Youngil Youm

IROS Conference 2008 Conference Paper

Dynamic crawl gait algorithm for quadruped robots

• Heeseon Hwang
• Youngil Youm

A velocity based gait generation algorithm with real time adaptation rules which are necessary for steady walking is suggested. Particularly, we have developed a steady crawl gait with duty factor beta = 0. 75. The main feature of the suggested algorithm is that it does not based on the foothold selection, and it can be used for the walking of blind robots on more realistic irregular terrain. The adaptation algorithms are the translational velocity modification to satisfy the steady gait requirement and the swing period modification to avoid the kinematic limitation. The suggested gait generation algorithm has been implemented in a simple quadruped robot which has totally eight actuated joints on the legs. Using the PD controller for the trajectory following and the adaptation algorithm of gait parameters, the steady periodic crawl gait on low irregular terrain has been demonstrated.

ICRA Conference 2007 Conference Paper

General ZMP Preview Control for Bipedal Walking

• Jonghoon Park
• Youngil Youm

An online pattern generator for bipedal walking control is designed based on the notion of ZMP preview control using the full dynamics model. The method is called the general ZMP preview control. Conventional implementation by Kajita is based on an approximated table-cart model, which neglects the actual system dynamics. This leads to erroneous ZMP tracking for real robots, even if the system tracks the generated COM pattern exactly. Numerical simulations are provided to show the advantage and character of the method

ICRA Conference 2007 Conference Paper

Landing Motion Control of Articulated Legged Robot

• Sanghak Sung
• Youngil Youm

This paper deals with the landing motion of an articulated legged robot. Humans use a peculiar crouching motion to land safely which can be characterized by body stiffness and damping. A stiffness controller formulation is used to realize this human behavior for the robot. Using this method, the landing motion is achieved with only the desired body stiffness and damping values, without desired COG (Center of Gravity) or joint paths. To achieve soft landing, variable body stiffness and damping values were optimized. PBOT, which has four links with flexible joints was used for validation of the landing controller. A body stiffness and damping controller was used as an outer landing control loop and a fast subsystem controller for flexible joints was used as an inner force control loop. Simulations and experimental results about the landing motion are presented to show the performance of the body stiffness and damping controller.

IROS Conference 2006 Conference Paper

Locomotion via Impact Switching between Decoupling Vector Fields

• Heeseon Hwang
• Kevin M. Lynch
• Youngil Youm

This paper investigates motion planning for underactuated systems with impacts, as in legged robots. Some such systems admit decoupling vector fields between impacts, and the system can be thought of as a kinematic system as it moves along the integral curves of these decoupling vector fields. This reduces motion planning to choosing a sequence of decoupling vector fields and impact transition times between these vector fields. Each transition must satisfy the condition that the image of the pre-impact state (through the impact mapping) leads to a post-impact state aligned with the new decoupling vector field. We derive this condition, extending previous work where transitions were only allowed at zero velocity. Our approach combines the benefits of computationally efficient kinematic planning with potentially faster execution times due to the fact that the system does not have to be slowed to zero velocity at the switches. Switches are restricted to a lower-dimensional configuration surface, however. We have applied this approach to motion planning for a planar two-link robot which locomotes by using a single revolute actuator at the joint between the links and by alternately clamping one of two possible pivot points to the ground

IROS Conference 2005 Conference Paper

Accurate multi-DOF kinesthetic haptic display using instantaneous restriction space

• Keehoon Kim
• Wan Kyun Chung
• Youngil Youm

This paper proposes an accurate kinesthetic haptic display method for a multi-DOF haptic interface. Position-position (p-p) architecture plays an important role in a haptic interface like four channel architecture since force reflection using only force sensor information induces a serious problem if a slave manipulator is constrained by unexpected obstacles the force sensor cannot detect. However, the conventional p-p architecture in literature has limitations to apply to a multi-DOF haptic interface. This paper indicates the limitation through an example and proposes a novel haptic display method using instantaneous restriction space (IRS). IRS can be calculated using Jacobian and joint angle error of a slave manipulator. Since the proposed method has the form of impedance two port architecture in the sense of data flow, it can be easily combined with the previous results of two-port haptic display framework in literature. The method is compared to the conventional p-p architecture through experiments.

ICRA Conference 2005 Conference Paper

Control of Ground Interaction at the Zero-Moment Point for Dynamic Control of Humanoid Robots

• Jonghoon Park
• Youngil Youm
• Wan Kyun Chung

In order for stable control of humanoid robots, ground contact forces should be properly controlled for compensating the dynamic disturbances caused by unactuated body movement. The stability in the sense of the zero-moment point (ZMP), guaranteeing secure contacts during control, is a necessary condition for stable motion control. Therefore, we propose a method to control the ground interaction at the ZMP, or ZMP interaction in short, by modifying the system reference acceleration. We also show that simultaneous control of the ZMP interaction and the body movements is not allowed in general. Simulation result is provided to corroborate the theoretical result.

IROS Conference 2005 Conference Paper

Second-order contact kinematics for regular contacts

• Jonghoon Park
• Wan Kyun Chung
• Youngil Youm

Second-order contact kinematics for regular contacts, such as surface-surface, curve-curve, curve-surface, and vertex-surface, are formulated in a unified framework, extending Montana's (1988) first-order contact kinematics for surface-surface contact only. Given two rigid bodies in contact with each other, the contact kinematics is the mathematical expression of the relative motion between them and the five dimensional contact coordinate vector. Second-order contact kinematics describes the second-order derivative of the contact coordinate vector in terms of the derivative of the relative twist. The result can be directly applied to geometric integration of contact dynamics.

