Effect of Joint Friction Compensation on a “Muscle-First” Motor-Assisted Hybrid Neuroprosthesis

Frontiers in Neurorobotics, 2020 · DOI: 10.3389/fnbot.2020.588950 · Published: December 11, 2020

Assistive Technology Neurology Biomechanics

Simple Explanation

This study explores how much energy people use when walking with a special device. This device helps people with weak muscles walk by combining electrical stimulation with a motorized exoskeleton. The main idea is to let the person's own muscles do as much of the work as possible, with the device only helping when needed. The device adds some resistance at the hip and knee joints. The study found that reducing the friction in the device's joints helps people use less energy when walking. This means that the device works better when it doesn't resist the person's movements.

Study Duration

Not specified

Participants

Six able-bodied subjects

Evidence Level

Original Research

Key Findings

1
Friction compensation reduced metabolic consumption while walking in the exoskeleton.
2
There was an average decrease of 8.8 ± 12.4 % while walking with friction compensation.
3
Peak swing phase knee angle increased by an average of 15.6 ± 7.7◦during friction compensation

Research Summary

This study assessed the metabolic energy consumption of walking with the external components of a “Muscle-First” Motor Assisted Hybrid Neuroprosthesis (MAHNP), which combines implanted neuromuscular stimulation with a motorized exoskeleton. Oxygen consumption was measured on six able-bodied subjects performing 6 min walk tests at three different speeds (0.4, 0.8, and 1.2 m/s) under two different conditions: one with the motors producing no torque to compensate for friction, and the other having the motors injecting power to overcome passive friction based on a feedforward friction model. Average oxygen consumption in the uncompensated condition across all speeds, measured in Metabolic Equivalent of Task (METs), was statistically different than the friction compensated condition. There was an average decrease of 8.8% for METs and 1.9% for heart rate across all speeds.

Practical Implications

Enhanced Exoskeleton Design

Minimizing joint friction in hybrid neuroprostheses can significantly reduce metabolic energy expenditure, making these devices more efficient and practical for users.

Improved Gait Kinematics

Friction compensation leads to gait patterns that more closely resemble natural walking, suggesting improvements in the comfort and effectiveness of the device.

Future Research Directions

Further studies should focus on other factors contributing to metabolic cost, such as gravity compensation and sagittal plane constraints, to optimize hybrid neuroprosthesis design and control.

Study Limitations

1
Peak knee angular velocities were 262.3 ± 93.1 ◦/s, about 60◦ faster than the conditions for deriving the friction compensation model.
2
Friction compensation was not found to have a significant effect on heart rate, and this is possibly due to high variability in metabolic steady state heart rate between subjects.
3
The small number of participants limits the study’s ability to evince general trends that may be exhibited in a larger population

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