CPG assistive motion control for variable stiffness actuators

We present a nonlinear feedback controller design for a variable stiffness actuator, that will force the closed-loop system to a stable limit cycle. The controller design synthesis allows for an inherent selection of limit cycle parameters, such as frequency and magnitude. The controller is based on the central pattern generator (CPG), that is a collection of neurons in the spinal cord of vertebrates and is used to control rhythmic movement, like, for example, breathing and walking. We develop a CPG impedance controller for our variable stiffness actuator MeRIA and validate it in an electromechanical test-bench environment. During these tests, the series elastic element of the actuator was changed in resemblance to the stiffness changes of the muscle-tendon system of vertebrates. Results on CPG controller performance under variable stiffness of the actuator are presented.