Travelling wave ultrasonic motor using the B08 flexural mode of a circular membrane

This paper describes the design, construction, and performance of a piezoelectric motor that uses the travelling B₀₈ mode of an 80-mm diameter circular membrane to drive a rotor by frictional contact. The motor is of a thin planar design, giving high torque of up to 0.33 Nm at low speed and has been developed as a design that can be made with lithographic techniques for miniaturization. Investigations of the free stator with a vibration pattern imager and impedance analyser gave the resonance frequency, mode, and electromechanical coupling of the stator. Motor speed as a function of frequency for a constant voltage and performance charts of speed, output power, and efficiency against torque are presented for a particular input voltage and rotor pre-load. The effects of two different lead zirconate titanate (PZT) ring dimensions have been investigated. Excitation of the B₀₉ mode has been observed, incommensurate with the piezoelectric excitation of the stator. This is discussed with relation to edge-clamping of the stator. Single standing wave motoring was observed, believed to arise from asymmetry of the stator and its perturbation of the B₀₈ resonance mode. Sources of power loss, including frame vibration and friction interface slip, are considered and discussed     

A standing wave-type noncontact linear ultrasonic motor

In this study, a novel standing wave-type noncontact linear ultrasonic motor is proposed and analyzed. This linear ultrasonic motor uses a properly controlled ultrasonic standing wave to levitate and drive a slider. A prototype of the motor was constructed by using a wedge-shaped aluminum stator, which was placed horizontally and driven by a multilayer PZT vibrator. The levitation and motion of the slider were observed. Assuming that the driving force was generated by the turbulent acoustic streaming in the boundary air layer next to the bottom surface of the slider, a theoretical model was developed. The calculated characteristics of this motor were found to agree quite well with the experimental results. Based on the experimental and theoretical results, guidelines for increasing the displacement and speed of the slider were obtained. It was found that increasing the stator vibration displacement, or decreasing the gradient of the stator vibration velocity and the weight per unit area of the slider, led to an increase of the slider displacement. It was also found that increasing the amplitude and gradient of the stator vibration velocity, or decreasing the weight per unit area of the slider and the driving frequency, gave rise to an increase of the slider speed. There exists an optimum roughness of the bottom surface of the slider at which the slider speed has a maximum     

A piezoelectric motor using flexural vibration of a thin piezoelectric membrane

This paper describes a new implementation of a disk-type piezoelectric motor, whose stator is a commercial available piezomembrane composed of a nickel alloy disk to which a piezoceramic disk is bonded. The two disks are concentric, and the total thickness is very small. Ultrasonic motors are based on the concept of driving a rotor by mechanical vibration excited on a stator, via the piezoelectric effect. The rotor is in contact with the stator, and the driving force is the frictional force between rotor and stator. To transform the mechanical vibration of the stator in the rotor rotation, a traveling wave must be excited on the stator surface. The proposed motor can be regarded as a disk-type, single wavelength motor in which the traveling wave is due to the natural flexural vibration of the piezomembrane at low frequency. The behavior of the stator is analyzed both theoretically, by using the theory of isotropic and homogeneous vibrating plates, and by means of a commercial finite element computer code, finding a good agreement with the experimental results. The main features of the motor are very small thickness, appreciable torque, and high speed, obtained with low input power at low voltage; the intended application is to substitute the moving-coil in analogic instrumentation.     

Numerical analysis of the symmetric hybrid transducer ultrasonicmotor

In this paper, operation of a symmetric hybrid transducer ultrasonic motor with output produced by two rotors connected together via a drive shaft is numerically analyzed and compared with the traditional asymmetric hybrid transducer motor design that produces its output from only one rotor. A one-dimensional finite element model for torsional vibration in the stator and a Coulomb friction model for rotor/stator contact associated with the longitudinal vibration of the motor are introduced. The calculation results demonstrate that the symmetric design is capable of performance comparable with the traditional asymmetric design when an optimum static spring force in the rotor/stator contact interface is applied during operation     

Flextensional ultrasonic motor using the contour mode of a square piezoelectric plate

This paper presents the design, fabrication, and characterization of a new type of standing wave piezoelectric ultrasonic motor. The motor uses a metallic flextensional amplifier, or cymbal, to convert the contour mode vibrations of a square piezoelectric ceramic plate into flexural oscillations, which are further converted to produce rotary actuation by means of an elastic-fin friction drive. The motor operates on a single-phase electrical supply. A beryllium copper rotor design with three-fin configuration was adopted, and the geometry was varied to include different material thicknesses, fin lengths, and inclinations. The best stall torque and no load speed for a 25-mm square motor were 0.72 Nmm and 895 r/minute, respectively. The behavior of the stator structure was analyzed by ANSYS finite element software using harmonic and modal analyses. The vibration mode estimated by finite element modeling (FEM) was confirmed by laser Doppler vibration measurements.     

