• Title/Summary/Keyword: Static friction

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Analysis of the Static Friction Coefficient of Contacting Rough Surfaces in Miniature Systems (거친 면 접촉의 정적 마찰계수 해석)

  • 김태종
    • Tribology and Lubricants
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    • v.19 no.4
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    • pp.230-236
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    • 2003
  • In applications such as MEMS and NEMS devices, the adhesion force and contact load may be of the same order of magnitude and the static friction coefficient can be very large. Such large coefficient may result in unacceptable and possibly catastrophic adhesion, stiction, friction and wear. To obtain the static friction coefficient of contacting real surfaces without the assumption of an empirical coefficient value, numerical simulations of the contact load, tangential force, and adhesion force are preformed. The surfaces in dry contact are statistically modeled by a collection of spherical asperities with Gaussian height distribution. The asperity micro-contact model utilized in calculation (the ZMC model), considers the transition from elastic deformation to fully plastic flow of the contacting asperity. The force approach of the modified DMT model using the Lennard-Jones attractive potential is applied to characterize the intermolecular forces. The effect of the surface topography on the static friction coefficient is investigated for cases rough, intermediate, smooth, and very smooth, respectively. Results of the static friction coefficient versus the external force are presented for a wide range of plasticity index and surface energy, respectively. Compared with those obtained by the GW and CEB models, the ZMC model is more complete in calculating the static friction coefficient of rough surfaces.

Research on the friction characteristics of multi purpose oils as mission (다용도 미션오일의 마찰특성에 관한 연구)

  • Myung, Byoung-Soo;Ryu, Hee-Bong;Lee, Yang-Kun
    • Journal of the Korean Society of Industry Convergence
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    • v.8 no.3
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    • pp.135-141
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    • 2005
  • The static friction coefficients of 4 samples against each different temperatures were similar values. Compared against RT, at $80^{\circ}C$ the static friction coefficients decreased from 0.130 to 0.116 that was equal from 88% to 90% of the static friction coefficients respectively. Otherwise the dynamic friction coefficients compared against RT, decreased from 0.138 to 0.088 which was from 71% to 77.5% respectively at $80^{\circ}C$. The noise characteristics were judged by s/d value. And when the s/d value was limited less than 0.8, noise concerns were released. At 3000 engaging cycles the static friction and the dynamic friction coefficient were 0.137 and 0.073 respectively. When plate pressure rose up to $195kg_f/cm^2$, the static friction coefficient decreased from 0.137 to 0.125 but this decreasing could be considered as stable. When speed rose up to 2200rpm, the static friction coefficient decrease from 0.14 to 0.13 but this decreasing could be considered as stable. At 3000 engaging cycles the amount of worn out was 0.04 : the thickness of disc was decrease from 4.72mm to 4.68mm. But regarding the normal operation condition, further more worn-out could not be expected. Therefore concerning worn-out, the basic oil could be considered as appropriate.

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Static Friction Compensation for Enhancing Motor Control Precision (모터 제어 정밀도 향상을 위한 정지 마찰력 보상)

  • Ryoo, Jung Rae;Doh, Tae-Yong
    • Journal of Institute of Control, Robotics and Systems
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    • v.20 no.2
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    • pp.180-185
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    • 2014
  • DC motor is a representative electric motor commonly utilized in various motion control fields. However, DC motor-based motion control systems suffer from degradation of position precision due to nonlinear static friction. In order to enhance control precision, friction model-based compensators have been introduced in previous researches, where friction models are identified and counter inputs are added to control inputs for cancelling out the identified friction forces. In this paper, a static friction compensator is proposed without use of a friction model. The proposed compensation algorithm utilizes internal state manipulation to generate compensation pulses, and related parameters are easily tuned experimentally. The proposed friction compensator is applied to a DC motor-based motion control system, and results are presented in comparison with those without a friction compensator.

Study on Torque Analysis of Micro-Electromagnetic Clutch by Using FEM (FEM을 이용한 Micro-Electromagnetic Clutch 토크해석)

  • Piao Changhao;Cho Chongdu;Kim Myunggu;Pan Qiang
    • The Transactions of the Korean Institute of Electrical Engineers B
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    • v.54 no.2
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    • pp.60-65
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    • 2005
  • This study tries to analyzes the static friction torque that generated in a micro-electromagnetic clutch by using FEM. For the purpose of design change and optimization of the micro-electromagnetic clutch, the static friction torque prediction is very important. We construct the axi symmetric FEM model for analyze the static friction torque and the real material properties are substituted to the FEM model. For a test, predicted static friction torque is compared with experimental one to discuss the rationality of torque analysis process. The analytical result agrees well to experimental data. explaining the validity of the mathematical process and FEM model.

