dave-in-nj:
If you have ever laid a quarter flat in a push-to-insert coin tray, you have an idea.
A small chamber that goes under the hopper, materials spill in and fill
Then when you pull it back the filled opening slides over an discharge hole and dispenses the materials.
The larger the opening, the greater the quantity.
You can have multiple slides to dispense different amounts.
using a gunpowder style, you can have one motor and one chamber per unit and dispense in any multiple of quantity.
the speed would be really fast. for one cup of tea you could make it even fun to watch.
As for the LEL or Lower Explosion Level, that is super easy to address. a ventilation system with air supplied above and the return/recirculate below would pull any debris from the air. Once used in offices to remove cigarette smoke, it can capture super fine particulate.
if this is for a tea house, the amount of circulation is massive. the dust problem is related for enclosed manufacturing facilities as the big letters in red implies on the link.
I've been looking at cereal,candy and rice dispensers and they all seems to use the same rubber multi-finned paddle. Seems to be very reliable however maybe a little inaccurate for my purpose. I may experiment.. I certainly get what you mean about the coin slider setup. I actually found this on thingy-verse which could be another approach.