• Tribology and Lubricants
• /
• 제12권1호
• /
• pp.47-55
• /
• 1996

In this study, steady state and perturbed pressures are experimentally measured under inherently compensated restrictors in externally pressurized air bearings. A piezo actuator is used for simulating small displacement perturbation in the air film. The pressures under the restrictors are measured by a miniature type pressure transducer and the height of the air film is measured by capacitance type gap sensors developed by Chapman's method. The perturbed pressure is obtained through Fourier transformation of the two signals. The measured perturbed pressures are in good agreement with the calculated values.

• Tribology and Lubricants
• /
• 제13권4호
• /
• pp.40-46
• /
• 1997

The externally pressurized air journal bearings which have two circumferential grooves with inherently compensated restrictors are analyzed. Two circumferential grooves with restrictors are made on the bearing surface in order to increase the stiffness and damping coefficients. In this paper, the dynamic characteristics such as stiffness and damping coefficients of this type of bearings are calculated. As a result of theoretical analysis, it is verified that there exist the groove depth and the distance between two grooves which generate the maximum stiffness at the given bearing dimensions.

• 한국정밀공학회지
• /
• 제32권2호
• /
• pp.135-140
• /
• 2015

It is an important thing for a designer to simulate and predict the performance of a spindle and a rotary table. In addition to the general performance such as static stiffness, the error motion performance information is beneficial to the designer in many cases. However for an aerostatic bearing the fluid film physical status should be calculated in order to simulate those performances and the calculation time is another obstacle for a simple performance simulation. In this paper the investigation on experiment and simulation is performed in order to find a more effective simulation method for the rotational error motion.

• Tribology and Lubricants
• /
• 제7권2호
• /
• pp.51-60
• /
• 1991

For the accurate run-out of a light rotor shaft the sliding bearings supplied with externally pressurized air are effectively applied, and it is important to predict the static and dynamic characteristics of rotor-bearing system. In this study direct numerical method is applied to solve the perturbed Reynolds' equation. To solve it the perturbed dimensionless mass flow rate is used as the boundary condition under the inherently-compensated restrictor. The dynamic characteristics of a rotor supported in the externally pressurized air bearings are analyzed, and as a result the orbit of the journal center is calculated. The theoretical results are investigated and discussed.

• Journal of Mechanical Science and Technology
• /
• 제15권9호
• /
• pp.1240-1247
• /
• 2001

A robust control design scheme using well-developed SISO techniques is proposed for maglev vehicles that are inherently unstable MIMO systems. The proposed separate control method has basically two control loops: a stabilizing loop by a pole-placement technique, and a performance loop using a novel optimal LQ loop-shaping technique. This paper shows that the coupling terms involved in maglev vehicles with multimagnets should not be neglected but compensated for their stability and performance robustness. The robustness properties of the proposed control system are then evaluated under variations of vehicle masses and air gaps through a computer simulation. This paper also describes the reason why the proposed control technique can be suggested as a tool using only SISO techniques in controlling unstable MIMO systems such as maglev vehicles.

• 소성∙가공
• /
• 제20권3호
• /
• pp.229-235
• /
• 2011

The formability of magnesium alloy sheets at room temperature is generally low because of the inherently limited number of slip systems, but higher at temperatures over $150^{\circ}C$. Therefore, prior to the practical application of these materials, the forming limits should be evaluated as a function of the temperature and strain rate. This can be achieved experimentally by performing a series of tests or analytically by deriving the corresponding modeling approaches. However, before the formability analysis can be conducted, a model of flow stress, which includes the effects of strain, strain rate and temperature, should be carefully identified. In this paper, such procedure is carried out for Mg alloy AZ31 and the concept of flow stress surface is proposed. Experimental flow stresses at four temperature levels ($150^{\circ}C$, $200^{\circ}C$, $250^{\circ}C$, $300^{\circ}C$) each with the pre-assigned strain rate levels of $0.01s^{-1}$, $0.1s^{-1}$ and $1.0s^{-1}$ are collected in order to establish the relationships between these variables. The temperature-compensated strain rate parameter which combines, in a single variable, the effects of temperature and strain rate, is introduced to capture these relationships in a compact manner. This study shows that the proposed concept of flow stress surface is practically relevant for the evaluation of temperature and strain dependent formability.

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 2004년도 ICCAS
• /
• pp.1958-1961
• /
• 2004

Ring Laser Gyroscopes used as navigational sensors inherently experience a lock-in region, where very low rotational rates are not measurable. Most RLG manufacturers use a mechanical dither motor that applies a small oscillatory rotational motion larger than this region to resolve this problem. Any input acceleration that bends this dithering axis causes flexure error, which is a noncommutative error that can not be compensated by simply using integrated gyro sensor output. This paper introduces noncommutative error equations that define attitude errors caused by flexure errors. In this paper, flexure error is classified as sensor level error if the sensing axis coincides with the dithering axis and as system level error if the two axes do not coincide. The relationship between gyro output and the rotation vector is introduced and is used to define the coordinate transformation matrix and angular motion. Equations are derived for both sensor level and system level flexure error analysis. These equations show that RLG based INS attitude error caused by flexure is directly proportional to time, amount of input acceleration and the dynamic frequency of the vehicle.