Study on Torque Analysis and Armature Shape Optimization of Electromagnetic Clutch by Using FEM (FEM을 이용한 Electromagnetic Clutch 토크해석과 전기자 치수최적화)

  • Piao, Changhao
    • The Transactions of the Korean Institute of Electrical Engineers B
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    • v.55 no.5
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    • pp.245-249
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    • 2006
  • This study tries to test and analyze the static friction torque generated by an electromagnetic clutch. Then the torque is improved by optimizing the shape of armature. For the purpose of design change and optimization of the electromagnetic clutch, the static friction torque prediction is very important. We construct an axi symmetric FEM model for analyzing the static friction torque and used a torque tester for evaluating the real torque. For a test, predicted static friction torque is compared with the experimental one to discuss the rationality of torque analysis process. The analytical result agrees well with experimental data, explaining the validity of the mathematical process and FEM model. After confirming the torque analysis process, the optimization process is investigated. The optimization result shows that the static torque is improved by changing the armature shape.

Physical Properties of Rapeseed (II) (유채 종자의 물리적 특성(II))

  • Hong, S.J.;Duc, Le Anh;Han, J.W.;Kim, H.;Kim, Y.H.;Keum, D.H.
    • Journal of Biosystems Engineering
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    • v.33 no.3
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    • pp.173-178
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    • 2008
  • Some physical properties of rapeseed were measured at five moisture levels of 10.03, 14.91, 20.07, 25.06 and 30.12% (w.b.), which include frictional properties (coefficient of static friction, emptying and filling angle of repose) and aerodynamic properties (terminal velocity and drag coefficient). The physical properties of rapeseed were evaluated as a function of seed moisture content. In the moisture content range, the coefficients of static friction, emptying and filling angle of repose increased linearly with increase of moisture content. The maximum values of coefficients of static friction were on the acrylic surface, varied from 0.34 to 0.43; the next is on the galvanized steel, varied from 0.30 to 0.38; and the minimum were on stainless steel surface, varied from 0.27 to 0.35. Emptying and filling angle of repose varied from 26.12 to 29.62 and 23.83 to 27.05 degrees, respectively. Terminal velocity increased linearly from 3.47 to 3.91 m/s with increase of moisture content. Drag coefficient varied from 1.84 to 1.64 as the moisture content increased. The relationship between drag coefficient and moisture content were expressed by non-linear equation.

Feeding Characteristics of Ball Guide in High Speed Spindle's Bearing Preload Units (고속 주축 베어링용 예압장치의 볼 가이드 이송특성)

  • Lee, Chan-Hong
    • Journal of the Korean Society of Manufacturing Technology Engineers
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    • v.20 no.6
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    • pp.685-691
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    • 2011
  • The Bearing preload units are used for stable rotational movements of high speed spindles. The feeding mechanism of the preload unit is important to prevent overheat of bearings and to keep constant bearing load under thermal deformation of spindle unit. In this study, ball slide guide and ball bush as feeding mechanism of preload unit are selected. The maximum static friction force, radial stiffness and damping ratio of ball slide guide with ball load, ball number and ball size are widely investigated. In conclusion, the surface of ball slide guide must be heat treated to reduce static friction force. The number and size of ball are increased to control sensitive bearing preload force.

Determination of DEM Input Parameters for Dynamic Behavior Simulation of Aggregates (골재의 동적 거동 모사를 위한 DEM 입력변수의 결정 연구)

  • Yun, Tae Young;Yoo, Pyeong Jun;Kim, Yeon Bok
    • International Journal of Highway Engineering
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    • v.16 no.1
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    • pp.21-30
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    • 2014
  • PURPOSES : Evaluation of input parameters determination procedure for dynamic analysis of aggregates in DEM. METHODS : In this research, the aggregate slump test and angularity test were performed as fundamental laboratory tests to determine input parameters of spherical particles in DEM. The heights spreads, weights of the simple tests were measured and used to calibrate rolling and static friction coefficients of particles. RESULTS : The DEM simulations with calibrated parameters showed good agreement with the laboratory test results for given dynamic condition. CONCLUSIONS : It is concluded that the employed calibration method can be applicable to determine rolling friction coefficient of DEM simulation for given dynamic conditions. However, further research is necessary to connect the result to the behavior of aggregate in packing and mixing process and to refine static friction coefficient.

Braking Characteristics of Friction Disk made of Carbon Paper for Wet-type Multiple Disk Brakes of Crane Turning Decelerator (크레인 선회감속기의 습식 다판 브레이크를 위한 카본 페이퍼 마찰 디스크의 제동 특성)

  • Cho, Yonsang;Bae, Myongho
    • Tribology and Lubricants
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    • v.28 no.3
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    • pp.112-116
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    • 2012
  • wet-type multiple disk brakes are very important parts of turning decelerator for deck crane, because they are advanced in durability and braking power, and can be designed compactly. Thus, we designed and made wet-type multiple disk brakes of turning decelerator for deck crane to be localization of these imported all. In this study, wet multiple disk brakes were made a comparative test with the 2 types materials of friction disk by the SAE No.2 dynamometer. The friction characteristics were measured and analyzed to decide a suitable material as wear depth of friction disk and dynamic and static friction coefficient.