Howon Lee

Hill climbing algorithm of an inverted pendulum

This research aims at the control of the inverted pendulum attached on the top plate of a mobile robot. Especially, when the mobile robot is climbing up the hill, the stable control of the inverted pendulum is a challenging problem. Considering the gravity of the pendulum according to the inclined angle, the mobile robot motion is controlled to keep the inverted pendulum upright while the mobile robot is changing the location. For this purpose, the dynamics of the mobile robot and inverted pendulum have been derived and utilized with the PID control algorithm to keep the inverted pendulum upright. Through the real experiments, the range of disturbance which can be overcome by the controller has been shown. And also the effectiveness and validity the derived dynamics have been shown with various disturbances.

Driving control of mobile inverted pendulum

This research aims at the control of the inverted pendulum attached on the top plate of a mobile robot. Conventional approaches focus on the balance of the pendulum while the mobile platform is moving. However in this research it is designed to follow the desired trajectory of the mobile robot. For the purpose, the acceleration as well as pose of the mobile platform need to be controlled. Especially, when the mobile robot is curvilinear motion, the stable control of the inverted pendulum is a challenging problem. The mobile robot motion is controlled to keep the inverted pendulum upright while the mobile robot is moving to the goal position. For this purpose, the dynamics of the mobile robot and inverted pendulum have been derived and utilized with the velocity estimator control algorithm to keep the inverted pendulum upright. Through the real experiments, the range of disturbance which can be overcome by the controller has been verified and utilized to control the pendulum. And also the effectiveness and validity the derived dynamics have been shown with various disturbances.

The biochemical composition of phytoplankton in the Laptev and East Siberian seas during the summer of 2013

The Laptev and East Siberian seas which are generally viewed as terrestrial organic matter (TerrOM)-dominated seas, are among the least biologically understood regions in the Arctic Ocean. During the summer of 2013, however, the TerrOM signature was negligible in our samples. We investigated the biochemical composition (carbohydrates [CHO], proteins [PRT], and lipids [LIP]) of phytoplankton-dominated particulate organic matter in order to improve our understanding of the physiological status of resident phytoplankton. Our chlorophyll-a values and the presence of SCMs and resting spores were associated with a cessation of the phytoplankton bloom. Despite the low inorganic nitrogen nutrients in the water column, the cellular PRT (39%) were comparable to CHO (42%) contents and the inorganic (dissolved nitrogen:dissolved phosphate) and organic (PRT:CHO) indices did not indicate a nitrogen stress of phytoplankton metabolism. Altogether, the phytoplankton were likely in a growth transition from the exponential to the stationary phase, resulting in CHO-dominated cells with moderate PRT. By comparing our biochemical analyses with the LIP-dominated (> 50%) ones in the Chukchi Sea (the summers of 2011 and 2012), we conclude that more severe nitrogen-limited conditions occurred in the Chukchi Sea. In a quality aspect, we suggest that consumers which feed on LIP-rich phytoplankton could have an advantage to overwinter while those feeding on CHO-rich phytoplankton will gain energy efficiently in a short term. Therefore, the biochemical composition of phytoplankton could be a valid integrator of surrounding environments in which phytoplankton grow and can be a good indicator of their nutritional value.

First in situ estimations of small phytoplankton carbon and nitrogen uptake rates in the Kara, Laptev, and East Siberian seas

