Browsing by Author "Suhonen, Mika"

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Modeling and Parameter and State Estimation of a Micro-Electro-Mechanical Fine-Pointing Actuator
(2010) Suhonen, Mika
School of Science | Master's thesis
The design and the manufacturing process of a two-axial micro-electro-mechanical fine-pointing actuator is outlined. The actuator is based on electrostatic actuation and capacitive detection. It is intended to be used in intersatellite optical links. A mathematical model for the actuator system is developed. The electro-mechanical model consists of a 3- degree-of-freedom model rigid-body model and nonlinear models for the electrostatic actuation and the capacitive measurement of the position and attitude of the moving part. Experiments are designed for obtaining data from which the various model parameters can be estimated. Probability models and estimators are developed for the actuator model parameters. The work discusses mainly maximum likelihood and least-squares methods. State estimation of the system is discussed. The model of the system is an ordinary differential equation system together with sampled measurements and zero-order hold actuation. Monte Carlo computer simulations are performed on the system with pseudo-random noise. The state of the system is estimated from the simulated measurement results with the Extended Kalman Filter, the Unscented Kalman Filter and a simple moving average filter. The accuracy of the estimates is determined by comparing them to the simulated state. The feedback controller and the digital signal processing hardware used in experiments are outlined. The controller employs feedback linearization and three independent PID controllers. Measurements are performed to estimate actuator parameters. The speed of the utilized digital signal processing hardware allowed only the simple moving average filter to be used in real-time experiments. Experiments where the actuator was in vacuum were conducted and the state of the actuator was estimated with the simple filter. An electrostatic actuator with constant-voltage boundary conditions has an unstable region where the plates of the actuator capacitor collapse together. Mechanical damping of the actuator in vacuum is very low. Stable operation of the actuator was achieved well within the open-loop unstable region with the rather slow control system which gives support to the accuracy of the model and the estimates.