U.S. patent application number 12/212811 was filed with the patent office on 2009-09-24 for multifunctional optical sensor comprising a photodetectors matrix coupled to a microlenses matrix.
Invention is credited to Davide Capello, Cosimo Carvignese, Roberto Finizio, Luca Liotti, Nereo Pallaro, Piermario Repetto.
Application Number | 20090236505 12/212811 |
Document ID | / |
Family ID | 35954120 |
Filed Date | 2009-09-24 |
United States Patent
Application |
20090236505 |
Kind Code |
A1 |
Pallaro; Nereo ; et
al. |
September 24, 2009 |
MULTIFUNCTIONAL OPTICAL SENSOR COMPRISING A PHOTODETECTORS MATRIX
COUPLED TO A MICROLENSES MATRIX
Abstract
Multifunctional optical sensor, comprising a matrix of
photodetectors of the CCD or CMOS type, having a sensitive area
divided into sub-areas, each of which, individually or combined
with others, is dedicated to a specific function of monitoring the
scene or measuring environmental parameters. The optical sensor
comprises a matrix of microlenses, each of which is set to focus
the radiation coming from a portion of solid angle on the
associated photodetector or cluster of mutually contiguous
photodetectors. Each function is associated to a single microlens
or to a single subgroup of mutually contiguous microlenses or to
multiple, not mutually contiguous microlenses or to multiple, not
mutually contiguous subgroups of microlenses. The angular
separation between the central directions of the portions of solid
angle subtended by adjacent photodetectors or adjacent clusters of
photodetectors is not constant within the matrix.
Inventors: |
Pallaro; Nereo; (Orbassano
(Torino), IT) ; Capello; Davide; (Orbassano (Torino),
IT) ; Repetto; Piermario; (Orbassano (Torino),
IT) ; Finizio; Roberto; (Orbassano (Torino), IT)
; Carvignese; Cosimo; (Orbassano (Torino), IT) ;
Liotti; Luca; (Orbassano (Torino), IT) |
Correspondence
Address: |
PATTERSON & SHERIDAN, L.L.P.
3040 POST OAK BOULEVARD, SUITE 1500
HOUSTON
TX
77056
US
|
Family ID: |
35954120 |
Appl. No.: |
12/212811 |
Filed: |
September 18, 2008 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11533089 |
Sep 19, 2006 |
7518099 |
|
|
12212811 |
|
|
|
|
Current U.S.
Class: |
250/227.2 |
Current CPC
Class: |
G01J 1/4228 20130101;
H01L 27/14627 20130101; G01J 1/0411 20130101; B60R 2300/108
20130101; H04N 7/181 20130101; B60R 2300/8093 20130101; B60R
2300/305 20130101; B60R 1/00 20130101; G01J 1/0407 20130101; H04N
5/2254 20130101; H04N 5/22541 20180801; G01J 1/4204 20130101; B60R
2300/8053 20130101; H01L 27/14625 20130101 |
Class at
Publication: |
250/227.2 |
International
Class: |
G02B 6/06 20060101
G02B006/06 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 19, 2005 |
EP |
05425654.0 |
Claims
1. A multifunctional optical sensor, comprising a matrix of
photodetectors of the CCD or CMOS type, having a sensitive area
divided into sub-areas, each of which, individually or combined
with others, is dedicated to a specific function of monitoring the
scene observed by the sensor or measuring environmental parameters,
wherein said optical sensor comprising a matrix of microlenses,
each microlens being set to focus radiation coming from a portion
of solid angle field of view on the associated photodetector or
cluster of mutually contiguous photodetectors, each function is
associated to a single microlens or to a single subgroup of
mutually contiguous microlenses or to multiple, not mutually
contiguous microlenses or to not mutually contiguous subgroups of
microlenses, the contiguous photodetectors able to be associated to
a function defining a sub-area, which is a region of interest
(ROI), and the angular separation between the central directions of
the portions of solid angle subtended by adjacent photodetectors or
adjacent clusters of photodetectors is not constant within the
matrix, wherein the not constant angular displacement is provided
by the sensor comprising a matrix of diaphragms being positioned
between the photodetectors matrix and the microlenses matrix, the
distances between the centres of the diaphragms being equal to the
dimensions of the microlenses, and the microlenses being centred on
a respective photodetector or cluster of photodetectors, each
microlens being designed in such a way as to select for each
photodetector or cluster of photodetectors a portion of the solid
angle subtended by each microlens.
2. The optical sensor as claimed in claim 1, wherein said
microlenses are designed with optical solutions of the refractive
kind, with total internal reflection, reflexive or a combination of
the above.
