Traveling Wave Ultrasonic Motor Research Articles

Neural Network Based Modeling and Predictive Position Control of Traveling Wave Ultrasonic Motor Using Chaotic Genetic Algorithm

Traveling wave ultrasonic motors (TWUSMs) possess heavy nonlinearities and load-dependent characteristics such as dead-zone. Therefore, modeling and controlling of TWUSMs are difficult and challenging tasks. In this paper, a Hammerstein model is proposed for rotary TWUSM (RTWUSM) which is proper for control purposes. This model is constructed using the chaotic genetic algorithm (CGA) and radial basis function neural network (RBFNN). Then, Model Predictive Controller (MPC) with online CGA optimizer is applied based on the presented model. Simulation results and their validation with the data derived from experiments demonstrate the effectiveness of the proposed model and controller.

An Ultrasonic Motor Precision Adjustable Speed Scheme Study and Analysis

In this paper, the traveling wave ultrasonic motor speed regulation method, such as voltage regulators, and phase modulation characteristics，are detailed studied. Comparing the advantages and disadvantages of each, the paper put forward the reversing pulse width adjustment scheme. Experiments show that the reversing pulse width adjustment method is a good speed regulation method, the dynamic, wide speed range and good linearity governor.

Chaotic operation and chaos control of travelling wave ultrasonic motor

The travelling wave ultrasonic motor, which is a nonlinear dynamic system, has complex chaotic phenomenon with some certain choices of system parameters and external inputs, and its chaotic characteristics have not been studied until now. In this paper, the preliminary study of the chaos phenomenon in ultrasonic motor driving system has been done. The experiment of speed closed-loop control is designed to obtain several groups of time sampling data sequence of the amplitude of driving voltage, and phase-space reconstruction is used to analyze the chaos characteristics of these time sequences. The largest Lyapunov index is calculated and the result is positive, which shows that the travelling wave ultrasonic motor has chaotic characteristics in a certain working condition Then, the nonlinear characteristics of travelling wave ultrasonic motor are analyzed which includes Lyapunov exponent map, the bifurcation diagram and the locus of voltage relative to speed based on the nonlinear chaos model of a travelling wave ultrasonic motor. After that, two kinds of adaptive delay feedback controllers are designed in this paper to control and suppress chaos in USM speed control system. Simulation results show that the method can control unstable periodic orbits, suppress chaos in USM control system. Proportion-delayed feedback controller was designed following and arithmetic of fuzzy logic was used to adaptively adjust the delay time online. Simulation results show that this method could fast and effectively change the chaos movement into periodic or fixed-point movement and make the system enter into stable state from chaos state. Finally the chaos behavior was controlled.

2A2-D12 楕円運動の観察による超音波モータのトルクモデルの構築(アクチュエータの機構と制御(2))

We propose modeling of the torque generated by a travelling wave ultrasonic motor using a high-speed camera with microscope (high-speed microscope) that can measure the ultrasonic vibration. Such modeling approach is useful for design of the motor dimensions and control of the motor output such as the rotational speed and torque. In this paper, we build a mechanical model with the amplitude of the elliptical motion to predict the motor torque. The high-speed microscope show the transient response of the elliptical motion and the resulting behavior determines the model parameters. The relation between the torque model and the experimental torque is examined by modulating the applied AC voltages.

Desing And Implementation Of A Digitally Controlled Compact Speed Driver For Travelling Wave Ultrasonic Motor

In this paper, a compact size digitally controlled speed driver for travelling wave ultrasonic motor was designed and implemented. Although the driver system is light in weight, simple, small in size, it is possible to enter speed and direction digitally as well as tracking the real motor speed, voltage and current on an LCD. The implemented system was tested in a laboratory for different speed and load cases and obtained results are presented.

Effect of Rotor Vibration on the Driving Characteristics of a Travelling Wave Ultrasonic Motor

We theoretically investigate the driving mechanism of a travelling wave ultrasonic motor that consists of a rotor and a stator, in consideration of the rotor vibration. As a result, we can make clear the inverse rotation phenomenon of the ultrasonic motor that could not be analyzed out of consideration of its vibration. And also, it is found that the driving characteristics are classified into six patterns due to the rotor vibration and that, in the case that the phase of the rotor vibration is opposite to that of the stator, the driving force becomes generally greater than in the case of the same phase. Furthermore, it is experimentally confirmed that, in the case of same phase, the rotating direction is normal ( opposite to a travelling wave direction ) if the amplitude of the rotor vibration is smaller than that of the stator.

