Ultrasonic Motor Research Articles

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.

Efficiency Model for Traveling Wave-Type Ultrasonic Motors Based on Contact Variables and Preload

The contact interface variables are difficult to measure for an ultrasonic motor. When the ultrasonic motor works under different preloads, the error between the traditional efficiency model and the real output is quite large. In order to solve these two problems, we propose a novel efficiency model. It takes measured preload and the feedback voltage data as the input, which may offer better accuracy and on-line ability. Firstly, the effect of the preload on the drive characteristics is investigated, and the relationship between preload and the change in motor energy input is analyzed. Secondly, a contact model based on measured preload and feedback voltage is built, providing a more accurate description of the contact variables. Finally, an efficiency model was developed with a new composite stator structure. A preload test rig for a 60 mm ultrasonic motor is built and real operating conditions are measured. The results show that the correlation coefficient of the present model is 0.991, larger than 0.925 of the conventional model. The proposed model is more consistent with the real working conditions for the motor.

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.

Preload Optimization Method for Traveling-Wave Rotary Ultrasonic Motor

Preload optimization is very important for ultrasonic motors’ design and application. In this paper, a novel method for a traveling-wave rotary ultrasonic motor is proposed. Firstly, based on linear regression and the analytic hierarchy process (AHP), the mapping between the drive characteristics, mechanical characteristics, speed stability, and preload of the traveling-wave-type rotary ultrasonic motor was established. Then, the characteristic curves of stalling torque, no-load speed, maximum efficiency, and speed stability with the change of preload method were measured with a new test platform. Finally, three traveling-wave rotary ultrasonic motors with optimized preload were used in a cooperative manipulator for validation. The experimental results showed that when the preload was optimized from 200 N to 310 N, the stalling torque of the motor increased by 20.7%, the maximum efficiency increased by 15.3%, the standard deviation of the speed decreased by 53.8%, and the no-load speed decreased by 5.5%. Therefore, it can be seen that the new preload optimization approach can significantly improve the performance indexes of ultrasonic motors and meet the practical requirements of direct-drive cooperative manipulators in engineering applications. The new preload optimization method offers advantages in motor output performance compared to conventional methods.

Thermal stability of the electromechanical properties in acceptor-doped and composite-hardened (Na1/2Bi1/2)TiO3–BaTiO3 ferroelectrics

Lead-free relaxor ferroelectrics are promising candidates for next-generation piezoelectric high-power devices, such as ultrasonic motors, transformers, and therapeutic ultrasonics. These applications require hard ferroelectrics with a broad operating temperature range. Recently, acceptor Zn2+ doping and composite formation with ZnO were proposed to induce hardening in Na1/2Bi1/2TiO3–BaTiO3 and simultaneously increase the depolarization temperature. Here, these two strategies are compared by studying the temperature dependence of electromechanical properties, ferroelectric loops, and nonlinear polarization harmonics. In the modified compositions, depolarization is associated with the shift of the ferroelectric-to-relaxor transition to higher temperatures, while the depolarization onset remains unchanged. This leads to broadening rather than translation of the depolarization region, accompanied by decoupling of the piezoelectric d33 and d31 coefficients. The temperature-dependent electromechanical response is stable for composites, while the Zn2+-doped samples exhibit strong temperature dependence akin to acceptor-doped Pb(Zr,Ti)O3. The thermal evolution of electromechanical coefficients is not related to the thermally induced decrease of the coercive/internal bias fields but instead to the ratio of irreversible-to-reversible nonlinear dynamics arising from displacements of domain walls or similar interfaces. The results demonstrate that mechanical stress-based hardening in the composites exhibits superior thermal stability, which can considerably improve the operational range of lead-free piezoelectric materials.

