U.S. patent application number 09/780517 was filed with the patent office on 2002-01-24 for inductively powered lamp unit.
This patent application is currently assigned to Auckland UniServices Limited. Invention is credited to Boys, John Talbot, Green, Andrew William.
Application Number | 20020008973 09/780517 |
Document ID | / |
Family ID | 26651365 |
Filed Date | 2002-01-24 |
United States Patent
Application |
20020008973 |
Kind Code |
A1 |
Boys, John Talbot ; et
al. |
January 24, 2002 |
Inductively powered lamp unit
Abstract
An inductively powered lamp unit 806 is fixed onto a substrate
and over a position where a primary inductive loop 803 is spread
apart (as at 807). At such sites, a horizontal (or at least
parallel to the surface of the substrate) component of alternating
magnetic flux is available. The conductors of the loop 802-803 can
be inserted in a slit 804 cut into the substrate. The spreading
apart of the conductors may be ensured with a spreader 808. A power
supply 801 may be a resonant supply operating at 40 kHz. The lamp
unit 806 does use a resonant pickup coil which can be shorted so as
to minimize coupling, and provide supply regulation. The lamp unit
can be controlled by signals transmitted over the primary loop.
Applications include roadway markers and fire escape egress
indicators, and underwater lighting.
Inventors: |
Boys, John Talbot;
(Auckland, NZ) ; Green, Andrew William; (Auckland,
NZ) |
Correspondence
Address: |
YOUNG & THOMPSON
745 SOUTH 23RD STREET 2ND FLOOR
ARLINGTON
VA
22202
|
Assignee: |
Auckland UniServices
Limited
Auckland
NZ
|
Family ID: |
26651365 |
Appl. No.: |
09/780517 |
Filed: |
February 12, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09780517 |
Feb 12, 2001 |
|
|
|
08793303 |
Mar 12, 1997 |
|
|
|
08793303 |
Mar 12, 1997 |
|
|
|
PCT/NZ95/00061 |
Jul 11, 1995 |
|
|
|
Current U.S.
Class: |
362/307 |
Current CPC
Class: |
F21W 2111/06 20130101;
H05B 39/00 20130101; H05B 47/185 20200101; H02J 50/40 20160201;
F21W 2131/401 20130101; H05B 45/38 20200101; E01F 9/559 20160201;
F21S 8/032 20130101; F21V 23/02 20130101; F21W 2111/02 20130101;
F21Y 2115/10 20160801; H02J 50/12 20160201; F21S 4/28 20160101 |
Class at
Publication: |
362/307 |
International
Class: |
F21V 007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 13, 1994 |
NZ |
264000 |
Claims
What is claimed is:
1. A method of supplying electricity to a discrete lamp unit,
comprising the steps of: forming a hole in stationary material;
positioning in the hole wiring capable of generating an alternating
inductive magnetic field outside the hole when an alternating
electrical current is passed through the wiring; covering the
wiring in the hole; and positioning remote from the wiring the
discrete lamp unit which is adapted to provide illumination when
energized inductively with an induced alternating electrical
current generated by the inductive magnetic field.
2. The method as claimed in claim 1, including the steps of forming
the hole as an elongate groove, positioning the wiring inside the
groove so that, in use, the alternating inductive magnetic field is
elongate and extends outside the groove.
3. The method as claimed in claim 2, including the steps of
positioning outside the groove a row of said discrete lamp
units.
4. The method as claimed in claim 3, including the step of forming
the groove along a track selected from the group consisting of a
road, a pathway, an aircraft runway, a quay, a corridor, a
pedestrian crossing, a swimming pool wall and a swimming pool
floor.
5. A loosely coupled inductively powered lamp unit comprising: a
housing having at least one window for transmitting light; one or
more lamps for radiating light; collection means for collecting
loosely coupled inductively transferred power from an alternating
primary magnetic field external of the housing and operating at
least one selected frequency, said collection means comprising a
resonant circuit within the housing having a resonant period
corresponding to a selected frequency and including at least one
inductance and at least one capacitance, wherein the one or more
lamps are light emitting diodes and the at least one inductance has
a winding adapted to be intersected by a portion of the alternating
magnetic field and thereby collect power as a secondary current;
means for limiting the maximum amount of secondary current
circulating in the resonant circuit; means for transferring power
at an output from the resonant circuit to the one or more lamps;
and means for controlling the power provided to the one or more
lamps.
6. The loosely coupled inductively powered lamp unit as claimed in
claim 5, wherein the one or more lamps consist of a plurality of
light emitting diodes in series.
7. The loosely coupled inductively powered lamp unit as claimed in
claim 6, wherein the means for limiting the amount of secondary
current circulating in the resonant circuit comprises a shorting
switch for closing a connection across the inductance, the shorting
switch being controlled by a controller provided with means for
sensing the magnitude of the output so that when the output exceeds
a first, higher, predetermined threshold the shorting switch is
closed for a period exceeding the resonant period of the circuit,
or when the output falls below a second, lower, predetermined
threshold the shorting switch is opened, thereby limiting the
secondary current flowing in the resonant circuit so that any
magnetic flux generated by the secondary current does not have a
significant counteracting effect on the primary field and so that
the output of the resonant circuit is not able to exceed a
predetermined maximum and so that the amount of light radiated from
the inductively powered lamp unit is, above a lower limit of
efficiency, substantially independent of the coupling efficiency
between the external magnetic field and the resonant circuit.
8. The loosely coupled inductively powered lamp unit as claimed in
claim 7, wherein the means for sensing the magnitude of the output
is configured so as to sense an output current.
9. The loosely coupled inductively powered lamp unit as claimed in
claim 7, wherein the one or more lamps are laser diodes.
