After the many hours that went into the initial hardware design, it became clear there was more work to be done. What followed was several weeks of contemplation, reflection, and mourning, but then it was time to suck it up and try again with a new approach: a vacuum system. (pun intended if you couldn't tell.. I'm guessing you could tell... I hope you could tell....)
The vacuum idea was different than most drink machines I've seen others make. It would address the problems from our initial design, but there were new challenges that needed to be addressed, mainly with how to plumb the system. Keeping in mind goals for the system to be reasonably low-cost, and simple, yet functional and compact led to the following design:
To pour a drink, there are essentially 4 steps, using 3 different flows or "cycles". These cycles are identified in the diagram as the "Fill Cycle", "Drain Drink Cycle", and "Drain Rinse Cycle". The different cycles represent different states of the blue solenoid valves, creating different flows in the system. To elaborate, let me walk you through a complete drink pouring process.
Step 1a: (Fill Cycle)
In the Fill Cycle, arrows having a light orange color indicate the flow. (Arrows with two colors apply to two different cycles.) To start the process, the vacuum pump turns on, and the valve connected between the rinse tank and the hose extending to the top of the mixing chamber opens. This creates a vacuum inside the mixing chamber. Notice that the vacuum hoses from and to the rinse tank do not extend down into the rinse solution. The rinse tank is a solid sealed container, so the vacuum created in the rinse container is also created in the mixing chamber. With the vacuum established, the individual ingredient valves can be opened to bring the ingredient from the bottle into the mixing chamber. The ingredient valves are opened one at a time, and timed according to a calibration factor to retrieve the appropriate amount.
Step 1b: (Line Purge)
After the ingredients have been sucked into the mixing chamber, there is still some liquid remaining in the line. To make sure it is included in the mix, the line is purged by opening the AIR (Line Purge) valve at the end of the ingredients valve array. A side-effect of this is that the air purging the line bubbles up through the mixture in the mixing chamber, effectively mixing the ingredients. Once the line is purged, the valves are closed and the vacuum pump is shut off.
Step 2: (Drain Drink Cycle)
The Drain Drink Cycle is fairly simple. In this cycle, the DRAIN DRINK valve opens at the bottom of the mixing chamber, and the AIR (Chamber Vac Release) valve opens, releasing the vacuum in the chamber and allowing the mixed solution to dispense into a cup. After a timed amount, the valves then close.
Step 3: (Rinse - Fill Cycle)
At this point, the consumer is happy and has left the drink machine. You might be thinking... "Like, ewww now the next person will get any leftover liquid in the mixing chamber contaminating their drink." This is a downfall to this vacuum system approach. The solution, is the rinse cycle. This step is the same as Step 1, but instead of ingredient valves opening, only the RINSE valve, second to last in the ingredient valve array, will open. This will flush the line and fill up the chamber. Then, the line will again purge like in Step 1b, and the air-bubbles will help agitate the rinse in the mixing chamber.
Step 4: (Drain Rinse Cycle)
Finally, the last thing to do is empty the rinse solution from the mixing chamber, but we don't want to simply spit this stuff out of the drink faucet! In the Drain Rinse Cycle, the vacuum pump activates, but instead of the vacuum being routed to the top of the mixing chamber, the CHAMBER DRAIN (DRAIN RINSE) valve opens, along with the AIR (CHAMBER VAC RELEASE) valve. In this way, the rinse solution in the mixing chamber is vacuumed back into the rinse chamber for re-use. Now, obviously there may still be some drops of rinse solution...
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