Object detection system

The present invention provides for a detection system for detecting an object, comprising optical elements including a radiation source of an electromagnetic nature and at least one detector detecting radiation reflected off the object from the radiation source. The system is configured so that trigonometric relationships are established between all or selected of the optical elements and the object. Using the angle of radiation from the radiation source and the angle of reflection into the detector, the system determines the range or distance, and/or velocity of the object relative to the system. While the use of one detector is sufficient to provide an angle measurement for the system to determine the object range and/or velocity, an additional detector may be used to increase accuracy and flexibility. The detectors of the system may have be normal-looking, or side-looking detectors, either of which detects intensity variations. Each detector uses a mask and a baffle in accordance with the concept of constructive occlusion, which improves the response characteristics of the detector. The mask occupies a predetermined position within the detector to enable the detector to provide a tailored response profile. The baffle is configured within the detector to partition a diffusely-reflective cavity within the detector. An LED array or a scanning light assembly may be used with the system as the radiation source.

BACKGROUND OF THE INVENTION 
The present invention relates generally to systems that determine an 
object's range and/or velocity, in particular, a system with optical 
elements having distinct radiation and detection properties for 
determining an object's relative distance or range, and/or velocity to the 
system. 
There are many uses for object detection systems. To improve building or 
vehicle security, object detection systems may be used to detect 
approaching thieves or vandals. To improve personal security, object 
detection systems may be used to detect the range of an assailant within 
which personal security devices may be deployed. In particular, aerosol 
repellents, such as the now widely-available "pepper sprays," or 
electronic debilitating devices, often prescribe an optimum range for 
effective use. Beyond the field of surveillance and security, object 
detecting systems may also improve levels of performance, productivity 
and/or safety in various industrial environments where collisions between 
objects and/or people are to be avoided. The risk of accidents or injury 
in the transport of heavy loads or even the parking of an automobile may 
be substantially reduced with the use of object detection systems. 
Conventional object detection systems or devices, in particular, those 
using optics, use lateral effects diodes. These diodes are typically 
expensive and have relatively poor performance levels. 
It should therefore be appreciated that there exists a definite need for a 
relatively simple and inexpensive object detection system, which can 
determine a distance or a range of an object with flexible operating 
parameters. It is also desired that the system be operative on the 
detected object within a minimum range, even substantially up to the point 
of contact between the object and the optical elements of the system, and 
that such optical elements of the system be relatively small in size, for 
example, on the order of an inch, or fractions thereof. It is further 
desired that the system be capable of detecting the velocity of a moving 
object and be relatively free from interference due to environmental 
impurities such as dirt or dust. The present invention addresses all of 
these desires and more. 
SUMMARY OF THE INVENTION 
The present invention resides generally in an optical detection system that 
detects the range or distance, and/or velocity of objects relative to the 
system. 
The present invention provides for a system having a plurality of optical 
elements, including a radiation source and at least one detector. The 
radiation source may emit radiation that is electromagnetic in nature and 
if so, preferably near the infrared spectrum. The detector is responsive 
to the radiation that is emitted from the radiation source and reflected 
off the object. 
The system is configured such that trigonometric relationships may be 
established between all or selected optical elements and the object whose 
distance or range to the system is to be determined. Applying the 
trigonometric relationships in conjunction with known physical parameters 
of the optical elements of the system, the system determines the range 
and/or velocity of the object. 
In one embodiment, the radiation source and the detector are aligned along 
a base line whose perpendicular distance to the object is defined as the 
range of the object. The radiation source and the detector are separated 
by a known distance along the base line and the system is enabled to 
determine the range of the object. In this embodiment, the system is 
configured such that the radiation source, the detector and the object are 
situated at three remote locations representing vertices of a triangle. By 
determining various angles between the optical elements and the object, 
the range of the object is derived. 