10. The loosely coupled inductively powered lamp unit as claimed in
claim 7, wherein the resonant inductance comprises one or more
coils, each coil being wrapped around an elongated member composed
of a ferromagnetic material having a midpoint, which member is
orientated when the lamp unit is placed in position so as to lie
with its midpoint substantially adjacent to a primary conductor
capable when energized of radiating a primary field, and
substantially at right angles to the direction of the primary
conductor.
11. The loosely coupled inductively powered lamp unit as claimed in
claim 7, wherein the lamp unit is a sealed housing adapted to be
mounted upon a surface of a substrate and has a low profile.
12. The loosely coupled inductively powered lamp unit as claimed in
claim 6, wherein the means for limiting the amount of secondary
current circulating in the resonant circuit comprises a shorting
switch for closing a connection across the inductance; the shorting
switch being controlled by a controller provided with means for
sensing the magnitude of the output in comparison to a reference
voltage and for sensing the phase of the secondary current, and for
closing the shorting switch for a part of each cycle of the
secondary current in proportion to the difference between the
output and the reference voltage, so that in use the magnitude of
the output is held at a substantially constant level, and also so
that the secondary current flowing in the resonant circuit is
controlled and does not have a significant counteracting effect on
the primary field, so that the output of the resonant circuit is
not able to exceed a predetermined maximum, and so that the amount
of light radiated from the inductively powered lamp unit is, above
a lower limit of coupling efficiency, substantially independent of
the coupling efficiency between the external magnetic field and the
resonant circuit.
13. The loosely coupled lighting installation comprising one or
more inductively powered lamp units as claimed in claim 7, each
affixed to a surface of a substrate, each lamp unit for emitting
light on being energized by inductive transfer of power across a
space from a primary conductor located on or beneath the surface of
the substrate; the primary conductor for carrying an alternating
current.
14. The loosely coupled lighting installation as claimed in claim
13, wherein in use the primary conductor radiates an external
alternating magnetic field which is predominantly parallel to the
surface of the substrate, at a frequency which is substantially the
same as the selected resonant period of the resonant circuit in at
least one of the lamp units; the frequency lying in the range of
between 200 Hz and 2 Mhz.
15. The loosely coupled lighting installation as claimed in claim
14, wherein the primary conductor radiates an external alternating
magnetic field at a frequency selected from a frequency range
between 10 kHz and 80 kHz.
16. The loosely coupled lighting installation as claimed in claim
15, wherein the light produced by the or each lamp unit is capable
of being controlled by control signals superimposed from time to
time on the alternating magnetic field radiated by the primary
conductor.
17. A loosely coupled, self-illuminated cat's eye, roadway marking
system, comprising: a power supply for producing an alternating
current at at least one selected frequency; an inductive power
distribution cable connected to the power supply and placed along
or beneath an area of a roadway to be marked; and at least one road
warning lamp unit located above or close to said power distribution
cable, each lamp unit comprising, a housing having at least one
window for transmitting light, one or more light emitting diodes
for radiating light, and collection means to collect loosely
coupled inductively transferred power from an external alternating
primary magnetic field from the inductive power distribution cable
operating at the at least one selected frequency, said collection
means comprising a resonant circuit within the housing having a
resonant period corresponding to a selected frequency and including
at least one inductance and at least one capacitance, the at least
one inductance having a winding adapted to be intersected by a
portion of the alternating magnetic field and thereby being for
collecting power as a secondary current, means for limiting the
maximum amount of secondary current circulating in the resonant
circuit, means for transferring power at an output from the
resonant circuit to the lamp or lamps, and means for controlling
the power provided to the lamp or lamps.
18. The loosely coupled roadway marking system as claimed in claim
17, wherein the inductive power distribution cable is a loop with
both conductors positioned one above the other in a substantially
vertical slit in the roadway.
19. The loosely coupled roadway marking system as claimed in claim
18, wherein the cable is spread apart at selected locations where
lamp units are to be located.
20. The loosely coupled roadway marking system as claimed in claim
19, wherein the power supply is capable of being controlled by
control signals superimposed from time to time on the alternating
magnetic field radiated by the primary conductor, and the at least
one road warning lamp unit is capable of detecting said control
signals and varying its light output in response thereto.
Description
RELATED APPLICATION
[0001] This application is a continuation of co-pending Application
Ser. No. 08/793,303, filed on Mar. 12, 1997. Application Ser. No.
08/793,303 is the national phase of PCT International Application
No. PCT/NZ95/00061 filed on Jul. 11, 1995 under 35 U.S.C. .sctn.
371. The entire contents of each of the above-identified
applications are hereby incorporated by reference.
TECHNICAL FIELD OF THE INVENTION
[0002] This invention relates to the field of electrically driven
lighting, to means for driving one or more lamps using inductive
power transfer, and more particularly but not exclusively to the
provision of emergency lights, indicating lights, and roadway
signal lighting powered from adjacent concealed cables.
BACKGROUND
[0003] Transmission of electrical power to articles which consume
power over significant gaps by means of inductive power transfer
has become increasingly feasible with developments in resonant
primary and resonant secondary conductors, means to control and
limit the resonant secondaries, and suitable energising power
supplies.
[0004] There are a number of applications where even a fixed source
of light is advantageously driven by an inductively powered source,
rather than by simple direct connections using conductive
materials.