3. A multifunctional optical sensor, comprising a matrix of
photodetectors of the CCD or CMOS type, having a sensitive area
divided into sub-areas, each of which, individually or combined
with others, is dedicated to a specific function of monitoring the
scene observed by the sensor or measuring environmental parameters,
wherein said optical sensor comprising a matrix of microlenses,
each microlens being set to focus radiation coming from a portion
of solid angle field of view on the associated photodetector or
cluster of mutually contiguous photodetectors, each function is
associated to a single microlens or to a single subgroup of
mutually contiguous microlenses or to multiple, not mutually
contiguous microlenses or to not mutually contiguous subgroups of
microlenses, the contiguous photodetectors able to be associated to
a function defining a sub-area, which is a region of interest
(ROI), and the angular separation between the central directions of
the portions of solid angle subtended by adjacent photodetectors or
adjacent clusters of photodetectors is not constant within the
matrix, wherein the not constant angular displacement is provided
by the sensor comprising a matrix of diaphragms being positioned
between the photodetectors matrix and the microlenses matrix, the
distances between the centres of the diaphragms being different
from the dimensions of the microlenses, the microlenses being a
matrix associated to a respective photodetector or group of
photodetectors and related diaphragms, the microobjectives allowing
to vary effective focal length while maintaining the back focal
length and thereby allow for a non-constant separation between the
central directions.
4. A multifunctional optical sensor, comprising a matrix of
photodetectors of the CCD or CMOS type, having a sensitive area
divided into sub-areas, each of which, individually or combined
with others, is dedicated to a specific function of monitoring the
scene observed by the sensor or measuring environmental parameters,
wherein said optical sensor comprising a matrix of microlenses,
each microlens being set to focus radiation coming from a portion
of solid angle field of view on the associated photodetector or
cluster of mutually contiguous photodetectors, each function is
associated to a single microlens or to a single subgroup of
mutually contiguous microlenses or to multiple, not mutually
contiguous microlenses or to not mutually contiguous subgroups of
microlenses, the contiguous photodetectors able to be associated to
a function defining a sub-area, which is a region of interest
(ROI), and the angular separation between the central directions of
the portions of solid angle subtended by adjacent photodetectors or
adjacent clusters of photodetectors is not constant within the
matrix, wherein the not constant angular displacement is provided
by said sensor not comprising a matrix of diaphragms and the matrix
of photodetectors being a high resolution matrix including active
photodetectors and inactive photodetectors, the active
photodetectors defining the central direction of the field of view
subtended by a respective microlens.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of co-pending U.S. patent
application Ser. No. 11/533,089, filed Sep. 19, 2006, which claims
benefit of European patent application serial number 05425654.0,
filed Sep. 19, 2005. Each application is herein incorporated by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a multifunctional optical
sensor, in particular for automotive use, comprising a matrix of
photodetectors of the CCD or CMOS type having a sensitive area
divided into sub-areas, which, individually or combined together,
are designated to specific functions of monitoring the scene or
measuring environmental parameters.
[0004] The scene monitoring functions include monitoring the scene
in front, behind or laterally to the vehicle. The frontal
monitoring detects, for example, the presence of a vehicle coming
from the opposite direction, the presence of a curve or the
movement of the vehicle towards the longitudinal demarcation lines
of the lane. The monitoring behind the vehicle can, for example,
aid parking maneuvers. The lateral monitoring detects, for example,
the vehicles that arrive laterally and that are not visible with
the external rear-view mirror, since they are in the so-called
"blind angle".
[0005] The measurement of environmental parameters comprises, for
example, the measurement of fog, rain, window fogging, illumination
and solar irradiation conditions.
[0006] 2. Description of the Related Art
[0007] The documents EP-A-1 418 089 and EP-A-1 521 226 by the same
Applicant describe multifunctional optical sensors, but refer to
multifunctional integration solutions on matrix of photodetectors
of the CCD or CMOS type by means of single aperture optics or
matrices of lenses positioned in front of the optical window of the
sensor. In the document EP-A-1 521 226, each function is associated
to a single lens (or to multiple lenses positioned on different
matrices) and said lens is associated to a subgroup of
photodetectors.
[0008] FIG. 1 shows a perspective view of an embodiment of the
sensor according to the invention of the document EP-A-1 418 089.
Use of single aperture optics limits the possibility of reducing
the size of the opto-mechanical system as a whole. Moreover, the
complexity of the process for the construction and assembly of the
system does not allow significantly to lower the costs of the
sensor for large volumes.
SUMMARY OF THE INVENTION
[0009] The object of the present invention is to provide an optical
sensor of the type defined above which enables to: [0010] optimise
the partition of the matrix: there is more freedom in defining the
shape (rectangular, trapezoidal, linear) and the co-ordinates of
the sub-areas of the photodetectors matrix associated to each
function, the photodetectors used solely for the separation of the
sub-areas are reduced or eliminated, the entire sensitive area is
used and it is possible to assign different directions and fields
of view to photodetectors belonging to the same sub-area/function
(as will be illustrated farther on); [0011] miniaturise the sensor
from the optics and chip viewpoint: using microlenses matrices, the
typical dimensions of single aperture optical systems are
eliminated, by optimising the partition of the matrix its format is
reduced; high miniaturisation simplifies integration on the
vehicle, enabling to insert the optical sensor in the rear-view
mirrors, near the roof, in the ceiling lamp, etc.; [0012] simplify
image processing: every photodetector or group of photodetectors
has its field of view and direction optimised in such a way as to
achieve a sort of optical "pre-processing"; [0013] reduce costs
thanks to optimised formats of the matrix, low cost microlens
fabrication processes, deposition of interference filters on the
surfaces of the microlens matrices adjacent to the
photodetectors.
