GB2128749A - Electronic compass with tilt compensation - Google Patents
Electronic compass with tilt compensation Download PDFInfo
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- GB2128749A GB2128749A GB08325212A GB8325212A GB2128749A GB 2128749 A GB2128749 A GB 2128749A GB 08325212 A GB08325212 A GB 08325212A GB 8325212 A GB8325212 A GB 8325212A GB 2128749 A GB2128749 A GB 2128749A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
- G01C17/00—Compasses; Devices for ascertaining true or magnetic north for navigation or surveying purposes
- G01C17/38—Testing, calibrating, or compensating of compasses
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Abstract
An electronic compass for land, sea or air vehicles comprises three magnetic sensors 4,5,6 arranged to be respectively responsive to orthogonal components of a magnetic field which includes the earth's magnetic field and a spurious magnetic field which is associated with the vehicle, for producing electrical signals corresponding to said components, tilt sensors 2,3 responsive to vehicle tilt with respect to the horizontal plane, data processor and storage means arranged to store signals derived from the sensors 4,5,6 as the vehicle is turned through a compass setting cycle, and signal processor means 18 to 28 responsive to electrical signals produced by the sensors 4,5,6 after the setting cycle has been completed and to the signals stored at 14 during the setting cycle, for providing compensated signals related to the bearing appertaining to the heading of the vehicle in which the effects of the spurious magnetic field are compensated for and further processor means 31,32 to which the compensated signals are applied and which is responsive to the tilt sensors 2,3 for modifying the compensated signals to produce output signals 33,34 appertaining to vehicle heading in which the effects of tilt are compensated for. A navigation system incorporating the compass can also monitor distance travelled or the vehicle velocity to derive the location of the vehicle. <IMAGE>
Description
SPECIFICATION
Compass
This invention relates to electronic compasses and to navigation systems including such compasses and more especially it relates to such compasses and navigation systems for use in vehicles.
The term vehicle when used herein is intended to include ships, boats or aircraft as well as land based vehicles such as cars, lorries or military vehicles and the term electronic compass as used herein defines a compass in which a bearing indication is afforded in dependence upon electronic signals provided by magnetic sensors responsive to the earths magnetic field.
Modern vehicles are constructed principally from steel or include significant steel parts having magnetic characteristics which distort the earth's magnetic field in and around the close proximity of the vehicle. Although electronic compasses per se are known, their use has hitherto been strictly limited in vehicles, since magnetic sensors essential to such compasses must either be placed on masts or extension arms in order to avoid spurious magnetic fields associated with the vehicle and the use of masts or the like is often not possible or at least undesirable, or be subjcted to an elaborate compensation process.
An important object of the present invention is to provide for a vehicle an electronic compass or a navigation system including such a compass, wherein spurious magnetic fields associated with the vehicle are compensated for, such that magnetic sensors forming a part of the compass may be accommodated within or close to the vehicle in which the compass is carried and additionally to provide means effective to compensate for the effects of vehicle tilt.
According to the present invention an electronic compass for vehicles comprises three magnetic sensors arranged in use to be respectively responsive to orthogonal components of a magnetic field which includes the earth's magnetic field and a spurious magnetic field which is associated with the vehicle, for producing electrical signals corresponding to said components, tilt sensor means responsive to vehicle tilt with respect to the horizontal plane, data processor and storage means arranged to store signals derived from the sensors as the vehicle is turned through a compass setting cycle, and signal processor means responsive to electrical signals produced by the sensors after the setting cycle has been completed and to the signals stored during the setting cycle, for providing compensated signals related to the bearing appertaining to the heading of the vehicle in which the effects of the spurious magnetic field are compensated for and further processor means to which the compensated signals are applied and which is responsive to the tilt sensor means for modifying the compensated signals to produce output signals appertaining to vehicle heading in which effects of tilt are compensated for.
By causing the vehicle to move through a predetermined compass setting cycle, data is made available and stored which appertains to three orthogonal axes, subsequently to be utilised by the signal processor to compensate for the spurious magnetic field associated with the vehicle, whereby the provision of signals indicative of a magnetic compass bearing appertaining to the heading of the vehicle is facilitated which is modified to compensate for vehicle tilt.
The setting cycle may be performed in any manner which will produce a response from each of the three sensors as the vehicle is moved through various headings and tilts. These will be chosen in accordance with the type of manoeuvre which can be carried out by the vehicle concerned.
The tilt sensor means may comprise mechanical or electro-mechanical tilt sensors responsie to vehicle tilt to which the three magnetic sensors are subject to provide the tilt of the magnetic sensors in two orthogonal planes.
If the magnetic field detected by the three orthogonal sensors is plotted in three dimensions in a co-ordinate system then a surface locus would be obtained for all values of vehicle bearing and tilt. Under ideal conditions this surface would be spherical but due to the effects of spurious magnetic fields associated with a vehicle, the ideal shape is distorted to the form of an ellipsoid.
