• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.05a
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• pp.143-149
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• 2002

Ball reducer with waved grooves has many advantages over other reducers for the high-reduction ratios, low noise and low energy loss, etc. The mechanism of force transmission is very similar to that of cam and follower in automobile valve train system especially in the contact geometry. In this study, we have investigated the traces of contact between ball and outer race and the working behaviors with a certain reduction ratio. In order to verify the contact behaviors between ball and outer race, which determines the critical endurance life the contact velocity and load are computed for a cycle. During some period of a cycle, the contact velocity reverses its direction very suddenly, which causes undesirable endurance performance of this machinery. From the computational investigation in this work, we hope to predict similar contact damages in other machinery due to this kind of contact behaviors, which is very common in many contact phenomena.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.491-495
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• 2004

The industries use polymer materials for many purposes for they have many merits. The costs of these materials take up too great a proportion of the overall cost of products that use these materials as their major material. It is advantage for polymer industries to reduce these costs. The microcellular foaming process was developed in the early 1980s to solve this problem and proved to be quite successful. Microcellular foaming process uses inert gases such as $CO_2$, $N_2$. As these gases solve into polymer matrices, many properties are changed. The microcellular foaming process makes the glass transition temperature of polymers to low, and diminish the residual stress of polymer matrices. Besides, the microcellular foaming process has several merits, impact strength elevation, thermal insulation, noise insulation, and raw material saving etc. This characteristic of microcellular foaming process has influenced by cell morphology. The cell morphology means cell size and cell density. The cell morphology has influenced by many factors. The examples of factor are pressure drop rate, foaming temperature, foaming time, saturation pressure, saturation time etc. Among their factors, pressure drop rate is the most important factor for cell morphology in microcellular foaming injection molding process. This paper describes about the cell morphology change in accordance with the pressure drop rate of microcellular foaming injection molding process.

• Journal of the korean Society of Automotive Engineers
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• v.14 no.5
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• pp.69-82
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• 1992

Vibration of intake menifold is important as it could worsen the noise levels radiated from surface itself and support bracket, and it eventually leads to the failures of a Throttle Position Sensor and an Idle Air Control Valve. In this study, structural modification method is proposed to reduce structural vibration of an intake manifold system. At first, vibration problems are identified through tests on a running engine. Then modal data acquired by modal testing and finite element analysis are helpful to understand vibration mechanism of the system, and used as the design guide when structural modifications are attempted. After the system model is validated by comparison of the modal data obtained from analysis and experiment, iterative calculations are performed to find optimized structure of the system by finite element analysis. As a result, a newly designed plenum bracket is suggested in such a way that the intake manifold is stiffened, and that design of the support bracket is suggested in such a way that the intake manifold is stiffened, and that design of the support bracket is changed in terms of bolting position, thickness, shape, and minimum weight increase. Finally, it is shown that a new design achieves a significant reduction of vibration of an intake manifold system and it is confirmed by tests on a running engine.

• Tribology and Lubricants
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• v.29 no.2
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• pp.105-110
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• 2013

Refrigeration and air-conditioning compressors used in home appliances, including refrigerators and air conditioners, are typically hermetic-type reciprocating compressors. Because the shell is sealed by welding, it should be designed to have a semi-permanent life. The energy consumption of a hermetic-type reciprocating compressor is low, but because it operates continuously to maintain a constant temperature inside the refrigerator, it has a certain base load. In this type of compressor, the driving motor operates at a high speed (about 3,000 - 3,600 rpm), which causes valve damage, friction, wear, and high-frequency noise. Many studies have been conducted to solve these problems. To enhance the reliability and efficiency of the reciprocating compressor, the design conditions and operating environment of journal bearings should be considered. Dynamic behavior analysis should be carried out in terms of the discharge pressure. The results showed that the load (discharge pressure) increases in the forward lookup zone and decreases in the backward lookup zone. When the revolution speed is increased, the maximum load decreases in the region where the maximum load operates.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.290-295
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• 2005

Hydraulic actuators are important in modern industry due to high power, fast response, and high stiffness. In recent years, hybrid actuation system, which combines electric and hydraulic technology in a compact unit, can be adapted to a wide variety of force, speed and torque requirements. Moreover, the hybrid actuation system has dealt with the energy consumption and noise problem existed in the conventional hydraulic system. Therefore, hybrid actuator has a wide range of application fields such as plastic injection-molding and metal forming technology, where force or pressure control is the most important technology. In this paper, the solution for force control of hybrid system is presented. However, some limitations still exist such as deterioration of the performance of transient response due to the variable environment stiffness. Therefore, intelligent switching control using Learning Vector Quantization Neural Network (LVQNN) is newly proposed in this paper in order to overcome these limitations. Experiments are carried out to evaluate the effectiveness of the proposed algorithm with large variation of stiffness of external environment. In addition, it is understood that the new system has energy saving effect even though it has almost the same response as that of valve controlled system.

