Type synthesis and reconfiguration analysis of a class of variable-DOF single-loop mechanisms

•A new method for type synthesis of variable-DOF single-loop mechanisms•A number of new variable-DOF single-loop mechanisms•Reconfiguration analysis using kinematic mapping and algebraic geometry•Example mechanisms with 1 to 2 DOF have two or three operation modes.•Obtained all the transition configurations between any two operation modes

This paper deals with the type synthesis and reconfiguration analysis of variable-DOF (degree-of-freedom) single-loop mechanisms — a class of reconfigurable mechanisms that DOF may change. A method is proposed to the type synthesis of variable-DOF single-loop mechanisms by inserting two joints to a multi-DOF single-loop overconstrained mechanism. Reconfiguration analysis of a variable-DOF single-loop 7R mechanism is then carried out using the kinematic mapping and algebraic geometry method. The analysis shows that the variable-DOF 7R mechanism may have one 2-DOF planar 5R operation mode and one or two 1-DOF spatial 7R operation modes depending on the link parameters of the mechanism. Transition configurations between each pair of operation modes are also identified. This work provides a framework for further investigation on variable-DOF single-loop mechanisms.