Kinematic decomposition of coupler plane and the study on the formation and distribution of coupler curves

Based on the kinematic decomposition of the coupler plane and the analysis of coupler limit positions in a four-bar linkage, the formation of coupler curves is studied and the coupler plane is divided into crank-zone, rocker-zone, coupler-zone and cross-zone. Shapes and features of coupler curves in different zones are then explained. To investigate further the variation and distribution of coupler curves in the cross-zone, several mark directions on the coupler plane and special crunode points on coupler curves in a four-bar linkage are defined and the coupler curves with special crunode points are examined. The influence of the phase relation between the transportation motion and the relative motion of the coupler on the shape of the coupler curve is then analyzed.