U.S. patent application number 12/282830 was filed with the patent office on 2009-03-26 for magnetic wheel.
This patent application is currently assigned to MATSWITCH TECHNOLOGY WORLDWIDE PTY LTD. Invention is credited to Franz Kocijan.
Application Number | 20090078484 12/282830 |
Document ID | / |
Family ID | 38508952 |
Filed Date | 2009-03-26 |
United States Patent
Application |
20090078484 |
Kind Code |
A1 |
Kocijan; Franz |
March 26, 2009 |
MAGNETIC WHEEL
Abstract
Magnetic circuit that has (a) a source of magnetic flux which
includes an electromagnet or one or more permanent magnets, (b) at
least two oppositely polarisable pole extension bodies associated
with the magnetic flux source, the bodies being disc, wheel, roller
or similarly shaped with an outer circumferential surface and held
rotatable about respective axes of rotation, and (c) a
ferromagnetic counter body which is arranged to cooperate with the
pole extension bodies such as to provide an external flux path for
the magnetic flux when in magnetic proximity or contact with the
circumferential surface of the pole extension bodies, which is
characterised in that the magnetic flux source is held stationary
relative to the rotatable pole extension bodies.
Inventors: |
Kocijan; Franz; (New South
Wales, AU) |
Correspondence
Address: |
SHERIDAN ROSS PC
1560 BROADWAY, SUITE 1200
DENVER
CO
80202
US
|
Assignee: |
MATSWITCH TECHNOLOGY WORLDWIDE PTY
LTD
Rawdon Island
AU
|
Family ID: |
38508952 |
Appl. No.: |
12/282830 |
Filed: |
March 6, 2007 |
PCT Filed: |
March 6, 2007 |
PCT NO: |
PCT/AU2007/000277 |
371 Date: |
October 22, 2008 |
Current U.S.
Class: |
180/167 ;
280/612; 335/302 |
Current CPC
Class: |
B60L 13/04 20130101;
B60L 2200/26 20130101; B66C 1/04 20130101; B66C 7/02 20130101; B66C
1/06 20130101; B66C 1/08 20130101 |
Class at
Publication: |
180/167 ;
335/302; 280/612 |
International
Class: |
B60L 13/04 20060101
B60L013/04; H01F 7/02 20060101 H01F007/02; A63C 1/20 20060101
A63C001/20 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 13, 2006 |
AU |
2006901247 |
Claims
1. Magnetic circuit having (a) one or more permanent magnets as a
source of magnetic flux, (b) at least two oppositely polarisable
pole extension bodies associated with the magnetic flux source, the
bodies being disc, wheel, roller or similarly shaped with an outer
circumferential surface and held rotatable about respective axes of
rotation, and (c) a counter body having ferromagnetic properties
which is arranged to cooperate with the rotatable pole extension
bodies in providing an external flux path for the magnetic flux
when in magnetic contact with the circumferential surface of the
pole extension bodies, the magnetic flux source being held
stationary relative to the rotatable pole extension bodies.
2. Vehicle capable of magnetically attaching to a magnetically
attractive substrate, including a vehicle body at which are
supported at least two wheel members and at least one magnet
exhibiting a N-- and a S-pole, wherein the wheel members include
magnetically passive but polarisable material, wherein the wheel
members and the magnet(s) are spatially located on the vehicle body
in a manner wherein the wheel members provide rotatable, oppositely
polarisable pole extension elements of the N-- and S-poles of the
otherwise stationary magnet(s), whereby resting of the wheel
members on the surface of a magnetically attractive substrate
creates a closed magnetic circuit encompassing the magnet, pole
extension wheel members and the substrate.
3. Support appliance capable of magnetically retaining attached to
it in an otherwise displaceable manner a magnetically attractive
body, including a support structure at which are mounted at least
two wheel or roller members arranged for rotation about respective
axes, and at least one magnet exhibiting a N-- and S-pole mounted
at the support body separate from the wheel or roller members,
wherein the wheel members include magnetically passive but
polarisable material, and wherein the wheel or roller members are
spatially located on the support structure in a manner wherein the
wheel members provide rotatable, oppositely polarisable pole
extension elements of the N-- and S-poles of the otherwise
stationary dipole magnet, whereby bringing a magnetically
attractive substrate into surface contact with the peripheral
surface of the wheel members creates a closed magnetic circuit
encompassing the magnet, pole wheel or roller members and the
substrate.
4. Vehicle according to claim 2, respectively, wherein the at least
one magnet is supported such as to maintain an air gap to the wheel
or roller pole extension members.
5. Appliance according to claim 3, respectively, further including
drive means arranged for transferring torque into at least one of
the wheel or roller members.
6. Vehicle according to claim 2, further including means for
self-propelling the vehicle on the substrate surface.
7. Vehicle according to claim 6, wherein the self-propelling means
include an arrangement for transferring torque to at least one of
the wheel members from an on-board motor.
8. Appliance according to claim 5, wherein the drive means include
one of a belt drive, a sprocket wheel drive, a chain drive or a
worm gear drive or combinations thereof.
9. Appliance according to claim 8, wherein the drive means include
one or more friction rollers disposed to transmit or receive torque
by engagement with an outer circumference of at least one of the
wheel members.
10. Appliance according to claim 9, wherein the friction rollers
incorporate ferromagnetic materials operatively arranged for
biasing the rollers into and holding contact with the wheel
member(s) through magnetic force.
11. Vehicle or appliance according to claim 8, wherein the drive
means include a gear box or arrangement.
12. Appliance according to claim 3, respectively, wherein one
dipole magnet is provided per wheel or roller member pair.
13. Appliance according to claim 12, wherein the dipole magnet is a
switchable permanent magnet device arranged for generating an
external magnetic field that can be varied between a maximum flux
density output in a fully on or active state and a minimum,
practically negligible flux density output in a fully off or
deactivated state.
14. Appliance according to claim 13, wherein the switchable
permanent magnet device includes one of a toggle switch for
changing and selecting between fully on and fully off states and an
incremental switch for setting and fixing a magnetic flux output
between fully on and fully off.
15. Appliance according to claim 12, wherein the wheel or roller
members are cup shaped in cross-section, and wherein the dipole
magnet extends with one of its poles into the cup shaped wheel or
roller.
16. Appliance according to claim 13, having at least four of said
wheels or rollers arranged in pairs, wherein one said switchable
permanent magnet device is present per each said wheel or roller
member pair, and further including a device for discretely
switching the two switchable permanent magnet devices independently
or jointly.
17. Magnetic circuit according to claim 1, wherein the rotatable
pole extension bodies are wheel shaped and have a cross-sectional
shape and dimensions to (a) minimise flux transfer losses from the
magnetic flux source into the rotatable pole wheels, (b) provide
relatively larger area virtual poles thereby to maximise flux
transfer outside of the direct physical contact zone between pole
extension wheels and substrate surface, and (c) maintain a
predetermined value of magnetic attraction force towards the
substrate.
18. Magnetic circuit according to claim 17, wherein the pole
extension wheels are cylindrically cup-shaped bodies having an
annular flange portion having an axial length which is a function
of the magnetic field strength of the magnetic flux source.
19. Magnetic circuit according to claim 18, wherein the cup-shaped
pole extension wheels have an axial length sufficient to cover the
magnetic flux source to an extent where the flux source exhibits
approx 70% of its maximum field strength.
20. Magnetic circuit according to claim 1, wherein the magnetic
flux source comprises switchable permanent magnet devices
switchable to exhibit an external magnet field between strong and
weak (practically zero) values.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to the field of magnetics, in
particular to the use of magnetic force to attach one object to
another whilst allowing movement of the objects relative to one
another in a magnetically attached state.
BACKGROUND OF THE INVENTION
[0002] There are numerous situations and applications where it is
desirable and/or necessary to secure or support one object to or on
another object whilst allowing for freedom of translational or
rotational movement of these objects relative to one another.
[0003] In the field of material handling, for example, roller
conveyors are used to transport sheet metal and other ferromagnetic
work pieces from one location to another. Gravity forces are relied
upon to ensure the work pieces remain on the conveyor rollers (some
of which may be driven and others being idle rollers) as these are
transported, and thus such conveyor systems will mostly have roller
transport paths extending substantially in a common horizontal
plane, unless additional, dedicated hold-down structures are
employed in restraining the work pieces from lifting-off from where
rollers are deployed along inclined travel path sections.
