Design and development of active vibration isolation system for free space optics communication

Free Space Optics (FSO) communication is a technology widely used today. It involves transmission of data from a transmitter to a receiver. In order to achieve successful data transmission, a continuous alignment between the transmitter and receiver telescope is needed. Misalignment could happen due to many factors. Vibration at the transmitter or the receiver is one of the factors that contribute to misalignment. In this work, active vibration isolation (AVI) system is designed and fabricated in order to improve the performance of the transmitter and receiver in an FSO link. First, a virtual prototype is designed. Then a real prototype is fabricated to implement AVI. The result after applying a controller to the AVI system shows 33.1% reduction in amplitude of displacement of the top plate, in other words reduction in amplitude of vibration

Active Vibration Isolation System (AVIS) using a voice coil actuator to improve free space optics communication

n Free Space Optic communication (FSOC), transmitter and receiver's alignment is vital to maintain the line of sight during the whole communication period. This is critical in data transmission over a long-distance. Vibration at either receiver or transmitter, causes misalignment and this affects FSOC. In this paper, AVIS, which can actively isolate FSO devices from low-frequency vibration from the ground, is designed and developed. The main goal is to reduce vibration from the top plate of the system where the telescope of the FSOC system is placed. An analytical model of the active vibration isolation is derived, and then the real prototype is fabricated. An imbalance mass system is used as an exciter for the system. Furthermore, for the cost-saving factor, a voice coil actuator which is modified from a conventional loudspeaker is used as an actuator for the system. LQR controller is implemented by using LabVIEW. The results show that the displacement level of the system with excitation frequencies 6 Hz, 12 Hz and 18 Hz are reduced more than 85 %. Moreover, it is proven that the loudspeaker not only costs lower but also gives a good performance for an AVIS

An Investigation on Structure-Vibration Isolator Interactions for Particular Performance

In engineering, particularly in certain application of vibration isolation, there is a need toachieve a special low or high supporting stiffness. There are two methods found to be effectivein providing these particular performances mainly nonlinear vibration isolation and/or activevibration isolation. To assess the efficiency of a nonlinear isolator, interaction analysis isnecessary, as for the structure control interactions, the dynamic characteristics of bothstructure and control system affect each other. There have been fewer publications thatconsider or discuss the interactions between a structure and a nonlinear vibration isolator, andbetween a structure and an active isolator. This thesis presents the study of the interactionbetween a beam and a nonlinear isolator and between a beam and an active isolator for lowand high supporting stiffness.For the beam- nonlinear isolator , the system consists of an elastic beam- like structureand a geometrically nonlinear isolation system in which a horizontal degree provides aphysical approach for realising the required horizontal force. The generalised dynamicequations of the proposed interaction system are derived, from which three reduced modelscan be obtained by introducing the related conditions into the generalised model. The modalsummation method is used to analyse the beam. The nonlinear dynamic behaviour onequilibria and stabilities of the system are investigated. The dynamic interaction mechanismbetween the nonlinear isolation system and the elastic structure is revealed. The beamnonlinear isolator design for low stiffness support and high stiffness support is discussed. Thenthe interaction between the beam and the active isolator is found, theoretical design strategiesof the active vibration isolation system are developed, and two cases are investigated; an activeisolator with low suspension frequency and an active isolator with high suspension frequency.It is found that the beam provides additional mass, stiffness and force to the nonlinearvibration isolator and to the active isolator. For the beam-nonlinear isolator and beam- activeisolator with low stiffness support, the requirement to perform ground vibration test wherebythe rigid mode of the beam must be less than one third of the first elastic natural frequency ofthe free-free beam has been satisfied. The condition to achieve high stiffness support has alsobeen satisfied. Nonlinear dynamical behaviour of the beam-nonlinear isolator indicates thatperiod doubling bifurcation occurs when the excitation force is 1 and excitation frequency is0.5Hz. Poincare maps reveals that the system form closed loops and no chaotic behaviour isobserved. Perfomance analysis in terms of force transmissibility of the nonlinear isolatorshows that the nonlinear isolator performs better than a linear isolator and also performsbetter than a hardening HSLDS mount. For the conceptual design of the beam-active isolator,the dynamic response of the system was done using Simulink Simscape blockset and is foundto be similar to the dynamic response found using Simulink alone. The investigated system inthe thesis can provide extremely low or high supporting stiffness and frequencies to satisfyspecial engineering applications for high precision vibration isolation

Investigation on the interaction analysis of beam-nonlinear isolator with low and high stiffness support

