1mm管式悬臂梁结构微型超声马达研究

Cantilevered Ultrasonic Micro-motors Using Piezoelectric Tubes with 1 mm Diameter

利用外径1.0mm,内径0.6mm的压电PZT陶瓷管,研制了相同结构的三种不同长度悬臂梁的管式微超声马达.为改善定子与转子之间的摩擦性能,在定子的自由端粘结金属帽形成复合定子.马达定子外壁均匀分为4个电极,内壁接地;为消除引线对定子振动的影响,电极通过固定座直接连接到驱动电路.通过不同质量的负载,调节定子和转子之间的预紧力.考虑定子管长和金属帽的影响,采用有限元方法分析定子共振频率和有效机电耦合系数随陶瓷管长度和金属帽质量的变化.结果表明,随着管长或金属帽质量的增加,定子共振频率和有效机电耦合系数下降.根据理论计算和实验测量,表明所研制的微型超声马达第一阶弯曲共振频率的理论分析值与实验测量值吻合.实验测量还表明,马达在定子共振频率附近具有最大转速;并且在相同预紧力下,马达转速随电压近似线性增加,当电压加至120V时,转速可达每秒85转;加大预紧力,马达输出力矩提高,当预紧力加至70mN时,输出力矩可达4.7μNm.

Compared with traditional electromagnetic motors, ultrasonic motors have many advantages, such as simple structures, quick response, no electromagnetic interference and so on. Tube-type ultrasonic micro-motors can operate in very small spaces, such as medical catheters, micro-robot and micro-craft drivers in the future because of their thin structures. Several tube-type ultrasonic micro-motors have been reported during the past decades. However, there are still some problems to solved, such as simplifying the structures and fixing the ceramic tube stators. Especially, little research has been done about the influence of pre-stress on the ultrasonic motors. In this paper, tube-type cantilevered ultrasonic micro-motors are presented. One end of the ceramic tube stator of the motor is fixed on a circuit board directly where no down-leads are used, and the other end is covered by a metalcap, which is used to imprave the friction between the stator and rotor and enhance the rotation speed and output torque of the motor. The external wall of the ceramic tube is divided into four electrodes for the input voltage signals to generate two vertical bending vibrations, and the internal wall of the ceramic tube is grounded. Then the driving mechanism of this kind of motors is also analyzed. The resonance frequency and effective electro-mechanical coupling factor of the composite stators are analyzed by a FEM method, in which the stator is composed of a ceramic tube and a metal-cap. The results show that the resonance frequency and effective electro-mechanical coupling factor decrease with the in crease of the tube length and the mass of the metal cap, and a moderate tube length and small metal-cap are very suitable. Three motors using PZT piezoelectric ceramic tube with the diameter of lmm and different lengths of 3.0 mm, 4.0 mm and 4.8 mm are manufactured. The resonance frequencies of these motors are measured by an impedance analyzer, which are in good agreement with the results of the FEM simulation. The rotation speeds of the micro-motors under different conditions are also measured by a laser vibrometer, which shows that rotation speeds of the motors increase with the applied voltage almost linearly, but decrease with the pre-stress increase. The motors have the maximum rotation speeds more than 60 r/s at their resonance frequencies as the pre-stress is suitable. Meanwhile, the pre-stress has little influence on the relations between the rotation speeds and the voltage variations. The average starting torques of the motors under different pre-stresses are also estimated by an ＂angular acceleration＂ method, which shows that the motors have large and stable output torques more than 3 - 4 μNm under a suitable pre-stress. At last, a possible explanation for the variation of the average starting torques of different motors with the pre-stresses is presented.