Optimising a driving mechanism mechanical design of EXOTIC exoskeleton—a review on upper limb exoskeletons driving systems and a case study

While designing rehabilitation exoskeletons is often realised based on experience and intuition, many processes can be computer-aided. This gives the opportunity to design lighter and more compact constructions. Hence, the devices can be fully wearable and have a wider range of motion. So far, mainly topology optimisation and parametric dimensional optimisations have been used for that. The presented study addresses the problem of automatic selection of the driving systems for exoskeletons. It consists of the literature review of the components used to actuate the joints of such constructions, optimisation algorithm development, and a case study on the EXOTIC exoskeleton. The method includes building a database of motors and gearboxes, computing inverse kinematics of a system to obtain angular trajectories from the task-oriented paths, iteration computing inverse dynamics to compute required torque and the search for the optimal solution according to the defined goal function. This approach enables single joint and multijoint optimisation, with the custom goal function minimising optionally masses, diameters or widths of the selected driving systems. The investigation consists of the 28 simulation trials for EXOTIC exoskeleton to compare results obtained for different aims. Moreover, to visualise the effect, the 1^st DOF driving mechanism is redesigned to obtain its minimum width based on the optimisation results. The optimal choice reduced the actuation mechanism mass by 15.3%, while its total dimensions by 17.5%, 8.5% and 26.2%, respectively. The presented approach is easily transferable to any other active exoskeleton and can contribute to designing compact and lightweight constructions. This is particularly important in assistive rehabilitation and can also be used in industrial assistance processes.