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Team Members

  • Jaehyun Bae

Motivation

DARPA Warrior Web Program

  • There has a been a lot of research into exoskeletons over the years to alleviate heavy loads that soldiers should burden, but strapping a person into a robotic outfit just isn't practical in a combat zone yet.
  • DARPA's Warrior Web program aims to build a lightweight suit that improves a soldier's endurance and overall effectiveness, while preventing injuries.
  • The main goals by developing the warrior web are
    1. To prevent and reduce musculoskeletal injuries. 
    2.  To augment positive work done by the muscles and reduce the physical burden

Harvard Exosuit


  • In order to develop an under-suit that doesn’t interrupt wearer’s free movement, researchers are trying to make it soft and deformable, but still capable of applying force to body joints.
  • Harvard Biodesign group, one of a project groups in this program, is trying to make their warrior web suit soft and light, and they call their suit harvard exosuit.
  • Experimental data proved that it can help loaded walking by reducing metabolic costs.

Challenges

  • it is difficult to analyze the effectivness of exist
  • It is difficult to find the optimal input force for actuators to reduce the metabolic cost
  • It is difficult to identify the effect of change of design parameters
  • The reasons for the challenges are
    1. The under-suit may be soft and deformable
    2. Hard to identify how external actuation assists loaded gait.
    3. Experimental metabolic cost data is inconsistent case by case

Project Goals

Through this project, I tried to resolve the challenges in developing exosuit with Opensim simulation. Simulation can help developing soft wearable exosuit as it can gives an intuition on how exosuit help muscles, and what are the key features that one should care about when developing the suit.

I hope this project construct a systematic way of analyzing and designing exosuit.

•Evaluate the effectiveness of wearing active actuator on metabolic cost reduction during loaded walking.
•
•Explain how exosuit can help loaded gait.
•
•Verify the impact of changes in design parameters.
•
•Find optimal control inputs for exosuit actuators.

Strategy

Experimental data

Two different types of data was collected from a same subject. 

One gait cycle of loaded walking (From left toe off to next left toe off)

One gait cycle of unloaded walking (From left toe off to next left toe off)

For both data, walking speed is identical, and loaded weight was 38kg. 

Modeling

  • How to model a subject wearing active actuator


    The diagram 

  • Sample models

Optimization process

The idea to optimize the control input force for the actuator is to take advantage of the optimization procedure in CMC tool. CMC procedure. CMC procedure contains static optimization process, and it tries to minimize the cost function J which can be represented as

When there is active actuators on OpenSim Model, the activation term in cost function becomes

and,

 

Assign large value of maximum force to each actuator to reduce the size of xactuator, so that the influence of actuator to J is diminished.

Result & Discussion

Metabolic cost change

 

Loaded walkingUnloaded walking

 

 

 

 

 

Optimal actuator input

 Loaded walkingUnloaded walking
Ankle actuator
Hip actuator

 

 

Analysis of optimal input force for ankle actuator

Best realistic actuation input force for ankle actuator

Biarticular actuator

Model

Simulation result

Discussion

Conclusion

Featured result

•Both hip actuator and ankle actuator can reduce the metabolic cost during walking
–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
•
•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 force
•
•Biarticular actuator doesn’t assist loaded walking very well and the force input is not consistent.
•
•
•
•Both hip actuator and ankle actuator can reduce the metabolic cost during walking
–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
•
•Optimal input of ankle actuator is consistent with gait cycle and muscle forces data, while that of hip actuator is not.
•
•The simulation methodology to use CMC as an optimization tool works, but more improvement is needed.
•
•Longer MA magnifies the effectiveness of Exosuit
•
•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 force
•
•Exosuit offers greater assist for loaded walking than unloaded walking
•
•Biarticular 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.
•
•CMC process doesn’t minimize metabolic cost. Instead, it minimizes 2-norm of activation.
•
•The experimental data is 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 used

References

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OpenSim is supported by the Mobilize Center , an NIH Biomedical Technology Resource Center (grant P41 EB027060); the Restore Center , an NIH-funded Medical Rehabilitation Research Resource Network Center (grant P2C HD101913); and the Wu Tsai Human Performance Alliance through the Joe and Clara Tsai Foundation. See the People page for a list of the many people who have contributed to the OpenSim project over the years. ©2010-2024 OpenSim. All rights reserved.