U.S. patent application number 10/843687 was filed with the patent office on 2005-06-02 for maritime safety system.
This patent application is currently assigned to Mobilarm Pty Ltd. Invention is credited to Pallister, Mark, Pallister, Vanessa, Ward, David.
Application Number | 20050118905 10/843687 |
Document ID | / |
Family ID | 34553065 |
Filed Date | 2005-06-02 |
United States Patent
Application |
20050118905 |
Kind Code |
A1 |
Pallister, Mark ; et
al. |
June 2, 2005 |
Maritime safety system
Abstract
A maritime safety system comprising at least one transmitter
unit (12, 14, 16, 18), each transmitter unit being arranged to
transmit successive signals by wireless communication at pseudo
random intervals and each transmitter unit (12, 14, 16, 18) having
an associated transmitter range, a base station (10) arranged to
receive said transmitted signals and an alarm device (20). The base
station (10) is arranged to cause the alarm device (20) to generate
an audible and/or visible alarm when a plurality of successive
signals from at least one of the transmitter units (12, 14, 16, 18)
are not detected, and the arrangement is such that when a
transmitter unit (12, 14, 16, 18) is disposed a distance from the
base station (10) which is greater than the transmission range
associated with the transmitter unit and a plurality of successive
signals are not detected, an audible and/or visible alarm is
generated.
Inventors: |
Pallister, Mark; (West
Perth, AU) ; Pallister, Vanessa; (West Perth, AU)
; Ward, David; (Menora, AU) |
Correspondence
Address: |
DAVIS WRIGHT TREMAINE, LLP
2600 CENTURY SQUARE
1501 FOURTH AVENUE
SEATTLE
WA
98101-1688
US
|
Assignee: |
Mobilarm Pty Ltd
West Perth
AU
|
Family ID: |
34553065 |
Appl. No.: |
10/843687 |
Filed: |
May 10, 2004 |
Current U.S.
Class: |
441/80 |
Current CPC
Class: |
B63C 9/0005 20130101;
G08B 21/088 20130101; G08B 21/0269 20130101 |
Class at
Publication: |
441/080 |
International
Class: |
B63C 009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 24, 2003 |
AU |
2003905841 |
Feb 19, 2004 |
AU |
2004900824 |
Claims
The invention claimed is:
1. A maritime safety system comprising: at least one transmitter
unit, each transmitter unit being arranged to transmit successive
signals by wireless communication at pseudo random intervals and
each transmitter unit having an associated transmitter range; a
base station arranged to receive said transmitted signals; and an
alarm device; said base station being arranged to cause the alarm
device to generate an audible and/or visible alarm when a plurality
of successive signals from a transmitter unit are not detected; the
arrangement being such that when a transmitter unit is disposed a
distance from the base station which is greater than the
transmission range associated with the transmitter unit and a
plurality of successive signals are not detected from the
transmitter unit, an audible and/or visible alarm is generated.
2. A maritime safety system as claimed in claim 1, wherein the base
station is arranged to cause the alarm to be generated when three
successive signals are not detected.
3. A maritime safety system as claimed in claim 1, wherein each
transmitter unit is arranged to transmit a signal once every second
at a pseudo random offset within each one second interval.
4. A maritime safety system as claimed in claim 1, wherein each
transmitter unit further comprises a pseudo random number generator
in the form of a linear feedback shift register (LFSR) to determine
the time at which to transmit the signals.
5. A maritime safety system as claimed in claim 4, wherein each
LFSR is seeded with a unique identification code.
6. A maritime safety system as claimed in claim 1, wherein the
transmitted signals are in the form of periodically transmitted
pulses.
7. A maritime safety system as claimed in claim 1, further
comprising a plurality of transmitter units, and wherein the system
is arranged so as to distinguish the transmitter units from each
other by incorporating a unique code into each transmitted
signal.
8. A maritime safety system as claimed in claim 7, wherein the
transmitter units are arranged to transmit signals at substantially
the same frequency and the base station is arranged such that only
signals of a predetermined frequency are detected.
9. A maritime safety system as claimed in claim 1, wherein the
transmitter units are arranged to transmit signals at different
frequencies and the base station is arranged to detect signals at
the different frequencies and to distinguish detected signals on
the basis of frequency.
10. A maritime safety system as claimed in claim 1, wherein the
base station further comprises a display for visibly displaying
information associated with the safety system to a user.
