Active vibration isolation by using voice coil actuator for free space optic communication

Abstract

In Free Space Optic (FSO) communication, the alignment between transmitter and receiver telescope is very important. The line of sight (LOS) of their optics must be aligned during the entire communication session. This is crucial in long distance data transmission. One of the factors that cause misalignment is vibration, either at the transmitter or the receiver. In this thesis, active vibration isolation (AVI) system which is able to actively isolate FSO devices from low frequency vibration from the ground is designed and developed. The main goal is to suppress vibration from the top plate of the system where the telescope of FSO system is mounted. 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 prototyping in order to analyze the behavior of the system before the real prototype is developed. Controllers are designed and some simulation studies are performed in MATLAB for this AVI system. Then the real prototype is developed according to the design. An imbalance mass system is used as exciter of the system. Furthermore for cost saving factor, voice coil actuator which is modified from conventional loudspeaker is used as actuator of the system. Gain Feedback controller and LQR controller are implemented by using LabVIEW. The time domain and frequency domain analysis are done to analyze the performance of the active vibration isolation system with excitation frequency in a range of 0 Hz to 20 Hz. For system with excitation frequency 6 Hz, the reduction of displacement for gain feedback controller and LQR controller are 30.78 % and 93.56 % respectively while for the system with excitation frequency 12 Hz, the reduction of displacement is 30.86 % and 86.02 % for gain feedback controller and LQR controller respectively. The reduction of displacement of the system with excitation frequency 18 Hz for gain feedback controller and LQR controller are 61.23 % and 90.04 % respectively. According to experimental and simulation results, we can conclude that both controllers manage to suppress vibration at low frequency. LQR controller shows a better performance compared to gain feedback controller.