U.S. patent application number 13/208125 was filed with the patent office on 2011-12-08 for laser range finding device and distance measurement method thereof.
Invention is credited to Pie-Yau Chien, Sheng Liang, Hua-Tang Liu, Yin-Long Luo, Peng-Fei Song.
Application Number | 20110299061 13/208125 |
Document ID | / |
Family ID | 40136121 |
Filed Date | 2011-12-08 |
United States Patent
Application |
20110299061 |
Kind Code |
A1 |
Luo; Yin-Long ; et
al. |
December 8, 2011 |
LASER RANGE FINDING DEVICE AND DISTANCE MEASUREMENT METHOD
THEREOF
Abstract
A distance measurement method for use in a laser range finding
device to measure a distance between the laser range finding device
and a target is disclosed. The method comprises the following
steps. A laser signal is sent to the target in a first time point.
A reflected laser signal reflected by the target is then received.
A digital signal having a plurality of signal values ranging from 0
to N is obtained by sampling the reflected laser signal with a
sampling signal, wherein N is an integer larger than two. A maximum
signal value among the signal values is obtained. The distance is
calculated according to the first time point and a second time
point where the maximum signal value is generated.
Inventors: |
Luo; Yin-Long; (Hang-Zhou,
CN) ; Liang; Sheng; (Hang-Zhou, CN) ; Song;
Peng-Fei; (Hang-Zhou, CN) ; Chien; Pie-Yau;
(Taichung Hsien, TW) ; Liu; Hua-Tang; (Taichung
Hsien, TW) |
Family ID: |
40136121 |
Appl. No.: |
13/208125 |
Filed: |
August 11, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12885852 |
Sep 20, 2010 |
8018580 |
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13208125 |
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12047350 |
Mar 13, 2008 |
7800737 |
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12885852 |
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Current U.S.
Class: |
356/5.01 ;
356/4.01 |
Current CPC
Class: |
G01S 7/4873
20130101 |
Class at
Publication: |
356/5.01 ;
356/4.01 |
International
Class: |
G01C 3/08 20060101
G01C003/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 25, 2007 |
TW |
96122879 |
Claims
1. A distance measurement method for use in a laser range finding
device to measure a distance between the laser range finding device
and a target, comprising: transmitting a laser signal to the target
at a first time point; receiving a reflected laser signal reflected
by the target; generating a digital signal by sampling the
reflected laser signal and creating a plurality of different
non-zero magnitude values for the digital signal that are each
associated with a time for the received reflected laser signal and
have a magnitude that corresponds to a magnitude of the received
reflected laser signal at the associated time; and calculating the
distance between the laser range finding device and the target
based on the generated digital signal.
2. The method of claim 1, wherein: the digital signal is generated
based on one reflected laser signal.
3. The distance measurement method of claim 1, wherein: the digital
signal is a signal with eight bits per data value.
4. The distance measurement method of claim 1, wherein: the digital
signal is a signal with more than one bit per data value.
5. The distance measurement method of claim 1, wherein: the digital
signal is generated by sampling the reflected laser signal with a
sampling signal.
6. The distance measurement method of clam 1, wherein: the
generated digital signal has a waveform that is similar to a
waveform of the received reflected laser signal.
7. A laser range finding device for measuring a distance between
the laser range finding device and a target, comprising: a
transmitter that transmits a laser signal to the target at a first
time point; a receiver that receives a reflected laser signal
reflected by the target; an analog-to-digital converter that
samples the reflected laser signal and generates a digital signal
by sampling the received reflected laser signal and creating a
plurality of different non-zero magnitude values that are each
associated with a time for the received reflected signal and have a
magnitude that corresponds to a magnitude of the received reflected
laser signal at the associated time such that the generated digital
signal has a waveform that is similar to a waveform of the received
reflected laser signal; and a processing unit that calculates the
distance between the laser range finding device and the target
based on the generated digital signal.
8. The laser range finding device of claim 7, wherein the
transmitter comprises: a laser diode; and a driving circuit that
controls the laser diode to transmit the laser signal to the
target.
