Transmission and actuation systems in cable-driven, walking-assistance exosuits based on postural and dynamic synergies

Abstract

The design of walking-assistance exosuits is becoming increasingly popular among those who aim at developing a light, affordable and wearable system. They are indeed an alternative to traditional exoskeletons, which tend to be bulkier and more expensive. The main advantages of exosuits, as opposed to exoskeletons, are their lower weight and price, as well as their increased wearability and kinematic compatibility with the user. Thus, it is key to optimize their design and, particularly, the number of actuators and the actuation scheme. One of the current, common ways to achieve better designs, is to conduct a Principal Component Analysis (PCA) on some of the involved variables to reduce their dimensionality and thus, simplify the actuation system. The goal of this paper is to analyze the different variables upon which PCA can be conducted and propose the resulting actuation schemes, comparing the results and determining the best design approach for the design of a synergy-based, gait-assistance exosuit. The study focuses on both postural and dynamic synergies to optimize their design. Here, both synergy types are reviewed from a design perspective, yielding different design criteria following a PCA-based study, each with their own set of advantages and disadvantages. Thus, the design of cable-driven exosuits is optimized via analysis of gait parameters related with its actuation, such as joint torque or cable extensions. Kinematics or postural synergies lead to a higher cumulative variance of the first principal component and the transmission system is simpler than the ones obtained through dynamic synergies.