[0004] In overhead conveying applications in enclosed surroundings,
eg large ware houses, it is known to install overhead rails to
which are secured wheeled carriages from which in turn may be
suspended crane head structures, grippers and similar attachment
devices. Gravity force is relied upon to hold the grooved carriage
wheels in engagement with and on top of the overhead guide rails,
and side brackets provide additional security against lateral
dislodgement from the rails.
[0005] In the field of high-rise building construction, it is known
to provide vertically extending rails which provide guidance for
working platforms which are suspended for vertical movement from
the top of the building in order to carry out maintenance work,
such as window cleaning, etc. The platforms incorporate gripper
mechanisms which form-fittingly engage over the rails to restrain
horizontal movement (eg swaying) whilst held vertically movable
along the rail.
[0006] In the field of robotics, in particular such using remote
controlled vehicles, it is known to incorporate into autonomous,
wheeled platform or self-tracked vehicles, a multitude of different
type of tools and implements by way of which specific tasks may be
carried out remotely by an operator. For example, gripper-arms can
be deployed from such vehicles to recover samples in difficult to
access or hostile environments. Whilst friction enhancing wheel and
track coatings may be used to increase adherence of the vehicle to
the surface in order to allow the vehicle to climb or descend along
steep inclines, there are limits to the steepness of the travel
path which such vehicle may safely master without tipping over or
sliding in uncontrolled manner.
[0007] The present invention was conceived having regard to
applications such as those listed above, and in particular to one
or more application environments where (a) ferromagnetic materials
require conveying or transporting, (b) the incorporation of or
presence of ferromagnetic structures would allow the use of magnets
as a source of force to secure objects to one another in
displaceable manner, (c) gravitational forces are absent to provide
for force-locking engagement of a movable object onto a dedicated
ferromagnetic material substrate or support surface, or (d) indeed
the presence of gravitational forces would necessitate the erection
of or provision of specialised support, guide or other retention
structures or measures to enable a vehicle, either self-propelled
or otherwise, to move along steeply inclined, vertical, and even
inclined or horizontal overhanging (eg ceiling) surfaces having
ferromagnetic properties. However, the below disclosed invention
and its underlying principles may find broader applications, also
replacing existing solutions currently not employing magnetic force
to achieve object coupling.
[0008] In using particular permanent magnets to secure objects to
one another, it is known that the magnetic attraction force is a
function of the type and amount of active magnetic material
employed, the geometry of the magnet's working face, air or other
magnetic leakage paths in the magnetic flux circuit encompassing
the active magnetic material and the body being subjected to the
magnetic attraction force, the ferromagnetic material properties of
the attracted body (ie its relative permeability and magnetic
saturation limits), and the orientation of the Normal force vector
between attracted objects relative to the gravity force vector. The
displacement force required will then be a function of the
effective attraction force and the coefficient of friction defined
between the surfaces of objects.
[0009] In other terms, the physical and geometrical factors, as
well as the functional energetic elements of the closed (or loaded)
magnetic circuit created between a first object (eg an object
carrying a permanent magnet) and a second object (eg ferromagnetic
sheet) will determine ultimately how strongly the objects are
attracted to one another, and whether these objects can be
displaced relative to one another whilst remaining attached to one
another.
[0010] The stronger planar surfaces of objects are `forced`
together by a magnetic attraction force, the more difficult it is
to displace them relative to one another whilst remaining attached
to one another, by exerting a force perpendicular to the attracting
force vector, for any given coefficient of friction which applies
for the pairing of materials of the two objects. It is also
recognised that magnetically attractive surfaces can have very
large friction coefficients, and this knowledge has found
expression in a wide range of technical solutions, such as magnetic
clamps, magnetic lifters, magnetic chucks, etc, where ferromagnetic
objects are to be firmly secured against displacement (assuming
normal operational condition) at a supporting structure that
incorporates magnetic active materials.
[0011] In seeking to enable magnetically coupled objects to move
more easily relative to one another, so called magnetic wheels have
been devised for selected industrial applications, eg
self-propelled welding and inspection robots.
[0012] In its simplest incarnation, a magnetic wheel may be
comprised of a solid disc of permanent magnetic material, eg a
disc-shaped Neodymium-Iron-Boron magnet, magnetised such that
opposite axial end faces of the magnet have different polarity
(here termed axially magnetised). One such disc each can be secured
on opposite terminal ends of a non-magnetisable axle member, which
in turn can be mounted to a vehicle chassis or frame, whereby the
discs may engage with their peripheral surface on a magnetically
attractive substrate surface and roll on such surface in a
magnetically attached state, compare for example U.S. Pat. No.
6,886,651 (Slocum et al.), column 12, lines 44 following. Each disc
(or wheel) will generate an at least partially closed loop magnetic
field extending into the substrate on which it rests, creating a
strong attractive force between the disc and substrate.
[0013] Slocum also discloses a somewhat more elaborate yet simple
magnetic wheel consisting of a disc-shaped, axially magnetised
magnetic core element sandwiched between two magnetically
attractive disc members (made of soft steel, permalloy or laminated
structures comprising such magnetisable but otherwise magnetically
passive materials) having a diameter that is somewhat larger than
the magnet core so that only the disc members can come with their
peripheral surfaces into contact with the magnetically attractive
surface on which the wheel is to magnetically engage. The disc
members thus represent pole extension pieces which concentrate the
magnetic flux originating in the magnetic core element and provide
a low reluctance path for such flux, thus improving the attractive
force between each wheel unit and magnetically attractive support
surface as compared to the wheel embodiment without pole extension
discs.
[0014] Slocum's magnetic wheels are incorporated into
self-propelled carriages that form part of a material
transportation system wherein such carriages can travel along
magnetically attractive surfaces that may include a ceiling,
vertical and inclined walls.
[0015] U.S. Pat. No. 5,809,099 discloses a laser-guided underwater
wall climbing robot for use in inspecting reactor pressure vessels,
which robot includes a self-propelled vehicle supperstructure that
incorporates four magnetic wheels used to provide the necessary
attraction force to allow the vehicle to travel along the
ferromagnetic inner surface of the reactor vessel. Each wheel
consists of a ring-shaped permanent magnet supported on a
non-magnetic axle shaft for rotation therewith, two steel discs of
slightly larger diameter than the magnet being magnetically
attached and secured to the opposite axial faces of the
ring-magnet, ie the discs provide magnetised pole extension pieces
as well as the peripheral engagement surface of the wheel unit,
similar to the Slocum wheel described above.
[0016] U.S. Pat. No. 5,853,655 describes a magnetic wheel guided
carriage for automated welding and cutting of ferromagnetic
substrates such as pipes, steel plates, wherein the magnetic wheels
consist of a plurality (eg three) of axially magnetised ring-shaped
magnets sandwiched between interleaving ring-shaped mild steel
discs (eg five) of a diameter that is larger than that of the
magnets. The stacked discs are mounted and secured against rotation
on a stainless steel sleeve which in turn will be received on an
axle of the carriage. Again, each wheel unit has a plurality of N--
and S-poles whose magnetic field extends into the ferromagnetic
substrate thereby creating at each wheel a closed magnetic flux
path securing the wheels to the substrate surface.
[0017] Other prior art patent documents are also known to deal with
aspects and methodologies that seek to address specific
shortcomings that `basic` magnetic wheels may exhibit in certain
application fields.
[0018] So for example, U.S. Pat. No. 3,690,393 (Guy) would seem to
aim to address the above mentioned problem that magnetically
attractive surfaces can have very large friction coefficients which
in certain applications can be detrimental. Guy describes a vehicle
having a frame on which is mounted a prime mover (eg electric
motor) which is coupled by suitable gearing to a live (or traction)
axle to which a pair of wheel assemblies are secured in order to
propel the vehicle. In one embodiment, one of the non-driven wheel
assemblies consist of a plurality of axially polarised annular
magnet discs secured to one another to form a cylindrical roller
wheel whose outer (peripheral) surface is coated with a thin layer
of a non-polarizable, anti-friction material, such as PTFE
(polytetrafluoroethylene) which minimises drag on the wheel
assembly as the vehicle frame is propelled.