ICRA Conference 2005 Conference Paper

Simulation Study of Fish Swimming Modes for Aquatic Robot System

• Eunjung Kim
• Youngil Youm

In this paper, we show the simulation result to find the suitable fish swimming modes (especially BCF swimming) for fishlike underwater robot system. To find the suitable swimming modes, we assume that they have the same length, volume, and weight, but they have the different numbers of actuator (joint). And we use the minimum number of joint for each swimming mode. We derive the dynamic equation for each system using Kane’s method and these results are compared by the result of DADS. We present the optimal solution of swimming mode for some aquatic locomotion, especially faster (high propulsive efficiency) and more maneuverable (quick turning motion).

ICRA Conference 2004 Conference Paper

A New Position Error based Robust Controller Design Framework of Teleoperation for Free to Contact Motion

• Kyongho Park
• Wan Kyun Chung
• Youngil Youm

There was a paper on robust controller design framework of teleoperation. This design method strongly depends on the initial setup of the system and can not be applied to the realistic situation which includes the transition motion as free to contact motion because the controllers were separately derived for the free motion and contact motion. Therefore, we want to propose a new design framework which can solve this dependence. To prove the effectiveness of the proposed method, comparative simulation with the existing four channel design method was performed.

ICRA Conference 2004 Conference Paper

Design and Dynamic Analysis of Fish Robot: PoTuna

• Eunjung Kim
• Youngil Youm

This paper presents the design and the analysis of a "fish-like underwater robot". In order to develop swimming robot like a real fish, extensive hydrodynamic analysis were made followed by the study of biology of the fishes especially its maneuverability and propel styles. Swimming mode is achieved by mimicking fish-swimming of carangiform. This is the swimming mode of the fast motion using its tail and peduncle for propulsion. In order to generate configurations of vortices that gives efficient propulsion, yawing and surging with a caudal fin is applied, and in order to submerge and maintain the body balance, pitching and heaving motion with a pair of pectoral fin is used. We have derived the equation of motion of PoTuna by two methods. In first method, we use the equation of motion of underwater vehicle with the potential flow theory for the power of propulsion. In second method, we apply the method of the equation of motion of UVM (underwater vehicle-manipulator). Then, we compared these results.

IROS Conference 2004 Conference Paper

Geometric numerical integration algorithms for articulated multi-body systems

• Jonghoon Park
• Wan Kyun Chung
• Youngil Youm

Numerical integration methods based on Lie group theoretic geometrical approaches are extended to articulated multi-body systems with rigid body displacements belonging to the special Euclidean group SE (3) as a part of generalized coordinate. Two Lie group integrators, Crouch-Grossman method and Munthe-Kaas method, are formulated for the equation of motion for articulated multi-body systems. The proposed methods provide singularity-free integration, unlike the Euler-angle method, while the integration always evolves on the underlying manifold structure, unlike the quarternion method. Numerical simulation result validates the methods by checking energy and momentum conservation at even integrated system state.

ICRA Conference 2004 Conference Paper

The Development of Postech Hand 5

• Juhyoung Lee
• Youngil Youm
• Wan Kyun Chung

We define that the end effector is the device which interacts with the environment or contacts objects to execute tasks. Up to now, many researchers have developed anthropomorphic robotic hands as end effectors. We discuss the problems in the development of a human-scale and motor-driven anthropomorphic robot hand. In this paper, PRH's design concept, kinematic design and developments of the actuator, transmission, and sensing device are presented. By imitating the physiology of human hands, we devised new metacarpalphalangeal joints and interphalangeal joints suitable for human-size motor-driven robot hands.

IROS Conference 2003 Conference Paper

A stable sequential inverse kinematics of flexible robots: explicit and implicit expansion methods

• Joono Cheong
• Youngil Youm
• Wan Kyun Chung

This paper deals with the sequential inverse kinematics for the high speed tracking of flexible robots. As a continuation of the implicit expansion method in, the explicit version of the sequential inverse kinematics is presented which is easier to be understood conceptually. The accuracy and stability of the two algorithms are compared and proved. Numerical study verifies the validity of the theoretical results.

IROS Conference 2003 Conference Paper

Design and analysis of a new 7-DOF parallel type haptic device: PATHOS-II

• Keehoon Kim
• Wan Kyun Chung
• Youngil Youm

Most tele-operation to manipulate an object consists of grasping and manipulation, and two or more 6-DOF haptic devices are usually used in master side. In this article, a new simply designed 7-DOF haptic device, PATHOS II is proposed for 1-DOF grasping and 6-DOF manipulation. The merits of a parallel type haptic device such as high stiffness and accuracy are natural characteristics of PATHOS-II with optimized workspace. Due to its unique symmetric structure, the isotropic manipulability is enhanced within the reachable workspace. This parallel type haptic device can be used in applications which need high precision, stiffness and isotropic manipulability.

