A dynamic model of a device with a parallel-serial structure to support the human lower limb.

BACKGROUND: Support systems designed for human lower limbs are usually characterized by a serial kinematic structure taking into account only one lower limb. To overcome the mobility range limitations, a new structure of the exoskeleton is proposed in this paper.

OBJECTIVE: The design process of the dynamic model for the support structure characterized by a parallel-serial mechanism is presented in the paper. The structure works as an exoskeleton and is designed to assist motion of the human lower limb in the process of rehabilitation.

METHODS: The structure of the support model was divided into linear (executive system) and nonlinear (the mechanical skeleton of the system) parts. The model of the executive system was designed and its parameters were estimated in the course of tests on a laboratory stand, as well as identification procedures. The nonlinear model was expressed by mathematical equations. The characteristic coefficients in the equation were determined based on a 3d CAD model.

RESULTS: To analyze the behavior of the mechanism, a simulation of dynamic responses was compared with experimental results for a real system consisting of a mechatronic device, actuator drivers, a controller, and programmed software.

CONCLUSIONS: The proposed new structure enables an increase of the range of rotation angles and can be fitted to an individual person. The derived model is in the analytical form and can also be easily adopted to the different versions of the exoskeleton and used in the design of control systems.