11. A maritime safety system as claimed in claim 10, wherein the
information is indicative of whether the or each transmitter unit
is operating correctly, whether any of the transmitter units
require charging, and/or of the or each relevant identifier
associated with the or each transmitter unit for which a signal has
not been detected for a predetermined period of time.
12. A maritime safety system as claimed in claim 1, wherein the
base station is arranged to interface with positioning means so as
to generate information indicative of the location of the base
station when a plurality of successive signals from at least one of
the transmitter units are not detected for a predetermined period
of time.
13. A maritime safety system as claimed in claim 12, wherein the
positioning means is a GPS-type positioning means arranged to
generate GPS positioning data indicative of the location of the
base station.
14. A maritime safety system as claimed in claim 1, wherein the
base station is arranged to interface with one or more external
devices and to transfer an actuation signal to one or more of the
external devices when a signal from at least one of the transmitter
units is not detected for a predetermined period of time, the
external devices including a further alarm device, a dan buoy
release, a self steering trip, an engine cut-out, a head-to-wind
command to the autopilot, and/or an emergency position indicating
radio beacon (EPIRB) assembly arranged to release an emergency
position indicating radio beacon (EPIRB).
15. A maritime safety system as claimed in claim 1, wherein the or
each transmitter unit includes a status indicating device which may
be in the form of an LED.
16. A maritime safety system as claimed in claim 15, wherein the or
each transmitter unit is arranged so that the LED is caused to
indicate different status conditions depending on the current
status and operation of the transmitter unit.
17. A maritime safety system as claimed in claim 1, wherein the or
each transmitter unit includes a rechargeable battery and a
charging device arranged to facilitate inductive charging of the
rechargeable batteries.
18. A maritime safety system as claimed in claim 1, wherein the or
each transmitter unit is arranged to transmit information
indicative of the current status and/or operation of the
transmitter unit.
19. A base station for a maritime safety system, the base station
being arranged to receive signals transmitted from at least one
transmitter unit by wireless communication, and the base station
being arranged to generate an actuation signal when a plurality of
successive signals from at least one of the transmitter units are
not detected; the arrangement being such that when a transmitter
unit is disposed a distance from the base station which is greater
than a transmission range associated with the transmitter unit, a
plurality of successive signals are not detected and the actuation
signal is generated.
20. A base station as claimed in claim 19, wherein the base station
is arranged to cause the alarm to be generated when three
successive signals are not detected.
21. A base station as claimed in claim 19, further comprising a
display for visibly displaying information associated with the
safety system to a user.
22. A base station as claimed in claim 21, wherein the information
is indicative of whether the or each transmitter unit is operating
correctly, whether any of the transmitter units require charging,
and/or of the or each relevant identifier associated with the or
each transmitter unit for which a signal has not been detected for
a predetermined period of time.
23. A base station as claimed in claim 19, wherein the base station
is arranged to interface with positioning means so as to generate
information indicative of the location of the base station when a
plurality of successive signals from at least one of the
transmitter units are not detected for a predetermined period of
time.
24. A base station as claimed in claim 23, wherein the positioning
means is a GPS-type positioning means arranged to generate GPS
positioning data indicative of the location of the base
station.
25. A base station as claimed in claim 19, wherein the base station
is arranged to interface with one or more external devices and to
transfer an actuation signal to one or more of the external devices
when a signal from at least one of the transmitter units is not
detected for a predetermined period of time, the external devices
including a further alarm device, a dan buoy release, a self
steering trip, an engine cut-out, a head-to-wind command to the
autopilot, and/or an emergency position indicating radio beacon
(EPIRB) assembly arranged to release an emergency position
indicating radio beacon (EPIRB).
26. A transmitter unit for a maritime system, the transmitter unit
being arranged to transmit successive signals by wireless
communication, each signal being transmitted at a pseudo random
offset relative to a predetermined time interval so as to thereby
reduce the likelihood during use of signal transmissions from two
transmitter units occurring simultaneously.
27. A transmitter unit as claimed in claim 26, wherein the
transmitter unit is arranged to transmit a signal once every second
at a pseudo random offset within each one second interval.
28. A transmitter unit as claimed in claim 26, wherein the
transmitter unit further comprises a pseudo random number generator
in the form of a linear feedback shift register (LFSR) to determine
the time at which to transmit the signals.
