Input link rotatability analysis of four-bar based Watt mechanisms with revolute and prismatic joints

• Input link rotatability analysis of Watt six-link mechanisms is presented.
• Four-bar based Watt mechanisms containing only revolute joints are analyzed.
• Four-bar based Watt mechanisms containing one prismatic joint are analyzed.
• Analysis is applicable to all assembly modes of the mechanisms.
• The presented analysis offers many advantages over the other approaches.

This paper presents the input link rotatability analysis of four-bar based Watt six-link mechanisms, having at the most one prismatic joint. All assembly modes of such Watt mechanisms are considered in the analysis. For all the cases considered, explicit mathematical conditions are obtained, which can be used to check the input link rotatability of a given Watt mechanism. Apart from being of theoretical importance, the presented analysis is suitable for implementation within an optimization scheme, is computationally efficient and can be utilized to ensure that the synthesized mechanism does not shift from one branch to another, when put to use in practice. When incorporated within an evolutionary optimization algorithm, it can be effectively used to handle the rotatability constraint. The approach can be easily extended to Watt mechanisms containing more than one prismatic joint.