U.S. patent application number 09/829319 was filed with the patent office on 2002-03-14 for remote attitude and position indicating system.
Invention is credited to Blevins, William Mark, Judkins, Eric, Rakes, Lonny, Schoess, Jeffrey Norman.
Application Number | 20020031050 09/829319 |
Document ID | / |
Family ID | 22723390 |
Filed Date | 2002-03-14 |
United States Patent
Application |
20020031050 |
Kind Code |
A1 |
Blevins, William Mark ; et
al. |
March 14, 2002 |
Remote attitude and position indicating system
Abstract
A method and apparatus using ultrasonic sensors for
determination of the pointing vector described by two points
separated in space in the coordinate frame of the measuring system.
For measurement, acoustic signals are transmitted from two emitters
whose spatially separated coordinates form the desired pointing
vector. Three detectors, associated receiver electronics and
software are required to compute six distinct spheres from the time
of flight measurements. The intersection of the three spheres,
associated with each emitter, describe the desired location in the
detector coordinate system of that emitter. With the coordinates of
each emitter, the pointing vector is computed using standard
geometry. A reference is required to determine the time of flight
of the signals to each detector. Another embodiment uses an active
reflective technique, where the timing is obtained through round
trip transmission and reception of the signal with a known fixed
delay at the vector points.
Inventors: |
Blevins, William Mark;
(Albuquerque, NM) ; Rakes, Lonny; (Rio Rancho,
NM) ; Judkins, Eric; (Albuquerque, NM) ;
Schoess, Jeffrey Norman; (Buffalo, MN) |
Correspondence
Address: |
Honeywell International Inc.
Law Dept. AB2
P. O. Box 2245
Morristown
NJ
07962-9806
US
|
Family ID: |
22723390 |
Appl. No.: |
09/829319 |
Filed: |
April 9, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60195925 |
Apr 10, 2000 |
|
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Current U.S.
Class: |
367/127 |
Current CPC
Class: |
F41G 3/02 20130101; G06F
3/0346 20130101; Y10S 367/907 20130101 |
Class at
Publication: |
367/127 |
International
Class: |
G01S 003/80 |
Claims
What is claimed is:
1. A method for determining a position and orientation of an
object, the method comprising the steps of: (a) providing two
linearly aligned emitters on the object; (b) providing at least
three co-linear detectors positioned in a field of view of the
emitters; (c) providing a geodetic reference to the detectors; (d)
transmitting a distinct signal from each emitter; (e) receiving the
distinct signals by each of the detectors; (f) deriving at least
six time of flight measurements from the distinct signals to the
detectors; (g) converting the at least six time of flight
measurements to distances; and (h) computing the position and
orientation of the object from the distances.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based on U.S. Provisional application
Ser. No. 60/195,925 entitled "Ultrasonic Remote Position and
Orientation Sensing System", filed on Apr. 10, 2000, the teachings
of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention (Technical Field)
[0003] The invention relates to a system for determining the
position and orientation of an object and more particularly a
method and apparatus for an acoustic based determination of an
arbitrary position and orientation of an object in space without
any physical tether or connection to the object and with no
alignments or predetermined spatial relationships between the
system and the target object.
[0004] 2. Background Art
[0005] The problem that this invention solves is efficient and
accurate initial laying of an indirect fire weapon system for
location and direction and subsequent attitude measurements
necessary to firing the weapon system accurately at a target.
Additionally, minimizing weight and power requirements as well as
minimizing hardware physically attached to the weapon is crucial to
the solution.
[0006] There are two methods that try to solve the problem. The
first is the method employed by self-propelled weapon systems. Self
propelled weapon systems use a three-axis attitude sensor and
global positioning system (GPS) to determine pointing data. The
second is a theoretical optical method. In this system, a barcode
is attached to the end of the tube, and a barcode reader is used to
measure the tube displacement and calculate azimuth.