29. A transmitter unit as claimed in claim 28, wherein the LFSR is
seeded with a unique identification code.
30. A transmitter unit as claimed in claim 26, wherein the
transmitted signals are in the form of periodically transmitted
pulses.
31. A transmitter unit as claimed in claim 26, wherein the
transmitter unit includes a status indicating device which may be
in the form of an LED.
32. A transmitter unit as claimed in claim 31, wherein the
transmitter unit is arranged so that the LED is caused to indicate
different status conditions depending on the current status and
operation of the transmitter unit.
33. A transmitter unit as claimed in claim 26, wherein the
transmitter unit includes a rechargeable battery and a charging
device arranged to facilitate inductive charging of the
rechargeable battery.
34. A transmitter unit as claimed in claim 26, wherein the
transmitter unit is arranged to transmit information indicative of
the current status and/or operation of the transmitter unit.
Description
CROSS REFERENCE TO RELATED APPLICATION(S)
[0001] This application claims priority to Australian Patent
Application No. 20044900824, filed Feb. 19, 2004, and Australian
Patent Application No. 2003905841, filed Oct. 24, 2003.
BACKGROUND OF THE INVENTION
[0002] When a member of the crew of a maritime vessel is lost
overboard, the time elapsed before an alarm is raised is critical.
This is particularly so in cold waters, where the chances of
survival of the crew member diminish rapidly with time. However,
even in warm waters, prompt recognition that the crew member is no
longer on the vessel greatly enhances the chances of locating the
crew member in a safe condition.
[0003] Existing systems for indicating that a crew member has
fallen overboard require the overboard crew member to activate an
alarm carried by the crew member, or another crew member on the
vessel to activate an alarm disposed on the vessel.
[0004] However, both of these arrangements can result in
appreciable delay, for example in a circumstance wherein the crew
member lost overboard is unconscious and therefore incapable of
activating the alarm, or in a circumstance wherein the absence of
the overboard crew member is not immediately noted by another crew
member.
[0005] The preceding discussion of the background to the invention
is intended to facilitate an understanding of the present
invention. However, it should be appreciated that the discussion is
not an acknowledgement or admission that any of the material
referred to was part of the common general knowledge in Australia
as at the priority date of the present application.
[0006] In the following description of the invention, except where
the context requires otherwise due to express language or necessary
implication, the word "comprise" or variations such as "comprises"
or "comprising" is used in an inclusive sense, i.e. to specify the
presence of the stated features but not to preclude the presence or
addition of further features in various embodiments of the
invention.
FIELD OF THE INVENTION
[0007] The present invention relates to a maritime safety system
and, in particular, to a maritime safety system of the type
intended to provide a warning when a member of the crew of a vessel
or an important article associated with the vessel is lost
overboard. The present invention also relates to a base station for
use with the maritime safety system.
BRIEF SUMMARY OF THE INVENTION
[0008] In accordance with a first aspect of the present invention,
there is provided a maritime safety system comprising:
[0009] at least one transmitter unit, each transmitter unit being
arranged to transmit successive signals by wireless communication
at pseudo random intervals and each transmitter unit having an
associated transmitter range;
[0010] a base station arranged to receive said transmitted signals;
and
[0011] an alarm device;
[0012] said base station being arranged to cause the alarm device
to generate an audible and/or visible alarm when a plurality of
successive signals from a transmitter unit are not detected;
[0013] the arrangement being such that when a transmitter unit is
disposed a distance from the base station which is greater than the
transmission range associated with the transmitter unit and a
plurality of successive signals are not detected from the
transmitter unit, an audible and/or visible alarm is generated.
[0014] In this way, an indication is provided to crew members on
the vessel that a crew member has potentially fallen overboard.
[0015] It will also be apparent that since an alarm is generated
when signals from a transmitter unit are not detected, the alarm
may indicate that the transmitter unit is damaged or that charging
of a battery in the transmitter unit is necessary. In this sense,
the system of the present invention is fail-safe in that an alarm
is generated in the event of transmitter unit failure.
[0016] Preferably, the base station is arranged to cause the alarm
to be generated when three successive signals are not detected.
[0017] In one arrangement, the transmitted signals are in the form
of pulses periodically transmitted by the or each transmitter
unit.
