Multi-directional Dynamic Mechanical Impedance of the Human Ankle; A Key to Anthropomorphism in Lower Extremity Assistive Robots

2014 ◽  
pp. 157-178 ◽  
Author(s):  
Mohammad Rastgaar ◽  
Hyunglae Lee ◽  
Evandro Ficanha ◽  
Patrick Ho ◽  
Hermano Igo Krebs ◽  
...  
Keyword(s):  
Lower Extremity ◽  
Mechanical Impedance ◽  
Dynamic Mechanical ◽  
Assistive Robots ◽  
Human Ankle

scholarly journals Interpretation of the Directional Properties of Voluntarily Modulated Human Ankle Mechanical Impedance

2010 ◽  
Author(s):  
Patrick Ho ◽  
Hyunglae Lee ◽  
Mohammad A. Rastgaar ◽  
Hermano Igo Krebs ◽  
Neville Hogan
Keyword(s):  
Muscle Activation ◽  
Mechanical Impedance ◽  
In Vivo Studies ◽  
General Representation ◽  
Quantitative Characterization ◽  
Ankle Impedance ◽  
Human Ankle ◽  
Electromyographic Recording

This article presents the results of two in-vivo studies providing measurements of human static ankle mechanical impedance. Accurate measurements of ankle impedance when muscles were voluntarily activated were obtained using a therapeutic robot, Anklebot, and an electromyographic recording system. Important features of ankle impedance, and their variation with muscle activity, are discussed, including magnitude, symmetry and directions of minimum and maximum impedance. Voluntary muscle activation has a significant impact on ankle impedance, increasing it by up to a factor of three in our experiments. Furthermore, significant asymmetries and deviations from a linear two-spring model are present in many subjects, indicating that ankle impedance has a complex and individually idiosyncratic structure. We propose the use of Fourier series as a general representation, providing both insight and a precise quantitative characterization of human static ankle impedance.

scholarly journals Estimation of the Two Degrees-of-Freedom Time-Varying Impedance of the Human Ankle

2018 ◽  
Vol 12 (1) ◽  
Author(s):  
Evandro Ficanha ◽  
Guilherme Ribeiro ◽  
Lauren Knop ◽  
Mo Rastgaar
Keyword(s):  
Degrees Of Freedom ◽  
Mechanical Impedance ◽  
Heel Strike ◽  
Time Varying ◽  
Two Degrees Of Freedom ◽  
Impedance Modulation ◽  
Ankle Stiffness ◽  
Human Ankle ◽  
Stiffness And Damping ◽  
And Inversion

An understanding of the time-varying mechanical impedance of the ankle during walking is fundamental in the design of active ankle-foot prostheses and lower extremity rehabilitation devices. This paper describes the estimation of the time-varying mechanical impedance of the human ankle in both dorsiflexion–plantarflexion (DP) and inversion–eversion (IE) during walking in a straight line. The impedance was estimated using a two degrees-of-freedom (DOF) vibrating platform and instrumented walkway. The perturbations were applied at eight different axes of rotation combining different amounts of DP and IE rotations of four male subjects. The observed stiffness and damping were low at heel strike, increased during the mid-stance, and decreases at push-off. At heel strike, it was observed that both the damping and stiffness were larger in IE than in DP. The maximum average ankle stiffness was 5.43 N·m/rad/kg at 31% of the stance length (SL) when combining plantarflexion and inversion and the minimum average was 1.14 N·m/rad/kg at 7% of the SL when combining dorsiflexion and eversion. The maximum average ankle damping was 0.080 Nms/rad/kg at 38% of the SL when combining plantarflexion and inversion, and the minimum average was 0.016 Nms/rad/kg at 7% of the SL when combining plantarflexion and eversion. From 23% to 93% of the SL, the largest ankle stiffness and damping occurred during the combination of plantarflexion and inversion or dorsiflexion and eversion. These rotations are the resulting motion of the ankle's subtalar joint, suggesting that the role of this joint and the muscles involved in the ankle rotation are significant in the impedance modulation in both DP and IE during gait.

Stochastic Estimation of Human Ankle Mechanical Impedance in Lateral/Medial Rotation

2014 ◽  
Author(s):  
Evandro M. Ficanha ◽  
Mohammad Rastgaar
Keyword(s):  
Degrees Of Freedom ◽  
Muscle Activation ◽  
Transfer Functions ◽  
Linear Time ◽  
Mechanical Impedance ◽  
Linear Time Invariant ◽  
Ankle Impedance ◽  
Human Ankle ◽  
Medial Rotation ◽  
The Difference

This article compares stochastic estimates of human ankle mechanical impedance when ankle muscles were fully relaxed and co-contracting antagonistically. We employed Anklebot, a rehabilitation robot for the ankle to provide torque perturbations. Surface electromyography (EMG) was used to monitor muscle activation levels and these EMG signals were displayed to subjects who attempted to maintain them constant. Time histories of ankle torques and angles in the lateral/medial (LM) directions were recorded. The results also compared with the ankle impedance in inversion-eversion (IE) and dorsiflexion-plantarflexion (DP). Linear time-invariant transfer functions between the measured torques and angles were estimated for the Anklebot alone and when a human subject wore it; the difference between these functions provided an estimate of ankle mechanical impedance. High coherence was observed over a frequency range up to 30 Hz. The main effect of muscle activation was to increase the magnitude of ankle mechanical impedance in all degrees of freedom of ankle.