Carbon and nitrogen uptake rates by small phytoplankton (0.7–5 μm) in the Kara, Laptev, and East Siberian seas in the Arctic Ocean were quantified using in situ isotope labeling experiments; this research, which was novel and part of the NABOS (Nansen and Amundsen Basins Observational System) program, took place from 21 August to 22 September 2013. The depth-integrated carbon (C), nitrate (NO−3 ), and ammonium (NH + 4 ) uptake rates by small phytoplankton ranged from 0.54 to 15.96 mg C m−2 h−1, 0.05 to 1.02 mg C m−2 h−1, and 0.11 to 3.73 mg N m−2 h−1, respectively. The contributions of small phytoplankton towards the total C, NO−3 , and NH + 4 varied from 25 % to 89 %, 31 % to 89 %, and 28 % to 91 %, respectively. The turnover times for NO−3 and NH + 4 by small phytoplankton found in the present study indicate the longer residence times (years) of the nutrients in the deeper waters, particularly for NO−3 . Additionally, the relatively higher C and N uptake rates by small phytoplankton obtained in the present study from locations with less sea ice concentration indicate the possibility that small phytoplankton thrive under the retreat of sea ice as a result of warming conditions. The high contributions of small phytoplankton to the total C and N uptake rates suggest the capability of small autotrophs to withstand the adverse hydrographic conditions introduced by climate change.

3D map building using the LRF and sinusoidal trajectory of a Quadrotor

In this paper propose a 3D mapping system using Quadrotor using the LRF and the sinusoidal trajectory algorithm. Instead of the expensive and bulky 3D-laser scanner, the LRF can be utilized and installed on the Quadrotor for the map building and the autonomous navigation. The high frequency noise caused by a Quadrotor moving in real time, was filtered using a hybrid median filter. By using a sine wave trajectory algorithm proposed in this paper, it is possible to save time 3D map, it can widen the measuring range. Scanning a 3D mapping experiments were performed to evaluate the interior walls of the sinusoidal trajectory performance algorithm.

Driving Control by Based upon the Slip Pattern of the Ball Robot

This paper proposes a driving course plans using the slip patterns of an Mecanum wheel Ball Robot. Slip of Mecanum wheel Ball Robot causes uncertainty on the driving. This solution is necessary in order to reduce the uncertainty of the robot. Analyzing the slip pattern according on the driving angle change of the robot, which was shown in the graph for slip pattern. On the basis of a formal slip pattern can establish the moving performance of the Mecanum wheel Ball Robot and the optimal path planning. Using a self-produced robots, the experiment on the optimal path planning using a slip pattern and the performance was evaluated.

Optimization of dual-arm configurations for multiple object handling

This paper proposes a stability analysis criterion for the multiple objects handling operation of dual arm manipulator to make optimal postures. When the dual-arm manipulator grasps a fixed object to carry it to a desired location, the dual-arm manipulator should hold the object stably and efficiently without losing the control. As a performance evaluation parameter, joint torque data from current sensors are utilized. From the current information, torque and power consumption in each joint are estimated. In this paper an optimal posture for an unstructured object is defined by a cost function formed by three factors: the holding forces, manipulability measure, and the power consumption. For the stable grasp, the forces of the dual-arm manipulators and the gravity force need to be well-balanced to make it minimum. The grasping force to the object is computed by using the pointing vector to the object and the joint torque. Manipulability measure which implies how efficiently the dual -arm manipulator can move the holding object together, can be represented by the intersection of the two manipulability ellipsoids for the left and right arms. Effectiveness of the proposed algorithm has been verified through the real experiments.

Obstacle avoidance algorithm of the underwater robot in the underwater environment

This paper proposes an algorithm that enables the safe navigation toward the destination without collisions to the obstacle in the two-dimensional underwater environment. Recently study about the underwater robot goes actively and above all, the navigation in the underwater environment have occurred a challenging problem for the underwater robots. Using the heuristic method, an effective motion for the navigation of the underwater robot is created and the most stable motion direction without collisions is calculated using the fuzzy theory. It creates total 3 cells for the robot to move along and each cell has its own weight so that the robot can select a next moving cell by priority in the same environment. In this paper, the navigation of the underwater robot in underwater environment has been observed through the simulations when effected on the force like buoyancy. It is confirmed that the obstacle avoidance can be successfully achieved by analyzing and changing the weights in the fuzzy algorithm according to the motion of the robot.