[0018] In order to distinguish signals transmitted from the or each
transmitter unit from signals received from other sources, the base
station may be arranged such that only signals of a predetermined
frequency are detected.
[0019] In one embodiment, a plurality of transmitter units are
provided and the system is arranged so as to distinguish the
transmitter units from each other by allocating a unique code to
each transmitter unit and incorporating a unique code into each
transmitted signal.
[0020] In addition, or alternatively, the transmitter units may be
arranged to transmit signals at different frequencies and the base
station may be arranged to detect signals at the different
frequencies and to distinguish detected signals on the basis of
frequency.
[0021] In one embodiment, the base station further comprises a
display for visibly displaying information associated with the
safety system to a user. The information may be indicative of the
status and/or operation of the transmitter units and may include
information indicative of whether the or each transmitter unit is
operating correctly, whether any of the transmitter units require
charging, information indicative of the or each relevant identifier
associated with the or each transmitter unit for which a signal has
not been detected for a predetermined period of time, and so on.
The display may be an LCD display.
[0022] The base station may also be arranged so as to interface
with positioning means useable to determine the location of the
base station. The positioning means may be a GPS-type positioning
means arranged to generate GPS positioning data indicative of the
location of the base station.
[0023] In one arrangement, the base station is arranged to
interface with the positioning means so as to generate information
indicative of the location of the base station when a plurality of
successive signals from at least one of the transmitter units are
not detected for a predetermined period of time.
[0024] The base station may also be arranged to interface with one
or more external devices and to transfer an actuation signal to one
or more of the external devices when a signal from at least one of
the transmitter units is not detected for a predetermined period of
time. The external devices may include a further alarm device, a
dan buoy release, a self steering trip, an engine cut-out or a
head-to-wind command to the autopilot. The external devices may
also include an emergency position indicating radio beacon (EPIRB)
assembly arranged to release an emergency position indicating radio
beacon (EPIRB) when a signal from at least one of the transmitter
units is not detected for a predetermined period of time.
[0025] In one arrangement, the system further includes a data
storage device arranged to cooperate with the base station so as to
store and selectively retrieve important system and transmitter
unit information.
[0026] The or each transmitter unit may include a housing formed of
at least partially transparent material so that any ingress of
water into the housing is readily identifiable by a user, operative
components of the transmitter unit being disposed in the
housing.
[0027] The or each transmitter unit may include means for securing
the transmitter unit to a person. The securing means may include a
tab provided with an aperture for receiving a lanyard or a clip for
attaching to an item of clothing.
[0028] The or each transmitter unit may include a status indicating
device which may be in the form of an LED.
[0029] In one arrangement, the or each transmitter unit is arranged
so that the LED is caused to indicate different status conditions
depending on the current status and operation of the transmitter
unit.
[0030] The or each transmitter unit may include a battery and a
charging device which may be an inductive coupling type charging
device for facilitating charging of the battery by interacting with
an incident changing magnetic field so as to generate an induced
voltage. The charging device may include a coil.
[0031] The or each transmitter unit may be arranged to transmit
information indicative of the current status and/or operation of
the transmitter unit.
[0032] In accordance with a second aspect of the present invention,
there is provided a base station for a maritime safety system, the
base station being arranged to receive signals transmitted from at
least one transmitter unit by wireless communication, and the base
station being arranged to generate an actuation signal when a
plurality of successive signals from at least one of the
transmitter units are not detected;
[0033] the arrangement being such that when a transmitter unit is
disposed a distance from the base station which is greater than a
transmission range associated with the transmitter unit, the
actuation signal is generated.
[0034] In accordance with a third aspect of the present invention,
there is provided a transmitter unit for a maritime system, the
transmitter unit being arranged to transmit successive signals by
wireless communication, each signal being transmitted at a pseudo
random offset relative to a predetermined time interval so as to
thereby reduce the likelihood during use of signal transmissions
from two transmitter units occurring simultaneously.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)
[0035] The present invention will now be described, by way of
example only, with reference to the accompanying drawings, in
which:
[0036] FIG. 1 is a diagrammatic representation of a maritime
security system in accordance with an embodiment of the present
invention with the system shown in a non-activated state;
[0037] FIG. 2 is a block diagram of a base station of the maritime
safety system shown in FIG. 1;
[0038] FIG. 3 is a diagrammatic representation of a transmitter
unit of the maritime safety system shown in FIG. 1; and
[0039] FIG. 4 is a diagrammatic representation of the maritime
safety system shown in FIG. 1 with the system shown in an activated
state.
