Note: Descriptions are shown in the official language in which they were submitted.
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CAPACITIVE SENSORS FOR VEHICULAR ENVIRONMENTS
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefd of the filing of U.S. Provisional Patent
Application Serial
No. 60/138,139, entitled "Capacitive Occupant Sensor Integrated in Airbag
Cover", filed on June 8,
1999, and the specification thereof is incorporated herein by reference. This
application also claims
the benefit of the filing of U.S. Provisional Patent Application Serial No.
60/121,653, entitled "Force-
Detecting Capacitive Sensor Embedded in a Transparency Product," filed on
February 24, 1999, and
the specification thereof is also incorporated herein by reference.
BACKGROUND OF THE INVENTION
Field of the Invention (Technical Field):
The present invention relates to capacitive sensors, particularly those
employed in automotive
vehicular environments.
Backcrround Art:
Sensor technologies are becoming increasingly important in the development of
safety and
convenience features of vehicles. Because of differing vehicle geometries and
extreme
environmental conditions to which they are subjected, the sensors presently
available are deficient in
many regards.
Automobile air bag systems are a well known means of attempting to reduce the
likelihood of
serious injury to passengers in collisions. These systems are designed to very
quickly inflate an air
bag in front of a passenger during a collision, so as to hopefully prevent the
passenger from colliding
with hard objects in the passenger compartment interior, particularly the
steering column and/or the
dashboard. Such systems typically sense that the vehicle is involved in a
collision, by using an
accelerometer to sense sudden deceleration of the vehicle. Rapid inflation of
the air bag may be
obtained by electrical ignition of a pyrotechnic substance which rapidly
generates a volume of gas
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sufficient to inflate the air bag, or by electrical opening of a valve for
release of compressed gas
stored in a chamber which is part of the air bag system.
The performance of an air bag system, in terms of its success or failure in
preventing serious
passenger injury, may be critically dependent on facts concerning the initial
position and subsequent
motion of the passenger, which are not made known to the system by an
accelerometer which
senses deceleration of the vehicle as a whole. Passenger head motion is
particularly important, due
to the seriousness of head injuries. For example, if the passenger is seated
too far forward, or has
hislher head too far forward, occupying the space into which the air bag will
deploy, the passenger
may be seriously injured by the deployment of the air bag intended to prevent
passenger injury. So
there is clearly a need for passenger position sensing apparatus, which can
prevent air bag
deployment when the passenger is already too far forward when the collision
begins.
But even if the passenger is not too far forward at the beginning of the
collision, the
passenger will tend to move rapidly forward, with the passenger's head leading
that motion, relative
to the vehicle, as the vehicle rapidly decelerates, and will tend to move into
the air bag deployment
space, at least in the case of forward collisions, and may be too far into the
air bag deployment
space, before the completion of air bag deployment, to escape injury from the
air bag deployment.
There are a number of factors which may strongly influence the forward motion
of the passenger, in
addition to initial position, in ways which may vary markedly from one
passenger to another. The
relative forward motion of the passenger will depend strongly on whether the
passenger has secured
a seat lap belt and/or shoulder harness prior to the collision. The
passenger's motion may also be
influenced somewhat by the strength of any tensing up reaction the passenger
has to the collision,
i.e., instinctively pushing forward with the feet against the floorboard to
restrain forward motion of the
body. Such a protective reaction may vary greatly from one passenger to
another, and may be
greatly reduced or wholly absent if the collision is too sudden, so that the
passenger has no time to
react, or if the passenger is intoxicated or otherwise impaired. Also
variation of the crash intensity by
itself will cause considerable variation in passenger acceleration. So there
is a need for systems
which account for various positional and motion data, and analyze that
information in making the yes
or no decision on air bag deployment. Overhead sensors offer an advantage over
those previously
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known systems having beam-emitting sensors located in front of the passenger,
as in air bag
systems with acoustic sensors mounted on the steering column, for which the
beam from the sensor
will at times by blocked from operating by the hands and/or forearms of the
driver.
The use of capacitive sensors offers advantages over beam - emitting sensors,
since each
capacitive coupling sensor functions by sensing the change in the capacitance
of a capacitor, caused
by the nearby presence of a person, an effect which is essentially
instantaneous (since propagated
at light speed), rather than requiring a finite, non-negligible beam travel
time as in the case of an
ultrasonic position sensor, and since the capacitive coupling sensor does not
require transmission
and detection of a beam which might be blocked. And the use of an overhead
array of capacitive
coupling proximity sensors, the signals from which are analyzed by a
microprocessor, allows
essentially instantaneous and continuous monitoring of passenger position and
motion through
triangulation based on the distances of the passenger to the various sensors
of the array, so that the
overhead sensor array can be used to accurately and continuously determine
fore - aft, diagonal, and
lateral passenger motion. Since the passenger's head will be closest to the
overhead sensors, this
method will be particularly sensitive to passenger head motion.
The current state of the art is reflected by the following patents: U.S.
Patent No. 5,702,123, to
Takahashi et al., entitled "Air Bag Apparatus for Passenger Seat"; U.S. Patent
No. 5,653,462, to
Breed et al., entitled "Vehicle Occupant Position and Velocity Sensor"; U.S.
Patent No. 5,602,734, to
Kithil, entitled "Automobile Air Bag Systems"; U.S. Patent No. 5,549,323, to
Davis, entitled "Plastic
Air Bag Cover Having an Integrated Occupant-Sensing Sensor Module"; U.S.
Patent No. 5,512,836,
to Chen et al., entitled "Solid-State Proximity Sensor"; U.S. Patent No.
5,366,241, to Kithil, entitled
"Automobile Air Bag System' ; U.S. Patent No. 5,802,479, to Kithil, entitled
"Motor Vehicle Occupant
Sensing Systems;" U.S. Patent No. 6,014,602, to Kithil, entitled "Motor
Vehicle Occupant Sensing
Systems;" U.S. Patent No. 5,363,051, to Jenstrom et al., entitled "Steering
Capaciflector Sensor";
and U.S. Patent No. 5,118,134, to Mattes et al., entitled "Method and
Apparatus for Protecting Motor
Vehicle Occupants".
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Capacitive sensor arrays are employed in the art for detection of persons,
including for
presence and position within automobiles. Further representative of the art
are U.S. Patent No.
3,864,668, entitled "Seat Belt Warning and Ignition Interlock System", to
Bickford; U.S. Patent No.
3,898,472, entitled "Occupancy Detector Apparatus for Automotive Safety
System", to Long; U.S.
Patent No. 4,796,013, entitled "Capacitive Occupancy Detector Apparatus", to
Yasuda et al.; and
U.S. Patent No. 4,887,024, entitled "Person Detecting Device", to Sugiyama et
al. U.S. Patent Nos.
4,972,154 and 5,394,097, entitled "Apparatus and Method for Measuring Wood
Grain Angle" and
"Dielectric Sensor", respectively, to Bechtel, et al., exemplify one and two-
sided fabrication of
electrodes on traditional printed circuit (PC) boards.
