U.S. patent application number 11/144971 was filed with the patent office on 2005-10-06 for automatic vehicle exterior light control.
Invention is credited to Bauer, Frederick T., Bechtel, Jon H., Stam, Joseph S..
Application Number | 20050219852 11/144971 |
Document ID | / |
Family ID | 22562212 |
Filed Date | 2005-10-06 |
United States Patent
Application |
20050219852 |
Kind Code |
A1 |
Stam, Joseph S. ; et
al. |
October 6, 2005 |
Automatic vehicle exterior light control
Abstract
A system for automatically controlling continuously variable
headlamps on a controlled vehicle includes an imaging system
capable of determining lateral and elevational locations of
headlamps from oncoming vehicles and tail lamps from leading
vehicles. The system also includes a control unit that can acquire
an image from in front of the controlled vehicle. The image covers
a glare area including points at which drivers of oncoming and
leading vehicles would perceive the headlamps to cause excessive
glare. The image is processed to determine if at least one oncoming
or leading vehicle is within the glare area. If at least one
vehicle is within the glare area, the headlamp illumination range
is reduced. Otherwise, the illumination range is set to full
illumination range.
Inventors: |
Stam, Joseph S.; (Holland,
MI) ; Bechtel, Jon H.; (Holland, MI) ; Bauer,
Frederick T.; (Holland, MI) |
Correspondence
Address: |
BRIAN J. REES
GENTEX CORPORATION
600 NORTH CENTENNIAL STREET
ZEELAND
MI
49464
US
|
Family ID: |
22562212 |
Appl. No.: |
11/144971 |
Filed: |
June 3, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11144971 |
Jun 3, 2005 |
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10617323 |
Jul 10, 2003 |
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6906467 |
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10617323 |
Jul 10, 2003 |
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10197834 |
Jul 18, 2002 |
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6593698 |
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10197834 |
Jul 18, 2002 |
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09938774 |
Aug 24, 2001 |
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6429594 |
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09938774 |
Aug 24, 2001 |
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09546858 |
Apr 10, 2000 |
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6281632 |
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09546858 |
Apr 10, 2000 |
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09157063 |
Sep 18, 1998 |
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6049171 |
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Current U.S.
Class: |
362/466 |
Current CPC
Class: |
B60Q 1/1423 20130101;
B60Q 2300/314 20130101; B60Q 2300/114 20130101; B60Q 2300/112
20130101; G06K 9/00825 20130101; B60Q 2300/3321 20130101; B60Q
2400/30 20130101; B60Q 2300/056 20130101; B60Q 1/085 20130101; B60Q
2300/132 20130101; B60Q 2300/42 20130101; B60Q 2300/054 20130101;
B60Q 2300/41 20130101; B60Q 1/18 20130101; B60Q 2300/312
20130101 |
Class at
Publication: |
362/466 |
International
Class: |
F21V 001/00 |
Claims
The invention claimed is:
1. An automatic exterior light control, comprising: an image array
sensor, said image array sensor comprising an array of pixel
sensors, wherein said image array sensor is configured and mounted
such that a field of view of said image array sensor substantially
passes through an associated windshield area that is wiped by a
windshield wiper.
2. An automatic exterior light control as in claim 1 wherein an
image array sensor aim is adjustable electronically.
3. An automatic exterior light control as in claim 1 wherein an
image array sensor aim is automatically adjusted.
4. An automatic exterior light control as in claim 1 comprising an
ambient light level input.
5. An automatic exterior light control as in claim 4 wherein
automatic exterior light control is enabled when an ambient light
level is below a threshold.
6. An automatic exterior light control as in claim 1 comprising an
exterior light control signal comprising a variable rate of
change.
7. An automatic exterior light control as in claim 1 comprising a
variable exterior light control signal threshold.
8. An automatic exterior light control as in claim 1 wherein at
least one image acquired from said image array sensor covers a
glare area including points at which drivers of oncoming and
leading vehicles would perceive the headlamps to cause excessive
glare, said image is processed to determine if at least one
oncoming or leading vehicle is within a glare area and if at least
one vehicle is within the glare area, the headlamp illumination
range is reduced.
9. An automatic exterior light control, comprising: an image array
sensor, said image array sensor comprising an array of pixel
sensors, wherein said image array sensor is configured and mounted
such that a field of view of said image array sensor is adjustable
electronically.
10. An automatic exterior light control as in claim 9 wherein an
image array sensor aim is automatically adjusted.
11. An automatic exterior light control as in claim 9 wherein said
image array sensor is configured and mounted such that a field of
view of said image array sensor substantially passes through an
associated windshield area that is wiped by a windshield wiper.
12. An automatic exterior light control as in claim 9 comprising an
ambient light level input.
13. An automatic exterior light control as in claim 12 wherein
automatic exterior light control is enabled when an ambient light
level is below a threshold.
14. An automatic exterior light control as in claim 9 comprising an
exterior light control signal comprising a variable rate of
change.
15. An automatic exterior light control as in claim 9 comprising a
variable exterior light control signal threshold.
16. An automatic exterior light control as in claim 9 wherein at
least one image acquired from said image array sensor covers a
glare area including points at which drivers of oncoming and
leading vehicles would perceive the headlamps to cause excessive
glare, said image is processed to determine if at least one
oncoming or leading vehicle is within a glare area and if at least
one vehicle is within the glare area, the headlamp illumination
range is reduced.
17. An automatic exterior light control, comprising: an image array
sensor, said image array sensor comprising an array of pixel
sensors; and a controller configured with an ambient light input,
wherein automatic exterior light control is enabled when an ambient
light level is below a threshold.
18. An automatic exterior light control as in claim 17 wherein said
ambient light input is derived from said image array sensor.
19. An automatic exterior light control as in claim 17 wherein an
image array sensor aim is adjustable electronically.
20. An automatic exterior light control as in claim 17 wherein an
image array sensor aim is automatically adjusted.
21. An automatic exterior light control as in claim 17 wherein said
image array sensor is configured and mounted such that a field of
view of said image array sensor substantially passes through an
associated windshield area that is wiped by a windshield wiper.
22. An automatic exterior light control as in claim 17 comprising
an exterior light control signal comprising a variable rate of
change.
23. An automatic exterior light control as in claim 17 comprising a
variable exterior light control signal threshold.
24. An automatic exterior light control as in claim 17 wherein at
least one image acquired from said image array sensor covers a
glare area including points at which drivers of oncoming and
leading vehicles would perceive the headlamps to cause excessive
glare, said image is processed to determine if at least one
oncoming or leading vehicle is within a glare area and if at least
one vehicle is within the glare area, the headlamp illumination
range is reduced.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 10/617,323, entitled "CONTINUOUSLY VARIABLE
HEADLAMP CONTROL," filed on Jul. 10, 2003, by Joseph S. Stam et
al., which is a continuation of U.S. patent application Ser. No.
10/197,834, entitled "CONTINUOUSLY VARIABLE HEADLAMP CONTROL,"
filed on Jul. 18, 2002, by Joseph S. Stam et al., now U.S. Pat. No.
6,593,698, which is a continuation of U.S. patent application Ser.
No. 09/938,774, entitled "CONTINUOUSLY VARIABLE HEADLAMP CONTROL,"
filed on Aug. 24, 2001, by Joseph S. Stam et al., now U.S. Pat. No.
6,429,594, which is a continuation of U.S. patent application Ser.
No. 09/546,858, entitled "CONTINUOUSLY VARIABLE HEADLAMP CONTROL,"
filed on Apr. 10, 2000, by Joseph S. Stam et al., now U.S. Pat. No.
6,281,632, which is a continuation of U.S. patent application Ser.
No. 09/157,063, entitled "CONTINUOUSLY VARIABLE HEADLAMP CONTROL,"
filed on Sep. 18, 1998, by Joseph S. Stam et al., now U.S. Pat. No.
6,049,171. The entire disclosure of each of the above-noted
applications is incorporated herein by reference. Priority under 35
U.S.C. .sctn.120 is hereby claimed to the filing dates of each of
the above-identified applications.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to automatically controlling
continuously variable headlamps to prevent excessive glare seen by
drivers in front of the headlamps.
[0003] Recently, headlamps producing a continuously variable
illumination range have become available. The illumination range
may be varied by one or both of changing the intensity of light and
changing the direction of light emitted by the headlamps.
[0004] Varying headlamp illumination intensity can be accomplished
in several different means. A first means is to provide a
pulse-width modulated (PWM) signal to the headlamp. By varying the
duty cycle of headlamp power, the headlamp illumination intensity
can be increased or decreased. This may be accomplished by
providing a PWM signal from a control system to a high power field
effect transistor (FET) in series with the headlamp bulb.
[0005] Another means of varying the power duty cycle of a headlamp
is to provide a PWM signal to a lamp driver integrated circuit such
as a Motorola MC33286. This integrated circuit provides the added
advantage of limiting the maximum inrush current to the headlamp,
thus potentially extending the life of the headlamp bulb.
[0006] Yet another means of varying headlamp illumination uses high
intensity discharge (HID) headlamps. HID lamps are a new, highly
efficient headlamp technology. The ballasts used to power HID
headlamps can be directly supplied with a control signal to vary
headlamp illumination intensity.
[0007] Still another means to vary the illumination intensity of a
headlamp is to provide an attenuating filter to absorb some of the
light emitted from the headlamp. An electrochromic filter may be
placed in front of the headlamp. By controlling the voltage applied
to the electrochromic filter, the amount of light absorbed and,
hence, the emitted illumination level, can be varied.
[0008] There are also several means available for changing the
direction of light emitted from headlamps. Headlamp aim can be
varied using actuators to move the headlamp housing relative to the
vehicle. Typically, these actuators are electric motors such as
stepper motors.
[0009] For headlamps with appropriately designed reflectors,
mechanically moving the light source relative to the reflector can
change headlamp beam direction as well as headlamp illumination
intensity.
[0010] HID headlamps provide several additional methods of aiming
the headlamp beam. Some of these methods involve deflecting or
perturbing the arc in such a way as to vary the lamp output. U.S.
Pat. No. 5,508,592 entitled "METHOD FOR DEFLECTING THE ARC OF AN
ELECTRODELESS HID LAMP" to W. Lapatovich et al., which is hereby
incorporated by reference, describes exciting the HID lamp with a
high-frequency radio signal. Modulating the signal causes the lamp
to operate at an acoustic resonance point, perturbing the arc from
its quiescent position. An alternative technique, known as
magnetodynamic positioning (MDP), uses a magnetic field to shape
the HID arc. MDP is being developed by Osram Sylvania Inc. of
Danvers, Mass.
[0011] A collection of methods for implementing continuously
variable headlamps is described in Society of Automotive Engineers
(SAE) publication SP-1323 entitled "Automotive Lighting
Technology," which is hereby incorporated by reference.