DETAILED DESCRIPTION OF THE INVENTION
[0040] Referring to the drawings, in FIG. 1 there is shown a
maritime safety system in accordance with an embodiment of the
invention during use. The system comprises a base station 10,
first, second, third and fourth transmitter units 12,14, 16 and 18
respectively, an alarm device 20 and a positioning means, in this
example in the form of a vessel global positioning system (GPS) 22.
In the present example, the safety system also includes an
emergency position indicating radio beacon (EPIRB) assembly 24
having an EPIRB 26 and an EPIRB releasing device 28.
[0041] During use, the base station 10, the alarm device 20, the
vessel positioning means 22 and the EPIRB assembly 24 are disposed
on a maritime vessel 30 and each of the transmitter units 12, 14,
16, 18 is secured to or otherwise carried by a crew member 32 of
the vessel 30. Each of the transmitter units 12,14,16, 18 is of
sufficient power that a signal transmitted by a transmitter unit
12, 14, 16,18 is capable of being received by the base station 10
provided that the transmitter unit 12, 14, 16, 18 is located within
a range 35 of the base station 10.
[0042] The base station 10 is arranged to receive signals from the
transmitter units 12, 14, 16, 18 and is arranged to distinguish the
transmitter signals from signals received from other sources, for
example by arranging the base station 10 such that only signals of
a predetermined frequency are detected and by arranging each
transmitter unit to periodically transmit a signal at the
predetermined frequency.
[0043] The nature of the signal transmitted by each transmitter
unit is such that the base station 10 is able to identify the
transmitter unit 12, 14, 16, 18 and distinguish the transmitter
units from each other. In this example, this is achieved by
allocating a unique identification code to each transmitter unit
12, 14, 16, 18 and incorporating the relevant unique identification
code into the signal transmitted by the relevant transmitter
unit.
[0044] However, it will be understood that other arrangements for
ensuring that the base station 10 is able to receive and
distinguish signals from the transmitter units are possible. For
example, the transmitter units may be arranged to transmit signals
at different frequencies.
[0045] In order to reduce the likelihood that one or more
transmitters will transmit signals simultaneously, the interval
between successive transmissions for each transmitter unit may be
different.
[0046] In this example, the transmitter units are arranged such
that each transmitter unit 12, 14, 16, 18 transmits a signal to the
base station 10 at pseudo random intervals, for example once every
second and at a random offset within each one second interval. Such
an asynchronous transmission protocol serves to reduce the
likelihood of two signal transmissions occurring
simultaneously.
[0047] In order to further reduce the likelihood of simultaneous
signal transmissions, the base station 10 is arranged so as to
generate an audible alarm only when several expected transmissions
are not received from a transmitter unit. For example, the base
station 10 may be arranged so as to expect a signal from each
transmitter unit every second and to generate an audible alarm when
three successive signal transmissions are not received from a
transmitter unit.
[0048] The base station 10 interfaces with the alarm device 20, the
vessel global positioning system 22 and the EPIRB assembly 24 such
that when three successive signals are not detected by the base
station 10 from at least one of the transmitter units 12, 14, 16,
18, the base station 10 generates an actuation signal which causes
the alarm device 20 to activate and generate an audible alarm.
Non-detection of three successive signals also causes the vessel
global positioning system 22 to log the location of the vessel 30
and the EPIRB releasing means 28 of the EPIRB assembly 24 to
activate and release the EPIRB 26 into the surrounding water.
[0049] The base station 10 is shown in more detail in FIG. 2. The
base station 10 includes a control unit 33 for controlling and
coordinating operations in the base station 10, one or more
receivers 34 for receiving transmissions from the transmitter units
12, 14, 16, 18, an LCD display 36 for visibly displaying
information associated with the safety system, and a data storage
device 38 for storing important system and operational
information.
[0050] The control unit 33 in this example includes a 16-bit
microprocessor with 16 MHz clocking speed. The control unit 33 is
arranged to interface with the alarm device 20 such that an audible
alarm is generated in response to receipt of an actuation signal
from the control unit 33 indicative that no signal has been
detected from at least one of the transmitter units 12, 14, 16, 18
by the or at least one of the receivers 34 for three successive
transmissions.
