Sangdeok Park

Accurate Modeling and Robust Hovering Control for a Quad---rotor VTOL Aircraft

Quad-robot type (QRT) unmanned aerial vehicles (UAVs) have been developed for quick detection and observation of the circumstances under calamity environment such as indoor fire spots. The UAV is equipped with four propellers driven by each electric motor, an embedded controller, an Inertial Navigation System (INS) using three rate gyros and accelerometers, a CCD (Charge Coupled Device) camera with wireless communication transmitter for observation, and an ultrasonic range sensor for height control. Accurate modeling and robust flight control of QRT UAVs are mainly discussed in this work. Rigorous dynamic model of a QRT UAV is obtained both in the reference and body frame coordinate systems. A disturbance observer (DOB) based controller using the derived dynamic models is also proposed for robust hovering control. The control input induced by DOB is helpful to use simple equations of motion satisfying accurately derived dynamics. The developed hovering robot shows stable flying performances under the adoption of DOB and the vision based localization method. Although a model is incorrect, DOB method can design a controller by regarding the inaccurate part of the model and sensor noises as disturbances. The UAV can also avoid obstacles using eight IR (Infrared) and four ultrasonic range sensors. This kind of micro UAV can be widely used in various calamity observation fields without danger of human beings under harmful environment. The experimental results show the performance of the proposed control algorithm.

RIC (robust internal-loop compensator) based flight control of a quad-rotor type UAV

A QRT (quad-rotor type) hovering robot system is developed for quick detection and observation of the circumstances under calamity environment such as indoor fire spots. The UAV (unmanned aerial vehicle) is equipped with four propellers driven by each electric motor, an embedded controller, an INS (inertial navigation system) using three rate gyros and accelerometers, a CCD (charge coupled device) camera with wireless communication transmitter for observation, and an ultrasonic range sensor for height control. The developed hovering robot shows stable flying performances under the adoption of RIC (robust internal-loop compensator) based disturbance compensation and the vision based localization method. Although a model is incorrect, RIC method can design a controller by regarding the inaccurate part of the model and sensor noises as disturbances. The UAV can also avoid obstacles using eight IRs (infrareds) and four ultrasonic range sensors. This kind of micro UAV can be widely used in various calamity observation fields without danger of human beings under harmful environment.

An Effective Kalman Filter Localization Method for Mobile Robots

An effective Kalman filter localization method for mobile robots is investigated in terms of the robust Kalman filter with perturbation estimator. In the recursive algorithm, the perturbation estimator produces equivalent perturbations with respect to the nominal state equation and the action model of a mobile robot is adaptively modified with the perturbation estimates. The integral control property of the perturbation estimator enables a great reduction of the localization error, specifically when the odometric disturbance is large. The Kalman filter recursive equations including predictor, corrector, perturbation estimator, and the corresponding covariance propagation equations are formulated systematically. The effectiveness of the proposed scheme is verified through simulation and experimental results for a wheeled mobile robot

Central pattern generator based reflexive control of quadruped walking robots using a recurrent neural network

This paper presents a novel Central Pattern Generator (CPG) model for controlling quadruped walking robots. The improvement of this model focuses on generating any desired waveforms along with accurate online modulation. In detail, a well-analyzed Recurrent Neural Network is used as the oscillators to generate simple harmonic periodic signals that exhibit limit cycle effects. Then, an approximate Fourier series is employed to transform those mentioned simple signals into arbitrary desired outputs under the phase constraints of several primary quadruped gaits. With comprehensive closed-form equations, the model also allows the user to modulate the waveform, the frequency and the phase constraint of the outputs online by directly setting the inner parameters without the need for any manual tuning. In addition, an associated controller is designed using leg coordination Cartesian position as the control state space based on which stiffness control is performed at sub-controller level. In addition, several reflex modules are embedded to transform the feedback of all sensors into the CPG space. This helps the CPG recognize external disturbances and utilize inner limit cycle effect to stabilize the robot motion. Finally, experiments with a real quadruped robot named AiDIN III performing several dynamic trotting tasks on several unknown natural terrains are presented to validate the effectiveness of the proposed CPG model and controller.

