Pruittikorn Smithmaitrie

Design and performance testing of an ultrasonic linear motor with dual piezoelectric actuators

In this work, design and performance testing of an ultrasonic linear motor with dual piezoelectric actuator patches are studied. The motor system consists of a linear stator, a pre-load weight, and two piezoelectric actuator patches. The piezoelectric actuators are bonded with the linear elastic stator at specific locations. The stator generates propagating waves when the piezoelectric actuators are subjected to harmonic excitations. Vibration characteristics of the linear stator are analyzed and compared with finite element and experimental results. The analytical, finite element, and experimental results show agreement. In the experiments, performance of the ultrasonic linear motor is tested. Relationships between velocity and pre-load weight, velocity and applied voltage, driving force and applied voltage, and velocity and driving force are reported. The design of the dual piezoelectric actuators yields a simpler structure with a smaller number of actuators and lower stator stiffness compared with a conventional design of an ultrasonic linear motor with fully laminated piezoelectric actuators.

Touching force response of the piezoelectric Braille cell

Purpose. The objective of this research is to investigate dynamic responses of the piezoelectric Braille cell when it is subjected to both electrical signal and touching force. Method. Physical behavior of the piezoelectric actuator inside the piezoelectric Braille cell is analyzed. The mathematical model of the piezoelectric Braille system is presented. Then, data of visually impaired people using a Braille Note is studied as design information and a reference input for calculation of the piezoelectric Braille response under the touching force. Results. The results show dynamic responses of the piezoelectric Braille cell. The designed piezoelectric bimorph has a settling time of 0.15 second. The relationship between the Braille dot height and applied voltage is linear. The behavior of the piezoelectric Braille dot when it is touched during operation shows that the dot height is decreased as the force increases. Conclusions. The result provides understanding of the piezoelectric Braille cell behavior under both touching force and electrical excitation simultaneously. This is the important issue for the design and development of piezoelectric Braille cells in senses of controlling Braille dot displacement or force-feedback in the future.

Dual piezoelecttic actuators for the traveling wave ultrasonic linear motor

The effect of a dual piezoelectric actuators ultrasonic linear motor is studied in this research. The two piezoelectric actuators are bonded with a linear elastic stator. The stator generates the traveling wave when the actuators are subjected to the harmonic excitations. Vibration characteristics of the linear stator are determined by using the finite element analysis, i.e., modal, harmonic and transient responses. In the experiment, the motor characteristics are tested, i.e., the maximum velocity, operating frequency and applied voltage. In addition, the relationship between the pre-load and velocity of the motor is reported. The result shows that the maximum velocity of the motor occurs at a specific per-load. The comparison of the operating frequency and harmonic response shows well agreement between the finite element and experimental results.

Characteristics of NR/CB Composites: Preparation Methods and Correlations of Electrical and Mechanical Properties

This work aims to correlate the electrical conductivity and mechanical properties of binary composites made of natural rubber (NR) and carbon black (CB). The samples were prepared using both a wet and dry mixing method before making the composites with a conventional rubber vulcanization process. The dry-mixing method was found to achieve higher electrical conductivity than the wet-mixing method. The composite made by efficient vulcanization (EV) had lower compression set than the composite made by conventional vulcanization (CV) and the compression set increased with an increase of CB. The highest tensile strength of the composite was found at CB content of 20 phr. The percolation threshold concentration of the binary composite was observed at 10 phr CB. Electrical conductivity of the composite depended on sample thickness where thinner samples had higher conductivity than the thick sample.

Validation of the Finite Element Model and Vibration Characteristic of the Piezoelectric Head Gimbal Assembly

The dual-stage head gimbal assembly of the hard disk drive utilizes the piezoelectric actuator to supplement the voice coil motor for the precision head positioning. Vibration characteristic of the head gimbal assembly system is analyzed by using the finite element method. The modal characteristic of the piezoelectric head gimbal assembly is measured by the laser doppler vibrometer and compared with the finite element result to validate the finite element model. The natural frequencies and vibration mode shapes are determined via the frequency response functions by measuring the system response at the side of the head slider and the top of the load beam. The crucial vibration modes that may cause the off-track positioning of the read/write head are reported. The comparison of natural frequencies and mode shapes show agreement of the finite element model and experiment testing.

Wave propagations of curvilinear motors driven by partially laminated piezoelectric actuators

A piezoelectric arc stator is the key component delivering driving actions to an ultrasonic curvilinear motor. The arc stator drives the rotor along the arc structure to any specific angular position. Usually conventional stators in ultrasonic motors are fully bounded with piezoelectric patch actuators. To reduce production costs while maintaining similar driving characteristics, an arc stator partially bonded with piezoelectric actuators is proposed and its dynamic characteristics are analyzed in this study. The effect of actuator locations on the wave propagation is investigated. Both analytical and finite element results demonstrate similar dynamic responses. That is, the response of the wave propagation depends on specific locations of piezoelectric actuators. One of the two configurations investigated shows that the partially laminated piezoelectric actuator pattern can also generate rather steady traveling waves on the stator with consistent wave amplitude. This implies that the partially laminated actuator technique could be an alternative actuator pattern to the fully laminated actuators in the design of ultrasonic curvilinear motors or other finite-length ultrasonic motors.

