Positioning refinement algorithm

• US 6,292,751 B1
• Filed: 02/08/2000
• Issued: 09/18/2001
• Est. Priority Date: 02/08/2000
• Status: Expired due to Term

• Current Assignee: OL Security LLC (Intellectual Ventures LLC), The United States of America As Represented By The Secretary of Agriculture
• Original Assignee: BAE Systems Plc
• Inventors: Frank, Mark
• Primary Examiner(s): Cuchlinski, Jr., William A.
• Assistant Examiner(s): MARC-COLEMAN, MARTHE Y
• Application Number:
  US09/500,274
• Time in Patent Office: 588 Days
• Field of Search: 701/207, 701/202, 701/221, 701/220, 702/150, 702/87
• US Class Current: 701/220
• CPC Class Codes: G01C 21/188 for accumulated errors, e.g. by coupling inertial systems with absolute positioning systems

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.

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.

2. The method of claim 1, wherein the function is a straight line with a slope proportional to the magnitude of the recorded indicated velocity.

3. The method of claim 1, where the IMU is mounted upon a vehicle for detecting mines and where the period of interest begins when a mine is detected and ends when the vehicle is positioned such that the mine is behind the vehicle and in close proximity thereto.

4. The method of claim 1, wherein a parameter of the function is determined by setting the function equal to the recorded indicated velocity and setting the time equal to the end of the period of interest.

5. The method of claim 1, further comprising the step of providing a computer processor for performing the step of deriving the accumulated error in position.

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.

7. The method of claim 6, wherein the function is a straight line with a slope proportional to the magnitude of the recorded indicated velocity.

8. The method of claim 6, wherein a parameter of the function is determined by setting the function equal to the recorded indicated velocity and setting the time equal to the end of the period of interest.

9. The method of claim 6, further comprising the step of providing a computer processor for deriving the accumulated error in position.

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, t₁, and position, P₁, of the IMU at a subsequent start of a period of interest after the first zero velocity update;

recording the time, t₂ and position, P₂, 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, V₂, indicated from the IMU; and

deriving an accumulated error in position, Δ

P_e, according to the following formula;

11. The method of claim 10, further comprising the step of computing a change in position, Δ

P_a, of the IMU according to the following formula;

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.