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Strategy
Experimental data
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For both data, walking speed is identical, and loaded weight was 38kg.
Modeling
How to model a subject wearing active actuator
Add explanation here- The diagram
Sample models
Loaded gait model
Add explanation here
Unloaded gait model
Optimization process
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| Loaded walking | Unloaded walking | ||||||||
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Loaded walking
I put together the metabolic cost changes in loaded gait case and unloaded walking case
The first thing to notice is that the metabolic cost is much lower during unloaded walking than loaded walking. Loaded walking costs only 75% metabolic energy compared to loaded walking. Also, we can see that ankle actuator works better to reduce metabolic cost than hip actuator, especially in loaded walking case.
In loaded walking case, ankle actuator reduces metabolic cost by 10%, while hip actuator reduces it by about 7%.
On the other hand, in unloaded walking case, ankle actuator reduces metabolic cost by 10%, while hip actuator reduces it by 1%.
Therefore, we can say that ankle actuator helps metabolic cost reduction better than hip actuator if we have an optimal actuator which has no maximum force limitation.
Optimal actuator input
| Loaded walking | Unloaded walking | |
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| Ankle actuator |  |  |
| Hip actuator |  |  |
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.
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
If we draw the sum of baseline uniarticular forces and active actuator input force together, we can see that the active actuator force follows baseline uniarticular muscle forces. The redline here is sum of baseline uniarticular forces and blue line is active actuator input force. 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.
Best realistic actuation input force for ankle actuator
Biarticular actuator
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| Loaded walking | Unloaded walking |
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ModelBiarticular actuator
Simulation result
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Conclusion
Featured result
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You can find the model that I used in htt~~~~