the
first and second rotating components comprise lips that extend into
the cavities, so as to secure the pole-piece structure in
position.
2. The pole-piece assembly as claimed in claim 1, wherein the first
and second rotating components are associated with an input shaft
or an output shaft.
3. The pole-piece assembly as claimed in claim 1, wherein the first
and second rotating components are located at opposite axial ends
of a magnetic gear assembly.
4. The pole-piece assembly as claimed in claim 1, wherein the one
or more channels extend in a direction parallel or substantially
parallel to the longitudinal axis of said pole-piece structure.
5. The pole-piece assembly as claimed in claim 1, wherein each said
cavities are provided between a first flange and a second flange,
and said lips slot into said cavities between said first and second
flanges.
6. The pole-piece assembly as claimed in claim 1, wherein the
solid, substantially non-magnetic material is cast or molded into
the channels.
7. The pole-piece assembly as claimed in claim 1, wherein the
non-magnetic material comprises a resin that is provided throughout
each channel, wherein the resin completely fills each channel.
8. The pole-piece assembly as claimed in claim 1, wherein there are
no air gaps between each channel and the solid, substantially
non-magnetic material.
9. The pole-piece assembly as claimed in claim 1, wherein said
pole-piece structure consists of a plurality of laminate plates and
said non-magnetic material.
10. The pole-piece assembly as claimed in claim 9, wherein each of
said plates comprises a plurality of solid portions arranged
alternately with a plurality of substantially hollow portions, and
one or more apertures are provided in said hollow portions.
11. The pole-piece assembly as claimed in claim 10, wherein each of
said plates are stacked such that said solid portions align so as
to form a plurality of magnetic pole-pieces in said pole-piece
structure.
12. The pole-piece assembly as claimed in claim 10, wherein said
plates are stacked such that said hollow portions align so as to
form said one or more channels extending from said first end of the
pole-piece structure to said second, opposite end of the pole-piece
structure.
13. The pole-piece assembly as claimed in claim 9, wherein each of
said laminate plates are formed from a single piece of
material.
14. The pole-piece assembly as claimed in claim 9, wherein said
laminate plates are held together by said the solid, substantially
non-magnetic material.
15. A magnetic gear assembly comprising: the pole-piece assembly as
claimed in claim 1; a plurality of inner permanent magnets; and a
plurality of outer permanent magnets located concentrically with
respect to said inner permanent magnets; wherein said pole-piece
structure is located between said inner and outer permanent magnets
and modulates the magnetic fields produced by said inner and outer
permanent magnets.
16. A method of securing a pole-piece structure in position,
comprising: casting or molding a substantially non-magnetic
material within each of one or more channels provided in a
pole-piece structure, such that a solid, substantially non-magnetic
material is provided within each channel, wherein the casting or
molding comprises casting or molding cavities at each of a first
end and a second end of said one or more channels; and providing a
first rotating component and a second rotating component, each of
said first and second rotating components comprising lips which
extend into said cavities.
17. The method as claimed in claim 16, wherein the casting or
molding cavities comprises casting or molding a first flange and a
second flange around each cavity, and said lips slot into said
cavities between said first and second flanges.
18. The method as claimed in claim 16, wherein each lip of said
first rotating component extends into each cavity at the first end
of said one or more channels, and each lip of said second rotating
component extends into each cavity at the second end of said one or
more channels.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of U.S. Ser.
No. 15/622,575 filed Jun. 14, 2017, which claims priority to
European Patent Application No. 16275085.5 filed Jun. 23, 2016, the
entire contents of which is incorporated herein by reference.
TECHNICAL FIELD
[0002] The present disclosure relates generally to a pole-piece
structure for a magnetic gear, and methods of manufacturing
same.
BACKGROUND
[0003] Magnetic gears are known and typically involve a concentric
array of annular components that rotate relative to one another in
order to rotate an output shaft at a different speed to an input
shaft.
