Control Of Large Space Structures Research Articles

Dynamics modeling and attitude-vibration hybrid control of a large flexible space structure

The challenges in the dynamic modeling and control of large flexible space structures (LFSSs) include the high number of degrees of freedom in the model, the geometric nonlinearities in the flexible components, and the nonlinear coupling effects between overall motions and vibrations of the structure. In this study, we propose a systematic method to solve the mentioned problems in the research of LFSSs. We use the referenced nodal coordinate formulation (RNCF) to build the dynamic model. The modeling method is general and the model can better describe the large deformations of flexible structures compared with the modal-based dynamic model. The key feature of our work is that we use a hybrid control strategy for the attitude and vibration control directly performing on the full-scale dynamic model. Specifically, the control strategy combines a proportional and derivative (PD) control algorithm based on SO(3) for the attitude control and an analytical linear-quadratic (LQ) vibration control method for the vibration control. The simulation results are presented to demonstrate the effectiveness of the proposed hybrid control strategy both in the three-axis attitude maneuver task and on-orbit pointing scenario.

Vibration Suppression for Flexible Plate with Tunable Magnetically Controlled Joint Stiffness/Damping

Large flexible solar panels have the properties of light weight, low stiffness, and weak damping, which leads to low-frequency and large-amplitude vibrations. The existing vibration control methods of solar panels mainly adopt intelligent piezoelectric structures. However, the disadvantage is that the large stroke drive and control are limited. In the present study, a semi-active vibration control approach is proposed for flexible space solar panels based on magnetically controlled joints. The magnetic stiffness comes from the linear relationship between the joint output torque and rotation angle. The magnetic damping stems from the eddy current damping resulting from the relative motion between the permanent magnet rotor and the stator core of the joint. Firstly, the coupling dynamic modeling of a flexible plate and magnetic joints is established by adopting the Lagrange equation and the assumed mode approach. Secondly, semi-active vibration control simulations of the coupled system are performed. Meanwhile, the influence of the variable joint stiffness on the system frequency-shift effect is studied. Finally, the experimental platform is built, and simultaneously, non-contact permanent magnets and airflow are used to simulate single- and multi- frequency excitations, respectively. The experimental results indicate that, in the range of 0.06–0.343 Hz, magnetic damping is the leading factor with magnetic stiffness being the auxiliary. Additionally, it is also experimentally verified that the dual joint actuation has good synchronization. This study provides a new solution for the low-frequency vibration control of large flexible space structures.

Distributed magnetic attitude control for large space structures

The utility of distributed magnetic torque rods for the attitude control of a large space structure is investigated. Distributed arrays of actuators offer advantages such as distributing structural loads, increasing fault tolerance, allowing structures to be designed modularly, and additionally the actuators may be integrated with on-orbit fabrication strategies. First, distributed torques are shown to effectively rotate highly flexible structures. This is compared with torques applied to the centre-of-mass of the structure, which cause large surface deformations and can fail to enact a rotation. This is demonstrated using a spring–mass model of a planar structure with embedded actuators. A distributed torque algorithm is then developed to control an individually addressable array of actuators. Attitude control simulations are performed, using the array to control a large space structure, again modelled as a spring–mass system. The attitude control system is demonstrated to effectively detumble a representative 75 × 75 m flexible structure, and perform slew manoeuvres, in the presence of both gravity-gradient torques and a realistic magnetic field model.

Active vibration control of large space structures: Modelling and experimental testing of offset piezoelectric stack actuators

