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Why The ESCORT Guardian
Alert® System
Uses Doppler Microwave Technology
There are various types of
systems in consideration for
discriminatory back up warning for trucks and automobiles. These
systems must alert the
driver/vehicle operator to potential collision situations
while the vehicle is backing.
These are NOT back-up
alarms that simply beep when a vehicle so equipped is in reverse; these are systems that
warn a driver ONLY when necessary to avoid a collision or backover
accident.
Despite the best efforts of
fleet operators and the common
sense of private vehicle drivers, backing accidents are all
too common; there are about 500
fatalities each year, mostly young children. Vehicles with large blind spots to the rear, especially
SUVs and vans, are becoming more
prevalent in cities and suburban environments where backing
in constricted space is normal
practice. The need for a technological solution
to this dangerous situation has
brought a number of, in our view, inadequate systems to market, some of which offer the
illusion of solving
the problem while only helping
in marginal fashion under ideal circumstances.
As if backing
is not dangerous enough, the false
sense of security that these systems give many drivers cause more accidents and in some cases
more reckless backing
than with no system at
all. Technology must provide a solution without adding
false expectation. Currently,
there are systems on the road with "holes" large
enough for an adult to pass
unnoticed and be run over during backing. Other
systems suffer chronic
weather-related performance restrictions and need
regular maintenance that is
obviously not going to happen in the real world.
However, Doppler
microwave radar offers excellent performance in all environments,
is maintenance-free and is
affordable. Also, as an additional incentive to automakers and vehicle owners, it is unobtrusive to
vehicle styling as it can be hidden behind the rear bumper skin.
ESCORT
Guardian Alert® has drawn the conclusion that Doppler microwave radar is the only system
that offers complete coverage to
the rear of the vehicle without compromising detection in any
way that allows people to go
undetected. Additionally, it senses only
diminishing distance between
the vehicle and any object, because without the
distance between the vehicle
and object diminishing, a collision cannot occur. This is
an important means by which
nuisance notifications are reduced.
As a further
means to reduce nuisance
notifications, The ESCORT Guardian Alert® also
does not warn if the diminishing
distance closing speed is under one-quarter of one mile-per-hour.
This is because normal backing
scenarios contemplate a backing speed of well over that rate, and if a backing speed is under that
rate, it is most likely because
the operator is aware of an obstruction and "inching" toward
it. This is an important
distinction of the Guardian Alert® as a "near unknown-objects detection sensor" as opposed to "parking
aids".
There are four
basic areas of compromise with
various back-up warning systems:
-
Environmental
issues
-
Passive
warning
-
Presence
sensing
-
Vibration and
durability issue
While each is
a separate limitation, most
systems suffer from more than one.
Environmental Issues cover a whole range of problems from precipitation
to illumination levels, with
condensation and road dirt causing the most and worst
system failures and performance
degradation.
Cameras and monitor systems, being
optical in nature, often do not
work well without sufficient light levels. Ice, dirt
and condensation may render these
systems totally useless. Condensation is a particular issue during early morning operation, and
heaters are sometimes used to
offset this issue. While some immediate maintenance may improve
some situations, heavy
precipitation may severely hinder their ability to detect
or warn the vehicle operator of an
obstacle in the path of a reverse-moving vehicle.
Infrared ranging systems suffer the
same as cameras; optics get dirty and don't work. Cleaning without sufficient water causes
scratches that over time further
degrade performance.
Ultrasonic systems do not work in
strong winds (over 12 mph) and
suffer from the transducers "clogging up" with damp road
dirt and salt. A major problem
attributable to ultrasonic sensor systems having multiple transducers (currently the automakers are using
such systems) is that the
transducers won't all clog up at once and fail totally. If they did,
the driver would stand some chance
of realizing the system had problems; however, they clog up randomly during forward motion (regular
driving). They fail to work (when
called upon by engaging reverse) individually or maybe in pairs, but
not as a whole set. For example, a
vehicle equipped with the reverse sensing system suffers clogging (failure) in three sensors - passenger
side outer, passenger side inner
and drivers side inner. The drivers side outer is fine, and so
when the vehicle is reversed back
towards a flat wall, the system reports it's warnings correctly, and the driver has no idea that the
system is suffering a 75% failure.
Shortly thereafter, the driver backs towards a supposedly
open area, unaware of a child in
the blind spot behind the passenger side of the
rear bumper. The three clogged
transducers fail to detect. therefore, no warnings
are given. Afterwards, the
driver insists that the system worked just fine a
little while earlier, and
general testing will substantiate that statement.
However, thorough testing will
reveal the lack of detection on the passenger
side. Ultrasonic sensors cannot self-test themselves
individually. Such sensors
either need to work in pairs
looking at each other, or with a target behind
the vehicle. Sensors that look
at each other will false alarm in normal operation
so they are either not arranged
to see each other or are operated in a ripple
(one at a time in sequence).