IROS Conference 2003 Conference Paper

Hopping through stiffness modulation method (STINIM)

• Sanghak Sung
• Youngil Youm
• Wan Kyun Chung

In this paper, we present hopping strategy which is more human-like for legged robot through stiffness modulation of a body. This method enables to reduce impact force on touch-down and adaption on ground stiffness change. Simple selected models are used to validate this method and singular perturbation method is used for control.

ICRA Conference 2002 Conference Paper

Characterization of Instability of Dynamic Control for Kinematically Redundant Manipulators

• Jonghoon Park
• Wan Kyun Chung
• Youngil Youm

In redundant manipulator research community, the phenomenon called torque instability has not yet been completely characterized using unanimous agreement on its mechanism. This article shows that the behavior is indeed caused by incomplete compensation of null dynamics related with self-motion. This instability can be avoided by proper control with compensation of nonlinear null dynamics, and we propose a method to stabilize conventional redundancy resolution schemes extended to dynamic controls.

IROS Conference 2002 Conference Paper

Inverse kinematics of multi-link flexible robots for high speed applications

• Joono Cheong
• Youngil Youm
• Wan Kyun Chung

This paper proposes an improved differential inverse kinematics algorithm which works good for high speed motion control. The dynamic constraint as well as the kinematic constraint is utilized for the inverse kinematics. The singular perturbation method helps to reduce inverse kinematics to be solvable. The numerical and experimental results show the performance of the proposed method clearly.

ICRA Conference 2002 Conference Paper

Obtaining Passivity of Micro-Teleoperation Handling a Small Inertia Object

• Kyongho Park
• Wan Kyun Chung
• Youngil Youm

There have been many bilateral micro-teleoperation systems handling a small object. Historically, Lawrence (1991) proposed the transparency-optimized architecture and passivity theorem for stability analysis of bilateral teleoperation. He claimed that unless the task(or environment) impedance contains a significant inertial behavior, passivity condition for transparency-optimized architecture can not be satisfied. To overcome this problem, we analyze and propose a method which can satisfy passivity condition for the micro-teleoperation system handling a small inertial object based on the structures originated by Lawrence and Hashtrudi-Zaad et al. (1999) and velocity-force scaling property of micro-teleoperation.

IROS Conference 2002 Conference Paper

PID composite controller and its tuning for flexible link robots

• Joono Cheong
• Wan Kyun Chung
• Youngil Youm

This paper proposes a PID-type composite controller for controlling flexible arms modeled by the singular perturbation approach, and investigates a tuning method based on the proposed controller structure. For the slow sub-controller, a PD plus disturbance observer is used, which eventually takes on PID form, and for the fast sub-controller, modal feedback PID control is utilized. The effects of design parameters of the controller on the closed loop response are investigated. Through simulation and experiments, the adequacy and performance of the proposed method are verified.

ICRA Conference 2002 Conference Paper

Real-Time ZMP Compensation Method using Null Motion for Mobile Manipulators

• Jinhyun Kim
• Wan Kyun Chung
• Youngil Youm
• Bum Hee Lee

The dynamic stability of a mobile manipulator using ZMP compensation is considered. A unified approach for the two subsystems is formulated using a redundant scheme. First, to conserve the dynamic stability of the system, we define the performance index for the redundant system using the ZMP (zero moment point). This performance index represents the stability of the whole mobile manipulator system. Then, the redundancy resolution problem for optimizing the given performance index is solved using the null motion. Finally, the performance of this method is demonstrated by simulation study.

IROS Conference 2001 Conference Paper

Development of human-mobile communication system using electrooculogram signals

• Youngmin Kim
• Nakju Lett Doh
• Youngil Youm
• Wan Kyun Chung

Present the development of a human-mobile robot communication system using electrooculogram (EOG) signals. An ideal velocity shape signal processing algorithm is proposed to extract position data where the eyes are focusing on from the noise and drift included in EOG signals. Additionally, an efficient algorithm for the detection of various eye-lip movements such as blink and wink is suggested. Two experiments were performed for the validation of the human-mobile communication system. One is point stabilization of a mobile robot, using extracted eye focusing position data. The other is a moving target following experiment using various eye-lip movements as mobile robot commands.

IROS Conference 2001 Conference Paper

Fast suppression of vibration for multi-link flexible robots using parameter adaptive control

• Joono Cheong
• Wan Kyun Chung
• Youngil Youm

A simple direct parameter update rule is presented to suppress the vibration more quickly by considering the dynamics of the flexible subsystem. Different from most of adaptive control schemes in multilink flexible robots, which are a model independent approach, the proposed adaptive control utilizes model parameters and updates them. Usually, the precise modeling of multi-link flexible robot is hard to obtain and even if we can get it, it is difficult to use in the online control tasks. For these reasons, a simplified model is used to describe the robot dynamics. The modelling errors and other structured uncertainty are considered as parameter perturbation. We verify the effectiveness of the proposed algorithm through experiments.

ICRA Conference 2001 Conference Paper

Input Preshaping Vibration Suppression of Beam-Mass-Cart Systems Using Robust Internal-Loop Compensator

• Bong Keun Kim
• Sangdeok Park
• Wan Kyun Chung
• Youngil Youm

In this paper, an input preshaping control method with robust disturbance attenuation algorithm is proposed to suppress vibration of a translating flexible beam carrying a fixed or moving mass. The input preshaping method is based on the analytic modeling of the system and frequency equation as a function of various parameters including the position of moving mass. By using a generalized framework for disturbance attenuation, it is shown that an input preshaping method can be easily designed to reduce single mode residual vibration and to get accurate positioning of a beam-mass-cart system in the presence of uncertainty and disturbance.

