Note: Descriptions are shown in the official language in which they were submitted.
CA 02313509 2000-07-06
The present invention relates to a system, (Vehicle Locating Device, (VLD)),
that when installed and set-up in a vehicle, has the capability of
electronically
determining and reporting its geographical position (fix) and current status.
The
position fix is determined using a Global Positioning System (GPS) Receiver
module. Additionally there is a back up redundant magnetic compass system that
complements the GPS data in the event the GPS satellites signal become
obstructed. The reporting function is preferably via a separate radio
frequency RF-
Modem transceiver. The main role of the system is that of a "Passive Vehicle
Locator", (PVL) device and the additional role being a "Passive Collision
Notification", (PCN) collision detection system. A reporting station or
monitoring
service receives and collects this data, and notifies the appropriate services
if it is
determined that the vehicle has been stolen or involved in a collision.
The details concerning the reporting station / message service is considered
outside the scope of this invention as it represents third party operation of
a GPS
system, other than the receipt and processing of positional data.
A dramatic increase in vehicle theft, (automobiles, snowmobiles, boats,
aeroplanes, etc.), for vehicle or parts resale has lead to an increase in
demand by
owners, police and insurance carriers for a measure to track and recover the
stolen
property. It is the intention of the applicant to provide the market with a
tool to help
aid in the recovery of stolen vehicles.
By means of a selected RF system transceiver from several radio frequency
(RF) technology systems and a small system controller in the vehicle a
watchful eye
can be kept on ones' property through a monitoring service centre. Although it
is not
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CA 02313509 2000-07-06
the design intent of the system to prevent the theft of the vehicle, measures
are built
into the system to prevent the vehicle from starting where possible. The
present
system will not prevent the theft of a vehicle if it is with engine running.
The system
will communicate the vehicle's location and particulars to the monitoring
service at
the request of the monitoring service or when triggered by the in-vehicle
system. The
monitoring service can then notify the appropriate authorities.
The system operates as a total passive system to the user, with "no user
requirements". The primary function of the system is to continuously derive
position
fixes from the GPS receiver and compliment any magnetic compass system while
the vehicle is operating and in the run mode and periodically when the vehicle
is off.
The fix obtained from the GPS receiver and compass is used by the system in
the
event of vehicle theft. The vehicle data is transmitted from the vehicle via a
lo-VHF
transceiver ~RF Modem uplink to a LEGS) system in one application of the
system.
This signal is then relayed from the LEGS to a ground ~,arth station (GES).
The
GES redirects the signal containing data to a designated monitoring service.
The
GPS and magnetic compass data collected by the in-vehicle system is
temporarily
stored to scratch pad memory and is routinely updated.
The key feature/function of the system is that of a collision and rate of
movement detection system. By means of an onboard two axis accelerometer,
shock and vibration data is continuously read while the vehicle is in the run
mode
and periodically when the vehicle is at rest. The system compares this data to
programmed limits and acts accordingly when required. The system will
communicate the collision "g" Force details to the monitoring service centre
as well
as the last fix.
Locating and recovering a distressed vehicle is an obviously important factor
in saving accident victims' lives and property. The ability to shave minutes
or
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CA 02313509 2000-07-06
seconds off the response time to an automobile accident is crucial when lives
are in
jeopardy. In some remote locations such as rural roads, a car accident may not
be
noticed until another person or automobile happens along. This could be hours
or
even days if for example an overturned car was off the road, buried in snow.
This
would also be particularly true if all the drivers and passengers were
rendered
unconscious by the impact, and or trapped inside wreckage.
A method of independently and instantly sending out a distress signal
indicating the vehicles geographical location (hx) to emergency response
authorities
could serve to cut down on the delay time between the accident event and
emergency services arrival. This is accomplished by:
Eliminating and/or reducing the time between when the accident occurred and
the time that a person finds the accident, (if no person was witness to the
accident) or reports a missing person(s).
Eliminating delay time from when a person finds the accident to when the
person
telephones the emergency services.
Eliminating the possibility that a emergency response unit is dispatched,
whilst a
closer unit is unaware or not dispatched to the call.
~ Minimizing the time used by the emergency services in locating the actual
accident spot. In many rural roads the area is not well identified, and a
stranger
to the area reporting an accident report may not be able to effectively
communicate the location.
