Topology optimization of compliant mechanisms based on the BESO method
Creators: name: Li, Yan
Publisher: name: RMIT University
Year: 2024

description: This dissertation explores topology optimization techniques for designing compliant mechanisms actuated by forces. For a compliant mechanism, it has the potential of reducing part count, mechanical joints, operation noise, and manufacturing and assembly costs over a traditional rigid-link mechanism. Thus the application of compliant mechanisms is becoming increasingly prevalent in medical instruments and mechanical devices. Optimization of compliant mechanisms has drawn intense attention of many researchers.<br><br>However, this design field has been facing many challenges and shortages in several aspects such as optimization method, optimization algorithm and resulting topology. For example, convergence problems often lead to vague solutions. Optimization algorithms are not very suitable to investigate the real physical significance. Furthermore, designs of compliant mechanisms using topology optimization techniques naturally lead to the introduction of hinges into final topologies. In addition, the previous design also focuses mainly on the optimal design of linear compliant mechanisms. In fact, optimizing nonlinear compliant mechanisms is proving quite necessary in real applications as the simulation is more accurate. Therefore, it is important to devote efforts to the modification of previous optimization techniques for constructing practical compliant mechanism designs.<br><br>This dissertation proposes a modified bi-directional evolutionary structural optimization (BESO) method for the optimal design of linear and geometrically nonlinear compliant mechanisms. Numerical algorithms based on the BESO method are developed through various objectives and constraints in compliant mechanism design. <br><br>Firstly, to consider functional behaviours of compliant mechanisms, sets of clear and suitable structural configurations are produced by quantifying various performance characteristics and changing the stiffness of attached springs. This implies that material distribution and hinge formation are demonstrated in this work. To achieve prescribed structural stiffness for optimized mechanisms, a new BESO algorithm is established for solving the proposed optimization problem by gradually updating design variables. The inverter and the gripper optimization problems serve to demonstrate the practicability and effectiveness of the proposed method. Besides this, a new formulation is established by considering desirable deformation and simultaneously precluding the formation of hinges in order to design hinge-free compliant mechanisms, verified by a large number of numerical experiments including rare 3D hinge-free designs. Furthermore, compliant mechanisms often undergo large displacement, in order to provide their functionality. Therefore, the research also addresses the optimal design of compliant mechanism with geometrically nonlinear behaviours. With the aid of the hard-kill BESO method, a new systemic design approach is developed to overcome the convergence difficulty caused by extreme deformation in the nonlinear finite element analysis. Large-displacement inverter design with the desired structural stiffness is provided based on a new evolutionary optimization technique involved in a developed multi-criteria flexibility-stiffness formulation. <br><br>Overall, the modified BESO method has effectively set up new optimizations, visualizing and analysing the resulting topologies for 2D and 3D compliant mechanism designs. The findings shown in this dissertation have also established appropriate techniques for designing various linear compliant mechanisms. In addition, an efficient and robust methodology has been provided for the topology optimization of geometrically nonlinear compliant mechanisms. Furthermore, the work has provided a solid foundation for creating a practical design tool in the form of a user-friendly computer program, which is suitable for the conceptual design of a wide range of compliant mechanisms.<br><br>