U.S. patent application number 09/383444 was filed with the patent office on 2001-11-15 for device and method to detect an object in a given area, especially vehicles, for the purpose of traffic control.
Invention is credited to HORBER, ERNST.
Application Number | 20010040514 09/383444 |
Document ID | / |
Family ID | 7821745 |
Filed Date | 2001-11-15 |
United States Patent
Application |
20010040514 |
Kind Code |
A1 |
HORBER, ERNST |
November 15, 2001 |
DEVICE AND METHOD TO DETECT AN OBJECT IN A GIVEN AREA, ESPECIALLY
VEHICLES, FOR THE PURPOSE OF TRAFFIC CONTROL
Abstract
When detecting an object in a given area, especially vehicles
for the purposes of traffic control, there appear to be
inaccuracies in the system based on measuring pulse propagation
times. In order to avoid such inaccuracies, a sample of observed
(measured) real values is compared with a gauging table having a
sample of values stored therein, so that pulse propagation time
measurements are no longer necessary.
Inventors: |
HORBER, ERNST; (NEUSITZ,
DE) |
Correspondence
Address: |
FITCH EVEN TABIN AND FLANNERY
120 SOUTH LA SALLE STREET
SUITE 1600
CHICAGO
IL
606033406
|
Family ID: |
7821745 |
Appl. No.: |
09/383444 |
Filed: |
August 26, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09383444 |
Aug 26, 1999 |
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PCT/EP98/01102 |
Feb 26, 1988 |
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Current U.S.
Class: |
340/933 |
Current CPC
Class: |
G01S 17/04 20200101;
G01S 17/58 20130101; G08G 1/01 20130101; G01S 7/4802 20130101 |
Class at
Publication: |
340/933 |
International
Class: |
G08G 001/01; G08G
001/095 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 27, 1997 |
DE |
197 08 014.6 |
Claims
What is claimed is:
1. Apparatus for detecting an object in a predetermined spatial
region, in particular vehicles for traffic monitoring, including at
least one transmitter (10) for generating and emitting radiation
pulses to the predetermined spatial region, at least one receiver
(12) which receives the radiation backscattered or reflected from
the predetermined spatial region and emits a detection signal
(U(t)) as a function of backscattered or reflected radiation, at
least two devices (15) for the detection of instantaneous values
(Ui) of the detection signal U(t) within corresponding time
intervals, a control device (14) which emits a control signal to
the transmitter (10) to trigger the emission of a radiation pulse,
and to the device (15) for the detection of instantaneous values
for fixing the time intervals for detection of the instantaneous
values, and a device (16, 17, 18) for comparison of a value pattern
that can be derived from the detected instantaneous values, with
stored value patterns.
2. Apparatus according to claim 1, wherein the detection signal
U(t) is fed in parallel to the at least two devices (15) for the
detection of instantaneous values.
3. Apparatus according to claim 1, wherein the devices (15) for the
detection of instantaneous values are instantaneous voltage
measuring devices (15; 15-1, 15-2, 15-n).
4. Apparatus according to claim 3, wherein each instantaneous
voltage measuring device (15) includes a switch (15a) which is open
in the untriggered state and which is operated by the control pulse
from the control device (14), and an integrating amplifier (15b) to
which the detection signal U(t) is fed when the switch (15a) is
closed.
5. Apparatus according to claim 1, including a device (16) for
digitalization of the detected instantaneous values and an
evaluating device (17) for deriving a value pattern from the
instantaneous values and for comparison of the value pattern with
stored value patterns.
6. Apparatus according to claim 5, wherein the stored value
patterns are filed in a calibration table.
7. Apparatus according to claim 6, wherein the value patterns filed
in the calibration table are assigned to given distances.
8. Apparatus according to claim 1, wherein the radiation pulse
radiated by the transmitter (10) is narrowly focused for the
distance measurement or wherein the radiation pulse radiated by the
transmitter (10) is fanned out for space monitoring.
9. Apparatus according to claim 1, wherein the radiation pulse is a
laser light pulse, preferably with a wavelength of about 860
nm.
10. Apparatus according to claim 9, wherein the full width at
half-maximum of the pulse is about 15 ns.
11. Apparatus according to claim 9, wherein the repetition rate of
the pulse is about 30 kHz.
