Traveling Wave Ultrasonic Motor Research Articles

Modal analysis and output characteristics of an ultrasonic motor with a square prismatic shell stator

Abstract A rotary traveling wave ultrasonic motor having a square prismatic shell stator is proposed. The stator contacts with the rotor through interference fit, and elastically deforms slightly, and then presses against the rotor. Then the pre-pressure is created by the initial deformation of the stator with simple structure. The in-plane modal problem of the stator is analyzed by numerical method as a folded beam and the results are compared with those from finite element method (FEM) and laser doppler measurement. The 3rd and 5th degenerate modes with repeat natural frequencies are selected as working modes, and the influence of actuating frequency and voltage on the no-load speed and stall torque is studied by multi-physics simulation for the operation of these two modes. A prototype is fabricated and the output characteristics were tested and compared with the simulated results. The 3rd working mode is found to have better performance and can reach a no-load speed of 205 rpm and maximum torque of 3.9 mN·m when the input is 28.0 kHz and 100V. The effect of the pre-pressure for the 3rd working mode is discussed further.

Design, Analysis, and Implementation of Wireless Traveling-Wave Ultrasonic Motors

Design, Analysis, and Implementation of Wireless Traveling-Wave Ultrasonic Motors

Design of a new cantilevered cylindrical traveling wave ultrasonic motor

In this paper, a composite excitation method is used to optimize the design of an existing cantilevered cylindrical ultrasonic motor to avoid vibration interference. Modal and transient simulation analysis of the stator structure was carried out by the finite element method. Optimized stator structure is simpler than the original motor. Simulation analysis results show that the circumferential amplitude is increased by more than 35% with 55.7% reduction in ceramic usage.

Design and experiment of a double-sided staggered conical teeth traveling wave ultrasonic motor

This paper proposed a double-sided staggered conical teeth traveling wave rotating ultrasonic motor based on in-plane bending mode, which reduces the difficulty of rotor preload application and improves the output characteristics of in-plane bending mode traveling wave rotating ultrasonic motor. The motor has four sets of drive teeth alternately distributed on both the inner and outer sides of the vibrator, with the drive teeth gap dedicated to accommodate the piezoelectric ceramic piece, and the staggered drive teeth on both sides of the vibrator are used to drive the rotor rotation. The motor operates in two in-plane third-order bending modes with the same frequency and orthogonal to each other, and is excited by four sets of piezoelectric ceramic disks spaced 90 degrees apart from the inner and outer sides. After the prototype was completed, its vibration characteristics and output performance were experimentally tested, and the actual effects of the three excitation schemes were compared. The experimental results show that the motor can provide a maximum output torque of 1.82 N·mm and a maximum no-load speed of 96.4 rpm when the excitation voltage is 300 V and the excitation frequency is 20.60 kHz.

A Double-Sided Tapered Teeth Traveling Wave Ultrasonic Motor Based on In-Plane Bending Mode

In order to improve the output torque of an in-plane bending mode traveling wave rotary ultrasonic motor, a double-sided tapered teeth traveling wave rotary ultrasonic motor was proposed. The motor is designed with three types of adaptive rotors that can be used for replacement in different output environments. Simulation analysis was conducted using ANSYS, and prototype production and experimental testing were conducted. The experimental results show that when the excitation voltage is 300 V and the excitation frequency is 22.665 kHz, the maximum output torque that the motor provide is 3.087 N·mm, and the maximum no-load speed is 295 rpm.

Design and Experiments of a New Internal Cone Type Traveling Wave Ultrasonic Motor

Design and Experiments of a New Internal Cone Type Traveling Wave Ultrasonic Motor

Laser-induced microtextured stators coupling with flexible rotors for low-voltage driving rotational piezoelectric motors

Traveling-wave ultrasonic motors promise widespread applications in precision engineering, medical, and aerospace field due to their high-power density, but suffer from low efficiency and stress gradient. In this case, the synergy effect of surface-functionalized friction regulation and interface coupling interference of wear loss/debris could effectively eliminate these deficiencies. Herein, we report a low-voltage driving rotational piezoelectric motor (PM30) that proceeds through laser-induced microtextured stators coupling with flexible rotors, which enables working at a rotational speed of 158 rpm and torque of 73 N·mm, respectively, under the condition of low-voltage (80Vp) and low-preload (40 N). Such operation parameters are far beyond the current reported results. Furthermore, FEM simulation and SEM observation demonstrated that the low-voltage driving and high-performance output are resulting from the combination of surface microtextured stators for friction enhancement and flexible rotors for displacement amplification with contact expansion, which regulates tangential friction and reshares the stresses distribution during the dynamic contact along with the rotary motion of rotors. This work provides a promising strategy to construct friction-stress regulation and energy-transformation enhancement toward energy-saving and high-efficient friction drive for piezoelectric devices.

