Jongkyu Park

Hysteresis compensation of piezoelectric actuators: the modified Rayleigh model.

In this study, we develop a novel modified Rayleigh model for hysteresis compensation in piezoelectric actuators. Piezoelectric actuators suffer from hysteresis, in large drive fields of more than 100 V, which can result in serious displacement errors. The typical phenomenological approach is to use the Rayleigh model; however, this model gives more than 10% difference with experiments at the large electric fields of more than 1kV/mm. Furthermore, there are no studies that apply the Rayleigh model to the compensation of precision actuators, such as stack actuators; it has only been applied in the study of the physical properties of piezoelectric materials. Therefore, we propose a modified Rayleigh model, in which each coefficient is defined differently according to whether the field is increasing or decreasing to account for asymmetry at the high fields. By applying a computer-based control from an inverse form of this modified Rayleigh model, we show that we can compensate for hysteresis to reduce the position error to less than five percent. This model has the merits of reducing complicated fitting procedures and of saving computation time compared to the Preisach model. Specifically, this model cannot only predict the hysteresis curves in all local fields using only one fitting procedure, but also make it possible to control the displacement of various piezo-based actuators without expensive sensors, based on the charge-based model.

Design of an ultrasonic sensor for measuring distance and detecting obstacles.

This paper introduces a novel method for designing the transducer of a highly directional ultrasonic range sensor for detecting obstacles in mobile robot applications. The transducer consists of wave generation, amplification, and radiation sections, and a countermass. The operating principle of this design is based on the parametric array method where the frequency difference between two ultrasonic waves is used to generate a highly directional low-frequency wave with a small aperture. The aim of this study was to design an optimal transducer to generate the two simultaneous longitudinal modes efficiently. We first derived an appropriate mathematical model by combining the continuum model of a bar and countermass with the compatibility condition between a piezoelectric actuator and a linear horn. Then we determined the optimal length of the aluminum horn and the piezoelectric actuator using a finite element method. The proposed sensor exhibited a half-power bandwidth of less than+/-1.3 degrees at 44.8 kHz, a much higher directivity than existing conventional ultrasonic range sensors.

Design of a Piezoelectric Energy-Harvesting Shock Absorber System for a Vehicle

Only ∼20% of a vehicles fuel consumption is used for overcoming air drag force and friction with the road. Vibration energy produced during driving is dissipated by shock absorbers in the vehicle suspension. A new Piezoelectric Energy-Harvesting Shock Absorber (PEHSA) system for vehicles has been developed to act as an energy harvester that converts vibration energy to electrical energy. Cylindrical piezoelectric transducers are combined with the cylinder of the shock absorber to generate electricity from changes in fluid pressure produced by piston vibrations. A multiphysics simulation was performed using COMSOL Multiphysics to determine the characteristics of the PEHSA system.

Design and Fabrication of Three Touch Point Thin Ultrasonic Rotary Motor

A novel structure three touch points thin ultrasonic rotary motor has been proposed to enable the actuator to use in small mobile equipment. A thin stator of simple structure is advantageous to use in tight spaces. Also, three points of contact enables to stable driving. Twelve ceramics plates were attached on upper and bottom side of the metal plate. When three phase alternating current sources are applied to the stator, elliptical displacements are generated at three inner edges of the stator. Modeling of the ultrasonic motor was done and the displacement characteristics were defined by using finite element analysis program. The effectiveness of the proposed design was verified by experiments. Characteristics of the motor such as speed, and input voltage were measured by using the driver and measurement equipment. Maximum displacement was appeared at frequency of minimum impedance. The resonance frequency was inversely proportional to the ceramic length. The maximum speed of 220 [rpm] was obtained at the resonance frequency, 76.4 [kHz]. The speed increase somewhat linearly with increasing applied voltage.

Design and Multi-physics Analysis of Anemovane Using the Piezoelectric Unimorph

We propose and describe an anemovane that can detect wind speed in all directions owing to its sea urchin-like shape. In this design, cantilevers project from the sphere, imitating sea-urchin prickles. When wind hits the cantilevers, the pressure sends a voltage signal through the piezoelectric unimorph bender. The velocity of the wind can then be calculated from this voltage signal. This research describes the theoretical analysis of the piezoelectric unimorph bender and the multi-physics analysis performed by combining the fluid, the solid structure, and the piezoelectric material, and the verification of the optimal design.