By using the stored values of magnetic field sensed during the setting cycle in a transform to convert the values of magnetic field measured on the ellipsoidal locus back to the spherical locus, output signals appertaining to true bearing or heading can be computed.
The spurious magnetic field associated with a vehicle may be considered to be the combination of a permanent magnetic field and an induced magnetic field, and by utilising signal values sensed and stored during the compass setting cycle, a transform is derived which is applied in the signal processor to provide compensation for the permanent magnetic field and the induced magnetic field associated with the vehicle, even if these fields are very large, whereby the provision of an unambiguous bearing indication is afforded.
Although a transform utilising a comprehensive set of stored values sufficient to define a complete three dimensional surface locus which is in the form of an ellipsoid would be ideal, a comparatively simple transform may be satisfactory which utilises a set of nine values which are spaced apart over the three dimensional surface of the ellipsoidal magnetic locus and which may be measured during a simple setting cycle vehicle manoeuvre or series of manoeuvres.
Accordingly the data storage means may include capacity to store data corresponding to or derived from the nine values sensed by each of the sensors during the setting cycle, these values being defined as x1 to x9, y, to y9 and z1 to z9 for the three orthogonal magnetic sensors respectively and the signal processor means may be adapted to solve an equation utilising these values to provide the bearing indication.
One embodiment of the invention will now be described solely by way of example with reference to the accompanying drawings in which:
Figure 1 is a somewhat schematic perspective view of an aircraft showing the three axes of interest x,y, and z;
Figure 2 is a diagram of a spherical locus of the magnetic field along the x,y,z axes as unaffected by spurious fields associated with other aircraft;
Figure 3 is a diagram of an ellipisoidal locus along the x,y,z axes of a magnetic field which includes spurious fields associated with the aircraft;
Figure 4 is a diagram of an ellipisoidal locus of a magnetic field which corresponds to the locus of Fig. 3 but with a component corresponding to the permanent magnetic field of the aircraft subtracted;;
Figure 5 is a diagram of an ellipsoidal locus corresponding to the locus of Fig. 4 but with its axes rotated such that they lie along the axes x, y and z; and
Figure 6 is a somewhat schematic block flow diagram illustrating various stages in mathematical processing associated with an electronic compass.
If operation of a compass is required on a vehicle whose attitude will at times be significantly tilted, such as an aircraft or a cross country vehicle, then use of a strapped down two axis sensor as described in Patent No. will lead to errors caused by the inability of the tilted sensors to sense the horizontal components of the earth's magnetic field. The technique described in Patent No. can however be extended to a three axis sensor where the three axes are arranged orthogonally.
Referring now to Fig. 1 a three axis magnetometer is mounted in the vehicle, e.g. in an aircraft, to measure the magnetic field sensed along the longitudinal axis of the aircraft, x, along the transverse axis of the aircraft, y, and along the vertical axis, z. The local magnetic field in the vicinity of these sensors is a combination of the earth's magnetic field and spurious magnetic fields due to the ferromagnetic parts of the vehicle. If no spurious magnetic field were present and the components of the earth's magnetic field along the x,y and z axes are plotted out then a spherical locus in 3 dimensions would be obtained for all values of bearing, pitch and roll of the vehicle as shown in Fig. 2. The sphere is centred on the origin of the co-ordinate system and an arbitary point is defined as 'A' on the surface of the locus.
In practice however the perfect spherical locus as shown in Fig. 2 is shifted from the origin of the co-ordinate system due to the permanent field of the vehicle and distorted into an ellipsoid due to the induced field of the vehicle to give the form of the locus shown in Fig. 3. In Fig. 3 the centre of the ellipsoid at point B has been shifted to a point (Px, Py Pz). In addition the sphere has been distorted into an ellipsoid with its major axes along definable directions such that the point 'A' is transformed to a point 'C' on the surface of the locus.In order to correct for this distortion of the sphere into an ellipsoid it is necessary to determine the parameters of the ellipsoid in order to convert the point C on the ellipsoid surface in Fig. 3 back into the equivalent point A on the spherical surface in Fig. 2. Then, from a knowledge of the x,y and z values for the spherical locus and the tilt of the vehicle in two planes, the bearing of the vehicle reltive to magnetic north can be derived.
The equation describing the ellipsoidal surface in Fig. 3 can be written as:ax2 + by2 + cz2 + 2fyz + 2gzx + 2hxy + 2ux + 2vy + 2wz = d2 where x = magnetic field sensed vehicle by the longitudinal vehicle sensor
y = magnetic field sensed by the transverse vehicle sensor
z= magnetic field sensed by the vertical vehicle sensor a,b,c,f,g,h,u,v,w,d are constants for a
defined location on the Earth's surface.
