• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.6
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• pp.465-472
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• 2013

In this paper, we suggest how to determine the parachute deploy position for accurate landing of a UAV at a desired position. The 9-DOF dynamic modeling of UAV-parachute system is required to construct the proposed algorithm based on neural network nonlinear function approximation technique. The input and output data sets to train the neural network are obtained from simulation results using UAV-parachute 9-DOF model. The input data consist of the deploy position, UAV's velocity, and wind velocity. The output data consist of the cross range and down range of landing positions. So we predict the relative landing position from the current UAV position. The deploy position is then determined through distance compensations for the relative landing positions from the desired landing position. The deploy position is consistently calculated and updated.

• Steel and Composite Structures
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• v.9 no.2
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• pp.131-158
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• 2009

This paper presents a modelling technique for the nonlinear analysis of composite steel-concrete beams with partial shear interaction. It extends the applicability of two stiffness elements previously derived by the authors using the direct stiffness method, i.e. the 6DOF and the 8DOF elements, to account for material nonlinearities. The freedoms are the vertical displacement, the rotation and the slip at both ends for the 6DOF stiffness element, as well as the axial displacement at the level of the reference axis for the 8DOF stiffness element. The solution iterative scheme is based on the secant method, with the convergence criteria relying on the ratios of the Euclidean norms of both forces and displacements. The advantage of the approach is that the displacement and force fields of the stiffness elements are extremely rich as they correspond to those required by the analytical solution of the elastic partial interaction problem, thereby producing a robust numerical technique. Experimental results available in the literature are used to validate the finite element proposed in the paper. For this purpose, those reported by Chapman and Balakrishnan (1964), Fabbrocino et al. (1998, 1999) and Ansourian (1981) are utilised; these consist of six simply supported beams with a point load applied at mid-span inducing positive bending moment in the beams, three simply supported beams with a point load applied at mid-span inducing negative bending moment in the beams, and six two-span continuous composite beams respectively. Based on these comparisons, a preferred degree of discretisation suitable for the proposed modelling technique expressed as a function of the ratio between the element length and depth is proposed, as is the number of Gauss stations needed. This allows for accurate prediction of the nonlinear response of composite beams.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.3
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• pp.666-672
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• 2017

Our research team is developing a 6-DOF manipulator for narrow workspaces in press forming processes, such as placing PEM nuts on the bottom of a chassis. In this paper, kinematic analysis was performed for the position control of the manipulator, along with structural analyses for position accuracy with different payloads. First, the Denavit-Hatenberg (DH) parameters are defined, and then the forward and backward kinematic equations are presented using the DH parameters. The kinematic model was verified by visual simulation using Coppelia Robotics' virtual robot experimentation platform (V-REP). Position accuracy analysis was performed through structural analyses of deflection due to self-weight and deflection under full payload (5 kgf) in fully opened and fully folded states. The maximum generated stress was 22.05 MPa in the link connecting axes 2 and 3, which was confirmed to be structurally safe when considering the materials of the parts.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.2
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• pp.704-710
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• 2017

Our research team is developing a 6-DOF manipulator that is adequate for the narrow workspace of press forming processes. This paper addresses the task sequence optimization methods for the manipulator to minimize the task-finishing time. First, a kinematic model of the manipulator is presented, and the anticipated times for moving among the task locations are computed. Then, a mathematical model of the task sequence optimization problem is presented, followed by a comparison of three meta-heuristic methods to solve the optimization problem: an ant colony system, simulated annealing, and a genetic algorithm. The simulation shows that the genetic algorithm is robust to the parameter settings and has the best performance in both minimizing the task-finishing time and the computing time compared to the other methods. Finally, the algorithms were implemented and validated through a simulation using Mathworks' Matlab and Coppelia Robotics' V-REP (virtual robot experimentation platform).