9. The laser range finding device of claim 7, wherein the receiver
comprises: an avalanche photodiode that receives the reflected
laser signal reflected by the target; a signal amplifier that
amplifies the reflected laser signal received by the avalanche
photodiode; and a filter circuit that performs a noise filtering to
the amplified reflected laser signal.
10. The laser range finding device of claim 7, further comprising:
a memory unit in communication with the processing unit, the memory
unit stores the digital signal; and a control circuit in
communication with the processing unit, the control circuit
receives a trigger signal from the processing unit so as to drive
the transmitter to transmit the laser signal and activate the
analog-to-digital converter.
11. The laser range finding device of claim 7, further comprising:
a displaying unit coupled to the processing unit for displaying the
distance between the laser range finding device and the target
calculated by the processing unit.
12. The laser range finding device of claim 14, wherein: the
digital signal is a signal with more than one bit per data
value.
13. The laser range finding device of claim 7, wherein: the digital
signal is a signal with eight bits per magnitude for the plurality
of different non-zero magnitude values.
14. The laser range finding device of claim 7, wherein: the
analog-to-digital converter samples the reflected laser signal with
a sampling signal to generate the digital signal.
15. The laser range finding device of claim 7, wherein: the
analog-to-digital converter generates the digital signal based on
one reflected laser signal.
16. A distance measurement method for use in a laser range finding
device to measure a distance between the laser range finding device
and a target, comprising: transmitting a laser signal to the target
at a first time point; receiving a reflected laser signal reflected
by the target; generating a digital signal having a plurality of
signal values by sampling the reflected laser signal, the signal
values range from 0 to N where N is a positive integer greater than
two; and calculating the distance between the laser range finding
device and the target based on the generated digital signal.
17. The method of claim 16, wherein: the digital signal is
generated based on one reflected laser signal.
18. The distance measurement method of claim 16, wherein: the
digital signal is a signal with more than one bit per data
value.
19. The distance measurement method of claim 16, wherein: the
digital signal is generated by sampling the reflected laser signal
with a sampling signal.
20. The distance measurement method of claim 16, wherein: the
generated digital signal has a waveform that is similar to a
waveform of the received reflected laser signal.
Description
[0001] This application is a continuation application of U.S.
patent application Ser. No. 12/885,852, "Laser Range Finding Device
& Distance Measurement Method Thereof," filed on Sep. 20, 2010,
by Luo, et al., which is a continuation application of U.S. patent
application Ser. No. 12/047,350, "Laser Range Finding Device &
Distance Measurement Method Thereof," filed on Mar. 13, 2008, by
Luo, et al., Now U.S. Pat. No. 7,800,737. which claims priority to
Taiwan Patent Application No. 96122879, filed Jun. 25, 2007, all of
which are incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to a laser range finding device and
distance measurement method thereof, and more precisely, to a laser
range finding device and distance measurement method for measuring
a distance between a laser range finding device and a target using
time of flight (TOF) of laser signals.
[0004] 2. Description of the Related Art
[0005] Generally, distance measurement methods using laser signals
can be classified into three types: phase, interference and pulse
feedback types. For a laser range measurement with a pulse type, a
distance between a laser range finding device and a target is
calculated by directly measuring time of flight of the laser light
pulse signal. When a laser diode is trigged by a driving circuit,
it generates a start pulse as a starting signal of a time distance
measurement system to start counting time. Then, after a reflected
laser signal has been received and amplified, the laser diode
generates a stop pulse to stop the time count. A counting circuit
measures a time difference between the start pulse and the stop
pulse to calculate and obtain a time of flight of the transmitted
laser pulse signal from the target to the laser range finding
device, thereby obtaining the distance between the laser range
finding device and the target using the calculated time of
flight.
[0006] However, when performing a long distance measurement (i.e.,
the target is far away from the laser range finding device), the
signal strength of the reflected signal received by the laser range
finding device may be very weak, such that the signal strength of
the received signal is only a little larger than that of a noise
signal. In this case, noise signal values may be erroneous
determined as the target signal if a predetermined threshold level
is set too small or the weak signal reflected from the target will
not be detected if the predetermined threshold level is set too
large.
[0007] It is therefore desired to provide methods and apparatuses
for improving the ability of the distance measured for the laser
range finding device.
