A novel method to model the effect of environmental constraint of geometry in the mechanism design

Abstract

Few studies have considered the effect of environmental constraints throughout the entire design process of mechanical systems. Neglecting such effect might lead to misunderstanding the kinematic performance of the mechanical systems. In our work, an environment-based design concept was proposed by using passive limbs to model and analyze geometrical constraints in each step of the theoretical design process. Redesigning of a thrust system in a shield machine is taken as an example for better demonstration of this design approach. A new equivalent model of the thrust system was synthesized by using passive limbs to express environmental constraints of geometry based on the shield behavior. The uniform kinematic model was developed for the integrated equivalent mechanism of the thrust system. The effectiveness of the passive limbs in expressing environmental constraints was then evaluated by kinematical analysis. A singularity analysis was performed to assess the consistency between the equivalent model and a real thrust system. The reachable angular workspace was also analyzed to demonstrate the influence of the passive limbs as an example of environment-based parameter design. A motion simulation was performed to demonstrate the improvement of the forward kinematics by using the passive limbs to solve the singularity problem. A dexterity performance index based on the proposed model was conducted to demonstrate the kinematical property of the thrust system.