Design and Application of a Constraint-Tuning Modified-Mode Ultrasonic Actuator
| Autor: | Lai, Ming Hung, 賴明宏 |
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| Rok vydání: | 2012 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 100 Using a piezoelectric unimorph vibrator with constraint-tuning modified-mode (CTMM) mechanism, a novel design of a thin-disc ultrasonic actuator was developed and validated to drive a linear slider. The theoretical estimation of in-plane wave propagation on a thin disc was introduced to explain the novel actuating mechanism, via a modal expansion technique, modal participation factors and derived green functions of planer waves. Applying four screws at the exact distribution of angles on the thin-disc vibrator, the actuating mechanism of ultrasonic modified modes is generated and propagated. The in-plane vibration modes could be tuned by these desired screw constraints on the piezoelectric vibrator. To implement the equilibrium structure force in bilateral directions, natural and forced harmonic analysis as well as impedance comparison with structural damping of FEM software ANSYS are also introduced into the constrained design. Hence, computing complexities in mathmatics to solve these multiple constraints in a thin disc could be avoided. There are two kind of modified modes chosen at the different resonant frequencies within the electromechanical coupling of piezoelectric material to pursue more efficiency in energy conversion. Experimental results have demonstrated that the proposed ultrasonic actuator with an adapted single-phase, bi-frequency LC resonant driving circuit is able to directly drive the optical sled in rightward and leftward movements to help the optical actuator to retirve the data in the optical storage dick. Based upon the driving variation of voltage amplitude and the preload on the CTMM ultrasonic actuator, the nonlinear phenomena, such as the frequency shifting in electromechanical resonance and the dead zone in moving response, could be suppressed completely by the PID-based SMC controller with output biases. Using system identification technique, an approximate second-order model of the linear stage could be obtained for the equivalent control term of the PID-based SMC controller. Through an estimated model error, the design of the switching control term was used to compensate for the shifting property of resonant frequencies under electromechanical coupling. A target-command-shaping function matched the responding speed of the system during tracking experiments. The SMC controller has the capacity for noise rejection to control the slider positioning in bilateral tracking motions pushed by the CTMM actuator. Its resolution is sufficient to approach the accuracy within a micrometer level and the controllable proficiency in the long moving distance of millimeters. Therefore, the theory, design, and implementation for CTMM actuators have the excellent agreement and controllability. A CTMM actuator, with the thickness of only 3 mm, is very suitable to develop the thin and slender driving mechanism. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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