| Multi-degree of freedom (MDOF) ultrasonic motor (USM) has the advantages of simple structure, easy assembly, and high mechanical integration. It is also convenient to drive and able to achieve the diversification of movement. Like all the other types of USM, MDOF USM can provide high resolution motion and avoid electromagnetic interference. Now it is widely used in the industry, such as joint of the robot, precision assembly, micro robot, medical apparatus and instruments, which makes it a hot topic in the field of USM research. Among all the MDOF USMs, the rotary-linear USM has high research value and broad application prospects, as its motion is a common form in real life. This type of USM can realize rotary and linear motion, respectively, while some can realize both. In this research, a new rotary-linear bar type USM based on one single stator was developed. Its working principle, mathematical model, finite element simulation, performance testing and structural optimization were reported. The main achievements are as follows.(1) A new rotary-linear2-DOF motor structure based on one single stator was introduced. By taking advantage of the slanted ceramics, two mode of stator motion can be derived. Those microscopic motion of stator can be converted into the macroscopic motion of rotor. The motor has a compact structure and needs only one single power source, which make it well qualified in miniaturized applications. The prototype motor had only25mm length and2.5mm diameter.(2) A driving methodology applied to the new motor was proposed. As the traditional USM driving method can not be applied due to its special structure, an asymmetric square-wave type voltage is used to drive the motor. The movement of the rotor can be derived by means of smooth impact drive method (SIDM) near the resonance frequency. By controlling the driving frequency, the mode of the rotor movement can be switched. Besides, the direction and speed of the rotor movement can be adjusted by changing the duty cycle and amplitude of the input voltage, respectively.(3) A modeling method based on complex losses was developed. An equivalent model on the modal analysis was build up to calculate the nature frequencies of the stator. Further, the piezoelectric loss factor and metal loss factor were used to deduce the harmonic amplitude of the stator end. So a mathematical model, which can calculate the maximum linear displacement and rotary angle approximately, was derived. A good match was found by comparing the results from the finite element model and mathematical model, which validated the correctness of the mathematical model.(4) An optimization method applied to the new motor was introduced. The proposed mothed aimed at optimizing the output character of the2-DOF stator, by adjusting the structural parameters. The concept of relative sensitivity coefficient was utilized in the comprehensive comparison. Several groups of the motor parameters were chosen. And according to those chosen parameters, the prototype motors were made. It was found that, the performance of the optimized motor has been improved significantly.This study proposed a new rotary-linear USM, which extended the application field of MDOF motors. The modeling and optimization method will play an active role in the characteristic analysis, structure design and optimization of ultrasonic motors. |
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