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

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Chapter 3 / Sensors / Seeker<br />

_ _<br />

the overshoot as shown in Figure 3-55. In practice the motor voltage and<br />

winding resistance limit the current and an artificially low limit is usually<br />

imposed below this value.<br />

Table 3-18 : Complex Gimbal Dynamic Characteristics<br />

MATH DESCRIPTION PITCH YAW UNITS<br />

SKKCZ Controller zero time constant 9.1 1.3 msec<br />

SKKCP Controller pole time constant 10.5 1.5 msec<br />

SKKA Controller/DAC gain 40 120 Amp/rad<br />

SKIM Motor current limit 6 12 Amps<br />

SKKM Motor gain 0.05 0.15 N-m/Amp<br />

SKζG Motor damping ratio 0.7 0.7<br />

SKωG Motor natural frequency 800 800 Hz<br />

SKJG Gimbal inertia 0.05 0.5 g m 2<br />

CLOSED LOOP RESPONSE ( DB )<br />

5<br />

0<br />

-5<br />

-10<br />

-15<br />

-20<br />

10 0<br />

3.9-9<br />

10 1<br />

FREQUENCY ( HZ )<br />

Figure 3-52 : Closed Loop Frequency Response<br />

The torque disturbances (SKτE) comprise spring, cogging and ripple torques.<br />

SK<br />

K<br />

G1Ψ<br />

SK<br />

K<br />

⋅ Ψ<br />

H<br />

B<br />

G5Ψ<br />

⋅<br />

+<br />

SK<br />

I<br />

K<br />

SK GΨ<br />

G2Ψ<br />

⋅ cos<br />

τ<br />

SK EΨ<br />

⋅ cos<br />

+<br />

: =<br />

10 2<br />

H<br />

( K ⋅ Ψ + K )<br />

H<br />

( K ⋅ Ψ + K )<br />

SK<br />

SK<br />

G6Ψ<br />

G3Ψ<br />

B<br />

B<br />

SK<br />

SK<br />

G7Ψ<br />

G4Ψ<br />

Equation 3.9-13<br />

The effect of gimbal mass imbalance leading to a cross coupling of the<br />

motor torque has been ignored. The outer (yaw) gimbal is usually<br />

connected by slip rings, the leads bringing power to the inner gimbals<br />

increasingly resist gimbal motion as the off-boresight angle increases.

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