U.S. patent application number 10/103748 was filed with the patent office on 2003-09-25 for continuous aimpoint tracking system.
Invention is credited to Blackwell, Frank J., Jungwirth, Patrick W., Skala, James A..
Application Number | 20030180692 10/103748 |
Document ID | / |
Family ID | 28040464 |
Filed Date | 2003-09-25 |
United States Patent
Application |
20030180692 |
Kind Code |
A1 |
Skala, James A. ; et
al. |
September 25, 2003 |
Continuous aimpoint tracking system
Abstract
The Continuous Aimpoint Tracking System is comprised of a
position detection device (PDD) and a laser pointing device (LPD)
that projects an infrared crosshair onto the PDD. The PDD is
coupled to a computer and comprises a multitude of photodiodes and
associated circuits, the photodiodes being evenly spaced and
arranged to form a frame that can be mounted on the computer so as
to surround the computer video display. When a "shot" is fired from
the LPD, the crosshair projection is interrupted briefly. The PDD
determines the position of the four crosshair intersections and
reports them to the computer which, in response, generates the
video signals that form the resolved aimpoint on the screen,
matching the LPD aimpoint to the video image. Further, the tracking
system determines the rotation of the LPD over a range of at least
10 degrees clockwise or counter-clockwise.
Inventors: |
Skala, James A.; (Hartselle,
AL) ; Blackwell, Frank J.; (Decatur, AL) ;
Jungwirth, Patrick W.; (Huntsville, AL) |
Correspondence
Address: |
Legal Office
(AMSAM-L-G-I, Mr. Fred M. Bush)
US Army Aviation and Missile Command
Redstone Arsenal
AL
35898-5000
US
|
Family ID: |
28040464 |
Appl. No.: |
10/103748 |
Filed: |
March 22, 2002 |
Current U.S.
Class: |
434/22 ;
89/41.06 |
Current CPC
Class: |
F41G 3/2633 20130101;
F41G 1/35 20130101 |
Class at
Publication: |
434/22 ;
89/41.06 |
International
Class: |
F41G 003/26; F41G
001/32; F41G 005/06 |
Goverment Interests
[0001] The invention described herein may be manufactured, used and
licensed by or for the Government for governmental purposes without
the payment to us of any royalties thereon.
Claims
We claim:
1. A continuous aimpoint tracking system for continuously tracking
the aimpoint and cant of a shooter, said system comprising: a
computer having a video display for displaying on said video
display the aimpoint and cant; a laser pointing device to be
manipulated by said shooter, said laser pointing device being
adapted for emitting laser aim signals and being positioned
relative to said video display so as to allow the shooter to aim
laser signals at any pre-selected area of said video display; a
position detection device, said detection device being coupled to
said computer and mounted thereon so as to frame said video
display, said detection device sensing said laser aim signals being
emitted from said pointing device and generating and sending
corresponding data packets to said computer, said computer
processing said data packets to produce and display video signals
indicative of the exact location of said aim signals on said video
display.
2. A continuous aimpoint tracking system for continuously tracking
the aimpoint and cant of a shooter as set forth in claim 1, wherein
said data packets are sent from said detection device to said
computer at a rate dictated by the application of said CATS.
3. A continuous aimpoint tracking system for continuously tracking
the aimpoint and cant as set forth in claim 2, wherein said
position detection device comprises: a plurality of photodiodes for
producing current signals in response to laser signals impinging
thereon, said photodiodes being disposed in a first and a second
horizontal rows, said horizontal rows being identical in structure
and function, and in a first and a second vertical columns, said
vertical columns being identical in structure and function, said
rows and columns jointly forming a frame suitable for mounting on
said video display of said computer so as to surround said video
display; a means for scanning said photodiodes in a pre-determined
sequence; a means for processing said current signals to yield
corresponding digital signals; and a plurality of bus lines coupled
between said photodiodes and said processing means, said digital
signals being subsequently converted into data packets and input to
said computer.