To meet demanding mission objectives, most current satellites for Earth and Universe observation are equipped with large flexible appendages. However, due to the coupling between spacecraft rigid and elastic dynamics, unwanted elastic vibrations of such flexible elements may compromise the achievement of pointing and stability requirements. Therefore, control solutions aiming at avoiding instabilities and, at worst, the failure of the mission, are currently needed. In this scenario, growing interest has been recently devoted to Active Vibration Control (AVC) strategies relying on the use of smart materials. Among them, piezoelectric patches are the most studied and tested devices for both actuating and sensing purposes. This paper aims to contribute to this line of research by investigating a different type of actuator, namely an Offset Piezoelectric Stack Actuator (OPSA), to assess its performance in damping out elastic vibrations of large space structures. Moreover, special attention is devoted to compare OPSA performance with standard patch actuators behaviour. In order to develop the AVC system, an equivalent electro-mechanical coupled Finite Element (FE) formulation is implemented, integrating both sensors and piezo-stack elements on the passive hosting structure. The final structural model including both electrical inputs/outputs, as well as modified mass and stiffness due to the additional piezo devices, is then obtained. A parametric analysis is carried out to optimize the maximum control action exerted by the OPSA device. Finally, the OPSA numerical model is experimentally validated by mounting it on a cantilever plate, representative of a scaled solar panel. Experimental data are used not only to verify the device expected functioning, but also to tune the parameters in the OPSA FE model, which can be finally integrated in a planar satellite dynamics simulator to evaluate the AVC system efficiency when performing attitude manoeuvres.

Robust Collocated Control of Large Flexible Space Structures

Agile maneuvering and precise pointing control require special attention for spacecraft equipped with large flexible appendages. A joint academia-industry research involving Sapienza University of Rome, Thales Alenia Space in France and the European Space Agency (ESA), investigates the use of innovative solutions to counteract the deterioration in pointing accuracy stemming from interactions between a rigid bus and the flexible structures during operations. Specifically, this paper aims at presenting the design of an attitude/vibration control architecture in a μ-synthesis framework. The architecture consists of an attitude control system combined with a distributed network of actuators/sensors at structural level for active vibration control purposes. A spacecraft equipped with an interferometric Ka-band SAR payload and two solar arrays is considered as a useful and challenging benchmark problem to assess the proposed methodology. The numerical simulations, carried out via both a linearized setting and a nonlinear simulator, have proved the effectiveness of the robust collocated control in comparison with a baseline PID controller.

Cooperative control of large flexible space structure by two planar robots

Cooperative control of large flexible space structure by two planar robots

Active vibration control of a hoop truss structure with piezoelectric bending actuators based on a fuzzy logic algorithm

Active vibration control of large flexible space structure is a challenging topic in the system dynamics and control of spacecraft. This paper proposes a novel approach for vibration control on a large hoop truss structure, typically used as mesh satellite antenna. First, to suppress the first-order bending modal response of the hoop truss structure with an initial disturbance, a piezoelectric bending actuator with excellent bending actuation performance was carefully designed as a key component of an active vibration control system. Then, the actuating characteristics of the actuator and the dynamic equations of the active structure were analyzed and formulated based on a finite element method. In order to improve the vibration-attenuating effect of the control system, a Mamdani-type fuzzy logic algorithm was employed in a closed-loop control system. Finally, simulations and experiments were implemented to validate the effectiveness of the proposed active control approach and structure. The experimental results showed that the decay time of first-order bending modal response (around 0.34 Hz) of control system reduces by 75% compared with that of the uncontrolled system. The results demonstrate that the proposed active vibration control system has good application potential in controlling the bending modes of a large flexible spacecraft.

Decentralized simple adaptive control for large space structures

A decentralized simple adaptive control is proposed for the vibration suppression of large space structures (LSS) with distributed actuators and sensors. The LSS is viewed as a set of connected substructures so that the dynamic substructuring method can be applied to establish the equations of motion for the LSS. Then, extraction and contraction of the subsystems are performed to form the perturbed equations of motion for each substructure. An output feedback control law only requiring the information of the local sensors is designed based on the simple adaptive control method. The stability of the overall system is rigorously proven.

Infinite-dimensional Kalman filter design for flexible curved beams based on PDE models

State observer design is a crucial step in active vibration control of large flexible space structures (LFSSs). Since the LFSSs often have lower natural frequencies, high modal density and low damping, the traditional observer design methods which use the modal truncation model are easily leading to the problem of observation spillover. Instead, the approaches directly using the partial differential equation (PDE) models of flexible structures can avoid the spillover problem, and are becoming the hotspot of research in this field. The presented research aimed at the flexible curved beams which are often used as support components in space antennas, and designed the infinite dimensional state observer for the in-plane vibration of cantilevered curved beams with weakly internal damping based on the theory of Kalman filtering. Firstly, a second order PDEs model for the in-plane vibration of the curved beam is established which considers the shear deformation and rotary inertia of the curved beam simultaneously, then by using the variable substitution method, the second order PDEs model is reduced to first order and transformed to an abstract state space model (SSM) in Hilbert space. The infinite-dimensional Kalman filter for the curved beam is designed using the SSM, and the explicit formula for the feedback gain operators of the Kalman filter are obtained based on the spectral factorization method in frequency domain. Finally, a numerical example is carried out to validate the effect of the presented infinite dimensional Kalman filter design method, and to reveal the effectiveness of the method on preventing the observation spillover.