The present invention provides apparatuses and methods addressing deficiencies
in the prior
art, as described in the description of the preferred embodiments, below. The
present invention
concerns systems for sensing characteristics of motor vehicles and occupants
for purposes such as
deployment of air bags during vehicle crashes, to monitor drowsy drivers, and
to determine crash
characteristics. More particularly it concerns systems in which the system
operation is affected not
only by information about the motion of the vehicle caused by crash forces,
but also measured data
concerning the motion of the passenger, so that the system will operate in a
manner to minimize the
risk of serious injury to the passenger. The present invention also
incorporates a microprocessor
having memory to track data and compare it to reference data, as well as an
algorithm to
compensate for temperature effects upon the sensors.
SUMMARY OF THE INVENTION (DISCLOSURE OF THE INVENTION)
The present invention is of a force-detecting capacitive sensor comprising at
least two
electrodes integral with a transparency product. At least one of the
electrodes can be a conductive
membrane or coating that is also integral with the transparency product. The
electrodes can be in a
parallel or a non-parallel configuration. The transparency product can be
glass, for example a
vehicle windshield.
The present invention is also a system for detecting force which imparts
momentary bending
to a transparency product. The system is comprised of at least one force-
detecting capacitive sensor
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integral with the transparency product. Preferably, the sensor or sensors are
configured for
discriminating different vehicle crash characteristics, and preferably work in
conjunction with a
vehicle occupant protection system having at least one occupant restraint
device.
The present invention is also a system for detecting a visibility condition of
a transparency
product, and the system comprises at least one capacitive sensor integral with
the transparency
product that is able to distinguish between a visibility condition and an
object in proximity to the
transparency product. Preferably, the system operates in conjunction with a
vehicle occupant
protection system to distinguish between a vehicle occupant in proximity to
the transparency product
and condensed moisture on the transparency product. Preferably, the system
further initiates a
response to modify the visibility condition.
The present invention is further a method of compensating for long-term
affects of
temperature on a sensing system. The method includes the steps of determining
the constant
desired sensor output; determining low frequency shifts due to temperature
affects; comparing the
constant desired sensor output to the low frequency shifts due to temperature
affects; and employing
a compensation algorithm to account for the difference.
Additionally, the present invention is a vehicle occupant detecting capacitive
sensor in
combination with a conductive panel functioning as a vehicle airbag door and
ground plane for the
capacitive sensor. Additional capacitive sensors can be included, and all of
the capacitive sensors
are fabricated on a substrate material adjacent to the conductive panel.
Preferably, the capacitive
sensors are each assigned to at least one triangle for discriminating occupant
proximity and
providing data to an airbag controller. Each of the capacitive sensors are
preferably circular.
The present invention is still further a method of configuring a capacitive
sensor and a
reference sensor on a dielectric substrate, and comprises the steps of
fabricating a reference sensor
and a capacitive sensor on a substrate; placing a monolithic ground on a
reverse side of the
substrate; attaching a printed circuit board to a deleted portion of the
monolithic ground; connecting
the reference sensor to electronic parts on the printed circuit board; and
compensating for changes in
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capacitive sensor output which are not related to proximity of a vehicle
occupant by comparing the
capacitive sensor output to the reference sensor output.
The present invention also is a method of detecting head motion indications of
a drowsy
vehicle operator. This method comprises the steps of representing the drowsy
vehicle operator's
head motion with a four-dimensional feature vector; training a feature
detection network; utilizing a
sleep detector to detect head motion that does not look like an alert
operator's head motion and does
look like a feature associated with a sleep nod; customizing the sleep
detector for individual vehicle
operators; and identifying the operator of a vehicle and modifying sleep
detector parameters based
on historical data attributable to the identified operator.
The present invention is further still a capacitive occupant sensing system
for a sunroof-
equipped vehicle to monitor an occupant's head position. The system consists
of a nested circle
capacitive sensor and at least one L-shaped capacitive sensor surrounding the
nested circle
capacitive sensor, and both the nested cirGe capacitive sensor and the L-
shaped capacitive sensor
are located adjacent the sunroof. Optionally, the system further comprises a
dummy sensor located
on the opposite side of the sunroof from the nested circle capacitive sensor
and the L-shaped
capacitive sensor. A method of sensing the occupant's head position in the
sunroof-equipped vehicle
with a dummy sensor and a nested circle capacitive sensor array comprises the
steps of positioning
a dummy sensor on an opposite side of the sunroof from the nested circle
capacitive sensor array
adjacent the sunroof; deriving a composite head position from the dummy sensor
head position and
the triangulated head position from the nested circle capacitive sensor array;
identifying the operator
by comparing the head coordinates of the operator to historical data
attributable to the identified
operator; and updating parameters which identify non-impairment conditions of
the operator.
A primary object of the present invention is to provide capacitive sensing
arrays and systems
for detecting force upon a transparency object, for sensing occupant head
position, for determining
vehicle crash characteristics, and for operating in conjunction with a vehicle
occupant safety system.
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Another object of the present invention is to provide a means for a reference
sensor to be
near a capacitive sensor.
Still another object of the present invention is to provide an electrode for
capacitive sensing
made from a conductive coating.
Yet another object of the present invention is to combine a capacitive sensor
with a
conductive panel that functions as a vehicle airbag door, as well as a ground
plane for the capacitive
sensor.
Yet still another object of the present invention is to provide a detection
algorithm for detecting
head motion indications of a drowsy vehicle operator specific to individual
operators.
A primary advantage of the present invention is that it can distinguish
between moisture upon
a transparency product and an object near a transparency product.
Another advantage of the present invention is that is compensates for long-
term temperature
effects upon sensors.
Another advantage of the present invention is that it identifies a vehicle
operator and adjusts
vehicle safety systems to be specific to the identified operator.
Yet another advantage of the present invention is that it defines a capacitive
sensor array,
including a dummy sensor, that is effective in detecting an occupant's head
position for a sunroof-
equipped vehicle.
Other objects, advantages and novel features, and further scope of
applicability of the present
invention will be set forth in part in the detailed description to follow,
taken in conjunction with the
accompanying drawings, and in part will become apparent to those skilled in
the art upon
examination of the following, or may be learned by practice of the invention.
