The basic idea here is to take a normal pen and have a computer control it. This is done by attaching the pen to a set of movable arms, the X and Y axes. The arms are controlled by stepper motors, allowing precise control of the pen. The computer will drive the stepper motors, and will also control a mechanism that raises and lowers the pen. Since this is nothing new, I found some links that go more in depth on the subject.
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