Equivalent pin models for dynamic analysis of compound rigid-flexure multi-body systems

Compliant joints are featured with adaptability to nonstructural environment, thus they are competent candidates for designing biomimetic fingers. However, compliant joints differ from typical pin joints in ways of large nonlinear deformations with moving rotation center and non-constant radius as well as repetitive motions with fatigue, which hinders their implementation in robotics and mechatronics. A proper design of compliant mechanism is necessary so that robotics knowledge can be applied to model and control compliant joints. For this purpose, a modeling method is proposed to design compliant joints for a flexure finger. It offers closed-form solutions for analyzing free-grasping manipulation of a finger, and formulation for approximating a compliant joint as a pin-joint with rotation center offset and radius modification. Within the framework of three-link flexure finger dynamics, a beam model is employed for the compliant joints. Three design configurations (straight, convex and concave) of compliant joints are compared in analysis of kinematics, dynamics and maximum stress.