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Designing a Mechanism for Fault Diagnosis of Space Reaction Wheel by Piezoelectric Sensors and Neglecting the Rotor Inertia

Abbasi, Meisam | 2011

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  1. Type of Document: M.Sc. Thesis
  2. Language: English
  3. Document No: 42315 (58)
  4. University: Sharif University of Technology, International Campus, Kish Island
  5. Department: Science and Engineering
  6. Advisor(s): Salarieh, Hassan; Zabihollah, Abolghasem
  7. Abstract:
  8. A Reaction Wheel (RW) is a torque actuator which is used for attitude control of a satellite. Reaction Wheels usually consist of a brushless DC motor which rotates a flywheel. When the flywheel is accelerated by the motor, the reaction torque of the motor applies to the base of the RW and therefore the satellite can rotate along the RW spin axis. Due to frictionless surrounding of a satellite in space, a very small disturbance in a reaction wheel structure during its function may lead to instability of satellite and decrease the satellite precision and performance. There are some important sources of disturbance in an RW. Some of them are: 1- Unbalances in wheel (offset of center of gravity of flywheel from rotation axis), 2- Misalignment in wheel shaft (angular misalignment of principle inertia and spin axis), 3- Bearing damages and 4- Motor/Driver fault. Before assembling an RW, its quality based on disturbance analysis must be checked. When the ranges of disturbances are smaller than standard values, the RW is permitted to be utilized in a satellite. In the literature, Miller used the measurement table with several load cells to measure the disturbance of the Reaction Wheel, while the test reaction wheel rotates on the measurement table, the disturbance force and torque are determined from the combination of the deflection signals from the supporting load cells, the disturbance simulates the elasticity of the supporting load cells and induces the vibration of the table. Taniwaki, used the air-floating disturbance detector. In this detector, the RW is mounted on an air-floating slide block. Three surfaces of the sliding block (bottom and two sides) are supported by two air pads (total six air pads). As a result, the slide block is constrained and has one degree of freedom in the x direction. Translational displacement motion caused by disturbance forces in measured with a CCD laser sensor, and disturbance forces are then calculated from displacements off-line. The main objective of this thesis is to design a system to analyze the reaction wheel disturbances by using the smart materials. For simplicity, two main mechanical disturbance sources that are the flywheel unbalance (static unbalance) and the wheel shaft misalignment (dynamic unbalance) are selected to be analyzed by the system. To this end a mechanism is designed to measure the unbalancing forces and moments of RW when it normally works (without need to be disassembled). The measurement signals are processed and type of the disturbance, their value and locations are estimated
  9. Keywords:
  10. Unbalance ; Measurement ; Misalignment ; Reaction Wheel (RW) ; Static Unbalance ; Dynamic Unbalance

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