Characteristics estimation of a traveling wave type ultrasonic motor

A method for calculating the load characteristics of a traveling-wave-type ultrasonic motor (TWUM) is proposed. A systematic method using an equivalent circuit is suggested for estimating the performance of the motor, including its electrical and the mechanical parts. In the proposed method, a governing equation for the motor is derived to describe the relation between the applied voltage at an electrical terminal, vibration velocities, and the external forces at mechanical terminals of a vibrator. A method for estimating the forces between the rotor and the vibrator of the motor is presented and used to calculate the load characteristics. The numerically calculated load characteristics are shown to agree well with the measured ones, confirming the validity of the method.     

A high-power traveling wave ultrasonic motor

In the present work, a traveling wave ultrasonic motor (TWUSM) is proposed. It is composed of an annular-shaped stator and two cone-shaped rotors that are pressed in contact to the borders of the inner surface of the stator. A rotating traveling wave has been generated in the stator by using as vibration generators two bolted Langevin transducers (BLT) opportunely shifted in space and in time. The vibrational behavior of the stator as well as the traveling wave generation has been simulated with the finite-element method (FEM) software. A prototype of the motor has been manufactured and experimentally characterized. It exhibits a static torque of about 0.8 N x m and a maximum angular speed of about 300 rpm. Possible variations of the present design aimed to increase output torque or minimize encumbrance are described and discussed.     

A cylindrical traveling wave ultrasonic motor using a circumferential composite transducer

This paper intends to present and verify a new idea for constructing traveling wave ultrasonic motors that may effectively avoid the drawbacks of conventional traveling wave motors using bonded PZT plates as the exciting elements. In the configuration of the motor's stator, a composite sandwich type transducer is used to excite a traveling wave in a cylinder with two cantilevers as the coupling bridges between the transducer and the cylinder. The design process of the stator is described using the FEM modal analysis method, and the establishment of traveling wave on the cylindrical stator was simulated by FEM transient analysis. To verify the theoretical analysis results, a laser Doppler scanner was employed to test the mode shapes of a prototype stator excited by the longitudinal and bending vibrations respectively. Finally, to validate the design idea, a prototype motor was fabricated and tested; the typical output features are no-load speed of 156 rpm and maximum torque of 0.75 N·m under exciting voltages of 70 V(rms) applied to excite the longitudinal vibration of the transducer and 200 V(rms) applied to excite the bending vibration.     

Characteristics of traveling wave ultrasonic motor under atmosphere and vacuum cycle condition

Under atmosphere and vacuum cycle condition, characteristics of a disc-type traveling wave ultrasonic motor (TWUSM) are tested, variations of rotation speed with time and load are also obtained. Two vacuum conditions used are low vacuum of 2 Pa and high vacuum of 5 × 10⁻³ Pa. The lower the environment pressure is, the smaller the rotation speed of TWUSM. And load characteristics of TWUSM in vacuum are poorer than that in atmosphere. Then, using polyfluortetraethylene (PTFE) composite and p-hydroxybenzoic acid polymer (Ekonol) composite as friction materials, load characteristics of TWUSM are compared. As a result, the load characteristics of Ekonol composite are better than the former one, which can hold bigger torque with higher speed. Both principle of ultrasonic motor and knowledge of tribology are applied to analyze the reason that stall torque of TWUSM in vacuum is smaller than in atmosphere.     

Design of a hybrid transducer type ultrasonic motor

The authors present a design method for a hybrid transducer-type ultrasonic motor (HTUSM) for practical use. They introduce a simple equivalent circuit that expresses the unique operation mechanism of the hybrid transducer-type motor. A numerical simulation based on the model enables them to predict the motor characteristics such as the maximum torque and the no-load revolution speed. In addition, for the purpose of efficient design and physical interpretation of the phenomena, they discuss analytically the maximum torque of a special case and develop two design charts for the prediction of the no-load speed of the motor.     

Evaluation of the effect of preload force on resonance frequencies for a traveling wave ultrasonic motor

In this paper, a novel method of numerical computation of the natural frequencies, depending on the most important running parameters for an ultrasonic motor, is described. The analyzed configuration by the Space Division of Alenia Spazio, Rome, within an Italian Space Agency (ASI) development program, is the flexural traveling wave one. The dynamic equations for the stator and the rotors of the ultrasonic motor are assumed into a differential system, whose equations are coupled by terms that represent interface generalized forces. In order to calculate natural frequencies of the motor-coupled terms of the equations are worked out with respect to the variables of the degrees of freedom. Hence, the mass, damping, and stiffness matrix for the whole system are obtained, then resonance frequencies, depending on the most important running parameters such as axial preload of the motor, are calculated. The results are compared with numerical ones, obtained by a finite element modeling (FEM) model, showing a good agreement.     

