• 한국정밀공학회지
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• 제28권6호
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• pp.687-693
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• 2011

Spring-mass models have been widely accepted to explain the basic dynamics of human gait. Researchers found that the leg stiffness increased with gait speed to increase energy efficiency. However, the difference of leg stiffness change with gait speed between the young and the elderly has not been verified yet. In this study, we calculated the lower limb stiffness of the elderly using walking model with an axial spring. Vertical stiffness was defined as the ratio of the vertical force change to the vertical displacement change. Seven young and eight elderly subjects participated to the test. The subjects walked on a 12 meter long, 1 meter wide walkway at four different gait speeds, ranging from their self-selected speed to maximum speed randomly. Kinetic and kinematic data were collected using three force plates and motion capture cameras, respectively. The vertical stiffness of the two groups increased as a function of walking speed. Maximum walking speed of the elderly was slower than that of the young, yet the walking speed correlated well with the optimal stiffness that maximizes propulsion energy in both groups. The results may imply that human may use apparent limb stiffness to optimize energy based on spring-like leg mechanics.

• 대한조선학회논문집
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• 제44권3호
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• pp.323-331
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• 2007

Proposed Manta-type Unmanned Undersea Vehicle(UUV) turned out to have the tendency of dynamic instability in vertical plane, and moreover to have that of so strong dynamic stability in horizontal plane as to cause another problem in turning motion due to negative value of sway damping lever. The authors discussed the changes in appendage design for improvement of dynamic stability of UUV in vertical and horizontal planes. As a result, the dynamic stability in vertical plane was improved by increasing the area of horizontal stern planes. and the dynamic stability in horizontal plane was also improved by removal of lower vertical plate and by adjusting the area and position of upper vertical plate simultaneously.

• 한국의류학회지
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• 제45권4호
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• pp.648-660
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• 2021

This study analyzes how sewing conditions for elastic bands on woven fabrics affect elongation. The directions of the elastic bands were vertical, horizontal, vertical and horizontal crossing, and horizontal and vertical crossing. Intervals between the elastic bands were 3.0 cm and 6.0 cm. The woven fabric was tailored for the elastic band sewing using warp, weft, and bias. Consequently, it was possible to visually confirm elongation differences according to the sewing condition of the elastic bands. A detailed examination demonstrated that the horizontal or vertical placement of elastic bands tailored in a crosswise direction produces high vertical elongation and low horizontal contraction. However, elastic bands sewed in crossing directions, regardless of warp and weft directions, resulted in both high vertical elongation and high horizontal contraction. In all cases, the more elastic bands were used, the higher the horizontal elongation. In conclusion, appropriate placements of elastic bands on woven fabric increases motion convenience.

• 대한기계학회논문집A
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• 제21권10호
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• pp.1718-1729
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• 1997

This paper describes motion errors due to acceleration and deceleration types of servo motors in NC machine tools. Motion errors are composed of two components : one is due to transient response of a servomechanism and the other comes from gain mismatching of positioning servo motors. It deals with circular interpolation to identify motion errors by using Interface card. Also in order to minimize motion errors, this study presents an effective method to optimize parameters which are connected with motion errors. The proposed method is based upon a second order polynomial regression model and it includes an orthogonal array method to make the effective results of experiments. The validity and reliability of the study were verified on a vertical machining center equipped with FANUC 0MC through a series of experiments and analysis.

• 한국정밀공학회지
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• 제28권5호
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• pp.599-605
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• 2011

A 3-D rehabilitation robot system is developed. The robot system is for the rehabilitation of upper extremities, especially the shoulder and elbow joints, and has 3-D workspace for occupational therapy to recover physical functions in activities of daily living(ADL). The rehabilitation robot system has 1 DOF in horizontal rotational motion and 2 DOF in vertical rotational motion, where all actuators are set on the ground. Parallelogram linkage mechanisms lower the equivalent inertia of the control elements as well as control forces. Also the mechanisms have high mechanical rigidity for the end effector and the handle. In this paper, a hybrid position/force controller is used for controlling positions and forces simultaneously The controller is tuned according to the robot posture. The active motion modes for rehabilitation program consist of active-resisted motion mode and active-free motion mode. The results of the experiments show that the proposed motion modes provide the intended forces effectively.