[0005] In most of the situations below, some of which are
particularly adverse for conventional lighting, a particularly
reliable lighting source is an advantage and in most of these
situations the nature of inductive powering of lights will
inherently enhance the reliability of a system over that using
alternative power supplies such as direct connections, internal
batteries, or solar cells with rechartable batteries. Some
situations include: where electrical isolation is necessary, as in
lights used in or near water such as in swimming pools or areas
where people work in contact with water,
[0006] where corrosive or conductive fluids are likely to
occur,
[0007] where sparks may cause explosions, as in coal mines and in
operating theatres or in certain other industrial sites where
flammable powders, gases, or the like are found,
[0008] where the added robustness of buried cables assists in
maintaining power transfer during exceptional circumstances,
[0009] where a surface on which lights are laid is prone to be
replaced, such as on a roadway with a tar sealed surface.
[0010] In our U.S. Pat. No. 5,293,328 we describe an inductive
power transfer system having particular application to a
multiplicity of vehicles.
OBJECT
[0011] It is an object of the present invention to provide an
improved system for the inductive transfer of electrical energy to
a source of light or one which will at least provide the public
with a useful choice.
STATEMENT OF THE INVENTION
[0012] In one aspect the invention provides an inductively powered
lamp unit; the lamp unit including one or more lamps capable of
radiating light and comprising means to
[0013] collect inductively transferred power from an external
alternating primary magnetic field; said collection means
comprising a resonant circuit having a resonant period and
including at least one inductance and at least one capacitance;
wherein the at least one inductance has a winding adapted to be
intersected by a portion of the alternating magnetic field and
thereby collect power as a secondary current, means capable of
limiting the maximum amount of secondary current circulating in the
resonant circuit, means to transfer power at an output from the
resonant circuit to the lamp or lamps,
[0014] and means to control the power provided to the lamp or
lamps.
[0015] Preferably the means capable of limiting the amount of
secondary current circulating in the resonant circuit comprises a
shorting switch capable of closing a connection across the
inductance; the shorting switch being controlled by a controller
provided with means capable of sensing the magnitude of the output
so that when the output exceeds a first, higher, predetermined
threshold the shorting switch is closed for a period exceeding the
resonant period of the circuit, or when the output falls below a
second, lower, predetermined threshold the shorting switch is
opened;
[0016] thereby limiting the secondary current flowing in the
resonant circuit so that any magnetic flux generated by the
secondary current does not have a significant counteracting effect
on the primary field and so that the output of the resonant circuit
is not able to exceed a predetermined maximum.
[0017] Preferably the means capable of sensing the magnitude of the
output is configured so as to sense an output current.
[0018] Alternatively the means capable of sensing the magnitude of
the output is configured so as to sense a relative or absolute
output light intensity.
[0019] Preferably the resonant inductance comprises one or more
coils, each coil being wrapped around an elongated member composed
of a ferromagnetic material having a midpoint, which member is
orientated when the lamp unit is placed in position so as to lie
with its midpoint substantially adjacent to a primary conductor
(capable when energised of radiating a primary field), and
substantially at right angles to the direction of the primary
conductor.
[0020] Preferably the lamp unit has a low profile and at least one
window capable of transmitting light; the unit being capable of
being attached to the surface of a roadway; and wherein the lamp or
lamps comprise one or more light-emitting diodes.
[0021] It is also preferable that the lamp unit is packaged in a
strong housing having a low profile and at least one window capable
of transmitting light; the unit being capable of being attached
onto the surface of a roadway, capable of withstanding loads
applied by a road vehicle driving over it, and not capable of
adversely affecting the integrity of the road vehicle nor
deflecting the road vehicle from its course.
[0022] Preferably the lamp unit also includes at least one
retroreflector unit for passively reflecting the light of vehicle
beams.
[0023] In another aspect the invention provides a lighting
installation comprising one or more inductively powered lamp units
as described above, each affixed to a surface of a substrate, each
lamp unit being capable of emitting light on being energised by
inductive transfer of power across a space from a primary conductor
located beneath the surface of the substrate; the primary conductor
carrying, when in use, an alternating current.
[0024] Preferably the primary conductor radiates an external
alternating magnetic field, at a frequency which is substantially
the same as the resonant circuit in at least one of the lamp units;
the frequency lying in the range of between 200 Hz and 2 MHz.
[0025] Preferably the primary conductor is laid down within a
substrate in the topology of a loop, connected at a first open end
to a power supply and having a second, closed end, the loop
comprising a pair of closely spaced conductors, though spread apart
in an axis substantially perpendicular to the surface of the
substrate at each site where a lamp unit is to be placed.
[0026] Preferably the one or more inductively powered lamp units
are placed upon the substrate so as to guide a moving person
(whether on foot or steering a vehicle) to pass along a particular
route.
[0027] Preferably one or more lamp units may be selectively
addressed using the primary conductor as a medium, so that the
light radiated therefrom may be changed from time to time.
[0028] Preferably selective addressing is accomplished by
superimposing a message over the primary current, in the form of
momentary variations of the amplitude of the primary current.
[0029] Preferably selective addressing is accomplished by
superimposing a message over the primary current, in the form of
momentary variations of the phase of the primary current.
[0030] Preferably selective addressing is accomplished by
superimposing a message over the primary current, in the form of
information carried within a carrier frequency, separate from the
frequency of the power for inductive transfer.
[0031] Preferably selective addressing is accomplished by setting
the frequency of the primary current so as to match the resonant
frequency of the resonant circuit of the addressed one or more lamp
units which, for this purpose, may each be provided with one of a
variety of resonant frequencies.
[0032] In another aspect the invention provides an installation for
laying out marking lights on a road, comprising a set of
inductively powered roadway markers, a primary energising loop
cable, and a power supply.
[0033] Preferably the power supply is capable of energising the
primary energising loop in response to an external triggering
event.
