Method and apparatus for calibrating the gyros of a strapdown inertial navigation system
First Claim
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1. In a method for adjusting the rate outputs of the gyros of an aircraft'"'"'s strapdown inertial navigation system for east gyro bias error wherein the cross-track velocity (VCT) of said aircraft is utilized to determine said east gyro bias error, the improvement comprising the steps of:
- a) taxiing said aircraft substantially along a heading; and
b) measuring north velocity (VN), east velocity (VE), heading (ψ
H) and time derivative of said heading (ψ
H) of said aircraft while taxiing said aircraft; and
c) determining a crab angle (β
) of said taxiing aircraft; and
d) determining a lever arm (RL) of said taxiing aircraft; and
e) determining cross heading velocity (Vc) and heading velocity (VH) of said taxiing aircraft according to the relationships;
space="preserve" listing-type="equation">V.sub.c =V.sub.E cos ψ
.sub.H -V.sub.N sin ψ
.sub.H
space="preserve" listing-type="equation">V.sub.H =V.sub.E sin ψ
.sub.H +V.sub.N cos ψ
.sub.H ;
thenf) determining VCT according to the relationship
space="preserve" listing-type="equation">V.sub.CT =V.sub.C -V.sub.H sin β
-R.sub.L ψ
.sub.H ;
theng) integrating VCT to generate a cross-track position PCT ; and
h) determining Kalman gain values for VN, VE, ψ
H, ψ
H, RL and β
;
theni) multiplying said Kalman gain values by said cross-track position PCT to determine VN, VE, ψ
H, ψ
H, RL and β
errors;
thenj) correcting VCT for said VN, VE, ψ
H, ψ
H, RL and β
errors; and
thenk) adjusting gyro output values in accordance with said corrected value of VCT.
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Abstract
A method and apparatus for minimizing the effect of lateral velocity transients upon an aircraft inertial instrument calibration process of the type in which cross-track velocity is measured and utilized to correct for the east component of gyro bias error. A "cross-track position" value is obtained by integration of the cross-track velocity. A Kalman filter calculates a plurality of gain values corresponding to measurements of crab angle, lever arm, north and east velocity, heading angle and rate of change of heading angle and those gain values are applied to the cross-track position value to obtain error values for each of such parameters. The calculated error values are then employed as corrections to, or calibrations of, the inertial instrument outputs.
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Citations
12 Claims
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1. In a method for adjusting the rate outputs of the gyros of an aircraft'"'"'s strapdown inertial navigation system for east gyro bias error wherein the cross-track velocity (VCT) of said aircraft is utilized to determine said east gyro bias error, the improvement comprising the steps of:
-
a) taxiing said aircraft substantially along a heading; and b) measuring north velocity (VN), east velocity (VE), heading (ψ
H) and time derivative of said heading (ψ
H) of said aircraft while taxiing said aircraft; andc) determining a crab angle (β
) of said taxiing aircraft; andd) determining a lever arm (RL) of said taxiing aircraft; and e) determining cross heading velocity (Vc) and heading velocity (VH) of said taxiing aircraft according to the relationships;
space="preserve" listing-type="equation">V.sub.c =V.sub.E cos ψ
.sub.H -V.sub.N sin ψ
.sub.H
space="preserve" listing-type="equation">V.sub.H =V.sub.E sin ψ
.sub.H +V.sub.N cos ψ
.sub.H ;then f) determining VCT according to the relationship
space="preserve" listing-type="equation">V.sub.CT =V.sub.C -V.sub.H sin β
-R.sub.L ψ
.sub.H ;then g) integrating VCT to generate a cross-track position PCT ; and h) determining Kalman gain values for VN, VE, ψ
H, ψ
H, RL and β
;
theni) multiplying said Kalman gain values by said cross-track position PCT to determine VN, VE, ψ
H, ψ
H, RL and β
errors;
thenj) correcting VCT for said VN, VE, ψ
H, ψ
H, RL and β
errors; and
thenk) adjusting gyro output values in accordance with said corrected value of VCT. - View Dependent Claims (2, 3, 4, 5)
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6. Apparatus for adjusting the rate outputs of the gyros of the strapdown inertial navigation system of an aircraft while taxiing for east gyro bias error by employing the relationship between cross-track velocity (VCT) and said error comprising, in combination:
-
a) means for continuously measuring north velocity (VN), east velocity (VE), heading (ψ
H) and rate of change of said heading (ψ
H) of said taxiing aircraft;b) means for continuously providing crab angle (β
) of said taxiing aircraft;c) means for continuously providing lever arm (RL) of said taxiing aircraft; d) means for continuously determining cross heading velocity (VC) and heading velocity (VH) of said taxiing aircraft from VN, VE and ψ
H ;e) means for continuously determining VCT from VC, VH, β
, RL and ψ
H ;f) means for integrating VCT to generate a cross-track position PCT ; g) a Kalman filter for receiving values of VN, VE, ψ
H, ψ
H, RL and β and
providing gain values in response thereto;h) means for multiplying said cross-track position by said gain values to generate error values of VN, VE, ψ
H, ψ
H, RL and β
;i) means for correcting VCT for said VN, VE, ψ
H, ψ
H, RL and β
error values; andj) means for adjusting the outputs of said gyros in accordance with the corrected value of VCT. - View Dependent Claims (7, 8, 9, 10, 11)
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12. A method for calibrating the gyros of a strapdown inertial navigation system of an aircraft comprising the steps of:
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a) measuring the rate outputs of said gyros while said aircraft is at rest at a first heading; and b) resolving said rate outputs into north and east coordinates;
thenc) determining the north component of gyro rate bias error along said north coordinate;
thend) rotating said aircraft to a second heading; and e) taxiing said aircraft substantially along said second heading;
thenf) determining the cross-track velocity of said aircraft from values of north and east velocity, heading and heading rate, crab angle and lever arm measured while taxiing; and g) integrating said cross-track velocity to generate a cross-track position; and h) generating Kalman gain vales of said north and east velocity, heading and heading rate, crab angle and lever arm;
theni) deriving error corrections to said cross-track velocity by multiplying said Kalman gain values by said cross-track position;
thenj) correcting said cross-track velocity with said error corrections;
thenk) deriving the east component of gyro bias error from said corrected cross-track velocity; and
thenl) adjusting the outputs of said gyros by correcting for said north and east components of gyro rate bias error based upon measurements made prior to takeoff.
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Current AssigneeNorthrop Grumman Systems Corporation (Northrop Grumman Corporation)
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Original AssigneeLitton Systems Incorporated (Northrop Grumman Corporation)
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InventorsDiesel, John W.
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Primary Examiner(s)Chin, Gary
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Application NumberUS08/039,725Time in Patent Office1,330 DaysField of Search364/449, 364/453, 364/454, 364/571.01, 364/571.02, 364/571.06, 73/1 R, 73/178 R, 73/504, 244/177US Class Current701/220CPC Class CodesG01C 21/166 Mechanical, construction or...G01C 25/005 initial alignment, calibrat...