Instrumented Walkway for Estimation of the Ankle Impedance in Dorsiflexion-Plantarflexion and Inversion-Eversion During Standing and Walking

2015 ◽  
Author(s):  
Evandro M. Ficanha ◽  
Guilherme Ribeiro ◽  
Mohammad Rastgaar Aagaah
Keyword(s):  
Degrees Of Freedom ◽  
Force Plate ◽  
Mechanical Impedance ◽  
Standing Position ◽  
Camera System ◽  
Ankle Impedance ◽  
System A ◽  
Human Ankle ◽  
Applied Forces ◽  
And Inversion

This paper describes in detail the fabrication of an instrumented walkway for estimation of the ankle mechanical impedance in both dorsiflexion-plantarflexion (DP) and in inversion-eversion (IE) directions during walking in arbitrary directions and standing. The platform consists of two linear actuators, each capable of generating ±351.3 N peak force that are mechanically coupled to a force plate using Bowden cables. The applied forces cause the force plate to rotate in two degrees of freedom (DOF) and transfer torques to the human ankle to generate DP and IE rotations. The relative rotational motion of the foot with respect to the shin is recorded using a motion capture camera system while the forces applied to the foot are measured with the force plate, from which the torques applied to the ankle are calculated. The analytical methods required for the estimation of the ankle torques, rotations, and impedances are presented. To validate the system, a mockup with known stiffness was used, and it was shown that the developed system was capable of properly estimating the stiffness of the mockup in two DOF with less than 5% error. Also, a preliminary experiment with a human subject in standing position was performed, and the estimated quasi-static impedance of the ankle was estimated at 319 Nm/rad in DP and 119 Nm/rad in IE.

scholarly journals Control of power-augmenting lower extremity exoskeleton while walking with heavy payload

2019 ◽  
Vol 16 (1) ◽  
pp. 172988141983053 ◽  
Author(s):  
Byunghun Choi ◽  
Changhoon Seo ◽  
Sanghoon Lee ◽  
Byungun Kim
Keyword(s):  
Lower Extremity ◽  
Control Strategy ◽  
Hybrid Control ◽  
Mechanical Impedance ◽  
Torque Control ◽  
Maximum Speed ◽  
Weight Shift ◽  
Gait Phase ◽  
And Control ◽  
Direct Feedback

This article presents a design and control framework for a prototype of lower extremity exoskeleton to enhance the human strength during locomotion. The hybrid control strategy is practically applied according to the two gait phases, that is, stance and swing. The weight shift method based on human’s weight shift information was proposed and implemented to acquire the detection of gait phase. In the stance phase, a stiff virtual wall method is applied to support the entire weight of the exoskeleton while carrying a heavy payload. Direct feedback and feed-forward torque control are used to reduce mechanical impedance in the swing phase. In experiments, to verify the performance of the proposed control strategy, a human subject wearing the prototype of power-augmenting lower extremity exoskeleton was able to walk with a 50-kg (110-lb) payload at a maximum speed of 1.67 m/s (6 km/h). Satisfactory results were obtained with regard to walking experiments with the heavy payload.

scholarly journals Impedance of the Human Ankle During Standing for Posture Control

2018 ◽  
Author(s):  
G. A. Ribeiro ◽  
E. Ficanha ◽  
L. Knop ◽  
M. Rastgaar
Keyword(s):  
Mechanical Impedance ◽  
Posture Control ◽  
Resultant Force ◽  
Order System ◽  
Time Varying ◽  
Ankle Impedance ◽  
Impedance Modulation ◽  
Human Ankle ◽  
Stiffness And Damping ◽  
Antagonistic Muscles

The stiffness and damping of anatomical joints can be modulated by muscle co-contraction, where antagonistic muscles contract simultaneously, increasing both the joint’s stiffness and damping. In a second order system, the mechanical impedance, or simply impedance, is a function of the system’s inertia, damping, and stiffness. The ankle impedance can be defined as the resultant force due to an external motion perturbation. The impedance modulation of the human ankle is required for stable walking. The estimation of the time-varying impedance modulation of the human ankle is the focus of research by different groups [1,2].

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