[0034] Preferably the power supply is capable of remotely
controlling one or more lamp units by means of the primary
energising loop.
[0035] Preferably the power supply is capable of remotely
controlling one or more lamp units by means of the primary
energising loop in response to an external triggering event.
[0036] In another aspect the invention provides an installation for
laying out marking lights along a fire escape route or egress route
in relation to a building, comprising a set of inductively powered
lamp units, a primary energising loop cable capable of being buried
within a substrate of the building, and a power supply having a
battery backup; the installation being capable of being activated
during an emergency.
[0037] Preferably the primary alternating current is a sine
wave.
[0038] Preferably it has a frequency in the range of from 500 Hz to
1 MHz, although more preferably it has a frequency in the range of
from about 10 KHz to about 50 KHz.
[0039] Preferably the alternating current is generated within a
resonant power converter.
[0040] Preferably the concealed primary cable is electrically
insulated and mechanically protected by being embedded within the
substrate. Optionally it may be sealed into a slit cut into the
substrate with a circular saw or the like.
[0041] Preferably the concealed cable comprises a pair of
conductors orientated substantially perpendicular to the surface of
the substrate, although optionally a pair of conductors may lie
side by side within parallel slits. Preferably the cable is
composed of a litz wire or other wire having a high
surface-to-volume ratio such as a strip.
[0042] In another aspect the invention provides a lamp unit within
a strong housing, comprising a resonant secondary or pickup coil
and capacitor, one or more light-emitting lamps, and optionally
power conditioning means.
[0043] Optionally the lamp unit has a low profile and may be
applied to a road surface.
[0044] Optionally the lamp unit also contains one or more
retro-reflector modules.
[0045] Preferably the power conditioning means comprises a current
limit and optionally this may be built into light-emitting diodes
or be an intrinsic property of metallic filament lamps.
[0046] In the case of light-emitting diodes, a pair of lamps or of
banks of lamps may be connected in inverse parallel in order to
utilise both half-cycles of an AC waveform.
[0047] In a further aspect the invention may provide a
road-markings set of lamps comprising a series of lamp units, an
embedded cable, and a power supply.
[0048] Optionally this invention may be used to highlight dangerous
portions of a highway. Optionally it may be energised by the
proximity of a vehicle.
[0049] In a related aspect the invention provides a pedestrian
crossing, comprising means to detect the presence of a waiting
pedestrian, sets of road markings, and a sequencer to energise the
road markings lamps for a period of time before signalling to the
pedestrian that a warning has been given.
[0050] In a yet further aspect the invention may provide a fire
escape indication set of lamps.
[0051] Preferably the power supply for the invention is driven from
a set of storage batteries so that it can operate in the at least
temporary absence of a mains supply.
DRAWINGS
[0052] The following is a description of a preferred form of the
invention, given by way of example only, with reference to the
accompanying diagrams.
[0053] FIG. 1: is an illustration of a section through a light
housing above a pair of primary conductors embedded in a
substrate.
[0054] FIG. 2: is a perspective view of a row of lights energised
inductively by alternating current in a concealed cable.
[0055] FIG. 3: illustrates energisation using a cable carried
within a single vertical slit.
[0056] FIG. 4: shows a typical circuit for use in a light housing
of the present invention.
[0057] FIG. 5: shows a preferred circuit including control of the
resonant pickup circuit.
[0058] FIG. 6: shows a preferred circuit like FIG. 5, also
including means for detecting and responding to control
impulses.
[0059] FIG. 7: shows the interior of a roadway marker incorporating
a pair of ferrite strips as pickup devices to collect inductive
power.
[0060] FIG. 8: shows the disposition of the primary inductive loop
in an installation.
[0061] FIG. 9: shows the flux about the primary conductors,
entering the ferrite mainly at its ends.
[0062] FIG. 10: shows options for controlling the output of
individual lamp units by way of currents within the primary
conductor.
PREFERRED EMBODIMENTS
[0063] One application of this invention is for `self-illuminated
"cats-eye style" roadway reflectors`. This specification describes
an installation for laying out a series of marking or warning
lights (which may also include retro-reflectors) along a generally
linear course, and particular applications for these lights include
roadway lighting. Here they may be substituted for the well-known
"cats-eye" retro-reflectors which are placed upon the road and
being of low profile, may be driven over. Many applications beyond
the known range of uses for "cats-eye" reflectors become available
for a system of self-powered units.
[0064] In relation to another application; fire egress lighting,
the type of energisation used in this invention offers advantages
over conventional lighting in that the invention is more resistant
to fire damage than other types of emergency guidance and therefore
will persist for a longer time.
[0065] We shall describe a basic type of light unit and cabling,
(Example 1) and a more advanced type of light unit (Example 2) as
reduced to practice, but it should be realised that these examples
are in no way limiting and that further examples, exploiting the
characteristic features of the invention, may become obvious to the
skilled reader.
[0066] In principle, we feed alternating current at preferably
about 36-40 KHz and at a sufficient current (typically 10-12 A)
into a cable buried within the substrate of the road or building or
the like, and provide radiated magnetic flux from the cable at
discrete sites for use in energising lamp units adapted for using
inductive power transfer. Although it is convenient and effective
to use resonating current and a resonant power supply to power the
primary inductive loop (the cable) power of similar characteristics
could be generated in other ways.
[0067] Principles of resonant pickup of inductive power do apply
for effective operation of the lamp units and the Examples
illustrate this.
EXAMPLE 1
[0068] Our most basic system comprises:
[0069] (a) A power supply 200, generating a sine-wave output of a
desired power level at usually around 40 KHz into a (mainly
inductive) resonating cable 201, and in the applications described
herein here at a power level of perhaps up to 100-200 watts
although much higher levels can be generated.