• Journal of the Korea Institute of Military Science and Technology
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• v.12 no.4
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• pp.540-547
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• 2009

In the near future, military robots are likely to be substituted for military personnel in the field of battle. The power system of a legged robot is considerably more complex than the one used for a land vehicle because of the coordination and stability issues due to the large number of degree of freedom. In this paper, a servovalve-piston combination system for a straight-line motion of robot leg is modeled as three degree of freedom based on double inputs and single output transfer function. The output is the displacement of piston from neutral. The inputs are valve displacement from neutral and arbitrary load force in this system. LQR(Linear Quadratic Regulator) technique is applied in order to achieve robust stability and fast responses of the system. The Kalman filter loop, rejection of disturbance and noise, riccati equation, filter gain matrix, and frequency domain equality are analyzed and designed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.9
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• pp.1139-1148
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• 1997

Compression waves propagating in a high-speed railway tunnel develops large pressure fluctuations on the train body or tunnel structures. The pressure fluctuations would cause an ear discomfort for the passengers and increase the aerodynamic resistance of trains. As a fundamental research to resolve the pressure wave phenomenon in the tunnel, experiments were carried out by using a shock tube with an open end. A blockage to model trains inside the tunnel was installed on the lower wall of shock tube, thus forming a sudden cross-sectional area reduction. The compression waves were obtained by the fast opening gate valve instead of a conventional diaphragm of shock tube and measured by the flush mounted pressure transducers with a high sensitivity. The experimental results were compared with the previous theoretical analyses. The results show that the ratio of the reflected to the incident compression wave at the sudden cross-sectional area reduction increases but the ratio of the passing to the incident compression wave decreases, as the incident compression wave becomes stronger. This experimental results are in good agreements with the previous theoretical ones. The maximum pressure gradient of the compression wave abruptly increases but the width of the wave front does not vary, as it passes over the sudden cross-sectional area reduction.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.865-870
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• 2001

For pneumatic system control, we need a data transmission system with high speed and high reliability or information interchange between main computer and solenoid valves and I/O devices. This paper presents a set of design techniques for a data communication system that is mainly used for pneumatic system control. For this purpose, we first designed hardware modules for an interface between central control module and local node that handles the operation of solenoid valves. In addition we developed a communication protocol for construction of RS-485 based multidrop network, and this protocol is basically designed with a kind of polling technique. Finally we evaluated performance of the developed system. The field test results show that, even under high noise environment, the data transmission of 375Kbps rate is possible up to 1,000m without using repeater. In addition, the system developed in this research is proved to be used easily for extension of a communication network because of its module structure.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.10
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• pp.3186-3198
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• 1996

When a robot is to have contact with its enviornment, such as a medi-care robot, it would be advantageous for the robot to have a high compliance. For this reason, a robot having not only a flexible link but also an actuator with compliance, is desirable. This paper is concerned with the position and vibration control of 1 degree of freedom flexible robot using a pneumatic artificial muscle actuator. The dynamics of the manipulator assumed to be and Euler-Bernoulli beam are derived on the basis of the linear mathematical modle. Although this pneumatic artifical muscle actuator has many merits for the compliance robot, it is difficult to make an effective control scheme of this system because of ths nonlinearity and uncertainty on the dynamics of the actuator. By designing a controller using .mu.-synthesis, robust performance against measurement noise, various modeling uncertainties on the dynamics of the servo valve, actuator and mainpulator, is achieved. The effectiveness of the proposed control method is illustrated through simulations and experiments.

• Journal of the Korean Society of Visualization
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• v.15 no.1
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• pp.11-18
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• 2017

A two-phase flow observed in a heat exchanger or nuclear power generation often has a profound effect on undesirable noise or flow characteristics. Void fraction, which refers to the ratio of gas (or liquid) to the total fluid, affects heat transfer coefficient, vibration and so forth. In other words, void fraction is one of most important parameters in two-phase flow since it contributes to comprehend the characteristics of two-phase flow. We developed a two-phase flow visualization system to measure cross-sectional and volumetric void fractions by using quick closing valves and image processing software. With this system, we could observe the plug, slug, and stratified flow patterns of two-phase flow and measure a myriad of void fractions. As a consequence of the experiment, we found that the estimated void fractions were largely coincident with the predictive values by Chisholm model.