Yun-Joo Nam

Performance Improvement of a Rotary MR Fluid Actuator Based on Electromagnetic Design

This study presents an electromagnetic design methodology for a rotary magnetorheological (MR) fluid actuator. In order to improve the performance of the MR fluid actuator, the magnetic field should be effectively applied to the MR fluid. Therefore, it is important that the magnetic circuit composed of the MR fluid, the ferromagnetic material for magnetic flux path, and the electromagnetic coil is well designed. For this purpose, two effective approaches are proposed: one is to shorten the magnetic flux path by removing the unnecessary bulk of the yoke in order to improve the static characteristic of the MR fluid actuator, and the other is to increase the magnetic reluctance of the magnetic circuit by minimizing the cross-sectional area of the yoke through which the magnetic flux passes in order to improve the dynamic and hysteretic characteristics. The effectiveness of the proposed design methodology is verified through magnetic analysis and a series of basic experiments.

Electromagnetic Design of a Magnetorheological Damper

This study presents an electromagnetic design methodology for the magnetorheological (MR) damper. To improve the performance of the MR damper, the magnetic field should be effectively supplied to the MR fluid. Therefore, it is important that the magnetic circuit composed with the MR fluid, the ferromagnetic yoke for forming the magnetic flux path, and the electromagnetic coil are well designed from the electromagnetic viewpoint. For this purpose, two effective approaches are proposed; one is to shorten the magnetic flux path by removing the unnecessary bulk of the yoke in order to improve the static characteristic of the MR damper, and the other is to increase the magnetic reluctance of the magnetic circuit by minimizing the cross-sectional area of the yoke through which the magnetic flux passes in order to improve the dynamic and hysteretic characteristics. After designing and manufacturing two MR dampers, the conventional type and the proposed type, their performances are evaluated and compared through the magnetic field analysis and a series of basic experiments. These results show that the proposed design methodology can be effectively used as a fundamental design material for expanding application fields of the MR damper.

Performance Evaluation of Two Different Bypass-type MR Shock Dampers

This article presents the performance evaluation of two different bypass-type magneto-rheological (MR) shock dampers for high impulsive force systems, one of which is a single-ended damper and the other a double-ended one. First of all, MR shock dampers are designed and manufactured on the basis of the Bingham properties of MR fluid and the result of the magnetic field analysis for the magnetic circuit. After experimental investigations on both the magnetic field-dependent damping force and the response characteristics, the quasi-steady state models describing the dynamic behavior of the proposed dampers are formulated. Then, a simple one degree-of-freedom mass-drop system as a test bench for the MR shock dampers is constructed, and the simple and practical control algorithm is proposed in consideration of dynamic characteristics of the shock control system. Finally, in order to investigate their dynamic characteristics and control performances under shock condition, a comparison study is conducted through a series of experiments and simulations. The results show the controllability and adaptability of the proposed MR shock dampers for shock or impulsive force as well as the effectiveness of the proposed control algorithm.

A hybrid haptic device for wide-ranged force reflection and improved transparency

This paper is concerned with the transparency improvement of a 1-DOF (degree-of-freedom) hybrid haptic device with the wide-ranged haptic reflection. The hybrid haptic device is actuated by the combination of an active actuator and a passive one. A noble hybrid concept for the haptic device is proposed for two purposes; one is to improve the transparency of the haptic device by compensating friction components qualitatively and quantitatively, and the other is to reflect the wide-ranged force or torque in large workspace. In the proposed hybrid actuation, the passive actuator is used as the main source of the reflective output, since it has the passivity property in nature so that the safety in interaction and the stability in haptic control can be concurrently guaranteed. The active actuator, which is active in nature, is used either for compensating back-driven components in the haptic system or for providing additional outputs in the haptic reflection larger than the maximum capacity of the passive actuator.

Kinematics and Optimization of 2-DOF Parallel Manipulator with Revolute Actuators and a Passive Leg

In this paper, a 2-DOF planar parallel manipulator with two revolute actuators and one passive constraining leg. The kinematic analysis of the mechanism is analytically performed: the inverse and forward kinematics problems are solved in closed forms, the workspace is derived systematically, and the three kinds of singular configurations are found. The optimal design to determine the geometric parameters and the operating limits of the actuated legs is performed considering the kinematic manipulability and workspace size. These results of the paper show the effectiveness of the presented manipulator.

