Positioning refinement algorithm

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First Claim
1. A method for correcting errors in position derived from an inertial measurement unit (IMU), comprising the steps of:
 performing a first zero velocity update at a time when the IMU is at rest;
recording the time and position of the IMU at a subsequent start of a period of interest after the first zero velocity update;
recording the time and position of the IMU at the end of the period of interest;
performing a second zero velocity update at the end of the period of interest with the IMU at rest, and then recording a velocity indicated from the IMU; and
deriving an accumulated error in position the deriving comprising a) approximating errors in velocity by a function of time with a parameter determined from the recorded indicated velocity, and b) integrating the function over the period of interest to determine the accumulated error in position during the period of interest.
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Abstract
A method is provided for correcting errors in position derived from an inertial measurement unit (IMU), by performing a first zero velocity update at a time when the IMU is at rest, recording the time and position of the IMU at a subsequent start of a period of interest after the first zero velocity update, recording the time and position of the IMU at the end of the period of interest, performing a second zero velocity update at the end of the period of interest with the IMU at rest, and then recording a velocity indicated from the IMU, and deriving an accumulated error in position from the recorded data, by approximating errors in velocity by a function of time with a parameter determined from the recorded indicated velocity, and integrating the function over the period of interest to determine the accumulated error in position during the period of interest.
34 Citations
View as Search Results
State Estimator for Rejecting Noise and Tracking and Updating Bias in Inertial Sensors and Associated Methods  
Patent #
US 20100292943A1
Filed 05/18/2009

Current Assignee
University of Utah Research Foundation

Sponsoring Entity
University of Utah Research Foundation

Methods and systems providing an adaptive threshold for a beam sharpened pulse radar  
Patent #
US 7,652,615 B2
Filed 05/26/2006

Current Assignee
Honeywell International Inc.

Sponsoring Entity
Honeywell International Inc.

Method and computerreadable storage medium with instructions for processing data in an internal navigation system  
Patent #
US 20090254276A1
Filed 04/08/2008

Current Assignee
ENSCO Incorporated

Sponsoring Entity
ENSCO Incorporated

Level, angle and distance measuring device  
Patent #
US 7,350,303 B2
Filed 11/14/2003

Current Assignee
Rock Angus James, Rock Alan George

Sponsoring Entity
Rock Angus James, Rock Alan George

INERTIAL MEASUREMENT UNIT LOCALIZATION TECHNIQUE FOR SENSOR NETWORKS  
Patent #
US 20080291042A1
Filed 05/23/2007

Current Assignee
Honeywell International Inc.

Sponsoring Entity
Honeywell International Inc.

Method and apparatus for compensating for acceleration errors and inertial navigation system employing the same  
Patent #
US 7,280,916 B2
Filed 06/16/2004

Current Assignee
Samsung Electronics Co. Ltd.

Sponsoring Entity
Samsung Electronics Co. Ltd.

METHODS AND SYSTEMS PROVIDING AN ADAPTIVE THRESHOLD FOR A BEAM SHARPENED PULSE RADAR  
Patent #
US 20070273572A1
Filed 05/26/2006

Current Assignee
Honeywell International Inc.

Sponsoring Entity
Honeywell International Inc.

Level, angle and distance measuring device  
Patent #
US 20060053645A1
Filed 11/14/2003

Current Assignee
Rock Angus James, Rock Alan George

Sponsoring Entity
Rock Angus James, Rock Alan George

Navigation of remote controlled vehicles  
Patent #
US 6,859,729 B2
Filed 10/21/2002

Current Assignee
OL Security LLC

Sponsoring Entity
BAE Systems Integrated Defense Solutions Inc

Navigation of remote controlled vehicles  
Patent #
US 20040078137A1
Filed 10/21/2002

Current Assignee
OL Security LLC

Sponsoring Entity
OL Security LLC

Method and apparatus for compensating for acceleration errors and inertial navigation system employing the same  
Patent #
US 20040260468A1
Filed 06/16/2004

Current Assignee
Samsung Electronics Co. Ltd.

