Maximum torque generation of SEA under velocity control

Nowadays, compliance is required in various research. Series Elastic Actuator (SEA) has been emerged as one of the promising actuator system, since it provides various benefits such as safety, force sensing, energy storing with its inherent compliance. While the SEA contributes not only to the human interacting robot but also to wide robotics area, there is still limitation in performance that is caused by non-linearity and discontinuous power transfer. The cause of these influence is arisen from the electric devices (e.g., sensor, motor) and mechanical characteristics (e.g., friction, gear backlash), since SEA consists of a motor, a spring and a gear reducer to amplify the output torque. We focus on improvement of maximum force control performance (i.e., control bandwidth) taking into consideration saturation characteristic of the motor drive. Especially velocity limitation which interrupts spring deformation tracking performance is concentrated in this research; the spring in SEA transforms displacement to output force and its performance depends on the position control performance of the SEA. A novel index called Maximum Torque Transmissibility (MTT) is defined to assess the ability to fully utilize maximum continuous motor torque input which is saturated by velocity output limitation condition. Novel and practical frequency bandwidth can be found based on the proposed MTT.