An ultrasonic piezoelectric motor utilizing axial-torsional coupling in a pretwisted non-circular cross-sectioned prismatic beam

A rotary piezoelectric motor design with simple structural components and the potential for miniaturization using a pretwisted beam stator is demonstrated in this paper. The beam acts as a vibration converter to transform axial vibration input from a piezoelectric element into combined axial-torsional vibration. The axial vibration of the stator modulates the torsional friction forces transmitted to the rotor. Prototype stators measuring 6.5 x 6.5 x 67.5 mm were constructed using aluminum (2024-T6) twisted beams with rectangular cross-section and multilayer piezoelectric actuators. The stall torque and noload speed attained for a rectangular beam with an aspect ratio of 1.44 and pretwist helix angle of 17.7 degrees C were 0.17 mNm and 840 rpm with inputs of 184.4 kHz and 149 mW, respectively. Operation in both clockwise and counterclockwise directions was obtained by choosing either 70.37 or 184.4 kHz for the operating frequency. The effects of rotor preload and power input on motor performance were investigated experimentally. The results suggest that motor efficiency is higher at low power input, and that efficiency increases with preload to a maximum beyond which it begins to drop.     

An ultrasonic motor driven by the phase-velocity difference between two traveling waves

This paper presents a new ultrasonic motor in which the rotor rotation speed is locked by the phase-velocity difference between the two traveling waves propagating on the stator and the rotor. First, the unique construction to excite two traveling waves both in the stator and the rotor is described. Then, the operation principle of the present motor is revealed by our careful experiments. Dynamics of the two traveling waves are measured by an in-plane laser Doppler vibrometer under various conditions, as well as the motor performances. Our experiments show that the rotation speed of the motor is equal to the phase-velocity difference between the two traveling waves on the contact surfaces of rotor and stator. It is confirmed that the rotor rotates so as to cancel the phase-velocity difference between the traveling vibrations along the circumferences of the rotor and stator. If the load does not exceed the maximum torque that is determined by the vibration amplitude, the rotation speed is subject only to the phase-velocity difference.     

Force transfer model and characteristics of hybrid transducer type ultrasonic motors

The characteristics of longitudinal-torsional hybrid transducer-type ultrasonic motors (HTUSM) are low speed and high torque. The discontinuous-surface-contact mode between the stator and the rotor is different from the many-point-contact mode of traveling wave motors, which is also an essential cause for high torque. Therefore, it is important to analyze its force transfer model between the rotor and the stator. In this paper, issues of using the method of equivalent circuit model are addressed. The relationships between the contact angle, preload, and physical parameters of frictional materials are given, according to the impulse conservation law axially. The equations describing output torque, amplitudes of longitudinal and torsional vibration, and parameters of the rotor are derived according to the principle that the work done by the load is equal to that by the driving force in one vibrating cycle. All factors that influence the mechanical characteristics are analyzed, and accuracy and suitability of the force transfer model are verified by comparison with the prototype motor. The formula for transfer efficiency on the stator/rotor interface is given, and the low-efficiency of this type motor is explained. The wide-working frequency range property of this type motor is shown with experimental results. Based on this study, the parameters of the rotor and preload are determined. The maximum torque of the prototype motor is up to 13.2 nm, and no-load speed of this type of motor is 12.5 rpm.     

Rotor Design and Finite Element Analysis of Traveling Wave Rotaty Ultrasonic Motor

The dynamic transfer mechanism of the traveling wave rotary ultrasonic motor rotor-stator' s contact surface is studied in the paper and the key parts stator and cone flexible rotor of ultrasonic motor are designed.The three-dimensional contact model and finite element model considering the radial sliding between the rotor and the stator are established. The relation between the stator surface particle that amplitude frequency characteristics,resonance speed,radial displacement of ultrasonic motor and the tooth height are analyzed. Mass point radial relative displacement of contact surface between the cone flexible rotor,flexible rotor and the stator are contrasted. The cone flexible rotor is better placed on the surface of the stator tooth through its elastic deformation is interpreted. The cone flexible rotor reduces the radial slip between the stator and the output efficiency of ultrasonic motor is improved. The displacement trajectory of the stator surface is synthesized in a row wave cycle. The method of the stator mass point elliptical motion drives the rotor rotation is verified.     

