• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.39 no.7
• /
• pp.605-611
• /
• 2011

Shimmy is a self-excited vibration in lateral and torsional directions of a landing gear during either the take-off or landing. It is caused by a couple of conditions such as a low torsional stiffness of the strut, a free-play in the landing gear, a wheel imbalance, or worn parts, and it may make the aircraft unstable. This study was performed for an analysis of the shimmy stability on a small aircraft. A nose landing gear was modeled as a linear system and characterized by state-equations which were used to analyze the stability both in the frequency and time-domain for predicting whether the shimmy occurs and investigating a good design range of the important parameters. The root-locus method and the 4th Runge-Kutta method were used for each analysis. Because the present system has a simple mechanism using a friction to reinforce the stability, the friction, a non-linear factor, was linearized by a describing function and considered in the analysis and observed the result of the instability reduction.

• Proceedings of the KIEE Conference
• /
• 2009.07a
• /
• pp.1640_1641
• /
• 2009

Dynamic friction and force ripple are the most predominant factors that affect the positioning accuracy of permanent magnet synchronous motor(PMSM) servo drives system, and it is desirable to compensate them in finite time with a continuous control law. In this paper, based on LuGre dynamic friction model, a robust adaptive skidding mode controller is proposed to compensate the nonlinear effect of friction and force ripple. The controller scheme consists of a PD component and a robust adaptive sliding mode controller for estimating the unknown system parameter. Using Lyapunov stability theorem, asymptotic stability analysis and position tracking performance are guaranteed. Simulation results well verify the feasibility and the effectiveness of the proposed scheme for high0precision motion trajectory tracking.

• Proceedings of the KSME Conference
• /
• 2003.11a
• /
• pp.1690-1695
• /
• 2003

In order to investigate the mechanism of brake squeal noise, the sound and vibration of an actua1 brake system were measured using a brake dynamometer. The experimental results show that disc run-out varies with brake line pressure and the factor of squeal generation is the run-out due to the misalignment of brake disk. A three degrees of freedom friction model is developed for the disk brake system where the run-out effect and nonlinear friction characteristic are considered. The results of numerical analysis of the model agree well with the experimental results. Also, the stability analysis of the model was performed to predict the generation of brake squeal due to the design parameter modification of brake systems. The results show that the squeal generation depends on the nm-out rather than the friction characteristic between the pad and the disk of brake.

• Journal of the Korean Society for Precision Engineering
• /
• v.16 no.5 s.98
• /
• pp.145-150
• /
• 1999

We have studied on the tribological characteristics of surface modification by Arc Ion Implantation(AIP) coating method. Coating materials were deposited by the Titanium carbide(TiC) and Titanium nitride(TiN). An experimental process was established to determine the tribological characteristics of friction and wear behaviour with the variation of applied load, temperature and the time by the Falex friction and wear test machine. The results, It can be improved that when the surface modification of hard coatings(TiC, TiN) was deposited steel, the tribological characteristics become better. It is argued that improved because of excellence of the anti-wear, the extreme pressure properties and the heat stability.

• Tribology and Lubricants
• /
• v.26 no.4
• /
• pp.246-253
• /
• 2010

Friction characteristics of the brake friction materials without environmentally regulated ingredients were examined to find their role in the brake performance. Five friction materials were produced based on a nearcommercial formulation by changing the relative amount of potentially hazardous ingredients to health and environment, such as $Sb_2S_3$, potassium titanate, and brass fiber. Tribological properties of the friction materials were obtained using a scale dynamometer and Krauss type tribometer. Results showed that the excluded three ingredients played important synergetic effects on tribological properties in terms of fade resistance, wear resistance and friction effectiveness. In particular, brass fibers played important roles in the friction stability by providing excellent thermal diffusivity at the friction interface. Potassium titanate whiskers showed excellent fade resistance and wear resistance compared to the substituted barite. Antimony trisulfide, on the other hand, showed little effect on the high temperature fade resistance and wear resistance, while it increased friction effectiveness at moderate temperatures. The friction materials without the three ingredients showed severe fade, indicating antisynergy effects.

• Tribology and Lubricants
• /
• v.14 no.1
• /
• pp.70-78
• /
• 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 Korean Geotechical Society Conference
• /
• 2005.03a
• /
• pp.179-184
• /
• 2005

Shear strength parameters obtained from filed survey are important factors in the analysis of slope stability. In this study, sensitivity analysis was performed to evaluate the effect of input parameters on the analysis of slope stability. The input parameters selected for sensitivity analysis were slope angle, cohesion, and friction angle. Monte-Carlo Simulation method was used for calculating input parameters and the factor of safety was computed by means of limit equilibrium method. A rock slope, which has failed in the field, was used for the sensitivity analysis in the analysis of slope stability. The result of analysis shows that the factor of safety of the rock slope was a little low. From partial correlation coefficient(PPC) of input parameters determined from the sensitivity analysis, slope stability was dependant on cohesion and slope angle. The effect of friction angle was lower than that of cohesion and slope angle on slope stability.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
• /
• 1999.06a
• /
• pp.240-246
• /
• 1999

The effect of microstructure of gray cast iron disk was investigated by using a pad-on-disk type friction tester. Three different rotors with different microstructures were studied in this work. They showed a pearlitic matrix, a ferritic matrix, and a martensitic structure, respectively. All of them have graphite flakes in common. Drag tests at different pressure and speed conditions were carried out to study friction stability, temperature rise during drags. The rotor containing pearlitic matrix showed lower values of friction coefficient, small amount of temperature rise, and less fading. The results showed that gray cast iron disk containing pearlitic matrix has good friction characteristics.

• Tribology and Lubricants
• /
• v.29 no.2
• /
• pp.98-104
• /
• 2013

Cu-matrix-sintered brake pads and heat-resistant low-alloy steel are commonly applied to basic brake systems in high-energy moving machines. We analyzed how the tribological characteristics are influenced by the inertial mass. A high inertial mass decreased the friction coefficient by about 15% compared to a low inertial mass under all velocity conditions. The wear rates of the friction materials increased with the inertial mass. Thus, the inertial mass influences the friction coefficient and wear rate of the friction materials and disk but not the friction stability.

• The Transactions of the Korean Institute of Electrical Engineers D
• /
• v.49 no.10
• /
• pp.555-562
• /
• 2000

We propose an adaptive nonlinear control algorithm for compensation of the stick-slip friction in a dynamic system. The friction force and mass of the system are estimated and compensated by adaptive control law. Especially, as the nonlinear control input in a small tracking error zone is enlarged by the nonlinear function, the steady state error is significantly reduced. The proposed algorithm is a direct adaptive control method based on the Laypunov stability theory, and its convergence is guaranteed under the bounded noise or torque disturbance. We verified the performance of the proposed algorithm by computer simulation on one-DOF mechanical system with friction.