[0070] (b) A cable 201 of up to 800-1000 m length having
closed-loop topology which is placed alongside the intended
position of a or each lamp unit 203, 204. We prefer to use litz
wire in installations where efficiency and long-term reliability at
high loading levels is important, although for cheapness ordinary
insulated copper (or aluminium) cables can be used.
[0071] (c) One or more lamp units 203, 204, 100, laid out in a
series like a chain, each of which units comprises a pickup coil
preferably resonant at the power supply frequency, one or more
lamps, and preferably power conditioning means. We generally prefer
light-emitting diodes as they are reliable.
[0072] The cable can be laid out as a single U-shaped loop or can
be run out along several branches, though preferably as a single
length without joins. A particular application may require tuning,
as only one length has the correct resonant frequency and for this
purpose the installer can either vary the resonating capacitors
within the power supply or add toroids (including air gaps) over
the cable to artificially increase its inductance and thereby
simulate a longer cable than is actually present. We prefer to run
the cable at a low power and at a low voltage, for safety's
sake.
[0073] As there are no exposed metallic conductors in an
inductively powered lighting system, it may be used for long
periods in a corrosive atmosphere or one where seawater is present.
The relative absence of risk of sparks allows its use in
inflammable or explosive situations.
[0074] FIG. 1 illustrates the road warning lamp 100 of Example 3 in
place on a road surface 102. In this drawing we have shown the
energising cables 109 in a parallel pair of slits 108, although
roading engineers prefer a single slit as 302 in FIG. 3. The lamp
100 comprises a tough housing 101, having a clear or translucent
window in front of an array of lights or preferably light-emitting
diodes 103. These diodes derive their power from a secondary pickup
coil 104 which is made resonant at about the preferred operating
frequency by a capacitor 106, and the lamps are driven through a
rectifier module 107. The slits 108 in the roadway 102 are
preferably filled with a matrix. FIG. 3 illustrates the vertical
wiring alternative, in which the secondary coil 304 is placed above
the slit 302 containing the pair of wires 305. Preferably the slit
is cut deeper at about the intended position of each lamp unit 306,
so that one of the cables 308 may be brought deeper and so increase
the inductive field available at that point. Between lamp units,
the cable 305 has a reduced inductance where its conducting members
are closer together and so an increased length of cable can be
driven with a limited voltage. A further way to enhance the
magnetic flux at a lamp site is to use a ferrite rod or peg as at
205 in FIG. 2. This may limit the freedom of placement of lamp
units. Ferrite may be incorporated within lamp units, as suggested
by the core of the inductor 401. At least one conductor may,
instead of being litz wire, be a flat strip of metal, as this will
raise the amount of surface available for carrying skin-effect
currents.
[0075] FIG. 4 shows one preferred circuit, in which 401 and 402
comprise a resonant circuit, 403 is a rectifier to make a DC
voltage, and 405 is a set of LED lamps in series. 404 may be a
shunt regulator acting as a current limiter, or a flasher module.
Preferably, 404 is a repetitively acting shorting switch (see 503
with 501, 502 in FIG. 5). If a current limiter is not used, the
operating current in the lamps may be set to the usual preferred
value of around 20 mA by choosing from a range of lamp units or
placing a lamp unit so as to give a predetermined brightness.
EXAMPLE 2
[0076] This portion of the specification describes a preferred
inductively powered lamp unit. There are two versions, shown as
FIG. 5 (no ability for external control) and FIG. 6 having internal
means for detecting and responding to control impulses. Certain
parts of these two circuits have been discussed in relation to FIG.
4.
[0077] The non-controlled circuit is shown as 500 in FIG. 5. The
resonant pickup coil 401 may actually comprise two coils 704 (as in
FIG. 7) wound around each ferrite strip 703, and if several coils
are used they are placed in series. The capacitor(s) of the
resonant circuit are shown at 402; here 247 nF and including
provision (pads) on the circuit board for adding a small "tuning"
capacitor. The resonant frequency is at about 40 KHz. The bridge
rectifier 403 is made up of four diodes (type BAT83), the output of
which is passed through an inductor 501 (7.5 mH) and through a
steering diode 502 (BAT83) to charge a capacitor 505 (33 FF, 25V ).
Power FET transistor 503 (type IFRD110) is used as a shorting
switch to short out the resonant circuit from time to time, each
time lasting for a number of cycles. Means to control the shorting
switch comprise the operational amplifier/comparator 506 (type
MC33171) which has at its inverting input a zener diode 510 (type
TC9491) as a voltage reference. The comparator compares the zener
voltage with a proportion of the current passed through the output
lamps at resistor 610 (30 ohms) (via a 1K resistor 509) and uses a
diode 507 (type BAT83) in series with a 68K resistor 508 as a
non-inverting feedback loop, for hysteresis. This control circuit
provides a controlled current centered on a design value and
fluctuating to a small extent about that value when the resonant
circuit is alternately shorted, then allowed to charge the
capacitor 505. Typically, there are about 500 shorting events per
second.
[0078] Providing current regulation of this type allows the lamp
unit to emit substantially a controlled amount of light regardless
of its position, within limits. Exact placement is not critical. It
is not uncommon for a marker on a hot, tar-sealed road to be
displaced laterally by tires of heavy vehicles and this regulation
provides some tolerance to displacement after positioning.
[0079] In our preferred circuit two chains (405) of high-intensity
(orange) light-emitting diodes (type HLMT-CL00) are used to radiate
light to one side of the lamp unit. Of course, other colours could
be used.
