Design of the Clutched Variable Parallel Elastic Actuator (CVPEA) for Lower Limb Exoskeletons.

The paper presents a novel clutched variable parallel elastic actuator (CVPEA) mainly consisting of a motor and a flat spiral spring in parallel to actuate the hip of lower limb exoskeletons in sagittal plane. To minimize the power and torque requirement for motor, we put forward three optimization methods including minimizing the rms motor power, the peak motor torque and the peak motor power to determine the optimal PE (parallel elastic) for CVPEA. It is proved that the mechanical energy reduction in the late stance period can be stored in the PE and can be later recycled in the early swing period in a gait cycle according to simulation results. Simulation results also show that using the optimal PE with stiffness of 0.037 Nm/rad, balance position of 0.452 rad determined by minimizing peak motor torque, the rms and peak motor torque, the rms and peak motor can be approximately reduced by 52.3%, 52.9%, 57.5% and 70.2%, respectively, when a subject wearing the CVPEA driven exoskeleton with body weight of 90kg walks at a speed of 0.8 m/s. With this optimal PE, the motor torque and power requirement are largest reduced.