4. A continuous aimpoint tracking system for continuously tracking
the aimpoint and cant as set forth in claim 3, wherein said
photodiodes are further disposed to maintain the exactly same
pre-selected spacing therebetween.
5. A continuous aimpoint tracking system for continuously tracking
the aimpoint and cant as set forth in claim 4, wherein every
n.sup.th photodiode in a pair of one horizontal row and one
vertical column is connected to the same bus line among said
plurality of bus lines.
6. A continuous aimpoint tracking system as set forth in claim 5,
wherein said means for sequential scanning comprises: a first and a
second microcontrollers, said first microcontroller being coupled
to scan said first row and said first column of said photodiodes
while said second microcontroller is coupled to scan said second
row and said second column of said photodiodes; a means for
isolating any selected photodiode from other photodiodes on the
same bus line so that sequential scanning can be performed by a
particular microcontroller among said microcontrollers, said
particular microcontroller being coupled to said selected
photodiode, said isolating means being coupled between said
photodiodes and said particular microcontroller.
7. A continuous aimpoint tracking system as set forth in claim 6,
wherein said first and second microcontrollers communicate with
each other so as to coordinate the scanning of said
photodiodes.
8. A continuous aimpoint tracking system as set forth in claim 7,
wherein one of said microcontrollers communicates with said
computer.
9. A continuous aimpoint tracking system as set forth in claim 8,
wherein said isolating means is a plurality of selecting switches,
each of said selecting switches being coupled between one of said
plurality of photodiodes and said particular microcontroller, said
selecting switches responding to commands from said particular
microcontroller to select a photodiode to be scanned at any point
in time.
10. A continuous aimpoint tracking system as set forth in claim 9,
wherein said means for processing said current signals comprises: a
plurality of identical processing units, each of said units
comprising a current amplifier coupled to one of said bus lines,
said current amplifier producing corresponding voltage signals in
response to said current signals received from said selected
photodiode; a digital potentiometer set at a pre-selected
attenuation step; a fixed attenuator coupled between said current
amplifier and said digital potentiometer, said attenuator receiving
said voltage signals from said current amplifier and rendering said
voltage signals acceptable to said potentiometer; an
analog-to-digital converter coupled to said particular
microcontroller, said converter producing digital output signals in
response to voltage input signals and transmitting said digital
output signals to said particular microcontroller; a voltage
amplifier coupled between said digital potentiometer and said
analog-to-digital converter, said voltage amplifier receiving
signals from said potentiometer and producing, in response,
low-impedance signals, said voltage amplifier further transmitting
said low-impedance signals to said analog-to-digital converter.
11. A continuous aimpoint tracking system as set forth in claim 10,
wherein said pre-selected attenuation step of said digital
potentiometer may be varied by said particular microcontroller.
12. A continuous aimpoint tracking system as set forth in claim 11,
wherein said current amplifier further cooperates with said
selecting switches and said bus line to provide current
balance.
13. A continuous aimpoint tracking system as set forth in claim 12,
wherein each of said horizontal rows contains therein 112
photodiodes and each of said vertical columns contains therein 96
photodiodes.
14. A continuous aimpoint tracking system as set forth in claim 13,
wherein said laser pointing device for emitting laser aim signals
comprises: a plurality of lasers for emitting infrared radiation; a
means for powering said lasers; a means for selectively activating
said lasers; and a means positioned to receive said infrared
radiation from said lasers, shape said radiation and subsequently
project said radiation in the form of a crosshair onto said
position detecting device.
15. A continuous aimpoint tracking system as set forth in claim 14,
wherein said plurality of lasers comprises: a first laser and a
second laser.
16. A continuous aimpoint tracking system as set forth in claim 15,
wherein said aimpoint tracking system further comprises: a firing
device, said laser pointing device being coupled to said firing
device to cooperate therewith.
