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the fastest acting insulin
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a typical injection syringe
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an intermediate acting insulin
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Final Project—Peristaltic Pump
For the final project I wanted to make an insulin mixing device for insulin-dependent diabetics like myself. Though I do not have to mix insulins, many type I diabetics do, and the process can be confusing and prone to errors. Such errors could mean either low or high blood sugar levels, the former leading to potential tragedies like car accidents and the latter leading to long-term systemic complications.
It is easy to make mistakes during this process, especially with impaired eyesight from diabetic retinopathy, or with hands that have lost coordination due to aging. If this process were streamlined and automated, the number of errors could be reduced.
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the fastest acting insulin
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a typical injection syringe
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an intermediate acting insulin
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My idea is to make a device that would mix insulins by computer control, to improve this currently manual process.
A peristaltic pump is a pump that moves fluid without a pump immersed in the propelled fluid. They are called peristaltic because peristalsis is the name for process by which consecutively constricting circular muscles move material in human intestines.
Below are photos showing how such pumps work. The rotation of the motor is in the direction indicated. The tube is made of medical silicon rubber, a flexible material. When the roller compresses the tubing, it cuts off fluid flow, but as the main wheel rotates, rotating the peripheral wheels, fluid is forced forward in the tubing.
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stage 1
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stage 2
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stage 3
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I wanted to make this kind of pump as the first step in developing the insulin mixer. The pumps available on the market cost in the neighborhood of $2000.
Below is the pump as I made it for the final review, at a cost of about $60.
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overall view |
overall view |
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a detail view of the wheel and tubing assembly |
To make the mounts for the brass fittings and the fluid tanks, I used the 3D printer. Since I made so many parts on the 3D printer, I essentially had the entire object constructed in a CAD model before making it, as shown below. The baseplate was made using the waterjet cutter.
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overall view
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plan view
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the constituent parts in my CAD model (first drive wheel
iteration shown)
There were several problems that I ran into. The first design the for wheel did not include wheels that roll on the tubing, instead I used three lobes, as shown below.
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| the first iteration of the drive wheel | the last iteration of the drive wheel, printed on the 3D printer, with embedded wheels |
When I installed this drive wheel I found that the action of the lobes pinching the tubing would pull the tubing off the brass mounts that it was connected to. Though I could have tried lubricating the tubing, instead I went to the design below, using wheels to eliminate the pulling action on the tube as it pinched between the roller and the wedge block mounted to the baseplate.
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drive wheel model
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drive wheel model
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drive wheel model, plan view (wireframe)
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The interesting part of this wheel is that I printed it as a single unit on the 3D printer. Since the support material can be dissolved away, this part has a shaft inside the outer wheels that is integral to the part. The wheels cannot be removed from the assembly. Though this is interesting because such a pre-assembled part is impossible to make in any way besides 3D printing, it also poses obvious problems of bearing fit and service life were one to use such an assembly in real-world conditions.
I had to increase the gap between the faces of the small wheel and the faces of the larger wheel to 0.020" to account for the inaccuracy of the 3D printer—not very precise—but it was a success to make this wheel—the third one I printed actually woks!!!
Though I did not come too close to realizing the insulin mixer, it was exciting to use the 3D printer in this way and a triumph for me to make a pump that actually drives fluid forward.