Structure Design And Optimization For Guide Unloading System Of Ultra-Precision Machine

In this paper, a new kind of guide's unloading system is designed for ultra-precision machine tool for large-scale aspheric optical element(national key project of the 10th five years plan). This unloading system not only has the characteristic of steady mechanical unloading, but also has the strong point of gas-lubricated. It can ensure the unloading system run steadily without friction, and can adjust the unloading weight accurately.Analyzes the unloading system influence to the precision of ultra-precision's guide , and designs the unloading system. Designs the spring's specific structure, this unloading spring can adjust the unloading weight accurately. It also designs the unloading air-floated flat's structure and calculates the bearing capacity, air-film thickness and air-film stiffness under different air pressure. The calculating result indicates that unloading weight should be more than 1000Kg, and the air pressure should be in 0.5~0.6MPa.The rigidity of the unloading spring is measured by loaded different weight. Variation of the guide's linearity error under the unloading system is measured. The experiment proves that this structure of unloading system can ensure the guide's linearity error and arrive the designing target. The guide's linearity error can achieve 0.375μm/600mm when unloading weight is 1200Kg.The unloading system will cause gas hammer phenomenon when the unloading weight is above 1000Kg and air pressure is above 0.5MPa. Base on the technology of gas-lubricated instability, this paper analyzes the structure factor that can lead to gas hammer phenomenon in the method of exclusion. The reason is that air-float flat bends when unloading weight loads, the deformation of air-float flat destroys the air-film thickness and the air-float surface's volume effects increment, all of this leads to gas hammer phenomenon.At last, the FEM model of unloading air-floated flat under different unloading weights is established by ANSYS. The stress and displacement distribution of unloading air-float flat are got. By analyzing the calculating result of FEM we know, when the displacement of Y direction of air-float flat is less than 12.5μm, the gas hammer phenomenon can be avoided. Base on the...