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Team Members

  • Jaehyun Bae

Motivation

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Best realistic actuation input force for ankle actuator

 

•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 for ankle actuator is not achievable. (>2000N)
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•Project Approach: Try different types of input forces for ankle actuators up to 400N, and compare the results to optimal control input case.

•Run CMC after setting the actuator input forces as a control constraints for each case.

As the optimal input force for ankle actuator is not achievable, I tried to find a realistic ankle actuator force which has its maximum force of 400N. My initial guess was to saturate the optimal input force that I found earlier at 400N. Therefore, I cut the optimal input force at 400N, and create new input force. I added this force profile to CMC tool as a control constraints, and run CMC again.

 

 

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.

–The result from new CMC procedure using 4000N Fmax and control input such that 0 ≤ xactuator ≤ 0.1

 

In these graphs, you can see a similaritly between the saturated optimal input and a results of new CMC procedure.

Loaded walkingUnloaded walking
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•Loaded walking
1.optimal: 10.35% reduction
2.Scaled: 1.34% reduction
3.Saturated: 1.84% reduction
•Unloaded walking
1.optimal: 10.62% reduction
2.Scaled: 3.02% reduction
3.Saturated: 3.46% reduction
•Saturated input is better than scaled input for MC reduction.
•Realistic force input can help unloaded walking better than loaded walking.

Discussion

 

•The input force resulted from new CMC works best for metabolic cost reduction
•New CMC result gives a force profile similar to saturated input force.
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ModelBiarticular actuator

Now that we know both ankle actuator hip actuator works well to reduce metabolic cost during loaded walking, the natural progress is to create biarticular actuator which can affect both ankle plantar flexion and hip extension. In order to reduce the number of actuator, I created biarticular actuator with 1 DOF, and see how much it reduces metabolic cost, and what it’s optimal input force is.

Simulation result

 

 

 

 

 

 

 

 

 

Loaded walking- rate of metabolic reduction

1.When ankle actuator is appended: 10.35%
2.When hip actuator V4 is appended: 6.62%
3.When biarticular actuator is appended: 3.12%

Control input is noisy, which makes it hard to realize

Biarticular actuator is not as effective as uni-articular actuators in terms of metabolic cost reduction.

 

Conclusion

Featured result

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