[0014] According to the present invention, said object is achieved
by a multifunctional optical sensor having the characteristics set
out in claim 1.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The present invention shall now be described in detail with
reference to the accompanying drawings, provided purely by way of
non limiting example, in which:
[0016] FIG. 1 shows a perspective view of an embodiment of the
sensor according to the invention of the document EP-A-1 418
089;
[0017] FIG. 2 is a schematic view showing the principle of
operation of an optical solution with single aperture;
[0018] FIG. 3 is a schematic view showing the principle of
operation of an optical solution based on microlens matrices;
[0019] FIG. 4 is a schematic view showing the principle of
operation of an optical system based on microlens matrices that
constitutes prior art;
[0020] FIG. 5 is a schematic view showing the principle of
operation of the optical system of the present invention according
to a first embodiment;
[0021] FIG. 6 is a schematic view showing the principle of
operation of the optical system of the present invention according
to a second embodiment;
[0022] FIGS. 7 and 8 are schematic views illustrating the principle
of operation of two variants of the optical system of FIG. 6;
[0023] FIG. 9 is a schematic view showing the principle of
operation of the optical system of the present invention according
to a third embodiment;
[0024] FIG. 10 shows the principle of operation of a microlens
matrix with high resolution, not operating with the aid of
diaphragms;
[0025] FIG. 11 is a schematic view showing the spaces of the
objects and of the images of two optical systems, constituted by a
single aperture optics (FIG. 11a) and by a 2D microlens matrix
(FIG. 11b), said optical systems being coupled to 2D photodetector
matrices with the same format;
[0026] FIG. 12 is a variant of FIG. 11b;
[0027] FIG. 13 is a schematic view showing the spaces of the
objects and of the images of an optical system constituted by a 1D
microlens matrix;
[0028] FIG. 14 is another variant of FIG. 11b;
[0029] FIG. 15 shows an example of an optical sensor with a matrix
of photodetectors with constant dimensions or pitch and microlenses
with different field of view on a road scenario;
[0030] FIG. 16 is an example of application of the optical sensor
of FIG. 15 on a road scenario;
[0031] FIG. 17 is an example of a matrix of subgroups of
photodetectors that frame the same portion of scene or different
portions of scene;
[0032] FIG. 18 is a variant of the use of the diaphragms of FIG. 17
for optical pre-processing functions;
[0033] FIGS. 19 and 20 show two examples of partition in sub-areas
of the sensitive area of the photodetector matrix, previously
described in the document EP-A-1 418 089 by the same Applicant;
[0034] FIG. 21 schematically shows an optical solution for
detecting rain based on a matrix of microlenses with different
focal length;
[0035] FIG. 22 shows an example of light wave guide coupled to the
photodetector matrix to perform the function of monitoring the
occupant of the vehicle;
[0036] FIG. 23 shows an example of partition into sub-areas of the
sensitive area of the photodetector matrix according to a preferred
characteristic of the present invention; and
[0037] FIG. 24 shows the possible positioning on the vehicle of
multifunction sensors for the "blind angle" function according to
the present invention.
DETAILED DESCRIPTION
[0038] The present invention relates to a multifunctional optical
sensor comprising a matrix of photodetectors of the CCD or CMOS
type and a matrix of microlenses, in which each microlens is
coupled to a subgroup (cluster) of photodetectors (pixels) or to a
single photodetector. The microlenses are grouped in subgroups,
each of which, individually or combined with others, is dedicated
to a specific function of monitoring the scene or measuring
environmental parameters.
[0039] The present invention is directed, in particular, to the
application on a motor vehicle of a multifunctional optical sensor
of the type mentioned above, which can be positioned for example:
[0040] in proximity to the windshield, e.g. in the interior
rear-view mirror, to carry out, for example, the following
functions: measurement of environmental illumination or entry into
a gallery, measurement of solar irradiation, detection of the
presence of raindrops on the windshield, detection of conditions of
internal or external fogging of the windshield, detection of the
presence of ice, detection of fog conditions and monitoring the
scene in front of the vehicle (vehicle crossing); additional
functions which can be integrated in addition or alternatively to
the vehicle crossing function are the functions: levelling, curve
or lane detection (for commanding adaptive headlights or for Lane
Warning), night vision (viewing scene in the near-infrared or NIR),
detection of vertical road signs, detection of pedestrians, black
box (storing images relating to frontal monitoring in a circular
memory buffer which can be used in case of accident); [0041] near
the rear window, to carry out the following functions: measurement
of environmental illumination, rain/fogging (internal and
external), ice, fog, rear monitoring (parking); additional
functions which can be integrated in addition or alternatively to
rear monitoring are: blind angle monitoring, levelling, lane
detection, black box; [0042] in the side mirrors to carry out the
functions: measurement of environmental illumination, fog, rear
monitoring (blind angle); additional functions which can be
integrated in addition or alternatively to blind angle monitoring
are: parking, levelling, lane detection, black box; [0043] in the
uprights of the windshield for the functions of: user
identification, occupant monitoring for the air-bag system.
[0044] The optical sensor according to the present invention can
also be used in other applications, such as: road infrastructures,
robotics, domotics, agriculture, etc.
[0045] The present invention shall now be described in detail with
reference to the operating principles of optical systems.