Sponsoring Entity
Samsung Electronics Co. Ltd.

Positioning and data integrating method and system thereof  
Patent #
US 6,516,272 B2
Filed 11/20/2001

Current Assignee
American GNC Corporation

Sponsoring Entity
American GNC Corporation

Method and apparatus for applying decimation processing to vehicle position data based upon data accuracy estimation  
Patent #
US 6,480,784 B2
Filed 03/20/2001

Current Assignee
Matsushita Electric Industrial Company Limited

Sponsoring Entity
Matsushita Electric Industrial Company Limited

Method and computerreadable storage medium with instructions for processing data in an internal navigation system  
Patent #
US 8,224,575 B2
Filed 04/08/2008

Current Assignee
ENSCO Incorporated

Sponsoring Entity
ENSCO Incorporated

ESTIMATION OF NDIMENSIONAL PARAMETERS WHILE SENSING FEWER THAN N DIMENSIONS  
Patent #
US 20120209520A1
Filed 02/08/2012

Current Assignee
Honeywell International Inc.

Sponsoring Entity
Honeywell International Inc.

Machine navigation system having integrity checking  
Patent #
US 8,700,324 B2
Filed 08/25/2010

Current Assignee
Caterpillar Incorporated

Sponsoring Entity
Caterpillar Incorporated

Estimation of Ndimensional parameters while sensing fewer than N dimensions  
Patent #
US 8,812,235 B2
Filed 02/08/2012

Current Assignee
Honeywell International Inc.

Sponsoring Entity
Honeywell International Inc.

Vision based zero velocity and zero attitude rate update  
Patent #
US 8,948,446 B2
Filed 01/19/2011

Current Assignee
Honeywell International Inc.

Sponsoring Entity
Honeywell International Inc.

State estimator for rejecting noise and tracking and updating bias in inertial sensors and associated methods  
Patent #
US 9,127,947 B2
Filed 05/18/2009

Current Assignee
University of Utah Research Foundation

Sponsoring Entity
University of Utah Research Foundation

Devices, Systems, and Methods Related to Tracking Location of Operator Control Units for Locomotives  
Patent #
US 20160229434A1
Filed 02/06/2015

Current Assignee
Control Solutions Enterprises Inc.

Sponsoring Entity
Control Solutions Enterprises Inc.

Position measurement correction using loopclosure and movement data  
Patent #
US 9,423,250 B1
Filed 08/23/2012

Current Assignee
The Boeing Co.

Sponsoring Entity
The Boeing Co.

Onvehicle equipment control system and vehicle  
Patent #
US 9,731,667 B2
Filed 07/10/2013

Current Assignee
Ibaraki Toyota Jidosha Kabushiki Kaisha

Sponsoring Entity
Ibaraki Toyota Jidosha Kabushiki Kaisha

Systems, methods, and apparatus for calibration of and threedimensional tracking of intermittent motion with an inertial measurement unit  
Patent #
US 9,810,549 B2
Filed 01/06/2012

Current Assignee
University of Utah Research Foundation

Sponsoring Entity
University of Utah Research Foundation

Heading inconsistency mitigation for inertial navigation using lowperformance inertial measurement units with relative aiding  
Patent #
US 9,909,877 B2
Filed 06/06/2016

Current Assignee
Honeywell International Inc.

Sponsoring Entity
Honeywell International Inc.

Devices, systems, and methods related to tracking location of operator control units for locomotives  
Patent #
US 10,023,210 B2
Filed 02/06/2015

Current Assignee
Control Solutions Enterprises Inc.

Sponsoring Entity
Laird Technologies Incorporated

Control system for work machine, work machine, and control method for work machine  
Patent #
US 10,120,388 B2
Filed 03/31/2016

Current Assignee
Komatsu

Sponsoring Entity
Komatsu

Inertial motion tracking device  
Patent #
US 10,274,509 B1
Filed 04/09/2015

Current Assignee
InertialWave Co.

Sponsoring Entity
InertialWave Co.