This equation can be solved in a number of ways to determine the constants in the equation, one example being to substitute nine separate x, y, z values into the equation, for different vehicle bearings and tilt, and to solve the resulting nine simultaneous equations for the nine coefficients a,b,c,f,g,h,u,v,w. Note that the constant d is a scaling factor, and can be given any convenient value.Choosing d2 = 1 and taking the values of the field measured as xj, y;, zj for nine independent points on the locus with i = 1 to 9, we obtain:
x12 y12 z12 2y1z1 2z1x1 2x1y1 2x1 2y1 2z1 a 1
x22 y22 z22 2y2z2 2z2x2 2x2y2 2x2 2y2 2z2 b 1 x32 y32 z32 2y3z3 2z3x3 2x3y3 2x3 2y3 2z3 c 1 x42 y42 z42 2y4z4 2z4x4 2x4y4 2x4 2y4 2Z4 f 1 x52 y52 z52 2y5z5 2z5x5 2x5y5 2x5 2y5 2z5 . g = 1
x62 y62 z62 2y6z6 2z6x6 2x6y6 2x6 2y6 2z6 h 1 X72 y72 Z72 2y7Z7 2Z7X7 2X7y7 2X7 2y7 2z7 u 1
x82 y82 z82 2y8z8 2z8x8 2x8y8 2x8 2y8 2z8 v 1
x92 y92 z92 2y9z9 2z9x9 2x9y9 2x9 2y9 2z9 w 1
Inverting this matrix, we obtain:
a x12 y12 z12 2y1z1 2z1x1 2x1y1 2x1 2y1 2z1 -1 1
b x22 y22 z22 2y2z2 2z2x2 2x2y2 2x2 2Y2 2z2 1
c x32 y32 z32 2y3z3 2z3x3 2x3y3 2x3 2y3 2z3 1
f x42 y42 z42 2y4z4 2z4x4 2x4y4 2x4 2y4 2z4 1
g = x52 y52 z52 2y5z5 2z5x5 2x5y5 2x5 2y5 2z5 1
h x62 y62 z62 2y6z6 2z6x6 2x6y6 2x6 2y6 2z6 1
u x72 y72 z72 2y7z7 2z7x7 2x7y7 2x7 2y7 2z7 1
v x82 y82 z82 2y8z8 2z8x8 2x8y8 2x8 2y8 2z8 1
w x92 y92 z92 2y9z9 2z9x9 2z9y9 2x9 2y9 2z9 1 from which the values of a,b,c,f,g,h,u,v and w can be derived.
One method of deriving and using the coefficient a,b,c,f,g,h,u,v,w to correct the magnetometer readings for the presence of the vehicle is illustrated. Nine calibration points need to be chosen in accordance with the type of manoeuvre which can be carried out by the vehicle-for instance four points from each of a left and right banked turn, plus one straight and level flight value form an acceptable set for an aircraft, while for a land vehicle the two sets of four points can be obtained in a different way by driving in a circle on ground having two different slopes.
Many other sets of manoeuvres and methods of selecting points can be devised, but in each case the objective is to measure the three components of magnetic field at nine points which are well spaced over the three dimensional surface of the magnetic locus which is in the form of the ellipsoid as shown in Fig. 3.
It is also possible to select more than nine points. In this case it is necessary to select the values of the constants a,b,c,f,g,h,u,v and w which provide the best fit of an ellipsoid through all the points selected.
The process of calculating the correction data for magnetic effects due to the vehicle is equivalent to the following process which will hereinafter be mathematically explained and also later described with reference to Fig. 6:
i) A translation of the x, y and z coordinate system to centre the ellipsoid by determination of
Px, Py, Pz, such that the point 'C' is transformed to a point 'D' on the surface of the locus
shown in Fig. 4;
ii) A rotation of the x, y and z coordinate system to the ellipsoid axes, such that the point 'D'
is transformed to a point 'E' on the surface of the locus shown in Fig. 5;
iii) Scaling of the x,y and z coordinate axes to change the ellipsoid to a sphere; and,
iv) Rotation of the sphere back to the correct orientation i.e. the inverse of step (ii), such that
the point 'E' is transformed to the point 'A' on Fig. 2.
The values to be used in the above processes are derived from the values obtained for a,b,c,f,g,h,u,v and w as follows. First the coordinates (Px,Py,P,) for the centre of the ellipsoid are given by:
Px Px bc-f2 gf-hc hf-bg l ' -u py = fg-hc ac-g2 hg-af -v x 1/det G Pz ,hf-bg hg-af ab-h2 -w where
a h g G = #h b f# g f c detG = the determinant of matrix G.
