Jongsuh Lee

Smooth Vibrotactile Flow Generation Using Two Piezoelectric Actuators

This paper proposes a method for generating a smooth directional vibrotactile flow on a thin plate. While actuating two piezoelectric actuators spatially across the plate, temporal sweeping of the input excitation frequency from zero to the first mode of the resonance frequency can smooth the perceived directional vibrotactile flow, as compared to a vibrotactile flow generated by conventional apparent tactile movement and phantom sensation methods. In order to ascertain important factors in the excitation pattern, a user study was conducted for three factors (amplitude (constant versus modulated), frequency (constant versus swept), and ending shape (sharp versus smooth)). The results showed that frequency sweeping in addition to amplitude modulation and smooth ending were the most important factors in smoothing vibrotactile flows. Moreover, an excitation signal with a smooth ending shape was important for generating nonspiky flows at the midpoint. In this study, a vibration isolation design is also proposed in order to substantially decrease the transmission of the actuator vibration to the mockup housing. As such, it is expected that the proposed vibrotactile flow generation method and vibration isolation design may be useful in applications including generating directional information in navigation maps or for identifying callers in mobile devices.This paper proposes a method for generating a smooth directional vibrotactile flow on a thin plate. While actuating two piezoelectric actuators spatially across the plate, temporal sweeping of the input excitation frequency from zero to the first mode of the resonance frequency can smooth the perceived directional vibrotactile flow, as compared to a vibrotactile flow generated by conventional apparent tactile movement and phantom sensation methods. In order to ascertain important factors in the excitation pattern, a user study was conducted for three factors (amplitude (constant versus modulated), frequency (constant versus swept), and ending shape (sharp versus smooth)). The results showed that frequency sweeping in addition to amplitude modulation and smooth ending were the most important factors in smoothing vibrotactile flows. Moreover, an excitation signal with a smooth ending shape was important for generating nonspiky flows at the midpoint. In this study, a vibration isolation design is also proposed in order to substantially decrease the transmission of the actuator vibration to the mockup housing. As such, it is expected that the proposed vibrotactile flow generation method and vibration isolation design may be useful in applications including generating directional information in navigation maps or for identifying callers in mobile devices.

3-D Vibration Measurement Using a Single Laser Scanning Vibrometer by Moving to Three Different Locations

3-D vibration measurement is achieved using a single laser scanning vibrometer (LSV) and laser scanner (LS) by moving them to three arbitrarily different locations from the principle that vibration analysis based on the frequency domain is independent of the vibration signal based on time domain. The proposed system has the same effect as using three sets of LSVs, and has an advantage of reducing equipment costs. Analytical approach of obtaining in-plane and out-of-plane vibration of surface is introduced using geometrical relations between three LSV coordinates and vibrations measured at three different locations. The proposed algorithm is verified by comparing the experimental results obtained by a three-axis accelerometer and a developed optical system with an LSV and an LS combined together.

Enhanced method to reconstruct mode shapes of continuous scanning measurements using the Hilbert Huang transform and the modal analysis method

Generally, it is time consuming to experimentally identify the operating deflection shape or mode shape of a structure. To overcome this problem, the Hilbert Huang transform (HHT) technique has been recently proposed. This technique is used to extract the mode shape from measurements that continuously measure the vibration of a region of interest within a structure using a non-contact laser sensor. In previous research regarding the HHT, two technical processes were needed to obtain the mode shape for each mode. The purpose of this study is to improve and complement our previous research, and for this purpose, a modal analysis approach is adapted without using the two technical processes to obtain an accurate un-damped impulse response of each mode for continuous scanning measurements. In addition, frequency response functions for each type of beam are derived, making it possible to make continuously scanned measurements along a straight profile. In this paper, the technical limitations and drawbacks of the damping compensation technique used in previous research are identified. In addition, the separation of resonant frequency (the Doppler effect) that occurs in continuous scanning measurements and the separation of damping phenomenon are also observed. The proposed method is quantitatively verified by comparing it with the results obtained from a conventional approach to estimate the mode shape with an impulse response.