12. Method for detecting an object in a predetermined spatial
region, in particular vehicles for traffic monitoring, with the
steps of: emitting at least one radiation pulse to the
predetermined spatial region, receiving the radiation backscattered
or reflected from the predetermined spatial region, generating a
detection signal as a function of the radiation backscattered or
reflected from the predetermined spatial region, detecting
instantaneous values of the detection signal within at least two
measurement time intervals, deriving a value pattern from the
detected instantaneous values and comparison of the value pattern
with stored value patterns.
13. Method according to claim 12, wherein the comparison of the
value pattern is carried out with the aid of value patterns stored
in a calibration table.
14. Method according to claim 13, wherein the comparison leads to a
distance filed in the calibration table as the result.
15. Method according to claim 12, wherein the measurement time
intervals almost completely cover a predetermined measurement time
range in which the backscattered or reflected radiation is
received.
16. Method according to claim 12, wherein the width of a
measurement time interval does not exceed the pulse width of the
received backscattered or reflected radiation.
17. Method according to claim 12, wherein each received pulse is
capable of detection in at least two measurement intervals offset
from each other in time.
18. Method according to claim 12, wherein the instantaneous values
are instantaneous voltage values.
19. Method according to claim 12, wherein the radiation pulse is a
laser light pulse, preferably with a wavelength of about 860
nm.
20. Method according to claim 19, wherein the full width at
half-maximum of the pulse is about 15 ns.
21. Method according to claim 19, wherein the repetition rate of
the pulse is about 30 kHz.
Description
[0001] The present invention concerns an apparatus and a method for
detecting an object in a predetermined spatial region, in
particular vehicles for traffic monitoring, according to the
introductory part of the claims.
[0002] An apparatus of this kind is known from DE 42 34 880. The
apparatus for detecting and recognising vehicles located on a
roadway includes two narrowly focused distance sensors in order to
be able to determine direction of travel, speed and vehicle length
at the same time. By measuring the vehicle height which is
determined from the measured, different distance values,
classification of the vehicle model is possible. In this case the
distance sensors are spaced apart in the direction of travel by a
distance which is substantially shorter than the length of the
vehicle. Also distance sensors have the advantage over ordinary
reflex light barriers that higher reliability and better detection
behaviour are achieved, as inaccuracies on account of
distinguishing between beams which are reflected by a moving
vehicle or by the road are reduced. To determine the speed, length
and direction of travel of the vehicle, a pulse run time
measurement is performed. A time measuring device for this purpose
measures the time which elapses between detection of the vehicle by
the first and second sensors.
[0003] From U.S. Pat. No. 5,321,490 is known an electronic object
sensor for detecting objects which are in the vicinity of the
sensor. Two focused, pulse-like laser beams diverging from each
other are directed onto the area to be examined. The two beams are
generated by means of a prism from a single laser beam emitted by a
laser diode. The object sensor includes a receiver for detecting
the beams reflected by an object in the area of observation. The
run time which a pulse-like beam emitted by the transmitter needs
until detection by the receiver is measured. The speed of an object
in the area of observation is calculated from the distance which
the two laser beams describe on the road surface, and the time
which elapses between detection of the vehicle by the first beam
and detection by the second beam.
[0004] From the reception of several successive pulses it is
possible to deduce the number of vehicles, the vehicle size and
shape, and hence the vehicle model.
[0005] A difficulty with the known systems however exists with
respect to greatly fluctuating signal amplitudes which arise on
account of the different reflection properties of the surfaces by
which the light is reflected (e.g. road surface, plastic parts,
windscreen or black metal parts). This means that surfaces the same
distance away cause reception signals with essentially the same run
time but different signal amplitude, which leads to difficulties in
determining and fixing the moment of reception of the reflected
signal. This causes in general uncertainty in time measurement of
entry of the object into the laser beam, and therefore needs
special precautions, for example an additional detector, in order
to be able to correct this error.
[0006] It is the problem of the present invention, in detecting an
object in a predetermined spatial region, in particular vehicles
for traffic monitoring, to avoid the inaccuracies arising in case
of run time measurements.
[0007] This problem is solved according to the invention.
[0008] A central concept consists in that detection of the object
in a given region takes place by a comparison of an observed
(measured) instantaneous value pattern with a previously determined
instantaneous value pattern stored in a calibration table.
