Abstract
In order to improve the life quality of lower extremity amputees, many researchers have studied the powered knee-ankle prosthesis. Various parameters must necessarily be adjusted for the finite state machine impedance model method. Hybrid zero-dynamic (HZD) assumptions are ideal, and with this method measurement information of existing sensors can be limited. The virtual constraint method offers better comprehensive performance at present and can realize the continuous control for the whole gait cycle. The problem with virtual constraint is mainly the selection of phase variables. The joint trajectory of the virtual constraint is derived from a healthy individual, but the joint trajectory of the amputee’s normal walking is difficult to obtain. In response to the above problems, this paper proposes an instinctive human joint trajectory, selecting the phase variable associated with the hip joint angle and angular velocity. The Fourier transform solves the expression of the joint trajectory, and the virtual constraint unifies the control method of the entire gait cycle. The simulation results prove the feasibility of the scheme.
Highlights
According to the relevant literature and the data of the Amputee Coalition and the Stroke Center [1,2,3], it is clear that the problems of restoring normal life functions for the lower extremity amputee continue to require additional study
The finite state machine impedance control method divides the human gait into four stages: early stance period, late stance period, early swing period, and late swing period [7]
A prosthesis based on Hybrid zero-dynamic (HZD) control assumes that the bipedal model is in contact with the ground on only one leg stance [8,9,10], i.e the gait stance period and the swing period respectively account for 50% of gait cycle
Summary
According to the relevant literature and the data of the Amputee Coalition and the Stroke Center [1,2,3], it is clear that the problems of restoring normal life functions for the lower extremity amputee continue to require additional study. The key problem of the virtual constraint is the selection of the phase variable and the method of parameterizing the joint trajectory on the unified control of the powered knee-ankle prosthesis. The method of parameterizing the joint trajectory by the phase variable is mainly the Bezier curve and the discrete Fourier transform. For existing virtual constraint control [11,13,14,15], the lower limb joint trajectory is derived from healthy individuals. The joint trajectory is obtained by a Bezier piecewise fitting using the joint trajectory of a healthy individual This process can adjust the shape of the curve depending on demand. The virtual constraint system uses discrete Fourier transform methods to ensure the periodic continuity of the joint trajectory.
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