Prototopea
2012 - 2017
This is LIM Innovations (LIM) flagship prosthetic device: Infinite Socket TF. LIM’s sockets are unique because of their modularity and adjustability. This was the first transtibial socket of its kind. LIM sockets uses a thermoplastic carbon fiber that can be remolded allowing patients to keep the same socket over large volume fluctuations. Additionally, the socket uses an adjustable seat to provide ischial containment to the residual limb granting the prosthesis with greater control.
Over my career at LIM, I worked on four Infinite socket versions and countless subassamblies directly used in the product or for manufacturing purposes.
I started working on this device as an R&D engineer in early 2012 with the rest of the awesome LIM Innovation team! This was a really exciting time because I was able to participate in foundational meetings that created LIM as well as work with industrial designers, engineers, and clinicians.
I contributed by being the onhand CNC machinist and prototyping engineer. I worked on many of the components, including many of the machined metal, plastic, sheet metal, technical fabric, injection molds, casting molds, and carbon fiber.
I engineered over 60+ fixtures for different types of machining, sheet metal, carbon fiber, and technical fabric components/assemblies. Many fixtures served multiple purposes as components required second and third operations for our manufactring process.
I designed, machined, and operated 3 injection molds for a small part run (<300) for use on a Morgan Press 7.5 cu. in. (5 oz.) max. single shot Injection molder.
I machined 300+ metal components for low volume production in preparation for our limited market release.
In late 2014 the device had a limited market release at AOPA (American Orthoic and Prosthetic Association), LIM began selling in much higher volumes. I scaled back some of the in-house manufacturing and began optimizing which components to outsource and finishing (powder coating, anodizing).
For our featured in Wired magazine’s 2014 article titled “FORGET CHEETAH BLADES. THIS PROSTHETIC SOCKET IS A REAL BREAKTHROUGH” I powdercoated all our components with a “Gun Metal” Black and it became an insant hit with our patients!
2015-2016
Modern prosthetic sockets are created by casting patient limbs in plaster then making limb positives. The positives are used to make clinical changes and confirm socket fit before making a finished socket. However, this process can take up to three weeks to create a physical socket!
The Pin Jig is a thermoplastic forming machine used to form components for two modular prosthetic sockets: Infinite Socket TF and Infinite Socket TT.
Each pin is actuated by an overhead CNC machine (not shown) to create a contour. Once the shape is achieved, internal plates lock the pins in place. The pins provide a rigid surface. Heated thermoplastic material is placed on the pin surface and locked in place inside a polycarbonate pressure box. Bladders inside the box pressurize and force the plastic to conform. Viola! Parts!
I completed the project over 10 months and served as the lead mechanical design and fabrication engineer. The project required mechanically designing, machining, and fabricating the entire device from scratch. The goal was to thermoform larger carbon-fiber struts reliability and faster than current methods while making it easily serviced.
Overall, the Pin Jig provided massive time savings compared to the traditional socket fabrication process by creating a complete socket skeleton in <2 hours! An entire socket could be shipped in 3 days! This technology underpinned LIM's fast and unique fabrication process.
An interlocking plate mechanism with an over-molded silicone gasket was used to lock the pins in place. The internal components could be easily machined and swapped in. Additionally, the plate mechanism supported 100 N per pin. This allowed for the device to be scaled up and form larger components. By creating larger components, LIM was able to accommodate larger patients sizes and improve its addressable market.
Lastly, I was able to minimize backlash when locking the pins in place and maintain limb fidelity (<0.5 mm) of the sockets by reaming the assembly as a single piece. High limb fidelity has been correlated with more comfortable sockets and higher product satisfaction.
2016 - 2017
This is the Infinite Socket TT by LIM Innovations for transtibial amputees. This was the first below-knee prosthetic socket developed by LIM Innovations
The two large humps at the brim are molded around the condyles of the knee to provide two points of contact while the rear strut is adjusted by the user with a Boa dial. Two adjustable air bladders can be inflated on either side of the tibial crest. This three-way pinch allows the socket to tighten to the residual limb and prevents rotation of the socket. This socket is unique for transtibial amputees because of its ability to flex but stay rigid enough to support 250 lbs weight.
I worked on the project as an R&D Engineer. In this role, I prototyped and fabricated many of the structural components. After the release of the Infinite Socket TF, our team began to push the limits of my fabrication knoweldge.
To address the largest below-knee population possible, we developed extremely complicated parts to save space. They were so hard to CNC machine and prototype!
