Traveling Wave Rotary 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.

A novel rotary ultrasonic motor based on multiple Langevin transducers: design, simulation, and experimental investigation

Traveling wave rotary ultrasonic motors (TRUSMs) have been applied in optical systems, robotics, biomedical and other fields. However, the disadvantages such as short working life, driving performance degradation, and low energy utilization significantly limit the long-term and stable operation of TRUSMs in advanced fields like aerospace mechanisms. To address the above issues, a novel rotary ultrasonic motor based on multiple Langevin transducers is proposed in this paper. First, the structural design, driving principle and general design criteria are described in detail. Then, the structural parameters are optimized by finite element simulation analysis. Second, a prototype is assembled controllably. Subsequently, the impedance test and vibration measurement are carried out. The results show that the traveling wave is successfully generated on the tooth-ring, and all the Langevin transducers are excited to the first-order longitudinal vibration modes, which strongly verify the correctness of design principle. Finally, the driving performance experiment is carried out. The experimental results show that the no-load speed is 62 r min−1 under the pre-pressure of 10 N. The stalling torque is 0.94 N m at the driving voltage of 500 Vp-p. The response characteristics show that the start/stop time are 4.6/5.5 ms, and the angular displacement resolution of clockwise/counterclockwise driving are 6.7/10.2 μrad. The motor proposed in this paper not only exhibits relatively high output performance with excellent vibration characteristics, but also maintains compactness of the structure. The sandwiched structure design effectively avoids the problem that the bonded-type piezoceramic rings in conventional TRUSMs are prone to damage or fall-off when vibrating for a long time. Furthermore, the general design criteria provide a new approach to develop high performance rotary ultrasonic motors. The proposed novel ultrasonic motor is expected to meet the demand for long-term and stable operation in aerospace mechanisms.

Improvement of energy conversion efficiency in traveling wave rotary ultrasonic motor by increasing friction coefficient

This article introduces a method of enhancing the energy conversion efficiency of a traveling wave rotary ultrasonic motor with a flexible rotor by increasing the friction coefficient at the stator–rotor interface. The increased friction coefficient leads to improvements in energy conversion efficiency by increasing the output power and reducing friction loss power. Experimental verification showed that the friction coefficient in the interface increased from 0.21 to 0.32, the maximum energy conversion efficiency increased from 36.8% to 46.3%, and the interface friction loss was reduced.

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 experimental study of electromagnetic clutch-type variable pre-pressure ultrasonic motor

The traveling-wave rotary ultrasonic motor (TRUM) technique has become increasingly mature deepening of related research and development of related technology. The unique friction drive mode of a TRUM provides the advantages of a low speed, large torque, fast response, and a self-locking feature for power failure but also suffers from a relatively low efficiency. Regarding speed control, the commonly used approach of combining frequency modulation and speed regulation has provided the advantages of high precision and a wide range. Still, the load-carrying capacity of a TRUM is reduced when the driving frequency deviates from the resonant point, which is not conducive to the characteristics of low speed and large torque of the TRUM. To address this limitation, this study uses the pre-pressure and designs an electromagnetic clutch-type variable pre-pressure self-adjusting ultrasonic motor based on the TRUM-70 hollow ultrasonic motor. In addition, the force and motion analyses are conducted on the core components, and the basic parameters of the electromagnetic mechanism are calculated according to the specific design requirements. Furthermore, the Maxwell equation is used to simulate the designed magnetic circuit, and a prototype is fabricated and assembled. The feasibility of the proposed motor design is verified through experimental study, and the performance of the motor is compared with those of conventional ultrasonic motors. The experimental results show that the proposed electromagnetic clutch-type variable pre-pressure ultrasonic motor can effectively improve the output efficiency of the motor, especially when the load varies significantly.

A novel traveling wave rotary ultrasonic motor with piezoelectric backup function

To fulfill high-reliability requirements for aerospace applications, a novel traveling wave rotary ultrasonic motor with a piezoelectric backup function (Backup motor) is proposed in this paper. The backup function is enabled by the addition of a set of piezoelectric ceramics (PZT). Based on the ultrasonic motor of the CSX-60, a cantilever-tooth backup motor (CTBM) is designed and fabricated. This backup motor can operate in three working modes according to the excitation settings of PZTs, namely normal mode, backup mode, and enhanced mode. The relationships between three working modes’ performances are analyzed by finite element (FE) analysis and prototype tests. The results show that backup mode, as the substitution, can nearly reach normal mode’s performance, while enhanced mode is obviously higher than others. Furthermore, a modified backup motor with straight-tooth (STBM) and different sizes of PZT is designed and tested as a supplement to verify the feasibility of the proposal. In addition, the effect of stress reduction on PZT damage is verified by extreme working experiments. The comparison between the two types of motors indicates that STBM can provide better frictional drive performance. This proposal can provide a new reference for the subsequent reliability study of ultrasonic motors.

