Varying mechanical compliance benefits energy efficiency of a knee joint actuator

Abstract In the field of wearable robots, actuator efficiency and user safety are frequently addressed by intentionally adding compliance to the actuation unit. However, the implications compliance has on the actuator’s overall performance in different conditions and activities are not fully understood, largely due to single task-focused experimental evaluations of these devices. To overcome this, our paper analyzes the effects that changing mechanical compliance has on the actuator’s overall performance in different ideal conditions in an experimental test setup. The torque performance and electrical energy consumption of an orthotic, adjustable-compliance knee joint actuator are evaluated during emulated walking and sit-to-stand-to-sit movements. Furthermore, the feasibility of combined operation of a dual mechanical compliance configuration during walking is investigated, and its outcomes reported in this work. The results demonstrate that varying mechanical compliance can lead up to 50% energy savings compared to a no-compliance configuration and show that, in general, changing compliance level leads to either energy-optimal or power-optimal actuator performance, but not both.