Self-calibrated azimuth and attitude accuracy enhancing method and system (SAAAEMS)

• US 8,005,635 B2
• Filed: 08/14/2008
• Issued: 08/23/2011
• Est. Priority Date: 08/14/2007
• Status: Active Grant

• Current Assignee: American GNC Corporation
• Original Assignee: American GNC Corporation
• Inventors: Lin, Ching-Fang
• Primary Examiner(s): Kundu, Sujoy K
• Application Number:
  US12/228,754
• Publication Number:
  US 20090089001A1
• Time in Patent Office: 1,104 Days
• Field of Search: 702/92, 702/93, 702/141, 342/357.11, 342/357.14, 735/033, 735/040.2, 735/040.3, 735/040.8, 735/041.8, 701/216
• US Class Current: 702/92
• CPC Class Codes: G01C 21/188 for accumulated errors, e.g. by coupling inertial systems with absolute positioning systems
• CPC Class Codes: G01C 25/005 initial alignment, calibration or starting-up of inertial devices

Abstract

A method and system for Self-calibrated Azimuth and Attitude Accuracy Enhancing are disclosed, wherein SAAAEMS approach is based on fully auto-calibration self-contained INS principles, not depending on magnetometers for azimuth/heading determination, and thus the system outputs and performance are not affected by the environmental magnetic fields. In order to reduce the system size and cost, this new innovative methods and algorithms are used for SAAAEMS system configuration and integration. Compared to a conventional INS for gyrocompassing, AGNC'"'"'s approach uses a smaller number of high accuracy sensors: SAAAEMS uses only one 2-axis high accuracy gyro (for example, one DTG) instead of 3-axis; the third axis gyro is a MEMS gyro. It uses only 2 high accuracy accelerometers instead of 3, since the two accelerometers are used only for gyrocompassing not for navigation. These two changes to the conventional INS system configuration remarkably reduce the whole system size and cost. SAAAEMS, uses dynamic gyrocompassing processing for isolation of Base motion disturbance/interference and vibration. SAAAEMS provides a method and system for using automatic methods for system calibration.

Claims

1. A self-calibrated azimuth and attitude accuracy enhancing system, which is a self-contained system, comprising:

two kinds of inertial sensors only, wherein the first kind of inertial sensor comprises a first one-axis gyro measuring an inertial angular rate; and

a second one-axis gyro measuring an inertial angular rate wherein said first one-axis gyro and said second one-axis gyro are not identical in direction;

wherein the second kind of inertial sensor comprises a first accelerometer measuring an acceleration; and

a second accelerometer measuring an acceleration wherein said first accelerometer and said second accelerometer are not identical in direction; and

a system processor processing said measurements of said first one-axis gyro, said second one-axis gyro, said first accelerometer, and said second accelerometer for determining an azimuth and attitude where said system is located through gyro-compassing processing based on measurement of the earth'"'"'s angular rate and gravity for obtaining the true north of a carrier of said system without magnetic interference and GPS signal jamming.

2. The system, as recited in claim 1, wherein the first kind of inertial sensor further comprises a third gyro for said system to work in dynamic state.

3. The system, as recited in claim 2, wherein said third gyro is a MEMS gyro.

4. The system, as recited in claim 3, wherein said first one-axis gyro, said second one-axis gyro, said first accelerometer, and said second accelerometer are measuring an earth'"'"'s angular velocity vector and a local gravity force vector.

5. The system, as recited in claim 4, further comprising:

one or more sensor signal filters for filtering signals of said first one-axis gyro, said second one-axis gyro, said first accelerometer, and said second accelerometer; and

an ADC (analog/digital convertor) circuit converting analog signals of said first one-axis gyro, said second one-axis gyro, said first accelerometer, and said second accelerometer into digital signals and feeding said digital signals into said system processor.

6. The system, as recited in claim 1, wherein said first one-axis gyro and said second one-axis gyro is a two-axis gyro.

7. The system, as recited in claim 2, wherein said first one-axis gyro and said second one-axis gyro is a two-axis gyro.

8. The system, as recited in claim 5, wherein said first one-axis gyro and said second one-axis gyro is a two-axis gyro.

9. A self-calibrated azimuth and attitude accuracy enhancing method, comprising steps of:

(a) powering on a SAAAEMS (self-calibrated azimuth and attitude accurate enhancing method and system) system and positioning said system on a stationary base;

(b) waiting for a predetermined period of time for gyros to fully start;

(c) getting two channel gyro and two channel accelerometer measurement data;

(d) performing sensor calibration and error compensation for both two channel gyro and two channel accelerometer measurement data by the following steps;

(d1) positioning said SAAAEMS system on a stationary base;

(d2) waiting for a predetermined period of time for gyros to fully start;

(d3) performing ADC to get two channel gyro measurement data;

(d4) processing said gyro measurement data by two (X, Y) low-pass filters;

(d5) averaging said gyro data over a predetermined time period;

(d6) using said standard deviation of said gyro data over a predetermined time period to verify if said SAAAEMS system is really on a stationary base;

(d7) saving said obtained data as group 1;

(d8) moving said SAAAEMS system to a second angular position and on a stationary base;

(d9) repeating step (d2) to step (d6), saving said obtained data as group 2;