ICRA Conference 2001 Conference Paper

Multiple Tasks Kinematics Using Weighted Pseudo-Inverse for Kinematically Redundant Manipulators

• Jonghoon Park
• Youngjin Choi
• Wan Kyun Chung
• Youngil Youm

This paper proposes a method to accommodate multiple tasks for redundancy utilization, which is based on a specific weighted pseudo-inverse. The proposed method also has task priority imposition property same as those conventional task priority based methods. In order to deal with general situations of task specification, the so-called semi-definitely weighted pseudo-inverse is devised.

ICRA Conference 2001 Conference Paper

On the Coarse/Fine Dual-Stage Manipulators with Robust Perturbation Compensator

• SangJoo Kwon
• Wan Kyun Chung
• Youngil Youm

A dual-stage, fast and fine robotic manipulator is presented. By adopting merits of both coarse and fine actuator, a desirable system having the capacity of large workspace with high resolution of motion is enabled. We constructed an ultra precision XY-manipulator with dual-stage structure where the PZT driven fine stage is mounted on the motor driven XY positioner and applied it to fine tracking controls and micro-teleoperations as a slave manipulator. We describe essential merits of the compound actuation mechanism and the control strategy to successfully utilize it with a proper servo system design. Through experimental results, the effectiveness of the coarse/fine manipulation by the dual stage manipulator is shown.

IROS Conference 2001 Conference Paper

On the optimal PID performance tuning for robotic manipulators

• Youngjin Choi
• Wan Kyun Chung
• Youngil Youm

Although most robotic manipulators have used the conventional PID or PID plus something, e. g. , gravity compensator, friction compensator, disturbance observer and so on, there exist still no general tuning rules which can adjust the PID control performance. The paper explains the tuning methods of inverse optimal PID control assuring the extended disturbance input-to-state stability and shows its validity through many experiments for a robotic manipulator.

IROS Conference 2001 Conference Paper

PTP motion control of XY positioning systems with a flexible beam

• Bong Keun Kim
• Sangdeok Park
• Wan Kyun Chung
• Youngil Youm

A PTP motion control method composed of a feedforward and feedback controller is proposed to get accurate positioning and to suppress vibration of a XY positioning system with a flexible beam. The input preshaping based on the analytic modeling and frequency equation of the system is proposed as a feedforward controller to produce desired responses. A feedback controller is proposed based on a robust internal-loop compensator to stabilize the whole system and to meet closed-loop performance. Experiments are carried out to show the validity of the proposed controller.

ICRA Conference 2000 Conference Paper

Analytic Jacobian of In-Parallel Manipulators

• Doik Kim
• Wan Kyun Chung
• Youngil Youm

A general formulation to obtain an analytic Jacobian matrix for in-parallel manipulators has not been developed yet, although several authors addressed it. This paper suggests a consistent approach to obtain the instantaneous kinematic relation of in-parallel manipulators, by extending the results of screw theory to the forward and inverse instantaneous relations, and gives a formula that can obtain a reciprocal screw analytically without considering geometric relations.

ICRA Conference 2000 Conference Paper

Bandwidth Modulation of Rigid Subsystem for the Class of Flexible Robots

• Joono Cheong
• Wan Kyun Chung
• Youngil Youm

Focuses on the design of rigid part motion control and the selection of bandwidth of the rigid subsystem. Based on the passivity approach and disturbance observer, we investigate the relationship between macro joint tracking performance and vibration suppression capability using the joint motion bandwidth parameter. For the flexibility isolated system, the independent sub-controllers for the rigid and flexible part are proposed just like the singular perturbation approach. The validity of the proposed method is verified by experiments.

ICRA Conference 2000 Conference Paper

Normalized Impact Geometry and Performance Index for Redundant Manipulators

• Jinhyun Kim
• Wan Kyun Chung
• Youngil Youm

We investigate the instantaneous impact phenomenon due to the collision between the manipulator and the environment for kinematically redundant manipulators. First, we define a normalized impact geometry in the viewpoint of normalized velocity change. We then reduce the impulsive effects under uncertain environment for redundant manipulators. A new impact performance index based on velocity direction is proposed. Finally, the performance of the proposed index is demonstrated by numerical examples and experiments.

IROS Conference 2000 Conference Paper

On hard contact force control

• Nukju Doh
• Wan Kyun Chung
• Youngil Youm

In this paper, we consider hard contact force control law which shows good performance as well as enhanced stability and robustness. First, we consider hard contact transition such as hammering when the manipulator's approaching velocity is high or the environment is very stiff. In hard contact, phase transition can be divided into two definitely different phases, "pre-transition phase" and "transition phase". Here we define the "pre-transition phase" and propose a novel controller named as "suppression controller" which is not only stable but also simple to implement. Based on this result, we suggest a hard contact force control scheme which is named "hybrid suppression controller". The effectiveness of these approaches are verified via experiments using POSTECH 1 DOF DD arm.

