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박천홍(Chun Hong Park),이영준(Young Joon Lee),홍성욱(Seong Wook Hong),이후상(Husang Lee) Korean Society for Precision Engineering 2005 한국정밀공학회지 Vol.22 No.5
A self-compensated water-hydrostatic bearing is well known to have advantages in stiffness. In this paper, its concept is extended to a hydrostatic journal bearing for achieving higher stiffness. The finite element method is applied to analyze the load characteristics of the self-compensated hydrostatic journal bearing. The analysis results reveal that the self-compensated journal bearing has higher load capacity and higher stiffness than conventional, fixed capillary journal bearings, and that this benefit degrades in the case of high eccentricity. Thus, a spindle system with self-compensated journal bearings must be designed to ensure a sufficiently large load capacity. A rectangular type capillary is also introduced with consideration of the practical application of the self-compensated hydrostatic journal bearing. Theoretical analysis results show that the rectangular type capillary is more beneficial than conventional annular type capillaries in practical use. The experimental verification on the analysis method is made to show that the experimental results are in good agreement with theoretical results.
전달함수를 이용한 다공질 공기베어링 스테이지의 운동오차해석
박천홍(Chun Hong Park),이후상(Husang Lee) Korean Society for Precision Engineering 2004 한국정밀공학회지 Vol.21 No.7
In order to analyze the motion errors of the aerostatic stage, it is necessary to consider the influence of the moment variation occurred inside the pads. In this paper, a motion error anaysis method utilizing the transfer functions on the reaction force and moment is proposed, and general characteristics of the transfer functions are discussed. Calculated motion errors by the proposed method show good agreement with the ones calculated by Multi Pad Method, which is considered the entire table as an analysis object. Also, by the introduction of the transfer function of motion errors, which represent the relationship between the spatial frequency components of the rail form error and motion errors, motional characteristics of the porous aerostatic stage can be generalized. In detail, the influence of the spatial frequencies is analyzed quantatively, and the patterns of the insensitive frequencies which almost do not affect the linear motion error or angular motion error according to the rail length ratio and the number of the pad are verified. The relationship between the moment variation occurred inside the pads and the motion errors is also verified together.
박천홍(Chun Hong Park),오윤진(Yoon Jin Oh),황주호(Joo Ho Hwang),이득우(Deug Woo Lee) Korean Society for Precision Engineering 2004 한국정밀공학회지 Vol.21 No.6
In order to discuss the availability of hydrostatic guideways driven by the core less linear motor to ultra precision machine tools, a prototype of guideway is designed and tested in this research. A coreless linear DC motor with the continuous force of 156 N and a laser scale with the resulution of 0.01 ㎛ are used as the feeding system. The experiments are performed on the static stiffness, motion accuracy, positioning accuracy, micro step response and variation of velocity. The guideway has the infinite axial stiffness within 50 N of applied load, and by the motion error compensation method using the Active Controlled Capillary, 0.08 ㎛ of linear motion error and 0.1 arcsec of angular motion error are acquired. The guideway also has 0.21 ㎛ of positioning error and 0.09 ㎛ of repeatability, and it shows the stable response against the 0.01 ㎛ resolution step command. The velocity variation of feeding system is less than 0.6%. From these results, it is confirmed that the hydrostatic guideway driven by the coreless linear motor is very useful for the ultra precision machine tools.