• Korean Journal of Remote Sensing
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• v.39 no.6_1
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• pp.1245-1254
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• 2023

Significant research has been conducted on the W-band synthetic aperture radar (SAR) system that utilizes the 77 GHz frequency modulation continuous wave (FMCW) radar. To reconstruct the high-resolution W-band SAR image, it is necessary to transform the point cloud acquired from the stereo cameras or the LiDAR in the direction of 6 degrees of freedom (DOF) and apply them to the SAR signal processing. However, there are difficulties in matching images due to the different geometric structures of images acquired from different sensors. In this study, we present the method to extract an optimized depth map by obtaining 6 DOF of the point cloud using a gradient descent method based on the entropy of the SAR image. An experiment was conducted to reconstruct a tree, which is a major road environment object, using the constructed W-band SAR system. The SAR image, reconstructed using the entropy-based gradient descent method, showed a decrease of 53.2828 in mean square error and an increase of 0.5529 in the structural similarity index, compared to SAR images reconstructed from radar coordinates.

• Transactions on Control, Automation and Systems Engineering
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• v.4 no.3
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• pp.217-223
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• 2002

The paper presents a single constraint equation of the direct kinematic solution of 6-dof (Stewart-Gough) platforms. Many research works have presented a single polynomial of the direct kinematics for several 6-dof platforms. However, the formulation of the polynomial has potential problems such as complicated formulation procedures and discrimination of the actual solution from all roots. This results in heavy computational burden and time-consuming task. Thus, to overcome these problems, we use a new formulation approach, called the Tetrahedron Approach, to easily derive a single constraint equation, not a polynomial one, of the direct kinematics and use two well-known numerical iterative methods to find the solution of the single constraint equation. Their performance and characteristics are investigated through a series of simulation.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.11a
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• pp.734-735
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• 2008

Shock absorber for rotorcraft landing gear should absorb landing impact during landing and isolate vibration to fuselage during taxiing. Double stage oleo-pneumatic shock absorber is known to have better performances than single stage oleo-pneumatic shock absorber. This paper deals with the z-direction translational acceleration at mass center, roil and pitch angular acceleration of fuselage for single and double stage oleo-pneumatic shock absorber at nose landing gear when a 6DOF rigid model is taxiing on the pound.

• Proceedings of the KIPE Conference
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• 2000.07a
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• pp.729-734
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• 2000

This paper proposes virtual-magnetic system by a force-reflecting interface to drive a ultrasonic motors(USMs) To approach virtual magnet in graphic the 6 dDOF force-reflecting interfaces provides force feedback to users as if I is magnetic-force, So users can feel real magnet Effectively to display the magnetic-force we need the interface with specific characteristics such as low inertia almost zero friction and very high stiffness As an actuator for the interface the USMs have many good advantage satisfied these conditions over conventional servo motors. To estimate capability of this virtual-magnetic system we did an experiment of magnetism based on coulomb's law when Coulmb's low apply this experiment it is vey conformable to real magnet

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.04a
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• pp.483-487
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• 1996

We consider the estimation of the position and orientation of 6 DOF motion bed (Stewart platform) from the measured cylinder length. The solution of forward kinematics is not solved yet as a useful realtime application tool because of the complity of the equation with multiple solutiple solutions. Hence we suggest an algorithm for the estimation of forward kinematics solution using Luenberger observer withnonlinear error correction term. The Luenberger observer withlinear model shows that the estimation error does not go to zero in steadystate due to the linearization error of the dynamic model. Hence the linear observer is modified using nonlinear measurement error equation and we prove thd practical stability of the estimation error dynamics of the proposed observer using lyapunov function.

• Journal of Industrial Technology
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• v.21 no.A
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• pp.97-103
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• 2001

This paper presents the development of the I/O Interface for the real time parallel data communication between controller of a six-axis industrial robot(CRS-A460) and an external computer. The proposed I/O Interface consists of the hardware I/O interface and the software that is downloaded to the robot controller and executed by the controller operating system. The constitution of the digital I/O Port for CRS-A460 robot controller and the digital I/O board for IBM-PC are presented as well as the Process Control Program of the robot controller. The developed protocol for the parallel data communication is described. The data communication is tested, and the performance is analysed. In particular, it is shown that the real-time constraint of the robot controller process is satisfied.