While the use of one detector and one radiation source is sufficient for 
determining the range and/or velocity of the object, another embodiment of 
the invention may also include an additional detector to improve 
flexibility and accuracy. Additional trigonometric relationships are 
established where the system is configured with the additional detector 
also lying on the base line, but opposing the first detector such that the 
radiation source is substantially situated between the two detectors. The 
system is configured such that the two detectors and the object are 
situated at three remote locations representing vertices of a triangle. 
The two detectors may but need not be at equal separation from the 
radiation source. With a known separation of the additional detector from 
the radiation source, and/or from the first detector, the system derives 
the range and/or velocity of the object with improved accuracy and 
flexibility. 
Processing electronics are provided in the system to process signals from 
the detectors and/or the radiation source representing respectively the 
angle of reflection and/or the angle of radiation, to determine the range. 
With additional processing, the velocity at which the object may move 
relative to the detection system may also be determined. 
Each detector of the system uses a mask and a baffle in accordance with the 
concept of constructive occlusion which improves the response 
characteristics of the detector. The mask occupies a predetermined 
position relative to the detector to enable the detector to provide a 
tailored response profile. The baffle is configured relative to the 
detector to partition a diffusely-reflective cavity within the detector, 
that receives the reflected radiation detected by the detector. 
The detector may be configured as a normal-looking detector detecting the 
direction at which the radiation enters the detector in terms of elevation 
angles and/or azimuthal angles. Alternatively, the detector may be 
configured as a side-looking detector detecting the direction at which the 
radiation enters the detector in terms of azimuth angles. The processing 
electronics is configured according to the type of detector used, which 
may include the use of a look-up table. When used in pairs, the detectors 
of the pair may be both normal-looking, both side-looking, or a one of 
each type. 
Other features and advantages of the present invention should become 
apparent from the following description of the preferred embodiments, 
taken in conjunction with the accompanying drawings, which illustrate, by 
way of example, the principles of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As shown in the exemplary drawings, the present invention resides in an 
optical object detection system 10 that determines a range or distance, 
and/or velocity of an object, without requiring complicated electrical 
wiring, expensive photodetector arrays, video cameras, or image 
processing. More specifically, the system measures properties of 
electromagnetic radiation, such as radiation intensity and/or frequency, 
to provide at least an angle from which a range and/or a velocity of the 
object may be determined by the system through the principles of 
trigonometry. 
The detection system 10 in one embodiment as shown in FIG. 1, has a 
plurality of optical elements, including a radiation source S and a 
detector D that are affixed to a mounting bracket 12. The radiation source 
S emits radiation toward an object O which in turn reflects the radiation 
toward the detector D. The radiation emitted by the radiation source S may 
be electromagnetic in nature. In that regard, the radiation source S may 
be an infrared light emitting diode, although it is understood by one of 
ordinary skill in the art that the radiation source may also be a visible 
light source, though it is not limited to either. 
The radiation source S and the detector D are situated along a base line L 
defined by the length of the mounting bracket 12 and are separated by a 
known distance T. The object O is located at a position as shown in a 
solid line, at a distance or range R.sub.a from the base line L and it 
defines an angle of radiation .alpha..sub.a with the radiation source S, 
and an angle of reflection .beta..sub.a with the detector D. The detector 
D determines the angle of reflection .beta..sub.a that is used by the 
system to determine the range R of the object O. 
It can be seen that the system is configured such that the object O and the 
optical elements S and D are at three remote locations that may represent 
vertices of a triangle .DELTA.OSD. In this configuration, the system 
determines the angles .alpha..sub.a and/or .beta..sub.a in the manner 
described hereinbelow, to determine the range R.sub.a that is the direct 
or perpendicular distance substantially between the object O and base line 
L. 
Where the object O is instead located at another position as shown in a 
broken line, the detector D determines a range R.sub.b, with a 
determination of an angle of radiation .alpha..sub.b and an angle of 
reflection .beta..sub.b of the triangle .DELTA.OSD, though it is 
understood by one of ordinary skill in the art that the sign of the angle 
of radiation is to be properly defined within a predetermined coordinate 
system to reflect the object's position relative to the boresight B. 
