Abstract In this work we present a new adjustable stiffness rotary series elastic actuator (ASRSEA) where the stiffness is adjusted by adjusting the length of spring elements using lockable pins. The design of spring elements is optimized for undergoing maximum deformation based on compliance maximization. To ensure symmetry, a pair of spiral spring elements that are equally phased out are used. On each spiral spring element, a guided movable pin that can be locked to a rigid back plate is mounted. By locking the pins to the back plate, the effective length of the spiral spring elements can be adjusted, resulting in adjustable stiffness of the SEA. The stiffness is determined using finite element analysis (FEA) and experimentally validated. An assembly is designed with the SEA and a rotational encoder to determine the torque transmitted by the SEA. This apparatus can be used for assist-as-needed (AAN) operation where the load torque can be calculated from the deformation of the SEA and input torque from motor can be adjusted according to user effort. Such AAN mode of operation enables simpler control of prime movers in assistive applications, thus increasing safety in human-robot interactions. Future work will focus on improving the AAN operation control using data from SEA to train machine learning methods.
Mittapally et al. (Fri,) studied this question.