BRIEF SUMMARY OF THE INVENTION
[0008] An embodiment of the invention provides and discloses a
distance measurement method for use in a laser range finding device
to measure a distance between the laser range finding device and a
target. The distance measurement method comprises the following
steps. First, a laser signal to the target is transmitted in a
first time point. Then, a reflected laser signal reflected by the
target is received. Next, a digital signal having a plurality of
signal values is obtained by sampling the reflected laser signal
with a sampling signal, wherein the signal values range from 0 to N
where N is a positive integer greater than two. A maximum signal
value among the signal values of the digital signal is then found.
Finally, the distance between the laser range finding device and
the target is calculated according to the first time point and a
second time point corresponding to the maximum signal value.
[0009] An embodiment of the invention also provides and discloses a
laser range finding device for measuring a distance between the
laser range finding device and a target. The laser range finding
device at least comprises a transmitter, a receiver, an
analog-to-digital converter and a system unit. The transmitter
transmits a laser signal to the target in a first time point. The
receiver receives a reflected laser signal reflected by the target.
The analog-to-digital converter samples the reflected laser signal
with a sampling signal to obtain a digital signal having a
plurality of signal values, wherein the signal values range from 0
to N where N is a positive integer greater than two. The system
unit finds a maximum signal value among the signal values of the
digital signal and calculates the distance between the laser range
finding device and the target according to the first time point and
a second time point that generates the maximum signal value.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The invention can be more fully understood by reading the
subsequent detailed description and examples with reference to the
accompanying drawings, wherein:
[0011] FIG. 1 schematically shows a block diagram of an embodiment
of a laser range finding device;
[0012] FIG. 2 is a block diagram illustrating an embodiment of a
laser range finding device according to the invention;
[0013] FIG. 3 is a signal waveform diagram;
[0014] FIG. 4 is a flowchart of an embodiment of a distance
measurement method according to the invention;
[0015] FIG. 5 is a flowchart of another embodiment of a distance
measurement method according to the invention;
[0016] FIG. 6 schematically shows an embodiment of a mapping table
according to the invention; and
[0017] FIG. 7 schematically shows an embodiment of a digital signal
according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0018] The following description is of the best-contemplated mode
of carrying out the invention. This description is made for the
purpose of illustrating the general principles of the invention and
should not be taken in a limiting sense. The scope of the invention
is best determined by reference to the appended claims.
[0019] The invention is now described with reference to FIGS. 1
through 7, which generally relate to a laser range finding devices
and distance measurement methods thereof. In the following detailed
description, reference is made to the accompanying drawings which
form a part hereof, shown by way of illustration of specific
embodiments. These embodiments are described in sufficient detail
to enable those skilled in the art to practice the invention, and
it is to be understood that other embodiments may be utilized and
that structural, logical and electrical changes may be made without
departing from the spirit and scope of the invention. The following
detailed description is, therefore, not to be taken in a limiting
sense. It should be understood that many of the elements described
and illustrated throughout the specification are functional in
nature and may be embodied in one or more physical entities or may
take other forms beyond those described or depicted.
[0020] The embodiments of the invention provide a laser range
finding device and distance measurement method thereof so as to
obtain a distance between the laser range finding device and a
target. In one embodiment, a laser range finding device is
provided. The laser range finding device performs a digitalization
operation for a received reflected laser signal by an
analog-to-digital converter (ADC) so as to generate a digital
signal comprising a multitude of signal values. Given the generated
digital signal that comprises a multitude of signal values,
original waveform and amplitude of the reflected laser signal can
be reserved so that the noise signal and the target signal can be
distinguished, thus, improving the ability to guard against noise
interference, to perform long distance measurements, and to shorten
the time for distance measurements.
[0021] In an embodiment of a distance method according to the
invention, the reflected laser signal is utilized to obtain a
digital signal comprising a plurality of signal values, and a
maximum signal value among all of the signal values of the digital
signal is then found. Next, a time of flight of the laser signal is
calculated using the time point which generates the maximum signal
value thereby obtaining the distance between the laser range
finding device and the target, wherein the time of flight of the
laser signal indicates a time difference from a first time point
that the laser signal is transmitted to a second time point that a
reflected laser signal is received.
