Simulation model of actuators of an orthotic robot

W Zakładzie Konstrukcji Urządzeń Precyzyjnych na Wydziale Mechatroniki Politechniki Warszawskiej trwają prace nad systemem do pionizacji i realizowania chodu osób z bezwładem kończyn dolnych. Projektowanie urządzenia jest wspomagane badaniami modelowymi. W artykule przedstawiono symulacyjny model elektromechanicznej części systemu opracowany w środowisku Matlab/SimMechanics. Model wykorzystano m.in. do wyznaczenia zapotrzebowania energetycznego układów wykonawczych i oceny błędów odwzorowania profili ruchu.In the Division of Design of Precision Devices at the Faculty of Mechatronics of Warsaw University of Technology works there are performed upon a system for verticalisation and substituting gait for people with paresis (Fig. 1). Works are supported with simulation software. Simulation model of the system actuators is described in the paper. The purpose of simulation was to estimate energy consumption of actuators and to assess quality of their movements. Main assumption for the model is that mechanisms activating user's legs are of a planar kind. Matlab-SimMechanics mathematical environment was used for modelling. Structure of the model is presented in Fig. 2. Parts of human body are sources of load for actuators as described by eq. (2) and (3). Their parameters are inserted into "body" blocs (Fig. 3), which represent stiff elements of mechanisms in the model. Mechanical contact between the device and a ground was modelled as reaction forces occurring in "foot" parts of the device when distance between them and the ground is less than the assumed value. The drives of actuators' employ DC motors equipped with reduction gearboxes (Fig. 4). Typical equations (4) - (9) were used for modelling DC motors and gears. Input signals are reference angular displacements of joints expressed in the form of functions approximating experimental data (Fig. 5). Simulation experiments revealed strong relation between length of gait cycle and energy consumption of actuators (Fig. 6). Reduction gear ratio also influences energy needs as well as quality of the device movements (Fig. 8). The model is being currently modified and enhanced in order to be used at the next stages of design process