[0004] In one type of configuration, an inner permanent magnet can
form an inner rotor and an outer permanent magnet can form an outer
stator. A rotational pole-piece structure can be located between
the inner and outer permanent magnets in order to provide a
concentration of magnetic lines of force therebetween, and modulate
the magnetic field so as to produce a gearing between the input and
output shafts. The pole-piece structure forms a torque path between
the input and output shafts without any mechanical contact. It is
possible to vary the arrangement such that the pole-piece is a
stator, and the two sets of permanent magnets rotate.
[0005] The gear ratio may be equal to the number of magnetic pole
pairs on the permanent magnet associated with the high speed shaft,
as compared to the number of magnetic pole pairs on the permanent
magnet associated with the low speed shaft. This implies an even
number of permanent magnets associated with each shaft.
[0006] Magnetic gears have known advantages in that, although
bearings are required to mount the shafts in the gear assembly, the
coupling between the moving parts is otherwise frictionless.
[0007] Pole-pieces, or "modulators" may be formed from laminate
plates. Typically these are held together by a chassis or
sub-carriage that extends through air gaps in the pole-piece. It is
desired to provide improvements to the mounting of the pole-piece
to the high or low speed shaft, or to the housing.
SUMMARY
[0008] In accordance with an aspect of the disclosure, there is
provided a pole-piece structure for a magnetic gear, comprising: a
plurality of laminate plates, wherein each plate comprises one or
more apertures and an aperture in each plate aligns with an
aperture in an adjacent plate to form one or more channels
extending from a first end of the laminate plates to a second,
opposite end of the laminate plates; wherein a solid, substantially
non-magnetic material is provided throughout each channel to hold
the plurality of laminate plates together.
[0009] The use of a solid, non-magnetic material to hold the plates
together has been found to provide an improved structure as
compared to conventional devices, which typically involve the use
of further components such as a metal frame or housing located
around the pole-piece to hold the pole-piece in position. In the
present disclosure, the pole-piece may be held in position using
the non-magnetic material provided throughout each channel.
[0010] The non-magnetic material may be non-metallic.
[0011] The non-magnetic material may be a resin, such that a resin
cast may be formed throughout each channel. The resin may be an
epoxy resin. The filler may be silica and the resin may be
silica-filled epoxy resin. The silica may be silica nanoparticles.
The resin may have a coefficient of thermal expansion of less then
about 50.times.10-6/.degree. C., 40.times.10-6/.degree. C.,
30.times.10-6/.degree. C. or 20.times.10-6/.degree. C.
[0012] The apertures may be aligned such that the one or more
channels formed by the apertures may run axially from the first end
of the laminate plates to the second, opposite end of the laminate
plates. The apertures may extend through the entire axial length of
each plate.
[0013] Each aperture and/or channel may have a uniform width and/or
cross-sectional area. The non-magnetic material may also have a
uniform width and/or cross-sectional area, which may match that of
the apertures and/or channel(s).
[0014] Each aperture and/or channel, and/or the non-magnetic
material may have a rectangular, or rounded rectangular shape or
cross-section. The non-magnetic material may have a substantially
cuboid shape throughout each channel.
[0015] The one or more channels may extend in a direction parallel
or substantially parallel to the longitudinal axis of the
pole-piece structure, and/or the magnetic gear assembly (described
below).
[0016] The non-magnetic material may be provided throughout each
channel such that the non-magnetic material completely fills the
channel.
[0017] There may be no air gaps within each channel and/or between
the laminate plates and/or between the radial wall thickness of the
plates.
[0018] The laminate plates may be stacked together and each plate
may contact an adjacent plate along an entirety of its
circumference.
[0019] The pole-piece structure may consist of the plurality of
laminate plates and the non-magnetic material.