• 한국인터넷방송통신학회논문지
• /
• 제12권2호
• /
• pp.153-158
• /
• 2012

본 논문에서는 통신 채널에서 발생되는 찌그러짐과 잡음의 영향을 최소화하기 위하여 사용되는 적응 등화 알고리즘인 CMA 와 MMA 의 성능을 비교하였다. 다른 방식에비해 비교적 간단한 연산으로 고속 등화가 가능한 알고리즘인 CMA (Constant Modulus Algorithm)와 이의 오차 함수를 변형한 MMA (Multi-Modulus Algorithm)의 성능을 분석하여 점대점 또는 점대다점의 디지털 전송에서 적용 가능성을 확인하였다. CMA 알고리즘은 수신 신호의 진폭만을 보상하며 위상은 보상하지 못하므로 별도의 PLL을 사용하여야 하지만, MMA 알고리즘은 진폭과 위상을 동시에 보상할 수 있음을 컴퓨터 시뮬레이션을 통하여 확인하였으며 이의 성능 비교를 위해서 적응 등화기에 필수적인 수렴 특성과 잔류 isi양을 사용하였고, 그 결과 수렴 특성에서는 MMA 방식이, 진폭 보상을 나타내는 잔류 isi 양에서는 CMA 방식이 우월함을 알 수 있었다.

• Smart Structures and Systems
• /
• 제20권4호
• /
• pp.483-498
• /
• 2017

Real-Time Hybrid Simulation (RTHS) is a powerful and cost-effective dynamic experimental technique. To implement a stable and accurate RTHS, time delay present in the experiment loop needs to be compensated. This delay is mostly introduced by servo-hydraulic actuator dynamics and can be reduced by applying appropriate compensators. Existing compensators have demonstrated effective performance in achieving good tracking performance. Most of them have been focused on their application in cases where the structure under investigation is subjected to inputs with relatively low frequency bandwidth such as earthquake excitations. To advance RTHS as an attractive technique for other engineering applications with broader excitation frequency, a discrete-time feedforward compensator is developed herein via various optimization techniques to enhance the performance of RTHS. The proposed compensator is unique as a discrete-time, model-based feedforward compensator. The feedforward control is chosen because it can substantially improve the reference tracking performance and speed when the plant dynamics is well-understood and modeled. The discrete-time formulation enables the use of inherently stable digital filters for compensator development, and avoids the error induced by continuous-time to discrete-time conversion during the compensator implementation in digital computer. This paper discusses the technical challenges in designing a discrete-time compensator, and proposes several optimal solutions to resolve these challenges. The effectiveness of compensators obtained via these optimal solutions is demonstrated through both numerical and experimental studies. Then, the proposed compensators have been successfully applied to RTHS tests. By comparing these results to results obtained using several existing feedforward compensators, the proposed compensator demonstrates superior performance in both time delay and Root-Mean-Square (RMS) error.

• 의료법학
• /
• 제21권3호
• /
• pp.77-116
• /
• 2020

현대 과학의 경험과 성과가 반영된 의약품의 사용으로 인류에게 질병의 치료와 건강 상태의 개선이라는 혜택이 주어지고 있다. 그러나 의약품은 질병의 치료라는 혜택 이외에도 본질적으로 피할 수 없는 부작용도 내포한다. 각국은 부작용으로 인한 피해의 최소화를 위해 시장진입 규제나 시판후조사 등의 조치를 취하고 있으나, 부작용의 발생은 피할 수 없다. 부작용으로 인한 손해의 발생이 불가항력이라도 그 점이 사전에 알려진 것이었다면, 의약품의 종류와 사용 형태에 따라서 처방한 의사나 복약지도를 담당하는 약사 등이 손해를 배상해야 한다. 의약품에 결함이 있어 손해가 발생하는 경우도 있는데, 손해 배상의 일반원칙을 그대로 적용해서는 결함으로 인한 부작용 피해자가 손해를 배상받기 쉽지 않다. 우리나라를 비롯한 여러 나라가 제조물 책임법을 통하여 피해자의 보호를 도모하고 있으며, 의약품도 제조물에 포섭되기 때문에 제조물 책임법을 통한 손해배상을 문의할 수 있는데, 이 때 주로 설계상의 결함이나 표시상의 결함이 문제될 수 있다. 제조물 책임법이 제정·시행되기 이전에도 의약품의 부작용으로 인한 손해는 발생하여왔다. 이러한 경우를 위해서 판례는 제조물 책임법과 유사한 법리를 발전시켜 왔고, 의약품 결함은 혈액제제와 관련하여 판례가 형성되어 왔다. 제조물 책임법 시행 이전에 제조된 의약품으로 인한 손해는 향후에도 발생할 수 있기에 판례 법리는 중요한 검토의 대상이다.