On Passive Limbs in the Design of Parallel Mechanisms

Abstract

Passive limbs in parallel mechanisms can be introduced during type synthesis in order to reduce the possibility of redesigning or to decrease the complexity of the latter control strategy. In this paper, to find out more influences passive limbs can have on the performance of parallel mechanisms, using the theory of reciprocal screws, a united modeling framework of parallel mechanisms with passive limbs and without passive limbs is established first and then the performance comparison is carried out between parallel mechanisms with passive limbs and without passive limbs. All the performance indexes are calculated based on Jacobian matrices. The comparison results indicate that parallel mechanisms with passive limbs perform better in architecture dexterity, linear velocity isotropy, angular velocity isotropy, force isotropy, torque isotropy, maximum values of torque, linear deformation isotropy, angular deformation isotropy and maximum values of angular deformation.