• Tribology and Lubricants
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• v.36 no.2
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• pp.68-74
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• 2020

In this study, the effect of the shape error of a guideway on the movement of a stage that uses an air bearing is analyzed. The shape error of moving parts supported by the air bearing is known not to affect the vibrations of moving parts as much as the magnitude of the shape error. This is called the "averaging effect." In this study, the effect of shape error on a guideway, as well as the averaging effect of an air-bearing system, is analyzed theoretically using a dynamic-analysis program. The dynamic-analysis program applies a commercially available code in COMSOL and solves the Reynolds equation between the stage and the guideway, along with the equation of motion of the stage. The stage is modeled as a two-degree-of-freedom system. The shape error is applied to the film thickness function in the form of a sine wave. The stage movement is analyzed using the fast Fourier transform process. The eccentricity and tilting are found to be proportional to the amplitude of the shape error of the guideway. Stage vibrations are less than 10% of the amplitude of the shape error on the guideway. This means that the averaging effect of the air bearing is verified quantitatively. Moreover, if the air supply position matches the shape error in the guideway, there is a notable change in eccentricity and tilting.

• Tribology and Lubricants
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• v.35 no.1
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• pp.59-64
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• 2019

When slipping occurs between two materials, the coefficients of friction must be considered because these values determine the overall efficiency of the machine or slip characteristics. Therefore, it is important to find the coefficient of friction between two materials. This paper focuses on obtaining the coefficient of friction between an aiming bolt and a retainer located in the headlamps of a vehicle. This bolt supports the headlamp, and if the bolt is loosened by external vibration, the angle of the light will change and block the vision of pedestrians or other drivers. In order to study these situations, the coefficient of friction between aiming bolts and retainers needs to be measured. In addition, the coefficient of friction of materials used in the headlamp should be obtained. To determine these two factors, a new device is designed for two cases: surface-surface contact and surface-line contact. To increase reliability of the results, the device is designed using an air-bearing stage which uses compressed air as lubricant to eliminate the friction of the stage itself. Experiments were carried out by applying various vertical forces, and the results show that the coefficient of friction can be measured consistently. The procedure for designing the device and the results are discussed.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2005.05a
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• pp.468-472
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• 2005

In this paper, the static and dynamic stiffness of the air bearing stage for micro-micro machine tool are examined experimentally. For stiffness and precision concerns, air bearing stages are adapted for 3-axis micro-milling machine which is size of $200x200\;mm^2$. The air bearings in the stage are preloaded by permanent magnets to achieve desired bearing clearance and stiffness for vertical direction. As the stiffness of the air bearing is primary interests, static stiffness test were performed on XY stage in Z direction and Z column in Y direction. Dynamic test were performed on XY stage and Z column, respectively. Both static and dynamic tests were performed in different air pressure conditions. The vertical stiffness of XY stage is about 9 N/ pm where Y stiffness of Z column is much smaller as $1\;N/{\mu}m$ because of the large moment generated by Y force on the column.