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Introduction
Introduction
The objective of this design project was to create an assistive grabber device for an elderly female patient at the Mason-Wright Retirement Community in Springfield, MA. The goal of our design was to provide a grabber that is sturdier than the current grabber of our patient and also to add a unique arm cuff component. The sturdier design allows our patient to grab heavier objects and the arm cuff component reduces stress on our patient’s hand. As my group's Analysis Lead, I was responsible for concept development and used finite element analysis to analyze the different designs.
Prototype
Prototype
The grabber’s claws are made out of aluminum and the body is carbon fiber, allowing for a lightweight but strong design. The grabber has a handle, which when pulled, closes the claws around the object being grabbed. Cables connect the claws to the handle through the hollow grabber body. Compression springs reset the claws to the open position when the handle is released. The arm cuff rests on the forearm, balancing the moment of the object in the claws. Though the prototype has 3D printed claw components, the final product would require the strength of aluminum claw components.
Calculations
Calculations
[1] Handgrip strength norms. Retrieved 4/30, 2019, from https://www.topendsports.com/testing/norms/handgrip.htm
[2] Friction and friction coefficients. Retrieved 4/30, 2019, from https://www.engineeringtoolbox.com/friction-coefficients-d_778.html
[3] Ramirez, J., Pavon, J., & Toro, A. (2015). Experimental assessment of friction coefficient between polypropylene and human skin using instrumented sclerometer. Journal of Engineering Tribology, 229(3), 259.
Analysis
Analysis
The forces that would act on the grabber when lifting a 10 pound object were applied onto the grabber in ANSYS Workbench along with supports that would be provided from the hand on the grabber. Using aluminum claw components, the minimum safety factor occurred on both the carbon fiber tube and the stationary handle (at their intersection). The maximum equivalent stress on the stationary handle was 23.6 MPa for a minimum safety factor of 1.743. The maximum equivalent stress on the carbon fiber shaft was 382.3 MPa for a minimum safety factor of 1.763. Hence, with aluminum claw components, the grabber should be able to safely handle 10 pounds.
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