[0020] Each of the plates may comprise a plurality of solid
portions arranged alternately with a plurality of substantially
hollow portions, and the one or more apertures may be provided in
the hollow portions. There may be at least 2, 4, 6, 8, 10, 12 or 14
solid portions and/or hollow portions in each of the plates, such
that at least 2, 4, 6, 8, 10, 12 or 14 channels may be provided in
the pole-piece structure. As discussed herein, a solid,
substantially non-magnetic material is provided throughout each
channel.
[0021] Each of the plates may be stacked such that the solid
portions align so as to form a plurality of magnetic pole-pieces in
the pole-piece structure.
[0022] The plates may be stacked such that the hollow portions
align so as to form the one or more channels extending from a first
end of the laminate plates to a second, opposite end of the
laminate plates.
[0023] Each of the solid portions may be smooth and/or free of
surface variations, such as protrusions, depressions, dimples,
undulations, etc.
[0024] Each of the plates may comprise a uniform radial width (or
radial wall thickness) and/or a uniform axial width, and may also
be smooth and/or free of surface variations (other than the
apertures formed by the hollow connecting portions).
[0025] Each of the laminate plates may be formed from a single
piece of material, for example a metal (e.g., sheet metal).
[0026] In accordance with an aspect of the disclosure, there is
provided a magnetic gear assembly comprising: a pole-piece
structure as claimed in any preceding claim; a plurality of inner
permanent magnets; and a plurality of outer permanent magnets
located concentrically with respect to the inner permanent magnets;
wherein the pole-piece structure is located between the inner and
outer permanent magnets and modulates the magnetic fields produced
by the inner and outer permanent magnets.
[0027] The pole-piece structure may be located between first and
second rotating components of the magnetic gear assembly. The first
and second rotating components may be associated with the input
shaft or the output shaft. The first and second rotating components
may be located at opposite axial ends of the magnetic gear
assembly.
[0028] The solid, substantially non-magnetic material may comprise
cavities at each axial end, and the first and second rotating
components may comprise flanges that extend into the cavities, so
as to hold the pole-piece structure in position. The flanges may at
least partially extend into each channel.
[0029] In accordance with an aspect of the disclosure, there is
provided a method of forming a pole-piece structure, comprising:
stacking a plurality of plates against one another, wherein each
plate comprises one or more apertures and an aperture in each plate
aligns with an aperture in an adjacent plate to form one or more
channels extending from a first end of the laminate plates to a
second, opposite end of the laminate plates; and casting or molding
a substantially non-magnetic material (e.g., a resin as described
above) within each of the one or more channels, such that a solid,
substantially non-magnetic material is provided within each channel
that holds the plurality of laminate plates together.
[0030] The apertures may be located at the same circumferential
location on each plate, and the plates may be stacked such that the
apertures align and the channels extend in a direction parallel or
substantially parallel to the longitudinal axis of the pole-piece
structure.
[0031] The pole-piece structure may initially be held in place by a
clamp or other suitable holding mechanism. The non-magnetic
material may be injected into each of the channels. The clamp or
other suitable holding mechanism may be removed once all of the
channels have been cast or molded with the non-magnetic
material.
[0032] The pole-piece structure according to this method may have
any of the features of the pole-piece structure described
above.
[0033] In accordance with an aspect of the disclosure, there is
provided a method of forming a magnetic gear assembly, comprising:
forming a pole-piece structure as described above, wherein the step
of stacking said plurality of plates comprises stacking the plates
between a first rotating component of the magnetic gear assembly
and a second rotating component of the magnetic gear assembly.
[0034] The step of casting or molding a substantially non-magnetic
material may be carried out after the step of stacking the
plurality of plates between first and second rotating components of
the magnetic gear assembly.
