• The Journal of Korean Academy of Prosthodontics
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• v.45 no.3
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• pp.345-353
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• 2007

Statement of problem. Implant abutment screw joints tend to loosen under clinical conditions. Abutment screw loosening results in loss of preload in function. Purpose. Anti-rotational inner post screw (ARIPS) systems were compared with conventional abutment screws to reduce screw loosening. Reverse torque values were evaluated. Material and methods. 32 implant assemblies (Warentec, Co, Ltd, Seoul, Korea) were organized as the 30-Ncm-torque conventional groups and 30-Ncm-torque ARIPS groups in external and internal system. The specimens were tested to 106 cycles at a load of 200N. Preload reverse torque, postload reverse torque, and the ratio of postload reverse torque to preload reverse torque were evaluated. The data were analyzed with unpaired t-test in external and internal systems. Results. In the ratio of postload reverse torque to preload reverse torque, the ARIPS groups showed significant differences than the conventional screw group in both external and internal system. Conclusion. Within the limitations of this study, abutment screw loosening was effectively reduced using ARIPS system.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.690-695
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• 2006

This paper described the Performance test and sound characteristics of helicopter 'Tail-Fan' anti-torque system. In this research, Korea Aerospace Research Institute(KARI) developed 'Tail-Fan' anti-torque system for a helicopter and carried out performance and sound capturing tests of even and uneven tail fans. The performance test is carried out and the noise signals which are generated during the test are saved with microphones at the same time. The performance test's results meet the design requirements. Tone-corrected perceived noise level is reduced by replacing the even product with the uneven one.

• International Journal of Aeronautical and Space Sciences
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• v.6 no.1
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• pp.89-96
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• 2005

Ducted fans have advantages in noise as well as operational safety aspects compared to conventional tail rotors and are used as an anti-torque system for various classes of helicopters. The final goal of this study is to develop a ducted fan anti-torque system which can replace conventional tail rotors of existing helicopters to achieve safety enhancement and low noise level. In this paper, a conceptual design process and the results are described. Initially, the design requirement and the design parameter characteristics are analysed, and then initial sizing and configuration design are performed. There are several configuration changes due to specific technical reasons in each case. Finally, the required power and the pitch link load are predicted as an initial estimation. The conceptual design technique for the ducted fan in this study can be easily applied to the design of other ducted fans such as the lift fan for unmanned aerial vehicle.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.8 s.113
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• pp.857-863
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• 2006

This paper described the performance test and sound characteristics of helicopter 'Tail-Fan' anti-torque system. In this research, Korea Aerospace Research Institute(KARI) developed 'Tail-Fan' anti-torque system for a helicopter and carried out performance and sound capturing tests of even and uneven tail fans. The performance test is carried out and the noise signals which are generated during the test are saved with microphones at the same time. The performance test's results meet the design requirements. Tone-corrected perceived noise level is reduced by replacing the even product with the uneven one.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.2526-2531
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• 2005

A practical pinch torque estimator based on the Kalman filter is proposed for low-cost anti-pinch window control systems. To obtain the accurate angular velocity from Hall-effect sensor measurements, the angular velocity calculation algorithm is executed with additional procedures for removing the measurement noises. Apart from the previous works using the angular velocity estimates and torque estimates for detecting the pinched condition, the torque rate is augmented to the system model and the proposed pinch estimator is derived by applying the steady-state Kalman filter recursion to the model. The motivation of this approach comes from the idea that the bias errors in torque estimates due to the motor parameter uncertainties can be almost eliminated by introducing the torque rate state. For detecting the pinched condition, a systematic way to determine the threshold level of the torque rate estimates is also suggested via the deterministic estimation error analysis. Simulation results are given to certify the pinch detection performance of the proposed algorithm and its robustness against the motor parameter uncertainties.

