• Journal of the Korean Society for Precision Engineering
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• v.27 no.3
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• pp.50-57
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• 2010

A high precision air bearing stage has been developed and calibrated. This linear-motor driven stage was designed to transport a glass or wafer with the X and Y following errors in nanometer regime. To achieve this level of precision, bar type mirrors were adopted for real time ${\Delta}X$ and ${\Delta}Y$ laser measurement and feedback control. With the laser wavelength variation and instability being kept minimized through strict environment control, the orthogonality of this type of control system becomes purely dependent upon the surface flatness, distortion, and assembly of the bar mirrors. Compensations for the bar mirror distortions and assembly have been performed using the self-calibration method. As a result, the orthogonality error of the stage was successfully decreased from $0.04^{\circ}$ to 2.48 arcsec.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.05a
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• pp.225-230
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• 2003

Many port states such as New Zealand, the USA, Australia and Canada have strict regulations to prevent ships which arrive in their port from discharging polluted ballast water which contain harmful aquatic organisms and pathogens. They are notified that transfer of polluted ballast water can cause serious injury to public health and damage to property and environment. For this reason, they perceived that the ballast exchange in deep sea is the most effective method, together with submitting the ballast management plan which contains the effective exchange method, ballast system and safety consideration. In this study, we make an effort to develop optimum ballast water exchange management and in result of that, it provide more convenient and stable process for preparing ballast water management plan.

• International Journal of Aeronautical and Space Sciences
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• v.8 no.1
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• pp.10-20
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• 2007

For spacecraft attitude control, reaction wheel (RW) steering laws with more than three wheels for three-axis attitude control can be derived by using a control allocation (CA) approach.1-2 The CA technique deals with a problem of distributing a given control demand to available sets of actuators.3-4 There are many references for CA with applications to aerospace systems. For spacecraft, the control torque command for three body-fixed reference frames can be constructed by a combination of multiple wheels, usually four-wheel pyramid sets. Multi-wheel configurations can be exploited to satisfy a body-axis control torque requirement while satisfying objectives such as minimum control energy.1-2 In general, the reaction wheel steering laws determine required torque command for each wheel in the form of matrix pseudo-inverse. In general, the attitude control command is generated in the form of a feedback control. The spacecraft body angular rate measured by gyros is used to estimate angular displacement also.⁵ Combination of the body angular rate and attitude parameters such as quaternion and MRPs(Modified Rodrigues Parameters) is typically used in synthesizing the control command which should be produced by RWs.¹ The attitude sensor signals are usually corrupted by noise; gyros tend to contain errors such as drift and random noise. The attitude determination system can estimate such errors, and provide best true signals for feedback control.⁶ Even if the attitude determination system, for instance, sophisticated algorithm such as the EKF(Extended Kalman Filter) algorithm⁶, can eliminate the errors efficiently, it is quite probable that the control command still contains noise sources. The noise and/or other high frequency components in the control command would cause the wheel speed to change in an undesirable manner. The closed-loop system, governed by the feedback control law, is also directly affected by the noise due to imperfect sensor characteristics. The noise components in the sensor signal should be mitigated so that the control command is isolated from the noise effect. This can be done by adding a filter to the sensor output or preventing rapid change in the control command. Dynamic control allocation(DCA), recently studied by Härkegård, is to distribute the control command in the sense of dynamics⁴: the allocation is made over a certain time interval, not a fixed time instant. The dynamic behavior of the control command is taken into account in the course of distributing the control command. Not only the control command requirement, but also variation of the control command over a sampling interval is included in the performance criterion to be optimized. The result is a control command in the form of a finite difference equation over the given time interval.⁴ It results in a filter dynamics by taking the previous control command into account for the synthesis of current control command. Stability of the proposed dynamic control allocation (CA) approach was proved to ensure the control command is bounded at the steady-state. In this study, we extended the results presented in Ref. 4 by adding a two-step dynamic CA term in deriving the control allocation law. Also, the strict equality constraint, between the virtual and actual control inputs, is relaxed in order to construct control command with a smooth profile. The proposed DCA technique is applied to a spacecraft attitude control problem. The sensor noise and/or irregular signals, which are existent in most of spacecraft attitude sensors, can be handled effectively by the proposed approach.

• The Journal of the Convergence on Culture Technology
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• v.10 no.3
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• pp.61-67
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• 2024

Soldiers serving in military units and institutions are subject to strict security policies and technologies because they handle sensitive and confidential information related to national security, so they are likely to experience security stress. The purpose of this study is to recognize the need to manage the security stress of military personnel and to suggest management measures. To this end, a literature study was conducted on 12 KCI(Korean Journal Citation Index) journals dealing with security stress. Since 2016, research on security stress has been conducted mainly through empirical analysis through surveys. Studies related to security stress were divided into studies dealing with factors that affect stress, the relationship between security stress and security compliance intentions, and factors that reduce security stress. In particular, it was confirmed that factors such as organizational justice, organizational technical support, and security feedback can alleviate security stress. Next, by applying the results of this literature study to the defense security environment, we presented security stress management measures for military personnel in terms of improving security-related organizational justice awareness, technical support, and security feedback. The significance of this study is that we recognized the need to manage military personnel's security stress and reviewed practical measures related to this.

• International conference on construction engineering and project management
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• 2013.01a
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• pp.539-545
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• 2013

Although individual-level factors (e.g., attitudes, personality) have long been associated with day-to-day attendance decisions, increasingly researchers have recognized "the social nature of attendance dynamics and their susceptibility to social control (Johns, 2008)." Implications of this social approach for research would be to focus attention on the causes and effects of absence culture (i.e., absence-related perceptions, beliefs, values), and the effects of absence culture on individual and group attendance within social units. Construction projects typically require workers to work in teams or crews on highly interdependent projects, and, thus, are particularly relevant contexts to study absence culture. In this paper we apply a system dynamics (SD) model to study absence culture by utilizing the advantages of SD in capturing a feedback process and state changes. We were particularly interested in: (a) the awareness of social norms within construction crews that pertained to attendance, (b) the interplay between formal attendance rules (policy) and these social norms, and (c) how these sources of influence affected the decision-making process of construction crew members. We expect that the results of this work will help construction organizations evaluate (or re-consider) the effects of their attendance control policies (e.g., timing, strength, and frequency) within a social context. Moreover, our findings suggest that the key to reducing excessive absences might be to invest time in influencing absence culture directly rather than imposing frequent and strict regulations - which, in turn, may inadvertently fortify a culture that works against the organization's interests.