Multisensor vehiclemounted mine detector  
Patent #
US 6,026,135 A
Filed 04/03/1998

Current Assignee
QSINE CORPORATION LIMITED

Sponsoring Entity
Her Majesty the Queen in right of Canada as represented by the Minister of National Defence

Sculling compensation in strapdown inertial navigation systems  
Patent #
US 5,890,093 A
Filed 11/01/1996

Current Assignee
Northrop Grumman Systems Corporation

Sponsoring Entity


Azimuthaxis drift rate determination in an inertial navigator  
Patent #
US 5,941,935 A
Filed 09/23/1996

Current Assignee
Fernandez Manuel

Sponsoring Entity


Apparatus and method for sensing motionlessness in a vehicle  
Patent #
US 5,736,923 A
Filed 07/11/1995

Current Assignee
Ansaldo STS SPA

Sponsoring Entity
UNION SWITCH SIGNAL INC.

Azimuth misalignment determination in an inertial navigator  
Patent #
US 5,789,671 A
Filed 08/15/1996

Current Assignee
Fernandez Manuel

Sponsoring Entity
Fernandez Manuel

Integrated spacing and orientation control system  
Patent #
US 5,524,524 A
Filed 10/24/1994

Current Assignee
TRACOR AEROSPACE INC.

Sponsoring Entity
TRACOR AEROSPACE INC.

Procedure for measuring angles and trajectories by means of gyros and inertial systems  
Patent #
US 5,331,578 A
Filed 09/11/1991

