We struggled with many different aspects of our device, and came up with a variety of original solutions to our challenges, but two of the biggest hurdles to overcome were:
Device to push the pills down:
Our device dispenses pills by pushing them down a track, but we had several options as far as what was going to impulse them to go down the “tube”: a conventional spring, a motorized plate or a constant-force spring.
First of all we considered using a regular spring. This would be convenient as they’re easy to find and very cheap. These would be coiled at the top of the track and as each pill was to be dispensed it would uncoil, until being at its maximum extension when all the pills had been dispensed. However, they don’t apply a constant force when they’re completely coiled as when they’re uncoiled, which would be hard to calibrate and might compress the capsules too much, potentially destroying them.
Secondly we considered using a motorized plate. This would provide a constant force, and – by making it the same size as the casing – it would correctly dispense the casings. However, this option was electronically very complex, as a circuit and motors would be required for them to be functional, so they would take up more space and energy. Also, this made it more probable to pose problems, as the more complex the device is the more chances it has of failing.
Finally, after much research, we found constant force springs: a durable and inexpensive type of spring that works in a very interesting way: the force it exerts over its range of motion is constant. That is, it does not obey Hooke's law. Generally constant-force springs are constructed as a rolled ribbon of spring steel such that the spring is relaxed when it is fully rolled up[1]. This could pose problems by applying a force to only one side of the pill capsules. Attaching a plate to the bottom of the spring, which would be lowered through guides on the walls would help the force be constantly applied to the entire surface of the casing, and therefore make this an easy way to apply a constant force without needing to motorize the device. Therefore we chose the last option, because it was inexpensive, was available in the desired sizes, optimized space and didn’t require motorizing, thus leading to a less costly and simpler device.
Analgesic storage options:
First of all, we thought of storing the pills in blisters, which would keep the pills sealed and therefore not let them spoil. However, that would mean that pharmaceutical companies needed to develop a new way of producing the blisters so they could fit in the device. Secondly, we thought of having strands of plastic packets with precut lines in between each dose, which would be cut when they were to be dispensed. However, these could potentially jam the machine or – if not cut at the exact location – open the next packet, jam, or get stuck under the blade. Another idea we had was to store them in gelatin-based clear capsules, which would be edible and able to store more than one pill. However, these could stick to the walls and be susceptible to heat, as well as easily break. Finally, we decided to use clear plastic capsules, of 2x2x2cm, which would allow more than one pill to fit into the capsule if necessary, be reusable and easily refillable, inexpensive and hard to deform (ideal for our spring and roller dispensing system).
[1] As it is unrolled, the restoring force comes primarily from the portion of the ribbon near the roll. Because the geometry of that region remains nearly constant as the spring unrolls, the resulting force is nearly constant (Springs How Products Are Made, 14 July 2007).
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