[0007] Towed or man portable, indirect fire weapon systems are laid
using a surveyed aiming circle. Once they are laid on an azimuth of
fire, and have accurate position, all further aiming is done using
optical sights and aiming references (aiming poles, collimators, or
distant aiming points). There are several problems with this
system/method of laying and subsequent pointing of indirect fire
weapons; currently, survey is required to accurately emplace a
mortar. An accurate survey is difficult to transfer to places where
indirect fire weapon systems are set up. Additionally, the time it
takes to emplace using an aiming circle is considered too long.
With an aiming circle the location where the weapon is place is
limited to a direct line of sight to the aiming circle. As a
result, the weapon is not placed optimally for tactical
considerations. While the use of an attitude sensor and GPS
eliminates the need for a survey, this method also has
shortcomings. The primary shortcomings of the self-propelled
pointing system are excess weight, and power requirements. A towed
or man portable solution cannot accommodate the equipment used on
the self-propelled system. Additionally, the self propelled system
is exposed to severe shock, vibration, and temperature, since it is
mounted on the tube. This results in unacceptable failure rates of
electronic components.
[0008] The second method is a system using optics to perform weapon
pointing. A barcode is attached to the end of the weapon's tube
with a barcode reader placed a few meters away. As the tube is
moved, the barcode reader picks up the displacement and performs
the calculations to determine azimuth and elevation. Because this
optical solution is theoretical, the accuracy requirements have not
been proven.
[0009] The current methods fail to address weight, power, accuracy,
and off tube mounting requirements.
[0010] All state of the art pointing systems require some type of
position and attitude measurement device, such as a global
positioning system (GPS) receiver and inertial navigation system
(INS). The current method for solving this problem most often
relies on installation of an Inertial Navigation System (gyroscopes
and accelerometers) on the object of interest. For many
applications this solution is prohibitively expensive. An optical
approach requires exact positioning and re-alignments should the
object's position change. Standard ultrasonic techniques demand
separate sensing modules for full three-dimensional determination
of orientation. A radio frequency solution requires extremely fast
detection electronics (rough calculations indicate such a system
would need to resolve 4.6 picoseconds to sense the minimum
incremental motion of a mortar tube).
[0011] There are several other prior art systems that attempt to
solve the orientation and position determination problem as
discussed above.
[0012] U.S. Pat. No. 4,853,863 to Cohen, et al., discloses a system
that uses light, ultrasound and string wound on encoded,
spring-loaded reels as mechanisms for calculations based on
distances, angle measurements and doppler shift measurements
(derivatives) which are then integrated to yield distance
measurements. The Cohen, et al., system calls for 3 emitters and 3
detectors, all non-collinear for obtaining the measurements. The
present invention utilizes 2 emitters (collinear) and 3 detectors
(non-collinear). Another distinction from Cohen, et al., is that
the present invention utilizes 6 distances coupled with a means of
locating the system reference frame on the geodetic grid and a
means of determining reference frame orientation to calculate
absolute attitude and position. No such enhancement is to be found
in Cohen, et al. In addition, Cohen, et al., does not reference
fire control applications as disclosed herein.
[0013] U.S. Pat. No. 5,280,457 to Figueroa, et al., discloses a
means for making absolute distance measurements using ultrasound
and a "strobe"signal. The device is designed to eliminate the speed
of sound as a system variable. Figueroa, et al., describes a means
to locate a single point in 3-space, unlike the present invention
which determines object position and orientation (6 degrees of
freedom) in 3-space. Figueroa, et al., also describes, as a means
to accomplish this, the use of one emitter and m+2 detectors to
operate in m dimensions, i.e. one emitter and 5 detectors for a 3D
system. Again, this is in contrast to the present invention, which
uses 2 and 3 respectively. And finally, no application other than a
self-calibrating means of locating a point is given Figueroa et
al.
[0014] The present system provides an easy to use means of making
accurate determinations of an object's position and orientation.
The object of interest can have an arbitrary orientation with
respect to the sensing device. The user does not need to establish
precise references or datum points when using the system.