An efficient performance evaluation method of the traveling wave rotary ultrasonic motor's flexible rotor.

For a traveling wave rotary ultrasonic motor, matching the stator with a proper flexible rotor can be challenging because of the actual contact mechanism's complexity. Due to the lack of effective evaluation and prediction means in the rotor design process, the prototype test is usually needed to truly measure how well it performs, leading to high cost and long design cycle. In order to solve this problem, an efficient performance evaluation method of the flexible rotor based on equivalent contact pressure is proposed. By the key parameters of the flexible rotor's contact surface (area and pressure), an equivalent pressure model of the contact surface is established, which reveals the influence law of the flexible rotor's structural parameters on the motor's output performance. It is doubly verified by dynamics simulation and experiments. The advantage of this method is that without dynamics computation and prototype test, only statics analysis can evaluate the matching score of flexible rotor and target stator quickly and accurately. This study is expected to provide support for the structure design and performance prediction of the traveling wave rotary ultrasonic motor's rotor, in which significant time and cost savings can be achieved.

A Design Method of Traveling Wave Rotary Ultrasonic Motors Driving Circuit under High Voltage Using Single-Sided Hertzian Contact Forced Oscillator Model.

Traveling wave rotary ultrasonic motors (TRUMs) are widely used in various industrial processes due to their attractive features, such as compact structure, high accuracy, and fast response. However, the major limiting factors of the operational performance of TRUMs under high-voltage excitation are the nonlinear behavior caused by the nonlinearities of the piezoelectric materials and the friction between the stator and rotor of the motor. In this study, a nonlinear dynamics model and an identification method are presented to directly design the driver circuit for suppressing the nonlinear behavior under high voltage excitation. Firstly, by studying the time-frequency characteristics of the isolated electrode voltage, a single-sided Hertzian contact forced oscillator model of TRUMs is established, involving the nonlinearities of the piezoelectric material and friction. Secondly, a harmonic balance nonlinear identification is proposed in the time domain for TRUMs. The influence of the voltage and preload on the nonlinear phenomena is discussed. Lastly, a novel driver circuit is proposed to suppress the nonlinearities using feedback from the isolated electrode. Experiments showed that the total harmonic distortion decreased by 89.4% under 500 Vpp. The proposed drive circuit design method is used to find a high excitation voltage and preload to achieve greater motor output power.

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.

Nonlinear Dynamic Modeling of Traveling Wave Rotary Ultrasonic Motors for Designing Driver Circuit

Nonlinear Dynamic Modeling of Traveling Wave Rotary Ultrasonic Motors for Designing Driver Circuit

Improvement mechanism of energy conversion efficiency in ultrasonic motor with flexible rotor

Flexible rotors are widely used in traveling wave rotary ultrasonic motors (TRUMs) because of their higher energy conversion efficiency; however, there have been few reports on how flexible rotors improve the energy conversion efficiency of ultrasonic motors. In this study, we investigate the improvement mechanism of energy conversion efficiency in TRUMs with flexible rotors. A 3D finite element (FE) model with full coupling among a piezoelectric coupled stator, rotor, friction layer, and the rigid–elastic contact interface of the stator and friction layer is established. To analyze the mechanism by which the efficiency of the TRUM is improved, the contact interface and rotor vibration information are extracted. Taking TRUM-60 as an example, the transient solution method and modal analysis method are used to solve the model. It is found that when the stator mode is B09, the flexible rotor mode is B19. The energy conversion efficiency of the TRUM is obtained from the ratio of output power to the electrical input power of the model solution. The results are validated using 3D vibration measurements and energy conversion efficiency experiments. The simulation result shows that the motor with flexible rotor improves the energy conversion efficiency compared with the motor with rigid rotor, which can be attributed to two reasons: first, the axial amplitude ratio of the flexible rotor to the stator is reduced; second, the flexible rotor reduces the radial friction. This study reveals the influence of flexible rotor on the output efficiency and can thus provide guidance for rotor design.