[0009] The advantages gained with the invention lie in particular
in that a distance measurement can be determined by detecting a
single backscattered or reflected radiation pulse without a
timekeeper being needed. With the invention, measurement of the run
time of a radiated pulse is completely avoided.
[0010] In traffic monitoring, traffic parameters such as for
example number of vehicles, direction of travel and distance
between the vehicles as well as vehicle speed, model, height and
length can be detected. Also the invention advantageously allows
detection of stationary vehicles within any selected time interval.
By detecting several successive backscattered and reflected pulses
it is possible to determine a profile of a vehicle. By a comparison
with different patterns or characteristic features stored in a
microprocessor unit, vehicle models can be recognised.
[0011] Another advantage of the invention lies in that the
apparatus can be used in all weather situations, owing to the
wavelength of the transmitter used. In addition the apparatus
constitutes a component which is precise, reliable and cheap and
requires only little maintenance.
[0012] By arranging three pairs of aligned laser diodes, of which
the central pair is arranged in such a way that the radiation is
directed perpendicularly relative to the area of observation, and
the pairs to the left and right of the central pair are inclined by
about .+-.120, detection of the whole roadway can be achieved. In
this case the apparatus is oriented vertically to the road surface.
However, the apparatus can be mounted horizontally and mobile in
vehicles. For the detection of traffic data of a multi-lane
roadway, a plurality of sensor apparatuses can be run in parallel.
Such an embodiment of the invention can similarly be used for
traffic control.
[0013] However, the application of the principle according to the
invention is not confined to the monitoring of traffic. Another
application of the invention is for example the security monitoring
of rooms.
[0014] A detailed description of the apparatus according to the
invention and the method according to the invention is given below
with the aid of the drawings, showing:
[0015] FIG. 1 a schematic view of an embodiment of the
invention;
[0016] FIG. 2 a schematic view of a device for detecting
instantaneous values; and
[0017] FIG. 3 a time-dependent detection signal which the receiver
delivers on account of the radiation backscattered or reflected
from the monitored spatial region.
[0018] The embodiment of an apparatus according to the invention
shown schematically in FIG. 1 includes a transmitter 10 which emits
a pulse-like energy beam in the direction of a region to be
monitored, for example above a road. The transmitter 10 is
preferably a laser diode whose light has a wavelength in the near
infrared range of typically 860 nm. By using a laser diode of class
1, danger to the human eye is excluded, and by the selected
wavelength it is ensured that the radiation emitted is hardly
impaired by external factors' such as for example poor sight or
darkness. The output power of the laser diode is typically 200
.mu.W.
[0019] When used for traffic monitoring, the transmitter 10 is
preferably mounted in such a way above the roadway to be monitored
(not shown) that the radiation is emitted vertically in the
direction of the roadway.
[0020] The emission of laser pulses by the transmitter 10 is
controlled by a control unit 14 by the control unit 14 emitting a
control signal to the transmitter 10, which triggers the laser
pulse by its ascending flank. In practice, the laser pulses
generated have a repetition rate of 30 kHz. The full width at
half-maximum of an individual pulse is typically 15 ns.
[0021] The laser beam is influenced, for example focused, by a lens
(not shown) mounted in front of the transmitter so that a pulsed
beam of suitable geometry is available for the observation of
vehicles in road traffic. In this connection it should be mentioned
that for the detection or recognition of objects in the space, for
example caused by a moving person, a beam of high divergence with
preferably a quasi-isotropic radiation characteristic is used to
ensure three-dimensional detection.
[0022] As already mentioned before, the pulsed beam is radiated
into a region of observation in which an object is located. The
radiation backscattered or reflected by this object is detected by
the receiver 12. The receiver 12 then delivers, for each
individually received pulse, a time-dependent detection signal
U(t). The control signal with which emission of the pulse is
triggered in the transmitter is fed to at least two devices 15-1,
15-2, , 15-n for the detection of instantaneous values of the
detection signal U(t). Preferably the control signal is delayed for
a predetermined length of time, so that the detection of
instantaneous values does not begin until the reflected pulse
actually reaches the receiver. In FIG. 1 the control pulse emitted
by the control unit 14 is shown with a pulse duration
t.sub.T-t.sub.0. In this case to denotes the start of the control
pulse and t.sub.T the end of the control pulse. t.sub.i denotes the
beginning of a corresponding measurement interval, which will be
described in more detail below.