Automatic system initiates communications seconds after the accident, instead
of
relying on a person to decide to call. Any person immediately on the scene can
concentrate on possibly removing the victims to a safe location, especially if
the
victim is in further danger, i.e. fire, drowning, cold, etc.
The relaying of the vehicles fix may also be utilized in locating vehicles
that
have been stolen or hijacked. Insurance companies and law enforcement agencies
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CA 02313509 2000-07-06
welcome this aid in locating stolen property. If a system is able to determine
if the
vehicle has been stolen and report the occurrence and location at routine time
intervals, the vehicle could more easily be located and recovered. While this
mode
would be less time sensitive than the accident location, it may happen that
innocent
persons may be in the car (kidnapped), thus the expedient interception and
recovery
of those vehicles is as critical as that of the location of accident vehicles.
A module, able to automatically perform this function independent of any user
interaction, would be an attractive feature to many people. People whose
occupations cause them to drive long distances and/or those who find
themselves
driving extensively outside of urban centres would be among those interested
in
fitting this type of equipment.
The main function of the VLD is to relay data pertaining to a disabled
vehicle's
geographical fix via low orbit satellite communications networks to ground
based
axed relay stations. This communication is initiated by one or more specific
sensor
input activations. The activation of one of these sensors is related to very
specific
events, i.e. very high rates of deceleration, sustained negative forces in X,
Y or Z
axis or vehicle rollover, airbag deployment.
Brief Descrit~tion of the Drawings
In drawings that illustrate the present invention by way of Example:
Figure 1 is a block diagram of the system of the present invention;
Figure 2 is a diagram illustrating the intersection of two satellite range
spheres;
Figure 3 is a diagram illustrating the intersection of three satellite range
spheres;
Figure 4 is a graph illustrating a GPS fix sampling rate algorithm; and
Figure 5 is a ULD block circuit diagram.
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CA 02313509 2000-07-06
Description
The Vehicle Locating Device or VLD is an integrated assembly consisting of
three minor components and/or subsystems contained to a rigid housing moulded
of
automotive grade plastics and die cast metals specific for the application.
The
complete system includes;
~ Main Multifunction Control Module,
~ Custom wire harness assembly,
~ Rechargeable battery pack,
~ GPS receiver,
~ Lo-VHF transceiver, (RF-Modem),
~ System antennas.
The two RF subsystems and antennae are of existing technology, registered to
their
respective companies and may be patented by those respective companies
accordingly.
Main Multifunction Control Mod ~ip,~ nn~
The multifunction control module, (MCM), is the primary control element, and
all features and system functions are controlled by this module. The MCM
contains a
two axis accelerometer type sensor, a magnetic compass, a serial communication
controller, a power regulator and battery control system, a non-volatile
memory array
and peripheral interface circuits. The core microprocessor has the built in
feature of
a flash upgrade-able memory.
The flash upgrade-able memory allows updates to the operating system
software contained within the core microprocessor. It is updated through a
simple
instrumentation hook-up via a serial communication port. There is no need of
an
expensive module replacement as would be the case for masked embedded
microprocessor based systems.
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CA 02313509 2000-07-06
The MCM serves as the system motherboard for the entire system and allows
the placement and connection of the two remaining Badio Frequency (RF)
subsystems and the connection of the rechargeable backup battery. The system
is
connected through to various points of the vehicle by means of a custom wire
harness assembly connected via the right angle header, J 1, (part of
motherboard
assembly).
The entire MCM is conformal coated with a high grade encapsulant type
material reducing the effects and influence of environmental conditions, e.g.:
dust,
humidity, oil, grease and water.
Global Positioning S~ sr tom,,.jGPS~I Receiver
The global positioning receiver is a minimum of an eight (8) channel receiver.
The GPS receiver is an integrated assembly, the module is installed and
connected
through to the MCM and is held in place by mechanical stand-off fasteners and
a
vertical system connector.
The GPS Receiver preferred for the purposes of this system definition is that
of a subsidiary company to Magellan Corporation. Technical Specifications
pertaining the GPS Receiver are provided by ' Magellan for the GPS 8A series
product.
Note: Non-differential GPS Receiver, standard fix accuracy, t 100 metres, 95%
of
the time. (~ 0° 00.053996' of arc of a degree of longitude at L
0° 00.0' N). Fix
update: 1 to 99 sec, user selectable, (note: receiver requires acfive
antenna).
