A New Planar Overconstrained Mechanism Generated by Merging Two Symmetric Watt’s Six-Bar Linkages that Perform Gear-Like Motion

Abstract This article explores the synthesis of a planar overconstrained mechanism potentially for a folding hinge application. Inspired by a folding hinge patent from a phone company, the author analyzes the linkage and discovers a special mechanism generated by merging two symmetric Watt’s six-bar linkages. The synthesis method involves finding a Watt’s six-bar linkage with gear-like input–output motion. The differential evolution optimization algorithm is used to determine the dimensions of the linkage that satisfy the synchronized motion. Numerical results demonstrate the successful synthesis of the overconstrained mechanism with extremely low error, validating its performance. The CAD model and prototyping further confirm its functionality. This article makes three significant contributions: First, it synthesizes a Watt’s six-bar linkage that performs approximate gear-like motion for the first time. Second, it introduces a novel planar overconstrained mechanism and presents a methodology for its synthesis. Finally, it proposes a potential design for synthesizing and implementing overconstrained mechanisms in foldable phone hinges, meeting requirements for compactness and durability.