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. 2022 Jan 11:15:790060.
doi: 10.3389/fnbot.2021.790060. eCollection 2021.

Control Framework for Sloped Walking With a Powered Transfemoral Prosthesis

Namita Anil Kumar  1 , Shawanee Patrick  1 , Woolim Hong  1 , Pilwon Hur  2
Affiliations

Control Framework for Sloped Walking With a Powered Transfemoral Prosthesis

Namita Anil Kumar et al. Front Neurorobot. .

Abstract

User customization of a lower-limb powered Prosthesis controller remains a challenge to this date. Controllers adopting impedance control strategies mandate tedious tuning for every joint, terrain condition, and user. Moreover, no relationship is known to exist between the joint control parameters and the slope condition. We present a control framework composed of impedance control and trajectory tracking, with the transitioning between the two strategies facilitated by Bezier curves. The impedance (stiffness and damping) functions vary as polynomials during the stance phase for both the knee and ankle. These functions were derived through least squares optimization with healthy human sloped walking data. The functions derived for each slope condition were simplified using principal component analysis. The weights of the resulting basis functions were found to obey monotonic trends within upslope and downslope walking, proving the existence of a relationship between the joint parameter functions and the slope angle. Using these trends, one can now design a controller for any given slope angle. Amputee and able-bodied walking trials with a powered transfemoral prosthesis revealed the controller to generate a healthy human gait. The observed kinematic and kinetic trends with the slope angle were similar to those found in healthy walking.

Keywords: biomedical; impedance control; rehabilitation; sloped walking; transfemoral prosthesis control.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1
Gait cycle with important kinematic moments used as switching conditions in a finite state machine.
Figure 2
Figure 2
Basis joint parameter functions: panels (A1,B1) represent the ankle stiffness (Nm/rad/kg) and damping (Nm/rad/kg) basis functions, while panels (A2,B2) are the corresponding weights. Panels (C1,D1) represent the knee stiffness (Nm/rad/kg) and damping (Nms/rad/kg) basis functions, while panels (C2,D2) are the corresponding weights.
Figure 3
Figure 3
Experimental set up: panel (A) is the powered transfemoral prosthesis, AMPRO II, panel (B) shows the amputee walking with AMPRO II in a motion capture environment.
Figure 4
Figure 4
Amputee results for upslope walking and downslope walking. The subfigures labeled (A) correspond to the AMPRO II ankle joint, (M) are for the Microprocessor knee prosthesis.
Figure 5
Figure 5
Able-bodied subject results for upslope walking and downslope walking. The subfigures labeled (U) correspond to the upslope walking, while those labeled (D) are for downslope walking.
Figure 6
Figure 6
Peak ankle push-off power experienced by the amputee with the microprocessor knee and AMPRO II. Also shown is the peak push-off power experienced by the able-bodied subject with AMPRO II.
Figure 7
Figure 7
Amputee results for level walking with AMPRO II at different speeds. The subfigures labeled (A1,A2) correspond to the ankle, while those labeled (K1,K2) are for the knee.
See this image and copyright information in PMC

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