Analysis and design of a novel constant torque four-bar mechanism

This study presents a novel constant torque mechanism based on a classical four-bar mechanism with springs. To the best of our knowledge, this is the first four-bar mechanism in the literature that transmits constant torque through input to output link for a specific interval. The proposed design is based on a constant force transmitting double-slider mechanism. A gearset can be replaced with the proposed mechanism for the cases where the motion stroke is small. Thus, this mechanism is superior to a gear train when manufacturing and cost is taken into consideration. Further, the design has two important advantages: The first advantage is the torque amplification capability and the second one is the direction of motion option. These characteristics cannot be achieved with a classical parallelogram type four-bar mechanism which has constant torque transmission capacity. A generalized design procedure for the mechanism is proposed using dimensionless parameters. Then, a design example is studied and to verify the proposed analytical model, dynamic simulation is carried out in RecurDyn software.