[0080] Variations to FIG. 5 include (for example) monitoring the
ambient light with a light-dependent resistor, so that the
brightness of the marker is proportional to daylight, or regulating
current in terms of actual light output rather than lamp
current.
[0081] FIG. 6 illustrates one means 600 for rendering the circuit
capable of being externally controlled. As suggested in FIG. 10, it
is possible to superimpose control signals over the resonant power
circulating in the primary loop. This circuit is well-adapted for
control by means of low-frequency tones or dual tones. FIG. 6,
which is a development of FIG. 5 and includes the components of
FIG. 5, also includes means to short-circuit the pickup coil 401
from time to time (typically once per millisecond) and during that
time read the current circulating in the primary loop. This circuit
is tentative because it appears that an application-specific
integrated circuit will be an appropriate implementation.
[0082] Box 602 represents a clock generator producing a pulse of 50
Fsec every 1 msec. (There is no requirement to synchronise all
clocks in all markers in an installation to pulse synchronously).
Its output is passed to (a) an AND gate 606 shared by the
comparator and supplying the gate of the power FET, 503. Its output
also goes to the control input of a sample and hold circuit 603,
which reads the current across a current sense resistor 601
inserted in the source lead of 503. At times when the switch 503 is
closed, the resistor will, after a cycle or two at 40 KHz, or about
50 Fsec, have a voltage on it representing the current in the
primary inductive loop at that time. This voltage is taken to the
signal input of the sample and hold circuit, and the output is
passed to a circuit 604 which comprises a tone detector.
[0083] In this simple example we have provided a resistor 605
between the tone detector output and an input of the comparator, so
that activation of the tone detector has an effect on the setting
of the comparator 506 and the mean brightness of the lamps is
altered as a result of detecting a specific tone carried within the
primary inductive loop. "Stealing time" from the action of the
comparator as for FIG. 5 is of little moment because the inherent
regulation can compensate. Repetitive sampling at a rate of about 1
KHz will satisfy the Nyquist criterion for control signals which
are single or multiple tones of up to about 250 Hz.
[0084] Clearly there are many possible options; such as whether or
not the tone detector outputs switch from one state to another
state on each tone detection, or change state only during a tone,
and there may be more than one tone and hence more than one action,
or the detector output may be treated as a code signal passed to a
microprocessor which will execute one of a series of actions on the
light output from the lamps 405. There may be a red series and a
yellow (or orange, green or blue or even infra-red) series of lamps
which can be driven separately, or separately controllable lamps
may face in various directions.
[0085] Highway Markers
[0086] In FIG. 7, we show a highway marker 700 from above. The
casing 701 encloses a pair of ferrite cores 703 (only one core and
coil is labelled) which are on each side of a printed-circuit board
702 bearing the circuit of FIG. 6 and along one edge a row of
light-emitting diodes 705. We have not also illustrated
retro-reflectors in this diagram, but they may be interspersed with
the diodes 705.
[0087] FIG. 8 shows part of a roadway installation in side view. A
power supply 801 puts power into a loop of cable forming a primary
inductive loop. In the portions where the two conductors are close
together (802) the flux tends to cancel out and the cable radiated
little flux. Hence it may be elongated. At positions (803) where a
lamp unit (804) may be placed, the cable is spread apart,
preferably using a spreader (805) to maintain spacing during and
after installation. The end of the loop remote from the cable is
shown at 806.
[0088] If the power supply is a resonant power supply, and this
type of energisation is economical and, by energising the cable
with a sine wave, minimises problems of radiation of radio or
electromagnetic energy, it is preferable to use litz wire for the
cables. We prefer 4 mm.sup.2 litz wire. Our typical resonant power
supplies are run at 24 volts, which allows for battery backup and
safe running and at 24 volts it can power about a 25 meter long
primary inductive pathway, and about 10-14 amperes at a 40 kHz
frequency circulates in the cable when in operation. Using a higher
voltage allows longer primary inductive loops to be used. If an
unusually short cable is used, its inductance may be boosted with a
lumped inductance, trimmed to make the installation resonate at 40
kHz.
EXAMPLE 3
[0089] Our basic system may be embellished by providing for control
of the output of the lamp units, either as a group or individually.
Preferably this control is more than simply turning the entire set
on or off. One approach is to provide each lamp unit in an
installation with control electronics that can detect signals of
some sort radiated from the primary conductor cable, because this
cable is already functionally connected with all operational
lamps.
[0090] It is possible to superimpose a message over the primary
current, in the form of momentary variations of the amplitude of
the primary current, which can be sensed within the or each lamp
unit as changes in the operational settings of the regulating
mechanism. Coding of the amplitude could follow any convenient
code, such as the letters of the ASCII coding system, or Morse
code, or some other system such as those used in serial bus digital
control, such as the I.sup.2C bus. This requires a small amount of
complexity in each lamp unit that is capable of being addressed.
Each "bit:" of the code would have to be sufficiently long in time
to "catch" any lamp unit that at the time has shorted its inductive
pickup coil, unless a separate data sensing arrangement was used.
Information may be carried within a carrier frequency, separate
from the frequency of the power for inductive transfer.
[0091] Variations of the phase of the primary current are another
way to transmit data.
[0092] A cheap way of addressing lamp units is to make a variety of
units each having a different resonant frequency. Then only those
lamp unit that resonate at the frequency of the transmitted power
can operate. If a resonant power supply is used, it might be
provided with subsidiary switchable resonating capacitors. By this
means it is possible to create a travelling wave of flashing
lights, for decorative or directional purposes.