The objects and
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advantages of the invention may be realized and attained by means of the
instrumentalities and
combinations particularly pointed out in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated into and form a part of the
specification,
illustrate several embodiments of the present invention and, together with the
description, serve to
explain the principles of the invention. The drawings are only for the purpose
of illustrating a
preferred embodiment of the invention and are not to be construed as limiting
the invention. In the
drawings:
Fig. 1 is a cross-sectional view of embedded electrodes and conductive coating
for capacitive
sensing embedded in a transparency product in accordance with the present
invention;
Fig. 2 shows a perspective view of multiple electrodes for capacitive sensing
applied to the
surface of a transparency product in accordance with the present invention;
Fig. 3 shows multiple parallel electrodes for capacitive sensing in a vehicle
windshield in
accordance with the present invention;
Fig. 4 shows multiple non-parallel electrode pairs for capacitive sensing
inside a transparency
product in accordance with the present invention;
Fig. 5 shows force-detecting electrodes for capacitive sensing located in each
corner of a
vehicle windshield in accordance with the present invention;
Figs. 6a-6c show an overhead view of a vehicle and the crash discrimination
capabilities of
force-detecting electrodes for capacitive sensing in the vehicle windshield
according to the present
invention;
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Figs. 7a and 7b show a side view and frontal view, respectively, of a rigid or
semi-rigid
conductive panel functioning as an airbag door for vehicles;
Figs. 7c and 7d show a side view and frontal view, respectively, of a rigid or
semi-rigid
conductive panel functioning as a ground plane for the capacitive sensor of
the present invention;
Figs. 8a and 8b show a plan view and a side view, respectively, of a substrate
with a diecut
connecting tail for mounting capacitive sensors in accordance with the present
invention;
Fig. 8c shows the substrate of Figs. 8a and 8b with the connecting tail
passing through an
opening in the conductive panel and connecting to an ASIC with a reference
sensor constructed on a
printed circuit board on which the ASIC is mounted in accordance with the
present invention;
Figs. 9a and 9b show a plan view and a side view, respectively, of four
circular sensors
fabricated on substrate material in accordance with the present invention;
Fig. 10 shows an assignment of the sensors of Figs. 9a and 9b to triangular
sets in
accordance with the present invention;
Fig. 11 shows an alternative embodiment of capacitive sensors and conductive
coating
embedded in a transparency product in accordance with the present invention;
Fig. 12 shows a graphical representation of capacitance versus proximity to a
windshield, or
glass, surface in accordance with the present invention;
Figs. 13a through 13c show a plan view, a cross-sectional view, and a reverse
side view of a
capacitive reference sensor adjacent to an occupant sensor in accordance with
the present
invention;
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Fig. 14 shows the long-term drift of capacitive signals due to temperature
effects for a
vehicular sensor;
Figs. 15a and 15b show a nested circle sensor and its application in an array
for a sunroof-
equipped vehicle in accordance with the present invention;
Fig. 16 shows the relationship of occupant head motion with respect to time
during a sleep
nod; and
Fig. 17 shows an example of a dummy sensor input for triangulating vehicle
occupant head
position in accordance with the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
(BEST MODES FOR CARRYING OUT THE INVENTION)
In a first embodiment, the present invention is comprised of two or more
electrically
conductive elements ("electrodes") formed integrally on or within a
transparency product, such as
glass, a window, or a vehicle windshield. In addition to conventional
electrodes, a conductive
membrane or coating is also an electrode. These electrodes develop a mutual
capacitance which is
affected by a force acting against the transparency product. The change of
capacitance between two
electrodes, or between an electrode and a conductive membrane or coating
acting as an electrode,
is herein referred to as "capacitive sensing." Two electrodes, or an electrode
and a conductive
coating, are referred to as a "capacitive sensor."
Fig. 1 shows a cross-sectional view of transparency product 18, such as a
window or
windshield, with embedded electrodes 22 and 22', and conductive membrane or
coating 28 therein.
Electrodes 22 and 22' have capacitance 20'. Electrodes 22 and 22' can
respectively have
capacitance 20" and 20 with conductive membrane or coating 28. Inner
transparency product
layer 24 and outer transparency product layer 26 sandwich electrodes 22 and
22' and conductive
coating 28. Laminating material 30 is adjacent electrodes 22 and 22' and
conductive coating 28.
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Fig. 2 shows a perspective view of electrodes 22 and 22' applied to the
surface of transparency
product 18 and having mutual capacitance 20' between them.
Of course, multiple electrodes can be formed on the transparency product. The
transparency
product is shown as vehicle windshield 40 in Fig. 3, which is comprised of
laminated glass containing
a conductive membrane or coating which acts in conjunction with one or more
electrodes such as 22
and 22'. While two electrode sets (or capacitive sensors) 50 and 50' are shown
in Fig. 3, multiple
sets of electrodes can be formed on or in a transparency product, or
windshield 40. The axes of any
two electrode sets embedded in or applied to a transparency product can be
parallel (as shown in
Fig. 3) or non-parallel (as shown in Fig. 4).
These capacitive sensors integral with a transparency product can be used as a
system for
detecting force which imparts momentary bending to the transparency product.
In such a system,
the sensor or sensors are configured for discriminating different vehicle
crash characteristics. This
system for detecting force can further include and operate in conjunction with
a vehicle occupant
protection system that has occupant restraint device(s).
When a force acts against the transparency product, the juxtaposition of an
electrode such
as 22 relative to any other electrode such as 22', and/or the juxtaposition of
any electrode relative to
conductive membrane or coating 28, is momentarily changed. This change causes
a change in
capacitance that exists between the electrodes or between an electrode and the
conductive
membrane or coating. The change in juxtaposition is caused by momentary
bending or vibration of
the transparency product.
The change in capacitance can be used to discriminate different vehicle crash
characteristics,
by portraying the characteristics of the force which acted upon the
transparency product, for
instance, amount of force, direction of force, duration of force, and
combinations thereof. These
characteristics may be utilized in a crash detection system for vehicle
restraint systems, to
discriminate the type and severity of crash, type of object impacted,
direction of impact, percentage
of vehicle structure involved in the crash, etc.
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Multiple electrodes may be integrated in transparency product 18, or
windshield 40, to further
refine the discrimination capabilities. For example, capacitive sensors 50,
50', 50" and 50"' can be
positioned in each corner of windshield 40, thereby giving four spatially
distributed points of reference
for crash detection and discrimination as shown in Fig. 5.
Attention is now turned to Figs. 6a-6c showing a top view of vehicle 60
traveling to the right
and impacting objects. Fig. 6a is an example of a frontal crash event with
object 46 generating crash
pulse 44 which radiates through vehicle 60, front-to-back, shown by dashed
lines. Fig. 6b shows an
example crash pulse 44' resulting from an off-center impact with another
vehicle 48. Fig. 6c shows
an example crash pulse 44" resulting from an impact with object 70 such as a
tree or pole. The
characteristics of crash pulse 44, 44', and 44" represent the effect of the
impact on vehicle velocity,
often referred to as delta-V. This, in large part, is a function of type of
object impacted, vehicle
structural rigidity, vehicle and impacted object velocities, percentage of
overlap of the vehicle and
impacted object, etc.
By reference to crash pulse 44, 44', and 44", characteristics detected by the
spatially
distributed electrodes upon windshield 40, such as shown in Fig. 5, the rate
of deceleration of the
vehicle may be calculated, angle of impact determined, percentage of vehicle
overlap with the
impacted object, and other useful information can be gained about the type of
object hit. This data
can be employed to optimize the vehicle occupant protection systems, for
example, by adjusting the
timing and amount of restraining forces generated by devices such as
retractable seat belts, airbags,
etc.