Novel piezoelectric crawling robot with multiple degrees of freedom

Traditional ultrasonic motors can usually produce either linear or rotational motion. Piezoelectrically driven structures with multiple degrees of freedom require two or more ultrasonic motors, and the manufacturing process is associated with some problems related to their complex structure and difficult control. This study proposes a new structure of a multi-degree-of-freedom piezoelectric crawling robot. Four modes are selected as the working modes, and mode superposition is used to produce the linear and rotational motion of the robot. This structure is designed based on a combination of size and topological optimization to adjust the frequency response consistency of the motor. The performance of the motor was tested on surfaces with different roughnesses. Its performance on the desk surface was the best. Its maximum linear speed is 37 mm/s, and its maximum rotational speed is 6.28 rad/s. The performance tests were performed under different loads. The linear motion speed of the motor reached its maximum value at 29.2 kHz, and the rotational motion speed reached its maximum value at 32.1 kHz.

Data-Driven Tuning of PID Controlled Piezoelectric Ultrasonic Motor

Ultrasonic motors employ resonance to amplify the vibrations of piezoelectric actuator, offering precise positioning and relatively long travel distances and making them ideal for robotic, optical, metrology and medical applications. As operating in resonance and force transfer through friction lead to nonlinear characteristics like creep and hysteresis, it is difficult to apply model-based control, so data-driven control offers a good alternative. Data-driven techniques are used here for iterative feedback tuning of a proportional integral derivative (PID) controller parameters and comparing between different motor driving techniques, single source and dual source dual frequency (DSDF). The controller and stage system used are both produced by the company Physik Instrumente GmbH, where a PID controller is tuned with the help of four search methods: grid search, Luus–Jaakola method, genetic algorithm, and a new hybrid method developed that combines elements of grid search and Luus–Jaakola method. The latter method was found to be quick to converge and produced consistent result, similar to the Luus–Jaakola method. Genetic Algorithm was much slower and produced sub optimal results. The grid search has also proven the DSDF driving method to be robust, less parameter dependent, and produces far less integral position error than the single source driving method.

Engineered hard piezoelectric materials of MnO2 doped PZT-PSN ceramics for sensors applications

ABSTRACT In this study, MnO2-doped 0.96Pb(Zr0.515,Ti0.485)O3-0.04Pb(Sb0.5,Nb0.5)O3 (0.96PZT-0.04PSN) hard piezoelectric ceramics were fabricated by employing a conventional mixed-oxide process. Hard piezoelectric materials are suitable for mechanical device applications such as transducers or piezoelectric ultrasonic motors owing to their high mechanical quality factor. To improve the hard piezoelectric properties, MnO2 was selected and doped into 0.96PZT-0.04PSN ceramics in this study. When MnO2 was introduced into piezoelectric lead zirconate titanate (PZT) ceramics, the resistivity and dielectric permittivity decreased, leading to an increase in the mechanical quality factor. MnO2-doped 0.96PZT-0.04PSN ceramics have a lower piezoelectric charge coefficient and dielectric permittivity compared to those of 0.96PZT-0.04PSN ceramics. However, an enhanced mechanical quality factor of 1600 was obtained for the 0.96PZT-0.04PSN ceramics doped with 0.5 wt% of MnO2. In contrast to other hard piezoelectric materials, MnO2 doped 0.96Pb(Zr0.515,Ti0.485)O3-0.04Pb(Sb0.5,Nb0.5)O3 ceramics have a high Qm value while having an appropriate piezoelectric charge coefficient d33 and electromechanical coupling coefficient kp.

Influence mechanism of surface texture on the output performance of an ultrasonic motor

PurposeThe purpose of this study is to investigate the influence mechanism of different interface component surface textures on the ultrasonic motor (USM) output performance.Design/methodology/approachThe energy transmission mechanism of the traveling-wave ultrasonic motor 60 (TRUM-60) was numerically and experimentally investigated by fabricating dimple textures with different feature types on the friction material and the stator.FindingsTextured friction material can increase the contact range effectively, and thus, can improve the friction characteristics of the interface and the output performance of the TRUM-60. The experimental results verified the expected influence mechanism and demonstrated that the use of either a textured friction material or stator has a very different effect on USM output performance. A textured PI-based friction material improved the TRUM-60 output performance, resulting in a maximum energy conversion efficiency of 57.11%. However, a textured stator degraded the TRUM-60 output performance, resulting in a minimum energy conversion efficiency of only 44.92%.Originality/valueThe results of this study provide a theoretical foundation for improved USM designs with textured interfaces.

