• International Journal of Control, Automation, and Systems
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• v.1 no.4
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• pp.401-411
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• 2003

Important results about two-degree-of-freedom PID controllers are surveyed for the tutorial purpose, including equivalent transformations, various explanations about the effect of the two-degree-of-freedom structure, relation to the preceded-derivative PID and the I-PD controllers, and an optimal tuning method.

• Journal of Institute of Control, Robotics and Systems
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• v.4 no.3
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• pp.360-371
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• 1998

In this paper, output precision characteristics of a planar 6 degree-of-freedom parallel mechanisms are investigated, where the 6 degree-of-freedom mechanism is formed by adding an additional link along with an actuated joint in each serial subchain of the planar 3 degree-of-freedom parallel mechanism. Kinematic analysis for the parallel mechanism is performed, and its first-order kinematic characteristics are examined via kinematic isotropic index, maximum and minimum input-output velocity transmission ratios of the mechanisms. Based on this analysis, two types of planar 6 degrees-of-freedom parallel manipulators are selected. Then, dynamic characteristics of the two selected planar 6 degree-of-freedom parallel mechanisms, via Frobenius norms of inertia matrix and power modeling array, are investigated to compare the magnitudes of required control efforts of both three large actuators and three small actuators when the link lengths of three additional links are changed. It can be concluded from the analysis results that each of these two planar 6 degrees-of-freedom parallel mechanisms has an excellent control-in-the-small characteristics and therefore, it can be very effectively employed as a high-precision macro-micro manipulator when both its link lengths and locations of small and large actuators are properly chosen.

• Journal of Korean Association for Spatial Structures
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• v.4 no.4 s.14
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• pp.85-89
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• 2004

A frame element embedded normal to a shear wall or slab (shell element) is common in the structural systems. In that case there is a need for a membrane or shell element to have a normal rotation degree of freedom at each node in order to have a good result of stresses. Even if Many other people studied this area, All man, Cook and Sabir are representative investigators in this area. In this research paper, Sabir's methods of vertex rotation stiffness matrix in a membrane element are studied. New stiffness of vertex rotation are proposed by taking advantage of beam stiffness theory. Rectangular elements stiffness with rotational degree of freedom are compared in accuracy ratio each other.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.4
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• pp.97-108
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• 1996

Optimal design of fault-tolerant, spatial type redundant manipulators is treated in this paper. Design objective is to guarantte three degree-of -freedom translational motions in the task space, upon failure of one arbitrary joint of 4 degree-of-freedom manipulators. Noticing the nonfault-tolerant characteristics of current, wrist-type industrial manipulators, five different fault-tolerant spatial-type manipulators which have 4 degree-of-freedom structures with one joint redundancy are suggested. Faault-tolerant character-sitics of two redundant manipulators anr investigated based on the analysis of the self-motion and the null-space elements. Finally, in order to maximize the fault-tolerant capability, optimal design is performed for a spatial-type manipulator with respect to the global isotropic index, and the performance enhancement of the optimized case is shown by simulation.

• Earthquakes and Structures
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• v.4 no.1
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• pp.109-132
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• 2013

Current codes incorporate simplified methods for the prediction of acceleration demands on secondary structural and non-structural elements at different levels of a building. While the use of simple analysis methods should be advocated, damage to both secondary structural and non-structural elements in recent earthquakes have highlighted the need for improved design procedures for such elements. In order to take a step towards the formation of accurate but simplified methods of predicting floor spectra, this work examines the floor spectra on elastic and inelastic single-degree of freedom systems subject to accelerograms of varying seismic intensity. After identifying the factors that appear to affect the shape and intensity of acceleration demands on secondary structural and non-structural elements, a new series of calibrated equations are proposed to predict floor spectra on single degree of freedom supporting structures. The approach uses concepts of dynamics and inelasticity to define the shape and intensity of the floor spectra at different levels of damping. The results of non-linear time-history analyses of a series of single-degree of freedom supporting structures indicate that the new methodology is very promising. Future research will aim to extend the methodology to multi-degree of freedom supporting structures and run additional verification studies.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1994.10a
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• pp.605-610
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• 1994

