I think that's an improvement upon Forrest M. Mims III's plotter scanner. (He's the one who hand-drew some of the books at Radio Shack, like Getting Started in Electronics, and the 555 timer application notes circuits.) IIRC, for an article for Computers & Electronics magazine, he rigged up a flatbed X-Y plotter with an optical sensor (maybe one of the cadium sulfide photoresistors that RS sold?), and the resolution was very low, but it was pretty inspiring to kids. (It also gave you another reason to crave a plotter, which you now saw was really a robot module.)