| Summary: | 博士 === 國立臺灣大學 === 機械工程學研究所 === 96 === In the micro-electro-mechanical systems (MEMS) regime, thermal actuators have been known for its advantages of high output force, low driving voltage and simple fabrication processes. This dissertation focuses on the dynamic control of the thermal actuation. For thermal actuators using heat resistor effect, the relation between input current and output heat is nonlinear, which also makes the relation between input current and output displacement nonlinear. To make the dynamic control feasible, a proper active heat sink is provided.
A theoretical model taking into account the thermoelastic coupling is first developed. The thermoelastic coupling arises from the coupling of the strain rate to the temperature field of the heat transport. The dynamic responses for a harmonically varying thermal load are simulated using the eigenmode expansion method. The thermoelastic coupling effects on the resonant frequency and the quality factor are evaluated for each eigenmode resonance of the deflection. In addition, the dynamic characteristic of thermal actuators is dominated by the first-order characteristic of the heat conduction. Influences of thermal cut-off frequency, thermal diffusivity, thermal convection, and thermal radiation on the dynamic thermal responses are then studied.
The active heat sink utilizes the commercial thermoelectric cooler. For thermal actuators operating under a DC/AC composite input current, active heat sink is designed to eliminate the effect of the nonlinear heat on the displacement. Therefore the thermal actuators can be actuated synchronously with the input current. Based on the control equations of the active heat, the scheme to control the input heat of thermal actuators is proposed.
A bimorph micro-cantilever beam was fabricated using micromachining techniques. Dynamic responses of thermal actuators were measured using laser Doppler vibrometer. For DC/AC composite input current with AC component being a single-frequency sinusoidal waveform, the measured waveform of the tip velocity is generally agreed with the simulation. The displacement amplitude is 90.4% of the simulated one. The influence of the generated double-frequency heat on the displacement can be reduced by incorporating the active heat sink. The displacement amplitude from double-frequency heat is reduced to 46.5 %. For input current with AC component composed of two sinusoidal frequencies, the displacement stemmed from the generated nonlinear heat can also be reduced with discrepancies from the simulation.
In this study, the thermo-mechanical behavior of thermal actuators was investigated theoretically and experimentally. The developed method for the dynamic control of the thermal actuators was also verified. The obtained results provide insights which enable and facilitate further optimization of the dynamic control of thermal actuators.
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