= a(bc-f2) - h(hc-gf) + g(hf-bg)
If the (x,y,z) component values are translated to the position of the centre of the ellipsoid then the equation of the ellipsoid in the new coordinate system would be the same as the ellipsoid equation above but with the terms in u,v and w equal to zero and d replaced by d1 where d12 = [aPx2 + bPy2 + cPz2 + 2fPyPz + 2gPxPz + 2hPxPy + 2uPx + 2vPy + 2wPz] + d2
To derive the direction cosines of the three orthogonal axes of the ellipsoid relative to the (x,y,z) coordinate system it is necessary to first obtain the three eigenvalues L1,L2,L3 of the matrix
G.These three values of L are obtained from the three solutions for L of the cubic equation:
L3-AL2 + BL - C = 0 where
A=a+b+c B = bc + ca + ab - f2 - g2 - h2 C = abc - af2 - bg2 - ch2 + 2fgh
The three solutions for L for the cubic equation are:
L1 = D, + 1/3 A
L2 = D2 + 1/3 A L3=D+ 1/3A where
D, =2+(P/3) cos (1/3a)
D2 = - 2 + #(P/3) cos (1/3α + 1/3II)
D3 = - 2 + #(P/3) cos (1/3α - 1/3II)
Q α = cos-1 # # 2(P/3)3/2 P = 1/3A2 - B
Q = 2[1/3A]3 - 1/3 AB + C
The direction cosines li, m;, ni of each of the three axes of the ellipsoid in turn can be found from the following equations using Li with i = 1, 2 and 3 to define each of the three axes of the ellipsoid.
Ri li =
Ro
Rm mi =
Ro
Rn ni =
Ro where
Rl = (b - Li)(c - Li) - f2
Rm = fg - h(c - Li)
Rn = fh - g(b - Li)
Ro = R,2 + Rm2 + Rn2
The scaling factors to convert the ellipspoid into a sphere of radius d1 are
Sx = + #L1 Sy = + #L2
Sz = + #L3 When the above data have been calculated, further data may be used to improve the accuracy if
x12 y12 z12 2y1z1 2z1x1 2x1y1 2x1 2y1 2z1 a 1
x22 y22 z22 2y2z2 2z2x2 2x2y2 2x2 2y2 2z2 b 1
x32 y32 z32 2y3z3 2z3x3 2x3y3 2x3 2y3 2z3 c 1 X42 y42 Z42 2y4z4 2z4x4 2x4y4 2X4 2y4 2z4 f 1 x52 y52 z52 2y5z5 2z5x5 2x5y5 2x5 2y5 2z5 . g = 1
x62 y62 z62 2y6x6 2z6x6 2x6y6 2x6 2y6 2z8 h 1 x72 y72 z72 2y7z7 2z7x7 2x,y7 2x7 2y7 2z7 u 1 x82 y82 z82 2y8z8 2z8x8 2x8y8 2x8 2y8 2z8 v 1
x92 y92 z92 2y9z9 2z9x9 2x9y9 2x9 2y9 2z9 w 1
Inverting this matrix, we obtain::
a x12 y12 z12 2y1z1 2z1x1 2x1y1 2x1 2y1 2z1 -1 1
b x22 y22 z22 2y2z2 2z2x2 2x2y2 2x2 2y2 2z2 1
c x32 y32 z32 2y3z3 2z3x3 2x3y3 2x3 2y3 2z3 1
f x42 y42 z42 2y4z4 2z4x4 2x4y4 2x4 2y4 2z4 1
g = x52 y52 z52 2y5z5 2z5x5 2x5y5 2x5 2y5 2z5 1
h x62 y62 z62 2y6z6 2z6x6 2x6y6 2x6 2Y6 2z6 1
u x72 y72 z72 2y7z7 2z7x7 2x7y7 2x7 2y7 2z7 1
v x82 y82 z82 2y8z8 2z8x8 2x8y8 2x8 2y8 2z8 1
w x92 y92 z92 2y9z9 2z9x9 2x9y9 2x9 2y9 2z9 1 from which the values of a,b,c,f,g,h,u,v and w can be derived.
One method of deriving and using the coefficient a,b,c,f,g,h,u,v,w to correct the magnetometer readings for the presence of the vehicle is illustrated. Nine calibration points need to be chosen in accordance with the type of manoeuvre which can be carried out by the vehicle-for instance four points from each of a left and right banked turn, plus one straight and level flight value form an acceptable set for an aircraft, while for a land vehicle the two sets of four points can be obtained in a different way by driving in a circle on ground having two different slopes.
Many other sets of manoeuvres and methods of selecting points can be devised, but in each case the objective is to measure the three components of magnetic field at nine points which are well spaced over the three dimensional surface of the magnetic locus which is in the form of the ellipsoid as shown in Fig. 3.
