Hybrid parallel compliant actuation for lower limb rehabilitation

• Applicant: Professor Dr.-Ing. Steffen Leonhardt
• Subject Area: Biomedical Systems Technology
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 392037132

Paralysis is a functional loss of a single or multiple muscles of the skeletal musculature. Corresponding to the cause of the paralysis various therapy approaches are possible. On the one hand, a rehabilitative training can be realised with automated motion therapy and, on the other hand, the compensation of missing motor function can be substituted by powered actuators. In this research project, a new class of actuators and control of exoskeletons and active orthosis are to be fundamentally researched, which are especially suitable for patients with residual function (hemiplegics, stroke survivors). The suitability for paraplegic patients is to be examined in a later phase of the project. As a core component, the project focuses on the design of novel variable-parallel-elastic actuators (VPEA) for the movement support of the lower limbs. In order to be able to fully control the energy flow into the parallel spring, the actuator is equipped with a brake and a clutch. This approach is intended to minimise the necessary actuator power consumption and to involve the patient with a residual movement function more intensively in the motion during therapy due. In parallel to the design of the actuator, a nonlinear dynamical model is to be researched, which also contains physiological and dynamic submodels of the overall system, in addition to the hybrid electromechanical model. The increased complexity of the actuator demands for a multiobjective control design. In addition to cascaded force and impedance controllers (assist as needed principle), the energy flow into the parallel elastic element has to be controlled. Moreover, the control synthesis has to be designed with respect to an overactuated system with multiple actuated joints. Furthermore, the controller has to guarantee interaction stability with respect to possible residual muscle function of its wearer. To be able to achieve these objectives, a cascaded control structure with possible combinations of robust control for switched systems, iterative learning control or model-predictive control are investigated.The goal is to create a proven rehabilitation system that can be used for both patient groups. After integration of the actuator into an existing exoskeleton structure and motion tests, a commercial FES system is also examined in combination with VPEA. For this purpose, a synergistic physiological controller is to be developed which uses the patient muscles and VPEA together for the movement. The overall goal of this work package is the extension of the exoskeleton applicability to the group of paraplegic patients.The actuators, including the underlying control system for the individual joints, are successively put into operation and tested. Finally the whole exoskeletal support system is validated in a treadmill study in a Chinese motion lab of the Tsinghua University of Peking with cross-parlayed patients recruited from a cooperating Chinese hospital.

• DFG Programme: Research Grants
• International Connection: China
• Partner Organisation: National Natural Science Foundation of China
• Cooperation Partner: Professor Dr. Linhong Ji