Accordingly, regardless of whether the object O is to one side or the other 
of the boresight B, the system 10 comprising the optical elements S and D 
determines the range of the object from the system. However, to improve 
accuracy and flexibility, the system 10 may include an additional detector 
D'. The system 10 is configured such that the detector D' is aligned with 
the detector D on the base line B. The system may be configured such that 
the detector D' opposes the detector D from across the radiation source S, 
or opposes the radiation source S from across the detector D. The system 
10 is illustrated in FIG. 1 in the former configuration. 
With a known separation T', which may but not need not be equal to the 
separation T, or a known total separation T", the additional detector D' 
provides an additional reflection angle in the manner described above for 
the detector D, that is used by the system for detecting the object O. 
Accordingly, the system is configured such that the two detectors D and D' 
and the object O are at three remote locations representing the vertices 
of a triangle .DELTA.ODD'. 
The angles of reflection are determined by the system using intensity 
variations in the reflected radiation detected within each of the 
detectors D and D'. Signals representing the intensity variations within 
each detector are processed by a processor or an electronics unit E and 
representations of the range and/or velocity of the object O may be 
displayed on a display, such as an oscilloscope 14. An acoustic or 
sound-emitting device 16, such as a horn or a beeper, responsive to the 
electronics unit E may be included with the system 10, to provide audible 
signals representative of the range and/or velocity of the object O. 
Referring to FIGS. 2A, 2B and 2C, an exemplary detector Dex is shown, 
having a mask 18, a baffle 20 and a cavity 22. A base 24 is provided 
within which the cavity 22 is formed. The cavity 22 may be any shape, 
including cylindrical or hemispherical as illustrated and defines an 
aperture 26, serving as a detection surface, that is surrounded by a 
shoulder 21 at the top plane of the base 24. Where the aperture 26 is 
circular, the mask 18 is disk-shaped. In accordance with the concept of 
constructive occlusion, the mask 18 is of a predetermined size and shape, 
and is positioned a predetermined distance from the aperture 26. The mask 
18 is thus within the hemispherical area which the cavity 52 faces. The 
mask 18, which need not be completely opaque so long as it provides a 
reduction in transmissivity, constructively occludes the aperture 24 to 
provide a predetermined acceptance ratio between the mask 18 and the 
aperture 26. Accordingly, the mask 18 may be configured such that the area 
of the cavity 22 exposed to the radiation is substantially constant and 
independent of the angle of radiation or incidence. It is noted that the 
term angle of radiation and angle of incidence are used interchangeably. 
In either instance, the angle addressed is the angle at which the 
reflected radiation enters the detector, relative to the detector. 
In most instances, the mask 18 enables the detector Dex to have a 
substantially uniform response for most angles of elevation .THETA., i.e., 
from the normal down to approximately 10-20 degrees from the horizon 
relative to the detector. For angles of .THETA. near the horizon of the 
field of view of the detector D.sub.ex, the baffle 20 enables the detector 
D to have substantially uniform response for those angles. 
The mask 18, the baffle 20, and the base 24 with the cavity 22 may all be 
formed of a suitable diffusely reflective material such as 
Spectralon.RTM.. Spectralon.RTM. is a highly reflective polymeric block 
material manufactured and sold by Labsphere Inc. of North Sutton, N.H. 
Spectralon.RTM. is easily machined, durable, and provides a highly 
efficient Lambertian surface having a reflectivity of over 99% in the 
visible or near-infrared wavelengths. A Lambertian reflective surface 
reflects light with a substantially uniform intensity in all directions. 
Alternatively, the mask 18, the baffle 20, and the base 24 with the cavity 
22 may be constructed of a block material, such as aluminum or plastic, 
and coated with diffuse reflective material, such as barium sulfate. The 
detector D.sub.ex includes a protective dome 30 allowing the transmission 
of radiation, to protect the various components of the detector D.sub.ex. 
