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

Chapter 3 / Sensors / Gyroscopes
_ _
1
GUI
W_BCB
WX_UCB
WY_UCB
FLOAT ANGLE
WZ_UCB
GYROSCOPE
INPUT
3.4-3
ROLL GYROSCOPE
I_WX_BCB
WX_UCB
WY_UCB
YAW GYROSCOPE
I_WZ_BCB
WZ_UCB
I_WX_INC
ROLL ANGLE
PITCH GYROSCOPE
I_WY_BCB
I_WY_INC
PITCH ANGLE
I_WZ_INC
YAW ANGLE
Figure 3-24 : Gyroscope Triad Model
The generic gyroscope model here is adequate for both IMU-1 and IMU-2
in §3.3.1. The reference data will be described in terms of IMU-1 although
IMU-2 reference inputs can be treated likewise.
3.4.3 Reference Angular Rate
The average inertial angular rate is processed at the reference rate (GSfR) of
800 Hz. The angular rate about each input axis depends on the alignment
and orthogonality of the case with respect to the missile body, and each
sensor relative to the case as shown Figure 3-25.
W_BCB
1
CASE
MISALIGNMENT
NON
ORTHOGONALITY
FLOAT ANGLE
2
CROSS
COUPLING
1
2
3
4
5
6
WX_UCB
1
WY_UCB
2
WZ_UCB
Figure 3-25 : Gyroscope Input Models
Mechanical instruments are also subject to cross-coupling errors that depend
on the float angle. These additional error sources are invoked by setting
MS_GS_ER bits 11-13 listed in Table 3-8. To deal with these errors
additional Cartesian axes associated with the IMU case, and each sensor
therein, are required. Frame “D” is fixed in the IMU and originates at a
common reference point (u), and describes the orientation of the case with
respect to the Missile Body frame. An orthogonal “sensor” frame is
attached to each gyroscope referred to as “R”, “P” and “Y” respectively,
their individual reference points coinciding with (u). The manufacturing
3