複合材料機械手臂原件研製

Abstract

因為複合材料具有較高的單位密度楊氏係數(E/ρ)與單位密度強度(S/ρ)，所以現今許多機械手臂傾向使用複合材料取代傳統金屬來製作，能夠在減輕重量的同時維持剛性。 本研究首先使用玻璃纖維來製作兩種不同疊層設計的複合材料機械手臂，待製作完成後進行負載實驗量測位移與應變值，還有Free vibration與Fixed vibration兩種邊界條件的自然頻率值，並與鋁製機械手臂進行比較，發現重量減輕60%左右，但剛性較差，原因是因為玻璃纖維的材料常數較鋁差。 本研究使用Ansys有限元素軟體對實驗進行分析模擬，利用隨機多起始點總域極小值演算法與窮舉法來對負載實驗的應變與Fixed vibration的頻率進行材料常數的反求，並將結果代入位移與Free vibration的分析中，來驗證建模與分析設定的準確性。 本研究最後利用驗證過的分析模型，以輕量化的同時擁有較高剛性為目標，設計一新的複合材料機械手臂。藉由重新設計新的疊層與使用高模數的碳纖維布，並加入45/-45的疊層，最後達到減重50%，剛性優於鋁製金屬機械手臂的結果。 本研究之主要貢獻為提出一套具複雜疊層設計的複合材料機械手臂的疊層設計與分析方式，可以就使用者的需求進行調整，來達到設計的目標。製成方面有別於使用prepreg或使用毛刷塗抹樹酯，先將複合材料乾布置於模具中，藉由管線同時灌入樹酯與抽氣，來達到乾濕分離的方法，使樹酯能夠混合均勻，且製作更為容易。

Nowadays, many studies tend to replace conventional metals with composite materials to manufacture robot arm, because composite materials have better Young’s modulus per unit density and stiffness per unit density. By using composite materials, it can reduce the mass of robot arm and maintain the stiffness at the same time. In this study, the robot arm is first made by glass fiber with two different deigns. We perform static and dynamic experiments to find its strain, displacement, and natural frequencies. By comparing robot arm made of aluminum with that of glass fiber, the robot arm made of glass fiber weighs 60% less but has worse stiffness. The reason of worse stiffness is because the stiffness properties of glass fiber are lower than aluminum. The finite element code ANSYS is used to analyze robot arm deformation and vibration. Two optimization methods are used to identify robot arm’s properties. The measured strain and first five vibration natural frequencies are used to identify three elastic constants of the composite material. The identified constants are then use to determine the displacement and the first five free vibration natural frequencies in the finite element analysis. The close agreement between the theoretical and experimental displacement and natural frequencies has verified the feasibility of the proposed material constants identification method. By using the verified element model, we can redesign the composite robot arm with the goal of having less weight and better stiffness. By having new layers placement, using carbon fiber with high modulus and adding 45/-45 layers, the composite robot arm eventually weighs 50% less and has better stiffness.