Design, optimization, and testing of a compliant quasizero constant-force mechanism for linear motion guidance

Abstract

Constant-force compliant mechanisms (CCFMs) offer certain advantages in motion guidance through actuation force reduction. However, existing CCFMs typically require an initial input to activate the constant-force characteristics, resulting in complex force behavior. To overcome such limitations and enhance the force reduction performance, this paper proposes a novel compliant quasizero constant-force mechanism (QZ-CCFM) design using a stiffness combination configuration. It has a mirror-symmetrical structure composed of two halves, with each half integrating a negative-stiffness mechanism and a positive-stiffness mechanism. When the constant-force feature is activated by preloading a specific displacement to each half, the opposite reaction forces can be self-balanced, thereby initializing the mechanism to the constant-force region. By optimizing the key design variables, the mechanism achieves a maximized constant-force stroke while minimizing force fluctuations. Several prototypes have been fabricated for experimental study. The results indicate that the QZ-CCFM can offer a quasizero constant force of 0$\pm$0.10 N over a stroke of 4.40 mm (i.e., $\pm$2.20 mm relative to the initial position) without an initial input. The quasizero constant-force feature of the QZ-CCFM provides a promising guiding mechanism for improving actuation efficiency and performance in practical applications, such as precision positioning systems and biomedical devices.