[0012] Automatic control of continuously variable headlamps offers
several potential benefits over automatic control of traditional
on-off headlamps. Greater flexibility for illumination is
available, allowing headlamp illumination to be better adapted to
driving conditions. Also, continuously varying the headlamp
illumination does not create rapid changes in illumination that may
startle the driver. Various methods have been devised to control
both continuously variable and conventional discrete headlamps. One
of the oldest methods is to aim the headlamp in the same direction
as steered wheels. Another method increases the illumination range
in proportion to increasing vehicle speed.
[0013] Still another method of controlling headlamps has been
developed for HID lamps. The increased brightness and bluish color
of the HID lamps is particularly disrupting to oncoming drivers.
Due to this disruptness effect, certain European countries require
headlamp leveling systems if HID lamps are used on a vehicle. These
headlamp leveling systems detect the pitch of the vehicle relative
to the road and adjust the vertical aim of the headlamps
accordingly. Advanced systems further use the speed of the vehicle
to anticipate small pitch disturbances caused by acceleration.
[0014] One problem with current continuously variable headlamp
control systems is the inability to consider oncoming or leading
vehicles in determining the illumination range of headlamps. One
prior art device is expressed in U.S. Pat. No. 4,967,319 entitled
"HEADLIGHT APPARATUS FOR AUTOMOTIVE VEHICLE" by Y. Seko. This
device utilizes vehicle speed along with the output from a
five-element linear optical sensor array directly coupled to a
headlamp. The headlamp incorporates motor drives to adjust the
elevational angle of illumination beams. This design requires a
separate sensing and control system for each headlamp or suggests
as an alternative a controlled headlamp only on the side of the
vehicle facing opposing traffic. This design presents many
problems. First, the optical sensor and associated electronics are
in close proximity to the hot headlamp. Second, placing the image
sensor on the lower front portion of the vehicle may result in
imaging surfaces being coated with dirt and debris. Third, placing
the image sensor close to the headlamp beam makes the system
subject to the masking effects of scattered light from fog, snow,
rain, or dust particles in the air. Fourth, this system has no
color discriminating capability and, with only five pixels of
resolution, the imaging system is incapable of accurately
determining lateral and elevational locations of headlamps or tail
lights at any distance.
[0015] What is needed is control of continuously variable headlamps
based on detection of oncoming headlamps and leading tail lights at
distances where headlamp illumination would create excessive glare
for the drivers of oncoming and leading vehicles.
SUMMARY OF THE INVENTION
[0016] The present invention may control continuously variable
headlamps based on detected headlamps from oncoming vehicles and
tail lights from leading vehicles. The control system may determine
the proper aim of headlamps in steerable headlamp systems and may
determine the proper intensity of headlamps in variable intensity
headlamp systems. Gradual changes in the region of headlamp
illumination may be supported. The control system also operates
correctly over a wide range of ambient lighting conditions.
[0017] The headlamp control system of the present invention may
determine the proper aim of headlamps in steerable headlamp
systems.
[0018] The headlamp control system of the present invention may
vary the intensity of headlamp beams continuously in response to
detected oncoming and leading vehicles.
[0019] The headlamp control system of the present invention may
operate such that the transition from high beam to low beam or from
low beam to high beam is gradual and thus not startling to the
vehicle driver.
[0020] The present invention also provides control of continuously
variable headlamps over a wide range of ambient lighting
conditions.
[0021] In carrying out the above objects and features of the
present invention, a method for controlling continuously variable
headlamps is provided. The method includes detecting an ambient
light level. The continuously variable headlamps are set to
daylight mode if the ambient light level is greater than a first
threshold. The headlamps are set to low beam mode if the ambient
light level is less than the first threshold but greater than a
second threshold. Automatic headlamp dimming is enabled if the
ambient light level is less than the second threshold.
[0022] In an embodiment of the present invention, automatic
headlamp dimming includes obtaining an image in front of the
headlamps. The image covers a glare area including points at which
a driver in a vehicle in front of the headlamps would perceive the
continuously variable headlamps as causing excessive glare if the
headlamps were at full range. The image is processed to determine
if the vehicle is within the glare area. If the vehicle is within
the glare area, the continuously variable headlamp illumination
range is reduced. Otherwise, the continuously variable headlamps
are set to full illumination range. In various refinements, the
continuously variable illumination range may be modified by
changing the intensity of light emitted, by changing the direction
of light emitted, or both.
[0023] In another embodiment of the present invention, reducing the
continuously variable headlamp illumination range includes
incrementally decreasing the illumination range. Obtaining the
image, processing the image, and incrementally decreasing
illumination range are repeated until the illumination range
produces a level of illumination at the oncoming or leading vehicle
position that would not be perceived as causing excessive glare by
the driver in the vehicle in front of the continuously variable
headlamps.
[0024] In still another embodiment of the present invention, the
ambient light level is determined by a multipixel image sensor
having an elevational angle relative to the controlled vehicle
having continuously variable headlamps. The method includes
acquiring a sequence of images, finding a stationary light source
in each image, calculating a measure of elevation for the
stationary light source in each image, and determining the
elevational angle based on the calculated measures of
elevation.
[0025] In a further embodiment of the present invention, the full
illumination range is reduced if at least one form of
precipitation, such as fog, rain, snow, and the like, is
detected.
[0026] In a still further embodiment of the present invention, each
continuously variable headlamp has an effective illumination range
varied by changing vertical direction aimed. Each effective
illumination range has an elevational direction corresponding to an
upper extent of the headlamp beam bright portion. The method
further includes acquiring a sequence of images. The elevational
direction is determined for at least one continuously variable
headlamp in each image of the sequence. A determination is then
made as to whether or not the sequence of images was taken during
travel over a relatively straight, uniform surface. If so, the
determined elevational directions are averaged to obtain an
estimate of actual elevational direction.
[0027] A system for controlling at least one continuously variable
headlamp on a controlled vehicle is also provided. Each
continuously variable headlamp has an effective illumination range
varied by changing at least one parameter from a set including
horizontal direction aimed, vertical direction aimed, and intensity
emitted. The system includes an imaging system capable of
determining lateral and elevational locations of headlamps from
oncoming vehicles and tail lamps from leading vehicles. The system
also includes a control unit that can acquire an image from in
front of the at least one headlamp. The image covers a glare area
including points at which the driver of a vehicle in front of the
headlamps would perceive the headlamps as causing excessive glare.
The image is processed to determine if at least one vehicle
including oncoming vehicles and leading vehicles is within the
glare area. If at least one vehicle is within the glare area, the
headlamp illumination range is reduced. Otherwise, the headlamp
illumination range is set to full illumination range.
[0028] In an embodiment of the present invention, the controlled
vehicle has at least one low beam headlamp with variable intensity
and at least one high beam headlamp with variable intensity. The
control unit reduces the illumination range by decreasing the
intensity of the high beam headlamp while increasing the intensity
of the low beam headlamp.
[0029] In another embodiment of the present invention wherein
headlamps produce illumination through heating at least one
filament, the control unit causes a low amount of current to flow
through each filament when the controlled vehicle engine is running
and when the headlamp containing the filament is not controlled to
emit light. The low amount of current heating the filament
decreases filament brittleness thereby prolonging filament
life.
[0030] In still another embodiment of the present invention, the
imaging system is incorporated into the rearview mirror mount. The
imaging system is aimed through a portion of the controlled vehicle
windshield cleaned by a windshield wiper.
[0031] In yet another embodiment of the present invention, the
controlled vehicle has a headlamp with a variable vertical aim
direction. The system further includes at least one sensor for
determining vehicle pitch relative to the road surface. The control
unit aims the headlamp to compensate for controlled vehicle pitch
variations. In a refinement, the controlled vehicle includes a
speed sensor. The control unit anticipates controlled vehicle pitch
changes based on changes in controlled vehicle speed.
[0032] In a further embodiment of the present invention, the
controlled vehicle includes headlamps with variable horizontal aim
direction. The control unit determines if a leading vehicle is in a
curb lane on the opposite side of the controlled vehicle from
oncoming traffic and is in the glare area. If no leading vehicle is
in one of the curb lanes, headlamp illumination range is reduced by
aiming the headlamps away from the direction of oncoming
traffic.
[0033] In a still further embodiment of the present invention, the
control unit reduces headlamp illumination range at a predetermined
rate over a predetermined transition time.
[0034] A system is also provided for controlling at least one
continuously variable headlamp having an effective illumination
range varied by changing vertical direction aimed. Each effective
illumination range has an elevational direction corresponding to an
upper extent of the headlamp beam bright portion. The system
includes an imaging system capable of determining lateral and
elevational locations of headlamps from oncoming vehicles. The
imaging system is mounted a vertical distance above each headlamp.
The system also includes a control unit for acquiring an image in
front of the headlamps. The image covers a glare area including
points at which the driver of the oncoming vehicle would perceive
the continuously variable headlamps to cause excessive glare. The
image is processed to determine if at least one oncoming vehicle is
within the glare area. If at least oncoming vehicle is within the
glare area, the elevational angle between the imaging system and
the headlamps of each of the at least one oncoming vehicles is
determined. If at least one oncoming vehicle is within the glare
area, the continuously variable headlamps are aimed such that the
elevational direction is substantially parallel with a line between
the imaging system and the headlamps of the oncoming vehicle
producing the greatest of the determined elevational angles.
[0035] A system is further provided for controlling continuously
variable headlamps. The system includes at least one moisture
sensor for detecting at least one form of precipitation such as
fog, rain, and snow. The system also includes a control unit to
reduce the headlamp full illumination range when precipitation is
detected.