The active GPS antenna is connected to the GPS receiver. The GPS receiver
supplies the necessary power to the antennae system. Technical Specifications
pertaining to the GPS Active Antennae are model dependant.
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CA 02313509 2000-07-06
The magnetic two axis compass monitors both X & Y directions relative to the
vehicle with an overall accuracy of 3%. The purpose of the compass is to
compliment the onboard GPS receiver system. The compass provides the host
controller updates on direction on demand. In the event GPS data and or
signals
from the GPS satellite array is lost or skewed the compass provides the back
up
direction data required to allow the system to calculate from the last valid
GPS
almanac data sets current direction and speed. In the event of theft the GPS
antenna might be shielded or covered over by the would be perpetrator not
knowing
of the existence of compass system or a valid system failure.
The Lo-VHF transceiver is a bi-directional digital RF-Modem. The modem
operates as similar to IEEE specifications) RS232-C and is limited to a data
baud
rate of 2,400 bps in the up-link direction and 4,800 bps in the downlink. The
RF-
Modem requires a separate antenna assembly commonly available.
The transceiver is an integrated assembly, the module is installed and
connected through to the MCM via mechanical stand-off fasteners and a system
connector.
The transceiver selected for the purposes of this system definition is that of
a
subsidiary company to Magellan Corporation. Technical Specifications
pertaining the
RF Modem Transceiver are provided by Orbcomm Magellan for the OM 200 series
product .
Custom Wire Harness Assembly
The wire harness assembly consists of system automotive grade connectors
and is fabricated using automotive electrical wiring and techniques. The gauge
and
CA 02313509 2000-07-06
rating of the wiring is as per standard automotive specifications and
practices for use
in passenger compartment and trunk deck.
The individual wires of the harness are colour coded to insure ease of
installation and identification, thus reducing risk of potential errors.
~ Motherboard design, flexibility of add-on module types,
~ Motherboard contains key system circuitry,
~ Integrated two (2) axis accelerometer used for impact/collision detection,
~ Integrated two (2) axis magnetic compass system,
~ Integrated power supply and "Battery Run Down Protection"
Integrated battery charge control system,
~ Standard automotive battery voltage range, ( 9-16 Vdc.),
~ Low standby current requirements,
~ Environmental conditions protected assemblies,
~ Electrical stress protected assemblies,
~ Ease of placement and installation to vehicle,
~ Extensive onboard system diagnostics,
~ Custom wire harness, matched to vehicle manufacturer,
~ Automotive grade custom wire harness assembly,
~ Flash memory capabilities type microprocessor, ease of OS update software,
~ Vehicle communication bus compatibility (where possible), J1850 or CAN 2.Ob,
System connects and monitors installed alarm system status,
~ System operates in a total passive mode of operation,
~ Simplified system set-up and registration with monitoring service,
completely
automated and passive to user and technician,
~ Auxiliary GPS signs! output.
~ "Set-up & Test" serial communication port,
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CA 02313509 2000-07-06
RF Transceiver flexibility and system design, the system can operate with
conventional cellular systems as well with LEO type transceivers.
* J1850 & CAN 2.Ob are in-vehicle structured bus protocol sysfems and
respective
specifications. Each manufacturer will have their own unique set of
instructions and
function per instruction list. Additionally not all vehicles will be equipped
with
systems as such, connection to other alternate onboar~al systems will be
required.
Detailed Svstem Descri ion OI r io -
Main Multifunc ion Control Module, ( !In "1
The system comprises four key elements to form the entire system. The rriain
multifunction control module (MCM) forms the nucleus of the system and
contains all
operating system parameters of features/functions and the system non-volatile
memory storage system and the two axis impact detection accelerometers and the
compliment two axis magnetic compass. The remaining two systems are the RF-
Modem transceiver that supports the two way communication requirement with the
LEO system in one application of the system. The GPS receiver and magnetic
compass requirement is to provide on demand by the MCM position data of which
is
from time to time updated and stored to non-volatile memory. Three temporary
buffers contained to the core microprocessor is utilized for temporary storage
containing the position data and updated in a FIFO manner, (First In, First
Out).
The system is completely passive to the user of the vehicle the system is
installed. Upon completion of the installation and initialization by a trained
technician
the system is ready for use. The system is self contained with little to no
serviceable
parts. Failure of the MCM will require replacement of the module assembly.
