Jintai Chung

Vibration absorber for reduction of the in-plane vibration in an optical disk drive

A new type of vibration absorber is developed to reduce the in-plane vibration of the feeding deck system in an optical disk drive. In order to derive the equations of motion for the feeding deck system with the absorbers, a vibration model is established. After the frequency response function is obtained from the equations, the effects of absorber mass, stiffness and damping are analyzed. The material properties and shape of the vibration absorber are determined from the analysis results. For the purpose of verification, the performance of the absorber is investigated through experiments. The test results show that the proposed absorber is able to considerably reduce vibration in a wide range of spindle motor speeds.

Vibrations of an Axially Moving Beam with Deployment or Retraction

The longitudinal and transverse vibrations of an axially moving beam are analyzed when the beam has deploying or retracting motion. Comparing the previous studies in which only the transverse displacement is considered, the present study simultaneously considers the longitudinal and transverse displacements when deriving the equations of motion. To include a nonlinear effect, the nonlinear von Karman strain theory is adopted. The derived equation of longitudinal motion is linear and uncoupled with the transverse motion, whereas the equation of transverse motion is nonlinear and coupled with the longitudinal motion. After computing numerical solutions from the equations, the longitudinal and transverse vibrations are analyzed with regard to the moving speed and acceleration of the beam. In addition, the present nonlinear analysis of a moving beam is compared with a previous linear analysis for the variations of the moving acceleration, moving speed, and Young’s modulus. The linear and nonlinear vibration a...

Free in-plane vibration of an axially moving membrane

The free in-plane vibration of an axially moving membrane is studied considering the effects of both the translating speed and aspect ratio of the membrane. Two sets of boundary conditions, which are free and fixed constraints in the lateral direction at boundaries with mass transport, are discussed in this study. From the extended Hamilton principle, the coupled equations of the longitudinal and lateral motions are derived. These equations are then discretized by using the Galerkin method. From the discretized equations, the natural frequencies and mode shapes are obtained for the variations of the translating speed and aspect ratio. The results show that the translating speed, aspect ratio, and boundary conditions have significant effects on the in-plane vibrations of the moving membrane.

Vibration and noise reduction of an optical disk drive by using a vibration absorber

Vibration and noise reduction of an optical disk drive by using a vibration absorber is presented in this paper. In optical disk drives such as CD-ROM or DVD drives, vibration may become one of serious problems to be resolved as the rotating speed and the storage capacity increase. It is practically difficult to overcome the off-track and off-focusing errors by only the servo control without reducing vibration. In particular, when an optical disk drive has a wavy spinning disk, it may suffer from severe vibration. Based on the vibration signals measured by a laser vibrometer and an accelerometer, the resonance frequency of the disk drive is identified. For reduction of the vibration around the resonance frequency, a vibration absorber is designed and it is equipped on the feeding deck of the drive. The proposed vibration absorber consists of a steel plate ring and a rubber bobbin, which play roles of inertia mass and a spring, respectively. During the design procedure of the absorber, a finite element model is used to determine the required fundamental natural frequency of the absorber. The test results of vibration and noise after being equipped with the absorber show that vibration and noise of the optical disk drive are considerably reduced.

Stability analysis for the flapwise motion of a cantilever beam with rotary oscillation

Abstract The flapwise motion of a cantilever beam with rotary oscillation is analyzed to investigate the dynamic stability of the beam. The cantilever beam is regarded as a system subjected to parametric excitation because the angular speed of the cantilever beam varies harmonically. To consider the stiffening effect due to the centrifugal force, this study adopts the linear partial differential equation of flapwise motion, which is derived by a modelling method using the stretch deformation instead of the conventional longitudinal deformation. After the partial differential equation is discretized by the Galerkin method, the method of multiple scales is applied. Using this method, the stability of the beam is analyzed for the variations of the oscillating frequency and the maximum angular speed. In addition, to verify the stability results, the time responses of flapwise motion are computed by the generalized- α time integration method.

