Design of an inverse dynamics model of a lower-limb assistance exosuit

Abstract

In the area of gait assistance, simple models based on cable-driven actuators with anchor points at the segments to be actuated stand out due to their high wearability, low weight and reduced cost. Force is transmitted from the actuators to the anchor points using cables, increasing user comfort by doing away with the rigid structures found in traditional exoskeletons. This paper deals with the inverse dynamics model to obtain joint torques needed during the gait cycle as a precursor to numerically dimension and design the components to develop an exosuit. A two-dimensional biomechanical model made up of seven segments was designed with three in each leg and one for the torso and torques in the hip, knee and ankle as the primary parameters. These torques are then distributed between the subject and the exosuit in different configurations. This model helps optimise the various characteristics of the exosuit such as the placement of anchor points, the exact number of actuators, cable arrangements among others. When finalising the force transmission system of the exosuit, it is possible to determine several variables such as: which joint(s) need the most external support and which ones are better left unactuated. The effect of the aforementioned design parameters on the force transmission, effectiveness of proposed designs in other literature can also be analysed.