Modeling of mechanisms of quasi-constant movement

Abstract

In practice for material pressing mechanisms are used that provide synchronous motion of components. Gears can satisfy this design specification accurately, but they are more expensive and difficult to manufacture than linkages, and not convenient to transmit the motion between two parallel axis with large center distance. Thus, when a quasi-constant transmission ratio within a wide range of driving link rotation is allowed, four-bar linkages are suitable to replace gears. The possibility of using a four-bar linkage mechanism to ensure opposite rotation of double cranks is analysed. A planar four-bar linkage is characterized by having four revolute joints with parallel axis. The synthesis of four-bar linkages will yield an approximation of transmission ratio between the input and output crank rotation. Crank displacement equations for antiparallelogram and similar forbar linkage mechanisms depending on the sizes of the links are presented. Antiparallelogram mechanism with ratios j = 30 between the center-distance and the crank length provide a transmission ratio u 13 = 1 ± 5 % for driving the crank angle in range 40-140 deg. The Matlab simulation showed quasi-constant transmission ratio u = 1 ± 2 % for the four-bar mechanisms with coupler length not equal with fixed center distance.