Interested in exploring how precisely the craft robo can ‘titrate’, I took it apart more. Specifically, I’m interested in if when you tell the craft robo to print a number of a dots in a row, if it always hits the paper with same force and to the same depth.
An interesting thing to see in the craft robo is how it applies the pressure to the rollers, which control the paper it’s printing on. (The craft robo is an effective x-y stage by moving the printer head in the x-dimension and the paper in the y-dimension.)
It has a neat little spring mechanism on each side to keep the top roller, which can move up and down, in tension with the bottom roller, which is fixed. Having a custom injection molder part that sits on top of the end of the roller allows them to use a standard spring size and still set the tension to the desired value.
But I was really interested in the mechanism for moving the pen.
They use a linear solenoid actuator and a simple linkage to move the pen holder. There weren’t any visible mechanical stops, so I’m guessing that there is a mechanical stop inside the linear actuator.
The printer software allows you to vary the force you’re using, which must mean the charge they run through the solenoid — higher charge, higher force on the solid core, higher force on the pen. However it’s still unclear if there’s variation in the depth. There could be, given that nothing is truly rigid.
Just for fun, a note on how Rapidograph drafting pens work:
They have a hollow cylinder which extends from the ink cartridge. But inside the cylinder is a thin metal wire. When the wire is compressed against the paper, it breaks the meniscus of the ink and allows it to write. This is actually pretty cool, as it allows you to write without ever having the touch the hollow cylinder to the paper, which might be important if you have very delicate applications.