Improvement of the longitudinal vibration system for the hybrid transducer ultrasonic motor

This paper presents a symmetric hybrid transducer ultrasonic motor designed to produce large longitudinal vibration stress in the rotor/stator contact interface for high-torque operation. The nodal plane of the longitudinal vibration mode was adjusted to match the rotor/stator contact interface, and the piezoelectric ceramic disks for the longitudinal vibration were installed at the nodal plane of the longitudinal vibration mode for effective excitation. An experimental motor, 20 mm in diameter, using the first torsional vibration mode and the second longitudinal vibration mode was manufactured. A maximum torque of 0.8 N.m was achieved in the prototype, an improvement over previous versions.     

高速定转子均质机转子叶片振动模态分析

采用对接加载模态综合分析法,将定转子均质机关键元件转子系统结构简化为叶-盘系统,对单个转子叶片进行有限单元划分,分析得出了转子转速为4 500 R／MIN时振动频率响应分布趋势;前10阶扩展模态分布具有一定的规律性,在初始4阶模态状态时频率波动小,且与系统固有频率近似;从第5阶模态以后分布波动较大, 且波动幅度很接近,约为20HZ。分析结果有利于定转子均质机关键元件转子系统结构的优化设计。     

Y形旋转超声波马达的设计与动态特性分析

为了探索和丰富旋转超声波马达的结构,使其满足响应精准且速度快以及控制简便的要求,设计了Y形旋转超声波马达,并对其结构及动态特性进行了分析。Y形旋转超声波马达将3组压电陶瓷片的横向振动复合成驱动足端面对转子的微幅驱动,通过摩擦耦合在惯性作用下推动转子顺时针或逆时针旋转。运用Workbench软件中的Design Exporation组件对Y形旋转超声波马达定子组件的结构尺寸进行了优化设计,提升了定子组件的性能。构建优化后Y形旋转超声波马达定子组件的有限元仿真模型,并通过模态分析获得了定子组件工作所需的固有振型,通过谐响应分析获得了定子组件的幅频特性曲线,通过瞬态分析获得了1个激励周期内定子组件的振动模态,验证了Y形旋转超声波马达的驱动机理。结果表明,Y形旋转超声波马达压电陶瓷片表面施加电压的最佳频率为20 739 Hz,对应的驱动足端面的振幅为6.95 μm。Y形旋转超声波马达结构简单且具有对称性,能效利用率高,对拓宽超声波马达的应用领域有重要参考价值。     

新型箝位式压电电机的设计研究

针对传统箝位式压电电机在谐振态下工作时,方波振动的箝位部分结构设计复杂问题,提出一种新型箝位式压电电机。该电机箝位部分与驱动部分均由同频正弦电压驱动实现正弦振动,通过定子对动子的箝位接触,实现动子单向输出运动。相较于传统箝位式压电电机和超声电机,该电机的定子结构设计无需采用模态简并,结构设计难度降低。利用有限元仿真确定定、动子结构参数,制造样机并搭建实验平台。对箝位部分分别采用正弦波与方波做激励,再对驱动部分进行波形对比,表明正弦波亦能达到预期效果。实验结果表明:准静态时,激励电压频率为250Hz、电压峰峰值Vp-p为10V时,步进距离为0.5μm,步进速度0.13mm/s;谐振态时,激励电压频率为540Hz、电压峰峰值Vp-p为70V时,步进距离为32μm,步进速度16.9mm/s;该电机可兼顾低频高分辨率和高频高速输出以实现跨尺度工作。     

Analysis of a disk-type piezoelectric ultrasonic motor using impedance matrices

The dynamic behavior and the performance characteristics of the disk-type traveling wave piezoelectric ultrasonic motors (USM) are analyzed using impedance matrices. The stator is divided into three coupled subsystems: an inner metal disk, a piezoelectric annular actuator with segmented electrodes, and an outer metal disk with teeth. The effects of both shear deformation and rotary inertia are taken into account in deriving an impedance matrix for the piezoelectric actuator. The impedance matrices for each subsystem then are combined into a global impedance matrix using continuity conditions at the interfaces. A comparison is made between the impedance matrix model and the three-dimensional finite element model of the piezoelectric stator, obtaining the resonance and antiresonance frequencies and the effective electromechanical coupling factors versus circumferential mode numbers. Using the calculated resonance frequency and the vibration modes for the stator and a brush model with the Coulomb friction for the stator and rotor contact, stall torque, and no-load speed versus excitation frequencies are calculated at different preloads. Performance characteristics such as speed-torque curve and the output efficiency of the USM also are estimated using the current impedance matrix and the contact model. The present impedance model can be shown to be very effective in the design of the USM.     