[0051] The control unit 33 may also be arranged to interface with
positioning means other than the vessel global positioning means,
such as an external active GPS antenna 40 arranged to supply GPS
data in the absence of GPS data from the vessel global positioning
means 22.
[0052] The control unit 33 is also arranged to interface with the
LCD display 36 so that information relevant to the status and/or
operation of the security system may be visibly communicated to a
user. For example, information indicative of the status and/or
operation of the transmitter units may be displayed, such as
whether the transmitter units are operating correctly, or whether
any of the transmitter units require charging. The display may also
show the or each relevant identifier indicative of the or each
transmitter unit 12, 14, 16, 18 for which a signal has not been
detected for a predetermined period of time. In the present
embodiment, the LCD display 36 is caused by the control unit 33 to
display the following conditions where appropriate:
[0053] "Logged on-battery good"
[0054] This indicates normal operation of a transmitter unit 12,
14, 16, 18.
[0055] "Logged on-battery low"
[0056] This indicates that the transmitter unit is operating but
the battery in the transmitter unit is low and needs
recharging.
[0057] "Not logged on"
[0058] This indicates that a transmitter unit is switched off.
[0059] "Charging"
[0060] This indicates that a transmitter unit is being
recharged.
[0061] "MOB"
[0062] This indicates that a signal has ceased being received from
a transmitter unit and the transmitter unit appears to be lost.
This condition causes an emergency response screen to be displayed.
An MOB condition also causes the control unit 33 to display an
identifier unique to the lost transmitter unit, the time that the
transmitter unit was lost and the GPS location of the vessel on the
LCD display 36. This information is also stored in the data storage
device 38.
[0063] Although the display used in the present embodiment is an
LCD display 36, it will be understood that other display devices
are envisaged, such as an LED display device.
[0064] The control unit 33 is also arranged to interface with the
data storage device 38 so as to save and selectively retrieve all
important system and transmitter unit information, for example in
the event that power to the base station 10 is lost. The data
storage device 38 may be in the form of a non-voltile memory.
[0065] Optionally, the control unit 33 may also be arranged so as
to interface with an external device 42 such that an appropriate
actuation signal is forwarded to the external device 42 when a
signal is not detected from one or more of the transmitter units
for a predetermined period of time. For example, the external
device 42 may be an additional alarm unit, a dan buoy release, a
self steering trip, an engine cut-out, a head-to-wind command to
the autopilot, and so on.
[0066] A transmitter unit 12 is shown in more detail in FIG. 3.
[0067] The transmitter unit 12, 14,16, 18 includes a housing 44, in
this example formed of lightweight impact resistant polycarbonate
material, the housing 44 being ultrasonically sealed so as to be
waterproof to a rating of IP68. The housing 44 is also at least
partially transparent so that any ingress of water into the housing
44 is readily identifiable by a user. Integral with the housing 44
is a tab 46 provided with an aperture 48 for receiving a
lanyard.
[0068] However, although each transmitter unit 12, 14, 16, 18 of
the present embodiment includes a tab 46 and an aperture 48 for
receiving a lanyard, it will be understood that other arrangements
for securing the transmitter unit to a person are envisaged. For
example, the housing may include a clip for attaching to an item of
clothing, a belt, and so on.
[0069] Inside the housing 44 is disposed a control unit 50 for
controlling and coordinating operations of the transmitter unit, a
transmitter 52 for periodically transmitting a signal under control
of the control unit 50, an indicating device in this example in the
form of an LED 54 for indicating transmitter unit status to a user,
a battery 56 for supplying electrical power to components of the
transmitter unit 12, 14, 16, 18, and a charging device 58 for
facilitating charging of the battery 56.
[0070] In the present example, the LED 54 is caused by the control
unit 50 to indicate different status conditions depending on the
current status and operation of the transmitter unit. For example,
the LED 54 may be caused to emit a short pulse of green light once
every two seconds so as to indicate that the battery 56 is
sufficiently charged and the transmitter unit is transmitting a
signal, to emit a short pulse of red light once every two seconds
so as to indicate that the battery charge is low and the
transmitter unit is transmitting a signal, to emit a relatively
long pulse of green light once every five seconds so as to indicate
that the transmitter unit is disposed in a charger and the battery
56 is fully charged, to continuously emit red light so as to
indicate that the transmitter unit is disposed in a charger and
charging is in process but is not yet complete, and to emit no
light so as to indicate that the transmitter unit is switched
off.