The first embodiment of the present invention is applicable to equivalent
constructions,
methodologies, and applications, including the following: 1 ) detecting glass
deflection as an
indication of possible intrusion, such as a burglary attempt; 2) detecting
glass deflection as an
indication of potential breakage, such as the effect of a strong windstorm on
plate glass used in
buildings; 3) forming the electrodes on a surface of a transparency product;
4) integrating the
electrodes in or on multiple discrete transparency products, such as front and
rear vehicle windows;
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and 5) employing equivalent devices spatially distributed on the windshield or
other transparency
product, to provide multiple points of detection of a crash pulse, such as
accelerometers or strain
gauges.
Conductive membrane or coating 28 depicted in Figs. 1 and 11 (discussed below)
and
discussed herein can be suitable visually-transparent electroconductive
coatings that can be used or
are present with the windshield substrate including those with one or more
coating layers. As used
herein "coating layer(s)" or "layer" includes one or more coating films or
films. The coating layer or
layers can be part of a "coating stack" or "stack" which includes one or more
coating layers and/or
coating films. Suitable electroconductive coating layers) such as metal layers
with or without metal
oxide and/or dielectric layers include the type present in products sold by
Pittsburgh Plate Glass
Industries (PPG) under its registered trademark SUNGATE~.
However, as will be appreciated by those skilled in the art, the present
invention is not limited
thereto and may be used over any type of coating layers. For instance tin
oxide coated glass
substrates, commercially available from PPG, may be advantageously employed
herein. Also,
substantially transparent conductive coated flexible substrates, such as ITO
deposited onto
substantially clear or tinted MYLAR~, may be used. Materials suitable for
forming the
electroconductive coating layer are well known to those skilled in the art
including inorganic, organic,
or blends and composites of inorganic and organic electrochemically active
materials. Exemplary
conducting materials are coatings of doped indium oxide, doped tin oxide,
doped zinc oxide and the
like, as well as all thin metallic coatings that are substantially
transparent, such as those of gold,
silver, aluminum, nickel alloy, and the like and those such as W03, V2O5,
Mo03, Nb2O5, Ti02,
CuO, Ni2O3, Ir2O3, Cr2O3, Co2O3, Mn2O3, and the like. Also one or more
optional intermediate
layers may be deposited between the metal layer and any dielectric layer.
It is also possible to employ multiple layer coatings, such as SUNGATE~ and as
taught in
U.S. Patent No. 4,806,220, to Finley, entitled "Method of Making Low
Emissivity Film for High
Temperature Processing," the teachings of which are hereby incorporated by
reference. Others
include those of the following: U.S. Patent No. 4,786,563, to Gillery, et al.,
entitled "Protective
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Coating for Low Emissivity Coated Articles;" U.S. Patent No. 4,610,771, to
Gillery, entitled "Sputtered
Films of Metal Alloy Oxides and Method of Preparation Thereof;" U.S. Patent
No. 4,716,086, to
Gillery, et al., entitled "Protective Overcoat for Low Emissivity Coated
Article;" and U.S. Patent No.
4,898,789, to Finley, entitled "Low Emissivity Film for Automotive Heat Load
Reduction," all hereby
incorporated by reference.
A suitable SUNGATE~ coating is one that is electrically conductive and is not
adversely
affected by temperatures up to about 1300 degrees F (704 degrees C) for
several minutes.
Windshields and windows with SUNGATE~ coatings can consist of a stack of the
metallic and
dielectric films sandwiched between two glass plates. Other coatings that may
be used in the
practice of the invention are taught in U.S. Patent No. 4,201,649, to Gillery,
entitled "Low Resistance
Indium Oxide Coatings," which teachings are hereby incorporated by reference.
Also suitable are
conductive coated glass comprising a multi-layer thin film structure, which
includes a thin coating of
fluorine-doped tin oxide with additional undercoating thin film layers
disposed between the fluorine-
doped tin oxide layer and the underlying glass substrate. Such a multi-layer
coating stack is made
from an on-line (preferably in-bath) pyrolytically-coated (preferably by
chemical vapor deposition)
float glass. The layers undercoating the doped tin oxide typically comprise a
silica/silicone layer and
a tin oxide layer. Also suitable is the transparent conducting coating layer
used in this invention of a
thin layer of ITO (In2O3 containing preferably approximately 5 to 20 mole
percentage of Sn02).
Typically, conducting coating layers are disposed on a substrate of glass or
plastic as a coating
having a thickness in the range of about 5 nm to about 10,000 nm, and
preferably about 10 nm to
about 1,000 nm. However, any thickness of the conducting coating layer may be
employed that
provides adequate conductance and which does not appreciably interfere with
the transmission of
light where required.
Such coating layers can be applied to visually transparent substrates by any
method known
to those skilled in the art. For instance substrates can have a sputtered
coating stack although
MSVD coatings and pyrolytic coatings can also be used. For sputtered coating
the substrate may be
made of any material, e.g., plastic, glass, metal or ceramic. In the practice
of this invention, the
substrate is preferably transparent, e.g., nylon, glass or a Mylar~ plastic
sheet. Preferably the
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substrate is glass. The glass may be of any composition having any optical
properties, e.g., any
value of visible transmittance, ultraviolet transmission, infrared
transmission and/or total solar energy
transmission. Types of glasses that may be used in practice of the invention,
but not limited thereto,
are disclosed in: U.S. Patent No. 4,746,347, to Sensi, entitled "Patterned
Float Glass Method;" U.S.
Patent No. 4,792,536, to Pecoraro, et al., entitled "Transparent Infrared
Absorbing Glass and Method
of Making;" U.S. Patent Nos. 5,240,886 and 5,385,872, to Gulotta, et al.,
entitled "Ultraviolet
Absorbing, Green Tinted Glass;" and U.S. Patent No. 5,393,593, to Gulotta, et
al., entitled "Dark
Gray, Infrared Absorbing Glass Composition and Coated Glass for Privacy
Glazing," the disclosures
of which are hereby incorporated by reference.
The sputtered coating stack may have any arrangement including, but not
limited to, a base
layer also referred to as a dielectric layer, a phase matching layer or an
antireflective layer; an
electroconductive metal layer usually a silver film but may be any noble
metal; a primer or protective
layer which may be, but not limited to, a deposited stainless steel film, a
deposited copper film or a
deposited titanium film and a second dielectric layer or antireflective layer.
Coating stacks that are
single silver film coating stacks that may be used in the practice of the
invention, but not limiting to
the invention are disclosed in: U.S. Patent No. 4,320,155, to Gillery,
entitled "Method for Coating an
Article to Alternately Reflect and Absorb Solar Energy;" U.S. Patent No.
4,512,863, to Criss, et al.,
entitled "Stainless Steel Primer for Sputtered Films;" U.S. Patent No.
4,594,137, to Gillery, et al.,
entitled "Stainless Steel Overcoat for Sputtered Films;" and U.S. Patent No.
4,610,771, supra. The
disclosures of the patents are hereby incorporated by reference.
