Mr. Dae Oen Lee Profile

Dae Oen Lee

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Proceedings Article | 9 March 2014 Paper

Development of vibration isolation platform for low amplitude vibration

Dae-Oen Lee, Geeyong Park, Jae-Hung Han

Proceedings Volume 9057, 905708 (2014) https://doi.org/10.1117/12.2044984

KEYWORDS: Vibration isolation, Optical isolators, Satellites, Prototyping, Cryocoolers, Performance modeling, Sensors, Satellite imaging, Silicon, Image resolution

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The performance of high precision payloads on board a satellite is extremely sensitive to vibration. Although vibration environment of a satellite on orbit is very gentle compared to the launch environment, even a low amplitude vibration disturbances generated by reaction wheel assembly, cryocoolers, etc may cause serious problems in performing tasks such as capturing high resolution images. The most commonly taken approach to protect sensitive payloads from performance degrading vibration is application of vibration isolator. In this paper, development of vibration isolation platform for low amplitude vibration is discussed. Firstly, single axis vibration isolator is developed by adapting three parameter model using bellows and viscous fluid. The isolation performance of the developed single axis isolator is evaluated by measuring force transmissibility. The measured transmissibility shows that both the low Q-factor (about 2) and the high roll-off rate (about -40 dB/dec) are achieved with the developed isolator. Then, six single axis isolators are combined to form Stewart platform in cubic configuration to provide multi-axis vibration isolation. The isolation performance of the developed multi-axis isolator is evaluated using a simple prototype reaction wheel model in which wheel imbalance is the major source of vibration. The transmitted force without vibration isolator is measured and compared with the transmitted force with vibration isolator. More than 20 dB reduction of the X and Y direction (radial direction of flywheel) disturbance is observed for rotating wheel speed of 100 Hz and higher.

Proceedings Article | 28 March 2012 Paper

Integrated framework for jitter analysis combining disturbance, structure, vibration isolator and optical model

Dae-Oen Lee, Jae-San Yoon, Jae-Hung Han

Proceedings Volume 8341, 834126 (2012) https://doi.org/10.1117/12.915428

KEYWORDS: Vibration isolation, Modulation transfer functions, Optical isolators, Actuators, Integrated optics, Performance modeling, Satellites, Diffraction, Systems modeling, Image filtering

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Micro-vibration induced by actuating components of the satellite can severely degrade the optical performance of high precision observation satellites. In this paper, an integrated analysis framework combining disturbance, structure, vibration isolator and optical system model is developed for evaluating the performance of optical payloads in the presence of micro-vibration, and the effectiveness of using a vibration isolator for performance enhancement. Reaction wheel generated disturbance, usually the largest anticipated disturbance, is modeled including the disturbances' interaction with the structural modes of the wheel. For structure modeling, a finite element program is used to solve for eigenvalues and eigenvectors of a structure model which are then used to create a state space model in modal form. A vibration isolator model capturing dynamics of an active isolator utilizing piezoelectric based actuator and load cell for feedback control is included to reduce the transmission of reaction wheel disturbances to the base structure. Dynamic response of the structure to reaction wheel disturbances is calculated with and without vibration isolator. The resulting jitter is used to obtain modulation transfer function (MTF) of diffraction limited optical system model, and the obtained MTF is used as spatial frequency filter for image simulation.

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