[0019] Guy also describes an electromagnetic wheel assembly, in
which a non-magnetic cylindrical shell encloses an electromagnetic
coil about an inner core element mounted on the wheel's axle for
rotation therewith. Magnetisable pole discs are arranged at the
axial ends of the shell member, and electrical energy can be
supplied to the magnet coil through wiper contacts secured to one
of the pole discs. Upon energization of the electromagnetic coil,
the pole discs will be polarised with opposite polarities. The
annular rims of the pole discs are again coated with a
non-magnetisable, low-friction material for rolling contact with
the magnetisable substrate surface oh which the vehicle is intended
to travel.
[0020] In contrast, U.S. Pat. No. 2,694,164 (Geppelt) discloses
magnetic wheels of a type used in conjunction with welding and
cutting torch carriages which are self-propelled over ferromagnetic
surfaces. The magnetic wheel units consist of an axle sleeve of non
magnetisable material received within an annular-cylindrical
permanent magnet which is magnetized in its axial direction, two
cylindrically cup shaped wheel members of soft steel material which
have their annular flanges extending towards each other and into
clamped close engagement with opposite sides of a non-magnetic
spacer disc that surrounds the magnet about the middle of its axial
length. The axial end faces of the magnet abut against the
respectively facing inner faces of the cup wheel members such as to
allow magnetic flux transfer from the magnet into the wheels
towards their peripheral surface, the spacer disc serving to ensure
magnetic decoupling of the two wheels whereby these will assume
opposite polaritries in accordance with the magnetic field
generated by the permanent magnet of the wheel. Geppelt outlines
that the decrease in wall thickness of the annular cup flanges
towards the spacer disc (as compared to a prior art embodiment with
uniform cup flange thickness) increases the attractive force that
may be exerted between the magnetic wheel and the substrate to
which it attaches.
[0021] In practical terms, and in light of the above description of
prior art magnetic wheel constructs, a technical challenge still
exists in devising methods and arrangements of magnetic flux
transfer from a magnet, as a source of magnetic force to attach one
object to another, through a wheel structure into a magnetically
attractive body, to meet specified operational load carrying
capacity or retention requirements.
[0022] In a more confined aspect, it would be desirable to provide
a vehicle which uses magnetic energy to secure such vehicle onto a
ferromagnetic substrate surface and in which the magnetic flux
transfer mechanism will allow for greater flexibility with regards
to magnetically coupling and decoupling of the vehicle from the
substrate surface.
[0023] In another more confined aspect, it would be desirable to
provide a magnetic support structure by means of which a
ferromagnetic object may be transported between locations in a
secured manner and wherein at the end of such transporting
operation the object may be safely and easily disengaged from the
support structure.
[0024] In another aspect, it would be desirable to provide a
magnetic gripper appliance which may be actuated in order to secure
an object thereto whilst allowing for freedom of movement of the
object in order to conduct machining or other operations on the
object.
[0025] The term `ferromagnetic` as used herein is intended to cover
not only metals and alloys but also composite materials which when
subjected to an external magnetic field will become magnetised and
subject to magnetisation forces.
[0026] Other aspects of the invention will become apparent below
from the following description of preferred embodiments
thereof.
SUMMARY OF THE INVENTION
[0027] In broad terms, the present invention can be defined as
residing in a magnetic circuit that has (a) a source of magnetic
flux which includes an electromagnet or one or more permanent
magnets, (b) at least two oppositely polarisable pole extension
bodies associated with the magnetic flux source, the bodies being
disc, wheel, roller or similarly shaped with an outer
circumferential surface and held rotatable about respective axes of
rotation, and (c) a ferromagnetic counter body which is arranged to
cooperate with the pole extension bodies such as to provide an
external flux path for the magnetic flux when in magnetic proximity
or contact with the circumferential surface of the pole extension
bodies, which is characterised in that the magnetic flux source is
held stationary relative to the rotatable pole extension
bodies.
[0028] Compared with what may be termed `traditional` magnetic
wheel circuits utilised in attaching one object to another, such as
those described above, the present invention physically decouples
the active magnetic source or component (eg electromagnet,
switchable permanent magnet, or conventional permanent magnet) from
the disc-, roller- or wheel-like pole extension pieces, wherein the
pole extension pieces remain free to rotate about their respective
axes of rotation but the associated magnetic flux source remains
stationary, ie it does not rotate with the pole extension
pieces.
[0029] Preferably, physically decoupling will be accompanied by
spatially separating the flux source from the rotatable pole
extension pieces, eg by maintaining a small air gap between these
components, see also below. The term `small` will depend on the
specific application and may for example be 0.1 mm (or smaller) up
to a few millimetres.
[0030] Vis a vis the above described prior art magnetic wheels, the
mass associated with the magnetic flux source is no longer subject
to rotation with the wheel, thereby reducing inertia moments at the
wheel structure proper, with all the concomitant advantages which
such reduced wheel mass brings with it. Physical decoupling of the
wheels from the magnetic flux source also enables greater
flexibility in devising or designing the flux source itself.
[0031] Equally, where the source of magnetic flux of a magnetic
wheel unit is an electro-magnet, such as described in U.S. Pat.
Nos. 3,690,393 or 6,886,651, physical decoupling of the magnetic
flux source from the rotatable wheels in accordance with the
invention simplifies the mechanism/arrangement required for
transferring electrical power into the magnet coil, given that the
later remains stationary and there is no need for brushes or pole
shoes otherwise required for transferring electricity through the
pole pieces (or otherwise) into the rotating electromagnet coil
armature.
[0032] Independently of the type of magnetic flux source utilised,
magnetic flux transfer from the source into the rotatable pole
extension members will be effected across a `working gap` that can
be air or could conceivably be a different fluid confined into the
volume present between flux source unit and pole wheels, the fluid
then preferentially providing a low magnetic reluctance path, ie a
magnetisable fluid that has a relative magnetic reluctance that is
less than air.
[0033] It will also be noted that in contrast with prior art
magnetic wheels, each of which comprises at least one N--S pole
pair, the invention can provide embodiments and arrangements
wherein each rotatable pole extension member assumes only one
polarity, ie either S-- or N-polarity, so that the closed magnetic
flux path will encompass flux transfer from one pole extension
member through the ferromagnetic counter body, which provides a low
reluctance magnetic flux path, and into the other pole extension
member. In other words, two such rotatable pole extension members
are necessary and sufficient for a closed flux transfer
circuit.
[0034] In the following, for ease of understanding, and unless it
appears differently in the specific context, the term `wheel` will
be used to encompass all types of rotatable pole extension bodies
such as unitary soft-steel discs, cylindrical rollers, pulleys and
other structures that generally comprise a rim and hub united by a
radial connection structure, eg spokes, face web, etc, and which
are capable of rotation about a stationary (axial) axis and which
serve to support a vehicle or work piece for translational or
rotational movement upon rotation of the rim.
[0035] In a more specific aspect, the present invention provides a
vehicle capable of magnetically attaching to a magnetically
attractive substrate, including a vehicle body at which are
supported at least two wheel members and at least one dipole
magnet, wherein the wheel members include magnetically passive but
polarisable material, wherein the wheel members and the dipole
magnet(s) are spatially located on the vehicle body in a manner
wherein the wheel members provide rotatable, oppositely polarisable
pole extension elements of the otherwise stationary dipole
magnet(s), whereby resting of the wheel members on the surface of
the substrate creates a closed magnetic circuit encompassing the
dipole magnet, pole piece wheel members and substrate.
[0036] In an alternate specific aspect of the invention, there is
provided a support structure capable of magnetically retaining
attached to it in an otherwise translationally or rotationally
displaceable manner a magnetically attractive substrate, including
a support body at which are mounted at least two wheel or roller
members arranged for rotation about respective axes, and at least
one dipole magnet mounted at the support body separate from the
wheel or roller members, wherein the wheel or roller members
include magnetically passive but polarisable material, and are
spatially located on the support structure in a manner wherein the
wheel or roller members provide rotatable, oppositely polarisable
pole extension elements of the otherwise stationary dipole
magnet(s), whereby bringing a ferromagnetic substrate into surface
contact with the peripheral surface of both the wheel or roller
members creates a closed magnetic circuit encompassing the dipole
magnet(s), pole extension wheel or roller members and
substrate.
