In this article, a novel approach is presented to identify the singularity free joint rotation space (JRS) of two-DOF seven-bar parallel manipulators. The configuration space of a seven-bar manipulator is expressed as joint rotation space sheets and each sheet may have one, two or four-sides. Each sheet represents a manipulator branch and each side of a sheet corresponds to a singularity free Joint rotation space. The article presents a logical approach to understand how the joint rotatability of one loop in a seven-bar manipulator is affected by the other loop, the formation of branches and its relationship to singularities. Based on the types of interaction between loops, manipulators are classified into three types. The paper offers an effective method to identify and understand the problems with branch and singularity of parallel manipulators. The concept and method can also be used in other types of parallel manipulators.

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