Magnetic Actuators and Suspension for Space Vibration Control

The research on microgravity vibration isolation performed at the University of Virginia is summarized. This research on microgravity vibration isolation was focused in three areas: (1) the development of new actuators for use in microgravity isolation; (2) the design of controllers for multiple-degree-of-freedom active isolation; and (3) the construction of a single-degree-of-freedom test rig with umbilicals. Described are the design and testing of a large stroke linear actuator; the conceptual design and analysis of a redundant coarse-fine six-degree-of-freedom actuator; an investigation of the control issues of active microgravity isolation; a methodology for the design of multiple-degree-of-freedom isolation control systems using modern control theory; and the design and testing of a single-degree-of-freedom test rig with umbilicals

Vibration isolation under isolator-structure interaction

This thesis analyses a general case of the vibration isolation (VI) problem, considering both a rigid and non-rigid supporting structures. The aim is to study changes on the behaviour of both systems isolators and supporting structure when the interaction phenomenon between them is considered. The influence of the VI task on the base response is evaluated. In addition, the effect of the base dynamics on the the VI and alignment problem is studied. The novel contribution to the knowledge of this thesis is formulation of a novel VI approach, which facilitates a holistic analysis of the problem considering all the systems involved on it. This approach is valid for any number of isolators and for any type of base structure. Moreover, different control objectives can be easily defined; evaluation of the interaction phenomenon on both the platform and base response for different VI techniques; demonstration of the importance of the isolator damping ratio on the influence that the VI task has on the base response; evaluation of the effects of the supporting structure dynamics on the VI and alignment problem when multiple isolators are involved; analysis of the Multiple-Input-Multiple-Ouput (MIMO) control strategy by comparison with the Single-Input-Single-Output (SISO) control strategy. This comparative has been made for the VI and alignment problem of multiple isolators on a non-rigid supporting structure and includes analysis of the effectiveness of the Coral Reefs Optimization algorithms to find nearly-optimal control gains in VI and alignment problems. Through the investigation made for this thesis, a number of significant results have been reached, which show the importance of the supporting structure dynamics on the VI and alignment task. Moreover, the interaction phenomenon, and its consequence on the base response, has been investigated experimentally. The results derived from this thesis conclude that, for most scenarios, the dynamics of the base affects the VI task. Also, the active VI (AVI) technique shows a greater influence on the base response than passive VI (PVI) technique, for most cases. It has been observed that the use of AVI technique can additionally be oriented to control vibrations of the supporting structure, while the VI task is developed. Significant differences have been found when multiple isolators are involved in the same task for the alignment and VI problem, depending on whether or not the dynamics of the base are considered. The best set of control gains for the rigid-support case (which lead to maximum damping ratio) differ from those obtained when the supporting structure is considered as a flexible system, for different cases analysed in this thesis. The MIMO control strategy has shown great improvement with respect to the use of the SISO control strategy. Also, the Coral Reefs Optimization algorithms have been demonstrated to be a suitable tool to find nearly-optimal solutions for this type of problems

Active vibration isolation using a six-axis orthogonal vibration isolation platform with piezoelectric actuators

Piezoelectric actuators (PEA) act an important role in active vibration control area due to the advantages of fast response, high output force, small size and light weight. A 6-axis orthogonal vibration isolation platform based on PEAs is designed, which satisfies the demands of heavy payload, small installation space and multi degree of freedom vibration isolation. The dynamic model of the six-axis orthogonal vibration isolation platform with PEAs is established using Newton-Euler method. With the layout of six PEAs around the axis of symmetry, the dynamic equations could be decoupled into two single-input-single-output (SISO) subsystems and two multi-input-multi-output (MIMO) subsystems. Based on the modal superposition method, the two MIMO subsystems are further decoupled. The control strategy for each SISO system is developed with LQR control method. To evaluate the effectiveness of the control method, the simulation and verification experiment are conducted. The simulation result and experimental data indicate that the decoupling control of the proposed six-axis orthogonal vibration isolation platform with piezoelectric actuators effectively reduces the vibration response of payload within the target frequency range of 20 Hz to 200 Hz

Optimization of force-limiting seismic devices connecting structural subsystems

This paper is focused on the optimum design of an original force-limiting floor anchorage system for the seismic protection of reinforced concrete (RC) dual wall-frame buildings. This protection strategy is based on the interposition of elasto-plastic links between two structural subsystems, namely the lateral force resisting system (LFRS) and the gravity load resisting system (GLRS). The most efficient configuration accounting for the optimal position and mechanical characteristics of the nonlinear devices is obtained numerically by means of a modified constrained differential evolution algorithm. A 12-storey prototype RC dual wall-frame building is considered to demonstrate the effectiveness of the seismic protection strategy

Vibration reduction for vision systems on board unmanned aerial vehicles using a neuro-fuzzy controller

In this paper, an intelligent control approach based on neuro-fuzzy systems performance is presented, with the objective of counteracting the vibrations that affect the low-cost vision platform onboard an unmanned aerial system of rotating nature. A scaled dynamical model of a helicopter is used to simulate vibrations on its fuselage. The impact of these vibrations on the low-cost vision system will be assessed and an intelligent control approach will be derived in order to reduce its detrimental influence. Different trials that consider a neuro-fuzzy approach as a fundamental part of an intelligent semi-active control strategy have been carried out. Satisfactory results have been achieved compared to those obtained by means of vibration reduction passive techniques

Control and structural optimization for maneuvering large spacecraft

Presented here are the results of an advanced control design as well as a discussion of the requirements for automating both the structures and control design efforts for maneuvering a large spacecraft. The advanced control application addresses a general three dimensional slewing problem, and is applied to a large geostationary platform. The platform consists of two flexible antennas attached to the ends of a flexible truss. The control strategy involves an open-loop rigid body control profile which is derived from a nonlinear optimal control problem and provides the main control effort. A perturbation feedback control reduces the response due to the flexibility of the structure. Results are shown which demonstrate the usefulness of the approach. Software issues are considered for developing an integrated structures and control design environment