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.     

An ultrasonic motor using bending vibrations of a short cylinder

An ultrasonic motor using bending vibrations of a short cylinder with free-free ends is proposed, and its performance and efficiency are discussed. The motor is small in size and realizes a high mechanical output of more than 1 W. The general principle of the motor, which uses traveling waves, is as follows. When a traveling wave propagates along an elastic object, particles at the surface move elliptically. A movable object (a slider or a rotor) pressed to the elastic object may be caused to move due to the frictional forces between it and the surface. A motor based on this principal has been constructed and studied. The vibration mode used is found to have an undesirable radial component, which restricts the efficiency of the motor to about 10% at best. A large amount of the energy supplied is lost by the slippage owing to the existence of the undesirable component. It is concluded that to derive larger output power, the frictional material needs to be carefully chosen.     

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。     

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.     

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.     

杆式行波超声电机运动机理的研究

本介绍了作发展的一种杆式行波超声电机的结构。基于振动和波动理论，深人研究了杆式行波超声电机的运行机理，推导了定子端面上任意质点运动轨迹，证明了在一定的激励条件下，定子端面沿Z向、径向和周向都可形成行波。描述了定子端面某些点的运动轨迹的空间分布。还提出了定、转子问最佳接触角和有效椭圆的概念。这些都为设计高效率的杆式超声电机提供了理论依据。     

Design of a traveling wave type ultrasonic motor

The purpose of the present paper is to establish a method of design for a traveling wave type ultrasonic motor. This method is based on two models for the ultrasonic motor. A two-dimensional elastic contact model is used for estimating the friction drive between the rotor and vibrator of the motor. Moreover, an electrical equivalent circuit is used to estimate the interaction between the electrical and mechanical parts of the vibrator. The proposed method is applied to the design of a prototype motor. To determine applicability of the method, the load characteristics of the prototype motor are measured. The measured characteristics agree with the required ones which are specified in advance. As a result, the validity of the proposed method is experimentally confirmed     

Piezoelectric stepper motor with direct coupling mechanism to achieve high efficiency and precise control of motion

The paper describes a piezoelectric motor that combines the merits of piezoelectric materials, such as high power density generated at electromechanical resonance, and a precise control of displacement. In the motor, a standing shear wave is excited at the resonance in the piezoelectric tube, and it produces high-frequency torsional vibrations of the stator. The vibrations are converted into unidirectional rotation of a rotor by using a direct coupling mechanism between the stator and the rotor in which a clutch drives the rotor via locking it. The direct coupling makes it possible to transmit the whole power generated in the piezoelectric tube to the rotor, and thus achieve the high efficiency of the motor. It also allows combining two regimes of operation: continuous rotation and a stepwise motion within a 360 degrees interval with a high resolution of angular displacement.     

Coupled tangential-axial resonant modes of piezoelectric hollow cylinders and their application in ultrasonic motors

This paper describes a tangential-axial eigen-mode of a piezoelectric hollow cylinder. A new type of piezoelectric ultrasonic motor using this oscillation mode has been developed. The motor is a traveling-wave-type motor. The stator of such a motor consists of a solid piezoelectric hollow cylinder, which, excited in the tangential-axial resonant mode by a three-phase electrical signal, will exhibit elliptical displacement and transfer rotation to the rotor. The behavior of the stator has been simulated with finite element method (FEM) software. The simulation results have been checked with single-point contact measurements on the surface of the ultrasonic motors. The paper closes with the introduction of new ultrasonic motors based on this oscillation mode.     

Sensorless Monitoring of a Motor-Drive Machanical System Based on Adaptive Signal Decomposition

1IntroductionSensorless techniques have been successfully applied to motor speed measurement, noise and vibra-tion identification, and machinery fault diagnosis. Although a variety of relevant techniques such asvibration analysis are nowavailable for the monitoring and diagnosis of a mechanical system, studiesof the sensorless techniques have been followed with great interest by many researchers. In the tech-nique, since the motor is regarded not only as a drive motor to provide mechanical ene…     

An estimation of load characteristics of an ultrasonic motor by measuring transient responses

To measure the characteristics of ultrasonic motors, such as the maximum torque, torque-speed relationship and the frictional coefficient at the contact surface, a method in which the torque is calculated from the transient responses is proposed. The rise curve that is the transitional change in the rotor speed soon after turning on the motor gives the load characteristics, while the fall curve that is the decay of the rotor speed after turning off the motor yields the frictional coefficient of the contact surface. This method requires only a short time (the transient time of the motor) to complete the measurement. The relations between the transient responses, the load characteristics and the frictional force are analyzed, and the method is applied to a hybrid transducer type rotary motor and a traveling wave type linear motor.     

A torque estimator for a traveling wave ultrasonic motor--application to an active claw

Depending on its electrical-to-mechanical energy conversion process, the torque on a traveling wave ultrasonic motor (TWUM)'s shaft is not directly proportional to a measurable electrical variable, such as current or voltage. But it is derived from a complicated process at the stator/rotor interface. The load torque is thus quite unknown, and this can be a disadvantage in applications in which a torque limitation is required or a torque measurement is needed. The aim of this article is to come up with a straightforward torque estimator on a TWUM. For that purpose, the motor is modeled; this modeling leads to different estimator strategies. More specifically, we chose a strategy for which a speed sensor is useless, relying only on the stator's resonant behavior. The parameters of the motor needed for the estimator are measured afterward, and some nonlinearities are identified and taken into account. Several experimental trials then are carried out to check the performance of the estimator. A claw actuated by a TWUM is presented because this is a typical application in which the knowledge of the torque helps guarantee the safety of the device.     

