Influences of the structures of aerostatic thrust bearings on their responses to the supply pressure control

• Main Authors: Tin-Way Lin, 林庭緯
• Other Authors: Sy-Wei Lo
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/02680064785590906952

碩士 === 國立雲林科技大學 === 機械工程系 === 103 === In this thesis the responses of three aerostatic thrust bearings, which adopt conventional, silicone, or three-pore capillary as the restrictor, to the control of supply air pressure are studied. The control algorithms used include constant value compensation and PID control. It is found from the experiments that for elevation between 8 m and 16 m, the conventional bearing gives the best static stiffness, then the silicone one, and the three-pore type has the poorest stiffness. In the experiment where the bearing is lifted up from its rest position of no air supply to the assigned elevation, it showed that the higher the bearing stiffness, the slower the stabilization speed when the algorithm of constant-value compensation is applied. Among them the silicone bearing soars abruptly since only very little amount of air can flow through the capillary, which is compressed to close by the air pressure in the early stage; and the bearing ascends fast as the air spurts from the opened nozzle once the capillary passes its threshold of deformation. Adopting the PID algorithm can make the feedback speed double or more and eliminate the problem of hasty soaring. However the phenomenon of the sudden change in elevation is not observed in the experiment of descending because the capillary has already been opened. Compared to the others, the descending speed of the silicone bearing is quite slow. The reason might be that the viscoelasticity of silicone delays the recovery of the capillary channel. In the test where the load is augmented suddenly, we found that sometimes the constant-value control is unable to prevent the bearing from the collapse of the air film and eventually leads to its contact with the platen. The PID control, however, can effectively alleviate the fluctuation of the floating height for all three kinds of bearings.