This paper presents the study of the interaction between a beam and a nonlinear isolator for low and high supporting stiffness. The system consists of an elastic beam-like structure and a geometrically nonlinear isolation system in which a horizontal degree provides a physical approach for realising the required horizontal force. The generalised dynamic equations of the system are derived and the modal summation method is used to analyse the beam. The dynamic interaction mechanism between the nonlinear isolation system and the elastic structure is revealed. The beam-nonlinear isolator design for low stiffness support and high stiffness support is discussed. It is found that the beam provides additional mass, stiffness and force to the nonlinear vibration isolator and the requirement to perform ground vibration test whereby the rigid mode of the beam must be less than one third of the first elastic natural frequency of the free-free beam has been satisfied. The condition to achieve high stiffness support has also been satisfied. Nonlinear dynamical behaviour of the beam-nonlinear isolator indicates that period doubling bifurcation occurs when the excitation force is 1 and excitation frequency is 0.5 Hz. Poincaré maps reveals that the system form closed loops and no chaotic behaviour is observed. Performance analysis in terms of force transmissibility of the nonlinear isolator shows that the nonlinear isolator performs better than a linear isolator and also performs better than a hardening HSLDS mount

An investigation on the effect of active vibration isolator on to a structure for low stiffness support

In certain vibration isolation applications, there is a need to achieve a particular low or high supporting stiffness. A method that can provide these particulars supporting stiffness is by using active vibration isolation. The isolation units have to be connected to the supported structure and the effect of the isolation unit on the structure is observed. This paper investigates the effect of a supporting system which is the active vibration isolator on to the beam frequency. It is found that a low stiffness support can be achieved using negative feedback gain and thus affects the beam frequency

Active vibration isolation system for free space optic communication: virtual prototyping using LabVIEW-SolidWorks

In Free Space Optic (FSO) communication, the alignment between transmitter and receiver telescope is very important. The line of sight of their optics must be aligned during the entire communication time; this is crutial in large distance data transmission. One of the factors that causes misalignment is vibration, either at the transmitter or the receiver. In this work, active vibration isolation (AVI) system is designed and developed to tackle this issue. An AVI system isolates FSO devices from direct disturbances or ground vibrations. The LQR controller is proposed and implimented with LabVIEW. A mathematical model of the isolator is derived and the prototype model of the AVI system is designed in SolidWorks. This prototype model is integrated with LabVIEW software to perform virtual prototypin

A generalised nonlinear isolator-elastic beam interaction analysis for extremely low or high supporting frequency

This paper presents an integrated analysis of a nonlinear isolator-elastic beam interaction system to obtain extremely low or high supporting frequency. The nonlinear suspension unit consists of two vertical inclined springs and two horizontal springs, of which the vertical ones are to generate nonlinear effect while the horizontal one to provide a physical mean for realising required horizontal forces in reported nonlinear isolation systems. The dynamic equations of the system are derived, based on which three reduced models are obtained by introducing the related conditions. The nonlinear dynamic behavour on equilibria and stablities of the system are investigated. The dynamic interaction mechanism between the nonlinear suspension system and the eleastic structures are revealed. It is investigated the two application cases: one for aircraft ground vibration tests requiring an extreme low suporting frequency and another involving structure dynamic tests in laboratory where a rigid supporting foundation is expected. High performance vibration isolators with very low or very high stiffness are widely required in engineering. For ground vibration tests (GVT) of aircrafts, the supporting frequency have to be lower than one third of its first elastic natural frequency for flutter analysis. The weight of a large aircraft is huge but its first elastic natural frequency is quite low so that the stiffness of suportor must have a big static stiffness to support the large weight and also a very low dynamic stiffness for a very low supporting frequency [1]. In laboratories, dynamic tests of structures are often expected to be fixed on a rigid foundation, for which the stiffenss of supportor must be extremelly high. Experiments show a quite “rigid” foundation for static tests could be very soft for high frequency dynamic tests. To design this type of supportors, one approach is using active feedback controls in passive systems to modify its dynamic stiffness [2-3], which requires energy supply, so that it is difficult if the required energy is huge. Another approach is useing nonlinear spring [1]. The investigations on nonlinear isolatorss were reported [4-6] and their behaviour on stabilities, birfurcations and chaos are also given [7-8]. Available publications seem not tackling nonlinear isolator-structure interactions. As for structure control interactions [9], the dynamic characteristics of both structures and control system are affected each other. To assess the efficiency of a nonlinear isolator, interactions analysis is necessary. This paper intends to discuss this proble

Design and fabrication of active vibration isolation system for free space optics communication

Free Space Optics (FSO) communication is a technology widely used today. It involves transmission of data from a transmitter to a receiver. In order to achieve successful data transmission, a continuous alignment between the transmitter and receiver telescope is needed. If not, misalignment will happen due to certain factors. Vibration at the transmitter or the receiver is one of the factors that contribute to misalignment. In this work, active vibration isolation (AVI) system is designed and fabricated in order to improve the performance of the transmitter and receiver in an FSO link. First, a virtual prototype is designed. Then a real prototype is fabricated to implement AVI. The result after applying a controller to the AVI system shows 33.1% reduction in amplitude of displacement of the top plate, in other words reduction in amplitude of vibration