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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.
- This actuation scheme is valid for both loaded gait and unloaded gait.
- This This force signal is clear and easy to implement in 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
- 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.
- Also, it is difficult to implement the optimal control input for hip actuator in real world
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I could explain how the optimal actuation input for ankle actuator could help loaded gait by investigating the change of plantar flexor muscle forces
- The gastrocnemius muscle forces
- are barely changed.
- Other plantarflexor muscle forces, including Soleus muscle forces, are significantly decreased.
- 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.
To sum up, we can say that ankle actuator assists uniarticular muscles during loaded walking.
Ankle actuator assists uni-articular muscles during loaded walking.
Best realistic actuation input force for ankle actuator
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Optimal input force when actuation force is limited to 400N
From the previous results, we found that the optimal force for hip actuator is small enough to be achieved by real actuator
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•On the other hand, the maximum force of the optimal force input , while the optimal input force for ankle actuator is not achievable. (>2000N)
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•Project Approach: Try different . Therefore, I tried different types of input forces for ankle actuators up to 400N, and compare the results to optimal control input case.
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•Run CMC after setting the actuator input forces as a control constraints for each case.
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My initial guess was to saturate the optimal input force that I found earlier at 400N.
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I generated an new input force which is identical to optimal input force
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up to 400N, and
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saturated once optimal input force exceeds 400N.
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And then, I run CMC after setting the actuator input forces as a control constraints
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for each case.
I compared the saturated optimal input to a new CMC results which was acquired with 4000N maximum actuation force and bounded control input between 0 and .1. The new CMC results also has maximum force of 400N as the control input is bounded, and it gives better input force in terms of metabolic cost reduction than a result of CMC which was acquired with an actuator with 400N actuation and conventional control input.
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In these graphs, you can see a similaritly between the saturated optimal input and a results of new CMC procedure.
Metabolic cost reduction
| Loaded walking | Unloaded walking |
|---|---|
 |  |
•Loaded walking
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