SLIP with swing leg augmentation as a model for running

Abstract

Abstract-Swing leg adjustment, repulsive leg function and balance are key elements in the control of bipedal locomotion. In simple gait models like spring-loaded inverted pendulum (SLIP), swing leg control can be applied to achieve stable running. The aim of this study is to investigate the ability of pendulum like swing leg motion for stabilizing running and reproducing a desired (human like) gait pattern. The employed running model consists of two sub-models: SLIP model for the stance phase and a pendulum based control for the swing phase. It is shown that with changing the pendulum length at each step, stable running gaits with widely different performances are achieved. The body vertical speed at take off is utilized as feedback information to tune the pendulum length as the control parameter. In particular, the effect of the pendulum length adjustment on the motion characteristics like horizontal speed, apex height and the stabilized system energy will be investigated. With this method key features of the human like swing leg motion e.g. leg retraction can be reproduced. Higher speeds correspond larger angular motion of each leg which is in agreement with experimental results in previous studies. The presented model also explains the swing-leg to stance-leg interaction mechanism which was not addressed in the underlying SLIP model. This conceptual model can be considered as a functional mechanical template for legged locomotion and can be used to build more complex models, e.g. having segmented legs or an upper body.

The biomechanics of running and running styles: a synthesis

“…Also, the CoP excursion and the effective leg length may change when runners tend to land more on the fore-foot at higher speeds (Breine et al, 2014;Lai et al, 2020). Lastly, pendulum effects of the segmented swing-leg on stiffness should be considered (Clark et al, 2017;Kugler & Janshen, 2010;Maykranz & Seyfarth, 2014;Rashty et al, 2014). Together, this would result in a complex model to estimate leg stiffness.…”

“…The swing leg motion is often ignored in SLIP models as they essentially describe the course of one step (technically a half-cycle). Rashty et al (Rashty et al, 2014) showed that by modelling the pendular motion of the swing leg in the conventional SLIP model, the generated momentum of the swing leg induces sequential steps. Consequently, the forward motion becomes more stable, which led the authors to suggest that the swing leg may help to reduce muscular force provided by the stance leg (Rashty et al, 2014).…”

Locomotor Sub-functions for Control of Assistive Wearable Robots

“…Instead of Velocity based leg adjustment, a second approach which can be considered as a template based control method for leg swinging is to assume a passive pendulum-like movement of the swing leg (Knuesel et al, 2005 ; Mohammadinejad et al, 2014 ). Mochon and McMahon presented a model comprising a stiff stance leg and a segmented swing leg (Mochon and McMahon, 1980 ) which provides a better match of human walking dynamics, compared with the inverted pendulum model.…”

“…However, swing leg movement is still a missing part in SLIP based models. In Mohammadinejad et al ( 2014 ), we presented a new model combining SLIP for stance leg with pendulum movement for the swing leg in running. In this model the pendulum length is adapted at each step to attenuate any perturbation or error from desired movement.…”

“…In this paper we explain how understanding bipedal locomotion using the concept of three locomotor sub-functions can be employed to design and control assistive wearable robots. In that respect, first, we survey our previous studies on combinations of the control concepts of three locomotor sub-functions to achieve stable gaits (Sharbafi et al, 2013b , 2014 , 2016 , 2017 ; Mohammadinejad et al, 2014 ; Oehlke et al, 2016 ; Sharbafi and Seyfarth, 2017 ; Zhao et al, 2017 ). Then, we show that considering such an architecture to control a wearable robot, an actuator can be designed with optimal performance for a range of motions required for different locomotor sub-functions.…”