• Title, Summary, Keyword: Center of Gravity

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A Experimental Study on the Measurement and Estimation of Vehicle Center of Gravity (차량무게중심의 측정 및 추정에 관한 연구)

  • Lee, Myung-Su;Kim, Sang-Sup
    • Transactions of the Korean Society of Automotive Engineers
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    • v.18 no.5
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    • pp.91-99
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    • 2010
  • The center of gravity on vehicle is a fundamentally important point for assessing and measuring the characteristics of vehicle dynamics. Especially, the center of gravity height on vehicles is the closest factor with respect to rollover accidents in a social issue nowadays. In this paper, the center of gravity height in conjunction with vehicle parameters of vehicle weight, driving axle and roof height after measured by vehicle weight and loading location by means of VCGM developed by KATRI with good performance that the accuracy was less than 0.6% and repeatability 0.3% for vehicles being used in the whole world was observed. As a result of study, the location of center of gravity height on vehicle was able to be estimated with only roof height on vehicle.

Body Impedance Control for Walking Stabilization of a Quadrupedal Robot (4족 보행 로봇의 걸음새 안정화를 위한 몸체 임피던스 제어)

  • Lee, Soo-Yeong;Hong, Ye-Seon
    • The Transactions of the Korean Institute of Electrical Engineers D
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    • v.49 no.5
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    • pp.257-263
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    • 2000
  • One of the basic assumptions in the static gait design for a walking robot is that the weight of leg should be negligible compared to that of body, so that the total gravity center is not affected by swing of a leg. Based on the ideal assumption of zero leg-weight, conventional static gait has been simply designed for the gravity center of body to be inside the support polygon, consisting of each support leg's tip position. In case that the weight of leg is relatively heavy, however, while the gravity center of body is kept inside the support polygon, the total gravity center of walking robot can be out of the polygon due to weight of a swinging leg, which causes instability in walking. Thus, it is necessary in the static gait design of a real robot a compensation scheme for the fluctuation in the gravity center. In this paper, a body impedance control is proposed to obtain the total gravity center based on foot forces measured from load cells of a real walking robot and to adjust its position to track the pre-designed trajectory of the corresponding ideal robot's body center. Therefore, the walking stability is secured even in case that the weight of leg has serious influence on the total gravity center of robot.

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Improved Method for Determining the Height of Center of Gravity of Agricultural Tractors

  • Kim, YuYong;Noh, JaeSeung;Shin, SeungYeop;Kim, ByoungIn;Hong, SunJung
    • Journal of Biosystems Engineering
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    • v.41 no.3
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    • pp.170-176
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    • 2016
  • Purpose: This study aimed to improve the method for determining the position of the center of gravity for agricultural tractors. Methods: The proposed method uses trigonometric functions and coordinate transformation. Data were measured according to the ISO 789-6 test procedures for the center of gravity of agricultural tractors. The height calculated using the proposed method was compared with that determined from an AutoCAD drawing. To find the center of gravity of the tractor, the algorithm for finding the intersection of the two lines was used. Results: The vertical height from the ground to the center of gravity is 682.06 mm. The vertical coordinates obtained from the calculation and the drawing were the same. Conclusions: The developed method uses trigonometric and polar coordinate transformation. The method was compared and verified with the AutoCAD drawing results. The results indicate that users can apply this developed method instead of the plotting method which is an inconvenient and time-consuming. Further, users can program Microsoft Excel to easily determine the vertical coordinate. In addition, researchers will propose this method to the ISO as a standard method for determining the center of gravity in accordance with ISO 789-6.

An Assumption on How Archimedes Found out the Center of Gravity of Cones in 《The Method》 (아르키메데스가 《The Method》에서 원뿔의 무게중심을 구한 방식에 대한 하나의 가설)

  • Park, Sun-Yong;Hong, Gap-Ju
    • Journal for History of Mathematics
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    • v.26 no.5_6
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    • pp.371-388
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    • 2013
  • In ${\ll}$The Method${\gg}$, Archimedes presented the famous heuristic technique for calculating areas, volumes and centers of gravity of various plane and solid figures, utilizing the law of the lever. In that treatise, Archimedes used the fact that the center of gravity of a cone lies one-quarter of the way from the center of the base to the vertex, but the proof of this is not extant in his works. This study analyzes the propositions and their relations of ${\ll}$The Method${\gg}$ focusing on the procedural characteristics of the 'method' of Archimedes. According to the result of that analysis, this study discusses the likely approach which was taken for Archimedes to find out the center of gravity of a cone.

Field Measurement of the Center of Gravity and the Moment of Inertia of Railway Vehicles Using Vibration (진동을 이용한 철도차량의 무게중심과 관성모멘트 현장 측정)

  • Song, Ki-Seok;Choi, Yeon-Sun
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.23 no.10
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    • pp.878-884
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    • 2013
  • The center of gravity and the moment of inertia of railway vehicles are important parameters for running safety and stability in railway vehicle design. However, the exact measurement of those is difficult in manufacturing field. The weight measurement of a railway vehicle beneath the wheel using a weight scale is off by a large amount. This paper suggests a measurement method for the center of gravity and the moment of inertia of railway vehicles using vibration. For the measurement a railway vehicle is suspended using four wires. Direct measurement of the tension of the wires and the period of swinging motion of the suspended railway vehicle with calculations give the exact location of the center of gravity and the moment of inertia in x, y, and z directions, respectively. This implementation was demonstrated using an experimental device and verified numerically.