Within the detector D.sub.ex, the baffle 20 occupies a volume V 
substantially between the bottom of the cavity 22 and the underside of the 
mask 18. The baffle 20 is configured as intersecting members 32 that 
partition the volume V into sections 36 that may be symmetrical. In one 
embodiment, there are two intersecting planar members 32a and 32b that 
partition the volume V into four symmetric sections or quadrants Qa, Qb, 
Qc and Qd. 
A quadrant detector is disclosed in U.S. patent application Ser. No. 
08/589,104, filed Jan. 23, 1996, entitled QUADRANT LIGHT DETECTOR now U.S. 
Pat. No. 5,705,804. The disclosure thereof is hereby incorporated by 
reference in its entirety. 
In accordance with a feature of the invention, radiation from the radiation 
source is reflected off the object and captured by one or both detectors. 
In particular, the four sections or quadrants Q capture the reflected 
radiation whereby the captured radiation intensity within a given quadrant 
depends on the elevation angle of incident of the incoming radiation, as 
well as the incoming radiation's overall intensity at any time. A 
significant function of the cavity 22 is to provide a diffusely reflective 
surface that averages the incoming radiation at the aperture 26 and the 
hemispheric shape is often preferred because of its azimuthal symmetry and 
ease of construction. As mentioned, other cavity shapes are acceptable. 
For purposes of describing the detector's operation, a working 
approximation is obtained by treating the cavity 22 as if it ere a 
diffusely reflective flat surface that averages the incident radiation in 
the plane of the aperture 26. 
As also shown in FIGS. 2A-2C, localized sensors, such as photodetectors, 
e.g., photodiodes, 40a, 40b, 40c, and 40d are provided in each of the 
detectors D1 and D2 of FIG. 1. In particular, each of the photodetectors 
40a-40d are associated with a distinct quadrant. Each photodiode generates 
an electrical signal based on the radiation intensity in the respective 
quadrant of the cavity. The photodiodes are commercially available and 
sold by United Detector Technologies (UDT) Sensors, Inc. of Hawthorne, 
Calif., as Model PIN-040A. Each photodiode has a responsive area of 0.8 
square millimeters and a noise equivalent power (NEP) of 
6.times.10.sup.-15 Watts/(Hertz).sup.0.5. Such a photodiode with a 
relatively small responsive area has significant advantages including low 
noise characteristics and efficiency. In the latter regard, the efficiency 
of the detector increases as the detector/hemisphere diameter or area 
ratio decreases, resulting in a smaller detector often having a greater 
sensitivity than a large detector. Using these photodiodes, the detectors' 
efficiency nears their asymptotic state with an aperture having a diameter 
being approximately 0.5" or less. 
It is understood by one of ordinary skill in the art that the 
photodetectors 40a-40d may be localized at the cavity 22, or at another 
location wherein the photodetectors 40a-40d remain responsive to incident 
radiation in the cavity 22 by means of light-conveying devices, such as 
fiber optics or optical waveguides, that efficiently transmit light into 
or away from the cavity 22 to such other location. 
Referring still to FIGS. 2A-2C, the members 32 of the baffle 20 have a 
thickness of approximately 3.0 mm for improved opacity, which is also 
sufficient for small holes to be bore through the baffle 20 to accommodate 
small signal wires 42 that allow electrical connection to the 
photodetectors 40a-40d from the base 18. It is noted that the baffle 20 
may be constructed out of Spectralon.RTM. doped with barium sulfate. 
Further, the reflectivity of the baffle 20 can be grated so that the 
baffle 20 can have an angle dependent reflectivity, if desired to 
compensate for any nonuniform effects. 
