• Tribology and Lubricants
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• v.39 no.2
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• pp.76-80
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• 2023

This paper describes an experimental investigation of the effect of cooling flow rate on gas foil thrust bearing (GFTB) performance. In a newly developed GFTB test rig, a non-contact type pneumatic cylinder provides static loads to the test GFTB and a high-speed motor rotates a thrust runner up to the maximum speed of 80 krpm. Force sensor, torque arm connected to another force sensor, and thermocouples measures the applied static load, drag torque, and bearing temperature, respectively, for cooling flow rates of 0, 25, and 50 LPM at static loads of 50, 100, and 150 N. The test GFTB with the outer radius of 31.5 mm has six top foils supported on bump foil structures. During the series of tests, the transient responses of the bearing drag torque and bearing temperature are recorded until the bearing temperature converges with time for each cooling flow rate and static load. The test data show that the converged temperature decreases with increasing cooling flow rate and increases with increasing static load. The drag torque and friction coefficient decrease with increasing cooling flow rate, which may be attributed to the decrease in viscosity and lubricant (air) temperature. These test results suggest that an increase in cooling flow rate improves GFTB performance.

• Journal of the Korean Society for Precision Engineering
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• v.9 no.2
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• pp.36-43
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• 1992

In this paper, a robot assembly wrist, which is able to assemble chamferless parts, has been developed. The RCC (Remote Center Compliance) structure is used as a basic structure. 5 position sensors and 4 pneumatic actuators are installed additionally to measure the deformation of RCC structure and correct the errors actively. Due to the restricted direction of actuation, a decision rule which selects the suitable actuator according to the position sensor signals is needed. For this purpose, a neural network is used and it is experimentally shown that the nerual network overcomes system's nonlinearity. This paper presents fundamental experiment results for the insertion of parts with several clearance.

• Journal of Institute of Control, Robotics and Systems
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• v.7 no.5
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• pp.432-437
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• 2001

Korea High Speed Train(KHST) is supposed to run up 350km/h, in which the braking system has a crucial role for the safety of the train. In the design st데 of the braking system, its very hard to ac-quire information data for design guidelines. A HILS(Hardware-In-the-Loop Simulation) system can be used to get design data which could simulate the braking system of the real train in real-time. In this paper, cars are modelled including car dynamics, brake blending algorithms, pneumatic actuator dynamics, the models of each braking devices, adhesive coefficients, and soon. Real-time braking time, distance, and other design parameters are simulated using a DSP board and C language which shows the validity of the proposed method.

• Journal of Institute of Control, Robotics and Systems
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• v.18 no.6
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• pp.519-525
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• 2012

Electric brake booster systems replace conventional pneumatic brake boosters with electric motors and rotary-todisplacement mechanisms including ECU (Electronic Control Unit). Electric booster brake systems require precise target pressure tracking and control robustness because vehicle brake systems operate properly given the large range of loading and temperature, actuator saturation, load-dependent friction. Also for the implement of imbedded control system, the controller should be selected considering the limited memory size and the cycle time problem of real brake ECU. In this study, based on these requirements, a sliding mode controller has been chosen and applied considering both model uncertainty and external disturbance. A mathematical model for the electric booster is derived and simulated. The developed sliding mode controller considering chattering problem has been compared with a conventional cascade PID controller. The effectiveness of the controller is demonstrated in some braking cases.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.12
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• pp.1128-1138
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• 2010

One of the typical problems in the precise vibration is resonance characteristics at low frequency disturbance due to a heavy mass. An electro-magnetic(EM) air spring is a kind of vibration control unit and active isolator. The EM air spring in this study aims at removing the low frequency resonance for semiconductor manufacturing. The mechanical and electronic parts in the active isolator are designed to operate under a weight of 2.5 tons. The EM spring is floated using air pressure in a pneumatic elastic chamber and actuated by EM levitation force. The actuator consists of a EM coil and a permanent magnetic plate which are installed inside of the chamber. An air mount was constructed for the experiment with a stone surface plate, 4 active air springs, 4 gap sensors, a DSP controller, and a multi-channel power amp. A PD control method and operating logic was applied to the DSP. Simulation using 1/4 model was carried out and compared with the experiments. The time duration and maximum peak at resonance frequency can be reduced sharply by the proposed system. The results show that the active system can avoid the resonance caused by the natural frequency of the passive system.