Mode-splitting and quasi-degeneracies in circular plate vibration problems: The example of free vibrations of the stator of a traveling wave ultrasonic motor

In systems with rotational symmetry, bending modes occur in doubly-degenerate pairs with two independent vibration modes for each repeated natural frequency. In circular plates, the standing waves of two such degenerate bending modes can be superposed with a 1/4 period separation in time to yield a traveling wave response. This is the principle of a traveling wave ultrasonic motor (TWUM), in which a traveling bending wave in a stator drives the rotor through a friction contact. The stator contains teeth to increase the speed at the contact region, and these affect the rotational symmetry of the plate. When systems with rotational symmetry are modified either in their geometry, or by spatially varying their properties or boundary conditions, some mode-pairs split into singlet modes having distinct frequencies. In addition, coupling between some pairs of distinct unperturbed modes also causes quasi-degeneracies in the perturbed modes, which leads their frequency curves to approach and veer away in some regions of the parameter space. This paper discusses the effects of tooth geometry on the behavior of plate modes under free vibration. It investigates mode splitting and quasi-degeneracies and derives analytic expressions to predict these phenomena, using variational methods and a degenerate perturbation scheme for the solution to the plate’s discrete eigenvalue problem; these expressions are confirmed by solving the discrete eigenvalue problem of the plate with teeth.

Non-linear Generalized Predictive Control of Traveling-wave Ultrasonic Motor

Based on the experimental data of an ultrasonic motor's dynamic response, the non-linear Hammerstein model of an ultrasonic motor driving system is obtained by using particle swarm optimization. This model uses motor-driven frequency as input and rotating speed as output. As such, the main characteristics of nonlinearity in the ultrasonic motor operation process can better be expressed with a relatively simple form and a kind of feasible modeling method for model identification of ultrasonic motor system is proposed. Based on this Hammerstein model, the self-tuning nonlinear generalized predictive speed control strategy of an ultrasonic motor is proposed and the tuning method of the controller's parameters is also discussed in detail. This control strategy utilizes the roll forecasting, optimization and online self-tuning methods to deal with the nonlinearity of the ultrasonic motor. The experiments with a variety of disturbances indicate the efficiency and robustness of the proposed strategy.

A rotary ultrasonic motor using radial bending mode of ring with nested PZT excitation

This study presents and verifies a new idea for constructing a rotary traveling wave ultrasonic motor (USM) that uses the radial bending mode of a ring. In the new design, 20 trapezoid cross section slots are cut symmetrically in the outer surface of a thick duralumin alloy ring, where 20 PZT stacks are nested. In each slot, two wedging blocks are set between the PZT stack and the two sides of the slot respectively to apply preloading on the PZT ceramics. Two radial bending modes of the stator that have a phase difference of a quarter wavelength on space are generated by using the d33 operating mode of the PZT elements, and then a flexural traveling wave is formed by the superimposing of two standing waves whose amplitudes are equal and phases are different by 90° temporally. Two conical rotors are pressed to each end of the ring type stator by a coiled spring. The finite element method (FEM) simulation is developed to validate the feasibility of the proposed motor. The maximal speed and torque of the prototype are tested to be 126 r/min and 0.8 N·m, respectively.

Integrated thin-film piezoelectric traveling wave ultrasonic motors

An integrated approach to the fabrication of thin-film piezoelectric traveling wave ultrasonic motors at the mm-scale is being developed for low power, high torque motors for small scale robotics, biomedical, and sensing applications. This paper describes the realization of ultrasonic motor stators ranging in diameter from 1 to 3mm using wafer scale MEMS fabrication techniques with lead zirconate titanate (PZT) thin films. Using laser Doppler vibrometry (LDV), controlled traveling waves were demonstrated in the bulk silicon elastic medium of the stator and the standing wave behavior was characterized for control purposes. Furthermore, the resonant modes of the fabricated stators were modeled using finite element models, and experimental results agree well with this analysis.

Analyses of the temperature field of traveling-wave rotary ultrasonic motors

In this paper, the transient and steady-state temperature field of a traveling-wave rotary ultrasonic motor is analyzed by the finite element method, based on a theoretical model of power loss of this motor in rated operation. Using this model, the temperature field of this motor is calculated and the effects of the heat conductivity of friction material, motor size, ambient temperature, and pressure on the temperature field are estimated. The calculated temperature distribution and transient temperature change agree with the experimental results. The variation of heat conductivity of the friction material has little effect on the minimum temperature in the motor but this variation seriously affects the maximum temperature in the motor when the heat conductivity of the friction material is lower than 0.5 W/(m°C). Two indices are defined to express the non-uniformity of temperature field and how quickly the temperature field reaches its steady state for traveling-wave ultrasonic motors of different sizes. It is found that traveling-wave ultrasonic motors with different sizes have different nonuniformity of temperature field and take different amounts of time to reach thermal steady state. The maximum temperature rise is lower when the ambient temperature is higher; the maximum temperature increases as the vacuum degree increases and it is not affected by the vacuum degree when the vacuum degree is too high (<10(-3) Pa).

Compound Speed Control of Ultrasonic Motor Using Two Variables

In order to obtain more stable speed response, this paper designs a compound speed controller for travelling wave ultrasonic motor. The controller uses two variables, frequency and voltage amplitude, as the controlled variables. Among them, the frequency controller finishes the correction of larger speed error, and the voltage amplitude controller is used to accomplish the fine-tuning of speed error. The problems such as the jumping phenomenon in speed response, and saturation of voltage amplitude, are solved by this control strategy. Experiments show that, the control strategy is effective, and the speed control response is good.

