Models of magneto-rheological fluids to be used in design of 3D exoskeleton model with four variable-length links of adjustable stiffness

The mathematical models of magneto-rheological fluids and the methods of their control based on the variation of the external magnetic field applied to them are examined in the article. The promising generation of exoskeletons with variable-length links with adjustable stiffness is also considered. The magneto-rheological fluid is used in the design of these links. The proper adjustment of the exoskeleton link stiffness during wearer’s motion paves the way for the creation of more comfortable exoskeleton models from the bio-mechanical point of view. Such exoskeletons are in demand in many branches of both healthcare and industry. The rigidity of magneto-rheological substances can be changed in a considerable range under the effect of magnetic field, which helps implementing exoskeleton links with adjustable stiffness. The exoskeleton link stiffness adjustment in real-time is a complex control problem. The response rate of the mechanisms using magneto-rheological substances is high. At the same time, the power consumption of the system that controls magneto-rheological link is insignificant comparing to other models, which allows creating more advanced exoskeleton models. The exoskeleton model including four variable-length links with adjustable stiffness for human lower limbs is considered in the article. The obtained differential equations of motion are presented in generalized form. The kinematic method of model motion control is proposed.