Piezoelectric micromotor using a metal-ceramic composite structure

This paper presents a new piezoelectric micromotor design, in which a uniformly electroded piezoelectric ring bonded to a metal ring is used as the stator. Four inward arms at the inner circumference of the metal ring transfer radial displacements into tangential displacements. The rotor ends in a truncated cone shape and touches the tips of the arms. A rotation takes place by exciting coupled modes of the stator element, such as a radial mode and a second bending mode of the arms. The behavior of the free stator was analyzed using the ATILA finite element software. Torque vs. speed relationship was measured from the transient speed change with a motor load. A starting torque of 17 muNm was obtained at 20 Vrms. The main features of this motor are low cost and easy assembly because of a simple structure and small number of components.     

不平衡磁拉力及对偏心转子系统振动的影响

研究了电机中由于相对偏心引起的不平衡磁拉力对转子系统振动的影响。首先把气隙磁导展开为Fourier级数的形式,通过转子或定子表面的Maxwell应力积分得到非线性不平衡磁拉力的解析表达式。然后代入到转子系统的运动方程中,采用隐式非线性NEWMARK积分法计算系统在不平衡磁拉力和质量偏心力作用下的动力响应,详细分析了电机参数对偏心转子系统振动的影响。研究结果为旋转机械轴系的动力分析及设计提供了理论依据。     

定子永磁型高速电机凸极转子强度分析

定子永磁型电机具有转子上既无永磁体也无绕组、功率密度高、效率高等优点,因此非常适合在高速下工作。然而由于凸极转子复杂的几何形状,对其强度进行分析只能采用有限元法等数值方法。基于弹性力学理论,建立了凸极转子强度的解析分析模型。分析了凸极转子的载荷分布,在此基础上,基于平面应力模型和应力函数法,推导了定子永磁型电机凸极转子的应力及变形的解析解;用有限元法对解析解的有效性进行了验证;分析了凸极转子的凸极高度及形状对转子强度的影响。结果表明,建立的凸极转子强度解析解在转子应力最大区域内的计算结果与有限元法的计算结果完全吻合,能够对定子永磁型高速电机凸极转子的最大应力进行精确分析,可为定子永磁型高速电机的转子设计提供支持。     

圆盘型非接触超声波马达定子的振动模拟与测试

介绍一种圆盘型非接触超声波马达的结构。利用有限元法计算了超声波马达定子在不同振动模态下的固有频率,并用激光测振仪对定子进行了测试,结果两者吻合较好。由于振幅和非接触马达的声辐射压力密切相关,因此通过谐响应分析计算了定子的振幅与定子驱动电压的关系,从而为马达的实验研究提供了理论依据。在最优模态B21下进行转子转速测试,测得最高转速为1600rpm。     

面内模态方形压电超声电机的工作机理与实验

针对利用面内模态的方形压电超声电机工作机理进行研究,利用有限元方法得出了方形超声电机定子的振动模态振型,以此为基础,分析了电机定子内圈小齿在平面内模态(3,1)和(R,1)下的位移特点,给出了一个周期内电机定子内圈6个小齿切向运动与法向运动的分析结果,得出了在定子平面内模态(3,1)和(R,1)下,定子内圈6个小齿能够推动转子转动的结论.制作了电机样机并完成了电机运转试验,得出了相应的电机特性曲线,对上述分析进行了验证.根据上述分析结果,可以进一步研制一种方形驻波超声电机.     

Effect of the hydrodynamic bearing on rotor/stator contact in a ring-type ultrasonic motor

A hybrid numerical analysis that includes the hydrodynamic bearing effect and elastic contact in a ring-type ultrasonic motor is presented. The two-dimensional time-dependent compressible Reynolds equation is solved numerically by a second-order time accurate, noniterative, factored implicit finite-difference algorithm. The rotor deformation is described by a one-dimensional Green's function. The contact problem is solved by an iteration method so that the contact condition and the hydrodynamic bearing condition are satisfied simultaneously. The results show that the hydrodynamic bearing effect, especially the squeeze effect, is significant for ultrasonic frequency contact of the rotor and stator. Surface roughness, contact area, and normal vibrating speed of the stator are important parameters in the hydrodynamic bearing. A disagreement between the friction coefficient needed in the numerical analysis and the experimentally measured one in a previous study.