[0037] In essence, whilst the first aspect is directed at providing
a vehicular implementation of the broader concept underlying the
invention, eg providing externally or self-propelled vehicle
embodiments capable of movement along inclined or vertical walls,
for example, the second aspect is intended to cover applications
where the wheels or roller members together with the support body
remain stationary such as in a conveyor apparatus for conveying of
ferromagnetic objects, such as steel plates, along a plurality of
magnetically polarisable roller members disposed along a conveying
pathway, or applications where the support body is itself carried
or mounted at another appliance, eg robotic arm, thereby to allow
the pole wheel members to magnetically engage against and secure
thereto a ferromagnetic object or work piece.
[0038] It will also be appreciated that whilst it is feasible to
employ conventional permanent magnets (ie such which always exhibit
an external magnetic field) as the source of magnetisation of the
pole extension wheels, the basic concept underlying the present
invention is particularly conducive towards implementation of
vehicular and other embodiments that utilise switchable permanent
magnet structures, such as disclosed in U.S. Pat. Nos. 6,707,360
and 7,012,495. Such switchable permanent magnet units combine the
advantages of electromagnets and conventional permanent magnets
without their respective main drawbacks, namely the need for an
electric power source to drive an electromagnet and the
non-variability of magnetic flux output of permanent magnets, ie a
switchable permanent magnet does not require an electric power
source and can be switched to exhibit an external magnetic field
between strong and weak (practically zero) and values between these
extremes. For more details, refer to said US patents, the contents
of which are incorporated herein by way of cross-reference.
[0039] The use of magnet units which are capable of providing a
variable magnetic flux, such as said switchable permanent magnet
units and electro-magnets, provides an important additional aspect
of the invention in that the variability of the magnetic attraction
force enables application and machine embodiments where a
ferromagnetic work piece can be selectively engaged by the
rotatable pole extension elements, magnetically secured thereto for
spatial manipulation upon activation of the magnetic flux source,
and ultimately released there from upon deactivation of the
magnet.
[0040] Before turning to additional aspects and application fields
of the present invention, as well as additional features that may
find inclusion in preferred embodiments of the above broad
inventive concepts, reference shall be made to the accompanying
FIGS. 1a, 1b and 1c, which represent highly schematic illustrations
that will help in understanding basic principles underlying the
present invention. It shall be understood that the below
explanations rely on approximations, idealisations and
simplifications of the in part relatively complex phenomena
observed and present in magnetic circuits.
[0041] Turning first to FIG. 1a, it illustrates what shall here be
termed as a Magnetic Wheel unit 10, consisting of two disc-shaped
wheels 12, 14 and a bar-(or cylindrically) shaped dipole permanent
magnet 16. These components represent a basic unit that can be
built upon, modified and incorporated in numerous applications of
the invention as explained below.
[0042] The magnet 16 will be a high coercive, ie rare-earth magnet
capable of inducing high magnetic flux densities across air gaps
(mainly) through its axial end faces 16a, 16b, and generate a
pulling force (magnetic attraction force) in a ferromagnetic body
towards the axial end faces as outlined above.
[0043] The discs 12, 14 have a circumferential contact surface 13a
and two axial faces 13b and 13c, and are made entirely of
ferromagnetic soft steel.
[0044] The discs 12, 14 are respectively located opposite an axial
end face 16a, 16b of magnet 16, keeping a fixed small air gap (not
illustrated in FIG. 1), such that each disc provides an oppositely
polarised pole extension for the respective N--- and S-pole 20, 22
of the magnet 16. Furthermore, the discs 12, 14 are supported at
not illustrated axle members about a common axis of rotation 18 to
allow rotation thereof, ie the discs can be termed as freely
spinning pole extension `wheel` pieces which otherwise maintain a
fixed spatial relationship to the dipole magnet 16, the axis of
rotation being parallel or coinciding with the N--S magnetisation
axis of the dipole.
[0045] Magnetic flux transfer from the magnet 16 to the discs 12,
14 will take place across the small air gaps between the facing
sides 13b of the discs and the poles 20, 22 of the magnet 16. The
gaps are intended to minimise friction loses at the interface
between magnet 16 and pole pieces 12, 14, but could be replaced
with magnetisable roller bearings that provide for direct physical
contact between discs 12, 14 and the magnet's axial end faces and
thus improved flux transfer between magnet and pole discs 12,
14.
[0046] When the surface of a ferromagnetic substrate, eg steel
sheet 24, is brought into contact with the peripheral surface 13a
of both pole discs 12, 14 of the Magnetic Wheel Unit 10, a closed
magnetic circuit will be created, wherein a closed magnetic flux
loop will comprise a path internal to the magnet 16 and pole
extension discs 14, 16, and a path external to the unit 10 between
the pole extension discs 14, 16 and the ferromagnetic substrate 24.
That is, the external magnetic field extends within the substrate
24, and this is schematically illustrated at 26 in FIG. 1a, and the
entire closed loop flux path at 27 in FIG. 1b.
[0047] The Magnetic Wheel Unit 10 will be attracted and remain
strongly secured to the substrate 24, despite the actual physical
contact area between the discs 12, 14 and the steel sheet 24 being
essentially confined to a line measuring the sum of the thicknesses
(ie widths) of the disc 12, 14. The free-spinning nature of the
disc wheels 12, 14 allows translational displacement of the unit 10
over the surface of the substrate 24 by applying but a very small
force traverse to the magnetic attraction force which attaches the
Wheel Unit 10 to the substrate 24. The small force requirement
stems from the relatively low rolling resistance coefficient
applicable to steel discs rolling on a steel substrate, which is
magnitudes smaller than the static and the kinetic friction
coefficients applicable to the same material-pair combination but
where the pole wheels 12, 14 are kept in an immobilised state with
respect to the magnet 16 and the surface on which such static
wheels would otherwise glide.
[0048] It would seem counterintuitive that despite the presence of
air gaps between magnetic flux source 16 and rotatable pole discs
12, 14, and a very small contact area between pole piece discs 12,
14 and substrate 24, the Magnetic Wheel unit 10 will remain
securely attached to the substrate. A prototype Magnetic wheel unit
10 embodying the principle illustrated in FIG. 1 with the permanent
magnetic flux source being a rare earth NdFeB magnet having a
50mm.times.40 mm `flux source area` (ie cross-section area of the
magnetic flux source normal to the polarisation axis of the magnet)
capable of delivery of 1.2 Tesla magnetic flux density, with two
soft steel discs (having a magnetic flux density saturation level
of around 2 Tesla) with a dimension of 25 mm width.times.90 mm
diameter and keeping an air gap towards the permanent magnet of
approx 1 to 2 mm is able to attach to a ferromagnetic steel sheet
of 35 mm thickness and carry a load equivalent to a `breakaway
force` of over 1200 Newton.
[0049] As noted, the actual physical contact zone or area between
substrate 24 and (rotatable) pole discs 12, 14 is very small (in
theory a line, given that deformation, ie `flattening` of the
soft-steel discs under load is negligible).
[0050] It has been noted that in the vicinity of the physical
contact area there exist so called `virtual pole areas`, where
noticeable flux transfer takes place across air, ie (a) from the
peripheral surface of the pole discs either side of the contact
zone towards the substrate surface and (b) from both faces of the
disc near the contact zone and the substrate surface. In the
present context, such air gaps do not represent and are not to be
mistaken as unwanted leakage paths, rather the effective magnetic
contact area between discs and substrate is enlarged, and the so
called virtual poles provide an additional means of flux transfer
(albeit at lower density values) from discs 12, 14 to substrate 24,
thereby adding to the total pulling power available to secure the
unit 10 onto the substrate 24 (or vice versa). These virtual pole
area extensions are schematically illustrated at 30a, 30b and 31a
and 31b in FIG. 1b and in FIG. 1c, and do contribute in maintaining
a closed magnetic circuit of sufficient quality at the interface
between substrate and Magnetic Wheel unit 10 for the exerted
attraction force to remain high, as exemplified above.
