Mechanical Engineering in Action

Joshua Petry just completed his junior year at Northwestern and is on track to graduate next spring with a degree in mechanical engineering. He came to Northwestern as a PSEO student and decided to continue as a traditional student in the School of Science and Engineering; his three older siblings are Northwestern alums, and although he was open to going somewhere else for college, his time here as a PSEO student helped to make up his mind.

Petry is in the honors program which has allowed him to do some extraordinary things. At a high level, students who participate in this are given an extra push to expand their learning by doing additional labs, research, calculations, and a project for an enhanced engineering experience. According to Joshua, two years of PSEO were helpful because they enabled him to work through Northwestern’s general requirements, giving him more time to focus on the intensive engineering classes in his junior and senior years, as well as the honors program.

When it came time for Joshua to decide what he wanted to focus on for his honors design project, it was an easy choice because he’s always been fascinated with prosthetics. To him, this field is a good way to display the gospel because something is being restored or redeemed that a person either lost in an accident or was born without. In his words,

“When someone has been injured and lost function, it’s so cool to be able to explore God’s creation of the hand and try to design something that mimics it to restore function.”

His advisor and one of his professors, Dr. Siu-Yue Tam, has been a phenomenal resource and guide for him as he’s been digging into this project. She connected him with two people with missing finger segments for whom he could create a device to restore some functionality.

The first voluntary participant was born without some of the segments of varied fingers across both hands. Joshua asked her, “What is something you just can’t do?” She responded: “Not all of my fingers reach the keys of a keyboard.” And his work in prosthetics began—gathering design inspiration by researching what’s currently on the market, designing a prototype, producing it via a 3D printer, assembling the device, testing it, adjusting the force necessary to type through calculations, modifying the design, printing the updated prototype, testing it, etc., until an effective design is reached.

The second participant, however, had a different need, having lost a portion of his pointer finger and the proximal stubs of his two middle fingers in a table saw accident 20 years ago. Although he has since adapted to this loss of function, sometimes without thinking, he will grab for something with that hand, unsuccessfully, of course. The prototype design for this would need to be different than the one for the first participant as Petry further understood that there is a motion component of the wrist connected to the finger function. For example, this is needed along with grip strength for grabbing a glass. Additionally, specific measurements were needed to create a prosthetic to fit him perfectly, taking into account the lengths of his other uninjured hand’s fingers and grip strength.

Joshua needed a 3D scanner to capture exact measurements for custom parts. With guidance from Dr. Tam, he researched 3D scanners and selected one for the project. But there was one more obstacle to be addressed: how to capture the entire hand without interrupting the scanner.

As a young boy, in addition to his inquisitive nature of wanting to understand how things worked, Petry loved building with Legos. Tapping into this hobby, he developed a stand for the 3D scanner that rides along a circular track to capture a 360-degree image of whatever is placed in the center. This was a perfect solution to capture the measurements needed for Client 2. The 3D images captured are then placed into CAD software so that precise measurements can be gathered.

Joshua hopes to continue work on these projects next year. The design process for prosthetics is extremely time-intensive because each detail is extremely individualized in both measurement and maneuverability. In addition to creating a fine-tuned prototype, time must be made to consult with each individual so they can try on the device and determine what further modifications are required. For some, this may seem too tedious a process; however for Joshua, it’s serving people by creating something that will restore lost function.  

According to Petry, “Designing prosthetics is a tangible way to help someone, and it would be a dream goal of mine to go into that field.” His favorite parts of the process have been meeting clients, designing, working with CAD, printing, and assembling prosthetics so that function can be restored. When he’s stuck in the design process, he goes to the Ultimate Engineer of the human body, God Himself, to ask for understanding. Not too long ago, after he had been in prayer about how to make something work, God gave him clarity.

“For the LORD gives wisdom;
From his mouth come knowledge and understanding…”
– Proverbs 2:6 (ESV)

If the field of prosthetics is what God has fashioned Joshua for, his honors project has started him on the path to realizing this dream. Petry is a very humble man; however, it would be remiss not to include that, according to Dr. Tam, Joshua’s level of design rivals the ongoing work of engineering students at a top-20 elite institution.

Keep up the great work, Joshua. We’re proud of you!