ICRA Conference 2000 Conference Paper

Pre-Transition Phase Control: Three Different Approaches

• Nakju Lett Doh
• Gyudong Jeon
• Wan Kyun Chung
• Youngil Youm

In this paper, we consider hard contact transition such as hammering when the manipulator's approaching velocity is high or the environment is very stiff. In contact transition, phase transition can be divided into two definitely different phases, "pre-transition phase" and "transition phase". Here we define the "pre-transition phase" and we propose three control methods. First, we propose a novel controller named as "suppression controller" which is not only stable but also simple to implement. Second, we present passive damper named as "flexible-damped joint" which is a good solution to circumvent the pre-transition phase. Third, we suggest a stable and simple controller which can maximize joint damping and minimize recontact velocity in the flexible-damped joint. It is named as "joint damping controller". The effectiveness of these three approaches are verified via experiments using the POSTECH 1-DOF DD arm.

ICRA Conference 2000 Conference Paper

Robust and Time-Optimal Control Strategy for Coarse/Fine Dual-Stage Manipulators

• SangJoo Kwon
• Wan Kyun Chung
• Youngil Youm

A robust and time optimal control strategy for dual-stage manipulator is presented. The time optimal trajectory for a mass-damper system is determined and given as a reference input to the system. The feedback controller is constructed so that the fine stage tracks the coarse stage errors. The controller is robustly designed as the "perturbation compensated sliding mode control" law, which is a combination of sliding mode controller and perturbation observer. In addition, a null motion controller which regulates the fine stage at its neutral position is designed based on the "dynamic consistency" and, as a result, the overall dual-stage servo system exhibits robust and time-optimal performance. The inherent merit and performance of the dual-stage system is shown by experiments.

ICRA Conference 2000 Conference Paper

Unified Motion Specification and Control of Kinematically Redundant Manipulators

• Jonghoon Park
• Wan Kyun Chung
• Youngil Youm

The kinematically decoupled joint space decomposition (KD-JSD) is proposed as a systematic method for synthesis of dynamic control of kinematically redundant manipulators. The method leads to a proper control for direct specification and control of the self-motion of kinematically redundant manipulators, as well as the task motion. To cover various possibilities in specifying desired self-motion behaviors the conventional gradient projection method and task priority based method are reformulated within the framework of the KD-JSD. The validity of the proposed control method is shown experimentally adopting a three degrees-of-freedom direct-drive planar redundant manipulator.

ICRA Conference 1999 Conference Paper

Control of a Car-Like Mobile Robot for Parking Problem

• Sungon Lee
• Youngil Youm
• Wan Kyun Chung

Deals with the parking problem of a car-like mobile robot. The parking problem corresponds to the point-stabilization problem of nonholonomic systems. We propose a simple and efficient algorithm for the problem with stability analysis. Using this algorithm, a car-like mobile robot could be controlled to move to a desired posture within a prescribed boundary. The performance is verified through simulations and experiments using a car-like mobile robot.

IROS Conference 1999 Conference Paper

Control of car-like mobile robots for posture stabilization

• Sungon Lee
• Youngil Youm
• Wan Kyun Chung

Deals with the posture stabilization problem of car-like mobile robots. For a long distance, path-planning should be done first. But, over a short distance like a parking maneuver, path planning is difficult since car-like mobile robots, different from the conventional differential drive mobile robot, have a limit on turning radius. The derivation of a control law is also difficult in the sense that there exists no smooth feedback control for this problem. We propose a simple and efficient algorithm for the problem with stability analysis. Using this algorithm, we can control a car-like mobile robot to move to a desired posture within a prescribed boundary. The performance is verified through simulations and experiments using a car-like mobile robot.

IROS Conference 1999 Conference Paper

On dynamical decoupling of kinematically redundant manipulators

• Jonghoon Park
• Wan Kyun 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.

ICRA Conference 1999 Conference Paper

Performance of Linear Decentralized H-Infinity Optimal Control for Industrial Robotic Manipulators

• Jonghoon Park
• Wan Kyun Chung
• Youngil Youm

Industrial manipulators are under various limitations against high quality motion control, for example friction and dynamic uncertainties, and simple control structure. A robust linear PID motion controller, called the reference error feedback, is proposed, which solves the nonlinear L/sub 2/-gain attenuation control problem. Making use of the fact that the single parameter L/sub 2/-gain /spl gamma/ controls the performance and robustness, we propose a simple and stable method of tuning the controller called the "square law". The analytical results are verified through experiments of six degrees of freedom industrial manipulator.

ICRA Conference 1998 Conference Paper

Analytic Nonlinear Hinfty Optimal Control for Robotic Manipulators

• Jonghoon Park
• Wan Kyun Chung
• Youngil Youm

Recent successes in nonlinear H/sub /spl infin// control design has been applied to control of robot manipulator systems. It is known that the existence of H/sub /spl infin// optimal control reduces to solvability of the Hamilton-Jacobi-Isaacs partial differential equation, which is very difficult to solve. In this article, a robust control in the sense of L/sub 2/-gain attenuation from an external disturbance and one due to model uncertainties is designed for a class of Euler-Lagrange system based on a class of analytic solution to the associated Hamilton-Jacobi-Isaacs equation.

IROS Conference 1998 Conference Paper

Analytic singularity expression for 6-DOF Stewart platform-type parallel manipulators

• Doik Kim
• Wan Kyun Chung
• Youngil Youm

The analytic expression for the singularities of 6-DOF SPM (Stewart-platform type parallel manipulator) is obtained using the concept of LSM (local structurization method) with extra sensors. The resulting equation, however, does not include sensor values, but is a function of design variables. The equation is basically a third-degree polynomial and it exactly provides singularity information for general SPMs. Several symbolic examples are shown to verify the exactness of the singularity equation by comparing it with the previously reported singularities.