[0036] These and other features, advantages, and objects of the
present invention will be further understood and appreciated by
those skilled in the art by reference to the following
specification, claims, and appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] In the drawings:
[0038] FIG. 1 is a diagram showing a continuously variable headlamp
illumination range together with oncoming and leading vehicles;
[0039] FIG. 2 is a block diagram of a control system according to
an embodiment of the present invention;
[0040] FIG. 3 is a flow diagram of a method for controlling
continuously variable headlamps in different ambient lighting
conditions according to the present invention;
[0041] FIG. 4 is a flow diagram of automatic headlamp dimming
according to the present invention;
[0042] FIG. 5 is a flow chart of a method for detecting tail lamps
according to an embodiment of the present invention;
[0043] FIG. 6 is a flow chart of a method for detecting headlamps
according to an embodiment of the present invention;
[0044] FIG. 7 is a schematic diagram illustrating reduction of
headlamp illumination range according to an embodiment of the
present invention;
[0045] FIG. 8 is a flow diagram of an alternative method for
reducing headlamp illumination range according to the present
invention;
[0046] FIG. 9 is an illustration of street lamp imaging according
to the present invention;
[0047] FIGS. 10a and 10b are schematic diagrams of apparent street
light elevational angle as a function of camera-to-vehicle
inclination angle;
[0048] FIG. 11 is a schematic diagram illustrating street lamp
elevational angle calculation according to an embodiment of the
present invention;
[0049] FIG. 12 is a graph illustrating street lamp elevational
angles for three different camera-to-vehicle inclination
angles;
[0050] FIG. 13 is a flow diagram of a method for calculating
camera-to-vehicle inclination angle according to an embodiment of
the present invention;
[0051] FIG. 14 is an imaging system that may be used to implement
the present invention;
[0052] FIG. 15 is a schematic diagram of image array sensor
subwindows that may be used to implement the present invention;
[0053] FIG. 16 is a schematic diagram of an embodiment of an image
array sensor that may be used to implement the present
invention;
[0054] FIGS. 17a through 17e are schematic diagrams of an
embodiment of the present invention;
[0055] FIG. 18 is a block diagram illustrating registers and
associated logic used to control the image control sensor according
to an embodiment of the present invention;
[0056] FIG. 19 is a timing diagram illustrating image array sensor
control signals for the logic in FIG. 18;
[0057] FIG. 20 is an ambient light sensor that may be used to
implement the present invention;
[0058] FIG. 21 is a diagram illustrating mounting of a moisture
sensor that may be used to implement the present invention; and
[0059] FIG. 22 is a diagram illustrating operation of a moisture
sensor that may be used to implement the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0060] Referring now to FIG. 1, a continuously variable headlamp
illumination range together with oncoming and leading vehicles is
shown. Controlled vehicle 20 includes at least one continuously
variable headlamp 22. Each headlamp 22 produces a variable region
of bright light known as illumination range 24. A driver in
oncoming vehicle 26 or leading vehicle 28 that is within
illumination range 24 may view headlamps as producing excessive
glare. This glare may make it difficult for the driver of oncoming
vehicle 26 or leading vehicle 28 to see objects on the road, to
read vehicle instruments, and to readjust to night viewing
conditions once vehicle 26, 28 is outside of illumination range 24.
Hence, illumination range 24 is perceived as a glare area by the
driver of oncoming vehicle 26 or leading vehicle 28.
[0061] The present invention attempts to reduce the level of glare
seen by the driver of oncoming vehicle 26 or leading vehicle 28 by
providing a control system that detects oncoming vehicle 26 or
leading vehicle 28 and reduces illumination range 24
accordingly.
[0062] Referring now to FIG. 2, a block diagram of a control system
according to an embodiment of the present invention is shown. A
control system for continuously variable headlamps, shown generally
by 40, includes imaging system 42, control unit 44, and at least
one continuously variable headlamp system 46. Imaging system 42
includes vehicle imaging lens system 48 operative to focus light 50
from a region generally in front of controlled vehicle 20 onto
image array sensor 52. Imaging system 42 is capable of determining
lateral and elevational locations of headlamps from oncoming
vehicles 26 and leading vehicles 28. In a preferred embodiment of
the present invention, vehicle imaging lens system 48 includes two
lens systems, one lens system having a red filter and one lens
system having a cyan filter. Lens system 48 permits image array
sensor 52 to simultaneously view a red image and a cyan image of
the same region in front of controlled vehicle 20. Image array
sensor 52 is preferably comprised of an array of pixel sensors.
Further details regarding vehicle imaging lens system 48 and image
array sensor 52 are described with regards to FIGS. 14 through 16
below.
[0063] In a preferred embodiment, imaging system 42 includes
ambient light lens system 54 operable to gather light 56 over a
wide range of elevational angles for viewing by a portion of image
array sensor 52. Ambient light lens system 54 is described with
regards to FIG. 20 below. Alternatively, light 50 focused through
vehicle imaging lens system 48 may be used to determine ambient
light levels. Alternatively, a light sensor completely separate
from imaging system 42 may be used to determine ambient light
levels.
[0064] In a preferred embodiment, imaging system 42 is incorporated
into the interior rearview mirror mount. Imaging system 42 is aimed
through a portion of the windshield of controlled vehicle 20
cleaned by at least one windshield wiper.
[0065] Control unit 44 accepts pixel gray scale levels 58 and
generates image sensor control signals 60 and headlamp illumination
control signals 62. Control unit 44 includes imaging array control
and analog-to-digital converter (ADC) 64 and processor 66.
Processor 66 receives digitized image data from and sends control
information to imaging array control and ADC 64 via serial link 68.
A preferred embodiment for control unit 44 is described with
regards to FIGS. 17 through 19 below.
[0066] Control system 40 may include vehicle pitch sensors 70 to
detect the pitch angle of controlled vehicle 20 relative to the
road surface. Typically, two vehicle pitch sensors 70 are required.
Each sensor is mounted on the chassis of controlled vehicle 20 near
the front or rear axle. A sensor element is fixed to the axle. As
the axle moves relative to the chassis, sensor 70 measures either
rotational or linear displacement. To provide additional
information, control unit 44 may also be connected to vehicle speed
sensor 72.
[0067] Control system 40 may include one or more moisture sensors
74. Precipitation, such as fog, rain, or snow, may cause excessive
light from headlamps 22 to be reflected back to the driver of
controlled vehicle 20. Precipitation may also decrease the range at
which oncoming vehicles 26 and leading vehicles 28 may be detected.
Input from moisture sensor 74 may therefore be used to decrease the
full range of illumination range 24. A moisture sensor that may be
used to implement the present invention is described with regards
to FIGS. 21 and 22 below.
[0068] Each continuously variable headlamp 22 is controlled by at
least one headlamp controller 76. Each headlamp controller 76
accepts headlamp illumination control signals 62 from control unit
44 and affects headlamp 22 accordingly to modify illumination range
24 of light 78 leaving headlamp 22. Depending on the type of
continuously variable headlamp 22 used, headlamp controller 76 may
vary the intensity of light 78 leaving headlamp 22, may vary the
direction of light 78 leaving headlamp 22, or both. Examples of
circuits that may be used for headlamp controller 76 are described
with regards to FIGS. 17d and 17e below.
[0069] In one embodiment of the present invention, control unit 44
can acquire an image covering a glare area including points at
which a driver of oncoming vehicle 26 or leading vehicle 28 would
perceive headlamps 22 to cause excessive glare. Control unit 44
processes the image to determine if at least one vehicle 26, 28 is
within the glare area. If at least one vehicle is within the glare
area, control unit 44 reduces illumination range 24. Otherwise,
headlamps 22 are set to full illumination range 24.
[0070] In a preferred embodiment of the present invention,
reductions to illumination range 24 and setting headlamps 22 to
full illumination range 24 occurs gradually. Sharp transitions in
illumination range 24 may startle the driver of controlled vehicle
20 since the driver may not be aware of the precise switching time.
A transition time of between one and two seconds is desired for
returning to full illumination range 24 from dimmed illumination
range 24 corresponding to low beam headlamps. Such soft transitions
in illumination range 24 also allow control system 40 to recover
from a false detection of oncoming vehicle 26 or leading vehicle
28. Since image acquisition time is approximately 30 ms, correction
may occur without the driver of controlled vehicle 20 noticing any
change.
[0071] For controlled vehicle 20 with both high beam and low beam
headlamps 22, reducing illumination range 24 may be accomplished by
decreasing the intensity of high beam headlamps 22 while increasing
the intensity of low beam headlamps 22. Alternately, low beam
headlamps can be left on continuously when ambient light levels
fall below a certain threshold.
[0072] For controlled vehicle 20 with at least one headlamp 22
having a variable horizontal aimed direction, the aim of headlamp
22 may be moved away from the direction of oncoming vehicle 26 when
illumination range 24 is reduced. This allows the driver of
controlled vehicle 22 to better see the edge of the road, road
signs, pedestrians, animals, and the like that may be on the curb
side of controlled vehicle 22. In a preferred embodiment, control
unit 44 may determine if any leading vehicle 28 is in a curb lane
on the opposite side of controlled vehicle 20 from oncoming traffic
and is in the glare area. If not, reducing illumination range 24
includes aiming headlamps 22 away from the direction of oncoming
traffic. If a leading vehicle is detected in a curb lane,
illumination range 24 is reduced without changing the horizontal
aim of headlamps 22.
[0073] Referring now to FIG. 3, a flow diagram of a method for
controlling continuously variable headlamps in different ambient
lighting conditions according to the present invention is shown.
For FIG. 3 and for each additional flow diagram shown, operations
are not necessarily sequential operations. Similarly, operations
may be performed by software, hardware, or a combination of both.
The present invention transcends any particular implementation and
aspects are shown in sequential flow chart form for ease of
illustration.
[0074] During twilight, different drivers or automated headlamp
systems will turn on headlamps and running lights at different
times. Since the present invention relies on detecting headlamps of
oncoming vehicles 26 and tail lamps of leading vehicles 28, there
may be a period of time between when controlled vehicle 20 has
headlamps turned on and when vehicles 26, 28 can be detected. To
accommodate various ambient light conditions at which headlamps and
tail lamps of vehicles 26, 28 may be turned on, an embodiment of
the present invention uses two thresholds for system operation.
[0075] The ambient light level is detected in block 90. In block
92, the ambient light level is compared to a day threshold. When
the ambient light level is greater than the day threshold,
headlamps are set to daylight mode in block 94. Daylight mode may
include turning on daylight running lamps (DRLs).
[0076] In an embodiment of the present invention wherein the
controlled vehicle includes headlamps, such as continuously
variable headlamps 22, which produce illumination by heating at
least one filament, the effective filament life may be extended by
causing a low amount of current to flow through the element when
the headlamp is not controlled to emit light. The amount of current
is large enough to heat the filament without causing the filament
to emit light. This heating makes the filament less brittle and,
hence, less susceptible to shock and vibration damage.
[0077] When ambient light levels fall below the day threshold, the
ambient light level is compared to the night threshold in block 96.
If the ambient light level is less than the day threshold but
greater than the night threshold, headlamps are set to low beam
mode in block 98. In low beam mode, either standard low beam
headlamps may be turned on or continuously variable headlamps 22
may be set to an illumination range 24 corresponding to a low beam
pattern. Running lights including tail lamps may also be turned
on.
[0078] When ambient light levels fall below the night threshold
level, automatic headlamp dimming is enabled in block 100. During
automatic headlamp dimming mode, control unit 44 acquires an image
in front of headlamps 22. The image covers the glare area including
points at which the drivers of oncoming vehicles 26 or leading
vehicles 28 would perceive headlamps 22 to cause excessive glare.
Control unit 44 processes the image to determine if any vehicles
26, 28 are within the glare area. If at least one vehicle 26, 28 is
within the glare area, control unit 44 reduces headlamp
illumination range 24. Otherwise, headlamp illumination range 24 is
set to full illumination range.