17. A continuous aimpoint tracking system as set forth in claim 16,
wherein said laser pointing device further comprises: a means for
detecting when said firing device has fired.
18. A continuous aimpoint tracking system as set forth in claim 17,
wherein said selectively activating means comprises: a first timer
coupled between said detecting means and said lasers, said first
timer interrupting said lasers' emission of infrared radiation for
a first pre-set duration of time upon detection of firing.
19. A continuous aimpoint tracking system as set forth in claim 18,
wherein said selectively activating means further comprises: a
second timer coupled to restrict said first timer so that said
first timer does not activate to interrupt said lasers' emission
again until said first timer times out.
20. A continuous aimpoint tracking system as set forth in claim 19,
wherein said selectively activating means still further comprises:
a third timer coupled between said first timer and said powering
means, said third timer turning off said powering means in response
to lack of first timer interruptions for a second pre-set duration
of time.
21. A continuous aimpoint tracking system as set forth in claim 20,
wherein said means for shaping and projecting a crosshair
comprises: a first cylindrical lens and a second cylindrical lens,
each of said lenses being positioned to receive said infrared laser
radiation from said first laser and said second laser,
respectively, and optically diffract said radiation into a
horizontal line and a vertical line, respectively, each line having
a pre-determined spread angle, said horizontal and vertical lines
together forming a crosshair.
22. A continuous aimpoint tracking system as set forth in claim 21,
wherein the length of said horizontal line spans at least twice the
distance between the outer edges of said vertical columns of said
photodiodes in said position detection device.
23. A continuous aimpoint tracking system as set forth in claim 22,
wherein said aimpoint tracking system still further comprises: a
filter placed between said photodiodes and said laser pointing
device, said filter minimizing the effect of ambient infrared
radiation.
24. A continuous aimpoint tracking system for continuously tracking
the aimpoint and cant of a shooter, said system comprising: a
computer having a display screen for displaying on said screen the
aimpoint and cant; a laser pointing device manipulable by said
shooter, said laser pointing device being suitable for emitting
laser aim signals and being positioned relative to said display
screen so as to allow the shooter to aim laser signals at any
pre-selected area of said screen; a position detection device
coupled to said computer, said position detection device having
therein a plurality of photodiodes for producing current signals in
response to laser signals impinging thereon, said photodiodes being
disposed in a first and a second horizontal rows, said horizontal
rows being identical in structure and function, and in a first and
a second vertical columns, said vertical columns being identical in
structure and function, said rows and columns jointly forming a
frame suitable for mounting on said screen of said computer so as
to surround said screen, said position detection device further
having therein a means for scanning said photodiodes in a
pre-determined sequence, a microcontroller coupled to scan said
photodiodes, a means for processing said current signals to yield
corresponding digital signals, a plurality of bus lines coupled
between said photodiodes and said processing means and a means for
isolating any selected photodiode from other photodiodes on the
same bus line so that sequential scanning can be performed by said
microcontroller, said isolating means being coupled between said
photodiodes and said microcontroller, said digital signals being
subsequently converted into data packets and input to said computer
and said computer processing said data packets to produce and
display video signals on said screen, said video signals being
indicative of the exact location of said aim signals and magnitude
of said cant.
25. A continuous aimpoint tracking system as set forth in claim 24,
wherein said means for processing said current signals comprises: a
plurality of identical processing units, each of said units
comprising a current amplifier coupled to one of said bus lines,
said current amplifier producing corresponding voltage signals in
response to said current signals received from said selected
photodiode; a digital potentiometer set at a pre-selected
attenuation step; a fixed attenuator coupled between said current
amplifier and said digital potentiometer, said attenuator receiving
said voltage signals from said current amplifier and rendering said
voltage signals acceptable to said potentiometer; an
analog-to-digital converter coupled to said microcontroller, said
converter producing digital output signals in response to voltage
input signals and transmitting said digital output signals to said
microcontroller; a voltage amplifier coupled between said digital
potentiometer and said analog-to-digital converter, said voltage
amplifier receiving signals from said digital potentiometer and
producing, in response, low-impedance signals, said voltage
amplifier further transmitting said low-impedance signals to said
analog-to-digital converter.