Included to the systems operational modes is an extensive collection of
system diagnostics. Should the system encounter any system problems a output
signal containing the problem data will be transmitted to the reporting
station or
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CA 02313509 2000-07-06
monitoring service (RS/MS) for further action. The action or protocol the
RS/MS are
to follow are dependant on the seriousness of the reported problem which
dictate
the final action. A "Priority List'; available to the RS/MS describes the
problems) or
condition(s). The problems) or conditions) are scaled by priority and/or
severity
accordingly.
The "Prove Out Cycle", (POC) is an integral part of the normal system
function and baseline diagnostics allowing for the verification of system
integrity and
operational worthiness. The POC is initiated at every key "ON" condition,
regardless
of engine crank cycle absence.
Continuous system diagnostics and monitoring, the MCM continuously
monitors all connected points through to the vehicle via the wiring harness
and
internal modules and systems contained within the MCM system including the RF-
Modem and GPS assemblies.
Failure Detection Diagnostics.
The Failure detection Diagnostics mode triggers the system to seek help,
either by means of communication with the RS/MS and by module mounted
diagnostic light emitting diode (LED) indicator. The LED indicator will light
solid when
a system failure is present, service is required to rectify the condition.
Within the description of the FMEA (Failure Modes & Effects Analysis) tables
there are accepted predictable failure mode conditions, these conditions can
be
deemed as catastrophic failures or conditions that could prevent the lighting
of the
system status LED and/or the communication via the RF-Modem through to the
RS/MS. The conditions and failure modes are known calculated quantities.
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The system will and does from time to time experience "Intermittent
Conditions" which are normal conditions and are an accepted series of
conditions of
which manifest themselves and later are not traceable or repeatable. These
conditions are problematic in nature, the MCM is capable of dealing with
common
(known intermittent quantities derived from the system Failure Mode and
Effects
Analysis (FMEA)), under most conditions intermittent conditions or commonly
referred to as intermittent flags (IF's) and are stored to the MCM's temporary
memory and after a given travelled distance of 200 kilometres or fixed usage
period
of time dependent on the type of IF the flags) are erased. However the
original
problem code is stored to permanent memory for later history retrieval and
perusal
by either a technician or the MCM system.
Should an IF recur, (repeated IF condition) the history will be available from
the MCM's non-volatile memory. After which and an election by the system will
be
carried out to transmit the conditions to the RS/MS at which time appropriate
action
and steps to rectify the problem and contact the user are initiated.
In-Vehicle technology supports multiple system level of communication
between various dedicated system modules. Contained to the vehicle are a
series of
electronic dedicated controllers, these units share a common communication bus
connecting all vehicle critical and non-critical functions. There are
currently several
methodologies to achieve this communication protocol and structure however,
the
most commonly used protocols are CAN 2.Ob and SAE-J1850.
Collision Detection.
The purpose of the integrated accelerometer is to support the Eassive
collision notification (PCN) function of the MCM. The two (2) axis
accelerometer
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CA 02313509 2000-07-06
continuously measures and monitors changes in X&Y and derived limited Z
planes.
In the event of a collision the system will assess the net impact "g" Force
and
forward the data in addition to other pertinent data to the RS/MS.
In those vehicles where the VLD is connected through to the in-vehicle
communication area network data is obtained of a vehicle collision by means of
the
onboard supplemental $estraint ~,ystem (SRS) control module when the system
engages the SRS air bag system. A duplication or redundancy is obvious,
however,
the detection systems being the integrated two axis accelerometer and the
vehicles'
own SRS "g" Force monitor provide differing levels of data acquisition and
comparison.
The VLD discerns vehicle rollover utilizing data from the two axis
accelerometer and the two axis magnetic compass. Rollover can also be detected
by the acceleration with the two (2) axis mode of sensing. Normally, at rest,
the
accelerometer will experience a derived 1g in the Z axis. Normal driving and
operation of the vehicle will not produce any less downward accelerations for
any
significant length of time. In the case of a rollover, the vehicle is expected
to undergo
a series of violent swings in all planes, the forces acting in the Z axis will
be derived
and indicative of the event. Thus the analytical software discerns a rollover
signature, and starts the reporting process to the RS/MS.
Radio Freguencyr, i(RF~1 Sub~yrstems
The VLD / MCM housing accommodates the two RF subsystems, being the
RF-Modem and the GPS Receiver.
