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

Abstract

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.

Validation of an Instrumented Walkway Designed for Estimation of the Ankle Impedance in Sagittal and Frontal Planes

“…This paper describes the continuation of the authors' work presented in [1] and validates the capability of the system to obtain the ankle time-varying impedance properly. First, the construction of the Instrumented Walkway presented in [1] is briefly described. Next, the construction of a mockup with mechanical characteristics similar to the human lower leg and active time-varying stiffness is described.…”

“…An Instrumented Walkway was designed and fabricated for estimation of the ankle mechanical impedance during walking in arbitrary directions [1]. The Instrumented Walkway consists of vibrating platform (Fig.…”

“…This range was chosen so the pre-load of the springs assure the springs are on their linear range of operation. The stiffness was estimated as described in the previous work, where stochastic methods were used to estimate the mechanical impedance of the mockup [1].…”

“…The data was sampled at 300 Hz by the camera system, and the force plate sampled the reaction force at 7200 Hz (down-sampled to 300 Hz in post-processing to match the camera system data). The impedance was calculated based on the angles and torques of the mockup, similar to the method described in previous work [1]. In summary the admittance Y(f) is defined as a transfer function correlating torque inputs τ(f) to displacement outputs θ(f):…”

“…Previous work developed by the authors described the design and fabrication of an Instrumented Walkway capable of continuously applying pseudo-random perturbation to the ankle in two DOFs during the entire stance phase of the gait [1]. The developed vibrating platform to be used in the Instrumented Walkway does not require the user to wear or carry any actuator other than reflective markers for motion capturing using a camera system.…”