26. A continuous aimpoint tracking system as set forth in claim 25,
wherein said laser pointing device for emitting laser aim signals
comprises: a plurality of lasers for emitting infrared radiation; a
means for powering said lasers; a means for selectively activating
said lasers; and a means positioned to receive said infrared
radiation from said lasers, shape said radiation and subsequently
project said radiation in the form of crosshair lines onto said
position detecting device.
27. A continuous aimpoint tracking system as set forth in claim 26,
wherein said aimpoint tracking system further comprises an aluminum
enclosure enclosing said position detection device, said enclosure
having horizontal and vertical slits so as to allow infrared
radiation to enter and impinge on said diodes.
28. A continuous aimpoint tracking system as set forth in claim 27,
wherein said photodiodes are disposed to maintain the exactly same
pre-selected spacing therebetween, said pre-selected spacing being
determined by the desired width, at said position detection device,
of said crosshair laser lines.
Description
BACKGROUND OF THE INVENTION
[0002] In the field of aimpoint tracking, the current technology
provides a fairly accurate system in which the weapon to which the
pointing device is mounted is tethered to the scene containing the
target. In this system, the pointing device transmits an infrared
sight against a prism at the target scene and receives the
reflected light back at the transmitter to determine aimpoint
position with respect to the prism. It offers a fairly continuous
tracking but the tether alters the touch or feel of the weapon.
This altered sensation reduces the effectiveness of the aimpoint
training, since in real-life use there are no tethers between the
weapons and the targets.
[0003] Another currently available tracking system has no tether
but fails to provide continuous tracking, showing only the point
where the bullet hit. It pulses a laser against an opaque sheet of
Plexiglas.RTM. and triangulates the position of the laser light
pulse to determine the position of the aimpoint.
SUMMARY OF THE INVENTION
[0004] The Continuous Aimpoint Tracking System 100 (hereinafter may
be referred to as the CATS) has the advantage of providing
continuous aimpoint tracking, yet requiring no tether. It reports
at a rate per second, the rate depending on the application to
which the CATS is put, exactly where, in a position detection
device of any given size, a laser pointing device is aimed. The
CATS also reports the rotation (cant) of the pointing device.
However, in a typical marksmanship training application, reporting
at any rate of over 100 times per second is adequate. For example,
applicants have demonstrated the operation of the CATS at a
reporting speed of 112.5 times per second.
[0005] Laser pointing device (LPD) 101 projects an infrared laser
crosshair onto position detection device (PDD) 103 that is placed
at a given distance away from the LPD, the distance dictating the
required spread angle of the crosshair lines from the LPD. The LPD
can be attached to anything that needs accurate aimpoint from a
distance of about 6 feet to about 60 feet. Of particular interest
is the use of LPD in conjunction with firearm 109 such as a pistol,
rifle or shotgun, which makes possible marksmanship training with a
real weapon but without the use of live ammunition.
[0006] The PDD onto which the crosshair is projected is coupled to
standard personal computer (PC) 107 and is comprised of a multitude
of photodiodes 301 and associated circuits, the photodiodes being
evenly spaced and arranged to form a frame that can be mounted on
the computer display so as to surround computer display screen 105.
The vertical crosshair line projecting from the LPD intersects the
top and the bottom edges of the PDD while the horizontal crosshair
line intersects the left and the right edges of the PDD. The PDD
determines the position of the four crosshair intersections and
reports them to the computer. When a "shot" is fired from the LPD,
the crosshair projection is interrupted briefly (for example, 18 to
20 milliseconds). The computer, in response, generates the video
signals that form the resolved aimpoint on the computer screen,
matching the LPD aimpoint to the video image.
