Youngil Youm

Pohang University of Science and Technology

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Trends

Author Order

Document Type

Co-Authors

Wan Kyun Chung

Pohang University of Science and Technology

123

Jonghoon Park

Yonsei University

Joono Cheong

Korea University

Nakju Lett Doh

Advanced Institute of Convergence Technology

Adrian E. Flatt

Ninewells Hospital

Won Jee Chung

Changwon National University

Yonghwan Oh

Korea Institute of Science and Technology

SangJoo Kwon

Korea Aerospace University

Sanghak Sung

Pohang University of Science and Technology

Sangdeok Park

Korea National University of Transportation

Cooperative Institutions

Pohang University of Science and Technology

Korea Institute of Science and Technology

Korea Advanced Institute of Science and Technology

Seoul National University

Yonsei University

Hanyang University

Sungkyunkwan University

Research Institute of Industrial Science and Technology

Korea Institute of Robot and Convergence

Samsung (South Korea)

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Field

Kinematic Control of a Redundant Manipulator via a Serially Cooperative Multi-Subarm Scheme

대한기계학회 춘추학술대회 (1990)

Won Jee Chung Wan Kyun Chung Youngil Youm

Manipulator (device)

Source

Cite

Citations (0)

Motion analysis of a moving elastic beam with a moving mass

S. Park Wan Kyun Chung Youngil Youm J.W. Lee

The vibrational motion of an elastic beam fixed on a moving cart and carrying a moving mass was investigated. The equations of motion which describes the total dynamics of the beam-mass-cart system were derived and the coupled dynamic equations were solved by unconstrained modal analysis. In modal analysis, the exact normal mode solutions corresponding to the eigenfrequencies for the position of the moving mass and the ratios of the weight of the beam-mass-cart system were used. Proper transformations of the time solutions between the normal modes for a position and those for the next position of the moving mass were also adopted. Numerical simulations were carried out to obtain the open-loop responses of the system in tracking the pre-designed path of the moving mass.

Position (finance)

Tracking (education)

Added mass

Dynamics

Moving load

10.1109/aim.1999.803161

Cite

Citations (3)

A novel robust tracking controller based on hierarchical perturbation compensation

SangJoo Kwon Wan Kyun Chung Youngil Youm

A robust tracking controller for mechanical systems is proposed by combining a robust perturbation compensator with a nominal tracking controller designed in a sliding mode control (SMC) frame. Basically, the robustness of the system is achieved by the perturbation compensator and this approach enables a smooth sliding mode in the control loop tracking without chattering problem. A unified view is given to a class of perturbation observers and three kinds of expressions for the perturbation of a plant is described. In terms of the view and expressions, we propose the feedforward perturbation observer (FFPO), the feedback perturbation observer (FBPO), and the sliding mode perturbation observer (SMPO). Then, by hierarchically adopting these three observers, the hierarchical perturbation compensator (HPC) is constructed. The adaptive and integral property of the HPC greatly enhances the performance and stability robustness of the system with just the necessary amount of control effort. Through the stability analysis, it is shown that the HPC has an inherent property to overcome the limit of existing perturbation observers. The experimental results for a mechanical system demonstrate the effectiveness of the proposed controller.

Feed forward

Robustness

10.1109/acc.2001.945602

Cite

Citations (3)

Hybrid Impedance Control of Redundant Manipulators: An Approach to Decouple Task Space and Null Space Motions

Intelligent Automation & Soft Computing (1999)

Yonghwan Oh Wan Kyun Chung Youngil Youm Munsang Kim

ABSTRACTIn this paper, an approach to resolve the kinematic redundancy and to control the motion/force of redundant manipulators is presented using the concept of a quasi-coordinate. Using this factorization, we can transform the joint space dynamics into a new decoupled form with dimensional consistency. Then by extracting the minimal null-motion component to control the internal motion of redundant manipulator, inertial decoupling of the task space and null-space motions for redundant manipulator is achieved. Combining the extracted null-motion component and task space variables, an extended Jacobian is constructed and using this extended Jacobian, we devise a new hybrid impedance controller for redundant manipulator. The unique feature of this controller is the ability to directly control the null space motion which is known to have strong effect on performance of task space motion. Some numerical examples are given to demonstrate the performance of the proposed control method.

Impedance Control

Null (SQL)

10.1080/10798587.1999.10750757

Cite

Citations (1)

On dynamical decoupling of kinematically redundant manipulators

J. Park Wei‐Pang Chung Youngil Youm

The kinematically decoupled joint space decomposition is proposed as a general coordinate transformation between the joint space and the task space of kinematically redundant manipulators. The method can describe the kinematic, force, and dynamic redundancy in a unified way using a minimal number of systematic motion variables. Based on the method, a set of equivalent dynamical models of redundant manipulators is constructed and its characteristics are studied focusing on the dynamical decoupling between the task and the null motion dynamics.

Decoupling (probability)

Dynamical decoupling

10.1109/iros.1999.811690

Cite

Citations (39)

Kinematics of the wrist. I. An experimental study of radial-ulnar deviation and flexion-extension.