Some components required multiple fixtures and realignment between tooling paths. I was constantly fabricating sheet metal components, laser-cut fabrics, carbon fiber components, textile vacuum molds, and urethane molds for various components.
By programming and automating 4-axis CNC mills, waterjets, routers, and laser cutters, I was able to fabricate many of these designs and provide manufacturing feedback.
My contributions allowed our team to understand how to develop many components in-house and optimize components for external manufactures.
This socket was featured in Core77 magazine’s contest Social Impact Award in 2017.
2017
I worked with Chris at You3Dit to create the Balk Box. During this time, I was a self-employed design engineer. I was brought on to help digital design, provide DFM, and run guided FEA simulations with Autodesk Inventor.
The Balk Box was designed to be a lightweight, stackable, and vacuum-sealed tote. With the ability to support an internal vacuum of 1.5 psi. In addition, the client wanted the device to be plastic injection molded at a price of $25 per unit (bottom and lid).
I provided several innovations to this project. I was able to improve its structural integrity by adding a slight wall curvature which improved the second-moment area. The curved wall was stiffer and able to stack however, compared to current totes, the wall would require more plastic.
To validate designs for the lid, I carried out FEA simulations on the interface between the lid, walls, and vacuum inlet. In the simulations, the lid kept experiencing plastic deformation along the interface edges at 1.5 psi. I added ribbing and channels throughout the lid. By optimizing the taper on the lid channels, I was able to provide an adequate stiffness while ensuring the device could still be plastic injection molded and stacked. However, this also added more plastic than current totes.
We were able to develop a feasible design within the scope of the original request. Preliminary testing with a full-scale 3D print showed that the device would work. Using our design and drawings, were able to get our design to a $35 price point. Due to the extra plastic, our device ended up being more expensive at the volume requested by the client.
2020-2021
WORK IN PROGRESS!
I was contracted by a stealth startup to design and prototype a miniaturized ratchet from some of their intellectual property. Over the course of the last year, I worked on this device during my free time and created 2 functional prototypes. There were three main objectives to consider: Size, overall functionality, and locking mechanisms.
As the lead mechanical design and fabrication engineer. I was able to design and sources components to produce an initial functional prototype. The initial prototype, confirm feasibility of the design but highlighted limitations regarding locking mechanisms.
The secondary prototype focus was on the locking mechanism. The ratcheting system served two different purposes on each side. However due to the unique ratchet release, springs were unable to fit. A compliant mechanisms was used instead to serve as a spring.
As this project is ongoing and under confidentially agreement, limited photos and description are shared.
2020 - 2021
Prosthetic Science and Technology Research Lab
Modern prosthetic sockets require methods of socket suspension. The T-Pin is a new socket suspension method design for quick-release on lanyard systems.
I worked on this project while working at Prosthetics Science and Technology Research Lab at the University of Washington as an engineering lead.
This project was an offshoot of the main DOD study being run. The study focused on an electromechanical ratcheting mechanism that would reel a cable attached to the limb into the prosthetic device.
The current system used a bolt with a through-hole to secure the cable. However, this method was difficult for subjects to use because of the small size, repeated twisting, and their inability to see the bottom of their limb when attaching. I was tasked with creating a small device that would replace the threaded bolt component with a quick connecting part.
There were three distinct design problems:
Connection from liner to clip
I used the classic T-nut and T-slot to make the connection from liner to clip. T-nuts are simple locking features that rely on material area and strength. The T-slotting feature could also be placed perpendicular to the load from the cabling system and take advantage of material strength. T-Nut and slots are also easily manufactured with various different methods.
Locking Mechanism
I designed a gate that would rotate around the T-Slot and close the T-slot. Using a torsion spring, it would automatically close the gate. A large benefit of this design is that under many loading conditions, the gate wouldn’t see a bulk of the load. This allowed for the material the be lighter and thinner which helped when selecting a torsional spring.
Clip to Cable
This portion of the design had already been partially developed from the previous system. An end knot was used at the end of the cable as a dead stop. However, the challenge was finding the space. I was able to use the space within the shaft that held the torsional spring in place.
Improved Donning and Doffing
Instron testing ensured the device survived for a minimum of 25 K walking cycles and ensured the device's maximum load is 3x safety factor and a 10x daily use safety factor.
In preliminary testing with users, subjects were able to save almost 30 seconds while doff or donning their device!