[0007] Further, the CATS is able to measure the rotation of the LPD
over a range of at least 10 degrees clockwise or counter-clockwise.
The CATS uses the measured rotation of the LPD as feedback to help
the shooter learn to keep the weapon at a level cant, the ability
to do which becomes more important as the distance to the target
increases. In addition to normal bullet ballistics, the computer
can simulate the effects of cant versus distance of a shot,
providing realism for a marksmanship trainer that is not possible
without the measurement of rotation.
DESCRIPTION OF THE DRAWING
[0008] FIG. 1 is an overall functional diagram of the Continuous
Aimpoint Tracking System (CATS).
[0009] FIG. 2 presents a detailed diagram of the laser pointing
device.
[0010] FIG. 3 presents a detailed diagram of the position detection
device.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0011] Referring now to the drawing wherein like numbers represent
like parts in each of the several figures and arrows indicate
signal paths, the structure and operation of the laser pointing
device and the position detection device are explained in
detail.
[0012] In use as a marksmanship trainer, the LPD is mounted onto
weapon 109 such that the intersection of the projected horizontal
and vertical infrared crosshairs is approximately the same as the
aimpoint of the weapon. The LPD is coupled to trigger mechanism 201
so that the LPD sees a "fire" signal when microphone 203 detects
the sound of the weapon's hammer as the weapon is "fired".
Similarly, if a trigger switch is required, trigger switch 205
produces the "fire" signal.
[0013] The LPD is powered by batteries 221. When battery switch 219
is closed, regulator 217 provides constant voltage to first and
second infrared lasers 225 and 227 and to the circuit until the
batteries are exhausted, at which time it produces an under voltage
signal. When power is applied to the circuit, latch 213 is set by
the Power-On Circuit 215, thereby allowing the lasers to be
continuously powered on.
[0014] The projected infrared crosshair can be formed in different
ways. One method involves a single laser using a binary optic
diffraction grating or a prism arrangement that optically converts
the single laser beam into a crosshair. The preferred method,
however, is to use first and second infrared lasers 225 and 227
whose output impinges on first cylindrical lens 229 and second
cylindrical lens 231, respectively, each of which lenses spreads
the laser beam output into a laser line with a fixed spread angle.
The center halves of the resultant laser lines are usable signals
that project from apertures 233 and 235, the ends of the two laser
lines being blocked by the same apertures. The orientation of the
laser lines is set at 90 degrees with respect to each other so that
the combination of the lines form the projected crosshair that is
detected by PDD 103. The ends of the projected crosshairs must be
at least twice the distance between the left and right edges of the
PDD. Therefore, the required minimum spread angle of the laser
lines depends on the distance from the LPD to the PDD. For a
typical small arms training application where the minimum distance
between the LPD and the PDD is 6 feet, a minimum spread of 24
degrees is required. To achieve 6 to 30 foot distance, one may use
7 mW lasers in the LPD with 60-degree spread angle cylindrical
lenses.
[0015] The projected laser crosshair lines are ideal and promote
the best PDD accuracy if they have a gausian distribution across
the width of the lines and the line width at the PDD from the
normal operating distance is twice the spacing of the PDD's
photodiodes. Optical methods such as using a prism arrangement or
cylindrical lenses as described above produce lines with gausian
distributions.
[0016] In a typical small arms training application, when weapon
109 is fired, first timer 207 turns lasers 225 and 227 off for a
given number of milliseconds (usually 18 to 20 milliseconds),
interrupting the laser crosshair. Second timer 209 is coupled to
restrict the first timer from activating again until the first
timer times out. If no firing of the weapon is detected for a given
number of consecutive minutes, as indicated by third timer 211, or
if an under voltage signal from regulator 217 appears, latch 213 is
reset, thereby removing power from the lasers entirely, i.e. laser
switch 223 opens. Because the lasers represent over 99% of the
power requirement of the LPD, this effectively turns the LPD off.