IROS Conference 1998 Conference Paper

Experiments on extended impedance control of redundant manipulator

• Yonghwan Oh
• Wan Kyun Chung
• Youngil Youm
• Il Hong Suh

An impedance control approach based on extended task space formulation is addressed to control kinematically redundant manipulators. Defining a weighted inner product in joint space, a minimal parameterization of the null space can be achieved. Based on this formulation, we propose a control law called inertially decoupled impedance controller by expanding the conventional impedance control approach to control the motion of the end-effector as well as the internal motion. Experimental results are given to demonstrate the performance of the proposed control methods.

ICRA Conference 1998 Conference Paper

Motion/Force Decomposition of Redundant Manipulator and its Application to Hybrid Impedance Control

• Yonghwan Oh
• Wan Kyun Chung
• Youngil Youm
• Il Hong Suh

An approach to resolve the kinematic redundancy and to control the motion/force of redundant manipulators is presented. By defining a proper metric in joint space, minimal parametrization of motion and force controlled subspaces as well as the null motion component is realized. With this formulation, control of both motion/force and internal motion of redundant manipulator can be achieved via a new hybrid impedance control method with inertial decoupling of each space. Some numerical examples are given to demonstrate the performance of the proposed control method.

IROS Conference 1998 Conference Paper

𝒽 ∞ robust motion control of kinematically redundant manipulators

• Jonghoon Park
• Wan Kyun Chung
• Youngil Youm
• Moonsang Kim

A robust motion control with special focus on kinematically redundant manipulators is proposed based on the kinematically decoupled (KD) joint space decomposition and the analytic nonlinear /spl Hscr//sub /spl infin// control. Within the /spl Hscr//sub /spl infin// control design, robustness can be achieved by formulating the disturbance input to include model uncertainties and external disturbances as well. The proposed /spl Hscr//sub /spl infin// control is based on the analytic solution of the related Hamilton-Jacobi-Isaccs equation, and does not require any further assumptions except the Euler-Lagrange properties. Two components of motion, task and null motion, of a redundant manipulator are robustly controlled by the proposed KD reference motion compensation (RMC) reference error feedback (REF) control.

IROS Conference 1997 Conference Paper

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.

ICRA Conference 1997 Conference Paper

Extended impedance control of redundant manipulators using joint space decomposition

• Yonghwan Oh
• Wan Kyun Chung
• Youngil Youm

An impedance control approach based on extended task space formulation is addressed to control the kinematically redundant manipulators. Defining a weighted inner product in joint space, a minimal parametrization of the null space can be achieved. Based on this formulation, we propose a control law called inertially decoupled impedance controller by expanding the conventional impedance control approach to control the motion of the end-effector as well as the internal motion. Some numerical simulations are given to demonstrate the performance of the proposed control methods.

ICRA Conference 1997 Conference Paper

Geometrical approach for the workspace of 6-DOF parallel manipulators

• Doik Kim
• Wan Kyun Chung
• Youngil Youm

Since parallel manipulators have relatively small workspace when compared to serial manipulators, it is important to determine the workspace in the design stage. However, due to the complexity of the closed-loop chain mechanism, the determination of the workspace is difficult. In this paper, a fully geometrical method for the determination of the workspace of 6-DOF parallel manipulators is presented using the concept of a 4-bar linkage. The reachable and dexterous workspace can be determined from the proposed algorithm. In order to evaluate the workspace, each leg is considered as an open chain, and two kinematic constraints-position and mechanism constraints-are developed. The proposed method is verified by simulation.

ICRA Conference 1997 Conference Paper

Robust control of manipulators using Hamiltonian optimization

• Youngjin Choi
• Wan Kyun Chung
• Youngil Youm

Although nonlinear H/sub /spl infin// control theory for systems with uncertainties has been developed, it has been rarely applied to robot manipulators. We derive Hamiltonian equations of motion and Hamiltonian matrix (Riccati equation) for robot manipulators to get an optimal controller. Using the H/sub /spl infin// framework, we specify the L/sub 2/ norm of the performance measure, which consists of the position and momentum error during the task when there are uncertainties in the dynamic model of robot manipulators. For practical application, a stationary solution of the Riccati equation for the end-point is suggested and evaluated by simulation.

IROS Conference 1997 Conference Paper

Singularity analysis of 6-DOF parallel manipulator with local structuralization method

• Doik Kim
• Wan Kyun Chung
• Youngil Youm

Generally, singularity analysis of 6-DOF parallel manipulators is very difficult and, as a result, the velocity relation has many uncertainties. Many researchers have reported that the forward position kinematics can be solved more easily with extra sensors. However, the relation of the velocity kinematics with extra sensors has not been fully studied yet. In this paper, an alternative method using the local structuralization method (LSM) for the analysis of singular configurations is presented. With LSM, the velocity relation can be represented in a simple form, and the result is totally equivalent to the conventional velocity relation. The velocity relation suggested in this paper gives a closed-form solution of singularities.

