Robotic Light Touch Assists Human Balance Control During Maximum Forward Reaching.

OBJECTIVE: We investigated how light interpersonal touch (IPT) provided by a robotic system supports human individuals performing a challenging balance task compared to IPT provided by a human partner. BACKGROUND: IPT augments the control of body balance in contact receivers without a provision of mechanical body weight support. The nature of the processes governing the social haptic interaction, whether they are predominantly reactive or predictive, is uncertain. METHOD: Ten healthy adult individuals performed maximum forward reaching (MFR) without visual feedback while standing upright. We evaluated their control of reaching behavior and of body balance during IPT provided by either another human individual or by a robotic system in two alternative control modes (reactive vs. predictive). RESULTS: Reaching amplitude was not altered by any condition but all IPT conditions showed reduced body sway in the MFR end-state. Changes in reaching behavior under robotic IPT conditions, such as lower speed and straighter direction, were linked to reduced body sway. An Index of Performance expressed a potential trade-off between speed and accuracy with lower bitrate in the IPT conditions. CONCLUSION: The robotic IPT system was as supportive as human IPT. Robotic IPT seemed to afford more specific adjustments in the human contact receiver, such as trading reduced speed for increased accuracy, to meet the intrinsic demands and constraints of the robotic system or the demands of the social context when in contact with a human contact provider.

A center of pressure progression model for walking with non heeled and heeled footwear.

BACKGROUND: Heeled footwear benefits people with movement disorder in the form of shoe lifts, wedges and inserts while its prolonged use causes foot injury in healthy people. There lies a need to detect parameters that affect COP progression of the foot and gait stability due to footwear. RESEARCH QUESTION: Do we have bipedal models that can estimate gait parameters corresponding to different center of pressure (COP) trajectories? METHOD: In this study, we propose a COP translation model that can account for non heeled to heeled footwear. We describe the COP progression as a function of the center of mass (COM) state. This model is used to generate stable steady state walking solutions for different COP profiles. We compare these model solutions with experimental data on non-heeled and heeled-gait. RESULTS: The bipedal model shows stability across different COP profiles. The model estimates GRF profile (R2=0.83 for 1.3 m/s ) for non heeled normal walking qualitatively and on the temporal scale. It estimates GRF due to heeled gait (R2=0.83 for 1.08 m/s) but is limited in estimation of heeled gait parameters. SIGNIFICANCE: A bipedal model that can generate stable steady state walking solutions for different forward progressing COP profiles can help in design of foot orthotics for patients with gait disorder and understand injuries occurring due to prolonged wear of rigid heeled footwear.

Suspending loads decreases load stability but may slightly improve body stability.

Here, we seek to determine how compliantly suspended loads could affect the dynamic stability of legged locomotion. We theoretically model the dynamic stability of a human carrying a load using a coupled spring-mass-damper model and an actuated spring-loaded inverted pendulum model, as these models have demonstrated the ability to correctly predict other aspects of locomotion with a load in prior work, such as body forces and energetic cost. We report that minimizing the load suspension natural frequency and damping ratio significantly reduces the stability of the load mass but may slightly improve the body stability of locomotion when compared to a rigidly attached load. These results imply that a highly-compliant load suspension could help stabilize body motion during human, animal, or robot load carriage, but at the cost of a more awkward (less stable) load.