An ultrasonic linear motor using ridge-mode traveling waves

A new type of ultrasonic linear motor is presented using traveling waves excited along a ridge atop a substrate. The ridge cross section was designed to permit only the fundamental mode to be excited during operation of the motor, with a Langevin transducer used as the source of vibration in this study. The ridge waveguide was first made of lossy media to avoid reflecting vibration energy back toward the vibration source, forming a traveling wave. A 5-mm-wide, 15-mm-tall rectangular acrylic ridge was used to move a slider placed upon it toward the vibration source, in opposition to the direction of the traveling wave transmitted along the waveguide ridge. Using a low-loss 3 x 6-mm aluminum rectangular ridge combined with a damper clamped onto the far end of the waveguide, similar results were obtained. To obtain bidirectional operation, the damper was replaced with a second Langevin transducer, giving a pair of transducers located perpendicularly to the ends of the ridge and driven with an appropriate phase difference. The moving direction of the slider was reversed by shifting this phase difference by about 180 degrees. With this simple configuration, it may soon be possible to fabricate a linear micromotor system on a silicon substrate or other semiconductor wafer adjacent to other electronic and optoelectronic devices.     

旋转型行波超声电机定子的子结构模型研究

按照旋转型行波超声电机定子的结构特点将其划分为几个较简单的子结构,分别对其进行了动态特性分析,最后在子结构模态综合法的基础上建立了整个定子的分析模型。该模型可以很方便地计算电机定子的各阶模态,并且由于运用Guyan静力法将定子齿单元的刚度和质量凝聚到基体之上,不仅恰当地描述了齿对定子动态特性的影响,而且达到了缩减计算量的目的。通过算例和实验说明此理论模型是可行的,可用于电机系统性能预测和参数优化设计。     

Design and construction of a traveling wave thermoacoustic refrigerator

A traveling wave thermoacoustic refrigerator was designed, constructed, and tested. This refrigerator was composed of a linear motor, a branched tube, and a looped tube. A regenerator, composed of many screen meshes, was installed inside the looped tube. When the linear motor delivers an acoustic wave to the branched and looped tubes, heat pumping occurs along the regenerator. In this work, the regenerator radius and position were numerically optimized and the performance of the optimized refrigerator was measured. At the optimized values of regenerator radius and position, the refrigerator achieves a minimum cold temperature of 232 K and about 20% of the Carnot coefficient of performance at 265 K.     

Contact analysis and mathematical modeling of traveling wave ultrasonic motors

An analysis of the contact layer and a mathematical modeling of traveling wave ultrasonic motors (TWUM) are presented for the guidance of the design of contact layer and the analyses of the influence of the compressive force and contact layer on motor performance. The proposed model starts from a model previously studied but differs from that model in that it adds the analysis of the contact layer and derives the steady-state solutions of the nonlinear equations in the frequency domain, rather than in the time domain, for the analyses of vibrational responses of the stator and operational characteristics of the motor. The maximum permissible compressive force of the motor, the influences of the contact layer material, the thickness of the contact layer, and the compressive force on motor performance have been discussed. The results show that by using the model, one can understand the influence of the compressive force and contact layer material on motor performance, guide the choice of proper contact layer material, and calculate the maximum permissible compressive force and starting voltage.     

Hybrid transducer type ultrasonic motor

A type of ultrasonic motor whose stator is composed of a torsional vibrator and multilayered piezoelectric actuators is proposed and has been fabricated for trial. The stator is operated at the resonance frequency of the torsional vibration. The vibrator generates the mechanical output force and the actuators control the frictional force. The construction provides for arbitrary Lissajous's figures at the contacting surface and contributes to large mechanical output power with high efficiency and bidirectional motion. It also gives greater freedom of design. The prototype motor produced a maximum torque of 7 kg-cm and a maximum efficiency of 33%     

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.     

Standing wave bi-directional linearly moving ultrasonic motor

A standing wave bi-directional linearly moving ultrasonic motor has been studied for the purpose of implementing a practical linear ultrasonic motor with simple structure, simple driving and high resolution. The fundamental principle of this linear motor is projections on the right sides of a standing wave crests generating thrust force right-diagonally on the slider pressed against the projections. Correspondingly, projections on the left sides of the wave crests make the slider move toward the left. In order to realize bi-directional actuating, vibration mode B3 or B4 is excited in a rectangular plate-type vibrator to make the projections on the right sides or the left sides of the wave crests. In this paper, the operation principle of the linear motor is demonstrated. Furthermore, a prototype linear ultrasonic motor of 40 mm in length, 10 mm in width is fabricated and investigated. The following performances have been achieved: maximum speed 200 mm/s, maximum force output 150 gf, and resolution less than 0.1 mum.     