It is also possible to select more than nine points. In this case it is necessary to select the values of the constants a,b,c,f,g,h,u,v and w which provide the best fit of an ellipsoid through all the points selected.
The process of calculating the correction data for magnetic effects due to the vehicle is equivalent to the following process which will hereinafter be mathematically explained and also later described with reference to Fig. 6:
i) A translation of the x, y and z coordinate system to centre the ellipsoid by determination of Px Py, Pz such that the point 'C' is transformed to a point 'D' on the surface of the locus
shown in Fig. 4;
ii) A rotation of the x, y and z coordinate system to the ellipsoid axes, such that the point 'D'
is transformed to a point 'E' on the surface of the locus shown in Fig. 5:
iii) Scaling of the x,y and z coordinate axes to change the ellipsoid to a sphere; and,
iv) Rotation of the sphere back to the correct orientation i.e. the inverse of step (ii), such that
the point 'E' is transformed to the point 'A' on Fig. 2.
The values to be used in the above processes are derived from the values obtained for a,b,c,f,g,h,u,v and w as follows. First the coordinates (Px,Py,Pz) for the centre of the ellipsoid are given by:
Px bc-f2 gf-hc hf-bg -u #py# = #fg-hc ac-g2 hg-af# #-v# x1/det G Pz hf-bg hg-af ab-h2 -w where a g h G = #h b f# g f c detG = the determinant of matrix G.
= a(bc-f2) - h(hc-gf) + g(hf-bg)
If the (x,y,z) component values are translated to the position of the centre of the ellipsoid then the equation of the ellipsoid in the new coordinate system would be the same as the ellipsoid equation above but with the terms in u,v and w equal to zero and d replaced by d, where d12 = [aPx2 + bPy2 + cPz2 + 2fPyP2 + 2gPxPz + 2hPxPy + 2uPx + 2vPy + 2wPJ + d2
To derive the direction cosines of the three orthogonal axes of the ellipsoid relative to the (x,y,z) coordinate system it is necessary to first obtain the three eigenvalues L,,L2,L3 of the matrix
G.These three values of L are obtained from the three solutions for L of the cubic equation:
L3 - AL2 + BL - C = 0 where A=a+b+c B = bc + ca + ab - f2 - g2 - h2
C = abc - af2 - bg2 - ch2 + 2fgh
The three solutions for L for the cubic equation are:
L1 = D1 + 1/3 A
L2 = D2 + 1/3 A
L3= D3+ 1/3 A where
D1 = 2 + #(P/3) cos (1/3α) D2 = - 2 + #(P/3) cos (1/3α + 1/3II)
D3 = - 2 + #(P/3) cos (1/3α - 1/3II)
Q α = cos-1 # # 2(P/3)3/2 P = 1/3A2 - B
Q = 2[1/3A]3 - 1/ 3 AB + C
The direction cosines l;, mi, n1 of each of the three axes of the ellipsoid in turn can be found from the following equations using L1 with i = 1, 2 and 3 to define each of the three axes of the ellipsoid.
R1 li=
Ro
Rm mi=
Ro
Rn ni=
Ro where
R1 = (b - L1)(c - Li) - f2
Rm = fg - h(c-Li)
Rn = fh - g(b-Li)
Ro = R12 + Rm2 + Rn2
The scaling factors to convert the ellipspoid into a sphere of radius d1 are
Sx = + #L1 s, = + +VL2 Sz = + #L3 When the above data have been calculated, further data may be used to improve the accuracy if required.
The operating sequence for the compass uses the calibration data derived above as follows.
Commencing with a magnetometer reading (x, y, z) taken simultaneously with an attitude reading (P, R), the first stage is to calculate a corrected magnetometer reading. This is done as follows, using the calibration data (Px,Py Pz) for translation, (l1, ml, n1) (12, m2, n2), (13, m3, n3) for rotation and (sx, sy, sz) for scaling.
Translation:
x1 = x - Px
y1 = y - Py z1 = z - Rotation:
x2 l1 m1 n1 x1 #y2# = #l2 m2 n2 # # # y1 z2 l3 m3 n3 z1 scaling:
x3 sx x2 #y3# = #sy y2 # z3 sz z2 Inverse rotation:
|x4 | |l1 l2 l3 | |x3| |y4 | = |m1 m2 m3 | . |y| |z4 | |n1 n2 n3 | |z3| The second stage is then to adjust the corrected magnetic readings for attitude:
BA zcosP sinPsinR sinPcosR | |x4| BB = O cosR -sinR | . |Y4| @Bc@ @-sinP sinRcosP cosRcosP | |z4| where P = pitch angle and R = roll angle. P and R are the Euler rotations relative to the x, y, z axes of the vehicle.
