Method for determining route angles
First Claim
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1. A method for automatic calibration of the course accuracy of a three-axis magnetometer that is fixedly mounted in an aircraft and is subject to interference fields and instrumental errors comprising the steps of:
- (a) determining initial reference direction, at a preselected calibration location characterized by a homogeneous magnetic field of known intensity and inclination that is free from anomalies, by means of at least one gyroscope having short-term stability;
then(b) determining the theoretical values of the mutually perpendicular reference components Tx, Ty and Tz of the earth'"'"'s magnetic field required for said calibration;
then(c) sweeping over all route angles and course angle ranges, within established limiting roll and pitch angle values, required for said calibration during a flight maneuver; and
(d) continuously observing during said flight maneuver the deviations Δ
Tx =Tx '"'"'-Tx, Δ
Ty =Ty '"'"'-Ty and Δ
Tz =Tz '"'"'-Tz of the instantaneous magnetic field components Tx'"'"', Ty'"'"', Tz'"'"' from the reference components Tx, Ty and Tz ; and
(e) reading said deviations into a computer;
then(f) recurrently computing, after the occurrence of each observation triplet, Δ
Tx, Δ
Ty and Δ
Tz, in accordance with the calibration functions;
space="preserve" listing-type="equation">Δ
T.sub.x =T.sub.x '"'"'-T.sub.x =A.sub.x +B.sub.x.sin ψ
+C.sub.x.cos ψ
+D.sub.x.Φ
+E.sub.x.Φ
.sup.2 +F.sub.x.θ
+G.sub.x.θ
.sup.2 ( 1a)
space="preserve" listing-type="equation">Δ
T.sub.y =T.sub.y '"'"'-T.sub.y =A.sub.y +B.sub.y.sin ψ
+C.sub.y.cos ψ
+D.sub.y.Φ
+E.sub.y.Φ
.sup.2 +F.sub.y.θ
+G.sub.y.θ
.sup.2 ( 1b)
space="preserve" listing-type="equation">Δ
T.sub.z =T.sub.z '"'"'-T.sub.z =A.sub.z +B.sub.z.sin ψ
+C.sub.z.cos ψ
+D.sub.z.Φ
+E.sub.z.Φ
.sup.2 +F.sub.z.θ
+G.sub.z.θ
.sup.2 ( 1c)where ψ
is the route angle, Φ
is the roll angle and θ
is the pitch angle, correction coefficientsAx, Bx, . . . GxAy, By, . . . GyAz, Bz, . . . Gzhaving initial conditions;
Ax, Bx, . . . Gx =0Ay, By, . . . Gy =0Az, Bz, . . . Gz =0up to a predeterminable accuracy;
then(g) transforming the instantaneous magnetic field components to corrected intensity components Txc, Tyc, Tzc in accordance with;
space="preserve" listing-type="equation">T.sub.x.sup.c =T.sub.x '"'"'+V.sub.x ( 2a)
space="preserve" listing-type="equation">T.sub.y.sup.c =T.sub.y '"'"'+V.sub.y ( 2b)
space="preserve" listing-type="equation">T.sub.z.sup.c =T.sub.z '"'"'+V.sub.z ( 2c)with the correction values
space="preserve" listing-type="equation">V.sub.x =-A.sub.x -B.sub.x.sin ψ
-C.sub.x.cos ψ
-D.sub.x.Φ
-E.sub.x.Φ
.sup.2 -F.sub.x.θ
-G.sub.x.θ
.sup.2 ( 3a)
space="preserve" listing-type="equation">V.sub.y =-A.sub.y -B.sub.y.sin ψ
-C.sub.y.cos ψ
-D.sub.y.Φ
-E.sub.y.Φ
.sup.2 -F.sub.y.θ
-G.sub.y.θ
.sup.2 ( 3b)
space="preserve" listing-type="equation">V.sub.z =-A.sub.z -B.sub.z.sin ψ
-C.sub.z.cos ψ
-D.sub.z.Φ
-E.sub.z.Φ
.sup.2 -F.sub.z.θ
-G.sub.z.θ
.sup.2 ( 3c);
and then(h) determining a corrected route angle ψ
cm from the equations of step (g).
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Abstract
A method for the determining route angle and for automatically calibrating course accuracy with a three-axis magnetometer fixed to an aircraft despite the presence of interfering vehicle magnetic fields and instrumentation errors. The method is accomplished in flight and includes numerous computations to compensate the magnetometer'"'"'s principal error sources. A calibration flight includes specified flight maneuvers (without change of position). The method is particularly suitable for helicopters equipped with three-axis magnetometers.