New type of piezoelectric ultrasonic motor

The authors describe a newly developed motor concept which allows a bidirectional piezoelectric ultrasonic motor to be operated with only a single voltage feed and thus only one power amplifier. The motor concept is based on the superposition of a longitudinal and a flexural oscillation of a rod-shaped resonator. In a way analogous to the generation of a Lissajous figure, this superposition produces a rotary movement of the resonator end by means of which a rotor is directly driven. By selecting the relative phase of the electrical stimulations of both modes, the speed can be continuously varied in both directions. The motor can be driven in both right and left directions with speeds of 0 to 300 r/min, and a freewheeling state can be set up by means of a suitable phase between the oscillation modes. In the off state, the motor blocks the motion.     

Optimization of a new type of ultrasonic linear motor

This paper presents the design, the properties, and the optimization study of a new type of ultrasonic linear motor. Numerical modeling has been carried out and simulations with software have been realized. To avoid performing a large number of simulations, sensitivity analysis has been carried out, in particular using design of experiments. The Doehlert method has been chosen in our study. The results found show that this preoptimization stage allows one to improve the deformation amplitude and to reduce the input parameter variation ranges. Finite element (FE) optimization is then carried out, and results show that the motion amplitudes can be increased compared to the initial design of the motor. Some experiments on prototypes show that the travel range of the motor has been increased while decreasing the applied voltage by a factor of 2.     

Novel modeling technique for the stator of traveling wave ultrasonic motors

Traveling wave ultrasonic motors (TWUM) are a promising type of piezoelectric transducers, which are based on the friction transmission of mechanical propagating waves. These waves are excited on the stator by using high Q piezoelectric ceramics. This article presents a modeling strategy, which allows for a quick and precise modal and forced analysis of the stator of TWUM. First-order shear deformation laminated plate theory is applied to annular subdomains (super-elements) of the stator. In addition to shear deformations, the model takes into account the effect of rotary inertia, the stiffness contribution of the teeth, and the linear varying thickness of the stator. Moreover, the formulation considers a more realistic function for the electric field inside the piezoelectric ceramic, i.e., a linear function, instead of the generally assumed constant electric field. The Ritz method is used to find an approximated solution for the dynamic equations. Finally, the modal response is obtained and compared against the results from classical simplified models and the finite element method. Thus, the high accuracy and short computation times of the novel strategy were demonstrated.     

Sensitivity analysis and optimization of a standing wave ultrasonic linear motor

This paper presents the sensitivity analysis of an ultrasonic linear motor using design of experiments (DOE) and the finite element (FE) optimization of its deformation amplitude. A first ultrasonic linear motor prototype has been built at the laboratory. A deformation amplitude of about 6.6 microm can be obtained by applying a 100 V voltage. The goal is to obtain a bigger deformation amplitude by varying the motor parameters, in particular the vibratory piece dimensions. First of all, a parametrization of the motor structure is carried out. Then, with the aim of reducing the variation ranges of the input parameters--but also to avoid performing a large number of simulations--a preoptimization stage is necessary. Thus, sensitivity analysis is carried out using design of experiments, which is a good way to obtain the influence of the input parameters on the objective function. Factorial designs have been chosen to find out the effects of each input factor but also the effect of their interactions. This method then is compared with Doehlert design technique, which is generally used for optimization approaches. The results show that it is absolutely necessary to take into account the quadratic terms in the model because they represent an important effect. The use of design of experiments revealed to be an interesting way to analyze numerically the ultrasonic motor as a preoptimization stage and already allows one to improve the deformation amplitude but also to reduce the input parameter variation ranges. Different FE optimization methods are then applied, and results show that the deformation amplitude can be increased by a factor higher than 10 compared to the initial design.     

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.     

Design and implementation of spherical ultrasonic motor

We present a mechanical design and implementation of spherical ultrasonic motor (SUSM) that is an actuator with multiple rotational degrees of freedom (multi-DOF). The motor is constructed of 3 annular stators and a spherical rotor and is much smaller and simpler than conventional multi-DOF mechanisms such as gimbals using servomotors. We designed a novel SUSM using experimental data from a single annular stator and a finite element method. The SUSM using a spherical rotor of diameter 20 mm without any reduction gear has demonstrated advantages of high responsiveness, good accuracy, and high torque at low speed. The dynamic implementation of SUSM was consistent with the driving model of SUSM based on a friction drive.     

行波型杆式超声电机定子的参数化有限元法优化设计

摘要：利用参数化有限元优化方法,对行波型杆式超声电机定子进行优化设计。首先,在确定电机定子初始结构的基础上,建立其参数化有限元模型。其次,对定子有限元模型进行模态分析,求解工作模态频率对各结构参数的灵敏度,选取灵敏度高的结构参数为设计变量,并以反映电机输出性能的重要参数作为目标函数。同时,设计了定子结构的优化方案,采用了零阶优化方法,对其结构进行优化设计。最后,根据优化结果,制作了定子样机。试验表明：定子工作模态和端面质点的振幅都满足了预期的设计要求,试验结果与优化设计结果相符。研究表明,利用该优化设计方法能有效地缩短超声电机设计周期。