Then the heading is given by
BB H = -tan-1 @ BA where by taking account of the sign of BB and BA the vehicle heading, H, can be defined from 0 to 360 and the dip angle by
Bc D = tan-1 # # BA2 + BB2 The resulting heading can then be displayed as a bearing indication to the pilot of the vehicle or combined with a vehicle velocity sensor giving the vehicle velocity along its longitudinal and, if necessary, along its transverse axis to provide a navigation system, see Patent Ref.
The foregoing mathematical treatment will be better understood if reference is made to the flow diagram Fig. 6.
Referring now to the flow diagram of Fig. 6, an electronic compass is mounted in an aeroplane 1 and includes a roll sensor 2 and a pitch sensor 3. Pitch and roll sensing are well established techniques and may be carried out with any known apparatus. The aircraft is arranged also to carry x,y and z magnetic sensors 4,5 and 6 which are respectively responsive to orthogonally related magnetic fields. Outputs from the x,y and z sensors 4,5 and 6 are fed via lines 7,8 and 9 to analogue to digital converters 10,11 and 12 respectively. The analogue to digital converters are arranged to feed a processor via a switch 13 in the position shown in the drawing is set for calibration such that signals from the A to D converters 10,11 and 12 are fed to a calibration section of the compass.The calibration section of the compass comprises a store 14 for the field measurements for xi, yi and zj each of which comprise nine independent points on the locus. The store 14 is fed from the switch 1 3 via input lines 1 5,1 6 and 1 7 respectively. The store 14 is arranged to feed a signal processor 1 8 which serves to compute the coefficients a,b,c,f, g,h,u,v and w respectively. The processor 18 is arranged to feed a translation unit 1 9 which operates to compute the parameters Px, Py and Pz respectively.A rotation processor 20 is provided which serves to compute the values li, mi and n for i = 1,2 and 3, and the rotation processor 20 is arranged to feed a scaling unit 21 which serves to compute the scaling factors sx, 5y and sz.
When the switch 1 3 is moved from calibration to run, input signals from the A to D converters 10,11 and 12 are fed via lines 22,23 and 24 to translation, rotation, scaling, and inverse rotation units 25,26,27 and 28 respectively which perform the functions hereinbefore described and which are serially connected and which serve to produce x4,y4 and z4 output signals as indicated in the drawing which are indicative of the magnetic field along x,y and z axes which would obtain in the absence of the aircraft.
The pitch and roll sensors 2 and 3 are arranged to feed A to D converters 29 and 30 which provide digital pitch and roll signals for a pitch and roll correction unit 31 to which signals from the inverse rotation unit 28 are fed. Output signals BA, BB and BC from the unit 31 computed as hereinbefore explained are fed to a processor 32 which serves to compute the vehicle heading and the dip angle of the earth's magnetic field and to provide appropriate output signals on the lines 33 and 34. The translation unit 25, the rotation unit 26, the scaling unit 27 and the inverse rotation unit 28 receive appropriate correction signals which have been derived and stored in processors 19,20 and 21 during the calibration cycle and which are then applied on lines 35,36,37 and 38 respectively from the calibration section of the compass.
The precise mode of operation of the units just before referred to with reference to Fig. 6 is described in the mathematical treatment of the system which has been previously therein before explained.
Claims (6)
1. An electronic compass for vehicles comprising three magnetic sensors arranged in use to be respectively responsive to orthogonal components of a magnetic field which includes the earth's magnetic field and a spurious magnetic field which is associated with the vehicle, for producing electrical signals corresponding to said components, tilt sensor means responsive to vehicle tilt with respect to the horizontal plane, data processor and storage means arranged to store signals derived from the sensors as the vehicle is turned through a compass setting cycle, and signal processor means responsive to electrical signals produced by the sensors after the setting cycle has been completed and to the signals stored during the setting cycle, for providing compensated signals related to the bearing appertaining to the heading of the vehicle in which the effects of the spurious magnetic field are compensated for and further processor means to which the compensated signals are applied and which is responsive to the tilt sensor means for modifying the compensated signals to produce output signals appertaining to vehicle heading in which the effects of tilt are compensated for.
2. An electronic compass for vehicles as claimed in claim 1 wherein the tilt sensor means comprises mechanical or electro-mechanical tilt sensors responsive to vehicle tilt to which the two magnetic sensors are subject, to provide the tilt of the magnetic sensors in two orthogonal planes.
3. An electronic compass for vehicles as claimed in claim 1 or claim 2 wherein the data storage means includes capacity to store data corresponding to or derived from nine values sensed by each of the sensors during the setting cycle and wherein the signal processor means is adapted to solve an equation utilising these values to provide the bearing indication.
4. An electronic compass for vehicles substantially as hereinbefore described with reference to the accompanying drawings.
