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University of California, San Diego
Department of Mechanical and Aerospace Engineering
MAE 156B Sponsored Senior Design Project
Canwin Tso, Jinho Hong, Andrew Kim, Isaac Gonzalez
CAD Models for our final design: Scour Pad/Magic Eraser Insert (Left), Hexagonal Plastic Insert (Right)
Background:
Colonoscopies and endoscopies are one of the most common surgeries performed by gastroenterologists in the United States. Both procedures are done to detect cancer as well as other diseases in the gastrointestinal system from mouth to rectum. The equipment used for these procedures is called an endoscope, which is a semi-rigid tube/camera that can navigate through a human body. Figure 1 includes a picture of an endoscope as well as how it is typically held by physicians. As shown below, colonoscopy requires the use of the right hand to torque and advance the tube through a twisty colon. The frequent use of the forearm as well as the high grasping force mean physicians are subject to repetitive stress injuries (RSI).
Figure 1. Typical Way of Holding an Endoscope
Objective:
Design Requirements
Materials
Cheap and disposable or expensive but easy to clean
Shape & Structure
Ergonomic
The way doctors hold an endoscope should not change
Safety Requirements
Must not pose a health hazard to the patients and the doctors
Manufacturing
Our design must be capable of mass production
The benefits of our designs should outweigh the cost of the manufacturing process
High Priority Objectives
Our design must give physicians the mechanical advantage needed to exert the necessary forces to perform the colonoscopy.
Our design should not change the colonoscopy procedure. In other words, doctors should be able to maintain the same level of dexterity with or without our device.
The device must alleviate the physical stress felt by the doctor during the procedure.
Second Priority Objectives
Our device must be ergonomic.
Our device can either be cheap and disposable or expensive but easy to clean.
Our device must be safe to use.
Approach:
In order to satisfy all the priorities listed in the objectives, we decided to go with a human hand augmentation tool. The general idea of this would be to give extra padding on the endoscope so that the user can apply force on a larger diameter.
The human muscle performs optimally at certain configurations. To find this optimal gripping distance, we found the paper 'Hand strength: the influence of grip span and grip type' by Charlotte Fransson. The grip span is defined in Figure 1 and the finger force for different finger grip spans is defined as in Figure 2. From this we can see that the finger force increases up to around 50mm in finger grip span. Therefore, we can approach the endoscope torquer tool by adding extra padding up to ~50mm so that the 12.3mm endoscope will feel like a thicker apparatus, giving a larger finger grip span. This larger grip span will not only give a mechanical advantage for torque through a larger diameter, but also allow the user to apply more force through the optimal configuration of the finger muscles.
Figure 1: Grip Span
Figure 2: Finger force for different grip span
Testing Procedure:
Cardboard Colon Test
Picture of The Cardboard Colon
Although we have access to the simulation lab on campus, we built a cardboard colon so we could simulate the feeling of performing a colonoscopy at home. Using the endoscope provided by our sponsors, we were able to initially test our device by navigating the endoscope through the cardboard colon.
Colonoscopy Simulation Lab
We were given access to the Colonoscopy Simulation Lab. Inside the lab is a machine that simulates the feeling of performing a colonoscopy. On top of the machine is a monitor that shows the live feed from the endoscope. According to our sponsors, the simulation lab is the closest thing to the procedure.
Performance:
Compared to a towel, both devices did a better job preventing slippage. Ergonomics also improved as physicians now have a consistent grip throughout the procedure. With an overall mean radius of 16 mm, both handles were able to decrease the lateral force needed to torque the endoscope by 60 percent. This decrease in force provided physicians with better control of the endoscope, leading to an increase in accuracy. However, despite the benefits of our devices, they have their flaws, too. For instance, the high friction of the scouring pads/magic eraser sheets meant translational motion of our device was hindered. Furthermore, although the hexagonal inserts did a fantastic job preventing slippage, it would only work if the compression force was applied directly from the top and bottom. Because of this, more research needs to be done to determine the best solutions to solve the issues above.
Executive Summary:
Executive Summary.docx.pdfPage updated
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