[0035] The first and second rotating components may be associated
with the input shaft or the output shaft. The first and second
rotating components may be located at opposite axial ends of the
magnetic gear assembly.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] Various embodiments will now be described, by way of example
only, and with reference to the accompanying drawings in which:
[0037] FIG. 1 shows an axial cross-section through a magnetic gear
assembly;
[0038] FIG. 2 shows a radial cross-section through the magnetic
gear assembly shown in FIG. 1;
[0039] FIG. 3A shows the laminate plates in isolation;
[0040] FIG. 3B shows an exploded view of the pole-piece
structure;
[0041] FIG. 4A shows a cross-section through part of the magnetic
pole-piece structure of FIG. 3;
[0042] FIG. 4B shows a close up of part of FIG. 4A;
[0043] FIG. 5 shows a perspective view of a connection between two
parts of the pole-piece structure of FIG. 4;
[0044] FIG. 6 shows a perspective view of part of the pole-piece
structure of FIG. 4.
DETAILED DESCRIPTION
[0045] The disclosure relates generally to a pole piece structure
(or "modulator") for use in, e.g. a magnetic gear or a magnetic
gear assembly, and methods of manufacturing a pole-piece structure
(or "modulator").
[0046] FIG. 1 shows a magnetic gear assembly 10 in accordance with
an embodiment.
[0047] The magnetic gear assembly 10 comprises a housing 5, as well
as an input shaft 12 and an output shaft 22. The input shaft 12
connects to an inner rotor 14 via, e.g. a spline connection 13, and
the inner rotor 14 connects to an inner rotor support 15. The inner
rotor 14 and inner rotor support 15 rotate together and are
supported by inner bearings 16. The inner rotor 14 and inner rotor
support 15 and/or the input shaft 12 could be a single-piece
component.
[0048] The inner rotor 14 supports an array of inner permanent
magnets 30 that rotate together with the input shaft 12 and inner
rotor 14.
[0049] The housing 5 is fixed in relation to the moving parts of
the magnetic gear assembly 10, and supports an array of outer
permanent magnets 40. The outer permanent magnets 40 are fixed to
the housing 5 via an outer support 6.
[0050] A pole-piece structure or modulator 50 is located between
the outer permanent magnets 40 and the inner permanent magnets 30.
The modulator 50 is carried by one or more extensions 24 of the
output shaft 22 and a modulator support 26. The extensions 24 and
modulator support 26 are carried by inner bearings 16 and outer
bearings 18 and, with the modulator 50, are rotatable with the
output shaft 22.
[0051] The modulator 50 is made of a magnetic material and acts to
modulate the magnetic fields produced by the inner and outer
permanent magnets. To do this, the modulator 50 comprises a number
of magnetic poles that are regularly spaced around its
circumference, which provide flux harmonics corresponding to the
magnet pole pairs on the inner and outer permanent magnets. This
causes the components to interact in a magnetically-geared manner.
The modulator 50 may form a torque path between the input shaft 12
and the output shaft 22 without any mechanical contact. Such theory
is known in the art and will not be repeated herein.
[0052] In the illustrated embodiment, the outer permanent magnets
40 do not rotate, although other embodiments are contemplated in
which the outer permanent magnets 40 rotate and the pole-piece
structure 50 is fixed. Also, in the illustrated embodiment the
input shaft 12 and inner rotor 14 is configured as a high-speed
rotor and the modulator 50 and output shaft 22 are configured as
the low-speed rotor. This is due to the lower number of inner
permanent magnets 30 when compared to the number of outer permanent
magnets 40. However, other embodiments are contemplated in which
the inner rotor 14 is configured as the low-speed rotor, by using a
higher number of inner permanent magnets than outer permanent
magnets.
[0053] FIG. 2 shows a radial cross-section through the magnetic
gear assembly 10.
[0054] The inner rotor 14 supports the inner permanent magnets 30.
In the illustrated embodiment, eight inner permanent magnets are
used but any number can be used as required. The inner permanent
magnets are arranged in alternating north 32 and south 34 poles.
Similarly, the outer permanent magnets 40 comprise alternating
north 42 and south 44 poles. Eighteen alternating poles are used in
the illustrated embodiment, although any number can be used as
required.
