Design and Experimental Validation of a Large-Displacement Constant-Force Mechanism

This paper presents the design and experimental validation of a passive large-displacement constant-force mechanism (CFM). Unlike previous studies, without using extra stiffness-compensation components and active control devices, the presented CFMs can utilize the interaction between the components of a cam and sliders to directly achieve the constant-force characteristic over the entire flexibly designed large displacement once the cam is advisably designed with the consideration of friction effect by using the profile curve identification method (PCIM). Corresponding to the different requirements of conventional and extreme engineering environments, two versions of the mechanism, the basic and ultra-large-displacement CFM models are proposed, respectively. The basic version is designed directly based on the PCIM, whereas the ultra-large-displacement CFM is proposed using the relay-mode action of the multistage sliders. According to the theoretical design method, we design and fabricate two corresponding CFM prototypes. Validation experiments are then conducted, and the results show that both of the prototypes can satisfy the design requirements and possess large-displacement constant-force characteristics owing to the consistency of experimental and design data. Therefore, the proposed design theory for the cam-based large-displacement CFMs is validated and the designed CFMs will have extensive applications in relevant fields for force regulation and overload protection.