High-Torque-Capacity Helical Flexures for Series Elastic Actuators

Series elastic actuators (SEAs) achieve output torque and stiffness control by managing the deformation of a spring arranged between the motor and the output. SEAs are ideal for tasks involving human-robot interaction and unstructured environments. The stiffness, size, and torque capacity of the spring are crucial for the performance of an SEA. To increase the torque capacity of an SEA while maintaining a compact size, this article proposes a novel helical flexure as the spring in an SEA. The helical flexure is formed on the thin wall of a tube to generate high torque output with minimal reaction forces and moments. The resulting compliant tube can be combined with other transmission components to reduce the number of components and allow the inner passage of cables and shafts. Simulation comparisons and experimental testing verify the merits of the proposed helical flexure. An SEA prototype is fabricated to demonstrate the performance of the new helical flexure during zero-torque and high-torque motion. It is expected that this new helical flexure will offer a competitive solution for designing compact springs used in various SEAs.