• Journal of Broadcast Engineering
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• v.26 no.5
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• pp.519-532
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• 2021

Recently, in various fields such as games, movies, and animation, content that uses motion capture to build body models and create characters to express in 3D space is increasing. Studies are underway to generate animations using RGB-D cameras to compensate for problems such as the cost of cinematography in how to place joints by attaching markers, but the problem of pose estimation accuracy or equipment cost still exists. Therefore, in this paper, we propose a system that inputs RGB images into a joint estimation network and converts the results into 3D data to create FBX format animations in order to reduce the equipment cost required for animation creation and increase joint estimation accuracy. First, the two-dimensional joint is estimated for the RGB image, and the three-dimensional coordinates of the joint are estimated using this value. The result is converted to a quaternion, rotated, and an animation in FBX format is created. To measure the accuracy of the proposed method, the system operation was verified by comparing the error between the animation generated based on the 3D position of the marker by attaching a marker to the body and the animation generated by the proposed system.

• International Journal of Aeronautical and Space Sciences
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• v.12 no.1
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• pp.43-56
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• 2011

An integrated system composed of guidance, navigation and control (GNC) system for autonomous proximity operations and the docking of two spacecraft was developed. The position maneuvers were determined through the integration of the state-dependent Riccati equation formulated from nonlinear relative motion dynamics and relative navigation using rendezvous laser vision (Lidar) and a vision sensor system. In the vision sensor system, a switch between sensors was made along the approach phase in order to provide continuously effective navigation. As an extension of the rendezvous laser vision system, an automated terminal guidance scheme based on the Clohessy-Wiltshire state transition matrix was used to formulate a "V-bar hopping approach" reference trajectory. A proximity operations strategy was then adapted from the approach strategy used with the automated transfer vehicle. The attitude maneuvers, determined from a linear quadratic Gaussian-type control including quaternion based attitude estimation using star trackers or a vision sensor system, provided precise attitude control and robustness under uncertainties in the moments of inertia and external disturbances. These functions were then integrated into an autonomous GNC system that can perform proximity operations and meet all conditions for successful docking. A six-degree of freedom simulation was used to demonstrate the effectiveness of the integrated system.

• Journal of Sensor Science and Technology
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• v.28 no.2
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• pp.81-87
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• 2019

One of the major issues in inertial and magnetic measurement unit (IMMU)-based 3D orientation estimation is compensation for magnetic disturbances in magnetometer signals, as the magnetic disturbance is a major cause of inaccurate yaw estimation. In the proposed approach, a kinematic constraint is used to provide a measurement equation in addition to the accelerometer and magnetometer signals to mitigate the disturbance effect on the orientation estimation. Although a Kalman filter (KF) is the most popular framework for IMMU-based orientation estimation, a complementary filter (CF) has its own advantages over KF in terms of mathematical simplicity and ease of implementation. Accordingly, this paper introduces a quaternion-based CF with a constraint-combined correction equation. Furthermore, the weight of the constraint relative to the magnetometer signal is adjusted to adapt to magnetic environments to optimally deal with the magnetic disturbance. In the results of our validation experiments, the average and maximum of yaw errors were $1.17^{\circ}$ and $1.65^{\circ}$ from the proposed CF, respectively, and $8.88^{\circ}$ and $14.73^{\circ}$ from the conventional CF, respectively, showing the superiority of the proposed approach.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.10
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• pp.1023-1030
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• 2015

The purpose of this paper is to present the basic mathematical modeling of a hexacopter, which could be used to develop proper methods for stabilization and trajectory control. A hexacopter consists of six rotors with three pairs of counter-rotating fixed-pitch blades. This mechanism is an under-actuated, dynamically unstable, six-degrees-of-freedom system. The whole motion of this object consists of translational and rotational motion in three dimensions, where the translational motion is created by changing the direction and magnitude of the upward propeller thrust. The hexacopter is controlled by adjusting the angular velocities of the rotors, which are spun by electric motors. It is assumed to be a rigid body; thus, the differential equation of the hexacopter dynamics can be derived from the Newton-Euler equation. The Euler-angle parametrization of the three-dimensional rotations contains singular points in the coordinate space that can cause failure of both the dynamical model and control. In order to avoid singularities, the rotations of the hexacopter are parametrized in terms of quaternions. This choice has been made considering the linearity of the quaternion formulation and their stability and efficiency. Further, control simulation of a hexacopter applying cascaded-PID control is also presented in this paper.

• 한국전산유체공학회:학술대회논문집
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• 2008.03a
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• pp.208-214
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• 2008

The equilibrium molecular-dynamic simulations have been performed to estimate the properties of the three kinds of fluids (the Lennard-Jones fluid, water and aqueous sodium-chloride solution) confined between two plates that are separated by 1.086 nm; included in the equilibrium properties are the density distribution and the static structure, and the diffusivity in the dynamic property. Three kinds of fluids considered in this study are. The water molecules are modeled by using the SPC/E model and the ions by the charged Lennard-Jones particle model. To treat the water molecules, we combined the quaternion coordinates with Euler angles. We also proposed a plausible algorithm to assign the initial position and direction of molecules. The influence of polarization of water molecules as well as the presence of ions in the solution on the properties will be addressed in this study. In addition, we performed the non-equilibrium molecular-dynamic simulation to compute the flow velocity for the case with the gravitational force acting on molecules.