[0079] Several benefits, in addition to reducing glare seen by
drivers of oncoming vehicles 26 and leading vehicles 28, are
achieved by the present invention. Studies have shown that many
drivers rarely use high beams either out of fear of forgetting to
dim the high beams, out of unfamiliarity with high beam controls,
or due to preoccupation with other aspects of driving. By
automatically providing the full range of illumination when
oncoming vehicles 26 and leading vehicles 28 are not present, the
driver of controlled vehicle 20 will experience greater
visibility.
[0080] Another benefit achieved by the present invention is the
ability to illuminate areas in front of controlled vehicle 20
currently not legally permitted.
[0081] Current limitations on high beam aiming are based, in part,
on not completely blinding the drivers of oncoming vehicles 26 if
the high beams are not dimmed. Using control system 40,
illumination range 24 may be expanded to better illuminate overhead
and roadside signs, greatly aiding in night navigation. Because the
present invention automatically decreases illumination range 24 due
to an approaching oncoming vehicle 26 or leading vehicle 28, the
risk of temporarily blinding the driver of vehicles 26, 28 is
greatly reduced.
[0082] Referring now to FIG. 4, a flow diagram of automatic
headlamp dimming according to the present invention is shown. The
methods described in FIGS. 4 through 6 are more fully described in
U.S. Pat. No. 5,837,994 entitled "CONTROL SYSTEM TO AUTOMATICALLY
DIM VEHICLE HEAD LAMPS" by Joseph S. Stam et al., the entire
disclosure of which is hereby incorporated by reference.
[0083] Control unit 44 is used to acquire and examine images
obtained through imaging system 42 to detect the presence of
vehicles 26, 28. An image is acquired through the cyan filter in
block 110. A loop, governed by block 112, selects the next pixel to
be processed. The next pixel is processed in block 114 to detect
the presence of headlamps. A method for detecting the presence of
headlamps is described with regards to FIG. 6 below. A check is
made to determine if any headlamps for oncoming vehicles 26 are
found in block 116. Generally, headlamps of oncoming vehicles 26
appear much brighter than tail lamps of leading vehicles 28. Hence,
the gain for images used to search for tail lamps is greater than
the gain used to search for headlamp images. Therefore, headlamps
of oncoming vehicles 26 appearing in an image used to search for
tail lamps may wash out the image. If no headlamps are found,
images are acquired through cyan and red filters in block 118. A
loop, governed by block 120, is used to select each image pixel
through the red filter and corresponding image pixel through the
cyan filter. Each red image pixel and corresponding cyan image
pixel are processed in block 122 to detect the presence of tail
lamps. A method that may be used to detect tail lamps using red and
cyan image pixels is described with regards to FIG. 5 below. Once
the check for headlamps is completed and, if no headlamps are
detected, the check for tail lamps is completed, the illumination
range is controlled in block 124. Various alternatives for
controlling illumination range 24 of continuously variable
headlamps 22 are described with regards to FIGS. 2 and 3 above and
to FIGS. 7 through 13 below.
[0084] Alternatives to the method shown in FIG. 4 are possible. For
example, the image obtained through the cyan filter in block 110
may be used as the image obtained through the cyan filter in block
116.
[0085] Referring now to FIG. 5, a flow chart of a method for
detecting tail lamps according to an embodiment of the present
invention is shown. Pixels in image array sensor 52 that image
light 50 through the red filter in vehicle imaging lens system 48
are examined.
[0086] The location of each pixel within image array sensor 52 is
first determined to be within the tail lamp window in block 130. In
a preferred embodiment of the present invention, image array sensor
52 contains more pixels than are necessary to acquire an image
through the red and cyan filters having sufficient resolution.
These additional pixels can be used to compensate for imperfections
in aiming imaging system 42 relative to controlled vehicle 20. By
including additional rows and columns of pixels, rows and columns
of pixels on the edge of image array sensor 52 may be disregarded
to compensate for aiming variations. Methods for aiming imaging
system 42 relative to controlled vehicle 20 will be described with
regards to FIGS. 9 through 13 below. If the pixel is not determined
to be within the tail lamp window, the flow diagram is exited and
the next pixel is selected for examination as in block 132.
[0087] If the pixel selected from the red image is within the tail
lamp window, the value of the pixel is compared to the
corresponding pixel from the cyan image in block 134. A decision is
made in block 136 based on the comparison. If the red pixel is not
N % greater than the cyan pixel, the next red pixel is determined
as in block 132. Several criteria may be used to determine the
value of N. N may be fixed. N may also be derived from the ambient
light level. N may further be based on the spatial location of the
examined pixel. Distant leading vehicle 28 in front of controlled
vehicle 20 may be subjected to illumination 24 at full range
intensity. Thus, a lower value for N may be used for pixels
directly in front of controlled vehicle 20 while a higher value for
N may be used for pixels corresponding to areas not directly in
front of controlled vehicle 20.
[0088] Once the examined pixel is determined to be sufficiently
red, one or more brightness thresholds are determined in block 138.
The intensity of the red pixel is then compared to the one or more
thresholds in block 140. If the examined red pixel is not
sufficiently bright enough, the next pixel to be examined is
determined as in block 132. The one or more thresholds may be based
on a variety of factors. A threshold may be based on the average
illumination level of surrounding pixels. It may also be based on
settings for image array sensor 52 and ADC 64. The average pixel
intensity over the entire image may also be used to set a
threshold. As in the case of N, the threshold may also be
determined by the pixel spatial location. For example, the
threshold for pixels outside of 6.degree. right and left of center
should correspond to a light level incident on image array sensor
52 of about 12 times as bright as the threshold of red light
directly in front of controlled vehicle 20 and pixels between a
3.degree. and 6.degree. lateral angle should have a light level
about 4 times as bright as a pixel imaged in front of controlled
vehicle 20. Such spatial varying thresholds help to eliminate false
tail lamp detection caused by red reflectors along the side of the
road.
[0089] Once the examined pixel is determined to be sufficiently red
and determined to have a sufficient illumination level, the pixel
is added to a tail lamp list in block 142. Pixels are filtered for
reflector recognition in block 144. The position of each pixel in
the tail lamp list is compared to the position of pixels in the
tail lamp lists from previous images to determine if the pixels
represent tail lamps or roadside reflectors. Several techniques may
be used. First, rapid rightward motion of a pixel over several
frames is a strong indication that the pixels are imaging a
stationary reflector. Also, since the speed at which controlled
vehicle 20 overtakes leading vehicle 28 is much less than the speed
at which controlled vehicle 20 would overtake a stationary
reflector, the rate of increase in brightness of pixels would be
typically much greater for a stationary reflector than for tail
lamps on leading vehicle 28. A decision is made in block 46 to
determine if the pixel is a reflector image. If not, a
determination is made that a tail lamp has been detected in block
148.
[0090] Referring now to FIG. 6, a flow chart of a method for
detecting headlamps according to an embodiment of the present
invention is shown. A pixel from image array sensor 52 is selected
from a region viewing light 50 through vehicle image lens system 48
having a cyan filter. The pixel to be examined is first checked to
determine if the pixel is within the headlamp window in block 160.
As in block 130 in FIG. 5 above, block 160 permits corrections in
the aiming of imaging system 42 by not using all rows and columns
of image array sensor 52. If the examined pixel is not within the
headlamp window, the flow chart is exited and the next pixel is
obtained as in block 162.
[0091] A check is made in block 164 to determine if the examined
pixel is greater than an upper limit. If so, a determination is
made that a headlamp has been detected in block 166 and the flow
chart is exited. The upper limit used may be a fixed value, may be
based on the ambient light level, and may also be based on the
spatial location of the examined pixel.
[0092] If the upper limit in intensity is not exceeded, one or more
thresholds are calculated in block 168. A comparison is made in
block 170 to determine if the intensity of the examined pixel is
greater than at least one threshold. If not, the next pixel to be
examined is determined in block 162. As in block 138 in FIG. 5
above, the one or more thresholds may be determined based on a
variety of factors. The ambient light level may be used. Also, the
average intensity of pixels surrounding the examined pixel may be
used. Further, the vertical and horizontal spatial location of the
examined pixel may be used to determine the threshold.
[0093] If the examined pixel is greater than at least one
threshold, the pixel is added to the headlamp list in block 172.
Each pixel in the headlamp list is filtered for recognition as a
street lamp in block 174. One filtering method that may be used is
to examine a sequence of pixels in successive frames corresponding
to a potential headlamp. If this light source exhibits alternating
current (AC) modulation, the light source is deemed to be a street
lamp and not a headlamp. Another method that may be used is the
relative position of the light source in question from frame to
frame. If the light source exhibits rapid vertical movement, it may
be deemed a street lamp. A determination is made in block 176 as to
whether or not the light source is a street lamp. If the light
source is not a street lamp, a decision is made that a headlamp has
been detected in block 178.
[0094] Referring to FIG. 7, a schematic diagram illustrating
reducing headlamp illumination range according to an embodiment of
the present invention is shown. Controlled vehicle 20 has
continuously variable headlamp 22 with adjustable elevational aim.
Imaging system 42 is mounted in the rearview mirror mounting
bracket and aimed to look through the windshield of controlled
vehicle 20. In this position, imaging system 42 is approximately
0.5 meters above the plane of continuously variable headlamps 22.
When oncoming vehicle 26 is detected, an angle is calculated
between the direction of vehicle forward motion 190 and the
headlamps of oncoming vehicle 26. This inclination angle 192 is
used to aim continuously variable headlamps 22. The elevational
direction of the upper extent of illumination range 24, indicated
by 194, is set to be approximately parallel with a line from
imaging system 42 to the headlamps of oncoming vehicle 26. This
places beam upper extent 194 approximately 0.5 meters below the
headlamps of oncoming vehicle 26, thereby providing aiming
tolerance, lighting the road nearly to oncoming vehicle 26, and
avoiding striking the eyes of the driver of oncoming vehicle 26. If
multiple vehicles 26 are detected, beam upper extent 194 is set to
be substantially parallel with the greatest of the determined
elevational angles 192.
[0095] In an embodiment, the adjustment range of continuously
variable headlamps 22 may be restricted, particularly when angle
192 is substantially above or below a normal level. When one or
more vehicle pitch sensors 70 are also used, control system 40 may
base the aiming of headlamps 22 on output from imaging system 42
when lamps of oncoming vehicles 26 or leading vehicles 28 have been
located and leveling control may be used otherwise. In yet another
embodiment, input from vehicle pitch sensors 70 may be used to
calculate a limit on how high to set beam upper extent 194 to keep
the beam elevation within regulated ranges. Inputs from vehicle
speed sensor 72 may be used to anticipate acceleration of
controlled vehicle 20 to maintain the proper inclination for beam
upper extent 194.