[0051] FIG. 1c illustrates a magnetic field line model with
measured flux density values at two soft-steel 90 mm
diameter.times.25 mm thickness pole discs 12, 14 having a magnetic
density saturation level of 2 Tesla, which are polarised with
opposite polarities and which are held in air in spaced apart
relationship on a magnetic substrate 24. It can be seen that on
either side of the essentially linear contact zone 28 between pole
wheels 12, 14 and substrate 24, a flux density of 2 Tesla will
reduce drastically (ie the virtual pole extensions exhibit reduced
flux densities), wherein at a linear distance of 10 mm the flux
density is reduced to about 15% of the value at the physical
contact area, and about 5% at a distance of 20 mm.
[0052] Flux transfer from the magnet 16 into the substrate 24 will
thus be influenced--and limited--by (a) the shape and dimensions of
the interface of the magnetic flux source (eg the flux delivery
component in a switchable permanent magnet device or electromagnet)
at the gap towards the pole discs, (b) `magnetic leakage` at the
air gap interfaces between the passive pole extension discs 12, 14
and magnetic flux source 16, (c) geometric and shape constraints of
the discs which may not be able to `support` (ie carry and deliver)
the same flux density at the given field strength which the magnet
16 generates, (d) the nature of the virtual poles in so far as
these cannot support the same flux density at the given field
strength which the ferromagnetic material of the discs 12, 14 can,
and (e) the total magnetic path length between flux source and
ferromagnetic substrate, recalling that the magnetic pulling force
by means of which any ferromagnetic body is attracted to a source
of magnetic flux will vary mathematically with the square of
magnetic flux density provided by the source and linearly with the
contact area between the source and the attached body.
[0053] For example, a magnetic wheel unit 10 using relatively
larger diameter pole discs 12, 14 as those described above, eg
3-times, will have a longer total magnetic path (due to increased
diameter of discs) and the magnetising force at the contact area
will be lower then and the virtual pole areas will be smaller (and
in extreme situations virtually non-existent).
[0054] The actual size, shape and geometric extent of the virtual
poles are not fixed but vary with the actual working and
application conditions. Generally speaking, the larger the virtual
pole zones can be made, the more magnetic flux transfer may take
place in the vicinity of the disc-substrate interface. An important
consideration is therefore the need to avoid or minimise
magnetising force losses.
[0055] Consequently, in accordance with another aspect underlying
the present invention, the pole wheels will be of such shape and
dimensions to cater for (a) optimised flux transfer from the
magnetic flux source into the rotatable pole wheels and (b) provide
relatively larger area virtual poles thereby to enable optimised
flux transfer also outside of the direct physical contact zone
between pole discs and substrate surface, whilst (c) maintaining
sufficient magnetic attraction force towards the substrate; an
important point is to avoid, as far as practically possible, losses
in magnetising force at each interface.
[0056] Having noted the difficulties regarding precise definition
of the virtual pole zones, assuming an idealised air-gap leakage
free magnetic flux path between magnet flux source (eg permanent
magnet) and rotatable pole wheels, it is possible to match the size
of the diameter-cross-sectional area of the wheel or roller poles
as best as constructional possible to the size of the magnetic flux
source area, ie the cross section of a pole in the dipole magnet
perpendicular to its magnetisation axis. Such measure will produce
an optimised, ie a higher magnetising force at the discs' working
interface (ie air gap) with the substrate as compared to cases
where the geometric dimensions of the wheel or roller pole
extensions are chosen arbitrarily or without regard to magnetic
flux transfer considerations.
[0057] For example, and all other parameters being equal, cup
shaped wheels or rollers which are disposed to surround with their
annular rim portion a determinable part of the respectively
associated pole of the dipole magnet and maintain a small air gap
between the wheel's internal disc face towards the axial end face
of the dipole magnet, exhibit a larger total area for flux transfer
into and out of such wheel than a simple planar disc-shaped wheel
where the flux transfer area is confined to the surface area facing
the axial end face of the dipole magnet. One could say cup shaped
wheels can `capture` a larger portion of the flux emanating from
the magnet which, absent the annular rim portion of the cup which
surrounds part of the magnetic flux source, would be lost as
`stray` flux, and use such additionally captured flux to generate a
higher magnetic attraction force towards a ferromagnetic substrate
than `plain disc-shaped` pole extension.
[0058] The actual depth of the rim portion of the cup-shaped wheel
or roller will depend on the nature of the magnetic flux source
being employed, and in particular the magnetic flux `output` member
of the magnetic flux delivery device. In essence, the cup depth
will represent a compromise between maximum flux transfer
considerations (optimised where the annular rim portion depth is
such as to extend and cover the whole length of the respective
North/South pole of the magnet) and desired magnetising force (ie
magnetic attraction force) which will be lower in the flux transfer
optimised rim configuration. An empirically determined relative
size of the annular rim with regards to its covering of the flux
source is provided below in connection with a specific embodiment
of the invention.
[0059] To conserve the magnetising force of the high coercitivity
flux source it is also desirable to minimise the volume of the
passive ferromagnetic material pole extension wheels. Viewed only
from a point of view of seeking to optimise flux transfer, a
theoretical necessary volume maximum is given where the effective
cross section of the flux source equals the diametrical
cross-section of the wheel divided by any applicable flux
compression/concentration factor (the latter is determined by
material specific flux density carrying capacity and the flux
source density output. For example, if a flux source can provide a
magnetic flux density of 1.2 Tesla and is able to generate a
magnetising force sufficient to induce in mild steel a flux density
of 2 Tesla, the compression factor is about 1.6). The practical
maximum will be lower because of total magnetic path length and
flux/wheel air gap losses.
[0060] Turning then to advantageous additional features that may be
incorporated in different embodiments of the above described broad
concepts.
[0061] In utilising a conventional, non-switchable magnet or
preferably a switchable permanent magnet arrangement as the
magnetic flux source, it will be appreciated that the magnetically
active material may be encased or otherwise disposed to cooperate
with other stationary pole pieces additional to the rotatable pole
extension elements (ie wheels), in which case the flux will
`originate` in the active material and be made `available` through
the other stationary pole pieces that will be disposed in facing
close proximity to the rotatable pole wheels. The specific shape of
the stationary pole pieces will also influence flux transfer
capabilities and have an effect on the maximum available
magnetising force, as the poles do represent a `load` for the
magnetic field generated by the active magnetic material (ie the
flux source)
[0062] In preferred embodiments of the above described Magnetic
wheel units 10, use is made of a switchable permanent magnet device
disclosed in said U.S. Pat. No. 7,012,495, different types of which
can be sourced from Magswitch Technology Worldwide Pty Ltd
(Australia) or its subsidiaries. In these flux source units, the
active magnetic material is constituted by two, diametrically
oppositely polarised, dipole permanent magnet cylinders, stacked
within a cylindrical chamber of a two-pole-piece housing such as to
allow rotation of the magnet discs relative to one another, thereby
enabling the respective half-circular N-- and S-pole sections of
the magnet discs to be brought in and out of axial alignment with
one another. The ferromagnetic (passive) two pole pieces of the
housing are magnetically separated or isolated along two axially
extending contact edges, wherein when the respective N-- and
S-poles of the stacked magnet discs are rotated into full
alignment, the diameter separating the N-- and S-poles of the
magnet discs will extend between the contact edges of the housing,
thereby causing one of the pole pieces to be polarised and provide
a N-pole pole extension and the other a S-pole pole extension.
[0063] Such switchable dipole magnet unit may then constitute the
magnetic flux source 16 in FIG. 1a, wherein flux transfer into the
rotatable pole discs 12, 14 will take place from the magnet discs
through the housing pole pieces and across the air gap between
housing pole pieces and the pole wheels located in facing proximity
to the two pole pieces of the housing, respectively. The wall
thickness and exterior shape of the pole piece housing can be
chosen to provide a flux source unit having a constant magnetic
field or approx. constant magnetic flux about the periphery of the
housing; and spatial orientation of the unit's housing with respect
to the rotatable pole wheels can be determined as required. The
specific choice of switchable permanent magnet unit can be made by
reference to information available from Magswitch Technology
Worldwide, depending on load carrying requirements.
