Comparative analysis of the dynamics of 3D electromechanical models of exoskeletons with 4 and 5 links of variable length and generalization to the case of an arbitrary finite number n of links

Abstract

The article discusses three spatial models of exoskeletons: with four, five and n links. In accordance with the biomechanics of the human musculoskeletal system, the models use cylindrical, combinations of two cylindrical hinges with mutually perpendicular axes of rotation, and spherical hinges. The change in angles between the links is controlled using electric drives located in the hinge area. Unlike those considered earlier, in this model, a section of variable length is assumed to be significant, and the drive that controls the change in the length of the link is located in this section. The models provide for the presence of a battery attached to the hip joint, simulated by a concentrated mass. In addition, the five-link model includes auxiliary elements that support the user's head in the form of a point mass. As a simplifying assumption, it is assumed that the entire mass of a section of variable length is concentrated in its middle. A drive that changes the length of a link can be implemented in the form of a rack or pinion gear with an electric motor. Using the method of software motion control, for the considered models with 4 and 5 links, the inverse problem of dynamics was solved and the influence of the body on the forces developed in the lower extremities of the exoskeleton was analyzed. The significant impact of adding a body on exoskeleton control has been established. Based on the analysis of the obtained systems of differential equations of motion, a generalization of the exoskeleton model to the case of an arbitrary finite number of links is proposed.