32 Citations
7 Claims
-
1. A method for automatic calibration of the course accuracy of a three-axis magnetometer that is fixedly mounted in an aircraft and is subject to interference fields and instrumental errors comprising the steps of:
-
(a) determining initial reference direction, at a preselected calibration location characterized by a homogeneous magnetic field of known intensity and inclination that is free from anomalies, by means of at least one gyroscope having short-term stability;
then(b) determining the theoretical values of the mutually perpendicular reference components Tx, Ty and Tz of the earth'"'"'s magnetic field required for said calibration;
then(c) sweeping over all route angles and course angle ranges, within established limiting roll and pitch angle values, required for said calibration during a flight maneuver; and (d) continuously observing during said flight maneuver the deviations Δ
Tx =Tx '"'"'-Tx, Δ
Ty =Ty '"'"'-Ty and Δ
Tz =Tz '"'"'-Tz of the instantaneous magnetic field components Tx'"'"', Ty'"'"', Tz'"'"' from the reference components Tx, Ty and Tz ; and(e) reading said deviations into a computer;
then(f) recurrently computing, after the occurrence of each observation triplet, Δ
Tx, Δ
Ty and Δ
Tz, in accordance with the calibration functions;
space="preserve" listing-type="equation">Δ
T.sub.x =T.sub.x '"'"'-T.sub.x =A.sub.x +B.sub.x.sin ψ
+C.sub.x.cos ψ
+D.sub.x.Φ
+E.sub.x.Φ
.sup.2 +F.sub.x.θ
+G.sub.x.θ
.sup.2 ( 1a)
space="preserve" listing-type="equation">Δ
T.sub.y =T.sub.y '"'"'-T.sub.y =A.sub.y +B.sub.y.sin ψ
+C.sub.y.cos ψ
+D.sub.y.Φ
+E.sub.y.Φ
.sup.2 +F.sub.y.θ
+G.sub.y.θ
.sup.2 ( 1b)
space="preserve" listing-type="equation">Δ
T.sub.z =T.sub.z '"'"'-T.sub.z =A.sub.z +B.sub.z.sin ψ
+C.sub.z.cos ψ
+D.sub.z.Φ
+E.sub.z.Φ
.sup.2 +F.sub.z.θ
+G.sub.z.θ
.sup.2 ( 1c)where ψ
is the route angle, Φ
is the roll angle and θ
is the pitch angle, correction coefficientsAx, Bx, . . . Gx Ay, By, . . . Gy Az, Bz, . . . Gz having initial conditions; Ax, Bx, . . . Gx =0 Ay, By, . . . Gy =0 Az, Bz, . . . Gz =0 up to a predeterminable accuracy;
then(g) transforming the instantaneous magnetic field components to corrected intensity components Txc, Tyc, Tzc in accordance with;
space="preserve" listing-type="equation">T.sub.x.sup.c =T.sub.x '"'"'+V.sub.x ( 2a)
space="preserve" listing-type="equation">T.sub.y.sup.c =T.sub.y '"'"'+V.sub.y ( 2b)
space="preserve" listing-type="equation">T.sub.z.sup.c =T.sub.z '"'"'+V.sub.z ( 2c)with the correction values
space="preserve" listing-type="equation">V.sub.x =-A.sub.x -B.sub.x.sin ψ
-C.sub.x.cos ψ
-D.sub.x.Φ
-E.sub.x.Φ
.sup.2 -F.sub.x.θ
-G.sub.x.θ
.sup.2 ( 3a)
space="preserve" listing-type="equation">V.sub.y =-A.sub.y -B.sub.y.sin ψ
-C.sub.y.cos ψ
-D.sub.y.Φ
-E.sub.y.Φ
.sup.2 -F.sub.y.θ
-G.sub.y.θ
.sup.2 ( 3b)
space="preserve" listing-type="equation">V.sub.z =-A.sub.z -B.sub.z.sin ψ
-C.sub.z.cos ψ
-D.sub.z.Φ
-E.sub.z.Φ
.sup.2 -F.sub.z.θ
-G.sub.z.θ
.sup.2 ( 3c);and then (h) determining a corrected route angle ψ
cm from the equations of step (g).
