• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.4
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• pp.464-469
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• 2019

Tapered roller bearings are used widely in vans, trucks, and trains because they can support the vehicle in a stable manner even under a heavy load. The cage of a tapered roller bearing maintains the gap between the rollers, which prevents friction wear and suppresses heating. If the cage is severely deformed due to resonance, the roller may not be able to roll smoothly and even leave the cage. Consequently, it is very important to analyze the dynamic characteristics of the cage for reliable performance of a bearing. The cage essentially has geometrical tolerance in the manufacturing process. In this paper, the effects of those geometrical imperfections on the dynamic characteristics of the cage were investigated. As a result, natural frequency separation occurred near the natural frequency of the ideal cage due to geometrical imperfections. In addition, the interval was proportional to the magnitude of the geometric error, and the interval increased with increasing mode number.

• Journal of the Korean Society for Precision Engineering
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• v.25 no.10
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• pp.115-121
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• 2008

This paper presents bisymmetric dual iron core lineal motor stage for heavy-duty high precision applications such as large area micro-grooving machines or high precision roll die machines. In this stage, two iron core linear motors are installed in laterally symmetric way to cancel out the attractive forces. Main focus was given to analyzing the effect of cogging force and moment for two different layouts, which are symmetric and half-pitch shifted ones. Experimental results showed that the symmetric layout is more adequate for high precision applications because of its clear moment cancellation effect. It was also verified that the effect of the residual cogging moment can be suppressed further by increasing the bearing stiffness. One problem of the symmetric layout is added cogging force which hinders smooth motion, but its effect was relatively small compared with that of moment cancellation.

• Journal of Mechanical Science and Technology
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• v.18 no.10
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• pp.1722-1729
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• 2004

This paper presents a design methodology for determining configurations of slider air bearings considering the randomness of the air-bearing surface (ABS) geometry by using the iSIGHT. A reliability-based design optimization (RBDO) problem is formulated to minimize the variations in the mean values of the flying heights from a target value while satisfying the desired probabilistic constraints keeping the pitch and roll angles within a suitable range. The reliability analysis is employed to estimate how the fabrication tolerances of individual slider parameters affect the final flying attitude tolerances. The proposed approach first solves the deterministic optimization problem. Then, beginning with this solution, the RBDO is continued with the reliability constraints affected by the random variables. Reliability constraints overriding the constraints of the deterministic optimization attempt to drive the design to a reliability solution with minimum increase in the objective. The simulation results of the RBDO are listed in comparison with the values of the initial design and the results of the deterministic optimization, respectively. To show the effectiveness of the proposed approach, the reliability analyses are simply carried out by using the mean value first-order second-moment (MVFO) method. The Monte Carlo simulation of the RBDO's results is also performed to estimate the efficiency of the proposed approach. Those results are demonstrated to satisfy all the desired probabilistic constraints, where the target reliability level for constraints is defined as 0.8.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.2
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• pp.109-117
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• 2009

This paper presents a linear air bearing stage with compensated motion errors by active control of preloads generated by magnetic actuators with combination of permanent and electromagnets. A 1-axis linear stage motorized with a linear motor with 240mm of travel range is built for verifying this design concept and tested its performances. The three motions of the table are controlled with four magnetic actuators driven by current amplifiers and a DSP based digital controller. Three motion errors were measured combined method with laser interferometer and two-probe method with $0.085{\mu}m$ of repeatability for straightness error. The measured motion errors were modeled as functions of the stage position, and compensation were carried out with feedforward control because the characteristics of the motion control with magnetic actuators are linear and independent for each degree-of-freedoms. As the results, the errors were reduced from $1.09{\mu}m$ to $0.11{\mu}m$ for the vertical motion, from 9.42 sec to 0.18 sec for the pitch motion and from 2.42 sec to 0.18 sec for roll motion.

