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Here are the figures of sample simulation models. I modified the RRA-adjusted model to create several different types of models for comparison.
Loaded gait models
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The path actuator supporting plantarflexion is attached to the heel and tibia, and the path actuator supporting hip extension is attached to the backpack and femur. For simplicity, the loaded mass was added directly to the torso.
Unloaded gait models
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Loaded walking | Unloaded walking | ||||||||
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- Metabolic cost reduction when active actuators are added to the loaded gait model:
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Loaded walking | Unloaded walking | |
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Ankle actuator | ||
Hip actuator |
Optimal input force for the ankle actuator:
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We can explain how the optimal actuation input for the ankle actuator helps loaded gait by investigating the change of plantarflexor muscle forces.
- The gastrocnemius muscle forces barely change.
- Other plantarflexor muscle forces, including soleus muscle forces, are significantly decreased.
- If we compare the active actuator input force with the sum of the baseline uniarticular forces, we can see that the active actuator force follows the sum of the baseline uniarticular muscle forces.
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Loaded walking | Unloaded walking |
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- Metabolic cost reduction when active actuators are added to loaded gait model:
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Now that we know both the ankle actuator and the hip actuator can reduce metabolic cost during loaded walking, a natural progression is to test actuators which can affect both ankle plantarflexion and hip extension. To reduce the number of actuators, I added single-degree-of-freedom biarticular actuators affecting ankle plantarflexion and hip extension to legs on both sides, and investigate the metabolic cost. The main idea in creating a biarticular actuator is to let the path actuator go through the axis of ankle joint rotation. I chose the attachment points of the ankle and hip actuators as the via points and end points of the biarticular actuator line, and also set the origin of the ankle joint rotation as one of the via points. By doing so, I created a biarticular actuator which combines the effects of the ankle and hip actuators.
Simulation result
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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 the reduction observed using either the ankle or hip actuator.
- Control input is complex, which makes it hard to realize.
- The biarticular actuator is not as effective as the uniarticular actuators in terms of metabolic cost reduction.
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