[0096] Referring now to FIG. 8, a flow diagram of an alternative
method for reducing headlamp illumination range according to the
present invention is shown. An image is acquired in block 200 and a
determination is made to see if any vehicle is within the glare
area in block 202. Techniques for determining the presence of
oncoming vehicle 26 or leading vehicle 28 have been described with
regards to FIGS. 4 through 6 above. If no vehicle is detected, the
illumination range is set to full range in block 204.
[0097] If a vehicle is detected within the glare area, the
illumination range is decreased incrementally in block 206. This
results in illumination range 24 being decreased at a predetermined
rate over a predetermined transition time. Several techniques are
available for decreasing illumination range 24. First, the
intensity of light emitted by continuously variable headlamp 22 may
be decreased. Second, headlamps 22 may be aimed downward. Third,
headlamps 22 may be aimed horizontally away from the direction of
oncoming vehicle 26. In a refinement of the last option, a check is
made to determine if any leading vehicles 28 are in curb lanes on
the opposite side of controlled vehicle 20 from oncoming vehicle
26. If any leading vehicles 28 are detected, continuously variable
headlamps 22 are not aimed toward the curb lane. The rate at which
illumination range 24 is decreased may be constant or may be a
function of parameters including the current inclination angle of
continuously variable headlamps 22, the estimated range of oncoming
vehicle 26 or leading vehicle 28, ambient light levels, and the
like.
[0098] Depending on the automatic headlamp dimming technique used,
precise measurements of camera-to-vehicle and headlamp-to-camera
angles may be required. Concerning the latter, the difference
between the direction that control system 40 commands of the beam
of continuously variable headlamp 22 versus the actual direction of
the beam of headlamp 22 relative to imaging system 42 is a critical
system parameter. For example, low beams are designed to provide a
very sharp transition from a relatively strong beam with beam upper
extent 194 projected about 1.5.degree. downward to a greatly
diminished intensity which is normally viewed by drivers of
vehicles 26, 28 in the path of the beams. Thus, errors of
0.5.degree., particularly in the elevational direction, are
significant. Errors of 2.degree. are likely to subject drivers of
vehicles 26, 28 to intolerable glare from direct, prolonged
exposure to brighter portions of illumination range 24 as if
headlamp 22 had not been dimmed at all. The position of
illumination range 24 relative to imaging system 42 may be
determined using control system 40.
[0099] In one embodiment, the position of illumination range 24 is
sensed directly relative to the lights of oncoming vehicles 26 and
leading vehicles 28 as adjustments to illumination range 24 are
being made. In an alternative embodiment, illumination range 24 is
momentarily delayed from returning to full range. A sequence of
images is taken containing beam upper extent 194. If controlled
vehicle 20 is in motion and the beam pattern stays the same in each
of the sequence of images, control vehicle 20 can be assumed to be
moving on a straight and level road. Beam upper extent 194 can then
be determined relative to imaging system 42 by looking for a sharp
transition between very bright and very dim regions in the output
of image array sensor 52. The intensity of illumination range 24
may also be varied during the sequence of images to ensure that the
bright-to-dim transition is actually caused by continuously
variable headlamp 22. Experimentation is required to determine a
reasonable minimum speed, length of time, and number of frames to
obtain satisfactorily consistent measurements for a particular
implementation.
[0100] A method for aiming imaging system 42 relative to controlled
vehicle 20 is to precisely position controlled vehicle 20 in front
of a target that can be seen by imaging system 42. This method is
ideally suited to the automobile manufacturing process where aiming
imaging system 42 may be incorporated with or replace current
headlamp aiming. Vehicle dealerships and repair shops may be
equipped with a similar targeting apparatus.
[0101] Referring now to FIGS. 9 through 13, a method for
establishing the aim of imaging system 42 relative to controlled
vehicle 20 that may be performed during the normal operation of
controlled vehicle 20 is described. This method may be used in
conjunction with the targeting method described above.
[0102] Referring now to FIG. 9, an illustration of street lamp
imaging is shown. Image 220 represents an output from imaging
system 42 showing how street lamp 222 might appear in a sequence of
frames. By noting changes in the relative position of street lamp
222 in image 220, the vertical and horizontal aim of imaging system
42 relative to controlled vehicle 20 forward motion can be
determined. For simplicity, the following discussion concentrates
on determining vertical angle. This discussion can be extended to
determining horizontal angle as well.
[0103] Referring now to FIGS. 10a and 10b, schematic diagrams of
apparent street light elevational angle as a function of
camera-to-vehicle inclination angle are shown. In FIG. 10a, imaging
system axis 230 is aligned with vehicle forward motion direction
190. Imaging system axis 230 can be thought of as a normal to the
plane of image array sensor 52. Over a sequence of images, street
lamp 222 appears to be approaching imaging system 42. The angle
between street lamp 222 and imaging system axis 230, shown by 232,
increases linearly.
[0104] In FIG. 10b, imaging system 42 is not aimed in the direction
of vehicle forward motion 190. In particular, vehicle forward
motion direction 190 and imaging system axis 230 form inclination
angle 234. Therefore, in a sequence of images, street lamp
elevational angle 232 appears to increase in a non-linear
fashion.
[0105] Referring now to FIG. 11, a schematic diagram illustrating
street lamp elevational angle calculation according to an
embodiment of the present invention is shown. Image array sensor 52
in imaging system 42 is represented as an array of pixels, one of
which is shown by 240. The number of pixels 240 shown in FIG. 11 is
greatly reduced for clarity. Vehicle imaging lens system 48 is
represented by single lens 242. Street lamp 222 is imaged by lens
242 onto image array sensor 52 as street lamp image 244. Street
lamp elevational angle 232, shown as 0, can be calculated by
equation 1: 1 tan ( ) = ( IRN - RRN ) PH FL )
[0106] where RRN (Reference Row Number) is the row number
corresponding to imaging system axis 230, RN (Image Row Number) is
the row number of street lamp image 244, PH is the row height of
each pixel 240, and FL is the focal length of lens 242 relative to
image array sensor 52.
[0107] Referring now to FIG. 12, a graph illustrating street lamp
elevational angles for three different camera-to-vehicle
inclination angles is shown. Curves 250, 252, 254 show the
cotangent of the inclination angle as a function of simulated
distance for street lamp 222 that is five meters high. Images are
taken at 20 meter intervals from 200 to 80 meters as controlled
vehicle 20 approaches street lamp 222. For curve 250, imaging
system axis 230 is aligned with vehicle forward motion direction
190. For curve 252, imaging system axis 230 is 0.5.degree. above
vehicle forward motion direction 190. For curve 254, imaging system
axis 230 is 0.5.degree. below vehicle forward motion direction 190.
Curve 250 forms a straight line whereas curve 252 is concave upward
and curve 254 is concave downward.
[0108] Referring now to FIG. 13, a flow diagram of a method for
calculating camera-to-vehicle inclination angle according to an
embodiment of the present invention is shown. A count of the number
of images taken is reset in block 260. The image count is compared
to the maximum count (max count) required in block 262. The number
of images required should be determined experimentally based on the
type of imaging system 42 used and the configuration of imaging
system 42 in controlled vehicle 22. If the image count is less than
the maximum count, the next image is acquired and the image count
is incremented in block 264.
[0109] A light source is found in the image in block 266. If this
is the first image in a sequence or if no suitable light source has
been previously found, a number of light sources may be marked for
potential consideration. If a light source has been found in a
previous image in the sequence, an attempt is made to find the new
position of that light source. This attempt may be based on
searching pixels in the last known location of the light source
and, if a sequence of positions is known, may be based on
extrapolating from the sequence of light source images to predict
the next location of the light source.
[0110] A check is made to determine if the light source is
stationary in block 268. One check is to determine if the light
source exhibits AC modulation by examining light source intensity
over successive images. Another check is to track the relative
position of the light source in the sequence of images. If the
light source is not stationary, the image count is reset in block
270. If the light source is stationary, an elevational measure is
calculated in block 272. A technique for calculating elevational
angle was described with regards to FIG. 11 above.
[0111] When each image in a sequence of max count images contains a
stationary light source, elevational measurements are validated in
block 274. As indicated with regards to FIG. 12 above, a sequence
of elevational measurements for a stationary light source, when
expressed as the cotangent of the angle as a function of distance,
forms either a straight line, a concave upward curve, or a concave
downward curve. The sequence of elevational measurements is
examined to ensure that the sequence fits one of these patterns. If
not, the sequence is discarded and a new sequence is obtained.
[0112] In an embodiment of the present invention, a check is made
to determine if the sequence of images was acquired during
relatively steady travel at a relatively constant speed. If not,
the sequence is discarded and a new sequence is obtained. Constant
speed can be checked using the output of speed sensor 72. Steady
travel may be checked by examining the relative positions of
stationary and non-stationary light sources over a sequence of
frames.
[0113] The image elevation relative to the vehicle is determined in
block 276. If the sequence of elevational measurements does not
form a straight line, inclination angle 234 may be estimated by
adding a constant value representing the radiant value correction
to each of the tangent values to arrive at a corrected tangent
value. The reciprocals of the new values are taken and analyzed to
determine the difference between successive values. If the
difference is zero, the correction value is the tangent of
inclination angle 234. If the sequence of differences is not zero,
the concavity of the new sequence is determined. If the concavity
direction of the new sequence is the same as the original sequence,
the correction value is increased. If the concavity directions are
opposite, the correction factor is decreased. A new sequence of
differences is then obtained and the process is repeated.
[0114] Referring now to FIG. 14, a cross-sectional drawing of an
imaging system that may be used to implement the present invention
is shown. A similar imaging system is more completely described in
U.S. Pat. No. 6,130,421, entitled "IMAGING SYSTEM FOR VEHICLE
HEADLAMP CONTROL" by Jon H. Bechtel et al., the entire disclosure
of which is hereby incorporated by reference. Imaging system 42
includes housing 280 which holds vehicle imaging lens system 48 and
image array sensor 52. Housing 280 defines aperture 282 which opens
onto a scene generally in front of controlled vehicle 20. Support
284 serves to hold red lens 286 and cyan lens 288 and serves to
prevent light coming through aperture 282 and not passing through a
lens 286, 288 from striking image array sensor 52. As is further
described with regards to FIG. 15 below, image array sensor 52 has
a first region for receiving light transmitted by red lens 286 and
a second, non-overlapping region for receiving light transmitted by
cyan lens 288. Aperture 282, the spacing between lenses 286, 288,
and baffle 290 are designed to minimize the amount of light passing
through one of lens 286, 288 and striking the portion of image
sensor 52 used to image light from the other of lens 286, 288.
[0115] An embodiment of lenses 286, 288 will now be described.
