Navigational aid

Claim 2

Apparatus for determining the attitude of a body operating in a gravitational field comprising: acceleration sensor means for measuring the total acceleration of the body in relation to a coordinate system fixed with respect to said body; inertial acceleration calculating means for calculating the total inertial component of the total acceleration in relation to said coordinate system; comparator means for comparing said measured total acceleration with said total inertial component thereby to generate data representative of the orientation of the gravitational component of acceleration in relation to said coordinate system; and attitude calculating means for receiving said data and for calculating the attitude of the body.

Claim 5

An arrangement for determining the attitude of a body operating in a gravitational field comprising: means for defining, with respect to said body, a coordinate system having three orthogonal axes; velocity sensor means for sensing body velocity magnitude and direction relative to said axes; rotation sensor means for sensing rotation of the body about each of said axes; acceleration sensor means for measuring the total acceleration of the body along each of said axes; inertial acceleration calculating means for receiving data from said velocity sensor means and said rotation sensor means and processing it to determine the total inertial component of acceleration of the body; comparator means for comparing said measured total acceleration with said total inertia component thereby to generate data representative of the orientation of the gravitational component of acceleration in relation to said coordinate system; and attitude calculating means for receiving said data and for calculating the attitude of the body.

Claim 6

An arrangement for determining the attitude of a body operating in a gravitational field comprising: means for defining, with respect to said body, a coordinate system having three orthogonal axes; velocity sensor means for sensing body velocity magnitude and direction relative to said axes; rotation sensor means for sensing rotation of the body about each of said axes; acceleration sensor means for measuring the total acceleration of the body along each of said axes; inertial acceleration calculating means for receiving data from said velocity sensor means and said rotation sensor means and processing it to determine the total inertial component of acceleration of the body; comparator means for comparing said measured total acceleration with said total inertia component thereby to generate data representative of the orientation of the gravitational component of acceleration in relation to said coordinate system; and attitude calculating means for receiving said data and for calculating the attitude of the body.

Claim 7

An arrangement according to claim 3 wherein the orthogonal set of axes are x, y, z axes, wherein said inertial acceleration calculating means determine a portion (x i , y i , z i respectively) of the inertial component of acceleration acting along the x, y, and z axes according to the following expressions: x.sub.i =l(V+V[q tan α-r tan β-l.sup.2 (tan α.sec.sup.2 α.α+tan β.sec.sup.2 β.β)]) y.sub.i =l(V tan α+V[r-p tan α-l.sup.2 sec.sup.2 α(tan α.tan β.α-sec.sup.2 β.β)]) z.sub.i =l(V tan β+V[p-p tan β-q-l.sup.2 sec.sup.2 β(tanα.tan β.β-sec.sup.2 α.α)]) wherein V is the speed of the vehicle relative to a non-accelerating frame of reference and V is the derivative of V with respect to time; α is the angle of incidence referred to the center of gravity of the vehicle and α is the derivative of α with the respect to time; β is the yaw angle referred to the center of gravity of the aircraft and β is the derivative of β with respect to time; p, q, and r are the rotations of the vehicle about axes x, y and z respectively, and l is the velocity vector cosine relative to the x axis, and wherein the acceleration sensor means measure the portion (x m y m z m respectively) of the total acceleration acting along the x, y and z axes, said arrangement further including means for deducing the pitch and bank angles of the vehicle (θ, φ) according to the following expressions: θ=arc sin [x.sub.m -x.sub.l)/g] φ=arc tan [.sub.m -y.sub.i)/(z.sub.m -z.sub.i)].

Claim 8

An arrangement according to claim 3, further including: integration means for integrating the data received from the rotation sensor means to determine an estimated attitude of the vehicle, and monitoring means for comparing the estimated attitude produced by integration with that produced by deduction of the gravitational component.

Claim 9

An arrangement according to claim 5, wherein the estimate produced by integration and that produced by deduction of the gravitational component are each weighted in terms of their reliability and combined to obtain a best estimate employing a Kalman filtering technique.

Claim 10

An arrangement according to claim 5, further comprising: monitoring means for monitoring the second derivative of the data received from one or more of the velocity, rotation and acceleration sensor means, the monitoring means including means for suppressing the estimate produced by deduction of the gravitational component should the second derivative exceed a predetermined value.

Claim 11

An arrangement according to claim 3, further including means for calculating the magnitude of the gravitational component and means for comparing the calculated magnitude with standard gravity thereby to serve as a monitor.

Claim 12

An arrangement according to claim 3, further including low frequency filter means for smoothing short term fluctuations in the body velocity magnitude data from the velocity sensor means, and delay means for delaying body velocity direction data from said velocity sensor means and data from each of the rotation and acceleration sensor means in such a manner as to synchronize said delayed data with said filtered data, whereby the arrangement produces a delayed estimate of the attitude of the vehicle.

Claim 13

An arrangement according to claim 9, further including integrating means for integrating the data from the rotation sensor means and for adding the integrated data to the delayed estimate of the attitude deduced from the gravitational component, thereby to update the delayed estimate of the attitude.

Claim 14

Apparatus for determining the attitude of the body operating in a gravitational field comprising: acceleration sensor means for measuring the total acceleration of the body in relation to a coordinated system fixed with respect to said body and for outputting data (x m , y m , z m ) representative of said measured total acceleration; inertial acceleration calculating means for calculating the total inertial component of the total acceleration in relation to said coordinate system and for outputting data (x i , y i , z i ) representative of said total inertial component; and attitude calculating means for receiving data output by said inertial acceleration calculating means and for processing it to determine the pitch and bank angles of the body (θ, φ) according to the following expressions: θ=arcsin [x.sub.m -x.sub.i)/g] φ=arctan [y.sub.m -y.sub.i)/(z.sub.m -z.sub.i)].

Claim 15

Apparatus for determining the attitude of the body operating in a gravitational field comprising: acceleration sensor means for measuring the total acceleration of the body in relation to a coordinated system fixed with respect to said body and for outputting data (x m , y m , z m ) representative of said measured total acceleration; inertial acceleration calculating means for calculating the total inertial component of the total acceleration in relation to said coordinate system and for outputting data (x i , y i , z i ) representative of said total inertial component; and attitude calculating means for receiving data output by said inertial acceleration calculating means and for processing it to determine the pitch and bank angles of the body (θ, φ) according to the following expressions: θ=arcsin [x.sub.m -x.sub.i)/g] φ=arctan [y.sub.m -y.sub.i)/(z.sub.m -z.sub.i)].