Efficiently tunable positive-negative stiffness actuator

摘要

Compliant actuators have found their place in areas of prosthetics, rehabilitation and robot locomotion because they enable safe human-robot and stable robot-environment interaction, both non-trivial to achieve using conventional rigid actuation. These actuators are capable of varying their equilibrium position and apparent output stiffness in a way humans change the resting position and compliance of their limbs. Just like antagonistically actuated human joints, these actuators require two motor units to provide control over the equilibrium position and the positive joint stiffness. Here we present a novel compliant actuation concept which affords control over the equilibrium position and joint stiffness using a single motor unit. In order to achieve this unconventional functionality, the actuator combines a passive positive feedback (negative stiffness) mechanism with an efficiently tunable negative feedback (positive stiffness) mechanism. This provides a novel design with two distinct operation modes, one leading to unprecedented stiffness tunability, while the other enabling equilibrium point controllability. We present the first practical implementation of this actuator using a prototype prosthetic limb design along with experimental data testifying the range of tunability, covering compliant to rigid behaviour, without paying much on the power input.