Exoskeleton Dynamics Simulation with the System of Three Variable-Length Links of Adjustable Stiffness

The article proposes a spatial model of an exoskeleton for the human musculoskeletal system, represented by three movable links of variable length and two-point masses. The stiffness of the links is controlled by changing the voltage supplied to the magnetic rheological fluid, which fills sections of variable length. The model can be used to develop comfortable exoskeletons, the kinematic characteristics of which are close to the kinematic characteristics of the human musculoskeletal system. The model dynamics equations are constructed using local coordinate systems.

The required laws of change of generalized coordinates are specified by the equations of program constraints that determine the dependence of differentiable periodic functions on time. Control moments and longitudinal forces are determined by methods of solving inverse dynamics problems and are realized by changing the magnetic field strengths, which affect the change in the stiffness of the magnetic-rheological fluid. The magnetic field strengths that control the stiffness of the link are implemented by step functions. An animation of the movement of the mechanism has been synthesized, showing the adequacy of the proposed modeling procedure. The constraints of the links are modeled by joints and motors that implement the necessary rotational motion. The dynamics of the model is controlled by changing the lengths of the links and the angles between the links.