Sang Bong Kim

Pole assignment in a specified disk

The problem of assigning all poles of a closed-loop system in a specified disk by state feedback is considered for both continuous and discrete systems. A state feedback control law is determined by using a discrete Riccati equation. This kind of pole assignment problem is named D -pole assignment, and its relation to the optimal control problem and its robustness properties are discussed. The gain and phase margins for all closed-loop poles to stay inside the specified disk D are determined for the proposed control.

Modeling and Simulation for PIG Flow Control in Natural Gas Pipeline

This paper deals with dynamic analysis of Pipeline Inspection Gauge (PIG) flow control in natural gas pipelines. The dynamic behaviour of PIG depends on the pressure differential generated by injected gas flow behind the tail of the PIG and expelled gas flow in front of its nose. To analyze dynamic behaviour characteristics (e.g. gas flow, the PIG position and velocity) mathematical models are derived. Two types of nonlinear hyperbolic partial differential equations are developed for unsteady flow analysis of the PIG driving and expelled gas. Also, a non-homogeneous differential equation for dynamic analysis of the PIG is given. The nonlinear equations are solved by method of characteristics (MOC) with a regular rectangular grid under appropriate initial and boundary conditions. Runge-Kutta method is used for solving the steady flow equations to get the initial flow values and for solving the dynamic equation of the PIG. The upstream and downstream regions are divided into a number of elements of equal length. The sampling time and distance are chosen under Courant-Friedrich-Lewy (CFL) restriction. Simulation is performed with a pipeline segment in the Korea gas corporation (KOGAS) low pressure system, Ueijungboo-Sangye line. The simulation results show that the derived mathematical models and the proposed computational scheme are effective for estimating the position and velocity of the PIG with a given operational condition of pipeline.

Regulator design with poles in a specified region

A design method for regulators having poles in a specified region by using conformal mapping is proposed and the following two problems of regulator design are considered. The first is how to design all poles of a closed-loop system in a specified region by state feedback, and the other is how to design optimal regulators of which the poles may be located in a specified region, i.e. how to obtain the weighting matrices of a quadratic criterion function which yields all its poles in a specified disc with radius r and centre a within the left-half complex plane for continuous systems and in the unit circle for discrete systems.

Sliding Mode Control of Two-Wheeled Welding Mobile Robot for Tracking Smooth Curved Welding Path

In this paper, a nonlinear controller based on sliding mode control is applied to a two-wheeled Welding Mobile Robot (WMR) to track a smooth curved welding path at a constant velocity of the welding point. The mobile robot is considered in terms of dynamics model in Cartesian coordinates under the presence of external disturbance, and its parameters are exactly known. It is assumed that the disturbance satisfies the matching condition with a known boundary. To obtain the controller, the tracking errors are defined, and the two sliding surfaces are chosen to guarantee that the errors converge to zero asymptotically. Two cases are to be considered : fixed torch and controllable torch. In addition, a simple way of measuring the errors is introduced using two potentiometers. The simulation and experiment on a two-wheeled welding mobile robot are provided to show the effectiveness of the proposed controller.

Speed control of PIG using bypass flow in natural gas pipeline

This paper introduces a simple nonlinear control method for pipeline inspection gauge (PIG) flow in a natural gas pipeline. The PIG is controlled using the amount of bypass flow across its body. The dynamic behavior of the PIG depends on the different pressure across its body and the bypass flow through it. The system dynamics includes: dynamics of driving gas flow behind the PIG, dynamics of expelled gas in front of the PIG, dynamics of bypass flow and dynamics of the PIG. The method of characteristics (MOC) and Runge-Kutta method are used to solve the dynamics of flow. To control the PIG velocity, a simple nonlinear controller is proposed based on the back-stepping method. The closed loop system is stable in the sense of Lyapunov stability. To derive such a controller, three system parameters should be measured: the PIG position, its velocity and the velocity of bypass flow across the PIG body. To show the effectiveness of the proposed controller, the simulation has been done with three cases: the PIG starts to move at its launcher, the PIG arrives at its receiver and the PIG restarts after stopping in the pipeline. The simulation results show that the proposed controller can be used for controlling the PIG velocity with good performance when it runs in the natural gas pipeline.

