GB2217455A

GB2217455A - Azimuth correction in navigation systems

Info

Publication number: GB2217455A
Application number: GB8830092A
Authority: GB
Inventors: Fritz Hofmann
Original assignee: Messerschmitt Bolkow Blohm AG
Current assignee: Airbus Defence and Space GmbH
Priority date: 1988-04-16
Filing date: 1988-12-23
Publication date: 1989-10-25
Anticipated expiration: 2008-12-23
Also published as: DE3812783A1; FR2633741A1; GB8830092D0; DE3812783C2; FR2633741B1; GB2217455B

Description

2/17455 2 JMe291188 e; 1 1 1 f 1 Automatic azimuth correction in inertial_

navigation systems The invention relates to method and apparatus for carrying out automatic azimuth correction in inertial navigation systems using determination of azimuthal deviation between navigational means, typically a module, of a carrier vehicle and a reference means at a ground or other control station, and has particular application for flying bodies such as commonly called guided missiles.

As is known, azimuth correction in inertial reference systems was originally fraught with considerable difficulties owing to precision requirements and possibly very large size of the guided missiles, which difficulties could only be resolved using very large and expensive apparatus. From our DEPS 36 22 064 automatic optical azimuth correction is known using an angularly adjustable reflector at the guided missile for oblique direction finding. A uniaxially scanning line detector and a biaxially adjustable transmitter are used in conjunction with control means and inertial frame guidance means of the navigation means/module of the missile.

JMe291188 That and other proposals arising internally of the Applicants have enabled reduction of costs for azimuth transmission between the control station and the missile by use of a so-called "transmission window" arranged on or in the (cellular) structure of the missile. However, that is not altogether desirable particularly where it militates against a simple construction.

It is an object of this invention to provide method and apparatus for automatic azimuth correction without requiring a transmission window, preferably further without significant reduction of advantages and accuracy previously achieved.

According to one aspect of this invention there is provided a method for determining azimuthal deviation between navigation means of a carrier and reference means at a ground or other control station, especially for guided flying bodies such as missiles launched in a vertical or other elevationally inclined direction, wherein with the carrier in an inclined launching attitude, roll and yaw deviations of the carrier are first evaluated using inertial coupling, then, after determining elevation of launching attitude azimuth differential between the ground station and the JMe291188 T 3 - navigation module is evaluated by computation According to another aspect of this invention there is provided apparatus for carrying out that method wherein the navigation means of the carrier has associated sensor means for comparing inclination of the navigation means with inclination of the intended launching axis and computing means for determining the azimuth differential from the inclination difference regarding navigation module/launching axis.

Practical implementation of method and apparatus embodying this invention will now be indicated by way of example, with reference to the accompanying drawings, in which:

Figure 1 shows diagrams for explaining calculation of inertial coupling in one position of a missile or other carrier vehicle; Figure 2 shows diagrams for explaining calculation of inertial coupling in a vertical position of a missile or other carrier vehicle; Figure 3 shows diagrams for explaining calculation of carrier vehicle reference data in its JMe291188 launching position; and 7 4 - Figure 4 shows one apparatus layout for: inertial navigation-sensor module (1) of a missile (7) or other carrier vehicle, inertial vertical reference of the launching axis using an accelerometer (2), azimuth reference at launcher (5) using a north-seeker device (3), bus system (4) for interconnecting devices 1 to 3, attitude axis, launcher and carrier vehicl themselves.

e To determine azimuthal difference between the navigation module (1) of the guided missile (7) and a reference shown at a ground control station (here, at 3, the axes of inclination of the ground station), first of all roll deviation ( cf r) and yaw deviation (cfq 1) between the ground station and the navigation module are measured inertially at various angles of inclination.

z d' For a known start-elevation - as will be shown later - in the example of a missile (FK) the azimuthal difference (AV) between the ground station and the navigation module of the FK - or of the carrier vehicle JMe291188 - - can be computed. The azimuthal difference will be determined by the inertial coupling.