Lenses 286, 288 may be manufactured on a single plate of polymer,
such as acrylic, shown as 292. The polymer may optionally include
infrared filtration, ultraviolet filtration, or both. Each lens
286, 288 is plano-convex with the forward facing surface convex and
aspheric. The front surface of each lens 286, 288 may be described
by equation 2: 2 Z = c r 2 1 + 1 - ( 1 + k ) c 2 r 2
[0116] where Z is the value of the height of the lens surface along
the optical surface as a function of the radial distance r from the
optical axis, c is the curvature, and k is the conic constant. For
the front surface of red lens 286, c equals 0.456 mm.sup.-1 and k
equals -1.0. For the front surface of cyan lens 288, c equals 0.446
mm.sup.-1 and k equals -1.0. Lenses 286, 288 have a diameter of 1.1
mm and have centers spaced 1.2 mm apart. At the center, each lens
286, 288 is 1.0 mm. Plate 292 is mounted to baffle 284 such that
the back of each lens 286, 288 is 4.0 mm in front of image array
sensor 52. This distance is indicated by focal length FL in FIG.
14. Red and cyan filters are printed onto the rear flat surfaces of
red lens 286 and cyan 288, respectively, using screen, pad, or
other printing techniques. The red filter substantially transmits
light of wavelengths longer than 625 nm while attenuating light of
wavelength shorter than 625 nm. The cyan filter substantially
transmits light of wavelength shorter than 625 nm while attenuating
light of wavelength longer than 625 nm. The preferable field of
view afforded by lenses 286 and 288 is 10.degree. high by
20.degree. wide.
[0117] Referring now to FIG. 15, a schematic diagram of image array
sensor subwindows that may be used to implement the present
invention are shown. Image array sensor 52 includes an array of
pixel sensors, one of which is indicated by 240, arranged in rows
and columns. Image array sensor 52 includes top border 302, bottom
border 304, left border 306, and right border 308 defining a region
covered by pixel sensors 240. Image array sensor 52 is divided into
several subwindows. Upper subwindow 310 is bounded by borders 308,
312, 314, and 316, and contains pixel sensors 240 struck by an
image projected through red lens 286. Lower subwindow 318 is
bounded by borders 308, 320, 314, and 322, and includes pixel
sensors 240 onto which an image is projected through cyan lens
288.
[0118] Lenses 286, 288 provide a field of view in front of
controlled vehicle 20 such as, for example, 22.degree. wide by
9.degree. high. A space between border 312 and top edge 302 and
between borders 316 and 324 allow for an elevational adjustment to
correct for misalignment of imaging system 42 in controlled vehicle
20. To accomplish the adjustment, upper subwindow 310, defined by
borders 312 and 316, are moved up or down within the range between
top edge 302 and border 324. Similarly, borders 320 and 322
represent boundaries for lower subwindow 318 that may be moved
between bottom edge 304 and border 326. Pixel sensors 240 that lie
within the region between borders 324 and 326 may receive light
from both red lens 286 and cyan lens 288. Therefore, this region is
not normally used as part of the active imaging area. Although only
elevational adjustment has been described, lateral adjustment is
also possible.
[0119] Pixel sensors 240 lying between left edge 306 and border 314
may be used for ambient light sensing. Ambient light sensing is
described with regards to FIG. 20 below.
[0120] In a preferred embodiment of the present invention, image
array sensor 52 includes a 256.times.256 array of square pixel
sensors 240. In an alternative embodiment, pixel sensor 52 includes
a 256.times.128 square array of rectangular pixels, resulting in a
vertical resolution greater than the horizontal resolution.
[0121] Referring now to FIG. 16, a schematic diagram of an
embodiment of an image array sensor that may be used to implement
the present invention is shown. Pixel sensor 240 and the technique
for correlated double sampling shown are described in U.S. Pat. No.
5,471,515 entitled "ACTIVE PIXEL SENSOR WITH INTRA-PIXEL CHARGE
TRANSFER" to E. Fossum et al., which is hereby incorporated by
reference. The circuitry described can be built using standard CMOS
processes. Devices similar to image array sensor 52 are available
from Photobit Corporation of Pasedena, Calif.
[0122] Image sensor array 52 includes an array of pixels 240. Light
striking photogate transistor 330 in each pixel 240 generates
electrical charge which is accumulated beneath photogate transistor
330. During charge collection, the gate of photogate transistor 330
is held at a positive voltage to create a well beneath photogate
transistor 330 to hold the accumulated charge. The gate of gate
electrode 332 is held at a less positive voltage, V.sub.TX, to form
a barrier to the flow of electrons accumulated beneath photogate
transistor 330. In an embodiment, V.sub.TX is 3.8 volts relative to
VSS. When charge readout is desired, the gate of photogate
transistor 330 is brought to a voltage less than V.sub.TX. The
accumulated charge then flows from photogate transistor 330 through
gate electrode 332 to the region beneath floating diffusion 334.
Floating diffusion 334 is connected to the gate of n-channel FET
336 which has its drain connected to supply voltage VDD. Typically,
VDD is 5.0 volts referenced to VSS. The gate of photogate
transistor 330 is returned to its original voltage. A potential
proportional to the accumulated charge can now be sensed at the
source of FET 336.
[0123] During charge transfer and readout, the gate of reset
electrode 338 is held at a low positive voltage to form a barrier
to electrodes beneath floating diffusion 334. When the gate of
reset electrode 338 is brought to a high positive voltage, charge
collected beneath floating diffusion 334 is transferred through the
region beneath reset electrode 338 and into drain diffusion 340
which is connected to VDD. This brings the source of FET 336 to an
initial or reset potential. By subtracting this reset potential
from the illumination potential proportional to accumulated charge,
a great degree of fixed pattern noise may be eliminated. This
technique is known as correlated double sampling.
[0124] Pixel sensors 240 are arranged in rows and columns. In a
preferred embodiment, all of the pixels in a row of a selected
subwindow are read simultaneously into readout circuits, one of
which is indicated by 342. One readout circuit 342 exists for each
column. The row to be read is selected by a row address, indicated
generally by 344. Row address 344 is fed into row decoder 346
causing the row select line 348 corresponding to row address 344 to
become asserted. When row select line 348 is asserted, n-channel
FET 350 is turned on, allowing the potential at the source of FET
336 to appear on column readout line 352. All pixels 240 in each
column are connected to a common column readout line 352. However,
since each pixel in the column has a unique row address, only one
row select line 348 can be asserted resulting in at most one FET
336 source potential appearing on column readout line 352.
[0125] Two control signals provide the timing for gating charge in
each pixel 240. Photogate signal (PG) 354 is a high asserting
signal indicating when charge is to be transferred from photogate
transistor 330 to floating diffusion 334. Each row has a gate 356
which ANDs PG signal 354 and row select line 348 to produce row PG
signal 358 which is connected to the gate of each photogate
transistor 330 in the row. Row reset signal (RR) 360 is a high
asserting signal indicating when floating diffusions 334 should be
returned to the reset potential. Each row has gate 362 which ANDs
RR signal 360 with the appropriate row select line 348 to produce
reset signal 364 which is connected to the gate of each reset
electrode 338 in the row.
[0126] Voltages at the source of FET 336 are dropped across load
FET 366 when FET 350 is on. Load FET 366 is an n-channel device
with a fixed gate voltage of V.sub.LN. In this embodiment, V.sub.LN
is approximately 1.5 volts referenced to VSS. Each pixel 240 may
contain load FET 366 or, as is shown in FIG. 16, one load FET 366
may be used for each column.
[0127] Readout circuit 342 provides sample-and-hold for potentials
on column readout line 352 as well as output buffering. Two input
signals control each readout circuit 342. Sample-and-hold reset
signal (SHR) 368 turns on n-channel FET 370 allowing the potential
on column readout line 352 to charge capacitor 372. Capacitor 372
is used to store the reset potential. Sample-and-hold illumination
signal (SHS) 374 turns on n-channel FET 376. This permits the
potential on column readout line 352 to charge capacitor 378.
Capacitor 378 is used to hold the illumination potential
proportional to the charge accumulated by photogate transistor
330.
[0128] At the end of a complete readout operation, the reset
potential and illumination potential from each pixel 240 in a
selected row are stored in capacitors 372, 378 in each readout
circuit 342. A column address, shown generally by 380, is input
into decoder 382 asserting corresponding column select line 384.
Each column select line 384 controls an associated readout circuit
342 to determine which readout circuit 342 will be driving common
output lines SIGOUT 386 holding the illumination potential and
RSTOUT 388 holding the reset potential. Buffer 390, with input
connected across capacitor 378 and output connected to SIGOUT 386,
and buffer 392, with input connected across capacitor 372 and
output connected to RSTOUT 388 in each readout circuit 342 are
enabled by the appropriate column select line 384.
[0129] Referring now to FIGS. 17a through 17e, a schematic diagram
of an embodiment of the present invention is shown. Much of the
circuitry shown in FIGS. 17a and 17b is described in U.S. Pat. No.
5,990,469, entitled "CONTROL CIRCUIT FOR IMAGE ARRAY SENSORS," to
Jon H. Bechtel et al., the entire disclosure of which is hereby
incorporated by reference.
[0130] In FIG. 17a, image array sensor 52 is shown as integrated
circuit chip U7. Biasing circuitry 400 is used to set the various
voltage levels, such as V.sub.TX and V.sub.LN, required by image
array sensor 52. Output SIGOUT 386 and RSTOUT 388 are the
illumination potential and reset potential respectively for pixel
240 selected by row address 344 and column address 380. Difference
amplifier 402, such as the AD 830 High Speed, Video Difference
Amplifier by Analog Devices, accepts SIGOUT 386 and RSTOUT 388 and
produces noise-reduced signal 404. ADC 406, such as LTC 1196 by
Linear Technology, accepts noise-reduced signal 404 and produces
digitized signal (ADDATA) 408. The analog-to-digital conversion is
started by asserting conversion signal (CONVST) 410. The converted
value is serially shifted out at a rate determined by the input ADC
clock signal (ADCLK) 412.
[0131] The integrated circuit designated U4 and associated
components regulate the approximately 12-volt car battery output to
a 5-volt VCC supply voltage. The integrated circuit U3 and
associated components produce a conditioned 5-volt supply
signal.
[0132] In FIG. 17b, application specific integrated circuit (ASIC)
414 is shown. ASIC 414 contains much of the logic for controlling
image array sensor 52 and ADC 406 as well as for communicating with
processor 66. In the embodiment shown, ASIC 414 is an XC4003E from
Xylinx. However, it is well known in the art that a wide range of
means are available for implementing the logic in ASIC 414
including discrete logic, custom VLSI integrated circuits, various
FPGAs, programmable signal processors, and microcontrollers. The
logic implemented by ASIC 414 is described with regards to FIG. 18
below. Serial memory 416, such as the AT17C65 by Atmel, is
configured to store and automatically download the code describing
the designed logical operation into ASIC 414 each time power is
first applied. Clock signal 418, labeled OSC, is generated by
processor 66 and drives the sequential logic in ASIC 414.
[0133] ASIC 414 communicates with processor 66 using three lines.
