• Journal of the Korean Society of Safety
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• v.19 no.1
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• pp.12-17
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• 2004

By using an experimental approach recently developed to determine the torque-tension relationship for bearing frictional characteristics of several typical bolted joints were studied. The experimental approach allows the direct determination of the bearing friction between the nut and its bearing surface. Detailed friction studies were made on the influences of the size and shape of the hole, the use of a slot in a bolted joint, contact area and position, and other factors such as turning speed, coating, and the use of wax on the bearing surface. The contact area and position of the washer have a marginal effect on the bearing friction. The organic coating on the nuts reduces the bearing friction significantly. Nuts with organic coating over a washer with zinc finish provide the smallest and the most consistent bearing friction. The results from the experimental investigation will be helpful for the better design of bolted joints bearing friction. The results from the experimental investigation Will be helpful for the better design of bolted joints.

• The Journal of Korean Academy of Prosthodontics
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• v.49 no.2
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• pp.168-176
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• 2011

Purpose: This study aims at investigating the influence of various insertion torques on thermal changes of bone. A proper insertion torque is derived based on the thermal analysis with two different implant designs. Materials and methods: For implant materials, bovine scapula bone of 15 - 20 mm thickness was cut into 35 mm by 40 - 50 mm pieces. Of these, the pieces having 2 - 3 mm thickness cortical bone were used as samples. Then, the half of the sample was immersed in a bath of $36.5^{\circ}C$ and the other half was exposed to ambient temperature of $25^{\circ}C$, so that the inner and surface temperatures reached $36.5^{\circ}C$ and $28^{\circ}C$, respectively. Two types of implants ($4.5{\times}10\;mm$ Br${\aa}$nemark type, $4.8{\times}10\;mm$ Microthread type) were inserted into bovine scapula bone and the temperature was measured by a thermocouple at 0.2 mm from the measuring point. Finite element method (FEM) was used to analyze the thermal changes at contacting surface assuming that the sample is a cube of $4\;cm{\times}4\;cm{\times}2\;cm$ and a layer up to 2 mm from the top is cortical bone and below is a cancellous bone. Boundary conditions were set on the basis of the shape of cavity after implants. SolidWorks was used as a CAD program with the help of Abaqus 6.9-1. Results: In the in-vitro experiment, the Microhead type implant gives a higher maximum temperature than that of the Br${\aa}$nemark type, which is attributed to high frictional heat that is associated with the implant shape. In both types, an Eriksson threshold was observed at torques of 50 Ncm (Br${\aa}$nemark) and 35 Ncm (Microthread type), respectively. Based on these findings, the Microthread type implant is more affected by insertion torques. Conclusion: This study demonstrate that a proper choice of insertion torque is important when using a specific type of implant. In particular, for the Microthread type implant, possible bone damage may be expected as a result of frictional heat, which compensates for initial high success rate of fixation. Therefore, the insertion torque should be adjusted for each implant design. Furthermore, the operation skills should be carefully chosen for each implant type and insertion torque.

• Proceedings of the KIEE Conference
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• 2002.06a
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• pp.187-190
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• 2002

In contrast to conventional electromagnetic motor, USM(Ultrasonic Motor), as piezoelectric ceramic applying ultrasonic mechanical vibration and as frictional-movement type motor, get rotational torque by elastic friction between stator and rotator, The USM, which is small motor without iron cores and coil as a simple structure, has little load weight, has character of high torque at low speed, and can apply a direct drive type without deceleration gear as low speed type. A response of USM from control input is satisfactory, and also generates much torque in low speed driving, and holding torque is much without supplying power. In this study, I designed and made Ultrasonic motor-digital multi controller(USM- DMC) using FPGA chip, A54SX72A made in Actel Corporation. By the minute, USM-DMC can control frequency, duty ratio, and phase difference of USM by llbit digital input from Pc. Therefore, when we use this controller, we can apply to typical parameter, frequency, phase difference, and voltage parameter, to control as well as we can do mixing control like phase-frequency, phase-voltage, frequency-voltage, frequency-phase-voltage, What is more, the strongest point is that it can trace frequency based on optimized frequency because we can input optimized resonant frequency while in motoring.

