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Team Member
- Jaehyun Bae
Project overview
Motivation
DARPA Warrior Web Program
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Metabolic cost change when active actuators are added to model
First, I investigated how much metabolic cost is reduced when active actuators are added to a model, and optimal input force is applied to actuators. I did simulation for both loaded and unloaded walking cases, and I compared the influence of hip actuator and ankle actuator to metabolic cost reduction.
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| Loaded walking | Unloaded walking | |
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| Ankle actuator |  |  |
| Hip actuator |  |  |
Optimal input force for Ankle actuator
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- Actuation is started right after the toe-off of a foot on the opposite side, and the peak force occurs 7.12% of gait cycle before toe off, and ends at the toe-off of a foot on the same side.
In hip actuator case, the optimal input force is very complex, and I could not find any intuition from it. My initial guess on the optimal input force of hip actuator was to follow the hip flexion angle change, but the result doesn’t follow it at all. The complexity may be due to the optimization procedure in CMC, and I will try to figure out the reason in a future. However, the good thing about hip actuator is that it doesn’t require large amount of force to reduce the metabolic cost. The maximum force in this optimal input is about 400N, which is significantly lower than ankle actuator input, and it is achievable.
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- This actuation scheme is valid for both loaded gait and unloaded gait
This force signal is clear and easy to implement real world. However, the maximum actuation force is about 2500 N, which is too high, so we need to deal with it if we want to use this profile.
Optimal input force for Hip actuator
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- Hip actuator can reduce the metabolic cost with lower maximum force than ankle actuator.
- However, it is hard to identify how the actuator assists walking.
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- Also, it is difficult to implement the optimal control input for hip actuator in real world
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Unloaded walking
This is the optimal input force result in unloaded case. Still, you can see that ankle actuator input profile is clean and goes well with our intuition, but hip actuator input profile isn’t.
Analysis of optimal input force for ankle actuator
This result shows how muscle force changes when a model has ankle actuators. The graphs show plantar flexor muscle forces, and first row is muscle forces of a baseline model, and the second row is the muscle forces of a model with ankle actuator.
The red line is The muscle forces of gastrocnemius, and it barely change when ankle actuators are added. However, other muscle forces, which are from uniarticular muscles, are significantly decreased. Therefore, we can say that ankle actuator assists uniarticular muscles during loaded walking
I could explain how the optimal actuation input for ankle actuator could help loaded gait by investigating the change of plantar flexor muscle forces
Ankle actuator assists uni-articular muscles during loaded walking.
Best realistic actuation input force for ankle actuator
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