Design Optimization and Validation of Compliant Bidirectional Constant Force Mechanisms

Abstract

Abstract Complaint constant force mechanisms (CFMs) have been applied in many applications, e.g., end effectors, micro grippers, etc., due to their inherent ability to maintain a constant force environment and increase energy storage efficiency. However, the typically designed uni-directional, i.e. tension or compression only, CFMs may not efficiently harvest energy from reversed cyclic loadings. Bidirectional compliant CFMs (Bi-CFM) are proposed to improve the energy storage efficiency for reversed loading conditions. Two different kinds of Bi-CFMs categorized based on their synthesis methods are proposed in this research: (1) Bidirectional Assembled CFM (BiAs) and, (2) Bidirectional Monolithic CFM (BiMo). The BiAs is designed with the combination of two existing compression CFMs in series. Alternatively, the newly proposed Incremental Complexity Design (ICD) method which involves gradually adding complexity to the graph-based topology selection and shape optimization is introduced to develop BiMo, leading to more efficient and systematic design optimization, while also enabling the exploration of simpler design solutions. Static and low frequency dynamic experimental validations were conducted on the Bi-CFMs with 3D-printed PLA. By iteratively increasing the complexity of the design, the variables associated with topology and shape optimizations are substantially reduced (89.5%–93.0%) compared with the literature, leading to enhanced computational efficiency. The BiAs, and the BiMo obtained from ICD both exhibit a high energy similarity index in analysis (0.95) and static experimental tests (0.83–0.88). Furthermore, the energy loss metric and energy similarity index for the BiMo is 26% lower and 6.3% higher on average than the BiAs during low frequency dynamic tests respectively. Usage of the proposed Bi-CFM would help increase energy storage efficiency and make a good contribution towards reversed cyclic loading fields, i.e. biomechanical engineering, wind energy storage, etc.