Current Assignee
Deutsche Telekom AG

Sponsoring Entity
Deutsche Telekom AG

12 Claims
 1. A method for correcting errors in position derived from an inertial measurement unit (IMU), comprising the steps of:
 performing a first zero velocity update at a time when the IMU is at rest;
recording the time and position of the IMU at a subsequent start of a period of interest after the first zero velocity update;
recording the time and position of the IMU at the end of the period of interest;
performing a second zero velocity update at the end of the period of interest with the IMU at rest, and then recording a velocity indicated from the IMU; and
deriving an accumulated error in position the deriving comprising a) approximating errors in velocity by a function of time with a parameter determined from the recorded indicated velocity, and b) integrating the function over the period of interest to determine the accumulated error in position during the period of interest.  View Dependent Claims (2, 3, 4, 5)
 performing a first zero velocity update at a time when the IMU is at rest;
 6. A method for determining the position of a mine relative to a vehicle upon which is mounted an inertial measurement unit (IMU), comprising the steps of:
 performing a first zero velocity update at a time when the vehicle is at rest;
recording the time and position of the vehicle at a subsequent start of a period of interest after the first zero velocity update, wherein the start of the period of interest is triggered by the detection of a mine;
recording the time and position of the vehicle at the end of the period of interest, wherein the end of the period of interest is triggered by the positioning of the vehicle such that the mine is behind the vehicle and in close proximity thereto;
performing a zero velocity update at the end of the period of interest with the vehicle at rest, and then recording a velocity indicated from the IMU; and
deriving an accumulated error in position the deriving comprising a) approximating errors in velocity by a function of time with a parameter determined from the recorded indicated velocity, and b) integrating the function over the period of interest to determine the accumulated error in position during the period of interest.  View Dependent Claims (7, 8, 9)
 performing a first zero velocity update at a time when the vehicle is at rest;
 10. A method for correcting errors in position derived from an inertial measurement unit (IMU), comprising the steps of:
 performing a first zero velocity update at a time when the IMU is at rest;
recording the time, t , and position, P1 , of the IMU at a subsequent start of a period of interest after the first zero velocity update;1
recording the time, t and position, P2 , of the IMU at the end of the period of interest;2
performing a second zero velocity update at the end of the period of interest with the IMU at rest, and then recording a velocity, V , indicated from the IMU; and2
deriving an accumulated error in position, ΔP , according to the following formula;e  View Dependent Claims (11)
 performing a first zero velocity update at a time when the IMU is at rest;
 12. A mine detection vehicle for determining the position of a mine, comprising:
 an inertial navigation system (INS) comprising an inertial measurement unit (IMU) mounted upon said vehicle;
a processor for determining errors in position derived from said IMU by processing recorded data obtained according to the following steps;
(1) performing a first zero velocity update at a time when the IMU is at rest;
(2) recording the time and position of the IMU at a subsequent start of a period of interest after the first zero velocity update;
(3) recording the time and position of the IMU at the end of the period of interest;
(4) performing a second zero velocity update at the end of the period of interest with the IMU at rest, and then recording a velocity indicated from the IMU, and (5) deriving an accumulated error in position the deriving comprising a) approximating errors in velocity by a function of time with a parameter determined from the recorded indicated velocity, and b) integrating the function over the period of interest to determine the accumulated error in position during the period of interest.
 an inertial navigation system (INS) comprising an inertial measurement unit (IMU) mounted upon said vehicle;
1 Specification
This invention relates to methods and apparatus for correcting errors associated with the use of an inertial measurement unit (IMU) to track positions, locations, or movements.
BACKGROUND OF THE INVENTIONInertial Measurement Units (IMUs) typically use accelerometers and gyros to track accelerations in order to calculate changes in position. Because of inherent errors in the sensors used in IMUs, random errors in the calculated position build with time. One current method of eliminating these errors is to use a second position sensor (e.g., a GPS or an odometer input) along with a Kalman filter to minimize errors from each of the position sensors. A second method is to stop and perform a Zero Velocity Update (ZVU) to recalibrate the sensors at the beginning of a period of interest.