SUMMARY OF THE INVENTION (DISCLOSURE OF THE INVENTION
[0015] The Remote Attitude and Position Indicating Device (RAPID)
is a system for determining the location and pointing attitude of
an object relative to a known coordinate system. The RAPID system
uses an ultrasonic based measurement technique to determine the
distances from two points on the object of interest to at least
three points forming a plane in the known coordinate system. The
derivation of the minimum six distances is accomplished by
transmitting a distinct acoustic signal from each of two emitters
and deriving the time of flight of each distinct signal from the
two detectors to at least three detectors. Measurement of time of
flight (TOF) relies on the fact that the acoustic signals travel at
the speed of sound. Derivation of the minimum, six TOF measurements
requires that the detection algorithm (hardware and/or software)
ascertain the instant when the acoustic signals were sent. This can
be accomplished using an RF pulse transmission, which occurs at the
same time as the acoustic pulse but is received instantaneously at
the detector and its associated receiver electronics. Similar
results can be obtained without a reference pulse by measuring the
round trip time of flight, where three acoustic signals are
transmitted to the two object transducers, conditioned and returned
to the transmitting transducer after a fixed delay. Upon derivation
of the minimum, six TOF values, six emitter/pair distances are
computed, for use in final computation of object orientation using
standard geometric equations.
[0016] The method described above is implemented via two primary
electronic assemblies. These consist of an emitter assembly and
detector assembly. Note that there are two emitter assemblies on
the object of interest. The emitter assembly contains the
electronic circuitry necessary to generate the required drive
signals for an acoustic emitter and the RF transceiver (in the case
of the RF reference system). The detector assembly contains the
electronic circuitry necessary to receive, amplify and process the
signals detected by a minimum of three transducers. This circuitry
may also include a RF transceiver for receipt of the "time sent"
reference signal. In the round trip measurement implementation, the
detector assembly would contain the electronics necessary to drive
the dual purpose transducers, and then receive, amplify and process
the returned signals. The detector assembly will accommodate an
interface to a attitude and heading reference device to enable
calculation of object orientation in a know coordinate system
(earth frame).
[0017] A primary object of the present invention is to enable
automation of mortar laying, targeting and displacement.
[0018] Another object of the present invention is to enhance the
lethality of the mortar platform.
[0019] Another object of the present invention is to connect the
mortar to the digital battlefield.
[0020] A primary advantage of the present invention is that the
system is minimally obtrusive to the weapons platform
[0021] Another advantage of the present invention is since the
primary electronics are not on the weapon, the environment is much
more friendly, thereby reducing cost impacts of the environmental
design requirements on the system
[0022] Yet another advantage of the present invention is that the
system is extremely light, further supporting its inclusion as part
of the manpack and towed mortar systems
[0023] Another advantage of the present invention is that the
system does not require special setup or calibration, thereby
improving operations and survivability
[0024] Another advantage of the present invention is that the
system accuracy is dependent on the accuracy of the
pitch/roll/heading system, thereby offering tailorable performance
and cost.
[0025] Other objects, advantages and novel features, and further
scope of applicability of the present invention will be set forth
in part in the detailed description to follow, taken in conjunction
with the accompanying drawings, and in part will become apparent to
those skilled in the art upon examination of the following, or may
be learned by practice of the invention. The objects and advantages
of the invention may be realized and attained by means of the
instrumentalities and combinations particularly pointed out in the
appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] The accompanying drawings, which are incorporated into and
form a part of the specification, illustrate several embodiments of
the present invention and, together with the description, serve to
explain the principles of the invention. The drawings are only for
the purpose of illustrating a preferred embodiment of the invention
and are not to be construed as limiting the invention. In the
drawings:
[0027] FIG. 1 shows the preferred position and orientation sensing
system.
[0028] FIG. 2 schematically shows the preferred emitter
assembly.
[0029] FIG. 3 shows the preferred detector module.