Dielectric and Piezoelectric Properties of Ta-modified (K0.53Na0.47)(Nb0.8Ta0.2)O3 Ferroelectric Ceramics

Ta-substituted Na0.53K0.475Nb0.8Ta0.2O3 ceramics were prepared through the solid-state reaction method. The crystallized single phases were confirmed by X-ray diffraction. The temperature dependences of the dielectric and piezoelectric properties were investigated. Ta substitution in Na0.5K0.5NbO3 enhanced the piezoelectric property, and the corresponding piezoelectric coefficient was estimated to be d33 = 160 pC/N. With increasing temperature, the planar electromechanical coupling coefficient (kp ) increased linearly up to the orthorhombic-tetragonal phase-transition temperature (TO-T ) and decreased as the temperature comes closer to the Curie temperature (Tc ).

Design and Analysis of Ultrasonic Motor for Driving Sphere Wheel

In this paper, a new omnidirectional driving system is proposed that is composed of an ultrasonic motor, a sphere wheel, and ball bearings. The sphere wheel is driven by an ultrasonic motor, which is a Λ-type motor developed in the previous research. If the piezo-ceramic plates of the ultrasonic motor vibrate at the resonant frequency, the displacement of the ellipse orbit is generated at a sharp end of Λ-type. Modal analysis and time domain analysis were performed. The proposed omnidirectional driving system was validated by analyzing its motion characteristics.

Design of an ultrasonic motor which has Nib shaped stator

In this study, simple ultrasonic motor of plate type stator was proposed. Stator of the proposed ultrasonic motor was composed of an elastic plate and ceramics. The elastic plate has one tip in the middle. The two ceramics were attached on the side surfaces of the elastic plate. The both polarization directions were directed to the upward outside directions. When two AC voltages which have basically 90 degree phase difference were applied to the two ceramics, elliptical displacements of the stator tips were obtained. FEA simulation(ATILA) was used to analyze elliptical displacement characteristics of the friction line tips depending on the width and thickness of elastic body and ceramic. Optimize the elliptical displacement by synchronizing the two resonant frequencies. Based on the FEA results, one model of motor which showed effective characteristics at contact line was chosen and fabricated. The output characteristics of the prototype motor based on the analysis data were measured. And characteristics of the motor were compared with the simulated results.

Design of a Honeycomb Shaped Piezoelectric Energy Harvester

In this paper, design of a hexagon shape piezoelectric generator was done by using Finite Element Method (FEM) and generating characteristics of the prototype generator were experimented. The generating device was composed of a thin hexagonal steel plate and a frame-shaped hexagonal ceramic which was attached on the steel plate. This structure has a merit to lessen the stress of ceramic when vibration is applied on the center of the plate. The output of the hexagon generator can be improved, because its area is larger than foursquare area when perimeter is same. Also, when array the generators on a surface it can get high efficiency compared with a round shape device, because there is no wasting space. The generator was named as honeycomb shape piezoelectric generator, because merits of this structure are similar to the merits of honeycomb of a bee. Design and analysis of the generator was done by simulating the output characteristics according to the change of parameters by using FEM program. Output characteristics were determined by varying the width, thickness and the number of lamination of the ceramics. The generating characteristics of the fabricated honeycomb shape generator were measured and compared with the FEM results.

Design and fabriction of micro-viscometer using the propagation of acoustic waves in micro-channel

A micro-viscometer for measuring viscosity changes in small amount of liquid in real time is designed and fabricated. The merits of the device are to use minimal liquid and to increase the sensitivity for measuring the viscosity. The micro-viscometer is composed of two chambers connected by several micro-channels. Each chamber has a unimorphic piezoelectric diaphragm for driving and sensing sound waves. The micro-channel plays a role as a waveguide and an attenuator of sound waves. Attenuation of sound wave is a function of the viscosity of the liquid. So, the output voltage of sensor is also changed as the viscosity of liquid is changed. After fabrication through micromachining, the device was tested on several viscous liquids, and then it was demonstrated that the device can play a role of a viscometer with high sensitivity. In this paper, we mainly discuss on the comparison between experimental results and newly simulated results.