[0055] The modulator 50 comprises an array of regularly spaced
magnetic portions 52 and substantially non-magnetic portions 54,
which are arranged in an alternating pattern. The magnetic portions
52 may be a solid piece of a magnetic metal, and the substantially
non-magnetic portions 54 may comprise apertures. These are
described in more detail below. As illustrated, the number of
magnetic and non-magnetic parts is chosen to be twenty-six, i.e.
the sum of the inner and outer permanent magnets, although any
number can be used as required.
[0056] A nominal air gap (not shown) is present between the
modulator 50 and each of the inner and outer arrays of permanent
magnets 30, 40. This means that torque is transferred between the
rotating magnetic parts of the magnetic gear assembly 10 in a
frictionless manner.
[0057] The pole-piece structure or modulator 50 is formed from a
plurality of laminate plates 100 that are stacked together. The
plates may be formed from or comprise silicon-iron.
[0058] As shown in FIG. 3A, each plate 100 may comprise a ring
having a plurality of regularly spaced and solid portions 102 that
are separated by hollow connecting portions 104. The connecting
portions 104 comprise one or more connectors 105 (FIG. 3C) that
extend circumferentially between the solid portions 102 to connect
the solid portions 102 together. In the illustrated embodiment, two
narrow connectors 105 are provided for each hollow portion 104,
although a single connector or more than two connectors may be used
as appropriate. Optionally, each plate 100 is a single-piece of
magnetic metal.
[0059] When stacked together, the solid portions 102 of the
laminate plates 100 align and form the magnetic portions 52 of the
modulator 50. Similarly, when stacked together the hollow
connecting portions 104 of the laminate plates 100 align to form
the substantially non-magnetic portions 54 of the modulator 50. The
word "substantially" is used to indicate that, whilst the hollow
portions may still comprise metal (e.g. magnetic) connectors 105,
the hollow portions 104 are mainly void between the connectors 105
to provide non-magnetic channels, as discussed in more detail
below.
[0060] The hollow portions 104 comprise apertures, which apertures
are the voids between the connectors 105 and the sides of the solid
portions 102. Thus, an aperture in each plate 100 aligns with an
aperture in an adjacent plate 100 to form one or more channels 106
extending from a first end of the laminate plates to a second,
opposite end of the laminate plates.
[0061] Referring now to FIG. 3B, this shows the laminate plates 100
in a semi-assembled state. In order to hold the laminate plates 100
in position, a non-magnetic material 150 is provided throughout
each channel 106 to hold the plurality of laminate plates 100
together. In the illustrated embodiment the non-magnetic material
is a resin cast 150 that extends throughout each channel 106 formed
by the apertures in the hollow portions 104 of the plates 100. Each
resin cast 150 extends from the first end of the laminate plates to
the second, opposite end of the laminate plates.
[0062] Each extension 24 of the modulator support 26 extends into a
respective one of the resin casts 150, which secures the modulator
50 to the output shaft 22 and modulator support 26. This
facilitates assembly of the magnetic gear assembly 10 since the
extensions 24 may be inserted into respective ends of the modulator
50.
[0063] The resin material is substantially non-magnetic and/or
otherwise has no magnetic permeability and will not affect or
influence the magnetic performance of the gearbox.
[0064] Some conventional arrangements use a chassis or sub-carriage
to carry the modulator. Such arrangements may have included bolts
extending through the modulator to hold it together, or a bonding
material such as glue. It has been found that this type of
architecture can compromise the performance of the magnetic gear.
This may be due to the inclusion of metal bolts through the plates,
or perforations and/or indentations in the solid magnetic portions,
leading to losses in performance and efficiency. The broadest
aspects of the present disclosure overcome this by using a resin
cast within each channel to hold the plurality of laminate plates
together.
