Active vibration isolation of multi-degree of freedom systems

This paper concerns the improvement of High-Static-Low-Dynamic-Stiffness (HSLDS) isolation systems with active damping control. Firstly, a single-degree-of-freedom (SDOF) model is adopted in which a HSLDS isolation system is modelled by Duffing's equation. Harmonic base displacement is considered and an approximate solution to the equation of motion is determined by application of the Harmonic Balance method, to first order expansion, from which an expression for the system's motion transmissibility is derived. The analytical results show that active damping control is capable of suppressing the resonance peak of the nonlinear SDOF system, whilst maintaining its effective isolation at high frequencies. The dynamic model is validated by an experiment involving a test rig which is designed to mimic the behaviour of a Duffing oscillator. The experimental results with active damping control are in good agreement with both analytical and numerical solutions.

2008

In this paper, a switching control approach is studied with applications to active vibration isolation. The control design is based on the concept of input-to-state stability of the resulting discontinuous feedback system with respect to disturbances. The switching control strategy demonstrates improved disturbance rejection under feedback combined with a small sensitivity to noise in the absence of such feedback. Herein the control effort needed to achieve improved performance is substantially reduced. To access the performance of the closed-loop system, the control scheme is tested on a commercially available isolation system.

Jurnal Teknologi, 2015

This paper presents the dynamic analysis of a linear isolator under active stiffness control. Firstly, the literature review on the active stiffness and the concept of skyhook spring are presented. Then, based on the theoretical equation govern the isolation system model, the effect of active stiffness control in the absolute motion transmissibility performance is studied. In addition, the force response of the isolation system under active stiffness control is also examined to highlight its benefits in improving the isolation system performance.

2005

Proceedings of the American Control Conference, 2009

The closed-loop performance of motion systems that suffer from non-stationary disturbances could benefit from knowledge of these disturbances. Indeed, if the disturbance could be measured, this measurement could be used to enable a linear parameter varying (LPV) controller to adapt itself to the current operating condition, resulting in a closed-loop system with an overall increased performance. In this paper, this idea is applied to an active vibration isolation system which suffers from non-stationary disturbances.

2019

The authors acknowledge the financial support provided by the UK Engineering and Physical Sciences Research Council (EPSRC) and Spanish Ministry of Science, Innovation and Universities (Research Project SEED-SD, RTI2018-099639-B-I00).

Journal of Vibration and Control, 2011

This paper demonstrates a new idea for vibration isolation. Two different techniques of frequency reduction are presented here; the first technique depends on using an active embedded control system with proportional plus integral compensator to reduce the stiffness and corner frequency of the isolator in an active state while keeping high rigidity in a passive state. This type of isolation has proven the ability to reduce the frequency modes to about 50% of the natural frequencies in a passive state. The second technique is based on using phase lead and lag compensators on the unity gain points of the open-loop transfer function. This document will concentrate on single axis isolation although the mentioned isolator can be used as one active leg (strut) in six-axis isolators (Stewart platforms). The experimental results show as well as the simulation ones that these frequency reduction techniques have high performance on the discussed single-axis systems which makes it promising to...

MATEC Web of Conferences, 2015

In many classes of applications like active vibration control and active noise control, the disturbances can be characterized by their frequencies content and their location in a specific region in the frequency domain. The disturbances can be of narrow band type (simple or multiple) or of broad band type. A model can be associated to these disturbances. The knowledge of the disturbance model as well as of the compensator system is necessary for the design of an appropriate control system in order to attenuate (or to reject) their effect upon the system to be controlled. The attenuation of disturbances by feedback is limited by the Bode Integral and the "water bed" effect upon the output sensitivity function. In such situations, the feedback approach has to be complemented by a "feedforward disturbance compensation" requiring an additional transducer for getting information upon the disturbance. Unfortunately in most of the situations the disturbances are unknown and time-varying and therefore an adaptive approach should be considered. The generic term for adaptive attenuation of unknown and time-varying disturbances is "adaptive regulation" (known plant model, unknown and time-varying disturbance model). The paper will review a number of recent developments for adaptive feedback compensation of multiple unknown and timevarying narrow band disturbances and for adaptive feedforward compensation of broad band disturbances in the presence of the inherent internal positive feedback caused by the coupling between the compensator system and the measurement of the image of the disturbance. Some experimental results obtained on a relevant active vibration control system will illustrate the performance of the various algorithms presented. This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Finite element analysis was used to predict the power transmission from an actively isolated vibrating rigid mass to a simply supported beam. Vibrational power transmission was used as the cost function to be minimised. The work demonstrated that neglect of power transmission due to moments in experimental work is the reason why negative power transmission in the vertical direction at some frequencies has been reported in the literature. Simulations show that under active control when power transmission in the vertical direction is used as a cost function to be minimised, the overall vibration isolation performance of the active isolator can be worse than without control.

The need for isolating structures from surrounding vibrations arises frequently in many engineering applications. Examples include the isolation of manufacturing operations against seismic inputs as well as the development of suspension systems in automotive applica-tions. We present a model-free active control method for the vibration isolation of a rigid item that is elastically mounted to a slender rod which is subject to axial vibrations. A controlled linear actuator is placed between the rod and the item. It allows the displacement of the item in relation to the rod, with the goal of reducing the vibration transmissibility from rod to item. The key idea for controller development is to consider the axial vibrations as a superposition of me-chanical waves traveling in opposite directions inside the rod. The actuator is then controlled in order to reflect the waves that are traveling towards the item, thus interrupting the energy prop-agation path between rod and item. We demonst...