Human Walking Locomotion Research Articles

Bipedal Model and Hybrid Zero Dynamics of Human Walking With Foot Slip

Abstract Foot slip is one of the major causes of falls in human locomotion. Analytical bipedal models provide an insight into the complex slip dynamics and reactive control strategies for slip-induced fall prevention. Most of the existing bipedal dynamics models are built on no foot slip assumption and cannot be used directly for such analysis. We relax the no-slip assumption and present a new bipedal model to capture and predict human walking locomotion under slip. We first validate the proposed slip walking dynamic model by tuning and optimizing the model parameters to match the experimental results. The results demonstrate that the model successfully predicts both the human walking and recovery gaits with slip. Then, we extend the hybrid zero dynamics (HZD) model and properties to capture human walking with slip. We present the closed-form of the HZD for human walking and discuss the transition between the nonslip and slip states through slip recovery control design. The analysis and design are illustrated through human walking experiments. The models and analysis can be further used to design and control wearable robotic assistive devices to prevent slip-and-fall.

Special Issue: Nonlinear and Computational Dynamics in Biomedical Applications

Special Issue: Nonlinear and Computational Dynamics in Biomedical Applications

Boosting the efficiency of a footstep piezoelectric-stack energy harvester using the synchronized switch technology

In this article, the self-supported power conditioning circuits are studied for a footstep energy harvester, which consists of a monolithic multilayer piezoelectric stack with a force amplification frame to extract electricity from human walking locomotion. Based on the synchronized switch harvesting on inductance (SSHI) technology, the power conditioning circuits are designed to optimize the power flow from the piezoelectric stack to the energy storage device under real-time human walking excitation instead of a simple sine waveform input, as reported in most literatures. The unique properties of human walking locomotion and multilayer piezoelectric stack both impose complications for circuit design. Three common interface circuits, for example, standard energy harvesting circuit, series-SSHI, and parallel-SSHI, are compared in terms of their output power to find the best candidate for the real-time-footstep energy harvester. Experimental results show that the use of parallel-SSHI circuit interface produces 74% more power than the standard energy harvesting counterpart, while the use of series-SSHI circuit demonstrates a similar performance in comparison to the standard energy harvesting interface. The reasons for such a huge efficiency improvement using the parallel-SSHI interface are detailed in this article.

Deformable force amplification frame promoting piezoelectric stack energy harvesting: Parametric model, experiments and energy analysis

This article presents a nonlinear parametric model of force amplification ratio and an electromechanical model to couple the deformable frame with the piezoelectric stack in order to promote high-efficiency energy harvesting from human walking locomotion. Two improved frames (Frames I and II) are developed based on the modeling and simulation results. The experiments verified these modeling and simulation results that improved frames demonstrate a higher amplification ratio (8.4 for Frame II and 8.0 for Frame I), in comparison to the original frame (3.5). The experiments also verified these results that under the simulated walking excitation (100 N, ~1.4 Hz), the piezoelectric stack coupled with Frame II produces 4.1 mJ energy during each step, higher than the stand-alone stack (0.16 mJ) and the stack with the original frame (0.64 mJ). Note that the energy conversion efficiency of Frame II (9.1%) is even lower than that of Frame I (10.7%) and the stand-alone stack (25.8%). As such, this article concludes that the energy output of the piezoelectric stack depends largely on the frame deformations in terms of seven coupled frame parameters, instead of only one frame parameter (tilt angle), as commonly used in the referenced literature.