[0046] FIG. 2 shows the single aperture optical solutions whereon
are based the documents EP-A-1 418 089 and EP-A-1 521 226: the lens
8 has a field of view FOV=2arctan(d/2f) where d=nd.sub.pixel is the
total dimension of the photodetector matrix 12, d.sub.pixel is the
dimension or pitch of the photodetector 12 and f is the focal
length of the optical system.
[0047] In general, to reduce the dimensions of the optical system,
and in particular the focal length f by a factor n, microlenses 14
can be used, each coupled to a photodetector 12, with linear
dimension of d/n=d.sub.pixel and focal length f.sub.1=f/n (FIG. 3).
In this case, each of the microlenses 14 has a field of view that
coincides with the global field of view,
FOV.sub.1=FOV=2arctan(d.sub.pixel/2f.sub.1).
[0048] To have a global field of view FOV that is the resultant of
the individual fields of view of each of the microlenses 14 it is
necessary to reduce the size of the active area of the
photodetectors 12 in such a way that their dimensions are
d.sub.pixel/n or equivalently to position diaphragms 18 having
aperture with dimension d.sub.pixel/n in front of the
photodetectors 12.
[0049] If the distance between the centres of the diaphragms 18 is
different from the dimensions of the microlenses 14, as shown in
FIG. 4 which constitutes prior art, in front of the photodetectors
matrix 12 is positioned a matrix of diaphragms 18 such that any
microlens 14 has an IFOV 16 with central direction 20 and a
constant angular separation .alpha.i between the central directions
20 (.alpha.1=.alpha.2=.alpha.3=.alpha.4). The sum of the individual
IFOV 16 determines the global field of view FOV. Each microlens 14
can also be separated from the contiguous microlens by a "baffle"
18' whose function is to prevent the radiation coming from a
contiguous microlens from reaching the non corresponding
photodetector.
[0050] If the angular separation .alpha.i between the central
directions 20 is not to be constant, as contained in claim 1 and
shown in FIG. 5, it is necessary to change the distances between
the centres of the diaphragms. FIG. 5 schematically shows a lateral
view of a portion of an optical sensor 10 which comprises a
photodetectors matrix 12 and a microlenses matrix 14 in which the
distance between the centres of the diaphragms 18 is different from
the distance between the centres of the microlenses 14. Each
microlens 14 is associated to a cluster of photodetectors 12 or to
a single photodetector. In the example of FIG. 5, the microlenses
14 are mutually identical. Each microlens 14 is set to focalise the
radiation coming from a portion of solid angle IFOV 16 on the
cluster of photodetectors 12 or on the single photodetector 12
associated to the microlens 14. FIG. 5 shows a matrix of diaphragms
18 positioned between the photodetectors matrix 12 and the
microlenses matrix 14. The diaphragm matrix 18 enables to select
for each photodetector 12 or cluster of photodetectors 12 the
portion of solid angle IFOV 16.
[0051] A difference with respect to the case of FIG. 4 is that the
angular separation .alpha.i between the central directions 20 of
the portions of solid angle 16 subtended by the microlenses 14 is
not constant. In the example of FIG. 5, the angles between the
central directions 20 are designated .alpha.1, .alpha.2, .alpha.3,
and they are such that .alpha.1.noteq..alpha.2.noteq..alpha.3. The
reason for this is that the distance between the centres of the
diaphragms 18 is not constant. Another difference is that the total
FOV is not the sum of the IFOV 16 and therefore the FOV can be
sub-sampled. To prevent the radiation coming from a contiguous
microlens 14 from reaching the non corresponding photodetector 12,
each microlens 14 can be separated from the contiguous microlens 14
by a "baffle" 18'.
[0052] If the angular separation .alpha.i between the central
directions 20 is not to be constant, but the distance between the
diaphragms 18 is to be equal to the dimensions of the microlenses
14, as shown in FIG. 6, the microlenses must be calculated adding a
prismatic component to the spherical component in order to have
microlenses operating with optical axis not coinciding their axis
of symmetry (off-axis). The IFOV 16 of each microlens will have
such central directions 20 that
.alpha.1.noteq..alpha.2.noteq..alpha.3. As in the case shown in
FIG. 6, the total FOV can be sub-sampled.
[0053] In order to cover a field of view larger than what is
possible with a refractive optical solution as described above,
solutions with microlenses of the kind with total internal
reflection, reflexive solutions and mixed solutions can be
considered. For example, FIG. 7 shows a microlens 22 operating by
total internal reflection associated to refractive off-axis
microlenses 14. FIG. 8 shows an optical sensor with a reflexive
lens 24 associated to refractive off-axis microlenses 14.
[0054] An additional possibility for obtaining a non constant
angular separation .alpha.i between the central directions 20 is to
use a matrix of micro-objectives, as shown in FIG. 9. The
micro-objectives 15 are composed by at least two superposed
micro-objectives. The doublet optical solution allows to vary
effective focal length (e.f.l.) maintaining the back focal length
(b.f.l.) equal for all micro-objectives. In this way, the distance
between the photodetectors matrix 12 and the micro-objectives
matrix 15 is constant (b.f.l.) whilst the possibility of varying
e.f.l. allows to have a non constant separation between the central
directions 20, i.e. .alpha.1.noteq..alpha.2.noteq..alpha.3. In this
case, the IFOV are varied at the same time.