The ratio between widths or diameters 27 and 29 of the mask 18 and the 
aperture 26, respectively, and distance 31 between the mask 18 and the 
aperture 26 are significant parameters in optimizing the detector's 
accuracy and response efficiency. A more accurate response is obtained as 
the mask/aperture diameter ratio approaches one. However, the detector's 
response efficiency or sensitivity decreases as the mask/aperture diameter 
ratio approaches one because the aperture's acceptance area necessarily 
decreases. It is understood by one of ordinary skill in the art that the 
dimensions and parameters of the detector of the system may be varied in 
accordance with the desired use or application for which the detector is 
intended. 
As variations on the constructively-occluded detectors that may be used 
with the system, the detectors may be normal-looking, or side-looking. 
Normal-looking detectors have a hemispheric field of view in terms of 
elevation angles of .THETA. relative to the detectors, such as the 
detector D.sub.ex of FIGS. 2A-2D. In contrast, side-looking detectors have 
substantially an azimuthal or "ring" field of view in terms of azimuth 
angles .rho. relative to the detectors. Side-looking detectors may be 
either floor mounted or wall mounted. FIGS. 3A and 3B illustrate cross 
sectional and top views, respectively, of a "floor" mounted, side-looking 
detector D.sub.F. The detector D.sub.F has a cylindrical cavity 50, with 
the photodetectors 40 mounted on the floor of the cavity 50. In this 
embodiment, the diameter 27 of the mask 18 is slightly greater than the 
diameter 29 of aperture 26. Incident radiation is captured by the detector 
D.sub.F between the mask 18 and the aperture 26 separated by the distance 
31. 
FIGS. 3C and 3D illustrate cross sectional and top views, respectively, of 
a wall mounted, side-looking detector D.sub.W. The detector D.sub.W also 
has a cylindrical cavity 50, but the photodetectors 40 are mounted on the 
side of the cavity 50. In this embodiment, the diameter 27 of the mask 18 
is nearly identical to the diameter 29 of the aperture 26. 
Both the detectors D.sub.F and D.sub.W have a panoramic view of the 
surrounding horizon region. The panoramic view may be a complete "ring" 
covering 360 degrees in azimuth angles, or may be a partial "ring" 
covering a lesser predetermined range of azimuth angles, as explained 
below. 
The side looking detectors D.sub.F and D.sub.W of FIGS. 3A-3D are typically 
mounted on a surface such that the detectors are responsive to azimuth 
angles .rho. of incident radiation. Even so, not all azimuth angles .rho. 
may be of interest or relevance. Accordingly, as best illustrated in FIGS. 
3B and 3D, one of the quadrants Q may be vacant and only three 
photodetectors are used to detect, for example, 150 degrees in the azimuth 
direction. Of course, if desired, four photodetectors may be used for 
determining the direction of incoming radiation around 360 degrees of 
azimuth angle .rho.. In that regard, it is understood by one of ordinary 
skill in the art that the configuration of the detectors D.sub.F and 
D.sub.W may be tailored or changed to meet the desired function and 
operation of the detector. 
FIGS. 3E and 3F illustrate cross sectional and top views, respectively, of 
a normal-looking detector D.sub.N. This detector is similar to the 
detector D.sub.ex of FIGS. 2A-2C in almost all respects, except its 
overall dimension is of smaller scale, as indicated by the dimensions 
shown in the illustration. Like the detectors of FIGS. 2A-2C, the detector 
D.sub.N of FIGS. 3E and 3F has a view of substantially the hemispherical 
area which the cavity 52 faces, in terms of elevation angles. The mask 18 
is a predetermined distance from the aperture 26 and is thus within the 
hemispherical area which the cavity 52 faces. The diameter 27 of the mask 
18 is slightly smaller than the diameter 29 of the aperture 26. Like the 
detector D.sub.ex of FIGS. 2A-2C, the detector D.sub.N has its 
photodetectors 40 mounted on the underside of the mask 18. 
