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. 2022 Oct:2022:9660-9667.
doi: 10.1109/iros47612.2022.9982037. Epub 2022 Dec 26.

Data-Driven Variable Impedance Control of a Powered Knee-Ankle Prosthesis for Sit, Stand, and Walk with Minimal Tuning

Cara G Welker  1 , T Kevin Best  1 , Robert D Gregg  1
Affiliations

Data-Driven Variable Impedance Control of a Powered Knee-Ankle Prosthesis for Sit, Stand, and Walk with Minimal Tuning

Cara G Welker et al. Rep U S. 2022 Oct.

Abstract

Although the average healthy adult transitions from sit to stand over 60 times per day, most research on powered prosthesis control has only focused on walking. In this paper, we present a data-driven controller that enables sitting, standing, and walking with minimal tuning. Our controller comprises two high level modes of sit/stand and walking, and we develop heuristic biomechanical rules to control transitions. We use a phase variable based on the user's thigh angle to parameterize both walking and sit/stand motions, and use variable impedance control during ground contact and position control during swing. We extend previous work on data-driven optimization of continuous impedance parameter functions to design the sit/stand control mode using able-bodied data. Experiments with a powered knee-ankle prosthesis used by a participant with above-knee amputation demonstrate promise in clinical outcomes, as well as trade-offs between our minimal-tuning approach and accommodation of user preferences. Specifically, our controller enabled the participant to complete the sit/stand task 20% faster and reduced average asymmetry by half compared to his everyday passive prosthesis. The controller also facilitated a timed up and go test involving sitting, standing, walking, and turning, with only a mild (10%) decrease in speed compared to the everyday prosthesis. Our sit/stand/walk controller enables multiple activities of daily life with minimal tuning and mode switching.

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Figures

Fig. 1.
Fig. 1.
A diagram of the high-level control FSM that dictates transitions between walking and sit/stand modes, determined by the thigh angle θt and angular velocity ωt, knee angle θk, and foot ground contact (FGC). We use these signals to detect prosthetic-side heelstrike or late stance to transition to walking. We transition to standing when the user is stationary with prosthesis ground contact, a vertical thigh, and an extended knee.
Fig. 2.
Fig. 2.
Final optimal trajectories for stiffness, damping, and equilibrium angle for the knee and ankle joint are plotted during the sit-to-stand motion with respect to the phase variable of normalized thigh angle. Positive equilibrium angles correspond to knee flexion and ankle dorsiflexion. Phase is 0 while sitting and 1 while standing.
Fig. 3.
Fig. 3.
Photos of the participant practicing sit/stand symmetry with the powered prosthesis during training. The bar on the screen depicted the real-time loading symmetry between the left and right foot. When the loading symmetry was outside the recommended range (± 15%), the bar turned yellow and then gradually red as it moved away from the centerpoint.
Fig. 4.
Fig. 4.
Comparisons between the behavior of our controller implemented on the powered prosthesis during relaxed sit/stand motions to the mean able-bodied data used in the impedance model development [31]. (a) Trajectory of the phase estimate, determined by normalized thigh angle. (b) Kinematic data at the knee and ankle joint. (c) Kinetic data at the knee and ankle joint. Shaded regions represent ±1 standard deviation.
Fig. 5.
Fig. 5.
Vertical loading for the biological and prosthetic leg over time is shown for the relaxed condition of both sit-to-stand and stand-to-sit. Although peak loading asymmetry is similar between the passive and powered prostheses, the powered prosthesis enables the user to reach symmetry more quickly for both sit-to-stand and stand-to-sit.
See this image and copyright information in PMC

References

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