[0055] For the optical systems described above, a possible
alternative to the use of the diaphragms 18 consists of using a
matrix with photo-detectors 12 having smaller size than the
diaphragms 18. Lastly for equal sizes of the sensitive area of the
photodetectors matrix 12 it is possible to have either a high
resolution photodetectors matrix 12, or a photodetectors matrix 12
with larger size and hence smaller resolution. As shown in FIG.
10a, using a low resolution photodetectors matrix 12, a diaphragms
matrix 18 is used to vary the central direction 20 associated to
each microlens 14 (case described in the previous optical
solutions). Instead, using a high resolution photodetectors matrix
12, FIG. 10b, only some photodetectors 12, corresponding to the
central direction 20 of the microlens 14 to be obtained, are
activated, and the others are rendered inactive, with no need to
use a diaphragms matrix 18. The advantages of using a high
resolution matrix consist of eliminating the diaphragms 18 and
being able to reconfigure (also while acquiring the images from the
matrix) the active photodetectors in such a way as to change the
central directions 20 of the fields of view. The disadvantages are
due to the fact that the displacement of the central directions 20
occurs by discrete steps (the minimum pitch is equal to the size of
the photodetector 12) and not continuously as when using the
diaphragms 18, and that to visualise the images requires
pre-processing for addressing the active photodetectors.
[0056] The microlenses of the optical sensor according to the
present invention can be constituted by GRIN (gradient index)
material. On the lower plane of some microlens or of some subgroup
of microlenses can be deposited a selective interferential coating
operating as a filter to transmit only the wavelengths of interest.
For some functions, for example, a NIR (near infrared) LED
illuminator can be used, the related spectral band has to be
selected with respect to the background.
[0057] The photodetectors matrix is in CCD or CMOS technology,
standard or with parallel architecture (pre-processing at the
photodetector level).
[0058] The integration of multiple functions on a photodetectors
matrix coupled to a microlenses matrix according to claim 1 is in
accordance with the following rules: [0059] each function is
associated to a single microlens or to multiple microlenses, not
mutually contiguous, or to a single subgroup of mutually contiguous
microlenses or to multiple, not mutually contiguous subgroups of
microlenses. [0060] each microlens is associated to a single
photodetector or to a subgroup (cluster) of photodetectors; [0061]
the contiguous photodetectors able to be associated to a function
define a sub-area (ROI or Region Of Interest); [0062] some
photodetectors can be used only for separating the sub-areas;
[0063] the angular separation between the central directions of the
fields of view (IFOV) relating to photodetectors or clusters of
adjacent photodetectors is not constant within the matrix.
[0064] The condition whereby the angular separation between the
central directions of the fields of view (IFOV) relating to
adjacent photodetectors or clusters of photodetectors is not
constant within the matrix occurs in the following cases: [0065]
there are adjacent sub-areas dedicated to as many functions in
which the fields of view of the sub-areas are different; [0066] at
least one of the functions integrated on the photodetectors matrix
is associated to a single subgroup of microlenses which subtends a
solid angle FOV, but, thanks to the fact that the central direction
of the field of view IFOV of each individual microlens can be
established independently, contiguous photodetectors or clusters or
photodetectors, associated to the subgroup of microlenses, do not
always have mutually adjacent IFOV (this case will be described and
illustrated more extensively in the subsequent paragraph "Matrix
shape"); [0067] the microlenses of at least one subgroup have
different and mutually contiguous fields of view, in such a way as
to obtain a different resolution inside the global field of view of
said subgroup (this case will be described and illustrated more
extensively in the paragraph "Frontal monitoring"); [0068] the
microlenses of at least one subgroup have equal but not mutually
contiguous fields of view, in such a way as to sample in non
continuous fashion the global field of view of said subgroup of
microlenses and therefore obtain a different resolution inside the
global field of view of said subgroup of microlenses (this case
will be described and illustrated more extensively in the paragraph
"Frontal monitoring");
[0069] The variation in angular separation between the central
directions of the fields of view relating to photodetectors or
clusters of photodetectors can be obtained: [0070] modifying the
distance between the centres of the diaphragms positioned in front
of the photodetector or cluster of photodetectors (FIG. 5); [0071]
modifying the prismatic component in the case of off-axis
microlenses matrices (FIG. 6).
[0072] The variation in the field of view of an individual
microlens can be obtained: [0073] modifying the diameter of the
diaphragms positioned in front of the photodetector or cluster of
photodetectors; [0074] using the solution with micro-objectives
(FIG. 9).
[0075] Based on the above rules, additional innovative elements can
be identified, which will be described individually hereafter,
relating to:
[0076] 1. matrix shape;
[0077] 2. frontal monitoring;
[0078] 3. zoom;
[0079] 4. optical pre-processing;
[0080] 5. matrix partition.
Matrix Shape
[0081] FIG. 11 is a schematic view showing the object and image
planes of two optical systems, the first one constituted by a
single aperture optics 8 (FIG. 11a) and the second one constituted
by a 2D matrix of microlenses 14 (FIG. 11b), said optical systems
being coupled to matrices 2D of photodetectors 12, said matrices
having the same format m.times.n.
