| Micro-displacement actuator(MDA), which is used as the motion and force transmission, is an important part of Microelectromechanical System(MEMS). Driven by actuators, the MDA transfer motion and force by the transmission parts such as micro- link or micro-gear. The linear MDA can accumulate and amplify the displacement of actuators. This dissertation presents a systemic research on drive mechanism, experimental testing, impact dynamic model and performance analysis. The main contributions of this dissertation are as follows.The transient temperature analysis model and the mechanical model of the actuator are developed. The simulations are implemented using the piecewise finite differential method. The displacements of the actuator under different driving conditions were calculated and measured, and the results from both modeling and experiment agree reasonably well. The special design method and micromachining process of MEMS were reviewed and several classical MDA of friction-type and meshing-type were designed. The problems and considerations which should be taken into consideration in design are discussed.A measuring system is set up for obtaining the motion characteristic of electrothermal friction linear micro actuator. The friction linear micro actuator with ∏-shape or T-shape constraints achieved the movement of push and pull under different driving conditions. The velocity of the slider can be controlled by changing the driving frequency, which increases with increasing of the driving frequency. It is shown in experiment that the function of part MDA made use of the Poly MUMPs has come true, but the performance still need to be improved.The impact dynamics model for the actuator units and the slider in a friction linear micro actuator is established, and its motion equation is also derived that takes into account friction and contact. The relative motion between the actuator head and the slider, as well as forward or backward movement of the slider were analyzed in detail, and then the influences of the actuator conditions and the structural parameters of the linear micro actuator on the movement mode of slider were also analyzed. The forward and backward movement displacement of the slider has been measured under different drive frequencies, and the experimental results are in good agreement with theoretical predictions. The theoretical results show that the motion direction of the slider can be changed by controllable driving frequency to the liner micro actuator with different structural parameters, and the stiffness and mass of the actuator units have significant influence on the movement mode of the slider. It is feasible to use a set of actuator to driving the slider to do bidirectional motion.To analyze the key failure modes of the MDA, both the design and the practical work condition of the actuator were take n into account. The failure during the design process is mainly caused by layout errors and design rule violations, while the thermal fatigue failure of the actuator under the alternating temperature loading was analyzed at the stage of application. Then some suggestions were made to improve the design, and some measures were pointed out to improve the characteristic and the reliability of the MDA.To counter the thermal fatigue failure of the electrothermal actuator caused by the alternating temperature loading due to alternating current(AC), the failure mechanisms of the thermal fatigue failure was analyzed. The relationships between temperature and frequency or amplitude of the AC were analyzed. The results showed that the structure and the applied voltage levels have significant influence on the temperature distributions and the stress of the electrothermal actuator, and the thermal fatigue failure caused by stress does not occur for the maximum stress below the yield stress of the material. Then the relationships between displacement and number of cycles of the electrothermal actuator with AC loading are tested, and it is indicated that the thermal fatigue failure won’t take place when the temperature of the electrothermal actuator below ductile-brittle transition temperature, otherwise, thermal fatigue failure will occur after long-term cyclic loading. It is confirmed that the temperature between 300 °C to 600 °C is comparatively suitable for the electrothermal actuator according to theoretical and experimental analysis, and the actuator is able to provide accurate and stable number of cycles for tens of millions. Finally, thermal fatigue failure mechanism of electrothermal actuator is analyzed. The analysis indicates that high temperature deformation is the direct reason for thermal fatigue failure. |
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