Actuator Control Reducing Vibration in Flexible Structures
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Solution Overview
Problem
Existing methods for controlling mechanical systems with flexible structure elements and actuators face challenges in reducing vibrations, particularly due to resonance issues caused by periodic control signals, which can lead to harmful perturbing torques and instability in satellite orbital control and payload pointing applications.
Innovation Solution
A method that modifies the timing of control increments by adding random or pseudo-random temporal deviations to the initial and/or final instants of application, altering the frequency content of the control signal to attenuate energy peaks at resonant frequencies, thereby reducing vibrations and minimizing resonance risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If periodic control signals are used to control actuators in mechanical systems with flexible structure elements, then control effectiveness is maintained, but resonance issues occur causing harmful perturbing torques and increased vibrations
Solution Approach 1:
The patent applies periodic control action by distributing the total speed increment into multiple small increments applied periodically over time. Instead of continuous thrust, the control system applies discrete control pulses at periodic intervals, which maintains control effectiveness while reducing the amplitude of individual thrust impulses and their associated vibrations.
Solution Approach 2:
The patent employs preliminary action by pre-calculating and planning the sequence of control increments before execution. The control system determines in advance the timing and magnitude of each incremental control action, allowing optimization of the control schedule to avoid resonant frequencies of flexible structure elements while achieving the desired orbital correction.
2Loss of time
If continuous thrust is applied to achieve speed increment, then control duration is minimized, but perturbing torques from misalignments exceed admissible limits causing satellite to go off target
Solution Approach 1:
The patent applies segmentation by dividing the continuous thrust requirement into multiple discrete control increments. Each increment is applied separately over a distributed time schedule, transforming one long continuous control action into many short periodic pulses. This segmentation reduces the cumulative effect of perturbing torques from thrust misalignments while achieving the same total speed increment.
3Loss of energy
If sampling period is increased to minimize valve opening/closing transients, then number of transients is reduced, but control precision and ability to respond to vibrations deteriorates
Solution Approach 1:
The patent applies parameter changes by systematically varying the sampling period and the number of increments throughout the control schedule. The control system adjusts these parameters to optimize the balance between minimizing valve transients (and associated fuel consumption) and maintaining sufficient control precision. The sampling period is chosen to be sufficiently large to reduce transient frequency but small enough to maintain control authority over flexible mode vibrations.
Data Source
AI summary
The aim of the method of controlling at least one mechanical system exhibiting at least one flexible structure element and at least one actuator or group of actuators is to reduce the level of vibrations of said element while controlling the actuator or group of actuators in such a way as to achieve at least one objective assigned to the mechanical system. The control consists of increments having to be carried out at a sampling period T, each of the increments being constant in amplitude in a sampling time interval extending between two successive sampling instants and each of the increments being applied during a duration which is less than or equal to the sampling period T. In each sampling interval, at least one of the initial and final instants of application of the increment is modified by adding a variable, random or pseudo-random, temporal deviation dT.