[0082] In FIG. 11a the photodetectors 12 subtend the IFOV according
to the laws of geometric optics applied to the lens 8: adjacent
portions of the plane of the objects are subtended in the image
plane by mutually contiguous photodetectors 12.
[0083] In FIG. 11b, which constitutes prior art like the previous
FIG. 11a, the single aperture lens is replaced by a microlenses
matrix 14 and the previous considerations continues to apply:
adjacent portions of the object plane are subtended in the image
plane by mutually contiguous photodetectors 12.
[0084] However, the central direction 20 of the field of view IFOV
of each individual microlens 14 can be established independently.
Therefore in FIG. 12 the microlenses 14 are so positioned that the
previous rule no longer applies and thus the angular separation
between the central directions 20 of the fields of view relating to
adjacent photodetectors is not constant within the matrix. However,
in this case a pre-processing for addressing the photodetectors is
necessary in order to visualise the images.
[0085] The previous example can be considered as a generalisation
of particular cases, two of which are illustrated below.
[0086] A 2D matrix of m.times.n photodetectors 12 having a single
aperture lens 8 with field of view of x horizontal degrees and y
vertical degrees (FIG. 11a) can be redesigned as a 1D linear matrix
of m.times.n photodetectors 12, in such a way that each microlens
14 associated to the corresponding photodetector 12 has a field of
view of x/m horizontal degrees and y/n vertical degrees with
central direction 20 such as to cover a portion of the global field
of view of x horizontal degrees and y vertical degrees (FIG.
13).
[0087] This can be useful, for example, when it is necessary to
perform the 2D monitoring of a scene and the surface available for
integrating the sensor is sufficient only for a 1D linear matrix of
m.times.n photodetectors and not for a 2D matrix of m.times.n
photodetectors.
[0088] The fact that the central direction 20 of the field of view
IFOV of each individual microlens 14 can be established
independently, can be used also to optimise the partition of the
photodetectors matrix into sub-areas dedicated to specific
functions and in particular to exploit the entire sensitive area of
the matrix.
[0089] FIG. 14 shows, by way of example, the case in which there is
a need to view a portion of scene with a field of view of x
horizontal degrees and y vertical degrees, where x=y, and the
sub-area available on the sensor 10, constituted by a matrix 2D of
photodetectors 12, is rectangular: if the same resolution has to be
maintained along the two axes x and y of the object plane, and
therefore the same field of view has to be maintained for each
microlens 12, the microlenses can be positioned on the rectangular
sub-area as shown in FIG. 14.
Frontal Monitoring
[0090] The format of the TV camera, used in systems with single
aperture lens for monitoring the scene in front of the vehicle,
depends mainly on two parameters: field of view FOV and resolution
R needed in the areas of the scene in which some objects have to be
discriminated with higher precision (e.g., horizontal signs on the
road surface). This means that in the other areas of the scene in
which there are no objects of interest the previous resolution R is
wholly redundant.
[0091] For most of the frontal monitoring functions, the format of
the camera must be at least CIF (320.times.256 pixels) or VGA
(640.times.480 pixels).
[0092] These formats are not compatible with the optical solutions
based on micro-optics matrices proposed above, where the size of
the photodetector is in the order of tens of microns, i.e. far
larger than that of the photodetectors (less than 10 microns) of
the standard matrices used today for consumer or automotive
applications. The use of photodetectors, with dimensions in the
order of tens of microns, combined with high resolution means
excessively expanding the total area of the chip and consequently
raising fabrication costs.
[0093] In the case of optical solutions based on micro-optics
matrices, it is necessary to design the subgroup of microlenses,
dedicated to the frontal monitoring function, so that the fields of
view IFOV of the individual photodetectors (or clusters of
photodetectors), mutually contiguous, are not kept constant for the
whole field of view FOV of the microlenses subgroup, but they are
defined on the basis of the resolutions actually required in the
different areas of the scene as shown in FIG. 15. Consequently, the
angular separation between the central directions of the fields of
view IFOV of the individual mutually contiguous photodetectors (or
clusters of photodetectors) is not constant.
[0094] This approach enables to define a higher resolution in the
point of escape of the images relative to that of the peripheral
area, as shown in FIG. 16. Proceeding from the point of escape
towards the outer edges of the matrix, both the field of view IFOV
of the individual photodetectors (or of the photodetectors
clusters) and the angular separation between the central direction
of the IFOV increase, or else only the angular separation between
the central directions of the IFOV increases, whilst the IFOV are
instead maintained constant, in order to sample non continuously
the portion of the scene that requires a lower resolution.
Zoom
[0095] The frontal scene monitoring functions are manifold (vehicle
crossing, Lane Warning, curve detection, vertical signs detection,
pedestrian monitoring, etc.).
[0096] To integrate all these functions on a same photodetectors
matrix, coupled with a single aperture lens, it is first of all
necessary to evaluate the functional specifications in terms of
field of view, minimum and maximum range, resolution of a reference
obstacle at the maximum distance. Combining these specifications
enables to define the format of the matrix, which will obviously be
sufficient for some functions and redundant for others. With this
approach, the format of the camera will definitely be greater than
VGA.