Since the time of flight of a sound wave is slow,
and the settling time of an
inductive pulse circuit is long, this causes
rapidly moving targets (over 5
mph) to go undetected before collision (see
disclaimer #1,
later).
Radar systems are unaffected by all known environmental
conditions. The
only exception is a metallic bumper-sticker, such as on a AAA bumper
sticker (and obviously this
limitation can easily be avoided), as radar cannot
see through metal.
Passive warning refers to the system's
failure to alert the operator or
driver to a dangerous condition while backing. Camera and
monitor systems do not beep or
flash lights at the driver if a target enters the
field of detection. If the driver
is not looking (concentrating) on the image in
the monitor, and/or if the
driver is distracted by other vehicles or events
and fails to see the target, a
collision can occur. Active warning systems beep
and flash lights.
They do not need to be looked at to
be effective because they are audible and visual.
Passive Warning
systems (cameras) stick out of the rear
of vehicles and look good to
the general public who understand their function
and see the fleet operator
making an effort towards safety. They also gain
favor with fleet operators
because they make the entire decision-making process of
the backing maneuver be that of
the operator. There is no warning issued from
the system for the driver to
interpret. The operator must observe the situation
(as best as can be done with
the system performance and environmental
conditions), make a judgment,
and act accordingly. If he has an accident, it's the
operator's fault not the
owner's. From the owner's perspective, if the system doesn't
work for whatever reason, it
can be observed to be not working, and the
operator should act accordingly
(not reverse). If maintenance has failed to keep
the system in good order, the
operator can see this and abort the reverse
maneuver. Fleet operators like
"blame-free" systems that look good to the general
public. Thus, many camera
systems are installed despite their failings.
Presence
Sensing systems
(all ultrasonic and some radar) warn of things that are there in
the field of detection even if
they will never, ever, collide with the vehicle.
They warn of targets that are
stationary, relative to the vehicle, or are moving
away from the vehicle. So, if
for example the ground happened to be in the field
of view, the system would
continuously alarm. As a result, such a system
is configured
not to see the
ground. Then, due to the possibility of a rearward
up-ramp or incline (in a driveway
for example), the clearance between the lower detection edge of the ultrasonic beam or presence
sensing radar is increased to about 8-inches (a 6 degree up-ramp requires 8-inches of
clearance for a 6-foot detection system), and allowing for road surface
perturbations and vehicle height due to variances with loading, this clearance is
raised to about 10 inches. The
result is that an average 200-pound adult lying face up would
go undetected under the beam.
Children who have slipped on wet or icy pavement trying to get out of the way of backing vehicles
will go
undetected.
The ultimate
conclusion to this situation is that the automakers have
stopped referring to these
systems as "reverse warning systems" and are now called
them "parking assist systems".
They actively specify them as going no lower than
the lowest part of the vehicle
(such lowest part that is not wheel or
tire-related) and no higher
that the top of the rear bumper. Somewhere in the owner's
manual this is explained, along
with all the other disclaimers these systems
require. As we all know,
generally an owner's manual is not well read so it is
reasonable to assume that most
drivers will think that such a system provides full
coverage or are unaware of it's
limitations (see disclaimer #2, later). Either way, it offers no
safety-related benefits to backing towards an unseen person
unless the person is
standing up.
It should be noted that most
presence-sensing systems installed
have an OFF button that overrides and defeats the system. This
is because while a vehicle is
stationary, with something in the detection zone
and being in reverse gear
causes endless, annoying warnings. The OFF switch
cancels these annoying alarms
and resets to normal operation the next time reverse
gear is selected. This is to
help limit the "nuisance" factor, but it does nothing
to cause the operator to retain
confidence in the reliability of the system to
warn him/her when
needed.
Vibrations and durability
issues are very important. Sometimes, when parked and unattended, vehicles can be
damaged by other vehicles,
shopping carts, etc. Tree limbs can brush the top rear edge of
vans and trucks, car washing
systems (especially dryers) can misalign cameras
and mirrors. Cross view mirrors
are bumped and put out of alignment by loading
docks and other vehicles from
the same fleet during off hour loading and parking.
The reliability
of optical (camera and mirror) systems is impaired by knocks
and bumps that go undetected
until it's too late. Vehicle vibration as well
as jolting from bumpy roads can
also cause misalignment if the mounting
structure is not robust enough.
Ultrasonic and radar systems also suffer problems due
to their exposure, depending on
mounting location; however, radar mounted behind the rear bumper is virtually indestructible unless a
serious collision causes the
bumper to be smashed. All Sense Technologies sensors are encased in an
almost indestructible
epoxy-type resin for long-term durability.
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