[0030] FIG. 4 shows the typical components in either of the
embodiments of the invention.
[0031] FIG. 5 is a flow chart showing a typical method of using the
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
(BEST MODES FOR CARRYING OUT THE INVENTION)
[0032] The present invention comprises a system for determining an
arbitrary position and orientation of an object in space without
any physical tether or connection to the object and with no
alignments or predetermined spatial relationships between the
system and the target object. The preferred system is shown in FIG.
1. As shown in FIG. 1, the object of interest 001 represents a
mortar tube. This object 001 includes two acoustic emitter
assemblies 100 mounted on the axis of the tube and separated by
some know distance. The detector box and three associated
transducers 200 are located at and establish the reference
coordinate system for measurement of the tube attitude. As will be
discussed in more detail, the six measured distances between
emitter/detector pairs are used to geometrically compute the
pointing vector formed by the two emitters on the tube.
[0033] The system comprises an emitter assembly 100 of FIG. 2 and a
detection/processing module 200 of FIG. 3 and associated
software.
[0034] The emitter assembly 100, as shown in FIG. 2, is comprised
of two ultrasonic transducers 108, a short-range radio frequency
transceiver 110, associated drive electronics 102, power supply 116
and RF antenna 106. The electronics 102 excite the ultrasonic
transducers 108 at the required resonant frequency. The
transmission of the two transducers 108 may be separated in phase
or in frequency in order to distinguish the signals at the
detectors. The circuitry also drives the RF transceiver 110 so that
it emits a suitable radio frequency pulse 112. The electronics for
the acoustic and radio frequency sub-circuits derive their timing
from an oscillator 104 and the phase relationship between the RF
112 and the acoustic pulses 114 is known. The RF pulse 112 serves
as a timing reference at the detector module 200 and allows
emitter-to-detector distances to be calculated directly from the
phase relationship of the detected RF and acoustic signals and
known parameters such as the speed of sound in air.
[0035] As shown in FIG. 3, the detector/processing module 200 is
comprised of three ultrasonic detectors 210, signal conditioning
electronics 216, threshold detection circuitry 218, a short range
RF transceiver 214, a processor sub-system 220 and 222 and antenna
212. A pitch/roll/heading sense sub-system 224 and 226 is required
to enable absolute position and attitude information to be obtained
at the detector/processing module 200. For certain applications,
like military applications, a GPS system and `battlefield internet`
capability would also be included. The meteorological data 228 is
received via the `battlefield internet`. The three ultrasonic
detectors 210 are mounted on the module 200 such that they are not
co-linear and thus they define a plane. The pitch/roll/heading
sensors 224 and 226 are precision mounted in the module 200 with
respect to this plane. Object position and orientation are
referenced to the synthetic coordinate system established by the
pitch/roll/heading sensors 224 and 226. The radio frequency pulse
230 is received at the detector module 200 and initializes the
threshold detection and comparison process 220. Acoustic signals
240 are received and processed such that originating acoustic
emitter is known. One possible embodiment of the detector design
includes a timing circuit, (embodied within 220) where the high
precision timer is triggered upon receipt of the RF reference pulse
230 and the time of flight measurement is obtained upon receipt of
the acoustic pulses 240. A threshold detection technique 218 may be
employed to determine the receipt of the acoustic pulse 240. The
time interval relative to the RF pulse for time-of-flight from each
of two emitters to each of three detectors results in a set of six
distinct time intervals 250 for each measurement cycle. These
intervals 250 are processed to determine six independent
emitter-to-detector distances 250. In certain applications such as
military applications, meteorological data 228 such as temperature,
pressure and humidity can be factored into the distance
determination to enhance accuracy. The set of all possible emitter
locations that could generate a given distance result, describe a
sphere in the system reference frame. The intersection of three
such spheres (one for each detector) is two points, only one of
which is a logical solution. This solution is the location of the
emitter that originated the acoustic pulses. When the analogous
computation has been performed on signals from the second emitter,
the object's (e.g. mortar tube) position and orientation are
completely determined. For military applications, one additional
transform computation (not shown) can be performed to map the
system reference frame to the geodetic coordinate system employed
in fire missions. The equations for computation of the vector
pointing angles, azimuth, and elevation are:
d1a=(A0.sup.2+A1.sup.2+A2.sup.2).sup.1/2
d2a=((A0-R.sub.20).sup.2+A1.sup.2+A2.sup.2).sup.1/2
d3a=(A0.sup.2+(A0-R.sub.30).sup.2+A2.sup.2).sup.1/2 (1)
d1b=(B0.sup.2+B1.sup.2+B2.sup.2).sup.1/2
d2b=((B0-R.sub.20).sup.2+B1.sup.2+B2.sup.2).sup.1/2
d3b=(B0.sup.2+(B0-R.sub.30).sup.2+B2.sup.2).sup.1/2
[0036] where R.sub.20 is distance between origin detector and
detector on x axis and R.sub.30 is distance between origin detector
and detector on y axis.
