Xiangdong Liu

A Precise and Robust Control Strategy for Rigid Spacecraft Eigenaxis Rotation

Eigenaxis rotation is generally regarded as a near-minimum time strategy for rapid attitude maneuver due to its constitution of the shortest angular path between two orientations. In this paper, the robust control problem of rigid spacecraft eigenaxis rotation is investigated via time-varying sliding mode control (TVSMC) technique. Both external disturbance and parameter variation are taken into account. Major features of this robust eigenaxis rotation strategy are first demonstrated by a TVSMC algorithm. Global sliding phase is proved as well as the closed-loop system stability. Additionally, the necessary condition for eigenaxis rotation is provided. Subsequently, to suppress the global chattering and improve the control accuracy, a disturbance observer-based time-varying sliding mode control (DOTVSMC) algorithm is presented, where the boundary layer approach is used to soften the chattering and a disturbance observer is designed to attenuate undesired effect. The spacecraft attitude is represented by modified Rodrigues parameter (MRP) for the non-redundancy. Finally, a numerical simulation is employed to illustrate the effectiveness of the proposed strategy, where the pulse-width pulse-frequency (PWPF) technique is utilized to modulate the on-off thrusters.

Time-varying sliding mode control for spacecraft attitude maneuver with angular velocity constraint

In this paper, the attitude control problem for uncertain spacecraft under angular velocity constraint is addressed. Both parametric uncertainty and external disturbance are considered in the spacecrafts dynamics. The spacecrafts attitude is represented by modified Rodrigues parameter (MRP) for its non-redundancy. A time-varying sliding mode control (TVSMC) algorithm is derived for attitude control system. The proposed control algorithm eliminates the reaching phase of the conventional time-invariant sliding mode control (SMC) and guarantees the sliding mode occurrence all the time. Moreover, the control parameter is adjusted to avoid the angular velocity constraint during the maneuver. Finally, a numerical simulation is employed to verify the proposed control algorithm.

Attitude tracking of rigid spacecraft without angular velocity measurements via passivity approach

In this paper, the attitude tracking problem of rigid spacecraft without inertial or relative angular velocity measurements is investigated. The minimal attitude description, the modified Rodrigues parameters (MRPs), are utilized as the attitude parameters for the non-redundancy. The inherent passivity of the system describing the attitude tracking motion of the spacecraft is exploited. Then an attitude tracking control law using feedback parts of relative angular velocity and relative MRPs is designed. Additionally, to remove the requirement of the relative angular velocity measurements, a lead filter is utilized to provide the information for the tracking control problem with relative attitude measurements only. Finally, a numerical simulation is employed to verify the proposed control algorithm.

Valve's dynamic damping characteristics — Measurement and identification

This paper proposes a novel method to test the dynamic damping characteristics of valve. The testing system employs the vertical movement pattern, and has a suspension support structure. Force sensors are installed to measure the dynamic friction of the working valve directly. Making use of LuGre friction model and both adaptive genetic algorithm and chaos particle swarm optimization algorithm, the valves dynamic damping parameters can be identified. Experiments have been carried out on a piston rod with a rubber ring and a steel cylinder. The results demonstrate the designed dynamic damping test system and the parameter identification algorithms are effective.