A fairly detailed exoskeleton variable-length link model with adjustable stiffness is considered in the article. The refinement of the previously created models in terms of discretization is made. The geometrical dimensions of the top and bottom rods, the cylinder, the cylinder covers, the piston that moves inside the cylinder with magneto-rheological fluid, as well as their masses and moments of inertia relative to coordinate axes are refined. The payload mass at the end of the link, resulting under the effect of other links or the attached actuator, is simulated by a homogeneous ball. The change of the mass in the bottom and top parts of the cylinder, and the change of the moment of inertia of the link as the magneto-rheological fluid flows inside the cylinder from one part to another through the piston with microchannels are made more precise. All these made it possible to bring the model closer to the real technical device. The mathematical model of a more accurate link model is compiled. The possible model of actuator, functioning based on the proposed refined model of the exoskeleton link with magnetorheological fluid, is described. The possibility of its functioning and the options to control it are studied. The accuracy estimation for the refined model in comparison to the previously created models is made. All the results presented were obtained in a program created in the universal software environment “Wolfram Mathematica”. The links of the proposed model can be used in designing next-generation exoskeletons, which are more comfortable comparing to the existing models.
The software, implementing mathematical models of 2D and 3D active exoskeletons with electric drives, has been developed in the environment of universal computer mathematical system "Wolfram Mathematica". Each model has the same structure and includes five mobile links. Generalization of these models for the case of arbitrary finite number of n links is made. The angles, calculated between the links of the models, are used in the software described in the article, which differ these models from the existing ones. Cylindrical hinges are used for the articulated interconnection of the links in the 2D model. As for the 3D model, the spherical hinges perfectly implement all mobility degrees available in the human musculoskeletal system. This fact also differ the proposed 3D model from the existing ones, which have limited mobility and use not only spherical, but also cylindrical hinges to join some links in order to reduce dimension of the system of differential equations of motion. The comparative analysis of the obtained mathematical models for the two mechanisms in the form of Lagrange equations of the second kind is made. The system of electromechanical equations for the model using asynchronous AC motor is listed. The solution of direct and inverse dynamics problems is given for 2D model. As for the 3D model, no numerical solution of the Cauchy problem has been obtained due to large dimension of the system of differential equations of motion and limited computing power. Therefore, the idea about exoskeleton motion control model based on artificial intelligence that needs to be developed is suggested.
The article describes the technical problems that arise when modeling exoskeletons with variable length links and electromechanical drives:the delay of the executive mechanisms of the exoskeleton with increased movements of the human musculoskeletal system, which has a negative effect on the dynamics of the joint movement of a person inside the exoskeleton. The consequence is the lack of synchronization in the joint work of the human-exoskeleton cyborgic system. This reduces the comfort of using exoskeletons. An analysis of the prospects for improving the technologies for controlling electromechanical models of exoskeletons based on neuro-fuzzy networks is presented. The prospects for autonomization of exoskeleton control with the help of neural networks are determined. An analysis of possible problems associated with the introduction of intelligent control of the exoskeleton was carried out, solutions were proposed for the use of a neuro-fuzzy network to control the electromechanical model of the exoskeleton.
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