A design framework for semi-active structural controlled adjustable constant force mechanisms

Semi-active adjustable constant force mechanisms (ACFMs) are an emerging alternative in applications where energy-efficient control of constant force environments is required. However, there is a lack of design strategies in the literature for semi-active ACFMs. This study addresses this gap by presenting a design strategy for ACFMs that semi-actively tunes the constant force by structural control. A design framework is presented which consists of an optimization of a high slenderness large stroke CFM followed by a parametric study on adjusting constant force through slenderness reduction by repositioning the boundary condition location. The design framework was able to change constant force ranging from 2-4 times with a stroke of 11-26% of the mechanism footprint respectively. A selected design with a larger force magnitude was fabricated and experimentally tested, demonstrating a change in constant force of 2.01 times which is comparable to that of active control designs and improved compactness, i.e., stroke of 11% of the footprint of the mechanism. In conclusion, the proposed ACFM design framework maximizes the initial CFM stroke and achieves constant force tuning by changing beam slenderness, resulting in compact and efficient ACFM designs.