Design, modeling and analysis of large-stroke compliant constant torque mechanisms

Precision operations, such as micro-injection and micro-assembly tasks, require accurate and constant torque output. Compliant constant torque mechanisms (CCTMs) can be considered as a potential alternative due to the characteristic of accurate and constant torque output without the need for complex control algorithms and structures. Therefore, it is essential to propose a general, designer-friendly, and efficient design methodology for the design of CCTMs. In this paper, we propose a methodology for designing compliant constant torque mechanisms based on a co-design process between Cartesian coordinate system and Frenet frame. We use geometrically exact beam theory to model the static deflection of the built-in flexible beams so as to analyze the overall mechanism. We transform the design of this mechanism into a typical constrained optimization problem, and solve it via highly efficient numerical methods to achieve the desired design objectives given the user-defined constraints and satisfy some specific engineering requirements. Our optimized design is thoroughly evaluated and validated through finite element method and experimental testing, demonstrating a significantly improved performance compared to existing designs.