[0022] FIG. 1 schematically shows a block diagram of an embodiment
of a laser range finding device 100. As shown in FIG. 1, a
transmitter in the laser range finding device 100 transmits a laser
signal to a target 110 and then a receiver receives the reflected
laser signal. The signal values of the reflected laser signal are
converted to a value of one or zero by a comparator, processed by a
signal processing unit to find out the time point that a target
signal is received so as to determine a distance to the target.
[0023] The comparator compares the inputted signal value to a
threshold level to determine an output value. A value "1" is
outputted when the inputted signal value is larger than or equal to
the threshold level, otherwise a value "0" is outputted. When the
target distance is extended, the signal strength of the reflected
laser signal received by the receiver will become relatively weak,
resulting in increased interference by noise signals. As a result,
for finding the target signal, the threshold level has to be set
very small such that noise signals may be erroneously determined as
the target signal should the signal value of the noise signal
exceed the threshold level. In this case, the target signal may not
be actually recognized thereby extending the time needed for
distance measurement.
[0024] FIG. 2 is a block diagram illustrating an embodiment of a
laser range finding device 200 according to the invention, for
measuring the distance therefrom to a target 260. The laser range
finding device 200 comprises a transmitter 210, a receiver 220, a
analog-to-digital converter (ADC) 230, a system on chip (SOC) 240
and a displaying unit 250. The transmitter 210 transmits a laser
signal L1 to the target 260 for measuring the distance. The
transmitter 210 further comprises a pulsed laser diode 212 and a
driving circuit 240, wherein the driving circuit 240 controls the
laser diode 212 to transmit the laser signal to the target 260.
[0025] The receiver 220 receives a reflected laser signal L2
reflected by the target 260, which comprises an avalanche
photodiode 222 for receiving the reflected laser signal reflected
by the target, a signal amplifier 224 for amplifying the reflected
laser signal received by the avalanche photodiode 222, and a filter
circuit 226 for performing a noise filtering to the amplified
reflected laser signal. The analog-to-digital converter 230 is
coupled to the receiver 220, performing a signal digitalization to
the reflected laser signal from the receiver 220 so as to obtain a
digital signal having a plurality of signal values. It is to be
understood that the digital signal has a specific waveform as same
as that of the reflected laser signal and all of the signal values
range from 0 to N where N is a positive integer greater than two.
Referring to FIG. 3, a signal waveform diagram is illustrated. In
FIG. 3, signals S1, S2 and S3 represent waveforms of the received
reflected laser signal L2, a digital signal that has been
digitalized by the comparator of the laser range finding device 100
in FIG. 1, and a digital signal that has been digitalized by the
analog-to-digital converter 230 of the laser range finding device
200 in FIG. 2, respectively. It is assumed that, in this
embodiment, the analog-to-digital converter 230 is an eight bits
analog-to-digital converter (ADC) so that the reflected signal is
converted to a digital signal that has a plurality of signal values
ranging from 0 to 255. As shown in FIG. 3, signal values of three
sampling points P1, P2 and P3 on the reflected laser signal S1 are
all converted to "1" on the digital signal S2 while those values of
the three sampling points P1, P2 and P3 on the reflected laser
signal S1 are respectively converted to "100", "250" and "105" on
the digital signal S3. It is observed that the output of the
digital signal S2 forming a waveform which is a square wave due to
each output of the digital signal S2 is determined by comparing the
inputted signal value to a threshold level, not representing that
the sampling point P2 has a maximum peak value or a maximum signal
value. The signal values of digital signal S3, however, may be
quantified as various signal values, not only representing that the
sampling point P2 has a maximum peak value or a maximum signal
value but also keeping a waveform as same as that of the original
signal S1.
[0026] The system on chip (SOC) 240 comprises a control logic unit
242, a memory unit 244 and a processing unit 246. The control logic
unit 242 is coupled to the processing unit 214, the transmitter 210
and the analog-to-digital converter 230, driving the transmitter
210 to transmit the laser signal to the target 260 and activating
the analog-to-digital converter starting signal conversion when it
receives a trigger signal from the processing unit 246. The memory
unit 244 stores a digital signal converted by the analog-to-digital
converter 230. Then, the processing unit 246 reads the stored
digital signal from the memory unit 244 and finds a maximum signal
value among all of the signal values of the digital signal to
calculate a time of flight of the laser signal so as to obtain the
distance between the laser range finding device 200 and the target
260.