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.

Generalized Minimum Variance Iterative Learning Speed Control of Ultrasonic Motor

Generalized Minimum Variance Iterative Learning Speed Control of Ultrasonic Motor

An embedded capacitive sensor for in-situ angular detection of micromotor

An embedded capacitive sensor in traveling wave ultrasonic motor is proposed for angular detection. Equivalent circuit model of the system is well studied that correlation between sensor structure, parasitic parameters and the property of detection signal is found. Sensor structure is optimized with innovate structural design including multi-layer shielding, planar isolation and differential detection design. The signal-to-noise ratio of the detection signal is found up to 40 ​dB and the angular detection accuracy during step motion is less than 0.1°.

Comparison study of bending and three-wave vibration modes for micro ultrasonic motors

Bending and three-wave vibration modes are the fundamental principle of millimeter-scale ultrasonic motors. The question is that which vibration mode is suitable for smaller ultrasonic motors with a scale of 1–2 mm or less. In this study, we fabricate prototype stators capable of generating the two vibration modes in the same structure and compare them in an equitable manner. The stators comprise a bronze cuboid with sides of 1 mm and four piezoelectric plates adhered to the four side surfaces. At the stator’s length ranging from 1 to 2 mm, the prototype motors change their electrical and mechanical characteristics, and examining these characteristics reveal the advantages of selecting the vibration modes. We evaluate the performance of micro ultrasonic motors using the two modes via FEM piezoelectric analyses, impedance measurements, and experiments for measuring motor outputs. The experimental results show that the bending mode is advantageous for generating a higher output at a longer stator with a length of 2 mm. At a shorter length of 1 mm, using the three-wave mode performs a higher efficiency, although the bending mode reduces the output.

Design and characterization of a thin linear ultrasonic motor for miniature focus systems

We present a miniature linear piezoelectric ultrasonic motor with a thin and hollow design, which can serve as an essential component of autofocusing features in next-generation camera modules. It consists of a thin square stator with a hole and an elastic cylindrical slider with a slit. The motor design, in which the slider inserted into the stator hole expands outward, enables a hollow structure for centering a lens and an optimal preload for enhancing the motor thrust force. In this study, we model the relationship between the dimensions and the preload statically to quantify the preload value and clarify the design methodology of the motor. After optimizing the preload empirically, we evaluate the fundamental characteristics experimentally. The stator with a side length of 4.5 mm and a thickness of less than 1 mm provides a thrust force of 12.9 mN that leads to a quick response, which is a requirement of autofocusing. Finally, the motor drive system with visual feedback control is used to demonstrate the positioning of an actual lens group in front of an image sensor to obtain clearer images.

Effect of velocity and interference depth on the tribological properties of alumina sliding with Cu: A molecular dynamics simulation

The friction performance of alumina sliding against copper was studied by molecular dynamics simulation to understand the wear mechanism of ultrasonic motors (USM) from an atomic dimension. Importantly, the influence of velocity and interference depth on the nanotribological properties of Cu-Al2O3 was studied. The simulated results showed that both friction and normal force increased with an increasing velocity and interference depth. Wear rate also increased with an increasing interference depth. The adhesive wear mechanism dominated the wear process of interface. This study will provide a theoretical guidance for exploring the wear mechanism of USM from a nanoscale.

Transfer matrix model and experimental validation for a radial-torsional ultrasonic motor

Traditional traveling-wave rotary ultrasonic motors have been widely used in many applications due to their excellent output performances. However, the structure optimization have be hindered by the specific requirements on the piezoelectric ceramics with complex polarizations and shapes. To address such issues, a compact type ultrasonic motor operating at radial-torsional conversion mode is proposed in this paper, which is simply excited by one ring type piezoelectric wafer with a single polarization. This motor basically consists of one rotor and one disk type stator, which can be divided into an outer ring, four connection beams and an inner ring. A ring type piezoelectric wafer is bonded to the bottom face of the outer ring. Upon an excitation signal at resonance frequency, the proposed motor is able to rotate, driven by the torsional vibration mode of the inner ring converted from the radial vibration mode of the outer ring via the connecting beams An electromechanical model utilizing the transfer matrix method is built to analyze the dynamic behavior of the motor. This transfer matrix model of the system could provide an effective approach for simulating the coupled mechanical and electrical properties. Based on the proposed model, the dynamic process for converting the radial vibration mode into the torsional mode is quantatively assessed. Last, the vibration characteristics of the prototype motor is tested by using a 3D laser Doppler vibrometer and the experimental results are in good agreement with the calculations, confirming the validity of the transfer matrix model and the feasibility of the motor design.

