Graph-based optimization of continuous extrusion path in FRP-AM for compliant mechanism fabrication

Abstract

Compliant mechanism is a functional mechanism achieved by elastic deformation, which is expected to reduce the number of mechanical parts or assembly costs. Additive manufacturing using fiber-reinforced polymers (FRP-AM) is easy to fabricate a complex structure using materials with different elasticities. FRP-AM has an advantage in changing mechanical properties partially in fabricated structure. This is suitable for design of compliant mechanisms. For FRP-AM fabrication, it is necessary to consider the path continuity of fiber-reinforced materials. However, the conventional structural optimization method has difficulty in considering the fiber path continuity. The purpose of this study is to propose a simultaneous optimization of the structure and the continuous fiber path for compliant mechanism fabricated with FRP-AM. In the proposed method, by representing the target structure as a two-dimensional graph, the continuity of the fiber path is dealt with efficiently. Then, the graph is encoded into a binary tree, and genetic programming is adopted in the optimization process to obtain the structure that achieves the desired deformation. A case study was conducted to evaluate the proposed method. The compliant mechanism design of a robot end-effector, which initially consists of 9 walls with certain length, was optimized to achieve the target deformation, which finally consists of 18 walls with different length. The resulted FRP structures have continuous fiber paths. The deformation error against the target value was under 1% in FEM simulation. In addition, the optimized structure was fabricated. From the experiment on its deformation, the deformation error was about 20%. It was because the optimized structure deforms mainly due to bending of walls, which the simple approximation element is difficult to handle precisely. In addition, the gripping test was conducted, it was confirmed that the proposed optimization method is useful for design optimization of compliant mechanism fabrication with FRP-AM.