• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.11
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• pp.2436-2441
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• 2002

Finite element technique considering adhesive forces is proposed and applied to analyze the behavior of elastic hemispherical asperity adhesively contacting the plane surface of semi -infinite rigid body. It is demonstrated that the finite element model simulates interfacial phenomena such as jump -to-contact and adhesion hysteresis that cannot be simulated with the currently available adhesive contact continuum models. This simulation aiso provides valuable information on contact pressure, contact region and stress distributions. This technique is anticipated to be utilized in designing a low-adhesion surface profile for MEMS/NEMS applications since various contact geometries can be analyzed with this technique.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.410-415
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• 2004

Molecular dynamics simulations of nanoimprint lithography in which a stamp with patterns is pressed onto amorphous poly-(methylmethacrylate) (PMMA) surface are performed to study the deformation of polymer. Force fields including bond, angle, torsion, inversion, van der Waals and electrostatic potential are used to describe the intermolecular and intramolecular force of PMMA molecules and stamp. Periodic boundary condition is used in horizontal direction and $Nos\acute{e}$-Hoover thermostat is used to control the system temperature. As the simulation results, the adhesion forces between stamp and polymer are calculated and the mechanism of deformation are investigated. The effects of the adhesion force and friction force on the polymer deformation are also studied to analyze the pattern transfer in nanoimprint lithography. The mechanism of polymer deformation is investigated by means of inspecting the indentation process, molecular configurational properties, and molecular configurational energies.

• Journal of the Korea Institute of Military Science and Technology
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• v.6 no.4
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• pp.9-21
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• 2003

This paper describes the practical implementation of a semiactive hydropneumatic suspension system to provide the high off-road performance of military tracked vehicles. Real gas behavior of a spring system, frictional forces of joints, and the dynamics of a continuously variable damper are considered. The control system is consisted of two control loops, an outer loop calculates a target spool position which can deliver the required damping force and an inner loop tracks the required spool position. Dynamic tests of the one axis model show that the semiactive suspension system considerably reduces the acceleration as well as velocity and displacement of the sprung mass than the passive one.

• Journal of Power System Engineering
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• v.21 no.6
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• pp.101-109
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• 2017

The pneumatic driving system has advantages such as high output power per weight and low heat generation rate. However, it is difficult to control the position because of its strong non-linearity such as large friction forces compared to driving force, and heat transfer characteristics that change during operation. Therefore, in order to achieve the control objectives, a robust controller should be designed considering modeling error and model uncertainty. In this paper, a sliding mode controller is designed to improve the position control performance of pneumatic cylinder driving system. Experimental results show that the designed controller achieves the designed control objectives even if the model of the cylinder driving system, such as the initial pressure inside the cylinder and the initial position of the piston is changed.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2001.10a
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• pp.111-116
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• 2001

In this paper, a simple 2 D.O.F. planar motion model is proposed in order to analyze the snake motion of a machining center cross head assembly, that is travelling on linear guide rails. In the proposed mathematical model, the friction between head and guide ways is neglected, and also the support structures including guide rails, rear- and side-panels of the machining center are assumed to be rigid. The equations of motion of the proposed model are derived and successfully solved to determine vibration responses of the head assembly due to some applied traction forces.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.7
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• pp.91-98
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• 2003

In the field of precision manufacturing demanding high positioning performance, the mechanical friction in positioning device deteriorates the quality of the product and increases the cost of production for positioning devices. Therefore, we propose a contract-free linear actuator using active magnetic bearing. The structure and operating principle of the proposed system are explained, and the magnetic forces are analyzed by magnetic circuit theory to design magnetic bearings and linear actuator. With the derived equation of motion, the stability is identified. Experimental results are presented to show the feasibility.

• Tribology and Lubricants
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• v.18 no.6
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• pp.402-410
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• 2002

In this study, a hydrodynamic analysis of the reciprocating compressor crankshaft considering a finite bearing modelling of the journal bearings used in small refrigeration compressors is performed. In the problem formulation of the compression mechanism dynamics, all corresponding hydrodynamic forces and moments are considered using the finite bearing analysis in order to determine the crankshaft trajectory at each step. The solution of the Reynolds' equation is determined numerically using a finite difference method and a Newton-Raphson procedure was employed in solving the dynamic equations of the crankshaft. The crankshaft orbits fur the finite bearing model and short bearing theory were used to compare the effect of the hydrodynamic farces of the journal bearings on the dynamic and lubrication characteristics of the crankshaft-journal bearing system. Results show that the finite bearing model for the journal bearings must be considered in calculating for the accurate dynamic characteristics of the reciprocating compressor crankshaft.

• Journal of the Korean Society of Clothing and Textiles
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• v.23 no.7
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• pp.971-979
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• 1999

The experiment was conducted on five different kinds of fabrics dyed with loess. The sewability of fabrics dyed with loess by measuring the maximum needle piercing forces(MPF) through fabrics has been studied, MPF measurement using tensile tester was done 60 times for each fabrics at fixed low speed of 300mm/min. The nature of the loess on the dyed fabrics was physically jammed betweenthe fibers or adhered to the surface of fibers in the form of the fine particles so that the MPF through fabrics increases extremely in proportion to the increase of loess uptake and the plying number of fabrics dyed with loess. This results indicate that the MPF through fabrics is affected by mean value of the coefficient of friction on the surface of fabric(MIU) and cloth cover factor(Kc) in this experiment. Fabric was finished with softner to decrease the MPF during sewing operation, The MPF through softner finished fabric was decreased remarkably.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.3
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• pp.614-620
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• 2009

The force distribution in multi-legged robots is a constrained, optimization problem. The solution to the problem is the set points of the leg contact forces for a particular system task. In this paper, an efficient and general formulation of the force distribution problem is developed using linear programming. The considered walking robot is a quadruped robot with a locked-joint failure, i.e., a joint of the failed leg is locked at a known place. For overcoming the drawback of marginal stability in fault-tolerant gaits, we define safety margin on friction constraints as the objective function to be maximized. Dynamic features of locked-joint failure are represented by equality and inequality constraints of linear programming. Unlike the former study, our result can be applied to various forms of walking such as crab and turning gaits. Simulation results show the validity of the proposed scheme.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.2
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• pp.120-127
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• 2008

The constant velocity joint(CVJ) used for transmitting torque to the front wheels is an important part in automotive drive system. There are several types of constant velocity joints. Typically, they are classified by fixed and plunging constant velocity joints. The axial force generated in plunging constant velocity joints influences significantly the noise, vibration and harshness. For heaps of time, many constant velocity joint markers have been studying and developing a valid method to reduce the axial force and extensive tests have been carried out on rigs. This paper presents the analysis method to predict the axial force of a double offset constant velocity joint(DOJ), a kind of plunging constant velocity joint, and the influence of ball-cage dimension tolerance on the axial force.