Team Member
Overview
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url | http://www.youtube.com/watch?v=AChL_93DUCw&feature=youtu.be |
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Motivation
DARPA Warrior Web Program
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The main idea to create biarticular actuator is to let the path actuator go through the axis of ankle joint rotation. I chose the attachment points of ankle actuator and hip actuator as the via points and end points of biarticular actuator line, and also set the origin of ankle joint rotation as one of the via points. By doing so, I create a biarticular actuator as a combination of ankle actuator and hip actuator synchronized in series.
Simulation result
I run CMC on loaded gait model with biarticular actuator. I set the maximum force of biarticular actuator to be 10,000N, in order to see the optimal input force and best metabolic cost reduction.
Optimal input | Metabolic cost reduction |
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- Metabolic cost reduction when biarticular actuators are added to loaded gait is 3.12% from baseline. It is much lower than reduction rate of ankle actuator or hip actuator.
- Control input is noisycomplex, which makes it hard to realize
- Biarticular actuator is not as effective as uni-articular actuators in terms of metabolic cost reduction.
Conclusion
- Both hip actuator and ankle actuator can reduce the metabolic cost during walkingThree types of active actuators are evaluated in terms of metabolic cost reduction and controllability
- If we can apply sufficient amount of force, it is better to apply force to ankle joint.
- If not, hip actuator is a good alternative, even though it is hard to control
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- Biarticular actuator doesn’t assist loaded walking very well and the force input is not consistent.
- Active actuators offer greater assist for loaded walking than unloaded walking when we can apply sufficient amount of force
- Optimal input of ankle actuator is consistent with gait cycle and muscle forces data, while that of hip actuator is not.
- The optimal input force for ankle actuator when it’s maximum force is bounded is similar to the general optimal input force saturated at maximum forceBiarticular actuator doesn’t assist loaded walking very well and the force input is not consistent.
Limitations
- The experimental data was obtained from a subject without exosuit. Exosuit may change the kinematics of a subject as well as GRF.
- The simulation methodology to use CMC as an optimization tool works, but more improvement is needed.
- CMC process doesn’t minimize metabolic cost. Instead, it minimizes 2-norm of activation.
- The experimental data is was only one gait cycle.
- More realistic actuator simulation is needed. (E.g. Combination of passive & active actuator).
Source code
You can find the model that I created for the project in SimTK website. You can reproduce the result using the model on the website. Please visit http://www.simtk.org/~~~
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