Start Control of Ultrasonic Motor Based on Neural Network

It is very hard for the traveling wave ultrasonic motor to start directly with high speed, because of their special running mechanism and the unique features. To solve this problem and realize the uitrasonic motor’s high-speed start control, speed controller with on-line self-tuning parameters is designed. Neural network is used to realize the online adjustment of controller’s parameters, to agree with the different starting request of different speed references, and make best use of motor’s ability. The experiments indicated that the motor start fast and accurately, the control algorithm is effective and reliable.

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.

Modeling and Compensation of the Internal Friction Torque of a Travelling Wave Ultrasonic Motor.

This paper deals with the control and experimentation of a one-degree-of-freedom haptic stick, actuated by a travelling wave ultrasonic motor. This type of actuator has many interesting properties such as low-speed operation capabilities and a high torque-to-weight ratio, making it appropriate for haptic applications. However, the motor used in this application displays nonlinear behavior due to the necessary contact between its rotor and stator. Moreover, due to its energy conversion process, the torque applied to the end-effector is not a straightforward function of the supply current or voltage. This is why a force-feedback control strategy is presented, which includes an online parameter estimator. Experimental runs are then presented to examine the fidelity of the interface.

Rigid Contact Model of Ultrasonic Motor Based on Finite Element Method

Rigid contact model of rotor/stator in ring type traveling wave ultrasonic motor without frictional material based on finite element method is proposed in this paper. First, the vibration of the stator is analyzed. Next, the rigid contact model is simulated by finite element method. Subsequently, the contact mechanism of the rotor/stator as well as performance of the ultrasonic motor is studied, and the performance of motors with two different kinds of rotor is compared. It is indicated that contact length of the rotor/stator along circumferential direction decreases from the outer to the inner edge and the stall torque increases and no-load speed decreases with preload force increasing. The result is identified as being useful in designing and analyzing the ultrasonic motor.

Friction Material Optimization Design for the Traveling Wave Ultrasonic Motor with Stator Contact Layer

Traveling wave ultrasonic motor (TWUSM) is driven by friction force between stator and rotor. Then friction material properties are very important on the output characteristics of TWUSM. Under the guidance of an optimization design principle of friction material, a kind of Ekonol composite friction material (EK2) was developed by modification study, orthogonal experimental design and regression analysis. Through the comparison between EK2 and other common friction materials, it was proved that the TWUSM with EK2 can get better running stability, higher output torque and longer lifetime. Therefore, EK2 is a good friction material which can satisfy the practical running needs of TWUSM.

Tribological Properties of Ekonol Composites Friction Material in Traveling Ware Ultrasonic Motor

Traveling wave ultrasonic motor (TWUSM) is driven by friction force between stator and rotor. As the friction materials of contact layer in traveling wave ultrasonic motor(TWUSM), tribological properties of Ekonol composites(EK2) have important effects on motor driving characteristics and service life. Then EK2 was stuck on the stator tooth of 40 type disc-shape TWUSM. Under different driven mode and friction combination, tribological properties of EK2 was tested，and the wear morphologies of EK2 surfaces are observed by SEM. Results show that there are ultrasonic antifriction phenomenon in stator/rotor contact interface under ultrasonic drive. Ultrasonic fatigue is the main wear mechanism of contact layer. When Ek2 combine with Cu rotor， contact layer can obtain bigger friction coefficient, higher output torque and better wear properties. Then Ek2 and Cu rotor is a good friction combination which can satisfy the actual running needs of TWUSM.

The Effects of Friction Coefficient on Driving Performance in Traveling Wave Ultrasonic Motor

Traveling wave ultrasonic motor (TWUSM) is driven by friction force between stator and rotor, so friction coefficient is an important parameter of contact interface. In fact, there have mutual influence and restriction in various parameters of contact interface. For a comprehensive study on friction coefficient, the interaction between friction coefficient and other parameters should be considered. Base on a new contact model with visco-elastic stator contact layer of TWUSM，coupling effects of two parameters on motor output characteristics were simulated with MATLAB. According to the simulation results, a design principle of friction coefficient was present. A kind of Ekonol composite friction material (EK2) was developed under the guidance of this principle. Comparing with other common friction material of TWUSM, it was proved that motor with EK2 can get better running stability, higher output torque and longer lifetime. Therefore, EK2 is a good friction material which can satisfy the actual running needs of TWUSM.

Research on Driving Technique for Traveling Wave Ultrasonic Motor

Considering the special working principle and the special requirements of driving power supply for traveling wave ultrasonic motors, its driving techniques about switching power supply are outlined in detail based on analyzing the electrical model, subsequently, a review technique about DDS and its development is provided .Finally, some key problems, such as improvement of driving system,system miniaturization and direct digital synthesizer are discussed, some of their solving schemes and the direction of studies on driving power supply are put forward.