CAPSTONE BLOG #2: 9/30/23

Our proposal is to build an affordable add-on that decreases the effort and time required for a single armed individual to tie, take out, and replace their trash. The goal of the solution is that, for an single-armed amputee, the full process of tying, removing, and replacing a trash bag takes a reduced amount of time compared to how it would with no assistance.

Based on the goals mentioned, maintaining a maximum time limit of 10 seconds and having a maximum trash load and securing force of 20 lbs will make the device more effective over manually tying the device. However, this will be one of the main challenges for this project. Having an optimized tying system that will meet these requirements is crucial for success. Currently, the design is relying on a rotating tying mechanism where a pole rotates up to 650 degrees and a hook that holds the bag to be able to go up and down 4 inches to secure the knot. To ensure this device will be useful for most single-arm amputees, the mounting portion of the device must be able to expand between different size ranges for kitchen trash cans between 10-18 inches and attach onto the sides of a trash can using 2 clamps. Depending on the material of the trashcan, the design of the mounting system must be able to resist any slippage after installation. This may become a challenge as it depends on the maximum trash load and strength of the clamps.


Table 1: Constraints


In terms of the tying mechanism, there are two key challenges to address. Since the overall goal of the tying mechanism is to “create a tight knot in under 10 seconds”, the two challenges are the time constraint and the creation of a “tight knot”. Completing a kinematic analysis to determine the linear and angular displacements between one mechanic to another will give insight to any potential optimizations required to meet the 10 second goal. The kinematic data on the tying mechanism will be accompanied by the study and application of knot theory. Analysis using knot theory will define both the position of a “tight knot” in the bag, and the process of how the un-tied bag reaches this position. Since the physical goal of the tying mechanism is to create a knot, the knot theory analysis will provide the quantifiable constraint as to whether the tying mechanism works or doesn’t. Figures 1 and 2 show information on knot theory and an example of kinematic analysis, respectively. 

Another aspect in the tying mechanism design is considering the trash load limit of 20 pounds. To verify this limit, an isolated FEA on the hooks will be done to ensure the system used to tie the bag will not be interrupted. 


The soft challenges identified by our team extend beyond the physical aspects of the project, requiring thoughtful consideration in our design approach. One significant challenge involves project documentation, where the emphasis is on maintaining the accuracy and currency of information, such as design requirements and technical analyses, throughout the duration of the project. Another soft challenge in measuring the team’s success is clear communication and constant feedback with clients and stakeholders. Establishing and nurturing transparent channels of communication is vital for aligning our design with their expectations. Additionally, we recognize the subjective nature of the results, prompting us to engage in experiments with stakeholders. This approach seeks to test the success rate of our device and collect measured opinions from diverse perspectives. Success measurement is intricately tied to the device's viability, a determination we aim to make through stakeholder experiments, ensuring that the device effectively meets the expectations. Furthermore, a soft challenge to be considered would be the expansion or reduction of the scope of the project. With consistent feedback from both the clients and stakeholders, the scope of the project will need to be adjusted accordingly to meet expectations and deadlines as required. 


Figure 1: Basic Knot Theory Concepts




Figure 2a and 2b: Examples of Kinematic Analysis

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