For SUNGATE~ coated glass, the layers are zinc stannate; the primer layer is
deposited as
metallic copper and the electroconductive layer is silver. The primer layer is
preferably deposited on
the air surface of a glass sheet cut from a float glass ribbon. The air
surface is the surface opposite
the surface of the float ribbon supported on the molten pool of metal e.g. as
disclosed in U.S. Patent
No. 4,055,407, to Heithoff, et al., entitled "Apparatus for the Manufacture of
Flat Glass Having a
Glass Refractory Delivery Piece and Method of Installation." The coating stack
described above is
disclosed in the above-mentioned U.S. Patent Nos. 4,610,771 and 4,786,563,
supra. The protective
layer is deposited over the coating stack.
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Another useful coating stack carried on the substrate can include a base layer
which may
include one or more films of different dielectric materials or antireflective
materials or phase matching
materials, a first elecroconductive metal layer, a primer layer to prevent
degradation of the metal
layer during sputtering of a dielectric layer or antireflective layer or phase
matching layer. The
dielectric layer may have one or more films. A second electroconductive metal
layer can be
deposited over the phase matching layer. A second primer layer can be
deposited on the second
metal layer and a dielectric layer or antireflective layer can be deposited
over the second primer
layer. Suitable double metal layer coating stacks include the type disclosed
in U.S. Patent No.
5,821,001 to Arbab et al. entitled "Coated Articles" which is hereby
incorporated by reference, and in
products sold by PPG Industries, Inc., under its trademark SUNGATE~ coated
glass.
Applicant's pending PCT Patent Application Serial No. US98/15505, entitled
"Capacitive
Sensing in Vehicles," disclose a capacitive sensor, made up of electrodes,
embedded in an
automotive windshield, to detect proximity of an occupant adjacent to a nearby
airbag system and to
disable or modify the output of the airbag system if an occupant is in a
dangerously close position.
The sensor relies on the physics of mutual capacitance caused to exist between
the electrode pair.
In a second embodiment of the present invention, a capacitive sensor or
sensors are used in
a system for detecting a visibility condition of a transparency product. The
system distinguishes
between a visibility condition and an object in proximity to the transparency
product, and the system
can operate in conjunction with a vehicle occupant protection system to
distinguish between a
vehicle occupant in proximity to the transparency product and a visibility
condition. The system
further initiates a response to modify the visibility condition.
Transparency products, such as windshields, are also subject to diminished
visibility
conditions from the presence of condensing moisture on the interior or
exterior surface. The
condensing moisture can be either in liquid form, such as condensed fog or
rain drops, or in solid
form, such as frost, snow or ice. In a second embodiment, the present
invention is also a system for
detecting a visibility condition of a transparency product and initiating a
response to modify the
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visibility condition. In this embodiment a capacitive sensor is integral with,
such as embedded in or
on, a transparency product 18, or windshield, and detects the condensed-
moisture and initiates a
countermeasure such as a fan to direct air against the windshield surface, a
heater/defroster to melt
ice or frost, windshield wiper action, etc.
Attention is now turned to Fig. 11. The sensor shown is comprised of either
two
electrodes 22 and 22' forming a capacitive sensor with capacitance 20', or a
single electrode 22"'
which forms a capacitive sensor with conductive coating 28 applied to the
transparency product to
form capacitance 20"' as shown in Fig. 11. In either case, the electrodes or
coating may be applied
to an internal or to an external surface of transparency product 18, or
windshield 40 (as shown in
Figs. 3, 5 and 6). Fig. 11 depicts the case of the electrodes) and coating
applied to an internal
surface of transparency product 18.
The capacitive sensor of the second embodiment of the present invention can be
configured
to differentiate an occupant who is touching the transparency product, or
windshield, from condensed
moisture on the transparency product, or windshield. The physical principle
underlying the
differentiation relates to the sensor response for an object which is
capacitively coupled to the vehicle
frame versus sensor response for an object which is not coupled to the frame.
A capacitively
coupled object represents an occupant, and an uncoupled object represents
condensed moisture on
the glass.
For the occupant case, the sensor capacitance (assuming nominal electrode
spacing in the
range of 0.375" to 1.5", and an amplitude-modulated signal using a charge-
sensitive amplifier
topology) typically exhibits an exponential shape with the capacitance
decreasing to a minimum
value as the occupant approaches and touches the glass. This is attributable
to the mutual
capacitance shielding effect caused by the positioning of the occupant with
respect to the electrode
pair. The occupant's highly conductive outer skin layer becomes a shunt
pathway to the vehicle
frame for the field energy.
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For the condensing moisture case the sensor capacitance under the same
assumptions
exhibits a maximum capacitance because the moisture layer on the glass has no
shunt pathway, and
therefore the moisture becomes capacitively coupled to the driven electrode
and amplifies the
oscillating drive signal. This signal exceeds the input specification of the
charge sensitive amplifier
thereby causing a saturated condition, in turn outputting a signal indicating
maximum capacitance.
Fig. 12 shows the relationship between capacitance and proximity to a glass
windshield surface. The
reversal points for the ungrounded case is shown at 142. Moisture upon the
windshield is
represented by plot 144. The occupant case is represented by plot 140. As is
well understood in the
art, the signal processing architecture which converts capacitance to voltage
can invert the signals,
so that the moisture on glass case exhibits a minimum output voltage and the
occupant case exhibits
a maximum output voltage.
A windshield-embedded sensing system designed to detect an occupant adjacent
to a
nearby airbag, must notify the airbag controller if a blocked sensor condition
is detected. This can
happen if condensing moisture is on the windshield surface. Because the sensor
capacitance
reaches a maximum value if moisture in on the glass, versus a minimum value if
an occupant is close
to or touching the glass, the airbag controller can distinguish the two cases
and cause the airbag
system to respond appropriately, for example bypassing the logical input from
the momentarily
blocked sensor.
Furthermore, once the blocked sensor condition is detected it can be
alleviated by
automatically activating the defroster and/or blower units in the vehicle.
When the condensed
moisture has sufficiently evaporated, the sensor response quickly changes from
the maximum signal
level associated with the condensed moisture. This data is monitored by the
airbag controller and the
airbag system reverts to its normal mode of operation with respect to occupant
detection.
In a third embodiment, the present invention is a capacitive occupant sensor
integral with an
airbag cover containing a rigid or semi-rigid conductive panel. The conductive
panel serves at least
two purposes: 1 ) upon initial expansion of the airbag, one or more edges of
the panel act in a cutting
manner to form an opening through the foam or plastic covering material which
covers the panel;
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and 2) the conductive panel serves as a ground plane for the capacitive
occupant sensor which is
sandwiched between the panel and the outer (visible) surface of the airbag
cover. The ground plane
shields the capacitive sensor from electronic interference that may couple to
the sensor electrodes
from sources such as engine electronics, and shields the capacitive fields
from extending into the
airbag unit, thus reducing sensitivity to road or engine vibration which may
be transmitted into the
airbag unit.
Attention is now turned to Figs. 7a-7d. Figs. 7a-7d show rigid or semi-rigid
conductive
panel 92 functioning as an airbag door and as a ground plane for a capacitive
sensor or sensors.
