  The ability to convert reciprocating, i.e., alternating, actuation into
rotary motion using linkages is hindered fundamentally by their poor torque
transmission capability around kinematic singularity configurations. Here, we
harness the elastic potential energy of a linear spring attached to the coupler
link of four-bar mechanisms to manipulate force transmission around the
kinematic singularities. We developed a theoretical model to explore the
parameter space for proper force transmission in slider-crank and rocker-crank
four-bar kinematics. Finally, we verified the proposed model and methodology by
building and testing a macro-scale prototype of a slider-crank mechanism. We
expect this approach to enable the development of small-scale rotary engines
and robotic devices with closed kinematic chains dealing with serial kinematic
singularities, such as linkages and parallel manipulators.