Traveling wave distortion of MEMS ultrasonic motor induced by anisotropic elasticity

It is crucial to study the problem of traveling wave distortion due to its severe effect on the stability and efficiency of traveling wave ultrasonic motors (TWUM). In this study, the anisotropic elasticity as a new factor causing the traveling wave distortion in MEMS TWUM was considered, and an electromechanical model considering the effect of anisotropic elasticity was established to evaluate the distorted traveling wave. Initially, the orthogonal modes of the stator were investigated using finite element simulation, and the orthogonal modes’ two defects induced by the anisotropic elasticity were observed, which included modal splitting and shape distortion. Subsequently, the electromechanical model was established based on the defective orthogonal modes using Hamilton’s principle and classical laminated plate theory. Additionally, the effect of modal splitting and shape distortion on the traveling wave distortion was investigated based on the electromechanical model. It demonstrated that B13 was the optimal orthogonal mode for the high-quality traveling wave. Finally, MEMS TWUMs were fabricated and tested to verify the theoretical results. The test results were obtained using a laser Doppler vibrometer, and it was observed that the traveling wave produced from B13 was optimal. The test results of rotational speed measured using a high-speed camera also verified that B13 was the optimal orthogonal mode for the traveling waves.

Nominal-Model-Based Sliding-Mode Control for Traveling-Wave Ultrasonic Motor.

Traveling-wave ultrasonic motors (TWUSMs) have strong nonlinearity and uncertainty, which are sensitive to the environment, disturbances, and load changes. Thus, precision control of TWUSMs is hard to achieve with traditional methods for complex driving mechanisms. A nominal-model-based sliding-mode control strategy with strong robustness is proposed to achieve accurate speed control of TWUSMs. Firstly, a second-order nominal model of the speed difference and output torque was deduced to construct a nonlinear sliding-mode surface; then, a nonlinear sliding-mode controller was designed with the collaborative regulation of frequency and the amplitude of two-phase control voltages. The global asymptotic stability of the controller was proved under bounded disturbances and parameter uncertainty. Finally, the effectiveness and accurate control were testified to and verified by the simulations and experiments, which showed good robustness and a disturbance rejection of the strategy for TWUSMs, with strong nonlinearity and uncertainty.

Two-Phase Stator Vibration Amplitude Compensation of Traveling-Wave Ultrasonic Motor

The consistency of the two-phase mode responses is essential to ensure the mechanical performance and stability of traveling-wave ultrasonic motors. Due to the asymmetry of the stator, inevitable manufacturing errors, or imbalance of the excitation voltages, the amplitudes of the two-phase standing waves cannot be exactly the same, resulting in unstable operating of USM. To improve the stability of the motor and decrease the velocity fluctuation, a closed-loop velocity control scheme considering two-phase consistency compensation based on the vibration amplitude of the stator is proposed. This scheme is implemented under the framework of the stator vibration amplitude-based velocity control and parallel resonance frequency tracking (VCBVF). Based on the relationship between the velocity and stator vibration amplitude (SVA), two-phase excitation signals are adjusted individually and simultaneously. Compared with the single-phase feedback VCBVF control scheme, experimental results show that the proposed scheme can reduce the overshoot from 17.50% to 6.90% and velocity fluctuations from 7.69 rpm to 2.40 rpm, under different load torques. The proposed scheme can compensate for the two-phase electrical inconsistency and improve the velocity stability and output power of motor operation under various conditions.

Contact analysis and performance evaluation of ring type traveling wave ultrasonic motors based on a surface contact model

A surface contact model of ring type traveling wave ultrasonic motors is proposed in this paper in order to describe the circular three-dimensional contact and friction problem between the stator and rotor accurately. Differing from previous contact models of traveling wave ultrasonic motors, the flexibility of the rotor, which results in the irregular shape of contact area and inhomogeneous distribution of contact pressure along radial direction, is taken into account in the proposed model. The normal contact between the stator and rotor is analyzed with finite element method and the tangential force transmission on the contact surface is investigated with analytical method. The contact pressures and the tangential stresses on the contact surface are obtained. Mechanical performances of the motor are also studied based upon the proposed model. Finally, torque-speed curves of a prototype motor are measured and compared with the calculated results of the proposed model, and good agreements are obtained. In addition, the proposed surface contact model is compared with previous line contact models. It is found that the calculated results of the surface contact model are closer to measured results than those of line contact models. The comparison results verify the accuracy of the proposed surface contact model.

