Design optimization and validation of compliant bidirectional constant force mechanisms

Mechanical vibration is a valuable energy source, ideal for storing energy from cyclic loads like human activities, ocean waves, and automotive vibrations. Compared to the typically designed unidirectional compliant Constant Force Mechanisms (CFMs), Bidirectional Compliant Constant Force Mechanisms (Bi-CFMs) improve energy storage efficiency in reversed cyclic loads. Two types of Bi-CFMs, Bidirectional Assembled CFMs (BiAs) and Bidirectional Monolithic CFMs (BiMo), are introduced in this research. BiAs combines two compression unidirectional CFMs, while BiMo is implemented with the Incremental Complexity Design (ICD) for systematic topology optimization. The ICD method incrementally adds complexity to the optimization, resulting in more computationally efficient and systematic design optimization and enabling exploration of geometrically simpler design solutions. The BiAs and BiMo designs achieved a high energy similarity index of 0.95 and 0.96 in analysis, respectively, as validated through static experimental tests. BiMo outperforms BiAs in low-frequency dynamic tests, with 16.5 % lower energy loss and 26.6 % higher energy similarity. Bi-CFMs enhance energy storage efficiency for reversed cyclic loads in various applications like biomechanical engineering, soft robotics, and renewable energy conversion.