Abstract
The high-precision speed control of gimbal servo systems is the key to generating high-precision torque for control moment gyroscopes (CMGs) in spacecrafts. However, the control performance of gimbal servo systems may be degraded significantly by disturbances, especially a dynamic imbalance disturbance with the same frequency as the high-speed rotor. For assembled CMGs, it is very difficult to measure the rotor imbalance directly by using a dynamic balancing machine. In this paper, a gimbal disturbance observer is proposed to estimate the dynamic imbalance of the rotor assembled in the CMG. First, a third-order dynamical system is established to describe the disturbance dynamics of the gimbal servo system, in which the rotor dynamic imbalance torque along the gimbal axis and the other disturbances are modeled to be periodic and bounded, respectively. Then, the gimbal disturbance observer is designed for the third-order dynamical system by using the total disturbance as a virtual measurement. Since the virtual measurement is derived from the inverse dynamics of the gimbal servo system, the information of the rotor dynamic imbalance can be obtained indirectly only using the measurements of gimbal speed and three-phase currents. Semi-physical experimental results demonstrate the effectiveness of the observer by using a CMG simulator.
Highlights
As a kind of angular momentum exchange actuator, control moment gyros (CMGs) have been widely used in spacecraft attitude control owing to their superior properties in simple structure, large torque, and high precision [1,2,3,4,5]
Tm produced by the motor, and dynamic imbalance torque Tdz produced by the rotor rotation and the gyroscopic torque Tg arising from the spacecraft motion
The aim of this paper is to measure the rotor dynamic imbalance of a CMG indirectly from the information of the gimbal motion, and the problem of indirect measurement can be formulated as follows: Design a gimbal disturbance observer for the CMG gimbal servo system to estimate the rotor dynamic imbalance torque Tdz from Equation (4) by using the information of gimbal velocity ω and electromagnetic torque Te, and calculate the quantity of the rotor dynamic imbalance according to Equation (3)
Summary
As a kind of angular momentum exchange actuator, control moment gyros (CMGs) have been widely used in spacecraft attitude control owing to their superior properties in simple structure, large torque, and high precision [1,2,3,4,5]. In order to obtain the information of the dynamic imbalance for the assembled rotor, field dynamic balancing techniques can be used without disassembly [24,25] These techniques are not suitable for the assembled CMGs owing to the effects of the gimbal motions. In order to obtain information about the dynamic imbalance for assembled rotors in CMGs, a gimbal disturbance observer is proposed in this paper. This observer is designed for a third-order system, describing dynamic imbalance disturbance and the other disturbances in the gimbal servo system.
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