Data is shifted serially between ASIC 414 and processor 66 on
master out slave in (MOSI) 420 at a rate determined by serial
peripheral serial clock (SPSCLK) 422 in a direction determined by
slave select (SSI) 424. When SSI 424 is asserted, processor 66 is
the master and ASIC 414 is the slave. Processor 66 shifts
instruction words into ASIC 414. In this mode, processor 66 drives
SPSCLK 422. During instruction execution, processor 66 deasserts
SSI 424 making ASIC 414 the master and processor 66 the slave. ASIC
414 shifts digitized, noise reduced intensity signals to processor
66. In this mode, ASIC 414 generates SPSCLK 422.
[0134] As technology improves, it is desirable to locate image
array sensor 52, difference amplifier 402, ADC 406, and the logic
implemented in ASIC 414 on a single integrated circuit chip. It may
be possible to include processor 66 on such a chip as well.
[0135] In FIG. 17c, processor 66 and associated electronics are
shown. Processor 66 may be an H8S2128 microcontroller from Hitachi.
Processor 66 generates instructions for ASIC 414 that determine, in
part, which subwindows of image array sensor 52 will be examined.
Processor 66 receives digitized intensities from each pixel 240 in
designated subwindows of image array sensor 62. Processor 66 uses
these intensities to carry out the methods described with regards
to FIGS. 3 through 13 above for controlling continuously variable
headlamps 22. One necessary function is control of the gain for
images acquired using image array sensor 52. As described with
regards to FIG. 4 above, the gain for an image used to detect the
tail lamps of leading vehicles 28 needs to be greater than the gain
for an image used to detect headlamps of oncoming vehicles 26. One
or more of several means are possible for controlling image array
sensor 52 gain. First, the integration time of pixels 240 can be
varied. Second, the reference voltage, VREF, of ADC 406 can be
changed. Third, difference amplifier 402 can have a variable,
controllable gain. Fourth, a variable aperture or a variable
attenuator, such as an electrochromic window, can be placed in the
path of light striking image array sensor 52.
[0136] The types and numbers of control signals required for
headlamps 22 depend on headlamp configuration in controlled vehicle
20. For the embodiment described below, controlled vehicle 20 has
two continuously variable high beam headlamps 22 and two
continuously variable low beam headlamps 22. Each high beam
headlamp 22 can be vertically and horizontally aimed using stepper
motors. The intensity of both high beam headlamps 22 is controlled
by a single PWM signal. The two low beam headlamps 22 are not
steerable but have intensities controlled by a single PWM signal.
It is apparent to one of ordinary skill in the art that the present
invention can control various configurations of continuously
variable headlamps 22.
[0137] Processor 66 includes a first set of control signals, shown
generally by 426, for controlling the aim of the left high beam
headlamp. A similar set of eight control signals, shown generally
by 428, are used to control the aim of the right high beam
headlamp. Labels have been left off right aim control signals 428
for clarity. A description of aim control signals 426, 428 is
provided with regard to FIG. 17e below. Processor 66 also generates
high beam modulated signal 430 which is buffered to become high
beam PWM signal 432. Identical circuitry may be connected to low
beam modulated signal 434. This circuitry has been omitted for
clarity. Headlamp controller 76 using PWM signal 432 is described
with regards to FIG. 17d below.
[0138] In FIG. 17d, headlamp system 46 includes incandescent
headlamp 22 and headlamp intensity controller 76. Headlamp
intensity controller 76 includes a power FET, such as the IRFZ44N
by International Rectifier. The intensity of light emitted by
headlamp 22 is proportional to the duty cycle of PWM signal 432. A
base frequency for PWM signal 432 of 2000 Hz is preferred. Higher
frequencies may increase the power dissipation of the power
FET.
[0139] In FIG. 17e, headlamp system 46 includes headlamp 22 with
variable vertical and horizontal aiming and headlamp controller 76
for providing aiming signals. Headlamp 22 includes vertical stepper
motor 440 for controlling vertical aim direction and horizontal
stepper motor 442 for controlling horizontal aim direction.
Headlamp 22 also includes vertical home switch 444 and horizontal
home switch 446 for indicating when headlamp 22 is in the home
position. Vertical home switch 444 produces vertical home signal
(VSW) 448. Horizontal home switch 446 produces horizontal home
signal (HSW) 450. Vertical motor 440 is driven by motor controller
452, such as the SAA1042 by Motorola. Motor controller 452 has
three inputs. Vertical direction (VDIR) 454 indicates the direction
of rotation of motor 440 for each positive edge on vertical clock
(VCLK) 456. Vertical step (VSTEP) indicates whether motor 440 will
make a full step or a half step for each applied pulse of VCLK 456.
Horizontal motor controller 460 has horizontal direction (HDIR)
462, horizontal clock (HCLK) 464, and horizontal step (HSTEP) 466
which function similar to VDIR 454, VCLK 456, and VSTEP 458 for
vertical motor controller 452.
[0140] In an alternative embodiment using HID headlamps, the
direction of light emitted from one or more headlamps 22 is changed
using MDP. HID headlamps operate by producing a charged arc in a
gas such as xenon. The arc may be perturbed by the presence of a
magnetic field. Reflectors may be designed such that various
perturbations of the arc produce changes in the direction,
intensity, or both of light emitted by HID headlamp 22.
[0141] Aim control signals 426, 428 from processor 66 may be
replaced by analog or digital outputs determining the direction for
aiming the output of HID headlamp 22. Headlamps utilizing MDP are
being developed by Osram Sylvania Inc. of Danvers, Mass.
[0142] Referring now to FIG. 18, a block diagram illustrating
registers and associated logic used to control the image control
sensor is shown. The logic described below is more completely
discussed in U.S. Pat. No. 5,950,469, entitled "CONTROL CIRCUIT FOR
IMAGE ARRAY SENSORS," to Jon H. Bechtel et al., the entire
disclosure of which is hereby incorporated by reference.
[0143] ASIC 414 includes control logic 480 which controls a
collection of registers and associated logic. All but two of the
registers are initially loaded with data from an instruction
serially shifted over MOSI 420 from processor 66. The path used to
initialize the registers, indicated by 482, is shown as a dashed
line in FIG. 18. The purpose for each of the registers and
associated logic will now be described.
[0144] ASIC 414 can specify two subwindows within image array
sensor 52. The first subwindow is specified by low and high column
addresses and low and high row addresses. The second subwindow is
specified as having a column offset and a row offset from the first
subwindow. Hence, the first and second subwindows have the same
size. These two subwindows may be upper subwindow 310 and lower
subwindow 318 described with regard to FIG. 15 above. As described
with regards to FIG. 16 above, readout and reset of each pixel 240
occurs by rows. Alternate rows from each subwindow are obtained.
Each pixel in the selected row of first subwindow is read and then
each pixel in the selected row of the second subwindow is read.
[0145] Five registers are used to specify column address 380.
Second subwindow column offset register (SCO) 484 holds the column
offset between the first subwindow and the second subwindow. Low
column register (LC) 486 holds the starting column value for the
first subwindow. High column register (HC) 488 holds the ending
column value of the first subwindow. Active column register (AC)
490 holds the value of the currently examined column in the first
subwindow. Column select register (CS) 492 holds column address
380. Multiplexer 494 is initially set so that register AC 490 is
loaded with the same column starting value as register LC 486 when
processor 66 shifts an instruction into ASIC 414. During
instruction execution, multiplexer 496 is initially set so that
register CS 492 is loaded with the value of register AC 490.
Register AC 490 is incremented to select each column in the first
subwindow until the content of register AC 490 is greater than the
final column value in register HC 488 as determined by comparator
498. Register AC 490 is then reloaded with the starting column
value from register LC 486 through multiplexer 494. Multiplexer 496
is then set so that register CS 492 is loaded with the sum of
register AC 490 and register SCO 484 produced by adder 499. As
register AC 490 is incremented, register CS 492 then holds
successive column addresses 380 of the second subwindow.
[0146] Row address 344 is specified using six registers. Second
subwindow row offset register (SRO) 500 holds the row offset
between the first subwindow and the second subwindow. Low row
register (LR) 502 holds the starting row address of the first
subwindow. High row register (HR) 504 holds the ending row address
of the first subwindow. RR 506 holds the address of the first
subwindow row for reset. ADC row register (AR) 508 holds the first
subwindow row to be read out for analog-to-digital conversion. Row
select register (RS) 510 holds row address 344. Register RR 506 and
register AR 508 are used to determine the integration time for each
pixel 240. If each row in image array sensor 52 is reset
immediately prior to readout, a very short integration time
results. If each row is reset immediately following readout, a
longer integration period results, the length of which depends on
the number of rows in the first subwindow. An additional means for
further extending integration time is described below. Four rows
must therefore be considered, the reset row of the first subwindow,
the reset row of the second subwindow, the conversion row of the
first subwindow, and the conversion row of the second subwindow.
Multiplexer 512 and multiplexer 514 are first set to pass the
contents of register RR 506 into register RS 510. This makes the
reset row of the first subwindow row address 344. Multiplexers 512,
514 are then set so that register RS 510 is loaded with the sum of
register RR 506 and register SRO 500 produced by adder 516. This
makes row address 344 the reset row of the second subwindow.
Multiplexers 512, 514 are then set to load register RS 510 with the
contents of register AR 508. This makes row address 344 the
conversion row of the first subwindow. Multiplexers 512, 514 are
then set so that register RS 510 is loaded with the sum of register
AR 508 and register SRO 500 produced by adder 516. This makes row
address 344 the conversion row of the second subwindow. Register RR
506 and register AR 508 are then incremented. When the contents of
register RR 506 are greater than the ending row value held in
register HR 504 as determined by comparator 518, register RR 506 is
reloaded with the starting row address of the first subwindow from
register LR 502 through multiplexer 520. When the value held in
register AR 508 is greater than the ending row address in register
HR 504 as determined by comparator 522, register AR 508 is loaded
with the starting address of the first subwindow from register LR
502.
[0147] Two registers allow an integration period greater than the
frame period, which is defined as the time required to convert each
row in the first subwindow. Integration frame delay register (IFD)
524 holds the two's complement of the number of frame periods for
each integration period.
[0148] Integration frame counter register (IFC) 526 is initially
loaded through multiplexer 528 with the value loaded into register
IFD 524 plus one provided by serial incrementer 530. Incrementer
530 has an output indicating overflow. If register IFD 524 is
initialized with negative one, incrementer 530 indicates an
overflow. This overflow signals control logic 480 to perform row
readouts during the next frame period. If an overflow does not
occur from incrementer 530, no row readout is performed during the
next frame period. At the end of each frame period, the contents of
register IFC 526 are passed through incrementer 530 by multiplexer
528 and incrementer 530 overflow is checked again. When overflow
occurs, multiplexer 528 gates the contents of register IFD 524
through incrementer 530 into register IFC 526 and the process is
repeated.