Decentralized Robust Optimal Control of Large Flexible Space Structures by Fourth Order Local Proper Controllers Using Displacement Output

Decentralized Robust Optimal Control of Large Flexible Space Structures by Fourth Order Local Proper Controllers Using Displacement Output

A New Mechanism for the Vibration Control of Large Flexible Space Structures With Embedded Smart Devices

Large flexible space structures (LFSS), such as solar panels and synthetic aperture radar antennae, are widely employed in spacecraft. Owing to their structural peculiarities in addition with the special environment in outer space, it is easy to be aroused for the structural vibration of LFSS. This kind of vibration is very harmful to spacecraft. In this paper, we proposed a new mechanism for the vibration control of LFSS. An embedded smart device with a piezoelectric ceramic stack was built up, also. First, the nonlinear theory of structural vibration coupled with inner forces was deduced. Second, the basic principle of the new mechanism with the piezoelectric ceramic stack was expounded. Third, the smart device manufacturing and the embedded techniques were introduced. Finally, taking several solar panel structures as illustrative examples, we carried out both digital simulations and ground experiments. The research results showed us that the proposed new mechanism is quite effective to the vibration control of LFSS. This paper gives a new way to solve the vibration control problem of LFSS, especially for those with low frequencies, which is very valuable for improving the accuracy and performance of spacecraft.

変位出力を用いたプロパーな局所コントローラによる大型柔軟宇宙構造物の分散ロバスト最適制御

This paper considers position and attitude control of large flexible space structures composed of a number of subsystems(substructures) which are interconnected by flexible links modeled by springs and dampers. It is assumed that sensors and actuators are collocated in each subsystem. The purpose of the paper is to propose a decentralized control method by local proper controllers using only displacement / angular displacement output, which makes both each closed-loop subsystem and an overall closed-loop system not only robustly stable against uncertainty of characteristic parameters such as mass, damping, and stiffness, but also optimal for a quadratic cost function.

Decentralized robust optimal control of large flexible space structures by local proper controllers using displacement output

Decentralized robust optimal control of large flexible space structures by local proper controllers using displacement output

2A15 Decentralized Robust Optimal Control of Large Flexible Space Structures by Local Proper Controllers Using Displacement Output(The 12th International Conference on Motion and Vibration Control)

2A15 Decentralized Robust Optimal Control of Large Flexible Space Structures by Local Proper Controllers Using Displacement Output(The 12th International Conference on Motion and Vibration Control)

Nonlinear dynamics and control of large deployable space structures composed of trusses and meshes

The space industry in China is eager to have the advanced technology of large space structures composed of trusses cables and meshes. Such a large space structure, deployed on orbit, may serve as the large antenna for different space missions. The important scientific basis of the technology is the nonlinear dynamics modeling, analysis and control of these space structures during their deployment and service. This review article surveys the advances in relevant researches and proposes three open problems as follows. The first is the flexible multibody dynamics for the deployment of such a space structure, especially the nonlinear dynamics modeling and analysis for the contacts and wraps of mesh under microgravity, the internal impacts in clearance joints, and the coupling between structure deployment and spacecraft attitude. The second is the dynamics analysis of the space structures after deployment and during service, especially the complicated nonlinear vibrations of the flexible structure with numerous backlash joints under periodic thermal impacts. The third is the dynamic control of the space structures after deployment and during service, especially the under-actuated and lower-powered control for structure vibrations and waves.