[0064] As noted above, it is conceivable to have the facing
surfaces of the pole wheels and magnetic flux source unit coated
with a low friction material and provide for the presence of soft
steel roller bearings at the interfaces unit--pole wheels. In
practical implementations it is however technically feasible to
maintain very small air gap tolerances between the movable and
stationary components whilst not significantly negatively affecting
magnetic flux transfer across the air gap. In the end, the specific
application environment will dictate air gap distance
requirements.
[0065] Equally, applications are conceivable where the pole wheels
are mounted to allow free rotation about an axle whilst allowing
displacement towards and away from the axial end faces of the
magnet, so that they can be selectively brought into and out of
frictional engagement therewith, whereby an integral clutch and/or
brake can be implemented at the magnetic wheel unit itself.
[0066] As already noted, vehicular and stationary implementations
of the invention may incorporate driven or idle pole wheels or
rollers. The circumferential surface of the wheels and rollers may
have a friction coefficient enhancing or reducing coating, as
required, for improving traction or reducing friction at the
wheel--substrate interface, depending on whether the wheels are
traction or idle wheels.
[0067] Coating materials may include thin-film rubbers, preferably
incorporating ferromagnetic particles, flecks, powders etc to
increase the value of relative magnetic permeability of such
coating to reduce flux transfer losses whilst maintaining the
improved friction coefficient which such rubberised coating
provides. The wheel contact surface can have different `textures`,
eg smooth for low traction or profiled to increase "bite" for
higher traction. Coating may also include processes and use of
substances aimed at increasing the overall hardness of the wheel or
roller surface, eg Titanium Nitride to achieve more slipperiness
(smooth surface) or higher friction (textured surface). Noise
reducing coatings are equally conceivable, whereas coating films
aimed at preventing extraneous matter adhering onto the
wheel/roller peripheral surface are particularly advantageous in
`dirty` application fields such as steel sheet handling operations,
use of magnetic wheel units in vehicles employed as remote
controlled painting, brazing, welding and other applications.
[0068] A device incorporating one or more magnetic wheel units of
the type generically discussed above, can advantageously
incorporate drive means, such as a motor, arranged for transferring
torque into at least one of the wheel or roller (pole piece)
members. The torque available at the wheel or roller members can
then be used to impart propulsion to an object in contact with the
wheels (eg metal sheet conveying), self-propel a vehicle
incorporating the magnetic wheel unit(s), or where the torque
transferred is a `negative` torque aimed at reducing the rotational
speed of the wheels where such are caused to rotate by an external
force, slow down or brake an object that is in frictional contact
with the wheels.
[0069] The pole extension wheel members can be made advantageously
from soft steel or other ferromagnetic passive materials. An
advantageous wheel design may consist of a composite material
consisting of a plastic material or rubber matrix in which is
dispersed a considerable amount of ferromagnetic material powder
for flux carrying purposes. Deformability of the pole extension
wheel at its interface with the substrate on which its rests under
magnetic load will enlarge the contact zone where flux transfer
takes place directly between wheel member and substrate, also
providing increased frictional engagement therewith.
[0070] It will be appreciated, that the external peripheral surface
of the pole piece wheels or rollers may be smooth, textured,
corrugated or provided with other type of protrusions, eg cog wheel
teeth. The choice of wheel surface properties may be such so as
cooperate with a complementarily prepared surface of the substrate
with which the magnetic wheel unit will interact. For example, in a
friction wheel gearbox and variable ratio drive arrangement
incorporating one or more basic magnetic wheel units having smooth,
non-corrugated pole wheels or rollers, the inherent slippage
functionality which such provide when rolling on another
smooth-surface object can be used to minimise overload conditions
as torque transfer is reduced due to slippage. Of course, where
slippage in the torque transfer between pole wheels or rollers and
substrate is not desirable, form-interlocking complementary pole
wheel or roller and substrate surfaces may be employed, eg surfaces
having gear teeth.
[0071] A particularly useful embodiment of the invention will be in
a vehicular application that includes means for self-propelling the
vehicle on the substrate surface, regardless of whether the means
for self-propelling include an arrangement for transferring torque
which cooperates with the pole wheels or rollers for the latter to
effect torque transfer onto a ground or wall surface, or whether
the propulsion unit is independent from the magnetic wheel unit(s)
present in such vehicle, eg a separate traction wheel drive.
[0072] The torque transferring arrangement can be devised to suit a
given application field, and may include one or more of a belt
drive, a sprocket wheel drive, a chain drive or a worm gear drive
or combinations thereof.
[0073] A preferred option for a torque transferring arrangement
includes one or more friction rollers disposed to transmit torque
by engagement with an outer circumference of at least one of the
pole wheel or roller members. The friction rollers may be
selectively brought in and out of engagement with and biased
against the wheel members using a separate mechanism, but
advantageously the friction rollers could incorporate ferromagnetic
materials operatively arranged for biasing the rollers into and
holding contact with the wheel member(s) through magnetic
force.
[0074] In yet a further vehicular, self-propelled device
implementation of the present invention, means can be provided for
restricting rotational movement of the pole wheel or roller members
in one direction only, eg so that the wheels can rotate either
clockwise or counter-clockwise, but not both. This measure
increases traction efficiency in slippage situations by removing
the otherwise present bi-directional free-wheeling characteristics
present in normal wheel axles.
[0075] Also, it is advantageous to provide mechanisms or implements
aimed at preventing roll-back of a vehicle employing one or more
Magwheel units having propelling (ie torque transmitting) wheel
members climbing along steeply inclined or vertical surfaces whilst
remaining magnetically attached thereto, One implementation sees
the provision of brake pads or blocks that are selectively movable
into a location between wheel member(s) and substrate surface
immediately behind the contact area wheel(s)--substrate surface,
thereby to provide a wedging action preventing backward rolling of
the wheel(s).
[0076] Another roll-back prevention mechanism may be constituted by
a see-saw like arresting frame, wherein a substantially u-- or
bracket shaped frame member is mounted for rotation about but
otherwise secured to a common axle to both pole wheels such that
the frame's two parallel lever arms can be rotated to come with
their respective terminal ends into forced engagement with the
substrate surface on which the wheels are magnetically attached.
The lever arms may themselves be constituted by bent bar sections,
eg L-bent arms pivoted at the intersection of the angled arm
portions at the axle, thereby to provide a pull lever arrangement
wherein the braking force is a leveraged factor of the magnetic
attraction force provided by the wheel assembly itself.
[0077] In a vehicular embodiment incorporating four or more pole
wheels, wherein a switchable permanent magnet device is associated
with one wheel pair, provision of a suitable mechanism that enables
the selective switching on and off (or variation of the magnetic
field intensity output) of the individual switchable magnets
provides a number of advantages. Not only will such selective
`magnetic activation and deactivation` of individual wheel pairs
facilitate operational disengagement of the vehicle from the
substrate, it will also facilitate the vehicle being able to climb
over step-like obstacles or transitions between a horizontal and a
steeply inclined or vertical surface, in that forward pair of
wheels reaching such path change location may be `demagnetised`
thereby to render them magnetically inoperative, whereby they can
then lift-off from the initial surface and engage the inclined
surface, whereupon they may be `remagnetised` and allow the vehicle
to transition onto the inclined surface. The rearward located wheel
pair will be switched accordingly as it too reaches the path
discontinuity.
[0078] Vehicular application fields of the invention include
motional robots which can be magnetically attached to ferromagnetic
substrates (ie structures and objects) like ship hulls, submarine
hulls, pipelines (inside and outside). Such robots may carry a
variety of appliances such as cameras, all types of sensors
employed in detecting of faults in a structure or perform other
tasks, eg transporting a cable through a pipeline, cleaning a
pipeline, etc. For example, underwater optical and structural
inspection of the hull of a moving and submerged submarine hull can
be accomplished using a remote-controlled robot having a
streamlined body in which are received a suitable number of
Magwheel units of general type discussed above, which allow the
robot to remain securely attached to the hull whilst being
propelled along a desired inspection path.