(d10) moving said SAAAEMS system to a third angular position and on a stationary base;

(d11) repeating step (d2) to step (d6), saving said obtained data as group 3;

(d12) moving said SAAAEMS system to a forth angular position and on a stationary base;

(d13) repeating step (d2) to step (d6), saving said obtained data as group 4;

(d14) constructing an initial vector r which includes an initial estimates of a gyro bias;

(d15) using said obtained 4 groups data to construct initial F(r) matrix;

(d16) using said obtained 4 groups data to construct an initial

10. The method as recited in claim 9, further comprising the steps of:

(h) using said calculated Ĉ

_bⁿ(t) as an initial value of said C_bⁿ¹(t) DCM based on said static gyrocompasing process as said SAAAEMS system initialization method;

(i) using said initial C_bⁿ¹(t) to transform said calibrated and compensated gyro input data from said B frame to a N1 frame;

(j) using said initial C_bⁿ¹(t) to transform said calibrated and compensated accelerometer input data from said B frame to said N1 frame;

(k) sending X and Y components of said transformed accelerometer input data to SAAAEMS estimator and controller to form a closed-loop control command;

(l) removing an earth angular velocity component from said transformed gyro input data;

(m) adding closed-loop control command from said SAAAEMS estimator and controller to said transformed gyro input data, to form a total SAAAEMS attitude update command;

(n) using said total SAAAEMS attitude update command to update said system attitude by an quaternion attitude update equation;

(o) transforming said updated quaternion attitude to DMC representation and get an updated DMC C_bⁿ¹(t);

(p) looping back to the step (i), using said updated C_bⁿ¹(t) to transform said calibrated and compensated gyro input data from said B frame to said N1 frame;

(q) using said updated C_bⁿ¹(t) to transform said calibrated and compensated accelerometer input data from said B frame to said N1 frame;

(r) repeating said step (i) to said step (q) to obtain real-time continuous C_bⁿ¹(t) updates; and

(s) calculating a real-time continuous SAAAEMS pitch/elevation, roll and azimuth/heading angles for system output during the loop.

11. A self-calibrated azimuth and attitude accuracy enhancing method, comprising steps of:

(a) powering on a SAAAEMS (self-calibrated azimuth and attitude accurate enhancing method and system) system and positioning said system on a stationary base;

(b) waiting for a predetermined period of time for gyros to fully start;

(c) getting two channel gyro and two channel accelerometer measurement data;

(d) performing sensor calibration and error compensation for both two channel gyro and two channel accelerometer measurement data by the following steps;

(d1) positioning said SAAAEMS system on a stationary base;

(d2) waiting for a predetermined period of time for gyros to fully start;

(d3) performing ADC to get two channel gyro measurement data;

(d4) processing said gyro measurement data by two (X, Y) low-pass filters;

(d5) averaging said gyro data over a predetermined time period;

(d6) using said standard deviation of said gyro data over a predetermined time period to verify if said SAAAEMS system is really on a stationary base;

(d7) saving said obtained data as group 1;

(d8) moving said SAAAEMS system to a second angular position and on a stationary base;

(d9) repeating step (d2) to step (d6), saving said obtained data as group 2;

(d10) moving said SAAAEMS system to a third angular position and on a stationary base;

(d11) repeating step (d2) to step (d6), saving said obtained data as group 3;

(d12) moving said SAAAEMS system to a forth angular position and on a stationary base;

(d13) repeating step (d2) to step (d6), saving said obtained data as group 4;

(d14) constructing an initial vector r which includes an initial estimates of a gyro bias;

(d15) using said obtained 4 groups data to construct initial F(r) matrix;

(d16) using said obtained 4 groups data to construct an initial

12. The method as recited in claim 11, further comprising the steps of:

(h) using said calculated a;

Ĉ

_bⁿ(t) as an initial value of said C_bⁿ¹(t) DCM based on said static gyrocompasing process as said SAAAEMS system initialization method;

(i) using said initial C_bⁿ¹(t) to transform said calibrated and compensated gyro input data from said B frame to a N1 frame;

(j) using said initial C_bⁿ¹(t) to transform said calibrated and compensated accelerometer input data from said B frame to said N1 frame;

(k) sending X and Y components of said transformed accelerometer input data to SAAAEMS estimator and controller to form a closed-loop control command;

(l) removing an earth angular velocity component from said transformed gyro input data;

(m) adding closed-loop control command from said SAAAEMS estimator and controller to said transformed gyro input data, to form a total SAAAEMS attitude update command;

(n) using said total SAAAEMS attitude update command to update said system attitude by an quaternion attitude update equation;

(o) transforming said updated quaternion attitude to DMC representation and get an updated DMC C_bⁿ¹(t);

(p) looping back to the step (i), using said updated C_bⁿ¹(t) to transform said calibrated and compensated gyro input data from said B frame to said N1 frame;

(q) using said updated C_bⁿ¹(t) to transform said calibrated and compensated accelerometer input data from said B frame to said N1 frame;

(r) repeating said step (i) to said step (q) to obtain real-time continuous C_bⁿ¹(t) updates; and

(s) calculating a real-time continuous SAAAEMS pitch/elevation, roll and azimuth/heading angles for system output during the loop.