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This paper presents an evolutionary soft-add topology optimization method for synthesis of compliant mechanisms. Unlike the traditional hard-kill or soft-kill approaches, a soft-add scheme is proposed in this study where the elements are equivalent to be numerically added into the analysis domain through the proposed approach. The objective function in this study is to maximize the output displacement of the analyzed compliant mechanism. Three numerical examples are provided to demonstrate the effectiveness of the proposed method. The results show that the optimal topologies of the analyzed compliant mechanisms are in good agreement with previous studies. In addition, the computational time can be greatly reduced by using the proposed soft-add method in the analysis cases. As the target volume fraction in topology optimization for the analyzed compliant mechanism is usually below 30% of the design domain, the traditional methods which remove unnecessary elements from 100% turn into inefficient. The effect of spring stiffness on the optimized topology has also been investigated. It shows that higher stiffness values of the springs can obtain a clearer layout and minimize the one-node hinge problem for two-dimensional cases. The effect of spring stiffness is not significant for the three-dimensional case.

This study presents a topology optimization method for design of complaint mechanisms with maximum output displacement as the objective function. Unlike traditional approaches, one special characteristic of this method is that the volume fraction, which is defined as the calculated volume divided by the full volume, remains the same value throughout the optimization process based on the proposed pseudodensity and sensitivity number update scheme. The pseudodensity of each element is initially with the same value as the prespecified volume fraction constraint and can be decreased to a very small value or increased to one with a small increment. Two benchmark problems, the optimal design of a force–displacement inverter mechanism and a crunching mechanism, are provided as the illustrative examples to demonstrate the effectiveness of the proposed method. The results agree well with the previous studies. The proposed method is a general approach which can be used to synthesize the optimal designs of compliant mechanisms with better computational efficiency.