DESIGN OF EIGHT-BAR LINKAGES WITH AN APPLICATION TO RECTILINEAR MOTION

This paper explores an automated methodology to design eight-bar linkages for five positions, by constraining the user defined 4R open chain and 6R closed chain using RR dyads. The application in focus is that of rectilinear motion. The paper lays down the rules for systematic selection of link pairs for the application of RR constraints, that help automate the synthesis of eight-bar linkages. The methodology performs a random search within the user specified tolerance zones around the task specifications to increase the number of candidate linkage solutions. These linkages are then subjected to forward kinematic analysis using the Dixon determinant elimination procedure to find all possible linkage configurations over the range of motion of the input link. Linkages that have all the task configurations on one branch ensure their smooth movement through them. The result is an array of defect-free eight-bars that can perform approximate rectilinear motion. This method provides increased flexibility and control over the synthesized linkage compared to other known rectilinear motion linkages, owing to the ability to specify the backbone chain. A couple of examples are presented to illustrate the results.