-
-
2. A method for automatic calibration of the course accuracy of a three-axis magnetometer that is fixedly mounted in an aircraft and is subject to interference fields and instrumental errors comprising the steps of:
-
(a) establishing an estimated initial reference direction at a preselected calibration location that is characterized by a homogeneous magnetic field of known intensity and inclination and free from anomalies;
then(b) determining the theoretical values of the mutually perpendicular reference components Tx, Ty and Tz of the earth'"'"'s magnetic field required for calibration from said estimated initial reference direction by means of a gyroscope having short-term stability;
then(c) sweeping all route angles and course angle ranges, within established limiting roll and pitch angle values, required for calibration during a flight maneuver; and (d) continuously observing during said flight maneuver the deviations Δ
Tx =Tx '"'"'-Tx, Δ
Ty =Ty '"'"'-Ty and Δ
Tz =Tz '"'"'-Tz of the instantaneous magnetic field components Tx '"'"', Ty '"'"', Tz '"'"' from the reference components Tx, Ty, Tz ; and(e) reading said deviations into a computer;
then(f) recurrently computing, after the occurrence of each observation triplet, Δ
Tx, Δ
Ty and Δ
Tz, in accordance with the calibration functions;
space="preserve" listing-type="equation">Δ
T.sub.x =T.sub.x '"'"'-T.sub.x =A.sub.x +B.sub.x.sin ψ
+C.sub.x.cos ψ
+D.sub.x.Φ
+E.sub.x.Φ
.sup.2 +F.sub.x.θ
+G.sub.x.θ
.sup.2 ( 1a)
space="preserve" listing-type="equation">Δ
T.sub.y =T.sub.y '"'"'-T.sub.y =A.sub.y +B.sub.y.sin ψ
+C.sub.y.cos ψ
+D.sub.y.Φ
+E.sub.y.Φ
.sup.2 +F.sub.y.θ
+G.sub.y.θ
.sup.2 ( 1b)
space="preserve" listing-type="equation">T.sub.z =T.sub.z '"'"'-T.sub.z =A.sub.z +B.sub.z.sin ψ
+C.sub.z.cos ψ
+D.sub.z.Φ
+E.sub.z.Φ
.sup.2 +F.sub.z.θ
+G.sub.z.θ
.sup.2 ( 1c)where ψ
designates the route angle, Φ
designates the roll angle and θ
designates the pitch angle, correction coefficientsAx, Bx, . . . Gx Ay, By, . . . Gy Az, Bz, . . . Gz having initial conditions Ax, Bx, . . . Gx =0 Ay, By, . . . Gy =0 Az, Bz, . . . Gz =0 up to a predeterminable accuracy;
then(g) transforming the instantaneous magnetic field components to corrected intensity components in accordance with;
space="preserve" listing-type="equation">T.sub.x.sup.c =T.sub.x '"'"'+V.sub.x ( 2a)
space="preserve" listing-type="equation">T.sub.y.sup.c =T.sub.y '"'"'+V.sub.y ( 2b)
space="preserve" listing-type="equation">T.sub.z.sup.c =T.sub.z '"'"'+V.sub.z ( 2c)with the correction values
space="preserve" listing-type="equation">V.sub.x =-A.sub.x -B.sub.x.sin ψ
-C.sub.x.cos --D.sub.x.Φ
-E.sub.x.Φ
.sup.2 -F.sub.x.θ
-G.sub.x.θ
.sup.2 ( 3a)
space="preserve" listing-type="equation">V.sub.y =-A.sub.y -B.sub.y.sin ψ
-C.sub.y.cos ψ
-D.sub.y.Φ
-E.sub.y.Φ
.sup.2 -F.sub.y.θ
-G.sub.y.θ
.sup.2 ( 3b)
space="preserve" listing-type="equation">V.sub.z =-A.sub.z -B.sub.z.sin ψ
-C.sub.z.cos ψ
-D.sub.z.Φ
-E.sub.z.Φ
.sup.2 -F.sub.z.θ
-G.sub.z.θ
.sup.2 ( 3c);then (h) determining a corrected route angle ψ
cm from the equations of step (g) by inserting the uncorrected value of route angle ψ
into equations 3(a), 3(b) and 3(c);
then(i) performing a further calibration flight between at least two reference points (P1, P2) of known coordinates (ρ
1, ρ
2 ;
λ
1, λ
2);
then(j) determining a course correction defined as ##EQU21## and where (Δ
X-Δ
X'"'"')=path difference in the latitudinal direction in flight between the reference points (P1, P2);(Δ
Y-Δ
Y'"'"')=path difference in the longitudinal direction in flight between the reference points (P1, P2);arc tan Δ
Y/Δ
X=route angle; andS=path traversed between the reference points (P1, P2); and
then(k) determining said corrected route angle as
space="preserve" listing-type="equation">ψ
.sub.m.sup.c =f(T.sub.x.sup.c, T.sub.y.sup.c, T.sub.z.sup.c)+V.sub.A ( 5b). - View Dependent Claims (3, 4, 5, 6, 7)
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Current AssigneeLitec-LP GmbH
-
Original AssigneeLitec-LP GmbH
-
InventorsBaumker, Manfred
-
Primary Examiner(s)Chin, Gary
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Application NumberUS06/944,804Time in Patent Office1,012 DaysField of Search364/449, 364/453, 364/454, 364/457, 364/460, 364/571.02, 33/355 R, 33/356, 33/357, 324/245, 324/246, 73/178 RUS Class Current702/93CPC Class CodesG01C 17/38 Testing, calibrating, or co...