[0093] Fire Egress Indication Lamps
[0094] This is--as a preferred example--a fire-exit indicating
network, which when energised provides a chain of illuminated
beacons 203, 204 along the floor of a building. The beacons are
intended to direct people to the nearest fire exit. In addition to
the basic system above, we would usually include means to supply
the power from batteries as in an emergency the mains power is
likely to fail, and means to cause the power supply to start up
when an emergency condition, such as a blackout at night, and/or a
fire alarm is in effect. The energising cable 201 is preferably
embedded into a concrete or similar floor, and may be embedded at a
depth of several inches as our inductive power transfer system is a
loosely coupled one that tolerates spacings of that order. The
energising cable is placed along the floors of passageways that
lead to fire exits, preferably along the centre lines of the
passageways. The drive voltage may be as low as 12 volts, depending
on the power required.
[0095] The lamp units are preferably light-emitting diodes or the
like, embedded in wear-resistant transparent or translucent
housings so that they remain capable of emitting visible light even
after years in position. Preferably the lit lamps display a clearly
understood and preferably standardised direction so that people in
panic are not confused. Optionally the lamps or the power supply
may be operated in an attention-getting flashing mode and
optionally the lamp units may also generate audible signals. In
fact, they may also generate vibrations so that blind people can
locate and use the indicators. Our preferred lamp units may have
bases about 10 cm square--containing the resonant pickup coil--with
a height of perhaps 5 mm, and have a top made of a wear-resistant
material such as polycarbonate or even glass. They may include
other electronic devices such as a voltage sensor and a switch to
short-circuit the coil when the voltage rises above a threshold.
(This means of regulation limits the tendency of a resonant
secondary to develop a large circulating current which tends to
block the primary current from reaching past this secondary coil to
reach others. On the other hand, as this application of inductive
power transfer has substantially constant operating parameters, and
it may be preferable to select a lamp unit for a particular
position from a range of units having various
brightnesses--actually flux collection and conversion
capabilities.
[0096] These illuminated display devices may be glued onto a
carpet, or let into holes cut in a carpet, or glued onto a hard
surface, and need no electrical connections. Thus replacement of
damaged or displaced units is not a skilled job. Typical buildings
where the devices may be used include hotels, schools, hospitals,
auditoriums, and other public buildings.
[0097] Advantages of this device include that the system is located
on or in floors where it is unlikely to be damaged until after
surrounding structures have been destroyed, and the floor location
is compatible with people who are keeping low or even forced to
crawl in order to avoid smoke and fumes. (Conventional practices of
placing often illuminated EXIT signs high up above doorways can
lead to obscuration by smoke).
[0098] The device has inherently a high reliability because the
destruction of any lamp unit by flames or the like does not
compromise the remainder--rendering its pickup coil an open circuit
or a short circuit does not substantially affect the primary
current and so the remainder of the lamp units may remain lit.
[0099] Furthermore the lamp units themselves are electrically
isolated, and the energising power supply is preferably provided
with fault detection means so that it provides no electrical
hazards in itself.
[0100] A variant of this device can be used in theatres, hotels,
houses and the like, and would be energised steadily or on pressure
on a sensing pressure pad, to better indicate the positions of
stairs in the dark.
[0101] Roadway-details
[0102] A similar arrangement can be used on roadways to better
indicate lanes routes hazards and other events to motorists. A
particular application is in providing warnings at pedestrian
crossings. In the pedestrian crossing application, the power supply
is connected to a reliable source of AC power and is arranged to be
energised when (for example) a person steps onto a contact pad at
the curbside, or when a conventional button is pushed. The
energising cables are placed along selected patterns and may be
embedded within slits cut with a diamond saw. As our inductive
power transfer system uses only loose coupling, the cables may be
several centimeters deep and even the later addition of further
road surfaces will not affect coupling of power from the cables.
The cables are preferably sealed in place, using a suitable
adhesive or the like so that the installation is substantially
permanent.
[0103] The preferred slit dimensions for slits cut into roadways is
5 mm wide by 10 mm deep, rather than the more idealised parallel
pair of slits shown in FIG. 2. (Roads tend to crack and chip
between parallel, close slits). Therefore we have also made a
modified arrangement in which one of the pair of wires forming the
cable is above the other, as shown in FIG. 3, and optionally in
order to enhance the flux at the position of a lamp we make the
slit deeper at that site and push one conductor further away from
the road surface at that point.
[0104] Preferably the cables are energised from a power supply
operating at 12 or 24 volts, compatible with storage batteries fed
from a wind generator or solar cells, although a higher voltage may
be needed to inject resonant power into a longer run of cable,
particularly if the more efficient litz wire is not available.
[0105] The lamp units may be built into the existing "cats-eye"
housings widely used on roadways to demarcate lanes by means of
retro-reflective inserts. Glues or other means to mount these
devices are well known and the dimensions of existing housings are
adequate for housing the power pickup coils, control electronics,
and lamps. In order to catch drivers' attention we expect that
high-intensity beams from light-emitting diode lamps will be used,
aimed towards oncoming traffic. These lamps may be pulsed in a
synchronised, attention-gathering manner by for example pulsing the
power supply on and off. As the preferred resonant frequency is
high, the decay time for power is small. Forty cycles of 40 KHz
power=1 millisecond. Alternatively the internal regulator within
each housing may be arranged to operate in a cyclic manner,
although this may not give as clear a signal of danger to an
approaching driver.
[0106] In the pedestrian crossing application, a vandal-proof
warning device would preferably comprise (a) a sensing pad for
detecting a waiting pedestrian, a sequencer to first energise the
array of warning lamps for a suitable time, and then means to
energise a "Cross now" or "Walk" signal of some type which may be
(a) conventional illuminated signs, (b) audible, and/or (c) made of
further lamps on the roadway, this time over the crossing itself
and orientated so that they are visible to the pedestrian.