PID-type sliding mode-based adaptive motion control of a 2-DOF piezoelectric ultrasonic motor driven stage

This paper presents a new scheme of adaptive sliding mode control (ASMC) for a piezoelectric ultrasonic motor driven X–Y stage to meet the demand of precision motion tracking while addressing the problems of unknown nonlinear friction and model uncertainties. The system model with Coulomb friction and unilateral coupling effect is first investigated. Then the controller is designed with adaptive laws synthesized to obtain the unknown model parameters for handling parametric uncertainties and offsetting friction force. The robust control term acts as a high gain feedback control to make the output track the desired trajectory fast for guaranteed robust performance. Based on a PID-type sliding mode, the control scheme has a simple structure to be implemented and the control parameters can be easily tuned. Theoretical stability analysis of the proposed novel ASMC is accomplished using a Lyapunov framework. Furthermore, the proposed control scheme is applied to an X–Y stage and the results prove that the proposed control method is effective in achieving excellent tracking performance.

Robust ultra-precision motion control of linear ultrasonic motors: A combined ADRC-Luenberger observer approach

This work introduces an output feedback Active Disturbance Rejection Control scheme applied to the nanoposition control of uncertain Linear Ultrasonic Motors. The proposed algorithm, which is termed as the ADRC-Luenberger Observer Controller (ADRC-LOC), is composed of a Proportional Derivative controller plus a Disturbance Observer, the latter producing an estimate of the unknown disturbances affecting the ultrasonic motor to counteract their effects. A Luenberger Observer, which is designed using the disturbance-free model of the ultrasonic motor, produces velocity and acceleration estimates from position measurements. The velocity estimate is used in the derivative action of the Proportional Derivative controller whereas the acceleration estimate feeds the Disturbance Observer. The stability analysis of the closed-loop system shows that its solutions are Uniformly Ultimately Bounded. The effectiveness of the proposed approach is tested by means of real-time experiments. These outcomes show that the position errors obtained with the proposed ADRC-LOC are in the range of 50–100 nm. A recently proposed Sliding Mode Controller is also tested for comparison purposes. The proposed approach may be applied to linear uncertain perturbed systems of arbitrary order.

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.

Middle-low temperature sintering and piezoelectric properties of CuO and Bi2O3 doped PMS-PZT based ceramics for ultrasonic motors

A ternary solid-solution piezoelectric ceramic of rare-earth oxides modified 0.03 Pb(Mn1/3Sb2/3)O3-0.97 Pb(Zr0.505Ti0.495)O3 + x wt.% CuO + y wt.% Bi2O3 (PMS-PZT + x wt.% CuO + y wt. % Bi2O3) (x, y = 0–0.2) was successfully prepared via a transient-liquid-phase sintering. Both Cu2+ and Bi3+ were believed to replace the A-site Pb ions and to evidently induce the lattice shrinkage and the distortion decrease. However, the addition of only a small amount of CuO was found to effectively reduce the sintering temperature, sustain good piezoelectric properties and predominant transgranular fracture modes, but obviously increase the average grain size and high-field dielectric loss. Further experimental results indicate that the grain growth of the ceramics was inhibited effectively and the high-field dielectric loss was reduced through CuO and Bi2O3 co-doping. The 0.05 wt% CuO and 0.15 wt% Bi2O3 co-doped PMS-PZT ceramics sintered at 1050 °C exhibit excellent dielectric and piezoelectric properties of d33 = 410 pC/N, kp = 0.62, Qm = 1478, εr = 1550, tan δ = 0.8% (400 V/mm) and Tc = 330 °C. The experimental results can provide a solid fundament for multilayer piezoelectric actuating devices.