I don't see why a motor speed signal would be required or even useful.
I assume you refer to an auger-type feeding system, dry bulk solids?
I have designed bulk solids dosing systems based on a knife gate, no auger, so also no speed signal available at all, and also there is no consistent flow rate because it depends on how much product is in the hopper, granule size, coefficient of friction of the granules, and bulk density of the product. I originally tried to base my algorithm on the Beverloo equation but that was more trouble than it was worth and didn't work well. It required prior knowledge of, and inputting parameters of the product to be dispense. Dumbing it way down was the ticket to success running any product, without having to know anything about its properties beforehand. The way it works is:
1. Start opening the valve rapidly and keep opening until 1/3 target weight reached. Then dwell at current position until 50% target weight.
2. Capture current position and start closing the valve with quasi-logarithmic relationship between valve position and difference between current weight and target weight, such that it tapers off to just dribble at around 96% and dwell at current position until 100% target weight.
3. Close the valve.
In the system I just described, there is only one feedback: weight.
(Technically valve position is also available as feedback but it isn't used for anything but position control in a separate controller).
So I don't see where or why auger motor speed enters the equation.
If I was going to design an auger based system I would approach it the same way, except it would be even simpler. Run the auger at full speed until about 95% of target weight, then taper off to a dribble before stopping at 100%.
I don't know if this is an academic assignment or a real world application but assuming real world, my advice is that the "dribble mode" at the end is absolutely critical because load cell readings jump around when weight is changing, and the faster that weight is changing, the more they jump around. If extreme precision is required i would even recommend coming to a complete stop prior to 100%, average the weight value for a few seconds, then calculate the required rotations to reach 99%, do the rotations, dwell and average again, then proceed to appropriate rotations to hit 100% on the nose.