Design of an Adjustable Constant Force Mechanism Based on Integrated Magnet-beam Structures and an Adjustable Lever Mechanism

This paper presents a novel adjustable constant force mechanism (CFM) based on integrated magnet-beam structures and an adjustable lever mechanism. Different from the designs based on the linear stiffness combination method, the proposed CFM is designed via nonlinear stiffness combination, where attractive magnets are used to generate full-stroke nonlinear negative stiffness, and spline-shaped beams are optimized to provide nonlinear positive stiffness. This enables the generation of full-stroke zero stiffness (i.e., constant force), thereby increasing the constant force region. Moreover, the nonlinear stiffness characteristic also enables force fluctuation compensation by adjusting the initial gap between magnets, ensuring a constant output force even in the presence of manufacturing errors. Additionally, by adjusting the lever ratio of the lever mechanism, the constant force magnitude can be adjusted to adapt to different applications. The working principle and mechanical design of the proposed adjustable CFM are introduced. The static model of the spline-shaped beam is developed, and an optimization study is conducted for parameter determination. Finally, a prototype is fabricated and experiments are carried out to verify the effectiveness of the proposed design.