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Thesis - Leigh Moody.pdf - Bad Request - Cranfield University

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Chapter 5 / Missile State Observer<br />

_ _<br />

5.8.2 Missile Accelerometer Measurement Update<br />

Airframe stabilisation is less dependent on high frequency accelerometer<br />

output compared with gyroscope data. Accelerometer data is therefore<br />

accumulated and used at 100 Hz.<br />

AC<br />

Z ~<br />

: =<br />

100<br />

~<br />

f<br />

B<br />

r,<br />

u<br />

5-14<br />

: =<br />

3<br />

∑ 400<br />

i : = 0<br />

~<br />

f<br />

B<br />

r,<br />

u<br />

( t )<br />

k − i<br />

Equation 5.8-6<br />

If the IMU and missile reference points are not coincident the estimated<br />

accelerometer measurements are determined as in §3.3.1.1,<br />

T<br />

B<br />

A<br />

⋅<br />

AC<br />

Z<br />

A<br />

A<br />

B B<br />

( &<br />

A E<br />

A G B B B<br />

P&<br />

m + 2 ⋅ TE<br />

⋅ ωC,<br />

E × P&<br />

m − TG<br />

⋅ g ) + ω&<br />

A,<br />

B × Pm,<br />

u + ωA,<br />

B × ωA,<br />

B × Pm<br />

d<br />

: =<br />

, u<br />

Equation 5.8-7<br />

Ignoring coriolis acceleration due to earth rate, assuming the tilt between<br />

LGA and Alignment frames is negligible, and the IMU reference point lies<br />

on the missile longitudinal axis,<br />

P<br />

XB<br />

m,<br />

u<br />

⋅<br />

⎛<br />

⎜<br />

⎝<br />

AC<br />

−<br />

ZG T<br />

B<br />

( 0 , 0 , g ) ⎞<br />

⎟ +<br />

B A<br />

Z ≅ TA<br />

⋅<br />

⎛<br />

⎜ P&<br />

&<br />

m −<br />

ϕ<br />

⎝<br />

d ⎠<br />

rB ( ω )<br />

A,<br />

B<br />

2<br />

,<br />

ω<br />

XB<br />

A,<br />

B<br />

ϕ<br />

⋅ ω<br />

B<br />

ARM<br />

YB<br />

A,<br />

B<br />

: =<br />

+ ω&<br />

ZB<br />

A,<br />

B<br />

,<br />

ω<br />

XB<br />

A,<br />

B<br />

⋅ ω<br />

ZB<br />

A,<br />

B<br />

ARM<br />

Equation 5.8-8<br />

− ω&<br />

YB<br />

A,<br />

B<br />

⎞<br />

⎟<br />

⎠<br />

T<br />

Equation 5.8-9<br />

The accumulation delay is accounted for using a cyclic stack not backward<br />

state propagation. The linearised measurement matrix comprises,<br />

AC<br />

AC<br />

[ 0 M H H ]<br />

H ≡ ∂ Z ∂ X : =<br />

M<br />

3x9<br />

AC<br />

ML<br />

AC<br />

MA<br />

Equation 5.8-10<br />

Apportioning the acceleration innovations to the missile linear dynamics,

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