[0079] The skilled person will further appreciate that sensor
systems, motion control equipment, either for remote controlled
operation or on-board controlled operation using signal processing
equipment, motor management electronics and power source, and other
type of vehicle management equipment can be accommodated in the
vehicle support structure of a self-propelled vehicle as required
by the specific application environment of the vehicle.
[0080] The skilled person would also be aware of different types of
axle systems and vehicle chassis types that could be employed in
creating a vehicle embodying the invention.
[0081] Further features and other aspects of the invention will be
noted also from the following description of a number of preferred
implementations and embodiments of the invention, with reference to
the accompanying drawing. It should be noted, however, that the
invention is not restricted to the application fields outlined
above, and may be implemented in different forms.
BRIEF DESCRIPTION OF THE DRAWINGS
[0082] FIG. 1a, 1b, and 1c are highly simplified schematic
illustrations of basic concepts underlying the present
invention;
[0083] FIG. 2a to 2c are schematic illustrations of different
configurations of rotatable pole wheel arrangements used with
different magnet configurations, wherein FIG. 2a also illustrates a
ferromagnetic friction roller used to impart (or receive) torque
from the rotatable pole wheels;
[0084] FIG. 3a to 3c are schematic illustrations of implements and
devices in which the present invention can be embodied.
[0085] FIGS. 4a, 4b and 4c are schematics by way of which is
illustrated how to optimise rotatable pole piece geometries with
regards to the chosen magnetic flux source in a magnetic wheel unit
as per FIG. 2a; and
[0086] FIG. 5 is a schematic illustration of a magnetic wheel unit
braking arrangement which translates some of the available magnetic
attraction force into a braking force.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0087] A basic magnetic wheel unit as illustrated in FIGS. 1a and
1b has already been described above. Such units can be incorporated
in numerous and different machines and appliances. It should be
noted that the active magnetic material (ie permanent magnets) or
other magnetic flux source (eg electromagnet) can be received
within a dedicated housing; thus, the actual shape of the magnetic
flux unit 16 in FIGS. 1 and 2 is illustrative only and not
representative of the actual shape of such units.
[0088] As can be best understood by having reference to FIGS. 2a to
2c, depending on the number of and specific types of dipole magnets
employed as magnetic flux source, magnetic wheel units having
different pole wheel numbers and arrangements are possible.
[0089] FIG. 2a illustrates a twin wheel configuration unit 10
utilising a single magnet 16 and two rotatable pole wheels 14, 16
as previously described with reference to FIG. 1a.
[0090] FIG. 2b illustrates an arrangement with two pairs of pole
wheels 12', 14', one pair at the N-- Pole and one at the S-pole of
the bipolar magnet 16', ie a four-wheel magnetic wheel unit 10'
with single magnetic flux source 16'.
[0091] FIG. 2c in contrast illustrates a four-wheel magnetic wheel
unit 10'' with two spaced apart magnetic flux sources 16'' (which
can but need not be identical with regards to magnetic flux density
delivery qualities), wherein each magnet 16'' is associated with
one pole wheel pair 12'', 14''. It may be noted that the
magnetisation axis extending between N-- and S-poles of the two
magnets 16'' are orientated in opposite directions to one another,
but this need not be the case in practical embodiments of such unit
10''.
[0092] The lines 17, 17' and 17'' in FIGS. 2a to 2c, respectively
illustrate in crude but figuratively correct manner external flux
transfer paths that will be present in the substrate 24 (being
represented by a steel plate) that respectively exist between the
polarised pole wheels of the different units 10, 10' and 10''.
Given that the magnetic permeability of the ferromagnetic substrate
is by magnitudes higher than that of the surrounding environment,
be it air or another fluid like water, and assuming the substrate
properties are such that no flux saturation takes place during flux
transfer into the substrate, one would not observe any magnetic
field outside the immediate vicinity of the contact area between
pole wheels and substrate (refer above to virtual pole extension
areas) and the closed magnetic circuit comprised of the pole
wheels, substrate and magnetic flux source device.
[0093] Magnetic wheel units 10 (or 10' or 10'') can be embedded and
embodied in a multitude of apparatus and devices for a variety of
applications.
[0094] Turning first again to FIG. 2a, it schematically illustrates
one methodology of effecting torque transfer either into or from
the pole wheels 12, 14 of unit 10, by means of a ferromagnetic
roller bar 35 whose axis of rotation 36 along the axial length of
the roller is positioned to extend parallel to the axis of rotation
18 of the pole wheel pair. The roller bar 35 has a smooth outer
peripheral surface and is held by any suitable mechanism (not
illustrated) such that it is in, or can be brought with its outer
surface into and out of frictional abutment on the smooth
peripheral surface 13a of both wheels 12, 14. This basic
architecture can then be employed to effect torque transfer, either
positive for propulsion purposes or negative for object braking
purposes. For example, rotation of roller bar 35 as per arrow 37,
eg by coupling the roller with the output shaft of an electro
motor, will impart counter-orientated rotation to wheels 12, 14 as
per arrow 38 which in turn will then either allow the entire unit
10 to move in translatory manner over a stationarily held substrate
24 as per arrows 39, or where the unit 10 is otherwise secured
against movement, impart movement onto an otherwise unsecured
substrate 24 as per arrows 40 in a direction opposite to 39.
[0095] In using an appropriately dimensioned ferromagnetic roller
bar 35, it is possible to `utilise` part of the magnetic energy
provided by the magnetic flux source 16 of unit 10 to maintain
roller 35 in frictional and magnetic contact with wheel members
12,14 whilst the majority of the available magnetic flux is
utilised to secure the unit 10 onto substrate 24. It will then also
be appreciated that where the magnetic flux source 16 is a
switchable permanent magnet device or an electromagnet, variable
torque transfer may be effected, dependent on the amount of flux
transferred into roller 35 (and substrate) through wheel pole
members 12, 14, and the friction coefficient that then will be
present between the abutting surfaces of wheels 12, 14 and roller
35. The architecture illustrated in FIG. 2a provides for an
inherent torque slippage functionality which can reduce torque
transfer between unit 10 and substrate 24 in conditions that may
otherwise lead to an overload.
[0096] A more specific application field for magnetic wheel units
include roller conveyor systems in various forms like overhead
sheet metal conveyors, one of which is schematically illustrated in
FIG. 3a. A plurality of 2-wheeled magnetic wheel units 100a to 100g
embodying the concept described with reference to FIG. 2a (but with
a different torque transmission architecture) are suspended from a
ceiling rail 150 in predetermined distance from one another along
the extension or travel path defined by rail 150. Each unit 100a to
100g includes one pair of pole wheels accommodated within a
suitable gondola-like housing in which is received a switchable
magnet that provides magnetic flux to the respective wheel-pairs. A
suitable motor is used to impart selective rotation to the pole
wheels of the units. A steel plate 140 can be conveyed along travel
path A held magnetically attached successively at units 100a to
100g. Alternatively, units 100a to g could be 4-wheeled units as
illustrated in FIG. 2b or 2c, in which case one wheel pair would be
driven and one pair could be magnetic idle pole wheels. In yet a
further alternative, guide rail 150 could be replaced with a chain
belt or similar conveyor line on which the units 100a to 100g can
be secured; the units 100a to 100g could then all comprise idle
pole wheels, given that locomotion is provided by the chain drive
itself.
[0097] FIG. 3b illustrates an application wherein a 4-wheel
magnetic wheel unit 200 embodying the concept illustrated in FIG.
2c serves as a magnetic vice for releasably securing a tubular
ferromagnetic work piece 224 whose outer surface is to be powder
coated by atomiser apparatus 260. The pole wheels 212, 214, 212'
(and the counterpart not illustrated fourth wheel member) are
respectively secured for rotation about axle bolts 213 and 213'
mounted at and within a box-like support body 232. The two magnets
(not shown) respectively associated with the pole wheel pairs 212,
214 (212') are mounted within the support body 232 in such manner
that the magnetic N--S pole axis of each switchable magnet
coincides axially with the axis of rotation b and b' of the
respectively associated pole wheel pairs. Ref numeral 250 serves to
denote a support member by means of which the magnetic vice unit
200 can be secured to a support structure, which itself could be an
articulated arm that would enable the vice unit 200 to be
orientated in space as desired.
