EZ Clips
Adrianna Bernardo, Hadden Kelley, Sam Li
Executive Summary
Arthritis affects over 50 million adults in the United States, causing joint pain and limited mobility in those afflicted by it. EZ Clips’ goal is to develop a device that allows for users suffering from arthritis of the hands and wrists to comfortably trim their nails while maximizing the efficiency of the applied user force. Design decisions were driven from user feedback on comfort and usability, as well as the desire to adhere to standard ergonomic guidelines.
The final prototype utilizes a hydraulic mechanism in a table top clipper to maximize the user’s applied force, while still allowing the user to cut their nails with minimal dexterity. While the target ratio of output force to input force was 18:1, the final device force ratio measured to only be 15:1. This is primarily due to the limitations of standard syringe sizes, as syringes were the primary building material of the prototypes.
Table of Contents
Background………………....…...3
Project Brief and User Profile.….4
Analysis……………………….….5
Concept Development…………..6
Prototyping……………………….7
Final Concept……………….…...8
2
Project Background
The common nail clipper design that is used today was patented over 70 years ago in 1947. Since the time that it was patented, little changes have been made to the design over the years.
Although it is a simple and common device, the current design of nail clippers does not meet the specific needs of the arthritic community, limiting many arthritic users from being able to maintain their personal hygiene by clipping their own nails. Specifically, current nail clippers:
Figure 1. 1947 patent drawings of nail clipper
3
User Profile and Project Brief
Arthritis currently affects roughly 22.7% of all adults in the United States, and of those affected, almost 50% are over the age of sixty five. The most common form is called osteoarthritis which results from the erosion of the cartilage at the ends of joints. All of this indicates that a large proportion of people are suffering from chronic joint pain and limited grip strength and mobility making even the simplest of tasks increasingly difficult.
EZ Clips’ goal is to develop a device that allows for users suffering from arthritis of the hands and wrists to comfortably trim their nails while maximizing the efficiency of the applied user force. User interviews helped to identify comfort, cutting efficiency, and minimizing user force as the primary objectives of the developed device.
Figure 2. Percentage affected by arthritis by age group
4
Engineering Analysis
Hydraulic systems take advantage of the distributive property of force applied to a liquid. This means that a small force exerted over a small area is equal to a large force exerted over a large area. Since minimizing user force was a primary objective of the device, hydraulic mechanisms were explored throughout the prototyping process.
Standard nail clippers tested had an output to input force ratio of 8:1. Because user testing showed that people with arthritis are roughly 2.24 times weaker than a normal person, the ideal output to input force ratio for the prototype was determined to be 18:1. Using the governing equation F2 = (A2/A1) * F1, It was calculated that to achieve the ideal ratio of applied forces, a hydraulic mechanism with a large pump of diameter 4.24 times the diameter of the smaller pump could be used.
Figure 6. Initial CAD model
Figure 5. Concept Drawing
5
Concept Development
The initial design was for the device to be a handheld clipper with the hydraulic mechanism inserted between the two handles. As the handles are squeezed together, the pressure forces the larger plunger to rise and squeeze the clipper head. This design was altered because it was ultimately too large and unwieldy especially for someone with limited hand strength.
The final prototype, which is discussed later, uses a similar hydraulic mechanism, but is simplified in design for ease of use.
Figure 4. Final mechanism design
Figure 3. Initial mechanism design
6
Prototyping
The first prototype was entirely 3D printed with the intention of making very precise parts. In actuality parts were incapable of a degree of precision that ensures watertightness. The second iteration was a similar design but making the device out of plastic syringes to ease waterproofing. This ended up being too clumsy to use with one hand because of the degree of separation between the handles. With arthritis, this would prove to be difficult and even painful. From this, the device would have to either be smaller or simplified in such a way that only one hand can comfortably operate it.
Figure 7. Initial prototype designs
Figure 8. First syringe mechanisms
Figure 9. First functional prototype
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Final Concept
Building off the need for one handed use, the final concept is designed to be mounted on a smooth flat surface with suction pads. A single vertical plunger is all that needs to be moved to squeeze the cutter head. This new design doesn’t require the user to hold the device which decreases the strain on their hands and wrists. The vertical plunger minimizes the force required by allowing the user to be assisted by gravity when pushing down.
Figure 10. User testing
Figure 11. Final prototype
Figure 12. Exploded CAD View
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