[0071] However, it will be understood that other arrangements may
be used so as to indicate transmitter unit status and/or
operation.
[0072] The transmitter unit 12, 14, 16, 18 is also arranged to
transmit a signal in the form of a data packet containing the
unique identification code associated with the transmitter unit
once per second.
[0073] In order to minimise the likelihood of simultaneous signal
transmissions by two or more transmitter units 12,14, 16, 18, each
transmitter is provided with a pseudo random number generator 57
which is used to determine the offset time within each one second
interval at which the transmitter unit transmits the signal. In the
present example, the pseudo random number generator 57 is in the
form of a linear feedback shift register (LFSR). The output of an N
bit LFSR ensures that 2N unit outputs will be generated before the
LFSR repeats its sequence. For example, if a 20 bit LFSR is shifted
every second, 220=1048576 different outputs will be generated every
twelve days before the LFSR repeats.
[0074] In order to further reduce the likelihood of multiple
successive simultaneous transmissions of two transmitter units,
each LFSR is seeded with the respective unique identification
code.
[0075] The data packet consists of word aligned data which is
organised in such a way as to allow a simple UART to be used to
transmit data.
[0076] Prior to transmission of a data packet, the transmitter 52
must be enabled for a minimum period, in this example 2 ms. During
this time, alternating 1s and 0s are transmitted at 20 Kbit/s. This
pattern allows the receiver 34 of the base station 10 to
distinguish a binary 1 from a binary 0. A preamble precedes the
remainder of the packet, the preamble containing a unique pattern
that can not occur within the data, flags or error check portion of
the data packet. The base station 10 uses the preamble to indicate
the start of a new data packet.
[0077] The remainder of each data packet comprises the unique
identification code, status flags, and an error check sequence,
with each byte of data being scrambled using an exclusive OR
process. The identification code and error check portions of the
data packet make use of a data scrambling technique to ensure that
a significant number of edge transitions occur on the transmitted
data.
[0078] Each transmitter 52 is arranged so as to transfer data at a
rate of 20 Kbit/s. With this transfer rate, in the present example,
the length of a data packet is of the order of 4.4 ms. Accordingly,
the total transmit time for each signal including 2 ms transmitter
enable time is of the order of 6.4 ms.
[0079] The control unit 50 in this example includes a
microprocessor which may be a 16-bit microprocessor with 16 MHz
clocking speed.
[0080] The control unit 50 may also be arranged to cause the
transmitter 52 to transmit information indicative of the current
status and/or operation of the transmitter unit 12, 14, 16, 18. For
example, the transmitter 52 may be caused to transmit information
indicative of whether the respective transmitter unit is operating
correctly, whether the respective transmitter unit requires
charging, and so on.
[0081] The transmitter 52 in this example is arranged to transmit
signals in the 433 MHz ISM band with FSK modulation to reduce
interference.
[0082] The charging device 58 in this example is an inductive
coupling type charging device and for this purpose may include a
coil and associated circuitry, the coil interacting with an
incident changing magnetic field so as to generate an induced
voltage across the coil useable to charge the battery 56.
[0083] During use, in the event that a crew member 32 falls
overboard as shown in FIG. 4, the distance between the transmitter
unit 14 associated with the overboard crew member 32 and the base
station 10 will exceed the range 35. Accordingly, since the
transmitter unit 14 is located outside of the range 35, even though
a signal is transmitted by the transmitter unit 14, the base
station 10 is incapable of detecting the signal. If three
successive expected signals are not detected from the transmitter
unit 14, the base station 10 sends an actuation signal to the alarm
device 20 which causes the alarm device 20 to generate an audible
alarm. The base station also causes the vessel positioning means 22
to log the position of the vessel 30 and the time that the crew
member 32 was lost overboard. In the present example, the base
station 10 also causes the EPIRB assembly 24 to release the EPIRB
26 into the surrounding water.
[0084] It will be appreciated that since immersion of a transmitter
unit in water has the effect of reducing the intensity of the
signal transmitted by the transmitter unit, during use, if the
transmitter unit is immersed in water, the signal will not be
detected by the base station and an alarm will be generated.
[0085] Modifications and variations as would be apparent to a
skilled addressee are deemed to be within the scope of the present
invention.
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