Optimal design of fault-tolerant, spatial type maniplators is treated in this paper. Design objective is to guarantte three degree-of-freedom translational motions in the task space, upon failure of one arbitrary joint of 4 degree-of -freedom manipulators. Realizing the nonfault-tolerant characteristics of current, wrist-type industrial manipulators, several 4 degree-of-freedom redundant structures with one joint redundancy are suggested as the fault-tolerant spatial -type manipulators. Fault-tolerant charactersitics are investigated basedon the analysis of the self-motion and the null-space elements, of a redundant manipulator. Finally, in order to maximize the fault-tolerant capability,optimal design is performed for a spatial-type manipulator with respect to the global isotropic index, and the performance enhancement of the optimized case is shown by simulation.

• Structural Engineering and Mechanics
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• v.51 no.4
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• pp.643-650
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• 2014

A chaotic vibration isolation system is designed according to the chaotic vibration theory in this paper. The strong nonlinearity is generated by the system. Line spectra in the radiated noise maybe easily detected caused by marine vessels. It is Important to reduce the line spectra by improving the acoustic stealth of marine vessels. A multi-degree-freedom (MDF) nonlinear vibration isolation system (NVIS) system is setup by the experiment and finite element method. The model is established with finite element method. The results show that the behavior of the device gradually varies from period bifurcation into chaotic state and the line spectrum is changed from single spectral structure into broadband spectral structure. It is concluded that chaotic vibration isolation is preferable contrasted on line spectra isolation.

• Journal of Electrical Engineering and Technology
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• v.12 no.4
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• pp.1649-1656
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• 2017

This paper addresses the control problem of a laboratory-level 2 degree-of-freedom helicopter. The exact fuzzy model in a Takagi - Sugeno form is constructed by the sector nonlinearity technique, and is then represented as a set of uncertain linear systems. Output-tracking controller is designed in terms of linear matrix inequalities and the closed-loop stability is rigorously analyzed. Experimental evaluation shows that the proposed method is of benefit to many real industrial plants.

• Journal of Korean Institute of Industrial Engineers
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• v.23 no.4
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• pp.779-791
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• 1997

The purpose of this study is to measure a perceived joint discomfort in the seated and standing position, and to provide ranking systems of perceived joint discomfort. Nineteen mole subjects with no history of musculo-skeletal disorders participated in the experiment. Their physical characteristics were: age $-25.4{\pm}2.7$years, stature $-171.9{\pm}6.0cm$, and body weight $-67.1{\pm}7.0kg$. The results showed that the perceived joint discomforts were different depending upon the joints involved in motion and their movement directions (degree of freedom of motions), which implied that the human body motions and their degrees of freedom should be classified into several distinct classes that need to be assigned different weights of postural stress. Therefore, three ranking systems based on the perceived joint discomforts were suggested, which were classified by the degree of freedom of motions and joints, by only degree of freedom motions, and by joints involved in motion, respectively. In the seated position, the hip movement was the most stressful, the bock was the second, and the shoulder was the third. Likewise, in the standing postures, the hip was the most, the bock was the second, and the ankle was the third. It was expected that these joint motion ranking systems could be used by practitioners of health and safety to improve the comfort of working postures in industry.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.2 no.4
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• pp.33-39
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• 2003

The stiffness of multi-articulated industrial robots is very weak, because their structure is an articulated type with some links and joints. Thus it is known that cutting processes for metals are not accepted in machine shop well, but they have a lot of merits for cutting processes, for example, drilling, tapping, and engraving etc, because of the characteristics of their high degree of freedom. The temptation of cutting aluminium was carried out to investigate the feasibility and the limitations or constraints for cutting metals on them. First the mode shapes of 6 degree of freedom welding robot were taken and analysed, and next the cutting processes were practically carried out on it. The results of study were found out to show the feasibility of cutting processes at drilling under 6mm of tool diameter, as well as to have some limitations and constraints, for examples, feed rate, depth of cut and cutting force etc.