Week 3: Ironing Out Some Details
Jack S -
Hello everyone, and welcome back to my project! This week, I spent my time deciding on some design changes as well as researching and purchasing specific products I hope to include in my final design.
First, I decided I would draw out my current design to visualize where some issues could arise. To recap, I plan to have two main forces acting upon the fingers of the wearer: the soft actuator that will extend the fingers upon inflation, and an elastic cord that will act against the actuator, pulling the fingers in. The cord will be a constant force, while the soft actuator will be controlled by the wearer, allowing them to open and close the hand by either overpowering the force of the cables (inflation) or eliminating resistance to the force of the cables (deflation). Originally, I planned to attach each cable to the fingertip area of a glove, then use small pieces of tubing to ensure the cable runs close to the finger on the outside of the glove. While this does provide the force necessary to close the finger, the cable attached to the fingertip area provides an uncomfortable barrier between the wearer and any external object. At the same time, the glove itself would also provide an unnecessary barrier. To address this, I will cut the fingertips off of each glove, then run the elastic cords under, rather than over, the glove to avoid using unnecessary tubing.
I also changed how the glove will be controlled by the user. I had planned to put a force sensor on the middle finger, with corresponding actuators and cables on the ring and pointer fingers. This way, the user could lightly press their fingers down on something, triggering the actuators to deflate and the hand to clasp down with force. Upon further investigation, this seems impractical. In a resting position, where the actuators are fully inflated and those two fingers are fully open, it would be difficult to move your middle finger down enough to trigger contraction, since the pointer and ring fingers (both attached to actuators) will remain fully extended until the middle finger makes contact with the object. I now plan to place the force sensor on the thumb to avoid this potential issue. Now, the user should be able to place their thumb on, for example, a doorknob, triggering the ring and pointer fingers to close with force and provide a good grip.
I also spent time this week ordering and researching specific parts I will need for this design. In previous weeks, I tried out multiple inflatable objects to find which one would work best in a soft actuator. I continued that this week, as I purchased a pack of long latex balloons (the ones used to make balloon animals). These were appealing to me as they are very durable, they form a long, cylindrical shape (unlike disposable gloves), and they are very cheap. Once I got the balloons, I tied a knot in the middle and put them inside the cylinder of fabric to test their durability. So far, they have withstood a lot of pressure before bursting, and I will need to compare them to disposable gloves to see which is more durable. I am waiting to test this until I receive the pump, which I also ordered this week, as it is hard to compare the two materials using a hand pump.
That brings me to the pump, another purchase I made this week. Since my Arduino has a 5V output, I decided I would first look in that range to avoid purchasing a relay, which could add both cost and weight to the final product. Luckily, I quickly found a 4.5-liter/minute air pump online that is compatible with my Arduino. Since this specific pump had no protection from backflow, meaning the air would leak out as soon as the pump is turned off, I found a valve from the same company that can also be controlled with the Arduino. After consulting with my site advisor (and before I had placed the order), we decided we should purchase multiple pumps. This will give me a few opportunities during construction, including combining the force of two pumps to have a 9-liter/minute air output, or hooking up one pump to act as a vacuum (if the valve cannot deflate the actuators at a reasonable rate). Finding these pumps was great, as I now know that my device will require neither a heavy pressurized air container nor a large pump that would need to be held in a backpack. I can now say with confidence that, barring a massive change, my final device will be wearable on a single arm, with no other attachments needed. I am very excited to put these pieces together in the coming weeks. Thank you for reading!
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