Dynamic modeling and its analysis for PIG flow through curved section in natural gas pipeline

Dynamic modeling and its analysis for the PIG (pipeline inspection gauge) flow through a 90/spl deg/ curved pipe with compressible and unsteady flow are studied. The PIG dynamics model is derived by using a Lagrange equation under the assumption that it passes through 3 different sections in the curved pipeline such that it moves into, inside and out of the curved section. The downstream and up stream flow dynamics including the curved sections are solved using the method of characteristic. The effectiveness of the derived mathematical models is estimated by simulation results for a low pressure natural gas pipeline including downward and upward curved sections. The simulation results show that the proposed model and solution can be used for estimating the PIG dynamics when we pig the pipeline including curved sections.

Verification of the Theoretical Model for Analyzing Dynamic Behavior of the PIG from Actual Pigging

This paper deals with verification of the theoretical model for dynamic behavior of Pipeline Inspection Gauge (PIG) traveling through high pressure natural gas pipeline. The dynamic behavior of the PIG depends on the differential pressure across its body. This differential pressure is generated by injected gas flow behind the tail of the PIG and expelled gas flow in front of its nose. To analyze the dynamic behavior characteristics such as gas flow in pipeline, and the PIG position and velocity, not only the mathematical models are derived, but also the theoretical models must be certified by actual pigging experiment. But there is not any found results of research on the experimental certification for dynamic behavior of the PIG. The reason is why the fabrication of the PIG as well as, a field application are very difficult. In this research, the effectiveness of the introduced solution using the method of characteristics (MOC) was certified through field application. In-line inspection tool, 30” geometry PIG, was fabricated and actual pigging was carried out at the pipeline segment in Korea Gas Corporation (KOGAS) high pressure system, Incheon LT(LNG Terminal) -Namdong GS(Governor Station) line. Pigging is fulfilled successfully. Comparison of simulation results with experimental results show that the derived mathematical models and the proposed computational schemes are effective for predicting the position and velocity of the PIG with a given operational conditions of pipeline.

Modeling and motion control of mobile robot for lattice type welding

This paper presents a motion control method and its simulation results of a mobile robot for a lattice type welding. Its dynamic equation and motion control methods for welding speed and seam tracking are described. The motion control is realized in the view of keeping constant welding speed and precise target line even though the robot is driven for following straight line or curve. The mobile robot is modeled based on Lagrange equation under nonholonomic constraints and the model is represented in state space form. The motion control of the mobile robot is separated into three driving motions of straight locomotion, turning locomotion and torch slider control. For the torch slider control, the proportional-integral-derivative (PID) control method is used. For the straight locomotion, a concept of decoupling method between input and output is adopted and for the turning locomotion, the turning speed is controlled according to the angular velocity value at each point of the corner with range of 90° constrained to the welding speed. The proposed control methods are proved through simulation results and these results have proved that the mobile robot has enough ability to apply the lattice type welding line.

Development of high speed rotating arc sensor and seam tracking controller for welding robots

The paper presents a seam tracking controller of high speed rotating arc sensor developed by a microprocessor based system. The seam tracking algorithm is based on the average current value at each interval region of four phase points on one relating cycle. To remove the noise effect for the measured current, the area during one rotating cycle is separated into four regions of front, rear, left and light. The average values at each region are calculated, using the regional current values and a low pass filter incorporating the moving average and exponential smoothing methods are adopted. The effectiveness is proven through the experimental results for several kinds of welding condition.

An optimal control method for biped robot with stable walking gait

This paper proposes an optimal control method for a 10 degree of freedom (DOF) biped robot with stable walking gait. The biped robot is modeled as a 3D inverted pendulum. From dynamic model of the 3D inverted pendulum and under the assumption that center of mass (COM) of the biped robot moves on a horizontal constraint plane, zero moment point (ZMP) equations of the biped robot depending on the coordinate of the center of the pelvis link obtained from the dynamic model of the biped robot are given based on the DdasiaAlembertpsilas principle. A walking pattern is generated based on ZMP tracking control systems that are constructed to track the ZMP of the biped robot to zigzag ZMP reference trajectory decided by the footprint of the biped robot. An optimal tracking controller is designed to control the ZMP tracking control system. From the trajectory of the COM of the biped robot and an arc reference input of the swinging leg, the inverse kinematics solved by the solid geometry method is used to compute the angles of each joint of the biped robot. The simulation and experimental results show the effectiveness of this proposed control method.