Most applications using IMUs require good absolute position accuracy over long distances, such as for use in a plane or a tank. Such applications are ideal for use of an IMU coupled with a secondary data source such as a Global Positioning System (GPS) to bound and correct errors in the IMU. A typical IMU operating in conjunction with the GPS may be capable of 10 meters in accuracy relative to a fixed reference point after traversing a distance of 100 miles.
In contrast, some applications, such as to which this invention applies, requires extremely accurate relative position data over short distances. In such applications, it is necessary to determine with high accuracy how far the IMU has moved since the last ZVU was performed.
Neither of the two methods described above are suitable when very high relative positional accuracy is required over very short distances. For example, where a vehicle is used to detect and destroy a land mine, 3 centimeters of accuracy in 6 meters of travel is required. These high levels of accuracy preclude the use of coarse sensors such as an odometer or GPS to eliminate the errors. The nature of these applications also prevents a ZVU from being performed at the beginning of each period of interest (i.e., sensing of a mine or false alarm). Other solutions to the problem of accumulation of errors from an IMU include the use of more expensive sensors with lower noise, and using additional external equipment. As an example, survey quality differential Real Time Kinematic (RTK) GPS can provide highly accurate positional data with the use of a ground based station at a known point, which is disadvantageous in some situations. Thus, to achieve the requisite high levels of accuracy would generally require an IMU using extremely accurate sensors costing approximately $100,000. Therefore, there is a need for methods and apparatus for generating highly accurate position data over short periods of travel using a less expensive IMU.
SUMMARY OF THE INVENTIONAn object of the present invention is, therefore, to provide methods and apparatus for generating highly accurate position data over short periods of travel using a relatively inexpensive IMU. This invention utilizes a method of estimating the random velocity errors in order to remove a portion of these errors from the position data.
The invention allows the use of a relatively inexpensive IMU by providing a method of estimating the accumulated error at the beginning and end of the period of interest, and then correcting for these errors. The method employs a ZVU at the end of the period of interest and uses a simple algorithm along with existing data from the IMU to correct for the accumulated errors and thereby provide more accurate position data.
The invention may be employed in a system for detecting and disabling mines as described herein, and may also be used to refine the accuracy of position determination in other applications as well.
The present invention provides several key advantages: (1) it provides highly accurate relative position data over short distances; (2) does not require external or groundbased equipment; (3) does not require stopping for calibration at the beginning of the period of interest; (4) does not require stopping for any length of time to gather data; (5) does not require the use of a second data source; and (6) allows the use of less expensive inertial sensors.
According to the present invention, a conventional IMU is provided for obtaining relative position data. A Zero Velocity Update (ZVU) is performed prior to the commencement of motion to calibrate the IMU. At some time after the commencement of motion a period of interest begins. At the start of the period of interest, the time and position of the IMU is recorded. At a later time, the period of interest ends. At the end of the period of interest, the motion of the IMU is stopped and the time and position of the IMU is again recorded. The velocity indicated by the IMU at the end of the period of interest is also recorded. Because the IMU is now at rest, any velocity indicated by the IMU is the result of errors accumulated during the time of motion of the IMU. The accumulation of error as a function of time is approximated by a function, f(t). From this function, the approximate amount of error at both the beginning and the end of the period of interest can be calculated. This error can then be subtracted from the position data for both the beginning and ending points of interest to minimize the error in the indicated relative change in position between these points.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGSFor a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