The lasers cannot be turned back on to resume operation of the LPD
until battery switch 219 is turned off and then back on.
[0017] While the LPD is pointed anywhere on computer video display
105, if the laser crosshair is interrupted for a given number of
milliseconds by firing of weapon 109, PDD 103 sends a "fire" event
data packet to computer 107. This is explained further with
reference to FIG. 3. It is noted here that even though it is
contemplated that the PDD comprises a plurality of photodiodes and
at least two microcontrollers to scan the photodiodes, the
microcontrollers are identical in structure and function and only
one is illustrated in FIG. 3. Therefore, the illustration is
presented as representative only. Further, the signal processing
units per microcontroller residing in the PDD are also multiple in
number, each unit comprising current amplifier 305, attenuator 307,
digital potentiometer 309, voltage amplifier 311 and
analog-to-digital (A/D) converter 313. The preferred embodiment of
the PDD envisions eight such signal processing units per
microcontroller. But since they are identical in structure and
function, again only one such unit is shown in FIG. 3 for
representative and illustrative purposes only.
[0018] The PDD is essentially a rectangular frame that is mounted
on video display (screen) 105 and surrounds the display without
blocking the video image appearing on the video display. The PDD is
plugged into a serial port or a universal serial bus (USB) port
(e.g. a communications port) of personal computer 107. The area of
video display 105 is the tracking area. Along the edges of the four
sides of the PDD's rectangular frame are a plurality of photodiodes
that are positioned to maintain a precise, pre-selected spacing
between them. To accommodate a crosshair laser line width of 0.3
inch at the PDD, the spacing between any two photodiodes in the
same horizontal row or vertical column should be 0.15 inch. The
desired number of the photodiodes depends on the desired size of
the tracking area. In a preferred embodiment of the PDD to be used
in small arms training, the top and bottom horizontal rows each has
112 infrared photodiodes while the left and right vertical columns
each has 96 photodiodes.
[0019] Two microcontrollers are employed to scan the photodiodes,
each microcontroller scanning half (one horizontal row and one
vertical column) of the PDD array perimeter. The two
microcontrollers communicate with each other so as to coordinate
the scanning of all of the 416 photodiodes in a sequential manner
and one of the microcontrollers is further programmed to
communicate with the computer. Among the photodiodes in the half of
the PDD array perimeter (one horizontal row and one vertical
column) that is coupled to be scanned by a particular
microcontroller between the two microcontrollers, every 8.sup.th
photodiode is connected to one bus line of an 8-line bus. Each of
the bus lines, in turn, is coupled to a signal processing unit
comprised of a current amplifier, a fixed attenuator, a digital
potentiometer, a voltage amplifier and an analog-to-digital
converter.
[0020] FIG. 3 shows one of the eight identical photodiode busses
and one of the eight identical signal processing units that are
coupled to a particular one of the two microcontrollers. The
decision to use two microcontrollers is based on the length, high
impedance and settling times of the analog bus, the desired
accuracy and the aimpoint position reporting speed. Accuracy
suffers if the bus does not have sufficient time to settle after a
photodiode selection has been made for scanning. Correspondingly,
if less accuracy is permissible (such as caused by noise from a
longer bus and/or the result of less settling time on the bus),
then the PDD can be built using one microcontroller.
[0021] Every 8.89 milliseconds, the PDD measures the signal
provided by each of photodiodes 301 with microcontroller 315
sequentially selecting each photodiode to be scanned. Diode
selection gate 303 acts as a selection switch sequentially to
connect a single selected diode to diode common 317. Each
photodiode has its own diode selection gate that is coupled to the
diode common and is selected by particular microcontroller 315.
While a selected photodiode is being scanned, all other photodiodes
on the same bus are isolated.
