This study presents an improved compound control algorithm that substantially enhances the anti-disturbance performance of a gear-drive gyro-stabilized platform with a floating gear tension device. The tension device can provide a self-adjustable preload to eliminate the gap in the meshing process. However, the weaker gear support stiffness and more complex meshing friction are also induced by the tension device, which deteriorates the control accuracy and the ability to keep the aim point of the optical sensors isolated from the platform motion. The modeling and compensation of the induced complex nonlinearities are technically challenging, especially when base motion exists. The aim of this research is to cope with the unmeasured disturbances as well as the uncertainties caused by the base lateral motion. First, the structural properties of the gear transmission and the friction-generating mechanism are analyzed, which classify the disturbances into two categories: Time-invariant and time-varying parts. Then, a proportional-integral controller is designed to eliminate the steady-state error caused by the time-invariant disturbance. A proportional multiple-integral-based state augmented Kalman filter is proposed to estimate and compensate for the time-varying disturbance that can be approximated as a polynomial function. The effectiveness of the proposed compound algorithm is demonstrated by comparative experiments on a gear-drive pointing system with a floating gear tension device, which shows a maximum 76% improvement in stabilization precision.
Azimuth transmission chain with anti-backlash mechanism
AZI
Azimuth
DA
Digital–analog converter
ELE
Elevation
ESO
Extended state observer
ISP
Inertially stabilized platforms
LGQ
Linear-quadratic-Gaussian
LOS
Light of sight
PI
Proportional-integral
PID
Proportional-integral-differential
PIO
Proportional-integral observer
PMI
Proportional multiple-integral
PMISAKF
Proportional multiple-integral-based state augmented Kalman filter
RMS
Root-mean-square
SAKF
State augmented Kalman filter
TGSPWAGT
Two-axis gyro-stabilized platform with anti-backlash gear-drive transmission
Constant but unknown coefficients
, , ,
Coefficients of Eq. (34)
, , , , , ,
Observer matrixes for the augmented state space
Discrete state matrix of
Discrete state matrix of
Damping coefficients of the anti-backlash spring
Damping coefficient of the gear mesh
Estimates of the (q-i) th derivative of time-varying disturbance
Estimate of the
Damping matrix
Estimation error. On behalf of
On behalf of
Transfer function of the tracking err error
State vector of Eq. (43)
Total equivalent force borne by the bearing
Gear force from the driving gear to the driven gear
Normal force
Pretightening force
Initial value of the pretightening force
Radial force
Tangential force
The closed-loop transfer function
Gyros model
Notch filter
Open loop transfer function
Stabilization loop controller
,
Inertias of the driving and driven gear, respectively
,
Equivalent inertias of the azimuth motor and the load, respectively
Number of iterations
Equivalent stiffness
Gain of a coefficient conversion
Integral gain of PI controller
Voltage conversion factor of the driver
Integral factors of the observer
Gear mesh stiffness coefficient
Proportional gain of PI controller
Stiffness coefficient of the anti-backlash spring
Motor moment coefficient
Observer gain
Stiffness matrix
Value of for iteration
Torque input matrix
,
Masses of the driving and driven gear, respectively
Mass matrix
Transmission ratio
, ,
Number, amplitude, and frequency of frequency components
,
enter of the rotation of the driving and driven gear, respectively
Changed rotation center of the driving gear
,
Meshing points in driving and driven gear
Covariance of the estimation error vector
Prediction of to the next iteration
Bearing gyration radius
,
Circle radius of the driving and driven gear, respectively
Variance of each order component of disturbance
Measurement noise
Process noise
Variance of the control voltage
Noise covariance of
Settling time of the stabilization loop
Base coupling disturbance
Total disturbance torque
Constant part of
Variable part of
Equivalent friction torque including the meshing friction and the rotation friction
Frictions exist between and within the gimbal’s rotating bearings
Friction torque in gear transmission
Input torque of the load
Output torque of the azimuth motor
Sampling time
Driving torque to the azimuth driving gear
Compensation voltage
Input voltage
Output vlotage of the PI controller
Noise input matrix
State variable of Eq. (34)
Estimate of
New vectors are constructed for an augmented state space
Estimate of the state
Generalized coordinate vector
Movement in the Y direction
Speed command
Residual gyro rate
,
Equivalent relative rotation speed of the driving and driven gear, respectively
,
Angular rate of the motor and the load, respectively
Undamped natural frequencies
Natural resonant frequency
Integral of the velocity residual
Angular disturbance
,
Rotation angle of the driving and driven gear, respecively
,
Rotation angle of the load and the motor with respect to the vehicle base, respecively
,
Rotate angle of the motor and the load, respecively
Constant meshing friction coefficient
Viscous damping friction coefficient of the bearing
Operating pressure angle
Damping ratio of the stabilization loop
Denominator damping factor
Molecular damping factor
Poles of the desired stabilization loop
Resolution of DA
Displacement increment of the rotation center of the driving gear
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