A modeling technique for active control design studies with application to spacecraft microvibrations

Abstract

Microvibrations, at frequencies between 1 and 1000 Hz, generated by on board equipment, can propagate throughout a spacecraft structure and affect the performance of sensitive payloads. To investigate strategies to reduce these dynamic disturbances by means of active control systems, realistic yet simple structural models are necessary to represent the dynamics of the electromechanical system. In this paper a modeling technique which meets this requirement is presented, and the resulting mathematical model is used to develop some initial results on active control strategies. Attention is focused on a mass loaded panel subjected to point excitation sources, the objective being to minimize the displacement at an arbitrary output location. Piezoelectric patches acting as sensors and actuators are employed. The equations of motion are derived by using Lagrange's equation with vibration mode shapes as the Ritz functions. The number of sensors/actuators and their location is variable. The set of equations obtained is then transformed into state variables and some initial controller design studies are undertaken. These are based on standard linear systems optimal control theory where the resulting controller is implemented by a state observer. It is demonstrated that the proposed modeling technique is a feasible realistic basis for in-depth controller design/evaluation studies.

Dynamic Mass of a Reaction Wheel Including Gyroscopic Effects: An Experimental Approach

“…Due to the dynamic mass imaginary complex nature (intended as composed by a real and an imaginary number) and therefore, the importance of the phase between the signals, a synchronisation procedure was required before their direct implementation in Eq. (20).…”

“…The latter required to be re-elaborated using Eq. (20), where the term a f is represents the PSD of the background noise in the free-free boundary condition and the term D w represents the RWA dynamic mass from FE model. The outcomes are shown in Fig.…”

“…(20). If the spectral contribution of the noise obtained in the two dierent congurations is signicantly dierent (hence the RWA excitation vectors are dierent) then the iterative process to calculate the dynamic mass of the RWA using Eq.…”

Modelling the effect of electrical harness on microvibration response of structures

“…The research has focused on many aspects related to microvibrations, starting with the sources [7,8], and throughout the years various methodologies have been proposed for their modelling and control [9][10][11][12], e.g., simulating the interface between sources and spacecraft structures and predicting payload pointing errors [13,14]. Among the difficulties related to microvibrations, one of the main ones is their analysis, having to deal with extremely low amplitudes (µg) and a bandwidth that goes up to several hundred Hz.…”

A stochastic methodology for predictions of the environment created by multiple microvibration sources

“…With the term microvibrations we generally refer to accelerations in the region of micro g, and generally these low level mechanical disturbances occur over a wide frequency range, from "zero" up to say 500-1000 Hz. In addition to the issue of their control and minimisation [10,11,12], because of the large bandwidth of the frequency range, the modelling and analysis of microvibrations pose a challenge. This is a particular issue in the mid-frequency range as many of the micro-vibration sources on board a spacecraft (e.g.…”