It works like old typewriters. You align the corners of the paper and then clamp it.
Compare that, at the time, to the top of line of a Gerber (or 3M) plotter that was the only one able to handle 12+ ft. It used an array of sensors that at runtime adjusted the clamping-wheels pressure to keep the paper/vinyl roll aligned.
It was around $15-18K, while my Ioline was ~$1,300.
So I have a 5' x 5' router table that I've modified to hold pens. I was using paint pens that require the nibs to be indented to get more paint to flow. They run out every 2-4 feet of line. It doesn't make great lines. Here is the machine re-loading a pen: https://www.instagram.com/p/CAD-tR1FU8J/
The "pens" i've made are a piece of delrin, with a 1/4" hole drilled down the middle and a piece of 1/4" F1 felt stuffed in there.
The first one is a perlin vector field plus a deformation. I haven't heard of those artists but I will look them up.
On the brush: That's a chinese calligraphy brush. I spent a bunch of time making a bearing holder to let the brush swivel freely. It didn't work. The brush is very, very hard to get to behave. A human will tilt it slightly in order to get the bristles to go in the right direction, but the CNC machine keeps everything completely orthogonal. Works for pens but not brushes.
Edit: Keith Peters' algorithmic stuff ( http://www.artfromcode.com/ ) does seem to share a lot of the same underlying techniques. Perlin flow fields and hex truchet tiles especially.
unfortunately sharpies aren’t very good. i use paint pens but they require significant pressure to open the valve behind the nib.
i am currently working on making my own markers...