• Journal of Aerospace System Engineering
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• v.12 no.2
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• pp.30-36
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• 2018

In this study, a small-scaled test system for a tip jet rotor was developed to contribute to the research on unmanned compound rotorcraft. The performance and dynamic characteristics of the tip jet rotor were investigated using the test system. The diameter of the tip jet rotor was set to 2m in consideration of the size of the test site and the pneumatic supply capacity of the. The rotating speed of the rotor was controlled by the pressure of the compressed air. The thrust and forces during the rotor rotation were measured using a load measuring device. A hydraulic actuator was installed for the dynamic test and full-bridge strain gages were attached to the root of each blade to measure the flap, lag, and torsion-wise responses generated when the rotor is excited by the actuator. The performance and dynamic characteristic tests were conducted at various rotor speeds and blade pitches. In order to check the validity of the test results, the results were also compared with the CAMRAD II analysis.

• Aerospace Engineering and Technology
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• v.1 no.1
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• pp.141-146
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• 2002

During dynamic flight by propulsion of rocket engine, in the atmosphere, the attitude control of flight vehicle can be accomplished by the aerodynamic fin actuator. But, in the outer space, the method of TVC(Thrust Vector Control) is only depend on for it. There are many systems which were developed for TVC. In our research, among them we adopted gimbal engine actuation system which could control the vector of thrust by swivelling rocket engine connected by gimbal. There are electro-hydraulic, electro-mechanical and pneumatic system which can be used as gimbal engine actuation system, but the electro-hydraulic system that has high ratio of output power to mass is preferred for the high power system. In this note, we made a mathematical model of the electro-hydraulic gimbal engine actuation system for the TVC of KSR-III in detail and on the base of this model we performed a simulation study. And then, we verified the model by making a comparison between the simulation and the experiments on the real system.

• Tribology and Lubricants
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• v.39 no.2
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• pp.81-85
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• 2023

This study presents an experimental investigation of the effects of surface roughness on gas foil thrust bearing (GFTB) performance. A high-speed motor with the maximum speed of 80 krpm rotates a thrust runner and a pneumatic cylinder applies static loads to the test GFTB. When the motor speed increases and reaches a specific speed at which a hydrodynamic film pressure generated within the gap between the thrust runner and test GFTB is enough to support the applied static load, the thrust runner lifts off from the test GFTB and the friction mechanism changes from the boundary lubrication to the hydrodynamic lubrication. The experiment shows a series of lift-off test and load-carrying capacity test for two thrust runners with different surface roughnesses. For a constant static load of 15 N, thrust runner A with its lower surface roughness exhibits a higher start-up torque but lower lift-off torque than thrust runner B with a higher surface roughness. The load capacity test at a rotor speed of 60 krpm reveals that runner A results in a higher maximum load capacity than runner B. Runner A also shows a lower drag torque, friction coefficient, and bearing temperature than runner B at constant static loads. The results imply that maintaining a consistent surface roughness for a thrust runner may improve its static GFTB performance.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.196-201
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• 2004

In biometric and biomedical applications, a special transporting mechanism must be designed for the ${\mu}$TAS (micro total analysis system) to move samples and reagents through the microchannels that connect the unit procedure components in the system. An important issue for this miniaturization and integration is microfluid management technique, i.e., microfluid transportation, metering, and mixing. In view of this, this study presents an optimal fuzzy sliding-mode control (OFSMC) design based on the 8051 microprocessor and implementation of a complete microfluidic manipulated system implementation of biochip system with a pneumatic pumping actuator, a feedback-signal photodiodes and flowmeter. The new microfluid management technique successfully improved the efficiency of molecular biology reaction by increasing the velocity of the target nucleic acid molecules, which increases the effective collision into the probe molecules as the target molecules flow back and forth. Therefore, this hybridization chip was able to increase hybridization signal 6-fold and reduce non-specific target-probe binding and background noises within 30 minutes, as compared to conventional hybridization methods, which may take from 4 hours to overnight. In addition, the new technique was also used in DNA extraction. When serum existed in the fluid, the extraction efficiency of immobilized beads with solution flowing back and forth was 88-fold higher than that of free-beads.

• KSTLE International Journal
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• v.3 no.2
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• pp.101-109
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• 2002

This paper presents the fabrication and performance inspection of a peristaltic micropump by flow simulation. The valve-less micropump using the diffuser/nozzle is consists of base plate, mid plate, top plate and connection tubes fur inlet and outlet. In detail, the base plate is composed of two diffuser nozzles and three chambers, the mid plate consists of a glass diaphragm for the volumetric change of the pumping chamber. The inlet and outlet tubes are connected at the top plate and the actuator fur pressing the diaphragm is located beneath the top plate. The micropump is fabricated on the silicon wafer by DRIE (Deep Reactive ion Etching) process. The pumping performances are tested by the pneumatic test rig and compared with the simulated results fur various dimensions of diffuser nozzles. The pumping characteristics of the micropump by the volumetric change at the pumping chamber is modeled and simulated by the commercial software of FLOW-3D. The simulated results shows that reverse flow is the inherent phenomena in the diffuser nozzle type micropump, but it can be reduced at the dual pumping chamber model.