• Transactions of the Korean Society of Automotive Engineers
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• v.3 no.4
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• pp.19-29
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• 1995

This paper discusses the stick-slip phenomenon of the driveline system of a vehicle in consideration of friction. Friction is operated on the between of flywheel and clutch disk. The expressions for obtaining the results have been derived from the equation of motion of a three degree of freedom frictional torsion vibration system which is made up driving part(engine, flywheel), driven part(clutch, transmission) and dynamic load part(vehicle body) by applying forth-order Rungekutta method. It was found that the great affect parameters of the stick-slip or stick motion were surface pressure force between flywheel and clutch disk, time decay parameter of surface pressure force and 1st torsional spring constant of clutch disk when driveline system had been affected by friction force. The results of this study can be used as basic design data of the clutch system for the ride quality improvement of a car.

• Transactions of the Korean Society of Automotive Engineers
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• v.24 no.4
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• pp.471-479
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• 2016

Cross-drilling and slotting on the frictional surface of a brake rotor are methods used for improving the performance of the brake system. These shapes have particular advantages, such as the shaving effect of a slotted shape, which maintains a clean pad-to-rotor contact surface, and the venting effect of a drilled shape, which provides passageways for the gas to escape. In order to understand the effect of the machined pattern on the brake performance aspect, an experimental method is adopted along with the dynamometer test. The cross-drilled rotor, slotted rotor, and mixed pattern rotor with cross-drilling and slotting machining are prepared and tested in terms of friction coefficient, temperature, braking torque, and noise.

• Tribology and Lubricants
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• v.23 no.3
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• pp.95-102
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• 2007

In recently designed diesel engines, the running conditions for piston pin bearings have become very severe due to combustion pressure and temperature increase. Moreover, the lead removal from the bush material has strongly reduced the capability of the anti friction material to accept asperity contacts. In this paper, before trying to find the pressure distributions on the oil film of piston pin bearings by the unsteady two dimensional thermohydrodynamic lubrication analysis in order to do the optimum design of the bearings of piston pin, it will be investigated the tendancy of piston pin rotating motion by calculating the friction coefficient at piston pin bearings, the oil film thickness and the frictional torques induced by hydrodynamic shear stress.

• Tribology and Lubricants
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• v.24 no.3
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• pp.133-139
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• 2008

In recently designed diesel engines, the running conditions for piston pin bearings have become very severe due to combustion pressure and temperature increase. In this paper, it will be investigated the tendency of piston pin rotating motion by calculating the friction coefficient at piston pin bearings, the oil film thickness and the frictional torques induced by hydrodynamic shear stress. Finally, the pressure distributions on the oil film of piston pin bearings will be found by two-dimensional lubrication analysis in order to help the optimum design of the bearings of piston pin. Specially, it is investigated the effects on the film pressure distribution due to the change in maximum combustion pressure.

• Transactions of the Korean Society of Automotive Engineers
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• v.4 no.2
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• pp.198-208
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• 1996

The plunge joints of C.V. Joint for vehicle tend to produce a cyclic axial disturbance at a frequency of three of six times shaft speed, in which this distrubance caused by internal frictional effect is related to joint angle, rotational speed, torque, and joint size. This principal axial thrust force might make vehicle shuddered when coinciding with vehicle frequency of tranverse direction, and be one of reasons to have driver feel uncomfortable, unesay, while driving vehicle. The paper makes analysis of axial thrust force & vehicle shudder through computer simulation, comparing the result with experimental data, and reviewing the effect by changing of variables such as dimensions and driving conditions.

• Tribology and Lubricants
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• v.12 no.3
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• pp.79-84
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• 1996

One of the greatest dangers in mechanical face seals is the formation of heat checking and thermal stress cracks on the sliding surfaces. These thermal distortions due to non-uniform heating lead to increase the leakage of the sealed fluids and wear, and with balance of the seal can cause the seal faces to part. In this study heat checking and thermal stress cracks are investigated experimentally. These thermal distortions are explained using the thermal models of the conatct geometries between the seal ring and the seal seat. To overcome these thermal problems, the thermohydrodynamic seal is presented. The newly developed mechanical seal may substantially reduce the friction torque, frictional heating which causes heat checking and thermal stress cracks, and wear.

• Journal of Institute of Control, Robotics and Systems
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• v.11 no.11
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• pp.920-929
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• 2005

This paper presents controller design method for nonlinear radar gimbal system with parameter uncertainty and time delay. In order to consider nonlinearity of gimbal bearing frictional torque, we firstly represent fuzzy model for the nonlinear gimbal system, which is achieved by fuzzy combination of linear models through nonlinear fuzzy membership functions. And secondly we propose a delay dependent fuzzy $H_\infty$ controller design method for the delayed fuzzy model with parameter uncertainty and design radar gimbal controller. The designed controller stabilize gimbal system and guarantee $H_\infty$ performance. A computer simulation is given to illustrate stabilized control performances of the designed controller.