Design of Port Plate in Gerotor Pump for Reduction of Pressure Pulsation

The pressure pulsation due to the gear geometry of the gerotor (generalized rotor) pump mainly occurs in an instant that the chamber of the gerotor enters the delivery port and leaves the suction one. Such a pressure pulsation may result in undesirable vibration and noise of pump components as well as cavitation in hydraulic system. Therefore, it is very important to examine the pressure characteristic of the gerotor pump at its design and analysis stages. In this paper, in order to reduce the pressure pulsation in the gerotor pump, the port plate with the relief grooves is designed by referring to as notch of vane pump and relief groove of piston pump. A series of the theoretical analyses on the pressure pulsation is performed in consideration of various design parameters of the port plate, including the installation positions of the port inlet/ outlet and the groove width, and the operating conditions such as rotational velocity and delivery pressure.

Magnetic Fluid Actuator Based on Passive Levitation Phenomenon

This article is concerned with the practical design and dynamic characteristics of a magnetic fluid actuator for which the working principle is based on the passive levitation of a non-magnetic body immersed in magnetic fluid subjected to magnetic field. This magnetic fluid actuator is composed of kerosene-based magnetic fluid HC-50, a pair of hollow solenoids whose north poles are placed face-to-face with each other, and a non-magnetic (paramagnetic) body made of aluminum. First of all, the design methodology for the magnetic fluid actuator is proposed based on the ferrohydrostatic relation including the gravitational force, the buoyancy force, and magnetic body force acting on magnetic fluid by magnetic field. After manufacturing the magnetic fluid actuator based on the proposed design criteria, its dynamic characteristics are experimentally investigated with the step and frequency responses of the displacement of the non-magnetic object to input coil currents. Through the comparison study between simulation analyses and experimental results, the effectiveness of the proposed magnetic fluid actuator is verified.

Workspace optimization and kinematic performance evaluation of 2-DOF parallel mechanisms

This paper presents the kinematics and workspace optimization of the two different 2-DOF (Degrees-of-Freedom) planar parallel mechanisms: one (called 2-RPR mechanism) with translational actuators and the other (called 2-RRR mechanism) with rotational ones. First of all, the inverse kinematics and Jacobian matrix for each mechanism are derived analytically. Then, the workspace including the output-space and the joint-space is systematically analyzed in order to determine the geometric parameters and the operating range of the actuators. Finally, the kinematic optimization of the mechanisms is performed in consideration of their dexterity and rigidity. It is expected that the optimization results can be effectively used as a basic material for the applications of the presented mechanisms to more industrial fields.

Performance evaluation on vibration control of MR landing gear

This paper is concerned with the applicability of the developed MR damper to the landing gear system for the attenuating undesired shock and vibration in the landing and taxing phases. First of all, the experimental model of the MR damper is derived based on the results of performance evaluations. Next, a simplified skyhook controller, which is one of the most straightforward, but effective approaches for improving ride comport in vehicles with active suspensions, is formulated. Then, the vibration control performances of the landing gear system using the MR damper are theoretically evaluated in the landing phase of the aircraft. A series of simulation analyses show that the proposed MR damper with the skyhook controller is effective for suppressing undesired vibration of the aircraft body. Finally, the effectiveness of the simulation results are additionally verified via HILS (Hardware-in-the-loop-simulation) method.

Position feedback control of a nonmagnetic body levitated in magnetic fluid

This paper is concerned with the position feedback control of a magnetic fluid actuator which is characterized by the passive levitation of a nonmagnetic body immersed in a magnetic fluid under magnetic fields. First of all, the magnetic fluid actuator is designed based on the ferrohydrostatic relation. After manufacturing the actuator, its static and dynamic characteristics are investigated experimentally. With the aid of the dynamic governing relation obtained experimentally and the proportional-derivative controller, the position tracking control of the actuator is carried out both theoretically and experimentally. As a result, the applicability of the proposed magnetic fluid actuator to various engineering devices is verified.