Fig. 7a shows a side view of conductive panel 92 adjacent vehicle instrument
panel 82. Airbag
deployment causes conductive panel 92 to cut through covering material 86,
that is foam or plastic,
in the area generally referred to as 84 by dashed lines. Airbag module 80 is
behind vehicle
instrument panel 82. Hinged portion 88 of conductive panel 92 allows
conductive panel 92 to move
upward to positions shown as 92' and 92". Fig. 7b shows a frontal view of
conductive panel 92
showing the cut edges of covering material by dashed lines at 84. Hinged
portion 88 of conductive
panel 92 is shown at the top. Fig. 7c shows conductive panel 92 as a ground
plane for a capacitive
sensor. Conductive panel 92 is connected to ground 100. Fig. 7d shows a
frontal view of conductive
panel 92 grounded. In this third embodiment, multiple capacitive occupant
sensors can be adjacent
to conductive panel 92, thereby providing to an airbag controller multiple
types of proximity, position,
and motion data according to the characteristics of the occupant who is
sensed.
In the third embodiment of the present invention, wherein a sensor is integral
with conductive
panel 92, the capacitive sensor, or sensors, is comprised of at least two
adjacent electrodes formed
against and electrically isolated from the panel preferably embedded between
covering material 86
and conductive panel 92. Assuming a single sensor is used made up of two
electrodes, one
electrode is connected to a driving means, such as an oscillator, with drive
electrode and the other
electrode receives signals, the sense electrode, which detects the mutual
capacitance caused to
exist due to capacitive coupling between the two or more electrodes. One means
of isolating the
electrodes from the panel is to form the electrodes on one surface of a non-
conducting substrate
material which is adhered to the conductive panel. The substrate material may
be flexible to allow
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conformance to curvatures in the panel. Also, the substrate material may
provide for a die-cut
connecting portion (such as described in applicant's U.S. Patent No.
5,844,486, entitled "Integral
Capacitive Sensor Array") with sufficient length to reach an application-
specific integrated circuit
(ASIC). This can be achieved by passing the connecting portion through a gap
in the conductive
panel to reach the integrated circuit connecting points, which are located on
the opposite side of the
panel from the substrate.
Substrate 110 is shown in Figs. 8a and 8b, not to scale. Diecut connecting
"tail" 112 is
shown connecting to ASIC 114 in Fig. 8b. Fig. 8c shows a side view of
connecting tail 112 as it
passes through an opening 122 in conductive panel 92 and connects to ASIC 114,
as well as an
optional reference sensor formed by electrodes 90 and 90' constructed on the
opposite side of
printed circuit board 116 to which ASIC 114 is mounted. Diecut connecting tail
112 of capacitive
sensor substrate 110 is shown passing through opening 122 in conductive panel
92. Ground 100 is
connected between conductive panel 92 and printed circuit board 116. An
additional opening
through conductive panel 92 is shown at 122' and is where reference capacitive
coupling fields 120
exist, as well as into covering material 86.
The sensor exhibits a decrease in electrode capacitive coupling when a highly
conductive
object, such as a person's body, enters the fields and shields a portion of
the mutual capacitance.
The shielding effect correlates to proximity of the conductive object to the
sensor electrodes.
In an alternative third embodiment of the capacitive sensor, the sensor is
comprised of one
electrode and a driven shield, such as described in U.S. Patent No. 5,166,679
(Vranish et.al.), such
that the highly conductive object which enters the capacitive field forms a
second electrode of the
capacitor, causing capacitive coupling to increase when the object moves
closer. In this
embodiment, conductive panel 92 comprises the driven shield.
The capacitive sensor driving means and the signal processing and analysis
means for the
received signals, are integrated in ASIC 114 which optimally is located
adjacent to hinged portion 88
of panel 92. Hinged portion 88 allows the remaining one or more edges to
rotate outward due to the
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rapid expansion force of airbag 80 as discussed above. This location for ASIC
114 is preferred so it
is not detached from panel 92 by rapidly expanding airbag 80 (not shown in
Fig. 8c). A further
benefit is gained if ASIC 114 avoids contact with airbag 80, thus preventing
abrasion or cutting of the
airbag fabric which could weaken the airbag integrity and lead to structural
failure. Non-contact can
be achieved by positioning ASIC 114 remote from the airbag fabric, or by
covering it with a smooth
material such as plastic or glue, etc.
ASIC 114 is preferably attached to printed circuit board 116 which provides
connecting
means for the two or more electrodes of the capacitive sensor or sensors, and
for ground.
Additionally, printed circuit board 116 may contain on one surface a reference
capacitive sensor
comprised of electrodes 90 and 90'. The function of the reference capacitive
sensor is to create
reference capacitive coupling fields 120 of very short range, nominally 1/4",
which are oriented into
the foam or plastic covering material 86. The reference sensor is sensitive to
the relative conductivity
and/or changes in thickness of the covering material, caused for example by
changes in temperature
with respect to time of covering material 86. By means of comparison which
includes signal
subtraction or division, such changes in the foam or plastic material may be
compensated for. In
another embodiment, the reference sensor may be formed on the substrate along
with the capacitive
sensor, in either case functionally positioned to detect changes in
conductivity or thickness of the
foam or plastic covering material.
In the preferred third embodiment, multiple sensors are fabricated on
substrate 110, adjacent
to conductive panel 92 (see Fig. 9a). Four sensors 118, 118', 118", and 118"'
comprised of circular
electrode pairs is one way of accomplishing this. The circular electrode
arrangement provides
generally hemispheric sensing fields, so that a person moving into a sensing
field from a non-
orthogonal angle causes a change in capacitance approximately equal to a
person moving into the
sensing field from an orthogonal angle (orthogonal being defined as relative
to the face of the
sensor). Sensors 118, 118', 118", and 118"' need not necessarily be perfectly
circular, other shapes
such as oval, can be used in accordance with the present invention. Substrate
110 is curved as
necessary to fit the contour of the interior of the vehicle instrument panel
as shown in Fig. 9b.
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With this arrangement, multiple data types can be provided to the airbag
control unit, which
can be used by a discrimination and decision algorithm. The algorithm uses the
multiple data types to
determine characteristics of the occupant moving into the one, or more,
sensing fields, and to make a
decision as to airbag deployment characteristics based on the occupant
discrimination.
For example, proximity data for any of the multiple sensors can be provided;
the first
derivative of proximity, or velocity, can be provided; the second derivative,
acceleration, can be
provided; or the third derivative, commonly referred to as "jerk", can be
provided. Additionally,
thresholds can be assigned to each data type, within the discrimination and
decision algorithm, which
thus may consist of any combination of proximity, velocity, acceleration, or
jerk thresholds.
Additionally, the four sensors 118, 118', 118", and 118"' can be assigned to
triangle sets, as
shown in Fig. 10, and triangulation methods can be applied to the proximity
data to determine exact
position of the occupant. Fig. 10 shows top triangle set 130 comprised of
sensors 118, 118' and
118". Left triangle set 132 is comprised of sensors 118, 118" and 118"'. Right
triangle set 134 is
comprised of sensors 118, 118' and 118"', and bottom triangle set 136 is
comprised of sensors 118',
118" and 118"'. This position data is then employed by the discrimination and
decision algorithm as
to airbag deployment characteristics.