Service-oriented reverse reengineering: 5W1H model-driven re-documentation and candidate services identification

The purpose of this paper is to propose a service-oriented reverse reengineering that consists of re-documentation and design recovery. To understand the legacy system, we need to re-document the legacy system in a highlevel abstraction by using UML visual models through an initial reverse engineering. For this re-documentation, we propose a new re-documentation technique called 5W1H (Why, Who, When, Where, What, and How) model-driven re-documentation. Based upon the re-documented software visual model, we attempt to identify the scope of locating the candidate services from a legacy system. To show the feasibility of our approach, two applications using different design methods and architectures are re-documented into visual models. After recovering design methods and architectural patterns from the visual models, which have been injected into source code implicitly or explicitly to bring clear separation of concerns, we locate the scope of candidate services from the legacy system. We can reduce the effort of identifying candidate services by using the visualized model since we can discover highly possible locations for reusable business logic effectively. The service-oriented reverse engineering using 5W1H re-documentation technique will help a service producer to easily discover the candidate services from a legacy system through software re-documentation.

Robust mobile robot localization with combined Kalman filter-perturbation estimator

In this paper, a robust localization method for mobile robot based on the combination of Kalman filter and perturbation estimator is presented. It remarkably enhances the robustness of localization performance, specifically when large odometric errors are occurred. The perturbation estimator in the combined Kalman filter (CKF) is to estimate systematic errors which perturbs the behavior of nominal state transition equation. Intrinsically, it has the property of integrating the innovation, i.e., the difference between measurement and predicted measurement and thus gives a chance of more reducing the gap between real states and their estimates. After formulation of the CKF recursion, we show how the design parameters can be determined and how much beneficial it is through simulation and experiment for a two-wheeled mobile robot under indoor GPS.

Foot Trajectory Generation of Hydraulic Quadruped Robots on Uneven Terrain

This paper proposes trot pattern generation and online control methods for a legged robot to carry heavy-loads and move fast on the uneven terrain. The trot pattern is generated from the frequency modulated pattern generation method based on the frequency modulated oscillator in order for the legged robots to operate outdoors with the static and dynamic mobility. The efficiency and performance of the proposed are verified through the computer simulation and experiments using qRT-1/-2. In experiments, qRT which is a 2-legged and 2-wheeled robot and a front drive system vehicle with hydraulic linear actuators is used. The robot has trotted gaits at speeds up to 1.3 m/s on the even surface, walked up and down the 20 degree inclines, and walked at 0.7 m/s on the uneven surface. Also it has carried over 100 kg of the total weights including over 40 kg of the payload.

Development of mobile robot systems for automatic diagnosis of boiler tubes in fossil power plants and large size pipelines

Two types of mobile robotic systems using an NDT (nondestructive testing) method are developed for automatic diagnosis of boiler tubes in fossil power plants and large size pipelines. The developed mobile robots crawl on the outer surface of the tubes and the pipelines to detect in-pipe defects such as pinholes, cracks and thickness reduction by corrosion and/or erosion using an EMAT (electromagnetic acoustic transducer). Automation of defect detection by mobile robotic systems for these large-scale structures helps to prevent significant problems without danger to human beings under the harmful environment.

Drift Reduction in Pedestrian Navigation System by Exploiting Motion Constraints and Magnetic Field

Pedestrian navigation systems (PNS) using foot-mounted MEMS inertial sensors use zero-velocity updates (ZUPTs) to reduce drift in navigation solutions and estimate inertial sensor errors. However, it is well known that ZUPTs cannot reduce all errors, especially as heading error is not observable. Hence, the position estimates tend to drift and even cyclic ZUPTs are applied in updated steps of the Extended Kalman Filter (EKF). This urges the use of other motion constraints for pedestrian gait and any other valuable heading reduction information that is available. In this paper, we exploit two more motion constraints scenarios of pedestrian gait: (1) walking along straight paths; (2) standing still for a long time. It is observed that these motion constraints (called “virtual sensor”), though considerably reducing drift in PNS, still need an absolute heading reference. One common absolute heading estimation sensor is the magnetometer, which senses the Earth’s magnetic field and, hence, the true heading angle can be calculated. However, magnetometers are susceptible to magnetic distortions, especially in indoor environments. In this work, an algorithm, called magnetic anomaly detection (MAD) and compensation is designed by incorporating only healthy magnetometer data in the EKF updating step, to reduce drift in zero-velocity updated INS. Experiments are conducted in GPS-denied and magnetically distorted environments to validate the proposed algorithms.

A new method in modeling Central Pattern Generators to control quadruped walking robots

Aiming to real easy application in several quadruped robot platforms, this paper introduces a new method of modeling central pattern generators (CPG) to control quadruped locomotion. Not only can this new model generate all the primary gaits of quadrupeds stably with limit cycle effect, but it also has the ability of tuning the periodic outputs with arbitrary waveforms. The core idea is to combine strong points of two mathematical tools: Fourier series and Recurrent neural networks. In addition, a new biomimetic controller is also introduced using the proposed CPG model and several reflex modules. Finally, dynamic simulations are performed to validate the efficiency of the proposed controller.