ICRA Conference 1997 Conference Paper

Task based design of modular robot manipulator using efficient genetic algorithm

• Wan Kyun Chung
• Jeongheon Han
• Youngil Youm
• Seungho Kim

A modular robot manipulator is a robotic system assembled from discrete joints and links into one of many possible manipulator configurations. This paper describes a task based design method of modular robot manipulators. A locking mechanism which provides quick coupling and decoupling is developed and a parallel connection method is devised reducing the number of components on each module. To automatically determine the optimal link lengths of a modular manipulator for a given, task, the algorithm is two step: determine the necessary configuration of the robot using kinematic equations and then determine the optimal link length using the proposed efficient genetic algorithm. Some of design examples are shown.

ICRA Conference 1996 Conference Paper

An easily attainable and effective bilateral control for teleoperation

• Jaebum Son
• Youngil Youm
• Wan Kyun Chung
• Kyuwon Jeong

Teleoperating system has been developed for several decades, and many control schemes for it have been suggested. But the implementation for real applications needs a very effective but simple controller. In this paper, an advanced control scheme to achieve this objective is suggested, which is the combination of a modified internal model controller and a variable filter for force reflection. The effectiveness of the proposed scheme is verified through experiment. Both responses of unconstrained and contact motions for the testbed-walls with different stiffness are shown.

ICRA Conference 1996 Conference Paper

Control input reconstruction using redundancy under torque limit

• Jonghoon Park
• Wan Kyun Chung
• Youngil Youm
• Moonsang Kim
• Mankeun Kim

Various physical limitations which intrinsically exist in the manipulator control system, for example kinematic limits and torque limit, cause some undesirable effects. Specifically, when one or more actuators are saturated in torque the expected control performance can not be achieved. The effect of torque limit, especially for redundant manipulators, is studied in this article, and a local and analytic method to reconstruct the control input using the redundancy is proposed based on the kinematically decoupled modeling of redundant manipulators. It results in exact compensation of the task motion dynamic error at the cost of the least null motion dynamic error. Numerical simulations help to verify the advantages of the proposed scheme.

ICRA Conference 1996 Conference Paper

Design of compliant motion controllers for kinematically redundant manipulators

• Jonghoon Park
• WanKyun Chang
• Youngil Youm

Design of a compliant motion controller using a redundant manipulator is addressed in this article. Specifically, a hybrid controller and an impedance controller are extended to general redundant manipulators based on the kinematically and geometrically decoupled joint space decomposition. Geometrically decoupled task space decomposition provides a systematic ways of geometric modeling of general constraints. Both controllers have the advantage that the closed-loop dynamics of the manipulator are decomposed into position-controlled, force-controlled, and null motion-controlled subspaces, and each are linearized, reshaped to desired dynamics, and decoupled from the others. A simple numerical simulations prove the applicability of the proposed algorithms.

IROS Conference 1996 Conference Paper

Reconstruction of inverse kinematic solution subject to joint kinematic limits using kinematic redundancy

• Jonghoon Park
• Wan Kyun Chung
• Youngil Youm
• Moonsang Kim

Various physical limitations which intrinsically exist in the manipulator inverse kinematic system, for example joint travel and velocity limits, cause some undesirable effects. Specifically, when one or more joints are limited the desired task velocity can not be anticipated. The effect of joint kinematic limits, especially for redundant manipulators, is studied in this article, and an analytic method to reconstruct the inverse kinematic solution using the redundancy is proposed based on the kinematically decoupled modeling of redundant manipulators. It results in no error in the task motion at the cost of the least error in the null motion. Numerical simulations help to verify the advantages of the proposed scheme.

ICRA Conference 1996 Conference Paper

Weighted decomposition of kinematics and dynamics of kinematically redundant manipulators

• Jonghoon Park
• Wan Kyun Chung
• Youngil Youm

The kinematics and dynamics of kinematically redundant manipulators are to be decomposed in consistent way with the joint space decomposition induced by the weighted pseudo-inverse operation. The weighted kinematically decoupled joint space decomposition results to a family of decomposed kinematics and dynamics, parametrized by the symmetric positive-definite weight matrix, in the task motion and weighted null motion space. The inertially-decoupled weighted decomposition is shown to be only possible with the inertia as the weight. Also, the feedback motion controller which is consistent with a specific joint space decomposition is developed. The controller realizes the decoupled and linearized reference acceleration tracking controller in the task motion and weighted null motion space.

ICRA Conference 1995 Conference Paper

Local Structurization for the Forward Kinematics of Parallel Manipulators Using Extra Sensor Data

• Kilryong Han
• Wan Kyun Chung
• Youngil Youm

This paper presents a new extra sensing approach of local structurization to the forward kinematics of 6-DOF Stewart platform manipulators (SPMs). It is shown that one extra sensor is sufficient for both a 3-3 SPM and a 6-3 SPM to exactly resolve the forward kinematic problem (FKP) of the SPMs in closed form, two for a 6-6 SPM. In previous researches, at least three extra sensors were needed for closed-form resolution of the FKP of a 6-6 SPM. As a basis for the new approach, two concepts, local structurization and mechanism partition, are introduced. The new scheme is described with graphical illustrations and verified through numerical examples. Consequently, the new scheme is suitable to real implementation, because its computation is very efficient.