<FGREF>FIG. 1</FGREF> is a flow chart of steps for implementing a method of the present invention.
<FGREF>FIG. 2</FGREF> shows a plot of velocity error as a function of time.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTSAn operational flow chart of steps for implementing the methods of the present invention is shown in FIG. 1. Initially, an inertial navigation system (INS), which incorporates a conventional IMU, is at rest, 100. A ZVU is performed prior to commencement of motion of the INS to calibrate the IMU, 100. Motion of the INS then commences and the INS operates in an unaided navigation mode, 102. At some time after the commencement of motion a period of interest begins. At the start of the period of interest, the time and position of the INS is recorded, 104. At a later time, the period of interest ends. At this time, the INS receives a stop notification 106 and comes to rest, 108, and the time and position of the INS is recorded, 100. The velocity along two horizontal axes, say north and east, is then recorded, 112. Because the IMU is at rest, any velocity indicated by the IMU is the result of errors accumulated during the time of motion of the IMU. With the information now obtained, an accurate determination of the position of the INS relative to its position at the start of the period of interest can be made 114.
The IMU produces measurements of acceleration over time which may be integrated once to produce a velocity history and twice to produce an indication of position. However, the accelerometer output of the IMU contains errors which are random in nature. Since velocity and position are obtained from integration of the IMU ouput, velocity and position errors accumulate over time. In the present invention, the velocity errors are approximated by a function with parameters that can be determined by evaluating the function at two instances of time: at an initial time when the IMU is at rest and the function is set equal to zero, and at the end of the period of interest when the function is set equal to the velocity recorded after the ZVU is performed when the IMU is at rest. Once the function is determined, it can be integrated over the period of interest to determine the error in position that has accumulated during the period of interest.
For example, if the accelerometer bias is constant, the velocity error will grow linearly with time, while position error grows as the square of time. <FGREF>FIG. 2</FGREF> shows velocity error as a function of time, assuming a constant bias in the accelerometer output:
<F>V<HIL><SB>e</SB></HIL>(t)=∫a<HIL><SB>e</SB></HIL>dt=a<HIL><SB>e</SB></HIL>t+b</F>
where V<HIL><SB>e</SB></HIL>(t) is the velocity error and a<HIL><SB>e </SB></HIL>is the constant acceleration error, and b is some initial velocity error. At time, t=0, V<HIL><SB>e</SB></HIL>(t) is zero because a ZVU was performed with the INS at rest. This yields b=0. At a later time, t<HIL><SB>1</SB></HIL>, when a period of interest begins, the time, t<HIL><SB>1</SB></HIL>, and an indicated position, P<HIL><SB>1</SB></HIL>, is recorded. At a still later time, t<HIL><SB>2</SB></HIL>, the period of interest ends, and the time, t<HIL><SB>2</SB></HIL>, and position P<HIL><SB>2</SB></HIL>, is recorded. The INS is stopped and the velocity V<HIL><SB>2</SB></HIL>, is recorded. Since the actual velocity of the INS is zero, V<HIL><SB>2</SB></HIL>, is equal to the velocity error, V<HIL><SB>e</SB></HIL>(t<HIL><SB>2</SB></HIL>), at time, t<HIL><SB>2</SB></HIL>:
<F>V<HIL><SB>e</SB></HIL>(t<HIL><SB>2</SB></HIL>)=a<HIL><SB>e</SB></HIL>t<HIL><SB>2</SB></HIL>=V<HIL><SB>2</SB></HIL></F>
From this equation we can determine the constant acceleration error, a<HIL><SB>e</SB></HIL>=V<HIL><SB>2</SB></HIL>/t<HIL><SB>2</SB></HIL>. The position error can now be determined by integrating the function for velocity error over the period of interest: <CWU><MATHUS><MATHEMATICA></MATHEMATICA><MATHML><math><mrow><mrow><mi>Δ</mi><mo></mo><mstyle><mtext> </mtext></mstyle><mo></mo><msub><mi>P</mi><mi>e</mi></msub></mrow><mo>=</mo><mrow><mrow><msub><mi>V</mi><mn>2</mn></msub><mo></mo><mrow><msubsup><mo>∫</mo><msub><mi>t</mi><mn>1</mn></msub><msub><mi>t</mi><mn>2</mn></msub></msubsup><mo></mo><mrow><mi>t</mi><mo></mo><mstyle><mtext> </mtext></mstyle><mo></mo><mrow><mo>ⅆ</mo><mi>t</mi></mrow></mrow></mrow></mrow><mo>=</mo><mrow><mfrac><msub><mi>V</mi><mn>2</mn></msub><mn>2</mn></mfrac><mo></mo><mrow><mo>(</mo><mrow><msubsup><mi>t</mi><mn>2</mn><mn>2</mn></msubsup><mo></mo><msubsup><mi>t</mi><mn>1</mn><mn>2</mn></msubsup></mrow><mo>)</mo></mrow></mrow></mrow></mrow></math></MATHML><EMI></EMI></MATHUS></CWU>
where ΔP<HIL><SB>e </SB></HIL>is the position error that accumulated from the beginning of the period of interest to the end of the period of interest.
