複合式渦輪分子真空幫浦之應力及自然頻率分析

Abstract

本文的主要目的是在分析複合式渦輪分子真空幫浦轉子在旋轉下應力的分佈並求出轉子的第一自然振動頻率。 文中首先探討葉片幾何外型對於葉片的自然振頻之影響，包括葉片的不同長度、置放角度及厚度等。接著以軸對稱元素來分析幫浦的應力分佈，探討不同元素的特性以及對於分析結果有何影響。然後探究偏心葉片之設計及對稱圓心之葉片設計兩者的旋轉應力，以Ansys分析出兩者之實際應力分佈，決定幫浦將採用對稱圓心葉片之設計。 最後分析幫浦轉子在不同轉速（36000rpm和50000rpm）下的應力分佈，並將轉子葉片分成三個模組，分析不同葉片模組間的頻率，得到單葉片葉輪之第一自然振頻可以模擬多葉片葉輪之第一自然振頻的結論。藉此可以減低幫浦設計的參數及難度。

The thesis investigates the stress of the rotor under rotating and finds the first natural frequency of the rotor of the compound turbo molecular pump. At first, we research the influence of the blade's geometric shape about the natural frequency, including following three parameters, the length of the blade, the height of the blade, and the setting angle of the blade. Next we analyze the stress of the rotor by F.E.M. with axisymmetric elements, and then compare the performances of these different types of elements. Next we perform the two types of blade design: the offsetted blade and the radial blade. From the actual stress distribution of these two cases, we decide to adopt the design of the radial blade. At last, we calculate the stress distribution of rotor at different speed (36000rpm and 50000 rpm), and divide the rotor's blades into three modules, analyze the vibration characteristics between these different modules. We conclude that frequency of a rotating disk with a single blade can simulate the frequency of a disk with multi-blades. Therefore we can reduce the parameter of the rotor, and simplify the whole design.