[0098] Whilst it is feasible to incorporate a motor unit in order
to drive one or more of the pole wheels of unit 200, the
illustrated embodiment simply serves to magnetically hold work
piece 240 securely in space whilst allowing rotation thereof as
indicated by arrow 252 about its longitudinal axis.
[0099] This same device 200 could be used to magnetically clamp two
tubular pipe sections in end to end abutting relationship, thereby
enabling other operations to be carried out, such as butt welding
of the pipe sections.
[0100] FIG. 3c illustrates in schematic perspective view a self
propelled prototype of a Magnetic Trolley (vehicle) 300, which
essentially consists of two identical, independently manually
switchable permanent magnet units 316 generally of the basic type
described in U.S. Pat. No. 7,012,495, two cup-shaped pole wheel
pairs 312, 314 respectively associated with the magnetic flux
sources 316, a prime mover in form of an electric motor 320, a
not-illustrated power supply for the motor, eg battery pack, a
drive train arrangement 318 for transferring torque from the motor
320 into all four of the pole wheels 312, 314, an on-board vehicle
control system 322 as would be employed in either remote wirelessly
controlled vehicles or on-board computer controlled vehicles, and a
shoe-box-like vehicle body 324 on which all of the aforementioned
components are mounted. The individual pole wheels 312, 314, which
are cylindrically cup shaped as detailed in FIGS. 4a and 4b, are
journaled at respective axle elements 326 fixed to the side walls
of the vehicle body 324. The drive train arrangement 318 includes a
belt and pulley system kinematically coupling all four wheels 312,
314 with a driven gear axle supported at body 324 whose cog wheel
meshes with a helical screw shaft coupled to an output shaft of the
electric motor 320. Reference numerals 328 and 329 serve to denote
lever arms utilised for switching of the magnets 316 between their
respective activated states, in which a strong external magnetic
field is emitted and present, and a deactivated state, in which the
magnets 316 are `turned-off and no external magnet field is
present.
[0101] As may be best appreciated with reference to FIGS. 4a to 4c,
which show a simplified isometric representation of an individual
magnetic source unit 316 with its associated pole wheel pair 312,
314, and top and front plan views along arrows IVb and IVc in FIG.
4a, the magnetic flux source units 316, which are respectively
secured within the vehicle body 324 in a fixed location between
each associated pole wheel pair 312, 314, are located such that the
N--S magnetic axis of each magnet unit 316 (in the activated state)
extends coaxially with the wheel axles 318. Each unit 316 extends
with its two respective axial ends into the cylindrical void 328
defined within the annular rim flange 330 of the wheels 312, 314
and to be in facing relationship with the terminal disc web 332 of
the wheels 312, 314. A very small air gap 334 is maintained between
the two stationary pole extension pieces 336, 338 that form the
housing of the unit 316 in which is received the two diametrically
polarised permanent magnet cylinders 340, 342 that provide the
active, but switchable, permanent magnetic flux source of the unit
316 (compare above and U.S. Pat. No. 7,012,495).
[0102] A prototype vehicle according to FIG. 3c (using the unit of
FIG. 4a) was constructed, using four cup-shaped pole wheels having
an outer diameter of 90 mm, a rim wall thickness of 25 mm, a disc
web thickness of 25 mm (thereby defining a flux transfer
cross-sectional area of 1375 mm2, see FIG. 4a, at 344) and made of
soft-steel having a magnetic flux saturation limit of about 2
Tesla. The peripheral surface of the cups was uncoated and machined
to a smooth finish as viewed by the naked eye.
[0103] The magnetic flux source units comprise each a switchable
permanent magnet unit of type M5040 sourced from Magswitch
Technology Worldwide and capable of delivering (in unloaded circuit
conditions) 1.2 Tesla at the relevant passive stationary pole
surface employed in flux transfer, wherein the magnetic flux area
of the active magnetic material (ie the two cylindrical, stacked
magnets) totals 2000 mm.sup.2 (see FIG. 4a at 346).
[0104] The choice of (available) magnetic flux source, ie M5040
magnets, which given the shape of the magnetic field generated in
the `turned-on` state are similar to wide pole magnets with
non-uniform magnetic field distribution, influences also their
spatial arrangement with respect to the cup-shaped wheels as well
as the dimension (in axial direction of the wheel members) which
the rim wall of the wheel should have in order to achieve an
optimised flux transfer and magnetic field force generated
attraction force. Because the wheel pole members constitute a load
with respect to available magnetic force, the depth of the rim
portion is chosen such that it covers (surrounds) the M5040 magnet
up to a location where the magnetic field intensity measured along
a line running perpendicular to the N--S-pole diameter separation
line is about 0.7 of the maximum field value, see FIG. 4c, which is
about 12.5 mm in the chosen configuration.
[0105] The total weight of the vehicle including all drive train
and control components, vehicle body and a welding appliance
mounted thereon was recorded at around 12 kg (a single magnetic
wheel unit consisting of magnetic flux source 316 and cup wheel
poles 312, 314 weighs about 3 Kg).
[0106] Load carrying experiments conducted with vehicle 300
demonstrated that the breakaway force required to vertically
lift-off the vehicle whilst in magnetic attachment on a horizontal
clean steel sheet amounts to around 2400N, and the vehicle was able
to generate a traction force of around 400N on a clean steel sheet
substrate.
[0107] Flux transfer efficiency between the active magnetic
material of the switchable flux units 316 and the substrate was
determined to be about 50%.
[0108] Experiments have been conducted which suggest that the
four-wheeled self-propelled trolley as described is capable of
safely transporting an additional payload equal its own weight
along a vertically inclined steel sheet.
[0109] It will then be appreciated that such trolleys may be used
to mount all kind of instruments and appliances that can be safely
conveyed along inclined, vertical and even overhanging
ferromagnetic surfaces, or may be incorporated into other
structures that require safe attachment to a ferromagnetic
structure in displaceable manner.
[0110] For example, switchable magnetic wheel units as illustrated
can be incorporated in all types of working platforms that are
suspended from above to carry out maintenance and other work on
vertically inclined ferromagnetic surfaces, eg a ship's hull,
thereby providing a means of safely magnetically attaching the
platform to the ship hull without inhibiting up and downward
movement of the platform.
[0111] Turning lastly to FIG. 5, it illustrates schematically a
magnetic wheel climb-crawler 500 incorporating a magnetic wheel
unit 510 of similar type to the one illustrated and described with
reference to FIGS. 4a to 4c, with similar dimensions as referred to
above, which additionally incorporates a motion arresting frame 520
which can be selectively swivelled in and out of engagement with
the substrate on which the unit 510 is attached for travel. The
frame 520 is a substantially u-- or bracket having two parallel
arms 522 and 524 incorporating a bent 525 along their length and a
traverse handle arm 526 at an opposite end to the free terminal
ends 521 and 523 of the arms 522, 524.
[0112] The frame 520 is mounted for rotation about but otherwise
secured to the common axle 528 of both pole wheels 512, 514 such
that the frame's two parallel lever arms can be rotated to come
with their respective terminal ends 512 and 523 into forced
engagement with the substrate surface 530 on which the pole
extension wheels 512, 514 are magnetically attached.
[0113] The lever arm geometries, in particular the ratio of length
L2 between the free ends of arms 522 and 524 and the pivot point at
528 and the length L1 between pivot point at 528 and the traverse
bar section 529, where force 532 may be exerted in order to rotate
the frame 520, will determine the leverage between the force 533
that can be applied at the contact point of the free ends of arms
522, 524 with the substrate and the reaction force 534 which is
provided by the magnetic attraction force exerted between wheels
512, 514 and substrate.
[0114] The principle of the device 500 can be employed in devices
intended for climbing a vertical ferromagnetic wall, where backward
slippage due to low friction coefficients between wheels and
substrate is insufficient to secure positive traction forces. It
will be appreciated that the arresting device may also be used to
counter forward slipping, as the relevant motion pattern of the
unit and the location of ground engagement of the arresting device
ahead or behind the pole wheels will dictate the functionality of
the arresting device.
* * * * *