[0027] FIG. 4 is a flowchart 400 of an embodiment of a distance
measurement method according to the invention. In this embodiment,
refer to both FIGS. 2 and 4. In step S410, a laser signal is
transmitted to the target 260 in a first time point T1. The time
point T1 is the starting time the laser signal begins transmission.
Meanwhile, the control logic unit 244 receives a trigger signal
from the processing unit 246 and prepares to perform the distance
measurement. Accordingly, during the first time point, the control
logic unit 242 drives the driving circuit 214 of the transmitter
210 to control the laser diode 212 to transmit the laser signal L1
to the target 260 and activates the analog-to-digital converter 230
starting signal conversion.
[0028] In step S420, a reflected laser signal L2 reflected by the
target 260 is then received by the avalanche photodiode 222 of the
receiver 220, amplified by the signal amplifier 224, filtered for
noise from the amplified reflected laser signal by the filter
circuit 226 to achieve a filtered result, and outputted (e.g,
signal S1 shown in FIG. 3) to the analog-to-digital converter 230.
In step S430, the analog-to-digital converter 230 converts the
reflected laser signal from the receiver 220 to a digital signal so
as to generate a digital signal having a plurality of signal
values.
[0029] For example, referring to FIG. 3, assume that the
analog-to-digital converter 230 is an eight bits analog-to-digital
converter, the reflected laser signal S1 will be converted to the
digital signal S3 having a plurality of signal values ranging from
0 to 255, in which the waveform of the digital signal S3 is as same
as that of the signal S3. After the digital signal has been
generated by the analog-to-digital converter 230, the digital
signal is stored in the memory unit 244.
[0030] In step S440, the processing unit 246 reads the stored
digital signal from the memory unit 244 and finds a maximum signal
value among all of the signal values of the digital signal. In step
S450, the processing unit 246 calculates a time of flight of the
laser signal using the first time point T1 and a second time point
T2 that generated the maximum signal value. In this embodiment, the
time of flight is defined as the time that the laser signal leaves
the laser diode 212 to the time it is received by the
analog-to-digital converter 230. In this case, the time of flight
T=T2-T1.
[0031] In step S460, the distance between the laser range finding
device 200 and the target 260 is determined by multiplying the
calculated time of flight T by the speed of e light. In this case,
the signal values are within a large range (i.e. 0 to N, N>2),
depending on the bit number of the used analog-to-digital
converter, such that a difference between the noise signal value
and the target signal value is larger than one. As a result, the
target signal can be easily and actually located and found,
shortening the time needed for distance measurement.
[0032] For ensuring the accuracy of the maximum signal value time
point, in one embodiment, a threshold level is further applied to
help determination of the maximum signal value (i.e. target
signal).
[0033] FIG. 5 is a flowchart 500 of another embodiment of a
distance measurement method according to the invention.
[0034] As shown in FIG. 5, in step S510, a threshold level
corresponding to environmental parameters (such as weather,
strength of sun light and noise of the test environment) is
obtained. The environmental parameters, such as strength of sun
light, can be repeatedly tested in advance to acquire a group of
corresponding statistical data to serve as threshold levels later.
To acquire the group of statistical data corresponding to the
environmental parameters, a number of laser signals are transmitted
to the sky and then reflected laser signals are received by the
receiver of the laser range finding device as sampled signals.
Next, the sampled signals are analyzed to find a relationship of
the average signal value AV which is an average value of those
sampled signal values and a difference .DELTA. V of the found
maximum signal value and a relative maximum signal value found in
an area outside of the maximum signal value within a predetermined
range. Once the relationship has been found, the threshold level
can be set as a value that exceeds a maximum value of the
difference .DELTA. V. For example, for the average signal value AV
ranging from 18000 to 19000, the measured possible range of the
difference .DELTA. V is from 0 to 40, so the threshold level can be
set as 42, for example, if the sampled average signal value AV is a
value that blows 19000.