The purpose of the GPS receiver of the MCM is to determine the
geographical position (fix) in degrees latitude and longitude of present
position. The
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CA 02313509 2000-07-06
module receives signals from a series of geo-synchronous satellites orbiting
in
precise locations over the earth.
The GPS receiver calculates the range from the receiver to each satellite.
Once the range to a satellite is determined, it follows that the receiver lies
somewhere on a sphere with its radius equal to the calculated range. The
position of
the satellite is the centre of that sphere. If the range to a second satellite
is found, a
second sphere can be superimposed around that satellite. The receiver position
now
lies somewhere on the circle where the two spheres intersect (see Figure 2).
This, (to be noted), is different than the circle of position concept in
standard
navigation terms as this circle is oriented with the centre axis ends
coinciding with
the position of the two satellites rather than the circle of position with a
radius = 90°-
ho with its' axis oriented between a celestial body and the geographical
position of
that body. With a third satellite, the sphere intercepting the circle results
in two
common points, the location is reduced to two points (see Figure 3). A fourth
satellite
therefore fixes the altitude of the receiver.
To determine the range from the satellite, the receiver requires two
variables:
elapse time and speed. A continuous radio signal is sent out by the satellites
and is
picked up by the receiver which multiplies the speed of the signal by the time
it took
the signal to travel from the satellite to the receiver. The signal packet
transmitted by
the satellite is divided into a random sequence, each division being different
from
each other, called pseudo-random code (PRC), the random sequence is repeated
continuously. The GPS receiver is programmed with this sequence and generates
it
internally, therefore, satellites and the receivers must be synchronized.
All GPS satellites have atomic clocks, the receiver extracts the satellite's
transmission and compares the incoming signal to its own internal signal. A
comparison of how much the satellite signal is lagging gives the travel elapse
time,
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CA 02313509 2000-07-06
multiplication of this by the speed factor: c=2.997 924 58 x 108 m'~s-1, the
official
WGS-84 speed of light, determines the distance or range to that satellite.
The spherical radii of the satellite signals are determined for the three or
four
different satellites. With the PRC, the satellite transmits its orbital
position data or
almanac. The GPS constellation is monitored by the Master Control Station,
(MCS)
at Schriever Air Force Base. Using data collected by five monitor stations
distributed
around the globe, the MCS assesses the GPS performance every 15 minutes by
conducting tolerance and validation checks of the measured pseudo ranges using
a
filter error management process.
Several brands of receivers have the capability to track as many as twelve
satellites (channels) simultaneously, the advantage being that it can select
two or
three sets of satellites that have the best "cut" or azimuth angle
characteristics as
well as healthy almanac data. Horizontal Dilution of Precision (HDOP) is
caused by a
poor satellite set angle geometry. If the GPS receiver is using satellites in
the same
area of the sky as opposed to being distributed across the horizon, the
location of
the receiver becomes increasingly uncertain. Thus a good geometric position,
or cut
between each of the satellites around the earth's horizon would be
120°.
With the advent of the Selective Availability (SA) deactivated by the US
Government allows for GPS derived data accuracy improvement. Thus the standard
precision that can be expected from an uncorrected GPS receiver is t 10 metres
95% of the time. For the purposes of the VLD module, this is considered the
working
error of the systems precision and will suffice for the requirement of
accuracy.
GPS Sam ling Rate.
The MCM routinely accesses the GPS data and stores it to memory. There
are always three sets of data available for comparison. The rate at which the
data is
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CA 02313509 2000-07-06
accessed is fixed however, the distance travelled of the vehicle at higher
velocity is
greater then that of a slower moving vehicle.
The speed of the vehicle can be determined any number of ways, by GPS
sampling, or from the vehicles own data bus, by external sensor or takeoff
from the
vehicle's instrumentation. The sampling rate or "Update Factor" relationship
is
illustrated in Figure 4.
If the VLD experiences an acceleration and/or deceleration greater than a
pre-set threshold (approximately 5 g's), the system will immediately try to
acquire a
current fix from the GPS satellite array and store this latest data to the non-
volatile
memory. In such a case the VLD is designed to aid in collision location. In
addition to
the location and time, the VLD can be configured and programmed to record the
previous speed, time, course (direction) and other pertinent parameters over a
pre-
set period of time.