Experimental investigation on mechanical characteristics of low-voltage driving traveling-wave ultrasonic motor with the flexible rotor

Classical traveling-wave ultrasonic motors (TWUMs) usually generate the elliptical clusters on the stator surface through the bending vibration of the annular stator on the basis of piezoelectric excitation, and the torque output and power transmission are realized by friction coupling under the rational preload. Stable and reliable working characteristics attracted the focus of various applications. High energy consumption and low efficiency are restricted factors for the service performance of motors. Displacement amplification and stress regulation based on flexible design become a possible approach to improve motor performances. In this study, a TWUM30 prototype was proposed with consideration of (sub) structure optimization, i.e., tooth height and backlash of the stator elastomer. The flexible design of the rotor structure was carried out for consideration of the contact area and stress regulation. After integrated bonding of the stator and PZT4, the electrical and vibration characteristics of the stator prototype are measured by an impedance analyzer and high-precision laser micro-displacement sensor. Results showed that the proposed TWUM30 is capable of operation under low-voltage driving (41.9 kHz @ 80 Vp), and the extreme mechanical performances presented the stall toque of 64mN∙m and the no-load speed of 153.8 rpm. With the combination of the flexible design and systematic integrated manufacturing of the stator/rotor, low-voltage driving of the TWUM30 motor under ultra-low preload was realized at low cost and the adverse effects of excessive preload were suppressed. This study is expected to provide support for high reliability design and long-life service of the TWUMs. It also provides a realistic possibility for the flexible design and application of energy-saving and high-efficient traveling-wave piezoelectric drivers.

A Low-Voltage Cylindrical Traveling Wave Ultrasonic Motor Incorporating Multilayered Piezoelectric Ceramics.

In-plane bending traveling wave ultrasonic motors (USM), which are compact in structure and flexible in design, have been widely applied in biological engineering, optical engineering, and aerospace engineering. However, the high driving voltage and complicated driving circuit of this kind of USM restrict their further miniaturization and electromechanical integration in these applications and bring some potential safety hazards. To solve this problem, a low-voltage-driving traveling wave USM incorporating cofired multilayer piezoelectric ceramics was proposed in this work. Four cofired piezoelectric ceramics were strategically designed to excite two orthogonal third-order in-plane bending modes with the same frequency of the USM. The principles of traveling wave synthesis and low-voltage-driving of the USM were deduced, and the stator dynamic design and transient dynamic simulation were carried out by finite-element method. The microproperties of cofired piezoelectric multilayer ceramics, the vibration characteristics of the stator, and the mechanical output performance of the USM were tested by experiments. The results indicated that the motor can work as low as 5 [Formula: see text]. A long stroke with a maximum forward and reverse rotational speeds of 187.7 and 176.6 r/min were obtained, respectively, and a maximum stalling torque of 4.8 mN · m at 47.3 kHz under 15 [Formula: see text] was achieved. The results showed that the proposed USM is small, low in driving voltage, and high in torque output, which has promising applications in aerospace, biomedicine, and other fields that require a lightweight and integration of driving devices.

Analysis of stator rotor of rotating traveling wave ultrasonic motor

Abstract As a new type of energy exchange device, the operation characteristics of ultrasonic motor is a hot issue in current research. In this paper, the thermo-electro-mechanical coupling model of the stator and rotor of the rotary traveling wave ultrasonic motor is constructed by finite element software. The frequency and amplitude of the working mode of the stator and rotor of the ultrasonic motor under different temperature conditions are studied, and the influence of the piezoelectric ceramic lamination on the working state of the ultrasonic motor is discussed. The following conclusions are drawn: with the increase of temperature, the resonant frequency of the working mode of the ultrasonic motor B09 decreases and the amplitude increases slightly; piezoelectric ceramic delamination can improve the amplitude-frequency characteristics of stator and rotor. Considering comprehensively, the superposition of two layers of piezoelectric ceramic plates is the most suitable structure.

Performance improvement of micro-ultrasonic motors using the thickness shear mode piezoelectric elements

We propose a one-millimeter-scale traveling-wave ultrasonic motor that uses a thickness shear mode (15-mode) piezoelectric elements with a high shear piezoelectric coefficient. This thickness shear mode makes the micromotor suitable for operating with higher energy efficiency than conventional micromotors and enables a low voltage operation and a high torque generation. In this study, we build a thickness shear mode-driven micro-ultrasonic motor and demonstrate the improvement in motor performance. A micromotor comprising a cube with a side length of 1 mm and four piezoelectric plates is fabricated, and its dynamic and static characteristics are evaluated experimentally. With an optimal preload mechanism, the micromotor obtains unprecedented performance measures: an efficiency of 2.1% and a torque of 40 µNm, which are 3–4 times larger than those of a comparable micromotor using typical expansion mode (31-mode) piezoelectric elements. Currently, the proposed motor is the most powerful micromotor in 1–2 millimeter-scale actuators and represents a new benchmark for micromotors.