A study on modeling of a piezoelectric motor

n this paper, a study on modeling of a piezoelectric transducer type rotary traveling wave ultrasonic motor (USM) is presented. First a mathematical model and numerical simulation results are achieved. The model is based on the theory of piezoelectricity and physic theory. An experimental model is worked out and compared to the numerical model. The influence of the temperature on characteristics such as the rotational speed of the motor is considered. The speed of the USM is measured at temperature between 17°Cand 50°C. To develop suitable control strategies for the drive, a fuzzy model type Takagi-Sugeno is used. The unknown parameters of the output membership functions are determined by least square method. Experimental data are used to examine the validity of the fuzzy model. Comparison between experimental and calculated data of the fuzzy model indicates that the fuzzy model can well describe the nonlinear characteristics among the frequency of driving voltage and rotating speed.

Improving the performance of ultrasonic motors in low-pressure, variable-temperature environments

Ultrasonic motor (USM) performance is dependent on the tribological characteristics of the interface between a stator and rotor, which are sensitive to ambient environments and driving parameters. Thus, the effects of vacuum and temperature on the mechanical output performance and energy conversion efficiency of a traveling wave rotary ultrasonic motor 60 (TRUM-60) with a novel micro-dimpled PI-based friction material and optimized input parameters were systematically investigated for the first time. The degree of vacuum had a negligible effect on the performance of the TRUM-60, whereas temperature influenced its mechanical output torque, rotational speed, and output power. The results can aid in the design of USM devices for aerospace applications.

An Analytical Model for the Stiffness of Slotted Disk Springs

The slotted disk spring is an important part of ultrasonic motors. Its mechanical properties directly affect the running stability of the motor. In this study, an analytical model is developed to solve the preload problem for slotted disk springs used in ultrasonic motors. The outer conical ring of the slotted disk spring is modeled using the conical shell theory. The inner separated teeth are modeled by the cantilever beam theory. An analytical mechanical model for the force-displacement relationship of the entire slotted disk spring is then developed. The results of the experiment based on a force-displacement transducer and the results from the analytical model, a finite element calculation, and the Schremmer formula are compared to validate the analytical model. The results show that the proposed model has the highest accuracy. Parameter-sensitivity analysis for the slotted disk spring is finally performed, and a new slotted disk spring with a long zero-stiffness interval is designed for a 40[Formula: see text]mm traveling wave rotary ultrasonic motor.

Improvement in step resolution and response time of ultrasonic motor by using a piezoelectric resonant shunting circuit as damping control.

Ultrasonic motors can be driven by burst voltage to obtain micro-stepping motion, and the corresponding step size depends on the load and cycle number of the applied ac driving voltage in one burst. The rotor of the motor achieves a step motion through a process of startup-acceleration-deceleration-stop. To obtain a large torque (or thrust force) and quick startup, a large vibration amplitude of a stator and a high growth rate are desired; thus, a large mechanical quality factor and a high electromechanical coupling factor are required. However, the stator vibration decays for a long time before it stops because of low mechanical energy loss; meanwhile, the rotor moves a big step. Hence, there is contradiction between thrust force and resolution/response time. This paper presents a new drive method to improve the step resolution and response time while keeping the torque by damping control. By simply adding a switch and a shunting damp circuit and connecting the shunting circuit to ultrasonic motors at the end of a drive burst signal, the stator vibration attenuates more rapidly and the step size is reduced. First, the damping effect of the piezoelectric system with a passive resonant shunting circuit (a resistor and an inductor connected in series) on the free stator of a bar-type rotary traveling wave ultrasonic motor has been tested. Next, a drive circuit comprising electronic switches and the shunting circuit is designed and utilized for measuring the performance of the motor. Experimental results have well proven the proposed method.

Mechanical optimization of a novel hollow traveling wave rotary ultrasonic motor

A novel hollow type of traveling wave rotary ultrasonic motor is proposed, optimized, fabricated, and tested in this study. Unlike conventional ultrasonic motors, this novel ultrasonic motor adopts a bran-new preloading method that preload is applied from the bottom of the stator through a wave spring, which can not only enhance the anti-overload ability but also extend the working life of the motor. According to this motor, a three-dimensional finite element model has been built by the commercial finite element software ADINA. In terms of the friction material and the preload, a detailed further optimization procedure is given after the initial design. Finally, the appropriate size and location of the friction layer and a proper preload for this motor have been determined. Almost all of the motor’s mechanical capacities, such as rotational speed, torque, and deformation, can be obtained by simulations in ADINA, which have good agreement with experimental results.