5. A navigation system including a compass as claimed in any preceding claim, distance measuring apparatus, and a computer responsive to the said apparatus and to signals derived from the compass for providing output signals indicative of location in terms of map coordinates.
6. A navigation system including a compass as claimed in any preceding claim comprising means for sensing the velocity of the vehicle in which the compass is mounted, data infeed means operable for providing data appertaining to an original map reference, navigation computer means responsive to data derived from the velocity indicator, the compass, and the data infeed means for providing data for display means whereby the display means is arranged to provide a display indicative of the position or location of the vehicle.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08325212A GB2128749B (en) | 1982-10-12 | 1983-09-21 | Electronic compass with tilt compensation |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8229134 | 1982-10-12 | ||
| GB08325212A GB2128749B (en) | 1982-10-12 | 1983-09-21 | Electronic compass with tilt compensation |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB8325212D0 GB8325212D0 (en) | 1983-10-26 |
| GB2128749A true GB2128749A (en) | 1984-05-02 |
| GB2128749B GB2128749B (en) | 1987-04-15 |
Family
ID=26284106
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB08325212A Expired GB2128749B (en) | 1982-10-12 | 1983-09-21 | Electronic compass with tilt compensation |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2128749B (en) |
Cited By (15)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2141551A (en) * | 1983-06-17 | 1984-12-19 | Honda Motor Co Ltd | Correction method for vehicle-mounted geomagnetic field sensors |
| DE3405933A1 (en) * | 1984-02-18 | 1985-08-22 | Teldix Gmbh, 6900 Heidelberg | Method for determining the course of a moving object |
| EP0214817A2 (en) * | 1985-09-03 | 1987-03-18 | British Aerospace Public Limited Company | Calibration of magnetic compasses |
| EP0225493A2 (en) * | 1985-12-11 | 1987-06-16 | The Laitram Corporation | Magnetic compass calibration |
| EP0226653A1 (en) * | 1985-12-20 | 1987-07-01 | LITEF GmbH | Method to determine heading by using and automatically calibrating a 3-axis magnetometer rigidly fitted in an aircraft |
| EP0229468A2 (en) * | 1985-12-19 | 1987-07-22 | Honeywell Inc. | Magnetic flux detector correction system |
| EP0321123A1 (en) * | 1987-12-17 | 1989-06-21 | Roke Manor Research Limited | Navigation compass calibration |
| US4972593A (en) * | 1989-01-17 | 1990-11-27 | The Charles Stark Draper Laboratory, Inc. | Method and apparatus for measuring the undistorted magnetic field of the earth |
| FR2728338A1 (en) * | 1994-12-19 | 1996-06-21 | Eurocopter France | METHOD AND DEVICE FOR SIMULTANEOUS IDENTIFICATION AND CORRECTION OF ERRORS DUE TO MAGNETIC DISTURBANCES AND POOR ALIGNMENTS IN MEASUREMENTS OF A MAGNETOMETER |
| US5682335A (en) * | 1995-04-10 | 1997-10-28 | Eurocopter France | Method and device for simultaneous identification and correction of errors in the measurements of a magnetometer |
| WO2003074969A2 (en) | 2002-03-01 | 2003-09-12 | Gentex Corporation | Electronic compass system |
| WO2005115079A3 (en) * | 2004-05-27 | 2006-05-11 | Nokia Corp | System, method, device and computer code product for improving the readability of an electronic compass |
| WO2007026238A1 (en) | 2005-09-02 | 2007-03-08 | Nokia Corporation | Calibration of 3d field sensors |
| GB2449538A (en) * | 2007-05-21 | 2008-11-26 | Suunto Oy | Calibrated electronic compass |
| EP2930466A1 (en) | 2014-04-09 | 2015-10-14 | Vectronix AG | Handheld observation device with a digital magnetic compass |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB850692A (en) * | ||||
| GB1339070A (en) * | 1970-04-01 | 1973-11-28 | Sperry Rand Corp | Magnetic compasses |
| GB1495213A (en) * | 1974-12-11 | 1977-12-14 | Nasa | Magnetic heading reference |
| GB1595926A (en) * | 1977-04-01 | 1981-08-19 | E Systems Inc | Compensation system for a magnetic compass utilizing a hall effect generator |
-
1983
- 1983-09-21 GB GB08325212A patent/GB2128749B/en not_active Expired
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB850692A (en) * | ||||
| GB1339070A (en) * | 1970-04-01 | 1973-11-28 | Sperry Rand Corp | Magnetic compasses |