Center of Gravity and a Characterization of Parabolas

  • KIM, DONG-SOO;PARK, SOOKHEE;KIM, YOUNG HO
    • Kyungpook Mathematical Journal
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    • v.55 no.2
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    • pp.473-484
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    • 2015
  • Archimedes determined the center of gravity of a parabolic section as follows. For a parabolic section between a parabola and any chord AB on the parabola, let us denote by P the point on the parabola where the tangent is parallel to AB and by V the point where the line through P parallel to the axis of the parabola meets the chord AB. Then the center G of gravity of the section lies on PV called the axis of the parabolic section with $PG=\frac{3}{5}PV$. In this paper, we study strictly locally convex plane curves satisfying the above center of gravity properties. As a result, we prove that among strictly locally convex plane curves, those properties characterize parabolas.

Feasible Positions of Towing Point and Center of Gravity for Towfish Attitude Control

  • Kim, Min-Kyu;Park, Dong-Jin;Kim, Jong-Hwa;Choi, Jin-Kyu
    • Journal of Ocean Engineering and Technology
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    • v.34 no.5
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    • pp.334-341
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    • 2020
  • Most towfish systems do not have propulsive devices and cannot compensate for perturbation motion, which can affect the observation data. This paper discusses attitude control of a towfish with elevators on the left and right tail wings to improve the quality of the observational data. Specifically, we investigate the relationships between the towing point, the center of gravity, and the drag forces produced by the elevators to clarify whether the elevators can control the attitude of the towfish sufficiently for various positions of the towing point and center of gravity. The feasible positions of the towing point and center of gravity are defined by mechanical analyses, and simulations are conducted to verify that the elevators can provide attitude control in these positions. The simulation results show that at some positions, the elevators can control the attitude quickly and sufficiently even if disturbances exist.

Measurement of Gravity Center for Rotor Blades by Compensation of Machining Error in Jig (지그의 가공오차 보정에 의한 블레이드 무게 중심 측정)

  • Kong, Jae-Hyun;Kim, Ki-Sung;Ye, Sang-Don;Chun, See-Young;Hur, Kwan-Do
    • Journal of the Korean Society for Precision Engineering
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    • v.27 no.12
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    • pp.41-47
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    • 2010
  • There are many unbalanced models such as helicopter's rotor blades, small-sized precision motor in industrial applications. In the real products, their gravity center usually does not accord with the desired gravity center. If the deviation is large between them, it can be a major cause of vibration and noise as the part of model rotate. Therefore the gravity center in the rotational parts should be controlled properly because of static and dynamic balancing of the parts. In the research, the rotor blade of unmanned helicopter has been selected to obtain the high quality of balancing. In order to achieve the purpose, measuring system has been developed. In the system applied principle is three point weighting method, which is one of the Multiple-point Weighting Method. It has circle fitting for compensation of machining error, after measuring the values. From this study, the results showed that the proposed measurement procedure gives reliable and precise gravity center.

Geometrically Invariant Image Watermarking Using Connected Objects and Gravity Centers

  • Wang, Hongxia;Yin, Bangxu;Zhou, Linna
    • KSII Transactions on Internet and Information Systems (TIIS)
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    • v.7 no.11
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    • pp.2893-2912
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    • 2013
  • The design of geometrically invariant watermarking is one of the most challenging work in digital image watermarking research area. To achieve the robustness to geometrical attacks, the inherent characteristic of an image is usually used. In this paper, a geometrically invariant image watermarking scheme using connected objects and gravity center is proposed. First, the gray-scale image is converted into the binary one, and the connected objects according to the connectedness of binary image are obtained, then the coordinates of these connected objects are mapped to the gray-scale image, and the gravity centers of those bigger objects are chosen as the feature points for watermark embedding. After that, the line between each gravity center and the center of the whole image is rotated an angle to form a sector, and finally the same version of watermark is embedded into these sectors. Because the image connectedness is topologically invariant to geometrical attacks such as scaling and rotation, and the gravity center of the connected object as feature points is very stable, the watermark synchronization is realized successfully under the geometrical distortion. The proposed scheme can extract the watermark information without using the original image or template. The simulation results show the proposed scheme has a good invisibility for watermarking application, and stronger robustness than previous feature-based watermarking schemes against geometrical attacks such as rotation, scaling and cropping, and can also resist common image processing operations including JPEG compression, adding noise, median filtering, and histogram equalization, etc.

Analysis of the 500M Short track speed skating starting motion according to the center of gravity position ratio (인체 무게 중심 분할에 따른 500m 숏트트랙 스피드 스케이팅 출발 기술 분석)

  • Back, Jin-Ho;Chung, Nam-Ju;Han, Ki-Hoon;Lee, Yong-Goo;Yoon, Dong-Seob;Lee, Yong-Sik
    • Korean Journal of Sport Biomechanics
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    • v.13 no.3
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    • pp.199-215
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    • 2003
  • The purpose of this study was to attempt new starting motion and supply present starting motion in the 500M short track speed skating according to the center of gravity position. The center of gravity position ratio was divided starting motion into five(type A : front 80%-back 20%, type B front 70%-back 30%, type C : front 50%-back 50%, type D : front 30%-back 70%, type E : front 20%-back 80%). The three dimension motion analysis with DLT(direct linear transformation) method was executed using two video cameras. The following conclusion was that It was appear that reaction and execution time in starting motion was the most short in type B. It was characteristic that step of skaters was shorten and center of gravity position ratio was not effect to change of the step in each event. It was appear that the displacement of type D and type E were longer than that type A and type B during the starting motion. It was appear that skill types of center of gravity position ratio to the front were lower than that to the back and contract a posture. Observing the above, it was conclusion that skill type B of center of gravity position ratio to the tent was more effect than that to the back. But it is important that these skill type was most used to the competition and estimate the result.