In accordance with a feature of the present invention, either the 
side-looking detectors D.sub.F and D.sub.W or the normal-looking detector 
D.sub.N may be used in the embodiment of the system shown in FIG. 1. Where 
the detectors D and D' in FIG. 1 are side-looking detectors, the angles of 
reflection .beta. and .beta.' defined within the system are detected as 
the azimuth angle .rho. defined within the detectors. Limiting the 
discussion to the detector D of FIG. 1 only, it follows that: 
EQU .beta.=.rho. Eqn. 1 
where in accordance with the detector configuration, 
EQU .rho.=tan.sup.-1 (Y/X) Eqn. 2 
and Y and X are output values of the detector electronics within the 
Cartesian coordinate system of FIG. 5, defined as follows: 
EQU X=(B+C)-(A+D)!/(A+B+C+D) Eqn. 3 
EQU Y=(A+B)-(C+D)!/(A+B+C+D) Eqn. 4 
A, B, C and D represent the output signal levels of four photodetectors, 
respectively. If anyone of the photodetectors is not provided, e.g., where 
the desired azimuthal field of view is less than 360 degrees, that 
photodetector makes no contribution to Equation 3 or 4. 
With the recognition that the boundaries of the quadrants are clearly 
delineated by the value of the tangent of the angle of radiation incident 
on one of those quadrants, Equation 2 with Equations 3 and 4 substituted 
therein becomes: 
##EQU1## 
Therefore, the angle of reflection .beta. for the system when using the 
side-looking detectors of FIGS. 3A-3D is defined as: 
##EQU2## 
For the normal-looking detector of FIGS. 3E and 3F, the above equations are 
applicable; however, the angle of reflection .beta. for the system is the 
elevation angle .THETA. of the detectors, that is provided by look-up 
table shown in Appendix A. In particular, the output of the photodetectors 
from the detector is still fed into Equations 3 and 4 for generating an X 
and a Y value for determining the azimuth angle .rho. as set forth in 
Equation 2 above; however, a length L is also determined using the X and Y 
values as follows: 
EQU L=(X.sup.2 +Y.sup.2).sup.1/2 Eqn. 7 
The azimuth angle .rho. and the length L are then used with the look-up 
table of Appendix A, to obtain an elevation angle .THETA.. For the 
normal-looking detector, the angle .THETA. is used by the system as the 
angle of reflection .beta. of the system. Note that depending on how the 
elevation angle is defined in the look-up table, the angle .THETA. may 
require a conversion to an angle .THETA.' where .THETA.'=90-.THETA.. In 
the look-up table of Appendix A, the angle .THETA. of 90 degrees is taken 
to be the normal relative to the detector. 
Once the angle of reflection .beta. of the system has been determined, the 
system applies the trigonometric relationships defined within the system 
to determine the range R of the object. FIG. 4 illustrates an exemplary 
set of trigonometric relationships used by the system 10 with the range 
source S and detectors D and D' of FIG. 1, to determine the range R and R' 
of the object O. For simplification, the discussion (along with FIG. 4) is 
limited to the radiation source S and the detector D only. 
As previously described, the radiation source S directs radiation at an 
angle .alpha..sub.1 toward the object O which is located at position 
P.sub.1. The object O reflects the radiation toward the detector D which 
receives the reflected radiation at an angle .beta..sub.1. The angle 
.alpha..sub.1 is known to the system as the angular position of the 
radiation source and the angle .beta..sub.1 is determined by the system in 
accordance with Equation 2 for the side-looking detectors, or Equations 2 
and 7 with the look-up table for the normal-looking detectors. With known 
trigonometric relationships, it follows from FIG. 4 that: 
EQU T.sub.D =R.sub.1 Tan .beta..sub.1 Eqn. 8 
EQU T.sub.S =R.sub.1 Tan .alpha..sub.1 Eqn. 9 
EQU T=T.sub.D +T.sub.S Eqn. 10 
where the total distance T is known. Substituting Equations 8 and 9 into 
Equation 10, it follows that the known separation T between the detector D 
and radiation source S may be expressed as: 
EQU T=R.sub.1 Tan .beta..sub.1 +R.sub.1 Tan .alpha..sub.1 Eqn. 11 
Solving for the range R.sub.1, it follows that: 
##EQU3## 
The range R.sub.1 can therefore be derived since the separation T, the 
angle of radiation .alpha., and the angle of reflection .beta. are all 
known to the system. 