An Improved Force Feedback Control Algorithm for Active Tendons

An active tendon, consisting of a displacement actuator and a co-located force sensor, has been adopted by many studies to suppress the vibration of large space flexible structures. The damping, provided by the force feedback control algorithm in these studies, is small and can increase, especially for tendons with low axial stiffness. This study introduces an improved force feedback algorithm, which is based on the idea of velocity feedback. The algorithm provides a large damping ratio for space flexible structures and does not require a structure model. The effectiveness of the algorithm is demonstrated on a structure similar to JPL-MPI. The results show that large damping can be achieved for the vibration control of large space structures.

Hysteresis-reduced dynamic displacement control of piezoceramic stack actuators using model predictive sliding mode control

Currently, piezoelectric actuators are being used in many applications from precision positioning control to active vibration control of large space structures. They can take the form of a solid-state device and are conveniently controlled by a voltage input. In spite of their relative ease of control, positioning accuracy and actuator longevity can be compromised by the hysteresis. Thus, the primary objective of this research is to minimize the hysteretic effect of a piezoelectric actuator in order to obtain a near linear relationship between the input voltage and the output displacement. The reduction of the hysteresis is accomplished by a newly developed control methodology named model predictive sliding mode control. A nonlinear energy-based hysteresis model is developed for a piezoelectric stack actuator and model predictive sliding mode control is applied to force the system state to reach a sliding surface in an optimal manner and track the reference signal accurately thereafter. To validate this new approach, simulations and experiments are conducted and the results highlight significantly improved hysteresis reduction in the displacement control of the piezoelectric stack actuator.

Sensor architecture for the robotic control of large flexible space structures

AbstractThe future construction and maintenance of very large space structures such as orbital solar power stations and telescopes will require teams of free‐flying space robots. For robots to effectively perform these tasks, they will require knowledge of the structure's vibrations. Here, a robotic based sensor architecture for the vibration estimation of very large structures is presented. It is shown that this information can be effectively estimated by combining data provided by free‐flying remote robot “observers” equipped with range sensors with structure‐mounted acceleration sensors. A modified Kalman filter fuses low‐bandwidth vision data from the remote sensing robots with the high bandwidth, but spatially sparse structure‐mounted acceleration sensors. Results from experimental studies are presented that confirm the effectiveness of this approach. 2007 Wiley Periodicals, Inc.

Stability of Large Space Structures Preserved Under Failures of Local Controllers

This note considers position and attitude control of large space structures composed of a number of subsystems (substructures) interconnected by flexible links. A decentralized control law of dynamic displacement feedback compatible with subsystems is applied under the assumption that sensors and actuators are collocated. It has been known that the overall closed-loop system is robustly stable against uncertainties in mass, damping, and stiffness, if rigid modes of each subsystem are controllable and observable. The objective of this note is to derive conditions for the overall system to be stable even when some local controllers fail. The conditions are expressed in terms of the stiffness (or damping) matrices and interconnection location matrices of the subsystems whose local controllers fail

Extensive Experiments on Genetic Algorithms for the Optimization of Piezoelectric Actuator Locations

For shape control of smart structures, we have developed a series of micro-genetic-algorithms for optimal placement of a large number of piezoelectric actuators. Here, we investigate the effect on the solution quality of 1) different random seed generators; 2) restart criteria in micro-genetic-algorithms, specifically the two parameters, the number of generations used for the inner loop and the level of diversity in the population; and 3) different numbers of actuators. We also report a comparison of our genetic algorithms with two heuristic integer programming algorithms: worst-out-best-in and exhaustive single point substitution proposed by Haftka and Adelman (Selection of Actuator Locations for Static Shape Control of Large Space Structures by Heuristic Integer Programming, Computers and Structures, Vol. 20, 1985, pp. 572-582). Using current genetic algorithms, we not only get better layouts of actuators than reported in our previous publications, but we also find that the most distinct nature of genetic algorithms is randomness and robustness. The best parameter setting of genetic algorithms is dependent on both the number of evaluations used for termination and the seed generator used. Moreover, the best parameter setting of genetic algorithms varies as the number of actuators changes. To get the highest quality of solutions, multiple runs using different random seed generators are necessary. The time of investigation can be significantly reduced using a coarse grain parallel computing. Comparison of our genetic algorithms with the worst-out-best-in and exhaustive single point substitution shows that for a group of runs our genetic algorithms usually converge faster in the first few thousand evaluations and are more likely to find better solutions than the worst-out-best-in and exhaustive single point substitution algorithms.