[0022] The signal of the selected photodiode appears as a small
current (example: 0 to about 600 nanoamps), generated in response
to the infrared radiation (in the form of crosshair) impinging on
the photodiode. Current amplifier 305, then, converts the
photodiode current to a voltage that provides enough current
through a high resistance (example: 1.5 megohm) to balance the
current of the photodiode so that the bus voltage can be kept at
the voltage common 319 potential. The voltage developed by the
current amplifier balances the photodiode's current and is of low
impedance. Fixed attenuator 307 reduces this voltage and applies
the reduced voltage across digital potentiometer 309 whose
attenuation step is set by particular microcontroller 315. All of
the digital potentiometers' settings are independently set for each
row and column of photodiodes, and all photodiode signals in any
one row or column are measured with all 8 digital potentiometers
set to the same step during a single scan of the row or column. The
output voltage from digital potentiometer 309 is input to fixed
gain voltage amplifier 311, which, in response, produces a low
impedance output signal. The output signal of the voltage amplifier
is, then, input to A/D converter 313, which yields a corresponding
8-bit digital value. The digital value is input to particular
microcontroller 315 which, in turn, sends corresponding data
packets to computer 107. Such data packets are sent from the PDD to
the computer at an exemplary rate of 112.5 data packets per second,
the result of the microcontrollers scanning all of the photodiodes
every 8.89 milliseconds.
[0023] When the laser crosshair projection from the LPD is crossing
inside the detection area of the PDD, the PDD determines the
positions of the laser crosshair crossings at its edges and reports
these to the computer 112.5 times per second. In response, the
computer determines the aimpoint relative to the PDD as the
intersection of the two lines formed by connecting the top and
bottom edge laser crosshair positions, and the left and right laser
crosshair positions. The computer determines the rotation angle
from the horizontal line of the crosshair because it gives the best
accuracy. The computer uses this information to update the video
image in the display area of the PDD as required. The computer can
adjust the aimpoint relative to the video image as required to
align the PDD to the displayed video image; therefore, the LPD
needs no aimpoint adjustment and the PDD needs no critical
alignment to the video image. Only the video image size is required
to be exact and the image linear. The aimpoint remains accurate
when the LPD is rotated to angles of up to about 10 degrees, as
long as the laser crosshair lines continue to intersect all four
edges of the PDD.
[0024] When weapon 109 is triggered, the LPD infrared crosshair
projection is interrupted briefly, most likely 18 to 20
milliseconds. When this happens, because the PDD saw the laser on
all four edges, then sees nothing for at least one scan (8.89
milliseconds), and then again sees the laser on all four edges, it
determines that the LPD has been triggered, and the PDD reports
this as a "fire event" to the computer. The computer uses the last
reported position of all four edges as the aimpoint at the moment
that the shot was fired. When the crosshair signals are
continuously (more than about 6 scan periods) detected on less than
all four edges of the PDD, the microcontroller reports this to the
computer as an "off screen" event. During the transitions that
occur during a "fire event" and between normal position reporting
and "off screen" events, there are scans that result in no reports
being sent to the computer.
[0025] Four LED indicators, one for each edge of the PDD, are
located and visible at one corner of the PDD to indicate whether or
not a laser crosshair line is touching each respective edge of the
PDD. The LED is off when any laser line is crossing its respective
edge of the PDD. When lasers 225 and 227 are momentarily
interrupted while the LPD is pointed toward the tracking area,
these LED indicators flash on.
[0026] The resolution of the aimpoint at the PDD, assuming a 13 by
10 inch tracking area, is approximately 0.0006 inch with the
accuracy being better than +/-0.01 inch. The photodiodes have
randomly different sensitivities, and the analog channels are not
perfectly matched. Therefore, to achieve the specified accuracies,
a one-time in-circuit calibration is required to equalize the gain
of all photodiodes. Calibration is performed by illuminating the
entire PDD with a uniform level of infrared radiation and running a
suitable PC-based calibration program. During calibration, the PDD
sends the raw digital values of all 416 photodiodes to the
calibration program. Several complete scan samples should be taken
and averaged. The high diode value of each row and column is
compared to all other diode values of the same row or column to
determine the multiplier needed to make all diode values equal to
the high diode value. When the calibration is successful, the
calibration constants are downloaded from the computer to the PDD,
which, then, uses these gain equalization multiplier values to
equalize the gain of the photodiodes during normal operation of the
Continuous Aimpoint Tracking System.