If the object O is instead at position P2 (shown in broken lines in FIG. 
4), it follows that a range R.sub.2 may be expressed as follows: 
##EQU4## 
where the angle of radiation .alpha..sub.2, as previously mentioned, is 
defined with a sign opposite to that of the radiation angle .alpha..sub.1. 
The trigonometric relationships used above may be used for the detector D', 
with the recognition that the two sets of relationships are but mirror 
images of each other. 
Referring to FIG. 6, the system may be configured such that the detectors D 
and D' are at substantially equal distance from the radiation source S 
along the base line L. Where the object O is on the boresight B of the 
radiation source S, it can be seen from the foregoing that both detectors 
D and D' detect substantially the same angle of reflection .beta.. In 
certain instances, such as in vehicle airbag deployment, it may be useful 
to determine whether the object, that is the passenger, is centered 
relative to the system. 
As the object O approaches the base line L from position P.sub.1 to 
position P.sub.2, the angle of reflection detected by both detectors D and 
D' increases from .beta..sub.1 to .beta..sub.2. Accordingly, the range 
determined by the system decreases from R.sub.1 to R.sub.2. For vehicle 
airbag application, it may be dangerous to deploy an airbag if the 
passenger is too close to the system. Accordingly, it may be desired that 
the airbag be enabled for deployment only if the detectors D and D detect 
a minimum angle of reflection from the passenger. 
Referring to FIG. 7, where the system is configured such that the detectors 
D and D' are at unequal distances from the radiation source S along the 
base line L, the range R may be determined as follows, where the total 
separation T* between the detectors D and D' is known: 
EQU T=R tan .beta. Eqn. 14 
EQU T'=R tan .beta.' Eqn. 15 
EQU T*=T+T' Eqn. 16 
Substituting Equations 14 and 15 into Equation 16, it follows that: 
EQU T*=R(tan .beta.+tan .beta.') Eqn. 17 
Accordingly, the range R may be expressed as follows: 
##EQU5## 
If the detectors D and D' are the normal-looking detectors D.sub.N of FIGS. 
3E and 3F, the detectors are oriented such that the cavities 52 open 
toward or face the object O; that is, they face a direction parallel with 
the boresight B. As mentioned, the angles .beta. and .beta.' of Equation 
18 are the respective elevation angles derived from look-up table of 
Appendix A for each detector, using Equations 2 and 7. Alternatively, if 
the detectors are the side-looking detectors of either FIGS. 3A and 3B or 
3C and 3D, the detectors are oriented such that the cavities 50 of the 
detectors face a direction 90 degrees from the boresight. As mentioned, 
the angles .beta. and .beta.' in Equation 16 are the respective azimuth 
angles as shown in Equation 2. 
The system 10 has been described so far as detecting the range and/or the 
velocity of an object positioned within the plane defined by the page of 
the drawings. Where the object O is outside of that plane, i.e., above or 
below the page, the system 10 employing the normal-looking detectors 
D.sub.ex may be configured to determine the range and/or velocity of the 
object, by recognizing the trigonometric relationships that extend beyond 
the plane and applying both the azimuth angle and the elevation angle 
detected by the detectors D.sub.ex to those relationships, in manners 
known to those of ordinary skill in the art. 
With respect to the radiation source S of the system, the radiation source 
S may be an LED array 80, as illustrated in FIGS. 11A-11C, where a 
particular direction of radiation is provided by selective activation of a 
particular LED 82.sub.ij and/or physical orientation of the LED array 80. 