Vibration analysis of a flexible rotating disk with angular misalignment

Abstract The dynamic characteristics and responses of a flexible rotating disk are analyzed, when the disk has angular misalignment that is defined by the angle between the rotation and symmetry axes. Based on the von Karman strain theory and the Kirchhoff plate theory, three equations of motion are derived for the transverse, radial and tangential displacements when the disk has angular misalignment. The derived equations are fully coupled partial differential equations through the transverse, radial and tangential displacements. In particular, the equation of transverse motion is non-linear while the others are linear. After these partial differential equations and the associated boundary conditions are transformed into a weak form, the weak form is discretized to a non-linear matrix–vector equation by using the finite element method. The non-linear equation is linearized in the neighbourhood of a dynamic equilibrium position, and then the natural frequencies and mode shapes are computed. In addition, the dynamic time responses are obtained by applying the generalized- α method. The effects of angular misalignment on the natural frequencies, the mode shapes and the dynamic responses are investigated. The analysis shows that the angular misalignment causes the natural frequency split and the out-of-plane mode with only one nodal diameter and no nodal circle has the largest frequency split. It is also found that the angular misalignment yields the amplitude modulations in the transverse, radial and tangential dynamic responses.

A Study on the Characteristic of Noise and Vibration in 3-phase Induction Motor for the Forklift

ABSTRACT This paper presents the reduction of acoustic noise generated by electromagnetic force in an induction motor of the electrical forklift. After summarizing the electromagnetic excitation forces due to the interaction between the stator/rotor slot permeance and the stator winding magnetomotive force, the effects of the electromagnetic force on the noise and vibration of an induction motor are analyzed. In order to experimentally identify the noise sources of the motor, the signal analyses for noise and vibration are performed by using waterfall plots of noise and vibration spectrums. It is found that severe noise and vibration are caused by the electromagnetic force when the mode number of the excitation shape for a stator is low. Furthermore, it is verified that the motor noise is amplified if the excitation frequency of the electromagnetic force coincides with one of the natural frequencies of the stator. It is experimentally demonstrated that this severe noise can be considerably reduced by structure modifications. Finally, some design guidelines are suggested to develop an induction motor with a low level of noise.

Dynamic time responses of a flexible spinning disk misaligned with the axis of rotation

Using the finite element method, this study investigates the dynamic time responses of a flexible spinning disk of which axis of rotation is misaligned with the axis of symmetry. The misalignment between the axes of symmetry and rotation is one of major vibration sources in optical disk drives such as CD-ROM, CD-R, CD-RW and DVD drives. Based upon the Kirchhoff plate theory and the von Karman strain theory, three coupled equations of motion for the misaligned disk are obtained: two of the equations are for the in-plane motion while the other is for the out-of-plane motion. After transforming these equations into two weak forms for the in-plane and out-of-plane motions, the weak forms are discretized by using newly defined annular sector finite elements. Applying the generalized-α time integration method to the discretized equations, the time responses and the displacement distributions are computed and then the effects of misalignment on the responses and the distributions are analyzed. The computation results show that the misalignment has an influence on the magnitudes of the in-plane displacements. It is also found that the misalignment results in the amplitude modulation or the beat phenomenon in the time responses of the out-of-plane displacement.

Comparison of efficacy for erectile function and lower urinary tract symptoms of tadalafil 20 mg on-demand and 5 mg once daily in patients with erectile dysfunction

Aim:  To compare the improvement in erectile dysfunction (ED) and lower urinary tract symptoms (LUTS) as well as safety of tadalafil dosed at 20 mg on‐demand and 5 mg once daily among ED patients.

A Study on Noise Reduction for the Driving System of a Forklift

In this study. the noise sources were identified and the noise and vibration were reduced for an industrial forklift. To identify the noise sourses, noise signals were measured by a microphone on a driver seat and these signals were analyzed with a waterfall plot. For this purpose, the gear mesh frequencies from the gear box of a reducer were not only investigated but noise/vibration sourses of an electric motor were also examined. Furthermore, the frequency response functions were obtained to confirm the vibration and noise sourses. It was found that severe vibration and noise were generated in the casing and the connecting part of the reducer. The severe vibration and noise could be reduced by a structure modification.