[0097] An alternative that reduces the format of the TV camera
entails the use of an optical zoom. However, the size and
complexity of an optical zoom make it difficult to integrate it
with other optical systems dedicated to the environmental
parameters measuring functions (note the complexity of the optical
sensor shown in FIG. 1, according to the invention of the document
EP-A-1 418 089). Moreover, the optical zoom increase the
fabrication costs of the sensor.
[0098] If a matrix of microlenses is used instead of single
aperture optical systems, the sub-area dedicated to frontal scene
monitoring can be optimised, increasing resolution in the areas
where details need to be discriminated (horizontal signs, obstacle
recognition, etc.) and reducing it in the areas where the necessary
information is more qualitative (road edges, horizon, etc.). This
is equivalent to processing the images with the optimal resolution,
as is made possible by an optical zoom.
[0099] The solutions for varying resolutions have already been
discussed in the previous paragraph "Frontal monitoring".
Optical Pre-Processing
[0100] The ability to design the microlenses matrix defining the
direction and amplitude of the field of view for each of them
allows to simplify image processing.
[0101] A possible optical pre-processing function consists of
applying optical filters in order to pre-transform the image for
subsequent processing. With a single aperture optics, a high
resolution is required even in non significant areas in order to
have sufficient resolution to identify some areas of the images.
Instead, using different fields of view for each microlens or
subgroups of microlenses, it is possible to define the sub-areas of
the matrix with appropriate resolution and field of view, in order
to simplify the image processing operation.
[0102] With reference to FIG. 17, an additional possibility
consists of defining on the sensitive area of the matrix k groups
of j photodetectors, each able to create (by means of a single
microlens or a matrix of j microlenses) the image of the same
portion of scene or of different portions of scene. On each group
of j photodetectors are positioned diaphragms with different
shapes. When a group of photodetectors frames a portion of scene
that matches the shape of the diaphragm, the signal is the highest.
This approach can be used, for example, for the Lane Warning
function, as shown in FIG. 17, in which there are k/2 groups of j
photodetectors which view the left part of the road scenario (type
1 region of interest) and k/2 groups of j photodetectors which view
the right part of the road scenario (type 2 region of
interest).
[0103] The example shown in FIG. 12 can now be analysed from a
different viewpoint. As explained above, the microlenses 14 are so
positioned that adjacent portions of the object plane are not
subtended, in the image plane, by mutually contiguous
photodetectors 12 and, therefore, the angular separation between
the central directions 20 of the fields of view relating to
adjacent photodetectors 12 is not constant within the matrix. Based
on this general example, it is possible to design k subgroups of
microlenses with such field of view as to view k portions of the
scene which exactly match the shape of the diaphragms of FIG. 17,
to select k positions of the horizontal demarcation lines. Said k
subgroups of microlenses, however, are positioned horizontally on
the photodetectors matrix: the first subgroup starting from the top
left corner of the matrix and proceeding rightwards, the second one
starting from the end of the first subgroup and proceeding
rightwards and so on; reaching the right edge of the matrix, the
subsequent line is started.
[0104] FIG. 18a shows the enlargement of both the subgroup of
photodetectors relating to an ROI and of the photodetectors
actually exposed to the radiation that passes through diaphragm.
FIG. 18b shows the positioning of the k.sup.th subgroup of
microlenses as described above.
[0105] The advantages of this solution are: the removal of the
diaphragms of FIG. 17, the use of a matrix with smaller format, the
elimination of any form of pre-processing for addressing the
photodetectors, mentioned in the example of FIG. 12.
Matrix Partition
[0106] The partition of the sensitive area of the photodetectors
matrix can have different configurations according to the number
and type of integrated functions.
[0107] FIG. 19 shows, by way of example, a first possible partition
of the sensitive area of the photodetectors matrix, already
mentioned in the document EP-A-1 418 089 by the same Applicant. The
same functions can be integrated differently according to the
inventive elements of the present patent application.
[0108] The so-called "twilight" function is performed by a sub-area
of the matrix that has to measure environmental illumination. The
number of photodetectors dedicated to this function can even be
reduced to just one and there are no constraints in terms of
positioning on the sensitive area of the matrix. According to a
preferred characteristic, a central photodetector (or a few
photodetectors) is surrounded (are surrounded) by eight or more
photodetectors that have different fields of view, the central
one(s) larger and the lateral ones smaller, in order to have
information both about the intensity of environmental lighting
(central photodetector(s)) and about the intensity and direction of
solar irradiation (lateral photodetectors). The information about
environmental illumination enables automatically to turn on/off the
headlights of the vehicles in conditions of poor illumination. The
information on the direction of the solar illumination enables to
optimise the air conditioning system of the vehicle, e.g. for
activating and regulating the air flows of multi-zone air
conditioning systems. According to an additional preferred
characteristic, some photodetectors are oriented towards the
dashboard of the vehicle to measure the radiation directed thereon
(diffused radiation on the photodetectors). The photodetectors
dedicated to the illumination and solar irradiation function can be
positioned separately from each other, i.e. in non contiguous
positions.
[0109] With regard to the fog detection function (based on active
technique), the number of photodetectors can even be reduced to
just one and there are no constraints in terms of positioning on
the sensitive area of the matrix.