A (O-)-position of the launcher base is defined by: the vertical axis intercept "zrg", the direction of the pivot axis "yrg" horizontally oriented for harmonizing purposes, and the orthogonal axis "xrg" relative to zrg and yrg. Mounted in the launcher base, parallel to the intercept zrg, are accelerometers "awz, awy, awx", for which awx (0) = 0; and awy (0) = 0.

From Figure 1, setting up for launch in open terrain involves tilting the launcher base relative to the (0-)-position by a longitudinal tilt angle (eb) and by a transverse tilt angle (0b), typical maximum 0.1 radian. This (b-) position is defined by: awx (b) = lg sin @b axy (b) = lg cos eb sin jb; The missile reference frame is aligned appromixately parallel to "xrb, yrb, and zrb" as a consequence of its mechanical installation. Then, the angles:

Cf r Roll deviation about the axis xmb cf ql = Yaw deviation about the axis zmb cp q 2 = Pitch deviation about the axis ymb JMe221288 6 - define relatively small discrepancies inevitable between launcher base and the missile reference frame. Given that /cfr/, /cf-ql/ and /cfq 2/ <about 50 mrad, the axial configuration of the system cfr,Cfq 1 and cfq 2 has only a minor effect.

Thus, the roll deviation ( r) can be computed f rom:

amy(b) = 19 cos eb sin (1 b +Cfr) (1) To determine the yaw deviation (cfq 1), in accordance with the inertial coupling illustrated in Fig. 2 in the vertical position, the base of the missile and the sensor module of the latter are so aligned about the axis yrb of the launcher that "zrv" with "awz" (v) = 0 is horizontally positioned. In this (v)-position, the yawing deviation (Cpq can be computed from:

amy(v) = lg sin (1 b + Cfq 1); (2) Further, the pitching deviation ( ? q 2) is given by:

amz(v) = lg cos 1 b sincf q 2; (3) Thus, the slight discrepancy of the FK-reference frame from the "zrb, yrb, xrb" coordinate system can be determined from the measured values of "awx(b), awy(b), amy(v) and amz(v)".

11 1 4 Me291138 7 As is apparent from the diagram of Figure 3, in the launch position (s- position) of the launcher, the vertical alignment of the FK-sensor module is directly obtainable from the reading of the accelerometers "amx(s), amy(s) and amz(s)". The azimuth is related to the axis "yrb" = vertical projection of the pivot axis of the launcher in the horizontal plane "xrg, yrg". By contrast, the axis "ym+sly = vertical projection of the axis "yms" in the horizontal plane is rotated by an angle given by the equation:

8y=(fr sin es + cr q 1 cos es + Cf q 2 delta; (4) where delta > 1.

Figures 1, 2 and 3 of the drawing illustrate the computational method in sufficient detail to make further explanation unnecessary. For the outline embodiment of Figure 4, the computations set out above are carried out before launch by a microprocessor contained in the sensor module 1 of the carrier vehicl 7.

iMe291188

Claims

1. A method for determining azimuthal deviation between navigation means of a carrier and reference means at a ground or other control station, especially for guided flying bodies such as missiles launched in a vertical or other elevationally inclined direction, wherein with the carrier in an inclined launching attitude, roll and yaw deviations of the carrier are first evaluated using inertial coupling, then, after determining elevation of launching attitude azimuth differential between the ground station and the navigation module is evaluated by computation.

2. Apparatus for carrying out the method according to Claim 1, wherein the navigation means of the carrier has associated sensor means for comparing inclination of the navigation means with inclination of the intended launching axis and computing means for determining the azimuth differential from the inclination difference regarding navigation module/launching axis.

3. A method of determining azimuthal deviation between navigation means of a carrier vehicle to be launched and a ground or other control station substantially as herein described with reference to and as shown in the accompanying drawings.

j i 1 1h JMe291188

4. Apparatus for determining azimuthal deviation between navigation means of a carrier vehicle and a control station arranged and adapted to operate substantially as herein described with reference to and as shown in the accompanying drawings.

Published 1989 at The Patent Office. State House, 607, '1 High Holborn, London WCIR 4TP. Further copies maybe obtained from The Patent Offtce. Sales Branch, St Mary Cray, OrpingUn, Kent BR5 MD. Printed by Multiplex techniques ltd, St Mary Cray, Kent, Con. 1/87