The array of four sensors can be assigned to each of four triangle sets, as
shown in Fig. 10.
An example table of the data types available from the 4-sensor arrangement is
shown below in Table
1.
Table 1
Sensor set ProximityThreshold3D positionVelocityAccelerationJerk
,
Sensor 1 X X X X X
Sensor 2 X X X X X
Sensor 3 X X X X X
Sensor 4 X X X X X
Top TriangleX X X X X X
Left TriangleX X X X X X
Right TriangleX X X X X X
Bottom TriangleI X X X X X X
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The third embodiment of the present invention is understood to include
equivalent forms,
methodologies, and applications. For example, the rigid or semi-rigid panel
may be formed of non-
conductive material to which is applied a conductive film thus forming the
ground plane to which the
capacitive sensor electrodes are applied; the conductive film may comprise the
driven shield
element, as described in the Vranish patent; the cutting edges of the panel
may be any number of
one or greater, e.g. an oval shape, rectangular shape, or polygonal shape; the
reference sensor may
be fabricated on a printed circuit board, on the sensor substrate, or in other
manners that accomplish
the intent of detecting changes in conductivity and/or thickness of the
covering material; the
positioning of the ASIC may be in any convenient location on or near the
panel; the multiple sensors
may comprise any number of sensors greater than one; the triangulation sets
may use various
assignments of the multiple sensors; the discrimination and decision algorithm
may utilize any
combination of data types, and may incorporate data from other sensors as
well.
While Fig. 8c shows a reference sensor, comprised of electrodes 90 and 90',
fabricated on
one side of printed circuit board 116, the invention can also be practiced by
fabricating the reference
sensor on the same substrate as the capacitive occupant sensor, as shown in
Figs. 13a-13c. Figs.
13a, 13b and 13c show a plan view, a cross-sectional view, and a reverse side
view of substrate 160
with reference sensor 150 adjacent to capacitive occupant sensor comprised of
drive electrode 152
and sense electrode 154. In the cross-sectional view shown in Fig. 13b, it can
be seen that printed
circuit board 116 is below monolithic ground 164 and substrate 160 is atop
monolithic ground 164.
Drive electrode 152 and sense electrode 154, which together form a capacitive
sensor, are shown
atop substrate 160, along with reference sensor 150 comprised of circular
electrodes. In this form of
the reference sensor, connections are provided either on a surface of
substrate 160, or through
substrate 160 to matching pins or thru-holes on printed circuit board 116
containing electronic parts.
The physical connection of the reference electrodes to the electronic parts
can be achieved by
commonly available materials such as conductive epoxy glue. The electronic
parts perform signal
conditioning and output a usable signal which is representative of the
reference condition. This
reference condition is used to compensate for changes in sensor output which
are not related to the
proximity of an occupant, as for example change in the dielectric constant of
the carrier materials due
to changes in temperature or humidity.
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As disclosed in applicant's U.S. Patent No. 5,844,486 the opposite side of the
sensor may be
comprised of a monolithic ground area. In Fig. 13c, the grounding material is
deleted for that
portion 162 of monolithic ground area 164 on which electronics printed circuit
board 116 is adhered,
because printed circuit board 116 itself contains a grounded area similar in
dimension to deleted
monolithic ground area 162. This feature simplifies the interconnections
between printed circuit
board 116 and the sensor electrodes.
Attention is now turned to Figs. 15a and 15b. Circular electrode arrangements
have
additional applications. Applicant's pending PCT Patent Application Serial No.
US97/06822 teaches
a capacitive occupant sensor for sunroof vehicles comprised of L-shaped
electrodes around each of
at least two corners of the sunroof, the disclosure of which is incorporated
herein. In some
applications or in some vehicles, it may be desired to employ one or more
additional sensors to
provide more accurate data relating to occupant head position. One geometry of
capacitive sensor
that achieves this objective is the fourth embodiment of the present
invention, a "nested circle"
design as shown in Figs. 15a and 15b. Fig. 15a shows nested circle sensor 180
with drive
electrode 186 and receive electrodes 182 and 188. Interconnects are shown at
184. Fig. 15b shows
sunroof opening 190 of a vehicle with L-sensors 192 and 192' adjacent sunroof
opening 190, and
nested circle sensor 180 in between.
The challenge of accurately detecting head position using overhead-mounted
capacitive
sensors in a sunroof vehicle is that the sensors may not be positioned
directly over the occupant's
head, thus the signal is relatively weak and the resolved head position may be
less than desired for
the particular application. It is possible in most of these vehicles to
improve the resolution by utilizing
an array of two "L" sensors and one "nested circle" sensor, as shown in Fig.
15b.
Attention is now turned to Fig. 17. Fig. 17 shows a vehicle having sunroof
190,
L-sensors 192 and 192', and nested circular sensor 180 adjacent sunroof 190.
Dummy sensor 206
is located on the opposite side of sunroof 190. An occupant's head 200 is
shown inside the vehicle
beneath sunroof 190. The fixed proximity output from dummy sensor 206 is shown
generally by the
arrow at 204. The proximity outputs from the sensor array which is comprised
of sensors 180, 192
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and 192', is shown generally by the arrows at 202 into occupant's head 200.
The head position
triangulation algorithm which accepts proximities from these three sensors
shown in Fig. 15b can be
made more accurate by inputting data from dummy sensor 206 as shown at "x."
Dummy sensor 206
is assumed to be located at an opposite side of sunroof 190, thus it is a much
greater distance from
occupant's head 200 than the active sensor array 180, 192, and 192'. Due to
this distance, the output
of dummy sensor 206 can be assumed a fixed value for all possible head
positions of the occupant.
A composite head position is derived, either by average or other statistical
weighting methods, which
incorporates the head position using dummy sensor 206 and the triangulated
position of the active
sensor array. An example is shown in Fig. 16. Fig. 16 depicts head motion of
the occupant during a
typical sleep nod and will be described further below. The method is analogous
to the triangulation
of occupant position from multiple triangles as described above with respect
to Fig. 10. In this
embodiment, the matrix of sensor proximity inputs to the triangulation
algorithm are shown as "*" and
the head position outputs are shown as P1, P2, P3, and P4 in Table 2. The
final answer of head
position is an average of the four values, which may be weighted according to
sensor noise, vehicle
geometry, experimental results, etc.:
Table 2
Algorithm
Iteration
1 2 3 4 Final Answer
S1
S2
S3
Dummy
Head XYZ P1 P2 P3 P4 weighted average of
(P1:P4)
In the present invention, the overhead capacitive sensing system includes a
microprocessor
with suitable memory to perform the comparison of actual vs. reference head
position, and to record
the typical head position of each occupant who operates a given vehicle. This
data is used to identify
the operator and to update the parameters which identify the non-impairment
conditions of the
operator.
Operator identification is achieved by comparing the head XYZ coordinates of a
particular
driver, to the XYZ coordinates of all drivers who have used the vehicle, and
selecting the closest
match. Given a head XYZ resolution of +/- 0.25' ; fore-aft seat positions of
+/- 5"; and operator
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seated height head positions of -1" to -9", a matrix of possible head
positions of about 4 x 10 x 8 =
320 positions is obtained for each longitudinal "slice" of the vehicle. Some
drivers may sit with their
head slightly off-center so the possible head positions can be several times
greater.