The indicated position, P<HIL><SB>2</SB></HIL>, at time, t<HIL><SB>2</SB></HIL>, is given by: <CWU><MATHUS><MATHEMATICA></MATHEMATICA><MATHML><math><mrow><msub><mi>P</mi><mn>2</mn></msub><mo>=</mo><mrow><mrow><msub><mi>P</mi><mi>a</mi></msub><mo></mo><mrow><mo>(</mo><msub><mi>t</mi><mn>2</mn></msub><mo>)</mo></mrow></mrow><mo>+</mo><mfrac><mrow><msub><mi>V</mi><mn>2</mn></msub><mo></mo><msubsup><mi>t</mi><mn>2</mn><mn>2</mn></msubsup></mrow><mn>2</mn></mfrac></mrow></mrow></math></MATHML><EMI></EMI></MATHUS></CWU>
where P<HIL><SB>a</SB></HIL>(t<HIL><SB>2</SB></HIL>) is the actual position of the INS at the end of the period of interest relative to its position at time t=0. Since P<HIL><SB>2</SB></HIL>, t<HIL><SB>2 </SB></HIL>and V<HIL><SB>2 </SB></HIL>are known, P<HIL><SB>a</SB></HIL>(t<HIL><SB>2</SB></HIL>) can be calculated directly as: <CWU><MATHUS><MATHEMATICA></MATHEMATICA><MATHML><math><mrow><mrow><msub><mi>P</mi><mi>a</mi></msub><mo></mo><mrow><mo>(</mo><msub><mi>t</mi><mn>2</mn></msub><mo>)</mo></mrow></mrow><mo>=</mo><mrow><msub><mi>P</mi><mn>2</mn></msub><mo></mo><mrow><msub><mi>V</mi><mn>2</mn></msub><mo></mo><mfrac><msubsup><mi>t</mi><mn>2</mn><mn>2</mn></msubsup><mn>2</mn></mfrac></mrow></mrow></mrow></math></MATHML><EMI></EMI></MATHUS></CWU>
Similarly, the actual position of the INS at the beginning of the period of interest relative to its position at time t=0 can also be calculated: <CWU><MATHUS><MATHEMATICA></MATHEMATICA><MATHML><math><mrow><mrow><msub><mi>P</mi><mi>a</mi></msub><mo></mo><mrow><mo>(</mo><msub><mi>t</mi><mn>1</mn></msub><mo>)</mo></mrow></mrow><mo>=</mo><mrow><msub><mi>P</mi><mn>1</mn></msub><mo></mo><mfrac><mrow><msub><mi>V</mi><mn>2</mn></msub><mo></mo><msubsup><mi>t</mi><mn>1</mn><mn>2</mn></msubsup></mrow><mn>2</mn></mfrac></mrow></mrow></math></MATHML><EMI></EMI></MATHUS></CWU>
Thus, the actual change in position during the period of interest is: <CWU><MATHUS><MATHEMATICA></MATHEMATICA><MATHML><math><mrow><mrow><mi>Δ</mi><mo></mo><mstyle><mtext> </mtext></mstyle><mo></mo><msub><mi>P</mi><mi>a</mi></msub></mrow><mo>=</mo><mrow><mrow><mrow><msub><mi>P</mi><mi>a</mi></msub><mo></mo><mrow><mo>(</mo><msub><mi>t</mi><mn>2</mn></msub><mo>)</mo></mrow></mrow><mo></mo><mrow><msub><mi>P</mi><mi>a</mi></msub><mo></mo><mrow><mo>(</mo><msub><mi>t</mi><mn>1</mn></msub><mo>)</mo></mrow></mrow></mrow><mo>=</mo><mrow><mrow><mo>(</mo><mrow><msub><mi>P</mi><mn>2</mn></msub><mo></mo><msub><mi>P</mi><mn>1</mn></msub></mrow><mo>)</mo></mrow><mo></mo><mrow><mfrac><msub><mi>V</mi><mn>2</mn></msub><mn>2</mn></mfrac><mo></mo><mrow><mo>(</mo><mrow><msubsup><mi>t</mi><mn>2</mn><mn>2</mn></msubsup><mo></mo><msubsup><mi>t</mi><mn>1</mn><mn>2</mn></msubsup></mrow><mo>)</mo></mrow></mrow></mrow></mrow></mrow></math></MATHML><EMI></EMI></MATHUS></CWU>
Although the velocity error was approximated by a straight line in this example, a person of ordinary skill in the art will recognize that other suitable functions for approximating velocity error may be employed in accordance with the method of the invention as herein disclosed.
The calculation of position errors is performed for each orthogonal direction for which motion may take place. For example, if the motion of the IMU is in a plane, position error is calculated for each of the two orthogonal axes that define the plane of motion.
The method of the present invention may be implemented by providing a computer processor for performing the computations and logical decisions required to implement the method for correcting position errors described herein. Programming the processor to implement the method is a relatively simple task for a person of ordinary skill in the art.
The method of the present invention described herein may be employed in a mine hunterkiller system. Such a system utilizes a vehicle upon which is mounted an INS comprising an IMU and a processor for deriving errors in position from recorded data obtained in accordance with the method herein described. Initially, the vehicle is at rest and a ZVU is performed on the IMU. The vehicle then commences motion. A period of interest begins when the vehicle detects a mine just in front of the vehicle and records its position relative to the vehicle. At that moment, the time and position of the vehicle is recorded. The vehicle then stops with the mine behind the vehicle and in close proximity thereto, so that the mine may be reached by a robotic arm. At that moment, the time and position is again recorded and a ZVU is performed. From this data the precise position of the mine relative to the vehicle can be accurately determined. Using this accurate position data, a robotic arm places a neutralizer atop the mine for later remote detonation.
Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made to the embodiments described herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.