复合式罩极电机扭转振动检测与分析

设计了一种复合式罩极电机,为双定子双转子结构,电机运行时定子绕组施加励磁,产生的旋转磁场带动转子旋转。分析了电机气隙磁场的特性,推导了电磁转矩公式,表明电机运行时存在扭转振动。研制了复合式罩极电机样机,利用传感器对电机在不同励磁状态下的转矩输出进行了检测,表明电机运行时存在扭转振动,且扭振幅值随两相励磁电压的相位差而变化,最后对变化规律进行了理论分析,结果表明:扭转振动波的相位差为两相励磁电压相位差的2倍。     

Modeling of a piezoelectric rotary ultrasonic motor

A piezoelectric rotary ultrasonic motor is modeled for the purpose of predicting, a priori, motor performance as a function of design parameters. The Rayleigh-Ritz assumed mode energy method is used to model the distributed piezoceramics and the traveling wave dynamics of the stator. Natural frequencies and modeshapes are obtained for a generally configured motor. Nonlinear normal and tangential interface forces between the rotor and stator are incorporated into the forcing function along with the linear piezoelectric forcing. Given the applied torque, applied axial loading, and piezo drive voltages as inputs to the model, general motor performance measures are obtained-namely speed, input power, output power, and efficiency. The approach presented here provides a general framework for modeling these motors as well as a design tool for optimizing prototypes with the added flexibility of allowing for a wide variety of geometries and materials     

Finite-element analysis of the rotor/stator contact in a ring-type ultrasonic motor

A way to understand mechanical characteristics of an ultrasonic motor is presented. First, the vibration mode of a stator is calculated using a finite-element method (FEM) code. The path of the elliptic motion of the stator's teeth is obtained. The computed vibration mode at the surface of the stator is compared with that measured by an electrooptical displacement transducer. Next, the contact condition of the rotor/stator is calculated. The displacement and velocity of the rotor/stator, the distortion of the stick/slip area, the rotational speed of the rotor, and the friction loss of the motor are obtained. The calculated rotor displacement and torque-rotational speed curve correspond closely to the experimentally measured ones. The internal loss of the rotor/stator and the loss of the supporting felt are measured. The total loss of these losses and the calculated friction loss agree with the measured total loss. The calculated and the measured efficiency of the motor also agree.     

二自由度行波型超声波电机定子的数学模型与实验研究

二自由度行波型超声波电机是一种新型多自由度超声波电机。本文从二自由度行波型超声波电机的驱动机理和基本结构出发,就电机的结构实现、驱动球转子的最佳定子结构进行了分析,利用所建立的有限元模型进行定子振动的模态分析和共振频率计算,提出了外缘大倾角内缘线接触的行波定子。然后建立定子的接触模型,对其机械性能进行分析。测试结果表明,修正的数学模型更加符合电机的实际运行特性。所研制样机的球转子直径为45mm,定子直径为30mm,实现的堵转力矩为120mNm,空转转速12r/min。本文工作为多自由度行波型超声波电机的优化设计、性能提高奠定了基础。     

旋转型行波超声电机理论模型的仿真研究

建立了旋转型行波超声电机定、转子间的摩擦驱动模型，不仅考虑了接触界面上的纵向分布力，而且分析接触力沿周向和径向上的分量，在此基础上结合定子和转子的动力学模型得到了整个电机的机电耦合模型。文章分析了预压力影响电机驱动频率的本质原因，说明该频率不能直接通过分析自由定子得到，最后通过数值计算分析了接触界面力对电机工作频率的影响，取得了与实验一致的结果。     

A piezoelectric motor using two orthogonal bending modes of a hollow cylinder

This paper proposes a compact ultrasonic motor with low manufacturing costs, a simpler driving circuit, and scalability. The stator of the motor presented in this paper consists of a hollow metal cylinder, whose outside surface was flattened on two sides at 90 degrees to each other, on which two rectangular piezoelectric plates were bonded. Because the cylinder has a partially square/partially circular outside surface, the stator has two degenerated bending modes that are orthogonal to each other. A wobbling motion is generated on the cylinder when only one piezoelectric plate is excited at a frequency between the two orthogonal bending modes. A rod through a pair of ferrules was used as the rotor of this motor. The prototype motor, whose stator was 2.4 mm in diameter and 10 mm in length, operated at 69.5 kHz, was experimentally characterized, and a maximum torque of 1.8 mNm was obtained.     

伺服电机转子位置检测的误差分析与补偿

针对伺服电机转子位置检测中存在安装不方便、成本高等问题,提出了基于隧道磁阻效应和时栅技术相结合的转子位置检测单元的设计方案。将空间正交的一对TMR传感单元嵌入在电机的前端盖上,实现嵌入式位置精密检测。根据检测单元转子位置解算原理,分析了检测单元的安装误差、电气误差、电磁噪声误差等引起的误差成分。提出了基于超限学习机的误差补偿方法,通过对真实值和测量值样本的训练得到模型最优参数,根据模型参数建立转子位置的误差模型。利用所得到误差模型实现对转子位置的误差补偿。实验结果表明,在2000r/min匀速工况下,补偿前转子位置最大测量误差为4.64°,补偿后转子位置误差为0.315°,精度提升了93.2%,为伺服电机转子位置检测提供了新的方法。     

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.