Damping analysis with respect to rolling speed by analytic solution of a flexible ring model and its frequency response function derivation by modal summation method

In this research, a modal approach has been adopted to analyze the dynamic characteristics of the rolling tire by a ring model. Previously, most of the researchers focused on the changes in natural frequencies with respect to the rotational speed (in global coordinate) only. In this research, the change in the damping has also been taken into account by including a damping term in the ring model equations. The bi-orthogonal property which is used to obtain the Frequency Response Functions (FRFs) of a rotor/bearing system described in Cartesian coordinate has been applied to the ring model described in cylindrical coordinate to obtain the FRFs. The obtained damping values and FRFs from the analytic model are then compared with experimental results. Moreover, the physical meanings of the results are analyzed, based on experimental data of a stationary tire and a rolling tire at 60 km/h and 100 km/h.

Preliminary study for smoother vibrotactile flow generation on thin plates by using piezoelectric actuators

This paper presents a preliminary study on a new vibrotactile rendering method which can make smoother directional vibrotactile flows on a thin plate. Both by actuating two piezoelectric actuators sequentially from one side to the opposite side and by controlling amplitude-modulated input excitation frequency from zero to the 1st mode of the resonant frequency of a thin plate, a user can feel a smoother directional vibrotactile flows on his/her palm as he/she touches the surface of the thin plate. Experimental results and a user study show that the proposed vibrotactile flow is smoother than the vibrotactile flow that can be generated by the traditional apparent tactile movement and phantom sensation generation methods. The smooth directional vibrotactile flow may be useful for identifying callers or give directional information in navigation maps in mobile devices.

Vibration Analysis of a Partially Connected Double-Beam System with the Transfer Matrix Method and Identification of the Slap Phenomenon in the System

This study concerns dynamic behavior of a partially connected double-beam system. This beam system is composed of two single beams and these beams are connected to each other by the distributed sti...

Topology Optimization of a Magnetic Resonator Using Finite-Difference Time-Domain Method for Wireless Energy Transfer

In this paper, a magnetic resonator for wireless energy transfer system is designed using topology optimization based on an electromagnetic wave analysis. To analyze the magnetic resonator, the finite-difference time-domain method in a 2-D transverse magnetic mode is used with a Gaussian pulse source and perfectly matched layers. The topology optimization using solid isotropic material with the penalization method of a magnetic resonator is conducted to maximize magnetic energy. After these approaches, the fast Fourier transform is used to obtain the response of the magnetic resonator system over a wide range of frequencies.

Reconstruction of the in-plane mode shape of a rotating tire with a continuous scanning measurement using the Hilbert–Huang transform

Generally, the dynamic characteristics (natural frequency, damping, and mode shape) of a structure can be estimated by experimental modal analysis. Among these dynamic characteristics, mode shape requires multiple measurements of the structure at different positions, which increases the experimental cost and time. Recently, the Hilbert-Huang transform (HHT) method has been introduced to extract mode-shape information from a continuous measurement, which requires vibration measurements from one position to another position continuously with a non-contact sensor. In this research study, an effort has been made to estimate the mode shapes of a rolling tire with a single measurement instead of using the conventional experimental setup (i.e., measurement of the vibration of a rolling tire at multiple positions similar to the case of a non-rotating structure), which is used to estimate the dynamic behavior of a rolling tire. For this purpose, HHT, which was used in the continuous measurement of a non-rotating structure in previous research studies, has been used for the case of a rotating system in this study. Ambiguous mode combinations can occur in this rotating system, and therefore, a method to overcome this ambiguity is proposed in this study. In addition, the specific phenomenon for a rotating system is introduced, and the effect of this phenomenon with regard to the obtained results through HHT is investigated.

Dynamic Characteristics of Double Layer Beam with Respect to Different Boundary Conditions

Beam is one of the most commonly used object to verify the vibration theory since its analytic solutions have been well derived. For a double layer beam case, however, there are difficulties to estimate dynamic behavior of the layered beam with the derived analytic solutions for a single layer beam. This study is regarding investigations of dynamic characteristic changes of double layer beams with respect to various boundary conditions.

Vibration Class at GIST, Korea

Vibration class covers vibration phenomena of mechanical systems due to dynamic load is studied. It covers from single DOF to multi DOF and theory as well as numerical and experimental methods. It deals various subjects: Lagrange equation, Laplace transformation, Fourier transformation, mode superposition, finite element method, experimental modal analysis, random vibration, vibro-acoustics and model validation.