[0037] The resulting distances (d1a, d2a, d3a, d1b, d2b, d3b) are
the coordinates for the emitters and azimuth and elevation is
computed as follows:
Q=[d1a, d2a, d3a]
P=[d1b, d2b, d3b] (2)
Mtube=P-Q
.phi..sub.xy=arctan(Mtube1/Mtube0)-Azimuth (3)
.phi..sub.xz=arctan(Mtube2/Mtube0)-Elevation (4)
[0038] This system could be implemented as a low cost solution with
an existing off-the-self pitch/roll/heading module 224 and 226. A
detector module 200 with an embedded Inertial Navigation System
would provide enhanced precision, and could allow one INS to serve
multiple weapons.
[0039] The preliminary design of the system relied on the use of a
phase locked loop (PLL) for acoustic pulse edge detection. A 75 kHz
sinusoidal acoustic pulse, of 1.6 millisecond duration, was input
to the PLL. This implementation was intended to result in a very
simplistic way of detecting the beginning and end of the acoustic
pulse. However, the PLL was not stable enough to perform edge
detection to the resolution required to obtain the distance
measurement accuracy specified for the system. The design was
changed to eliminate the PLL and the acoustic pulse was input to a
fast A/D and processed via a digital signal processor. While other
similar known techniques can be utilized, this technique allowed
measurement of the pulse edge for TOF measurements to within 50
microseconds. This implementation yielded final azimuth and
elevation computations to within 10 mils (0.56 degree) accuracy
with averaging.
[0040] The present invention will interface to GPS and
pitch/roll/heading sensors 224 and 226 to provide the reference
coordinate system and position information to the
detector/processing module 200. The detector/processing module 200
will also be capable of interfacing to other systems, such as
communication radios, which, in the case of the fire control system
application, will provide meteorological data (not shown).
[0041] The preferred embodiment of the system does not require a RF
reference pulse. In this embodiment, the desired distance
measurements are derived through round trip measurement of the time
of flight of a transmitted acoustic pulse. The typical components
for the system are shown in FIG. 4. The transmitted pulses are
received at the weapon system transducer 108, amplified 312,
reshaped 314 and retransmitted back to the detector/processing
module 400. The delay in the active electronics at the weapon
system is fixed. Therefore, the distance is equal to half of the
total time of flight, less the fixed delay in the electronics.
[0042] In either embodiment, the principal detector assembly drive
electronics are the same. Transducers 108 when excited by an input
signal produced by the drive electronics at the proper frequency
produce an acoustic pulse at the resonant frequency of the
transducers 108/210. The signal is received at the detecting
transducer 210. The acoustic pulse excites the transducer 210
resulting in a voltage signal with characteristics corresponding to
the frequency and amplitude of the signal received. This signal is
conditioned and retransmitted (in the case of the preferred
embodiment) or triggers the measurement of time of flight (in the
case of RF reference pulse embodiment). The processing
electronics/software captures the TOF measurement for each
emitter-detector pair (or round trip TOF) and then computes the
desired azimuth and elevation via a mathematical implementation of
equations (1), (2), (3), and (4).
