Abstract: Study of workspace of plane closed-loop robot is one of basic problems. By using the implicit function theorem, the condition of the flexible workspace boundary of plane closed-loop five-bar mechanism is derived. That is the output bar and conjoint connecting link are folded of extended, as while as another connecting-link and conjoint coupler. Then with the workspace intersection of two two-revolute open chains and rotational range of a connecting-link of four-bar mechanism, it is analyzed that boundary curve construction of plane closed-loop five-bar mechanism which fulfills the requirement of workspace boundary condition. Based on the analyses, corresponding mathematical models are setted up. And it put forth solution algorithm of plane closed – loop five-bar mechanism. Finally some examples are given to validate these mathematical models.

Key words: Flexible workspace, Implicit function theorem, Plane closed – loop five-bar mechanism