Patient-cooperative control of variable impedance actuators (PatRiA)

• Applicant: Professor Dr.-Ing. Steffen Leonhardt
• Subject Area: Automation, Mechatronics, Control Systems, Intelligent Technical Systems, Robotics
• Term: from 2018 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 359716418

The aim of this project is the investigation of novel methods for patient-cooperative control of variable impedance actuators (VIA). The focus lies on the development of a synthesis framework to compute a feedback controller which is, at the same time, able to provide a stable and gentle interaction between patient and VIA and guarantees interaction stability between robot and patient. The synthesis framework is developed such that it can be used for any kind of VIA. For the force/torque control-loop, the investigated synthesis procedure has to take into account the time-varying behaviour of actuator output impedance, as well as any coupling in the multivariable VIA plant. A novel synthesis procedure is to be developed, that is based on Hinf-optimal control via linear matrix inequalities, with interaction stability as an additional constraint. In case of algorithm convergence problems or too conservative optimisation results, an alternative approach employing a Cayley-transformation and nonsmooth Hinf-optimisation is investigated. Since the goal of this project is to develop a patient-cooperative control, a variable degree of support is to be achieved via parameterisation of a structurally fixed cascaded impedance controller. The synthesis procedure has to provide a space of controller parameters that guarantees stable interaction between robot and patient. A novel approach using uncertain transfer functions and polynomial positivity via the Bernstein expansion algorithm will be investigated. Moreover, non-heuristic procedures should be investigated that are able to adjust the impedance parameters (via control and physical interaction) based on the patient s motor state. The developed patient-cooperative control strategies are validated in two VIA actuators that were developed at the Chair for Information Technology. For the estimation of the patient s motor state, a body sensor network is available. Finally, the developed methods are validated with subjects in a test-bench that was specifically designed for movement support of the knee joint.

• DFG Programme: Research Grants
• Co-Investigator: Dr.-Ing. Berno Misgeld