[0027] Depending on the environment in which the CATS is used, the
performance of the CATS can be much improved by use of filters
placed in front of the photodiodes. Saturation of the analog
circuits occurs when the ambient infrared illumination level drives
the current amplifier to saturation, rendering the PDD inoperative.
Prior to saturation of the analog circuits, as the ambient infrared
radiation level increases, the laser power must also increase to
maintain the same performance level of the PDD. The most effective
way to reduce the ambient infrared radiation level is to install a
bandpass filter in front of the photodiodes to eliminate all
infrared radiation above the LPD laser's wavelength (the
photodiodes themselves have a built-in filter to block all visible
light). This significantly improves the overall performance of the
PDD because the bandpass filter passes about 80% of the laser
signal, while removing about 80% of the signal from normal ambient
infrared sources. Alternatively, or in combination with the
bandpass filter, a set of circular polarization filters can be
installed, one in front of the lasers at the LPD, and another in
front of the photodiodes. However, this method requires about 50%
more initial laser power to achieve the same signal at the PDD. The
best scenario is to use no filters and avoid operating the CATS in
areas where high levels of ambient infrared illumination are
present.
[0028] The CATS can be used to measure and improve the cant of the
shooter manipulating the weapon. Long-distance shooters need to be
especially aware of the cant of their weapon because a cant of 1
degree can cause the bullet to miss by several feet from a distance
of 1600 meters (1 mile).
[0029] With the LPD attached to anything that rotates over a small
angle (5.degree. being the maximum sweep), the sweep of the laser
lines in the tracking area at a distance of 15 feet away from the
LPD provides two axis rotational measurements to 0.0003 degrees and
a cant measurement to 0.006 degrees. These three angular
measurements represent all three degrees of movement that are
available from a single point in space: azimuth, elevation and
rotation.
[0030] Although a particular embodiment and form of this invention
has been illustrated, it is apparent that various modifications and
embodiments of the invention may be made by those skilled in the
art without departing from the scope and spirit of the foregoing
disclosure. One such modification is using a standard "universal"
multi-device television remote control transmitter 111 to act as an
instructor console to control several PDD's in the same room. For
example, if seven PDD's are used, each PDD is assigned a number
from 1 to 7 that corresponds to the remote's various devices, like
"TV", "VCR", etc. When a selected PDD sees a command that has the
coding of the selected device, it responds by forwarding the
command to computer 107, causing various actions to take place.
Another modification is to enclose the PDD in an aluminum enclosure
with slits cut on the front side near the outer edges to allow the
laser crosshair projections to reach the photodiodes that are in
line behind the slits. This reduces the ambient infrared
illumination levels impinging on the photodiodes, thus improving
performance of the PDD. The aluminum enclosure further acts as a
static shield for the high impedance analog circuitry associated
with the nano ampere range signals that are generated by the
photodiodes. Additionally, the enclosure may have adjustable mounts
that fit almost any brand of video monitor, and may be held in
place by Velcro on the brackets. Yet another modification is to
enclose the computer and the video display (as a Thin Film
Transistor Liquid Crystal Display) in the aluminum enclosure with
the PDD, making an all-in-one system.
[0031] To those skilled in the art of position and angular
measurement, the invention described above can be applied to other
uses where a non-contact, non-tethered, high-precision method of
measurement of position and/or angle is required. One example is a
numerical controlled machine tool. Another exemplary application is
a two-axes high precision angular resolver for machines. Computer
games are another potential application.
[0032] Accordingly, the scope of the invention should be limited
only by the claims appended hereto.
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