Pill Cutter - Progress Blog 4: 11/23/2021

Hello and welcome back to our team's fourth blog post! This is a blog for the University of Houston's Mechanical Engineering Capstone Team 35: Progress Blog 4.

First off, we would like to talk about the work the team has completed up to now. Thus far, the team has completed the final device concept and is ready for the next stage of the fabrication process. These include the justification analysis, improvement changes, and materials selection.

In terms of the final design, the concept is composed of: a multi-shape disk with different pill sizes and shapes, a class II lever cutting mechanism, a curved blade, and a storage container with varying fin heights acting as the “secondary blades”, creating a surface defect to aid the rest of the cutting. The overall final design concept is shown below in figure 1.

Figure 1: Multi-Shape Disk Pill Cutter

In terms of the justification analysis, the team has performed a blade analysis test to determine which type of blades would give the pill the cleanest cut. The blades used for the analysis test include a curved blade, a serrated blade, a straight thin blade, and a straight wide blade. From our observation from the test of cutting the pill from two cutting angles -a center cut and an edge cut- the curved blade gave the cleanest amongst the four blades. As a result, this verifies the team's primary ideal: the more initial points of contact with the pill, the more of a “clean-cut” the blade produces. The results from this analysis are shown in figure 2, and the final blade design is shown in figure 3.

Figure 2: Blade Analysis Results

Figure 3: Final Blade Design

In addition to the blade analysis, the team also performed the finite element stress analysis on the CAD model of the device. From the FEA analysis, the team determined a stress concentration occurring at the start of the lever arm near the pin; this indicates a possible failure if the stress concentration is left unaddressed. For that reason, the team modified the lever arm to reduce the stress concentration by removing the sharp corner at the bottom of the connection and increasing the area of connection between the hinge and the arm. The result from the FEA analysis is displayed in figure 4, and the modified lever arm: in figure 5.

Figure 4: FEA analysis of the CAD model

Figure 5: The Modified Area of The Lever Arm

Besides the justification analysis and modifications, the team also completed the selection of the materials for each component of the device. The blade will be made using stainless steel, as stainless steel is one of the most commonly used materials in pharmaceutical devices due to its durability and the ability to withstand corrosive chemical reactions. The storage container will be made with orange translucent PLA filament, which helps to prevent ultraviolet light from degrading the pills in a photochemical reaction. The rest of the device will be made in PLA filament with no restrictions in color.

Finally, we, the team, plan on using the time during the winter break to look for potential vendors for the components, raw materials, and measuring instruments needed to fabricate our device. Additionally, we are looking into scheduling consultations with both the 3D printing lab and machinists for fabricating currently-non-existing components. Once we are back from winter break, we will assemble the storing system and pill-cutting system of our prototype as a whole.