Gunhee Jang 교수

A method of identifying the rotor position of a brushless DC (BLDC) motor and driving a motor smoothly from standstill without any position sensors is presented. This is done by monitoring the current responses to the inductance variation on the rotor position. The rotor position at standstill is detected by comparing the first and second differences of six current pulses injected into every two phases of the motor. Once the motor starts up, a pulse train, composed of long and short pulses, is i

A complete method is presented to calculate the stiffness and the damping coefficients in a hydrodynamic bearing considering five degrees of freedom for a general rotor-bearing system. Perturbation equations are obtained from Reynolds equation by assuming the small amplitude motion of a bearing center, and are solved by the finite element method. Their characteristics due to eccentricity and misalignment are investigated for herringbone groove journal and thrust bearings in the spindle motor of

This research presents a nonlinear model to analyze the ball bearing vibration due to the waviness in a rigid rotor supported by two or more ball bearings. The waviness of a ball and each races is modeled by the superposition of sinusoidal function, and the position vectors of inner and outer groove radius center are defined with respect to the mass center of the rotor in order to consider five degrees of freedom of a general rotor-bearing system. The waviness of a ball bearing is introduced to

The pole-teeth-winding configuration in brushless dc motors determines torque and unbalanced magnetic force which are the resultants of the tangential and the normal magnetic force in a small air gap, respectively. This paper calculated torque and unbalanced magnetic force using FEM, Maxwell stress tensor to investigate the influence of pole-teeth-winding patterns on the performance from two common designs, i.e. the rotational symmetric 12-pole 9-tooth (12P9S) motor and the rotational unsymmetri

This research investigates the dynamic characteristics of a herringbone grooved journal bearing with plain sleeve (GJPS) and a plain journal bearing with herringbone grooved sleeve (PJGS) under static and dynamic load. FEM is used to solve the Reynolds equation in order to calculate the pressure distribution in a fluid film. Reaction forces and friction torque are obtained by integrating the pressure and shear stress along the fluid film, respectively. Dynamic behaviors of a journal, such as orb

The Reynolds equation, incorporating Elrod’s cavitaton algorithm, is discretized on a rectangular grid in computational space through coordinate mapping in order to accurately analyze a herringbone grooved journal bearing of a spindle motor in a computer hard disk drive. The pressure distribution and cavitation area are determined by using the finite volume method. Predicted results are compared to experimental data of previous researchers. It was found that positive pressure is developed within

This paper presents a method to determine the improved commutation position of a brushless DC (BLDC) motor in such a way as to generate the symmetric terminal voltages of the nonenergized phase at the beginning and end of the commutation period. If the BLDC motor is energized at the exact commutation position, the terminal voltage of the nonenergized phase at the beginning of commutation is equal to the terminal voltage at the end of commutation, and the waveform of the terminal voltage should b

A principal source of vibration in permanent magnet (PM) motors and generators is the traveling forces on the stator induced by the rotating permanent magnets. These forces are transmitted through the stator and to the surrounding system. The magnetic forces were calculated from the flux density by finite element methods (FEMs). The dynamic reactions at the motor mounting points, which provide the forcing function to the base system, were also calculated by FEMs. The vibration characteristics an

This paper proposes a method to calculate the characteristics of a coupled fluid dynamic journal and thrust bearing of a hard disk drive (HDD) spindle motor. The governing equations for the journal and thrust bearings are the two-dimensional Reynolds equations in the θz and rθ planes, respectively. The finite element method is appropriately applied to analyze the coupled bearing under the conditions of the continuity of mass and pressure at the interface between the journal and thrust bearings.

This paper presents an analytical method to investigate the stability of a hydrodynamic journal bearing with rotating herringbone grooves. The dynamic coefficients of the hydrodynamic journal bearing are calculated using the FEM and the perturbation method. The linear equations of motion can be represented as a parametrically excited system because the dynamic coefficients have time-varying components due to the rotating grooves, even in the steady state. Their solution can be assumed as a Fouri