Design and control of a mechanical rotary variable impedance actuator

To realize different tasks in human-robotic interaction, various mechanical variable stiffness actuators are being investigated. A mechanical-rotary impedance actuator (the MeRIA) is presented that is based on the controllable effective length of a mechanical bending bar, which can be implemented into an orthosis for future research on rehabilitation training. The actuator provides joint motion and variable stiffness, simultaneously. The control task can be decoupled to be a decentralized control structure for which the controller of the two motor power sources can be designed respectively. For the movement control-loop, a cascaded impedance controller with position-torque-velocity control-loops are designed to maintain a stable and safe working environment. Using an H∞ loop-shaping methodology, a robust stabilization torque controller is achieved. The trade-off between the actuators performance and stability is taken into account to obtain a desired shape as a precondition of an H∞ controller synthesis. The actuator is tested on a test bench using rapid control prototyping. A model reduction algorithm is implemented to simplify the controller, and a prefilter design reduces the control-loop overshoot, thereby improving the robust stability and tracking performance during application. Experiments show that the MeRIA meets all the requirements for a mechanical device attached to the body.