Realization of the Ultrasonic Motor Speed Control System Based on H-Bridge

In view of the requirement that the speed of rotor speed of ultrasonic motor can be stabilized quickly, combined with the mathematical model of two-phase traveling wave ultrasonic motor, we designed the rotor speed stability control strategy of the two-phase traveling wave ultrasonic motor based on voltage and current double feedback. We simulated, analyzed, and verified the designed strategy using Matlab/Simulink simulation tool. The rationality of the simulation results proves the correctness of the designed control strategy, which lays a theoretical foundation for the production design of two-phase traveling wave ultrasonic motor.

A multi-degree-of-freedom clamping type traveling-wave ultrasonic motor

This paper proposes a multi-degree-of-freedom (multi-DOF) ultrasonic motor with four stators clamping a spherical rotor. The stator surface teeth are inclined at a certain angle, using the inclined surface to contact the rotor and transfer energy. The motor frame is exquisitely designed in which substrates hold four identical stators to drive the rotor to achieve a multi-DOF rotation. COMSOL Multiphysics performs the stator's modal analysis and harmonic response analysis to illustrate the vibration mode and frequency response. A prototype is fabricated to verify the operating principle and conduct the performance tests. The experimental results indicate that the motor can reach a no-load speed of 100r/min, and the stalling torque is 150mNm under a preload of 113 N. The results also denote the motor has a high load-carrying capacity with a maximum load torque of 143mNm and accurate operation with a maximum error of 0.15 mm.

Reducing static friction to improve backdrivability in torque control of traveling wave ultrasonic motor

In this study, we aimed to improve the backdrivability and torque control of a traveling wave ultrasonic motor (TWUSM). Because of its operating principle, a TWUSM has strong holding torque. While this feature is useful for maintaining the rotor in a fixed position in many applications, it can be problematic for applications that require backdrivability, such as assistive exoskeletons or haptic devices. We used the theoretical contact model, which considers tangential elasticity, to calculate the torque–speed characteristics of a TWUSM. To evaluate backdrivability, we simulated not only the case in which the TWUSM drives the output shaft actively, but also the case in which the output torque opposes the rotation direction and the TWUSM is driven by an external torque passively. According to the analysis of the contact force distribution, the holding torque was reduced because the sticking contact area was decreased by stator vibration. To verify the simulation results, we built an experimental setup to measure the actual torque characteristics, and the obtained results agreed with the simulation. Furthermore, using the same experimental setup, we compared two torque control methods, driving frequency control and phase difference control. As the theoretical model predicted, the latter method resulted in higher control accuracy.

Development of a Rotary Ultrasonic Motor with Double-Sided Staggered Teeth.

Based on the conventional structure of traveling wave ultrasonic motor, a rotary ultrasonic motor with double-sided staggered teeth was proposed. Both sides of the stator could be used to actuate the rotors to rotate and output torque. Moreover, the staggered teeth in the stator could be dedicated to accommodating the piezoelectric ceramic chips. Under the excitation of two alternating voltages with a 90° phase difference, a traveling wave could be generated in the ring-like stator. Then, a rotary motion could be realized by means of the friction between the rotors and the driving teeth of the stator. The finite element method was adopted to analyze the motion trajectories of the driving tips. Moreover, the experimental results showed that the load-free maximum speed and maximum output torque of the prototype were 99 rpm and 0.19 N·m at a voltage of 150 Vp with a frequency of 28.25 kHz.

Contact modeling and performance evaluation of ring type traveling wave ultrasonic motors considering stator teeth

A contact model of ring type traveling wave ultrasonic motors is proposed in this paper in order to investigate the dynamic contact and friction drive mechanism between the stator and rotor. Differing from previous contact models of ring type traveling wave ultrasonic motors, the Dahl friction model is adopted and the stator teeth are taken into account in the proposed model. The normal stress, the tangential stress, and the torque-speed characteristics of the motor are evaluated in detail based on the proposed model. Finally, the torque-speed values of the prototype motor are measured and compared with the calculation ones. The results show that the calculation values are in good agreement with the experimental values, which validates the proposed model. Moreover, the proposed contact model is compared with previous contact models that adopt Coulomb friction law and meanwhile ignore stator teeth by assuming teeth surfaces to be continuous. The comparison results show that the proposed model is more accurate than previous models.