Fault-tolerant control of flexible satellite with magnetic actuation and reaction wheel

The attitude fault-tolerant control of a flexible satellite actuated by reaction wheels and magnetic torquer bars is investigated in this article. A low earth orbit is considered for moment perturbations such as drag and gravity gradient. Furthermore, the flexible panels attached to a rigid central body are modeled through the assumed mode approach by a finite set of bending modal motion. The ordinary differential equations of their generalized coordinates are found using Lagrange’s equation, and the resulting dynamical model is validated by comparing its simulation results to the NX Siemens software results. Finally, a fault-tolerant controller based on sliding mode control is suggested and tested in different scenarios. It is showed that the proposed control method tolerates the actuators’ faults and controls the satellite’s attitude while desaturating the reaction wheels.

Frequency–Amplitude Relationship of a Nonlinear Symmetric Panel Absorber Mounted on a Flexible Wall

This study addresses the frequency–amplitude relationship of a nonlinear symmetric panel absorber mounted on a flexible wall. In many structural–acoustic works, only one flexible panel is considered in their models with symmetric configuration. There are very limited research investigations that focus on two flexible panels coupled with a cavity, particularly for nonlinear structural–acoustic problems. In practice, panel absorbers with symmetric configurations are common and usually mounted on a flexible wall. Thus, it should not be assumed that the wall is rigid. This study is the first work employing the weighted residual elliptic integral method for solving this problem, which involves the nonlinear multi-mode governing equations of two flexible panels coupled with a cavity. The reason for adopting the proposed solution method is that fewer nonlinear algebraic equations are generated. The results obtained from the proposed method and finite element method agree reasonably well with each other. The effects of some parameters such as vibration amplitude, cavity depth and thickness ratio, etc. are also investigated.

Two Actuation Methods for a Complete Morphing System Composed of a VGTM and a Compliant Parallel Mechanism

Presented in this paper is a complete morphing system consisting of a variable geometry truss manipulator (VGTM) that is fully covered by a flexible panel skin. Two approaches are studied for morphing control. The first one is to have the VGTM act as a driving mechanism and the flexible panels as a passive system. In this case, the VGTM is composed of active members and passive lockable members. It is shown that the morphing system can reach the desired shapes through intermediate steps. The second method is to have the flexible panels act as drivers and the VGTM as a passive supporting structure. In this case, the VGTM is only composed of passive lockable members. The morphing system can also achieve the desired poses through intermediate steps. The control strategies of the two methods are discussed along with kinematic analysis, a comparison study is conducted to show their pros and cons, and two prototypes are fabricated to verify the feasibility of two actuation methods.

Analysis of Structure–Acoustic Coupling Characteristics Between Adjacent Flexible Panels and Enclosed Cavity

This article studies the structure–acoustic coupling mechanism between two adjacent flexible panels and an enclosed cavity by analytical and mathematical methods based on modal expansion methods and impedance mobility techniques. The results show that the coupling relations among subsystem modes of the coupled system have selectivity characteristics. The coupling strength depends on the normalized mode–shape coupling coefficients. The coupling relationship between two flexible panels is established through the enclosed cavity. The structural–acoustic coupling effect mainly affects the low-order modes of the coupled system, especially the first-order modes of the panels and cavity. When one panel is weakly coupled with the cavity, the two flexible panels are decoupled. The vibration of the panel only depends on its structural characteristics and external excitation, and the panel radiates sound into the cavity. The vibration of another panel depends not only on its structural characteristics but also on its coupling effect with the cavity.

Dynamic Coupling and Control of Flexible Space Robots

The dynamic modeling and coupling effect of a space robot are complex when the flexible manipulator and solar panels are considered. This paper investigates the dynamic coupling effect and control of a flexible space robot with flexible manipulators and flexible panels. The equations of motion are derived for the robot model both of the rigid-flexible type and flexible-flexible type. The flexible space robot dynamic model is verified by comparison with the results generated by the ADAMS software, for which good agreement has been obtained. The dynamic coupling matrix of the flexible space robot is derived based on the dynamic model. The effects of the central rigid body mass and the joints angle on the dynamic coupling are analyzed. A control method is proposed to manipulate the flexible space robot based on the system dynamic model. The multiple-impulse robust (MIR) input shaper is used to suppress the vibration of flexible structures in the proposed controller. Appropriate design parameter and frequency scaling factor are selected for the MIR input shaper to suppress the flexible vibration. The flexible space robot control is conducted to illustrate the effect of the proposed controller. It is shown that the proposed control method can realize the desired joints manipulation, while suppressing the vibration of the flexible manipulators and flexible panels.