| GB1495213A (en) * | 1974-12-11 | 1977-12-14 | Nasa | Magnetic heading reference |
| GB1595926A (en) * | 1977-04-01 | 1981-08-19 | E Systems Inc | Compensation system for a magnetic compass utilizing a hall effect generator |
Cited By (29)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2141551A (en) * | 1983-06-17 | 1984-12-19 | Honda Motor Co Ltd | Correction method for vehicle-mounted geomagnetic field sensors |
| DE3405933A1 (en) * | 1984-02-18 | 1985-08-22 | Teldix Gmbh, 6900 Heidelberg | Method for determining the course of a moving object |
| EP0214817A2 (en) * | 1985-09-03 | 1987-03-18 | British Aerospace Public Limited Company | Calibration of magnetic compasses |
| EP0214817A3 (en) * | 1985-09-03 | 1988-06-29 | British Aerospace Public Limited Company | Calibration of magnetic compasses |
| EP0225493A2 (en) * | 1985-12-11 | 1987-06-16 | The Laitram Corporation | Magnetic compass calibration |
| EP0225493A3 (en) * | 1985-12-11 | 1989-05-03 | The Laitram Corporation | Magnetic compass calibration |
| EP0229468A2 (en) * | 1985-12-19 | 1987-07-22 | Honeywell Inc. | Magnetic flux detector correction system |
| EP0229468A3 (en) * | 1985-12-19 | 1989-04-26 | Honeywell Inc. | Magnetic flux detector correction system |
| EP0226653A1 (en) * | 1985-12-20 | 1987-07-01 | LITEF GmbH | Method to determine heading by using and automatically calibrating a 3-axis magnetometer rigidly fitted in an aircraft |
| US4870602A (en) * | 1985-12-20 | 1989-09-26 | Litef Gmbh | Method for determining route angles |
| EP0321123A1 (en) * | 1987-12-17 | 1989-06-21 | Roke Manor Research Limited | Navigation compass calibration |
| US4972593A (en) * | 1989-01-17 | 1990-11-27 | The Charles Stark Draper Laboratory, Inc. | Method and apparatus for measuring the undistorted magnetic field of the earth |
| US5654635A (en) * | 1994-12-19 | 1997-08-05 | Eurocopter France | Method and device for simultaneous identification and correction of errors due to magnetic perturbations and to misalignments in the measurements of a magnetometer |
| EP0718598A1 (en) * | 1994-12-19 | 1996-06-26 | EUROCOPTER FRANCE, Société Anonyme dite: | Correction of the errors of a magnetometer |
| FR2728338A1 (en) * | 1994-12-19 | 1996-06-21 | Eurocopter France | METHOD AND DEVICE FOR SIMULTANEOUS IDENTIFICATION AND CORRECTION OF ERRORS DUE TO MAGNETIC DISTURBANCES AND POOR ALIGNMENTS IN MEASUREMENTS OF A MAGNETOMETER |
| US5682335A (en) * | 1995-04-10 | 1997-10-28 | Eurocopter France | Method and device for simultaneous identification and correction of errors in the measurements of a magnetometer |
| EP1488196A4 (en) * | 2002-03-01 | 2011-07-06 | Gentex Corp | Electronic compass system |
| EP1488196A2 (en) * | 2002-03-01 | 2004-12-22 | Gentex Corporation | Electronic compass system |
| WO2003074969A2 (en) | 2002-03-01 | 2003-09-12 | Gentex Corporation | Electronic compass system |
| WO2005115079A3 (en) * | 2004-05-27 | 2006-05-11 | Nokia Corp | System, method, device and computer code product for improving the readability of an electronic compass |
| KR100895988B1 (en) | 2004-05-27 | 2009-05-07 | 노키아 코포레이션 | System, method, device and computer code product for improving the readability of an electronic compass |
| WO2007026238A1 (en) | 2005-09-02 | 2007-03-08 | Nokia Corporation | Calibration of 3d field sensors |
| EP1929246A1 (en) * | 2005-09-02 | 2008-06-11 | Nokia Corporation | Calibration of 3d field sensors |
| EP1929246A4 (en) * | 2005-09-02 | 2012-03-14 | Nokia Corp | Calibration of 3d field sensors |
| GB2449538A (en) * | 2007-05-21 | 2008-11-26 | Suunto Oy | Calibrated electronic compass |
| GB2449538B (en) * | 2007-05-21 | 2010-11-10 | Suunto Oy | Compass device and method for a compass device |
| US7905026B2 (en) | 2007-05-21 | 2011-03-15 | Suunto Oy | Compass device and method for a compass device |
| EP2930466A1 (en) | 2014-04-09 | 2015-10-14 | Vectronix AG | Handheld observation device with a digital magnetic compass |
| US9918044B2 (en) | 2014-04-09 | 2018-03-13 | Safran Vectronix Ag | Handheld observation device comprising a digital magnetic compass |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2128749B (en) | 1987-04-15 |
| GB8325212D0 (en) | 1983-10-26 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| 732 | Registration of transactions, instruments or events in the register (sect. 32/1977) | ||
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19960921 |