[0023] The detection signal U(t) is fed to the devices 15-1, 15-2,
. . . , 15-n for the detection of instantaneous values of the
detection signal U(t), which in the embodiment described here are
instantaneous voltage measuring devices 15-1, 15-2, . . . , 15-n
for the measurement of instantaneous voltages in corresponding time
intervals. The measurement intervals are stipulated by the control
unit 14 and are such that, for reasons of sensitivity, the width of
the intervals does not substantially exceed the pulse width of the
received reflected pulse. The intervals can have different widths
and overlap in time. They should however completely cover the whole
time range in order to avoid "blind" distance zones. The number of
measurement intervals can be optimised according to the required
precision of measurement, but every received pulse must be capable
of detection in at least two measurement intervals offset from each
other in time.
[0024] As can be seen in FIG. 2, each instantaneous voltage
measuring device 15 includes a switch 15a open in the untriggered
state and an integrating amplifier 15b for measuring an
instantaneous voltage Ui of the detection signal U(t) within a
given range of measuring times. The control pulse from the control
unit 14 is fed via a delay circuit 15c to the switch 15a, with the
result that the control pulse from the control unit 14 after a
given delay closes the switch 15a of the instantaneous voltage
measuring device 15 for a predetermined time interval. In the
process, closing of the switches 15a of the different instantaneous
voltage measuring devices 15-1, 15-2, . . . , 15-n is offset from
each other in time, so that the whole measurement range in which
the backscattered or reflected radiation can be received is
completely covered. Thus each instantaneous voltage measuring
device 15-1, 15-2, . . . , 15-n delivers an instantaneous voltage
value U1, U2, . . . , Un of the detection signal U(t), as shown in
FIG. 3 for ten different instantaneous voltage values (U1-U10). In
this way a set of instantaneous voltage values is obtained
according to the invention from the time-dependent detection signal
U(t). It should be mentioned that the instantaneous voltage value
U.sub.i can be the voltage integral over the interval i, or the
voltage at the end of the interval, or some other value
characteristic of the interval. In general a set of n instantaneous
voltage values U1, U2, . . . , Un is produced for each pulse
detected by the receiver.
[0025] The instantaneous voltage values U1, U2, . . . , Un are then
in the embodiment shown in FIG. 1 transmitted to a device 16 for
digitalisation which includes a multiplexer and an
analogue-to-digital converter (not shown). Evaluation then takes
place in an evaluating device 17 to which the digitalised values
are fed and which advantageously includes a microprocessor by means
of which the digitalised values are processed.
[0026] In a preferred embodiment a set of quotients of adjacent
instantaneous voltage values U.sub.i/U.sub.i+1 is calculated from
the instantaneous voltage values obtained from each measurement
pulse. In this way a quotient pattern (or instantaneous voltage
pattern) is determined for each measurement pulse radiated by the
transmitter 10. By a subsequent comparison of the instantaneous
voltage pattern with experimentally determined instantaneous
voltage patterns which are stored in a calibration table 18
connected to the evaluating device 17, the distance between an
object located in the region of observation and the measuring
device can be determined directly. For the application within the
scope of traffic monitoring, this means: If the distance determined
differs from the constant distance between measuring device and
road, in this way the presence of a vehicle in the monitored
spatial region is detected.
[0027] For an object moving in the area of observation, the profile
of the object which is characteristic of the moving object can be
determined from the detection of successively radiated pulses
received by the receiver device, on the basis of the distance
varying from one pulse to the next. For instance, in case of
traffic monitoring, a profile of moving vehicles can thus be
determined and the vehicle model classified in addition.
[0028] By arranging a second measuring device of identical
construction, which is arranged at a distance from the first
measuring device in the direction of movement of the object, the
speed of a moving object can be determined. Each of the measuring
devices emits a focused pulse-like laser beam in the direction of
the region of observation. A moving object is then recorded by the
first measuring device as described above, and then an
instantaneous voltage pattern is formed. By the reception of
successive radiation pulses a profile of the moving object is thus
determined, as discussed before. On account of the movement of the
object, the latter is also detected by the second measuring device
and a further profile of the moving object is determined. Next the
time which elapses between recording of the object by the first
measuring device and by the second measuring device can be
determined. By means of the measured elapsed time, the speed of the
object can be determined.
* * * * *