The Human Dynamics & Controls Lab (HDCL) focuses on improving mobility through the development of assistive devices. As an undergraduate researcher, I was part of the Portable Powered Ankle Foot Orthosis (PPAFO) team. For individuals who have weakened muscles below the knee, the PPAFO provides torque assistance during various phases of the gait cycle. Our group worked closely with individuals who had suffered from a stroke or had Parkinson's Disease.

During my time in the lab, I provided 3D modeling skills and also assisted my graduate mentor with conducting various studies of the PPAFO. I ran a study to test the number of steps which could be taken under varying setup conditions of the PPAFO. Finally, I worked a project to address the need to capture ankle angle in a mobile lab setting, for example at nursing homes.

Modeling the System

I modeled the PPAFO device using PTC Creo to develop imagery for lab presentations, and improve the lab's ability to visualize future iterations of the design in CAB. It was also a fantastic way for me to gain a better understanding of how the PPAFO system functioned.

PPAFO Longevity Study

Increase Walking Assistance

The walking assistance provided by the PPAFO is limited by the size of the pressurized CO2 source. An improved design added the ability to recycle compressed air allowing for increased walking time.

Putting the Design through its Paces

Testing considered three variables: CO2 bottle size, controller type, and pneumatic circuit configuration. The goal was to determine how many steps could be taken when considering different variables.

Recycling for the Win

Depending on the controller type used, longevity increased between 20%-50%.

PPAFO Longevity Study Results

PPAFO without Energy Capturing

PPAFO with Energy Recycling

Portable Ankle Angle Capture Device (PAAC)

PAAC Testing

Why measure ankle angle?

Standard motion capture systems cannot be easily transported. An understanding of an individual’s range of motion about the angle is a key data set needed when studying the PPAFO.

Design Goals: Portable & Low Cost

I developed various designs using PTC Creo. Based on the design criteria, one design was selected for initial prototyping.

Verify Accuracy

I tested the PAAC design in conjunction with a motion capture system to determine sensor correlation to current standards of motion capture.


Initial testing of the PAAC successfully produced ankle angle read outs but also indicated there was room for improvement in the design. One area for design improvement was the attachment method to the foot and shin which had a tendency to shift during testing. The ankle angle readout also varied slightly from the motion capture results which indicated that the Matlab program needed refining. At the end of the year, the work I had started was passed on to a summer research student to further the project.

PAAC Design Options

Paper Prototype

Plastic Prototype