Jong-Seok Rho

Analysis of temperature rise for piezoelectric transformer using finite-element method

Analysis of heat problem and temperature field of a piezoelectric transformer, operated at steady-state conditions, is described. The resonance frequency of the transformer is calculated from impedance and electrical gain analysis using a finite-element method. Mechanical displacement and electric potential of the transformer at the calculated resonance frequency are used to calculate the loss distribution of the transformer. Temperature distribution using discretized heat transfer equation is calculated from the obtained losses of the transformer. Properties of the piezoelectric material, dependent on the temperature field, are measured to recalculate the losses, temperature distribution, and new resonance characteristics of the transformer. Iterative method is adopted to recalculate the losses and resonance frequency due to the changes of the material constants from temperature increase. Computed temperature distributions and new resonance characteristics of the transformer at steady-state temperature are verified by comparison with experimental results

Design and characteristic analysis of L1B4 ultrasonic motor considering contact mechanism

Up to the present time, the analysis and design of ultrasonic motors (USMs) have been performed using rough analytic methods or commercial analysis tools without considering the complex contact mechanisms. As a result, it was impossible to achieve an exact analysis and design of a USM. In order to address the problem, we proposed the analysis and design methodology of an L1B4 USM using a three-dimensional finite element method combined with an analytic method that considers complex contact mechanisms in linear operation. This methodology is applicable to many other kinds of USMs which use resonance modes and contact mechanisms. Also, we designed and prototyped the mechanical system and driving circuit of the L1B4 USM, and finally validated the proposed analysis and design methodology by comparing their outcomes with experimental data.

Identification of material constants for piezoelectric transformers by three-dimensional, finite-element method and a design-sensitivity method

In this paper, an inversion scheme for piezoelectric constants of piezoelectric transformers is proposed. The impedance of piezoelectric transducers is calculated using a three-dimensional finite element method. The validity of this is confirmed experimentally. The effects of material coefficients on piezoelectric transformers are investigated numerically. Six material coefficient variables for piezoelectric transformers were selected, and a design sensitivity method was adopted as an inversion scheme. The validity of the proposed method was confirmed by step-up ratio calculations. The proposed method is applied to the analysis of a sample piezoelectric transformer, and its resonance characteristics are obtained by numerically combined equivalent circuit method.

Characteristic analysis and design of a B 14 rotary ultrasonic motor for a robot arm taking the contact mechanism into consideration

The ultrasonic motor (USM) has many merits for use in a robot arm application. Therefore, the disk-type traveling wave B14 rotary ultrasonic motor (RUSM) is proposed in this paper for that application. Up to the present time, the analysis and design of the USM have been almost always performed using rough analytic methods or using commercial analysis tools. As a result, it was impossible to achieve an exact analysis and design of the USM. In order to address this problem, this paper proposes the analysis and design methodology of the B14 RUSM using a numerical method (3-D FEM) combined with an analytic method taking the contact mechanism into consideration in a linear operation. This methodology is applicable to many other kinds of USMs that use similar mechanisms. In addition, the mechanical system and the driving circuit of the B14 RUSM are designed and prototyped. Finally, the proposed analysis and design methodology is validated by comparing its outcomes with the experimental data. Also, the appropriateness of the suggested RUSM for the application of a robot arm was verified

Analysis of ultrasonic linear motor by using finite element method and equivalent circuit

In this paper, the three-dimensional finite element method and construction of an equivalent-circuit for the linear ultrasonic motor, is presented. The validity of the three-dimensional finite element routine in this paper is experimentally confirmed by analyzing the impedance of a piezoelectric transducer. Using this confirmed finite element routine, the impedance and vibration mode of a linear ultrasonic motor are calculated. Elliptical motion of the contact point between vibrator and rail of a linear ultrasonic motor is shown for determination of the contact point. Using the finite element method and analytic equations, characteristics of linear ultrasonic motor, such as thrust force, speed, losses, power and efficiency, are calculated. And the results are confirmed by experiment. Finally, equivalent circuit parameters of the linear ultrasonic motor are obtained by three-dimensional finite element method and analytic equations.

Inversion of piezoelectric material coefficients by using finite element method with Asymptotic Waveform Evaluation

In this paper, a fast inversion scheme for piezoelectric constants of piezoelectric transformer is proposed. The effects of material coefficients on piezoelectric transformers are investigated by using three-dimensional finite element method (FEM) which is confirmed experimentally. A design sensitivity method adopted as an inversion scheme and Asymptotic Waveform Evaluation (AWE) is used for fast frequency sweep.