Mobility Lift

Engineering Capstone, Northeastern University

Created in 2018

Progress Bar_test.png

In my senior year of undergraduate study, a project came to the attention of our professors that varied a great deal from the traditional research-lab based prompts. Instead, a family in North Carolina had come to us and said:

"Our 16-year old boy ha Congenital Cytomegalovirus (cCMV) and cannot function on his own. Can you help him?"

The team was myself and four other bioengineering students (with focuses in medical devices and biomechanics). It would be unfair to say the team was just us five students; we had a great deal of support from our faculty adviser, Dr. Jeffery Ruberti, the bioengineering faculty at Northeastern University, and the family we were working with. To protect subject privacy, I will be referring to our 16-year old friend as John. John's primary caregiver is his grandmother who remained enthusiastic and involved throughout the entire project. Together, we worked to create a bespoke solution for a small family wanting to continue doing what they loved.

IMG_20181204_172516.jpg

The team conducted weeks of research and interviews with doctors and specialists to best understand John's condition and what his daily life would look like. A weekly call with his grandmother also helped us paint a picture of what their needs were, but perhaps more importantly, what John's strengths were. Initial brainstorms led us in paths of exploring the joys or music to a self correcting exoskeleton, and from this we landed on two concepts.
1. A device to help correct his 47 degree spinal misalignment

2. A device to help his grandmother pick him out out of the wheelchair.

process.JPG

Sketch showing the original process John's grandmother used to lift him out of his chair. It is a highly physical process and is unsustainable as the grandmother ages and as John gets bigger.

Meetings with surgeons, chiropractors, and even a team of legal risk professionals led us to make the decision to move away from any spinal adjustment device, and down a path of what I will now refer to as a mobility lift. We knew in any design we would have to fit/work around John's current wheelchair (as we could not physically modify it). John's grandmother made the specification that she wanted something that didn't use external power (aka no batteries), and something that she could potentially use on her own. Taking this information, we designed 5 initial proposals shown below in my sketches.

From these proposals, we settled on the bar hinge lift as the most feasible to complete in the remaining time (3 months), and also the safest in terms of initial calculations. We continued to call it the bar hinge lift as it utilizes the same mechanical principles as a bar hinge, popular on the backs of many doors.

One team member took to FEA modeling and projected the tipping angles, counterweights, and friction specs in order to secure the subject's safety with a safety factor of 10. With this safety factor in mind, we began to spec and design the material components of the lift. 

The whole time, we were conscious of the wheelchair and made a decision early on to use telescoping tubing for easy storage and size adjustability.

Bar hinge sketch and foam model for demonstrative purposes

While the team worked on compiling our reports and presentations, I created a quick CAD model of the design. The model was meant to be representative with parts for construction, and to assist visualize the angles that the bars would be optimized at (from calculations and FEA). The model also saw the first visualization of a double band braking system. The brake provides variable braking that increases the friction on a cable system (to prevent buckling) as the angle of the LT and L2. The picture shown on the right calls out the individual subsystems of the design.

a1ec3d47b981029e749aa5f9c610260f.png

CAD renderings of the bar hinge lift. The CAD chair model is to spec dimensions of John's wheelchair after taking measurements of the exact model of wheelchair. The red lines represent a cable system which acts as a safety brake during the transfer.

In the physical construction, I worked on testing the telescoping tubing, creating anchor points for a sling to be hooked on to, and in creating the foot of the device.
We chose a carbon fiber telescoping tubing for the arms of the device for both the safety factor and to save weight. I tested the tubes on an Instron tested in compression as singular tubes as well as in telescoping formation. We discovered a serious slippage in the telescoping formation, which I solved temporarily with a friction tape at the points of the telescoping connectors, and in the long term with a designed cam lock.

The sling anchor points were 3D printed using a carbon fiber blend filament, Onyx. Although the design looks like it could have a stress riser, an FEA with the chosen material dispels this fear within our safety factor.

The foot is there to provide extra stabilization and a person may stand on this part to provide a counterweight (optional, but recommended). I chose to make the foot folding so it may be stored under the base of the wheelchair, as this is the only removable component of the total system. The end of L2 is placed into the foot, and once it is locked in place, the device is ready to use.

When the prototype was finished, the tests with dumb weights were completed (tested with up to 90lb of weight, the weight of John), we had a surprise visit from someone very special.

John and his grandmother were going to load up in the car and drive 16 hours to come and see our work and test it with John's wheelchair. 

There are few words I can say that really explain the joy of getting to meet the family I had only known on the phone for 6-months. Even with John's disability, the love and excitement in his eyes was clear, and his grandmother was ready to get to work with us to suit up John's wheelchair. 

Everything attached as planned and in fact, stored better than we expected. We did not test with John that day, but instead with his actual sling and a series of weights. We were all overjoyed at seeing the device operate, even John who at this point was rolling on the floor making excited noises.

As an added anecdote, we finally saw first hand how the grandmother had to lift John out of his chair and it was more physically taxing than we were lead to believe, with a full on army carry in the process. The grandmother laughed and said, "It's like moving an 85lb sack of wiggly cement."

The prototype has since been signed off in a release to John and his grandmother to use, and may be developed further by local universities or small organizations. Unfortunately our team has been dispersed across the globe and is between school and full time employment. Before graduating, we released the IP rights from the University to our hands and applied for a provisional patent through the University. The university did not accept (fund) our provisional patent application, but the sketches below show some possible thoughts on how this lift could be used in hospital beds to aid in lifting patients.