[0110] For the tunnel function, the number of photodetectors can
even be reduced to just one and there are no constraints in terms
of positioning on the sensitive area of the matrix. According to a
preferred characteristic, a photodetector (a few photodetectors)
has (have) a frontal field of view of about 20.degree. and a second
photodetector (a few photodetectors) a smaller field of view, e.g.
about 10.degree..
[0111] The sub-area of the sensitive matrix marked with "frontal
monitoring" performs the so-called "Lane Warning" function.
Preferably, the area of interest (i.e. the area that is used
effectively for image processing) is a trapezoid and therefore the
number of photodetectors dedicated to this function is reduced from
the one described in the document EP-A-1 418 089 by the same
Applicant. Preferably, the field of view of the photodetectors are
smaller (higher resolution) in the areas of the images in which the
lane demarcation lines could be located. This enables to reduce the
number of photodetectors dedicated to this functions.
[0112] The area called "frontal monitoring", alternatively or in
addition to the "Lane Warning" function, can be dedicated to the
vehicle crossing detection function. According to a preferred
characteristic, the area of interest (i.e. the area that is used
effectively for image processing) is a trapezoid and therefore the
number of photodetectors dedicated to this function is reduced from
the one described in the document EP-A-1 418 089 by the same
Applicant. The fields of view of the photodetectors are smaller
(higher resolution) in the areas of the image where the potential
indicators of the presence of headlights of a crossed vehicle or of
taillights of a vehicle that precedes the reference vehicle (the
one whereon the sensor is mounted) could be located. According to a
preferred characteristic, two subgroups of photodetectors are
provided to perform this function: the photodetectors of the first
subgroup have fields of view that assure long range monitoring of
the scene to detect vehicles that arrive from the opposite lane,
and the photodetectors of the second subgroup have fields of view
that assure short range monitoring of the scene to detect the
vehicles that precede the reference vehicle.
[0113] According to a preferred characteristic, a set of
photodetectors positioned in the unused areas of the sub-area for
the frontal monitoring function can be dedicated to lateral
monitoring i.e. to the detection of the presence of a curve for
commanding the adaptive headlights of the vehicle.
[0114] The portion of sensitive area called "frontal monitoring"
can serve a combination of multiple functions, e.g. Lane Warning,
vehicle crossing, curve detection, etc. The sub-area dedicated to
such functions is preferably constituted by photodetectors whose
microlenses have optimised directions and fields of view: high
resolution only in the areas where the objects of interest for the
processing algorithms could be located, low resolution in non
interesting areas (e.g. the horizon). The result is comparable to
the one that would be obtained with an optical zoom.
[0115] FIG. 20 shows a second example of partition of the sensitive
area of the photodetectors matrix, already described in the
document EP-A-1 418 089 by the same Applicant. The same functions
can be integrated according to the inventive elements of the
present patent application.
[0116] For the rain/fogging function, there are no constraints in
terms of positioning on the sensitive area of the matrix. In the
solution described in the document EP-A-1 418 089, in order to have
the rain drops on a same image plane, the optical axis had to be
perpendicular to the windshield. According to the present
invention, the use of microlenses allows to maintain the optical
axis of the microlenses matrix parallel to the road plane. It is
possible to compensate for the different distance between the
photodetectors matrix and the windshield whereon the rain drops lie
by designing microlenses with different focal length, as shown in
the schematic representation of FIG. 21. In this figure, the
windshield of the vehicle is designated by the number 30. The
number 32 schematically indicates water drops deposited on the
outer surface of the windshield. The references 14', 14'', 14'''
designate microlenses with different focal length positioned in
such a way that the respective focalisation points fall on the
plane of the photodetectors independently of the different distance
of the microlenses relative to the windshield.
[0117] With reference to FIG. 22, the number 36 designates device
able to perform the function of monitoring the vehicle occupant.
The photodetectors matrix, designated by the reference 38, is
oriented towards the front of the vehicle. Some photodetectors 40,
e.g. positioned in the bottom left and right corner of the matrix
38, are used to determine the position of the driver and the
presence, type and position of the passenger. Since this function
does not require optics capable of creating the image of the entire
vehicle but only of monitoring and discriminating the presence of
passengers, a number of photodetectors equal, for example, to 9 is
indicated. Since the interior of the vehicle is positioned to the
rear of the active side of the photodetectors matrix 38, to view
the scene an optical system 42 is used, able to receive the image
positioned to the rear of the photodetectors matrix. For instance,
the optical system 42 can be a wave guide element as shown in FIG.
22. Alternatively, the optical system 42 can comprise prismatic
elements (not shown). The field of view of the optical system is
designated by the reference number 44.
[0118] FIG. 23 shows an additional possibility of partition of the
useful surface of the photodetectors matrix. This partition enables
to integrate a higher number of functions on a matrix with a
reduced format (e.g., CIF).
[0119] FIG. 24 shows the possible arrangement of sensors 10
according to the present invention for performing the function of
viewing the blind angle. According to a preferred characteristic of
the invention, to perform this function each sensor 10 can have two
different fields of view to cover different directions and
distances, so that the arriving vehicle crosses the two beams at
different times, generating a stepped signal that can be used to
signal the danger.
* * * * *