[0043] The present invention is unique in its implementation for
derivation of azimuth and elevation for a weapons system. The
active reflector embodiment is also unique as it eliminates the
need for a reference pulse from which to base time of flight. The
time of flight is obtained purely from the acoustic signal.
[0044] The transducers 210 may be driven in numerous ways to
produce different characteristic signals. In particular, the pulse
duration and shape may be altered to accommodate desired
performance in range and signal decoding/integrity. This allows
flexibility in both the drive and receive circuitry.
[0045] The processing element may take several forms, including
programmable logic devices, microprocessors and digital signal
processors. The power supply could be batteries or other type of
portable supply such as solar cells.
[0046] The sensors and electronics may be combined to form an
integrated package whose input is an unconditioned drive signal and
whose output is a TOF measurement or a trigger indicating receipt
of a valid acoustic pulse edge.
[0047] Additional acoustic sensors may be added for use in
calibration of speed of sound variations due to temperature and
other air column effects. Additional sensors will also improve
accuracy of measurement and eliminate ambiguities in coordinate
position measurements.
[0048] As discussed, the RF transceivers may be eliminated in the
active reflector embodiment. It is also possible to eliminate the
need for a processor if the algorithms are implemented in hardware
and/or firmware.
[0049] It is also possible to implement the present invention using
passive reflection. That is, the acoustic pulses would be
transmitted and reflected off of the surface of the weapon
system.
[0050] The software and/or firmware in the system will support two
functions in the system. The first function will be control of the
hardware. This will include initialization and reset functions for
such devices as analog to digital converters and time of flight
measurement timer (if implemented in hardware). The software will
then read the time of flight (TOF) measurements and compute the
desired azimuth and elevation outputs per the equations (1), (2),
(3), and (4). These equations form the algorithms for computation
of the desired weapon pointing angles. The angles will be converted
to the coordinate system of the pitch/roll/heading sensors 224 and
226 by the software. The software will also include a user
interface function, which provides pointing cues to the weapons
system operator. These cues will provide information for
positioning the weapon at the correct attitude necessary to hit its
target.
[0051] No user alignments are required. For the proposed military
application as shown in FIG. 1, the field soldier would set up his
mortar 001, set the detector module 200 on the ground one to three
meters away and turn both the emitter assembly 100 and detector
module 200 on. Five seconds later, his gun `knows` where it is and
where it's aimed. Ease of use is a prime benefit of this system.
FIG. 5 is a flow chart showing a typical method for using the
preferred embodiment in a mortar tube application.
[0052] While originally conceived as a user-friendly fire control
system for mortar applications, the method described herein can be
used in any situation where non-contact sensing of position and
orientation would be needed. There are a number of possible
applications, including:
[0053] Sensing the position/orientation of more than one mortar
with a single detector module. In principle, unique emitter carrier
frequencies (or pulse trains) and complementary receiving
electronics would allow more than one weapon to be served by a
single detection module.
[0054] The invention can be used on larger weapon systems, such as
tank tubes. In addition to providing targeting information, the
system could replace the tube-droop sensing system (currently a
laser/reflector/detector implementation) as well.
[0055] Recreational target shooters or the operators of shooting
ranges might employ such a system to provide a `no hassle` bore
sighting service.
[0056] Owners of high-end telescopes for amateur astronomy could
find this system very attractive, especially when interfaced with
one of the precision mount drives.
[0057] Although the invention has been described in detail with
particular reference to these preferred embodiments, other
embodiments can achieve the same results. Variations and
modifications of the present invention will be obvious to those
skilled in the art and it is intended to cover in the appended
claims all such modifications and equivalents. The entire
disclosures of all references, applications, patents, and
publications cited above, are hereby incorporated by reference.
* * * * *