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

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Chapter 3 / Sensors / Gyroscopes<br />

_ _<br />

GS<br />

γ<br />

( ) T<br />

γ , γ ,<br />

: =<br />

γ<br />

3.4-8<br />

R<br />

P<br />

Y<br />

Equation 3.4-7<br />

Applying a masking matrix [GXM] to deal with the different Spin axis<br />

orientations, and relating the Spin axis to individual sensor (R,P,Y) axes,<br />

ω<br />

U<br />

C,<br />

B<br />

: =<br />

⎛<br />

⎜<br />

⎜<br />

⎜<br />

⎝<br />

ω<br />

ω<br />

ω<br />

XR<br />

C, Β<br />

XP<br />

C, Β<br />

XY<br />

C, Β<br />

⎞<br />

⎟<br />

⎟<br />

⎟<br />

⎠<br />

−<br />

GS<br />

For the configuration selected,<br />

⎛<br />

⎜<br />

γ ⊗ ⎜<br />

⎜<br />

⎝<br />

[ GXM ]<br />

[ GXM ]<br />

: =<br />

⎡ 0<br />

⎢<br />

⎢<br />

1<br />

⎢⎣<br />

−1<br />

3.4.4 Measured Angular Rate and Angular Increments<br />

⋅<br />

⎡<br />

⎢<br />

⎢<br />

⎢<br />

⎣<br />

1<br />

0<br />

0<br />

ω<br />

ω<br />

⎤<br />

⎥<br />

⎥<br />

⎥⎦<br />

YR<br />

C, Β<br />

ZR<br />

C, Β<br />

ω<br />

ω<br />

XP<br />

C, Β<br />

ZP<br />

C, Β<br />

ω<br />

ω<br />

XY<br />

C, Β<br />

YY<br />

C, Β<br />

⎤ ⎞<br />

⎥<br />

⎟<br />

⎥<br />

⎟<br />

⎥<br />

⎟<br />

⎦ ⎠<br />

Equation 3.4-8<br />

Equation 3.4-9<br />

Non-gyroscopic torques, and imperfect electronics, that cause application<br />

dependent measurement errors are subject to physical constraints, financial<br />

and technical trade-offs. Ignoring rotor speed variation drift, float angular<br />

velocity and acceleration, Savage’s model of a single axis mechanical<br />

gyroscope expressed in (I,O,S) axes reduces to,<br />

ω<br />

~<br />

I<br />

C,<br />

B<br />

: =<br />

ϕ<br />

SF<br />

⎛<br />

⎜ I<br />

I ⎛ J ⎞<br />

⋅ ω<br />

⋅ ω ⋅ ω −<br />

⎜<br />

⎜ S − J I S JO<br />

&<br />

I<br />

⋅ ωC,<br />

B + GSB<br />

+<br />

⎟ C,<br />

B C,<br />

B<br />

⎝<br />

⎝ HW<br />

⎠<br />

HW<br />

O<br />

C,<br />

B<br />

⎞<br />

⎟<br />

⎠<br />

Equation 3.4-10<br />

The float inertia about the axes is denoted by (JI, JO, JS), and (HW) is the<br />

angular momentum of the rotor about the spin axis. Float dynamics, anisoelastic<br />

drift, and output rate induced errors are minimising by careful design.<br />

This leaves constant bias (GSB) and scale factor errors common to both<br />

optical and mechanical sensors. These errors are controlled by the bit<br />

pattern of MS_GS_ER listed in Table 3-9. Bits 22-23 reserved in Table 3-6<br />

for ADC errors, are replaced by PWM errors in mechanical sensors, and<br />

fringe counting in optical systems. The anti-aliasing filter and quantised<br />

noise associated with the ADC, controlled by bits 21 and 24, are not<br />

applicable.<br />

The inertial angular rate is corrupted at the reference rate by a time delay<br />

and 2 nd order dynamics,

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