View Source

Team Members

Jaehyun Bae

Motivation

DARPA Warrior Web Program

OpenSim Documentation > Modeling, Evaluation, and Control Optimization of Exosuit with OpenSim > DARPA.png

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 exosuit
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.

Goals

Through this projects, I would like to

Project Goals

Through this project, I tried to resolve the challenges in developing exosuit with Opensim simulation. Simulation can help developing exosuit because

It can help systematic analysis

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

Sample models

OpenSim Documentation > Modeling, Evaluation, and Control Optimization of Exosuit with OpenSim > LoadedModelSample.png

OpenSim Documentation > Modeling, Evaluation, and Control Optimization of Exosuit with OpenSim > UnloadedModel2.png

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

J = \sum_{i=1}^{n_x} x_i^2 + \sum_{j=1}^{n_q} w_j \left( \ddot{q}_j\,^* - \ddot{q}_j \right)^2

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

x = \begin{bmatrix} x_{muscle} \\ x_{actuator} \end{bmatrix}

and,

F_{actuator} = F_{actuator}^{max} \times x_{actuator}

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

Metabolic cost change

Loaded walking	Unloaded walking

Team Members

Motivation

DARPA Warrior Web Program

Harvard Exosuit

Challenges

Goals

Project Goals

Strategy

Experimental data

Modeling

How to model a subject wearing active actuator

Sample models

Optimization process

Result

Metabolic cost change

Optimal actuator input

Analysis of optimal input force for ankle actuator

Best realistic actuation input force for ankle actuator

Discussion

Conclusion

References