A Rotary Traveling Wave Ultrasonic Motor With Four Groups of Nested PZT Ceramics: Design and Performance Evaluation.

This study proposes a rotary traveling wave ultrasonic motor utilizing the B (0, 5) axial bending mode of a ring-shaped stator. The proposed motor had a compact structure as only four groups of piezoelectric (PZT) ceramics were nested into the stator to produce a bending traveling wave, a new design method was proposed utilized less PZT ceramics to reduce the volume and to improve the mechanical output characteristics. The operating principle of the proposed motor was illustrated. The finite element analysis was performed to obtain the vibration modes and the motion trajectories of the stator. A prototype was manufactured to validate the operating principle. The two standing waves and the motion trajectories of the driving tips were measured. The results denoted that this motor obtained an output speed of 53.86 r/min under a preload of 0.69 N when the frequency and voltage were 24.86 kHz and 250 Vp-p, the maximum stall torque was tested as about [Formula: see text] under the preload of 3.14 N. Finally, this study was compared with a previous design and it was found that the volume was reduced markedly; furthermore, the no-load speed, the efficiency, the torque density and the power density were improved significantly.

Design of Travelling-Wave Rotating Ultrasonic Motor under High Overload Environments: Impact Dynamics Simulation and Experimental Validation

Nowadays, piezoelectric actuators are widely used, but are rarely applied in high overload environments due to th difficulty implementing them. Traveling wave rotary ultrasonic motors (TRUMs) have the characteristics of variable structure and are insensitive to overload, endowing them with the potential ability of high overload resistance. In this study, four TRUMs with different rotor structures are designed to work under the high-impact acceleration of 10,000 g through modifying the rotors with a designed slotted disc spring. The dynamics model is established, the impact process is simulated, and the results are analyzed successively. The high-impact test, deformation measurement and performance test of the motors are carried out to verify the modification. The results show that performance of the TRUMs with a disc spring declines much less than those without a disc spring after the high-impact test. The TRUM-4 with the modified rotor and disc spring has the best performance, the speed of which decreased only 1.6% at the torque of 0.15 N m, and it is considered to be capable of withstanding the high acceleration of 10,000 g. This work is significance for guiding the ultrasonic motors’ optimization to expand their application in high-overload environments.

Design and Experiment of a Large-Aperture Hollow Traveling Wave Ultrasonic Motor with Low Speed and High Torque

To realize applications involving low speed and high torque in the high-performance actuator industry, especially in the aerospace field, we propose a novel 70H traveling wave rotary ultrasonic motor (TRUM) with an outer diameter of 70 mm and an aperture ratio of 53% (the ratio between the aperture and outer diameter). The power transmission mechanism between the stator and the rotor is analyzed, and a method for realizing low-speed–high-torque characteristics of TRUMs is proposed. ANSYS software is used to simulate the modal parameters of the stator, and the ratio β between the normal amplitude and the tangential vibration velocity of the stator is proposed. The larger the value of β, the lower the speed and the higher the torque. Furthermore, two prototype motors are fabricated, namely, 70HA and 70HB. Compared with 70HA, the maximum no-load speed of the improved 70HB (50 rpm) is decreased by 23.1% and the maximum stall torque (2.4 N∙m) is increased by 100%. Besides this, with a smaller mass of 210 g and a higher torque density of 11.43 N∙m/kg, 70HB has fundamentally different mechanical characteristics.

Dynamic preload control of traveling wave rotary ultrasonic motors for energy efficient operation

Ultrasonic motors (USM) have great potential to become the actuators of the next generation. However, the current control schemes of USM are still suffering from some shortcomings including limitation of output speed and torque range, and excessive heat generation. Driving schemes based solely on frequency control suffer from reduced efficiencies across most of its operation band due to having a single optimum driving frequency around resonance. In this paper, the effect of preload on USM driving characteristics was demonstrated and it was clarified that preload can affect the driving efficiency, resonance frequency, and output power range. Dynamic preload control has, thus, been proposed as a supplementary controller besides frequency control to enhance the USM performance. The results show that compared to static preload, dynamic preload can expand the output power range of USM (up to 5 W) while keeping a maximum driving efficiency (up to 22%).