[0107] In cases where the currents in the buried cables are likely
to affect inductive sensors used for controlling automatic traffic
lights, the operating frequency can be selected to be separated
from that used by the traffic light, and the relatively low
harmonic content of the resonant power means that a simple trap
tuned to the fundamental frequency should reject any interference
to the traffic light sensor.
[0108] In case further buried cables are used to provide power to
moving vehicles according to our inductive power transfer
principles, a separation in frequency should minimise any
cross-interference between cables or affecting the pickup coils. It
may well be preferable to adopt a different frequency of perhaps 40
KHz for these low-power lighting devices and run the vehicle power
cables at 10 KHz, whereupon the tuned resonant circuits of the
lighting devices should not develop any significant power when
exposed to magnetic flux at a 10 KHz cycle rate.
[0109] Variations
[0110] In order to arrange for switching of lanes on a roadway, for
example at a bridge where diurnal reversals in the flow of traffic
promote the use of more lanes in one direction than another at one
time, lane switching may be accomplished by linear arrays of
illuminated housings which are laid on the road along predetermined
lines or courses, and illuminated as required in order to steer
cars into lanes.
[0111] These types of lights can also be used to demarcate sharp
corners and the like and enhance areas of poor visibility. Here
they have the advantage over conventional reflectors that by
generating their own light they are effective outside (and
particularly to either side of) the region illuminated by the
headlights of a car. Preferably warning lights intended for
motorists are intermittently energised by the approach of a motor
vehicle, using a pressure pad or a proximity sensing device so that
they can be maintained from a rechargeable storage battery with a
solar cell as a source of power. When in operation, the bands of
light emitted from the arrays of lamp units may extend far beyond
the range of the driver's headlights.
[0112] Underwater Variations
[0113] As inductive power transfer is inherently unaffected by
non-magnetic materials that may appear or disappear in the gap, it
may be used under water. Accordingly a series of housings
containing lamps may be placed on the bottom (and sides, and edges)
of a swimming pool to indicate lanes, and energised as required by
buried cables concealed in the substance of the pool floor. These
lamp units may be fixed in place, and various combinations
energised by selecting particular runs of cable for various
combinations of lamp unit spacing. Alternatively they may be
clipped into retaining clips as and when required. Magnets,
particularly magnets formed from ferrites, may be used to
temporarily locate lamp units. Adjacent, magnetically soft ferrites
may be included to act as flux concentrators.
[0114] Options
[0115] A light housing could be provided with more than one pickup
coil and ancillary light sources, so that by changing the frequency
of the power in the primary cable, different colours of light (for
example) could be produced. Power modulation may also be arranged
to select different lamps. Light emitting diodes are at present
available in red, orange, yellow, green and blue, although the
latter two are not particularly bright. Laser diodes of various
visible colours may soon become cheap enough for use in this
application, where their enhanced beam-forming ability will aid in
the detection of these lights at a distance. Light-emitting diodes
have an advantage in that their ON-voltage can be used to provide a
degree of intrinsic regulation as shown in FIGS. 3 and 4 where even
the rectifier can be deleted if a second string of LEDs with the
opposite polarity is placed across the first string.
[0116] As the light housings will generally be fixed it is possible
to extend the cable length by bringing the wires close together
unless, at the site of a lamp, they are spread apart so that the
magnetic field increases. To further enhance the field, a loop can
be constructed in the primary cable, or a magnetically permeable
coupler such as a ferrite can be used.
[0117] In situations where lateral variations in lighting may
extend beyond the "tram-track" layout of primary coils, one wire
may be placed above the other, providing a more diffuse field. If
this field is weaker, a ferrite flux concentrator may be provided
to increase the power available within the secondary device.
[0118] Movable lights may be mounted on a light track or on a
surface such as a wall, ceiling, or table in such a way that they
can be held in position without requiring direct electrical contact
with the power source. In one example wall mountable lights can be
mounted in one or more plastic channel members attached to the wall
and may be allowed to slide along a channel member to a desired
position whilst picking up inductive power from a primary circuit
embedded in the wall or in the base of the channel member. As the
attachment of the light to the surface does not require any direct
electrical contacts whether sliding or stationary it is possible to
adopt any number of different attachment means for the location or
placement of the lights. The lights may take any desired shape or
design.
[0119] In the case of a photographic studio the lights may have a
base containing the resonant pickup and an arm or stem extending
therefrom which a suitable reflector or light housing is mounted
and containing the light source. In such a case it is preferable to
position the primary resonant circuit (or circuits) in a sinuous
pattern in the wall or ceiling so that the lamp bases can be placed
anywhere on the surface and still receive enough resonant power to
activate its light source. An advantage of placing the primary
cables in a "slit configuration" as previously described is that
the primary cables generate an external alternating magnetic field
which is predominately parallel to the surface of the substrate,
allowing the lamp base to be moved from side to side of the "slit"
containing the pair of cables and still receive enough power for
its light source.
[0120] Advantages
[0121] Inductively powered lamp units in accordance with this
invention have a variety of uses where direct contact between the
power cables and the lamp units is undesirable. Examples of such
uses include lights used in or near water such as in swimming pools
or areas where people work in contact with water, lights used in
corrosive environments or where conductive fluids are likely to
occur, lights used in mines and in operating theatres or in certain
other industrial sites where flammable powders, gases, or the like
are found, and lights used in roadways, or where the lights need to
be moved relative to the power supply (eg in display areas or in
photographic studios).
[0122] Finally, it will be appreciated that various alterations and
modifications may be made to the foregoing without departing from
the scope of this invention as set forth.
* * * * *