Abstract
This paper describes the fabrication and initial evaluation of a vibrating platform with two degrees of freedom (DOF) to estimate the human ankle's mechanical impedance in two DOFs; namely dorsiflexion–plantarflexion (DP) and inversion–eversion (IE). The device consists of an actuation and a force plate module. The actuation module generates torque perturbations up to 168 N·m in DP and 26 N·m in IE in the force plate module using Bowden cables. This provides a low-profile system that can be installed in a walkway. The frame of the force plate module rotates in two DOFs, applying torque perturbations to the human ankle in DP and IE. The ankle's rotations are measured using a motion capture camera system. The analytical and numerical approaches for estimation of the ankle's torques, rotations, and impedances are presented. A system validation using a mockup was conducted to verify the system's ability to estimate the impedance of a physical system in two DOFs. The developed system was capable of identifying the mockup's physical properties up to 15 Hz. The mockup's impedance magnitude at 0.9 Hz using a stochastic identification method was shown to be within 1.68% and 0.54% of the mockup's stiffness in DP and IE, respectively.
Highlights
The human ankle function is significant during walking and standing
This paper presents the design and initial validation of the developed instrumented vibrating platform that is capable of applying torque perturbations to the ankle in two degrees of freedom (DOF)
The results showed that the torque generated by the dynamics of the force plate module frame and springs and the torques generated by the motors were properly decoupled from the force plate measurements and their effects were not present in the impedance estimation
Summary
The human ankle function is significant during walking and standing. During walking, the ankle supports the body weight, generates propulsion, and contributes in stability, while rotating and generating torques in DP, IE, and internal external-internal directions[1]. The developed device expands the functionality of the Perturberator developed by Rouse et al [31] to estimate the time-varying impedance of the ankle in both DP and IE by applying torque perturbations to the ankle in those two DOFs. The paper describes the hardware and analytical methods for estimation of the impedance of the human ankle in two DOF. It first describes in detail the design and fabrication of the instrumented vibrating platform It discusses the evaluation of the developed system using an ankle-foot mockup to demonstrate the capability of the system and the developed protocols in identifying the mechanical impedance of a physical system in two DOFs. The analytical methods to calculate the ankle torques and angles based on the information obtained from the force plate and camera system are explained. The stochastic identification method that was used for impedance estimation of the anklefoot mockup based on the ankle angles and torques is presented
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