For a typical passenger car, relatively few operators use the vehicle while it
is under a single
ownership - using an example of a family of two adults and two teenage
drivers, sharing three
vehicles, most often one wage earner will drive one vehicle, the other wage
earner will drive the
second vehicle, and the two teen drivers share the remaining vehicle. Thus, it
is a simple matter to
compare an operator's actual head position to stored head positions for the
vehicle and to infer which
of the four drivers is operating the particular vehicle. Given this selection,
it is also possible to select
a history of time vs. position profiles for that operator, to update the
profile, and then use the updated
profile to better discriminate impairment from non-impairment, as described
below in the example.
However, sensor output of any of the embodiments of the present invention, as
well as other
sensing systems, can be affected by temperature. For many types of sensors, it
is difficult to
compensate for exposure to extreme temperatures over long time periods. This
is particularly true for
transportation vehicles which may be serviceable for decades, are likely to be
located in widely
varying climates over the years, and thus are exposed to much more than day-
night, week-to-week,
and seasonal temperature extremes.
It is possible with some sensors to compensate for long term changes in output
by employing
a non-zero sensor response which is sensitive only to the effects of these
temperature changes. If
the non-zero response shifts slowly, in most cases it can be safely assumed
this slow shift is due to
temperature and not due to a sensed condition.
For a capacitive occupant sensor employed in a vehicle, this technique is
particularly
appropriate because the presence of an occupant will cause high frequency
shifts in sensor output
which are readily distinguishable from very low frequency shifts attributable
to long-term temperature
effects. This concept is depicted in Fig. 14. Fig. 14 shows long-term drift of
capacitive signals due to
temperature affects. The constant desired sensor output is shown by the
constant horizontal
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line 172. Curved line 170 represents long-term drift of the capacitive signals
due to temperature
affects. A compensation algorithm can account for the difference between the
long-term drift 170
and the constant desired sensor output 172 at those places denoted 174, 176
and 178.
Industrial Applicability:
The invention is further illustrated by the following non-limiting example.
Example
Applicant's issued U.S. Patent No. 5,691,693, entitled "Impaired
Transportation Vehicle
Operator System," discloses a system for detecting impairment of the operating
ability of
transportation vehicle operators due to sleepiness, intoxication or other
causes, and providing
various alerting means of the impairment condition. The detection means is an
array of capacitive
coupling sensors placed in the vehicle headliner to sense operator head
position and motion, the
output of which is compared to normal head motion profiles and impaired head
motion profiles.
Using capacitive sensors of the present invention, an example of a
mathematical description of the
sleep detection algorithm is described below.
Attention is now turned to Fig. 16. The signature head motion shown in Fig. 16
is an
example of a characteristic sleep nod motion in the vertical (z) direction.
Note that the more positive
z-axis represents downward motion. The signature represents a sequence of
physiological events.
The shoulder is due to slow initial dropping of the head, followed by a sharp
drop during a free-fall
period (labeled as the rise). A plateau follows this as the head is caught.
The head is brought up
sharply with an overshoot, ending in final recovery to initial position.
The network architecture to represent this signature uses a typical four-
dimensional feature
vector:
x(t~ _ (shoulder/rise, plateau/rise, overshoot/rise, recovery/rise).
There is a feature vector associated with each sample time. These features are
used to train
a feature detection network.
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The
detection
algorithm
uses
the
following
CNLS
neural
network:
N number
of
inputs
to
the
feature
vector
x input
feature
vector
of
dimension
N
M number
of
kernels
kernel
width
parameter
a; adjustable
linear
parameter
c; j E characteristic
l,M input
feature
vector
(exemplar)
the
network
t time
p; = L c; The square in the argument
(x) exp /3~x )2 is a dot product.
- J
x
~
~
u; (x) Kernel
= P'
p.i
~x~
=I
M
~p(x) ~ Network
_ a;u; Architecture
(x)
%=I
Derivation of the architecture is based on an output variable y that depends
stochastically on
a stochastic input variable x. The expectation of y given x is
E(y~x) = Jdy y Pr~y~x) .
From Bayes' Theorem
Pr(Y~x) = Pr(y n x)
Pr~x)
yields
E(y~x~ = f dy y Pry ~ x)
Prrx)
Use a kernel approximation for the probability distributions.
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Pry n x) ~ 1 ~ yr~ ~Y~P,~ ~x~
M ;_,
where ~ (y) is a local probability kernel with mean a; and p,{x) is a local
probability kernel with a
mean c;. The input probability density is
M
Pr~x) = f dy Pry n x) = 1 ~ P.i ~x) .
M .;_~
The expectation reduces to
M
E~y~x~ _ ~ a.~ a ~ ~x~
where
u.~ ~x~ = Pu ~x~
p.i ~x~
7=1
20
If we associate the network with the expectation, then the CNLS Net is
recovered.
As a measurement of entropy, the quantity u;(x) can be interpreted as the
probability that the
output will be a~ given the input was x. This allows us to define entropy as:
H~x~ _ -~ u.~ ~x)log2 ~u.~ ~x)~.
Entropy is a measure of the "normalcy" of a feature x. It is the negative of
information, which
is a measure of "surprise." The probability that a feature is unusual is
Pr~surprise~x~ = 2-H(x)
The probability that a feature is usual is
Prrnormal~x) =1- 2-H(x)
The algorithm utilizes an anomaly detector to detect an inverse condition,
e.g. head motion
that does not look like a normal (alert) operator's head motion. Exemplars,
c;, form the centers of a
set of kernels,u,{x). These kernels are used to calculate entropy, HA(x). The
probability that a feature
is anomalous is then
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PrA =
The algorithm also utilizes a "spike" detector based on exemplars of sleep nod
behavior. The
features from these nods were used as exemplars of sleepy behavior. These
exemplars were used
to calculate entropy HS(x). The probability that the feature has the proper
shape for a sleep nod is
given by
Pr~Shape~x~ =1- 2-Hv (X)
An amplitude/width/sideways motion filter is applied so that the final
probability that the
feature looks like a spike is
Prs = ~1- 2-H~'~~X~ ~B
where B is one if the vertical change in head motion is within a user
specified window and the lateral
change in head motion is less than a user specified threshold. Otherwise B is
zero.
The sleep detector is a composite of the anomaly detector and the spike
detector. It is the
probability that the feature does not look like an awake driver AND also does
look like a feature
associated with a sleep nod. This probability is
PrD =2, Hn~x~~l-2-Hs~x~~.
The anomaly detector can be customized for individual drivers, as discussed
above.
Although the invention has been described in detail with particular reference
to these
preferred embodiments, other embodiments can achieve the same results.
Variations and
modifications of the present invention will be obvious to those skilled in the
art and it is intended to
cover in the appended claims all such modifications and equivalents. The
entire disclosures of all
references, applications, patents, and publications cited above are hereby
incorporated by reference.