[0065] The use of resin casts (or other non-magnetic material)
extending through the structure of the modulator also means that
the plates, while pressed against each other, are not connected to
one another for example by welding or other means. This increases
the magnetic permeability between the plates further, since a weld
could potentially introduce some unwanted eddy currents by creating
a path for torque to be transmitted.
[0066] The resin casts 150 may be formed prior to attachment of the
modulator 50 to the rest of the assembly. Alternatively, the resin
could be injected into a partially formed or near-complete
assembly.
[0067] In accordance with the disclosure, each plate 100 is held in
position through the use of one or more resin casts 150 extending
axially throughout the modulator 50. When the structure is formed,
substantially all of the channel(s) may be filled with resin, and
this may prevent radial movement of the plates. There may be
substantially no air gaps in the modulator 50, for example between
the plates and/or within the channels.
[0068] Using a resin cast in the manner described herein means that
the laminate plates 100 can be formed without any indentations or
other surface features. The solid portions 105 may be smooth, for
example, and/or both sides of each plate 100 may be flat. This is
because they are not required to attach to one another, as they may
be clamped together between the output shaft 24 and modulator
support 26. Some of the plates 100 are shown in FIG. 3B in
isolation, from which it can be seen that each plate 100 may be
flat and smooth on both sides. This smoothness further increases
the magnetic permeability between the plates.
[0069] The resin material may be arranged and configured to
transmit torque to the output shaft. This is achieved in the
illustrated embodiment by connecting the resin casts 150 to
extensions 24 and modulator support 26, so that movement (e.g.,
rotation) of the resin casts 150 due to the pole-pieces of the
modulator 50 causes movement (e.g., rotation) of the extensions 24
and modulator support 26, and in turn rotation of the output shaft
22. In other words, the resin casts 150 are on the primary load
path of the magnetic gear, and transmit torque to the output shaft
22.
[0070] FIG. 4A shows a cross-section through the output shaft 22,
extensions 24, modulator support 26 and modulator 50 of the
embodiment of the pole-piece structure 10 described above. For
clarity, other components of the pole-piece structure 10 are not
shown. FIG. 4B shows a close-up of part of FIG. 4A.
[0071] It can be seen from FIGS. 4A and 4B that the modulator 50 is
connected to the output shaft 22 using a plurality of lips 60 that
extend into respective hollow portions 156 located at opposite ends
of each resin cast 150. The extensions 24 and modulator support 26
also comprise respective annular platforms 62 that support an inner
surface of the modulator 50.
[0072] FIG. 5 shows a perspective view of the components shown in
FIG. 3 prior to their assembly, as well as further details of the
end of each resin cast 150. Some features are omitted for clarity
purposes.
[0073] Each resin cast 150 terminates in an end portion comprising
a first flange 152 and a second flange 154, wherein the hollow
portions 156 are located between the first flange 152 and the
second flange 154. As will be appreciated, the modulator 50 and
extensions 24 may be moved towards one another in the direction of
arrow 600, and the lips 60 slot into respective hollow portions 156
(or cavities) of the resin casts 150 to secure the modulator 50 to
the output shaft 22. The platform 62 slides underneath the
modulator 50 whilst maintaining contact to provide its function of
supporting the modulator 50 in use. The same procedure is used to
insert the modulator support 26 into the modulator 50.
[0074] Other arrangements for connecting the modulator 50 to the
output shaft 22 are contemplated, and the broadest aspects of this
disclosure are not limited to the arrangements shown in respect of
FIGS. 4A, 4B and 5.
[0075] FIG. 6 shows the modulator 50 connected to and assembled
with the output shaft 22, extensions 24 and modulator support 26.
It can be seen that the lips 60 extend into respective hollow
portions of the resin casts 150 as discussed above.
[0076] Although the present disclosure has been described with
reference to preferred embodiments, it will be understood by those
skilled in the art that various changes in form and detail may be
made without departing from the scope of the accompanying
claims.
* * * * *