Validation of a lower limb exoskeleton assist device focusing on viscous properties: verification of assist effectiveness by measuring muscle activity

Abstract Because exoskeletal assistive devices are worn directly by a person, enhancing cooperation is important. However, existing assistive devices have problems in terms of their cooperation with human behaviors. This is because existing assistive devices are driven by estimating the wearer’s movement intention based on predetermined movement time and device angle information. Although these methods are expected to work as expected, in practice, it is difficult to achieve the expected behavior. Therefore, an assistance method is required to reduce such misalignment with time and misalignment between the device and wearer. Therefore, this study focused on the viscoelastic properties that generate force in response to movement and are expected to enhance coordination. In a previous study, the authors confirmed the effects of viscoelastic properties or an assistive device with variable stiffness. However, viscous characteristics during movement have not been considered. In this study, we aimed to improve the coordination by focusing on the viscous characteristics. The viscous torque outputs in response to the angular velocity are expected to be driven in response to actual human motion. In this study, the viscous torque was calculated as the product of the command viscosity coefficient and the joint angular velocity and was applied to a lower-limb exoskeleton-type assist device equipped with a magneto-viscous fluid brake and a planetary gear mechanism. In addition, a viscous command that changes the torque according to speed (proposed method), a time command that changes the output value according to the passage of time, and an angle command that changes the command value according to the angle information of the device were applied to the assist device, and surface EMG measurements and command signals were compared. The target movement was a seated movement, and the left and right vastus medialis and semimembranosus muscles were measured. More than half of the subjects showed a decrease in myopotential for five subjects for all three command methods, confirming the effectiveness of the viscous command.