Journal of Bone and Joint Surgery (1978)

Youngil Youm R Y McMurthy Adrian E. Flatt T E Gillespie

The kinematics of the wrist during radial-ulnar deviation and flexion-extension were studied in several ways. In six fresh cadaver wrists, the forearm was fixed in full pronation, each motion was constrained to one plane, and two metal markers were placed in each of the finger metacarpals, as well as in the radius and all of the carpal bones except the pisiform and greater multangular. Radial ulnar and flexion-extension movements in these wrists were studied roentgenographically. In the wrists of six normal volunteers, a similar roentgenographic analysis was carried out and the trajectories of wrist motions also were studied using light-emitting diodes. Finally, roentgenographic measurements were made on 100 wrists of normal subjects. From these studies, it was concluded that: (1) during each of these motions, rotation occurs about a fixed axis located within the head of the capitate, and the location of each axis is not changed by the position of the hand in either plane; (2) the distance from the base of the third metacarpal to the distal articular surface of the radius (the carpal height), measured along the proximally projected axis of the third metacarpal on posteroanterior roentgenograms, is constant throughout radial-ulnar deviation of the normal wrist and can be used as a measure of carpal collapse; and (3) the perpendicular distance of the fixed axis of rotation for radial-ulnar deviation from the distally projected longitudinal axis of the ulna can be used as a quantitative measurement of the amount of translation of the carpus in pathological conditions.

Ulnar deviation

10.2106/00004623-197860040-00001

Cite

Citations (589)

MECHANICAL CHARACTERISTICS OF REFLEX DURIGN UPRIGHT POSTURE IN PARALYZED SUBJECTS

International Journal of Modern Physics B (2008)

Yong Chul Kim Youngil Youm Bumsuk Lee Youngho Kim Hyeonki Choi

The characteristics of flexor reflexes have been investigated in the previous studies with human subjects who were seated or supine position. However, researchers did not describe how the spinal circuits are used in different hip angles for paralyzed subjects, such as the standing position with walker or cane. In upright posture the compatibility between a flexor reflex of leg and body balance is a special problem for lower limb injured subjects. Therefore, the purpose of this study was to investigate the effects of hip angle change on the flexor reflex evoked in standing paralyzed subjects supported by walker. In this study, six spinal cord injured and four stroke subjects were recruited through the inpatient physical therapy clinics of Korea national rehabilitation hospital. A single axis electronic goniometer was mounted on the lateral side of the hip joint of the impaired limb to record movements in the sagittal plane at this joint. The electronic goniometer was connected to a data acquisition system, through amplifiers to a computer. Since subject' posture influenced characteristics of the flexion reflex response, the subjects were supported in an upright posture by the help of parallelogram walder. Two series of tests were performed on each leg. The first series of the tests investigated the influence of hip angle during stationary standing posture on flexion reflex response. The hip angle was adjusted by the foot plate. The second examined the effect of the voluntary action of subject on swing motion during the gait. The electrically induced flexion reflex simultaneously produced the flexion of the hip, knee and dorsiflexion of the ankle enabling the swing phase of walking. Form the experimental results we observed that the reflex response of hip joint was largerwith the hip in the extended position than in the flexed position during standing posture. Under voluntary movement on flexion reflex during gaint, the peak hip angle induced by stimulation was increased in spinal cord injury and stroke patients by subject' voluntary movement.

Supine position

Proprioception

Goniometer

Force platform

Stretch reflex

10.1142/s0217979208047377

Cite

Citations (0)

Two-Step Controller for 3-D Flexible Link Manipulators: Bandwidth Modulation and Modal Feedback Approach

Journal of Dynamic Systems Measurement and Control (2002)

Joono Cheong Wan Kyun Chung Youngil Youm

For joint tracking control of flexible robots, this paper presents a two-step design of controller: the bandwidth modulation with modal feedback approach. First, we focus on the design of rigid part’s motion controller considering the bandwidth of the rigid subsystem. We investigate the relationship between macro joint tracking performance and vibration suppression capability using the bandwidth parameter. After adjusting the bandwidth of rigid motion, the composite control, which is the second step consisting of rigid and flexible sub-controllers, is applied like singular perturbation approach. As the flexible sub-controller, we propose a direct modal feedback controller that is very simple, but effective to suppress the vibration. The validity and effectiveness of the proposed method are verified by experiments using a POSTECH 3-D flexible robot.

10.1115/1.1514240

Cite

Citations (8)

New Resolution Scheme of the Forward Kinematics of Parallel Manipulators Using Extra Sensors

Journal of Mechanical Design (1996)

Kilryong Han Wan Kyun Chung Youngil Youm

This paper presents a new closed-form resolution scheme of the forward kinematics of parallel manipulators based on two concepts, local structurization and mechanism partition. This scheme is applied to 6-DOF Stewart platform manipulators and the effectiveness of this scheme is verified through numerical examples. It is shown that one extra sensor is sufficient for both 3-3 SPM and 6-3 SPM to exactly resolve the forward kinematic problem (FKP) in closed form and two sensors for 6-6 SPM. In previous research, at least three extra sensors were needed for closed-form resolution of the FKP for 6-6 SPM. Consequently, the new resolution scheme is efficient to implement and easy for real-time applications for the control of parallel manipulators.

Stewart platform

Forward kinematics

10.1115/1.2826872

Cite

Citations (44)

Disturbance observer based motion control of redundant manipulators using weighted decomposition

Yonghwan Oh Wan Kyun Chung Youngil Youm Il Hong Suh

Design of a motion tracking controller is proposed for kinematically redundant manipulators. Using the weighted inner product in joint space, a minimal parametrization of the null space can be achieved. Combining this minimal set of null motion with kinematic relation, we obtain a new extended task space formulation. Based on this formulation, a trajectory tracking control law is proposed based on the momentum feedback disturbance observer (MFDOB). The performance of the proposed controller is verified through experiments with a planar three-link direct-drive manipulator.

Observer (physics)

Parametrization (atmospheric modeling)

10.1109/iros.1997.656602

Cite

Citations (3)