[0035] This relationship of the average signal value AV and the
corresponding threshold level can be acquired in advance and stored
in a mapping table of the memory unit. FIG. 6 schematically shows
an embodiment of a mapping table 600 according to the invention.
The mapping table 600 has an average value AV field representing
the average signal value AV and a threshold level field in which
each average value AV field corresponds to a threshold level. For
example, by looking up the mapping table, the threshold level is
set as 42 if the average value AV is 18500, while the threshold
level is set as 62 if the average value AV is 19501.
[0036] Accordingly, in step S520, a second larger signal value
located in an area outside of the maximum signal value within a
predetermined range is found. Note that the predetermined range can
be freely adjusted and it is normally a value around the maximum
signal value so as to prevent performing erroneous comparisons. For
example, in this embodiment, a relative maximum value (i.e. the
second larger signal value) is defined as a maximum signal value
acquired in an area outside of a time interval that utilizes the
second time point as a reference central point and ranged from a
time point that is one time unit prior to the second time point to
a time point that is one time unit subsequent to the second time
point, in which the time unit can be one cycle of the sampling
signal of the reflected laser signal. The predetermined range can
be defined as, for example, a time interval that utilizes the
maximum signal value as a reference central point within three
yards, but is not limited thereto.
[0037] FIG. 7 schematically shows an embodiment of a digital signal
according to the invention. As shown in FIG. 7, the signal value at
a point V1 is found as the maximum signal value, and a relative
maximum signal value (i.e. the signal value at a point V2) is thus,
found in an area outside of the signal value of the point V1 within
a predetermined range.
[0038] Next, in step S530, it is determined that whether a
difference .DELTA. V (i.e. V1-V2) between the maximum signal value
and the relative maximum signal value is not less than a selected
threshold level. If so (Yes in step S530), the found maximum signal
value is determined as the target signal thereby the second time
point that the maximum signal value has occurred is recognized as
being correct (step S540). If not (No in step S530), it implies
that the found maximum signal value may be a noise signal,
therefore, the laser signal is re-transmitted to perform another
measurement (step S550).
[0039] In addition, referring to FIG. 7, a maximum value would be
found after the time point that the maximum signal value has
occurred (as the signal value at time point T3 shown in FIG. 7) due
to the property of the hardware devices (such as the analog
filter). Such property of the hardware devices, therefore, may be
used to help determination of the target signal.
[0040] In one embodiment, a relative minimum signal value can be
acquired after the maximum signal value has occurred, and then it
is determined that whether a difference .DELTA. V2 (i.e. V1-V3)
between the maximum signal value and the relative minimum signal
value is not less than a second threshold level. If so, the found
maximum signal value is determined as the target signal thereby the
second time point that the maximum signal value has occurred is
recognized as being correct. If not, it implies that the found
maximum signal value may be a noise signal, therefore, the laser
signal is re-transmitted to perform another measurement. In another
embodiment, when the difference .DELTA. V between the maximum
signal value and the second larger signal value (the relative
maximum signal value) is less than the selected threshold level (No
in step S530), it is further determined that whether the difference
.DELTA. V2 (i.e. V1-V3) between the maximum signal value and the
relative minimum signal value is not less than a second threshold
level. If so, the found maximum signal value is determined as the
target signal and thereby the second time point that the maximum
signal value has occurred is recognized as being correct. If not,
it implies that the found maximum signal value may be a noise
signal, therefore, the laser signal is re-transmitted to perform
another measurement.
[0041] It is to be noted that, as would be apparent to those
skilled in the art, the although only one set of laser signals are
illustrated, it is also possible to transmit a number of sets of
laser signals for distance measurement. In this case, the receiver
is capable of receiving a number of reflected laser signals
corresponding to the transmitted ones and accumulating or averaging
these received reflected laser signals so as to perform further
processes using the accumulated or averaged signals. The invention
is therefore capable of application in distance measurement for a
plurality of sets of laser signals.
[0042] While the invention has been described by way of example and
in terms of preferred embodiment, it is to be understood that the
invention is not limited thereto. To the contrary, it is intended
to cover various modifications and similar arrangements (as would
be apparent to the skilled in the art). Therefore, the scope of the
appended claims should be accorded to the broadest interpretation
so as to encompass all such modifications and similar
arrangements.
* * * * *