• 한국전산유체공학회:학술대회논문집
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• 2008.10a
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• pp.208-214
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• 2008

The equilibrium molecular-dynamic simulations have been performed to estimate the properties of the three kinds of fluids (the Lennard-Jones fluid, water and aqueous sodium-chloride solution) confined between two plates that are separated by 1.086 nm; included in the equilibrium properties are the density distribution and the static structure, and the diffusivity in the dynamic property. Three kinds of fluids considered in this study are. The water molecules are modeled by using the SPC/E model and the ions by the charged Lennard-Jones particle model. To treat the water molecules, we combined the quaternion coordinates with Euler angles. We also proposed a plausible algorithm to assign the initial position and direction of molecules. The influence of polarization of water molecules as well as the presence of ions in the solution on the properties will be addressed in this study. In addition, we performed the non-equilibrium molecular-dynamic simulation to compute the flow velocity for the case with the gravitational force acting on molecules.

• Journal of computational fluids engineering
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• v.14 no.1
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• pp.24-34
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• 2009

The equilibrium molecular-dynamic simulations have been performed to estimate the properties of the three kinds of fluids confined between two plates that are separated by 1.086 nm; included in the statical properties are the density distribution and the static structure, and the autocorrelation velocity function in the dynamic property. Three kinds of fluids considered in this study are the Lennard-Jones fluid, water and aqueous sodium-chloride solution. The water molecules are modeled by using the SPC/E model and the ions by the charged Lennard-Jones particle model. To treat the water molecules, we combined the quaternion coordinates with Euler angles. We also proposed a plausible algorithm to assign the initial position and direction of molecules. The influence of polarization of water molecules as well as the presence of ions in the solution on the properties will be addressed in this study. In addition, we performed the non-equilibrium molecular-dynamic simulation to compute the flow velocity for the case with the gravitational force acting on molecules.

• Advances in aircraft and spacecraft science
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• v.5 no.4
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• pp.459-475
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• 2018

In the field of aerospace engineering, accurate control of a spacecraft's orientation is often very important to mission success. Therefore, attitude control is a technically plentiful and extensively studied subject in controls literature during recent decades. This investigation of spacecraft attitude control is assumed to address two important aspects of the problem solutions. One sliding mode anti-disturbance control for utilization of faulty actuator components and another one disturbance observer based control to improve the pointing accuracy in the absence of anti-vibration equipment for the elastic appendages like a solar panel. Simultaneous occurrence of vibration due to flexible appendages and reaction degradation due to failure in attitude actuators complicates this case. The advantage of this method is acquisition proper control by the combination of disturbance observer and sliding mode compensation that form a fault tolerant control for the concerned satellite attitude control system. Furthermore, the proposed composite method indicates that occurrence the failure in actuators and even elastic solar panel vibration effect may be handled directly without reconfiguring the control components or providing piezoelectric devices. It's noteworthy, attitude quaternion and angular velocity commands are robustly tracked via controllers to become inclined to zero.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.23 no.1
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• pp.49-55
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• 2015

This paper deals with dynamic modeling and controller design of a future Korean lunar module planned to be launched 2020's in Korea. For dynamic modeling of the lunar module, we first assume the lunar module as a rigid body. And we derive equations of motion for the lunar module by considering allocation of main thrusters and reaction thrusters. With the equation of motion, we design the controller based on the quaternion. A Pulse Width Pulse Frequency modulator(PWPFM) is selected for generating on/off signal. Finally, we construct a 2-phase descent mode including initial guidance mode, terminal guidance mode. The MATLAB simulation is performed for evaluating the descent ability and final landing velocity. The dynamic modeling and descent simulation of the lunar module in this paper could be applied for developing the future work of the Korean lunar exploration program.

• Journal of Institute of Control, Robotics and Systems
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• v.7 no.8
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• pp.703-710
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• 2001

The nonlinear observers are proposed for a nonlinear system. To improve the characteristics such as stability, convergence, and $H^{\infty}$ filter performance criterion, we utilize an $H^{\infty}$ filter Riccati equation or a modified $H^{\infty}$ filter Riccati equation with a freedom parameter. Using the Lyapunov function method, the characteristics of the observers are analyzed. Then the in-flight alignment for a strapdown inertial navigation system(SDINS) is designed using the proposed observer. And the additive quaternion error model is especially used to reduce the uncertainty of the SDINS error model. Simulation results show that the observer with the modified $H^{\infty}$ filter Riccati equation effectively improves the performance of the in-flight alignment.