IROS Conference 1995 Conference Paper

Specification and control of motion for kinematically redundant manipulators

• Jonghoon Park
• Wan Kyun Chung
• Youngil Youm

Useful specification and stable control of motions for redundant manipulators are two important application aspects. In this article, the dynamic controller which can stabilize the output motion and the null motion is proposed, which has also a unified null motion specification algorithm in it. It is distinctive in that it renders the closed loop system dynamics linear and decoupled in the null space as well as the output space. All the work in this article are based on the kinematically decomposed modeling.

ICRA Conference 1994 Conference Paper

Behaviors of Extended Jacobian Method for Kinematic Resolutions of Redundancy

• Jonghoon Park
• Wan Kyun Chung
• Youngil Youm

The characteristic of an inverse kinematic solution for redundant manipulators using EJM is exploited with the sufficient condition for EJM. A new analytic perspective other than the well-known algebraic and less-known geometric one on algorithmic singularity of EJM is proposed, on the basis of optimization process. The characteristic of a solution with EJM is shown to be able to change only by crossing the algorithmic singularity thereof. A 3-DOF planar redundant robot is analyzed when EJM is applied with the manipulability as an example. >

ICRA Conference 1994 Conference Paper

Implementation of Passive Hardware Damper for Force and Impact Control

• Yonghwan Oh
• Wan Kyun Chung
• K. W. Jeong
• Youngil Youm

This paper deals with the modeling and implementation of a robot system for force and impact control using a newly developed passive hardware damper. The system with passive damper is modeled and based on the model, the stability of the whole system with respect to force feedback gain is analyzed. The limitations of the conventional velocity feedback to produce damping characteristic is discussed. Experiments are performed with/without passive damper to verify the effectiveness of the passive damping method and it is shown that the passive damper can help the system make stable contact during the contact period especially with highly stiff environment. >

ICRA Conference 1994 Conference Paper

Stiffness Analysis and Control of Redundant Manipulators

• Hyouk Ryeol Choi
• Wan Kyun Chung
• Youngil Youm

In this paper, two points are addressed as for the stiffness control of redundant manipulators. The first is, through the joint stiffness analysis, a generalized stiffness model between the joint and taskspace stiffness. Differing from the previous stiffness model, this model shows the existence of the additional stiffness concerning the configuration change and force. The second is the joint stiffness control scheme of redundant manipulators based on the developed model, called orthogonal stiffness decomposition control. The effectiveness of the proposed model and control method is verified through simulations and experiments. >

IROS Conference 1993 Conference Paper

Dynamic control of redundant manipulators using full row-rank minors of Jacobian

• Won Jee Chung
• Wan Kyun Chung
• Youngil Youm

A dynamic control method that outperforms existing local torque optimization techniques for kinematically redundant manipulators is proposed. The proposed method resolves redundancy at the acceleration level. The command acceleration is composed of two terms: the minimum-norm acceleration and the null-space acceleration, which is intermittently added to the minimum-norm acceleration according to a kinematic criterion to globally reduce excessively large torque requirements. In particular, both the generation and the control of null-space acceleration is based on the property of full row-rank minors of a Jacobian matrix, i. e. , the aspect, which is a function of a manipulator's configuration. Numerical simulations illustrated good capability from the viewpoint of torque optimization and global stability.

IROS Conference 1993 Conference Paper

Stiffness analysis of multi-fingered robot hands

• Hyouk Ryeol Choi
• Wan Kyun Chung
• Youngil Youm

The stiffness of a grasp is analyzed on the basis of the generalized virtual stiffness (GVS) model. Considering that the normal and lateral stiffness of the finger usually are not decoupled due to kinematics and mechanical design, GVS is formulated as coupled virtual springs. The authors relate GVS to the effective fingertip stiffness including the additional stiffness at the joint space. Based on the grasp stiffness formulation, simulations were carried out, focusing on the grasp stability.

IROS Conference 1992 Conference Paper

New Dexterity Index Based On Effective Minors For Planar Redundant Manipulators

• Won Jee Chung
• Wan Kyun Chung
• Youngil Youm

ICRA Conference 1991 Conference Paper

Inverse kinematics of planar redundant manipulators using virtual link and displacement distribution schemes

• Won Jee Chung
• Wan Kyun Chung
• Youngil Youm

A method for the inverse kinematic problem of planar manipulators with multiple degrees of redundancy is proposed. The method starts by decomposing a redundant arm into a series of the local arms which are either two-link or three-link planar manipulator modules and by connecting the conjunction points between local arms with virtual links. In addition to virtual links, a displacement distribution scheme where the displacement of an end-effector is allocated to those of local arms according to displacement distribution criteria is also proposed. To effectively guide the proposed schemes, a dexterity index called the configuration index is utilized. Computer simulations of redundant manipulators using the proposed method are demonstrated as numerical examples. >

IROS Conference 1991 Conference Paper

J-minor based dynamic control (JMDC) for kinematically redundant manipulators

• Won Jee Chung
• Wan Kyun Chung
• Youngil Youm

This paper presents a real-time dynamic control method for kinematically redundant manipulators. The proposed method aims at reducing excessive joint torques, which have caused the instability of conventional local torque minimization algorithms, by preserving the signs of full row rank minors of the manipulator Jacobian. It is shown by computer simulations that these minors have close relation with the dynamics of redundant manipulators, which has not been treated carefully. The proposed method is found to be effective for torque reduction when compared with conventional approaches including the inertia-weighted pseudoinverse method, the null space vector method, and the redundancy decomposition control method. >