• Journal of Biosystems Engineering
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• 제25권3호
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• pp.179-186
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• 2000

Interactions between wheel lug surfaces and soil were analyzed through wheel motion. In this paper, lug surfaces such as trailing and leading lug sides and a lug face were analyzed and reported. The interactions between the surfaces and soil were expressed as the horizontal and vertical directions of resultant forces acting on the surfaces. There analysis indicated qualitatively that (1) the trailing lug side is mainly related to produce motion resistance and reaction to dynamic load, (2) the lug face is related to produce not only the motion resistance, the reaction to the dynamic load but also the traction and (3) the leading lug side is mainly related to produce the traction and the reaction to the dynamic load. Experiments were conducted to prove the results of the motion analysis. Normal and tangential forces acting on the surfaces were measured, and the traction, the motion resistance and the reaction to the dynamic load were calculated with wheel rotational and lug design angles. The experiments proved that the results of wheel motion analyses above mentioned as (1), (2) and obtained from the analysis were correct.

• 로봇학회논문지
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• 제17권4호
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• pp.500-507
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• 2022

In this study, a motion planning method based on the integer representation of contact status between wheels and the ground is proposed for planning swing motion of a 6×6 wheel-legged robot to cross large obstacles and gaps. Wheel-legged robots can drive on a flat road by wheels and overcome large obstacles by legs. Autonomously crossing large obstacles requires the robot to perform complex motion planning of multi-contacts and wheel-rolling at the same time. The lift-off and touch-down status of wheels and the trajectories of legs should be carefully planned to avoid collision between the robot body and the obstacle. To address this issue, we propose a planning method for swing motion of robot legs. It combines an integer representation of discrete contact status and a trajectory optimization based on the direct collocation method, which results in a mixed-integer nonlinear programming (MINLP) problem. The planned motion is used to control the joint angles of the articulated legs. The proposed method is verified by the MuJoCo simulation and shows that over 95% and 83% success rate when the height of vertical obstacles and the length of gaps are equal to or less than 1.68 times of the wheel radius and 1.44 times of the wheel diameter, respectively.

• 한국기계연구소 소보
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• 통권17호
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• pp.157-165
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• 1987

The SWATH concept hull form which is capable of high speed navigation with small oscillatory motions in waves, was developed from the catamaran type hull forms. This paper describes how the motion of a SWATH ship in irregular waves can be reduced by regulating the stabilizing fins. The optimal regulator and LQG (Linear Quadratic Gaussian) controller for vertical plane motion have been applied for both platforming mode and contouring mode controls. The calculations of hydrodynamic coefficients and external forces are possible for defining the system equation for the design purpose of motion control. Performances of the controlled system are compared with those of original system.

• The Journal of the Acoustical Society of Korea
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• 제17권2E호
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• pp.53-58
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• 1998

In this paper, we study the response of several anisotropic systems to buried transient line loads. The problem is mathematically formulated based on the equations of motion in the constitutive relations. The load is in form of a normal stress acting with arbitrary axis on the plane of monoclinic symmetry. Plane wave equation is coupled with vertical shear wave, longitudinal wave and horizontal shear wave. We first considered the equation of motion in reference coordinate system, where the line load is coincident with symmetry axis of the orthotrioic material. Then the equation of motion is transformed with respect to general coordiante system with azimuthal angle by using transformation tensor. The load is first described as a body force in the equations of the motion for the infinite media and then it is mathematically characterized. Subsequently the results for semi-infinite spaces is also obtained by using superposition of the infinite medium solution together with a scattered solution from the free surface. Consequently explicit solutions for the displacements are obtained by using Cargniard-DeHoop contour. Numerical results which are drawn from concrete examples of orthotropic material belonging to monoclinic symmetry are demonstrated.

• 한국정밀공학회지
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• 제26권4호
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• pp.64-71
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• 2009

A 3-D rehabilitation robot system is developed in this paper. The robot system is for the rehabilitation of upper extremities, especially the shoulder and elbow joints, and has 3-D workspace for enabling occupational therapy to recover physical functions in activities of daily living(ADL). The rehabilitation robot system, which is driven by actuators, has 1 DOF in horizontal rotational motion and 2 DOF in vertical rotational motion, where all actuators are set on the ground. Parallelogram linkage mechanisms lower the equivalent inertia of the control elements as well as control forces. Also the mechanisms have high mechanical rigidity for the end effector and the handle. Passive motion mode experiments have been performed to evaluate the proposed robot system. The results of the experiments show and excellent performance in simulating spasticity of patients.