Appropriately complex modelling of healthy human walking

Abstract

XVI

Autonomous Assistance-as-Needed Control of a Lower Limb Exoskeleton With Guaranteed Stability

“…The second technique used to reduce the complexity of the dynamic model, presented in [17], eliminates the need for branch chain modelling of the torso by representing the center of mass (CoM) of each link with an additional eccentric component (see Figure 3). Although the eccentric component of the CoM is irrelevant for most of the joints, it becomes crucial in the formulation of the torso dynamics.…”

“…Although the eccentric component of the CoM is irrelevant for most of the joints, it becomes crucial in the formulation of the torso dynamics. The torso dynamics are included by modelling the link connecting the stance hip joint to the swing hip joint as having a length of [17]. By including a non-zero eccentricity at the link connecting the stance hip joint to the swing hip joint of the biped, the dynamic effect of the unmodelled torso link is modeled without the need for branch chain modelling.…”

“…As a result, roughly 20% of healthy human walking goes unmodelled and can not be considered in the analysis of proposed control policies. Achieving the noninstantaneous double support phase of gait is done by constraining the motion of the trailing foot link of the fully actuated model such that the toe remains on the ground until the biped moves into the swing phase [17]. Two constraint equations are used,…”

“…In the case of this bipedal walker, the dependant angles were chosen to be the trailing legs knee and ankle joint. Defferentiating the constraint equations twice allows for the constraint forces (λ f1 , λ f2 ) on the trailing toe to be determined to ensure toe remains in contact with the ground throughout the double support phase [17]. The constraint force equations are added to the formulation of the dynamics, thus ensuring that they are actively considered throughout double support:…”

“…The Lagrangian dynamic model accurately represents the different phases of gait present in typical human locomotion, including non-instantaneous double support phase, fully actuated swing and stance phase, and an underactuated phase during terminal stance. The model provides an accurate representation of human walking despite its simple structure by combining the work done in [16] and [17]. Model validation is shown in Section II of this paper.…”