Equivalent four-bar linkage has been proved to be a simple and general approach for the identification of the singularity (dead center position) of single-DOF complex planar linkages. Based on the concept of equivalent four-bar linkage, this paper proposes the concept of equivalent five-bar linkage and extend this concept to analyze the singularity (dead center position) of three different topologies of two-DOF seven-bar planar linkages for the first time. The five links chosen from the two-DOF seven-bar linkage compose one equivalent five-bar linkage. A singular position may happen when the three passive joints of one equivalent five-bar linkage become collinear. When the equivalent five-bar linkage is at the singular position, the whole two-DOF seven-bar planar linkage must be also at the position of singularity. The propose method offers another geometric insights for the singularity analysis of two-DOF seven-bar planar linkages and other multiple-DOF planar linkages.
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