[0149] Reset frame count register (RFC) 532 is initialized with the
two's complement of the number of frames to be read plus one. This
value is used to indicate the number of times in which an
instruction shifted in from processor 66 is to be repeated. At the
end of each frame in which all rows of the first and second
subwindows have been read, the overflow output of incrementer 534
is examined. If an overflow has occurred, the instruction is
completed and no further processing occurs. If no overflow has
occurred, the contents of register RFC 532 are passed through
multiplexer 536 and incremented by incrementer 534.
[0150] Outputs from comparators 498, 518, 522 and incrementers 530,
534 are used by control logic 480 to generate internal control
signals for multiplexers 494, 496, 520, 512, 514, 528, 536 and
incrementers for registers 490, 506, 508 as well as for external
control signals such as PG 354, RR 360, SHS 374, SHR 368, CONVST
410, and ADCLK 412.
[0151] Referring now to FIG. 19, a timing diagram illustrating
image array sensor control signals is shown. The timing diagram is
provided to show timing relationships between signals and not
necessarily precise times between signal events.
[0152] The beginning of the timing diagram in FIG. 19 corresponds
with the start of an instruction execution by ASIC 414. Row address
(ROW) 344 is first set to the starting row of the first subwindow,
as shown by 550. Signals RR 360 and PG 354 are then asserted
dumping any charge that may be beneath photogate 330 in each pixel
240 in row 550, as shown generally by 552. Row address 344 is then
set to the first row of the second subwindow, as shown by 554.
Again, signals RR 360 and PG 354 are asserted, as shown by 556, to
reset all pixels 240 in second subwindow first row 554. Row address
344 is then set to the first subwindow second row, as shown by 558,
and signals RR 360 and PG 354 are asserted as shown by 560. This
process continues by alternately resetting the next row from the
first subwindow then the corresponding row from the second
subwindow.
[0153] At some point in the future, the time arrives to read the
values from each pixel 240 in the first row of the first subwindow.
Row address 344 is again set to first subwindow first row address
550. Signal RR 360 is asserted, as shown by 562, to dump any charge
under floating diffusion 334. Next, signal SHR 564 is asserted to
gate the reset potential for each pixel 240 in first subwindow
first row 550 into capacitor 372 of corresponding column readout
circuit 342. Next, signal PG 354 is asserted, as shown by 566, to
transfer charge accumulated under photogates 330 to floating
diffusions 334. Signal SHS 374 is then asserted, as shown by 568,
to gate the illumination potential for each pixel 240 into
capacitor 378 of corresponding column readout circuit 342.
Integration period 569 is the time between deasserting signal PG
354 during reset 569 and asserting signal PG 354 during readout
566.
[0154] The conversion process for each column in first subwindow
first row 550 can now begin. Column address (COL) 380 is set to
first window first column, as shown by 570. Signal CONVST 410 is
then asserted at 572. This causes ADC 406 to begin conversion. ASIC
414 provides a sequence of clock pulses on ADCLK 412 and receives
the digitized illumination value serially on ADDATA 408. ASIC 414
immediately shifts the data to processor 66 over MOSI 420 as shown
by 574. In the example shown in FIG. 19, each subwindow contains
only four columns. The addresses for first subwindow second column
576, third column 578, and fourth column 580 are successively used
as column address 380, and the conversion process is repeated.
[0155] Row address 344 can then be set to second subwindow first
row 554 and the sequence of assertions for signals RR 360, SHR 368,
PG 354, and SHS 374 repeated to load column readout circuits 342
with reset and illumination potentials. Column address 380 can be
set to second subwindow first column 382 and the conversion
sequence can be repeated.
[0156] Note that, since the conversion process uses reset and
illumination potentials stored in readout circuits 342 and column
address 380 but not row address 344 and that row reset requires row
address 344 but not column address 380 or readout circuits 342, row
reset may be interleaved with the conversion process. This is seen
in FIG. 19 where, following assertion of SHS signal 374 at 568, row
address 344 is set to the first subwindow n.sup.th row address 584
and signals RR 360 and PG 354 are asserted at 586 to reset all
pixels 240 in first subwindow n.sup.th row 584.
[0157] Referring now to FIG. 20, an ambient light sensor that may
be used to implement the present invention is shown. The ambient
light sensor may be incorporated into imaging system 42. The
ambient light sensor is described more fully in U.S. Pat. No.
6,130,421, entitled "IMAGING SYSTEM FOR VEHICLE HEADLAMP CONTROL,"
to Jon H. Bechtel et al., the entire disclosure of which is hereby
incorporated by reference.
[0158] Ambient light lens system 54 includes baffle 600 built onto
the front of housing 280. Baffle 600 is angled at an angle .theta.
of approximately 45.degree. with the horizontal of controlled
vehicle 20. Baffle 600 defines aperture 602 opening towards the
front of controlled vehicle 20. Aperture 602 may be trapezoidal
such that the projection of aperture 602 onto a vertical surface
would form a rectangle on the vertical surface. Lens 604 is mounted
in one side of aperture 602. The width of lens 604 is approximately
the same as the diameter of red lens 286 or cyan lens 288. Lens 604
accepts light rays over a wide elevational range, such as vertical
ray 606 and horizontal ray 608, and directs these rays into an
approximately horizontal direction. Lens 604 is positioned so that
a blurred, inverted image of lens 604 is projected by red lens 286
onto one edge of image array sensor 52 between top border 302 and
border 316 to form red sky image 610. Lens 604 is also positioned
so that a blurred, inverted image of lens 604 is projected by cyan
lens 288 between bottom border 304 and border 320 to form cyan sky
image 612. The active length of lens 604 is made short enough to
permit the entire active length to be projected onto red sky image
610 and cyan sky image 612.
[0159] Red sky image 610 and cyan sky image 612 are examined in
processor 66 to determine an ambient light level. The intensity
values may be averaged to determine ambient light levels. Lens 604
may be designed so that light 56 from different ranges of
elevational angles appears in different regions of lens 604. In
this case, light levels from different ranges of elevational angles
may be weighted higher than from other ranges of elevation angles
when an average is determined. For example, near vertical light may
be weighted highest and near horizontal light may be weighted
lowest. Also, since red sky image 610 and cyan sky image 612 are
correlated, intensities as a function of color may be obtained. For
example, the effective ambient light level may be increased for a
blue sky as compared with a cloudy sky.
[0160] Referring now to FIG. 21, a diagram illustrating mounting of
a moisture sensor that may be used to implement the present
invention is shown. Moisture sensor 74, as well as imaging system
42, may be constructed into mounting bracket 620 of interior
rearview mirror 622. Moisture sensor 74 may be mounted two to three
inches behind windshield 624 of controlled vehicle 20.
[0161] Referring now to FIG. 22, a diagram illustrating operation
of a moisture sensor that may be used to implement the present
invention is shown. Moisture sensor 74 and associated control
system are described in U.S. Pat. No. 5,923,027, entitled "MOISTURE
SENSOR AND WINDSHIELD FOG DETECTOR," by Joseph S. Stam et al.,
which is hereby incorporated by reference.
[0162] Moisture sensor 74 includes image array sensor 630, lens
632, and light source 634. Lens 632 is designed to focus windshield
624 onto image array sensor 630. Moisture sensor 74 operates in two
modes, one for detecting droplets on windshield 624 and one for
detecting fog on windshield 624. The first mode uses the focusing
effect of a droplet of water. When windshield 624 is dry, the scene
appearing on image array sensor 630 will be blurred since the scene
has an effective focal length of infinity and lens 632 is focused
on windshield 624. If droplets of water due to precipitation, such
as rain or snow, are present on windshield 624, portions of the
scene viewed by image array sensor 630 will be more sharply
focused. Since an unfocused scene has less high frequency spatial
components than a sharply focused scene, examining the output of
image array sensor 630 for high spatial frequency components will
provide an indication of droplets on windshield 624. In the second
operating mode, light source 634 shines a beam of light, shown
generally by 636, onto windshield 624. If no fog is present on
windshield 624, beam 636 will pass through windshield 624 and will
not be seen by image array sensor 630. If fog is present on the
interior of window 624, beam 636 will be reflected as interior
light spot 638 which will be detected by image array sensor 630.
Likewise, if fog is on the exterior but not the interior of window
624, beam 636 will be reflected as exterior light spot 640 which
will be seen by image array sensor 630. If light spot 638, 640 is
seen by image array 630, the relative height of light spot 638, 640
in the image can be used to determine whether the fog is on the
interior or exterior of windshield 624.
[0163] Image array sensor 630 may be similar in construction to
image array sensor 52. However, the number of pixels required for
image array sensor 630 is significantly less than for image array
sensor 52. A 64.times.64 array of pixels is considered to be
appropriate for image array sensor 630. The angle of windshield 624
in current passenger cars is about 27.degree.. Such a configuration
may cause raindrops and other moisture to be at different distances
from the image sensor depending on where the moisture is on
windshield 624. To help compensate for this problem, the top of
image array sensor 630 may be angled approximately 10.degree.
toward windshield 624.
[0164] In a preferred embodiment, lens 632 is a single biconvex
lens having a 6 mm diameter, front and rear radius of curvature of
7 mm for each surface, and a center thickness of 2.5 mm. The front
surface of lens 632 may be positioned 62 mm from the outer surface
of windshield 624. Mounting bracket 620 may form a stop of about 5
mm directly in front of lens 632. Image array sensor 630 may be
located about 8.55 mm from the rear surface of lens 632.
[0165] Light source 634 is preferably a light emitting diode (LED).
Light source 634 either emits highly collimated light or, as in the
embodiment shown in FIG. 22, lens 642 is used to focus the light
from light source 634 onto windshield 624. Light source 634 may
emit visible light or, preferably, infrared light so as not to
create a distraction for the driver of the controlled vehicle 20.
Light source 634 may be positioned a few millimeters above lens 632
and angled so that beam 636 strikes windshield 624 in an area
imaged by image array sensor 630.
[0166] The output from image array sensor 630 must be processed in
a manner similar to the output of image array sensor 52. A separate
image array control and ADC, similar to control and ADC 64, and
processor, similar to processor 66, may be provided for this
purpose. Alternately, a separate imaging array control and ADC may
be used with processor 66. A further embodiment is to use the same
control unit 44 for the output of both image array sensor 52 and
moisture sensor 74. Processor 66 would control which image array
sensor 52, 630 was being examined.
[0167] The above description is considered that of the preferred
embodiments only. Modifications of the invention will occur to
those skilled in the art and to those who make or use the
invention. Therefore, it is understood that the embodiments shown
in the drawings and described above are merely for illustrative
purposes and not intended to limit the scope of the invention,
which is defined by the following claims as interpreted according
to the principles of patent law, including the doctrine of
equivalents.
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