Alternatively, the system may use a mirror scanning assembly 84 in 
conjunction with an LED source 86, as illustrated in FIG. 12. 
FIG. 8 illustrates exemplary electronics for the unit E (FIG. 1) for 
processing the output values of the detector D. The radiation source S may 
be driven by a clock 60 to emit radiation pulses. The clock 60 also drives 
the analog to digital converter 62 which receives the analog outputs from 
the detector D detecting the reflected radiation off the object O, 
converts them to digital form and transfers the digital values through 
computer interface 64 to CPU 66 with memory 67. The angular position of 
the radiation source S may be controlled by a angular control 68 which 
provides the angle .alpha. through the computer interface 64 to the CPU 
66. The CPU 66 processing the results to determine the angle of incoming 
radiation and thus the range of the objection, may in turn drive an alarm 
70 and/or the display 12 to indicate the range. Where the CPU 66 also 
provides a velocity of the object O, the clock 60 may provide timing 
sequences to the CPU 66, and the alarm 70 and/or the display 12 may also 
indicate such velocity. 
FIG. 9 is a flow chart of an exemplary program activating an audio signal 
when the object O is within a predetermined range. For example, this 
program may be used for avoiding collisions between a vehicle and a wall. 
The program consists of two tasks, running substantially simultaneously, 
in parallel. The process begins (100), and in the first task, the counter 
is initialized (102). The clock, then in its first state, activates the 
radiation source (104) and then resulting range R.sub.i is detected (106) 
and stored in memory (108). The counter is incremented (110). This task 
continues to detect the range R.sub.i so long as the program is operating. 
Proceeding concurrently with this task is a second task which begins by 
reading the stored range R.sub.i (112) and comparing it with a 
predetermined range R.sub.0 (114). If the range R.sub.i is greater than 
the set range value of R.sub.0, the alarm will not be activated (116); 
otherwise, the alarm will be activated (118). So long as the program is in 
operation, the values of R.sub.i is compared with R.sub.0. 
FIG. 10 is a flow chart of a modified program that includes the 
determination of a velocity value, for example, to indicate whether the 
vehicle is approaching the wall within a safe speed. The program is 
similar to that of FIG. 9 with like reference numerals indicating like 
steps, except that in the second task, both the range R.sub.i and the 
range R.sub.1+1 are read (120) and a change in range .DELTA.R is 
calculated therefrom (122). The change in range .DELTA.R is then used to 
calculate a velocity V by dividing the change in range .DELTA.R by the 
change in time .DELTA.t (124), which is provided by the clock that drives 
the radiation pulses. The velocity V is compared with a set velocity value 
of V.sub.0 (126), and if the velocity V is greater a set velocity V.sub.0, 
the alarm is activated (118); otherwise, the alarm is deactivated (116). 
It is understood by one of ordinary skill in the art that the program can 
be varied to provide range, velocity or even acceleration values, and to 
activate different warning or indication signals and/or displays. 
The system can also be configured to detect the range of multiple objects. 
For example, if a second object O.sub.2 in addition to the object O is 
being detected by the system 10 and the second object O.sub.2 has a 
radiation reflection characteristic distinguishable from that of the 
object O, photodetectors 41.sub.A, 41.sub.B, 41.sub.C and 41.sub.D 
spectrally responsive to the radiation reflection characteristic of the 
object O.sub.2 may be arranged within the detector D as illustrated in 
FIG. 2D. 
It can be seen that the present invention provides a relatively simple and 
cost effective system that can detect the range of an object, without a 
large number of optical elements or complex processing electronics. 
Although the foregoing discloses the presently preferred embodiments of 
the present invention, it is understood that the those skilled in the art 
may make various changes to the preferred embodiments shown and described 
without departing from the scope of the invention. Accordingly, the 
invention is defined only by the following claims.