Harmonic Wave Propagation of Ultrasonic Arc Stators

A piezoelectric curvilinear arc stator designed for an ultrasonic curvilinear motor is studied in this research. Design of piezoelectric curvilinear arc stator is proposed and its governing equations and vibration behavior are investigated. Then, analysis of forced vibration response or driving characteristics to harmonic excitations in the modal domain is conducted. Finite element modeling and analysis of the arc stator are also discussed. Analytical results of free vibration characteristics are compared favorably with the finite element results. Harmonic analyses of the three finite element models reveal changes of dynamic behaviors of three models and also imply operating frequencies with significant traveling wave component. Study of mathematical and finite element simulation results suggests that stable traveling waves can be generated to drive a motor on the proposed curvilinear arc stator system.© 2003 ASME

Micro-Control Actions of Actuator Patches Laminated on Hemispherical Shells

Spherical shell-type structures and components appear in many engineering systems, such as radar domes, pressure vessels, storage tanks, etc. This study is to evaluate the micro-control actions and distributed control effectiveness of segmented actuator patches laminated on hemispheric shells. Mathematical models and governing equations of the hemispheric shells laminated with distributed actuator patches are presented first, followed by formulations of distributed control forces and micro-control actions including meridional/circumferential membrane and bending control components. Due to difficulties in analytical solution procedures, assumed mode shape functions based on the bending approximation theory are used in the modal control force expressions and analyses. Spatially distributed electromechanical actuation characteristics resulting from various meridional and circumferential actions are evaluated. Distributed control forces, patch sizes, actuator locations, micro-control actions, and normalized control authorities of a free-floating hemispheric shell are analyzed in a case study. Parametric analysis indicates that 1) the control forces and membrane/bending components are mode and location dependent and 2) the meridional/circumferential membrane control actions dominate the overall control effect.Copyright

Micro-Signals and Modal Potentials of Nonlinear Deep and Shallow Conical Shells

Conventional sensors, such as proximeters and accelerometers, are add-on devices usually adding additional weights to structures and machines. Health monitoring of flexible structures by electroactive smart materials has been investigated over the years. Thin-film piezoelectric material, e.g., polyvinylidene fluoride (PVDF) polymeric material, is a lightweight and dynamic sensitive material appearing to be a perfect candidate in monitoring structure’s dynamic state and health status of flexible shell structures with complex geometries. The complexity of shell structures has thwarted the progress in studying the distributed sensing of shell structures. Linear distributed sensing of various structures have been studied, like beam, plate, cylindrical shell, conical shell, spherical shell, paraboloidal shell and toroidal shell. However, distributed sensing control of nonlinear shell structures has not been carried out rigorously. This study is to present the microscopic signals, modal voltages and distributed micro-sensing components of truncated nonlinear conical shells laminated with distributed infinitesimal piezoelectric neurons. Signal generation of distributed neuron sensors laminated on conical shells is defined first. The dynamic signal of truncated nonlinear conical shell consists of microscopic linear and nonlinear membrane strain components and linear bending strain component based on the von Karman geometric nonlinearity. Micro-signals, modal voltages and distributed sensing components of two different truncated nonlinear conical shells are investigated and their sensitivities discussed.Copyright

Development and Validation of 3D Finite Element Models for Prediction of Orthodontic Tooth Movement

Objectives The aim of this study was to develop and validate three-dimensional (3D) finite element modeling for prediction of orthodontic tooth movement. Materials and Methods Two orthodontic patients were enrolled in this study. Computed tomography (CT) was captured 2 times. The first time was at T0 immediately before canine retraction. The second time was at T4 precisely at 4 months after canine retraction. Alginate impressions were taken at 1 month intervals (T0–T4) and scanned using a digital scanner. CT data and scanned models were used to construct 3D models. The two measured parameters were clinical tooth movement and calculated stress at three points on the canine root. The calculated stress was determined by the finite element method (FEM). The clinical tooth movement was measured from the differences in the measurement points on the superimposed model. Data from the first patient were used to analyze the tooth movement pattern and develop a mathematical formula for the second patient. Calculated orthodontic tooth movement of the second patient was compared to the clinical outcome. Results Differences between the calculated tooth movement and clinical tooth movement ranged from 0.003 to 0.085 mm or 0.36 to 8.96%. The calculated tooth movement and clinical tooth movement at all reference points of all time periods appeared at a similar level. Differences between the calculated and clinical tooth movements were less than 0.1 mm. Conclusion Three-dimensional FEM simulation of orthodontic tooth movement was achieved by combining data from the CT and digital model. The outcome of the tooth movement obtained from FEM was found to be similar to the actual clinical tooth movement.