Antagonistic Parallel Elastic Actuator Using Preloaded Composite Spiral Torsion Springs

Parallel elastic actuators (PEA) are widely applied for robotic applications with asymmetric load requirement. The elastic components are included in the systems aiming to reduce the actuation peak torque required from the electric motors. However, higher torque may be required during the opposite motion. The fused deposition modeling technique allows fabrication of 3D printed composite spiral torsion springs for compact modular PEAs. The antagonistic design enables using the springs to support moment in bidirectional. Preloading is substantially required to ensure the winding deformation of both springs. The design of spring stiffness and equilibrium is the major challenge to minimize the actuation peak torque and power consumption. In this paper, the behavior of the parallel elastic actuator with preloaded springs while subjected to the pure stiffness load is observed in three cases: the PEA's spring has lower, higher, and the same stiffness as the load. The position and current of the brushless DC motor driven by the ODrive Pro motor controller are recorded. The experimental setup allows characterization of the spring component and the PEA using different number of spring stacks. The results of this study can be used as a reference for further designing of antagonistic PEAs with preload for asymmetric load support.