• 제어로봇시스템학회:학술대회논문집
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• 1996.10b
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• pp.1476-1479
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• 1996

The ring rolling process is one of the best known ring production method. The present model based control system was designed for rings with rectangle cross-section yet. An Adaptive Fuzzy Control for Closed-Die Ring-Rolling was developed in order to enhance the flexibility of the radial-axial ring rolling machine and to produce the rings with highly complex cross-section profile, roller bearing rings. A fuzzy method was implemented because of its simple application and to utilize the known process knowledge. The quality of the control system was estimated by die filling grad, which is strong dependent on the rising time of the controller. The rolling process parameters were also varied to determine their influence on filling of the ring profile. Die filling met the requirement of the industry.

• Proceedings of the Korea Concrete Institute Conference
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• 1995.04a
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• pp.268-273
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• 1995

In recent years, precast prestressed concrete segmental box girder bridges have been increasingly constructed Expansion disphragm segment of this type bridge transfers forces from the superstructure onto bearing or column, and plays an important roll of anchorage zone for longitudinal prestressed forces. Non-linear stresses occur inside of diaphragms by these extensive concentrated forces. In this study, the strut-and-tie models are proposed to design an expansion segment rationally. A formula to determine the effective transverse prestressed forces is proposed on the basis of these models. The present study is expected to provide an effective tool to design expansion segment of prestressed concrete bridges rationally.

• 제어로봇시스템학회:학술대회논문집
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• 2002.10a
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• pp.66.5-66
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• 2002

Flatness of strip at aluminum cold rolling is one of the important quality parameters of rolled products. The reasons for this are perhaps obvious: for many of the end uses, subsequent processing requires a flat product poor flatness on-line can lead to reduced running speeds and hence to lower production levels. Amongst the reasons for lower running speeds is the increased risk of strip breaks. The Alcan Ulsan plant developed an automatic flatness control system on conventional four high mills for a year. This system compose of three parts as Intel RMX 3.3 operating system, advanced techniques, and flatness error analysis system. Strip flatness be measured by air bearing roll, passing the s...

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.6
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• pp.871-878
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• 2003

With the development of micro -technology, the demand for micro actual ing device is increasing. But, it is difficult to achieve high resolution and wide bandwidth with the conventional contact systems. So, the contact-free systems which are suspended or levitated by magnetic force or air bearing were proposed. These systems can be applied to high precision stages and alignment apparatuses. This paper describes a magnetically suspended system with four degrees of freedom which are composed of three rotations (roll, pitch, yaw), and one translation ( z). The operating principle and the structure of the system are similar to variable reluctance type electric machines. In this study, the force analysis is executed using magnetic circuit and virtual work principle, and the equations that describe the dynamics of the system are presented. The multivariable PID controller is adapted to the system and the experiment is executed.

• Tribology and Lubricants
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• v.23 no.2
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• pp.49-55
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• 2007

A numerical analysis of elastohydrodynamic lubrication of elliptical contacts with both rolling and spinning has been carried out. A finite difference method with non-uniform grid systems and the Newton-Raphson method are applied to solve the problems. The velocity vectors resulting from combined spinning and rolling/sliding motion lead to asymmetric pressure distributions and film shapes. Pressure distributions, film contours and variations of the minimum and central film thicknesses are compared with various spin-roll ratios. Reduction of the minimum film thickness under spinning is remarkable whereas the central film thickness is relatively less. The spin motion have large effect on variations of the minimum film thickness with load parameter which are small in pure rolling/sliding cases. Therefore present numerical scheme can be used in the analysis of general elliptical contact EHL problems and further studies are required.

• Journal of Mechanical Science and Technology
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• v.18 no.1
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• pp.37-44
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• 2004

This paper presents an approach to optimally design the air bearing surface (ABS) of the head slider by using the approximation methods. The reduced basis concept is used to reduce the number of design variables. In the numerical calculation, the progressive quadratic response surface modeling (PQRSM) is used to handle the non-smooth and discontinuous cost function. A multi-criteria optimization problem is formulated to enhance the flying performances over the entire recording band during the steady state and track seek operations. The optimal solutions of the sliders, whose target flying heights are 12 nm and 9 nm, are automatically obtained. The flying heights during the steady state operation become closer to the target values and the flying height variations during the track seek operation are smaller than those for the initial one. The pitch and roll angles are also kept within suitable ranges over the recording band.