Note: The technique and technology described supporting the activity of multi
point
data acquisition is patented and registered to Ardtech Technologies Inc., and
is
known as the "Data Collection 1~1/aterfall Memory System" (DCVIlMS) and is
part of a
separate system. This technology allows for the capturing and storing of ten
(ten)
seconds of data prior to an event.
The most recent fix is temporarily stored to the Lyon-volatile ~.emory (NVM)
array as Fix 1, indexing the preceding fix to Fix 2, the previous fix before
that one to
Fix 3 and so on, commonly referred to as a "FIFO" operation explained earlier
to this
document. The NVM has the capacity to record three fixes, and one static set
of
data utilized by the micro-controller.
Additionally, the MCM continuously via the magnetic compass estimates a
Dead Reckoning (DR) position based on last known good data from the GPS
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CA 02313509 2000-07-06
receiver and current speed and bearing. This DR and GPS data is constantly
updated and continuously calculated and in the event the GPS receiver was
unable
to acquire a usable fix, e.g.: the antenna was shielded from satellites, or
the unit
suffered a power interruption and was performing a (warm) boot at the time DR
would be available to provide a running DR.
Custom Wire Harness,
The custom wire harness is required to interconnect the various sensors (if
any) and vehicle connection points to the MCM, as well as derive supply power
from
the vehicle, (+12Vdc and Gnd.). It will also include antennae required for the
GPS
and RF-Modem transceiver system for the selected technology.
The main wire harness is an assembly of specialized automotive grade wire
and connectors. A primary wire harness plugs into the MCM unit, and is
terminated
with various connectors. Various extension harnesses allow connection of the
primary wire harness to optional remote sensors, power and ignition pickup
points.
The antennae wires will also emanate from the MCM unit. Special coaxial
type connectors and wire are utilized.
Brake Input,
Derived from the vehicle system bus, the brake input can be used in
conjunction with the two axis accelerometer system for the purposes of data
collection for the Detected Collision Waterfall Memory System, (DCWMS). The
data
stored in the memory would indicate speed at which the brakes were applied,
rate of
deceleration, speed of impact, etc. This input signal can also be derived from
the
brake pedal switch.
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-CA 02313509 2000-07-06
Derived from the vehicle system bus and can be included as an optional item
to those vehicles that are not equipped with automated systems. The speed
input
signal is used for such things as the look ahead algorithms, accident
reconstruction.
The look ahead algorithm is incorporated to predict where the vehicle should
be within a certain time period, much like a Dead Reckoning (DR) position.
Thus if
the GPS signal is blocked or it was not capable of delivering a good fix, the
VLD in
conjunction with the magnetic compass would "PredicY'the next position, based
on
its last known fix, speed and bearing and compass data. The technique for
predicting the next position could be based on one of several techniques, such
as
cosine law or meridonal parts. It would be able to deliver a usable DR
position this
for only a short elapse time as change in bearing or altitude would not be
compensated for. As soon as the GPS module is able to deliver a good fix, the
DR
position would be thrown out. Otherwise this data would be stored and relayed
as
part of the location data.
Rechargeable Battery and Charge S~ stem,
The MCM has a built in series of rechargeable battery cells, these cells
require periodic conditioning and recharging. The cells are required to
provide power
to the VLD after a power interruption occurs. The amount of energy available
from
the cells from a full charge allows for up to two (1.5) hours of continuous
usage
before requiring a recharge.
The battery charger system is an intelligent battery charge control system.
There are no user serviceable parts contained with the exception of battery
replacement by a qualified technician.
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CA 02313509 2000-07-06
The battery is contained to the MCM enclosure, the compartment section
housing the battery is reinforced and sectioned away from other local
circuitry.
Enclosure
The enclosure of the MCM contains the main circuit board and the plugged on
daughter boards, (GPS receiver and the RF-Modem). The enclosure is a metal die
cast moulded assembly for the bottom half with optional side inserts for
various
connector configurations.
The bottom half is characterized by the protrusion of several reinforced
mounting tabs or feet and or various through holes for screw mounting to the
vehicle. Moulded inside the bottom half is mounting bosses and guides for
securing
the circuit boards. Reinforcing ribs are also integral to the bottom half for
stiffness
and strength. The tray is designed to accommodate a layer of conformal coating
and
encapsulation.
The top cover is a simple aluminium stamped assembly and is affixed to the
bottom half with a combination of metal screws.
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