• Tribology and Lubricants
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• v.14 no.1
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• pp.70-78
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• 1998

Two different friction materials (organic and low-metallic pads) for automotive brakes were studied to investigate the anti-fading phenomena during stop. The anti-fading phenomena were pronounced more in the case of using low metallic friction materials than organic friction materials. The main cause of the anti-fading phenomena was the high dependence of friction coefficient on a sliding speed. The anti-fading was prominent when the initial brake temperature was high in the case of low-metallic friction materials due to the strong stick-slip event at high temperature. On the other hand, the anti-fading was not severe in organic friction materials and the effect was reduced at high braking temperature due to the thermal decomposition of organic friction materials. The strong stickslip phenomena of low metallic friction materials at high temperature induced high torque oscillations during drag test. During this experiment two different braking control modes (pressure controlled and torque controlled modes) were compared. The type of the control mode used for brake test significantly affected the friction characteristics.

• Proceedings of the KIPE Conference
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• 2004.07b
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• pp.891-894
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• 2004

This paper estimate coefficient of adhesion through speed sensor-less vector control and load torque disturbance observer used for maximum tractive force control. And also proposes anti-slip control algorithm, which controls torque force of motor in order to keep the estimated adhesion force in maximum adhesion by controlling PI torque with the differential value of estimated adhesion force coefficient.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.10a
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• pp.123-126
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• 2003

This paper describes the development procedure for Tail-Fan system which has the role of anti-torque and yaw control in helicopter. A detailed design of Tail-Fan system was done and structural analysis also was done. After finishing detailed design, Detailed drawings were generated for manufacture. Through detailed design and manufacture, required techniques were achieved for helicopter development. After validation through performance and stability test, acquired techniques will be applied to development of Korea Multi-role Helicopter(KMH) which will be launched

• Journal of Magnetics
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• v.14 no.4
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• pp.168-171
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• 2009

We propose a new type of spin torque nano-oscillator structure with an exchange- biased free rotating layer. The proposed spin torque nano-oscillator consists of a fixed layer and a free rotating layer with an additional anti-ferromagnetic layer, which leads to an exchange bias in the free rotating layer. The spin dynamics of the exchange-biased free rotating layer can be described as an additional exchange field because the exchange bias manifests itself by the existance of a finite exchange bias field. The exchange bias field plays a similar role to that of a finite external field. Hence, microwave generation can be achieved without an external field in the proposed structure.

• The Journal of Korean Academy of Prosthodontics
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• v.43 no.5
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• pp.671-683
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• 2005

Statement of problem: The most commonly reported problem associated with dental implant restoration is the loosening of the screws. Purpose: This study compared the efficacy of an implant system incorporating an anti-rotational locking sleeve(Anti-Rotating Inner Post Screw System(ARIPS-system)) with other, traditional implant systems as a means of minimizing vibration loosening. Materials and methods: Three implant systems were examined; the conventional external hex type, the ARIPS-system, and the internal taper type implant system 30 specimens(10 samples per group)were fabricated and each abutment screw was secured to the implant future with 32Ncm of torque force and loosening torque was measured using a Torque Gauge. The procedure was repeated 3 times, recording initial loosening torque each time. The re-tightened abutment screw was subjected to a cyclic load having a maximum forte of 200N and minimum of 20N at 2Hz over a period of 12,600 cycles. after which the loosening torque was measured. Measured values were calaulated for statistical analysis. Analysis of measured value was performed by 3 methods: (i) as a percentage average of the initial 3 loosening-torque values(initial loosening value) to the tightening torque of 32Ncm, (ii) as a percentage of the loosening torque value after a load of 200N(experimental value) to the initial loosening value, and (iii) as a percentage of the experimental value to the 32Ncm of tightening torque. The analyses shows the amount of initial loosening at the screw, loosening by repetitive load and the the final loosening value. Results: The results of this study were as follows (1) Percentage of initial loosening value to tightening-torque was increased in order of external hex, ARIPS-system and internal taper and all values between each groups showed statistical significance (p<0.05). (2) Percentage of experimental value to initial loosening value was increased in order of external hex, ARIPS-system and internal taper. Value of internal taper showed significant difference with those of external hex and ARIPS-system (p<0.05). (3) Percentage of experimental value to tightening torque was increased in order of external hex, ARIPS-system and internal taper and all values between each groups showed statistical significance (p<0.05). Conclusion: The results of the analysis of the final loosening level value, which are closely correlated to clinical use, show that the ARIPS-system can be a useful means of minimizing abutment screw loosening when compared to the external hex type system. Although further clinical studies need to be made, the ARIPS-system should be considered to maximize the long-term success of the implant prosthesis.